Diffusion and convection of gaseous and fine particulate from a chimney

Particle dispersion from a high chimney is considered and an expression for the subsequent concentration of the particulate deposited on the ground is derived. We consider the general case wherein the effects of both diffusion and convection on the steady state ground concentration of particulate are incorporated. Two key parameters emerge from this analysis: the ratio of diffusion to convection and the nondimensionalised surface mass transfer rate. We also solve the inverse problem of recovering these two parameters given the boundary concentration profile and provide an estimate of the concentration flux above the chimney stack

Simple approach to include external resistances in the Monte Carlo simulation of MESFETs and HEMTs

The contact and external series resistances play an important role in the performance of modern 0.1-0.2 μm HEMT's. It is not possible to include these resistances directly into the Monte Carlo simulations. Here we describe a simple and efficient way to include the external series resistances into the Monte Carlo results of the intrinsic device simulations. Examples of simulation results are given for a 0.2 μm pseudomorphic HEMT

Data user's note: Apollo 15 lunar photography

Brief descriptions are given of the Apollo 15 mission objectives, photographic equipment, and photographic coverage and quality. The lunar photographic tasks were: (1) ultraviolet photography of the earth and moon; (2) photography of the gegenschein from lunar orbit; (3) service module orbital photographic tasks; and (4) command module photographic tasks

Cognitive control and discourse comprehension in schizophrenia.

Cognitive deficits across a wide range of domains have been consistently observed in schizophrenia and are linked to poor functional outcome (Green, 1996; Carter, 2006). Language abnormalities are among the most salient and include disorganized speech as well as deficits in comprehension. In this review, we aim to evaluate impairments of language processing in schizophrenia in relation to a domain-general control deficit. We first provide an overview of language comprehension in the healthy human brain, stressing the role of cognitive control processes, especially during discourse comprehension. We then discuss cognitive control deficits in schizophrenia, before turning to evidence suggesting that schizophrenia patients are particularly impaired at processing meaningful discourse as a result of deficits in control functions. We conclude that domain-general control mechanisms are impaired in schizophrenia and that during language comprehension this is most likely to result in difficulties during the processing of discourse-level context, which involves integrating and maintaining multiple levels of meaning. Finally, we predict that language comprehension in schizophrenia patients will be most impaired during discourse processing. We further suggest that discourse comprehension problems in schizophrenia might be mitigated when conflicting information is absent and strong relations amongst individual words are present in the discourse context."There is no "centre of Speech" in the brain any more than there is a faculty of Speech in the mind.The entire brain, more or less, is at work in a man who uses language"William JamesFrom The Principles of Psychology, 1890"The mind in dementia praecox is like an orchestra without a conductor"Kraepelin, 1919

Detecting a rotation in the epsilon Eridani debris disc

The evidence for a rotation of the epsilon Eridani debris disc is examined. Data at 850 micron wavelength were previously obtained using the Submillimetre Common User Bolometer Array (SCUBA) over periods in 1997-1998 and 2000-2002. By chi-square fitting after shift and rotation operations, images from these two epochs were compared to recover proper motion and orbital motion of the disc. The same procedures were then performed on simulated images to estimate the accuracy of the results. Minima in the chi-square plots indicate a motion of the disc of approximately 0.6'' per year in the direction of the star's proper motion. This underestimates the true value of 1'' per year, implying that some of the structure in the disc region is not associated with epsilon Eridani, originating instead from background galaxies. From the chi-square fitting for orbital motion, a counterclockwise rotation rate of ~2.75 degrees per year is deduced. Comparisons with simulated data in which the disc is not rotating show that noise and background galaxies result in approximately Gaussian fluctuations with a standard deviation +/-1.5 degrees per year. Thus counterclockwise rotation of disc features is supported at approximately a 2-sigma level, after a 4-year time difference. This rate is faster than the Keplerian rate of 0.65 degrees per year for features at ~65 AU from the star, suggesting their motion is tracking a planet inside the dust ring. Future observations with SCUBA-2 can rule out no rotation of the epsilon Eridani dust clumps with ~4-sigma confidence. Assuming a rate of about 2.75 degrees per year, the rotation of the features after a 10-year period could be shown to be >1 degree per year at the 3-sigma level.Comment: 8 pages, 6 figure

Magnetic activity on AB Doradus: Temporal evolution of starspots and differential rotation from 1988 to 1994

Surface brightness maps for the young K0 dwarf AB Doradus are reconstructed from archival data sets for epochs spanning 1988 to 1994. By using the signal-to-noise enhancement technique of Least-Squares Deconvolution, our results show a greatly increased resolution of spot features than obtained in previously published surface brightness reconstructions. These images show that for the exception of epoch 1988.96, the starspot distributions are dominated by a long-lived polar cap, and short-lived low to high latitude features. The fragmented polar cap at epoch 1988.96 could indicate a change in the nature of the dynamo in the star. For the first time we measure differential rotation for epochs with sufficient phase coverage (1992.05, 1993.89, 1994.87). These measurements show variations on a timescale of at least one year, with the strongest surface differential rotation ever measured for AB Dor occurring in 1994.86. In conjunction with previous investigations, our results represent the first long-term analysis of the temporal evolution of differential rotation on active stars.Comment: accepted by MNRAS 18 pages 18 figure

