10,368 research outputs found
Miniature probes for use in gas turbine testing
Several examples of miniature probes (null type as well as fixed position) are presented which have proved useful in aircraft and space power systems component testing and are applicable to automotive gas turbine testing. These probes are used to determine component or system performance from the measurement of gas temperature as well as total and static pressure, and flow direction. Detailed drawings of the sensors are presented along with experimental data covering the flow characteristics over the range of intended use
Performance of mass flux probe in a Mach 3 stream
Performance of mass flux probe in Mach 3 strea
Enthalpy and stagnation temperature determination of a high temperature laminar flow gas stream Patent
Measuring conductive heat flow and thermal conductivity of laminar gas stream in cylindrical plug to simulate atmospheric reentr
Recovery and radiation corrections and time constants of several sizes of shielded and unshielded thermocouple probes for measuring gas temperature
Performance characteristics were experimentally determined for several sizes of a shielded and unshielded thermocouple probe design. The probes are of swaged construction and were made of type K wire with a stainless steel sheath and shield and MgO insulation. The wire sizes ranged from 0.03- to 1.02-mm diameter for the unshielded design and from 0.16- to 0.81-mm diameter for the shielded design. The probes were tested through a Mach number range of 0.2 to 0.9, through a temperature range of room ambient to 1420 K, and through a total-pressure range of 0.03 to 0.2.2 MPa (0.3 to 22 atm). Tables and graphs are presented to aid in selecting a particular type and size. Recovery corrections, radiation corrections, and time constants were determined
A new approach to the pulsed thermocouple for high gas temperature measurements
Pulsed thermocouple systems can be used to measure gas temperatures above the melting point of the thermocouple by various techniques of short term of intermittent exposure of the thermocouple operating at lower temperatures. An approach is described which uses a thermocouple cooled by a small jet of inert gas. When a measurement is to be made, the cooling jet is turned off and the thermocouple allowed to heat up to near its melting point, at which time the cooling is reapplied. The final temperature which the thermocouple should have attained is then calculated by extrapolating an exponential curve fit to the data. Temperature measurements can be recorded and displayed in near real time by using modern high-speed computing systems to perform these calculations. Examples of the technique applied to high temperature jet engine combustor development are presented
Observation of the Thermal Casimir Force is Open to Question
We discuss theoretical predictions for the thermal Casimir force and compare
them with available experimental data. Special attention is paid to the recent
claim of the observation of that effect, as predicted by the Drude model
approach. We show that this claim is in contradiction with a number of
experiments reported so far. We suggest that the experimental errors, as
reported in support of the observation of the thermal Casimir force, are
significantly underestimated. Furthermore, the experimental data at separations
above m are shown to be in agreement not with the Drude model approach,
as is claimed, but with the plasma model. The seeming agreement of the data
with the Drude model at separations below m is explained by the use of
an inadequate formulation of the proximity force approximation.Comment: 12 pages, 4 figures, to appear in Int. J. Mod. Phys.
Precise comparison of theory and new experiment for the Casimir force leads to stronger constraints on thermal quantum effects and long-range interactions
We report an improved dynamic determination of the Casimir pressure between
two plane plates obtained using a micromachined torsional oscillator. The main
improvements in the current experiment are a significant suppression of the
surface roughness of the Au layers deposited on the interacting surfaces, and a
decrease in the experimental error in the measurement of the absolute
separation. A metrological analysis of all data permitted us to determine both
the random and systematic errors, and to find the total experimental error as a
function of separation at the 95% confidence level. In contrast to all previous
experiments on the Casimir effect, our smallest experimental error (%) is achieved over a wide separation range. The theoretical Casimir
pressures in the experimental configuration were calculated by the use of four
theoretical approaches suggested in the literature. All corrections to the
Casimir force were calculated or estimated. All theoretical errors were
analyzed and combined to obtain the total theoretical error at the 95%
confidence level. Finally, the confidence interval for the differences between
theoretical and experimental pressures was obtained as a function of
separation. Our measurements are found to be consistent with two theoretical
approaches utilizing the plasma model and the surface impedance over the entire
measurement region. Two other approaches to the thermal Casimir force,
utilizing the Drude model or a special prescription for the determination of
the zero-frequency contribution to the Lifshitz formula, are excluded on the
basis of our measurements at the 99% and 95% confidence levels, respectively.
Finally, constraints on Yukawa-type hypothetical interactions are strengthened
by up to a factor of 20 in a wide interaction range.Comment: 43 pages, 15 figures, elsart.cls is used. Accepted for publication in
Annals of Physics. (Several misprints in the text are corrected.
Aspects of Nucleon Chiral Perturbation Theory
I review recent progress made in the calculation of nucleon properties in the
framework of heavy baryon CHPT. Topics include: Compton scattering,
scattering, the anatomy of a low-energy constant and the induced pseudoscalar
form factor.Comment: plain TeX (macro included), 12pp, lecture delivered at the workshop
on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
Comment on "Anomalies in electrostatic calibration for the measurement of the Casimir force in a sphere-plane geometry"
Recently W. J. Kim, M. Brown-Hayes, D. A. R. Dalvit, J. H. Brownell, and R.
Onofrio [Phys. Rev. A, v.78, 036102(R) (2008)] performed electrostatic
calibrations for a plane plate above a centimeter-size spherical lens at
separations down to 20-30 nm and observed "anomalous behavior". It was found
that the gradient of the electrostatic force does not depend on separation as
predicted on the basis of a pure Coulombian contribution. Some hypotheses which
could potentially explain the deviation from the expected behavior were
considered, and qualitative arguments in favor of the influence of patch
surface potentials were presented. We demonstrate that for the large lenses at
separations of a few tens nanometers from the plate, the electrostatic force
law used by the authors is not applicable due to possible deviations of the
mechanically polished and ground lens surface from a perfect spherical shape. A
model is proposed which explains the observed "anomalous behavior" using the
standard Coulombian force.Comment: 9 pages, 3 figure
Dual Brane Pairs, Chains and the Bekenstein-Hawking Entropy
A proposal towards a microscopic understanding of the Bekenstein-Hawking
entropy for D=4 spacetimes with event horizon is made. Since we will not rely
on supersymmetry these spacetimes need not be supersymmetric. Euclidean
D-branes which wrap the event horizon's boundary will play an important role.
After arguing for a discretization of the Euclidean D-brane worldvolume based
on the worldvolume uncertainty relation, we count chainlike excitations on the
worldvolume of specific dual Euclidean brane pairs. Without the need for
supersymmetry it is shown that one can thus reproduce the D=4
Bekenstein-Hawking entropy and its logarithmic correction.Comment: 14 pages, 1 figur
- …