bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular and Functional Characterizations of Gastrula Organizer Cells Derived from Human Embryonic Stem Cells
Authors: Sharon Nadav , Mor Ishay , Golan-lev Tamar , Fainsod Abraham , Benvenisty Nissim
Published: February 2011

The Spemann-Mangold organizer is the structure that provides the signals, which initiate pattern formation in the developing vertebrate embryo, affecting the main body axes. Very little is known about axial induction in the gastrulating human embryo, as research is hindered by obvious ethical restrictions. Human embryonic stem cells (hESCs) are pluripotent cells derived from the pregastrula embryo that can differentiate in culture following a program similar to normal embryonic development but without pattern formation. Here, we show that in hESC-derived embryoid bodies, we can induce differentiation of cells that harbor markers and characteristics of the gastrula-organizer. Moreover, genetic labeling of these cells enabled their purification, and the discovery of a comprehensive set of their secreted proteins, cell surface receptors, and nuclear factors characteristic of the organizer. Remarkably, transplantation of cell populations enriched for the putative human organizer into frog embryos induced a secondary axis. Our research demonstrates that the human organizer can be induced in vitro and paves the way for the study of pattern formation and the initial regulation of body axis establishment in humans.
Model Based Systems Engineering with Department of Defense Architectural Framework
Authors: Piaszczyk Chris
Published: February 2011

This paper presents a methodology for Model Based Systems Engineering (MBSE) utilizing the guidelines provided by the Department of Defense Architectural Framework (DoDAF). MBSE focuses the system engineering process on system modeling. Thus, requirements derivation, system design, integration, verification, and validation activities all center around the model of the system. System models can be built in many ways. This paper presents an approach using DoDAF. Visual accessibility of the DoDAF views facilitates full participation by all system stakeholders, including the customers, developers, and implementers, and enables the necessary dialogue. The approach promotes communications among the members of the development team and speeds up the iterations of the systems engineering process. The paper illustrates the utility of the DoDAF artifacts by means of a simplified but comprehensive, easy to follow, illustrative example. © 2011 Wiley Periodicals, Inc. Syst Eng
An architectural systems engineering methodology for addressing cyber security
Authors: Bayuk Jennifer L. , Horowitz Barry M.
Published: February 2011

This paper discusses important shortcomings of current approaches to systems security engineering. The value and limitations of perimeter security designs are examined. An architectural approach to systems security engineering is introduced as a complementary means for strengthening current approaches. Accordingly, this paper outlines a methodology to identify classes of new reusable system security solutions and an architectural framework based on reuse of the patterns of solutions. It also introduces a new methodology for security metrics intended to stimulate critical solution design tradeoff analyses as part of security design reuse considerations. Examples of problems, potential architectural solutions, and corresponding security metrics are provided. © 2011 Wiley Periodicals, Inc. Syst Eng
Mining large medical claims database to identify high‐risk patients: The case of antidepressant utilization
Authors: Huang Samuel H. , Li Hua , Mo Dengyao , Wulsin Lawson R.
Published: February 2011

Data mining techniques have been applied to discover knowledge from large observational data sets. In this paper, we focus on mining large medical claims databases to identify high‐risk patients. Patient selection, feature extraction, and feature selection are three important processing steps before popular data mining techniques are successfully applied. Both patient selection and feature extraction require domain knowledge. The episode treatment group methodology is a useful tool for organizing medical claims data. It is used for patient selection and feature extraction in this paper. The specific goal of the study is to identify patients with major depression who have a high risk of receiving inadequate antidepressant medication. A nationwide medical claims database covering a 5‐year period is used for this study. The records of 31,721 high‐risk patients and 50,022 comparison patients were examined for 18 features that include patient demographics, episode factors, and comorbidity factors. After supervised feature selection, three features were selected and analyzed using the classification and regression tree method. The result showed that it is possible to use two of the features (number of non‐antidepressant medications used and average number of claims during an episode of major depression) to identify a group of high‐risk patients. These patients are 2.67 times more likely to have inadequate antidepressant medication than the comparison patients. © 2011 John Wiley & Sons, Inc. WIREs Data Mining Knowl Discov 2011 1 154‐163 DOI: 10.1002/widm.5

This article is categorized under:

Application Areas > Health Care

Fundamental Concepts of Data and Knowledge > Knowledge Representation
Technology at the Zoo: The Influence of a Touchscreen Computer on Orangutans and Zoo Visitors
Authors: Perdue Bonnie M. , Clay Andrea W. , Gaalema Diann E. , Maple Terry L. , Stoinski Tara S.
Published: February 2011

A computer‐controlled touchscreen apparatus (hereafter referred to as “touchscreen”) in the orangutan exhibit at Zoo Atlanta provides enrichment to the animals and allows cognitive research to take place on exhibit. This study investigated the impact of the touchscreen on orangutan behavior and visibility, as well as its impact on zoo visitors. Despite previous research suggesting that providing a single computer system may negatively affect orangutan behavior, there was not a significant increase in aggression, stereotypic, or distress‐related behaviors following the activation of the on‐exhibit touchscreen. We also investigated the possibility that zoo visitors may be negatively affected by technology because it deviates from naturalism. However, we did not find a change in stay time or overall experience rating when the computer was turned on. This research was the first to assess visitor attitudes toward technology at the zoo, and we found that visitors report highly positive attitudes about technology for both animals and visitors. If subjects visited the exhibit when the computer was turned on, they more strongly agreed that orangutans benefit from interacting with computerized enrichment. This study is the first investigation of an on‐exhibit touchscreen in group‐housed apes; our findings of no negative effects on the animals or zoo visitors and positive attitudes toward technology suggest a significant value of this practice. Zoo Biol 31:27;–39, 2012. © 2011 Wiley Periodicals, Inc.
Substrate Pretreatment can Reduce the Alcohol Requirement During Biodiesel Production Via in Situ Transesterification
Authors: Haas Michael J. , Wagner Karen M.
Published: February 2011

