bluuebunny/crossref_metadata_2025 huggingface dataset:
The pollination mechanism of Abies amabilis
Authors: Chandler Luke M , Owens John N
Published: June 2004

The development and function of the pollination mechanism were studied in Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes growing in clonal seed orchards. Two adaxial ovules developed on each scale after dormancy and each ovule formed a funnel-like integument tip with a nucellus at the base of the shallow funnel. At receptivity, the seed cones were erect and the ovules inverted. No pollination drop was observed in fresh specimens but lipid microdrops were secreted on the rim and inner surface of the funnel. Water applied as spray beaded on all cone surfaces except where microdrops were present. Surfaces of the cone were observed using scanning electron microscopy to determine the presence and ultrastructure of the waxy cuticle. All surfaces that were not wettable with water were covered with epicuticular wax. Pollen did not adhere firmly to cone surfaces having epicuticular wax but adhered to the microdrops on the funnel. Drops of water picked up pollen as they moved over the waxy surfaces toward the cone axis. There, the inverted ovules were arranged in a tight helix around the cone axis. Beads of water, often containing pollen, settled on the scale surface just below the funnels and then touched and wetted the inside of the funnels, forming a column of water from the scale surface below to the funnel above. The saccate, buoyant pollen then floated up and into the funnel. Experiments were done to determine the effect of pollen application on pollen uptake into the ovule: without water, with water applied before or after pollen was applied, or as a pollenwater mix. Results support the hypothesis that A. amabilis, and likely other Abies species, lacks a conspicuous pollination drop and water as rain or dew substitutes for a pollination drop.
Short-term impact of forest soil compaction and organic matter removal on soil mesofauna density and oribatid mite diversity
Authors: Battigelli Jeffrey P , Spence John R , Langor David W , Berch Shannon M
Published: June 2004

This study examines the short-term impact of forest soil compaction and organic matter removal on soil mesofauna, in general, and oribatid mite species, in particular. Both soil compaction and organic matter removal reduced the density of soil mesofauna. Stem-only harvesting reduced total mesofauna densities by 20% relative to uncut forest values. A combination of whole-tree harvest and forest floor removal with heavy soil compaction significantly reduced total soil mesofauna densities by 93% relative to the uncut forest control. Removal of the forest floor represents a substantial loss of habitat for most soil mesofauna. The forest floor apparently buffered the mineral soil by limiting both the impact of soil compaction and fluctuations in soil temperature and moisture. The relative abundance of Prostigmata and Mesostigmata increased with treatment severity, whereas that of Oribatida decreased. Species richness of the oribatid mite fauna was reduced as the severity of treatments increased. The number of rare oribatid species (those representing <1% of the total oribatid mite sample) decreased by 40% or more relative to the uncut forest control. Evenness also decreased as treatment severity increased. Oppiella nova and Suctobelbella sp. near acutidens were the dominant oribatid species in both the forest floor and mineral soil, regardless of treatment. Soil compaction and organic matter removal significantly impacted the density and diversity of soil mesofauna and oribatid mite fauna in the short term at these study sites.
Modeling dead wood in Fennoscandian old-growth forests dominated by Norway spruce
Authors: Ranius Thomas , Jonsson Bengt Gunnar , Kruys Nicholas
Published: June 2004

If equilibrium is assumed in unmanaged forests, the volume of coarse woody debris (CWD), VCWD, may be calculated from (i) the volume of living trees, Vliving, (ii) average volume of a dead stem in relation to when it was alive, k, (iii) tree mortality rate, m, and (iv) residence time of CWD, t, by the equation VCWD = Vlivingkmt. We parameterized this equation with data from Norway spruce (Picea abies (L.) Karst.) dominated forests in Fennoscandia. The Vliving was assumed to be directly proportional to forest productivity. Tree mortality data were from the National Forest Inventory, while it was difficult to find quantitative data on k and t. The predicted amounts (74138 m3/ha, with larger amounts in the south) and size distribution (a negative exponential distribution of the number of stems) of CWD corresponded fairly well to averages from field inventories. By using a computer simulation program, the variability in tree mortality, density of living trees, and residence time of CWD were considered. In the simulations, the amount of CWD varied widely between 1-ha plots, especially for individual decay classes. Therefore, this model could be used to predict averages from larger landscapes unaffected by large disturbances, while no model can predict the amount of CWD at individual plots.
Structural stocking guides: a new look at an old friend
Authors: Gove Jeffrey H
Published: June 2004

A parameter recovery-based model is developed that allows the incorporation of diameter distribution information directly into stocking guides. The method is completely general in applicability across different guides and forest types and could be adapted to other systems such as density management diagrams. It relies on a simple measure of diameter distribution shape, the basal area larger than quadratic mean stand diameter, to estimate the parameters of the unknown distribution. This latter quantity is shown to have high correlation with stocking guide variables in northeastern forest types. A primary objective of this new type of guide is that its use should require a minimal amount of new information from the user and that the underlying model should be as simple as possible.
Influence of elevated CO2, nitrogen, and Pinus elliottii genotypes on performance of the redheaded pine sawfly, Neodiprion lecontei
Authors: Saxon Milam E , Davis Micheal A , Pritchard Seth G , Runion G Brett , Prior Stephen A , Stelzer Hank E , Rogers Hugo H , Dute Roland R
Published: June 2004

