Capacity Bounds for a Class of Interference Relay Channels

The capacity of a class of Interference Relay Channels (IRC) -the Injective Semideterministic IRC where the relay can only observe one of the sources- is investigated. We first derive a novel outer bound and two inner bounds which are based on a careful use of each of the available cooperative strategies together with the adequate interference decoding technique. The outer bound extends Telatar and Tse's work while the inner bounds contain several known results in the literature as special cases. Our main result is the characterization of the capacity region of the Gaussian class of IRCs studied within a fixed number of bits per dimension -constant gap. The proof relies on the use of the different cooperative strategies in specific SNR regimes due to the complexity of the schemes. As a matter of fact, this issue reveals the complex nature of the Gaussian IRC where the combination of a single coding scheme for the Gaussian relay and interference channel may not lead to a good coding scheme for this problem, even when the focus is only on capacity to within a constant gap over all possible fading statistics.Comment: 23 pages, 6 figures. Submitted to IEEE Transactions on Information Theory (revised version

A Novel Transmission Scheme for the KK-user Broadcast Channel with Delayed CSIT

The state-dependent $K$-user memoryless Broadcast Channel~(BC) with state feedback is investigated. We propose a novel transmission scheme and derive its corresponding achievable rate region, which, compared to some general schemes that deal with feedback, has the advantage of being relatively simple and thus is easy to evaluate. In particular, it is shown that the capacity region of the symmetric erasure BC with an arbitrary input alphabet size is achievable with the proposed scheme. For the fading Gaussian BC, we derive a symmetric achievable rate as a function of the signal-to-noise ratio~(SNR) and a small set of parameters. Besides achieving the optimal degrees of freedom at high SNR, the proposed scheme is shown, through numerical results, to outperform existing schemes from the literature in the finite SNR regime.Comment: 30 pages, 3 figures, submitted to IEEE Transactions on Wireless Communications (revised version

On the Secrecy Degress of Freedom of the Multi-Antenna Block Fading Wiretap Channels

We consider the multi-antenna wiretap channel in which the transmitter wishes to send a confidential message to its receiver while keeping it secret to the eavesdropper. It has been known that the secrecy capacity of such a channel does not increase with signal-to-noise ratio when the transmitter has no channel state information (CSI) under mild conditions. Motivated by Jafar's robust interference alignment technique, we study the so-called staggered multi-antenna block-fading wiretap channel where the legitimate receiver and the eavesdropper have different temporal correlation structures. Assuming no CSI at transmitter, we characterize lower and upper bounds on the secrecy degrees of freedom (s.d.o.f.) of the channel at hand. Our results show that a positive s.d.o.f. can be ensured whenever two receivers experience different fading variation. Remarkably, very simple linear precoding schemes provide the optimal s.d.o.f. in some cases of interest.Comment: to appear in Proc. of IEEE International Symposium on Information Theory (ISIT2010

A Comparative Study of Insertion Loss of Traffic Noise Barriers in Georgia

In this paper, three types of traffic noise barriers, interlocking steel panels, precast concrete panels, and Paragon panel 23-T, were evaluated in terms of insertion loss. Field test was conducted for the noise barriers recently installed as part of the Northwest Express Project in Georgia. The noise insertion loss was measured as noise difference in A-weighted decibels (dBA) immediately before and after the barriers. The insertion loss was then evaluated by correlating with noise barrier types and other influential variables, including the separation distance of barriers from traffic, the level of traffic, wind speed, and pavement types. The results showed that under prevailing conditions represented by other influential variables, all three barrier types achieved an insertion loss in the range of 7.02 dBA to 13.58 dBA, exceeding the noise reduction design goal of 7 dBA as stated in the Georgia Department of Transportation’s noise abatement policy. Among the three, the Paragon panel 23-T barriers effected the highest insertion loss, followed by the precast concrete panel barriers and the interlocking steel panel barriers

