bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular orientation distributions during injection molding of liquid crystalline polymers: Ex situ investigation of partially filled moldings
Authors: Fang Jun , Burghardt Wesley R. , Bubeck Robert A.
Published: October 2011

The development of molecular orientation in thermotropic liquid crystalline polymers (TLCPs) during injection molding has been investigated using two‐dimensional wide‐angle X‐ray scattering coordinated with numerical computations employing the Larson–Doi polydomain model. Orientation distributions were measured in “short shot” moldings to characterize structural evolution prior to completion of mold filling, in both thin and thick rectangular plaques. Distinct orientation patterns are observed near the filling front. In particular, strong extension at the melt front results in nearly transverse molecular alignment. Far away from the flow front shear competes with extension to produce complex spatial distributions of orientation. The relative influence of shear is stronger in the thin plaque, producing orientation along the filling direction. Exploiting an analogy between the Larson–Doi model and a fiber orientation model, we test the ability of process simulation tools to predict TLCP orientation distributions during molding. Substantial discrepancies between model predictions and experimental measurements are found near the flow front in partially filled short shots, attributed to the limits of the Hele–Shaw approximation used in the computations. Much of the flow front effect is however “washed out” by subsequent shear flow as mold filling progresses, leading to improved agreement between experiment and corresponding numerical predictions. POLYM. ENG. SCI.,, 2011. © 2011 Society of Plastics Engineers
Cofactor‐binding sites in proteins of deviating sequence: Comparative analysis and clustering in torsion angle, cavity, and fold space
Authors: Stegemann Björn , Klebe Gerhard
Published: October 2011

Small molecules are recognized in protein‐binding pockets through surface‐exposed physicochemical properties. To optimize binding, they have to adopt a conformation corresponding to a local energy minimum within the formed protein–ligand complex. However, their conformational flexibility makes them competent to bind not only to homologous proteins of the same family but also to proteins of remote similarity with respect to the shape of the binding pockets and folding pattern. Considering drug action, such observations can give rise tounexpected and undesired cross reactivity. In this study, datasets of six different cofactors (ADP, ATP, NAD(P)(H), FAD, and acetyl CoA, sharing an adenosine diphosphate moiety as common substructure), observed in multiple crystal structures of protein–cofactor complexes exhibiting sequence identity below 25%, have been analyzed for the conformational properties of the bound ligands, the distribution of physicochemical properties in the accommodating protein‐binding pockets, and the local folding patterns next to the cofactor‐binding site. State‐of‐the‐art clustering techniques have been applied to group the different protein–cofactor complexes in the different spaces. Interestingly, clustering in cavity (Cavbase) and fold space (DALI) reveals virtually the same data structuring. Remarkable relationships can be found among the different spaces. They provide information on how conformations are conserved across the host proteins and which distinct local cavity and fold motifs recognize the different portions of the cofactors. In those cases, where different cofactors are found to be accommodated in a similar fashion to the same fold motifs, only a commonly shared substructure of the cofactors is used for the recognition process. Proteins 2012. © 2011 Wiley Periodicals, Inc.
Uncertainty in carbon exchange modelling in a forest canopy due to kB−1 parametrizations
Authors: Hong J. , Kim J. , Byun Y. H.
Published: October 2011

The difference in turbulent transfer efficiency between momentum and scalars, represented by kB−1, has been the subject of considerable interest in micrometeorology, and various parametrizations have been proposed to address this issue. The simple kB−1 parametrizations that are based on either empirical formulations or K‐theory are still popularly used in the land surface models despite their theoretical deficiencies. Moreover, the impact of the uncertainty in this parameter on modelling surface carbon exchange has not been previously estimated. In this study, we examined the uncertainties of the simulated gross primary productivity (GPP), ecosystem respiration (RE), and net ecosystem exchange (NEE ≡ RE–GPP) for a forest canopy due to kB−1 parametrizations. The tested parametrizations included not only the schemes that set kB−1 as a constant or as a function of only the Reynolds number (popularly used in the land surface model), but also the schemes that express kB−1 as a function of plant phenology derived from the Lagrangian theory. Except for parametrizations that produced aerodynamic resistance as large as canopy resistance over a tall forest canopy, the variabilities of GPP and RE induced by kB−1 parametrizations were less than 2% of the annual GPP and RE, respectively. Nevertheless, the model produced approximately 10% variability of NEE values with changes in the kB−1 parametrizations (203±24 g C m−2year−1) because the simulated RE was less sensitive to the kB−1 parametrizations than the simulated GPP due to the negative feedback among kB−1, temperature, and RE. Our findings reveal that kB−1 parametrizations should be suitably applied in land surface modelling for better simulation of the global carbon cycle. Copyright © 2011 Royal Meteorological Society and British Crown Copyright, the Met Office
Receptor binding affinity based comparative QSAR study of testosterone derivatives
Authors: Khan Ahmad Khalid Raza , Khan Suhail Ahmad , Mishra Sunil , Khan Tajuddin , Ansari Mohiuddin , Khan Badshah Hasan
Published: October 2011

