bluuebunny/crossref_metadata_2025 huggingface dataset:
Conjugate ground and multisatellite observations of compression‐related EMIC Pc1 waves and associated proton precipitation
Authors: Usanova M. E. , Mann I. R. , Kale Z. C. , Rae I. J. , Sydora R. D. , Sandanger M. , Søraas F. , Glassmeier K.‐H. , Fornacon K.‐H. , Matsui H. , Puhl‐Quinn P. A. , Masson A. , Vallières X.
Published: July 2010

We present coordinated ground satellite observations of solar wind compression‐related dayside electromagnetic ion cyclotron (EMIC) waves from 25 September 2005. On the ground, dayside structured EMIC wave activity was observed by the CARISMA and STEP magnetometer arrays for several hours during the period of maximum compression. The EMIC waves were also registered by the Cluster satellites for half an hour, as they consecutively crossed the conjugate equatorial plasmasphere on their perigee passes at L ∼ 5. Simultaneously, conjugate to Cluster, NOAA 17 passed through field lines supporting EMIC wave activity and registered a localized enhancement of precipitating protons with energies >30 keV. Our observations suggest that generation of the EMIC waves and consequent loss of energetic protons may last for several hours while the magnetosphere remains compressed. The EMIC waves were confined to the outer plasmasphere region, just inside the plasmapause. Analysis of lower‐frequency Pc5 waves observed both by the Cluster electron drift instrument (EDI) and fluxgate magnetometer (FGM) instruments and by the ground magnetometers show that the repetitive structure of EMIC wave packets observed on the ground cannot be explained by the ultra low frequency (ULF) wave modulation theory. However, the EMIC wave repetition period on the ground was close to the estimated field‐aligned Alfvénic travel time. For a short interval of time, there was some evidence that EMIC wave packet repetition period in the source region was half of that on the ground, which further suggests bidirectional propagation of wave packets.
Quantification of the precipitation loss of radiation belt electrons observed by SAMPEX
Authors: Tu Weichao , Selesnick Richard , Li Xinlin , Looper Mark
Published: July 2010

Based on SAMPEX/PET observations, the rates and the spatial and temporal variations of electron loss to the atmosphere in the Earth's radiation belt were quantified using a drift diffusion model that includes the effects of azimuthal drift and pitch angle diffusion. The measured electrons by SAMPEX can be distinguished as trapped, quasi‐trapped (in the drift loss cone), and precipitating (in the bounce loss cone). The drift diffusion model simulates the low‐altitude electron distribution from SAMPEX. After fitting the model results to the data, the magnitudes and variations of the electron lifetime can be quantitatively determined based on the optimum model parameter values. Three magnetic storms of different magnitudes were selected to estimate the various loss rates of ∼0.5–3 MeV electrons during different phases of the storms and at L shells ranging from L = 3.5 to L = 6.5 (L represents the radial distance in the equatorial plane under a dipole field approximation). The storms represent a small storm, a moderate storm from the current solar minimum, and an intense storm right after the previous solar maximum. Model results for the three individual events showed that fast precipitation losses of relativistic electrons, as short as hours, persistently occurred in the storm main phases and with more efficient loss at higher energies over wide range of L regions and over all the SAMPEX‐covered local times. In addition to this newly discovered common feature of the main phase electron loss for all the storm events and at all L locations, some other properties of the electron loss rates, such as the local time and energy dependence that vary with time or locations, were also estimated and discussed. This method combining model with the low‐altitude observations provides direct quantification of the electron loss rate, a prerequisite for any comprehensive modeling of the radiation belt electron dynamics.
Comparative appraisal of linear inverse models constructed via distinctive parameterizations (comparing distinctly inverted models)
Authors: Chiao Ling‐Yun , Fang Hui‐Yuan , Gung Yuan‐Cheng , Chang Yu‐Hsuan , Hung Shu‐Huei
Published: July 2010

Most geophysical inverse problems deal with models of the continuous Earth structure. The classical Backus‐Gilbert's theory demonstrates that the resolvable model variation is the truth viewed through the resolution kernel that is woven by the data kernels. The actual numerical resolution amounts to the inversion of the Gram matrix formed by the inner products among data kernels. However, due to the usually sizable amount of data constraints and/or imperfection of the forward theory, the practical implementations are usually tackled through certain a priori finite parameterizations based on rather arbitrary choices of bases such as spatial voxels, splines, spherical harmonics, or spherical wavelets. The cross assessment on the consistency among inverse models parameterized or regularized differently has long been downplayed. It is shown in this study that straightforward conversions among different model representations also enable the direct conversions of the Gram matrices. This leads to significant flexibility in formulating the forward data rule in one representation and then carrying out the actual inversion in an alternate domain. Furthermore, it is also fairly easy to convert both the model covariance and resolution matrices across different representations. These conversions thus enable direct assessments across inverse models obtained via different parameterizations and different regularization schemes. An example utilizing preliminary results of an experiment of ambient noise tomography of a plate boundary region of complex tectonics for the northeast coast and offshore area of Taiwan is shown to demonstrate such comparisons.
Thermally stimulated “runaway” downhole flow in a superhydrostatic ocean crustal borehole: Observations, simulations, and inferences regarding crustal permeability
Authors: Davis Earl E. , LaBonte Alison , He Jiangheng , Becker Keir , Fisher Andrew
Published: July 2010

