bluuebunny/crossref_metadata_2025 huggingface dataset:
A procedure for the solution of multicomponent reactive transport problems
Authors: De Simoni M. , Carrera J. , Sánchez‐Vila X. , Guadagnini A.
Published: November 2005

Modeling transport of reactive solutes is a challenging problem, necessary for understanding the fate of pollutants and geochemical processes occurring in aquifers, rivers, estuaries, and oceans. Geochemical processes involving multiple reactive species are generally analyzed using advanced numerical codes. The resulting complexity has inhibited the development of analytical solutions for multicomponent heterogeneous reactions such as precipitation/dissolution. We present a procedure to solve groundwater reactive transport in the case of homogeneous and classical heterogeneous equilibrium reactions induced by mixing different waters. The methodology consists of four steps: (1) defining conservative components to decouple the solution of chemical equilibrium equations from species mass balances, (2) solving the transport equations for the conservative components, (3) performing speciation calculations to obtain concentrations of aqueous species, and (4) substituting the latter into the transport equations to evaluate reaction rates. We then obtain the space‐time distribution of concentrations and reaction rates. The key result is that when the equilibrium constant does not vary in space or time, the reaction rate is proportional to the rate of mixing, ∇TuD ∇u, where u is the vector of conservative components concentrations and D is the dispersion tensor. The methodology can be used to test numerical codes by setting benchmark problems but also to derive closed‐form analytical solutions whenever steps 2 and 3 are simple, as illustrated by the application to a binary system. This application clearly elucidates that in a three‐dimensional problem both chemical and transport parameters are equally important in controlling the process.
Residential water demand with endogenous pricing: The Canadian Case
Authors: Reynaud Arnaud , Renzetti Steven , Villeneuve Michel
Published: November 2005

In this paper, we show that the rate structure endogeneity may result in a misspecification of the residential water demand function. We propose to solve this endogeneity problem by estimating a probabilistic model describing how water rates are chosen by local communities. This model is estimated on a sample of Canadian local communities. We first show that the pricing structure choice reflects efficiency considerations, equity concerns, and, in some cases, a strategy of price discrimination across consumers by Canadian communities. Hence estimating the residential water demand without taking into account the pricing structures' endogeneity leads to a biased estimation of price and income elasticities. We also demonstrate that the pricing structure per se plays a significant role in influencing price responsiveness of Canadian residential consumers.
Effective discharge analysis of ecological processes in streams
Authors: Doyle Martin W. , Stanley Emily H. , Strayer David L. , Jacobson Robert B. , Schmidt John C.
Published: November 2005

Discharge is a master variable that controls many processes in stream ecosystems. However, there is uncertainty of which discharges are most important for driving particular ecological processes and thus how flow regime may influence entire stream ecosystems. Here the analytical method of effective discharge from fluvial geomorphology is used to analyze the interaction between frequency and magnitude of discharge events that drive organic matter transport, algal growth, nutrient retention, macroinvertebrate disturbance, and habitat availability. We quantify the ecological effective discharge using a synthesis of previously published studies and modeling from a range of study sites. An analytical expression is then developed for a particular case of ecological effective discharge and is used to explore how effective discharge varies within variable hydrologic regimes. Our results suggest that a range of discharges is important for different ecological processes in an individual stream. Discharges are not equally important; instead, effective discharge values exist that correspond to near modal flows and moderate floods for the variable sets examined. We suggest four types of ecological response to discharge variability: discharge as a transport mechanism, regulator of habitat, process modulator, and disturbance. Effective discharge analysis will perform well when there is a unique, essentially instantaneous relationship between discharge and an ecological process and poorly when effects of discharge are delayed or confounded by legacy effects. Despite some limitations the conceptual and analytical utility of the effective discharge analysis allows exploring general questions about how hydrologic variability influences various ecological processes in streams.
Long‐term exposure to the new nicotinic antagonist 1,2‐bisN‐cytisinylethane upregulates nicotinic receptor subtypes of SH‐SY5Y human neuroblastoma cells
Authors: Riganti Loredana , Matteoni Cosetta , Di Angelantonio Silvia , Nistri Andrea , Gaimarri Annalisa , Sparatore Fabio , Canu‐Boido Caterina , Clementi Francesco , Gotti Cecilia
Published: November 2005

Nicotinic drug treatment can affect the expression of neuronal nicotinic acetylcholine receptors (nAChR) bothin vivoandin vitrothrough molecular mechanisms not fully understood. The present study investigated the effect of the novel cytisine dimer 1,2‐bisN‐cytisinylethane (CC4) on nAChR natively expressed by SH‐SY5Y neuroblastoma cells in culture.

CC4 lacked the agonist properties of cytisine and was a potent antagonist (IC50=220 nM) on nAChRs. Chronic treatment of SH‐SY5Y cells with 1 mMCC4 for 48 h increased the expression of3H‐epibatidine (3H‐Epi; 3–4‐fold) or125I‐α‐bungarotoxin (125I‐αBgtx; 1.2‐fold) sensitive receptors present on the cell membrane and in the intracellular pool. Comparable data were obtained with nicotine or cytisine, but not with carbamylcholine,d‐tubocurarine, di‐hydro‐β‐erythroidine or hexametonium.

Immunoprecipitation and immunopurification studies showed that the increase in3H‐Epi‐binding receptors was due to the enhanced expression ofα3β2 andα3β2β4 subtypes without changes in subunit mRNA transcription or receptor half‐life. The upregulation was not dependent on agonist/antagonist properties of the drugs, and did not concern muscarinic or serotonin receptors.

