bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of flagellar hook compliance on motility of monotrichous bacteria: A modeling study
Authors: Shum H. , Gaffney E. A.
Published: June 2012

A crucial structure in the motility of flagellated bacteria is the hook, which connects the flagellum filament to the motor in the cell body. Early mathematical models of swimming bacteria assume that the helically shaped flagellum rotates rigidly about its axis, which coincides with the axis of the cell body. Motivated by evidence that the hook is much more flexible than the rest of the flagellum, we develop a new model that allows a naturally straight hook to bend. Hook dynamics are based on the Kirchhoff rod model, which is combined with a boundary element method for solving viscous interactions between the bacterium and the surrounding fluid. For swimming in unbounded fluid, we find good support for using a rigid model since the hook reaches an equilibrium configuration within several revolutions of the motor. However, for effective swimming, there are constraints on the hook stiffness relative to the scale set by the product of the motor torque with the hook length. When the hook is too flexible, its shape cannot be maintained and large deformations and stresses build up. When the hook is too rigid, the flagellum does not align with the cell body axis and the cell “wobbles” with little net forward motion. We also examine the attraction of swimmers to no-slip surfaces and find that the tendency to swim steadily close to a surface can be very sensitive to the combination of the hook rigidity and the precise shape of the cell and flagellum.
Constrained spin-density dynamics of an iron-sulfur complex: Ferredoxin cofactor
Authors: Ali Md. Ehesan , Nair Nisanth N. , Staemmler Volker , Marx Dominik
Published: June 2012

The computation of antiferromagnetic exchange coupling constants J by means of efficient density-based approaches requires in practice to take care of both spin projection to approximate the low spin ground state and proper localization of the magnetic orbitals at the transition metal centers. This is demonstrated here by a combined approach where the extended broken–symmetry (EBS) technique is employed to include the former aspect, while spin density constraints are applied to ensure the latter. This constrained EBS (CEBS) approach allows us to carry out ab initio molecular dynamics on a spin-projected low spin potential energy surface that is generated on-the-fly by propagating two coupled determinants and thereby accessing the antiferromagnetic coupling along the trajectory. When applied to the prototypical model of the oxidized [2Fe-2S] cofactor in Ferredoxins, [Fe2S2(SH)4]2−, at room temperature, CEBS leads to remarkably good results for geometrical structures and coupling constants J.
Using sharp transitions in contact angle hysteresis to move, deflect, and sort droplets on a superhydrophobic surface
Authors: Nilsson Michael A. , Rothstein Jonathan P.
Published: June 2012

In order to make an effective droplet-based microfluidic device, one must be able to precisely control a number of key processes including droplet positioning, motion, coalescence, mixing, and sorting. In a typical three-dimensional device, these processes are well understood. However, for planar or open microfluidic devices, many of these processes have yet to be demonstrated. In this paper, a series of superhydrophobic surfaces created by sanding Teflon are used as the microfluidics platform. The superhydrophobic surfaces used in this study all have advancing contact angles of 150° but have contact angle hysteresis that were varied smoothly from 3° to 30° as the grit size of the sandpaper is changed. Drop motion was initiated by placing the surface on an inclined plane. To deflect and move droplets along the surface, single and multiple transition lines in receding contact angle were created by spatially varying the surface roughness of the Teflon. The degree of droplet deflection was studied as a function of droplet size, droplet speed, and the angle that the transition line in contact angle hysteresis made with the principle direction of droplet motion. Droplet deflections across a single transition as large as 140% the droplet diameter were observed. The droplet deflection was found to increase with increasing difference in contact angle hysteresis across the transition and increasing transition angles up to about 40°. The largest deflections were observed over a very narrow range of droplet velocities corresponding to a range in Weber numbers between 0.1 and 0.2. This narrow range in Weber number suggests that transitions in receding contact angle can be used to sort drops based on velocity, size or wetting properties with a strong degree of selectivity. The direction of deflection was observed to change depending on whether the drops transitioned from a region of low to high or high to low contact angle hysteresis. In a transition from low to high hysteresis, a large portion of the drop's kinetic energy is converted into interfacial energy as the receding contact line of the drop is deformed. Alternatively, a transition from high to low hysteresis results in some of the drop's interfacial energy converted into kinetic energy as the deformation of the droplet is reduced. The result is either a reduction or increase in the droplet's velocity normal to the line of transition depending on the sign of the transition in contact angle hysteresis. Finally, single and multiple stripes of different contact angle hysteresis are also shown to be effective at deflecting droplets.
Structure and stability of the finite-area von Kármán street
Authors: Luzzatto-Fegiz Paolo , Williamson Charles H. K.
Published: June 2012

