6,323 research outputs found
Measurement of Magnetization Dynamics in Single-Molecule Magnets Induced by Pulsed Millimeter-Wave Radiation
We describe an experiment aimed at measuring the spin dynamics of the Fe8
single-molecule magnet in the presence of pulsed microwave radiation. In
earlier work, heating was observed after a 0.2-ms pulse of intense radiation,
indicating that the spin system and the lattice were out of thermal equilibrium
at millisecond time scale [Bal et al., Europhys. Lett. 71, 110 (2005)]. In the
current work, an inductive pick-up loop is used to probe the photon-induced
magnetization dynamics between only two levels of the spin system at much
shorter time scales (from ns to us). The relaxation time for the magnetization,
induced by a pulse of radiation, is found to be on the order of 10 us.Comment: 3 RevTeX pages, including 3 eps figures. The paper will appear in the
Journal of Applied Physics as MMM'05 conference proceeding
Magnetic susceptibility of ultra-small superconductor grains
For assemblies of superconductor nanograins, the magnetic response is
analyzed as a function of both temperature and magnetic field. In order to
describe the interaction energy of electron pairs for a huge number of
many-particle states, involved in calculations, we develop a simple
approximation, based on the Richardson solution for the reduced BCS Hamiltonian
and applicable over a wide range of the grain sizes and interaction strengths
at arbitrary distributions of single-electron energy levels in a grain. Our
study is focused upon ultra-small grains, where both the mean value of the
nearest-neighbor spacing of single-electron energy levels in a grain and
variations of this spacing from grain to grain significantly exceed the
superconducting gap in bulk samples of the same material. For these ultra-small
superconductor grains, the overall profiles of the magnetic susceptibility as a
function of magnetic field and temperature are demonstrated to be qualitatively
different from those for normal grains. We show that the analyzed signatures of
pairing correlations are sufficiently stable with respect to variations of the
average value of the grain size and its dispersion over an assembly of
nanograins. The presence of these signatures does not depend on a particular
choice of statistics, obeyed by single-electron energy levels in grains.Comment: 40 pages, 12 figures, submitted to Phys. Rev. B, E-mail addresses:
[email protected], [email protected], [email protected]
Nonlinear c-axis transport in Bi_2Sr_2CaCu_2O_(8+d) from two-barrier tunneling
Motivated by the peculiar features observed through intrinsic tunneling
spectroscopy of BiSrCaCuO mesas in the normal state,
we have extended the normal state two-barrier model for the c-axis transport
[M. Giura et al., Phys. Rev. B {\bf 68}, 134505 (2003)] to the analysis of
curves. We have found that the purely normal-state model reproduces all
the following experimental features: (a) the parabolic -dependence of
in the high- region (above the conventional pseudogap temperature),
(b) the emergence and the nearly voltage-independent position of the "humps"
from this parabolic behavior lowering the temperature, and (c) the crossing of
the absolute curves at a characteristic voltage . Our
findings indicate that conventional tunneling can be at the origin of most of
the uncommon features of the c axis transport in
BiSrCaCuO. We have compared our calculations to
experimental data taken in severely underdoped and slightly underdoped
BiSrCaCuO small mesas. We have found good agreement
between the data and the calculations, without any shift of the calculated
dI/dV on the vertical scale. In particular, in the normal state (above
) simple tunneling reproduces the experimental dI/dV quantitatively.
Below quantitative discrepancies are limited to a simple rescaling of
the voltage in the theoretical curves by a factor 2. The need for such
modifications remains an open question, that might be connected to a change of
the charge of a fraction of the carriers across the pseudogap opening.Comment: 7 pages, 5 figure
Effects of social disruption in elephants persist decades after culling.
BACKGROUND
Multi-level fission-fusion societies, characteristic of a number of large brained mammal species including some primates, cetaceans and elephants, are among the most complex and cognitively demanding animal social systems. Many free-ranging populations of these highly social mammals already face severe human disturbance, which is set to accelerate with projected anthropogenic environmental change. Despite this, our understanding of how such disruption affects core aspects of social functioning is still very limited.
RESULTS
We now use novel playback experiments to assess decision-making abilities integral to operating successfully within complex societies, and provide the first systematic evidence that fundamental social skills may be significantly impaired by anthropogenic disruption. African elephants (Loxodonta africana) that had experienced separation from family members and translocation during culling operations decades previously performed poorly on systematic tests of their social knowledge, failing to distinguish between callers on the basis of social familiarity. Moreover, elephants from the disrupted population showed no evidence of discriminating between callers when age-related cues simulated individuals on an increasing scale of social dominance, in sharp contrast to the undisturbed population where this core social ability was well developed.
