bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Equilibrium Relative Humidity on the Mechanical Signatures of Brittle Food Materials
Authors: Rohde Florian , Normand Mark D. , Peleg Micha
Published: March 2005

Three brittle commercial bakery products (bread sticks, pretzels, and zwiebacks) were compressed after equilibration at five relative humidity levels with a computer‐interfaced Universal Testing Machine. Their mechanical signatures are presented in the form of conventional force—time relationships, power spectra calculated by the fast Fourier transform, Richardson plots from which the apparent fractal dimension was calculated, and displays of the symmetrized‐dot pattern (SDP) produced from the original force—time relationships. It is demonstrated that, although the original force—time relationships were irregular and irreproducible, consistent patterns and values did emerge in the transformed data. Plasticization, as a result of moisture sorption, is clearly expressed in the disappearance of the high‐frequency region of the power spectrum and a drastic decrease in the magnitude of the apparent fractal dimension. The differences among the shapes of the original force—deformation curves before and after moisture sorption are also clearly evident from the SDP displays, but the sensitivity of the method needs to be established with a larger experimental data base.
Enzymatic Esterification by Surfactant‐Coated Lipase in Organic Media
Authors: Goto Masahiro , Kamiya Noriho , Miyata Masaki , Nakashio Fumiyuki
Published: March 2005

Surfactant‐coated lipases have been prepared with a synthesized surfactant. Preparation conditions to obtain a suitable surfactant‐coated lipase were investigated. The enzymatic activity of the lipase in an organic solvent significantly increased with the coating of the surfactant. The esterification rate from the surfactant‐coated lipase was much higher than that from the powder lipase. An aliphatic solvent showed higher activity than did alcohol, aromatic, and chloric solvents. Among them, isooctane gave the highest activity. The reactivity of the surfactant‐coated lipase depends on the pH of the aqueous solution in the preparation and on the buffer solution. Surfactant‐coated lipase prepared in the middle pH range using phosphate buffer showed high enzymatic activity. The surfactant‐coated lipase was thermostable at high temperature compared to the native lipase. A kinetic study enabled a ping‐pong bi‐bi reaction mechanism with alcohol inhibition to be suggested. From the kinetic analysis, it was found that an alcohol substrate inhibits enzymatic esterification by lipase. The reaction rate of the coated lipase was about 100 times that of the powder lipase.
Intracellular Expression of Vitreoscilla Hemoglobin Alters the Aerobic Metabolism of Saccharomyces cerevisiae
Authors: Chen Wilfred , Hughes Dallas E. , Bailey James E.
Published: March 2005

Vitreoscilla hemoglobin (VHb) has been expressed in Saccharomyces cerevisiae, and its influence on yeast aerobic metabolism has been investigated. New expression vectors were constructed to express VHb constitutively under the control of the ADH‐1 promoter. The presence of VHb was shown by Western blot analysis. VHb has been shown to localize predominantly in the cytoplasm. Batch fermentation results indicated that the wild‐type strain expressing VHb exhibited a shift in the carbon flux toward ethanol production, with no significant alteration in the specific growth rate. This effect was not observed if cells were grown under respiration inhibition, indicating that the metabolic effect of VHb is likely linked to respiration. Expression of VHb in the adh° strain MC65‐2A, which produces ethanol only via a respiration‐coupled pathway, revealed that ethanol production was decreased and cells reached a higher final cell density in a culture of the VHb‐expressing strain. Growth enhancement due to expression of VHb was observed only during the final stage of culture growth when the acetaldehyde produced during the first growth phase was used as a substrate. This metabolic effect of intracellular VHb was seen more clearly in an acetaldehyde fed‐batch fermentation in which VHb‐expressing cells grew to at least 3‐fold higher final cell density. These results suggest that the action of VHb is likely linked to electron transfer.
A Model of Mechanical Changes in Biomaterials at and around Their Glass Transition
Authors: Peleg Micha
Published: March 2005

The transition of biological and food materials from a glassy to a leathery or rubbery state and the accompanying loss of stiffness, hardness, or strength are tranditionally described by a relationahip between the magnitudes of these parameters and the temperature, moisture, or water activity. At the transition region, the curve depicting such a relationship has a sigmoidal shape that can be described by the model, Y(X) = Ys/{1 + exp[X ‐ Xc)/a]}, where X is either temperature, moisture content, or water activity, Y(X) is a mechanical parameter (e. g., modulus), Ys is the latter's magnitude in the glassy state (assumed to be practically constant), Xc is a characteristic temperature, moisture, or aw level of the transition, and a is a constant. This model was tested with the published data of various biomaterials (baker's yeast, casein, coffee creamer, luncheon meat, sodium caseinate, sucrose/glucose glass, wheat grains, and bread). In all cases, it gave a consistent description of the mechanical changes at and around the transition and had a very satisfactory fit.
Modeling of Bacterial Growth under Multiply‐Limiting Conditions. Experiments under Carbon‐ or/and Nitrogen‐Limiting Conditions
Authors: Straight Jeffrey V. , Ramkrishna Doraiswami
Published: March 2005

