bluuebunny/crossref_metadata_2025 huggingface dataset:
The dependence of contrail formation on the weather pattern and altitude in the North Atlantic
Authors: Irvine E. A. , Hoskins B. J. , Shine K. P.
Published: June 2012

Aircraft flying through cold ice‐supersaturated air produce persistent contrails which contribute to the climate impact of aviation. Here, we demonstrate the importance of the weather situation, together with the route and altitude of the aircraft through this, on estimating contrail coverage. The results have implications for determining the climate impact of contrails as well as potential mitigation strategies. Twenty‐one years of re‐analysis data are used to produce a climatological assessment of conditions favorable for persistent contrail formation between 200 and 300 hPa over the north Atlantic in winter. The seasonal‐mean frequency of cold ice‐supersaturated regions is highest near 300 hPa, and decreases with altitude. The frequency of occurrence of ice‐supersaturated regions varies with large‐scale weather pattern; the most common locations are over Greenland, on the southern side of the jet stream and around the northern edge of high pressure ridges. Assuming aircraft take a great circle route, as opposed to a more realistic time‐optimal route, is likely to lead to an error in the estimated contrail coverage, which can exceed 50% for westbound north Atlantic flights. The probability of contrail formation can increase or decrease with height, depending on the weather pattern, indicating that the generic suggestion that flying higher leads to fewer contrails is not robust.
Dust transport from non‐East Asian sources to the North Pacific
Authors: Hsu Shih‐Chieh , Huh Chih‐An , Lin Chuan‐Yao , Chen Wei‐Nai , Mahowald Natalie M. , Liu Shaw‐Chen , Chou C. C. K. , Liang Mao‐Chang , Tsai Chuen‐Jinn , Lin Fei‐Jan , Chen Jen‐Ping , Huang Yi‐Tang
Published: June 2012

It is generally thought that East Asia dominates the supply of eolian dust to the North Pacific. Here we show the first data‐based evidence of dust primarily from non‐East Asian sources even during March 2010 when a super dust storm from East Asia struck the western Pacific. Chemical characteristics of aerosol samples collected at a high‐mountain site in Taiwan show variable inputs from eolian dust and biomass burning. From backward trajectory analyses, satellite observation and model simulation, dust origins can be traced to the Middle East and North Africa, suggesting an integrated source from the global dust belt. Our global model results demonstrate that dust deposition in the North Pacific is primarily contributed by non‐East Asian sources with an eastward decrease along the Westerlies.
On near‐tail bubble penetration into geosynchronous altitude
Authors: Kim H.‐S. , Lee D.‐Y. , Ohtani S. , Park M.‐Y. , Ahn B.‐H.
Published: June 2012

Dipolarization of the magnetic field at the near‐Earth tail is usually associated with the local reduction of pV5/3 compared to that of the background, where p is the plasma pressure and V is the volume of the unit magnetic flux tube. This can be interpreted as a bubble, which can propagate earthward by the interchange process. How deep such a bubble can penetrate earthward, and what is the critical factor are critical questions that need to be answered. In this paper, we examine these issues by comparing near‐tail observations by inner probes of THEMIS with geosynchronous magnetic observations by GOES. We identified a number of bubble events associated with near‐tail dipolarization, which we call “tail bubble,” and checked geosynchronous disturbances. We find a statistical trend that geosynchronous disturbance is more likely to occur when associated with (or when hit by) an earthward moving tail bubble with a more‐depleted pV5/3. We estimated the background pV5/3 profile statistically and used it to determine expected equilibrium (or stop) positions for earthward moving bubbles where the bubble's pV5/3 is equal to that of the background. Statistically, we find that the equilibrium position is more inward for tail bubbles with a lower pV5/3, for which the probability of causing geosynchronous disturbance is higher. For example, the probability of a tail bubble being associated with geosynchronous disturbance is 75% if the bubble's equilibrium position is <8 RE. However, for all the events studied here, the bubble equilibrium positions are still outside the geosynchronous altitude. Although this result may be subject to change due to the uncertainty in estimating pV5/3 and the limited number of the events identified near geosynchronous altitude, we suggest that an overshooting of the penetrating bubbles beyond equilibrium positions is a possible explanation.
Non‐Fickian dispersion of groundwater age
Authors: Engdahl Nicholas B. , Ginn Timothy R. , Fogg Graham E.
Published: June 2012

We expand the governing equation of groundwater age to account for non‐Fickian dispersive fluxes using continuous random walks. Groundwater age is included as an additional (fifth) dimension on which the volumetric mass density of water is distributed and we follow the classical random walk derivation now in five dimensions. The general solution of the random walk recovers the previous conventional model of age when the low‐order moments of the transition density functions remain finite at their limits and describes non‐Fickian age distributions when the transition densities diverge. Previously published transition densities are then used to show how the added dimension in age affects the governing differential equations. Depending on which transition densities diverge, the resulting models may be nonlocal in time, space, or age and can describe asymptotic or preasymptotic dispersion. A joint distribution function of time and age transitions is developed as a conditional probability and a natural result of this is that time and age must always have identical transition densities. This implies that a transition density defined for age can substitute for a density in time and this has implications for transport model parameter estimation. We present examples of simulated age distributions from a geologically based, heterogeneous domain that exhibit non‐Fickian behavior and show that the non‐Fickian model provides better descriptions of the distributions than the Fickian model.
Mama Grizzly and the polar bears
Authors: Jacobs Howy
Published: June 2012

