bluuebunny/crossref_metadata_2025 huggingface dataset:
PPARα–LXR as a novel metabolostatic signalling axis in skeletal muscle that acts to optimize substrate selection in response to nutrient status
Authors: Caton Paul W. , Holness Mark J. , Bishop-Bailey David , Sugden Mary C.
Published: July 2011

LXR (liver X receptor) and PPARα (peroxisome-proliferator-activated receptor α) are nuclear receptors that control the expression of genes involved in glucose and lipid homoeostasis. Using wild-type and PPARα-null mice fed on an LXR-agonist-supplemented diet, the present study analysed the impact of pharmacological LXR activation on the expression of metabolically important genes in skeletal muscle, testing the hypothesis that LXR activation can modulate PPAR action in skeletal muscle in a manner dependent on nutritional status. In the fed state, LXR activation promoted a gene profile favouring lipid storage and glucose oxidation, increasing SCD1 (stearoyl-CoA desaturase 1) expression and down-regulating PGC-1α (PPARγ co-activator-1α) and PDK4 (pyruvate dehydrogenase kinase 4) expression. PPARα deficiency enhanced LXR stimulation of SCD1 expression, and facilitated elevated SREBP-1 (sterol-regulatory-element-binding protein-1) expression. However, LXR-mediated down-regulation of PGC-1α and PDK4 was opposed and reversed by PPARα deficiency. During fasting, prior LXR activation augmented PPARα signalling to heighten FA (fatty acid) oxidation and decrease glucose oxidation by augmenting fasting-induced up-regulation of PGC-1α and PDK4 expression, effects opposed by PPARα deficiency. Starvation-induced down-regulation of SCD1 expression was opposed by antecedent LXR activation in wild-type mice, an effect enhanced further by PPARα deficiency, which may elicit increased channelling of FA into triacylglycerol to limit lipotoxicity. Our results also identified potential regulatory links between the protein deacetylases SIRT1 (sirtuin 1) and SIRT3 and PDK4 expression in muscle from fasted mice, with a requirement for PPARα. In summary, we therefore propose that a LXR–PPARα signalling axis acts as a metabolostatic regulatory mechanism to optimize substrate selection and disposition in skeletal muscle according to metabolic requirement.
The circularly permuted yellow fluorescent protein cpYFP that has been used as a superoxide probe is highly responsive to pH but not superoxide in mitochondria: implications for the existence of superoxide ‘flashes’
Authors: Schwarzländer Markus , Logan David C. , Fricker Mark D. , Sweetlove Lee J.
Published: July 2011

The properties of a cpYFP [circularly permuted YFP (yellow fluorescent protein)] reported to act as a superoxide sensor have been re-examined in Arabidopsis mitochondria. We have found that the probe has high pH sensitivity and that dynamics in the cpYFP signal disappeared when the matrix pH was clamped by nigericin. In contrast, genetic and pharmacological manipulation of matrix superoxide had no detectable effect on the cpYFP signal. These findings question the existence of superoxide flashes in mitochondria.
Characterization of the dehydratase WcbK and the reductase WcaG involved in GDP-6-deoxy-manno-heptose biosynthesis in Campylobacter jejuni
Authors: McCallum Matthew , Shaw Gary S. , Creuzenet Carole
Published: July 2011

The capsule of Campylobacter jejuni strain 81-176 comprises the unusual 6-deoxy-α-D-altro-heptose, whose biosynthesis and function are not known. In the present study, we characterized enzymes of the capsular cluster, WcbK and WcaG, to determine their role in 6-deoxy-altro-heptose synthesis. These enzymes are similar to the Yersinia pseudotuberculosis GDP-manno-heptose dehydratase/reductase DmhA/DmhB that we characterized previously. Capillary electrophoresis and MS analyses showed that WcbK is a GDP-manno-heptose dehydratase whose product can be reduced by WcaG, and that WcbK/WcaG can use the substrate GDP-mannose, although with lower efficiency than heptose. Comparison of kinetic parameters for WcbK and DmhA indicated that the relaxed substrate specificity of WcbK comes at the expense of catalytic performance on GDP-manno-heptose. Moreover, although WcbK/WcaG and DmhA/DmhB are involved in altro- versus manno-heptose synthesis respectively, the enzymes can be used interchangeably in mixed reactions. NMR spectroscopy analyses indicated conservation of the sugar manno configuration during catalysis by WcbK/WcaG. Therefore additional capsular enzymes may perform the C3 epimerization necessary to generate 6-deoxy-altro-heptose. Finally, a conserved residue (Thr187 in WcbK) potentially involved in substrate specificity was identified by structural modelling of mannose and heptose dehydratases. Site-directed mutagenesis and kinetic analyses demonstrated its importance for enzymatic activity on heptose and mannose substrates.
Helicase dissociation and annealing of RNA-DNA hybrids by Escherichia coli Cas3 protein
Authors: Howard Jamieson A. L. , Delmas Stephane , Ivančić-Baće Ivana , Bolt Edward L.
Published: July 2011

