bluuebunny/crossref_metadata_2025 huggingface dataset:
Anode length optimization in a modified plasma focus device for optimal x-ray yields
Authors: Neog N. K. , Mohanty S. R. , Hotta E.
Published: January 2006

The effect of anode length and operating gas pressure on the x-ray emission from a nitrogen-filling modified plasma focus device has been investigated. The time-resolved investigation of x ray was carried out by using a five-channel photodiode x-ray spectrometer. The maximum x-ray yield is seen to increase with the increase in the anode length from 110 to 125 mm. Further increase in the anode length to 130 mm causes the x-ray yields to decrease. The highest x-ray yield of 4.5 J into 4πsr was found for 125 mm anode length, which is 0.2% of the input energy. The average x-ray photon energy was estimated by using half-value thickness method and found to be 8.4 keV. The electron temperature of the plasma was estimated to be around 3 keV by x-ray intensity ratio method. The space-resolved x-ray-emitting zones for all the anodes were captured by a pinhole-based x-ray imaging camera and the images were scanned for different gray levels by using a MATLAB computing software. These gray level spectra show that the image for a 125 mm anode length is more intense than that for the other anode. In addition to this, the gray level spectrum shows some highly dense spot inside the image, which is the so-called hot spot, emitting relatively higher energy x rays. Our results indicate that the plasma focus device could be optimized to a great extent for optimal x-ray yield by using an appropriate anode length.
Rashba spin-orbit effect on spin-tunneling time in a ferromagnetic∕semiconductor∕ferromagnetic heterojunction with a tunnel barrier
Authors: Zhang Ying-Tao , Li You-Cheng
Published: January 2006

The electronic transport properties are studied theoretically in a ferromagnetic∕semiconductor∕ferromagnetic heterojunction with a tunnel barrier. The Rashba spin-orbit interaction in the semiconductor and the significant quantum size are taken into account simultaneously. It is found that the tunnel barrier plays a decisive role in the transmission coefficients of spin-up and spin-down electrons. On the basis of the group velocity concept and the particle current conservation principle, the spin-tunneling time is obtained as a function of the intensity of the Rashba spin-orbit coupling and the length of the semiconductor, respectively. It is shown that as the length of the semiconductor increases, the behavior of the spin-tunneling time oscillates slightly. Both the Rashba spin-orbit coupling and the tunnel barrier damps the motion of electrons, and so the tunneling time of electrons is increased.
First-principles calculations of band structures and dynamic optical properties of CsCdBr3 and RbCdI3∙H2O crystals
Authors: Huang S.-P. , Cheng W.-D. , Wu D.-S. , Li X.-D. , Lan Y.-Z. , Li F.-F. , Shen J. , Zhang H. , Gong Y.-J.
Published: January 2006

We report the band structures as well as frequency-dependent (dynamic) linear and nonlinear optical properties of CsCdBr3 and RbCdI3∙H2O crystals calculated within density functional theory with a nonlocal gradient correction, including the dielectric function, linear and nonlinear refractive indices, frequency doubling, and self-focusing of light. The electronic origin of the optical susceptibilities is described and the critical power of light self-focusing is estimated for these two crystals.
Resonant infrared laser-induced desorption of methane condensed on NaCl(100): Isotope mixture experiments
Authors: Redlich Britta , Zacharias Helmut , Meijer Gerard , von Helden Gert
Published: January 2006

Resonantly enhanced infrared laser-induced desorption of methane condensed on a single-crystal NaCl(100) surface is observed after excitation with the widely tunable infrared laser output of the free-electron laser at the free-electron laser for infrared experiments facility using mass spectroscopic detection and time-of-flight analysis. Desorption of methane is observed only when the exciting light is in resonance with an internal vibrational mode of the molecule. Different intramolecular modes of the three methane isotopologues under study—CH4, CD4, and CD3H—are excited; the degenerate deformation mode ν4 is observed for CH4 and CD4 at 7.69 and 10.11μm, respectively, as well as the ν2 and ν4 modes of CD3H at 7.79, 9.75, and 9.98μm. The desorption signals for the pure layers of these different methane isotopologues as well as for different mixtures of two of these are investigated as a function of the infrared wavelength and the laser fluence. The desorption behavior for pure and mixed layers is compared and the underlying desorption mechanism is discussed.
Degradation of hexagonal silicon-carbide-based bipolar devices
Authors: Skowronski M. , Ha S.
Published: January 2006