Mis‐reporting of the science behind climate change has called into question the judgement and integrity of scientists. Howy argues that better communication between scientists and journalists is needed, to restore public confidence in both.
Mutant p53 interactome identifies nardilysin as a p53R273H‐specific binding partner that promotes invasion
Authors: Coffill Cynthia R , Muller Patricia A J , Oh Hue Kian , Neo Suat Peng , Hogue Kelly A , Cheok Chit Fang , Vousden Karen H , Lane David P , Blackstock Walter P , Gunaratne Jayantha
Published: June 2012

The invasiveness of tumour cells depends on changes in cell shape, polarity and migration. Mutant p53 induces enhanced tumour metastasis in mice, and human cells overexpressing p53R273H have aberrant polarity and increased invasiveness, demonstrating the ‘gain of function’ of mutant p53 in carcinogenesis. We hypothesize that p53R273H interacts with mutant p53‐specific binding partners that control polarity, migration or invasion. Here we analyze the p53R273H interactome using stable isotope labelling by amino acids in cell culture and quantitative mass spectrometry, and identify at least 15 new potential mutant p53‐specific binding partners. The interaction of p53R273H with one of them—nardilysin (NRD1)—promotes an invasive response to heparin binding–epidermal growth factor‐like growth factor that is p53R273H‐dependant but does not require Rab coupling protein or p63. Advanced proteomics has thus allowed the detection of a new mechanism of p53‐driven invasion.
Group I and II mammalian PAKs have different modes of activation by Cdc42
Authors: Baskaran Yohendran , Ng Yuen‐Wai , Selamat Widyawilis , Ling Felicia Tay Pei , Manser Ed
Published: June 2012

p21‐activated kinases (PAKs) are Cdc42 effectors found in metazoans, fungi and protozoa. They are subdivided into PAK1‐like (group I) or PAK4‐like (group II) kinases. Human PAK4 is widely expressed and its regulatory mechanism is unknown. We show that PAK4 is strongly inhibited by a newly identified auto‐inhibitory domain (AID) formed by amino acids 20 to 68, which is evolutionarily related to that of other PAKs. In contrast to group I kinases, PAK4 is constitutively phosphorylated on Ser 474 in the activation loop, but held in an inactive state until Cdc42 binding. Thus, group II PAKs are regulated through conformational changes in the AID rather than A‐loop phosphorylation.
Accelerated aging: a low energy, solvent-free alternative to solvothermal and mechanochemical synthesis of metal–organic materials
Authors: Cliffe Matthew J. , Mottillo Cristina , Stein Robin S. , Bučar Dejan-Krešimir , Friščić Tomislav
Published: June 2012

We describe a conceptually novel “accelerated aging” approach for the synthesis of metal–organic materials.
Desulfovibrio vulgaris bacterioferritin uses H2O2 as a co-substrate for iron oxidation and reveals DPS-like DNA protection and binding activities
Authors: Timóteo Cristina G. , Guilherme Márcia , Penas Daniela , Folgosa Filipe , Tavares Pedro , Pereira Alice S.
Published: June 2012

A gene encoding Bfr (bacterioferritin) was identified and isolated from the genome of Desulfovibrio vulgaris cells, and overexpressed in Escherichia coli. In vitro, H2O2 oxidizes Fe2+ ions at much higher reaction rates than O2. The H2O2 oxidation of two Fe2+ ions was proven by Mössbauer spectroscopy of rapid freeze-quenched samples. On the basis of the Mössbauer parameters of the intermediate species we propose that D. vulgaris Bfr follows a mineralization mechanism similar to the one reported for vertebrate H-type ferritins subunits, in which a diferrous centre at the ferroxidase site is oxidized to diferric intermediate species, that are subsequently translocated into the inner nanocavity. D. vulgaris recombinant Bfr oxidizes and stores up to 600 iron atoms per protein. This Bfr is able to bind DNA and protect it against hydroxyl radical and DNase deleterious effects. The use of H2O2 as an oxidant, combined with the DNA binding and protection activities, seems to indicate a DPS (DNAbinding protein from starved cells)-like role for D. vulgaris Bfr.
Redox properties of the disulfide bond of human Cu,Zn superoxide dismutase and the effects of human glutaredoxin 1
Authors: Bouldin Samantha D. , Darch Maxwell A. , Hart P. John , Outten Caryn E.
Published: June 2012

