bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo simulation of terahertz quantum cascade laser structures based on wide-bandgap semiconductors
Authors: Bellotti Enrico , Driscoll Kristina , Moustakas Theodore D. , Paiella Roberto
Published: June 2009

Wide-bandgap semiconductors such as GaN∕AlGaN and ZnO∕MgZnO quantum wells are promising for improving the spectral reach and high-temperature performance of terahertz quantum cascade lasers, due to their characteristically large optical phonon energies. Here, a particle-based Monte Carlo model is developed and used to quantify the potential of terahertz sources based on these materials relative to existing devices based on GaAs∕AlGaAs quantum wells. Specifically, three otherwise identical quantum cascade structures based on GaN∕AlGaN, ZnO∕MgZnO, and GaAs∕AlGaAs quantum wells are designed, and their steady-state carrier distributions are then computed as a function of temperature. The simulation results show that the larger the optical phonon energies (as in going from the AlGaAs to the MgZnO to the AlGaN materials system), the weaker the temperature dependence of the population inversion. In particular, as the temperature is increased from 10to300K, the population inversions are found to decrease by factors of 4.48, 1.50, and 1.25 for the AlGaAs, MgZnO, and AlGaN structure, respectively. Based on these results, the AlGaN and MgZnO devices are then predicted to be in principle capable of laser action without cryogenic cooling.
The effect of postannealing on the electrical properties of well-aligned n-ZnO nanorods/p-Si heterojunction
Authors: Liu Shu-Yi , Chen Tao , Jiang Yu-Long , Ru Guo-Ping , Qu Xin-Ping
Published: June 2009

This work investigates the effects of postannealing on the electrical properties of the n-ZnO nanorods/p-Si heterojunction. Well-aligned ZnO nanorods are grown on the p-Si substrate with a ZnO seed layer through a hydrothermal method. The as-grown ZnO nanorods are grown along the preferential [0001] direction with high single crystalline quality. The rectifying characteristics of the heterojunction are effectively improved and the rectification ratio is increased tens of times after annealing in air. The leakage current is decreased by two orders of magnitude and the forward-bias injection efficiency is largely enhanced after annealing. The photoluminescence and x-ray photoelectron spectroscopy results show that annealing in the air ambient can effectively reduce the loosely adsorbed oxygen on the surface of the ZnO nanorods so that the bound free electrons can be released, which can result in larger carrier concentration and improve the injection efficiency of the n-ZnO nanorods/p-Si structure in the forward voltage.
Effect of evaporation on blinking properties of the glycerol microdrop Raman laser
Authors: Sharma R. , Mondia J. P. , Schäfer J. , Lu Z. H. , Wang L. J.
Published: June 2009

We present long-term measurements of the blinking (on/off) behavior of the glycerol microdroplet Raman laser and demonstrate the dependency of the lasing bursts on the evaporation rate of the microdroplet. Electrodynamic levitation is used to study the glycerol microdroplets. Single and multimode lasing are achieved and shown here for droplets of 10.3 and 44.7 μm in diameter, respectively. Typical threshold fluences are measured to be between 200 and 390 mJ/cm2. Lasing occurs in temporally separated nearly symmetric bursts which increase in frequency and decrease in duration as the evaporation rate of the droplet is increased. Hence, we conclude that the Raman lasing blinking is caused by double resonances in the evaporating droplet and show that it can be manipulated by controlling the droplet’s evaporation rate.
Intrinsic rotation driven by the electrostatic turbulence in up-down asymmetric toroidal plasmas
Authors: Camenen Y. , Peeters A. G. , Angioni C. , Casson F. J. , Hornsby W. A. , Snodin A. P. , Strintzi D.
Published: June 2009

The transport of parallel momentum by small scale fluctuations is intrinsically linked to symmetry breaking in the direction of the magnetic field. In tokamaks, an up-down asymmetry in the equilibrium proves to be an efficient parallel symmetry breaking mechanism leading to the generation of a net radial flux of parallel momentum by the electrostatic turbulence [Y. Camenen et al., Phys. Rev. Lett. 102, 125001 (2009)]. This flux is neither proportional to the toroidal rotation nor to its gradient and arises from an incomplete cancellation of the local contributions to the parallel momentum flux under the flux surface average. The flux of parallel momentum then depends on the asymmetry of the curvature drift and on the extension of the fluctuations around the low field side midplane. In this paper, the mechanisms underlying the generation of the flux of parallel momentum are highlighted and the main dependences on plasma parameters investigated using linear gyrokinetic simulations.
Thermoelectric properties of AgPbmSbTem+2 (12≤m≤26) at elevated temperature
Authors: Dow H. S. , Oh M. W. , Park S. D. , Kim B. S. , Min B. K. , Lee H. W. , Wee D. M.
Published: June 2009

In this study, the thermoelectric properties of AgPbmSbTem+2 (LAST-m, m=12, 16, 18, 20, 22, and 26), including the Seebeck coefficient, the electrical resistivity, and the thermal conductivity, were studied in the temperature range from 323 to 773 K. The Seebeck coefficient and the electrical resistivity exhibited the behavior of a degenerate semiconductor. The measured results of the carrier concentration supported the conclusions of the electrical transport properties. The lowest electrical resistivity and the thermal conductivity were observed, which leads to the best thermoelectric performance in LAST-18 and the dimensionless figure of merit ZT value of 0.8 at 773 K.
Europium doping of zincblende GaN by ion implantation
Authors: Lorenz K. , Roqan I. S. , Franco N. , O’Donnell K. P. , Darakchieva V. , Alves E. , Trager-Cowan C. , Martin R. W. , As D. J. , Panfilova M.
Published: June 2009

