bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal variability of biogenic isoprene emissions from a temperate estuary
Authors: Exton D. A. , Suggett D. J. , Steinke M. , McGenity T. J.
Published: March 2012

Isoprene is important for its atmospheric impacts and the ecophysiological benefits it affords to emitting organisms; however, isoprene emissions from marine systems remain vastly understudied compared to terrestrial systems. This study investigates for the first time drivers of isoprene production in a temperate estuary, and the role this production may play in enabling organisms to tolerate the inherently wide range of environmental conditions. Intertidal sediment cores as well as high and low tide water samples were collected from four sites along the Colne Estuary, UK, every six weeks over a year. Isoprene concentrations in the water were significantly higher at low than high tide, and decreased toward the mouth of the estuary; sediment production showed no spatial variability. Diel isoprene concentration increased with light availability and decreased with tidal height; nighttime production was 79% lower than daytime production. Seasonal isoprene production and water concentrations were highest for the warmest months, with production strongly correlated with light (r2 = 0.800) and temperature (r2 = 0.752). Intertidal microphytobenthic communities were found to be the primary source of isoprene, with tidal action acting as a concentrating factor for isoprene entering the water column. Using these data we estimated an annual production rate for this estuary of 681 μmol m−2 y−1. This value falls at the upper end of other marine estimates and highlights the potentially significant role of estuaries as isoprene sources. The control of estuarine isoprene production by environmental processes identified here further suggests that such emissions may be altered by future environmental change.
Lithospheric and upper mantle structure of the northeastern Tibetan Plateau
Authors: Yue Han , Chen Y. John , Sandvol Eric , Ni James , Hearn Thomas , Zhou Shiyong , Feng Yongge , Ge Zengxi , Trujillo Andrea , Wang Yanbin , Jin Ge , Jiang Mingming , Tang Youcai , Liang Xiaofeng , Wei Songqiao , Wang Haiyang , Fan Wenyuan , Liu Zheng
Published: March 2012

We use receiver functions calculated for data collected by the INDEPTH‐IV seismic array to image the three‐dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern Tibet. Our results indicate an average crustal thickness of 65 to 70 km in northern Tibet. In addition, we observe a 20 km Moho offset beneath the northern margin of the Kunlun Mountains, a 10 km Moho offset across the Jinsha River Suture and gently northward dipping Moho beneath the Qaidam Basin. A region in the central Qiangtang Terrane with higher than normal crustal Vp/Vs ratio of ∼1.83 can be the result of the Eocene magmatic event. In the Qiangtang Terrane, we observe a significant lithospheric mantle discontinuity beneath the Bangong‐Nujiang Suture at 80 km depth which dips ∼10° to the north, reaching ∼120 km depth. We interpret this feature as either a piece of Lhasa Terrane or remnant oceanic slab underthrust below northern Tibet. We detect a ∼20 km depression of the 660‐km discontinuity in the mantle transition zone beneath the northern Lhasa Terrane in central Tibet, which suggests this phase transition has been influenced by a dense and/or cold oceanic slab. A modest ∼10 km depression of the 410‐km discontinuity located beneath the northern Qiangtang Terrane may be the result of localized warm upwelling associated with small‐scale convection induced by the penetration of the sinking Indian continental lithosphere into the transition zone beneath the central Tibetan Plateau.
Impact of Greenland's topographic height on precipitation and snow accumulation in idealized simulations
Authors: Hakuba M. Z. , Folini D. , Wild M. , Schär C.
Published: March 2012

The Greenland Ice Sheet (GrIS) is one of the most dominant orographic obstacles for atmospheric flow in the Northern Hemisphere. Within an idealized framework, we investigate the potential impact of a reduced Greenland topography upon precipitation, snow accumulation, and atmospheric circulation over the GrIS. Using the global atmospheric model ECHAM5‐HAM at about 1° spatial resolution (T106) and with present‐day climatological mean conditions, we perform four 16‐year sensitivity experiments that are identical except for the height of the GrIS topography: one control simulation with the present‐day Greenland topography, and three simulations with topographies reduced to 75%, 50%, and 25% of the present‐day height. This simple reduction of the GrIS topography (as compared to realistic melt dynamics) leads to an overall increase in annual total precipitation and snow accumulation, composed of significant increases in eastern, northern, and central Greenland and decreases on the western slopes. In principle, this gain in snow accumulation raises the possibility of a negative feedback that would stabilize the height of the GrIS. However, this feedback is likely overcompensated by enhanced ablation (positive feedback), as surface air temperatures strongly increase with reduced topographic height. The analysis of changes in circulation patterns indicates that flatter topographies allow the atmospheric flow to penetrate farther inland, enabling precipitation in regions that are presently desert‐like. Prominent circulation features change, in particular the all‐season Greenland Anticyclone and wintertime Icelandic Low become weaker with lower topography.
Climate change projection of snowfall in the Colorado River Basin using dynamical downscaling
Authors: Wi Sungwook , Dominguez Francina , Durcik Matej , Valdes Juan , Diaz Henry F. , Castro Christopher L.
Published: March 2012

