bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar cycle effect delays onset of ozone recovery
Authors: Dameris M. , Matthes S. , Deckert R. , Grewe V. , Ponater M.
Published: February 2006

Short‐ and long‐term changes of total ozone are investigated by means of an ensemble simulation with the coupled chemistry‐climate model E39/C for the period 1960 to 2020. Past total ozone changes are well simulated on both, long (decadal) and short (monthly) timescales. Even the 2002 Antarctic ozone anomaly appears in the ensemble. The model results indicate that the 11‐year solar cycle will delay the onset of a sustained ozone recovery. The lowest global mean total ozone values occur between 2005 and 2010, although stratospheric chlorine loading is assumed to decline after 2000. E39/C results exhibit a significant increase of total ozone after the beginning of the next decade, following the upcoming solar minimum. The observed ozone increase in the second half of the 1990s is reproduced by E39/C and is identified as a combined post‐Pinatubo and solar cycle effect rather than the beginning of a sustainable ozone recovery.
First detection of meso‐thermospheric Nitric Oxide (NO) by ground‐based FTIR solar absorption spectroscopy
Authors: Wiacek A. , Jones N. B. , Strong K. , Taylor J. R. , Mittermeier R. L. , Fast H.
Published: February 2006

We report the first detection of mesospheric‐lower thermospheric (MLT, 50–130 km) NO from ground‐based FTIR solar absorption spectra using Lorentz‐ and Doppler‐broadened solar absorption lines in the stratosphere and in the MLT, respectively. We present the first characterization of vertical sensitivity in the FTIR NO retrieval and show that MLT NO partial columns can be retrieved with ∼1 independent piece of information using a climatological NO profile extending up to 130 km. The information content analysis also improves the characterization of stratospheric partial column retrievals and is relevant to NO results obtained at other Network for the Detection of Stratospheric Change (NDSC) FTIR sites. We apply our approach to spectra recorded at Complementary NDSC site Toronto (43.66°N, 79.40°W) during the solar storms of Oct–Nov 2003 and at Primary NDSC site Eureka (80.05°N, 86.42°W) during Feb–Mar 2004. MLT NO enhancements are found at Eureka, while possible enhancements at Toronto cannot be attributed to a particular altitude.
SST forcing of decadal Indian Monsoon rainfall variability
Authors: Kucharski F. , Molteni F. , Yoo J. H.
Published: February 2006

Using ensemble integrations of an Atmospheric General Circulation Model (AGCM) forced globally with observed sea surface temperature (SST) anomalies it is shown that the observed decadal variability of Indian monsoon rainfall (IMR) can be reproduced, although amplitudes are somewhat overestimated. A second AGCM ensemble forced only in the Indian Ocean region suggests that the local Indian Ocean SST forcing is contributing significantly to the decadal IMR variability. Here, cold (warm) equatorial SSTs cause low‐level divergence (convergence) that in turn modifies the local Hadley circulation and strengthens (weakens) the Indian monsoon circulation. This result is complementary to previous findings that IMR variability is mainly determined by an atmospheric teleconnection with ENSO.
High‐pressure alloying of iron and xenon: “Missing” Xe in the Earth's core?
Authors: Lee Kanani K. M. , Steinle‐Neumann Gerd
Published: February 2006

Ab initio quantum mechanical calculations show that xenon (Xe) can be alloyed with hexagonal close‐packed iron at high pressure through substitutional incorporation, with a favorable enthalpy of formation for the alloy relative to the separate elemental solids, suggesting that Xe is soluble in the Earth's iron‐rich core (up to ∼0.8 mol %). This alloying behavior and the possible presence of a significant amount of Xe in the core are important for understanding the accretion and evolution of the Earth and its atmosphere.
Small‐scale, spatially distributed water management practices: Implications for research in the hydrologic sciences
Authors: Potter Kenneth W.
Published: February 2006

Traditional water resources management in the United States relies heavily on the use of centralized facilities, such as regional wastewater treatment plants and flood control reservoirs. Increasing concern for human impacts on aquatic systems and diminished federal support for large water management projects are motivating the increased use of small‐scale, widely distributed practices, such as treatment wetlands and infiltration practices. These practices, which exploit or enhance natural systems and processes, can be used alone or in conjunction with traditional practices to enhance performance and reduce environmental impacts. The use of smaller, more distributed water management practices challenges the hydrological science community to improve its capacity for assessing and predicting hydrologic conditions and to make this capacity accessible to water resource practitioners.
Hydrologic synthesis: Across processes, places, and scales
Authors: Blöschl Günter
Published: February 2006

Hydrologic synthesis, I believe, is needed in at least three respects: across processes, where the challenge is how to represent complex interacting dynamic systems including feedbacks between system components; across places, where the challenge is how to synthesize the plethora of case studies around the world in the past decades; and across scales, where one is interested in the general characteristics of processes as a function of space and time scales for the same site or an ensemble of sites. Seeking explanations for patterns, puzzles, and paradoxes is the way toward synthesis, and this should be pursued through two approaches. The first is to engage in more complex model building, but model complexity may ultimately limit the practical applicability of these models. The alternative is to seek more parsimonious avenues to synthesis. One of them is classification and similarity concepts which, generally speaking, can be profitably used when the processes are not fully understood. This often is the case in hydrology. Among the key unresolved issues and research challenges in hydrology is separating the predictable and the unpredictable. Synthesis, I think, needs to focus on the patterns of predictability. There is also an important, alternative, role of models in water resources management using models as communication tools. The best model then is not the most accurate one but the one that serves best the purpose of reaching a consensus among the players.
Purinoceptors as therapeutic targets for lower urinary tract dysfunction
Authors: Ford Anthony P D W. , Gever Joel R. , Nunn Philip A. , Zhong Yu , Cefalu Joseph S. , Dillon Michael P. , Cockayne Debra A.
Published: February 2006