Whole‐cell patch clamp analysis of CC4‐treated cells demonstrated larger nicotine‐evoked inward currents with augmented sensitivity to the blockersα‐conotoxin MII or methyllycaconitine.

In conclusion, chronic treatment with CC4 increased the number of nAChRs containingβ2 andα7 subunits on the plasma membrane, where they were functionally active. In the case ofβ2‐containing receptors, we propose that CC4, by binding to intracellular receptors, triggered a conformational reorganisation of intracellular subunits that stimulated preferential assembly and membrane‐directed trafficking ofβ2‐containing receptor subtypes.

British Journal of Pharmacology(2005)146, 1096–1109. doi:10.1038/sj.bjp.0706434
Protein S modulates the anticoagulant action of recombinant human activated protein C: a comparison between neonates and adults
Authors: Cvirn Gerhard , Koestenberger Martin , Leschnik Bettina , Male Christoph , Kutschera Joerg , Ferstl Ulrika , Muntean Wolfgang , Juergens Guenther , Gallistl Siegfried
Published: November 2005

Recombinant human‐activated protein C (rhAPC, Drotrecogin alpha (activated), Xigris™) has been shown to reduce organ damage and decrease mortality in severe sepsis. Since protein S (PS) serves as a potentiating cofactor of activated protein C and since PS levels are low in neonatal plasma, we hypothesized that the anticoagulant effect of rhAPC would be decreased in cord plasma compared to adult plasma.

We demonstrate that the anticoagulant action of 0.3 μg ml−1 rhAPC (5 nmol l−1) was decreased in cord plasma compared to adult plasma, and dose dependently increased in cord plasma in the presence of increasing activities of PS.

Correspondingly, the anticoagulant action of rhAPC decreased in adult plasma in the presence of decreasing activities of PS.

The low anticoagulant action of rhAPC in cord compared to adult plasma is attributable to low neonatal levels of PS, and as previously shown, to low neonatal levels of TFPI and AT.

Our laboratory experiments do not allow definite conclusions for clinical situations. However, we speculate that the anticoagulant efficacy of rhAPC is impaired in neonates and in clinical situations associated with consumption and/or inhibition of PS, AT, and TFPI, such as severe sepsis.

British Journal of Pharmacology (2005) 146, 1082–1086. doi:10.1038/sj.bjp.0706436
In vitro and in vivo pharmacological characterization of the novel UT receptor ligand [Pen5,DTrp7,Dab8]urotensin II(4–11) (UFP‐803)
Authors: Camarda Valeria , Spagnol Martina , Song Wei , Vergura Raffaella , Roth Adelheid L , Thompson Jonathan P , Rowbotham David J , Guerrini Remo , Marzola Erika , Salvadori Severo , Cavanni Paolo , Regoli Domenico , Douglas Stephen A , Lambert David G , Calò Girolamo
Published: November 2005

The novel urotensin‐II (U‐II) receptor (UT) ligand, [Pen5,DTrp7,Dab8]U‐II(4–11) (UFP‐803), was pharmacologically evaluated and compared with urantide in in vitro and in vivo assays.

In the rat isolated aorta, UFP‐803 was inactive alone but, concentration dependently, displaced the contractile response to U‐II to the right, revealing a competitive type of antagonism and a pA2 value of 7.46.

In the FLIPR [Ca2+]i assay, performed at room temperature in HEK293hUT and HEK293rUT cells, U‐II increased [Ca2+]i with pEC50 values of 8.11 and 8.48. Urantide and UFP‐803 were inactive as agonists, but antagonized the actions of U‐II by reducing, in a concentration‐dependent manner, the agonist maximal effects with apparent pKB values in the range of 8.45–9.05. In a separate series of experiments performed at 37°C using a cuvette‐based [Ca2+]i assay and CHOhUT cells, urantide mimicked the [Ca2+]i stimulatory effect of U‐II with an intrinsic activity (α) of 0.80, while UFP‐803 displayed a small (α=0.21) but consistent residual agonist activity. When the same experiments were repeated at 22°C (a temperature similar to that in FLIPR experiments), urantide displayed a very small intrinsic activity (α=0.11) and UFP‐803 was completely inactive as an agonist.

In vivo in mice, UFP‐803 (10 nmol kg−1) antagonized U‐II (1 nmol kg−1)‐induced increase in plasma extravasation in various vascular beds, while being inactive alone.

In conclusion, UFP‐803 is a potent UT receptor ligand which displays competitive/noncompetitive antagonist behavior depending on the assay. While UFP‐803 is less potent than urantide, it displayed reduced residual agonist activity and as such may be a useful pharmacological tool.

British Journal of Pharmacology (2006) 147, 92–100. doi:10.1038/sj.bjp.0706438
Angiotensin II and angiotensin II receptor blocker modulate the arrhythmogenic activity of pulmonary veins
Authors: Chen Yi‐Jen , Chen Yao‐Chang , Tai Ching‐Tai , Yeh Hung‐I , Lin Cheng‐I , Chen Shih‐Ann
Published: November 2005

Angiotensin II receptor blockers (AIIRBs) have been shown to prevent atrial fibrillation. The pulmonary veins (PVs) are the most important focus for the generation of atrial fibrillation. The aim of this study was to evaluate whether angiotensin II or AIIRB may change the arrhythmogenic activity of the PVs.

Conventional microelectrodes and whole‐cell patch clamps were used to investigate the action potentials (APs) and ionic currents in isolated rabbit PV tissue and single cardiomyocytes before and after administering angiotensin II or losartan (AIIRB).