As the limiting substrate is altered, a microorganism's internal structure is also altered by invoking different metabolic pathways for the utilization of the limiting substrate. Transitions between pathways are moderated by the processes of metabolic regulation and are observed under steady‐state and transient conditions. Under nitrogen‐limited steady‐state conditions, the effects of overflow metabolism are observed in the form of polysaccharide synthesis and excess carbon oxidation, two phenomena that are not observed under carbon‐limited conditions. Furthermore, during transient periods following dilution rate shifts, metabolic lags are observed to be a function of the size of the shift as well as the limiting substrate. The latter observation indicates the preference of one reaction pathway over another as the status of glucose or NH4+ is altered from limiting to nonlimiting. This paper presents steady‐state and transient results from continuous culture experiments using Escherichia coli W. Singly‐limiting conditions, when either glucose or ammonia is the limiting substrate, are investigated. Transient conditions are created by quickly increasing or decreasing the dilution rate of the fermentor. By utilizing the control strategies identified by Straight and Ramkrishna (1994) for regulating the processes commonly found within metabolic pathways, a cybernetic model is developed and compared to the steady‐state and transient experimental results. Due to the incorporation of metabolic pathways, the development of the model accounts for lumped biosynthetic intermediates in addition to key enzymes that catalyze different cellular processes. The model also accounts for an internal resource that is optimally allocated toward the synthesis of the key enzymes. Furthermore, the model incorporates the effects of maintenance processes and overflow metabolism. Upon incorporating nitrogen utilization, the kinetic aspects of the model do not explicitly reduce to those of previous cybernetic models; however, the regulatory structure is in complete agreement with previous cybernetic models proposed for carbon utilization.
Optimum Infection Conditions for Recombinant Protein Production in Insect Cell (Bm5) Suspension Culture
Authors: Zhang Junli , Kalogerakis Nicolas , Behie Leo A. , Iatrou Kostas
Published: March 2005

The baculovirus/insect cell expression system is an efficient and practical method for the production of many active therapeutic proteins on a large scale. The advantages of suspension cultures have been demonstrated with the study of a baculovirus/insect cell (BmNPV/Bm5) expression system for the production of recombinant chloramphenicol acetyltransferase (CAT), a model heterologous protein. Key infection parameters such as infection time and multiplicity of infection were examined systematically for the maximization of protein production. Furthermore, emphasis was placed on the development of possible medium replenishment strategies, which were necessary to achieve higher volumetric protein production from the infection of high‐density cell cultures without sacrificing specific protein productivity. The highest protein production was achieved with the infection of suspended cells in the mid to late exponential growth phase.
Effect of Modulated Glucose Uptake on High‐Level Recombinant Protein Production in a Dense Escherichia coli Culture
Authors: Chou Chih‐Hsiung , Bennett George N. , San Ka‐Yiu
Published: March 2005

Methyl α‐glucoside (α‐MG) is a metabolically inert glucose analog sharing the same phosphotransferase system with glucose. The potential of using this compound, which acts as a nontoxic competitive inhibitor, to modulate glucose uptake and subsequently reduce the acetate accumulation rate was investigated. In a complex medium, no significant effect on the growth rate was observed when the α‐MG to glucose ratio was low. The effect of α‐MG supplementation on the production of a model recombinant protein, CadA‐β‐galactosidase, under the regulation of a pH‐inducible promoter in a batch culture was also examined. It was observed that the amount of acetate accumulation was drastically reduced in the presence of α‐MG. More importantly, recombinant protein productivity was significantly improved. A very high volumetric productivity of approximately 1.6 g/L recombinant protein in a dense culture with an OD600 of 35 was obtained in a simple batch fermentation. Even at this high cell density, the specific protein productivity was maintained at a high level and was estimated to account for about 40% of the total cellular protein.
Effects of Ionic and Zwitterionic Surfactants on the Stabilization of Bovine Catalase
Authors: Spreti N. , Bartoletti A. , Profio P. Di , Germani R. , Savelli G.
Published: March 2005

The activity and stability of beef liver catalase have been investigated in the presence of different ionic and zwitterionic surfactants. All cationic and zwitterionic surfactants used in this work have no effect on the initial activity of catalase, but several of them allow the enzyme to retain a high residual activity for longer periods of time than those observed in the absence of any additives. However, the interactions between surfactants and catalase appear to be very peculiar, and certain zwitterionic surfactants have been found to remarkably slow down enzyme degradation, with the enzyme completely preserving its activity after several weeks at temperatures of up to 30 °C. This effect is probably due to an interaction between the surfactant and the intersubunit region of the protein; this interaction could stabilize the quaternary structure of the enzyme.
Extractive Cultivation of Escherichia coli Using Poly(ethylene glycol)/Phosphate Aqueous Two‐Phase Systems To Produce Intracellularβ‐Galactosidase
Authors: Kuboi Ryoichi , Umakoshi Hiroshi , Komasawa Isao
Published: March 2005

Escherichia coli cells were found to grow in poly(ethylene glycol) (PEG)/phosphate aqueous two‐phase systems by selecting the phase‐forming components and their concentrations, the tie‐line length, and the phase volume ratio properly. The cells cultivated up to an optical density at 660 nm of 1.0 were disrupted by ultrasonic irradiation to release and recover overproduced β‐galactosidase. The surviving cells were found to grow immediately after ultrasonic irradiation. The PEG/phosphate (KH2‐PO4‐K2HPO4) system with added Na2SO4 was the one optimized for extractive cultivation of E. coli cells, where β‐galactosidase was selectively partitioned to the top phase while total soluble proteins and cells partitioned to the bottom phase. This integrated process was extended to a semicontinuous operating mode, where the top phase containing β‐galactosidase was removed following intermittent ultrasonic irradiation and the bottom phase containing cells was recycled together with the new top phase solution to repeat production and recovery of β‐galactosidase.
Surfactant‐Coated Lipase Suitable for the Enzymatic Resolution of Menthol as a Biocatalyst in Organic Media
Authors: Kamiya Noriho , Goto Masahiro , Nakashio Fumiyuki
Published: March 2005

