bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the 6-minute walk test with established parameters for assessment of cardiopulmonary capacity in adults with complex congenital cardiac disease
Authors: Niedeggen Andreas , Skobel Erik , Haager Philipp , Lepper Wolfgang , Mühler Eberhard , Franke Andreas
Published: July 2005

Background:Objective assessment of the cardiopulmonary capacity in patients with complex congenital cardiac disease often remains difficult in clinical practice. The cardiopulmonary exercise test and determination of the levels of brain natriuretic peptide in the plasma are established tests, but expensive. The 6-minute walk test is also validated, but has not often been used in patients with heart failure due to congenital heart disease, nor compared with other tests. We sought to compare its value with the results of cardiopulmonary exercise testing and measuring the levels of brain natriuretic peptide in the plasma.Methods:We carried out a standardized 6-minute walk test in 31 patients with complex congenital cardiac disease on the same day that they underwent cardiopulmonary exercise testing and determination of levels of brain natriuretic peptide in the plasma. Of the patients, 7 had functionally univentricular hearts, 9 had transposition, 9 had tetralogy of Fallot, 3 had common arterial trunk, and 3 had pulmonary atresia with intact interventricular septum. Uptakes of oxygen at peak exercise, and at the anaerobic threshold, were determined using cardiopulmonary exercise testing, and classified as suggested by Weber. The 6-minute walk test was performed according to a standard protocol.Results:There was a significant correlation between brain natriuretic peptide, oxygen uptakes at peak exercise and 6-minute walk. The correlation between the 6-minute walk test and oxygen uptakes at the anaerobic threshold, however, was not significant.Conclusions:The 6-minute walk test can be performed easily, is inexpensive, widely available, and correlates well with measurements of brain natriuretic peptide and cardiopulmonary exercise testing, even in patients with corrected or palliated congenital cardiac malformations. A cut-off value of 450 metres in the 6-minute walk test allows a semi-quantitative classification in analogy to the classification suggested by Weber for cardiopulmonary exercise testing, and to a level of brain natriuretic peptide in the plasma of less or more than 100 picograms per millilitre.
A very unusual combination of straddling and overriding of the tricuspid valve associated with clefting of the mitral valve
Authors: Eberhardt Liane , Chetaille Philippe , Kreitmann Bernard
Published: July 2005

We describe a patient in whom we found dual orifices in a straddling and overriding tricuspid valve, with two normally sized ventricles and a cleft in the mitral valve. The patient underwent successful surgical repair. We discuss the concept of “double-orifice right atrium”, as well as the need to differentiate the isolated cleft of the morphologically mitral valve from the zone of apposition between the left ventricular components of the bridging leaflets seen in the setting of atrioventricular septal defect with common atrioventricular junction. We emphasise the unusual association of these abnormalities of the right and left atrioventricular valves in patients with separate atrioventricular junctions.
Ottoman financial integration with Europe: foreign loans, the Ottoman Bank and the Ottoman public debt
Authors: ELDEM EDHEM
Published: July 2005

Between 1854 and 1881, the Ottoman Empire went through one of the most critical phases of the history of its relations with European powers. Beginning with the first foreign loan contracted in 1854, this process was initially dominated by a modest level of indebtedness, coupled with sporadic and inconsequential attempts by western powers to impose some control over the viability of the operation. From 1863 on, a second and much more intense phase began, which eventually led to a snowballing effect of accumulated debts. The formal bankruptcy of the Empire in 1875 resulted in the collapse of the entire system in one of the most spectacular financial crashes of the period. It was only six years later, in 1881, that a solution was found in the establishment of the Ottoman Public Debt Administration that would control a large portion of state revenues. The new system restored the financial stability of the Empire, but profoundly modified its rapports de force with Europe by imposing on it a form of foreign control that would have been unthinkable only ten or twenty years earlier. While bringing a much-needed stability to the flailing Ottoman financial situation and thus opening the way to economic development, the new system also radically changed the very nature of the process of integration, by introducing an imperialist dimension that had been lacking in the previous decades.
Role of daily surface forcing in setting the temperature and mixed layer structure of the Southern Ocean
Authors: Kamenkovich Igor V.
Published: July 2005

The role of high‐frequency surface forcing in setting the temperature and mixed layer structure in the Southern Ocean is investigated in an ocean general circulation model. The analysis suggests that daily fluctuations in the momentum flux, and the enhanced vertical mixing they produce, have the biggest effect on the time‐mean temperature and mixed layer structure. In particular, summertime (December–February) surface temperatures are cooler, subsurface temperatures are warmer, and the mixed layer is thicker in the experiment with daily forcing than in the one without. The wintertime mixed layer in the Pacific sector is, however, thinner in the presence of daily forcing owing to the enhanced density contrast between the mixed layer and the ocean below. Daily fluctuations in the surface momentum flux are the leading cause of the high‐frequency temperature variability at the high latitudes of the Southern Ocean, whereas the daily variability in the surface heat flux is more important at the midlatitudes. Since the air and sea‐surface temperatures do not co‐vary on short timescales in this study, daily fluctuations in the air temperature/humidity cause substantial variability in the air‐sea turbulent exchanges of heat. The high‐frequency part of the wave number–frequency spectrum of the daily sea surface temperatures is interpreted using a conceptual model of the response of the Southern Ocean to passing atmospheric storms. For high‐to‐medium frequencies, the preferred wavelengths in the conceptual model are determined by fast atmospheric advection; preferred low frequencies, in contrast, are determined by slow oceanic advection.
Denitrification under glacial and interglacial conditions: A physical approach
Authors: Meissner Katrin J. , Galbraith Eric D. , Völker Christoph
Published: July 2005

