bluuebunny/crossref_metadata_2025 huggingface dataset:
Enzymatic Esterification of Fatty Acid Mixtures from Milk Fat and Anhydrous Milk Fat with Canola Oil in Supercritical Carbon Dioxide
Authors: Yu Zer‐Ran , Rizvi Syed S. H. , Zollweg John A.
Published: March 2005

The ester ethyl oleate was synthesized from oleic acid and ethanol by using the lipase, Candida cylindracea, immobilized on Celite 545 and in supercritical carbon dioxide (SC‐CO2) as the solvent. The enzymatic esterification reaction is much faster in SC‐CO2 than in organic solvents. This technique was then applied to the hydrolysis products of milk fat to determine the feasibility of using it as a process to enhance flavor. Gas chromatographic (GC) analysis of the ethyl esters showed that short‐chain fatty acids (C4‐C8) esterify more completely than long‐chain fatty acids (C16‐C18). The technique was then applied to interesterify a mixture of triglycerides from canola oil (CNO) and anhydrous milk fat (AMF). The starting mixture contained predominantly C52‐C56 triglycerides from the CNO and C32‐C38 triglycerides from the AMF. The product exhibited predominantly the C42‐C50 and C54 triglycerides.
Applications of Ultrafast HPLC to Process Development of Recombinant DNA‐Derived Proteins
Authors: Olson Kenneth C. , Gehant Richard L.
Published: March 2005

The application of ultrafast HPLC to the development of recovery processes for proteins produced by recombinant DNA technology has been explored using wide‐pore HPLC resins and instrumentation designed for rapid analysis. High‐resolution analysis of complex samples was achieved with a total analysis time of less than 5 min from injection to injection. Fractions collected during preparative chromatography were analyzed by SDS gel electrophoresis and fast HPLC. Specific proteins in the fractions were detected and quantitated by fast HPLC providing real‐time analysis for pooling. The technique was also applied to the formidable task of detecting and quantitating protein variants during the development of recovery processes. Several examples of post‐translational variant detection are shown. Ultrafast HPLC is a new analytical tool that can be applied to the development of robust manufacturing processes producing therapeutic proteins essentially free of known impurities and variants.
Mathematical Modeling of the Production of Cyclosporin A by Tolypocladium inflation: Effect of L‐Valine
Authors: Agathos Spiros N. , Lee Jaegwan
Published: March 2005

A mathematical model was developed to describe the kinetics of submerged fungal growth, consumption of nutrients, and production of the immunosuppressant drug, cyclosporin A (CyA). Special emphasis was placed on the experimentally observed stimulatory effect of L‐valine on CyA production. The proposed model was based on kinetic information and emerging mechanistic data on CyA biosynthesis. It was assumed that L‐valine acts as both precursor and inducer of the CyA‐synthesizing multienzyme (CyA synthetase), and an unmethylated intermediate of CyA was postulated in the biosynthetic process. The model consisted of two parts: one describing cell growth and substrate consumption and the other addressing the kinetics of internal properties such as endogenous valine, biosynthetic enzyme, CyA intermediate, and CyA. The success of this extensive model was confirmed by its ability to simulate adequately the kinetic profiles of both external and internal variables. For instance, the model correctly predicted the time course of intracellular L‐valine accumulation. In addition, both the optimal level and timing of exogenous L‐valine addition could be predicted for maximum drug production. This study suggests rational new ways of improving the fungal production process of this important immunosuppressant.
Optimal Design of an Enzymatic Reactor for Flow Injection Analysis
Authors: Poch M. , Montesinos J. L. , Valle M. Del , Alonso J. , Araujo A. , Lima J. L. F. C.
Published: March 2005

A simulation procedure for the optimization of enzymatic reactors used in sandwich flow injection systems is evaluated. The system is modeled as a plug‐flow reactor with axial dispersion. To calibrate it, dispersion coefficients can be evaluated using residence time distribution techniques; meanwhile, enzymatic kinetics must be determined for the system considered, according to the values of the substrate conversion attained. The model has been linked to an optimization routine based on the Powell algorithm. The proposed approach has been evaluated in a system performing simultaneous determinations of glucose and glycerol, considered the common carbon sources in a fermentation process.
Dehalogenation by Cytochrome P‐450cam: Effect of Oxygen Level on the Decomposition of l,2‐Dibromo‐3‐chloropropane
Authors: Koe Gary S. , Vilker Vincent L.
Published: March 2005

A P‐450cam monooxygenase enzyme system, obtained through separate purification of the three protein subunits, was used as a biocatalyst in the dehalogenation of 1,2‐dibromo‐3‐chloropropane (DBCP). Incubations in a solution containing the reconstituted enzyme system were performed in two oxygen environments, oxygen‐rich (oxygen‐saturated solution) and oxygen‐lean (oxygen concentration reduced to 1% of saturation), and analyzed for hydrocarbon and bromide ion (Br‐) product formation and the kinetics of DBCP decomposition. l‐Bromo‐3‐chloroacetone (BCA) was identified by gas chromatography‐mass spectrometry as a major product of oxygen‐rich incubations, while 3‐chloro‐l‐propene (allyl chloride) was verified as an oxygen‐lean product. The identification of these two products suggests that P‐450cam activity is occurring in two separate mechanisms, oxidative and reductive, which is governed by the availability of oxygen. This suggestion is further supported by differences that were observed in the DBCP decomposition rate, which is an order of magnitude slower under oxygen‐lean conditions, and differences in bromide ion formation, where approximately one Br‐stoichiometric equivalent is released per mole of DBCP lost under oxygen‐rich conditions versus approximately two Br‐ stoichiometric equivalents for oxygen‐lean conditions.
Concentrating Cellulases Using a Temperature‐Sensitive Hydrogel: Effect of Gel Particle Size and Geometry
Authors: Park Chang‐Ho , Orozco‐Avila Ignacio
Published: March 2005