Enantioselective esterification of menthol with fatty acids using a surfactant‐coated lipase was carried out in organic media. The surfactant‐coated lipase originating from Candida cylindracea appeared to be highly enantioselective and good biocatalyst for the resolution of racemic menthol. The enzymatic activity of the lipase in organic media was significantly increased by a coating with a nonionic surfactant. The reaction rate of the coated lipase was more than 100 times that of the powder lipase. In order to investigate the effect of the organic solvent on enantioselectivity, 19 kinds of solvents were employed. The nature of the organic solvent strongly affected the efficiency of the biocatalyst and the enantioselectivity. Among them, isooctane was the best organic solvent from the viewpoint of reaction rate and enantioselectivity. The effect of reaction temperature on esterification was also investigated. The optimal reaction temperature was around 35 °C. The enzymatic activities using n‐saturated fatty acids with different alkyl chain lengths were compared, and long‐chain fatty acids were found to be better substrates than shorter ones. The relationship between the initial rate of the esterification and the carbon number of the fatty acid was not linear. These results suggest that there are inherent Km values for each fatty acid.
Tissue Plasminogen Activator Coexpressed in Chinese Hamster Ovary Cells with α(2,6)‐Sialyltransferase Contains NeuAcα(2,6)Galβ(1,4)Gl‐N‐AcR Linkages
Authors: Minch Sherrill L. , Kallio Pauli T. , Bailey James E.
Published: March 2005

Genetic alteration of the set of oligosaccharide biosynthesis enzymes expressed in a genetically engineered host cell line is a plausible strategy for manipulating the oligosaccharides on a cloned glycoprotein coexpressed in that cell line. This hypothesis was verified for the particular case of sialylation of recombinant human tissue plasminogen activator (tPA) expressed by an engineered Chinese hamster ovary (CHO) cell line. The gene for rat liver, β‐galactoside α(2,6)‐sialyltransferase (2,6‐ST) was cloned behind the MMTV promoter in the vector pMSG and transfected into a tPA‐expressing CHO cell line. Selected and screened transfectants exhibited significantly greater surface fluorescence than controls in flow cytometric analyses of cells labeled with Sumbacus nigru agglutinin (SNA)‐biotin and streptavidin‐R‐phycoerythrin; SNA specifically binds to NeuAcα(2,6)Galβ(1,4)Glc‐N‐AcR linkages, which are synthesized by 2,6‐ST and which are not normally found on CHO cells. SNA blots of partially purified tPA from the culture supernatant demonstrated that tPA synthesized in the 2,6‐ST transfectants possessed terminal NeuAcα(2,6)Galβ(1,4)Glc‐N‐AcRlinkages, while tPA from the original recombinant CHO cell line did not. Besides possibly allowing the production of glycoproteins in cell culture with glycosylation more closely resembling that in humans, extensions of this strategy have the potential to tailor the pharmacokinetics, targeting, and antigenic properties of cloned glycoproteins.
Model‐Based Optimization of Equipment and Control for Heat Flux Measurements in a Laboratory Fermentor
Authors: Van Kleeff Bastiaan H. A. , Kuenen J. Gijs , Honderd Ger , Heijnen Sef J.
Published: March 2005

The measurement of microbially‐produced heat in standard laboratory fermentors was studied with the help of a mathematical model describing the heat flows. The improvements that were indicated by the modeling work were implemented in the experimental setup. Tests showed that both the standard deviation in the heat measurement and the response time for the experimental setup improved through use of the modeling results.
A velocity map ion-imaging study on ketene photodissociation at 208 and 213nm: Rotational dependence of product angular anisotropy
Authors: Liu Jie , Wang Fengyan , Wang Hua , Jiang Bo , Yang Xueming
Published: March 2005

Photodissociation dynamics of ketene following excitation at 208.59 and 213.24nm have been investigated using the velocity map ion-imaging method. Both the angular distribution and translational energy distribution of the CO products at different rotational and vibrational states have been obtained. No significant difference in the translational energy distributions for different CO rotational state products has been observed at both excitation wavelengths. The anisotropy parameter β is, however, noticeably different for different CO rotational state products at both excitation wavelengths. For lower rotational states of the CO product, β is smaller than zero, while β is larger than zero for CO at higher rotational states. The observed rotational dependence of angular anisotropy is interpreted as the dynamical influence of a peculiar conical intersection between the B11 excited state and A21 state along the CS-I coordinate.
III-V compliant substrates implemented by nanocavities introduced by ion implantation
Authors: Chicoine M. , Beaudoin C. , Roorda S. , Masut R. A. , Desjardins P.
Published: March 2005

A concept for the implementation of a compliant substrate using a buried layer of nanocavities is presented. The purpose of this nanocavity layer is to mechanically decouple a thin substrate layer from the rest of the substrate in order to relax stress in mismatched epilayers. The nanocavities were created by helium implantation in InP(001) followed by thermal annealing under a phosphorous rich atmosphere. Metalorganic vapor phase epitaxy of InAsP∕InP heterostructures grown simultaneously on substrates with nanocavities and on conventional substrates were characterized by high-resolution x-ray diffraction, transmission electron microscopy, and optical absorption. It is found that strain relaxation is enhanced for heterostructures grown on substrates with nanocavities and that the dislocations propagate partly in the compliant layer instead of the epilayer. The critical thickness of heterostructures grown on conventional substrates is roughly double that of structures grown on substrates containing nanocavities.
Controlling the properties of InGaAs quantum dots by selective-area epitaxy
Authors: Mokkapati S. , Lever P. , Tan H. H. , Jagadish C. , McBean K. E. , Phillips M. R.
Published: March 2005

