bluuebunny/crossref_metadata_2025 huggingface dataset:
Pre-Tommotian age of the lower Pestrotsvet Formation in the Selinde section on the Siberian platform: carbon isotopic evidence
Authors: KOUCHINSKY ARTEM , BENGTSON STEFAN , PAVLOV VLADIMIR , RUNNEGAR BRUCE , VAL'KOV ANATOLIJ , YOUNG EDWARD
Published: August 2005

Carbon isotopic data from the Selinde section in the southeastern part of the Siberian platform area are correlated with the reference isotopic profile from the Lower Cambrian stratotype sections of the Lena–Aldan region, but also show additional δ13C excursions unrecognized there. The chemostratigraphic correlation suggests that the geological and fossil record of the lower Pestrotsvet Formation in the Selinde section has a deeper history than the stratotype region. This conclusion is important for both constraining the age of the earliest Cambrian marine transgression on the Siberian platform and providing a clearer understanding of the pace and order of early Cambrian geochemical and biological events.
Ontogeny of plasma membrane Ca2+ ATPase isoforms in the
neural retina of the postnatal rat
Authors: RENTERÍA RENÉ C. , STREHLER EMANUEL E. , COPENHAGEN DAVID R. , KRIZAJ DAVID
Published: August 2005

Calcium ion (Ca2+) signaling has been widely implicated in
developmental events in the retina, but little is known about the specific
mechanisms utilized by developing neurons to decrease intracellular
Ca2+. Using immunocytochemistry, we determined the expression
profiles of all known isoforms of a key Ca2+ transporter, the
plasma membrane Ca2+ ATPase (PMCA), in the rat retina. During
the first postnatal week, the four PMCA isoforms were expressed in
patterns that differed from their expression in the adult retina. At
birth, PMCA1 was found in the ventricular zone and nascent cell processes
in the distal retina as well as in ganglion and amacrine cells. After the
first postnatal week, PMCA1 became restricted to photoreceptors and cone
bipolar cells. By P10 (by postnatal day 10), most inner retinal PMCA
consisted of PMCA2 and PMCA3. Prominent PMCA4 expression appeared after
the first postnatal week and was confined primarily to the ON sublamina of
the inner plexiform layer (IPL). The four PMCA isoforms could play
distinct functional roles in the development of the mammalian retina even
before synaptic circuits are established. Their expression patterns are
consistent with the hypothesis that inner and outer retinal neurons have
different Ca2+ handling needs.
Connections of contralaterally projecting isthmotectal axons and
GABA-immunoreactive neurons in Xenopus tectum: An ultrastructural
study
Authors: RYBICKA KRYSTYNA KIELAN , UDIN SUSAN B.
Published: August 2005

To investigate the circuitry that mediates binocular interactions in
the tectum of Xenopus frogs, we have begun to identify the tectal
cells that receive ipsilateral eye input relayed via the nucleus
isthmi. Isthmotectal axons were labeled with horseradish peroxidase, and
thin sections were labeled by postembedding immunogold reaction with
antibodies to γ-aminobutyric acid (GABA). Ultrastructural examination
reveals that many isthmotectal axons terminate on GABA-immunoreactive
dendrites. Other isthmotectal axons contact postsynaptic structures that
are unlabeled but have an appearance consistent with previously described
GABA-poor zones of GABA-immunoreactive dendrites. We also examined the
unlabeled inputs to the dendrites that were postsynaptic to filled
isthmotectal axons. The most common nonisthmic inputs to those dendrites
were GABA-immunoreactive processes with symmetric morphology.
Surprisingly, we found only one input with the retinotectal
characteristics of densely packed round, clear vesicles and minimal GABA
immunoreactivity. These results indicate that isthmotectal axons synapse
onto inhibitory interneurons, that retinotectal and isthmotectal axons do
not synapse close to each other on the same dendrites, and that inhibitory
connections are the closest neighbors to isthmotectal synapses.
Unilateral paralytic strabismus in the adult cat induces plastic changes in interocular disparity along the visual midline: Contribution of the corpus callosum
Authors: MILLERET C. , BUSER P. , WATROBA L.
Published: August 2005

Neurones activated through the corpus callosum (CC) in the cat visual cortex are known to be almost entirely located at the 17/18 border. They are orientation selective and display receptive fields (RFs) distributed along the central vertical meridian of the visual field (“visual midline”). Most of these cells are binocular, and many of them are activated both from the contralateral eye through the CC, and from the ipsilateral eyeviathe direct retino-geniculo-cortical (GC) pathway. These two pathways do not carry exactly the same information, leading to interocular disparity between pairs of RFs along the visual midline. Recently, we have demonstrated that a few weeks of unilateral paralytic strabismus surgically induced at adulthood does not alter the cortical distribution of these units but leads to a loss of their orientation selectivity and an increase of their RF size, mainly toward the ipsilateral hemifield when transcallosally activated (Watroba et al., 2001). To investigate interocular disparity, here we compared these RF changes to those occurring in the same neurones when activated through the ipsilateral direct GC route. The 17/18 transition zone and the bordering medial region within A17 were distinguished, as they display different interhemispheric connectivity. In these strabismics, some changes were noticed, but were basically identical in both recording zones. Ocular dominance was not altered, nor was the spatial distribution of the RFs with respect to the visual midline, nor the amplitude of position disparity between pairs of RFs. On the other hand, strabismus induced a loss of orientation selectivity regardless of whether neurones were activated directly or through the CC. Both types of RFs also widened, but in opposite directions with respect to the visual midline. This led to changes in incidences of the different types of position disparity. The overlap between pairs of RFs also increased. Based on these differences, we suggest that the contribution of the CC to binocular vision along the midline in the adult might be modulated through several intrinsic cortical mechanisms.
Avant que/de: possibles passages à la connexion temporelle
Authors: LE DRAOULEC ANNE
Published: August 2005

