bluuebunny/crossref_metadata_2025 huggingface dataset:
Total electron content (TEC) forecasting by Cascade Modeling: A possible alternative to the IRI‐2001
Authors: Senalp Erdem Turker , Tulunay Ersin , Tulunay Yurdanur
Published: August 2008

The ionospheric parameter, total electron content (TEC) is one of the key parameters in navigation and telecommunication applications. A small group at METU in Ankara has been developing data driven models in order to forecast the ionospheric parameters since 1990. In particular, results on forecasting TEC values one hour in advance by using their Neural Network Model—METU‐NN have been reported previously. Since then, some work has been done in order to increase the performance of the METU‐NN. In this paper, the most recent advanced model of the Neural Network containing Cascade Modeling (METU‐NN‐C) based on the Hammerstein systems is introduced. To demonstrate the performance of the METU‐NN‐C model, the Chilbolton and the Hailsham TEC values are considered during severe Space Weather conditions in some periods of 2001 and 2002. The authors have considered the METU‐NN‐C model as an alternative to the IRI‐2001. In order to facilitate a comparison, IRI‐2001 Hailsham TEC values are compared with those of the METU‐NN‐C by taking observed values as a basis.
Impulsive plane‐wave reflection from a homogeneous plasma half space
Authors: Zwietasch T. , Rothwell E. J. , Cossmann S. M.
Published: August 2008

The reflected‐field impulse response for a plane wave obliquely incident on a lossy plasma half space is determined analytically by the inversion of the frequency‐domain reflection coefficient. Both TE and TM incident field polarizations are considered. The resulting expressions involve simple functions and, at most, one or two convolutions of these functions. The simplicity of the expressions allows the temporal behavior of the reflected field to be predicted on the basis of the physical parameters of the plasma. The expressions are validated numerically by comparison to the inverse fast Fourier transform of the frequency‐domain reflection coefficient. A comparison to the response of a laboratory plasma shows good agreement.
Recent extension driven by mantle upwelling beneath the Admiralty Mountains (East Antarctica)
Authors: Faccenna Claudio , Rossetti Federico , Becker Thorsten W. , Danesi Stefania , Morelli Andrea
Published: August 2008

Northern Victoria Land is located at the boundary between an extended, presumably hot, region (West Antarctic Rift System) and the thick, possibly cold, East Antarctic craton. The style and timing of Tertiary deformation along with relationships with the magmatic activity are still unclear, and contrasting models have been proposed. We performed structural and morphotectonic analyses at the NE termination of northern Victoria Land in the Admiralty Mountains area, where the relationship between topography, tectonics, and magmatism is expected to be well pronounced. We found evidence of two subsequent episodes of faulting, occurring concurrently with the Neogene McMurdo volcanism. The first episode is associated with dextral transtension, and it is overprinted by extensional tectonics during the emplacement of large shield alkaline volcanoes. Upper mantle seismic tomography shows that the extensional regime is limited to regions overlying a low‐velocity anomaly. We interpret this anomaly to be of thermal origin, and have tested the role of large‐scale upwelling on lithosphere deformation in the area. The results of this integrated analysis suggest that the morphotectonic setting of the region and the magmatism is likely the result of upwelling flow at the boundary between the cold cratonic and the hot stretched province (WARS), at work until recent time in this portion of the northern Victoria Land.
Fault zone architecture and deformation processes within evaporitic rocks in the upper crust
Authors: De Paola N. , Collettini C. , Faulkner D. R. , Trippetta F.
Published: August 2008

Recently, in the Northern Apennines, geophysical data have identified the Triassic Evaporites (TE, anhydrites and dolomites) as the source region of the major extensional earthquakes of the area (M ∼ 6). In order to characterize fault zone architecture and deformation processes within the TE, we have studied exhumed evaporite‐bearing normal faults within the upper crust. The structure of large displacement (>100 m) normal faults is given by 1) a zoned fault core with a wider portion of fault‐parallel foliated Ca‐sulphates (ductile deformation), overprinted by an inner fault core (IFC) of localized brittle deformation, and 2) wide (dolostones) to absent (Ca‐sulphates) damage zones of fault fracture patterns. Fault rock assemblage within the IFC is characterized by fault breccia, gouge, and cataclasites of different grain size. Most of the deformation within the IFC is localized along thin and fault parallel principal slip surfaces (PSS) made of dolomite‐rich fine‐grained cataclasite. SEM analyses show an evolution from Ca‐ to St‐ to gypsum‐rich mineralization, due to episodic fluid flow events channeled along the fault zones during different stages of fault exhumation. The development of the observed fault geometry can be explained by a mechanical fault evolution model where initial faulting occurs along broad and ductile shear zones within the anhydrites and causes fracturing within the dolostones. Progressive deformation within the fault core leads to the development of fault parallel dolomite‐rich cataclastic layers. Their reactivation coupled with transient fluid overpressures can produce embrittlement and localization of brittle deformation within the IFC.
Aqueous and isotope geochemistry of mineral springs along the southern margin of the Tibetan plateau: Implications for fluid sources and regional degassing of CO2
Authors: Newell Dennis L. , Jessup Micah J. , Cottle John M. , Hilton David R. , Sharp Zachary D. , Fischer Tobias P.
Published: August 2008

