394 research outputs found
Spin-bias driven magnetization reversal and nondestructive detection in a single molecular magnet
The magnetization reversal in a single molecular magnet (SMM) weakly coupled
to an electrode with spin-dependent splitting of chemical potentials (spin
bias) is theoretically investigated by means of the rate equation. A
microscopic mechanism for the reversal is demonstrated by the avalanche
dynamics at the reversal point. The magnetization as a function of the spin
bias shows hysteresis loops tunable by the gate voltage and varying with
temperature. The nondestructive measurement to the orientation of giant spin in
SMM is presented by measuring the fully polarized electric current in the
response to a small spin bias. For Mnac molecule, its small transverse
anisotropy only slightly violates the results above. The situation when there
is an angle between the easy axis of the SMM and the spin quantization
direction of the electrode is also studied.Comment: 17 pages, 12 figure
(Sr_3Sc_2O_5)Fe_2As_2 as a possible parent compound for FeAs-based superconductors
A new compound with the FeAs-layers, namely (Sr_3Sc_2O_5)Fe_2As_2
(abbreviated as FeAs-32522), was successfully fabricated. It has a layered
structure with the space group of I4/mmm, and with the lattice constants a =
4.069 and c = 26.876 . The in-plane Fe ions construct a square
lattice which is close to that of other FeAs-based superconductors, such as
REFeAsO (RE = rare earth elements) and (Ba,Sr)Fe_2As_2. However the inter
FeAs-layer spacing in the new compound is greatly enlarged. The temperature
dependence of resistivity exhibits a weak upturn in the low temperature region,
but a metallic behavior was observed above about 60 K. The magnetic
susceptibility shows also a non-monotonic behavior. Interestingly, the
well-known resistivity anomaly which was discovered in all other parent
compounds, such as REFeAsO, (Ba,Sr)Fe_2As_2 and (Sr,Ca,Eu)FeAsF and associated
with the Spin-Density-Wave (SDW)/structural transition has not been found in
the new system either on the resistivity data or the magnetization data. This
could be induced by the large spacing distance between the FeAs-planes,
therefore the antiferromagnetic correlation between the moments of Fe ions in
neighboring FeAs-layers cannot be established. Alternatively it can also be
attributed to the self-doping effect between Fe and Sc ions. The Hall
coefficient R_H is negative but strongly temperature dependent in wide
temperature region, which indicates the dominance of electrical conduction by
electron-like charge carriers and probably a multi-band effect or a spin
related scattering effect. It is found that the magnetoresistance cannot be
described by the Kohler's rule, which gives further support to above arguments.Comment: 5 pages, 5 figures, some contents added, and one figure adde
Effects of Transcutaneous Electrical Acustimulation on Refractory Gastroesophageal Reflux Disease
Objective. To investigate effects and possible mechanisms of transcutaneous electrical acustimulation (TEA) performed by a wearable watch-size stimulator for refractory gastroesophageal reflux disease (RGERD). Methods. Twenty patients diagnosed as RGERD were enrolled in the study and randomly divided into four groups: esomeprazole group (Group A), esomeprazole combined with TEA group (Group B), esomeprazole combined with sham-TEA group (Group C), and esomeprazole combined with domperidone group (Group D). HRM and 24 h pH-impedance monitoring and GerdQ score were used to measure related indexes before and after treatment. Results. (1) TEA significantly increased LESP, compared with PPI treatment only or PPI plus sham-TEA. After pairwise comparison, LESP of Group B was increased more than Group A (P=0.008) or Group C (P=0.021). (2) PPI plus TEA decreased not only the number of acid reflux episodes but also the number of weak acid reflux episodes (P=0.005). (3) Heartburn and reflux symptoms were improved more with PPI + TEA than with PPI treatment only or PPI plus sham-TEA (GerdQ scores, P=0.001). Conclusion. TEA can improve symptoms in RGERD patients by increasing LESP and decreasing events of weak acid reflux and acid reflux; addition of TEA to esomeprazole significantly enhances the effect of TEA
Effects and Mechanisms of Transcutaneous Electroacupuncture on Chemotherapy-Induced Nausea and Vomiting
Nausea and vomiting are one of the major complications of chemotherapy for cancers. The aim of this study is to investigate the emetic effects and mechanisms involving serotonin and dopamine of needleless transcutaneous electroacupuncture (TEA) at Neiguan (PC6) and Jianshi (PC5) on chemotherapy-induced nausea and vomiting in patients with cancers. Seventy-two patients with chemotherapy were randomly divided into sham-TEA group (sham-TEA, n=34) and TEA group (n=38). TEA was performed at PC 6 and PC 5 (1 h, bid) in combination with granisetron. Sham-TEA was delivered at nonacupoints using the same parameters. We found the following. (1) In the acute phase, the conventional antiemetic therapy using Ondansetron effectively reduced nausea and vomiting; the addition of TEA did not show any additive effects. In the delayed phase, however, TEA significantly increased the rate of complete control (P<0.01) and reduced the nausea score (P<0.05), compared with sham-TEA. (2) TEA significantly reduced serum levels of 5-HT and dopamine in comparison with sham-TEA. Those results demonstrate that needleless transcutaneous electroacupuncture at PC6 using a watch-size digital stimulator improves emesis and reduces nausea in the delayed phase of chemotherapy in patients with cancers. This antiemetic effect is possibly mediated via mechanisms involving serotonin and dopamine
