Adjacent Networks Research Articles

Surface dynamics of polydimethylsiloxane rubber

The surfaces of polydimethylsiloxane (PDMS) RTV rubber display macroscopic and microscopic (as detected in the atomic force microscope) morphological changes, when heated to 250–280°C, in the presence of air. The separation between adjoining PDMS film surfaces disappears in the same temperature range and the film pieces are effectively soldered, as verified by scanning electron microscopy and by mechanical testing. Mechanical failure of films joined by soldering is cohesive or interfacial, depending on the extent of film ageing, during film preparation. These results are interpreted by considering that PDMS network chains undergo scission, at the above temperatures. As a result, reactive chain segments can migrate at the rubber surface and across the rubber-rubber interface; their recombination forms a new network, from two adjacent networks.

Extracellular matrix arrangement in the papillary muscles of the adult rat heart. Alterations after doxorubicin administration and experimental hypertension.

In the present study, we analyzed the components of the extracellular matrix (ECM) and its arrangement at the level of the papillary muscles in the adult rat heart using light and transmission and scanning electron microscopy techniques. Our results reveal that after a single dose (6 mg/kg) of dexorubicin to cause a significant decrease and disorganization of the endomysium and perimysium in the first week after injection, affecting the endomysial struts and perimysial strands. Degenerating myocytes and alterations of the coiled perimysial fibers were characteristic 4 weeks after treatment. After 8 weeks, ultrastructural alterations at the level of the plasma membrane of the myocytes and adjacent collagen network were present in the tip of the papillary muscles. These alterations may be responsible for the inefficiency of the valvular apparatus as an initial factor implicated in doxorubicin-induced congestive heart failure. Experimental hypertension, produced by constriction of the abdominal aorta, induced hypertrophy of the left ventricle, with increased perimysium and endomysium of the ECM at the level of the papillary muscles 4 weeks after aortic banding. Interstitial and perivascular fibrosis were observed 8 weeks after surgical treatment, and macrophages around the degenerating myocytes were characteristic 16 weeks after treatment. These alterations of the ECM network have been correlated with their possible implication in ventricular biomechanical properties.

Cell and oxygen flow in arterioles controlling capillary perfusion.

Measurements of hemodynamic and oxygen transport characteristics in the arterioles that control capillary perfusion in striated muscle were used to compare oxygen flow into adjacent capillary networks. Observations were made in arterioles arising consecutively (branches 1-3 and the last branch) from a single transverse arteriole. During maximal dilation [after 5 min of exposure to superfusate with 10(-4) M adenosine (ADO)], mean cell flow into branches decreased significantly with increasing axial distance along the transverse arteriole, from 8.47 +/- 2.43 x 10(3) (SE) cells/s in branch 1 to 5.56 +/- 2.14 x 10(3), 3.21 +/- 1.30 x 10(3), and 4.00 +/- 1.33 x 10(3) cells/s in successive branches. During control, cell fluxes were not significantly different by position (2.21 +/- 1.12, 1.31 +/- 0.42, 0.97 +/- 0.31, and 1.23 +/- 0.40 cells/s in branches 1, 2, and 3 and the last branch, respectively). Branch diameters during ADO were not significantly different by position (26.2 +/- 2.9, 24.5 +/- 1.4, 22.0 +/- 2.8, and 26.7 +/- 2.7 microns, respectively). Hemoglobin saturations during ADO were not different (59.6 +/- 2.2, 60.6 +/- 2.3, 60.3 +/- 2.3, and 61.0 +/- 2.3%, respectively), whereas mean oxygen flow into branch 1 significantly exceeded that into branches 2 and 3 and the last branch (1.40 +/- 0.40 vs. 0.60 +/- 0.17, 0.53 +/- 0.22, and 0.66 +/- 0.22 pl/min, respectively). During control, oxygen flows were not significantly different between branches. Thus, both cell and oxygen flow into these arterioles vary in a systematic way dependent on their relative branch position; regulatory processes serve to make oxygen supply more uniform.