The quantitative structure activity relationship models of 22 testosterone derivatives have been made with the help of topological and quantum chemical parameters. The molecular modeling and geometry optimization have been carried out with CAChe Pro software. The calculations of topological and quantum chemical parameters have been done by MOPAC 2007. The statistical parameters are calculated by STATISTICA and SSP software. The study indicates that the topological parameters better predict the receptor binding affinity of testosterone derivatives, whereas quantum chemical parameters better predict androgenic potency of testosterone derivatives as indicated by correlation coefficient, standard error, standard error of estimation, p value, t value, and degree of freedom of the quantitative structure activity relationship (QSAR) models. The predicted activity values obtained by these QSAR models are close to observed activity. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012
Pharmacology of P2X receptors
Authors: Syed Nawazish‐i‐Husain , Kennedy Charles
Published: October 2011

P2X receptors are ligand‐gated cation channels that mediate many of the extracellular actions of adenosine 5′‐triphosphate (ATP). The genes encoding seven different P2X subunits, P2X1–7, have been cloned and when expressed alone all P2X subunits form functional receptors, except P2X6, which usually only assembles in a heteromeric form. Subunits can also interact with each other and to date seven functional heteromultimers with pharmacological and/or biophysical properties that differ from the individual homomultimers have been identified: P2X2/3, P2X4/6, P2X1/5, P2X2/6, P2X1/4, P2X1/2, and possibly P2X4/7. These are distributed widely throughout the body and are involved in many physiological and pathophysiological processes. ATP is an agonist at all subtypes and few selective agonists and no useful antagonists were available when P2X receptors were first defined. Subsequently, nonselective antagonists, such as suramin and PPADS, were discovered and since then, and particularly in the past decade, numerous potent and subtype‐selective antagonists have been developed. These include NF449 and RO‐1 at P2X1 receptors; PSB‐1011 at P2X2 receptors; A317491, compound A, RO‐3, and AF‐353 at P2X3 and P2X2/3 receptors; 5‐BDBD at P2X4 receptors; and A740003, A438079, A804598, GSK314181A, AZ10606120, AZ11645373, AZD‐9056, CE‐224535, and EVT‐401 at P2X7 receptors. The therapeutic usefulness of these compounds is currently being investigated in a variety of disorders, including thrombosis (P2X1), chronic neuropathic and inflammatory pain (P2X3, P2X2/3, P2X4, P2X7), dysfunctional urinary bladder (P2X1, P2X3, P2X2/3), rheumatoid arthritis and osteoarthritis (P2X7), and depression (P2X7). WIREs Membr Transp Signal 2012, 1:16–30. doi: 10.1002/wmts.1

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Calcium channels of schistosomes: unresolved questions and unexpected answers
Authors: Salvador‐Recatalà Vicenta , Greenberg Robert M.
Published: October 2011

Parasitic flatworms of the genus Schistosoma are the causative agents of schistosomiasis, a highly prevalent, neglected tropical disease that causes significant morbidity in hundreds of millions of people worldwide. The current treatment of choice against schistosomiasis is praziquantel (PZQ), which is known to affect Ca2+ homeostasis in schistosomes, but which has an undefined molecular target and mode of action. PZQ is the only available antischistosomal drug in most parts of the world, making reports of PZQ resistance particularly troubling. Voltage‐gated Ca2+ (Cav) channels have been proposed as possible targets for PZQ, and, given their central role in the neuromuscular system, may also serve as targets for new anthelmintic therapeutics. Indeed, ion channels constitute the majority of targets for current anthelmintics. Cav channel subunits from schistosomes and other platyhelminths have several unique properties that make them attractive as potential drug targets, and that could also provide insights into structure–function relationships in, and evolution of, Cav channels. WIREs Membr Transp Signal 2012, 1:85–93. doi: 10.1002/wmts.19

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Kainate receptors in developing presynaptic terminals
Authors: Lauri Sari , Taira Tomi
Published: October 2011

The formation of neuronal circuitry involves a period of activity‐dependent fine‐tuning and maturation of the connectivity, during which some of the nascent synapses are strengthened and others are eliminated. Many of the mechanisms utilized in this process are developmentally downregulated and replaced with synaptic machinery typical of adult‐type transmission. The kainate‐type of ionotropic glutamate receptors (KARs) modulate transmission and excitability of the neuronal networks in a complex manner, and thereby contribute to generation of patterned activity critical for plasticity and information processing. The expression, activation, and signaling of KARs is altered during early postnatal development and it is becoming evident that these receptors have specific functions during synapse maturation. In particular, developmentally restricted functions have been described for presynaptically located KARs in both areas CA3 and CA1 of the hippocampus. Although the exact mechanisms and receptor subunits responsible for these effects are still largely unclear, it is evident that KARs regulate synapse dynamics and plasticity in the neonatal brain and might be critically important in linking neuronal activity to morphogenesis at immature synapses. WIREs Membr Transp Signal 2012, 1:45–55. doi: 10.1002/wmts.3

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Horizontal transfer of RNAs: exosomes as mediators of intercellular communication
Authors: Ramachandran Saraswathi , Palanisamy Viswanathan
Published: October 2011

Multicellular organisms are similar to biological communities, consisting of various cell types; thus, inter‐cell communication is critical for the functioning of the whole system that ultimately constitutes a living being. Conventional models of cellular exchange include signaling molecules and direct contact‐mediated cell communications. Exosomes, small vesicles originating from an inward budding of the plasma membrane, represent a new avenue for signaling between cells. This interchange is achieved by packaging RNA species into exosomes endowed with specific cell surface‐targeting motifs. The delivered RNA molecules are functional, and mRNA can be translated into new proteins, while microRNAs (miRNAs) target host mRNAs in the recipient cell. RNA involved in transmitting information or molecules between cells is called exosomal RNA (esRNA). This review summarizes the characteristics of exosomes, specifically focusing on their role in the horizontal transfer of cellular information. WIREs RNA 2012, 3:286–293. doi: 10.1002/wrna.115

