bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Area and Anchorage‐Dependent Growth of Chinese Hamster Ovary Cells
Authors: Ruaan R.‐C. , Tsai G.‐J. , Tsao G. T.
Published: March 2005

Cell growth can be affected by many factors. For study of the cell responses under various environmental changes, the traditional method using batch cultures may not provide precise answers. It sometimes even leads to misapprehension. A flow system was therefore designed to eliminate the variations in chemical environment during the cell growth. An anchorage Chinese hamster ovary (CHO) cell line was chosen for study under this system. With the help of time‐lapse video recording and image analysis, it was found that the exposed surface area (Ae) of Chinese hamster ovary (CHO) cells was significantly affected by the serum concentration (S) in the medium. Cells appeared to be larger when cultivated in medium of low serum content. Comparing the growth rates of cells on different substrata, we have found that, although they were different at a given serum concentration, the growth curves could be correlated to a Monod type equation by replacing the substrate term with AeS. Furthermore, when we studied the effect of density‐dependent inhibition of cell growth, we found that there exists a minimum value of AeS required for stimulating cell proliferation. Once AeS falls below this value, cell proliferation stops. These observations seemed to indicate that the interaction between serum factors and cell surface, i.e., AeS, is an important parameter of the growth of CHO cells.
Kinetics of Hepatocyte Spheroid Formation
Authors: Peshwa Madhusudan V. , Wu Florence J. , Follstad Brian D. , Cerra Frank B. , Hu Wei‐Shou
Published: March 2005

Cultured hepatocytes have been explored for use in a bioartificial liver. Spheroids formed by cultured hepatocytes exhibit enhanced liver‐specific functions. The kinetics of spheroid formation, using rat hepatocytes, was studied on positively charged surfaces that were either uncoated or coated with collagen or (hydroxyethyl)methacrylate (HEMA). Optimal spheroid formation was obtained on positively charged (Primaria) surfaces at inoculum densities in the range of (3–9) × 104 cells/cm2. Cells initially attached and spread out on the surface. Subsequent retraction led to the emergence of small clumps of cells attached to the surface, from which spheroids formed and shed off into suspension. The process of spheroid formation took more than 72 h and was accompanied by a decrease in the surface area occupied by attached cells. Optical sectioning of fluorescently stained spheroids using confocal microscopy indicated that most of the cells in the spheroid were viable. Spheroids also maintained a constant albumin synthesis rate for over 7 days in culture. Spheroid formation was evaluated in terms of the changes in spheroid diameter, the surface area covered by attached cells, and the total protein content of the fraction of cells that formed spheroids. The quantitative methodologies developed were used to assess the effect of inoculum cell concentration on spheroid formation and to evaluate the kinetics of spheroid formation on different surfaces both favorable and nonfavorable to spheroid formation.
Production and Characterization of a Novel Tissue‐Type Plasminogen Activator Derivative in Escherichia coli
Authors: Saito Yoshimasa , Ishii Yoshinori , Sasaki Hitoshi , Hayashi Masako , Fujimura Takao , Imai Yuko , Nakamura Sachiko , Suzuki Shingo , Notani Joji , Asada Takashi , Horiai Haruo , Kobayashi Masakazu , Niwa Mineo
Published: March 2005

We have created a novel thrombolytic agent by the combination of mutation with partial deletion of tissue‐type plasminogen activator (t‐PA). We constructed Escherichia coli expression vectors for (i) native t‐PA (nt‐PA) and its derivatives; (ii) K1K2P, consisting of kringle 1 (K1), kringle 2 (K2), and protease (P) domains; (iii) K2P, consisting of K2 and P domains; (iv) D‐nt‐PA, (v) D‐K1K2P; and (vi) D‐K2P. The latter three are point mutants of nt‐PA, K1K2P, and K2P, respectively, in which Arg275 (number corresponds to that of nt‐PA) has been mutated to Asp. The production of nt‐PA and its derivatives was remarkably improved by (i) removal of the 3× noncoding region of nt‐PA cDNA from expression vectors and (ii) expression in mutant E. coliderived from E. coli HB101, which is insensitive to heat‐shock inductions. The proteins produced were precipitated as insoluble aggregates in the cells and were renatured to active forms by extraction with 8 M urea followed by dialysis against a redox buffer containing GSH and GSSG. The renaturation yield depended on the pH of the buffer and the number of disulfide bonds of the proteins (nt‐PA ≪ K1K2P < K2P). The mutation of Arg275 (the plasmin cleavage site) caused an increase in the catalytic enhancement by fibrin and a decrease of the interaction with plasminogen activator inhibitors. Among them, D‐K2P was selected as a candidate for a new thrombolytic agent because of (i) its facility of renaturation and purification to homogeneity and (ii) its high catalytic enhancement by fibrin, as compared with nt‐PA or other derivatives produced by the same system. It was produced in large amounts and characterized by structural analysis, as well as by biological and pharmacological activities. The disulfide linkages of D‐K2P were found to be identical to those of nt‐PA (Bowes) on the kringle 2 and protease domains. Although its specific activity is approximately one‐fourth that of nt‐PA (Bowes), it shows higher fibrin acceleration and a longer half‐life in blood than nt‐PA (Bowes). In the preliminary pharmacological studies, D‐K2P exhibited more potential thrombolytic effect than recombinant nt‐PA (alteplase) by both bolus and infusional administrations in the rabbit thrombus model. It was also more effective in canine coronary thrombosis. These results may indicate that plasma half‐life and fibrin acceleration play important roles in the thrombolytic agent.
Partitioning of Vancomycin Using Poly(ethy1ene glycol)‐Coupled Ligands in Aqueous Two‐Phase Systems
Authors: Singh Manish , Clark William M.
Published: March 2005

