bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of a cafeteria diet on insulin production and clearance in rats
Authors: Castell-Auví Anna , Cedó Lídia , Pallarès Victor , Blay Mayte , Ardévol Anna , Pinent Montserrat
Published: December 2011

The aim of the present study was to determine the effects of a cafeteria diet on the function and apoptosis of the pancreas, and the activity and expression of the insulin-degrading enzyme (IDE). Female Wistar rats were fed either with a cafeteria diet or a control diet for 17 weeks, and blood and tissues were then collected for analysis. The cafeteria diet-treated rats had higher plasma insulin and C-peptide levels (P < 0·05), showing increased insulin secretion by the pancreas. Insulin protein and gene expression levels were higher in the pancreas of obese rats, as was its transcriptional controller, pancreatic duodenal homeobox 1 (P < 0·05). Feeding a cafeteria diet down-regulated the gene expression of the anti-apoptotic marker B-cell/lymphoma 2 (BCL2), and up-regulated the protein levels of BCL2-associated X protein, a pro-apoptotic marker (P < 0·05). The cafeteria diet caused lipid accumulation in the pancreas and modified the expression of key genes that control lipid metabolism. To assay whether insulin clearance was also modified, we checked the activity of the IDE, one of the enzymes responsible for insulin clearance. We found increased liver IDE activity (P < 0·05) in the cafeteria diet-fed animals, which could, in part, be due to an up-regulation of its gene expression. Conversely, IDE gene expression was unmodified in the kidney and adipose tissue; although when the adipose tissue weight was considered, the insulin clearance potential was higher in the cafeteria diet-treated rats. In conclusion, treatment with a cafeteria diet for 17 weeks in rats mimicked a pre-diabetic state, with ectopic lipid accumulation in the pancreas, and increased the IDE-mediated insulin clearance capability.
Genetic variation amongClonorchis sinensisisolates from different geographic regions in China revealed by sequence analyses of four mitochondrial genes
Authors: Liu G.H. , Li B. , Li J.Y. , Song H.Q. , Lin R.Q. , Cai X.Q. , Zou F.C. , Yan H.K. , Yuan Z.G. , Zhou D.H. , Zhu X.Q.
Published: December 2011

The present study examined sequence variation in four mitochondrial (mt) genes, namely cytochromecoxidase subunits 1 (cox1) and 2 (cox2), and NADH dehydrogenase subunits 1 and 2 (nad1andnad2) amongClonorchis sinensisisolates from different endemic regions in China, and their phylogenetic relationships with other zoonotic trematodes were reconstructed. A portion of thecox1andcox2genes (pcox1and pcox2), andnad1andnad2genes (pnad1and pnad2) were amplified separately from individual liver flukes by polymerase chain reaction (PCR) and the amplicons were subjected to sequencing from both directions. The intra-specific sequence variations withinC. sinensiswere 0–1.6% for pcox1, 0–1.4% for pcox2, 0–0.9% for pnad1and 0–1.0% for pnad2. Phylogenetic analyses based on the combined sequences of pcox1, pcox2, pnad1and pnad2revealed that all theC. sinensisisolates grouped together and were closely related toOpisthorchis felineus. These findings revealed the existence of intra-specific variation in mitochondrial DNA (mtDNA) sequences amongC. sinensisisolates from different geographic regions, and demonstrated that mtDNA sequences provide reliable genetic markers for phylogenetic studies of zoonotic trematodes.
Electron drift caused by rf field gradient creates many plasma phenomena: An attempt to distinguish the cause and the effect
Authors: XAPLANTERIS C. L. , FILIPPAKI E. D. , MISTAKIDIS I. S. , XAPLANTERIS L. C.
Published: December 2011

Many experimental data along with their theoretical interpretations on the rf low-temperature cylindrical plasma have been issued until today. Our Laboratory has contributed to that research by publishing results and interpretative mathematical models. With the present paper, two issues are being examined; firstly, the estimation of electron drift caused by the rf field gradient, which is the initial reason for the plasma behaviour, and secondly, many new experimental results, especially the electron-neutral collision frequency effect on the other plasma parameters and quantities. Up till now, only the plasma steady state was taken into consideration when a theoretical elaboration was carried out, regardless of the cause and the effect. This indicates the plasma's complicated and chaotic configuration and the need to simplify the problem. In the present work, a classification about the causality of the phenomena is attempted; the rf field gradient electron drift is proved to be the initial cause.
Two new European species from the heterogeneous Caloplaca holocarpa group (Teloschistaceae)
Authors: VONDRÁK Jan , KHODOSOVTSEV Alexander , ŠOUN Jaroslav , VONDRÁKOVÁ Olga
Published: December 2011