Migration of Ca II H bright points in the internetwork

The migration of magnetic bright point-like features (MBP) in the lower solar atmosphere reflects the dispersal of magnetic flux as well as the horizontal flows of the atmospheric layer they are embedded in. We analyse trajectories of the proper motion of intrinsically magnetic, isolated internetwork Ca II H MBPs (mean lifetime 461 +- 9 s) to obtain their diffusivity behaviour. We use seeing-free high spatial and temporal resolution image sequences of quiet-Sun, disc-centre observations obtained in the Ca II H 3968 {\AA} passband of the Sunrise Filter Imager (SuFI) onboard the Sunrise balloon-borne solar observatory. Small MBPs in the internetwork are automatically tracked. The trajectory of each MBP is then calculated and described by a diffusion index ({\gamma}) and a diffusion coefficient (D). We further explore the distribution of the diffusion indices with the help of a Monte Carlo simulation. We find {\gamma} = 1.69 +- 0.08 and D = 257 +- 32 km^2/s averaged over all MBPs. Trajectories of most MBPs are classified as super-diffusive, i.e., {\gamma} > 1, with the determined {\gamma} being to our knowledge the largest obtained so far. A direct correlation between D and time-scale ({\tau}) determined from trajectories of all MBPs is also obtained. We discuss a simple scenario to explain the diffusivity of the observed, relatively short-lived MBPs while they migrate within a small area in a supergranule (i.e., an internetwork area). We show that the scatter in the {\gamma} values obtained for individual MBPs is due to their limited lifetimes. The super-diffusive MBPs can be well-described as random walkers (due to granular evolution and intergranular turbu- lence) superposed on a large systematic (background) velocity, caused by granular, mesogranular and supergranular flows.Comment: 10 pages, 7 figures, 3 table

UV Spectroscopy of AB Doradus with the Hubble Space Telescope. Impulsive flares and bimodal profiles of the CIV 1549 line in a young star

We observed AB Doradus, a young and active late type star (K0 - K2 IV-V, P= 0.514 d) with the Goddard High Resolution Spectrograph of the post-COSTAR Hubble Space Telescope with the time and spectral resolutions of 27 s and 15 km, respectively. The wavelength band (1531 - 1565 A) included the strong CIV doublet (1548.202 and 1550.774, formed in the transition region at 100 000 K). The mean quiescent CIV flux state was close to the saturated value and 100 times the solar one. The line profile (after removing the rotational and instrumental profiles) is bimodal consisting of two Gaussians, narrow (FWHM = 70 km/s) and broad (FWHM =330km/s). This bimodality is probably due to two separate broadening mechanisms and velocity fields at the coronal base. It is possible that TR transient events (random multiple velocities), with a large surface coverage, give rise to the broadening of the narrow component,while true microflaring is responsible for the broad one. The transition region was observed to flare frequently on different time scales and magnitudes. The largest impulsive flare seen in the CIV 1549 emission reached in less than one minute the peak differential emission measure (10**51.2 cm-3) and returned exponentially in 5 minutes to the 7 times lower quiescent level.The 3 min average line profile of the flare was blue-shifted (-190 km/s) and broadened (FWHM = 800 km/s). This impulsive flare could have been due to a chromospheric heating and subsequent evaporation by an electron beam, accelerated (by reconnection) at the apex of a coronal loop.Comment: to be published in AJ (April 98), 3 tables and 7 figures as separate PS-files, print Table 2 as a landscap

Estimating the masses of extra-solar planets

All extra-solar planet masses that have been derived spectroscopically are lower limits since the inclination of the orbit to our line-of-sight is unknown except for transiting systems. It is, however, possible to determine the inclination angle, i, between the rotation axis of a star and an observer's line-of-sight from measurements of the projected equatorial velocity (v sin i), the stellar rotation period (P_rot) and the stellar radius (R_star). This allows the removal of the sin i dependency of spectroscopically derived extra-solar planet masses under the assumption that the planetary orbits lie perpendicular to the stellar rotation axis. We have carried out an extensive literature search and present a catalogue of v sin i, P_rot, and R_star estimates for exoplanet host stars. In addition, we have used Hipparcos parallaxes and the Barnes-Evans relationship to further supplement the R_star estimates obtained from the literature. Using this catalogue, we have obtained sin i estimates using a Markov-chain Monte Carlo analysis. This allows proper 1-sigma two-tailed confidence limits to be placed on the derived sin i's along with the transit probability for each planet to be determined. While a small proportion of systems yield sin i's significantly greater than 1, most likely due to poor P_rot estimations, the large majority are acceptable. We are further encouraged by the cases where we have data on transiting systems, as the technique indicates inclinations of ~90 degrees and high transit probabilities. In total, we estimate the true masses of 133 extra-solar planets. Of these, only 6 have revised masses that place them above the 13 Jupiter mass deuterium burning limit. Our work reveals a population of high-mass planets with low eccentricities and we speculate that these may represent the signature of different planetary formation mechanisms at work.Comment: 40 pages, 6 tables, 2 figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Society after editing of Tables 1 & 6 for electronic publication. Html abstract shortened for astro-ph submissio