Showing papers by "University of Tsukuba published in 1996"

Edge state in graphene ribbons: Nanometer size effect and edge shape dependence.

Abstract: Finite graphite systems having a zigzag edge exhibit a special edge state. The corresponding energy bands are almost flat at the Fermi level and thereby give a sharp peak in the density of states. The charge density in the edge state is strongly localized on the zigzag edge sites. No such localized state appears in graphite systems having an armchair edge. By utilizing the graphene ribbon model, we discuss the effect of the system size and edge shape on the special edge state. By varying the width of the graphene ribbons, we find that the nanometer size effect is crucial for determining the relative importance of the edge state. We also have extended the graphene ribbon to have edges of a general shape, which is defined as a mixture of zigzag and armchair sites. Examining the relative importance of the edge state for graphene ribbons with general edges, we find that a non-negligible edge state survives even in graphene ribbons with less developed zigzag edges. We demonstrate that such an edge shape with three or four zigzag sites per sequence is sufficient to show an edge state, when the system size is on a nanometer scale. The special characteristics of the edge state play a large role in determining the density of states near the Fermi level for graphite networks on a nanometer scale.

Peculiar Localized State at Zigzag Graphite Edge

Abstract: We study the electronic states of graphite ribbons with edges of two typical shapes, armchair and zigzag, by performing tight binding band calculations, and find that the graphite ribbons show striking contrast in the electronic states depending on the edge shape. In particular, a zigzag ribbon shows a remarkably sharp peak of density of states at the Fermi level, which does not originate from infinite graphite. We find that the singular electronic states arise from the partly flat bands at the Fermi level, whose wave functions are mainly localized on the zigzag edge. We reveal the puzzle for the emergence of the peculiar edge state by deriving the analytic form in the case of semi-infinite graphite with a zigzag edge. Applying the Hubbard model within the mean-field approximation, we discuss the possible magnetic structure in nanometer-scale micrographite.

Exchange Monte Carlo Method and Application to Spin Glass Simulations

Abstract: We propose an efficient Monte Carlo algorithm for simulating a “hardly-relaxing” system, in which many replicas with different temperatures are simultaneously simulated and a virtual process exchanging configurations of these replicas is introduced. This exchange process is expected to let the system at low temperatures escape from a local minimum. By using this algorithm the three-dimensional ± J Ising spin glass model is studied. The ergodicity time in this method is found much smaller than that of the multi-canonical method. In particular the time correlation function almost follows an exponential decay whose relaxation time is comparable to the ergodicity time at low temperatures. It suggests that the system relaxes very rapidly through the exchange process even in the low temperature phase.

Long-Term Lymphohematopoietic Reconstitution by a Single CD34-Low/Negative Hematopoietic Stem Cell

Abstract: Hematopoietic stem cells (HSCs) supply all blood cells throughout life by making use of their self-renewal and multilineage differentiation capabilities. A monoclonal antibody raised to the mouse homolog of CD34 (mCD34) was used to purify mouse HSCs to near homogeneity. Unlike in humans, primitive adult mouse bone marrow HSCs were detected in the mCD34 low to negative fraction. Injection of a single mCD34(lo/-), c-Kit+, Sca-1(+), lineage markers negative (Lin-) cell resulted in long-term reconstitution of the lymphohematopoietic system in 21 percent of recipients. Thus, the purified HSC population should enable analysis of the self-renewal and multilineage differentiation of individual HSCs.

Spectroscopic evidence for a pseudogap in the normal state of underdoped high- T c superconductors

Abstract: IT is well known that BCS mean-field theory is remarkably successful in describing conventional superconductors. A central concept of BCS theory is the energy gap in the electronic excitation spectrum below the superconducting transition temperature, Tc. The gap also serves as the order parameter: quite generally, long-range phase coherence and a non-zero gap go hand-in-hand1. But in underdoped high-Tc superconductors there is considerable evidence that a pseudogap (a suppression of spectral weight) is already formed in the normal state above Tc—first, from studies of the spin excitation spectrum2–5,24, which measure a 'spin gap', and later from a variety of other probes6–10. Here we present a study of underdoped Bi2Sr2CaCu2O8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES), which directly measures the momentum-resolved electron excitation spectrum of the CuO2 planes. We find that a pseudogap with d-wave symmetry opens up in the normal state below a temperature T* > Tc, and develops into the d-wave superconducting gap once phase coherence is established below Tc.

Phase-contrast X-ray computed tomography for observing biological soft tissues.

