bluuebunny/crossref_metadata_2025 huggingface dataset:
A combined electron microprobe (EMP) and Raman spectroscopic study of the alteration products in Martian meteorite MIL 03346
Authors: Kuebler K. E.
Published: November 2012

We examine the secondary alteration products in MIL 03346 using Raman spectroscopic and electron microprobe traverses. Discussion focuses on the single olivine in ,177 supplemented with observations from ,168 and ,169. Traverses start at the rim and progress into the interior. Dark brown, nearly opaque, laihunite [Fe2+Fe3+2(SiO4)2] is present as overgrowths, and 20–50µm veins of reddish‐brown stilpnomelane [(K,Na,Ca)4(Ti0.1,Al2.3,Fe3+35.5,Mn0.8,Mg9.3) (Si63Al9)(O,OH)206∗n(H2O)] occur inside the olivine. Stilpnomelane crosscuts and postdates the laihunite; veins are in sharp contact with the host olivine but lined by ~5µm films of jarosite [KFe3+3(SO4)2(OH)6] from a later generation of alteration. An interstitial laihunite also hosts stilpnomelane. The most recent secondary phases are gypsum and bassanite in our X‐ray maps of ,168 and ,169. Ca‐sulfates were not observed in X‐ray maps of ,177 but were detected in our Raman point count. All sulfates are believed to be Martian. The groundmass of MIL indicates rapid cooling from elevated temperatures withfO2near QFM. Reports of laihunite synthesis by olivine oxidation at elevated temperatures (100–800°C) suggest the overgrowths formed during consolidation. In terrestrial rocks, stilpnomelane is a product of late diagenesis to garnet‐grade metamorphism. In MIL, stilpnomelane appears to be a secondary phase formed at the lower end of this stability range, at conditions akin to diagenesis. Raman spectra indicate that the stilpnomelane, jarosite, and Ca‐sulfates are hydrated. The stilpnomelane contains Cl−and was followed by jarosite, a product of acid alteration, and the deposition of Ca‐sulfates and halide salts from more neutral chloride solutions.
A near‐field sea level record of East Antarctic Ice Sheet instability from 32 to 27 Myr
Authors: Gallagher Stephen J. , Villa Giuliana , Drysdale Russell N. , Wade Bridget S. , Scher Howie , Li Qianyu , Wallace Malcolm W. , Holdgate Guy R.
Published: November 2012

Fossil, facies, and isotope analyses of an early high‐paleolatitude (55°S) section suggests a highly unstable East Antarctic Ice Sheet from 32 to 27 Myr. The waxing and waning of this ice sheet from 140% to 40% of its present volume caused sea level changes of +25 m (ranging from ‐30 to +50 m) related to periodic glacial (100,000 to 200,000 years) and shorter interglacial events. The near‐field Gippsland sea level (GSL) curve shares many similarities to the far‐field New Jersey sea level (NJSL) estimates. However, there are possible resolution errors due to biochronology, taphonomy, and paleodepth estimates and the relative lack of lowstand deposits (in NJSL) that prevent detailed correlations with GSL. Nevertheless, the lateral variations in sea level between the GSL section and NJSL record that suggest ocean siphoning and antisiphoning may have propagated synchronous yet variable sea levels.
Measuring Biexponential Transverse Relaxation of the ASL Signal at 9.4 T to Estimate Arterial Oxygen Saturation and the Time of Exchange of Labeled Blood Water into Cortical Brain Tissue
Authors: Wells Jack A , Siow Bernard , Lythgoe Mark F , Thomas David L
Published: November 2012

The transverse decay of the arterial spin labeling (ASL) signal was measured at four inflow times in the rat brain cortex at 9.4 T. Biexponential T2 decay was observed that appears to derive from different T2 values associated with labeled water in the intravasculature (IV) and extravascular (EV) compartments. A two compartment biexponential model was used to assess the relative contribution of the IV and EV compartments to the ASL signal, without assuming a value for T2 of labeled blood water in the vessels. This novel methodology was applied to estimate the exchange time of blood water into EV tissue space and the oxygen saturation of blood on the arterial side of the vasculature. The mean exchange time of labeled blood water was estimated to be 370 ± 40 ms. The oxygen saturation of the arterial side of the vasculature was significantly less than 100% (~85%), which may have implications for quantitative functional magnetic resonance imaging studies where the arterial oxygen saturation is frequently assumed to be 100%.
Purinergic Receptors Regulate Myogenic Tone in Cerebral Parenchymal Arterioles
Authors: Brayden Joseph E , Li Yao , Tavares Matthew J
Published: November 2012

Myogenic tone is a fundamental aspect of vascular behavior in resistance arteries. This contractile response to changes in intravascular pressure is critically involved in blood flow autoregulation in tissues such as the brain, kidneys, and heart. Myogenic tone also helps regulate precapillary pressure and provides a level of background tone upon which vasodilator stimuli act to increase tissue perfusion when appropriate. Despite the importance of these processes in the brain, little is known about the mechanisms involved in control of myogenic tone in the cerebral microcirculation. Here, we report that pharmacological inhibition of P2Y4 and P2Y6 pyrimidine receptors nearly abolished myogenic tone in cerebral parenchymal arterioles (PAs). Molecular suppression of either P2Y4 or P2Y6 receptors using antisense oligodeoxynucleotides reduced myogenic tone by 44% ± 8% and 45% ± 7%, respectively. These results indicate that both receptor isoforms are activated by increased intravascular pressure, which enhances the activity of voltage-dependent calcium channels and increases myogenic tone in PAs. Enhancement or inhibition of ectonucleotidase activity had no effect on parenchymal arteriolar myogenic tone, indicating that this response is not mediated by local release of nucleotides, but rather may involve direct mechanical activation of P2Y receptors in the smooth muscle cells.
Mrp1 is Essential for Sphingolipid Signaling to P-Glycoprotein in Mouse Blood–Brain and Blood–Spinal Cord Barriers
Authors: Cartwright Tara A , Campos Christopher R , Cannon Ronald E , Miller David S
Published: November 2012