Springs issuing from different faults and shear zones along the crest of the Himalayas tap three different levels of crust beneath the Tibetan Plateau. From structurally highest to lowest these are the Tingri Graben, the South Tibetan Detachment System (STDS), and the Ama Drime massif (ADM). The aqueous chemistry reflects water‐rock interactions along faults and is consistent with mapped rock types. Major ion chemistry and calculated temperatures indicate that spring waters have circulated to greater depths along the N‐S trending faults that bound the Tingri Graben and Ama Drime detachment (ADD) compared to the STDS, suggesting that these structures penetrate to greater depths. Springs have excess CO2, N2, He, and CH4 compared to meteoric water values, implying addition from crustal sources. The 3He/4He ratios range from 0.018 to 0.063 RA and are consistent with a crustal source for He. The δ13C values of dissolved inorganic carbon (DIC) and CO2 gas range from −5.5 to +3.8‰ and −13.1 to −0.3‰ versus Peedee belemnite, respectively. Sources of carbon are evaluated by calculating isotopic trajectories associated with near‐surface effervescence of CO2. Positive δ13C values of the Tingri graben and STDS springs are consistent with decarbonation of marine carbonates as the source of CO2. Negative values for the ADD springs overlap with mantle values but are best explained by metamorphic devolatilization of reduced sedimentary carbon. The δ15N values of N2 range from −2.2 to +2.1‰ (versus AIR) and are explained by mixtures of air‐derived nitrogen, metamorphic devolatilization of sedimentary nitrogen, and nitrogen from near‐surface biogenic processes. CO2 flux is estimated by scaling from individual springs (∼105 mol a−1 per spring) to extensional structures across the southern limit of the Tibetan Plateau and likely contributes between 108 and 1011 mol a−1 (up to 10%) to the global carbon budget.
Joint modeling of lithosphere and mantle dynamics elucidating lithosphere‐mantle coupling
Authors: Ghosh A. , Holt W. E. , Wen L. , Haines A. J. , Flesch L. M.
Published: August 2008

We provide new insights into the lithosphere‐mantle coupling problem through a joint modeling of lithosphere dynamics and mantle convection and through comparison of model results with the high resolution velocity gradient tensor model along the Earth's plate boundary zones. Using a laterally variable effective viscosity lithosphere model, we compute depth integrated deviatoric stresses associated with both gravitational potential energy (GPE) differences and deeper mantle density buoyancy‐driven convection. When deviatoric stresses from horizontal basal tractions, associated with deeper density buoyancy‐driven convective circulation of the mantle, are added to those from GPE differences, the fit between the model deviatoric stress field and the deformation indicators improves dramatically in most areas of continental deformation. We find that the stresses induced by the horizontal tractions arising from deep mantle convection contribute approximately 50% of the magnitude of the Earth's deviatoric lithospheric stress field. We also demonstrate that lithosphere‐asthenosphere viscosity contrasts and lateral variations within the lithospheric plate boundary zones play an important role in generating the right direction and magnitude of tractions that yield an optimal match between deviatoric stress tensor patterns and the deformation indicators.
Effect of internal gravitational coupling on Titan's non‐synchronous rotation
Authors: Karatekin Ö. , Van Hoolst T. , Tokano T.
Published: August 2008

Variations in the spin period of Titan have been detected by the Cassini radar observations. Angular momentum exchange between Titan's surface and the atmosphere over seasonal time scales corresponding to Saturn's orbital period of 29.5 year is the most likely cause of the observed non‐synchronous rotation. The measured rotation rate can be explained if Titan's icy crust is rotationally decoupled from the interior in the presence of a subsurface ocean. However, we show that Titan is likely to rotate almost as a rigid body even when it has an internal ocean because of a substantial internal gravitational coupling between the crust and the interior. The predicted surface rotation rate will be further reduced due to Saturn's torque, but can approach to the observed value if other factors, such as larger atmospheric torque, smaller equatorial flattening or viscous relaxation of the icy crust are considered.
Newly discovered submarine flank eruption at Stromboli volcano (Aeolian Islands, Italy)
Authors: Di Roberto A. , Bertagnini A. , Pompilio M. , Gamberi F. , Marani M. P. , Rosi A. M.
Published: August 2008

The NW submarine portion of Stromboli volcano has been investigated by deep‐towed sidescan sonar, bathymetric surveys, video camera runs and dredging during two research cruises in 2002 and 2004. The surveys resulted in the identification of an extensive pillow lava field (106‐107m3) at about 2300 m of water depth and 9 km from the shoreline of Stromboli Island. The pillow lavas have a unique composition that does not match any known subaerial product, although a limited affinity exists with those erupted during the Neostromboli eruptive cycle of the island (13–6 ka). This is the first finding of a submarine eruption on the northern side of Stromboli and improves the knowledge of its flank activity and volcanic hazards. This eruption is interpreted as marking the onset of a new volcanic cycle from the edifice periphery fed by a new, distinct magma mixed with traces of the previous magma that survived the emptying of the Neostromboli magma chamber.
Detection of motion and heterogeneity in Earth's liquid outer core
Authors: Dai Wei , Song Xiaodong
Published: August 2008