Only a few years ago, an account of degradation of silicon carbide high-voltage p-i-n diodes was presented at the European Conference on Silicon Carbide and Related Compounds (Kloster Banz, Germany, 2000). This report was followed by the intense effort of multiple groups utilizing varied approaches and subsequent progress in both fundamental understanding of this phenomenon and its elimination. The degradation of SiC p-i-n junctions is now well documented to be due to the expansion of Shockley-type stacking faults in the part of the devices reached by the electron-hole plasma. The faults can gradually cover most of the junction area, impeding current flow and, as a result, increasing the on-state resistance. While in most semiconductors stacking faults are electrically inactive, in hexagonal silicon carbide polytypes (4H- and 6H-SiC) they form quantum-well-like electron states observed in luminescence and confirmed by first-principles calculations. The stacking-fault expansion occurs via motion of 30° silicon-core partial dislocations. The Si–Si bond along the dislocation line induces a deep level in the SiC band gap. This state serves as both a radiative and a nonradiative recombination center and converts the electron-hole recombination energy into activation energy for the dislocation motion. Dislocation motion is typically caused by shear stress, but in the case of SiC diodes, the driving force appears to be intrinsic to the material or to the fault itself, i.e., the fault expansion appears to lower the energy of the system. Stable devices can be fabricated by eliminating stacking-fault nucleation sites. The dominant type of such preexisting defects is the segment of basal plane dislocations dissociated into partials. The density of such defects can be reduced to below 1cm−2 by conversion of all basal plane dislocations propagating from the substrate into threading ones in the epitaxial layer. Remarkable progress in fabrication of low basal plane dislocation density material offers hope of bipolar SiC devices being available commercially in the near future.
Stabilization and positioning of a spin vortex in nanostructured ferromagnetic thin films
Authors: Su Yuanchang , Tao Ruibao
Published: January 2006

Spin vortex is a very common structure in ferromagnetic thin films, but it can be easily shifted by an in-plane applied field. The paper demonstrates that the vortex can be positioned over certain regions of the film due to the position of the hole made in the thin film. The calculation clearly shows that the hole can stabilize the spin vortex and sharpen the M-H loop transition, and may have potential applications in nanomagnets.
Structural, morphological, and electrical characterization of heteroepitaxial ZnO thin films deposited on Si (100) by pulsed laser deposition: Effect of annealing (800°C) in air
Authors: Jejurikar S. M. , Banpurkar A. G. , Limaye A. V. , Date S. K. , Patil S. I. , Adhi K. P. , Misra P. , Kukreja L. M. , Bathe Ravi
Published: January 2006

Pulsed laser deposition technique was used for growing thin films of ZnO on Si (100) substrate held at different temperatures (Ts). All the as-deposited films have shown a preferential c-axis orientation associated with varying grain size as a function of Ts ranging from 100to600°C. Current-voltage (I-V) characteristics of these films show Ohmic behavior over the entire Ts range studied. These films were subjected to annealing at 800°C in air ambient for 4h. The grain size was observed to increase after the annealing process for all the films deposited at different Ts. Interestingly, these annealed films show nonlinear variation of current with applied voltage, very similar to the one observed in doped ZnO varistors. The nonlinear parameters such as the asymmetric behavior of change in current on the polarity reversal of voltage, the plateau region, and the break down voltage are observed to depend on Ts. This nonlinear behavior can perhaps be explained on the basis of electronic conduction model proposed for the bulk, doped ZnO varistors. The role of insulating intergranular layers between the disoriented microcrystallites is expected to be similar to that played by insulating intergranular layers in the doped ZnO varistors.
Interface effects in highly oriented films of the Heusler alloy Co2MnSi on GaAs(001)
Authors: Singh L. J. , Barber Z. H. , Kohn A. , Petford-Long A. K. , Miyoshi Y. , Bugoslavsky Y. , Cohen L. F.
Published: January 2006

Highly (001) oriented thin films of Co2MnSi have been grown on lattice-matched GaAs(001) without a buffer layer. Stoichiometric films grown at the highest substrate temperature of 689 K showed the lowest resistivity (33μΩcm at 4.2 K) and the lowest coercivity (14 Oe). Twofold in-plane magnetic anisotropy was observed due to the inequivalence of the ⟨110⟩ directions, and this was attributed to the nature of the bonding at the reconstructed GaAs surface. Interfacial reactions resulted in the formation of an epitaxial Mn-As region and a thin interfacial layer that was Co-Ga rich. This prevented the desired lattice matching and resulted in films with a saturation magnetization slightly below the bulk value. In spite of this, the spin polarization of the free surface was measured to be 55%, similar to bulk material.
Gauged Wess–Zumino model in noncommutative Minkowski superspace
Authors: Cook James S.
Published: January 2006

We develop a gauged Wess–Zumino model in noncommutative Minkowski superspace. This is the natural extension of the work of Carlson and Nazaryan, which extended N=1∕2 supersymmetry written over deformed Euclidean superspace to Minkowski superspace. We investigate the coupling of the vector and chiral superfields. Noncommutativity is implemented by replacing products with star products. Although, in general, our star product is nonassociative, we prove that it is associative to the first order in the deformation parameter C. We show that our model reproduces the N=1∕2 theory in the appropriate limit, namely when the deformation parameters C¯α̇β̇=0. Essentially, we find the N=1∕2 theory and a conjugate copy. As in the N=1∕2 theory, a reparametrization of the gauge parameter, vector superfield, and chiral superfield are necessary to write standard C-independent gauge theory. However, our choice of parametrization differs from that used in the N=1∕2 supersymmetry, which leads to some unexpected new terms.
Observation of resonant tunneling through a self-assembled InAs quantum dot layer
Authors: Aslan B. , Liu H. C. , Gupta J. A. , Wasilewski Z. R. , Aers G. C. , Raymond S. , Buchanan M.
Published: January 2006