At the blood–brain and blood–spinal cord barriers, P-glycoprotein, an ATP-driven drug efflux pump, is a major obstacle to central nervous system (CNS) pharmacotherapy. Recently, we showed that signaling through tumor necrosis factor-α (TNF-α), sphingolipids, and sphingosine-1-phosphate receptor 1 (S1PR1) rapidly and reversibly reduced basal P-glycoprotein transport activity in the rat blood–brain barrier. The present study extends those findings to the mouse blood–brain and blood–spinal cord barriers and, importantly, identifies multidrug resistance-associated protein 1 (Mrp1, Abcc1) as the transporter that mediates S1P efflux from brain and spinal cord endothelial cells. In brain and spinal cord capillaries isolated from wild-type mice, TNF-α, sphingosine, S1P, the S1PR agonist fingolimod (FTY720), and its active, phosphorylated metabolite, FTY720P, reduced P-glycoprotein transport activity; these effects were abolished by a specific S1PR1 antagonist. In brain and spinal cord capillaries isolated from Mrp1-null mice, neither TNF-α nor sphingosine nor FTY720 reduced P-glycoprotein transport activity. However, S1P and FTY720P had the same S1PR1-dependent effects on transport activity as in capillaries from wild-type mice. Thus, deletion of Mrp1 alone terminated endogenous signaling to S1PR1. These results identify Mrp1 as the transporter essential for S1P efflux from the endothelial cells and thus for inside-out S1P signaling to P-glycoprotein at the blood–brain and blood–spinal cord barriers.
Identification of transcriptional and phosphatase regulators as interaction partners of human ADA3, a component of histone acetyltransferase complexes
Authors: Zencir Sevil , Sike Adam , Dobson Melanie J. , Ayaydin Ferhan , Boros Imre , Topcu Zeki
Published: November 2012

ADA (alteration/deficiency in activation) 3 is a conserved component of several transcriptional adaptor and HAT (histone acetyltransferase) complexes that regulate RNA polymerase II-mediated gene expression. Within the HAT complexes ADA3 is associated with ADA2 and the HAT GCN5 (general control non-repressed 5). ADA3 plays roles in diverse cellular processes and also in malignancies by modulating GCN5 catalytic activity and/or by interactions with other regulators. To gain a better understanding of ADA3 function, we used a yeast two-hybrid approach to screen a human fetal cDNA library for proteins that interacted with hADA3 (human ADA3). We identified three novel hADA3-interacting partners, a transcriptional regulator, AATF (apoptosis-antagonizing transcription factor), and regulatory subunits of the PP1 (protein phosphatase 1) and PP2A (protein phosphatase 2A) [PPP1R7 (PP1 regulatory subunit 7) and PPP2R5D (PP2A 56 kDa regulatory subunit δ isoform) respectively]. Analysis of truncated versions of hADA3 indicated that the C-terminal ADA2-interacting domain was not required for these interactions. Fluorescent microscopy analysis and co-immunoprecipitation provided support for the co-localization and interaction of hADA3 with these proteins in human cells. Expression of the interacting proteins altered expression of an hADA3-regulated reporter gene, suggesting functional consequences for the interactions. The detected interactions of hADA3 might extend the spectrum of mechanisms by which ADA3 can contribute to the regulation of gene expression and shed light on processes mediated by these newly identified ADA3 partners.
Biomineralization of selenium by the selenate-respiring bacteriumThauera selenatis
Authors: Butler Clive S. , Debieux Charles M. , Dridge Elizabeth J. , Splatt Peter , Wright Matthew
Published: November 2012

Bacterial anaerobic respiration using selenium oxyanions as the sole electron acceptor primarily result in the precipitation of selenium biominerals observed as either intracellular or extracellular selenium deposits. Although a better understanding of the enzymology of bacterial selenate reduction is emerging, the processes by which the selenium nanospheres are constructed, and in some cases secreted, has remained poorly studied. Thauera selenatis is a Gram-negative betaproteobacterium that is capable of respiring selenate due to the presence of a periplasmic selenate reductase (SerABC). SerABC is a molybdoenzyme that catalyses the reduction of selenate to selenite by accepting electrons from the Q-pool via a dihaem c-type cytochrome (cytc4). The product selenite is presumed to be reduced in the cytoplasm, forming intracellular selenium nanospheres that are ultimately secreted into the surrounding medium. The secretion of the selenium nanospheres is accompanied by the export of a ~95 kDa protein SefA (selenium factor A). SefA has no cleavable signal peptide, suggesting that it is also exported directly for the cytoplasmic compartment. It has been suggested that SefA functions to stabilize the formation of the selenium nanospheres before secretion, possibly providing reaction sites for selenium nanosphere creation or providing a shell to prevent subsequent selenium aggregation. The present paper draws on our current knowledge of selenate respiration and selenium biomineralization in T. selenatis and other analogous systems, and extends the application of nanoparticle tracking analysis to determine the size distribution profile of the selenium nanospheres secreted.
Development of a proteoliposome model to probe transmembrane electron-transfer reactions
Authors: White Gaye F. , Shi Zhi , Shi Liang , Dohnalkova Alice C. , Fredrickson James K. , Zachara John M. , Butt Julea N. , Richardson David J. , Clarke Thomas A.
Published: November 2012