The lateral variations in the fluid outer core are believed to be very small from fluid dynamics calculations. Seismological studies on the issue have been limited and controversial. A great challenge is to sort out influences from heterogeneity in the mantle or the inner core. Using high‐quality earthquake waveform doublets, we found that waves passing through the fluid core over a few years are significantly more variable than those passing through the mantle only. We interpret the temporal variability as the result of the fluid motion of the heterogeneous materials in the outer core. The level of heterogeneity in the fluid outer core is constrained to be ±0.022 s (95% confidence) in seismic travel times through the core, negligible for most seismological studies. However, the estimated velocity perturbation, about 10−3 for small‐scale heterogeneity (10 km) or 10−4 for large‐scale heterogeneity (1000 km), borders or exceeds the high‐end estimates of the lateral variations that can be supported by dynamic forces within the fluid core. The source of the heterogeneity is not clear at present.
Power line harmonic radiation observed by satellite: Properties and propagation through the ionosphere
Authors: Němec F. , Santolík O. , Parrot M. , Bortnik J.
Published: August 2008

We present results of a systematic survey of power line harmonic radiation events observed by the low‐altitude DEMETER spacecraft. Altogether, 88 events (45 with frequency spacing 50/100 Hz and 43 with frequency spacing 60/120 Hz) have been found by an automatic identification procedure and confirmed by visual inspection. Frequency‐Time intervals of individual lines forming the events have been found by an automated procedure, and the corresponding frequency‐time spectrograms have been fitted by a 2d‐Gaussian model. It is shown that the mean time duration of the lines forming the events is 20 seconds, with median being 12 seconds (this corresponds to the spatial dimensions of 156/90 km, respectively). The full width at half maximum of the frequency range of the lines is less than 3 Hz in the majority of cases. Moreover, the lines with larger bandwidth and the lines with the largest intensities often occur off exact multiples of base power system frequency. This can be explained either by wave‐particle interactions that take place and modify the radiated electromagnetic wave or by the improperly operating radiating power system. Full‐wave calculation of the efficiency of coupling of electromagnetic waves through the ionosphere has been done to show that it can explain lower intensity of events observed by satellite during the day as compared with those observed during the night. Estimated radiated peak power on the ground is larger for events observed during the day than for events observed during the night, and more events are observed during the day than during the night.
Assessment of global annual atmospheric energy balance from satellite observations
Authors: Lin Bing , Stackhouse Paul W. , Minnis Patrick , Wielicki Bruce A. , Hu Yongxiang , Sun Wenbo , Fan Tai‐Fang , Hinkelman Laura M.
Published: August 2008

Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface as well as latent and sensible heat over the oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation‐based turbulent heat flux estimates. Global annual means of the TOA net radiation obtained from both satellite direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 W/m2, respectively. The estimated atmospheric and surface heat imbalances are about −8 and 9 W/m2, respectively, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and the likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget: the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements has significantly reduced the bias errors in the observed global energy budgets of the climate system.
Characterizing the glycome of the mammalian immune system
Authors: Haslam Stuart M , Julien Sylvain , Burchell Joy M , Monk Clare R , Ceroni Alessio , Garden Oliver A , Dell Anne
Published: August 2008

The outermost layer of all immune cells, the glycocalyx, is composed of a complex mixture of glycoproteins, glycolipids and lectins, which specifically recognize particular glycan epitopes. As the glycocalyx is the cell's primary interface with the external environment many biologically significant events can be attributed to glycan recognition. For this reason the rapidly expanding glycomics field is being increasingly recognized as an important component in our quest to better understand the functioning of the immune system. In this review, we highlight the current status of immune cell glycomics, with particular attention being paid to T‐ and B‐lymphocytes and dendritic cells. We also describe the strategies and methodologies used to define immune cell glycomes.
Open Notebook Science - Falcipain-2 Preliminary Results
Authors: Bradley Jean-Claude , Rosenthal Philip , Guha Rajarshi , Mirza Khalid , Gut Jiri
Published: August 2008

This talk was presented by Jean-Claude Bradley at the American Chemical Society meeting in Philadelphia on August 20, 2008. An introduction to Open Notebook Science is presented followed by an illustration of how ONS can be used in drug discovery. New data relating to the anti-malarial activity of Ugi products on 2 falcipain-2 docking sites is detailed. The docking calculations were provided by Rajarshi Guha and the enzyme and in vitro assays on Plasmodium falciparum were provided by Phil Rosenthal and Jiri Gut. Most of the syntheses were carried out by Khalid Mirza in the Bradley group.Screencast available at: "http://video.google.com/videoplay?docid=3251406956070376532&hl=en":http://video.google.com/videoplay?docid=3251406956070376532&hl=en
Salt-stress-induced association of phosphatidylinositol 4,5-bisphosphate with clathrin-coated vesicles in plants
Authors: König Sabine , Ischebeck Till , Lerche Jennifer , Stenzel Irene , Heilmann Ingo
Published: August 2008

