3,917 research outputs found
Disordered hyperuniformity in two-component non-additive hard disk plasmas
We study the behavior of a two-component plasma made up of non-additive hard
disks with a logarithmic Coulomb interaction. Due to the Coulomb repulsion,
long-wavelength total density fluctuations are suppressed and the system is
globally hyperuniform. Short-range volume effects lead to phase separation or
to hetero-coordination for positive or negative non-additivities, respectively.
These effects compete with the hidden long-range order imposed by
hyperuniformity. As a result, the critical behavior of the mixture is modified,
with long-wavelength concentration fluctuations partially damped when the
system is charged. It is also shown that the decrease of configurational
entropy due to hyperuniformity originates from contributions beyond the
two-particle level. Finally, despite global hyperuniformity, we show that in
our system, the spatial configuration associated with each component separately
is not hyperuniform, i.e., the system is not "multihyperuniform.
Cryogenic scanning force microscopy of quantum Hall samples: Adiabatic transport originating in anisotropic depletion at contact interfaces
Anisotropic magneto resistances and intrinsic adiabatic transport features
are generated on quantum Hall samples based on an (Al,Ga)As/GaAs
heterostructure with alloyed Au/Ge/Ni contacts. We succeed to probe the
microscopic origin of these transport features with a cryogenic scanning force
microscope (SFM) by measuring the local potential distribution within the
two-dimensional electron system (2DES). These local measurements reveal the
presence of an incompressible strip in front of contacts with insulating
properties depending on the orientation of the contact/2DES interface line
relatively to the crystal axes of the heterostructure. Such an observation
gives another microscopic meaning to the term 'non-ideal contact' used in
context with the Landauer-B\"uttiker formalism applied to the quantum Hall
effect.Comment: 5 pages, 4 figure
Effective interactions and phase behaviour for a model clay suspension in an electrolyte
Since the early observation of nematic phases of disc-like clay colloids by
Langmuir in 1938, the phase behaviour of such systems has resisted theoretical
understanding. The main reason is that there is no satisfactory generalization
for charged discs of the isotropic DLVO potential describing the effective
interactions between a pair of spherical colloids in an electrolyte. In this
contribution, we show how to construct such a pair potential, incorporating
approximately both the non-linear effects of counter-ion condensation (charge
renormalization) and the anisotropy of the charged platelets. The consequences
on the phase behaviour of Laponite dispersions (thin discs of 30 nm diameter
and 1 nm thickness) are discussed, and investigation into the mesostructure via
Monte Carlo simulations are presented.Comment: LaTeX, 12 pages, 11 figure
On phase behavior and dynamical signatures of charged colloidal platelets
We investigate the competition between anisotropic excluded-volume and
repulsive electrostatic interactions in suspensions of thin charged colloidal
discs, by means of Monte-Carlo simulations and dynamical characterization of
the structures found. We show that the original intrinsic anisotropy of the
electrostatic potential between charged platelets, obtained within the
non-linear Poisson-Boltzmann formalism, not only rationalizes the generic
features of the complex phase diagram of charged colloidal platelets such as
Gibbsite and Beidellite clays, but also predicts the existence of novel
structures. In addition, we find evidences of a strong slowing down of the
dynamics upon increasing density.Comment: 6 pages, 6 Figure
Optomechanically induced transparency
Coherent interaction of laser radiation with multilevel atoms and molecules
can lead to quantum interference in the electronic excitation pathways. A
prominent example observed in atomic three-level-systems is the phenomenon of
electromagnetically induced transparency (EIT), in which a control laser
induces a narrow spectral transparency window for a weak probe laser beam. The
concomitant rapid variation of the refractive index in this spectral window can
give rise to dramatic reduction of the group velocity of a propagating pulse of
probe light. Dynamic control of EIT via the control laser enables even a
complete stop, that is, storage, of probe light pulses in the atomic medium.
