bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetism in galaxies – Observational overview and next generation radio telescopes
Authors: Beck Rainer
Published: June 2011

The strength and structure of cosmic magnetic fields is best studied by observations of radio continuum emission, its polarization and its Faraday rotation. Fields with a well-ordered spiral structure exist in many types of galaxies. Total field strengths in spiral arms and bars are 20–30 μG and dynamically important. Strong fields in central regions can drive gas inflows towards an active nucleus. The strongest regular fields (10–15 μG) are found in interarm regions, sometimes forming “magnetic spiral arms” between the optical arms. The typical degree of polarization is a few % in spiral arms, but high (up to 50%) in interarm regions. The detailed field structures suggest interaction with gas flows. Faraday rotation measures of the polarization vectors reveals large-scale patterns in several spiral galaxies which are regarded as signatures of large-scale (coherent) fields generated by dynamos. – Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission traces low-energy cosmic ray electrons which can propagate further away from their origin. LOFAR (30–240 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way. Polarization at higher frequencies (1–10 GHz), to be observed with the EVLA, MeerKAT, APERTIF and the SKA, will trace magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP and the SKA are dedicated to measure magnetic fields in distant intervening galaxies and clusters, and will be used to model the overall structure and strength of the magnetic field in the Milky Way.
On the solution of the Kompaneets equation in cosmological context: a numerical code to predict the CMB spectrum under general conditions
Authors: Burigana C. , Procopio P. , De Rosa A.
Published: June 2011

Interpretation of current and future data calls for a continuous improvement in the theoretical modeling of CMB spectrum. We describe the new version of a numerical code, KYPRIX, specifically written to solve the Kompaneets equation in a cosmological context under general assumptions. We report on the equation formalism, and structure and computational aspects of the code. New physical options have been introduced in the current code version: the cosmological constant in the terms controlling the general expansion of the Universe, the relevant chemical abundances, and the ionization history, from recombination to cosmological reionization. We present some of fundamental tests we carried out to verify the accuracy, reliability, and performance of the code. All the tests demonstrate the reliability and versatility of the new code version and its accuracy and applicability to the scientific analysis of current CMB spectrum data and of much more precise measurements that will be available in the future.
An XMM-Newton view of a small sample of Seyfert, 1 Galaxies
Authors: Cardaci M. V. , Hagele G. F. , Santos-Lleó M. , Krongold Y. , Díaz A. I. , Rodriguez-Pascual P.
Published: June 2011

We present a detailed analysis of all the X-ray data taken by the XMM-Newton satellite of a small sample of five Seyfert 1 galaxies: ESO 359-G19, HE 1143-1810, CTS A08.12, Mkn 110, and UGC 11763. Our aim is to characterize the different components of the material that print the absorption and emission features in the X-ray spectra of these objects. The continuum emission was studied through the EPIC spectra taking advantage of the spectral range of these cameras. The high resolution RGS spectra were analyzed in order to characterize the absorbing features and the emission line features that arise in the spectra of these sources.
How can vorticity be produced in irrotationally forced flows?
Authors: Sordo Fabio Del , Brandenburg Axel
Published: June 2011

A spherical hydrodynamical expansion flow can be described as the gradient of a potential. In that case no vorticity should be produced, but several additional mechanisms can drive its production. Here we analyze the effects of baroclinicity, rotation and shear in the case of a viscous fluid. Those flows resemble what happens in the interstellar medium. In fact in this astrophysical environment supernovae explosion are the dominant flows and, in a first approximation, they can be seen as spherical. One of the main difference is that in our numerical study we examine only weakly supersonic flows, while supernovae explosions are strongly supersonic.
Numerical study of jets produced by conical wire arrays on the Magpie pulsed power generator
Authors: Bocchi Matteo , Chittenden Jerry P. , Ciardi Andrea , Suzuki-Vidal Francisco , Hall Gareth N. , de Grouchy Phil , Lebedev Sergei V. , Bott Simon C.
Published: June 2011

With the aim to model jets produced by conical wire arrays on the MAGPIE generator, and to strengthen the link between laboratory and astrophysical jets, we performed three-dimensional magneto-hydro-dynamic numerical simulations using the code GORGON and successfully reproduced the experiments. We found that a minimum resolution of ~100 μm is required to retrieve the unstable character of the jet. Moreover, arrays with less wires produce more unstable jets with stronger magnetic fields around them.
Magnetic field amplification by relativistic shocks in a turbulent medium
Authors: Mizuno Yosuke , Pohl Martin , Niemiec Jacek , Zhang Bing , Nishikawa Ken-Ichi , Hardee Philip E.
Published: June 2011

We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneities, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in our two-dimensional simulations. The magnetic energy spectrum is flatter than Kolmogorov and indicates that a so-called small-scale dynamo is operating in the postshock region. We also find that the amount of magnetic-field amplification depends on the direction of the mean preshock magnetic field.
3D turbulent reconnection driven current-sheet dynamics: solar applications
Authors: Bettarini Lapo , Lapenta Giovanni
Published: June 2011