The mineral-respiring bacterium Shewanella oneidensis uses a protein complex, MtrCAB, composed of two decahaem cytochromes brought together inside a transmembrane porin to transport electrons across the outer membrane to a variety of mineral-based electron acceptors. A proteoliposome system has been developed that contains Methyl Viologen as an internalized electron carrier and valinomycin as a membrane-associated cation exchanger. These proteoliposomes can be used as a model system to investigate MtrCAB function.
Long-range electron transport to Fe(III) oxide via pili with metallic-like conductivity
Authors: Lovley Derek R.
Published: November 2012

The mechanisms for Fe(III) oxide reduction by Geobacter species are of interest because Geobacter species have been shown to play an important role in Fe(III) oxide reduction in a diversity of environments in which Fe(III) reduction is a geochemically significant process. Geobacter species specifically express pili during growth on Fe(III) oxide compared with growth on soluble chelated Fe(III), and mutants that cannot produce pili are unable to effectively reduce Fe(III) oxide. The pili of Geobacter sulfurreducens are electrically conductive along their length under physiologically relevant conditions and exhibit a metallic-like conductivity similar to that observed previously in synthetic organic metals. Metallic-like conductivity in a biological protein filament is a previously unrecognized mechanism for electron transport that differs significantly from the more well-known biological strategy of electron hopping/tunnelling between closely spaced redox-active proteins. The multihaem c-type cytochrome OmcS is specifically associated with pili and is necessary for Fe(III) oxide reduction. However, multiple lines of evidence, including the metallic-like conductivity of the pili and the fact that OmcS molecules are spaced too far apart for electron hopping/tunnelling, indicate that OmcS is not responsible for long-range electron conduction along the pili. The role of OmcS may be to facilitate electron transfer from the pili to Fe(III) oxide. Long-range electron transport via pili with metallic-like conductivity is a paradigm shift that has important implications not only for Fe(III) oxide reduction, but also for interspecies electron exchange in syntrophic microbial communities as well as microbe–electrode interactions and the emerging field of bioelectronics.
Rab11 proteins in health and disease
Authors: Kelly Eoin E. , Horgan Conor P. , McCaffrey Mary W.
Published: November 2012

Comprising over 60 members, Rab proteins constitute the largest branch of the Ras superfamily of low-molecular-mass G-proteins. This protein family have been primarily implicated in various aspects of intracellular membrane trafficking processes. On the basis of distinct subfamily-specific sequence motifs, many Rabs have been grouped into subfamilies. The Rab11 GTPase subfamily comprises three members: Rab11a, Rab11b and Rab25/Rab11c, which, between them, have been demonstrated to bind more than 30 proteins. In the present paper, we review the function of the Rab11 subfamily. We describe their localization and primary functional roles within the cell and their implication, to date, in disease processes. We also summarize the protein machinery currently known to regulate or mediate their functions and the cargo molecules which they have been shown to transport.
Electron transfer at the cell–uranium interface in Geobacter spp.
Authors: Reguera Gemma
Published: November 2012

The in situ stimulation of Fe(III) oxide reduction in the subsurface stimulates the growth of Geobacter spp. and the precipitation of U(VI) from groundwater. As with Fe(III) oxide reduction, the reduction of uranium by Geobacter spp. requires the expression of their conductive pili. The pili bind the soluble uranium and catalyse its extracellular reductive precipitation along the pili filaments as a mononuclear U(IV) complexed by carbon-containing ligands. Although most of the uranium is immobilized by the pili, some uranium deposits are also observed in discreet regions of the outer membrane, consistent with the participation of redox-active foci, presumably c-type cytochromes, in the extracellular reduction of uranium. It is unlikely that cytochromes released from the outer membrane could associate with the pili and contribute to the catalysis, because scanning tunnelling microscopy spectroscopy did not reveal any haem-specific electronic features in the pili, but, rather, showed topographic and electronic features intrinsic to the pilus shaft. Pili not only enhance the rate and extent of uranium reduction per cell, but also prevent the uranium from traversing the outer membrane and mineralizing the cell envelope. As a result, pili expression preserves the essential respiratory activities of the cell envelope and the cell's viability. Hence the results support a model in which the conductive pili function as the primary mechanism for the reduction of uranium and cellular protection in Geobacter spp.
Role of the Rab11 pathway in negative-strand virus assembly
Authors: Bruce Emily A. , Stuart Amanda , McCaffrey Mary W. , Digard Paul
Published: November 2012

As intracellular pathogens, enveloped viruses must usurp the host cell machinery for many stages of the viral life cycle in order to produce a new generation of infectious virions. In one of the less understood steps of viral assembly, viral components including the transmembrane glycoproteins, structural proteins and the viral genome must be targeted to the site of viral budding, where they assemble and are incorporated into a newly formed virion that gains a lipid envelope from a cellular membrane. Recent work has revealed that the cellular recycling endosome pathway, in particular Rab11, plays an important role in the assembly of negative-strand RNA viruses such as respiratory syncytial virus, influenza A virus, Andes virus and Sendai virus. The present mini-review discusses this emerging field and explores the potential roles of the Rab11 pathway in the trafficking, assembly and budding steps of these viruses.
MMBL proteins: from lectin to bacteriocin
Authors: Ghequire Maarten G.K. , Loris Remy , De Mot René
Published: November 2012