The Caloplaca holocarpa group contains members of the family Teloschistaceae with a strongly reduced thallus and conspicuous yellow, orange or red apothecia. In the absence of well-defined thallus characters, taxa of this group must be identified mainly by apothecial characters and are as a result often difficult to separate. The species of this group have been shown not to form a monophyletic entity, with representatives of other Teloschistaceae with more complex thalli intermixed among them. Caloplaca skii and C. syvashica are recognized here as two homogeneous clades with Caloplaca holocarpa-like phenotypes. Caloplaca skii, which is widespread in southern Europe, resembles C. cerinelloides but is distinguished by its smaller and narrower ascospores and by growing predominantly on xerophilous shrubs. Caloplaca syvashica is restricted to shrubs in salt marshes in the northern Black Sea region. It is similar to the British Caloplaca suaedae and Australian C. yarraensis, but differs from both, mainly in ascospore characters. Caloplaca yarraensis is closely related to the new C. syvashica but arguments against their conspecificity are emphasised. A key for epiphytic C. holocarpa-like Teloschistaceae from Europe is provided.
A preliminary survey of lichen associated eukaryotes using pyrosequencing
Authors: BATES Scott T. , BERG-LYONS Donna , LAUBER Christian L. , WALTERS William A. , KNIGHT Rob , FIERER Noah
Published: December 2011

Although various eukaryotic organisms, such as arthropods, endolichenic/lichenicolous fungi, and nematodes, have been isolated from lichens, the diversity and structure of eukaryotic communities associated with lichen thalli has not been well studied. In addressing this knowledge gap, we used bar-coded pyrosequencing of 18S rRNA genes to survey eukaryotes associated with thalli of three different lichen species. In addition to revealing an expected high abundance of lichen biont-related 18S genes, sequences recovered in our survey showed non-biont fungi from the Ascomycota also have a substantial presence in these thalli. Our samples additionally harboured fungi representing phyla (Blastocladiomycota, Chytridiomycota) that have not been isolated previously from lichens; however, their very low abundance indicates an incidental presence. The recovery of Alveolata, Metazoa, and Rhizaria sequences, along with recent work revealing the considerable bacterial diversity in these same samples, suggests lichens function as minute ecosystems in addition to being symbiotic organisms.
Malmographina, a new genus for Graphina malmei (Ascomycota: Ostropales: Graphidaceae)
Authors: CÁCERES Marcela Eugenia da Silva , RIVAS PLATA Eimy , LÜCKING Robert
Published: December 2011

The new genus Malmographina Cáceres, Rivas Plata & Lücking is introduced for Opegrapha plicosa Meissn. (syn. Graphis malmei Redinger), with the new combination Malmographina plicosa (Meiss.) Cáceres, Rivas Plata & Lücking. The taxon is characterized by prominent, striate, orange-pigmented, non-carbonized lirellae, a more or less clear hymenium, and large, muriform, hyaline ascospores. Malmographina is most similar to Hemithecium in lirellae morphology and anatomy, but in a molecular phylogenetic analysis falls within a clade containing Phaeographis and other genera with usually inspersed hymenium and brown ascospores. Within that clade, it is thus far the only taxon that has persistently hyaline ascospores. It is otherwise similar to Pallidogramme but does not cluster within that genus. A preliminary phylogenetic analysis of the Phaeographis clade confirms monophyly of the genera Halegrapha, Pallidogramme, and Platygramme, and suggests that Phaeographis should be divided into several generic lineages and that Leiorreuma and Sarcographa perhaps be merged.
Attractors with irrational rotation number
Authors: HERNÁNDEZ-CORBATO LUIS , ORTEGA RAFAEL , RUIZ DEL PORTAL FRANCISCO R.
Published: December 2011

Let h: 2 → 2 be a dissipative and orientation preserving homeomorphism having an asymptotically stable fixed point. Let U be the region of attraction and assume that it is proper and unbounded. Using Carathéodory's prime ends theory one can associate a rotation number, ρ, to h|U. We prove that any map in the above conditions and with ρ ∉ induces a Denjoy homeomorphism in the circle of prime ends. We also present some explicit examples of maps in this class and we show that, if the infinity point is accessible by an arc in U, ρ ∉ if and only if Per(h) = Fix(h) = {p}.
Management Actions in a With-Profits Fund
Authors: Tuley P. J.
Published: December 2011

The management of a fund requires a number of decisions as to the fair treatment of policyholders. This paper first considers the difference between the regulatory requirement to treat customers fairly and the longstanding concept within the profession of policyholders' reasonable expectations. The paper then goes on to consider the bearing of risks within the fund, and thus the interactions between the inherited estate and the asset share so often used to guide payouts to customers. Management actions are discussed in normal, and abnormal, times. Lastly, the considerations of distribution of the inherited estate are considered.
Actuarial Aspects of Internal Models for Solvency II
Authors: Brooks D. , Care R. J. , Chaplin M. B. , Kaufman A. M. , Morgan K. A. , Roberts D. N. , Skinner J. M. E. , Huntington-Thresher D. J. K. , Tuley P. J. , Wong D. L.
Published: December 2011

The draft paper sets out the authors' views of what good practice for the actuarial aspects of internal models will look like in 2012, the year Solvency II is expected to be implemented. Actuaries working on internal models can expect to have to follow such practices if their internal models are to be approved for use in calculating regulatory capital. The paper is therefore relevant for actuaries who plan to work on internal model implementation for Solvency II.