L'étude mettra en évidence l'existence de subordonnées introduites par avant que (ou avant de) dont le contenu, au lieu d'être présupposé (comme c'est généralement le cas pour les subordonnées temporelles), fait l'objet d'une assertion. Le phénomène a déjà été identifié et largement étudié à propos des subordonnées introduites par un quand dit ‘inverse’. Dans la subordination inverse, le quand joue le rôle discursif d'un connecteur temporel – qu'on définira très simplement par l'établissement d'une relation temporelle entre deux propositions assertées. Nous nous appuierons sur ce phénomène bien reconnu pour explorer le cas comparable quoique moins clairement identifié de avant que/de à rôle de connecteur temporel.
The status and conservation of hornbills in Cambodia
Authors: SETHA TAN
Published: August 2005

Internal security problems from the 1960s up until 1998 prevented any fieldwork in Cambodia. Since then, the situation has improved greatly and the Royal Government of Cambodia, in collaboration with international conservation NGOs, has been conducting general biological surveys across the country. Survey reports were used to investigate current occurrence of hornbills. Historically, three hornbill species — Great Hornbill Buceros bicornis, Wreathed Hornbill Aceros undulatus and Oriental Pied Hornbill Anthracoceros albirostris — were known from Cambodia. Recent surveys show that populations of Great and Wreathed Hornbills have declined significantly since the 1960s, while Oriental Pied is still common. A fourth hornbill species, Brown Hornbill Anorrhinus tickelli, was reported in 1998 in Kirirom National Park spanning the border of Koh Kong and Kompong Speu provinces in south-west Cambodia. Conservation priorities and priorities for future surveys are being developed.
Size matters: the effects of forest fragmentation and resource availability on the endemic Sumba Hornbill Aceros everetti
Authors: SITOMPUL ARNOLD F. , KINNAIRD MARGARET F. , O'BRIEN TIMOTHY G.
Published: August 2005

We examined the influence of forest fragmentation and resource availability on the abundance and distribution of Sumba Hornbill Aceros everetti, a large, canopy-dwelling bird endemic to Sumba Island, Indonesia. Hornbill numbers were estimated monthly from August 1998 to September 1999. Estimates were made in three large (≥1,000 ha) and three small (<1,000 ha) forest fragments, using a standard line transect method. Phenological patterns of canopy trees were assessed in 10 × 50 m plots. Our data indicated that forest patch size may be a better predictor of Sumba Hornbill abundance and distribution than overall resource availability. Hornbills occurred at higher densities in large forests (6/km2) than small forests (2.4/km2). Small forests produced more fruit/ha per month but lacked a number of important hornbill food species. Monthly fruit availability in large and small forest fragments had no significant effect on fluctuations in hornbill density. However, hornbill densities were significantly higher in forests with high densities of strangling figs, after controlling for patch size, and in larger forests hornbill densities correlated with the abundance of ripe figs. We hypothesize that small patches still have conservation value if they are within hornbill ranging distance, and speculate that Sumba's forests are in a dynamic phase before the full impact of fragmentation has been expressed.
What Divides Us? The Image and Organization of Political
Science
Authors: Grant J. Tobin
Published: August 2005

The question “What is political science?” is nearly as old as the
discipline itself. Political science continually self-examines the
discipline to evaluate who we are and how we have changed. In
addition, there are numerous studies of groups within political
science, including political science in the U.S. South and women in
political science. There are also reviews of the development and
state of subfields, e.g., urban politics , international relations,
comparative politics, and political theory. Each of these histories
provides an image of what political science is or what it should be.
These self-reviews provide images of the discipline that shape our
identities as political scientists and advance the progress of
political science. Even if the images do not affect future
directions in political science, they are “an important dimension of
identity and critical reflection on the theory and practice of
political science”. Developing and critiquing these images are
important academic exercises. J. Tobin
Grant is assistant professor, department of political science,
Southern Illinois University, Carbondale. He is coauthor (with
Thomas Rudolph) of Expression vs. Equality: The Politics
of Campaign Finance Reform (Ohio State University
Press, 2004). I thank
Badredine Arfi, Gregory Kasza, Scott McClurg, Thomas Rudolph,
Edward Schatz, and Herbert Weisberg for their comments and
suggestions on this article.
Steady state phreatic surfaces in sloping aquifers
Authors: Loáiciga Hugo A.
Published: August 2005

