bluuebunny/crossref_metadata_2025 huggingface dataset:
Versatile piezoelectric pulsed molecular beam source for gaseous compounds and organic molecules with femtomole accuracy for UHV and surface science applications
Authors: Schießer Alexander , Schäfer Rolf
Published: August 2009

This note describes the construction of a piezoelectric pulsed molecular beam source based upon a design presented in an earlier work [D. Proch and T. Trickl, Rev. Sci. Instrum. 60, 713 (1988)]. The design features significant modifications that permit the determination of the number of molecules in a beam pulse with an accuracy of 1×1011 molecules per pulse. The 21 cm long plunger-nozzle setup allows the molecules to be brought to any point of the UHV chamber with very high intensity. Furthermore, besides typical gaseous compounds, also smaller organic molecules with a vapor pressure higher than 0.1 mbar at room temperature may serve as feed material. This makes the new design suitable for various applications in chemical and surface science studies.
Electronic structure of epitaxial graphene nanoribbons on SiC(0001)
Authors: Deretzis I. , La Magna A.
Published: August 2009

We present electronic structure calculations of few-layer epitaxial graphene nanoribbons on SiC(0001). Trough an atomistic description of the graphene layers and the substrate within the extended Hückel theory and real/momentum space projections we argue that the role of the heterostructure’s interface becomes crucial for the conducting capacity of the studied systems. The key issue arising from this interaction is a Fermi level pinning effect introduced by dangling interface bonds. Such phenomenon is independent from the width of the considered nanostructures, compromising the importance of confinement in these systems.
Superheating of liquid xenon in metal tubes
Authors: Baidakov V. G. , Kaverin A. M.
Published: August 2009

The method of measuring the lifetime has been used to investigate the kinetics of spontaneous boiling-up of superheated xenon in copper tubes. In experiments the temperature dependence of the mean lifetime has been determined at pressures of 1.48 and 1.98 MPa. The data obtained have been compared with homogeneous nucleation theory. It has been found that experimental values of the attainable superheating temperature and the derivative (∂ ln J/∂T)p are systematically lower than their theoretical values. A description of experimental data in the framework of heterogeneous nucleation theory has shown that for the agreement of theory and experiment with the use of a macroscopic model of nucleation on a smooth surface it is necessary to take the value of the equilibrium contact angle θ0 equal to 70°, which is not a characteristic for a xenon-metal system. Taking into account the contribution of the energy of the three-phase contact solid wall-liquid-gas in a microscopic nucleation model makes it possible to reconcile heterogeneous nucleation theory and experimental data at a contact angle θ0 close to zero, with the linear tension taken equal to −6×10−12 J/m and the microscopic contact angle θ∗≃57°. The number of weakened sites, on which bubbles may form, is always smaller than the number of molecules adjacent to the solid wall.
Origin choice and petal loss in the flower garden of spiral wave tip trajectories
Authors: Gray Richard A. , Wikswo John P. , Otani Niels F.
Published: August 2009

Rotating spiral waves have been observed in numerous biological and physical systems. These spiral waves can be stationary, meander, or even degenerate into multiple unstable rotating waves. The spatiotemporal behavior of spiral waves has been extensively quantified by tracking spiral wave tip trajectories. However, the precise methodology of identifying the spiral wave tip and its influence on the specific patterns of behavior remains a largely unexplored topic of research. Here we use a two-state variable FitzHugh–Nagumo model to simulate stationary and meandering spiral waves and examine the spatiotemporal representation of the system’s state variables in both the real (i.e., physical) and state spaces. We show that mapping between these two spaces provides a method to demarcate the spiral wave tip as the center of rotation of the solution to the underlying nonlinear partial differential equations. This approach leads to the simplest tip trajectories by eliminating portions resulting from the rotational component of the spiral wave.
Metal-oxide-semiconductor capacitors with ZrO2 dielectrics grown on In0.53Ga0.47As by chemical beam deposition
Authors: Engel-Herbert Roman , Hwang Yoontae , Cagnon Joël , Stemmer Susanne
Published: August 2009

Zirconium oxide films were grown by chemical beam deposition with zirconium tert-butoxide as the source on (2×4) reconstructed, n-type In0.53Ga0.47As surfaces obtained after As decapping. Optimized growth conditions yielded ZrO2/In0.53Ga0.47As interfaces that were free of second phases. Capacitance-voltage (CV) measurements with different top electrodes showed a frequency dispersion of less than 2% per decade in accumulation. The accumulation capacitance and horizontal position of the CV curve were independent of temperature, while the inversion capacitance was strongly temperature dependent. Flat band voltages correlated with the work function of the metal electrode.
Photovoltaic effects in BiFeO3
Authors: Yang S. Y. , Martin L. W. , Byrnes S. J. , Conry T. E. , Basu S. R. , Paran D. , Reichertz L. , Ihlefeld J. , Adamo C. , Melville A. , Chu Y.-H. , Yang C.-H. , Musfeldt J. L. , Schlom D. G. , Ager J. W. , Ramesh R.
Published: August 2009

