4,417 research outputs found
Heavy fermion superconductivity and magnetic order in non-centrosymmetric
is a novel heavy fermion superconductor, crystallising in the
structure as a tetragonally distorted low symmetry variant of the
structure type. exhibits antiferromagnetic order at
K and enters into a heavy fermion superconducting state at
K. Large values of T/K and T refer to heavy quasiparticles forming Cooper pairs. Hitherto, is the first heavy fermion superconductor without a center of
symmetry.Comment: 4 pages, 4 figure
On centralizer algebras for spin representations
We give a presentation of the centralizer algebras for tensor products of
spinor representations of quantum groups via generators and relations. In the
even-dimensional case, this can be described in terms of non-standard
q-deformations of orthogonal Lie algebras; in the odd-dimensional case only a
certain subalgebra will appear. In the classical case q = 1 the relations boil
down to Lie algebra relations
Size effect on magnetism of Fe thin films in Fe/Ir superlattices
In ferromagnetic thin films, the Curie temperature variation with the
thickness is always considered as continuous when the thickness is varied from
to atomic planes. We show that it is not the case for Fe in Fe/Ir
superlattices. For an integer number of atomic planes, a unique magnetic
transition is observed by susceptibility measurements, whereas two magnetic
transitions are observed for fractional numbers of planes. This behavior is
attributed to successive transitions of areas with and atomic planes,
for which the 's are not the same. Indeed, the magnetic correlation length
is presumably shorter than the average size of the terraces. Monte carlo
simulations are performed to support this explanation.Comment: LaTeX file with Revtex, 5 pages, 5 eps figures, to appear in Phys.
Rev. Let
Generalized entropy and temperature in nuclear multifragmentation
In the framework of a 2D Vlasov model, we study the time evolution of the
"coarse-grained" Generalized Entropy (GE) in a nuclear system which undergoes a
multifragmentation (MF) phase transition. We investigate the GE both for the
gas and the fragments (surface and bulk part respectively). We find that the
formation of the surface causes the growth of the GE during the process of
fragmentation. This quantity then characterizes the MF and confirms the crucial
role of deterministic chaos in filling the new available phase-space: at
variance with the exact time evolution, no entropy change is found when the
linear response is applied. Numerical simulations were used also to extract
information about final temperatures of the fragments. From a fitting of the
momentum distribution with a Fermi-Dirac function we extract the temperature of
the fragments at the end of the process. We calculate also the gas temperature
by averaging over the available phase space. The latter is a few times larger
than the former, indicating a gas not in equilibrium. Though the model is very
schematic, this fact seems to be very general and could explain the discrepancy
found in experimental data when using the slope of light particles spectra
instead of the double ratio of isotope yields method in order to extract the
nuclear caloric curve.Comment: 26 pages, 9 postscript figures included, Revtex, some figures and
part of text changed, version accepted for publication in PR
One-body dissipation and chaotic dynamics in a classical simulation of a nuclear gas
In order to understand the origin of one-body dissipation in nuclei, we
analyze the behavior of a gas of classical particles moving in a
two-dimensional cavity with nuclear dimensions. This "nuclear" billiard has
multipole-deformed walls which undergo periodic shape oscillations. We
demonstrate that a single particle Hamiltonian containing coupling terms
between the particles' motion and the collective coordinate induces a chaotic
dynamics for any multipolarity, independently on the geometry of the billiard.