A temperature‐sensitive poly (N‐isopropylacrylamide) hydrogel was used to concentrate cellulases from Trichoderma reesei. The effect of gel size and geometry on separation efficiency and weight change rate was studied. Gel weight change was reproducible over six cycles of short swelling and collapsing (2 h each) experiments, but the gel weight change capacity of small and large cubes was 90% and 62% of small extruded gel, respectively. The gel weight change capacity of large extruded gel and chopped gel was comparable to that of small extruded gel. Cellulase separation efficiency increased up to 64% for large cubes, but it was lower than 80–97% for comparably sized solutes reported in the literature. Small extruded gel reached its equilibrium weight in 2–3 h, but it took more than 200 times longer for gel disks to reach equilibrium weights. Initial solution flux (surface‐specific water release/sorption rate) during swelling and collapsing was 1065–2450 g/m2·h, but flux decreased rapidly with time. Skin formation was partially responsible for the slower weight change rate of larger gels, but chopped gel also formed skin at collapse temperatures higher than 37 °C. Skin formation was not observed for small extruded gel up to 50 °C. During gel disk collapsing experiments, transparent bubbles trapping pressurized water initially were observed all over the gel surface, and some of the bubbles on the disk edge did not collapse until the gel approached an equilibrium weight.
Thermal Time Distributions in Tubular Heat Exchangers during Aseptic Processing of Fluid Foods
Authors: Bhamidipati S. , Singh R. K.
Published: March 2005

The objectives of this study were to develop a mathematical model for thermal time distributions (TTD) in tubular heat exchangers and to perform a computer simulation to study the role of TTD in food process design. A computer simulation of heat transfer to a pseudoplastic fluid with variable thermophysical properties heated in a tubular heat exchanger was carried out. A power law model, with the flow behavior consistency indices modeled as temperature‐dependent properties, is used to described the flow behavior of the fluid. The coupled continuity, momentum, and energy equations with corresponding boundary conditions for constant wall temperature and heat flux are solved numerically by a Dufort‐Frankel finite difference technique. Thermal processing models are then applied to obtain TTD by tracking fluid elements along the flow path in a heating section. TTD and F curves are used to evaluate process effectiveness. Two tube radii (0.0254 and 0.0382 m) and two wall temperatures (125 and 130 °C) were studied. Increasing the wall temperature from 125 to 130 °C reduced the length of the heat exchanger by 11.3%. Increasing the tube radius by 150% caused an 84.2 % increase in the length of the heating section.
A Kinetic Model for Substrate and Energy Consumption of Microbial Growth under Substrate‐Sufficient Conditions
Authors: Zeng A.‐P. , Deckwer W.‐D.
Published: March 2005

The growth of heterotrophic microorganisms can be classified into substrate‐limited and substrate‐sufficient growth according to the relative availability of the substrate (carbon and energy source) and other nutrients. It is generally observed that the consumption rates of substrate and energy (ATP) are higher under substrate‐sufficient conditions than under conditions of substrate limitation. The excess substrate and ATP consumption is often influenced by the residual concentration of substrate in a. relatively wide range. To account for these effects, a kinetic model is proposed to describe substrate and ATP consumption rates of microbial growth under substrate‐sufficient conditions. According to the model, the specific substrate consumption rate of a substrate‐sufficient culture can be expressed as the sum of the substrate consumption rate under substrate‐limited conditions at the corresponding specific growth rate and an additional consumption rate due to excess substrate. The same kinetic form also applies to the specific ATP consumption rate and to the specific oxygen consumption rate of an aerobic culture, respectively. The linear equations for substrate and ATP consumption rates of Pirt and of Stouthamer and Bettenhausen can be used for substrate‐limited growth. The excess of substrate and ATP consumption rates at carbon surplus can be described in a form similar to that of Michaelis&β;Menten kinetics. The proposed kinetic model has been verified with experimental data from three continuous cultures representing both anaerobic and aerobic microbial growth on substrates with low and high degrees of reductance. Using this model, the parameters maximum growth yield and maintenance requirement (both in terms of substrate and ATP) of a culture under different growth limitations can be better defined and quantified. The range of residual substrate concentrations in which the specific rates of substrate and ATP consumption are affected can also be assessed. This information should be helpful in designing medium and reactor operating conditions and in interpreting experimental results obtained under different limiting conditions.
Fractionation of Citrus Oils Using a Membrane‐Based Extraction Process
Authors: Brose Daniel J. , Chidlaw Mark B. , Friesen Dwayne T. , Lachapelle Ed D. , Van Eikeren Paul
Published: March 2005

A membrane‐based extraction process is described for the fractionation of citrus oils to produce an oil stream enriched in oxygenated components. The process relies on the high selectivity of cyclodextrins (CDs) to preferentially bind the desirable oxygenates. In the process, low‐temperature citrus oil flows on one side of a nonporous membrane, and an aqueous CD solution flows on the other side of the membrane. Oxygenates diffuse through the water‐swollen hydrophilic membrane and preferentially partition into the aqueous CD solution. The aqueous CD solution is then heated and circulated past a second membrane, where the CD/oxygenate complex dissociates and the liberated oxygenates diffuse into a citrus oil solution. Disassociated CD is recycled to the first membrane. Data are presented on the effect of temperature and CD type on the partitioning of oxygenates from orange oil into aqueous CD solutions. Operation of a pilot‐scale test loop that capitalizes on the high selectivity of CDs and the temperature dependence of the CD binding is described for the production of oxygenate‐enriched orange oil.
Biosorption of Heavy Metals
Authors: Volesky B. , Holan Z. R.
Published: March 2005