CRISPR (clustered regularly interspaced short palindromic repeat)/Cas (CRISPR-associated) is a nucleic acid processing system in bacteria and archaea that interacts with mobile genetic elements. CRISPR DNA and RNA sequences are processed by Cas proteins: in Escherichia coli K-12, one CRISPR locus links to eight cas genes (cas1, 2, 3 and casABCDE), whose protein products promote protection against phage. In the present paper, we report that purified E. coli Cas3 catalyses ATP-independent annealing of RNA with DNA forming R-loops, hybrids of RNA base-paired into duplex DNA. ATP abolishes Cas3 R-loop formation and instead powers Cas3 helicase unwinding of the invading RNA strand of a model R-loop substrate. R-loop formation by Cas3 requires magnesium as a co-factor and is inactivated by mutagenesis of a conserved amino acid motif. Cells expressing the mutant Cas3 protein are more sensitive to plaque formation by the phage λvir. A complex of CasABCDE (‘Cascade’) also promotes R-loop formation and we discuss possible overlapping roles of Cas3 and Cascade in E. coli, and the apparently antagonistic roles of Cas3 catalysing RNA–DNA annealing and ATP-dependent helicase unwinding.
Brown adipose tissue mitochondria: modulation by GDP and fatty acids depends on the respiratory substrates
Authors: De Meis Leopoldo , Ketzer Luisa A. , Camacho-Pereira Juliana , Galina Antonio
Published: July 2011

The UCP1 [first UCP (uncoupling protein)] that is found in the mitochondria of brown adipocytes [BAT (brown adipose tissue)] regulates the heat production, a process linked to non-shivering thermogenesis. The activity of UCP1 is modulated by GDP and fatty acids. In this report, we demonstrate that respiration and heat released by BAT mitochondria vary depending on the respiratory substrate utilized and the coupling state of the mitochondria. It has already been established that, in the presence of pyruvate/malate, BAT mitochondria are coupled by faf-BSA (fatty-acid-free BSA) and GDP, leading to an increase in ATP synthesis and mitochondrial membrane potential along with simultaneous decreases in both the rates of respiration and heat production. Oleate restores the uncoupled state, inhibiting ATP synthesis and increasing the rates of both respiration and heat production. We now show that in the presence of succinate: (i) the rates of uncoupled mitochondria respiration and heat production are five times slower than in the presence of pyruvate/malate; (ii) faf-BSA and GDP accelerate heat and respiration as a result and, in coupled mitochondria, these two rates are accelerated compared with pyruvate/malate; (iii) in spite of the differences in respiration and heat production noted with the two substrates, the membrane potential and the ATP synthesized were the same; and (iv) oleate promoted a decrease in heat production and respiration in coupled mitochondria, an effect different from that observed using pyruvate/malate. These effects are not related to the production of ROS (reactive oxygen species). We suggest that succinate could stimulate a new route to heat production in BAT mitochondria.
HIV-TAT-fused FHIT protein functions as a potential pro-apoptotic molecule in hepatocellular carcinoma cells
Authors: Yu Gui-Rong , Qin Wei-Wei , Li Ji-Peng , Hua Wei , Meng Yan-Ling , Chen Rui , Yan Bo , Wang Lei , Zhang Xiang , Jia Lin-Tao , Zhao Jing , Zhang Rui , Yang An-Gang
Published: July 2011

Accumulating evidence has demonstrated that FHIT (fragile histidine triad) is a bona fide tumour suppressor gene in a large fraction of human tumours, including hepatocellular cancer. A virus-based delivery system has been developed to transfer the FHIT gene into many types of cancer cells to inhibit growth or even induce apoptosis. However, a protein-based replacement strategy for FHIT has not been performed in cancer cells. Here, we used HIV-TAT (transactivator of transcription)-derived peptide to transfer the purified FHIT protein into HCC (hepatocellular carcinoma) cells and determine the biological effect of this fusion protein in inducing apoptosis. Affinity chromatography was used to purify TAT peptide-fused human FHIT (TAT–FHIT) protein from BL21 Escherichia coli. Immunofluorescence staining and Western blot analysis were performed to identify the expression and internalization of TAT–FHIT in HCC cells compared with the purified FHIT protein. Our study showed that TAT–FHIT protein can translocate into cancer cells in 1 h after incubation at 37°C. Furthermore, the results of MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay, Annexin-V staining and Western blotting demonstrated that TAT–FHIT can robustly inhibit growth and induce apoptosis of HCC cells in vitro. In addition, a mechanistic study showed that both exogenous and intrinsic apoptotic pathways were involved in TAT–FHIT-mediated apoptosis and this effect could be attenuated partially by a mitochondrial protector TAT-BH4, indicating that mitochondrion plays a critical role in TAT–FHIT-mediated pro-apoptotic effect in cancer cells. Taken together, our study suggests that TAT–FHIT is a potential pro-apoptotic molecule in HCC cells and strengthen the hypothesis of its therapeutic application against HCC.
Binding affinities of vascular endothelial growth factor (VEGF) for heparin-derived oligosaccharides
Authors: Zhao Wenjing , McCallum Scott A. , Xiao Zhongping , Zhang Fuming , Linhardt Robert J.
Published: July 2011

