Universal quantum computation with the Orbital Angular Momentum of a single photon

We prove that a single photon with quantum data encoded in its orbital angular momentum can be manipulated with simple optical elements to provide any desired quantum computation. We will show how to build any quantum unitary operator using beamsplitters, phase shifters, holograms and an extraction gate based on quantum interrogation. The advantages and challenges of these approach are then discussed, in particular the problem of the readout of the results.Comment: First version. Comments welcom

Delayed commutation in quantum computer networks

In the same way that classical computer networks connect and enhance the capabilities of classical computers, quantum networks can combine the advantages of quantum information and communications. We propose a non-classical network element, a delayed commutation switch, that can solve the problem of switching time in packet switching networks. With the help of some local ancillary qubits and superdense codes we can route the information after part of it has left the network node.Comment: 4 pages. 4 figures. Preliminar versio

An extreme event between the Little Ice Age and the 20th century: the snow avalanche cycle of 1888 in the Asturian Massif (Northern Spain)

Between the late Little Ice Age (LIA) cold stage and the early 20th century warmer scenario, a transitional regime characterized by an unstable climatic pattern generated a series of climate extremes affecting mid-latitude mountainous areas, as the Asturian Massif. There, the 1888 snow avalanche cycle appears as the most significant event, standing out among the rest of avalanche cycles recorded in this area during the 1800-2015 period both in terms of the number of damaging avalanches and damages caused by them. Among the factors that explain this event stands out the orographic precipitation phenomenon; the interaction of a cold and wet air mass originating from the North Atlantic with the relief of the Massif, which led to extraordinary snow thicknesses (>2 m) at very low altitudes (500 m a.s.l.), especially in the north-facing, Asturian versant of the Cantabrian Mountains. This allowed the triggering of avalanches in slopes gentler and in lower altitudes than usual, covering longer distances; consequently, avalanches reached more easily the settlements, generally placed at the bottom of the valley or in middle slope positions. The greater impact on the settlements, which suffered 84% of the damages, was the cause of this episode’s high socioeconomic impact (29 people dead, 34 injured, 123 heads of cattle dead, 124 buildings destroyed). These events occurred at a time when the mountain villages were highly populated and subjected to intense exploitation, coinciding with the development of new communication infrastructures in the upper parts of the Massif. Therefore, the 1888 episode constitutes a good example of both the impact of hydrometeorological events in mountain environments under high demographic pressure, and of climate extremes involved in a transition period from cold to warmer weather conditions.Entre la Pequeña Edad de Hielo (PEH) y las primeras décadas del siglo XX, un régimen de transición climática caracterizado por su inestabilidad generó una serie de eventos extremos que afectaron a las zonas montañosas de latitudes medias, como el Macizo Asturiano. Allí, el ciclo de aludes de 1888 fue el acontecimiento más significativo, destacando entre el resto de ciclos de avalanchas registrados en esta área entre 1800 y 2015 tanto por el número de avalanchas dañinas que se registraron como por los daños que estas causaron. Entre los factores que explican este acontecimiento destaca el fenómeno de las precipitaciones orográficas; la interacción de una masa de aire frío y húmedo (procedente del Atlántico Norte) con el relieve del Macizo, condujo a espesores de nieve extraordinarios (> 2 m) a muy bajas altitudes (500 m s.n.m.), especialmente en la vertiente asturiana (orientada al norte). Esto permitió el desencadenamiento de avalanchas en pendientes más suaves y a altitudes más bajas de lo habitual, cubriendo distancias más largas que en otros episodios. En consecuencia, estas avalanchas alcanzaron más fácilmente los asentamientos, tradicionalmente situados en el fondo del valle o en posiciones de media ladera. El mayor impacto en los asentamientos, que sufrieron el 84% de los daños, fue la causa del alto coste socioeconómico de este episodio (29 personas muertas, 34 heridas, 123 cabezas de ganado muertas, 124 edificios destruidos). Estos acontecimientos ocurrieron en un momento en que los núcleos de montaña estaban muy poblados y sometidos a una intensa explotación, coincidiendo además con el desarrollo de nuevas infraestructuras de comunicación en las partes altas del Macizo. Por lo tanto, el episodio de 1888 constituye un buen ejemplo tanto del impacto de los eventos hidrometeorológicos en ambientes montañosos bajo alta presión demográfica, como de los eventos extremos propios de un período de transición de condiciones climáticas frías a más cálidas.info:eu-repo/semantics/publishedVersio

Análisis comparativo de diferentes aproximaciones para el estudio del proteoma de Saccharomyces cerevisiae

