799 research outputs found
Photoemission kinks and phonons in cuprates
One of the possible mechanisms of high Tc superconductivity is Cooper pairing
with the help of bosons, which change the slope of the electronic dispersion as
observed by photoemission. Giustino et al. calculated that in the high
temperature superconductor La1.85Sr0.15CuO4 crystal lattice vibrations
(phonons) should have a negligible effect on photoemission spectra and
concluded that phonons do not play an important role. We show that the
calculations employed by Giustino et al. fail to reproduce huge influence of
electron-phonon coupling on important phonons observed in experiments. Thus one
would expect these calculations to similarly fail in explaining the role of
electron-phonon coupling for the electronic dispersion.Comment: To appear in Nature as a Brief Communiction Arisin
Produção de alimentos em sistemas agroflorestais de base agroecológica no cerrado na Região Sul de Mato Grosso do Sul.
Joint Elastic Side-Scattering Lidar and Raman Lidar Measurements of Aerosol Optical Properties in South East Colorado
We describe an experiment, located in south-east Colorado, USA, that measured
aerosol optical depth profiles using two Lidar techniques. Two independent
detectors measured scattered light from a vertical UV laser beam. One detector,
located at the laser site, measured light via the inelastic Raman
backscattering process. This is a common method used in atmospheric science for
measuring aerosol optical depth profiles. The other detector, located
approximately 40km distant, viewed the laser beam from the side. This detector
featured a 3.5m2 mirror and measured elastically scattered light in a bistatic
Lidar configuration following the method used at the Pierre Auger cosmic ray
observatory. The goal of this experiment was to assess and improve methods to
measure atmospheric clarity, specifically aerosol optical depth profiles, for
cosmic ray UV fluorescence detectors that use the atmosphere as a giant
calorimeter. The experiment collected data from September 2010 to July 2011
under varying conditions of aerosol loading. We describe the instruments and
techniques and compare the aerosol optical depth profiles measured by the Raman
and bistatic Lidar detectors.Comment: 34 pages, 16 figure
Encouraging versatile thinking in algebra using the computer
In this article we formulate and analyse some of the obstacles to understanding the notion of a variable, and the use and meaning of algebraic notation, and report empirical evidence to support the hypothesis that an approach using the computer will be more successful in overcoming these obstacles. The computer approach is formulated within a wider framework ofversatile thinking in which global, holistic processing complements local, sequential processing. This is done through a combination of programming in BASIC, physical activities which simulate computer storage and manipulation of variables, and specific software which evaluates expressions in standard mathematical notation. The software is designed to enable the user to explore examples and non-examples of a concept, in this case equivalent and non-equivalent expressions. We call such a piece of software ageneric organizer because if offers examples and non-examples which may be seen not just in specific terms, but as typical, or generic, examples of the algebraic processes, assisting the pupil in the difficult task of abstracting the more general concept which they represent. Empirical evidence from several related studies shows that such an approach significantly improves the understanding of higher order concepts in algebra, and that any initial loss in manipulative facility through lack of practice is more than made up at a later stage
SHAPING OF ION PULSES FROM AN ELECTRON BEAM ION SOURCE FOR PARTICLE INJECTION INTO ACCELERATORS*
Abstract Electron Beam Ion Sources (EBISs) provide highly charged ions (HCIs) for many applications, amongst others for particle injection into accelerators. Although EBISs are limited in ion output they feature a lot of advantages which qualify them for accelerator injection. The ion pulses extracted from the ion sources can be directly injected into an accelerator sequence which however requires ion pulses with distinct shape and length. The ions are produced by trapping in a high density electron beam for a certain time with electrostatic potentials providing for their axial trapping. Due to the ion energy distribution within the trapping region ion extraction can be controlled by controlling the trapping potential. A specific time dependent control mode of the trapping potential thus allow for the production of ion pulses with designated shape and length. Source parameters such as working gas pressure, electron beam current and energy influence the energy distribution of the ions which in turn influence the pulse shaping
Phase Diagram of the Two-Channel Kondo Lattice
The phase diagram of the two-channel Kondo lattice model is examined with a
Quantum Monte Carlo simulation in the limit of infinite dimensions.
Commensurate (and incommensurate) antiferromagnetic and superconducting states
are found. The antiferromagnetic transition is very weak and continuous;
whereas the superconducting transition is discontinuous to an odd-frequency
channel-singlet and spin-singlet pairing state.Comment: 5 pages, LaTeX and 4 PS figures (see also cond-mat/9609146 and
cond-mat/9605109
Giant phonon anomalies and central peak due to charge density wave formation in YBaCuO
The electron-phonon interaction is a major factor influencing the competition
between collective instabilities in correlated-electron materials, but its role
in driving high-temperature superconductivity in the cuprates remains poorly
understood. We have used high-resolution inelastic x-ray scattering to monitor
low-energy phonons in YBaCuO (superconducting
K), which is close to a charge density wave (CDW) instability. Phonons in a
narrow range of momentum space around the CDW ordering vector exhibit extremely
large superconductivity-induced lineshape renormalizations. These results imply
that the electron-phonon interaction has sufficient strength to generate
various anomalies in electronic spectra, but does not contribute significantly
to Cooper pairing. In addition, a quasi-elastic "central peak" due to CDW
nanodomains is observed in a wide temperature range above and below ,
suggesting that the gradual onset of a spatially inhomogeneous CDW domain state
with decreasing temperature is a generic feature of the underdoped cuprates
Herpes simplex virus 1 amplicon vector-mediated siRNA targeting epidermal growth factor receptor inhibits growth of human glioma cells in vivo
In primary glioblastomas and other tumor types, the epidermal growth factor receptor (EGFR) is frequently observed with alterations, such as amplification, structural rearrangements, or overexpression of the gene, suggesting an important role in glial tumorigenesis and progression. In this study, we investigated whether posttranscriptional gene silencing by vector-mediated RNAi to inhibit EGFR expression can reduce the growth of cultured human gli36 glioma cells. To "knock down" EGFR expression, we have created HSV-1-based amplicons that contain the RNA polymerase III-dependent H1 promoter to express double-stranded hairpin RNA directed against EGFR at two different locations (pHSVsiEGFR I and pHSVsiEGFR II). We demonstrate that both pHSVsiEGFR I and pHSVsiEGFR II mediated knock-down of transiently transfected full-length EGFR or endogenous EGFR in a dose-dependent manner. The knock-down of EGFR resulted in the growth inhibition of human glioblastoma (gli36-luc) cells both in culture and in athymic mice in vivo. Cell cycle analysis and annexin V staining revealed that siRNA-mediated suppression of EGFR induced apoptosis. Overall HSV-1 amplicons can mediate efficient and specific posttranscriptional gene silencing. Copyright © The American Society of Gene Therapy
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