bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of radially symmetric travelling waves in reaction–diffusion equations
Authors: Roussier Violaine
Published: February 2012

The asymptotic behaviour as

t

goes to infinity of solutions

u(x,t)

of the multidimensional parabolic equation

u_t=Δu+F(u)

is studied in the “bistable” case. More precisely, we consider the stability of spherically symmetric travelling waves with respect to small perturbations. First, we show that such waves are stable against spherically symmetric perturbations, and that the perturbations decay like

(\log\,t)/t^2

as

t

goes to infinity. Next, we observe that this stability result cannot hold for arbitrary (i.e., non-symmetric) perturbations. Indeed, we prove that there exist small perturbations such that the solution

u(x,t)

does not converge to a spherically symmetric profile as

t

goes to infinity. More precisely, for any direction

k\in S^{n−1}

, the restriction of

u(x,t)

to the ray

\{x=kr | r⩾0\}

converges to a

k

-dependent translate of the one-dimensional travelling wave.

On étudie le comportement pour les grands temps des solutions

u(x,t)

de l’équation parabolique

u_t=Δu+F(u)

dans le cas “bistable” et dans tout l’espace, en dimension supérieure. Plus précisément, on s’intéresse à la stabilité d’ondes progressives à symétrie sphérique pour de petites perturbations. Dans un premier temps, on montre que cette famille d’ondes est stable pour des perturbations à symétrie sphérique et que cette perturbation décroît comme

(\log\,t)/t^2

quand

t

tend vers l’infini. On montre ensuite que cette stabilité est mise en défaut pour des perturbations quelconques. En effet, on met en évidence des perturbations pour lesquelles la solution ne tend pas vers une onde à symétrie sphérique : dans chaque direction

k\in S^{n−1}

, la restriction de

u(x,t)

au rayon

\{x=kr | r⩾0\}

converge vers un translaté de l’onde progressive unidimensionnelle dépendant de 

k

.
Statistical mechanics of the N-point vortex system with random intensities on a bounded domain
Authors: Neri Cassio
Published: February 2012

The system of

N

point vortices on a bounded domain

Ω

is considered under the hypothesis that vortex intensities are independent and identically distributed random variables with respect to a law

P

supported on a bounded subset of

ℝ

. It is shown that, in the limit

N→+∞

, the 1-vortex distribution on

Ω

is a minimizer of the free energy functional (a combination of entropy and energy functionals) and is associated to (some) solutions of the following non-linear Poisson Equation (called Mean Field Equation):

\tag{1}
\begin{cases}
- \Delta u\left(x\right) = \left[\int \int e^{ - \beta ru\left(y\right)}\text{dy}P\left(\text{d}r\right)\right]^{ - 1}\int r_{1}e^{ - \beta ru\left(x\right)}P\left(\text{d}r\right), & \forall x \in \Omega , \\ u\left(x\right) = 0, & \forall x \in \partial \Omega .
\end{cases}

Le systéme de

N

vortex ponctuels sur un domaine

Ω

borné est considéré sous l’hypothèse que les intensités des vortex sont des variables aléatoires indépendentes et identiquement distribuées selon la loi

P

de support inclus dans un borné de

ℝ

. On montre que, à la limite quand

N→+∞

, la distribution d’un seul vortex dans

Ω

est un minimiseur de la fonctionnelle d’énergie libre (qui est une composition de l’entropie et de l’énergie) et qui est associée à (certaines) solutions de l’équation de Poisson non linéaire (dite de Champ Moyen) (1).
The growth impact of transport infrastructure investment: A regional analysis for China (1978–2008)
Authors: Yu Nannan , De Jong Martin , Storm Servaas , Mi Jianing
Published: February 2012

This study aims to explore the impact of transport capital stock on economic growth in Chinese regions. Using panel data for a sample of 28 provinces and municipalities over the period 1978–2008, the empirical findings show that there is significant spatial variation in the productivity effects of transport infrastructure in China. The highest output elasticity in the connection provinces of the central region means that transport investments there will yield the highest economic returns, which is in line with “the emergence of new economic center” theory. From a policy perspective, China had best give priority to the development of transport facilities in the backland region to realize the rise of Central China.
Hypercortisolism Caused by Ritonavir Associated Inhibition of CYP 3A4 Under Inhalative Glucocorticoid Therapy. 2 Case Reports and a Review of the Literature
Authors: Bernecker C. , West T. , Mansmann G. , Scherbaum W. , Willenberg H.
Published: February 2012

Recent in vitro and in vivo studies have shown a potent inhibition of cytochrome P450 CYP3A4 through human immune deficiency virus (HIV) protease inhibitors (PIs). The PI ritonavir is described as the most potent compound within these CYP3A4 inhibitors. We present 2 cases who developed the sequelae of glucocorticoid excess following ritonavir therapy and inhalative glucocorticoid treatment: A 60-year-old HIV positive man developed the typical symptoms of Cushing’s syndrome and a 52-year-old HIV positive man developed severe osteoporosis.
Effects of Short and Prolonged Mild Intracellular Nitric Oxide Manipulations on Various Aspects of Insulin Secretion in INS-1E β-Cells
Authors: Natali A. , Santini E. , Delbarba A. , Baldi S. , Venturi E. , Tulipani A. , Nisoli E. , Ferrannini E.
Published: February 2012

We aimed at evaluating the impact of short and prolonged mild manipulations of intracellular nitric oxide (NO) bioavailability on the main features of insulin secretion and whether NO promotes mitochondrial biogenesis in isolated β-cells.

