6,110 research outputs found
Heavy Fermions and Quantum Phase Transitions
Quantum phase transitions arise in many-body systems due to competing
interactions that promote rivaling ground states. Recent years have seen the
identification of continuous quantum phase transitions, or quantum critical
points, in a host of antiferromagnetic heavy-fermion compounds. Studies of the
interplay between the various effects have revealed new classes of quantum
critical points, and are uncovering a plethora of new quantum phases. At the
same time, quantum criticality has provided fresh insights into the electronic,
magnetic, and superconducting properties of the heavy-fermion metals. We review
these developments, discuss the open issues, and outline some directions for
future research.Comment: review article, 26 pages, 4 figure
HSV-2- and HIV-1- permissive cell lines co-infected by HSV-2 and HIV-1 co-replicate HSV-2 and HIV-1 without production of HSV-2/HIV-1 pseudotype particles
BACKGROUND: Herpes simplex virus type 2 (HSV-2) is a major cofactor of human immunodeficiency virus type 1 (HIV-1) sexual acquisition and transmission. In the present study, we investigated whether HIV-1 and HSV-2 may interact at the cellular level by forming HIV-1 hybrid virions pseudotyped with HSV-2 envelope glycoproteins, as was previously reported for HSV type 1. METHODS: We evaluated in vitro the production of HSV-2/HIV-1 pseudotypes in mononuclear CEM cells and epithelial HT29 and P4P cells. We analyzed the incorporation into the HIV-1 membrane of HSV-2 gB and gD, two major HSV-2 glycoproteins required for HSV-2 fusion with the cell membrane, in co-infected cells and in HIV-1-infected P4P cells transfected by plasmids coding for gB or gD. RESULTS: We show that HSV-2 and HIV-1 co-replicated in dually infected cells, and gB and gD were co-localized with gp160. However, HIV-1 particles, produced in HIV-1-infected cells expressing gB or gD after transfection or HSV-2 superinfection, did not incorporate either gB or gD in the viral membrane, and did not have the capacity to infect cells normally non-permissive for HIV-1, such as epithelial cells. CONCLUSION: Our results do not support the hypothesis of HSV-2/HIV-1 pseudotype formation and involvement in the synergistic genital interactions between HIV-1 and HSV-2
Epitaxial growth of FeSeTe thin films on CaF substrates with high critical current density
In-situ epitaxial growth of FeSeTe thin films is demonstrated
on a non-oxide substrate CaF. Structural analysis reveals that compressive
stress is moderately added to 36-nm thick FeSeTe, which pushes
up the critical temperature above 15 K, showing higher values than that of bulk
crystals. Critical current density at = 4.5 K reaches 5.9 x 10
Acm at = 10 T, and 4.2 x 10 Acm at = 14 T.
These results indicate that fluoride substrates have high potential for the
growth of iron-based superconductors in comparison with popular oxide
substrates.Comment: 9 pages, 3 figures, to be published in Applied Physics Express 4,
053101 (2011
A gate-variable spin current demultiplexer based on graphene
Spintronics, which utilizes spin as information carrier, is a promising
solution for nonvolatile memory and low-power computing in the post-Moore era.
An important challenge is to realize long distance spin transport, together
with efficient manipulation of spin current for novel logic-processing
applications. Here, we describe a gate-variable spin current demultiplexer
(GSDM) based on graphene, serving as a fundamental building block of
reconfigurable spin current logic circuits. The concept relies on electrical
gating of carrier density dependent conductivity and spin diffusion length in
graphene. As a demo, GSDM is realized for both single-layer and bilayer
graphene. The distribution and propagation of spin current in the two branches
of GSDM depend on spin relaxation characteristics of graphene. Compared with
Elliot-Yafet spin relaxation mechanism, D'yakonov-Perel mechanism results in
more appreciable gate-tuning performance. These unique features of GSDM would
give rise to abundant spin logic applications, such as on-chip spin current
modulators and reconfigurable spin logic circuits.Comment: 18 pages,3 figures,1 tabl
Impact of corpus callosum fiber tract crossing on polarimetric images of human brain histological sections: ex vivo studies in transmission configuration.
SIGNIFICANCE
Imaging Mueller polarimetry is capable to trace in-plane orientation of brain fiber tracts by detecting the optical anisotropy of white matter of healthy brain. Brain tumor cells grow chaotically and destroy this anisotropy. Hence, the drop in scalar retardance values and randomization of the azimuth of the optical axis could serve as the optical marker for brain tumor zone delineation.
AIM
The presence of underlying crossing fibers can also affect the values of scalar retardance and the azimuth of the optical axis. We studied and analyzed the impact of fiber crossing on the polarimetric images of thin histological sections of brain corpus callosum.
APPROACH
We used the transmission Mueller microscope for imaging of two-layered stacks of thin sections of corpus callosum tissue to mimic the overlapping brain fiber tracts with different fiber orientations. The decomposition of the measured Mueller matrices was performed with differential and Lu-Chipman algorithms and completed by the statistical analysis of the maps of scalar retardance, azimuth of the optical axis, and depolarization.
RESULTS
Our results indicate the sensitivity of Mueller polarimetry to different spatial arrangement of brain fiber tracts as seen in the maps of scalar retardance and azimuth of optical axis of two-layered stacks of corpus callosum sections The depolarization varies slightly () with the orientation of the optical axes in both corpus callosum stripes, but its value increases by 2.5 to 3 times with the stack thickness.