Recent observations show a decrease in the fraction of precipitation falling as snowfall in the western United States. In this work we evaluate a historical and future climate simulation over the Colorado River Basin using a 35 km continuous 111 year simulation (1969–2079) of the Weather Research and Forecasting (WRF) regional climate model with boundary forcing from the Hadley Centre for Climate Prediction and Research/Met Office's HadCM3 model with A2 emission scenario. The focus of this work is to (1) evaluate the simulated spatiotemporal variability of snowfall in the historical period when compared to observations and (2) project changes in snowfall and the fraction of precipitation that falls as snow during the 21st century. We find that the spatial variability in modeled snowfall in the historical period (1981–2005) is realistically represented when compared to observations. The trends of modeled snowfall are similar to the observed trends except at higher elevations. Examining the continuous 111 year simulation, we find the future projections show statistically significant increases in temperature with larger increases in the northern part of the basin. There are statistically insignificant increases in precipitation, while snowfall shows a statistically significant decrease throughout the period in all but the highest elevations and latitudes. The fraction of total precipitation falling as snow shows statistically significant declines in all regions. The strongest decrease in snowfall is seen at high elevations in the southern part of the basin and low elevations in the northern part of the basin. The regions of most intense decreases in snow experience a decline of approximately 50% in snowfall throughout the 111 year simulation period. The regions of strongest declines in snowfall roughly correspond to the region of migration of the zero degree Celsius line and emphasize snowfall dependence on both altitude and latitude.
Investigating the mesoscale impact of artificial reservoirs on frequency of rain during growing season
Authors: Degu Ahmed M. , Hossain Faisal
Published: March 2012

The specific question that this study pursued is “Have large dams modified the downwind frequency of rainfall in the mesoscale during growing season?” Rigorously quality controlled precipitation data comprising 3055 stations from the Global Historical Climatology Network (GHCN) were analyzed with 92 large dams in the U.S. Using 30 years of atmospheric reanalysis data, the wind rose diagram for each dam was derived from wind data at the 850 mb level. Around 96 (78) GHCN downwind (upwind) precipitation stations were identified that were within 100 km (mesoscale) of dams. The Mediterranean and humid subtropical climates were found to have experienced the highest and statistically significant change in trend in precipitation frequency downwind and within 100 km of dams during the growing season. The warm summer continental climatic region was found to have exhibited the next most modification. Paired analyses were performed as a function of predam and postdam and at upwind and downwind locations. For Mediterranean climates, the stations studied were found to have experienced a generally weak trend in precipitation frequency before the construction of the selected dams and a systematically more impacted trend during the postdam period. However, using precipitation observations alone, the specific role played by irrigation dams could not be distinguished from other types of dams in this study. Analysis of humidity records, however, revealed that dams can increase the moistening of the air mass by about 5%–15% (in terms of vapor pressure) as it passes downwind, while the effect can also be marginal for other dams. In summary, our study reveals that it is easier to establish a physically intuitive connection between large dams and downwind frequency of rain, but it is much more difficult to demonstrate this connection consistently for all the downwind stations in the mesoscale without the use of additional geophysical data (e.g., topography, land use, and land cover patterns) and mesoscale atmospheric modeling.
Analyzing the combined influence of solar activity and El Niño on streamflow across southern Canada
Authors: Fu Congsheng , James April L. , Wachowiak Mark P.
Published: March 2012

It is well known that the spatial and temporal patterns in streamflow can be correlated with many teleconnections, e.g., solar activity and climatic phenomena such as El Niño. However, fewer studies have attempted to analyze both the influence of solar activity and large scale climatic phenomena on natural processes, particularly hydrological processes. In this study we examine long term records of solar activity and El Niño for their combined influence on streamflow across southern Canada. Data used in the analysis include sunspot number, sea surface temperature anomaly in Niño region 3.4, and annual mean streamflow from 50 Canadian Reference Hydrometric Basin Network (RHBN) stations with record lengths ≥50 years (14 of them ≥90 years). Analysis is performed using Fourier spectrum analysis (FSA), continuous wavelet transform (CWT), and cross wavelet transform coherence analysis (WTC). Results of FSA show that for almost all the 14 RHBN stations with record lengths of ≥90 years, streamflow exhibits periodicities of approximately 11 and 22 years (which is in accordance with solar activity), as well as shorter term periodicities consistent with El Niño (2–7 years). WTC analysis confirms the correlation between these periodicities (2–7 years, 11 years, 22 years) in streamflow with solar activity and El Niño records. Both solar activity and El Niño's influences on annual mean streamflow in 18–32 year bands are common, while the influence of El Nino is more extensive in the 2–7 and ∼11 year bands. Through examination of correlations between solar activity and streamflow, El Niño and streamflow, and finally El Niño and solar activity, WTC analysis has identified that solar activity affects El Niño first, and this influence is then transferred by El Niño to streamflow. This study expands on earlier efforts examining linkages between El Niño and streamflow across southern Canada to an examination of linkages between solar activity, El Niño, and streamflow.
Seismic evidence of tectonic control on the depth of water influx into incoming oceanic plates at subduction trenches
Authors: Lefeldt M. , Ranero C. R. , Grevemeyer I.
Published: March 2012

