Quantum phase transition of the randomly diluted heisenberg antiferromagnet on a square lattice

Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S.     

Prominent signal intensity of T1/T2 prolongation in subcortical white matter of the anterior temporal region on conventional screening MRI of late preterm infants with normal development

Purpose

This study discusses prominent signal intensity of T₁/T₂ prolongation of subcortical white matter within the anterior temporal region in premature infant brains that radiologists may encounter when interpreting conventional screening MRIs.

Materials and Methods

T₁- and T₂-weighted images of 69 preterm and term infants with no neurological abnormalities or developmental delays were evaluated retrospectively for areas of prominent signal intensity of T₁/T₂ prolongation in white matter. We measured signal intensities of anterior temporal white matter, deep temporal white matter, frontopolar white matter and subcortical white matter of the precentral gyrus. We accessed chronological changes in signal intensity in the anterior and deep temporal white matter. We also analyzed variance tests among the signal intensity ratios to the ipsilateral thalamus of white matter areas by gestational age.

Results

There was high frequency of prominent signal intensity of T₁/T₂ prolongation in the temporal tip, particularly at a gestational age of 36–38 weeks. Signal intensity ratio of the anterior temporal white matter was lower on T₁-weighted images and higher on T₂-weighted images, and the finding became less prominent with increasing gestational age. The signal intensity ratios of anterior temporal white matter at a gestational age of 36–37 weeks and 38–39 weeks were significantly different from other regions.

Conclusion

Prominent signal intensity of T₁/T₂ prolongation of subcortical white matter of the anterior temporal region is seen in normal premature infants, especially those at 36–39 gestational weeks. Although it is a prominent finding, radiologists should understand that these findings do not represent a pathological condition.     

Observing in-phase single-quantum 15N multiplets for NH2/NH3+ groups with two-dimensional heteronuclear correlation spectroscopy

Two-dimensional (2D) F1-(1)H-coupled HSQC experiments provide 3:1:1:3 and 1:0:1 multiplets for AX(3) and AX(2) spin systems, respectively. These multiplets occur because, in addition to the 2S(y)H(z)(a)-->2S(y)H(z)(a) process, the coherence transfers such as 2S(y)H(z)(a)-->2S(y)H(z)(b) occurring in t(1) period provide detectable magnetization during the t(2) period. Here, we present a 2D F1-(1)H-coupled (1)H-(15)N heteronuclear correlation experiment that provides a 1:3:3:1 quartet for AX(3) spin system and a 1:2:1 triplet for AX(2). The experiment is a derivative of 2D HISQC experiment [J. Iwahara, Y.S. Jung, G.M. Clore, Heteronuclear NMR spectroscopy for lysine NH(3) groups in proteins: unique effect of water exchange on (15)N transverse relaxation. J. Am. Chem. Soc. 129 (2007) 2971-2980] and contains a scheme that kills anti-phase single-quantum terms generated in the t(1) period. The purge scheme is essential to observe in-phase single-quantum multiplets. Applications to the NH(2) and NH(3)(+) groups in proteins are demonstrated.     

Chemical carcinogenesis studies in nonhuman primates

This review covers chemical carcinogenesis studies in nonhuman primates performed by the National Cancer Institute, USA, to provide hitherto unavailable information on their susceptibility to compounds producing carcinogenic effects in rodents. From autopsy records of 401 breeders and untreated controls, incidences of spontaneous malignant tumors were found to be relatively low in cynomolgus (1.9%) and rhesus monkeys (3.8%), but higher in African green monkeys (8%). Various chemical compounds, and in particular 6 antineoplastic agents, 13 food-related compounds including additives and contaminants, 1 pesticide, 5 N-nitroso compounds, 3 heterocyclic amines, and 7 "classical" rodent carcinogens, were tested during the 34 years period, generally at doses 10 approximately 40 times the estimated human exposure. Results were inconclusive in many cases but unequivocal carcinogenicity was demonstrated for IQ, procarbazine, methylnitrosourea and diethylnitrosamine. Furthermore, negative findings for saccharine and cyclamate were in line with results in other species. Thus susceptibility to carcinogens is at least partly shared by nonhuman primates and rodents.     

Activity enhancement of CuZn-impregnated FSM-16 by modification with 1,3-butanediol for steam reforming of methanol

Catalytic activities of CuZn-impregnated FSM-16 catalysts, prepared by the conventional impregnation method and a modified impregnation method with 1,3-butanediol, in steam reforming of methanol were examined. The catalytic activity of the modified CuZn-impregnated FSM-16 was remarkably higher than that of the one prepared by the conventional impregnation method. Characterization of the catalysts by XRD and TPR showed that the enhancement in catalytic activity is due to an improvement in copper dispersion. The amount of 1,3-butanediol, the calcination temperature, and the amount of metal loading were varied to seek the optimal catalyst with the highest methanol conversion. Besides 1,3-butanediol, other organic compounds such as 1,3-propanediol, ethylene glycol, and citric acid also resulted in an enhancement in catalytic activity, while propanol did not.From Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 64–72.Original English Text Copyright © 2005 by Jakdetchai, Takayama, Nakajima.This article was submitted by the authors in English.     

First asymmetric total synthesis of Us-7 and -8, novel D-seco Corynanthe-type oxindole alkaloids from Uncaria attenuata: structure revision of Us-7 and determination of absolute stereochemistry

[reaction: see text] Starting from (S)-glycidol, the asymmetric total synthesis of novel D-seco Corynanthe-type oxindoles Us-7 and Us-8 was accomplished. The structure of Us-7 was revised from the reported structure 1 with the (3R,7S) form to structure 22 with (3S,7R), and the absolute stereochemistry at C15 of both alkaloids was established.     

Differential scanning coulometric titrometry: Application to the system CoNiO at 1000°C

A novel technique involving solid state coulometric titration using stabilized zirconia electrolytes is presented. The method is termed differential scanning coulometric titrometry (DSCT). It is useful for the phase equilibrium studies of multicomponent oxide systems. In the DSCT, two independent and isostructural galvanic cells are used. One is a sample cell in which a sample is charged, while the other is a reference cell without a sample. Under the condition that oxygen activities in both cells are equal to each other, coulometric titration is carried out continuously in both cells. The difference between the titration currents provided to both cells corresponds to the amount of oxygen which is allowed to react with a sample per unit time. If the difference is recorded with respect to the oxygen activity, it starts to deviate from a base line when the sample starts to be oxidized or reduced. This method was successfully applied to the system CoNiO at 1000°C. The phase diagram of the system and related thermodynamic data were obtained.