Cornelis Zwaan, 1928-1999

Cornelis (\Kees") Zwaan was a well-known solar physicist at Utrecht University in The Netherlands. To- gether with his graduate students he also ventured out to other cool stars, concentrating on their magnetic activity. He has been a member of the AAS and the Solar Physics Division and had close ties with many American astro- physicists. He died from cancer in his house at Doorn, The Netherlands on June 16, 1999. He had had major surgery in 1998, but recovered so fast that we and his other friends expected to have him with us much longer. The end came far too soon

A spiral structure in the disk of EX Draconis on the rise to outburst maximum

We report on the R-band eclipse mapping analysis of high-speed photometry of the dwarf nova EX Dra on the rise to the maximum of the November 1995 outburst. The eclipse map shows a one-armed spiral structure of ~180 degrees in azimuth, extending in radius from R ~0.2 to 0.43 R_{L1} (where R_{L1} is the distance from the disk center to the inner Lagrangian point), that contributes about 22 per cent of the total flux of the eclipse map. The spiral structure is stationary in a reference frame co-rotating with the binary and is stable for a timescale of at least 5 binary orbits. The comparison of the eclipse maps on the rise and in quiescence suggests that the outbursts of EX Dra may be driven by episodes of enhanced mass-transfer from the secondary star. Possible explanations for the nature of the spiral structure are discussed.Comment: To appear in the Astrophysical Journal Letters; 8 pages, 2 figures; coded with AAS latex styl

The Quiet-Sun Photosphere and Chromosphere

The overall structure and the fine structure of the solar photosphere outside active regions are largely understood, except possibly important roles of a turbulent near-surface dynamo at its bottom, internal gravity waves at its top, and small-scale vorticity. Classical 1D static radiation-escape modelling has been replaced by 3D time-dependent MHD simulations that come closer to reality. The solar chromosphere, in contrast, remains ill-understood although its pivotal role in coronal mass and energy loading makes it a principal research area. Its fine structure defines its overall structure, so that hard-to-observe and hard-to-model small-scale dynamical processes are the key to understanding. However, both chromospheric observation and chromospheric simulation presently mature towards the required sophistication. The open-field features seem of greater interest than the easier-to-see closed-field features.Comment: Accepted for special issue "Astrophysical Processes on the Sun" of Phil. Trans. Royal Soc. A, ed. C. Parnell. Note: clicking on the year in a citation opens the corresponding ADS abstract page in the browse

HST/FOS Time-resolved spectral mapping of IP Pegasi at the end of an outburst

We report an eclipse mapping analysis of time-resolved ultraviolet spectroscopy covering three eclipses of the dwarf nova IP Pegasi on the late decline of the 1993 May outburst. The eclipse maps of the first run show evidence of one spiral arm, suggesting that spiral structures may still be present in the accretion disc 9 days after the onset of the outburst. In the spatially resolved spectra the most prominent lines appear in emission at any radius, being stronger in the inner disc regions. The spectrum of the gas stream is clearly distinct from the disc spectrum in the intermediate and outer disc regions, suggesting the occurrence of gas stream overflow. The full width half maximum of C IV is approximately constant with radius, in contrast to the expected $v\propto{R^{-1/2}}$ law for a gas in Keplerian orbits. This line probably originates in a vertically extended region (chromosphere + disc wind). The uneclipsed component contributes $\sim{4}$ % of the flux in C IV in the first run, and becomes negligible in the remaining runs. We fit stellar atmosphere models to the spatially resolved spectra. The radial run of the disc color temperature for the three runs is flatter than the expected $T\propto{R^{-3/4}}$ law for steady-state optically thick discs models, with $T\simeq{20000}$ K in the inner regions and $T\simeq{9000}$ K in the outer disc regions. The solid angles that result from the fits are smaller than expected from the parameters of the system. The radial run of the solid angle suggests that the disc is flared in outburst, and decreases in thickness toward the end of the outburst.Comment: 14 pages, 14 figures, in press in Astronomy & Astrophysic

HST/FOS Eclipse Observations of the Nova-like Cataclysmic Variable UX Ursae Majoris

