38,940 research outputs found
Nanostructuring of glass micro-nanowires
In the past decade, glass fiber tapers with micron or sub-micron diameter have attracted much attention and found a wide range of applications in optics [1] including mode filtering, supercontinuum generation, high-Q resonators and resonant sensing, optical trapping and optical propulsion. Nanofabrication can add new application opportunities, like Fabry-Perot resonators, Scanning near-field optical microscopy (SNOM) probe and surface plasmon resonators
MAC Layer performance analysis of dense small cell networks with full duplex
© 2018 IEEE. The study of full duplex (FD) is important because it has been identified as one of the candidate technologies for the 5th-generation (5G) networks. Small cell networks (SCNs) are envisioned to embrace the FD transmission technology in order to increase the spectral efficiency of wireless systems. In this paper, for the first time, we consider FD communications in a realistic small cell networks (SCN) scenario, where base stations (BSs) can select FD or half-duplex (HD) mode according to the real-time downlink (DL)/uplink (UL) traffic. We present analytical results on the probabilities of BS mode selection, which match the simulation results well
On the Vertex Operators of the Elliptic Quantum Algebra }
A realization of the elliptic quantum algebra for
any given level is constructed in terms of three free boson fields and
their accompanying twisted partners. It can be viewed as the elliptic
deformation of Wakimoto realization. Two screening currents are constructed;
they commute or anti-commute with modulo total
q-differences. The free fields realization for two types vertex operators
nominated as the type and the type vertex operators are presented. The
twisted version of the two types vertex operators are also obtained. They all
play crucial roles in calculating correlation functions.Comment: 23 page
H-Alpha and Hard X-Ray Observations of a Two-Ribbon Flare Associated with a Filament Eruption
We perform a multi-wavelength study of a two-ribbon flare on 2002 September
29 and its associated filament eruption, observed simultaneously in the H-alpha
line by a ground-based imaging spectrograph and in hard X-rays by RHESSI. The
flare ribbons contain several H-alpha bright kernels that show different
evolutional behaviors. In particular, we find two kernels that may be the
footpoints of a loop. A single hard X-ray source appears to cover these two
kernels and to move across the magnetic neutral line. We explain this as a
result of the merging of two footpoint sources that show gradually asymmetric
emission owing to an asymmetric magnetic topology of the newly reconnected
loops. In one of the H-alpha kernels, we detect a continuum enhancement at the
visible wavelength. By checking its spatial and temporal relationship with the
hard X-ray emission, we ascribe it as being caused by electron beam
precipitation. In addition, we derive the line-of-sight velocity of the
filament plasma based on the Doppler shift of the filament-caused absorption in
the H-alpha blue wing. The filament shows rapid acceleration during the
impulsive phase. These observational features are in principal consistent with
the general scenario of the canonical two-ribbon flare model.Comment: 15 pages, 5 figures, accepted for publication in Ap
Three realizations of quantum affine algebra
In this article we establish explicit isomorphisms between three realizations
of quantum twisted affine algebra : the Drinfeld ("current")
realization, the Chevalley realization and the so-called realization,
investigated by Faddeev, Reshetikhin and Takhtajan.Comment: 15 page
Evolution of the Fermi surface with carrier concentration in Bi_2Sr_2CaCu_2O_{8+\delta}
We show, by use of angle-resolved photoemission spectroscopy, that underdoped
Bi_2Sr_2CaCu_2O_{8+\delta} appears to have a large Fermi surface centered at
(\pi,\pi), even for samples with a T_c as low as 15 K. No clear evidence of a
Fermi surface pocket around (\pi/2,\pi/2) has been found. These conclusions are
based on a determination of the minimum gap locus in the pseudogap regime T_c <
T < T^*, which is found to coincide with the locus of gapless excitations in
momentum space (Fermi surface) determined above T^*. These results suggest that
the pseudogap is more likely of precursor pairing rather than magnetic origin.Comment: 4 pages, revtex, 4 postscript color figure
Extraction of the Electron Self-Energy from Angle Resolved Photoemission Data: Application to Bi2212
The self-energy , the fundamental function which
describes the effects of many-body interactions on an electron in a solid, is
usually difficult to obtain directly from experimental data. In this paper, we
show that by making certain reasonable assumptions, the self-energy can be
directly determined from angle resolved photoemission data. We demonstrate this
method on data for the high temperature superconductor
(Bi2212) in the normal, superconducting, and pseudogap phases.Comment: expanded version (6 pages), to be published, Phys Rev B (1 Sept 99
Internal stress wave measurements in solids subjected to lithotripter pulses
Semiconductor strain gauges were used to measure the internal strain along the axes of spherical and disk plaster specimens when subjected to lithotripter shock pulses. The pulses were produced by one of two lithotripters. The first source generates spherically diverging shock waves of peak pressure approximately 1 MPa at the surface of the specimen. For this source, the incident and first reflected pressure (P) waves in both sphere and disk specimens were identified. In addition, waves reflected by the disk circumference were found to contribute significantly to the strain fields along the disk axis. Experimental results compared favorably to a ray theory analysis of a spherically diverging shock wave striking either concretion. For the sphere, pressure contours for the incident P wave and caustic lines were determined theoretically for an incident spherical shock wave. These caustic lines indicate the location of the highest stresses within the sphere and therefore the areas where damage may occur. Results were also presented for a second source that uses an ellipsoidal reflector to generate a 30-MPa focused shock wave, more closely approximating the wave fields of a clinical extracorporeal lithotripter
Magnetic Reconnection resulting from Flux Emergence: Implications for Jet Formation in the lower solar atmosphere?
We aim at investigating the formation of jet-like features in the lower solar
atmosphere, e.g. chromosphere and transition region, as a result of magnetic
reconnection. Magnetic reconnection as occurring at chromospheric and
transition regions densities and triggered by magnetic flux emergence is
studied using a 2.5D MHD code. The initial atmosphere is static and isothermal,
with a temperature of 20,000 K. The initial magnetic field is uniform and
vertical. Two physical environments with different magnetic field strength (25
G and 50 G) are presented. In each case, two sub-cases are discussed, where the
environments have different initial mass density. In the case where we have a
weaker magnetic field (25 G) and higher plasma density (
cm), valid for the typical quiet Sun chromosphere, a plasma jet would be
observed with a temperature of 2--3 K and a velocity as high as
40 km/s. The opposite case of a medium with a lower electron density
( cm), i.e. more typical for the transition region,
and a stronger magnetic field of 50 G, up-flows with line-of-sight velocities
as high as 90 km/s and temperatures of 6 10 K, i.e. upper
transition region -- low coronal temperatures, are produced. Only in the latter
case, the low corona Fe IX 171 \AA\ shows a response in the jet which is
comparable to the O V increase. The results show that magnetic reconnection can
be an efficient mechanism to drive plasma outflows in the chromosphere and
transition region. The model can reproduce characteristics, such as temperature
and velocity for a range of jet features like a fibril, a spicule, an hot X-ray
jet or a transition region jet by changing either the magnetic field strength
or the electron density, i.e. where in the atmosphere the reconnection occurs.Comment: 11 pages, 13 figures, 2 table
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