120 research outputs found
Changes of some blood indices and myocardial electrolyte content during hypokinesia
Using special hypokinetic cages, the volume changes of circulating blood, its hematocrit and protein content, volume ratios between extra- and intracellular liquids in the body, as well as electrolyte content in the blood and myocardium during hypokinesia were investigated experimentally in rabbits
Experimental investigation of the role of thyrocalcitonin in the prophylaxis of disturbances in the water-salt and mineral metabolism during a 30-day hypokinesia
The effect of thyrocalcitonin (TCT) injections on the metabolism of water and electrolytes in free-moving and immobilized chinchilla hares is described. Calcium excretion from immobilized animals was elevated, but normalized in those also receiving TCT injections. TCT also normalized water content and excretion rates
Errors in quantum optimal control and strategy for the search of easily implementable control pulses
We introduce a new approach to assess the error of control problems we aim to
optimize. The method offers a strategy to define new control pulses that are
not necessarily optimal but still able to yield an error not larger than some
fixed a priori threshold, and therefore provide control pulses that might be
more amenable for an experimental implementation. The formalism is applied to
an exactly solvable model and to the Landau-Zener model, whose optimal control
problem is solvable only numerically. The presented method is of importance for
applications where a high degree of controllability of the dynamics of quantum
systems is required.Comment: 13 pages, 3 figure
Optimal control of atom transport for quantum gates in optical lattices
By means of optimal control techniques we model and optimize the manipulation
of the external quantum state (center-of-mass motion) of atoms trapped in
adjustable optical potentials. We consider in detail the cases of both non
interacting and interacting atoms moving between neighboring sites in a lattice
of a double-well optical potentials. Such a lattice can perform
interaction-mediated entanglement of atom pairs and can realize two-qubit
quantum gates. The optimized control sequences for the optical potential allow
transport faster and with significantly larger fidelity than is possible with
processes based on adiabatic transport.Comment: revised version: minor changes, 2 references added, published versio
High Fidelity Quantum Gates in the Presence of Dispersion
We numerically demonstrate the control of motional degrees of freedom of an
ensemble of neutral atoms in an optical lattice with a shallow trapping
potential. Taking into account the range of quasimomenta across different
Brillouin zones results in an ensemble whose members effectively have
inhomogeneous control fields as well as spectrally distinct control
Hamiltonians. We present an ensemble-averaged optimal control technique that
yields high fidelity control pulses, irrespective of quasimomentum, with
average fidelities above 98%. The resulting controls show a broadband spectrum
with gate times in the order of several free oscillations to optimize gates
with up to 13.2% dispersion in the energies from the band structure. This can
be seen as a model system for the prospects of robust quantum control. This
result explores the limits of discretizing a continuous ensemble for control
theory
Quantum spin field effect transistor
We propose, theoretically, a new type of quantum field effect transistor that
operates purely on the flow of spin current in the absence of charge current.
This spin field effect transistor (SFET) is constructed without any magnetic
material, but with the help of spin flip mechanism provided by a rotating
external magnetic field of uniform strength. The SFET generates a constant
instantaneous spin current that is sensitively controllable by a gate voltage
as well as by the frequency and strength of the rotating field. The
characteristics of a Carbon nanotube based SFET is provided as an example
Carbon nanotube-based quantum pump in the presence of superconducting lead
Parametric electron pump through superconductor-carbon-nanotube based
molecular devices was investigated. It is found that a dc current, which is
assisted by resonant Andreev reflection, can be pumped out from such molecular
device by a cyclic variation of two gate voltages near the nanotube. The pumped
current can be either positive or negative under different system parameters.
Due to the Andreev reflection, the pumped current has the double peak structure
around the resonant point. The ratio of pumped current of N-SWNT-S system to
that of N-SWNT-N system (I^{NS}/I^N) is found to approach four in the weak
pumping regime near the resonance when there is exactly one resonant level at
Fermi energy inside the energy gap. Numerical results confirm that in the weak
pumping regime the pumped current is proportional to the square of the pumping
amplitude V_p, but in the strong pumping regime the pumped current has the
linear relation with V_p. Our numerical results also predict that pumped
current can be obtained more easily by using zigzag tube than by using armchair
tube
Quantized Adiabatic Charge Transport in a Carbon Nanotube
The coupling of a metallic Carbon nanotube to a surface acoustic wave (SAW)
is proposed as a vehicle to realize quantized adiabatic charge transport in a
Luttinger liquid system. We demonstrate that electron backscattering by a
periodic SAW potential, which results in miniband formation, can be achieved at
energies near the Fermi level. Electron interaction, treated in a Luttinger
liquid framework, is shown to enhance minigaps and thereby improve current
quantization. Quantized SAW induced current, as a function of electron density,
changes sign at half-filling.Comment: 5 pages, 2 figure
Charge-Stripe Ordering From Local Octahedral Tilts: Underdoped and Superconducting La2-xSrxCuO4 (0 < x < 0.30)
The local structure of La2-xSrxCuO4, for 0 < x < 0.30, has been investigated
using the atomic pair distribution function (PDF) analysis of neutron powder
diffraction data. The local octahedral tilts are studied to look for evidence
of [110] symmetry (i.e., LTT-symmetry) tilts locally, even though the average
tilts have [010] symmetry (i.e., LTO-symmetry) in these compounds. We argue
that this observation would suggest the presence of local charge-stripe order.
We show that the tilts are locally LTO in the undoped phase, in agreement with
the average crystal structure. At non-zero doping the PDF data are consistent
with the presence of local tilt disorder in the form of a mixture of LTO and
LTT local tilt directions and a distribution of local tilt magnitudes. We
present topological tilt models which qualitatively explain the origin of tilt
disorder in the presence of charge stripes and show that the PDF data are well
explained by such a mixture of locally small and large amplitude tilts.Comment: 11 two-column pages, 11 figure
Exact SO(8) Symmetry in the Weakly-Interacting Two-Leg Ladder
A perturbative renormalization group analysis of interacting electrons on a
two-leg ladder reveals that at half-filling any weakly repulsive system scales
onto an exactly soluble Gross-Neveu model with a hidden SO(8) symmetry. The
half-filled ground state is a Mott insulator with short-range d-wave pair
correlations. We extract the exact energies, degeneracies, and quantum numbers
of *all* the low energy excited multiplets. One energy (mass) m octets contains
Cooper pair, magnon, and density-wave excitations, two more octets contain
single-particle excitations, and a mass \sqrt{3}m antisymmetric tensor contains
28 "bound states". Exact single-particle and spin gaps are found for the
lightly-doped (d-wave paired one-dimension Bose fluid) system. We also
determine the four other robust phases occuring at half-filling for partially
attractive interactions. All 5 phases have distinct SO(8) symmetries, but share
S.C. Zhang's SO(5) as a common subgroup.Comment: RevTex, 35 pages with 15 figure
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