bluuebunny/crossref_metadata_2025 huggingface dataset:
Perplexities of pertussis: recent global epidemiological trends and their potential causes
Authors: JACKSON D. W. , ROHANI PEJMAN
Published: January 2013

Recent much-publicized increases in pertussis case reports in some countries with high vaccine coverage have raised concerns about its current and future control. The ubiquity of this trend, however, remains unexamined. In an attempt to paint a global picture, we used case counts to determine which countries experienced statistically significant trends in incidence over the past two decades and to map changes in incidence during this period. These data reveal that pertussis resurgence is not a universal phenomenon. The heterogeneity in incidence trends, even in countries with superficially similar demography, socioeconomic conditions and vaccination programmes, is striking and requires explanation. In this opinion piece, we review and assess the multifaceted proposed explanations incorporating evolution, population dynamics, and the details of immunization programmes. While we do not solve the riddle that is pertussis epidemiology, we highlight critical aspects that are likely to hold the key to understanding its worldwide epidemiology.
Large-scale occupancy surveys in East Antarctica discover new Adélie penguin breeding sites and reveal an expanding breeding distribution
Authors: Southwell Colin , Emmerson Louise
Published: January 2013

Knowledge of spatial distribution is fundamental to ecological studies and crucial for conservation and management of species and biodiversity, but detailed, large-scale spatial data are lacking for most taxa. Although the Adélie penguin is one of the most intensively studied Antarctic vertebrates, spatial data that could aid in ecological study and conservation management are incomplete. We undertook a large-scale survey of the current breeding distribution of Adélie penguins along 3800 km of the East Antarctic coastline. The survey increased the number of known breeding locations by 50% and revealed that the breeding distribution has expanded in some parts of the survey region over the past two to three decades. The expanding breeding distribution may reflect underlying population dynamics of sustained growth and resultant density dependent effect on dispersal and movement from established breeding sites to new sites. The comprehensive, large-scale distribution data from this study will form a baseline for assessing any future changes in Adélie penguin breeding distribution, provide data for developing spatial models for predicting future changes in breeding distribution under plausible scenarios of environmental change, and contribute to the development of metapopulation models by providing estimates of local colonization and extinction probabilities under specific conditions of metapopulation change.
On radial stationary solutions to a model of non-equilibrium growth
Authors: ESCUDERO CARLOS , HAKL ROBERT , PERAL IRENEO , TORRES PEDRO J.
Published: January 2013

We present the formal geometric derivation of a non-equilibrium growth model that takes the form of a parabolic partial differential equation. Subsequently, we study its stationary radial solutions by means of variational techniques. Our results depend on the size of a parameter that plays the role of the strength of forcing. For small forcing we prove the existence and multiplicity of solutions to the elliptic problem. We discuss our results in the context of non-equilibrium statistical mechanics.
Counting civil society: deconstructing elite participation in the provincial English city, 1900–1950
Authors: HAYES NICK
Published: January 2013

With few dissenting voices, the historiography of twentieth-century urban civil society has been relayed through a prism of continuing and escalating elite disengagement. Within a paradigm of declinism, academics, politicians and social commentators contrast a past offering a richness of social commitment against a present characterized by lowering standards in urban governance. Put simply, the right sorts of people were no longer volunteering. Yet the data for such claims is insubstantial, and the applied methodology flawed. What are lacking are detailed empirical studies which offer flexible measures of status across a range of voluntary and political activities, so that we can better understand the social trends of urban volunteering across the first 50 years of the twentieth century.
Iodine and iron status of pregnant women in Lubumbashi, Democratic Republic of Congo
Authors: Habimana Laurence , Twite Kabange E , Wallemacq Pierre , De Nayer Philippe , Daumerie Chantal , Donnen Philippe , Kalenga Muenze K , Robert Annie
Published: January 2013

Objective

Adequate iodine and Fe intakes are imperative during pregnancy to prevent fetal defects, but such data are not available in the Democratic Republic of Congo. We aimed to assess iodine and Fe status in pregnant women from Lubumbashi.

Design

Cross-sectional study. We measured urinary iodine concentration (UIC) in random urine samples using a modified Sandell–Kolthoff digestion method; the WHO reference medians were used to classify iodine intake as deficient, adequate, more than adequate or excessive. Serum ferritin concentrations were measured by immunoenzymatic assay and considered insufficient when <12 ng/ml.

Setting

Maternity units from rural, semi-urban and urban areas of Lubumbashi, Democratic Republic of Congo.

Subjects

Two hundred and twenty-five randomly selected pregnant women attending prenatal consultation, seventy-five postpartum women and seventy-five non-pregnant women as controls.

Results

Overall median UIC in pregnant women was 138 (interquartile range: 105–172) μg/l, indicating iodine deficiency, whereas postpartum and non-pregnant women had adequate iodine intake: median UIC = 144 μg/l and 204 μg/l, respectively. Median UIC values were lower in late pregnancy than in early pregnancy: in the first, second and third trimester respectively 255 μg/l, 70 μg/l and 88 μg/l in the rural area; 306 μg/l, 166 μg/l and 68 μg/l in the semi-urban area; and 203 μg/l, 174 μg/l and 99 μg/l in the urban area. Fe was insufficient in 39 % of pregnant women compared with 21 % of non-pregnant and postpartum women. In the third trimester, deficiencies in both iodine and Fe were high: 40 %, 12 % and 18 % in the rural, semi-urban and urban areas, respectively.

