Ribbon homology cobordisms

We study 4-dimensional homology cobordisms without 3-handles, showing that they interact nicely with Thurston geometries, character varieties, and instanton and Heegaard Floer homologies. Using these, we derive obstructions to such cobordisms, with topological applications.Comment: 50 pages, 6 figures. Major reorganization of sections for improved exposition. Result on Dehn surgery extended from Seifert fibered homology spheres to rational homology sphere

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

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

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 $B$. The coupling of Fermi arcs on opposite surfaces broadens the Landau levels with a band width that oscillates periodically in $1/B$. 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 $1/B$-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

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

Construction and classification of Z₂s-linear Hadamard codes

The Z₂s-additive and Z₂Z₄-additive codes are subgroups of Z₂s^n and Z₂^α × Z₄^β, respectively. Both families can be seen as generalizations of linear codes over Z₂ and Z₄. A Z₂s-linear (resp. Z₂Z₄-linear) Hadamard code is a binary Hadamard code which is the Gray map image of a Z₂s-additive (resp. Z₂Z₄-additive) code. It is known that there are exactly ⌊(t−1)/2⌋ and ⌊t/2⌋ nonequivalent Z₂Z₄-linear Hadamard codes of length 2ᵗ, with α=0 and α≠0, respectively, for all t≥3. In this paper, new Z₂s-linear Hadamard codes are constructed for s>2, which are not equivalent to any Z₂Z₄-linear Hadamard code. Moreover, for each s>2, it is claimed that the new constructed nonlinear Z₂-linear Hadamard codes of length 2ᵗ are pairwise nonequivalent

Determinación de la betalactamasa en cepas de Neisseria gonorrhoeae

The appearance of strains of N. gonorrhoeae resistant to different antibiotics, which could be caused by plasmids or by mutations, require constant surveillance so as to revise the schemes of treatment. In our country the existent studies to determine the problem of strains of N. gonorrhoeae resistent to penicilin have been scarce therefore it was decided to determine the presence of beta lactamase and antimicrobe susceptibility from isolates of this pathogen obtained from different health services around the country. From 89 strains studied 46 (52%) were producers of beta lactamase; 11% of these presented resistance to spectinomycin and 96% to tetracycline. In the strains which did not produce beta lactamase, 61% were resistant to tetracycline and 2% to penicilin: additionally 98% of the NPBL strains presented a moderate sensitivity to penicilin. All the PBL and NPBL strains were sensitive to ceftriaxone. This data confirms the circulation of PBL strains of N. gonorrhoeae throughout different regions of the country and supports the recommendation to maintain surveillance, permitting the determination of the real frequency of these strains in our country.La aparición de cepas de N. gonorrhoeae resistentes a diferentes antibióticos, la cual puede estar mediada por plásmidos o por mutaciones, requiere una continua vigilancia, con el fin de revisar los esquemas de tratamiento. En nuestro medio, los estudios realizados para establecer el problema de resistencia de cepas de N. gonorrhoeae a la penicilina han sido escasos, por esto decidimos determinar, en aislamientos de este patógeno obtenidos en diferentes servicios de salud del país, la presencia de la betalactamasa y la susceptibilidad antimicrobiana. De 89 cepas estudiadas, 46 (52%) fueron productoras de beta lactamasa (PBL); 11% de ellas presentaron resistencia a la espectinomicina y 96% a la tetraciclina. En las cepas no productoras de beta lactamasa, el 61% fue resistente a la tetraciclina y el 2% a la penicilina; adicionalmente el 98% de las cepas NPBL presentaron una sensibilidad moderada a la penicilina. Todas las cepas, PBL y NPBL, fueron sensibles a la ceftriaxona. Estos datos confirman la circulación de cepas de N. gonorrhoeae PBL en diferentes regiones del país y apoyan la recomendación de mantener una vigilancia que nos permita conocer la verdadera frecuencia de ellas en nuestro medio