By using a recently developed numerical method, we explore in detail the possible inviscid equilibrium flows for a Kármán street comprising uniform, large-area vortices. In order to determine stability, we make use of an energy-based stability argument (originally proposed by Lord Kelvin), whose previous implementation had been unsuccessful in determining stability for the Kármán street [P. G. Saffman and J. C. Schatzman, “Stability of a vortex street of finite vortices,” J. Fluid Mech. 117, 171–186 (1982)10.1017/S0022112082001578]. We discuss in detail the issues affecting this interpretation of Kelvin's ideas, and show that this energy-based argument cannot detect subharmonic instabilities. To find superharmonic instabilities, we employ a recently introduced approach, which constitutes a reliable implementation of Kelvin's stability ideas [P. Luzzatto-Fegiz and C. H. K. Williamson, “Stability of conservative flows and new steady fluid solutions from bifurcation diagrams exploiting a variational argument,” Phys. Rev. Lett. 104, 044504 (2010)10.1103/PhysRevLett.104.044504]. For periodic flows, this leads us to organize solutions into families with fixed impulse I, and to construct diagrams involving the flow energy E and horizontal spacing (i.e., wavelength) L. Families of large-I vortex streets exhibit a turning point in L, and terminate with “cat's eyes” vortices (as also suggested by previous investigators). However, for low-I streets, the solution families display a multitude of turning points (leading to multiple possible streets, for given L), and terminate with teardrop-shaped vortices. This is radically different from previous suggestions in the literature. These two qualitatively different limiting states are connected by a special street, whereby vortices from opposite rows touch, such that each vortex boundary exhibits three corners. Furthermore, by following the family of I = 0 streets to small L, we gain access to a large, hitherto unexplored flow regime, involving streets with L significantly smaller than previously believed possible. To elucidate in detail the possible solution regimes, we introduce a map of spacing L, versus impulse I, which we construct by numerically computing a large number of steady vortex configurations. For each constant-impulse family of steady vortices, our stability approach also reveals a single superharmonic bifurcation, leading to new families of vortex streets, which exhibit lower symmetry.
Nonlinear relativistic single-electron Thomson scattering power spectrum for incoming laser of arbitrary intensity
Authors: Álvarez-Estrada R. F. , Pastor I. , Guasp J. , Castejón F.
Published: June 2012

The classical nonlinear incoherent Thomson scattering power spectrum from a single relativistic electron with incoming laser radiation of any intensity, investigated numerically by the present authors in a previous publication, displayed both an approximate quadratic behavior in frequency and a redshift of the power spectrum for high intensity incoming radiation. The present work is devoted to justify, in a more general setup, those numerical findings. Those justifications are reinforced by extending suitably analytical approaches, as developed by other authors. Moreover, our analytical treatment exhibits differences between the Doppler-like frequencies for linear and circular polarization of the incoming radiation. Those differences depend nonlinearly on the laser intensity and on the electron initial velocity and do not appear to have been displayed by previous authors. Those Doppler-like frequencies and their differences are validated by new Monte Carlo computations beyond our previuos ones and reported here.
Tuning the electron energy by controlling the density perturbation position in laser plasma accelerators
Authors: Brijesh P. , Thaury C. , Phuoc K. T. , Corde S. , Lambert G. , Malka V. , Mangles S. P. D. , Bloom M. , Kneip S.
Published: June 2012

A density perturbation in an underdense plasma was used to improve the quality of electron bunches produced in the laser-plasma wakefield acceleration scheme. Quasi-monoenergetic electrons were generated by controlled injection in the longitudinal density gradients of the density perturbation. By tuning the position of the density perturbation along the laser propagation axis, a fine control of the electron energy from a mean value of 60 MeV to 120 MeV has been demonstrated with a relative energy-spread of 15 ± 3.6%, divergence of 4 ± 0.8 mrad, and charge of 6 ± 1.8 pC.
Parallel transport of long mean-free-path plasma along open magnetic field lines: Parallel heat flux
Authors: Guo Zehua , Tang Xian-Zhu
Published: June 2012

In a long mean-free-path plasma where temperature anisotropy can be sustained, the parallel heat flux has two components with one associated with the parallel thermal energy and the other the perpendicular thermal energy. Due to the large deviation of the distribution function from local Maxwellian in an open field line plasma with low collisionality, the conventional perturbative calculation of the parallel heat flux closure in its local or non-local form is no longer applicable. Here, a non-perturbative calculation is presented for a collisionless plasma in a two-dimensional flux expander bounded by absorbing walls. Specifically, closures of previously unfamiliar form are obtained for ions and electrons, which relate two distinct components of the species parallel heat flux to the lower order fluid moments such as density, parallel flow, parallel and perpendicular temperatures, and the field quantities such as the magnetic field strength and the electrostatic potential. The plasma source and boundary condition at the absorbing wall enter explicitly in the closure calculation. Although the closure calculation does not take into account wave-particle interactions, the results based on passing orbits from steady-state collisionless drift-kinetic equation show remarkable agreement with fully kinetic-Maxwell simulations. As an example of the physical implications of the theory, the parallel heat flux closures are found to predict a surprising observation in the kinetic-Maxwell simulation of the 2D magnetic flux expander problem, where the parallel heat flux of the parallel thermal energy flows from low to high parallel temperature region.
Ion-acoustic solitons in negative ion plasma with two-electron temperature distributions
Authors: Mishra M. K. , Tiwari R. S. , Chawla J. K.
Published: June 2012

