48,959 research outputs found
The Cylindrical Antenna with Tapered Resistive Loading Scientific Report No. 5
Current, input impedance, and far field pattern of cylindrical antenna with tapered resistive loadin
Role of internal gases and creep of Ag in controlling the critical current density of Ag-sheathed Bi2Sr2CaCu2Ox wires
High engineering critical current density JE of >500 A/mm2 at 20 T and 4.2 K
can be regularly achieved in Ag-sheathed multifilamentary Bi2Sr2CaCu2Ox
(Bi-2212) round wire when the sample length is several centimeters. However,
JE(20 T) in Bi-2212 wires of several meters length, as well as longer pieces
wound in coils, rarely exceeds 200 A/mm2. Moreover, long-length wires often
exhibit signs of Bi-2212 leakage after melt processing that are rarely found in
short, open-end samples. We studied the length dependence of JE of
state-of-the-art powder-in-tube (PIT) Bi-2212 wires and gases released by them
during melt processing using mass spectroscopy, confirming that JE degradation
with length is due to wire swelling produced by high internal gas pressures at
elevated temperatures [1,2]. We further modeled the gas transport in Bi-2212
wires and examined the wire expansion at critical stages of the melt processing
of as-drawn PIT wires and the wires that received a degassing treatment or a
cold-densification treatment before melt processing. These investigations
showed that internal gas pressure in long-length wires drives creep of the Ag
sheath during the heat treatment, causing wire to expand, lowering the density
of Bi-2212 filaments, and therefore degrading the wire JE; the creep rupture of
silver sheath naturally leads to the leakage of Bi-2212 liquid. Our work shows
that proper control of such creep is the key to preventing Bi-2212 leakage and
achieving high JE in long-length Bi-2212 conductors and coils
A simple theory of dipole antennas
Simple and quantitatively accurate representation of current distribution in dipole antenna
Absence of magnetic long range order in YCrSbO: bond-disorder induced magnetic frustration in a ferromagnetic pyrochlore
The consequences of nonmagnetic-ion dilution for the pyrochlore family
Y()O ( = magnetic ion, = nonmagnetic
ion) have been investigated. As a first step, we experimentally examine the
magnetic properties of YCrSbO ( = 0.5), in which the magnetic
sites (Cr) are percolative. Although the effective Cr-Cr spin exchange
is ferromagnetic, as evidenced by a positive Curie-Weiss temperature,
= 20.1(6) K, our high-resolution neutron powder
diffraction measurements detect no sign of magnetic long range order down to 2
K. In order to understand our observations, we performed numerical simulations
to study the bond-disorder introduced by the ionic size mismatch between
and . Based on these simulations, bond-disorder ( 0.23)
percolates well ahead of site-disorder ( 0.61). This model
successfully reproduces the critical region (0.2 < < 0.25) for the N\'eel
to spin glass phase transition in Zn(CrGa)O, where
the Cr/Ga-sublattice forms the same corner-sharing tetrahedral network as the
-sublattice in Y()O, and the rapid drop in
magnetically ordered moment in the N\'eel phase [Lee , Phys. Rev. B
77, 014405 (2008)]. Our study stresses the nonnegligible role of bond-disorder
on magnetic frustration, even in ferromagnets
The spectral energy distribution of galaxies at z > 2.5: Implications from the Herschel/SPIRE color-color diagram
We use the Herschel SPIRE color-color diagram to study the spectral energy
distribution (SED) and the redshift estimation of high-z galaxies. We compiled
a sample of 57 galaxies with spectroscopically confirmed redshifts and SPIRE
detections in all three bands at , and compared their average SPIRE
colors with SED templates from local and high-z libraries. We find that local
SEDs are inconsistent with high-z observations. The local calibrations of the
parameters need to be adjusted to describe the average colors of high-z
galaxies. For high-z libraries, the templates with an evolution from z=0 to 3
can well describe the average colors of the observations at high redshift.
Using these templates, we defined color cuts to divide the SPIRE color-color
diagram into different regions with different mean redshifts. We tested this
method and two other color cut methods using a large sample of 783
Herschel-selected galaxies, and find that although these methods can separate
the sample into populations with different mean redshifts, the dispersion of
redshifts in each population is considerably large. Additional information is
needed for better sampling.Comment: 17 pages, 14 figures, accepted for publication in A&
Electroweak Theory Without Higgs Bosons
A perturbative SU(2)_L X U(1)_Y electroweak theory containing W, Z, photon,
ghost, lepton and quark fields, but no Higgs or other fields, gives masses to
W, Z and the non-neutrino fermions by means of an unconventional choice for the
unperturbed Lagrangian and a novel method of renormalisation. The
renormalisation extends to all orders. The masses emerge on renormalisation to
one loop. To one loop the neutrinos are massless, the A -> Z transition drops
out of the theory, the d quark is unstable and S-matrix elements are
independent of the gauge parameter xi.Comment: 27 pages, LaTex, no figures; revised for publication; accepted by
Int. J. Mod. Phys. A; includes biographical note on A. F. Nicholso
Photoluminescence and spectral switching of single CdSe/ZnS colloidal nanocrystals in poly(methyl methacrylate)
Emission from single CdSe nanocrystals in PMMA was investigated. A fraction
of the nanocrystals exhibiting switching between two energy states, which have
similar total intensities, but distinctly different spectra were observed. We
found that the spectral shift characteristic frequency increases with the pump
power. By using the dynamic shift in the spectral position of emission peaks,
we were able to correlate peaks from the same nanocrystal. The measured
correlation is consistent with assignment of low energy lines to phonon
replicas.Comment: 5 pages, 4 figure
Anti-correlation and subsector structure in financial systems
With the random matrix theory, we study the spatial structure of the Chinese
stock market, American stock market and global market indices. After taking
into account the signs of the components in the eigenvectors of the
cross-correlation matrix, we detect the subsector structure of the financial
systems. The positive and negative subsectors are anti-correlated each other in
the corresponding eigenmode. The subsector structure is strong in the Chinese
stock market, while somewhat weaker in the American stock market and global
market indices. Characteristics of the subsector structures in different
markets are revealed.Comment: 6 pages, 2 figures, 4 table
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