Only within the past decade has the potential of metal biosorption by biomass materials been well established. For economic reasons, of particular interest are abundant biomass types generated as a waste byproduct of large‐scale industrial fermentations or certain metal‐binding algae found in large quantities in the sea. These biomass types serve as a basis for newly developed metal biosorption processes foreseen particularly as a very competitive means for the detoxification of metal‐bearing industrial effluents. The assessment of the metal‐binding capacity of some new biosorbents is discussed. Lead and cadmium, for instance, have been effectively removed from very dilute solutions by the dried biomass of some ubiquitous species of brown marine algae such as Ascophyllum and Sargassum, which accumulate more than 30% of biomass dry weight in the metal. Mycelia of the industrial steroid‐transforming fungi Rhizopus and Absidia are excellent biosorbents for lead, cadmium, copper, zinc, and uranium and also bind other heavy metals up to 25% of the biomass dry weight. Biosorption isotherm curves, derived from equilibrium batch sorption experiments, are used in the evaluation of metal uptake by different biosorbents. Further studies are focusing on the assessment of biosorbent performance in dynamic continuous‐flow sorption systems. In the course of this work, new methodologies are being developed that are aimed at mathematical modeling of biosorption systems and their effective optimization. Elucidation of mechanisms active in metal biosorption is essential for successful exploitation of the phenomenon and for regeneration of biosorbent materials in multiple reuse cycles. The complex nature of biosorbent materials makes this task particularly challenging. Discussion focuses on the composition of marine algae polysaccharide structures, which seem instrumental in metal uptake and binding. The state of the art in the field of biosorption is reviewed in this article, with many references to recent reviews and key individual contributions.
Fnr, a Global Transcriptional Regulator of Escherichia coli, Activates the Vitreoscilla Hemoglobin (VHb) Promoter and Intracellular VHb Expression Increases Cytochrome d Promoter Activity
Authors: Tsai Philip S. , Kallio Pauli T. , Bailey James E.
Published: March 2005

The oxygen‐regulated promoter (Pvhb) of the Vitreoscilla hemoglobin gene has been applied to direct high‐level expression of several cloned proteins, including Vitreoscilla hemoglobin (VHb), which improves productivity of many aerobic processes. In an effort to gain a better understanding of the regulation of Pvhb, and to guide further optimization of this technology, we investigated whether the Escherichia coli global regulatory molecules Fnr and the Arc system (ArcA and ArcB), which control the expression of various genes under either aerobic or anaerobic conditions, also regulate Pvhb activity in E. coli. The activity of Pvhb and the expression of VHb in E. coli were activated by Fnr, but were relatively unaffected by the Arc system under microaerobic conditions (DO less than 2% air saturation). We also examined the possibility of VHb affecting cytochrome d promoter activity during microaerobiosis. The presence of VHb increased the activity of β‐galactosidase from a cytochrome d promoter‐lacZ fusion by 1.5‐fold. This indicates that VHb affects oxygen‐regulated transcription of E. coli genes and may contribute to the modified physiology observed in VHb‐expressing E. coli.
Noncompetitive Immunoassays Using Bifunmctional Unilamellar Vesicles or Liposomes
Authors: Singh Anup K. , Kilpatrick Peter K. , Carbonell Ruben G.
Published: March 2005

Small unilamellar vesicles (SUVs) functionalized with an enzyme label and with specific ligands for biological molecules are useful as signal enhancement vehicles in the development of enzyme‐linked immunoadsorbent assays and other biosensor applications. Bifunctional vesicles were prepared by covalently attaching horseradish peroxidase (HRP) and an antibody to the outside of the lipid bilayer of an SUV. The reaction conditions were optimized to obtain 7–12 antibody molecules and 100–200 HRP molecules per vesicle. The enzyme retained 70–80% of its specific activity after immobilization, and the presence of immobilized proteins on the vesicle surface apparently increased the vesicle stability. To minimize the background signal and maximize the specific signal, the immunoassay protocol was optimized with respect to (1) the type and concentration of blocking agent, (2) the diluents for HRP‐antibodyvesicles and sample, (3) the incubation period, and (4) the incubation temperature. The bifunctional vesicles were used in a noncompetitive immunoassay to detect d‐dimer, a fibrin dimer formed at the early stages of thrombosis. A second conjugate, HRP‐antibody, was prepared, characterized, and used as a control against which to compare the assay using vesicles. The assay results using vesicles led to a detection limit for d‐dimer in human plasma 9 times lower than what was achieved using the conventional enzyme‐antibody conjugate assay.
Studies on Affinity Constants of Hapten‐Specific Monoclonal Antibodies Using an Antibody‐Immobilized ELISA
Authors: Chu Kent S. , Jin Shan , Guo Jingrong , Jue Marina , Huang John J.
Published: March 2005