Lower urinary tract symptoms (LUTS) are present in many common urological syndromes. However, their current suboptimal management by muscarinic and α1‐adrenoceptor antagonists leaves a significant opportunity for the discovery and development of superior medicines. As potential targets for such therapeutics, purinoceptors have emerged over the last two decades from investigations that have established a prominent role for ATP in the regulation of urinary bladder function under normal and pathophysiological conditions. In particular, evidence suggests that ATP signaling via P2X1 receptors participates in the efferent control of detrusor smooth muscle excitability, and that this function may be heightened in disease and aging. ATP also appears to be involved in bladder sensation, via activation of P2X3 and P2X2/3 receptors on sensory afferent neurons, both within the bladder itself and possibly at central synapses. Such findings are based on results from classical pharmacological and localization studies in non‐human and human tissues, knockout mice, and studies using recently identified pharmacological antagonists – some of which possess attributes that offer the potential for optimization into candidate drug molecules. Based on recent advances in this field, it is clearly possible that the development of selective antagonists for these receptors will occur that could lead to therapies offering better relief of sensory and motor symptoms for patients, while minimizing the systemic side effects that limit current medicines.

British Journal of Pharmacology (2006) 147, S132–S143. doi:10.1038/sj.bjp.0706637
Protection of Adult Mouse Progenitor Cells and Human Glioma Cells by de novo Decorin Expression in an Oxygen- and Glucose-Deprived Cell Culture Model System
Authors: Santra Manoranjan , Katakowski Mark , Zhang Rui Lan , Meng He , Jiang Feng , Chopp Michael
Published: February 2006

We employed an in vitro hypoxia cell culture model system and gene transfer technology to examine the effect of the decorin gene on cell survival against oxygen and glucose deprivation (OGD). Ectopic expression of decorin in subventricular zone (SVZ) cells from adult male mouse brain and human glioblastoma U-87 cells kept the cells viable against 24 h of OGD. Fewer than 1% of decorin-synthesizing cells were apoptotic after 12 h of OGD. In contrast, 100% of the control cells were apoptotic even after 4h of OGD. De novo decorin synthesis in SVZ and U-87 cells induced expression of p21, p27 and Ras, AKT (acutely transforming retrovirus AKT8 in rodent T-cell lymphoma), and phosphorylated AKT. Blocking of phosphoinositide 3-kinase (PI-3K), Ras, and the epidermal growth factor receptor with specific inhibitors had no effect on induction of Ras, p21, and p27 at the messenger RNA level in decorin-synthesizing SVZ and U-87 cells. PI-3K inhibitors significantly increased apoptosis in decorin-expressing cells. Our data indicate that induction of p21, p27, Ras, AKT, and phosphorylated AKT by decorin inhibits apoptosis and protects U-87 and SVZ cells against OGD. Therefore, our data suggest that decorin is a potent trophic factor that protects neuronal progenitor cells and glioma cells from OGD.
Spheromak formation and sustainment studies at the sustained spheromak physics experiment using high-speed imaging and magnetic diagnostics
Authors: Romero-Talamás C. A. , Holcomb C. , Bellan P. M. , Hill D. N.
Published: February 2006

A high-speed imaging system with shutter speeds as fast as 2ns and double frame capability has been used to directly image the formation and evolution of the sustained spheromak physics experiment (SSPX) [E. B. Hooper et al., Nucl. Fusion 39, 863 (1999)]. Reproducible plasma features have been identified with this diagnostic and divided into three groups, according to the stage in the discharge at which they occur: (i) breakdown and ejection, (ii) sustainment, and (iii) decay. During the first stage, plasma descends into the flux conserver shortly after breakdown and a transient plasma column is formed. The column then rapidly bends and simultaneously becomes too dim to photograph a few microseconds after formation. It is conjectured here that this rapid bending precedes the transfer of toroidal to poloidal flux. During sustainment, a stable plasma column different from the transient one is observed. It has been possible to measure the column diameter and compare it to CORSICA [A. Tarditi et al., Contrib. Plasma Phys. 36, 132 (1996)], a magnetohydrodynamic equilibrium reconstruction code which showed good agreement with the measurements. Elongation and velocity measurements were made of cathode patterns also seen during this stage, possibly caused by pressure gradients or E×B drifts. The patterns elongate in a toroidal-only direction which depends on the magnetic-field polarity. During the decay stage the column diameter expands as the current ramps down, until it eventually dissolves into filaments. With the use of magnetic probes inserted in the gun region, an X point which moved axially depending on current level and toroidal mode number was observed in all the stages of the SSPX plasma discharge.
Exact decoupling of the Dirac Hamiltonian. IV. Automated evaluation of molecular properties within the Douglas-Kroll-Hess theory up to arbitrary order
Authors: Wolf Alexander , Reiher Markus
Published: February 2006