Abstract: Biological soft tissues are almost transparent to hard X rays and therefore cannot be investigated without enhancement with a contrast medium, such as iodine. On the other hand, phase–contrast X–ray imaging is sensitive to light elements1–8. This is because the X–ray phase shift cross section is almost a thousand times larger than the X–ray absorption cross section for light elements such as hydrogen, carbon, nitrogen and oxygen4,5. Hence, phase–contrast X–ray imaging is a promising technique for observing the structure inside biological soft tissues without the need for staining and without serious radiation exposure. We have devised a means of observing biological tissues in three dimensions using a novel X–ray computed tomography (CT) by modifying the phase–contrast technique. To generate appropriate CT input data, we used phase–mapping images obtained using an X–ray interferometer6 and computer analysis of interference patterns9. Now, we present a three–dimensional observation result of a nonstained sample of a cancerous rabbit liver, using a synchrotron X–ray source. Phase–contrast X–ray CT was able to clearly differentiate the cancer lesion from the normal tissue. Moreover, fine structures corresponding to cancerous degeneration and fibrous tissues were clearly depicted.

Structural basis of calcium-induced E-cadherin rigidification and dimerization

Abstract: THE cadherins mediate cell adhesion and play a fundamental role in normal development1 They participate in the maintenance of proper cell–cell contacts: for example, reduced levels of epithelial cadherin (E-cadherin) correlate with increased invasiveness in many human tumour cell types2,3 The cadherins typically consist of five tandemly repeated extracellular domains, a single membrane-spanning segment and a cytoplasmic region4–6 The N-terminal extracellular domains mediate cell–cell contact7while the cytoplasmic region interacts with the cytoskeleton through the catenins8 Cadherins depend on calcium for their function: removal of calcium abolishes adhesive activity, renders cadherins vulnerable to proteases (reviewed in ref 4) and, in E-cadherin, induces a dramatic reversible conformational change in the entire extracellular region9 We report here the X-ray crystal structure at 20 A resolution of the two N-terminal extracellular domains of E-cadherin in the presence of calcium The structure reveals a two-fold symmetric dimer, each molecule of which binds a contiguous array of three bridged calcium ions Not only do the bound calcium ions linearize and rigidity the molecule, they promote dimerization Although the N-terminal domain of each molecule in the dimer is aligned in a parallel orientation, the interactions between them differ significantly from those found in the neural cadherin (N-cadherin) N-terminal domain (NCD1) structure10 The E-cadherin dual-domain structure reported here defines the role played by calcium in the cadherin-mediated formation and maintenance of solid tissues

Inhibition of myocardial endothelin pathway improves long-term survival in heart failure

Abstract: Occlusion of the diseased coronary artery in humans causes acute myocardial infarction, survivors of which have a high risk for the development of chronic heart failure. Cardiac myocytes and vascular endothelial cells produce endothelin-1 (refs 2-4), which increases the contractility of cardiac muscle and of vascular smooth muscle cells. Endothelin-1 also exerts long-term effects such as myocardial hypertrophy, and causes cellular injury in cardiac myocytes. Production of endothelin-1 is markedly increased in the myocardium of rats with heart failure, and acute application of an endothelin-receptor antagonist decreases myocardial contractility in such rats, indicating that myocardial endothelin-1 may help to support contractility of the failing heart. But we report here that the upregulated myocardial endothelin system may contribute to the progression of chronic heart failure, because long-term treatment with an endothelin-receptor antagonist greatly improved the survival of rats with chronic heart failure. This beneficial effect was accompanied by significant amelioration of left ventricular dysfunction and prevention of ventricular remodelling, in which there is usually an increase in the ventricular mass and cavity enlargement of the ventricle.

Ataxia and epileptic seizures in mice lacking type 1 inositol 1,4,5-trisphosphate receptor

Abstract: The inositol 1,4,5-trisphosphate (InsP3) receptor acts as an InsP3-gated Ca2+ release channel in a variety of cell types. Type 1 InsP3 receptor (IP3R1) is the major neuronal member of the IP3R family in the central nervous system, predominantly enriched in cerebellar Purkinje cells but also concentrated in neurons in the hippocampal CA1 region, caudate-putamen, and cerebral cortex. Here we report that most IP3R1-deficient mice generated by gene targeting die in utero, and born animals have severe ataxia and tonic or tonic-clonic seizures and die by the weaning period. An electroencephalogram showed that they suffer from epilepsy, indicating that IP3R1 is essential for proper brain function. However, observation by light microscope of the haematoxylin-eosin staining of the brain and peripheral tissues of IP3R1-deficient mice showed no abnormality, and the unique electrophysiological properties of the cerebellar Purkinje cells of IP3R1-deficient mice were not severely impaired.

