Chromosome structure inside the nucleus

Recent in situ three-dimensional structural studies have provided a new model for the 30 nm chromatin fiber. In addition, research during the past year has revealed some of the molecular complexity of non-histone chromosomal proteins. Still to come is the unification of molecular insights with chromosomal architecture.     

On the structure and composition of Kelex 100

Since 1976, the manufacturing process for Kelex 100 (Registered trade name of Sherex Chemical Co., Dublin, Ohio) has been changed. The major constituents of post-1976 Kelex 100 have been identified by gas-liquid chromatography, mass spectrometry and infra-red spectroscopy.     

DNA structure properties and phospholipid composition of Salmonella derby

The properties of DNA structure and the phospholipid content of Salmonella derby cells were studied with respect to their plasmid content and radiosensitivity. The role of R-plasmid in determining the qualitative and quantitative compositions of S. derby phospholipids was revealed. The radiosensitivity of plasmid-carrying S. derby mutants was shown to be most likely determined by the structure of DNA, its GC content, and the level of methylation. We suggest that the phospholipid molecules and their interaction with DNA play a key role in formation of the radio-resistance of plasmid-free S. derby cells.     

The composition and structure of chromite during reduction with carbon

Examination of grains of chromite, subjected to varying degrees of reduction by heating chromite-graphite mixtures, using a scanning electron microscope and electronprobe microanalyser. Initially reduction of iron from chromite to form metallic iron, with a small chromium content, at the surface. Iron diffusion from within the grains to the surface with continued reduction and contraction of the core of unaltered chromite. Reduction of chromium as the main reaction when the core has disappeared and observation of a second skrinking core, this time of chromium. Increase of the chromium content of the metal phase and forming of the carbide (Cr, Fe)₇C₃ during this period. Reduction within the grains when the chromium core has disappeared. MgAl₂O₄ containing up to 6 percent chromium as final residue of the original chromite for the experimental conditions.     

Influence of pellet composition and structure on carbothermic reduction of silica

The melting zone in a cupola has temperatures greater than 1773 K and a reducing atmosphere. This condition is suitable for the carbothermic reduction of silica. The key to the applicability of carbothermic reduction of silica for ferroalloy production is rapid in situ production of SiC and its subsequent dissolution in the hot metal. The main objective of this investigation was to study the kinetics of the carbothermic reduction process and determine the optimum parameters for rapid and complete in situ conversion of silica to SiC. At temperatures above 1773 K, the key reactions in the carbothermic reduction process are (1) SiO₂ (s)+CO (g)=SiO (g)+CO₂ (g), (2) SiO (g)+2C (s)=SiC (s)+CO (g), (3) C (s)+CO₂ (g)=2CO (g). To meet the objective of this study, conditions must be such that the surface reactions occurring at the carbon and silica surfaces are rate limiting and the entire silica is converted to SiC. Pellet composition and structure in terms of carbon to silica ratio, their particle sizes, and compaction pressure that ensure surface reaction is rate controlling were determined. The gas-solid reaction kinetics was mathematically modeled in terms of the process parameters. The reaction kinetics improved by reducing both carbon and silica particle sizes. However, below a certain critical particle size, there was no significant improvement in the reaction kinetics. For complete conversion of SiO₂ (s) to SiC (s), excess carbon and critical porosity are necessary to ensure that the entire SiO (g) generated by Reaction [1] is consumed via Reaction [2] within the pellet.     

The composition and structure of depressive symptomatology in renal disease.

