Quantum Backflow States from Eigenstates of the Regularized Current Operator

We present an exhaustive class of states with quantum backflow -- the phenomenon in which a state consisting entirely of positive momenta may have negative current and the probability flows in the opposite direction to the momentum. They are characterized by a general function of momenta subject to very weak conditions. Such a family of states is of interest in the light of a recent experimental proposal to measure backflow. We find one particularly simple state which has surprisingly large backflow -- about 41 percent of the lower bound on flux derived by Bracken and Melloy. We study the eigenstates of a regularized current operator and we show how some of these states, in a certain limit, lead to our class of backflow states. This limit also clarifies the correspondence between the spectrum of the regularized current operator, which has just two non-zero eigenvalues in our chosen regularization, and the usual current operator.Comment: 16 pages, 2 figure

Terminal velocities of luminous, early-type SMC stars

Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are used to determine terminal velocities for 11 O and B-type giants and supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV resonance lines. Using archival data from observations with the Goddard High-Resolution Spectrograph and the International Ultraviolet Explorer telescope, terminal velocities are obtained for a further five B-type supergiants. We discuss the metallicity dependence of stellar terminal velocities, finding no evidence for a significant scaling between Galactic and SMC metallicities for Teff < 30,000 K, consistent with the predictions of radiation driven wind theory for supergiant stars. A comparison of the $v_\infty / v_{esc}$ ratio between the SMC and Galactic samples, while consistent with the above statement, emphasizes that the uncertainties in the distances to galactic O-stars are a serious obstacle to a detailed comparison with theory. For the SMC sample there is considerable scatter in this ratio at a given effective temperature, perhaps indicative of uncertainties in stellar masses.Comment: 28 pages, 8 figures, accepted by ApJ; minor revisions prior to acceptanc

The First Galaxies: Clues from Element Abundances

It has recently become possible to measure directly the abundances of several chemical elements in a variety of environments at redshifts up to z = 5. In this review I summarise the latest observations of Lyman break galaxies, damped Lyman alpha systems and the Lyman alpha forest with a view to uncovering any clues which these data may offer to the first episodes of star formation. The picture which is emerging is one where the universe at z = 3 already included many of the components of today's galaxies--even at these early times we see evidence for Populations I and II stars, while the `smoking gun' for Population III objects may be hidden in the chemical composition of the lowest density regions of the IGM, yet to be deciphered.Comment: 15 pages, LaTex, 8 Postscript Figures. To appear in the Philosophical Transactions of The Royal Society, Series

Structural behaviour of copper chloride catalysts during the chlorination of CO to phosgene

The interaction of CO with an attapulgite-supported Cu(II)Cl2 catalyst has been examined in a micro-reactor arrangement. CO exposure to the dried, as-received catalyst at elevated temperatures leads to the formation of CO2 as the only identifiable product. However, phosgene production can be induced by a catalyst pre-treatment where the supported Cu(II)Cl2 sample is exposed to a diluted stream of chlorine. Subsequent CO exposure at ~ 370°C then leads to phosgene production. In order to investigate the origins of this atypical set of reaction characteristics, a series of x-ray absorption experiments were performed that were supplemented by DFT calculations. XANES measurements establish that at the elevated temperatures connected with phosgene formation, the catalyst is comprised of Cu+ and a small amount of Cu2+. Moreover, the data show that unique to the chlorine pre-treated sample, CO exposure at elevated temperature results in a short-lived oxidation of the copper. On the basis of calculated CO adsorption energies, DFT calculations indicate that a mixed Cu+/Cu2+ catalyst is required to support CO chemisorption

Localization and genomic structure of human deoxyhypusine synthase gene on chromosome 19p13.2-distal 19p13.1

The amino acid hypusine is formed post-translationally in a single cellular protein, the eukaryotic translation initiation factor 5A, by two enzymes, namely deoxyhypusine synthase and deoxyhypusine hydroxylase. Hypusine is found in all eukaryotes and in some archaebacteria, but not in eubacteria. The deoxyhypusine synthase cDNA was cloned and mapped by fluorescence in situ hybridization on chromosome 19p13.11-p13.12. Rare cDNAs containing internal deletions were also found. We localized the deoxyhypusine synthase gene on a high resolution cosmid/BAC contig map of chromosome 19 to a region in 19p13.2-distal 19p13.1 between MANB and JUNB. Analysis of the genomic exon/intron structure of the gene coding region showed that it consists of nine exons and spans a length of 6.6kb. From observation of the genomic structure, it seems likely that the internally deleted forms of mature RNA are the result of alternative splicing, rather than of artifacts

Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. II. Optical and Near Infrared Star Formation History of the Starburst Cluster NGC 2070 in 30 Doradus

We present a study of the recent star formation of 30 Doradus in the Large Magellanic Cloud (LMC) using the panchromatic imaging survey Hubble Tarantula Treasury Project (HTTP). In this paper we focus on the stars within 20 pc of the center of the massive ionizing cluster of 30 Doradus, NGC 2070. We recovered the star formation history by comparing deep optical and NIR color-magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs generated with the latest PARSEC models, which include all stellar phases from pre-main sequence to post- main sequence. For the first time in this region we are able to measure the star formation using intermediate and low mass stars simultaneously. Our results suggest that NGC2070 experienced a prolonged activity. In particular, we find that the star formation in the region: i) exceeded the average LMC rate ~ 20 Myr ago; ii) accelerated dramatically ~ 7 Myr ago; and iii) reached a peak value 1-3 Myr ago. We did not find significant deviations from a Kroupa initial mass function down to 0.5 Msun. The average internal reddening E(B-V) is found to be between 0.3 and 0.4 mag.Comment: Submitted to Ap

A Black Deer at Black Cave: New Pictograph Radiocarbon Date for the Lower Pecos, Texas

A Pecos River style painting of a black deer from Black Cave Annex (41VV76a) in southwest Texas was radiocarbon dated. Using plasma oxidation and accelerator mass spectrometry, we obtained an age of 1465 ± 40 RCYBP (2 sigma calibrated age range of A.D. 470-660). This age is younger than the accepted age range for Pecos River style paintings, which is approximately 4000-3000 years B.P. This new measurement in association with other younger dates prompts us to question whether the Pecos River style endured for a longer time period than previously thought. More radiocarbon research is needed in order to understand how this anomalous result might fit within the Lower Pecos Canyonlands rock art chronology

Emergent singular solutions of non-local density-magnetization equations in one dimension

We investigate the emergence of singular solutions in a non-local model for a magnetic system. We study a modified Gilbert-type equation for the magnetization vector and find that the evolution depends strongly on the length scales of the non-local effects. We pass to a coupled density-magnetization model and perform a linear stability analysis, noting the effect of the length scales of non-locality on the system's stability properties. We carry out numerical simulations of the coupled system and find that singular solutions emerge from smooth initial data. The singular solutions represent a collection of interacting particles (clumpons). By restricting ourselves to the two-clumpon case, we are reduced to a two-dimensional dynamical system that is readily analyzed, and thus we classify the different clumpon interactions possible.Comment: 19 pages, 13 figures. Submitted to Phys. Rev.

Synthetic spectra of H Balmer and HeI absorption lines. II: Evolutionary synthesis models for starburst and post-starburst galaxies

We present evolutionary stellar population synthesis models to predict the spectrum of a single-metallicity stellar population, with a spectral sampling of 0.3 A in five spectral regions between 3700 and 5000 A. The models, which are optimized for galaxies with active star formation, synthesize the profiles of the hydrogen Balmer series (Hb, Hg, Hd, H8, H9, H10, H11, H12 and H13) and the neutral helium absorption lines (HeI 4922, HeI 4471, HeI 4388, HeI 4144, HeI 4121, HeI 4026, HeI 4009 and HeI 3819) for a burst with an age ranging from 1 to 1000 Myr, and different assumptions about the stellar initial mass function. Continuous star formation models lasting for 1 Gyr are also presented. The input stellar library includes NLTE absorption profiles for stars hotter than 25000 K and LTE profiles for lower temperatures. The temperature and gravity coverage is 4000 K <Teff< 50000 K and 0.0< log g$< 5.0, respectively. The models can be used to date starburst and post-starburst galaxies until 1 Gyr. They have been tested on data for clusters in the LMC, the super-star cluster B in the starburst galaxy NGC 1569, the nucleus of the dwarf elliptical NGC 205 and a luminous "E+A" galaxy. The full data set is available for retrieval at http://www.iaa.es/ae/e2.html and at http://www.stsci.edu/science/starburst/, or on request from the authors at [email protected]: To be published in ApJS. 48 pages and 20 figure

Sodium Density Associates with Nighttime Systolic Blood Pressure in Young Healthy Adults

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