bluuebunny/crossref_metadata_2025 huggingface dataset:
Runaway breakdown and electrical discharges in thunderstorms
Authors: Milikh Gennady , Roussel‐Dupré Robert
Published: December 2010

This review considers the precise role played by runaway breakdown (RB) in the initiation and development of lightning discharges. RB remains a fundamental research topic under intense investigation. The question of how lightning is initiated and subsequently evolves in the thunderstorm environment rests in part on a fundamental understanding of RB and cosmic rays and the potential coupling to thermal runaway (as a seed to RB) and conventional breakdown (as a source of thermal runaways). In this paper, we describe the basic mechanism of RB and the conditions required to initiate an observable avalanche. Feedback processes that fundamentally enhance RB are discussed, as are both conventional breakdown and thermal runaway. Observations that provide clear evidence for the presence of energetic particles in thunderstorms/lightning include γ‐ray and X‐ray flux intensifications over thunderstorms, γ‐ray and X‐ray bursts in conjunction with stepped leaders, terrestrial γ‐ray flashes, and neutron production by lightning. Intense radio impulses termed narrow bipolar pulses (or NBPs) provide indirect evidence for RB particularly when measured in association with cosmic ray showers. Our present understanding of these phenomena and their enduring enigmatic character are touched upon briefly.
Subsurface Images Shed Light on Past Tsunamis in India
Authors: Nair Rajesh R. , Buynevich Ilya , Goble Ronald J. , Srinivasan P. , Murthy S. G. N. , Kandpal S. C. , Vijaya Lakshmi C. S. , Trivedi D.
Published: December 2010

The 2004 Indian Ocean tsunami caused massive devastation and left a lasting impact along many of the major coastal regions in South Asia, including the coast of Tamil Nadu, a state in the southeastern tip of India. Following the event, sand deposits draped the low‐lying areas and buried the muddy sediments of the coastal plain [Babu et al., 2007; Srinivasalu et al., 2007]. In addition, erosional features related to the tsunami, such as channels and scarps, have been observed along many parts of the coast (Figure 1a). This tsunami, along with a recorded history of intense monsoons, has highlighted the need for focused research on the role of extreme events in shaping the geological character of India's coastal plains.
New AGU Journal on Earth Systems Modeling
Authors: Cook Bill
Published: December 2010

The American Geophysical Union is pleased to announce that effective immediately, it is the new publisher of the Journal of Advances in Modeling Earth Systems (JAMES). JAMES is a peer‐reviewed, open‐access, all‐electronic journal that advances the science of Earth systems modeling by offering high‐quality scientific research articles. JAMES was founded by the Center for Multiscale Modeling of Atmospheric Processes, a U.S. National Science Foundation—sponsored Science and Technology Center, and the journal began publishing peer‐reviewed articles in the summer of 2009. Until now, the journal has been published by the Institute of Global Environment and Society.
Causes and biogeochemical implications of regional differences in silicification of marine diatoms
Authors: Baines Stephen B. , Twining Benjamin S. , Brzezinski Mark A. , Nelson David M. , Fisher Nicholas S.
Published: December 2010

Diatoms facilitate the export of organic carbon and associated nutrient elements in the ocean because their dense opaline silica shells provide ballast to sinking particles. Marine ecosystem models generally assume that cellular silicification is either constant or varies solely due to physiological responses. Using a cell‐specific technique, synchrotron‐based X‐ray fluorescence (SXRF) microscopy, we show that diatom cells in the cold, high‐silicic‐acid waters of the Antarctic Zone of the Southern Ocean (SOAZ) had 6 times more Si per volume than did those inhabiting the warm, low‐silicic‐acid waters of eastern equatorial Pacific (EEP). Ratios of Si:P and Si:S differed less than this because cellular P and S concentrations were higher in SOAZ cells. Resulting differences in excess density and frustule surface area‐to‐volume ratios should result in more efficient removal and slower dissolution of biogenic silica in the SOAZ compared to the EEP. Moreover, the difference between the excess densities of diatoms and nondiatoms was 15‐fold greater in the SOAZ than in the EEP. Several possible causes of the regional differences in silicification are evaluated. Differences in cell volume between regions and additions of silicic acid and iron had minor effects on silicification. Instead, cellular silicification varied substantially among diatom morphological types within each region, suggesting that community composition largely determined the community silicification in these regions. We suggest that ecological processes may cause much larger systematic regional and temporal differences in cellular stoichiometry than is currently accommodated by ecosystem models.
Rapid, continuous streaking of tremor in Cascadia
Authors: Ghosh Abhijit , Vidale John E. , Sweet Justin R. , Creager Kenneth C. , Wech Aaron G. , Houston Heidi , Brodsky Emily E.
Published: December 2010