Water transported by slabs into the mantle at subduction zones plays key roles in tectonics, magmatism, fluid and volatiles fluxes, and most likely in the chemical evolution of the Earth's oceans and mantle. Yet, incorporation of water into oceanic plates before subduction is a poorly understood process. Several studies suggest that plates may acquire most water at subduction trenches because the ocean crust and uppermost mantle there are intensely faulted caused by bending and/or slab pull, and display anomalously low seismic velocities. The low velocities are interpreted to arise from a combination of fluid‐filled fractures associated to normal faulting and mineral transformation by hydration. Mantle hydration by transformation of nominally dry peridotite to water‐rich serpentinite could potentially create the largest fluid reservoir in slabs and is therefore the most relevant for the transport of water in the deep mantle. The depth of fracturing by normal‐fault earthquakes is usually not well constrained, but could potentially create deep percolation paths for water that might hydrate up to tens of kilometers into the mantle, restrained only by serpentine stability. Yet, interpretation of deep intraplate mineral alteration remains speculative because active‐source seismic experiments have sampled only the uppermost few kilometers of mantle, leaving the depth‐extent of anomalous velocities and their relation to faulting unconstrained. Here we use a joint inversion of active‐source seismic data, and both local and regional earthquakes to map the three dimensional distribution of anomalous velocities under a seismic network deployed at the trench seafloor. We found that anomalous velocities are restrained to the depth of normal‐fault micro‐earthquake activity recorded in the network, and are considerably shallower than either the rupture depth of teleseismic, normal‐fault earthquakes, or the limit of serpentine stability. Extensional micro‐earthquakes indicate that each fault in the region slips every 2–3 months which may facilitate regular water percolation. Deeper, teleseismic earthquakes are comparatively infrequent, and possibly do not cause significant fracturing that remains open long enough to promote alteration detectable with our seismic study. Our results show that the stability field of serpentine does not constrain the depth of potential mantle hydration.
Pickup ions and ion cyclotron wave amplitudes upstream of Mars: First results from the 1D hybrid simulation
Authors: Cowee M. M. , Gary S. P. , Wei H. Y.
Published: March 2012

Observations upstream of Mars show strong and persistent plasma wave activity near the local proton cyclotron frequency. These waves are thought to be generated by unstable populations of newborn ions produced by ionization of the Martian hydrogen exosphere. It is generally believed that the amplitudes of the waves are related to the energy of the local pickup ion population, such that the observed spatial and temporal distribution of the wave amplitudes could be used as a diagnostic of local exospheric structure and loss rate. To understand the relationship between wave amplitudes and ion pickup rate, we carry out a parametric study using the 1D hybrid simulation (kinetic ions, fluid electrons) for varying pickup rates and pickup geometry for the Martian planetary environment. Our results indicate that, contrary to expectations, the observed local ion cyclotron wave amplitudes cannot be easily related to local ion pickup rates because the growth time of the instability is long compared to the transit time of the waves past Mars. Additionally, we find the amount of pickup ion energy lost to wave growth is not a constant over all injection rates and wave amplitudes are likely affected by propagation through regions of spatially non‐uniform ion production. Because the waves in the upstream region are in a state of growth rather than saturated, the simulations suggest the pickup ion distributions are likely only partially scattered.
Spherical‐Earth finite element model of short‐term postseismic deformation following the 2004 Sumatra earthquake
Authors: Hu Yan , Wang Kelin
Published: March 2012

Decadal‐scale postseismic deformation of subduction earthquakes has been widely modeled using a Maxwell viscoelastic Earth with a mantle‐wedge viscosity of about 1019 Pa s. Short‐term postseismic deformation within a few years after the earthquake remains a more challenging problem because of the predominance of afterslip of the megathrust and the potentially more complex mantle rheology. Questions include the necessity of invoking the transient rheology and the relative importance of contributions from afterslip and viscoelastic relaxation. In this work, we address these questions by developing a spherical‐Earth viscoelastic finite element model for the short‐term postseismic deformation following the magnitude 9.2 Sumatra earthquake of 2004. The model consists of elastic overriding and subducting plates and a viscoelastic mantle of bi‐viscous Burgers rheology, with the continental mantle (mantle wedge) being less viscous than the oceanic mantle by a factor of ten. Primary observational constraints for the short‐term postseismic deformation include ∼1 year net displacements of nine near‐field GPS sites and ∼3 year time series from three far‐field sites several hundred kilometers from the 2004 rupture zone. Model results indicate that the afterslip of the fault must be at work within the first few years after the earthquake. The observed deformation is best explained with a model that includes both the afterslip and transient rheology. In the preferred model, the transient and steady state viscosities of the mantle wedge are 5 × 1017 Pa s and 1019 Pa s, respectively.
Induction of type I IFNs by intracellular DNA‐sensing pathways
Authors: Cavlar Taner , Ablasser Andrea , Hornung Veit
Published: March 2012

