PEtite modeling is a tough industry to break into. Especially since most modeling agencies won't represent models unless they're 5 feet and 9 inches tall or taller. Have you had people tell you're cute? Do you hear all the time "you should be a model"? But you just don't qualify for the strict standards that most modeling angencies have?

Rest assured there is a career out there for the petite model. There is work in the worlds of the fashion, commercial, editorial and many other industries for the less 5 feet 9 inch models. There is even work for models as short as 5 feet tall.

Most of the work in the petite modeling industry involoves close up pictures of the face, hands, feet or other body parts instead of the body as a whole. The fashion modeling industry, however is very body focused, that is why they have such stringent height requirements for their models.

As a petite or avearage size model you would probably not be working much in the fashion industry so bodily imperfections and height are not usually factors. Evan a fairly average looking person can be very successful in this industry if they are willing to work hard, get the job done and show clients they are easy to work with.

So how do you get in to this specialized segment of the modeling market? First, remember the focus in this market is very much on the face rather than the figure. To make it in this market you need to have nice skin, a good bone structure, good teeth, and be cute. Most of your success will also be based on the look that is "in" at the moment.

To find out if you have any chance of success as a petite model you need to get an evaluation from an agency or someone who has contact with clients within the industry. This will tell you if you have the look that their clients are hiring at the moment.

If you are told you just don't have the right look at the moment don't despair. The modeling industry moves at a fast pace, and what's not in now could be the rave in the next 6 months.

The models in this segment of the market are often paid very well because advertisers usually focus more on the look of the models face than her figure. Advertisers usually have more money to spend than many clients in the fashion industry and a good model could make as much as $125.00 per hour on her first job.

Not cute? Do you think you don't have that "glamourous" look that could get you high paying jobs as a model. Don't despair, even a normal person can get high paying jobs in this industry if they are easy to work with and sparkle on camera. A plain model who exhibits spark and vitality is more likely to get the job than a beautiful model who is lifeless.

Photographers and clients would rather work with a model who is vibrant and easy to work with than a beautiful one who is honery, does not take instructions well, and acts "snobby" or conceited on the job. Putting too high a price on yourself in this highly competative industry many times will cause clients to pass you on for a more pleasant model.

Rest assured there is plenty of work in this industry if you have the looks, talent, and are easy to work with.

When you think of modeling, do you picture 16 year old, waifish thin and very exotic looking girl? If so,think again. Even though the modelng business is oversaturated with the most beautiful women in the world, an average-looking person can still have a nitche within the business.

Fashion modeling is the most prestigious category of the modeling industry, because about a dozen of fashion models have actually achieved the status of celebrities.Fashion modeling industry is not open to everyone and has very strict standards: height, weight, age and measurement requirements. Fashion models have to stay very thin to fit the clothes they are modeling, and even though many people in the industry might deny it, the pressure to have zero body fat is enormous in the fashion world. If you are tall and thin and lucky enough to have an agent who’d send you to castings (meetings with clients or photographers who can potentially hire you,) be prepared to do about six meetings a day, which wouldn’t necessarily result in any jobs.

If you are lucky enough to actually get a modeling job, most editorial projects (such as magazines) don’t pay a lot, and it takes an average fashion model a few years to build up her portfolio to start getting big fashion campaigns and other high-paying modeling gigs.

Travel for fashion shows or for editorial work can be exhausting, and many young women have trouble coping with pressure, related to the industry and its standards. Therefore – drug use, eating disorders, unfinished education and other issues, mentioned way too frequently in the media.

Not everything about the world of fashion modeling is dark and hard, but unfortunately, there are very few models who can actually make it to the top and enjoy the fame and fortune it offers. The biggest problem of fashion modeling today is competition. Because the industry has been raised to its highly prestigious status, it is simply impossible to provide all gorgeous hopefuls with enough work. This is why many aspiring fashion models give up modeling after spending six months in a tiny model apartment in Paris or Milan, watching their hungry roommates steal their food or do drugs.

I remember leaving home at 17 and going to Milan on a contract with a big fashion agency. I lived in a two-bedroom apartment with five other models, who all had eating disorders to some degree. Some girls did drugs. The atmosphere overall was extremely competitive, which reflected the way fashion modeling operates in general. The way my roommates greeted me was always the same: “So, are you working tomorrow? What are you shooting for? How much does it pay?”

The most common misconception about modeling is that the industry revolves around fashion. Closer look reveals, however, that fashion modeling is not the only option for someone who tries to be a model.

You can choose many different paths in her career, focusing on one direction or trying out a few.

Commercial, fitness, fit and showroom, glamour and fetish, artistic, convention and parts modeling could be easier, less competitive and healthier options for the aspiring models.

“There is simply more money in commercial print. You can make $3000 a day,” says Frank Marsi, commercial photographer, “You can also work much longer, there are commercial models in their late thirties.”

Have you seen cell-phone ads? They usually feature good looking, but not outrageously gorgeous people. This is how commercial models look like. Catalogues, some billboards, most advertisements and TV commercials use commercial models. As long as there is advertising, there is a need for people who look right to sell the product.

The height and weight requirements in commercial modeling are not as drastic as in fashion, and they very from job to job. A catalogue, for example, would require a taller model for clothes to look good, but an anti-balding shampoo ad would feature a middle-aged gentleman, who’d be the perfect model for that particular product.

I remember shooting for a commercial job for a pajama catalogue about a year ago. All I had to do was sit on a sofa wearing a pajama and pretend to be reading. I made $1300 that day.

To become a commercial model, you would need a composite card with about five pictures that look natural and pretty. Start by finding a good local commercial photographer, who’d shoot your photos. Then you can visit modeling agencies and show them your photos. Always check up on the photographer’s or agency’s reputation by asking for references, before committing to anything.

To get into the world of TV commercials, the best option is to send your headshots to casting directors who cast for commercial work. If they like you for a commercial role, you’d have to audition. If you do get the part, the pay could be anywhere from $10000 and up.

Fitness modeling is obviously for the fit. Protein bar ads, health shakes ads, sports clothes ads, fitness magazines – they all use fitness models. Muscle And Fitness magazine photographer Brian Moss finds most of his models at fitness conventions and contests, although he sometimes looks for his models on the internet.

Moss says that fitness modeling is easy to break into, if you have the right look.” I found this girl once and told her she’d have a cover in a year. She ended up doing two covers,” Moss says.

Fitness models should have great muscle definition and work out regularly. “There are many girls, there are many beautiful bodies, but there are very few beautiful girls with beautiful bodies. I mean, athletic, of course,” Moss says.

The pay for fitness magazine shoots is about $150 a day. “You shouldn’t confuse publicity with money,” says Moss. Magazine jobs could lead to doing commercial fitness work, which pays more.

The best place for a fitness model to start her career is to get involved with contests and fitness conventions, info on which could be found on the Internet.

Fit and showroom modeling could be somewhat boring work, but it pays well. Showrooms pay about $300 a day and fittings pay $100-$200 an hour. Showroom models show the clothing samples to clients. Generally, showroom work is booked through agencies and it is very seasonal – it’s busy after the fashion show season.