Heparin and HS (heparan sulfate) exert their wide range of biological activities by interacting with extracellular protein ligands. Among these important protein ligands are various angiogenic growth factors and cytokines. HS binding to VEGF (vascular endothelial growth factor) regulates multiple aspects of vascular development and function through its specific interaction with HS. Many studies have focused on HS-derived or HS-mimicking structures for the characterization of VEGF165 interaction with HS. Using a heparinase 1-prepared small library of heparin-derived oligosaccharides ranging from hexasaccharide to octadecasaccharide, we systematically investigated the heparin-specific structural features required for VEGF binding. We report the apparent affinities for the association between the heparin-derived oligosaccharides with both VEGF165 and VEGF55, a peptide construct encompassing exclusively the heparin-binding domain of VEGF165. An octasaccharide was the minimum size of oligosaccharide within the library to efficiently bind to both forms of VEGF and a tetradecasaccharide displayed an effective binding affinity to VEGF165 comparable to unfractionated heparin. The range of relative apparent binding affinities among VEGF and the panel of heparin-derived oligosaccharides demonstrate that the VEGF binding affinity likely depends on the specific structural features of these oligosaccharides, including their degree of sulfation, sugar-ring stereochemistry and conformation. Notably, the unique 3-O-sulfo group found within the specific antithrombin binding site of heparin is not required for VEGF165 binding. These findings afford new insight into the inherent kinetics and affinities for VEGF association with heparin and heparin-derived oligosaccharides with key residue-specific modifications and may potentially benefit the future design of oligosaccharide-based anti-angiogenesis drugs.
Hypoxic regulation of mesenchymal stem cell migration: the role of RhoA and HIF‐1α
Authors: Raheja Leah F. , Genetos Damian C. , Wong Alice , Yellowley Clare E.
Published: July 2011

A variety of pathologies such as skeletal fracture, neoplasia and inflammation compromise tissue perfusion and thereby decrease tissue oxygen tension. We and others have demonstrated that hypoxia is a potent stimulant for MSC (mesenchymal stem cell) recruitment and differentiation, yet to date little research has focused on the effects of oxygen tension on MSC migration. In the present study, we examined the effects of hypoxia and the potential role of the GTPase RhoA and HIF‐1α (hypoxia‐inducible factor 1α) on MSC migration. Our results demonstrate that hypoxia decreases MSC migration through an HIF‐1α and RhoA‐mediated pathway. The active GTP‐bound form of RhoA was reduced in 1% oxygen, whereas activation of RhoA under hypoxic conditions rescued migration. Furthermore, stabilization of HIF‐1α under normoxic conditions attenuated cell migration similar to that of hypoxia. These results suggest that hypoxia negatively affects MSC migration by regulating activation of GTPases. These results highlight the importance of oxygen in regulating the recruitment of progenitor cells to areas of ischaemic tissue damage.
Mesenchymal stem cell injection ameliorates chronic renal failure in a rat model
Authors: Villanueva Sandra , Ewertz Ernesto , Carrión Flavio , Tapia Andrés , Vergara César , Céspedes Carlos , Sáez Pablo J. , Luz Patricia , Irarrázabal Carlos , Carreño Juan E. , Figueroa Fernando , Vio Carlos P.
Published: July 2011

CKD (chronic kidney disease) has become a public health problem. The therapeutic approaches have been able to reduce proteinuria, but have not been successful in limiting disease progression. In this setting, cell therapies associated with regenerative effects are attracting increasing interest. We evaluated the effect of MSC (mesenchymal stem cells) on the progression of CKD and the expression of molecular biomarkers associated with regenerative effects. Adult male Sprague–Dawley rats subjected to 5/6 NPX (nephrectomy) received a single intravenous infusion of 0.5×106 MSC or culture medium. A sham group subjected to the same injection was used as the control. Rats were killed 5 weeks after MSC infusion. Dye tracking of MSC was followed by immunofluorescence analysis. Kidney function was evaluated using plasma creatinine. Structural damage was evaluated by H&E (haematoxylin and eosin) staining, ED-1 abundance (macrophages) and interstitial α-SMA (α-smooth muscle actin). Repairing processes were evaluated by functional and structural analyses and angiogenic/epitheliogenic protein expression. MSC could be detected in kidney tissues from NPX animals treated with intravenous cell infusion. This group presented a marked reduction in plasma creatinine levels and damage markers ED-1 and α-SMA (P<0.05). In addition, treated rats exhibited a significant induction in epitheliogenic [Pax-2, bFGF (basic fibroblast growth factor) and BMP-7 (bone morphogenetic protein-7)] and angiogenic [VEGF (vascular endothelial growth factor) and Tie-2] proteins. The expression of these biomarkers of regeneration was significantly related to the increase in renal function. Many aspects of the cell therapy in CKD remain to be investigated in more detail: for example, its safety, low cost and the possible need for repeated cell injections over time. Beyond the undeniable importance of these issues, what still needs to be clarified is whether MSC administration has a real effect on the treatment of this pathology. It is precisely to this point that the present study aims to contribute.
Microfluidic wet spinning of chitosan-alginate microfibers and encapsulation of HepG2 cells in fibers
Authors: Lee Bo Ram , Lee Kwang Ho , Kang Edward , Kim Dong-Sik , Lee Sang-Hoon
Published: June 2011

