Separate Structural Elements Research Articles

Fracture of a Circular Disk with Mixed Conditions on the Boundary

A model of a circular disk fracture based on consideration of the fracture process zone near the curvilinear crack tip is suggested. It is considered that mixed boundary conditions are given on the boundary of the disk. It is accepted that the fracture process zone is a finite length layer with a material with partially broken bonds between its separate structural elements (end zone). Analysis of equilibrium limit of the curvilinear crack is performed on the basis of ultimate extension of the material bonds.

Cracking in a circular disk under mixed boundary conditions

A model of cracking in a circular disk with mixed boundary conditions on the boundary is suggested. It is assumed that the cracking process zone is a finite length layer containing a material with partially disturbed bonds between separate structural elements in the plastic flow state at constant stress. Limit equilibrium analysis of the zone of weakened interparticle bonds of the material (prefracture) is performed on the basis of the criterion of critical opening of prefracture zone faces.

Fracture of a composite reinforced by unidirectional fibers

An elastic medium weakened by a periodic system of circular holes filled with homogeneous elastic fibers whose surface is coated with a homogeneous film is considered. A fracture model for a medium with a periodic structure is proposed, which is based on an analysis of the fracture zone near the crack tip. It is assumed that the fracture zone is a layer of finite length containing a material with partially broken bonds between separate structural elements (end zone). The fracture zone is considered as part of the crack. The bonds between crack faces in the end zone are modeled by applying the cohesive forces caused by the presence of bonds to the crack surface. An analysis of the limit equilibrium of shear cracks in the end zone of the model is performed on the basis of a nonlocal fracture criterion together with a force condition for the motion of crack tip and a deformation condition for determining the motion of faces of end-zone cracks. In the analysis, relationships between the cohesive forces and the shear of crack faces are established, the stress state near the crack is assessed with account of external loading, cohesive forces, and fiber arrangement, and the critical external loads as functions of geometric parameters of the composite are determined.

MANUSCRIPT BOOK AS A SOURCE OF RESEARCH: HISTORY OF A CODEX IN THE GDL

When conducting research, it is important for a historian to examine not only the event or object of interest, but all of the decisive circumstances, chronology, places and persons invol­ved as well. It is in order to attain this goal, that sources of information are collected, analysed and in­terpreted. Humanitarian disciplines tend to research manuscripts as material artefacts, literary texts or means of cultural transactions. However, it is not common in Lithuania for manuscripts to be used as a source of research. A manuscript, copied in the 15th century GDL, was chosen to illustrate this statement. The book was sometime later divided into two parts that are now stored separately in the National Library of Russia and the Wroblewski Library of the Lithuanian Academy of Sciences. This article was written in order to determine the history of manuscript book Collection of Sermons by Isaac of Nineveh, while at the same time presenting ways to use manuscripts as a legitimate source in cultu­ral and historical research. The study was carried out by using codicological and comparative methods as well as analysis of literature and archival sources. Detailed codicological descriptions of both books were written. The hypothesis, that the two codices, which were copied by hand at the start of 15th century, are two parts of one exemplar, was proven true on the basis of the results that were obtained. The article contains information about the historical and cultural contexts surrounding the birth of this book. The history of how the codex was copied and stored is reconstructed and the persons invol­ved in the process are discussed in the article as well. The complex research of the dated exemplar reve­als that the manuscript book as well as its separate structural elements and the materials it was made of can be used as a source of information for research in at least several scientific disciplines such as history, literature and bibliography. The codex itself could be considered as an interdisciplinary source of research. The postscript, which remained in the codex, contains two colophons and the Praise for Witold. This text is published at the end of the article in its original orthography.

Asp433 in the closing gate of ASIC1 determines stability of the open state without changing properties of the selectivity filter or Ca2+ block