I’ve done a lot of bridal showroom work, where I tried on a lot of wedding dresses for a week or so. The work was exhausting, because you have to stay on your feet for the whole day, but I was happy with the pay.

Fittings involve trying on samples of designer clothing, having your measurements taken and telling the designer how does the garment feel. Fit models have to be a specific size.

Michelle Rogo, booker from Fit agency in New York says that the best part about being a fit model is that “you are in a comfortable atmosphere all the time, without too much hostility or competition.” Female fit models range from size four to size 14, but size eight gets the most work For males it’s the medium size that fits the most.

Fit models can keep working for a very long time as long as they keep their measurements. “Our oldest model gets the most work and she is in her 50’s,” says Rogo.

I do fit modeling quite frequently. It’s not the most glamorous of industries, but the pay is certainly worth it. I have a company that hires me for a week of fittings couple of times a year and I am always looking forward to these weeks!

The best way to become a fit model would be to visit your local fashion design school. Calling modeling agencies and asking if they have a fit division helps, too. More independent-minded fit models can try calling clothing companies directly.

Glamour, fetish and artistic modeling are for the brave among us. If you decide to model in these categories, be prepared to take your clothes off. There is a big debate going on about the differences between those three styles, but generally, glamour photographs involve at least partial nudity and lingerie, artistic photos are usually black and white and require full nudity, while fetish is everything in between, sometimes involving leather, chains and/or fishnets.

To model in these exciting, but risky categories, you have to be at least 18 years old. There is more work for females, so male models should probably concentrate on other areas. Modeling agencies aren’t the best source of unconventional or nude work, so you might want to check out some web resources, such as glamourmodels.com or garageglamour.com. When dealing with web photographers, don’t forget to ask for samples of their work and references, because safety is very important.

For those with exceptionally beautiful body parts, such as hands, feet, etc. there is parts modeling. To get into this huge and well-paying market you would need photos of your best body part to show to modeling agencies in your area. For more information, visit partsmodels.com

Modeling can be very fun, exciting and well-paid work that doesn’t have to involve starving and breaking your high heels while walking to millions of castings. If you really want to model, you are likely to find your niche in that business. And remember, the most important qualities that make a good model, regardless of the category she or he chooses to work in, are: confidence, patience, persistence, and punctuality.

Good luck!

Anastasia has enjoyed a very successful modeling career in major European capitals of fashion, as well as in the United States. She walked the catwalk for Prada and was photographed for Maxim and Glamour.

Anastasia is a published author of Diary of a Model - book, based a true story of glamorous photoshoots and fashionable parties. A must read for anyone interested in the inner workings of the business!

Swimsuit modeling is a very competitive field and the number of top models herein increase and decrease on daily basis. Once you decide to be a swimsuit model, the first job is to do a lot of research in order to find the right agency for your promotion. The city of New York is known as one of the major cities for modeling opportunities. Hard work, attraction, connections and luck - all play a part in deciding where you end up in this profession. No matter where you are based, if you sign with a big and popular agency that's based in New York as most of them are, there is a fairly good chance that you'll end up well. But it is important to know that there is always a demand for models in minor markets such as Chicago, Philadelphia and Phoenix.

Swim suit modeling very necessarily demands a good body. Being a swimsuit model might seem easy but coming back to reality, modeling is just another job at the end of the day. It's hard to make a good living and even harder to sustain it for more than a few years. Only a very few make it into the upper echelons of the profession. The supermodels that we are so used to seeing around must have initially had to take on secondary jobs just to make their ends meet. Many models end up doing this job only for a few years as it is pressurizing to live on a daily diet of rejection and keep up to look a particular way. Such pressures can take a severe psychological toll and may even be a risk to life.

It is usually the young models with training and experience that are most wanted as swimsuit models. There are various training schools out there that teach ramp walk, picture posing and hone your present skills as young models. It will also help you when you audition for a modeling agency. Having a models portfolio and gaining some basic instruction is important if you are considering taking up modeling as a full-time career. It is a swimsuit models duty to select swimsuit-modeling agents, who are correct for them. You can mail your picture and resume to all of the modeling agencies in your area. Every major city has well-established modeling agencies so you must get in touch with a few to get their opinions. Some of the best lingerie models modeling agencies look for bikini models but they may vary according to their requirements and choices. Picking an agent for swimsuit models that is well known and established is important.

Who wants to be a model? The answer is "EVERYONE." It's a fact! They may not admit it but deep inside every one desires be a model. A career in modeling can be financially satisfying and can offer several opportunities for you to blossom as a perfectionist. The key to success in the modeling industry is to have confidence in one's self. There are a lot of doubts that arise before someone enters this profession. For example; "can I really become a model?" or "why do I wish to become a model in the first place?" The answer to the second one may be fame, money or may be a childhood fantasy. It may be just anything but that reason has to be embraced and used as a motivational force to be successful in this industry.

To become a model, your look has to be marketable. A firm would have to trust that your face or body on their product would help them increase their sales. If you think you can handle the pressure of constant rejections then you are ready and you have crossed the first hurdle of this glamorous world. There are different types of modeling for e.g. fashion, commercial or specialty. Fashion modeling includes ramp walks, clothing campaigns, or posing for magazines, catalogues and showroom displays.

Fashion agencies usually have very specific requirements in terms of height, weight and age. These are strict due to industry standard for clothing samples. Rarely would an agency accept people, who fall short on these requirements even if the latter have unusually beautiful looks. Commercial modeling is employing models to sell products for household or industrial use. These comprise of cars, hair products, alcoholic and non-alcoholic beverages, household appliances, industrial appliances, machinery etc. Commercial agencies usually have no physical limitations and they are open to hiring people of all ages, sizes and ethnic backgrounds. Specialty agencies generally represent talent with special bodies or faces. These may include full figured models, bodybuilders, athletic builds or even body part modeling.

It is very important to find the right agency that may be interested in promoting you as a model. First you should call up the agencies and then send them some of your finest pictures. Also you must give about 4-6 weeks for them to reply. If an agency is interested in you they will definitely call you, however if chasing them with phone calls might just put them off. You need patience before you reach the glamour and publicity levels. Modeling profession is really hard work and can be surprisingly boring, tedious and even emotionally stressful.

If you are tall, slim and have the confidence to face the camera anywhere then modeling is the career for you. You are also required to have the tenancy, tolerance, aptitude, interpersonal skills, determination and business sense. Modeling can be a fun, exciting, and courageous experience, however, the chances of becoming a successful or famous model are not many due to tough competition. Agencies that provide you with work make a commission on your fee (15 to 20%), so beware of agencies that ask for money before even starting the work. Also it is important to check and see if they are reputable and real. One must keep copies of all-important papers such as contracts etc as they may be needed in case of a dispute. It is wise to remain with a reputable agency, as constantly switching agencies may give you a status of being unprofessional.

Successful people have followed certain strategies or models to achieve successes. Whether they are athletes, who always perform at the highest level, or businessmen who own titan companies, or salesmen who always exceed their sales targets every month, what make them achieve all these successes?