In the tissue preparations, angiotensin II induced delayed after‐depolarizations (1, 10, and 100 nM) and accelerated the automatic rhythm (10 and 100 nM). Angiotensin II (100 nM) prolonged the AP duration and increased the contractile force (10 and 100 nM). Losartan (1 and 10 μM) inhibited the automatic rhythm. Losartan (10 μM) prolonged the AP duration and reduced the contractile force (1 and 10 μM).

Angiotensin II reduced the transient outward potassium current (Ito) but increased the L‐type calcium, delayed rectifier potassium (IK), transient inward (Iti), pacemaker, and Na+–Ca2+exchanger (NCX) currents in the PV cardiomyocytes. Losartan decreased theIto,IK,Iti, and NCX currents.

In conclusion, angiotensin II and AIIRB modulate the PV electrical activity, which may play a role in the pathophysiology of atrial fibrillation.

British Journal of Pharmacology(2006)147, 12–22. doi:10.1038/sj.bjp.0706445
Human colonic myocytes are involved in postischemic inflammation through ADAM17‐dependent TNFα production
Authors: Jarry Anne , Bach‐Ngohou Kalyane , Masson Damien , Dejoie Thomas , Lehur Paul‐Antoine , Mosnier Jean‐François , Denis Marc G , Laboisse Christian L
Published: November 2005

The aim of this study was to identify human colonic resident cells able to initiate an inflammatory response in postischemic injury.

Postischemic colonic injury, a condition relevant to various clinical settings, involves an inflammatory cascade in intestinal tissues through the recruitment of circulating inflammatory cells. However, there is no information on the nature of resident cells of the different intestinal layers able to initiate a postischemic inflammatory response. It is however an important issue in the context of a pharmacological approach of the early phase of intestinal ischemia.

We reasoned that maintaining the different colonic layers as explant cultures in an oxygenated medium immediately after colonic resection, that is, after an ischemic period, would allow one to identify the resident cells able to initiate an inflammatory cascade, without interference of recruited inflammatory/immune cells. To this end, we designed an explant culture system that operationally defines three compartments in surgical specimens of the human colon, based on the microdissected layers, that is, mucosa, submucosa (containing muscularis mucosae) and muscularis propria. To validate the results obtained in explant cultures in the clinical setting of ischemic colitis, eight cases of sigmoid volvulus were examined.

Only the myocytes‐containing explants produced tumor necrosis factor alpha (TNFα), via an ADAM17 (a disintegrin and metalloproteinase‐17)‐dependent pathway, as shown by the abrogation of TNFα production by the inhibitor Tapi‐2. Immunofluorescence studies identified nonvascular and vascular myocytes as resident cells coexpressing TNFα and ADAM17, both in our postischemic explant system and in surgical specimens from ischemic colitis patients. Finally, time‐course experiments on explanted tissues showed that TNFα production by myocytes was an early event triggered by a postischemic oxidative stress involving nuclear factor kappa B (NF‐κB).

In conclusion, this study identifies human intestinal myocytes as resident cells able to initiate an inflammatory reaction through TNFα production in postischemic conditions, and delineates two points of control in TNFα production, NF‐κB and ADAM17, which can be targeted by pharmacological manipulation.

British Journal of Pharmacology (2006) 147, 64–72. doi:10.1038/sj.bjp.0706449
Perturbation of collisional plasma flow around a charged dust particle: Kinetic analysis
Authors: Schweigert I. V. , Schweigert V. A. , Peeters F. M.
Published: November 2005

The ion density and electric potential distribution are found within the linear kinetic approach using the dielectrical permittivity of a flowing collisional plasma around a charged particle. The parameters of the disturbed plasma flow near the dust particle are also calculated numerically through a self-consistent solution of the ion kinetic equation and the Poisson equation with the particle-in-cell Monte Carlo collision algorithm. Scaling laws are formulated from an analysis of the linear kinetic equation. Comparison of the ion and potential distributions for sub- and supersonic ion flows in the collisional and collisionless regimes lends support to these scaling laws for flowing plasmas.
Multistage interaction of a shock wave and a strong vortex
Authors: Zhang Shuhai , Zhang Yong-Tao , Shu Chi-Wang
Published: November 2005

The interaction between a shock wave and a strong vortex is simulated systematically through solving the two-dimensional, unsteady compressible Navier–Stokes equations using a fifth-order weighted essentially nonoscillatory finite difference scheme. Our main purpose in this study is to characterize the flow structure and the generation of sound waves of the shock–strong vortex interaction. The simulations show that the interaction of a shock wave and a strong vortex has a multistage feature. It contains the interaction of the shock wave and the initial vortex, of the reflected shock wave and the deformed vortex and of the shocklets and the deformed vortex. The shocklets are generated by the secondary interaction. Due to the complex reflected shock structure, there exist interactions between the reflected shock waves and the sound waves. Many pressure waves are embedded in the second and third sound waves.
Plasmonic response in a one-dimensional periodic structure of metallic rods
Authors: Pradarutti B. , Rau C. , Torosyan G. , Beigang R. , Kawase K.
Published: November 2005

The frequency response of a two-dimensional structure of metallic cylindrical rods having one-dimensional periodicity is reported. The structure is excited under transverse electric incidence of terahertz radiation, where the periodicity is of the size of the diameter of the rods. The response shows metallic behavior and leads to an effective plasma frequency which determines the lowest frequency of transmission. The results are confirmed by three independent investigations: An approximate analytic theory, computational simulations, and experiments.
The accuracy of ab initio molecular geometries for systems containing second-row atoms
Authors: Coriani Sonia , Marchesan Domenico , Gauss Jürgen , Hättig Christof , Helgaker Trygve , Jørgensen Poul
Published: November 2005