A constriction formed by the crossing of the second transmembrane domains of ASIC1, residues G432 to G436, forms the narrowest segment of the pore in the crystal structure of chicken ASIC1, presumably in the desensitized state, suggesting that it constitutes the “desensitization gate” and the “selectivity filter.” Residues Gly-432 and Asp-433 occlude the pore, preventing the passage of ions from the extracellular side. Here, we examined the role of Asp-433 and Gly-432 in channel kinetics, ion selectivity, conductance, and Ca2+ block in lamprey ASIC1 that is a channel with little intrinsic desensitization in the pH range of maximal activity, pH 7.0. The results show that the duration of open times depends on residue 433, with Asp supporting the longest openings followed by Glu, Gln, or Asn, whereas other residues keep the channel closed. This is consistent with residue Asp-433 forming the pore’s closing gate and the properties of the side chain either stabilizing (hydrophobic amino acids) or destabilizing (Asp) the gate. The data also show residue 432 influencing the duration of openings, but here only Gly and Ala support long openings, whereas all other residues keep channels closed. The negative charge of Asp-433 was not required for block of the open pore by Ca2+ or for determining ion selectivity and unitary conductance. We conclude that the conserved residue Asp-433 forms the closing gate of the pore and thereby determines the duration of individual openings while desensitization, defined as the permanent closure of all or a fraction of channels by the continual presence of H+, modulates the on or off position of the closing gate. The latter effect depends on less conserved regions of the channel, such as TM1 and the extracellular domain. The constriction made by Asp-433 and Gly-432 does not select for ions in the open conformation, implying that the closing gate and selectivity filter are separate structural elements in the ion pathway of ASIC1. The results also predict a significantly different conformation of TM2 in the open state that relieves the constriction made by TM2, allowing the passage of ions unimpeded by the side chain of Asp-433.

Application of borehole optical televiewing to investigating the 3-D structure of glaciers: implications for the formation of longitudinal debris ridges, midre Lovénbreen, Svalbard

AbstractDigital optical televiewing (OPTV) of hot-water-drilled boreholes is evaluated as a technique for the investigation of englacial ice and debris structures on the basis of six boreholes drilled in the terminus region of midre Lovénbreen, Svalbard. The resulting OPTV logs successfully reveal several visually distinctive englacial ice properties and deformation structures (e.g. oblique englacial fractures imaged here for the first time). Combining these OPTV logs with surface mapping has resulted in the identification of eight separate structural elements, several of which can be interpolated onto 3-D grids at a node spacing of 1 m vertically and 10 m horizontally. Basally derived englacial sediment layers are also found to be intercalated with primary stratification, elevated into near-vertical planes around a central fold axis by large-scale lateral folding. The analysis also allows supraglacial longitudinal debris ridges to be subclassified into two types: a previously described (type-I) form, which are the exposed fold axes of large-scale lateral folds, and a new (type-II) form experiencing secondary deformation by small-scale horizontal folding in association with vertical displacements across arcuate shear planes in response to longitudinally compressive stresses near the glacier terminus. Although using boreholes to investigate glacier structure is limited (e.g. by parallelism with vertical planes), applying OPTV to multiple boreholes at midre Lovénbreen has successfully revealed a range of 3-D structural elements at high spatial resolution. As such, interpolating between multiple OPTV logs overcomes many of the problems associated with interpretations made solely on the basis of surface-based structural mapping, and combining the two techniques represents a powerful glaciological tool.

The stabilization of nanodisperse silver in a sulfo cation exchanger

Silver-ion exchanger (electron ion exchanger, EI) composites with equivalent silver and hydrogen counterion contents were prepared by chemical deposition. Microscopic and X-ray data showed that silver nanoparticles and their ensembles isolated from each other and stabilized by a polymeric matrix were formed. Contact of Ag0-EI in the H+ form with solutions of silver salts caused the occurrence of two processes, ion exchange and metal recrystallization. These processes were interrelated because they involved one common particle, the silver counterion. Recrystallization proceeded by the electron-ion mechanism, but, because of matrix isolation of silver particles, electron transfer occurred inside separate structural elements (ensembles of particles) rather than over the whole composite volume. The transfer of silver ions largely occurred over ionogenic matrix centers, which substantially decreased their mobility. The low electronic conductivity of the composite and limited mobility of counterions were charge stabilization factors, which hindered recrystallization and, along with matrix stabilization, contributed to the retention of nanosized silver particles.