Nonvolcanic tremor is a recently discovered weak seismic signal associated with slow slip on a fault plane and has potential to answer many questions about how faults move. Its spatiotemporal distribution, however, is complex and varies over different time scales, and the causal physical mechanisms remain unclear. Here we use a beam backprojection method to show rapid, continuous, slip‐parallel streaking of tremor over time scales of several minutes to an hour during the May 2008 episodic tremor and slip event in the Cascadia subduction zone. The streaks propagate across distances up to 65 km, primarily parallel to the slip direction of the subduction zone, both updip and downdip at velocities ranging from 30 to 200 km/h. We explore mainly two models that may explain such continuous tremor streaking. The first involves interaction of slowly migrating creep front with slip‐parallel linear structures on the fault. The second is pressure‐driven fluid flow through structurally controlled conduits on the fault. Both can be consistent with the observed propagation velocities and geometries, although the second one requires unlikely condition. In addition, we put this new observation in the context of the overall variability of tremor behavior observed over different time scales.
Can global models ignore the chemical composition of aerosols?
Authors: Roesler E. L. , Penner J. E.
Published: December 2010

The number of cloud droplets formed from a population of aerosols depends on the aerosol number concentration, NA, the size distribution, and the chemical composition. The cloud albedo effect occurs when increasing NA causes increases to the droplet concentration, ND. We examined the effects of changing aerosol size, composition, and number on ND within the United States. We found that changing the water‐soluble organic carbon (WSOC) fraction from 50% to 0.05% in the fine mode aerosol and from 50% to 95% in the coarse mode aerosol decreased ND by an average of 34%. Our results show that the changes to the aerosol composition cause over a 20% change to ND, a magnitude previously estimated to cause a 1 W m−2 change in radiative forcing. Given the realistic range of aerosol compositions used here, it is not possible for global models to correctly calculate the cloud albedo effect if composition is ignored.
Satellite observations cap the atmospheric organic aerosol budget
Authors: Heald Colette L. , Ridley David A. , Kreidenweis Sonia M. , Drury Easan E.
Published: December 2010

Limited understanding of the production and loss of organic aerosol (OA) to the atmosphere has resulted in poorly constrained source estimates ranging from 140 to 910 TgCyr−1 [Goldstein and Galbally, 2007]. We use satellite observations to quantitatively estimate the atmospheric burden of organic aerosol and the associated production. We find that attributing the mid‐visible continental aerosol optical depth (AOD) observed by the MISR satellite entirely to OA implies a global source of 430 TgCyr−1 of sub‐micron OA. We use a model (GEOS‐Chem) to remove the contribution of inorganic aerosol, dust and soot from the observed AOD and derive a continental OA production of 150 TgCyr−1 (equivalent burden of 2.5 TgC), with 80% uncertainty. This result significantly reduces the uncertainty in the global OA budget and provides an upper limit for the “missing source” of OA.
Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm
Authors: Hosokawa K. , Tsugawa T. , Shiokawa K. , Otsuka Y. , Nishitani N. , Ogawa T. , Hairston M. R.
Published: December 2010

During a magnetic storm on 14–16 December 2006, a polar cap tongue of ionization (TOI) was detected by an all‐sky imager (ASI) at Resolute Bay, Canada (74.73°N, 265.07°E). We investigate the temporal evolution and spatial structure of the TOI in detail by combining the optical data with other observations (e.g., solar wind, GPS total electron content, SuperDARN, and DMSP and NOAA POES satellites). The TOI was observed as a bright and elongated 630 nm airglow plume for 4 h during the main phase of the storm. This interval corresponded to a period of prolonged stable large‐amplitude southward IMF during a coronal mass ejection (CME). One to one and a half hours before the appearance of TOI, the polar cap boundary expanded rapidly far equatorward, and a positive ionospheric storm occurred. This implies that both the “expansion of the high‐latitude plasma convection” and “build up of the source plasma in the midlatitudes” are necessary conditions for the formation of a TOI. Because both of them were triggered by a major southward turning of the IMF, the prolonged large‐amplitude southward IMF orientation in the trailing part of the CME was primarily responsible for the generation of TOI. After its appearance, the TOI exhibited dynamic motion in the dawn to dusk direction. Simultaneous SuperDARN data suggest that a longitudinal progression of subauroral polarization stream controlled this dynamic motion. The optical TOI was found to be a continuous stream elongated in the noon‐midnight direction although it contained some mesoscale patterns. Absence of large‐scale temporal changes in the cusp plasma flow during the stable IMF period allowed the TOI to remain continuous without being broken into polar cap patches. The mesoscale structures within the TOI were probably produced by small‐scale velocity fluctuations in the cusp plasma flow. The TOI as visualized with the all‐sky airglow imager was found to be much more dynamic and much more complicated than we ever thought. The current study indicates that such a behavior of the TOI was presumably caused by a combination of temporal variations in the global‐scale plasma circulation system, expansion and contraction of the polar cap area, and plasma density changes in the dayside low to midlatitudes.
Antibodies targeting Cancer stem cells, A novel pattern in Immunotherapy
Authors: Alam Sarfaraz
Published: December 2010

