4,141 research outputs found
Dynamical polarization of graphene under strain
We study the dependence of the plasmon dispersion relation of graphene on
applied uniaxial strain. Besides electron correlation at the RPA level, we also
include local field effects specific for the honeycomb lattice. As a
consequence of the two-band character of the electronic band structure, we find
two distinct plasmon branches. We recover the square-root behavior of the
low-energy branch, and find a nonmonotonic dependence of the strain-induced
modification of its stiffness, as a function of the wavevector orientation with
respect to applied strain.Comment: Phys. Rev. B, accepte
Heavy Superheated Droplet Detectors as a Probe of Spin-independent WIMP Dark Matter Existence
At present, application of Superheated Droplet Detectors (SDDs) in WIMP dark
matter searches has been limited to the spin-dependent sector, owing to the
general use of fluorinated refrigerants which have high spin sensitivity. Given
their recent demonstration of a significant constraint capability with
relatively small exposures and the relative economy of the technique, we
consider the potential impact of heavy versions of such devices on the
spin-independent sector. Limits obtainable from a -loaded SDD
are estimated on the basis of the radiopurity levels and backgrounds already
achieved by the SIMPLE and PICASSO experiments. With 34 kgd exposure,
equivalent to the current CDMS, such a device may already probe to below
10 pb in the spin-independent cross section.Comment: 9 pages, 4 figures, accepted Phys. Rev.
To what extent can dynamical models describe statistical features of turbulent flows?
Statistical features of "bursty" behaviour in charged and neutral fluid
turbulence, are compared to statistics of intermittent events in a GOY shell
model, and avalanches in different models of Self Organized Criticality (SOC).
It is found that inter-burst times show a power law distribution for turbulent
samples and for the shell model, a property which is shared only in a
particular case of the running sandpile model. The breakdown of self-similarity
generated by isolated events observed in the turbulent samples, is well
reproduced by the shell model, while it is absent in all SOC models considered.
On this base, we conclude that SOC models are not adequate to mimic fluid
turbulence, while the GOY shell model constitutes a better candidate to
describe the gross features of turbulence.Comment: 14 pages, 4 figures, in press on Europhys. Lett. (may 2002
Froth-like minimizers of a non local free energy functional with competing interactions
We investigate the ground and low energy states of a one dimensional non
local free energy functional describing at a mean field level a spin system
with both ferromagnetic and antiferromagnetic interactions. In particular, the
antiferromagnetic interaction is assumed to have a range much larger than the
ferromagnetic one. The competition between these two effects is expected to
lead to the spontaneous emergence of a regular alternation of long intervals on
which the spin profile is magnetized either up or down, with an oscillation
scale intermediate between the range of the ferromagnetic and that of the
antiferromagnetic interaction. In this sense, the optimal or quasi-optimal
profiles are "froth-like": if seen on the scale of the antiferromagnetic
potential they look neutral, but if seen at the microscope they actually
consist of big bubbles of two different phases alternating among each other. In
this paper we prove the validity of this picture, we compute the oscillation
scale of the quasi-optimal profiles and we quantify their distance in norm from
a reference periodic profile. The proof consists of two main steps: we first
coarse grain the system on a scale intermediate between the range of the
ferromagnetic potential and the expected optimal oscillation scale; in this way
we reduce the original functional to an effective "sharp interface" one. Next,
we study the latter by reflection positivity methods, which require as a key
ingredient the exact locality of the short range term. Our proof has the
conceptual interest of combining coarse graining with reflection positivity
methods, an idea that is presumably useful in much more general contexts than
the one studied here.Comment: 38 pages, 2 figure
The role of proteasome inhibitors in multiple myeloma bone disease and bone metastasis: Effects on osteoblasts and osteocytes