Recent analysis of sedimentary δ15N records over the last 200,000 years has shown an expansion of water column denitrification zones during warmer periods and a shrinkage of these oxygen‐poor regions during glacial periods. Two different mechanisms could be responsible for driving the changes in the denitrification records: variations in local productivity leading to a change in remineralization rates and/or changes in the ocean circulation and ocean temperature resulting in variations of the physical supply of dissolved oxygen. Here we focus on the “supply” mechanism by using a fully coupled atmosphere‐ocean‐sea ice‐land surface scheme model (the University of Victoria Earth System Climate Model) to examine oxygen supply under varying physical conditions while maintaining an invariant biological oxygen utilization scheme. We show that circulation changes can be the cause for the observed changes in dissolved oxygen in the glacial ocean. Lower temperatures and enhanced formation of Antarctic Intermediate Water and North Pacific Intermediate Water during glacial periods increase the physical supply of oxygen and therefore decrease water column denitrification. In our Last Glacial Maximum simulations the change in water characteristics in the eastern tropical Pacific is important enough to reduce denitrification by 46% to 65% compared to present‐day conditions, depending on the wind fields used as boundary conditions. The consequences of our findings could be substantial for the near future. With a warming climate, denitrification zones could expand, leading to changes in the biological pump and the flux of N2O into the atmosphere.
Role of algal aggregation in vertical carbon export during SOIREE and in other low biomass environments
Authors: Jackson George A. , Waite Anya M. , Boyd Philip W.
Published: July 2005

Additions of iron to surface regions of the ocean have induced an increase in phytoplankton biomass, but do not necessarily trigger increases in carbon export from surface waters. Using new size‐characterization of settling particles from the Southern Ocean Iron Release Experiment (SOIREE) and an extremely simple, mechanistic aggregation model, we show that removal of phytoplankton from surface waters via sedimentation was controlled by the formation of larger, faster sinking particles via coagulation. We demonstrate that in low biomass regions, where concentrations do not reach the critical concentration needed for massive sedimentation, carbon export is nevertheless still contingent upon the detailed mechanics of particle aggregation. There is therefore a direct dependence of export flux on the extent of aggregation during blooms, verification critical to the success of hydrodynamic models in predicting export.
Nonlinear regression modeling of nutrient loads in streams: A Bayesian approach
Authors: Qian Song S. , Reckhow Kenneth H. , Zhai Jun , McMahon Gerard
Published: July 2005

A Bayesian nonlinear regression modeling method is introduced and compared with the least squares method for modeling nutrient loads in stream networks. The objective of the study is to better model spatial correlation in river basin hydrology and land use for improving the model as a forecasting tool. The Bayesian modeling approach is introduced in three steps, each with a more complicated model and data error structure. The approach is illustrated using a data set from three large river basins in eastern North Carolina. Results indicate that the Bayesian model better accounts for model and data uncertainties than does the conventional least squares approach. Applications of the Bayesian models for ambient water quality standards compliance and TMDL assessment are discussed.
A novel assay method for an amino acid racemase reaction based on circular dichroism
Authors: Noda Masafumi , Matoba Yasuyuki , Kumagai Takanori , Sugiyama Masanori
Published: July 2005

We have established a novel assay method based on circular dichroism that can be used for the kinetic study of the activity of amino acid racemases, such as ALR (alanine racemase). Although an enzyme-coupled assay method has been used to measure racemase activity, the CD method is superior to the enzyme assay because it can accurately determine the immediate changes of an enantiomer on racemization between its L- and D-forms. The enzyme-coupled assay requires D-amino acid oxidase, which is inactivated by an inhibitor of ALR, D-cycloserine. This indicates that the inhibitory kinetic study for ALR with D-cycloserine by the enzyme-coupled assay method is restricted to the analysis of only the reaction resulting in the formation of L-Ala from D-Ala. However, since the CD assay does not require the coupled enzyme, it can be used to comprehensively evaluate the reactions that result in the formation both of D-Ala from L-Ala and of L-Ala from D-Ala at several substrate concentrations. Streptomyces ALR also catalyses the formation of D-Ser from L-Ser and of L-Ser from D-Ser, but the catalytic constants (kcat) are 4- and 10-fold lower than those for the formation of D-Ala from L-Ala and of L-Ala from D-Ala respectively.
Comparative characterization of rat deoxyribonuclease 1 (Dnase1) and murine deoxyribonuclease 1-like 3 (Dnase1l3)
Authors: Napirei Markus , Wulf Swantje , Eulitz Dirk , Mannherz Hans Georg , Kloeckl Thomas
Published: July 2005

