bluuebunny/crossref_metadata_2025 huggingface dataset:
Fibronectin promotes proplatelet formation in the human megakaryocytic cell line UT‐7/TPO
Authors: Kawaguchi Tatsuya , Hatano Ryo , Yamaguchi Kyoji , Nawa Katsuhiko , Hashimoto Ryuji , Yokota Hiroshi
Published: October 2011

We investigated PPF (proplatelet formation) in the human megakaryocytic cell line UT‐7/TPO in vitro and signal transduction pathways responsible for PPF. The megakaryocytic cell lines are useful for studying megakaryocyte biology, although PPF is induced only in the presence of phorbol ester. TPO (thrombopoietin) stimulates megakaryocyte proliferation and differentiation; however, no PPF occurred in the megakaryocytic cell lines, even after the addition of TPO. Therefore, factors other than TPO may play an important role in the process of PPF. As PPF occurs in the bone marrow in vivo, we noted extracellular matrix proteins and found that soluble FN (fibronectin) induced potent PPF in UT‐7/TPO without phorbol ester. A Western blot analysis showed that the expression of integrins was not increased by FN treatment. Anti‐β1 antibody and the RGD (arginine‐glycine‐aspartate) peptide inhibited FN‐induced PPF. This result indicates that the signal originated from integrin β1, which is essential to inducing PPF in UT‐7/TPO. Results of the experiments using several inhibitors suggest that activation of the MEK [MAPK (mitogen‐activated protein kinase)/ERK (extracellular‐signal‐regulated kinase) kinase]–ERK and PI3K (phosphoinositide 3‐kinase) pathways are necessary for PPF. The phosphorylation of ERK gradually increased for 2 h after the addition of soluble FN, which suggests that activation of ERK is essential for the initial induction of FN‐induced PPF in UT‐7/TPO. UT‐7/TPO is a useful cell line that enables us to study the signals of PPF without effects of chemical compounds.
STIM1/Orai1 contributes to sex differences in vascular responses to calcium in spontaneously hypertensive rats
Authors: Giachini Fernanda R. C. , Lima Victor V. , Filgueira Fernando P. , Dorrance Anne M. , Carvalho Maria Helena C. , Fortes Zuleica B. , Webb R. Clinton , Tostes Rita C.
Published: October 2011

Sex differences in Ca2+-dependent signalling and homoeostasis in the vasculature of hypertensive rats are well characterized. However, sex-related differences in SOCE (store-operated Ca2+ entry) have been minimally investigated. We hypothesized that vascular protection in females, compared with males, reflects decreased Ca2+ mobilization due to diminished activation of Orai1/STIM1 (stromal interaction molecule 1). In addition, we investigated whether ovariectomy in females affects the activation of the Orai1/STIM1 pathway. Endothelium-denuded aortic rings from male and female SHRSP (stroke-prone spontaneously hypertensive rats) and WKY (Wistar–Kyoto) rats and from OVX (ovariectomized) or sham female SHRSP and WKY rats were used to functionally evaluate Ca2+ influx-induced contractions. Compared with females, aorta from male SHRSP displayed: (i) increased contraction during the Ca2+-loading period; (ii) similar transient contraction during Ca2+ release from the intracellular stores; (iii) increased activation of STIM1 and Orai1, as shown by the blockade of STIM1 and Orai1 with neutralizing antibodies, which reversed the sex differences in contraction during the Ca2+-loading period; and (iv) increased expression of STIM1 and Orai1. Additionally, we found that aortas from OVX-SHRSP showed increased contraction during the Ca2+-loading period and increased Orai1 expression, but no changes in the SR (sarcoplasmic reticulum)-buffering capacity or STIM1 expression. These findings suggest that augmented activation of STIM1/Orai1 in aortas from male SHRSP represents a mechanism that contributes to sex-related impaired control of intracellular Ca2+ levels. Furthermore, female sex hormones may negatively modulate the STIM/Orai1 pathway, contributing to vascular protection observed in female rats.
Darbepoetin enhances endothelium-dependent vasomotor function in patients with stable coronary artery disease only after preceding ischaemia/reperfusion
Authors: Tilling Lindsey , Hunt Joanne , Donald Ann , Clapp Brian , Chowienczyk Phil
Published: October 2011

Vasoprotective effects of erythropoietin in animal models are mediated by endothelium-derived NO and/or mobilization of EPCs (endothelial progenitor cells) and may be enhanced by ischaemia: whether they are present in humans is unknown. We examined whether the erythropoietin analogue darbepoetin improves FMD (flow-mediated dilatation), a measure of endothelium-derived NO, and whether this is influenced by preceding I/R (ischaemia/reperfusion). A total of 36 patients (50–75 years) with stable coronary artery disease were randomized to receive a single dose of darbepoetin (300 μg) or saline placebo. FMD was measured at the brachial artery using high-resolution ultrasound. CD133+/CD34+/VEGFR2+ (vascular endothelial growth factor receptor 2) circulating EPCs were enumerated by flow cytometry. Measurements were made immediately before darbepoetin/placebo and at 24 h, 72 h and 7 days. At 24 h, FMD was repeated after 20 min of I/R of the upper limb. A further group of 11 patients was studied according to the same protocol, all receiving darbepoetin, with omission of forearm I/R at 24 h. Immunoreactive erythropoietin peaked at 24 h and remained elevated at approximately 50-fold of baseline at 72 h. FMD did not differ significantly between groups at 24 h (before I/R). At 72 h (48 h after I/R), FMD was greater (by 2.3±0.5% in the darbepoetin compared with the placebo group, a 66% increase over baseline; P<0.001) and greater than FMD at the same time point without preceding I/R (P<0.01). Increases in CD133+/CD34+/VEGFR2+ cells after darbepoetin did not differ according to the presence or absence of preceding I/R. Preceding I/R is required for darbepoetin to enhance endothelial function, possibly by increasing expression of the erythropoietin receptor and by a mechanism likely to involve Akt/NO rather than circulating EPCs.
Flexible resistive random access memory using solution-processed TiOx with Al top electrode on Ag layer-inserted indium-zinc-tin-oxide-coated polyethersulfone substrate
Authors: Jung Seungjae , Kong Jaemin , Song Sunghoon , Lee Kwanghee , Lee Takhee , Hwang Hyunsang , Jeon Sanghun
Published: October 2011