Ion–acoustic solitons in a warm positive and negative ion species with different masses, concentrations, and charge states with two electron temperature distributions are studied. Using reductive perturbation method, Korteweg de-Vries (KdV) and modified-KdV (m-KdV) equations are derived for the system. The soliton solution of the KdV and m-KdV equations is discussed in detail. It is found that if the ions have finite temperatures, then there exist two types of modes, namely slow and fast ion-acoustic modes. It is also investigated that the parameter determining the nature of soliton (i.e., whether the system will support compressive or rarefactive solitons) is different for slow and fast modes. For the slow mode, the parameter is the relative temperature of the two ion species; whereas for the fast mode, it is the relative concentration of the two ion species. At a critical concentration of negative ions, both compressive and rarefactive solitons coexist. The amplitude and width of the solitons are discussed in detail at critical concentration for m-KdV solitons. The effect of the relative temperature of the two-electron and cold-electron concentration on the characteristics of the solitons are also discussed.
Note: Tip enhanced Raman spectroscopy with objective scanner on opaque samples
Authors: Nicklaus Mischa , Nauenheim Christian , Krayev Andrey , Gavrilyuk Vasili , Belyaev Alexey , Ruediger Andreas
Published: June 2012

We report on 14 nm lateral resolution in tip-enhanced Raman spectroscopy mapping of carbon nanotubes with an experimental setup that has been designed for the analysis of opaque samples in confocal side-access through a novel piezo-driven objective scanner. The objective scanner allows for fast and stable laser-to-tip alignment and for the adjustment of the focus position with sub-wavelength precision to optimize the excitation of surface plasmons. It also offers the additional benefit of imaging the near-field generated Raman scattering at the gap between tip and sample as direct control of the tip enhancement.
Electrical shielding box measurement of the negative hydrogen beam from Penning ion gauge ion source
Authors: Wang T. , Yang Z. , Dong P. , long J. D. , He X. Z. , Wang X. , Zhang K. Z. , Zhang L. W.
Published: June 2012

The cold-cathode Penning ion gauge (PIG) type ion source has been used for generation of negative hydrogen (H−) ions as the internal ion source of a compact cyclotron. A novel method called electrical shielding box dc beam measurement is described in this paper, and the beam intensity was measured under dc extraction inside an electrical shielding box. The results of the trajectory simulation and dc H− beam extraction measurement were presented. The effect of gas flow rate, magnetic field strength, arc current, and extraction voltage were also discussed. In conclusion, the dc H− beam current of about 4 mA from the PIG ion source with the puller voltage of 40 kV and arc current of 1.31 A was extrapolated from the measurement at low extraction dc voltages.
Role of fluid density in shaping eruption currents driven by frontal particle blow-out
Authors: Carroll C. S. , Turnbull B. , Louge M. Y.
Published: June 2012

We study the role of suspension density in eruption currents, a regime of gravity-driven flow that is sustained by massive, localized blow-out of particles acting as a steady source of heavier fluid injected into a uniform flow at high Reynolds number. Inspired by the potential flow solution of Saffman and Yuen [“Finite-amplitude interfacial waves in the presence of a current,” J. Fluid Mech. 123, 459–476 (1982)10.1017/S0022112082003152], we show that the relative density difference between the two fluids swells the size of the current's head without changing its shape, while inducing a velocity jump at the interface. We test this inviscid theory against inviscid and large-eddy-simulations. We also conduct experiments in a water flume, where a line source of fluorescent brines of various densities is injected in a cross-stream and visualized with a narrow sheet of light. Simulations and experiments reveal that, with isotropic velocity distribution on a finite source, eruption currents expand further and develop interface oscillations, but the inviscid theory still captures relative swelling induced by density. We compare predictions to the static pressure data of McElwaine and Turnbull [“Air pressure data from the Vallee de la Sionne avalanches of 2004,” J. Geophys. Res. 110, F03010, doi:10.1029/2004JF000237 (2005)] in powder snow avalanches.
A compact collinear polarization gating scheme for many cycle laser pulses
Authors: Kolliopoulos G. , Carpeggiani P. A. , Rompotis D. , Charalambidis D. , Tzallas P.
Published: June 2012

We demonstrate the generation of a broadband coherent continuum extreme-ultraviolet (XUV) radiation produced by the interaction of gases with a many-cycle infrared (IR) laser field, utilizing a compact collinear many cycle-polarization gating (CMC-PG) device. The spectral width of the XUV radiation can support isolated pulses of 200 asec duration. The CMC-PG device forms a high energy content ultra-short temporal gate in a many-cycle laser pulse, within which the XUV emission is taking place. The gate width has been measured and is in agreement with the theoretical calculations. The simplicity, the compactness, the long term stability, and the high IR energy output within the gate, make the CMC-PG device an ideal tool for generating energetic isolated attosecond pulses and measure the carrier-envelope phase of a high-power many-cycle laser field.
Depletion layer formation in suspensions of elastic capsules in Newtonian and viscoelastic fluids
Authors: Pranay Pratik , Henríquez-Rivera Rafael G. , Graham Michael D.
Published: June 2012