Presence of hematopoietic stem cells in the adult liver

Abstract: Recently, cases have been reported in which a mixed chimeric state of blood cells is established after liver transplantation. Because the established chimerism may have aided in the induction of donor-specific tolerance, the mechanism responsible for this chimerism is of clinical importance. To establish this, we examined cells in adult mouse liver and identified the presence of c-kit+ Sca-1+ Lin(lo/-) cells. These cells were capable of forming in vivo as well as in vitro colonies. Furthermore, the cells could reconstitute bone marrow of lethally irradiated recipient mice for at least 12 months. These data obtained from the mouse study strongly suggest that hematopoietic stem cells residing in the donor liver are responsible for mixed chimerism and maintenance of tolerance after liver transplantation.

Essential role of the posterior morphogen nanos for germline development in Drosophila

Abstract: IN many animal groups, factors required for germline formation are localized in germ plasm1, a region of the egg cytoplasm. In Drosophila embryos, germ plasm is located in the posterior pole region and is inherited in pole cells, the germline progenitors. Transplantation experiments have demonstrated that germ plasm contains factors that can form germline2–4, and germ plasm also directs abdomen formation5. Genetic analysis has shown that a common mechanism directs the localization of the abdomen and germline-forming factors to the posterior pole6–12. The critical factor for abdomen formation is the nanos (nos) protein (nanos)13–15. Here we show that nos is also essential for germline formation in Drosophila; pole cells lacking nanos activity fail to migrate into the gonads, and so do not become functional germ cells. In such pole cells, gene expression, which normally initiates within the gonad, begins prematurely during pole-cell migration. Premature activation of genes in germline precursors may mean that these cells fail to develop normally. A function for nos protein in Drosophila germline formation is compatible with observations of its association with germ plasm in other animals16–18.

Diversity and inheritance of inter-simple sequence repeat polymorphisms in Douglas-fir (Pseudotsuga menziesii) and sugi (Cryptomeria japonica).

Abstract: We studied inter-simple sequence repeat (ISSR) polymorphism and inheritance in Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and sugi (Cryptomeria japonica D. Don) megagametophytes using primers that anneal to simple repeats of various lengths, sequences, and non-repetitive motifs at the 5' and 3' ends. Products were visualized on agarose gels with ethidium bromide staining. More than 60% of the 96 primers tested gave interpretable banding patterns in both Douglas-fir and sugi, and the useful primers were in complete agreement among species. Dinucleotide repeat primers were the majority of those tested, and gave all of the useful banding patterns. The 24 best primers were used for segregation studies, yielding a total of 77 loci distributed among two Douglas-fir families and one sugi family. Approximately 90% of the 24 primers showed polymorphism within at least one of the three families. The average number of variable loci per primer was 1.6. Primers based on (AG) n repeats gave the largest number of polymorphic loci; 16 primer-family combinations yielded 24 segregating loci. However, primer based on (GT) n repeats gave the most loci per primer studied (mean of 2.0). All markers displayed apparent dominance (band presence vs absence), and all but three segregation ratios (4%) fit Mendelian expectations: Because they employ longer primers than do RAPDs, have a high degree of polymorphism, conform well to Mendelian expectations, and do not require use of acrylamide gels for analysis, ISSRs may be useful markers for PCR-based genome maps and population studies of conifers.

Endogenous endothelin-1 participates in the maintenance of cardiac function in rats with congestive heart failure : Marked increase in endothelin-1 production in the failing heart

Abstract: Background Although it was demonstrated that circulating endothelin-1 (ET-1) levels are elevated in congestive heart failure (CHF), the production and roles of ET-1 in the failing heart are not known. We investigated the production of ET-1 in the heart and the density of myocardial ET receptors in rats with CHF. We also investigated the effects of intravenously infused BQ-123, an endothelinA (ETA) receptor antagonist, on both heart rate and myocardial contractility in rats with CHF. Methods and Results We used the left coronary artery–ligated rat model of CHF (CHF rats). Three weeks after surgery, the rats developed CHF. Plasma ET-1 concentration was significantly higher in the CHF rats than in the sham-operated rats (P<.01). In the left ventricle, the expression of prepro–ET-1 mRNA was markedly higher in the CHF rats than in the sham-operated rats. The peptide level of ET-1 in the left ventricle was also significantly higher in the CHF rats than in the sham-operated rats (500±41 versus 102±10 pg/g tissue...