Deoxyribonuclease 1 (DNASE1, DNase I) and deoxyribonuclease 1-like 3 (DNASE1L3, DNase γ, DNase Y, LS-DNase) are members of a DNASE1 protein family that is defined by similar biochemical properties such as Ca2+/Mg2+-dependency and an optimal pH of about 7.0 as well as by a high similarity in their nucleic acid and amino acid sequences. In the present study we describe the recombinant expression of rat Dnase1 and murine Dnase1l3 as fusion proteins tagged by their C-terminus to green fluorescent protein in NIH-3T3 fibroblasts and bovine lens epithelial cells. Both enzymes were translocated into the rough endoplasmic reticulum, transported along the entire secretory pathway and finally secreted into the cell culture medium. No nuclear occurrence of the nucleases was detectable. However, deletion of the N-terminal signal peptide of both nucleases resulted in a cytoplasmic and nuclear distribution of both fusion proteins. Dnase1 preferentially hydrolysed ‘naked’ plasmid DNA, whereas Dnase1l3 cleaved nuclear DNA with high activity. Dnase1l3 was able to cleave chromatin in an internucleosomal manner without proteolytic help. By contrast, Dnase1 was only able to achieve this cleavage pattern in the presence of proteases that hydrolysed chromatin-bound proteins. Detailed analysis of murine sera derived from Dnase1 knockout mice revealed that serum contains, besides the major serum nuclease Dnase1, an additional Dnase1l3-like nucleolytic activity, which, in co-operation with Dnase1, might help to suppress anti-DNA autoimmunity by degrading nuclear chromatin released from dying cells.
A short guided tour through functional and structural features of saposin-like proteins
Authors: Bruhn Heike
Published: July 2005

SAPLIPs (saposin-like proteins) are a diverse family of lipid-interacting proteins that have various and only partly understood, but nevertheless essential, cellular functions. Their existence is conserved in phylogenetically most distant organisms, such as primitive protozoa and mammals. Owing to their remarkable sequence variability, a common mechanism for their actions is not known. Some shared principles beyond their diversity have become evident by analysis of known three-dimensional structures. Whereas lipid interaction is the basis for their functions, the special cellular tasks are often defined by interaction partners other than lipids. Based on recent findings, this review summarizes phylogenetic relations, function and structural features of the members of this family.
Probing peroxisomal β-oxidation and the labelling of acetyl-CoA proxies with [1-13C]octanoate and [3-13C]octanoate in the perfused rat liver
Authors: Kasumov Takhar , Adams Jillian E. , Bian Fang , David France , Thomas Katherine R. , Jobbins Kathryn A. , Minkler Paul E. , Hoppel Charles L. , Brunengraber Henri
Published: July 2005

We reported previously that a substantial fraction of the acetyl groups used to synthesize malonyl-CoA in rat heart is derived from peroxisomal β-oxidation of long-chain and very-long-chain fatty acids. This conclusion was based on the interpretation of the 13C-labelling ratio (malonyl-CoA)/(acetyl moiety of citrate) measured in the presence of substrates that label acetyl-CoA in mitochondria only (ratio <1.0) or in both mitochondria and peroxisomes (ratio >1.0). The goals of the present study were to test, in rat livers perfused with [1-13C]octanoate or [3-13C]octanoate, (i) whether peroxisomal β-oxidation contributes acetyl groups for malonyl-CoA synthesis, and (ii) the degree of labelling homogeneity of acetyl-CoA proxies (acetyl moiety of citrate, acetate, β-hydroxybutyrate, malonyl-CoA and acetylcarnitine). Our data show that (i) octanoate undergoes two cycles of peroxisomal β-oxidation in liver, (ii) acetyl groups formed in peroxisomes contribute to malonyl-CoA synthesis, (iii) the labelling of acetyl-CoA proxies is markedly heterogeneous, and (iv) the labelling of C1+2 of β-hydroxybutyrate does not reflect the labelling of acetyl-CoA used in the citric acid cycle.
Cloning of ABCA17, a novel rodent sperm-specific ABC (ATP-binding cassette) transporter that regulates intracellular lipid metabolism
Authors: Ban Nobuhiro , Sasaki Mayumi , Sakai Hiromichi , Ueda Kazumitsu , Inagaki Nobuya
Published: July 2005

The A subclass of the ABC (ATP-binding cassette) transporter superfamily has a structural feature that distinguishes it from other ABC transporters, and is proposed to be involved in the transmembrane transport of endogenous lipids. Here we have cloned mouse and rat full-length cDNAs of ABCA17, a novel ABC transporter belonging to the A subclass. Mouse and rat ABCA17 proteins comprise 1733 and 1773 amino acid residues respectively, having 87.3% amino acid identity; mouse ABCA17 has amino acid identities of 55.3% and 36.7% with mouse ABCA3 and sea urchin ABCA respectively. RNA blot and quantitative real-time PCR analyses showed that ABCA17 mRNA is expressed exclusively in the testis. Examination of testis by in situ hybridization showed that ABCA17 mRNA is expressed in germ cells, mainly spermatocytes, in the seminiferous tubule. Immunoblot analysis using a specific antibody showed that ABCA17 is a protein of 200 kDa, and immunohistochemical analysis demonstrated that the protein is detected in the anterior head of sperm and elongated spermatids. ABCA17 was localized in the endoplasmic reticulum in transiently transfected HEK293 cells. Metabolic labelling analysis showed that intracellular esterified lipids, including cholesteryl esters, fatty acid esters and triacylglycerols, were significantly decreased in HEK293 cells stably expressing ABCA17 compared with untransfected cells. These results suggest that ABCA17 may play a role in regulating lipid composition in sperm.
Electrostatic stabilization in a pre-organized polar active site: the catalytic role of Lys-80 in Candida tenuis xylose reductase (AKR2B5) probed by site-directed mutagenesis and functional complementation studies
Authors: Kratzer Regina , Nidetzky Bernd
Published: July 2005

