bluuebunny/crossref_metadata_2025 huggingface dataset:
Susceptibility for homeostatic plasticity is down‐regulated in parallel with maturation of the rat hippocampal synaptic circuitry
Authors: Huupponen J. , Molchanova S. M. , Taira T. , Lauri S. E.
Published: March 2007

Homeostatic regulation, i.e. the ability of neurons and neuronal networks to adjust their output in response to chronic alterations in electrical activity is a prerequisite for the pronounced functional plasticity in the developing brain. Cellular mechanisms of homeostatic plasticity have mainly been studied in cultured preparations. To understand the developmental time frame and properties of homeostatic plasticity under more physiological conditions, we have here compared the effects of activity deprivation on synaptic transmission in acutely isolated and cultured hippocampal slices at different stages of development. We find that transmission at both glutamatergic and GABAergic synapses is strongly and rapidly (15 h) regulated in the opposite directions in response to inactivity during narrow, separated time windows early in development. Following this critical period of synaptic development, induction of the homeostatic response requires longer periods (40 h) of inactivity. At glutamatergic synapses, activity blockade led to an increase in the amplitude and frequency of mEPSCs, and the threshold for induction of this response was increased during development. In contrast, homeostatic regulation at GABAergic synapses was expressed in a qualitatively distinct manner at different developmental stages. Immature neurons responded rapidly to inactivity by regulating mIPSC frequency, while longer activity blockade led to a decrease in the mIPSC amplitude independent of the neuronal maturation. The susceptibility of immature networks to homeostatic regulation may serve as a safety mechanism against rapid runaway destability during the time of intense remodelling of the synaptic circuitry.
A G Protein-Coupled Receptor Is a Plasma Membrane Receptor for the Plant Hormone Abscisic Acid
Authors: Liu Xigang , Yue Yanling , Li Bin , Nie Yanli , Li Wei , Wu Wei-Hua , Ma Ligeng
Published: March 2007

The plant hormone abscisic acid (ABA) regulates many physiological and developmental processes in plants. The mechanism of ABA perception at the cell surface is not understood. Here, we report that a G protein–coupled receptor genetically and physically interacts with the G protein α subunit GPA1 to mediate all known ABA responses in
Arabidopsis
. Overexpressing this receptor results in an ABA-hypersensitive phenotype. This receptor binds ABA with high affinity at physiological concentration with expected kinetics and stereospecificity. The binding of ABA to the receptor leads to the dissociation of the receptor-GPA1 complex in yeast. Our results demonstrate that this G protein–coupled receptor is a plasma membrane ABA receptor.
Surprising Arginine Biosynthesis: a Reappraisal of the Enzymology and Evolution of the Pathway in Microorganisms
Authors: Xu Ying , Labedan Bernard , Glansdorff Nicolas
Published: March 2007

Major aspects of the pathway of de novo arginine biosynthesis via acetylated intermediates in microorganisms must be revised in light of recent enzymatic and genomic investigations. The enzymeN-acetylglutamate synthase (NAGS), which used to be considered responsible for the first committed step of the pathway, is present in a limited number of bacterial phyla only and is absent fromArchaea. In manyBacteria, shorter proteins related to the Gcn5-relatedN-acetyltransferase family appear to acetylatel-glutamate; some are clearly similar to the C-terminal, acetyl-coenzyme A (CoA) binding domain of classical NAGS, while others are more distantly related. Short NAGSs can be single gene products, as inMycobacteriumspp. andThermusspp., or fused to the enzyme catalyzing the last step of the pathway (argininosuccinase), as in members of theAlteromonas-Vibriogroup. How these proteins bind glutamate remains to be determined. In someBacteria, a bifunctional ornithine acetyltransferase (i.e., using both acetylornithine and acetyl-CoA as donors of the acetyl group) accounts for glutamate acetylation. In manyArchaea, the enzyme responsible for glutamate acetylation remains elusive, but possible connections with a novel lysine biosynthetic pathway arose recently from genomic investigations. In someProteobacteria(notablyXanthomonadaceae) andBacteroidetes, the carbamoylation step of the pathway appears to involveN-acetylornithine orN-succinylornithine rather than ornithine. The productN-acetylcitrulline is deacetylated by an enzyme that is also involved in the provision of ornithine from acetylornithine; this is an important metabolic function, as ornithine itself can become essential as a source of other metabolites. This review insists on the biochemical and evolutionary implications of these findings.
Colicin Biology
Authors: Cascales Eric , Buchanan Susan K. , Duché Denis , Kleanthous Colin , Lloubès Roland , Postle Kathleen , Riley Margaret , Slatin Stephen , Cavard Danièle
Published: March 2007

Colicins are proteins produced by and toxic for some strains ofEscherichia coli. They are produced by strains ofE. colicarrying a colicinogenic plasmid that bears the genetic determinants for colicin synthesis, immunity, and release. Insights gained into each fundamental aspect of their biology are presented: their synthesis, which is under SOS regulation; their release into the extracellular medium, which involves the colicin lysis protein; and their uptake mechanisms and modes of action. Colicins are organized into three domains, each one involved in a different step of the process of killing sensitive bacteria. The structures of some colicins are known at the atomic level and are discussed. Colicins exert their lethal action by first binding to specific receptors, which are outer membrane proteins used for the entry of specific nutrients. They are then translocated through the outer membrane and transit through the periplasm by either the Tol or the TonB system. The components of each system are known, and their implication in the functioning of the system is described. Colicins then reach their lethal target and act either by forming a voltage-dependent channel into the inner membrane or by using their endonuclease activity on DNA, rRNA, or tRNA. The mechanisms of inhibition by specific and cognate immunity proteins are presented. Finally, the use of colicins as laboratory or biotechnological tools and their mode of evolution are discussed.
Anatomy of the sural nerve in a computer-assisted model: implications for surgical minimal-invasive Achilles tendon repair
Authors: Citak Musa , Knobloch Karsten , Albrecht Knut , Krettek Christian , Hufner Tobias
Published: March 2007

Background:Sural nerve injuries are an evident risk especially of minimal-invasive surgical Achilles tendon repair. However, detailed anatomical studies focusing on the relationship of the sural nerve with the Achilles tendon at various levels are scarce, even pending in two planes.