The performance of the standard hierarchy of ab initio models—that is, Hartree–Fock theory, second-order Møller–Plesset theory, coupled-cluster singles-and-doubles theory, and coupled-cluster singles-doubles-approximate-triples theory—in combination with correlation-consistent basis sets is investigated for equilibrium geometries of molecules containing second-row elements. From an analysis on a collection of 31molecules (yielding statistical samples of 41 bond distances and 13 bond angles), the statistical errors (mean deviation, mean absolute deviation, standard deviation, and maximum absolute deviation) are established at each level of theory. The importance of core correlation is examined by comparing calculations in the frozen-core approximation with calculations where all electrons are correlated.
Selective OD bond dissociation of HOD: Photodissociation of vibrationally excited HOD in the 5νOD state
Authors: Akagi Hiroshi , Fukazawa Hiroshi , Yokoyama Keiichi , Yokoyama Atsushi
Published: November 2005

Exclusively selective OD bond dissociation of HOD has been demonstrated by the ultraviolet photodissociation at 243.1nm through the fourth overtone state of the OD stretching mode (5νOD). Branching ratio between the OH and OD bond dissociation channels has been determined by detecting H and D atoms, utilizing a (2+1) resonance-enhanced multiphoton ionization (REMPI) process. The OD bond dissociation has been solely observed with the branching ratio Φ(D+OH)∕Φ(H+OD)>12, which has been determined by the detection limit for the H atom. Time-dependent wave-packet calculations reveal two important features for the highly selective OD bond dissociation: (1) strong local-mode character of the 5νOD state and (2) limitation of the total excitation energy lower than the saddle point between the OH and OD dissociation channels in the Ã state. Additionally, the recoil velocity and angular distribution of the nascent D atom are roughly evaluated by analyzing the Doppler-resolved REMPI spectrum. Based on these results, the dynamics of the selective OD dissociation has been discussed in detail.
Self-assembled network of carbon nanotubes synthesized by chemical vapor deposition in alumina porous template
Authors: Kouklin N.
Published: November 2005

Relying on self-assembly principles and mechanisms to engineer new and previously unachievable devices and systems on nano- and microscales is a highly promising field of research today. In this work, a self-assembly of partially exposed and free-standing carbon nanotubes (CNTs) grown in the pores of alumina matrix into a quasiperiodic two-dimensional static network is reported. The network pattern is analyzed with a fast Fourier transformation and reveals a short-range order, which does not replicate that of underlying alumina template. The network formation is likely to be driven by short-range interactions involving hydrophobic-hydrophobic interactions and van der Waals forces balanced by mechanical deformation forces. The work might help realize new possibilities for self-guided, bottom-up, and large scale assembly of multifunctional and electrically conductive CNTs grown in alumina matrix for applications in electronic circuits, sensor networks and interconnects.
On neutral-beam injection counter to the plasma current
Authors: Helander P. , Akers R. J. , Eriksson L.-G.
Published: November 2005

It is well known that when neutral beams inject ions into trapped orbits in a tokamak, the transfer of momentum between the beam and the plasma occurs through the torque exerted by a radial return current. It is shown that this implies that the angular momentum transferred to the plasma can be larger than the angular momentum of the beam, if the injection is in the opposite direction to the plasma current and the beam ions suffer orbit losses. On the Mega-Ampere Spherical Tokamak (MAST) [R. J. Akers, J. W. Ahn, G. Y. Antar, L. C. Appel, D. Applegate, C. Brickley et al., Plasma Phys. Controlled Fusion 45, A175 (2003)], this results in up to 30% larger momentum deposition with counterinjection than with co-injection, with substantially increased plasma rotation as a result. It is also shown that heating of the plasma (most probably of the ions) can occur even when the beam ions are lost before they have had time to slow down in the plasma. This is the dominant heating mechanism in the outer 40% of the MAST plasma during counterinjection.
Three-dimensional simulations of a platelet-shaped spheroid near a wall in shear flow
Authors: Mody Nipa A. , King Michael R.
Published: November 2005

We have investigated the three-dimensional motion of an oblate spheroid-shaped particle or “platelet” close to an infinite planar wall in shear flow. The completed double layer-boundary integral equation method modified to include a flat surface boundary was used to compute the effects of the wall on the flow behavior of a platelet of aspect ratio 0.25. Platelet simulations were initiated with the platelet having its axis of symmetry normal to the surface. The platelet is observed to demonstrate three distinct regimes of flow, the dominant regime of flow being dependent on its initial height from the surface. Platelets further than 1.2 platelet radii from the surface display a “modified” Jeffery orbit with periodic rotational motion in the direction of flow (regime I). The presence of the wall retards platelet flow and more importantly introduces periodic lateral motion normal to the wall. When the platelet starts flowing at a height between 1.1 and 0.75 platelet radii from the surface (regime II), it is found to dip down and then “pole vault” off of the surface. Periodic platelet rotation and contact with the surface then ensues with no drift of the platelet away from the surface. In the third regime of flow, a platelet with an initial height of 0.7 platelet radii and below demonstrates wobble motion. The platelet neither rotates nor contacts the surface, but instead, moves laterally in a periodic manner as it translates in the direction of flow. Flow behavior typical of regime III is not observed at all spheroid aspect ratios. The range of initial heights that demonstrate regime III flow diminishes with increasing aspect ratio and regime III disappears completely above an aspect ratio of 0.41. If a platelet located at heights relevant to regime III is given an initial tilt about the y axis or x axis (where x is the flow direction), the resulting flow may either continue in regime III or shift to regime II, depending on the tilt angle. There is a small critical angle of tilt, the magnitude of which depends on the initial platelet height, above which the platelet flow behavior immediately transitions from regime III flow to that of regime II. Tilts about the x axis induce fully three-dimensional flow with rotational motion occurring about all three axes. Therefore, even small tilts about the x axis that are below the critical tilt angles can cause platelet flow to transform from regime III to II eventually at some point downstream. Thus, a platelet flowing close to the surface in linear shear has ample opportunity to contact the surface, an important event for initiating receptor-ligand binding of blood platelets to the injured vascular endothelium during the onset of hemostasis.
Yellow-to-violet up-conversion luminescence in neodymium-doped sol-gel GeO2∕γ-glycidoxypropyltrimethoxysilane hybrid planar waveguides
Authors: Que Wenxiu , Sun Z. , Hu X.
Published: November 2005

