1,808,069 research outputs found
Emergence of Classical Orbits in Few-Cycle Above-Threshold Ionization
The time-dependent Schr\"odinger equation for atomic hydrogen in few-cycle
laser pulses is solved numerically. Introducing a positive definite quantum
distribution function in energy-position space, a straightforward comparison of
the numerical ab initio results with classical orbit theory is facilitated.
Integration over position space yields directly the photoelectron spectra so
that the various pathways contributing to a certain energy in the photoelectron
spectra can be established in an unprecedented direct and transparent way.Comment: 4 pages, 4 figures REVTeX (manuscript with higher resolution figures
available at http://www.dieterbauer.de/publist.html
Observation of explosive collisionless reconnection in 3D nonlinear gyrofluid simulations
The nonlinear dynamics of collisionless reconnecting modes is investigated,
in the framework of a three-dimensional gyrofluid model. This is the relevant
regime of high-temperature plasmas, where reconnection is made possible by
electron inertia and has higher growth rates than resistive reconnection. The
presence of a strong guide field is assumed, in a background slab model, with
Dirichlet boundary conditions in the direction of nonuniformity. Values of ion
sound gyro-radius and electron collisionless skin depth much smaller than the
current layer width are considered. Strong acceleration of growth is found at
the onset to nonlinearity, while at all times the energy functional is well
conserved. Nonlinear growth rates more than one order of magnitude higher than
linear growth rates are observed when entering into the small- regime
A Lattice QCD Analysis of the Strangeness Magnetic Moment of the Nucleon
The outcome of the SAMPLE Experiment suggests that the strange-quark
contribution to the nucleon magnetic moment, G_M^s(0), may be greater than
zero. This result is very difficult to reconcile with expectations based on the
successful baryon magnetic-moment phenomenology of the constituent quark model.
We show that careful consideration of chiral symmetry reveals some rather
unexpected properties of QCD. In particular, it is found that the valence
u-quark contribution to the magnetic moment of the neutron can differ by more
than 50% from its contribution to the Xi^0 magnetic moment. This hitherto
unforeseen result leads to the value G_M^s(0) = -0.16 +/- 0.18 with a
systematic error, arising from the relatively large strange quark mass used in
existing lattice calculations, that would tend to shift G_M^s(0) towards small
positive values.Comment: RevTeX, 20 pages, 12 figure
Nucleon and Pion Form Factors in Different Forms of Relativistic Quantum Mechanics
Calculations of form factors in different forms of relativistic kinematics
are presented. They involve the instant, front and point forms. In the two
first cases, different kinematical conditions are considered while in the
latter case, both a Dirac-inspired approach and a hyperplane-based one are
incorporated in our study. Numerical results are presented for the pion form
factors with emphasis on both the low and high Q**2 range. A new argument is
presented, explaining why some approaches do considerably much better than
other ones whenonly a single-particle current is considered.Comment: To appear in the proceedings of MENU04 (Beijing, Aug. 29- Sept. 4,
2004
The hidden geometric character of relativistic quantum mechanics
The presentation makes use of geometric algebra, also known as Clifford
algebra, in 5-dimensional spacetime. The choice of this space is given the
character of first principle, justified solely by the consequences that can be
derived from such choice and their consistency with experimental results. Given
a metric space of any dimension, one can define monogenic functions, the
natural extension of analytic functions to higher dimensions; such functions
have null vector derivative and have previously been shown by other authors to
play a decisive role in lower dimensional spaces. All monogenic functions have
null Laplacian by consequence; in an hyperbolic space this fact leads
inevitably to a wave equation with plane-like solutions. This is also true for
5-dimensional spacetime and we will explore those solutions, establishing a
parallel with the solutions of the Dirac equation. For this purpose we will
invoke the isomorphism between the complex algebra of 4x4 matrices, also known
as Dirac's matrices. There is one problem with this isomorphism, because the
solutions to Dirac's equation are usually known as spinors (column matrices)
that don't belong to the 4x4 matrix algebra and as such are excluded from the
isomorphism. We will show that a solution in terms of Dirac spinors is
equivalent to a plane wave solution. Just as one finds in the standard
formulation, monogenic functions can be naturally split into positive/negative
energy together with left/right ones. This split is provided by geometric
projectors and we will show that there is a second set of projectors providing
an alternate 4-fold split. The possible implications of this alternate split
are not yet fully understood and are presently the subject of profound
research.Comment: 29 pages. Small changes in V3 suggested by refere
The size of flavor changing effects induced by the symmetry breaking sector
It has recently been shown that strong interactions underlying electroweak
symmetry breaking will induce four-fermion amplitudes proportional to m_t^2,
which in turn will influence a variety of flavor changing processes. We argue
that the size of these effects are likely to be far below the current
experimental bounds.Comment: 5 pages, LaTeX, 1 figur
Tensile creep-rate of pyrolytic carbon
Stress-change technique, combined with a graphical-interpolation analysis, yields data on the stress and temperature dependence of the creep rate over broad strain and stress or temperature ranges on as-deposited, substrate-nucleated, pyrolytic carbon
Process development
An overview is given of seven process development activities which were presented at this session. Pulsed excimer laser processing of photovoltaic cells was presented. A different pulsed excimer laser annealing was described using a 50 w laser. Diffusion barrier research focused on lowering the chemical reactivity of amorphous thin film on silicon. In another effort adherent and conductive films were successfully achieved. Other efforts were aimed at achieving a simultaneous front and back junction. Microwave enhanced plasma deposition experiments were performed. An updated version of the Solar Array Manufacturing Industry Costing Standards (SAMICS) was presented, along with a life cycle cost analysis of high efficiency cells. The last presentation was on the evaluation of the ethyl vinyl acetate encapsulating system
- …