Moreover, the risk quantification techniques discussed in the paper can also be used in the Own Risk Solvency Assessment (ORSA) process also required by Solvency II. The paper is therefore relevant to actuaries working in companies that are not planning to apply to use an internal model.

The paper covers both life and non-life insurance and reinsurance, and reviews current practice as well as setting out possible future practice. This leads to identification of areas for research by the Profession to prepare for 2012 and an indication of the directions this work might take.

The paper is effectively a work in progress, and readers should ask themselves what they should do in response to the ideas discussed.
Mainstreaming the continuum approach to the management of plant genetic resources for food and agriculture through national strategy
Authors: Mba Chikelu , Guimaraes Elcio P. , Guei Gouantoueu R. , Hershey Clair , Paganini Michela , Pick Barbara , Ghosh Kakoli
Published: December 2011

Global food security could be imperilled by the combined pressures from the effects of continually evolving climatic conditions, demographics and other socio-economic factors, the demands of the livestock, bioenergy and fibre industries for food-based substrates, the static or decreasing availability of natural resources for agriculture and the impracticality of increased use of economically and environmentally costly agricultural inputs. The optimal harnessing of plant genetic resources for food and agriculture (PGRFA) in manners that translate their repertoire of hidden potentials into significantly enhanced crop productivities has been severally identified as crucial to achieving the required considerably significant increases in food production. The scope of the problems and the plausible means for addressing them compel the devising of novel and more efficient ways for deploying PGRFA in need-based crop improvement programmes. We posit a continuum approach to the management of PGRFA which links seamlessly the effective conservation and access to PGRFA through their use in developing superior and resilient crop varieties to the provision of their high-quality seeds and planting materials to the growers. To achieve the mainstreaming of this paradigm, we propose the institutionalization of overarching national PGRFA strategies that prescribe result-oriented action plans spanning above three components of the management of PGRFA for a country's priority crops. We also describe the strategy as a means for identifying and assigning responsibilities to critical stakeholders and providing for the governance of all aspects of PGRFA activities over specific time frames. Steps to developing and adopting a national PGRFA strategy are also suggested.
Using SSR markers to map genetic diversity and population structure ofSolanum pimpinellifoliumfor development of a core collection
Authors: Rao Eguru Sreenivasa , Kadirvel Palchamy , Symonds Rachael C. , Geethanjali Subramaniam , Ebert Andreas W.
Published: December 2011

The present study was undertaken to examine the population structure of theSolanum pimpinellifoliumcollection maintained by AVRDC – The World Vegetable Center – and to construct a core set of this collection. Out of the entire collection of 322 accessions, a diverse subset of 190 accessions was chosen representing 14 countries of origin. Data on 32 qualitative and 22 quantitative phenotypic traits (IPGRI–AVRDC descriptor traits) and 48 simple sequence repeat markers evenly distributed over the genome were used to develop the core set. A total of 377 alleles were detected with 7.85 alleles per locus, on average. Of these, 52 alleles at 28 loci were extremely rare-frequency alleles. The 190 accessions clustered into two main populations and an admixture group. Population I (PopI) included 99 accessions, 93 of which originated from Peru. Population II (PopII) contained 49 accessions, the majority of which originated from Ecuador and Mexico. The remaining 42 accessions were classified as admixture group. The two main populations were further subdivided into five subgroups. Values ofFstamong the five sub-populations were significant (average pairwiseFstof 0.296), suggesting a real difference between these populations. A clear differentiation was observed among and within populations based on geography. Peruvian accessions were genetically more diverse than accessions originating in Ecuador and Mexico. Within the Peruvian group, a gradual increase in genetic diversity was observed from southern to northern Peru. The constructed core collection consists of 75 accessions representing 23.4% of AVRDC's entireS. pimpinellifoliumcollection and 39.5% of the subset used in this study. It is a well-balanced core with a good representation of the different populations (31 accessions from PopI, 22 from PopII and 22 from the Admixture group) and geographic origins (40 accessions from Peru, 17 from Ecuador, 14 from Mexico and four from other countries).
Preferences for tap water attributes within couples: An exploration of alternative mixed logit parameterizations
Authors: Scarpa Riccardo , Thiene Mara , Hensher David A.
Published: December 2011

Preferences for attributes of complex goods may differ substantially among members of households. Some of these goods, such as tap water, are jointly supplied at the household level. This issue of jointness poses a series of theoretical and empirical challenges to economists engaged in empirical nonmarket valuation studies. While a series of results have already been obtained in the literature, the issue of how to empirically measure these differences, and how sensitive the results are to choice of model specification from the same data, is yet to be clearly understood. In this paper we use data from a widely employed form of stated preference survey for multiattribute goods, namely choice experiments. The salient feature of the data collection is that the same choice experiment was applied to both partners of established couples. The analysis focuses on models that simultaneously handle scale as well as preference heterogeneity in marginal rates of substitution (MRS), thereby isolating true differences between members of couples in their MRS, by removing interpersonal variation in scale. The models employed are different parameterizations of the mixed logit model, including the willingness to pay (WTP)‐space model and the generalized multinomial logit model. We find that in this sample there is some evidence of significant statistical differences in values between women and men, but these are of small magnitude and only apply to a few attributes.
Studies provide new insights into Japan's March 2011 tsunami
Authors: Balcerak Ernie
Published: December 2011