The ability of physical pretreatment of the feedstock to reduce the alcohol requirement for high yield fatty acid methyl esters (FAME) production during the in situ transesterification of soybeans was investigated. Four physical treatments were studied: (a) dehulling and flaking, (b) dehulling, flaking and passage through a twin screw extruder, (c) passage through an expander type extruder, or (d) conversion to a flour‐like consistency (1–10 μm particles) via disruption in a Pulsewave disintegrator. Following drying, optimal reaction conditions for high yield, room temperature, in situ transesterification of the lipid‐linked fatty acids resident in these materials were determined. Expander and Pulsewave pretreatment did not substantially reduce the amount of methanol required for high level FAME production below that required for flaked soybeans. However, the combination of flaking, extrusion and drying achieved a minimum nearly threefold reduction in the methanol requirement compared with that for soybeans that had been only flaked and dried. The flaking/extrusion/drying regime resulted in a minimum optimal molar ratio for (methanol/substrate fatty acid) of 9:1 for effective in situ transesterification. This is a 20‐fold reduction in methanol usage compared to the previously reported ratio of 181:1 for the use of flaked‐only soybeans. (Haas et al. in J Am Oil Chem Soc 81:83–89, 2004).
Dissection of the thoracic aorta following cardiopulmonary resuscitation
Authors: Oren-Grinberg Achikam , Shahul Sajid , Sarge Todd
Published: February 2011

An 86-year-old patient was admitted to the ICU with multiple trauma injury following a fall down ten stairs. Shortly after ICU admission the patient went into cardiac arrest and resuscitation efforts, including cardiopulmonary resuscitation (CPR), were initiated. Transesophageal echocardiogram was performed to guide therapy and, after regaining heart rhythm and blood pressure, the echocardiogram exam demonstrated critical aortic stenosis and type-B aortic dissection. The aortic dissection was not present on initial chest computerized tomography done on admission to the hospital. The aortic dissection appears to have resulted from the CPR performed to revive the patient.
Further insights into the strange role of bacterial endosymbionts in whitefly, Bemisia tabaci: Comparison of secondary symbionts from biotypes B and Q in China
Authors: Chu D. , Gao C.S. , De Barro P. , Zhang Y.J. , Wan F.H. , Khan I.A.
Published: February 2011

The percentage infection of secondary symbionts (SS) (Wolbachia, Arsenophonus, Rickettsia, Hamiltonella, Fritschea and Cardinium) in the exotic Bemisia tabaci (Genn.) invaders, commonly known as biotypes B and Q from China, were determined by PCR. In total, 373 biotype B and 1830 biotype Q individuals were screened for the presence of SS. Biotype B was more abundant than biotype Q from 2005 to 2006, and biotype Q was more abundant from 2007 to 2009. Each of the SS, with the exception of Fritschea, was detected in both biotypes B and Q; Fritschea was found in none of the samples examined. For biotype B, the percentage infection of Hamiltonella was the highest (92.0%) followed by Rickettsia (70.2%). For biotype Q, the percentage infection of Hamiltonella was again the highest (73.3%). Arsenophonus was the least common of the SS observed in both biotypes B and Q. The percentage infection of Wolbachia, Rickettsia and Hamiltonella in biotype B was each significantly higher than in biotype Q, whereas the percentage infection of Cardinium in biotype B was significantly lower than in biotype Q. The percentage infection of SS in biotypes B and Q varied from year to year over the period 2005–2009. Furthermore, within biotype Q, two distinct subgroups were identified which differ from each other in terms of their SS complement. We discuss these results in the light of the potentially influential factors and roles of the SS.
Single-dielectric barrier discharge plasma actuator modelling and validation
Authors: MERTZ BENJAMIN E. , CORKE THOMAS C.
Published: February 2011

Single-dielectric barrier discharge (SDBD) plasma actuators have gained a great deal of world-wide interest for flow-control applications. With this has come the need for flow-interaction models of plasma actuators that can be used in computational flow simulations. SDBD plasma actuators consist of two electrodes: one uncovered and exposed to the air and the other encapsulated by a dielectric material. An AC electric potential is supplied to the electrodes. When the AC potential is large enough, the air in the region over the encapsulated electrode ionizes. The ionized air in the presence of the electric field results in a space–time dependent body force vector field. The body force is the mechanism for flow control. This study describes a semi-empirical model that has been developed to capture the dynamic nature of the local air ionization and time-dependent body force vector distribution. Validation of the model includes comparisons to experimentally measured space–time charge distribution and the time-resolved and time-averaged body force. Two flow simulations are then used to further validate the SDBD plasma actuator model. These involved an impulsively started plasma actuator in still air, and the flow around a circular cylinder in which plasma actuators were used to suppress the Karman vortex street. In both cases, the simulations agreed well with the experiments.
Long working hours and symptoms of anxiety and depression: a 5-year follow-up of the Whitehall II study
Authors: Virtanen M. , Ferrie J. E. , Singh-Manoux A. , Shipley M. J. , Stansfeld S. A. , Marmot M. G. , Ahola K. , Vahtera J. , Kivimäki M.
Published: February 2011

Background

Although long working hours are common in working populations, little is known about the effect of long working hours on mental health.

