bluuebunny/crossref_metadata_2025 huggingface dataset:
Children’s Intuitive Teleology: Shifting the Focus of Evolution Education Research
Authors: Kampourakis Kostas , Palaiokrassa Eirini , Papadopoulou Maria , Pavlidi Vasiliki , Argyropoulou Myrto
Published: March 2012

Research has shown that children usually provide teleological explanations for the features of organisms and artifacts, from a very early age (3–4 years old). However, there is no consensus on whether teleological explanations are given in the same manner for non-living natural objects as well. The present study aimed to document the teleological explanations of 5- to 8-year-old children for particular features (color and shape) of organisms, artifacts and non-living natural objects. In addition, it was examined if there was any correlation between these explanations and children’s explanations for the usefulness of those features. Our results indicate a developmental shift in children’s teleological explanations, from a non-selective teleology in pre-school to a selective one in the second grade. In the latter case, children provided teleological explanations mostly for the shape of the feet of organisms and for the shape of artifacts, whereas pre-school children provided teleological explanations for non-living natural objects as well, both for the color and for the shape in all cases. Our results are not conclusive and further research is required, including a larger spectrum of students, since teleology is one of the most important conceptual obstacles in understanding evolution that persists even into adulthood. We conclude by proposing a particular research program for this purpose.
The Proximate Determinants of Educational Homogamy: The Effects of First Marriage, Marital Dissolution, Remarriage, and Educational Upgrading
Authors: Schwartz Christine R. , Mare Robert D.
Published: March 2012

This paper adapts the population balancing equation to develop a framework for studying the proximate determinants of educational homogamy. Using data from the National Longitudinal Survey of Youth on a cohort of women born between 1957 and 1964, we decompose the odds of homogamy in prevailing marriages into four proximate determinants: (1) first marriages, (2) first and later marital dissolutions, (3) remarriages, and (4) educational attainment after marriage. The odds of homogamy among new first marriages are lower than among prevailing marriages, but not because of selective marital dissolution, remarriage, and educational attainment after marriage, as has been speculated. Prevailing marriages are more likely to be educationally homogamous than new first marriages because of the accumulation of homogamous first marriages in the stock of marriages. First marriages overwhelmingly account for the odds of homogamy in prevailing marriages in this cohort. Marital dissolutions, remarriages, and educational upgrades after marriage have relatively small and offsetting effects. Our results suggest that, despite the high prevalence of divorce, remarriage, and continued schooling after marriage in the United States, the key to understanding trends in educational homogamy lies primarily in variation in assortative mating into first marriage.
Habitat preference of sea cucumbers:Holothuria atraandHolothuria edulisin the coastal waters of Sri Lanka
Authors: Dissanayake D.C.T. , Stefansson G.
Published: March 2012

Despite their economic importance, the ecology of many sea cucumber species is poorly understood and factors influencing their habitat preferences remain largely unexplained. The distribution and habitat preference of two sea cucumber species;Holothuria atraandHolothuria eduliswere studied off the north-west coast of Sri Lanka by underwater visual census in October 2008. The relationships between the density of each species and the habitat variables, such as mean grain size, organic content (% of dry weight), gravel (%), silt–mud (%), and depth, were examined using a generalized additive model. All these variables except silt–mud have significant influence (P < 0.05) on the habitat association ofH. atra. The shallow water (<10 m) seagrass habitat with sediments characterized by 2–3.5% organic content, 15–25% of gravel and coarse sand (0.7–1.2 mm) were the most preferred conditions byH. atra. High densities ofH. eduliswere found in the shallow (<10 m) depths of rocky areas with algae and seagrass. Favoured bottom sediment conditions ofH. eduliswere mainly similar to the conditions preferred byH. atra, except organic content which did not significantly influence the habitat preference of this species. The preference towards the specific habitat characteristics seems to be associated with their feeding and protection. An understanding of habitat preference would be useful to improve the management of these sea cucumber populations and enable more precise stock assessment.
Are non-loricate ciliates a primary contributor to ecological pattern of planktonic ciliate communities? A case study in Jiaozhou Bay, northern China
Authors: Jiang Yong , Zhang Wei , Zhu Mingzhuang , Al-Rasheid Khaled A. S. , Xu Henglong
Published: March 2012

The contribution of non-loricate ciliate assemblage to the ecological pattern of a ciliated protozoan community was studied based on a 1-year (June 2007–May 2008) dataset collected from Jiaozhou Bay, northern China. Samples were collected biweekly from five sampling sites. Results showed that: (1) the non-loricate ciliate assemblages were the primary components and significantly correlated with the total ciliate communities in terms of species number, abundance and biomass; (2) the ecological pattern of non-loricate ciliate assemblages was significantly related to that of both total ciliate communities and variations in environmental variables; and (3) spatio-temporal variations in biodiversity (richness, diversity and evenness of species) indices of non-loricate ciliate assemblages were significantly correlated with those of total ciliate communities and the environmental conditions, especially nutrients nitrate nitrogen, nitrite nitrogen and soluble reactive phosphorous. These results suggest that the non-loricate ciliates are a primary contributor to the ecological pattern of total ciliate communities and might be used as a potential bioindicator for bioassessment in marine ecosystems.
Prevalence of GB virus type C viraemia in MSM with or without HIV-1 infection in Beijing, China
Authors: LIU Z. , LI L. , CHEN Z. , XU M. , ZHANG T. , JIAO Y. , SHENG B. , CHEN D. , WU H.
Published: March 2012