If the coupling terms are switched off the "wall formula" predictions are
recovered. We discuss the dissipative behavior of the wall motion and its
relation with the order-to-chaos transition in the dynamics of the microscopic
degrees of freedom.Comment: 16 pages, 12 postscript figures included, revtex, new version
completely revised accepted by Physical Review C and scheduled to appear in
the issue of november 199
Seebeck Effect in Magnetic Tunnel Junctions
Creating temperature gradients in magnetic nanostructures has resulted in a
new research direction, i.e., the combination of magneto- and thermoelectric
effects. Here, we demonstrate the observation of one important effect of this
class: the magneto-Seebeck effect. It is observed when a magnetic configuration
changes the charge based Seebeck coefficient. In particular, the Seebeck
coefficient changes during the transition from a parallel to an antiparallel
magnetic configuration in a tunnel junction. In that respect, it is the analog
to the tunneling magnetoresistance. The Seebeck coefficients in parallel and
antiparallel configuration are in the order of the voltages known from the
charge-Seebeck effect. The size and sign of the effect can be controlled by the
composition of the electrodes' atomic layers adjacent to the barrier and the
temperature. Experimentally, we realized 8.8 % magneto-Seebeck effect, which
results from a voltage change of about -8.7 {\mu}V/K from the antiparallel to
the parallel direction close to the predicted value of -12.1 {\mu}V/K.Comment: 16 pages, 7 figures, 2 table
On the derivative of the associated Legendre function of the first kind of integer order with respect to its degree
In our recent works [R. Szmytkowski, J. Phys. A 39 (2006) 15147; corrigendum:
40 (2007) 7819; addendum: 40 (2007) 14887], we have investigated the derivative
of the Legendre function of the first kind, , with respect to its
degree . In the present work, we extend these studies and construct
several representations of the derivative of the associated Legendre function
of the first kind, , with respect to the degree , for
. At first, we establish several contour-integral
representations of . They are then
used to derive Rodrigues-type formulas for with . Next, some closed-form
expressions for are
obtained. These results are applied to find several representations, both
explicit and of the Rodrigues type, for the associated Legendre function of the
second kind of integer degree and order, ; the explicit
representations are suitable for use for numerical purposes in various regions
of the complex -plane. Finally, the derivatives
, and , all with , are evaluated in terms
of .Comment: LateX, 40 pages, 1 figure, extensive referencin
Backbending region study in 160,162Dy using incomplete fusion reactions
18 pĂĄgs.; 17 figs.; 3 tabs. ; PACS number(s): 23.20.Lv, 23.20.En, 27.70.1q, 21.60.CsThe incomplete fusion reactions 7Liâ158,160Gd at beam energies of 8 MeV/nucleon have been used to study the first band crossing region in the heavy stable Dy isotopes 160,162Dy. The Îł rays were detected in the GASP spectrometer in coincidence with fast charged particles detected in the ISIS silicon ball. We succeeded to observe the first backbending in 162Dy at a crossing frequency of â Ï â 350 keV, a value much higher than expected from other nuclei in this mass region. Moreover, for the first time in a nucleus with a very large interaction strength, the yrare band in 160Dy could be established up to rather high spin (I= 20â) allowing for a precise determination of the interaction strength between the ground state and the Stockholm band, |Vg-S| = 219(2) keV. Together with |Vg-S| = 14(2) kev determined for the corresponding interaction in 162Dy, a full oscillation of the strengths from one node to the next could be observed within an isotopic chain. In addition to the ground state and Stockholm bands, many other known bands in the two nuclei were considerably extended to higher spin and the experimental results are compared to calculations within the projected shell model. ©2002 The American Physical SocietyThis work has been supported by Deutsches Bundesministerium fur Bildung,
Wissenschaft, Forschung und Technologie (BMBF). A.J. acknowledges
support by the Deutsche Forschungsgemeinschaft
(DFG).Peer Reviewe
Timing of Intervention Affects Brain Electrical Activity in Children Exposed to Severe Psychosocial Neglect
Background: Early psychosocial deprivation has profound effects on brain activity in the young child. Previous reports have shown increased power in slow frequencies of the electroencephalogram (EEG), primarily in the theta band, and decreased power in higher alpha and beta band frequencies in infants and children who have experienced institutional care. Methodology/Principal Findings: We assessed the consequences of removing infants from institutions and placing them into a foster care intervention on brain electrical activity when children were 8 years of age. We found the intervention was successful for increasing high frequency EEG alpha power, with effects being most pronounced for children placed into foster care before 24 months of age. Conclusions/Significance: The dependence on age of placement for the effects observed on high frequency EEG alpha power suggests a sensitive period after which brain activity in the face of severe psychosocial deprivation is less amenabl
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