Affinity partitioning describes a process in which a biospecific ligand is used to manipulate the partitioning behavior of a biomolecule by coupling a ligand to one of the phase‐forming polymers. It combines the high selectivity of affinity chromatography with the scalability of aqueous two‐phase extractions. Fundamental studies have been made on the factors affecting affinity partitioning of the antibiotic vancomycin using a series of polymer—ligands composed of the D‐Ala‐D‐Ala peptide coupled to poly(ethy1ene glycol) in methoxypoly(ethy1ene g1ycol)/dextran aqueous two‐phase systems. The effects of varying the ligand molecular weight, the ligand binding interaction, the number of binding sites, the tie‐line length, and the aggregation of vancomycin have been measured. A modification of the Flanagan and Barondes model for affinity partitioning has been suggested to explain the results. The modified model accounts for the changes in the surface properties of the biomaterial on complex formation.
A Dynamic Light Scattering Study of β‐Galactosidase: Environmental Effects on Protein Conformation and Enzyme Activity
Authors: Yang Shang‐Tian , Marchio Jack L. , Yen Jyh‐Wen
Published: March 2005

Dynamic light scattering (DLS) is a useful technique for analyzing the size, shape, and other structural characteristics of protein molecules in solution. The effects of various environmental conditions on the structure and activity of Aspergillus oryzae β‐galactosidase were studied. DLS was used to determine protein particle size under various salt, pH, and temperature conditions. Changes in the activity and stability of this enzyme caused by different environmental conditions were found to correlate well with the size changes of the protein particles. This change in protein size can be attributed to protein unfolding and aggregation under extreme conditions. The presence of the enzyme substrate, lactose, in the protein solution greatly enhanced enzyme stability by inhibiting aggregation.
Effects of Solution Properties on Solute and Permeate Flux in Bovine Serum Albumin‐IgG Ultrafiltration
Authors: Nel Russell G. , Oppenheim S. F. , Rodgers V. G. J.
Published: March 2005

It has been observed that bovine serum albumin (BSA, 69 000 Da) exhibits high rejection in a pH 7.4, 0.15 M NaCl solution containing low concentrations of immuno‐γ‐globulins (IgG, 155000 Da). Although it is apparent that this phenomenon is likely due to the complex interactions of the proteins as well as to simple steric hindrance, it is not clear to what extent these resistances contribute to the solute flux loss. This study investigates how variations in IgG concentration, solution pH, and ionic strength can affect the solute and the permeate fluxes for the ultrafiltration of BSA through 100 000 MWCO cellulosic membranes in a batch cell. The results showed that, unlike cases performed at pH 7.4 in 0.15 M NaCl, the presence of IgG may increase the transport of BSA under certain conditions. This study does show the potential value and insights that will result from further binary protein ultrafiltration research.
Resemblance of Immobilized Trichoderma viride Fungal Spores in an Alginate Matrix to a Composite Material
Authors: Nussinovitch A.
Published: March 2005

Trichoderma uiride fungal spores were immobilized in alginate gels. The mechanical properties of these gels were tested by compression using a universal testing machine. The properties of the immobilized preparations are presented in terms of their corrected stress at failure, Hencky's strain at failure, and the modulus of deformability. Results are also presented as the ratio between mechanical properties of gels with or without microorganisms, and the occupied volume of the tested gel. A simple mathematical model for composite materials was found to properly describe the relative stress at failure vs the phase volume of the fungal spores. Random loose packing of the spores in the matrix is proposed.
Wind influence on a coastal buoyant outflow
Authors: Whitney Michael M. , Garvine Richard W.
Published: March 2005

This paper investigates the interplay between river discharge and winds in forcing coastal buoyant outflows. During light winds a plume influenced by the Earth's rotation will flow down shelf (in the direction of Kelvin wave propagation) as a slender buoyancy‐driven coastal current. Downwelling favorable winds augment this down‐shelf flow, narrow the plume, and mix the water column. Upwelling favorable winds drive currents that counter the buoyancy‐driven flow, spread plume waters offshore, and rapidly mix buoyant waters. Two criteria are developed to assess the wind influence on a buoyant outflow. The wind strength index (Ws) determines whether a plume's along‐shelf flow is in a wind‐driven or buoyancy‐driven state. Ws is the ratio of the wind‐driven and buoyancy‐driven along‐shelf velocities. Wind influence on across‐shelf plume structure is rated with a timescale (ttilt) for the isopycnal tilting caused by wind‐driven Ekman circulation. These criteria are used to characterize wind influence on the Delaware Coastal Current and can be applied to other coastal buoyant outflows. The Delaware buoyant outflow is simulated for springtime high–river discharge conditions. Simulation results and Ws values reveal that the coastal current is buoyancy‐driven most of the time (∣Ws∣ < 1 on average). Wind events, however, overwhelm the buoyancy‐driven flow (∣Ws∣ > 1) several times during the high‐discharge period. Strong upwelling events reverse the buoyant outflow; they constitute an important mechanism for transporting fresh water up shelf. Across‐shelf plume structure is more sensitive to wind influence than the along‐shelf flow. Values of ttilt indicate that moderate or strong winds persisting throughout a day can modify plume width significantly. Plume widening during upwelling events is accompanied by mixing that can erase the buoyant outflow.
Antiparallel versus component merging at the magnetopause: Current bifurcation and intermittent reconnection
Authors: Karimabadi Homa , Daughton William , Quest Kevin B.
Published: March 2005