Lys-80 of Candida tenuis xylose reductase (AKR2B5) is conserved throughout the aldo–keto reductase protein superfamily and may prime the nearby Tyr-51 for general acid catalysis to NAD(P)H-dependent carbonyl group reduction. We have examined the catalytic significance of side-chain substitutions in two AKR2B5 mutants, Lys-80→Ala (K80A) and Asp-46→Asn Lys-80→Ala (D46N K80A), using steady-state kinetic analysis and restoration of activity with external amines. Binding of NAD+ (Kd=24 μM) and NADP+ (Kd=0.03 μM) was 10- and 40-fold tighter in K80A than the wild-type enzyme, whereas binding of NADH (Kd=51 μM) and NADPH (Kd=19 μM) was weakened 2- and 16-fold in this mutant respectively. D46N K80A bound NAD(P)H and NAD(P)+ uniformly approx. 5-fold less tightly than the wild-type enzyme. The second-order rate constant for non-covalent restoration of NADH-dependent reductase activity (kmax/Kamine) by protonated ethylamine was 0.11 M−1·s−1 for K80A, whereas no detectable rescue occurred for D46N K80A. After correction for effects of side-chain hydrophobicity, we obtained a linear free energy relationship of log (kmax/Kamine) and amine group pKa (slope=+0.29; r2=0.93) at pH 7.0. pH profiles of log (kcat/Km) for carbonyl group reduction by wild-type and D46N K80A revealed identical and kinetically unperturbed pKa values of 8.50 (±0.20). Therefore the protonated side chain of Lys-80 is not an essential activator of general acid catalysis by AKR2B5. Stabilized structurally through the salt-link interaction with the negatively charged Asp-46, it is proposed to pull the side chain of Tyr-51 into the catalytic position, leading to a preorganized polar environment of overall neutral charge, in which approximation of uncharged reactive groups is favoured and thus hydride transfer from NAD(P)H is strongly preferred. Lys-80 affects further the directional preference of AKR2B5 for NAD(P)H-dependent reduction by increasing NAD(P)H compared with NAD(P)+-binding selectivity.
Functional and structural characterization of the myoglobin from the polychaete Ophelia bicornis
Authors: Sanna M. Teresa , Manconi Barbara , Castagnola Massimo , Giardina Bruno , Masia Daniela , Messana Irene , Olianas Alessandra , Patamia Maria , Petruzzelli Raffaele , Pellegrini Mariagiuseppina
Published: July 2005

The myoglobin of the polychaete annelid Ophelia bicornis was isolated, purified to homogeneity and characterized. The primary structure, obtained from cDNA and protein sequencing, consists of 139 amino acid residues. The alignment with other globin sequences showed that O. bicornis myoglobin misses the pre-A helix and the first six residues of the A helix. The presence of a PheB10-GlnE7 haem distal residue pair is in agreement with the measured oxygen affinity (P50=0.85 mmHg; 1 mmHg=0.133 kPa) and the only slightly higher autoxidation rate constant (0.28 h−1) with respect to that of the sperm whale myoglobin mutant E7 His→Gln (0.21 h−1) and to elephant myoglobin (0.1 h−1). Oxygen-binding co-operativity was found to be absent under all the examined experimental conditions. The resistance of O. bicornis myoglobin towards autoxidation seems to confirm the important role of part of the A helix in the stability of the globin. The higher pKa of the acid–alkaline ferric transition of O. bicornis with respect to Asian elephant myoglobin, as well as the higher absorbance ratio of its ferric form to the oxy form measured in the Soret region (γmet/γoxy) with respect to that of the African elephant myoglobin, suggested a stronger interaction between the distal glutamine and the water molecule at the sixth co-ordinate position.
Characterization of a novel NADP+-dependent D-arabitol dehydrogenase from the plant pathogen Uromyces fabae
Authors: Link Tobias , Lohaus Gertrud , Heiser Ingrid , Mendgen Kurt , Hahn Matthias , Voegele Ralf T.
Published: July 2005

We have identified and characterized a novel NADP+-dependent D-arabitol dehydrogenase and the corresponding gene from the rust fungus Uromyces fabae, a biotrophic plant pathogen on broad bean (Vicia faba). The new enzyme was termed ARD1p (D-arabitol dehydrogenase 1). It recognizes D-arabitol and mannitol as substrates in the forward reaction, and D-xylulose, D-ribulose and D-fructose as substrates in the reverse reaction. Co-factor specificity was restricted to NADP(H). Kinetic data for the major substrates and co-factors are presented. A detailed analysis of the organization and expression pattern of the ARD1 gene are also given. Immunocytological data indicate a localization of the gene product predominantly in haustoria, the feeding structures of these fungi. Analyses of metabolite levels during pathogenesis indicate that the D-arabitol concentration rises dramatically as infection progresses, and D-arabitol was shown in an in vitro system to be capable of quenching reactive oxygen species involved in host plant defence reactions. ARD1p may therefore play an important role in carbohydrate metabolism and in establishing and/or maintaining the biotrophic interaction in U. fabae.
Numerical simulations of a thermocline in a pressure-driven flow between two infinite horizontal plates
Authors: Moestam Robert , Davidson Lars
Published: July 2005

