Showing papers by "Academia Sinica published in 1994"

Magnetoelectric effect in composites of piezoelectric and piezomagnetic phases

Abstract: The magnetoelectric effect in composites of piezoelectric and piezomagnetic phases is investigated theoretically. The magnetoelectric effect is totally absent in these two constituent phases, and so it is a new property of the composites. A generalized theoretical framework based on a Green's function method and perturbation theory is proposed to treat the coupled magnetoelectric behavior in the composites. Explicit relations for determining the effective magnetoelectric effect in the composites are derived, and the different approximate expressions for the magnetoelectric coefficient of the fibrous composites with 1-3 or 3-1 connectivity of phases are given. To illustrate the technique, numerical calculations of the magnetoelectric coefficients of the BaTiO3-CoFe2O4 composites for various phase compositions and particle shapes are performed. The theoretical estimates are shown to be in agreement with available experimental results, and also show the interesting magnetoelectric behavior of the composites.

Identification of early visual evoked potential generators by retinotopic and topographic analyses

Abstract: This study investigated the cortical sources of the early (50-250 ms) components of the pattern-onset visual evoked potential (VEP) VEPs were recorded in response to a small circular checkerboard stimulus that was flashed over a range of visual field positions Temporally and spatially overlapping VEP components were distinguished by differences in retinotopic sensitivity and scalp topography, and by inverse dipole modeling The C1 component (50-80 ms) was found to change its polarity and topography systematically as a function of stimulus position in a manner consistent with the retinotopic organization of the striate cortex The P1 component (comprised of the P75 and P100 subcomponents) had a time course that overlapped the C1 but could be distinguished from the C1 by its differing topography and reduced sensitivity to stimulus position The P1 generators were localized to the lateral extrastriate cortex Inverse dipole models were consistent with these striate and extrastriate source locations for the C1 and P1, respectively The N1 component (120-180 ms) was found to originate from several spatially distinct generators that differed in their retinotopic organization © 1995 Wiley-Liss, Inc

Normal Forms and Bifurcation of Planar Vector Fields

Abstract: Preface 1. Center manifolds 2. Normal forms 3. Codimension one bifurcations 4. Codimension two bifurcations 5. Bifurcations with codimension higher that two Bibliography Index.

Sources of attention-sensitive visual event-related potentials.

Abstract: In a study of the neural processes that mediate visual attention in humans, 32-channel recordings of event-related potentials were obtained from 14 normal subjects while they performed a spatial attention task. The generator locations of the early C1, P1, and Nl components of the visual evoked response were estimated by means of topographic maps of voltage and current source density in conjunction with dipole modelling. The topography of the C1 component (ca. 85 ms post-stimulus) was consistent with a generator in striate cortex, and this component was unaffected by attention. In contrast, the P1 and Nl components (ca. 95 and 170ms) exhibited current density foci at scalp sites overlying lateral extrastriate cortex and were larger for attended stimuli than for unattended stimuli. The voltage topographies in the 75–175 ms latency range were modeled with a 5-dipole configuration consisting of a single striate dipole and left-right pairs of dipoles located in lateral extrastriate and inferior occipito-temporal areas. This model was found to account for the voltage topographies produced by both attended and unattended stimuli with low residual variance. These results support the proposal that visual-spatial attention modulates neural activity in extrastriate visual cortex but does not affect the initial evoked response in striate cortex.

Gerchberg–Saxton and Yang–Gu algorithms for phase retrieval in a nonunitary transform system: a comparison

Abstract: A detailed comparison of the original Gerchberg-Saxton and the Yang-Gu algorithms for the reconstruction of model images from two intensity measurements in a nonunitary transform system is presented. The Yang-Gu algorithm is a generalization of the Gerchberg-Saxton algorithm and is effective in solving the general amplitude-phase-retrieval problem in any linear unitary or nonunitary transform system. For a unitary transform system the Yang-Gu algorithm is identical to the Gerchberg-Saxton algorithm. The reconstruction of images from data corrupted with random noise is also investigated. The simulation results show that the Yang-Gu algorithm is relatively insensitive to the presence of noise in data. In all cases studied the Yang-Gu algorithm always resulted in a highly accurate recovered phase.