INS-1E β-cells were exposed to either the intracellular NO donor, hydroxylamine (HA), or the NO synthase inhibitor, L-nitro-arginine-methyl-ester (l-NAME), at concentrations lower than 2.0 mM. Glucose and arginine-induced insulin secretion (GIIS and AIIS) were measured after short (1 h) or prolonged (48 h) exposure to l-NAME 1.0 and 2.0 mM or HA 0.4 and 0.8 mM, lower concentrations were also evaluated for the 1 h effects. Basal insulin secretion (BIS), with either HA or l-NAME added to culture media, and peroxisome proliferators-activated receptor γ coactivator 1α (PGC-1α), nuclear respiratory factor-1 (NRF-1), and mitochondrial DNA transcription factor-A (Tfam) gene expression during chronic HA supplementation were also measured.

Neither l-NAME nor HA affected insulin release at glucose 3.3 mM or in cell culture (BIS). Both short and prolonged cell exposure to l-NAME potentiated GIIS though with a flat dose-response curve while HA inhibited GIIS only at the highest concentration. AIIS was prevented by short exposure to l-NAME and potentiated by HA, while it did not respond to prolonged incubations. Prolonged cell exposure to HA had no effect on PGC-1α, NRF-1 or Tfam gene expression.

In INS1E cells an intact NO synthesis is necessary to limit insulin release in response to acute glucose gradients and to fully respond to arginine while intracellular NO enrichment above the physiologic levels further inhibits GIIS and potentiate AIIS only when excessive. Prolonged NO manipulations do not affect AIIS, BIS or mitochondrial biogenesis.
Recombinant Human TSH Increases Uptake and Effective Half-life of Radioiodine in Thyroid Hormone Secreting Metastases of Follicular Thyroid Cancer
Authors: Schneider C. , Dietlein M. , Eschner W. , Schmidt M. , Kahraman D. , Kobe C.
Published: February 2012

Follicular thyroid cancer with thyroid hormone secreting metastases is an extremely rare condition, with only a few cases reported world-wide.

We here present the case of a 64-year-old female patient affected by follicular thyroid cancer with extensive thyroid hormone secreting metastases leading to TSH-suppression.

We have also summarized the relevant diagnostic and therapeutic approaches and describe, for the first time, the effects of rhTSH-application in this rare tumor entity.

In this patient, we found that rhTSH increased 131I-uptake into the thyroid hormone secreting metastases and prolonged the effective half-life of 131I. These effects of rhTSH should be considered when fixed activities of 131I are prescribed.
Serum Procalcitonin and Calcitonin Normal Values Before and After Calcium Gluconate Infusion
Authors: Giovanella L.
Published: February 2012

To evaluate and compare serum procalcitonin (PCT) and calcitonin (hCT) levels before and after stimulation with intravenous calcium gluconate in selected thyroid healthy subjects.

There were enrolled 78 healthy blood donors with no history of thyroid disease, renal disease, neuroendocrine tumours, infections or inflammatory diseases, and taking no proton-pump inhibitors medication. Serum PCT and hCT were measured before and after intravenous injection of 2.5 mg/kg calcium gluconate.

Undetectable basal PCT values were found in all subjects while a marginal increase occurred only in 2 male subjects after stimulation. The basal and stimulated 95th percentile hCT values were 7.80 pg/mL and 102 pg/mL in males and 5.20 pg/mL and 78.5 pg/mL in females, respectively.

Our data suggest that calcium gluconate physiologically stimulate the release of mature hCT molecule from the parafollicular C-cells with no or minimal effects on the PCT release. Our preliminary results form a reliable reference platform for basal and calcium-stimulated PCT measurements in clinical studies.
New methods for high current fast ion beam production by laser-driven acceleration
Authors: Margarone D. , Krasa J. , Prokupek J. , Velyhan A. , Torrisi L. , Picciotto A. , Giuffrida L. , Gammino S. , Cirrone P. , Cutroneo M. , Romano F. , Serra E. , Mangione A. , Rosinski M. , Parys P. , Ryc L. , Limpouch J. , Laska L. , Jungwirth K. , Ullschmied J. , Mocek T. , Korn G. , Rus B.
Published: February 2012

An overview of the last experimental campaigns on laser-driven ion acceleration performed at the PALS facility in Prague is given. Both the 2 TW, sub-nanosecond iodine laser system and the 20 TW, femtosecond Ti:sapphire laser, recently installed at PALS, are used along our experiments performed in the intensity range 1016−1019 W/cm2. The main goal of our studies was to generate high energy, high current ion streams at relatively low laser intensities. The discussed experimental investigations show promising results in terms of maximum ion energy and current density, which make the laser-accelerated ion beams a candidate for new-generation ion sources to be employed in medicine, nuclear physics, matter physics, and industry.
Progress in the MITICA beam source design
Authors: Zaccaria P. , Agostinetti P. , Marcuzzi D. , Pavei M. , Pilan N. , Rizzolo A. , Sonato P. , Spada F. , Trevisan L.
Published: February 2012

