84,685 research outputs found
Note on the limits to the local Mach number on an aerofoil in subsonic flow
It has been noted in some experiments that the local Mach
number just ahead of a shock wave on an aerofoil in subsonic flow is
limited, values of the limit of the order of 1.4 are usually quoted.
This note presents two lines of thought indicating how such a limit
may arise. The first starts with the observation that the pressure
after the shock will not be higher than the rain stream pressure.
Fig.1 shows the calculated relation between local Mach number ahead
of the shock (Mâ
1
), shock inclination (S), mainstream Mach number (M1)
and pressure coefficient just aft of the shock. âą
(Cp) It is noted
that, for given M1 , Cp and .5 ,two shocks are possible in general,
a strong one for which Ms , > 1.48, and a weak one for which MS1 < 1.48,
and it is argued that the latter is the more likely. The second
approach is based on the fact that a relation between stream deflection
(8) and Mach number for the flow in the limited supersonics regions on
a number of aerofoils has been derived from some. experimental data.
Further analysis of experimental data is required before this relation
can be accepted as general. If it is accepted, however, then it
indicates that the Mach numbers increase above unity for a given
deflection is about one-third of that given by simple wave theory
(Fig.2). An analysis of the possible deflections on aerofoils of
various thicknesses (Fig.3) then indicates that deflections corresponding
to local Mach numbers of the order of 1,5 or higher are unlikely except
at incidences of the order of5 ° or more, and may then be more likely
for thick wings than for thin wings. Flow breakaway will make the
attainment of such high local Mach numbers less likely
High dispersion observations of Venus during 1972. The CO2 band at 7820 angstrom
Photographic plates of Venus which show the spectrum of the carbon dioxide band at 7820A were obtained at Table Mountain Observatory in September-October 1972. These spectra showed a semi-regular 4-day variation in the CO2 abundance over the disk of the planet. Evidence for temporal variations in the rotational temperature of this band and temperature variations over the disk was found. The two quantities, CO2 abundance and temperature, do not show any obvious relationship; however, an increase in the temperature usually is accompanied by a decrease in the abundance of CO2. The average temperature, found from a curve of growth analysis assuming a constant CO2 line of width, is 249 plus or minus 1.4 K (one standard deviation)
Theoretical Predictions of Superconductivity in Alkali Metals under High Pressure
We calculated the superconductivity properties of alkali metals under high
pressure using the results of band theory and the rigid-muffin-tin theory of
Gaspari and Gyorffy. Our results suggest that at high pressures Lithium,
Potassium, Rubidium and Cesium would be superconductors with transition
temperatures approaching . Our calculations also suggest that Sodium
would not be a superconductor under high pressure even if compressed to less
than half of its equilibrium volume. We found that the compression of the
lattice strengthens the electron-phonon coupling through a delicately balanced
increase of both the electronic and phononic components of this coupling. This
increase of the electron-phonon coupling in Li is due to an enhancement of the
- channel of the interaction, while in the heavier elements the -
channel is the dominant component.Comment: 6 pages, 8 figure
Chiral extrapolation and physical insights
It has recently been established that finite-range regularisation in chiral
effective field theory enables the accurate extrapolation of modern lattice QCD
results to the chiral regime. We review some of the highlights of
extrapolations of quenched lattice QCD results, including spectroscopy and
magnetic moments. The resonance displays peculiar chiral features in
the quenched theory which can be exploited to demonstrate the presence of
significant chiral corrections.Comment: 6 pages, 5 figures, presented at LHP2003, Cairns, Australi
Hadron structure on the back of an envelope
In order to remove a little of the mysticism surrounding the issue of
strangeness in the nucleon, we present simple, physically transparent estimates
of both the strange magnetic moment and charge radius of the proton. Although
simple, the estimates are in quite good agreement with sophisticated
calculations using the latest input from lattice QCD. We further explore the
possible size of systematic uncertainties associated with charge symmetry
violation (CSV) in the recent precise determination of the strange magnetic
moment of the proton. We find that CSV acts to increase the error estimate by
0.003 \mu_N such that G_M^s = -0.046 +/- 0.022 \mu_N.Comment: 9 pages, 1 figure, Invited talk at First Workshop on Quark-Hadron
Duality and the Transition to pQCD, Frascati, June 6-8 200
Chiral Symmetry and the Intrinsic Structure of the Nucleon
Understanding hadron structure within the framework of QCD is an extremely
challenging problem. In order to solve it, it is vital that our thinking should
be guided by the best available insight. Our purpose here is to explain the
model independent consequences of the approximate chiral symmetry of QCD for
two famous results concerning the structure of the nucleon. We show that both
the apparent success of the constituent quark model in reproducing the ratio of
the proton to neutron magnetic moments and the apparent success of the Foldy
term in reproducing the observed charge radius of the neutron are coincidental.
That is, a relatively small change of the current quark mass would spoil both
results.Comment: RevTeX, 10 pages, 2 figure
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