Method

We examined the association between long working hours and the onset of depressive and anxiety symptoms in middle-aged employees. Participants were 2960 full-time employees aged 44 to 66 years (2248 men, 712 women) from the prospective Whitehall II cohort study of British civil servants. Working hours, anxiety and depressive symptoms, and covariates were measured at baseline (1997–1999) followed by two subsequent measurements of depressive and anxiety symptoms (2001 and 2002–2004).

Results

In a prospective analysis of participants with no depressive (n=2549) or anxiety symptoms (n=2618) at baseline, Cox proportional hazard analysis adjusted for baseline covariates showed a 1.66-fold [95% confidence interval (CI) 1.06–2.61] risk of depressive symptoms and a 1.74-fold (95% CI 1.15–2.61) risk of anxiety symptoms among employees working more than 55 h/week compared with employees working 35–40 h/week. Sex-stratified analysis showed an excess risk of depression and anxiety associated with long working hours among women [hazard ratios (HRs) 2.67 (95% CI 1.07–6.68) and 2.84 (95% CI 1.27–6.34) respectively] but not men [1.30 (0.77–2.19) and 1.43 (0.89–2.30)].

Conclusions

Working long hours is a risk factor for the development of depressive and anxiety symptoms in women.
Being and Becoming: Children as Audiences
Authors: Johanson Katya , Glow Hilary
Published: February 2011

In this article, Katya Johanson and Hilary Glow examine the ways in which performing arts companies and arts policy institutions perceive the needs of children as audiences. Historically, children have been promoted as arts audiences. Some of these represent an attempt to fashion the adults of the future – as audiences, citizens of a nation, or members of a specific community. Other rationales focus on the needs or rights of the child, such as educational goals or the provision of an antidote to the perceived corrupting effect of electronic entertainment. Drawing on interviews with performing arts practitioners, the authors explore some of these themes through case studies of three children's theatre companies, identifying the development of policy rationales for the support of practices directed at children which are primarily based on pedagogical principles. The case studies reveal a shift away from educational goals for children's theatre, and identify a new emphasis on the importance of valuing children's aesthetic choices, examining how these trends are enacted within the case-study organizations, and the implications of these trends for company programming. Hilary Glow is Senior Lecturer and Director of the Arts Management Program at Deakin University, Victoria. She has published articles on cultural policy and the audience experience in various journals, and in a monograph on Australian political theatre (2007). Katya Johanson lectures and researches in the School of Communication and Creative Arts at Deakin University. She has published on Australian cultural policy and on the relationship between art, politics and national identity. With Glow she is the author of a monograph on Australian indigenous performing arts (2009).
Pain and Patriotism on the Armenian Stage
Authors: Brown Mark
Published: February 2011

Report on the Armenian theatre showcase held in Yerevan from 15 to 19 June 2010.
Cryptic species, biogeographic complexity and the evolutionary history of theEctemnorhinusgroup in the sub-Antarctic, including a description ofBothrometopus huntleyi, n. sp.
Authors: Grobler G.C. , Bastos A.D.S. , Treasure A.M. , Chown S.L.
Published: February 2011

The biogeography of the South Indian Ocean Province (SIP) biotas has long been controversial. Much of the discussion has been based on interpretation of species distributions, based on morphological or anatomical delimitations. However, molecular phylogenetic approaches elsewhere have recently shown that interpretations based solely on morphological data may be misleading. Nonetheless, few studies have employed molecular phylogenetic approaches to understand the biogeography of the SIP biotas. We do so here for theEctemnorhinusgroup of genera, a monophyletic unit of weevils endemic to the region. We use mitochondrial cytochrome oxidase I DNA sequence data to reconstruct relationships among 13 species and 22 populations in the generaPalirhoeus,BothrometopusandEctemnorhinus. On the basis of this analysis we find little support for separating the genusPalirhoeusfromBothrometopus, and little support for the morphologically-based species groups currently recognized withinBothrometopus. Using a molecular clock we show that dispersal among islands probably took place against the prevailing wind direction. These data also support a previous hypothesis of radiation of the epilithic generaBothrometopusandPalirhoeusduring the Pliocene/early Pleistocene, but reject the hypothesis that the genusEctemnorhinusradiated following the last glacial maximum. We show thatBothrometopus parvulus(C.O. Waterhouse) on the Prince Edward Islands comprises two species that are not sister taxa. We name the second speciesBothrometopus huntleyin. sp. and provide a description thereof.
Look how far we have come
Authors: CLAGUE CHRISTOPHER
Published: February 2011