Antibody targeting of cancer is showing clinical and commercial success after deep research and development over the last 3 decades. They have the great potential to deliver long-term cures but a shift in thinking towards a cancer stem cell (CSC) model for tumour development is certain to have an impact on how antibodies are selected and developed, the targets they bind to and the drugs used in combination with them. CSCs have been identified from many human tumours and share many of the characteristics of normal stem cells such as the ability to renew and metabolically or physically protect themselves from xenobiotic and DNA damage. Targeting CSCs could be a strategy to improve the outcome of cancer therapy. Monoclonal antibodies are clinically and commercially established which makes them great for therapeutic effect.The aim of this review is to examine the biology of cancer stem cells, consider the markers defining them and their survival, and at the same time describe the new antibody-focused strategies emerging to target them for more effective treatment of cancer.
FreePub: Collecting and Organizing Scienti*c Material Using Mindmaps
Authors: Dalamagas Theodore , Farmakakis Tryfon , Maragkakis Manolis , Hatzigeorgiou Artemis Hatzigeorgiou
Published: December 2010

This paper presents a creativity support tool, called FreePub,to collect and organize scientifi*c material using mindmaps. Mindmaps are visual, graph-based representations of concepts, ideas, notes, tasks, etc. They generally take a hierarchical or tree branch format, with ideas branching into their subsections. FreePub supports creativity cycles. A user starts such a cycle by setting up her domain of interest using mindmaps. Then, she can browse mindmaps and launch search tasks to gather relevant publications from several data sources. FreePub, besides publications, identifies helpful supporting material (e.g., blog posts, presentations). All retrieved information from FreePub can be imported and organized in mindmaps. FreePub has been fully implemented on top of FreeMind, a popular open-source, mindmapping tool.
Multivariate Linkage Scan for Metabolic Syndrome Traits in Families With Type 2 Diabetes
Authors: Edwards Karen L. , Wan Jia Y. , Hutter Carolyn M. , Fong Pui Yee , Santorico Stephanie A.
Published: December 2010

The purpose of this study was to evaluate evidence for linkage to interrelated quantitative features of the metabolic syndrome (MetS). Data on eight quantitative MetS traits (body weight, waist circumference, systolic and diastolic blood pressure, high‐density lipoprotein (HDL) cholesterol, triglycerides (TGs), and fasting glucose and insulin measurements) and a 10 cM genome scan were available for 78 white families (n = 532 subjects). These data were used to conduct multipoint, multivariate linkage analyses, including tests for coincident linkage and complete pleiotropy. The strongest evidence for linkage from the bivariate analyses was observed on chromosome 1 (1p22.2) (HDL‐TG; univariate lod score equivalent (lodeq = 3.99)) with stronger results from the trivariate analysis at the same location (HDL‐TG‐Insulin; lodeq = 4.32). Seven additional susceptibility regions (lodeq scores >1.9) were observed (1p36, 1q23, 2q21.2, 8q23.3, 14q23.2, 14q32.11, and 20p11.21). The results from this study indicate that several correlated traits of the MetS are influenced by the same gene(s) that account for some of the clustering of the MetS features.
Association of Subcutaneous and Visceral Adiposity With Albuminuria: The Framingham Heart Study
Authors: Foster Meredith C. , Hwang Shih‐Jen , Massaro Joseph M. , Hoffmann Udo , DeBoer Ian H. , Robins Sander J. , Vasan Ramachandran S. , Fox Caroline S.
Published: December 2010

Microalbuminuria is a common condition associated with increased incidence of cardiovascular events and mortality. Abdominal obesity is associated with microalbuminuria, but studies linking visceral adipose tissue (VAT) and microalbuminuria are limited. Our objective was to determine the associations of albuminuria with VAT and subcutaneous adipose tissue (SAT). We performed a cross‐sectional study in the Framingham Multi‐Detector Computed Tomography (MDCT) cohort (n = 3,099, 48.2% women, mean age 53 years). VAT and SAT volumes were measured using computed tomography. Urinary albumin‐to‐creatinine ratio (UACR) was calculated from spot urine samples. Microalbuminuria was defined as a UACR >25 mg/g in women or >17 mg/g in men. Overall, 7.9% (n = 244) of the sample had microalbuminuria. Among men, VAT (odds ratio (OR) 1.48 per s.d., P < 0.0001) and SAT (OR 1.37 per s.d., P = 0.0002) were associated with microalbuminuria in minimally adjusted models, which remained significant after multivariable adjustment (VAT OR 1.34 per s.d., P = 0.001; SAT OR 1.28 per s.d., P = 0.005). Additionally, when considered jointly, VAT (P = 0.002) but not SAT (P = 0.2) was associated with microalbuminuria. In women, VAT was associated with microalbuminuria after minimal adjustment (OR 1.28, P = 0.01), but not after multivariable adjustment (OR 1.03, P = 0.8). In multivariable models in women, SAT was associated with a decreased odds of having microalbuminuria (OR 0.75 per s.d., P = 0.03). In conclusion, VAT is associated with microalbuminuria in men but not women. Albuminuria may be a manifestation of visceral adiposity.
Obesity Is Associated With Reduced White Matter Integrity in Otherwise Healthy Adults*
Authors: Stanek Kelly M. , Grieve Stuart M. , Brickman Adam M. , Korgaonkar Mayuresh S. , Paul Robert H. , Cohen Ronald A. , Gunstad John J.
Published: December 2010