An array of boreholes, drilled through a regionally continuous hydrologically confining layer of sediments into extrusive igneous basement rocks of the Juan de Fuca Ridge eastern flank, has been instrumented with CORK hydrologic observatories for long‐term monitoring and fluid sampling. Omission of seals between nested casing strings reaching into basement at one site created a low‐resistance connection between basement and the overlying water column, and despite the natural superhydrostatic state of basement water at that location, a “runaway” condition of cold seawater downhole flow into the crust was established, which persisted for more than 4 years. The existence of this condition, along with perturbations generated by it and by initial drilling operations observed at a properly sealed hole 2.4 km away, have been used with analytic and finite element model solutions to constrain formation permeability. The minimum threshold permeability allowing stable downhole flow is roughly 4 × 10−13 m2. A value of permeability similar to this (3–4 × 10−13 m2) is estimated on the basis of the elapsed time for initial perturbations to propagate between the sites (∼2.5 days). The amplitude of the long‐term flow perturbation observed at the sealed site (roughly 1.7 kPa) is smaller than that predicted by modeling (5–10 kPa). Models for flow in an anisotropically permeable layer show that this could be the consequence of low vertical permeability (e.g., arising from massive volcanic or sediment interlayering) or high permeability in the direction of the tectonic fabric generated at the ridge axis. Disagreement between the permeabilities estimated here with previous large‐scale estimates appropriate for the cross‐strike direction (the primary direction between the borehole sites) (10−10–10−9 m2) is difficult to reconcile; it is possible that the holes are poorly connected to zones of high permeability that facilitate the large lateral fluid and heat fluxes previously inferred at this young crustal site.
Planning, implementation, and first results of the Tropical Composition, Cloud and Climate Coupling Experiment (TC4)
Authors: Toon Owen B. , Starr David O. , Jensen Eric J. , Newman Paul A. , Platnick Steven , Schoeberl Mark R. , Wennberg Paul O. , Wofsy Steven C. , Kurylo Michael J. , Maring Hal , Jucks Kenneth W. , Craig Michael S. , Vasques Marilyn F. , Pfister Lenny , Rosenlof Karen H. , Selkirk Henry B. , Colarco Peter R. , Kawa Stephan R. , Mace Gerald G. , Minnis Patrick , Pickering Kenneth E.
Published: July 2010

The Tropical Composition, Cloud and Climate Coupling Experiment (TC4), was based in Costa Rica and Panama during July and August 2007. The NASA ER‐2, DC‐8, and WB‐57F aircraft flew 26 science flights during TC4. The ER‐2 employed 11 instruments as a remote sampling platform and satellite surrogate. The WB‐57F used 25 instruments for in situ chemical and microphysical sampling in the tropical tropopause layer (TTL). The DC‐8 used 25 instruments to sample boundary layer properties, as well as the radiation, chemistry, and microphysics of the TTL. TC4 also had numerous sonde launches, two ground‐based radars, and a ground‐based chemical and microphysical sampling site. The major goal of TC4 was to better understand the role that the TTL plays in the Earth's climate and atmospheric chemistry by combining in situ and remotely sensed data from the ground, balloons, and aircraft with data from NASA satellites. Significant progress was made in understanding the microphysical and radiative properties of anvils and thin cirrus. Numerous measurements were made of the humidity and chemistry of the tropical atmosphere from the boundary layer to the lower stratosphere. Insight was also gained into convective transport between the ground and the TTL, and into transport mechanisms across the TTL. New methods were refined and extended to all the NASA aircraft for real‐time location relative to meteorological features. The ability to change flight patterns in response to aircraft observations relayed to the ground allowed the three aircraft to target phenomena of interest in an efficient, well‐coordinated manner.
Direct Sun measurements of NO2 column abundances from Table Mountain, California: Intercomparison of low‐ and high‐resolution spectrometers
Authors: Wang Shuhui , Pongetti Thomas J. , Sander Stanley P. , Spinei Elena , Mount George H. , Cede Alexander , Herman Jay
Published: July 2010

The NO2 total column abundance, was measured with a direct Sun viewing technique using three different instruments at NASA Jet Propulsion Laboratory's (JPL) Table Mountain Facility in California during an instrument intercomparison campaign in July 2007. The instruments are a high‐resolution (∼0.001 nm) Fourier transform ultraviolet spectrometer (FTUVS) from JPL and two moderate‐resolution grating spectrometers, multifunction differential optical absorption spectroscopy (MF‐DOAS) (∼0.8 nm) from Washington State University and Pandora (∼0.4 nm) from NASA Goddard Space Flight Center. FTUVS uses high spectral resolution to determine the absolute NO2 column abundance independently from the exoatmospheric solar irradiance using rovibrational NO2 absorption lines. The NO2 total column is retrieved after removing the solar background using Doppler‐shifted spectra from the east and west limbs of the Sun. The FTUVS measurements were used to validate the independently calibrated measurements of multifunction differential optical absorption spectroscopy (MF‐DOAS) and Pandora. The latter two instruments start with measured high‐Sun spectra as solar references to retrieve relative NO2 columns and then apply modified Langley or “bootstrap” methods to determine the amounts of NO2 in the references to obtain the absolute NO2 columns. The calibration offset derived from the FTUVS measurements is consistent with the values derived from Langley and bootstrap calibration plots of the NO2 slant column measured by the grating spectrometers. The calibrated total vertical column abundances of NO2, from all three instruments are compared showing that MF‐DOAS and Pandora data agree well with each other, and both data sets agree with FTUVS data to within (1.5 ± 4.1)% and (6.0 ± 6.0)%, respectively.
The 16 April 2010 major volcanic ash plume over central Europe: EARLINET lidar and AERONET photometer observations at Leipzig and Munich, Germany
Authors: Ansmann A. , Tesche M. , Groß S. , Freudenthaler V. , Seifert P. , Hiebsch A. , Schmidt J. , Wandinger U. , Mattis I. , Müller D. , Wiegner M.
Published: July 2010