Steady state groundwater flow driven by constant recharge in an unconfined aquifer overlying sloping bedrock is shown to be represented, using the Dupuit approximation, by an ordinary differential equation of the Abel type y(x) · y′(x) + a · y(x) + x = 0, whose analytical solution is derived in this work. This article first investigates the case of zero saturated thickness at the upstream boundary, a flow system reminiscent of perched groundwater created by percolation of precipitation or irrigation in a sloping aquifer fully draining at its downstream boundary. A variant of this flow system occurs when the phreatic surface mounds and produces groundwater discharge toward the upstream boundary. This variant is a generalization of the classical groundwater flow problem involving two lakes connected by an aquifer, the latter being on sloping terrain in this instance. Analytical solutions for the phreatic surface's steady state geometry are derived for the case of monotonically declining hydraulic head as well as for the case of a mounded phreatic surface. These solutions are of practical interest in drainage studies, slope stability, and runoff formation investigations. It is shown that the flow factor a = − tan β (where K, N, and tan β are the hydraulic conductivity, vertical recharge, and aquifer slope, respectively) has a commanding role on the phreatic surface's solutions. Two computational examples illustrate the implementation of this article's results.
Characterizing a large shear‐zone with seismic and magnetotelluric methods: The case of the Dead Sea Transform
Authors: Maercklin N. , Bedrosian P. A. , Haberland C. , Ritter O. , Ryberg T. , Weber M. , Weckmann U.
Published: August 2005

Seismic tomography, imaging of seismic scatterers, and magnetotelluric soundings reveal a sharp lithologic contrast along a ∼10 km long segment of the Arava Fault (AF), a prominent fault of the southern Dead Sea Transform (DST) in the Middle East. Low seismic velocities and resistivities occur on its western side and higher values east of it, and the boundary between the two units coincides partly with a seismic scattering image. At 1–4 km depth the boundary is offset to the east of the AF surface trace, suggesting that at least two fault strands exist, and that slip occurred on multiple strands throughout the margin's history. A westward fault jump, possibly associated with straightening of a fault bend, explains both our observations and the narrow fault zone observed by others.
Synaptic plasticity disruption by amyloid β protein: modulation by potential Alzheimer's disease modifying therapies
Authors: Rowan M.J. , Klyubin I. , Wang Q. , Anwyl R.
Published: August 2005

AD (Alzheimer's disease) is characterized by a progressive and devastating mental decline that is usually presaged by impairment of a form of memory dependent on medial temporal lobe structures, including the hippocampus. The severity of clinical dementia correlates positively with the cerebral load of the AD-related protein Aβ (amyloid β), particularly in its soluble form rather than the insoluble fibrillar Aβ found in amyloid plaques. Recent research in animal models of AD has pointed to a potentially important role for rapid disruptive effects of soluble species of Aβ on neural function in causing a relatively selective impairment of memory early in the disease. Our experiments assessing the mechanisms of Aβ inhibition of LTP (long-term potentiation), a correlate of memory-related synaptic plasticity, in the rodent hippocampus showed that low-n oligomers were the soluble Aβ species primarily responsible for the disruption of synaptic plasticity in vivo. Exogenously applied and endogenously generated anti-Aβ antibodies rapidly neutralized and prevented the synaptic plasticity disrupting effects of these very potent Aβ oligomers. This suggests that active or passive immunotherapeutic strategies for early AD should target Aβ oligomers in the brain. The ability of agents that reduce nitrosative/oxidative stress or antagonize stress-activated kinases to prevent Aβ inhibition of LTP in vitro points to a key role of these cellular mechanisms at very early stages in Aβ-induced neuronal dysfunction. A combination of antibody-mediated inactivation of Aβ oligomers and pharmacological prevention of cellular stress mechanisms underlying their synaptic plasticity disrupting effects provides an attractive strategy in the prevention of early AD.
Evidence suggesting that Homo neanderthalensis contributed the H2 MAPT haplotype to Homo sapiens
Authors: Hardy J. , Pittman A. , Myers A. , Gwinn-Hardy K. , Fung H.C. , de Silva R. , Hutton M. , Duckworth J.
Published: August 2005

The tau (MAPT) locus exists as two distinct clades, H1 and H2. The H1 clade has a normal linkage disequilibrium structure and is the only haplotype found in all populations except those derived from Caucasians. The H2 haplotype is the minor haplotype in Caucasian populations and is not found in other populations. It shows no recombination over a region of 2 Mb with the more common H1 haplotype. The distribution of the haplotype and analysis of the slippage of dinucleotide repeat markers within the haplotype suggest that it entered Homo sapiens populations between approx. 10000 and 30000 years ago. However, sequence comparison of the H2 haplotype with the H1 haplotype and with the chimp sequence suggests that the common founder of the H1 and H2 haplotypes was far earlier than this. We suggest that the H2 haplotype is derived from Homo neanderthalensis and entered H. sapiens populations during the co-existence of these species in Europe from approx. 45000 to 18000 years ago and that the H2 haplotype has been under selection pressure since that time, possibly because of the role of this H1 haplotype in neurodegenerative disease.
ARL1 has an essential role in Trypanosoma brucei
Authors: Price H.P. , Goulding D. , Smith D.F.
Published: August 2005

Myristoyl-CoA protein:NMT (N-myristoyl transferase) catalyses the N-myristoylation of cellular proteins with a range of functions and is essential for viability in the protozoan parasites, Leishmania major and Trypanosoma brucei. In our investigations to define the essential downstream targets of NMT, we have focused on the ARF (ADP-ribosylation factor) family of proteins, as growth arrest in Saccharomyces cerevisiae mutants with reduced NMT activity correlates with decreased modification of members of this group of proteins. We have identified nine ARF/ARLs (where ARL stands for ARF-like) encoded in the T. brucei and T. cruzi genomes and ten in L. major. The T. brucei ARL1 protein is expressed only in the mammalian bloodstream form of the parasite, in which it is localized to the Golgi apparatus. RNAi (RNA interference) has been used to demonstrate that ARL1 is essential for viability in these infective cells. Before cell death, depletion of ARL1 protein results in disintegration of the Golgi structure and a delay in exocytosis of the abundant GPI (glycosylphosphatidylinositol)-anchored VSG (variant surface glycoprotein) to the parasite surface.
Function and regulation of RhoE
Authors: Riento K. , Villalonga P. , Garg R. , Ridley A.
Published: August 2005