Existing work demonstrates that obesity is independently associated with cognitive dysfunction and macrostructural brain changes; however, little is known about the association between obesity and white matter (WM) integrity. We explore this relationship in a large cohort of otherwise healthy subjects. The present study classified 103 adult participants from the Brain Resource International Database between 21 and 86 years of age without history of neurological, medical, or psychiatric illness according to BMI (normal weight, overweight, obese) and subjected them to diffusion tensor imaging (DTI). Resulting fractional anisotropy (FA) indexes for the corpus callosum and fornix were examined in relation to BMI and age in a multiple regression framework. Results indicated that increasing BMI was independently associated with lower FA in the genu, splenium, and fornix, and a BMI × age interaction emerged for FA in the splenium and body of the corpus callosum. When categorized, obese persons demonstrated lower FA than normal and overweight persons for all WM indexes, but no FA differences emerged between overweight and normal persons. Results indicate both a direct association between obesity and reduced WM tract integrity and an interaction between obesity and aging processes on certain WM tracts in otherwise healthy adults. While such findings suggest a possible role for adiposity in WM dysfunction and associated cognitive deficits, prospective studies are needed to clarify the nature of these relationships and elucidate underlying mechanisms.
High temperature Seebeck coefficient metrology
Authors: Martin J. , Tritt T. , Uher C.
Published: December 2010

We present an overview of the challenges and practices of thermoelectric metrology on bulk materials at high temperature (300 to 1300 K). The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at high temperature. This has led to the implementation of nonideal practices that have further complicated the confirmation of reported high ZT materials. To ensure meaningful interlaboratory comparison of data, thermoelectric measurements must be reliable, accurate, and consistent. This article will summarize and compare the relevant measurement techniques and apparatus designs required to effectively manage uncertainty, while also providing a reference resource of previous advances in high temperature thermoelectric metrology.
Ground and excited electronic states of azobenzene: A quantum Monte Carlo study
Authors: Dubecký M. , Derian R. , Mitas L. , Štich I.
Published: December 2010

Large–scale quantum Monte Carlo (QMC) calculations of ground and excited singlet states of both conformers of azobenzene are presented. Remarkable accuracy is achieved by combining medium accuracy quantum chemistry methods with QMC. The results not only reproduce measured values with chemical accuracy but the accuracy is sufficient to identify part of experimental results which appear to be biased. Novel analysis of nodal surface structure yields new insights and control over their convergence, providing boost to the chemical accuracy electronic structure methods of large molecular systems.
Electronic coupling matrix elements from charge constrained density functional theory calculations using a plane wave basis set
Authors: Oberhofer Harald , Blumberger Jochen
Published: December 2010

We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn–Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken–Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q−) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, $( {\langle {| {H_{\rm ab} } |^2 } \rangle } )^{1/2} = 6.7\, \hbox{mH},$(⟨|H ab |2⟩)1/2=6.7mH, is significantly higher than the value obtained for the minimum energy structure, $| {H_{\rm ab} } | = 3.8\, \hbox{mH}$|H ab |=3.8mH. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q− in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.
Finite element analysis and design of cubic high-pressure anvils based on the principle of lateral support
Authors: Han Qi-Gang , Li Ming-Zhe , Jia Xiao-Peng , Ma Hong-An
Published: December 2010

This article theoretically investigates the lateral support on cubic high-pressure anvil using finite element analysis. The results show that to gain the same chamber pressure, the value of system oil pressure can be decreased by reducing the lateral support area and the anvils’ lifetime is extended when the lateral support area grows. The optimal lateral support area to maximize anvils’ lifetime is 27.96 cm2. Furthermore, the chamber pressure will increase by about 6.99% when the value of lateral support area reduces from 33.16 to 27.96 cm2 under same hydraulic rams. Our simulation results have been verified by many high-pressure synthesis experiments and illustrated by breakage of anvils.
Growth and electrical properties of Na1/2Bi1/2TiO3–BaTiO3 lead-free single crystal with morphotropic phase boundary composition
Authors: Chen Chao , Jiang Xiangping , Li Yueming , Wang Feifei , Zhang Qinhui , Luo Haosu
Published: December 2010

In present work, lead-free single crystal 0.94Na1/2Bi1/2TiO3–0.06BaTiO3 (NBBT94/6) with dimension of Φ40 mm×10 mm was grown by a precisely controlled top seeded solution growth method. The crystal structure measurement result indicates that the NBBT94/6 single crystal exhibits the feature of rhombohedral-tetragonal phase coexistence at room temperature. The crystallographic orientation dependence of electrical properties for NBBT94/6 single crystal was investigated in detail. The remnant polarizations (Pr) of ⟨001⟩, ⟨001⟩, and ⟨111⟩ oriented crystals are 16.02 μC/cm2, 22.16 μC/cm2, and 27.23 μC/cm2, respectively. The corresponding coercive fields (Ec) are 24.89, 20.72, and 15.36 kV/cm. Moreover, a double hysteresis loop appears at the depolarization temperature. High piezoelectric properties d33 of 360 pC/N and kt of 62% were obtained in the ⟨001⟩ oriented crystals due to the engineered domain configuration which make them promising candidates for environmental friendly solid-state actuator applications.
Alternative stable scroll waves and conversion of autowave turbulence
Authors: Foulkes A. J. , Barkley D. , Biktashev V. N. , Biktasheva I. V.
Published: December 2010

