bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic variation in the mitochondrial cytochrome c oxidase subunit 1 within Progamotaenia festiva (Cestoda: Anoplocephalidae) from macropodid marsupials
Authors: BEVERIDGE I. , SHAMSI S. , HU M. , CHILTON N. B. , GASSER R. B.
Published: April 2007

Genetic variation was examined in the anoplocephalid cestode Progamotaenia festiva, from Australian marsupials, in order to test the hypothesis that P. festiva, is a complex of sibling species and to assess the extent of host switching reported previously based on multilocus enzyme electrophoresis (MEE). Polymerase chain reaction (PCR)-based single-strand conformational polymorphism (SSCP) was used for the analysis of sequence variation in the cytochrome c oxidase subunit 1 (cox1) gene among 179 specimens of P. festiva (identified based on morphology and predilection site in the host) from 13 different host species, followed by selective DNA sequencing. Fifty-three distinct sequence types (haplotypes) representing all specimens were defined. Phylogenetic analyses of these sequence data (utilizing maximum parsimony and neighbour-joining methods) revealed 12 distinct clades. Other heterologous species, P. ewersi and P. macropodis, were used as outgroups and the remaining bile-duct inhabiting species, P. diaphana and P. effigia, were included in the analysis for comparative purposes. The latter 2 species were nested within the clades representing P. festiva. Most clades of P. festiva identified were restricted to a single host species; one clade primarily in Macropus robustus was also found in the related host species M. antilopinus in an area of host sympatry; another clade occurring primarily in M. robustus occurred also in additional kangaroo species, M. rufus and M. dorsalis. High levels of genetic divergence, the existence of distinct clades and their occurrence in sympatry provide support for the hypothesis that P. festiva represents a complex of numerous species, most of which, but not all, are host specific. Three distinct clades of cestodes were found within a single host, M. robustus, but there was no evidence of within-host speciation.
Single-legged hopping robotics research—A review
Authors: Sayyad Ajij , Seth B. , Seshu P.
Published: April 2007

Inspired by the agility of animal and human locomotion, the number of researchers studying and developing legged robots has been increasing at a rapid rate over the last few decades. In comparison to multilegged robots, single-legged robots have only one type of locomotion gait, i.e., hopping, which represents a highly nonlinear dynamical behavior consisting of alternating flight and stance phases. Hopping motion has to be dynamically stabilized and presents challenging control problems. A large fraction of studies on legged robots has focused on modeling and control of single-legged hopping machines. In this paper, we present a comprehensive review of developments in the field of single-legged hopping robots. We have attempted to cover development of prototype models as well as theoretical models of such hopping systems.
Verändert Schulkleidung die Lerneinstellung von Grundschülern und die Einschätzung des Zusammenhalts in der Klasse?
Authors: Spörer Nadine , Brunstein Joachim C.
Published: April 2007

Zusammenfassung. In einer Längsschnittstudie mit 251 Grundschülern wurde untersucht, ob das Tragen einheitlicher Schulkleidung schulische Einstellungen verändert. Es wurden 155 Schüler einer Grundschule, in der freiwillig Schulkleidung getragen wurde (Versuchsschule), und 96 Schüler einer Parallelschule ohne einheitliche Bekleidung acht Monate vor sowie sechs Monate nach Einführung der Schulkleidung befragt. Zum Prätest bestanden keine Unterschiede zwischen den Schulen. Zum Posttest berichteten Schüler der Versuchsschule über eine niedrigere Lernfreude als Schüler der Parallelschule. Hinsichtlich der Variablen Klassenklima, soziale Integration und Anstrengungsbereitschaft unterschieden sich die Schüler nicht. Weiterhin zeigte sich, dass innerhalb der Versuchsschule Mädchen häufiger Schulkleidung wählten als Jungen. Zudem entschieden sich Kinder ohne Migrationshintergrund im Vergleich zu Kindern mit Migrationshintergrund häufiger für Schulkleidung. Bezogen auf die schulischen Einstellungen gab es jedoch keine Unterschiede zwischen Trägern und Nichtträgern innerhalb der Versuchsschule.
Selbstregulation in der Verhandlungsführung
Authors: Otto Barbara , Lang Alexander , Schmitz Bernhard
Published: April 2007

Zusammenfassung. Im Folgenden wird die Entwicklung und Evaluation eines Verhandlungstrainings dargestellt, dessen theoretische Grundlage das Selbstregulationsmodell von Zimmerman (2000) bildet. Die Intervention besteht aus vier Einheiten, in denen die Themenbereiche allgemeine Kommunikation, Verhandlungsvorbereitung, Argumentation und Umgang mit unfairen Verhandlungsweisen behandelt werden. Die Stichprobe setzt sich aus 42 berufstätigen Personen zusammen, die in Großunternehmen rekrutiert wurden. Die Evaluation erfolgte anhand eines Vortest-Nachtest-Kontrollgruppendesigns. Sowohl mithilfe von Fragebögen als auch mit Videoszenarien wurde der Lerngewinn der Trainingsteilnehmer in Hinblick auf selbstregulierte Fähigkeiten, verhandlungsspezifisches Wissen, verhandlungsbezogene Selbstwirksamkeit und Verhandlungsverhalten überprüft. Der Vortest-Nachtest-Vergleich ergab, dass die Teilnehmer nach dem Training über verbesserte selbstregulatorische Kompetenzen und gesteigerte verhandlungsspezifische Selbstwirksamkeit verfügten. Ebenfalls ließ sich am Ende des Trainings eine hartnäckigere Verhandlungsweise der Trainingsteilnehmer feststellen, die gleichzeitig durch ein erhöhtes Maß an volitionaler Kontrolle und Fairness gekennzeichnet ist. In fast allen erhobenen Skalen ließen sich mittlere bis große Effektstärken nachweisen.
Elternzeit: Ein Risiko für die Karriere?
Authors: Wiese Bettina S.
Published: April 2007