We report a photovoltaic effect in ferroelectric BiFeO3 thin films. The all-oxide heterostructures with SrRuO3 bottom and tin doped indium oxide top electrodes are characterized by open-circuit voltages ∼0.8–0.9 V and external quantum efficiencies up to ∼10% when illuminated with the appropriate light. Efficiencies are at least an order of magnitude larger than the maximum efficiency under sunlight (AM 1.5) thus far reported for ferroelectric-based devices. The dependence of the measured open-circuit voltage on film thickness suggests contributions to the large open-circuit voltage from both the ferroelectric polarization and band offsets at the BiFeO3/tin doped indium oxide interface.
Influence of the carrier gas molar mass on the particle formation in a vapor phase
Authors: Braun S. , Römer F. , Kraska T.
Published: August 2009

The influence of the molar mass of a carrier gas on the formation of nanoparticles in the vapor phase is investigated. The function of the carrier gas atmosphere is the regulation of the particle temperature by collisions with the cluster surface. The aim of this work is to optimize the carrier gas in a simulation in order to mimic a large amount of carrier gas atoms by few gas atoms with effective parameters. In this context the efficiency of the heat exchange with the carrier gas depending on its molar mass is analyzed. As a result one finds for varying molar masses and unchanged interaction parameters a competition between the efficiency and the number of the collisions. For too small molar masses the energy exchange per collision is too small while for too high masses the carrier gas atoms become very slow, decreasing the number of collisions.
Josephson effect between electron-doped and hole-doped iron pnictide single crystals
Authors: Zhang Xiaohang , Saha Shanta R. , Butch Nicholas P. , Kirshenbaum Kevin , Paglione Johnpierre , Greene Richard L. , Liu Yong , Yan Liqin , Oh Yoon Seok , Kim Kee Hoon , Takeuchi Ichiro
Published: August 2009

We have observed the Josephson effect in junctions formed between single crystals of SrFe1.74Co0.26As2 and Ba0.23K0.77Fe2As2. The ac Josephson effect was observed under microwave irradiation in the I-V characteristics. By applying an in-plane magnetic field, the critical current is completely modulated and shows a relatively symmetric diffraction pattern consistent with the intermediate junction limit. The observation of the Josephson effect in the p-n bicrystal structure not only has significant implications for designing phase-sensitive junctions to probe the pairing symmetry of iron pnictide superconductors, but also represents an important step in developing all iron pnictide devices for applications.
An investigation of the magnetic state dependent low frequency noise in magnetic tunnel junctions
Authors: Guo Feng , McKusky Greg , Dahlberg E. Dan
Published: August 2009

The low frequency noise in magnetic tunnel junctions was studied as a function of applied magnetic field. In magnetic states where the magnetization is reversing, the measurement indicates a 1/f2 spectrum whereas at all other applied fields a 1/f spectrum is observed. The 1/f2 spectra are found to be an artifact of the magnetic after effect. Without the artificial influence of the magnetic after effect, only 1/f spectra are observed.
Lateral migration of a small spherical buoyant particle in a wall-bounded linear shear flow
Authors: Takemura Fumio , Magnaudet Jacques
Published: August 2009

Lateral migration velocities of solid spherical particles suspended in a linear wall-bounded shear flow are measured for Reynolds number, Re<2 (Re=2RU/ν, where R is the particle radius, U is the local slip velocity between the particle and the fluid, and ν is the kinematic viscosity of the suspending fluid). The velocity parallel to the wall and the distance between the particle and the wall are measured as a function of time, allowing the lateral migration velocity and the slip velocity of the particle to be determined. The measured velocities are compared to the theoretical predictions of McLaughlin [“The lift on a small sphere in wall-bounded linear shear flows,” J. Fluid Mech. 246, 249 (1993)] and Magnaudet et al. [J. Fluid Mech. 476, 115 (2003)] corresponding to the situation where the wall lies in the Oseen region and in the Stokes region of the flow disturbance produced by the particle, respectively. A good agreement is observed in both regimes with the corresponding prediction. The measurements are used to build an empirical fit capable of predicting the migration velocity whatever the distance between the particle and the wall.
Role of conformational dynamics in kinetics of an enzymatic cycle in a nonequilibrium steady state
Authors: Min Wei , Xie X. Sunney , Bagchi Biman
Published: August 2009

Enzyme is a dynamic entity with diverse time scales, ranging from picoseconds to seconds or even longer. Here we develop a rate theory for enzyme catalysis that includes conformational dynamics as cycling on a two-dimensional (2D) reaction free energy surface involving an intrinsic reaction coordinate (X) and an enzyme conformational coordinate (Q). The validity of Michaelis–Menten (MM) equation, i.e., substrate concentration dependence of enzymatic velocity, is examined under a nonequilibrium steady state. Under certain conditions, the classic MM equation holds but with generalized microscopic interpretations of kinetic parameters. However, under other conditions, our rate theory predicts either positive (sigmoidal-like) or negative (biphasic-like) kinetic cooperativity due to the modified effective 2D reaction pathway on X-Q surface, which can explain non-MM dependence previously observed on many monomeric enzymes that involve slow or hysteretic conformational transitions. Furthermore, we find that a slow conformational relaxation during product release could retain the enzyme in a favorable configuration, such that enzymatic turnover is dynamically accelerated at high substrate concentrations. The effect of such conformation retainment in a nonequilibrium steady state is evaluated.
Variation in the μ-opioid receptor gene (OPRM1) is associated with dispositional and neural sensitivity to social rejection
Authors: Way Baldwin M. , Taylor Shelley E. , Eisenberger Naomi I.
Published: August 2009