We provide a complete three-dimensional picture of the reconnecting dynamics of a current-sheet. Recently, a two-dimensional non-steady reconnection dynamics has been proved to occur without the presence of any anomalous effect (Lapenta, 2008, Skender & Lapenta, 2010, Bettarini & Lapenta, 2010) but such a picture must be confirmed in a full three-dimensional configuration wherein all instability modes are allowed to drive the evolution of the system, i.e. to sustain a reconnection dynamics or to push the system along a different instability path. Here we propose a full-space analysis allowing us to determine the longitudinal and, possibly, the transversal modes driving the different current-sheet disruption regimes, the corresponding characteristic time-scales and to study system's instability space- parameter (plasma beta, Lundquist and Reynolds numbers, system's aspect ratio). The conditions leading to an explosive evolution rather then to a diffusive dynamics as well as the details of the reconnection inflow/outflow regime at the disruption phase are determined. Such system embedded in a solar-like environment and undergoing a non-steady reconnection evolution may determine the formation both of jets and waves influencing the dynamics and energetic of the upper layers and of characteristic down-flows as observed in the low solar atmosphere.
Assessing the detail needed to capture rainfall‐runoff dynamics with physics‐based hydrologic response simulation
Authors: Mirus Benjamin B. , Ebel Brian A. , Heppner Christopher S. , Loague Keith
Published: June 2011

Concept development simulation with distributed, physics‐based models provides a quantitative approach for investigating runoff generation processes across environmental conditions. Disparities within data sets employed to design and parameterize boundary value problems used in heuristic simulation inevitably introduce various levels of bias. The objective was to evaluate the impact of boundary value problem complexity on process representation for different runoff generation mechanisms. The comprehensive physics‐based hydrologic response model InHM has been employed to generate base case simulations for four well‐characterized catchments. The C3 and CB catchments are located within steep, forested environments dominated by subsurface stormflow; the TW and R5 catchments are located in gently sloping rangeland environments dominated by Dunne and Horton overland flows. Observational details are well captured within all four of the base case simulations, but the characterization of soil depth, permeability, rainfall intensity, and evapotranspiration differs for each. These differences are investigated through the conversion of each base case into a reduced case scenario, all sharing the same level of complexity. Evaluation of how individual boundary value problem characteristics impact simulated runoff generation processes is facilitated by quantitative analysis of integrated and distributed responses at high spatial and temporal resolution. Generally, the base case reduction causes moderate changes in discharge and runoff patterns, with the dominant process remaining unchanged. Moderate differences between the base and reduced cases highlight the importance of detailed field observations for parameterizing and evaluating physics‐based models. Overall, similarities between the base and reduced cases indicate that the simpler boundary value problems may be useful for concept development simulation to investigate fundamental controls on the spectrum of runoff generation mechanisms.
Neuroreceptor Quantitation in vivo by the Steady-State Principle Using Constant Infusion or Bolus Injection of Radioactive Tracers
Authors: Lassen Niels A.
Published: June 2011

The approaches hitherto used for measuring the kinetic constants Kd and Bmax of neuroreceptors in vivo all violate the steady state of the system. This complicates the kinetic analysis as approximations must be made, introducing errors of unknown magnitude. The present study presents the theory for designing experiments in which the steady state is preserved. It is based on maintaining a constant degree of receptor binding (occupancy) throughout the experiment. This is achieved by administering by prolonged intravenous infusion the non-radioactive ligand one wishes to study. The fraction of receptor sites not occupied by the “cold” ligand is measured by using trace amounts of a radioactive ligand binding to the same receptor. A minimum of two studies at different occupancies must be performed. In this presentation it is proposed to make the second study at essentially zero receptor occupancy by administering the tracer alone. The pair of tracer studies, the one without and the other with infusion of cold ligand, allows calculation of the cold ligand's equilibrium dissociation constant Kd. In the special case when tracer and cold ligands are chemically identical, then Bmax can also be calculated. Two different modes of tracer administration can be used. If the tracer is also infused at a constant rate for a long time, then the occupancy of receptor sites by the cold ligand can be calculated by measuring the equilibrium tracer concentrations in brain and plasma. If the tracer is administered as an intravenous bolus injection, then the area under the brain and plasma radioactivity curves or compartmental analysis must be used. The bolus injection approach, described in this paper for the first time, has the highest overall counting efficiency and should therefore be particularly suited for studies in man using positron emission tomography (PET) or single photon emission tomography (SPECT). Tracer infusion is the method of choice for animal experiments, as only one set of values are needed, those at long time, as can be obtained post vivo by counting samples of brain or by using autoradiographic techniques. The steady-state principle shows that ligands with very low Kd values, i.e., with very high affinity, are not suited for receptor quantitation.
Cerebral Artery Dilatation Maintains Cerebral Oxygenation at Extreme Altitude and in Acute Hypoxia—An Ultrasound and MRI Study
Authors: Wilson Mark H , Edsell Mark EG , Davagnanam Indran , Hirani Shashivadan P , Martin Dan S , Levett Denny ZH , Thornton John S , Golay Xavier , Strycharczuk Lisa , Newman Stanton P , Montgomery Hugh E , Grocott Mike PW , Imray Christopher HE ,   for the Caudwell Xtreme Everest Research Group
Published: June 2011