Motivated by observations of the effects of drag-reducing polymer additives on various aspects of blood flow, suspensions of fluid-filled elastic capsules in Newtonian fluids and dilute solutions of high molecular weight (drag-reducing) polymers are investigated during plane Couette flow in a slit geometry. A simple model is presented to describe the cross-stream distribution of capsules as a balance of shear-induced diffusion and wall-induced migration due to capsule deformability. The model provides a theoretical prediction of the dependence of capsule-depleted layer thickness on the capillary number. A computational approach is then used to directly study the motion of elastic capsules in a Newtonian fluid and in polymer solutions. Capsule membranes are modeled using a neo-Hookean constitutive model and polymer molecules are modeled as bead-spring chains with finitely extensible nonlinearly elastic springs, with parameters chosen to loosely approximate 4000 kDa poly(ethylene oxide). Simulations are performed with a Stokes flow formulation of the immersed boundary method for the capsules, combined with Brownian dynamics for the polymer molecules. Results for an isolated capsule near a wall indicate that the wall-induced migration depends on the capillary number and is strongly reduced by addition of polymer. Numerical simulations of suspensions of capsules in Newtonian fluid illustrate the formation of a capsule-depleted layer near the walls. The thickness of this layer is found to be strongly dependent on the capillary number. The shear-induced diffusivity of the capsules, on the other hand, shows only a weak dependence on capillary number. These results thus indicate that the mechanism of wall-induced migration is the primary source for determining the capillary number dependence of the depletion layer thickness. Both the wall-induced migration and the shear-induced diffusive motion of the capsules are attenuated under the influence of polymer; reduction of migration dominates, however, so the net effect of polymers on the capsule suspension is to reduce the thickness of the capsule-depleted layer. This prediction is in qualitative agreement with experimental observations.
Investigation on heat transfer between two coaxial cylinders for measurement of thermal accommodation coefficient
Authors: Yamaguchi Hiroki , Kanazawa Kazuaki , Matsuda Yu , Niimi Tomohide , Polikarpov Alexey , Graur Irina
Published: June 2012

The heat flux between two coaxial cylinders was measured in the range from the free molecular to the early transitional flow regimes for extraction of the thermal accommodation coefficient using an approximate relation on the pressure dependence of the heat flux. The experimental coaxial cylinders' geometry has been traditionally implemented for the measurement of the thermal accommodation coefficient using the low-pressure method; however, the actual experimental setup was characterized by large temperature difference and large cylinders' radius ratio. Compared to the original low-pressure method, much higher pressure range was applied. In order to verify assumptions in the accommodation coefficient extraction, the heat flux under measurement conditions was simulated numerically by the nonlinear S-model kinetic equation. Very good agreement was found between the measured and the simulated heat flux. The proposed procedure of the thermal accommodation coefficient extraction was discussed in detail and verified. The temperature dependence of the thermal accommodation coefficient was also found.
The slow spreading of several viscous films over a deep viscous pool
Authors: Foster J. M. , Please C. P. , Fitt A. D.
Published: June 2012

In this study, a previously derived two-dimensional model is used to describe the slow spreading of viscous films on the surface of a quiescent deep viscous pool due to gravity. It is assumed that the densities and viscosities of the fluids in the films and pool are comparable, but may be different. It is also assumed that surface tension effects are negligible. The fluid in the films and in the pool are both modelled using the Stokes flow equations. By exploiting the slenderness of the spreading films, asymptotic techniques are used to analyse the flow. It is shown that the dominant forces controlling the spreading are gravity and the tangential stress induced in the films by the underlying pool. As a consequence, the rate of spreading of the films is independent of their viscosity. For the case special of a symmetric configuration of films on the surface of the pool, the flow is studied by assuming that the solution becomes self-similar and hence the problem is recast in a self-similar coordinate system. Stokeslet analysis is then used to derive a singular integral equation for the stresses on the interfaces between the films and the pool. The form of this integral equation depends on the configuration of spreading films that are to be considered. A number of different cases are then studied, namely, a single film, two films, and an infinite periodic array of films. Finally, some results are derived that apply to a general symmetric configuration of films. It is shown that the profile of a spreading film close to its front (where the film thickness becomes zero) is proportional to x1/4. It is also shown that fronts move, and hence, the distance between adjacent fronts increases proportional to t1/3.
The onset of steady vortices in Taylor-Couette flow: The role of approximate symmetry
Authors: Cliffe K. A. , Mullin T. , Schaeffer D.
Published: June 2012