Selective growth of InGaAs quantum dots on GaAs is reported. It is demonstrated that selective-area epitaxy can be used for in-plane bandgap energy control of quantum dots. Atomic force microscopy and cathodoluminescence are used for characterization of the selectively grown dots. Our results show that the composition, size, and uniformity of dots are determined by the dimensions of the mask used for patterning the substrate. Properties of dots can be selectively tuned by varying the mask dimensions. A single-step growth of a thin InGaAs quantum well and InGaAs quantum dots on the same wafer is demonstrated. By using a single-step growth, dots luminescing at different wavelengths, in the range 1150–1230nm, in different parts of the same wafer are achieved.
Dependence of the programming window of silicon-on-insulator nanocrystal memories on channel width
Authors: Fiori G. , Iannaccone G. , Molas G. , De Salvo B.
Published: March 2005

In this letter, we investigate the observed dependence of the programming window of silicon-on-insulator (SOI) nanocrystal memories on the width of the channel. Indeed, experiments show that the obtained threshold voltage shift after programming strongly increases with decreasing channel width. We show that such behavior is due to the preferential injection of electrons, during the program operation, from regions close to the edges of the SOI channel, where the electric field is stronger. As a consequence, charge is mostly stored in the dots in the oxide region surrounding the edges, and therefore is more and more effective as the channel width is decreased. Our conjecture is verified through dedicated three-dimensional simulations and checked against other mechanisms proposed in the literature.
A copper(I) protein possibly involved in the assembly of Cu
A
center of bacterial cytochrome
c
oxidase
Authors: Banci Lucia , Bertini Ivano , Ciofi-Baffoni Simone , Katsari Efthalia , Katsaros Nikolaos , Kubicek Karel , Mangani Stefano
Published: March 2005

Sco1 and Cox17 are accessory proteins required for the correct assembly of eukaryotic cytochrome
c
oxidase. At variance with Sco1, Cox17 orthologs are found only in eukaryotes. We browsed bacterial genomes to search proteins functionally equivalent to Cox17, and we identified a class of proteins of unknown function displaying a conserved gene neighborhood to bacterial Sco1 genes, all sharing a potential metal binding motif H(M)X
10
MX
21
HXM. Two members of this group, DR1885 from
Deinococcus radiodurans
and CC3502 from
Caulobacter crescentus
, were expressed, and their interaction with copper was investigated. The solution structure and extended x-ray absorption fine structure data on the former protein reveal that the protein binds copper(I) through a histidine and three Mets in a cupredoxin-like fold. The surface location of the copper-binding site as well as the type of coordination are well poised for metal transfer chemistry, suggesting that DR1885 might transfer copper, taking the role of Cox17 in bacteria. On the basis of our results, a possible pathway for copper delivery to the Cu
A
center in bacteria is proposed.
A spatially localized rhomboid protease cleaves cell surface adhesins essential for invasion by
Toxoplasma
Authors: Brossier Fabien , Jewett Travis J. , Sibley L. David , Urban Sinisa
Published: March 2005

Apicomplexan parasites cause serious human and animal diseases, the treatment of which requires identification of new therapeutic targets. Host-cell invasion culminates in the essential cleavage of parasite adhesins, and although the cleavage site for several adhesins maps within their transmembrane domains, the protease responsible for this processing has not been discovered. We have identified, cloned, and characterized the five nonmitochondrial rhomboid intramembrane proteases encoded in the recently completed genome of
Toxoplasma gondii
. Four
T. gondii
rhomboids (TgROMs) were active proteases with similar substrate specificity. TgROM1, TgROM4, and TgROM5 were expressed in the tachyzoite stage responsible for the disease, whereas TgROM2 and TgROM3 were expressed in the oocyst stage involved in transmission. Although both TgROM5 and TgROM4 localized to the cell surface in tachyzoites, TgROM5 was primarily at the posterior of the parasite, whereas adhesins were sequestered in internal micronemes. Upon microneme secretion, as occurs during invasion, the MIC2 adhesin was secreted to the apical end and translocated to the posterior, the site of cleavage, where it colocalized only with TgROM5. Moreover, only TgROM5 was able to cleave MIC adhesins in a cell-based assay, indicating that it likely provides the key protease activity necessary for invasion.
T. gondii
rhomboids have clear homologues in other apicomplexans including malaria; thus, our findings provide a model for studying invasion by this deadly pathogen and offer a target for therapeutic intervention.
Osteocalcin protein sequences of Neanderthals and modern primates
Authors: Nielsen-Marsh Christina M. , Richards Michael P. , Hauschka Peter V. , Thomas-Oates Jane E. , Trinkaus Erik , Pettitt Paul B. , Karavanić Ivor , Poinar Hendrik , Collins Matthew J.
Published: March 2005