The successful encapsulation of human hepatocellular carcinoma (HepG2) cells would greatly assist a broad range of applications in tissue engineering. Due to the harsh conditions during standard chitosan fiber fabrication processes, encapsulation of HepG2 cells in chitosan fibers has been challenging. Here, we describe the successful wet-spinning of chitosan-alginate fibers using a coaxial flow microfluidic chip. We determined the optimal mixing conditions for generating chitosan-alginate fibers, including a 1:5 ratio of 2% (w/w) water-soluble chitosan (WSC) solution to 2% (w/w) alginate solution. Ratio including higher than 2% (w/w) WSC solution increased aggregation throughout the mixture. By suspending cells in the WSC–alginate solution, we successfully fabricated HepG2 cell-laden fibers. The encapsulated HepG2 cells in the chitosan-alginate fibers were more viable than cells encapsulated in pure alginate fibers, suggesting that cross-linked chitosan provides a better environment for HepG2 cells than alginate alone. In addition, we found that the adhesion of HepG2 cells on the chitosan-alginate fiber is much better than that on the alginate fibers.
A modular cell culture device for generating arrays of gradients using stacked microfluidic flows
Authors: Sip Christopher G. , Bhattacharjee Nirveek , Folch Albert
Published: June 2011

Microfluidics has become increasingly important for the study of biochemical cues because it enables exquisite spatiotemporal control of the microenvironment. Well-characterized, stable, and reproducible generation of biochemical gradients is critical for understanding the complex behaviors involved in many biological phenomena. Although many microfluidic devices have been developed which achieve these criteria, the ongoing challenge for these platforms is to provide a suitably benign and physiologically relevant environment for cell culture in a user-friendly format. To achieve this paradigm, microfluidic designs must consider the full scope of cell culture from substrate preparation, cell seeding, and long-term maintenance to properly observe gradient sensing behavior. In addition, designs must address the challenges associated with altered culture conditions and shear forces in flow-based devices. With this consideration, we have designed and characterized a microfluidic device based on the principle of stacked flows to achieve highly stable gradients of diffusible molecules over large areas with extremely low shear forces. The device utilizes a benign vacuum sealing strategy for reversible application to pre-established cell cultures. We apply this device to an existing culture of breast cancer cells to demonstrate the negligible effect of its shear flow on migratory behavior. Lastly, we extend the stacked-flow design to demonstrate its scalable architecture with a prototype device for generating an array of combinatorial gradients.
Bile canaliculi formation by aligning rat primary hepatocytes in a microfluidic device
Authors: Nakao Yosuke , Kimura Hiroshi , Sakai Yasuyuki , Fujii Teruo
Published: June 2011

In this study, we propose a microfluidic cell culture device mimicking the microscopic structure in liver tissue called hepatic cords. The cell culture area of the device was designed to align hepatocytes in two lines in a similar way to hepatic cords. Thanks to the structural design together with a cell seeding procedure, rat primary hepatocytes were successfully aligned in two lines and cultured under perfusion condition. It is shown that aligned hepatocytes gradually self-organize and form bile canaliculi along the hepatic cord-like structure. The present technique to culture hepatocytes with functional bile canaliculi could be used as an alternative to animal testing in the field of drug discovery and toxicological studies, and also be beneficial to tissue engineering applications.
Exploitation of physical and chemical constraints for three-dimensional microtissue construction in microfluidics
Authors: Choudhury Deepak , Mo Xuejun , Iliescu Ciprian , Tan Loo Ling , Tong Wen Hao , Yu Hanry
Published: June 2011

There are a plethora of approaches to construct microtissues as building blocks for the repair and regeneration of larger and complex tissues. Here we focus on various physical and chemical trapping methods for engineering three-dimensional microtissue constructs in microfluidic systems that recapitulate the in vivo tissue microstructures and functions. Advances in these in vitro tissue models have enabled various applications, including drug screening, disease or injury models, and cell-based biosensors. The future would see strides toward the mesoscale control of even finer tissue microstructures and the scaling of various designs for high throughput applications. These tools and knowledge will establish the foundation for precision engineering of complex tissues of the internal organs for biomedical applications.
Valence-driven electrical behavior of manganese-modified bismuth ferrite thin films
Authors: Wu Jiagang , Wang John , Xiao Dingquan , Zhu Jianguo
Published: June 2011

BiFe0.95R0.05O3 (Mn2+, Mn3+, and Mn4+) thin films with (110) orientation were fabricated on SrRuO3/Pt/TiO2/SiO2/Si(100) substrates via rf sputtering. With the increasing valence of Mn in BiFe0.95R0.05O3, the concentration of Fe2+ increases, whereas the concentration of oxygen vacancies decreases. The electrical properties of BiFe0.95R0.05O3 are correlated with the valence of Mn. Their leakage current density is dependent on the concentration of oxygen vacancies caused by different valences of Mn. Their P-E loops become better with the increasing valence of Mn owing to a lower leakage current density in high electric field regions, and a large remanent polarization of 2Pr ∼ 145.2 μC/cm2 is obtained for the Mn4+-doped film. For the Mn2+-doped bismuth ferrite film, the space-charge-limited conduction and Schottky barrier dominate its leakage behavior under a negative electric field, the Ohmic conduction and Schottky barrier are involved in the leakage behavior under a positive electric field, and the interface-limited Fowler–Nordheim tunneling is their dominant mechanism in a high electric field region. In contrast, an Ohmic conduction dominates the leakage behavior of Mn3+- and Mn4+-doped films regardless of negative and positive directions or measurement temperatures.
Direct selected multireference configuration interaction calculations for large systems using localized orbitals
Authors: Ben Amor Nadia , Bessac Fabienne , Hoyau Sophie , Maynau Daniel
Published: July 2011