In Part III [J. Chem. Phys. 124, 064102 (2005)] of this series of papers on exact decoupling of the Dirac Hamiltonian within transformation theory, we developed the most general account on how to treat magnetic and electric properties in a unitary transformation theory on the same footing. In this paper we present an implementation of a general algorithm for the calculation of magnetic as well as electric properties within the framework of Douglas-Kroll-Hess theory. The formal and practical principles of this algorithm are described. We present the first high-order Douglas-Kroll-Hess results for property operators. As for model properties we propose to use the well-defined radial moments, i.e., expectation values of rk, which can be understood as terms of the Taylor-series expansion of any property operator. Such moments facilitate a rigorous comparison of methods free of uncertainties which may arise in a direct comparison with experiment. This is important in view of the fact that various approaches to two-component molecular properties may yield numerically very small terms whose approximate or inaccurate treatment would not be visible in a direct comparison to experimental data or to another approximate computational reference. Results are presented for various degrees of decoupling of the model properties within the Douglas-Kroll-Hess scheme.
Complete mapping of the morphologies of some linear and graft fluorinated co-oligomers in an aprotic solvent by dissipative particle dynamics
Authors: Sema Özen Alimet , Sen Unal , Atilgan Canan
Published: February 2006

The mesoscopic morphologies of linear and graft fluorinated block copolymers of ABCBA and C:BA types, respectively, have been investigated by using dissipative particle dynamics method. Self-assembly in a selective solvent has been examined by the introduction of dimethylformamide as the choice of solvent. By comparing the solubility parameters calculated using atomistic simulations, fluorine-containing segments are found to be immiscible both with other segments of the polymer and with the solvent. Morphologies of the pure linear and graft copolymers were lamellar and cylindrical, respectively. Interfacial tension versus concentration curves have been used to explain the self-assembly behavior of copolymers in solution, as well as to predict the kinetic mechanisms responsible for this behavior.
Information theoretical properties of Tsallis entropies
Authors: Furuichi Shigeru
Published: February 2006

A chain rule and a subadditivity for the entropy of type β, which is one of the nonadditive entropies, were derived by Daróczy. In this paper, we study the further relations among Tsallis type entropies which are typical nonadditive entropies. The chain rule is generalized by showing it for Tsallis relative entropy and the nonadditive entropy. We show some inequalities related to Tsallis entropies, especially the strong subadditivity for Tsallis type entropies and the subadditivity for the nonadditive entropies. The subadditivity and the strong subadditivity naturally lead to define Tsallis mutual entropy and Tsallis conditional mutual entropy, respectively, and then we show again chain rules for Tsallis mutual entropies. We give properties of entropic distances in terms of Tsallis entropies. Finally we show parametrically extended results based on information theory.
Separation of noncommutative differential calculus on quantum Minkowski space
Authors: Bachmaier Fabian , Blohmann Christian
Published: February 2006

Noncommutative differential calculus on quantum Minkowski space is not separated with respect to the standard generators, in the sense that partial derivatives of functions of a single generator can depend on all other generators. It is shown that this problem can be overcome by a separation of variables. We study the action of the universal L-matrix, appearing in the coproduct of partial derivatives, on generators. Powers of the resulting quantum Minkowski algebra valued matrices are calculated. This leads to a nonlinear coordinate transformation which essentially separates the calculus. A compact formula for general derivatives is obtained in form of a chain rule with partial Jackson derivatives. It is applied to the massive quantum Klein-Gordon equation by reducing it to an ordinary q-difference equation. The rest state solution can be expressed in terms of a product of q-exponential functions in the separated variables.
Accurate and efficient method for the treatment of exchange in a plane-wave basis
Authors: Sorouri A. , Foulkes W. M. C. , Hine N. D. M.
Published: February 2006

We describe an accurate and efficient extension of Chawla and Voth’s [J. Chem. Phys. 108, 4697 (1998)] plane-wave based algorithm for calculating exchange energies, exchange energy densities, and exchange energy gradients with respect to wave-function parameters in systems of electrons subject to periodic boundary conditions. The theory and numerical results show that the computational effort scales almost linearly with the number of plane waves and quadratically with the number of k vectors. To obtain high accuracy with relatively few k vectors, we use an adaptation of Gygi and Baldereschi’s [Phys. Rev. B 34, 4405 (1986)] method for reducing Brillouin-zone integration errors.
Wagging the contact line: Transverse and longitudinal waves
Authors: Saritha S. , Neogi P.
Published: February 2006

Kinetics of wetting has been explored where the contact line not only sees a steady spreading but also has longitudinal or transverse oscillations imposed on it. The latter case is realized when spreading takes place over a rough surface. The effects of the imposed motion are small, which seem to be due to low spreading rates and small dynamic contact angles used in this study. However, a singularity is seen in viscous dissipation during the movement on the model rough surface, which is interpreted here as an instability that is similar to Haines’ jumps and stick-slip phenomena, with possible entrainment of the displaced fluid. This is the first time that all of these have been associated with each other.
Constant surface-tension molecular-dynamics simulation methods for anisotropic systems
Authors: Aoki Keiko M. , Yoneya Makoto , Yokoyama Hiroshi
Published: February 2006

