Parallax

Errors due to parallax can also be avoided by means of the Shellbach stripe, and the use of the now well-known Shellbach burette is consequently to be strongly recommended. 

It will be clear that the precautions to be taken in reading a burette should also be taken when using apparatus of a similar character, e.g. the barometer, eudiometer, mercury manometer, etc. 

References.—For a second method of calibrating weights, see Richards, y. Amer. Chem. Soc. 1900, 2S, 144 Zeitschr. physikal. Chem., 1900, S3,605. 

For a discussion of the accuracy of pipettes and burettes, see Wagner, Zeitschr. physikal. Cheni., 1899, 28, 193. 

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In contrast to AFM, which directly provides accurate height mfonnation in a limited range, quantitative assessment of the surface topography by SEM is possible by measuring die parallax of stereo pairs [45]. 

When actually taking a reading on the scale S during an experiment, a small lens is used, and the usual precautions must be taken to avoid an error by parallax. ... 

This is sometimes made of mirror glass in order to eliminate the error due to parallax, t Manufactured by Edwards High Vacuum Ltd. This is essentially a form of McLeod gauge. 

Second, when filling a pipet or volumetric flask, set the liquid s level exactly at the calibration mark. The liquid s top surface is curved into a meniscus, the bottom of which should be exactly even with the glassware s calibration mark (Figure 2.6). The meniscus should be adjusted with the calibration mark at eye level to avoid parallax errors. If your eye level is above the calibration mark the pipet or volumetric flask will be overfilled. The pipet or volumetric flask will be underfilled if your eye level is below the calibration mark. 

Parallax errors are occasioned by failure to read the thermometer from a position exactly normal to its tube axis. Parallax can be reduced by taking the mean of several observations by skilled observers but can be eliminated only by use of a filar telescope mounted so as to move along an axis parallel to the thermometer stem. 

In a dynamic event, one obtains only one X-ray per X-ray head, as opposed to a number of optical photographs taken through a given optical lens. Often several X-ray heads are used to show the evolution of the deformation, but each X-ray views the event from a different angle and it is not uncommon to view the event orthogonally. This can be used to advantage to determine the location of certain features through parallax. For a review on this technique, see Isbell (1987). 

A graticule is normally provided on the screen to assist in the measurement. Parallax errors can cause problems unless this graticule is actually engraved on the screen itself, and the final accuracy will depend on the degree of beam focusing which can be achieved. Accuracy of better than 1.5 per cent should be possible in most cases. 

The use of a light beam as an indicator avoids the errors caused by friction with a normal pointer, while a hairline incorporated in the projection fens eliminates errors due to parallax, and with the scale at a distance of 1 m from the mirror, a sensitivity of up to 1 500 mm/ tA can be achieved. 

As with other graduated glassware, burettes are produced to both Class A and Class B specifications in accordance with the appropriate standard [BS 846 (1985) ISO 385 (1984)], and Class A burettes may be purchased with BST Certificates. All Class A and some Class B burettes have graduation marks which completely encircle the burette this is a very important feature for the avoidance of parallax errors in reading the burette. Typical values for the tolerances permitted for Class A burettes are ... 

Palladium, D. of as dimethylglyoximate. (g) 463 as nioximate, (g) 474 by EDTA, (ti) 329 Paper chromatography 229 see Thin layer chromatography Parallax errors due to, 85 Parallel determinations 132 Partial ionic equations 850, (T) 851 Partition chromatography 13. 217 Partition coefficient 162 Patton and Reeder s indicator 317, 328 Peptisation 419. 421... 

Something else should be said about the impact of accommodation- When the (general) theory concerned is strongly supported independently of the fact at issue, the accommodation of some fact, even in this ad hoc way, may well still supply the best explanation that science can currently supply for that fact. So, for example, the best explanation in, say, 1700 for the observation of no stellar parallax was surely the Copemican one—that there must in fact be an apparent parallactic motion but that even the nearest stars are so far away as to make the effect too small to be detected by even the best available telescopes. (Here, as before with Ptolemy and with scientific creationism, we use the phenomenon—no observed parallax—to fix (in this case in a rather loose way) an otherwise free parameter in the theory (distance to the nearest star).)... 

We have determined the positions of our stars in H-R diagrams for the appropriate Fe and [a/Fe] abundances, using Teff obtained by Method 1 and the absolute magnitudes, Mv, derived from Hipparcos parallaxes. The good agreement between the gravities obtained from the evolutionary tracks ([4]) and those from Method 1 suggests that non-LTE effects are unlikely in Method 1. 