Plants exposed to hyperosmotic stress undergo changes in membrane dynamics and lipid composition to maintain cellular integrity and avoid membrane leakage. Various plant species respond to hyperosmotic stress with transient increases in PtdIns(4,5)P2; however, the physiological role of such increases is unresolved. The plasma membrane represents the outermost barrier between the symplast of plant cells and its apoplastic surroundings. In the present study, the spatio-temporal dynamics of stress-induced changes in phosphoinositides were analysed in subcellular fractions of Arabidopsis leaves to delineate possible physiological roles. Unlabelled lipids were separated by TLC and quantified by gas-chromatographic detection of associated fatty acids. Transient PtdIns(4,5)P2 increases upon exposure to hyperosmotic stress were detected first in enriched plasmamembrane fractions, however, at later time points, PtdIns(4,5)P2 was increased in the endomembrane fractions of the corresponding two-phase systems. When major endomembranes were enriched from rosette leaves prior to hyperosmotic stress and during stimulation for 60 min, no stress-induced increases in the levels of PtdIns(4,5)P2 were found in fractions enriched for endoplasmic reticulum, nuclei or plastidial membranes. Instead, increased PtdIns(4,5)P2 was found in CCVs (clathrin-coated vesicles), which proliferated several-fold in mass within 60 min of hyperosmotic stress, according to the abundance of CCV-associated proteins and lipids. Monitoring the subcellular distribution of fluorescence-tagged reporters for clathrin and PtdIns(4,5)P2 during transient co-expression in onion epidermal cells indicates rapid stress-induced co-localization of clathrin with PtdIns(4,5)P2 at the plasma membrane. The results indicate that PtdIns(4,5)P2 may act in stress-induced formation of CCVs in plant cells, highlighting the evolutionary conservation of the phosphoinositide system between organismic kingdoms.
Genetically modified adenoviral vector with the protein transduction domain of Tat improves gene transfer to CAR-deficient cells
Authors: Liu Shihai , Mao Qinwen , Zhang Weifeng , Zheng Xiaojing , Bian Ye , Wang Dongyang , Li Huijin , Chai Lihong , Zhao Junli , Xia Haibin
Published: August 2008

The transduction efficiency of Ad (adenovirus) depends, to some extent, on the expression level of CAR (coxsackievirus and Ad receptor) of a target cell. The low level of CAR on the cell surface is a potential barrier to efficient gene transfer. To overcome this problem, PTD.AdeGFP (where eGFP is enhanced green fluorescent protein) was constructed by modifying the HI loop of Ad5 (Ad type 5) fibre with the Tat (trans-activating) PTD (protein transduction domain) derived from HIV. The present study showed that PTD.AdeGFP significantly improved gene transfer to multiple cell types deficient in expression of CAR. The improvement in gene transfer was not the result of charge-directed binding between the virus and the cell surface. Although PTD.AdeGFP formed aggregates, it infected target cells in a manner different from AdeGFP aggregates precipitated by calcium phosphate. In addition, PTD.AdeGFP was able to transduce target cells in a dynamin-independent pathway. The results provide some new clues as to how PTD.AdeGFP infects target cells. This new vector would be valuable in gene-function analysis and for gene therapy in cancer.
Case Studies in Effective Treatment of Central Auditory Processing Disorders
Authors: Ferre Jeanane M. , Wickman Fotini M.
Published: August 2008

The behavioral characteristics of central auditory processing disorder (CAPD) are similar to those of other neurocognitive and communicative disorders. Differential diagnosis is used to “tease out” the auditory specific deficit. Differential intervention combines specific management strategies with specific rehabilitative procedures to minimize the impact of the CAPD and improve skills. A compelling body of research supports the use of specific types of therapeutic rehabilitation for listeners with CAPD; however, additional research is needed regarding treatment outcomes for specific auditory deficits. Single-subject case studies can provide evidence of treatment effectiveness in a clinical setting. This paper presents two cases that provide evidence that the inclusion of deficit specific auditory treatment into the overall intervention plan of students with specific central auditory processing disorder can reduce the deficit and minimize its impact in a relatively short period of time.
Toward Evidence-Based Practice in the Auditory Processing Disorder Clinic
Authors: Johnstone Patti M.
Published: August 2008

Audiologists are seeking evidence to guide clinical decision-making regarding the tests used to diagnose auditory processing disorder (APD) in children. Novel research paradigms using a population health framework hold promise in helping clinicians understand the prevalence, profile, and social underpinnings of APD in the general pediatric population. In addition, tests employing novel stimuli like speech-evoked auditory potentials or spatial and vocal cues may lead the way toward a new and more reliable APD test battery.
Visible photoemission from InN
Authors: Glesener J. W. , Estrera J. P.
Published: August 2008

At 5.8eV, InN has one of the highest electron affinities of any semiconductor. Upon applying cesium and oxygen to a previously hydrogen cleaned InN surface, visible photoemission was observed. The InN spectral response confirms the standard model of photoemission yield with an inclusion of a tunneling factor for the electron escape probability. The existence of photoemission beyond 950nm supports the case for a lower bandgap in this material.
Crawling beneath the free surface: Water snail locomotion
Authors: Lee Sungyon , Bush John W. M. , Hosoi A. E. , Lauga Eric
Published: August 2008