We demonstrated a flexible resistive random access memory (FReRAM) device using a solution-processed TiOx active layer with an Al top electrode on an Ag layer-inserted indium-zinc-tin-oxide (IAI)-coated polyethersulfone substrate (Al/TiOx/IAI). Its feasibility of FReRAM application was evaluated through the comparison of electrical and mechanical characteristics with devices having different structure such as Ag/TiOx/Ag, Al/TiOx/indium-tin-oxide, and Al/TiOx/Al. As a result, our FReRAM device exhibited greater FReRAM performance such as stable memory characteristics under mechanically bent conditions and robustness to repetitive bending cycles. In addition, the device was thermally stable up to 85 °C, despite its flexible electrode and polymer substrate.
Influence of wetting layers and quantum dot size distribution on intermediate band formation in InAs/GaAs superlattices
Authors: Huang S. , Semichaevsky A. V. , Webster L. , Johnson H. T. , Goldman R. S.
Published: October 2011

We examine the influence of the wetting layers (WLs) and the quantum dot (QD) size distribution on the sub-bandgap external quantum efficiency (EQE) of QD solar cells. We use a finite-element Schrödinger-Poisson model that considers QD and wetting layer shapes, sizes, and spacings from cross-sectional scanning tunneling and atomic force micrographs. A comparison between experiments and computations reveals an insignificant contribution of the WL to the sub-bandgap EQE and a broadening of sub-bandgap EQE associated with a variation in QD sizes in the growth direction.
A portable fluorescence detector for fast ultra trace detection of explosive vapors
Authors: Xin Yunhong , He Gang , Wang Qi , Fang Yu
Published: October 2011

This paper developed a portable detector based on a specific material-based fluorescent sensing film for an ultra trace detection of explosives, such as 2,4,6-trinitrotoluene (TNT) or its derivate 2,4-dinitrotoluene (DNT), in ambient air or on objects tainted by explosives. The fluorescent sensing films are based on single-layer chemistry and the signal amplification effect of conjugated polymers, which exhibited higher sensitivity and shorter response time to TNT or DNT at their vapor pressures. Due to application of the light emitting diode and the solid state photomultiplier and the cross-correlation-based circuit design technology, the device has the advantages of low-power, low-cost, small size, and an improved signal to noise ratio. The results of the experiments showed that the detector can real-time detect and identify of explosive vapors at extremely low levels; it is suitable for the identification of suspect luggage, forensic analyses, or battlefields clearing.
Effects of band-tails on the subthreshold characteristics of nanowire band-to-band tunneling transistors
Authors: Khayer M. Abul , Lake Roger K.
Published: October 2011

High source doping is required to support the high electric fields necessary to provide sufficient drive currents in interband tunnel field effect transistors (TFETs). High doping is associated with band-tails in the density of states that decay exponentially into the bandgap with decay constants that can be comparable to the room temperature thermal energy kBT. This compromises the core operational principal of a TFET of a hard energy cut-off to the injected channel carrier distribution provided by the source valence band edge. If the band-tails are limited to the source region, they have minimal effect for short channels ≤10 nm, since the leakage current is dominated by direct, coherent tunneling through the channel. For longer 20 nm channels, source band-tails can double the inverse subthreshold slope but still leave it below the ideal 60 mV/decade value with on-off current ratios greater than 106 using a supply voltage of 0.4 V. Band-tails both in the source and channel are more detrimental for both 10 and 20 nm channels. On-off current ratios are reduced to ≥103 and ≥104 for the 10 nm and 20 nm channel devices, respectively.
Impact of metal nano layer thickness on tunneling oxide and memory performance of core-shell iridium-oxide nanocrystals
Authors: Banerjee W. , Maikap S. , Tien T.-C. , Li W.-C. , Yang J.-R.
Published: October 2011