Aim:To determine the position and course of the sural nerve in relation to the Achilles tendon in two planes after trans-section and computer-assisted determination.

Methods:The exact course of the sural nerve was determined in 10 cadavers (55.3 years, 19–89 years), using a computer-assisted method in two planes (transversal/sagittal).

Results:The sural nerve crossed the Achilles tendon at 11 (8.7–12.4) cm proximal to the tuber calcanei. The distance between the lateral crossing and the proximal musculotendineus junction was 35 (20–58) mm. Starting from the tuber calcanei, the distance was 2/2 mm (transversal/sagittal plane) at 11 cm proximal to the tuber calcanei, 4/4 mm at 10 cm proximal, 5/6 mm at 9 cm, 8/10 mm at 5 cm and 11/18 mm at the tuber calcanei.

Conclusion:In the lateral crossing region of the sural nerve and the lateral proximal Achilles tendon 9–12 cm proximal to the tuber calcanei, a close relationship of both anatomical structures can be visualised using computer-assisted measurements; caution is suggested to prevent sural nerve entrapment in either open or percutaneous Achilles tendon repair.
Does plyometric training improve vertical jump height? A meta-analytical review
Authors: Markovic Goran
Published: March 2007

The aim of this study was to determine the precise effect of plyometric training (PT) on vertical jump height in healthy individuals. Meta-analyses of randomised and non-randomised controlled trials that evaluated the effect of PT on four typical vertical jump height tests were carried out: squat jump (SJ); countermovement jump (CMJ); countermovement jump with the arm swing (CMJA); and drop jump (DJ). Studies were identified by computerised and manual searches of the literature. Data on changes in jump height for the plyometric and control groups were extracted and statistically pooled in a meta-analysis, separately for each type of jump. A total of 26 studies yielding 13 data points for SJ, 19 data points for CMJ, 14 data points for CMJA and 7 data points for DJ met the initial inclusion criteria. The pooled estimate of the effect of PT on vertical jump height was 4.7% (95% CI 1.8 to 7.6%), 8.7% (95% CI 7.0 to 10.4%), 7.5% (95% CI 4.2 to 10.8%) and 4.7% (95% CI 0.8 to 8.6%) for the SJ, CMJ, CMJA and DJ, respectively. When expressed in standardised units (ie, effect sizes), the effect of PT on vertical jump height was 0.44 (95% CI 0.15 to 0.72), 0.88 (95% CI 0.64 to 1.11), 0.74 (95% CI 0.47 to 1.02) and 0.62 (95% CI 0.18 to 1.05) for the SJ, CMJ, CMJA and DJ, respectively. PT provides a statistically significant and practically relevant improvement in vertical jump height with the mean effect ranging from 4.7% (SJ and DJ), over 7.5% (CMJA) to 8.7% (CMJ). These results justify the application of PT for the purpose of development of vertical jump performance in healthy individuals.
Ecological characteristics of modern diatom assemblages from Axel Heiberg Island (High Arctic Canada) and their application to paleolimnological inference models
Authors: Michelutti Neal , Smol John P. , Douglas Marianne S.V.
Published: March 2007

Relationships between modern surface sediment diatom assemblages and measured water chemistry variables were examined from 30 lakes and ponds on Axel Heiberg Island (Nunavut) in the Canadian High Arctic. Canonical correspondence analysis with forward selection and Monte Carlo permutation tests identified dissolved organic carbon, dissolved inorganic carbon, specific conductance, and pH as the measured environmental variables explaining significant proportions of the diatom variance. Canonical correspondence analysis axis 1 represented a gradient of specific conductance, and axis 2 was influenced primarily by pH. To increase the signal-to-noise ratio in our reconstructions, the species data sets were refined to include only taxa that had significant responses to either conductivity or pH, as determined by Huisman Olff Fresco models of species–environment relationships. Diatom-based inference models were subsequently developed for both lakewater specific conductance (r2boot= 0.75, root mean square error of prediction = 0.22) and lakewater pH (r2boot= 0.31, root mean square error of prediction = 0.57) using weighted averaging techniques. These data contribute to our understanding of diatom biogeography throughout the Canadian Arctic and have implications for regional paleoclimatic reconstructions in these climatically and environmentally sensitive regions.
Geese and grazing lawns: responses of the grassFestuca rubrato defoliation in a subarctic coastal marsh
Authors: O P. C. , Kotanen P. M. , Abraham K. F.
Published: March 2007

