408 research outputs found
Ultrafast quasiparticle relaxation dynamics in normal metals and heavy fermion materials
We present a detailed theoretical study of the ultrafast quasiparticle
relaxation dynamics observed in normal metals and heavy fermion materials with
femtosecond time-resolved optical pump-probe spectroscopy. For normal metals, a
nonthermal electron distribution gives rise to a temperature (T) independent
electron-phonon relaxation time at low temperatures, in contrast to the
T^{-3}-divergent behavior predicted by the two-temperature model. For heavy
fermion compounds, we find that the blocking of electron-phonon scattering for
heavy electrons within the density-of-states peak near the Fermi energy is
crucial to explain the rapid increase of the electron-phonon relaxation time
below the Kondo temperature. We propose the hypothesis that the slower Fermi
velocity compared to the sound velocity provides a natural blocking mechanism
due to energy and momentum conservation laws.Comment: 10 pages, 11 figure
Bcc He as a Coherent Quantum Solid
In this work we investigate implications of the quantum nature of bcc %
He. We show that it is a unique solid phase with both a lattice structure and
an Off-Diagonal Long Range Order of coherently oscillating local electric
dipole moments. These dipoles arise from the local motion of the atoms in the
crystal potential well, and oscillate in synchrony to reduce the dipolar
interaction energy. The dipolar ground-state is therefore found to be a
coherent state with a well defined global phase and a three-component complex
order parameter. The condensation energy of the dipoles in the bcc phase
stabilizes it over the hcp phase at finite temperatures. We further show that
there can be fermionic excitations of this ground-state and predict that they
form an optical-like branch in the (110) direction. A comparison with
'super-solid' models is also discussed.Comment: 12 pages, 8 figure
Multicomponent theory of buoyancy instabilities in magnetized plasmas: The case of magnetic field parallel to gravity
We investigate electromagnetic buoyancy instabilities of the electron-ion
plasma with the heat flux based on not the magnetohydrodynamic (MHD) equations,
but using the multicomponent plasma approach when the momentum equations are
solved for each species. We consider a geometry in which the background
magnetic field, gravity, and stratification are directed along one axis. The
nonzero background electron thermal flux is taken into account. Collisions
between electrons and ions are included in the momentum equations. No
simplifications usual for the one-fluid MHD-approach in studying these
instabilities are used. We derive a simple dispersion relation, which shows
that the thermal flux perturbation generally stabilizes an instability for the
geometry under consideration. This result contradicts to conclusion obtained in
the MHD-approach. We show that the reason of this contradiction is the
simplified assumptions used in the MHD analysis of buoyancy instabilities and
the role of the longitudinal electric field perturbation which is not captured
by the ideal MHD equations. Our dispersion relation also shows that the medium
with the electron thermal flux can be unstable, if the temperature gradients of
ions and electrons have the opposite signs. The results obtained can be applied
to the weakly collisional magnetized plasma objects in laboratory and
astrophysics.Comment: Accepted for publication in Astrophysics & Space Scienc
Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRuRhO
The solid-solution SrRuRhO () is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4 to the enhanced paramagnetic
4. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at .
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO. Furthermore, another
anomaly in the specific heat was observed at .Comment: Accepted for publication in PR
Electron Dynamics in NdCeCuO: Evidence for the Pseudogap State and Unconventional c-axis Response
Infrared reflectance measurements were made with light polarized along the a-
and c-axis of both superconducting and antiferromagnetic phases of electron
doped NdCeCuO. The results are compared to
characteristic features of the electromagnetic response in hole doped cuprates.