Zusammenfassung. In einer Serie von drei experimentellen Studien wird der Frage nachgegangen, welche Einflüsse Informationen bezüglich der Inanspruchnahme von Elternzeiten auf das berufsbezogene Fremdurteil haben. Die vorgestellten Untersuchungen (Gesamtstichprobe N = 428) basieren auf einem Szenarioansatz, bei dem eine Frau nach der Geburt eines Kindes Angaben zur geplanten weiteren Berufstätigkeit macht (keine Auszeit, ein-, zwei-, dreijährige Auszeit). Die teils mit Studierenden, teils mit Berufstätigen als Beurteiler durchgeführten Studien zeigen, dass Frauen, die durchgehend Voll- oder vorübergehend Teilzeit arbeiten wollen, bezüglich beruflicher Eigenschaften positiver beurteilt werden als Frauen, welche eine längere familienbedingte berufliche Auszeit (> 1 Jahr) planen.
Psychopathologisches Profil bei Tic- und Zwangsstörungen
Authors: Roessner Veit , Becker Andreas , Rothenberger Aribert
Published: April 2007

Zusammenfassung. Neben der Kernsymptomatik und manch symptomatischer Überlappung von Tic- und Zwangsstörungen ist für eine therapierelevante Diagnostik auch das breitere psychopathologische Profil von Bedeutung. Daher ist es Ziel dieser Arbeit anhand des mit der Child Behavior Checklist (CBCL) erhobenen allgemeinen psychopathologischen Profils diese diagnostischen Schritte zu erleichtern und zu präzisieren. Die Diskriminanzanalyse der CBCL-Skalen von 49 Kindern und Jugendlichen mit alleiniger Zwangsstörung und 67 mit alleiniger Ticstörung (kein Gruppenunterschied in Alter und Geschlechtsverteilung) erbrachte eine hohe Güte der Unterscheidung anhand der CBCL-Skalen Schizoid/Zwanghaft, Angst/Depressivität sowie Sozialer Rückzug. Auf diesen drei CBCL-Skalen zeigten die Patienten mit einer Zwangsstörung höhere Werte als die Kinder und Jugendlichen mit einer Ticstörung. Daher sind die genannten Skalen im klinischen Alltag für die orientierende Differenzialdiagnostik von Tic- und/oder Zwangsstörungen geeignet und können ein gezieltes und ökonomisches weiteres Vorgehen leiten.
Diagnostik von Zwangsstörungen im Kindes- und Jugendalter
Authors: Goletz Hildegard , Döpfner Manfred
Published: April 2007

Zusammenfassung. Die Komplexität von Zwangsstörungen macht eine umfassende Diagnostik erforderlich. Die Diagnostik von Zwangsstörungen ist in eine multimodale Verhaltens- und Psychodiagnostik integriert, die eine detaillierte Erfassung der individuellen Zwangssymptomatik, einschließlich ihrer aufrechterhaltenden Bedingungen, Beeinträchtigungen, komorbiden Störungen und Probleme impliziert. Die spezifischen Aspekte des diagnostischen Vorgehens bei Kindern und Jugendlichen mit Zwangsstörungen sowie deren Bezugspersonen (einschließlich Beziehungsaufbau, Exploration familiärer Beziehungen, der Zwangssymptomatik sowie komorbider Auffälligkeiten des Kindes bzw. Jugendlichen und psychischer Auffälligkeiten der Bezugspersonen, Exploration eines gemeinsamen Störungskonzeptes, Behandlungsziele und Behandlungsplanung) werden dargelegt. Die deutschsprachigen spezifischen diagnostischen Verfahren, einschließlich neuer Verfahren, werden detailliert beschrieben.
Tic- und Zwangsstörungen
Authors: Döpfner Manfred , Rothenberger Aribert
Published: April 2007

Zusammenfassung. In diesem Übersichtsartikel werden die Gemeinsamkeiten und Unterschiede von Tic- und Zwangsstörungen auf verschiedenen Ebenen dargestellt. In der Psychopathologie unterscheiden sich beide Phänomene zunächst deutlich - Tics sind plötzlich auftretende, unwillkürliche, motorische Bewegungen oder Vokalisationen. Zwänge sind wiederholte, zweckmäßige und beabsichtigte Verhaltensweisen. Es gibt jedoch fließende Übergänge, die sich vor allem bei den Just-Right-Zwängen manifestieren, die bei Tourette-Störungen gehäuft auftreten. Die diagnostischen Strategien und die dabei hilfreichen Instrumente werden vorgestellt. In der Therapie haben sich bei beiden Störungen sowohl verhaltenstherapeutische als auch pharmakotherapeutische Verfahren bewährt. Es wird eine Übersicht über den Stand der empirischen Evidenz gegeben. Die Behandlung von kombinierten Tic- und Zwangsstörungen wird speziell erörtert.
Neurobiologie bei Tic- und Zwangsstörungen
Authors: Roessner Veit , Rothenberger Aribert
Published: April 2007