The intramolecular disulfide bond in hSOD1 [human SOD1 (Cu,Zn superoxide dismutase 1)] plays a key role in maintaining the protein's stability and quaternary structure. In mutant forms of SOD1 that cause familial ALS (amyotrophic lateral sclerosis), this disulfide bond is more susceptible to chemical reduction, which may lead to destabilization of the dimer and aggregation. During hSOD1 maturation, disulfide formation is catalysed by CCS1 (copper chaperone for SOD1). Previous studies in yeast demonstrate that the yeast GSH/Grx (glutaredoxin) redox system promotes reduction of the hSOD1 disulfide in the absence of CCS1. In the present study, we probe further the interaction between hSOD1, GSH and Grxs to provide mechanistic insight into the redox kinetics and thermodynamics of the hSOD1 disulfide. We demonstrate that hGrx1 (human Grx1) uses a monothiol mechanism to reduce the hSOD1 disulfide, and the GSH/hGrx1 system reduces ALS mutant SOD1 at a faster rate than WT (wild-type) hSOD1. However, redox potential measurements demonstrate that the thermodynamic stability of the disulfide is not consistently lower in ALS mutants compared with WT hSOD1. Furthermore, the presence of metal cofactors does not influence the disulfide redox potential. Overall, these studies suggest that differences in the GSH/hGrx1 reaction rate with WT compared with ALS mutant hSOD1 and not the inherent thermodynamic stability of the hSOD1 disulfide bond may contribute to the greater pathogenicity of ALS mutant hSOD1.
The RNA-binding protein CUG-BP1 increases survivin expression in oesophageal cancer cells through enhanced mRNA stability
Authors: Chang Elizabeth T. , Donahue James M. , Xiao Lan , Cui Yuhong , Rao Jaladanki N. , Turner Douglas J. , Twaddell William S. , Wang Jian-Ying , Battafarano Richard J.
Published: June 2012

Survivin, a member of the IAP (inhibitor of apoptosis protein) family, plays important roles in maintaining cellular homoeostasis and regulating cell-cycle progression. This IAP is overexpressed in oesophageal cancer cells, leading to uncontrolled cell growth and resistance to apoptosis. CUG-BP1 (CUG-binding protein 1) is an RNA-binding protein that regulates the stability and translational efficiency of target mRNAs. In the present paper, we report that CUG-BP1 is overexpressed in oesophageal cancer cell lines and human oesophageal cancer specimens. CUG-BP1 associates with the 3′-untranslated region of survivin mRNA, thereby stabilizing the transcript and elevating its expression in oesophageal cancer cells. Our results show that overexpression of CUG-BP1 in oesophageal epithelial cells results in increased survivin mRNA stability and consequently survivin protein expression. Conversely, silencing CUG-BP1 in oesophageal cancer cells destabilizes survivin mRNA, lowering the level of survivin protein. In addition, we have found that altering CUG-BP1 expression modulates susceptibility to chemotherapy-induced apoptosis. Overexpression of CUG-BP1 in oesophageal epithelial cells increases resistance to apoptosis, whereas silencing CUG-BP1 makes oesophageal cancer cells more susceptible to chemotherapy-induced apoptosis. Co-transfection experiments with small interfering RNA directed against survivin suggest that the anti-apoptotic role for CUG-BP1 is not entirely dependent on its effect on survivin expression.
Revealing a natural marine product as a novel agonist for retinoic acid receptors with a unique binding mode and inhibitory effects on cancer cells
Authors: Wang Shanshan , Wang Zhao , Lin Shengchen , Zheng Weili , Wang Rui , Jin Shikai , Chen Jinan , Jin Lihua , Li Yong
Published: June 2012

Retinoids display anti-tumour activity on various cancer cells and therefore have been used as important therapeutic agents. However, adverse side effects and RA (retinoic acid) resistance limit further development and clinical application of retinoid-based therapeutic agents. We report in the present paper the identification of a natural marine product that activates RARs (RA receptors) with a chemical structure distinct from retinoids by high-throughput compound library screening. Luffariellolide was uncovered as a novel RAR agonist by inducing co-activator binding to these receptors in vitro, further inhibiting cell growth and regulating RAR target genes in various cancer cells. Structural and molecular studies unravelled a unique binding mode of this natural ligand to RARs with an unexpected covalent modification on the RAR. Functional characterization further revealed that luffariellolide displays chemotherapeutic potentials for overcoming RA resistance in colon cancer cells, suggesting that luffariellolide may represent a unique template for designing novel non-retinoid compounds with advantages over current RA drugs.
Primary human endothelial cells secrete agents that reduce responsiveness to lysophosphatidic acid (LPA)
Authors: Park Eun Young , Kazlauskas Andrius
Published: June 2012

The plasma level of LPA (lysophosphatidic acid) (200–600 nM) is well within the range that promotes proliferation and migration of vascular ECs (endothelial cells), yet vessels are quiescent and stable. In this report, we considered one explanation for this paradox: that ECs secrete agents that attenuate responsiveness to LPA. Indeed, we observed that CM (conditioned medium) from confluent, quiescent cultures of primary HUVECs (human umbilical vein ECs) contained an agent that inhibited LPA-mediated signalling events and cellular responses. The putative inhibitor, which we tentatively call ILMR (inhibitor of LPA-mediated responsiveness) seemed to act on cells (instead of at the level of LPA) by suppressing the ability of LPA receptor 1 to signal. The amount and/or activity of ILMR was regulated by growth factors; exposing HUVECs to VEGF-A (vascular endothelial growth factor A), but not bFGF (basic fibroblast growth factor), reduced the amount and/or activity of ILMR in CM. We conclude that in addition to promoting angiogenesis directly, VEGF-A can also act indirectly by modulating the bioactivity of angiomodulators such as LPA.
Enhanced phosphorylation of Na+–Cl− co-transporter in experimental metabolic syndrome: role of insulin
Authors: Komers Radko , Rogers Shaunessy , Oyama Terry T. , Xu Bei , Yang Chao-Ling , McCormick James , Ellison David H.
Published: June 2012