Direct numerical simulations of pressure-driven flow between two infinite horizontal plates with a stabilizing temperature difference imposed on the plates are presented, for different Grashof numbers. A thermocline-like solution is obtained. The thermocline decorrelates velocity fluctuations which results in a high mean flow velocity. Temperature fluctuations decorrelate from the vertical velocity fluctuations and it is found that although ⟨T′2⟩ and ⟨υ′2⟩ increase with Grashof number, ⟨υ′T′⟩ decreases. It is argued from the simulations that this behavior is due to internal gravity waves. It is also found that the demands on the size of the computational box increase with Grashof number.
Reliable treatment of electrostatics in combined QM/MM simulation of macromolecules
Authors: Schaefer Patricia , Riccardi Demian , Cui Qiang
Published: July 2005

A robust approach for dealing with electrostatic interactions for spherical boundary conditions has been implemented in the QM/MM framework. The development was based on the generalized solvent boundary potential (GSBP) method proposed by Im et al. [J. Chem. Phys. 114, 2924 (2001)], and the specific implementation was applied to the self-consistent-charge density-functional tight-binding approach as the quantum mechanics (QM) level, although extension to other QM methods is straightforward. Compared to the popular stochastic boundary-condition scheme, the new protocol offers a balanced treatment between quantum mechanics/molecular mechanics (QM/MM) and MM/MM interactions; it also includes the effect of the bulk solvent and macromolecule atoms outside of the microscopic region at the Poisson–Boltzmann level. The new method was illustrated with application to the enzyme human carbonic anhydrase II and compared to stochastic boundary-condition simulations using different electrostatic treatments. The GSBP-based QM/MM simulations were most consistent with available experimental data, while conventional stochastic boundary simulations yielded various artifacts depending on different electrostatic models. The results highlight the importance of carefully treating electrostatics in QM/MM simulations of biomolecules and suggest that the commonly used truncation schemes should be avoided in QM/MM simulations, especially in simulations that involve extensive conformational samplings. The development of the GSBP-based QM/MM protocol has opened up the exciting possibility of studying chemical events in very complex biomolecular systems in a multiscale framework.
Generation-recombination effects on dark currents in CdTe-passivated midwave infrared HgCdTe photodiodes
Authors: Jozwikowska A. , Jozwikowski K. , Antoszewski J. , Musca C. A. , Nguyen T. , Sewell R. H. , Dell J. M. , Faraone L. , Orman Z.
Published: July 2005

The effect of an abrupt CdTe∕HgCdTe passivation heterointerface on generation recombination and dark currents in n-on-p midwave infrared photodiodes with 5.2-μm cut-off wavelength has been investigated. Experimentally, it was observed that the zero-bias-dynamic resistance, R0, at low temperatures scales with the perimeter of the n-on-p junction, rather than with the junction area, suggesting that surface effects are dominant. The diode current–voltage characteristics at low temperatures indicate significant contributions from tunneling effects, which is the dominant leakage current mechanism for reverse bias greater than approximately 30mV. These two observations suggest that the region where the junction terminates at the CdTe∕HgCdTe abrupt interface is responsible for the above effects. A two-dimensional model has been developed to investigate the dark current mechanisms in the vicinity of the junction termination at CdTe∕HgCdTe interface, which also takes into account the effect of dislocations on generation-recombination processes. Calculated profiles of the energy bands and electric field along different cross sections of the photodiode indicate that the electric field achieves a maximum value of the order of mid −105V∕cm in the region where the junction terminates at the CdTe∕HgCdTe interface. The presence of such a high localized electric field in this area decreases the ionization energy of trap levels in the band gap and, hence, increases efficiency of the Shockley–Read–Hall generation-recombination processes. In addition to diffusion, generation recombination, and trap-assisted tunneling mechanisms, the calculations of dynamic resistance include Poole–Frenkel and phonon-trap-assisted tunneling effects. The best fit to the zero bias dynamic resistance versus temperature results has been obtained using an aerial dislocation density in the bulk of the HgCdTe layer equal to 106cm−2. Although the direct band-to-band tunneling and impact ionization processes were also considered, their contributions are shown to be insignificant.
Dielectric properties and microstructure of nano-MgO dispersed Ba0.3Sr0.7TiO3 thin films prepared by sputter deposition
Authors: Wang Sea-Fue , Chu Jinn P. , Lin Chen Chun , Mahalingam T.
Published: July 2005

In this study, thin films prepared from the targets of Ba0.3Sr0.7TiO3 (BST), BST∕5mol%MgO,BST∕10mol%MgO, and BST∕20mol%MgO composites, using radio frequency magnetron sputtering, have been reported. As-deposited films were found to be amorphous and began to crystallize after annealing at temperatures of 650 °C and above. The addition of MgO in the BST films resulted in the hindrance of crystallization and inhibition of grain growth. MgO was substituted into the BST lattices to a certain degree. High-resolution transmission electron microscopy results revealed some MgO dispersed in the BST matrix. The MgO dispersed in the dense BST matrix was found to be around 25 nm in size. The dielectric constant was estimated to be 90 for the pure BST film annealed at 700 °C, and observed to be slightly reduced with the MgO addition. The dielectric losses of the Ba0.3Sr0.7TiO3 (0.006) and BST∕MgO films (0.002–0.004) were much less than those of the Ba0.6Sr0.4TiO3(0.013) and Ba0.7Sr0.3TiO3 films (0.11–0.13). The leakage current was smaller for the BST∕10mol%MgO film compared to the pure BST film and this low leakage current may be attributed to the substitution of Mg in the B sites of BST lattices which might have behaved as an electron acceptors.
Characterization of buried photonic crystal waveguides and microcavities fabricated by deep ultraviolet lithography
Authors: Märki Iwan , Salt Martin , Herzig Hans Peter , Stanley Ross , El Melhaoui L. , Lyan P. , Fedeli J. M.
Published: July 2005