In coastal marshes on James Bay and southern Hudson Bay, Canada, the grass Festuca rubra L. is heavily used for forage by both Snow (Chen caerulescens caerulescens (Linnaeus)) and Canada Geese ( Branta canadensis (Linnaeus)). On Akimiski Island, James Bay, this grass occurs in a mosaic of short, heavily grazed patches and tall, lightly grazed patches. We investigated whether short plants are primarily a plastic morphological response to grazing by geese. Over two growing seasons, we measured growth of short patches protected from grazing and of tall patches subjected to mowing treatments, with unmanipulated short and tall controls. Protection resulted in rapid conversion from a short growth form to a tall form, similar in height and biomass to plants in tall control plots. Mowed tall plants also rapidly recovered to near tall control values for height and biomass. A single 3 week treatment episode often permitted nearly full recovery to tall form. In some cases, more sustained protection was required, but repeated mowing ultimately may have reduced growth rates. These results indicate that the morphology of individual plants of Festuca rubra plastically recovers from changes in defoliation pressure. Consequently, short patches likely represent grazing lawns maintained by intensive foraging by geese.
Interspecific competition in a pecan–cotton alleycropping system in the southern United States: Production physiology
Authors: Zamora Diomides S. , Jose Shibu , Nair P.K.R. , Ramsey Craig L.
Published: March 2007

A study was conducted on a Red Bay sandy loam soil (Rhodic Paleudult) in Jay, Florida, USA, to investigate how interspecific interactions between pecan ( Carya illinoensis K. Koch) and cotton ( Gossypium hirsutum L.) would affect cotton leaf morphology and gas exchange and thereby biomass and lint yield. We quantified specific leaf area (SLA), specific leaf nitrogen (SLN), net photosynthesis (A), transpiration, stomatal conductance, and net canopy photosynthetic index (CNPI) from cotton with and without aboveground and belowground interactions. To separate roots of cotton and pecan, polyethylene-lined trenches were installed (barrier treatment) parallel to tree rows in half the number of plots. Results showed that SLA for barrier and nonbarrier plants was 61% and 47% higher, respectively, compared with the monoculture cotton. Monoculture plants exhibited higher CNPI (70.7 μmol·m–2·s–1) compared with the barrier (52.7 μmol·m–2·s–1) and nonbarrier plants (18.3 μmol·m–2·s–1). SLN was similar for both the barrier and nonbarrier plants; however, it was lower than the monoculture. A positive curvilinear relationship between A and SLN was observed, with peak A (28 μmol·m–2·s–1) observed between 2.2 and 2.4 mg N·m–2. Significant curvilinear relationships between CNPI and aboveground biomass and lint yield were also observed for all treatments. These findings indicate that competitive interactions in alleycropping regulate leaf level traits such as SLA and SLN by altering water and light availability, which in turn exert a profound influence on aboveground biomass and lint yield for cotton plants.
Proglacial succession of biological soil crusts and vascular plants: biotic interactions in the High Arctic
Authors: Breen Katie , Lévesque Esther
Published: March 2007

To evaluate the hypothesis that biological soil crusts facilitate the establishment and maintenance of vascular plants during succession, we studied the distribution patterns of crusts and vascular plants along a High Arctic glacier foreland and compared the success of plants growing in and out of crusted substrate. Multivariate analyses determined that distance from the glacier and crust cover were the most important variables, explaining 11% and 9% of the variance in the vegetation data, respectively. Surfaces colonized by biological soil crusts generally supported higher plant densities and showed positive associations with the most dominant, long-lived plant species such as Saxifraga oppositifolia L., Salix arctica Pall., and Dryas integrifolia Vahl. Crusts facilitate plant establishment and growth in early and midsuccession but may compete for available resources further along the chronosequence. This study recognizes subtle direct influences of crust on vegetation density but also draws attention to a much larger overall positive effect on community structure. Succession on this foreland proceeds via a “directional-replacement” model and supports a well-developed community of biological soil crusts and vascular plants with greater species richness, cover, and density compared with other glacier foreland vegetation communities previously investigated on Ellesmere Island, Nunavut.
Inhibition fields for phyllotactic pattern formation: a simulation studyThis article is one of a selection of papers published on the Special Theme of Shoot Apical Meristems.
Authors: Smith Richard S. , Kuhlemeier Cris , Prusinkiewicz Przemyslaw
Published: March 2007

Most theories of phyllotaxis are based on the idea that the formation of new primordia is inhibited by the proximity of older primordia. Several mechanisms that could result in such an inhibition have been proposed, including mechanical interactions, diffusion of a chemical inhibitor, and signaling by actively transported substances. Despite the apparent diversity of these mechanisms, their pattern-generation properties can be captured in a unified manner by inhibition fields surrounding the existing primordia. In this paper, we introduce a class of fields that depend on both the spatial distribution and the age of previously formed primordia. Using current techniques to create geometrically realistic, growing apex surfaces, we show that such fields can robustly generate a wide range of spiral, multijugate, and whorled phyllotactic patterns and their transitions. The mathematical form of the inhibition fields suggests research directions for future studies of phyllotactic patterning mechanisms.
Sexual differences in shoot and leaf dynamics in the dioecious tree Salix sachalinensis
Authors: Ueno Naoto , Kanno Hiroshi , Seiwa Kenji
Published: March 2007

