Showing papers by "University of Tsukuba published in 1991"

Phenomenological theory of unconventional superconductivity

Abstract: This article is a review of recent developments in the phenomenological description of unconventional superconductivity. Starting with the BCS theory of superconductivity with anisotropic Cooper pairing, the authors explain the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional superconductivity. This is used to classify the possible superconducting states in a system with given crystal symmetry, including strong-coupling effects and spin-orbit interaction. On the basis of the BCS theory the unusual low-temperature properties and the (resonant) impurity scattering effects are discussed for superconductors with anisotropic pairing. Using the Ginzburg-Landau theory, the authors study several bulk properties of such superconductors: spontaneous lattice distortion, upper critical magnetic field, splitting of a phase transition due to uniaxial stress. Two possible mechanisms for ultrasound absorption are discussed: collective modes and damping by domain-wall motion. The boundary conditions for the Ginzburg-Landau theory are derived from a correlation function formulation and by group-theoretical methods. They are applied to a study of the Josephson and proximity effects if unconventional superconductors are involved there. The magnetic properties of superconductors that break time-reversal symmetry are analyzed. Examples of current and magnetic-field distributions close to inhomogeneities of the superconducting order parameter are given and their physical origin is discussed. Vortices in a superconductor with a multicomponent order parameter can exhibit various topological structures. As examples the authors show fractional vortices on domain walls and nonaxial vortices in the bulk. Furthermore, the problem of the possible coexistence of a superconducting and a magnetically ordered phase in an unconventional superconductor is analyzed. The combination of two order parameters that are almost degenerate in their critical temperature is considered with respect to the phase-transition behavior and effects on the lower and upper critical fields. Because heavy-fermion superconductors---which are possible realizations of unconventional superconductivity---have been the main motivation for the phenomenological studies presented here, the authors compare the theoretical results with the experimental facts and data. In particular, they emphasize the intriguing features of the compound U${\mathrm{Pt}}_{3}$ and consider in detail the alloy ${\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Th}}_{x}{\mathrm{Be}}_{13}$.

A pivoting algorithm for convex hulls and vertex enumeration of arrangements and polyhedra

Abstract: We present a new pivot-based algorithm which can be used with minor modification for the enumeration of the facets of the convex hull of a set of points, or for the enumeration of the vertices of an arrangement or of a convex polyhedron, in arbitrary dimension. The algorithm has the following properties:(a)Virtually no additional storage is required beyond the input data.(b)The output list produced is free of duplicates.(c)The algorithm is extremely simple, requires no data structures, and handles all degenerate cases.(d)The running time is output sensitive for nondegenerate inputs.(e)The algorithm is easy to parallelize efficiently. For example, the algorithm finds thev vertices of a polyhedron inRd defined by a nondegenerate system ofn inequalities (or, dually, thev facets of the convex hull ofn points inRd, where each facet contains exactlyd given points) in timeO(ndv) andO(nd) space. Thev vertices in a simple arrangement ofn hyperplanes inRd can be found inO(n2dv) time andO(nd) space complexity. The algorithm is based on inverting finite pivot algorithms for linear programming.

Volume transition in a gel driven by hydrogen bonding

Abstract: INTERACTIONS between macromolecules fall into four categories: ionic, hydrophobic, van der Waals and hydrogen bonding. Phase transitions in polymer gels provide a means of studying these interactions. Many gels will undergo reversible, discontinuous volume changes in response to changes in, for example, temperature, gel composition or light irradiation1–5. These transitions result from the competition between repulsive intermolecular forces, usually electrostatic in nature, that act to expand the polymer network, and an attractive force that acts to shrink it. Volume transitions in gels have been observed that are driven by all of the above-mentioned forces except hydrogen bonding (ref 6–10; T.T. et al, unpublished data; H. Inomata et al., personal communication). Here we report on a phase transition in an interpenetrating polymer network of poly(acrylamide) and poly(acrylic acid) that completes this picture—it is controlled by cooperative 'zipping' interactions between the molecules which result from hydrogen bonding. Cooperativity is an essential feature of the interactions, in that independent hydrogen bonds would not provide a sufficient driving force for the transition. A further novel characteristic of this phase transition is that the swelling (in water) is induced by an increase rather than a decrease in temperature.

Molecular and cellular mechanism of endothelin regulation. Implications for vascular function.