An enzyme‐linked immunosorbent assay to measure affinity constants of hapten‐specific monoclonal antibodies has been developed. In this method an antibody‐immobilizing format is used. Antibody affinity toward hapten—enzyme tracer is first calculated by using Scatchard's method. Using this affinity, antibody‐hapten affinity is then calculated by following the principles of chemical thermodynamics and mass conservation. The affinity from this method agrees with the IC50 values in ELISA. This method is useful in early determination of affinity during monoclonal antibody development. Compared with the antigen‐coated format, this method avoids the problem of distinguishing binding of unliganded antibody and singly liganded antibody to antigens on solid phase.
Purification and Characterization of an Amyloglucosidase from Termitomyces clypeatus That Liberates Glucose From Xylan
Authors: Ghosh A. K. , Naskar A. K. , Jana M. L. , Khowala S. , Sengupta S.
Published: March 2005

An amyloglucosidase was purified to homogeneity from the culture filtrate of Termitomyces clypeatus, using the following steps: ammonium sulfate fractionation, DEAE‐Sephadex chromatography, and HP‐GPLC on an Ulstropac TSK‐G3000 SWG column. The enzyme was a glycoprotein with a minimum molecular weight of 56 000. It had appreciable activity on glycogen and amylopectin, moderate activity on maltose, and little activity on panose. The enzyme, unlike fungal amyloglucosidase (Aspergillus niger), could liberate glucose from xylans. The enzyme had Km = 1.81 mg/mL and Vm = 82.1 μmol/min/mg for starch hydrolysis and Km = 4.36 mg/mL and Vm = 57.7 μmol/min/mg for the hydrolysis of larch wood xylan. Among the different inhibitors, NBS and CDTA were the most potent. Previously the enzyme was shown [Khowala, S.; et al. Appl. Microbiol. Technol. 1992, 37, 287–292] to have synergistic activity on xylan hydrolysis similar to other xylanolytic enzymes: α‐arabinofuranosidase or α‐glucuronidase. Since the amyloglucosidase was not active on cellulose, arabinogalactan, or β‐glucans, which may be present as contaminants in xylan, the probable liberation of glucose directly from xylan by the enzyme was indicated.
Effects of ring shadowing on the detection of electrostatic discharges at Saturn
Authors: Mendillo Michael , Moore Luke , Clarke John , Mueller‐Wodarg Ingo , Kurth William S. , Kaiser M. L.
Published: March 2005

A long‐standing discrepancy exists in determinations from observations and modeling of the diurnal variation of the peak electron density of Saturn's ionosphere. Using a new Saturn‐Thermosphere‐Ionosphere‐Model (STIM), we examine the suggestion by Burns et al. (1983) that Saturn's rings shadow its ionosphere causing radio penetration “holes”, thereby allowing lightning‐induced radio signals (Saturn electrostatic discharges, SEDs) to escape. This lessens the need to invoke globally enhanced loss processes to account for Voyager era observations of nighttime peak density (Nmax) as low as 103 e/cm3 from the SEDs. We find radio frequency “windows” produced by ring shadowing that were narrow and confined to low latitudes during the Voyager era, but are now broadly distributed over northern mid‐latitudes during the Cassini era. If lightning sources occur only at near‐equatorial latitudes, then the far less frequent detection of SEDs by Cassini early in its mission would be consistent with the current ionospheric morphology.
Spatial and diurnal variation of precipitation systems over Asia observed by the TRMM Precipitation Radar
Authors: Hirose Masafumi , Nakamura Kenji
Published: March 2005

The spatial and diurnal variation of rainfall over Asia was investigated using the spaceborne radar data for four seasons during 1998–2003. The regional variation of the prevailing precipitation systems most closely associated with the maximum hourly rainfall was shown by examining the fine spatial distribution of rainfall amount and scale‐based precipitation systems. Small precipitation systems (<102 km2) occurred most frequently around early afternoon over most land. The south facing slopes of the Himalayas, especially south of Mount Everest and the upper portion of the Brahmaputra valley, is the most obvious region of the daytime genesis of the convective systems over the Asian landmass. Over the Tibetan Plateau the occurrence of the small systems was larger than over inland India and the foothills. Large systems (>104 km2) developed mostly in the evening over nearly flat landmasses. Wide‐spread systems with intense rain pixels developed over the foothills of the Himalayas in late night–early morning period, which was distinct from the daytime convection. Over ocean, in addition to the morning signature, spatially inhomogeneous and systematic characteristics were evident over the offshore region, for example, around the maritime continent. Large systems, which are strongly associated with terrain, have a great influence on the total number of rain pixels and the total amount of rainfall. For 86% of the region where large system is dominant the time of maximum rainfall is within 3 hours of the time of maximum rainfall for large systems.
Identification and characterization of the human ARD1–NATH protein acetyltransferase complex
Authors: ARNESEN Thomas , ANDERSON Dave , BALDERSHEIM Christian , LANOTTE Michel , VARHAUG Jan E. , LILLEHAUG Johan R.
Published: March 2005

