Showing papers by "University of Arkansas published in 2009"

Observation of PT-Symmetry Breaking in Complex Optical Potentials

Abstract: In 1998, Bender and Boettcher found that a wide class of Hamiltonians, even though non-Hermitian, can still exhibit entirely real spectra provided that they obey parity-time requirements or PT symmetry. Here we demonstrate experimentally passive PT-symmetry breaking within the realm of optics. This phase transition leads to a loss induced optical transparency in specially designed pseudo-Hermitian guiding potentials.

Formation of high-quality I-III-VI semiconductor nanocrystals by tuning relative reactivity of cationic precursors.

Abstract: A method for the synthesis of nearly monodisperse CuInS2 semiconductor nanocrystals (from <2 to 20 nm) was developed using generic and air-stable chemicals in a non-coordinating solvent. Such “greener” approaches also allowed the reaction temperatures to be below 200 °C. By introducing reactivity-controlling ligands for Cu, namely thiols, control of the Cu:In stoichiometric ratio in the nanocrystals was achieved. Amines were identified as catalytic reagents for the rapid oxidation of the CuInS2 nanocrystals, which could be prevented by the formation of CuInS2/ZnS core/shell nanocrystals by a one-pot approach. CuInS2/ZnS core/shell nanocrystals also showed greatly improved optical properties, with photoluminescence quantum yield up to about 30% and an emission peak position tunable from 500 to 950 nm. The versatility of the synthetic strategy was demonstrated by extending it to the synthesis of AgInS2 nanocrystals by simply replacing the copper salt by a silver salt.

Golden carbon nanotubes as multimodal photoacoustic and photothermal high-contrast molecular agents

Abstract: Carbon nanotubes have shown promise as contrast agents for photoacoustic and photothermal imaging of tumours and infections because they offer high resolution and allow deep tissue imaging. However, in vivo applications have been limited by the relatively low absorption displayed by nanotubes at near-infrared wavelengths and concerns over toxicity. Here, we show that gold-plated carbon nanotubes-termed golden carbon nanotubes-can be used as photoacoustic and photothermal contrast agents with enhanced near-infrared contrast ( approximately 10(2)-fold) for targeting lymphatic vessels in mice using extremely low laser fluence levels of a few mJ cm(-2). Antibody-conjugated golden carbon nanotubes were used to map the lymphatic endothelial receptor, and preliminary in vitro viability tests show golden carbon nanotubes have minimal toxicity. This new nanomaterial could be an effective alternative to existing nanoparticles and fluorescent labels for non-invasive targeted imaging of molecular structures in vivo.

In vivo magnetic enrichment and multiplex photoacoustic detection of circulating tumour cells

Abstract: The spread of cancer cells between organs, a process known as metastasis, is the cause of most cancer deaths. Detecting circulating tumour cells -- a common marker for the development of metastasis -- is difficult because ex vivo methods are not sensitive enough owing to limited blood sample volume and in vivo diagnosis is time-consuming as large volumes of blood must be analysed. Here, we show a way to magnetically capture circulating tumour cells in the bloodstream of mice followed by rapid photoacoustic detection. Magnetic nanoparticles, which were functionalized to target a receptor commonly found in breast cancer cells, bound and captured circulating tumour cells under a magnet. To improve detection sensitivity and specificity, gold-plated carbon nanotubes conjugated with folic acid were used as a second contrast agent for photoacoustic imaging. By integrating in vivo multiplex targeting, magnetic enrichment, signal amplification and multicolour recognition, our approach allows circulating tumour cells to be concentrated from a large volume of blood in the vessels of tumour-bearing mice, and this could have potential for the early diagnosis of cancer and the prevention of metastasis in humans.