GB virus C (GBV-C) is frequently identified in patients co-infected with human immunodeficiency virus type 1 (HIV-1) due to the similar transmission routes. However, it remains unclear how these two viruses interact with each other and how one virus affects the replication of the other in the human body. In this study, we performed a case-control study to determine whether GBV-C viraemia could prevent the acquisition of HIV-1 infection, and a cohort study to determine the prevalence, genotypic characteristics and incidence of GBV-C infection in men who have sex with men (MSM) populations in Beijing, China. The prevalence of GBV-C infection in HIV-1-negative subjects was similar to that in HIV-1-positive subjects. Before HIV-1 acquisition, the prevalence of GBV-C was 17·7%, which increased to 27·2% at the acute stage and to 34% at the chronic stage. Genotype 3 was the major genotype of GBV-C in both groups. A significantly positive correlation was observed between the CD4+ T-cell counts and GBV-C viral loads at the acute stage of HIV infection. At the chronic stage (12 months later), this correlation was no longer significant, although it was still positive. Overall, this study demonstrated that pre-existing GBV-C viraemia could not prevent the acquisition of HIV-1 infection and transmission of HIV-1 significantly increased the prevalence of GBV-C viraemia.
The epidemiology of published norovirus outbreaks: a review of risk factors associated with attack rate and genogroup
Authors: MATTHEWS J. E. , DICKEY B. W. , MILLER R. D. , FELZER J. R. , DAWSON B. P. , LEE A. S. , ROCKS J. J. , KIEL J. , MONTES J. S. , MOE C. L. , EISENBERG J. N. S. , LEON J. S.
Published: March 2012

The purpose of this study was to examine global epidemiological trends in human norovirus (NoV) outbreaks by transmission route and setting, and describe relationships between these characteristics, viral attack rates, and the occurrence of genogroup I (GI) or genogroup II (GII) strains in outbreaks. We analysed data from 902 reverse transcriptase–polymerase chain reaction-confirmed, human NoV outbreaks abstracted from a systematic review of articles published from 1993 to 2011 and indexed under the terms ‘norovirus’ and ‘outbreak’. Multivariate regression analyses demonstrated that foodservice and winter outbreaks were significantly associated with higher attack rates. Foodborne and waterborne outbreaks were associated with multiple strains (GI+GII). Waterborne outbreaks were significantly associated with GI strains, while healthcare-related and winter outbreaks were associated with GII strains. These results identify important trends for epidemic NoV detection, prevention, and control.
Psychiatric Comorbidity in Women with Chronic Pelvic Pain
Authors: Meltzer-Brody Samantha , Leserman Jane
Published: March 2012

Chronic pain syndromes are often treatment refractory and pose an enormous burden of suffering for the individual. Chronic pelvic pain (CPP) is generally defined as noncyclic pain of at least 6 months duration and severe enough to require medical care or cause disability. CPP has been estimated to have a prevalence of 15% among women of reproductive age. Women are at increased risk for both major depression and chronic pain syndromes such as CPP, and are more likely to report antecedent stressful events, have higher rates of physical and sexual abuse, and subsequently develop posttraumatic stress disorder. High rates of sexual and physical abuse and other trauma have been shown among women with CPP, including symptoms of dyspareunia (pain during intercourse), dysmenorrhea (pain during menstruation), and vulvar pain. A detailed and comprehensive evaluation of the patient with CPP should include a thorough gynecologic exam and a full mental health assessment. Treatment of CPP must include an integrated approach targeted at both the psychiatric comorbidity and pain symptoms. A multidisciplinary treatment team offers the best chance for success with CPP, and it is critical to suggest psychiatric treatment (psychopharmacology and/or psychotherapy) in addition to traditional medical and surgical approaches.
Female Sexual Disorders: Assessment, Diagnosis, and Treatment
Authors: Kingsberg Sheryl A. , Knudson Gail
Published: March 2012

Sexual health is important to overall health and quality of life. Sexual problems have been associated with relationship problems and may interfere with overall health and they may also be a marker for other undiagnosed comorbid medical conditions. In order for healthcare professionals to manage the sexual health concerns of their patients, it is important for them to understand what constitutes good sexual health. To that end, it is necessary to have a working knowledge of the evolving theoretical models offered to describe a healthy sexual response as well as an understanding of the neurobiology of sexual function. The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Revised lists six primary female sexual disorders: hypoactive sexual desire disorder, sexual aversion disorder, female sexual arousal disorder, female orgasmic disorder,dyspareunia, and vaginismus. Despite a growing awareness of the high prevalence of sexual disorders they are not typically identified nor treated. There are a number of reasons why clinicians fail to identify and treat sexual problems including insufficient training in sexual medicine and communication skills, time-constraints, and embarrassment. Treatment for female sexual problems is usually individualized and may include a combination of office-based education and basic counseling, cognitive-behavioral psychotherapy, pharmacotherapy, and treatment of concomitant medical conditions.
A Complex Case of Neuro-Behçet's Disease in a Patient Previously Diagnosed with multiple Sclerosis: A Case Report
Authors: Shamim Afroz , Budman Cathy L.
Published: March 2012