In the dioecious tree Salix sachalinensis Fr. Schm., females invested a greater amount of biomass to reproductive organs compared with males, indicating a greater reproductive cost in females. To elucidate mechanisms for the compensation of reproductive costs in females, we examined differences between the sexes in resource allocation, leaf and shoot dynamics, and leaf photosynthetic ability. In individual 1-year-old shoots, greater vegetative shoot biomass was observed in females than in males, although the mean mass of individual vegetative shoots was lower in females than in males. In both sexes, vegetative shoots at the proximal end of 1-year-old shoots completed their annual leaf production earliest and began shedding leaves earliest, although the light conditions did not differ from those at the terminal end. The leaf and shoot structure and dynamics in S. sachalinensis suggest effective carbon gain for both sexes by always placing new leaves with high photosynthetic rates at terminal shoot positions. In females, in particular, the net carbon gain would be increased by reducing construction and respiration costs and tissue loss by placing inexpensive small shoots in proximal shoot positions. To investigate to what extent the photosynthetic capacity of short-lived shoots compensated for reproductive costs in females, 80% of the vegetative-shoot buds were removed from 1-year-old shoots in females and males to simulate natural shoot shedding. In the current year, shoot removal did not reduce reproductive investment, but strongly reduced the diameter growth of 1-year-old shoots, in which the reduction was much greater in females than in males. In the following year, a reduction in reproductive investment was observed in females. Females of S. sachalinensis compensated for reproductive costs, not only by investing a greater amount of biomass in vegetative shoots, but also by using a more effective system of carbon acquisition (rapid leaf turnover on inexpensive shoots) than males.
Electron-donating methoxyl group position effect on properties of diarylethene derivatives having a pyrazole unit
Authors: Yang Tianshe , Pu Shouzhi , Chen Bing , Xu Jingkun
Published: March 2007

New types of asymmetrical photochromic diarylethene derivatives having a pyrazole unit, namely 1-[1,3,5-trimethyl-1-pyrazol-4-yl],2-[2-methyl-5-(4-methoxylphenyl)-1-thien-3-yl]perfluorocyclopentene (1a), 1-[1,3,5-trimethylpyrazol-4-yl],2-[2-methyl-5-(3-methoxylphenyl)-1-thien-3-yl] perfluorocyclopentene (2a), 1-[1,3,5-trimethyl-pyrazol-4-yl],2-[2-methyl-5-(2-methoxylphenyl)-1-thien-3-yl]perfluorocyclopentene (3a), and 1-[1,3,5-trimethyl-pyrazol-4-yl],2-[2-methyl-5-phenyl-1-thien-3-yl]perfluorocyclopentene (4a), were synthesized. Their optical and electrochemical properties, such as photochromism, photochromic cyclization–cycloreversion kinetics, and fluorescence and electrochemical properties were investigated in detail. The results show that all of these compounds have good photochromism, high cycloreversion quantum yield, and relatively strong fluorescence. Their cyclization-cycloreversion processes were determined to be zeroth to first order reactions. The oxidations of diarylethenes 1a–4a were initiated at 0.73, 1.11, 0.79, and 1.03 V, respectively. Furthermore, introduction of the electron-donating methoxyl group at different positions of the terminal phenyl ring was found to strongly influence these optical and electrochemical properties.Key words: photochromism, diarylethene, electron-donating group, optical and electrochemical properties.
Asymmetric synthesis, crystal structure, and antidepressant activity of 2-aryl-3-alkyl-5-methyl-2-morpholinol hydrochlorides
Authors: Cao Gao , Hu Ai-Xi , Xiao Xin-Rong
Published: March 2007

2-Aryl-3-alkyl-5-methyl-2-morpholinols were synthesized from the reactions of chiral 2-aminopropan-1-ol with 2-bromo-1-phenylpropan-1-one, 2-bromo-1-(3-chlorophenyl)propan-1-one, 1-(4-(benzyloxy)phenyl)-2-bromopropan-1-one, 2-bromo-1-(6-methoxy- naphthalen-2-yl)propan-1-one, and 1-(4-(benzyloxy)phenyl)pentan-1-one in N-methyl-2-pyrrolidone (NMP), respectively. The 2-aryl-3-alkyl-5-methyl-2-morpholinols were reacted with hydrogen chloride to give the hydrochloride salts with yields of 56%–77%. The structures of the products were proven by means of their 1H NMR, IR, and MS spectroscopic data. The stereochemical properties of representative products were established unambiguously by the X-ray single crystal analysis. The antidepressant activities of the title compounds were assayed by the mouse forced swimming test (FST). The FST results confirm the antidepressant properties of our products.Key words: morpholinol hydrochloride, hemiacetal, chiral synthesis, X-ray diffraction, absolute configuration, antidepressant activity.
Montmorillonite K-10 clay as reusable heterogeneous catalyst for the microwave-mediated solventless synthesis of phthalazinetetraones
Authors: Habibi Davood , Mahmoodi Nosratollah , Marvi Omid
Published: March 2007

Different phthalazino[2,3-b]phthalazine-5,7,12,14-tetraones were synthesized in a simple and environmentally benign method from the reaction of some phthalic anhydrides with semicarbazide or thiosemicarbazide using montmorillonite K-10 clay as solid heterogeneous acidic catalyst and microwaves under solvent-free conditions in good yields and short reaction times. The present method has many obvious advantages compared with those reported in the literature, including high efficiency, higher yield, operational simplicity, environmental benignity, and the possibility of recycling the solid clay. The solid clay catalyst used in the first cycle of the reactions was successfully recovered and reused in the second cycle, showing a gradual decrease in activity.Key words: montmorillonite K-10 clay, microwave, solvent-free condition, phthalazinetetraones, semicarbazide, thiosemicarbazide.
Rhenium and manganese modified activated carbon as catalyst for methanol decomposition
Authors: Tsoncheva T , Vankova S , Bozhkov O , Mehandjiev D
Published: March 2007

Bicomponent manganese and rhenium modified activated carbon materials, prepared by different methods, are studied and compared with the corresponding monocomponent materials as catalysts in methanol decomposition to CO and hydrogen. The best catalytic activity and stability is observed for the sample obtained by simultaneous deposition of Mn and Re precursors. The complex character of the catalytic active centre, including manganese and rhenium irons in various oxidative states, is discussed. The determining role of the Mn(II) ions in the improvement of the catalytic properties is assumed.Key words: rhenium, manganese, activated carbon, methanol decomposition.
Biradical radiationless decay channel in adenine and its derivatives
Authors: Zgierski Marek Z , Patchkovskii Serguei , Lim Edward C
Published: March 2007