Scientific understanding of social pain—the hurt feelings resulting from social rejection, separation, or loss—has been facilitated by the hypothesis that such feelings arise, in part, from some of the same neural and neurochemical systems that generate the unpleasant feelings resulting from physical pain. Accordingly, in animals, the painkiller morphine not only alleviates the distress of physical pain, but also the distress of social separation. Because morphine acts on the μ-opioid receptor, we examined whether variation in the μ-opioid receptor gene (OPRM1), as measured by the functional A118G polymorphism, was associated with individual differences in rejection sensitivity. Participants (n= 122) completed a self-report inventory of dispositional sensitivity to social rejection and a subsample (n= 31) completed a functional MRI session in which they were rejected from an online ball-tossing game played with two supposed others. The A118G polymorphism was associated with dispositional sensitivity to rejection in the entire sample and in the fMRI subsample. Consistent with these results, G allele carriers showed greater reactivity to social rejection in neural regions previously shown to be involved in processing social pain as well as the unpleasantness of physical pain, particularly the dorsal anterior cingulate cortex (dACC) and anterior insula. Furthermore, dACC activity mediated the relationship between the A118G polymorphism and dispositional sensitivity to rejection, suggesting that this is a critical site for μ-opioid-related influence on social pain. Taken together, these data suggest that the A118G polymorphism specifically, and the μ-opioid receptor more generally, are involved in social pain in addition to physical pain.
Electrodeposition of metals from supercritical fluids
Authors: Ke Jie , Su Wenta , Howdle Steven M. , George Michael W. , Cook David , Perdjon-Abel Magda , Bartlett Philip N. , Zhang Wenjian , Cheng Fei , Levason William , Reid Gillian , Hyde Jason , Wilson James , Smith David C. , Mallik Kanad , Sazio Pier
Published: August 2009

Electrodeposition is a widely used materials-deposition technology with a number of unique features, in particular, the efficient use of starting materials, conformal, and directed coating. The properties of the solvent medium for electrodeposition are critical to the technique's applicability. Supercritical fluids are unique solvents which give a wide range of advantages for chemistry in general, and materials processing in particular. However, a widely applicable approach to electrodeposition from supercritical fluids has not yet been developed. We present here a method that allows electrodeposition of a range of metals from supercritical carbon dioxide, using acetonitrile as a co-solvent and supercritical difluoromethane. This method is based on a careful selection of reagent and supporting electrolyte. There are no obvious barriers preventing this method being applied to deposit a range of materials from many different supercritical fluids. We present the deposition of 3-nm diameter nanowires in mesoporous silica templates using this methodology.
Study of free oligosaccharides derived from the bacterial
N
-glycosylation pathway
Authors: Nothaft Harald , Liu Xin , McNally David J. , Li Jianjun , Szymanski Christine M.
Published: August 2009

The food-borne pathogen
Campylobacter jejuni
is one of the leading causes of bacterial gastroenteritis worldwide and the most frequent antecedent in neuropathies such as the Guillain-Barré and Miller Fisher syndromes.
C. jejuni
was demonstrated to possess an
N
-linked protein glycosylation pathway that adds a conserved heptasaccharide to >40 periplasmic and membrane proteins. Recently, we showed that
C. jejuni
also produces free heptasaccharides derived from the
N
-glycan pathway reminiscent of the free oligosaccharides (fOS) produced by eukaryotes. Herein, we demonstrate that
C. jejuni
fOS are produced in response to changes in the osmolarity of the environment and bacterial growth phase. We provide evidence showing the conserved WWDYG motif of the oligosaccharyltransferase, PglB, is necessary for fOS release into the periplasm. This report demonstrates that fOS from an
N
-glycosylation pathway in bacteria are potentially equivalent to osmoregulated periplasmic glucans in other Gram-negative organisms.
Melatonin modulates visual function and cell viability in the mouse retina via the MT1 melatonin receptor
Authors: Baba Kenkichi , Pozdeyev Nikita , Mazzoni Francesca , Contreras-Alcantara Susana , Liu Cuimei , Kasamatsu Manami , Martinez-Merlos Theresa , Strettoi Enrica , Iuvone P. Michael , Tosini Gianluca
Published: August 2009

A clear demonstration of the role of melatonin and its receptors in specific retinal functions is lacking. The present study investigated the distribution of MT1 receptors within the retina, and the scotopic and photopic electroretinograms (ERG) and retinal morphology in wild-type (WT) and MT1 receptor-deficient mice. MT1 receptor transcripts were localized in photoreceptor cells and in some inner retinal neurons. A diurnal rhythm in the dark-adapted ERG responses was observed in WT mice, with higher a- and b-wave amplitudes at night, but this rhythm was absent in mice lacking MT1 receptors. Injection of melatonin during the day decreased the scotopic response threshold and the amplitude of the a- and b-waves in the WT mice, but not in the MT1
−/−
mice. The effects of MT1 receptor deficiency on retinal morphology was investigated at three different ages (3, 12, and 18 months). No differences between MT1
−/−
and WT mice were observed at 3 months of age, whereas at 12 months MT1
−/−
mice have a significant reduction in the number of photoreceptor nuclei in the outer nuclear layer compared with WT controls. No differences were observed in the number of cells in inner nuclear layer or in ganglion cells at 12 months of age. At 18 months, the loss of photoreceptor nuclei in the outer nuclear layer was further accentuated and the number of ganglion cells was also significantly lower than that of controls. These data demonstrate the functional significance of melatonin and MT1 receptors in the mammalian retina and create the basis for future studies on the therapeutic use of melatonin in retinal degeneration.
The equilibrium intrinsic crystal–liquid interface of colloids
Authors: Hernández-Guzmán Jessica , Weeks Eric R.
Published: August 2009