Abstract: It is now well recognized that vascular endothelium plays an important role in regulation of vascular tonus. The endothelial cell produces not only vasodilators such as endothelium-derived relaxing factor (EDRF) and prostacyclin, but also vasoconstrictors, that is, thromboxane and endothelin (ET). ET was initially isolated from a conditioned medium of the cultured porcine aortic endothelial cells.' It consists of 21 amino acid residues including two intramolecular disulfide bonds (Figure 1). This peptide is the most potent vasoconstrictive peptide so far known. When it is injected intravenously, a longlasting pressor response is observed.1 Because of these unique pharmacological properties, ET has been thought to play an important role in the maintenance of blood pressure or in the generation of hypertension and vasospasm. The aim of this article is to review the rationale for ET-induced vasoconstriction, particularly from the standpoint of molecular and cellular aspects and the importance of ET in the pathogenesis of hypertension and vasospasm.

Local and Remote Responses to Excessive Snow Mass over Eurasia Appearing in the Northern Spring and Summer Climate A Study with the MRI * GCM

Abstract: The effect of excessive snow mass over the Eurasian continent on the spring and summer climate is investigated by using the MRI * GCM. The ensemble mean of the four runs (SNOW runs) with the excessive snow mass of 5 cm (water equivalent) at the beginning of March over the snow cover area of the continent is compared with that of the control runs, to deduce the effect of the snow mass on the climatic parameters in the later seasons. The main results are summarized as follows: (1) In spring, the albedo effect is dominated in the lower latitudes particularly over the Tibetan Plateau. The reduced net radiation by the anomalous snow cover balances the reduced surface sensible and latent heat fluxes, which account for the significant decrease of surface temperature, cloudiness and total diabatic heating over there in the SNOW runs. (2) In summer, in contrast, the snow-hydrological effect is significant, particularly in the mid-latitudes. The increase of ground wetness in the SNOW runs causes anomalous cooling and higher pressure near the surface. A moderate signal of the weakened Asian summer monsoon is also obtained. However, the increase of evaporation activates cumulus convection, which partly compensates for the decrease of total diabatic heating by the cooling near the surface. This evaporation/convection feedback seems to work, on the other hand, to sustain the increased ground wetness throughout the summer. (3) The atmospheric teleconnection patterns induced by the anomalous snow cover over the Tibetan Plateau and east Asia significantly appear over the north Pacific and the North American continent in spring through late summer. These anomalous circulations cause the considerable decrease of surface temperature over the northeastern part of North America. (4) The implication of these results for the Ice Age issue is also briefly discussed.

Increased plasma level of endothelin-1 and coronary spasm induction in patients with vasospastic angina pectoris.

Abstract: To elucidate the pathogenic contribution of a potent vasoconstrictor, endothelin-1, to coronary artery spasm, we provoked spasm with intracoronary administration of acetylcholine or ergonovine and performed sensitive immunoassays of plasma levels of endothelin-1 and atrial natriuretic factor (ANF) in the peripheral vein and coronary sinus of patients with a tentative diagnosis of vasospastic angina (VSA, n = 19). The validity of coronary sinus blood sampling was verified by simultaneous measurement of the ANF level. The plasma endothelin-1 levels in venous and coronary sinus blood of the spasm-provoked patients (n = 12) were 1.71-fold and 2.16-fold higher, respectively, than those of nonprovoked cases (n = 5, p less than 0.01). During left coronary spasm, the endothelin-1 level in coronary sinus transiently decreased from 2.27 +/- 0.14 to 1.76 +/- 0.14 pg/ml (p less than 0.01) and returned to the control level (1.98 +/- 0.20 pg/ml) after the spasm resolved, whereas the change was equivocal during right coronary spasm. In contrast, the patients in whom spasm was not provoked showed no changes and maintained low endothelin-1 levels both before and after the maximal provocation (0.90 +/- 0.13 versus 0.90 +/- 0.13 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin-1 is an autocrine/paracrine growth factor for human cancer cell lines.