Arguably, bacteriocins deployed in warfare among related bacteria are among the most diverse proteinacous compounds with respect to structure and mode of action. Identification of the first prokaryotic member of the so-called MMBLs (monocot mannose-binding lectins) or GNA (Galanthus nivalis agglutinin) lectin family and discovery of its genus-specific killer activity in the Gram-negative bacteria Pseudomonas and Xanthomonas has added yet another kind of toxin to this group of allelopathic molecules. This novel feature is reminiscent of the protective function, on the basis of antifungal, insecticidal, nematicidal or antiviral activity, assigned to or proposed for several of the eukaryotic MMBL proteins that are ubiquitously distributed among monocot plants, but also occur in some other plants, fish, sponges, amoebae and fungi. Direct bactericidal activity can also be effected by a C-type lectin, but this is a mammalian protein that limits mucosal colonization by Gram-positive bacteria. The presence of two divergent MMBL domains in the novel bacteriocins raises questions about task distribution between modules and the possible role of carbohydrate binding in the specificity of target strain recognition and killing. Notably, bacteriocin activity was also demonstrated for a hybrid MMBL protein with an accessory protease-like domain. This association with one or more additional modules, often with predicted peptide-hydrolysing or -binding activity, suggests that additional bacteriotoxic proteins may be found among the diverse chimaeric MMBL proteins encoded in prokaryotic genomes. A phylogenetic survey of the bacterial MMBL modules reveals a mosaic pattern of strongly diverged sequences, mainly occurring in soil-dwelling and rhizosphere bacteria, which may reflect a trans-kingdom acquisition of the ancestral genes.
Resistance is futile: the bacteriocin model for addressing the antibiotic resistance challenge
Authors: Riley Margaret A. , Robinson Sandra M. , Roy Christopher M. , Dennis Morgan , Liu Vivian , Dorit Robert L.
Published: November 2012

Pathogenic bacteria resistant to many or all antibiotics already exist. With the decline in microbiological research at pharmaceutical companies, the high rate at which resistance has evolved and spread has demanded a novel approach to addressing this critical human health issue. In the present paper, we propose a new paradigm in antibiotic discovery and development, one that applies ecological and evolutionary theory to design antimicrobial drugs that are more difficult and/or more costly to resist. In essence, we propose to simply adopt the strategies invented and applied by bacteria for hundreds of millions of years. Our research focuses on bacteriocins, powerful biological weapons, and their use as alternative therapeutics in human health.
Colicin M, a peptidoglycan lipid-II-degrading enzyme: potential use for antibacterial means?
Authors: Touzé Thierry , Barreteau Hélène , El Ghachi Meriem , Bouhss Ahmed , Barnéoud-Arnoulet Aurélie , Patin Delphine , Sacco Emmanuelle , Blanot Didier , Arthur Michel , Duché Denis , Lloubès Roland , Mengin-Lecreulx Dominique
Published: November 2012

Colicins are proteins produced by some strains of Escherichia coli to kill competitors belonging to the same species. Among them, ColM (colicin M) is the only one that blocks the biosynthesis of peptidoglycan, a specific bacterial cell-wall polymer essential for cell integrity. ColM acts in the periplasm by hydrolysing the phosphoester bond of the peptidoglycan lipid intermediate (lipid II). ColM cytotoxicity is dependent on FkpA of the targeted cell, a chaperone with peptidylprolyl cis–trans isomerase activity. Dissection of ColM was used to delineate the catalytic domain and to identify the active-site residues. The in vitro activity of the isolated catalytic domain towards lipid II was 50-fold higher than that of the full-length bacteriocin. Moreover, this domain was bactericidal in the absence of FkpA under conditions that bypass the import mechanism (FhuA–TonB machinery). Thus ColM undergoes a maturation process driven by FkpA that is not required for the activity of the isolated catalytic domain. Genes encoding proteins with similarity to the catalytic domain of ColM were identified in pathogenic strains of Pseudomonas and other genera. ColM acts on several structures of lipid II representative of the diversity of peptidoglycan chemotypes. All together, these data open the way to the potential use of ColM-related bacteriocins as broad spectrum antibacterial agents.
Molecular basis of Charcot–Marie–Tooth type 2B disease
Authors: Bucci Cecilia , De Luca Maria
Published: November 2012

CMT2B (Charcot–Marie–Tooth type 2B) disease is an autosomal dominant peripheral neuropathy whose onset is in the second or third decade of life, thus in adolescence or young adulthood. CMT2B is clinically characterized by severe symmetric distal sensory loss, reduced tendon reflexes at ankles, weakness in the lower limbs and muscle atrophy, complicated by ulcerations that often lead to amputations. Four missense mutations in the gene encoding the small GTPase Rab7 cause the CMT2B neuropathy. Rab7 is a ubiquitous protein that regulates transport to late endosomes and lysosomes in the endocytic pathway. In neurons, Rab7 is important for endosomal trafficking and signalling of neurotrophins, and for retrograde axonal transport. Recent data on CMT2B-causing Rab7 mutant proteins show that these proteins exhibit altered koff rates and, as a consequence, they are mainly in the GTP-bound state and bind more strongly to Rab7 effector proteins. Notably, expression of CMT2B-causing Rab7 mutant proteins strongly inhibit neurite outgrowth in several cells lines and alter NGF (nerve growth factor) trafficking and signalling. These data indicate that Rab7 plays an essential role in neuronal cells and that CMT2B-causing Rab7 mutant proteins alter neuronal specific pathways, but do not fully explain why only peripheral neurons are affected in CMT2B. In the present paper, we discuss the current understanding of the molecular and cellular mechanisms underlying CMT2B, and we consider possible hypotheses in order to explain how alterations of Rab7 function lead to CMT2B.
The Rab family of proteins: 25 years on
Authors: Kelly Eoin E. , Horgan Conor P. , Goud Bruno , McCaffrey Mary W.
Published: November 2012