Model of acceptance with peer support: a social network perspective to understand employees' system use

Abstract: Prior research has extensively studied individual adoption and use of information systems, primarily using beliefs as predictors of behavioral intention to use a system that in turn predicts system use. We propose a model of acceptance with peer support (MAPS) that integrates prior individual-level research with social networks constructs. We argue that an individual's embeddedness in the social network of the organizational unit implementing a new information system can enhance our understanding of technology use. An individual's coworkers can be important sources of help in overcoming knowledge barriers constraining use of a complex system, and such interactions with others can determine an employee's ability to influence eventual system configuration and features. We incorporate network density (reflecting "get-help" ties for an employee) and network centrality (reflecting "give-help" ties for an employee), drawn from prior social network research, as key predictors of system use. Further, we conceptualize valued network density and valued network centrality, both of which take into account ties to those with relevant system-related information, knowledge, and resources, and employ them as additional predictors. We suggest that these constructs together are coping and influencing pathways by which they have an effect on system use. We conducted a 3-month long study of 87 employees in one business unit in an organization. The results confirmed our theory that social network constructs can significantly enhance our understanding of system use over and above predictors from prior individual-level adoption research.

The Relationship Between Perceptions of Organizational Politics and Employee Attitudes, Strain, and Behavior: A Meta-Analytic Examination

Abstract: The current study tested a model that links perceptions of organizational politics to job performance and “turnover intentions” (intentions to quit). Meta-analytic evidence supported significant, b...

Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 1: Fine particle composition and organic source apportionment

Abstract: . Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and complementary instrumentation. Mass concentrations, diurnal cycles, and size distributions of inorganic and organic species are similar to results from the CENICA supersite in April 2003 with organic aerosol (OA) comprising about half of the fine PM mass. Positive Matrix Factorization (PMF) analysis of the high resolution OA spectra identified three major components: chemically-reduced urban primary emissions (hydrocarbon-like OA, HOA), oxygenated OA (OOA, mostly secondary OA or SOA), and biomass burning OA (BBOA) that correlates with levoglucosan and acetonitrile. BBOA includes several very large plumes from regional fires and likely also some refuse burning. A fourth OA component is a small local nitrogen-containing reduced OA component (LOA) which accounts for 9% of the OA mass but one third of the organic nitrogen, likely as amines. OOA accounts for almost half of the OA on average, consistent with previous observations. OA apportionment results from PMF-AMS are compared to the PM2.5 chemical mass balance of organic molecular markers (CMB-OMM, from GC/MS analysis of filters). Results from both methods are overall consistent. Both assign the major components of OA to primary urban, biomass burning/woodsmoke, and secondary sources at similar magnitudes. The 2006 Mexico City emissions inventory underestimates the urban primary PM2.5 emissions by a factor of ~4, and it is ~16 times lower than afternoon concentrations when secondary species are included. Additionally, the forest fire contribution is at least an order-of-magnitude larger than in the inventory.

Individual Swift Trust and Knowledge-Based Trust in Face-to-Face and Virtual Team Members

Abstract: Traditionally, trust has been seen as a result of personal knowledge of an individual's past behavior. In this view, trust develops gradually over time based on an individual's cognitive assessment of the other person's behavior. However, high levels of trust have been observed among members of virtual teams, who often have little prior history of working together and may never meet each other in person. To integrate these two seemingly contradictory views of trust, this study manipulated team member characteristics and team member behavior to empirically test a two-stage theoretical model of trust formation and the influence of information and communication technologies (ICT) on trust formation. The results indicate that category-based processing of team member characteristics and an individual's own disposition to trust dominated the initial formation of swift trust. Once individuals accumulated sufficient information to assess a team member's trustworthiness, the effects of swift trust declined and knowledge-based trust formed using team members' behaviors (perceived ability, integrity, and benevolence) became dominant. The use of ICT increased perceived risk of team failure, which reduced the likelihood that team members would engage in future trusting behaviors.