Resonant tunneling through a self-assembled InAs quantum dot (QD) layer using a new design is reported: The QD layer surrounded by undoped GaAs barriers is clad by two GaInNAs∕GaAs short period superlattice regions which serve as injector and collector of electrons. Clear observation of three- to zero-dimensional resonant tunneling is presented in electrophotoluminescence measurement results, and supported with current–voltage and capacitance–voltage characteristics.
Reliability of field programmable magnetic logic gate arrays
Authors: Reiss G. , Meyners D.
Published: January 2006

In concepts for logic circuits using hysteretic magnetoresistive effects, one gains advantages of magnetic thin-film elements, e.g., nonvolatility, radiation hardness and nondestructive readout. The requirements concerning reproducibility of resistance and magnetoresistance, however, are much more stringent than for memory applications. Using experimental data of magnetic logic circuits, we show that the variances of resistance and magnetoresistance, and the amplitude of the magnetoresistance, determine the yield of working logic gates. The current magnetoresistance of 75% for CoFeB∕Al2O3 junctions is close to the minimum required value. More than 250% obtained with MgO barriers, however, will allow a fault tolerant production.
Mechanism of the anomalous temperature dependence of coercivity in Sm(Co,Fe,Cu,Zr)z high-temperature magnets
Authors: Rong Chuan-bing , Zhang Hong-wei , Shen Bao-gen , Liu J. Ping
Published: January 2006

Coercivity mechanism of the precipitation-hardened Sm(Co,Fe,Cu,Zr)z high-temperature magnets was found to vary with temperature by measurements of reversible magnetization. The magnetization reversal is mainly controlled by domain-wall pinning when temperature is lower than 800K, while is mainly dominated by nucleation at higher temperature. It is interesting to find that the anomalous temperature dependence of coercivity Hc(T) near Curie temperature of the 1:5 phase is caused by the fast drop of intergranular exchange coupling. This mechanism can also explain the coercivity behavior that the anomalous Hc(T) tends to disappear with increasing z value.
Field emission from Ni-disilicide nanorods formed by using implantation of Ni in Si coupled with laser annealing
Authors: Ok Young-Woo , Seong Tae-Yeon , Choi Chel-Jong , Tu K. N.
Published: January 2006

We report on the formation of Ni-disilicide (NiSi2) nanorods using Ni and Si implantation combined with a laser annealing process. We found that NiSi2 nanorods are formed when the as-implanted Si samples are laser annealed at the energy density of 700mJ∕cm2. Based on the Fowler–Nordheim theory, field emission behavior of the NiSi2 nanorod samples has been characterized. The turn-on field and a field enhancement factor were measured to be 7.6V∕μm and about 630, respectively. A possible mechanism is given to describe how the NiSi2 nanorods embedded in crystallized Si are formed during the laser annealing.
Nanoepitaxy of InAs∕InP quantum dots by metalorganic vapor phase epitaxy for 1.55μm emitters
Authors: Benoit J. M. , Le Gratiet L. , Beaudoin G. , Michon A. , Saint-Girons G. , Kuszelewicz R. , Sagnes I.
Published: January 2006

We report here on the structural and optical properties of selectively grown InAs∕InP quantum dots. Our approach combines electron-beam lithography, reactive ion etching, and selective low-pressure metalorganic vapor phase epitaxy, which allows the growth of nanometer-scale InAs quantum dots directly on InP substrate and an improved control of their size uniformity and density. These nanogrown InAs dots exhibit a high-efficiency photoluminescence band pointed at 1.55μm at room temperature.
Electrically robust ultralong nanowires of NiSi, Ni2Si, and Ni31Si12
Authors: Zhang Zhen , Hellström Per-Erik , Östling Mikael , Zhang Shi-Li , Lu Jun
Published: January 2006

Mass fabrication of directly accessible, ultralong, uniform Si nanowires is realized by employing a controllable and reproducible method based on standard Si technology. High-conductivity polycrystalline Ni-silicide nanowires around 30 nm by 30 nm in cross section, able to support extremely high currents at ∼108A∕cm2, are obtained by means of solid-state reaction of the Si nanowires with subsequently deposited Ni films. By properly adjusting the Ni film thickness, NiSi, Ni2Si, and Ni31Si12 nanowires characterized with distinct resistivity and temperature coefficient of resistance are obtained. Upon annealing, the electrical continuity of the nanowires breaks at temperatures about 0.7 times the melting points of the silicides.
Conduction-band electron effective mass in Zn0.87Mn0.13Se measured by terahertz and far-infrared magnetooptic ellipsometry
Authors: Hofmann T. , Schade U. , Agarwal K. C. , Daniel B. , Klingshirn C. , Hetterich M. , Herzinger C. M. , Schubert M.
Published: January 2006