Abstract: We studied whether a novel vasoconstrictor peptide, endothelin-1 (ET-1), is synthesized by and released from human carcinoma cell lines, and whether ET-1 stimulates proliferation of these tumor cells. ET-1-like immunoreactivity was released from both HeLa and HEp-2 cells as a function of time. Reverse-phase HPLC of the conditioned media from HeLa cells revealed a major peak coeluting with standard ET-1. Northern blot analysis demonstrated the expression of mRNA for ET-1 precursor in both tumor cell lines. Both cell lines contained a single class of specific binding sites for ET-1. ET-1 dose-dependently induced increases in cytosolic free Ca2+ concentration in fura-2-loaded tumor cells, whose effect was completely abolished by chelating extracellular Ca2+ or by Ca(2+)-channel blocker. ET-1 stimulated proliferation of the quiescent cell lines in a dose-dependent manner, whose effect was inhibited by Ca(2+)-channel blocker. Polyclonal antibody for ET-1 inhibited proliferation of these cell lines, whereas nonimmune serum had no effect. These results demonstrate that ET-1 is synthesized by and released from human epithelial carcinoma cell lines, and that exogenous and endogenous ET-1 stimulates proliferation of the cells possibly through Ca2+ influx, suggesting its role as an autocrine/paracrine growth factor for certain tumor cells.

Saccharide-sensitive phase transition of a lectin-loaded gel

Abstract: A GEL system that swells and shrinks in response to specific molecules could serve as the basis for technological applications of polymer gels, for example as sensors, drug-delivery devices and actuators. Here we describe a lectin-loaded polymer gel that undergoes distinct swelling behaviour in response to different saccharides. The gel consists of a covalently cross-linked polymer network of N-isopropylacrylamide in which the lectin, concanavalin A, is immobilized. Concanavalin A displays selective binding affinities for certain saccharides. The gel undergoes a volume phase transition at ∼34 °C. When the saccharide dextran sulphate is added (as the sodium salt DSS) to the gel, it swells to a volume up to five times greater at temperatures close to this transition, and the transition itself changes from discontinuous to continuous. Replacing DSS with the non-ionic saccharide α-methyl-D-mannopyranoside brings about collapse of the gel back to almost its native volume. This process is reversible and repeatable. These results point to a general principle for the design of such molecule-specific systems.

Generalized phase-shifting interferometry

Abstract: We describe a generalized phase-shifting interferometry for which the reference phases are directly evaluated at each time that the interference fringe data are read. The reference phases are obtained from the additional straight fringes on the interfering plane by the fast-Fourier-transform method. According to error estimation, the repeatabilities in the measurements of optical surfaces are λ/500 rms, when the generalized algorithm with eight data acquisitions is used.

Interdependence between safety-control policy and multiple-sensor schemes via Dempster-Shafer theory

Abstract: The Dempster-Shafer (D-S) theory has been gaining popularity in fields where incomplete knowledge is a factor. The author explores the application of the D-S theory in system reliability and safety. Inappropriate application of the D-S theory to safety-control policies can degrade plant safety. This is proven in two phases: (1) a unified combination rule for fusing information on plant states given by independent knowledge sources such as sensors or human operators is developed; and (2) combination rules cannot be chosen in an arbitrary manner, i.e., the best choice of combination rules depends on whether the safety-control policy is fault-warning or safety-preservation. >

The Monsoon Year — A New Concept of the Climatic Year in the Tropics

Abstract: The concept of “monsoon year” is proposed as a unit year of climatic anomalies (i.e., the climatic year) in the tropics. This monsoon year is defined as one year starting just before the northern summer monsoon season. It is also argued that this climatic year in the tropics is physically based upon the characteristic nature of the coupled ocean/land/atmosphere system over the Asian monsoon/Pacific Ocean sector.

SINEs: Short interspersed repeated elements of the eukaryotic genome

Abstract: Much of the eukaryotic genome is composed of a variety of repetitive sequences. Amongst these, there are two kinds of retroposons (sequence elements derived from nonviral cellular RNA): SINEs (short interspersed elements) and LINEs (long interspersed elements). Amplification of SINEs occurs in a single germ cell, and the members of SINEs spread and become fixed in populations through genetic drift. SINEs can be regarded as phylogenetic landmarks: they are specific to one species, a few species, a genus or in some cases a family, indicating a specific time of amplification during evolution. Recent studies concerning the structure and origin of many SINEs revealed that retroposons are more widespread in animal genomes than was previously thought.

Descending input from the hypothalamic paraventricular nucleus to sympathetic preganglionic neurons in the rat.

