Modelling spatial recall, mental imagery and neglect

We present a computational model of the neural mechanisms in the pari-etal and temporal lobes that support spatial navigation, recall of scenes and imagery of the products of recall. Long term representations are stored in the hippocampus, and are associated with local spatial and object-related features in the parahippocampal region. Viewer-centered representations are dynamically generated from long term memory in the parietal part of the model. The model thereby simulates recall and im-agery of locations and objects in complex environments. After parietal damage, the model exhibits hemispatial neglect in mental imagery that rotates with the imagined perspective of the observer, as in the famous Milan Square experiment [1]. Our model makes novel predictions for the neural representations in the parahippocampal and parietal regions and for behavior in healthy volunteers and neuropsychological patients.

Effects of Early-Adolescent, Mid-Adolescent, or Adult Stress on Morphine Conditioned Place Preference

Early-life stress is correlated with negative mental health outcomes, including illicit drug abuse. One mechanism that may contribute to drug abuse is stress-induced elevation of drug reward. Place conditioning paradigms show that exposure to uncontrollable stress as an adult enhances opiate conditioned place preference, CPP. The present work addressed whether early-adolescent, mid-adolescent, or adult stress amplified morphine CPP. Male Sprague-Dawley rats were randomly assigned to stress or no stress conditions and received stress during early-, mid-adolescence, or adulthood. Stressors were unpredictable consisting of exposure to synthetic fox odor (trimethylthiazoline) and an elevated platform. Morphine place conditioning occurred during adulthood, and all animals received either morphine (15 mg/kg) on the initially non-preferred side or saline (1 ml/kg) on the initially preferred side. A post-test was conducted and time on non-preferred side was analyzed. A 2 (S/NS) x 2 (pre-/post-test) x 3 (early-adolescent/mid-adolescent/adult) mixed ANOVA revealed a significant main effect of test, F(1,42)=115.90, p \u3c .001

X-Rays from the Nearby Solitary Millisecond Pulsar PSR J0030+0451 - the Final ROSAT Observations

We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451. The pulsar was one of the last targets observed in DEC-98 by the ROSAT PSPC. X-ray pulses are detected on a $4.5\sigma$ level and make the source the $11^{th}$ millisecond pulsar detected in the X-ray domain. The pulsed fraction is found to be $69\pm18$. The X-ray pulse profile is characterized by two narrow peaks which match the gross pulse profile observed at 1.4 GHz. Assuming a Crab-like spectrum the X-ray flux is in the range $f_x= 2-3\times 10^{-13}$ erg s$^{-1}$ cm$^{-2}$ ($0.1-2.4$ keV), implying an X-ray efficiency of $L_x/\dot{E}\sim 0.5-5 \times 10^{-3} (d/0.23 {kpc})^2$.Comment: Accepted for publication in Ap

The Struve-Sahade effect in the optical spectra of O-type binaries I. Main-sequence systems

We present a spectroscopic analysis of four massive binary systems that are known or are good candidates to display the Struve-Sahade effect (defined as the apparent strengthening of the secondary spectrum of the binary when the star is approaching, and the corresponding weakening of the lines when it is receding). We use high resolution optical spectra to determine new orbital solutions and spectral types of HD 165052, HD 100213, HD 159176 and DH Cep. As good knowledge of the fundamental parameters of the considered systems is necessary to examine the Struve-Sahade effect. We then study equivalent width variations in the lines of both components of these binaries during their orbital cycle. In the case of these four systems, variations appear in the equivalent widths of some lines during the orbital cycle, but the definition given above can any longer be valid, since it is now clear that the effect modifies the primary spectrum as much as the secondary spectrum. Furthermore, the lines affected, and the way in which they are affected, depend on the considered system. For at least two of them (HD 100213 and HD 159176) these variations probably reflect the ellipsoidal variable nature of the system.Comment: 12 pages, 20 figures, in press A&

The cosmic dust analyzer: Experimental evaluation of an impact ionization model

A thermal equilibrium plasma model is used to process data from an impact ionization time-of-flight mass spectrometer in order to convert the raw ion data to relative abundances of the elemental constituents of cosmic dust particles

A 2 component X-ray spectrum from SMC X-1

Both HEAO-1 A2 and Einstein SSS observations of SMC X-1 are presented. An unpulsed soft component is found with a blackbody temperature of 0.16 keV and an area for the emission region of 10 to the 15th power sq cm to 10 to the 17th power sq cm. The hard X-ray component is pulsed; the phase averaged spectrum is a power law with alpha approximately 0.5 keV up to 17 keV above which it steepens. The SSS sets an upper limit of 4 x 10 to the 21st power H cm/2 to any absorption and is consistent with that expected from the wind of SK160. Absorption dips with a timescale of several hundred seconds are seen immediately following an eclipse exit and are probably caused by inhomogeneities in the wind of SK160

Spectroscopic study of the O-type runaway supergiant HD 195592

The scope of this paper is to perform a detailed spectroscopic study of the northern O-type supergiant HD 195592. We use a large sample of high quality spectra in order to investigate its multiplicity, and to probe the line profile variability. Our analysis reveals a clear spectroscopic binary signature in the profile of the He {\sc i} $\lambda$ 6678 line, pointing to a probable O + B system. We report on low amplitude radial velocity variations in every strong absorption line in the blue spectrum of HD 195592. These variations are ruled by two time-scales respectively of 5.063 and about 20 days. The former is firmly established, whilst the latter is poorly constrained. We report also on a very significant line profile variability of the H $\beta$ line, with time scales strongly related to those of the radial velocities. Our results provide significant evidence that HD 195592 is a binary system, with a period that might be the variability time-scale of about 5 days. The second time scale may be the signature of an additional star moving along a wider orbit provided its mass is low enough, even though direct evidence for the presence of a third star is still lacking. Alternatively, the second time-scale may be the signature of a variability intrinsic to the stellar wind of the primary, potentially related to the stellar rotation.Comment: 9 pages, 5 postscript figures, accepted for publication in New Astronom

α\alpha-Particle Spectrum in the Reaction p+11^{11}B→α+8Be∗→3α\to \alpha + ^8Be^*\to 3\alpha

Using a simple phenomenological parametrization of the reaction amplitude we calculated $\alpha$-particle spectrum in the reaction p+$^{11}$B$\to \alpha + ^8Be^*\to 3\alpha$ at the resonance proton energy 675 KeV. The parametrization includes Breit-Wigner factor with an energy dependent width for intermediate $^8Be^*$ state and the Coulomb and the centrifugal factors in $\alpha$-particle emission vertexes. The shape of the spectrum consists of a well defined peak corresponding to emission of the primary $\alpha$ and a flat shoulder going down to very low energy. We found that below 1.5 MeV there are 17.5% of $\alpha$'s and below 1 MeV there are 11% of them.Comment: 6 pages, 3 figure