Ultra-low Amplitude Variables in the LMC -- Classical Cepheids, Pop. II Cepheids, RV Tau Stars and Binary Variables

A search for variable stars with ultra-low amplitudes (ULA), in the millimag range, has been made in the combined MACHO and OGLE data bases in the broad vicinity of the Cepheid instability strip in the HR diagram. A total of 25 singly periodic and 4 multiply periodic ULA objects has been uncovered. Our analysis does not allow us to distinguish between pulsational and ellipsoidal (binary) variability, nor between LMC and foreground objects. However, the objects are strongly clustered and appear to be associated with the pulsational instability strips of LMC Pop. I and II variables. When combined with the ULA variables of Buchler et al (2005) a total of 20 objects fall close to the classical Cepheid instability strip. However, they appear to fall on parallel period-magnitude relations that are shifted to slightly higher magnitude which would confer them a different evolutionary status. Low amplitude RV Tauri and Pop. II Cepheids have been uncovered that do not appear in the MACHO or OGLE catalogs. Interestingly, a set of binaries seem to lie on a PM relation that is essentially parallel to that of the RV Tauri/Pop. II Cepheids.Comment: 13 pages, 13 (color) figures. Astrophysical Journal (accepted for publlication

Modulations in Multi-Periodic Blue Variables in the LMC

As shown by Mennickent, et al(2003), a subset of the blue variable stars in the Large Magellanic Cloud exhibit brightness variability of small amplitude in the period range 2.4 to 16 days as well as larger amplitude variability with periods of 140 to 600 days, with a remarkably tight relation between the long and the short periods. Our re-examination of these objects has led to the discovery of additional variability. The Fourier spectra of 11 of their 30 objects have 3 or 4 peaks above the noise level and a linear relation of the form f_a = 2(f_b - f_L) among three of the frequencies. An explanation of this relation requires an interplay between the binary motion and that of a third object. The two frequency relations together with the Fourier amplitude ratios pose a challenging modeling problem.Comment: 4 pages, 3 figures, Astrophysical Journal (in press

Ultra-Low Amplitude Cepheids in the Large Magellanic Cloud

The MACHO variables of LMC Field 77 that lie in the vicinity of the Cepheid instability strip are reexamined. Among the 144 variables that we identify as Cepheids we find 14 that have Fourier amplitudes <0.05 mag in the MACHO red band, of which 7 have an amplitude <0.006 mag : we dub the latter group of stars ultra-low amplitude (ULA) Cepheids. The variability of these objects is verified by a comparison of the MACHO red with the MACHO blue lightcurves and with those of the corresponding OGLE LMC stars. The occurrence of ULA Cepheids is in agreement with theory. We have also discovered 2 low amplitude variables whose periods are about a factor of 5--6 smaller than those of F Cepheids of equal apparent magnitude. We suggest that these objects are Cepheids undergoing pulsations in a surface mode and that they belong to a novel class of Strange Cepheids (or Surface Mode Cepheids) whose existence was predicted by Buchler et al. (1997).Comment: 4 pages, 5 figures, slightly revised, to appear in ApJ Letter

Feedback cooling of a single trapped ion

Based on a real-time measurement of the motion of a single ion in a Paul trap, we demonstrate its electro-mechanical cooling below the Doppler limit by homodyne feedback control (cold damping). The feedback cooling results are well described by a model based on a quantum mechanical Master Equation.Comment: 4 pages, 3 figure

همانژیواندوتلیومای اپیتلیویید کبدی بدخیم اولیه، یک مرور جامع از متون تحقیقی با تأکید بر درمان جراحی

زمینه و هدف: همانژیواندوتلیـومای اپیتلیویید کبدی (HEH) بدخیم، یک تومـور عروقی بدخیـم نادر با علت ناشناخته و سیر طبیعی متغیر است. نویسندگان این مقاله، مـرور جامعی از متـون تحقیقی در مـورد HEH را با تمـرکز بر پیامدهای بالینی پس از راهبـردهای درمانی متفاوت، ارائه می‌دهند. مواد و روش‌ها: در این مـرور، تمامی مجمـوعه‌های منتشر شده در مورد بیماران مبتلا به HEH (تعداد 434 بیمـار) از نخستین توصیف این بیمـاران در سال 1984 تا مقالة حاضر مـورد تحلیل قـرار گرفت. پارامتـرهای مرور شده شامل: داده‌های جمعیت ـ شناختی، تظاهـرات بالینی، روش‌های درمانی و پیامـدهای بالینی بود. یافته‌ها: میانگین سنی بیماران مبتلا به HEH، 7/41 سال و نسبت مرد به زن، 2 به 3 بود. شایعترین تظاهـرات بالینی: درد ربع فـوقانی راست شکم، هپاتومگالی و کاهش وزن بود. اغلـب بیماران با تومور چند کانونی که هر دو لـوب را درگیـر کرده، مـراجعه کردند. شایعترین مناطق درگیری خارج کبدی در زمان تشخیص: ریه، صفاق، گـره‌های لنفـاوی و استخوان بود. شایعتـرین تدابیـر درمانی: پیـوند کبد (LTx)‌ (8/44% از بیمـاران)، پیگیـری بدون درمان (8/24% از بیماران)، شیمی درمانی یا پرتو درمانی (21% از بیماران)، و رزکسیـون کبد (LRx) (4/9% از بیمـاران) بود. میـزان بقـای یک و پنـج سالة پس از LTx به ترتیب 96% و 5/54%، پس از عـدم درمان به ترتیب 3/39% و 5/4% پس از شیمـی درمانی یا پرتودرمانی به ترتیب 3/73% و 30% و پس از LRx به ترتیب 100% و 75% بود. نتیجه‌گیـری: LRx درمان انتخـابی برای بیمـاران مبتلا به HEH قابل رزکسیـون است، با این وجـود، به دلیل چند مـرکزی بودن HEH کبـدی، LTx به عنوان درمـان انتخـابی پیشنهـاد شده است. علاوه بر این، LTx گزینة قابل قبـولی برای بیمارانی است که HEH با تظاهـرات خارج کبدی دارند. شاید بتوان بیماران کاملاً گزینش شده را تحت LTx از اهـداء کنندة زنده (با حفـظ منبع اهـداء) قـرار داد. نقش درمان‌های کمکی مختلف برای بیمارن مبتلا به HEH همچنان نامعلـوم است