We propose a simulation method for liquid-liquid interface under constant surface tension and constant normal pressure. The method introduces an anisotropic factor in the cell dynamics which avoids artifacts such as continuous expansion or contraction of the cell lengths. This allows simulation of a full range of surface tensions including when the value is 0, i. e, hydrostatic pressure.
Statistical theory of electromagnetic weak turbulence
Authors: Yoon Peter H.
Published: February 2006

The weak turbulence theory as commonly found in the literature employs electrostatic approximation and is applicable to unmagnetized plasmas only. To this date, fully electromagnetic generalization of the existing weak turbulence theory based upon statistical mechanical approach remains largely incomplete. Instead, electromagnetic effects are incorporated into the weak turbulence formalism by means of the semiclassical approach. The present paper reformulates the fully electromagnetic weak turbulence theory from classical statistical mechanical (i.e., the Klimontovich) approach.
Resonance parametric instability in microwave gas discharges produced by circular polarization fields
Authors: Ghorbanalilu M. , Shokri B.
Published: February 2006

By studying the interaction between an intense microwave field with circular polarization weaker than an atomic field with a dilute gas, and making use of the electron distribution function (EDF), which is nonequilibrium and anisotropic, the interaction between high-frequency electric field with produced plasma is studied. By solving the dispersion equation for two different limits, it is found that the produced plasma is unstable and parametric resonance hydrodynamic instability takes place on this kind of plasma.
Laboratory observation of secondary shock formation ahead of a strongly radiative blast wave
Authors: Hansen J. F. , Edwards M. J. , Froula D. H. , Gregori G. , Edens A. D. , Ditmire T.
Published: February 2006

High Mach number blast waves were created by focusing a laser pulse on a solid pin, surrounded by nitrogen or xenon gas. In xenon, the initial shock is strongly radiative, sending out a supersonic radiative heat wave far ahead of itself. The shock propagates into the heated gas, diminishing in strength as it goes. The radiative heat wave also slows, and when its Mach number drops to two with respect to the downstream plasma, the heat wave drives a second shock ahead of itself to satisfy mass and momentum conservation in the heat wave reference frame; the heat wave becomes subsonic behind the second shock. For some time both shocks are observed simultaneously. Eventually the initial shock diminishes in strength so much that it can longer be observed, but the second shock continues to propagate long after this time. This sequence of events is a new phenomenon that has not previously been discussed in the literature. Numerical simulation clarifies the origin of the second shock, and its position is consistent with an analytical estimate.
Continuum model for the breathing oscillation of a spherical complex plasma
Authors: Sheridan T. E.
Published: February 2006

A nonlinear equation of motion for the breathing oscillation of a spherical complex plasma is derived. A spherical complex plasma, or “dust ball,” is a three-dimensional arrangement of n identical charged particles interacting through a shielded Coulomb force (i.e., a Yukawa potential) with a Debye length λ and confined by a three-dimensional, isotropic, parabolic potential well for which the single-particle oscillation frequency is ω0. The dependence of the equilibrium radius R0 and small-amplitude breathing frequency ωbr on λ is computed. Exact analytical results are given for the continuum limit n→∞ (i.e., a spherical Yukawa fluid). The squared breathing frequency (ωbr∕ω0)2=3 for the unshielded Coulomb interaction (1∕λ→0), irrespective of n, and increases to (ωbr∕ω0)2=5 as 1∕λ→∞. The effects of a finite number of particles are modeled by assuming an inner cutoff for the Yukawa potential a distance a from any point in the complex plasma sphere. Three physical regimes are identified: a Coulomb regime where λ⪢R0 and corrections to the infinite-λ case are small, a nearest-neighbor regime, where R0⪢a>λ and nearest-neighbor interactions dominate, and a plasma regime where R0⪢λ≳a and continuum plasma theory is applicable. For 1∕λ→∞, (ωbr∕ω0)2∼a∕λ in the nearest-neighbor regime, while (ωbr∕ω0)2∼5 in the plasma regime.
Variational principle for linear stability of flowing plasmas in Hall magnetohydrodynamics
Authors: Hirota M. , Yoshida Z. , Hameiri E.
Published: February 2006

Linear stability of equilibrium states with flow is studied by means of the variational principle in Hall magnetohydrodynamics (MHD). The Lagrangian representation of the linearized Hall MHD equation is performed by considering special perturbations that preserves some constants of motion (the Casimir invariants). The resultant equation has a Hamiltonian structure which enables the variational principle. There is however some difficulties in showing the positive definiteness of the quadratic form in the presence of flow. The dynamically accessible variation is a more restricted class of perturbations which, by definition, preserves all the Casimir invariants. For such variations, the quadratic form (the second variation of Hamiltonian) can be positive definite. Some conditions for stability are derived by applying this variational principle to the double Beltrami equilibrium.
Magnetic island induced bootstrap current on island dynamics in tokamaks
Authors: Shaing K. C. , Spong D. A.
Published: February 2006

When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in ∣B∣ is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)]. Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter ∣Δ′∣ for the island to be unstable. This lower limit depends on the local poloidal plasma beta βp, the ratio of the plasma pressure to the poloidal magnetic field pressure. If βp is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.
The effect of safety factor and magnetic shear on turbulent transport in nonlinear gyrokinetic simulations
Authors: Kinsey J. E. , Waltz R. E. , Candy J.
Published: February 2006

