ASCA Discovery of an X-ray Pulsar in the Error Box of SGR1900+14

We present a 2 - 10 keV ASCA observation of the field around the soft gamma repeater SGR1900+14. One quiescent X-ray source was detected in this observation, and it was in the SGR error box. In 2 - 10 keV X-rays, its spectrum may be fit by a power law with index -2.2, and its unabsorbed flux is 9.6 x 10^-12 erg cm^-2 s^-1. We also find a clear 5.16 s period. The properties of the three well-studied soft gamma repeaters are remarkably similar to one another, and provide evidence that all of them are associated with young, strongly magnetized neutron stars in supernova remnants.Comment: Accepted for publication in the Astrophysical Journal Letter

Efficiency of the Incomplete Enumeration algorithm for Monte-Carlo simulation of linear and branched polymers

We study the efficiency of the incomplete enumeration algorithm for linear and branched polymers. There is a qualitative difference in the efficiency in these two cases. The average time to generate an independent sample of $n$ sites for large $n$ varies as $n^2$ for linear polymers, but as $exp(c n^{\alpha})$ for branched (undirected and directed) polymers, where $0<\alpha<1$. On the binary tree, our numerical studies for $n$ of order $10^4$ gives $\alpha = 0.333 \pm 0.005$. We argue that $\alpha=1/3$ exactly in this case.Comment: replaced with published versio

Energy Flow in the Cryptophyte PE545 Antenna Is Directed by Bilin Pigment Conformation

Structure-based calculations are combined with quantitative modeling of spectra and energy transfer dynamics to detemine the energy transfer scheme of the PE545 principal light-harvesting antenna of the cryptomonad Rhodomonas CS24. We use a recently developed quantum-mechanics/molecular mechanics (QM/MM) method that allows us to account for pigment-protein interactions at atomic detail in site energies, transition dipole moments, and electronic couplings. In addition, conformational flexibility of the pigment-protein complex is accounted for through molecular dynamics (MD) simulations. We find that conformational disorder largely smoothes the large energetic differences predicted from the crystal structure between the pseudosymmetric pairs PEB50/61C-PEB50/61D and PEB82C-PEB82D. Moreover, we find that, in contrast to chlorophyll-based photosynthetic complexes, pigment composition and conformation play a major role in defining the energy ladder in the PE545 complex, rather than specific pigment-protein interactions. This is explained by the remarkable conformational flexibility of the eight bilin pigments in PE545, characterized by a quasi-linear arrangement of four pyrrole units. The MD-QM/MM site energies allow us to reproduce the main features of the spectra, and minor adjustments of the energies of the three red-most pigments DBV19A, DBV19B, and PEB82D allow us to model the spectra of PE545 with a similar quality compared to our original model (model E from Novoderezhkin et al. Biophys. J.2010, 99, 344), which was extracted from the spectral and kinetic fit. Moreover, the fit of the transient absorption kinetics is even better in the new structure-based model. The largest difference between our previous and present results is that the MD-QM/MM calculations predict a much smaller gap between the PEB50/61C and PEB50/61D sites, in better accord with chemical intuition. We conclude that the current adjusted MD-QM/MM energies are more reliable in order to explore the spectral properties and energy transfer dynamics in the PE545 complex

HST Observations of SGR 0526-66: New Constraints on Accretion and Magnetar Models

Soft Gamma-ray Repeaters (SGRs) are among the most enigmatic sources known today. Exhibiting huge X- and Gamma-ray bursts and flares, as well as soft quiescent X-ray emission, their energy source remains a mystery. Just as mysterious are the Anomalous X-ray pulsars (AXPs), which share many of the same characteristics. Thanks to recent Chandra observations, SGR 0526-66, the first SGR, now appears to be a transition object bridging the two classes, and therefore observations of it have implications for both SGRs and AXPs. The two most popular current models for their persistent emission are accretion of a fossil disk or decay of an enormous (~10^15 G) magnetic field in a magnetar. We show how deep optical observations of SGR 0526-66, the only SGR with small enough optical extinction for meaningful observations, show no evidence of an optical counterpart. These observation place strong new constraints on both accretion disk and magnetar models, and suggest that the spectral energy distribution may peak in the hard-UV. Almost all accretion disks are excluded by the optical data, and a magnetar would require a ~10^15-10^16 G field.Comment: 23 pages, 5 figures. Accepted by Ap