Localization of ribosomal DNA in Rhagoletis pomonella (Diptera: Tephritidae) by in situ hybridization.

The ribosomal DNA (rDNA) of Rhagoletis pomonella was localized within both salivary gland polytene chromosomes and somatic cell mitotic chromosomes by in situ hybridization using the heterospecific Drosophila melanogaster rDNA clone, Dm238. In situ hybridization analysis of polytene nuclei showed that R. pomonella rDNA is located in the nucleolus and adjacent granular network of chromosome 1. The site of origin of rDNA is within this isomorphic granular network. The preservation of nucleolar ultrastructure in some polytene chromosome preparations allowed light microscope localization of R. pomonella rDNA to the apparent periphery of fibrillar centres within fibrillar complexes. In somatic cell nuclei, DM238 hybridized to the nucleolus organizing region (NOR) located on chromosome 1 at the site of the secondary constriction. The frequency distribution of heteromorphisms for rDNA content, differential appearance of secondary constrictions, non-pairing of the NOR and differences in homologue lengths suggests that the structural differentiation of this region in chromosome 1 is sex linked. This the first published description of the salivary gland polytene chromosomes from R. pomonella, and we include a tentative karyotype description, polytene chromosome maps and comments on their suitability for banding and molecular analysis.

Identification of the epiplasmins, a new set of cortical proteins of the membrane cytoskeleton in Paramecium

ABSTRACT In most ciliates, the epiplasm, a superficial cytoskeletal layer of variable thickness, both surrounds basal bodies and interacts tightly with adjacent membrane networks; it constitutes the predominant structure in Paramecium cell ghosts. Previous indirect data suggested several cortical proteins as potential constituents of the epiplasm. New sharp monoclonal antibodies presented in this paper, positive both on immunotransfers and in immunocytochemical tests carried out on permeabilized cells and ultrathin sections, definitively identify the epiplasmins: a set of about twenty protein bands ranging from 45 to 33 kDa and making up the bulk of the epiplasmic layer. The complete epiplasmin pattern characterized from gradient-purified cortex is also present in unfractionated whole cells, confirming that the pattern is not generated artifactually. Comparative one-step extractions, performed either in 1 M KI or in 4 M urea, solubilize the epiplasmins as a whole, indicating that all of them share very similar biochemical properties. Two-dimensional electrophoresis shows the great complexity of this epiplasmin group. Epiplasmin solu-bilization properties are discussed with respect to other models of membrane-cytoskeleton interaction developed among protists and metazoans and also to intermediate filaments, specially lamins. Immunofluorescent labelling combined with confocal microscopy permits a more detailed study of epiplasm formation at the level of the fission furrow, with new insights into two successive steps of epiplasm growth. A first series of interspecific reactions has been carried out with one of the anti-epiplasmin antibodies, yielding results which are discussed in an evolutionary framework.

The fracture behavior of a directionally solidified FeCrMnC superalloy

The fracture behavior of a directionally solidified alloy, containing Fe-15Cr-15Mn-2Mo-1.5C-1Si-1Nb (where the composition is in weight per cent), has been investigated in both transverse and longitudinal orientations at room temperature in laboratory air. The directional solidification (DS) process resulted in an aligned polycrystal, with individual grains sharing a common (001) zone axis, and a network of interdendritic chromium-rich M 7C 3 blocky carbides and niobium-rich MC script carbides. A heat treatment, which simulates the brazing cycle used to assemble the heater heads found in prototype automotive Stirling engines, was applied to all specimens prior to the fracture experiments. Interestingly and unexpectedly, the specimens which were oriented with the crack propagation plane parallel to the DS direction, identified as the transverse orientation (T-L), exhibited a toughness value which was twice that of the orientation in which the crack propagated perpendicular to the DS direction, the longitudinal orientation (L-T). For the T-L orientation, the fracture path was observed to progress through the dendrite cores, resulting in a significant amount of plastic deformation and energy absorption during the fracture process. Extensive crack bifurcation and tortuosity constituted another mechanism by which the toughness was increased for the T-L orientation. For the L-T orientation, fracture proceeded in a brittle cleavage fashion, with the propagating crack passing predominantly through the less tough interdendritic carbide network and tearing through the f.c.c. matrix only as it traversed between adjacent carbide networks.

