376 research outputs found
A New Unconventional Antiferromagnet, YbPt
We report the synthesis and basic properties of single crystals of a new
binary compound, YbPt. The Yb ions in this compound are fully
trivalent, and heat capacity measurements show that the crystal field scheme
involves a doublet ground state, well separated from the excited states, which
are fully occupied above 150 K. The heat capacity displays a large,
weakly first order anomaly at 2.4 K, where a cusp is observed in the magnetic
susceptibility signalling the onset of antiferromagnetic order. The entropy
associated with this order is the full Rln2 of the doublet ground state,
however the magnetic susceptibility in the ordered phase is dominated by a
large and temperature independent component below the Neel temperature. The
heat capacity in the ordered state originates with ferromagnetic spin waves,
giving evidence for the inherently local moment character of the ordered state.
The electrical resistivity is unusually large, and becomes quadratic in
temperature exactly at the Neel temperature. The absence of analogous Fermi
liquid behavior in the heat capacity and the magnetic susceptibility implies
that YbPt is a low electron density system, where the Fermi surface
is further gapped by the onset of magnetic order.Comment: 8 pages, 9 figure
High pressure insulator-metal transition in SmB6
We report the temperature and pressure dependence of the electrical resistivity and Hall constant of single crystal SmB6 for temperatures ranging from 1.2 K to room temperature, and pressures from 1 bar to 80 kbar. Our results indicate that at low pressures SmB6 is an insulator, but undergoes a sudden transition to metallic behavior at a pressure of 50 kbar.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31646/1/0000580.pd
Principles of crystal growth of intermetallic and oxide compounds from molten solutions
We present a tutorial on the principles of crystal growth of intermetallic
and oxide compounds from molten solutions, with an emphasis on the fundamental
principles governing the underlying phase equilibria and phase diagrams of
multicomponent systems.Comment: 43 pages, 24 figures; Philosophical Magazine, 201
Electronic transport in EuB
EuB is a magnetic semiconductor in which defects introduce charge
carriers into the conduction band with the Fermi energy varying with
temperature and magnetic field. We present experimental and theoretical work on
the electronic magnetotransport in single-crystalline EuB. Magnetization,
magnetoresistance and Hall effect data were recorded at temperatures between 2
and 300 K and in magnetic fields up to 5.5 T. The negative magnetoresistance is
well reproduced by a model in which the spin disorder scattering is reduced by
the applied magnetic field. The Hall effect can be separated into an ordinary
and an anomalous part. At 20 K the latter accounts for half of the observed
Hall voltage, and its importance decreases rapidly with increasing temperature.
As for Gd and its compounds, where the rare-earth ion adopts the same Hund's
rule ground state as Eu in EuB, the standard antisymmetric
scattering mechanisms underestimate the of this contribution by several
orders of magnitude, while reproducing its almost perfectly. Well below
the bulk ferromagnetic ordering at = 12.5 K, a two-band model
successfully describes the magnetotransport. Our description is consistent with
published de Haas van Alphen, optical reflectivity, angular-resolved
photoemission, and soft X-ray emission as well as absorption data, but requires
a new interpretation for the gap feature deduced from the latter two
experiments.Comment: 35 pages, 12 figures, submitted to PR
Envisioning the future of aquatic animal tracking: Technology, science, and application
Electronic tags are significantly improving our understanding of aquatic animal behavior and are emerging as key sources of information for conservation and management practices. Future aquatic integrative biology and ecology studies will increasingly rely on data from electronic tagging. Continued advances in tracking hardware and software are needed to provide the knowledge required by managers and policymakers to address the challenges posed by the world's changing aquatic ecosystems. We foresee multiplatform tracking systems for simultaneously monitoring the position, activity, and physiology of animals and the environment through which they are moving. Improved data collection will be accompanied by greater data accessibility and analytical tools for processing data, enabled by new infrastructure and cyberinfrastructure. To operationalize advances and facilitate integration into policy, there must be parallel developments in the accessibility of education and training, as well as solutions to key governance and legal issues
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Exploring the physiological, neurophysiological and cognitive performance effects of elevated carbon dioxide concentrations indoors
Rationale: An accumulation of CO2 in occupied indoor spaces is correlated to negative impacts on
concentration, sleepiness and aspects of cognitive performance. However factors such as: (a) the
relative effect of CO2 itself compared to other pollutants; (b) the minimum necessary exposure time
for cognitive performance to be affected; and (c) the physiological drivers of cognitive performance
reductions due to increased indoor CO2 concentrations are not yet clear. Method: A within-subjects
counterbalanced study design was used to test cognitive performance, subjective and physiological
parameters of 31 volunteers during short (< 40 minutes) exposures to normal CO2 (830 ppm) and high
CO2 (2,700 ppm, raised by introducing pure CO2 alongside the occupant generated CO2). The study
was conducted in a small naturally ventilated office and EEG was used as an objective indicator of
sleepiness. Results: The addition of pure CO2 to the room resulted in the absence of an expected
learning effect in two cognitive performance test battery components without measurably affecting
any of the physiological, psychological, or reported comfort, sick building syndrome and health
variables measured. However participants who had slept less the previous night appeared more
susceptible to becoming sleepier as a result of the increased CO2. Contributions: The results suggest
(1) the addition of pure CO2 may influence aspects of cognitive performance after only short
exposures (2) these changes occur in the absence of clear physiological drivers, (3) lack of sleep may mediate people’s response to higher CO2 concentration
Search for the standard model Higgs boson decaying to a pair in events with no charged leptons and large missing transverse energy using the full CDF data set
We report on a search for the standard model Higgs boson produced in
association with a vector boson in the full data set of proton-antiproton
collisions at TeV recorded by the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45 fb. We
consider events having no identified charged lepton, a transverse energy
imbalance, and two or three jets, of which at least one is consistent with
originating from the decay of a quark. We place 95% credibility level upper
limits on the production cross section times standard model branching fraction
for several mass hypotheses between 90 and . For a Higgs
boson mass of , the observed (expected) limit is 6.7
(3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let
Search for the standard model Higgs boson decaying to a bb pair in events with one charged lepton and large missing transverse energy using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data
collected with the CDF II detector at the Tevatron corresponding to an
integrated luminosity of 9.45 fb-1. In events consistent with the decay of the
Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a
neutrino, we set 95% credibility level upper limits on the WH production cross
section times the H->bb branching ratio as a function of Higgs boson mass. At a
Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) times
the standard model value.Comment: Submitted to Phys. Rev. Lett (v2 contains clarifications suggested by
PRL
Search for the standard model Higgs boson decaying to a bb pair in events with two oppositely-charged leptons using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a Z boson in data collected with the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45/fb. In events
consistent with the decay of the Higgs boson to a bottom-quark pair and the Z
boson to electron or muon pairs, we set 95% credibility level upper limits on
the ZH production cross section times the H -> bb branching ratio as a function
of Higgs boson mass. At a Higgs boson mass of 125 GeV/c^2 we observe (expect) a
limit of 7.1 (3.9) times the standard model value.Comment: To be submitted to Phys. Rev. Let
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