Intracellular membrane trafficking requires the complex interplay of several classes of trafficking proteins. Rab proteins, the largest subfamily of the Ras superfamily of small G-proteins, are central regulators of all aspects of intracellular trafficking processes including vesicle budding and uncoating, motility, tethering and fusion. In the present paper, we discuss the discovery, evolution and characterization of the Rab GTPase family. We examine their basic functional roles, their important structural features and the regulatory proteins which mediate Rab function. We speculate on outstanding issues in the field, such as the mechanisms of Rab membrane association and the co-ordinated interplay between distinct Rab proteins. Finally, we summarize the data implicating Rab proteins in an ever increasing number of diseases.
Shewanella oneidensis MR-1 chemotaxis proteins and electron-transport chain components essential for congregation near insoluble electron acceptors
Authors: Harris H. Wayne , El-Naggar Mohamed Y. , Nealson Kenneth H.
Published: November 2012

Shewanella oneidensis MR-1 cells utilize a behaviour response called electrokinesis to increase their speed in the vicinity of IEAs (insoluble electron acceptors), including manganese oxides, iron oxides and poised electrodes [Harris, El-Naggar, Bretschger, Ward, Romine, Obraztsova and Nealson (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 326–331]. However, it is not currently understood how bacteria remain in the vicinity of the IEA and accumulate both on the surface and in the surrounding medium. In the present paper, we provide results indicating that cells that have contacted the IEAs swim faster than those that have not recently made contact. In addition, fast-swimming cells exhibit an enhancement of swimming reversals leading to rapid non-random accumulation of cells on, and adjacent to, mineral particles. We call the observed accumulation near IEAs ‘congregation’. Congregation is eliminated by the loss of a critical gene involved with EET (extracellular electron transport) (cymA, SO_4591) and is altered or eliminated in several deletion mutants of homologues of genes that are involved with chemotaxis or energy taxis in Escherichia coli. These genes include chemotactic signal transduction protein (cheA-3, SO_3207), methyl-accepting chemotaxis proteins with the Cache domain (mcp_cache, SO_2240) or the PAS (Per/Arnt/Sim) domain (mcp_pas, SO_1385). In the present paper, we report studies of S. oneidensis MR-1 that lend some insight into how microbes in this group can ‘sense’ the presence of a solid substrate such as a mineral surface, and maintain themselves in the vicinity of the mineral (i.e. via congregation), which may ultimately lead to attachment and biofilm formation.
High order standing-wave plasmon resonances in silver u-shaped nanowires
Authors: Rodríguez-Fortuño Francisco J. , Ortuño Rubén , García-Meca Carlos , Martí Javier , Martínez Alejandro
Published: November 2012

Optical measurements of the transmission spectra through nanofabricated planar arrays of silver u-shaped nanowires on a silicon substrate resonating at infrared frequencies are performed. Good agreement with the numerically simulated surface plasmon standing wave resonances supported by the structures is found. Such resonances exhibit field enhancement and are able to provide magnetic and electric responses when used as the unit cell of a metamaterial. The magnetic excitation of the resonators using oblique incidence is shown to be drastically reduced by the existence of a high index substrate such as silicon.
Percutaneous permeation measurement of topical phthalocyanine by photoacoustic technique
Authors: Silva Emanoel P. O. , Barja Paulo R. , Cardoso Luiz E. , Beltrame Milton
Published: November 2012

This investigation have studied photoacoustic (PA) technique to percutaneous permeation of topical hydroxy-(29H,31H-phthalocyaninate) aluminum (PcAlOH) on pig ear skin. The PcAlOH was incorporated in an emulsion (O/W) (1 mg/dl) with assessed stability parameters of: pH, short and long term stability tests (in the several conditions). The skin was prepared through a heat separation technique, and with a scalpel, the outer skin of the cartilage was removed. The skins were then cut into 4 cm2 pieces and treated with sodium bromide 2 mol/L for 6 h at 37 °C. The epidermis layer was washed with purified water, dried, and stored under reduced pressure until use. The skin permeation kinetics was determined by photoacoustic technique in an open photoacoustic cell. Short (after preparation) and long-term stability tests showed no phase separation. The emulsion developed pH 7.6 and after incorporating the pH was unchanged. The typical times for percutaneous permeation of the emulsion base and emulsion + PcAlOH were 182 (±6) and 438 (±3) s, respectively. This study indicated that the formulations containing PcAlOH have stabile characteristics and show promising results in absorption into the skin. The presence of the photosensitive agent in the formulation contributed significantly to the greater absorption time than observed in the base formulation. The used photoacoustic technical to examine the penetration kinetics of PcAlOH in pig ear skin was adequate and may be employed in the determination of the percutaneous permeation of phthalocyanines.
Enhanced ferromagnetism and glassy state in phase separated La0.95Sr0.05MnO3 + δ
Authors: De K. , Das S. , Roy A. , Dhak P. , Willinger M. , Amaral J. S. , Amaral V. S. , Giri S. , Majumder S. , Silva C. J. R. , Gomes M. J. M. , Mahapatra P. K.
Published: November 2012