Slash pine (Pinus elliottii Engelm. var. elliottii) seedlings were grown in open-top chambers receiving ambient or elevated atmospheric CO2 (~365 or ~720 µL·L1). Seedlings received low or high soil nitrogen treatments (0.02 or 0.2 mg N·g1) and represented three families varying in resistance to fusiform rust (Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme (Hedgc. & N. Hunt) Burdsall & G. Snow). Following 18 months of exposure to treatment conditions, current-year needles were fed to larvae of the redheaded pine sawfly (Neodiprion lecontei (Fitch)). Needle N concentration and water content were lower in elevated-CO2 and in low-N treatments. Total phenolics increased under high-CO2 and low-N conditions and were highest in the resistant family. Condensed tannins did not vary on the basis of CO2 or N but were higher in needles from the resistant family. Alterations in needle chemistry were associated with variations in sawfly growth and development. Larvae performed most poorly on the family most resistant to fusiform rust, suggesting that the mechanism for resistance was similar in both cases. Relative consumption rates increased with CO2-enriched needle diets but were depressed for resistant needles, suggesting deterrence from the higher total phenolics in this family. Diets using CO2-enriched needles or resistant needles or needles from low-N fertilization treatments resulted in lower relative growth rates for the larvae. Days to pupation increased for larvae fed CO2-enriched and low-N needles. These results suggest that the redheaded pine sawfly could suffer as the level of atmospheric CO2 continues to rise.
Height development of Scots pine on peatlands: describing change in site productivity with a site index model
Authors: Hökkä Hannu , Ojansuu Risto
Published: June 2004

The effect of site properties and forest drainage on the dominant height development of Scots pine (Pinus sylvestris L.) stands in peatland sites was studied using data from permanent sample plots located in natural and drained sites in northern Finland. The Korf model was used to describe the height development of dominant trees in natural sites. The effect of drainage on height development was accounted for by a term giving a nonlinear height increase for drained sites as a function of the time elapsed since drainage. The variance component model was applied to account for the hierarchical data structure. Natural height development after 30 years of age at DBH was significantly slower in PF sites (sparsely forested pine fens) than in PS sites (genuine forested pine swamps). Within PF sites, there were further differences in relation to nutrient availability. Temperature sum explained the variation in the intercept. In PS sites, drainage resulted in a moderate increase in the maximum attainable height, while in PF sites, drainage improved site productivity by 80%85% in terms of the attainable height. The asymptote for drained stands was dependent on stand age at the time of drainage. Differences between the two major groups were assumed to be due to initial differences in site water regime.
Persistence of early growth of planted Picea mariana seedlings following clear-cutting and drainage in Quebec wetlands
Authors: Roy Vincent , Plamondon André P , Bernier Pierre Y
Published: June 2004

A study was carried out to test the persistence of the early effects of forest drainage and planting position on the growth of black spruce (Picea mariana (Mill.) BSP) seedlings planted in eight drained forested wetland cutovers. Initial results, 2 years after planting, had shown that seedling response was most affected by planting position within the microtopography, and to a lesser extent, by distance to the drainage ditch. Persistence of these effects was tested by measuring the survival and growth rates of seedlings for an additional 4 years after planting. Increased growth owing to raised planting position was maintained over time. The small effect of distance to ditch on seedling growth observed after two growing seasons did not evolve into larger differences over time, and after 6 years there was no significant effect of distance to drainage ditch. Given the marginal growth improvements of black spruce seedlings planted closer to the ditch, drainage networks with narrow ditch spacing are not necessary on these site types after clear-cutting.
Using crown condition variables as indicators of forest health
Authors: Zarnoch S J , Bechtold W A , Stolte K W
Published: June 2004

Indicators of forest health used in previous studies have focused on crown variables analyzed individually at the tree level by summarizing over all species. This approach has the virtue of simplicity but does not account for the three-dimensional attributes of a tree crown, the multivariate nature of the crown variables, or variability among species. To alleviate these difficulties, we define composite crown indicators based on geometric principles to better quantify the entire tree crown. These include crown volume, crown surface area, and crown production efficiency. These indicators were then standardized to a mean of 0 and variance of 1 to enable direct comparison among species. Residualized indicators, which can also be standardized, were defined as the deviation from a regression model that adjusted for tree and plot conditions. Distributional properties were examined for the three composite crown indicators and their standardized-residualized counterparts for 6167 trees from 250 permanent plots distributed across Virginia, Georgia, and Alabama. Comparisons between the composite crown indicators and their associated standardized residual indicators revealed that only two or three plots were jointly classified as poor by both when thresholds were set at the lower 5 percentiles of statistical distributions. In contrast, 19-21 other plots were classified differently, emphasizing that different aspects of crown condition are being summarized when the raw values are adjusted and standardized. Generally, crown volume and crown surface area behaved similarly, while crown production efficiency was substantially different.
Forest floor microarthropod abundance and oribatid mite (Acari: Oribatida) composition following partial and clear-cut harvesting in the mixedwood boreal forest
Authors: Lindo Zoë , Visser Suzanne
Published: June 2004