Zusammenfassung. Erst in den letzten Jahren wird auch in der Forschung vermehrtes Augenmerk auf die Überschneidung von Tic- und Zwangsstörungen gerichtet. Während in Übersichtsarbeiten zum gemeinsamen Auftreten von Tic- und Zwangsstörungen die zahlreichen Befunde zu Phänomenologie, begleitender Psychopathologie, Epidemiologie und daraus resultierenden Therapieimplikationen breiten Raum einnehmen, sind die Untersuchungsergebnisse hinsichtlich ätiologischer und pathophysiologischer Gemeinsamkeiten in entsprechenden Arbeiten unterrepräsentiert. Daher wird mit dieser Arbeit ein Überblick über den aktuellen neurobiologischen Forschungsstand zu den Gemeinsamkeiten und Unterschieden von Tic- und Zwangsstörungen gegeben.
On the large wind shear and fast meridional transport above the mesopause
Authors: Liu H.‐L.
Published: April 2007

Unexpectedly strong winds/shears and fast meridional transport above the mesopause have been revealed from previous rocket and satellite observations. Using Richardson number criteria for dynamic stability, we estimate the maximum wind shears allowable by the background static stability, which peaks above the mesopause. These maximum shears are in general agreement with the large wind shears inferred from the rocket measurements at low and mid‐latitudes, indicating the close relationship between the latter and the stability constraint set by the background atmosphere. Diagnostic calculations also indicate that the meridional transport in this region may not be well understood solely by examining the mean meridional circulation, and large amplitude tides/planetary waves can play an important role in the bulk transport of tracers. Strong stochastic winds, presumably due to gravity waves, do not seem to significantly change the large scale pattern of the transport but may extend the range of the tracer movement.
Electron acceleration due to inertial Alfvén waves in a non‐Maxwellian plasma
Authors: Watt C. E. J. , Rankin R.
Published: April 2007

We investigate parallel electron acceleration due to inertial Alfvén wave pulses in the presence of Lorentzian (kappa) distribution functions which possess high‐energy tails. A linear kinetic dispersion relation for inertial Alfvén waves is derived whose solutions are used to guide the analysis of the simulation results. The dispersion relation solutions show that the parallel phase velocity of linear waves is unchanged when Lorentzian distribution functions are considered instead of Maxwellian distribution functions. The solutions also indicate that Landau damping is increased for low values of spectral index, κ, implying that wave‐particle interactions are enhanced for Lorentzian distribution functions. We test this hypothesis by performing self‐consistent kinetic simulations and show that the energy content of resonant beam electrons significantly increases with decreasing κ. The dependence of this process on pulse amplitude and perpendicular scale length is investigated, and it is shown that for the same pulse parameters, resonant electron beams are generated more efficiently in a Lorentzian plasma compared to a Maxwellian plasma. The energy range of resonant beam electrons are also presented, and it is noted that for low values of κ it is possible to generate electrons with energy of a few keV, even for relatively small‐amplitude pulses with peak perpendicular electric fields of the order of 20 mV/m. We also show that the percentage of wave Poynting flux which is converted into electron energy flux depends upon the value of κ, the perpendicular scale length, and the initial amplitude of the inertial Alfvén wave.
Intensity of geomagnetic storms depends on the X‐line location in the plasma sheet
Authors: Kan J. R. , Xing X. , Wolf R. A.
Published: April 2007

Magnetic reconnection in the plasma sheet, known as the near‐Earth X‐line (NEXL), is observed within ∼30 RE from Earth during substorms. In the absence of substorms, the reconnection X‐line is observed beyond ∼30 RE, denoted as mid‐distant‐tail X‐line (MDXL). During quasi‐periodic substorms, convection is enhanced by the NEXL to intensify the ring current of major storms with Dst < ∼ −100 nT. During extended periods without substorms, convection is driven by the MDXL to intensify the ring current of minor storms with Dst > ∼ −100 nT. Motivated by observations, we propose a ring current injection conjecture to order the storm intensity: Ring current intensity increases if the X‐line forms closer to Earth. We carry out a rough entropy analysis as a first step toward theoretical investigation of the ring current injection conjecture. We show that substorm‐associated near‐Earth reconnection of closed plasma sheet field lines cannot provide the ring current particles for a major magnetic storm. However, we find that near‐Earth reconnection of tail lobe field lines in a few strong substorm events could provide the particles for the storm‐time ring current, if the X‐line is located earthward of ∼15 RE with an uncertainty up to ∼25 RE.
Collisionless damping of parametrically unstable Alfvén waves
Authors: Araneda J. A. , Marsch E. , Viñas A. F.
Published: April 2007

Linear Vlasov theory and one‐dimensional hybrid simulations are used to study the parametric instabilities of a circularly polarized parallel propagating Alfvén wave in a homogeneous, magnetized, and collisionless plasma. We discuss the linear and the weakly nonlinear development of the instabilities of the Alfvén waves, including kinetic effects, and investigate the structure, the growth, and the damping of the driven ion acoustic‐like waves. The dispersion relation reproduces the fluid characteristics of the instabilities in the case that protons are cold but contains an infinite number of roots in the general case. We show that at low proton plasma βp (βp ≈ 0.1), kinetic effects break the degeneracy of the mode‐coupling solutions of the fluid theory, and we unambiguously identify the growing and the damped modes. We find that contrary to traditional thought, kinetic effects are important even for very low‐βp in the late stages of the linear evolution, leading to a dephasing effect between the plasma pressure and the density fluctuations. The relevance of the results to the experimental identification of the instabilities, to the generation of local turbulence, and to the reduction of cross helicity in the solar wind are pointed out.
Analysis of the 3–7 October 2000 and 15–24 April 2002 geomagnetic storms with an optimized nonlinear dynamical model
Authors: Spencer E. , Horton W. , Mays M. L. , Doxas I. , Kozyra J.
Published: April 2007