This paper reports on over 100 nonlinear simulations used to systematically study the effects of safety factor q and magnetic shear ŝ on turbulent energy and particle transport due to ion temperature gradient (ITG) modes and trapped electron modes (TEM) for several reference cases using the GYRO gyrokinetic code. All the simulations are collisionless, electrostatic, and utilize shifted circle geometry. The motivation is to create a database for benchmarking and testing of turbulent transport models. In simulations varying q, it is found that the ion and electron energy transport exhibit an offset linear dependence on q for 1⩽q⩽4. This result is valid for cases in which the spectrum is dominated by either TEM or ITG modes. The particle transport also follows a linear q dependence if the diffusivity D is positive (outward). If a particle pinch is predicted, however, then D is found to be insensitive to q. In kinetic electron simulations varying the magnetic shear ŝ, the particle transport can exhibit a null flow at a particular value of ŝ. In the vicinity of the null flow point, the transport spectrum shows that some modes drive an inward flow while others drive an outward flow. For negative magnetic shear, the magnetohydrodynamic α parameter is shown to be stabilizing for both the energy and particle transport but can be destabilizing for large positive shear. Compared to the ITG dominated case, the TEM cases show the same linear q dependence, but a weaker ŝ dependence is exhibited for positive magnetic shear values when TEM modes dominate the spectrum. In general, the q, ŝ, and α dependence of the transport including kinetic electrons is consistent with ITG adiabatic electron simulation results.
Doping concentration dependence of room-temperature ferromagnetism for Ni-doped ZnO thin films prepared by pulsed-laser deposition
Authors: Liu Xiaoxue , Lin Fangting , Sun Linlin , Cheng Wenjuan , Ma Xueming , Shi Wangzhou
Published: February 2006

High-quality Ni-doped ZnO thin films of single phase with preferred c-axis growth orientation were formed on Si (100) substrates by pulsed-laser deposition at room temperature. The films exhibited room-temperature ferromagnetic behaviors with saturation magnetic moment per Ni atom of 0.37μB,0.26μB,0.25μB and 0.21μB for the Ni concentration of 1, 3, 5, and 7 at. %, respectively. The decrease of ferromagnetism with doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Ni–ZnO thin films, not from any secondary phase.
Optical waveguiding using thermal gradients across homogeneous liquids in microfluidic channels
Authors: Tang Sindy K. Y. , Mayers Brian T. , Vezenov Dmitri V. , Whitesides George M.
Published: February 2006

This letter describes the design and operation of a liquid-core liquid-cladding (L2) optical waveguide composed of a thermal gradient across a compositionally homogeneous liquid flowing in a microfluidic channel at low Reynolds number. Two streams of liquid at a higher temperature (the cladding) sandwich a stream of liquid at a lower temperature (the core). This temperature difference results in a contrast in refractive index across the width of the channel that is sufficient to guide light. The use of a single homogeneous liquid in this L2 system simplifies recycling, and facilitates closed-loop operation. Furthermore, with radiative and inline heating of the liquids, it should be possible to reconfigure this optical system with considerable flexibility.
Combined centroid-envelope dynamics of intense, magnetically focused charged beams surrounded by conducting walls
Authors: Fiuza K. , Rizzato F. B. , Pakter R.
Published: February 2006

In this paper we analyze the combined envelope-centroid dynamics of magnetically focused high-intensity charged beams surrounded by conducting walls. Similar to the case where conducting walls are absent, it is shown that the envelope and centroid dynamics decouple from each other. Mismatched envelopes still decay into equilibrium with simultaneous emittance growth, but the centroid keeps oscillating with no appreciable energy loss. Some estimates are performed to analytically obtain characteristics of halo formation seen in the full simulations.
THz Zenneck surface wave (THz surface plasmon) propagation on a metal sheet
Authors: Jeon Tae-In , Grischkowsky D.
Published: February 2006

We present an experimental study of the propagation of the THz Zenneck surface wave on an aluminum sheet, now more commonly denoted as the THz surface plasmon (TSP). Here, the TSP pulse is generated by coupling the THz pulse from a metal parallel-plate waveguide onto the aluminum sheet; the propagated TSP pulse is detected at the output end of the sheet using a standard photoconductive dipole antenna. We separate the associated free-space THz pulse from the TSP pulse using a curved sheet. The observed weakly guided TSP propagation has the expected low group velocity dispersion, but also has anomalously high attenuation and much tighter binding to the metal surface than predicted by Zenneck theory.
Signal mixing in a multiple input transistor laser near threshold
Authors: Feng M. , Holonyak N. , Chan R. , James A. , Walter G.
Published: February 2006

A single-emitter multiple-input transistor laser has been realized and demonstrated in signal mixing, yielding in the stimulated-recombination region near laser threshold frequency conversion with simultaneously an electrical and optical output signal. In the unique nonlinear region of compression of the transistor I-V characteristics (β≡ΔIC∕ΔIB, βspon>βstim), input signals f1=2GHz and f2=2.1GHz are converted into mf1±nf2 ranging from 0.1to8.4GHz. Stimulated emission (enhanced recombination) changes the transistor into a special form of nonlinear element, a special form of electronic processor or “switch.”
Organic field effect transistor mobility from transient response analysis
Authors: Dunn Lawrence , Basu Debarshi , Wang Liang , Dodabalapur Ananth
Published: February 2006

