Compact Cycle Research Articles

The cytoskeleton and associated proteins during cleavage, compaction and blastocyst differentiation in the pig

Abstract The organization of the cytoskeleton during early pig embryogenesis was investigated by using fluorescence and electron microscopy. The early morphogenesis of the pig embryo differed from that of the mouse, the standard model of the early mammalian development. In the pig, both compaction and polarization were gradual, and definitive polarization of cell surface microville occurred first shortly before blastocyst formation; the compaction and polarization of the mouse embryo are completed as early as at the 8 cell stage. Furthermore, the pig morula undergoes cycles of compaction and decompaction throughout its development. Distinct changes in the distribution of actin and the actin-associated proteins α-fodrin, vinculin and E-cadherin coincided with these events. In the pig, all these molecules were evenly distributed at all aspects of the blastomeres during early cleavage and then gradually accumulated in regions of intercellular contacts toward the blastocyst stage; microfilaments in trophectoderm cells formed a cortical meshwork associated with apical microvilli and adherent junctions (zonula adherens). In the mouse, the corresponding changes occur earlier, at the 8 cell stage. Microtubules formed a network-like cortical layer beneath the microvilli at the free outer surfaces of pig blastomeres. Cytokeratin bundles were not observed until the early blastocyst, where they characteristically associated with newly formed desmosomes. In both species a close correlation between morphologically defined developmental stages and the organization of the cytoskeleton: actin and actin-associated proteins are involved in polarization and compaction, whereas the appearance of intermediate filament bundles coincides with the building of the first epithelium, the trophectoderm; it is in the timing of events that a contrast between species is observed.

Residual stresses in cyclic powder compaction

The behavior of a powder during isostatic compaction is simulated by a hollow sphere model. A flexible one-dimensional finite element analysis is presented for a hypoelastic and strain-hardening plastic behavior of the matrix at finite strains. Results are given for various cases, and the residual stresses after one or several compaction cycles are discussed.

Behaviour of soils (lateritic) subjected to multi-cyclic compaction

A study was made of the influence of multi-recycling/recompaction (referred to as multi-cyclic compaction) on some basic properties of a Pre-cambrian—rock-derived lateritic sample used mainly for embankment construction in Western Nigeria. The sample was recycled several times while gradation, consistency and shear characteristics were investigated as the compaction cycle progressed. As a result of disintegration of the “micro-clusters”, in which state lateritic soils exist in situ, the soil became better graded (U c and percentage of fines increased) and less plastic (PI decreases); the friction angle, φ, decreases; while cohesion, C, increases, up to about cycle 8 after which they stabilize. In practical terms, dry density increases with better grading resulting in the reduction of permeability and compressibility characteristics. As a result, recycled soil requires less effort to achieve a pre-determined density, while air drying could bring the soil back to its original state through further aggregation or micro-clustering.

Activation of maternal centrosomes in unfertilized sea urchin eggs.

Centrosomes are undetectable in unfertilized sea urchin eggs, and normally the sperm introduces the cell's microtubule-organizing center (MTOC) at fertilization. However, artificial activation or parthenogenesis triggers microtubule assembly in the unfertilized egg, and this study explores the reappearance and behavior of the maternal centrosome. During activation with A23187 or ammonia, microtubules appear first at the cortex; centrosomal antigen is detected diffusely throughout the entire cytoplasm. Later, the centrosome becomes more distinct and organizes a radial microtubule shell, and eventually a compact centrosome at the egg center organizes a monaster. In these activated eggs, centrosomes undergo cycles of compaction and decompaction in synchrony with the chromatin, which also undergoes cycles of condensation and decondensation. Parthenogenetic activation with heavy water (50% D2O) or the microtubule-stabilizing drug taxol (10 microM) induces numerous centrosomal foci in the unfertilized sea urchin egg. Within 15 min after incubation in D2O, numerous fine centrosomal foci are detected, and they organize a connected network of numerous asters which fill the entire egg. Taxol induces over 100 centrosomal foci by 15 min after treatment, which organize a corresponding number of asters. The centrosomal material in either D2O- or taxol-treated eggs aggregates with time to form fewer but denser foci, resulting in fewer and larger asters. Fertilization of eggs pretreated with either D2O or taxol shows that the paternal centrosome is dominant over the maternal centrosome. The centrosomal material gradually becomes associated with the enlarged sperm aster. These experiments demonstrate that maternal centrosomal material is present in the unfertilized egg, likely as dispersed undetectable material, which can be activated without paternal contributions. At fertilization, paternal centrosomes become dominant over the maternal centrosomal material.

Frequency stability of a tunable diode laser mounted in a compact Stirling cycle cooler

A tunable diode laser (TDL) has been operated with a compact lightweight closed-cycle Stirling cooler. The laser linewidth has been measured near 80 K and found to be about half of that when using more massive closed-cycle coolers. Novel applications include balloon-borne and aircraft- adapted instruments, where size, weight, and power requirements place stringent demands on necessary TDL cooling systems.