Salmonellosis Outbreaks in the United States Due to Fresh Produce: Sources and Potential Intervention Measures

Abstract: Foodborne Salmonella spp. is a leading cause of foodborne illness in the United States each year. Traditionally, most cases of salmonellosis were thought to originate from meat and poultry products. However, an increasing number of salmonellosis outbreaks are occurring as a result of contaminated produce. Several produce items specifically have been identified in outbreaks, and the ability of Salmonella to attach or internalize into vegetables and fruits may be factors that make these produce items more likely to be sources of Salmonella. In addition, environmental factors including contaminated water sources used to irrigate and wash produce crops have been implicated in a large number of outbreaks. Salmonella is carried by both domesticated and wild animals and can contaminate freshwater by direct or indirect contact. In some cases, direct contact of produce or seeds with contaminated manure or animal wastes can lead to contaminated crops. This review examines outbreaks of Salmonella due to con...

A Control Theory Perspective on Agile Methodology Use and Changing User Requirements

Abstract: In this paper, we draw on control theory to understand the conditions under which the use of agile practices is most effective in improving software project quality. Although agile development methodologies offer the potential of improving software development outcomes, limited research has examined how project managers can structure the software development environment to maximize the benefits of agile methodology use during a project. As a result, project managers have little guidance on how to manage teams who are using agile methodologies. Arguing that the most effective control modes are those that provide teams with autonomy in determining the methods for achieving project objectives, we propose hypotheses related to the interaction between control modes, agile methodology use, and requirements change. We test the model in a field study of 862 software developers in 110 teams. The model explains substantial variance in four objective measures of project quality---bug severity, component complexity, coordinative complexity, and dynamic complexity. Results largely support our hypotheses, highlighting the interplay between project control, agile methodology use, and requirements change. The findings contribute to extant literature by integrating control theory into the growing literature on agile methodology use and by identifying specific contingencies affecting the efficacy of different control modes. We discuss the theoretical and practical implications of our results.

RFID for Better Supply-Chain Management through Enhanced Information Visibility

Abstract: Mostly fueled by mandates, adoption, and implementation of the RFID, technology in the retail industry is growing rapidly. At these early stages of adoption, one puzzling issue for retailers and suppliers is the compelling business case for RFID. In order to explore the potential business case for RFID, we conducted a case study using actual RFID data collected by a major retailer for the cases shipped by one of its major suppliers. We show the physical layout of the RFID readers on a partial supply-chain covering product movement from distribution centers to retail stores. First, in the analysis phase, we identify several performance metrics that can be computed from the RFID readings. Next, using this RFID data, we compute the values of those performance metrics. These values represent mean time between movements at different locations. Then, we discuss how these measures can assist in improving logistical performance at a micro supply chain level of operations between a distribution center and a retail store. We present how such information can be valuable to both the retail store operator and the supplier. We also discuss the initial lessons learned from actual RFID data collected in the field, in terms of data quality issues.

Call for mixed analysis: A philosophical framework for combining qualitative and quantitative approaches

Abstract: We provide a philosophical justification for analyzing qualitative and quantitative data within the same study. First, we present several recent typologies of analyses in social science research th...

Evidence for room-temperature multiferroicity in a compound with a giant axial ratio.

Abstract: In the search for multiferroic materials magnetic compounds with a strongly elongated unit-cell (large axial ratio $c/a$) have been scrutinized intensely However, none was hitherto proven to have a switchable polarization, an essential feature of ferroelectrics Here, we provide evidence for the epitaxial stabilization of a monoclinic phase of ${\mathrm{BiFeO}}_{3}$ with a giant axial ratio ($c/a=123$) that is both ferroelectric and magnetic at room temperature Surprisingly, and in contrast with previous theoretical predictions, the polarization does not increase dramatically with $c/a$ We discuss our results in terms of the competition between polar and antiferrodistortive instabilities and give perspectives for engineering multiferroic phases

Evidence for Increased Aggressiveness in a Recent Widespread Strain of Puccinia striiformis f. sp. tritici Causing Stripe Rust of Wheat