One of the major unresolved issues regarding magnetic reconnection at the dayside magnetopause is the location where reconnection first occurs during periods of a large interplanetary magnetic field By. In order to address this issue, we examine and contrast the onset of reconnection in the presence and absence of a finite guide field (By). In an accompanying paper (Karimabadi et al., 2005) we showed that in case of one linearly unstable mode, tearing saturates at amplitudes too small to be of relevance to transport at the magnetopause, even in the antiparallel case. However, we show that in general a number of modes are simultaneously unstable at the magnetopause. This process is aided by the presence of electron temperature anisotropy which broadens the unstable spectrum, extending it to very short wavelengths. Multimode tearing gets past the single mode stabilization and grows to large amplitudes in several stages: the initial linear stage, the coalescence process which proceeds at a slower growth rate, the growth and dominance of the longest wavelength in the system, and a final explosive phase which leads to a saturated state with a bifurcated current sheet. The aspect ratio of the magnetic island at the end of the explosive phase is ∼0.2. This is in good agreement with the aspect ratio of the magnetic island structure at Earth's magnetopause reconstructed from the single‐spacecraft data by Hau and Sonnerup (1999). We find that in addition to coalescence, there can occur stretching of the X lines. This leads to a recurrent reconnection process where only a single, rather than a pair of magnetic structures are periodically produced, reminiscent of flux transfer events. Although the detailed properties of the various interacting modes are altered in the presence of a guide field, the basic scenario including the final explosive phase of the system remains even for very large guide fields. We calculate the steady state reconnection rate as a function of guide field and plasma beta and show that fast reconnection is obtained even for modest values of guide field. Detailed application of these results to the magnetopause is discussed. One key finding is that it takes a very weak guide field of less than 0.07 of the magnetosheath field to transition away from the antiparallel reconnection. The linear growth rate of isotropic tearing compared to convection time is fast only for thin sheets. In the absence of electron temperature anisotropies, both antiparallel and component merging remain competitive as long as the guide field is not too strong (≤0.4). Local condition, most importantly the shear flow, is identified as one effect that may change the behavior of reconnection in the antiparallel versus component merging.
How permeable is the edge of the Arctic vortex: Model studies of winter 1999–2000
Authors: Steinhorst Hildegard‐Maria , Konopka Paul , Günther Gebhard , Müller Rolf
Published: March 2005

The edge of the Arctic vortex constitutes a strong barrier to transport; however, the extent of isolation of the vortex air as a function of altitude and season is relatively poorly quantified. In this study, by examining the transport of midlatitude air parcels across the vortex edge into the vortex, we analyze the permeability of the vortex edge. With the three‐dimensional version of CLaMS (Chemical Lagrangian Model of the Stratosphere) we explore the dilution of the vortex air due to mixing in winter 1999–2000. An artificial, passive tracer was initialized on 1 December 1999 inside the polar vortex with a value of 100% and with a value of zero outside the polar vortex. Using several different definitions of the vortex edge, the resulting intrusions of midlatitude air into the vortex show the same mean features. This demonstrates that the diagnosed dilution does not strongly depend on the details of the definition of the vortex edge. At about the end of March 2000, the vertical structure of the vortex consisted of well‐isolated, pure vortex layers around 500 K and 750 K, with some more diluted layers in between and at the vortex bottom. The influence of wave activity on the evolution of the intrusion layers is studied. The divergence of the Eliassen‐Palm flux shows such a high variability during the whole period that it is not possible to assess a direct causality of certain intrusion layers and some specific patterns. Some characteristics of the vortex edge, in particular the shape of the gradient of potential vorticity (PV), can influence the dilution of the vortex. In cases without a distinct maximum in the PV gradient, the defined “vortex edge” may vary substantially from day to day. The comparison of some properties of the vortex (wind speed, PV field, area of the vortex, the maximum of the PV gradient) of undisturbed versus diluted layers and the variation in time of the intrusions were analyzed. All observed intrusions begin in conditions of weak PV gradient, indicating that the value of the maximum of the PV gradient may be used as a quantitative measure of the permeability of the vortex edge.
On the reconstruction of seasonal oceanic precipitation in the presatellite era
Authors: Efthymiadis Dimitrios , New Mark , Washington Richard
Published: March 2005

A fundamental limitation of gridded precipitation data sets is the paucity of observations over the oceans in the presatellite era. We have evaluated the capabilities and limitations of reconstructing oceanic precipitation using land‐based precipitation records. The reconstruction method is based on eigenvector projection, where eigenvectors (or empirical orthogonal functions) of precipitation variability in the Climate Prediction Center (CPC) merged analysis of precipitation (CMAP) gauge/satellite precipitation data set, with near‐global coverage from 1979 to present, are projected onto land‐only data. The approach has useful skill in areas of the tropics where interannual variability is mainly associated with El Niño–Southern Oscillation (ENSO) activity. Reconstruction is less skillful in non‐ENSO years and is primarily restricted to within 1000–2000 km of land‐based data. Analogous dependencies hold for the extratropical oceans, where precipitation is best reconstructed close to land data and/or in areas where precipitation variability is locally associated with major atmospheric circulation patterns. Using the National Centers for Environmental Prediction‐National Center for Atmospheric Research reanalysis precipitation as a “proxy” for observations in the presatellite era yields similar results, and in addition, illustrates the limitations to the approach when applied in the presatellite era (prior to 1979): skill is greatest in oceanic areas that are close to land observations and/or dominated by persistent atmospheric or atmosphere‐ocean patterns. Overall, the technique would appear to have some value in providing a qualitative picture of oceanic precipitation variability in the presatellite era, but estimation errors preclude use of the data for quantitative analyses.
Exact sequence analysis for three-dimensional hydrophobic-polar lattice proteins
Authors: Schiemann Reinhard , Bachmann Michael , Janke Wolfhard
Published: March 2005

