31,975 research outputs found
Sign Changes of Intrinsic Spin Hall Effect in Semiconductors and Simple Metals: First-Principles Calculations
First-principles calculations are applied to study spin Hall effect in
semiconductors and simple metals. We found that intrinsic spin Hall
conductivity (ISHC) in realistic materials shows rich sign changes, which may
be used to distinguish the effect from the extrinsic one. The calculated ISHC
in n-doped GaAs can be well compared with experiment, and it differs from the
sign obtained from the extrinsic effect. On the other hand, the ISHC in W and
Au, which shows opposite sign respectively, is robust and not sensitive to the
disorder.Comment: 4 pages, 4 figure
Protecting dissipative quantum state preparation via dynamical decoupling
We show that dissipative quantum state preparation processes can be protected
against qubit dephasing by interlacing the state preparation control with
dynamical decoupling (DD) control consisting of a sequence of short
-pulses. The inhomogeneous broadening can be suppressed to second order of
the pulse interval, and the protection efficiency is nearly independent of the
pulse sequence but determined by the average interval between pulses. The DD
protection is numerically tested and found to be efficient against
inhomogeneous dephasing on two exemplary dissipative state preparation schemes
that use collective pumping to realize many-body singlets and linear cluster
states respectively. Numerical simulation also shows that the state preparation
can be efficiently protected by -pulses with completely random arrival
time. Our results make possible the application of these state preparation
schemes in inhomogeneously broadened systems. DD protection of state
preparation against dynamical noises is also discussed using the example of
Gaussian noise with a semiclasscial description.Comment: 9 pages, 8 figure
Studies of the role of nf-κb in controlling osteoclast differentiation and bone loss
Increased osteoclast (OC) bone resorption and/or decreased osteoblast (OB) bone formation contribute to bone loss in osteoporosis and rheumatoid arthritis (RA). Findings of the basic and translational research presented in this thesis demonstrate a number of mechanisms by which cytokine-induced NF-κB activation controls bone resorption and formation: 1) Tumour necrosis factor-α (TNF) expands pool of OC precursors (OCPs) by promoting their proliferation through stimulation of the expression of macrophage colony stimulating factor (M-CSF) receptor, c-Fms, and switching M-CSF-induced resident (M2) to inflammatory (M1) macrophages with enhanced OC forming potential and increased production of inflammatory factors through induction of NF-κB RelB; 2) Similar to RANKL, TNF sequentially activates transcriptional factors NF-κB p50 and p52 followed by c-Fos and then NFATc1 to induce OC differentiation. However, TNF alone nduces very limited OC differentiation. In contrast, it pre-activates OCPs to express cFos which cooperates with interleukin-1 (IL-1) produced by these OCPs in an autocrine mechanism by interacting with bone matrix to mediate the OC terminal differentiation and bone resorption from these pre-activated OCPs. 3) TNF-induced OC formation is independent of RANKL but it also induces NF-κB2 p100 to limit OC formation and bone
resorption, and thus p100 deletion accelerates joint destruction and systemic bone loss in TNF-induced RA; 4) TNF receptor associated factor-3 (TRAF3) limits OC
differentiation by negatively regulating non-canonical NF-κB activation and RANKL induces TRAF3 ubiquitination and lysosomal degradation to promote OC differentiation.
