Garbage In, Garbage Out

1. Garbage In, Garbage Out • Garbage In, Garbage Out (abbreviated to GIGO) is a phrase in the field of computer science or ICT. It is used primarily to call attention to the fact that computers will unquestioningly process the most nonsensical of input data and produce nonsensical output, and is a pun on FIFO (First In, First Out). It was most popular in the early days of computing, but applies even more today, when powerful computers can spew out mountains of erroneous information in a short time. The actual term "Garbage in, Garbage out", coined as a teaching mantra by George Fuechsel, an IBM 305 RAMAC technician/instructor in New York, soon contracted to the acronym GIGO. Early programmers were required to test virtually each program step and cautioned not to expect that the resulting program would "do the right thing" when given imperfect input. The underlying principle was probably cited by Charles Babbage, inventor of the first programmable device, who said: • On two occasions I have been asked,—"Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" [...] I am not able rightly to comprehend the kind of confusion of ideas that could provoke such a question.[1] • From Wikipedia, the free source of all true and perfect knowledge • Charles Babbage, FRS (December 26, 1791 London, England – October 18, 1871

2. 4.10 At% Pb Same data as following slide

3. Does anyone see a problem here? 12.78 at% Pb Same data as previous slide

4. Oops!

5. If contrast and Brightness are set to zero and the screen is pure, white...

6. Feedback on Labs 5/6 “Vapor pressure” is a “reserved term” Refers to the pressure of a vapor in thermodynamic equilibrium with a condensed phase of the same material Will be discussed at length next week Vapor: “…a substance in the gas phase at a temperature lower than its critical temperature.” Wikipedia Critical temperature of water is 374 C Critical temperature of nitrogen is -147 C

7. Feedback on Labs 5/6 “Affect” is always a verb • “Changing the probe current affects the probe diameter.” • If you use “effect” as a verb, you are most likely using it incorrectly. Assume it is always a noun. • X-rays interact with electrons in solids via the Photoelectric effect. • Forgetting to turn on the HV has a profound effect on your image. • “Effect” as a verb means “to cause”. If you never use “effect” as a verb, you will be safe.

8. Spot size ≠ probe diameter! • “The actual focused area of the electron beam on the specimen is referred to as the spot size. Both the focused beam area and the beam current increase with Spot Size.”

9. Feedback on Labs 5/6 • “…it is possible to flood the chamber with ionizable gas, which interacts with the charging layer, thus providing a path to ground [1].” • [1] FEI Powerpoint presentation • Students reported that beam scattering in LowVac degrades image quality • Helix detector • WD < 1 mm! • Runs in immersion mode • Killer images at 500kX

10. Gold on glass with Helix detector Nominal precision is 3%. How many digits do you get? Resolution is 1.6 nm

11. Feedback on Labs 5/6 • “We also varied the kV between 2 and 5.” • Let’s discuss the concept vs. the units. • To establish a causal relationship you may change only one parameter at a time. • New failure mode: screen completely white when you first start up • Still white at zero contrast and brightness • Look under the processing page • Somebody has left the “display” option on “Inverse”

14. Flat: Not tilted Smooth on micron scale How many significant figures? Backwards: Accuracy should be ± 1-2% Precision 1-2%

16. Limits

17. What do you expect to see? What elements can you rule out? (“Peak ID” can find some amazing stuff!)

20. (Standard) Sample

25. ZNi > ZFe

28. Corrections are an iterative process: taking one component into consideration affects others

39. Absorption

42. We are experimentalists! Try both on known materials; which gives most accurate answer?

45. n.b.

46. n.b.