The three Rnd proteins, Rnd1, Rnd2 and RhoE/Rnd3, are a subset of Rho family proteins that are unusual in that they bind but do not hydrolyse GTP, and are therefore not regulated by the classical GTP/GDP conformational switch of small GTPases. Increased expression of each Rnd protein induces loss of stress fibres in cultured fibroblasts and epithelial cells, acting antagonistically to RhoA, which stimulates stress fibre formation. RhoE is farnesylated and localizes partly on membranes, including the Golgi and plasma membrane, and in the cytosol. RhoE inhibits RhoA signalling in part by binding to the RhoA-activated serine/threonine kinase ROCK I (Rho-associated kinase I), thereby preventing it from phosphorylating its targets. RhoE activity is itself regulated by phosphorylation by ROCK I on multiple sites. RhoE phosphorylation enhances its stability, leading to an increase in RhoE levels. In addition, phosphorylation reduces its association with membranes and correlates with its ability to induce loss of stress fibres. RhoE also acts independently of ROCK to inhibit cell cycle progression, in part by preventing translation of cyclin D1, and to inhibit transformation of fibroblasts by oncogenic H-Ras. RhoE is therefore a multifunctional protein whose localization and actions are regulated by phosphorylation.
The role of the retinoblastoma protein (Rb) in the nuclear localization of BAG-1: implications for colorectal tumour cell survival
Authors: Clemo N.K. , Arhel N.J. , Barnes J.D. , Baker J. , Moorghen M. , Packham G.K. , Paraskeva C. , Williams A.C.
Published: August 2005

Although the retinoblastoma susceptibility gene RB1 is inactivated in a wide variety of human cancers, the retinoblastoma protein (Rb) has been shown to be overexpressed in colon cancers, which is linked to the anti-apoptotic function of the protein. However, the mechanisms by which Rb regulates apoptosis are yet to be fully elucidated. We have established that Rb interacts with the anti-apoptotic BAG-1 (Bcl-2 associated athanogene-1) protein, and that a decrease in nuclear localization of BAG-1 is detectable when the interaction between Rb and BAG-1 is disrupted by expression of the E7 viral oncoprotein. Interestingly, although reported as deregulated in colorectal cancers, we have found that BAG-1 expression is also altered in small adenomas, where its localization was found to be predominantly nuclear. In addition, we have established that maintenance of high nuclear BAG-1 in vitro increases the resistance of adenoma-derived cells to γ-radiation-induced apoptosis. Our work suggests a novel function for Rb, involving modulation of the subcellular localization of BAG-1. We have found predominant nuclear BAG-1 localization in small adenomas, and suggest that BAG-1 may promote colorectal tumour cell survival by making colonic epithelial cells less sensitive to DNA damage.
Regulation of tetrapyrrole biosynthesis in higher plants
Authors: Moulin M. , Smith A.G.
Published: August 2005

Plant tetrapyrroles are the most abundant biomolecules on the earth and are cofactors of many apoproteins essential for plant function. The four end-products sirohaem, chlorophyll, haem and phytochromobilin are synthesized by a common branched pathway, which is tightly regulated to ensure a continuous supply to the cognate apoproteins. This may induce strong competition between different branches of the pathway for common substrates. In addition, the intermediates, which are phototoxic, must not be allowed to accumulate in the cell. The major control points are during the synthesis of the initial precursor, ALA (5-aminolaevulinic acid), and at the branch points for the insertion of metal ions into the porphyrin macrocycle. A recent study has also suggested that tetrapyrroles are involved in the communication between the chloroplast and the nucleus, strengthening the necessity for tight regulation. However, intermediates remain difficult to quantify mainly due to their low content and the different properties of the intermediates. In this paper, we summarize the regulation of this pathway and we detail why it is important to have an accurate method for the determination of tetrapyrroles in plants.
Biodiversity of cytochrome P450 redox systems
Authors: McLean K.J. , Sabri M. , Marshall K.R. , Lawson R.J. , Lewis D.G. , Clift D. , Balding P.R. , Dunford A.J. , Warman A.J. , McVey J.P. , Quinn A.-M. , Sutcliffe M.J. , Scrutton N.S. , Munro A.W.
Published: August 2005

P450s (cytochrome P450 mono-oxygenases) are a superfamily of haem-containing mono-oxygenase enzymes that participate in a wide range of biochemical pathways in different organisms from all of the domains of life. To facilitate their activity, P450s require sequential delivery of two electrons passed from one or more redox partner enzymes. Although the P450 enzymes themselves show remarkable similarity in overall structure, it is increasingly apparent that there is enormous diversity in the redox partner systems that drive the P450 enzymes. This paper examines some of the recent advances in our understanding of the biodiversity of the P450 redox apparatus, with a particular emphasis on the redox systems in the pathogen Mycobacterium tuberculosis.
Vitamin B12: chemistry and biochemistry
Authors: Kräutler B.
Published: August 2005