Neodymium-doped GeO2∕γ-glycidoxypropyltrimethoxysilane hybrid planar waveguide films were prepared by a low-temperature sol-gel technique from an organic-inorganic hybrid system for photonic applications. Optical properties such as refractive index, thickness, propagation modes, and attenuation coefficient of the hybrid planar waveguides were investigated by using a prism coupling technique. An intense room-temperature yellow-to-violet up-conversion emission at 397nm (D3∕24→I13∕24) was measured from the hybrid planar waveguide film heated at a low temperature of 100°C upon excitation with a xenon lamp at the wavelength of 580nm. In addition to this intense violet emission, a relatively weak ultraviolet emission at 376nm and a blue emission at 468nm were also observed. The mechanism of the up-conversion emission is proposed, and they indicate that the excited-state absorption process originating from the long-lived F3∕24 excited state should be responsible for the up-conversion process.
Spectral shape analysis of ultraviolet luminescence in n-type ZnO:Ga
Authors: Makino T. , Segawa Y. , Yoshida S. , Tsukazaki A. , Ohtomo A. , Kawasaki M. , Koinuma H.
Published: November 2005

Thin films of laser molecular-beam epitaxy grown n-type Ga-doped ZnO were investigated with respect to their optical properties. Intense room-temperature photoluminescence (PL) in the near-band edge (NBE) region was observed. Moreover, its broadening of PL band was significantly larger than predicted by theoretical results modeled in terms of potential fluctuations caused by the random distribution of donor impurities. In addition, the line shape was rather asymmetrical. To explain these features of the NBE bands, a vibronic model was developed accounting for contributions from a series of phonon replicas.
High-density and high-ρR fuel assembly for fast-ignition inertial confinement fusion
Authors: Betti R. , Zhou C.
Published: November 2005

Scaling relations to optimize implosion parameters for fast-ignition inertial confinement fusion are derived and used to design high-gain fast-ignition targets. A method to assemble thermonuclear fuel at high densities, high ρR, and with a small-size hot spot is presented. Massive cryogenic shells can be imploded with a low implosion velocity VI on a low adiabat α using the relaxation-pulse technique. While the low VI yields a small hot spot, the low α leads to large peak values of the density and areal density. It is shown that a 750kJ laser can assemble fuel with VI≃1.7×107cm∕s, α≃0.7, ρ≃400g∕cc, ρR≃3g∕cm2, and a hot-spot volume of less than 10% of the compressed core. If fully ignited, this fuel assembly can produce high gains of interest to inertial fusion energy applications.
Dielectric functions and electronic band structure of lead zirconate titanate thin films
Authors: Lee Hosun , Kang Youn Seon , Cho Sang-Jun , Xiao Bo , Morkoç Hadis , Kang Tae Dong , Lee Ghil Soo , Li Jingbo , Wei Su-Huai , Snyder P. G. , Evans J. T.
Published: November 2005

We measure pseudodielectric functions in the visible-deep ultraviolet spectral range of Pb(ZrxTi1−x)O3 (x=0.2,0.56,0.82) (PZT), Pb0.98Nb0.04(Zr0.2Ti0.8)0.96O3, Pb0.91La0.09(Zr0.65Ti0.35)0.98O3, and Pb0.85La0.15Ti0.96O3 films grown on platinized silicon substrates using a sol-gel method and on (0001) sapphire using a radio-frequency sputtering method. Using a parametric optical constant model, we estimate the dielectric functions (ϵ) of the perovskite oxide thin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical-point model, we determine the parameters of the critical points. In the second derivative spectra, the lowest band-gap energy peak near 4eV is fitted as a double peak for annealed PZTs due to the perovskite phase. As-grown PZTs have mainly pyrochlore phase and the lowest band-gap peak is fitted as a single peak. We also examine the effect of dopants La and Nb, which substitute at Pb and Zr (Ti) sites, respectively. We found three band gaps Ea(∼3.9eV), Eb(∼4.5eV), and Ec(∼6.5eV) in the order of increasing energy. The Ea and Eb band-gap energies were not sensitive to Zr composition. We discuss the change of critical-point parameters for PZTs in comparison to the band-structure calculations based on local-density approximation. The near constancy of the lowest band-gap energy independent of Zr composition is consistent with the band-structure calculations.
Characterization of a-Si:H∕c-Si interfaces by effective-lifetime measurements
Authors: Garín M. , Rau U. , Brendle W. , Martín I. , Alcubilla R.
Published: November 2005