The observations were performed at ESO using the 1.52m telescope and FEROS. The obtained spectra have high nominal resolving power (R 48000), and S/N 500 at maximum and a coverage from 4000 A to 9200 A. Many spectra were acquired for all sample stars. The atmospheric parameters (Teff, log g, [Fe/H] and microturbulence velocities) have been obtained through an iterative and totally self-consistent procedure from Fe lines of the observed spectrum. The initial values of Teg were obtained from a (B-V) vs Teg calibration and log were determined from Hipparcos parallaxes and evolutionary tracks. The [O/Fe] abundances were derived by fitting synthetic spectra to the observed one. 

Chemical abundances are inferred from the EW of the lines. Selected lines and atomic data are from our previous paper [5], from [4] and. Stellar parameters were first inferred from Geneva photometry and Hipparcos parallaxes. Then temperatures, microturbulence velocities, gravities and metallicities were iteratively changed in order to i) obey the excitation equilibrium of the Fe I lines ii) require that Fe I and Fe II abundances agree within 0.1-0.15 dex and iii) require that Fe I lines with different equivalent widths (EW) give the same iron abundance. 

Boothroyd Sackmann (1999). Thus, to solve the 3He problem in terms of extra-mixing in low-mass stars, the vast majority of them (90%-100%) must be affected by this phenomenon (Galli et al. 1997). The same conclusion has been reached independently by Charbonnel do Nascimento (1998) on the basis of the statistics of carbon isotopic ratios in a sample of red-giant stars with accurate Hipparcos parallaxes. 

So a star with a parallax angle of 0.1 arcsec is at a distance of 10 pc, which can be converted to SI units by knowing the Earth s orbit. One parsec is 3.26... 

Parallax calculations are the only absolute measure of distance... 

The distances to Betelgeuse, Aldebaran and Spica are given in Appendix B. Calculate the distance to these stars in parsecs and identify which distances can be measured on Earth using parallax. 

Parsec A unit of distance resulting from a stellar parallax of 1 arcsecond, equal to 3.26... 

The most metal-deficient stars comprise field stars in the solar neighbourhood (where in some cases distances and luminosities can be found from parallaxes) and stars in globular clusters where the morphology of the HR diagram can be studied (Fig. 4.8). Such stars are of particular interest because their content of heavy elements (synthesized in still earlier generations of stars) is so low that they can... 

Paraformaldehyde, 2 623 22 123 Paraformaldehyde solids, 22 119 para-hydrogen, 23 759, 760—761, 764 vapor pressure of, 23 764 Parainfluenza vaccine, 25 498 Paraldehyde, 2 103 Parallax errors, in liquid-in-glass thermometers, 24 465 Parallel-counterflow exchanger, heat-exchanger effectiveness for, 23 255 Parallel flow heat exchangers heat-exchanger effectiveness for,... 

Systematic errors usually arise from specific shortcomings in the measuring instrument, the observer, or the way in which the measurement is taken. Sources of systematic error include a badly calibrated measuring device, a faulty instrument movement, an incorrect action by the experimenter (e.g., misreading a volume measurement), or the parallax effect when incorrectly viewing a scale. Repeating the measurement does not necessarily help, because the error may be repeated, and the analyst may... 

In Fig. 6, we report the radius an the mass of the compact star RX J1856.5-3754 inferred by Walter Lattimer (2002) (see also Kaplan et al. 2002) from the fit of the full spectral energy distribution for this isolated radio-quite neutron star , after a revised parallax determination (Kaplan et al. 2002) which implies a distance to the source of 117 12 pc. Comparing the mass-radius box for RX J1856.5-3754 reported in Fig. 6 with the theoretical determination of the MR relation for different equations of state, one concludes that RX J1856.5-3754 could be (see e.g. Fig. 2 in Walter Lattimer, 2002) either an hadronic star or an hybrid or strange star (see also Drake et al. 2002). 

Parallax error is one of the main sources of error in liquid measurements. Figure 4.2 illustrates that the liquid surface in a container is not even, and a meniscus is formed. For most liquids the surface is concave. The uneven surface is due to surface tension, and if not read properly, may result in an error commonly known as parallax error. When a container with graduations for volumes has a liquid in it, the reading must always be made at the bottom of the meniscus. The parallax error is shown in Figure 4.2. 

British Standards Institution (B.S. 846 1962) has laid down specifications for burettes and these are produced to either Class A or Class B specifications. All Class A and a few of Class B burettes have graduations that extend right round the barrel (or stem) of the burette to minimise errors due to parallax while taking the exact burette reading. It may be noted that Class B burettes are normally graduated on one side only. Permitted tolerances on capacity for burettes used in common practice are stated in Table 2.2. 

A. Chattopadhyay and E. London, Parallax method for direct measurement of membrane penetration depth utilizing fluorescence quenching by spin-labeled phospholipids, Biochemistry 26, 39-45 (1987). 

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