Rotating spiral and scroll waves (vortices) are investigated in the FitzHugh–Nagumo model of excitable media. The focus is on a parameter region in which there exists bistability between alternative stable vortices with distinct periods. Response functions are used to predict the filament tension of the alternative scrolls and it is shown that the slow-period scroll has negative filament tension, while the filament tension of the fast-period scroll changes sign within a hysteresis loop. The predictions are confirmed by direct simulations. Further investigations show that the slow-period scrolls display features similar to delayed after-depolarization and tend to develop into turbulence similar to ventricular fibrillation (VF). Scrolls with positive filament tension collapse or stabilize, similar to monomorphic ventricular tachycardia (VT). Perturbations, such as boundary interaction or shock stimulus, can convert the vortex with negative filament tension into the vortex with positive filament tension. This may correspond to transition from VF to VT unrelated to pinning.
Note: A table-top blast driven shock tube
Authors: Courtney Michael W. , Courtney Amy C.
Published: December 2010

The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer that explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.
Correlation between growth kinetics and nanoscale resistive switching properties of SrTiO3 thin films
Authors: Muenstermann Ruth , Menke Tobias , Dittmann Regina , Mi Shaobo , Jia Chun-Lin , Park Daesung , Mayer Joachim
Published: December 2010

We deliberately fabricated SrTiO3 thin films deviating from ideal stoichiometry and from two-dimensional layer-by-layer growth mode, in order to study the impact of well pronounced defect arrangements on the nanoscale electrical properties. By combining transmission electron microscopy with conductive-tip atomic force microscopy we succeeded to elucidate the microstructure of thin films grown by pulsed laser deposition under kinetically limited growth conditions and to correlate it with the local electrical properties. SrTiO3 thin films, grown in a layer-by-layer growth mode, exhibit a defect structure and conductivity pattern close to single crystals, containing irregularly distributed, resistive switching spots. In contrast to this, Ti-rich films exhibit short-range-ordered, well-conducting resistive switching units. For Ti-rich films grown in a kinetically more restricted island growth mode, we succeeded to identify defective island boundaries with the location of tip-induced resistive switching. The observed nanoscale switching behavior is consistent with a voltage driven oxygen vacancy movement that induces a local redox-based metal-to-insulator transition. Switching occurs preferentially in defect-rich regions, that exhibit a high concentration of oxygen vacancies and might act as easy-diffusion-channels.
Enhanced efficiency of CdMgZnSe down-converted light emitting diodes using light extraction features fabricated by laser-speckle lithography
Authors: Yang Zhaohui H. , Haase Michael A. , Leatherdale Catherine A. , Smith Terry L.
Published: December 2010

We report a method of making a wavelength converted, light-emitting diode (LED) having light extraction features based on coherent speckle patterns. These patterns have random feature size, random feature distribution, and random feature shape. The features were produced using a maskless lithography process based on exposing photoresist with a laser-induced coherent optical speckle pattern. A wet chemical etching process was then used to transfer the resist pattern into the underlying surface of the semiconductor wavelength converter layer. The external quantum efficiency of a wavelength converter with emitting surfaces having such extraction features showed a twofold increase compared to a wavelength converter without extraction features. While demonstrated here using semiconductor wavelength converters, this approach could also be applied to light extraction in conventional LED structures.
Magnetic trends in GaxMn1−xN, AlxMn1−xN, and InxMn1−xN ternary systems: A first-principles study
Authors: Boukra A. , Zaoui A. , Ferhat M.
Published: December 2010

We have performed first-principles calculations using the full-potential linearized augmented plane-wave method to investigate the magnetic properties of Al1−xMnxN, Ga1−xMnxN, and In1−xMnxN semiconductors, for x=0.25, 0.50, and 0.75 in their ordered zinc-blend ferromagnetic phase. For the structural properties, we found strong positive deviation from Vegard’s law regarding the variation in the lattice parameter which is in direct contrast with conventional III-V alloys. In addition, we found that In1−xMnxN exhibits a half-metallic characteristic for all Mn composition. A total magnetic moment of 4 μB was found for all In1−xMnxN compositions, and for half-metallic phases of Al1−xMnxN and Ga1−xMnxN, respectively. The Mn atom is the main source of the total magnetic moment in these alloys, while the contributions from Al, Ga, In, and N are negligible.
Hopf solitons in the Nicole model
Authors: Gillard Mike , Sutcliffe Paul
Published: December 2010

The Nicole model is a conformal field theory in a three-dimensional space. It has topological soliton solutions classified by the integer-valued Hopf charge, and all currently known solitons are axially symmetric. A volume-preserving flow is used to construct soliton solutions numerically for all Hopf charges from 1 to 8. It is found that the known axially symmetric solutions are unstable for Hopf charges greater than 2 and new lower energy solutions are obtained that include knots and links. A comparison with the Skyrme–Faddeev model suggests many universal features, though there are some differences in the link types obtained in the two theories.
Wavelength selection in the crown splash
Authors: Zhang Li V. , Brunet Philippe , Eggers Jens , Deegan Robert D.
Published: December 2010