New data, field studies, modeling efforts, and surveys are revealing a wealth of information about the devastating tsunami that followed the 11 March 2011 Tohoku earthquake. The earthquake and resulting tsunami caused massive destruction and the loss of about 20,000 lives. At the AGU Fall Meeting last week in San Francisco, Calif., scientists reported a variety of new insights about the tsunami and its effects and about tsunami defense mechanisms, ways to forecast tsunami inundation, and public perception of risk. For example, part of the reason the tsunami generated by the Tohoku quake was so large and destructive was that it was a “merging tsunami.” Merging tsunamis, which have been hypothesized but not previously observed with certainty, grow in size dramatically when seafloor topography alters the direction in which the waves are traveling and causes two waves to merge into a larger wave. The alteration of wave paths by complex ocean‐floor topography makes it difficult to predict where the largest waves will strike land. “Tsunamis often destroy some coastal areas while leaving others with little damage,” explained Tony Song of the NASA Jet Propulsion Laboratory, California Institute of Technology, at a 5 December press conference.
Severe droughts have occurred in the northeastern United States
Authors: Balcerak Ernie
Published: December 2011

People do not usually consider the northeastern United States to be a drought‐prone region, but new evidence shows that mega‐droughts have occurred there in the past. Dorothy Peteet of Columbia University and NASA's Goddard Institute for Space Studies reported at the AGU Fall Meeting in San Francisco, Calif., on her analysis of sediment cores in marshes in New York State. Different chemicals flow into a marsh from freshwater upriver and from saltwater from the ocean; higher concentrations of bromine and calcium, which are more common in saltwater, indicate a drier period. The data indicate that at least three mega‐droughts occurred in the past 6000 years, the longest during what scientists term as the “Medieval warm period,” which lasted from about 850 C.E. to 1350 C.E. “People don't think of this area as threatened by droughts because we've been in a wet period,” Peteet said.
Computer programing for geosciences: Teach your students how to make tools
Authors: Grapenthin Ronni
Published: December 2011

When I announced my intention to pursue a Ph.D. in geophysics, some people gave me confused looks, because I was working on a master's degree in computer science at the time. My friends, like many incoming geoscience graduate students, have trouble linking these two fields. From my perspective, it is pretty straightforward: Much of geoscience evolves around novel analyses of large data sets that require custom tools—computer programs—to minimize the drudgery of manual data handling; other disciplines share this characteristic. While most faculty adapted to the need for tool development quite naturally, as they grew up around computer terminal interfaces, incoming graduate students lack intuitive understanding of programing concepts such as generalization and automation. I believe the major cause is the intuitive graphical user interfaces of modern operating systems and applications, which isolate the user from all technical details. Generally, current curricula do not recognize this gap between user and machine. For students to operate effectively, they require specialized courses teaching them the skills they need to make tools that operate on particular data sets and solve their specific problems. Courses in computer science departments are aimed at a different audience and are of limited help.
The stratosphere: Dynamics, transport, and chemistry
Authors: Schultz Colin
Published: December 2011

On an October weekend in 2008, scientists gathered in New York City for PlumbFest, a symposium and celebration centered on the field of stratospheric research. Thirteen influential speakers explored the latest developments in the study of the middle atmosphere. The presentations, formalized and collected, became the AGU monographThe Stratosphere: Dynamics, Transport, and Chemistry, edited by Lorenzo M. Polvani, Adam H. Sobel, and Darryn W. Waugh. In this interview, Waugh talks toEos about the origins of PlumbFest, the Antarctic ozone hole, and the role the stratosphere plays in controlling the weather.
Reconciling late Miocene climate and carbon dioxide levels
Authors: Balcerak Ernie
Published: December 2011

The Miocene epoch, about 23–5 million years ago, was warmer than today. However, reconstructions indicate that it also had levels of atmospheric carbon dioxide (CO2) similar to preindustrial values. Scientists have had difficulty reconciling the Miocene temperatures and CO2 levels in models. Knorr et al. ran simulations using a coupled atmosphere‐ocean general circulation model to try to simulate a warm late Miocene climate with preindustrial CO2 levels. They analyzed the importance of tectonic factors and vegetation changes driving the late Miocene climate and found that the temperature could largely be explained by the vegetation distribution, thus showing that the warmer late Miocene climate can be reconciled with the preindustrial CO2 concentrations. (Geophysical Research Letters, doi:10.1029/2011GL048873, 2011)
Sudden stratospheric warming did not cool the thermosphere
Authors: Balcerak Ernie
Published: December 2011

In January 2009 a sudden stratospheric warming event occurred, in which temperatures in the stratosphere increased by 70 K. A previous study indicated that this sudden stratospheric warming led to strong cooling higher up in the atmosphere, in the upper thermosphere. However, a new analysis by Fuller‐Rowell et al. shows that that is probably not the case. The authors analyzed three different models and found that there was no evidence for any large‐scale decrease in upper thermosphere temperature or density caused by the sudden stratospheric warming event. Rather, they found that the observed decrease could be explained by small changes in geomagnetic activity that occurred at the same time. (Geophysical Research Letters, doi:10.1029/2011GL048985, 2011)
Heat played key role in Amazon droughts
Authors: Balcerak Ernie
Published: December 2011

