WPT-R basics - Wonderlic Personnel Test Updated: 2023

Welcome to the ME 270 course website for the Fall 2023 term. The material on this site is a complement to the lecture book for the course. And, all material here is accessible without the need to log in. Please review the resources that are available to you in the links on the left sidebar of the page. Logging in is required only for adding comments to the blog posts. Read me for instructions in logging in to the website. 

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When you’re starting out in astrophotography, the myriad technical terms can be daunting. Gain? Offset? Flat darks — or is it dark flats? Let’s clear up some common areas of confusion.

We’ll start with gain. Setting the gain value affects a camera’s electronic gain, which is reported in electrons per analog-to-digital unit, or e–/ADU. A common belief is that adjusting the gain changes the sensitivity of the camera. However, it’s more accurate to say that it changes the way the camera quantizes light as it converts photons into a digital signal.

A camera sensor converts photons to electrons, which are then collected and read out at the end of the exposure. The amount of charge is converted to digital units of pixel brightness, from black to white. The scale depends on the camera’s bit depth: A 12-bit sensor has a range of 0 to 4,095 ADU, while a 16-bit sensor has a range of 0 to 65,535 ADU. Shooting at unity gain means 1 electron = 1 ADU. At low gain, it will take multiple electrons to add 1 ADU to a pixel’s total count. At high gain, each electron adds multiple ADU to that pixel.

A higher gain reduces the well depth, or how many electrons it takes to saturate the pixel. This gives the appearance of higher sensitivity and allows for shorter exposures at the expense of dynamic range — the range of brightness values the camera can record in a single shot. Lower gain allows you to use the full well depth of the pixel, making smaller gradations between brightness values and thus increasing contrast and dynamic range; however, you lose signal when not enough electrons accumulate to step one whole ADU. If you’re not sure where to start, unity gain is a good compromise.

Offset is the amount of charge that is preloaded into the pixels to prevent them from reporting zero. This avoids losing any small amount of signal. There is not necessarily an optimum offset, but you do need to determine how large an offset is sufficient. At your camera’s shortest exposure setting and while covered, adjust the offset until the histogram curve separates from the left edge of the histogram, indicating that no pixels are reporting zero.

Dark calibration images help reduce the noise that accumulates from heat and electronics during a long exposure. This can’t remove the random shot noise — the statistical noise inherent to capturing low numbers of photons. But it can reduce fixed-pattern noise (caused by variations in pixel response, leading some pixels to consistently read brighter or dimmer) and hot pixels (defective pixels that read much too bright).

To create a master dark, cover the camera and take at least 10 shots with the same exposure time, camera temperature, gain, and offset as your light frames. The camera does not need to be on the telescope. I usually take 50 to 100 darks for better statistics, as you will be averaging (stacking) the frames to create a master dark. I keep a darks library for different temperatures and settings. (Bias frames are no longer necessary for today’s modern CMOS cameras, and can actually cause problems instead.)

Flat frames correct for vignetting (darkening of the corners) and dust spots. These don’t need to be taken at the same temperature nor exposure time as your light frames, but they do need to be at the same gain and offset, and the camera must be on the telescope in the same orientation and focus. A properly exposed flat image should have the histogram peak roughly centered. For color cameras, it can be difficult to get all three red, green, and blue peaks in the center; just make sure they are not falling off the left or right sides of the graph. Adjust the exposure time to change the histogram peak location.

Flat darks are dark frames for your flats — just like you use a master dark to calibrate your lights. These are not always necessary, but if you experience problems with flats appearing to overcorrect your lights, try calibrating your flats with flat darks. These, like dark frames, can be taken off the telescope if necessary, and should be around the same temperature and have the same exposure time as the flats.

Now that you are armed with knowledge of common astrophotography camera terms, you are ready to take great astrophotos. Bring on the photons!

Salmiak, a Scandinavian salt licorice, is definitely an acquired taste. Sometimes the confection is a little sweet, but often it’s this unique (if slightly addictive) combination of bitterness and salinity, a flavor profile so distinct that it helped inform a major scientific discovery. 

For decades, the scientific and culinary communities have recognized five basic tastes: salty, sweet, sour, bitter and umami. However, researchers from the University of Southern California Dornsife College of Letters, Arts and Scientists believe that there may be one more called ammonium chloride, also called salmiak salt, which happens to be the ingredient that gives salmiak its signature salted pucker. “If you live in a Scandinavian country, you will be familiar with and may like this taste,” USC Dornsife neuroscientist Emily Liman said in a release. 

Liman and her team of researchers published their findings earlier this month in the journal “Nature Communications.” They wrote in the introduction to the study that ammonium — and its gas, ammonia — are generally noxious to humans and other animals. High tissue concentrations of ammonium found in conditions, such as hyperammonemia, can be life-threatening. 