Local fluctuation of the spectrum of a multidimensional Anderson tight binding model

Abstract: We consider the Anderson tight binding modelH=−Δ+V acting inl 2(Z d ) and its restrictionH Λ to finite hypercubes Λ⊂Z d . HereV={V x ;x∈Z d } is a random potential consisting of independent identically distributed random variables. Let {E j (Λ)} j be the eigenvalues ofH Λ, and let ξ j (Λ,E)=|Λ|(E j (Λ)−E),j≧1, be its rescaled eigenvalues. Then assuming that the exponential decay of the fractional moment of the Green function holds for complex energies nearE and that the density of statesn(E) exists atE, we shall prove that the random sequence {ξ j (Λ,E)} j , considered as a point process onR 1, converges weakly to the stationary Poisson point process with intensity measuren(E)dx as Λ gets large, thus extending the result of Molchanov proved for a one-dimensional continuum random Schrodinger operator. On the other hand, the exponential decay of the fractional moment of the Green function was established recently by Aizenman, Molchanov and Graf as a technical lemma for proving Anderson localization at large disorder or at extreme energy. Thus our result in this paper can be summarized as follows: near the energyE where Anderson localization is expected, there is no correlation between eigenvalues ofH Λ if Λ is large.

Comparing Policy Networks: Labor Politics in the U.S., Germany, and Japan

Abstract: The United States, Germany, and Japan - the world's three most powerful and successful free market societies - differ strikingly in how their governments relate to their economies. Comparing Policy Networks reports the results of collaborative research by three teams investigating the social organization and policymaking processes of national labor policy domains in the United States, Germany, and Japan during the 1980s. The researchers gathered information about policy goals, communication patterns, and political support connections from 350 key national organizations, including labor unions, business associations, public interest groups, government agencies, and political parties. These networks reveal similar conflict divisions between business and labor interests, but also distinctive patterns within each nation. Unique combinations of informal policy-making networks and the national political institutions may in part explain the differences in power structures and legislative decisions.

Electronic structure of early 3d-transition-metal oxides by analysis of the 2p core-level photoemission spectra.

Abstract: The electronic structures of a wide range of early transition-metal (TM) compounds, including Ti and V oxides with metal valences ranging from 2+ to 5+ and formal d-electron numbers ranging from 0 to 2, have been investigated by a configuration-interaction cluster model analysis of the core-level metal 2p x-ray photoemission spectra (XPS). Inelastic energy-loss backgrounds calculated from experimentally measured electron-energy-loss spectra (EELS) were subtracted from the XPS spectra to remove extrinsic loss features. Parameter values deduced for the charge-transfer energy Delta and the d-d Coulomb repulsion energy U are shown to continue the systematic trends established previously for the late TM compounds, giving support to a charge-transfer mechanism for the satellite structures. The early TM compounds are characterized by a large metal d-ligand p hybridization energy, resulting in strong covalency in these compounds. Values for Delta and U suggest that many early TM compounds should be reclassified as intermediate between the charge-transfer regime and the Mott-Hubbard regime.

Hypertension Induced in Pregnant Mice by Placental Renin and Maternal Angiotensinogen

Abstract: Maternal hypertension is a common complication of pregnancy and its pathophysiology is poorly understood This phenomenon was studied in an animal model by mating transgenic mice expressing components of the human renin-angiotensin system When transgenic females expressing angiotensinogen were mated with transgenic males expressing renin, the pregnant females displayed a transient elevation of blood pressure in late pregnancy, due to secretion of placental human renin into the maternal circulation Blood pressure returned to normal levels after delivery of the pups Histopathologic examination revealed uniform enlargement of glomeruli associated with an increase in urinary protein excretion, myocardial hypertrophy, and necrosis and edema in the placenta These mice may provide molecular insights into pregnancy-associated hypertension in humans

MesP1: a novel basic helix-loop-helix protein expressed in the nascent mesodermal cells during mouse gastrulation