The twisted skeleton of 1,9-diaminononane incatena-[catena-,?-(1,9-diaminononane)cadmium(II) tetra-? -cyanonickelate(II)]-o-xylene(2/1)

The Hofmann-danon-typeo-xylene clathrate Cd[NH2(CH2)9NH2]Ni(CN)4·0.5(CH3)2C6H4, crystallizes in the triclinic space groupPĪ witha = 15.118(3),b = 14.048(4),c = 7.325(1) A, α = 91.50(2), β = 131.66(3), and γ = 107.50(2)°,V = 1051(1) A3 andZ = 2. The structure, refined toR = 0.047 using 2851 reflections, reveals a three-dimensional host framework built of the layers of a two-dimensionalcatena-[cadmium tetra-μ-cyanonickelate(Il)] network and of the ambidentate 1,9-diaminononane (danon) bridging the Cd atoms in adjacent networks. The guesto-xylene molecule is accommodated in the cavity formed in the interlayer space similar to that in the Hofmann-daotn-type. The skeleton of the danon in the Cd-NC9N-Cd linkage takes a (gauche)2(trans)8 conformation twisted at the (gauche)2 part in contrast with the all-trans conformation of 1,8-diaminononane in the Hofmann-daotn-type clathrate. The twisted (gauche)2 part of the danon skeleton occupies the interlayer space to such an extent that void space available for the guest o-xylene molecule decreases to half that in the Hofmann-daotn-type clathrate Cd[NH2(CH2)8NH2]Ni(CN)4·G.

Microvasculature of the Thyroid Gland in the Common Tree Shrew (<i>Tupaia glis</i>): Microvascular Corrosion Cast/Scanning Electron Microscopy Study

A thyroid vascular cast of the common tree shrew (Tupaia glis) was obtained by injection of Batson's No. 17 plastic mixture into the ascending aorta. The cast was studied under the scanning electron microscope. It was found that each half of the gland is supplied by a large superior and a rather small inferior thyroid artery. After plunging into the gland, the arteries divide into smaller branches that are the interlobular, intralobular and follicular arteries (afferent vessels). The basket-like capillaries arising from the follicular arteries and encapsulating thyroid follicles are of large diameter and are arranged in a single layer. The follicular side of the capillary casts was observed to contain numerous small and some large projecting knobs compatible with the presence of fenestrations in the endothelial cells. On the other hand, endothelial nuclear imprints were found mainly on the stromal surface of the follicular capillary casts. Transfollicular capillaries connecting the adjacent follicular capillary networks were also observed. Blood from the follicular capillaries either drains into the follicular veins (efferent vessels) or abruptly drains into the intralobular veins before proceeding to intralobular and interlobular veins, respectively. The interlobular veins are collected into a few small superior, a few larger middle and a few even larger inferior thyroid veins. These veins drain directly into the laryngeal vein lying adjacent to the deep surface of the thyroid gland before joining the jugular vein. Venous valves were identified outside the thyroid gland. In addition, the glomerular capillary island of the parathyroid gland was often seen at the cranioanterolateral and sometimes at the cranioposterolateral aspect of the thyroid gland.

Catena-μ-(1,9-Diaminononane)cadmium(II) Array in the Crystal Structure of catena-[Bis-catena-μ-(1,9-diaminononane)cadmium(II) cis-Di-μ-cyano-dicyanonickelate(II)]-(2,4-Xylidine) (1/2) Different from That in the 2,3-Isomer Analog

Abstract In a novel three-dimensional host framework of the title inclusion compound the ambidentate 1,9-diaminononane (danon) makes a two-dimensional catena-μ-network with Cd atoms in contrast with the catena-bis-μ-danon double-1D chain structure in the 2,3-xylidine analog. The 3D framework of the metal-complex host is accomplished by catena-μ-dicyano linkage of –NCNi(CN)2CN– between adjacent networks.

