Rashba spin precession in quantum Hall edge channels

Quasi--one dimensional edge channels are formed at the boundary of a two-dimensional electron system subject to a strong perpendicular magnetic field. We consider the effect of Rashba spin--orbit coupling, induced by structural inversion asymmetry, on their electronic and transport properties. Both our analytical and numerical results show that spin--split quantum--Hall edge channels exhibit properties analogous to that of Rashba--split quantum wires. Suppressed backscattering and a long spin life time render these edge channels an ideal system for observing voltage--controlled spin precession. Based on the latter, we propose a magnet--less spin--dependent electron interferometer.Comment: 7 pages, 6 figure

Accurate mass-radius ratios for Hyades white dwarfs

We use the ESPRESSO spectrograph at the Very Large Telescope to measure velocity shifts and gravitational redshifts of eight bona fide Hyades white dwarfs, with an accuracy better than 1.5 percent. By comparing the gravitational redshift measurements of the mass-to-radius ratio with the same ratios derived by fitting the \textit{Gaia} photometry with theoretical models, we find an agreement to better than one per cent. It is possible to reproduce the observed white dwarf cooling sequence and the trend of the mass-to-radius ratios as a function of colour using isochrones with ages between 725 and 800 Myr, tuned for the Hyades. One star, EGGR\,29, consistently stands out in all diagrams, indicating that it is possibly the remnant of a blue straggler. We also computed mass-to-radius ratios from published gravities and masses, determined from spectroscopy. The comparison between photometric and spectroscopic stellar parameters reveals that spectroscopic effective temperature and gravity are systematically larger than the photometric values. Spectroscopic mass-to-radius ratios disagree with those measured from gravitational redshift, indicating the presence of systematics affecting the white dwarf parameters derived from the spectroscopic analysis.Comment: MNRAS, accepted for pubblicatio

Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae

We report the discovery of three stars that, along with the prototype LP40-365, form a distinct class of chemically peculiar runaway stars that are the survivors of thermonuclear explosions. Spectroscopy of the four confirmed LP 40-365 stars finds ONe-dominated atmospheres enriched with remarkably similar amounts of nuclear ashes of partial O- and Si-burning. Kinematic evidence is consistent with ejection from a binary supernova progenitor; at least two stars have rest-frame velocities indicating they are unbound to the Galaxy. With masses and radii ranging between 0.20-0.28 Msun and 0.16-0.60 Rsun, respectively, we speculate these inflated white dwarfs are the partly burnt remnants of either peculiar Type Iax or electron-capture supernovae. Adopting supernova rates from the literature, we estimate that ~20 LP40-365 stars brighter than 19 mag should be detectable within 2 kpc from the Sun at the end of the Gaia mission. We suggest that as they cool, these stars will evolve in their spectroscopic appearance, and eventually become peculiar O-rich white dwarfs. Finally, we stress that the discovery of new LP40-365 stars will be useful to further constrain their evolution, supplying key boundary conditions to the modelling of explosion mechanisms, supernova rates, and nucleosynthetic yields of peculiar thermonuclear explosions.Comment: 22 pages, 14 figures, 6 tables. Accepted for publication on MNRA

Stellar archaeology with Gaia: the Galactic white dwarf population

Gaia will identify several 1e5 white dwarfs, most of which will be in the solar neighborhood at distances of a few hundred parsecs. Ground-based optical follow-up spectroscopy of this sample of stellar remnants is essential to unlock the enormous scientific potential it holds for our understanding of stellar evolution, and the Galactic formation history of both stars and planets.Comment: Summary of a talk at the 'Multi-Object Spectroscopy in the Next Decade' conference in La Palma, March 2015, to be published in ASP Conference Series (editors Ian Skillen & Scott Trager

Dissipation effects in spin-Hall transport of electrons and holes

We investigate the spin-Hall effect of both electrons and holes in semiconductors using the Kubo formula in the correct zero-frequency limit taking into account the finite momentum relaxation time of carriers in real semiconductors. This approach allows to analyze the range of validity of recent theoretical findings. In particular, the spin-Hall conductivity vanishes for vanishing spin-orbit coupling if the correct zero-frequency limit is performed.Comment: 5 pages, no figures, version to appear in Phys. Rev.