Coupled-cluster calculations of increasing accuracy (approximate doubles: CC2; doubles: EOM-CCSD; connected triples: CR-EOM-CCSD(T)) for CIS-optimized potential energy profiles of adenine and its derivatives indicate that the ultrafast internal conversion of the optically excited π π* state occurs through a state switch to a biradical state, which intersects the ground state at a lower energy. The electronic nature of the biradical state is defined by an electronic configuration in which one unpaired electron occupies a π* orbital confined to the five-membered ring. The second unpaired electron is localized very strongly on a p-type C2 atomic orbital of the six-membered ring. The biradical state minimum has a strongly puckered six-membered ring and a C2–H bond, which is twisted nearly perpendicular to the average ring plane. Consistent with the biradical-mediated internal conversion, the π π* state lifetime is extremely short in adenine and 9-methyladenine, which have barrierless crossing to the biradical state. The lifetime is slightly longer in N,N-dimethyladenine, which has a small barrier for the state switch. In 2-aminopurine the biradical state is found above the π π* state, preventing the biradical state switch and dramatically increasing the lifetime. These results, combined with an earlier work on pyrimidine bases, strongly suggest the importance of a direct decay of the doorway π π* state via a biradical state switch in the photophysics of DNA, even though the nature of the biradical state is somewhat different in purines and pyrimidines.Key words: adenine, guanine, DNA damage, radiationless decay, biradical, ab initio, coupled clusted.
Fluoride detection based on fluorescence enhancement of thioureido naphthalene derivative
Authors: Chakraborty Sourav , Tarr Matthew A
Published: March 2007

A novel thioureido naphthalene derivative was synthesized and characterized. The compound proved itself as an effective fluoride sensor with respect to selectivity and sensitivity. In acetonitrile, the fluorescence intensity increased by 40-fold with the addition of 5 equiv. of fluoride. Fluorescence intensity did not substantially change with other halides, suggesting that the thioureido protons interact strongly with fluoride but not with other halides. The enhanced fluorescence is due to increased quantum efficiency of the fluoride complex.Key words: fluoride sensing, thioureido compound, fluorescence.
CATION DISTRIBUTION OF MnFe2O4 NANOPARTICLES SYNTHESIZED UNDER AN INDUCED MAGNETIC FIELD
Authors: WANG JUN , WU YEJUN , ZHU YUEJIN
Published: March 2007

Nanoparticles of MnFe 2 O 4 have been synthesized under an induced magnetic field by a hydrothermal process. A strong correlation between the cation distribution and the magnetic properties of MnFe 2 O 4 nanoparticles has been identified. From the results of Mössbauer spectroscopy it has been found that the nanoparticles synthesized under zero magnetic fields have 21% inversion occupancy in the tetrahedral sites by Fe 3+ cations, while this value decreases to 10% in the sample formed under a 0.25 T magnetic field. The results explain well the decrease in saturation magnetization from 62.2 emu/g to 52.8 emu/g for the sample formed under a magnetic field. This provides an understanding on how to control the inner structure in order to control the magnetic properties of these spinel ferrite nanoparticles.
PHENOMENOLOGICAL MODEL FOR CREEP BEHAVIOR INCu–8.5 at.%AlALLOY
Authors: ABO-ELSOUD M.
Published: March 2007

Creep experiments were conducted on Cu –8.5 at.% Al alloy in the intermediate temperature range, 673–873 K, corresponding to 0.46–0.72 Tm, where Tmis the absolute melting temperature. The present analysis reveals the presence of two distinct deformation regions (climb and viscous glide) in the plot of log [Formula: see text] versus log σ. The implications of these results on the transition from power-law to exponential creep regime are examined. The results indicated that the rate-controlling mechanism for creep is the obstacle-controlled dislocation glide. A phenomenological model is proposed, which assumes that cell boundaries with sub-grains act as sources and obstacles to gliding dislocations.
SPIN DYNAMICS IN STRONGLY CORRELATED ELECTRON SYSTEMS
Authors: SHERMAN A. , SCHREIBER M.
Published: March 2007

Magnetic properties of the two-dimensional t-J model are reviewed. Some of these properties are close to those observed in cuprate perovskites. In particular, the magnetic response of the model is characterized by the intensive peak at the antiferromagnetic wave vector and at some transfer frequency. The peak splits into several incommensurate maxima for lower and higher frequencies. We discuss mechanisms which are responsible for these peculiarities in the model, which might also refer to cuprates.
INFLUENCE OF POST-TREATMENT ON OPTICAL PROPERTIES OF Sc:Ce:Cu:LiNbO3 CRYSTALS
Authors: MA DECAI , WANG BIAO , WANG RUI , WANG HAI , LIU HONGCHENG , LI QINGKUN
Published: March 2007

The congruent Sc(3 mol%):Ce:Cu:LiNbO 3 single crystals were grown by the Czochralski method and three kinds of different samples were prepared by proper reduction or oxidation post-treatment processes. The extrinsic defect structures of samples were determined by infrared transmittance spectra. Two-wave coupling and light induced scattering experiments were used to measure the photorefractive properties. It is found that the reduction treatment made erasure time and diffraction efficiency decrease, but light-induced scattering resistance increase; the inverse case occurred with oxidation treatment. Analysis indicated that photoconductivity change was responsible for photorefractive properties.
THE EFFECT OF FINANCIAL INFORMATION QUALITY ON ABILITY TO ACCESS EXTERNAL FUNDS AND PERFORMANCE OF SMES IN THAILAND
Authors: SARAPAIVANICH NARUANARD , KOTEY BERNICE
Published: March 2007