The effects of partial and clear-cut harvesting on abundance and community composition of forest floor microarthropods and oribatid mites were investigated in conifer and deciduous stands of the mixedwood boreal forest. Soil samples from clearcuts, strip-cut corridors in a partial cut, green-tree retention patches in a partial cut, and uncut control sites were collected 2.5 years after harvest and microarthropods were extracted, enumerated, and identified. Densities of microarthropod suborders were lower in the strip-cut corridors of the deciduous stands and significantly lower in the suborder Oribatida (oribatid mites). Changes in microarthropod community composition, decreased relative abundance of prostigmatid mites, and increased relative abundance of mesostigmatid mites were observed in corridor and clear-cut treatments. Lowered abundances and changes in community composition are likely due to compaction of the forest floor during harvesting. Selected oribatid mite species showed significantly lower abundances in clearcuts than in uncut sites, but diversity indices for oribatid mites were generally not significantly different between uncut sites and clearcuts. Changes in oribatid mite communities following harvesting were thus more quantitative (absolute abundance) than qualitative (diversity, composition), and as a result, use of oribatid mites as biological indicators of disturbance is limited because of the lack of changes in species composition.
Successional status and root foraging for phosphorus in seven tropical tree species
Authors: Blair Brent C , Perfecto Ivette
Published: June 2004

In this study, the impact of localized nutrient patches on above- and belowground growth of tropical trees was examined. Seedlings of seven tree species (Albizia guachapele Kunth (Dugand), Cedrela odorata L., Ceiba pentandra (L.) Gaertn., Cordia alliodora (Ruiz & Pavón) Oken, Dalbergia retusa Hemsl., Gliricidia sepium (Jacq.) Kunth ex Walp., and Swietenia macrophylla King) of varying successional status were used in a greenhouse container experiment. Treatments of homogeneous and heterogeneous P fertilization were used to determine each species' ability to forage morphologically for P. In each pot, root length density, average root diameter, and root length to shoot ratio were measured. It was hypothesized that early successional species would be most effective at taking advantage of the heterogeneous soil environment. This prediction was based on studies showing a high degree of soil heterogeneity in early successional forest environments and the need for plants to take advantage of this variability. The study found great variability in the foraging capacity between species, but the hypothesis that successional status and root foraging ability are related was not supported in the species tested. Overall, five of the seven species examined showed some indication that they were taking advantage of local nutrient patches. In four of these species, increased root length density was detected in P patches (A. guachapele, C. odorata, G. sepium, and S. macrophylla) and one species had decreased root width in the P patches (G. sepium). When comparisons were made between homogeneously and heterogeneously fertilized pots, G. sepium and C. alliodora appeared to take advantage of the heterogeneous resource. Both of these species increased aboveground growth in the heterogeneous pots and C. alliodora also had a decreased root to shoot ratio.
The source of heme for vascular heme oxygenase I: heme uptake in rat aorta
Authors: Bui Loc , Rish Kimberly , Jaronczyk Kinga , Bourque Stephane , McLaughlin Brian E , Brien James F , Marks Gerald S , Smith Ann , Nakatsu Kanji
Published: June 2004

During the last decade, heme oxygenase (HO) and carbon monoxide (CO) have garnered substantial research interest in terms of cell and organ regulation, especially as they bear on the central nervous system, organ transplantation, and the cardiovascular system. While the enzymatic mechanism, substrates, and products of HO are well known, it is not clear whether the cardiovascular system derives its supply of the heme substrate through de novo synthesis or uptake from the extracellular milieu. The objective of the present study was to test the latter possibility in rat aorta and to determine the influence of plasma proteins that bind heme in vivo, viz. hemopexin and albumin. Aortic tissue was exposed to [14C]heme in vitro, and the concentration and time dependence of heme uptake was assessed. The presence of hemopexin or albumin in the incubation medium dramatically decreased heme uptake by the aorta. Heme uptake by aortic tissue was not altered after induction of HO-1, which would be expected to increase tissue heme demand. In summary, the rat, isolated aorta was capable of obtaining heme from its external milieu, but this was obtunded in the presence of the plasma proteins hemopexin or albumin. For normal physiological situations, heme uptake may not be a usual source of substrate for vascular HO and hemoenzymes such as nitric oxide synthase, soluble guanylyl cyclase, and cyclooxygenase.Key words: heme uptake, vasculature, heme oxygenase, hemopexin.
The source of heme for vascular heme oxygenase II: de novo heme biosynthesis in rat aorta
Authors: Jaronczyk Kinga , Bui Loc , Soong Jonathan M , McLaughlin Brian E , Marks Gerald S , Brien James F , Nakatsu Kanji
Published: June 2004

