Mach-Zehnder Interferometric device for spin filtering in a GaAs/AlGaAs electron gas

A spin filtering device using quantum spin interference is theoretically proposed in a GaAs/AlGaAs electron gas that has both Rashba and Dresselhaus spin-orbit couplings. The device achieves polarized electron currents by separating spin up and spin down components without a magnetic field gradient. We find two broad spin filtering regimes, one where the interferometer has symmetrical arms, where a small magnetic flux is needed to achieve spin separation, and the other with asymmetric arms where the change in path length renders an extra phase emulating the effects of a magnetic field. We identify operating points for the device where optimal electron polarization is achieved within value ranges found in a 2D electron gas. Both device setups apply for arbitrary incoming electron polarization and operate at broad energy ranges within the incoming electron band

Mesoscopic rings with Spin-Orbit interactions

A didactic description of charge and spin equilibrium currents on mesoscopic rings in the presence of Spin-Orbit interaction is presented. Emphasis is made on the non trivial construction of the correct Hamiltonian in polar coordinates, the calculation of eigenvalues and eigenfunctions and the symmetries of the ground state properties. Spin currents are derived following an intuitive definition and then a more thorough derivation is built upon the canonical Lagrangian formulation that emphasizes the SU(2) gauge structure of the transport problem of spin 1/2 fermions in spin-orbit active media. The quantization conditions that follow from the constraint of single-valued Pauli spinors are also discussed. The targeted students are those of a graduate Condensed Matter Physics course

Two electron entanglement enhancement by an inelastic scattering process

In order to assess inelastic effects on two fermion entanglement production, we address an exactly solvable two-particle scattering problem where the target is an excitable scatterer. Useful entanglement, as measured by the two particle concurrence, is obtained from post-selection of oppositely scattered particle states. The $S$ matrix formalism is generalized in order to address non-unitary evolution in the propagating channels. We find the striking result that inelasticity can actually increase concurrence as compared to the elastic case by increasing the uncertainty of the single particle subspace. Concurrence zeros are controlled by either single particle resonance energies or total reflection conditions that ascertain precisely one of the electron states. Concurrence minima also occur and are controlled by entangled resonance situations were the electron becomes entangled with the scatterer, and thus does not give up full information of its state. In this model, exciting the scatterer can never fully destroy phase coherence due to an intrinsic limit to the probability of inelastic events.Comment: 8 pages, to appear in Phys. Rev

Perfect spin filtering device through a Mach Zehnder interferometer in GaAs/AlGaAs electron gas

Spin filtering through quantum spin interference is addressed exactly, in two dimensions, in a medium that has both Rashba and Dresselhaus spin-orbit couplings and an applied external magnetic field. The problem is addressed from the fully non-Abelian Gauge formulation. We propose an experimentally feasible electronic Mach Zehnder Interferometer and solve for the perfect spin filtering conditions. We find two broad solutions, one where filtering is achieved in the original incoming basis, that is purely a non-Abelian solution, and the other where one needs a tilted axis to observe the polarized output spinor. The latter solution is well approximated by an Abelianized approximation. Both solutions apply for arbitrary incoming polarization, and are only limited by the randomness of the incoming spinor state.Comment: published version, one figure adde

Agricultural practices and food gathering during the Sierras de Córdoba’s Late Pre-Hispanic Period (Argentina): The archaeobotanical record of C. Pun. 39

El estudio arqueobotánico realizado en el sitio multipropósito C.Pun.39 (valle de Punilla, Córdoba), en el marco de las estrategias de subsistencia de las sociedades prehispánicas tardías (1000-300 AP), permitió la observación de restos vegetales a nivel macro y microscópico. Entre los macrorrestos carbonizados, se documentó la presencia de un fruto de maíz (Zea mays), así como semillas de poroto común cultivado (Phaseolus vulgaris aff. var. vulgaris), poroto pallar (Phaseolus cf. P. lunatus) y algarrobo (Prosopis cf. P. nigra). Entre los restos adheridos a artefactos cerámicos y de molienda se identificaron microfósiles de maíz, zapallo (Cucurbita sp.), chañar (Geoffroea decorticans) y algarrobo (Prosopis sp.). Los datos obtenidos permiten discutir la presencia e importancia prehispánica de algunos cultígenos, así como el aprovechamiento de frutos silvestres, de los cuales sólo se tenían evidencias arqueológicas indirectas.The archaeobotanical study carried out on the residential site C.Pun.39 (Punilla Valley, Córdoba), within subsistence strategies framework of Late Prehispanic societies (1000-300 BP), allowed us the observation of macro and micro plant remains. Among charred macro-remains not only maize kernel (Zea mays) was documented but also common bean (Phaseolus vulgaris aff. var. vulgaris), lima bean (Phaseolus cf. P. lunatus) and algarrobo seeds (Prosopis cf. P. nigra). Among micro-remains incorporated into pottery and grinding artifact, maize, squash (Cucurbita sp.), chañar (Geoffroea decorticans) and algarrobo (Prosopis sp.) were identified. The results show us the presence and prehispanic importance of some crops as well as wild fruits, where little direct archaeological evidence existed

Emergency care for women irregular migrants who arrive in Spain by small boat: a qualitative study

