2,070 research outputs found
Method to preserve the chiral-symmetry protection of the zeroth Landau level on a two-dimensional lattice
The spectrum of massless Dirac fermions on the surface of a topological
insulator in a perpendicular magnetic field contains a -independent
"zeroth Landau level", protected by chiral symmetry. If the Dirac equation is
discretized on a lattice by the method of "Wilson fermions", the chiral
symmetry is broken and the zeroth Landau level is broadened when has
spatial fluctuations. We show how this lattice artefact can be avoided starting
from an alternative nonlocal discretization scheme introduced by Stacey. A key
step is to spatially separate the states of opposite chirality in the zeroth
Landau level, by adjoining and regions.Comment: Contribution to a special issue of Annals of Physics in memory of
Kostya Efeto
Tangent fermions: Dirac or Majorana fermions on a lattice without fermion doubling
I. Introduction
II. Two-dimensional lattice fermions
III. Methods to avoid fermion doubling (sine dispersion, sine plus cosine
dispersion, staggered lattice dispersion, linear sawtooth dispersion, tangent
dispersion)
IV. Topologically protected Dirac cone
V. Application: Klein tunneling (tangent fermions on a space-time lattice,
wave packet propagation)
VI. Application: Strong antilocalization (transfer matrix of tangent
fermions, topological insulator versus graphene)
VII. Application: Anomalous quantum Hall effect (gauge invariant tangent
fermions, topologically protected zeroth Landau level)
VIII. Application: Majorana metal (Dirac versus Majorana fermions, phase
diagram)
IX. OutlookComment: review article, 26 pages, 13 figures; V2: added three appendices, and
provided code for the various implementation
Magnetic breakdown spectrum of a Kramers-Weyl semimetal
We calculate the Landau levels of a Kramers-Weyl semimetal thin slab in a
perpendicular magnetic field . The coupling of Fermi arcs on opposite
surfaces broadens the Landau levels with a band width that oscillates
periodically in . We interpret the spectrum in terms of a one-dimensional
superlattice induced by magnetic breakdown at Weyl points. The band width
oscillations may be observed as -periodic magnetoconductance oscillations,
at weaker fields and higher temperatures than the Shubnikov-de Haas
oscillations due to Landau level quantization. No such spectrum appears in a
generic Weyl semimetal, the Kramers degeneracy at time-reversally invariant
momenta is essential.Comment: 13 pages, 18 figure
Dynamical simulation of the injection of vortices into a Majorana edge mode
The chiral edge modes of a topological superconductor can transport fermionic
quasiparticles, with Abelian exchange statistics, but they can also transport
non-Abelian anyons: Majorana zero-modes bound to a {\pi}-phase domain wall that
propagates along the boundary. Such an edge vortex is injected by the
application of an h/2e flux bias over a Josephson junction. Existing
descriptions of the injection process rely on the instantaneous scattering
approximation of the adiabatic regime, where the internal dynamics of the
Josephson junction is ignored. Here we go beyond that approximation in a
time-dependent many-body simulation of the injection process, followed by a
braiding of the mobile edge vortex with an immobile Abrikosov vortex in the
bulk of the superconductor. Our simulation sheds light on the properties of the
Josephson junction needed for a successful implementation of a flying Majorana
qubit.Comment: 13 pages 12 figure
Traumatic brain injury: Failure of the intravenous route for the administration of bone marrow stromal stem cells as treatment of chronic neurological sequels
Objetivo: Estudiar el posible efecto terapéutico de la administración intravenosa de células madre estromales
(CME) obtenidas de médula ósea para tratar las secuelas neurológicas en fase crónica tras una lesión cerebral
traumática.
Material y método: Se realizó un modelo de lesión cerebral traumática en ratas Wistar adultas y se estudió el
déficit neurológico inducido en el curso de los dos meses siguientes, por medio del test mNSS y el test Smart.
Tras ese tiempo, en fase de secuelas crónicamente establecidas, se administraron intravenosamente 15 x 106
CME (n:10) o suero fisiológico (n:10). En los dos meses siguientes se estudió la posible modificación de las secuelas
neurológicas.
Resultados: Cuando se compararon los resultados de la valoración funcional entre ambos grupos experimentales,
no se observaron diferencias estadísticamente significativas.
Conclusión: Nuestros resultados sugieren que el trasplante de CME por vía intravenosa, en una fase de secuelas
crónicamente establecidas tras una lesión traumática cerebral grave, no tiene efecto terapéuticoObjective: We studied the possible therapeutic effect of intravenous administration (noninvasive method) of
BMSCs to treat neurological sequels in a chronic stage after TBI.
Material and method: A model of TBI in adult Wistar rats was performed and we studied the neurological deficit
induced in the course of two months, through the mNSS and Smart tests. After this time, with established
sequels, 15 x 106 BMSCs (n = 10) or saline (n = 10) were administered intravenously. Changes in the neurological
deficits were studied in two months.
Results: Comparison of functional changes between both experimental groups showed no statistically significant
differences.