We have exactly enumerated all sequences and conformations of hydrophobic-polar (HP) proteins with chains of up to 19 monomers on the simple cubic lattice. For two variants of the HP model, where only two types of monomers are distinguished, we determined and statistically analyzed designing sequences, i.e., sequences that have a nondegenerate ground state. Furthermore we were interested in characteristic thermodynamic properties of HP proteins with designing sequences. In order to be able to perform these exact studies, we applied an efficient enumeration method based on contact sets.
Controlling the size of nanostructures in thin films via blending of block copolymers and homopolymers
Authors: Peng Juan , Gao Xiang , Wei Yuhan , Wang Hanfu , Li Binyao , Han Yanchun
Published: March 2005

The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy.
Pulsed laser photolysis and quantum chemical-statistical rate study of the reaction of the ethynyl radical with water vapor
Authors: Carl Shaun A. , Minh Thi Nguyen Hue , Elsamra Rehab M. I. , Tho Nguyen Minh , Peeters Jozef
Published: March 2005

The rate coefficient of the gas-phase reaction C2H+H2O→products has been experimentally determined over the temperature range 500–825K using a pulsed laser photolysis-chemiluminescence (PLP-CL) technique. Ethynyl radicals (C2H) were generated by pulsed 193nm photolysis of C2H2 in the presence of H2O vapor and buffer gas N2 at 15Torr. The relative concentration of C2H radicals was monitored as a function of time using a CH* chemiluminescence method. The rate constant determinations for C2H+H2O were k1(550K)=(2.3±1.3)×10−13cm3s−1, k1(770K)=(7.2±1.4)×10−13cm3s−1, and k1(825K)=(7.7±1.5)×10−13cm3s−1. The error in the only other measurement of this rate constant is also discussed. We have also characterized the reaction theoretically using quantum chemical computations. The relevant portion of the potential energy surface of C2H3O in its doublet electronic ground state has been investigated using density functional theory B3LYP∕6-311++G(3df,2p) and molecular orbital computations at the unrestricted coupled-cluster level of theory that incorporates all single and double excitations plus perturbative corrections for the triple excitations, along with the 6-311++G(3df,2p) basis set [(U)CCSD(T)∕6-311++G(3df,2p)] and using UCCSD(T)∕6-31G(d,p) optimized geometries. Five isomers, six dissociation products, and sixteen transition structures were characterized. The results confirm that the hydrogen abstraction producing C2H2+OH is the most facile reaction channel. For this channel, refined computations using (U)CCSD(T)∕6-311++G(3df,2p)∕∕(U)CCSD(T)∕6-311++G(d,p) and complete-active-space second-order perturbation theory/complete-active-space self-consistent-field theory (CASPT2/CASSCF) [B. O. Roos, Adv. Chem. Phys. 69, 399 (1987)] using the contracted atomic natural orbitals basis set (ANO-L) [J. Almlöf and P. R. Taylor, J. Chem. Phys.86, 4070 (1987)] were performed, yielding zero-point energy-corrected potential energy barriers of 17kJmol−1 and 15kJmol−1, respectively. Transition-state theory rate constant calculations, based on the UCCSD(T) and CASPT2/CASSCF computations that also include H-atom tunneling and a hindered internal rotation, are in perfect agreement with the experimental values. Considering both our experimental and theoretical determinations, the rate constant can best be expressed, in modified Arrhenius form as k1(T)=(2.2±0.1)×10−21T3.05exp[−(376±100)∕T]cm3s−1 for the range 300–2000K. Thus, at temperatures above 1500K, reaction of C2H with H2O is predicted to be one of the dominant C2H reactions in hydrocarbon combustion.
Conformal symmetries of Einstein’s field equations and initial data
Authors: Sharma Ramesh
Published: March 2005

This paper examines the initial data for the evolution of the space–time solution of Einstein’s equations admitting a conformal symmetry. Under certain conditions on the extrinsic curvature of the initial complete spacelike hypersurface and sectional curvature of the space–time with respect to sections containing the normal vector field, we have shown that the initial hypersurface is conformally diffeomorphic to a sphere or a flat space or a hyperbolic space or the product of an open real interval and a complete 2-manifold. It has been further shown that if the initial hypersurface is compact, then it is conformally diffeomorphic to a sphere. Finally, the conformal symmetries of a generalized Robertson–Walker space–time have been described.
On deformations of standard R-matrices for integrable infinite-dimensional systems
Authors: Szablikowski Błażej M. , Błaszak Maciej
Published: March 2005