We report here protein sequences of fossil hominids, from two Neanderthals dating to ≈75,000 years old from Shanidar Cave in Iraq. These sequences, the oldest reported fossil primate protein sequences, are of bone osteocalcin, which was extracted and sequenced by using MALDI-TOF/TOF mass spectrometry. Through a combination of direct sequencing and peptide mass mapping, we determined that Neanderthals have an osteocalcin amino acid sequence that is identical to that of modern humans. We also report complete osteocalcin sequences for chimpanzee (
Pan troglodytes
) and gorilla (
Gorilla gorilla gorilla
) and a partial sequence for orangutan (
Pongo pygmaeus
), all of which are previously unreported. We found that the osteocalcin sequences of Neanderthals, modern human, chimpanzee, and orangutan are unusual among mammals in that the ninth amino acid is proline (Pro-9), whereas most species have hydroxyproline (Hyp-9). Posttranslational hydroxylation of Pro-9 in osteocalcin by prolyl-4-hydroxylase requires adequate concentrations of vitamin C (
l
-ascorbic acid), molecular O
2
, Fe
2+
, and 2-oxoglutarate, and also depends on enzyme recognition of the target proline substrate consensus sequence Leu-Gly-Ala-Pro-9-Ala-Pro-Tyr occurring in most mammals. In five species with Pro-9–Val-10, hydroxylation is blocked, whereas in gorilla there is a mixture of Pro-9 and Hyp-9. We suggest that the absence of hydroxylation of Pro-9 in
Pan
,
Pongo
, and
Homo
may reflect response to a selective pressure related to a decline in vitamin C in the diet during omnivorous dietary adaptation, either independently or through the common ancestor of these species.
From liberation to reconstruction: Theory & practice in the life of Harold Wolpe
Authors: Burawoy Michael
Published: March 2005

Writings from exile have a long and distinguished pedigree. Trotsky wrote his History of the Russian Revolution while in exile in Turkey and The Revolution Betrayedin Norway; Lenin wrote Imperialism: The Highest Stage of Capitalism in Zurich and had to escape to Finland to write State and Revolution; Luxemburg wrote The Accumulation of Capitalin Switzerland, and Gramsci wrote his Prison Notebooksunder the eye of fascist jail guards. Marx wrote his Capital while exiled in London which is also where Harold Wolpe wrote his most important analyses of South Africa. Being in exile gave him the space to develop a new research program for the study of South Africa, its present, its past, and its future.

This is a shortened version of The Harold Wolpe Memorial Lecture, presented in July 2004 in South Africa. Among the ideas on which it reflects are those Wolpe originally published in ROAPE and which this issue revisits. It is not only a tribute to Wolpe's singular contribution to the African liberation struggle but also an acute reflection of the struggles for liberation and reconstruction that lie ahead, the political practice they demand, the uses of state power required for these tasks and the obligations of intellectual responsibility they impose. See, http://www.wolpetrust.org.za/index.htm
Gauge-field-theory solution of the elastic state of a screw dislocation in a dispersive (non-local) crystalline solid
Authors: Sharma P , Ganti S
Published: March 2005

The relaxed state of a type of topological defect (screw dislocation) located in a dispersive (non-local) elastic solid is discussed from a viewpoint of gauge field theory. The starting point of this work is the non-local elastic Lagrangian, that is, like its classic elastic counterpart, globally gauge invariant under the Euclidean group of transformations

O
(3)▹

(3). When compared with gauge solutions of the same problem predicated on the classical elastic Lagrangian, the present solution sheds some interesting insights into the nature of non-locality-gauge field interactions. Both the

(3) gauge theory of dislocations (predicated on breaking of the translational symmetry) and the phenomenological non-local elasticity introduce their own respective characteristic length-scale parameters in the elastic equilibrium of dislocations while removing unphysical singularities. In the present work we show that, surprisingly, attempts to elucidate gauge interactions in a dispersive or non-local medium lead to functionally the same solution as in the gauge theory based on local elasticity, albeit, the gauge length-scale must be replaced by an effective length-scale measure. In particular, the non-local and the gauge length-scale combine in a nonlinear fashion to yield the aforementioned effective length-scale. Our results allow one to immediately write the solution of most screw dislocation problems in the gauge non-local theory of defects, provided the counterpart gauge solution based on classical elasticity is known.
Analysis of Concurrent Grain Growth During Creep of Polycrystalline Alumina
Authors: Chokshi Atul H. , Porter John R.
Published: March 2005

During low‐stress creep experiments in a fine‐grained alumina, the strain rates decreased continuously with time due to the occurrence of concurrent grain growth. The grain‐growth kinetics were independent of the applied stress and depended only on the time of exposure to the elevated test temperature. An analysis of the effect of concurrent grain growth was consistent with experimental observations.
Intergranular Films and Pore Surfaces in Synroc C: Structure, Composition, and Dissolution Characteristics
Authors: COOPER J. A. , COUSENS D. R. , HANNA J. A. , LEWIS R. A. , MYHRA S. , SEGALL R. L. , SMART R. St. C. , TURNER P. S. , WHITE T. J.
Published: March 2005

High‐resolution electron microscopy and scanning electron microscopy were used to determine the distribution of intergranular films, triple‐point regions, and microvoids in synroc C. Diffraction contrast derived from interphase films, which were 1 to 3 nm thick, and from triple points showed them to be ill‐defined crystallographically, and they may be described as glassy. Pores were usually several micrometers in extent and occurred principally in rutile‐rich areas. The chemical composition of these structural features was obtained using analytical transmission electron microscopy, secondaryion mass spectrometry, X‐ray photoelectron spectroscopy, and scanning Auger microscopy. Within intergranular films, elemental enhancement of cesium, sodium, potassium, and aluminum, and possibly silicon and molybdenum, was observed. Enhancement of cesium, sodium, phosphorus, aluminum, and silicon was found in triple‐point regions. Fracture faces preferentially expose boundaries between grains, and ion exchange of
Preparation of Amorphous Silicas Doped with Organic Molecules by the Sol‐Gel Process
Authors: Makishima Akio , Tani Toshiro
Published: March 2005

Molecular dispersions of amorphous siliceous materials doped with organic molecules were prepared by a sol‐gel process in which Si(OC2H5)4 was hydrolyzed in neutral or acidic solution. An amorphous silica which was doped with quinizarin on the order of 5×10−5 mol/mol SiO2 showed photochemical hole burning at ∼4 K.
Seeding with γ‐Alumina for Transformation and Microstructure Control in Boehmite‐Derived α‐Alumina
Authors: McArdle James L. , Messing Gary L.
Published: March 2005

