581 research outputs found
Stereotaxic gamma knife surgery in treatment of critically located pilocytic astrocytoma: preliminary result
BACKGROUND: Low-grade gliomas are uncommon primary brain tumors, located more often in the posterior fossa, optic pathway, and brain stem and less commonly in the cerebral hemispheres. CASE PRESENTATIONS: Two patients with diagnosed recurrent cystic pilocytic astrocytoma critically located within the brain (thalamic and brain stem) were treated with gamma knife surgery. Gamma knife surgery (GKS) did improve the patient's clinical condition very much which remained stable later on. Progressive reduction on the magnetic resonance imaging (MRI) studies of the solid part of the tumor and almost disappearance of the cystic component was achieved within the follow-up period of 36 months in the first case with the (thalamic located lesion) and 22 months in the second case with the (brain stem located lesion). CONCLUSION: Gamma knife surgery represents an alternate tool in the treatment of recurrent and/or small postoperative residual pilocytic astrocytoma especially if they are critically locate
Entanglement renormalization of anisotropic XY model
The renormalization group flows of the one-dimensional anisotropic XY model
and quantum Ising model under a transverse field are obtained by different
multiscale entanglement renormalization ansatz schemes. It is shown that the
optimized disentangler removes the short-range entanglement by rotating the
system in the parameter space spanned by the anisotropy and the magnetic field.
It is understood from the study that the disentangler reduces the entanglement
by mapping the system to another one in the same universality class but with
smaller short range entanglement. The phase boundary and corresponding critical
exponents are calculated using different schemes with different block sizes,
look-ahead steps and truncation dimensions. It is shown that larger truncation
dimension leads to more accurate results and that using larger block size or
look-ahead step improve the overall calculation consistency.Comment: 5 pages, 3 figure
The Structure of the [Zn_In - V_P] Defect Complex in Zn Doped InP
We study the structure, the formation and binding energies and the transfer
levels of the zinc-phosphorus vacancy complex [Zn_In - V_P] in Zn doped p-type
InP, as a function of the charge, using plane wave ab initio DFT-LDA
calculations in a 64 atom supercell. We find a binding energy of 0.39 eV for
the complex, which is neutral in p-type material, the 0/-1 transfer level lying
0.50 eV above the valence band edge, all in agreement with recent positron
annihilation experiments. This indicates that, whilst the formation of
phosphorus vacancies (V_P) may be involved in carrier compensation in heavily
Zn doped material, the formation of Zn-vacancy complexes is not.
Regarding the structure: for charge states Q=+6 to -4 the Zn atom is in an
sp^2 bonded DX position and electrons added/removed go to/come from the
remaining dangling bonds on the triangle of In atoms. This reduces the
effective vacancy volume monatonically as electrons are added to the complex,
also in agreement with experiment. The reduction occurs through a combination
of increased In-In bonding and increased Zn-In electrostatic attraction. In
addition, for certain charge states we find complex Jahn-Teller behaviour in
which up to three different structures, (with the In triangle dimerised,
antidimerised or symmetric) are stable and are close to degenerate. We are able
to predict and successfully explain the structural behaviour of this complex
using a simple tight binding model.Comment: 10 pages text (postscript) plus 8 figures (jpeg). Submitted to Phys.
Rev.
Autonomous Non-Equilibrium Self-Assembly and Molecular Movements Powered by Electrical Energy
The ability to exploit energy autonomously is one of the hallmarks of life. Mastering such processes in artificial nanosystems can open technological opportunities. In the last decades, light- and chemically driven autonomous systems have been developed in relation to conformational motion and self-assembly, mostly in relation to molecular motors. In contrast, despite electrical energy being an attractive energy source to power nanosystems, its autonomous harnessing has received little attention. Herein we consider an operation mode that allows the autonomous exploitation of electrical energy by a self-assembling system. Threading and dethreading motions of a pseudorotaxane take place autonomously in solution, powered by the current flowing between the electrodes of a scanning electrochemical microscope. The underlying autonomous energy ratchet mechanism drives the self-assembly steps away from equilibrium with a higher energy efficiency compared to other autonomous systems. The strategy is general and might be extended to other redox-driven systems
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Microarray detection of human parainfluenzavirus 4 infection associated with respiratory failure in an immunocompetent adult.
A pan-viral DNA microarray, the Virochip (University of California, San Francisco), was used to detect human parainfluenzavirus 4 (HPIV-4) infection in an immunocompetent adult presenting with a life-threatening acute respiratory illness. The virus was identified in an endotracheal aspirate specimen, and the microarray results were confirmed by specific polymerase chain reaction and serological analysis for HPIV-4. Conventional clinical laboratory testing using an extensive panel of microbiological tests failed to yield a diagnosis. This case suggests that the potential severity of disease caused by HPIV-4 in adults may be greater than previously appreciated and illustrates the clinical utility of a microarray for broad-based viral pathogen screening
The Myth of Carbon Offsets
The RCRC’s mandate is to help identify and incubate fiscal, monetary, and financial regulatory policy solutions that will put the United States on track for net-zero emissions before 2050. Informed by the work of many scientists, regulators, climate advocates, and international organizations, we take a broadly critical view of the many carbon credit markets and offsetting strategies that have developed thus far and urge policymakers, firms, and other organizations to reevaluate and refine this approach. This paper discusses some of the foundational challenges associated with the practice of offsetting and presents recommendations to chart an alternative path forward
Chemically Induced Mismatch of Rings and Stations in [3]Rotaxanes
The mechanical interlocking of molecular components can lead to the appearance of novel and unconventional properties and processes, with potential relevance for applications in nanoscience, sensing, catalysis, and materials science. We describe a [3]rotaxane in which the number of recognition sites available on the axle component can be changed by acid-base inputs, encompassing cases in which this number is larger, equal to, or smaller than the number of interlocked macrocycles. These species exhibit very different properties and give rise to a unique network of acid-base reactions that leads to a fine pKa tuning of chemically equivalent acidic sites. The rotaxane where only one station is available for two rings exhibits a rich coconformational dynamics, unveiled by an integrated experimental and computational approach. In this compound, the two crown ethers compete for the sole recognition site, but can also come together to share it, driven by the need to minimize free energy without evident inter-ring interactions
Crystal Undulator As A Novel Compact Source Of Radiation
A crystalline undulator (CU) with periodically deformed crystallographic
planes is capable of deflecting charged particles with the same strength as an
equivalent magnetic field of 1000 T and could provide quite a short period L in
the sub-millimeter range. We present an idea for creation of a CU and report
its first realization. One face of a silicon crystal was given periodic
micro-scratches (grooves), with a period of 1 mm, by means of a diamond blade.
The X-ray tests of the crystal deformation have shown that a sinusoidal-like
shape of crystalline planes goes through the bulk of the crystal. This opens up
the possibility for experiments with high-energy particles channeled in CU, a
novel compact source of radiation. The first experiment on photon emission in
CU has been started at LNF with 800 MeV positrons aiming to produce 50 keV
undulator photons.Comment: Presented at PAC 2003 (Portland, May 12-16
Entanglement renormalization and boundary critical phenomena
The multiscale entanglement renormalization ansatz is applied to the study of
boundary critical phenomena. We compute averages of local operators as a
function of the distance from the boundary and the surface contribution to the
ground state energy. Furthermore, assuming a uniform tensor structure, we show
that the multiscale entanglement renormalization ansatz implies an exact
relation between bulk and boundary critical exponents known to exist for
boundary critical systems.Comment: 6 pages, 4 figures; for a related work see arXiv:0912.164
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