Simple deformations, with a parameter ϵ, of classical R-matrices which follow from decomposition of appropriate Lie algebras, are considered. As a result nonstandard Lax representations for some well-known integrable systems are presented and integrable evolution equations are constructed.
Effects of thermal annealing on deep-level defects and minority-carrier electron diffusion length in Be-doped InGaAsN
Authors: Xie S. Y. , Yoon S. F. , Wang S. Z.
Published: March 2005

We report the effects of ex situ thermal annealing on the deep-level defects and the minority-carrier electron diffusion length in Be-doped, p-type In0.03Ga0.97As0.99N0.01 grown by solid source molecular-beam epitaxy. Deep-level transient spectroscopy measurements reveal two majority-carrier hole traps, HT1 (0.18 eV) and HT4 (0.59 eV), and two minority-carrier electron traps, ET1 (0.09 eV) and ET3 (0.41 eV), in the as-grown sample. For the sample with postgrowth thermal annealing, the overall deep-level defect-concentration is decreased. Two hole traps, HT2 (0.39 eV) and HT3 (0.41 eV), and one electron trap, ET2 (0.19 eV), are observed. We found that the minority-carrier electron diffusion length increases by ∼30% and the leakage current of the InGaAsN∕GaAsp-n junction decreases by 2–3 orders after thermal annealing. An increase of the net acceptor concentration after annealing is also observed and can be explained by a recently proposed three-center-complex model.
Infrared refractive indices of liquid crystals
Authors: Li Jun , Wu Shin-Tson , Brugioni Stefano , Meucci Riccardo , Faetti Sandro
Published: March 2005

The refractive indices of E7 liquid-crystal mixture were measured at six visible and two infrared (λ=1.55 and 10.6μm) wavelengths at different temperatures, using Abbe and wedged cell refractometer methods, respectively. The experimental data of the visible wavelengths fit the extended Cauchy equations well. Using the extended Cauchy equations, we can extrapolate the refractive indices of E7 to IR. The extrapolated results almost strike through the measured data. Thus, the extended Cauchy equations can be used to link the visible refractive indices to infrared, where the refractive index measurements are more difficult.
Edge capillary-gravity waves on a sloping beach
Authors: Muzylev Sergey V. , Bulgakov Sergey N. , Duran-Matute Matias
Published: March 2005

It is shown how the solution for velocity potential may be determined when the effect of surface tension is included in the linearized theory of Ursell-type edge waves over a plane-sloping beach. The problem is examined without making a hydrostatic assumption. Explicit solutions for edge capillary-gravity waves are given and the dispersion equation is obtained. The influence of capillarity on gravity waves is discussed.
Hydrogen passivation effect in nitrogen-doped ZnO thin films
Authors: Li Xiaonan , Keyes Brian , Asher Sally , Zhang S. B. , Wei Su-Huai , Coutts Timothy J. , Limpijumnong Sukit , Van de Walle Chris G.
Published: March 2005

The role of hydrogen in nitrogen-doped ZnO thin films was studied by Fourier transform infrared (FTIR) absorption and modeled by first-principles calculations to understand the difficulty of doping ZnO p-type with nitrogen. Nitrogen-doped ZnO films were fabricated by low-pressure metal-organic chemical vapor deposition (MOCVD). High levels of nitrogen incorporation were observed, but the acceptor concentrations remained low. Theoretical analysis suggests there is a high probability that NO− and H+ charged defects combine to form the neutral defect complexes, thereby compensating the nitrogen-related acceptors. Calculated values of the vibrational frequencies of the related infrared modes agree well with the measured spectra. Thus, we believe the difficulty of achieving p-type doping in MOCVD-grown ZnO films is due, at least partially, to inadvertent passivation by hydrogen.
Field emission of carbon nanotubes on anodic aluminum oxide template with controlled tube density
Authors: Chen Po-Lin , Chang Jun-Kai , Kuo Cheng-Tzu , Pan Fu-Ming
Published: March 2005

The tube number density of aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH4∕H2 feed ratio during the CNT growth. We ascribe the variation of the tube density as a function of the CH4∕H2 feed ratio to the kinetic competition between outgrowth of cobalt-catalyzed CNTs from the AAO pore bottom and deposition of the amorphous carbon (a-C) overlayer on the AAO template. A pore-filling ratio of 18% to 82% for the nanotubes overgrown out of nanopores on the AAO template can be easily achieved by adjusting the CH4∕H2 feed ratio. Enhanced field emission properties of CNTs were obtained by lowering the tube density on AAO. However, at a high CH4 concentration, a-C by-product deposit on the CNT surface can degrade the field emission property due to a high energy barrier and significant potential drop at the emission site.
Self-recovery of stressed nanomembranes
Authors: Jiang Chaoyang , Rybak Beth M. , Markutsya Sergiy , Kladitis Paul E. , Tsukruk Vladimir V.
Published: March 2005

Long-term stability and self-recovery properties were studied for the compliant nanomembranes with a thickness of 55nm free suspended over openings of several hundred microns across. These nanomembranes were assembled with spin-assisted layer-by-layer routines and were composed of polymer multilayers and gold nanoparticles. In a wide pressure range, the membranes behave like completely elastic freely suspended plates. Temporal stability was tested under extreme deformational conditions close to ultimate strain and very modest creep behavior was observed. A unique “self-recovery” ability of these nanomembranes was revealed in these tests. We observed a complete restoration of the initial nanomembrane shape and properties after significant inelastic deformation. These unique micromechanical properties are suggested to be the result of strong Coulombic interaction between the polyelectrolyte layers combined with a high level of biaxial orientation of polymer chains and in-plane prestretching stresses.
Effects of hydrogen on the morphology and electrical properties of GaN grown by plasma-assisted molecular-beam epitaxy
Authors: Dong Y. , Feenstra R. M. , Greve D. W. , Moore J. C. , Sievert M. D. , Baski A. A.
Published: March 2005