The optically thickest volcanic ash plume ever measured over Germany was monitored with multiwavelength Raman lidars and Sun photometer at Leipzig and Munich. When this ash layer, originating from the Eyjafjoll eruptions in southern Iceland, crossed Leipzig between 2.5 and 6 km height on 16 April 2010, the total 500 nm aerosol optical depth reached 1.0, and the ash–related optical depth was about 0.7. Volume light–extinction coefficients (40–75–minute mean values) measured over Leipzig and Munich at 355 and 532 nm reached values of 400–600 Mm−1 and ash mass concentrations were on the order of 1000 ± 350 μg/m3 in the center of the main ash layer. Extinction–to–backscatter ratios ranged from 55 ± 5 sr (Munich) to 60 ± 5 sr (Leipzig) in the main ash layer, and the particle linear depolarization ratio was close to 0.35 at both wavelengths. Rather low photometer–derived Ångström exponents (500–1640 nm wavelength range) indicated the presence of a significant amount of large ash particles with diameters >20 μm.
Role of slowly settling particles in the ocean carbon cycle
Authors: Alonso‐González Iván J. , Arístegui Javier , Lee Cindy , Sanchez‐Vidal Anna , Calafat Antoni , Fabrés Joan , Sangrá Pablo , Masqué Pere , Hernández‐Guerra Alonso , Benítez‐Barrios Verónica
Published: July 2010

Here we present results from sediment traps that separate particles as a function of their settling velocity, which were moored in the Canary Current region over a 1.5‐year period. This study represents the longest time series using “in situ” particle settling velocity traps to date and are unique in providing year‐round estimates. We find that, at least during half of the year in subtropical waters (the largest ocean domain), more than 60% of total particulate organic carbon is contained in slowly settling particles (0.7–11 m d−1). Analyses of organic biomarkers reveal that these particles have the same degradation state, or are even fresher than rapidly sinking particles. Thus, if slowly settling particles dominate the exportable carbon pool, most organic matter would be respired in surface waters, acting as a biological source of CO2 susceptible to exchange with the atmosphere. In the context of climate change, if the predicted changes in phytoplankton community structure occur, slowly settling particles would be favored, affecting the strength of the biological pump in the ocean.
Groundwater processes in Hebes Chasma, Mars
Authors: Grindrod Peter M. , Balme Matthew R.
Published: July 2010

We describe a conceptual model of groundwater processes at Hebes Chasma, Mars, which can account for the distribution of hydrated minerals and their subsequent evolution. At Hebes Chasma, pressure gradients set up by the large central mound, Hebes Mensa, could cause groundwater to be sourced predominantly from beneath the central region, if such water were present. Evaporation of upwelling groundwater would cause monohydrates to form at or near the surface through efflorescence, and polyhydrates to form inside the central mound through subflorescence. This crystallization could lead to an excess pore pressure, causing large‐scale weakening and subsequent collapse that can reveal the interior polyhydrated deposits. If evaporation is high compared to groundwater inflow, then increased crystallization would promote the formation of collapse zones. If evaporation is low compared to groundwater inflow then there would be a greater chance for water reaching the surface and the possible formation of karst landforms.
Transit time scattering of energetic electrons due to equatorially confined magnetosonic waves
Authors: Bortnik J. , Thorne R. M.
Published: July 2010

Recent analysis using quasilinear theory (QLT) has shown that magnetosonic (MS) waves are able to accelerate electrons to relativistic energies on fast time scales (∼1 day). However, the large obliquity of the wave and typical equatorial confinement of the MS wave power create conditions that bring into question the fundamental applicability of QLT to this problem. In this paper, a test particle code is used to model the interaction of energetic electrons with fast MS waves, to test the results of QLT analysis, and to investigate any potential nonlinear effects. It is found that in the expected Landau‐resonant region, test particle results show good agreement with QLT, but outside this region, the spatial confinement of the low‐frequency waves introduces a new source of scattering which we call “transit time diffusion.” Although this mechanism is weaker than resonant scattering, it is nevertheless able to interfere with the Landau resonance to create nulls in the energy‐pitch angle diffusion map, and the scattering persists even when resonant diffusion is completely removed.
Reply to comment by P. M. Bellan on “Comment on ‘Ice iron/sodium film as cause for high noctilucent cloud radar reflectivity’”
Authors: Rapp Markus , Lübken Franz‐Josef
Published: July 2010

