Beam-based Feedback Simulations for the NLC Linac

Extensive beam-based feedback systems are planned as an integral part of the Next Linear Collider (NLC) control system. Wakefield effects are a significant influence on the feedback design, imposing both architectural and algorithmic constraints. Studies are in progress to assure the optimal selection of devices and to refine and confirm the algorithms for the system design. We show the results of initial simulations, along with evaluations of system response for various conditions of ground motion and other operational disturbances.Comment: 3 pages. Linac2000 conferenc

Radiative acceleration and transient, radiation-induced electric fields

The radiative acceleration of particles and the electrostatic potential fields that arise in low density plasmas hit by radiation produced by a transient, compact source are investigated. We calculate the dynamical evolution and asymptotic energy of the charged particles accelerated by the photons and the radiation-induced electric double layer in the full relativistic, Klein-Nishina regime. For fluxes in excess of $10^{27}$ ${\rm erg} {\rm cm}^{-2} {\rm s}^{-1}$, the radiative force on a diluted plasma (n\la 10^{11} cm$^{-3}$) is so strong that electrons are accelerated rapidly to relativistic speeds while ions lag behind owing to their larger inertia. The ions are later effectively accelerated by the strong radiation-induced double layer electric field up to Lorentz factors $\approx 100$, attainable in the case of negligible Compton drag. The asymptotic energies achieved by both ions and electrons are larger by a factor 2--4 with respect to what one could naively expect assuming that the electron-ion assembly is a rigidly coupled system. The regime we investigate may be relevant within the framework of giant flares from soft gamma-repeaters.Comment: 14 pages, 7 figures, ApJ, in press (tentatively scheduled for the v. 592, 2003 issue

Grazer control of the fine-scale distribution of phytoplankton in warm-core Gulf Stream rings

We measured in situ rates of primary production, zooplankton grazing and the fine-scale distribution of zooplankton abundance, along with continuous observations of salinity, temperature and fluorescence in vertical profiles of two warm-core Gulf Stream rings and a station in the northern Sargasso Sea. A subsurface chlorophyll maximum was located within the pycnocline at all nineteen of the pump stations. In the majority of pump profiles, subsurface chlorophyll maxima coincided with maxima in particulate organic carbon and ATP. However, neither zooplankton biomass or numerical abundance were related to chlorophyll concentrations. Maxima in zooplankton biomass and grazing generally occurred at depths of highest primary production. Zooplankton grazing and biomass were more closely coupled to phytoplankton production per unit chlorophyll (P-chl) rather than production per unit volume (absolute production). Our results suggest that after the seasonal thermocline is established, phytoplankton removal by zooplankton is greatest in the upper water column where P-chl is higher. This phytoplankton removal by zooplankton limits the amount of absolute primary production in the upper water column and results in a subsurface maximum of absolute production at depths where grazing pressure is reduced. In contrast, the subsurface chlorophyll maximum, likely formed from both production at depth and sinking, does not appear to be a site of enhanced zooplankton grazing activity

Preliminary evaluation of spectral, normal and meteorological crop stage estimation approaches

Several of the projects in the AgRISTARS program require crop phenology information, including classification, acreage and yield estimation, and detection of episodal events. This study evaluates several crop calendar estimation techniques for their potential use in the program. The techniques, although generic in approach, were developed and tested on spring wheat data collected in 1978. There are three basic approaches to crop stage estimation: historical averages for an area (normal crop calendars), agrometeorological modeling of known crop-weather relationships agrometeorological (agromet) crop calendars, and interpretation of spectral signatures (spectral crop calendars). In all, 10 combinations of planting and biostage estimation models were evaluated. Dates of stage occurrence are estimated with biases between -4 and +4 days while root mean square errors range from 10 to 15 days. Results are inconclusive as to the superiority of any of the models and further evaluation of the models with the 1979 data set is recommended

Living with early-stage dementia: a review of qualitative studies

A

On the Radio Occultation Method for Studying Planetary Atmospheres

The problem of determining the refractivity profile of a planetary atmosphere from optical or radio occultation data is identical in principle to the problem of determining the variation of seismic velocities in the earth from the observed travel times of seismic body waves. In either case, a complete set of data can be inverted uniquely, the only constraints being those fundamental to geometric optics. Expressions are given for converting observed Doppler shifts to the index of refraction as a function of depth in the atmosphere. The effect of various approximations on the analysis is discussed; it is found that a ‘thin atmosphere’ approximation simplifies the mathematics and preserves the singularity at the critical ray curvature

Phasing of gravitational waves from inspiralling eccentric binaries at the third-and-a-half post-Newtonian order

We obtain an efficient description for the dynamics of nonspinning compact binaries moving in inspiralling eccentric orbits to implement the phasing of gravitational waves from such binaries at the 3.5 post-Newtonian (PN) order. Our computation heavily depends on the phasing formalism, presented in [T. Damour, A. Gopakumar, and B. R. Iyer, Phys. Rev. D \textbf{70}, 064028 (2004)], and the 3PN accurate generalized quasi-Keplerian parametric solution to the conservative dynamics of nonspinning compact binaries moving in eccentric orbits, available in [R.-M. Memmesheimer, A. Gopakumar, and G. Sch\"afer, Phys. Rev. D \textbf{70}, 104011 (2004)]. The gravitational-wave (GW) polarizations $h_{+}$ and $h_{\times}$ with 3.5PN accurate phasing should be useful for the earth-based GW interferometers, current and advanced, if they plan to search for gravitational waves from inspiralling eccentric binaries. Our results will be required to do \emph{astrophysics} with the proposed space-based GW interferometers like LISA, BBO, and DECIGO.Comment: 22 pages including 2 figures; submitted to PR

Pair-induced spectral changes and variability in compact X-ray sources

Inverse Compton scattering of ultraviolet photons by GeV electrons produces γ-rays which in turn create electron–positron pairs if the source is sufficiently compact. The pairs modify the emergent radiation spectrum through their own inverse Compton scattering and through thermal Comptonization after they have cooled to sub-relativistic temperatures. Recent calculations of spectral reprocessing under these conditions are extended to situations in which the Thomson optical depth of the pair plasma exceeds unity, and to demonstrate time-dependent behaviour explicitly. The relevance of our results to X-ray observations of active galactic nuclei, binary X-ray sources and γ-ray bursters is discussed briefly

Prospects for gravitational-wave observations of neutron-star tidal disruption in neutron-star/black-hole binaries

For an inspiraling neutron-star/black-hole binary (NS/BH), we estimate the gravity-wave frequency f_td at the onset of NS tidal disruption. We model the NS as a tidally distorted, homogeneous, Newtonian ellipsoid on a circular, equatorial geodesic around a Kerr BH. We find that f_td depends strongly on the NS radius R, and estimate that LIGO-II (ca. 2006-2008) might measure R to 15% precision at 140 Mpc (about 1 event/yr under current estimates). This suggests that LIGO-II might extract valuable information about the NS equation of state from tidal-disruption waves.Comment: RevTeX, 4 pages, 2 EPS figures. Revised slightly, corrected typo