Eu was implanted into high quality cubic (zincblende) GaN (ZB-GaN) layers grown by molecular beam epitaxy. Detailed structural characterization before and after implantation was performed by x-ray diffraction (XRD) and Rutherford backscattering/channeling spectrometry. A low concentration (<10%) of wurtzite phase inclusions was observed by XRD analysis in as-grown samples with their (0001) planes aligned with the {111} planes of the cubic lattice. Implantation of Eu causes an expansion of the lattice parameter in the implanted region similar to that observed for the c-lattice parameter of wurtzite GaN (W-GaN). For ZB-GaN:Eu, a large fraction of Eu ions is found on a high symmetry interstitial site aligned with the ⟨110⟩ direction, while a Ga substitutional site is observed for W-GaN:Eu. The implantation damage in ZB-GaN:Eu could partly be removed by thermal annealing, but an increase in the wurtzite phase fraction was observed at the same time. Cathodoluminescence, photoluminescence (PL), and PL excitation spectroscopy revealed several emission lines which can be attributed to distinct Eu-related optical centers in ZB-GaN and W-GaN inclusions.
Effect of anisotropy on anomalous Hall effect in Tb–Fe thin films
Authors: Babu V. Hari , Markandeyulu G. , Subrahmanyam A.
Published: June 2009

The electrical and Hall resistivities of TbxFe100−x thin films in the temperature range 13–300 K were investigated. The sign of Hall resistivity at 300 K is found to change from positive for x=28 film to negative for x=30 film, in accordance with the compensation of Tb and Fe moments. All the films are seen to have planar magnetic anisotropy at 13 K. The temperature coefficients of electrical resistivities of the amorphous films with 19≤x≤51 are seen to be negative. The temperature dependence of Hall resistivity of these films is explained on the basis of random magnetic anisotropy model. The temperature dependences of Hall resistivities of the x=22 and 41 films are seen to exhibit a nonmonotonous behavior due to change in anisotropy from perpendicular to planar. The same behavior is considered for the explanation regarding the probable formation of Berry phase curvature in these films.
A structural, magnetic, and Mössbauer spectral study of the TbCo4−xFexB compounds with x=, 1, and 2
Authors: Mayot Hervé , Isnard Olivier , Grandjean Fernande , Long Gary J.
Published: June 2009

The TbCo4−xFexB compounds with x=0, 1, and 2 have been investigated by x-ray and neutron diffraction, magnetic measurements, and iron-57 Mössbauer spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase of approximately 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mössbauer spectra of the TbCo4−xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of approximately 1.7μB, and small iron hyperfine fields of approximately 16 T. The compensation temperature of the TbCo4−xFexB compounds decreases continuously from 400 to 350 K between x=0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects the strong hybridization of the 3d orbitals of the 6i site transition metal with the boron 2p orbitals.
Optical, structural, and magnetic properties of cobalt nanostructure thin films
Authors: Schmidt D. , Kjerstad A. C. , Hofmann T. , Skomski R. , Schubert E. , Schubert M.
Published: June 2009

We report on optical, structural, and magnetic properties of two substantially different cobalt nanostructure thin films deposited at an oblique angle of incidence of 85° away from the substrate normal. Comparison is made between an achiral columnar thin film grown without substrate rotation and a chiral nanocoil sculptured thin film by glancing angle deposition with substrate rotation. Generalized spectroscopic ellipsometry is employed to determine geometrical structure properties and the anisotropic optical constants of the films in the spectral range from 400 to 1000 nm. The magnetic properties are analyzed with a superconducting quantum interference device magnetometer. Both nanostructure thin films show highly anisotropic optical properties such as strong form birefringence and large dichroism. In particular, Co slanted columnar thin films are found to possess monoclinic optical properties. Magnetic measurements at room temperature show hysteresis anisotropy with respect to a magnetic field either parallel or perpendicular to the nanostructures’ long axis. We find extremely large coercive fields of approximately 3 kOe for our achiral columnar nanostructures.
Characterization of rhenium oxide films and their application to liquid crystal cells
Authors: Cazzanelli E. , Castriota M. , Marino S. , Scaramuzza N. , Purans J. , Kuzmin A. , Kalendarev R. , Mariotto G. , Das G.
Published: June 2009

Rhenium trioxide exhibits high electronic conductivity, while its open cubic crystal structure allows an appreciable hydrogen intercalation, generating disordered solid phases, with protonic conductivity. Rhenium oxide thin films have been obtained by thermal evaporation of ReO3 powders on different substrates, maintained at different temperatures, and also by reactive magnetron sputtering of a Re metallic target. A comparative investigation has been carried out on these films, by using micro-Raman spectroscopy and x-ray diffraction. Two basic types of solid phases appear to grow in the films: a red metallic HxReO3 compound, with distorted perovskite structures, like in the bulk material, and ordered HReO4 crystals based on tetrahedral perrhenate ions. Because of its conduction properties, the electrical and electro-optical behaviors of ReO3 films deposited on standard indium tin oxide/glass substrate have been tested inside asymmetric nematic liquid crystal cells, showing an appreciable capability of rectification of their electro-optical response, in similar way to tungsten trioxide.
Magnetism of crystalline and amorphous La0.67Ca0.33MnO3 nanoparticles
Authors: Bhowmik R. N. , Poddar Asok , Ranganathan R. , Mazumdar Chandan
Published: June 2009