Multiple sclerosis (MS) and Neuro-Behçet's disease (NBD) have been associated with a range of neuropsychiatric symptoms, including fatigue, cognitive impairment, depression, bipolar disorder, anxiety, sexual dysfunction, and other behavioral disturbances that are characterized by remissions and exacerbations at different points during the course of the disease. We present an interesting case of NBD in a 48-year-old female who had previously been diagnosed with MS. Exploration of this patient's various neuropsychiatric symptoms, their misattribution first to psychopathology and then subsequently to a variety of neurological problems exemplifies the potential pitfalls in diagnosis of a seemingly rare disorder. The role of psychosocial stress-related inflammatory changes in the patient's behavioral and neurological symptoms is explored as well as the potential psychological and medical effects of delayed diagnosis and treatment.
Temperature versus salinity gradients below the ocean mixed layer
Authors: Helber Robert W. , Kara A. Birol , Richman James G. , Carnes Michael R. , Barron Charlie N. , Hurlburt Harley E. , Boyer Timothy
Published: March 2012

We characterize the global ocean seasonal variability of the temperature versus salinity gradients in the transition layer just below the mixed layer using observations of conductivity temperature and depth and profiling float data from the National Ocean Data Center's World Ocean Data set. The balance of these gradients determines the temperature versus salinity control at the mixed layer depth (MLD). We define the MLD as the shallowest of the isothermal, isohaline, and isopycnal layer depths (ITLD, IHLD, and IPLD), each with a shared dependence on a 0.2°C temperature offset. Data are gridded monthly using a variational technique that minimizes the squared analysis slope and data misfit. Surface layers of vertically uniform temperature, salinity, and density have substantially different characteristics. By examining differences between IPLD, ITLD, and IHLD, we determine the annual evolution of temperature or salinity or both temperature and salinity vertical gradients responsible for the observed MLD. We find ITLD determines MLD for 63% and IHLD for 14% of the global ocean. The remaining 23% of the ocean has both ITLD and IHLD nearly identical. It is found that temperature tends to control MLD where surface heat fluxes are large and precipitation is small. Conversely, salinity controls MLD where precipitation is large and surface heat fluxes are small. In the tropical ocean, salinity controls MLD where surface heat fluxes can be moderate but precipitation is very large and dominant.
An automated dust detection using SEVIRI: A multiyear climatology of summertime dustiness in the central and western Sahara
Authors: Ashpole Ian , Washington Richard
Published: March 2012

Here we present an automated dust detection scheme using the Infrared (IR) channels of the Spinning Enhanced Visible and Infrared Imager (SEVIRI), carried on board Meteosat Second Generation (MSG) satellites, from which dust scheme images that are now widely used in Saharan dust studies are created. This provides an objective, readily reproducible and quick way to build up climatologies of dust presence which compares well with subjectively identified dust presence in the daytime hours. At nighttime the automated detection scheme is less reliable due to the strong diurnal cycle of surface temperatures. Our SEVIRI Dust Flag (SDF) is compared to Aerosol Optical Depth (AOD) from the surface and found to successfully and consistently identify moderate‐heavy dust outbreaks, although success rate is lower in the early morning and late evening. SDF corresponds to Absorbing Aerosol Index (AAI) from the Ozone Monitoring Instrument (OMI) that is also indicative of moderate‐heavy dust outbreaks across the central and western Sahara, but there are differences in the spatial patterns of climatologies created over a number of years that are likely to be due to the different sensitivities of the detection schemes. Despite these discrepancies, SDF and AAI both place dust hot spots in southern Algeria and across its southern borders with Mali and Niger, and SDF climatologies for June–August 2004–2010 reveal that there is a substantial degree of interannual variability in dust presence in the central and western Sahara in the boreal summer.
Quantifying total suspended sediment export from the Burdekin River catchment using the loads regression estimator tool
Authors: Kuhnert Petra M. , Henderson Brent L. , Lewis Stephen E. , Bainbridge Zoe T. , Wilkinson Scott N. , Brodie Jon E.
Published: March 2012

The loads regression estimator (LRE) was introduced by Wang et al. (2011) as an improved approach for quantifying the export of loads and the corresponding uncertainty from river systems, where data are limited. We extend this methodology and show how LRE can be used to analyze a 24 year record of total suspended sediment concentrations for the Burdekin River. For large catchments with highly variable discharge such as that of the Burdekin River, it is important to quantify loads and their uncertainties accurately to determine the current load and to monitor the effect of changes in catchment management. The extended methodology incorporates (1) multiple discounted flow terms to represent the effect of flow history on concentration, (2) a term that captures sediment trapping and spatial sources of flow in terms of the ratio of flow from above the Burdekin Falls Dam, and (3) catchment vegetation cover. Furthermore, we validated model structure and performance in relation to the application tested. We also considered errors in gauged flow rates of 10% that were consistent with the literature. The results for the Burdekin site indicate substantial variability in loads across years. The inclusion of vegetation cover as a predictor had a significant impact on total suspended sediment (TSS) concentration, with values up to 2.1% lower noted per increasing percentage of vegetation cover. TSS concentration was up to 38% lower in years with greater proportions of flow from above the dam. The extended LRE methodology resulted in improved model performance. The results suggest that management of vegetation cover in dry years can reduce TSS loads from the Burdekin catchment, and this is the focus of future work.
Comparison of forecasts of mean monthly water level in the Paraguay River, Brazil, from two fractionally differenced models
Authors: Prass Taiane S. , Bravo Juan Martin , Clarke Robin T. , Collischonn Walter , Lopes Sílvia R. C.
Published: March 2012