In 2005 the Amazon region suffered a major drought in which a shortage of precipitation affected 2.5 million square kilometers of land, which resulted in significant tree loss. An even more widespread drought hit the region in 2010, affecting 3.2 million square meters of land. A new study by Toomey et al. shows that the loss of biomass during those events was due not only to a lack of moisture but also to heat stress. The researchers analyzed land surface temperature data from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite to look for a relationship among heat anomaly, precipitation anomaly, and forest stress during the droughts.
Climatological patterns over South America derived from COSMIC radio occultation data
Authors: Hierro R. , Llamedo P. , de la Torre A. , Alexander P. , Rolla A.
Published: December 2011

Meteorological phenomena are closely linked to the presence of water vapor. They mainly originate and develop in the troposphere, where almost all the atmospheric water is concentrated. The Global Positioning System radio occultation (GPS RO) technique provides vertical profiles of refractivity from which other properties such as temperature and water vapor can be derived. The GPS RO capability to reproduce global, synoptic, and regional climatological patterns over South America, which is a mostly oceanic continent, is tested. From FORMOSAT‐3/COSMIC mission data (2006–2010), our previous knowledge regarding global and synoptic/regional patterns of temperature, equivalent potential temperature, specific humidity, and pressure is verified. Special cases such as baroclinic disturbances arriving at South American midlatitudes and storm events over a mountain region near the Andes are analyzed. The temporal evolution and the latitude‐longitude distribution in several layers of the variables listed above are well described with this technique.
Mineral dust aerosols over the Sahara: Meteorological controls on emission and transport and implications for modeling
Authors: Knippertz Peter , Todd Martin C.
Published: December 2011

Atmospheric mineral dust has recently become an important research field in Earth system science because of its impacts on radiation, clouds, atmospheric dynamics and chemistry, air quality, and biogeochemical cycles. Studying and modeling dust emission and transport over the world's largest source region, the Sahara, is particularly challenging because of the complex meteorology and a very sparse observational network. Recent advances in satellite retrievals together with ground‐ and aircraft‐based field campaigns have fostered our understanding of the spatiotemporal variability of the dust aerosol and its atmospheric drivers. We now have a more complete picture of the key processes in the atmosphere associated with dust emission. These cover a range of scales from (1) synoptic scale cyclones in the northern sector of the Sahara, harmattan surges and African easterly waves, through (2) low‐level jets and cold pools of mesoscale convective systems (particularly over the Sahel), to (3) microscale dust devils and dusty plumes, each with its own pronounced diurnal and seasonal characteristics. This paper summarizes recent progress on monitoring and analyzing the dust distribution over the Sahara and discusses implications for numerical modeling. Among the key challenges for the future are a better quantification of the relative importance of single processes and a more realistic representation of the effects of the smaller‐scale meteorological features in dust models. In particular, moist convection has been recognized as a major limitation to our understanding because of the inability of satellites to observe dust under clouds and the difficulties of numerical models to capture convective organization.
Developing novel non-hydroxamate histone deacetylaseinhibitors: the chelidamic warhead
Authors: Valente Sergio , Conte Mariarosaria , Tardugno Maria , Nebbioso Angela , Tinari Gabriella , Altucci Lucia , Mai Antonello
Published: December 2011

The dimethyl 4-hydroxypyridine-2,6-dicarboxylate is a valuable scaffold for HDAC inhibitor design as a replacement of the well-known hydroxamate function.
The thermally-induced reaction of thin Ni films with Si: Effect of the substrate orientation
Authors: Gaudet S. , Desjardins P. , Lavoie C.
Published: December 2011

The solid-state reaction between thin Ni films and Si substrates was investigated using in situ synchrotron x-ray diffraction as well as ex situ three-dimensional reciprocal space maps and transmission electron microscopy analyses. Our results indicate that the orientation of the crystalline Si substrate strongly affects the reaction pathways, thereby altering the phase formation sequence upon annealing. On Si(001), the reaction begins with the formation of orthorhombic Ni2Si grains having a strong fiber texture. The metastable hexagonal θ phase and the NiSi phase then form through texture inheritance. The reaction on Si(111) is characterized by the appearance of multiple epitaxial phases. The as-prepared Ni samples contain a small amount of θ. Upon annealing, epitaxially textured Ni2Si along with other very thin epitaxial interfacial layers that may contain NiSi2 first appear. Once Ni2Si has completely consumed Ni, epitaxial Ni3Si2 grows while the complete consumption of Ni2Si triggers the formation of NiSi. Texture inheritance on Si(001) facilitates the nucleation and growth of NiSi, thus explaining the lower formation temperature on Si(001) than on Si(111).
Molecular simulation of fluid-solid interfaces at nanoscale
Authors: Ould-Kaddour F. , Levesque D.
Published: December 2011