A successful antimicrobial immune response involves the coordinate action of cells and soluble factors, with the cytokine family of type I interferons (IFNs) having a central role. Type I IFNs are not only crucial in conferring immediate antimicrobial, most importantly antiviral effects, but they also have an essential role in bridging the innate with the adaptive immune response. Therefore, production of these key cytokines must be tightly controlled. To this effect the host has evolved a set of pattern recognition receptors (PRRs) that reliably and specifically detect the presence of microbial pathogens before mounting an IFN response. Most PRR pathways that are known to induce type I IFNs are triggered upon recognition of nucleic acids. This mode of sensing is not straightforward, as large amounts of RNA and DNA are also present within the host. Nevertheless, in some cases distinct molecular features that are present within foreign nucleic acids but absent in endogenous nucleic acids, allow the host to reliably discriminate between ‘self’ and ‘non‐self’. At the same time, compartmentalization of PRRs within subcellular organelles that are usually devoid of host nucleic acids, but are sites of pathogen localization, is another principle that enables the host to distinguish self from non‐self. The latter mode of sensing applies to the detection of microbial DNA within the cytoplasm, a compartment in which host DNAs are usually not present. Despite the past years’ tremendous progress in the field of innate immunity, our understanding of cytoplasmic DNA sensing mechanisms is only beginning to form/take form. In this review, we outline the recent advancements in the elucidation of intracellular DNA‐sensing pathways and discuss the future directions of this emerging field.
Codonopsis pilosula twines either to the left or to the right
Authors: Lin Gonghua , Zhao Fang , Nevo Eviatar , Zhang Tongzuo , Su Jianping
Published: March 2012

We report the twining handedness of Codonopsis pilosula, which has either a left- or right-handed helix among different plants, among different tillers within a single plant, and among different branches within a single tiller. The handedness was randomly distributed among different plants, among the tillers within the same plants, but not among the branches within the same tillers. Moreover, the handedness of the stems can be strongly influenced by external forces, i.e. the compulsory left and right forming inclined to produce more left- and right-handed twining stems, respectively, and the reversing could make a left-handed stem to be right-handed and vice versa. We also discuss the probable mechanisms these curious cases happen.
Lyme Borreliosis During Pregnancy
Authors: Lakos András , Solymosi Norbert
Published: March 2012

One of the authors (AL) presented a poster on 34 pregnancies of maternal Lyme borreliosis (Lb) in 1995. It was striking that untreated Lb associated with higher probability of adverse outcome but the number of patients were small and the statistical power was low. We have recently published a paper on 95 maternal Lb and the outcome of their pregnancies. Since the closure of the database for that manuscript the number of the pregnant women with Borrelia infection observed in our Centre increased to 124, and the statistical analysis strengthened our previous doubtful observations and reached significant results in important aspects by now. This series is the largest study to date on this topic. Treatment was administered parenterally to 87 (70%) women and orally to 25 (20.0%). Infection remained untreated in 12 (10%) pregnancies. Adverse outcomes were seen in 7/87 (8%), 9/25 (36%), 8/12 (67%), of the parenterally, orally treated and untreated women, respectively. In comparison to patients treated with antibiotics, untreated women had a significantly higher risk of adverse pregnancy outcomes (OR: 11.62, p<0.001). Mothers treated orally comparing to iv. treatment had an increased chance (OR: 6.28) to have an adverse outcome (p=0.001). In the adverse pregnancy outcome, the most impressive difference was between the untreated and parenterally treated women (OR: 21.44, p<0.001). The probability of adverse outcome increased by the exposition time (from the first maternal symptom to the treatment or delivery). When the exposition time has reached four months, the probability of adverse outcome increased by 33%. We had no chance to examine the bacterial invasion of the foetus. Loss of the pregnancy (N=9), small for gestational age or preterm birth (N=7) were the most prevalent adverse outcomes in our series. The other complications were heterogeneous. Our results indicate that untreated or orally treated maternal Borrelia burgdorferi s.l. infection is associated with adverse outcomes. 'Congenital Lyme disease' similar to the Hutchinson's triad in syphilis is unlikely.
FAIRE-seq data analysis of Chlamydomonas reinhardtii under carbon deprivation
Authors: Urbina-Gómez David , Vischi Winck Flavia , Müller-Röber Bernd , Riaño-Pachón Diego Mauricio
Published: March 2012

