8,735 research outputs found
The seaweeds of Kenya: Checklist, history of seaweed study, coastal environment, and analysis of seaweed diversity and biogeography
The seaweeds of Kenya are relatively well documented in comparison with the marine floras of other countries in the Indian Ocean. A checklist is provided of the seaweeds recorded, which includes a total of 386 species (214 red algae, 116 green algae and 56 brown algae), plus an additional 19 infra-specific taxa. This is the first detailed list for almost 30 years, with a 29% increase in species compared to the previous listing. The history of seaweed study in Kenya and the Kenyan coastal environment as a habitat for seaweeds are discussed in detail. An ordination analysis of the global biogeographic relationships of the Kenyan seaweed flora shows clearly the internal consistency of the Indo-Pacific seaweed flora at this large scale. Data on Indian Ocean relationships show that the Kenyan flora produces a distinct grouping of seaweed floras from Tanzania, Madagascar, Mozambique and the Indian Ocean coast of South Africa, which is somewhat separated from the floras of the rest of the Indian Ocean. The data reveal that Mozambiquan seaweeds are seriously understudied, with only 26% of the Kenyan flora having been recorded in that country, compared with 68% in Tanzania, 41% in Madagascar, and 43% in South Africa
Multilevel blocking approach to the fermion sign problem in path-integral Monte Carlo simulations
A general algorithm toward the solution of the fermion sign problem in
finite-temperature quantum Monte Carlo simulations has been formulated for
discretized fermion path integrals with nearest-neighbor interactions in the
Trotter direction. This multilevel approach systematically implements a simple
blocking strategy in a recursive manner to synthesize the sign cancellations
among different fermionic paths throughout the whole configuration space. The
practical usefulness of the method is demonstrated for interacting electrons in
a quantum dot.Comment: 4 pages RevTeX, incl. two figure
Performance of an Operating High Energy Physics Data Grid: D0SAR-Grid
The D0 experiment at Fermilab's Tevatron will record several petabytes of
data over the next five years in pursuing the goals of understanding nature and
searching for the origin of mass. Computing resources required to analyze these
data far exceed capabilities of any one institution. Moreover, the widely
scattered geographical distribution of D0 collaborators poses further serious
difficulties for optimal use of human and computing resources. These
difficulties will exacerbate in future high energy physics experiments, like
the LHC. The computing grid has long been recognized as a solution to these
problems. This technology is being made a more immediate reality to end users
in D0 by developing a grid in the D0 Southern Analysis Region (D0SAR),
D0SAR-Grid, using all available resources within it and a home-grown local task
manager, McFarm. We will present the architecture in which the D0SAR-Grid is
implemented, the use of technology and the functionality of the grid, and the
experience from operating the grid in simulation, reprocessing and data
analyses for a currently running HEP experiment.Comment: 3 pages, no figures, conference proceedings of DPF04 tal
Dynamics of laser-driven proton acceleration exhibited by measured laser absorptivity and reflectivity
Proton acceleration from nanometer thin foils with intense laser pulses is investigated experimentally. We analyzed the laser absorptivity by parallel monitoring of laser transmissivity and reflectivity with different laser intensities when moving the targets along the laser axis. A direct correlation between laser absorptivity and maximum proton energy is observed. Experimental results are interpreted in analytical estimation, exhibiting a coexistence of plasma expansion and light-sail form of radiation pressure acceleration (RPA-LS) mechanisms during the entire proton acceleration process based on the measured laser absorptivity and reflectivity
The Optimal Gravitational Lens Telescope
Given an observed gravitational lens mirage produced by a foreground
deflector (cf. galaxy, quasar, cluster,...), it is possible via numerical lens
inversion to retrieve the real source image, taking full advantage of the
magnifying power of the cosmic lens. This has been achieved in the past for
several remarkable gravitational lens systems. Instead, we propose here to
invert an observed multiply imaged source directly at the telescope using an
ad-hoc optical instrument which is described in the present paper. Compared to
the previous method, this should allow one to detect fainter source features as
well as to use such an optimal gravitational lens telescope to explore even
fainter objects located behind and near the lens. Laboratory and numerical
experiments illustrate this new approach
Time-variation of Jupiter's internal magnetic field consistent with zonal wind advection