“Thus, it is not surprising that animals from the nematode C. elegans to fruit flies and humans have evolved multiple mechanisms to detect ammonium/ammonia,” they wrote. “Ammonium has a unique and strong taste, described as a combination of bitter, salty, and a little sour.” 

For decades scientists have known that the tongue responds strongly to ammonium chloride, but weren’t sure which receptors were responsible for being able to do so. Liman and her team, which includes scientists from the University of Colorado Medical School, theorized that the same protein that detects sour tastes, OTOP1, might respond to ammonium chloride, too. 

According to a release from the university, the researchers tested this hypothesis by introducing the OTOP1 gene into lab-grown human cells. Some of these cells were then exposed to acid and ammonium chloride and “the results showed that ammonium chloride activated the OTOP1 receptor just as effectively as acid.” 

“Further tests on mice confirmed that those with the OTOP1 gene avoided ammonium chloride, while those without it didn’t mind the taste,” the release continued. 

As this finding would indicate, many animals, including humans, find the taste of ammonium chloride to be aversive — but as the popularity of salmiak would indicate, that’s not universally the case. 

“While no one knows what twisted soul was the first to add NH4CL, ammonium chloride, to licorice root extract and sugar, some suspect old-time pharmacies used the salty compound for housemade cough syrups, as it is powerful enough to clear your sinuses,” wrote Andrew Richdale for “Saveur.” “By the 1930s, licorice bits loaded with the expectorant had blown up across and beyond the Nordic region, including Holland, the world's largest consumer of the treat. The tang of salmiak is so popular in the region today, it's used to flavor pastries, tobacco packets, and even meat dishes.”

So, what will it take for the scientific community at large to sign on to the idea of another basic taste? If it’s anything like umami’s ascension to the group, the answer may simply be time. 

In the early 1900s, a chemist named Dr. Kikunae Ikeda of Tokyo Imperial University observed there was a quality in Dashi — a clear, savory stock made from kombu and dried bonito flakes — that was distinct from the other four basic tastes: sweet, salty, bitter and sour. Ikeda said that the flavor is “usually so faint and overshadowed by other stronger tastes that it is often difficult to recognize it unless attention is specifically directed towards it,” however it could not be produced by any combination of the other four basic tastes. 

Eventually, Ikeda found that the taste, which he called “umami,” was made of glutamate, an amino acid that is one of the building blocks of protein. With his newfound knowledge, Ikeda went on to found the company Ajinomoto and started mass producing the food additive monosodium glutamate or MSG. However, the broader scientific community didn’t begin to recognize umami as a discernible taste until the mid-1980s, nearly eight decades after Ikeda’s original findings. 

Through the years, other research teams have advocated for yet other tastes to be added to the Big Four (now the Big Five with the addition of umami). In 2016,  Juyun Lim at Oregon State University in Corvallis posited that humans could taste the “starchiness” associated with carbohydrate-rich foods. “Asians would say it was rice-like, while Caucasians described it as bread-like or pasta-like. It’s like eating flour,” she told The New Scientist. 

A year prior, a paper published in the journal “Chemical Senses” argued that we were missing another basic taste called oleogustus, or the unique taste of fat. One of the study authors, Richard D. Mattes, told TIME that while there is no single definition of what makes something a basic taste, for it to be recognized by other scientists, it really  needs to meet several categories. According to him, “the stimulus should have a unique structure, it should bind or interact with a unique receptor, it should be carried by the taste nerves to the central nervous system where taste information is decoded, and it should have a particular function.” 

For now, the scientists behind the ammonium chloride study plan to explore the OTOP1 receptor’s response to ammonium chloride, hoping to uncover more about its evolutionary significance.

Editor’s note: Consultant Bill Tobin of WJT Assoc. spends his time helping molders diagnose molding problems, and offers his comments on some basics of cooling your molds.

It isn’t rocket science to understand that a mold is really a heat exchanger. The heat you put into the plastic to melt it must be removed enough not to shrink or warp a part. Most people put in 7/16-inch-diameter waterlines. Why? Two rules of thumb:

• The drill size for a 1/4-inch pipe tap is 7/16 inch, which allows you to put in the quick disconnect nipple without having to redrill the hole in order to tap the threads.
• Waterlines control heat within three diameters of themselves. The 7/16-inch size is a happy medium between many small lines and the fact that larger lines don’t particularly increase the heat exchange benefit. With a minimum of 1.5 gal/min through this circuit we will get turbulent flow—the optimum cooling situation.

Yet, simply having the right diameter waterline is only one of the three elements of good cooling. Assume you have a thin tube-shaped part, about 3 inches long. One end has an ID of 1/4 inch and the lower end is about 3/4 inch in diameter. A good tool designer, moldmaker, or molder would immediately say these cores should probably be made of P-20 or beryllium copper. (While on its face many people would reject beryllium copper because of its insufficient hardness, accurate developments have allowed this metal to be almost as hard as P-20.)