The paper compares forecasts of mean monthly water levels up to six months ahead at Ladário, on the Upper Paraguay River, Brazil, estimated from two long‐range dependence models. In one of them, the marked seasonal cycle was removed and a fractionally differenced model was fitted to the transformed series. In the other, a seasonal fractionally differenced model was fitted to water levels without transformation. Forecasts from both models for periods up to six months ahead were compared with forecasts given by simpler “short‐range dependence” Box‐Jenkins models, one fitted to the transformed series, the other a seasonal autoregressive moving average (ARMA) model. Estimates of parameters in the four models (two “long‐range dependence”, two “short‐range dependence”) were updated at six‐monthly intervals over a 20 year period, and forecasts were compared using root mean square errors (rmse) between water‐level forecasts and observed levels. As judged by rmse, performances of the two long‐range dependence models, and of the ARMA (1,1) short‐range dependence model, were very similar; all three out‐performed the seasonal short‐range dependence ARMA model. There was evidence that all models performed better during recession periods, than on the hydrograph rising limb.
U.S. trade dispute with China over rare earth elements
Authors: Showstack Randy
Published: March 2012

The U.S. government has brought a new trade case against China over rare earth elements (REE) as well as tungsten and molybdenum, President Barack Obama announced on 13 March. Japan and the European Union also have taken similar actions against China about REEs, which are a group of 17 chemically similar metallic elements that are used in a variety of electronic, optical, magnetic, and catalytic applications. REEs are plentiful in the Earth's crust, although China currently has about 37% of the world's reserves and accounts for more than 95% of the world's production of the elements, according to the British Geological Survey. The United States has requested consultations with China at the World Trade Organization (WTO) concerning “China's unfair export restraints on rare earths, as well as tungsten and molybdenum,” the Office of the United States Trade Representative announced in a 13 March statement.
Ronald Greeley (1939–2011)
Authors: Spudis Paul D.
Published: March 2012

Ronald Greeley, Regent's Professor at Arizona State University, passed away on 27 October 2011 at his home in Tempe. Ron was one of the most prominent and productive planetary scientists of the past 40 years. He leaves behind a record of scientific understanding and numerous former students to carry on his legacy of discovery. Ron was educated in geology at Mississippi State University (B.S., 1962, and M.S., 1963) and the University of Missouri‐Rolla (Ph.D., 1966)
Fichtner receives 2011 Keiiti Aki Young Scientist Award: Citation
Authors: Shearer Peter
Published: March 2012

Andreas Fichtner received the 2011 Keiiti Aki Young Scientist Award at the 2011 AGU Fall Meeting, held 5–9 December in San Francisco, Calif. The award recognizes the scientific accomplishments of a young scientist who makes outstanding contributions to the advancement of seismology.
Fichtner receives 2011 Keiiti Aki Young Scientist Award: Response
Authors: Fichtner Andreas
Published: March 2012

Andreas Fichtner received the 2011 Keiiti Aki Young Scientist Award at the 2011 AGU Fall Meeting, held 5–9 December in San Francisco, Calif. The award recognizes the scientific accomplishments of a young scientist who makes outstanding contributions to the advancement of seismology.
Remote sensing of volcanic ash properties
Authors: Balcerak Ernie
Published: March 2012

Remote sensing is an important tool to track hazardous volcanic plumes, providing an overview of the ash cloud. Francis et al. describe a method of using infrared data from instruments on board the Meteosat satellite to detect volcanic ash and derive quantitative measurements of its physical properties. They demonstrated their technique using data from the 2010 Eyjafjallajökull eruption and validated their retrieved properties against space‐borne and airborne lidar data. They show that their retrieved properties are realistic, and the method should help improve ash cloud analysis and forecasting. (Journal of Geophysical Research‐Atmospheres, doi:10.1029/2011JD016788, 2012)
When will warming‐induced rainfall changes be perceptible?
Authors: Balcerak Ernie
Published: March 2012

Global climate change is not only changing temperatures but also altering precipitation. These changes in precipitation have been studied on large regional levels, but studies have not been able to identify changes in observed precipitation on smaller spatial scales. Natural interannual variability also makes it difficult to perceive precipitation changes caused by global warming at a statistically significant level. Using general circulation climate models to study future precipitation changes, Mahlstein et al. estimated how much global temperatures would need to increase for the warming‐induced precipitation changes to be clearly noticeable on local or regional scales. They found that temperatures would need to be 1.4°C warmer than they were in the early twentieth century for regional precipitation changes to be statistically significant. The authors note that this is likely to occur by the end of this century. (Geophysical Research Letters, doi:10.1029/2011GL050738, 2012
Protection of cells from nitric oxide‐mediated apoptotic death by glutathione C60 derivative
Authors: Hu Zhen , Zhang Chunhua , Tang Peiyi , Li Cuiyun , Yao Yuhuan , Sun Shaofan , Zhang Li , Huang Yudong
Published: March 2012

