A Family of Hybrid Space-Time Codes for MIMO Wireless Communications

Hybrid MIMO space-time codes combine the benefits of spatial multiplexing with diversity gain to achieve both high spectral efficiency and link reliability. In this paper, we present a family of hybrid codes, known as LD STBC-VBLAST codes, along with a receiver architecture suitable for low-complexity hardware implementation. We show that, under Rayleigh fading, the performance of LD STBC-VBLAST codes is superior to other recently proposed hybrid codes. We also present a technique to derive, from a given propagation scenario, spatially correlated MIMO channel models adequate for space-time coding performance analysis. Using this technique, we evaluate the performance of LD STBC-VBLAST codes under several correlated channels.ITESO, A.C.ITSONCINVESTAV-IPNPROME

EFECTO DE LA LONGITUD DEL DIÁMETRO EN LA ESTABILIDAD TÉRMICA DE LA CAPA LIBRE DE LAS MEMORIAS RAM MAGNÉTICAS

ResumenUna de las nuevas aplicaciones del magnetismo en medios de almacenamiento de datos son las memorias RAM magnéticas (MRAM, por sus siglas en inglés). El periodo de tiempo que se puede mantener un bit en una MRAM está íntimamente relacionado con la estabilidad térmica del dispositivo, la cual depende de las propiedades de los materiales utilizados y de la geometría. En el presente trabajo presentamos un estudio de cómo afecta el diámetro del dispositivo a la estabilidad térmica de una MRAM. A partir de los resultados obtenidos es posible explicar que al incrementar del diámetro de una MRAM, en algún punto el proceso de inversión de la magnetización deja de ser una rotación coherente y se convierte un movimiento de pared de dominio, lo cual a su vez ocasiona que la barrera de energía no sea proporcional al volumen, presentándose una disminución en el valor de la barrera de energía.Palabras Claves: Almacenamiento, Estabilidad, MEP, MRAM. EFFECT OF THE LENGTH OF THE DIAMETER ON THE THERMAL STABILITY OF THE FREE LAYER OF MAGNETIC RAM MEMORIESAbstractOne of the novel applications of magnetism in data storage is the use of Magnetic Random Access Memories (MRAM). The period that a bit can be stored in such a device is closely related to the thermal stability, which in turn depends on the materials used, and on the geometry. In the present work, we performed a study on the effect of the junction diameter on the thermal stability of an MRAM. From our results it is possible to explain the reason why when the diameter of an MRAM in increased the reversal process goes from coherent rotation to domain wall movement, leading to a decrease in the energy barrier.Keywords: MEP, MRAM, Storage, Stability

Reconstructing Native American Population History

The peopling of the Americas has been the subject of extensive genetic, archaeological and linguistic research; however, central questions remain unresolved1–5. One contentious issue is whether the settlement occurred via a single6–8 or multiple streams of migration from Siberia9–15. The pattern of dispersals within the Americas is also poorly understood. To address these questions at higher resolution than was previously possible, we assembled data from 52 Native American and 17 Siberian groups genotyped at 364,470 single nucleotide polymorphisms. We show that Native Americans descend from at least three streams of Asian gene flow. Most descend entirely from a single ancestral population that we call “First American”. However, speakers of Eskimo-Aleut languages from the Arctic inherit almost half their ancestry from a second stream of Asian gene flow, and the Na-Dene-speaking Chipewyan from Canada inherit roughly one-tenth of their ancestry from a third stream. We show that the initial peopling followed a southward expansion facilitated by the coast, with sequential population splits and little gene flow after divergence, especially in South America. A major exception is in Chibchan-speakers on both sides of the Panama Isthmus, who have ancestry from both North and South America

Association Between Preexisting Versus Newly Identified Atrial Fibrillation and Outcomes of Patients With Acute Pulmonary Embolism