We report the ferromagnetism of La0.67Ca0.33MnO3 in bulk polycrystalline, nanocrystalline, and amorphous phases. The structural change from crystalline phase to amorphous phase exhibited a systematic decrease in TC (paramagnetic to ferromagnetic transition temperature) and spontaneous magnetization (MS). The experimental results suggested few more interesting features, e.g., appearance of large magnetic irreversibility in the temperature dependence of magnetization, lack of magnetic saturation at high magnetic field, blocking of magnetization below TB, and enhancement of coercivity. In addition, the magnetic phase transition near to TC changes from first order character in bulk sample to second order character in nanocrystalline and amorphous samples. We understand the observed magnetic features as the effects of decreasing particle size and increasing magnetic (spin-lattice) disorder. The magnetic dynamics of amorphous samples is distinctly different from the nanocrystalline samples and also found to be comparable with the properties of reported amorphous ferromagnetic nanoparticles.
Multiple negative differential resistances in crossed carbon nanotubes
Authors: Al Ahmad M. , Dragoman D. , Dragoman M. , Plana R. , Ting J.-H. , Huang F.-Y. , Li T.-L.
Published: June 2009

An oscillatory dependence of the drain current on the drain voltage is found in a nanostructure consisting of two crossing semiconductor carbon nanotubes that are suspended over a dielectric trench, which is backed by a doped silicon substrate that acts as a gate. Alternating positive and negative differential resistance regions are generated as a function of the drain-source voltage values and can be slightly shifted by the gate voltage. Moreover, the negative differential resistance is retrieved in a large bandwidth, of up to 100 MHz, when the structure is excited with ac signals.
Rayleigh–Taylor instability in elastic-plastic solids
Authors: Piriz A. R. , Cela J. J. López , Tahir N. A.
Published: June 2009

The linear analysis of incompressible Rayleigh–Taylor instability is carried out for thick solid plates accelerated uniformly by a constant pressure. The instability threshold is found and the boundary for the elastic to plastic transition is also determined. It is demonstrated that transition from the elastic to the plastic regime is a necessary condition for the onset of instability but not a sufficient one. The theory is in excellent quantitative agreement with the results of two-dimensional numerical simulations and reveals the main physical mechanisms that control the instability.
Si
+
ion implantation for strain relaxation of pseudomorphic Si1−xGex/Si(100) heterostructures
Authors: Buca D. , Minamisawa R. A. , Trinkaus H. , Holländer B. , Mantl S. , Loo R. , Caymax M.
Published: June 2009

A mechanism of strain relief of pseudomorphic Si1−xGex/Si(100) heterostructures by Si+ ion implantation and annealing is proposed and analytically modeled. The degree of strain relaxation is presented as a function of Ge content and implantation and annealing parameters. Rutherford backscattering spectrometry/channeling, Raman spectroscopy, and transmission electron microscopy are employed to quantify the efficiency of the relaxation process and to examine the quality of the samples, respectively. The mechanism and the conditions for strain relaxation are discussed in terms of dislocation loop formation in the implanted range with emphasis on loop formation in the compressively strained SiGe layer. The detrimental effect of local amorphization of the SiGe layer on its relaxation and on strain transfer to the Si-cap layer is also addressed.
Structural characterization and magnetic profile of annealed CoFeB∕MgO multilayers
Authors: Vadalá M. , Zhernenkov K. , Wolff M. , Toperverg B. P. , Westerholt K. , Zabel H. , Wisniowski P. , Cardoso S. , Freitas P. P.
Published: June 2009

Magnetic tunnel junctions (MTJ) have become of strategic importance due to the large tunneling magnetoresistance ratio (TMR) that they can achieve at room temperature. The largest TMR values observed until now were recorded in MTJs with MgO barriers and CoFeB electrodes after annealing of the junction above the recrystallization temperature of the amorphous CoFeB layers. We have used x-ray reflectivity combined with polarized neutron reflectivity to characterize the structure and the magnetism of [Co60Fe20B20∕MgO]14 multilayers, where the MgO layers were prepared by different methods and annealed at different temperatures. We have found that the MgO preparation method as well as the annealing temperature play a significant role in the systems. A gradient in thickness together with a variation of the scattering length density along the multilayer stacks induce a process of underoxidation or overoxidation, strictly dependent on the MgO production method.
Pulse-induced low-power resistive switching in HfO2 metal-insulator-metal diodes for nonvolatile memory applications
Authors: Walczyk Ch. , Wenger Ch. , Sohal R. , Lukosius M. , Fox A. , Dąbrowski J. , Wolansky D. , Tillack B. , Müssig H.-J. , Schroeder T.
Published: June 2009

The conduction process as well as the unipolar resistive switching behavior of Au∕HfO2∕TiN metal-insulator-metal structures were investigated for future nonvolatile memory applications. With current-voltage measurements performed at different temperatures (200–400K), the Poole–Frenkel effect as conduction process was identified. In particular, we extracted a trap energy level at ϕt=0.35±0.05eV below the HfO2 conduction band to which a microscopic origin is tentatively assigned. From current-voltage measurements of Au∕HfO2∕TiN structures, low-power (as low as 120μW) resistive switching was observed. The required forming process is shown to be an energy-induced phenomenon. The characteristics include electric pulse-induced resistive switching by applying pulses up to 100μs and a retention time upon continuous nondestructive readout of more than 104s.
Shared-mode assisted resonant energy transfer in the weak coupling regime
Authors: Hennebicq E. , Beljonne D. , Curutchet C. , Scholes G. D. , Silbey R. J.
Published: June 2009