The dehydration, transformation, and densification of boehmite (γ‐AlOOH) are enhanced by addition of γ‐Al2O3 seed particles. α‐Al2O3 microstructures with uniform 1‐ to 2‐μm grain size and sintered densities 98% of theoretical are achieved at 1300°C Thermal analysis shows that γ‐Al2O3 seed particles transform to α‐Al2O3 before the matrix, thus controllably nucleating the transformation of θ‐AI2O3 to α‐Al2O3.
Crystallography of the Tetragonal to Monoclinic Transformation in MgO‐Partially‐Stabilized Zirconia
Authors: MUDDLE B. C. , HANNINK R. H. J.
Published: March 2005

The structure of monoclinic ZrO2 particles dispersed in MgO‐partially‐stabilized zirconia has been examined systematically using transmission electron microscopy and electron micro‐diffraction. In both particles transformed athermally and those transformed under stress, the product of the martensitic tetragonal to monoclinic transformation comprises parallel variants of the monoclinic structure. The monoclinic domains extend either parallel or normal to the original precipitate habit plane and, to within the accuracy of the technique, adjacent pairs are twin related. For particles with domains parallel to the particle habit plane the boundary between variants is (001)m and the orientation relationship between tetragonal and monoclinic lattices is such that (001)m‖ (001)t and [100]m‖ [100]t. In particles with transverse domains, the domain boundaries are parallel to (100)m, and the orientation relationship is given by (100)m‖ (100)t and [001]m‖ [001]t. In each case the lattice correspondence implied between parent and product lattices is such that the cm axis is parallel to the Cm axis. The microcracking associated with transformed particles appears closely related to the substructure adopted by the particles and the origin of this microcracking is briefly discussed.
Effect of Some Additives on the Specific Surface of Alumina Obtained from Aluminum‐Ammonium Alum
Authors: Bogdanov B. I. , Chomakov Iv. , Iliev Y. , Tanev P.
Published: March 2005

The effect of Al(NO3)3·9H2O, AlCl3·6H2O, Al(CH3COO)3, and NH4F on the specific surface of Al2O3 obtained from aluminum‐ammonium alum by calcining was studied. It was found that the use of these additives makes it possible to obtain Al2O3 with specific surface varying from 1 to 135 m2/g after thermal treatment in the interval from 1273 to 1423 K. The changes in the morphology and structure of powederd Al2O3 obtained from alum containing these additives were studied by electron microscope observations.
Reaction During Sintering of Barium Titanate with Lithium Fluoride
Authors: Guha J. P. , Anderson H. U.
Published: March 2005

The reactions occurring during sintering of stoichiometric BaTiO3 with small additions of LiF were studied at temperatures between 700° and 900°C. BaTiO3 reacts with LiF to form a cubic solid solution and Li2TiO3 During sintering, the cubic solid solution coexists with Li2Ti03 and forms a liquid phase at 740°± 5°C. The occurrence of a liquid phase at this temperature results in an enhancement of the sintering process and leads to the development of a highly dense microstructure.
Relationship between the Strength of Ceramic/Metal Joints in Tensile and Three‐Point Bending
Authors: Suganuma Katsuaki , Okamoto Taira , Koizumi Mitsue , Shimada Masahiko
Published: March 2005

The tensile strength and the three‐point bending strength of Si3N4/Al/Invar joints were compared. The fracture modes in both tests were almost the same. Statistical treatments of the strengths showed that both strengths had a similar Weibull slope of ∼6. The three‐point bending strength was 2.5 times greater than the tensile strength. This magnification was slightly greater than that obtained from the relation of the effective areas in both tests.
Comparative Single‐Point Diamond Scratching Behavior of a Cordierite Glass and Glass‐Ceramic
Authors: Donaldson Kimberly Yates , Hasselman D. P. H.
Published: March 2005

A comparative study was conducted of the single‐point diamond scratching response of a cordierite glass and glass‐ceramic. For the glass, deformation and material removal occurred by viscous flow at the lowest values of load, viscous flow combined with crack formation adjacent to the contact area over the intermediate load range, and extensive spoiling at the highest values of load. The density of the spalls and spall size were found to be proportional and inversely proportional to perpendicular scratching load, respectively. The glass‐ceramic exhibited plastic flow and abrasive wear at loads as low as could be reliably measured, the particle size of the debris being of the order of the grain size. At the highest ranges of load, the glass‐ceramic exhibited material removal by spall formation with a spall size proportional to load. At the lower ranges of load, the widths of the scratch for the glass and glass‐ceramic were comparable. However, at the highest values of load tne size of the spall of the glass‐ceramic was significantly less than the size of the spall in the glass.
Effective Transformation Strain in Binary Elastic Composites
Authors: McMeeking Robert M.
Published: March 2005

This communication concerns the strain in a binary elastic composite when one component undergoes a transformation such as a martensitic phase change. The results are significant when the transforming phase has elastic properties which are different from those of the matrix material. The estimates are pertinent to transformation toughening of ceramic composites. Experimental data for transformation toughening are reviewed in the context of the theoretical results.
Stress‐Induced Transformation and Plastic Deformation for Y2O3‐Containing Tetragonal Zirconia Polycrystals
Authors: MATSUI M. , SOMA T. , ODA I.
Published: March 2005