In the framework of the development of the ITER neutral beam (NB) system, a test facility is planned to be built in Padova. A full size prototype of the ITER heating NB injector (MITICA) shall be built and tested at full beam power (17 MW) as per ITER requirements. The design of the MITICA beam source has further progressed following updated optimization and overall integration criteria. In the paper, the major design choices and revisions are presented, together with some results of numerical analyses carried out in order to assess the electrostatic and thermo-mechanical behaviour of the source.
A 3D Monte Carlo code for the modeling of plasma dynamics and beam formation mechanism in electron cyclotron resonance ion sources
Authors: Neri L. , Mascali D. , Celona L. , Gammino S. , Ciavola G.
Published: February 2012

The code here presented is the first part of a Monte Carlo (MC) self-consistent 3D plasma simulator. It is yet able to solve the equation of motion for thousands of independent charged particles. The procedure allows to understand the consequences of each phenomenon introduced in the evolution steps of the code. MC random selection of starting parameters is used for each particles; the environmental conditions enclosed in the simulation are ECRIS magnetic field, resonant electromagnetic wave, initial plasma density distribution and MC calculation of Spitzer collision. The results of the first simulations explain some typical effects as the hollow beam formation and the main plasma deconfinement mechanism.
Quaternary memory device fabricated from a single layer Fe film
Authors: Yoo Taehee , Khym S. , Lee Hakjoon , Lee Sangyeop , Lee Sanghoon , Liu X. , Furdyna J. K. , Lee Dong Uk , Kyu Kim Eun
Published: February 2012

A cross-shaped Hall device was fabricated from a single-crystal bcc Fe film having two in-plane magnetic easy axes. When a current pulse is applied to a Au strip patterned on top of the Fe Hall device, multiple domains with two orthogonal magnetization directions form in the Fe Hall device during magnetization reversal. Distributions of such domain that result in four different Hall resistance states can then be obtained by applying appropriate current pulses to the Au strip of the device. The writing of each Hall resistance state is then performed by applying a sequence of current pulses to the Au strip that generate magnetic fields required to achieve a desired domain distribution in the Fe film. Time dependent measurements show remarkably robust temporal stability for all four Hall resistance states. The demonstration of the writing process for the four distinct states in this Fe Hall device by current pulse sequences provides the possibility of realizing a practical room-temperature quaternary memory device in a single ferromagnetic film.
Enhancing and broadening absorption properties of frequency selective surfaces absorbers using FeCoB-based thin film
Authors: Ren Wenyi , Nie Yan , Xiong Xuan , Zhang Cui , Zhou Yan , Gong Rongzhou
Published: February 2012

In this paper, the influence of FeCoB-based magnetic film on the absorption properties of traditional frequency selective surface (FSS) was investigated experimentally. A single-layer Minkowski fractal planar frequency selective surface was chosen, and the laser etching technique was proposed to fabricate aluminum-based FSS (AFSS) samples. Magnetic films were prepared by radio frequency magnetron sputtering, with the targets of Fe40Co40B20 and SiO2. It is found that after the magnetic film is incorporated, the bandwidth under −10 dB increases by 33.3% from 5.08 to 6.78 GHz and the peak value of reflectivity decreases from −12.46 to −38.41 dB. The 3.1-mm-thick radar absorber is relatively light and could obtain the reflectivity of −38.41 with −20 dB bandwidth of 1.85 GHz. As a consequence, under the circumstance that the total thickness of the sample maintains relatively constant, the magnetic thin film can effectively improve the absorption properties of the sample.
Fabrication of a fully magnetic impeller for improvement of the magnetic properties of a pump with a power harvester
Authors: Kim Sung Hoon , Shin Jaewon , Hashi Shuichiro , Ishiyama Kazushi , Ozaki Masaru , Matsumura Syuji
Published: February 2012

An all-in-one wireless pump with a power generator was developed for use in biomedical applications. The developed pump is driven by an external rotating magnetic field. Thus, the performance of the system is limited by the magnetic properties of the rotor. To improve the magnetic properties of the magnetic all-in-one pump, a fully magnetic impeller was fabricated with magnetic powder (Sm2Fe17N3) because sintered magnetic materials have a lower degree of freedom for shape. The magnetic moment (M) and coercive force (Hc) of the fully magnetic impeller are 0.993 Am2 and 0.82 MA/m, respectively. We analyzed the magnetic properties of the fully magnetic impeller using simulation and experiments. In addition, we investigated the improved performance of the all-in-one pump system using the fully magnetic impeller.
Spin accumulation created electrically in an n-type germanium channel using Schottky tunnel contacts
Authors: Kasahara K. , Baba Y. , Yamane K. , Ando Y. , Yamada S. , Hoshi Y. , Sawano K. , Miyao M. , Hamaya K.
Published: February 2012

Using high-quality Fe3Si/n+-Ge Schottky-tunnel-barrier contacts, we study spin accumulation in an n-type germanium (n-Ge) channel. In the three- or two-terminal voltage measurements with low bias current conditions at 50 K, Hanle-effect signals are clearly detected only at a forward-biased contact. These are reliable evidence for electrical detection of the spin accumulation created in the n-Ge channel. The estimated spin lifetime in n-Ge at 50 K is one order of magnitude shorter than those in n-Si reported recently. The magnitude of the spin signals cannot be explained by the commonly used spin diffusion model. We discuss a possible origin of the difference between experimental data and theoretical values.
Relativistic critical density increase and relaxation and high-power pulse propagation
Authors: Weng S. M. , Mulser P. , Sheng Z. M.
Published: February 2012

