6,703 research outputs found
The effects of isometric work on heart rate, blood pressure, and net oxygen cost
Isometric exercise effects on heart rate, blood pressure, and net oxygen cos
Enhanced Molecular Orientation Induced by Molecular Anti-Alignment
We explore the role of laser induced anti-alignment in enhancing molecular
orientation. A field-free enhanced orientation via anti-alignment scheme is
presented, which combines a linearly polarized femtosecond laser pulse with a
half-cycle pulse. The laser pulse induces transient anti-alignment in the plane
orthogonal to the field polarization, while the half-cycle pulse leads to the
orientation. We identify two qualitatively different enhancement mechanisms
depending on the pulse order, and optimize their effects using classical and
quantum models both at zero and non-zero temperature
Saturation Effects in Deep Inelastic Scattering at low and its Implications on Diffraction
We present a model based on the concept of saturation for small and
small . With only three parameters we achieve a good description of all Deep
Inelastic Scattering data below . This includes a consistent treatment
of charm and a successful extrapolation into the photoproduction regime. The
same model leads to a roughly constant ratio of diffractive and inclusive cross
section.Comment: 24 pages, 12 figures, Latex-fil
Orienting coupled quantum rotors by ultrashort laser pulses
We point out that the non-adiabatic orientation of quantum rotors, produced
by ultrashort laser pulses, is remarkably enhanced by introducing dipolar
interaction between the rotors. This enhanced orientation of quantum rotors is
in contrast with the behavior of classical paired rotors, in which dipolar
interactions prevent the orientation of the rotors. We demonstrate also that a
specially designed sequence of pulses can most efficiently enhances the
orientation of quantum paired rotors.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
Saturation and geometric scaling in DIS at small x
We present various aspects of the saturation model which provides good
description of inclusive and diffractive DIS at small x. The model uses parton
saturation ideas to take into account unitarity requirements. A new scaling
predicted by the model in the small x domain is successfully confronted with
the data.Comment: Presented at New Trends in HERA Physics 2001, Ringberg Castle,
Tegernsee, Germany, 17-22 June 2001, minor corrections, some references adde
Double logarithms, , and the NLO DGLAP evolution for the non-singlet component of the nucleon spin structure function,
Theoretical predictions show that at low values of Bjorken the spin
structure function, is influenced by large logarithmic corrections,
, which may be predominant in this region. These corrections are
also partially contained in the NLO part of the standard DGLAP evolution. Here
we calculate the non-singlet component of the nucleon structure function,
, and its first moment, using a unified evolution
equation. This equation incorporates the terms describing the NLO DGLAP
evolution and the terms contributing to the resummation. In order
to avoid double counting in the overlapping regions of the phase-space, a
unique way of including the NLO terms into the unified evolution equation is
proposed. The scheme-independent results obtained from this unified evolution
are compared to the NLO fit to experimental data, GRSV'2000. Analysis of the
first moments of shows that the unified evolution including the
resummation goes beyond the NLO DGLAP analysis. Corrections
generated by double logarithms at low influence the -dependence of the
first moments strongly.Comment: 13 pages, latex, 2 figures; Appendix adde
Loading a Bose-Einstein Condensate onto an Optical Lattice: an Application of Optimal Control Theory to The Non Linear Schr\"odinger Equation
Using a set of general methods developed by Krotov [A. I. Konnov and V. A.
Krotov, Automation and Remote Control, {\bf 60}, 1427 (1999)], we extend the
capabilities of Optimal Control Theory to the Nonlinear Schr\"odinger Equation
(NLSE). The paper begins with a general review of the Krotov approach to
optimization. Although the linearized version of the method is sufficient for
the linear Schr\"odinger equation, the full flexibility of the general method
is required for treatment of the nonlinear Schr\"odinger equation. Formal
equations for the optimization of the NLSE, as well as a concrete algorithm are
presented. As an illustration, we consider a Bose-Einstein condensate initially
at rest in a harmonic trap. A phase develops across the BEC when an optical
lattice potential is turned on. The goal is to counter this effect and keep the
phase flat by adjusting the trap strength. The problem is formulated in the
language of Optimal Control Theory (OCT) and solved using the above
methodology. To our knowledge, this is the first rigorous application of OCT to
the Nonlinear Schr\"odinger equation, a capability that is bound to have
numerous other applications.Comment: 11 pages, 4 figures, A reference added, Some typos correcte
A global analysis of inclusive diffractive cross sections at HERA
We describe the most recent data on the diffractive structure functions from
the H1 and ZEUS Collaborations at HERA using four models. First, a Pomeron
Structure Function (PSF) model, in which the Pomeron is considered as an object
with parton distribution functions. Then, the Bartels Ellis Kowalski Wusthoff
(BEKW) approach is discussed, assuming the simplest perturbative description of
the Pomeron using a two-gluon ladder. A third approach, the Bialas Peschanski
(BP) model, based on the dipole formalism is then described. Finally, we
discuss the Golec-Biernat-W\"usthoff (GBW) saturation model which takes into
account saturation effects. The best description of all avaible measurements
can be achieved with either the PSF based model or the BEKW approach. In
particular, the BEKW prediction allows to include the highest
measurements, which are dominated by higher twists effects and provide an
efficient and compact parametrisation of the diffractive cross section. The two
other models also give a good description of cross section measurements at
small with a small number of parameters. The comparison of all predictions
allows us to identify interesting differences in the behaviour of the effective
pomeron intercept and in the shape of the longitudinal component of the
diffractive structure functions. In this last part, we present some features
that can be discriminated by new experimental measurements, completing the HERA
program.Comment: 32 pages, 18 figure
Combined electrical transport and capacitance spectroscopy of a field effect transistor
We have measured both the current-voltage (-)
and capacitance-voltage (-) characteristics of a
field effect transistor. From the measured capacitance
we calculate the electron surface density and show that its gate voltage
dependence follows the theoretical prediction resulting from the
two-dimensional free electron model. This model allows us to fit the measured
- characteristics over the \emph{entire range} of
. Combining this experimental result with the measured
current-voltage characteristics, we determine the field effect mobility as a
function of gate voltage. We show that for our device this improved combined
approach yields significantly smaller values (more than a factor of 4) of the
electron mobility than the conventional analysis of the current-voltage
characteristics only.Comment: to appear in Applied Physics Letter
Four point function of R-currents in N=4 SYM in the Regge limit at weak coupling
We compute, in N=4 super Yang-Mills theory, the four point correlation
function of R-currents in the Regge limit in the leading logarithmic
approximation at weak coupling. Such a correlator is the closest analog to
photon-photon scattering within QCD, and there is a well-defined procedure to
perform the analogous computation at strong coupling via the AdS/CFT
correspondence. The main result of this paper is, on the gauge theory side, the
proof of Regge factorization and the explicit computation of the R-current
impact factors.Comment: 21 pages, 10 figures, typos correcte
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