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Medium 9780596003234

4. Users, Passwords, and Authentication

Slice ePub May 27, 2014

Good account security is part of your first line of defense against system abuse. People trying to gain unauthorized access to your system often try to acquire the usernames and passwords of legitimate users. After an attacker gains initial access, he is free to snoop around, looking for other security holes to exploit to attain successively higher privileges. Its much easier to compromise a system from a local account than from outside.[30]

Because most internal users are not malicious, many systems have better defenses against outsiders than against authorized users. Accordingly, the best way to keep your system secure is to keep unauthorized users out of the system in the first place. This means teaching your users what good account security means and making sure they adhere to good security practices.

This chapter explains the Unix user account and password systems. Well explain these basic concepts, discuss the mechanics for picking and maintaining a good password, and finally show you how passwords are implemented in the Unix environment. In Chapter 19, well describe in detail how to protect your accounts from many different types of attacks.

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Medium 9781930538757

7 Planning Your Study: Quantitative Research Designs

Slice ePub May 26, 2015

“Design is not just what it looks like and feels like. Design is how it works.”

–Steve Jobs

Christine Hedges


• Good research questions will determine the design you choose for your study.

• Two broad categories of quantitative design are experimental and non-experimental. Myriad research designs exist within each category.

• Assuring validity is important when designing a quantitative study.

• Staff nurses who are designing quantitative studies should consider various aspects of the their study and consult with an experienced researcher before deciding upon a design.

A finished product appears so seamless. When you attend a symphony, the sublime tones reach your senses in perfection, never hinting at the hours of orchestral rehearsal and preparation that came before. Likewise, your excellent nursing care appears effortless and expert to your patient—the patient does not see your educational preparation, nursing care plan, or practice guidelines that prepared you to provide expert care.

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Medium 9781449356439

2. DIT (Do-It-Together)

Slice ePub June 15, 2015

I thought I was pretty original: starting from the very beginning, getting back to the basics, and really trying to understand how things are made. But about three months into my Zero to Maker journey, I came across a story that made my approach and experience seem pretty tame. I learned about Thomas Thwaites and his heroic attempt to build a toaster from scratch. He started with the rawest of materials—copper, iron ore, melted plastic—and set out to end up with the cute little appliance that graces many a kitchen counter.

His story began in 2008 when Thwaites, then a student at the Royal College of Art and Design in the United Kingdom, first hatched his now infamous Toaster Project.[3] His inspiration was a line of science fiction from Douglas Adams’ Mostly Harmless, one of the Hitchhiker’s Guide to the Galaxy installments:

Left to his own devices he couldn’t build a toaster. He could just about make a sandwich and that was it.

The presumption here is that we are looking at a bemused human being on a distant planet, with outsized expectations to civilize low-tech species that inhabited the world. The hero, however, quickly realizes that without the support of the entire human species, he cannot muster the technological know-how to accomplish the feat of creating a toaster.

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Medium 9781449310646

7. Resolution, By the Numbers

Slice ePub May 27, 2014

Assume an ideal detector. Ideal = perfect 100% fidelity; thus it only returns data intrinsic to source with no noise, has perfectly square pixels, and there are no optical defects, lens flare, etc. That is, its the sensor equivalent of physics frictionless vacuum.

Your target is a star with a possible exoplanet. Your detector receives 52 photons. We presume thats what your detector of a given size captures for the entire exposure. What happens when we try to catch it with different imaging detectors? Remember, no matter how we slice it, we only get 52 photons.

Those 52 photons are incident on a single detector (say, 1cm1cm). It is divided in this example into pixels. Each pixel is like a little bucket that collects the photons. We visualize the pixels shown in Figure7-1.

Figure7-1.Four detectors, each covering the same area, but with increasing spatial resolution

Figure7-2 shows a 22 pixel image. Figure7-3 shows a 44 pixel image.

Figure7-2.22 pixel image

Figure7-3.44 pixel image

Table7-1 shows the number of photons in a 22 pixel image.

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Medium 9781591202264

9. Minerals

Slice ePub July 14, 2014


There is a wide variety of minerals present in the body. It would be surprising if there were not, since life originated in the seas, which contain almost all the minerals. It would require too much of the cell’s energy to keep its interior free of minerals, while it is energy-conserving to incorporate minerals into enzyme reactions that could coordinate with the protein molecules. Minerals present in the greatest amounts in the primitive seas would most likely have been used, while very rare elements would play a minor role. Theoretically, every mineral element could have been used, with each having an optimum range, playing the role life had shaped for it.

When the optimum range is very close to zero, these elements are needed in trace amounts. When the optimum range is greater, milligram and gram amounts are needed. The optimum is determined by the ease with which these elements can be eliminated and by the presence of mechanisms developed to deal with them. For example, copper is required in doses of 2 milligrams (mg) per day; less than this will cause a deficiency, and much more will cause copper toxicity. Zinc is required in doses of 15 mg per day; less will result in a deficiency, but as zinc is water-soluble and easily excreted, the body can tolerate fairly large amounts. A man needs 10 mg of iron a day. Giving 20 mg a day for many years may cause a problem for a man, but a woman needs 20 mg a day as she loses iron with her menstrual periods.

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