Within the CuO planes the frequency dependent scattering rate,
1/, is depressed below 650 cm; this behavior is a
hallmark of the pseudogap state. While in several hole doped compounds the
energy scales associated with the pseudogap and superconducting states are
quite close, we are able to show that in NdCeCuO
the two scales differ by more than one order of magnitude. Another feature of
the in-plane charge response is a peak in the real part of the conductivity,
, at 50-110 cm which is in sharp contrast with the
Drude-like response where is centered at . This
latter effect is similar to what is found in disordered hole doped cuprates and
is discussed in the context of carrier localization. Examination of the c-axis
conductivity gives evidence for an anomalously broad frequency range from which
the interlayer superfluid is accumulated. Compelling evidence for the pseudogap
state as well as other characteristics of the charge dynamics in
NdCeCuO signal global similarities of the cuprate
phase diagram with respect to electron and hole doping.Comment: Submitted to PR
Theory and Applications of Non-Relativistic and Relativistic Turbulent Reconnection
Realistic astrophysical environments are turbulent due to the extremely high
Reynolds numbers. Therefore, the theories of reconnection intended for
describing astrophysical reconnection should not ignore the effects of
turbulence on magnetic reconnection. Turbulence is known to change the nature
of many physical processes dramatically and in this review we claim that
magnetic reconnection is not an exception. We stress that not only
astrophysical turbulence is ubiquitous, but also magnetic reconnection itself
induces turbulence. Thus turbulence must be accounted for in any realistic
astrophysical reconnection setup. We argue that due to the similarities of MHD
turbulence in relativistic and non-relativistic cases the theory of magnetic
reconnection developed for the non-relativistic case can be extended to the
relativistic case and we provide numerical simulations that support this
conjecture. We also provide quantitative comparisons of the theoretical
predictions and results of numerical experiments, including the situations when
turbulent reconnection is self-driven, i.e. the turbulence in the system is
generated by the reconnection process itself. We show how turbulent
reconnection entails the violation of magnetic flux freezing, the conclusion
that has really far reaching consequences for many realistically turbulent
astrophysical environments. In addition, we consider observational testing of
turbulent reconnection as well as numerous implications of the theory. The
former includes the Sun and solar wind reconnection, while the latter include
the process of reconnection diffusion induced by turbulent reconnection, the
acceleration of energetic particles, bursts of turbulent reconnection related
to black hole sources as well as gamma ray bursts. Finally, we explain why
turbulent reconnection cannot be explained by turbulent resistivity or derived
through the mean field approach.Comment: 66 pages, 24 figures, a chapter of the book "Magnetic Reconnection -
Concepts and Applications", editors W. Gonzalez, E. N. Parke
Autoinflammatory periodic fever, immunodeficiency, and thrombocytopenia (PFIT) caused by mutation in actin-regulatory gene WDR1
The importance of actin dynamics in the activation of the inflammasome is becoming increasingly apparent. IL-1β, which is activated by the inflammasome, is known to be central to the pathogenesis of many monogenic autoinflammatory diseases. However, evidence from an autoinflammatory murine model indicates that IL-18, the other cytokine triggered by inflammasome activity, is important in its own right. In this model, autoinflammation was caused by mutation in the actin regulatory gene WDR1 We report a homozygous missense mutation in WDR1 in two siblings causing periodic fevers with immunodeficiency and thrombocytopenia. We found impaired actin dynamics in patient immune cells. Patients had high serum levels of IL-18, without a corresponding increase in IL-18-binding protein or IL-1β, and their cells also secreted more IL-18 but not IL-1β in culture. We found increased caspase-1 cleavage within patient monocytes indicative of increased inflammasome activity. We transfected HEK293T cells with pyrin and wild-type and mutated WDR1 Mutant protein formed aggregates that appeared to accumulate pyrin; this could potentially precipitate inflammasome assembly. We have extended the findings from the mouse model to highlight the importance of WDR1 and actin regulation in the activation of the inflammasome, and in human autoinflammation
The surface detector array of the Telescope Array experiment
The Telescope Array (TA) experiment, located in the western desert of
Utah,USA, is designed for observation of extensive air showers from extremely
high energy cosmic rays. The experiment has a surface detector array surrounded
by three fluorescence detectors to enable simultaneous detection of shower
particles at ground level and fluorescence photons along the shower track. The
TA surface detectors and fluorescence detectors started full hybrid observation
in March, 2008. In this article we describe the design and technical features
of the TA surface detector.Comment: 32 pages, 17 figure
New air fluorescence detectors employed in the Telescope Array experiment
Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been
observing ultra high energy cosmic rays to understand their origins. The
experiment involves a surface detector (SD) array and three fluorescence
detector (FD) stations. FD stations, installed surrounding the SD array,
measure the air fluorescence light emitted from extensive air showers (EASs)
for precise determination of their energies and species. The detectors employed
at one of the three FD stations were relocated from the High Resolution Fly's
Eye experiment. At the other two stations, newly designed detectors were
constructed for the TA experiment. An FD consists of a primary mirror and a
camera equipped with photomultiplier tubes. To obtain the EAS parameters with
high accuracies, understanding the FD optical characteristics is important. In
this paper, we report the characteristics and installation of new FDs and the
performances of the FD components. The results of the monitored mirror
reflectance during the observation time are also described in this report.Comment: 44 pages, 23 figures, submitted to NIM-
- …