Renal disease is an increasingly common illness among middle-aged and older adults, and is often associated with depression. The Center for Epidemiologic Studies Depression Scale (CES–D) is a widely used self-report screening measure on which responses generally conform to a 4-factor structure, with each factor loading onto a higher-order Depression factor. The current study examines whether this structure is supported among individuals with renal disease (both predialysis and posttransplant kidney disease patients). Persons with renal disease (n = 225) and healthy control participants (n = 230) were recruited from Vancouver General Hospital and the community. Participants completed the CES–D as part of an extended assessment. Confirmatory factor analytic models were computed for the renal disease and healthy control groups. Results support a 4-factor structure for CES–D responses in persons with renal disease and healthy controls. The hierarchical structure of CES–D responses also appears invariant between groups. Factor structure was similar between groups; only for Depressive Affect was the strength of association with the second-order factor greater among the renal disease than healthy control participants. Findings support similarity of CES–D factor structures between patients with renal disease and healthy individuals. Results suggest that the CES–D's 4 factors contribute to measurement of a higher-order Depression factor in both groups; furthermore, 3 of 4 factors appear invariant between groups. As such, this measure can be used confidently to quantify depressive symptoms in individuals with renal disease. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Secondary structure composition and pH-dependent conformational changes of soluble recombinant HLA-DM

HLA-DM catalyzes the release of invariant chain fragments from newly synthesized major histocompatibility complex (MHC) class II molecules, stabilizes empty class II molecules, and edits class II-associated peptides by preferentially releasing those that are loosely bound. The ability of HLA-DM to carry out these functions in vitro is pH dependent, with an optimum at pH 4.5-5.5 and poor activity at pH 7. The structural basis for these properties of HLA-DM is unknown. Sequence homology suggests that HLA-DM resembles classical, peptide-binding MHC class II molecules. In this study, we examined whether HLA-DM has a secondary structure composition consistent with an MHC fold and whether HLA-DM changes conformation between pH 5 and pH 7. Far-UV circular dichroism (CD) spectra of recombinant soluble HLA-DM (sDM) indicate that HLA-DM belongs to the alpha/beta class of proteins and structurally resembles both MHC class I and class II molecules. The CD peak around 198 nm increases upon going from neutral to endosomal pH and drops sharply upon denaturation below pH 3.5, distinguishing at least three states of sDM: the denatured state and two highly similar folded states. Fluorescence emission spectra show a slight blue-shift and a approximately 20% drop in intensity at pH 5 compared with pH 7. Unfolding experiments using guanidinium chloride show that the stability of sDM is somewhat reduced but not lost at pH 5. These results indicate that sDM undergoes a pH-dependent conformational change between neutral and endosomal pH. The change seems to involve both hydrogen bonding patterns and the hydrophobic core of sDM and may contribute to the pH dependence of DM activity.     

Effects on composite composition and structure from compound loading during hot pressing

Translated from Poroshkovaya Metallurgiya, No. 5(341), pp. 1–4, May, 1991.     

Cell-wall composition and structure of yeast cells and conjugation tubes of Tremella mesenterica

Cell walls prepared from vegetative yeast cells and from hormone-induced conjugation tubes of the basidiomycete Tremella mesenterica had similar compositions. Evidence was found for 1,3-alpha-glucan (yeast 38%, tube 25%), 1,3-beta-1,6-beta-glucan (yeast 33%, tube 48%) and chitin (both less than 3%) in the walls. The walls also contained xylose (5 to 7%), mannose (6%), glucuronic acid (approx. 2%), and traces of galactose. Protein amounted to less than 2% of the wall weight. The cell capsule was very insoluble and could not be removed from the cell wall. The conjugation hormone did not appear to exert its effect on cell shape by causing gross changes in wall composition.     

Effect of annealing on the composition and structure of TiC and TaC powders

Conclusions The least deviations of the compositions of TiC and TaC from stoichiometric are caused by annealing specimens in graphite crucibles in a pure argon atmosphere. In our work it proved impossible to obtain specimens of precisely stoichiometric composition. A dominant influence on the recrystallization of titanium and tantalum carbides is exerted by the decarburization and lattice defect formation processes. X-ray diffraction and scanning electron microscopical investigations have revealed the existence of substantial differences b tween the structural changes occurring in TiC during high-temperature treatment and in metals during recrystallization. In the process under consideration the following stages may be distinguished: decarburization of the carbide, accompanied by the appearance of lattice distortions; progressive mosaic block disorientation linked with growth in stress of the second kind, followed by fragmentation of large crystals; recovery in the fragmented crystals.Translated from Poroshkovaya Metallurgiya, No. 11(203), pp. 99–105, November, 1979.     

