3,040 research outputs found
Bandgap properties of two-dimensional low-index photonic crystals
We study the bandgap properties of two-dimensional photonic crystals created
by a lattice of rods or holes conformed in a symmetric or asymmetric triangular
structure. Using the plane-wave analysis, we calculate a minimum value of the
refractive index contrast for opening both partial and full two-dimensional
spectral gaps for both TM and TE polarized waves. We also analyze the effect of
ellipticity of rods and holes and their orientation on the threshold value and
the relative size of the bandgap.Comment: 5 pages, 6 figures, App. Phys. B. styl
Entanglement in spin-1/2 dimerized Heisenberg systems
We study entanglement in dimerized Heisenberg systems. In particular, we give
exact results of ground-state pairwise entanglement for the four-qubit model by
identifying a Z_2 symmetry. Although the entanglements cannot identify the
critical point of the system, the mean entanglement of nearest-neighbor qubits
really does, namely, it reaches a maximum at the critical point.Comment: Four pages, three figures, accepted in Communications in Theoretical
Physic
On optimal summable graphs
For a graph G , let Ï ( G ) and ÎŽ ( G ) denote, respectively, its sum number and minimum degree. Trivially, Ï ( G ) â„ ÎŽ ( G ) . A nontrivial connected graph G is called a k -optimum summable graph , where k â„ 1 , if Ï ( G ) = ÎŽ ( G ) = k . In this paper, we show that if G is a k -optimum summable graph of order n , k â„ 3 , then (1) n â„ 2 k ; (2) the complete bipartite graph K k,n â k is not a spanning subgraph of G . We also describe new families of k -optimum summable graphs for k â„ 1
Differential selectivity of CIITA promoter activation by IFN-γ and IRF- 1 in astrocytes and macrophages: CIITA promoter activation is not affected by TNF-α
During demyelinating disease of the central nervous system (CNS), locally elevated cytokine levels may induce upregulation of MHC class II molecules on otherwise low expressing or negative cell types such as microglia and astrocytes, since IFN-γ has been shown to induce MHC class II expression on these cell types in vitro. While many transcription factors are involved with MHC class II expression, only the class II transactivator (CIITA) is tightly coordinated with IFN-γ-inducibility. Control of CIITA gene expression is complex, involving four distinct promoters, two of which (promoters III and IV) are IFN-γ-inducible in certain cell types. Here we demonstrate that IFN-γ treatment of rat astrocytes induces only CIITA promoter IV activity in contrast to the murine macrophage cell line RAW 264.7 that uses both IFN-γ-inducible promoters. In contrast to previously published reports, promoter IV activation is completely dependent upon an intact interferon regulatory factor-1 (IRF-1) but not STAT1 binding site using promoter constructs specifically mutated at these positions. Importantly, while TNF-α is able to synergize with IFN-γ to increase astrocyte MHC class II expression in vitro, we show that treatment of rat astrocytes with TNF-α has no effect on CIITA promoter activity. These data demonstrate that TNF-α augments MHC class II expression through a mechanism downstream or independent of CIITA induction
Mass spectrum of the axial-vector hidden charmed and hidden bottom tetraquark states
In this article, we perform a systematic study of the mass spectrum of the
axial-vector hidden charmed and hidden bottom tetraquark states using the QCD
sum rules, and identify the as an axial-vector tetraquark state
tentatively.Comment: 24 pages, 38 figures, slight revisio
Temperature dependence of Vortex Charges in High Temperature Superconductors
Using a model Hamiltonian with d-wave superconductivity and competing
antiferromagnetic (AF) interactions, the temperature (T) dependence of the
vortex charge in high T_c superconductors is investigated by numerically
solving the Bogoliubov-de Gennes equations. The strength of the induced AF
order inside the vortex core is T dependent. The vortex charge could be
negative when the AF order with sufficient strength is present at low
temperatures. At higher temperatures, the AF order may be completely suppressed
and the vortex charge becomes positive. A first order like transition in the T
dependent vortex charge is seen near the critical temperature T_{AF}. For
underdoped sample, the spatial profiles of the induced spin-density wave and
charge-density wave orders could have stripe like structures at T < T_s, and
change to two-dimensional isotropic ones at T > T_s. As a result, a vortex
charge discontinuity occurs at T_s.Comment: 5 pages, 5 figure
Characterization of unresolved and unclassified sources detected in radio continuum surveys of the Galactic plane
The continuum emission from 1 to 2 GHz of The HI/OH/Recombination line survey of the inner Milky Way (THOR) at 0.5) of the FIRST survey indicates that these sources might be high z extragalactic compact objects. The similar pattern of one-point and two-point statistics of unclassified and compact sources with extragalactic surveys and simulations confirms the extragalactic origin of these sources
Upper critical field calculations for the high critical temperature superconductors considering inhomogeneities
We perform calculations to obtain the curve of high temperature
superconductors (HTSC). We consider explicitly the fact that the HTSC possess
intrinsic inhomogeneities by taking into account a non uniform charge density
. The transition to a coherent superconducting phase at a critical
temperature corresponds to a percolation threshold among different
superconducting regions, each one characterized by a given .
Within this model we calculate the upper critical field by means of an
average linearized Ginzburg-Landau (GL) equation to take into account the
distribution of local superconducting temperatures . This
approach explains some of the anomalies associated with and why
several properties like the Meissner and Nernst effects are detected at
temperatures much higher than .Comment: Latex text, add reference
Interaction Properties of the Periodic and Step-like Solutions of the Double-Sine-Gordon Equation
The periodic and step-like solutions of the double-Sine-Gordon equation are
investigated, with different initial conditions and for various values of the
potential parameter . We plot energy and force diagrams, as functions
of the inter-soliton distance for such solutions. This allows us to consider
our system as an interacting many-body system in 1+1 dimension. We therefore
plot state diagrams (pressure vs. average density) for step-like as well as
periodic solutions. Step-like solutions are shown to behave similarly to their
counterparts in the Sine-Gordon system. However, periodic solutions show a
fundamentally different behavior as the parameter is increased. We
show that two distinct phases of periodic solutions exist which exhibit
manifestly different behavior. Response functions for these phases are shown to
behave differently, joining at an apparent phase transition point.Comment: 17pages, 15 figure
Dynamics of Entanglement in One-Dimensional Spin Systems
We study the dynamics of quantum correlations in a class of exactly solvable
Ising-type models. We analyze in particular the time evolution of initial Bell
states created in a fully polarized background and on the ground state. We find
that the pairwise entanglement propagates with a velocity proportional to the
reduced interaction for all the four Bell states. Singlet-like states are
favored during the propagation, in the sense that triplet-like states change
their character during the propagation under certain circumstances.
Characteristic for the anisotropic models is the instantaneous creation of
pairwise entanglement from a fully polarized state; furthermore, the
propagation of pairwise entanglement is suppressed in favor of a creation of
different types of entanglement. The ``entanglement wave'' evolving from a Bell
state on the ground state turns out to be very localized in space-time. Further
support to a recently formulated conjecture on entanglement sharing is given.Comment: 25 pages, 21 figures; revte
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