We use confocal microscopy to study an equilibrated crystal–liquid interface in a colloidal suspension. Capillary waves roughen the surface, but locally the intrinsic interface is sharply defined. We use local measurements of the structure and dynamics to characterize the intrinsic interface, and different measurements find slightly different widths of this interface. In terms of the particle diameter
d
, this width is either 1.5
d
(based on structural information) or 2.4
d
(based on dynamics), both not much larger than the particle size. This work is the first direct experimental visualization of an equilibrated crystal–liquid interface.
Glass rheology: From mode-coupling theory to a dynamical yield criterion
Authors: Brader Joseph M. , Voigtmann Thomas , Fuchs Matthias , Larson Ronald G. , Cates Michael E.
Published: August 2009

The mode coupling theory (MCT) of glasses, while offering an incomplete description of glass transition physics, represents the only established route to first-principles prediction of rheological behavior in nonergodic materials such as colloidal glasses. However, the constitutive equations derivable from MCT are somewhat intractable, hindering their practical use and also their interpretation. Here, we present a schematic (single-mode) MCT model which incorporates the tensorial structure of the full theory. Using it, we calculate the dynamic yield surface for a large class of flows.
Nob1 binds the single-stranded cleavage site D at the 3′-end of 18S rRNA with its PIN domain
Authors: Lamanna Allison C. , Karbstein Katrin
Published: August 2009

Ribosome assembly is a hierarchical process that involves pre-rRNA folding, modification, and cleavage and assembly of ribosomal proteins. In eukaryotes, this process requires a macromolecular complex comprising over 200 proteins and RNAs. Whereas the rRNA modification machinery is well-characterized, rRNA cleavage to release mature rRNAs is poorly understood, and in yeast, only 2 of 8 endonucleases have been identified. The essential and conserved ribosome assembly factor Nob1 has been suggested to be the endonuclease responsible for generating the mature 3′-end of 18S rRNA by cleaving at site D. Here we provide evidence that recombinant Nob1 forms a tetramer that binds directly to pre-rRNA analogs containing cleavage site D. Analysis of Nob1's affinity to a series of RNA truncations, as well as Nob1-dependent protections of pre-rRNA in vitro and in vivo demonstrate that Nob1's binding site centers around the 3′-end of 18S rRNA, where our data also locate Nob1's suggested active site. Thus, Nob1 is poised for cleavage at the 3′-end of 18S rRNA. Together with prior data, these results strongly implicate Nob1 in cleavage at site D. In addition, our data provide evidence that the cleavage site at the 3′-end of 18S rRNA is single-stranded and not part of a duplex as commonly depicted. Using these results, we have built a model for Nob1's interaction with preribosomes.
Enhanced surface hydrophobicity by coupling of surface polarity and topography
Authors: Giovambattista Nicolas , Debenedetti Pablo G. , Rossky Peter J.
Published: August 2009

We use atomistic computer simulation to explore the relationship between mesoscopic (liquid drop contact angle) and microscopic (surface atomic polarity) characteristics for water in contact with a model solid surface based on the structure of silica. We vary both the magnitude and direction of the solid surface polarity at the atomic scale and characterize the response of an aqueous interface in terms of the solvent molecular organization and contact angle. We show that when the topography and polarity of the surface act in concert with the asymmetric charge distribution of water, the hydrophobicity varies substantially and, further, can be maximal for a surface with significant polarity. The results suggest that patterning of a surface on several length scales, from atomic to μm lengths, can make important independent contributions to macroscopic hydrophobicity.
Substantial similarity in amygdala neuronal activity during conditioned appetitive and aversive emotional arousal
Authors: Shabel Steven J. , Janak Patricia H.
Published: August 2009

The amygdala is important for determining the emotional significance of environmental stimuli. However, the degree to which appetitive and aversive stimuli are processed by the same or different neuronal circuits within the amygdala remains unclear. Here we show that neuronal activity during the expression of classically conditioned appetitive and aversive emotional responses is more similar than expected by chance, despite the different sensory modalities of the eliciting stimuli. We also found that the activity of a large number of cells (> 43%) was correlated with blood pressure, a measure of emotional arousal. Together, our results suggest that a substantial proportion of neuronal circuits within the amygdala can contribute to both appetitive and aversive emotional arousal.
Vertical perceptual span and the processing of visual signals in reading
Authors: Cauchard Fabrice , Eyrolle Hélène , Cellier Jean‐Marie , Hyönä Jukka
Published: August 2009