Heme is an essential prosthetic group or substrate for many proteins, including hemoglobin, and hemo enzymes such as nitric oxide synthase, soluble guanylyl cyclase, and heme oxygenase (HO). HO is responsible for the breakdown of heme into equimolar amounts of biliverdin, iron, and carbon monoxide, the latter of which is thought to play a role in the regulation of vascular tone. It is not clear whether the source of heme for cardiovascular functions is derived from uptake from the extracellular milieu or synthesis. In this study, we tested the hypothesis that blood vessels obtain their supply of heme for HO through de novo synthesis. Adult male Sprague–Dawley rat aorta was incubated at 37 °C in Krebs' solution with 1 µM [14C]δ-aminolevulinic acid (ALA). [14C]ALA uptake was linear for about 30 min and reached a plateau at approximately 100 min. The radioactivity was incorporated into porphyrins and heme as determined by esterification of14C-labelled metabolites and thin-layer chromatography. The first and rate-limiting step of heme biosynthesis is catalyzed by ALA synthase (ALA-S), the activity of which was determined in rat aorta using a radiometric assay, ~250 nmol·(g wet mass)–1·h–1. Inducing HO-1 in rat aorta with S-nitroso-N-acetyl penicil la mine (500 µM) did not increase ALA-S activity as compared with basal activity levels of the enzyme. It appears that there is a sufficient amount of heme available under basal ALA-S activity conditions to meet the increased demand for heme resulting from HO-1 induction. These observations indicate that the complete enzymatic pathway for de novo heme biosynthesis resides in rat aorta and furthermore indicate that de novo heme synthesis is capable of supplying a substantial portion of the heme substrate for HO in the aorta.Key words: heme biosynthesis, vasculature, carbon monoxide, heme oxygenase, δ-aminolevulinic acid synthase.
Spinal excitation and inhibition decrease as humans age
Authors: Kido Aiko , Tanaka Naofumi , Stein Richard B
Published: June 2004

Although changes in the soleus H-reflex (an electrical analog of the tendon jerk) with age have been examined in a number of studies, some controversy remains. Also, the effect of age on inhibitory reflexes has received little attention. The purpose of this paper was to examine some excitatory and inhibitory reflexes systematically in healthy human subjects having a wide range of ages. We confirmed that both the maximum H-reflex (Hmax) and the maximum M-wave (Mmax) (from direct stimulation of motor axons) decrease gradually with age. The decrease in Hmax was larger so the Hmax/Mmax ratio decreased dramatically with age. Interestingly, the modulation of the H-reflex during walking was essentially the same at all ages, suggesting that the pathways that modulate the H-reflex amplitude during walking are relatively well preserved during the aging process. We showed for the first time that the short-latency, reciprocal inhibitory pathways from the common peroneal nerve to soleus muscle and from the tibial nerve to the tibialis anterior muscle also decreased with age, when measured as a depression of ongoing voluntary activity. These results suggest that there may be a general decrease in excitability of spinal pathways with age. Thus, the use of age-matched controls is particularly important in assessing abnormalities resulting from disorders that occur primarily in the elderly.Key words: H-reflex, reciprocal inhibition, age.
Gold sodium thiomalate improves membrane potential impaired by high-frequency stimulation
Authors: Aoki Takako , Oba Toshiharu
Published: June 2004

Effects of gold sodium thiomalate (GSTM) on membrane potential and tetanus tension were examined to elucidate whether the gold compound improves mechanical and electrical muscle dysfunction produced by continuous repeated stimulation of frog skeletal muscles. Continuous stimulation (50 Hz for 2 min, 0.05 ms pulse duration) to the sartorius muscle depolarized the membrane, decreased action potential amplitude, and prolonged action potential duration. GSTM (0.1 mM), unlike thiomalic acid (0.1 mM), markedly decreased impairment of these electrical parameters produced during the stimulation period. In the presence of 500 units/mL of catalase, fatigue stimulation still lengthened by 1.5-fold the half-duration of the action potential after a 5-min rest. The prolongation was, however, smaller than that in controls (no catalase). Application of both catalase and GSTM led to no further changes in action potential compared with the application of catalase alone. GSTM did not affect resting tension of single toe muscle fibers though it suppressed the maximum tension after continuous stimulation. These findings suggest that GSTM can inhibit excitable dysfunction of skeletal muscles subjected to continuous stimulation and that such protective effects of GSTM may be partially mediated by H2O2.Key words: gold sodium thiomalate, catalase, continuous stimulation, resting and action potentials, force, frog skeletal muscle.
Toxic effect of chloromycetin on the ultrastructures of the motor neurons of the Chinese tree shrew (Tupaia belangeri)
Authors: Yu Farong , Yu Fahong , Li Rende , Wang Rui
Published: June 2004

This paper describes the toxic effects of chloromycetin on the motor neurons of the Chinese tree shrew (Tupaia belangeri chinensis) with horse radish peroxidase (HRP) as the labeling enzyme. When chloromycetin was administered orally at 2.5 mg/kg (body weight)/day for 3 days, Chinese tree shrews showed evidence of neurotoxicity. This included damage in cortical motor neuron synapses ending on neurons of the red nucleus and the ultrastructural changes in the mitochondria such as swelling of these organelles and blurring of their cristae. There was an increase of the mitochondrial matrix density and of the thickness of the synaptic membranes. These observations indicate that chloromycetin can lead to ultrastructural change of terminals of the cortical motor axons, and that Chinese tree shrews are sensitive animal model for chloromycetin neurotoxicity.Key words: chloromycetin, red nuclei, motor neuron, ultrastructure, Chinese tree shrew, Tupaia belangeri.
Effect of age on mechanical properties of rat mesenteric small arteries
Authors: Laurant Pascal , Adrian Mark , Berthelot Alain
Published: June 2004

