3,761 research outputs found
Observation of a uniform temperature dependence in the electrical resistance across the structural phase transition in thin film vanadium oxide ()
An electrical study of thin films in the vicinity of the structural
phase transition at shows (a) that the electrical resistance
follows over the -range,
covering both sides of the structural transition, and (b) a history dependent
hysteresis loop in upon thermal cycling. These features are attributed here
to transport through a granular network.Comment: 3 pages, 3 color figure
Spin diffusion of correlated two-spin states in a dielectric crystal
Reciprocal space measurements of spin diffusion in a single crystal of
calcium fluoride (CaF) have been extended to dipolar ordered states. The
experimental results for the component of the spin diffusion parallel with the
external field are cm/s for the
[001] direction and cm/s for the
[111] direction. The diffusion rates for dipolar order are significantly faster
than those for Zeeman order and are considerably faster than predicted by
simple theoretical models. It is suggested that constructive interference in
the transport of the two spin state is responsible for this enhancement. As
expected the anisotropy in the diffusion rates is observed to be significantly
less for dipolar order compared to the Zeeman case.Comment: 4 pages, 2 figures. Resubmitted to PRL - new figure added /
discussion expande
Simulations of Information Transport in Spin Chains
Transport of quantum information in linear spin chains has been the subject
of much theoretical work. Experimental studies by nuclear spin systems in
solid-state by NMR (a natural implementation of such models) is complicated
since the dipolar Hamiltonian is not solely comprised of nearest-neighbor
XY-Heisenberg couplings. We present here a similarity transformation between
the XY-Heisenberg Hamiltonian and the grade raising Hamiltonian, an interaction
which is achievable with the collective control provided by radio-frequency
pulses in NMR. Not only does this second Hamiltonian allows us to simulate the
information transport in a spin chain, but it also provides a means to observe
its signature experimentally
On Simulating Liouvillian Flow From Quantum Mechanics Via Wigner Functions
The interconnection between quantum mechanics and probabilistic classical
mechanics for a free relativistic particle is derived in terms of Wigner
functions (WF) for both Dirac and Klein-Gordon (K-G) equations. Construction of
WF is achieved by first defining a bilocal 4-current and then taking its
Fourier transform w.r.t. the relative 4-coordinate. The K-G and Proca cases
also lend themselves to a closely parallel treatment provided the Kemmer-
Duffin beta-matrix formalism is employed for the former. Calculation of WF is
carried out in a Lorentz-covariant fashion by standard `trace' techniques. The
results are compared with a recent derivation due to Bosanac.Comment: 9 pages, Latex; email: [email protected]
Universal Control of Nuclear Spins Via Anisotropic Hyperfine Interactions
We show that nuclear spin subsystems can be completely controlled via
microwave irradiation of resolved anisotropic hyperfine interactions with a
nearby electron spin. Such indirect addressing of the nuclear spins via
coupling to an electron allows us to create nuclear spin gates whose
operational time is significantly faster than conventional direct addressing
methods. We experimentally demonstrate the feasibility of this method on a
solid-state ensemble system consisting of one electron and one nuclear spin.Comment: RevTeX4, 8 pages, 8 figure
Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze
Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (±10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20±4 W m^(−2)) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate
Decay of highly-correlated spin states in a dipolar-coupled solid
We have measured the decay of NMR multiple quantum coherence intensities both
under the internal dipolar Hamiltonian as well as when this interaction is
effectively averaged to zero, in the cubic calcium fluoride (CaF2) spin system
and the pseudo one-dimensional system of fluoroapatite. In calcium fluoride the
decay rates depend both on the number of correlated spins in the cluster, as
well as on the coherence number. For smaller clusters, the decays depend
strongly on coherence number, but this dependence weakens as the size of the
cluster increases. The same scaling was observed when the coherence
distribution was measured in both the usual Zeeman or z basis and the x basis.
The coherence decay in the one dimensional fluoroapatite system did not change
significantly as a function of the multiple quantum growth time, in contrast to
the calcium fluoride case. While the growth of coherence orders is severely
restricted in this case, the number of correlated spins should continue to
grow, albeit more slowly. All coherence intensities were observed to decay as
Gaussian functions in time. In all cases the standard deviation of the observed
decay appeared to scale linearly with coherence number.Comment: 7 pages, 9 figures. submitted to PR
A sequential study of circulating immune complexes, complement mediated IC solubilisation and immunoglobulins in borderline tuberculoid patients with and without reactions
Sequential estimates of the levels of circulating immune complexes (CIC), complement
catabolic fragment C3d, complement-mediated immune complex solubilization (CMS) and
immunoglobulins were made in 24 newly diagnosed patients with borderline tuberculoid
leprosy over a 20 month period after initiation of chemotherapy.
Fourteen of these patients had not suffered from reversal reactions either at the time
of presentation or during the follow-up period. The levels of CIC were elevated in them
from the third to the eleventh month after starting chemotherapy and immunoglobulin G
(IgG) levels were elevated upto eight months. The concentrations of C3d and
immunoglobulins A (IgA) and M (IgM) were normal in these patients.
The other ten patients had reversal reaction at the time of diagnosis which subsided
by the third month after starting treatment. They did not have reversal reactions later. The
levels of CIC and IgG were elevated and those of CMS were depressed throughout the
study period. Serum C3d level was initially elevated but came down to normal by the third
month while IgA and IgM levels were within normal limits.
The relevance of these findings to the genesis of reversal reaction is discussed in this
communication
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