In the present study, we investigated the activity of the thiazide-sensitive NCC (Na+–Cl− co-transporter) in experimental metabolic syndrome and the role of insulin in NCC activation. Renal responses to the NCC inhibitor HCTZ (hydrochlorothiazide), as a measure of NCC activity in vivo, were studied in 12-week-old ZO (Zucker obese) rats, a model of the metabolic syndrome, and in ZL (Zucker lean) control animals, together with renal NCC expression and molecular markers of NCC activity, such as localization and phosphorylation. Effects of insulin were studied further in mammalian cell lines with inducible and endogenous expression of this molecule. ZO rats displayed marked hyperinsulinaemia, but no differences in plasma aldosterone, compared with ZL rats. In ZO rats, natriuretic and diuretic responses to NCC inhibition with HCTZ were enhanced compared with ZL rats, and were associated with a decrease in BP (blood pressure). ZO rats displayed enhanced Thr53 NCC phosphorylation and predominant membrane localization of both total and phosphorylated NCC, together with a different profile in expression of SPAK (Ste20-related proline/alanine-rich kinase) isoforms, and lower expression of WNK4. In vitro, insulin induced NCC phosphorylation, which was blocked by a PI3K (phosphoinositide 3-kinase) inhibitor. Insulin-induced reduction in WNK4 expression was also observed, but delayed compared with the time course of NCC phosphorylation. In summary, we report increased NCC activity in hyperinsulinaemic rodents in conjunction with the SPAK expression profile consistent with NCC activation and reduced WNK4, as well as an ability of insulin to induce NCC stimulatory phosphorylation in vitro. Together, these findings indicate that hyperinsulinaemia is an important driving force of NCC activity in the metabolic syndrome with possible consequences for BP regulation.
Effects of prasugrel on platelet inhibition during systemic endotoxaemia: a randomized controlled trial
Authors: Spiel Alexander O. , Derhaschnig Ulla , Schwameis Michael , Bartko Johann , Siller-Matula Jolanta M. , Jilma Bernd
Published: June 2012

P2Y12 receptor antagonists have become a mainstay for the treatment of CVD (cardiovascular diseases). However, they have rarely been evaluated under pathophysiological conditions apart from arterial diseases. We hypothesized interactions between prasugrel and enhanced vWF (von Willebrand Factor) release in a model of systemic inflammation, and compared the pharmacodynamic effects of prasugrel against placebo on agonist-induced platelet aggregation and shear-induced platelet plug formation. A total of 20 healthy male volunteers were enrolled in a double-blind placebo-controlled two-way crossover trial. Each volunteer received either placebo or a 60 mg loading dose of prasugrel 2 h before endotoxin or placebo infusion. Platelet inhibition was measured with MEA (multiple electrode aggregometry), the PFA-100 system and the VASP (vasodilator-stimulated phosphoprotein) phosphorylation assay. Prasugrel blunted various platelet aggregation pathways, including those induced by ADP (−81%), AA (arachidonic acid) (−60%), ristocetin (−75%; P<0.001 for all) and, to a lesser degree, collagen or TRAP (thrombin-receptor-activating peptide). Prasugrel decreased shear-induced platelet plug formation, but vWF release during endotoxaemia partly antagonized the inhibitory effect of prasugrel as measured with the PFA-100 system. Endotoxaemia acutely decreased ristocetin and TRAP-induced platelet aggregation, and enhanced ristocetin-induced aggregation after 24 h. Strong in vivo blockade of P2Y12 inhibits a broad spectrum of platelet aggregation pathways. However, vWF release may reduce prasugrel's effects under high-shear conditions.
The Use and Productivity of Past Tense Morphology in Specific Language Impairment: An Examination of Danish
Authors: Vang Christensen Rikke , Hansson Kristina
Published: June 2012

Purpose

The authors' primary goal was to investigate the potential of past tense inflection as a clinical marker of Danish specific language impairment (SLI). They also wished to test the predictions of the extended optional infinitive (EOI) account and processing based accounts of SLI on Danish.

Method

Using sentence completion and sentence repetition tasks, the authors investigated the use of past tense by 3 groups (
n
= 11 in each group): (a) children with SLI whose ages ranged from 5;2 (years;months) to 7;11; (b) children with typical language development matched on chronological age; and (c) children with typical language development matched on vocabulary.

Results

Participants with SLI were less likely to produce past tense than were both typically developing control groups. In particular, only the children with SLI had difficulties with accurately producing past tense verbs during the sentence repetition task. Past tense accuracy was associated with children’s productive vocabulary levels and proficiency with a nonword repetition task.

Conclusion

Past tense use is potentially a clinical marker of Danish SLI, but more research is needed to confirm this. Results provided mixed support for competing accounts of SLI.

Supplemental Material

https://doi.org/10.23641/asha.6170387
Audiovisual Speech Perception in Children With Developmental Language Disorder in Degraded Listening Conditions
Authors: Meronen Auli , Tiippana Kaisa , Westerholm Jari , Ahonen Timo
Published: June 2012

Purpose

The effect of the signal-to-noise ratio (SNR) on the perception of audiovisual speech in children with and without developmental language disorder (DLD) was investigated by varying the noise level and the sound intensity of acoustic speech. The main hypotheses were that the McGurk effect (in which incongruent visual speech alters the auditory speech percept) would be weaker for children with DLD than for controls and that it would get stronger with decreasing SNR in both groups.

