Virginia Tech

About: Virginia Tech is a education organization based out in Blacksburg, Virginia, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 42053 authors who have published 95234 publications receiving 2905142 citations. The organization is also known as: VT & Virginia Polytechnic Institute and State University.

Alternative Polymer Systems for Proton Exchange Membranes (PEMs)

Abstract: Fuel cells have the potential to become an important energy conversion technology. Research efforts directed toward the widespread commercialization of fuel cells have accelerated in light of ongoing efforts to develop a hydrogen-based energy economy to reduce dependence on foreign oil and decrease pollution. Proton exchange membrane (also termed “polymer electrolyte membrane”) (PEM) fuel cells employing a solid polymer electrolyte to separate the fuel from the oxidant were first deployed in the Gemini space program in the early 1960s using cells that were extremely expensive and had short lifetimes due to the oxidative degradation of their sulfonated polystyrene-divinylbenzene copolymer membranes. These cells were considered too costly and short-lived for real-world applications. The commercialization of Nafion by DuPont in the late 1960s helped to demonstrate the potential interest in terrestrial applications for fuel cells, although its major focus was in chloroalkali processes. PEM fuel cells are being developed for three main applications: automotive, stationary, and portable power. Each of these applications has its unique operating conditions and material requirements. Common themes critical to all high performance proton exchange membranes include (1) high protonic conductivity, (2) low electronic conductivity, (3) low permeability to fuel and oxidant, (4) low water transport through diffusion and electro-osmosis, (5) oxidative and hydrolytic stability, (6) good mechanical properties in both the dry and hydrated states, (7) cost, and (8) capability for fabrication into membrane electrode assemblies (MEAs). Nearly all existing membrane materials for PEM fuel cells rely on absorbed water and its interaction with acid groups to produce protonic conductivity. Due to the large fraction of absorbed water in the membrane, both mechanical properties and water transport become key issues. Devising systems that can conduct protons with little or no water is perhaps the greatest challenge for new membrane materials. Specifically, for automotive applications the U.S. Department of Energy has currently established a guideline of 120 °C and 50% relative humidity as target operating conditions, and a goal of 0.1 S/cm for the protonic conductivity of the membrane. New membranes that have significantly reduced methanol permeability and water transport (through diffusion and electro-osmotic drag) are required for portable power oriented direct methanol fuel cells (DMFCs), where a liquid methanol fuel highly diluted in water is used at generally <90 °C as the source of protons. Unreacted methanol at the anode can diffuse through the membrane and react at the cathode, lowering the voltage efficiency of the cell and reducing the system’s fuel efficiency. The methanol is usually delivered to the anode as a dilute, for example, 1 M (or less), solution (3.2 wt %), and relatively thick Nafion 117 (1100 EW, 7 mil ∼ 178 μm thick) is used to reduce methanol crossover. The dilute methanol feed increases the system’s complexity and reduces the energy density of the fuel, while the thick Nafion membrane increases the resistive losses of the cell, especially when compared to the thinner membranes that are used in hydrogen/air systems. The presence of excessive amounts of water at the cathode through diffusion and electro-osmosis * To whom correspondence should be addressed. E-mail: jmcgrath@vt.edu. † Sandia National Laboratory. ‡ Case Western Reserve University. § Los Alamos National Laboratory. | Virginia Polytechnic Institute and State University. 4587 Chem. Rev. 2004, 104, 4587−4612

A review of power harvesting using piezoelectric materials (2003–2006)

Abstract: The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. Current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of a disposable nature to allow the device to function over extended periods of time. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. A number of sources of harvestable ambient energy exist, including waste heat, vibration, electromagnetic waves, wind, flowing water, and solar energy. While each of these sources of energy can be effectively used to power remote sensors, the structural and biological communities have placed an emphasis on scavenging vibrational energy with piezoelectric materials. This article will review recent literature in the field of power harvesting and present the current state of power harvesting in its drive to create completely self-powered devices.

A Vision of 6G Wireless Systems: Applications, Trends, Technologies, and Open Research Problems

Abstract: The ongoing deployment of 5G cellular systems is continuously exposing the inherent limitations of this system, compared to its original premise as an enabler for Internet of Everything applications. These 5G drawbacks are spurring worldwide activities focused on defining the next-generation 6G wireless system that can truly integrate far-reaching applications ranging from autonomous systems to extended reality. Despite recent 6G initiatives (one example is the 6Genesis project in Finland), the fundamental architectural and performance components of 6G remain largely undefined. In this article, we present a holistic, forward-looking vision that defines the tenets of a 6G system. We opine that 6G will not be a mere exploration of more spectrum at high-frequency bands, but it will rather be a convergence of upcoming technological trends driven by exciting, underlying services. In this regard, we first identify the primary drivers of 6G systems, in terms of applications and accompanying technological trends. Then, we propose a new set of service classes and expose their target 6G performance requirements. We then identify the enabling technologies for the introduced 6G services and outline a comprehensive research agenda that leverages those technologies. We conclude by providing concrete recommendations for the roadmap toward 6G. Ultimately, the intent of this article is to serve as a basis for stimulating more out-of-the-box research around 6G.

Role of superoxide dismutases (SODs) in controlling oxidative stress in plants

Abstract: Reactive O2 species (ROS) are produced in both unstressed and stressed cells. Plants have welldeveloped defence systems against ROS, involving both limiting the formation of ROS as well as instituting its removal. Under unstressed conditions, the formation and removal of O2 are in balance. However, the defence system, when presented with increased ROS formation under stress conditions, can be overwhelmed. Within a cell, the superoxide dismutases (SODs) constitute the first line of defence against ROS. Specialization of function among the SODs may be due to a combination of the influence of subcellular location of the enzyme and upstream sequences in the genomic sequence. The commonality of elements in the upstream sequences of Fe, Mn and CuuZn SODs suggests a relatively recent origin for those regulatory regions. The differences in the upstream regions of the three FeSOD genes suggest differing regulatory control which is borne out in the research literature. The finding that the upstream sequences of Mn and peroxisomal CuuZn SODs have three common elements suggests a common regulatory pathway. The tools are available to dissect further the molecular basis for antioxidant defence responses in plant cells. SODs are clearly among the most important of those defences, when coupled with the necessary downstream events for full detoxification of ROS.