Vitamin B12, the ‘antipernicious anaemia factor’, is required for human and animal metabolism. It was discovered in the late 1940s and its unique corrin ligand was revealed approx. 10 years later by X-ray crystallography. The B12-coenzymes are cofactors in various important enzymatic reactions and are particularly relevant in the metabolism of anaerobic microorganisms. Microorganisms are the only natural sources of the B12-derivatives, whereas most spheres of life (except for the higher plants) depend on these cobalt corrinoids.
Pressure device for resonant magnetic x-ray scattering
Authors: Kernavanois Nolwenn , Deen Pascale P. , Paolasini Luigi , Braithwaite Daniel
Published: August 2005

A pressure device has been developed and adapted to resonant x-ray magnetic scattering (RXMS) technique. The system is optimized for diffraction studies and allows a wide angular aperture in the scattering plane. Pressure changes are made in situ with pressure determination by the ruby fluorescence method. Since the whole device is compatible with a standard Orange cryostat, an extended (p,T) phase space, with T=1.4–300K and p=0–30kbar, can now be probed by RXMS. As an illustration, first results on Ce(CoxFe1−x)2 single crystal are presented. Such a pressure device can be equally used for other than RXMS techniques as shown with the study at low temperature of SmS under pressure using x-ray fluorescence measurements.
Electron-stimulated sputtering of thin amorphous solid water films on Pt(111)
Authors: Petrik Nikolay G. , Kimmel Greg A.
Published: August 2005

The electron-stimulated sputtering of thin amorphous solid water films deposited on Pt(111) is investigated. The sputtering appears to be dominated by two processes: (1) electron-stimulated desorption of water molecules and (2) electron-stimulated reactions leading to the production of molecular hydrogen and molecular oxygen. The electron-stimulated desorption of water increases monotonically with increasing film thickness. In contrast, the total sputtering—which includes all electron-stimulated reaction channels—is maximized for films of intermediate thickness. The sputtering yield versus thickness indicates that erosion of the film occurs due to reactions at both the water/vacuum interface and the Pt/water interface. Experiments with layered films of D2O and H2O demonstrate significant loss of hydrogen due to reactions at the Pt/water interface. The electron-stimulated sputtering is independent of temperature below ∼80K and increases rapidly at higher temperatures.
Gold nanoclusters on amorphous carbon synthesized by ion-beam deposition
Authors: Thune Elsa , Carpene Ettore , Sauthoff Katharina , Seibt Michael , Reinke Petra
Published: August 2005

Gold clusters have been deposited by a monoenergetic, mass-selected ion beam with low energies (20–350eV) on amorphous carbon substrates in order to minimize the influence of the surface crystallinity and the ion-induced structural changes. Gold has been used as a model system, due to the poor reactivity with carbon, to study the ion-energy dependence, the temporal evolution, and the influence of the temperature on the cluster distribution. The cluster size is very sensitive to the energy and the mean size strongly decreases from 4 to less than 1nm as the ion energy increases. We can also note that the size distribution becomes broader. For impact energies below 100eV, surface processes dominate the cluster nucleation and growth. If higher energies are used, an increasing number of ions is implanted below the surface and different processes control the cluster formation. When the energy increases above 350eV, the cluster size drastically drops below 5nm. The samples are analyzed with different methods such as atomic force microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy to determine their size distribution, composition, and structure.
Temperature dependence of the thermo-optic coefficient of lithium niobate, from 300 to 515 K in the visible and infrared regions
Authors: Moretti Luigi , Iodice Mario , Della Corte Francesco G. , Rendina Ivo
Published: August 2005

The temperature dependence of the thermo-optic coefficients of lithium niobate has been measured in the temperature range between 320 and 515 K for both wavelengths of 632 and 1523 nm and for ordinary and extraordinary refractive indices. The experimental data, carried out by means of a simple interferometric technique, have been compared with two theoretical models that follow different approaches for treating the thermo-optic effect. The experimental results show good agreement with the theoretical ones.
A modified Poisson–Boltzmann analysis of the capacitance behavior of the electric double layer at low temperatures
Authors: Bhuiyan L. B. , Outhwaite C. W. , Henderson D.
Published: August 2005

The modified Poisson–Boltzmann theory is used to analyze the anomalous behavior of the electric double layer capacitance for small surface charge at low temperatures and densities. Good agreement is found with simulation and recent density-functional theory results. Negative adsorption is also found in line with theory and simulation. An unsatisfactory feature is the relatively poor structure in this region due to the inherent approximations in the theory. This feature is unimportant in relation to the capacitance results but has implications when calculating adsorption properties.
Lattice vibrations and phase-transition soft mode in near stoichiometric lithium niobate crystals
Authors: Xia H. R. , Sun S. Q. , Cheng X. F. , Dong S. M. , Xu H. Y. , Gao L. , Cui D. L.
Published: August 2005

At room temperature, Raman-scattering investigations of near stoichiometric lithium niobate (S-LN) crystals theoretically and experimentally reveal an effect of the lattice vacant positions on the Raman spectra. At high temperature, Raman peaks of the mode ν5 vary sensitively and intensely with the increase of the temperature. A condensed soft optical-phonon mode originates from the triply degenerate symmetric in-plane O–Nb–O bending. The paraelectric-ferroelectric structural transition occurs at about 1170°C. The composition homogeneity and optical uniformity of the S-LN crystals are demonstrated to be excellent compared with those of the congruent lithium niobate.
Long lifetime, triggered, spark-gap switch for repetitive pulsed power applications
Authors: Winands G. J. J. , Liu Z. , Pemen A. J. M. , van Heesch E. J. M. , Yan K.
Published: August 2005