Deformability of hierarchic cable roof

The hierarchic structure is formed by the negative Gaussian curvature type saddle-shaped cable roofs by suspending separate roof’s corners to a higher level cable structure. These systems can be inter-combined to form wider roof areas. In order to reduce the complexity and the amount of calculation, and to avoid a calculation matrix convergence problem, calculation of stresses and displacements of complicated hierarchically subordinated structures with various geometrical parameters of a hierarchic roof could be accomplished by the sub-structuring method. The effect of interdependencies of separate structural elements and a higher level cable structure can be determined by the iterative approximation method. The following structural possibilities to decrease the deformability of a hierarchic cable roof were considered: increase in cable’s stiffness and decrease in cable’s dead weight. Steel and hybrid composite cable with increased specific strength used on the base of carbon fiber reinforced plastic (CFRP), glass fiber reinforced plastic (GFRP), Liquid Crystal Polymer (LCP) Vectra and steel were considered as materials of hierarchic cable structure. It was stated that increase in cable’s stiffness at tension has the most significant influence upon the deformability of hierarchic cable roof.

Targeting and Assembly of Rat Mitochondrial Translocase of Outer Membrane 22 (TOM22) into the TOM Complex

Tom22 is a preprotein receptor and organizer of the mitochondrial outer membrane translocase complex (TOM complex). Rat Tom22 (rTOM22) is a 142-residue protein, embedded in the outer membrane through the internal transmembrane domain (TMD) with 82 N-terminal residues in the cytosol and 41 C-terminal residues in the intermembrane space. We analyzed the signals that target rTOM22 to the mitochondrial outer membrane and assembly into the TOM complex in cultured mammalian cells. Deletions or mutations were systematically introduced into the molecule, and the intracellular localization of the mutant constructs in HeLa cells was examined by confocal microscopy and cell fractionation. Their assembly into the TOM complex was also examined using blue native gel electrophoresis. These experiments revealed three separate structural elements: a cytoplasmic 10-residue segment with an acidic alpha-helical structure located 30 residues upstream of the TMD (the import sequence), TMD with an appropriate hydrophobicity, and a 20-residue C-terminal segment located 22 residues downstream of the TMD (C-tail signal). The import sequence and TMD were both essential for targeting and integration into the TOM complex, whereas the C-tail signal affected the import efficiency. The import sequence combined with foreign TMD functioned as a mitochondrial targeting and anchor signal but failed to integrate the construct into the TOM complex. Thus, the mitochondrial-targeting and TOM integration signal could be discriminated. A yeast two-hybrid assay revealed that the import sequence interacted with two intramolecular elements, the TMD and C-tail signal, and that it also interacted with the import receptor Tom20.

Local stochastic analysis of microcracking and non-elastic behavior of ceramics

A failure model is considered and applied to n-phase brittle materials such as ceramics. Non-elastic behavior of ceramics is considered as a stochastic process that involves cracking of separate structural elements. Application is made to single-phase ceramic with various statistical distributions of the grain sizes. Use is made of an effective continuum and a statistical description of the failure process. The theoretical calculations agree with data obtained from acoustic emission.

Microstructural engineering of ceramic-matrix layered composites: Effect of grain-size dispersion on single-phase ceramic strength

A failure model is considered which can be applied to n-phase brittle materials (in particular to ceramics). The authors attempt to solve a physical problem of the description of failure of a micro-inhomogeneous solid as stochastic process of the cracking of separate structural elements. The particular model is executed for n=1 (case of single-phase ceramics) and is applied for the description of the mechanical behaviour of single-phase ceramic layers with various statistical distributions of the grains sizes. An effective continuum and a statistical description of the failure process is used. There are four stages in the process. The first stage is loading without microcracking and the second stage is a stable non-localized microcracking before maximum stress. The third stage is a stable localized microcracking after stress maximum and the fourth stage is an unstable (catastrophic) fracture. The trends of the theoretical calculations agree with data obtained from acoustic emission studies.

THE USE OF SHOCK TRANSMISSION UNITS IN BRIDGING.

Keywords W S ATKINS, COLEBRAND BRIDGES, BRIDGING, SHOCKS, TRANSMISSION, UNITS, MECHANISMS, LINK, STRUCTURES, STRUCTURAL, ELEMENTS, DECKS, SUPPORTS, IMPACT, LOADING, LOADS, STRENGTHENING, MOVEMENT, FORCES, DESIGN, MANUFACTURE, SUBSTRUCTURES, MULTI SPAN, EARTHQUAKES, ZONES, CONSTRUCTION, CONTINUOUS, VIADUCTS... Show All

Simulation of the physical effects of the interaction of molten fuel with the coolant

The method proposed makes it possible to obtain computational estimates of the intensity of a steam explosion inside a reactor vessel and in the space below the reactor inside the melt trap. The computational investigations of the intensity of a steam explosion inside a VVER vessel in the most likely scenario of a serious accident with efflux of melt into the bottom pressurized chamber show that under certain conditions a high pressure capable of destroying separate structural elements can develop.