An electronic method for analyzing the transient response of a pentacene organic field effect transistor at time scales below 100ns is presented with analysis that allows extraction of estimated field-dependent device mobility from the measured carrier velocity. A second technique we propose is the use of T-SPICE simulations of transient response data of the device behavior between ∼100ns and ∼3μs. These results are compared with lower field-effect mobilities extracted from the transient data at 250μs and the dc drain current (Id) versus source-drain voltage (Vds) characteristics in the saturation regime. This trend of decreasing mobility with increasing time is perhaps due to the absence of the bias stress effect at small time scales.
Improvement in electron holographic phase images of focused-ion-beam-milled GaAs and Si p-n junctions by in situ annealing
Authors: Cooper David , Twitchett Alison C. , Somodi Philippa K. , Midgley Paul A. , Dunin-Borkowski Rafal E. , Farrer Ian , Ritchie David A.
Published: February 2006

Low temperature (200–600°C) annealing in the transmission electron microscope (TEM) is used to provide a significant noise reduction in phase images of focused-ion-beam-milled GaAs and Si p-n junctions recorded using off-axis electron holography, as well as increasing the measured phase shifts across the junctions. Our results suggest that annealing removes defects resulting from Ga+ implantation and reactivates dopant atoms in the thin TEM specimens. In GaAs, electrically inactive surface layer thicknesses are reduced from 80to17nm on each specimen surface after annealing at 500°C. In Si the improvement is from 25to5nm.
Modulation of photoemission spectra of In2O3 nanowires by the variation in Zn doping level
Authors: Hsin C. L. , He J. H. , Chen L. J.
Published: February 2006

The growth of In2O3 nanowires on Si substrate with different zinc doping levels has been achieved by a vapor transport and condensation method. The atomic percentage in doping level is approximately proportional to the weight of ZnO powder added in the source. The ultraviolet (UV) and green light photoemissions of the In2O3 nanowires are depressed and enhanced, respectively, with the doping level of Zn impurity. The UV and green light peaks are attributed to oxygen vacancy and zinc impurity energy levels. Similar tuning by other impurities can be expected and will be beneficial for possible optoelectronic applications.
Magnetoresistance of atomic-scale electromigrated nickel nanocontacts
Authors: Keane Z. K. , Yu L. H. , Natelson D.
Published: February 2006

We report measurements of the electron transport through atomic-scale constrictions and tunnel junctions between ferromagnetic electrodes. Structures are fabricated using a combination of e-beam lithography and controlled electromigration. Sample geometries are chosen to allow independent control of electrode bulk magnetizations. As junction size is decreased to the single channel limit, conventional anisotropic magnetoresistance (AMR) increases in magnitude, approaching the size expected for tunneling magnetoresistance (TMR) upon tunnel junction formation. Significant mesoscopic variations are seen in the magnitude and sign of the magnetoresistance, and no evidence is found of large ballistic magnetoresistance effects.
Channel-width dependence of low-frequency noise in process tensile-strained n-channel metal-oxide-semiconductor transistors
Authors: Lu Ming-Pei , Lee Wen-Chin , Chen Ming-Jer
Published: February 2006

Low-frequency noise measurement in process tensile-strained n-channel metal-oxide-semiconductor field-effect transistors yields the density of the interface states, exhibiting a decreasing trend while decreasing the channel width. This finding corroborates the group of Pb centers caused by the lattice mismatch at (100) Si-SiO2 interface as the origin of the underlying interface states. The inverse narrow width effect appears to be insignificant, substantially confirming the validity of the noise measurement. The present noise experiment therefore points to the enhancement of the tensile strain in the presence of channel narrowing, which in turn reduces the lattice mismatch.
Propagation of surface plasmons on Ag and Cu extended one-dimensional arrays on silicon substrates
Authors: Sundararajan Sri Priya , Steele Jennifer Marie , Halas Naomi J.
Published: February 2006

Propagating surface plasmon waves can be supported by Cu and Ag periodic array, or grating, structures on silicon substrates. The plasmon dispersion characteristics, such as group velocity and bandgap associated with these structures are measured experimentally. In the infrared region of the spectrum (1.3–1.6μm) the properties of surface plasmons supported by these Ag and Cu periodic structures are virtually indistinguishable. The plasmon dispersion can be modified by varying either the grating period or the plasmon order. The plasmonic bandgap for this array geometry increases with increasing plasmon order.
Phosphorescence of red Os(fptz)2(PPh2Me)2 doped organic light-emitting devices with n and p hosts
Authors: Liu Tswen-Hsin , Hsu Shih-Feng , Ho Meng-Hung , Liao Chi-Hung , Wu Yao-Shan , Chen Chin H. , Tung Yung-Liang , Wu Pei-Chi , Chi Yun
Published: February 2006

We have applied a stericly-hindered red phosphorescent dopant Os(fptz)2(PPh2Me)2 [fptz=3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, PPh2Me=phosphine ligand] in p-type 4,4′-N,N′-dicarbazole-biphenyl or n-type bis(2-methyl-8-quinolinolato)(p-phenylphenolato) aluminum host and found that the latter produced higher luminance efficiency at lower doping concentration. We present a model to rationalize this phenomenon in which the n-type host impedes hole transport, which leads to narrower recombination zone near the hole transport layer/emission layer interface than the p-type host, hence, more effective recombination.
Realtime study of plume ejection dynamics in silicon laser ablation under 5ns pulses
Authors: Ren Jun , Yin Xiaobo , Orlov Sergei S. , Hesselink Lambertus
Published: February 2006