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Molecular dynamics simulations of nanosheets of polymeric carbon nitride and comparison with experimental observations

A computational study of the properties of polymeric carbon nitride using molecular dynamics is presented. The analysis of ideal infinite-extent sheets permits to evaluate the effect of temperature on the network of hydrogen bonds responsible for the linkage of the material. The weakening of this binding mechanism at sufficiently high temperatures, together with the inter-layer interactions characteristic of this type of 2D materials, is shown to determine the conformation properties of polymeric carbon nitride at the nanoscale. The results obtained from the simulation of finite samples in the canonical ensemble at varying temperatures are consistent with those from the characterization of our experimentally synthesized samples. Hydrogen bonding between adjacent polymer ribbons leads this process and is the cause of the typical crumpled structure of this material

A counterfactual Rydberg gate for photons

Quantum computation with photons requires efficient two photon gates. We put forward a two photon entangling gate which uses an intermediate atomic system. The system includes a single Rydberg atom which can switch on and off photon absorption in an ensemble using the dipole blockade. The gate is based in a counterfactual protocol. The mere possibility of an absorption that can only occur with a vanishing probability steers the photons to the desired final state.Comment: 4 Figures. 6 pages of tex

The SASSCAL contribution to climate observation, climate data management and data rescue in Southern Africa

A major task of the newly established "Southern African Science Service Centre for Climate Change and Adaptive Land Management" (SASSCAL; www.sasscal.org) and its partners is to provide science-based environmental information and knowledge which includes the provision of consistent and reliable climate data for Southern Africa. Hence, SASSCAL, in close cooperation with the national weather authorities of Angola, Botswana, Germany and Zambia as well as partner institutions in Namibia and South Africa, supports the extension of the regional meteorological observation network and the improvement of the climate archives at national level. With the ongoing rehabilitation of existing weather stations and the new installation of fully automated weather stations (AWS), altogether 105 AWS currently provide a set of climate variables at 15, 30 and 60 min intervals respectively. These records are made available through the SASSCAL WeatherNet, an online platform providing near-real time data as well as various statistics and graphics, all in open access. This effort is complemented by the harmonization and improvement of climate data management concepts at the national weather authorities, capacity building activities and an extension of the data bases with historical climate data which are still available from different sources. These activities are performed through cooperation between regional and German institutions and will provide important information for climate service related activities

Evidence For The Production Of Slow Antiprotonic Hydrogen In Vacuum

We present evidence showing how antiprotonic hydrogen, the quasistable antiproton-proton (pbar-p) bound system, has been synthesized following the interaction of antiprotons with the hydrogen molecular ion (H2+) in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events, evidence is presented for antiprotonic hydrogen production with sub-eV kinetic energies in states around n=70, and with low angular momenta. The slow antiprotonic hydrogen may be studied using laser spectroscopic techniques.Comment: 5 pages with 4 figures. Published as Phys. Rev. Letters 97, 153401 (2006), in slightly different for

Cryptic MHC Polymorphism Revealed but Not Explained by Selection on the Class IIB Peptide-Binding Region

The immune genes of the major histocompatibility complex (MHC) are characterized by extraordinarily high levels of nucleotide and haplotype diversity. This variation is maintained by pathogen-mediated balancing selection that is operating on the peptide-binding region (PBR). Several recent studies have found, however, that some populations possess large clusters of alleles that are translated into virtually identical proteins. Here, we address the question of how this nucleotide polymorphism is maintained with little or no functional variation for selection to operate on. We investigate circa 750–850 bp of MHC class II DAB genes in four wild populations of the guppy Poecilia reticulata. By sequencing an extended region, we uncovered 40.9% more sequences (alleles), which would have been missed if we had amplified the exon 2 alone. We found evidence of several gene conversion events that may have homogenized sequence variation. This reduces the visible copy number variation (CNV) and can result in a systematic underestimation of the CNV in studies of the MHC and perhaps other multigene families. We then focus on a single cluster, which comprises 27 (of a total of 66) sequences. These sequences are virtually identical and show no signal of selection. We use microsatellites to reconstruct the populations' demography and employ simulations to examine whether so many similar nucleotide sequences can be maintained in the populations. Simulations show that this variation does not behave neutrally. We propose that selection operates outside the PBR, for example, on linked immune genes or on the “sheltered load” that is thought to be associated to the MHC. Future studies on the MHC would benefit from extending the amplicon size to include polymorphisms outside the exon with the PBR. This may capture otherwise cryptic haplotype variation and CNV, and it may help detect other regions in the MHC that are under selection