Análisis y comparación de políticas de transporte urbano China-España

El crecimiento económico en China ha sido muy importante en las dos últimas décadas, provocando un incremento de la urbanización, fenómeno que también se ha producido en España, aunque en menor medida. Las pautas de movilidad han experimentado cambios significativos, debido a que la dispersión urbana ha provocado un incremento en el número de viajes, en las distancias de viaje y en los niveles de motorización de la población, que en las ciudades de China ha crecido, sólo en 2007, en torno a un 10%, mientras que en las ciudades españolas lo ha hecho en un 5%. Esta nueva situación ha provocado un cambio en las pautas de viaje, sobre todo en China, ya que el peso de la bicicleta en el reparto modal de viajes ha disminuido entre 10 y 20 puntos porcentuales, mientras que el transporte público, y sobre todo, el uso del coche, han aumentado. Las políticas implementadas por los gobiernos locales, regionales y nacionales también han influido: así, en China, se ha fomentado el uso del coche como motor de crecimiento económico y desarrollo social, mientras que en España, desde distintas administraciones, se viene fomentado el uso del transporte público frente al uso del coche. Estas similitudes y diferencias entre ambos países hace interesante realizar un análisis comparativo de la movilidad en las principales ciudades chinas y españolas, utilizándose algunos indicadores socioeconómicos y de movilidad. El objetivo del análisis es comparar las diferentes políticas llevadas a cabo en ambos países y evaluar la efectividad de las mismas y las diferencias de resultados conseguidos

Poxviruses in bats … so what?

Poxviruses are important pathogens of man and numerous domestic and wild animal species. Cross species (including zoonotic) poxvirus infections can have drastic consequences for the recipient host. Bats are a diverse order of mammals known to carry lethal viral zoonoses such as Rabies, Hendra, Nipah, and SARS. Consequent targeted research is revealing bats to be infected with a rich diversity of novel viruses. Poxviruses were recently identified in bats and the settings in which they were found were dramatically different. Here, we review the natural history of poxviruses in bats and highlight the relationship of the viruses to each other and their context in the Poxviridae family. In addition to considering the zoonotic potential of these viruses, we reflect on the broader implications of these findings. Specifically, the potential to explore and exploit this newfound relationship to study coevolution and cross species transmission together with fundamental aspects of poxvirus host tropism as well as bat virology and immunology

Phase-tunable multiple Andreev reflections in a quantum spin Hall strip

A quantum spin Hall strip where different edges are contacted by $s$-wave superconductors with a phase difference $\phi$ supports Majorana Kramers pairs (MKPs). We study the transport properties of this setup in a four-terminal normal metal (N)/insulator (I)/superconductor (S) and S/I/S junction. The tunneling spectroscopy for the N/I/S junction reveals that the signature of MKPs is that the conductance is quantized by $4e^2/h$ at zero bias and suppressed at the gap edges. In the S/I/S junction, the subharmonic gap structure displays a phase-tuned even-odd effect, where all odd spikes disappear in the presence of MKPs and the remaining even spikes split when superconductors forming the junction have different gaps. We explain these features by showing that midgap bound states enhance the transmission of the even order multiple Andreev reflections, while the reduced density of states at the gap edges suppresses the odd order ones.Comment: 9 pages, 5 figure

Enhanced Superconductivity and Suppression of Charge-density Wave Order in 2H-TaS2_2 in the Two-dimensional Limit

As superconductors are thinned down to the 2D limit, their critical temperature $T_c$ typically decreases. Here we report the opposite behavior, a substantial enhancement of $T_c$ with decreasing thickness, in 2D crystalline superconductor 2H-TaS$_2$. Remarkably, in the monolayer limit, $T_c$ increases to 3.4 K compared to 0.8 K in the bulk. Accompanying this trend in superconductivity, we observe suppression of the charge-density wave (CDW) transition with decreasing thickness. To explain these trends, we perform electronic structure calculations showing that a reduction of the CDW amplitude results in a substantial increase of the density of states at the Fermi energy, which contributes to the enhancement of $T_c$. Our results establish ultra-thin 2H-TaS$_2$ as an ideal platform to study the competition between CDW order and superconductivity