Recent work has suggested that correlations in the environments of chromophores can lead to a change in the dynamics of excitation transfer in both the coherent and incoherent limits. An example of this effect that is relevant to many single molecule experiments occurs in the standard Förster model for resonant energy transfer (RET). The standard formula for the FRET rate breaks down when the electronic excitations on weakly interacting donor and acceptor couple to the same vibrational modes. The transfer rate can then no longer be factored into donor emission and acceptor absorption lineshapes, but must be recast in terms of a renormalized phonon reorganization energy accounting for the magnitude and sign of the excitation-vibration couplings. In this paper, we derive theoretically how the FRET rate depends on the shared mode structure and coupling, examine the simplified case of Gaussian lineshapes and then provide a quantitative calculation for a system of current interest.
Diffractive grating structure for coherent light source production
Authors: Lee S. Y. , Jing Y. C. , Luo T. , Pang X. , Wang X. , Ng K. Y.
Published: June 2009

A diffractive structure of cavities is designed to produce resonances at very high frequencies. This type of cavity structure may be useful for producing controllable coherent synchrotron radiation by microbunching the particle beam.
Dust grain oscillations in two-dimensional hexagonal dusty plasma crystals in the presence of a magnetic field
Authors: Farokhi B. , Shahmansouri M. , Shukla P. K.
Published: June 2009

The influence of a constant magnetic field on the propagation of dust-lattice waves in a two-dimensional hexagonal strongly coupled dusty plasma crystal is considered. The expression for the wave dispersion relation clearly shows that high- and low-frequency dust lattice vibrations exist as a result of the coupling between the longitudinal and transverse dust lattice modes due to the Lorentz force acting on the charged dust particles. It is found that in an external magnetic field the damping rate of the high-frequency (low-frequency) dust lattice wave is increased (decreased). For special values of the wave number and the direction of the wave propagation, the imaginary part of low-frequency is zero and the imaginary part of high-frequency attains a maximum value. The present investigation indicates that the damping rates depend on direction of the external magnetic field. The polarization of dust lattice wave modes is found for different magnetic field strengths and for different directions.
Materials design of half-metallic graphene and graphene nanoribbons
Authors: Wu Menghao , Wu Xiaojun , Gao Yi , Zeng X. C.
Published: June 2009

Through patterned chemical modification, we show that both graphene sheets and zigzag-edged graphene nanoribbons (ZGNRs) can be converted to half-metals as long as the unmodified carbon strip (or width of ZGNRs) is sufficiently wide. Periodically functionalized graphene can mimic electronic behavior of edge-modified ZGNRs as the edge-modified zigzag carbon chains effectively divide a graphene sheet into a series of identical ZGNRs.
Phase synchronization analysis by assessment of the phase difference gradient
Authors: Vejmelka Martin , Paluš Milan , Lee W. T.
Published: June 2009

Phase synchronization is an important phenomenon of nonlinear dynamics and has recently received much scientific attention. In this work a method for identifying phase synchronization epochs is described which focuses on estimating the gradient of segments of the generalized phase differences between phase slips in an experimental time series. In phase synchronized systems, there should be a zero gradient of the generalized phase differences even if the systems are contaminated by noise. A method which tests if the gradient of the generalized phase difference is statistically different from zero is reported. The method has been validated by numerical studies on model systems and by comparing the results to those published previously. The method is applied to cardiorespiratory time series from a human volunteer measured in clinical settings and compared to synchrogram analysis for the same data. Potential problems with synchrogram analysis of experimental data are discussed.
Coarse graining and scaling in dissipative particle dynamics
Authors: Füchslin Rudolf M. , Fellermann Harold , Eriksson Anders , Ziock Hans-Joachim
Published: June 2009

Dissipative particle dynamics (DPD) is now a well-established method for simulating soft matter systems. However, its applicability was recently questioned because some investigations showed an upper coarse-graining limit that would prevent the applicability of the method to the whole mesoscopic range. This article aims to re-establish DPD as a truly mesoscopic method by analyzing the problems reported by other authors and by presenting a scaling scheme that allows one to apply DPD simulations directly to any desired length scale.
Evaluation of electromagnetic enhancement of surface enhanced hyper Raman scattering using plasmonic properties of binary active sites in single Ag nanoaggregates
Authors: Itoh Tamitake , Yoshikawa Hiroyuki , Yoshida Kenichi , Biju Vasudevanpillai , Ishikawa Mitsuru
Published: June 2009

We found a binary active site of surface enhanced Raman scattering (SERS) and surface enhanced hyper Raman scattering (SEHRS) in single Ag nanoaggregates by single particle spectroscopy. The intensity fluctuation of SEHRS was canceled by dividing SEHRS intensity by SERS intensity on the basis of the binary active site analysis. Thanks to the identification of the plasmons common to both SERS and SEHRS we revealed that an enormous enhancement in SEHRS is ascribed to the electromagnetic (EM) enhancement entirely coupled with longitudinal plasmon modes excluding other kinds of enhancement factors. Our results indicate that EM enhancement factors of metal nanostructures are estimated from spectral information on the longitudinal plasmon resonance band obtained by the scattering or absorption spectra of the nanostructures.
Electronic properties of potassium doped FePc from electron energy-loss spectroscopy
Authors: König A. , Roth F. , Kraus R. , Knupfer M.
Published: June 2009