This article studies theoretically and experimentally the recombination at the amorphous/crystalline silicon interface of a heterojunction with intrinsic thin layer (HIT) structure without metallization. We propose a physical model to calculate the interface recombination rate under illumination. This model calculates the effective lifetime τeff as a function of the average excess minority carrier concentration ⟨Δn⟩. In order to test the model, we prepared a set of HIT structures. The dependence of τeff vs ⟨Δn⟩ of the samples is measured using the quasi-steady-state photoconductance technique. By fitting our model to the experimental data, we determine the a-Si:H∕c-Si interface parameters and the doping density of the amorphous layer.
Fault tolerance calculations for clocked quantum-dot cellular automata devices
Authors: Khatun M. , Barclay T. , Sturzu I. , Tougaw P. D.
Published: November 2005

We present a numerical study of fault tolerance properties in quantum-dot cellular automata (QCA) devices. A full-basis quantum method is used for calculations of the Hamiltonian, and a statistical model has been introduced to simulate the influence of position defects of the dots within cells on the logical output. Combined effects of temperature and cell defects on a shift register have been studied. Uniform and normal distributions have been used for the cell defect simulations. Normal distribution simulations produce realistic results compared to the uniform distribution. In order to show the operational limit of a device, parameters such as “displacement factor” and “success rate” are introduced. Results show that the fault tolerance of a QCA device is strongly dependent on temperature as well as on the cell defects. The robustness of a shift register is also dependent on the size of the device.
Characteristics of a low-frequency-driven ferroinductor-coupled discharge
Authors: Felsteiner J. , Slutsker Ya. Z. , Vaisberg P. M.
Published: November 2005

We present characteristics of a low-frequency (LF) inductively coupled discharge where, instead of using an inductorlike rf antenna, we used a ferromagnetic core with a primary winding (“ferroinductor”). A dense (>1012cm−3), highly ionized (30%–40%) plasma was obtained in this ferroinductor at gas pressures as low as 10−4Torr. In a wide range of comparatively low frequencies the core and winding losses were found to be small compared with the LF driving power delivered to the plasma. The driving frequency could be very low compared with typical inductively coupled discharges. The input impedance was found to be almost purely active (cosφ≈0.9), and it was possible to achieve various input resistances (e.g., 50Ω) in the whole investigated range of frequencies, powers, and pressures, which made unnecessary any matching box between the LF driver and the ferroinductor-coupled plasma device. Such a combination of properties makes this kind of discharge attractive for many applications.
Reduced temperature-quenching of photoluminescence from indium nitride nanotips grown by metalorganic chemical vapor deposition
Authors: Shi Shih-Chen , Chen Chia-Fu , Hsu Geng-Ming , Hwang Jih-Shang , Chattopadhyay Surojit , Lan Zon-Huang , Chen Kuei-Hsien , Chen Li-Chyong
Published: November 2005

We report metalorganic chemical vapor deposition of indium nitride (InN) nanotips with apex angles of 10° and length and base diameter of around 1μm and 200 nm, respectively. The structure of the hexagonal InN nanotips growing along [002] was studied by electron microscopy and x-ray diffraction, and the optical properties were studied using temperature-dependent photoluminescence (PL) measurements. A narrow emission peak with a 18 meV full width at half maximum positioned at 0.77 eV was obtained with no visible emission. A PL quenching of only 14% was observed with a temperature scan of 15–320 K.
Double-transducer structure for picosecond ultrasound generation
Authors: Li Ta-Ching , Pu Nen-Wen , Lwo Ben-Je , Pan En-Yea , Kao Chin-Hsing
Published: November 2005

We report a double-transducer technique for more effective generation of picosecond acoustic waves. A tungsten layer, which is buried under a transparent film and a thin top metal transducer, plays the role of a bottom laser-acoustic transducer as well as a high-impedance acoustic reflector. The pulse shape and the induced piezoreflectance response of the acoustic wave launched by the bottom transducer are different from the conventional top transducer. The effect of the bottom transducer depends on the thicknesses and optical constants of the top transducer and the transparent film. The accuracy of velocity measurement can be raised owing to more efficient energy utilization, halved pulse broadening and attenuation of the tungsten-launched waves, and the added signatures on the reflectance curve.
Uncooled bolometer response of a low noise La2∕3Sr1∕3MnO3 thin film
Authors: Méchin Laurence , Routoure Jean-Marc , Guillet Bruno , Yang Fan , Flament Stéphane , Robbes Didier , Chakalov Radoslav A.
Published: November 2005

We report measurements of the optical responses of a La2∕3Sr1∕3MnO3 (LSMO) sample at a wavelength of 533 nm in the 300–400 K range. At 335 K the temperature coefficient of the resistance of a 100-μm-wide, 300-μm-long LSMO line was 0.017K−1 and the normalized Hooge parameter was 9×10−30m3, which is among the lowest reported values. We then measured an optical sensitivity at I=5mA of 10.4VW−1 and corresponding noise equivalent power (NEP) values of 8.1×10−10WHz−1∕2 and 3.3×10−10WHz−1∕2 at 30 Hz and above 1 kHz, respectively. Simple considerations on bias current conditions and thermal conductance G are finally given for further sensitivity improvements using LSMO films.
Low-frequency phase locking in high-inductance superconducting nanowires
Authors: Hadfield R. H. , Miller A. J. , Nam S. W. , Kautz R. L. , Schwall R. E.
Published: November 2005