Land snails move via adhesive locomotion. Through muscular contraction and expansion of their foot, they transmit waves of shear stress through a thin layer of mucus onto a solid substrate. Since a free surface cannot support shear stress, adhesive locomotion is not a viable propulsion mechanism for water snails that travel inverted beneath the free surface. Nevertheless, the motion of the freshwater snail, Sorbeoconcha physidae, is reminiscent of that of its terrestrial counterparts, being generated by the undulation of the snail foot that is separated from the free surface by a thin layer of mucus. Here, a lubrication model is used to describe the mucus flow in the limit of small-amplitude interfacial deformations. By assuming the shape of the snail foot to be a traveling sine wave and the mucus to be Newtonian, an evolution equation for the interface shape is obtained and the resulting propulsive force on the snail is calculated. This propulsive force is found to be nonzero for moderate values of the capillary number but vanishes in the limits of high and low capillary number. Physically, this force arises because the snail’s foot deforms the free surface, thereby generating curvature pressures and lubrication flows inside the mucus layer that couple to the topography of the foot.
Hydrogen trapping state associated with the low temperature thermal desorption spectroscopy peak in hydrogenated nanostructured graphite
Authors: Miyabe Yumiko , Yoshida Tomoko , Muto Shunsuke , Kiyobayashi Tetsu , Wasada Hiroaki
Published: August 2008

Hydrogenated nanostructured graphite has been reported to exhibit a characteristic peak at around 600–800 K in thermal desorption spectroscopy (TDS). The origin of this peak is still controversial. We have reexamined it based on a combination Fourier transform infrared (FT-IR), electron diffraction, and electron energy-loss spectroscopy (EELS) study. The FT-IR spectrum of HNG exhibited an unknown broad absorption band at very low frequencies around 660 cm−1, which almost disappeared by annealing up to 800 K. Electron diffraction as well as plasmon peaks in EELS detected unusual shrinkage and subsequent expansion of the graphene interlayer distance by hydrogen incorporation and desorption with annealing, which were well correlated with the change in intensity of the 660 cm−1 IR band. An energetically stable configuration was found by theoretical model calculations based on GAUSSIAN03. All the present results are consistent with our previous studies, which suggested that hydrogen is loosely trapped between graphene layers [S. Muto et al., Jpn. J. Appl. Phys. 44, 2061 (2005); T. Kimura et al., J. Alloys Compd. 413, 150 (2006)].
Measurement of tropospheric RO2 and HO2 radicals by a laser-induced fluorescence instrument
Authors: Fuchs Hendrik , Holland Frank , Hofzumahaus Andreas
Published: August 2008

A new method (ROxLIF) for the measurement of atmospheric peroxy radicals (HO2 and RO2) was developed using a two-step chemical conversion scheme and laser-induced fluorescence (LIF) for radical detection. Ambient air is sampled into a differentially pumped flow reactor, in which atmospheric ROx radicals (=RO2+RO+HO2+OH) are chemically converted to HO2 by a large excess of NO and CO at reduced pressures (ROx mode). When only CO is added as a reagent, the sum of atmospheric HO2+OH is converted to HO2 (HOx mode). At the reactor outlet, part of the air flow is transferred into a low-pressure detection chamber, where the HO2 is further converted by reaction with NO to OH, which is then detected with high sensitivity by LIF at 308 nm. The ROxLIF technique has been implemented in an existing LIF instrument that is also capable of measuring atmospheric OH. From the concurrent measurements of ROx, HOx and OH, concentrations of HO2 and RO2 can be determined. The system is calibrated using the quantitative photolysis of water vapor at 185 nm as a radical source. Addition of CO or hydrocarbons to the calibration gas yields well-defined concentrations of HO2 or RO2, respectively, providing an estimated accuracy for the calibration of about 20%. The ROxLIF technique is extremely sensitive and has detection limits (signal-to-noise ratio=2) of about 0.1 pptv of HO2 or RO2 at a time resolution of 1 min. The paper describes the technique and its calibration, discusses the chemistry in the conversion reactor and possible interferences, and gives an example of ambient air measurements to demonstrate the performance of the new technique.
Reversible work function changes induced by photoisomerization of asymmetric azobenzene dithiol self-assembled monolayers on gold
Authors: Ah Qune Lloyd F. N. , Akiyama H. , Nagahiro T. , Tamada K. , Wee Andrew T. S.
Published: August 2008

We measured reversible changes in the work function (ΔϕAu) of gold substrates modified by asymmetric azobenzene dithiol self-assembled monolayers (SAMs) following photoisomerization and thermal recovery of the azo unit. The azobenzene derivative SAMs were photoisomerized to cis form by UV irradiation. ΔϕAu was monitored in real time during thermal recovery to trans form by ultraviolet photoelectron spectroscopy using a synchrotron light source. Changing the substituted functional group in the p′ position of the azobenzene from electron donating to electron withdrawing resulted in opposite responses of ΔϕAu against photoisomerization. Hence, a direct correlation between ΔϕAu and changes in molecular dipole moments was obtained.
Analysis of oxygen induced anisotropy crossover in Pt/Co/MOx trilayers
Authors: Manchon A. , Ducruet C. , Lombard L. , Auffret S. , Rodmacq B. , Dieny B. , Pizzini S. , Vogel J. , Uhlíř V. , Hochstrasser M. , Panaccione G.
Published: August 2008