Conclusions

Our data suggest that pregnant women are at risk of iodine and Fe deficiencies in Lubumbashi. Country policies fighting against iodine and Fe deficiencies during pregnancy should be reinforced.
Twin Registries Worldwide: An Important Resource for Scientific Research
Authors: Hur Yoon-Mi , Craig Jeffrey M.
Published: January 2013

Twins can provide unique opportunities to study causal influences on variation in human behaviors, development, and diseases. During the past 10 years, the number of twin registries has increased rapidly across the globe and we thought it timely to bring these to the attention of our readership. In this special issue, we invited papers on twin registries and cohorts from 28 countries representing five continents. Subjects covered include how to establish and maintain twin registries, accurately assess zygosity, collect biospecimens, and other important issues related to twin studies. This special issue shows that over 1.5 million twins and their families are participating in twin studies worldwide. Research interests will be highlighted, with the aim of fostering collaborative research.
Angstbezogenes Kontrollerleben
Authors: Helbig-Lang Sylvia , Schneider Annegret , Petermann Franz
Published: January 2013

Theoretischer Hintergrund: Subjektive Kontrollüberzeugungen werden als wesentlicher Faktor in der Entstehung und Aufrechterhaltung von Angststörungen diskutiert. Der Angstkontrollfragebogen (AKF) stellt das einzige Verfahren dar, das auf die Erfassung angstspezifischer Kontrollüberzeugungen zielt. Fragestellung: Wie ist die psychometrische Güte einer deutschen Übersetzung des AKF zu beurteilen? Methode: Untersuchung des AKF in einer nicht-klinischen und einer klinischen Stichprobe. Ergebnisse: Der AKF Gesamtscore wies befriedigende Reliabilitätskennwerte auf; darüber hinaus wurden Hinweise auf konvergente Validität gefunden. Allerdings stellen die Ergebnisse die Spezifität des Verfahrens für Angsterleben in Frage. Wie bereits in Studien zur Originalversion konnte keine überzeugende Faktorenstruktur etabliert werden. Schlussfolgerungen: Der AKF stellt eine potentiell wichtige Ergänzung nicht-symptomspezifischer Maße zur Erklärung von Psychopathologie dar, bedarf jedoch insbesondere hinsichtlich seiner latenten Struktur weiterer Überprüfung.
Entwicklung und Validierung eines Fragebogens zur Erfassung von hypochondrischem Sicherheitsverhalten
Authors: Weck Florian , Brehm Ursula , Schermelleh-Engel Karin
Published: January 2013

Theoretischer Hintergrund: Sicherheitsverhalten wird für die Aufrechterhaltung von hypochondrischen Ängsten ein wichtiger Stellenwert beigemessen. Fragestellung: In der vorliegenden Untersuchung soll die Güte eines Fragebogens zur Erfassung von Sicherheitsverhalten bei vorliegender Hypochondrie (FSVH) überprüft werden. Methode: Zur Validierung wurden eine Patientenstichprobe (N = 108) und eine Online-Stichprobe (N = 503) herangezogen. Ergebnisse: Mittels explorativer und konfirmatorischer Faktorenanalysen ließen sich die Faktoren Rückversicherungs- und Vermeidungsverhalten extrahieren. Es zeigten sich deutliche Hinweise für die konvergente und diskriminante Validität des FSVH. Für den FSVH fanden sich signifikant höhere Werte für Patienten mit Hypochondrie als für solche mit Angststörungen, somit war es möglich, mittels des FSVH zwischen diesen beiden Störungsgruppen mit hoher Genauigkeit zu diskriminieren. Schlussfolgerung: Der FSVH stellt eine geeignete Ergänzung zu etablierten Verfahren dar.
The Adaptation of the Cerebral Circulation to Pregnancy: Mechanisms and Consequences
Authors: Cipolla Marilyn J
Published: January 2013

The adaptation of the cerebral circulation to pregnancy is unique from other vascular beds. Most notably, the growth and vasodilatory response to high levels of circulating growth factors and cytokines that promote substantial hemodynamic changes in other vascular beds is limited in the cerebral circulation. This is accomplished through several mechanisms, including downregulation of key receptors and transcription factors, and production of circulating factors that counteract the vasodilatory effects of vascular endothelial growth factor (VEGF) and placental growth factor. Pregnancy both prevents and reverses hypertensive inward remodeling of cerebral arteries, possibly through downregulation of the angiotensin type 1 receptor. The blood–brain barrier (BBB) importantly adapts to pregnancy by preventing the passage of seizure provoking serum into the brain and limiting the permeability effects of VEGF that is more highly expressed in cerebral vasculature during pregnancy. While the adaptation of the cerebral circulation to pregnancy provides for relatively normal cerebral blood flow and BBB properties in the face of substantial cardiovascular changes and high levels of circulating factors, under pathologic conditions, these adaptations appear to promote greater brain injury, including edema formation during acute hypertension, and greater sensitivity to bacterial endotoxin.
Comparisons of Analysis Methods for Proof‐of‐Concept Trials
Authors: Karlsson KE , Vong C , Bergstrand M , Jonsson EN , Karlsson MO
Published: January 2013

Drug development struggles with high costs and time consuming processes. Hence, a need for new strategies has been accentuated by many stakeholders in drug development. This study proposes the use of pharmacometric models to rationalize drug development. Two simulated examples, within the therapeutic areas of acute stroke and type 2 diabetes, are utilized to compare a pharmacometric model–based analysis to a t‐test with respect to study power of proof‐of‐concept (POC) trials. In all investigated examples and scenarios, the conventional statistical analysis resulted in several fold larger study sizes to achieve 80% power. For a scenario with a parallel design of one placebo group and one active dose arm, the difference between the conventional and pharmacometric approach was 4.3‐ and 8.4‐fold, for the stroke and diabetes example, respectively. Although the model‐based power depend on the model assumptions, in these scenarios, the pharmacometric model–based approach was demonstrated to permit drastic streamlining of POC trials.

CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e23; doi:10.1038/psp.2012.24; advance online publication 16 January 2013
An analysis and validation pipeline for large-scale RNAi-based screens
Authors: Plank Michael , Hu Guang , Silva A. Sofia , Wood Shona H. , Hesketh Emily E. , Janssens Georges , Macedo André , de Magalhães João Pedro , Church George M.
Published: January 2013

Large-scale RNAi-based screens are a major technology, but require adequate prioritization and validation of candidate genes from the primary screen. In this work, we performed a large-scale pooled shRNA screen in mouse embryonic stem cells (ESCs) to discover genes associated with oxidative stress resistance and found several candidates. We then developed a bioinformatics pipeline to prioritize these candidates incorporating effect sizes, functional enrichment analysis, interaction networks and gene expression information. To validate candidates, we mixed normal cells with cells expressing the shRNA coupled to a fluorescent protein, which allows control cells to be used as an internal standard and thus we could detect shRNAs with subtle effects. Although we did not identify genes associated with oxidative stress resistance, as a proof-of-concept of our pipeline we demonstrate a detrimental role of Edd1 silencing in ESC growth. Our methods may be useful for candidate gene prioritization of large-scale RNAi-based screens.
Electron paramagnetic resonance oxygen imaging in vivo
Authors: Epel, Boris , Halpern Howard
Published: January 2013

This review covers the last 15 years of the development of EPR in vivo oxygen imaging. During this time, a number of major technological and methodological advances have taken place. Narrow line width, long relaxation time, and non-toxic triaryl methyl radicals were introduced in the late 1990s. These not only improved continuous wave (CW) imaging, but also enabled the application of pulse EPR imaging to animals. Recent developments in pulse technology have brought an order of magnitude increase in image acquisition speed, enhancement of sensitivity, and considerable improvement in the precision and accuracy of oxygen measurements. Consequently, pulse methods take up a significant part of this review.
High-frequency and -field electron paramagnetic resonance of transition metal ion (d block) coordination complexes
Authors: Telser Joshua , Ozarowski Andrew , Krzystek J.
Published: January 2013

High-frequency and -field electron paramagnetic resonance (HFEPR), in its current configuration (frequencies up to 1THz; fields up to 35T), has been applied to transition metal complexes for over twenty years, whilst early examples of this technique go back nearly fifty years. In this Report are described HFEPR (limited to frequencies above those generated by most commercial instruments) studies on paramagnetic transition metal ion molecular complexes. These coordination complexes are chiefly of the d block ions, and specifically 3d (first row transition metals), but selected examples of studies on 4d, 5d and 4f ions will also be discussed. The period from 2006 will primarily be covered with an emphasis on results reported within the last several years. The subject emphasis will be on mono- or dinuclear complexes; however, polynuclear systems will also be reviewed. Computational/theoretical studies that are closely related to experimental work will be described as well. Speculation as to new targets for application of HFEPR within this general area will be entertained throughout the Report.
Molecular interpretation of EPR parameters - computational spectroscopy approaches
Authors: Pietrzyk Piotr , Podolska Katarzyna , Sojka Zbigniew
Published: January 2013

DFT and post HF computation machinery used for the calculation of EPR parameters have been surveyed. The role of electron correlation, relativity treatment, spin polarization and contamination, and basis set customisation has been outlined and illustrated using recent literature data. Various aspects of molecular interpretation of spin Hamiltonian parameters regarding the structural, dynamical and environmental effects have been covered and illustrated using selected examples. It is presumed that such non-technical précis of current theoretical framework of the computational EPR spectroscopy may be useful for the broader audience to follow the case studies, and may serve also as a practical guide of the present state of the art in this rapidly developing field.
Amino acid sensing in dietary-restriction-mediated longevity: roles of signal-transducing kinases GCN2 and TOR
Authors: Gallinetti Jordan , Harputlugil Eylul , Mitchell James R.
Published: January 2013

DR (dietary restriction), or reduced food intake without malnutrition, is associated with extended longevity, improved metabolic fitness and increased stress resistance in a wide range of organisms. DR is often referred to as calorie restriction, implying that reduced energy intake is responsible for its widespread and evolutionarily conserved benefits. However, recent data indicate dietary amino acid restriction as a key mediator of DR benefits. In fruitflies, an imbalance in essential amino acid intake is thought to underlie longevity benefits of DR. In mammals, reduced dietary protein or essential amino acid intake can extend longevity, improve metabolic fitness and increase stress resistance. In the present paper we review two evolutionarily conserved signal transduction pathways responsible for sensing amino acid levels. The eIF2α (eukaryotic initiation factor 2α) kinase GCN2 (general amino acid control non-derepressible 2) senses the absence of one or more amino acids by virtue of direct binding to uncharged cognate tRNAs. The presence of certain amino acids, such as leucine, permits activation of the master growth regulating kinase TOR (target of rapamycin). These two signal transduction pathways react to amino acid deprivation by inhibiting general protein translation while at the same time increasing translation of specific mRNAs involved in restoring homoeostasis. Together, these pathways may contribute to the regulation of longevity, metabolic fitness and stress resistance.
Breaking on through to the other side: protein export through the bacterial Sec system
Authors: Chatzi Katerina E. , Sardis Marios F. , Karamanou Spyridoula , Economou Anastassios
Published: January 2013