Several factors have been identified in the literature as affecting SME performance, in particular ability to access finance. Access to finance is in turn influenced by variables in both the enterprise's internal and external environment. It is held that SMEs are unable to access external finance because they are not investment ready. They lack the necessary information and knowledge of their businesses to approach finance providers or to be successful in accessing funds if they do. Face-to-face interviews using structured questionnaire were conducted to collect primary data from 407 SMEs operating in the trading sector in 3 provinces- Bangkok, Chiang-Mai and Khon-Kan. Results of the structural equation modelling (SEM) reveal that quality of financial information has significant positive effect on performance and on owner-managers' perception of their ability to access external capital. A significant positive effect of their perception of ability to access capital on performance was also found.
GLOBAL CONSERVATIVE MULTIPEAKON SOLUTIONS OF THE CAMASSA–HOLM EQUATION
Authors: HOLDEN HELGE , RAYNAUD XAVIER
Published: March 2007

We show how to construct globally defined multipeakon solutions of the Camassa–Holm equation. The construction includes in particular the case with peakon-antipeakon collisions. The solutions are conservative in the sense that the associated energy is constant for almost all times. Furthermore, we construct a new set of ordinary differential equations that determines the multipeakons globally. The system remains globally well-defined.
STABILITY OF RAREFACTION WAVES AND VACUUM STATES FOR THE MULTIDIMENSIONAL EULER EQUATIONS
Authors: CHEN GUI-QIANG , CHEN JUN
Published: March 2007

We are interested in properties of the multidimensional Euler equations for compressible fluids. Rarefaction waves are the unique solutions that may contain vacuum states in later time, in the context of one-dimensional Riemann problem, even when the Riemann initial data are away from the vacuum. For the multidimensional Euler equations describing isentropic or adiabatic fluids, we prove that plane rarefaction waves and vacuum states are stable within a large class of entropy solutions that may contain vacuum states. Rarefaction waves and vacuum states are also shown to be global attractors of entropy solutions in L∞, provided initial data are L∞ ∩ L1 perturbations of Riemann initial data. Our analysis applies to entropy solutions with arbitrarily large oscillation, and no bounded variation regularity is required.
HIGH-FIELD LIMIT FROM A KINETIC EQUATION TO MULTIDIMENSIONAL SCALAR CONSERVATION LAWS
Authors: BERTHELIN F. , MAUSER N. J. , POUPAUD F.
Published: March 2007

We study the relaxation of kinetic BGK models involving a high-field term within the transport operator. They lead us to multidimensional scalar conservation laws with a flux-function which is perturbed with respect to classical relaxation. The proof of the relaxation limit makes modified Maxwellians to appear. We consider "pseudo distribution functions" which can take negative values and we introduce appropriate admissible states. This is a first step towards adapting this analysis to quantum kinetic BGK models.
Local inhibitory reflexes excited by mucosal application of nutrient amino acids in guinea pig jejunum
Authors: Gwynne R. M. , Bornstein J. C.
Published: March 2007

The motility of the gut depends on the chemicals contained in the lumen, but the stimuli that modify motility and their relationship to enteric neural pathways are unclear. This study examined local inhibitory reflexes activated by various chemical stimulants applied to the mucosa to characterize effective physiological stimuli and the pathways they excite. Segments of the jejunum were dissected to allow access to the circular muscle on one-half of the preparation while leaving the mucosa intact on the circumferentially adjacent half. Chemicals were transiently applied to the mucosa, and responses were recorded intracellularly in nearby circular muscle cells. The amino acids l-phenylalanine, l-alanine, or l-tryptophan (all 1 mM) evoked inhibitory junction potentials (IJPs; latency 150–300 ms, amplitude 3–8 mV, each n > 6) that were blocked by TTX and partially blocked by antagonists of P2X receptors and/or a combination of antagonists at 5-HT3and 5-HT4receptors. The putative mediators 5-HT (10 μM), ATP (1 mM), and CCK-8 (1–10 μM) elicited IJPs mediated via 5-HT3, P2X, and CCK-B receptors, respectively. Responses were only partially reduced by the effective antagonists. IJPs evoked by electrically stimulating the mucosa were unaffected by antagonists that reduced chemically evoked responses. Both chemically and electrically evoked IJPs were resistant to nicotinic, NK1, NK3, α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, N-methyl-d-aspartate, or CGRP receptor blockade. We conclude that mucosal stimulation by amino acids activates local neural pathways whose pharmacology depends on the nature of the stimulus. Transmitters involved at some synapses in these pathways remain to be identified.
Functional and molecular characterization of the fluid secretion mechanism in human parotid acinar cells
Authors: Nakamoto Tetsuji , Srivastava Alaka , Romanenko Victor G. , Ovitt Catherine E. , Perez-Cornejo Patricia , Arreola Jorge , Begenisich Ted , Melvin James E.
Published: March 2007

