2,371 research outputs found
Letter from P.C. Garvin, M.D. to Governor Washburn offering medical services, July 3, 1862
https://digitalmaine.com/adj_gen_corr_town_acton/1003/thumbnail.jp
Boeing 747 aircraft with large external pod for transporting outsize cargo
The effect on structural arrangement, system weight, and range performance of the cargo pod payload carrying capability was determined to include either the bridge launcher or a spacelab module on a Boeing 747 aircraft. Modifications to the carrier aircraft and the installation time required to attach the external pod to the 747 were minimized. Results indicate that the increase in pod size was minimal, and that the basic 747 structure was adequate to safely absorb the load induced by ground or air operation while transporting either payload
Experimental study of nonlinear conductance in small metallic samples
We have directly observed current-dependent, nonlinear contributions to the conductance fluctuations of phase-coherent metallic wires and loops. The fluctuations in the current-voltage curves are reproducible, asymmetric about I=0, and in qualitative agreement with theoretical predictions. In ac measurements, the nonlinear terms also generate large harmonic signals of the conductance fluctuations whose dependence on the drive current can be understood qualitatively. The spectra of harmonics from loops and wires have different dependences on the voltage across the sample
Temperature Dependence of the Normal-Metal Aharonov-Bohm Effect
The amplitude of h/e periodic oscillations in the magnetoresistance of very small normal-metal (Au) rings, as well as the harmonic h/2e, have been studied as a function of temperature. The amplitudes depend on the temperature T roughly as T-1/2, as expected from the averaging of conduction channels in the absence of inelastic scattering, but may not be entirely consistent with this model. At the lowest T, the size of the fluctuations in the conductance is about ΔG∼e2/h, as predicted recently
Two-Bit Gates are Universal for Quantum Computation
A proof is given, which relies on the commutator algebra of the unitary Lie
groups, that quantum gates operating on just two bits at a time are sufficient
to construct a general quantum circuit. The best previous result had shown the
universality of three-bit gates, by analogy to the universality of the Toffoli
three-bit gate of classical reversible computing. Two-bit quantum gates may be
implemented by magnetic resonance operations applied to a pair of electronic or
nuclear spins. A ``gearbox quantum computer'' proposed here, based on the
principles of atomic force microscopy, would permit the operation of such
two-bit gates in a physical system with very long phase breaking (i.e., quantum
phase coherence) times. Simpler versions of the gearbox computer could be used
to do experiments on Einstein-Podolsky-Rosen states and related entangled
quantum states.Comment: 21 pages, REVTeX 3.0, two .ps figures available from author upon
reques
Direct Observation of Ensemble Averaging of the Aharonov-Bohm Effect in Normal-Metal Loops
Aharonov-Bohm magnetoconductance oscillations have been measured in series arrays of 1, 3, 10, and 30 submicron-diameter Ag loops. At constant temperature, the amplitude of the h/e oscillations is observed to decrease as the square root of number of loops, while the amplitude of h/2e conductance oscillations, measured in the same samples, is independent of the number of series loops. This is direct confirmation of the ensemble averaging properties of h/e oscillations in multiloop systems. The amplitude of the h/e oscillations is in good agreement with recent calculations
Flux Periodicities in Loops of Nodal Superconductors
Supercurrents in superconducting flux threaded loops are expected to
oscillate with the magnetic flux with a period of hc/2e. This is indeed true
for s-wave superconductors larger than the coherence length xi_0. Here we show
that for superconductors with gap nodes, there is no such strict condition for
the supercurrent to be hc/2e rather than hc/e periodic. For nodal
superconductors, the flux induced Doppler shift of the near nodal states leads
to a flux dependent occupation probability of quasi-particles circulating
clockwise and counter clockwise around the loop, which leads to an hc/e
periodic component of the supercurrent, even at zero temperature. We analyze
this phenomenon on a cylinder in an approximative analytic approach and also
numerically within the framework of the BCS theory. Specifically for d-wave
pairing, we show that the hc/e periodic current component decreases with the
inverse radius of the loop and investigate its temperature dependence
Universal scaling of nonlocal and local resistance fluctuations in small wires
Resistance fluctuations in small metal samples result from coherent transport of the carriers. The wave functions of the carriers extend into regions which are not accessible classically. We have directly measured the length dependence of the nonlocal magnetoresistance fluctuations in Sb and Au wires by studying regions of our samples separated from the classical current path by a distance L which varied from 3Lcphi down to 0.2Lcphi (where Lcphi is the phase coherence length for the carriers in the metal). These fluctuations decay exponentially with L/Lcphi. Measurements along the classical current paths scale more slowly with L/Lcphi than predicted by the analytical theory but are in agreement with numerical simulations. We have also studied the length dependence of the magnetic field correlation scale BC, and we find that it is in qualitative agreement with a recent model calculation that accounts for the voltage probes
Torsional response and stiffening of individual multi-walled carbon nanotubes
We report on the characterization of torsional oscillators which use
multi-walled carbon nanotubes as the spring elements. Through
atomic-force-microscope force-distance measurements we are able to apply
torsional strains to the nanotubes and measure their torsional spring constants
and effective shear moduli. We find that the effective shear moduli cover a
broad range, with the largest values near the theoretically predicted value.
The data also suggest that the nanotubes are stiffened by repeated flexing.Comment: 4 page
Asymmetry in the Magnetoconductance of Metal Wires and Loops
Universal conductance fluctuations in wires and Aharonov-Bohm oscillations in loops are not symmetric about H=0. The observation of asymmetry in the periodic oscillations is possible when the phase-coherence length of the wave function is comparable to the separation of the voltage probes. In both cases, four-probe measurements yield resistances which depend on lead configuration. The asymmetries appear like Hall voltages, and are consistent with Onsager\u27s relations
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