1,605 research outputs found
Folds and Buckles at the Nanoscale: Experimental and Theoretical Investigation of the Bending Properties of Graphene Membranes
The elastic properties of graphene crystals have been extensively investigated, revealing unique properties in the linear and nonlinear regimes, when the membranes are under either stretching or bending loading conditions. Nevertheless less knowledge has been developed so far on folded graphene membranes and ribbons. It has been recently suggested that fold-induced curvatures, without in-plane strain, can affect the local chemical reactivity, the mechanical properties, and the electron transfer in graphene membranes. This intriguing perspective envisages a materials-by-design approach through the engineering of folding and bending to develop enhanced nano-resonators or nano-electro-mechanical devices. Here we present a novel methodology to investigate the mechanical properties of folded and wrinkled graphene crystals, combining transmission electron microscopy mapping of 3D curvatures and theoretical modeling based on continuum elasticity theory and tight-binding atomistic simulations
Water relations of grapevine cv. Cortese with different training systems
Leaf (LWP) and stem water potential and stomatal conductance (SC) were measured during the day on grapevines trained with four different systems: traditional trellis, central curtain, Y trellis and double curtain. During most of the day LWP was lower and the stem to leaf water potential gradient was higher in the traditional trellis than in the other systems. On the contrary, very few differences were found as regards SC. Osmotic potential changed little during the day and among treatments. Traditional trellis vines had lower yield and total sugar production. The conclusion is drawn that training systems can affect water relations and in this way influence yield and must quality.Relations hydriques de vignes du cépage Cortese élevées sous différents systèmes de conduiteLe potentiel hydrique des feuilles (LWP) et des tiges et la conductance stomatique (SC) ont été mésurés le long du jour sur des plantes de vigne élevés sous quatre systèmes de conduite: vigne palissée en taille Guyot, rideau simple, système Y, rideau double. Pendant la plupart du jour LWP a été plus réduit dans les vignes en Guyot tandis que le gradient de potentiel entre feuille et tige a été plus éléve chez le même système de conduite. Au contraire, les différences au niveau de SC ont été négligeables. Le potentiel osmotique de la feuille a peu changé le long du jour et entre les systemès de conduite. Les vignes en Guyot ont produit moins de raisins et de sucre. Le mode de conduite peut affecter les relations hydriques de la vigne et donc modifier la production et la qualité du moût
Recent results of a seismically isolated optical table prototype designed for advanced LIGO
The Horizontal Access Module Seismic Attenuation System (HAM-SAS) is a mechanical device expressly designed to isolate a multipurpose optical table and fit in the tight space of the LIGO HAM Ultra-High-Vacuum chamber. Seismic attenuation in the detectors' sensitivity frequency band is achieved with state of the art passive mechanical attenuators. These devices should provide an attenuation factor of about 70dB above 10Hz at the suspension point of the Advanced LIGO triple pendulum suspension. Automatic control techniques are used to position the optical table and damp rigid body modes. Here, we report the main results obtained from the full scale prototype installed at the MIT LIGO Advanced System Test Interferometer (LASTI) facility. Seismic attenuation performance, control strategies, improvements and limitations are also discussed
Relativistic Green functions in a plane wave gravitational background
We consider a massive relativistic particle in the background of a
gravitational plane wave. The corresponding Green functions for both spinless
and spin 1/2 cases, previously computed by A. Barducci and R. Giachetti
\cite{Barducci3}, are reobtained here by alternative methods, as for example,
the Fock-Schwinger proper-time method and the algebraic method. In analogy to
the electromagnetic case, we show that for a gravitational plane wave
background a semiclassical approach is also sufficient to provide the exact
result, though the lagrangian involved is far from being a quadratic one.Comment: Last paper by Professor Arvind Narayan Vaidya, 18 pages, no figure
Anti-de Sitter boundary in Poincare coordinates
We study the space-time boundary of a Poincare patch of Anti-de Sitter (AdS)
space. We map the Poincare AdS boundary to the global coordinate chart and show
why this boundary is not equivalent to the global AdS boundary. The Poincare
AdS boundary is shown to contain points of the bulk of the entire AdS space.