The impact of a drop onto a liquid layer produces a splash that results from the ejection and dissolution of one or more liquid sheets, which expand radially from the point of impact. In the crown splash parameter regime, secondary droplets appear at fairly regularly spaced intervals along the rim of the sheet. By performing many experiments for the same parameter values, we measure the spectrum of small-amplitude perturbations growing on the rim. We show that for a range of parameters in the crown splash regime, the generation of secondary droplets results from a Rayleigh–Plateau instability of the rim, whose shape is almost cylindrical. In our theoretical calculation, we include the time dependence of the base state. The remaining irregularity of the pattern is explained by the finite width of the Rayleigh-Plateau dispersion relation. Alternative mechanisms, such as the Rayleigh–Taylor instability, can be excluded for the experimental parameters of our study.
Quantification of energy loss mechanisms in organic light-emitting diodes
Authors: Meerheim Rico , Furno Mauro , Hofmann Simone , Lüssem Björn , Leo Karl
Published: December 2010

The external quantum efficiency of organic light-emitting diodes (OLEDs) is limited by several loss mechanisms. By applying a numerical model for the efficiency analysis of OLED devices, we analyze the distribution of the different energy loss mechanisms in bottom and top emission organic light-emitting diodes. We validate the findings by the comparison with experimental data measured on red state-of-the-art p-i-n devices containing the red phosphorescent emitting dye iridium(III)bis[2-methyldibenzo-(f, h)quinoxaline](acetylacetonate) [Ir(MDQ)2(acac)]. The model is used to design extremely efficient bottom and top emission diodes with 21% and 27% external quantum efficiencies, respectively.
GaN-based surface-emitting laser with two-dimensional photonic crystal acting as distributed-feedback grating and optical cladding
Authors: Kawashima Shoichi , Kawashima Takeshi , Nagatomo Yasuhiro , Hori Yuichiro , Iwase Hideo , Uchida Takeshi , Hoshino Katsuyuki , Numata Aihiko , Uchida Mamoru
Published: December 2010

We demonstrate GaN-based distributed-feedback surface-emitting lasers grown on sapphire substrates with a two-dimensional (2D) square-lattice photonic crystal (PhC) that forms a high-aspect-ratio void array (void diameter: 65 nm and depth: 220 nm). The 2D PhC layer acts as both distributed-feedback grating and p-type optical cladding of a separate confinement heterostructure. To form the 2D PhC in the nitride semiconductor layers, we developed an embedding process that uses mass-transport phenomena. Crystallographic facets appeared on the inner walls of the embedded voids. Room-temperature lasing action was observed at 406.0 nm for a PhC lattice constant of 162.5 nm. The threshold current density was 9.7 kA/cm2 for a 120-μm-square p-contact electrode.
Propulsive force measurements and flow behavior of undulatory swimmers at low Reynolds number
Authors: Sznitman J. , Shen X. , Sznitman R. , Arratia P. E.
Published: December 2010

The swimming behavior of the nematode Caenorhabditis elegans is investigated in aqueous solutions of increasing viscosity. Detailed flow dynamics associated with the nematode’s swimming motion as well as propulsive force and power are obtained using particle tracking and velocimetry methods. We find that C. elegans delivers propulsive thrusts on the order of a few nanonewtons. Such findings are supported by values obtained using resistive force theory; the ratio of normal to tangential drag coefficients is estimated to be approximately 1.4. Over the range of solutions investigated here, the flow properties remain largely independent of viscosity. Velocity magnitudes of the flow away from the nematode body decay rapidly within less than a body length and collapse onto a single master curve. Overall, our findings support that C. elegans is an attractive living model to study the coupling between small-scale propulsion and low Reynolds number hydrodynamics.
Direct minority carrier lifetime measurements and recombination mechanisms in long-wave infrared type II superlattices using time-resolved photoluminescence
Authors: Connelly Blair C. , Metcalfe Grace D. , Shen Hongen , Wraback Michael
Published: December 2010

We present a direct optical measurement of minority carrier lifetime as a function of temperature and excitation density in long-wave infrared InAs/GaSb type II superlattices using time-resolved photoluminescence. Results indicate that carrier lifetime is dominated by Shockley–Read–Hall recombination, with a lifetime of 30 ns at 77 K. Below 40 K, we observe a freeze-out of carriers and increased contributions from radiative recombination. High-injection measurements yield a radiative recombination coefficient of 1.8×10−10 cm3/s and an upper limit of the Auger recombination coefficient of 10−28 cm6/s at 60 K. An acceptor level of ∼20 meV above the valence band is also determined.
rf mode switching in a relativistic magnetron with diffraction output
Authors: Liu Meiqin , Michel Cedric , Prasad Sarita , Fuks Mikhail I. , Schamiloglu Edl , Liu Chun-Liang
Published: December 2010

