3,837 research outputs found
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
Monolithic microwave integrated circuit water vapor radiometer
A proof of concept Monolithic Microwave Integrated Circuit (MMIC) Water Vapor Radiometer (WVR) is under development at the Jet Propulsion Laboratory (JPL). WVR's are used to remotely sense water vapor and cloud liquid water in the atmosphere and are valuable for meteorological applications as well as for determination of signal path delays due to water vapor in the atmosphere. The high cost and large size of existing WVR instruments motivate the development of miniature MMIC WVR's, which have great potential for low cost mass production. The miniaturization of WVR components allows large scale deployment of WVR's for Earth environment and meteorological applications. Small WVR's can also result in improved thermal stability, resulting in improved calibration stability. Described here is the design and fabrication of a 31.4 GHz MMIC radiometer as one channel of a thermally stable WVR as a means of assessing MMIC technology feasibility
Long Term Failure in Compacted Clay Slopes
The results of field, laboratory, and analytical investigations of recurring slope failures along the Mississippi River Levee are presented. Observations from slide trenching operations are described. Laboratory measured shear strengths are compared to effective strengths at failure back-calculated for two slides. Factors influencing the long term behavior of the levee materials and the mechanism of failure are discussed
Significant enhancement of irreversibility field in clean-limit bulk MgB2
Low resistivity ("clean") MgB2 bulk samples annealed in Mg vapor show an
increase in upper critical field Hc2(T) and irreversibility field Hirr(T) by a
factor of 2 in both transport and magnetic measurements. The best sample
displayed Hirr above 14 T at 4.2 K and 6 T at 20 K. These changes were
accompanied by an increase of the 40 K resistivity from 1.0 to 18 microohm-cm
and a lowering of the resistivity ratio from 15 to 3, while the critical
temperature Tc decreased by only 1-2 K. These results point the way to make
prepare MgB2 attractive for magnet applications.Comment: 3 pages, 4 figures, submitted to Applied Physics Letter
Enhancement of the upper critical field of Nb3Sn utilizing disorder introduced by ball milling the elements
Nb3Sn was prepared by milling Nb and Sn powder mixtures followed by limited
reactions to restrict disorder recovery. Although disorder reduced the
superconducting critical temperature Tc, the concomitant electron scattering
increased the upper critical field mu0Hc2 to as high as 35 T at 0 K, as
determined by the Werthamer-Helfand-Hohenberg equation. Hc2 was higher for
longer milling times and lower annealing temperatures. Substitution of 2% Ti
for Nb did not appreciably enhance Hc2, suggesting that alloying mitigates the
benefits of disorder. Since alloyed Nb3Sn wires have mu0Hc2(0) approximately 29
T, wires based on heavily milled powders could extend the field range for
applications if they can be made with high current density
Slide Stabilization With Gravel Trenches
A different method of slide stabilization using gravel trenches is described. The design, construction, and performance monitoring of the gravel trenches are discussed together with a history of the slide, description of the soils, and mechanism of failure. The applications and limitations of this method of slide stabilization are also evaluated
Uncovering the Hidden Order in URu2Si2 by Impurity Doping
We report the use of impurities to probe the hidden order parameter of the
strongly correlated metal URu_2Si_2 below the transition temperature T_0 ~ 17.5
K. The nature of this order parameter has eluded researchers for more than two
decades, but is accompanied by the development of a partial gap in the single
particle density of states that can be detected through measurements of the
electronic specific heat and nuclear spin-lattice relaxation rate. We find that
impurities in the hidden order phase give rise to local patches of
antiferromagnetism. An analysis of the coupling between the antiferromagnetism
and the hidden order reveals that the former is not a competing order parameter
but rather a parasitic effect of the latter.Comment: 4 pages, 4 figure
Gravity localization on thick branes: a numerical approach
We introduce a numerical procedure to investigate the spectrum of massive
modes and its contribution for gravity localization on thick branes. After
considering a model with an analytically known Schroedinger potential, we
present the method and discuss its applicability. With this procedure we can
study several models even when the Schroedinger potential is not known
analytically. We discuss both the occurrence of localization of gravity and the
correction to the Newtonian potential given by the massive modes.Comment: 22 pages, 12 figure
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