The Euclidean AdS space is also discussed. In this case one can define a
semi-global chart that divides the AdS space in the same way as the
corresponding Euclidean Poincare chart.Comment: In this revised version we add a discussion of the physical
consequences of the choice of a coordinate system for AdS space. We changed
figure 1 and added more references. Version to be published in Gen. Relat.
Grav
Core-mantle boundary deformations and J2 variations resulting from the 2004 Sumatra earthquake
The deformation at the core-mantle boundary produced by the 2004 Sumatra
earthquake is investigated by means of a semi-analytic theoretical model of
global coseismic and postseismic deformation, predicting a millimetric
coseismic perturbation over a large portion of the core-mantle boundary.
Spectral features of such deformations are analysed and discussed. The
time-dependent postseismic evolution of the elliptical part of the gravity
field (J2) is also computed for different asthenosphere viscosity models. Our
results show that, for asthenospheric viscosities smaller than 10^18 Pa s, the
postseismic J2 variation in the next years is expected to leave a detectable
signal in geodetic observations.Comment: 14 pages, 8 figures, 1 table. It will appear in Geophysical Journal
Internationa
Pion and Vector Meson Form Factors in the Kuperstein-Sonnenschein holographic model
We study phenomenological aspects of the holographic model of chiral symmetry
breaking recently introduced by Kuperstein and Sonnenschein (KS). As a first
step, we calculate the spectrum of vector and axial-vector mesons in the KS
model. We numerically compute various coupling constants of the mesons and
pions. Our analysis indicates that vector meson dominance is realized in this
model. The pion, vector meson and axial-vector meson form factors are obtained
and studied in detail. We find good agreement with QCD results. In particular,
the pion form factor closely matches available experimental data.Comment: v1: 27 pages, 9 figures, 4 tables; v2: minor changes, added more
general discussion of vector meson dominance; v3: minor changes and
additions, version accepted for publication in JHE
Conditioned Unitary Transformation on biphotons
A conditioned unitary transformation ( polarization rotation) is
performed at single-photon level. The transformation is realized by rotating
polarization for one of the photons of a polarization-entangled biphoton state
(signal photon) by means of a Pockel's cell triggered by the detection of the
other (idler) photon after polarization selection. As a result, polarization
degree for the signal beam changes from zero to the value given by the idler
detector quantum efficiency. This result is relevant to practical realization
of various quantum information schemes and can be used for developing a new
method of absolute quantum efficiency calibration
Glueball Regge trajectories from gauge/string duality and the Pomeron
The spectrum of light baryons and mesons has been reproduced recently by
Brodsky and Teramond from a holographic dual to QCD inspired in the AdS/CFT
correspondence. They associate fluctuations about the AdS geometry with four
dimensional angular momenta of the dual QCD states. We use a similar approach
to estimate masses of glueball states with different spins and their
excitations. We consider Dirichlet and Neumann boundary conditions and find
approximate linear Regge trajectories for these glueballs. In particular the
Neumann case is consistent with the Pomeron trajectory.Comment: In this revised version we made some additional remarks on the text.
We also included 2 more references. The glueball spectrum and Regge
trajectories are unchanged. 10 pages, 2 eps figure
Nonperturbative SUSY Correlators at Finite Temperature
We calculate finite temperature effects on a correlation function in the two
dimensional supersymmetric nonlinear O(3) sigma model. The correlation function
violates chiral symmetry and at zero temperature it has been shown to be a
constant, which gives rise to a double-valued condensate. Within the bilinear
approximation we find an exact result in a one-instanton background at finite
temperature. In contrast to the result at zero temperature we find that the
correlation function decays exponentially at large distances.Comment: Latex, 27 pages, 1 Postscript figur
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