We have studied the electronic structure of potassium doped iron phthalocyanine (FePc) phases using electron energy-loss spectroscopy. The electronic excitation spectrum of FePc is rather complex and comprises both π-π∗ transitions of the phthalocyanine ligand and transitions that involve the Fe 3d orbitals. This allows deeper insight into the orbital occupation in FePc. Potassium doping, i.e., the addition of electrons to the FePc molecules causes significant changes in the electronic excitations, which signal filling of π∗ as well as Fe 3d orbitals.
Locally induced charged states in La0.89Sr0.11MnO3 single crystals
Authors: Mamin R. F. , Bdikin I. K. , Kholkin A. L.
Published: June 2009

Scanning probe microscopy was used to create and to detect local bias induced charged states in La0.89Sr0.11MnO3 single crystals at room temperature. The lifetime of these nonequilibrium states exceeds 100 h. These bias induced states display also a ferroelectriclike hysteresis with piezoelectric contrast reversed by the applied field. Such states showing reversible multifunctional properties are attractive for modern semiconductor technology with its focus on nonvolatile random-access memories.
Mössbauer studies of complex materials: Energy versus time domain
Authors: Planckaert N. , Callens R. , Demeter J. , Laenens B. , Meersschaut J. , Sturhahn W. , Kharlamova S. , Temst K. , Vantomme A.
Published: June 2009

We present a critical comparison between conventional Mössbauer spectroscopy on the one hand and energy and time resolved nuclear resonant scattering on the other hand. The three Mössbauer techniques are evaluated by the characterization of the complex magnetic structure of an Fe3Al alloy. It is shown how the different scattering processes and detection schemes, which are involved in the respective configurations, determine the specific strengths of the three techniques and how they are optimally suited for the characterization of materials of varying complexity and reduced sizes.
Terahertz generation in GaN diodes operating in pulsed regime limited by self-heating
Authors: Barry E. A. , Sokolov V. N. , Kim K. W. , Trew R. J.
Published: June 2009

The conditions for pulsed regime operation of terahertz power generation in vertical nanoscale GaN-based diodes are investigated via self-consistent simulation of the high-field electron transport in the active channel and thermal transport in the entire device structure. The combined electrothermal model allows for a detailed analysis of the dynamical local distributions of the electric field, drift-velocity, and lattice temperature. We show that stable generation is achievable with a self-heating limited output power of 2.25 W at an operation frequency of 0.71 THz for a pulse width of 3 ns with a few tens of nanosecond duty cycle.
Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon
Authors: Busselez R. , Lefort R. , Guendouz M. , Frick B. , Merdrignac-Conanec O. , Morineau D.
Published: June 2009

Glycerol and trehalose-glycerol binary solutions are glass-forming liquids with remarkable bioprotectant properties. Incoherent quasielastic neutron scattering is used to reveal the different effects of nanoconfinement and addition of trehalose on the molecular dynamics in the normal liquid and supercooled liquid phases, on a nanosecond time scale. Confinement has been realized in straight channels of diameter D=8 nm formed by porous silicon. It leads to a faster and more inhomogeneous relaxation dynamics deep in the liquid phase. This confinement effect remains at lower temperature where it affects the glassy dynamics. The glass transitions of the confined systems are shifted to low temperature with respect to the bulk ones. Adding trehalose tends to slow down the overall glassy dynamics and increases the nonexponential character of the structural relaxation. Unprecedented results are obtained for the binary bioprotectant solution, which exhibits an extremely non-Debye relaxation dynamics as a result of the combination of the effects of confinement and mixing of two constituents.
Magnetic states of zigzag graphene nanoribbons from first principles
Authors: Wu Fang , Kan Erjun , Xiang Hongjun , Wei Su-Huai , Whangbo Myung-Hwan , Yang Jinlong
Published: June 2009

The nature of the magnetic states of zigzag graphene nanoribbons (ZGNRs) was explored on the basis of density functional calculations to understand why they are apparently nonmagnetic. Our study shows that the magnetic moments of ZGNRs are destroyed by p-type or n-type carrier doping with ∼1013 carriers/cm2 per ribbon, which is close to the amount of unpaired spins that ZGNRs are expected to have. Thus the extrinsic sources of carrier doping should be removed to observe the expected magnetic character of ZGNRs.
Solitary wake field microdynamics of the pulsed laser induced microbubbles in three-dimensional dusty plasma liquids
Authors: Tsai Chen-Yu , Teng Lee-Wen , Chang Mei-Chu , Tseng Yu-Ping , I Lin
Published: June 2009

The Eulerian/Lagrangian dynamics in the narrow wake field of the dusty plasma bubble is explored by directly tracking dust motion at the microscopic level. The bubble is induced by the focused laser pulse ablation in three-dimensional quiescent dusty plasma liquids operated in the pressure higher than the critical pressure for the self-excitation of dust acoustic wave by the downward ion wind. It is found that, after bubble expansion ceases, the collective excitation maintains its width and travels downward as a solitary wave, led by an ultrasonic rarefaction front contributed by the dust motion below the lower boundary, and trailed by the few compressional crests with descending crest heights and speeds in the narrow wake, under the symmetry breaking by the downward ion flow. The quick damping of the waves propagating along other directions leads to a narrow wake. Increasing the background pressure causes the more isotropic collapsing of the bubble without wake field oscillation. The role played by dust motion on interacting with and sustaining the wake field evolution is identified and discussed.
Fast pressure probe measurements of a high-velocity plasma plume
Authors: Messer S. , Case A. , Bomgardner R. , Phillips M. , Witherspoon F. D.
Published: June 2009