We determine the electron effective mass parameter m*=0.086±0.004m0 of thin-film n-type low-chlorine-doped Zn0.87Mn0.13Se with free-charge-carrier concentration N=4.5×1017cm−3 and optical mobility μ=300±20cm2∕(Vs) using magneto-optic generalized ellipsometry in the terahertz and far-infrared spectral domain for wave numbers from ω=30–650cm−1. The room-temperature measurements were carried out with magnetic fields up to 3 T. We employ synchrotron and black-body radiation sources for the terahertz and far-infrared spectral regions, respectively. Comparison with previous experimental results from samples with considerably higher free electron density and theoretical calculations suggest that our value is sufficiently unaffected by band nonparabolicity and provides a good approximation of the Γ-point conduction band mass in Zn0.87Mn0.13Se. We further provide optical phonon mode parameters and the high-frequency dielectric constant.
Michael Heidelberger and the demystification of antibodies
Authors: Van Epps Heather L.
Published: January 2006

Having defined the protein nature of antibodies under the tutelage of Oswald Avery, Michael Heidelberger was the first to apply mathematics to the reaction of antibodies and their antigens (the “precipitin reaction”). Heidelberger's calculations launched decades of research that helped reveal the specificity, function, and origin of antibodies.
MultiLoc: prediction of protein subcellular localization using N-terminal targeting sequences, sequence motifs and amino acid composition
Authors: Höglund Annette , Dönnes Pierre , Blum Torsten , Adolph Hans-Werner , Kohlbacher Oliver
Published: January 2006

Motivation: Functional annotation of unknown proteins is a major goal in proteomics. A key annotation is the prediction of a protein's subcellular localization. Numerous prediction techniques have been developed, typically focusing on a single underlying biological aspect or predicting a subset of all possible localizations. An important step is taken towards emulating the protein sorting process by capturing and bringing together biologically relevant information, and addressing the clear need to improve prediction accuracy and localization coverage.

Results: Here we present a novel SVM-based approach for predicting subcellular localization, which integrates N-terminal targeting sequences, amino acid composition and protein sequence motifs. We show how this approach improves the prediction based on N-terminal targeting sequences, by comparing our method TargetLoc against existing methods. Furthermore, MultiLoc performs considerably better than comparable methods predicting all major eukaryotic subcellular localizations, and shows better or comparable results to methods that are specialized on fewer localizations or for one organism.

Availability:  

Contact:  hoeglund@informatik.uni-tuebingen.de
Isaac Newton's alchemical notes in the Royal Society
Authors: Young John T
Published: January 2006

A substantial 16-folio alchemical manuscript entirely in the hand of Isaac Newton, thought lost since 1936, was recently discovered among the Royal Society's previously uncatalogued Miscellaneous Manuscripts. This paper is intended to supplement a full online diplomatic transcription of this important document with a short account of how the manuscript came to be lost and found again, a summary of its content, evidence about its sources, composition and dating, and suggestions as to the lines on which subsequent research might proceed. Like most of Newton's alchemical writings, the work in question is largely if not wholly derivative, and it may be a conflation of what was originally conceived as two or more distinct documents. A few parts of it, however, may contain elements of Newton's own commentary and/or records of his own laboratory practice. No definitive conclusions are offered about such possibilities: the aim is rather to draw attention to the document's existence and significance and to encourage further, more detailed research on it.
A history of Kaye and Laby
Authors: Ambrose Douglas
Published: January 2006

Two young researchers at the Cavendish Laboratory in the early part of the twentieth century made a collection of physical data that was published and has been known for nearly 100 years not by its title but by their names, ‘Kaye and Laby’. A brief account of the careers of the authors is followed by discussion of the development of the
Tables of physical and chemical constants
.
Effects of human papillomavirus type 16 oncoproteins on survivin gene expression
Authors: Borbély Ágnes A. , Murvai Melinda , Kónya József , Beck Zoltán , Gergely Lajos , Li Fengzhi , Veress György
Published: January 2006

Survivin has recently been identified as a novel member of the inhibitor of apoptosis (IAP) gene family. The product of this gene not only suppresses apoptosis but also controls cell division. Survivin is undetectable in most terminally differentiated normal tissues but is expressed in embryonic and fetal organs and is present in most malignant tumours. Human papillomaviruses (HPV) are thought to play an important role in the development of cervical cancer. By interfering in the cell cycle, the viral oncoproteins (E6 and E7) can induce the immortalization of the host cell. The transcriptional effects of the HPV-16 E6 and E7 proteins on the survivin promoter in transiently transfected cell lines using luciferase tests were examined. HPV-16 E6, but not E7, was found to significantly transactivate the survivin promoter. Experiments performed in different cancer cell lines and with different E6 mutants indicated that the effect of E6 on the survivin promoter is largely dependent on p53 status. In accordance with this, the p53 tumour suppressor protein downregulated the expression of survivin. As E6 is able to interact with p53 and induces its ubiquitin-dependent degradation, it appears that the transactivation effect of E6 on survivin is mediated by the p53 degradation pathway. Transduction of HPV-16 E6 and E7 into human embryonic fibroblast cells showed that the HPV oncoproteins can upregulate endogenous survivin mRNA. Importantly, cell cycle synchronization experiments showed that the effect of HPV-16 E6 on survivin transcription is independent of the cell cycle.
Human CD46-transgenic mice in studies involving replication-incompetent adenoviral type 35 vectors
Authors: Verhaagh Sandra , de Jong Esmeralda , Goudsmit Jaap , Lecollinet Sylvie , Gillissen Gert , de Vries Margreet , van Leuven Kees , Que Ivo , Ouwehand Krista , Mintardjo Ratna , Weverling Gerrit Jan , Radošević Katarina , Richardson Jennifer , Eloit Marc , Lowik Clemens , Quax Paul , Havenga Menzo
Published: January 2006