More than one-third of cellular proteomes traffic into and across membranes. Bacteria have invented several sophisticated secretion systems that guide various proteins to extracytoplasmic locations and in some cases inject them directly into hosts. Of these, the Sec system is ubiquitous, essential and by far the best understood. Secretory polypeptides are sorted from cytoplasmic ones initially due to characteristic signal peptides. Then they are targeted to the plasma membrane by chaperones/pilots. The translocase, a dynamic nanomachine, lies at the centre of this process and acts as a protein-conducting channel with a unique property; allowing both forward transfer of secretory proteins but also lateral release into the lipid bilayer with high fidelity and efficiency. This process, tightly orchestrated at the expense of energy, ensures fundamental cell processes such as membrane biogenesis, cell division, motility, nutrient uptake and environmental sensing. In the present review, we examine this fascinating process, summarizing current knowledge on the structure, function and mechanics of the Sec pathway.
Coherent structures, intermittent turbulence, and dissipation in high-temperature plasmas
Authors: Karimabadi H. , Roytershteyn V. , Wan M. , Matthaeus W. H. , Daughton W. , Wu P. , Shay M. , Loring B. , Borovsky J. , Leonardis E. , Chapman S. C. , Nakamura T. K. M.
Published: January 2013

An unsolved problem in plasma turbulence is how energy is dissipated at small scales. Particle collisions are too infrequent in hot plasmas to provide the necessary dissipation. Simulations either treat the fluid scales and impose an ad hoc form of dissipation (e.g., resistivity) or consider dissipation arising from resonant damping of small amplitude disturbances where damping rates are found to be comparable to that predicted from linear theory. Here, we report kinetic simulations that span the macroscopic fluid scales down to the motion of electrons. We find that turbulent cascade leads to generation of coherent structures in the form of current sheets that steepen to electron scales, triggering strong localized heating of the plasma. The dominant heating mechanism is due to parallel electric fields associated with the current sheets, leading to anisotropic electron and ion distributions which can be measured with NASA's upcoming Magnetospheric Multiscale mission. The motion of coherent structures also generates waves that are emitted into the ambient plasma in form of highly oblique compressional and shear Alfven modes. In 3D, modes propagating at other angles can also be generated. This indicates that intermittent plasma turbulence will in general consist of both coherent structures and waves. However, the current sheet heating is found to be locally several orders of magnitude more efficient than wave damping and is sufficient to explain the observed heating rates in the solar wind.
Translocation and encapsulation of siRNA inside carbon nanotubes
Authors: Mogurampelly Santosh , Maiti Prabal K.
Published: January 2013

We report spontaneous translocation of small interfering RNA (siRNA) inside carbon nanotubes (CNTs) of various diameters and chirality using all atom molecular dynamics simulations with explicit solvent. We use umbrella sampling method to calculate the free energy landscape of the siRNA entry and translocation event. Free energy profiles show that siRNA gains free energy while translocating inside CNT, and barrier for siRNA exit from CNT ranges from 40 to 110 kcal/mol depending on CNT chirality and salt concentration. The translocation time τ decreases with the increase of CNT diameter with a critical diameter of 24 Å for the translocation. In contrast, double strand DNA of the same sequence does not translocate inside CNT due to large free energy barrier for the translocation. This study helps in understanding the nucleic acid transport through nanopores at microscopic level and may help designing carbon nanotube based sensor for siRNA.
Hybrid chromophore/template nanostructures: A customizable platform material for solar energy storage and conversion
Authors: Kolpak Alexie M. , Grossman Jeffrey C.
Published: January 2013

Challenges with cost, cyclability, and/or low energy density have largely prevented the development of solar thermal fuels, a potentially attractive alternative energy technology based on molecules that can capture and store solar energy as latent heat in a closed cycle. In this paper, we present a set of novel hybrid photoisomer/template solar thermal fuels that can potentially circumvent these challenges. Using first-principles computations, we demonstrate that these fuels, composed of organic photoisomers bound to inexpensive carbon-based templates, can reversibly store solar energy at densities comparable to Li-ion batteries. Furthermore, we show that variation of the template material in combination with the photoisomer can be used to optimize many of the key performance metrics of the fuel—i.e., the energy density, the storage lifetime, the temperature of the output heat, and the efficiency of the solar-to-heat conversion. Our work suggests that the solar thermal fuels concept can be translated into a practical and highly customizable energy storage and conversion technology.
Nuclear stopping power in warm and hot dense matter
Authors: Faussurier Gérald , Blancard Christophe , Gauthier Maxence
Published: January 2013