We present results of the optical characterization of silicon photonic crystal waveguides and microcavities that are completely buried in a silicon dioxide cladding and are fabricated by deep ultraviolet (UV) lithography. The advantages of buried waveguides and deep UV lithography are discussed. Transmission spectra and loss factors for photonic crystal waveguides, as well as quality factors for resonant microcavities, are obtained. The observed characteristics are in good agreement with three-dimensional simulations.
Strain fields in InAs∕GaAs quantum wire structures: Inclusion versus inhomogeneity
Authors: Pan E. , Han F. , Albrecht J. D.
Published: July 2005

This paper studies the elastic fields in InAs∕GaAs quantum wire (QWR) structures arising from the lattice mismatch between InAs and GaAs. The present treatment is different from recent analyses based on the Eshelby inclusion approach where the QWR material, for simplicity, is assumed to be the same as the matrix/substrate. Here, a more complete treatment is developed taking into account the structural inhomogeneity using the boundary integral equation method. We implement our model using discrete boundary elements at the interface between the QWR and its surrounding matrix. The coefficients of the algebraic equations are derived exactly for constant elements using our recent Green’s-function solutions in the Stroh formalism. For both (001) and (111) growth directions, our results show that while the elastic fields far from the QWR are approximated well by the homogeneous inclusion approach, for points within or close to the QWR, the differences between the fields computed with the simplified inclusion and complete inhomogeneity models can be as large as 10% for the test system. These differences in the strain fields will have strong implications for the modeling of the quantized energy states of the quantum wire nanostructures. Since the strain fields inside and close to the wire are more important than the exterior strain fields from the standpoint of the confined electronic states, we suggest that in the vicinity of the QWR, the inhomogeneity model be used with proper elastic constants, while the simple exact inclusion model be used in the bulk of surrounding medium.
Depolarized light scattering from liquid crystals as a factor for black level light leakage in liquid-crystal displays
Authors: Yoneya Makoto , Utsumi Yuka , Umeda Yoshiyuki
Published: July 2005

Depolarized light scattering due to thermally excited orientational fluctuations of liquid-crystal directors was investigated in the context of the black level light leakage in liquid-crystal displays. Particular attention was given on the comparison between homogeneous and homeotropic liquid-crystal alignments which are both used as black states of liquid-crystal displays. The homeotropic alignment was found to have lower light-scattering intensity and less light leakage than the homogeneous alignment in the small scattering angle regions. The dependency of the scattering intensity on the cell gap and the extrapolation length was also evaluated. The cell gap and the extrapolation length were found to have a large influence.
Friction force microscopy as an alternative method to probe molecular interactions
Authors: Lekka Małgorzata , Kulik Andrzej J. , Jeney Sylvia , Raczkowska Joanna , Lekki Janusz , Budkowski Andrzej , Forró László
Published: July 2005

Friction force microscopy was applied to study protein–carbohydrate interactions that are important in many cellular recognition processes. The expression and structure of carbohydrates can be investigated using lectins as molecular probes since they recognize different types of sugar molecules. Lectins (concanavalin A and lentil lectin, recognizing mannose-type carbohydrates) were attached to the probing tip and carboxypeptidase Y (possessing complementary carbohydrates) was immobilized on a modified glass surface using microcontact printing. The results obtained from friction force maps and dependencies on the loading rate (measured in a physiological buffer) were divided in two distinct groups. The first group of results obtained for lectin–protein complexes was assigned to molecular recognition events, whereas the other including all control measurements was attributed to nonspecific interaction. All results presented here indicate that friction force microscopy can be successfully employed to study recognition processes.
Swift heavy-ion-induced epitaxial crystallization of buried Si3N4 layer
Authors: Som T. , Satpati B. , Sinha O. P. , Kanjilal D.
Published: July 2005

We report on swift heavy-ion-beam-induced epitaxial crystallization of a buried Si3N4 layer. We observe good epitaxial crystallization at 200 °C, which is a much lower temperature than that required for the conventional solid phase epitaxial growth. High-resolution transmission electron microscopy and selected area diffraction patterns have been used to study the 100-MeV Ag8+-ion-beam-induced epitaxial growth of the Si3N4 layer. A possible mechanism of recrystallization is discussed on the basis of synergetic effects of electronic and nuclear energy-loss processes along the trajectory of the swift heavy ions at elevated temperatures.
Effects of double substitution on the magnetic properties of Nd2Fe17−x−yTixAly: A combined investigation of x-ray diffraction, neutron diffraction, and magnetic measurement
Authors: Liu X. F. , Lv J. Y. , Han S. B. , Peng J. , Wang H. , Hu Z. B. , Chen D. F. , Xue Y. J. , Li J. H.
Published: July 2005