Importantly, a lysosomal inhibitor that inhibits TRAF3 degradation prevents ovariectomy-induced bone loss; 5) RelB and Notch NICD bind RUNX2 to inhibit OB differentiation and RelB:p52 dimer association with NICD inhibit OB differentiation by enhancing the binding of RBPjκ to Hes1. These findings suggest that non-canonical NF- κB signaling could be targets to develop new therapies for RA or osteoporosis. For example 1) Agents that degrade TNF-induced RelB could block M1 macrophage differentiation to inhibit inflammation and joint destruction for the therapy of RA; 2)Agents that prevent p100 processing or TRAF3 degradation could inhibit bone resorption and also stimulate bone formation simultaneously for the therapy of osteoporosis
Study on QoS support in 802.11e-based multi-hop vehicular wireless ad hoc networks
Multimedia communications over vehicular ad hoc networks (VANET) will play an important role in the future intelligent transport system (ITS). QoS support for VANET therefore becomes an essential problem. In this paper, we first study the QoS performance in multi-hop VANET by using the standard IEEE 802.11e EDCA MAC and our proposed triple-constraint QoS routing protocol, Delay-Reliability-Hop (DeReHQ). In particular, we evaluate the DeReHQ protocol together with EDCA in highway and urban areas. Simulation results show that end-to-end delay performance can sometimes be achieved when both 802.11e EDCA and DeReHQ extended AODV are used. However, further studies on cross-layer optimization for QoS support in multi-hop environment are required
Does a proton "bubble" structure exist in the low-lying states of 34Si?
The possible existence of a "bubble" structure in the proton density of
Si has recently attracted a lot of research interest. To examine the
existence of the "bubble" structure in low-lying states, we establish a
relativistic version of configuration mixing of both particle number and
angular momentum projected quadrupole deformed mean-field states and apply this
state-of-the-art beyond relativistic mean-field method to study the density
distribution of the low-lying states in Si. An excellent agreement with
the data of low-spin spectrum and electric multipole transition strengths is
achieved without introducing any parameters. We find that the central
depression in the proton density is quenched by dynamic quadrupole shape
fluctuation, but not as significantly as what has been found in a beyond
non-relativistic mean-field study. Our results suggest that the existence of
proton "bubble" structure in the low-lying excited and states
is very unlikely.Comment: 6 pages, 8 figures and 1 table, accepted for publication in Physics
Letters
Covariant description of shape evolution and shape coexistence in neutron-rich nuclei at N\approx60
The shape evolution and shape coexistence phenomena in neutron-rich nuclei at
, including Kr, Sr, Zr, and Mo isotopes, are studied in the
covariant density functional theory (DFT) with the new parameter set PC-PK1.
Pairing correlations are treated using the BCS approximation with a separable
pairing force. Sharp rising in the charge radii of Sr and Zr isotopes at N=60
is observed and shown to be related to the rapid changing in nuclear shapes.
The shape evolution is moderate in neighboring Kr and Mo isotopes. Similar as
the results of previous Hartree-Fock-Bogogliubov (HFB) calculations with the
Gogny force, triaxiality is observed in Mo isotopes and shown to be essential
to reproduce quantitatively the corresponding charge radii. In addition, the
coexistence of prolate and oblate shapes is found in both Sr and
Zr. The observed oblate and prolate minima are related to the low
single-particle energy level density around the Fermi surfaces of neutron and
proton respectively. Furthermore, the 5-dimensional (5D) collective Hamiltonian
determined by the calculations of the PC-PK1 energy functional is solved for
Sr and Zr. The resultant excitation energy of state and
E0 transition strength are in rather good
agreement with the data. It is found that the lower barrier height separating
the two competing minima along the deformation in Zr gives
rise to the larger than that in Sr.Comment: 1 table, 11 figures, 23 page
A Unified and Complete Construction of All Finite Dimensional Irreducible Representations of gl(2|2)
Representations of the non-semisimple superalgebra in the standard
basis are investigated by means of the vector coherent state method and
boson-fermion realization. All finite-dimensional irreducible typical and
atypical representations and lowest weight (indecomposable) Kac modules of
are constructed explicitly through the explicit construction of all
particle states (multiplets) in terms of boson and fermion
creation operators in the super-Fock space. This gives a unified and complete
treatment of finite-dimensional representations of in explicit form,
essential for the construction of primary fields of the corresponding current
superalgebra at arbitrary level.Comment: LaTex file, 23 pages, two references and a comment added, to appear
in J. Math. Phy
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