Elizabeth Gaskell, 'North and South' : traducció i anàlisi

La idea principal d'aquest treball és traduir un capítol de l'obra North and South, d'Elizabeth Gaskell. Hem escollit un capítol (VII) que reflecteix l'estil narratiu de l'autora per tal d'analitzar-lo i contextualitzar l'obra dins d'un marc històric, cultural i social, que també ens serveix per entendre la vida de l'autora. Analitzem tant els problemes lingüístics del procés de traducció com les dificultats de documentació i de les diferències extralingüístiques (salt generacional, dialectologia, termes especialitzats, referents culturals, etc.). Finalment, completem el treball amb una proposta de traducció al català del capítol esmentat, sense oblidar-nos del comentari de traducció on s'hi troben exemples dels tipus de problemes que hem esmentat prèviamentLa finalidad de este trabajo es la traducción y el análisis de un capítulo (en concreto del capítulo VII) de la novela costumbrista de Elizabeth Gaskell North and SouthThe purpose of this project is the translation and the analysis of one chapter (chapter VII) from North and South, a costumbrist novel written by Elizabeth Gaskell, a Victorian write

Pathological elongation of the internal carotid artery: surgical treatment and immediate postoperative results

Scopul lucrării. În structura cauzelor dezvoltării insuficienței cerebrovasculare, elongarea patologică a arterei carotide interne ocupă locul 2, după afectarea aterosclerotică. Prevalența dolicoarteriopatiei la populația generală se estimează a fi de la 10 la 40 %, iar de la 16% până la 56 % din pacienți au în anamnestic deficit neurologic tranzitor sau permanent. Scopul lucrării este optimizarea tehnicilor chirurgicale și aprecierea eficienței postoperatorii imediate la pacienții cu elongare patologică a arterei carotide interne. Materiale și metode. Studiul efectuat reprezintă o analiză retrospectivă a 243 pacienți, tratați în cadrul IMSP SCR ,,Timofei Moșneaga”, secția de Chirurgie Vasculară în perioada 2002-2022. Rezultate. La pacienții supuși studiului s-a efectuat 258 intervenții chirurgicale. Rezultatele imediate au fost: la 230 pacienți (89.14 %) a dispărut simptomatologia preoperatorie, AVC ischemic s-a înregistrat la 1 pacient, sindrom coronarian acut sau deces nu s-a înregistrat la nici un pacient din lotul studiat. Concluzii. Luând în considerare rata mică de complicații periprocedurale precum și eficacitatea postoperatorie imediată evidentă, putem spune că intervenția chirurgicală în tratamentul elongărilor patologice ale arterelor carotide interne reprezintă o metoda sigură și eficientă pentru prevenirea accidentelor vasculare cerebrale acute și îmbunătățirea calității vieții pacienților.Aim of study. Among the causes contributing to the development of cerebrovascular insufficiency, pathological elongation of the internal carotid artery ranks second after atherosclerotic involvement. The prevalence of dolichoarteriopathy in the general population is estimated to range from 10% to 40%, and between 16% and 56% of patients have a history of transient or permanent neurological deficits. The aim of this study was to optimize surgical techniques and assess immediate postoperative efficacy in patients with pathological elongation of the internal carotid artery. Materials and methods. This study represents a retrospective analysis of 243 patients treated at the State Medical and Pharmaceutical University "Timofei Moșneaga", Department of Vascular Surgery, between 2002 and 2022. Results. A total of 258 surgical interventions were performed in the study group. The immediate results were as follows: symptomatology disappeared in 230 patients (89.14%), one patient experienced an ischemic stroke, and no cases of acute coronary syndrome or death were recorded among the studied patients. Conclusions. Considering the low rate of periprocedural complications and the evident immediate postoperative effectiveness, it can be concluded that surgical intervention for the treatment of pathological elongation of the internal carotid artery is a safe and efficient method for preventing acute cerebrovascular accidents and improving the quality of life for patients