Method

The participants were 8-year-old children with DLD and a sample of children with normal language development. In the McGurk stimuli, the consonant uttered by the voice differed from that articulated by the face. Three sound intensities (24, 36, and 48 dB) and noise levels (−12, 0, and +6 dB) were used. Perception of unisensory visual speech was also measured.

Results

The children with DLD experienced a weak McGurk effect, that is, a weak influence of visual speech on audiovisual speech perception, which remained rather constant across SNR levels. The children with DLD were inaccurate at lipreading.

Conclusions

Children with DLD have problems in perceiving spoken consonants presented audiovisually and visually. The weaker McGurk effect could be accounted for by the poorer lipreading ability of children with DLD.
A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials
Authors: Félix V. , Jannot Y. , Degiovanni A.
Published: June 2012

Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10−1 to 105 Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.
Fourier transform infrared spectroscopy approach for measurements of photoluminescence and electroluminescence in mid-infrared
Authors: Zhang Y. G. , Gu Y. , Wang K. , Fang X. , Li A. Z. , Liu K. H.
Published: June 2012

An improved Fourier transform infrared spectroscopy approach adapting to photoluminescence and electroluminescence measurements in mid-infrared has been developed, in which diode-pumped solid-state excitation lasers were adopted for photoluminescence excitation. In this approach, three different Fourier transform infrared modes of rapid scan, double modulation, and step scan were software switchable without changing the hardware or connections. The advantages and limitations of each mode were analyzed in detail. Using this approach a group of III–V and II–VI samples from near-infrared extending to mid-infrared with photoluminescence intensities in a wider range have been characterized at room temperature to demonstrate the validity and overall performances of the system. The weaker electroluminescence of quantum cascade lasers in mid-infrared band was also surveyed at different resolutions. Results show that for samples with relatively strong photoluminescence or electroluminescence out off the background, rapid scan mode is the most preferable. For weaker photoluminescence or electroluminescence overlapped with background, double modulation is the most effective mode. To get a better signal noise ratio when weaker photoluminescence or electroluminescence signal has been observed in double modulation mode, switching to step scan mode should be an advisable option despite the long data acquiring time and limited resolution.
A full Stokes vector ellipsometry measurement system for in situ diagnostics in dynamic experiments
Authors: Bakshi L. , Eliezer S. , Appelbaum G. , Nissim N. , Perelmutter L. , Mond M.
Published: June 2012

A fast ellipsometry system with a resolution of only a few nanoseconds that can simultaneously measure all four Stokes parameters was developed for use in dynamic experiments. Due to its fine temporal resolution, the system is useful for a wide variety of dynamic setups, two of which are presented, fast foil heating and shock compression. As a test case the optical properties of nickel were measured in a fast foil heating setup. The complex index of refraction and emissivity at 532 nm and in the range of 1000–1900 K are presented. It was found that the emissivity monotonously increases below and above the melting point while an abrupt increase of about 2% was observed at the phase transition. These results are in accordance with the literature. Shock compression experiments included sample-free surface measurements. Samples of 1020 steel were shocked up to 25 GPa on the Hugoniot curve. The measured optical properties under these conditions showed a significant change; the value of the emissivity was doubled.
Tokamak-edge toroidal rotation due to inhomogeneous transport and geodesic curvature
Authors: Stoltzfus-Dueck T.
Published: June 2012

In a model kinetic ion transport equation for the pedestal and scrape-off layer, passing-ion drift orbit excursions interact with spatially inhomogeneous but purely diffusive transport to cause the orbit-averaged diffusivities to depend on the sign of ν∥, preferentially transporting counter-current ions for realistic parameter values. The resulting pedestal-top intrinsic rotation is typically co-current, reaches experimentally relevant values, and is proportional to pedestal-top ion temperature Ti|pt over plasma current Ip, as observed in experiment. The rotation drive is independent of the toroidal velocity and its radial gradient, representing a residual stress. Co-current spin-up at the L-H transition is expected due to increasing Ti|pt and a steepening of the turbulence intensity gradient. A more inboard (outboard) X-point leads to additional co- (counter-) current rotation drive. Beyond intrinsic rotation, comparison of heat and momentum transport reveals that neutral beam injection must be significantly unbalanced in the counter-current direction to cause zero toroidal rotation at the pedestal top.
Generation of tunable, 100–800 MeV quasi-monoenergetic electron beams from a laser-wakefield accelerator in the blowout regime
Authors: Banerjee S. , Powers N. D. , Ramanathan V. , Ghebregziabher I. , Brown K. J. , Maharjan C. M. , Chen S. , Beck A. , Lefebvre E. , Kalmykov S. Y. , Shadwick B. A. , Umstadter D. P.
Published: June 2012