Economics has changed enormously since Professor Ha-Joon Chang burst onto the scene in the early 1990s. His critiques of mainstream economics are far more applicable to the discipline at that time than they are now. Whatever the shortcomings of the current literature on institutions and development, progress is not being held back by conceptual blinders imposed by economic orthodoxy. Game theory and behavioral economics have enriched the menu of models acceptable in the professional journals. More important, empirical standards have greatly advanced. Behavioral models are being confronted with computerized games and even with in-the-field experiments, especially in poor countries where recruiting experimental subjects is cheaper. The recent literature does not merely undermine traditional assumptions; it offers parsimonious interpretations that help us to understand the economy and the polity better than before.
Dynamic rating curve assessment in unstable rivers using Ornstein‐Uhlenbeck processes
Authors: Reitan Trond , Petersen‐Øverleir Asgeir
Published: February 2011

The procedure of fitting rating curves in channels where the stage‐discharge relationship is subject to changes driven by morphological processes remains one of the major unsolved problems in hydrometry. This paper addresses this issue by formulating the stage‐discharge relationship as a steady flow, one‐segmented power law model with parameters that are viewed as stochastic processes with characteristics associated with the temporal instabilities of the channel elements governing the stage‐discharge relationship. A Bayesian analysis with informative priors and time‐stage‐discharge measurements as forcing data is used to determine the most plausible model and its posterior parameter distributions using Markov chain Monte Carlo simulation techniques and particle filtering. The proposed framework is applied to data from gauging stations in two unstable rivers and one stable river in Norway.
Functional model of water balance variability at the catchment scale: 2. Elasticity of fast and slow runoff components to precipitation change in the continental United States
Authors: Harman C. J. , Troch P. A. , Sivapalan M.
Published: February 2011

Assessing the sensitivity of annual streamflow to precipitation is challenging due to the complexity of the processes that control the water balance. A low‐dimensional model can be useful to interrogate data in regional assessments of a large number of catchments, and can provide insights into the broad similarities and differences between catchments' behaviors. This work assesses the sensitivity to precipitation of total annual streamflow, as well as its slow and fast flow components, within the framework of the Ponce and Shetty water balance model. This framework assumes that there are upper limits on the ability of a catchment to store and evaporate water, and there are minimum threshold amounts of precipitation and wetting (precipitation minus fast flow) needed to initiate fast and slow runoff. The flow elasticities (percent of change in flow per percent of change in annual precipitation) were estimated for 405 catchments in the Model‐Parameter Estimation Experiment data set (including an assessment of parameter uncertainty). The elasticity of total discharge was 2.1 on average across the catchments, which is consistent with other studies. The fast component was higher (≈ 2.4) and slow flow was lower (≈ 2.0). Elasticities were highest and most variable in arid areas. The variations in elasticity between sites were shown to be primarily controlled by the two threshold parameters. The thresholds were a high proportion of mean annual precipitation in arid sites where only a small proportion of catchment wetting is released as slow flow. This provides some insight into previous observations that the sensitivity is correlated with climate.
Thrombotic distal middle cerebral artery occlusion produced by topical FeCl3 application: A novel model suitable for intravital microscopy and thrombolysis studies
Authors: Karatas Hulya , Erdener Sefik Evren , Gursoy-Ozdemir Yasemin , Gurer Gunfer , Soylemezoglu Figen , Dunn Andrew K , Dalkara Turgay
Published: February 2011

Intravital or multiphoton microscopy and laser-speckle imaging have become popular because they allow live monitoring of several processes during cerebral ischemia. Available rodent models have limitations for these experiments; e.g., filament occlusion of the proximal middle cerebral artery (MCA) is difficult to perform under a microscope, whereas distal occlusion methods may damage the MCA and the peri-arterial cortex. We found that placement of a 10% FeCl3-soaked filter paper strip (0.3 × 1 mm2) on the duramater over the trunk of the distal MCA through a cranial window for 3 minutes induced intraarterial thrombus without damaging the peri-arterial cortex in the mouse. This caused a rapid regional cerebral blood flow decrease within 10 minutes and total occlusion of the MCA segment under the filter paper in 17 ± 2 minutes, which resulted in a typical cortical infarct of 27 ±4 mm3 at 24 hours and moderate sensorimotor deficits. There was no significant hemispheric swelling or hemorrhage or mortality at 24 hours. Reperfusion was obtained in half of the mice with tissue plasminogen activator, which allowed live monitoring of clot lysis along with restoration of tissue perfusion and MCA flow. In conclusion, this relatively simple and noninvasive stroke model is easy to perform under a microscope, making it suitable for live imaging and thrombolysis studies.
Star and miktoarm star block (co)polymers viaself-assembly of ATRP generated polymer segments featuring Hamilton wedge and cyanuric acid binding motifs
Authors: Altintas Ozcan , Tunca Umit , Barner-Kowollik Christopher
Published: February 2011

The self-assembly of well-defined ATRP prepared polymers with terminal and mid-chain Hamilton wedge as well as cyanuric acid binding motifs is demonstrated to be an efficient avenue to star and miktoarm star block copolymers.
An improved coarse-grained model of solvation and the hydrophobic effect
Authors: Varilly Patrick , Patel Amish J. , Chandler David
Published: February 2011

