Acta Medica Okayama7012004Folding of the triangular lattice in a discrete three-dimensional space: density-matrix renormalization-group studyENYoshihiroNishiyama<p>Folding of the triangular lattice in a discrete three-dimensional space is investigated numerically. Such "discrete folding" has come about through theoretical investigation, since Bowick and co-workers introduced it as a simplified model for the crumpling of the phantom polymerized membranes. So far, it has been analyzed with the hexagon approximation of the cluster variation method (CVM). However, the possible systematic error of the approximation was not fully estimated; in fact, it has been known that the transfer-matrix calculation is limited in the tractable strip widths Lless than or equal to6. Aiming to surmount this limitation, we utilized the density-matrix renormalization group. Thereby, we succeeded in treating strip widths up to L=29 which admit reliable extrapolations to the thermodynamic limit. Our data indicate an onset of a discontinuous crumpling transition with the latent heat substantially larger than the CVM estimate. It is even larger than the latent heat of the planar (two-dimensional) folding, as first noticed by the preceding CVM study. That is, contrary to our naive expectation, the discontinuous character of the transition is even promoted by the enlargement of the embedding-space dimensions. We also calculated the folding entropy, which appears to lie within the best analytical bound obtained previously via combinatorics arguments.</p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama7312006Transfer-matrix approach to three-dimensional bond percolation:an application of novotny's formalismENYoshihiroNishiyama<p>A transfer-matrix simulation scheme for the three-dimensional (d=3) bond percolation is presented. Our scheme is based on Novotny's transfer-matrix formalism, which enables us to consider arbitrary (integral) number of sites N constituting a unit of the transfer-matrix slice even for d=3. Such an arbitrariness allows us to perform systematic finite-size-scaling analysis of the criticality at the percolation threshold. Diagonalizing the transfer matrix for N=4,5,...,10, we obtain an estimate for the correlation-length critical exponent nu=0.81(5).</p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama7022004Multicriticality of the three-dimensional Ising model with plaquette interactions: an extension of novotny's transfer-matrix formalismENYoshihiroNishiyama<p>A three-dimensional Ising model with the plaquette-type (next-nearest-neighbor and four-spin) interactions is investigated numerically. This extended Ising model, the so-called gonihedric model, was introduced by Savvidy and Wegner as a discretized version of the interacting (closed) surfaces without surface tension. The gonihedric model is notorious for its slow relaxation to the thermal equilibrium (glassy behavior), which deteriorates the efficiency of the Monte Carlo sampling. We employ the transfer-matrix (TM) method, implementing Novotny's idea, which enables us to treat an arbitrary number of spins N for one TM slice even in three dimensions. This arbitrariness admits systematic finite-size-scaling analyses. Accepting the extended parameter space by Cirillo , we analyzed the (multi-) criticality of the gonihedric model for Nless than or equal to13. Thereby, we found that, as first noted by Cirillo analytically (cluster-variation method), the data are well described by the multicritical (crossover) scaling theory. That is, the previously reported nonstandard criticality for the gonihedric model is reconciled with a crossover exponent and the ordinary three-dimensional-Ising universality class. We estimate the crossover exponent and the correlation-length critical exponent at the multicritical point as phi=0.6(2) and (nu) over dot =0.45(15), respectively.</p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama7142005Finite-size-scaling analysis of the XY universality class between two and three dimensions: an application of novotny's transfer-matrix methodENYoshihiroNishiyama<p>Based on Novotny's transfer-matrix method, we simulated the (stacked) triangular Ising antiferromagnet embedded in the space with the dimensions variable in the range 2 <= d <= 3. Our aim is to investigate the criticality of the XY universality class for 2 <= d <= 3. For that purpose, we employed an extended version of the finite-size-scaling analysis developed by Novotny, who utilized this scheme to survey the Ising criticality (ferromagnet) for 1 <= d <= 3. Diagonalizing the transfer matrix for the system sizes N up to N=17, we calculated the d-dependent correlation-length critical exponent nu(d). Our simulation result nu(d) appears to interpolate smoothly the known two limiting cases, namely, the Kosterlitz-Thouless (KT) and d=3 XY universality classes, and the intermediate behavior bears close resemblance to that of the analytical formula via the 1/N-expansion technique. Methodological details including the modifications specific to the present model are reported.</p>No potential conflict of interest relevant to this article was reported.Okayama University Medical SchoolActa Medica Okayama0386-300X5221998The Usefulness of <sup>99m</sup>Tc-Technegas Scintigraphy for Diagnosing Pulmonary Impairment Caused by Pulmonary Emphysema97103ENKatashiSatohKazueTakahashiTakuyakobayashiYukaYamamotoYoshihiroNishiyamaMasatadaTanabeArticle10.18926/AMO/31317<p>X-ray computed tomography (CT) has been used for diagnosis of pulmonary emphysema because it can reveal the morphology of low attenuation areas. Recently, 99mTc-Technegas imaging, one of several types of scintigraphic techniques, has been used for ventilation scintigraphy. Technegas scintigraphy was performed on 15 patients with pulmonary emphysema, and we compared the extent and degree of abnormal findings on Technegas scintigraphy with the extent of low attenuation areas shown by CT. We classified the findings of Technegas imaging into three grades, from mild to severe, according to the extent of peripheral irregularity and central hot spot formation. We also classified the findings of CT as centrilobular emphysema into three grades from mild to severe according to the extent of low attention areas in the peripheral lung fields. In 5 cases, CT and Technegas assessment resulted in equivalent diagnoses. In eight cases, Technegas images showed more detailed findings than CT images. In the two remaining cases, which were diagnosed as panlobular emphysema on CT, Technegas images showed the severe stage. Technegas scintigraphy was useful for diagnostic assessment of pulmonary emphysema, especially for panlobular emphysema, which is difficult to distinguish from the normal lung condition by CT assessment.</p>
No potential conflict of interest relevant to this article was reported.