High-power laser pulse propagation in an overdense plasma due to the relativistic critical density increase has been investigated in one dimension. In a first step the conditions for the existence of a relativistic critical density are delimited and supported by particle-in-cell simulations. Its accurate determination is made possible by the installation of a new numerical diagnostics. Guided by this we show that the critical density increase strongly depends on both laser polarization and plasma density profile. Further, we find a new relaxation time ranging from several to many laser cycles, which sets a limit for short laser pulse manipulation and tailoring. Paramountly, it is proved that in the power optics domain the pulse propagation velocity is inhibited by the relativistic energy density in the medium and by the efficient reflection, in contrast to the group velocity from standard dispersion optics.
Changes in density fluctuations as a result of resonant magnetic perturbations correlate with the density inverse scale length
Authors: Mordijck S. , Moyer R. A. , McKee G. R.
Published: February 2012

In this paper we show that the changes in ion-scale density fluctuations ñ/n induced by resonant magnetic perturbations (RMPs) exhibit the same trends as modifications to the inverse density scale length, a/Ln in the pedestal area. In a series of ITER similar shape (ISS) H-mode discharges in DIII-D, the n = 3 even parity RMP-coil current is varied from 4 kA up to 6.2 kA. The application of n = 3 RMPs results in an increase of a/Ln in the plasma core and a reduction in the pedestal area. Comparing the changes in a/Ln with the changes in density ion-scale fluctuations ñ/n shows that at ΨN=0.95, the ñ/n follows the trends in a/Ln. This suggests that the changes in ñ/n are due to changes in the underlying density gradient rather than due to the RMPs directly in ISS H-mode discharges in DIII-D.
Formation and structure of 360 and 540 degree domain walls in thin magnetic stripes
Authors: Jang Youngman , Bowden S. R. , Mascaro Mark , Unguris J. , Ross C. A.
Published: February 2012

360°, 540°, and other complex transverse domain walls have been created in narrow cobalt wires connected to injection pads by cycling a magnetic field perpendicular to the wire length. The composite walls, formed by impingement of 180° transverse walls of alternating chirality, are stable over a wide field range. The structure of the walls observed at remanence by scanning electron microscopy with polarization analysis and by magnetic force microscopy is in good quantitative agreement with the prediction of micromagnetic simulations.
Lowering the excitation threshold of a random laser using the dynamic scattering states of an organosiloxane smectic A liquid crystal
Authors: Morris Stephen M. , Gardiner Damian J. , Qasim Malik M. , Hands Philip J. W. , Wilkinson Timothy D. , Coles Harry J.
Published: February 2012

Smectic A liquid crystals, based upon molecular structures that consist of combined siloxane and mesogenic moieties, exhibit strong multiple scattering of light with and without the presence of an electric field. This paper demonstrates that when one adds a laser dye to these compounds it is possible to observe random laser emission under optical excitation, and that the output can be varied depending upon the scattering state that is induced by the electric field. Results are presented to show that the excitation threshold of a dynamic scattering state, consisting of chaotic motion due to electro-hydrodynamic instabilities, exhibits lower lasing excitation thresholds than the scattering states that exist in the absence of an applied electric field. However, the lowest threshold is observed for a dynamic scattering state that does not have the largest scattering strength but which occurs when there is optimization of the combined light absorption and scattering properties.
Phononic crystal diffraction gratings
Authors: Moiseyenko Rayisa P. , Herbison Sarah , Declercq Nico F. , Laude Vincent
Published: February 2012

When a phononic crystal is interrogated by an external source of acoustic waves, there is necessarily a phenomenon of diffraction occurring on the external enclosing surfaces. Indeed, these external surfaces are periodic and the resulting acoustic diffraction grating has a periodicity that depends on the orientation of the phononic crystal. This work presents a combined experimental and theoretical study on the diffraction of bulk ultrasonic waves on the external surfaces of a 2D phononic crystal that consists of a triangular lattice of steel rods in a water matrix. The results of transmission experiments are compared with theoretical band structures obtained with the finite-element method. Angular spectrograms (showing frequency as a function of angle) determined from diffraction experiments are then compared with finite-element simulations of diffraction occurring on the surfaces of the crystal. The experimental results show that the diffraction that occurs on its external surfaces is highly frequency-dependent and has a definite relation with the Bloch modes of the phononic crystal. In particular, a strong influence of the presence of bandgaps and deaf bands on the diffraction efficiency is found. This observation opens perspectives for the design of efficient phononic crystal diffraction gratings.
Schlieren imaging in a dielectric barrier discharge actuator for airflow control
Authors: Cristofolini A. , Neretti G. , Roveda F. , Borghi C. A.
Published: February 2012

The operation of a surface dielectric barrier discharge actuator for airflow control has been experimentally investigated. The actuator is constituted by an electrode pair separated by a dielectric Teflon sheet. Several ac supply conditions have been utilized. An electrohydrodynamics interaction was induced in still air, and several fluid-dynamic regimes were obtained. Visualization of the plasma boundary layer during the discharge ignition phase and during the steady state regime was obtained by utilizing a Schlieren diagnostic technique. The vortex morphology and propagation velocities at all supply conditions utilized have been evaluated. Velocity profiles perpendicular to the actuator surface, obtained from Pitot tube measurements, and line intensity profiles, determined by means of Schlieren imaging, have been determined for the steady regime operation. The integral along a line perpendicular to the actuator surface of the light intensity of the Schlieren image has been calculated. The profile obtained is in good agreement with the Pitot velocity profile in all the supply conditions investigated. Numerical simulations were also performed. The calculations confirm the relation between the flow velocity distribution in the boundary layer and the gas density distribution, which is the cause of the Schlieren image.
First-principles investigation of pressure-induced phase transition in LiNbO3
Authors: Nakamura Kaoru , Higuchi Sadao , Ohnuma Toshiharu
Published: February 2012