We study the effect of introducing hydrogen gas through the rf-plasma source during plasma-assisted molecular-beam epitaxy of GaN(0001). The well-known smooth-to-rough transition that occurs for this surface as a function of decreasing Ga flux in the absence of H is found to persist even with H present, although the critical Ga flux for this transition increases. Under Ga-rich conditions, the presence of hydrogen is found to induce step bunching (facetting) on the surface. Conductive atomic force microscopy reveals that leakage current through dislocation cores is significantly reduced when hydrogen is present during the growth.
Probing local water contents of in vitro protein films by ultrasonic force microscopy
Authors: Szoszkiewicz Robert , Kulik Andrzej J. , Gremaud Gerard , Lekka Malgorzata
Published: March 2005

By means of ultrasonic force microscopy and lateral force microscopy we measure adhesion hysteresis and friction on protein films of bovine serum albumin and concanavalin A at local scales. Our investigations at different relative humidities (less than 5% and at 50% relative humidity) correspond to dehydrated and hydrated states of proteins. We demonstrate that a substantial increase of adhesion hysteresis with relative humidity is sensitive measure of protein–water binding capacity at local scales.
High-intensity terahertz radiation from a microstructured large-area photoconductor
Authors: Dreyhaupt A. , Winnerl S. , Dekorsy T. , Helm M.
Published: March 2005

We present a planar large-area photoconducting emitter for impulsive generation of terahertz (THz) radiation. The device consists of an interdigitated electrode metal-semiconductor-metal (MSM) structure which is masked by a second metallization layer isolated from the MSM electrodes. The second layer blocks optical excitation in every second period of the MSM finger structure. Hence charge carriers are excited only in those periods of the MSM structure which exhibit a unidirectional electric field. Constructive interference of the THz emission from accelerated carriers leads to THz electric field amplitudes up to 85V∕cm when excited with fs optical pulses from a Ti:sapphire oscillator with an average power of 100mW at a bias voltage of 65V applied to the MSM structure. The proposed device structure has a large potential for large-area high-power THz emitters.
Computed tomographic reconstruction based on x-ray refraction contrast
Authors: Maksimenko Anton , Ando Masami , Hiroshi Sugiyama , Yuasa Tetsuya
Published: March 2005

Computed tomographic (CT) reconstruction technique is widely used in many fields of research. Commonly the CT-reconstruction is based on the x-ray absorption contrast. However, recently, methods for generating other x-ray contrasts have been developed. One of them is the refraction contrast which provides information on the deflection of the x-ray beam when penetrating through the object. This contrast has certain advantages and allows us to observe details invisible in the absorption images. Thus, CT based on the refraction contrast must have the same advantages. However, it requires a new mathematical algorithm and software. This letter is dedicated to the solution of the problem including theoretical consideration on the mathematical model which is the basis for the computer modeling and experimental realization of the technique. Actual experimental results together with the reconstructed images are presented and described.
Molecular and Crystal Structure of Two Anthracene Derivatives and their 1,4-Endoperoxides. Influence of the Aromatic Ring Distortion upon the Steric Acceleration of the 1,4-Addition of Singlet Oxygen
Authors: Lahrahar Nacer , Bouas-Laurent Henri , Desvergne Jean-Pierre , Marsau Pierre , Rigaudy Jean
Published: March 2005

The X-ray structure determination of two anthracene derivatives, namely
1,2,3,4-tetramethylanthracene (TMA) and
1,2,3,4-tetramethyl-9,10-diphenylanthracene (TMDPA), and of their
endoperoxides, 1,2,3,4- tetramethyl-1,4-dihydro-1,4-epidioxyanthracene (TMAPO)
and 1,2,3,4-tetramethyl-9,10-diphenyl-1,4-dihy- dro-1,4-epidioxyanthracene
(TMDPAPO), has been performed. The compared analysis of the conformations of
the four molecular structures strongly suggests that the steric acceleration
observed for singlet oxygen addition to TMDPA should be attributed to the
important distortion of the anthracene nucleus.
The Synthesis, Stereochemistry and Properties of Linear and Branched Chain Tetraethylenepentaamine Cobalt(III) Complexes
Authors: Buckingham David A. , Jackson W. Gregory , Marzilli Patricia A. , Sargeson Alan M.
Published: March 2005