The relativistic magnetron with diffraction output (RMDO) has demonstrated nearly 70% efficiency in recent simulations. This letter reports a rapid mode switching technique in the RMDO using a low power, short-pulse, external single frequency signal. The MAGIC electromagnetic finite-difference-time-domain particle-in-cell code used in simulations demonstrated that an input signal of 300 kW is sufficient to switch neighboring modes in a gigawatt output power A6 RMDO with a transparent cathode, whereas for the original A6 magnetron configuration with radial extraction driven by a transparent cathode 30 MW is required. This frequency agility adds additional versatility to this high power microwave source.
Combined light and electron scattering for exploring hydrogen in thin metallic films
Authors: Prinz Jan , Pálsson Gunnar K. , Korelis Panagiotis T. , Hjörvarsson Björgvin
Published: December 2010

We present a method, combining optical transmission with electrical resistance, to study the hydrogen uptake in thin transition metal films. The change in optical transmission is used to determine the hydrogen concentration, while the change in resistance serves as an indicator for the ordering of hydrogen. We identify phase boundaries and regions of high and low orders as well as changes in the ordering temperature. As a demonstration of this approach we compare the hydrogen uptake of 50 and 10 nm single-crystal vanadium films. The ordered phase is found to be extended to higher temperatures in the thinner sample.
Solution processed inverted tandem polymer solar cells with self-assembled monolayer modified interfacial layers
Authors: Hau Steven K. , Yip Hin-Lap , Chen Kung-Shih , Zou Jingyu , Jen Alex K.-Y.
Published: December 2010

Inverted tandem bulk-heterojunction solar cells with comparable efficiency to single layer devices have been demonstrated by utilizing two thin layers (∼50 nm) of poly-(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester as the active material and a fullerene self-assembled monolayer (C60-SAM) to modify the interfaces between the ZnO buffer layer and the active layer. Single and tandem solar cells without the SAM modification have much lower efficiencies than the ones with modification. The successful demonstrations of inverted tandem devices with SAM modification give promise of further device improvements if active materials with complementary absorption can be used.
Near-field optical transducer for nanomechanical resonators
Authors: Basarir O. , Bramhavar S. , Ekinci K. L.
Published: December 2010

We show that a single-mode tapered-fiber waveguide can be used as a sensitive transducer to couple to the motion of a nanomechanical resonator. When the waveguide and the resonator are sufficiently close to each other, small mechanical oscillations of the resonator can be actuated efficiently by the optical dipole force. Scattering of evanescent waves confined around the waveguide and the ensuing modulation in the optical transmission through the waveguide allow for sensitive detection of the resonator oscillations. Using this technique, we have measured high-frequency nanomechanical resonances with a ∼150 fm Hz−1/2 noise floor at a detection power of ∼100 μW. The tapered-fiber waveguide provides a single seamless transduction interface between the device chip and the measurement equipment, thus offering potential for use outside of the research laboratory.
Piezoelectric response of single-crystal PbZr1−xTixO3 near morphotropic phase boundary predicted by phase-field simulation
Authors: Cao Y. , Sheng G. , Zhang J. X. , Choudhury S. , Li Y. L. , Randall C. A. , Chen L. Q.
Published: December 2010

The piezoelectric property of hypothetic single-crystal PbZr1−xTixO3 (PZT) is studied using phase-field simulations. The dependence of piezoelectric coefficient (d33) on PbTiO3 compositions (x) near the morphotropic phase boundary of PZT was obtained. Using the existing thermodynamic description of PZT, it is shown that d33 reaches a peak value of 720 pC/N at x=0.47 which is more than three times of that for the ceramic counterpart. The relation between the domain structure of the poled PZT single crystals and the enhancement of d33 near the MPB composition is discussed.
Electronic structures of c-plane and a-plane AlN/ZnO heterointerfaces determined by synchrotron radiation photoemission spectroscopy
Authors: Liu J. W. , Kobayashi A. , Ueno K. , Toyoda S. , Kikuchi A. , Ohta J. , Fujioka H. , Kumigashira H. , Oshima M.
Published: December 2010

c -plane and a-plane AlN films have been grown on single-crystal ZnO substrates by pulsed laser deposition at room temperature. The electronic structures of c-plane and a-plane AlN/ZnO heterojunctions have been characterized by synchrotron radiation photoemission spectroscopy. Based on the binding energies of core-levels and valence-band maximum values, the valence-band offsets have been found to be 0.4±0.1 and 0.1±0.1 eV for the c-plane and a-plane AlN/ZnO heterojunctions, respectively. Both heterojunctions show type-II band configurations with conduction band offsets of 3.0±0.1 and 2.7±0.1 eV, respectively. The potential on the ZnO side bends downward toward the interface for the a-plane AlN/ZnO heterojunction. However, that bends upward toward the interface for the c-plane AlN/ZnO heterojunction. This phenomenon is explained well by the effect of spontaneous polarization in AlN and ZnO.
Superconducting gap induced barrier enhancement in a BiFeO3-based heterostructure
Authors: Lu C. L. , Wang Y. , You L. , Zhou X. , Peng H. Y. , Xing G. Z. , Chia E. E. M. , Panagopoulos C. , Chen L. , Liu J.-M. , Wang J. , Wu T.
Published: December 2010