Protein acetyltransferases and deacetylases have been implicated in oncogenesis, apoptosis and cell cycle regulation. Most of the protein acetyltransferases described acetylate ε-amino groups of lysine residues within proteins. Mouse ARD1 (homologue of yeast Ard1p, where Ard1p stands for arrest defective 1 protein) is the only known protein acetyltransferase catalysing acetylation of proteins at both α- (N-terminus) and ε-amino groups. Yeast Ard1p interacts with Nat1p (N-acetyltransferase 1 protein) to form a functional NAT (N-acetyltransferase). We now describe the human homologue of Nat1p, NATH (NAT human), as the partner of the hARD1 (human ARD1) protein. Included in the characterization of the NATH and hARD1 proteins is the following: (i) endogenous NATH and hARD1 proteins are expressed in human epithelial, glioma and promyelocytic cell lines; (ii) NATH and hARD1 form a stable complex, as investigated by reciprocal immunoprecipitations followed by MS analysis; (iii) NATH–hARD1 complex expresses N-terminal acetylation activity; (iv) NATH and hARD1 interact with ribosomal subunits, indicating a co-translational acetyltransferase function; (v) NATH is localized in the cytoplasm, whereas hARD1 localizes both to the cytoplasm and nucleus; (vi) hARD1 partially co-localizes in nuclear spots with the transcription factor HIF-1α (hypoxia-inducible factor 1α), a known ε-amino substrate of ARD1; (vii) NATH and hARD1 are cleaved during apoptosis, resulting in a decreased NAT activity. This study identifies the human homologues of the yeast Ard1p and Nat1p proteins and presents new aspects of the NATH and hARD1 proteins relative to their yeast homologues.
Calcium-induced tertiary structure modifications of endo-β-1,3-glucanase from Pyrococcus furiosus in 7.9 M guanidinium chloride
Authors: CHIARALUCE Roberta , GIANESE Giulio , ANGELACCIO Sebastiana , FLORIO Rita , van LIESHOUT Johan F. T. , van der OOST John , CONSALVI Valerio
Published: March 2005

The family 16 endo-β-1,3 glucanase from the extremophilic archaeon Pyrococcus furiosus is a laminarinase, which in 7.9 M GdmCl (guanidinium chloride) maintains a significant amount of tertiary structure without any change of secondary structure. The addition of calcium to the enzyme in 7.9 M GdmCl causes significant changes to the near-UV CD and fluorescence spectra, suggesting a notable increase in the tertiary structure which leads to a state comparable, but not identical, to the native state. The capability to interact with calcium in 7.9 M GdmCl with a consistent recovery of native tertiary structure is a unique property of this extremely stable endo-β-1,3 glucanase. The effect of calcium on the thermodynamic parameters relative to the GdmCl-induced equilibrium unfolding has been analysed by CD and fluorescence spectroscopy. The interaction of calcium with the native form of the enzyme is studied by Fourier-transform infrared spectroscopy in the absorption region of carboxylate groups and by titration in the presence of a chromophoric chelator. A homology-based model of the enzyme is generated and used to predict the putative binding site(s) for calcium and the structural interactions potentially responsible for the unusual stability of this protein, in comparison with other family 16 glycoside hydrolases.
Activation and assembly of the NADPH oxidase: a structural perspective
Authors: GROEMPING Yvonne , RITTINGER Katrin
Published: March 2005

The NADPH oxidase of professional phagocytes is a crucial component of the innate immune response due to its fundamental role in the production of reactive oxygen species that act as powerful microbicidal agents. The activity of this multi-protein enzyme is dependent on the regulated assembly of the six enzyme subunits at the membrane where oxygen is reduced to superoxide anions. In the resting state, four of the enzyme subunits are maintained in the cytosol, either through auto-inhibitory interactions or through complex formation with accessory proteins that are not part of the active enzyme complex. Multiple inputs are required to disrupt these inhibitory interactions and allow translocation to the membrane and association with the integral membrane components. Protein interaction modules are key regulators of NADPH oxidase assembly, and the protein–protein interactions mediated via these domains have been the target of numerous studies. Many models have been put forward to describe the intricate network of reversible protein interactions that regulate the activity of this enzyme, but an all-encompassing model has so far been elusive. An important step towards an understanding of the molecular basis of NADPH oxidase assembly and activity has been the recent solution of the three-dimensional structures of some of the oxidase components. We will discuss these structures in the present review and attempt to reconcile some of the conflicting models on the basis of the structural information available.
All-electron and relativistic pseudopotential studies for the group 1 element polarizabilities from K to element 119
Authors: Lim Ivan S. , Schwerdtfeger Peter , Metz Bernhard , Stoll Hermann
Published: March 2005

Two-component and scalar relativistic energy-consistent pseudopotentials for the group 1 elements from K to element 119 are presented using nine electrons for the valence space definition. The accuracy of such an approximation is discussed for dipole polarizabilities and ionization potentials obtained at the coupled-cluster level as compared to experimental and all-electron Douglas–Kroll results.
Effects of lattice mismatch and bulk anisotropy on interband tunneling in broken-gap heterostructures
Authors: Zakharova A. , Yen S. T. , Nilsson K. , Chao K. A.
Published: March 2005

We have studied the effects of bulk anisotropy and the strain induced by lattice mismatch on the interband tunneling in broken-gap single-barrier InAs∕AlSb∕GaSb heterostructures and double-barrier InAs∕AlSb∕GaSb∕InAs∕AlSb∕GaSb heterostructures. We have used the eight-band k∙p model and the scattering matrix method, combined with the Burt envelope function theory, to calculate the interband transmission coefficients through the broken-gap heterostructures. We have found a noticeable anisotropy of the transmission coefficients when the magnitude of the in-plane wave vector increases to around 0.25nm−1. We have also found that the strain and the bulk anisotropy of quasiparticle dispersion produce additional peaks in the tunneling probability. For the double-barrier resonant-tunneling structures we discover a large spin splitting of the resonant-tunneling peaks caused by the lack of inversion symmetry. A strong influence of the strain induced by lattice mismatch appears in the current–voltage characteristics of the studied broken-gap heterostructures. In InAs∕AlSb∕GaSb structures the interband tunneling processes into the heavy-hole states contribute mainly to the peak current density if the sample is grown on InAs, but if the sample is grown on GaSb the interband tunneling processes into the light-hole states become the main contribution to the peak current density. As a result, the structure grown on GaSb has a much larger peak current density. This phenomenon was observed experimentally.
Imaging the “missing” bands in the resonance-enhanced multiphoton ionization detection of methyl radical
Authors: Zhang Bailin , Zhang Jinghui , Liu Kopin
Published: March 2005