We explore the possible high-pressure phase transition of LiNbO3 using an evolutionary algorithm combined with first-principles calculations. A NaIO3-type structure with Pnma symmetry was predicted as the room temperature phase, and an apatite-like structure with P63/m symmetry was predicted as the high temperature, high-pressure phase. These predictions are consistent with the experimental findings of Mukaide et al. [J. Appl. Phys. 93, 3852 (2003)]. Interestingly, however, the thermodynamic stability of the Cmcm phase was found to be greater than that of the Pnma phase below 50 GPa. In order to explain this, we investigated the possible deformation paths between R3c and high-pressure phases and found that a high energy barrier hinders Cmcm formation, despite its greater thermodynamic stability. In sum, our results indicate that an understanding of the atomistic mechanisms behind phase transition is essential in order to correctly predict phase transition behavior.
Thickness-dependent converse magnetoelectric coupling in bi-layered Ni/PZT thin films
Authors: Li Zheng , Hu Jiamian , Shu Li , Gao Ya , Shen Yang , Lin Yuanhua , Nan C. W.
Published: February 2012

The converse magnetoelectric (ME) effect was investigated in bi-layered Ni/Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Si substrates, with different thicknesses of Ni thin layers. By using an AC-mode magneto-optical Kerr effect method, it was revealed that the electric-voltage induced magnetization variation was dependent on the thickness of the Ni thin layer. The results showed that the Ni/PZT bilayered films with thick (about 40 nm) Ni films presented a dominative strain mediated ME coupling, whereas an interface-charge and strain co-mediated ME coupling might coexist in the Ni/PZT bilayered films with decreasing thickness (e.g., about 10 nm) of Ni films.
Oscillatory bubbles induced by geometrical constraint
Authors: Pailha M. , Hazel A. L. , Glendinning P. A. , Juel A.
Published: February 2012

We show that a simple change in pore geometry can radically alter the behavior of a fluid-displacing air finger, indicating that models based on idealized pore geometries fail to capture key features of complex practical flows. In particular, partial occlusion of a rectangular cross section can force a transition from a steadily propagating centered finger to a state that exhibits spatial oscillations formed by periodic sideways motion of the interface at a fixed distance behind the moving finger tip. We characterize the dynamics of the oscillations, which suggest that they arise from a global homoclinic connection between the stable and unstable manifolds of a steady, symmetry-broken solution.
Coherent control and time-dependent density functional theory: Towards creation of wave packets by ultrashort laser pulses
Authors: Raghunathan Shampa , Nest Mathias
Published: February 2012

Explicitly time-dependent density functional theory (TDDFT) is a formally exact theory, which can treat very large systems. However, in practice it is used almost exclusively in the adiabatic approximation and with standard ground state functionals. Therefore, if combined with coherent control theory, it is not clear which control tasks can be achieved reliably, and how this depends on the functionals. In this paper, we continue earlier work in order to establish rules that answer these questions. Specifically, we look at the creation of wave packets by ultrashort laser pulses that contain several excited states. We find that (i) adiabatic TDDFT only works if the system is not driven too far from the ground state, (ii) the permanent dipole moments involved should not differ too much, and (iii) these results are independent of the functional used. Additionally, we find an artifact that produces fluence-dependent excitation energies.
Assessment of ozone generation in dry air fed silent discharge reactors
Authors: Yehia Ashraf
Published: February 2012

Two equations have been derived in this paper for expecting the ozone generation inside dry air fed silent discharge reactors. The derived equations have been built on theories of the silent discharges and their applications, reported in the literature. The two equations have been investigated individually with experimental results for ozone generated by silent discharges in coaxial cylindrical reactors. The reactors were stressed with an ac voltage and fed by dry air flowing with constant rates at atmospheric pressure and room temperature. The results, that have been calculated by the two equations individually, have agreed with the experimental results over the whole range of the investigated parameters. Subsequently, the two derived equations represent suitable criteria for expecting the ozone concentration generated by silent discharges in dry air fed coaxial cylindrical reactors under any discharge conditions in range of the investigated parameters.
Kinetic pathways to peptide aggregation on surfaces: The effects of β-sheet propensity and surface attraction
Authors: Morriss-Andrews Alex , Shea Joan-Emma
Published: February 2012