There recently has been a debate about whether polar mesosphere summer echoes (PMSE) are caused by radar scattering from electrons in a metal layer on mesospheric ice particle surfaces as proposed by Bellan (2008) or from electrons in the gas phase as has been the conventional assumption for decades. In a comment to Bellan (2008) we showed strong experimental evidence against the metal film hypothesis and concluded that it should be dismissed. In his reply to our comment, Bellan (2010) does not invalidate our arguments but instead criticizes the “classical” PMSE theory which is strongly supported by experiments and is by now accepted by most scientists. In the current reply, we address this criticism point by point and conclude that the arguments presented by Bellan (2010) neither invalidate our criticism of the metal film hypothesis nor do they question the “classical” PMSE theory.
Atrial Natriuretic Peptide is Eliminated from the Brain by Natriuretic Peptide Receptor-C-Mediated Brain-to-Blood Efflux Transport at the Blood—Brain Barrier
Authors: Ito Shingo , Ohtsuki Sumio , Katsukura Yuki , Funaki Miho , Koitabashi Yusuke , Sugino Akihiko , Murata Sho , Terasaki Tetsuya
Published: July 2010

Cerebral atrial natriuretic peptide (ANP), which is generated in the brain, has functions in the regulation of brain water and electrolyte balance, blood pressure and local cerebral blood flow, as well as in neuroendocrine functions. However, cerebral ANP clearance is still poorly understood. The purpose of this study was to clarify the mechanism of blood–brain (BBB) efflux transport of ANP in mouse. Western blot analysis showed expression of natriuretic peptide receptor (Npr)-A and Npr-C in mouse brain capillaries. The brain efflux index (BEI) method confirmed elimination of [125I]human ANP (hANP) from mouse brain across the BBB. Inhibition studies suggested the involvement of Npr-C in vivo. Furthermore, rapid internalization of [125I]hANP by TM-BBB4 cells (an in vitro BBB model) was significantly inhibited by Npr-C inhibitors and by two different Npr-C-targeted short interfering RNAs (siRNAs). Finally, treatment with 1α,25-dihydroxyvitamin D3(1,25(OH)2D3) significantly increased Npr-C expression in TM-BBB4 cells, as determined by liquid chromatography–tandem mass spectrometry (LC-MS/MS)-based targeted absolute proteomics. Our results indicate that Npr-C mediates brain-to-blood efflux transport of ANP at the mouse BBB as a pathway of cerebral ANP clearance. It seems likely that levels of natriuretic peptides in the brain are modulated by 1,25(OH)2D3through upregulation of Npr-C expression at the BBB.
Inhibition of GSK3β enhances both adhesive and signalling activities of β‐catenin in mouse embryonic stem cells
Authors: Sineva Galina S. , Pospelov Valery A.
Published: July 2010

Background. GSK3β (glycogen synthase kinase 3β) regulates the expression level and activity of various target proteins, including β‐catenin. β‐Catenin is a co‐activator of Wnt‐dependent genes as well as a partner for transmembrane cadherins to mediate cell‐to‐cell adhesion. In some cases, inhibition of GSK3β activity was shown to promote self‐renewal of ESCs (embryonic stem cells), but immediate effects of GSK3β inhibitors in these cells still remain elusive.

Results. Here, we address the effects of GSK3β inhibitors BIO (6‐bromoindirubin‐3′‐oxime) and CHIR99021 on mESCs (mouse ESCs), focusing on modulation of β‐catenin activities. We found that, upon GSK3β inhibition, the colonies of undifferentiated mESCs acquire a more compact morphology. This change is paralleled by two somewhat polar effects: (i) the accumulation of the β‐catenin, which is co‐localized with E‐cadherin at the plasma membrane, and the cytoplasmic, tyrosine unphosphorylated β‐catenin, which is able to bind the GST (glutathione transferase)‐fused cytoplasmic domain of E‐cadherin; and (ii) the accumulation of the tyrosine phosphorylated β‐catenin and its nuclear translocation that is accompanied by activation of the Tcf (T‐cell factor)/β‐catenin‐dependent transcription of Top‐Flash reporter. The Tcf‐mediated activation, however, does not affect most of the analysed Wnt‐responsive genes involved in EMT (epithelial—mesenchymal transition) or cell‐cycle progression, suggesting that the adhesive function of β‐catenin is dominant over transcription in undifferentiated mESCs. Treatment with BIO decreases proliferation rates of mESCs. This is not due to apoptosis, but rather to accumulation of cells in G1 phase of the cell cycle and is accompanied by down‐regulation of the c‐myc mRNA content.

Conclusion. Our results suggest that inhibition of GSK3β activity in mESCs enhances both the β‐catenin/E‐cadherin‐mediated adhesion and the Tcf/β‐catenin‐dependent transcription, but does not activate transcription in most of the examined genes involved in EMT and cell cycle progression.
Mechanisms and functions of p38 MAPK signalling
Authors: Cuadrado Ana , Nebreda Angel R.
Published: July 2010

The p38 MAPK (mitogen-activated protein kinase) signalling pathway allows cells to interpret a wide range of external signals and respond appropriately by generating a plethora of different biological effects. The diversity and specificity in cellular outcomes is achieved with an apparently simple linear architecture of the pathway, consisting of a core of three protein kinases acting sequentially. In the present review, we dissect the molecular mechanisms underlying p38 MAPK functions, with special emphasis on the activation and regulation of the core kinases, the interplay with other signalling pathways and the nature of p38 MAPK substrates as a source of functional diversity. Finally, we discuss how genetic mouse models are facilitating the identification of physiological functions for p38 MAPKs, which may impinge on their eventual use as therapeutic targets.
Pharmacogenetics and human genetic polymorphisms
Authors: Daly Ann K.
Published: July 2010