Described are the syntheses, isolation and resolution of many diastereoisomers
of pentaaminecobalt(III) complexes obtained from commercial-grade
tetraethylenepentaamine. They contain both linear (tetraen;
3,6,9-triazaundecane-1,11-diamine) and branched chain (trenen;
3-(2-aminoethyl)-3,6-diazaoctane-1,8- diamine) isomers of
C8H23N5 and
are free of the many other amines present in the original (crude) pentaamine
mixture. A dimeric bridging peroxocobalt(III) complex
[Co2(C8H23N5)2O2]
(ClO4)4 has been isolated and
converted into a mixture of
s-[Co(trenen)X]n+
and α-anti β-,
α-syn β- and
α-α-[Co(tetraen)X]2+
complexes (X = Cl¯, Br¯, N3¯), and
the various isomers have been separated by a combination of fractional
crystallization and ion-exchange chromatography. In addition, some X =
NO3¯ and OH2 derivatives have
been made by a kinetic route, including the unstable
α-syn β isomers. Many of the complexes have
been resolved into their enantiomers, and visible, o.r.d. and c.d. spectra are
reported. An X-ray crystallographic analysis of a prototype of each of the
four isomeric complexes (X = Cl¯ or
N3¯) has been determined previously, thereby
establishing the identity of many related complexes. Stereoretentive reactions
are used to correlate these related isomers, and 13 C
and 1 H n.m.r. spectra are reported. The pure trenen and
tetraen ligands have been recovered from the CoIII
complexes and can be distinguished by 13 C n.m.r.
spectroscopy
Reaction of Imidazoles with Cyanogen Bromide: Cyanation at N 1 or Bromination at C 2?
Authors: McCallum Peter B. W. , Grimmett M. Ross , Blackman Allan G. , Weavers Rex T.
Published: March 2005

The reaction in acetonitrile solution of a number of imidazoles(1H-, 1-methyl-, 2-methyl-, 4-methyl-, 1,2-, 1,4- and1,5-dimethyl-, 1-ethyl-, 1-benzyl- and 1-butyl-imidazole) and imidazolecomplexes([Co(NH3)5(imH)](ClO4)3,[Co(NH3)5(im)](ClO4)2 and[Co(NH3)5(1-Meim)](ClO4)3) with BrCN has beenstudied. Those imidazoles bearing an N-alkyl substituent and having a hydrogenat C2 react to give the 2-bromo products, while the N-H imidazoles react togive N-cyano derivatives. The product(s) from thereaction of 1,2-dimethylimidazole with BrCN could not be characterized. Of thecomplexes, only[Co(NH3)5(im)](ClO4)2 reacts, giving the 2-bromoproduct. Our observations suggest a lone pair on a ring nitrogen atom isnecessary for an imidazole to react with BrCN, and a possible mechanism issuggested. The X-ray structure of 2-methylimidazole-1-carbonitrile isreported. Crystal data (–143°C) forC5H5N3:monoclinic, P21/c, a10·201(5), b 7·110(3),c 7·227(3) Å, β 100·47(2)°,V 515·4(4) Å 3 , Z 4,dcalcd 1·380 gcm¯3 . Refinement of the structure converged withR1 0·0444 for 1183reflections with Fo >4F(Fo) andwR2 0·1259 for all 1278data.
[1H,15N] N.M.R. Kinetic Studies of Reactions of cis- and trans-[PtCl2(15NH3)(c-C6H1115NH2)] with Guanosine 5'-Monophosphate
Authors: Barton Sarah J. , Barnham Kevin J. , Habtemariam Abraha , Frey Urban , Sue Rodney E. , Sadler Peter J.
Published: March 2005

cis-[PtCl2(15NH3)(c-C6H11NH2)]
is an active metabolite of the oral platinum(IV) anticancer drug
cis,trans,cis-[PtCl2(CH3CO2)2(NH2)(c-C6H11NH2)].
Since it is likely that guanine bases on DNA are targets for this drug, we
have analysed the kinetics of reaction of this platinum(II) metabolite with
guanosine 5′-monophosphate (5′-GMP) at 310 K, pH 7, using
[1H, 15N] n.m.r.
methods. Reactions of the trans isomer are reported for
comparison. The reactions proceed via aquated intermediates, and, for the
cis isomer, the rates of aquation and substitution of
H2O by 5′-GMP are 2-5 times faster
trans to the amine ligand
(c-C6H11NH2)
compared to trans to NH3 for both the first and second
steps. For the trans complex, the first aquation step is
c. 3 times faster than for the cis complex, as expected
from the higher trans influence of Cl¯, whereas the
rate of the second aquation step (trans to N7 of
5′-GMP) is comparable to that trans to
NH3. These findings have implications for the courses of
reactions with DNA.
Complexes of 6A-(2-Aminoethylamino)-6A-deoxy-b-cyclodextrin and 6A-[Bis(carboxylatomethyl)amino]-6A-deoxy-b-cyclodextrin with (R)- and (S)-Tryptophanate and (R)- and (S)-Phenylalaninate in Aqueous Solution. A pH Titrimetric and N.M.R. Spectroscopic Study
Authors: Sandow Melissa , May Bruce L. , Clements Philip , Easton Christopher J. , Lincoln Stephen F.
Published: March 2005

The 1 : 1 host–guest complexes formed by
6A-(2-aminoethylamino)-6A-deoxy-β-cyclodextrin
and (R)- and (S)-tryptophanate are
characterized by log(K/dm3
mol–1) = 4.83±0.02 and
4.72±0.03, respectively, and for those formed with
(R)- and (S)-phenylalaninate
log(K/dm3
mol–1) = 3.82±0.05 and
4.12±0.02, respectively, in aqueous solution at 298.2 K and
I = 0.10 mol dm–3
(NaClO4), where K is the stability
constant. The corresponding values for the analogous complexes formed by
6A-[bis(carboxylatomethyl)amino]-6A-deoxy-β-cyclodextrin
are 3.4±0.1, 3.3±0.1, 4.02±0.06 and 4.00±0.06,
respectively. Host–guest complexes are also formed by the monoprotonated
substituted β-cyclodextrins. 1H n.m.r. spectroscopy
(ROESY) indicates that the guests are complexed with their indole and phenyl
entities inside the annuli of the substituted β-cyclodextrin
hosts.
Termination of spiral waves during cardiac fibrillation via shock-induced phase resetting
Authors: Gray Richard A. , Chattipakorn Nipon
Published: March 2005