This article is categorized under:

Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs

RNA in Disease and Development > RNA in Development
Crystal Growth of Al‐Rich Complex Metallic Phases in the System Al–Cr–Fe Using the Czochralski Method
Authors: Bauer Birgitta , Gille Peter
Published: October 2011

Complex metallic phases in the Al–Cr–Fe system are considered to be interesting because of their enhanced resistance against corrosion. Single crystal growth of the Al4(Cr,Fe) and Al13(Fe,Cr)4 phases, which is a prerequisite for detailed studies is presented herein for the first time. Along with their binary end members Al4Cr and Al13Fe4 growth of cm3‐size crystals was achieved by using the Czochralski method from Al‐rich solutions at temperatures of approximately 1000 °C. Special emphasis is put on the refinement of the Al‐rich corner of the ternary phase diagram in determining the 1000 °C equilibria between the incongruent melts and the corresponding ternary solid solutions. Our findings confirm earlier data on the existence region of Al13(Fe,Cr)4, but significantly differ from those with respect to the so called Al4(Cr,Fe) phase. It is shown that the existence region of Al4(Cr,Fe) decomposes into four regions of structurally different phases depending on the Cr/Fe ratio. Binary μ‐Al4Cr crystallizes in the hexagonal space group P63/mmc and can dissolve only up to about 1 At‐% iron. More Fe‐rich alloys crystallize in the orthorhombic space group Cmcm (about 2 At‐% iron) or Immm (containing between 3 and about 6 At‐% iron). For crystals containing about 7 At‐% iron the structure belongs to the space group R$\bar{3}$. The grown single crystals were characterized by electron probe microanalysis revealing only weak segregation effects. The structural perfection of the orthorhombic phase was studied using X‐ray topography with the Lang technique. Significant anisotropic properties of this phase allow to discuss structural similarities with decagonal quasicrystals.
Holocene vegetation and climate change recorded in alpine bog sediments from the Borreguiles de la Virgen, Sierra Nevada, southern Spain
Authors: Jiménez-Moreno Gonzalo , Anderson R. Scott
Published: October 2011

High-resolution pollen and magnetic susceptibility (MS) analyses have been carried out on a sediment core taken from a high-elevation alpine bog area located in Sierra Nevada, southern Spain. The earliest part of the record, from 8200 to about 7000 cal yr BP, is characterized by the highest abundance of arboreal pollen andPediastrum, indicating the warmest and wettest conditions in the area at that time. The pollen record shows a progressive aridification since 7000 cal yr BP that occurred in two steps, first shown by a decrease inPinus, replaced by Poaceae from 7000 to 4600 cal yr BP and then by Cyperaceae,Artemisiaand Amaranthaceae from 4600 to 1200 cal yr BP.Pediastrumalso decreased progressively and totally disappeared at ca. 3000 yr ago. The progressive aridification is punctuated by periodically enhanced drought at ca. 6500, 5200 and 4000 cal yr BP that coincide in timing and duration with well-known dry events in the Mediterranean and other areas. Since 1200 cal yr BP, several changes are observed in the vegetation that probably indicate the high-impact of humans in the Sierra Nevada, with pasturing leading to nutrient enrichment and eutrophication of the bog,Pinusreforestation andOleacultivation at lower elevations.
The Institutional Foundations of Personal Finance: Innovation in U.S. Savings Banks, 1880s–1920s
Authors: Wadhwani R. Daniel
Published: October 2011

The system of personal finance that developed in the United States was more fragmented than comparative arrangements in most industrializing countries, where savings banks had become large, diversified financial institutions. The federalist political structure of the U.S., combined with lobbying by existing intermediaries, inhibited the establishment of a centralized public provider of financial services for households such as emerged elsewhere. Moreover, the United States did not develop strong, diversified savings institutions at the local level, due in part to regulations that stifled innovation by savings banks and in part to the risk-averse organizational culture of the banks themselves. These factors enabled the proliferation of specialized intermediaries that aggressively marketed new financial services to households and facilitated the growth of new patterns of financial behavior among ordinary Americans.
Americanization through Credit? Consumer Credit in Germany, 1860s–1960s
Authors: Logemann Jan
Published: October 2011

This study of the American impact on German consumer credit reveals that the notion of post–World War II Americanization emerging through credit-induced consumption is more complicated than has been previously acknowledged. The postwar debate in Germany over consumer credit as an American import had antecedents in a longer, previously overlooked, history of consumer credit. Moreover, the concept of Americanization remains misleading from a comparative perspective: First, examples of indigenous German institutional consumer lending predate the postwar period. Second, differences in both the forms and quantitative weight of consumer lending defy the notion of convergence. Third, different social and political contexts prevented a wholesale adoption in Germany of an American model of credit financing, despite repeated transatlantic transfers.
THE EFFECTS OF PRUNING AT DIFFERENT TIMES ON THE GROWTH, PHOTOSYNTHESIS AND YIELD OF CONILON COFFEE (COFFEA CANEPHORA) CLONES WITH VARYING PATTERNS OF FRUIT MATURATION IN SOUTHEASTERN BRAZIL
Authors: MORAIS L. E. , CAVATTE P. C. , MEDINA E. F. , SILVA P. E. M. , MARTINS S. C. V. , VOLPI P. S. , JÚNIOR S. ANDRADE , MACHADO FILHO J. A. , RONCHI C. P. , DAMATTA F. M.
Published: October 2011