Wild-type strains of mice do not express CD46, a high-affinity receptor for human group B adenoviruses including type 35. Therefore, studies performed to date in mice using replication-incompetent Ad35 (rAd35) vaccine carriers may underestimate potency or result in altered vector distribution. Here, it is reported that CD46 transgenic mice (MYII-strain) express CD46 in all major organs and that it functions as a receptor for rAd35 vectors. Similar to monkeys and humans, MYII mice highly express CD46 in their lungs and kidneys and demonstrate low expression in muscle. Upon intravenous administration, rAd35 vector genomes as well as expression are detected in lungs of MYII mice, in contrast to wild-type littermates. Expression was predominantly detected in lung epithelial cells. Upon intramuscular administration, the initial level of luciferase expression is higher in MYII mice as compared with wild-type littermates, in spite of the fact that CD46 expression is low in muscle of MYII mice. The higher level of expression in muscle of MYII mice results in prolonged gene expression as assessed by CCD camera imaging for luciferase activity. Finally, a significant dose-sparing effect in MYII mice as compared with wild-type littermates on anti-SIVgag CD8+T-cell induction following intramuscular vaccination with an rA35.SIVgag vaccine was observed. This dose-sparing effect was also observed when reinfusing dendritic cells derived from MYII mice after exposure to rAd35.SIVgag vaccine as compared with rAd35.SIVgag exposed dendritic cells from wild-type littermates. It was concluded that MYII mice represent an interesting preclinical model to evaluate potency and safety of rAd35 vectors.
Stability of the BK polyomavirus genome in renal-transplant patients without nephropathy
Authors: Takasaka Tomokazu , Goya Nobuyuki , Ishida Hideki , Tanabe Kazunari , Toma Hiroshi , Fujioka Tomoaki , Omori So , Zheng Huai-Ying , Chen Qin , Nukuzuma Souichi , Kitamura Tadaichi , Yogo Yoshiaki
Published: January 2006

To clarify the stability of the BK polyomavirus (BKPyV) genome in renal transplant (RT) recipients, three to five complete BKPyV genomes from each of six RT recipients with surviving renal allografts were molecularly cloned. The complete sequences of these clones were determined and compared in each patient. No nucleotide difference was detected among clones in two patients, and a few nucleotide variations were found among those in four patients. In each of these patients a parental sequence (usually the major sequence), from which variant sequences (usually minor sequences) with nucleotide substitutions would have been generated, were identified. A comparison between the parental and variant sequences in each patient identified a single nucleotide substitution in each variant sequence. From these findings, it was concluded that the genome of BKPyV is stable in RT recipients without nephropathy, with only minor nucleotide substitutions in the coding region.
Host-induced avirulence of hibiscus chlorotic ringspot virus mutants correlates with reduced gene-silencing suppression activity
Authors: Meng Chunying , Chen Jun , Peng Jinrong , Wong Sek-Man
Published: January 2006

Post-transcriptional gene silencing (PTGS) and virus-encoded gene-silencing suppressors are defence and counterdefence strategies developed by host and pathogens during evolution. Using a green fluorescence protein-based transient suppression system, the coat protein (CP) of Hibiscus chlorotic ringspot virus (HCRSV) was identified as a strong gene-silencing suppressor. CP suppressed sense RNA-induced but not dsRNA-induced local and systemic PTGS. This is different from another virus in the genus Carmovirus, Turnip crinkle virus (TCV), the CP of which strongly suppresses dsRNA-induced PTGS. HCRSV CP domain deletion mutants lost their suppression function, indicating that the complete CP is essential for suppression of PTGS. When CP was expressed from a Potato virus X (PVX) vector, it was able to enhance the symptom severity and to increase the accumulation of PVX RNA. Here, it is proposed that HCRSV CP suppresses PTGS at the initiation step, which is different from TCV CP. In addition, a previous study demonstrated that CP mutants resulting from serial passage of HCRSV in its local lesion host also showed a significantly reduced suppression function, indicating that host-induced mutations that lead to avirulence of HCRSV in kenaf correlate with its reduced ability to suppress PTGS.
Multiple Heme Oxygenase Family Members Contribute to the Biosynthesis of the Phytochrome Chromophore in Arabidopsis
Authors: Emborg Thomas J. , Walker Joseph M. , Noh Bosl , Vierstra Richard D.
Published: January 2006