We present a method to estimate the nuclear component of the stopping power of ions propagating in dense matter. Three kinds of effective pair potentials are proposed. Results from the warm dense matter regime and the domain of high energy density physics are presented and discussed for proton and helium. The role of ionic temperature is examined. The nuclear stopping power can play a noticeable role in hot dense matter.
Production rate and diameter analysis of spherical monodisperse microbubbles from two-dimensional, expanding-nozzle flow-focusing microfluidic devices
Authors: Wang Shiying , Dhanaliwala Ali H. , Chen Johnny L. , Hossack John A.
Published: January 2013

Flow-focusing microfluidic devices (FFMDs) can produce microbubbles (MBs) with precisely controlled diameters and a narrow size distribution. In this paper, poly-dimethyl-siloxane based, rectangular-nozzle, two-dimensional (2-D) planar, expanding-nozzle FFMDs were characterized using a high speed camera to determine the production rate and diameter of Tween 20 (2% v/v) stabilized MBs. The effect of gas pressure and liquid flow rate on MB production rate and diameter was analyzed in order to develop a relationship between FFMD input parameters and MB production. MB generation was observed to transition through five regimes at a constant gas pressure and increasing liquid flow rate. Each MB generation event (i.e., break-off to break-off) was further separated into two characteristic phases: bubbling and waiting. The duration of the bubbling phase was linearly related to the liquid flow rate, while the duration of the waiting phase was related to both liquid flow rate and gas pressure. The MB production rate was found to be inversely proportional to the sum of the bubbling and waiting times, while the diameter was found to be proportional to the product of the gas pressure and bubbling time.
Generalized extended Navier-Stokes theory: Correlations in molecular fluids with intrinsic angular momentum
Authors: Hansen J. S. , Daivis Peter J. , Dyre Jeppe C. , Todd B. D. , Bruus Henrik
Published: January 2013

The extended Navier-Stokes theory accounts for the coupling between the translational and rotational molecular degrees of freedom. In this paper, we generalize this theory to non-zero frequencies and wavevectors, which enables a new study of spatio-temporal correlation phenomena present in molecular fluids. To discuss these phenomena in detail, molecular dynamics simulations of molecular chlorine are performed for three different state points. In general, the theory captures the behavior for small wavevector and frequencies as expected. For example, in the hydrodynamic regime and for molecular fluids with small moment of inertia like chlorine, the theory predicts that the longitudinal and transverse intrinsic angular velocity correlation functions are almost identical, which is also seen in the molecular dynamics simulations. However, the theory fails at large wavevector and frequencies. To account for the correlations at these scales, we derive a phenomenological expression for the frequency dependent rotational viscosity and wavevector and frequency dependent longitudinal spin viscosity. From this we observe a significant coupling enhancement between the molecular angular velocity and translational velocity for large frequencies in the gas phase; this is not observed for the supercritical fluid and liquid state points.
CO oxidation on h-BN supported Au atom
Authors: Gao Min , Lyalin Andrey , Taketsugu Tetsuya
Published: January 2013

The mechanism of CO oxidation by O2 on Au atoms supported on the pristine and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. It is found that O2 binds stronger than CO on an Au atom supported on the defect free h-BN surface and h-BN surface with nitrogen vacancy (VN@h-BN), but weaker than CO on a free Au atom or Au trapped by a boron vacancy (VB@h-BN). The excess of the positive or negative charge on Au can considerably change its catalytic properties and enhance activation of the adsorbed O2. Coadsorption of CO and O2 on Au, Au/VN@h-BN, and Au/VB@h-BN results in additional charge transfer to O2. Various pathways of the CO oxidation reaction by molecular oxygen are studied. We found two different pathways for CO oxidation: a two-step pathway where two CO2 molecules are formed independently, and a self-promotion pathway where oxidation of the first CO molecule is promoted by the second CO molecule. Interaction of Au with the defect-free and defected h-BN surface considerably affects the CO oxidation reaction pathways and barriers. Therefore, Au supported on the h-BN surface (pristine or defected) cannot be considered as pseudo-free atom and support effects have to be taken into account, even when the interaction of Au with the support is weak.
Structural study of Al2O3-Na2O-CaO-P2O5 bioactive glasses as a function of aluminium content
Authors: Smith J. M. , King S. P. , Barney E. R. , Hanna J. V. , Newport R. J. , Pickup D. M.
Published: January 2013

Calcium phosphate based biomaterials are extensively used in the context of tissue engineering: small changes in composition can lead to significant changes in properties allowing their use in a wide range of applications. Samples of composition (Al2O3)x(Na2O)0.11-x(CaO)0.445(P2O5)0.445, where x = 0, 0.03, 0.05, and 0.08, were prepared by melt quenching. The atomic-scale structure has been studied using neutron diffraction and solid state 27Al MAS NMR, and these data have been rationalised with the determined density of the final glass product. With increasing aluminium concentration the density increases initially, but beyond about 3 mol. % Al2O3 the density starts to decrease. Neutron diffraction data show a concomitant change in the aluminium speciation, which is confirmed by 27Al MAS NMR studies. The NMR data reveal that aluminium is present in 4, 5, and 6-fold coordination and that the relative concentrations of these environments change with increasing aluminium concentration. Materials containing aluminium in 6-fold coordination tend to have higher densities than analogous materials with the aluminium found in 4-fold coordination. Thus, the density changes may readily be explained in terms of an increase in the relative concentration of 4-coordinated aluminium at the expense of 6-fold aluminium as the Al2O3 content is increased beyond 3 mol. %.
Reactive adsorption of ammonia and ammonia/water on CuBTC metal-organic framework: A ReaxFF molecular dynamics simulation
Authors: Huang Liangliang , Bandosz Teresa , Joshi Kaushik L. , van Duin Adri C. T. , Gubbins Keith E.
Published: January 2013