The economics of coffee plantations is intrinsically linked to pruning, which can improve the canopy architecture and thereby increase productivity. However, recommended pruning times on conilon coffee plantations have been made on an entirely empirical basis. In this study, by evaluating growth, photosynthetic gas exchanges, starch accumulation and crop productivity, the effects of pruning at different times between harvest and flowering were investigated for six conilon coffee clones with distinct stages of fruit maturation (early, intermediate and late). Clones with an early maturation stage were pruned at four different times: 0, 30, 60 and 90 days after harvest (DAH). Intermediate clones were pruned at 0, 30 and 60 DAH, and late clones were pruned at 0 and 30 DAH. Overall, the rates of shoot growth and net photosynthesis, the stomatal conductance and the crop yield were not affected by the pruning treatments in any of the clones. In addition, pruning times did not affect the concentrations of starch or the photochemical efficiency of photosystem II. The carbon isotope composition ratio was marginally affected by the treatments. These results suggest that the pruning time after harvests is relatively unimportant and pruning operations can be scheduled to optimise the use of labour, which directly impacts the production costs of coffee.
Epifauna diversity and ecology on intertidal flats in the tropical Niger Delta, with remarks on the gastropod speciesHaminoea orbignyana
Authors: Zabbey Nenibarini , Malaquias Manuel António E.
Published: October 2011

Here we report novel data on the ecology and diversity of West African estuarine biological communities, with emphasis on the opisthobranch gastropod,Haminoea orbignyana. Macrofaunal samples were obtained from five intertidal flats within Bodo Creek in the lower Niger Delta during two years (May 2006–April 2008) to investigate diversity and community assemblages of epimacrofauna. A total of 601 individuals belonging to 18 species were recorded, with density varying between 4 ind.m−2and 660 ind.m−2. Gastropods (predominantlyPachymelania auritaandH. orbignyana) accounted for 92.3% of the community abundance, followed by malacostraca crustaceans (7.7%). Diversity varied (P < 0.05) between locations, with the mangrove swamp station having higher richness, diversity and evenness values than the open intertidal flat locations. The speciesH. orbignyanawas only found on downstream sampling sites reaching a maximum density of 52 ind.m−2. The species seems to recruit during November/December and likely attains a maximum life span of about 18 months.
Invariants of the dihedral group D2p in characteristic two
Authors: KOHLS MARTIN , SEZER MÜFİT
Published: October 2011

We consider finite dimensional representations of the dihedral group D2p over an algebraically closed field of characteristic two where p is an odd prime and study the degrees of generating and separating polynomials in the corresponding ring of invariants. We give an upper bound for the degrees of the polynomials in a minimal generating set that does not depend on p when the dimension of the representation is sufficiently large. We also show that p + 1 is the minimal number such that the invariants up to that degree always form a separating set. We also give an explicit description of a separating set.
A geometric definition of the Mañé-Mather set and a Theorem of Marie-Claude Arnaud.
Authors: BERNARD PATRICK , DOS SANTOS JOANA OLIVEIRA
Published: October 2011

We study some properties of Lipschitz exact Lagrangian manifolds isotopic to the zero section. We prove that if such a manifold is invariant under an optical Hamiltonian, then it must be a Lipschitz graph. This extends a recent result of Marie–Claude Arnaud. We also obtain a new geometric description of the Mañé–Mather invariant set.
Characterization of staphylococci contaminating automated teller machines in Hong Kong
Authors: ZHANG M. , O'DONONGHUE M. , BOOST M. V.
Published: October 2011

Environmental staphylococcal contamination was investigated by culture of 400 automated teller machines (ATMs). Isolates were characterized for antibiotic and antiseptic susceptibility, carriage of antiseptic resistance genes (QAC genes), and spa types. MRSA, which was similar to local clinical isolates, was present on two (0·5%) of the 62 (15·5%) ATMs that yielded Staphylococcus aureus. QAC genes were more common in coagulase-negative staphylococci (qacA/B 26·0%, smr 14%) than S. aureus (11·3% qacA/B, 1·6% smr). QAC-positive isolates had significantly higher minimum inhibitory concentrations/minimum bactericidal concentrations to benzalkonium chloride and chlorhexidine digluconate. QAC gene presence was significantly associated with methicillin and tetracycline resistance. Survival of staphylococci, including MRSA, on common access sites may be facilitated by low disinfectant concentrations, which select for disinfectant-tolerant strains, while co-selecting for antibiotic-resistance determinants. Disinfection procedures should be performed correctly to help prevent spread of resistant pathogens from reservoirs in the community.
First report of methicillin-resistantStaphylococcus aureusCordobes/Chilean clone involved in nosocomial infections in Brazil
Authors: BECKER A. P. , SANTOS O. , CASTRUCCI F. M. , DIAS C. , D'AZEVEDO P. ALVES
Published: October 2011