We present a coarse-grained lattice model of solvation thermodynamics and the hydrophobic effect that implements the ideas of Lum–Chandler–Weeks theory [J. Phys. Chem. B 134, 4570 (1999)] and improves upon previous lattice models based on it. Through comparison with molecular simulation, we show that our model captures the length-scale and curvature dependence of solvation free energies with near-quantitative accuracy and 2–3 orders of magnitude less computational effort, and further, correctly describes the large but rare solvent fluctuations that are involved in dewetting, vapor tube formation, and hydrophobic assembly. Our model is intermediate in detail and complexity between implicit-solvent models and explicit-water simulations.
UV–visible absorption of small gold clusters in neon: Aun (n = 1–5 and 7–9)
Authors: Lecoultre S. , Rydlo A. , Félix C. , Buttet J. , Gilb S. , Harbich W.
Published: February 2011

We present optical absorption spectra in the UV–visible range (1.5 eV < E < 6 eV) for mass selected neutral gold clusters Aun (n = 1–5 and 7–9) embedded in solid Ne at 7 K. The experimental spectra are compared with time-dependent density functional calculations. Electronic transitions are distributed over the whole energy range without any concentration of the oscillator strength in a small energy window, characteristic for the more s-like metals such as the alkalis or silver. Contrary to the case of silver and partly copper clusters, transitions issued from mainly d-type states are significantly involved in low energy transitions. The measured integrated cross section is smaller (<20%) than expected from a free-electron system, manifesting the strong screening of the s electrons due to the proximity of the s and d levels in gold.
Quantum dynamics of hydrogen interacting with single-walled carbon nanotubes: Multiple H-atom adsorbates
Authors: McAfee Jason L. , Poirier Bill
Published: February 2011

In a previous paper [J. L. McAfee and B. Poirier, J. Chem. Phys. 130, 064701 (2009)], using spin-polarized density functional theory (DFT), the authors reported a binding energy of 0.755 eV, for a single hydrogen atom adsorbed on a pristine (unrelaxed) (5,5) single-walled carbon nanotube (SWNT) substrate. A full three-dimensional (3D) potential energy surface (PES) for the SWNT–H system was also developed, and used in a quantum dynamics calculation to compute all rovibrational bound states, and associated equatorial and longitudinal adsorbate migration rates. A highly pronounced preference for the latter migration pathway at ambient temperatures was observed. In this work, we extend the aforementioned study to include multiple H-atom adsorbates. Extensive DFT calculations are performed, in order to ascertain the most relevant dynamical pathways. For two adsorbates, the SWNT–H–H system is found to exhibit highly site-specific binding, as well as long-range correlation and pronounced binding energy enhancement. The latter effect is even more pronounced in the full-hydrogenation limit, increasing the per-adsorbate binding energy to 2.6 eV. To study migration dynamics, a single-hole model is developed, for which the binding energy drops to 2.11 eV. A global 3D PES is developed for the hole migration model, using 40 radial × 18 cylindrical ab initio geometries, fit to a Fourier basis with radially dependent expansion coefficients (rms error 4.9 meV). As compared with the single-adsorbate case, the hole migration PES does not exhibit separate chemisorption and physisorption wells. The barrier to longitudinal migration is also found to be much lower. Quantum dynamics calculations for all rovibrational states are then performed (using a mixed spectral basis/phase-space optimized discrete variable representation), and used to compute longitudinal migration rates. Ramifications for the use of SWNTs as potential hydrogen storage materials are discussed.
Improved hydrogen ionization rate in enhanced glow discharge plasma immersion ion implantation by enlarging the interaction path using an insulating tube
Authors: Wang Zhuo , Zhu Ying , Li Liu He , Lu Qiu Yuan , He Fu Shun , Dun Dan Dan , Li Fen , Fu Ricky K. Y. , Chu Paul K.
Published: February 2011

A small pointed hollow anode and large tabular cathode are used in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). Electrons are repelled from the substrate by the electric field formed by the negative voltage pulses and concentrate in the vicinity of the anode to enhance the self-glow discharge process. To extend the application of EGD-PIII to plasma gases with low ionization rates, an insulating tube is used to increase the interaction path for electrons and neutrals in order to enhance the discharge near the anode. Results obtained from numerical simulation based on the particle-in-cell code, finite element method, and experiments show that this configuration enhances the ionization rate and subsequent ion implant fluence. The process is especially suitable for gases that have low ionization rates such as hydrogen and helium.
A novel target-type low pressure drop bidirectional optoelectronic air flow sensor for infant artificial ventilation: Measurement principle and static calibration
Authors: Saccomandi Paola , Schena Emiliano , Silvestri Sergio
Published: February 2011