Yttria‐containing tetragonal zirconia polycrystals with low thermal stability showed plastic deformation with a maximum bending strain of 0.8% due to the stress‐induced tetragonal to monoclinic transformation. The strain rate depended on applied stress and temperature. The temperature at which the transformation rate is maximum increases with increasing applied stress. Changes in microstructure and crystallographic structure after plastic deformation were examined by transmission electron microscopy and X‐ray analyses. The mechanism of plastic deformation is discussed in relation to the tetragonal to monoclinic transformation.
Tetragonal Zirconia Polycrystals Reinforced with SiC Whiskers
Authors: CLAUSSEN N. , WEISSKOPF K.‐L. , RüHLE M.
Published: March 2005

The microstructure and the mechanical properties of hot‐pressed tetragonal ZrO2 polycrystals (TZP) reinforced with up to 30 vol% SiC whiskers were studied. The SiC whisker‐TZP composites were stable under the hot‐pressing conditions at 1450°C. Annealing in an oxidizing atmosphere at ∼1000°C resulted in glass formation and microcracking caused by whisker oxidation and transformation of the ZrO2 grains near the whiskers to monoclinic symmetry. The fracture toughness was markedly improved by the dispersed whiskers (∼12 Mpa·m1/2 at 30 vol% SiC) compared to the values measured for the matrix (∼6 Mpa·m1/2). The flexural strength of the hot‐pressed TZP‐30 vol% SiC whisker composite at 1000°C (∼400 MPa) was twice that of the TZP matrix.
Microstructure and Mechanical Properties of Mullite Prepared by the Sol‐Gel Method
Authors: Ismail M. G. M. U. , Nakai Zenjiro , Sōmiya Shigeyuki
Published: March 2005

Mullite (3Al2O3·2SiO2) of stoichiometric composition was prepared by mixing boehmite sol and silica dispersion and gelling at a pH of 3. Complete mullitization takes place at or above 1300°C. Ultrafine mullite powder prepared by calcining gel at 1400°C and attrition milling could be sintered to >98% (theoretical density) at 1650°C for 1.5 h. The flexural strength of the sintered body at room temperature was 405 MPa and 350 MPa at 1300°C. Only traces of a secondary phase were observed along the grain boundary.
Morphology of Tetragonal ZrO2 in a Ternary (Mg,Y)‐PSZ
Authors: LEE RAN‐RONG , HEUER ARTHUR H.
Published: March 2005

The precipitation of tetragonal (t) ZrO2 in a ternary (Mg,Y)‐PSZ has been studied. Nucleation of t‐ZrO2 occurs homogeneously, as in other PSZ's, and coarsened precipitates are multivariant and have an unusual tetrahedral morphology.
Laser‐Driven Pyrolysis: Synthesis of TiO2 from Titanium Isopropoxide
Authors: Rice Gary W.
Published: March 2005

Laser‐driven pyrolysis of the titanium alkoxide Ti(OCHMe2)4 yields TiO2 powder. The pyrolysis can be conducted using the pure alkoxide vapor or by using argon, ethylene, or ethylene| oxygen carrier gases. The powder is principally anatase, but contains some rutile when the pyrolysis is conducted at very high temperatures.
Structural Role of Zinc Oxide in Silica and Soda‐Silica Glasses
Authors: ROSENTHAL ALLAN B. , GAROFALINI STEPHEN H.
Published: March 2005

The structures of amorphous zinc silicate and sodium zinc silicate have been studied using the molecular dynamics computer simulation technique. Results showed that bond lengths and coordination numbers for the individual atomic species fit within the range of results from a number of crystalline and glassy silicates. Discrete ZnO4 tetrahedra were seen to exist to a higher degree in the sodium zinc silicate system due to charge compensation from neighboring sodium atoms. Simulation results are also compared to EXAFS data of low concentrations of zinc oxide in silica and sodium silicate glasses. The local environment of oxygen in the simulated systems is also discussed.
Static and Cyclic Fatigue Behavior of a Sintered Silicon Nitride at Room Temperature
Authors: KAWAKUBO TAKASHI , KOMEYA K.
Published: March 2005

The static and cyclic fatigue behavior of sintered silicon nitride was investigated at room temperature. Flexure specimens, with an indentation‐induced flaw at the center, were tested under a static or cyclic load applied by four‐point bending. Sintered silicon nitride was shown to be susceptible to static and cyclic fatigue failure. Comparing the static and cyclic fatigue lifetimes at frequencies from 0.01 to 10 Hz, it was shown that minimum time to failure was almost the same, in spite of differences in loading mode or frequency. However, cyclic stress decreased the scatter in lifetime by reducing the upper limit. Moreover, the cyclic fatigue limit was significantly lower than the static fatigue limit. High‐magnification fractography revealed a fatigue failure dominated by intergranular cracking with partial transgranular failure at perpendicularly elongated crystals. This suggests that the intergranular fatigue crack can be arrested at grain‐boundary triplets, and also can be reactivated by subsequent cyclic loading. The crack growth rate, calculated from the fatigue lifetime, showed three characteristic regions having a plateau at 70% to 90% of the fracture toughness, which suggests a possible intergranular stress corrosion cracking mechanism resembling that in glass or alumina.
High‐Temperature Characteristics of Transition Al2O3 Powder with Ultrafine Spherical Particles
Authors: Hirayama Tsukasa
Published: March 2005