For every outcome that is produced, it is a result of an action. To achieve success, one may need to take a lot of different actions so as to find out what is the best action that will produce the best outcome.

Everyone can achieve what they want if they find out what are the exact strategies or actions that successful role models of their desired industry did. By finding out what they did, and applying the same action, you will be able to produce similar results. It will save you the most precious asset of your life, which is time.

You will not need to spend the time on trial and error to find out the right action to take, if you model somebody who has already found it.

We have been subconsciously modeling people since we were young. When we are babies, we tend to model how our parents walked, and we transformed ourselves from the days of crawling to walking. If a child finds that his or her father is very righteous and responsible, the child will most probably adopt the same characteristics of his father when he or she grows up.

Therefore, modeling for excellence is the way to do it. Look for a role model who has achieved everything in your field of industry or interest, and model him or her now.

The author is the co-founder of HomeBizGears.com

HomeBizGears.com strives to provide the resources and gears for you to start YOUR own Internet Business. At HomeBizGears.com, you can find lessons on Internet Business, useful links and articles.

To become a top model in the industry you have to be bright and attractive. If you are much talented and attractive even then you will have to do some of the following tasks to get not only a modeling assignment but to reach at the top. You will have to understand the various modeling types so that you can choose a specific type of modeling that is suitable for you. There are market demands for certain types of models more often than others. You will have to learn and understand the type of job required for each type of modeling and a few types are mentioned here.

Some of the common types of modeling include fashion modeling, hobby modeling, sports modeling, glamour modeling, trade show modeling, product modeling, commercial modeling and body parts modeling. Fashion modeling is much in demand and has tough standards for getting a modeling assignment in this type of modeling. Glamour modeling is also in high demand. In glamour modeling your photos and sometimes semi nude or nude photos are used for generating sexual feeling. Glamour modeling is also known as body modeling as here your body is at sale. The other more common modeling type is commercial product modeling. In this type of modeling you are asked to act in an ad. You can find in details about all the types of fashion modeling in fashion books or fashion magazines.

Once you go through the literature available for fashion modeling and decide a specific type of modeling then it is the tough job ahead. You will have to make an action plan for yourself for the coming years ahead. For achieving your goal to become a top model, you will have to give yourself the right direction. Improving your modeling skills with the help or guidance from an expert needs your foremost priority. You will not only be improving your skills, but at the same time you will need to change your attitude. You should show the people associated with the modeling industry that your attitude is highly professional.

To become a top model you need to have highest level of self-confidence. You need to improve your networking skills and find the modeling assignments for you. As more and more assignment you will get, chances to become a top model will increase. You should also be willing to travel, as sometimes the modeling assignment will require your presence in another city, state or country. You should also have an excellent body and you will also require maintaining your body continuously. Having all these qualities in you will make a route for you in the modeling industry and you will become a top model in the coming years.

Q. With the holiday season upon us, I've got some worries about my kids. Each year, they seem to be less and less grateful for what they receive, and want more and more stuff. I'm afraid of what this will lead to, and wonder what you would suggest for how to teach our kids to be grateful.

A. I am asked this question often at this time of year.

Part of the problem is that we live in a culture that not only doesn't support the concept of gratitude, it teaches the exact opposite.

In order to teach gratitude and appreciation, here are three suggestions:

Model gratitude in your own life

Do you complain a lot? Your kids are listening and will copy you.

Make things last. Don't just throw something out if it can be fixed.

Talk with your kids about' what you are grateful for in life. Tell your kids, often, what you appreciate about them.

Go slow on the big things

When we rent Chuck E. Cheese for a 3-year-old's birthday party, send kids to middle school dances in limos, and buy 16-year-olds brand-new cars, just what are we teaching them? What are they going to expect, (demand) next year?

We forget to ask the same question the scientists in the movie "Jurassic Park" forgot to ask: Just because we can do something, does it necessarily mean we should?

Have regular "gratitude times in your family

Make it a regular part of your dinner conversation to share what your are grateful for that day.

Make it a part of the bedtime ritual to share what you are grateful for in your life.

Stochastic modeling was used to predict nitrogen dioxide and fine particles [particles collected with an upper 50% cut point of 2.5 [micro]m aerodynamic diameter (PM2.5)] levels at 1,669 addresses of the participants of two ongoing birth cohort studies conducted in Munich, Germany. Alternatively, the Gaussian multisource dispersion model IMMI[S.sup.net/em] was used to estimate the annual mean values for N[O.sub.2] and total suspended particles (TSP) for the 40 measurement sites and for all study subjects. The aim of this study was to compare the measured N[O.sub.2] and P[M.sub.2.5] levels with the levels predicted by the two modeling approaches (for the 40 measurement sites) and to compare the results of the stochastic and dispersion modeling for all study infants (1,669 sites). N[O.sub.2] and P[M.sub.2.5] concentrations obtained by the stochastic models were in the same range as the measured concentrations, whereas the N[O.sub.2] and TSP levels estimated by dispersion modeling were higher than the measured values. However, the correlation between stochastic- and dispersion-modeled concentrations was strong for both pollutants: At the 40 measurement sites, for N[O.sub.2], r = 0.83, and for PM, r = 0.79; at the 1,669 cohort sites, for N[O.sub.2], r = 0.83 and for PM, r = 0.79. Both models yield similar results regarding exposure estimate of the study cohort to traffic-related air pollution, when classified into tertiles; that is, 70% of the study subjects were classified into the same category. In conclusion, despite different assumptions and procedures used for the stochastic and dispersion modeling, both models yield similar results regarding exposure estimation of the study cohort to traffic-related air pollutants. Key words: air pollutants, dispersion modeling, GIS, stochastic modeling, traffic. doi:10.1289/ehp.7662 available via http://dx.doi.org/[Online 15 April 2005]

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Recent interest has focused on traffic-related air pollution and the potential health effects associated with exposure (Kunzli et al. 2000). The acute health effects of short-term exposures to traffic-related pollution have been widely demonstrated, but much less is known about the chronic effects of exposure. Several studies have found associations between chronic morbidity or mortality and traffic-related pollution (e.g., Brunekreef et al. 1997; Heinrich and Wichmann 2004; Hock et al. 2002a; Weiland et al. 1994; Wjst et al. 1993). On the other hand, a number of studies have found no detectable effects (Magnus et al. 1998; Wilkinson et al. 1999). Thus, the extent to which the long-term exposure to air pollution contributes to chronic health effects remains unknown. Much of the uncertainty relates to the problems of potential confounding variables and of reliable estimates of exposure to traffic-related pollution at the individual or small-area level, across large populations and cities. To date, most assessments of the health impacts of long-term exposure have involved between-city comparisons using a limited number of monitors within each city. Such between-city comparisons are subject to exposure misclassification because they rely on a small number of monitors. A recently conducted study in four European countries [SAVIAH (Small-Area Variation in Air Pollution and Health)] found important variations in the concentrations of nitrogen dioxide and sulfur dioxide on a small scale within cities (Lebret et al. 2000). Several other studies have documented important within-city variation of concentration, especially related to nearness to motorized traffic and location within the city--for example, center versus suburb (Bernard et al. 1997; Cyrys et al. 1998; Raaschou-Nielsen et al. 2000).

