Ultrafast Momentum Imaging of Pseudospin-Flip Excitations in Graphene

The pseudospin of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photo-excited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization, and are maximum perpendicular to it. Here, we use time- and angle-resolved photoemission spectroscopy to investigate the resulting unconventional hot carrier dynamics, sampling carrier distributions as a function of energy and in-plane momentum. We first show that the rapidly-established quasi-thermal electron distribution initially exhibits an azimuth-dependent temperature, consistent with relaxation through collinear electron-electron scattering. Azimuthal thermalization is found to occur only at longer time delays, at a rate that depends on the substrate and the static doping level. Further, we observe pronounced differences in the electron and hole dynamics in n-doped samples. By simulating the Coulomb- and phonon-mediated carrier dynamics we are able to disentangle the influence of excitation fluence, screening, and doping, and develop a microscopic picture of the carrier dynamics in photo-excited graphene. Our results clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photo-control experiments and optoelectronic device applications.Comment: 23 pages, 12 figure

Characterization of Photoreceivers for LISA

LISA will use quadrant photo receivers as front-end devices for the phase meter measuring the motion of drag-free test masses in both angular orientation and separation. We have set up a laboratory testbed for the characterization of photo receivers. Some of the limiting noise sources have been identified and their contribution has been either measured or determined from the measured data. We have built a photo receiver with a 0.5 mm diameter quadrant photodiode with an equivalent input noise of better than 1.8 pA/(square root of)Hz below 20 MHz and a 3 dB bandwidth of 34 MHz

Policitemia vera en un perro : su diagnóstico y su tratamiento

En este artículo presentamos un caso clínico de policitemia vera (eritrocitosis) canina con un nivel de eritropoyetina en suero normal. Fue diagnosticado y tratado mediante flebotomías repetidas, en un primer momento y con hidroxyurea posteriormente

Remark on charge conjugation in the non relativistic limit

We study the non relativistic limit of the charge conjugation operation $\cal C$ in the context of the Dirac equation coupled to an electromagnetic field. The limit is well defined and, as in the relativistic case, $\cal C$, $\cal P$ (parity) and $\cal T$ (time reversal) are the generators of a matrix group isomorphic to a semidirect sum of the dihedral group of eight elements and $\Z_2$. The existence of the limit is supported by an argument based in quantum field theory. Also, and most important, the limit exists in the context of galilean relativity. Finally, if one complexifies the Lorentz group and therefore the galilean spacetime $x_\mu$, then the explicit form of the matrix for $\cal C$ allows to interpret it, in this context, as the complex conjugation of the spatial coordinates: $\vec{x} \to \vec{x}^*$. This result is natural in a fiber bundle description.Comment: 8 page

Isotropization of Bianchi type models and a new FRW solution in Brans-Dicke theory

Using scaled variables we are able to integrate an equation valid for isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD) theory. We analyze known and new solutions for these models in relation with the possibility that anisotropic models asymptotically isotropize, and/or possess inflationary properties. In particular, a new solution of curve ($k\neq0$) Friedmann-Robertson-Walker (FRW) cosmologies in Brans-Dicke theory is analyzed.Comment: 15 pages, 4 postscript figures, to appear in Gen. Rel. Grav., special issue dedicated in honour of Prof. H. Dehne

Tracking primary thermalization events in graphene with photoemission at extreme timescales

Direct and inverse Auger scattering are amongst the primary processes that mediate the thermalization of hot carriers in semiconductors. These two processes involve the annihilation or generation of an electron-hole pair by exchanging energy with a third carrier, which is either accelerated or decelerated. Inverse Auger scattering is generally suppressed, as the decelerated carriers must have excess energies higher than the band gap itself. In graphene, which is gapless, inverse Auger scattering is instead predicted to be dominant at the earliest time delays. Here, $<8$ femtosecond extreme-ultraviolet pulses are used to detect this imbalance, tracking both the number of excited electrons and their kinetic energy with time- and angle-resolved photoemission spectroscopy. Over a time window of approximately 25 fs after absorption of the pump pulse, we observe an increase in conduction band carrier density and a simultaneous decrease of the average carrier kinetic energy, revealing that relaxation is in fact dominated by inverse Auger scattering. Measurements of carrier scattering at extreme timescales by photoemission will serve as a guide to ultrafast control of electronic properties in solids for PetaHertz electronics.Comment: 16 pages, 8 figure