In this paper, we present results on a scalable high-energy electron source based on laser wakefield acceleration. The electron accelerator using 30–80 TW, 30 fs laser pulses, operates in the blowout regime, and produces high-quality, quasi-monoenergetic electron beams in the range 100–800 MeV. These beams have angular divergence of 1–4 mrad, and 5%–25% energy spread, with a resulting brightness 1011 electrons mm−2 MeV−1 mrad−2. The beam parameters can be tuned by varying the laser and plasma conditions. The use of a high-quality laser pulse and appropriate target conditions enables optimization of beam quality, concentrating a significant fraction of the accelerated charge into the quasi-monoenergetic component.
Experimental study of parametric dependence of electron-scale turbulence in a spherical tokamak
Authors: Ren Y. , Guttenfelder W. , Kaye S. M. , Mazzucato E. , Bell R. E. , Diallo A. , Domier C. W. , LeBlanc B. P. , Lee K. C. , Smith D. R. , Yuh H.
Published: June 2012

Electron-scale turbulence is predicted to drive anomalous electron thermal transport. However, experimental study of its relation with transport is still in its early stage. On the National Spherical Tokamak Experiment (NSTX), electron-scale density fluctuations are studied with a novel tangential microwave scattering system with high radial resolution of ±2 cm. Here, we report a study of parametric dependence of electron-scale turbulence in NSTX H-mode plasmas. The dependence on density gradient is studied through the observation of a large density gradient variation in the core induced by an edge localized mode (ELM) event, where we found the first clear experimental evidence of density gradient stabilization of electron-gyro scale turbulence in a fusion plasma. This observation, coupled with linear gyro-kinetic calculations, leads to the identification of the observed instability as toroidal electron temperature gradient (ETG) modes. It is observed that longer wavelength ETG modes, k⊥ρs≲10 (ρs is the ion gyroradius at electron temperature and k⊥ is the wavenumber perpendicular to local equilibrium magnetic field), are most stabilized by density gradient, and the stabilization is accompanied by about a factor of two decrease in electron thermal diffusivity. Comparisons with nonlinear ETG gyrokinetic simulations show ETG turbulence may be able to explain the experimental electron heat flux observed before the ELM event. The collisionality dependence of electron-scale turbulence is also studied by systematically varying plasma current and toroidal field, so that electron gyroradius (ρe), electron beta (βe), and safety factor (q95) are kept approximately constant. More than a factor of two change in electron collisionality, νe*, was achieved, and we found that the spectral power of electron-scale turbulence appears to increase as νe* is decreased in this collisonality scan. However, both linear and nonlinear simulations show no or weak dependence with the electron-ion collision frequency, νe/i. Instead, other equilibrium parameters (safety factor, electron density gradient, for example) affect ETG linear growth rate and electron thermal transport more than νe/i does. Furthermore, electron heat flux predicted by the simulations is found to have an order-of-magnitude spatial variation in the experimental measurement region and is also found to be much smaller than experimental levels except at one radial location we evaluated. The predicted electron heat flux is shown to be strongly anti-correlated with density gradient, which varies for a factor of three in the measurement region, which is in agreement with the density gradient dependence study reported in this paper.
Modeling the propagation of whistler-mode waves in the presence of field-aligned density irregularities
Authors: Streltsov A. V. , Woodroffe J. , Gekelman W. , Pribyl P.
Published: June 2012

We present a numerical study of propagation of VLF whistler-mode waves in a laboratory plasma. Our goal is to understand whistler propagation in magnetic field-aligned irregularities (also called channels or ducts). Two cases are examined, that of a high-frequency (ω>Ωce/2) whistler in a density depletion duct and that of a low-frequency (ω<Ωce/2) whistler in a density enhancement. Results from a numerical simulation of whistler wave propagation are compared to data from the UCLA Los Angeles Physics Teachers Alliance Group plasma device and whistler propagation in pre-existing density depletion and density enhancement ducts is demonstrated.
Comparison of two experimental methods for the mechanical characterization of thin or thick films from the study of micromachined circular diaphragms
Authors: Malhaire C.
Published: June 2012

The purpose of this study was to compare two experimental methods and evaluate the effectiveness of a set of analytical models in order to measure the initial stress and the Young's modulus value of thin and thick film materials. Two types of experiments were performed on micromachined circular diaphragms: bulge testing and vibrometry. The range of validity and accuracy of the analytical models with respect to the vibration of the diaphragms was discussed from the finite element simulations. It was shown that the a/t ratio should be considered carefully to determine the value of the Young's modulus by vibrometry with an acceptable error. A relative error of approximately ±10% on E was obtained for a/t ≤ 750. For 750 ≤ a/t ≤ 1000, the value of the dimensionless parameter k must also be considered. It has been shown that the residual stress value can be obtained with an accuracy of 10% or less, given that k > 12. As an illustration, experimental methods and models were applied to the characterization of a thick electroplated gold film and a sputter-deposited Inconel thin film. Circular structures were defined by vertical sidewalls etched on the back of a Si wafer using the deep reactive ion etching technique. In addition to analytical models, parametric finite element simulations and a design optimization technique were used to determine the material's mechanical properties. The static deflections of the diaphragms were measured as a function of the applied pressure. The resonant frequencies and mode shapes of the vibrating structures were observed under vacuum by white-light interferometric microscopy. For gold, it was found that E = (53 ± 20) GPa and σ0 = (180 ± 10) MPa. For Inconel, it was found that E = (157 ± 14) GPa and σ0 = (172 ± 5) MPa.
Cathodoluminescence insights into the ionic disorder of photocatalytic anatase films
Authors: Pezzotti Giuseppe , Leto Andrea , Battiston Simone , Minella Marco , Zhu Wenliang
Published: June 2012