Abstract: Milus, E. A., Kristensen, K., and Hovmoller, M. S. 2009. Evidence for increased aggressiveness in a recent widespread strain of Puccinia striiformis f. sp. tritici causing stripe rust of wheat. Phytopathology 99:89-94. Stripe rust (yellow rust) of wheat, caused by Puccinia striiformis f. sp. tritici, has become more severe in eastern United States, Australia, and elsewhere since 2000. Recent research has shown that this coincided with a global spread of two closely related strains that were similar based on virulence phenotype and amplified fragment length polymorphism. The objective of this research was to quantify differences in aggressiveness among isolates representative of the pre-2000 and post-2000 populations. Representative isolates were evaluated at low (10 to 18°C) and high (12 to 28°C) temperature regimes for latent period, lesion length, lesion width, lesion area, and spore production on adult plants of a susceptible wheat cultivar with no known genes for resistance to stripe rust. “New” isolates (since 2000) were significantly more aggressive than “old” isolates (before 2000) for all variables. At the low temperature regime, new isolates sporulated 2.1 days (16%) sooner, grew 0.3 mm per day (18%) faster, produced 999 (140%) more spores per inoculation site per day, and produced 6.5 (71%) more spores per mm 2 of lesion per day compared with old isolates. At the high temperature regime, new isolates sporulated 3 days (26%) sooner, grew 0.2 mm per day (18%) and 2.2 mm 2 per day (88%) faster, grew 1.2 mm (50%) wider, produced 774 (370%) more spores per inoculation site per day, and produced 6.2 (159%) more spores per mm2 of lesion per day than old isolates. New isolates showed significant adaptation to the warm temperature regime for all variables. Based on these results and previously published models for stripe rust epidemics, recent severe stripe rust epidemics were most likely enhanced by the pathogen’s increased aggressiveness, especially at higher temperature. Furthermore, these results demonstrate that wheat rust fungi can adapt to warmer temperatures and cause severe disease in previously unfavorable environments.

Synthesis of Cu-Doped InP Nanocrystals (d-dots) with ZnSe Diffusion Barrier as Efficient and Color-Tunable NIR Emitters

Abstract: Efficient Cu-doped InP quantum dots (Cu:InP d-dots) emitters were successfully synthesized by epitaxial growth of a ZnSe diffusion barrier for the dopants. The Cu dopant emission of the Cu:InP/ZnSe core/shell d-dots covered the important red and near-infrared (NIR) window for biomedical applicaitons, from 630 to 1100 nm, by varying the size of the InP host nanocrystals. These new d-dots emitters not only compensate for the emission wavelength of the existing noncadmium d-dots emitters, Cu- and Mn-doped ZnSe d-dots (450-610 nm), but also offer a complete series of efficient nanocrystal emitters based on InP nanocrystals. The one-pot synthetic scheme for the formation of Cu:InP/ZnSe core/shell d-dots was successfully established by systematically studying the doping process, the dopant concentration-dependent photophysical properties, and the dopant diffusion during shell epitaxy, etc. Complete elimination of InP bandgap emission and efficient pure dopant emission (with photoluminescence quantum yield as high as between 35-40%) of the core/shell d-dots were achieved by optimizing the final doping level and the diffusion barrier thickness.

Offshore information systems project success: the role of social embeddedness and cultural characteristics

Abstract: Agency theory has served as a key basis for identifying drivers of offshore information system project success. Consequently, the role of relational factors in driving project success has been overlooked in this literature. In this paper, we address this gap by integrating the social embeddedness perspective and the culture literature to theorize how and why relational factors affect the success of offshore IS projects that are strategic in nature. We identify organizational and interpersonal cultural differences as critical success factors in this context. Using data from a longitudinal field study of 155 offshore IS projects managed by 22 project leaders, we found evidence of a relationship between hypothesized relational factors and two measures of offshore IS project success--namely, project cost overruns and client satisfaction-- over and above the effects of project characteristics and agency factors. Specifically, we found that information exchange, joint problem solving, and trust reduce project cost overruns and improve client satisfaction. We also found a relationship between cultural differences at the organizational and team level, and offshore IS project success. The model explained 40 percent and 41 percent of the variance in project cost overruns and client satisfaction, respectively, for projects with a client representative. For projects with no client representative, the model explained 35 percent and 37 percent of the variance in project cost overruns and client satisfaction, respectively. Collectively, the results have important theoretical and practical implications for how client-- vendor relationships should be managed when partnering with offshore firms and designing offshore IS project teams.