A computationally optimized low‐dimensional nonlinear dynamical model of the magnetosphere‐ionosphere system called WINDMI is used to analyze two large geomagnetic storm events, 3–7 October 2000 and 15–24 April 2002. These two important storms share common features such as the passage of magnetic clouds, shock events from coronal mass ejections, triggered substorms, and intervals of sawtooth oscillations. The sawtooth oscillations resemble periodic substorms but occur in association with strong or building ring current populations and have injection regions that are unusually close to the Earth and unusually wide in magnetic local times (Henderson et al., 2006; Borovsky et al., 2007). The April 2002 event includes one of the best examples of sawtooth events ever observed. On 18 April 2002, sawtooth oscillations were clearly visible when solar wind conditions (IMF Bz, density, pressure) were relatively steady with a slowly varying Dst. In this study, WINDMI is used to model the 3–7 October 2000 and 15–24 April 2002 geomagnetic activity. WINDMI results are evaluated focusing on the sawtooth intervals and the overall prediction of the westward auroral electrojet (AL) index and Dst index. The input to the model is the dynamo driving voltage derived from the fluctuating solar wind plasma and the interplanetary magnetic field measured by the ACE satellite. The output of the model is a field‐aligned current proportional to the AL index and the energy stored in the ring current which is proportional to the Dst index. The model parameters are optimized using a genetic algorithm (GA) to obtain solutions that simultaneously have least mean square fit to the AL and Dst indices and also exhibit substorms of period 2–4 hours. The GA optimization results show that the model is able to predict the Dst index reliably and captures the timing and periodicity of the sawtooth signatures in the AL index reasonably well for both storm events.
Two‐dimensional characterization of hydraulic heterogeneity by multiple pumping tests
Authors: Li Wei , Englert Andreas , Cirpka Olaf A. , Vanderborght Jan , Vereecken Harry
Published: April 2007

The conventional analysis of pumping tests by type‐curve methods is based on the assumption of a homogeneous aquifer. Applying these techniques to pumping test data from real heterogeneous aquifers leads to estimates of the hydraulic parameters that depend on the choice of the pumping and observation well positions. In this paper, we test whether these values may be viewed as pseudo‐local values of transmissivity and storativity, which can be interpolated by kriging. We compare such estimates to those obtained by geostatistical inverse modeling, where heterogeneity is assumed in all stages of estimation. We use drawdown data from multiple pumping tests conducted at the test site in Krauthausen, Germany. The geometric mean values of transmissivity and storativity determined by type‐curve analysis are very close to those obtained by geostatistical inversion, but the conventional approach failed to resolve the spatial variability of transmissivity. In contrast, the estimate from geostatistical inversion reveals more structure. This indicates that the estimates of the type‐curve approaches can not be treated as pseudo‐local values. Concerning storativity, both analysis methods show strong fluctuations. Because the variability of all terms making up the storativity is small, we believe that the estimated variability of storativity is biased. We examine the influence of measurement error on estimating structural parameters of covariance functions in the inversion. We obtain larger correlation lengths and smaller prior variances if we trust the measured data less.
Estimating precipitation errors using spaceborne surface soil moisture retrievals
Authors: Crow W. T. , Bolten J. D.
Published: April 2007

Limitations in the availability of ground‐based rain gauge data currently hamper our ability to quantify errors in global precipitation products over data‐poor areas of the world. Over land, these limitations may be eased by approaches based on interpreting the degree of dynamic consistency existing between precipitation estimates and remotely‐sensed surface soil moisture retrievals. This paper demonstrates how such an approach can be implemented using a Kalman filter tuning procedure to reliably estimate daily rainfall errors in global precipitation products without reliance on ground‐based rainfall observations.
Structural insights into a new homodimeric self‐activated GTPase family
Authors: Gras Stéphanie , Chaumont Valérie , Fernandez Bernard , Carpentier Philippe , Charrier‐Savournin Fabienne , Schmitt Sophie , Pineau Charles , Flament Didier , Hecker Arnaud , Forterre Patrick , Armengaud Jean , Housset Dominique
Published: April 2007

The human XAB1/MBDin GTPase and its close homologues form one of the ten phylogenetically distinct families of the SIMIBI (after signal recognition particle, MinD and BioD) class of phosphate‐binding loop NTPases. The genomic context and the partners identified for the archaeal and eukaryotic homologues indicate that they are involved in genome maintenance—DNA repair or replication. The crystal structure of PAB0955 from Pyrococcus abyssi shows that, unlike other SIMIBI class G proteins, these highly conserved GTPases are homodimeric, regardless of the presence of nucleotides. The nucleotide‐binding site of PAB0955 is rather rigid and its conformation is closest to that of the activated SRP G domain. One insertion to the G domain bears a strictly conserved GPN motif, which is part of the catalytic site of the other monomer and stabilizes the phosphate ion formed. Owing to this unique functional feature, we propose to call this family as GPN‐loop GTPase.
Hemicalcin, a new toxin from the Iranian scorpion Hemiscorpius lepturus which is active on ryanodine-sensitive Ca2+ channels
Authors: Shahbazzadeh Delavar , Srairi-Abid Najet , Feng Wei , Ram Narendra , Borchani Lamia , Ronjat Michel , Akbari Abolfazl , Pessah Isaac N. , De Waard Michel , El Ayeb Mohamed
Published: April 2007