This article reports measurements of stagnation pressure on a contoured coaxial gun, now installed at the Maryland Centrifugal Experiment [R. Ellis et al., Phys. Plasmas 12, 055704 (2005)]. The impact of the plasma on the stationary probe is consistent with adiabatic compression and supersonic flow. Measured pressure signals are consistent with a shock traveling at 110 km/s and a following flow with speed of 90 km/s. At late times, the pressure profile is consistent with an adiabatically expanding plasma that fills the vacuum chamber.
A reliable method of manufacturing metallic hierarchical superhydrophobic surfaces
Authors: Pogreb Roman , Whyman Gene , Barayev Reuven , Bormashenko Edward , Aurbach Doron
Published: June 2009

A method of manufacturing hierarchical metallic surfaces demonstrating superhydrophobic properties is presented. The surfaces showed apparent contact angles as high as 153° and sliding angles of 10° for 50–100 μl droplets. The Cassie-like model [A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944)], considering the hierarchical topography of the relief, predicts apparent contact angles in a satisfactory agreement with the measured values.
Observation of stimulated Raman scattering in silicon nanocomposites
Authors: Sirleto L. , Ferrara M. A. , Nicotra G. , Spinella C. , Rendina I.
Published: June 2009

In this paper, we report on the observation of stimulated Raman scattering in silicon nanocomposites, consisting of silicon nanoparticles dispersed in SiO2 matrix prepared by sol-gel method. Using a 1427nm cw pump laser, amplification of Stokes signal, at 1542.2nm, up to 1.4dB∕cm is demonstrated. A preliminary valuation of approximately a fivefold enhancement of the gain coefficient in Raman amplifier based on silicon nanocomposites with respect to silicon and a significant reduction of threshold power are also reported. These results have a potential interest for silicon-based Raman lasers.
Structural and electronic properties of the planar C-skeleton polymers
Authors: Nakamura Jun , Arimura Nariaki , Hirayama Motoi , Natori Akiko
Published: June 2009

Atomic arrangements and electronic properties of two-dimensional C-based compounds having the diamondlike skeletons terminated with hydrogen atoms and/or hydroxyl groups, named graphane (poly-C2H2) and planar polymethanol (poly-C2OH2), have been investigated using first-principles calculations within the density functional theory. These planar polymers have direct gaps of 3.32 eV (only with hydrogen terminators) and 1.88 eV (with hydrogen and OH terminators), while crystalline diamond has an indirect band gap. The optical dipole transition between band edges, especially for the planar polymethanol, can be allowed.
Interface structure and the chemical states of Pt film on polar-ZnO single crystal
Authors: Nagata T. , Volk J. , Yamashita Y. , Yoshikawa H. , Haemori M. , Hayakawa R. , Yoshitake M. , Ueda S. , Kobayashi K. , Chikyow T.
Published: June 2009

The interface structures and the chemical states between the Pt layer and polar-ZnO single crystal were investigated. Two-dimensional x-ray diffraction images revealed that Zn-polar ZnO had less mosaicity than the O-polar one. Angle-resolved hard x-ray photoelectron spectroscopy was used to investigate the chemical states of the interface. At the interface of the Pt/Zn-polar ZnO, zinc diffusion into the Pt layer, forming PtZn and ZnPtO bonds, was found. For the O-polar ZnO, in contrast, PtO was predominantly formed at the interface. Zinc diffusion prevented oxidization of the Pt layer and affected the mosaicity of the interface.
Women's fear of childbirth and preference for cesarean section – a cross‐sectional study at various stages of pregnancy in Sweden
Authors: NIEMINEN KATRI , STEPHANSSON OLOF , RYDING ELSA LENA
Published: June 2009

Objective. To investigate Swedish women's level of antenatal fear of childbirth at various gestational ages, and factors associated with intense fear and with preference for cesarean section. Design. A cross‐sectional study. Setting. All antenatal clinics in four geographical areas. Sample. Thousand six hundred and thirty‐five pregnant women at various gestational ages recruited during September–October 2006. Method. A questionnaire completed at the antenatal clinic. The women reported their appraisal of the approaching delivery according to the Wijma Delivery Expectancy/Experience Questionnaire (W‐DEQ). Main outcome measures. The level of fear of childbirth and preferred mode of delivery. Results. Mean W‐DEQ score was 62.8. The prevalence of intense fear of childbirth (W‐DEQ score ≥85) was 15.8% and very intense fear (tocophobia) (W‐DEQ score ≥100) 5.7%. Nulliparous women had a higher mean score than parous women, but more parous women reported an intense fear. Preference for cesarean section was associated with fear of childbirth (OR 11.79, 6.1–22.59 for nulliparous and OR 8.32, 4.36–15.85 for parous women) and for parous women also with a previous cesarean section (OR 18.54, 9.55–35.97), or an instrumental vaginal delivery (OR 2.34, 1.02–5.34). The level of fear of childbirth was not associated with the gestational age. Conclusions. When a woman requests a cesarean section, both primary fear of birth and traumatic childbirth experiences need to be considered and dealt with. The W‐DEQ can be used at any time during pregnancy in order to identify pregnant women who suffer from intense fear of childbirth.
Computed tomographic pulmonary angiography in the assessment of severity of acute pulmonary embolism and right ventricular dysfunction
Authors: Nural M. S. , Elmali M. , Findik S. , Yapici O. , Uzun O. , Sunter A. T. , Erkan L.
Published: June 2009

Background: The distinction between severe pulmonary embolism (PE) and right heart dysfunction is important for predicting patient mortality.