The influence of the glutathione C60 derivative on the cytotoxicity of a highly reactive free radical NO (nitric oxide) has been investigated. Consistent with its cytoprotective abilities, the derivative scavenges ROS (reactive oxygen species) and RNS (reactive nitrogen species) both in vitro and under cell‐free conditions. Moreover, the glutathione C60 derivative protected PC12 cells from the cytotoxic effect of the NO‐releasing compound, SNP (sodium nitroprusside). Addition of glutathione C60 derivative alone did not induce apoptosis and necrosis. The results suggest that the glutathione C60 derivative has the potential to prevent NO‐mediated cell death without evident toxicity.
Time dependent changes in extreme ultraviolet reflectivity of Ru mirrors from electron-induced surface chemistry
Authors: Kanjilal A. , Catalfano M. , Harilal S. S. , Hassanein A. , Rice B.
Published: March 2012

Time dependent changes in 13.5 nm extreme ultraviolet (EUV) reflectivity of Ru mirrors due to variations in surface composition were investigated. The surface properties of Ru films were analyzed in situ by means of X-ray photoelectron spectroscopy (XPS), and further verified by Auger electron spectroscopy (AES). Moreover, the impact on EUV reflectivity (EUVR) with time was examined in situ via continuous and/or discrete EUV exposures. The rapid decrease in EUVR was observed in the presence of photoelectrons (PEs) from Ru mirror of the EUV setup, whereas no significant variation was recorded by screening out additional PEs. Detailed XPS and AES analyses suggest that carbon deposition via dissociation of residual hydrocarbons plays a dominant role in the presence of additional PEs, and thus reduces the reflectivity rapidly. Using EUV photoelectron spectroscopy, systematic reduction of the secondary electron yield from the Ru mirror surface was observed in consecutive scans, and therefore supports the formation of carbonaceous Ru surface in the presence of additional PEs.
Differential alternating current chip calorimeter for in situ investigation of vapor-deposited thin films
Authors: Ahrenberg M. , Shoifet E. , Whitaker K. R. , Huth H. , Ediger M. D. , Schick C.
Published: March 2012

Physical vapor deposition can be used to produce thin films with interesting material properties including extraordinarily stable organic glasses. We describe an ac chip calorimeter for in situ heat capacity measurements of as-deposited nanometer thin films of organic glass formers. The calorimetric system is based on a differential ac chip calorimeter which is placed in the vacuum chamber for physical vapor deposition. The sample is directly deposited onto one calorimetric chip sensor while the other sensor is protected against deposition. The device and the temperature calibration procedure are described. The latter makes use of the phase transitions of cyclopentane and the frequency dependence of the dynamic glass transition of toluene and ethylbenzene. Sample thickness determination is based on a finite element modeling of the sensor sample arrangement. In the modeling, a layer of toluene was added to the sample sensor and its thickness was varied in an iterative way until the model fit the experimental data.
Atomistic simulations of rare events using gentlest ascent dynamics
Authors: Samanta Amit , E Weinan
Published: March 2012

The dynamics of complex systems often involve thermally activated barrier crossing events that allow these systems to move from one basin of attraction on the high dimensional energy surface to another. Such events are ubiquitous, but challenging to simulate using conventional simulation tools, such as molecular dynamics. Recently, E and Zhou [Nonlinearity 24(6), 1831 (2011)]10.1088/0951-7715/24/6/008 proposed a set of dynamic equations, the gentlest ascent dynamics (GAD), to describe the escape of a system from a basin of attraction and proved that solutions of GAD converge to index-1 saddle points of the underlying energy. In this paper, we extend GAD to enable finite temperature simulations in which the system hops between different saddle points on the energy surface. An effective strategy to use GAD to sample an ensemble of low barrier saddle points located in the vicinity of a locally stable configuration on the high dimensional energy surface is proposed. The utility of the method is demonstrated by studying the low barrier saddle points associated with point defect activity on a surface. This is done for two representative systems, namely, (a) a surface vacancy and ad-atom pair and (b) a heptamer island on the (111) surface of copper.
Accumulation of air in polymeric materials investigated by laser-induced breakdown spectroscopy
Authors: Yip W. L. , Mothe E. , Beldjilali S. , Hermann J.
Published: March 2012

We report on spectroscopic analyses of plasmas produced by laser irradiation of nitrogen-free and nitrogen-containing polymer materials. Ultraviolet laser pulses of 5 ns duration and 4 mJ energy were focused onto the samples with a fluence of about 20 Jcm−2. The plasma emission was analyzed with an Echelle spectrometer equipped with a gated detector. Comparing the spectra recorded during ablation in air and argon, it is shown that the spectral line emission of atomic nitrogen originates from the excitation of the ambient air, whereas the CN molecular bands are essentially emitted from the ablation plume. Furthermore, the measurements demonstrate an additional contribution of nitrogen emission from the air molecules accumulated in the polymer. Storage under vacuum over a duration of the order of one day leads to the release of the absorbed air. As a consequence of the air absorption, the measurement of elemental composition of polymers via laser-induced breakdown spectroscopy is particularly difficult. Here, we quantify the atmospheric contribution to the plume emission during polymer analysis.
Calculations of two-fluid linear response to non-axisymmetric fields in tokamaks
Authors: Ferraro N. M.
Published: March 2012