Abstract: The descending projection of the hypothalamic paraventricular nucleus (PVN) to the sympathetic preganglionic neurons (SPNs) in the upper thoracic cord of the rat was studied. PVN-fibers were labeled by anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L), while SPNs were retrogradely labeled with cholera toxin subunit B (CTb) which was injected into the superior cervical ganglion. SPNs labeled with CTb were mainly observed in the nucleus intermediolateralis (IML) pars principalis and pars funicularis, and a small number of them were in the nucleus intercalatus (IC) and central autonomic nucleus (CA). SPNs found in the IML had dendrites that projected in various directions. Five types of dendritic projections were noted: medial, rostral, caudal, lateral (including dorsolateral) and ventral. Longitudinal dendritic bundles interconnected each cell cluster in the IML. Medial dendrites of the IML, together with dendrites of the IC and CA, formed transverse dendritic bundles extending from the IML to the central canal. The transverse dendritic bundles disentangled near the midline and formed a loose dendritic plexus in the region just dorsal to the central canal. PVN-fibers labeled with PHA-L were observed primarily in lamina I and intermediate gray (lamina VII). Although varicose PVN-fibers and SPNs coexisted in the IML, the tight packing of the dendritic bundles prevented any clear demonstration of direct contacts between them. On the other hand, PVN-fibers were occasionally found to appose and wind around the primary or secondary dendrites of some SPNs of the CA and IC. These dendrites were studded with varicosities of PVN-fibers for a short length, and terminal boutons of PVN-fibers were also seen to make contact directly with the dendrites. The results of this study substantiated a direct connection between the PVN and SPNs, using a combination of immunohistochemical techniques for PHA-L and CTb. The possible involvement of a direct pathway from the PVN to SPNs in cardiovascular regulation is discussed.

Hypertension Associated with Endothelin-Secreting Malignant Hemangioendothelioma

Abstract: Endothelin-1, a potent vasoconstrictor peptide that has recently been isolated from the supernatant of cultured porcine aortic endothelial cells (1), is involved in some vascular disorders (2). Mal...

Topographical localisation of endothelin mRNA and peptide immunoreactivity in neurones of the human brain.

Abstract: The distribution of endothelin mRNA and immunoreactivity in the human brain was investigated using the technique of in situ hybridization and immunocytochemistry. Cryostat sections from 22 cases of neurologically normal adult human brain, collected 3–7 h post-mortem were hybridized with 35S-labelled complementary (c)RNA probes prepared from the 3′ non-coding region of endothelin-1 cDNA, and the chromosomal genes encoding endothelin-2 and -3. In situ hybridization with all three cRNA probes revealed labelled neuronal cell bodies in laminae III–VI of the parietal, temporal and frontal cortices. Labelled cells were also seen, scattered throughout the para- and periventricular; supraoptic and lateral hypothalamic nuclei, the caudate nucleus, amygdala, hippocampus, basal nucleus of Meynert, substantia nigra, raphe nuclei, Purkinje cell layer of the cerebellum and in the dorsal motor nuclei of the vagus of the medulla oblongata. The distribution of neurones immunoreactive to endothelin was similar to that of endothelin mRNA, although fewer immunoreactive cells throughout the brain, were noted. Immunoreactive fibres were present mainly in the cortex and hypothalamus, and to a lesser extent in the brain stem. Combined in situ hybridization and immunocytochemistry on the same section revealed the presence of endothelin-1 mRNA and immunoreactivity in the same cortical neuronal cell. Colocalisation studies in the cortex revealed endothelin-1 mRNA and immunoreactivity in a number of cells which also expressed neuropeptide Y mRNA and immunoreactivity. In the hypothalamus and basal nucleus of Meynert endothelin immunoreactivity was colocalised to a subset of neurophysin- and galanin-immunoreactive cell bodies respectively. Endothelin mRNA and immunoreactivity was also seen in some blood vessel endothelial cells. The findings of endothelin mRNAs and immunoreactivity in heterogenous neuronal populations further emphasises the potential role of endothelin as a neuropeptide, probably having diverse actions in the nervous system of man.

Formation of stationary alternate bars in a steep channel with mixed-size sediment: a flume experiment

Abstract: Alternate bars were formed by sediment transport in a flume with Froude-modelled flow and relative roughness characteristic of gravel-boulder channels with steep slopes The flume (03 m wide × 75 m long) was filled with a sand-gravel mixture, which was also fed into the top of the flume at a constant rate under constant discharge Channel slope was set at 003 Initially, coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream Sorting in the pool directed coarse particles onto the next bar head downstream Alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting, flow, and channel morphology During episodes of bar construction, unsorted bedload invaded interior bar surfaces and was deposited Persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar-head erosion and bedload transport over bars Likely factors leading to bar-head stabilization in modelled gravel-bed channels are coarse mixed-size sediment, steep channel gradients, and shallow depths