The onset of steady cellular motion in Taylor-Couette flow between a pair of finite length cylinders is studied. This is most often portrayed in the literature as an example of a simple pitchfork bifurcation where the trivial state of rotary Couette flow is replaced by cellular motion above a critical Reynolds number. However, numerous experiments and simulations of the Navier-Stokes equations, as well as the detailed numerical bifurcation study reported here, all lead to the following, seemingly paradoxical, conclusion: On the one hand, no matter how long the apparatus, finite-length effects greatly perturb the disconnected branch of the pitchfork of the periodic model. This corresponds to anomalous-mode flows which are observed to exist above a range of Reynolds number that is at least a factor of two greater than the value corresponding to the onset of cells. On the other hand, in long cylinders these effects appear to change the connected branch of normal-mode flows only minimally. We propose a resolution of this paradox in terms of a symmetry breaking bifurcation. The relevant symmetry, which is only approximate, is between two normal-mode flows with large, and nearly equal, numbers of cells. Additionally, our numerical calculations establish a scaling law that quantifies the magnitude of finite-length effects on normal-mode flows at large lengths.
Investigation of the global phase behavior of polymer mixtures in the shield region
Authors: Gençaslan Mustafa
Published: June 2012

This paper is a contribution of our systematic investigation of the global phase behaviors of the chain molecules mixtures, i.e., polymer mixture solutions. The phase behavior of fluid mixtures is understood by the critical lines in fluid-gas diagrams. The critical lines of binary fluid system may, under circumstances, exhibit closed loops in the critical lines. A distinction is made between free critical loops, as described by type VI in the Scott and van Konynenburg classification, and “rooted” critical loops, as found in the shield region. We define rooted loops as closed critical lines that are attached to the critical line structure by means of unstable critical line. We obtain the rooted loops in the global phase diagrams of the polymer mixture solutions within the framework of a model that combines the lattice gas model of Schouten, ten Seldam and Trappeniers with the Flory–Huggins theory, and we present the influence of the chain length of long molecules on the rooted critical loops. We present the results in the density-density and the temperature (T)–pressure (P) planes in detail.
Ohmic contact to n-AlGaN through bonding state transition at TiAl interface
Authors: Zhang Binbin , Lin Wei , Li Shuping , Zheng Yu , Yang Xu , Cai Duanjun , Kang Junyong
Published: June 2012

We report the optimized ohmic contact to high Al content n-AlGaN through modification of the interfacial bonding state of TiAl alloy. First-principles calculations demonstrate that the change of interfacial bonding state (N rich to Al rich) at the TiAl/n-AlGaN interface is crucial for the formation of low barrier contact. The significant electron-transfer and strong orbital hybridization between the Ti atoms and the nearest Al atoms plays a key role in lowering the contact barrier. After treatment of the TiAl/n-AlGaN sample via rapid thermal annealing, perfectly linear I-V characteristic is achieved and the elemental profile by Auger electron spectroscopy confirms the N-rich-to-Al-rich local state transition in the interfacial layers.
Dual beam photoacoustic infrared spectroscopy of solids using an external cavity quantum cascade laser
Authors: Dehghany M. , Michaelian K. H.
Published: June 2012

Quantum cascade laser-based instrumentation for dual beam photoacoustic (PA) spectroscopy is described in this article. Experimental equipment includes a 4.55 μm (2141–2265 cm−1) continuous wave external cavity quantum cascade laser (EC-QCL), two gas-microphone PA cells, and two lock-in amplifiers. Correction for the time and wavenumber dependence of the laser output is effected through real-time division of the PA signals derived from the sample and reference channels. Source-compensated mid-infrared absorption spectra of carbon black powder and aromatic hydrocarbon solids were obtained to confirm the reliability of the method. Absorption maxima in the EC-QCL PA spectra of hydrocarbons are better defined than those in Fourier transform infrared spectra acquired under similar conditions, enabling the detection of several previously unknown bands.
Influence of the nonthermal plasma shielding on the ion collisions in Lorentzian semiclassical plasmas
Authors: Ki Dae-Han , Jung Young-Dae
Published: June 2012

The influence of the nonthermal plasma shielding on the elastic ion-ion collision is investigated in dense Lorentzian semiclassical plasmas. The effective interaction potential and phase theory are applied to obtain the scattering phase shift and collision cross section as functions of the spectral index of the Lorentzian plasma, impact parameter, collision energy, and plasma parameters. The result shows that the nonthermal plasma shielding effect reduces the magnitude of the scattering phase shift. It is also found that the nonthermal plasma shielding effect suppresses the ion-ion collision cross section. Hence, we have found that the ion-ion collision cross sections in thermal plasmas are always greater than those in nonthermal plasmas. In addition, it is found that the nonthermal shielding effect on the collision cross section increases with an increase of the Debye length in Lorentzian semiclassical plasmas.
Shape control of nickel nanostructures incorporated in amorphous carbon films: From globular nanoparticles toward aligned nanowires
Authors: El Mel A. A. , Bouts N. , Grigore E. , Gautron E. , Granier A. , Angleraud B. , Tessier P. Y.
Published: June 2012