Stone artefacts on the seabed at a submerged freshwater spring confirm a drowned cultural landscape in Murujuga, Western Australia

We report the discovery and identification of five ancient stone artefacts associated with a submerged freshwater spring at the underwater archaeological site WH1 in Murujuga (Dampier Archipelago), Western Australia. A limiting date applied to the site based on timing of inundation suggests it was occupied in the Late Pleistocene or Early Holocene. The site is situated well below the intertidal zone having been recorded at 14 m depth in Flying Foam Passage. This discovery highlights the high potential of these submerged springs as archaeological survey targets. We discuss results of a recent survey that expands the number of confirmed artefacts located at WH1 and the geomorphological context in a large calcareous depression associated with a freshwater source. This study demonstrates how submerged landscape research using a suite of technologies can reveal archaeological assemblages in this tropical geomorphological environment, and that adapted techniques could be applied to other tropical conditions such as mangrove coasts, large deltaic plains, or reef-building environments. There are likely thousands of drowned archaeological sites on the continental shelf of the tropics, extending from the intertidal zone to the lowest point of the culturally occupied landmass, at approximately 130 m below modern sea level

Understanding the Cool DA White Dwarf, G29-38

The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and compositions, critical to understanding post main sequence evolution, along with their cooling rates, allowing us to calibrate their ages directly. The most important set of white dwarf variables to measure are the oldest of the pulsators, the cool DAVs, which have not previously been explored through asteroseismology due to their complexity and instability. Through a time-series photometry data set spanning ten years, we explore the pulsation spectrum of the cool DAV, G29-38 and find an underlying structure of 19 (not including multiplet components) normal-mode, probably l=1 pulsations amidst an abundance of time variability and linear combination modes. Modelling results are incomplete, but we suggest possible starting directions and discuss probable values for the stellar mass and hydrogen layer size. For the first time, we have made sense out of the complicated power spectra of a large-amplitude DA pulsator. We have shown its seemingly erratic set of observed frequencies can be understood in terms of a recurring set of normal-mode pulsations and their linear combinations. With this result, we have opened the interior secrets of the DAVs to future asteroseismological modelling, thereby joining the rest of the known white dwarf pulsators.Comment: 29 pages including 5 figures To appear in ApJ 1 Mar 9

Quantitative Models of the Mechanisms That Control Genome-Wide Patterns of Transcription Factor Binding during Early Drosophila Development

Transcription factors that drive complex patterns of gene expression during animal development bind to thousands of genomic regions, with quantitative differences in binding across bound regions mediating their activity. While we now have tools to characterize the DNA affinities of these proteins and to precisely measure their genome-wide distribution in vivo, our understanding of the forces that determine where, when, and to what extent they bind remains primitive. Here we use a thermodynamic model of transcription factor binding to evaluate the contribution of different biophysical forces to the binding of five regulators of early embryonic anterior-posterior patterning in Drosophila melanogaster. Predictions based on DNA sequence and in vitro protein-DNA affinities alone achieve a correlation of ∼0.4 with experimental measurements of in vivo binding. Incorporating cooperativity and competition among the five factors, and accounting for spatial patterning by modeling binding in every nucleus independently, had little effect on prediction accuracy. A major source of error was the prediction of binding events that do not occur in vivo, which we hypothesized reflected reduced accessibility of chromatin. To test this, we incorporated experimental measurements of genome-wide DNA accessibility into our model, effectively restricting predicted binding to regions of open chromatin. This dramatically improved our predictions to a correlation of 0.6–0.9 for various factors across known target genes. Finally, we used our model to quantify the roles of DNA sequence, accessibility, and binding competition and cooperativity. Our results show that, in regions of open chromatin, binding can be predicted almost exclusively by the sequence specificity of individual factors, with a minimal role for protein interactions. We suggest that a combination of experimentally determined chromatin accessibility data and simple computational models of transcription factor binding may be used to predict the binding landscape of any animal transcription factor with significant precision