50,466 research outputs found
Theory of selective excitation in Stimulated Raman Scattering
A semiclassical model is used to investigate the possibility of selectively
exciting one of two closely spaced, uncoupled Raman transitions. The duration
of the intense pump pulse that creates the Raman coherence is shorter than the
vibrational period of a molecule (impulsive regime of interaction). Pulse
shapes are found that provide either enhancement or suppression of particular
vibrational excitations.Comment: RevTeX4,10 pages, 5 figures, submitted to Phys.Rev.
Single grain (LRE)-Ba-Cu-O superconductors fabricated by top seeded melt growth in air
We have recently reported a practical processing method for the fabrication in air of large, single grain (LRE)-Ba-Cu-O [where LRE Nd, Sm, Eu and Gd] bulk superconductors that exhibit high Tc and high Jc. The process is based initially on the development of a new type of generic seed crystal that can promote effectively the epitaxial nucleation of any (RE)-Ba-Cu-O system and, secondly, by suppressing the formation of (LRE)/Ba solid solution in a controlled manner within large LRE-Ba-Cu-O grains processed in air. In this paper we investigate the degree of homogeneity of large grain Sm-Ba-Cu-O superconductors fabricated by this novel process. The technique offers a significant degree of freedom in terms of processing parameters and reproducibility in the growth of oriented single grains in air and yields bulk samples with significantly improved superconducting and field-trapping properties compared to those processed by conventional top seeded melt growth (TSMG)
Distinction Between Inflection and Derivation of Learning Reduplication in Mandarin
Reduplication as a word-formation process in Mandarin, which is one of the most difficult knowledge to comprehend for scholar and student. Theoretically this research offers an approach that is different from what has been made by previous researchers. Using the M.D.S Simatupang free context approach this research contrasts the reduplicative forms of all word classes and shows the relationships between them (AA, AABB, ABAB, ABB) and their basic forms (A, AB), then based on test of categorical word and test of lexical decomposition as proposed by J.W.M Verhaar, this study analyzes and explains reduplication and inflectional reduplication in Mandarin in order to students understand as their meaning vocabularies. As a result, this research examines the derivational and inflectional reduplication in Mandarin all at once can disseminate the use of morphological theory. In addition, this study discusses Mandarin reduplication based on various word classes that are contained as a basis for the relevant form of reduplication. Beginner research results will be presented in this study in order to stimulate more complete writing, it will be better if this research can be disseminated in order to add learning and reading material for future research
Temperature-Dependent Frequency Shifts in Collective Excitations of a Bose-Einstein Condensate
By including the contribution of the thermal cloud to the Lagrangian of the
condensate of a Bose gas, we extend the time-dependent variational method at
zero temperature to study temperature-dependent low collective excitation
modes. A Gaussian trial wave function of the condensate and a static
distribution density of the thermal cloud are used, and analytical expressions
for temperature-dependent excitation frequencies obtained. Theoretical results
are compared with measurements in the JILA and MIT experiments.Comment: 13 pages, RevTex, 2 EPS figure
On the distribution of estimators of diffusion constants for Brownian motion
We discuss the distribution of various estimators for extracting the
diffusion constant of single Brownian trajectories obtained by fitting the
squared displacement of the trajectory. The analysis of the problem can be
framed in terms of quadratic functionals of Brownian motion that correspond to
the Euclidean path integral for simple Harmonic oscillators with time dependent
frequencies. Explicit analytical results are given for the distribution of the
diffusion constant estimator in a number of cases and our results are confirmed
by numerical simulations.Comment: 14 pages, 5 figure
Entanglement in Relativistic Quantum Field Theory
I present some general ideas about quantum entanglement in relativistic
quantum field theory, especially entanglement in the physical vacuum. Here,
entanglement is defined between different single particle states (or modes),
parameterized either by energy-momentum together with internal degrees of
freedom, or by spacetime coordinate together with the component index in the
case of a vector or spinor field. In this approach, the notion of entanglement
between different spacetime points can be established. Some entanglement
properties are obtained as constraints from symmetries, e.g., under Lorentz
transformation, space inversion, time reverse and charge conjugation.Comment: 5 pages. v1: Submitted for publication in May 2004. v2: minor
correction
The Schrodinger-like Equation for a Nonrelativistic Electron in a Photon Field of Arbitrary Intensity
The ordinary Schrodinger equation with minimal coupling for a nonrelativistic
electron interacting with a single-mode photon field is not satisfied by the
nonrelativistic limit of the exact solutions to the corresponding Dirac
equation. A Schrodinger-like equation valid for arbitrary photon intensity is
derived from the Dirac equation without the weak-field assumption. The
"eigenvalue" in the new equation is an operator in a Cartan subalgebra. An
approximation consistent with the nonrelativistic energy level derived from its
relativistic value replaces the "eigenvalue" operator by an ordinary number,
recovering the ordinary Schrodinger eigenvalue equation used in the formal
scattering formalism. The Schrodinger-like equation for the multimode case is
also presented.Comment: Tex file, 13 pages, no figur
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Mechanistic Study Of Plasma Damage Of Low k Dielectric Surfaces
Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O-2, N-2/H-2, N-2 and H-2 in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.Microelectronics Research Cente
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