The growth of nickel/carbon nanocomposite thin films by a hybrid plasma process, which combines magnetron sputtering and plasma enhanced chemical vapor deposition, has been investigated. This study has shown that the films consist of nickel-rich nanostructures embedded in an amorphous carbon matrix. The size, the distribution, the density, and the shape of these nanostructures are directly dependent to the total carbon content within the films. At low carbon content (∼28 at. %), dense nanowire array perpendicularly oriented to the surface of the substrate can be fabricated. For an intermediate carbon concentration (∼35 at. %), the nickel phase was organized into elongated nanoparticles. These nanoparticles became spherical when reaching a higher carbon content (∼54 at. %). The extensive structural study allowed the representation of a structure zone diagram, as well as, the development of a scenario describing the growth mechanisms that take place during the deposition of such nanocomposite material.
Spin reorientation and the magnetocaloric effect in HoyEr(1−y)N
Authors: von Ranke P. J. , Alvarenga T. S. T. , Alho B. P. , Nóbrega E. P. , Ribeiro P. O. , Carvalho A. Magnus G. , de Sousa V. S. R. , Caldas A. , de Oliveira N. A.
Published: June 2012

We report on the magnetic and magnetocaloric effect calculations in rare earth mononitrides HoyEr(1−y)N (y = 0, 0.5, 0.75, and 1). The magnetic Hamiltonian includes the crystalline electrical field in both magnetic sublattices; disorder in exchange interactions among Ho-Ho, Er-Er, and Ho-Er magnetic ions and the Zeeman effect. The theoretical results for the magnetic entropy change and adiabatic temperature change are in good agreement with the available experimental data. Besides, ferrimagnetic arrangement, inverse magnetocaloric effect, and spin reorientation transition (spin flop process) were predicted and quantitatively described.
The deformation units in metallic glasses revealed by stress-induced localized glass transition
Authors: Huo L. S. , Ma J. , Ke H. B. , Bai H. Y. , Zhao D. Q. , Wang W. H.
Published: June 2012

We report that even in quasi-static cyclic compressions in the apparent elastic regimes of the bulk metallic glasses, the precisely measured stress-strain curve presents a mechanical hysteresis loop, which is commonly perceived to occur only in high-frequency dynamic tests. A phenomenological viscoelastic model is established to explain the hysteresis loop and demonstrate the evolutions of the viscous zones in metallic glasses during the cyclic compression. The declining of the viscosity of the viscous zones to at least 1 × 1012 Pa s when stress applied indicates that stress-induced localized glass to supercooled liquid transition occurs. We show that the deformation units of metallic glasses are evolved from the intrinsic heterogeneous defects in metallic glasses under stress and the evolution is a manifestation of the stress-induced localized glass transition. Our study might provide a new insight into the atomic-scale mechanisms of plastic deformation of metallic glasses.
Recent progress of the HCN interferometer on J-TEXT tokamak
Authors: Gao L. , Zhuang G. , Wang Zhi Jiang , Chen W. , Chen J. , Li Q. , Liu Y.
Published: June 2012

A multichannel far-infrared HCN laser interferometer has been developed to measure plasma electron density for the J-TEXT tokamak. Initial operation of a seven chords system with 7 cm spacing and a 0.1 ms temporal resolution is described. Density modulation experiments in J-TEXT show that it is possible to obtain information on particle transport by precise measurement of the density perturbation amplitude and phase spatial variation. An optical configuration upgrade has been implemented in order to improve phase resolution.
Time-resolved ion energy distribution measurements using an advanced neutral particle analyzer on the MST reversed-field pinch
Authors: Eilerman S. , Anderson J. K. , Reusch J. A. , Liu D. , Fiksel G. , Polosatkin S. , Belykh V.
Published: June 2012

An advanced neutral particle analyzer (ANPA) capable of simultaneously measuring hydrogen and deuterium ions of energies up to 45 keV has recently been developed for use on the Madison Symmetric Torus. The charge-to-mass separation allows for separate analysis of bulk deuterium ions and hydrogen ions injected with a 1 MW, 25 keV neutral beam. Orientation of the ANPA allows sampling of different regions of ion velocity space; a radial viewport favors collection of ions with high v⊥/|v| while a recently installed tangential viewport favors ions with high v||/|v|, such as those from the core-localized fast ion population created by the neutral beam. Signals are observed in the ANPA's highest energy channels during periodic magnetic reconnection events, which are drivers of anisotropic, non-Maxwellian ion energization in the reversed-field pinch. ANPA signal strength is dependent on the background neutral density, which also increases during magnetic reconnection events, so careful analysis must be performed to identify the true change in the ion distribution. A Monte Carlo neutral particle tracing code (NENE) is used to reconstruct neutral density profiles based on Dα line emission, which is measured using a 16-chord filtered photodiode array.
Acidic ionic liquid/water solution as both medium and proton source for electrocatalytic H
2
evolution by [Ni(P
2
N
2
)
2
]
2+
complexes
Authors: Pool Douglas H. , Stewart Michael P. , O’Hagan Molly , Shaw Wendy J. , Roberts John A. S. , Bullock R. Morris , DuBois Daniel L.
Published: June 2012

The electrocatalytic reduction of protons to H
2
by

(where

in the highly acidic ionic liquid dibutylformamidium bis(trifluoromethanesulfonyl)amide shows a strong dependence on added water. A turnover frequency of 43,000–53,000 s
-1
has been measured for hydrogen production at 25 °C when the mole fraction of water (
χ

