6,185 research outputs found
Multivariate Design of Experiments for Engineering Dimensional Analysis
We consider the design of dimensional analysis experiments when there is more
than a single response. We first give a brief overview of dimensional analysis
experiments and the dimensional analysis (DA) procedure. The validity of the DA
method for univariate responses was established by the Buckingham -Theorem
in the early 20th century. We extend the theorem to the multivariate case,
develop basic criteria for multivariate design of DA and give guidelines for
design construction. Finally, we illustrate the construction of designs for DA
experiments for an example involving the design of a heat exchanger
Low radiation dose in computed tomography: the role of iodine
Recent approaches to reducing radiation exposure during CT examinations typically utilize automated dose modulation strategies on the basis of lower tube voltage combined with iterative reconstruction and other dose-saving techniques. Less clearly appreciated is the potentially substantial role that iodinated contrast media (CM) can play in low-radiation-dose CT examinations. Herein we discuss the role of iodinated CM in low-radiation-dose examinations and describe approaches for the optimization of CM administration protocols to further reduce radiation dose and/or CM dose while maintaining image quality for accurate diagnosis. Similar to the higher iodine attenuation obtained at low-tube-voltage settings, high-iodine-signal protocols may permit radiation dose reduction by permitting a lowering of mAs while maintaining the signal-to-noise ratio. This is particularly feasible in first pass examinations where high iodine signal can be achieved by injecting iodine more rapidly. The combination of low kV and IR can also be used to reduce the iodine dose. Here, in optimum contrast injection protocols, the volume of CM administered rather than the iodine concentration should be reduced, since with high-iodine-concentration CM further reductions of iodine dose are achievable for modern first pass examinations. Moreover, higher concentrations of CM more readily allow reductions of both flow rate and volume, thereby improving the tolerability of contrast administration
Statistical mechanical description of liquid systems in electric field
We formulate the statistical mechanical description of liquid systems for
both polarizable and polar systems in an electric field in the
-ensemble, which is the pendant to the thermodynamic description in
terms of the free energy at constant potential. The contribution of the
electric field to the configurational integral in
the -ensemble is given in an exact form as a factor in the
integrand of . We calculate the contribution of the
electric field to the Ornstein-Zernike formula for the scattering function in
the -ensemble. As an application we determine the field induced
shift of the critical temperature for polarizable and polar liquids, and show
that the shift is upward for polarizable liquids and downward for polar
liquids.Comment: 6 page
Cosmological Inflation with orbifold moduli as inflatons
Cosmological inflation is studied in the case where the inflaton is the
overall modulus for an orbifold. General forms of the (non-perturbative)
superpotential are considered to ensure that is modular
invariant. We find generically that these models do not produce a potential
flat enough for slow roll to a supersymmetric minimum, although we do find a
model which produces up to 20 e-folds of inflation to a non-supersymmetric
minimum.Comment: LaTeX file, 16 pages including 5 figures, v3 is the published versio
Heterogeneity of oxygen reactivity: key for selectivity of partial methanol oxidation on gold surfaces
Recent evidence for low-temperature oxidation of methyl formate on Au(332) may affect the selectivity of gold catalysts during partial oxidation of methanol. Under isothermal conditions, overoxidation of methyl formate is significantly slower than methanol oxidation which can be attributed to special oxygen species required for overoxidation
Performance of Hamamatsu 64-anode photomultipliers for use with wavelength--shifting optical fibres
Hamamatsu R5900-00-M64 and R7600-00-M64 photomultiplier tubes will be used
with wavelength--shifting optical fibres to read out scintillator strips in the
MINOS near detector. We report on measurements of the gain, efficiency,
linearity, crosstalk, and dark noise of 232 of these PMTs, of which 219 met
MINOS requirements.Comment: 15 pages, 12 figures. Accepted by Nucl. Inst. Meth.
QCD-based description of one-particle inclusive B decays
We discuss one-particle inclusive B decays in the limit of heavy b and c
quarks. Using the large-N_C limit we factorize the non-leptonic matrix
elements, and we employ a short distance expansion. Modeling the remaining
nonperturbative matrix elements we obtain predictions for various decay
channels and compare them with existing data.Comment: LaTeX, 22 pages, 6 figures (eps); analytical and numerical results
unchanged, misrepresentation of experimental data in Fig. 5 corrected, final
published versio
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