We present results of nanosecond laser ablation of silicon over a broad range of laser intensities, investigated by studying the time evolution of the ablation plume ejection, which, as measured by transmission of a probe beam, consists of a fast ejection phase followed by a delayed slow ejection phase. Experimental results indicate that different physical processes dominate at different ablation stages. The laser intensity threshold for the appearance of the slow ejection is ∼30GW∕cm2. The plume kinetics parameters extracted from our experiments agree well with estimations based on blast wave and homogeneous nucleation theories, providing a physical explanation for the observed ablation rate dependence on the laser light intensity.
Effect of the lossy layer thickness of metal cylindrical waveguide wall on the propagation constant of electromagnetic modes
Authors: Luo Jirun , Jiao Chongqing
Published: February 2006

Based on the dispersion equation of electromagnetic mode, the propagation problem in a lossy cylindrical waveguide is studied. The analytic formula of propagation constant for any mode in the waveguide is presented, which includes the effect of the lossy layer thickness on the waveguide wall. The analysis with the analytic formula shows that the lossy layer thickness has great effect on the propagation constant when the thickness is 1.5 times smaller than the skin depth of good conductor (δ).
Effect of interlayer magnetic coupling on the Jc of YBa2Cu3O7/insulator/YBa2Cu3O7 trilayers
Authors: Wang X. , Wu J. Z.
Published: February 2006

We have studied critical current density (Jc) in YBa2Cu3O7−x/insulator/YBa2Cu3O7−x trilayers as the interlayer magnetic coupling is reduced by increasing the insulator thickness (tI). Although the thickness of both YBa2Cu3O7−x layers were fixed at 0.25μm, the self- and weak-field Jc of the trilayer sample increases monotonically with tI from the lowest value for a 0.5-μm-thick YBa2Cu3O7−x film at tI=0, and saturates at the Jc value for a 0.25-μm-thick YBa2Cu3O7−x film at tI≈20nm. This result suggests an intimate correlation between Jc and magnetic coupling of vortex segments in two YBCO layers.
Effects of adenosine triphosphate on the vase life of cut carnation flowers
Authors: Song L. , Liu H. , Su X. , You Y. , Jiang Y.
Published: February 2006

The addition of adenosine triphosphate (ATP) to vase solutions at a concentration of 0.01−0.50 mmol/L markedly extended the vase life of cut carnation flowers at 25°C and 80−90% relative humidity. The most beneficial effect on vase life was observed at 0.1 mmol/L ATP, with a 28% extension over non-ATP-treated flowers. Furthermore, the addition of ATP at 0.1 mmol/L increased flower size by 12% by the end of the vase-holding period and significantly extended the time to maximum flower expansion by 1.7 days, compared with non-ATP-treated flowers held in distilled water. Our data suggest that exogenous ATP supply is an effective method to extend the vase life of cut carnation flowers.
Engineering a biospecific communication pathway between cells and electrodes
Authors: Collier Joel H. , Mrksich Milan
Published: February 2006

Methods for transducing the cellular activities of mammalian cells into measurable electronic signals are important in many biotechnical applications, including biosensors, cell arrays, and other cell-based devices. This manuscript describes an approach for functionally integrating cellular activities and electrical processes in an underlying substrate. The cells are engineered with a cell-surface chimeric receptor that presents the nonmammalian enzyme cutinase. Action of this cell-surface cutinase on enzyme substrate self-assembled monolayers switches a nonelectroactive hydroxyphenyl ester to an electroactive hydroquinone, providing an electrical activity that can be identified with cyclic voltammetry. In this way, cell-surface enzymatic activity is transduced into electronic signals. The development of strategies to directly interface the activities of cells with materials will be important to enabling a broad class of hybrid microsystems that combine living and nonliving components.
Simple fold composition and modular architecture of the nuclear pore complex
Authors: Devos Damien , Dokudovskaya Svetlana , Williams Rosemary , Alber Frank , Eswar Narayanan , Chait Brian T. , Rout Michael P. , Sali Andrej
Published: February 2006

The nuclear pore complex (NPC) consists of multiple copies of ≈30 different proteins [nucleoporins (nups)], forming a channel in the nuclear envelope that mediates macromolecular transport between the cytosol and the nucleus. With <5% of the nup residues currently available in experimentally determined structures, little is known about the detailed structure of the NPC. Here, we use a combined computational and biochemical approach to assign folds for ≈95% of the residues in the yeast and vertebrate nups. These fold assignments suggest an underlying simplicity in the composition and modularity in the architecture of all eukaryotic NPCs. The simplicity in NPC composition is reflected in the presence of only eight fold types, with the three most frequent folds accounting for ≈85% of the residues. The modularity in NPC architecture is reflected in its hierarchical and symmetrical organization that partitions the predicted nup folds into three groups: the transmembrane group containing transmembrane helices and a cadherin fold, the central scaffold group containing β-propeller and α-solenoid folds, and the peripheral FG group containing predominantly the FG repeats and the coiled-coil fold. Moreover, similarities between structures in coated vesicles and those in the NPC support our prior hypothesis for their common evolutionary origin in a progenitor protocoatomer. The small number of predicted fold types in the NPC and their internal symmetries suggest that the bulk of the NPC structure has evolved through extensive motif and gene duplication from a simple precursor set of only a few proteins.
Directing electron transfer within Photosystem I by breaking H-bonds in the cofactor branches
Authors: Li Yajing , van der Est Art , Lucas Marie Gabrielle , Ramesh V. M. , Gu Feifei , Petrenko Alexander , Lin Su , Webber Andrew N. , Rappaport Fabrice , Redding Kevin
Published: February 2006

