702 research outputs found
Susceptibility inhomogeneity and non-Fermi liquid behavior in UCu_{5-x}Pt_x
Transverse-field muSR shifts and relaxation rates have been measured in the
non-Fermi liquid (NFL) alloy system UCu_{5-x}Pt_x, x = 1.0, 1.5, and 2.5. At
low temperatures the fractional spread in Knight shifts delta K/K approx
deltachi/chi is gtrsim 2 for x = 1, but is only half this value for x = 1.5 and
2.5. In a disorder-driven scenario where the NFL behavior is due to a broadly
distributed (Kondo or Griffiths-phase cluster) characteristic energy E, our
results indicate that delta E/E_{rm av} approx (delta K/K)_{T=0} is similar for
UCu_{5-x}Pd_x (x = 1 and 1.5) and UCu_4Pt, but is reduced for UCu_{5-x}Pt_x, x
= 1.5 and 2.5. This reduction is due to a marked increase of E with increasing
x; the spread delta E is found to be roughly independent of x. Our results
correlate with the observed suppression of other NFL anomalies for x > 1 in
UCu_{5-x}Pt_x but not in UCu_{5-x}Pd_x, and are further evidence for the
importance of disorder in the NFL behavior of both these alloy systems.Comment: 4 pages, 2 figures, submitted to 10th International Conference on
Muon Spin Rotation, Relaxation, and Resonance, Oxford, UK, August 200
Spin dynamics in a structurally ordered non-Fermi liquid compound: YbRh_2Si_2
Muon spin relaxation (muSR) experiments have been carried out at low
temperatures in the non-Fermi-liquid heavy-fermion compound YbRh_2Si_2. The
longitudinal-field muSR relaxation function is exponential, indicative that the
dynamic spin fluctuations are homogeneous. The relaxation rate 1/T_1 varies
with applied field as H^{-y}, y = 1.0 \pm 0.1, which implies a scaling law of
the form \chi''(\omega) \propto \omega^{-y} f(\omega/T), \lim_{x\to0} f(x) = x
for the dynamic spin susceptibility.Comment: 5 pages, 2 figures. To be published in proceedings of musr2002
(Physica B
Dynamic Scaling in Diluted Systems Phase Transitions: Deactivation trough Thermal Dilution
Activated scaling is confirmed to hold in transverse field induced phase
transitions of randomly diluted Ising systems. Quantum Monte Carlo calculations
have been made not just at the percolation threshold but well bellow and above
it including the Griffiths-McCoy phase. A novel deactivation phenomena in the
Griffiths-McCoy phase is observed using a thermal (in contrast to random)
dilution of the system.Comment: 4 pages, 4 figures, RevTe
muSR and NMR in f-electron non-Fermi liquid materials
Magnetic resonance (muSR and NMR) studies of f-electron non-Fermi-liquid
(NFL) materials give clear evidence that structural disorder is a major factor
in NFL behavior. Longitudinal-field muSR relaxation measurements at low fields
reveal a wide distribution of muon relaxation rates and divergences in the
frequency dependence of spin correlation functions in the NFL systems
UCu_{5-x}Pd_x and CePtSi_{1-x}Ge_x. These divergences seem to be due to slow
dynamics associated with quantum spin-glass behavior, rather than quantum
criticality as in a uniform system, for two reasons: the observed strong
inhomogeneity in the muon relaxation rate, and the strong and
frequency-dependent low-frequency fluctuation observed in U(Cu,Pd)_5 and
CePt(Si,Ge). In the NFL materials CeCu_{5.9}Au_{0.1},
Ce(Ru_{0.5}Rh_{0.5})_2Si_2, CeNi_2Ge_2, and YbRh_2Si_2 the low-frequency weight
of the spin fluctuation spectrum is much weaker than in the disordered NFL
systems.Comment: 10 pages, 4 figures. To be published in proceedings of muSR2002
(Physica B
Medidas da transpiração em porta-enxertos de citros
Estudou-se a variação diurna da transpiração de quatro porta -enxertos de citros, durante 12 horas, em intervalos de 60 minutos, pelo método das pesagens. Verificou-se que não ocorreu diferenças estatÃsticas na marcha diária da transpiração, entre Poncirus trifoliata, Citrus aurantium (laranja Azeda), Citrus sinensis (laranja Caipira) e Citrus limonia (limão Cravo). O limoeiro Cravo mostrou, nas condições estudadas, área foliar superior à Poncirus, laranja Azeda e laranja Caipira. Observou-se ainda uma correlação positiva entre a área foliar e a transpiração dos quatro porta-enxertos de citros.Diurnal transpiration rates of four citrus rootstocks were measured during 12 hours separated by intervals of 60 minutes, through the weighing method. Plants of Poncirus trifoliata, Citrus aurantium, Citrus sinensis, and Citrus limonia do not present statistical differences in the daily march of transpiration. In the studied conditions C. limonia showed higher leaf area than P. trifoliata, C. aurantium, and C. sinensis. There was a positive correlation between leaf area and transpiration of the four citrus rootstodks
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
Silicic conduits as supersized tuffisites:Clastogenic influences on shifting eruption styles at Cordón Caulle volcano (Chile)
Understanding the processes that drive explosive-effusive transitions during large silicic eruptions is crucial to hazard mitigation. Conduit models usually treat magma ascent and degassing as a gradual, unidirectional progression from bubble nucleation through magmatic fragmentation. However, there is growing evidence for the importance of bi-directional clastogenic processes that sinter fragmented materials into coherent clastogenic magmas. Bombs that were ejected immediately before the first emergence of lava in the 2011–2012 eruption at Cordón Caulle volcano (Chile) are texturally heterogeneous composite assemblages of welded pyroclastic material. Although diverse in density and appearance, SEM and X-ray tomographic analysis show them all to have been formed by multi-generational viscous sintering of fine ash. Sintering created discrete clasts ranging from obsidian to pumice and formed a pervasive clast-supporting matrix that assembled these clasts into a conduit-sealing plug. An evaluation of sintering timescales reveals texturally disparate bomb components to represent only minutes of difference in residence time within the conduit. Permeability modelling indicates that the plug was an effective conduit seal, with outgassing potential—even from high-porosity regions—being limited by the inability of gas to flow across tendrils of densely sintered inter-clast matrix. Contrary to traditional perspectives, declining expressions of explosivity at the surface need not be preceded or accompanied by a decline in fragmentation efficiency. Instead, they result from tips in balance between the opposing processes of fragmentation and sintering that occur in countless cycles within volcanic conduits. These processes may be particularly enhanced at silicic fissure volcanoes, which have laterally extensive subsurface plumbing systems that require complex magma ascent pathways. The textures investigated here reveal the processes occurring within silicic fissures to be phenomenologically identical to those that have been inferred to occur in tuffisite veins: silicic conduits are essentially supersized examples of edifice-penetrating tuffisites
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
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