In the present work, we purified and characterized a novel toxin named hemicalcin from the venom of the Iranian chactoid scorpion Hemiscorpius lepturus where it represents 0.6% of the total protein content. It is a 33-mer basic peptide reticulated by three disulfide bridges, and that shares between 85 and 91% sequence identity with four other toxins, all known or supposed to be active on ryanodine-sensitive calcium channels. Hemicalcin differs from these other toxins by seven amino acids at positions 9 (leucine/arginine), 12 (alanine/glutamic acid), 13 (aspartic acid/asparagine), 14 (lysine/asparagine), 18 (serine/glycine), 26 (threonine/alanine) and 28 (proline/isoleucine/alanine). In spite of these differences, hemicalcin remains active on ryanodine-sensitive Ca2+ channels, since it increases [3H]ryanodine binding on RyR1 (ryanodine receptor type 1) and triggers Ca2+ release from sarcoplasmic vesicles. Bilayer lipid membrane experiments, in which the RyR1 channel is reconstituted and its gating properties are analysed, indicate that hemicalcin promotes an increase in the opening probability at intermediate concentration and induces a long-lasting subconductance level of 38% of the original amplitude at higher concentrations. Mice intracerebroventricular inoculation of 300 ng of hemicalcin induces neurotoxic symptoms in vivo, followed by death. Overall, these data identify a new biologically active toxin that belongs to a family of peptides active on the ryanodine-sensitive channel.
Neurogranin binds to phosphatidic acid and associates to cellular membranes
Authors: Domínguez-González Irene , Vázquez-Cuesta Silvia N. , Algaba Alicia , Díez-Guerra F. Javier
Published: April 2007

Neurogranin (Ng) is a 78-amino-acid-long protein concentrated at dendritic spines of forebrain neurons that is involved in synaptic plasticity through the regulation of CaM (calmodulin)-mediated signalling. Ng features a central IQ motif that mediates binding to CaM and is phosphorylated by PKC (protein kinase C). We have analysed the subcellular distribution of Ng and found that it associates to cellular membranes in rat brain. In vitro binding assays revealed that Ng selectively binds to PA (phosphatidic acid) and that this interaction is prevented by CaM and PKC phosphorylation. Using the peptide Ng-(29–47) and a mutant with an internal deletion (Ng-IQless), we have shown that Ng binding to PA and to cellular membranes is mediated by its IQ motif. Ng expressed in NIH-3T3 cells accumulates at peripheral regions of the plasma membrane and localizes at intracellular vesicles that can be clearly visualized following saponin permeabilization. This distribution was affected by PLD (phospholipase D) and PIP5K (phosphatidylinositol 4-phosphate 5-kinase) overexpression. Based on these results, we propose that Ng binding to PA may be involved in Ng accumulation at dendritic spines and that Ng could modulate PA signalling in the postsynaptic environment.
Amide solvent protection analysis demonstrates that amyloid-β(1–40) and amyloid-β(1–42) form different fibrillar structures under identical conditions
Authors: Olofsson Anders , Lindhagen-Persson Malin , Sauer-Eriksson A. Elisabeth , Öhman Anders
Published: April 2007

AD (Alzheimer's disease) is a neurodegenerative disorder characterized by self-assembly and amyloid formation of the 39–43 residue long Aβ (amyloid-β)-peptide. The most abundant species, Aβ(1–40) and Aβ(1–42), are both present within senile plaques, but Aβ(1–42) peptides are considerably more prone to self-aggregation and are also essential for the development of AD. To understand the molecular and pathological mechanisms behind AD, a detailed knowledge of the amyloid structures of Aβ-peptides is vital. In the present study we have used quenched hydrogen/deuterium-exchange NMR experiments to probe the structure of Aβ(1–40) fibrils. The fibrils were prepared and analysed identically as in our previous study on Aβ(1–42) fibrils, allowing a direct comparison of the two fibrillar structures. The solvent protection pattern of Aβ(1–40) fibrils revealed two well-protected regions, consistent with a structural arrangement of two β-strands connected with a bend. This protection pattern partly resembles the pattern found in Aβ(1–42) fibrils, but the Aβ(1–40) fibrils display a significantly increased protection for the N-terminal residues Phe4–His14, suggesting that additional secondary structure is formed in this region. In contrast, the C-terminal residues Gly37–Val40 show a reduced protection that suggests a loss of secondary structure in this region and an altered filament assembly. The differences between the present study and other similar investigations suggest that subtle variations in fibril-preparation conditions may significantly affect the fibrillar architecture.
Phylogenetic and specificity studies of two-domain GNA-related lectins: generation of multispecificity through domain duplication and divergent evolution
Authors: Van Damme Els J. M. , Nakamura-Tsuruta Sachiko , Smith David F. , Ongenaert Maté , Winter Harry C. , Rougé Pierre , Goldstein Irwin J. , Mo Hanqing , Kominami Junko , Culerrier Raphaël , Barre Annick , Hirabayashi Jun , Peumans Willy J.
Published: April 2007