The impact of iridium-oxide (IrOx) nano layer thickness on the tunneling oxide and memory performance of IrOx metal nanocrystals in an n-Si/SiO2/Al2O3/IrOx/Al2O3/IrOx structure has been investigated. A thinner (1.5 nm) IrOx nano layer has shown better memory performance than that of a thicker one (2.5 nm). Core-shell IrOx nanocrystals with a small average diameter of 2.4 nm and a high density of ∼2 × 1012/cm2 have been observed by scanning transmission electron microscopy. The IrOx nanocrystals are confirmed by x-ray photoelectron spectroscopy. A large memory window of 3.0 V at a sweeping gate voltage of ±5 V and 7.2 V at a sweeping gate voltage of ± 8 V has been observed for the 1.5 nm-thick IrOx nano layer memory capacitors with a small equivalent oxide thickness of 8 nm. The electrons and holes are trapped in the core and annular regions of the IrOx nanocrystals, respectively, which is explained by Gibbs free energy. High electron and hole-trapping densities are found to be 1.5 × 1013/cm2 and 2 × 1013/cm2, respectively, due to the small size and high-density of IrOx nanocrystals. Excellent program/erase endurance of >106 cycles and good retention of 104 s with a good memory window of >1.2 V under a small operation voltage of ± 5 V are obtained. A large memory size of >10 Tbit/sq. in. can be designed by using the IrOx nanocrystals. This study is not only important for the IrOx nanocrystal charge-trapping memory investigation but it will also help to design future metal nanocrystal flash memory.
Sign change of tunnel magnetoresistance ratio with temperature in epitaxial Fe/MgO/Co2MnSn magnetic tunnel junctions
Authors: Tanaka M. A. , Hori T. , Mibu K. , Kondou K. , Ono T. , Kasai S. , Asaka T. , Inoue J.
Published: October 2011

Bias-voltage dependence of tunnel magnetoresistance (TMR) was investigated for epitaxial magnetic tunnel junctions of Fe/MgO/Co2MnSn at various temperatures. The magnetoresistance measurement showed sign change of TMR ratio as a function of bias voltage. Sign change in TMR effect was also observed with changing temperature at a fixed bias voltage around 0 mV. These tunneling behaviors can be explained by a modified Jullière’s model adopting an interaction between tunnel electrons and localized spins of magnetic impurities within the tunnel barrier. The temperature dependent sign change was qualitatively explained by the theoretical calculation.
Surface spin effects in La-doped CoFe2O4 nanoparticles prepared by microemulsion route
Authors: Burianova Simona , Poltierova Vejpravova Jana , Holec Petr , Plocek Jiri , Niznansky Daniel
Published: October 2011

A comparative study of pure CoFe2O4 nanoparticles and La-doped CoFe2O4 nanoparticles, prepared by microemulsion route has been performed. The samples were characterized using x-ray diffraction and transmission electron microscopy in order to obtain average particle size. The doping of small amount of La3+ ions (up to 3 molar %) causes significant reduction of the particle size using the identical preparation route. The samples were investigated by magnetization measurements, which revealed the coercivity values strongly dependent on particle size, but not significantly on level of La3+ doping. Detailed in-field Mössbauer spectroscopy studies were performed in order to determine spin canting angles and cation distribution within the spinel network. The non-negligible canting angles up to 40° in the La-doped samples were observed. The presence of the spin surface effects was also supported by magnetic measurement as the magnetization did not saturate even in considerably high magnetic fields (7 T). Moreover, significantly reduced values of the saturation magnetization were obtained. The observed features originated by the surface spin disorder in nanosized particles are explained in the frame of the core-shell model.
Electric quadrupole excitation in surface plasmon resonance of metallic composite nanohole arrays
Authors: Wu Shan , Liu Jianqiang , Zhou Lin , Wang Qianjin , Zhang Yi , Wang Guodong , Zhu Yongyuan
Published: October 2011

We present an experimental and theoretical study on the composite nanostructures composed of the LT-shaped metallic nanohole arrays. Multiple resonance transmission peaks are observed in the optical transmission spectra. By analyzing their electric field distributions on the interface, we infer the electric dipole and the electric quadrupole plasmonic resonances contribute to these transmission peaks. The electric quadrupole is a subradiant mode, which cannot be directly excited by the incident light. Here, we demonstrate that the surface plasmon polaritons can excite the electric quadrupole plasmonic resonance mode through the near-field interaction.
Role of the first coordination shell in determining the equilibrium structure and dynamics of simple liquids
Authors: Toxvaerd Søren , Dyre Jeppe C.
Published: October 2011

The traditional view that the physical properties of a simple liquid are determined primarily by its repulsive forces was recently challenged by Berthier and Tarjus, who showed that in some cases ignoring the attractions leads to large errors in the dynamics [L. Berthier and G. Tarjus, Phys. Rev. Lett. 103, 170601 (2009);10.1103/PhysRevLett.103.170601 J. Chem. Phys. 134, 214503 (2011)10.1063/1.3592709]. We present simulations of the standard Lennard-Jones liquid at several condensed-fluid state points, including a fairly low density state and a very high density state, as well as simulations of the Kob-Andersen binary Lennard-Jones mixture. By varying the range of the forces via a shifted-forces cutoff, results for the thermodynamics, dynamics, and structure show that the determining factor for getting the correct statics and dynamics is not whether or not the attractive forces per se are included in the simulations. What matters is whether or not interactions are included from all particles within the first coordination shell – the attractive forces can thus be ignored, but only at extremely high densities. The recognition of the importance of a local shell in condensed fluids goes back to van der Waals; our results confirm this idea and thereby the basic picture of the old hole and cell theories for simple condensed fluids.
Density evolution measurement of hydrogen plasma in capillary discharge by spectroscopy and interferometry methods
Authors: Jang D. G. , Kim M. S. , Nam I. H. , Uhm H. S. , Suk H.
Published: October 2011

