10,226 research outputs found
Lunar orbiting microwave beam power system
A microwave beam power system using lunar orbiting solar powered satellite(s) and surface rectenna(s) was investigated as a possible energy source for the Moon's surface. The concept has the potential of reduced system mass by placing the power source in orbit. This can greatly reduce and/or eliminate the 14 day energy storage requirement of a lunar surface solar system. Also propellants required to de-orbit to the surface are greatly reduced. To determine the practicality of the concept and the most important factors, a zero-th order feasibility analysis was performed. Three different operational scenarios employing state of the art technology and forecasts for two different sets of advanced technologies were investigated. To reduce the complexity of the problem, satellite(s) were assumed in circular equatorial orbits around the Moon, supplying continuous power to a single equatorial base through a fixed horizontal rectenna on the surface. State of the art technology yielded specific masses greater than 2500 kg/kw, well above projections for surface systems. Using advanced technologies the specific masses are on the order of 100 kg/kw which is within the range of projections for surface nuclear (20 kg/kw) and solar systems (500 kg/kw). Further studies examining optimization of the scenarios, other technologies such as lasers transmitters and nuclear sources, and operational issues such as logistics, maintenance and support are being carried out to support the Space Exploration Initiative (SEI) to the Moon and Mars
An accurate formula for the period of a simple pendulum oscillating beyond the small-angle regime
A simple approximation formula is derived here for the dependence of the
period of a simple pendulum on amplitude that only requires a pocket calculator
and furnishes an error of less than 0.25% with respect to the exact period. It
is shown that this formula describes the increase of the pendulum period with
amplitude better than other simple formulas found in literature. A good
agreement with experimental data for a low air-resistance pendulum is also
verified and it suggests, together with the current availability/precision of
timers and detectors, that the proposed formula is useful for extending the
pendulum experiment beyond the usual small-angle oscillations.Comment: 15 pages and 4 figures. to appear in American Journal of Physic
Niobium-based superconducting nano-devices fabrication using all-metal suspended masks
We report a novel method for the fabrication of superconducting nanodevices
based on niobium. The well-known difficulties of lithographic patterning of
high-quality niobium are overcome by replacing the usual organic resist mask by
a metallic one. The quality of the fabrication procedure is demonstrated by the
realization and characterization of long and narrow superconducting lines and
niobium-gold-niobium proximity SQUIDs
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'Can you be a doctor, even if you faint?' The tacit lessons of cadaveric dissection
Background: The undergraduate Medicine course at the University of Cambridge has included cadaveric dissection as part of its anatomy teaching for over three centuries. In recent years, medical schools in the UK and the US have debated whether cadaveric dissection is a useful and efficient way of teaching anatomy. Existing research on this subject has focused narrowly on the knowledge-acquisition for medical students afforded through dissection, and thus we have broadened the scope of such considerations to include the emotional responses of medical students to the dissection process.
Subjects and methods: The basis for this paper is a phenomenological analysis of response data gathered from 56 first year medical students at the University of Cambridge through written questionnaires and discussion groups before and after their first experiences of cadaveric dissection.
Results: Our research suggests that there are in fact many more lessons taught and acquired through studying in the dissection room: they are tacit, emotional, experiential and dispositional.
Conclusions: When this wider picture of the value of dissection is considered, a much stronger case for the continued inclusion of cadaveric dissection in the medical curriculum can be made, as it is a valuable and unique educational experience
Nonadiabatic Pauli susceptibility in fullerene compounds
Pauli paramagnetic susceptibility is unaffected by the electron-phonon
interaction in the Migdal-Eliashberg context. Fullerene compounds however do
not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic
effects are expected to be relevant in these materials. In this paper we
investigate the Pauli spin susceptibility in nonadiabatic regime by following a
conserving approach based on Ward's identity. We find that a sizable
renormalization of due to electron-phonon coupling appears when
nonadiabatic effects are taken into account. The intrinsic dependence of
on the electron-phonon interaction gives rise to a finite and negative isotope
effect which could be experimentally detected in fullerides. In addition, we
find an enhancement of the spin susceptibility with temperature increasing, in
agreement with the temperature dependence of observed in fullerene
compounds. The role of electronic correlation is also discussed.Comment: Revtex, 10 pages, 8 figures include
Coulomb gas representation of quantum Hall effect on Riemann surfaces
Using the correlation function of chiral vertex operators of the Coulomb gas
model, we find the Laughlin wavefunctions of quantum Hall effect, with filling
factor , on Riemann sufaces with Poincare metric. The same is done
for quasihole wavefunctions. We also discuss their plasma analogy.Comment: 10 pages, LaTex, the paper is completely rewritten, It will be
appeared in : Jour. Phys. A 32 (1999
The Modular Group, Operator Ordering, and Time in (2+1)-Dimensional Gravity
A choice of time-slicing in classical general relativity permits the
construction of time-dependent wave functions in the ``frozen time''
Chern-Simons formulation of -dimensional quantum gravity. Because of
operator ordering ambiguities, however, these wave functions are not unique. It
is shown that when space has the topology of a torus, suitable operator
orderings give rise to wave functions that transform under the modular group as
automorphic functions of arbitrary weights, with dynamics determined by the
corresponding Maass Laplacians on moduli space.Comment: 8 pages, LaTe
Thermal Conductivity near H_c2 for spin-triplet superconducting States with line nodes in Sr_2RuO_4
We calculate the thermal conductivity kappa in magnetic fields near H_c2 for
spin-triplet superconducting states with line nodes vertical and horizontal
relative to the RuO_2-planes. The method for calculating the Green's functions
takes into account the spatial variation of the order parameter and
superconducting flow for the Abrikosov vortex lattice. For in-plane magnetic
field we obtain variations of the in-plane kappa with two-fold symmetry as a
function of rotation angle where the minima and maxima occur for field
directions parallel and perpendicular to the heat flow. The amplitude of the
variation decreases with increasing impurity scattering and temperature. At
higher temperatures the minima and maxima of the variation are interchanged.
Since the results for vertical and horizontal line nodes are almost the same we
cannot say which of the two pairing models is more compatible with recent
measurements of kappa in Sr_2RuO_4. The observed four-fold modulation of kappa
in YBa_2Cu_3O_(7-\delta) is obtained for d-wave pairing by taking into account
the particular shape of the Fermi surface and the finite temperature effect.
The results for kappa for the f-wave pairing state with horizontal line nodes
disagree in some respects with the measurements on UPt_3.Comment: 8 pages, 6 figures. To be published in Phys. Rev.
Polarization Diffusion from Spacetime Uncertainty
A model of Lorentz invariant random fluctuations in photon polarization is
presented. The effects are frequency dependent and affect the polarization of
photons as they propagate through space. We test for this effect by confronting
the model with the latest measurements of polarization of Cosmic Microwave
Background (CMB) photons.Comment: 4 pages, 1 figur
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