A re-investigation of the occurrence and taxonomic distribution of proteins built up of protomers consisting of two tandem arrayed domains equivalent to the GNA [Galanthus nivalis (snowdrop) agglutinin] revealed that these are widespread among monotyledonous plants. Phylogenetic analysis of the available sequences indicated that these proteins do not represent a monophylogenetic group but most probably result from multiple independent domain duplication/in tandem insertion events. To corroborate the relationship between inter-domain sequence divergence and the widening of specificity range, a detailed comparative analysis was made of the sequences and specificity of a set of two-domain GNA-related lectins. Glycan microarray analyses, frontal affinity chromatography and surface plasmon resonance measurements demonstrated that the two-domain GNA-related lectins acquired a marked diversity in carbohydrate-binding specificity that strikingly contrasts the canonical exclusive specificity of their single domain counterparts towards mannose. Moreover, it appears that most two-domain GNA-related lectins interact with both high mannose and complex N-glycans and that this dual specificity relies on the simultaneous presence of at least two different independently acting binding sites. The combined phylogenetic, specificity and structural data strongly suggest that plants used domain duplication followed by divergent evolution as a mechanism to generate multispecific lectins from a single mannose-binding domain. Taking into account that the shift in specificity of some binding sites from high mannose to complex type N-glycans implies that the two-domain GNA-related lectins are primarily directed against typical animal glycans, it is tempting to speculate that plants developed two-domain GNA-related lectins for defence purposes.
Definition of the minimal fragments of Sti1 required for dimerization, interaction with Hsp70 and Hsp90 and in vivo functions
Authors: Flom Gary , Behal Robert H. , Rosen Luke , Cole Douglas G. , Johnson Jill L.
Published: April 2007

The molecular chaperone Hsp (heat-shock protein) 90 is critical for the activity of diverse cellular client proteins. In a current model, client proteins are transferred from Hsp70 to Hsp90 in a process mediated by the co-chaperone Sti1/Hop, which may simultaneously interact with Hsp70 and Hsp90 via separate TPR (tetratricopeptide repeat) domains, but the mechanism and in vivo importance of this function is unclear. In the present study, we used truncated forms of Sti1 to determine the minimal regions required for the Hsp70 and Hsp90 interaction, as well as Sti1 dimerization. We found that both TPR1 and TPR2B contribute to the Hsp70 interaction in vivo and that mutations in both TPR1 and TPR2B were required to disrupt the in vitro interaction of Sti1 with the C-terminus of the Hsp70 Ssa1. The TPR2A domain was required for the Hsp90 interaction in vivo, but the isolated TPR2A domain was not sufficient for the Hsp90 interaction unless combined with the TPR2B domain. However, isolated TPR2A was both necessary and sufficient for purified Sti1 to migrate as a dimer in solution. The DP2 domain, which is essential for in vivo function, was dispensable for the Hsp70 and Hsp90 interaction, as well as Sti1 dimerization. As evidence for the role of Sti1 in mediating the interaction between Hsp70 and Hsp90 in vivo, we identified Sti1 mutants that result in reduced recovery of Hsp70 in Hsp90 complexes. We also identified two Hsp90 mutants that exhibit a reduced Hsp70 interaction, which may help clarify the mechanism of client transfer between the two molecular chaperones.
On a q-analog of a Sahi result
Authors: Bershtein Olga
Published: April 2007

We obtain a q-analog of a well-known Sahi result on the joint spectrum of S(GLn×GLn)-invariant differential operators with polynomial coefficients on the vector space of complex n×n matrices.
Effect of secondary electron emission on the Jeans instability in a dusty plasma
Authors: Sarkar Susmita , Roy Banamali , Maity Saumyen , Khan Manoranjan , Gupta M. R.
Published: April 2007

In this paper the effect of secondary electron emission on Jeans instability in a dusty plasma has been investigated. Due to secondary electron emission, dust grains may have two stable equilibrium states out of which one is negative and the other is positive. Here both cases have been considered separately. It has been shown that secondary electron emission enhances Jeans instability when equilibrium dust charge is negative. It has also been shown that growth rate of Jeans instability reduces with increasing secondary electron emission when equilibrium dust charge is positive.
Electrostatics of proteins in dielectric solvent continua. I. Newton’s third law marries qE forces
Authors: Stork Martina , Tavan Paul
Published: April 2007

The authors reformulate and revise an electrostatic theory treating proteins surrounded by dielectric solvent continua [B. Egwolf and P. Tavan, J. Chem. Phys. 118, 2039 (2003)] to make the resulting reaction field (RF) forces compatible with Newton’s third law. Such a compatibility is required for their use in molecular dynamics (MD) simulations, in which the proteins are modeled by all-atom molecular mechanics force fields. According to the original theory the RF forces, which are due to the electric field generated by the solvent polarization and act on the partial charges of a protein, i.e., the so-called qE forces, can be quite accurately computed from Gaussian RF dipoles localized at the protein atoms. Using a slightly different approximation scheme also the RF energies of given protein configurations are obtained. However, because the qE forces do not account for the dielectric boundary pressure exerted by the solvent continuum on the protein, they do not obey the principle that actio equals reactio as required by Newton’s third law. Therefore, their use in MD simulations is severely hampered. An analysis of the original theory has led the authors now to a reformulation removing the main difficulties. By considering the RF energy, which represents the dominant electrostatic contribution to the free energy of solvation for a given protein configuration, they show that its negative configurational gradient yields mean RF forces obeying the reactio principle. Because the evaluation of these mean forces is computationally much more demanding than that of the qE forces, they derive a suggestion how the qE forces can be modified to obey Newton’s third law. Various properties of the thus established theory, particularly issues of accuracy and of computational efficiency, are discussed. A sample application to a MD simulation of a peptide in solution is described in the following paper [M. Stork and P. Tavan, J. Chem. Phys., 126, 165106 (2007).
Shock patterns in a slightly underexpanded sonic jet controlled by radial injections
Authors: Chauvet Nicolas , Deck Sebastien , Jacquin Laurent
Published: April 2007