The equilibrium states of vapor and liquid coexistent phases in contact with a solid surface are studied at the nanoscale by molecular dynamics simulations for a temperature close to the fluid triple point. The characteristics of the solid-fluid interfaces are determined when the interaction strength between the fluid and the solid varies in order to go from a situation of complete drying to that of complete wetting. From the vapor-liquid density profiles of liquid drops lying on the substrate surface or menisci of liquid films confined in slit pores, the contact angles made by the vapor-liquid interface with the solid are computed. The angle values are similar for the drops and the films. They are also in good qualitative agreement with the estimates obtained through the Young's relation from the surface tensions associated with the vapor-solid, liquid-solid, and vapor-liquid interfaces. However, at this scale, the uncertainties inherent to the angle computation and, to a lesser extent, to size effects seem to preclude that the quantitative agreement between the angle estimates obtained from the interface geometry and calculated from the Young's relation can be better than few degrees.
Rotational tunneling in CH4 II: Disorder effects
Authors: Press Werner , Krasnow Igor , Zamponi Michaela , Prager Michael
Published: December 2011

Transitions within the tunneling multiplet of CH4 in phase II have been measured in an experiment at the backscattering instrument BASIS of the Neutron Source SNS. They all involve transitions from or to T-states. A statistical model is put forward which accounts for local departures from tetrahedral symmetry at the sites of ordered molecules. Different from previous work, in which discrete sets of overlap matrix elements have been studied, now large numbers of elements as well as the ensemble of T-states are considered. The observed neutron spectra can be explained rather well, all based on the pocket state formalism of A. Hüller [Phys. Rev. B 16, 1844 (1977)]. A completely new result is the observation and simulation of transitions between T-states, which give rise to a double peaked feature close to the elastic position and which reflect the disorder in the system. CH2D2 molecules in the CH4 matrix are largely responsible for the disorder and an interesting topic for their own sake. The simple model presented may lend itself to a broader application.
Chasing charge localization and chemical reactivity following photoionization in liquid water
Authors: Marsalek Ondrej , Elles Christopher G. , Pieniazek Piotr A. , Pluhařová Eva , VandeVondele Joost , Bradforth Stephen E. , Jungwirth Pavel
Published: December 2011

The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ∼30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H2O+ + H2O → OH + H3O+. The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM/MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ∼40 fs time resolution and broadband spectral probing across the near-UV and visible are presented and direct comparisons with the theoretical simulations are made. Within the sensitivity and time resolution of the current measurement, a matching spectral signature is not detected. This result is used to place an upper limit on the absorption strength and/or lifetime of the localized H2O+(aq) species.
Pressure distribution in a quasi-hydrostatic pressure medium: A finite element analysis
Authors: Tempere Jacques , Silvera Isaac F.
Published: December 2011

The highest quality pressures on samples in a diamond anvil cell (DAC) at high pressures are produced using quasi-hydrostatic pressurization media such as helium or hydrogen. In this paper we carry out a finite element analysis of pressure distributions in a DAC using helium and non-hydrostatic argon pressurization media. We find that samples and ruby chips are at substantially higher pressures than the pressurization media, although this is sharply reduced by using helium, which has a low yield strength for the shear modulus. The deviations in pressure of the different samples (and ruby) from the pressurization media differ and depend on their elastic constants. Our observations may account for the distribution of pressures in metallic markers found in a recent calibration of the ruby scale to high pressures.
Spin-orbit relativistic long-range corrected time-dependent density functional theory for investigating spin-forbidden transitions in photochemical reactions
Authors: Nakata Ayako , Tsuneda Takao , Hirao Kimihiko
Published: December 2011

A long-range corrected (LC) time-dependent density functional theory (TDDFT) incorporating relativistic effects with spin-orbit couplings is presented. The relativistic effects are based on the two-component zeroth-order regular approximation Hamiltonian. Before calculating the electronic excitations, we calculated the ionization potentials (IPs) of alkaline metal, alkaline-earth metal, group 12 transition metal, and rare gas atoms as the minus orbital (spinor) energies on the basis of Koopmans’ theorem. We found that both long-range exchange and spin-orbit coupling effects are required to obtain Koopmans’ IPs, i.e., the orbital (spinor) energies, quantitatively in DFT calculations even for first-row transition metals and systems containing large short-range exchange effects. We then calculated the valence excitations of group 12 transition metal atoms and the Rydberg excitations of rare gas atoms using spin-orbit relativistic LC-TDDFT. We found that the long-range exchange and spin-orbit coupling effects significantly contribute to the electronic spectra of even light atoms if the atoms have low-lying excitations between orbital spinors of quite different electron distributions.
High coherent bi-chromatic laser with gigahertz splitting produced by the high diffraction orders of acousto-optic modulator used for coherent population trapping experiments
Authors: Yun Peter , Tan Bozhong , Deng Wei , Gu Sihong
Published: December 2011