A previous study by Pollatsek et al. (1993) claims that the perceptual span in reading is restricted to the fixated line, i.e. readers typically focus their visual attention on the line of text being read. The present study investigated whether readers make use of content structure signals (paragraph indentations and topic headings) present several lines away from the currently fixated line. We reasoned that as these signals are low‐resolution visual objects (as opposed to letter and word identity), readers may attend to them even if they are located some distance away from the fixated line. Participants read a hierarchically organized multi‐topic expository text containing structure signals in either a normal condition or a window condition, where the text disappeared above and below a vertical 3° gaze‐contingent region. After reading, participants were asked to produce a written recall of the text. The results showed that the overall reading rate was not affected by the window. Nevertheless, the headings were reread more in the normal condition than in the window one. In addition, more topics were recalled in the normal than in the window condition. We interpret the results as indicating that the readers visually attend to useful text layout features while considering bigger units than single text lines. The perception of topic headings located away from the fixated line may favour long‐range regressions towards them, which in turn may favour text comprehension. This claim is consistent with previous studies that showed that look‐back fixations to headings are performed with an integrative intent.
‘Parisomania’? Jack Hylton and the French Connection
Authors: Mawer Deborah
Published: August 2009

Like many figures in popular music, the British dance bandleader and entrepreneur Jack Hylton (1892–1965) has been largely forgotten. Through concert tours of France and nostalgic recordings with Chevalier, Hylton forged a connection which peaked at the Paris Opéra. Despite his large French-related repertory, which included ‘jazz’ arrangements of Stravinsky's Mavra, Ravel's Boléro and chansons, his American-influenced style was ultimately international. If his obsession justified the quip of ‘Parisomania’, there was reason in his madness.
Use of 2π-PSD systems for quasielastic neutron time-of-flight experiments
Authors: Lechner R.E.
Published: August 2009

Very-large-area detector systems for low-energy-transfer time-of-flight spectrometers are discussed. Four different kinds of linear position-sensitive detector arrays with spherical- or cylindrical-zone geometries are considered. A non-uniform sample–detector distance is involved, varying by up to 40% for cylindrical symmetry using 5 m long linear position-sensitive detectors (PSDs). Integration over large solid-angle regions causes practical consequences for data treatment, but no serious problems for spectrometer performance. We demonstrate that energy-resolution function, PWR optimization, and duration of spectral periods are essentially not deteriorated. Consequences for the normalization of measured neutron scattering data and mechanical detector implementation are discussed.
Introducing the inverted-geometry time-of-flight backscattering instrument, MARS at SINQ
Authors: Tregenna-Piggott Philip L.W. , Juranyi Fanni , Allenspach Peter
Published: August 2009

The design and performance of the new inverted-geometry time-of-flight backscattering instrument, Mica Analyzer high Resolution inverted time-of-flight backscattering Spectrometer (MARS) located at SINQ, at the Paul Scherrer Institut, is described. The spectrometer boasts high resolution over a large neutron energy transfer range, reaching 1 µeV at the elastic line. The foremost distinguishing feature is the moveable analyzer banks, allowing resolution matching between the primary and secondary instrument, thus achieving optimal intensity. A wide Q-range is obtained by selecting different mica analyzer reflections, rendering MARS a highly versatile spectrometer with applications foreseen across many branches of the physical and biological sciences.
A new thermal triple-axis spectrometer at the research reactor FRJ-2
Authors: Conrad H. , Brückel TH. , Budwig A. , Bussmann K. , Engels R. , Fracassi V. , Heinen J. , Heybutzki H. , Ioffe A. , Küssel E. , Kulessa T. , Pap M. , Schmitz B. , Suxdorf F. , Zeiske T.
Published: August 2009

A high intensity triple-axis spectrometer is described, which has been commissioned only a year before the final shut-down of the FRJ-2 reactor in May 2006. It was designed both as an instrument for quasi-elastic scattering with polarisation analysis on an area detector, and as a triple-axis spectrometer with polarization analysis for measurements of magnetic and nuclear inelastic scattering. The instrument features two exchangeable monochromators (Cu [200] and PG [002]), which enable both horizontal and vertical focusing. High monochromatic neutron current densities at the sample position of up to 4×107cm−2 s−1 (for pyrolytic graphite at 34 meV) and energies of up to 117 meV (with copper) have been achieved at the FRJ-2 (thermal flux density: 3×1014cm−2 s−1). The utilization of 3He filters both as polarizer and analyzer will enable polarization analysis for high-energy neutrons. The spectrometer is presently being prepared for installation at the new Chinese research reactor CARR at the China Institute of Atomic Energy in Fang Shan near Beijing.
Primary spectrometer neutron optics simulations for a new cold neutron backscattering spectrometer
Authors: Bordallo H.N. , Frick B. , Schober H. , Seydel T.
Published: August 2009