Conclusions: Our results suggest that transplantation of BMSCs intravenously, at a stage of established sequels
after severe TBI, has no therapeutic effectEsta investigación ha sido financiada por FUNDACIÓN MAPFR
The prognostic role of circulating tumor cells (CTCs) in lung cancer
© 2018 Kapeleris, Kulasinghe, Warkiani, Vela, Kenny, O'Byrne and Punyadeera. Lung cancer affects over 1. 8 million people worldwide and is the leading cause of cancer related mortality globally. Currently, diagnosis of lung cancer involves a combination of imaging and invasive biopsies to confirm histopathology. Non-invasive diagnostic techniques under investigation include "liquid biopsies" through a simple blood draw to develop predictive and prognostic biomarkers. A better understanding of circulating tumor cell (CTC) dissemination mechanisms offers promising potential for the development of techniques to assist in the diagnosis of lung cancer. Enumeration and characterization of CTCs has the potential to act as a prognostic biomarker and to identify novel drug targets for a precision medicine approach to lung cancer care. This review will focus on the current status of CTCs and their potential diagnostic and prognostic utility in this setting
Security devices based on liquid crystals doped with a colour dye
Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices.
Employing liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. Rubbed polyimide is used as alignment layer on each substrate of the LC cell. By rubbing the polyimide in different directions in each substrate it is possible to create any kind of symbols, drawings or motifs with a greyscale; the more complex the created device is, the more difficult is to fake it.
To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant colour dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display can obviously be used as backlight as well
Spectroscopic and Theoretical Study of CuI Binding to His111 in the Human Prion Protein Fragment 106-115
The ability of the cellular prion protein (PrPC) to bind copper in vivo points to a physiological role for PrPC in copper transport. Six copper binding sites have been identified in the nonstructured N-terminal region of human PrPC. Among these sites, the His111 site is unique in that it contains a MKHM motif that would confer interesting CuI and CuII binding properties. We have evaluated CuI coordination to the PrP(106-115) fragment of the human PrP protein, using NMR and X-ray absorption spectroscopies and electronic structure calculations. We find that Met109 and Met112 play an important role in anchoring this metal ion. CuI coordination to His111 is pH-dependent: at pH >8, 2N1O1S species are formed with one Met ligand; in the range of pH 5-8, both methionine (Met) residues bind to CuI, forming a 1N1O2S species, where N is from His111 and O is from a backbone carbonyl or a water molecule; at pH <5, only the two Met residues remain coordinated. Thus, even upon drastic changes in the chemical environment, such as those occurring during endocytosis of PrPC (decreased pH and a reducing potential), the two Met residues in the MKHM motif enable PrPC to maintain the bound CuI ions, consistent with a copper transport function for this protein. We also find that the physiologically relevant CuI-1N1O2S species activates dioxygen via an inner-sphere mechanism, likely involving the formation of a copper(II) superoxide complex. In this process, the Met residues are partially oxidized to sulfoxide; this ability to scavenge superoxide may play a role in the proposed antioxidant properties of PrPC. This study provides further insight into the CuI coordination properties of His111 in human PrPC and the molecular mechanism of oxygen activation by this site.Fil: Arcos López, Trinidad. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Qayyum, Munzarin. University of Stanford; Estados UnidosFil: Rivillas Acevedo, Lina. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Miotto, Marco César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina. Max Planck Laboratory for Structural Biology; ArgentinaFil: Grande Aztatzi, Rafael. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Fernandez, Claudio Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina. Max Planck Laboratory for Structural Biology; ArgentinaFil: Hedman, Britt. University of Stanford; Estados UnidosFil: Hodgson, Keith O.. University of Stanford; Estados UnidosFil: Vela, Alberto. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Solomon, Edward I.. University of Stanford; Estados UnidosFil: Quintanar, Liliana. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; Méxic
G-band Spectral Synthesis in Solar Magnetic Concentrations
Narrow band imaging in the G-band is commonly used to trace the small
magnetic field concentrations of the Sun, although the mechanism that makes
them bright has remained unclear. We carry out LTE syntheses of the G-band in
an assorted set of semi-empirical model magnetic concentrations. The syntheses
include all CH lines as well as the main atomic lines within the band-pass. The
model atmospheres produce bright G-band spectra having many properties in
common with the observed G-band bright points. In particular, the contrast
referred to the quiet Sun is about twice the contrast in continuum wavelengths.
The agreement with observations does not depend on the specificities of the
model atmosphere, rather it holds from single fluxtubes to MIcro-Structured
Magnetic Atmospheres. However, the agreement requires that the real G-band
bright points are not spatially resolved, even in the best observations. Since
the predicted G-band intensities exceed by far the observed values, we foresee
a notable increase of contrast of the G-band images upon improvement of the
angular resolution. According to the LTE modeling, the G-band spectrum emerges
from the deep photosphere that produces the continuum. Our syntheses also
predict solar magnetic concentrations showing up in continuum images but not in
the G-band . Finally, we have examined the importance of the CH
photo-dissociation in setting the amount of G-band absorption. It turns out to
play a minor role.Comment: To appear in ApJ, 554 n2 Jun 20, 33 pages and 9 figure
Fully Convolutional Networks for Continuous Sign Language Recognition
Continuous sign language recognition (SLR) is a challenging task that
requires learning on both spatial and temporal dimensions of signing frame
sequences. Most recent work accomplishes this by using CNN and RNN hybrid
networks. However, training these networks is generally non-trivial, and most
of them fail in learning unseen sequence patterns, causing an unsatisfactory
performance for online recognition. In this paper, we propose a fully
convolutional network (FCN) for online SLR to concurrently learn spatial and
temporal features from weakly annotated video sequences with only
sentence-level annotations given. A gloss feature enhancement (GFE) module is
introduced in the proposed network to enforce better sequence alignment
learning. The proposed network is end-to-end trainable without any
pre-training. We conduct experiments on two large scale SLR datasets.
Experiments show that our method for continuous SLR is effective and performs
well in online recognition.Comment: Accepted to ECCV202
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