H
2
O

) is 0.72. The same catalyst in acetonitrile with added dimethylformamidium trifluoromethanesulfonate and water has a turnover frequency of 720 s
-1
. Thus, the use of an ionic liquid/aqueous solution enhances the observed catalytic rate by more than a factor of 50, compared to a similar acid in a traditional organic solvent. Complexes

(X = H, OMe,CH
2
P(O)(OEt)
2
, Br) are also catalysts in the ionic liquid/water mixture, and the observed catalytic rates correlate with the hydrophobicity of
X
.
Nanoparticle-based therapy in an in vivo microRNA-155 (miR-155)-dependent mouse model of lymphoma
Authors: Babar Imran A. , Cheng Christopher J. , Booth Carmen J. , Liang Xianping , Weidhaas Joanne B. , Saltzman W. Mark , Slack Frank J.
Published: June 2012

MicroRNA-155 (miR-155) is an oncogenic microRNA that regulates several pathways involved in cell division and immunoregulation. It is overexpressed in numerous cancers, is often correlated with poor prognosis, and is thus a key target for future therapies. In this work we show that overexpression of miR-155 in lymphoid tissues results in disseminated lymphoma characterized by a clonal, transplantable pre-B-cell population of neoplastic lymphocytes. Withdrawal of miR-155 in mice with established disease results in rapid regression of lymphadenopathy, in part because of apoptosis of the malignant lymphocytes, demonstrating that these tumors are dependent on miR-155 expression. We show that systemic delivery of antisense peptide nucleic acids encapsulated in unique polymer nanoparticles inhibits miR-155 and slows the growth of these “addicted” pre-B-cell tumors in vivo, suggesting a promising therapeutic option for lymphoma/leukemia.
Splitting CO
2
into CO and O
2
by a single catalyst
Authors: Chen Zuofeng , Concepcion Javier J. , Brennaman M. Kyle , Kang Peng , Norris Michael R. , Hoertz Paul G. , Meyer Thomas J.
Published: June 2012

The metal complex [(tpy)(Mebim-py)Ru
II
(S)]
2+
(tpy = 2,2
′
 : 6
′
,2
′′
-terpyridine; Mebim-py = 3-methyl-1-pyridylbenzimidazol-2-ylidene; S = solvent) is a robust, reactive electrocatalyst toward both water oxidation to oxygen and carbon dioxide reduction to carbon monoxide. Here we describe its use as a single electrocatalyst for CO
2
splitting, CO
2
 → CO + 1/2 O
2
, in a two-compartment electrochemical cell.
Electron transfer-based combination therapy of cisplatin with tetramethyl-
p
-phenylenediamine for ovarian, cervical, and lung cancers
Authors: Luo Ting , Yu Jianqing , Nguyen Jenny , Wang Chun-Rong , Bristow Robert G. , Jaffray David A. , Zhou Xiao Zhen , Lu Kun Ping , Lu Qing-Bin
Published: June 2012

The platinum-based chemotherapy is the standard treatment for several types of cancer. However, cancer cells often become refractory with time and most patients with serious cancers die of drug resistance. Recently, we have discovered a unique dissociative electron-transfer mechanism of action of cisplatin, the first and most widely used platinum-based anticancer drug. Here, we show that the combination of cisplatin with an exemplary biological electron donor,
N
,
N
,
N
′,
N
′-tetramethyl-
p
-phenylenediamine (TMPD), may overcome the resistance of cancer cells to cisplatin. Our steady-state absorption and fluorescence spectroscopic measurements confirm the effective dissociative electron-transfer reaction between TMPD and cisplatin. More significantly, we found that the combination of 100 μM TMPD with cisplatin enhances double-strand breaks of plasmid DNA by a factor of approximately 3.5 and dramatically reduces the viability of cisplatin-sensitive human cervical (HeLa) cancer cells and highly cisplatin-resistant human ovarian (NIH:OVCAR-3) and lung (A549) cancer cells. Furthermore, this combination enhances apoptosis and DNA fragmentation by factors of 2–5 compared with cisplatin alone. These results demonstrate that this combination treatment not only results in a strong synergetic effect, but also makes resistant cancer cells sensitive to cisplatin. Because cisplatin is the cornerstone agent for the treatment of a variety of human cancers (including testicular, ovarian, cervical, bladder, head/neck, and lung cancers), our results show both the potential to improve platinum-based chemotherapy of various human cancers and the promise of femtomedicine as an emerging frontier in advancing cancer therapy.
Conservation of complex knotting and slipknotting patterns in proteins
Authors: Sułkowska Joanna I. , Rawdon Eric J. , Millett Kenneth C. , Onuchic Jose N. , Stasiak Andrzej
Published: June 2012

While analyzing all available protein structures for the presence of knots and slipknots, we detected a strict conservation of complex knotting patterns within and between several protein families despite their large sequence divergence. Because protein folding pathways leading to knotted native protein structures are slower and less efficient than those leading to unknotted proteins with similar size and sequence, the strict conservation of the knotting patterns indicates an important physiological role of knots and slipknots in these proteins. Although little is known about the functional role of knots, recent studies have demonstrated a protein-stabilizing ability of knots and slipknots. Some of the conserved knotting patterns occur in proteins forming transmembrane channels where the slipknot loop seems to strap together the transmembrane helices forming the channel.
Evidence for a spontaneous gapped state in ultraclean bilayer graphene
Authors: Bao Wenzhong , Velasco Jairo , Zhang Fan , Jing Lei , Standley Brian , Smirnov Dmitry , Bockrath Marc , MacDonald Allan H. , Lau Chun Ning
Published: June 2012

