Repeated experiments

In analytical chemistry, a number of identical measurements are taken and then an error is estimated by computing the standard deviation. With computational experiments, repeating the same step should always give exactly the same result, with the exception of Monte Carlo techniques. An error is estimated by comparing a number of similar computations to the experimental answers or much more rigorous computations. 

Fatigue. Engineering components often experience repeated cycles of load or deflection during their service fives. Under repetitive loading most metallic materials fracture at stresses well below their ultimate tensile strengths, by a process known as fatigue. The actual lifetime of the part depends on service conditions, eg, magnitude of stress or strain, temperature, environment, surface condition of the part, as well as on the microstmcture. 

A major difference between extrusion and IM is that the extruder processes plastics at a lower pressure and operates continuously. Its pressure usually ranges from 1.4 to 10.4 MPa (200 to 1,500 psi) and could go to 34.5 or 69 MPa (5,000 or possibly 10,000 psi). In IM, pressures go from 14 to 210 MPa (2,000 to 30,000 psi). However, the most important difference is that the IM melt is not continuous it experiences repeatable abrupt changes when the melt is forced into a mold cavity. With these significant differences, it is actually easier to theorize about the extrusion melt behavior as many more controls are required in IM. 

Collisions in the gas phase, whether they result in a reaction or not, are timed somewhat uniformly. In solutions, however, solute pairs undergo multiple collisions within a solvent cage. Once two solute species are in one cage, they are likely to remain neighbors for some time, during which they experience repeated collisions. 

Phase cycling As employed in modern NMR experiments, repeating the pulse sequence with all the other parameters being kept constant and only the phases of the pulse (s) and the phase-sensitive detector reference being changed. The FIDs are acquired and coadded. The procedure is used to eliminate undesired coherences or artifact signals, or to produce certain desired effects (e.g., multiple-quantum filtration). 

Consensus guidelines indicate that inhaled corticosteroid therapy should be considered for symptomatic patients with stage III or IV disease (FEVj less than 50%) who experience repeated exacerbations despite bronchodilator therapy. 

Ketamine is rapidly metabolized by the body, so the hallucinogenic effects of ketamine wear off within an hour or so after taking the drug. However, users say they often experience repeated flashbacks, or sudden memories of the visions or feelings experienced while on the drug. These flashbacks can persist for days, weeks, months, or even a year after a particular trip. 

The experimental setup consists of two coaxial tubes (Fig. 4.6) [18], one of which, e.g. the inner one, containing a solution of an inert probe substance and the paramagnetic solute, and the other containing a solution of only the inert probe substance in the same solvent. The shifts of the probe substance differ in the two solutions, and two different signals are observed. Their chemical shift separation is measured, and the experiment repeated with the same solution in the outer... 

Fig. 9. IR spectra of increasing doses of ethylene oxide adsorbed at 298 K on fully dehydrated MgO [experiment repeated on the basis of Zecchina and Stone (259)].

A mass, m, of adsorbent (weighing w0 in vacuum) is now introduced and the experiment repeated using the same amount of gas. If adsorption is detectable at the given T, p, the volume V will usually be less than V° and the apparent weight of the adsorbent will increase from w° to w. 

For the pituitary hormones, and pancreatic hormones, analytical methods are in general available with species specific reagents for the mouse, rat, dog, pig and to a limited extent for rabbit. Steroid hormones can be measured readily by an array of analytical methods. Application of gene arrays and studies on gene expression are not recommended for single-dose experiments, repeated dose exposure is required (3-7 days). 

Do further experiments. Many scientists test the generality with experiments, repeating each other s woik and doing other experiments related to those. 

When we have the possibility to obtain the real residual variances (2-3 experiments repeated in the Dj and D2 blocks), we can suggest to validate the following hypothesis abc = abc = is rejected, we can conclude... 