Vascular changes in peripheral corneal destructive disease

A clinical classification of peripheral corneal destructive disease is presented. These syndromes all start within 2 mm of the limbus and are accompanied by varying degrees of vaso-occlusion of the adjacent limbal vascular networks. Close observation of the configuration, integrity and pattern of the limbal vessels can indicate whether the disease is active, quiescent or brought under control with treatment.

The blood vascular architecture of the rat thyroid gland: A scanning electron microscope study of corrosion casts.

The blood vascular bed of the rat thyroid gland was reproduced by injection of a methacrylate casting medium and observed with a scanning electron microscope. The rat thyroid gland received the superior and inferior thyroid arteries and emitted the superior and inferior thyroid veins. Anastomosis between the interlobular arteries or between the interlobular veins was frequently observed in the thyroid gland. The arteriovenous anastomosis was rarely observed between the terminal branches of the lobular arteries and veins. The thyroid blood vascular bed was divided into lobular units which consisted of basket-like capillary networks surrounding the thyroid follicles; a small lobular unit consisted of a few networks, whereas a large one of fifty or more networks. Sizes and forms of the networks varied widely in each case. However, the networks in the superficial layers of the lateral parts of the thyroid gland were typically most developed. Regardless of its size and form, each network always received a proper efferent vessel continuous with the lobular vein, though it was sometimes provided with an accessory afferent or efferent vessel. Only occasionally were the adjacent networks fused with each other or connected by transfollicular capillaries. Thus, the present data suggest that each follicular capillary network is a fairly independent functional-unit in the thyroid microcirculation. The capillaries of the network were sinusoidal in nature and sometimes protruded fine projections which indicated the neogenesis of capillaries. The blood vascular bed of the newborn rat thyroid gland was not always differentiated into basket-like capillary networks.

The Intermountain Power Project 1600 MW HVDC transmission system

The 1660 MW HVDC transmission system of the Intermountain Power Project (IPP) is designed to deliver energy from a coal-fired, two-unit generating plant in Delta, Utah, to load centers in southern California, USA. To minimize disturbance to the adjacent AC network and the relatively isolated generating plant, several special control features as well as high short-time and steady-state overload capability are required in the design of the IPP HVDC converter stations. The power system reliability requirements of the Western Systems Coordinating Council (WSCC) on the DC transmission system resulted in the specification of guaranteed reliability and availability requirements. The main features in the design of the main circuit equipment, HVDC controls, and the reliability and availability consideration of the IPP transmission system are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Devising a cooperation policy for emergency networks.

A mathematical programming model is proposed to select an optimal cooperation policy between autonomous service networks for dispatching purposes. In addition to traditional characteristics such as network topology and station location, this model takes into account 'political' constraints on minimum response-time in certain subzones. Such constraints are translated into performance requirements, which are imposed on the cooperation policy. Testing the model under different assumptions can be useful for analysing various cooperation policies. The paper formulates a mathematical programming model, derives example policies for various circumstances, and tests the sensitivity of the resultant policies to some parameters, such as the penalty for not providing service, and distances between adjacent networks. The paper suggests also a less constrained approach, which entails a linear programming model. A comparison between the two approaches is presented.

Three-dimensional aspects of blood vessels in thyroids from normal, low iodine diet-treated, TSH-treated, and PTU-treated rats.