Extraordinary Hall effect and x-ray spectroscopy measurements have been performed on a series of Pt/Co/MOx trilayers (M=Al, Mg, Ta, etc.) in order to investigate the role of oxidation in the onset of perpendicular magnetic anisotropy at the Co/MOx interface. It is observed that varying the plasma oxidation time modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. We focused on the influence of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The interfacial electronic structure is analyzed via x-ray photoelectron spectroscopy measurements. It is shown that the maximum of out-of-plane magnetic anisotropy corresponds to the appearance of a significant density of Co–O bondings at the Co/AlOx interface.
Thickness-dependent structural and electrical properties of multiferroic Mn-doped BiFeO3 thin films grown epitaxially by pulsed laser deposition
Authors: Zhu X. H. , Béa H. , Bibes M. , Fusil S. , Bouzehouane K. , Jacquet E. , Barthélémy A. , Lebeugle D. , Viret M. , Colson D.
Published: August 2008

Thickness dependence of structural and electrical properties of multiferroic Mn-doped BiFeO3 (BFMO) thin films, grown on SrTiO3 (001) substrates with a bottom electrode of SrRuO3, was investigated. Very good ferroelectric properties were obtained in the thicker BFMO films with a typical remanent polarization of ∼65 μC/cm2, while ferroelectric polarization switching was too difficult to detect using a conventional technique in the thinnest BFMO films due to a much higher coercive field and an increase in the tunneling current. Their ferroelectric nature, however, was demonstrated by piezoresponse force microscopy, and excellent insulating properties and homogeneity were achieved in the films.
Phonon backscattering and thermal conductivity suppression in sawtooth nanowires
Authors: Moore Arden L. , Saha Sanjoy K. , Prasher Ravi S. , Shi Li
Published: August 2008

The effect of surface roughness on phonon transport in a nanowire has often been described by treating the surface as flat with a specularity parameter (p) in the range between 0 and 1. A lower thermal conductivity limit is approached at p=0 for diffuse surface. It is demonstrated here by Monte Carlo simulation that sawtooth roughness on a nanowire can cause phonon backscattering and suppress the thermal conductivity below the diffuse surface limit. The backscattering effect can be accounted for only by a negative p if the detail of the surface roughness is ignored.
Indium tin oxide modified transparent nanotube thin films as effective anodes for flexible organic light-emitting diodes
Authors: Li Jianfeng , Hu Liangbing , Liu Jun , Wang Lian , Marks Tobin J. , Grüner George
Published: August 2008

Sn-doped In2O3 (ITO) modified single-walled carbon nanotube (SW-CNT) transparent electrodes are fabricated on flexible polyethyleneterephthalate (PET) substrates by stamp printing SW-CNT films, followed by room temperature ion-assisted deposition of ITO. Polymer light-emitting diodes (PLEDs) using such film as anodes exhibit superior performance versus CNT-only controls. Flexible PLEDs with the following structure: PET/CNT(30 nm)-ITO(45 nm)/poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate)/[poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)diphenylamine)]+{4,4′-bis[(p-trichlorosilyl propylphenyl)-phenylamino]biphenyl}/[poly(9,9-dioctylfluorene-co-benzothiadiazole)]/CsF/Al, achieve a maximum light output of 8900cd∕m2 with a current efficiency of 4.5cd∕A. Bending test comparisons with ITO/PET show the ITO modified CNT/PET electrodes to be far more mechanically flexible.
Modeling shock waves in orthotropic elastic materials
Authors: Vignjevic Rade , Campbell James C. , Bourne Neil K. , Djordjevic Nenad
Published: August 2008

A constitutive relationship for modeling of shock wave propagation in orthotropic materials is proposed for nonlinear explicit transient large deformation computer codes (hydrocodes). A procedure for separation of material volumetric compression (compressibility effects equation of state) from deviatoric strain effects is formulated, which allows for the consistent calculation of stresses in the elastic regime as well as in the presence of shock waves. According to this procedure the pressure is defined as the state of stress that results in only volumetric deformation, and consequently is a diagonal second order tensor. As reported by Anderson et al. [Comput. Mech. 15, 201 (1994)], the shock response of an orthotropic material cannot be accurately predicted using the conventional decomposition of the stress tensor into isotropic and deviatoric parts. This paper presents two different stress decompositions based on the assumption that the stress tensor is split into two components: one component is due to volumetric strain and the other is due to deviatoric strain. Both decompositions are rigorously derived. In order to test their ability to describe shock propagation in orthotropic materials, both algorithms were implemented in a hydrocode and their predictions were compared to experimental plate impact data. The material considered was a carbon fiber reinforced epoxy material, which was tested in both the through-thickness and longitudinal directions. The ψ decomposition showed good agreement with the physical behavior of the considered material, while the ζ decomposition significantly overestimated the longitudinal stresses.
Ultrafast dynamics of photoexcited charge carriers in nanocrystalline diamond
Authors: Němec P. , Preclíková J. , Kromka A. , Rezek B. , Trojánek F. , Malý P.
Published: August 2008

We report on ultrafast charge carrier dynamics in sub-band-gap energy states in nanocrystalline diamond self-supporting membranes prepared by plasma-enhanced chemical vapor deposition technique. The obtained data are hence not influenced by the substrate effects. Results of the femtosecond transient transmission and photoluminescence laser spectroscopy indicate relaxation of photoexcited carriers with the time constants of the order of 1 ps. This is attributed to an ultrafast spatial separation of holes and electrons at the surface of nanocrystals. Only the carrier population photoexcited in energy levels of 1.68 eV silicon related center decays on a much longer time scale with the time constant of 2.4 ns.
Suppression of the intermode plasmon scattering due to total internal reflection of oblique plasmons in a multichannel high-electron-mobility transistor
Authors: Popov V. V.
Published: August 2008