The term pharmacogenetics was first used in the late 1950s and can be defined as the study of genetic factors affecting drug response. Prior to formal use of this term, there was already clinical data available in relation to variable patient responses to the drugs isoniazid, primaquine and succinylcholine. The subject area developed rapidly, particularly with regard to genetic factors affecting drug disposition. There is now comprehensive understanding of the molecular basis for variable drug metabolism by the cytochromes P450 and also for variable glucuronidation, acetylation and methylation of certain drugs. Some of this knowledge has already been translated to the clinic. The molecular basis of variation in drug targets, such as receptors and enzymes, is generally less well understood, although there is consistent evidence that polymorphisms in the genes encoding the β-adrenergic receptors and the enzyme vitamin K epoxide reductase is of clinical importance. The genetic basis of rare idiosyncratic adverse drug reactions had also been examined. Susceptibility to reactions affecting skin and liver appears to be determined in part by the HLA (human leucocyte antigen) genotype, whereas reactions affecting the heart and muscle may be determined by polymorphisms in genes encoding ion channels and transporters respectively. Genome-wide association studies are increasingly being used to study drug response and susceptibility to adverse drug reactions, resulting in identification of some novel pharmacogenetic associations.
Large-scale statistical analysis of early failures in Cu electromigration, Part II: Scaling behavior and short-length effects
Authors: Gall Martin , Hauschildt Meike , Hernandez Richard
Published: July 2010

The first part of this study, presented in a separate paper, focused on the early failure mechanisms in down-flow electromigration. Since bimodality can occur at very small percentage levels, specific test structures were designed based on the Wheatstone Bridge technique. The use of these structures enabled a tested sample size past 800,000 for the 90 nm technology node, allowing a direct analysis of electromigration failure mechanisms at the single-digit ppm regime. The activation energy for the down-flow early failure mechanism was determined to be 0.83±0.01 eV, significantly lower than the usually reported activation energy of about 0.90 eV for electromigration-induced diffusion along Cu/SiCN interfaces. Very short experimental lifetimes due to small, slit-shaped voids under vias were found to control the chip lifetime at operating conditions. In this second part of our large-scale, statistical study, we will discuss the electromigration scaling behavior across 90, 65, and 45 nm technologies. Results indicate that the early failure mechanism follows the expected dependency, i.e., the lifetimes scale with the interconnect line height and the critical void size. The slitlike character of the early failure void morphology also raises concerns about the validity of the short-length effect for this mechanism. A very small amount of Cu depletion may cause failure even before a stress gradient is established. We therefore conducted large-scale statistical experiments close to the critical current density-length product (jL)∗. The results indicate that at very small failure percentages, the critical product extrapolates to about 2100±300 A/cm for SiCOH-based dielectrics in 90 nm technology. This value represents a decrease from the previously determined (jL)∗ product of about 3000±500 A/cm for the same dielectric material and technology node, acquired with single link interconnects. Utilizing the advantages of the Wheatstone Bridge technique, the total sample size encompassing 90, 65, and 45 nm technologies was increased past 1.2×106.
Anomalous diffusion in the interphase cell nucleus: The effect of spatial correlations of chromatin
Authors: Fritsch Christian C. , Langowski Jörg
Published: July 2010

The metabolism of a living cell requires a permanent transfer of molecules throughout the cell and beyond its bounds. Within cell nuclei, molecules are predominantly driven by diffusion, which is influenced by the chromatin network. We propose a quantity related to the pair correlation function to measure the diffusion-relevant clumpiness of chromatin. Using Monte Carlo lattice simulations, we investigate to what extent diffusion can be anomalous due to obstruction by the chromatin network. Chromatin is simulated by a wormlike chain on a lattice, which exhibits different types of loop-induced compartmentalization on a subchromosomal level. Our simulation results show that the proposed measure of clumpiness is suitable to quantify the compartmentalization of chromatin and to connect it to diffusion anomaly parameters, critical molecule sizes for trapping and the transition lengths at which diffusion becomes normal at long times.
Spatially uniform calibration of a liquid xenon detector at low energies using K83mr
Authors: Manalaysay A. , Undagoitia T. Marrodán , Askin A. , Baudis L. , Behrens A. , Ferella A. D. , Kish A. , Lebeda O. , Santorelli R. , Vénos D. , Vollhardt A.
Published: July 2010

A difficult task with many particle detectors focusing on interactions below ∼100 keV is to perform a calibration in the appropriate energy range that adequately probes all regions of the detector. Because detector response can vary greatly in various locations within the device, a spatially uniform calibration is important. We present a new method for calibration of liquid xenon (LXe) detectors, using the short-lived K83mr. This source has transitions at 9.4 and 32.1 keV, and as a noble gas like Xe, it disperses uniformly in all regions of the detector. Even for low source activities, the existence of the two transitions provides a method of identifying the decays that is free of background. We find that at decreasing energies, the LXe light yield increases, while the amount of electric field quenching is diminished. Additionally, we show that if any long-lived radioactive backgrounds are introduced by this method, they will present less than 67×10−6 events kg−1 day−1 keV−1 in the next generation of LXe dark matter direct detection searches.
Photogating effect as a defect probe in hydrogenated nanocrystalline silicon solar cells
Authors: Li Hongbo B. T. , Schropp Ruud E. I. , Rubinelli Francisco A.
Published: July 2010