In this article a critical component for pulsed power applications is described: the heavy-duty switch. The design of a coaxial, high repetition rate, large average power, and long lifetime spark-gap switch is discussed. The switch is used with a fail-free LCR trigger circuit. Critical issues for switch design are presented together with experimental results. It is observed that the switch has a good stability, and its lifetime is estimated to be in the order of 1010 shots (∼106C) at 10J∕pulse, 60kV and 100ns pulses. Measurements were performed with 20 and 34kV average switching voltage (100ns pulses, energy per pulse 0.4 and 0.75J, respectively). For up to 450pulses∕s (pps), pre-firing can be prevented by increasing the gap pressure (up to 2.5 and 7bars, respectively), no gas flush is required. Above 450pps, up to 820pps, a forced gas flow of maximal 35Nm3∕h, is required for stable operation. Measurements on the time delay and jitter of the switch demonstrate that these values are influenced by pressure, flow, and pulse repetition rate. For 34kV average switching voltage the time delay and time jitter vary between 35 and 250 and 10 and 80μs, respectively. For 20kV average switching voltage these values are: 30–160 and 4–50μs. During a test run of 2.5h (at 100Hz, 0.75J∕pulse) the feasibility of the switch was proved, and the switching voltage jitter was less than 0.7%.
Direct observation of a fully strained dead layer at Ba0.7Sr0.3TiO3∕SrRuO3 interface
Authors: He J. Q. , Vasco E. , Jia C. L. , Wang R. H.
Published: August 2005

Epitaxial SrRuO3∕Ba0.7Sr0.3TiO3 (BST)/SrRuO3 thin film capacitors were prepared on SrTiO3 substrates by pulsed laser deposition. The structures of stacked BST films with different thicknesses were investigated by transmission electron microscopy. A distinctive layer of about 3nm of thickness was identified within BST films thicker than 9nm at the interface with the SrRuO3 bottom electrode. The distinctive layer is misfit dislocation-free showing pseudoconstant lattice parameters. Misfit dislocations are formed at the interface between the distinctive layer and the BST film bulk layer relaxing the latter as the film thickness increases. The effect of the distinctive layer on the system dielectric response is discussed within the framework of an interfacial dead-layer model.
Development of a microwave transmission setup for time-resolved measurements of the transient complex conductivity in bulk samples
Authors: Schins J. M. , Prins P. , Grozema F. C. , Abellón R. D. , de Haas M. P. , Siebbeles L. D. A.
Published: August 2005

We describe and characterize a microwave transmission setup for the measurement of radiation-induced transient conductivities in the frequency range between 26 and 38GHz (Q band). This technique combines the virtues of two already existing techniques. On one hand, the microwave transmission technique is well established for the determination of (quasi)static conductivities, but requires adaptations to be suitable to the determination of transient conductivities with 1ns temporal resolution. On the other hand, the transient conductivity technique is well established, too, but in its present form (using a reflection configuration) it suffers from a poor signal to noise ratio due to unwanted interferences. These interferences are due to the circulator, which diverts part of the incoming microwave flux directly to the detector. We characterized the transmission setup by measuring the real and imaginary components of the conductivity of pulse irradiated CO2 gas at different pressures, and compared these results to predictions of the Drude model. CO2 was chosen as a test sample because of its well characterized behavior when irradiated with MeV electron pulses, and the fact that a wide range of the ratios of imaginary to real components of the conductivity are obtainable by just controlling the pressure. For intrinsic bulk isolators (either powders or in solution) pulse-induced conductivity changes as small as 10−8S∕m can be measured with nanosecond time resolution. The ratio of the imaginary to real part of the conductivity can be measured in the range from 0.084 to 28, which means that the dynamic range has been increased more than 100-fold with respect to the customary reflection setup.
Experimental demonstration of complete photonic band gap in two-dimensional photonic crystal slabs
Authors: Takayama Sei-ichi , Kitagawa Hitoshi , Tanaka Yoshinori , Asano Takashi , Noda Susumu
Published: August 2005

The realization of a photonic band gap (PBG)—not only for transverse electric (TE), but also transverse magnetic (TM)-like polarization modes in two-dimensional photonic crystal slab—is of interest for various applications. Such a complete PBG has been investigated theoretically in two-dimensional structures of which thickness is infinity. However, a complete PBG has not been demonstrated in feasible two-dimensional slab structure. In this letter, we propose two-dimensional photonic crystal slabs consisting of a triangular lattice of triangular air holes to achieve a complete PBG, and report the transmission spectra of fabricated samples. The results indicate that the degeneracy between the first and second band at the J point for TM-like polarization mode is solved, and PBG for TM-like polarization mode is obtained. Finally, we confirm the overlap of PBG between TE- and TM-like polarization modes.
Transition from diffuse to filamentary domain in a 9.5GHz microwave-induced surface discharge
Authors: Popović S. , Exton R. J. , Herring G. C.
Published: August 2005