Ultrafine transition Al2O3 powder with spherical particles was prepared by an arc‐discharge method. High‐temperature characteristics were found to be superior to those of commercial A12O3 powders by DTA, specific surface‐area measurements, XRD, and TEM. The powder studied transformed to α‐phase at about 1335°C. After heat treatment at 1260°C for 1 h, the specific surface area of the powder decreased from 25.0 to 17.3 m2/g. Some particles were able to retain the transition phase even after 106 h at 1160°C.
Direct Measurement of Piezoelectric Strain Using a Diffraction Grating
Authors: YAMAMOTO TAKASHI , KAWASE MASATOSHI , SATO HEIHACHI
Published: March 2005

Piezoelectric strain under a large de electric field, D33 is directly measured by using an electrically controllable diffraction (ECD) grating. The ECD grating consists of a lead lanthanum zirconate titanate piezoelectric ceramic with 65 pairs of grooves having 40‐μm width and 80‐μm period on its surface. The operational principle for the diffraction grating and the procedure for obtaining D33 are described. D33 is measured experimentally with a He‐Ne 3.39‐μm laser, yielding a value of 5.9 × 10−9 m/V under a dc electric field of 1 kV/mm. This value is discussed along with the piezoelectric constant d33 calculated from a conventional electrical resonant method.
Dissolution Kinetics of Crystalline and Amorphous Silica in Hydrofluoric‐Hydrochloric Acid Mixtures
Authors: LIANG DA‐TUNG , READEY DENNIS W.
Published: March 2005

The dissolution kinetics of crystalline and amorphous silica were studied as a function of time, temperature, concentration of HF, concentration of HC1, and crystallographic orientation. The results indicate that dissolution is a surface reaction‐controlled process. The dissolution rate depends strongly on HF concentration and weakly on HC1 concentration. The dissolution rates depend on crystallographic direction in α‐quartz and are slower than for fused silica. The rate‐controlling step is thought to be a ligand exchange process at the surface.
Environmental Effects on the Static Fatigue of Silica Optical Fiber
Authors: MATTHEWSON M. JOHN , KURKJIAN CHARLES R.
Published: March 2005

The static fatigue properties of silica optical fiber are measured in 90°C aqueous environment for various pH s in the range 0 to 14 and for distilled water. The effect of a UV‐curable urethane acrylate protective coating is evaluated by directly comparing coated and bare fiber. It is found that both higher pH and (at long times) the presence of the protective coating increase the fatigue rate. Enhanced fatigue is observed in which the stress corrosion parameter, n, is significantly less than the accepted value of ∼20 measured from short‐term experiments.
Synthesis of the Orthorhombic Phase of 2Y˙ZrO2
Authors: Ohtaka Osamu , Kume Shoichi , Iwami Tsutomu , Urabe Kazunori
Published: March 2005

A mixture of tetragonal and monoclinic 2Y˙ZrO2 (2 mol% Y2O3–ZrO2) powder was treated from 400° to 800°C and from 4 to 7 GPa for 30 min. The products were identified by powder XRD, Raman spectroscopy, and TEM. Results indicated that an orthorhombic phase was synthesized at T=400° to 600°C and P>4 GPa. The lattice parameters were obtained as a=0.505, b=0.525, and c=0.509 nm; the density was 6.17 Mg/m3. The orthorhombic phase always coexisted with the tetragonal phase in the products. The amounts of the tetragonal phase before and after treatment remained largely unchanged, whereas the amount of new orthorhombic phase was nearly the same as the decreased amount of the monoclinic phase. It was assumed, therefore, that only the monoclinic phase transformed into the orthorhombic phase.
Suspension Processing of Al2O3/SiC Whisker Composites
Authors: SACKS MICHAEL D. , LEE HAE‐WEON , ROJAS OSWALDO E.
Published: March 2005

Homogeneous Al2O3 powder/SiC whisker compacts were prepared by suspension processing. By optimizing the conditions for particle/whisker codispersion, castable suspensions could be prepared at total‐solids concentrations 50 vol%. Green bodies with high relative density (∼66% to 70%) were obtained with SiC whisker contents in the range of 5 to 30 vol%. Although densification was severely inhibited by the SiC whiskers, significantly higher sintered densities were obtained by suspension processing compared to dry processing.
Extrinsic OH− Absorption in Transparent Polycrystalline Lanthana‐Doped Yttria
Authors: Wei George C.
Published: March 2005

Transparent lanthana‐doped yttria fabricated by transient solid second‐phase sintering under wet hydrogen typically has a broad absorption band with a peak at 3.08 μm. The absorption band shift observed in samples treated in wet deuterium indicated that the 3.08‐μm absorption was due to OH− ions. The diffusion rates of hydrogen defects in lanthana‐doped yttria were determined in the temperature range from 1000° to 1400°C. The changes in the concentrations of OH− ions upon anneals were determined by measuring infrared absorbance at 3.08 μm. The diffusion coefficient is 1.3 × 10−7, 9.9 × 10−7, and 4.1 × 10−6 cm2/s at 1000°, 1200°, and 1400°C, respectively, with an activation energy of 140 kJ/mol. Annealing in a controlled oxygen partial‐pressure environment can remove the OH− absorption band and bring the total absorption in the 3‐ to 5‐μm range closer to the intrinsic values.
Hydrothermal Preparation of Ultrafine Ferrites and Their Sintering
Authors: Komarneni Sridhar , Fregeau Elizabeth , Breval Else , Roy Rustum
Published: March 2005

Ultrafine and nearly spherical ferrites such as NiFe2O4, ZnFe2O4, NixZn1−xFe2O4, Mn0.5Zn0.5Fe2O4, and CoFe2O4 were prepared under mild hydrothermal conditions by precipitating from metal nitrates with aqueous ammonia. These hydrothermal ferrite powders were shown to sinter to almost theoretical density at 1000°C without any sintering aids.