The measurement of the spectrally resolved collection efficiency is of great importance in solar cell characterization. Under standard conditions the bias light is a solar simulator or a light source with a similar broadband irradiation spectrum. When a colored blue or red bias light is used instead, an enhanced collection efficiency effect, in the literature known as the photogating effect, can be observed under certain conditions. While most of the published reports on such effect were on solar cells with amorphous silicon based absorber layers, we have shown that the enhanced collection efficiency could be also present in thin film silicon solar cells where hydrogenated nanocrystalline silicon (nc-Si:H) is used as the absorber layer. In this article we present detailed experimental results and simulations aiming at a better understanding of this phenomenon. We show that the collection efficiency is strongly dependent on the intensity of bias light and the intensity of the monochromatic light. These experimental results are consistent with the computer predictions made by our code. We also show that the photogating effect is greatly enhanced when nanocrystalline silicon cells are built with an improperly doped p-layer or with a defective p/i interface region due to the reduced internal electric field present in such cells. The existence of this effect further proves that carrier transport in a nc-Si:H solar cell with an i-layer made close to the phase transition regime is influenced to a large extent by drift transport. The study of this effect is proposed as an alternative approach to gain a deeper understanding about the carrier transport scenarios in thin film solar cells, especially nanocrystalline silicon solar cells.
A new all-digital time differential γ-γ angular correlation spectrometer
Authors: Nagl Matthias , Vetter Ulrich , Uhrmacher Michael , Hofsäss Hans
Published: July 2010

A new digital time differential perturbed angular correlation spectrometer, designed to measure the energy of and coincidence time between correlated detector signals, here correlated γ photons, is presented. The system overcomes limitations of earlier digital approaches and features improved performance and handling. By consequently separating the data recording and evaluation, it permits the simultaneous measurement of decays with several γ-ray cascades at once and avoids the necessity of premeasurement configuration. Tests showed that the spectrometer reaches a time resolution of 460 ps [using a Co60 sample and Lu1.8Y0.2SiO5:Ce (LYSO) scintillators, otherwise better than 100 ps], an energy resolution that is equivalent to the limit of the used scintillation material, and a processing capability of more than 200 000 γ quanta per detector and second. Other possible applications of the presented methods include nuclear spectroscopy, positron emission tomography, time of flight studies, lidar, and radar.
Frequency-feature based antistrong-disturbance signal processing method and system for vortex flowmeter with single sensor
Authors: Xu Ke-Jun , Luo Qing-Lin , Wang Gang , Liu San-Shan , Kang Yi-Bo
Published: July 2010

Digital signal processing methods have been applied to vortex flowmeter for extracting the useful information from noisy output of the vortex flow sensor. But these approaches are unavailable when the power of the mechanical vibration noise is larger than that of the vortex flow signal. In order to solve this problem, an antistrong-disturbance signal processing method is proposed based on frequency features of the vortex flow signal and mechanical vibration noise for the vortex flowmeter with single sensor. The frequency bandwidth of the vortex flow signal is different from that of the mechanical vibration noise. The autocorrelation function can represent bandwidth features of the signal and noise. The output of the vortex flow sensor is processed by the spectrum analysis, filtered by bandpass filters, and calculated by autocorrelation function at the fixed delaying time and at τ=0 to obtain ratios. The frequency corresponding to the minimal ratio is regarded as the vortex flow frequency. With an ultralow-power microcontroller, a digital signal processing system is developed to implement the antistrong-disturbance algorithm, and at the same time to ensure low-power and two-wire mode for meeting the requirement of process instrumentation. The water flow-rate calibration and vibration test experiments are conducted, and the experimental results show that both the algorithm and system are effective.
Tangential soft-x ray imaging for three-dimensional structural studies in a reversed field pinch
Authors: Onchi T. , Ikezoe R. , Oki K. , Sanpei A. , Himura H. , Masamune S.
Published: July 2010

Tangential soft-x ray (SXR) imaging diagnostic has been developed and three-dimensional (3D) structure of the internal magnetic surface has been deduced by comparing the experimental and calculated two-dimensional SXR images in a reversed field pinch. The SXR imaging system, consisting of a MCP, a fluorescent plate, and an intensified charge coupled device camera, has been installed in REversed field pinch of Low-Aspect-ratio eXperiment (RELAX) machine. Major characteristics of an experimental SXR image could be reproduced by numerical calculations of the image using a single island model, suggesting a helical hot core in RELAX. The SXR imaging system could be useful for 3D structural studies when tangential and vertical simultaneous imaging systems would be installed, with appropriate numerical modeling of 3D structure of the magnetic surfaces.
The behavior of NaOH at the air-water interface: A computational study
Authors: Wick Collin D. , Dang Liem X.
Published: July 2010

Molecular dynamics simulations with a polarizable multistate empirical valence-bond model were carried out to investigate NaOH dissociation and pairing in water bulk and at the air-water interface. It was found that NaOH readily dissociates in the bulk and the effect of the air-water interface on NaOH dissociation is fairly minor. Also, NaOH complexes were found to be strongly repelled from the air-water interface, which is consistent with surface tension measurements. At the same time, a very strong preference for the hydroxide anion to be oriented toward the air was found that persisted a few angstroms toward the liquid from the Gibbs dividing surface of the air-water interface. This was due to a preference for the hydroxide anion to have its hydrogen pointing toward the air and the fact that the sodium ion was more likely to be found near the hydroxide oxygen than hydrogen. As a consequence, the simulation results show that surfaces of NaOH solutions should be negatively charged, in agreement with experimental observations, but also that the hydroxide has little surface affinity. This provides the possibility that the surface of water can be devoid of hydroxide anions, but still have a strong negative charge.
Instabilities and transient behaviors of a liquid film flowing down a porous inclined plane
Authors: Liu Rong , Liu Qiusheng
Published: July 2010