Transcranial Doppler is a widely used noninvasive technique for assessing cerebral artery blood flow. All previous high altitude studies assessing cerebral blood flow (CBF) in the field that have used Doppler to measure arterial blood velocity have assumed vessel diameter to not alter. Here, we report two studies that demonstrate this is not the case. First, we report the highest recorded study of CBF (7,950 m on Everest) and demonstrate that above 5,300 m, middle cerebral artery (MCA) diameter increases ( n = 24 at 5,300 m, 14 at 6,400 m, and 5 at 7,950 m). Mean MCA diameter at sea level was 5.30 mm, at 5,300 m was 5.23 mm, at 6,400 m was 6.66 mm, and at 7,950 m was 9.34 mm ( P<0.001 for change between 5,300 and 7,950 m). The dilatation at 7,950 m reversed with oxygen. Second, we confirm this dilatation by demonstrating the same effect (and correlating it with ultrasound) during hypoxia (FiO2 = 12% for 3 hours) in a 3-T magnetic resonance imaging study at sea level ( n = 7). From these results, we conclude that it cannot be assumed that cerebral artery diameter is constant, especially during alterations of inspired oxygen partial pressure, and that transcranial 2D ultrasound is a technique that can be used at the bedside or in the remote setting to assess MCA caliber.
Current Issues: A Group Supervisory Approach to Preschool Fluency Therapy
Authors: Subramanian Anu
Published: June 2011

Blended individual-group supervision (BIGS) was described by Murphy and Watson (2004) as a technique to combine both individual and group supervision styles using the tenets of the teaching clinic (Dowling, 1979). The present article uses a modified version of BIGS to supervise student clinicians working with preschool children who exhibit dysfluencies. The therapy techniques used include direct techniques such as speaking in fast and slow rates of speech and choral reading. Parent education is an integral part of the therapy process. This includes providing parents with information about stuttering and fluency enhancing conditions while also giving parents the opportunity to utilize these techniques in the session. Student clinicians learn to incorporate fluency enhancing conditions in sessions and to have close interaction with parents. Therapy for older children (5-year-olds) integrates more direct strategies to reduce dysfluencies. Supervisory meetings are comprised of group meetings, and students come prepared with questions and interact with each other and the clinical supervisor in order to plan and implement therapy.
Analysis of heart rate variability signal in meditation using second-order difference plot
Authors: Goswami Damodar Prasad , Tibarewala Dewaki Nandan , Bhattacharya Dilip Kumar
Published: June 2011

In this article, the heart rate variability signal taken from subjects practising different types of meditations have been investigated to find the underlying similarity among them and how they differ from the non-meditative condition. Four different groups of subjects having different meditation techniques are involved. The data have been obtained from the Physionet and also collected with our own ECG machine. For data analysis, the second order difference plot is applied. Each of the plots obtained from the second order differences form a single cluster which is nearly elliptical in shape except for some outliers. In meditation, the axis of the elliptical cluster rotates anticlockwise from the cluster formed from the premeditation data, although the amount of rotation is not of the same extent in every case. This form study reveals definite and specific changes in the heart rate variability of the subjects during meditation. All the four groups of subjects followed different procedures but surprisingly the resulting physiological effect is the same to some extent. It indicates that there is some commonness among all the meditative techniques in spite of their apparent dissimilarity and it may be hoped that each of them leads to the same result as preached by the masters of meditation. The study shows that meditative state has a completely different physiology and that it can be achieved by any meditation technique we have observed. Possible use of this tool in clinical setting such as in stress management and in the treatment of hypertension is also mentioned.
On the numerical simulation of the diffuse arc in a vacuum interrupter
Authors: Langlois Y. , Chapelle P. , Jardy A. , Gentils F.
Published: June 2011

A 2D two-fluid numerical model is developed for the description of the diffuse arc in a vacuum interrupter under the possible influence of an axial magnetic field (AMF). This model incorporates the energy balance equations for both ions and electrons and takes into account the three components of the self-generated magnetic field. The possibility of both supersonic (at low current density) and subsonic (at high current density) plasma flow regimes is considered. Data from the literature are used to specify the values of the plasma parameters near the cathode, and the boundary conditions on the anode boundary rely on a simplified model of the anode sheath. Simulation results are presented for both ion flow regimes, with special attention to the current and plasma flow features. It is shown that there is always a contraction of the current flow, whereas the dynamics of the ions throughout the interelectrode gap is strongly influenced by their flow regime near the cathode. Finally, the influence of various operating parameters (presence of an AMF, gap length) on the current constriction at the anode is discussed.
Time-domain analysis and experimental examination of cumulative second-harmonic generation by primary Lamb wave propagation
Authors: Deng Mingxi , Xiang Yanxun , Liu Liangbing
Published: June 2011