The strategies available for treating salivary gland hypofunction are limited because relatively little is known about the secretion process in humans. An initial microarray screen detected ion transport proteins generally accepted to be critically involved in salivation. We tested for the activity of some of these proteins, as well as for specific cell properties required to support fluid secretion. The resting membrane potential of human acinar cells was near −51 mV, while the intracellular [Cl−] was ∼62 mM, about fourfold higher than expected if Cl ions were passively distributed. Active Cl−uptake mechanisms included a bumetanide-sensitive Na+-K+-2Cl−cotransporter and paired DIDS-sensitive Cl−/HCO3−and EIPA-sensitive Na+/H+exchangers that correlated with expression of NKCC1, AE2, and NHE1 transcripts, respectively. Intracellular Ca2+stimulated a niflumic acid-sensitive Cl−current with properties similar to the Ca2+-gated Cl channel BEST2. In addition, intracellular Ca2+stimulated a paxilline-sensitive and voltage-dependent, large-conductance K channel and a clotrimazole-sensitive, intermediate-conductance K channel, consistent with the detection of transcripts for KCNMA1 and KCNN4, respectively. Our results demonstrate that the ion transport mechanisms in human parotid glands are equivalent to those in the mouse, confirming that animal models provide valuable systems for testing therapies to prevent salivary gland dysfunction.
Hypoxic incubation blunts the development of thermogenesis in chicken embryos and hatchlings
Authors: Azzam Milène A. , Szdzuy Kirsten , Mortola Jacopo P.
Published: March 2007

We asked to what extent sustained hypoxia during embryonic growth might interfere with the normal development of thermogenesis. White Leghorn chicken eggs were incubated at 38°C either in normoxia (Nx, 21% O2) or in hypoxia [Hx, 15% O2, from embryonic day 5 (E5) until hatching]. The Hx embryos had lower body weight (W) throughout incubation, and hatching was delayed by about 10 h. For both groups, all measurements were conducted in normoxia. At embryonic day E11, the static temperature-oxygen consumption (ambient T-V̇o2) curve was typically ectothermic (Q10= 1.92–1.94) and similar between Nx and Hx. Toward the end of incubation (E20), the Q10averaged 1.41 ± 0.06 in Nx and 1.79 ± 0.08 in Hx ( P < 0.005), indicating that the onset of the thermogenic response in Hx lagged behind Nx. In the 1-day-old hatchlings (H1), body weight did not significantly differ between Nx and Hx. At H1, the T-V̇o2curves were endothermic-type, and more so in the older (>8 h old) than in the newly hatched (<8 h old) chicks, whether examined statically or dynamically as a function of time. In either case, the thermogenic responses of Hx were lower than those of Nx. In a 43–31°C thermocline, the preferred T of the Hx hatchlings was around 37.3°C, and similar to Nx, suggesting a similar setpoint for thermoregulation. We conclude that hypoxic incubation blunted the development of thermogenesis. This could be interpreted as an example of epigenetic regulation, in which an environmental perturbation during early development alters the phenotypic expression of a regulatory system.
Myocardial infarct size measurement in the mouse chronic infarction model: comparison of area- and length-based approaches
Authors: Takagawa Junya , Zhang Yan , Wong Maelene L. , Sievers Richard E. , Kapasi Neel K. , Wang Yan , Yeghiazarians Yerem , Lee Randall J. , Grossman William , Springer Matthew L.
Published: March 2007

Efficacy of potential treatments for myocardial infarction (MI) is commonly assessed by histological measurement of infarct size in rodent models. In experiments involving an acute MI setting, measurement of the infarcted area in tissue sections of the left ventricle is a standard approach to determine infarct size. This approach has also been used in the chronic infarct setting to measure infarct area several weeks post-MI. We tested the hypothesis that, because wall thinning is known to occur in the chronic setting, the area measurement approach would be less appropriate. We compared infarct measurements in tissue sections based on 1) infarct area, 2) epicardial and endocardial infarct arc lengths, and 3) midline infarct arc length. Infarct sizes from all three measurement approaches correlated significantly with left ventricular ejection fraction and wall motion abnormality. However, the infarct size values derived from the area measurement approach were significantly smaller than those from the other two measurement approaches, and the range of values obtained was compressed 0.4-fold. The midline method allowed detection of the expected size differences between infarcts of variable severity resulting from proximal vs. distal ligation of the coronary artery. Segmental infarct size was correlated with segmental wall motion abnormality. We conclude that both area- and length-based measurements can be used to determine relative infarct size over a wide range of severity, although the area-based measurements are substantially more compressed due to wall thinning, and that the estimation of infarct midlines is a simple, reliable approach to infarct size assessment.
Changes in stretch reflexes and muscle stiffness with age in prepubescent children
Authors: Grosset Jean-Francois , Mora Isabelle , Lambertz Daniel , Pérot Chantal
Published: March 2007

Musculo-articular stiffness of the triceps surae (TS) increases with age in prepubescent children, under both passive and active conditions. This study investigates whether these changes in muscle stiffness influence the amplitude of the reflex response to muscle stretch. TS stiffness and reflex activities were measured in 46 children (7–11 yr old) and in 9 adults. The TS Hoffmann reflex (H reflex) and T reflex (tendon jerk) in response to taping the Achilles tendon were evaluated at rest and normalized to the maximal motor response (Mmax). Sinusoidal perturbations of passive or activated muscles were used to evoke stretch reflexes and to measure passive and active musculoarticular stiffness. The children's Hmax-to-Mmaxratio did not change with age and did not differ from adult values. The T-to-Mmaxratio increased with age but remained significantly lower than in adults. Passive stiffness also increased with age and was correlated with the T-to-Mmaxratio. Similarly, the children's stretch reflex and active musculoarticular stiffness were significantly correlated and increased with age. We conclude that prepubescent children have smaller T reflexes and stretch reflexes than adults, and the lower musculoarticular stiffness is mainly responsible for these smaller reflexes, as indicated by the parallel increases in reflex and stiffness.
Genetic variation of the β2-adrenergic receptor is associated with differences in lung fluid accumulation in humans
Authors: Snyder Eric M. , Beck Kenneth C. , Turner Stephen T. , Hoffman Eric A. , Joyner Michael J. , Johnson Bruce D.
Published: March 2007