With aging, large arteries become stiffer and systolic blood pressure consequently increases. Less is known, however, about the age-related change in mechanics of small resistance arteries. The aim of this study was to determine whether aging plays a role in the stiffening of the small mesenteric arteries of rats. Intra-arterial systolic, diastolic, mean and pulse pressures were measured in male Wistar rats aged 2, 4, 15 and 26 months. The passive mechanical properties of the wall of isolated perfused and pressurized arterial segments of mesenteric small arteries were also investigated. Intra-arterial systolic, diastolic and mean blood pressures tended to decrease with age and were significantly lower in the oldest rats (26-month-old group). Pulse pressure was significantly higher in the 15- and 26-month-old groups than in the two younger groups. Under isobaric conditions, increasing age is associated with an outward hypertrophic remodeling of the mesenteric arteries. Under relaxed conditions, incremental distensibility in response to increasing intravascular pressure did not change with aging. As a function of strain (under isometric conditions), stress shifted to the left as age increased, indicating an age-related vascular stiffening. Under isobaric conditions or in relation to wall stress, the elastic modulus was greater in the adult 15-month-old rats than in the younger rats. These findings suggest that distensibility seems to be preserved with aging, despite stiffness of the wall components, probably by arterial wall geometric adaptation, which limits the pulse pressure damage. It is interesting to note that elastic modulus in mesenteric arteries from the oldest rats (26-month-old), examined in relation to wall stress and intravascular pressure, did not differ from that of the youngest rats, thus suggesting that elasticity of wall components had been restored.Key words: age, arteries, elastic modulus, stiffness, pressure.
A TOPOLOGICAL VIEW ON BARYON NUMBER CONSERVATION
Authors: MATUTE ERNESTO A.
Published: June 2004

We argue that the charge fractionalization in quarks has a hidden topological character related to a broken [Formula: see text] symmetry between integer-charged bare quarks and leptons. The mechanism is a tunneling process occurring in time between standard field configurations of a pure gauge form with different topological winding numbers associated with integer-charged bare quarks in the far past and future. This transition, which nonperturbatively normalizes local bare charges with a universal accumulated value, corresponds to a specific topologically nontrivial configuration of the weak gauge fields in Euclidean spacetime. The outcome is an effective topological charge equal to the ratio between baryon number and the number of fermion generations associated with baryonic matter. The observed conservation of baryon number is then related to the conservation of this bookkeeping charge on quarks. Baryon number violation may only arise through topological effects as in decays induced by electroweak instantons. However, stability of a free proton is expected.
ADSORPTION SITES OF THE PRODUCTS OF GeH4 ON ASYMMETRIC Si(100)(2×1) SURFACE
Authors: KATıRCıOĞLU ŞENAY
Published: June 2004

The decomposition of GeH 4 on Si (100)(2×1) was investigated on different adsorption models of fragments using density functional theory method. The most probable adsorption model of fragments corresponding to the growth steps of SiGe film has been obtained by geometry optimization and single value total energy calculations. The relative adsorption energies of GeH 3, GeH 2 and GeH have been found to be -5.6, -5.1, and -4.5 eV for their most probable adsorption models respectively. It has been found that, the asymmetric dimer bond rows of Ge on Si (100) surface can be constructed by following the adsorption models corresponding to the relative adsorption energies of GeH 3, GeH 2 and GeH .
QUANTUM TUNNELING OF MESOSCOPIC SPIN IN BOSE–EINSTEIN CONDENSATES
Authors: ZHAO HUA , LIANG J.-Q.
Published: June 2004

In this paper the exact quantum phase model is derived with the help of a mesoscopic spin model from weakly linked two-component Bose–Einstein condensates. It is shown that the π-phase state which is seen to be the degenerate ground state exists only in an extreme limit of parameter, Δ≪1. π-phase state becomes metastable in the parameter region 0<Δ<1 and unstable when Δ≥1. The low-lying energy band resulted from the quantum tunneling is obtained explicitly by means of instanton method. We also analyze the phase-dissipation due to quantum tunneling. Moreover, the decay of the metastable π-phase state via quantum tunneling is studied and the life time is found analytically.
COLLAPSE AND REVIVAL EFFECT IN A MESOSCOPIC LC CIRCUIT
Authors: LUO HAI-MEI , JI YING-HUA , LIU JIE
Published: June 2004

This paper studied the time evolution of quantum state in a mesoscopic LC circuit with the coupling energy caused by mesoscopic capacitor acting as a tunnel junction. It indicates that the state of the junction evolves into the quantum superposition of two coherent states and, in the state, nonclassical squeezing properties of the circuit appear. It also indicates that the dynamic behavior of the current shows collapse and revival phenomenon. The research in the paper will be helpful to miniaturize integrate circuits and electric components. It will be also important for the utilization of mesoscopic circuits to evolve the quantum states, which work as information carriers.
EFFECT OF CHARGE–PLASMON INTERACTION TO THE EFFECTIVE MASS OF A CHARGED PARTICLE IN SOLIDS
Authors: PINSOOK UDOMSILP , SA-YAKANIT VIRULH , BOVORNRATANARAKS THITI
Published: June 2004