Unusual high temperature ferromagentism is reported for La0.95Sr0.05MnO3+δ with Curie temperatures (TC1 and TC2) TC1 at 290 K and TC2 ∼ 150 K. Weak antiferromagnetism (AFM) is thought to give low moment, low temperature irreversibility, and non-saturation up to 10 T at 5 K. A short-range ferromagnetism is predicted from well-defined hysteresis at 5 K and field-cooled (FC) magnetization curves. Strong irreversibility between zero field-cooled (ZFC) and FC at 5 T is due to “hard” spins, not from ferromagnetic clusters. Field-dependent peak shift of spin freezing temperature in ZFC, memory effect, magnetic relaxation shows cluster glass like transition in the system. A metal-insulator transition at 115 K also implies a completion of percolation of short range ferromagnetic clusters, giving an onset of metallic state at 115 K. A complete magnetic phase diagram is presented showing its temperature dependent rich magnetic behavior.
Fundamental properties of field emission-driven direct current microdischarges
Authors: Rumbach Paul , Go David B.
Published: November 2012

For half a century, it has been known that the onset of field emission in direct current microdischarges with gap sizes less than 10 μm can lead to breakdown at applied voltages far less than predicted by Paschen's law. It is still unclear how field emission affects other fundamental plasma properties at this scale. In this work, a one-dimensional fluid model is used to predict basic scaling laws for fundamental properties including ion density, electric field due to space charge, and current-voltage relations in the pre-breakdown regime. Computational results are compared with approximate analytic solutions. It is shown that field emission provides an abundance of cathode electrons, which in turn create large ion concentrations through ionizing collisions well before Paschen's criterion for breakdown is met. Breakdown due to ion-enhanced field emission occurs when the electric field due to space charge becomes comparable to the applied electric field. Simple scaling analysis of the 1D Poisson equation demonstrates that an ion density of n+ ≈ 0.1VAε0/qd2 is necessary to significantly distort the electric field. Defining breakdown in terms of this critical ion density leads analytically to a simple, effective secondary emission coefficient γ′ of the same mathematical form initially suggested by Boyle and Kisliuk [Phys. Rev. 97, 255 (1955)].
Effect of processing kinetics on the structure of ferromagnetic-ferroelectric-ferromagnetic interfaces
Authors: Sankara Rama Krishnan P. S. , Ramasse Q. M. , Liang Wen-I , Chu Ying-Hao , Nagarajan V. , Munroe P.
Published: November 2012

Trilayer heterostructures consisting of a ferroelectric bismuth ferrite (BFO) film sandwiched between ferromagnetic lanthanum strontium manganese oxide (LSMO) films were fabricated using pulsed laser deposition. Both BFO thicknesses (20 nm, 5 nm) and cooling rates were varied to investigate the role of processing parameters on the chemistry of the interfaces. The interfaces were investigated using a dedicated aberration corrected scanning transmission electron microscope (STEM) operated at 100 kV via STEM-high angle annular dark field (STEM-HAADF) and STEM-electron energy loss spectroscopy (STEM-EELS) modes. Combined analysis through STEM-HAADF and STEM-EELS revealed the formation of lattice distortion in certain regions of the BFO layer for the ∼5 nm film. Piezoresponse force microscopy (PFM) studies of the ∼5 nm BFO sample revealed weak ferroelectric domain switching. Stacking fault defects with mixed valence manganese (Mn-B site cation) were formed in the top LSMO layer when the heterostructure was cooled at a slower rate irrespective of BFO thickness, thereby demonstrating the effect of processing kinetics on the physical integrity of the heterostructure.
A new, definitive analysis of a very old spectrum: The highly perturbed A2Πu–X 2Πg band system of the chlorine cation (${\rm Cl}_2^ +$ Cl 2+)
Authors: Gharaibeh Mohammed A. , Clouthier Dennis J. , Kalemos Apostolos , Lefebvre-Brion Hélène , Field Robert W.
Published: November 2012

The laser-induced fluorescence spectrum of jet-cooled chlorine cation has been recorded in the 500−312 nm region with high sensitivity and rigorous vibrational and spin-orbit cooling. More than 80 bands of the highly vibrationally perturbed A 2Πu−X 2Πg electronic transition have been detected and shown to originate from the Ω = 3/2 spin-orbit component of v = 0 of the ground state. The spectrum extends some 3700 cm−1 to the red of any previously published report and the 0–0 band has been identified for the first time. The bands have regular rotational structure but exhibit irregular vibrational intervals and isotope splittings. Our ab initio studies show that the perturbations are due to a ΔΩ = 0 spin-orbit interaction between the A2Π3/2u and B2Δ 3/2u states which have an avoided crossing at ∼2.5 Å, which corresponds to v ≈ 4 of the A state. The nonadiabatic coupled equations have been solved for this two-state interaction after constructing the diabatic potentials including only the diagonal (ΔΛ = 0) spin-orbit coupling, yielding low-lying vibrational energy levels, isotope splittings, and rotational constants in good agreement with experiment. The calculations show that many of the observed bands are actually transitions to predominantly B state vibrational levels, which borrow oscillator strength from the A−X transition through spin-orbit mixing. Starting from the coupled equations solutions, we have fitted the experimental data using an effective Hamiltonian matrix that includes the vibrational energy levels of the A and B states and a single electronic spin-orbit coupling term $H_{{\rm SO}}^{AB}$H SO AB which has a value of 240 cm−1. Transitions up to v′ = 32 in both states have been satisfactorily fitted for all three chlorine isotopologues, providing a quantitative description of the perturbations. Transitions to higher levels are complicated by interactions with other electronic states.
Complexity and simplicity of optimal control theory pulses shaped for controlling vibrational qubits
Authors: Shyshlov Dmytro , Babikov Dmitri
Published: November 2012