Mechanisms of peptide aggregation on hydrophobic surfaces are explored using molecular dynamics simulations with a coarse-grained peptide representation. Systems of peptides are studied with varying degrees of backbone rigidity (a measure of β-sheet propensity) and degrees of attraction between their hydrophobic residues and the surface. Multiple pathways for aggregation are observed, depending on the surface attraction and peptide β-sheet propensity. For the case of a single-layered β-sheet fibril forming on the surface (a dominant structure seen in all simulations), three mechanisms are observed: (a) a condensation-ordering transition where a bulk-formed amorphous aggregate binds to the surface and subsequently rearranges to form a fibril; (b) the initial formation of a single-layered fibril in the bulk depositing flat on the surface; and (c) peptides binding individually to the surface and nucleating fibril formation by individual peptide deposition. Peptides with a stiffer chiral backbone prefer mechanism (b) over (a), and stronger surface attractions prefer mechanism (c) over (a) and (b). Our model is compared to various similar experimental systems, and an agreement was found in terms of the surface increasing the degree of fibrillar aggregation, with the directions of fibrillar growth matching the crystallographic symmetry of the surface. Our simulations provide details of aggregate growth mechanisms on scales inaccessible to either experiment or atomistic simulations.
Constant tip-surface distance with atomic force microscopy via quality factor feedback
Authors: Fan Lin , Potter Daniel , Sulchek Todd
Published: February 2012

The atomic force microscope (AFM) is a powerful and widely used instrument to image topography and measure forces at the micrometer and nanometer length scale. Because of the high degree of operating accuracy required of the instrument, small thermal and mechanical drifts of the cantilever and piezoactuator systems hamper measurements as the AFM tip drifts spatially relative to the sample surface. To compensate for the drift, we control the tip-surface distance by monitoring the cantilever quality factor (Q) in a closed loop. Brownian thermal fluctuations provide sufficient actuation to accurately determine cantilever Q by fitting the thermal noise spectrum to a Lorentzian function. We show that the cantilever damping is sufficiently affected by the tip-surface distance so that the tip position of soft cantilevers can be maintained within 40 nm of a setpoint in air and within 3 nm in water with 95% reliability. Utilizing this method to hover the tip above a sample surface, we have the capability to study sensitive interactions at the nanometer length scale over long periods of time.
Electronic states and the influence of oxygen addition on the optical absorption behaviour of manganese phthalocyanine
Authors: Friedrich R. , Hahn T. , Kortus J. , Fronk M. , Haidu F. , Salvan G. , Zahn D. R. T. , Schlesinger M. , Mehring M. , Roth F. , Mahns B. , Knupfer M.
Published: February 2012

The effects of electronic states and air exposure on the spectroscopic properties of manganese phthalocyanine (MnPc) have been examined. The observed features of the Q-band in the absorption spectra can be explained by intrinsic electronic properties of MnPc, i.e., the formation of singly charged molecules by charge transfer excitations. However, the reaction of MnPc with atmospheric molecular oxygen leads to deviations in peak intensities but does not change the fundamental characteristics of the spectra. Nevertheless, the reaction with oxygen changes the spin state from S = 3/2 to S = 1/2. X-ray diffraction measurements also indicate a slow diffusion process of the oxygen into the MnPc crystal. We discuss both influences to explain the behaviour of MnPc in various spectroscopic methods (EELS, ellipsometry, PES). Furthermore, we support the experimental investigations by detailed ab-initio calculations of spectroscopic properties using methods of the density functional theory framework.
Mechanism of OH radical hydration: A comparative computational study of liquid and supercritical solvent
Authors: Swiatla-Wojcik Dorota , Szala-Bilnik Joanna
Published: February 2012

Flexible models of the radical and water molecules including short-range interaction of hydrogen atoms have been employed in molecular dynamic simulation to understand mechanism of •OH hydration in aqueous systems of technological importance. A key role of H-bond connectivity patterns of water molecules has been identified. The behavior of •OHaq strongly depends on water density and correlates with topological changes in the hydrogen-bonded structure of water driven by thermodynamic conditions. Liquid and supercritical water above the critical density exhibit the radical localization in cavities existing in the solvent structure. A change of mechanism has been found at supercritical conditions below the critical density. Instead of cavity localization, we have identified accumulation of water molecules around •OH associated with the formation of a strong H-donor bond and diminution of non-homogeneity in the solvent structure. For all the systems investigated, the computed hydration number and the internal energy of hydration ΔhU showed approximately linear decrease with decreasing density of the solvent but a degree of radical-water hydrogen bonding exhibited non-monotonic dependence on density. The increase in the number of radical-water H-acceptor bonds is associated with diminution of extended nets of four-bonded water molecules in compressed solution at ∼473 K. Up to 473 K, the isobaric heat of hydration in compressed liquid water remains constant and equal to −40 ± 1 kJ mol−1.
Electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with cationic ordering
Authors: Zhu Min , Lin Yong , Lo Edward W. C. , Wang Qiong , Zhao Zhengjie , Xie Wenhui
Published: February 2012

Employing first-principles electronic structure calculations, the electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with Ni/Mn and Co/Mn ordering in (001), (110), and (111) directions are investigated. The ground states of La2NiMnO6 and La2CoMnO6 are ferromagnetic semiconducting with alternative Ni/Mn and Co/Mn ordering along the (111) direction. Furthermore, it is found that La2NiMnO6 and La2CoMnO6 are half-metal with Ni/Mn or Co/Mn ordering along (001) and (110) after considering the effect of electronic correlation. Our results would be helpful in exploring more spintronics materials.
The reflex gyrotron
Authors: Goldenberg A. L. , Savilov A. V. , Yulpatov V. K.
Published: February 2012