Plasma density is one of the most important parameters for laser wakefield acceleration using a gas-filled capillary waveguide. We measured the evolving hydrogen plasma densities in capillary discharge by using two different diagnostics methods at the same time, i.e., the Stark-effect-based spectroscopy and the transverse interferometry methods. It was found that there is a rather large difference between two methods and the phenomenon is explained in view of self-absorption. The correlation was obtained and the result is quite useful for capillary-plasma-based laser wakefield acceleration research.
Tuning the inter-shell splitting in self-assembled CdTe quantum dots
Authors: Kukliński K. , Kłopotowski Ł. , Fronc K. , Wiater M. , Wojnar P. , Rutkowski P. , Voliotis V. , Grousson R. , Karczewski G. , Kossut J. , Wojtowicz T.
Published: October 2011

We present photoluminescence studies of highly excited single self-assembled CdTe quantum dots under continuous-wave and pulsed excitations. We observe appearance of emission bands related to sequential filling of s-, p- and d-shells. We analyze the inter-shell splitting for five samples, in which the dots were formed from a strained CdTe layer of different width. We find that by increasing the CdTe layer width, the inter-shell splitting increases. In a time resolved measurement, we observe a radiative cascade between transitions involving one, two, and more than two excitons.
Dual ground-state pulse generation from a passively mode-locked InAs/InGaAs quantum dot laser
Authors: Mesaritakis Charis , Simos Christos , Simos Hercules , Krestnikov Igor , Syvridis Dimitris
Published: October 2011

In this paper, we present experimental results related to tunable dual wavelength passive mode locking of two independent ground state sub-bands in a multi section InAs/InGaAs quantum dot laser. The emission of these sub-bands is related to gain suppression at the center of the ground state emission, whereas their wavelength separation is tunable with injection current. Through the mechanism of passive mode locking two independent pulses were obtained, with typical pulse width in the order of 17 ps.
Coalescence of 3-phenyl-propynenitrile on Cu(111) into interlocking pinwheel chains
Authors: Luo Miaomiao , Lu Wenhao , Kim Daeho , Chu Eric , Wyrick Jon , Holzke Connor , Salib Daniel , Cohen Kamelia D. , Cheng Zhihai , Sun Dezheng , Zhu Yeming , Einstein T. L. , Bartels Ludwig
Published: October 2011

3-phenyl-propynenitrile (PPN) adsorbs on Cu(111) in a hexagonal network of molecular trimers formed through intermolecular interaction of the cyano group of one molecule with the aromatic ring of its neighbor. Heptamers of trimers coalesce into interlocking pinwheel-shaped structures that, by percolating across islands of the original trimer coverage, create the appearance of gear chains. Density functional theory aids in identifying substrate stress associated with the chemisorption of PPN's acetylene group as the cause of this transition.
Disordered quantum walks in one lattice dimension
Authors: Ahlbrecht Andre , Scholz Volkher B. , Werner Albert H.
Published: October 2011

We study a spin-$\frac{1}{2}$12-particle moving on a one-dimensional lattice subject to disorder induced by a random, space-dependent quantum coin. The discrete time evolution is given by a family of random unitary quantum walk operators, where the shift operation is assumed to be deterministic. Each coin is an independent identically distributed random variable with values in the group of two-dimensional unitary matrices. We derive sufficient conditions on the probability distribution of the coins such that the system exhibits dynamical localization. Put differently, the tunneling probability between two lattice sites decays rapidly for almost all choices of random coins and after arbitrary many time steps with increasing distance. Our findings imply that this effect takes place if the coin is chosen at random from the Haar measure, or some measure continuous with respect to it, but also for a class of discrete probability measures which support consists of two coins, one of them being the Hadamard coin.
On Dirac equation on a time scale
Authors: Hovhannisyan Gro
Published: October 2011

We consider the non-autonomous linear Dirac equation on a time scale containing important discrete, continuous, and quantum time scales. A representation of the solutions is established via an approximate solutions in terms of unknown phase functions with the error estimates. JWKB and other asymptotic representations are discussed. The adiabatic invariants of the Dirac equation are described by using a small parameter method. We also calculate the transition probabilities for the Dirac equation. Using the asymptotic solutions we show that the electron-positron transition probability during a long period of time is about 1/3. Since this probability is high, there is a simple explanation of the stability of the revolution of an electron about the proton only by the electromagnetic field. Indeed when the electron is far from the proton, it is attracted by the electromagnetic field of the proton. When the electron approaches closer to the proton, it turns to the positron which is repelling from the proton by the same electromagnetic field.
Large-area transparent conductive few-layer graphene electrode in GaN-based ultra-violet light-emitting diodes
Authors: Kim Byung-Jae , Lee Chongmin , Jung Younghun , Hyeon Baik Kwang , Mastro Michael A. , Hite Jennifer K. , Eddy Charles R. , Kim Jihyun
Published: October 2011

We report on the development of a large-area few-layer graphene (FLG)—based transparent conductive electrode as a current spreading layer for GaN-based ultraviolet (UV) light-emitting diodes (LEDs). Large-area FLG was deposited on Cu using the chemical vapor deposition (CVD) method and subsequently transferred to the surface of the UV LED. UV light at a peak of 372 nm was emitted through the FLG-based transparent conductive electrode. The current spreading effects of FLG were clearly evident in both the optical images of electroluminescence (EL) and current-voltage (I-V) characteristics. Degradation of the FLG-based transparent conductive electrode could be induced by high power operation. Our results indicate that a large-area FLG-based electrode on GaN offers excellent current spreading and ultra-violet transparency properties when compared to the standard optoelectronic indium tin oxide (ITO) contact layer.
Mercedes–Benz water molecules near hydrophobic wall: Integral equation theories vs Monte Carlo simulations
Authors: Urbic T. , Holovko M. F.
Published: October 2011