Methicillin-resistantStaphylococcus aureus(MRSA) commonly causes infection in hospitalized patients. Resistance is due to the acquisition ofmecA gene located on the chromosomal element SCCmecand to date 12 types have been identified. Specific epidemic clones of MRSA have emerged with enhanced ability to spread within and among hospitals and to cross national boundaries. We studied 30 isolates from patients with MRSA infections at two hospitals in Porto Alegre city from April to December, 2008 and determined their SCCmectype by PCR. Representative strains were typed by PFGE. Eighteen (60%) isolates carried SCCmectype III and had PFGE profiles clonally related to the previously characterized Brazilian epidemic clone, and 11 (36·7%) isolates with pulsotypes closely related to the Cordobes/Chilean clone harboured SCCmectype I. To the best of our knowledge, this is the first report of the appearance of Cordobes/Chilean clone involved in nosocomial infection in Brazil.
Use of Gravity Recovery and Climate Experiment terrestrial water storage retrievals to evaluate model estimates by the Australian water resources assessment system
Authors: van Dijk A. I. J. M. , Renzullo L. J. , Rodell M.
Published: October 2011

Terrestrial water storage (TWS) estimates retrieved from the Gravity Recovery and Climate Experiment (GRACE) satellite mission were compared to TWS modeled by the Australian Water Resources Assessment (AWRA) system. The aim was to test whether differences could be attributed and used to identify model deficiencies. Data for 2003–2010 were decomposed into the seasonal cycle, linear trends and the remaining de‐trended anomalies before comparing. AWRA tended to have smaller seasonal amplitude than GRACE. GRACE showed a strong (>15 mm yr−1) drying trend in northwest Australia that was associated with a preceding period of unusually wet conditions, whereas weaker drying trends in the southern Murray Basin and southwest Western Australia were associated with relatively dry conditions. AWRA estimated trends were less negative for these regions, while a more positive trend was estimated for areas affected by cyclone Charlotte in 2009. For 2003–2009, a decrease of 7–8 mm yr−1 (50–60 km3 yr−1) was estimated from GRACE, enough to explain 6%–7% of the contemporary rate of global sea level rise. This trend was not reproduced by the model. Agreement between model and data suggested that the GRACE retrieval error estimates are biased high. A scaling coefficient applied to GRACE TWS to reduce the effect of signal leakage appeared to degrade quantitative agreement for some regions. Model aspects identified for improvement included a need for better estimation of rainfall in northwest Australia, and more sophisticated treatment of diffuse groundwater discharge processes and surface‐groundwater connectivity for some regions.
Macromolecular design of poly(vinyl alcohol) by RAFT polymerization
Authors: Smith Anton A. A. , Hussmann Thomas , Elich Joseph , Postma Almar , Alves Marie-Helene , Zelikin Alexander N.
Published: October 2011

Modern tools of polymer design yield superior PVA with drastically enhanced utility in biomedicine.
Scaling of light emission from detonating bare Composition B, 2,4,6-trinitrotoluene [C7H5(NO2)3], and PE4 plastic explosive charges
Authors: Mostert Frederik J. , Olivier Marius
Published: October 2011

It is well known that an intense flash of light is emitted when an explosive charge is detonated. The light emission continues well beyond the actual detonation process due to shock excitation of the air molecules around the charge, as well as post-detonation reactions in the expanding products of the detonation. Various researchers have studied these emissions, and it has been established that there are features in such emission spectra that can be regarded as characteristic for a specific explosive composition and configuration. In this study, the emission characteristics at wavelengths between 650 and 940 nm were experimentally investigated for cylindrical bare Composition B, 2,4,6-trinitrotoluene [C7H5(NO2)3], and PE4 plastic explosive charges in the mass (M) range of 0.5 kg to 4 kg. The results show that the light emission parameters scale to M1/3 consistent with other explosive blast parameters such as pressure and impulse (so-called Hopkinson’s scaling). It is also shown that for bare charges, two distinct regions in time can be distinguished for the light emission, namely, light from the early time frame, while the charge is detonating (and slightly beyond), and light from the expanding products of the explosive (the “fireball”). It is argued that in the first region, ionization effects and shock excitation of the air molecules around the charge dominate the light emission. The dominance of these effects fizzles out rapidly as the blast wave expands from the charge, leaving only light emission from the expanding products of the detonation.
Photo-induced Ag deposition on periodically poled lithium niobate: Concentration and intensity dependence
Authors: Sun Yang , Eller Brianna S. , Nemanich Robert J.
Published: October 2011

This research focuses on the formation of Ag nanopatterns on periodically poled lithium niobate (PPLN). The photo-induced process employs UV-light exposure while the PPLN is immersed in a AgNO3 solution. The Ag deposition was consistent with previous results, showing preferential deposition along the domain boundary as well as an increased density of particles on the positive domain surface in comparison to the negative domain. By tuning the chemical solution concentration and the UV-light intensity, the Ag+ ion flux and the electron flux are varied and the deposition pattern could be controlled to either enhance the nanowire-like structures along the domain boundary or create a more uniform deposition pattern over the positive and negative domains. To understand the deposition process, we investigated the relationship between the Ag+ ion flux because of diffusion and the electron flux initiated by the UV exposure of the ferroelectric surface. The subsequent results suggest that this relationship is responsible for the different deposition patterns. The observed variation of boundary-enhanced or boundary-depressed deposition is explained by consideration of the electric field distribution and the ratio of the Ag+ ion and photon flux. The results establish that the ratio can be controlled by varying the solution concentration and/or UV-light intensity to generate enhanced nanowire-like structures along the domain boundary or a more uniform deposition pattern over the positive and negative surface. Moreover, the specific value of the Ag+/photon flux ratio where the pattern changes is dependent on other factors including the nucleation limited growth mechanism and the Stern layer on the lithium niobate.
Lattice thermal conductivity of ultra high temperature ceramics ZrB2 and HfB2 from atomistic simulations
Authors: Lawson John W. , Daw Murray S. , Bauschlicher Charles W.
Published: October 2011