Within the second-order perturbation approximation, the physical process of cumulative second-harmonic generation by the primary Lamb wave propagation has been investigated in the time domain. Based on the preconditions that the transfer of energy from the primary Lamb wave to the double frequency Lamb wave is not zero and that the phase velocity matching condition is satisfied, we focus on analyzing the influence of mismatching of the group velocities on the generation of the second harmonic by propagation of a primary Lamb wave tone burst with a finite duration. Our analysis indicates that the time-domain envelope of the second harmonic generated is dependent on the propagation distance when both the duration of the primary Lamb wave tone burst and the group velocity mismatch are given. Furthermore, it can be concluded that the integrated amplitude of the time-domain second harmonic, which quantifies the efficiency of the second-harmonic generation, grows with the propagation distance even when the group velocity matching condition is not satisfied. The experimental examination has been performed, and it verifies our theoretical analysis.
Kinetic description of quasi-stationary axisymmetric collisionless accretion disk plasmas with arbitrary magnetic field configurations
Authors: Cremaschini Claudio , Miller John C. , Tessarotto Massimo
Published: June 2011

A kinetic treatment is developed for collisionless magnetized plasmas occurring in high-temperature, low-density astrophysical accretion disks, such as are thought to be present in some radiatively inefficient accretion flows onto black holes. Quasi-stationary configurations are investigated, within the framework of a Vlasov-Maxwell description. The plasma is taken to be axisymmetric and subject to the action of slowly time-varying gravitational and electromagnetic fields. The magnetic field is assumed to be characterized by a family of locally nested but open magnetic surfaces. The slow collisionless dynamics of these plasmas is investigated, yielding a reduced gyrokinetic Vlasov equation for the kinetic distribution function. For doing this, an asymptotic quasi-stationary solution is first determined, represented by a generalized bi-Maxwellian distribution expressed in terms of the relevant adiabatic invariants. The existence of the solution is shown to depend on having suitable kinetic constraints and conditions leading to particle trapping phenomena. With this solution, one can treat temperature anisotropy, toroidal and poloidal flow velocities, and finite Larmor-radius effects. An asymptotic expansion for the distribution function permits analytic evaluation of all the relevant fluid fields. Basic theoretical features of the solution and their astrophysical implications are discussed. As an application, the possibility of describing the dynamics of slowly time-varying accretion flows and the self-generation of magnetic field by means of a “kinetic dynamo effect” are discussed. Both effects are shown to be related to intrinsically kinetic physical mechanisms.
Simulations of the confinement of ubiquitin in self-assembled reverse micelles
Authors: Tian Jianhui , García Angel E.
Published: June 2011

We describe the effects of confinement on the structure, hydration, and the internal dynamics of ubiquitin encapsulated in reverse micelles (RM). We performed molecular dynamics simulations of the encapsulation of ubiquitin into self-assembled protein/surfactant reverse micelles to study the positioning and interactions of the protein with the RM and found that ubiquitin binds to the RM interface at low salt concentrations. The same hydrophobic patch that is recognized by ubiquitin binding domains  in vivo is found to make direct contact with the surfactant head groups, hydrophobic tails, and the iso-octane solvent. The fast backbone N-H relaxation dynamics show that the fluctuations of the protein encapsulated in the RM are reduced when compared to the protein in bulk. This reduction in fluctuations can be explained by the direct interactions of ubiquitin with the surfactant and by the reduced hydration environment within the RM. At high concentrations of excess salt, the protein does not bind strongly to the RM interface and the fast backbone dynamics are similar to that of the protein in bulk. Our simulations demonstrate that the confinement of protein can result in altered protein dynamics due to the interactions between the protein and the surfactant.
Spectral conversion for solar cell efficiency enhancement using YVO4:Bi3+,Ln3+ (Ln = Dy, Er, Ho, Eu, Sm, and Yb) phosphors
Authors: Huang X. Y. , Wang J. X. , Yu D. C. , Ye S. , Zhang Q. Y. , Sun X. W.
Published: June 2011

Bi3+–Ln3+ (Ln = Dy, Er, Ho, Eu, and Sm) co-doped YVO4 phosphors are proposed as UV-absorbing luminescent converter candidate to enhance the power conversion efficiency and photochemical stability of dye-sensitized solar cells (DSSCs). The phosphors can efficiently convert UV photons in a broad range from 250 to 400 nm into visible emissions, which can be absorbed by DSSCs. Efficient broadband down-conversion UV light into near-infrared emission around 1000 nm was achieved in the YVO4:Bi3+,Yb3+ phosphors. The energy transfer from V5+–Bi3+ charge-transfer state to Yb3+ was shown to be a cooperative down-conversion type by the luminescence spectra, energy transfer efficiency, and luminescence decay curves. The YVO4:Bi3+,Yb3+ phosphors are promising for boosting the efficiency of crystalline silicon solar cells by down-converting the UV part of the solar spectrum to near-infrared photons with a twofold increase in the photon number. This research may open up promising new perspectives for designing novel luminescent materials for photovoltaic cells with high efficiency.
Three-dimensional nanojunction device models for photovoltaics
Authors: Wangperawong Artit , Bent Stacey F.
Published: June 2011

A model is developed to describe the behavior of three-dimensionally nanostructured photovoltaic devices, distinguishing between isolated radial pn junctions and interdigitated pn junctions. We examine two specific interdigitated architectures, the point-contact nanojunction and the extended nanojunction, which are most relevant to experimental devices reported to date but have yet to be distinguished in the field. The model is also applied to polycrystalline CdTe devices with inverted grain boundaries. We demonstrate that for CdTe/CdS solar cells using low-quality materials, the efficiency of the extended nanojunction geometry is superior to other designs considered.
Analysis of backside-electrode and gate-field-plate effects on buffer-related current collapse in AlGaN/GaN high electron mobility transistors
Authors: Horio Kazushige , Onodera Hiraku , Nakajima Atsushi
Published: June 2011