For the genome-wide identification of nucleosome depleted regions under carbon deprivation, we analyze an available set of data from an assay of formaldehyde-assisted isolation of regulatory elements followed by sequencing (FAIRE-seq). Mapping to the sequenced nuclear genome of C.reinhardtii, followed by the identification of the enrichment-sequenced fragments was performed. We examined the location of these fragments relative to annotated genes. The related genes were associated to the corresponding Gene-Ontology (GO), for an evaluation of over-representate GO categories. Some genes, link with functions or locations, that have been previous described, indicating the success of the method finding carbon-metabolism related fragments.
Virology and molecular pathogenesis of HPV (human papillomavirus)associated oropharyngeal squamous cell carcinoma
Authors: Miller Daniel L. , Puricelli Michael D. , Stack M. Sharon
Published: March 2012

The current literature fully supports HPV (human papillomavirus)-associated OPSCC (oropharyngeal squamous cell carcinoma) as a unique clinical entity. It affects an unambiguous patient population with defined risk factors, has a genetic expression pattern more similar to cervical squamous cell carcinoma than non-HPV-associated HNSCC (head and neck squamous cell carcinoma), and may warrant divergent clinical management compared with HNSCC associated with traditional risk factors. However, a detailed understanding of the molecular mechanisms driving these differences and the ability to exploit this knowledge to improve clinical management of OPSCC has not yet come to fruition. The present review summarizes the aetiology of HPV-positive (HPV+) OPSCC and provides a detailed overview of HPV virology and molecular pathogenesis relevant to infection of oropharyngeal tissues. Methods of detection and differential gene expression analyses are also summarized. Future research into mechanisms that mediate tropism of HPV to oropharyngeal tissues, improved detection strategies and the pathophysiological significance of altered gene and microRNA expression profiles is warranted.
Calculation of electron-hole recombination probability using explicitly correlated Hartree-Fock method
Authors: Elward Jennifer M. , Thallinger Barbara , Chakraborty Arindam
Published: March 2012

The electron-hole explicitly correlated Hartree-Fock method (eh-XCHF) is presented as a general strategy for investigation of electron-hole correlation and computation of electron-hole recombination probability. The eh-XCHF method is a variational method which uses explicitly correlated wavefunction that depends on the electron-hole inter-particle distances. It is shown that the explicitly correlated ansatz provides a systematic route to variationally minimize the total energy. The parabolic quantum dot is used as the benchmark system and the eh-XCHF method is used for computation of the ground state energy and electron-hole recombination probability. The results are compared to Hartree-Fock and explicitly correlated full configuration interaction (R12-FCI) calculations. The results indicate that an accurate description of the electron-hole wavefunction at short electron-hole inter-particle distances is crucial for qualitative description of the electron-hole recombination probability. The eh-XCHF method successfully addresses this issue and comparison of eh-XCHF calculations with R12-FCI shows good agreement. The quality of the mean field approximation for electron-hole system is also investigated by comparing HF and R12-FCI energies for electron-electron and electron-hole systems. It was found that performance of the mean field approximation is worse for the electron-hole system as compared to the corresponding electron-electron system.
A second-order perturbation theory route to vibrational averages and transition properties of molecules: General formulation and application to infrared and vibrational circular dichroism spectroscopies
Authors: Bloino Julien , Barone Vincenzo
Published: March 2012

A general formulation to compute anharmonic vibrational averages and transition properties at the second-order of perturbation theory is derived from the Rayleigh-Schrödinger development. This approach is intended to be applicable to any property expanded as a Taylor series up to the third order with respect to normal coordinates or their associated momenta. The equations are straightforward to implement and can be easily adapted to various properties, as illustrated for the case of electric and magnetic dipole moments. From those, infrared and vibrational circular dichroism spectra can be readily obtained. This fully automatic procedure has been applied to several chiral molecules of small-to-medium sizes and compared to the standard double harmonic approximation and to experimental data.
Ab-initio molecular modeling of interfaces in tantalum-carbon system
Authors: Balani Kantesh , Bakshi Srinivasa Rao , Mungole Tarang , Agarwal Arvind
Published: March 2012

Processing of ultrahigh temperature TaC ceramic material with sintering additives of B4C and reinforcement of carbon nanotubes (CNTs) gives rise to possible formation of several interfaces (Ta2C-TaC, TaC-CNT, Ta2C-CNT, TaB2-TaC, and TaB2-CNT) that could influence the resultant properties. Current work focuses on interfaces developed during spark plasma sintering of TaC-system and performing ab initio molecular modeling of the interfaces generated during processing of TaC-B4C and TaC-CNT composites. The energy of the various interfaces has been evaluated and compared with TaC-Ta2C interface. The iso-surface electronic contours are extracted from the calculations eliciting the enhanced stability of TaC-CNT interface by 72.2%. CNTs form stable interfaces with Ta2C and TaB2 phases with a reduction in the energy by 35.8% and 40.4%, respectively. The computed Ta-C-B interfaces are also compared with experimentally observed interfaces in high resolution TEM images.
Multiexcitonic emission from single elongated InGaAs/GaAs quantum dots
Authors: Dusanowski Ł. , Sęk G. , Musiał A. , Podemski P. , Misiewicz J. , Löffler A. , Höfling S. , Reitzenstein S. , Forchel A.
Published: March 2012