The nature of ionic disorder and the effect of structural defects on the photocatalytic function of anatase are revisited in the light of direct experimental evidence retrieved on the molecular scale by cathodoluminescence (CL) spectroscopy. CL spectra, collected on different types of photocatalytically efficient or inefficient anatase films, embodied a composite optical response of electron-compensating majority types of ionic disorder in the anatase lattice. This paper describes the dual experimental output obtained by systematically monitoring optically active off-stoichiometry sites, as follows: (i) quantitative analyses of film stoichiometry including the interactions of different lattice-defect populations; and (ii) stability/evolution of off-stoichiometry sites upon post-fabrication annealing cycles and their effects on the photocatalytic activity of the films. CL experiments provided us with direct access to the structural state of the defective anatase lattice, thus unfolding some missing detail about the complex physicochemical interactions behind its photocatalytic efficiency.
Effects of lateral current injection in GaN multi-quantum well light-emitting diodes
Authors: Kivisaari Pyry , Oksanen Jani , Tulkki Jukka
Published: June 2012

In conventional multi-quantum well (MQW) LEDs, typically only one QW emits light due to a very nonuniform carrier distribution. We show by numerical simulations that by adopting a genuinely two-dimensional LED structure enabling lateral hole current injection into the QWs it becomes possible to achieve a more even carrier distribution potentially enabling smaller droop and uniform light emission from all the QWs in the MQW stack. We also show that the uneven emission may be explained with standard current transport models as quasi-Fermi losses between successive quantum wells. We demonstrate our findings by studying three different LED structures and comparing our results to published experimental results.
Approximate inclusion of four-mode couplings in vibrational coupled-cluster theory
Authors: Zoccante Alberto , Seidler Peter , Hansen Mikkel Bo , Christiansen Ove
Published: June 2012

The vibrational coupled cluster (VCC) equations are analyzed in terms of vibrational Møller-Plesset perturbation theory aiming specifically at the importance of four-mode couplings. Based on this analysis, new VCC methods are derived for the calculation of anharmonic vibrational energies and vibrational spectra using vibrational coupled cluster response theory. It is shown how the effect of four-mode coupling and excitations can be efficiently and accurately described using approximations for their inclusion. Two closely related approaches are suggested. The computational scaling of the so-called VCC[3pt4F] method is not higher than the fifth power in the number of vibrational degrees of freedom when up to four-mode coupling terms are present in the Hamiltonian and only fourth order when only up to three-mode couplings are present. With a further approximation, one obtains the VCC[3pt4] model which is shown to scale with at most the fourth power in the number of vibrational degrees of freedom for Hamiltonians with both three- and four-mode coupling levels, while sharing the most important characteristics with VCC[3pt4F]. Sample calculations reported for selected tetra-atomic molecules as well as the larger dioxirane and ethylene oxide molecules support that the new models are accurate and useful.
Theoretical study of the nuclear spin-molecular rotation coupling for relativistic electrons and non-relativistic nuclei
Authors: Aucar Ignacio A. , Gómez Sergio S. , de Azúa Martín C. Ruiz , Giribet Claudia G.
Published: June 2012

A theoretical study of the relation between the relativistic formulation of the nuclear magnetic shielding and spin-rotation tensors is presented. To this end a theoretical expression of the relativistic spin-rotation tensor is formulated, considering a molecular Hamiltonian of relativistic electrons and non-relativistic nuclei. Molecular rotation effects are introduced considering the terms of the Born-Oppenheimer decomposition, which couple the electrons and nuclei dynamics. The loss of the simple relation linking both spectral parameters in the non-relativistic formulation is further analyzed carrying out a perturbative expansion of relativistic effects by means of the linear response within the elimination of the small component approach. It is concluded that relativistic effects on the spin-rotation tensor are less important than those of the nuclear magnetic shielding tensor.
Revisiting the mean-field picture of dipolar effects in solution NMR
Authors: Chen Y. Morris , Branca R. T. , Warren W. S.
Published: June 2012

For more than three decades, the classical or mean-field picture describing the distant dipolar field has been almost always simplified to an effective field proportional to the local longitudinal magnetization, differing only by a scale factor of 1.5 for homomolecular (identical resonance frequency) and heteromolecular interactions. We re-examine the underlying assumptions, and show both theoretically and experimentally that the mathematical framework needs to be modified for modern applications such as imaging. We demonstrate new pulse sequences which produce unexpected effects; for example, modulating an arbitrarily small fraction of the magnetization can substantially alter the frequency evolution. Thus, matched gradient pulse pairs (a seemingly innocuous module in thousands of existing pulse sequences) can alter the time evolution in highly unexpected ways, particularly with small flip angle pulses such as those used in hyperpolarized experiments. We also show that specific gradient pulse combinations can retain only dipolar interactions between unlike spins, and the dipolar field can generate a secular Hamiltonian proportional to Ix.
The steepest S curve of spreading and collecting flows: Discovering the invading tree, not assuming it
Authors: Cetkin E. , Lorente S. , Bejan A.
Published: June 2012