Two-dimensional transient analysis of gate-field-plate AlGaN/GaN high electron mobility transistors with a backside electrode is performed by considering a deep donor and a deep acceptor in a buffer layer. Effects of introducing a field plate and a backside electrode on buffer-related lag and current collapse are studied. It is shown that gate field plate introduction is effective in reducing lag and current collapse when the acceptor density in the buffer layer is high. On the other hand, backside electrode introduction is shown to be effective in reducing drain lag and current collapse, particularly when the acceptor density in the buffer layer is relatively low, because the fixed potential at the backside electrode reduces electron injection into the buffer layer and the resulting trapping effects.
Surface damage on diamond membranes fabricated by ion implantation and lift-off
Authors: Drumm V. S. , Alves A. D. C. , Fairchild B. A. , Ganesan K. , McCallum J. C. , Jamieson D. N. , Prawer S. , Rubanov S. , Kalish R. , Feldman L. C.
Published: June 2011

Thin membranes with excellent optical properties are essential elements in diamond based photonic systems. Due to the chemical inertness of diamond, ion beam processing must be employed to carve photonic structures. One method to realize such membranes is ion-implantation graphitization followed by chemical removal of the sacrificial graphite. The interface revealed when the sacrificial layer is removed has interesting properties. To investigate this interface, we employed the surface sensitive technique of grazing angle channeled Rutherford backscattering spectroscopy. Even after high temperature annealing and chemical etching a thin layer of damaged diamond remains, however, it is removed by hydrogen plasma exposure.
Enhanced magnetoresistance in naturally oxidized MgO-based magnetic tunnel junctions with ferromagnetic CoFe/CoFeB bilayers
Authors: Schreiber D. K. , Choi Y-S , Liu Yuzi , Chiaramonti Ann N. , Seidman David N. , Petford-Long A. K.
Published: June 2011

Three-dimensional elemental distributions in magnetic tunnel junctions containing naturally oxidized MgO tunnel barriers are characterized using atom-probe tomography. Replacing the CoFeB free layer (reference layer) with a CoFe/CoFeB (CoFeB/CoFe) bilayer increases the magnetoresistance from 105% to 192% and decreases the resistance-area product from 14.5 to 3.4 Ω μm2. The CoFe/CoFeB bilayer improves the compositional uniformity within the free layer by nucleating CoFeB crystals across the entire layer, resulting in a homogeneous barrier/free layer interface. In contrast, the simple CoFeB free layer partially crystallizes with composition differences from grain to grain (5–30 nm), degrading the tunnel junction performance.
Coercivity of ordered arrays of magnetic Co nanowires with controlled variable lengths
Authors: Vivas L. G. , Yanes R. , Chubykalo-Fesenko O. , Vazquez M.
Published: June 2011

Ordered hexagonal arrays of Co nanowires were prepared using anodic aluminum oxide templates, varying the nanowire length in a controlled way. The measured coercivity values were shown to decrease with the increase in the nanowire aspect ratio, in contrast to the behavior expected from the shape anisotropy. The measurements were interpreted considering the change in the preferred crystalline structure, from fcc cubic to hcp hexagonal in small and high aspect ratio nanowires, respectively. The experimental evolution of coercivity with nanowires length is interpreted considering micromagnetic simulations taking into account the change in their crystalline structure.
Low temperature near-field scanning optical microscopy on infrared and terahertz photonic-crystal quantum cascade lasers
Authors: Moldovan-Doyen I. C. , Xu G. , Greusard L. , Sevin G. , Strupiechonski E. , Beaudoin G. , Sagnes I. , Khanna S. P. , Linfield E. H. , Davies A. G. , Colombelli R. , De Wilde Y.
Published: June 2011

We report the development of a scattering-type near-field scanning optical microscope (sNSOM) which operates at temperatures down to 100 K with a scanning range of up to 400 μm. We have used this sNSOM to map the electromagnetic near-field on mid-IR and terahertz (THz) surface emitting quantum cascade lasers with photonic-crystal resonators. Mid-IR devices operate at λ=7.5 μm (40 THz) while THz devices operate at λ≈110 μm (2.7 THz). The near-field images—in agreement with numerical calculations—demonstrate an instrument resolution of 100's nm.
Note: Stacked rings for terahertz wave-guiding
Authors: de Rijk E. , Macor A. , Hogge J-Ph. , Alberti S. , Ansermet J-Ph.
Published: June 2011

We demonstrate the construction of corrugated waveguides using stacked rings to propagate terahertz frequencies. The waveguide allows propagation of the same fundamental mode as an optical-fiber, namely, the HE11 mode. This simple concept opens the way for corrugated wave-guides up to several terahertz, maintaining beam characteristics as for terahertz applications.
Low-loss asymmetric strip-loaded slot waveguides in silicon-on-insulator
Authors: Ding Ran , Baehr-Jones Tom , Kim Woo-Joong , Boyko Bryan , Bojko Richard , Spott Alexander , Pomerene Andrew , Hill Craig , Reinhardt Wesley , Hochberg Michael
Published: June 2011