Terahertz radiation impinging on multichannel high-electron-mobility transistors (HEMTs) with comparable lateral and transverse gated-channel dimensions excites oblique plasmons modes that experience the total internal reflection from the gate edges. This reflection prevents leakage of the gated plasmon energy into the ungated plasmons modes of ungated device regions. These results can explain significant shrinking of the gated plasmon resonance linewidth in the multichannel HEMT.
Partially coherent extreme ultraviolet interference lithography for 16nm patterning research
Authors: Goldstein M. , Wüest A. , Barnhart D.
Published: August 2008

Conditions are reported under which a partially coherent plasma source of 13.5nm wavelength radiation is found to be suitable for interference lithography. The predicted resolution exceeds the capability of present imaging systems and is comparable to synchrotron-based approaches. Methods borrowed from ray tracing are utilized for a partially coherent interference analysis, and a rigorous coupled wave theory is applied to optimize grating efficiency. The results suggest that a compact patterning tool with a resolution of 16nm is possible by a careful selection of the design parameters.
Strain-compensated InAs/GaNAs quantum dots for use in high-efficiency solar cells
Authors: Oshima Ryuji , Takata Ayami , Okada Yoshitaka
Published: August 2008

We have investigated GaAs-based p-i-n quantum dot solar cells (QDSCs) with 10 up to 20 stacked layers of self-assembled InAs quantum dots (QDs) grown by atomic hydrogen-assisted molecular beam epitaxy. The net average lattice strain was minimized by using the strain-compensation technique, in which GaNAs dilute nitrides were used as spacer layers. The filtered short-circuit current density beyond GaAs bandedge was 2.47 mA/cm2 for strain-compensated QDSC with 20 stacks of InAs QD layers, which was four times higher than that for strained QDSC with identical cell structure.
Anomaly of the rotational nonergodicity parameter of glass formers probed by high field electron paramagnetic resonance
Authors: Bercu V. , Martinelli M. , Massa C. A. , Pardi L. A. , Rössler E. A. , Leporini D.
Published: August 2008

Exploiting the high angular resolution of high field electron paramagnetic resonance measured at 95, 190, and 285 GHz we determine the rotational nonergodicity parameter of different probe molecules in the glass former o-terphenyl and polybutadiene in a model-independent way. Our results clearly show a characteristic change in the temperature of the nonergodicity parameter proving a rather sharp dynamic crossover in both systems, in contrast to previous results from other techniques.
Topology of chaotic mixing patterns
Authors: Thiffeault Jean-Luc , Finn Matthew D. , Gouillart Emmanuelle , Hall Toby
Published: August 2008

A stirring device consisting of a periodic motion of rods induces a mapping of the fluid domain to itself, which can be regarded as a homeomorphism of a punctured surface. Having the rods undergo a topologically complex motion guarantees at least a minimal amount of stretching of material lines, which is important for chaotic mixing. We use topological considerations to describe the nature of the injection of unmixed material into a central mixing region, which takes place at injection cusps. A topological index formula allow us to predict the possible types of unstable foliations that can arise for a fixed number of rods.
Detection of seizure rhythmicity by recurrences
Authors: Harrison Mary Ann F. , Frei Mark G. , Osorio Ivan
Published: August 2008

Epileptic seizures show a certain degree of rhythmicity, a feature of heuristic and practical interest. In this paper, we introduce a simple model of this type of behavior, and suggest a measure for detecting and quantifying it. To evaluate our method, we develop a set of test segments that incorporate rhythmicity features, and present results from the application of this measure to test segments. We then analyze electrocorticogram segments containing seizures, and present two examples. Finally, we discuss the similarity of our method to techniques for detecting unstable periodic orbits in chaotic time series.
GaSb based light emitting diodes with strained InGaAsSb type I quantum well active regions
Authors: Suchalkin Sergey , Jung Seungyong , Kipshidze Gela , Shterengas Leon , Hosoda Takashi , Westerfeld David , Snyder Donald , Belenky Gregory
Published: August 2008

Mid-IR (λ≈3–3.5 μm) light emitting diodes with quinternary AlInGaAsSb barriers and InGaAsSb strained quantum wells grown on GaSb substrates have been demonstrated. The devices produced a quasi-cw emission power of 0.7 mW at room temperature and 2.5 mW at T=80 K.
Low-voltage high-performance C60 thin film transistors via low-surface-energy phosphonic acid monolayer/hafnium oxide hybrid dielectric
Authors: Acton Orb , Ting Guy , Ma Hong , Jen Alex K.-Y.
Published: August 2008

C 60 -based organic thin film transistors (OTFTs) have been fabricated using a n-octadecylphosphonic acid self-assembled monolayer/sol-gel processed hafnium oxide hybrid dielectric. With the combination of high capacitance (580 nF/cm2) and low leakage current density (8×10−9 A/cm2), this hybrid dielectric yields C60 OTFTs operating under 1.5 V with an average n-channel saturation field-effect mobility of 0.28 cm2/V s, high on-off current ratio of 105, and low subthreshold slope of 100 mV/decade. The low surface energy of the n-octadecylphosphonic acid allows C60 to form a thin film with large grains that provide an efficient charge carrier pathway for the low-voltage OTFTs.
Two-species mixing in a nested Penning trap for antihydrogen trapping
Authors: Ordonez C. A. , Weathers D. L.
Published: August 2008