To overcome these problems, some studies used surrogate variables, such as distance to major road or traffic intensity (objectively determined or self-reported) (Brunekreef et al. 1997; van Vliet et al. 1997; Weiland et al. 1994; Wjst et al. 1993) to account for within-city variability in exposure. A disadvantage of t2hese exposure indicators is that they are frequently not validated, and it may therefore be unclear what the actual exposure contrast is.

A potential solution to these problems is the use of geographic information systems (GIS) in which geographic data can be either used for the development of dispersion models (Bellander et al. 2001; Pershagen et al. 1995) or combined with concentration measurements to estimate exposures for individual members of large study populations by regression (stochastic) models (Brauer et al. 2003; Briggs et al. 1997; Gehring et al. 2002).

So far, epidemiologic studies used either stochastic or dispersion modeling, but not both in parallel. Only in the international collaborative study on the risks of development of childhood asthma and other allergic diseases [TRAPCA (Traffic-Related Air Pollution on Childhood Asthma) study (Brauer et al. 2002; Gehring et al. 2002)] were both approaches (stochastic and dispersion modeling) used in parallel to predict the outdoor exposure to N[O.sub.2] and particulate matter (PM) for 1,669 study participants. For the stochastic modeling, N[O.sub.2] and particles collected with an upper 50% cut point of 2.5 [micro]m aerodynamic diameter (P[M.sub.2.5]) were measured at 40 sites spread over the city area to estimate the annual average concentrations of these pollutants. This data set offers the unique opportunity to evaluate the result of the dispersion and stochastic modeling. The aim of the study is to compare the measured levels of the two pollutants with the levels predicted by the two modeling approaches (for the 40 measurement sites) and to compare the results of the stochastic and dispersion modeling for all 1,669 study participants.

Cross-platform, design-oriented form.Z v5.5 combines surface and solid, polygonal, and smooth modeling; NURBS; and parametrics. Bend Along Curve tool bends objects along any freely flowing 3D curve, and API includes methods for automating script development. With direct key and mouse driven navigation, interface offers scenes palette and contextual menu. LWA files and their predefined material can be imported and accessed by rendering procedures.

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August 1, 2005 - Siggraph 2005, Los Angeles, California: AutoDesSys, Inc., the developer of form.Z, is pleased to introduce form.Z 5.5 and present a sneak preview of the next release, version 6.0, at its Booth # 1447.

Live demonstrations will cover case studies of the modeling and rendering process, with emphasis on newer tools, such as smooth parametric modeling and cloning. On the rendering side, setting up a variety of rendering effects will be demonstrated, including the recently released HDRI based environment light. All this will be applied to a model of the sarcophagus of King Tutankhamen, the Egyptian "boy" Pharaoh, currently exhibited in Los Angeles.

In addition, AutoDesSys will preview some significant new tools in the just released form.Z 5.5 and in the forthcoming form.Z 6.0.
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form*Z 5.5 includes a number of new tools, interface enhancements, file translators and improved versions of smooth modeling, rendering and network rendering. The most impressive new modeling tool is Bend along Curve, which bends an object along any freely flowing 3D curve. For example, this operation can take a linear object like a pencil and give it the shape of a pretzel. Direct key and mouse driven navigation, scenes palette, and a contextual menu are the main interface improvements. A completely revised DWG/DXF translator now supports Autocad 2004 and 2006 files. LWA (LightWork Archive) files and their predefined material, originating from a variety of real life manufacturers, can now be imported and accessed by the rendering procedures. An improved version of the form*Z API includes new methods for automating script development making form*Z scripts easier to develop.

Object animation is the most significant feature of form.Z 6.0. This new feature enables objects and lights to be animated directly in form.Z. The new animation features expand upon the currently available camera animation capabilities. Like all tools in form.Z, animation is a design tool. Animation can be used for traditional design visualization or as a way of generating 3D forms from the animation process. The combination of animation transformation, parameter animation, morphing and deformation create a new dimension in design exploration and form generation. These are, of course, forms that cannot be created with classical traditional methods and imply results that can only be produced by artificially creative processes. form.Z 6.0 is scheduled to be released later this year.

"The addition of object animation will bring form.Z full circle", said Chris Yessios, President of AutoDesSys. "This is something that our users have wished for and the beauty of it is that they will not only have the opportunity to animate objects, but do it as part of the design process and without the need to switch applications or leave the form.Z environment. form.Z has long been hailed as the ultimate modeling cross platform program. It will now empower its users to explore forms even they had not suspected that they existed."

The July/August 2005 issue of ID Magazine, dedicated to the juried "51st Annual Design Review" features a number of form.Z users who won awards of Design Distinction and Best of Category in the environment, furniture, and equipment categories. The recently published in.form.Z 2005, AutoDesSys' annual newsletter, is a celebration of form.Z user work. It is a testimony to the combination of creativity and technology, the application of the digital to the demands of design in a variety of industries. The credits for the cover image go to Giorgio Borruso whose virtual study of the Fornarina store that opened at the Mandalay Bay Hotel in Las Vegas is featured. He won numerous awards for the design concept, including the Store of the Year Award. Copies of in.form.Z 2005 are available at the AuotDesSys Booth # 1447 at Siggraph 2005 or by writing to us.

form.Z is a cross platform design oriented 3D modeler that combines surface and solid modeling, polygonal and smooth (resolution independent) modeling, NURBS and parametrics. form.Z includes 2D drafting, information management, raytrace and radiosity rendering, animation, an open architecture with an API and script language that offer further means for customization.

C International Journal of Digital Accounting Research and can not be used without prior permission of the publisher.

This article discusses how prepayment and default constitute competing risks in mortgage lending, provides examples of the importance of using a combined approach when evaluating the risk of whole loans and MBS, and concludes with practical implications of using the competing risks framework.

Though it may seem apt, the phrase "competing risks" in the title of this article does not refer to the annual budget battle between various risk management functions within large financial institutions. Rather, it is a framework for modeling the impact of separate causes for attrition. In the mortgage world, these are the separate, but interdependent, risks of prepayment and default. For prime mortgages (whole loans) and for mortgage-backed securities (MBS), prepayment risk has long dominated the issue of credit risk. Historically, in the secondary market, the three government-sponsored enterprises (GSEs) guaranteed the credit risk of most conforming mortgage loans, which represented the bulk of the primary market.

However, a recent issue of Inside Mortgage Finance (IMF, June 10, 2005) noted the following fact: "During the first three months of the year, non-prime lenders churned out an estimated $184 billion in new loans. Putting that into perspective, more than one out of every four loans--or 28.5%--of all new mortgages made during the first quarter of the year went to borrowers in the subprime and Alt A categories." Moreover, SMR Research Corporation estimates over $700 billion in junior liens outstanding at the end of 2004 (Home Equity Loans: 2005 Outlook). Therefore, loans with greater credit risk represent a significant and increasing portion of the primary mortgage market.
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A large number of these loans, and the associated credit risk, are held on the balance sheets of large financial institutions. The IMF estimated that the 50 largest financial services holding companies held a combined $1.01 trillion in whole loans during that same first quarter of 2005. Moreover, according to Inside MBS & ABS (July 17, 2005), a weekly newsletter published by the IMF, Fannie Mae and Freddie Mac bought $212 billion in nonconforming MBS during 2004, assuming much of the credit risk for the underlying mortgages. (1) Thus, the increasing credit risk in the system is held by a large number of institutions, and even the GSEs now must learn to assess the greater credit risk from nonconforming products.

