2,194 research outputs found
Congruences of lines in , quadratic normality, and completely exceptional Monge-Amp\`ere equations
The existence is proved of two new families of locally Cohen-Macaulay sextic
threefolds in , which are not quadratically normal. These
threefolds arise naturally in the realm of first order congruences of lines as
focal loci and in the study of the completely exceptional Monge-Amp\`ere
equations. One of these families comes from a smooth congruence of multidegree
which is a smooth Fano fourfold of index two and genus 9.Comment: 16 page
Magnetism and Superconductivity in (RE)Ni2B2C: The Case of TmNi2B2C
The recently reported coexistence of an oscillatory magnetic order with the
wave vector Q=0.241 \AA^{-1} and superconductivity in TmNi2B2C is analyzed
theoretically. It is shown that the oscillatory magnetic order and
superconductivity interact predominantly via the exchange interaction between
localized moments (LM's) and conduction electrons, while the electromagnetic
interaction between them is negligible. In the coexistence phase of the clean
TmNi2B2C the quasiparticle spectrum should have a line of zeros at the Fermi
surface, giving rise to the power law behavior of thermodynamic and transport
properties. Two scenarios of the origin of the oscillatory magnetic order in
TmNi2B2C are analyzed: a) due to superconductivity and b) independently on
superconductivity. Experiments in magnetic field are proposed in order to
choose between them.Comment: 12 pages with 2 PS figures, RevTe
Superhydrophobic structures on 316L stainless steel surfaces machined by nanosecond pulsed laser
In this paper nanosecond laser machining process was developed to improve the hydrophobicity of AISI 316L stainless steel surface. A geometrical model of laser machined Gaussian micro hole, together with constrain conditions, was established for the first time to predict surface contact angle and optimize structure geometries for maximizing its hydrophobicity. The effects of processing laser power and pitch of microstructures on the topography of the machined surface were investigated through laser machining experiment. Subsequently, the water droplet contact angle was measured to evaluate the hydrophobicity of different specimens. Results show that under the laser power of 10 W and 14 W, with the increase of the pitch of microstructures, the contact angle increases until it reaches its peak value then drops gradually. Under the large pitch of microstructure, the contact angle will increase with the increase of the processing laser power. Under the same pitch of microstructure, the contact angle will increase with the increase of ten-point height of surface topography, Sz which is a better parameter than Sa (arithmetical mean height) to characterise hydrophobicity of surface with Gaussian holes. This study shows that large Sz is an essential condition to form the stable and robust Cassie–Baxter state, i.e. a condition to achieve superhydrophobicity. The comparison between the predicted and measured contact angles in experiments shows that the proposed model can accurately predict contact angle and optimize the geometries of the microstructure to achieve maximum hydrophobicity
Perturbative QCD Fragmentation Functions for and Production
The dominant production mechanism for bound states in high
energy processes is the production of a high energy or quark,
followed by its fragmentation into the state. We calculate the
fragmentation functions for the production of the S-wave states and
to leading order in the QCD coupling constant. The fragmentation
probabilities for and
are approximately and , while those
for and are smaller by almost two
orders of magnitude.Comment: Latex, 12 pages, 3 figures available upon request, NUHEP-TH-93-
Dynamic instability in resonant tunneling
We show that an instability may be present in resonant tunneling through a
quantum well in one, two and three dimensions, when the resonance lies near the
emitter Fermi level. A simple semiclassical model which simulates the resonance
and the projected density of states by a nonlinear conductor, the Coulomb
barrier by a capacitance, and the time evolution by an iterated map, is used.
The model reproduces the observed hysteresis in such devices, and exhibits a
series of bifurcations leading to fast chaotic current fluctuations.Comment: 7 pages, 2 figure
A Review of Unsupervised Spectral Target Analysis for Hyperspectral Imagery
One of great challenges in unsupervised hyperspectral target analysis is how to obtain desired knowledge in an unsupervised means directly from the data for image analysis. This paper provides a review of unsupervised target analysis by first addressing two fundamental issues, "what are material substances of interest, referred to as targets?" and "how can these targets be extracted from the data?" and then further developing least squares (LS)-based unsupervised algorithms for finding spectral targets for analysis. In order to validate and substantiate the proposed unsupervised hyperspectral target analysis, three applications in endmember extraction, target detection and linear spectral unmixing are considered where custom-designed synthetic images and real image scenes are used to conduct experiments
Realistic constraints on the doubly charged bilepton couplings from Bhabha scattering with LEP data
Upper limits on doubly charged bilepton couplings and masses are extracted
from LEP data for Bhabha scattering at energy range GeV
using standard model program ZFITTER which calculates radiative corrections. We
find that at 95% C.L. for scalar and
vector bileptons.Comment: 5 pages, 1 EPS figur
A batch-service queueing model with a discrete batch Markovian arrival process
Queueing systems with batch service have been investigated extensively during the past decades. However, nearly all the studied models share the common feature that an uncorrelated arrival process is considered, which is unrealistic in several real-life situations. In this paper, we study a discrete-time queueing model, with a server that only initiates service when the amount of customers in system (system content) reaches or exceeds a threshold. Correlation is taken into account by assuming a discrete batch Markovian arrival process (D-BMAP), i.e. the distribution of the number of customer arrivals per slot depends on a background state which is determined by a first-order Markov chain. We deduce the probability generating function of the system content at random slot marks and we examine the influence of correlation in the arrival process on the behavior of the system. We show that correlation merely has a small impact on the threshold that minimizes the mean system content. In addition, we demonstrate that correlation might have a significant influence on the system content and therefore has to be included in the model
Decoupling of superconducting layers in magnetic superconductor RuSr_{2}GdCu_{2}O_{8}
We propose the model for magnetic properties of the magnetic superconductor
RuSrGdCuO, which incorporates the theory of the
superconducting/ferromagnetic multilayers. The transition line , on
which the Josephson coupled superconducting planes are decoupled, i.e. , is calculated as a function of the exchange energy . As the
result of this decoupling a nonmonotonic behavior of magnetic properties, like
the lower critical field , Josephson plasma frequency, etc. is realized
near (or by crossing) the line. The obtained results are used in
analyzing the newly discovered antiferromagnetic ruthenocuprate
RuSrGdCuO with possible weak ferromagnetic order in the RuO
planes.Comment: 12 pages, 3 figs embede
Approach to the semiconductor cavity QED in high-Q regimes with q-deformed boson
The high density Frenkel exciton which interacts with a single mode
microcavity field is dealed with in the framework of the q-deformed boson. It
is shown that the q-defomation of bosonic commutation relations is satisfied
naturally by the exciton operators when the low density limit is deviated. An
analytical expression of the physical spectrum for the exciton is given by
using of the dressed states of the cavity field and the exciton. We also give
the numerical study and compare the theoretical results with the experimental
resultsComment: 6 pages, 2 figure
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