In this work, we present both experimental data and simulations of multiexcitonic emission spectra of single self-assembled elongated In0.3Ga0.7As/GaAs quantum dots. The emission spectra reveal an unusual evolution with the increased excitation power density. First, a biexciton line appears simultaneously with its low energy sideband, the origin of which has already been postulated previously and related to the interaction of a quantum dot biexciton with excitons generated in the surrounding wetting layer. A further increase of the excitation causes a disappearance of the exciton line accompanied with a transformation of the biexciton sharp line and its sideband into a redshifting broad emission band. The latter recalls a typical feature of the transition from excitonic emission into electron-hole plasma called Mott transition, which is possible to occur in wire-like structures under the conditions of very high carrier densities. However, we propose an alternative explanation and show that this behavior can be well explained based on a multilevel rate equation model, indicating that such a dependence of the emission spectra is a fingerprint of a formation of multiexcitonic states. Further, we discuss the importance of various quantum system parameters as the radiative lifetimes or spectral linewidths.
Highly versatile concept for precise tailoring of nanogranular composites with a gas aggregation cluster source
Authors: Gojdka B. , Zaporojtchenko V. , Hrkac V. , Xiong J. , Kienle L. , Strunskus T. , Faupel F.
Published: March 2012

A concept for the precise tailoring of a wide variety of nanogranular composites with a gas aggregation cluster source and a magnetron is presented. Electrical charging of the preformed clusters and the substrate in a plasma is discussed as a fundamental physical hindrance for conventional co-sputtering with a cluster source. The proposed concept overcomes this hindrance and is experimentally demonstrated for the deposition of a dielectric aluminum nitride matrix with embedded magnetic cobalt clusters. Chemical, magnetic, and structural analyses of the composite confirm the feasibility of the proposed concept as a versatile route for the preparation of nanocomposites.
Optimization of orbital-specific virtuals in local Møller-Plesset perturbation theory
Authors: Kurashige Yuki , Yang Jun , Chan Garnet K.-L. , Manby Frederick R.
Published: March 2012

We present an orbital-optimized version of our orbital-specific-virtuals second-order Møller-Plesset perturbation theory (OSV-MP2). The OSV model is a local correlation ansatz with a small basis of virtual functions for each occupied orbital. It is related to the Pulay–Saebø approach, in which domains of virtual orbitals are drawn from a single set of projected atomic orbitals; but here the virtual functions associated with a particular occupied orbital are specifically tailored to the correlation effects in which that orbital participates. In this study, the shapes of the OSVs are optimized simultaneously with the OSV-MP2 amplitudes by minimizing the Hylleraas functional or approximations to it. It is found that optimized OSVs are considerably more accurate than the OSVs obtained through singular value decomposition of diagonal blocks of MP2 amplitudes, as used in our earlier work. Orbital-optimized OSV-MP2 recovers smooth potential energy surfaces regardless of the number of virtuals. Full optimization is still computationally demanding, but orbital optimization in a diagonal or Kapuy-type MP2 approximation provides an attractive scheme for determining accurate OSVs.
The implementation of a self-consistent constricted variational density functional theory for the description of excited states
Authors: Ziegler Tom , Krykunov Mykhaylo , Cullen John
Published: March 2012

We present here the implementation of a self-consistent approach to the calculation of excitation energies within regular Kohn-Sham density functional theory. The method is based on the n-order constricted variational density functional theory (CV(n)-DFT) [T. Ziegler, M. Seth, M. Krykunov, J. Autschbach, and F. Wang, J. Chem. Phys. 130, 154102 (2009)]10.1063/1.3114988 and its self-consistent formulation (SCF-CV(∞)-DFT) [J. Cullen, M. Krykunov, and T. Ziegler, Chem. Phys. 391, 11 (2011)]10.1016/j.chemphys.2011.05.021. A full account is given of the way in which SCF-CV(∞)-DFT is implemented. The SCF-CV(∞)-DFT scheme is further applied to transitions from occupied π orbitals to virtual π* orbitals. The same series of transitions has been studied previously by high-level ab initio methods. We compare here the performance of SCF-CV(∞)-DFT to that of time dependent density functional theory (TD-DFT), CV(n)-DFT and ΔSCF-DFT, with the ab initio results as a benchmark standard. It is finally demonstrated how adiabatic TD-DFT and ΔSCF-DFT are related through different approximations to SCF-CV(∞)-DFT.
Multiphonon effects on the optical emission spectra of the nitrogen-vacancy center in diamond at different temperatures
Authors: Ma Wen-Long , Li Shu-Shen
Published: March 2012