In the context of molecular quantum computation the optimal control theory (OCT) is used to obtain shaped laser pulses for high-fidelity control of vibrational qubits. Optimization is done in time domain and the OCT algorithm varies values of electric field in each time step independently, tuning hundreds of thousands of parameters to find one optimal solution. Such flexibility is not available in experiments, where pulse shaping is done in frequency domain and the number of “tuning knobs” is much smaller. The question of possible experimental interpretations of theoretically found OCT solutions arises. In this work we analyze very accurate optimal pulse that we obtained for implementing quantum gate CNOT for the two-qubit system encoded into the exited vibrational states of thiophosgene molecule. Next, we try to alter this pulse by reducing the number of available frequency channels and intentionally introducing systematic and random errors (in frequency domain, by modifying the values of amplitudes and phases of different frequency components). We conclude that a very limited number of frequency components (only 32 in the model of thiophosgene) are really necessary for accurate control of the vibrational two-qubit system, and such pulses can be readily constructed using OCT. If the amplitude and phase errors of different frequency components do not exceed ±3% of the optimal values, one can still achieve accurate transformations of the vibrational two-qubit system, with gate fidelity of CNOT exceeding 0.99.
Photodissociation of N-methylformamide isolated in solid parahydrogen
Authors: Ruzi Mahmut , Anderson David T.
Published: November 2012

We report FTIR studies of the 193 nm photodecomposition of N-methylformamide (NMF) isolated in solid parahydrogen (pH2) matrices at 1.9 K. By studying the detailed photokinetics we can distinguish between primary and secondary photoproducts. We observe single exponential decay of the NMF precursor upon irradiation and identify three competing primary dissociation channels: HCO + NHCH3; H + CONHCH3; and CO + CH3NH2 with branching ratios of 0.46(7):0.032(8):0.51(6), respectively. Two of the primary photoproducts (NHCH3 and CONHCH3) are observed for the first time using IR spectroscopy and assigned via ab initio calculations of the vibrational frequencies and intensities of these radicals. The dominant radical formation channel HCO + NHCH3 is consistent with efficient C–N peptide bond fission at this wavelength and escape of the nascent radical pair from the pH2 solvent cage. The significant branching 0.51(6) measured for the molecular channel CO + CH3NH2 is unexpected and raises important questions about the details of the in situ photochemistry. Starting from the NMF precursor, we observe and characterize spectroscopically a wide variety of secondary photoproducts including CH2NH, HCN, HNC, HNCO, CH3NCO, CH4, and NH3.
Adjustment of ablation shapes and subwavelength ripples based on electron dynamics control by designing femtosecond laser pulse trains
Authors: Yuan Yanping , Jiang Lan , Li Xin , Wang Cong , Lu Yongfeng
Published: November 2012

A quantum model is proposed to investigate femtosecond laser pulse trains processing of dielectrics by including the plasma model with the consideration of laser particle-wave duality. Central wavelengths (400 nm and 800 nm) strongly impact the surface plasmon field distribution, the coupling field intensity distribution (between the absorbed intensity and the surface plasma), and the distribution of transient localized free electron density in the material. This, in turn, significantly changes the localized transient optical/thermal properties during laser materials processing. The effects of central wavelengths on ablation shapes and subwavelength ripples are discussed. The simulation results show that: (1) ablation shapes and the spacing of subwavelength ripples can be adjusted by localized transient electron dynamics control using femtosecond laser pulse trains; (2) the adjustment of the radii of ablation shapes is stronger than that of the periods of subwavelength ripples.
Swing switching of spin-torque valves
Authors: Dunn Tom , Kamenev Alex
Published: November 2012

We propose a method for inducing magnetization reversal using an AC spin current polarized perpendicular to the equilibrium magnetization of the free magnetic layer. We show that the critical AC spin current is significantly smaller than the corresponding DC one. The effect is understood as a consequence of the underdamped nature of the spin-torque oscillators. It allows to use the kinetic inertia to overcome the residual energy barrier, rather than suppressing the latter by a large spin current. The effect is similar to a swing which may be set into high amplitude motion by a weak near-resonant push. The optimal AC frequency is identified as the upper bifurcation frequency of the corresponding driven nonlinear oscillator. Together with fast switching times it makes the perpendicular AC method to be the most efficient way to realize spin-torque memory valve.
Line-source excitation of realistic conformal metasurface cloaks
Authors: Padooru Yashwanth R. , Yakovlev Alexander B. , Chen Pai-Yen , Alù Andrea
Published: November 2012

Following our recently introduced analytical tools to model and design conformal mantle cloaks based on metasurfaces [Padooru et al., J. Appl. Phys. 112, 034907 (2012)], we investigate their performance and physical properties when excited by an electric line source placed in their close proximity. We consider metasurfaces formed by 2-D arrays of slotted (meshes and Jerusalem cross slots) and printed (patches and Jerusalem crosses) sub-wavelength elements. The electromagnetic scattering analysis is carried out using a rigorous analytical model, which utilizes the two-sided impedance boundary conditions at the interface of the sub-wavelength elements. It is shown that the homogenized grid-impedance expressions, originally derived for planar arrays of sub-wavelength elements and plane-wave excitation, may be successfully used to model and tailor the surface reactance of cylindrical conformal mantle cloaks illuminated by near-field sources. Our closed-form analytical results are in good agreement with full-wave numerical simulations, up to sub-wavelength distances from the metasurface, confirming that mantle cloaks may be very effective to suppress the scattering of moderately sized objects, independent of the type of excitation and point of observation. We also discuss the dual functionality of these metasurfaces to boost radiation efficiency and directivity from confined near-field sources.
On the applicability of laser ionization for simulating hypervelocity impacts
Authors: Mocker Anna , Grün Eberhard , Sternovsky Zoltán , Drake Keith , Kempf Sascha , Hornung Klaus , Srama Ralf
Published: November 2012