Two-Dimensional Polymers with Random Short-Range Interactions

We use complete enumeration and Monte Carlo techniques to study two-dimensional self-avoiding polymer chains with quenched ``charges'' $\pm 1$. The interaction of charges at neighboring lattice sites is described by $q_i q_j$. We find that a polymer undergoes a collapse transition at a temperature $T_{\theta}$, which decreases with increasing imbalance between charges. At the transition point, the dependence of the radius of gyration of the polymer on the number of monomers is characterized by an exponent $\nu_{\theta} = 0.60 \pm 0.02$, which is slightly larger than the similar exponent for homopolymers. We find no evidence of freezing at low temperatures.Comment: 4 two-column pages, 6 eps figures, RevTex, Submitted to Phys. Rev.

Lattice Resistance to Dislocation Motion at the Nanoscale

In this letter we propose a model that demonstrates the effect of free surface on the lattice resistance experienced by a moving dislocation in nanodimensional systems. This effect manifests in an enhanced velocity of dislocation due to the proximity of the dislocation line to the surface. To verify this finding, molecular dynamics simulations for an edge dislocation in bcc molybdenum are performed and the results are found to be in agreement with the numerical implementations of this model. The reduction in this effect at higher stresses and temperatures, as revealed by the simulations, confirms the role of lattice resistance behind the observed change in the dislocation velocity.Comment: 4 Figure

Strange Star Heating Events as a Model for Giant Flares of Soft Gamma-ray Repeaters

Two giant flares were observed on 5 March 1979 and 27 August 1998 from the soft gamma-ray repeaters SGR 0526-66 and SGR 1900+14, respectively. The striking similarity between these remarkable bursts strongly implies a common nature. We show that the light curves of the giant bursts may be easily explained in the model where the burst radiation is produced by the bare quark surface of a strange star heated, for example, by impact of a massive comet-like object.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Letter

Probing reflection from aerosols with the near-infrared dayside spectrum of WASP-80b

The presence of aerosols is intimately linked to the global energy budget and the composition of a planet's atmospheres. Their ability to reflect incoming light prevents energy from being deposited into the atmosphere, and they shape spectra of exoplanets. We observed five near-infrared secondary eclipses of WASP-80b with the Wide Field Camera 3 (WFC3) aboard the \textit{Hubble Space Telescope} to provide constraints on the presence and properties of atmospheric aerosols. We detect a broadband eclipse depth of $34\pm10$\,ppm for WASP-80b. We detect a higher planetary flux than expected from thermal emission alone at $1.6\sigma$, which hints toward the presence of reflecting aerosols on this planet's dayside, indicating a geometric albedo of $A_g<0.33$ at 3$\sigma$. We paired the WFC3 data with Spitzer data and explored multiple atmospheric models with and without aerosols to interpret this spectrum. Albeit consistent with a clear dayside atmosphere, we found a slight preference for near-solar metallicities and for dayside clouds over hazes. We exclude soot haze formation rates higher than $10^{-10.7}$ g cm$^{-2}$s$^{-1}$ and tholin formation rates higher than $10^{-12.0}$ g cm$^{-2}$s$^{-1}$ at $3\sigma$. We applied the same atmospheric models to a previously published WFC3/Spitzer transmission spectrum for this planet and found weak haze formation. A single soot haze formation rate best fits both the dayside and the transmission spectra simultaneously. However, we emphasize that no models provide satisfactory fits in terms of the chi-square of both spectra simultaneously, indicating longitudinal dissimilarity in the atmosphere's aerosol composition.Comment: Published in ApJ Letters (20 Oct 2023