Studies on the interaction of the carbohydrate binding module 3 from the Clostridium thermocellum CipA scaffolding protein with cellulose and paper fibres

The adsorption of a carbohydrate binding module (CBM3) from the Clostridium thermocellum scaffolding protein (CipA) to cellulose was analysed in this work. The effect of CBM-PEG on the drainability of E. globulus and P. sylvestris pulps and on the physical properties of the respective papersheets was also studied. The CBM binding to cellulose is often described as “irreversible”, but this classification does not fully characterize this interaction. Indeed, the results obtained demonstrate that, although the adsorption on cellulose is rather stable, CBM inter-fibre mobility may be observed. The results also showed that the CBM-PEG conjugate improves the drainability of E. globulus and P. sylvestris pulps without affecting the physical properties of the papersheets.This research was supported by Fundacao para a Ciencia e a Tecnologia under grant POCTI/BIO/45356/2002

Ancient Migratory Events in the Middle East: New Clues from the Y-Chromosome Variation of Modern Iranians

Knowledge of high resolution Y-chromosome haplogroup diversification within Iran provides important geographic context regarding the spread and compartmentalization of male lineages in the Middle East and southwestern Asia. At present, the Iranian population is characterized by an extraordinary mix of different ethnic groups speaking a variety of Indo-Iranian, Semitic and Turkic languages. Despite these features, only few studies have investigated the multiethnic components of the Iranian gene pool. In this survey 938 Iranian male DNAs belonging to 15 ethnic groups from 14 Iranian provinces were analyzed for 84 Y-chromosome biallelic markers and 10 STRs. The results show an autochthonous but non-homogeneous ancient background mainly composed by J2a sub-clades with different external contributions. The phylogeography of the main haplogroups allowed identifying post-glacial and Neolithic expansions toward western Eurasia but also recent movements towards the Iranian region from western Eurasia (R1b-L23), Central Asia (Q-M25), Asia Minor (J2a-M92) and southern Mesopotamia (J1-Page08). In spite of the presence of important geographic barriers (Zagros and Alborz mountain ranges, and the Dasht-e Kavir and Dash-e Lut deserts) which may have limited gene flow, AMOVA analysis revealed that language, in addition to geography, has played an important role in shaping the nowadays Iranian gene pool. Overall, this study provides a portrait of the Y-chromosomal variation in Iran, useful for depicting a more comprehensive history of the peoples of this area as well as for reconstructing ancient migration routes. In addition, our results evidence the important role of the Iranian plateau as source and recipient of gene flow between culturally and genetically distinct population

Sex Determination in the Squalius alburnoides Complex: An Initial Characterization of Sex Cascade Elements in the Context of a Hybrid Polyploid Genome

BACKGROUND:Sex determination processes vary widely among different vertebrate taxa, but no group offers as much diversity for the study of the evolution of sex determination as teleost fish. However, the knowledge about sex determination gene cascades is scarce in this species-rich group and further difficulties arise when considering hybrid fish taxa, in which mechanisms exhibited by parental species are often disrupted. Even though hybridisation is frequent among teleosts, gene based approaches on sex determination have seldom been conducted in hybrid fish. The hybrid polyploid complex of Squalius alburnoides was used as a model to address this question. METHODOLOGY/PRINCIPAL FINDINGS:We have initiated the isolation and characterization of regulatory elements (dmrt1, wt1, dax1 and figla) potentially involved in sex determination in S. alburnoides and in the parental species S. pyrenaicus and analysed their expression patterns by in situ hybridisation. In adults, an overall conservation in the cellular localization of the gene transcripts was observed between the hybrids and parental species. Some novel features emerged, such as dmrt1 expression in adult ovaries, and the non-dimorphic expression of figla, an ovarian marker in other species, in gonads of both sexes in S. alburnoides and S. pyrenaicus. The potential contribution of each gene to the sex determination process was assessed based on the timing and location of expression. Dmrt1 and wt1 transcripts were found at early stages of male development in S. alburnoides and are most likely implicated in the process of gonad development. CONCLUSIONS/SIGNIFICANCE:For the first time in the study of this hybrid complex, it was possible to directly compare the gene expression patterns between the bisexual parental species and the various hybrid forms, for an extended set of genes. The contribution of these genes to gonad integrity maintenance and functionality is apparently unaltered in the hybrids, suggesting that no abrupt shifts in gene expression occurred as a result of hybridisation

Large-scale production of cellulose-binding domains : adsorption studies using CBD-FITC conjugates

A method for the gram-scale production of cellulose-binding domains (CBD) through the proteolytic digestion of a commercial nzymatic preparation (Celluclast) was developed. The CBD obtained, isolated from Trichoderma reesei cellobiohydrolase I, is highly pure and heavily glycosylated. The purified peptide has a molecular weight of 8.43 kDa, comprising the binding module, a part of the linker, and about 30% glycosidic moiety. Its properties may thus be different from recombinant ones expressed in bacteria. CBDfluorescein isothiocyanate conjugates were used to study the CBD-cellulose interaction. The presence of fluorescent peptides adsorbed on crystalline and amorphous cellulose fibers suggests that amorphous regions have a higher concentration of binding sites. The adsorption is reversible, but desorption is a very slow process.Fundação para a Ciência e a Tecnologia (FCT