Purpose: To identify the role of computed tomographic pulmonary angiography (CTPA) in the assessment of the severity of acute PE and right ventricular dysfunction.

Material and Methods: Eighty-five patients suspected of having PE, as diagnosed by CTPA and scintigraphy, were divided into three groups: hemodynamically unstable PE (HUPE) (n = 20), hemodynamically stable PE (HSPE) (n = 33), and no PE (n = 32). For each patient, obstruction scores, including short-axis diameters of the right ventricle (RV) and left ventricle (LV), main pulmonary artery, and superior vena cava (SVC), were measured. The RV/LV short-axis ratios were calculated. The shapes of the interventricular septum and the reflux of the contrast medium into the inferior vena cava (IVC) were evaluated. The mortality due to PE within a 1-month follow-up period was recorded.

Results: The median CTPA obstruction score (HUPE 64%, HSPE 28%, P < 0.001), median RV/LV short-axis ratio (HUPE 1.4, HSPE 1.0, P < 0.01), median RV diameter (HUPE 55 mm, HSPE 42 mm, P < 0.001), median SVC diameter (HUPE 23 mm, HSPE 19 mm, P < 0.01), interventricular septum convex toward the LV (HUPE 70%, HSPE 18%, P < 0.001), and reflux of the contrast medium into the IVC (HUPE 65%, HSPE 33%, p < 0.05) were significantly different between the HUPE and HSPE groups. With ROC analysis, the CTPA obstruction score and RV/LV short-axis ratio threshold values for the HUPE patients were calculated to be 48% (95% sensitivity, 76% specificity) and 1.1 (85% sensitivity, 76% specificity), respectively. Three patients in the HUPE group died within the first 24 hours. Logistic regression methods revealed only the RV diameter as a significant predictor of death (odds ratio 1.24; 95% CI 1.04–1.48; P = 0.01).

Conclusion: This study found that the parameters useful for distinguishing HUPE and HSPE included CTPA obstruction score, RV and SVC diameters, RV/LV short-axis ratio, interventricular septum shape, and reflux into the IVC. RV dilatation may be a significant predictor for mortality.
Diagnostic accuracy of 18f-2-deoxy-fluoro-d-glucose positron emission tomography for pn1 lymph nodes in patients with lung cancer
Authors: Nakagawa M. , Hara M. , Sakurai K. , Ozawa Y. , Mizuno A. , Tamaki T. , Nishio M. , Shibamoto Y.
Published: June 2009

Background: Nodal status has been reported to be one of the most important factors affecting survival in patients with lung cancer. For determining treatment strategy, accurate evaluation of nodal status is expected.

Purpose: To evaluate the accuracy of 18F-2-deoxy-fluoro-D-glucose (FDG) positron emission tomography (PET) for diagnosing nodal status in lung cancer patients with pathologically proven N1 (pN1) lymph node metastases, in comparison with that of computed tomography (CT).

Material and Methods: Nineteen pN1 patients with primary lung cancer undergoing preoperative CT and FDG-PET were investigated. The diagnosis was confirmed by surgery in all patients. Lymph nodes were considered to be positive when uptake higher than the surrounding mediastinum level was visually observed. Radiological and pathological correlation was investigated, and the association between FDG uptake and the size of metastatic nodes was evaluated.

Results: Of the 19 pN1 patients, nodal stage determined by FDG-PET was cN0 in eight, cN1 in four, cN2 in six, and cN3 in one. Thus, FDG-PET provided correct N-staging in 21%, under-staging in 42%, and over-staging in 37%. FDG-PET could not depict pN1 lymph node in six (32%) of 19 patients. In two patients (11%), mild symmetrical hilar and mediastinal accumulation was found and considered as benign physiological uptake. In six patients (32%), the ipsilateral mediastinal uptake was depicted and diagnosed as cN2. One patient was diagnosed as cN3 because of FDG accumulation at the supraclavicular fossa. On CT, nodal staging was cN0 in nine, cN1 in six, and cN2 in four. CT staging was therefore correct in 32%, underestimated in 47%, and overestimated in 21%.

Conclusion: The diagnostic accuracy of FDG-PET (21%) was low and similar to that of CT (32%); under- and over-diagnosis were found in similar proportions. The limitation of FDG-PET should be recognized when nodal staging might alter the therapeutic strategy in patients with primary lung cancer.
Book Reviews
Authors: Skaane Per
Published: June 2009

Crushed Stone-like Calcifications: The Most Frequent Malignant Type (Breast Cancer: Early Detection with Mammography). By L. Tabar, T. Tot, & P. B. Dean. Stuttgart: Georg Thieme Verlag, 2008. ISBN: 978-3-13-148531-1. 312 pages, 1022 illustrations. Price (hardcover): EUR 109.95
Radiofrequency ablation of colorectal liver metastases downstaged by chemotherapy
Authors: Knudsen Anders Riegels , Kannerup Anne-Sofia , Mortensen Frank Viborg , Nielsen Dennis Tønner
Published: June 2009

Background: Radiofrequency ablation (RFA) continues to evolve, improving the potentials of this technique. It is now a widely used procedure in the treatment of patients with unresectable colorectal liver metastases, increasing the number of potentially curable patients.

Purpose: To evaluate the long-term survival of patients treated by RFA for colorectal liver metastases after downstaging by systemic chemotherapy.