The effects of double substitution of Ti and Al for Fe on the structural and magnetic properties of Nd2Fe17−x−yTixAly compounds were investigated. A series of Nd2Fe17−x−yTixAly compounds (0⩽x⩽1.0;0⩽y⩽3) were prepared by arc melting techniques in high pure Ar atmosphere. Rietveld analyses of x-ray and neutron diffractions indicate that all the samples crystallize in the rhombohedral Th2Zn17-type structure. The lattice parameters a, c and the unit-cell volumes of Nd2Fe17−x−yTixAly increase linearly with increasing aluminum content for a given Ti content and increase with the increase of Ti content for a given Al content. The addition of Ti atoms has a positive effect on the increasing rates of the a axis and the unit-cell volume on the Al content, but has a negative effect on the increasing rate of the c axis. Neutron-diffraction analyses indicate that Ti atoms and Al atoms prefer to take 6c sites and 18h sites, respectively, in doubly substituted Nd2Fe17−x−yTixAly but the site occupancies change slightly compared to that in the corresponding singly substituted compounds. The effects of Ti and Al substitutions on the bond lengths in the doubly substituted compounds are quite different from that in the singly substituted compounds. The Curie temperature measurements show that a higher Ti content results in a slower increase of TC on the Al content in Nd2Fe17−x−yTixAly (y⩽3). The TC of doubly substituted Nd2Fe16.5−yTi0.5Aly are higher than that of singly substituted Nd2Fe17−yAly when Al content is low (y⩽0.8) but reversely for y>0.8. For a given Ti content, the Ms of Nd2Fe17−x−yTixAly with x=0,0.5 first both increase a little and then decrease with the increase of Al content. The Ms of Nd2Fe17−x−yTixAly decreases with the increase of Ti content for a given Al content.
Comment on “Multireference configuration-interaction calculations for positronium halides” [J. Chem. Phys. 122, 054302 (2005)]
Authors: Mitroy J. , Bromley M. W. J.
Published: July 2005

Large-scale configuration–interaction calculations of the binding energies and annihilation rates of the positronium halides, PsF, PsCl, PsBr, and PsI [S. L. Saito, J. Chem. Phys. 122 054302 (2005)], have made erroneous predictions about the structures of these atoms. The predictions were based on small annihilation rates, which result from using a small basis and additionally invalid estimates of the contributions from single-particle orbitals with ℓ>8.
Lattice defects and magnetic ordering in plutonium oxides: A hybrid density-functional-theory study of strongly correlated materials
Authors: Prodan Ionut D. , Scuseria Gustavo E. , Sordo José A. , Kudin Konstantin N. , Martin Richard L.
Published: July 2005

Experimental studies of actinide oxides are challenging, and conventional electronic structure calculations fail to qualitatively reproduce the scarce data. We employ a new generation of hybrid density functionals to model a defective plutonium dioxide lattice. The procedure is first tested against stoichiometric bulk PuO2 and Pu2O3, for which predictions agree well with experiment where known. The interstitial oxygen in PuO2.25 is found to be singly charged, consistent with experimental observations and contrary to the O2− previously proposed theoretically.
Low resistance WSix-based ohmic contacts on n-type GaN
Authors: Pan Chang-Chi , Chen Ming-Shung , Lee Chia-Ming , Chyi Jen-Inn
Published: July 2005

Low contact resistance, high reflectivity, and high thermal stability Ti∕WSix∕Ti∕Au multilayer ohmic contact to n-type GaN has been demonstrated. Specific contact resistivity as low as 1×10−6Ωcm2 is obtained in a metallization scheme of Ti∕WSi0.05∕Ti∕Au (20∕40∕20∕200nm) after thermal annealing at 800°C for 3min in N2 ambient. Its specific contact resistivity maintains at the same level after heat treatment at 300°C for 96h. In addition, the optical reflectivity in the wavelength range of 350–450nm is about twofold higher than that of the conventional Ti∕Al∕Ti∕Au (30∕100∕40∕120nm) contact. The former also exhibits much smoother surface and better edge acuity, which is essential for devices sensitive to critical dimension control.
Improvement of field emission from printed carbon nanotubes by a critical bias field
Authors: Lee H. J. , Moon S. I. , Kim J. K. , Lee Y. D. , Nahm S. , Yoo J. E. , Han J. H. , Lee Y. H. , Hwang S. W. , Ju B. K.
Published: July 2005

By applying a critical bias field instead of conventional surface treatments, the electron emission properties of screen-printed nanotubes were investigated through scanning electron microscopy and emission current-voltage characteristics. After the surface treatment, at the bias field of 2.5V∕μm, the electron emission current density with good uniform emission sites reached the value of 2.13mA∕cm2, which was 400 times higher than that of the untreated sample, and the turn-on voltage decreased markedly from 700to460V. In addition, the enhancement of the alignment of carbon nanotubes to the vertical direction was observed, resulting in an increase in the field-enhancement factor.
Selective etching of epitaxial MnAs films on GaAs(001): Influence of structure and strain
Authors: Mohanty J. , Takagaki Y. , Hesjedal T. , Däweritz L. , Ploog K. H.
Published: July 2005

Strain in epitaxial MnAs thin films on GaAs(001) substrates plays an important role in the coupled magnetostructural phase transition. As a result of strain, the phase transition from the ferromagnetic α phase to the paramagnetic β phase proceeds over a wide temperature range and the coexisting phases form a periodic stripe array. Employing suitable wet chemical etchants, the two MnAs phases can be etched selectively. Perpendicular to the α-β-stripe structure, the built-up strain relaxes in the course of the etching process by the formation of cracks. The combination of both strain relaxation mechanisms allows for the defined patterning of two-dimensional arrays of nanomagnets. Through micromagnetic investigations, it is possible to identify the location of α- and β-MnAs which helps to clarify two major aspects of the etching process. First, it is possible to determine the etch rates of α- and β-MnAs and follow the complex interplay of strain and phase composition during the etching process. Second, as strain reflects itself in a shifted phase-transition temperature, temperature-dependent micromagnetic studies allow to determine the strain environment of the cracks.
Real-time nonlinear feedback control of pattern formation in (bio)chemical reaction-diffusion processes: A model study
Authors: Brandt-Pollmann U. , Lebiedz D. , Diehl M. , Sager S. , Schlöder J.
Published: July 2005