[abridged abstract] We present and analyze Hubble Space Telescope observations of the eclipsing nova-like cataclysmic variable UX UMa obtained with the Faint Object Spectrograph. Two eclipses each were observed with the G160L grating (covering the ultraviolet waveband) in August of 1994 and with the PRISM (covering the near-ultraviolet to near-infrared) in November of the same year. The system was 50% brighter in November than in August, which, if due to a change in the accretion rate, indicates a fairly substantial increase in Mdot_acc by >~ 50%. Model disk spectra constructed as ensembles of stellar atmospheres provide poor descriptions of the observed post-eclipse spectra, despite the fact that UX UMa's light should be dominated by the disk at this time. Suitably scaled single temperature model stellar atmospheres with T_eff = 12,500-14,500 K actually provide a better match to both the ultraviolet and optical post-eclipse spectra. Evidently, great care must be taken in attempts to derive accretion rates from comparisons of disk models to observations. One way to reconcile disk models with the observed post-eclipse spectra is to postulate the presence of a significant amount of optically thin material in the system. Such an optically thin component might be associated with the transition region (``chromosphere'') between the disk photosphere and the fast wind from the system, whose presence has been suggested by Knigge & Drew (1997).Comment: 35 pages, including 12 figures; to appear in the ApJ (Vol. 499

The PDE4 inhibitor rolipram reverses object memory impairment induced by acute tryptophan depletion in the rat

The selective type IV phosphodiesterase inhibitor, rolipram, has been shown to improve long-term memory and can reverse the cholinergic deficit caused by scopolamine. However, the underlying mechanisms of action of rolipram remain obscure. The present study investigates the effect of rolipram in a serotonergic-deficit model of acute tryptophan depletion (ATD). In addition, the levels of plasma tryptophan (TRP) were compared to object recognition performance. The experiments were conducted using male Wistar rats. The time-dependent effect of ATD treatment (a gelatin-based protein mixture) on plasma TRP levels (0, 1, 3, and 6 h after injection) and object recognition task (ORT) performance (0.5, 1, 3, and 6 h after ATD treatment) was examined. The effect of rolipram (0, 0.01, 0.03, and 0.1 mg/kg, i.p.) was tested in the condition in which ATD induced a clear memory deficit. ATD significantly lowered the plasma TRP ratio (TRP/Sigma large neutral amino acid) with a maximum of 48%, approximately 1 h after administration. Furthermore, ATD impairs ORT performance when administered 3 h before testing. Rolipram (0.1 mg/kg) reversed the memory deficit induced by ATD in a dose-dependent manner. On the basis of previous studies and the ability to reverse a serotonergic deficit, we suggest that rolipram may act through elevation of cyclic adenosine monophosphate levels and subsequent increase in neurotransmitter release

Cognitive functioning in meningioma patients:A systematic review

This systematic review evaluates relevant findings and methodologic aspects of studies on cognitive functioning in meningioma patients prior to and/or following surgery with or without adjuvant radiotherapy. PubMed and Web of Science electronic databases were searched until December 2015. From 1012 initially identified articles, 11 met the inclusion criteria for this review. Multiple methodological limitations were identified which include the lack of pre-treatment assessments, variations in the number and types of neuropsychological tests used, the normative data used to identify patients with cognitive deficits, and the variety of definitions for cognitive impairment. Study results suggest that most of meningioma patients are faced with cognitive deficits in several cognitive domains prior to surgery. Following surgery, most of these patients seem to improve in cognitive functioning. However, they still have impairments in a wide range of cognitive functions compared to healthy controls. Suggestions are given for future research. Adequate diagnosis and treatment of cognitive deficits may ultimately lead to improved outcome and quality of life in meningioma patients

Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim

Multicolor (BVRI) light curves of the eclipsing classical nova V Per are presented, and a total of twelve new eclipse timings are measured for the system. When combined with previous eclipse timings from the literature, these timings yield a revised ephemeris for the times of mid-eclipse given by HJD = 2,447,442.8260(1) + 0.107123474(3) E. The eclipse profiles are analyzed with a parameter-fitting model that assumes four sources of luminosity: a white dwarf primary star, a main-sequence secondary star, a flared accretion disk with a rim, and a bright spot at the intersection of the mass-transfer stream and the disk periphery. A matrix of model solutions are computed, covering an extensive range of plausible parameter values. The solution matrix is then explored to determine the optimum values for the fitting parameters and their associated errors. For models that treat the accretion disk as a flat structure without a rim, optimum fits require that the disk have a flat temperature profile. Although models with a truncated inner disk (R_in >> R_wd) result in a steeper temperature profile, steady-state models with a temperature profile characterized by T(r) \propto r^{-3/4} are found only for models with a significant disk rim. A comparison of the observed brightness and color at mid-eclipse with the photometric properties of the best-fitting model suggests that V Per lies at a distance of ~ 1 kpc.Comment: Accepted for publication in The Astrophysical Journal. Thirty-nine pages, including 9 figures. V2 - updated to include additional references and related discussion to previous work overlooked in the original version, and to correct a typo in the ephemeris given in the abstract. V3 - Minor typos corrected. The paper is scheduled for the 20 June 2006 issue of the ApJ. V4 - An error in equation (9) has been corrected. The results presented in the paper were not affected, as all computations were made using the correct formulation of this equatio