We report ReaxFF molecular dynamics simulations for reactive adsorption of NH3 on dehydrated CuBTC metal-organic framework. If the temperature is moderate (up to 125 °C), the dehydrated CuBTC demonstrates a good hydrostatic stability for water concentrations up to 4.0 molecules per copper site. However, if the temperature increases to 550 K, the dehydrated CuBTC will collapse even at a small water concentration, 1.0 H2O molecule per copper site. When NH3 molecules are adsorbed in the channel and micropores of CuBTC, they prefer to chemisorb to the copper sites rather than forming a dimer with another NH3 molecule. The formation of equimolar Cu2(NH2)4 and (NH4)3BTC structures is observed at 348 K, which is in good agreement with previous experimental findings. The dehydrated CuBTC framework is partially collapsed upon NH3 adsorption, while the Cu–Cu dimer structure remains stable under the investigated conditions. Further calculations reveal that the stability of CuBTC is related to the ammonia concentration. The critical NH3 concentration after which the dehydrated CuBTC starts to collapse is determined to be 1.0 NH3 molecule per copper site. Depending on whether NH3 concentration is below or above the critical value, the dehydrated CuBTC can be stable to a higher temperature, 378 K, or can collapse at a lower temperature, 250 K. H2O/NH3 mixtures have also been studied, and we find that although water molecules do not demonstrate a strong interaction with the copper sites of CuBTC, the existence of water molecules can substantially prevent ammonia from interacting with CuBTC, and thus reduce the amount of chemisorbed NH3 molecules on CuBTC and stabilize the CuBTC framework to some extent.
Preferential concentration and settling of heavy particles in homogeneous turbulence
Authors: Dejoan A. , Monchaux R.
Published: January 2013

Voronoï diagrams are used to analyze one-way coupling direct numerical simulation data of heavy particles settling in homogeneous turbulence. Preferential concentration and clustering of the inertial particles are analyzed for an extended range of particle Stokes and Rouse numbers. Influence of preferential concentration on the settling velocity enhancement is addressed from statistics of particle and flow field quantities conditioned on the local concentration. While gravity is found to have almost no influence on the global characteristics of preferential concentration, the conditional statistics bring out a refined preferential sampling of the flow field resulting from the gravitational effects. This preferential sampling shows that beside the descending fluid velocity contribution, the settling velocity is further increased by the descending fluid acceleration. This effect cannot be detected from global estimations of the particle concentration field. A 2D analysis of the Voronoï cells is also presented to investigate their shape and orientation. It is found that clusters can be represented as 2D elongated manifolds. Their shape is shown to be similar in zero and non-zero gravity fields while Voronoï cells tend to be more elongated for Stokes numbers around unity. Under the gravity effects, they tend to be preferentially oriented perpendicularly to the gravitational axis.
Nonlinear Raman forward scattering of a short laser pulse in a collisional transversely magnetized plasma
Authors: Paknezhad Alireza
Published: January 2013

Nonlinear Raman forward scattering (NRFS) of an intense short laser pulse with a duration shorter than the plasma period through a homogenous collisional transversely magnetized plasma is investigated theoretically when ponderomotive, relativistic and collioninal nonlinearities are taken into account. The plasma is embedded in a uniform magnetic field perpendicular to both, the direction of propagation and electric vector of the radiation field. Nonlinear wave equation is set up and Fourier transformation method is used to solve the coupled equations describing NRFS instability. Finally, the growth rate of this instability is obtained. Thermal effects of plasma electrons and effect of the electron-ion collisions are examined. It is found that the growth rate of Raman forward scattering first decreases on increasing electron thermal velocity, minimizes at an optimum value, and then increases. Our results also show that the growth rate increases by increasing the electron-ion collisions.
Dust-acoustic shock formation in dusty plasmas with non-thermal ions
Authors: Asgari H. , Muniandy S. V. , Wong C. S.
Published: January 2013

In this study, the nonlinear Burgers equation in the presence of the dust charge fluctuation is derived and the shock-like solution is determined. It is well known that in order to have a monotonic or oscillatory shock wave, a source of dissipation is needed. By using the experimental data reported in the laboratory observation of self-excited dust-acoustic shock waves [Heinrich et al., Phys. Rev. Lett. 103, 115002 (2009)], it is shown that dust charge fluctuation can be considered as a candidate for the source of dissipation needed for the dust-acoustic shock formation. By examining the effects of non-thermal ions on dust-acoustic shock's characteristics, a possible theoretical explanation for the discrepancies observed between theory and experiment is proposed.
Heat capacities of mass selected deprotonated water clusters
Authors: Zamith Sébastien , Labastie Pierre , L’Hermite Jean-Marc
Published: January 2013

Heat capacities of mass selected deprotonated water clusters (H2O)n−1OH− have been measured in the size range n = 48–118, as a function of temperature. We have found that they undergo a melting-like transition in the range 110–130 K. The transition temperature is size dependent with a strong correlation with the dissociation energy around the shell closure at n = 55.
Nondecaying long range effect of surface decoration on the charge state of NV center in diamond
Authors: Hu Wei , Li Zhenyu , Yang Jinlong , Hou Jianguo
Published: January 2013