The oxidative cleavage of heme by heme oxygenases (HOs) to form biliverdin IXα (BV) is the committed step in the biosynthesis of the phytochrome (phy) chromophore and thus essential for proper photomorphogenesis in plants. Arabidopsis (Arabidopsis thaliana) contains four possible HO genes (HY1, HO2–4). Genetic analysis of the HY1 locus showed previously that it is the major source of BV with hy1 mutant plants displaying long hypocotyls and decreased chlorophyll accumulation consistent with a substantial deficiency in photochemically active phys. More recent analysis of HO2 suggested that it also plays a role in phy assembly and photomorphogenesis but the ho2 mutant phenotype is more subtle than that of hy1 mutants. Here, we define the functions of HO3 and HO4 in Arabidopsis. Like HY1, the HO3 and HO4 proteins have the capacity to synthesize BV from heme. Through a phenotypic analysis of T-DNA insertion mutants affecting HO3 and HO4 in combination with mutants affecting HY1 or HO2, we demonstrate that both of the encoded proteins also have roles in photomorphogenesis, especially in the absence of HY1. Disruption of HO3 and HO4 in the hy1 background further desensitizes seedlings to red and far-red light and accelerates flowering time, with the triple mutant strongly resembling seedlings deficient in the synthesis of multiple phy apoproteins. The hy1/ho3/ho4 mutant can be rescued phenotypically and for the accumulation of holo-phy by feeding seedlings BV. Taken together, we conclude that multiple members of the Arabidopsis HO family are important for synthesizing the bilin chromophore used to assemble photochemically active phys.
Patch use behaviour in benthic fish depends on their long‐term growth prospects
Authors: Stenberg Marika , Persson Anders
Published: January 2006

Animals foraging in a heterogeneous environment may combine prior information on patch qualities and patch sample information to maximize intake rate. Prior information dictates the long‐term expectations, whereas prior information in combination with patch sample information determines when to leave an individual food patch. We examined patch use behaviour of benthic feeding fish in their natural environment at different spatial scales to test if they could determine patch quality and if patch use behaviour was correlated with environmental quality. In seven lakes along a gradient of environmental quality (measured as maximum benthivore size), we made repeated measurements of giving‐up density (GUD) in artificial food patches of different qualities. At the largest spatial scale, between lakes, we tested if giving‐up densities revealed the long‐term growth expectation of benthic fish. At the local scale of patches and micro patches we tested for the ability of benthic fish to assess patch quality, and how this ability depended on the patch exploitation levels between the different lakes. We found that GUD was positively related to maximum size of bream, suggesting that short‐term behavioural decisions reflected long‐term growth expectations. Benthic fish discriminated between nearby rich and poor patches, but not between rich and poor micropatches within a food patch. This suggests that the foraging scale of benthic fish lies between the patch and micro patch scale in our experiments. We conclude that patch use behaviour of benthic fish can provide a powerful measure of habitat quality that reveals how benthic fish perceive their environment.
Redefining the community: a species‐based approach
Authors: K. Dodds Walter , A. Nelson Jennifer
Published: January 2006

We propose that effective community size can be defined on the basis of the web of indirect interactions experienced on average by each individual species. Indirect interaction chains are composed of links provided by direct interactions. We analyzed previously published data on 20 assemblages of species. Chain strengths were estimated by the weakest link and by the product of link strength. The average strength of the interaction chain decreased with increasing numbers of links with both models. Positive indirect interactions in chains with an even number of links offset negative direct interactions. We set the community size by the chain length where 95% of the indirect interactions are weaker than 10% of the mean of the absolute value of direct interaction strength. Using the multiplicative model, seven assemblages had a community size (web of interaction length) of three links, one of four links, and the remainder of communities were too small to set community size. The analysis suggests that effective communities of size are rarely investigated in ecological experiments.
Natural and artificial floral damage induces resistance in Nemophila menziesii (Hydrophyllaceae) flowers
Authors: McCall Andrew C.
Published: January 2006

Resistance to leaf herbivory is well‐documented in plants. In contrast, resistance to herbivory in flowers has received very little attention, even though reproductive tissues are often essential for plant reproduction. Plants may protect reproductive tissues with a range of defenses from constitutive to induced, although ecological costs associated with constitutive defense or resistance are expected to be higher than costs associated with induced responses. Induced responses in flowers may be effective against floral herbivores while minimizing the negative impacts of resistance on pollinators. This study examines induced responses in Nemophila menziesii (Hydrophyllaceae), a plant that frequently receives high levels of floral herbivory. I report that natural caterpillar herbivory increased levels of resistance against caterpillars later in the season. Similarly, artificial clipping to flowers consistently reduced natural damage to flowers vs unclipped controls over two years. Neither whole‐plant nor individual seed set was affected by the reduction of floral damage. Induced resistance in reproductive tissues may benefit plants that are exposed to both floral herbivory and pollinator activity and can be an important link between plant antagonists and plant mutualists.
Combined impacts of Allee effects and parasitism
Authors: Deredec Anne , Courchamp Franck
Published: January 2006

Despite their individual importance for population dynamics and conservation biology, the combined impacts of Allee effects and parasitism have received little attention. We built a mathematical model to compare the dynamics of populations with or without Allee effects when infected by microparasites. We show that the influence of an Allee effect takes the form of a tradeoff. The presence of an Allee effect in host populations may protect them, by reducing the range of population sizes that allow parasite spread. Yet if infection spreads, the Allee effect weakens host populations by reducing their size and by widening the range of parasite species that lead them to extinction. These results have important implications for predicting the survival of threatened populations or the success of reintroductions, and may help define size ranges within which given populations should be maintained to prevent both epidemics and Allee effects driven extinctions.
Habitat complexity and consumer‐mediated positive feedbacks on a Caribbean coral reef
Authors: Lee Sarah C.
Published: January 2006