To prepare the coherent population trapping (CPT) states with rubidium and cesium, the commonly used atoms in CPT studies, a coherent bi-chromatic light field with frequency difference of several GHz is a basic requirement. With a 200 MHz center frequency acousto-optic modulator (AOM), we have realized bi-chromatic laser fields with several GHz frequency splits through high diffraction orders. We have experimentally studied the coherence between two frequency components of a bi-chromatic laser beam, which is composed of ±6 orders with frequency split of 3 GHz diffracted from the same laser beam, and the measured residual phase noise is \documentclass[12pt]{minimal}\begin{document}$\Delta \phi ^{2}<0.019\ \text{rad}^{2}$\end{document}Δφ2<0.019rad2. The bi-chromatic laser fields were used to prepare CPT states with 85Rb and 87Rb atoms, and high contrast CPT signals were obtained. For CPT states preparation, our study result shows that it is a feasible approach to generate the bi-chromatic light field with larger frequency splits through high diffraction orders of AOM.
Point defect engineering strategies to suppress A-center formation in silicon
Authors: Chroneos A. , Londos C. A. , Sgourou E. N. , Pochet P.
Published: December 2011

We investigate the impact of tin doping on the formation of vacancy-oxygen pairs (VO or A-centers) and their conversion to VO2 clusters in electron-irradiated silicon. The experimental results are consistent with previous reports that Sn doping suppresses the formation of the A-center. We introduce a model to account for the observed differences under both Sn-poor and Sn-rich doping conditions. Using density functional theory calculations, we propose point defect engineering strategies to reduce the concentration of the deleterious A-centers in silicon. We predict that doping with lead, zirconium, or hafnium will lead to the suppression of the A-centers.
Trapping of metal atoms in the defects on graphene
Authors: Tang Yanan , Yang Zongxian , Dai Xianqi
Published: December 2011

The binding of a single metal atom (Pt, Pd, Au, and Sn) nearby a single-vacancy (SV) on the graphene is investigated using the first-principles density-functional theory. On the pristine graphene (pri-graphene), the Pt, Pd, and Sn prefer to be adsorbed at the bridge site, while Au prefers the top site. On the graphene with a single-vacancy (SV-graphene), all the metal atoms prefer to be trapped at the vacancy site and appear as dopants. However, the trapping abilities of the SV-graphene are varied for different metal atoms, i.e., the Pt and Pd have the larger trapping zones than do the others. The diffusion barrier of a metal atom on the SV-graphene is much higher than that on the pri-graphene, and the Pt atom has the largest diffusion barrier from the SV site to the neighboring bridge sites. On the SV-graphene, more electrons are transferred from the adatoms (or dopants) to the carbon atoms at the defect site, which induces changes in the electronic structures and magnetic properties of the systems. This work provides valuable information on the selectivity of lattice vacancy in trapping metal atoms, which would be vital for the atomic-scale design of new metal-carbon nanostructures and graphene-based catalysts.
The observation of unoccupied quantum-well states in Bi thin film grown on Si(111) by two-photon photoemission spectroscopy
Authors: Fujimasa Shuji , Imamura Masaki , Takahashi Kazutoshi , Yamamoto Isamu , Azuma Junpei , Kamada Masao
Published: December 2011

We have performed angle-resolved two-photon photoemission (AR-2PPE) measurements of Bi thin film with the thickness of 12 bilayers grown on Si(111) surface. From the excitation photon-energy dependence of AR-2PPE spectra, we have obtained the energy dispersion of unoccupied electronic states in the energy range between 2.0 and 3.0 eV above the EF. The observed electronic states are attributed to the unoccupied quantum-well states due to quantization of the 6 p-derived bulk bands along the Γ-T direction.
Crystallization properties and their drift dependence in phase-change memory studied with a micro-thermal stage
Authors: Ahn Chiyui , Lee Byoungil , Jeyasingh Rakesh G. D. , Asheghi Mehdi , Hurkx G. A. M. , Goodson Kenneth E. , Philip Wong H.-S.
Published: December 2011

The crystallization properties of phase-change memory (PCM) cells are studied at microsecond time scales using a novel micro-thermal stage. The time for recrystallization due to thermal disturbances is measured for varying amorphous volume fractions and annealing temperatures. PCM cells of intermediate resistances programmed with three different programming schemes are investigated and compared. For multi-bit programming, controlling the pulse-tail duration may be preferable as it has better retention characteristics than pulse-amplitude modulation or current-filament control. The effect of incomplete crystalline filaments on crystallization speed is experimentally investigated in this work, and the Arrhenius parameters are extracted from our crystallization time measurements to support a proposed unified mechanism for crystallization and drift. We have also found that recrystallization can be suppressed by more than 20% when there is a second of delay time between thermal disturbances.
Size-dependent elastic properties of crystalline polymers via a molecular mechanics model
Authors: Zhao Junhua , Guo Wanlin , Zhang Zhiliang , Rabczuk Timon
Published: December 2011