The complete nucleotide sequence and gene organization of carp (Cyprinus carpio) mitochondrial genome.

Abstract: The complete sequence of the carp mitochondrial genome of 16,575 base pairs has been determined. The carp mitochondrial genome encodes the same set of genes (13 proteins, 2 rRNAs, and 22 tRNAs) as do other vertebrate mitochondrial DNAs. Comparison of this teleostean mitochondrial genome with those of other vertebrates reveals a similar gene order and compact genomic organization. The codon usage of proteins of carp mitochondrial genome is similar to that of other vertebrates. The phylogenetic relationship for mitochondrial protein genes is more apparent than that for the mitochondrial tRNA and rRNA genes.

Elastic-wave stimulation of oil production; a review of methods and results

Abstract: Numerous observations accumulated principally during the last 40 years show that seismic waves generated from earthquakes and cultural noise may alter water and oil production In some cases wave excitation may appreciably increase the mobility of fluids The effect of elastic waves on the permeability of saturated rock has been confirmed in numerous laboratory experiments Two related applications have arisen from these findings In the first application, high-power ultrasonic waves are applied for downhole cleaning of the near-wellbore in producing formations that exhibit declining production as a result of the deposition of scales and precipitants, mud penetration, etc In many cases, ultrasound effectively removes the barriers to oil flow into the well The ultrasonic method is reported to be successful in 40-50 percent of the cases studied In the case of successful treatment, the effect of improved permeability may last up to several months Whereas this method has a very local effect, a second application is used to stimulate the reservoir as a whole Here seismic frequency waves are applied at the earth’s surface by arrays of vibroseis-type sources This method has produced promising results; however, further testing and understanding of the mechanisms are necessary

Nonparametric Estimation of Mean Functionals with Data Missing at Random

Abstract: This article considers a distribution-free estimation procedure for a basic pattern of missing data that often arises from the wellknown double sampling in survey methodology. Without parametric modeling of the missing mechanism or the joint distribution, kernel regression estimators are used to estimate mean functionals through empirical estimation of the missing pattern. A generalization of the method of Cheng and Wei is verified under the assumption of missing at random. Asymptotic distributions are derived for estimating the mean of the incomplete data and for estimating the mean treatment difference in a nonrandomized observational study. The nonparametric method is compared with a naive pairwise deletion method and a linear regression method via the asymptotic relative efficiencies and a simulation study. The comparison shows that the proposed nonparametric estimators attain reliable performances in general.

Receptor binding redefined by a structural switch in a mutant human insulin.

Abstract: CRYSTAL structures of insulin have been determined in various distinct forms1–5, the relevance of which to receptor recognition has long been the subject of speculation2,6,7. Recently the crystal structure of an inactive insulin analogue has been determined and, surprisingly, found to have a conformation identical to native insulin8,9. On this basis Dodson and colleagues have suggested that the known insulin crystal structures reflect an inactive conformation, and that a change in conformation is required for activity—specifically, the carboxy terminal residues of the B-chain are proposed to separate from the amino terminal residues of the A-chain8. Here we report the solution structure of an active insulin mutant7,10, determined by two-dimensional NMR, which supports this hypothesis. In the mutant, the carboxy terminal β-turn and β-strand of the B-chain are destabilized and do not pack across the rest of the molecule. We suggest that analogous detachment of the carboxy terminal region of the B-chain occurs in native insulin on binding to its receptor. Our finding that partial unfolding of the B-chain exposes an alternative protein surface rationalizes the receptor-binding properties of a series of anomalous insulin analogues7,11–13, including a mutant insulin associated with diabetes mellitus in man14,15.