A typical problem of low-power short-wavelength gyrotrons is that a too long cavity is required to provide the start of rf oscillations. Therefore, it is attractive to realize a gyrotron with a long enough operating region but relatively low diffraction Q-factor of the operating cavity. In this work, we propose a gyrotron with reflecting of electrons back to the operating cavity. Such a scheme provides significant decrease of the starting current and considerable efficiency enhancement.
Tantalum nitride superconducting single-photon detectors with low cut-off energy
Authors: Engel A. , Aeschbacher A. , Inderbitzin K. , Schilling A. , Il’in K. , Hofherr M. , Siegel M. , Semenov A. , Hübers H.-W.
Published: February 2012

Materials with a small superconducting energy gap are expected to favor a high detection efficiency of low-energy photons in superconducting nanowire single-photon detectors. We developed a TaN detector with smaller gap and lower density of states at the Fermi energy than in comparable NbN devices, while other relevant parameters remain essentially unchanged. The observed reduction of the minimum photon energy required for direct detection is in line with model predictions of ≈1/3 as compared to NbN.
Mechanically compliant grating reflectors for optomechanics
Authors: Kemiktarak Utku , Metcalfe Michael , Durand Mathieu , Lawall John
Published: February 2012

We demonstrate micromechanical reflectors with a reflectivity as large as 99.4% and a mechanical quality factor Q as large as 7.8 × 105 for optomechanical applications. The reflectors are silicon nitride membranes patterned with sub-wavelength grating structures, obviating the need for the many dielectric layers used in conventional mirrors. We have employed the reflectors in the construction of a Fabry-Perot cavity with a finesse as high as F = 1200, and used the optical response to probe the mechanical properties of the membrane.
Large converse magnetoelectric response in Rosen-type transformer and Terfenol-D laminated composite
Authors: Zhou Jian-Ping , Wang Pan , Yang Jia , Liu Peng , Zhang Huai-Wu
Published: February 2012

A magnetoelectric laminate composite was proposed by combing a piezoelectric transformer and a Terfenol-D plate. Converse magnetoelectric effect was researched by using an induction method with frequency, bias magnetic field, ac voltage, and Terfenol-D thickness. A giant converse magnetoelectric coefficient of 35.7 G/V was obtained at half-wavelength vibration mode in the composite with the Terfenol-D thickness of 0.7 mm, which is a great improvement in comparison with the previous reports. The magnetoelectric distribution exhibited that the converse magnetoelectric effect was dominated by the stress in the composite.
How to impose stick boundary conditions in coarse-grained hydrodynamics of Brownian colloids and semi-flexible fiber rheology
Authors: Groot Robert D.
Published: February 2012

Long-range hydrodynamics between colloidal particles or fibers is modelled by the fluid particle model. Two methods are considered to impose the fluid boundary conditions at colloidal surfaces. In the first method radial and transverse friction forces between particle and solvent are applied such that the correct friction and torque follows for moving or rotating particles. The force coefficients are calculated analytically and checked by numerical simulation. In the second method a collision rule is used between colloidal particle and solvent particle that imposes the stick boundary conditions exactly. The collision rule comprises a generalisation of the Lowe-Anderson thermostat to radial and transverse velocity differences.
Investigation of the band offsets caused by thin Al2O3 layers in HfO2 based Si metal oxide semiconductor devices
Authors: Kornblum Lior , Meyler Boris , Cytermann Catherine , Yofis Svetlana , Salzman Joseph , Eizenberg Moshe
Published: February 2012

Ultrathin dielectric capping layers are a prominent route for threshold voltage control in advanced Si devices. In this work the position of an Al2O3 layer inside a HfO2-based stack is systematically varied and investigated following a low and a high temperature anneal. Electrical results are compared with a sub-nanometer resolution materials characterization, showing a diffusion of Al to the bottom HfO2 interface. A correlation is found between the presence of Al at the bottom interface and a flatband voltage increase. Based on these findings, we propose to use the position of the Al2O3 for fine-tuning the threshold voltage.
Surprising complexity of the Asf1 histone chaperone-Rad53 kinase interaction
Authors: Jiao Yue , Seeger Karsten , Lautrette Aurelie , Gaubert Albane , Mousson Florence , Guerois Raphael , Mann Carl , Ochsenbein Françoise
Published: February 2012

The histone chaperone Asf1 and the checkpoint kinase Rad53 are found in a complex in budding yeast cells in the absence of genotoxic stress. Our data suggest that this complex involves at least three interaction sites. One site involves the H3-binding surface of Asf11 with an as yet undefined surface of Rad53. A second site is formed by the Rad53-FHA1 domain binding to Asf1-
T
270
phosphorylated by casein kinase II. The third site involves the C-terminal 21 amino acids of Rad53 bound to the conserved Asf1 N-terminal domain. The structure of this site showed that the Rad53 C-terminus binds Asf1 in a remarkably similar manner to peptides derived from the histone cochaperones HirA and CAF-I. We call this binding motif, (
R
/
K
)
R
(
I
/
A
/
V
) × (
L
/
P
), the AIP box for Asf1-Interacting Protein box. Furthermore, C-terminal Rad53-
F
820
binds the same pocket of Asf1 as does histone
H
4-
F
100
. Thus Rad53 competes with histones H3-H4 and cochaperones HirA/CAF-I for binding to Asf1. Rad53 is phosphorylated and activated upon genotoxic stress. The Asf1-Rad53 complex dissociated when cells were treated with hydroxyurea but not methyl-methane-sulfonate, suggesting a regulation of the complex as a function of the stress. We identified a
rad53
mutation that destabilized the Asf1-Rad53 complex and increased the viability of
rad9
and
rad24
mutants in conditions of genotoxic stress, suggesting that complex stability impacts the DNA damage response.
Significance analysis of xMap cytokine bead arrays
Authors: Won Joong-Ho , Goldberger Ofir , Shen-Orr Shai S. , Davis Mark M. , Olshen Richard A.
Published: February 2012