Associative version of Henderson-Abraham-Barker theory is applied for the study of Mercedes–Benz model of water near hydrophobic surface. We calculated density profiles and adsorption coefficients using Percus-Yevick and soft mean spherical associative approximations. The results are compared with Monte Carlo simulation data. It is shown that at higher temperatures both approximations satisfactory reproduce the simulation data. For lower temperatures, soft mean spherical approximation gives good agreement at low and at high densities while in at mid range densities, the prediction is only qualitative. The formation of a depletion layer between water and hydrophobic surface was also demonstrated and studied.
Investigation of thermal transport degradation in rough Si nanowires
Authors: Luisier Mathieu
Published: October 2011

Thermal transport through 〈100〉 and 〈110〉 rough Si nanowires is investigated using an atomistic quantum transport approach based on a modified Keating model and the wave function formalism. The thermal conductance, resistance, and conductivity are calculated for different nanowire lengths and the root mean square of the rough surfaces. The simulation results show that thermal transport is diffusive in rough nanowires without surrounding oxide layers. Its degradation, as compared to ideal structures, cannot be attributed to phonon localization effects, but to the properties of the phonon band structure. Phonon bands with an almost flat dispersion cannot propagate through disordered structures due to the mode mismatch between adjacent unit cells.
Imaging the formation of a p-n junction in a suspended carbon nanotube with scanning photocurrent microscopy
Authors: Buchs Gilles , Barkelid Maria , Bagiante Salvatore , Steele Gary A. , Zwiller Val
Published: October 2011

We use scanning photocurrent microscopy (SPCM) to investigate individual suspended semiconducting carbon nanotube devices where the potential profile is engineered by means of local gates. In situ tunable p-n junctions can be generated at any position along the nanotube axis. Combining SPCM with transport measurements allows a detailed microscopic study of the evolution of the band profiles as a function of the gates voltage. Here we study the emergence of a p-n and a n-p junctions out of a n-type transistor channel using two local gates. In both cases the I - V curves recorded for gate configurations corresponding to the formation of the p-n or n-p junction in the SPCM measurements reveal a clear transition from resistive to rectification regimes. The rectification curves can be fitted well to the Shockley diode model with a series resistor and reveal a clear ideal diode behavior.
Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch
Authors: Aguado Andrés , López José M.
Published: October 2011

We locate the putative global minimum structures of NaxCs55 − x and LixCs55 − x nanoalloys through combined empirical potential and density functional theory calculations, and compare them to the structures of 55-atom Li-Na and Na-K nanoalloys obtained in a recent paper [A. Aguado and J. M. López, J. Chem. Phys. 133, 094302 (2010)10.1063/1.3479396]. Alkali nanoalloys are representative of isovalent metallic mixtures with a strong tendency towards core-shell segregation, and span a wide range of size mismatches. By comparing the four systems, we analyse how the size mismatch and composition affect the structures and relative stabilities of these mixtures, and identify useful generic trends. The Na-K system is found to possess a nearly optimal size mismatch for the formation of poly-icosahedral (pIh) structures with little strain. In systems with a larger size mismatch (Na-Cs and Li-Cs), frustration of the pIh packing induces for some compositions a reconstruction of the core, which adopts instead a decahedral packing. When the size mismatch is smaller than optimal (Li-Na), frustration leads to a partial amorphization of the structures. The excess energies are negative for all systems except for a few compositions, demonstrating that the four mixtures are reactive. Moreover, we find that Li-Cs and Li-Na mixtures are more reactive (i.e., they have more negative excess energies) than Na-K and Na-Cs mixtures, so the stability trends when comparing the different materials are exactly opposite to the trends observed in the bulk limit: the strongly non-reactive Li-alkali bulk mixtures become the most reactive ones at the nanoscale. For each material, we identify the magic composition xm which minimizes the excess energy. xm is found to increase with the size mismatch due to steric crowding effects, and for LixCs55 − x the most stable cluster has almost equiatomic composition. We advance a simple geometric packing rule that suffices to systematize all the observed trends in systems with large size mismatch (Na-K, Na-Cs, and Li-Cs). As the size mismatch is reduced, however, electron shell effects become more and more important and contribute significantly to the stability of the Li-Na system.
OH···X (X = O, S) hydrogen bonding in thetrahydrofuran and tetrahydrothiophene
Authors: Biswal Himansu S. , Wategaonkar Sanjay
Published: October 2011