We report on low-loss asymmetric strip-loaded slot waveguides in silicon-on-insulator fabricated with 248 nm photolithography. Waveguide losses were 2 dB/cm or less at wavelengths near 1550 nm. A 40 nm strip-loading allows low-resistance electrical contact to be made to the two slot arms. The asymmetric design suppresses the TE1 mode while increasing the wavelength range for which the TE0 mode guides. This type of waveguide is suitable for building low insertion-loss, high-bandwidth, low drive-voltage modulators, when coated with an electro-optic polymer cladding.
Radiation induced control of electric field in Au/CdTe/In structures
Authors: Franc J. , Dědič V. , Sellin P. J. , Grill R. , Veeramani P.
Published: June 2011

In this contribution we demonstrate both experimentally and theoretically the possibility to control the profile of internal electric field by compensation of the space charge formed by carriers trapped at deep levels QT with space charge present due to band bending at the metal/CdTe interface QM. The demonstrated mechanism represents a promising way to decrease the problems associated with charge collection efficiency in CdTe x-ray detectors operated at high fluxes of x-ray photons.
Theoretical analysis of carrier mobility in organic field-effect transistors
Authors: Xu Yong , Balestra Francis , Ghibaudo Gerard
Published: June 2011

A theoretical analysis of the carrier mobility in organic transistors is presented. We noticed that the assumption of zero potential at open/quasi-free surface may cause a large deviation of the areal charge density in the organic film, greater in thinner-film transistors. Taking into account this effect, the effective mobility is obtained using the Kubo–Greenwood integral, which provides the total conductivity in the band and thus in the whole organic film. The mobility is studied with respect to gate voltage and temperature, for various disorder and transport diffusivity levels, enabling a better insight of the carrier mobility in organic transistors.
μ-Conotoxins that differentially block sodium channels NaV1.1 through 1.8 identify those responsible for action potentials in sciatic nerve
Authors: Wilson Michael J. , Yoshikami Doju , Azam Layla , Gajewiak Joanna , Olivera Baldomero M. , Bulaj Grzegorz , Zhang Min-Min
Published: June 2011

Voltage-gated sodium channels (VGSCs) are important for action potentials. There are seven major isoforms of the pore-forming and gate-bearing α-subunit (NaV1) of VGSCs in mammalian neurons, and a given neuron can express more than one isoform. Five of the neuronal isoforms, NaV1.1, 1.2, 1.3, 1.6, and 1.7, are exquisitely sensitive to tetrodotoxin (TTX), and a functional differentiation of these presents a serious challenge. Here, we examined a panel of 11 μ-conopeptides for their ability to block rodent NaV1.1 through 1.8 expressed inXenopusoocytes. Although none blocked NaV1.8, a TTX-resistant isoform, the resulting “activity matrix” revealed that the panel could readily discriminate between the members of all pair-wise combinations of the tested isoforms. To examine the identities of endogenous VGSCs, a subset of the panel was tested on A- and C-compound action potentials recorded from isolated preparations of rat sciatic nerve. The results show that the major subtypes in the corresponding A- and C-fibers were NaV1.6 and 1.7, respectively. Ruled out as major players in both fiber types were NaV1.1, 1.2, and 1.3. These results are consistent with immunohistochemical findings of others. To our awareness this is the first report describing a qualitative pharmacological survey of TTX-sensitive NaV1 isoforms responsible for propagating action potentials in peripheral nerve. The panel of μ-conopeptides should be useful in identifying the functional contributions of NaV1 isoforms in other preparations.
The Role Played by Contaminated Surfaces in the Transmission of Nosocomial Pathogens
Authors: Otter Jonathan A. , Yezli Saber , French Gary L.
Published: June 2011

Studies in the 1970s and 1980s suggested that environmental surface contamination played a negligible role in the endemic transmission of healthcare-associated infections. However, recent studies have demonstrated that several major nosocomial pathogens are shed by patients and contaminate hospital surfaces at concentrations sufficient for transmission, survive for extended periods, persist despite attempts to disinfect or remove them, and can be transferred to the hands of healthcare workers. Evidence is accumulating that contaminated surfaces make an important contribution to the epidemic and endemic transmission ofClostridium difficile,vancomycin-resistant enterococci, methicillin-resistantStaphylococcus aureus, Acinetobacter baumannii, Pseudomonas aeruginosa,and norovirus and that improved environmental decontamination contributes to the control of outbreaks. Efforts to improve environmental hygiene should include enhancing the efficacy of cleaning and disinfection and reducing the shedding of pathogens. Further high-quality studies are needed to clarify the role played by surfaces in nosocomial transmission and to determine the effectiveness of different interventions in reducing associated infection rates.
Electronic Memorandum Decreases Unnecessary Antimicrobial Use for Asymptomatic Bacteriuria and Culture-Negative Pyuria
Authors: Linares Leslie A. , Thornton David J. , Strymish Judith , Baker Errol , Gupta Kalpana
Published: June 2011

Objectives.

Asymptomatic bacteriuria/candidiuria (ASB) and culture-negative pyuria (CNP) are common and often result in inappropriate antibiotic use. We aimed to evaluate whether a standardized educational memorandum could reduce antimicrobial utilization for ASB/CNP.