We theoretically investigate the multiphonon effects on the optical emission spectra of the negatively charged nitrogen-vacancy (NV−) center in diamond and find that the fluorescence emission spectra described by the single frequency model agree quite well with the experimental data. From a comparison between our theory and the experimental results, we also find a reduction of the anti-Stokes shift of the emission spectra at high temperature. This is contradictory to the linear hole-phonon interaction model. We resolve this contradiction by adding the quadratic hole-phonon interaction to our model. Our theoretical analyses show that this may reduce the lattice relaxation energy. As a consequence, fewer phonons are emitted in the optical transition, therefore explaining the reduction of the anti-Stokes shift at high temperature.
Acoustically induced current flow in graphene
Authors: Miseikis V. , Cunningham J. E. , Saeed K. , O’Rorke R. , Davies A. G.
Published: March 2012

We demonstrate the directed control of charge carriers in graphene using the electric field that accompanies the propagation of surface acoustic waves (SAWs) on a piezoelectric surface. Graphene grown by chemical vapor deposition was transferred to the surface of lithium niobate, allowing its direct integration with interdigital transducers used for SAW generation and detection. Radio frequency (RF) signal applied to the transducers at their resonant frequency was found to generate a direct current flow by the transport of p-type charge carriers. The acoustically induced current scales linearly with the applied RF power and can be observed even in presence of a counter-flow current induced by an applied bias.
The origin of non-Drude terahertz conductivity in nanomaterials
Authors: Shimakawa K. , Itoh T. , Naito H. , Kasap S. O.
Published: March 2012

The Drude-Smith (DS) model hitherto has been a well accepted model for the terahertz conductivity of nanomaterials, even though its physical basis is not clear. It is shown that a series sequence of transport involving grains and grain boundaries produces a Lorentzian-type energy loss and dominates the THz conductivity in nanomaterials, which is able to explain both the real and imaginary parts of the conductivity. The present model represents a completely different point of view than the standard Drude-Smith model.
Insights into the mechanism of Alzheimer’s β-amyloid aggregation as a function of concentration by using atomic force microscopy
Authors: Mustata Gina-Mirela , Shekhawat Gajendra S. , Lambert Mary P. , Viola Kirsten L. , Velasco Pauline T. , Klein William L. , Dravid Vinayak P.
Published: March 2012

The size and shape of Alzheimer’s β-amyloid structures, as well as the kinetics of their self-assembly, exhibits a very pronounced dependence on concentration and environment. In the present study, we are reporting the direct observation of Aβ oligomers and fibrils assemblies using atomic force microscopy imaging in fluid environment. These results demonstrate that in the Aβ preparations at lower concentrations, predominant are the globular, smaller oligomers, while for higher concentrations, globular oligomers co-exist with higher molecular weight fibrillar structures. At higher concentrations, the fibril formation is a dynamic and continuous process, yielding amyloid fibrils with multiple structures and diameters.
Thermal contact conductance of demountable in vacuum copper-copper joint between 14 and 100 K
Authors: Mykhaylyk V. B. , Burt M. , Ursachi C. , Wagner A.
Published: March 2012

Thermal contact conductance (TCC) at material interfaces has a great impact upon the efficiency of cooling in cryogenic instruments, and is thus a crucial design parameter. Lack of reliable numerical data for demountable in vacuum bare (uncoated, dry, and without interposers) copper-copper joints prompted us to carry out systematic studies of TCC over the temperature range 14–100 K. We measured TCC as function of applied force for the contacts with surface roughness Ra = 0.2, 1.6, and 3.2 μm. It is seen that with increasing temperature, the TCC of bare Cu-Cu contact initially rises following a generic power law dependency Tγ with γ = 1.25 ± 0.02, reaching a maximum value at 40–50 K. TCC then decreases as temperature continues to rise towards 100 K. We show results that match those in the literature from low (4–20 K) and high (100–300 K) temperature domains, resulting in a unified smooth curve of temperature dependency of TCC for bare Cu-Cu joints. Temperature dependence is then described in a phenomenological model, accounting for the effects of changes in bulk conductivity and surface hardness with temperature. This model consistently explains the observed power law dependence of TCC as function of applied force and changes caused by roughness of contact surfaces.
Two-channel impedance spectroscopy for the simultaneous measurement of two samples
Authors: Singh Lokendra P. , Richert Ranko
Published: March 2012