The zero-frequency linear plasma response to static applied non-axisymmetric fields is calculated using a resistive two-fluid model in diverted, toroidal geometry. Within this model, the effects on the plasma response of resistivity, rotation, differential ion and electron velocity, and dissipation are explored. Rotation is generally found to inhibit the formation of islands in the plasma, in qualitative agreement with theoretical results. When two-fluid effects are included, it is found that the penetration of the non-axisymmetric fields is generally greatest when the part of the electron rotation perpendicular to the equilibrium magnetic field is small at the mode-rational surface. Strong rotation shear in the edge is found to enhance the plasma response there. The entire plasma, including the separatrix and scrape-off layer, is included in the computational domain.
Theoretical study of shear horizontal wave propagation in periodically layered piezoelectric structure
Authors: Zhao J. , Pan Y. , Zhong Z.
Published: March 2012

In this paper, the propagation of the shear horizontal wave (SH-wave) in the single piezoelectric layer and periodically layered piezoelectric structure is studied. Both the dispersion equation and transmission coefficients are derived to reveal the wave behavior of the corresponding structures when the piezoelectricity is ignored or the electrical circuit is open and closed. The zero-order mode of the piezoelectricity-ignored single plate is not dispersive and every higher order mode is dispersive with a cut-off frequency. Same features are found for the electrically open and closed cases except that the zero-order mode of the latter case is no more non-dispersive. The pass bands of the piezoelectricity-ignored periodically layered structure appear when the normalized frequency is an even integer under the normal incidence, and new stop bands will appear from the pass bands as the incident angle increases. The same features are observed for the band gaps of the electrically open and closed cases except that the zero-order mode of the latter case is dispersive. The stop bands of the periodic structure will change in a cycle as the geometric ratio increases from zero to one.
Kinetics of electron attachment to OH and HNO3 and mutual neutralization of Ar+ with NO2− and NO3− at 300 and 500 K
Authors: Shuman Nicholas S. , Miller Thomas M. , Viggiano A. A.
Published: March 2012

The electron attachment rate constant to nitric acid (HNO3) has been measured in a flowing afterglow-Langmuir probe (FALP) apparatus at 300 and 500 K using three independent methods: the traditional FALP technique of monitoring electron depletion, “one-gas” VENDAMS (variable electron and neutral density attachment mass spectrometry), and “two-gas” VENDAMS. The three measurements are in agreement with a 300 K weighted average of 1.4 ± 0.3 × 10−7 cm3 s−1, 2 to 10 times higher than previously reported values. Attachment is primarily dissociative yielding NO2− as previously reported, but for the first time a small endothermic channel to produce OH− was also observed at 500 K. From the one-gas VENDAMS data, associative attachment to the OH produced in the primary attachment was found to occur with an effective two body rate constant of $ 1.2 \pm _{0.7}^3 \times 10$1.2±0.73×10−11 cm3 s−1 at 300 K, the first reported rate constant for this radical species. Finally, ion-ion neutralization rate constants of NO2− and NO3− with Ar+ were determined to be $5.2 \pm _{2.5}^{1.5}$5.2±2.51.5 × 10−8 and 4.5 ± 2.5 × 10−8 cm3 s−1 at 300 K, respectively.
Magnetic and structural properties of the Fe layers in CoO/Fe/Ag(001) heterostructure
Authors: Bali Rantej , Soares Márcio M. , Ramos Aline Y. , Tolentino Hélio C. N. , Yildiz Fikret , Boudot Clemence , Proux Olivier , De Santis Maurizio , Przybylski Marek , Kirschner Jürgen
Published: March 2012

The influence of interfacial oxidation on the magnetic behaviour of CoO covered Fe/Ag(001) is reported. Coverage with CoO causes the formation of a mixed Fe2O3-Fe3O4 interfacial oxide layer. The depth of the Fe-oxide varies with the thickness of pre-covered Fe and above 8 monolayers (MLs) of Fe the oxide depth becomes constant at 2 ML. Differences in exchange bias and coercivity obtained from magnetic field and zero field cooling nearly vanish above 8 ML Fe thickness, showing a direct correlation between the magnetic behaviour of Fe and structure of the interfacial Fe-oxide layer.
Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas
Authors: Rice J. E. , Greenwald M. J. , Podpaly Y. A. , Reinke M. L. , Diamond P. H. , Hughes J. W. , Howard N. T. , Ma Y. , Cziegler I. , Duval B. P. , Ennever P. C. , Ernst D. , Fiore C. L. , Gao C. , Irby J. H. , Marmar E. S. , Porkolab M. , Tsujii N. , Wolfe S. M.
Published: March 2012

Ohmic energy confinement saturation is found to be closely related to core toroidal rotation reversals in Alcator C-Mod tokamak plasmas. Rotation reversals occur at a critical density, depending on the plasma current and toroidal magnetic field, which coincides with the density separating the linear Ohmic confinement regime from the saturated Ohmic confinement regime. The rotation is directed co-current at low density and abruptly changes direction to counter-current when the energy confinement saturates as the density is increased. Since there is a bifurcation in the direction of the rotation at this critical density, toroidal rotation reversal is a very sensitive indicator in the determination of the regime change. The reversal and confinement saturation results can be unified, since these processes occur in a particular range of the collisionality.
Second-harmonic generation reveals the oxidation steps in semiconductor processing
Authors: Vanbel M. K. , Valev V. K. , Vincent B. , Afanas’ev V. V. , Locquet J.-P. , Van Elshocht S. , Caymax M. , Verbiest T.
Published: March 2012