Spreading and collecting flows are united by the flow design known as the S-curve: when plotted versus time, the size of the domain that is filled or emptied has a history that is shaped as an S. Here, we show that the fastest spreading or collecting (i.e., the steepest S curve) is discovered by allowing the tree architecture to morph freely, toward greater access over time, in accord with the constructal law of design in nature. The angles between the lines of the invading flow architecture can be selected such that the overall flow proceeds the fastest, covering the greatest territory at any moment. The design is a sequence of two distinct phenomena: “invasion” by channels and branches that grow fast, and “consolidation” by slow diffusion perpendicular to the channels. Invasion and consolidation collaborate hand-in-glove to facilitate the spreading or collecting over the available finite area or volume.
Note: Measurement of the runaway electrons in the J-TEXT tokamak
Authors: Chen Z. Y. , Zhang Y. , Zhang X. Q. , Luo Y. H. , Jin W. , Li J. C. , Chen Z. P. , Wang Z. J. , Yang Z. J. , Zhuang G.
Published: June 2012

The runaway electrons have been measured by hard x-ray detectors and soft x-ray array in the J-TEXT tokamak. The hard x-ray radiations in the energy ranges of 0.5–5 MeV are measured by two NaI detectors. The flux of lost runaway electrons can be obtained routinely. The soft x-ray array diagnostics are used to monitor the runaway beam generated in disruptions since the soft x-ray is dominated by the interaction between runaway electrons and metallic impurities inside the plasma. With the aid of soft x-ray array, runaway electron beam has been detected directly during the formation of runaway current plateau following the disruptions.
Origin of thickness dependent dc electrical breakdown in dielectrics
Authors: Chen George , Zhao Junwei , Li Shengtao , Zhong Lisheng
Published: June 2012

A model based on space charge dynamics under high dc electric field has been proposed to explain commonly observed thickness dependent breakdown of polymeric material. The formation and dynamics of space charge will result in local electric field enhancement that has a direct impact on dielectric breakdown. The simulation results show that the breakdown depends on the sample thickness with a power index of 0.143, indicating the space charge and its dynamics are responsible for thickness dependent breakdown. The model also predicts the effect of voltage ramping rate on the electrical breakdown strength.
Structural and electrical studies of ultrathin layers with Si0.7Ge0.3 nanocrystals confined in a SiGe/SiO2 superlattice
Authors: Vieira E. M. F. , Martín-Sánchez J. , Rolo A. G. , Parisini A. , Buljan M. , Capan I. , Alves E. , Barradas N. P. , Conde O. , Bernstorff S. , Chahboun A. , Levichev S. , Gomes M. J. M.
Published: June 2012

In this work, SiGe/SiO2 multi-layer (ML) films with layer thickness in the range of a few nanometers were successfully fabricated by conventional RF-magnetron sputtering at 350 °C. The influence of the annealing treatment on SiGe nanocrystals (NCs) formation and crystalline properties were investigated by Raman spectroscopy and grazing incidence x-ray diffraction. At the annealing temperature of 800 °C, where well defined SiGe NCs were observed, a thorough structural investigation of the whole ML structure has been undertaken by Rutherford backscattering spectroscopy, grazing incidence small angle x-ray scattering, high resolution transmission electron microscopy, and annular dark field scanning transmission electron microscopy. Our results show that the onset of local modifications to the ML composition takes place at this temperature for annealing times of the order of a few tens of minutes with the formation of defective regions in the upper portion of the ML structure. Only the very first layers over the Si substrate appear immune to this problem. This finding has been exploited for the fabrication of a defect free metal-oxide-semiconductor structure with a well-defined single layer of SiGe NCs. A memory effect attributed to the presence of the SiGe NCs has been demonstrated by high frequency capacitance-voltage measurements.
Plasmonic absorption enhancement in organic solar cells by nano disks in a buffer layer
Authors: Kim Inho , Seok Jeong Doo , Seong Lee Taek , Seong Lee Wook , Lee Kyeong-Seok
Published: June 2012

We demonstrate using finite-difference-time-domain calculations that embedding Ag nano disks (NDs) in the buffer layers of thin P3HT:PCBM organic solar cells can enhance optical absorption in the active layers at specific wavelength range. We show that the aspect ratio of the NDs is a key parameter for strong plasmonic absorption enhancement. Two different plasmonic absorption bands are observed stemming from optical refractive index differences among the layers surrounding the NDs in the solar cell devices. One absorption band by the surface plasmon mode localized at the interface of indium tin oxide/ND, which is undesirable for plasmonic absorption enhancement in the active layer, become negligible as the aspect ratio of the diameter-to-height increased. The other absorption band by the dipole-like surface plasmon mode, which plays a main role in enhancing the absorption in the active layer, is spectrally tunable by adjusting the aspect ratio of the NDs. The influences of diameter, height, and coverage of the NDs on optical absorption in the active layer are discussed. Embedding the optimal size NDs in the buffer layer leads to the enhanced total absorption in the 50 nm thick active layer by 16% relative to that without the NDs, and the optical absorption keeps enhanced with increasing the active layer thickness up to 90 nm. However, further increases in the active layer thickness are detrimental to absorption enhancement, which is considered to be caused by destructive interference between scattered light by the NDs and incident light.