Síndrome de intestino corto en niños: actualidades en su diagnóstico y manejo

ResumenEl síndrome de intestino corto (SIC) se refiere a la suma de alteraciones funcionales que resultan de una reducción crítica en la longitud del intestino, y que en ausencia de un tratamiento adecuado se manifiestan con diarrea crónica, deshidratación crónica, desnutrición, pérdida de peso, deficiencia de nutrimentos y electrolitos, así como falla para crecer que se presenta con mayor frecuencia durante el periodo neonatal. El objetivo de este artículo es realizar una revisión de la literatura médica sobre la definición, las causas más frecuentes de SIC así como entender la fisiopatología, los factores pronósticos y tratamiento.Se realizó una búsqueda de artículos en PubMed, considerando la información existente en niños con SIC de 20 años hasta la fecha, utilizando las palabras clave “síndrome de intestino corto”. De un total de 784 artículos potenciales, se realizó una selección de 82 artículos donde realizamos la revisión de la literatura médica. Los pacientes con SIC son todo un reto para su tratamiento, por lo que se debe establecer un manejo multidisciplinario enfocado en mantener un soporte nutricional óptimo que cubra las necesidades para crecimiento, desarrollo y asimismo, disminuir al máximo la presencia de complicaciones a corto, mediano y largo plazo. El diagnóstico y manejo de un niño con SIC, implica un equipo de profesionales expertos en el manejo gastroenterológico, pediátrico y nutricional. El pronóstico del niño estará en función al manejo oportuno, así como longitud de la resección intestinal y presencia o no de válvula ileocecal.AbstractShort bowel syndrome (SBS) refers to the sum of the functional alterations that are the result of a critical reduction in the length of the intestine, which in the absence of adequate treatment, presents as chronic diarrhea, chronic dehydration, malnutrition, weight loss, nutriment and electrolyte deficiency, along with a failure to grow that is present with greater frequency during the neonatal period. The aim was to carry out a review of the literature encompassing the definition and the most frequent causes of SBS, together with an understanding of its physiopathology, prognostic factors, and treatment.An Internet search of PubMed articles was carried out for the existing information published over the last 20 years on SBS in children, using the keywords “short bowel syndrome”. From a total of 784 potential articles, 82 articles were chosen for the literature review. The treatment of patients presenting with SBS is quite a challenge and therefore it is necessary to establish multidisciplinary management with a focus on maintaining optimal nutritional support that covers the necessities of growth and development and at the same time provides a maximum reduction of short, medium, and long-term complications. The diagnosis and treatment of a child with SBS require a team of professionals that are experts in gastroenterologic, pediatric, and nutritional management. The outcome for the child will be directly related to opportune management, as well as to the length of the intestinal resection and the presence or absence of the ileocecal valve

Induced Gravity and the Attractor Dynamics of Dark Energy/Dark Matter

Attractor solutions that give dynamical reasons for dark energy to act like the cosmological constant, or behavior close to it, are interesting possibilities to explain cosmic acceleration. Coupling the scalar field to matter or to gravity enlarges the dynamical behavior; we consider both couplings together, which can ameliorate some problems for each individually. Such theories have also been proposed in a Higgs-like fashion to induce gravity and unify dark energy and dark matter origins. We explore restrictions on such theories due to their dynamical behavior compared to observations of the cosmic expansion. Quartic potentials in particular have viable stability properties and asymptotically approach general relativity.Comment: 11 pages, 10 figures, accepted in JCAP, results unchanged, an explanation added on perfect fluids for general spinor Lagrangian

Los conflictos socioambientales y la construcción de alternativas: experiencias de agricultura periurbana en el sur de la zona metropolitana de Guadalajara, Jalisco, México

El crecimiento desordenado de la zona metropolitana de Guadalajara, Jalisco, México, ha ocasionado una serie de conflictos socioambientales que impactan los recursos naturales y la calidad de vida de los habitantes del entorno periurbano. Ante ello, diversos actores locales se han orientado a construir alternativas a estos conflictos y allí es crucial el papel de la agricultura familiar periurbana, sustentable y multifuncional. En este trabajo se da cuenta de la experiencia del Instituto Tecnológico y de Estudios Superiores de Occidente, que lleva a cabo en la región un proyecto de acompañamiento e investigación participativa, donde se ha formado a los agricultores locales en la transición hacia agriculturas más sustentables, con el que se han demostrado las experiencias de agricultura periurbana, su viabilidad y sus aportaciones a la sustentabilidad regional, y se ha favorecido la articulación de los actores locales con organizaciones regionales y nacionales. Estos procesos se realizan en un tejido social fuerte que es la base para la construcción de alternativas a los conflictos socioambientales. The disordered sprawl of Guadalajara, Jalisco, Mexico has caused a number of environmental conflicts that impact the environment and quality of life of the residents of the suburban surroundings. In response, diverse local actors have focused on building alternatives to these conflicts where it is crucial the role of peri-urban, sustainable and multifunctional family agriculture. The Western Institute of Technology and Higher Education, holds in the region a project of accompaniment and participatory research, which has qualified local farmers in the transition to more sustainable agriculture and demonstrate the feasibility of the experiences of periurban agriculture and their contributions to regional sustainability, finally it has favored the articulation of local regional and national actors. These processes get done inside a strong social network which is the base to the construction of alternatives to socioenvironmental conflicts