Investigation into the structure and phase composition of powder aluminum-phosphorus master alloys

Powder aluminum-phosphorus master alloys for modifying hypereutectic silumins are developed. Optimal treatment modes of powder mixtures in a high-energy planetary mill which give minimal losses of the starting material and the microstructure with the uniform and dispersed distribution of particles of excess phases in the aluminum matrix are selected. The phase composition of formed master alloys is investigated by electron probe microanalysis. The high efficiency of modifying the hypereutectic silumin Al-17 wt % Si by introducing phosphorus (0.008 wt %) using fabricated master alloys is shown.     

Charging composition and structure optimisation in the sintering process (Part I)

In this paper, an optimisation system for charging composition and structure in the sintering process was established in order to reduce the sinter cost in the ironmaking process. The system comprised four modules: sinter metallurgical performance testing and analysis, sintering burdening design and optimisation, sintering matching calculation, and sinter component and property prediction. The data for the first module came from actual production values of a steelworks and from testing in the laboratory. Based on material balance theory, the second module used a linear programming method to optimise sinter cost, quality and quantity. The third module was built to predict the sintering production data. The fourth module can be used to predict some composition and properties of the sinter based on a Back-Propagation neural network. The system integrated all of these modules using Visual Basic and MATLAB. As the result, the optimum charging composition and structure of sinter which satisfies all constraint conditions can be obtained. Compared with traditional production testing and hand calculation in the sintering process the system can reduce the sinter cost and greatly decrease the production risk. Industrial application proves that the system is very useful and efficient in reducing sinter cost while ensuring output quantity and quality.     

Change in composition and structure of chromium-carbonitride nanopowder on storage and heating in gases

The changes in composition and structure of chromium-carbonitride nanopowder on storage and heating in gases are investigated. On annealing in argon and nitrogen at 1273–1373 K, the carbonitride is converted to nitride Cr₃C₂; on annealing in hydrogen, the carbide Cr₇C₃ is produced. The conversion to Cr₃C₂ is accompanied by enlargement of the nanopowder as a result of solid-phase coalescence. The interaction of carbonitride with atmospheric gases (oxygen and water vapor), which involves adsorption and diffusion, is accompanied by considerable increase in oxidation within the first 24 h. The temperature at which oxidation begins in air depends on the size of the nanoparticles: it rises from 542 to 568 K with increase in size from 22 to 53 nm. The dependence of the degree of oxidation and the temperature at which oxidation begins on the particle size is determined.     

The composition,structure, and properties of calcium-hydride powder of titanium carbide

The technology of obtaining titanium carbide powders by reduction-carbidization of titanium dioxide with calcium hydride and carbide at temperatures up to 1200°C is developed. The dispersity of the TiC particles is determined by thermal desorption and scanning electron microscopy: the average size of crystals is no larger than 1 μm. It is revealed by the methods of coulometry and energy dispersive spectrometry that calcium-hydride titanium carbide is characterized by a high content of bound carbon and a low content (0.01–0.03 wt %) of free carbon. It is established by X-ray structural analysis and transmission electron microscopy that TiC particles are uniform (their composition is close to stoichiometric TiC_1.0) and are single crystals. The investigation of the structure and properties of hard alloys of the compositions 60% TiC + 29.6% Ni + 10.4% Mo and 72% TiC + 18.3% Ni and 9.7% Mo, which were obtained on the basis of calcium-hydride titanium carbide powders, showed that they completely satisfy the requirements to tungsten-free hard alloys.