PHLB09H3 Chapter : chp 6.docx

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17 Apr 2012

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Human research has lead to great advancements and disagreements among philosophers and scientists. On one side, human research has led to the development of medical science why the development of vaccines and treatments for polio, measles, yellow fever, hepatitis, and others. On the other side it has also led down to some dark paths: nazi experiments, tuskegee study, radiation and children. To deal with such problems among human research numerous codes of ethics outlined on principles governing human research or clinical trials: the nuremberg code, declaration of helenski, the belmont report. A human research or a clinical trial is normally an intervention of a drug or a treatment procedure to determine the best possible effect. Clinical trials can derive reliable answers because they are carefully configured, minimize bias and avoid errors. A typical clinical trial consists of two groups: control group and the experimental group. The control group is further divided into placebo control group and active control group.

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A stent is a small, tubular device implanted into arteries orsome other hollow organ in order to provide structural supportagainst collapse. Some modern stents can even provide gradual drugdelivery. Clinical failures are some of the most serious reasonsfor continual R&D into stent improvement. Models are anindispensable part of further research as experimental testing isoften expensive and time-consuming. For example, a stent with a10-year life expectancy corresponds to approximately 400 millioncyclic loadings from heartbeats!

A common design for a stent is a hollow woven mesh of helicalwire, as shown in the above figure. Much like Chinese finger traps,a change in length is accompanied by a corresponding change inradius of the stent. The goal of this problem is to examine howthis deformations are coupled.

(a) Letâs start out by looking at a single helix of wire.Convince yourself that we can parametrize the curve of the wireby:

x(Î¸) =rcosÎ¸

y(Î¸) = rsinÎ¸

z(Î¸) = (lÎ¸/2Ï)sinÎ±

where r is the radius and Î± is the âlead angleâ of the helix -the angle the wire makes with the xy-plane as it crosses it, and lis the length of wire in one turn of the helix. Determine thislength of wire l in one turn of the helix by using l =â« ds withappropriate bounds, where ds =â(dx²+dy²+dz² ). Express l in terms of rand Î±.

In research in cardiology and exercise physiology, it is often important to know the mass of blood pumped by a person's brain in one stroke. This information can be obtained by means of a ballistocardiograph. The instrument works as follows: The subject lies on a horizontal pallet floating on a film of air. Friction on a pallet is negligible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed v, and the body and platform move in the opposite direction with speed V. The speed of the blood can be determined independently (e.g., by observing an ultrasound Doppler shift). Assume that the blood's speed is 50.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves at a speed of in 0.160 s after one heartbeat. Calculate the mass of the blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. This simplified example illustrates the principle of ballistocardiography, but in practice, a more sophisticated model of heart function is used.

lemondinosaur475

Theory: Topics that you should be familiar with are: significantfigures, least count and estimated fraction, systematic and randomerrors, accuracy versus precision, percent difference and percenterror. These topics should have been covered in class already (orperhaps in an introduction to the lab manual or in a handout). Itis assumed that the instructor has discussed how to use the massbalance, etc.
Introduction: The goal of section I of this experiment is tomeasure (to the correct least count and estimated fraction) andcalculate (to the correct number of significant figures) thedensity of a metal ball and compare it to a table of accepteddensities (?=7.8x103 kg/m3).
To accomplish this goal keep in mind that: ? = m/V and Vsphere =(4/3) p r3
In the space below create a data table, show your calculations indetail, and compare your measured answer to accepted values givenabove. (Would you calculate a percent error or a percentdifference?)
1
II. Is g (the acceleration due to gravity) a constant? If so, whatis it?
1) SetuptheFree-FallApparatusasdemonstratedbytheinstructor.
2)MeasurethetimeittakesforthemetalballtofallthroughthesuggesteddisplacementsshowninDataTable 1. Be sure to do 4 trials for each fall and take the averageof your time and displacement. For each trial measure thedisplacement and record your results as precisely as possible. Becareful how you measure the displacement!
Data Table 1
Displacement (meters) Time
Trial 1
___.40___ m .281 s
______.40_ m .284 s
___.40____ m .283 s
____.40___ m .285 s
Average Displacement =.40 m Average time .0285 s
Trial 2
____.60___ m .357 s
____.60___ m .358 s
_____.60__ m .347 s
____.60___ m .347 s
Time (seconds)
Average Displacement = .60 Average Time = .352
Trial3
_.80____ m .402 s
_.80____ m .401 s
_.80______ m .402 S
_.80___ m .401 s
Average Displacement = .80 m Average Time =.401 s

Trial4
__ 1.00____ m .454 s
___1.00____ m .453 s
___1.00____ m .463 s
___1.00____ m .453 s
Average Displacement = 1.00 m Average Time =.455 s
3)PlotDisplacement(usetheaveragedisplacement)asafunctionofTime(usetheaveragetime)usingacomputer software that you know the best. (Does Displacement orTime go on the âverticalâ (or y) axis? Make sure that you label theaxes of your graph properly and give the graph a descriptivetitle.), Please include (0,0) point.
4)UsetheCurveFitFunctiontotrytofindthecurvethatistheclosestfitforthegraph.Whichofthefollowing curve types gives the best fit? Try each to findout.
a) linear fit? b) quadratic (power 2)? c) exponential? d) Power?
The curve with the correlation coefficient (R) closest to 1 has theclosest fit. (e.g. 0.997 is better than 0.956)
5)Printthecurvewiththeclosestfit(oneforeachmemberofthelabgroup).Besureyourgraphincludesthe equation for your fit.
6)Canyoudeterminetheexperimentalaccelerationofgravityfromthisgraph?Explainhowandshowyourwork.
7)Ifalinearfunctionisnotthebestfitofyourplotfromstep3),howwouldyouplotdisplacementandtimeso that the resulting plot is linear? Explain. (Ask your instructorfor a hint if you are not sure of what to do, but be sure to thinkabout it for a while before you ask.)
3
8)Printacopyofthegraphforeachlabpartnershowingalinearfittoyourdataandproperlylabeledaxes.
9)Canyoudeterminetheexperimentalaccelerationduetogravityfromthisgraph?Explainandshowyourwork.
10) How do your experimental values of âgâ compare with theaccepted value (g = 9.80 m/s2) for the acceleration of gravity?Give a mathematical comparison using what you learned aboutmeasurements previously. (Show work)
4
Question and further procedures
1. What is the greatest source of error in performing theexperiment? Is this error random or systematic? Explain.
2. At this point you should have calculated g in two different ways(A quadratic graph, and a linear graph). Which technique do youthink is best? Do all two techniques give the same answer? If not,which technique do you think has the most error?
3. How might you modify your procedures to determine whether or notg depends on the mass of the falling object? Do the experiment andcalculate g using your favorite technique.

PHLB09H3 Chapter : chp 6.docx

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