In-situ measurements, the direct interception and analysis of dust particles by spacecraft-based instrumentation, provide insights into the dynamical, physical and chemical properties of cosmic dust. The most sensitive detection methods for dust particles in space are based on impact ionization. Laser ionization is used for the test, development, and calibration of impact ionization instruments and to complement laboratory based particle impact experiments. A typical setup uses a 355 nm Nd-YAG laser with a pulse length of about 5 ns. It is necessary to investigate the properties of both processes with respect to their comparability. A study was performed to find out to what extent laser ionization can be used to simulate impact ionization. The findings show that laser ionization and impact ionization show similarities, which can be used to test the functionality of dust impact detectors, especially time-of-flight instruments. Our paper provides information on what extent these similarities hold and where their limits are.
Size-dependent phase transition of graphite to superhard graphite under high pressure at room temperature
Authors: Liu Cailong , Han Yonghao , Li Quan , Ma Yanzhang , Ma Yanming , Gao Chunxiao
Published: November 2012

In situ electrical resistivity measurement of graphite compressed in two different pressure cycles in one single experiment at room temperature in the pressure range of 0-34 GPa has been reported. The electrical results indicate that less superhard graphite formed in the second cycle than in the first one. Our experiments identify the phase transition of the graphite at 15.1 and 17.9 GPa for the first and second pressure cycles, respectively, and explain why the superhard post-graphite cannot indent diamond films. The scanning electron microscopy of the graphite powders before and after pressure annealing helps to support the conclusion that both the phase transitions and the formation of superhard post-graphite are sensitive to the grain size of the initial graphite sample under high pressure.
Heat treatment induced martensitic accommodation and adaptive anisotropy in melt spun Ni55Mn22Ga23 (at. %) ribbons
Authors: Singh Satnam , Roy R. K. , Ghosh M. , Mitra A. , Panda A. K.
Published: November 2012

The effect of annealing on melt spun Ni55Mn22Ga23 (at. %) ribbon has been addressed in terms of structural, thermal, thermomagnetic, and magnetic field induced strain (MFIS) behaviour. In comparison to as-spun ribbons, the samples annealed within the L21 domain at 1073 K for 30 h with subsequent furnace cooling, showed a rise in martensitic transformation temperature. This was endorsed from electron microscopy studies revealing change in morphology of martensite plate and stacking of dislocations in a preferential orientation. The mechanism is associated to martensitic accommodation which enhanced ferro-elastic magnetic coupling and also lowered magnetic coercivity. Such accommodations and adaptive anisotropy improved the MFIS behavior in the annealed sample.
Two-bit multi-level phase change random access memory with a triple phase change material stack structure
Authors: Gyanathan Ashvini , Yeo Yee-Chia
Published: November 2012

This work demonstrates a novel two-bit multi-level device structure comprising three phase change material (PCM) layers, separated by SiN thermal barrier layers. This triple PCM stack consisted of (from bottom to top), Ge2Sb2Te5 (GST), an ultrathin SiN barrier, nitrogen-doped GST, another ultrathin SiN barrier, and Ag0.5In0.5Sb3Te6. The PCM layers can selectively amorphize to form 4 different resistance levels (“00,” “01,” “10,” and “11”) using respective voltage pulses. Electrical characterization was extensively performed on these devices. Thermal analysis was also done to understand the physics behind the phase changing characteristics of the two-bit memory devices. The melting and crystallization temperatures of the PCMs play important roles in the power consumption of the multi-level devices. The electrical resistivities and thermal conductivities of the PCMs and the SiN thermal barrier are also crucial factors contributing to the phase changing behaviour of the PCMs in the two-bit multi-level PCRAM device.
Theoretical investigation of the proton transfer mechanism in guanine-cytosine and adenine-thymine base pairs
Authors: Xiao Shiyan , Wang Lei , Liu Yuan , Lin Xiangsong , Liang Haojun
Published: November 2012

Ab initio constrained molecular dynamics and metadynamics were employed to investigate the mechanism of proton transfer in guanine-cytosine (GC) and adenine-thymine (AT) base pairs in the gas phase at room temperature. It is shown that double proton transfer (DPT) in the GC base pair is a concerted and asynchronous mechanism, and three pathways with a similar free energy barrier start from the canonical GC and end up in its “rare” imino-enol tautomer. The activation energy for the route that the DPT starts from the hydrogen atom movement in the O6(G)-N4(C) bridge is approximately 1.0 kcal/mol higher than that which starts in the N1(G)-N3(C) bridge. For the AT base pair, a stable intermediate state is identified in the two-dimensional free energy surface of the DPT event. We found that the movement of the hydrogen atom in the N1(A)-N3(T) bridge occurs before the movement of the hydrogen atom in the N6(A)-O4(T) bridge. Thus, it is demonstrated that the DPT in AT base pairs is a stepwise and an asynchronous mechanism.