Background Atrial fibrillation (AF) may exist before or occur early in the course of pulmonary embolism (PE). We determined the PE outcomes based on the presence and timing of AF. Methods and Results Using the data from a multicenter PE registry, we identified 3 groups: (1) those with preexisting AF, (2) patients with new AF within 2 days from acute PE (incident AF), and (3) patients without AF. We assessed the 90-day and 1-year risk of mortality and stroke in patients with AF, compared with those without AF (reference group). Among 16 497 patients with PE, 792 had preexisting AF. These patients had increased odds of 90-day all-cause (odds ratio [OR], 2.81; 95% CI, 2.33-3.38) and PE-related mortality (OR, 2.38; 95% CI, 1.37-4.14) and increased 1-year hazard for ischemic stroke (hazard ratio, 5.48; 95% CI, 3.10-9.69) compared with those without AF. After multivariable adjustment, preexisting AF was associated with significantly increased odds of all-cause mortality (OR, 1.91; 95% CI, 1.57-2.32) but not PE-related mortality (OR, 1.50; 95% CI, 0.85-2.66). Among 16 497 patients with PE, 445 developed new incident AF within 2 days of acute PE. Incident AF was associated with increased odds of 90-day all-cause (OR, 2.28; 95% CI, 1.75-2.97) and PE-related (OR, 3.64; 95% CI, 2.01-6.59) mortality but not stroke. Findings were similar in multivariable analyses. Conclusions In patients with acute symptomatic PE, both preexisting AF and incident AF predict adverse clinical outcomes. The type of adverse outcomes may differ depending on the timing of AF onset.info:eu-repo/semantics/publishedVersio

Cálculo de la incertidumbre estándar mediante la técnica de Monte Carlo para la medición de la topografía y del campo de desplazamiento mediante ESPI

La ventaja del uso de las técnicas interferométricas basados en el patrón de moteado ESPI (electronic speckle pattern interferometry) es única ya que se pueden hacer mediciones muy precisas de los campos de desplazamientos que ocurren en la superficie de algún elemento mecánico cuando se deforma. Sin embargo, cuando se utiliza la iluminación divergente, se observa que la medición de los campos de desplazamientos está en función de la topografía del objeto. Por tal motivo, antes de evaluar las deformaciones mecánicas por la técnica ESPI con iluminación divergente es necesario conocer la topografía del objeto. La estimación de la incertidumbre estándar de las mediciones de los campos de desplazamiento debe de contemplar la incertidumbre de las mediciones de la topografía que se propaga debido a la ley generalizada de la propagación de la incertidumbre. En este trabajo se muestra el uso de la técnica de Monte Carlo para el cálculo de la incertidumbre estándar para la las mediciones de los campos de desplazamiento y la topografía de superficie de objetos mediante la técnica de interferometría electrónica del patrón de moteado con iluminación dual y divergente

An exact solution for the level-crossing rate and the average duration of fades of the envelope of sum-of-cisoids processes

Authors version of an article published in the journal: Procedia Technology. Also available from the publisher at: http://dx.doi.org/10.1016/j.protcy.2012.03.004Sum-of-cisoids (SOC) processes provide a physically and numerically appealing framework for the modelling and simulation of a wide class of mobile radio channels. This paper is concerned with the problem of finding a general solution for the level-crossing rate (LCR) and the average duration of fades (ADF) of the envelope of SOC processes. Exact expressions are derived for the LCR and the ADF by taking into account that the inphase component, the quadrature component, and the time derivatives of the inphase and quadrature components of SOC processes are in general mutually correlated. The validity of the theoretical results is confirmed by simulation results. This study reveals new insight into the fading behaviour of SOS-based multipath fading channel models. The results of this study are indispensable for the performance assessment of mobile radio channel simulators employing the SOC principle