These recent developments increase the importance of default risk vis-a-vis prepayment risk for mortgage lenders, whether they are portfolio lenders or buyers of MBS. However, the presence of prepayment risk limits the applicability of traditional approaches to default modeling. The competing risks framework for modeling prepayment and default confers important advantages relative to these traditional approaches, particularly in the context of valuation, risk management, and capital allocation.

The Need for Hazard Models

As with other types of consumer assets, it is important to address the timing of the default event, and to account for static predictive variables. But mortgages are unique in offering the borrower an important and valuable option to prepay the loan early. Other consumer loans are prepayable, but only mortgages offer a significant financial reward for careful use of the option. This poses a particular challenge for default modelers. (2) Consumers frequently use the prepayment option when it is to their advantage. When interest rates reached 30-year lows in 2003, the monthly prepayment rate for prime mortgages reached nearly 7%. The average lives of mortgages vary enormously due to differing prepayment rates and lead to significantly different cumulative losses for mortgages with similar credit characteristics. As a result, building an accurate life-of-loan loss model for mortgages is very difficult.

Prepayment modelers take a different approach (as illustrated by the fact that the life-of-loan prepayment rate is a concept unheard of in the industry), using what are called hazard models. A hazard model is simply a model designed to predict the probability of attrition given that the subject has not yet left. For prepayment, this means predicting the probability of prepayment in a given month for all borrowers who have not yet prepaid. This methodology sees heavy use in prepayment modeling. (3) Hazard models for prepayment commonly include age and current rate levels as explanatory variables.

While the hazard modeling is well understood by investors and by Wall Street, technique has less commonly been applied to mortgage default. Hazard models, however, are frequently used in assessing the risk of default or bankruptcy for corporate bonds. (4) In the case of mortgages, a hazard model would predict the probability that the mortgage defaults in a particular month, given that it has not yet defaulted or prepaid. Such a model typically would include age, current house-price levels, and borrower FICO scores as explanatory variables.

InfoSWMM for ArcGIS v4 facilitates evaluation, management, rehabilitation, and operation of wastewater and stormwater collection systems. It addresses all operations of sewer systems, from analysis and design to management functions such as water quality assessment, pollution prediction, urban flooding, real-time control, and record keeping. Program helps manage urban runoff and wet weather water quality problems, optimizing BMP and LID designs, and meeting SSO and CSO regulations.

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Unsurpassed Capabilities Set New Standard For Ease, Power, and Performance

in Geocentric Urban Drainage Modeling

Broomfield, Colorado USA, August 24, 2005 - In its ongoing quest to equip the global wastewater industry with the world's most comprehensive and innovative GIS-centric modeling and design solutions, MWH Soft, a leading global provider of environmental and water resources applications software, today announced the worldwide availability of the V4 Generation of InfoSWMM for ArcGIS (ESRI, Redlands, CA). The release marks the most significant milestone to date in the evolution of the company's flagship urban drainage modeling product, firmly establishing it as the number one choice for the effective evaluation, management, rehabilitation and operation of wastewater and stormwater collection systems.

As a full-featured urban drainage network analysis and design program, InfoSWMM delivers the highest rate of return in the industry. All operations of a typical sewer system - from analysis and design to management functions such as water quality assessment, pollution prediction, urban flooding, real-time control and record keeping - are addressed in a single, fully integrated geoengineering environment. The program offers users unprecedented power in managing urban runoff and wet weather water quality problems in combined, sanitary and storm sewers; optimizing BMP and LID designs; and meeting SSO and CSO regulations. The model also offers highly sophisticated Real-Time Control (RTC) schemes for the operational management of wastewater systems and hydraulic structures. The unparalleled performance modeling of InfoSWMM sets new benchmarks in scalability, reliability, functionality and flexibility within the powerful ArcGIS environment.
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Underlining MWH Soft's leadership in the wastewater industry, InfoSWMM reflects the company's ongoing commitment to delivering pioneering technology that raises the bar for urban drainage network modeling standards, helping to shape the future of this critical sector. Focused on expanded geospatial functions and performance, InfoSWMM V4 offers important cutting-edge GIS features and a wide array of enhancements that set an unprecedented standard for GIS-based modeling. These improvements greatly simplify, accelerate, and integrate urban drainage network engineering, helping wastewater engineers develop better designs and operational improvements faster and more efficiently.

Key additional tools include a Transect Extractor that uses advanced GIS technology to automatically create channel cross-sections from a DEM or contour elevation data by simply drawing a line on the map. Stations and elevations can be extracted at equal distances or at each change in slope. Another new feature, a Dry Weather Flow (DWF) Allocator, automatically and reliably computes and assigns wastewater loads generated by various customer categories. Wastewater loads can be calculated based on land use, population, or meter data, then allocated by customer type or merged into a single base flow. In addition, InfoSWMM 4.0 now supports an unlimited number of dry weather base flows, which can be managed and tracked by customer type (industrial, residential, etc.) at each junction. Different hourly, daily, monthly, and weekend patterns can be applied to each base flow at a junction, providing the ultimate flexibility for estimating sanitary loads throughout a long-term continuous simulation.

InfoSWMM is quickly becoming the must-have solution for comprehensive enterprise-wide geospatial urban drainage engineering. With an intuitive working environment and new cutting-edge features and improvements, V4 Generation delivers unmatched capabilities to the wastewater industry, backed by unparalleled technical support. "Just eight months ago, we introduced the world to InfoSWMM and set a new standard of excellence in urban drainage modeling and management software," said Paul F. Boulos, Ph.D, President and Chief Operating Officer of MWH Soft. "Now we're pleased to introduce another major evolutionary release that underscores our ongoing commitment to delivering superior value. InfoSWMM is not only the world's first and only urban drainage modeling solution certified by the National Association of GIS-Centric Software (NAGCS); its powerful hydraulic computational engine is also endorsed by the USEPA and certified by FEMA. We are proud to ship a significantly refined tool set that will have an immediate impact on our clients' productivity and performance."

Andover, Mass.-based Lattix Inc. on Monday announced the release of its software architecture management solution for Eclipse projects.

Lattix LDM for Eclipse is part of the company's new 2.5 version of Lattix LDM (Lightweight Dependency Model), said Neeraj Sangal, president and founder of Lattix.

The Lattix plug-in enables developers to visualize and maintain the architecture of their projects, and uses system interdependencies to build blueprints of large, complex systems, Sangal said.

"We use a dependency structure matrix," Sangal said. "The concept of a dependency structure matrix comes from system engineering. We can do tens of thousands of classes in a model."