Background: this study aimed to describe and understand the experiences and health needs of women irregular migrants during emergency care provision upon arrival in Spain by small boat. Methods: a qualitative study based on Gadamer’s phenomenology was used. The data collection included 13 in-depth interviews with women irregular migrants and 10 in-depth interviews with key informants. The study took place in the Spanish Red Cross’ facilities between February 2017 and April 2018. Results: two main themes emerged from the data analysis: the need for emergency care focused on women irregular migrants with the sub-themes ‘Women irregular migrants as objects of sexual exploitation’ and ‘The mother-child dyad as the axis in human trafficking’; and developing an emergency care gender policy for women irregular migrants, with the subthemes ‘Healthcare in a police-controlled setting: detecting weaknesses’ and ‘Promoting screening and safety protocols focused on women irregular migrants’. Conclusions: women irregular migrants who arrive in Spain by small boat have specific needs and healthcare problems. Due to strict safety conditions during emergency care provision, rape and human trafficking can go unnoticed. Implications: interdisciplinary care protocols and new health policies that have a gender perspective are needed to improve the emergency care provided to women irregular migrants

Accompanied child irregular migrants who arrive to Spain in small boats: experiences and health needs

The European Union is the preferred destination of child irregular migrants arrived from northern Africa, who risk their lives crossing the Mediterranean Sea in small boats. Accompanied Child Irregular Migrants (AChIMs) are exposed to physical and psychological risk. The objective of our study is to describe and understand the experiences and health needs of AChIMs who arrive to Spain in small boats, through the testimony of adults who accompany them on the journey. A qualitative study, based on Gadamer's hermeneutic phenomenology, was performed. After obtaining approval from the Ethics and Research Committee, we conducted in-depth interviews on 32 adults who travelled with AChIMs. Two main themes emerged: (1) The journey a child should never have to take, with the subthemes 'AChIMs as a paradigm of vulnerability' and 'Crossing the sea, playing with death' and (2) Characterising emergency care to AChIMs, with the subthemes 'Prioritising specific care', 'Identifying high-risk situations' and 'The detaining of innocent children'. AChIMs, along with adults, risk their lives in such a dangerous and perilous journey, therefore, finding out about their experiences may contribute to improving the treatment of their specific health needs during the phases of rescue and emergency care

Dynamic equivalence between atomic and colloidal liquids

We show that the kinetic-theoretical self-diffusion coefficient of an atomic fluid plays the same role as the short-time self-diffusion coefficient D_S in a colloidal liquid, in the sense that the dynamic properties of the former, at times much longer than the mean free time, and properly scaled with D_S, will indistinguishable from those of a colloidal liquid with the same interaction potential. One important consequence of such dynamic equivalence is that the ratio D_L/ D_S of the long-time to the short-time self-diffusion coefficients must then be the same for both, an atomic and a colloidal system characterized by the same inter-particle interactions. This naturally extends to atomic fluids a well-known dynamic criterion for freezing of colloidal liquids[Phys. Rev. Lett. 70, 1557 (1993)]. We corroborate these predictions by comparing molecular and Brownian dynamics simulations on (soft- and hard-sphere) model systems, representative of what we may refer to as the "hard-sphere" dynamic universality class

Revising the diversity within the Dwarf Dog-faced Bat, Molossops temminckii (Chiroptera, Molossidae), with the revalidation of the endangered Molossops griseiventer

The genus Molossops includes two monotypic species of insectivore bats distributed in South America: Molossops neglectus and Molossops temminckii. Both can be differentiated, based on sizes, M. temminckii being smaller (forearm less than 33 mm). Despite being monotypic, at least two additional subspecies have been described for M. temminckii, of which M. temminckii griseiventer from the inter-Andean Valley of the Magdalena River in Colombia might represent a valid taxon. To test the taxonomic status of M. t. griseiventer, we reviewed specimens of M. temminckii from cis- and trans-Andean localities in Colombia. We used Cytochrome-b and Cytochrome Oxidase I comparisons to test the phylogenetic position of cis- and trans-Andean samples and compared qualitative morphology, morphometric and bioacoustics. Our results show that M. t. griseiventer is differentiated from cis-Andean specimens, providing further evidence of its validity at the species level. Furthermore, M. temminckii (sensu stricto) is also distributed in Colombia, but both M. griseiventer and M. temminckii are allopatric, with the Andes acting as a barrier. The specific identity of the specimens from the Caribbean Region of Colombia needs a new evaluation, but our results clearly show that the diversity of Molossops is underestimated

Optimal Nitrogen Fertilization to Reach the Maximum Grain and Stover Yields of Maize (Zea mays L.): Tendency Modeling

Utilization of maize stover to the production of meat and milk and saving the grains for human consumption would be one strategy for the optimal usage of resources. Variance and tendency analyses were applied to find the optimal nitrogen (N) fertilization dose (0, 100, 145, 190, 240, and 290 kg/ha) for forage (F), stover (S), cob (C), and grain (G) yields, as well as the optimal grain-to-forage, cob-to-forage, and cob-to-stover ratios (G:F, C:F, and C:S, respectively). The study was performed in central Mexico (20.691389° N and −101.259722° W, 1740 m a.m.s.l.; Cwa (Köppen), 699 mm annual precipitation; alluvial soils). N-190 and N-240 improved the individual yields and ratios the most. Linear and quadratic models for CDM, GDM, and G:F ratio had coefficients of determination (R2) of 0.20–0.46 (p < 0.03). Cubic showed R2 = 0.30–0.72 (p < 0.02), and the best models were for CDM, GDM, and the G:F, C:F, and C:S DM ratios (R2 = 0.60–0.72; p < 0.0002). Neither SHB nor SDM negatively correlated with CDM or GDM (r = 0.23–0.48; p < 0.0001). Excess of N had negative effects on forage, stover, cobs, and grains yields, but optimal N fertilization increased the proportion of the G:F, C:F, and C:S ratios, as well as the SHB and SDM yields, without negative effects on grain production