On the basis of density functional theory, stability and electronic structure of nitrogen-vacancy (NV) centers in surface modified diamond have been studied. Surface decoration is traditionally expected to only have influence on those NV centers close to the surface. However, our calculations indicate that its effect to charged NV centers is nondecaying and long-range, where the formation energy of the charged NV center converges to a value typically different for different types of surface decoration. Such a nondecaying long range effect is due to the electrostatic potential shift induced by the surface dipole layer, and it leads to the preference of NV− center for oxygen saturated diamond and NV0 for hydrogenated one. Our work demonstrates that surface functionalization can be used to modify the relative stabilities of differently charged defects in nonmetallic materials.
Attachment cross-sections of protonated and deprotonated water clusters
Authors: Zamith Sébastien , de Tournadre Grégoire , Labastie Pierre , L’Hermite Jean-Marc
Published: January 2013

Attachment cross-sections of water molecules onto size selected protonated (H2O)nH+ and deprotonated (H2O)n − 1OH− water clusters have been measured in the size range n = 30–140 for 10 eV kinetic energy of the clusters in the laboratory frame. Within our experimental accuracy, the attachment cross-sections are found to have the same magnitude and size dependence for both species. It is shown that electrostatic interactions are likely to play a role even for the largest sizes investigated.
Radial x-ray diffraction of tungsten tetraboride to 86 GPa under nonhydrostatic compression
Authors: Xiong Lun , Liu Jing , Bai Ligang , Li Yanchun , Lin Chuanlong , He Duanwei , Peng Fang , Lin Jung-Fu
Published: January 2013

Investigations of the equation of state of tungsten tetraboride (WB4) have been performed under nonhydrostatic compression to 85.8 GPa using radial x-ray diffraction techniques in a diamond anvil cell at room temperature. The hexagonal structure of WB4 is found to be stable up to the highest pressure of 85.8 GPa. The radial x-ray diffraction data yield a bulk modulus K0 = 319(5) GPa with K0′ = 4.1(0.2) at ψ = 54.7°. With a fixed K0′ of 4, the derived K0 is 323(1) GPa. The bulk modulus obtained from fits of diffraction data at ψ = 0° and 90° is 196(6) GPa and 507(13) GPa, respectively. The values gradually increased from ψ = 0° to 90°, showing the compressibility of the sample strongly depends on the stress environment. In addition, the compressibility of the unit cell axes (a- and c-axes) of WB4 demonstrates an almost isotropic nature with pressure increasing.
Uniaxial pressure setup for piezoresistance and magnetoresistance measurements in Heusler materials
Authors: Bourgault D. , Porcar L. , Bruyère C. , Jacquet P. , Courtois P.
Published: January 2013

We report on a new uniaxial pressure experimental setup for electrical resistivity measurements working in a 77 K–500 K temperature range and in a magnetic field up to 8 T. Such a continuous uniaxial pressure device enables the study of the piezoresistance and the pressure induced change in electrical properties of bulk samples. Strong influence of uniaxial pressure on transport properties is shown for Ni–Co–Mn–In Heusler single crystal material. A shift of the martensite–austenite first order transformation temperature is measured with an applied uniaxial pressure leading to an electrical resistance changed by up to 120%.
Monolayer graphene oxide as a building block for artificial muscles
Authors: Rogers Geoffrey W. , Liu Jefferson Z.
Published: January 2013

The electromechanical actuation of a highly ordered compound of graphene oxide (GO) is shown via ab initio simulations to produce high-performance quantum-mechanical responses, which mimic the behaviour of mammalian skeletal muscle. In addition to large expansive strains (∼10%), this GO compound (asymmetrically unzipped C4O) exhibits large contractive strains of −4.8% upon −0.15 e/C-atom electron injection. Furthermore, as these contractive strains are coupled with equally high stresses (∼100 GPa) and short response times (∼1 ns), we show that this GO material meets all of the functional requirements of an artificial muscle building block.
Gate voltage induced topological phase transition in hexagonal boron-nitride bilayers
Authors: Zhai Xuechao , Jin Guojun
Published: January 2013

Single or few-layer hexagonal boron nitride sheets usually have very large band gaps, which greatly hinders their applications in electronic circuits. In this letter, we propose a way to significantly reduce the band gap of hexagonal boron-nitride bilayer (BNBL) by applying an interlayer bias voltage. In the presence of the intrinsic and Rashba spin-orbit couplings, we demonstrate whether gated BNBL is topologically nontrivial depends strongly on its stacking type. For AA-stacking BNBL with inversion symmetry, the strong topological insulator phase is obtained, and phase boundaries are analytically given. We also observe a re-entrant phase behavior from a normal insulator to a topological insulator then to a normal insulator, which is switched by the gate voltage. For AB-stacking BNBL, it is always topologically trivial but exhibits an unusual quantum Hall phase with four degenerate low-energy states localized at a single edge. These findings provide potential applications of BNBLs in electronics and spintronics.
Response functions of Fuji imaging plates to monoenergetic protons in the energy range 0.6–3.2 MeV
Authors: Bonnet T. , Comet M. , Denis-Petit D. , Gobet F. , Hannachi F. , Tarisien M. , Versteegen M. , Aleonard M. M.
Published: January 2013