Green's Function Theory of the Two-Dimensional Heisenberg Model : Spin Wave in Short Range Order

Abstract: The two dimensional Heisenberg model is studied with a Green's function decoupling scheme in the ferromagnetic and the antiferromagnetic cases. We employ Kondo and Yamaji's formulation and improve it quantitatively. The present theory does not violate the rotational symmetry and the sum rule of the correlation function. We calculate excitation spectrum, long range order, correlation functions, correlation length, energy, and spin susceptibility. The results are compared with those of the Monte Carlo simulations and the experiments of La 2 CuO 4 . Qualitative and semi-quantitative agreements are obtained. In particular, the temperature dependence of the susceptibility indicated by Monte Carlo simulations is reproduced over all temperature region.

Shikonin production and secretion by hairy root cultures of Lithospermum erythrorhizon.

Abstract: Hairy root cultures of Lithospermum erythrorhizon were established by transformation of in vitro grown shoots with Agrobacterium rhizogenes 15834. Hairy roots cultured on Murashige and Skoog solid medium did not produce any red pigments. However, the hairy roots cultured in Root Culture solid or liquid media produced a large amount of red pigments, which were released to the medium. The addition of adsorbents to the culture medium stimulated shikonin production by ca. 3-fold. Using this method an air-lift fermenter system was established, equipped with a XAD-2 column, which continuously produced ca. 5 mg/day of shikonin during a period of more than 220 days.

Chromosomal assignments of the human endothelin family genes: the endothelin-1 gene (EDN1) to 6p23-p24, the endothelin-2 gene (EDN2) to 1p34, and the endothelin-3 gene (EDN3) to 20q13.2-q13.3.

Abstract: Chromosomal assignments of the genes for the human endothelin family, the endothelin-1 gene (EDN1), the endothelin-2 gene (EDN2), and the endothelin-3 gene (EDN3), were accomplished by in situ hybridization to human metaphase chromosomes using a 3H-labeled human preproendothelin cDNA probe for each endothelin. The chromosomal assignment of the EDN2 was also performed by Southern blot analysis of somatic cell hybrid DNAs. EDN1, EDN2, and EDN3 were mapped to 6p23-p24, 1p34, and 20q13.2-q13.3, respectively.

Multifractal analysis of spatial distribution of microearthquakes in the Kanto region

Abstract: SUMMARY The spatial distribution of earthquakes is a fractal, which is characterized by a fractal dimension. However, if a spatial distribution has a heterogeneous fractal structure, a single value of fractal dimension [e.g. Do (capacity dimension) or D2 (correlation dimension)] is not enough to characterize it. From a multifractal viewpoint, we analysed the spatial distribution of microearthquakes in the Kanto region by using a local density function. Generalized dimensions, D,, of the spatial distribution were calculated from the slopes of generalized correlation integrals, C,(r) versus distance r, on a log-log plot, examining the self-similarity of the spatial distribution of microearthquakes. Self-similar structures are held well at scales from 1.26 to 12.6 km. Our results suggest that the spatial distribution of microearthquakes in the Kanto region is not a homogeneous fractal structure but a heterogeneous one with generalized dimensions D2 = 2.2 h D3 2 - .? D, = 1.7. The value of D,, the lower limit of fractal dimension, is the fractal dimension of the most intensive clustering in the heterogeneous fractal set. The fractal dimension of the most intensive clustering of microearthquakes in the Kanto region is 1.7.

Shaping and reshaping of salmonid genomes by amplification of tRNA-derived retroposons during evolution.

Abstract: Three families of tRNA-derived repeated retroposons in the genomes of salmonid species have been isolated and characterized. These three families differ in sequence, but all are derived from a tRNA(Lys) or from a tRNA species structurally related to tRNA(Lys). The salmon Sma I family is present in the genomes of two species of the genus Oncorhynchus but not in other species, including five other species of the same genus. The charr Fok I family is present only in four species and subspecies of the genus Salvelinus. The third family, the salmonid Hpa I family, appears to be present in all salmonid species but is not present in species that are not members of the Salmonidae. Thus, the genome of proto-Salmonidae was originally shaped by amplification and dispersion of the salmonid Hpa I family and then reshaped by amplification of the Sma I and Fok I families in the more recently evolved species of salmon and charr, respectively. We speculate that amplification and dispersion of retroposons may have played a role in salmonid speciation.