3,611 research outputs found
Low-energy limit of the three-band model for electrons in a CuO plane
The three-band model with the O-O direct hopping near to unit filling is
considered. We present the general procedure of reduction of this model to the
low-energy limit. At unit filling the three-band model in the charge-transfer
limit is reduced to the Heisenberg model and we calculate the superexchange
constant. For the case of the small electron doping the three-band model is
reduced to the model and we calculate electron hopping parameters at the
nearest and next neighbors. We derive the structure of corrections to the
model and calculate their magnitude. The values of the hopping parameters for
electron- and hole-doping differ approximately at 40 %.Comment: 10 pp. (LATEX
Plasma Magnetosphere Formation Around Oscillating Magnetized Neutron Stars
The notion of death line of rotating pulsars is applied to model of
oscillating neutron stars. It is shown that the magnetosphere of typical
non-rotating oscillating stars may not contain secondary plasma to support the
generation of radio emission in the region of open field lines of plasma
magnetosphere.Comment: Accepted for publication in Astrophysics & Space Scienc
Super-high temperature sensitivity of long-period gratings in B/Ge co-doped fiber
Long period fiber grating (LPFG) can be used as active gain controlling device in EDFA. However, LPFGs fabricated in the standard telecom fiber only have a typical temperature sensitivity of 3-10nm/100°C, which may not be sufficient for implementing tuneable filters capable of wide tuning range and high tuning efficiency. In this paper, we report a theoretical and experimental investigation of thermal properties of LPFGs fabricated in B/Ge co-doped optical fiber. We have found that the temperature sensitivity of the LPFGs in the B/Ge fiber is considerably increased compared with those produced in the standard fiber. The LPFGs written in the B/Ge fiber have achieved, on average, one order of magnitude higher sensitivity than that of the LPFGs produced in the standard telecom fiber. We have also identified that the thermal response of LPFG is strongly dependent on the order of the coupled resonant cladding mode. The maximum sensitivity of 1.75nm/°C achieved by the 10th cladding mode of the 240μm LPFG is nearly 24 times that of the minimum value (0.075nm/C) exhibited by the 30th mode of the 34μm LPFG. Such devices may lead to high-efficiency and low-cost thermal/electrical tunable loss filters or sensors with extremely high temperature resolution
Importing Timber, Exporting Ecological Impact
Covering 32% of the planet, boreal forests are one of the last relatively intact terrestrial biomes, and are a critical carbon sink in global climate dynamics. Mature and old-growth boreal forests provide a large number of products that are culturally and economically important, from wood-based lumber, pulp, and fuel wood, to numerous nonwood products. Intensive wood harvest and conservation of naturally dynamic intact forests tend to be mutually exclusive; where biodiversity is highly valued, wood harvests are limited or banned outright. The authors of this Policy Forum advise that increasing domestic forest protection without decreasing demand for wood necessitates an increase in foreign imports, which introduces a negative impact on forest biodiversity elsewhere. In some cases, exporting impact across the border may cause negative impacts to boomerang back into the country's protected forests
Study of f_0(980) and f_0(1500) from B_s \to f_0(980)\pi, f_0(1500)\pi Decays
In this paper, we analyze the scalar mesons and from
the decays within Perturbative
QCD approach. From the leading order calculations, we find that (a) in the
allowed mixing angle ranges, the branching ratio of is about , which is smaller than
that of (the difference is a few times even one
order); (b) the decay is better to distinguish
between the lowest lying state or the first excited state for ,
because the branching ratios for two scenarios have about one-order difference
in most of the mixing angle ranges; and (c) the direct CP asymmetries of for two scenarios also exists great difference. In
scenario II, the variation range of the value according to the mixing angle is very small, except for
the values corresponding to the mixing angles being near or
, while the variation range of in scenario I is very large. Compared with the future data for
the decay , it is ease to determine the nature
of the scalar meson .Comment: 16 pages, 3 figures, Revte
High frequency magnetic permeability of nanocomposite film
The high frequency magnetic permeability of nanocomposite film consisting of
the single-domain spherical ferromagnetic particles in the dielectric matrix is
studied. The permeability is assumed to be determined by rotation of the
ferromagnetic inclusion magnetic moments around equilibrium direction in AC
magnetic field. The composite is modeled by a cubic array of ferromagnetic
particles. The magnetic permeability tensor is calculated by solving the
Landau-Lifshits-Gilbert equation accounting for the dipole interaction of
magnetic particles. The permeability tensor components are found as functions
of the frequency, temperature, ferromagnetic inclusions density and magnetic
anisotropy. The obtained results show that nanocomposite films could have
rather high value of magnetic permeability in the microwave range
Degree-distribution Stability of Growing Networks
In this paper, we abstract a kind of stochastic processes from evolving
processes of growing networks, this process is called growing network Markov
chains. Thus the existence and the formulas of degree distribution are
transformed to the corresponding problems of growing network Markov chains.
First we investigate the growing network Markov chains, and obtain the
condition in which the steady degree distribution exists and get its exact
formulas. Then we apply it to various growing networks. With this method, we
get a rigorous, exact and unified solution of the steady degree distribution
for growing networks.Comment: 12 page
Nanotribological Investigation of Polymer Brushes with Lithographically Defined and Systematically Varying Grafting Densities.
Following controlled photodeprotection of a 2-nitrophenylpropyloxycarbonyl-protected (aminopropyl)triethoxysilane (NPPOC-APTES) film and subsequent derivatization with a bromoester-based initiator, poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC) brushes with various grafting densities were grown from planar silicon substrates using atom transfer radical polymerization (ATRP). The grafting density correlated closely with the extent of deprotection of the NPPOC-APTES. The coefficient of friction for such PMPC brushes was measured by friction force microscopy in water and found to be inversely proportional to the grafting density due to the osmotic pressure that resists deformation. Deprotection of NPPOC-APTES via near-field photolithography using a range of writing rates enabled the fabrication of neighboring nanoscopic polymeric structures with dimensions ranging from 100 to 1000 nm. Slow writing rates enable complete deprotection to occur; hence, polymer brushes are formed with comparable thicknesses to macroscopic brushes grown under the same conditions. However, the extent of deprotection is reduced at higher writing rates, resulting in the concomitant reduction of the brush thickness. The coefficient of friction for such polymer brushes varied smoothly with brush height, with lower coefficients being obtained at slower writing rate (increasing initiator density) because the solvated brush layer confers greater lubricity. However, when ultrasharp probes were used for nanotribological measurements, the coefficient of friction increased with brush thickness. Under such conditions, the radius of curvature of the tip is comparable to the mean spacing between brush chains, allowing the probe to penetrate the brush layer leading to a relatively large contact area
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