CONCLUSIONS
The crossing brain fiber tracts measured in transmission induce the drop in values of scalar retardance and randomization of the azimuth of the optical axis at optical path length of . It suggests that the presence of nerve fibers crossing within the depth of few microns will be also detected in polarimetric maps of brain white matter measured in reflection configuration
The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances
down to 27.9 Rs, allowing solar wind turbulence and acceleration mechanisms to
be studied in situ closer to the Sun than previously possible. The turbulence
properties were found to be significantly different in the inbound and outbound
portions of PSP's fourth solar encounter, likely due to the proximity to the
heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the
streamer belt wind, the turbulence was found to have lower amplitudes, higher
magnetic compressibility, a steeper magnetic field spectrum (with spectral
index close to -5/3 rather than -3/2), a lower Alfv\'enicity, and a "1/f" break
at much lower frequencies. These are also features of slow wind at 1 au,
suggesting the near-Sun streamer belt wind to be the prototypical slow solar
wind. The transition in properties occurs at a predicted angular distance of
~4{\deg} from the HCS, suggesting ~8{\deg} as the full-width of the streamer
belt wind at these distances. While the majority of the Alfv\'enic turbulence
energy fluxes measured by PSP are consistent with those required for
reflection-driven turbulence models of solar wind acceleration, the fluxes in
the streamer belt are significantly lower than the model predictions,
suggesting that additional mechanisms are necessary to explain the acceleration
of the streamer belt solar wind
Electromagnetic wave diffraction by periodic planar metamaterials with nonlinear constituents
We present a theory which explains how to achieve an enhancement of nonlinear
effects in a thin layer of nonlinear medium by involving a planar periodic
structure specially designed to bear a trapped-mode resonant regime. In
particular, the possibility of a nonlinear thin metamaterial to produce the
bistable response at a relatively low input intensity due to a large quality
factor of the trapped-mode resonance is shown. Also a simple design of an
all-dielectric low-loss silicon-based planar metamaterial which can provide an
extremely sharp resonant reflection and transmission is proposed. The designed
metamaterial is envisioned for aggregating with a pumped active medium to
achieve an enhancement of quantum dots luminescence and to produce an
all-dielectric analog of a 'lasing spaser'.Comment: 18 pages, 13 figure
Sex differences in cancer mechanisms
We now know that cancer is many different diseases, with great variation even within a single histological subtype. With the current emphasis on developing personalized approaches to cancer treatment, it is astonishing that we have not yet systematically incorporated the biology of sex differences into our paradigms for laboratory and clinical cancer research. While some sex differences in cancer arise through the actions of circulating sex hormones, other sex differences are independent of estrogen, testosterone, or progesterone levels. Instead, these differences are the result of sexual differentiation, a process that involves genetic and epigenetic mechanisms, in addition to acute sex hormone actions. Sexual differentiation begins with fertilization and continues beyond menopause. It affects virtually every body system, resulting in marked sex differences in such areas as growth, lifespan, metabolism, and immunity, all of which can impact on cancer progression, treatment response, and survival. These organismal level differences have correlates at the cellular level, and thus, males and females can fundamentally differ in their protections and vulnerabilities to cancer, from cellular transformation through all stages of progression, spread, and response to treatment. Our goal in this review is to cover some of the robust sex differences that exist in core cancer pathways and to make the case for inclusion of sex as a biological variable in all laboratory and clinical cancer research. We finish with a discussion of lab- and clinic-based experimental design that should be used when testing whether sex matters and the appropriate statistical models to apply in data analysis for rigorous evaluations of potential sex effects. It is our goal to facilitate the evaluation of sex differences in cancer in order to improve outcomes for all patients
Quantum Criticality and Novel Phases: Summary and Outlook
This conference summary and outlook provides a personal overview of the
topics and themes of the August 2009 Dresden meeting on quantum criticality and
novel phases. The dichotomy between the local moment and the itinerant views of
magnetism is revisited and refreshed in new materials, new probes and new
theoretical ideas. New universality and apparent zero temperature phases of
matter move us beyond the old ideas of quantum criticality. This is accompanied
by alternative pairing interactions and as yet unidentified phases developing
in the vicinity of quantum critical points. In discussing novel order, the
magnetic analogues of superconductivity are considered as candidate states for
the hidden order that sometimes develops in the vicinity of quantum critical
points in metallic systems. These analogues can be thought of as "pairing" in
the particle-hole channel and are tabulated. This analogy is used to outline a
framework to study the relation between ferromagnetic fluctuations and the
propensity of a metal to nematic type phases which at weak coupling correspond
to Pomeranchuk instabilities. This question can be related to the fundamental
relations of Fermi liquid theory.Comment: Conference summary for the 2009 Dresden Meeting on Quantum
Criticality and Novel Phases. 7 pages and 4 figures. The associated
presentation may be found at
http://www.theory.bham.ac.uk/staff/schofield/talks/Dresden
Spin torque resonant vortex core expulsion for an efficient radio-frequency detection scheme
Spin-polarised radio-frequency currents, whose frequency is equal to that of
the gyrotropic mode, will cause an excitation of the core of a magnetic vortex
confined in a magnetic tunnel junction. When the excitation radius of the
vortex core is greater than that of the junction radius, vortex core expulsion
is observed, leading to a large change in resistance, as the layer enters a
predominantly uniform magnetisation state. Unlike the conventional spin-torque
diode effect, this highly tunable resonant effect will generate a voltage which
does not decrease as a function of rf power, and has the potential to form the
basis of a new generation of tunable nanoscale radio-frequency detectors
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