There exists an international quest to trap neutral antimatter in the form of antihydrogen for scientific study. One method that is being developed for trapping antihydrogen employs a nested Penning trap. Such a trap serves to mix positrons and antiprotons so as to produce low energy antihydrogen atoms. Mixing is achieved when the confinement volumes of the two species overlap one another. In the work presented here, a theoretical understanding of the mixing process is developed by analyzing a mixing scheme that was recently reported [G. Gabrielse et al., Phys. Rev. Lett. 100, 113001 (2008)]. The results indicate that positron space charge or collisions among antiprotons may substantially reduce the fraction of antiprotons that have an energy suitable for antihydrogen trapping.
Resonant coherent Bragg rod analysis of strained epitaxial heterostructures
Authors: Kumah D. P. , Riposan A. , Cionca C. N. , Husseini N. S. , Clarke R. , Lee J. Y. , Millunchick J. M. , Yacoby Y. , Schlepütz C. M. , Björck M. , Willmott P. R.
Published: August 2008

The resonant response of the complex x-ray scattering factor has been used in conjunction with the coherent Bragg rod analysis phase-retrieval algorithm to determine the composition and strain profiles of ultrathin layers of GaAs grown on InGaAs buffers. The buffer layers are nominally latticed matched with the InP substrate and the subsequent GaAs growth is compared at two different temperatures: 480 and 520°C. We show that electron density maps extracted from Bragg rod scans measured close to the Ga and As K-edges can be used to deconvolute roughness and intermixing. It is found that indium incorporation and roughening lead to a significant reduction of the strain in this system.
Direct observation of the size dependence of Dexter energy transfer from polymer to small PbS quantum dots
Authors: Zhang Yating , Xu Zhangcheng
Published: August 2008

Small PbS quantum dots (QDs) with diameters ranging from 2.5 to 3 nm were synthesized directly in the conjugated polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) at 70 °C. To monitor the size dependence of Dexter energy transfer [D. L. Dexter, J. Chem. Phys. 21, 836 (1953)] from MEH-PPV to PbS QDs, the photoluminescence of MEH-PPV is measured for a series of samples with varying QD sizes controlled by the reaction time. A decreased transfer rate is observed for PbS QDs with a diameter of about 2.65 nm due to the minimum overlap between the emission spectrum of MEH-PPV and the 1Se-1Sh and 1Pe-1Sh transitions of PbS QDs.
Confining and slowing airborne sound with a corrugated metawire
Authors: Christensen J. , Huidobro P. A. , Martín-Moreno L. , García-Vidal F. J.
Published: August 2008

In this letter we present a theoretical study on the acoustic wave propagation along a periodically corrugated perfect rigid wire surrounded by air. It is shown how acoustic surface waves (ASWs) can be engineered with their propagation properties controlled by geometrical means. These highly localized ASWs give rise to strong acoustical field confinement along the wire, whereas the slowing down of sound decelerate the group velocity down to zero. What is believed to be a promising feature of these low-loss propagation properties is the ability to tune sensing and screening applications with good transducer coupling.
Diamond solid state ionization chambers for x-ray absorption spectroscopy applications
Authors: De Sio A. , Bocci A. , Pace E. , Castellano C. , Cinque G. , Tartoni N. , D’Acapito F.
Published: August 2008

The photoresponse of a diamond detector has been compared with a standard ionization chamber in x-ray absorption spectroscopy applications. A photoconductive device based on a nitrogen-doped single crystal diamond has been tested by synchrotron radiation. Time stability and linearity have been studied by x rays at 10 keV to assess its performances. Finally, extended x-ray absorption fine structure at the Fe K-edge was carried on a standard iron target using both the diamond device and the IC. Spectroscopical results have been compared including references to literature.
Different curvatures of tunable liquid microlens via the control of laminar flow rate
Authors: Seow Y. C. , Liu A. Q. , Chin L. K. , Li X. C. , Huang H. J. , Cheng T. H. , Zhou X. Q.
Published: August 2008

This letter reports the tunable liquid microlens using three laminar flows injected into an expansion chamber. Different lens shapes and curvatures can be achieved and tuned through the control of three flow rates. The expansion chamber is designed to improve the fluidic stability and maintain the ideal lens shape for precise microscale optical measurement. The optical aberration is also eliminated by minimizing the diffusive broadening at the interfaces. The collimation and focusing capabilities of three liquid microlenses are demonstrated. The tunable liquid microlens is promising as a tool to realize different optical components that can be integrated onto a microchip.
Thermochemical control of oil droplet motion on a solid substrate
Authors: Song Chaeyeon , Kim Kipom , Lee Kyuyong , Pak Hyuk Kyu
Published: August 2008

Through the thermochemical control of a liquid droplet on a solid substrate, we investigated the motion of the droplet and the underlying mechanism. Depending on the contact angle of the running droplet on the substrate with a chemical gradient coating, we observed two different behaviors for the droplet under local laser heating: reversing for a contact angle larger than a critical value (∼90°) and passing for a smaller value. The motion at the laser heating position was found to be closely related to the contact angle change, indicating that capillary flow plays an important role in the thermally induced motion of the droplet.