This Brief Communication is focused on the shock patterns appearing in supersonic round jets subjected to azimuthal disturbances, such as those produced by discrete radial injections. First, it is highlighted that slightly underexpanded sonic jets exhibit a lens-shaped shock wave that is clearly different from the standard Mach disk. This pattern is observed in many propulsive jets. Second, when azimuthal perturbations are imposed, the shock-wave structure is shown to evolve under the action of transverse mass flows toward a pattern resembling a Mach disk configuration. An analysis of these patterns is conducted using the theory of characteristics.
Self-assembly of periodic nanoclusters of Si and Ge along atomically straight steps of a vicinal Si(111)
Authors: Sekiguchi Takeharu , Yoshida Shunji , Shiren Yohei , Itoh Kohei M. , Mysliveček Josef , Voigtländer Bert
Published: April 2007

The very initial stage of the molecular beam epitaxy of Si and Ge on Si(111)−7×7 substrates with atomically straight steps has been studied by scanning tunneling microscopy and spectroscopy. The atomically straight steps have been prepared on a miscut Si(111) substrate by annealing at 830 °C with kink-up direct current. The length of the steps can be maximized by selecting a proper annealing time. The steps have a well-defined U(2, 0) step-edge structure. The growth of both Si and Ge at temperatures between 250 and 400 °C starts with formation of a single-adatom-row nanowire (0.67 nm in width) along the lower edge of each U(2, 0) step. Subsequent growth of Si and Ge at temperatures between 250 and 300 °C results in formation of one-dimensional arrays of nanoclusters (less than 2.0 nm in width) in the unfaulted halves of the 7×7 structure along the upper step edges. Scanning tunneling spectroscopy reveals localized electronic states of the nanoclusters. Differences between the growth of Si and Ge nanoclusters are discussed.
Excited excitonic states observed in semiconductor quantum dots using polarization resolved optical spectroscopy
Authors: Troncale V. , Karlsson K. F. , Oberli D. Y. , Byszewski M. , Malko A. , Pelucchi E. , Rudra A. , Kapon E.
Published: April 2007

We present results on the polarization-resolved photoluminescence emitted from InGaAs/AlGaAs single quantum dots (QDs) grown in inverted tetrahedral pyramids. The emitted light was detected for two mutually perpendicular linear polarization directions in the less conventional cleaved-edge geometry, in addition to the standard top-emission geometry. Whereas the in-plane linear polarization was isotropic, as a consequence of the high symmetry of the system, we found a strong polarization anisotropy of the edge-emitted light revealing QD states of predominantly heavy- or light-hole character. By temperature control of the charge state, several neutral and charged light-hole like exciton complexes were identified. In particular, a biexciton showing a twofold radiative recombination path, leading to two nearly perpendicularly polarized emission multiplets, was identified. These results are also of technological relevance for any design of optoelectronic QD-integrated devices.
Detection of single electron spin resonance in a double quantum dot
Authors: Koppens F. H. L. , Buizert C. , Vink I. T. , Nowack K. C. , Meunier T. , Kouwenhoven L. P. , Vandersypen L. M. K.
Published: April 2007

Spin-dependent transport measurements through a double quantum dot are a valuable tool for detecting both the coherent evolution of the spin state of a single electron, as well as the hybridization of two-electron spin states. In this article, we discuss a model that describes the transport cycle in this regime, including the effects of an oscillating magnetic field (causing electron spin resonance) and the effective nuclear fields on the spin states in the two dots. We numerically calculate the current flow due to the induced spin flips via electron spin resonance, and we study the detector efficiency for a range of parameters. The experimental data are compared with the model and we find a reasonable agreement.
Atomic scale study of the impact of the strain and composition of the capping layer on the formation of InAs quantum dots
Authors: Ulloa J. M. , Çelebi C. , Koenraad P. M. , Simon A. , Gapihan E. , Letoublon A. , Bertru N. , Drouzas I. , Mowbray D. J. , Steer M. J. , Hopkinson M.
Published: April 2007

The impact of the capping material on the structural properties of self-assembled InAs quantum dots (QDs) was studied at the atomic scale by cross-sectional scanning tunneling microscopy. Capping with lattice matched layers and with strained layers was analyzed. When the different capping materials are lattice matched to the substrate, the differences in the QD properties can be dominated by chemical effects: InAs/InP QDs capped with InP have a 2 ML smaller height than those capped with InGaAs or InGaAsP due to As/P exchange induced decomposition. The height of the dots is found to be much more strongly affected when strained capping layers are used. InAs/GaAs, QDs capped with InGaAs are considerably taller than typical GaAs-capped dots. When GaAsSb is used as the capping layer, the dots are almost full pyramids with a height of 9.5 nm, indicating that dot decomposition is almost completely suppressed. This indicates that the dot/capping layer strain plays a major role in inducing dot decomposition during capping.
Electrical manipulation of spin-orbit coupling in semiconductor heterostructures
Authors: Sih Vanessa , Awschalom David D.
Published: April 2007

The spin-orbit interaction offers an avenue for the electrical generation and manipulation of electron spin polarization in semiconductors without magnetic materials or magnetic fields. In semiconductor heterostructures, the spin-orbit coupling modifies the electron g factor and introduces momentum-dependent spin splittings. In addition, spin-orbit coupling enables the electrical generation of spin polarization through these spin splittings and the spin Hall effect. Here we present an overview of recent measurements of spin dynamics, spin splittings, and electrically generated spin polarization. We demonstrate manipulation of the spin-orbit coupling using electric and magnetic fields to change the orbital motion of the electrons and using strain and quantum confinement to tune the spin splittings in semiconductor heterostructures.
Seeing emergent phases in quantum Hall double layers
Authors: Pellegrini Vittorio , Luin Stefano , Karmakar Biswajit , Pinczuk Aron , Dennis Brian S. , Pfeiffer Loren N. , West Ken W.
Published: April 2007