In this article, hydrogen bonding interaction between p-cresol (p-CR) and cyclic ether, tetrahydrofuran (THF) and thioether, tetrahydrothiophene (THT) has been investigated. Two-color resonantly enhanced two-photon ionization in conjunction with the fluorescence detected IR (FDIR) spectroscopy was used to record the changes in the OH stretching frequency in these complexes. The FDIR spectra showed existence of a single conformer of the p-CR·THF and two conformers of the p-CR·THT complex. With the help of computed IR spectra and atoms-in-molecules analysis, the two conformers of p-CR·THT were assigned as the complex of p-CR with THT (C2)/THT (CS). The redshift of OH stretching frequency for the p-CR·THF complex was greater compared to those for the conformers of the p-CR·THT complex. The binding energies of the p-CR·THF and p-CR·THT complexes were computed to be 7.42 and 6.15 kcal/mole. These were of the same order as those for the acyclic analogs, diethylether (DEE), and diethylsulfide (DES), of the solvent molecules under investigation. Although the DEE and THF consist of same number of carbon atoms, the dispersion energy contribution was much higher (43%) for DEE than that for THF (30%). In the case of sulfur analogs, however, it was similar (∼50%) in the case of both DES well as THT complexes. All the computed H-bond indicators for these two complexes nicely correlate with the observed redshift of the O–H stretch.
Ab initio calculations on Li-ion migration in Li2FeSiO4 cathode material with a P21 symmetry structure
Authors: Su Dawei , Ahn Hyojun , Wang Guoxiu
Published: October 2011

We have systematically investigated the diffusion mechanism of Li ions in Li2FeSiO4 and its delithiated product LiFeSiO4 based on the P21 symmetry using the first principle method. Calculations on the energy barriers for possible spatial hopping pathways predicted that the activation barriers along the [101] direction and Li ion layer in the ac plane are relatively low, which can ensure the facile lithium diffusion along those directions. The results indicate that Li2FeSiO4 with the P21 symmetry is an ionic conductor for Li ions with two-dimensional diffusion.
Large internal stress-assisted twin-boundary motion in Ni2MnGa ferromagnetic shape memory alloy
Authors: Nie Z. H. , Cong D. Y. , Liu D. M. , Ren Y. , Pötschke M. , Roth S. , Wang Y. D.
Published: October 2011

The twin boundary motion driven by thermo-magnetic coupling was in-situ studied in a NiMnGa single crystal using high-energy x-ray diffraction technique. An unstable martensite with an internal stress of ∼8 MPa was obtained through a thermo-magnetic training. The triple martensite variants assisted by internal stress are distinct from the self-accommodated martensite twin variants with a stress-free state, and a single martensite-variant can be actuated only by a magnetic field of ∼0.34 T, equivalent to an actuator stress of about 1.3 MPa. The generation of so large internal stress among variants is attributed to the altered martensite nucleation sites triggered by external fields during thermo-magnetic training.
Microfabricated optofluidic ring resonator structures
Authors: Scholten Kee , Fan Xudong , Zellers Edward. T.
Published: October 2011

We describe the fabrication and preliminary optical characterization of rugged, Si-micromachined optofluidic ring resonator (μOFRR) structures consisting of thin-walled SiOx cylinders with expanded midsections designed to enhance the three-dimensional confinement of whispering gallery modes (WGMs). These μOFRR structures were grown thermally at wafer scale on the interior of Si molds defined by deep-reactive-ion etching and pre-treated to reduce surface roughness. Devices 85-μm tall with 2-μm thick walls and inner diameters ranging from 50 to 200 μm supported pure-mode WGMs with Q-factors >104 near 985 nm. Advantages for eventual vapor detection in gas chromatographic microsystems are highlighted.
Anomalous Hall effect measurements on capped bit-patterned media
Authors: Ranjbar M. , Piramanayagam S. N. , Wong S. K. , Sbiaa R. , Chong T. C.
Published: October 2011

The role of a small exchange coupling between isolated single-domain magnetic dots through a thin continuous film—in a system called capped bit-patterned media (CBPM)—has been studied experimentally using anomalous Hall effect measurements. The exchange coupling, provided by the thin continuous layer, was effective in reducing the switching field distribution (SFD) and coercivity under optimized conditions. SFD increases and coercivity decreases for very high values of exchange coupling due to the formation of multi-domains. Besides reducing SFD, the CBPM also exhibit potential writability advantage at higher densities, indicating their potential application as bit-patterned media.
Reproducible electrochemical etching of silver probes with a radius of curvature of 20 nm for tip-enhanced Raman applications
Authors: Lloyd J. S. , Williams A. , Rickman R. H. , McCowen A. , Dunstan P. R.
Published: October 2011

The performance of tip-enhanced Raman spectroscopy (TERS) largely depends on probe optimisation. An electrochemical etch using nitric acid and ethanol produces sharp silver probes with radius of curvature between 20 and 60 nm. Optimisation also identified controllable tapers; rough or smooth. Boundary element method simulations comparing the response to 532 nm excitation of silver and gold probes reveal no discernable field enhancement at the gold apex, but strong localised enhancement is observed at the silver apex. The motivation for employing this method of etching silver probes can also be seen in the signal enhancement observed in preliminary TERS data presented.
Nitrogen flux induced GaN nanostructure nucleation at misfit dislocations on Al2O3(0001)
Authors: Kesaria Manoj , Shivaprasad S. M.
Published: October 2011

The work demonstrates the dominant role of nitrogen flux rate on GaN nanostructure formation on bare Al2O3(0001). In nitrogen rich conditions, wurtzite c-oriented GaN nanowall honeycomb network is formed as strain relaxation pathway of nucleation at edge dislocations. A specific nitrogen flux rate in a plasma assisted molecular beam epitaxy growth is necessary for fixed Ga flux and substrate temperature to form columnar self assembled nanostructures. It is argued that kinetically hindering diffusion of Ga adatoms and the low sticking coefficient of r and m planes of nanowalls promote 1-dimension nanocolumn formation at screw dislocations formed at the GaN-Sapphire interface.
Field emission from hydrogen titanate nanotubes
Authors: Chakraborty Indrani , Chatterjee Sriparna , Ayyub Pushan
Published: October 2011