Abstract: A subtractive hybridization strategy was used to isolate putative genes involved in the development of mouse primordial germ cells (PGC). Complimentary DNA was amplified on RNA isolated from the base of the allantois where PGC are located in the 7.5 days post coitum (dpc) mouse embryo. It was then subtracted by hybridization with cDNA amplified on RNA of the anterior region where PGC are absent. A novel gene thus isolated is designated as Mesp1 and encodes a possible transcription factor MesP1 containing a basic helix-loop-helix motif. Its earliest expression was observed at the onset of gastrulation, as early as 6.5 dpc, in the nascent mesodermal cells that first ingressed at the end of the primitive streak. These expressing cells in the lateral and extraembryonic mesoderm showed a wing-shaped distribution. Its initial expression was soon down-regulated at 7.5 dpc before the completion of gastrulation, except at the proximal end of the primitive streak which included the extraembryonic mesoderm and the base of allantois. At 8 dpc, the expression at the base of the allantois moved laterally. This distribution between 7.0 and 8.0 dpc was similar to that of PGC detected by the alkaline phosphatase activity. However, the expression of Mesp1 was down-regulated thereafter, when PGC entered in the migration stage. After birth, Mesp1 expression was detected only in mature testes, but in a different isoform from that expressed in the embryo. Mesp1 was mapped to the mid region of chromosome 7, near the mesodermal deficiency gene (mesd). However, a Southern hybridization study clearly showed that Mesp1 was distinctly different from mesd. The amino acid sequence and its expression pattern suggest that MesP1 plays an important role in the development of the nascent mesoderm including PGC.

Relationship between Falls and Stride Length Variability in Senile Dementia of the Alzheimer Type

Abstract: In this study, 97 patients with senile dementia of the Alzheimer type (SDAT) in a nursing home were followed over a period of 2 years, and the relationship between falls and gait function was examined. The findings indicated that the number of fallers was significantly higher in moderate-stage SDAT patients than in the mild-stage patients. In the moderate-stage SDAT patients, walking speed and stride length, measured as indices to evaluate gait function, were significantly lower, and the stride length variability was significantly higher than in mild-stage patients. When comparing the gait indices of fallers and non-fallers by the severity of dementia, a significant difference was observed only in stride length variability. The gait abnormality associated with advanced severity in dementia is believed to be a factor affecting falling. In particular, stride length variability appeared to be an effective predictor of falling.

The phylogenetic relationship between the Chlamydomonadales and Chlorococcales inferred from 18SrDNA sequence data

Abstract: SUMMARY Nuclear-encoded small subunit ribosomal RNA gene (185rDNA) sequences were determined for Chlamydomonas moewusii Gerloff and five chlorococcalean algae (Chlorococcum hypnosporum Starr; Chlorococcum oleofaciens Trainor et Bold; Chlorococcum sp.; Tetracystis aeria Brown et Bold; Protosiphon botryoides (Kutzingl Klebs). All these algae are characterized by a clockwise CCW) flagellar apparatus. Phylogenetic trees were constructed from sequences from these algae together with 20 green algae. All algae with a CW flagellar apparatus form a monophyletic clade (CW group). Three principal clades can be recognized in the CW group, although no morphological character supports monophyly of any of these three clades. The 185rDNA trees clearly demonstrate the non-monophyly of the Chlamydomonadales and Chlorococcales, suggesting that vegetative morphology does not reflect phylogenetic relationships in the CW group. The paraphyly or polyphyly of the genus Chlamydomonas and Chlorococcum are also revealed. Present analysis suggests that the presence or absence of a zoospore's cell wall and the multinucleate condition have limited taxonomic values at higher taxonomic ranks.

Requirement for a noncoding RNA in Drosophila polar granules for germ cell establishment.

Abstract: In Drosophila embryos, germ cell formation is induced by specialized cytoplasm at the posterior of the egg, the pole plasm. Pole plasm contains polar granules, organelles in which maternally produced molecules required for germ cell formation are assembled. An untranslatable RNA, called Polar granule component (Pgc), was identified and found to be localized in polar granules. Most pole cells in embryos produced by transgenic females expressing antisense Pgc RNA failed to complete migration and to populate the embryonic gonads, and females that developed from these embryos often had agametic ovaries. These results support an essential role for Pgc RNA in germline development.

Trajectory Tracking Control for Navigation of the Inverse Pendulum Type Self-Contained Mobile Robot

Abstract: In this paper, we discuss the trajectory control for a wheeled inverse pendulum type mobile robot. The robot has two independent driving wheels on the same axle, and a gyro type sensor to measure the inclination angular velocity of the body and rotary encoders to measure wheel rotation. The purpose of this work is to make a robot autonomously navigate in a plane while keeping its own balance. The control algorithm consists of three parts: balance and velocity control, steering control and straight line tracking control. We designed and implemented a vehicle command system for such robot to control using the proposed algorithm. Experiments of the navigation in a real indoor environment have been performed using our experimental robot “Yamabico Kurara”.