An analytical molecular mechanics model is developed to obtain the size-dependent elastic properties of crystalline polyethylene. An effective “stick-spiral” model is adopted in the polymer chain. Explicit equations are derived from the Lennard-Jones potential function for the van der Waals force between any two polymer chains. By using the derived formulas, the nine size-dependent elastic constants are investigated systematically. The present analytical results are in reasonable agreement with those from present united-atom molecular dynamics simulations. The established analytical model provides an efficient route for mechanical characterization of crystalline polymers and related materials toward nanoelectromechanical applications.
Experimental characterization and modeling of the bending strain effect on flexible microwave diodes and switches on plastic substrate
Authors: Qin Guoxuan , Yang Laichun , Seo Jung-Hun , Yuan Hao-Chih , Celler George K. , Ma Jianguo , Ma Zhenqiang
Published: December 2011

In this letter, comprehensive experimental characterization and modeling of the bending strain effect on flexible microwave diodes and switches are conducted. The flexible microwave devices/circuits indicate different performance dependence with bending strains under different bias conditions. It is observed that individual diodes and switch circuits have the same dominant factors (series resistance and inductance) for radio frequency properties under bending conditions. More importantly, variations of the dominant factors are almost only dependent on the strains and regardless of diode areas or connection topology. The study provides guidelines for designing and using high-speed diodes/switches for flexible monolithic microwave integrated circuits.
Characterization of low viscosity polymer solutions for microchip electrophoresis of non-denatured proteins on plastic chips
Authors: Yasui Takao , Reza Mohamadi Mohamad , Kaji Noritada , Okamoto Yukihiro , Tokeshi Manabu , Baba Yoshinobu
Published: December 2011

In this paper, we study characteristics of polymers (methylcellulose, hypromellose ((hydroxypropyl)methyl cellulose), poly(vinylpyrrolidone), and poly(vinyl alcohol)) with different chemical structures for microchip electrophoresis of non-denatured protein samples in a plastic microchip made of poly(methyl methacrylate) (PMMA). Coating efficiency of these polymers for controlling protein adsorption onto the channel surface of the plastic microchip, wettability of the PMMA surface, and electroosmotic flow in the PMMA microchannels in the presence of these polymers were compared. Also relative electrophoretic mobility of protein samples in solutions of these polymers was studied. We showed that when using low polymer concentrations (lower than the polymer entanglement point) where the sieving effect is substantially negligible, the interaction of the samples with the polymer affected the electrophoretic mobility of the samples. This effect can be used for achieving better resolution in microchip electrophoresis of protein samples.
Non-universal behavior well above the percolation threshold and thermal properties of core-shell-magnetite-polymer fibers
Authors: Vempati Sesha , Babu Veluru Jagadeesh , Karunakaran Raghuraman G. , Raghavachari Dhamodharan , Srinivasan Natarajan T.
Published: December 2011

Aligned nanocomposite electrospun fibers are investigated for electrical (dc, ac, and dielectric) and thermal properties (10−40 wt.%). This nanocomposite consists of poly(methylmethacrylate) (PMMA) grafted core-shell magnetite (CSM) nanoparticles and PMMA. Electrical properties as a function of tunnel gap (in between the CSM nanoparticles) are studied as the polymer shell stays intact and the “cores” do not touch each other well above the percolation threshold. The depleted improvement in dc conductivity (σdcwt%) with increasing wt.% (the improvement percentage: σdc10 to σdc20 ≈ 100%; σdc20 to σdc30 ≈ 40% and σdc30 to σdc40 ≈ 1.2%) affirms the non-touching “cores” of CSM. Interestingly, the observed ac conductive behavior (0.1−13 MHz) in the high end of the frequency range is in clear contrast to that of a typical percolating system, in fact it does not explicitly follow the universal power law. Some of the obtained critical exponents are not accommodated by the universal theory and significantly different from the present theoretical/experimental predictions. Additionally, an improvement in thermal stability of ∼30 °C and an overall increase in glass transition temperature are reported.
Magnetocaloric effect and its implementation in critical behavior study of Mn4FeGe3−xSix intermetallic compounds
Authors: Halder Madhumita , Yusuf S. M. , Nigam A. K.
Published: December 2011

Magnetocaloric effect in Mn4FeGe3−xSix compounds has been studied by dc magnetization measurements. For the parent compound Mn4FeGe3, the paramagnetic to ferromagnetic transition temperature TC is above room temperature (320 K), which initially remains constant for small Si substitution at the Ge site and then decreases marginally with an increase in Si concentration. A large change in magnetic entropy at the TC, under a magnetic field variation of 50 kOe, with typical values of 5.9, 6.5, 5.9, and 4.4 J kg−1 K−1for x = 0, 0.2, 0.6, and 1 samples, respectively, along with a broad operating temperature range and a negligible hysteresis make Mn4FeGe3−xSix series a promising candidate for magnetic refrigerant material around room temperature. Mn4FeGe3−xSix series is found to undergo a second-order magnetic phase transition. The field dependence of the magnetic entropy change has been brought out and implemented to deduce the critical exponents. The critical behavior study shows that the magnetic interactions for x = 0 and 0.2 samples have two different behaviors below and above TC. Below TC, it follows the mean field theory with long-range magnetic interaction and above TC it follows the Heisenberg three-dimensional model with short-range or local magnetic interaction. The magnetic exchange interactions for the x = 0.6 and 1 samples follow the mean-field theory.