Monitoring oxidation steps is an important factor during the fabrication of semiconductor devices, because transistor performance can be greatly affected by defects in the passivation layer. As an example, we discuss the formation of a gate stack in metal oxide semiconductor (MOS) devices using Ge as an alternative channel material. Building an MOS gate stack on Ge requires passivation of the interface between the dielectric (typically a high-k material such as Al2O3 or HfO2, grown by means of atomic layer deposition (ALD)) and the Ge channel. Such passivation can be obtained from a very thin Si layer, epitaxially grown on Ge. The Si surface receives an oxidizing clean (O3 or wet chemical clean) before the ALD step. In this work, second-harmonic generation (SHG) data are presented for silicon layers with varying thickness, grown with either trisilane (Si3H8) or silane (SiH4) and with various cleaning steps. The trend in second-harmonic response upon azimuthal rotation of the samples was comparable for both silane and trisilane as a Si precursor. Our results show that upon oxidation, the SHG intensity reduces, most likely due to a reduction of the amount of crystalline Si, which is converted to SiO2.
A bio-inspired approach to enhancing wind power conversion
Authors: Song YongDuan , Cai WenChuan , Li Peng , Hu YongSheng
Published: March 2012

The primary objective of this investigation is to develop a new control method for wind turbines that can increase their wind energy capture efficiency. Since the resultant wind turbine system dynamics are profoundly nonlinear and coupled with significant uncertainties, traditional model-based control is found to be not only structurally complex but also computationally expensive. Here, we explore two sets of control algorithms to enhance wind to electrical energy conversion. The first accounts for system nonlinearities and external disturbances by integrating variable structure control with adaptive control. The second accommodates the nonlinearities arising from rotor aerodynamics and pitch (actuation) dynamics, as well as external disturbances, through a method inspired by a 1st order human memory/learning model. The second method allows direct maximum power coefficient tracking for winds under the rated speed and ensures rated power output for winds over the rated speed. Basically, it uses the system current and most recent memorized responses, together with past control experience, to generate new control actions. Both rotor dynamics and actuation (pitch) dynamics are reflected indirectly through the observed/measured system response at each instant, and are embedded within the control mechanism. Thus, there is no need for detailed information on the system model or system parameters in the control’s design and implementation. The efficacy of both proposed approaches is analyzed through numerical simulations.
Rare backflow and extreme wall-normal velocity fluctuations in near-wall turbulence
Authors: Lenaers Peter , Li Qiang , Brethouwer Geert , Schlatter Philipp , Örlü Ramis
Published: March 2012

Rare negative streamwise velocities and extreme wall-normal velocity fluctuations near the wall are investigated for turbulent channel flow at a series of Reynolds numbers based on friction velocity up to Reτ = 1000. Probability density functions of the wall-shear stress and velocity components are presented as well as joint probability density functions of the velocity components and the pressure. Backflow occurs more often (0.06% at the wall at Reτ = 1000) and further away (up to y+ = 8.5) from the wall for increasing Reynolds number. The regions of backflow are circular with an average diameter, based on ensemble averages, of approximately 20 viscous units independent of Reynolds number. A strong oblique vortex outside the viscous sublayer is found to cause this backflow. Extreme wall-normal velocity events occur also more often for increasing Reynolds number. These extreme fluctuations cause high flatness values near the wall (F(v) = 43 at Reτ = 1000). Positive and negative velocity spikes appear in pairs, located on the two edges of a strong streamwise vortex as documented by Xu et al. [Phys. Fluids 8, 1938 (1996)]10.1063/1.868973 for Reτ = 180. The spikes are elliptical and orientated in streamwise direction with a typical length of 25 and a typical width of 7.5 viscous units at y+ ≈ 1. The negative spike occurs in a high-speed streak indicating a sweeping motion, while the positive spike is located in between a high and low-speed streak. The joint probability density functions of negative streamwise and extreme wall-normal velocity events show that these events are largely uncorrelated. The majority of both type of events can be found lying underneath a large-scale structure in the outer region with positive sign, which can be understood by considering the more intense velocity fluctuations due to amplitude modulation of the inner layer by the outer layer. Simulations performed at different resolutions give only minor differences. Results from experiments and recent turbulent boundary layer simulations show similar results indicating that these rare events are universal for wall-bounded flows. In order to detect these rare events in experiments, measurement techniques have to be specifically tuned.
Vibrational modes of GaAs hexagonal nanopillar arrays studied with ultrashort optical pulses
Authors: Sakuma Hirotaka , Tomoda Motonobu , Otsuka Paul H. , Matsuda Osamu , Wright Oliver B. , Fukui Takashi , Tomioka Katsuhiro , Veres Istvan A.
Published: March 2012

We investigate the vibrational modes of a triangular array of anisotropic, hexagonal GaAs nanopillars on a GaAs substrate through ultrafast changes in optical reflectivity. By comparison with simulations, we identify GHz resonances, mode shapes, and damping. In addition, by varying the pillar diameter, height, and pitch, we distinguish collective and localized modes. A proper understanding of substrate-attached nanostructure dynamics will lead to better characterization of nanosensors based on perturbations to vibrational resonances.
Efficient broad-spectrum parallel tandem organic solar cells based on the highly crystalline chloroaluminum phthalocyanine films as the planar layer
Authors: Chen Weichao , Qiao Xiaolan , Yang Jianbing , Yu Bo , Yan Donghang
Published: March 2012