Three small features were uncovered in the (2+1) resonance-enhanced multiphoton ionization spectra of CD3 produced from a crossed-beam reaction of F+CHD3 near reaction threshold. Taking the velocity mapped images of these features revealed several well-resolved ringlike structures. By conservation of energy, these spectral features were unambiguously assigned to the “missing” bands of 111, 311, and 411 in the literature. These assignments enable all four modes of excitation of this important radical being detected, which could have significant impact on future dynamics studies of the mode specificity of methyl radical.
Midgut epithelial responses of different mosquito–
Plasmodium
combinations: The actin cone zipper repair mechanism in
Aedes aegypti
Authors: Gupta Lalita , Kumar Sanjeev , Han Yeon Soo , Pimenta Paulo F. P. , Barillas-Mury Carolina
Published: March 2005

In vivo
responses of midgut epithelial cells to ookinete invasion of three different vector–parasite combinations,
Aedes aegypti
–
Plasmodium gallinaceum
,
Anopheles stephensi
–
Plasmodium berghei
, and
A. stephensi
–
P. gallinaceum
, were directly compared by using enzymatic markers and immunofluorescence stainings. Our studies indicate that, in
A. aegypti
and
A. stephensi
ookinetes traverse the midgut via an intracellular route and inflict irreversible damage to the invaded cells. These two mosquito species differ, however, in their mechanisms of epithelial repair.
A. stephensi
detaches damaged cells by an actin-mediated budding-off mechanism when invaded by either
P. berghei
or
P. gallinaceum
. In
A. aegypti
, the midgut epithelium is repaired by a unique actin cone zipper mechanism that involves the formation of a cone-shaped actin aggregate at the base of the cell that closes sequentially, expelling the cellular contents into the midgut lumen as it brings together healthy neighboring cells. Invasion of
A. stephensi
by
P. berghei
induced expression of nitric oxide synthase and peroxidase activities, which mediate tyrosine nitration. These enzymes and nitrotyrosine, however, were not induced in the other two vector–parasite combinations examined. These studies indicate that the epithelial responses of different mosquito–parasite combinations are not universal. The implications of these observations to validate animal experimental systems that reflect the biology of natural vectors of human malarias are discussed.
Capitalising Culture: Liverpool 2008
Authors: Jones Paul , Wilks-Heeg Stuart
Published: March 2005

This article analyses the political, economic and social contexts of Liverpool's successful bid to become European Capital of Culture, 2008. It highlights the juxtaposition in the Liverpool 2008 process of discourses of urban entrepreneurialism and a strong emphasis on community involvement. While the bid is part of a wider shift in governance in the city that has helped reverse local economic decline, it is argued that the increasingly ‘boosterist’ character of cultural policy in the city raises a number of concerns. In particular, the article highlights the tensions arising from the re-branding of Liverpool as ‘The World in One City’ and the threat that the emphasis on culture as economic development poses to ‘alternative’ culture in the city.
Low effective population size and evidence for inbreeding in an overexploited flatfish, plaice (Pleuronectes platessaL.)
Authors: Hoarau Galice , Boon Eva , Jongma Dorris N , Ferber Steven , Palsson Jonbjorn , Van der Veer Henk W , Rijnsdorp Adriaan D , Stam Wytze T , Olsen Jeanine L
Published: March 2005

Overexploitation and subsequent collapse of major worldwide fisheries has made it clear that marine stocks are not inexhaustible. Unfortunately, the perception remains that marine fishes are resilient to large population reductions, as even a commercially ‘collapsed’ stock will still consist of millions of individuals. Coupled with this notion is the idea that fisheries can, therefore, have little effect on the genetic diversity of stocks. We used DNA from archived otoliths collected between 1924 and 1972 together with 2002 juvenile's tissue to estimate effective population size (Ne) in plaice (Pleuronectes platessa).Ne was estimated at 20 000 in the North Sea and 2000 in Iceland. These values are five orders of magnitude smaller than the estimated census size for the two locations. Populations examined between 1924 and 1960 were in Hardy–Weinberg equilibrium, whereas populations examined after approximately 1970 were not. Extensive testing was performed to rule out genotyping artefacts and Wahlund effects. The significant heterozygote deficiencies found from 1970 onward were attributed to inbreeding. The emergence of inbreeding between 1950 and 1970 coincides with the increase in fishing mortality after World War II. Although the biological mechanisms remain speculative, our demonstration of inbreeding signals the need for understanding the social and mating behaviour in commercially important fishes.
ZrO2‐Transformation‐Toughened Glass‐Ceramics Prepared by the Sol‐Gel Process from Metal Alkoxides
Authors: NOGAMI M. , TOMOZAWA M.
Published: March 2005

Glasses of composition 3ZrO2O · 2SiO2 were prepared by the sol‐gel process from metal alkoxides. Tetragonal ZrO2 was precipitated by appropriate heat treatment at 1000° to 1200°C. The fracture toughness of these glass‐ceramics increased with increasing crystallite size of the tetragonal ZrO2, reaching ∼5.0 MN/m3/2 at a size of ∼40 nm. The higher fracture toughness was attributed to tetragonal → monoclinic ZrO2 transformation toughening.
Stress Distribution in Multiphase Systems: II, Composite Disks with Cylindrical Interfaces
Authors: OEL H. J. , FRECHETTE V. D.
Published: March 2005