Theoretical and empirical evidence suggest that positive feedbacks can increase resilience in ecological communities. On Caribbean coral reefs, there have been striking shifts from physically complex communities with high coral cover to relatively homogenous communities dominated by macroalgae, which have persisted for decades. However, little is known about positive feedbacks that may maintain coral reef community states. Here, I explore a potential consumer‐mediated feedback on a Jamaican reef by examining how grazing by a keystone herbivore (Diadema antillarum) is enhanced by physical structure, which offer refugia from predation. Surveys revealed that habitat complexity and Diadema density were positively related. Increasing habitat complexity by adding physical structure significantly decreased macroalgal cover and increased the proportion of urchins in algal habitats in field manipulations. Experimental increases in urchin density also decreased macroalgal cover, but did not affect the proportion of urchins in algal habitats. These results suggest that the low habitat complexity of macroalgal‐dominated reefs may inhibit an urchin‐mediated shift to coral dominance and that positive feedbacks must be considered in reef restoration efforts.
Consequences of differing competitive abilities between juvenile and adult plants
Authors: Lamb Eric G. , Cahill James F.
Published: January 2006

The competitive ability of perennial plants can change with life‐stage, but whether these changes have fitness consequences is unknown. We present a simple model of two components of fitness, mortality and flowering rates, for two grassland species with very different patterns of competitive ability and life‐stage. Achillea millefolium seedlings are poor competitors while the adults are good competitors. In contrast, Solidago missouriensis seedlings and adults have similar competitive ability. Models of the two species show that the overall effects of competition on growth are more important than interspecific differences in competitive ability in determining mortality and flowering rates, though the higher seedling competitive ability of S. missouriensis relative to A. millefolium seedlings does result in slightly lower mortality and higher flowering rates for the former species. Simulations where both average competitive ability and relative seedling and adult competitive ability are varied predict that dominant species with high overall competitive ability should experience no advantage or disadvantage from varying competitive ability through development. When overall competitive ability is moderate, the relative costs and benefits of differential competitive abilities among adults and seedlings are variable. High seedling competitive ability relative to adult competitive ability should be favored among species with low overall competitive ability. We predict that communities with high intensity of competition should have a high frequency of species with high seedling competitive ability, while communities with lower intensity of competition should have species with a wide range of relative seedling and adult competitive ability.
Using a proxy of plant productivity (NDVI) to find key periods for animal performance: the case of roe deer
Authors: Pettorelli Nathalie , Gaillard Jean‐Michel , Mysterud Atle , Duncan Patrick , Chr. Stenseth Nils , Delorme Daniel , Van Laere Guy , Toïgo Carole , Klein Francois
Published: January 2006

Animals in seasonal environments are affected by climate in very different ways depending on season and part of the climatic effects operates indirectly through the plants. Vegetation conditions in spring and summer are regarded as decisive for the reproductive success and the offspring's condition of large herbivores, but objective ways to determine key periods during the growing season have not been done often due to limitations in plant data. Using satellite data (NDVI), we determined how plant productivity from birth to fall influences the following winter body mass of roe deer fawns. We do this in two populations, the first inhabiting the low productive Chizé reserve in south western France with an oceanic climate and the second from Trois Fontaines, a highly productive forest with continental climate in east France. The effect of plant productivity was similar for male and female fawn mass, as expected from the weak intensity of sexual selection in roe deer life history traits. We found contrasting results between sites, with a strong effect of plant productivity in spring (April‐May) in the Chizé population, but no effect in the Trois Fontaines population. The relatively low variability in winter fawn body mass could account for the absence of NDVI effects at Trois Fontaines. However, such results might also point to a limitation in the use of the NDVI, since the relationship between the canopy and the plant productivity at the ground level might be weak in the highly productive forest of Trois Fontaines.
Identification of health problems at 18 months of age – a task for physicians or child health nurses?
Authors: Magnusson M. , Sundelin C. , Westerlund M.
Published: January 2006

Background Several studies have questioned the rationality of repeated routine health examinations by physicians during the first years of life. The aim of the present study was to evaluate the population‐based 18‐month health examination and compare the yield of new health problems identified by physicians in 1994 with the yield identified by child health centre (CHC) nurses in 2000.

Methods Two populations of children were invited to their 18‐month health examination during one year, the first in 1994 and the second in 2000. In 1994 the population consisted of 4075 and in 2000 of 2968 children who were registered in Uppsala county, Sweden, for census purposes in December 31 each year. Data from a county health register as well as child health records and information regarding referrals were analysed to categorize the health problems by type, severity and action taken.

Results On the whole few new verified health problems were detected by the health examinations at the 18 month health examinations: 2.3% in 1994 and 1.7% in 2000. In 1994, when the physicians carried out the examinations, the most common health problems were somatic problems, particularly moderate transient infections. In 2000, when the nurses carried out the examinations, the dominant problems were speech problems. Peculiarly enough a couple of children with the same severe health problems, gluten allergy and problems in the autistic spectrum, were identified both in 1994 and in 2000. In addition the nurses in 2000 identified seven children with severe speech problems. No additional severe health problems were identified by the physicians in 1994.