The transition from the low-pressure diffuse to the high-pressure filamentary domain of a 9.5GHz microwave-induced surface discharge in air is recorded. The discharge employs several half-wavelength initiators that locally enhance the electric field to achieve breakdown in the higher-pressure subcritical region. Visible light imaging illustrates the qualitative changes in discharge morphology over the pressure range 4.5to760Torr (0.6to100kPa).
Nanoscale imaging of grain orientations and ferroelectric domains in (Bi1−xLax)4Ti3O12 films for ferroelectric memories
Authors: Yang B. , Park N. J. , Seo B. I. , Oh Y. H. , Kim S. J. , Hong S. K. , Lee S. S. , Park Y. J.
Published: August 2005

We report results of nanoscopic investigation of grain crystallographic orientations and ferroelectric domains by electron backscatter diffraction (EBSD) technique and piezoresponse force microscope (PFM), respectively, in (Bi1−xLax)4Ti3O12 (BLT) films for ferroelectric semiconductor memories. It is demonstrated that the EBSD technique is useful in characterizing nanoscale grain crystallographic orientations of BLT films. Comparison studies of grain orientations by EBSD technique and switching properties of ferroelectric domains by PFM show that c-axis parallel to normal oriented grains with almost linear dielectric properties have platelike morphology. However, a- or b-axis oriented grains with superior ferroelectric properties have ellipsoidal morphology with a size of less than 0.2μm in long axis. Consequently, the suppression of the platelike structures through process controls is important for the realization of high-density BLT-based memories.
Root architectural tradeoffs for water and phosphorus acquisition
Authors: Ho Melissa D. , Rosas Juan Carlos , Brown Kathleen M. , Lynch Jonathan P.
Published: August 2005

Root architectural traits that increase topsoil foraging are advantageous for phosphorus acquisition but may incur tradeoffs for the acquisition of deep soil resources such as water. To examine this relationship, common bean genotypes contrasting for rooting depth were grown in the field and in the greenhouse with phosphorus stress, water stress and combined phosphorus and water stress. In the greenhouse, water and phosphorus availability were vertically stratified to approximate field conditions, with higher phosphorus in the upper layer and more moisture in the bottom layer. Under phosphorus stress, shallow-rooted genotypes grew best, whereas under drought stress, deep-rooted genotypes grew best. In the combined stress treatment, the best genotype in the greenhouse had a dimorphic root system that permitted vigorous rooting throughout the soil profile. In the field, shallow-rooted genotypes surpassed deep-rooted genotypes under combined stress. This may reflect the importance of early vegetative growth in terminal drought environments. Our results support the hypothesis that root architectural tradeoffs exist for multiple resource acquisition, particularly when resources are differentially localised in the soil profile. Architectural plasticity and root dimorphism achieved through complementary growth of distinct root classes may be important means to optimise acquisition of multiple soil resources.
Parallel evolution of chimeric fusion genes
Authors: Jones Corbin D. , Begun David J.
Published: August 2005

To understand how novel functions arise, we must identify common patterns and mechanisms shaping the evolution of new genes. Here, we take advantage of data from three
Drosophila
genes,
jingwei
,
Adh-Finnegan
, and
Adh-Twain
, to find evolutionary patterns and mechanisms governing the evolution of new genes. All three of these genes are independently derived from
Adh
, which enabled us to use the extensive literature on
Adh
in
Drosophila
to guide our analyses. We discovered a fundamental similarity in the temporal, spatial, and types of amino acid changes that occurred. All three genes underwent rapid adaptive amino acid evolution shortly after they were formed, followed by later quiescence and functional constraint. These genes also show striking parallels in which amino acids change in the
Adh
region. We showed that these early changes tend to occur at amino acid residues that seldom, if ever, evolve in
Drosophila Adh
. Changes at these slowly evolving sites are usually associated with loss of function or hypomorphic mutations in
Drosophila melanogaster
. Our data indicate that shifting away from ancestral functions may be a critical step early in the evolution of chimeric fusion genes. We suggest that the patterns we observed are both general and predictive.
Absence of behavioral abnormalities and neurodegenerationin vivodespite widespread neuronal huntingtin inclusions
Authors: Slow Elizabeth J. , Graham Rona K. , Osmand Alexander P. , Devon Rebecca S. , Lu Ge , Deng Yu , Pearson Jacqui , Vaid Kuljeet , Bissada Nagat , Wetzel Ronald , Leavitt Blair R. , Hayden Michael R.
Published: August 2005

We have serendipitously established a mouse that expresses an N-terminal human huntingtin (htt) fragment with an expanded polyglutamine repeat (≈120) under the control of the endogenous human promoter (shortstop). Frequent and widespread htt inclusions occur early in shortstop mice. Despite these inclusions, shortstop mice display no clinical evidence of neuronal dysfunction and no neuronal degeneration as determined by brain weight, striatal volume, and striatal neuronal count. These results indicate that htt inclusions are not pathogenicin vivo. In contrast, the full-length yeast artificial chromosome (YAC) 128 model with the identical polyglutamine length and same level of transgenic protein expression as the shortstop demonstrates significant neuronal dysfunction and loss. In contrast to the YAC128 mouse, which demonstrates enhanced susceptibility to excitotoxic death, the shortstop mouse is protected from excitotoxicity, providingin vivoevidence suggesting that neurodegeneration in Huntington disease is mediated by excitotoxic mechanisms.
Mapping the landscape of biomedical research in Nigeria since 1967
Authors: Nwagwu Williams
Published: August 2005