An optoelectronic target-type volumetric air flow-rate transducer for bidirectional measurements is presented. The sensor is composed of a T-shaped target and two nominally identical LED-photodiode couples which are operated in differential mode. The sensitive surfaces of the photodiodes are differentially shadowed by the deflection of the target, which in turn depends on the gas flow-rate. The principle of operation is described in mathematical terms and the design parameters have been optimized in order to obtain the highest sensitivity along with minimal pressure drop and reduced dimensions. The sensor is placed in a 20 mm diameter hose and was tested with air flow-rate in the typical temperature range of mechanical ventilation between 20 and 40 °C. The theoretical model was validated through experiments carried out in the volumetric flow range from −7.0 to +7.0 l min−1. The nonlinear behavior allows sensitivities equal to 0.6 V l−1 min for flow rates ranging from −2.0 to +2.0 l min−1, equal to 2.0 V l−1 min for flow rates ranging from −3.0 to −2.0 l min−1 and from +2.0 to +3.0 l min−1, up to 5.7 V l−1 min at higher flow rates ranging from −7.0 to −3.0 l min−1 and from +3.0 to +7.0 l min−1. The linear range extends from 3.0 to 7.0 l min−1 with constant sensitivity equal to 5.7 V l−1 min. The sensor is able to detect a flow-rate equal to 1.0 l min−1 with a sensitivity of about 400 mV l−1 min. The differential nature of the output minimizes the influence of the LEDs’ power supply variations and allows to obtain a repeatability in the order of 3% of full scale output. The small pressure drop produced by the sensor placed in-line the fluid stream, of about 2.4 Pa at 7 l min−1, corresponds to a negligible fluid dynamic resistance lower than 0.34 Pa l−1 min.
Time-dependent density functional theory of open quantum systems in the linear-response regime
Authors: Tempel David G. , Watson Mark A. , Olivares-Amaya Roberto , Aspuru-Guzik Alán
Published: February 2011

Time-dependent density functional theory (TDDFT) has recently been extended to describe many-body open quantum systems evolving under nonunitary dynamics according to a quantum master equation. In the master equation approach, electronic excitation spectra are broadened and shifted due to relaxation and dephasing of the electronic degrees of freedom by the surrounding environment. In this paper, we develop a formulation of TDDFT linear-response theory (LR-TDDFT) for many-body electronic systems evolving under a master equation, yielding broadened excitation spectra. This is done by mapping an interacting open quantum system onto a noninteracting open Kohn–Sham system yielding the correct nonequilibrium density evolution. A pseudoeigenvalue equation analogous to the Casida equations of the usual LR-TDDFT is derived for the Redfield master equation, yielding complex energies and Lamb shifts. As a simple demonstration, we calculate the spectrum of a C2 + atom including natural linewidths, by treating the electromagnetic field vacuum as a photon bath. The performance of an adiabatic exchange-correlation kernel is analyzed and a first-order frequency-dependent correction to the bare Kohn–Sham linewidth based on the Görling–Levy perturbation theory is calculated.
Confined high-mobility electron gas at the Ruddlesden–Popper type heterointerfaces
Authors: Matvejeff M. , Nishio K. , Takahashi R. , Lippmaa M.
Published: February 2011

We study the transport properties of Ruddlesden–Popper type interfaces grown on SrTiO3 substrates, showing that in contrast to perovskite-type interfaces, no mobile carriers are observed in the substrate even when La ions of the rocksalt layer are in direct contact with the Ti-terminated surface of SrTiO3. Annealing at 800 °C and above can, however, be used to perform local chemical doping of the interface by La-ion diffusion into the SrTiO3 substrate, forming a metallic interface with confined high-mobility carriers. The technique can be used to reliably fabricate δ-doped perovskite quantum wells with sheet carrier densities below 1013 cm−2.
Graphene Q-switched, tunable fiber laser
Authors: Popa D. , Sun Z. , Hasan T. , Torrisi F. , Wang F. , Ferrari A. C.
Published: February 2011

We demonstrate a wideband-tunable Q-switched fiber laser exploiting a graphene saturable absorber. We get ∼2 μs pulses, tunable between 1522 and 1555 nm with up to ∼40 nJ energy. This is a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.
Role of charge photodesorption in self-synchronized breakdown of surface streamers in air at atmospheric pressure
Authors: Guaitella O. , Marinov I. , Rousseau A.
Published: February 2011

A surface dielectric barrier discharge configuration with two identical high voltage electrodes is investigated in air at atmospheric pressure. Synchronized breakdown of streamers on both electrodes is evidenced by statistical study. The light emitted by plasma filament on one electrode can trigger the breakdown of streamers on the other electrode. The role of photodesorption of negative charges deposited on the Pyrex dielectric barrier is responsible for these self-synchronized breakdowns. The binding energy of negative charges photodesorbed is estimated to be lower than 3.5 eV.
An efficient micromixer based on multidirectional vortices due to baffles and channel curvature
Authors: Tsai Rei-Tang , Wu Chih-Yang
Published: February 2011

An efficient planar micromixer based on multidirectional vortices in a curved channel with radial baffles is proposed and examined in this work. The curvature of the microchannel and the radial baffles induce vortices in different directions. The multidirectional vortices and the converging-diverging flow caused by the baffles contribute together to the enhancement of mixing. The micromixer is fabricated with polydimethylsiloxane by a single planar microlithography process and the mixing behaviors are observed by a confocal spectral microscope imaging system to validate the simulation obtained by a commercial code. The simulation and experimental results are in reasonable agreement. The concentration distributions and flow patterns obtained reveal the following trends. (i) The mixing efficiency of the basic C-shaped micromixer with the first baffle attached to the internal cylinder and the second attached to the external cylinder is better than that of the C-shaped micromixer with inverted arrangement of baffles. (ii) When the radius of the curved channel and the width of the passage between the baffle and the cylindrical wall are small enough and the Reynolds number (Re) is large enough, an extra separation vortex develops in the downstream of the second baffle. This phenomenon is one of the reasons of trend (i). (iii) A micromixer consisting of a few basic C-shaped micromixers connected by straight channels may generate a high degree of mixing for the case with a large Re.
Matter wave switching in Bose–Einstein condensates via intensity redistribution soliton interactions
Authors: Rajendran S. , Lakshmanan M. , Muruganandam P.
Published: February 2011