The alterations of bone remodeling are typical of multiple myeloma (MM) patients where the uncoupled and unbalanced bone remodeling caused the onset of osteolytic lesions. Moreover, bone metastasis occurs in the majority of patients with breast and prostate cancer. Skeletal-related events negatively impact on quality of life by increasing the vulnerability to fractures. Several bone-targeting treatments have been developed to control bone pain and pathological fractures, including bisphosphonates and Denosumab. Nevertheless, these agents act by inhibiting osteoclast activity but do not improve bone formation. Proteasome inhibitors (PIs) have shown bone anabolic effects and encouraging results in stimulating osteoblast differentiation and bone healing. Among these, the first-in-class bortezomib and the second-generation PIs, carfilzomib, and ixazomib regulate the bone remodeling process by controlling the degradation of several bone proteins. PIs have been recently proven to also be efficacious in blocking MM-induced osteocyte death providing new possible therapeutic use in the management of bone loss. PIs have significant side effects that limit their use as bone anabolic strategy. Multiple alternative approaches have been made. The conjugation of PIs with bisphosphonates, which can target them to bone, showed good results in terms of bone anabolic activity. However, the clinical implications of these effects require further investigations
Collective modes of doped graphene and a standard 2DEG in a strong magnetic field: linear magneto-plasmons versus magneto-excitons
A doped graphene layer in the integer quantum Hall regime reveals a highly
unusual particle-hole excitation spectrum, which is calculated from the
dynamical polarizability in the random phase approximation. We find that the
elementary neutral excitations in graphene in a magnetic field are unlike those
of a standard two-dimensional electron gas (2DEG): in addition to the
upper-hybrid mode, the particle-hole spectrum is reorganized in linear
magneto-plasmons that disperse roughly parallel to , instead of
the usual horizontal (almost dispersionless) magneto-excitons. These modes
could be detected in an inelastic light scattering experiment.Comment: 8 pages, 3 figures. Version accepted for publication in Phys. Rev.
Electron-electron interactions in decoupled graphene layers
Multi-layer graphene on the carbon face of silicon carbide is an intriguing
electronic system which typically consists of a stack of ten or more layers.
Rotational stacking faults in this system dramatically reduce inter-layer
coherence. In this article we report on the influence of inter-layer
interactions, which remain strong even when coherence is negligible, on the
Fermi liquid properties of charged graphene layers. We find that inter-layer
interactions increase the magnitudes of correlation energies and decrease
quasiparticle velocities, even when remote-layer carrier densities are small,
and that they lessen the influence of exchange and correlation on the
distribution of carriers across layers.Comment: 8 pages, 4 figures, submitte
Anomalous spin-resolved point-contact transmission of holes due to cubic Rashba spin-orbit coupling
Evidence is presented for the finite wave vector crossing of the two lowest
one-dimensional spin-split subbands in quantum point contacts fabricated from
two-dimensional hole gases with strong spin-orbit interaction. This phenomenon
offers an elegant explanation for the anomalous sign of the spin polarization
filtered by a point contact, as observed in magnetic focusing experiments.
Anticrossing is introduced by a magnetic field parallel to the channel or an
asymmetric potential transverse to it. Controlling the magnitude of the
spin-splitting affords a novel mechanism for inverting the sign of the spin
polarization.Comment: 4 pages, 3 figure
Ground-state properties of the one-dimensional electron liquid
We present calculations of the energy, pair-correlation function (PCF), static structure factor (SSF), and momentum density (MD) for the one-dimensional electron gas using the quantum Monte Carlo method. We are able to resolve peaks in the SSF at even-integer multiples of the Fermi wave vector, which grow as the coupling is increased. Our MD results show an increase in the effective Fermi wave vector as the interaction strength is raised in the paramagnetic harmonic wire; this appears to be a result of the vanishing difference between the wave functions of the paramagnetic and ferromagnetic systems. We have extracted the Luttinger liquid exponent from our MDs by fitting to data around kF, finding good agreement between the exponent of the ferromagnetic infinitely thin wire and the ferromagnetic harmonic wire
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