3,624 research outputs found
Casimir energy density in closed hyperbolic universes
The original Casimir effect results from the difference in the vacuum
energies of the electromagnetic field, between that in a region of space with
boundary conditions and that in the same region without boundary conditions. In
this paper we develop the theory of a similar situation, involving a scalar
field in spacetimes with compact spatial sections of negative spatial
curvature.Comment: 10 pages. Contribution to the "Fifth Alexander Friedmann
International Seminar on Gravitation and Cosmology," Joao Pessoa, Brazil,
2002. Revised version, with altered Abstract and one new referenc
Adsorption studies of DNA origami on silicon dioxide
Self-assembled DNA nanostructures promise low-cost ways to create nanoscale shapes. DNA nanostructures can also be used to position particles with nanometer precision. Yet, reliable and low-cost ways of integrating the structures with MEMS technology still have to be developed and innovations are of great interest to the field. We have examined in detail the adherence of DNA origami tiles on silicon oxide surfaces of wafers in dependence on pH-value and magnesium ion concentration. The results of this work will help to pursue new strategies of positioning DNA nanostruc-tures on SiO2. Precise control over the strength of structure-surface adhesion is a prerequisite of relia-ble processes
Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interaction
Chiral magnets are an emerging class of topological matter harbouring
localized and topologically protected vortex-like magnetic textures called
skyrmions, which are currently under intense scrutiny as a new entity for
information storage and processing. Here, on the level of micromagnetics we
rigorously show that chiral magnets cannot only host skyrmions but also
antiskyrmions as least-energy configurations over all non-trivial homotopy
classes. We derive practical criteria for their occurrence and coexistence with
skyrmions that can be fulfilled by (110)-oriented interfaces in dependence on
the electronic structure. Relating the electronic structure to an atomistic
spin-lattice model by means of density-functional calculations and minimizing
the energy on a mesoscopic scale applying spin-relaxation methods, we propose a
double layer of Fe grown on a W(110) substrate as a practical example. We
conjecture that ultrathin magnetic films grown on semiconductor or heavy metal
substrates with symmetry are prototype classes of materials hosting
magnetic antiskyrmions.Comment: 20 pages (11 pages + 9 pages supplementary material
Inflammation and Microvasculopathy in Renal Ischemia Reperfusion Injury
Acute renal failure (ARF) severely worsens prognosis of hospitalized patients. The most frequent cause of intrarenal ARF is transient or prolonged renal hypoperfusion (ischemia). Ischemia primarily affects the function and structure of tubular epithelial cells, which, in severe cases, is characterized by epithelial cell necrosis. Nevertheless, ischemia does not exclusively lead to alterations of epithelial cells but also causes interstitial inflammation and interstitial microvasculopathy. Both inflammation and microvasculopathy are particularly important in terms of postischemic kidney repair. Postischemic microvasculopathy is characterized by endothelial cell swelling with subsequent microvascular occlusion. Thus, reperfusion is inhibited (no-reflow phenomenon). Such endothelial cell dysfunction offers new therapeutic perspectives in ischemic ARF. Newer observations point towards the role of the so-called endothelial progenitor cells (EPCs) in the treatment of ARF. Systemic administration of EPCs to mice with bilateral renal ischemia mitigates postischemic endothelial cell dysfunction and protects animals from acute renal failure
The power spectrum of the circular noise
The circular noise is important in connection to Mach's principle, and also
as a possible probe of the Unruh effect. In this letter the power spectrum of
the detector following the Trocheries-Takeno motion in the Minkowski vacuum is
analytically obtained in the form of an infinite series. A mean distribution
function and corresponding energy density are obtained for this particular
detected noise. The analogous of a non constant temperature distribution is
obtained. And in the end, a brief discussion about the equilibrium
configuration is given.Comment: accepted for publication in GR
Resonant vibrations, peak broadening and noise in single molecule contacts: beyond the resonant tunnelling picture
We carry out experiments on single-molecule junctions at low temperatures,
using the mechanically controlled break junction technique. Analyzing the
results received with more than ten different molecules the nature of the first
peak in the differential conductance spectra is elucidated. We observe an
electronic transition with a vibronic fine structure, which is most frequently
smeared out and forms a broad peak. In the usual parameter range we find strong
indications that additionally fluctuations become active even at low
temperatures. We conclude that the electrical field feeds instabilities, which
are triggered by the onset of current. This is underscored by noise
measurements that show strong anomalies at the onset of charge transport
Finite-Temperature Fidelity-Metric Approach to the Lipkin-Meshkov-Glick Model
The fidelity metric has recently been proposed as a useful and elegant
approach to identify and characterize both quantum and classical phase
transitions. We study this metric on the manifold of thermal states for the
Lipkin-Meshkov-Glick (LMG) model. For the isotropic LMG model, we find that the
metric reduces to a Fisher-Rao metric, reflecting an underlying classical
probability distribution. Furthermore, this metric can be expressed in terms of
derivatives of the free energy, indicating a relation to Ruppeiner geometry.
This allows us to obtain exact expressions for the (suitably rescaled) metric
in the thermodynamic limit. The phase transition of the isotropic LMG model is
signalled by a degeneracy of this (improper) metric in the paramagnetic phase.
Due to the integrability of the isotropic LMG model, ground state level
crossings occur, leading to an ill-defined fidelity metric at zero temperature.Comment: 18 pages, 3 figure
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