Exhumation of the Dabie Shan ultra-high-pressure rocks and accumulation of the Songpan-Ganzi flysch sequence, central China

Abstract: The presence of coesite- and diamond-bearing ultra-high-pressure (UHP) metamorphic rocks in the Dabie and Sulu regions, central China, suggests that a >100-km-thick crustal section (4 x 106 km6 in volume) has been denuded. This volume is comparable to that represented by the 10-15-km-thick Middle to Upper Triassic flysch rocks in the Songpan-Ganzi region. Regional geology and radiometric dates are compatible with an interpretation that the majority of these sedimentary rocks were derived from denudation of the orogenic belt between North and South China blocks following their latest Paleozoic to Triassic collision. This correlation implies a high denudation rate of ∼4 mm/yr that may have been in part promoted by tropical precipitation and extreme topographic relief for as long as 25 m.y.

A diverse new primate fauna from middle Eocene fissure-fillings in southeastern China

Abstract: We report the discovery of a fauna of primates from Eocene (approximately 45 Myr) deposits in China having a diversity greater than in European and North American localities of similar antiquity From the many forms that will illuminate questions of primate phylogeny comes evidence for a basal radiation of primitive simians

Controlling spatiotemporal chaos in coupled map lattice systems.

Abstract: A spatiotemporal system is modeled by a coupled map lattice. Feedback pinnings are used to control chaos of the system by stabilizing a certain unstable reference state. As the pinning distribution is dense enough, the unstable state can be stabilized. If the density is low, the reference state may not be approached asymptotically. In this case, however, the pinnings can still effectively suppress chaos and produce rich spatiotemporal structures. If a solution is locally stable while the transient process to this state is extremely long and chaotic, pinnings of very low density can well control the transient chaos.

Patterns and Structures of the Currents in Bohai, Huanghai and East China Seas

Abstract: The Bohai Sea (BS), Huanghai Sea (HS) and East China Sea (ECS) are a continuous system that consists of two sub-systems: the warm and saline current system of oceanic origin (Kuroshio and its branches and extensions) and the less saline coastal current system. The former moves northward and northeastward and the latter generally southward. The current pattern of these seas is roughly in the form of a cyclonic gyre as shown in Fig. 1, with the Kuroshio-Tsushima Warm Current - HS Warm Current and its extension on the east side and the China Coastal Current including the southern BS Coastal Current, HS Coastal Current, and ECS Coastal Current) on the west side. Along the western coast of Korea, the West Korea Coastal Current flows southward.

Petrogenesis of garnet‐bearing ultramafic rocks and associated eclogites in the Su‐Lu ultrahigh‐P metamorphic terrane, eastern China

Abstract: Ultramafic blocks that themselves contain eclogite lenses in the Triassic Su-Lu ultrahigh-P terrane of eastern China range in size from hundreds of metres to kilometres. The ultramafic blocks are enclosed in quartzofeldspathic gneiss of early Proterozoic age. Ultramafic rocks include garnetiferous lherzolite, wehrlite, pyroxenite, and hornblende peridotite. Garnet lherzolites are relatively depleted in Al2O3 (<3.8wt%), CaO (<3.2%) and TiO2 (<0.11 wt%), and are low in total REE contents (several p.p.m.), suggesting that the rocks are residual mantle material that was subjected to low degrees of partial melting. The eclogite lenses or layers within the ultramafic rocks are characterized by higher MgO and CaO, lower Al2O3 and TiO2 contents, and a higher CaO/Al2O3 ratio compared to eclogites enclosed in the quartzofeldspathic gneiss. Scatter in the plots of major and trace elements vs. MgO, REE patterns and La, Sm and Lu contents suggest that some eclogites were derived from melts formed by various degrees (0.05–0.20) of partial melting of peridotite, and that other eclogites formed by accumulation of garnet and clinopyroxene ± trapped melt in the upper mantle. Both ultramafic and eclogitic rocks have experienced a complex metamorphic history. At least six stages of recrystallization occurred in the ultramafic rocks based on an analysis of reaction textures and mineral compositions. Stage I is a high temperature protolith assemblage of Ol + Opx + Cpx + Spl. Stage II consists of the ultrahigh-pressure assemblage Ol + Cpx + Opx + Grt. Stage III is manifested by the appearance of fine-grained garnet after coarse-grained garnet. Stage IV is characterized by formation of kelyphitic rims of fibrous Opx and Cpx around garnet, and replacement of garnet by spinel and pargasitic-hornblende. Stage V is represented by the assemblage Ol + Opx + Prg-Hbl + Spl. The mineral assemblages of stages VIA and VIB are Ol + Tr-Amp + Chl and Serp + Chl ± talc, respectively. Garnet and orthopyroxene all show a decrease in MgO with retrogressive recrystallization and Na2O in clinopyroxene also decreases throughout this history. Eclogites enclosed within ultramafic blocks consist of Grt + Omp + Rt ± Qtz ± Phn. A few quartz-bearing eclogites contain rounded and oval inclusion of polycrystalline quartz aggregates after coesite in garnet and omphacite. Minor retrograde features include thin symplectic rims or secondary amphiboles after Cpx, and ilmenite after rutile. P-T estimates indicate that the ultrahigh-metamorphism (stage II) of ultramafic rocks occurred at 820-900d C and 36-41 kbar and that peak metamorphism of eclogites occurred at 730-900d C and >28 kbar. Consonant with earlier plate tectonic models, we suggest that these rocks were underplated at the base of the continental crust. The rocks then underwent ultrahigh-pressure metamorphism and were tectonically emplaced into thickened continental crust during the Triassic collision between the Sino-Korean and Yangtze cratons.