A selected multireference configuration interaction (CI) method and the corresponding code are presented. It is based on a procedure of localization that permits to obtain well localized occupied and virtual orbitals. Due to the local character of the electron correlation, using local orbitals allows one to neglect long range interactions. In a first step, three topological matrices are constructed, which determine whether two orbitals must be considered as interacting or not. Two of them concern the truncation of the determinant basis, one for occupied/virtual, the second one for dispersive interactions. The third one concerns the truncation of the list of two electron integrals. This approach permits a fine analysis of each kind of approximation and induces a huge reduction of the CI size and of the computational time. The procedure is tested on linear polyene aldehyde chains, dissociation potential energy curve, and reaction energy of a pesticide-Ca2+ complex and finally on transition energies of a large iron system presenting a light-induced excited spin-state trapping effect.
Stopping power for a charged particle moving through three-dimensional nonideal finite-temperature electron gases
Authors: Zhang Ya , Song Yuan-Hong , Wang You-Nian
Published: July 2011

We investigate the interaction of a charged particle with nonideal 3D electron gases by using the quantum hydrodynamic (QHD) theory. The stopping power for a nonideal electron gas at a finite-temperature has been theoretically analyzed and numerically calculated. In our calculation, the impact of nonideality and temperature on stopping power is stressed and clearly presented. The QHD dielectric function is obtained and compared to random-phase approximation result. It is shown that the QHD theory can properly describe the stopping power for higher particle velocities greater than the Bohr velocity.
Effect of oxygen defects on ferromagnetic of undoped ZnO
Authors: Liu Weijing , Li Wenwu , Hu Zhigao , Tang Zheng , Tang Xiaodong
Published: July 2011

Undoped ZnO nano-particles were synthesized by a solution route and annealed in N2, O2, and Ar, respectively. X-ray diffraction and X-ray photoelectron spectroscopy measurements show that the samples possess typical wurtzite structure and have no other impurity phases. Magnetization loops for the ZnO samples were measured and clearly show typical ferromagnetic saturation behavior. With the combination of defect analysis based on photoluminescence spectroscopy and first-principles calculations of the possible magnetic defect centers in ZnO, the effect of defects on the nature and origin of ferromagnetism was investigated. The results suggest oxygen defects, especially singly ionized oxygen vacancies, play a crucial role in mediating ferromagnetism in the undoped ZnO system.
Realising epitaxial growth of GaN on (001) diamond
Authors: van Dreumel G. W. G. , Tinnemans P. T. , van den Heuvel A. A. J. , Bohnen T. , Buijnsters J. G. , ter Meulen J. J. , van Enckevort W. J. P. , Hageman P. R. , Vlieg E.
Published: July 2011

By an extensive investigation of the principal growth parameters on the deposition process, we realized the epitaxial growth of crystalline wurtzite GaN thin films on single crystal (001) diamond substrates by metal organic chemical vapor deposition. From the influence of pressure, V/III ratio, and temperature, it was deduced that the growth process is determined by the mass-transport of gallium precursor material toward the substrate. The highest temperature yielded an improved epitaxial relationship between grown layer and substrate. X ray diffraction (XRD) pole figure analysis established the presence of two domains of epitaxial layers, namely (0001) 〈101−0〉 GaN∥ (001)[110] diamond and (0001) 〈101−0〉 GaN∥ (001) [11−0] diamond, which are 90∘ rotated with respect to each other. The presence of these domains is explained by the occurrence of areas of (2×1) and (1×2) surface reconstruction of the diamond substrate. When applying highly misoriented diamond substrates toward the [110] diamond direction, one of the growth domains is suppressed and highly epitaxial GaN on (001) diamond is realized.
Amorphization of C60 nanotubes under pressure
Authors: Hu J. Y. , Liang S. C. , Piao G. Z. , Zhang S. J. , Zhang Q. H. , Yang Y. , Zhao Q. , Zhu K. , Liu Y. L. , Tang L. Y. , Li Y. C. , Liu J. , Jin C. Q. , Yu R. C.
Published: July 2011

C60 nanotubes with diameters of smaller than 500 nm are fabricated by a modified liquid–liquid interfacial precipitation method. In situ angle dispersive synchrotron x ray diffraction and Raman scattering under pressures have been employed to study the structure evolution of the C60 nanotubes. The experimental results indicate that there is a pressure induced irreversible amorphization at 40.1 GPa. An isostructural phase transition occurs in the pressure range of 9.29–12.2 GPa, which is probably relative to the changes in the bonding type of C60 nanotubes.
A comparative study on electrical transport properties of thin films of Ge1Sb2Te4 and Ge2Sb2Te5 phase-change materials
Authors: Xu Ling , Tong Liang , Geng Lei , Yang Fei , Xu Jun , Su Weining , Liu Dong , Ma Zhongyuan , Chen Kunji
Published: July 2011