Multiple unstable spiral waves rotating around phase singularities (PSs) in the heart, i.e., ventricular fibrillation (VF), is the leading cause of death in the industrialized world. Spiral waves are ubiquitous in nature and have been extensively studied by physiologists, mathematicians, chemists, and biologists, with particular emphasis on their movement and stability. Spiral waves are not easy to terminate because of the difficulty of “breaking” the continuous spatial progression of phase around the PSs. The only means to stop VF (i.e., cardiac defibrillation) is to deliver a strong electric shock to the heart. Here, we use the similarities between spiral wave dynamics and limit cycle oscillators to characterize the spatio-temporal dynamics of VF and defibrillation via phase-resetting curves. During VF, only PSs, including their formation and termination, were associated with large phase changes. At low shock strengths, phase-resetting curves exhibited characteristics of weak (type 1) resetting. As shock strength increased, the number of postshock PSs decreased to zero coincident with a transition to strong (type 0) resetting. Our results indicate that shock-induced spiral wave termination in the heart is caused by altering the phase around the PSs, such that, depending on the preshock phase, sites are either excited by membrane depolarization (phase advanced) or exhibit slowed membrane repolarization (phase delay). Strong shocks that defibrillate break the continuity of phase around PSs by forcing the state of all sites to the fast portion of state space, thus quickly leading to a “homogeneity of state,” subsequent global repolarization and spiral wave termination.
Tetanic Stimulation of the Peripheral Nerve before Transcranial Electrical Stimulation Can Enlarge Amplitudes of Myogenic Motor Evoked Potentials during General Anesthesia with Neuromuscular Blockade
Authors: Kakimoto Meiko , Kawaguchi Masahiko , Yamamoto Yuri , Inoue Satoki , Horiuchi Toshinori , Nakase Hiroyuki , Sakaki Toshisuke , Furuya Hitoshi
Published: March 2005

Background

Neuromuscular blockade can suppress myogenic motor evoked potentials (MEPs). The authors hypothesized that tetanic stimulation (TS) of the peripheral nerve before transcranial stimulation may enhance myogenic MEPs during neuromuscular blockade. In the current study, the authors evaluated MEP augmentations by TS at different levels of duration, posttetanic interval, neuromuscular blockade, and stimulus intensity.

Methods

Thirty-two patients undergoing propofol-fentanyl-nitrous oxide anesthesia were examined. Train-of-five stimulation was delivered to C3-C4, and MEPs were recorded from the abductor hallucis muscle. In study 1, TS with a duration of 1, 3, or 5 s was delivered at 50 Hz to the tibial nerve 1, 3, or 5 s (interval) before transcranial stimulation, and the effects of TS on MEP amplitude were evaluated. In study 2, TS-induced MEP augmentations were evaluated at the neuromuscular blockade level (%T1) of 50% or 5%. In study 3, MEP augmentations by TS at stimulus intensities of 0, 5, 25, and 50 mA were evaluated.

Results

The application of TS significantly enlarged the amplitudes of MEPs at the combinations of duration (3, 5 s) and interval (1, 3, 5 s) compared with those without TS. TS-induced MEP augmentations were similarly observed at %T1 of both 50% and 5%. TS-induced MEP augmentations were observed at stimulus intensities of 25 and 50 mA.

Conclusions

The results indicate that TS of the peripheral nerve before transcranial stimulation can enlarge the amplitude of MEPs during general anesthesia with neuromuscular blockade. TS of the peripheral nerve can be intraoperatively applied as a method to augment myogenic MEP responses.
Does Preoperative Coronary Angioplasty Improve Perioperative Cardiac Outcome?
Authors: Godet Gilles , Riou Bruno , Bertrand Michèle , Fléron Marie-Hélène , Goarin Jean-Pierre , Montalescot Gilles , Coriat Pierre
Published: March 2005

Background

Percutaneous coronary intervention (PCI) is performed in patients with coronary artery disease who are undergoing major noncardiac procedures to reduce perioperative cardiac morbidity and mortality. However, the impact of this approach on postoperative outcome remains controversial.

Methods

The authors analyzed a cohort of 1,152 patients after abdominal aortic surgery in which 78 patients underwent PCI. A propensity score analysis was performed. Also, using a logistic regression model, the authors determined variables associated with a severe postoperative coronary event or a death in patients without PCI. Then, in patients with PCI, they compared the expected and observed outcome.

Results

Five variables (age > 75 yr, blood transfusion > 3 units, repeated surgery, preoperative hemodialysis, and previous cardiac failure) independently predicted (with 94% correctly classified) a severe postoperative coronary event, and five variables (age > 75 yr, repeated surgery, previously abnormal ST segment/T waves, previous hypertension, and previous cardiac failure) independently predicted (with 97% correctly classified) postoperative death. In the PCI group, the observed percentages of patients with a severe postoperative coronary event (9.0% [95% confidence interval, 4.4-17.4]) or death (5.1% [95% confidence interval, 2.0-12.5]) were not significantly different from the expected percentages (8.2 and 6.9%, respectively). When all patients were pooled together, the odds ratios of PCI were not significant. The propensity score analysis provided a similar conclusion.

Conclusion

PCI did not seem to limit significantly cardiac risk or death after aortic surgery.