Determination of the time dependency (secular variation) of a planet’s magnetic field provides a window into understanding the dynamo responsible for generating its field. However, of the six Solar System planets with active dynamos, secular variation has been firmly established only for Earth. Here, we compare magnetic field observations of Jupiter from the Pioneer 10 and 11, Voyager 1 and Ulysses spacecraft (acquired 1973–1992) with a new Juno reference model (JRM09). We find a consistent, systematic change in Jupiter’s field over this 45-year time span, which cannot be explained by changes in the magnetospheric field or by changing the assumed rotation rate of Jupiter. Through a simplified forward model, we find that the inferred change in the field is consistent with advection of the field by Jupiter’s zonal winds, projected down to 93–95% of Jupiter’s radius (where the electrical conductivity of the hydrogen envelope becomes sufficient to advect the field). This result demonstrates that zonal wind interactions with Jupiter’s magnetic field are important and lends independent support to atmospheric and gravitational-field determinations of the profile of Jupiter’s deep winds
Red Parkes-Quasars: Evidence for Soft X-ray Absorption
The Parkes Half-Jansky Flat Spectrum Sample contains a large number of
sources with unusually red optical-to-near-infrared continua. If this is to be
interpreted as extinction by dust in the line-of-sight, then associated
material might also give rise to absorption in the soft X-ray regime. This
hypothesis is tested using broadband (0.1-2.4 keV) data from the {\it ROSAT}
All-Sky Survey provided by Siebert et al. (1998). Significant (
confidence level) correlations between optical (and near-infrared)--to--soft
X-ray continuum slope and optical extinction are found in the data, consistent
with absorption by material with metallicity and a range in gas-to-dust ratio
as observed in the local ISM. Under this simple model, the soft X-rays are
absorbed at a level consistent with the range of extinctions (
magnitudes) implied by the observed optical reddening. Excess X-ray absorption
by warm (ionised) gas, (ie. a `warm absorber') is not required.Comment: 23 pages of text, 3 figures, to appear in Jan 10 (1999) issue of The
Astrophysical Journa
Classification and nondegeneracy of Toda system with singular sources
We consider the following Toda system \Delta u_i + \D \sum_{j = 1}^n
a_{ij}e^{u_j} = 4\pi\gamma_{i}\delta_{0} \text{in}\mathbb R^2, \int_{\mathbb
R^2}e^{u_i} dx -1\delta_0a_{ij}\gamma_i=0\forall \;1\leq i\leq n\gamma_i+\gamma_{i+1}+...+\gamma_j \notin \mathbb Z1\leq i\leq
j\leq nu_i$ is \textit{radially symmetric} w.r.t. 0.
(iii) We prove that the linearized equation at any solution is
\textit{non-degenerate}. These are fundamental results in order to understand
the bubbling behavior of the Toda system.Comment: 28 page
Science Goals and Overview of the Radiation Belt Storm Probes (RBSP) Energetic Particle, Composition, and Thermal Plasma (ECT) Suite on NASA’s Van Allen Probes Mission
The Radiation Belt Storm Probes (RBSP)-Energetic Particle, Composition, and Thermal Plasma (ECT) suite contains an innovative complement of particle instruments to ensure the highest quality measurements ever made in the inner magnetosphere and radiation belts. The coordinated RBSP-ECT particle measurements, analyzed in combination with fields and waves observations and state-of-the-art theory and modeling, are necessary for understanding the acceleration, global distribution, and variability of radiation belt electrons and ions, key science objectives of NASA’s Living With a Star program and the Van Allen Probes mission. The RBSP-ECT suite consists of three highly-coordinated instruments: the Magnetic Electron Ion Spectrometer (MagEIS), the Helium Oxygen Proton Electron (HOPE) sensor, and the Relativistic Electron Proton Telescope (REPT). Collectively they cover, continuously, the full electron and ion spectra from one eV to 10’s of MeV with sufficient energy resolution, pitch angle coverage and resolution, and with composition measurements in the critical energy range up to 50 keV and also from a few to 50 MeV/nucleon. All three instruments are based on measurement techniques proven in the radiation belts. The instruments use those proven techniques along with innovative new designs, optimized for operation in the most extreme conditions in order to provide unambiguous separation of ions and electrons and clean energy responses even in the presence of extreme penetrating background environments. The design, fabrication and operation of ECT spaceflight instrumentation in the harsh radiation belt environment ensure that particle measurements have the fidelity needed for closure in answering key mission science questions. ECT instrument details are provided in companion papers in this same issue. In this paper, we describe the science objectives of the RBSP-ECT instrument suite on the Van Allen Probe spacecraft within the context of the overall mission objectives, indicate how the characteristics of the instruments satisfy the requirements to achieve these objectives, provide information about science data collection and dissemination, and conclude with a description of some early mission results
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