We use Feynman variational path integral method to study the effective mass of a charged particle in solids in which plasmons are an elementary excitation. This approach has an advantage as the ground state energy and the effective mass can be expressed analytically. We examine a particular case, i.e. the motion of a slow positron in metals. We find that the effective mass increases with rs. The results are compared with those of a similar approach and of experiments. Nevertheless, the effect of the charge–plasmon interaction cannot fully account for the large positron effective mass in metals. The discrepancies are discussed.
TEMPERATURE- AND FIELD-INDUCED VALENCE TRANSITION IN A MODEL FOR INTERMEDIATE VALENCE SYSTEMS
Authors: GANGADHAR REDDY G. , RAMAKANTH A. , GHATAK S. K.
Published: June 2004

Motivated by the experimental studies on the temperature- and field-induced valence transitions in Yb- and Eu-based rare earth compounds, a model calculation is performed. For this purpose, the periodic Anderson model, supplemented by the Falicov–Kimball term is chosen to describe the fluctuating valence systems. The model is solved first by decoupling the Falicov–Kimball term and then taking the intrasite Coulomb interaction strength to infinity. The resulting coupled equations for the spin dependent average occupations of the localized and itenerant states and the excitonic correlations have been solved self-consistently for different constellations of model parameters. The model calculations show that it is possible to induce valence transitions in the system by either varying the temperature or the field or both. The results obtained bear a rather striking similarity to the experimental observations not only in general but also in most of the details.
RECENT ADVANCES IN UNCONVENTIONAL DENSITY WAVES
Authors: DÓRA BALÁZS , MAKI KAZUMI , VIROSZTEK ATTILA
Published: June 2004

The unconventional density wave (UDW) was speculated on as a possible electronic ground state in the excitonic insulator in 1968. The recent surge of interest in UDW's is partly due to the proposal that the pseudogap phase in high Tc cuprate superconductors is a d-wave density wave (d-DW).

Here we review our recent works on UDW's within the framework of mean field theory. In particular, we have shown that many properties of the low temperature phase (LTP) in α-( BEDT-TTF )2 MHg ( SCN )4, with M = K , Rb and Tl , are well characterized in terms of the unconventional charge density wave (UCDW). In this identification the Landau quantization of the quasiparticle motion in a magnetic field (the Nersesyan effect) plays the crucial role. Indeed, the angle-dependent magnetoresistance and the negative giant Nernst effect are two hallmarks of UDW's.
A+B→0 ENHANCED DIFFUSION-CONTROLLED REACTIONS UNDER STATIONARY REGIME CONDITION THROUGH THOMPSON'S APPROACH
Authors: NASSIF CLÁUDIO , SILVA P. R.
Published: June 2004

In this work, Thompson's method is used to study the A+B→0 reactions controlled by anomalous and brownian diffusion in the case of an external homogeneous source (h) of particles A and B under sthequiometric condition (the same input rate h) and also in the special case of the stationary regime. So the novelty in the present work is that we are able to obtain for such kind of reactions (σ=1) the static critical exponent δ of concentration [Formula: see text], the dynamical exponent for the relaxation time Δ'(τh~h-Δ') and the exponent for the concentration decaying ξ(∊~τ-ξ), with all these quantities evaluated in the limit h→0 (zero-field-rate). We also get scaling relations among new critical indexes. After we go further by obtaining more general results for such exponents so that we are able to include also the case of A+A→0(A) reactions within an unified scheme as already made before by introducing a general effective action (Aσ,γ). Thus, when we consider the case σ=0 (A,+A→0(A) reactions) we recover those critical exponents (δ,Δ',ξ) for anomalous coalescence reactions of type kA→lA(l<k). And when we even make γ=2 (brownian diffusion) we get the exponents previously given by Rácz, and also some results obtained by Lee and Oliveira. Thompson's method is a simple alternative way to the renormalization group scheme and has been shown to be a good description for long-time regime.
DEPENDENCE OF GIANT MAGNETORESISTANCE ON THE THICKNESS OF MAGNETIC AND NON-MAGNETIC LAYERS IN DUAL SPIN VALVES
Authors: WANG YONG , XU MING , MAI ZHENHONG
Published: June 2004

Based on the previous semi-classical model, we have performed calculation of the giant magnetoresistance (GMR) as a function of the thickness of the top/bottom or center ferromagnetic layers and the non-magnetic layer in dual spin valves. Our results are in good agreement with that reported in experiment, i.e., a GMR maximum is observed when the thickness of the top/bottom magnetic layer is at 20 ~ 40 Å; the GMR value decreases monotonically with the increase of the non-magnetic layer thickness. By considering the "pin-hole" effect, the variation of GMR versus the thickness of the center magnetic layer is also found to be consistent with the experimental result. These calculations will be helpful in the design of high-quality spin-valve structures.
1/f NOISE COMPONENT CONDITIONED BY BUILT-IN ELECTRIC FIELD IN SEMICONDUCTORS
Authors: ASRIYAN H. V. , GASPARYAN F. V.
Published: June 2004