We have measured the responses of Fuji MS, SR, and TR imaging plates (IPs) to protons with energies ranging from 0.6 to 3.2 MeV. Monoenergetic protons were produced with the 3.5 MV AIFIRA (Applications Interdisciplinaires de Faisceaux d’Ions en Région Aquitaine) accelerator at the Centre d’Etudes Nucléaires de Bordeaux Gradignan (CENBG). The IPs were irradiated with protons backscattered off a tantalum target. We present the photo-stimulated luminescence response of the IPs together with the fading measurements for these IPs. A method is applied to allow correction of fading effects for variable proton irradiation duration. Using the IP fading corrections, a model of the IP response function to protons was developed. The model enables extrapolation of the IP response to protons up to proton energies of 10 MeV. Our work is finally compared to previous works conducted on Fuji TR IP response to protons.
Hyperpolarizabilities of one and two electron ions under strongly coupled plasma
Authors: Sen Subhrangsu , Mandal Puspajit , Kumar Mukherjee Prasanta , Fricke Burkhard
Published: January 2013

Systematic investigations on the hyperpolarizabilities of hydrogen and helium like ions up to nuclear charge Z = 7 under strongly coupled plasma environment have been performed. Variation perturbation theory has been adopted to evaluate such properties for the one and two electron systems. For the two electron systems coupled Hartree-Fock theory, which takes care of partial electron correlation effects, has been utilised. Ion sphere model of the strongly coupled plasma, valid for ionic systems only, has been adopted for estimating the effect of plasma environment on the hyperpolarizability. The calculated free ion hyperpolarizability for all the systems is in good agreement with the existing data. Under confinement hyperpolarizabilities of one and two electron ions show interesting trend with respect to plasma coupling strength.
N-type conductivity and properties of carbon-doped InN(0001) films grown by molecular beam epitaxy
Authors: Himmerlich M. , Knübel A. , Aidam R. , Kirste L. , Eisenhardt A. , Krischok S. , Pezoldt J. , Schley P. , Sakalauskas E. , Goldhahn R. , Félix R. , Mánuel J. M. , Morales F. M. , Carvalho D. , Ben T. , García R. , Koblmüller G.
Published: January 2013

In this work, we have analyzed the effect of intentional carbon doping on molecular beam epitaxy grown In-polar InN epilayers using carbon bromide (CBr4) as dopant source. Hall effect measurements, high resolution X-ray diffraction, atomic force microscopy, transmission electron microscopy, secondary ion mass spectrometry, spectroscopic ellipsometry, as well as X-ray photoelectron spectroscopy were employed to characterize the influence of different dopant concentrations on the electrical, optical, crystallographic, morphological, and electronic properties of InN. It was found that the electron concentration increases linearly with the incorporation of carbon pointing towards the effect of n-type doping and that incorporated C impurities reduce the electron mobility within the InN films. This correlation is further reflected in associated properties such as the onset of optical absorption, the plasmon frequency, the effective electron mass and the position of the bulk and surface Fermi level. Furthermore, it is found that the dislocation densities are independent of carbon incorporation, ruling them out as origin for the increased n-type conductivity and reduced carrier mobility in these epilayers.
Structurally manipulating electron-spin polarization via δ-doping in a magnetic nanostructure
Authors: Lu Mao-Wang , Wang Zhi-Yong , Liang Yu-Li , An Yan-Bo , Li Li-Qiong
Published: January 2013

We theoretically investigate the control of the electron-spin polarization in a spin filter by a tunalbe δ-doping, where the device and the δ-doping can be realized experimentally by depositing a ferromagnetic stripe on top of semiconductor heterostructure and using molecular beam epitaxy or metal-organic chemical-vapor deposition, respectively. The δ-doping dependent transmission and conductance are numerically calculated for InAs material system. It is shown that both amplitude and sign of electron-spin polarization vary dramatically with the weight and/or the location of the δ-doping. Thus, it is possible to open a new door for effectively manipulating spin-polarized source, and the considered nanostructure can serve as a spin filter with a structurally controllable spin polarization by the δ-doping.
Enhanced piezoelectric and ferroelectric properties in the BaZrO3 substituted BiFeO3-PbTiO3
Authors: Fan Longlong , Chen Jun , Li Sha , Kang Huajun , Liu Laijun , Fang Liang , Xing Xianran
Published: January 2013

BiFeO3-PbTiO3 (BF-PT) compounds possess very high Curie temperature and tetragonality compared to other PbTiO3-based piezoceramics. The BaZrO3 (BZ), with weakly ferroelectric active cations, was introduced into the BiFeO3-PbTiO3 to reduce the tetragonality (c/a) and improve the piezoelectric property. For the (0.8-x)BiFeO3-0.2BaZrO3-xPbTiO3, the BaZrO3 substitution can effectively decrease the tetragonality (c/a) from 1.18 to 1.02 for those compositions near the morphotropic phase boundary. The piezoelectric property of BiFeO3-PbTiO3 can be much enhanced with an optimal piezoelectric constant ∼270 pC/N with a reduced TC of 270 °C. Both the temperature dependent dielectric properties and polarization loops verified the existence of antiferroelectric relaxor, which was not observed in previous reported BiFeO3-PbTiO3 based materials.