613 research outputs found
Middle Atlantic Outer Continental Shelf Environmental Studies Volume 1: Executive Summary
Increasing demand for petroleum and natural gas in the United States has led to a need for development of reliable new domestic sources. The Outer Continental Shelf of the United States holds great interest among the oil companies for possible exploration and development of oil and gas resources to meet this need. This interest was demonstrated for the Middle Atlantic Outer Continental Shelf in the oil companies\u27 response to the lease sale conducted in August 1976. Of the 154 tracts comprising 876,750 acres offered for lease in August 1975 for exploratory drilling in the Baltimore Canyon Trough (Figure 1), oil compa~ies purchased drilling rights to 101 tracts comprising 575,011 acres. The Bureau of Land Management Environmental Studies Program was established to provide information needed for prediction, assessment, and management of impacts on the human marine and coastal environments of the Outer Continental Shelf and the nearshore area which may be affected by these drilling activities. The studies are designed to: 1. Provide information on the status of the environment upon which the prediction of the impacts of Outer Continental Shelf oil and gas development for leasing decisionmaking may be based, 2. provide information on the ways and extent that Outer Continental Shelf development can potentially impact the human, marine, biological, and coastal areas, 3. ensure that information already available or being collected under the program is in a form that can be used in the decisionmaking process associated with a specific leasing action or with the longer term Outer Continental Shelf minerals management responsibilities, and 4. provide a basis for furture monitoring of Outer Continental Shelf operations
Similarity of Fermi Surface in the Hidden Order State and in the Antiferromagnetic State of URu2Si2
Shubnikov-de Haas measurements of high quality URu2Si2 single crystals reveal
two previously unobserved Fermi surface branches in the so-called hidden order
phase. Therefore about 55% of the enhanced mass is now detected. Under pressure
in the antiferromagnetic state, the Shubnikov-de Haas frequencies for magnetic
fields applied along the crystalline c axis show little change compared with
the zero pressure data. This implies a similar Fermi surface in both the hidden
order and antiferromagnetic states, which strongly suggests that the lattice
doubling in the antiferromagnetic phase due to the ordering vector QAF = (0 0
1) already occurs in the hidden order. These measurements provide a good test
for existing or future theories of the hidden order parameter.Comment: 4 pages, 4 figure
Thermoelectric power quantum oscillations in the ferromagnet UGe
We present thermoelectric power and resistivity measurements in the
ferromagnet UGe as a function of temperature and magnetic field. At low
temperature, huge quantum oscillations are observed in the thermoelectric power
as a function of the magnetic field applied along the axis. The frequencies
of the extreme orbits are determined and an analysis of the cyclotron masses is
performed following different theoretical approaches for quantum oscillations
detected in the thermoelectric power. They are compared to those obtained by
Shubnikov-de Haas experiments on the same crystal and previous de Haas-van
Alphen experiments. The agreement of the different probes confirms
thermoelectric power as an excellent probe to extract simultaneously both
microscopic and macroscopic information on the Fermi-surface properties.
Band-structure calculations of UGe in the ferromagnetic state are compared
to the experiment.Comment: 10 figures, 12 pages, accepted for publication in Phys. Rev.