CONCLUSIONS
Key decision-making abilities that are fundamental to living in complex societies could be significantly altered in the long-term through exposure to severely disruptive events (e.g. culling and translocation). There is an assumption that wildlife responds to increasing pressure from human societies only in terms of demography, however our study demonstrates that the effects may be considerably more pervasive. These findings highlight the potential long-term negative consequences of acute social disruption in cognitively advanced species that live in close-knit kin-based societies, and alter our perspective on the health and functioning of populations that have been subjected to anthropogenic disturbance
Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process
Manufacturing superconducting circuits out of ultrathin films is a
challenging task when it comes to patterning complex compounds, which are
likely to be deteriorated by the patterning process. With the purpose of
developing high-T superconducting photon detectors, we designed a novel
route to pattern ultrathin YBCO films down to the nanometric scale. We believe
that our method, based on a specific use of a focused-ion beam, consists in
locally implanting Ga^{3+} ions and/or defects instead of etching the film.
This protocol could be of interest to engineer high-T superconducting
devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to
treat other sensitive compounds.Comment: 13 pages, 7 figure
Tunnel and thermal c-axis transport in BSCCO in the normal and pseudogap state
We consider the problem of c-axis transport in double-layered cuprates, in
particular with reference to BiSrCaCuO
compounds. We exploit the effect of the two barriers on the thermal and tunnel
transport. The resulting model is able to describe accurately the normal state
c-axis resistivity in BiSrCaCuO, from the
underdoped side up to the strongly overdoped. We extend the model, without
introducing additional parameters, in order to allow for the decrease of the
barrier when an external voltage bias is applied. The extended model is found
to describe properly the c-axis resistivity for small voltage bias above the
pseudogap temperature , the c-axis resistivity for large voltage bias
even below , and the differential curves taken in mesa structures.Comment: 12 pages, 6 figures. Submitted to Superconductor Science and
Technolog
Electrical conductivity beyond linear response in layered superconductors under magnetic field
The time-dependent Ginzburg-Landau approach is used to investigate nonlinear
response of a strongly type-II superconductor. The dissipation takes a form of
the flux flow which is quantitatively studied beyond linear response. Thermal
fluctuations, represented by the Langevin white noise, are assumed to be strong
enough to melt the Abrikosov vortex lattice created by the magnetic field into
a moving vortex liquid and marginalize the effects of the vortex pinning by
inhomogeneities. The layered structure of the superconductor is accounted for
by means of the Lawrence-Doniach model. The nonlinear interaction term in
dynamics is treated within Gaussian approximation and we go beyond the often
used lowest Landau level approximation to treat arbitrary magnetic fields. The
I-V curve is calculated for arbitrary temperature and the results are compared
to experimental data on high- superconductor
YBaCuO.Comment: 8 pages, 3 figure
Establishing pastures under wheat crops
RECENT surveys indicate that in the medium and high rainfall cereal and sheep areas as much as half the new pasture sown is sown with a crop.
In the drier wheatbelt areas the figure is 20 to 30 per cent
Plasma inflammatory cytokines and survival of pancreatic cancer patients.
OBJECTIVES: Inflammation and inflammatory conditions have been associated with pancreatic cancer risk and progression in a number of clinical, epidemiological, and animal model studies. The goal of the present study is to identify plasma markers of inflammation associated with survival of pancreatic cancer patients, and assess their joint contribution to patient outcome.
METHODS: We measured circulating levels of four established markers of inflammation (C-reactive protein (CRP), interleukin-6 (IL-6), soluble tumor necrosis factor receptor type II (sTNF-RII), and macrophage inhibitory cytokine-1 (MIC-1)) in 446 patients enrolled in an ongoing prospective clinic-based study. Hazard ratios (HRs) and 95% confidence intervals (CI) for death were estimated using multivariate Cox proportional hazards models.
RESULTS: Overall mortality was significantly increased in patients in the top quartile of CRP (HR = 2.52, 95% CI: 1.82-3.49), IL-6 (HR = 2.78, 95% CI: 2.03-3.81), sTNF-RII (HR = 2.00, 95% CI: 1.46-2.72), and MIC-1 (HR = 2.53, 95% CI: 1.83-3.50), compared to those in the bottom quartile (P-trend
CONCLUSION: Individual elevated plasma inflammatory cytokines are associated with significant and dramatic reductions in pancreatic cancer patient survival. Furthermore, we observed an independent combined effect of those cytokines on patient survival, suggesting that multiple inflammatory pathways are likely involved in PDAC progression. Future research efforts to target the inflammatory state using combination strategies in pancreatic cancer patients are warranted
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