We have investigated the electrical properties of Ge1Sb2Te4 and Ge2Sb2Te5 thin films in the temperature range of 27 to 200 °C. The optical bandgap values obtained from the measured absorption spectra for amorphous Ge1Sb2Te4 and Ge2Sb2Te5 are 0.70 and 0.90 eV, respectively. The results of the in situ temperature dependence of the sheet resistance demonstrate that both Ge1Sb2Te4 and Ge2Sb2Te5 thin films in the amorphous phase exhibit a temperature-activated electrical conductivity with activation energy values of 0.42 and 0.45 eV, respectively. These results show that our experimental results agree well with the predictions of Mott’s model. The temperature dependent carrier mobility was measured accurately using the surface acoustic wave method, which is an appropriate method for materials with low conductivities and low mobility. Typical values of drift mobility for amorphous Ge1Sb2Te4 and Ge2Sb2Te5 thin films at room temperature are round 10−3 cm2/(Vs) and 10−2 cm2/(Vs), respectively. The values of drift mobility remain small below 140 °C when the films are in an amorphous state. The drift mobility increases gradually as the temperature increases in the temperature range of 140–160 °C and shows dramatic changes above 160 °C. In general, the mobility of amorphous Ge2Sb2Te5 is 3 to 5 times higher than that of amorphous Ge1Sb2Te4. The smaller mobility for Ge1Sb2Te4 films might suggest that amorphous Ge1Sb2Te4 film has more vacancies, which results in more disordering as compared to that of Ge2Sb2Te5.
A cold energy mixture theory for the equation of state in solid and porous metal mixtures
Authors: Zhang X. F. , Qiao L. , Shi A. S. , Zhang J. , Guan Z. W.
Published: July 2011

Porous or solid multi-component mixtures are ubiquitous in nature and extensively used as industrial materials such as multifunctional energetic structural materials (MESMs), metallic and ceramic powder for shock consolidation, and porous armor materials. In order to analyze the dynamic behavior of a particular solid or porous metal mixture in any given situation, a model is developed to calculate the Hugoniot data for solid or porous mixtures using only static thermodynamic properties of the components. The model applies the cold energy mixture theory to calculate the isotherm of the components to avoid temperature effects on the mixtures. The isobaric contribution from the thermodynamic equation of state is used to describe the porous material Hugoniot. Dynamic shock responses of solid or porous powder mixtures compacted by shock waves have been analyzed based on the mixture theory and Hugoniot for porous materials. The model is tested on both single-component porous materials such as aluminum 2024, copper, and iron; and on multi-component mixtures such as W/Cu, Fe/Ni, and Al/Ni. The theoretical calculations agree well with the corresponding experimental and simulation results. The present model produces satisfactory correlation with the experimentally obtained Hugoniot data for solid porous materials over a wide pressure range.
Effects of Na content on the luminescence behavior, conduction type, and crystal structure of Na-doped ZnO films
Authors: Lai Jian-Jhong , Lin Yow-Jon , Chen Ya-Hui , Chang Hsing-Cheng , Liu Chia-Jyi , Zou Yi-Yan , Shih Yu-Tai , Wang Meng-Chieh
Published: July 2011

This study investigates the effect of Na content on the structural, optical, and electrical properties of sol-gel Na-doped ZnO films using x-ray diffraction, photoluminescence, and conductivity measurements. It is shown that a p-type conversion of the Na-doped ZnO film might be due to a combined effect of the increased substitutional-Na density and the decreased oxygen-vacancy (VO) density. However, excess Na incorporation into ZnO shows an ambiguous carrier type due to the increase in the donorlike VO density. These results indicate that compensation effects limit the hole concentration in the Na-doped ZnO films. In addition, when more Na is substituted into the ZnO system, the difference in the ionic radii of Zn2+ and Na+ starts playing an increasingly important role, causing the presence of tensile stress in the Na-doped ZnO film.
Anisotropic diffusion in confined colloidal dispersions: The evanescent diffusivity
Authors: Swan James W. , Brady John F.
Published: July 2011

We employ an analogy to traditional dynamic light scattering to describe the inhomogeneous and anisotropic diffusion of colloid particles near a solid boundary measured via evanescent wave dynamic light scattering. Following this approach, we generate new expressions for the short-time self- and collective diffusivities of colloidal dispersions with arbitrary volume fraction. We use these expressions in combination with accelerated Stokesian dynamics simulations to calculate the diffusivities in the limit of large and small scattering wave numbers for evanescent penetration depths ranging from four particle radii to one-fifth of a particle radius and volume fractions from 10% to 40%. We show that at high volume fractions, and larger penetration depths, the boundaries have little effect on the dynamics of the suspension parallel to the wall since, to a first approximation, the boundary acts hydrodynamically much as another nearby particle. However, near and normal to the wall, the diffusivity shows a strong dependence on penetration depth for all volume fractions. This is due to the lubrication interactions between the particles and the boundary as the particle moves relative to the wall. These results are novel and comprehensive with respect to the range of penetration depth and volume fraction and provide a complete determination of the effect of hydrodynamic interactions on colloidal diffusion adjacent to a rigid boundary.
AlN photonic crystal nanocavities realized by epitaxial conformal growth on nanopatterned silicon substrate
Authors: Néel D. , Sergent S. , Mexis M. , Sam-Giao D. , Guillet T. , Brimont C. , Bretagnon T. , Semond F. , Gayral B. , David S. , Checoury X. , Boucaud P.
Published: June 2011