Resonantly driven coherent oscillations in a solid-state quantum emitter

Abstract: Two experiments observe the so-called Mollow triplet in the emission spectrum of a quantum dot—originating from resonantly driving a dot transition—and demonstrate the potential of these systems to act as single-photon sources, and as a readout modality for electron-spin states. Single-quantum emitters emit only one photon at a time1,2, but the properties of the photon depend on how the emitter is excited3. Incoherent excitation is simple and broadly used with solid-state emitters such as quantum dots, but does not allow direct manipulation of the quantum state. Coherent, resonant excitation on the other hand is used in pump–probe techniques to examine the quantum state of the emitter4, but does not permit collection of the single-photon emission. Coherent control with simultaneous generation of photons has been an elusive goal in solid-state approaches, where, because of strong laser scattering at the detection wavelength, measurement of resonant emission has been limited to cross-polarized detection5 or Stokes-shift techniques6,7. Here we demonstrate that a semiconductor quantum dot in a microcavity can be resonantly driven and its single-photon emission extracted background free. Under strong continuous-wave excitation, the dot undergoes several Rabi oscillations before emitting, which are visible as oscillations in the second-order correlation function. The quantum-dot states are therefore ‘dressed’, resulting in a Mollow-triplet emission spectrum. Such coherent control will be necessary for future high-efficiency sources of indistinguishable single photons3,8, which can be used for quantum key distribution9 or through post-selection10 to generate entangled photon pairs11,12.

Phenomenological characteristics of attentional biases towards threat: A critical review.

Abstract: Although research has consistently revealed the presence of a general attentional bias towards threat, empirical and theoretical ambiguity exists in determining whether attentional biases are comprised of facilitated attention to threat, difficulty in disengagement from threat, or both, as well as whether attentional biases reflect automatic or strategic processes. This paper reviews empirical investigations across four common assessment tasks: the Stroop (masked and unmasked), dot probe, visual search, and the Posner tasks. Although the review finds inconsistencies both within and between assessment tasks, the evidence suggests that attentional biases towards threat are comprised of each of the phenomenological characteristics addressed in this paper. Contemporary theoretical models of attentional biases in anxiety are summarized and critically reviewed in light of the current evidence. Suggestions for future research are addressed, including a need to investigate the psychometric properties of the assessment tasks, to utilize consistent theoretically driven operationalizations of attentional biases, and to provide a temporal description of the characteristics of attentional biases towards threat.

World-trade web: Topological properties, dynamics, and evolution

Abstract: This paper studies the statistical properties of the web of import-export relationships among world countries using a weighted-network approach. We analyze how the distributions of the most important network statistics measuring connectivity, assortativity, clustering, and centrality have coevolved over time. We show that all node-statistic distributions and their correlation structure have remained surprisingly stable in the last 20 years—and are likely to do so in the future. Conversely, the distribution of positive link weights is slowly moving from a log-normal density towards a power law. We also characterize the autoregressive properties of network-statistics dynamics. We find that network-statistics growth rates are well-proxied by fat-tailed densities like the Laplace or the asymmetric exponential power. Finally, we find that all our results are reasonably robust to a few alternative, economically meaningful, weighting schemes.

Dynamic linear models

Abstract: In this chapter we discuss the basic notions about state space models and their use in time series analysis. The dynamic linear model is presented as a special case of a general state space model, being linear and Gaussian. For dynamic linear models, estimation and forecasting can be obtained recursively by the well-known Kalman filter.