We review recent studies by optics methods of emergent phases in the quantum Hall (QH) regimes of double layers with finite tunneling at Landau level filling factor ν=1. In measurements of spin excitations by inelastic light scattering and of elastically scattered Rayleigh light under the application of in-plane magnetic fields, we uncovered evidence of a quantum phase transition that occurs when a many-body tunneling gap collapses. The transformation can be regarded as a transition from an incompressible highly correlated QH state to a compressible composite-fermion bilayer system. The correlated QH state is characterized by the presence of populations of bound electron-hole pairs across the tunneling gap. Quantitative determinations of the density of such excitonic pairs are obtained from inelastic light scattering spectra of spin excitations. The correlated QH state displays resonant Rayleigh scattering with unusual temperature dependence.
Trimming Si surfaces for molecular electronics
Authors: Caldas M. J. , Calzolari A. , Cucinotta C. S.
Published: April 2007

In the last two decades significant progress has been made in developing methodologies (fabrication and analysis) for organic functionalization of semiconductors, in view of applications in molecular electronics, nano-bio devices, and surface nanopatterning in general. A strategic route is the functionalization of Si surfaces to exploit both the existing Si technology and the strength of the Si-C bond. It is also interesting to take advantage of Si-O chemistry, creating Si-O-C covalent bridges and trying at the same time to protect the interface from spurious oxidation. The microscopic understanding of interactions at the organic/semiconductor interfaces, required to proceed in these directions is, however, still poor. Theoretical studies can thus be very helpful to identify relevant model systems, and predict the effects on the electronic structure. Here, we use state-of-the-art ab initio methods to investigate alkyl monolayers on the perfectly hydrogenated Si(100) surface, bonded through single Si-C or double Si-OO-C bridges. Our results point to structural differences between bridging mechanisms, leading to different overall surface orderings. We find also relevant electronic differences. Our results always show a sharp frontier between the organic and inorganic electronic states, with a well defined energy barrier. For configurations with a Si-C bridge the top valence states are free from molecular contributions, while in the case of bonding through the Si-OO-C double bridge the results point to a contribution from the interface oxygen atoms.
Rotationally inelastic collisions of SO(XΣ−3) with H2: Potential energy surface and rate coefficients for excitation by para-H2 at low temperature
Authors: Lique F. , Senent M.-L. , Spielfiedel A. , Feautrier N.
Published: April 2007

Rotational excitation of the interstellar species SO(XΣ−3) with H2 is investigated. The authors present a new four-dimensional potential energy surface for the SO–H2 system, calculated at an internuclear SO distance frozen at its experimental minimum energy distance. It was obtained at the RCCSD(T) level using the aug-cc-pVTZ basis sets for the four atoms. Bond functions were placed at mid-distance between the SO center of mass and the center of mass of H2 for a better description of the van der Waals interaction. Close coupling calculations of the collisional excitation cross sections between the fine structure levels of SO by collisions with para-H2 are calculated at low energies which yield, after Boltzmann thermal average, rate coefficients up to 50K. The exact level splitting is taken into account. The propensity rules between fine structure levels are studied. It is shown that F-conserving cross sections are much larger, especially for high-N rotational levels, than F-changing cross sections, as found previously for SO–He collisions and expected from theoretical considerations. The new rate coefficients are compared with previous results obtained for this molecule and they find that important differences exist that can induce important consequences on astrophysical modeling. Comparison with excitation by collision with He shows that the rate coefficients differ by important factors that cannot be only explained by the reduced mass ratio in the thermal average. This may be due to differences between the potential energy surfaces as well as to the contribution of the different reduced masses in the scattering equations.
Field emission from multiwall carbon nanotubes on paper substrates
Authors: Lyth S. M. , Silva S. R. P.
Published: April 2007

The authors report extremely low electron field emission thresholds from acid oxidized multiwall carbon nanotubes deposited on paper substrates by dip coating in an aqueous nanotube ink. Using paper substrates of differing surface roughness, field emission threshold fields ranging from 0.8to11.6V∕μm were observed, varying in an approximate inverse linear log relationship with the surface roughness of the underlying paper substrate. This study shows how field emission from supported nanotube films can be tailored via the morphology of the scaffold substrate, and how these composite electrodes can be straightforwardly fabricated on cheap, flexible substrates.
Simple phenomenological determination of contact stiffness and elastic modulus of Ce-based bulk metallic glasses through nanoindentation
Authors: Li W. H. , Shin Keesam , Lee C. G. , Wei B. C. , Zhang T. H.
Published: April 2007

The viscoelastic deformation of Ce-based bulk metallic glasses (BMGs) with low glass transition temperature is investigated at room temperature. Contact stiffness and elastic modulus of Ce-based BMGs cannot be derived using the conventional Oliver-Pharr method [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)]. The present work shows that the time dependent displacement of unloading segments can be described well by a generalized Kelvin model. Thus, a modified Oliver-Pharr method is proposed to evaluate the contact stiffness and elastic modulus, which does, in fact, reproduce the values obtained via uniaxial compression tests.
High current permanent discharges in air induced by femtosecond laser filamentation
Authors: Houard A. , D’Amico C. , Liu Y. , Andre Y. B. , Franco M. , Prade B. , Mysyrowicz A. , Salmon E. , Pierlot P. , Cleon L.-M.
Published: April 2007

Filaments created in air by an intense femtosecond laser pulse in the presence of an electric field generate a highly conductive permanent plasma column.