The determinants for Sm protein binding to Xenopus U1 and U5 snRNAs are complex and non-identical.

The Sm binding sites of different spliceosomal U small nuclear RNAs (snRNAs), the RNA structural elements required for interaction with common snRNP proteins, have been considered to be similar or identical. Here we show that this is not the case. Instead, structural and sequence features unique to U1 or U5 snRNAs that contribute to common protein binding are identified. The determinants of Sm protein binding in both RNAs are complex, consisting in U5 of minimally two and in U1 of minimally four separate structural elements. Even the most conserved features of the two RNAs, single-stranded regions whose generalized sequence is PuA(U)nGPu, are not functionally interchangeable in protein binding. At least one of the newly defined RNA elements functions in assembly with the common proteins, but is not required for their stable binding thereafter. U1, but not U5, snRNP requires a trimethyl guanosine cap structure for its transport to the nucleus. This is not a consequence of the differences in common snRNP binding to the two RNAs, but is due to structural features of U1 RNA that do not contribute to Sm protein binding.

An algorithm for comparing RNA secondary structures and searching for similar substructures

To access the functional informations carried by RNA molecules at the level of their secondary structure interactions, we propose a comparison method based on a tree edit algorithm which takes into account the tree structure of RNA foldings. Any secondary structure is translated into a tree involving all its elementary substructures; then a shorter condensed tree is built in which any unbranched helix interspersed with bulges and interior loops is taken as a single node. This method includes several parameters: a comparison matrix between structural units, gap penalties, and the scoring between nodes of the condensed trees. Their effects have been analysed using as a model a rapidly divergent domain of the large ribosomal RNA, for which structural variation during evolution is well known. This method allows one to recognize precisely, in large target molecules, definite substructures that present with the query molecules only a limited set of closely related secondary structure features; it is still efficient if intervening features, which can correspond to insertion/deletion of entire stem regions, separate such structural elements. When coupled with a hierarchical clustering algorithm, this method is suitable for classifying RNA molecules according to their secondary structure homologies.

The sites of neurotoxicity in alpha-cobratoxin.

We have chemically modified groups of amino acids in the sequence of alpha-cobratoxin and have studied the derivatives as to their affinity of binding to the acetylcholine receptor protein from Torpedo marmorata. (i) The toxin derivatives which were fully modified at lysine (penta-epsilon-N,N-dimethyl lysine; penta-epsilon-N-acetyl lysine), arginine (penta-N7,N8-(1,2-dihydroxycyclohex-1,2-ylene arginine), and tyrosine (mononitrotyrosine) all had significant remaining toxicity and affinity of binding. (ii) The "extra" disulfide of alpha-cobratoxin was selectively reduced and alkylated. Depending on the charge, size, and hydrophobicity of the attached groups, derivatives were obtained that bound to the acetylcholine receptor with higher (di-S-carboxyamidomethyl), about equal (di-S-pyridylethyl), or lower (di-iodoacetaminoethylnaphthylamine-5-sulfonic acid) affinity than the unmodified toxin. (iii) A fully reduced and carbamidomethylated derivative of alpha-cobratoxin obtained by repeating the procedure for selective reduction six times still bound with appreciable affinity (KD approximately 3 X 10(-6) M) to the acetylcholine receptor. We conclude that neither a single positively charged residue nor tyrosine nor the integrity of the disulfides is absolutely essential for toxicity. Furthermore, the single tyrosine and the area around the extra disulfide do not participate in the binding to the receptor. Together with previous findings on this interaction, this suggests a multipoint attachment of toxin and receptor involving several locally separate structural elements of the toxin.

The morphology of polypropylene granules and its link with the titanium trichloride texture

The morphology of polypropylene granules forming directly in the polymerization process was studied by scanning electron microscopy, and by adsorption and mercury-porometric methods. Separate structural elements were isolated which consisted of the polypropylene granules and a link was established between these and the structural elements of the catylast particles. A mechanism of formation of such granules has been established on the basis of the findings; it is suggested that the granules form on the internal surfaces of the porous catalyst.