At the charge neutrality point, bilayer graphene (BLG) is strongly susceptible to electronic interactions and is expected to undergo a phase transition to a state with spontaneously broken symmetries. By systematically investigating a large number of single-and double-gated BLG devices, we observe a bimodal distribution of minimum conductivities at the charge neutrality point. Although
σ
min
is often approximately 2–3 
e
2
/
h
(where
e
is the electron charge and
h
is Planck’s constant), it is several orders of magnitude smaller in BLG devices that have both high mobility and low extrinsic doping. The insulating state in the latter samples appears below a transition temperature
T

c

of approximately 5 K and has a
T
 = 0 energy gap of approximately 3 meV. Transitions between these different states can be tuned by adjusting disorder or carrier density.
A Reappraisal of Investing in Commodity Futures Markets
Authors: Sanders Dwight R. , Irwin Scott H.
Published: June 2012

Investments into commodity‐linked products have grown considerably in recent years. Unlike investments in equities, commodity futures markets produce no earnings; the source of returns is thus unclear. This paper examines returns to static long‐only U.S. commodity futures investments over five decades and finds that returns to individual futures markets are zero, and the returns to futures market portfolios depend critically on portfolio weighting schemes. Historical portfolio returns are not statistically different from zero and are driven by price episodes such as that of 1972‐1974. In other periods, portfolio returns are zero or negative. Overall, the case for long‐only investment in commodities may not be as strong as that implied in some studies (e.g., Gorton and Rouwenhorst, 2006a). If so, the growth in long‐only commodity investments may naturally subside and ease the policy debate regarding speculative position limits.
The effect of decreasing seasonal sea-ice cover on the winter Bering Sea pollock fishery
Authors: Pfeiffer Lisa , Haynie Alan C.
Published: June 2012

Pfeiffer, L., and Haynie, A. C. 2012. The effect of decreasing seasonal sea-ice cover on the winter Bering Sea pollock fishery. – ICES Journal of Marine Science, 69: . The winter fishing season for eastern Bering Sea pollock (Theragra chalcogramma) is during the period of maximum seasonal sea-ice extent, but harvesters avoid fishing in ice-covered waters. Global climate models predict a 40% reduction in winter ice cover by 2050, with potential implications for the costs incurred by vessels travelling to and around their fishing grounds and the value of their catch. Additionally, it may open entirely new areas to fishing. Using retrospective data from 1999 to 2009, a period of extensive annual climate variation, the variation in important characteristics of the fishery is analysed. When ice is present, it restricts a portion of the fishing grounds, but in general, ice-restricted areas have lower expected profits at the time of restriction than the areas left open. Some areas show a change in effort in warm years relative to cold, but the global redistribution of effort attributable to ice cover is small. This is largely because the winter fishery is driven by the pursuit of roe-bearing fish whose spawning location is stable in the southern part of the fishing grounds.
Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?
Authors: Gårdmark Anna , Östman Örjan , Nielsen Anders , Lundström Karl , Karlsson Olle , Pönni Jukka , Aho Teija
Published: June 2012

Gårdmark, A., Östman, Ö., Nielsen, A., Lundström K., Karlsson O., Pönni, J., and Aho, T. 2012. Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates? – ICES Journal of Marine Science, 69: . Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973–2009. Accounting for predation increased the herring SSB 16% (maximum 19%), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change.
Modelling the abundance of grey seals (Halichoerus grypus) along the Norwegian coast
Authors: Øigård Tor Arne , Frie Anne Kirstine , Nilssen Kjell Tormod , Hammill Mike Osborne
Published: June 2012

Øigård, T. A., Frie, A. K., Nilssen, K. T., and Hammill, M. O. 2012. Modelling the abundance of grey seals (Halichoerus grypus) along the Norwegian coast. – ICES Journal of Marine Science, 69: . An age-structured population dynamics model of the Norwegian grey seal (Halichoerus grypus) population has been developed. The model is of a Bayesian character in the sense that priors for various parameters were used. Model runs indicated an increase in the abundance of the total Norwegian grey seal population during the last 30 years, suggesting a total of 8740 (95% confidence interval: 7320–10 170) animals in 2011. A total catch of 707 (95% confidence interval: 532–882) grey seals would maintain the population size at the 2011 level. Model runs suggest that current catch levels will likely result in a reduction in the population size in Sør-Trøndelag and Nord-Trøndelag counties, and an increase in the population size in Rogaland, Nordland, Troms, and Finnmark counties. The model runs assumed that 80% of the seals taken in Rogaland came from the UK and that 50 and 55% of the catches in Troms and Finnmark, respectively, were immigrants from Russia.