Material and Methods: In a retrospective review of our prospective colorectal liver metastasis RFA database, 36 patients (20 males, 16 females; median age 67 years) were identified during an 8-year period (1999–2007). All patients were initially unsuitable for local treatment, and referred to systemic chemotherapy by our multidisciplinary team. Multinodularity and/or location of tumor was the main cause of patients being unsuitable for local treatment. Chemotherapy mainly consisted of 5-fluorouracil and leucovorin combined with oxaliplatin or irinotecan. After downstaging with chemotherapy, patients were treated by RFA. Patients with extrahepatic disease were excluded from RFA treatment. Pre- and posttreatment evaluation was performed with multidetector computed tomography (MDCT) scans.

Results: The median time from diagnosis of hepatic metastases to first RFA was 10 months. A total of 158 tumors were treated with RFA during the study period. Median follow-up period was 27 months. The estimated median survival time after diagnosis of hepatic metastasis was 39 months, with a 5-year survival rate of 34%.

Conclusion: In selected patients with colorectal liver metastases downstaged by chemotherapy, RFA is an important modality that may contribute to improved survival. Furthermore, all patients responding to systemic chemotherapy should be re-evaluated by a multidisciplinary team.
Private Lives
Authors: Rozenberg Joshua
Published: June 2009

Joshua Rozenberg considers the impact of an ever expanding privacy law
The Press Strikes Back
Authors: Roque Harry
Published: June 2009

Journalists in the Philippines are challenging the use of libel actions to silence reporting, says Harry Roque
A Matter of Honour
Authors: McNamara Lawrence
Published: June 2009

Lawrence McNamara puts reputation in the balance and considers why it needs legal protection
Law Warp
Authors: Brett Alastair
Published: June 2009

Libel online is governed by arcane legislation that even pre-dates the invention of the light bulb. It’s time for reform, says Alastair Brett
Tiananmen Remembered
Authors: Dan Wang , Xinran
Published: June 2009

Wang Dan, a leading figure in the 1989 protests, talks to the writer Xinran about the fallout and the legacy
Global Snapshot
Authors: Spencer Oliver
Published: June 2009

Around the world, defamation legislation cripples free speech. Oliver Spencer separates the bad from the worst in a survey
Through the Looking-Glass
Authors: Abrams Floyd
Published: June 2009

English libel law turns US protection for free speech on its head. Floyd Abrams considers how the UK became an international libel tribunal
In God’s Name
Authors: Haraszti Miklos
Published: June 2009

The growing trend for criminalising criticism of religion is a declaration of war on freedom of speech, says Miklos Haraszti
A Bias for Freedom
Authors: Kampfner John
Published: June 2009

The Index on Censorship Freedom of Expression Awards took place in April. Chief executive John Kampfner reports on the evening
Retinal Vascular Caliber and Diabetes in a Multiethnic Asian Population
Authors: JEGANATHAN V. SWETHA E. , SABANAYAGAM CHARUMATHI , TAI E. SHYONG , LEE JEANNETTE , LAMOUREUX ECOSSE , SUN CONG , KAWASAKI RYO , WONG TIEN Y.
Published: June 2009

Objective: The aim of this study was to examine the relationship of retinal vascular caliber with diabetes and impaired fasting glucose (IFG) in a multiethnic Asian population.

Methods: This work was a population‐based cross‐sectional study comprising 3,404 Singaporean Chinese, Indian, and Malay participants. Retinal arteriolar and venular diameters, CRAE and CRVE, respectively were measured from digital retinal photographs. Diabetes was defined as physician‐diagnosis of diabetes, self‐reported use of diabetic medication, or fasting plasma glucose (FPG) ≥ 7 mmol/L; IFG as FPG 6.1–6.9 mmol/L.

Results: After adjusting for age, gender, ethnicity, systolic blood pressure, body mass index, total cholesterol, triglycerides, smoking, and vascular caliber (Model 3), participants with diabetes had both larger CRAE and CRVE, compared to those with normal fasting glucose (NFG) or IFG. In a multivariate analysis, including clinical risk factors and CRVE, mean CRAE increased from 143.6 μm in NFG to 145.3 μm with diabetes (P for trend = 0.01). On the other hand, each mmol/L increase in FPG was associated with a 0.51‐μm increase in CRVE (P=0.006). In a subgroup analysis stratified by ethnicity, the association between FPG and larger CRVE was predominantly present among ethnic Indians (0.9‐μm increase in CRVE per mmol/L increase in FPG).

Conclusion: Diabetes was associated with larger retinal arteriolar diameters and glucose level was associated with larger retinal venular diameters in this multiethnic Asian population. The magnitude of association between glucose level and venular widening was stronger among ethnic Indians.
Emergency Legal Preparedness for Hospitals and Health Care Personnel
Authors: Hodge James G. , Garcia Andrea M. , Anderson Evan D. , Kaufman Torrey
Published: June 2009

During the past decade, hospital emergency preparedness has become a focus of local, state, and federal governments seeking to address emergencies or disasters that affect the public health. Integral to hospital emergency preparedness are numerous legal challenges that hospitals and their health care personnel face during declared states of emergencies. In this article, we evaluate legal requirements for hospital emergency preparedness, key legal concerns that hospitals should consider in emergency preparedness activities, and how the changing legal landscape during emergencies necessitates real-time decision making. We then analyze legal issues including negligence, discrimination, and criminal culpability that may arise during or after medical triage. Finally, we examine the legal risks of evading preparedness, specifically asking how a hospital and its personnel may be held liable for failing to plan or prepare for an emergency. (Disaster Med Public Health Preparedness. 2009;3(Suppl 1):S37–S44)