Design, Setting, and Patients.

Quasi-experimental study with a control group, from a convenience sample of inpatients with abnormal urinalysis or urine culture results in a Veterans Affairs hospital.

Intervention.

An educational memorandum outlining guidelines for diagnosis and treatment of ASB was placed in the chart of patients with ASB/CNP who were receiving antimicrobials.

Methods.

The records of patients meeting inclusion criteria were abstracted for demographics, comorbidities, antimicrobials, and symptoms suggestive of possible urinary tract infection (UTI). Patients were categorized as having ASB, CNP, or UTI. The number of antimicrobial-days attributed to ASB/CNP was compared between the control group and the intervention group.

Results.

Charts of 301 patients with abnormal urine results were reviewed. Thirty of 117 (26%) patients in the control group received antimicrobials for ASB/CNP for an average of 6.3 days. In the intervention group, 24 of 92 (26%) patients received antimicrobials for ASB/CNP for an average of 2.2 days (t-test: P<.001). Adverse events from antimicrobials for ASB/CNP occurred in 3 of the 30 (10%) patients in the control group. There were no adverse events from untreated ASB/CNP in the intervention group.

Conclusions.

ASB and CNP resulted in antimicrobial exposure in more than one-quarter of our study patients. Placing a standardized memorandum in the electronic record was associated with a 65% relative reduction in antimicrobial-days for ASB and CNP.
Enhancement in photo-induced hydrophilicity of TiO2/CNT nanostructures by applying voltage
Authors: Abdi Yaser , Khalilian Maryam , Arzi Ezatollah
Published: June 2011

Carbon nanotube (CNT) arrays were synthesized by plasma-enhanced chemical vapour deposition on a silicon substrate. Cabbage-like TiO2nanostructures on the CNTs were produced by atmospheric-pressure chemical vapour deposition. Scanning electron microcopy was used to study the morphology of the TiO2/CNT structures while x-ray diffraction and Fourier transform infrared (FTIR) spectroscopy were used to verify the characteristics of the prepared nanostructures. Their hydrophilicity under UV and visible light was investigated and compared with the activity of thin films of TiO2. The TiO2/CNTs showed a highly improved photocatalytic activity in comparison with the TiO2film. The excellent visible-light-induced hydrophilicity of the TiO2/CNTs was attributed to the generation of electron–hole pairs by visible light excitation with a low recombination rate. The results of this study showed that the fabricated cabbage-like TiO2/CNT nanostructures have a super-hydrophilic surface without further UV irradiation. Electrical measurements showed that a p–n junction was formed at the interface of the TiO2/CNTs. Consequently, a super-hydrophilic surface was achieved by applying an electric bias voltage. Visible-light- and electro-induced hydrophilicity of the obtained nanostructure was reported in this work.
Latest investigations on fluctuations, ELM filaments and turbulent transport in the SOL of ASDEX Upgrade
Authors: Müller H.W. , Adamek J. , Cavazzana R. , Conway G.D. , Fuchs C. , Gunn J.P. , Herrmann A. , Horaček J. , Ionita C. , Kallenbach A. , Kočan M. , Maraschek M. , Maszl C. , Mehlmann F. , Nold B. , Peterka M. , Rohde V. , Schweinzer J. , Schrittwieser R. , Vianello N. , Wolfrum E. , Zuin M.
Published: June 2011

This paper presents turbulence investigations in the scrape-off layer (SOL) of ASDEX Upgrade in ohmic, L-mode and H-mode discharges using electrostatic and electromagnetic probes. Detailed studies are performed on small scale turbulence and on ELM filaments. Simultaneous measurements of floating and plasma potential fluctuations revealed significant differences between these quantities. Large errors can occur when the electric field is extracted from floating potential measurements, even in ohmic discharges. Turbulence studies in ohmic plasmas show the existence of density holes inside the separatrix and blobs outside. Close to the separatrix a reversal of the poloidal blob propagation velocity occurs. Investigations on the Reynolds stress in the scrape-off layer (SOL) show its importance for the momentum transport in L-mode while its impact for momentum transport during ELMs in H-mode is rather small. In the far SOL the electron density and temperature were measured during type-I ELMy H-mode at ASDEX Upgrade resolving ELM filaments. Strong density peaks and temperatures of several 10 eV were detected during the ELM events. Additional investigations on the ions in ELM filaments by a retarding field analyser indicate ion temperatures of 50–80 eV. ELMs also expel current concentrated in filaments into the SOL. Furthermore, discharges with small ELMs were studied. In N2 seeded discharges the type-I ELM frequency rises and the ELM duration decreases. For discharges with small type-II ELMs the mean turbulent radial particle flux is increased over the mean particle flux in type-I ELM discharges at otherwise similar plasma parameters.
Systematic design of a sawtooth period feedback controller using a Kadomtsev–Porcelli sawtooth model
Authors: Witvoet G. , de Baar M.R. , Westerhof E. , Steinbuch M. , Doelman N.J.
Published: June 2011