An essay on synthetic chemistry of colloidal nanocrystals

Abstract: The central goal of synthetic chemistry of colloidal nanocrystals at present is to discover functional materials. Such functional materials should help mankind to meet the tough challenges brought by the rapid depletion of natural resources and the significant increase of population with higher and higher living standards. With this thought in mind, this essay discusses the basic guidelines for developing this new branch of synthetic chemistry, including rational synthetic strategies, functional performance, and green chemistry principles.

Association of mitochondrial function and feed efficiency in poultry and livestock species.

Abstract: As grain prices have increased dramatically in the past year, understanding the fundamental genetic, cellular, and biochemical mechanisms responsible for feed efficiency (FE; g of gain/g of feed) or residual feed intake (RFI; an alternative feed efficiency trait that quantifies interanimal variation in DMI that is unexplained by differences in BW and growth rate) in livestock and poultry is extremely important with respect to maintaining viable meat production practices in the United States. Although breed and diet have long been known to affect mitochondrial function, few studies have investigated differences in mitochondrial function and biochemistry due to interanimal phenotypic differences in FE or RFI (i.e., variation among animals of the same breed and fed the same diet). This paper reviews existing literature on relationships of mitochondrial function and biochemistry with FE and RFI in poultry and livestock. The overall goal of all of this paper is to assist the development of tools (e.g., genetic markers or biomarkers) to aid commercial breeding companies in genetic selection that, in turn, will help maintain viable livestock and poultry industries in the United States and around the world.

Temporal and Spatial Interference between Four-Wave Mixing and Six-Wave Mixing Channels.

Abstract: Using phase control between four-wave mixing (FWM) and six-wave mixing (SWM) channels in a four-level atomic system, we demonstrate temporal and spatial interferences between these two nonlinear optical processes. Efficient and coexisting FWM and SWM signals are produced in the same electromagnetically induced transparency window via atomic coherence. The temporal interference has a femtosecond time scale corresponding to the optical transition frequency. Such studies of intermixing between different order nonlinear optical processes with a controllable phase delay can have important applications in high-precision measurements, coherence quantum control, and quantum information processing.

MID-IR LUMINOSITIES AND UV/OPTICAL STAR FORMATION RATES AT z< 1.4

Abstract: Ultraviolet (UV) nonionizing continuum and mid-infrared (IR) emission constitute the basis of two widely used star formation (SF) indicators at intermediate and high redshifts. We study 2430 galaxies with z 10^(11) L_⊙, yet with little current SF. For them a reasonable amount of dust absorption of stellar light (but presumably higher than in nearby early-type galaxies) is sufficient to produce the observed levels of IR, which includes a large contribution from intermediate and old stellar populations. In our sample, which contains very few ultraluminous IR galaxies, optical and X-ray active galactic nuclei do not contribute on average more than ~50% to the mid-IR luminosity, and we see no evidence for a large population of "IR excess" galaxies.

Stability of perchlorate hydrates and their liquid solutions at the Phoenix landing site, Mars

Abstract: [1] We studied the low-temperature properties of sodium and magnesium perchlorate solutions as potential liquid brines at the Phoenix landing site. We determined their theoretical eutectic values to be 236 ± 1 K for 52 wt% sodium perchlorate and 206 ± 1 K for 44.0 wt% magnesium perchlorate. Evaporation rates of solutions at various concentrations were measured under martian conditions, and range from 0.07 to 0.49 mm h ―1 for NaClO 4 and from 0.06 to 0.29 mm h ―1 for Mg(ClO 4 ) 2 . The extrapolation to Phoenix landing site conditions using our theoretical treatment shows that perchlorates are liquid during the summer for at least part of the day, and exhibit very low evaporation rates. Moreover, magnesium perchlorate eutectic solutions are thermodynamically stable over vapour and ice during a few hours a day. We conclude that liquid brines may be present and even stable for short periods of time at the Phoenix landing site.