University of Virginia

About: University of Virginia is a education organization based out in Charlottesville, Virginia, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 52543 authors who have published 113268 publications receiving 5220506 citations. The organization is also known as: U of V & UVa.

Advantages of diffuse radiation for terrestrial ecosystem productivity

Abstract: [1] Clouds and aerosols alter the proportion of diffuse radiation in global solar radiation reaching the Earth's surface. It is known that diffuse and direct beam radiation differ in the way they transfer through plant canopies and affect the summation of nonlinear processes like photosynthesis differently than what would occur at the leaf scale. We compared the relative efficiencies of canopy photosynthesis to diffuse and direct photosynthetically active radiation (PAR) for a Scots pine forest, an aspen forest, a mixed deciduous forest, a tallgrass prairie and a winter wheat crop. The comparison was based on the seasonal patterns of the parameters that define the canopy photosynthetic responses to diffuse PAR and those that define the responses to direct PAR. These parameters were inferred from half-hourly tower CO2 flux measurements. We found that: (1) diffuse radiation results in higher light use efficiencies by plant canopies; (2) diffuse radiation has much less tendency to cause canopy photosynthetic saturation; (3) the advantages of diffuse radiation over direct radiation increase with radiation level; (4) temperature as well as vapor pressure deficit can cause different responses in diffuse and direct canopy photosynthesis, indicating that their impacts on terrestrial ecosystem carbon assimilation may depend on radiation regimes and thus sky conditions. These findings call for different treatments of diffuse and direct radiation in models of global primary production, and studies of the roles of clouds and aerosols in global carbon cycle.

Hardware Trojan Attacks: Threat Analysis and Countermeasures

Abstract: Security of a computer system has been traditionally related to the security of the software or the information being processed. The underlying hardware used for information processing has been considered trusted. The emergence of hardware Trojan attacks violates this root of trust. These attacks, in the form of malicious modifications of electronic hardware at different stages of its life cycle, pose major security concerns in the electronics industry. An adversary can mount such an attack with an objective to cause operational failure or to leak secret information from inside a chip-e.g., the key in a cryptographic chip, during field operation. Global economic trend that encourages increased reliance on untrusted entities in the hardware design and fabrication process is rapidly enhancing the vulnerability to such attacks. In this paper, we analyze the threat of hardware Trojan attacks; present attack models, types, and scenarios; discuss different forms of protection approaches, both proactive and reactive; and describe emerging attack modes, defenses, and future research pathways.

Biogenic Hydrocarbons in the Atmospheric Boundary Layer: A Review

Abstract: Nonmethane hydrocarbons are ubiquitous trace atmospheric constituents yet they control the oxidation capacity of the atmosphere. Both anthropogenic and biogenic processes contribute to the release of hydrocarbons to the atmosphere. In this manuscript, the state of the science concerning biosynthesis, transport, and chemical transformation of hydrocarbons emitted by the terrestrial biosphere is reviewed. In particular, the focus is on isoprene, monoterpenes, and oxygen-ated hydrocarbons. The generated science during the last 10 years is reviewed to explain and quantify hydrocarbon emissions from vegetation and to discern impacts of biogenic hydrocarbons on local and regional atmospheric chemistry. Furthermore, the physiological and environmental processes controlling biosynthesis and production of hydrocarbon compounds are reported on. Many advances have been made on measurement and modeling approaches developed to quantify hydrocarbon emissions from leaves and forest ecosystems. A synthesis of the atmospheric chemistry of biogenic hydrocarbons and their role in the formation of oxidants and aerosols is presented. The integration of biogenic hydrocarbon kinetics and atmospheric physics into mathematical modeling systems is examined to assess the contribution of biogenic hydrocarbons to the formation of oxidants and aerosols, thereby allowing us to study their impacts on the earth's climate system and to develop strategies to reduce oxidant precursors in affected regions.

Maintaining Mobility in Late Life. I. Demographic Characteristics and Chronic Conditions

Abstract: To assess the role of demographic factors and chronic conditions in maintaining mobility in older persons, this study utilized longitudinal data collected as part of the Established Populations for Epidemiologic Studies of the Elderly between 1981 and 1987 on 6,981 men and women aged 65 years and older in East Boston, Massachusetts; Iowa and Washington counties, Iowa; and New Haven, Connecticut. Results are presented for those who at baseline reported intact mobility, defined as the ability to climb stairs and walk a half mile without help, and who were followed annually for up to 4 years for changes in mobility status. Age, income, education, and chronic conditions present at baseline and occurring during follow-up were evaluated for their association with loss of mobility. Over the follow-up period, 55.1% of subjects maintained mobility, 36.2% lost mobility, and 8.7% died without evidence of mobility loss prior to death. In both men and women, increasing age and lower income levels were associated with increased risk of losing mobility, even after controlling for the presence of chronic conditions at baseline. After adjustment for age, income, and chronic conditions, lower education levels were a significant risk factor for mobility loss in men, but not in women. Baseline reports of previous heart attack, stroke, high blood pressure, diabetes, dyspnea, and exertional leg pain were associated with small but significant risks for mobility loss. There was a stepwise increase in the risk of mobility loss according to the number of chronic conditions present at baseline that was very consistent between men and women. The occurrence during the study of a new heart attack, stroke, cancer, or hip fracture was associated with a substantially greater risk of mobility loss than was associated with the presence of these conditions at baseline.

A radio pulsar/x-ray binary link.

Abstract: Radio pulsars with millisecond spin periods are thought to have been spun up by the transfer of matter and angular momentum from a low-mass companion star during an x-ray-emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have been detected. Here we report on detection and follow-up observations of a nearby radio millisecond pulsar (MSP) in a circular binary orbit with an optically identified companion star. Optical observations indicate that an accretion disk was present in this system within the past decade. Our optical data show no evidence that one exists today, suggesting that the radio MSP has turned on after a recent LMXB phase.