Lattix LDM for Eclipse uses a dependency structure matrix to deliver a scaleable representation of an entire system. And the LDM approach gives architects and developers the opportunity to analyze their architecture, edit the structure, create what-if scenarios, set design rules and share the architecture with others.

The Lattix LDM for Eclipse plug-in also enables developers and architects to map architecture to code, test architecture and detect architectural problems while coding, and to refactor architecture.
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"Our approach is lightweight, and models do not get obsolete," Sangal said. "You can update the model mechanically."

Lattix announced its membership in the Eclipse Foundation earlier this month. Sangal said the membership and the new plug-in are a response to customer demand.

"We were driven to it by our customers," he said. "We have customers who have Java and they said they wanted to see our technology on Eclipse."

Moreover, "Eclipse customers were demanding the capability to map their application architecture to the actual code," Sangal said. "They now will have the means to test the architecture, detect violations while coding and prevent architectural erosion."

The osmotic pressure of chondroitin sulfate (CS) solution in contact with an aqueous 1:1 salt reservoir of fixed ionic strength is studied using a recently developed coarse-grained molecular model. The effects of sulfation type (4- vs. 6-sulfation), sulfation pattern (statistical distribution of sulfate groups along a chain), ionic strength, CS intrinsic stiffness, and steric interactions on CS osmotic pressure are investigated. At physiological ionic strength (0.15 M NaCl), the sulfation type and pattern, as measured by a standard statistical description of copolymerization, are found to have a negligible influence on CS osmotic pressure, which depends principally on the mean volumetric fixed charge density. The intrinsic backbone stiffness characteristic of polysaccharides such as CS, however, is demonstrated to contribute significantly to its osmotic pressure behavior, which is similar to that of a solution of charged rods for the 20-disaccharide chains considered. Steric excluded volume is found to play a negligible role in determining CS osmotic pressure at physiological ionic strength due to the dominance of repulsive intermolecular electrostatic interactions that maintain chains maximally spaced in that regime, whereas at high ionic-strength steric interactions become dominant due to electrostatic screening. Osmotic pressure predictions are compared to experimental data and to well-established theoretical models including the Donnan theory and the Poisson-Boltzmann cylindrical cell model.
Articular cartilage is an avascular tissue that provides a low-friction, protective lining to the ends of contacting bones during joint locomotion. The tissue consists of a dense extracellular matrix of aggrecan and type II collagen that is maintained by a sparse volume fraction (~2%) of cells. Aggrecan is a high-molecular-weight proteoglycan (1-3.5 MDa) that consists of a linear protein backbone (~300 [Angstrom] contour length) with ~100 covalently bound anionic chondroitin sulfate (CS) glycosaminoglycans (GAGs), as well as a smaller molecular-weight fraction of keratin sulfate GAGs and other oligosaccharides (Fig. 1) (1,2). With the aid of link protein, aggrecan associates noncovalently with high-molecular-weight hyaluronic acid to form supramolecular complexes, helping to retain it in the extracellular matrix. The high negative charge density presented by the CS chains on aggrecan generates an osmotic swelling pressure that maintains articular cartilage in a hydrated state (60-80% water by weight) even under substantial compressive loads, and plays a central role in determining its compressive mechanical properties (3,4).

The CS constituent of aggrecan varies in chemical composition depending on the state of health or disease of articular cartilage (osteoarthritis or rheumatoid arthritis), anatomical site, depth within the cartilage layer, and age of the organism (5-12). For example, the fraction of 6-sulfated CS disaccharides in human femoral condyle cartilage increases with age from ~0.5 to 0.8 from birth to the age of 20 years with a concomitant decrease in 4-sulfation, after which it plateaus. Additionally, the concentration of 6-sulfated CS disaccharides in knee synovial fluid has been observed to be significantly lower in rheumatoid arthritis and osteoarthritis than in healthy tissue (10) and the concentration of 4-sulfated CS disaccharides higher in osteoarthritic hip cartilage, with only slight changes in overall GAG content (13). Considering the important role that CS plays in determining the mechanical properties of articular cartilage and these observed variations in CS chemical composition, it is of significant biological interest to understand the connection between CS composition and its osmotic pressure and conformation in detail. It is also of primary interest to gain a comprehensive understanding of the molecular origin of the mechanical properties of GAGs and proteoglycans due to their important role in tissue engineering and biomaterials applications, as well as in other native biological tissues such as the corneal stroma and central nervous system (1,14-16).

The specific objectives of this study are twofold. First, we investigate the effects of CS chemical composition, namely sulfation type, sulfation pattern, and molecular weight, on CS osmotic pressure under physiological conditions (0.15 M NaCl) to gain insight into the potentially relevant biomechanical function of these variations. Second, we evaluate the relative roles played by intrinsic versus electrostatic CS backbone stiffness as well as steric excluded volume interactions to gain a better understanding of the molecular origin of CS osmotic pressure. The latter aim is to aid in the development and application of analytical models of cartilage biomechanics (17-19). Toward this end, we employ a recently developed coarse-grained molecular model that enables the computation of solution conformational and thermodynamic properties of GAGs (20). The model uses systematic coarse-graining from an all-atom representation of the disaccharide building blocks of GAGs to achieve computational tractability that enables the simulation of physiologically relevant system sizes while retaining the underlying chemical identity of the sugars. In our previous work, we applied the coarse-grained model to chondroitin (CH), chondroitin 4-sulfate (C4S), chondroitin 6-sulfate (C6S), and hyaluronic acid in infinitely dilute solution and studied the effects of sulfation type, ionic strength, and pH on their conformation and titration behavior (20). In the current work, we demonstrate theoretically that the model is also directly applicable to the computation of GAG osmotic pressure, and we use it to investigate mechanistically the CS chemical composition-osmotic pressure relationship. Osmotic pressure predictions are compared with experimental data of Ehrlich and others (21), and contrasted with two well-established models of polyelectrolyte solutions-the Donnan theory and the Poisson-Boltzmann cylindrical cell model. Although the ultimate aim of this line of research is to study the physiological solution conformation and mechanical properties of aggrecan, the current investigation into the solution behavior of CS is viewed as a valuable and necessary step toward that end, both for purposes of model validation and because we believe that a fundamental understanding of the solution properties of aggrecan requires a comprehensive understanding of the properties of its biochemical constituents.

Designed for system management on zSeries[R] and System/390[R], Tivoli[R] Performance Modeler for z/OS[R] v2.2 provides PC-based performance modeling and capacity planning tool that can model impact of changing number and speed of CPUs, disk I/O response times, and paging rates as well as LPAR definitions and parameter changes. Software supports modeling up to 40 workloads, processors with up to 64 central processors, and zSeries Application Assist Processors.

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At a glance

IBM Tivoli Performance Modeler for z/OS V2.2 is a PC-based capacity planning and performance modeling tool for OS/390[R] or z/OS-based mainframe computers that can be used to:

Model up to 40 workloads within a single LPAR

Model processors with up to 64 central processors
Model the IBM System z9 family of processors

Help extract zAAP specific information

Help gather, edit, and report on day-to-day workload data

Model "what-if" versus actual scenarios

Provide multiple image modeling capability

For ordering, contact:

Your IBM representative, an IBM Business Partner, or IBM Americas Call Centers at 800-IBM-CALL (Reference: YE001).