Using time dependent nonlinear (s-wave scattering length) coupling between the components of a weakly interacting two component Bose–Einstein condensate (BEC), we show the possibility of matter wave switching (fraction of atoms transfer) between the components via shape changing/intensity redistribution (matter redistribution) soliton interactions. We investigate the exact bright–bright N-soliton solution of an effective one-dimensional (1D) two component BEC by suitably tailoring the trap potential, atomic scattering length, and atom gain or loss. In particular, we show that the effective 1D coupled Gross–Pitaevskii equations with time dependent parameters can be transformed into the well known completely integrable Manakov model described by coupled nonlinear Schrödinger equations by effecting a change of variables of the coordinates and the wave functions under certain conditions related to the time dependent parameters. We obtain the one-soliton solution and demonstrate the shape changing/matter redistribution interactions of two and three-soliton solutions for the time-independent expulsive harmonic trap potential, periodically modulated harmonic trap potential, and kinklike modulated harmonic trap potential. The standard elastic collision of solitons occur only for a specific choice of soliton parameters.
A post-Hartree–Fock study of pressure-induced phase transitions in solid nitrogen: The case of the α, γ, and ε low-pressure phases
Authors: Erba A. , Maschio L. , Salustro S. , Casassa S.
Published: February 2011

We have performed fully periodic ab initio post-Hartree–Fock calculations on three low-temperature molecular phases of solid nitrogen, namely α, γ, and ε. The aim is to characterize the pressure-induced transitions among these phases, which are prototypical molecular crystals, through a periodic local-MP2 method, implemented in the CRYSCOR program. Cohesive energies are computed using extended correlation consistent molecular basis sets, up to quintuple-ζ quality. The MP2 description of equilibrium volumes, pressure–volume curves, and transition pressures is found to be in good agreement with the experiments.
Experimental analysis of dominant instabilities in coaxial jets
Authors: Segalini A. , Talamelli A.
Published: February 2011

An experimental analysis of the dominant instabilities in the near field of two coaxial jets is presented and discussed. Different inner/outer jet velocity pairs (Ui,Uo) have been tested in order to investigate the effect of both velocity ratio ru=Uo/Ui and Reynolds number. Three main instabilities have emerged depending on the velocity ratio. For ru<0.75, the coaxial jets dynamic is driven by the inner shear layer. For ru>1.6, the outer shear layer dominates the near field vortex dynamics while for ru nearly unitary, the vortex shedding behind the separating wall imposes its own dynamics. A new scaling relationship is proposed to improve the estimation of the shedding frequency with respect to the one found in literature.
The Beryllium tetramer: Profiling an elusive molecule
Authors: Ascik Peter N. , Wilke Jeremiah J. , Simmonett Andrew C. , Yamaguchi Yukio , Schaefer Henry F.
Published: February 2011

The structure and energetics of Be4 are investigated using state-of-the-art coupled-cluster methods. We compute the optimized bond length, dissociation energy, and anharmonic vibrational frequencies. A composite approach is employed, starting from coupled-cluster theory with single, double, and perturbative triple excitations extrapolated to the complete basis set (CBS) limit using Dunning's correlation consistent cc-pCVQZ and cc-pCV5Z basis sets. A correction for full triple and connected quadruple excitations in the smaller cc-pCVDZ basis set is then added, yielding an approximation to CCSDT(Q)/CBS denoted c∼CCSDT(Q). Corrections are included for relativistic and non-Born–Oppenheimer effects. We obtain De = 89.7 kcal mol−1, D0 = 84.9 kcal mol−1, and re = 2.043 Å. Second-order vibrational perturbation theory (VPT2) is applied to a full quartic force field computed at the c∼CCSDT(Q) level of theory, yielding Be = 0.448 cm−1 and fundamental frequencies of 666 (a1), 468 (e), and 571 (t2) cm−1. Computations on the spectroscopically characterized Be2 molecule are reported for the purpose of benchmarking our methods. Perturbative estimates of the effect of quadruple excitations are found to be essential to computing accurate parameters for Be2; however, they seem to exert a much smaller influence on the structure and energetics of Be4. Our extensive characterization of the Be4 bonding potential energy surface should aid in the experimental identification of this thermodynamically viable but elusive molecule.
New two-dimensional quantum models with shape invariance
Authors: Cannata F. , Ioffe M. V. , Nishnianidze D. N.
Published: February 2011

Two-dimensional quantum models which obey the property of shape invariance are built in the framework of polynomial two-dimensional supersymmetric quantum mechanics. They are obtained using the expressions for known one-dimensional shape invariant potentials. The constructed Hamiltonians are integrable with symmetry operators of fourth order in momenta, and they are not amenable to the conventional separation of variables.
Relativistic kinetic model for energy deposition of intense laser-driven electrons in fast ignition scenario
Authors: Wu Sizhong , Zhou Cangtao , Zhu Shaoping , Zhang Hua , He Xiantu
Published: February 2011