The future new cold neutron backscattering spectrometer IN16B at the Institut Laue-Langevin is being designed to maintain the extremely high energy resolution of the existing backscattering spectrometer IN16 (approximately 0.4 µeV full width at half maximum in a standard configuration). Simultaneously, a phase space transformation (PST) device will significantly increase the flux at the sample position at the expense of an acceptably more divergent incoming beam. A wide wavelength band (Δλ/λ ≈ 10%) has to be offered to the PST device in order to achieve a significant flux gain by a factor of at least 4. Thus, IN16B will have to be located at the end of a cold neutron guide, whilst the present IN16 is located at a side position along a guide. In order to optimize the layout of individual components and to estimate the instrument performance, the Monte Carlo simulation programs McStas and VITESS have been used. McStas and VITESS offer a general framework to compose virtual neutron scattering instruments and support both reactor and spallation neutron sources. In this paper, we report on studies to optimize the neutron delivery towards the PST device, with an emphasis on results from McStas. The simulations of IN16B were performed for two different hypothetical guide end positions, namely a shorter guide with 58Ni coating and existing gaps and instruments upstream, and a longer dedicated guide with a ballistic layout and supermirror coating. For the simulations, different models of the available cold neutron moderator sources have been taken into account. A neutron velocity selector and an elliptical focus guide were optimized for the purposes of IN16B.
Intermediate nonlinear regimes of line-tied g mode and ballooning instability
Authors: Zhu P. , Hegna C.C. , Sovinec C.R. , Bhattacharjee A. , Germaschewski K.
Published: August 2009

A theoretical framework has been developed to describe the nonlinear regimes of line-tied g modes in slab geometry and ballooning instabilities in toroidal configurations. Recent experimental observation and numerical simulations demonstrate a persistence of ballooning-like filamentary structures well into the nonlinear stage of edge localized mode (ELM) activity in H-mode plasmas. Our theory is based on an expansion using two small scale lengths, the mode displacement across magnetic flux surfaces and the mode width in the most rapidly varying direction, both normalized by the equilibrium scale length. When the mode displacement across the magnetic flux surface is much less than the mode width in the most rapidly varying direction, the mode is in the linear regime. When the mode displacement grows to the order of the mode width in the rapidly varying direction, the plasma remains incompressible to lowest order, and the Cowley–Artun regime is obtained. The detonation regime, where the nonlinear growth of the mode could be finite-time singular, is accessible when the system is sufficiently close to marginal stability. At higher levels of nonlinearity, the system evolves to the intermediate nonlinear regime, when the mode displacement across the magnetic flux surface becomes comparable to the mode width in the same direction. During this phase, the nonlinear growth of the mode in the parallel and perpendicular directions are coupled, and sound wave physics contributes to nonlinear stability. The governing equations for the line-tied g mode and the ballooning instability in the intermediate nonlinear regime have been derived. A remarkable feature of the nonlinear equations is that solutions of the associated local linear mode equations continue to be valid solutions into the intermediate nonlinear regime in a Lagrangian reference frame. This property has been confirmed in the full ideal MHD simulations of both the line-tied g mode in a shearless slab and the ballooning instability in a tokamak, and may help explain the growth and persistence of the filamentary structures observed in ELM experiments well into the nonlinear phase.
Operational limits during high power long pulses with radiofrequency heating in Tore Supra
Authors: Ekedahl A. , Bucalossi J. , Basiuk V. , Brémond S. , Colas L. , Corre Y. , Delchambre E. , Douai D. , Dumont R. , Dunand G. , Giruzzi G. , Goniche M. , Hong S. , Imbeaux F. , Kazarian F. , Lombard G. , Manenc L. , Meyer O. , Millon L. , Mitteau R. , Monier-Garbet P. , Moreau P. , Pégourié B. , Rimini F.G. , Saint-Laurent F. , Samaille F. , Schwob J.L. , Tsitrone E.
Published: August 2009

Issues related to the limitations and optimization of long pulse operation at high radiofrequency (RF) power levels in the Tore Supra tokamak are presented. An increasing operational limitation was encountered during the experimental campaigns in 2006–2007, affecting the high power and long pulse performance. This limitation was characterized by the sudden appearance of a multifaceted asymmetric radiation from the edge (MARFE), often followed by a disruption. The analyses revealed that the limitation could be linked to over-heating and flaking of the carbon re-deposition layers on the main plasma facing components (PFCs). The carbon deposits on all PFCs were therefore completely removed during the winter shutdown 2007–2008. Following this, a remarkable improvement in the injected power capability was observed, resulting in almost 12 MW of injected power during 10 s, without any of the previous signs of limitation (MARFE, disruption).

Furthermore, the RF antennas are subject to localized heat loads due to RF sheath effects and interaction by fast particles, effects which need to be minimized in particular for long pulse operation. Experimental results concerning the heat load on the antennas, caused by fast ion losses in the presence of magnetic ripple, are presented in this paper.
Edge plasma physics issues for the Fusion Advanced Studies Torus (FAST) in reactor relevant conditions
Authors: Maddaluno G. , Zagórski R. , Ridolfini V. Pericoli , Apicella M.L. , Calabrò G. , Crisanti F. , Cucchiaro A. , Pizzuto A. , Ramogida G.
Published: August 2009