We report the synthesis and characterization of an epitaxial heterostructure composed of multiferroic BiFeO3 and superconducting YBa2Cu3O7−δ thin films grown on (001) SrTiO3. Both the superconductivity of YBa2Cu3O7−δ and the ferroelectricity of BiFeO3 are retained in the heterostructure. Current density-electric field characteristics measured from 30 to 170 K suggest a Schottky-emission-like transport at the BiFeO3/YBa2Cu3O7−δ interface. Furthermore, the temperature dependence of the barrier height shows an anomalous enhancement at TC, indicating an intimate coupling between the multiferroic and the superconducting layers.
Electroluminescence of green CdSe/ZnS quantum dots enhanced by harvesting excitons from phosphorescent molecules
Authors: Zhang Y. Q. , Cao X. A.
Published: December 2010

We demonstrated the enhancement of electroluminescence from green CdSe/ZnS quantum dots (QDs) in hybrid QD/organic light-emitting diodes (LEDs) by employing blue phosphorescent dyes bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (FIrpic) as efficient exciton harvesters and energy transfer donors. Precise control over the position and concentration of the donors doped in a fluorescent host led to complete exciton energy transfer from FIrpic molecules located within the Förster distance of ∼8 nm from the QD layer, and a 2.5-fold increase in the quantum efficiency of the QD-LEDs.
Role of silicon in silicon-indium-zinc-oxide thin-film transistor
Authors: Chong Eugene , Kim Seung Han , Lee Sang Yeol
Published: December 2010

Silicon effect on the performance of amorphous silicon-indium-zinc-oxide (a-SIZO) films has been investigated for thin-film transistor applications depending on composition ratio and annealing-temperature. X-ray diffraction, x-ray photoelectron spectroscopy, and time-of-flight secondary-ion-mass-spectrometry have been used to characterize the properties of SIZO thin-film channel layer with different Si concentrations and annealing-temperatures. Those results revealed that Si is more strongly binding with oxygen since their high metal-oxygen bonding-strength and low standard electric potential, which result in implying Si, allow the amorphous oxide semiconductors to achieve oxide-lattice structures even at a low-temperature of 150 °C.
Cavity-enhanced localized plasmon resonance sensing
Authors: Ameling Ralf , Langguth Lutz , Hentschel Mario , Mesch Martin , Braun Paul V. , Giessen Harald
Published: December 2010

We present a method to enhance the sensing properties of a localized plasmon sensor. The concept is based on the combination of localized plasmons in nanostructures and a photonic microcavity. Metal nanorods that are placed at Bragg distance above a metal mirror form a Fabry–Pérot microcavity and constitute a coupled photonic-plasmonic system. The localized plasmon resonances of the nanorods and the phase shifts upon plasmon excitation are extremely sensitive to changes in the refractive index of the material surrounding the nanorods. Compared to the plasmonic nanorods alone, the coupled photonic-plasmonic system allows for a much more sensitive detection of small refractive index changes.
DNA base (cytosine) modified/capped ultrasmall Gd2S3:Eu3+ gadofluoroprobes for platelet isolation
Authors: Dutta Ranu K. , Sharma Prashant K. , Pandey Avinash C.
Published: December 2010

The present letter deals with the synthesis of ultrasmall Gd2S3:Eu3+ nanoparticles and their surface modification with “cytosine,” a nucleobase present in DNA/RNA. These nanoparticles show orthorhombic (Pnma) crystal symmetry with excellent magnetic and luminescent characters simultaneously. In contrast to the previous reports, cytosine modified nanoparticles do not show a significant change in their structural and magnetic properties, whereas luminescence is enhanced slightly owing to the surface passivation. The in vitro studies show better accumulation of blood platelets with cytosine modified nanoparticles as compared to unmodified posing them a potential candidate for platelet isolation from the plasma for different applications and studies.
Real-time single-shot three-dimensional and contrast-enhanced optical coherence imaging using phase coherent photorefractive quantum wells
Authors: Kabir A. , Dongol A. , Wang X. , Wagner H. P.
Published: December 2010

We demonstrate two real-time optical coherence imaging acquisition modes using all-optical phase coherent photorefractive ZnSe quantum wells as dynamic holographic films. These films use the coherence of excitons for time-gating which provides depth information of an object according to the brightness profile of its holographic image. This quality allows depth-resolved imaging of moving particles with a resolution of a few micrometers in a single-shot three-dimensional mode. In a complementary contrast-enhanced mode moving particles are imaged by the local enhancement of a static reference hologram, enabling optical coherence imaging at a large depth-of-field.
The growth and radial analysis of Si/Ge core-shell nanowires
Authors: Chang Hsu-Kai , Lee Si-Chen
Published: December 2010

Si/Ge core-shell nanowires, which possess uniform diameters around 100 nm, were synthesized at low temperature using a chemical vapor deposition process. The radial structures of Si/Ge nanowires were investigated via cross-sectional transmission electron microscopy analysis. The data from energy dispersive x-ray spectroscopy confirmed the coaxial structures of our nanowires, which consistently determined the core to be polycrystalline Si and the shell to be crystalline Ge. The optical properties of Si/Ge core-shell nanowires were also discussed from Raman measurement. The method presented in this study will allow efficient fabrication of core-shell nanostructures and may be promising for future device application.