The influence of the built-in electric field on the low-frequency current fluctuations in n-type non-degenerate homogeneous semiconductors at presence of constant external electric and magnetic fields is examined. The problem is considered by means of Langevin-type Boltzmann transport equations for the electron and phonon systems at domination of electron–acoustic phonon scatterings. For the first time, it is shown that within the context of the introduced problem, the spectral density of the current noise contains 1/f component specified by the built-in electric field. By form it is similar to the empiric Hooge formula. On the basis of the computations, a model explaining the physical mechanism of the origin of the additional component of 1/f noise, conditioned by the presence of the built-in electric field in semiconductor, is proposed. For the Hooge parameter, a comparison with the experimental data of generally observed 1/f noise for Si samples is carried out. The comparison shows that at some "favorable" conditions, the level of this new component of the 1/f noise can reach the level of the generally observed 1/f noise.
INVESTIGATION OF FOUR-WAVE MIXING OF MATTER WAVES IN BOSE–EINSTEIN CONDENSATES
Authors: SUN CHUNLIU , HANG CHAO , HUANG GUOXIANG , HU BAMBI
Published: June 2004

We investigate the four-wave mixing of matter wave packets created from a Bose–Einstein condensate, realized experimentally by utilizing light pulses to create two high-momentum wave packets via Bragg diffraction from a stationary condensate. Based on the Gross–Pitaevskii equation, a set of nonlinearly coupled envelope equations including self- and cross-phase modulational effects are derived systematically using a method of multiple-scales. The exact and explicit analytical solutions are provided for the coupled envelope equations and the evolution of the wave packets after turning off trapping potential is discussed and compared with experiment.
ROBUST PROFILE VERIFICATION SCHEME BASED ON EAR REFERENCE COORDINATE SYSTEM
Authors: KIM BYUNG-GYU , JUNG SUNG-YUN , PARK DONG-JO
Published: June 2004

In this paper, a novel profile verification scheme based on the ear, contour lines and feature points from head profile images is proposed. From the side image of a human head taken by a CCD camera, the contour line of the image is extracted by the simple filling method and morphological filtering. Based on the reference coordinate set by using ear images enrolled in the database a priori, the features of the contour line such as the tip of the nose, bottom of the nose, eye point and so on are extracted. The contour of the given image is divided into segments by utilizing the extracted feature points. The directional code of each segment is proposed and the length of the segment is computed for generating the feature vector. The verification of the given profile is performed by matching these feature vectors with those of the enrolled database. The experimental results show validity of the developed method for feature extraction and profile verification.
INTEGRATED HANDWRITING RECOGNITION AND INTERPRETATION USING FINITE-STATE MODELS
Authors: TOSELLI A. H. , JUAN A. , GONZÁLEZ J. , SALVADOR I. , VIDAL E. , CASACUBERTA F. , KEYSERS D. , NEY H.
Published: June 2004

The interpretation of handwritten sentences is carried out using a holistic approach in which both text image recognition and the interpretation itself are tightly integrated. Conventional approaches follow a serial, first-recognition then-interpretation scheme which cannot adequately use semantic–pragmatic knowledge to recover from recognition errors. Stochastic finite-sate transducers are shown to be suitable models for this integration, permitting a full exploitation of the final interpretation constraints. Continuous-density hidden Markov models are embedded in the edges of the transducer to account for lexical and morphological constraints. Robustness with respect to stroke vertical variability is achieved by integrating tangent vectors into the emission densities of these models. Experimental results are reported on a syntax-constrained interpretation task which show the effectiveness of the proposed approaches. These results are also shown to be comparatively better than those achieved with other conventional, N-gram-based techniques which do not take advantage of full integration.
CONSTRUCTING RIBBON SURFACE-LINKS FROM REAL LINE CONFIGURATIONS
Authors: TAYAMA IKUO
Published: June 2004

For a real line configuration L, we construct a ribbon surface-link which has the same group as L. If L is a general position line configuration or a central line configuration, the constructed ribbon surface-link has the minimum genus.
LEGENDRIAN SURGERY IS NOT CATEGORY-PRESERVING FOR TIGHT CONTACT STRUCTURES
Authors: KIM JIN-HONG
Published: June 2004

The aim of this paper is to show that the Seifert fibered space Σ(-½, ⅓, ⅓) over S2does not admit any tight contact structures. As a consequence, we can conclude that Legendrian surgery is not category-preserving for tight contact structures on closed 3-manifolds.
CEMAP: COST-EFFECTIVE MOBILE AGENT PLANNING
Authors: BAEK JIN-WOOK , YEO JAE-HEUNG , KIM GYU-TAE , YEOM HEON-YOUNG
Published: June 2004

Two significant performance factors in Mobile Agent Planning (MAP) for distributed information retrieval are the number of mobile agents and the total execution time. Using fewer mobile agents results in less network traffic and consumes less bandwidth. Regardless of the number of agents used, the total execution time for a task must be kept to a minimum. A retrieval service must minimize both these factors for better system performance, and at the same time, it must be able to supply the required information to users as quickly as possible. In this paper, we propose heuristic algorithms, called Cost-Effective MAP (CEMAP), to minimize both the number of mobile agents and the total execution time under the condition that the turnaround time is kept to a minimum. Although these algorithms tend to slightly increase the planning cost, a simulation study shows that these algorithms enhance the system performance significantly. By adopting these algorithms, systems can maintain lower network traffic while satisfying the minimum turnaround time.
Market-Based Evaluation for Models to Predict Bond Ratings
Authors: Chan Konan , Jegadeesh Narasimhan
Published: June 2004