Decays of the b(c)-meson

Abstract: The decays of the [ital B][sub [ital c]] meson are calculated systematically by introducing a suitable approach. The obtained results are discussed and compared with those obtained by other approaches.

Expression of alpha-amylases, carbohydrate metabolism, and autophagy in cultured rice cells is coordinately regulated by sugar nutrient.

Abstract: A rice suspension cell culture system has been established to study how sugar depletion regulates alpha-amylase expression, carbohydrate metabolism, and other physiological and cellular changes. It is shown here that a group of 44 kDa alpha-amylases are constitutively expressed whether or not the cells are starved of sucrose. However, expression of a new group of alpha-amylases of 46 kDa is dramatically induced when cells are starved of sucrose. Cellular sugar and starch were rapidly consumed and metabolic activity was decreased in the starved cells. Extensive autophagy also occurred in the starved cells, which caused an increase in vacuolar volume and degradation of cytoplasmic constituents including amyloplasts. Immunocytochemical studies revealed that alpha-amylases are localized in starch granules within amyloplasts, in cell walls, and in some of the vacuoles. The presence of putative signal sequences in the N-termini of nine rice alpha-amylases suggests hitherto unidentified pathways for import of alpha-amylases into amyloplasts. The studies show that differential alpha-amylase expression, carbohydrate metabolism, metabolic activity, and vacuolar autophagy are coordinately regulated by the sugar level in the medium. As the starved suspension cells exhibit some sugar-regulated characteristics of alpha-amylase expression in germinating rice embryos as well as physiological changes similar to those in senescing cells, this system represents an ideal tool for studying cellular, biochemical, and molecular biological aspects of alpha-amylase gene regulation, carbohydrate metabolism, senescence, and protein targeting in plants.

Algebraic and geometric reasoning using Dixon resultants

Abstract: Dixon's method for computing multivariate resultants by simultaneously eliminating many variables is reviewed. The method is found to be quite restrictive because often the Dixon matrix is singular, and the Dixon resultant vanished identically yielding no information about solutions for many algebraic and geometry problems. We extend Dixon's method for the case when the Dixon matrix is singular, but satisfies a condition. An efficient algorithm is developed based on the proposed extension for extracting conditions for the existence of affine solutions of a finite set of polynomials. Using this algorithm, numerous geometric and algebraic identities are derived for examples which appear intractable with other techniques of triangulation such as the successive resultant method, the Gro¨bner basis method, Macaulay resultants and Characteristic set method. Experimental results suggest that the resultant of a set of polynomials which are symmetric in the variables is relatively easier to compute using the extended Dixon's method.