Niobium nitride nanowires show considerable promise as high-speed single-photon detectors. We report the observation of an anomalous low-frequency (∼10MHz) response in long, superconducting NbN nanowires (100nm wide, 4nm thick, and 500μm long). This behavior, although strikingly reminiscent of the ac Josephson effect, can be explained by a relaxation oscillation resulting from the high kinetic inductance of the type II nanowire. We simulate all of the observed effects using a simple resistive-hotspot/series-inductor model. The voltage pulses observed are indistinguishable from the pulses induced by visible photons, and our observations suggest noise-induced relaxation oscillations are one mechanism for the dark counts in photon detectors.
Wavelength-codified fiber laser hydrogen detector
Authors: Ortigosa-Blanch A. , Díez A. , González-Segura A. , Cruz J. L. , Andrés M. V.
Published: November 2005

We report a scheme for an optical hydrogen detector that codifies the information in wavelength. The system is based on an erbium-doped fiber laser with two coupled cavities and a Palladium-coated tapered fiber within one of the laser cavities. The tapered fiber acts as the hydrogen-sensing element. When the sensing element is exposed to a hydrogen atmosphere, its attenuation decreases changing the cavity losses. This change leads the system to switch lasing from the wavelength of the auxiliary cavity to the characteristic wavelength of the cavity which contains the sensing element. The detection level can be shifted by adjusting the reflective elements of the cavity containing the sensing element.
In solid localization of finger impacts using acoustic time-reversal process
Authors: Ing Ros Kiri , Quieffin Nicolas , Catheline Stefan , Fink Mathias
Published: November 2005

Time reversal in acoustics is a very efficient solution to focus sound back to its source in a wide range of materials including reverberating media. It expresses the following properties: A wave still has the memory of its source location. The concept presented in this letter first consists in detecting the acoustic waves in solid objects generated by a slight finger knock. In a second step, the information related to the source location is extracted from a simulated time reversal experiment in the computer. Then, an action (turn on the light or a compact disk player, for example) is associated with each location. Thus, the whole system transforms solid objects into interactive interfaces. Compared to the existing acoustic techniques, it presents the great advantage of being simple and easily applicable to inhomogeneous objects whatever their shapes. The number of possible touch locations at the surface of objects is shown to be directly related to the mean wavelength of the detected acoustic wave.
Residual strain around a step edge of artificial Al∕Si(111)-7×7 nanocluster
Authors: Liu Zhanwei , Xie Huimin , Fang Daining , Dai Fulong , Xue Qikun , Liu Hong , Jia Jinfeng
Published: November 2005

During artificial Al∕Si(111)-7×7 nanocluster fabrication by using surface-mediated clustering, original step with an atomically straight edge becomes curved and irregular because of stronger attractive interaction between Al atoms and Si atoms. Surface residual strain around step edges has been studied by using digital geometric phase technique. The results show that the residual strain is compressive and there is larger compressive stress near both of the up and down step edges.
Spatial location of transport-limiting traps in TiO2 nanoparticle films in dye-sensitized solar cells
Authors: Kopidakis N. , Neale N. R. , Zhu K. , van de Lagemaat J. , Frank A. J.
Published: November 2005

The dependence of the electron diffusion coefficient and photoinduced electron density on the internal surface area of TiO2 nanoparticle films in dye-sensitized solar cells was investigated by photocurrent transient measurements. The internal surface area was varied by altering the average particle size of the films. The density of electron traps in the films is found to change in direct proportion with the internal surface area, indicating that the traps are located predominately at the surface of TiO2 particles instead of in the bulk of the particles or at interparticle grain boundaries. The observed scaling of the electron diffusion coefficient with the internal surface area suggests that surface traps limit transport in TiO2 nanoparticle films. These results address a long-standing issue in the understanding of electron transport in dye-sensitized TiO2 solar cells.
Lagrangian statistics of particle pairs in homogeneous isotropic turbulence
Authors: Biferale L. , Boffetta G. , Celani A. , Devenish B. J. , Lanotte A. , Toschi F.
Published: November 2005

We present a detailed investigation of the particle pair separation process in homogeneous isotropic turbulence. We use data from direct numerical simulations up to Rλ∼280 following the evolution of about two million passive tracers advected by the flow over a time span of about three decades. We present data for both the separation distance and the relative velocity statistics. Statistics are measured along the particle pair trajectories both as a function of time and as a function of their separation, i.e., at fixed scales. We compare and contrast both sets of statistics in order to gain insight into the mechanisms governing the separation process. We find very high levels of intermittency in the early stages, that is, for travel times up to order ten Kolmogorov time scales. The fixed scale statistics allow us to quantify anomalous corrections to Richardson diffusion in the inertial range of scales for those pairs that separate rapidly. It also allows a quantitative analysis of intermittency corrections for the relative velocity statistics.
Lanthanum distribution and dielectric properties of intergrowth Bi5−xLaxTiNbWO15 ferroelectrics
Authors: Yi Z. G. , Li Y. X. , Zeng J. T. , Yang Q. B. , Wang D. , Lu Y. Q. , Yin Q. R.
Published: November 2005