The β2-adrenergic receptors (β2AR) play an important role in lung fluid regulation. Previous research has suggested that subjects homozygous for arginine at amino acid 16 of the β2AR (Arg16) may have attenuated receptor function relative to subjects homozygous for glycine at the same amino acid (Gly16). We sought to determine if the Arg16Gly polymorphism of the β2AR influenced lung fluid balance in response to rapid saline infusion. We hypothesized that subjects homozygous for Arg at amino acid 16 ( n = 14) would have greater lung fluid accumulation compared with those homozygous for Gly ( n = 15) following a rapid intravenous infusion of isotonic saline (30 ml/kg over 17 min). Changes in lung fluid were determined using measures of lung density and tissue volume (computerized tomography imaging) and measures of pulmonary capillary blood volume (Vc) and alveolar-capillary conductance (DM, determined from the simultaneous assessment of the diffusing capacities of the lungs for carbon monoxide and nitric oxide). The saline infusion resulted in elevated catecholamines in both genotype groups (Arg16 283 ± 117% vs. Gly16 252 ± 118%, P > 0.05). The Arg16 group had a larger decrease in DMand increase in lung tissue volume and lung water after saline infusion relative to the Gly16 group (DM−13 ± 14 vs. 0 ± 26%, P < 0.05; lung tissue volume 13 ± 11 vs. 3 ± 11% and lung water +90 ± 66 vs. +48 ± 144 ml, P = 0.10, P < 0.05, for Arg vs. Gly16, respectively, means ± SD). These data suggest that subjects homozygous for Arg at amino acid 16 of the β2AR have a greater susceptibility for lung fluid accumulation relative to subjects homozygous for Gly at this position.
Creatine uptake in brain and skeletal muscle of mice lacking guanidinoacetate methyltransferase assessed by magnetic resonance spectroscopy
Authors: Kan Hermien E. , Meeuwissen Esther , van Asten Jack J. , Veltien Andor , Isbrandt Dirk , Heerschap Arend
Published: March 2007

Creatine (Cr) levels in skeletal muscle and brain of a mouse model of Cr deficiency caused by guanidinoacetate methyltransferase absence (GAMT−/−) were studied after Cr supplementation with 2 g·kg body wt−1·day−1Cr for 35 days. Localized1H magnetic resonance spectroscopy (MRS) was performed in brain (cerebellum and thalamus/hippocampus) and in hind leg muscle of GAMT−/−mice before and after Cr supplementation and in control (Con) mice. As expected, a signal for Cr was hardly detectable in MR spectra of GAMT−/−mice before Cr supplementation. In the thalamus/hippocampus region of these mice, an increase in N-acetylasparate (NAA) was observed. During Cr administration, Cr levels increased faster in skeletal muscle compared with brain, but this occurred only during the first day of supplementation. Thereafter, Cr levels increased by 0.8 mM/day in all studied locations. After 35 days of Cr supplementation, Cr levels in all locations were higher compared with Con mice on a Cr-free diet and NAA levels normalized. Only because of the repeated MRS measurements performed in this longitudinal Cr supplementation study on GAMT−/−mice were we able to discover the initial faster uptake of Cr in skeletal muscle compared with brain, which may represent muscular Cr uptake independent of Cr transporter expression. Our results can provide the basis for additional experiments to optimize Cr supplementation in GAMT deficiency, as increases in brain Cr are slow in patients after Cr supplementation.
Glucocorticoid Receptor, Nuclear Factor κB, Activator Protein-1 and C-Jun N-Terminal Kinase in Systemic Lupus Erythematosus Patients
Authors: Oikonomidou Olga , Vlachoyiannopoulos Panayiotis G. , Kominakis Antonios , Kalofoutis Anastasios , Moutsopoulos Haralampos M. , Moutsatsou Paraskevi
Published: March 2007

Objective: Due to the crucial role of the glucocorticoid receptor (GR), nuclear factor ĸB (NFĸB), activator protein-1 (AP-1) and c-jun N-terminal kinase (JNK) in regulating inflammatory mediators and immune responses, we investigated their potential role in systemic lupus erythematosus (SLE). Patients and Methods: Whole cell and nuclear extracts from peripheral blood lymphocytes, isolated from 25 SLE patients and 25 controls, were immunoblotted using GR, p65/NFĸB, c-fos and JNK1 antibodies. The electrophoretic mobility shift assay (EMSA) assessed GR, NFĸB and AP-1-DNA binding in nuclear aliquots. Associations with the disease state and the doses of corticosteroids administered were studied. Results: (i) SLE patients had lower GR-DNA binding (p < 0.001), NFĸB-DNA binding (p < 0.001) and whole cell c-fos (p < 0.01) but higher nuclear NFĸB (p < 0.01). (ii) SLE patients and controls had similar AP-1-DNA binding, nuclear c-fos, GR and JNK, whole cell GR, NFĸB and JNK. (iii) No differences were detected between active and non-active SLE or high- and low-dose corticosteroid patients. (iv) In SLE, increases in GR-DNA binding were associated with increases in NFĸB-DNA binding (p < 0.0001), and increases in nuclear JNK were associated with increases in AP-1-DNA binding (p < 0.01). (v) In controls, increases in GR-DNA binding were associated with increases in AP-1-DNA binding (p < 0.001). Conclusion: We suggest disturbed GR, NFĸB, AP-1 and JNK signaling in SLE, characterized by a reduced GR- and NFĸB-DNA binding, a significant association between GR-mediated and NFĸB-driven pathways, and a significant correlation between nuclear JNK- and AP-1-driven pathways. These disturbances may contribute to abnormal cytokine production and the etiopathogenesis of SLE.