An original method to fabricate III-nitride photonic crystal membranes without etching of III-N materials is reported. A photonic crystal pattern is first realized in a silicon substrate. GaN quantum dots embedded in a thin AlN layer are then grown by conformal epitaxy using ammonia-based molecular beam epitaxy on the top of the patterned silicon substrate and a free-standing membrane is achieved by selective etching of the silicon substrate through the holes of the photonic crystal. Room temperature microphotoluminescence measurements show a quality factor as high as 1800 at 425 nm on a modified L3 cavity. Possibility to achieve lasing with this system is discussed.
Temperature-dependent magnetic anisotropies in epitaxial Fe/CoO/MgO(001) system studied by the planar Hall effect
Authors: Cao W. N. , Li J. , Chen G. , Zhu J. , Hu C. R. , Wu Y. Z.
Published: July 2011

Exchange-induced in-plane magnetic anisotropies in a single-crystalline Fe/CoO/MgO(001) system were quantitatively investigated using the planar Hall effect as a function of temperature. Field cooling can induce a strong uniaxial anisotropy in Fe film with the easy axis along the CoO〈110〉 directions close to the cooling field direction. The exchange coupling also induces a 4-fold anisotropy with the easy axis along the CoO〈100〉 directions. Our results prove that the strong magneto-crystalline anisotropy of CoO antiferromagnetic spin plays a significant role in exchange-induced anisotropy.
Superlensing effect of an anisotropic metamaterial slab with near-zero dynamic mass
Authors: Zhou Xiaoming , Hu Gengkai
Published: July 2011

A metamaterial slab of anisotropic mass with one diagonal component being infinity and the other being zero is demonstrated to behave as a superlens for acoustic imaging beyond the diffraction limit. The underlying mechanism for extraordinary transmission of evanescent waves is attributed to the zero mass effect. Microstructure design for such anisotropic lens is also presented. In contrast to the anisotropic superlens based on Fabry-Pérot resonant mechanism, the proposed lens operates without the limitation on lens thickness, thus more flexible in practical applications. Numerical modeling is performed to validate the proposed ideas.
Optimal signal-to-noise ratio for silicon nanowire biochemical sensors
Authors: Rajan Nitin K. , Routenberg David A. , Reed Mark A.
Published: July 2011

The signal-to-noise ratio (SNR) for silicon nanowire field-effect transistors operated in an electrolyte environment is an essential figure-of-merit to characterize and compare the detection limit of such devices when used in an exposed channel configuration as biochemical sensors. We employ low frequency noise measurements to determine the regime for optimal SNR. We find that SNR is not significantly affected by the electrolyte concentration, composition, or pH, leading us to conclude that the major contributions to the SNR come from the intrinsic device quality. The results presented here show that SNR is maximized at the peak transconductance.
Gravity Probe B concludes its 50-year quest
Authors: Blau Steven K.
Published: July 2011

A conceptually simple experiment confirmed two predictions of general relativity, but not with the hoped-for precision.
Focus on software
Authors: Mandelis Andreas
Published: July 2011

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Latrophilin 1 and its endogenous ligand Lasso/teneurin-2 form a high-affinity transsynaptic receptor pair with signaling capabilities
Authors: Silva John-Paul , Lelianova Vera G. , Ermolyuk Yaroslav S. , Vysokov Nickolai , Hitchen Paul G. , Berninghausen Otto , Rahman M. Atiqur , Zangrandi Alice , Fidalgo Sara , Tonevitsky Alexander G. , Dell Anne , Volynski Kirill E. , Ushkaryov Yuri A.
Published: July 2011

Latrophilin 1 (LPH1), a neuronal receptor of α-latrotoxin, is implicated in neurotransmitter release and control of presynaptic Ca
2+
. As an “adhesion G-protein-coupled receptor,” LPH1 can convert cell surface interactions into intracellular signaling. To examine the physiological functions of LPH1, we used LPH1’s extracellular domain to purify its endogenous ligand. A single protein of ∼275 kDa was isolated from rat brain and termed Lasso. Peptide sequencing and molecular cloning have shown that Lasso is a splice variant of teneurin-2, a brain-specific orphan cell surface receptor with a function in neuronal pathfinding and synaptogenesis. We show that LPH1 and Lasso interact strongly and specifically. They are always copurified from rat brain extracts. Coculturing cells expressing LPH1 with cells expressing Lasso leads to their mutual attraction and formation of multiple junctions to which both proteins are recruited. Cells expressing LPH1 form chimerical synapses with hippocampal neurons in cocultures; LPH1 and postsynaptic neuronal protein PSD-95 accumulate on opposite sides of these structures. Immunoblotting and immunoelectron microscopy of purified synapses and immunostaining of cultured hippocampal neurons show that LPH1 and Lasso are enriched in synapses; in both systems, LPH1 is presynaptic, whereas Lasso is postsynaptic. A C-terminal fragment of Lasso interacts with LPH1 and induces Ca
2+
signals in presynaptic boutons of hippocampal neurons and in neuroblastoma cells expressing LPH1. Thus, LPH1 and Lasso can form transsynaptic complexes capable of inducing presynaptic Ca
2+
signals, which might affect synaptic functions.
Power of discourse or discourse of the powerful?
Authors: Holzscheiter Anna
Published: July 2011