This article maps the biomedical literature of Nigeria by source/origin of publications and authorships from 1967 to 2002. This mapping is expected to provide crucial information to both government and others taking funding and related decisions regarding biomedical research in Nigeria. Data was collected from MEDLINE. Scientists publishing on Nigerian biomedicine have written 6,820 articles in 295 journals/sources. Only eight of the 121 local journals that published biomedical research in Nigeria during the period were included in MEDLINE's listing (2.72%), while there were 32 (10.84%) regional and 255 (86.44%) external journals used. Local journals appeared to be more heavily used than regional and external ones. It was also shown that MEDLINE does not adequately represent Nigeria's biomedical literature.
Active Nercc1 Protein Kinase Concentrates at Centrosomes Early in Mitosis and Is Necessary for Proper Spindle Assembly
Authors: Roig Joan , Groen Aaron , Caldwell Jennifer , Avruch Joseph
Published: August 2005

The Nercc1 protein kinase autoactivates in vitro and is activated in vivo during mitosis. Autoactivation in vitro requires phosphorylation of the activation loop at threonine 210. Mitotic activation of Nercc1 in mammalian cells is accompanied by Thr210 phosphorylation and involves a small fraction of total Nercc1. Mammalian Nercc1 coimmunoprecipitates γ-tubulin and the activated Nercc1 polypeptides localize to the centrosomes and spindle poles during early mitosis, suggesting that active Nercc has important functions at the microtubular organizing center during cell division. To test this hypothesis, we characterized the Xenopus Nercc1 orthologue (XNercc). XNercc endogenous to meiotic egg extracts coprecipitates a multiprotein complex that contains γ-tubulin and several components of the γ-tubulin ring complex and localizes to the poles of spindles formed in vitro. Reciprocally, immunoprecipitates of the γ-tubulin ring complex polypeptide Xgrip109 contain XNercc. Immunodepletion of XNercc from egg extracts results in delayed spindle assembly, fewer bipolar spindles, and the appearance of aberrant microtubule structures, aberrations corrected by addition of purified recombinant XNercc. XNercc immunodepletion also slows aster assembly induced by Ran-GTP, producing Ran-asters of abnormal size and morphology. Thus, Nercc1 contributes to both the centrosomal and the chromatin/Ran pathways that collaborate in the organization of a bipolar spindle.
Acclimation of unicellular cyanobacteria to macronutrient deficiency: emergence of a complex network of cellular responses
Authors: Schwarz Rakefet , Forchhammer Karl
Published: August 2005

Cyanobacteria are equipped with numerous mechanisms that allow them to survive under conditions of nutrient starvation, some of which are unique to these organisms. This review surveys the molecular mechanisms underlying acclimation responses to nitrogen and phosphorus deprivation, with an emphasis on non-diazotrophic freshwater cyanobacteria. As documented for other micro-organisms, nutrient limitation of cyanobacteria elicits both general and specific responses. The general responses occur under any starvation condition and are the result of the stresses imposed by arrested anabolism. In contrast, the specific responses are acclimation processes that occur as a result of limitation for a particular nutrient; they lead to modification of metabolic and physiological routes to compensate for the restriction. First, the general acclimation processes are discussed, with an emphasis on modifications of the photosynthetic apparatus. The molecular mechanisms underlying specific responses to phosphorus and nitrogen-limitation are then outlined, and finally the cross-talk between pathways modulating specific and general responses is described.
Induction of the SOS regulon of Haemophilus influenzae does not affect phase variation rates at tetranucleotide or dinucleotide repeats
Authors: Sweetman Wendy A. , Moxon E. Richard , Bayliss Christopher D.
Published: August 2005

Haemophilus influenzaehas microsatellite repeat tracts in 5′ coding regions or promoters of several genes that are important for commensal and virulence behaviour. Changes in repeat number lead to switches in expression of these genes, a process referred to as phase variation. Hence, the virulence behaviour of this organism may be influenced by factors that alter the frequency of mutations in these repeat tracts. InEscherichia coli, induction of the SOS response destabilizes dinucleotide repeat tracts.H. influenzaeencodes a homologue of theE. coliSOS repressor, LexA. TheH. influenzaegenome sequence was screened for the presence of the minimal consensus LexA-binding sequence fromE. coli, CTG(N)10CAG, in order to identify genes with the potential to be SOS regulated. Twenty-five genes were identified that had LexA-binding sequences within 200 bp of the start codon. AnH. influenzaenon-inducible LexA mutant (lexANI) was generated by site-directed mutagenesis. This mutant showed increased sensitivity, compared with wild-type (WT) cells, to both UV irradiation and mitomycin C (mitC) treatment. Semi-quantitative RT-PCR studies confirmed thatH. influenzaemounts a LexA-regulated SOS response following DNA assault. Transcript levels oflexA,recA,recN,recX,ruvAandimpAwere increased in WT cells following DNA damage but not inlexANIcells. Induction of theH. influenzaeSOS response by UV irradiation or mitC treatment did not lead to any observable SOS-dependent changes in phase variation rates at either dinucleotide or tetranucleotide repeat tracts. Treatment with mitC caused a small increase in phase variation rates in both repeat tracts, independently of an SOS response. We suggest that the difference betweenH. influenzaeandE. coliwith regard to the effect of the SOS response on dinucleotide phase variation rates is due to the absence of any of the knowntrans-lesion synthesis DNA polymerases inH. influenzae.