Highly multiplexed assays using antibody coated, fluorescent (xMap) beads are widely used to measure quantities of soluble analytes, such as cytokines and antibodies in clinical and other studies. Current analyses of these assays use methods based on standard curves that have limitations in detecting low or high abundance analytes. Here we describe SAxCyB (Significance Analysis of xMap Cytokine Beads), a method that uses fluorescence measurements of individual beads to find significant differences between experimental conditions. We show that SAxCyB outperforms conventional analysis schemes in both sensitivity (low fluorescence) and robustness (high variability) and has enabled us to find many new differentially expressed cytokines in published studies.
Design of a binding scaffold based on variable lymphocyte receptors of jawless vertebrates by module engineering
Authors: Lee Sang-Chul , Park Keunwan , Han Jieun , Lee Joong-jae , Kim Hyun Jung , Hong Seungpyo , Heu Woosung , Kim Yu Jung , Ha Jae-Seok , Lee Seung-Goo , Cheong Hae-Kap , Jeon Young Ho , Kim Dongsup , Kim Hak-Sung
Published: February 2012

Repeat proteins have recently been of great interest as potential alternatives to immunoglobulin antibodies due to their unique structural and biophysical features. We here present the development of a binding scaffold based on variable lymphocyte receptors, which are nonimmunoglobulin antibodies composed of Leucine-rich repeat modules in jawless vertebrates, by module engineering. A template scaffold was first constructed by joining consensus repeat modules between the N- and C-capping motifs of variable lymphocyte receptors. The N-terminal domain of the template scaffold was redesigned based on the internalin-B cap by analyzing the modular similarity between the respective repeat units using a computational approach. The newly designed scaffold, termed “Repebody,” showed a high level of soluble expression in bacteria, displaying high thermodynamic and pH stabilities. Ease of molecular engineering was shown by designing repebodies specific for myeloid differentiation protein-2 and hen egg lysozyme, respectively, by a rational approach. The crystal structures of designed repebodies were determined to elucidate the structural features and interaction interfaces. We demonstrate general applicability of the scaffold by selecting repebodies with different binding affinities for interleukin-6 using phage display.
Protein-flexibility mediated coupling between photoswitching kinetics and surrounding viscosity of a photochromic fluorescent protein
Authors: Kao Ya-Ting , Zhu Xinxin , Min Wei
Published: February 2012

Recent advances in fluorescent proteins (FPs) have generated a remarkable family of optical highlighters with special light responses. Among them, Dronpa exhibits a unique capability of reversible light-regulated on-off switching. However, the environmental dependence of this photochromism is largely unexplored. Herein we report that the photoswitching kinetics of the chromophore inside Dronpa is actually slowed down by increasing medium viscosity outside Dronpa. This finding is a special example of an FP where the environment can exert a hydrodynamic effect on the internal chromophore. We attribute this effect to protein-flexibility mediated coupling where the chromophore’s
cis-trans
isomerization during photoswitching is accompanied by conformational motion of a part of the protein β-barrel whose dynamics should be hindered by medium friction. Consistent with this mechanism, the photoswitching kinetics of Dronpa-3, a structurally more flexible mutant, is found to exhibit a more pronounced viscosity dependence. Furthermore, we mapped out spatial distributions of microviscosity in live cells experienced by a histone protein using the photoswitching kinetics of Dronpa-3 fusion as a contrast mechanism. This unique reporter should provide protein-specific information about the crowded intracellular environments by offering a genetically encoded microviscosity probe, which did not exist with normal FPs before.
DNA cleavage and opening reactions of human topoisomerase IIα are regulated
via
Mg
2+
-mediated dynamic bending of gate-DNA
Authors: Lee Sanghwa , Jung Seung-Ryoung , Heo Kang , Byl Jo Ann W. , Deweese Joseph E. , Osheroff Neil , Hohng Sungchul
Published: February 2012

Topoisomerase II resolves intrinsic topological problems of double-stranded DNA. As part of its essential cellular functions, the enzyme generates DNA breaks, but the regulation of this potentially dangerous process is not well understood. Here we report single-molecule fluorescence experiments that reveal a previously uncharacterized sequence of events during DNA cleavage by topoisomerase II: nonspecific DNA binding, sequence-specific DNA bending, and stochastic cleavage of DNA. We have identified unexpected structural roles of Mg
2+
ions coordinated in the TOPRIM (topoisomerase-primase) domain in inducing cleavage-competent DNA bending. A break at one scissile bond dramatically stabilized DNA bending, explaining how two scission events in opposing strands can be coordinated to achieve a high probability of double-stranded cleavage. Clamping of the protein
N
-gate greatly enhanced the rate and degree of DNA bending, resulting in a significant stimulation of the DNA cleavage and opening reactions. Our data strongly suggest that the accurate cleavage of DNA by topoisomerase II is regulated through a tight coordination with DNA bending.