Photosystem I has two branches of cofactors down which light-driven electron transfer (ET) could potentially proceed, each consisting of a pair of chlorophylls (Chls) and a phylloquinone (PhQ). Forward ET from PhQ to the next ET cofactor (F
X
) is described by two kinetic components with decay times of ≈20 and ≈200 ns, which have been proposed to represent ET from PhQ
B
and PhQ
A
, respectively. Immediately preceding each quinone is a Chl (ec3), which receives a H-bond from a nearby tyrosine. To decrease the reduction potential of each of these Chls, and thus modify the relative yield of ET within the targeted branch, this H-bond was removed by conversion of each Tyr to Phe in the green alga
Chlamydomonas reinhardtii
. Together, transient optical absorption spectroscopy performed
in vivo
and transient electron paramagnetic resonance data from thylakoid membranes showed that the mutations affect the relative amplitudes, but not the lifetimes, of the two kinetic components representing ET from PhQ to F
X
. The mutation near ec3
A
increases the fraction of the faster component at the expense of the slower component, with the opposite effect seen in the ec3
B
mutant. We interpret this result as a decrease in the relative use of the targeted branch. This finding suggests that in Photosystem I, unlike type II reaction centers, the relative efficiency of the two branches is extremely sensitive to the energetics of the embedded redox cofactors.
Functional dissection of YabA, a negative regulator of DNA replication initiation in
Bacillus subtilis
Authors: Noirot-Gros Marie-Françoise , Velten M. , Yoshimura M. , McGovern S. , Morimoto T. , Ehrlich S. D. , Ogasawara N. , Polard P. , Noirot Philippe
Published: February 2006

The regulation of initiation of DNA replication is crucial to ensure that the genome is replicated only once per cell cycle. In the Gram-positive bacterium
Bacillus subtilis
, the function of the YabA protein in initiation control was assigned based on its interaction with the DnaA initiator and the DnaN sliding clamp in the yeast two-hybrid and on the overinitiation phenotype observed in a
yabA
null strain. However, YabA is unrelated to known regulators of initiation and interacts with several additional proteins that could also be involved directly or not in initiation control. Here, we investigated the specific role of YabA interactions with DnaA and DnaN in initiation control by identifying single amino acid changes in YabA that disrupted solely the interaction with DnaA or DnaN. These disruptive mutations delineated specific interacting surfaces involving a Zn
2+
-cluster structure in YabA. In
B. subtilis
, these YabA interaction mutations abolished both initiation control and the formation of YabA foci at the replication factory. Upon coexpression of deficient YabA mutants, mixed oligomers formed foci at the replisome and restored initiation control, indicating that YabA acts within a heterocomplex with DnaA and DnaN. In agreement, purified YabA oligomerized and formed complexes with DnaA and DnaN. These findings underscore the functional association of YabA with the replication machinery, indicating that YabA regulates initiation through coupling with the elongation of replication.
Design of a mimic of nonamyloidogenic and bioactive human islet amyloid polypeptide (IAPP) as nanomolar affinity inhibitor of IAPP cytotoxic fibrillogenesis
Authors: Yan Li-Mei , Tatarek-Nossol Marianna , Velkova Aleksandra , Kazantzis Athanasios , Kapurniotu Aphrodite
Published: February 2006

Protein aggregation into cytotoxic oligomers and fibrils
in vivo
is linked to cell degeneration and the pathogenesis of >25 uncurable diseases, whereas the high aggregation propensity and insolubility of several bioactive polypeptides and proteins
in vitro
prevent their therapeutic use. Aggregation of human islet amyloid polypeptide (IAPP) into pancreatic amyloid is strongly associated with the pathogenesis of type II diabetes. IAPP is a 37-residue polypeptide that acts as a neuroendocrine regulator of glucose homeostasis. However, IAPP misfolds and self-associates into cytotoxic aggregates and fibrils even at nanomolar concentrations. Because IAPP aggregation causes β-cell death and prohibits therapeutic application of IAPP in diabetes, we pursued a minimalistic chemical design approach to generate a molecular mimic of a nonamyloidogenic and bioactive IAPP conformation that would still be able to associate with IAPP and thus inhibit its fibrillogenesis and cytotoxicity. We show that the double N-methylated full length IAPP analog [(N-Me)G24, (N-Me)I26]-IAPP (IAPP-GI) is a highly soluble, nonamyloidogenic, and noncytotoxic IAPP molecular mimic and an IAPP receptor agonist. Moreover, IAPP-GI binds IAPP with low nanomolar affinity and completely blocks IAPP cytotoxic self-assembly and fibrillogenesis with activity in the low nanomolar concentration range. Importantly, IAPP-GI dissociates cytotoxic IAPP oligomers and fibrils and is able to reverse their cytotoxicity. Bifunctional soluble IAPP mimics that combine bioactivity with the ability to block and reverse IAPP cytotoxic self-assembly are promising candidates for the treatment of diabetes. Moreover, our amyloid disease inhibitor design concept may be applicable to other protein aggregation diseases.