ESR of YbRh2Si2 and 174YbRh2Si2 : local and itinerant properties
Below the Kondo temperature the heavy Fermion compound YbRhSi
shows a well defined Electron Spin Resonance (ESR) with local Yb
properties. We report a detailed analysis of the ESR intensity which gives
information on the number of ESR active centers relative to the ESR of well
localized Yb in YPd:Yb. The ESR lineshape is investigated regarding
contributions from itinerant centers. From the ESR of monoisotopic
YbRhSi we could exclude unresolved hyperfine contributions
to the lineshape.Comment: 3 Figure
High pressure phase diagrams of CeRhIn and CeCoIn studied by ac calorimetry
The pressure-temperature phase diagrams of the heavy fermion antiferromagnet
CeRhIn and the heavy fermion superconductor CeCoIn have been studied
under hydrostatic pressure by ac calorimetry and ac susceptibility measurements
using diamond anvil cells with argon as pressure medium. In CeRhIn, the use
of a highly hydrostatic pressure transmitting medium allows for a clean
simultaneous determination by a bulk probe of the antiferromagnetic and
superconducting transitions. We compare our new phase diagram with the previous
ones, discuss the nature (first or second order) of the various lines, and the
coexistence of antiferromagnetic order and superconductivity. The link between
the collaps of the superconducting heat anomaly and the broadening of the
antiferromagnetic transition points to an inhomogeneous appearence of
superconductivity below GPa. Homogeneous bulk
superconductivity is only observed above this critical pressure. We present a
detailed analysis of the influence of pressure inomogeneities on the specific
heat anomalies which emphasizes that the observed broadening of the transitions
near is connected with the first order transition. For CeCoIn we show
that the large specific heat anomaly observed at at ambient pressure is
suppressed linearly at least up to 3 GPa
Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure
The mechanism of drastic change of Fermi surfaces as well as transport
anomalies near P=Pc=2.35 GPa in CeRhIn5 is explained theoretically. The key
mechanism is pointed out to be the interplay of magnetic order and Ce-valence
fluctuations. We show that the antiferromagnetic state with "small" Fermi
surfaces changes to the paramagnetic state with "large" Fermi surfaces with
huge enhancement of effective mass of electrons with keeping finite c-f
hybridization. This explains the drastic change of the de Haas-van Alphen
signals. Furthermore, it is also consistent with the emergence of T-linear
resistivity simultaneous with the residual resistivity peak at P=Pc in CeRhIn5.Comment: 5 pages, 3 figures, submitted to Journal of Physical Society of Japa
Antiferromagnetism and Superconductivity in CeRhIn
We discuss recent results on the heavy fermion superconductor CeRhIn
which presents ideal conditions to study the strong coupling between the
suppression of antiferromagnetic order and the appearance of unconventional
superconductivity. The appearance of superconductivity as function of pressure
is strongly connected to the suppression of the magnetic order. Under magnetic
field, the re-entrance of magnetic order inside the superconducting state shows
that antiferromagnetism nucleates in the vortex cores. The suppression of
antiferromagnetism in CeRhIn by Sn doping is compared to that under
hydrostatic pressure.Comment: 6 pages, 8 figures, to be published in Proc. Int. Conf. Heavy
Electrons (ICHE2010) J. Phys. Soc. Jpn. 80 (2011
Suppression of hidden order in URu2Si2 under pressure and restoration in magnetic field
We describe here recent inelastic neutron scattering experiments on the heavy
fermion compound URu2Si2 realized in order to clarify the nature of the hidden
order (HO) phase which occurs below T_0 = 17.5 K at ambient pressure. The
choice was to measure at a given pressure P where the system will go, by
lowering the temperature, successively from paramagnetic (PM) to HO and then to
antiferromagnetic phase (AF). Furthermore, in order to verify the selection of
the pressure, a macroscopic detection of the phase transitions was also
achieved in situ via its thermal expansion response detected by a strain gauge
glued on the crystal. Just above P_x = 0.5 GPa, where the ground state switches
from HO to AF, the Q_0 = (1, 0, 0) excitation disappears while the excitation
at the incommensurate wavevector Q_1 = (1.4, 0, 0) remains. Thus, the Q_0 = (1,
0, 0) excitation is intrinsic only in the HO phase. This result is reinforced
by studies where now pressure and magnetic field can be used as tuning
variable. Above P_x, the AF phase at low temperature is destroyed by a magnetic
field larger than H_AF (collapse of the AF Q_0 = (1, 0, 0) Bragg reflection).
The field reentrance of the HO phase is demonstrated by the reappearance of its
characteristic Q_0 = (1, 0, 0) excitation. The recovery of a PM phase will only
be achieved far above H_AF at H_M approx 35 T. To determine the P-H-T phase
diagram of URu2Si2, macroscopic measurements of the thermal expansion were
realized with a strain gauge. The reentrant magnetic field increases strongly
with pressure. Finally, to investigate the interplay between superconductivity
(SC) and spin dynamics, new inelastic neutron scattering experiments are
reported down to 0.4 K, far below the superconducting critical temperature T_SC
approx 1.3 K as measured on our crystal by diamagnetic shielding.Comment: 5 pages, 7 figures, ICN 2009 conference proceeding
Inelastic contribution of the resistivity in the hidden order in URu2Si2
In the hidden order of URu2Si2 the resistivity at very low temperature shows
no T^2 behavior above the transition to superconductivity. However, when
entering the antiferromagnetic phase, the Fermi liquid behavior is recovered.
We discuss the change of the inelastic term when entering the AF phase with
pressure considering the temperature dependence of the Grueneisen parameter at
ambient pressure and the influence of superconductivity by an extrapolation of
high field data.Comment: 5 pages, 2 figures, SCES conference proceedin
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