Atomistic Green-Kubo simulations are performed to evaluate the lattice thermal conductivity for single crystals of the ultra high temperature ceramics ZrB2 and HfB2. Recently developed interatomic potentials are used for these simulations. Heat current correlation functions show rapid oscillations, which can be identified with mixed metal-Boron optical phonon modes. Results for temperatures from 300K to 1000K are presented.
Thermal conductivity enhancement of nanofluids containing graphene nanosheets
Authors: Sen Gupta Soujit , Manoj Siva V. , Krishnan Sreenath , Sreeprasad T. S. , Singh Pawan K. , Pradeep T. , Das Sarit K.
Published: October 2011

This paper envisages a mechanism of heat conduction behind the thermal conductivity enhancement observed in graphene nanofluids. Graphene nanofluids have been prepared, characterized, and their thermal conductivity was measured using the transient hot wire method. The enhancements in thermal conductivity are substantial even at lower concentrations and are not predicted by the classical Maxwell model. The enhancement also shows strong temperature dependence which is unlike its carbon predecessors, carbon nanotube (CNT) and graphene oxide nanofluids. It is also seen that the magnitude of enhancement is in-between CNT and metallic/metal oxide nanofluids. This could be an indication that the mechanism of heat conduction is a combination of percolation in CNT and Brownian motion and micro convection effects in metallic/metal oxide nanofluids, leading to a strong proposition of a hybrid model.
An explicit physics-based model of ionic polymer-metal composite actuators
Authors: Pugal David , Kim Kwang J. , Aabloo Alvo
Published: October 2011

The Poisson-Nernst-Planck system of equations is used to simulate the charge dynamics due to ionic current and resulting time-dependent displacement of ionic polymer-metal composite (IPMC) materials. Measured data show that currents through the polymer of IPMC cause potential gradients on the electrodes. Existing physics based models of IPMC do not explicitly consider how this affects the charge formation near the electrodes and resulting actuation of IPMC. We have developed an explicit physics based model that couples the currents in the polymer to the electric current in the continuous electrodes of IPMC. The coupling is based on the Ramo-Shockley theorem. The circular dependency concept is used to explain how the dependency between the ionic current and the potential drop in the electrodes is calculated and how they affect each other. Simulations were carried out using the finite element method. Calculated potential gradients, electric currents, and tip displacement of IPMC were validated against experimental data. We also show how the model is general in respect to the different types of currents in the polymer and how it can be used in more complicated cases such as 3D simulations.
Curvature-induced secondary microflow motion in steady electro-osmotic transport with hydrodynamic slippage effect
Authors: Lim Jin-Myoung , Chun Myung-Suk
Published: October 2011

In order to exactly understand the curvature-induced secondary flow motion, the steady electro-osmotic flow (EOF) is investigated by applying the full Poisson-Boltzmann/Navier-Stokes equations in a whole domain of the rectangular microchannel. The momentum equation is solved with the continuity equation as the pressure-velocity coupling achieves convergence by employing the advanced algorithm, and generalized Navier’s slip boundary conditions are applied at the hydrophobic curved surface. Two kinds of channels widely used for lab-on-chips are explored with the glass channel and the heterogeneous channel consisting of glass and hydrophobic polydimethylsiloxane, spanning thin to thick electric double layer (EDL) problem. According to a sufficiently low Dean number, an inward skewness in the streamwise velocity profile is observed at the turn. With increasing EDL thickness, the electrokinetic effect gets higher contribution in the velocity profile. Simulation results regarding the variations of streamwise velocity depending on the electrokinetic parameters and hydrodynamic fluid slippage are qualitatively consistent with the predictions documented in the literature. Secondary flows arise due to a mismatch of streamline velocity between fluid in the channel center and near-wall regions. Strengthened secondary flow results from increasing the EDL thickness and the contribution of fluid inertia (i.e., electric field and channel curvature), providing a scaling relation with the same slope. Comparing with and between the cases enables us to identify the optimum selection in applications of curved channel for enhanced EOF and stronger secondary motion relevant to the mixing effect.
Ion-implantation induced nano distortion layer and its influence on nonlinear optical properties of ZnO single crystals
Authors: Zheng C. C. , Xu S. J. , Ning J. Q. , Chen Y. N. , Lu X. H. , Ling C.-C. , Che C. M. , Gao G. Y. , Hao J. H. , Brauer G. , Anwand W.
Published: October 2011

Second harmonic generation (SHG) and X-ray diffraction rocking curves of high-quality ZnO single crystals implanted by different ions (He, Cu, and Zn) were investigated. Interestingly, it was found that both He- and Zn-implanted samples show a convinced increment in SHG efficiency while the Cu-implanted one does not. X-ray diffraction rocking curves of the samples show satellite structures, and the simulations firmly reveal the formation of quasi-interfaces inside He- and Zn-implanted crystals. These quasi-interfaces lead to SHG improvement in the two samples. Polarization dependence of SHG of the samples on the excitation light also evidences this conclusion.
Auger recombination rates in ZnMgO from first principles
Authors: Heinemann Markus , Heiliger Christian
Published: October 2011