Stress distributions calculated for thin disks having a cylindrical inclusion were found to agree with those measured for glass specimens cooled to room temperature after they were sealed. Maximum circumferential stress in the sheath was independent of inclusion size, but the more rapid decrease of this stress with distance from the inclusion makes crack extension from the interface impossible for inclusions below a certain size. For larger inclusions, flaws above a critical size can be expected to grow and to terminate after a certain distance.
Impact of Small Steel Spheres on the Surfaces of “Normal” and “Anomalous” Glasses
Authors: CHAUDHRI M.M. , KURKJIAN C.R.
Published: March 2005

High‐speed photography (framing rate of 106 s‐1) has been used to follow the formation and growth of damage in a number of oxide glasses when impacted with 1‐mm‐diameter steel balls at velocities of 150 m· s‐1 or higher. Silicate, germanate, and borate glasses were studied in order to clarify the importance of “anomalous” vs “normal” elastic characteristics on their impact behavior. As expected it was found that glasses in these systems which are “anomalous” showed impact behavior which had earlier been seen in silica and borosilicate glass, whiie those glasses which are “normal” showed behavior similar to that shown by soda‐lime silica glass. On the other hand, although B2O3 has been characterized as “normal,” its impact, as well as its quasi‐static behavior, appears to put it in a class by itself. In this case, no cracking is observed during loading up to 150 m·s‐1, while radial and lateral cracking are seen during unloading.
Ferroelastic Domain Switching as a Toughening Mechanism in Tetragonal Zirconia
Authors: Virkar Anil V. , Matsumoto Roger L. K.
Published: March 2005

X‐ray diffraction data are presented in support of the existence of ferroelasticity in tetragonal zirconia. Reorientation of ferroelastic domains by externally applied stress is proposed as a toughening mechanism. Toughening by this mechanism can occur in addition to transformation toughening and also explains high toughness of some zirconias which exhibit no transformation to the monoclinic form. Zirconia ceramics toughened by the ferroelastic mechanism have the potential to retain high toughness at elevated temperature unlike transformation toughening.
Simulation of Microstructure Development During the Hydration of a Cement Compound
Authors: JENNINGS HAMLIN M. , JOHNSON STEVEN K.
Published: March 2005

A mathematical model which simulates the development of microstructure during the hydration of tricalcium silicate (C3S) is described. It is part of a program to develop a model which will quantitatively connect variables associated with different observable characteristics in cement‐based systems, from the time of mixing onwards. The core of the model is a mathematical description of all significant aspects of a selected volume of hydrating material. Output is either a numerical description of some aspect of the system or a graphic representation of the microstructure. The model is versatile and interactive and provides the ability to test the consequences of individual hypotheses in a system which has complex interconnected cause‐effect relationships. It has the potential for predicting microstructure and bulk properties resulting from a wide variety of hydration conditions. It might also serve as a prototype for other materials which are formed through reaction bonding of powder compacts, including fired ceramics, chemically bonded ceramics, and products of powder metallurgy.
Influence of Surface Stress on indentation Cracking
Authors: GREEN D. J. , MALONEY B. R.
Published: March 2005

A simple, two‐dimensional fracture mechanics analysis was used to determine the influence of nonuniform residual surface stresses on the formation of radial indentation cracks. The indentation behavior depends on the depth of the compressive stresses, such that the apparent fracture toughness passes through a maximum with increasing indentation load. The analysis was used to estimate the surface stress from indentation data for a zirconia‐toughened ceramic and was compared to previous X‐ray diffraction measurements of this stress. The comparison gives only fair agreement; the sources of possible error are discussed. Such surface stresses also influence the accuracy of KIC measurements when an indentation crack length technique is used; surface preparation is a critical factor in the measurement. Finally, the KIC values obtained from indentation crack sizes were compared with those obtained by the double‐cantilever‐beam technique.
Structural Characterization of High‐Temperature Zirconia Ceramics by Perturbed Angular Correlation Spectroscopy
Authors: JAEGER HERBERT , GARDNER JOHN A. , HAYGARTH JOHN C. , RASERA ROBERT L.
Published: March 2005

Perturbed angular correlation spectra of γ‐rays emitted following the decay of dilute 181Hf in several zirconia ceramics are reported. Spectra for monoclinic and tetragonal zirconia, a tetragonal zirconia/yttria alloy, a cubic zirconia/yttria alloy, and two mixed tetragonal/cubic‐phase zirconia/yttria alloys were measured as a function of temperature to 1470°C. The spectrum observed for each phase has a unique signature, and the spectrum of mixed‐phase materials can be used to determine the relative amounts of the different phases. These data give a cubic/(cubic + tetragonal) phase boundary that is somewhat lower in temperature than indicated by current phase diagrams.
Characterization of the Spinel Phase from SiO2‐Al2O3 Xerogels and the Formation Process of Mullite
Authors: OKADA KIYOSHI , ŌTSUKA NOZOMU
Published: March 2005