Preliminary study of the performance characteristics of a mhd generator for the compact fusion advanced rankine cycle

The feasibility of high enthalpy extraction from the in-situ radiation-catalyzed MHD generator is studied numerically as a part of the compact fusion advanced Rankine cycle for fusion reactors. The cesium seeded mercury is selected as the working medium, which is superheated by synchrotron radiation from the fusion plasma. In the MHD channel, electrons are heated by Joule dissipation, leading the electron temperature to be higher than that of the mercury vapor. A new type of disk configuration is proposed in the present paper, which is referred to as a disk type generator with separate channels. By using this type of generator, the enthalpy extraction ratio reaches about 59.44% in the case of multi-power take-offs. The obtained cycle efficiency is about 32.1% for a simple cycle. In the case of the recuperative cycle the efficiency becomes about 35.8%. If some amorphous thermoelectric conversion can be installed, the cycle efficiency reaches about 41.7%, which is similar to conventional steam-turbine cycles.

Microwave heating of flowing slightly-ionized gases in a compact fusion advanced rankine (CFAR) cycle

A compact fusion advanced closed-Rankine cycle (CFAR) based on the less expensive “in-situ” nonequilibrium MHD (magnetohydrodynamic) conversion with assistance from synchrotron radiation superheat in the “microwave” tokamak using synchrotron radiation both for MHD energy conversion and current drive is studied for the improvement of tokamak fusion reactor economy. In this CFAR concept, superheat of flowing slightly-ionized gases by synchrotron radiation energy plays a very important role in the system cycle efficiency, using solely MHD electrical power generation. This paper describes a two-dimensional microwave superheat model and examines the above envisaged concept, which is a key issue in the CFAR cycle.

Differentiability and topology of labyrinths in the disc and annulus

IT IS WELL-KNOWN that vector fields on the disc, or more generally on a planar surface, do not exhibit complicated global phenomena: by the Poincare-Bendixson theorem, every recurrent orbit is either a singularity or a simple closed curve. The situation is completely different for line fields. In particular, it was shown in [6] that it is possible for an orbit of a line field to lose itself in a labyrinth, i.e. to enter a disc and stay inside for ever without either going to a singularity or spiralling towards a compact cycle. Line fields in the disc and the annulus were studied and classified in [6], under the assumption that the singularities are thorns and tripods. It was also asked in [6] to what extent line fields with nontrivial recurrence can be differentiable. We intend in this paper first to partially answer this question, then to extend the classification in [6] to the case when singularities are thorns and saddles with any number of prongs. First we discuss differentiability. There are several natural definitions of C’differentiability for singular line fields (even for orientable ones). First one can require the line field to be C’ in the complement of the singularities; it was pointed out in [6] that being C” in this sense does not restrict the dynamics of the foliation. Another notion of differentiability imposes strong C’ local models near the singularities (see 92). Assuming C2-differentiability in this sense, we prove that the Poincart-Bendixson theorem continues to hold; that is, every orbit entering a disc and staying inside has to go to a singularity or spiral towards a compact cycle. The proof is inspired in part by Denjoy’s theorem about C2 vector fields on the torus. This is in sharp contrast with the fact due to Cherry [l], that on the torus minus a disc there are vector fields (Cm in the above sense) where every orbit coming in from the boundary stays inside forever and does not spiral towards a compact cycle. A very interesting question is whether the Poincare-Bendixson theorem continues to hold for line fields with hyperbolic-type singularities; by this we mean that the natural holonomy maps obtained by following a separatrix through a singularity are of the same form as for hyperbolic vector fields. In $3 and $4 of this paper, we extend the results of [6] to line fields with thorns and n-prong saddles. For the disc, the situation is not essentially different from the case of thorns and tripods. However, for the annulus, the study is quite different and more complicated. In both cases, we obtain a topological structure theorem for the foliation. In several instances the proofs we give simplify arguments in [6].