We investigate direct electron-electron-hole interband Auger recombination for wurtzite Zn1-xMgxO alloys in the range 0 ≤ x ≤ 1. Recombination rates are computed by interpolating the band structure and transition matrix elements from ab initio calculations of bulk ZnO, Zn0.5Mgn0.5O, and MgO primitive cells. We find that interband Auger recombination is most probable for Mg concentrations around 50%, where ZnMgO does not exist in a stable wurtzite phase. Since, for low Mg concentrations, the calculated Auger coefficients are far below 10−32 cm6/s, we do not expect significant nonradiative loss through direct interband recombination in wurtzite ZnMgO.
Microstructure and mechanical properties of copper subjected to cryogenic laser shock peening
Authors: Ye Chang , Suslov Sergey , Lin Dong , Liao Yiliang , Fei Xueling , Cheng Gary J.
Published: October 2011

In this study, an innovative materials processing technique, cryogenic laser shock peening (CLSP), is investigated. Copper is processed by laser shock peening (LSP) at the cryogenic temperature and compared with LSP at room temperature (RT-LSP). The microstructure of copper after processing is characterized by transmission electron microscopy (TEM). Nanotwins were observed in copper after CLSP due to the effect of cryogenic temperature. In addition, more energy is stored in the material as defects (dislocations) by CLSP compared to RT-LSP. Because of these unique microstructure changes, it is found that high material strength with good thermal stability is achieved after CLSP. The mechanical properties after CLSP, RT-LSP, and as-received are compared.
High resolution photoluminescence spectroscopy of donors in undoped and In-doped ZnO grown by metalorganic vapor phase epitaxy
Authors: Watkins S. P. , Deng Z. W. , Li D. C. , Huang H.
Published: October 2011

We report the observation of photoluminescence (PL) transitions in ZnO epilayers grown by metalorganic vapor phase epitaxy (MOVPE) on C-sapphire substrates with linewidths as low as 0.2 meV at 4.2 K. A dominant donor bound exciton (D0X) peak at 3361.0 meV is observed in all undoped samples together with the corresponding ionized donor bound exciton (D+X) peak at 3372.9 meV. The addition of In dopant using trimethylindium results in the appearance of the I9 transition at 3357.8 meV, which has been previously attributed to In D0X transitions. By intentionally doping the epilayers with In we can calibrate the PL energy spectra, and thereby identify the dominant D0X transition in undoped material at 3361.0 meV as due to Ga donors. The In and Ga identifications are also confirmed by the observation of two electron satellites. High temperature annealing under O2 results in a strong reduction of the In and Ga transitions, and the appearance of a third line which we attribute to Al out-diffusing from the sapphire substrate. Temperature dependent PL measurements on In-doped samples above 4 K show additional lines due to well-resolved D0X (B) transitions separated by 4.6 meV for both Ga and In donors due to the crystal field splitting of the valence band. The line intensities are modeled by simple Boltzmann statistics. On the basis of comparison with accepted values of the I9 transition energy in homoepitaxial ZnO samples, we deduce a strain-induced blueshift of ∼ 1.2 meV which is consistent with residual compressive strain induced in the ZnO films due to the smaller in-plane effective lattice constant of sapphire.
Highly effective gold nanoparticle-enhanced biosensor array on the wettability controlled substrate by wiping
Authors: Kim Jongsu , Park Hyunkyu , Kang Bongchul , Ku Renata , Ham Chulho , Yang Minyang
Published: October 2011

We demonstrate the use of a highly effective biosensor array to fulfill the requirements of high intensity, reduced nonspecific adsorption (NSA), and low sample usage. The mixed self-assembled monolayers (SAMs), consisting of methyl-terminated and methoxy-(polyethylene glycol (PEG))-terminated silanes, were newly applied as the background layer to reduce the background NSA via wettability control. The surface was modified by a plasma process with a pattern mask. Gold nanoparticles (AuNPs) were grafted within pattern-modified regions to increase intensity and were modified with protein G variants with cysteine residues to immobilize the antibody proteins directly. The target protein samples were selectively dewetted by the high throughput wiping process, while retaining semi-contact with the substrate. The data revealed that the background NSA was significantly reduced by 78% with selective dewetting compared to the standard method. Furthermore, the peak intensity was improved 5 times by applying AuNPs as compared to that of a planar surface, and the protein requirement was significantly reduced versus the standard process.
Procedure for measuring electrical resistivity of anisotropic materials: A revision of the Montgomery method
Authors: dos Santos C. A. M. , de Campos A. , da Luz M. S. , White B. D. , Neumeier J. J. , de Lima B. S. , Shigue C. Y.
Published: October 2011