Hydrothermally synthesized hydrogen titanate (H2Ti3O7) nanotube meshes and arrays exhibit excellent field emission characteristics. The turn-on field is as low as 1.4 V μm−1 for the mesh and 2.6 V μm−1 for the array, while the electric field corresponding to an emission current density of 10 μA cm−2 is 2 V μm−1 (mesh) and 3.8 V μm−1 (array). The H2Ti3O7 nanotube mesh has one of the lowest reported turn-on voltages and highest enhancement factors. The emission current also shows good long term stability. We attribute the efficient field emission to the presence of mid-gap states arising from the negative surface charge on the H2Ti3O7 nanotubes.
Penetration depth in near-field radiative heat transfer between metamaterials
Authors: Basu Soumyadipta , Francoeur Mathieu
Published: October 2011

In this letter, we investigate the penetration depth in near-field radiative heat transfer between metamaterials when surface polaritons are excited at both electrical and magnetic resonances. The analyses show that based on the optical properties of the metamaterial, two different penetration depths can be defined corresponding to electrical and magnetic resonances. Depending upon the scattering rate of the metamaterial, it is possible to selectively enhance or reduce the penetration depth of near-field thermal radiation at electric and magnetic resonances. The results obtained from this study will benefit applications of metamaterials in near-field energy harvesting.
Magnetism of cobalt nanoclusters on graphene on iridium
Authors: Vo-Van Chi , Schumacher Stefan , Coraux Johann , Sessi Violetta , Fruchart Olivier , Brookes Nick B. , Ohresser Philippe , Michely Thomas
Published: October 2011

The structure and magnetic properties of Co clusters, comprising 26–2700 atoms, self-organized or not on the graphene/Ir(111) moiré, were studied in situ with the help of scanning tunneling microscopy and x-ray magnetic circular dichroism. Surprisingly, the small clusters have almost no magnetic anisotropy. We find indication for a magnetic coupling between the clusters.
Non-destructive observation of in-grown stacking faults in 4H-SiC epitaxial layer using mirror electron microscope
Authors: Hasegawa Masaki , Ohno Toshiyuki
Published: October 2011

Mirror electron microscope (MEM) observation has been conducted for a 4-μm-thick n-doped 4H-SiC epitaxial layer. If the sample is simultaneously illuminated with ultraviolet (UV) light of a slightly greater energy than the bandgap energy of 4H-SiC, in-grown stacking faults (IGSFs) can be clearly observed in MEM images. These observations were performed non-destructively, as almost all irradiated electrons returned without impinging the sample surface due to the negative voltage applied to the sample. High spatial resolution observation via MEM showed that multiple IGSFs were stacked up. The phenomenon in which the contrast of the IGSFs vanished in the absence of UV illumination and under UV illumination with a lower energy than the bandgap energy revealed that the origin of the contrast was the negative charging of IGSFs trapping electrons excited by UV light.
Polarization switching at the nanoscale in ferroelectric copolymer thin films
Authors: Gaynutdinov R. V. , Mitko S. , Yudin S. G. , Fridkin V. M. , Ducharme Stephen
Published: October 2011

The polarization switching kinetics were measured at the nanoscale in continuous thin films of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The dependence of the switching rate on voltage for a 54-nm thick film exhibits extrinsic nucleation and domain-growth type kinetics with no true threshold coercive field, and is qualitatively different from the behavior of an 18-nm thick film, which exhibits intrinsic switching kinetics, and a true threshold field. The results are consistent with studies of thin film capacitors of much larger area and with a recent refinement of the theory of the critical size for intrinsic switching.
Optical investigation of reduced graphene oxide by spectroscopic ellipsometry and the band-gap tuning
Authors: Shen Y. , Zhou P. , Sun Q. Q. , Wan L. , Li J. , Chen L. Y. , Zhang D. W. , Wang X. B.
Published: October 2011

Spectroscopic ellipsometry was used to characterize the optical response of few layer reduced graphene oxide and graphene oxide in visible range. Lorentz oscillator model is added to analyze the ellipsometric parameters. The experiment shows the optical response of few layer reduced graphene oxide and monolayer exfoliated graphene in visible range is quite similar with slight difference due to the structure defects. The Lorentz oscillator model gives experimental support to investigate the band-gap tuning through the reduction process in details.
Effect of temperature on CO detection sensitivity of ZnO nanorod-gated AlGaN/GaN high electron mobility transistors
Authors: Lo Chien-Fong , Chu B. H. , Pearton S. J. , Dabiran A. , Chow P. P. , Doré S. , Hung S. C. , Chen C. W. , Ren F.
Published: October 2011