One of the most crucial steps for a fast ignition scenario is the energy deposition into the highly compressed deuterium-tritium core plasmas via intense laser-produced relativistic electrons. Based on fundamental principles, a kinetic model is developed by considering both binary collisions and the contribution due to collective process. The collision operator is exactly simplified by taking into account relativistic effects within the context of fast ignition. It is expressed in a differential form with the help of two analogous Rosenbluth potentials. The explicit formulation of a relativistic kinetic equation in three-dimensional momentum space is obtained by expanding the potential functions in terms of spherical harmonics, in which only simple differentiations and integrations are involved. Fast electron number is well conserved in this model. The range and penetration depth are also discussed.
Atom-centered symmetry functions for constructing high-dimensional neural network potentials
Authors: Behler Jörg
Published: February 2011

Neural networks offer an unbiased and numerically very accurate approach to represent high-dimensional ab initio potential-energy surfaces. Once constructed, neural network potentials can provide the energies and forces many orders of magnitude faster than electronic structure calculations, and thus enable molecular dynamics simulations of large systems. However, Cartesian coordinates are not a good choice to represent the atomic positions, and a transformation to symmetry functions is required. Using simple benchmark systems, the properties of several types of symmetry functions suitable for the construction of high-dimensional neural network potential-energy surfaces are discussed in detail. The symmetry functions are general and can be applied to all types of systems such as molecules, crystalline and amorphous solids, and liquids.
Multifunctional Ti1−xTaxO2: Ta doping or alloying?
Authors: Barman A. Roy , Motapothula M. , Annadi A. , Gopinadhan K. , Zhao Y. L. , Yong Z. , Santoso I. , Ariando  , Breese M. , Rusydi A. , Dhar S. , Venkatesan T.
Published: February 2011

Useful electronic, magnetic, and optical properties have been proposed and observed in thin films of Ti1−xMxO2 (M=Ta,Nb,V). In this work, we have studied phase formation for films of Ti1−xTaxO2 prepared by pulsed laser deposition. We show that substitutional Ta in TiO2 results in a different material system in terms of its electronic properties. Moss–Burstein shift is ruled out by comparing the electrical transport data of anatase and rutile TiO2. Vegard’s law fit to the blueshift data and the high energy optical reflectivity studies confirm the formation of an alloy with a distinct band structure.
Asymmetric double-shifted characteristics in epitaxial (002) exchange-biased IrMn/CoFe bilayers
Authors: Huang Hsin-Hung , Yang Chih-Yen , Lin Hsiu-Hau , Lai Chih-Huang
Published: February 2011

Symmetric and asymmetric double-shifted loops were observed at room temperature in epitaxial (002) Ir20Mn80/Co50Fe50 samples placed in a setting field applied along collinear and noncollinear directions with the deposition-field direction, respectively. A coherent rotation model with extra unidirectional exchange and uniaxial anisotropies induced by the noncollinear setting field is proposed to explain the asymmetric double-shifted loops. Due to the existence of the biaxial magnetocrystalline anisotropy, the noncollinear setting field results in two interfacial Ir20Mn80 spin orientations, where the major spins determine the direction to observe double-shifted loops and the minor spins determine the field-shift and the asymmetry of double-shifted loops.
Cation-ordering effects in the single layered manganite La2/3Sr4/3MnO4
Authors: Nelson-Cheeseman B. B. , Shah A. B. , Santos T. S. , Bader S. D. , Zuo J.-M. , Bhattacharya A.
Published: February 2011

Epitaxial La1−xSrxMnO3⋅SrO (x=1/3) films were synthesized as random alloys and cation-ordered analogs to probe how cation ordering affects the properties of a two dimensional manganite. The films show evidence for a spin glass like phase below 20 K and weak ferromagnetic ordering up to 130 K. There is a dramatic difference in magnetic anisotropy and the low temperature transport mechanism depending on the cation order, which is consistent with differences in Mn 3d orbital occupancies. This work indicates that cation ordering can significantly alter the Mn 3d orbital ground state in these correlated electron systems.
Study of a hydrogen-bombardment process for molecular cross-linking within thin films
Authors: Liu Y. , Yang D. Q. , Nie H.-Y. , Lau W. M. , Yang J.
Published: February 2011

A low-energy hydrogen bombardment method, without using any chemical additives, has been designed for fine tuning both physical and chemical properties of molecular thin films through selectively cleaving C–H bonds and keeping other bonds intact. In the hydrogen bombardment process, carbon radicals are generated during collisions between C–H bonds and hydrogen molecules carrying ∼10 eV kinetic energy. These carbon radicals induce cross-linking of neighboring molecular chains. In this work, we focus on the effect of hydrogen bombardment on dotriacontane (C32H66) thin films as growing on native SiO2 surfaces. After the hydrogen bombardment, XPS results indirectly explain that cross-linking has occurred among C32H66 molecules, where the major chemical elements have been preserved even though the bombarded thin film is washed by organic solution such as hexane. AFM results show the height of the perpendicular phase in the thin film decreases due to the bombardment. Intriguingly, Young's modulus of the bombarded thin films can be increased up to ∼6.5 GPa, about five times of elasticity of the virgin films. The surface roughness of the thin films can be kept as smooth as the virgin film surface after thorough bombardment. Therefore, the hydrogen bombardment method shows a great potential in the modification of morphological, mechanical, and tribological properties of organic thin films for a broad range of applications, especially in an aggressive environment.