Efficient parallel tandem organic solar cells are demonstrated by using the highly crystalline chloroaluminum phthalocyanine (AlClPc) films as the planar layer. Their broad photoresponse from 400–900 nm is contributed to the strong near-infrared absorption of the AlClPc films and the good complementarity between AlClPc and zinc phthalocyanine. Importantly, the high external quantum efficiency is obtained in the entire response range with the peak value 65% due to the high carrier mobility of the AlClPc films, and correspondingly the high power conversion efficiency of 3.5% is attributed to the large short circuit current density of 12.15 mA/cm2.
Band gap tuning in ferroelectric Bi4Ti3O12 by alloying with LaTMO3 (TM = Ti, V, Cr, Mn, Co, Ni, and Al)
Authors: Seok Choi Woo , Nyung Lee Ho
Published: March 2012

We fabricated ferroelectric Bi4Ti3O12 (BiT) single crystalline thin films site-specifically substituted with LaTMO3 (TM = Al, Ti, V, Cr, Mn, Co, and Ni) on SrTiO3 substrates by pulsed laser epitaxy. When transition metals are incorporated into a certain site of BiT, some of BiT-LaTMO3 showed a substantially decreased band gap, coming from the additional optical transition between oxygen 2p and TM 3d states. Specifically, all alloys with Mott insulators revealed a possibility of band gap reduction. Among them, BiT-LaCoO3 showed the largest band gap reduction by ∼1 eV, positioning itself as a promising material for highly efficient opto-electronic devices.
Structure and ion transport in Li3Fe2(PO4)3 synthesized by solution combustion technique
Authors: Vijayan Lakshmi , Cheruku Rajesh , Govindaraj G.
Published: March 2012

Li3Fe2(PO4)3 is interesting because of its technological application and environmentally benign nature. Nanocrystalline Li3Fe2(PO4)3 is synthesized by a solution combustion technique. The role of fuels/complexing agents in deciding the structural parameters and ac electrical behavior is investigated in this study. Antiferromagnetic nature and direct bandgap energy of 3.09 eV are recognized in the material. Enhanced conduction is established through mobility of Li+ ion in four co-ordination in the modified monoclinic symmetry and high temperature stability through orthorhombic symmetry. Quality of electrical data is confirmed through a Kramers-Kronig test and electrical relaxation parameters are obtained from modulus analysis. Scaling analysis of modulus data confirmed the time-temperature superposition principle.
Quantum-dot nano-cavity lasers with Purcell-enhanced stimulated emission
Authors: Gregersen N. , Suhr T. , Lorke M. , Mørk J.
Published: March 2012

We present a rate equation model for quantum-dot light-emitting devices that take into account Purcell enhancement of both spontaneous emission and stimulated emission as well as the spectral profile of the optical and electronic density-of-states. We find that below threshold the β-factor in a quantum-dot nanolaser depends strongly on the pump. For quantum dots with linewidth comparable to that of the cavity, we then show that an otherwise non-lasing device can lase due to Purcell enhancement of the stimulated emission. Finally, we compare the rate equation model to a microscopic model and obtain good agreement.
Nonlocal spin transports in nanopillar-based lateral spin valve
Authors: Nonoguchi S. , Nomura T. , Kimura T.
Published: March 2012

A different type lateral spin valve structure consisting of a pair of the closely located Permalloy nanopillars on a uniform copper film has been developed. From the bias-current and temperature dependences of the spin signal, the nanopillar lateral spin valve was found to have several advantages for generating the pure spin current over the conventional lateral spin valves. We also show that the limitation of the generating spin current can be enhanced by increasing the number of the spin injectors.
Carrier dynamics and conductivity of SnO2 nanowires investigated by time-resolved terahertz spectroscopy
Authors: Tsokkou Demetra , Othonos Andreas , Zervos Matthew
Published: March 2012

THz spectroscopy has been applied to investigate the photo-induced and intrinsic conductivity in SnO2 nanowires using the Drude-Smith model. The refractive index of the nanowires was found to decrease from 2.4 to 2.1 with increasing THz frequency and the dc mobility of the non-excited nanowires was determined to be 72 ± 10 cm2/Vs. Measurements reveal that scattering times are carrier density dependent, while a strong suppression of long transport is evident. Intensity-dependent measurements provided an estimate of the Auger coefficient found to be γ = (7.2 ± 2.0) × 10−31 cm6/s.
Aging associated domain evolution in the orthorhombic phase of 〈001〉 textured (K0.5Na0.5)Nb0.97Sb0.03O3 ceramics
Authors: Yao Jianjun , Li Jiefang , Viehland D. , Chang Yunfei , Messing Gary L.
Published: March 2012

Aging effect due to domain evolution in (K0.5,Na0.5)Nb0.97Sb0.03O3 〈001〉 textured ceramics was investigated by piezoresponse force microscopy. We find that aging effect is pronounced in the orthorhombic single phase field. A more uniform and finer domain structure on the order of several hundred nanometers was observed after aging and is believed to originate from defect-migration. After poling, large domains (∼10 μm) with smooth boundaries were found in the aged condition due to the more readily redistribution of uniform and finer domain structures after aging.