This article discusses the relevance of discourse analytical approaches for a specific field of social inquiry in international political studies: the creation and transformation of international norms. It starts from the assumption that contemporary discourse scholarship in the discipline of International Relations is a vibrant yet still under-explored area of social constructivist research. The field is still characterized by a rather sharp rift between postmodern notions of discourse on the one hand, and more pragmatic, positivist studies on communicative rationality on the other. By exploring the transformation of powerful global discourses on childhood and children’s rights during the negotiations leading to the 1989 Convention on the Rights of the Child, the article will argue that for a fuller understanding of such norm-changing events a two-dimensional perspective on discourse is essential which combines elements from both branches of IR discourse research. In discussing this case, the article will show that the concept of discourse can both serve to identify historical meaning-patterns and social conventions (in this case attached to the child and the phase of childhood) and, at the same time, highlight the real-time communicative processes and communicative strategies among a distinct set of policy-makers in the course of which such meaning conventions are transformed. Following the tradition of Critical Discourse Analysis (CDA), the approach stresses the value of incorporating the ‘social environment’ into discourse analysis, since it allows identifying specific sets of socially shared semantics within the institutional setting as well as to account for specific interpersonal dynamics and exclusionary practices that expand and transform these semantics.
Torque–velocity characteristics and contractile rate of force development in elite badminton players
Authors: Andersen Lars L. , Larsson Benny , Overgaard Hanne , Aagaard Per
Published: July 2011

Elite badminton requires muscular endurance combined with appropriate maximal and explosive muscle strength. The musculature of the lower extremities is especially important in this context since rapid and forceful movements with the weight of the body are performed repeatedly throughout a match. In the present study, we examined various leg‐strength parameters of 35 male elite badminton players who had been performing resistance exercises as part of their physical training for several years. The badminton players were compared with an age‐matched reference group, the members of whom were physically active on a recreational basis, and to the same reference group after they had performed resistance training for 14 weeks. Maximal muscle strength of the knee extensor (quadriceps) and flexor muscles (hamstrings) was determined using isokinetic dynamometry. To measure explosive muscle strength, the contractile rate of force development was determined during maximal isometric muscle contractions. In general, the badminton players showed greater maximal muscle strength and contractile rate of force development than the reference group: mean quadriceps peak torque during slow concentric contraction: 3.69 Nm · kg−1, s=0.08 vs. 3.26 Nm · kg−1, s=0.8 (P<0.001); mean hamstring peak torque during slow concentric contraction: 1.86 Nm · kg−1, s=0.04 vs. 1.63 Nm · kg−1, s=0.04 (P<0.001); mean quadriceps rate of force development at 100 ms: 24.4 Nm · s−1·kg−1, s=0.5 vs. 22.1 Nm·s−1 · kg−1, s=0.6 (P<0.05); mean hamstring rate of force development at 100 ms: 11.4 Nm · s−1·kg−1, s=0.3 vs. 8.9 Nm · s−1 · kg−1, s=0.4 (P<0.05). However, after 14 weeks of resistance training the reference group achieved similar isometric and slow concentric muscle strength as the badminton players, although the badminton players still had a higher isometric rate of force development and muscle strength during fast (240° · s−1) quadriceps contractions. Large volumes of concurrent endurance training could have attenuated the long‐term development of maximal muscle strength in the badminton players. The badminton players had a higher contractile rate of force development than the reference group before and after resistance training. Greater explosive muscle strength in the badminton players might be a physiological adaptation to their badminton training.
Spectral parameters of surface electromyography and performance in swim bench exercises during the training of elite and junior swimmers
Authors: Ganter Nico , Witte Kerstin , Edelmann‐Nusser Jürgen , Heller Mario , Schwab Karin , Witte Herbert
Published: July 2011

Spectral parameters of surface electromyography (EMG) are used to assess intramuscular coordination in terms of fatigue and motor unit recruitment. The aim of the present study was to examine changes in performance and EMG spectral parameters of the propulsive muscles during a swim bench exercise in swimmers to determine the intra‐individual effects of different training periods in the normal training process. Ten swimmers of different ages and standards were investigated in a longitudinal study. Electromyograms of the relevant muscles (triceps longum, triceps lateralis, and latissimus dorsi) were recorded during the tests, and spectral parameters calculated using time‐variant spectral analysis. In the elite swimmers, we observed variation in performance throughout the training season with respect to training load, whereas for the junior swimmers there was a trend to improve performances irrespective of training load. Correlations with performance were observed for the median frequencies of the triceps longus for the elite athletes. Performances and frequencies were increased in the taper period, whereas they were reduced after periods of high training loads. For the junior swimmers, no such correlations were observed. Based on our results, spectral parameters could provide information about the fatigue of the neuromuscular system of elite swimmers during periods of high training loads and enhanced intramuscular coordination in the taper period before competition.
Switching to Perennial Energy Crops Under Uncertainty and Costly Reversibility
Authors: Song Feng , Zhao Jinhua , Swinton Scott M.
Published: June 2011

We study a farmer's decision to convert traditional cropland into land for growing dedicated energy crops, taking into account sunk conversion costs and uncertainties in crop returns. The optimal decision rules differ significantly from the expected net present value rule, which ignores uncertainties, and from real options models that allow only one‐way conversion into energy crops. These models also predict drastically different patterns of land conversions into and out of energy crops over time. Using corn–soybean rotation and switchgrass as examples, we show that the model predictions are sensitive to assumptions about stochastic processes of the returns. Government policies might have unintended consequences: subsidizing conversion costs into switchgrass may not much affect proportions of land in switchgrass in the long run.