Cooling the Core
With the core cut to configuration, we now need to cool it (our second element). Conventional cooling choices are either a baffle or a bubbler. Here is where most people tend to fall into a trap. If the water is directed up the tube with the bubbler or on one side with a baffle we still have to maintain the cooling characteristics with turbulent flow. We must be sure our bubbler or baffle is not so constrained that the entire system is strangled and turbulent flow stops.

The next concern with this insert is proximity. If we can’t get the water close enough to the heat, it won’t make any difference if it’s turbulent or not. This is especially a problem with thin protruding cores. If you can’t get the waterline near the source of heat, bring the heat to the waterline. This is done with the use of gas pins—hollow pins that contain a low-boiling liquid (sometimes Freon). One tip of the pin is heated, and it immediately transmits the heat to the other end of the pin, which should be located in the middle of the waterline.

Managing Heat
Two other important factors are where to put waterlines, and how to hook them up. Nearly everyone cools the cores and cavities, but the most common mistake is not getting sufficient cooling to the runners, sucker pins, stripper plates, and (most importantly) the sprue—whether it is a hot runner or conventional design. Anywhere there is heat it should be managed. If you have a stripper plate on the ejector side with sucker pins holding the runner and it is not cooled, it’s just a matter of time before (1) it heats up and starts galling the pins because of thermal expansion, or (2) the sucker pins are so hot and the plate is so warm that the runner will not stick to the sucker pins and will come off the plate like a wet noodle.

Internal looping should be serial. The water circuit should be able to enter the mold and find its way out again without splitting into separate paths. When water circuits are split internally in the mold, turbulent flow can be measured on the in and out, but how do you know this is what’s happening in the mold? Water will always take the path of least resistance. Therefore, if there is a parallel circuit but one leg is constricted and the other isn’t, the water will have a tendency not to flow into the restricted portion.

Parallel circuits, which are a form of an internal manifold, should be avoided at all costs. The machine manifolds work because they are usually fed by 2-inch or larger lines. So long as the plant water can maintain the pressure, the parallel machine manifold will deliver pressure to each line equally. Bringing a waterline to the mold and then making a small manifold or splitter to allow that one line to be split into multiple lines will only work if the pressure and flow out of your mini-manifold is equal to the pressure of the line in.

While this is possible, it is also difficult. If you must have a manifold on the mold, put it on externally with large pipes as the inlet, and split it into smaller lines to the mold so that the circuits can be balanced before the handles of the valves are taken off and welded into place.

Waterlines and water circulation in a mold are easy. However, simple oversights like the ones mentioned here can turn the best mold into a loser.

Look at your machines and molds. It is interesting to note that most machines come with undersized manifolds, which usually require looping. There is even a philosophy in some shops where, if the manifolds have only four inlets and outlets per side, the tool will be specified as built with no more than that number. This constriction brings some interesting challenges to the moldbuilder. And for the molder, mold setup often ends up looking like a can of worms with external splitting manifolds, jumpers, and waterlines all over the mold.

Have your intern do some interviews with the setup crew. Look specifically for how much time is wasted and how often the mold setup is delayed looking for the right length waterline. Either the techs cannot find the right length or the current hose is worn or leaking and therefore useless. Find the average time per setup. Find the cost in lost production per hour. Multiply these two numbers together. This is the average loss of money per job. Have the intern find out how many times molds have been hung in the past year and multiply that figure by the average loss. Many will find this number is a semifantastic amount of lost money and machine time.

Now have your intern do a simple study. Usually waterlines can be classified into four categories: long, medium, short, and jumpers. Have the intern measure as many lines as possible and these categories and lengths will become glaringly apparent. Here’s the tricky part. Color-code your hoses. For example, red is long, blue is medium, black is short. Any worn or leaking hose is cut down to a good section and is recycled into a jumper.

Setup sheets can now become easier by identifying the number of long, medium, short, and jumpers for each mold. These are now color-coded and easier to locate. If a particular length is not available, it can be taken off another press that isn’t using it. Also, keep in mind that waterline hose is embarrassingly cheap compared to the downtime.

A second project is another exercise in dispelling silliness. Spend a few hundred dollars and buy a set of manifolds with more outlets. With a mold in the press that is looped, have the intern measure the flow of the water in gal/min, and note the scrap and cycle time for a typical run. Install the new manifolds without looping. Instead, hook up as many direct circuits as possible to the manifold. Take the same measurements the next time this same mold is run. The results will be dramatic. The scrap will go down, and the cycle time will shorten. Technicians will learn that any time there is a loop where there could be a direct circuit, a penalty will be paid in terms of productivity.

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