Overview

IBM Tivoli[R] Performance Modeler for z/OS[R] V2.2 is a PC-based performance modeling and capacity planning tool that runs on Microsoft Windows. It can be as portable as your PC or laptop. IBM Tivoli Performance Modeler for z/OS V2.2 is designed for system management on the IBM zSeries[R] and System/390[R] (S/390[R]).

With growing operating system complexity and the huge impact of responding to workload changes, basic Central Processor Unit (CPU) utilization is generally no longer sufficient information for performing capacity planning. IBM Tivoli Performance Modeler for z/OS V2.2 can be used to model the impact of changing:

Number and speed of CPUs

Disk I/O response times

Paging rates (auxiliary and expanded memory paging)

Logical partition (LPAR) definitions and parameter changes

New in V2.2:

Support for modeling up to 40 workloads, up from 20 workloads within a single LPAR.

Support for modeling processors with up to 64 central processors. This includes support for modeling the IBM System z9 family of processors.

Support for zSeries Application Assist Processors (zAAPs). zAAP is an optional feature for zSeries 990 and zSeries 890.

Key prerequisites

Any PC that runs Microsoft Windows 2000 or Windows XP (recommended 300 MHz, or greater)

IBM z/OS Resource Measurement Facility (RMF), or equivalent software (such as CMF MONITOR from BMC Software)

What is news? More precisely, when is news? Lately, the division has become starker between news that reports the details of past events, and "news" that is a forecast, a best guess, of the outcome of past events, or even of future events.

For some time, I have found fiction of increasingly little interest why should I care about made-up people, when real people have far more interesting lives and are, to boot, real? Much of what passes for "news" I find similarly uncompelling, because it is mere speculation. Worse by far, though, is the "news" that is speculation about speculation.

An example: A hurricane threatens--let's call it Cassandra. The TV news anchor, who has flown into the town most likely to be destroyed cuts to a guy in a sports coat with a computer screen. He is an "expert" on such matters, who confirms that when the storm hits in a couple of days, an apocalypse will ensue, with insured losses that will cause the collapse of insurance and reinsurance companies and disrupt shipping for generations.

When Cassandra takes a slight turn and misses the populated areas altogether, there's nary a change in anyone's routine. As Hurricane Katrina approached New Orleans late in August, the catastrophe modeling agencies fell over each other to forecast the estimated cost of insured losses from a storm that had not yet hit anything. On Friday, Aug. 26, three days before Katrina made its second landfall, RMS forecast insured losses at $1 to $2 billion. AIR Worldwide's estimate that day was a maximum of $600 million. Guess who made the evening "news"?

On Sunday afternoon, RMS upped the ante: "greater than" and possibly "far more devastating than" $9 billion. Monday morning, as the storm hit, EQECAT forecast losses for U.S. insurers from Hurricane Katrina of $30 billion.

By Monday evening, Aug. 29, after the worst of things, estimates were "between $10 billion and $25 billion." The hurricane, in other words, followed a more or less predictable line, while the financial forecasts were all over the map.

What public service was fulfilled by these estimates? And why were they so wildly inaccurate? The only answer to the latter question is a losing proposition: hurricanes are erratic, and impossible to forecast with any accuracy, right up to and after the event. That being the ease, why issue speculative reports containing more hot air than the hurricane itself?

The agencies' forecasts were picked up by news organizations and parlayed into dire predictions of the washing-away of the city of New Orleans by a 28-foot tidal wave. RM8 provided a statistic: New Orleans had $40 billion of insured values, and the surrounding parishes some $110 billion.

The modeling agencies shouted "Fire!" in a crowded media room. The agencies have been very kind to me in terms of access in the past, but really, they must desist from this sort of behavior. The fact is that we really won't know the true losses for weeks, maybe months.

To all the instant experts, prognosticators, seers, pundits and other purveyors of opinion who masquerade as news analysts by forecasting, I would paraphrase Bambi's mother: "If you don't have anything factual to say, don't say anything at all."

The electrical effects of dislocations has been studied by modeling zero-bias resistance-area product (R^sub 0^A) of long wavelength infrared diodes fabricated in molecular beam epitaxy (MBE)-grown HgCdTe-Si epitaxial films. Results show that dislocations influence both 40 K and 78 K R^sub 0^A products in high dislocation density (HgCdTe/Si) material. In low dislocation density samples (HgCdTe/CdZnTe), the variations in 78 K R^sub 0^A are limited by the composition (x) variations in Hg^sub 1-x^Cd^sub x^Te material, whereas dislocation contribution dominates the variations at 40 K. The origin of relatively large spread in 40 K R^sub 0^A in both types of samples is traced to the statistical variations in the core charges of dislocations. It is concluded that additional alternatives besides the reduction of dislocation density (such as control of core charges), may also need attention in order to make Si a viable substrate material for the growth of HgCdTe epitaxial layers suitable for devices operating at 40 K.

Key words: HgCdTe-on-Si, infrared detectors, long wavelength infrared (LWIR), zero-bias resistance-area productIn pursuit of developing low-cost technology to fabricate high density, large size, long wavelength infrared (LWIR) detector arrays for thermal imaging applications, recent years have witnessed considerable activity on the growth of HgCdTe epitaxial layers on Si substrates by molecular beam epitaxy (MBE) technique.1-8 Short wavelength infrared (SWIR) and mid-wavelength infrared (MWIR) arrays have been previously reported in the literature, using MBE-grown HgCdTe epitaxial layers on 4-in. (211) Si substrates.2-6 These arrays are generally operated at 77 K, where contribution of dislocations is within tolerable limits for some tactical applications. High dislocation density in the range of mid-10^sup 6^ cm^sup -2^ in these epitaxial layers has, however, prevented the realization of uniform LWIR arrays suitable for operation at 40 K for some strategic applications. Thus, present thinking appears to revolve around efforts to reduce the dislocation densities in HgCdTe/Si below 10^sup 6^ cm^sup -2^, as is the case with the HgCdTe/CdZnTe system. Given the large (19%) mismatch between the lattice-parameters of Si and HgCdTe (a^sub Si^ = 5.43 A^sup 0^, a^sub HgTe^ = 6.453 A^sup 0^, and a^sub CdTe^ = 6.48 A^sup 0^), as compared to lattice-matched CdZnTe substrates, it may not be entirely possible to match the dislocation density levels in the two systems. With such a possibility in mind, this paper proposes to explore the basic origin of the large spread of 40 K R^sub 0^A product by modeling the reported results of LWIR diodes fabricated in HgCdTe/Si epitaxial layers.

