15,873 research outputs found
Convergence Rates for Newton’s Method at Singular Points
If Newton’s method is employed to find a root of a map from a Banach space into itself and the derivative is singular at that root, the convergence of the Newton iterates to the root is linear rather than quadratic. In this paper we give a detailed analysis of the linear convergence rates for several types of singular problems. For some of these problems we describe modifications of Newton’s method which will restore quadratic convergence
Density of bulk trap states in organic semiconductor crystals: discrete levels induced by oxygen in rubrene
The density of trap states in the bandgap of semiconducting organic single
crystals has been measured quantitatively and with high energy resolution by
means of the experimental method of temperature-dependent
space-charge-limited-current spectroscopy (TD-SCLC). This spectroscopy has been
applied to study bulk rubrene single crystals, which are shown by this
technique to be of high chemical and structural quality. A density of deep trap
states as low as ~ 10^{15} cm^{-3} is measured in the purest crystals, and the
exponentially varying shallow trap density near the band edge could be
identified (1 decade in the density of states per ~25 meV). Furthermore, we
have induced and spectroscopically identified an oxygen related sharp hole bulk
trap state at 0.27 eV above the valence band.Comment: published in Phys. Rev. B, high quality figures:
http://www.cpfs.mpg.de/~krellner
Integrating Students into Interdisciplinary Health and Health Disparities Research Teams
Major initiatives by the U.S. Department of Health and Human Services as well as the World Health Organization have produced a large and compelling body of evidence on how to reduce health disparities, which entails having a clear understanding of how social factors shape health and healthcare outcomes. Specifically, there is a need for healthcare professionals to understand social determinants of health (e.g., low socioeconomic status, lack of health insurance, and poor education) and how these lead to disparities in health for people of minority racial and ethnic groups. Little is known about how students are developed as health disparities researchers or how their research experiences impact their views about addressing social determinants of health as a career goal. The purpose of this paper is to describe how health and human sciences students were integrated into three minority HIV prevention and testing projects using the lifelong learning for health professionals (LLHP) principles and activities framework, which entails a focus on: (a) education, (b) community, and (c) organization in the planning, development, implementation, and evaluation of interdisciplinary research
Implementing Quantum Gates by Optimal Control with Doubly Exponential Convergence
We introduce a novel algorithm for the task of coherently controlling a
quantum mechanical system to implement any chosen unitary dynamics. It performs
faster than existing state of the art methods by one to three orders of
magnitude (depending on which one we compare to), particularly for quantum
information processing purposes. This substantially enhances the ability to
both study the control capabilities of physical systems within their coherence
times, and constrain solutions for control tasks to lie within experimentally
feasible regions. Natural extensions of the algorithm are also discussed.Comment: 4+2 figures; to appear in PR
Late Time Barium Cloud Striations and Their Possible Relationship to Equatorial Spread F
An active experiment has been conducted in space that allows a test for the theory of nonlinear development of striations in large barium clouds. The results are in excellent agreement with a computer simulation of the ExB instability reported by Scannapiecoe t al. (1976). The power law irregularity spectrum predicted by the theory and verified by the experiment is shown here to be due to wave steepeninga nd not_top lasmat urbulence.T he barium cloud resultsa re remarkably similar to bottomside equatorial spread F. A possible role of the E x B instability in bottomside equatorial spread F is discussed as a supplement to the Rayleigh-Taylor instability during the postsunset rise of the F layer and during anomalousp lasma uplifts which occur during geomagneticallya ctive period
Multipole strength function of deformed superfluid nuclei made easy
We present an efficient method for calculating strength functions using the
finite amplitude method (FAM) for deformed superfluid heavy nuclei within the
framework of the nuclear density functional theory. We demonstrate that FAM
reproduces strength functions obtained with the fully self-consistent
quasi-particle random-phase approximation (QRPA) at a fraction of computational
cost. As a demonstration, we compute the isoscalar and isovector monopole
strength for strongly deformed configurations in Pu by considering huge
quasi-particle QRPA spaces. Our approach to FAM, based on Broyden's iterative
procedure, opens the possibility for large-scale calculations of strength
distributions in well-bound and weakly bound nuclei across the nuclear
landscape.Comment: 5 pages, 3 figure
Eddy turbulence parameters inferred from radar observations at Jicamarca
Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007). In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1&times;10<sup>3</sup> m<sup>2</sup>/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007) is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density
Superconductivity and Stoichiometry in the BSCCO-family Materials
We report on magnetization, c-axis and ab-plane resistivity, critical
current, electronic band structure and superconducting gap properties. Bulk
measurements and photoemission data were taken on similar samples.Comment: 4 pages, latex, to be published in Journal of Superconductivity. two
figures available from Jian Ma at [email protected]
Crit II Electric, Magnetic, and Density Measurements Within an Ionizing Neutral Stream
Measurements from rocket borne sensors inside a high velocity neutral barium beam show a factor of six increasei n plasmad ensityi n a movingi onizingf ront. This region-wacso -locatedw ith intensef luctuatinge lectric fields( $E • 300m V/m) at frequenciewse llu ndert he lower hybrid frequency for a barium plasina. Large quasi-DC electric and magnetic field fluctuations were also detected with a large componento f the current and the electricf ield. parallelt o Bo. An Alfv6n wavew ith a finite electricf ield componentp arallel to the geomagneticfi eld was observed to propagatea longB o, wherei t wasd etectedb y ami nstrumented sub-payload
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