Three-dimensional images of blood vessels in thyroid glands from normal, low iodine diet-treated, thyroid-stimulating hormone (TSH)-treated and propylthiouracil (PTU)-treated rats were investigated by use of the corrosion-cast method. The vascular casts made by the injection of methacrylate resin were observed with the scanning electron microscope. In normal animals, each follicle is surrounded by a clearly defined basket-like capillary network, which is generally independent of adjacent networks, though a few anastomoses or common capillaries are sometimes seen. In low iodine diet-treated or TSH-treated animals, the capillaries in the basket-like network become markedly dilated and fuse with one another. Though the vascular casts of PTU-treated animals are similar to those of low iodine diet-treated or TSH-treated ones in some aspects, most basket-like networks become distorted and irregular in shape, and the capillaries are heterogeneously dilated and show many buds, branches and anastomoses. We consider that these peculiar changes in the thyroid of the PTU-treated animals are due not only to the elevation of serum TSH but also to other unknown factors. It is clear that the distribution and morphology of the thyroid capillaries are extremely affected and changed by functional states of the gland.

Horizontal strain across the Wasatch Front near Salt Lake City, Utah

Two adjacent geodetic networks span a 105‐km extent of the Wasatch fault zone in north‐central Utah. One of the networks, located in the vicinity of Salt Lake City, was observed by the National Ocean Service/National Geodetic Survey (NOS/NGS) in 1962–1963 (triangulation mode) and again in 1973–1974 (combined triangulation‐trilateration mode). To the north, in the vicinity of Ogden, the U.S. Geological Survey (USGS) performed five separate trilateration surveys of the second network during the 1972–1981 interval. When fit to a model assuming both temporal and spatial homogeneity for the strain rate, the two independent data sets yield mutually consistent strain rate tensors. Subsets of the NOS/NGS data, however, suggest spatial variation in the strain field, and a subset of the USGS data indicates a possible temporal variation in the strain rate. The quality of the data is such that we are uncertain whether or not these apparent variations represent actual tectonic signals. The strain rate tensors for the two complete data sets suggest an underlying deformational pattern characterized by east‐west (E‐W) maximum principal strain (extension positive). This pattern may also be inferred from regional seismicity and Quaternary geology. The suspected variations would imply that the area to the north of Salt Lake City experienced significant E‐W compression preceding 1978, in contradiction to the underlying strain pattern. This compression may be caused by the mountainous block, eastward adjacent to the fault zone, displacing westward along a shallow‐angle, west dipping detachment surface. We speculate on the existence of an E‐W trending zone of weakness, for example, secondary faults, located north of Salt Lake City to explain how the stress field to the north may be decoupled from that to the south where E‐W compression has not been detected. While seismic and geologic information contribute some plausibility to our speculations, the evidence for the existence of the suspected variations is inconclusive.

The 1979 Homestead Valley Earthquake Sequence, California: Control of aftershocks and postseismic deformation

The coseismic slip and geometry of the March 15, 1979, Homestead Valley, California, earthquake sequence are well constrained by precise horizontal and vertical geodetic observations and by data from a dense local seismic network. These observations indicate 0.52±0.10 m of right‐lateral slip and 0.17±0.04 m of reverse slip on a buried vertical 6‐km‐long and 5‐km‐deep fault and yield a mean static stress drop of 7.2±1.3 MPa. The largest shock had MS = 5.6. Observations of the ground rupture revealed up to 0.1 m of right‐lateral slip on two mapped faults that are subparallel to the modeled seismic slip plane. In the 1.9 years since the earthquakes, geodetic network displacements indicate that an additional 60±10 mm of postseismic creep took place. The rate of postseismic shear strain (0.53±0.13 μrad/yr) measured within a 30×30‐km network centered on the principal events was anomalously high compared to its preearthquake value and the postseismic rate in the adjacent network. This transient cannot be explained by postseismic slip on the seismic fault but rather indicates that broadscale release of strain followed the earthquake sequence. We have calculated the postearthquake stress field caused by the modeled coseismic slip. We assume that failure is promoted when the sum of the shear stress plus 0.75 times the faultopening stress increases. Most aftershocks concentrate at points where the stresses are enhanced by 0.3 MPa (3 bars) or more; aftershocks are nearly absent where postearthquake stresses decrease by 0.3–0.5 MPa. Isolated off‐fault clusters of aftershocks that locate at one fault length from the rupture plane are explainable by this hypothesis. We find that ground rupture and postseismic creep take place where near‐surface stresses are calculated to increase within the preexisting fault zones. Two patches that extend 4 km from both ends of the seismic fault exhibited neither aftershocks nor measurable postseismic creep. The sensitivity of aftershocks and ground rupture to changes in stress that are less than 5% of the earthquake stress drop demonstrates that the region around the earthquakes was within a few percent of its failure threshold before the main shocks. The preearthquake stress field and the stress required for failure must also have been nearly uniform.