MODEL

The Rockwell group used (211) Si/ZnTe/CdTe substrates to grow HgCdTe epilayers by MBE. The structure of the active layers consisted of an n-HgCdTe absorber layer (LWIR) followed by a wider bandgap P-layer. Diodes were fabricated in double-layer planar heterostructure (DLPH) architecture by selective area ion implantation. Arsenic was implanted through photoresist windows and followed by annealing for cap layer diffusion and activation of arsenic. The diodes were finally passivated with a CdTe layer. Similar diodes fabricated on the epitaxial layers grown on bulk CdZnTe substrates were also studied for comparison. It was reported that, at 78 K, diode performances of MBE LWIR HgCdTe on Si are comparable to that of LWIR HgCdTe on bulk CdZnTe substrates, both in terms of R^sub 0^A values and their variations. However, at 40 K, comparable diode performance in terms of R^sub 0^A value is occasionally obtained due to very large variations in R^sub 0^A. In the following paragraphs, we discuss the comparison of the experimental results with the theory in both types of diodes, with the objective of tracing the origin of large variations in R^sub 0^A at 40 K.

Figure 1 shows a plot of R^sub 0^A product of small area (~10^sup -6^-10^sup -5^ cm^sup 2^) LWIR HgCdTe diodes fabricated in epitaxial layers grown on bulk CdZnTe substrates. The dislocation density in the epitaxial layers has been stated as 8 × 10^sup 4^ cm^sup -2^. The experimental data (discrete points) shown here has been taken from Figs. 4a and Ua of Ref. 8. It is clearly observed that R^sub 0^A product of the diodes exhibit a much larger spread at 40 K than at 78 K. Let us first discuss R^sub 0^A variations at 40 K, which can be explained in more than one way as discussed below.

Discussions given in the following paragraphs are based on the understanding that, at 40 K, thermal diffusion current contribution is negligibly small and that the impedance of dislocations that intersect the junction dominates the diode impedance.

Tobin et al.14 explained variations of 40 K R^sub 0^A product in a variable area diode array by assuming Poisson distribution of defects/dislocations within the base material, implying that the dislocations were nonuniformly distributed. It can be clearly seen from Eq. 1, that R^sub 0^A will be independent of diode area for a uniform distribution of dislocations. Poisson statistics were then used to calculate the probability that a diode of a given size had a particular number of dislocations. In this model, small area diodes in an array exhibited a larger spread than the larger area diodes. Though the model is able to qualitatively explain R^sub 0^A variations in a variable area array of HgCdTe diodes at 40 K, it does not appear to conform to the real-time situation encountered in practice. For example, consider the 40 K R^sub 0^A spread shown in Fig. 1. Experimental values vary by an order of magnitude from 10^sup 5^ to 10^sup 6^ ohm-cm^sup 2^. At the given dislocation density of 8 × 10^sup 4^ cm^sup -2^ in the base material, a small area diode (10^sup -6^-10^sup -5^ cm^sup 2^) can either have zero or one dislocation within the diode area, which is insufficient to explain the large spread shown in Fig. 1. In fact, an order of magnitude variation of R^sub 0^A in diodes of similar areas here demands variations in the number of dislocations (within the diode area) from 0 to 9. This is only possible if some local regions in the base material have variable dislocation densities varying up to 9 × 10^sup 6^ cm^sup -2^. In practice, this appears to be a highly unlikely event, especially when efforts are focused to fabricate uniform arrays with very high operability.

We present a coarse-grained approach for modeling the thermodynamic stability of single-domain globular proteins in concentrated aqueous solutions. Our treatment derives effective protein-protein interactions from basic structural and energetic characteristics of the native and denatured states. These characteristics, along with the intrinsic (i.e., infinite dilution) thermodynamics of folding, are calculated from elementary sequence information using a heteropolymer collapse theory. We integrate this information into Reactive Canonical Monte Carlo simulations to investigate the connections between protein sequence hydrophobicity, protein-protein interactions, protein concentration, and the thermodynamic stability of the native state. The model predicts that sequence hydrophobicity can affect how protein concentration impacts native-state stability in solution. In particular, low hydrophobicity proteins are primarily stabilized by increases in protein concentration, whereas high hydrophobicity proteins exhibit richer nonmonotonic behavior. These trends appear qualitatively consistent with the available experimental data. Although factors such as pH, salt concentration, and protein charge are also important for protein stability, our analysis suggests that some of the nontrivial experimental trends may be driven by a competition between destabilizing hydrophobic protein-protein attractions and entropie crowding effects.
Proteins in their native states play an important role in many biological processes and pharmaceutical applications. They participate in almost every aspect of the biochemical transport and regulation required for living organisms. They also serve as therapeutic drugs for targeting infectious diseases and cancer. However, most proteins, under most conditions, exhibit only marginal thermodynamic stability. As a result, minor sequence mutations or even small perturbations to solution parameters (e.g., pH, temperature, concentration, etc.) can result in protein denaturation (1).

This has important practical consequences. Unfolded or misfolded proteins look and behave differently than they do in their native states (2). They lack the highly specific molecular structure necessary for biological activity. Moreover, since unfolded proteins generally expose a significant number of hydrophobic core residues to the aqueous solvent, they have a tendency to associate and form non-native aggregates in solution. Unwanted protein aggregation and subsequent precipitation pose enormous problems in biological and pharmaceutical contexts (3,4). These processes are connected, although in a manner still imperfectly understood, to a number of debilitating diseases such as Parkinson's, Alzheimer's, Huntington's, and Down's syndrome (5-9). They are also known to cause rapid degradation of pharmaceutical formulations, reducing the shelf life of promising new drugs and restricting the strategies available for purification, handling, and delivery of therapeutics (10-15).

Given the technological and practical importance of pro tein stability, there is an urgent need to develop a generic understanding of the thermodynamic driving forces for protein unfolding, aggregation, crystallization, and phase separation. One way to facilitate this understanding is to build models that can account for, at various levels of sophistication, three vital aspects of stability for the native and denatured states: the relationship between protein sequence and structure, protein-protein interactions, and the global phase behavior of protein solutions. This is a formidable challenge because proteins are inherently large and complex molecules. Moreover, proteins encounter a wide variety of solution environments in biological and pharmaceutical processes, exposing them to thermal, mechanical, osmotic, and chemical stresses. To describe protein behavior under these conditions, one must also have a reliable method for accounting for hydrophobic interactions (16-23), which are a dominant force (24,25) in biomolecular folding and assembly events. These interactions have been particularly challenging to model because they exhibit subtle dependencies on both the state of the solution and the size and shape of the participating solutes.

Although each of the aforementioned aspects of protein stability have been long appreciated, theoretical investigations have focused more on their independent study than on devising strategies for integrating them into a single model. For example, models developed to investigate the single-molecule protein folding problem (26-30) are almost exclusively too complicated to be extended, either theoretically or via computer simulation, to investigate the collective behavior of thousands of proteins and millions of water molecules in solution. On the other hand, many recent theoretical models introduced to study the thermodynamics of crystallization or liquid-liquid phase separation in protein solutions (31-40), although insightful in many respects, do not consider sequence information, the polymeric character of the individual proteins, or the possibility of protein unfolding. Despite the development of some powerful coarse-grained models that address some of these issues (41-60), theoretical methods that can provide a comprehensive understanding of the protein stability problem are still lacking.