The nonmodal linear stability of a falling film over a porous inclined plane has been investigated. The base flow is driven by gravity. We use Darcy’s law to describe the flow in the porous medium. A simplified one-sided model is used to describe the fluid flow. In this model, the influence of the porous layer on the flow in the film can be identified by a parameter β. The instabilities of a falling film have traditionally been investigated by linearizing the governing equations and testing for unstable eigenvalues of the linearized problem. However, the results of eigenvalue analysis agree poorly in many cases with experiments, especially for shear flows. In the present paper, we have studied the linear stability of three-dimensional disturbances using the nonmodal stability theory. Particular attentions are paid to the transient behavior rather than the long time behavior of eigenmodes predicted by traditional normal mode analysis. The transient behaviors of the response to external excitations and the response to initial conditions are studied by examining the pseudospectral structures and the energy growth function G(t). Before we study the nonmodal stability of the system, we extend the results of long-wave analysis in previous works by examining the linear stabilities for streamwise and spanwise disturbances. Results show that the critical conditions of both the surface mode and the shear mode instabilities are dependent on β for streamwise disturbances. However, the spanwise disturbances have no unstable eigenvalue.
Ab initio energy landscape of LiF clusters
Authors: Doll K. , Schön J. C. , Jansen M.
Published: July 2010

A global search for possible LiF cluster structures is performed up to (LiF)8. The method is based on simulated annealing, where all the energies are evaluated on the ab initio level. In addition, the threshold algorithm is employed to determine the energy barriers for the transitions among these structures, for the cluster (LiF)4, again on the ab initio level, and the corresponding tree graph is obtained.
Ab initio study of the 1 Δ2-X̃ Π2 electronic transition of C2As
Authors: Jerosimić Stanka , Stojanović Ljiljana , Perić Miljenko
Published: July 2010

We report the results of ab initio calculations on the 1 Δ2-X̃ Π2 spectral system of C2As. The present study is closely related to the recent comprehensive experimental and theoretical work by Wei et al. [J. Chem. Phys. 129, 134307 (2008)]. By means of the state-average complete active space self-consistent field and multireference configuration interaction approach, we computed the vertical excitation energies to the low-lying doublet electronic species, potential surfaces and spin-orbit constants for the X̃ Π2 and 1 Δ2 states, as well as the components of the electric dipole moment for the transition between these two species. Using these data, we calculated the vibronic energy levels, the spin-orbit structure of the spectrum, and the vibronic transition moments of the X̃ Π2-1 Δ2 system. The results of the present study for the X Π2 state agree with those derived from experimental findings by Wei et al., they elucidate the vibronic and spin-orbit structure in the 1 Δ2 species, and offer predictions for experimental searches of heretofore unobserved electronic states.
Coherent interfacial bonding on the FeAs tetrahedron in Fe/Ba(Fe1−xCox)2As2 bilayers
Authors: Thersleff T. , Iida K. , Haindl S. , Kidszun M. , Pohl D. , Hartmann A. , Kurth F. , Hänisch J. , Hühne R. , Rellinghaus B. , Schultz L. , Holzapfel B.
Published: July 2010

We demonstrate the growth of epitaxial Fe/Ba(Fe1−xCox)2As2 bilayers on MgO(001) and (La,Sr)(Al,Ta)O3(001) single crystal substrates using pulsed laser deposition (PLD). This architecture produces a coherent interfacial bond between body-centered cubic iron and Ba(Fe1−xCox)2As2 (Ba–122). The superconducting transition temperatures for both bilayers remain close to that of the PLD target. Direct observation of interfacial bonding between Fe and the Ba–122 FeAs sublattice by atomic resolution transmission electron microscopy implies that this bilayer architecture may work for other iron pnictide systems and pave the way for their fabrication into superconducting/ferromagnetic heterostructures.
Magnetic field induced inversion in the effect of particle size on powder cohesiveness
Authors: Espin M. J. , Valverde J. M. , Quintanilla M. A. S. , Castellanos A.
Published: July 2010

Experimental measurements are reported on the tensile yield stress of magnetofluidized beds of fine magnetic powders operated in the cross-flow configuration. In the absence of externally applied magnetic field the yield stress of the powder depends on particle size as expected, i.e., it increases as bead size is decreased. This trend is however inverted when an external magnetic field is applied. It is suggested that the average orientation of interparticle contacts relative to the direction of the field as affected by particle size plays a relevant role on the magnetic yield stress of these systems.
The effect of volume fraction concentration on the thermal conductivity and thermal diffusivity of nanofluids: Numerical and experimental
Authors: Ali Faris Mohammed , Yunus W. Mahmood Mat , Moksin Mohd Maarof , Talib Zainal Abidin
Published: July 2010