Quantum theory of electronic double-slit diffraction
The phenomena of electron, neutron, atomic and molecular diffraction have
been studied by many experiments, and these experiments are explained by some
theoretical works. In this paper, we study electronic double-slit diffraction
with quantum mechanical approach. We can obtain the results: (1) When the slit
width is in the range of we can obtain the obvious
diffraction patterns. (2) when the ratio of , order are missing in
diffraction pattern. (3)When the ratio of , there isn't missing order in diffraction pattern. (4) We
also find a new quantum mechanics effect that the slit thickness has a
large affect to the electronic diffraction patterns. We think all the
predictions in our work can be tested by the electronic double-slit diffraction
experiment.Comment: 9pages, 14figure
Information-technology approach to quantum feedback control
Quantum control theory is profitably reexamined from the perspective of
quantum information, two results on the role of quantum information technology
in quantum feedback control are presented and two quantum feedback control
schemes, teleportation-based distant quantum feedback control and quantum
feedback control with quantum cloning, are proposed. In the first feedback
scheme, the output from the quantum system to be controlled is fed back into
the distant actuator via teleportation to alter the dynamics of system. The
result theoretically shows that it can accomplish some tasks such as distant
feedback quantum control that Markovian or Bayesian quantum feedback can't
complete. In the second feedback strategy, the design of quantum feedback
control algorithms is separated into a state recognition step, which gives
"on-off" signal to the actuator through recognizing some copies from the
cloning machine, and a feedback (control) step using another copies of cloning
machine. A compromise between information acquisition and measurement
disturbance is established, and this strategy can perform some quantum control
tasks with coherent feedback.Comment: 10 pages,submitte
Entanglement in spin-one Heisenberg chains
By using the concept of negativity, we study entanglement in spin-one
Heisenberg chains. Both the bilinear chain and the bilinear-biquadratic chain
are considered. Due to the SU(2) symmetry, the negativity can be determined by
two correlators, which greatly facilitate the study of entanglement properties.
Analytical results of negativity are obtained in the bilinear model up to four
spins and the two-spin bilinear-biquadratic model, and numerical results of
negativity are presented. We determine the threshold temperature before which
the thermal state is doomed to be entangled.Comment: 7 pages and 4 figure
Bubbling AdS and droplet descriptions of BPS geometries in IIB supergravity
This paper focuses on supergravity duals of BPS states in N=4 super
Yang-Mills. In order to describe these duals, we begin with a sequence of
breathing mode reductions of IIB supergravity: first on S^3, then S^3 x S^1,
and finally on S^3 x S^1 x CP^1. We then follow with a complete supersymmetry
analysis, yielding 1/8, 1/4 and 1/2 BPS configurations, respectively (where in
the last step we take the Hopf fibration of S^3). The 1/8 BPS geometries, which
have an S^3 isometry and are time-fibered over a six-dimensional base, are
determined by solving a non-linear equation for the Kahler metric on the base.
Similarly, the 1/4 BPS configurations have an S^3 x S^1 isometry and a
four-dimensional base, whose Kahler metric obeys another non-linear,
Monge-Ampere type equation.
Despite the non-linearity of the problem, we develop a universal bubbling AdS
description of these geometries by focusing on the boundary conditions which
ensure their regularity. In the 1/8 BPS case, we find that the S^3 cycle
shrinks to zero size on a five-dimensional locus inside the six-dimensional
base. Enforcing regularity of the full solution requires that the interior of a
smooth, generally disconnected five-dimensional surface be removed from the
base. The AdS_5 x S^5 ground state corresponds to excising the interior of an
S^5, while the 1/8 BPS excitations correspond to deformations (including
topology change) of the S^5 and/or the excision of additional droplets from the
base. In the case of 1/4 BPS configurations, by enforcing regularity
conditions, we identify three-dimensional surfaces inside the four-dimensional
base which separate the regions where the S^3 shrinks to zero size from those
where the S^1 shrinks.Comment: 94 pages, 6 figures, latex, typos corrected, references added, one
new Appendi
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