1,152 research outputs found
Scalable and Fault Tolerant Group Key Management
To address the group key management problem for modern networks this research proposes a lightweight group key management protocol with a gossip-based dissemination routine. Experiments show that by slightly increasing workload for the key update mechanism, this protocol is superior to currently available tree-based protocols with respect to reliability and fault tolerance, while remaining scalable to large groups. Java simulations show that the protocol efficiently distributes keys to large groups in the midst of up to 35 percent node failure rates. In addition, it eliminates the need for logical key hierarchy while preserving an overall reduction in rekey messages to rekey a group. The protocol provides a simple “pull” mechanism to ensure perfect rekeys in spite of the primary rekey mechanism’s probabilistic guarantees, without burdening key distribution facilities. Parameters for overlay management and gossip are improved to minimize rekey message traffic while remaining tolerant to node failure
Elastic Tensor of SrRuO
The six independent elastic constants of SrRuO were determined using
resonant ultrasound spectroscopy on a high-quality single-crystal specimen. The
constants are in excellent agreement with those obtained from pulse-echo
experiments performed on a sample cut from the same ingot. A calculation of the
Debye temperature using the measured constants agrees well with values obtained
from both specific heat and M\"{o}ssbauer measurements.Comment: 4 pages, 2 figures, 2 tables, submitted to PR
Transport in Ultraclean YBaCuO: neither Unitary nor Born Impurity Scattering
The thermal conductivity of ultraclean YBaCuO was measured at
very low temperature in magnetic fields up to 13 T. The temperature and field
dependence of the electronic heat conductivity show that two widespread
assumptions of transport theory applied to unconventional superconductors fail
for clean cuprates: impurity scattering cannot be treated in the usual unitary
limit (nor indeed in the Born limit), and scattering of quasiparticles off
vortices cannot be neglected. Our study also sheds light on the long-standing
puzzle of a sudden onset of a "plateau" in the thermal conductivity of Bi-2212
versus field.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Ultrasonic attenuation in magnetic fields for superconducting states with line nodes in Sr2RuO4
We calculate the ultrasonic attenuation in magnetic fields for
superconducting states with line nodes vertical or horizontal relative to the
RuO_2 planes. This theory, which is valid for fields near Hc2 and not too low
temperatures, takes into account the effects of supercurrent flow and Andreev
scattering by the Abrikosov vortex lattice. For rotating in-plane field
H(theta) the attenuation alpha(theta)exhibits variations of fourfold symmetry
in the rotation angle theta. In the case of vertical nodes, the transverse T100
sound mode yields the weakest(linear)H and T dependence of alpha, while the
longitudinal L100 mode yields a stronger (quadratic) H and T dependence. This
is in strong contrast to the case of horizontal line nodes where alpha is the
same for the T100 and L100 modes (apart from a shift of pi/4 in field
direction) and is roughly a quadratic function of H and T. Thus we conclude
that measurements of alpha in in-plane magnetic fields for different in-plane
sound modes may be an important tool for probing the nodal structure of the gap
in Sr_2RuO_4.Comment: 5 pages, 6 figures, replaced in non-preprint form, to appear in Phys.
Rev.
Interlayer pair tunneling and gap anisotropy in YBaCuO
Recent ARPES measurement observed a large -axis gap anisotropy,
, in clean YBaCuO. This
indicates that some sub-dominant component may exist in the -wave
dominant gap. We propose that the interlayer pairing tunneling contribution can
be determined through the investigation of the order parameter anisotropy.
Their potentially observable features in transport and spin dynamics are also
studied.Comment: 4 pages, 3 figure
Quasiparticle transport in the vortex state of YBa_2Cu_3O_6.9
The effect of vortices on quasiparticle transport in cuprate superconductors
was investigated by measuring the low temperature thermal conductivity of
YBa_2Cu_3O_6.9 in magnetic fields up to 8 T. The residual linear term (as T \to
0) is found to increase with field, directly reflecting the occupation of
extended quasiparticle states. A study for different Zn impurity concentrations
reveals a good agreement with recent calculations for a d-wave superconductor,
thereby shedding light on the nature of scattering by both impurities and
vortices. It also provides a quantitative measure of the gap near the nodes.Comment: 4 pages, 2 included eps figures, significant new analysis wrt other
experiments, to appear in Phys Rev Lett 29 March 199
Cross-country discrepancies on public understanding of stress concepts: evidence for stress-management psychoeducational programs
Low-Energy Quasiparticles in Cuprate Superconductors: A Quantitative Analysis
A residual linear term is observed in the thermal conductivity of
optimally-doped Bi-2212 at very low temperatures whose magnitude is in
excellent agreement with the value expected from Fermi-liquid theory and the
d-wave energy spectrum measured by photoemission spectroscopy, with no
adjustable parameters. This solid basis allows us to make a quantitative
analysis of thermodynamic properties at low temperature and establish that
thermally-excited quasiparticles are a significant, perhaps even the dominant
mechanism in suppressing the superfluid density in cuprate superconductors
Bi-2212 and YBCO.Comment: Revised version with additional page, figure, table and reference; to
appear in Physical Review B (1 August 2000
More on FOX News: FOXA1 on the horizon of estrogen receptor function and endocrine response
Estrogen receptor α (ER) is a major driver of breast cancer and the target of endocrine therapy. Full disclosure of the cofactors regulating ER interactions with chromatin and its transcriptional regulatory activity is still elusive. Novel genome-wide profiling tools have mapped ER binding events in breast cancer cells and delineated cofactors important in ER activity. Among these, the Forkhead protein FOXA1 is emerging as a key factor dictating global chromatin structure and the transcriptional function of ER in breast and non-breast cancer cells. The significance of FOXA1 in the chromatin interactions and transcriptional regulation of both estrogen- and tamoxifen-bound ER, and in supporting tamoxifen-resistant cell growth, may impact current endocrine therapies
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