Geometry and arithmetic cycles attached to [formula omitted]—I

IN THE study of the arithmetics of modular curves and in the classical theory of automorphic forms on the upper half plane with respect to subgroups of SL,(Z), modular symbols have served as an indispensable tool linking geometry and arithmetic (e.g. [S], [l 11). There is a natural generalization of this notion to the case of an arithmetic subgroup r of a reductive algebraic Q-group G as, for example, suggested by Mazur [ 123. The construction produces families of relative cycles in the arithmetic quotient X/T, where X denotes the symmetric space attached to G. In analogy with the classical case, there then arise various problems concerning these cycles; but they have not yet been solved in any great generality. In particular, one may ask under what conditions one obtains non-vanishing homology classes for X/‘T in this way, or, what is the relation between modular symbols and automorphic forms with respect to r, especially those which contribute to the cohomology of r. Moreover, can one get some information on special values of L-functions associated to automorphic forms out of modular symbols? (cf. [S], [12]). Being modest in our aim, we will focus on the case G = SL3/Q and a torsion-free subgroup r of finite index in SL, (Z). T’hen r acts properly on the associated symmetric space X = SO(3)\SL,(Iw), and the quotient X/r is a five-dimensional, non-compact, complete Riemannian manifold of finite volume. Recall that X/r may be viewed as the interior of a compact manifold R/r with boundary and that the inclusion is a homotopy equivalence [4]. Given an admissible parabolic Q-subgroup P of SL3 (R) one has the associated modular symbol (cf. 92), which gives rise to relative cycles of degree 2 (3) if P is a Bore1 subgroup (resp. a maximal parabolic one). One knows that H2 (B/r, Z(J?/T),C) is generated by cycles of the first type [2]. This paper is mainly devoted to the study of the geometry of modular symbols in the second case and their non-trivial contribution to the cohomology of r (cf. 5.2, 5.3). This result will be achieved by showing that the modular cycles in question have a positive intersection number with certain associated compact cycles in X/r. These so-called hyperbolic cycles are two-dimensional submanifolds C(6) in X/r attached to indefinite ternary quadratic forms b over Q, and C(6) is compact if b does not represent zero over Q. This natural idea to show that the modular cycles are cohomologically non-zero was originally carried out by Millson and Raghunathan [13], [14] in the context of compact arithmetic quotients of, for example, SO(p,q). By analysing the intersection number of hyperbolic cycles with complementary hyperbolic ones they proved that there are uniform arithmetic subgroups, so that the hyperbolic cycles considered in the corresponding locally symmetric space are non-bounding. On the other hand, such hyperbolic cycles also occur naturally as fix point components of involutions (cf. [lo], [13], [15]). From the results of Rohlfs [ 151, the fix point components of an involution on X/r can be parametrized by the first non-abelian cohomology set H’ (9, r) attached to g = { 1, p) (cf. 94 for definition). Since a modular cycle in X/T may also be interpreted as a fix point component of a certain

Elastic properties of granular materials under uniaxial compaction cycles

Data on andesitic and basaltic sands are presented showing compressional sound velocity, density, and creep as functions of uniaxial loading through several compaction cycles. Maximum pressures over which acoustic measurements were made were in the range from 600 to 700 bars. The dynamic elastic modulus varies with pressure in a manner analogous to that of a static elastic modulus defined by small pressure perturbations on a typical compaction cycle. After several compaction cycles, two compressional elastic moduli apparently exist at low pressure (thus two modes of compressional wave propagation through the samples are indicated). The elastic moduli observations are briefly discussed in terms of a general expression for compressibility.

The Zeta Sedimentation Ratio

Abstract The zeta sedimentation ratio (ZSR) is a measurement similar to the determination of the erythrocyte sedimentation rate (ESR) but possesses sevaral advantages. It is unaffected by anemia and responds in a linear manner to increase in fibrinogen and/or gamma globulin. The normal range is identical for males and females. A blood sample, contained within a vertically oriented capillary tube, is subjected to four cycles of dispersion and compaction. At the conclusion of this process, the hematocrit of the blood in the red cell-containing portion of the capillary tube is measured. This hematocrit, a measure of the closeness with which red cells will approach each other under a standardized stress, is the ZSR.

The Heat Equation Method of Milgram and Rosenbloom for Open Riemannian Manifolds

In a pair of notes [12] in the Proceedings of the National Academy of Sciences, Milgram and Rosenbloom introduced a generalized heat equation into the theory of harmonic integrals and used it to obtain a proof of the existence assertion of Hodge's theorem. The theory of integral equations of Volterra type played an important role in the presentation, which was restricted to compact manifolds. This restriction to compact manifolds was eased by Spencer [15], who extended the methods to apply to a class of complete manifolds in which strong restrictions are put on the curvature tensor. A generalization in a different direction was made by Yosida [18], who replaced the integral equation methods by Hilbert space methods and obtained results for open manifolds. Spencer [17] used these methods in examining Green's and Neumann's boundary value problems for A. Lax and Milgram have used Hilbert space techniques in applying the heat equation method to the study of certain partial differential equations. Yosida showed that the equation (a at)at = Aat can be solved in such a way that if a (with finite norm) is the initial value of at, then a. is in the space of those norm-finite forms 3 for which Ai = 0. (We take the sign of A to be such that for functions A reduces to the negative of the Laplace-Beltrami operator.) He described his results as an ergodic theorem in which the solution of the diffusion equation leads to a stochastic procedure for going from a form to its harmonic part. For closed manifolds he obtained additional information adequate to demonstrate Hodge's existence theorem. The methods used in this paper are patterned after those of Yosida but lead to a more complete generalization of the results of Milgram and Rosenbloom. Denoting the solution of the heat equation with initial value a by Wta, the main results are (complete hypotheses below): W. is the projection onto the harmonic forms (those forms with finite norm for which both da and ba are zero). If a is closed, Wta is closed. If a is closed, the periods of Wta on compact cycles are independent of t, 0 < t < cc? Thus W. projects a onto a harmonic form with the same periods.