The carbon monoxide (CO) detection sensitivities of ZnO nanorod-gated AlGaN/GaN high electron mobility transistors were measured over a range of temperatures from 25–150 °C. Once the sensor was exposed to the CO-containing ambient, the drain current, I, of the high electron mobility transistors increased due to chemisorbed oxygen on the ZnO surface reacting with CO, forming CO2 and releasing electrons to the oxide surface. Although the sensor could detect CO as low as 100 ppm at room temperature, the detection sensitivity, ΔI/I, was only around 0.23%. By increasing the sensor temperature to 150 °C, the detection sensitivity was improved by a factor of over 30% to 7.5%.
Room temperature direct gap electroluminescence from Ge/Si0.15Ge0.85 multiple quantum well waveguide
Authors: Chaisakul Papichaya , Marris-Morini Delphine , Isella Giovanni , Chrastina Daniel , Izard Nicolas , Le Roux Xavier , Edmond Samson , Coudevylle Jean-René , Vivien Laurent
Published: October 2011

We report room temperature direct gap electroluminescence (EL) from a Ge/Si0.15Ge0.85 multiple quantum well (MQW) waveguide. The excitonic direct gap transition and the dependence of the EL intensity on the injection currents and temperature are clearly observed. EL from the Ge/SiGe MQWs is shown to have a transverse-electric polarization. These results demonstrate the strong potential of the Ge/Si0.15Ge0.85 MQWs in terms of the realization of a monolithically integrated light source on the Si platform.
Determination of spatio-spectral properties of individual modes within multimode waveguides using spectrally resolved near-field scanning optical microscopy
Authors: Berry S. A. , Gates J. C. , Brocklesby W. S.
Published: October 2011

Near-field scanning optical microscopy (NSOM) is used to measure the relative group velocity and relative amplitude of modes in a multimode waveguide with an incoherent broadband light source. A spectrally resolving NSOM probe was used to observe localized spectral interference in the multimode waveguide. Fourier analysis was used to identify temporal delays. The modes can be further identified by their temporally discriminated spatial profile which is based on the product of their fields. This data provide the relative amplitude and phases of the modes.
State Dirigisme in Megaprojects: Governing the 2014 Winter Olympics in Sochi
Authors: Müller Martin
Published: October 2011

This paper examines the preparation for the 2014 Winter Olympic Games in Sochi, Russia, and links it to debates on state rescaling and urban entrepreneurialism in megaprojects. It is argued that the Olympic megaproject in Sochi follows a model of state dirigisme which accords a salient role to the national state. Although private sector companies act as investors, the national state steers the planning process and directs the investment. This arrangement is reflected in a business–state relationship in which the boundaries between the public and the private sector become blurred, as the state establishes directive control over companies. The model of state dirigisme is underpinned by a nationalist narrative which frames the Olympic Games not primarily as a stimulus for economic development and global competitiveness but as a contribution to Russian greatness. This mode of governing the Olympic Games deviates from the model of entrepreneurial governance and the concomitant state rescaling, dominant in megaprojects in North America and Western Europe, in according a prominent role to the national state rather than to market-led development pushed by cities as lead actors.
The other Side of the Knowledge Economy: ‘Reproductive’ Employment and Affective Labours in Oxford
Authors: McDowell Linda , Dyson Jane
Published: October 2011

A marked feature of current narratives about economic change is their epochal or transformative character. An older rhetoric about the shift from Fordism to post-Fordism has been replaced by a widely accepted story about the ‘new’ knowledge economy, as well as a less-dominant narrative about new forms of affective or immaterial labour. In both cases, as with post-Fordist claims, the significance of women's changing labour-market participation patterns has been down-played. Each of the new transformation stories bases its claims on a productionist analysis, rather than on the different forms that the necessary labour of reproduction now takes. Here we critically assess the epochal narratives, arguing that, if the reproductive side of the economy, including public sector services (once termed collective consumption) and both public and private forms of commodified domestic labour are the focus, a narrative of continuity rather than transformation more accurately captures labour-market change. We briefly illustrate these theoretical arguments by an analysis of Oxford's labour market which is dominated by public sector employment and so is an exemplary city in which to explore the reproductive side of the economy.
(PRODUCT)RED™: How Celebrities Push the Boundaries of ‘Causumerism’
Authors: Ponte Stefano , Richey Lisa Ann
Published: October 2011

(PRODUCT)RED™ (hereafter RED) is a cobranding initiative launched in 2006 by the aid celebrity Bono to raise money from product sales to support The Global Fund to Fight AIDS, Tuberculosis and Malaria. In this paper we argue that RED is shifting the boundaries of ‘causumerism’ (shopping for a better world) by enrolling consumers in ways that do not rely on accurate knowledge of the products or specific understanding of the cause that The Global Fund engages but, instead, rely on a system of more general, affective affinity between the ‘aid celebrities’ who are behind RED (such as Bono) and the consumers who buy iconic brand products to help ‘distant others’. While in many other forms of causumerism, labels or certification systems ‘prove’ that a product is just, in RED, aid celebrities provide the proof. From the consumer point of view both labels and celebrities provide a similar simplification of complex social, economic, and environmental processes. At the same time, we argue that there are important distinctions as well—labels and certifications are ultimately about improving the conditions of production, whereas RED is about accepting existing production and trade systems and donating a proportion of sales income to help distant others in Africa. The iconic brands sitting under the RED umbrella also play an important role as they offer a consistent and known venue for channeling consumer affect. We argue that celebrity validation, backed up by iconic brands, facilitates at least three shifts in the realm of causumerism: from ‘conscious consumption’ (mainly based on product-related information) to ‘compassionate consumption’ (mainly based on the management of consumer affect); from attention to the product and its production process toward the medical treatment of the ‘people with the problem’ (AIDS patients in Africa); and from addressing the causes of problems to solving their manifestations.