Previous studies have examined different statistical models to predict corporate bond ratings. However, these papers use agency ratings as the benchmark to assess models and ignore the evidence that agency ratings may not be accurate in a timely manner. In this paper, we propose a new approach which incorporates ex-post bond returns to evaluate rating prediction models. Relative rating strength portfolios, formed by buying under-rated bonds with agency ratings lower than model ratings and selling over-rated bonds with agency ratings higher than model ratings, are employed to test the performance of different statistical models in rating predictions. Our results show that one version of multiple discriminant analysis model can generate a statistically significant abnormal return of 5% over a 5-year horizon. The ordered probit model which is believed to possess theoretical advantages in classifying bonds does not perform better. This suggests that using traditional measures to evaluate models can be misleading. The existence of a profitable trading strategy also raises the concern of market efficiency in the corporate bond market.
The Determinants of Returns on China-Concept Stocks Listed in Taiwan Stock Market
Authors: Yang Chau-Chen , Lee Cheng-Few , Lin Chung-Jiun , Chung Ya-Ting
Published: June 2004

We use a probit selection model to investigate whether the relation between stock returns and their fundamental determinants varies for China-concept and non-China-concept stocks. In addition, an ordered probit selection model is used as well to explore whether the determinants of stock returns change due to the different level of investments in China. There are a lot of reasons for Taiwanese firms to invest in China. The stock of a firm with capital investments in China is called China-concept stock. A firm can decide whether to go for its capital investments in China or not. It is interesting to investigate whether a firm's decision to invest in China affects the determination of stock returns or not. This investment decision should not be treated as exogenous in examining the determinants of stock returns. Hence, a two-stage selection model is employed for this purpose. We find that heavy-level-investment-in-China firms do exhibit a different relation between stock returns and their fundamental determinants. Book-to-market ratio is the most important determinant of stock returns for all firms.
Bid-Ask Bounce and the Intraday Performance of Limit Orders: Evidence from the Taiwan Stock Exchange
Authors: Liang Yu-Li , Jiang Ching-Hai , Huang Yen-Sheng
Published: June 2004

This paper examines the performance of limit orders versus market orders using intraday transaction prices for all stocks listed on the Taiwan Stock Exchange over the first three months of 1999. The results indicate that executed limit orders significantly outperform market orders. Moreover, even after including the impact of unfilled limit orders, the unconditional limit orders still perform slightly better than the corresponding market orders. The superior performance of limit orders is consistent with the explanation that limit order traders benefit from the bid-ask bounce driven by liquidity trading in the Taiwan stock market. By replacing the buy and sell prices by the bid-ask average, the superior profitability of limit orders decline significantly.
The Informative Content of the Net-Buy Information of Institutional Investors: Evidence from the Taiwan Stock Market
Authors: Chiao Chaoshin , Lin Ko-I
Published: June 2004

This paper studies the informative content of the NB (net-buy) information of institutional investors, including foreign investors (FIs), security investment trust companies (SITCs), and security dealers (SDs), in the Taiwan stock market. First, with/without considering prevailing market frictions, the investment strategies based on the NB trading volume and dollar trading volume of SITCs, outperform the market and those strategies based on those of FIs and SDs. Second, on average, institutional investors trade mostly large and growth stocks. Third, evidence supports negative leading roles of the aggregate/disaggregate NB dollar trading volumes of FIs over those of SITCs.
Risk Sharing in Mortgage Loan Agreements
Authors: Neo Poh Har , Ong Seow Eng
Published: June 2004

This paper examines whether risk sharing exists in mortgage loan agreements. Specifically, we analyze the effect of the number of co-borrowers on foreclosure risk, using data from Singapore. Through the estimation of probit model, the results consistently show that co-borrowers significantly reduce the foreclosure risk, suggesting the existence of risk sharing among the co-borrowers. In addition, foreclosure risk is reduced proportionately with the number of co-borrowers. Further analysis shows that low-rise properties required a larger number of co-borrowers than high-rise properties in order to share risk effectively. Interestingly, low-rise properties experience a greater decline in the foreclosure likelihood than high-rise properties for every increase in the number of co-borrowers.
WIGNER ROTATIONS, BELL STATES, AND LORENTZ INVARIANCE OF ENTANGLEMENT AND VON NEUMANN ENTROPY
Authors: SOO CHOPIN , LIN CYRUS C. Y.
Published: June 2004

We compute, for massive particles, the explicit Wigner rotations of one-particle states for arbitrary Lorentz transformations; and the explicit Hermitian generators of the infinite-dimensional unitary representation. For a pair of spin 1/2 particles, Einstein–Podolsky–Rosen–ell entangled states and their behaviour under the Lorentz group are analyzed in the context of quantum field theory. Group theoretical considerations suggest a convenient definition of the Bell states which is slightly different from the conventional assignment. The behaviour of Bell states under arbitrary Lorentz transformations can then be described succinctly. Reduced density matrices applicable to systems of identical particles are defined through Yang's prescription. The von Neumann entropy of each of the reduced density matrix is Lorentz invariant; and its relevance as a measure of entanglement is discussed, and illustrated with an explicit example. A regularization of the entropy in terms of generalized zeta functions is also suggested.