To have reliable predictions of the thermal loads on the divertor plates and of the core plasma purity in the proposed Fusion Advanced Studies Torus (FAST) tokamak, numerical self-consistent simulations have been made for the H-mode and steady-state scenario by using the 2D multi-fluid code COREDIV. In the simulations full W plasma facing components, foreseen for basic operation, as well as liquid lithium divertor targets have been considered. Impurity seeding, for reducing divertor heat loads, was allowed. The overall picture shows that, marginally in the intermediate and, necessarily in the high density H-mode scenarios (average density 〈ne〉 = 2 × 1020 m−3and 5 × 1020 m−3, respectively), impurity seeding should be foreseen with W as target material; however, only a small amount of Ar (0.03% atomic concentration), not affecting the core purity, is sufficient to maintain the divertor peak loads below 18 MW m−2, which represents the safety limit for the W monoblock technology, presently accepted for the ITER divertor tiles. Li always needs additional impurities for decreasing divertor heat loads. At low plasma densities (but ⩾1.3 × 1020 m−3), typical of steady-state regimes, W alone is effective in dissipating the input power by radiative losses, without excessive core contamination. Impurity seeding would lead to excessive W sputtering by Ar and too highZeff. The impact of unmitigated giant (1.5 MJ) type I edge localized modes on the W divertor targets was also analysed: the resulting maximum energy load of 1 MJ m−2, larger than the tolerable one by a factor of 3, seems not difficult to recover by foreseen mitigation tools.
Integrated scenario with type-III ELMy H-mode edge: extrapolation to ITER
Authors: Rapp J. , Corre Y. , Andrew Y. , de Baar M.R. , Beurskens M. , Brezinsek S. , Brix M. , Devaux S. , Eich T. , Felton R. , Fundamenski W. , Giroud C. , Howell D. , Huber A. , Jachmich S. , Joffrin E. , Korotkov A. , Matthews G.F. , McDonald D.C. , Meigs A. , Monier-Garbet P. , Morgan P. , Nunes I. , van Rooij G.J. , Sauter O. , Stamp M.F. , Telesca G. , de Vries P.C. , Zagorski R.
Published: August 2009

One of the most severe problems for fusion reactors is the power load on the plasma facing components. The challenge is to develop operation scenarios, which combine sufficient energy confinement with benign heat loads to the plasma facing components. The radiative type-III ELMy H-mode seems a possible solution for such an integrated ITER scenario. Nitrogen seeded type-III ELMy H-modes for the standard inductive scenario and the high beta stationary hybrid scenario are investigated with respect to their transient and steady-state power fluxes to the divertor, confinement properties, edge operational space, core operational space, plasma purity and MHD behaviour. A large database of highly radiative type-III ELMy H-modes on JET is used for extrapolations to ITER. On this basis the transient heat load should be acceptable for ITER. It was found that the scaling of the confinement time with respect to the ion gyroradius is close to the gyro-Bohm scaling. Scalings with respect to the plasma collisionality suggest that the confinement will be good enough for an ITER scenario at 17 MA with a power amplification factor (Q) of 10 and might be marginally good enough for a Q = 10 scenario at 15 MA. Those extrapolations are supported by simulations with an integrated core/edge model COREDIV. In addition the hybrid scenario with type-III edge localized modes has been proven to have improved edge conditions without any modification of the central plasma current profile, indicating it is compatible with a high beta operation for a steady-state ITER Q = 5 scenario.
Integrated simulation of ELM energy loss and cycle in improved H-mode plasmas
Authors: Hayashi N. , Takizuka T. , Aiba N. , Oyama N. , Ozeki T. , Wiesen S. , Parail V.
Published: August 2009

The energy loss due to an edge localized mode (ELM) crash and its cycle have been studied by using an integrated core transport code with a stability code for peeling–ballooning modes and a transport model of scrape-off-layer (SOL) and divertor plasmas. The integrated code reproduces a series of ELMs with the following characteristics. The ELM energy loss increases with decreasing collisionality and the ELM frequency increases linearly with the input power, as seen in experiments of type-I ELMs. A transport model with the neoclassical transport in the pedestal connected to the SOL parallel transport reproduces a lowered inter-ELM transport in the case of low collisionality so that the ELM loss power is enhanced as observed in experiments. The inter-ELM energy confinement time evaluated from simulation results agrees with the scaling based on the JT-60U data. The steep pressure gradient in the core just beyond the pedestal top, desirable for improved H-mode plasmas with the H
H98y2 factor above unity, is found to enhance the ELM energy loss and reduce the ELM frequency so that the ELM loss power remains constant. The steep pressure gradient in the core beyond the pedestal top broadens eigenfunction profiles of unstable modes and possibly induces subsequent instabilities. In the subsequent instabilities, when a large energy is transported to the vicinity of the separatrix by the instabilities, a subsequent instability arises near the separatrix and makes an additional loss.
Consequences of finite transport on the effectiveness of ECCD for neoclassical tearing mode stabilization in ITER
Authors: Bertelli N. , Westerhof E.
Published: August 2009