This article reports on the effect of aluminum (Al) volume fraction concentration on the thermal conductivity and thermal diffusivity of Al nanoparticles suspended in water, ethylene glycol, and ethanol based fluids prepared by the one step method. The Al nanoparticles were independently produced and then mixed with a base fluid to produce the nanoparticles suspension. The thermal conductivity and thermal diffusivity of the nanofluids were measured using the hot wire-laser beam displacement technique. The thermal conductivity and thermal diffusivity were obtained by fitting the experimental data to the numerical data simulated for Al in distilled water, ethylene glycol, and ethanol. The thermal conductivity and thermal diffusivity of the nanofluids increase with an increase in the volume fraction concentration.
Photoelectrical imaging and characterization of point contacts in pentacene thin-film transistors
Authors: Tsen Adam W. , Cicoira Fabio , Malliaras George G. , Park Jiwoong
Published: July 2010

We report the spatially resolved electrical response of bottom-contact pentacene thin-film transistors to a scanning, focused laser. We find that pentacene films make point-like electrical contacts to the underlying gold electrodes and are able to image them with diffraction-limited resolution. We can further estimate the interfacial resistance associated with hole-injection at an individual point contact, and show that optical activation of one alone increases device current significantly.
The effect of energy level offset between Ir dopant and carbazole hosts on the emission efficiency
Authors: Kwon Soonnam , Wee Kyung-Ryang , Won Kim Jeong , Kang Sang Ook
Published: July 2010

The interface energy offsets of various carbazole hosts and iridium(III) [bis(4,6-difluorophenyl) pyridinato-N,C2′]-tetrakis(1-pyrazolyl)borate (FIr6) and their influence on the efficiency were investigated. Vacuum level shifted by +0.12 eV for bis(4-(N-carbazolyl)phenyl)dimethylsilane (Me2SiCBP2) and FIr6 interface, which was negligible for other hosts and FIr6 interface. As a result, the hole injection from the host to the guest was almost barrier free to reach a high efficiency of 17.1% in the Me2SiCBP2 based device. It dropped to 14% when N, N′-dicarbazolyl-3,5-benzene (mCP) was used as the host, which is the reminiscent of the existence of a hole injection barrier (−0.16 eV).
Ultraviolet photochemistry of buta-1,3- and buta-1,2-dienes: Laser spectroscopic absolute hydrogen atom quantum yield and translational energy distribution measurements
Authors: Hanf A. , Volpp H.-R. , Sharma P. , Mittal J. P. , Vatsa R. K.
Published: July 2010

Using pulsed H-atom Lyman-α laser-induced fluorescence spectroscopy along with a photolytic calibration approach, absolute H-atom product quantum yields of ϕH-b13d=(0.32±0.04) and ϕH-b12d=(0.36±0.04) were measured under collision-free conditions for the 193 nm gas-phase laser flash photolysis of buta-1,3- and buta-1,2-diene at room temperature, which demonstrate that nascent H-atom formation is of comparable importance for both parent molecules. Comparison of the available energy fraction, fT-b13d=(0.22±0.03) and fT-b12d=(0.13±0.01), released as H+C4H5 product translational energy with results of impulsive and statistical energy partitioning modeling calculations indicates that for both, buta-1,3- and buta-1,2-diene, H-atom formation is preceded by internal conversion to the respective electronic ground state (S0) potential energy surfaces. In addition, values of σb-1,3-d-Lα=(3.5±0.2)×10−17 cm2 and σb-1,2-d-Lα=(4.4±0.2)×10−17 cm2 for the previously unknown Lyman-α (121.6 nm) radiation photoabsorption cross sections of buta-1,3- and buta-1,2-diene in the gas-phase were determined.
Surface morphology and magnetic anisotropy of obliquely deposited Co/Si(111) films
Authors: Fang Ya-Peng , He Wei , Liu Hao-Liang , Zhan Qing-Feng , Du Hai-Feng , Wu Qiong , Yang Hai-Tao , Zhang Xiang-Qun , Cheng Zhao-Hua
Published: July 2010

We report an investigation on magnetic anisotropy of Co/Si(111) films deposited at oblique incidence. An in-plane uniaxial magnetic anisotropy (UMA) with the easy axis perpendicular to the incident flux plane was observed to superimpose on sixfold magnetocrystalline anisotropy of Co films. We built a total energy model to investigate the magnetization reversal mechanism around hard axis. The simulated value of UMA is Ku=1.7×105 erg/cm3, which is consistent with Kshape=1.1×105 erg/cm3 calculated from scanning tunneling microscope image. This good agreement suggests the in-plane UMA is mainly originated from the shape of the oblique deposited Co stripes.
Optoelectrofluidic field separation based on light-intensity gradients
Authors: Lee Sanghyun , Park Hyun Jin , Yoon Jin Sung , Kang Kwan Hyoung
Published: July 2010

Optoelectrofluidic field separation (OEFS) of particles under light -intensity gradient (LIG) is reported, where the LIG illumination on the photoconductive layer converts the short-ranged dielectrophoresis (DEP) force to the long-ranged one. The long-ranged DEP force can compete with the hydrodynamic force by alternating current electro-osmosis (ACEO) over the entire illumination area for realizing effective field separation of particles. In the OEFS system, the codirectional illumination and observation induce the levitation effect, compensating the attenuation of the DEP force under LIG illumination by slightly floating particles from the surface. Results of the field separation and concentration of diverse particle pairs (0.82–16 μm) are well demonstrated, and conditions determining the critical radius and effective particle manipulation are discussed. The OEFS with codirectional LIG strategy could be a promising particle manipulation method in many applications where a rapid manipulation of biological cells and particles over the entire working area are of interest.