A procedure for determining the electrical resistivity of anisotropic materials is presented. It offers several improvements to the well-known Montgomery method. One improvement, in particular, is the ability to obtain the electrical resistivity for all three axes of an orthorhombic crystal analytically, rather than using the iterative approach suggested by Montgomery for the third axis. All necessary equations are derived and their application in determining the tensor components of the electrical resistivity is explained in detail. Measurements on isotropic specimens were executed in order to test the foundations of the method. Measurements on anisotropic samples are compared with measurements obtained by using the standard four-probe method, revealing good agreement.
Current-voltage-time characteristics of the reactive Ar/N2 high power impulse magnetron sputtering discharge
Authors: Magnus F. , Sveinsson O. B. , Olafsson S. , Gudmundsson J. T.
Published: October 2011

The discharge current and voltage waveforms have been measured in a reactive high power impulse magnetron sputtering (HiPIMS) Ar/N2 discharge with a Ti target for 400 μs long pulses. We observe that the current waveform in the reactive Ar/N2 HiPIMS discharge is highly dependent on the pulse repetition frequency, unlike the non-reactive Ar discharge. The current is found to increase significantly as the frequency is lowered. This is attributed to an increase in the secondary electron emission yield during the self-sputtering phase, when the nitride forms on the target at low frequencies. In addition, self-sputtering runaway occurs at lower discharge voltages when nitrogen is added to the discharge. This illustrates the crucial role of self-sputtering in the behavior of the reactive HiPIMS discharge.
Method for measuring energy generation and efficiency of dielectric elastomer generators
Authors: Kaltseis Rainer , Keplinger Christoph , Baumgartner Richard , Kaltenbrunner Martin , Li Tiefeng , Mächler Philipp , Schwödiauer Reinhard , Suo Zhigang , Bauer Siegfried
Published: October 2011

Dielectric elastomer generators convert mechanical into electrical energy at high energy density, showing promise for large and small scale energy harvesting. We present an experiment to monitor electrical and mechanical energy flows separately and show the cycle of energy conversion in work-conjugate planes. A specific electrical energy generated per cycle of 102mJ/g, at a specific average power of 17mW/g, is demonstrated with an acrylic elastomer in a showcase generation cycle. The measured mechanical to electrical energy conversion efficiency is 7.5%. The experiment may be used to assess the aptitude of specifically designed elastomers for energy harvesting.
Structure and magnetic properties of ternary Tb-Fe-B nanoparticles and nanoflakes
Authors: Liu R. M. , Yue M. , Liu W. Q. , Zhang D. T. , Zhang J. X. , Guo Z. H. , Li W.
Published: October 2011

The structure and magnetic properties were studied for the ternary Tb-Fe-B nanoparticles and nanoflakes prepared by surfactant-aid high energy ball milling and subsequent size-selection. For the nanoparticles, significant room-temperature coercivity up to 10.6 kOe was achieved with the average particle size of 31.4 nm, but it decreases substantially to 400 Oe as the size is down to 8.2 nm. For the nanoflakes, the thickness is in the range of 50-80 nm while the length is about 1.1 μm, and high coercivity of 22.1 kOe and strong magnetic anisotropy were obtained simultaneously, indicating that the nanoflakes possess excellent permanent magnetic properties.
Realization of high efficiency orange and white organic light emitting diodes by introducing an ultra-thin undoped orange emitting layer
Authors: Zhao Yongbiao , Chen Jiangshan , Ma Dongge
Published: October 2011

In this paper, we report on high efficiency orange and white organic light emitting diodes (OLEDs) by introducing an ultra-thin undoped orange emitting layer (less than 1 nm) adjacent to the electron-transporting layer. The orange OLEDs showed a high external quantum efficiency (EQE) of 16.4% at 1000 cd/m2, and the resulting four-color white OLEDs emitted an EQE of 15.5% and a maximum color render index (CRI) of 87 at luminance of 1000 cd/m2. Further analysis on the EQE of the white OLEDs makes us confident that this design has the possibility to realize 100% internal quantum efficiency (IQE) by using much more highly efficient phosphorescent emitters.
Complex Bragg grating writing using direct modulation of the optical fiber with flexural waves
Authors: Oliveira Roberson A. , Marques Carlos A. F. , Cook Kevin , Canning John , Nogueira Rogério N. , Pohl Alexandre A. P.
Published: October 2011

A flexural wave is applied to an optical fiber during the process of Bragg grating inscription using the direct writing method through a phase mask. Using this approach, we can dither the writing process to allow complex grating writing. Examples we demonstrate are tunable sampled gratings and phase-shifted gratings.
Molecular simulations of H2 adsorption in metal-porphyrin frameworks: A potential new material evaluation
Authors: Xiong Ruichang , Keffer David J.
Published: October 2011

Path integral grand canonical Monte Carlo (PI-GCMC) simulations using standard force fields are carried out to calculate the adsorption of H2 in five metal-porphyrin frameworks (MPFs), a new class of metal organic framework (MOF)-type materials. These simulations are performed at 77 K and room temperature (300 K). The adsorption isotherms of H2 in IRMOF-1 and IRMOF-10 are also calculated as a comparison. All calculations indicate that all MPFs adsorbed a higher weight fraction of H2 than both IRMOF-1 and IRMOF-10, with one exception (MPF-2). The gravimetric hydrogen capacities are still well short of practical goals. The MPFs provide additional adsorption sites due to the porphyrin. A statistical mechanical lattice model predicts the adsorption well at room temperature. The prediction by this model showed that a weight fraction of hydrogen of 6 wt. % adsorbed in pores of the size found in IRMOF-1 at ambient temperature and modest pressures required a binding energy of about 17 kJ/mole, which is consistent with other findings.