Two kinds of xerogels were prepared by the slow and rapid hydrolyses of tetraethoxysilane and aluminum nitrate nonahydrate dissolved in ethanol. Xerogels prepared by slow hydrolysis crystallized mullite directly from the amorphous state on firing whereas those formed by rapid hydrolysis crystallized a spinel phase before mullite formation. The composition of the spinel phase was characterized by various methods to be near SiO2·6Al2O3. The process of mullite formation is discussed in relation to the structures of the starting materials.
Kinetics of Crack Tip Blunting of Glasses
Authors: HIRAO KAZUYUKI , TOMOZAWA MINORU
Published: March 2005

When abraded or indented glasses are annealed, a strength increase of 20% to 30% is observed. Crack tip blunting and removal of tensile residual stress near the crack tip have both been proposed to explain this phenomenon. In order to resolve which is the more likely mechanism, the kinetics of strength increase of soda‐lime, borosilicate, and high‐silica glasses were measured as a function of heat‐treatment temperature and atmosphere. The sinusoidal profile decay of corrugated glass surfaces of the soda‐lime glass was also investigated at similar temperatures and atmospheres. From these two complementary measurements, it was concluded that the observed strength increase of glasses upon annealing is caused by crack tip blunting, most likely due to viscous flow assisted by water diffused from the atmosphere.
Crystal Growth Kinetics of 4K2O·CaO·10SiO2 from Its Own Melt and Two Other Melts in the K2O‐CaO‐SiO2 System
Authors: QIAN Z. , TOLT T. L. , COOPER A. R.
Published: March 2005

Crystal growth of 4K2O·CaO·10SiO2 from its own melt occurred with a faceted interface, while crystal growth from a melt ∼4 wt% richer in silica than the crystal showed dendritic morphology and growth from a melt ∼5 wt% leaner in silica showed dendritic growth at undercoolings <10°C and faceted growth at undercoolings >30°C. The crystal growth velocities in all cases were independent of time and fit well the empirical relation In [U/(Tl‐T)1.6] =A – Q/T, where U is velocity, A and Q are constants, and Tl, is the liquidus temperature of the melt. The crystal growth data for the three melt compositions lie together in a narrow swath when plotted using the above equation. An explanation for this behavior is proposed which suggests that the phase boundary reaction aided by nucleation at surface sites provided by screw dislocations determines the growth kinetics even when the melt and crystal have different compositions.
Heterogeneous Dissolution of Refractory Oxides in Molten Calcium‐Aluminum Silicate
Authors: Bates J. Lambert
Published: March 2005

The dissolution of Al2O3, MgAl2O4. Y3Al5O12, MgO, and other refractory oxides in molten Ca‐Al silicates is heterogeneous over significant temperature and silicate composition ranges with the formation of at least one solid reaction product at the oxide‐silicate interface.
Effects of Cation Substitution on Electrical and Thermal Transport Properties of YCrO3 and LaCrO3
Authors: WEBER WILLIAM J. , GRIFFIN CURTIS W. , BATES J. LAMBERT
Published: March 2005

High‐temperature electrical conductivity, Seebeck coefficient, and thermal conductivity measurements were used to study the effects of different cation substituents on electrical and thermal transport in YCrO3 and LaCrO3. The substitution of divalent Ca and Sr for Y and La, respectively, resulted in the formation of small polarons as charge carriers. The additional substitution of Mn for Cr resulted in the formation of a second charge carrier associated with the Mn. The electrical conductivity results were consistent with thermally activated transport by hopping of a temperature‐independent carrier concentration. The activation energies were 0.20 and 0.12 eV for (Y,Ca)CrO3 and (La,Sr)CrO3, respectively, and increased to about 0.50 eV with the substitution of Mn for Cr. The Seebeck coefficient increased linearly with temperature and decreased with substituent concentration for both (Y,Ca)CrO3 and (La,Sr)CrO3. The substitution of Mn for Cr resulted in a Seebeck coefficient with a more complex dependence on temperature and substituent concentration. The thermal conductivity did not change significantly with either cation substitution or temperature.
Oxygen Self‐Diffusion in Lithium‐Doped Single‐Crystal Magnesium Oxide
Authors: Oishi Yasumichi , Ando Ken , Yasumura Kenji
Published: March 2005

Oxygen self‐diffusion coefficients for a single‐crystal MgO doped with 400 ppm Li were determined at 848° to 1300°C by isotope exchange technique using 18O as the tracer. The diffusion coefficient increased with increasing temperature in the lower temperature range, as described by D = 7.8 × 10−4 exp[−279 (kJ/mol)/RT] cm2/s, which was interpreted to be an extrinsic diffusion due to the oxygen vacancies introduced by substitutional Li ions. The oxygen diffusivity tended to decrease above 1050°C, presumably becauuse of evaporation of Li2O.
Growth of Twinned β ‐Silicon Carbide Whiskers by the Vapor‐Liquid‐Solid Process
Authors: de Jong Remco , Mccauley Ronald A. , Tambuyser Paul
Published: March 2005

Whiskers of twinned SiC in the cubic form were produced by the vapor‐liquid‐solid process as a byproduct of the corrosion of silicon nitride. These whiskers were characterized and their properties related to their use in reinforced materials.
Thermal Expansion and Thermal Expansion Anisotropy of SiC Polytypes
Authors: LI Z. , BRADT R. C.
Published: March 2005

The principal axial coefficients of thermal expansion for the (3C), (4H), and (6H) polytypes of SiC are considered to identify the structural role of the stacking layer sequence as it affects the thermal expansion. A general equation based on the fractions of cubic and hexagonal layer stacking is developed that expresses the principal axial thermal expansion coefficients of all of the SiC polytypes. It is then applied to address the thermal expansion anisotropy of the noncubic SiC structures.