Bi 5 − x La x Ti Nb W O 15  (x=0–1.50) ceramics prepared by conventional solid-state reaction were studied using x-ray diffraction (XRD), dielectric spectroscopy and Raman scattering techniques. The XRD analysis implied that single-phase intergrowth bismuth layered perovskite structure was obtained for all the samples and when x=0.75, the Bi3+ in (Bi2O2)2+ layer begins to be substituted by La3+. The dielectric spectra showed that, when Bi3+ in (Bi2O2)2+ is substituted, the Curie temperature becomes diffusive and the dielectric permittivity at room temperature is increased in a wide frequency range. Especially when x=1.50, the dielectric permittivity reaches its maximum of 270, nearly two times larger than that of the La3+ undoped sample. The Raman scattering experiments evidenced further that Bi3+ in (Bi2O2)2+ is substituted when x⩾0.75 and revealed the orthorhombic distortion of the octahedra is responsible for the increase of the dielectric permittivity at x⩾1.25.
Cell Scaffolds with Three-Dimensional Order: The Role of Modelling in Establishing Design Guidelines
Authors: Shanbhag Sachin , Lee Jungwoo , Kotov Nicholas A.
Published: November 2005

The architectural uniformity of highly ordered cell scaffolds with inverted colloidal crystal geometry is exploited by modelling the movement of cells and nutrients in the scaffold using Brownian dynamics simulations. The extent of cell–scaffold interaction and the diffusion of the cells in the scaffold are explicitly examined. A procedure to identify a suitable region in the available design space is suggested and evaluated against earlier experimental observations.
New Camphor-Derived Selenonium Ylides: Enantioselective Synthesis of Chiral Epoxides
Authors: Li Xin-Liang , Wang Yi , Huang Zhi-Zhen
Published: November 2005

Optically pure selenonium salts 3 as the precursors of two new chiral selenonium ylides 4 can be synthesized stereoselectively from natural d-camphor in good yields. It is found that the reaction of the selenonium salt 3b, an aldehyde, and potassium tert-butoxide can take place smoothly in ‘one-pot’ via the formation of selenonium ylide 4b, to give chiral trans-diaryl epoxides 5 in good yields with good diastereoselectivities and enantioselectivities.
Processing Windows for Forming Silk Fibroin Biomaterials into a 3D Porous Matrix
Authors: Kim Hyeon Joo , Kim Hyun Suk , Matsumoto Akira , Chin In-Joo , Jin Hyoung-Joon , Kaplan David L.
Published: November 2005

In the present study we clarify phase diagrams related to silk fibroin processing into three-dimensional porous structures useful for biomaterials and for scaffolds in tissue engineering. All-aqueous and organic solvent (hexafluoroisopropanol) modes of processing are compared relative to solution concentration of silk protein polymer and size of porogen (NaCl particles). The results clarify the range of conditions under which these biomaterial matrices can be formed, with a broader range of pore sizes and smoother surface morphology generated from the organic solvent process. These structures are directly applicable to fundamental studies of protein-based biomaterial assembly as well as cell interactions and tissue formation with these systems.
Synthesis and Characterization of SAMs and Tethered Bilayer Membranes from Unsymmetrically Substituted 1,2-Dithianes
Authors: Burns Christopher J. , Field Leslie D. , Petteys Brian J. , Ridley Damon D.
Published: November 2005

The synthesis of a series of new membrane-forming compounds, based on previously established components used in an ion-channel switch (ICS) biosensor (Nature 1997, 387, 580) is described. All new compounds are derived from 4,5-dihydroxy-1,2-dithiane, and contain a hydrophilic reservoir section (based on ethylene glycol units) and a lypophilic section (based on the natural lipid phytanol). Ellipsometry and contact angle measurements indicate that self-assembled monolayers (SAMs) formed from the new materials possess thicknesses and membrane packing comparable to previously reported biosensor components. Tethered bilayer lipid membranes (t-BLMs) incorporating the novel materials were studied using impedance spectroscopy with the ion-carrier valinomycin. The electrical behavior and calculated membrane thickness of the t-BLMs are comparable to those derived from the standard ICS components and this demonstrates that the novel membrane-forming compounds form stable membranes that are sufficiently fluid to transport potassium ions in the presence of valinomycin.
Increased-Valence or Electronic Hypervalence for a Diatomic One-Electron Bond
Authors: Harcourt Richard D.
Published: November 2005

With a and b as overlapping atomic orbitals to form the A–B bonding molecular orbital ψab = a + kb, it is deduced that for k ≠ 0, 1, or ∞, either the A atom or the B atom in the one-electron bond valence bond structure (A · B) exhibits increased-valence or electronic hypervalence, namely its valence exceeds unity. The result is illustrated using the results of STO-6G valence bond calculations for the one-electron bond of LiH+ and an excited state for H2CN. Valencies for the ground-states of H2+, H2, and H2− are also considered.
Application of the Palladium(0)-Catalyzed Ullmann Cross-Coupling Reaction in a Total Synthesis of (±)-Aspidospermidine and thus Representing an Approach to the Lower Hemisphere of the Binary Indole - Indoline Alkaloid Vinblastine
Authors: Banwell Martin G. , Lupton David W. , Willis Anthony C.
Published: November 2005

As part of ongoing studies directed towards the construction of the anti-cancer agent vinblastine (1), the related but structurally less complex natural product aspidospermidine (3) has been synthesized. Two approaches to target 3 were pursued. In the first, which was unsuccessful, the amine-tethered enone 6 was prepared but this failed to engage in the pivotal intramolecular conjugate addition reaction to give the bicyclic system 5. In contrast, the related compound 46, incorporating tethered enone and azide moieties, engaged in an intramolecular 1,3-dipolar cycloaddition reaction to give, presumably via an intermediate triazoline, the isolable and ring-fused aziridine 47. This was then converted, over two steps, into the previously reported tetrahydrocarbazole 4. Application of established protocols to this last compound allowed for the installation of the E-ring of the title alkaloid 3 and completion of the total synthesis.