Conclusions According to the present study, there is no evidence that health examinations carried out by nurses are of lower quality in detecting health problems than those carried out by physicians. The organization and content of the health surveillance programme ought to be reconsidered with respect to available resources and importance of the close relationship established between nurse and family already in the newborn period.
Post‐partum depression and infant growth in a South African peri‐urban settlement
Authors: Tomlinson M. , Cooper P. J. , Stein A. , Swartz L. , Molteno C.
Published: January 2006

Aim To examine the association between maternal post‐natal depression and infant growth.

Background Infant growth has recently been shown, in two studies from South Asia, to be adversely affected by maternal depression in the early post‐partum period. It is uncertain whether a similar association obtains in developing countries outside Asia.

Method A sample of 147 mother–infant dyads was recruited from a peri‐urban settlement outside Cape Town and seen at 2 and 18 months post partum.

Results No clear effect of post‐partum depression on infant growth was found. Although maternal depression at 2 months was found to be associated with lower infant weight at 18 months, when birthweight was considered this effect disappeared.

Conclusions Possible explanations for the non‐replication of the South Asian findings are considered.
Strength in diversity: fish sanctuaries and deep‐water pools in Lao PDR
Authors: BAIRD I. G.
Published: January 2006

Abstract  Fish sanctuaries are types of aquatic protected areas common throughout the landlocked country of Lao PDR. The key to their successful implementation in Laos appears to be local support. Therefore, they fit well within the context of community‐based fisheries/co‐management programmes. Fish sanctuaries are almost always established in deep‐water pools, which serve as important dry season refuges for fish. The best‐known fish sanctuaries in Laos are known as Fish Conservation Zones (FCZs), and are found in the mainstream Mekong River in Khong district, Champasak province, southern Laos. In Khong, there is increasing evidence that FCZs established by villagers, but with government support, are important places of concentration for various fish species. FCZs can benefit fish stocks, especially relatively sedentary species, but also highly migratory ones. FCZs are not panaceas for solving all the fisheries problems in Laos or the Mekong River Basin, but they represent important management tools that should not be overlooked.
Concurrent assessment of fish and habitat in warmwater streams in Wyoming
Authors: QUIST M. C. , HUBERT W. A. , RAHEL F. J.
Published: January 2006

Abstract  Fisheries research and management in North America have focused largely on sport fishes, but native non‐game fishes have attracted increased attention due to their declines. The Warmwater Stream Assessment (WSA) was developed to evaluate simultaneously both fish and habitat in Wyoming streams by a process that includes three major components: (1) stream‐reach selection and accumulation of existing information, (2) fish and habitat sampling and (3) summarisation and evaluation of fish and habitat information. Fish are sampled by electric fishing or seining and habitat is measured at reach and channel‐unit (i.e. pool, run, riffle, side channel, or backwater) scales. Fish and habitat data are subsequently summarised using a data‐matrix approach. Hierarchical decision trees are used to assess critical habitat requirements for each fish species expected or found in the reach. Combined measurements of available habitat and the ecology of individual species contribute to the evaluation of the observed fish assemblage. The WSA incorporates knowledge of the fish assemblage and habitat features to enable inferences of factors likely influencing both the fish assemblage and their habitat. The WSA was developed for warmwater streams in Wyoming, but its philosophy, process and conceptual basis may be applied to environmental assessments in other geographical areas.
Patients and nurses’ perceptions of ward environmental factors and support systems in the care of suicidal patients
Authors: Sun Fan‐Ko , Long Ann , Boore Jennifer , Tsao Lee‐Ing
Published: January 2006

Aims.  The aims of this paper are to present and discuss the findings that emerged from a qualitative study exploring nurses and patients’ views of the acute psychiatric ward (the context) and the type of care received (the intervening conditions).

Background.  The phenomenon of suicide and the nursing care of people who are suicidal have previously been investigated. However, literature demonstrates that there is a dearth of information exploring the importance of the ward context in the care of suicidal patients and the intervening conditions that are used by professionals in the care of suicidal patients.

Method.  Qualitative research using the grounded theory approach.

Data collection and analysis.  Fifteen patients who had either suicidal ideas or had attempted suicide and 15 psychiatric nurses were interviewed and observed. Data were analysed using open, axial and selective coding.

Findings.  A substantive theory of suicide‐nursing care was developed. For the purpose of this paper, the two categories that emerged in the ‘context’ element of the paradigm model are explored. They were: team working and the psychiatric ward environment. In addition, the four categories from the ‘intervening conditions’ are discussed. They were: nurses’ attitudes and beliefs have an effect on caring, barriers to caring, patients’ negative thoughts and feelings about the care provided and support systems.

Conclusion.  The findings indicated that the context of the ward environment and the intervening conditions used by nurses in the nursing care of suicidal patients helped to define some of the complex dynamics that impacted on the development of a therapeutic relationship within the practice of suicide‐nursing care.

Relevance to clinical practice.  Environmental factors as well as the nurses’ knowledge and skills and the type of support patients receive impact on the care of suicidal patients. These findings could help to enhance and advance suicide‐nursing care.