Theoretical and experimental studies related to manipulation of pattern formation in self-organizing reaction-diffusion processes by appropriate control stimuli become increasingly important both in chemical engineering and cellular biochemistry. In a model study, we demonstrate here exemplarily the application of an efficient nonlinear model predictive control (NMPC) algorithm to real-time optimal feedback control of pattern formation in a bacterial chemotaxis system modeled by nonlinear partial differential equations. The corresponding drift-diffusion model type is representative for many (bio)chemical systems involving nonlinear reaction dynamics and nonlinear diffusion. We show how the computed optimal feedback control strategy exploits the system inherent physical property of wave propagation to achieve desired control aims. We discuss various applications of our approach to optimal control of spatiotemporal dynamics.
Characterization of electron emission from relaxed InAs quantum dots capped with InGaAs
Authors: Chen J. F. , Hsiao R. S. , Wang C. K. , Wang J. S. , Chi J. Y.
Published: July 2005

The effect of strain relaxation in a relaxed InAs quantum dot (QD) capped with InGaAs is investigated by admittance and deep-level transient spectroscopy (DLTS). Strain relaxation markedly increases the emission time in the QD region and extends carrier depletion to the bottom GaAs layer. The experimental data show the presence of relaxation traps in the QD region and the neighboring bottom GaAs layer. The electron emission from the QD region is governed by a trap located at 0.17–0.21 eV below the QD ground state. The electron-escape process is identified as thermal activation at high temperatures and direct tunneling at low temperatures from the trap. In the bottom GaAs layer near the QD, DLTS reveals a relaxation trap at 0.37–0.41 eV relative to the GaAs conduction band. The energy difference between these two traps is comparable to the QD ground-state energy relative to the GaAs conduction-band edge, suggesting that the two traps may be the same trap which is pinned to the GaAs conduction band. The considerable difference between their properties may result from different atoms surrounding the trap.
Enhanced piezoelectric properties of barium titanate single crystals with different engineered-domain sizes
Authors: Wada Satoshi , Yako Koichi , Kakemoto Hirofumi , Tsurumi Takaaki , Kiguchi Takanori
Published: July 2005

For tetragonal barium titanate (BaTiO3) single crystals, an electric field (E-field) applied along the [111]c direction can induce an engineered-domain configuration in these crystals. In this study, such engineered-domain configurations of different domain sizes were induced in BaTiO3 single crystals, and their piezoelectric properties were investigated as a function of domain size. Prior to this study, the dependences of the domain configuration on the temperature and E-field were investigated using a polarizing microscope in order to understand the optimum poling condition for fine- and coarse-domain configurations. We found that above the Curie temperature (TC) of 132.2 °C, when an E-field above 6.0kV∕cm was applied along the [111]c direction, an engineered domain with a fine-domain configuration appeared. Moreover, it was also found that this fine-domain configuration remained stable at room temperature without the E-field. On the other hand, the coarse-domain configuration was obtained upon poling at just below TC. Finally, the piezoelectric properties of 31 resonators with different domain sizes of 40–5.5μm were measured. As a result, it was found that the piezoelectric properties, such as d31 and k31, increased significantly with decreasing domain size.
On the coalescence speed of bubbles
Authors: Thoroddsen S. T. , Etoh T. G. , Takehara K. , Ootsuka N.
Published: July 2005

Two bubbles brought into contact will coalesce rapidly. We study experimentally the initial coalescence motions in the neck region connecting the two bubbles, using an ultrahigh-speed video camera. The air bubbles are grown in ethyl alcohol, at the ends of two opposing vertical needles, until they come into contact. The growth rate of the neck is measured and modeled with a capillary/inertial balance. The instantaneous profile in the neck forms a circular arc, with the ratio of the two principal radii of curvatures increasing linearly in time.
Electro-optical and dielectric relaxation studies of an antiferroelectric liquid-crystal mixture (W-132A)
Authors: Srivastava A. K. , Agrawal V. K. , Dabrowski R. , Otón J. M. , Dhar R.
Published: July 2005

Electro-optical properties and dielectric relaxation phenomenon have been investigated for antiferroelectric liquid-crystal mixture W-132A exhibiting SmA*, SmC*, and wide temperature range (∼0–48°C) induced SmCA* phases. Spontaneous polarization, tilt angle, response time, viscosity, relaxation frequency, dielectric strength, and distribution parameter have been determined as a function of temperature. Switching process has been studied in the antiferroelectric SmCA* phase with the help of transmission intensity-voltage characteristics. Impedance spectroscopy of the material under the planar anchoring conditioning of the sample has been carried out in the frequency range of 1Hz–10MHz. Usual soft-mode dielectric relaxation in the SmA* phase and Goldstone mode in the SmC* phase have been observed. A tendency of the soft mode to penetrate into the SmC* phase and that of the Goldstone mode into the SmCA* phase have been observed. The dielectric spectrum of the SmCA* phase exhibits two absorption peaks, namely, PL and PH modes which are separated by about two decades of frequency. PL is related to in-phase azimuthal angle fluctuation of the molecules in antitilt pairs, whereas PH is due to the antiphase fluctuation of the molecules in antitilt pairs.