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.

Early geochemical environment of Mars as determined from thermodynamics of phyllosilicates

Abstract: There is abundant evidence that liquid water once existed on the surface of Mars. Today's martian atmosphere is too thin to sustain the sort of greenhouse effect that could create a climate warm enough to support liquid water but, one theory goes, there may have been a carbon dioxide-rich atmosphere in the past. The apparent absence of carbonates and the low escape rates of carbon dioxide, however, have argued against that explanation. Now a thermodynamic study of clay minerals recently discovered by the OMEGA spectro-imaging instrument on-board Mars Express, has provided a clearer picture of the primitive geochemical conditions on Mars. What emerges is an atmosphere with very low carbon dioxide levels. Other greenhouse gases — methane seems the most likely — may therefore have been involved in sustaining a warm and wet climate on Mars. The apparent absence of carbonates and the low escape rates of carbon dioxide are indicative of an early Martian atmosphere with low levels of carbon dioxide. Calculations of aqueous equilibria of phyllosilicates that were recently observed on Mars now suggest low partial pressure of carbon dioxide at the time. This implies that other greenhouse gases may have played a key role in sustaining a warm and wet climate on early Mars. Images of geomorphological features that seem to have been produced by the action of liquid water have been considered evidence for wet surface conditions on early Mars1. Moreover, the recent identification of large deposits of phyllosilicates, associated with the ancient Noachian terrains2,3 suggests long-timescale weathering4 of the primary basaltic crust by liquid water2,5. It has been proposed that a greenhouse effect resulting from a carbon-dioxide-rich atmosphere sustained the temperate climate required to maintain liquid water on the martian surface during the Noachian6,7. The apparent absence of carbonates and the low escape rates of carbon dioxide8, however, are indicative of an early martian atmosphere with low levels of carbon dioxide. Here we investigate the geochemical conditions prevailing on the surface of Mars during the Noachian period using calculations of the aqueous equilibria of phyllosilicates. Our results show that Fe3+-rich phyllosilicates probably precipitated under weakly acidic to alkaline pH, an environment different from that of the following period, which was dominated by strongly acid weathering9 that led to the sulphate deposits identified on Mars10,11,12. Thermodynamic calculations demonstrate that the oxidation state of the martian surface was already high, supporting early escape of hydrogen. Finally, equilibrium with carbonates implies that phyllosilicate precipitation occurs preferentially at a very low partial pressure of carbon dioxide. We suggest that the possible absence of Noachian carbonates more probably resulted from low levels of atmospheric carbon dioxide, rather than primary acidic conditions13. Other greenhouse gases may therefore have played a part in sustaining a warm and wet climate on the early Mars.

Research Commentary---NeuroIS: The Potential of Cognitive Neuroscience for Information Systems Research

Abstract: This paper introduces the idea of drawing upon the cognitive neuroscience literature to inform IS research (herein termed “NeuroIS”). Recent advances in cognitive neuroscience are uncovering the neural bases of cognitive, emotional, and social processes, and they offer new insights into the complex interplay between IT and information processing, decision making, and behavior among people, organizations, and markets. The paper reviews the emerging cognitive neuroscience literature to propose a set of seven opportunities that IS researchers can use to inform IS phenomena, namely (1) localizing the neural correlates of IS constructs, (2) capturing hidden mental processes, (3) complementing existing sources of IS data with brain data, (4) identifying antecedents of IS constructs, (5) testing consequences of IS constructs, (6) inferring the temporal ordering among IS constructs, and (7) challenging assumptions and enhancing IS theories. The paper proposes a framework for exploring the potential of cognitive neuroscience for IS research and offers examples of potentially fertile intersections of cognitive neuroscience and IS research in the domains of design science and human-computer interaction. This is followed by an example NeuroIS study in the context of e-commerce adoption using fMRI, which spawns interesting new insights. The challenges of using functional neuroimaging tools are also discussed. The paper concludes that there is considerable potential for using cognitive neuroscience theories and functional brain imaging tools in IS research to enhance IS theories.

Understanding muscle markers: Aggregation and construct validity

Abstract: Musculoskeletal markers are frequently used to reconstruct past lifestyles and activity patterns. Yet, the reliability of muscle marker measurements has been called into question because they allegedly fail to correlate with cross-sectional properties and exercise patterns, and are confounded by body size. In this study, the principle of aggregation was used to sum muscle markers over 7 insertion sites (4 humeral, 2 radial, and 1 ulnar) and examine the effects on them of body size, age, sex, and cross-sectional properties. Analyses were made of a sample of 91 (66 males, 25 females) Native British Columbians (3500-1500 years BP) and 18th century Quebec prisoners. Muscle markers were measured using three-point observer rating scales; size was measured by standard methods; age and sex were determined through pelvic, cranial, and dental morphology; and cross-sectional properties were calculated from radiographs. Whereas any single muscle marker component failed to correlate with age, size, sex, or cross-sections, aggregate muscle marker correlated with: age, r = 0.49; size, r = 0.38; sex, r = 0.40; and, cross-sections, r = 0.38; P < 0.001. Older individuals had greater muscle markers, as did larger individuals, males, and those with more robust cross-sections. Based on partial correlations and regression analyses, age was the best overall predictor of aggregate muscle marker.

Laser nano-manufacturing - State of the art and challenges

Abstract: This paper provides an overview of advances in laser based nano-manufacturing technologies including surface nano-structure manufacturing, production of nano materials (nanoparticles, nanotubes and nanowires) and 3D nano-structures manufacture through multiple layer additive techniques and nano-joining/forming. Examples of practical applications of laser manufactured nanostructures, materials and components are given. A discussion on the challenge and outlooks in laser nano-manufacturing is presented.