Differential effects of rotation, plant residue and nitrogen fertilizer on microbial biomass and organic matter in an Australian alfisol

Abstract: Measurements of microbial biomass C in an Alfisol topsoil commenced in the ninth year of a field trial, which had been set up to determine the influence of agronomic practices on plant yields and soil properties. Management practice and time of sampling over a 5-year monitoring period affected the magnitude and direction of changes in the concentrations of microbial biomass C, which did not consistently relate to changes in the concentrations of soil organic matter C and N. Microbial biomass C was (a) higher in soils under a wheat-pasture rotation than under continuous wheat, but only during the first 3 years of monitoring, (b) higher in soils where plant residues were incorporated or retained on the soil surface than where residues were burned, but (c) lower in N-fertilized soils than in unfertilized soils. Measured differences in biomass C between treatments were generally much less than predicted, when based on calculations of biomass C accumulation from the decomposition of known amounts of returned plant residues. By contrast with biomass C, organic matter contents were consistently higher where practices resulted in greater residue return, viz. in soils under the rotation which included a pasture phase, in N-fertilized soils, and in soils where residues were incorporated or were left on the soil surface. The decreased biomass C contents in N-fertilized soils (despite a greater return of plant residues and an increased accumulation of soil organic C and N), were partly attributable to an effect of fertilizer in decreasing soil pH, which directly affected biomass assay performance. Nevertheless, after correction for pH changes, N fertilizer application practice decreased biomass C as a percentage of soil organic C, due it is deduced, to increased death rates of decomposer organisms. Rates of C and N mineralization expressed as percentages of soil organic matter C and N were unaffected by N-fertilizer practices. We have concluded that short- and long-term factors influenced biomass C under the various management practices. Changing soil environmental conditions may with time partly offset, or even reverse, trends based solely on considerations of energy supply (i.e. plant residue return). In the wider context, the value of microbial biomass as an index of sustainability is better appraised when differences in time scale for the expression of factors influencing the processes of C turnover in soil are also considered.

Reduction of Cr(VI) by a Consortium of Sulfate-Reducing Bacteria (SRB III).

Abstract: A consortium of bacteria with tolerance to high concentrations of Cr(VI) (up to 2,500 ppm) and other toxic heavy metals has been obtained from metal-refinishing wastewaters in Chengdu, People9s Republic of China This consortium consists of a range of gram-positive and gram-negative rods and has the capacity to reduce Cr(VI) to Cr(III) as amorphous precipitates which are associated with the bacterial surfaces An endospore-producing, gram-positive rod and a gram-negative rod accumulate the most metallic precipitates, and, over time, 80 to 95% of Cr can be removed from concentrations ranging from 50 to 2,000 ppm (096 to 3845 mM) Kinetic studies revealed a first-order constant for Cr removal of 01518 h-1 for an initial concentration of 1,000 ppm (193 mM), and the sorption isothermal data could be interpreted by the Freundlich relationship The sorption was not entirely due to a passive interaction with reactive sites on the bacterial surfaces since gamma-irradiated, killed cells could not immobilize as much metal When U or Zn was added with the Cr, it was also removed and could even increase the total amount of Cr immobilized The consortium was tolerant to small amounts of oxygen in the headspace of tubes, but active growth of the bacteria was a requirement for Cr immobilization through Cr(VI) reduction, resulting in the lowering of Eh Our data suggest that the reduction was via H2S This consortium has been named SRB III, and it may be useful for the bioremediation of fluid metal-refining wastes Images

Mechanical theorem proving in geometries

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Evidence for Monophyly and Arthropod Affinity of Cambrian Giant Predators

Abstract: The Chinese Early Cambrian Chengjiang fauna includes three different anomalocaridids, a globally spread, extinct marine group including the largest known Cambrian animals. Anomalocaridids were active predators, and their presence implies that a complex ecosystem appeared abruptly in the earliest Phanerozoic. Complete specimens display several sets of characters shared only with some other exclusively Cambrian forms. This evidence indicates that anomalocaridids, Opabinia, and Kerygmachela form a monophyletic clade. Certain features indicate arthropod affinities of the lade, and for this group an unnamed (sub)phylum-level taxon within an arthropod (super)phylum is proposed.