One of the main aims of the ITER electron cyclotron resonance heating (ECRH) system, in particular of the Upper Port Launcher, is the control of magnetohydrodynamics instabilities. This control typically requires non-inductively driven currents with a high degree of localization, i.e. with a very narrow profile. A numerical analysis of the effect of the radial diffusion of the EC driven current carrying electrons has been performed in order to estimate the effectiveness of electron cyclotron current drive (ECCD) for neoclassical tearing mode (NTM) stabilization. In particular, Fokker–Planck calculations including radial diffusion for the case of the ITER ECRH Upper Port Launcher are presented. These show a significant decrease in the local current density when radial diffusion at a rate of only 1 m2 s−1 is included and consequently a broadening of the profile with a drop in the predicted efficiency for NTM control. Furthermore, it is shown that a simple formula combining the effect of the radial diffusion and the width of the EC power deposition profile reproduces quite accurately the maximum EC driven current density, which is the more relevant number in determining the NTM suppression figure of merit, for typical ITER parameters.
A retrospective analysis to explore the applicability of fish biomarkers and sediment bioassays along contaminated salinity transects
Authors: Schipper Cor A. , Lahr Joost , van den Brink Paul J. , George Steve G. , Hansen Peter-Diedrich , da Silva de Assis Helena C. , van der Oost Ron , Thain John E. , Livingstone Dave , Mitchelmore Carys , van Schooten Frederik-Jan , Ariese Freek , Murk Albertinka J. , Grinwis Guy C. M. , Klamer Hans , Kater Belinda J. , Postma Jaap F. , van der Werf Bert , Vethaak A. Dick
Published: August 2009

Schipper, C. A., Lahr, J., van den Brink, P. J., George, S. G., Hansen, P-D., da Silva de Assis, H. C., van der Oost, R., Thain, J. E., Livingstone, D., Mitchelmore, C., van Schooten, F-J., Ariese, F., Murk, A. J., Grinwis, G. C. M., Klamer, H., Kater, B. J., Postma, J. F., van der Werf, B., and Vethaak, A. D. 2009. A retrospective analysis to explore the applicability of fish biomarkers and sediment bioassays along contaminated salinity transects. – ICES Journal of Marine Science, 66: 2089–2105. Biological-effects monitoring in estuarine environments is complex as a result of strong gradients and fluctuations in salinity and other environmental conditions, which may influence contaminant bioavailability and the physiology and metabolism of the organisms. To select the most robust and reliable biological-effect methods for monitoring and assessment programmes, a large-scale field study was conducted in two estuarine transects in the Netherlands. The locations ranged from heavily polluted harbour areas (the ports of Rotterdam and Amsterdam) to cleaner coastal and freshwater sites. Assessment methods used included a variety of biomarkers in flounder (Platichthys flesus) and a range of in vitro (sediment extracts) and in vivo bioassays. Multivariate statistical analysis was applied to investigate correlations and relationships between various biological effects and contaminant levels in flounder liver or sediments. Several biological methods seemed to be too much affected by salinity differences for routine use in estuaries. The most discriminative biomarkers in the study were hepatic metallothionein content and biliary 1-OH pyrene in fish. Mechanism-based in vitro assays DR-CALUX and ER-CALUX applied to sediment extracts for screening of potential toxicity were much more responsive than in vivo bioassays with macro-invertebrates using survival as an endpoint.
Progress in modelling herring populations: an individual-based model of growth
Authors: Russo Tommaso , Mariani Stefano , Baldi Paolo , Parisi Antonio , Magnifico Giuseppe , Clausen Lotte Worsøe , Cataudella Stefano
Published: August 2009

Russo, T., Mariani, S., Baldi, P., Parisi, A., Magnifico, G., Clausen, L. W., and Cataudella, S. 2009. Progress in modelling herring populations: an individual-based model of growth. – ICES Journal of Marine Science, 66: 1718–1725. Stock assessment may gain from taking into account individual variations in growth, because size is a key predictor of survival and reproduction. In trying to understand patterns in empirical observations, a major challenge is to model the changes in the size distribution of a cohort with age. We introduce an individual-based growth model that is founded on the use of a stochastic class of processes called subordinators. This modelling approach has several desirable features, because it (i) can take account of both individual and environmental sources of random variations, (ii) has the property of letting size increase monotonically, and (iii) ensures that the mean size-at-age follows the widely accepted von Bertalanffy equation. The parameterization of the model is tested on two Atlantic herring (Clupea harengus) datasets collected from the stocks of North Sea autumn spawners (ICES Divisions IVa, IVb, and IVc) and western Baltic spring spawners (ICES Subarea III). The size distributions obtained from the subordinator model largely match the observed size distributions, suggesting that this approach might be successfully implemented to support the assessment of commercial fish stocks, such as when modelling of size variability is required.
Aberration correction past and present
Authors: Hawkes P. W.
Published: August 2009

Electron lenses are extremely poor: if glass lenses were as bad, we should see as well with the naked eye as with a microscope! The demonstration by Otto Scherzer in 1936 that skilful lens design could never eliminate the spherical and chromatic aberrations of rotationally symmetric electron lenses was therefore most unwelcome and the other great electron optician of those years, Walter Glaser, never ceased striving to find a loophole in Scherzer’s proof. In the wartime and early post-war years, the first proposals for correcting
C
s
were made and in 1947, in a second milestone paper, Scherzer listed these and other ways of correcting lenses; soon after, Dennis Gabor invented holography for the same purpose. These approaches will be briefly summarized and the work that led to the successful implementation of quadupole–octopole and sextupole correctors in the 1990s will be analysed. In conclusion, the elegant role of image algebra in describing image formation and processing and, above all, in developing new methods will be mentioned.