Here, we demonstrate optomechanically induced transparency (OMIT)--formally
equivalent to EIT--in a cavity optomechanical system operating in the resolved
sideband regime. A control laser tuned to the lower motional sideband of the
cavity resonance induces a dipole-like interaction of optical and mechanical
degrees of freedom. Under these conditions, the destructive interference of
excitation pathways for an intracavity probe field gives rise to a window of
transparency when a two-photon resonance condition is met. As a salient feature
of EIT, the power of the control laser determines the width and depth of the
probe transparency window. OMIT could therefore provide a new approach for
delaying, slowing and storing light pulses in long-lived mechanical excitations
of optomechanical systems, whose optical and mechanical properties can be
tailored in almost arbitrary ways in the micro- and nano-optomechanical
platforms developed to date
Primary radiotherapy in progressive optic nerve sheath meningiomas: a long-term follow-up study
Background/aims: To report the outcome of primary radiotherapy in patients with progressive optic nerve sheath meningioma (ONSM). Methods: The clinical records of all patients were reviewed in a retrospective, observational, multicentre study. Results: Thirty-four consecutive patients were included. Twenty-six women and eight men received conventional or stereotactic fractionated radiotherapy, and were followed for a median 58 (range 51–156) months. Fourteen eyes (41%) showed improved visual acuity of at least two lines on the Snellen chart. In 17 (50%) eyes, the vision stabilised, while deterioration was noted in three eyes (9%). The visual outcome was not associated with age at the time of radiotherapy (p=0.83), sex (p=0.43), visual acuity at the time of presentation (p=0.22) or type of radiotherapy (p=0.35). Optic disc swelling was associated with improved visual acuity (p<0.01) and 4/11 patients with optic atrophy also showed improvement. Long-term complications were dry eyes in five patients, cataracts in three, and mild radiation retinopathy in four. Conclusion: Primary radiotherapy for patients with ONSM is associated with long-term improvement of visual acuity and few adverse effects.Peerooz Saeed, Leo Blank, Dinesh Selva, John G. Wolbers, Peter J.C.M. Nowak, Ronald B. Geskus, Ezekiel Weis, Maarten P. Mourits, Jack Rootma
Eta Carinae across the 2003.5 Minimum: Analysis in the visible and near infrared spectral region
We present an analysis of the visible through near infrared spectrum of Eta
Carinae and its ejecta obtained during the "Eta Carinae Campaign with the UVES
at the ESO VLT". This is a part of larger effort to present a complete Eta
Carinae spectrum, and extends the previously presented analyses with the
HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near
UV is characterized by the ejecta absorption. At longer wavelengths, stellar
wind features from the central source and narrow emission lines from the
Weigelt condensations dominate the spectrum. However, narrow absorption lines
from the circumstellar shells are present. This paper provides a description of
the spectrum between 3060 and 10,430 A, including line identifications of the
ejecta absorption spectrum, the emission spectrum from the Weigelt
condensations and the P-Cygni stellar wind features. The high spectral
resolving power of VLT/UVES enables equivalent width measurements of atomic and
molecular absorption lines for elements with no transitions at the shorter
wavelengths. However, the ground based seeing and contributions of nebular
scattered radiation prevent direct comparison of measured equivalent widths in
the VLT/UVES and HST/STIS spectra. Fortunately, HST/STIS and VLT/UVES have a
small overlap in wavelength coverage which allows us to compare and adjust for
the difference in scattered radiation entering the instruments' apertures. This
paper provides a complete online VLT/UVES spectrum with line identifications
and a spectral comparison between HST/STIS and VLT/UVES between 3060 and 3160
A.Comment: 13 pages, 11 figures + atlas. The paper accepted for the ApJS and is
accompanied with an atlas in the online edition pape
Geochemical composition of k-rich lavas from the lena trough (Arctic ocean)
Mid-ocean ridge basalts (MORB) from the Arctic Ocean have been significantly less studied than those from other oceans. The Arctic ridges (Gakkel Ridge and Lena Trough) are ultraslow-spreading ridges with low melt productivity and are thus the best locations to investigate mantle heterogeneity. We report the major and trace element and Sr-Nd-Pb-Hf isotope compositions of basalts generated along the Lena Trough and the westernmost part of the Gakkel Ridge in the Arctic Ocean. Basalts from the northern Lena Trough and westernmost Gakkel Ridge (NLT-WGR) have compositions close to normal MORB. The geochemical composition of the NLT-WGR lavas confirms a binary mixing model involving melts from a depleted MORB mantle source and a Spitsbergen amphibole-bearing subcontinental lithospheric mantle (SCLM) source. In contrast, in the central part of the Lena Trough (CLT), the basalts are alkalic with relatively high Mg-number (60-65), high SiO2 (51·0-51·6 wt %), Al2O. 3 (18·1-18·4 wt %), Na2O (4·0-4·2 wt %), K 2O (1·0-1·6 wt %), K2O/TiO2 (0·6-0·9) and (La/Sm)PM (1·4-1·8), and low FeO (6·5-6·8 wt %) contents. These basalts display isotope variations with .87Sr/.86Sr ranging from 0·70361 to 0·70390, .143Nd/144Nd from 0·51283 to 0·51290 (e{open} Nd + 3·7 to +5·2), 176Hf/177Hf from 0·28313 to 0·28322 (e{open}Hf + 11·6 to +14·9) and .206Pb/204Pb from 17·752 to 17·884, .207Pb/204Pb from 15·410 to 15·423 and .208Pb/. 204Pb from 37·544 to 37·670. These isotope compositions clearly distinguish the CLT lavas from those generated along the Gakkel Ridge. For the CLT lavas, involvement of a phlogopite- or amphibole- and (possibly garnet)-bearing SCLM source component is proposed. Owing to SCLM contamination along the entire length of the Lena Trough, we classify the Lena Trough as an ocean-continent transition boundary. Magmatism similar to that observed in the Lena Trough would be expected to occur wherever ocean spreading initiates. © The Author 2011. Published by Oxford University Press. All rights reserved
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