University of Arkansas

About: University of Arkansas is a education organization based out in Fayetteville, Arkansas, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 17225 authors who have published 33329 publications receiving 941102 citations. The organization is also known as: Arkansas & UA.

Application of nonlocal elastic shell theory in wave propagation analysis of carbon nanotubes

Abstract: Wave propagation in carbon nanotubes (CNTs) is studied based on the proposed nonlocal elastic shell theory. Both theoretical analyses and numerical simulations have explicitly revealed the small-scale effect on wave dispersion relations for different CNT wavenumbers in the longitudinal and circumferential directions and for different wavelengths in the circumferential direction. The applicability of the proposed nonlocal elastic shell theory is especially explored and analyzed based on the differences between the wave solutions from local and nonlocal theories in numerical simulations. It is found that the newly proposed nonlocal shell theory is indispensable in predicting CNT phonon dispersion relations at larger longitudinal and circumferential wavenumbers and smaller wavelength in the circumferential direction when the small-scale effect becomes dominant and hence noteworthy. In addition, the asymptotic frequency, phase velocities and cut-off frequencies are also derived from the nonlocal shell theory. Moreover, an estimation of the scale coefficient is provided based on the derived asymptotic frequency. The research findings not only demonstrate great potential of the proposed nonlocal shell theory in studying vibration and phonon dispersion relations of CNTs but also signify limitations of local continuum mechanics in analysis of small-scale effects, and thus are of significance in promoting the development of nonlocal continuum mechanics in the design of nanostructures.

Biological production of ethanol from coal synthesis gas

Abstract: The anaerobic bacteriaClostridium ljungdahlii produces ethanol and acetate from CO, CO2, and H2 in synthesis gas. Early studies with the bacterium showed that relatively high concentrations of ethanol could be produced by lowering the fermentation pH and eliminating yeast extract from the medium in favor of a defined medium. This article presents the results from a medium development study based on the aerobic bacteriumEscherichia coli. The results of continuous-reactor studies in a continuously stirred tank reactor (CSTR) with and without cell recycle are shown to demonstrate the utility of this improved medium.

The Market Valuation of Corporate Reputation

Abstract: We provide evidence that corporate reputation has value relevance, as measured by its ability to explain the firm's market value of equity at the end of the fiscal period. Corporate reputation is assessed using a summary measure from the Fortune survey of ‘America's most admired companies.’ The Fortune measure serves as a proxy for intangible assets, such as internally generated goodwill, customer service, and intellectual capital. We demonstrate that this summary measure of non-financial information adds to market value, even after controlling for the financial performance ‘halo’ effects on the Fortune ratings.

Ultrasmall near-infrared non-cadmium quantum dots for in vivo tumor imaging.

Abstract: The high tumor uptake of ultrasmall near-infrared quantum dots (QDs) attributed to the enhanced permeability and retention effect is reported. InAs/InP/ZnSe QDs coated by mercaptopropionic acid (MPA) exhibit an emission wavelength of about 800 nm (QD800-MPA) with very small hydrodynamic diameter (<10 nm). Using 22B and LS174T tumor xenograft models, in vivo and ex vivo imaging studies show that QD800-MPA is highly accumulated in the tumor area, which is very promising for tumor detection in living mice. The ex vivo elemental analysis (Indium) using inductively coupled plasma (ICP) spectrometry confirm the tumor uptake of QDs. The ICP data are consistent with the in vivo and ex vivo fluorescence imaging. Human serum albumin (HSA)-coated QD800-MPA nanoparticles (QD800-MPA-HSA) show reduced localization in mononuclear phagocytic system-related organs over QD800-MPA plausibly due to the low uptake of QD800-MPA-HSA in macrophage cells. QD800-MPA-HSA may have great potential for in vivo fluorescence imaging.

Optimal Status Update for Age of Information Minimization with an Energy Harvesting Source

Abstract: In this paper, we consider a scenario where an energy harvesting sensor continuously monitors a system and sends time-stamped status updates to a destination. The destination keeps track of the system status through the received updates. We use the metric Age of Information (AoI), the time that has elapsed since the last received update was generated, to measure the "freshness" of the status information available at the destination. We assume energy arrives randomly at the sensor according to a Poisson process, and each status update consumes one unit of energy. Our objective is to design optimal online status update policies to minimize the long-term average AoI, subject to the energy causality constraint at the sensor. We consider three scenarios, i.e., the battery size is infinite, finite, and one unit only, respectively. For the infinite battery scenario, we adopt a best-effort uniform status update policy and show that it minimizes the long-term average AoI. For the finite battery scenario, we adopt an energy-aware adaptive status update policy, and prove that it is asymptotically optimal when the battery size goes to infinity. For the last scenario where the battery size is one, we first show that within a broadly defined class of online policies, the optimal policy should have a renewal structure, i.e., the status update epochs form a renewal process, and the length of each renewal interval depends on the first energy arrival over that interval only. We then focus on a renewal interval, and prove that if the AoI in the system is below a threshold when the first energy arrives, the sensor should store the energy and hold status update until the AoI reaches the threshold, otherwise, it updates the status immediately. We analytically characterize the long-term average AoI under such a threshold-based policy, and explicitly identify the optimal threshold.