The overheads of transnetwork fragmentation

The number of fragments generated between adjacent networks is derived for different fragmentation schemes. This result is extended to cover fragmentation over more complex transnetwork systems. This allows the calculation of the number of fragments received at a packet destination. The effects of fragmentation on the receiver are examined using a simple model of packet processing.

Microstructural study of hot-deformed cemented carbides

Abstract The microstructure of cemented transition-metal carbides has been characterized in both the as-sintered condition and after uniaxial plastic compression at temperatures of 1100 and 1400°C. Both the dislocation structure and the dislocation density were non-uniform within the same sample for all compositions and conditions investigated. These findings are attributed to the large but localized internal stresses developed during liquid-phase sintering and to localized differential thermal contraction on cooling from liquid-phase sintering. Later evidence suggested the presence of a thin film of Go at two-grain interfaces, although it could not be detected by X-ray microchemical analysis because of limited spatial resolution. The likely mechanism of high-temperature deformation is grain-boundary sliding. WC grain shapes were significantly less sharp and angular for samples compressed at 1400°C then for those compressed at 1100°C. It is suggested that this rounding of WC grains occurred as a consequence of a solution and reprecipitation process, which also may have resulted in a larger effective load-supporting cross-sectional area between adjacent WC networks, leading to the previously reported levelling (rather than sharp decrease) of compressive yield stress with respect to temperature as the temperature exceeds the binder liquidus.

The Crystal Structure of Ammonium Diaminodiphosphate

AbstractAmmonium diaminodiphosphate, (NH4)2(P2O4(NH2)2), monoclinic with the space group P21/c and cell dimensions a = 7.634(4), b = 8.237(4), c = 7.127(4) Å and β = 116.63(4)°. There are two formula units per unit cell. The structural analysis with visually estimated data yielded an R value of 0.084 for 508 unique observed reflections. The centrosymmetric diaminodiphosphate anions are linked through NH…O hydrogen bonds from the ammonium cations into infinite chains lying in the [010] plane. Adjacent twodimensional networks of this nature are connected to one another through both the cations and through direct NH…O hydrogen bonds. The following bond lengths were obtained: PP 2.186(4), PO 1.473(6) and 1.512(5), PN 1.663(5) Å.

General dynamic theory of macromolecular networks. I. Definitions and classification

AbstractThe problem of the structural theory of macromolecular networks is formulated and discussed in general terms. The conditions required for a system to become a homogeneous macromolecular network are defined and discussed. Networks are divided according to the nature of their junctions into three classes: energetic (with chemical or quasi‐chemical crosslinks), topological (with entangled chains), and contact (with frictional interactions). The main features of these three classes are discussed. A distribution density function ψ describing the configurations of macromolecules in network systems is introduced. The phase space of variables is 4(N + 1)‐dimensional and includes the coordinates of (N + 1) vectors hi joining the adjacent network junctions and (N + 1) contour lengths li of the network chains. The system of simultaneous equations required for the determination of the function ψ includes the equation of continuity, kinematic equations for the deformation velocity of the individual junctions, the force balance equation needed for the determination of sliding rates li, kinetic equations for the processes of junction breakage and reformation, and the equilibrium distribution of network junctions defining the initial conditions for the distribution function ψ.