A systematic methodology for structured design of feedback controllers for the sawtooth period is presented, based on dedicated identification of the sawtooth dynamics. Therefore, a combined Kadomtsev–Porcelli model of a sawtoothing plasma actuated by an electron cyclotron current drive system has been set-up. This is used to derive the linearized input–output relations (transfer functions) from the varying deposition location of the electron cyclotron waves (ECW) to the sawtooth period. These transfer functions are derived around a large collection of operating points. Assessment of these control-relevant transfer functions shows that a sawtooth period controller requires an integral (I) action to guarantee closed-loop stability with zero steady-state error. Additional proportional-integral (PI) action can be applied to further increase the closed-loop performance. The parameters of both the I and PII controllers have been optimized in terms of stability, performance and robustness. Moreover, the effect of the mechanical ECW launcher on the closed-loop performance is studied for realistic cases. It is shown that the launcher dynamics seriously affects the achievable closed-loop performance in present-day experiments.
Ideal magnetohydrodynamic simulations of unmagnetized dense plasma jet injection into a hot strongly magnetized plasma
Authors: Liu Wei , Hsu Scott C.
Published: June 2011

We present results from three-dimensional ideal magnetohydrodynamic simulations of unmagnetized dense plasma jet injection into a uniform hot strongly magnetized plasma, with the aim of providing insight into core fuelling of a tokamak with parameters relevant for ITER and National Spherical Torus Experiment (NSTX). Unmagnetized dense plasma jet injection is similar to compact toroid injection but with much higher plasma density and total mass, and consequently lower required injection velocity. Mass deposition of the jet into the background appears to be facilitated via magnetic reconnection along the jet's trailing edge. The penetration depth of the plasma jet into the background plasma is mostly dependent on the jet's initial kinetic energy, and a key requirement for spatially localized mass deposition is for the jet's slowing-down time to be less than the time for the perturbed background magnetic flux to relax due to magnetic reconnection. This work suggests that more accurate treatment of reconnection is needed to fully model this problem. Parameters for unmagnetized dense plasma jet injection are identified for localized core deposition as well as edge localized mode (ELM) pacing applications in ITER and NSTX-relevant regimes.
Arithmetic theory of harmonic numbers
Authors: Sun Zhi-Wei
Published: June 2011

Harmonic numbers

H

k

=

∑

0
>
j
⩽
k

1

/

j
 
(
k
=
0
,
1
,
2
,
…
)

H_{k}=\sum _{0>j\leqslant k}1/j\ (k=0,1,2,\ldots )

play important roles in mathematics. In this paper we investigate their arithmetic properties and obtain various basic congruences. Let

p
>
3

p>3

be a prime. We show that
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="sigma-summation Underscript k equals 1 Overscript p minus 1 Endscripts StartFraction upper H Subscript k Baseline Over k 2 Superscript k Baseline EndFraction identical-to 0 left-parenthesis normal m normal o normal d p right-parenthesis comma sigma-summation Underscript k equals 1 Overscript p minus 1 Endscripts upper H Subscript k Superscript 2 Baseline identical-to 2 p minus 2 left-parenthesis normal m normal o normal d p squared right-parenthesis comma sigma-summation Underscript k equals 1 Overscript p minus 1 Endscripts upper H Subscript k Superscript 3 Baseline identical-to 6 left-parenthesis normal m normal o normal d p right-parenthesis comma">

∑

k
=
1

p
−
1

H

k

k

2

k

≡
0
 
(

m
o
d

 
p
)
,
 

∑

k
=
1

p
−
1

H

k

2

≡
2
p
−
2
 
(

m
o
d

 

p

2

)
,
 

∑

k
=
1

p
−
1

H

k

3

≡
6
 
(

m
o
d

 
p
)
,

\begin{equation*} \sum _{k=1}^{p-1}\frac {H_{k}}{k2^{k}}\equiv 0\ (\mathrm {mod} \ p),\ \sum _{k=1}^{p-1}H_{k}^{2} \equiv 2p-2\ (\mathrm {mod} \ p^{2}), \ \sum _{k=1}^{p-1}H_{k}^{3}\equiv 6\ (\mathrm {mod} \ p),\end{equation*}

and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="sigma-summation Underscript k equals 1 Overscript p minus 1 Endscripts StartFraction upper H Subscript k Superscript 2 Baseline Over k squared EndFraction identical-to 0 left-parenthesis normal m normal o normal d p right-parenthesis provided p greater-than 5 period">

∑

k
=
1

p
−
1

H

k

2

k

2

≡
0
 
(

m
o
d

 
p
)

provided 
 
p
>
5.

\begin{equation*} \sum _{k=1}^{p-1}\frac {H_{k}^{2}}{k^{2}}\equiv 0\ (\mathrm {mod} \ p)\qquad \text {provided }\ p>5. \end{equation*}

(In contrast, it is known that

∑

k
=
1

∞

H

k

/

(
k

2

k

)
=

π

2

/

12

\sum _{k=1}^{\infty }H_{k}/(k2^{k})=\pi ^{2}/12

and

∑

k
=
1

∞

H

k

2

/

k

2

=
17

π

4

/

360

\sum _{k=1}^{\infty }H_{k}^{2}/k^{2}=17\pi ^{4}/360

.) Our tools include some sophisticated combinatorial identities and properties of Bernoulli numbers.