Texas A&M University

About: Texas A&M University is a education organization based out in College Station, Texas, United States. It is known for research contribution in the topics: Population & Finite element method. The organization has 72169 authors who have published 164372 publications receiving 5764236 citations.

Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

Abstract: We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.

The Electrocatalysis of Oxygen Evolution on Perovskites

Abstract: Measurements of the oxygen evolution reaction have been made on eighteen substituted perovskites containing first‐row transition metal ions. Rates are reported at equilibrium and at an overpotential of 0.3V. Electrode kinetic parameters are given, including roughness factors. The rate does not depend on semiconductor‐type properties. It increases as the pH of zero charge, at which the occupancy of OH− and H+ at the interface becomes equal, moves in an alkaline direction, with decrease of magnetic moment, with decrease of stability of the perovskite lattice, with decrease of the enthalpy of formation of the transition metal hydroxides, and with increase in the number of d‐electrons in the transition metal ion. The accuracy of the roughness factor measurements are affected by weakness in knowledge of true double layer capacities. The value assumed here, 60 μF cm−2, may be accurate to only ± 100%. Models are given which suggest that the pores are active throughout. The correlations between the rate and electronic properties are consistent with rate‐determining steps which involve desorption of OH radicals, e.g., . An MO discussion suggests that the electrocatalysis increases with increased occupancy of the antibonding orbitals of MZ‒OH. Earlier interpretations include the concept that an increase of the rate occurs because of increasing overlap between the orbitals of the transition metal ion and the spσorbital of O. However, this theory is based on only three different materials, in which rate‐determining step changes. An interpretation based upon nonstoichiometry is shown to be consistent with observed trends, but insufficient to explain their magnitude. The electrical and chemical contributions to the rate are analyzed. The value of agr; is related via bond strength considerations to the MZ‒OH bond strengths. The relative electrocatalysis discussed is limited to an overpotential which corresponds to a practical range of rates on the faster catalysts. A volcano relation for oxygen evolution on perovskites seems likely. Future electrocatalysts are predicted.

Trichoderma : the genomics of opportunistic success

Abstract: Trichoderma is a genus of common filamentous fungi that display a remarkable range of lifestyles and interactions with other fungi, animals and plants. Because of their ability to antagonize plant-pathogenic fungi and to stimulate plant growth and defence responses, some Trichoderma strains are used for biological control of plant diseases. In this Review, we discuss recent advances in molecular ecology and genomics which indicate that the interactions of Trichoderma spp. with animals and plants may have evolved as a result of saprotrophy on fungal biomass (mycotrophy) and various forms of parasitism on other fungi (mycoparasitism), combined with broad environmental opportunism.

A rapid method for extraction of cotton (Gossypium spp.) genomic DNA suitable for RFLP or PCR analysis

Abstract: Extraction of high-quality genomic DNA fromGossypium (cotton) species is difficult due to high levels of polysaccharide, oxidizable quinones, and other interfering substances. We describe a procedure that consistently permits isolation of cotton genomic DNA of satisfactory size and quality for RFLP and PCR analysis, as well as for most routine cloning applications. Several antioxidants, phenol-binding reagents, and phenol oxidase inhibitors are used throughout the procedure, and most polysaccharides are eliminated early in the procedure by isolation of nuclei.

Midgap surface states as a novel signature for dxa2-xb2-wave superconductivity.

Abstract: It is shown that a sizable areal density of midgap states exists on a {110} surface of a ${\mathit{d}}_{\mathit{x}\mathit{a}}^{2}$-${\mathit{x}}_{\mathit{b}}^{2}$-wave superconductor, which can either have vacuum or an insulator at the surface, or be separated from vacuum or an insulator by a clean, size-quantized, normal metal overlayer. These ``midgap'' states have many observable consequences---some of which are briefly discussed here---which can be used as a clear signature to distinguish between d-wave and anisotropic s-wave superconductors.