Similarly the instruments of chemistry must be simple, so that their changing power is easy to understand and apply. In short, Boerhaave s rules make experiments repeatable. The results of Boerhaave s chemistry will approach truth, for if an experiment has the same result at all times it must be true. It follows that the chemist can form a judgement based on a thorough knowledge of particulars. Boerhaave argued ... 

Typically, in cases where some minor impurity is isolated instead of the expected product, the whole stuff is washed into the waste and the experiment repeated with purified reactants and greater control over the reaction conditions. If Pedersen had followed this pattern of behavior (especially because product 214 was unable to complex the cation and therefore useless from the viewpoint of the initial practical request ), he probably would never again have had the chance to go to Stockholm to receive the Nobel Prize subsequently awarded to him (together with Donald Cram and Jean-Marie Lehn) in 1987. Fortunately, peculiarities displayed by 214 did not escape Pedersen s attention. In fact, while ether 214 was only slightly soluble in methanol, its solubility increased dramatically in the presence of sodium hydroxide. Additional tests showed that this effect was not base dependent and could be observed with many sodium salts, as well as with many other salts of inorganic cations. Even more intriguing was the observation that inorganic salts which were... 

Over 90% of individuals who have one manic episode will have additional episodes. And approximately 60-70% of manic episodes occur just before or after periods of major depression. While this may paint a rather bleak picture, it should be noted that some experts hold that while up to 40% of those with bipolar disorder will experience repeating cycles, they rarely experience long-term physical or mental impairment. And most people with bipolar disorder have periods with almost no symptoms in which they essentially function normally. 

Gaussian distribution A symmetrical bell-shaped curve described by the equation y = Aexp(—The value of x is the deviation of a variable from its mean value. The variance of such measurements (the square of the e.s.d.) is fl/2. In many kinds of experiments, repeated measurements follow such a Gaussian or normal error distribution. 

Dilute 1 c.c. of this aniline solution with 10 c.c. of water, and add a small quantity of a filtered water solution of bleaching powder. A violet colouration takes place by this reaction (Runge s), the most minute quantity of free aniline may be detected. If in this experiment the solution should not remain clear, but a dirty violet precipitate separate out, a too concentrated solution has been used the aniline water is diluted further, and the experiment repeated. If a salt of aniline is to be tested, it is dissolved in water, treated with alkali, the free aniline extracted with ether, this latter evaporated, and the residue dissolved in water. Then proceed exactly as just directed. 

If even after long standing an abundant separation of crystals does not take place, the cause is probably due to the large percentage of anhydride in the fuming sulphuric acid. Under these conditions it is diluted with concentrated acid, and the experiment repeated. If on the other hand the acid is too weak, the benzene will not dissolve in it. In this case, during the sulphonation the mixture is not cooled, and the reaction is allowed to take place at 40-50°. 

For comparison the titanium electrodes were replaced with graphite electrodes and the above experiment repeated under the same conditions with fresh and pure methanol in the three-necked flask. After arcing for 10 min and after filtration the solution obtained was analyzed by HPLC-DAD. The polyyne C8H2 was by far the most abundant molecular species detected followed by C10H2 and CgHo. The polyyne C12H2 was present in detectable amounts. The other byproducts, essentially PAHs, were present in trace amounts relative to C8H2. Naphthalene and acenaphthalene were identified. 

The above buffer mixture was diluted to one-tenth its concentration and the experiment repeated. The pitnus. b.p.b. was found to be 9.09. 

A special situation arises frequently in "X, "Y correlations with a transition metal nucleus whose low receptivity enforces an indirect detection scheme, and the very large shift range of the metal must thus be covered in FI. In order to determine the chemical shift with sufficient accuracy in a short time, the measurement is normally carried out in two steps. First, a rough estimate of S( "Y) is determined by acquiring a spectrum with a small number of tj increments and a large fl spectral window. The Y-carrier frequency is then set near on-resonance, and the experiment repeated with a reduced spectral width, which allows to verify that the cross-peaks are not folded and affords S( "Y) with the desired accuracy. 

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