A proposal to measure the similarity between retinal vessel segmentations images

We propose a novel approach for the assessment of the similarity of retinal vessel segmentation images that is based on linking the standard performance metrics of a segmentation algorithm, with the actual structural properties of the images through the fractal dimension. Method: We apply our methodology to compare the vascularity extracted by automatic segmentation against manually segmented images. Results: We demonstrate that the strong correlation between the standard metrics and fractal dimension is preserved regardless of the size of the subimages analyzed. Discussion or Conclusion: We show that the fractal dimension is correlated to the segmentation algorithm’s performance and therefore it can be used as a comparison metric.Proponemos una nueva metodología para establecer la similitud entre imágenes segmentadas de la red vascular de la retina. El método está basado en vincular métricas estándar con propiedades estructurales a través de la dimensión fractal. Método: Aplicamos nuestra metodología para comparar la vascularidad de imágenes de la retina extraídas de forma automática contra segmentaciones hechas de forma manual. Resultados: Demostramos que existe una fuerte correlación entre las métricas estándar y la dimensión fractal y que esta prevalece incluso si se divide la imagen en sub-imágenes. Discusión o Conclusión: Mostramos que la dimensión fractal esta correlacionada con el rendimiento del algoritmo de segmentación y por tanto puede ser usado como métrica

Carrier Diversity Incorporation to Low-Complexity Near-ML Detection for Multicarrier Systems over V2V Radio Channel

Inter-carrier interference (ICI) in vehicle to vehicle (V2V) orthogonal frequency division multiplexing (OFDM) systems is a common problem that makes the process of detecting data a demanding task. Mitigation of the ICI in V2V systems has been addressed with linear and non-linear iterative receivers in the past; however, the former requires a high number of iterations to achieve good performance, while the latter does not exploit the channel’s frequency diversity. In this paper, a transmission and reception scheme for low complexity data detection in doubly selective highly time varying channels is proposed. The technique couples the discrete Fourier transform spreading with non-linear detection in order to collect the available channel frequency diversity and successfully achieving performance close to the optimal maximum likelihood (ML) detector. When compared with the iterative LMMSE detection, the proposed system achieves a higher performance in terms of bit error rate (BER), reducing the computational cost by a third-part when using 48 subcarriers, while in an OFDM system with 512 subcarriers, the computational cost is reduced by two orders of magnitude

IMPLEMENTACIÓN DE GESTIÓN DE SERVICIOS DE TECNOLOGÍAS DE LA INFORMACIÓN DESDE EL DISEÑO DE UN LABORATORIO UNIVERSITARIO PARA LA ENSEÑANZA DE REDES DE CÓMPUTO (IMPLEMENTATION OF INFORMATION TECHNOLOGY SERVICES MANAGEMENT FROM THE DESIGN OF A UNIVERSITY LABORATORY FOR THE TEACHING OF COMPUTER NETWORKS)

Resumen En el presente trabajo describimos como se resolvieron los dos principales problemas que enfrentaba la carrera de ingeniería en informática del Instituto Tecnológico Superior de Purísima del Rincón: falta de un laboratorio de redes y falta de control en los procesos. Se incorporó la gestión de servicios de TI (Tecnologías de la Información) basado en las buenas prácticas descritas por ITIL (Information Technology Infrastructure Library) en un laboratorio de redes para CCNA (Cisco Certified Network Associate). Su implementación se realizó en cinco fases. La primera fue el diseño lógico y físico del laboratorio. En la segunda fase se seleccionaron los estándares para el cableado estructurado, y se empezó una solicitud para ser aceptados como academia Cisco. En la tercera fase se puso en funcionamiento el laboratorio CCNA. En la cuarta fase se configuró la seguridad perimetral en los equipos. Por último, a través de ITIL se estandarizaron las solicitudes de préstamo, prácticas y mantenimiento de los equipos. Palabras Clave: Estándares de calidad, laboratorio de redes, servicios de TI. Abstract This paper describes how the two principal problems faced by the computer science engineering at the Instituto Superior de Purísisma del Rincon were solved: lack of a networking laboratory and lack of control on the processes. The IT (Information Technology) service management best practice framework known as ITIL (Information Technology Infrastructure Library) was implemented in the networking lab for the CCNA (Cisco Certified Network Associate) certification. This work was carried out in five phases. The first was the logical and physical design of the laboratory. In the second phase, the standards for structured cabling were selected, and the Cisco academy requirements were fulfilled. In the third phase, the CCNA laboratory was made operational. In the fourth phase, perimeter security was configured. Finally, through ITIL, laboratory scheduling, laboratory equipment loan requests, and equipment maintenance were standardized. Keywords: quality standards, networking laboratory, IT services