We describe a dielectric relaxation technique, which allows one to obtain a very accurate comparison of the behavior of two different samples. The key feature is the simultaneous impedance measurement on two capacitors that can share a common center electrode, implying that the same voltage is applied to both samples and that only a single gain/phase analyzer is required. The capabilities of this technique have been examined by comparing the dynamics of protonated and deuterated 1-propanol samples using this dual-channel analyzer in the frequency range of 10−2–106 Hz and in the temperature range of 110–160 K, after calibrating the system using the same sample in both, channel 1 and channel 2. For many supercooled liquids, the high sensitivity of the dielectric relaxation behavior on temperature prevents a meaningful comparison of nearly identical dynamics on the basis of two separate measurements. Based on this dual-channel method, we observe that a deuterated 1-propanol sample displays small but systematic deviations from the relaxation spectra of its protonated counterpart, which would not be observable in separate dielectric measurements. Many other applications can be envisioned where simultaneous or differential impedance measurements are advantageous.
Thin film measurement system for moving objects based on a laterally distributed linear variable filter spectrometer
Authors: Murr Patrik J. , Wiesent Benjamin R. , Hirth Florian , Koch Alexander W.
Published: March 2012

Instantaneous measurement of optical or geometrical parameters of thin layers is an ambitious aim in many industrial applications. These layers have a variety of use-cases, such as optical bandpassing, dielectric permittivity, or lubrication. Mostly, these layers are in motion due to the production process. In order to observe process parameters, the motion usually has to be disrupted. Thus, the increase of production time due to control purposes is an undesirable drawback of this otherwise suitable technique. In this publication, we present a solution to this particular drawback of most production process monitoring systems exemplarily for film thickness measurement. We show the realization of a measurement principle which has, to our knowledge, never been published before in this application. Therefore, we exploit the advantages of the combination of a linear variable filter with a complementary metal oxide semiconductor sensor array. By an apt readout sequence, this measurement system is able to measure transmission spectra while the target is in motion. We show that this measurement system is able to measure film thicknesses of objects in the range of several 100 nm thickness at up to a velocity of 4 m/s. A reproducibility below 2 nm was acquired.
Electron temperature in electrically isolated Si double quantum dots
Authors: Rossi A. , Ferrus T. , Williams D. A.
Published: March 2012

Charge-based quantum computation can be attained through reliable control of single electrons in lead-less quantum systems. Single-charge transitions in electrically isolated double quantum dots (DQDs) realised in phosphorus-doped silicon can be detected via capacitively coupled single-electron tunnelling devices. By means of time-resolved measurements of the detector’s conductance, we investigate the dots’ occupancy statistics in temperature. We observe a significant reduction of the effective electron temperature in the DQD as compared to the temperature in the detector’s leads. This sets promises to make isolated DQDs suitable platforms for long-coherence quantum computation.
Nonpolar nitrous oxide dimer: Observation of combination bands of (14N2O)2 and (15N2O)2 involving the torsion and antigeared bending modes
Authors: Rezaei M. , Michaelian K. H. , Moazzen-Ahmadi N.
Published: March 2012

Spectra of the nonpolar nitrous oxide dimer in the region of the N2O ν1 fundamental band were observed in a supersonic slit-jet apparatus. The expansion gas was probed using radiation from a quantum cascade or a tunable diode laser, with both lasers employed in a rapid-scan signal averaging mode. Four bands were observed and analyzed: new combination bands involving the intermolecular conrotation of the monomers (Ag antigeared bend) for (14N2O)2 and (15N2O)2, the previously reported torsional combination band for (14N2O)2 with improved signal-to-noise ratio, and the same torsional combination band for (15N2O)2. The resulting frequencies for the intermolecular antigeared mode are 96.0926(1) and 95.4912(1) cm−1 for (14N2O)2 and (15N2O)2, respectively. This is the third of the four intermolecular frequencies which has now been measured experimentally, the others being the out-of-plane torsion and the geared bend modes. Our experimental results are in good agreement with two recent high level ab initio theoretical calculations.
Efficiency enhancement in dye sensitized solar cells through co-sensitization of TiO2 nanocrystalline electrodes
Authors: Saxena Vibha , Veerender P. , Chauhan A. K. , Jha P. , Aswal D. K. , Gupta S. K.
Published: March 2012

We have demonstrated that co-sensitization of TiO2 electrode with an inexpensive rhodamine 19 perchlorate laser dye along with N3 dye not only enhances the incident-photon-to-current conversion efficiency but also reduces dark current. Consequently, the devices yield an average power efficiency of 4.7% as against 2.3% and 0.6% obtained for N3 and rhodamine 19 perchlorate dye based devices, respectively. The improvement in efficiency is attributed to the enhanced dye absorption on TiO2 electrode as well as reduced dye aggregation that resulted from the usage of two dyes on different anchoring sites of single TiO2 electrode.
Probing crossover from analogous weak antilocalization to localization by an Aharonov-Bohm interferometer on topological insulator surface
Authors: Fu Zhen-Guo , Zhang Ping , Li Shu-Shen
Published: March 2012

We propose a scanning tunneling microscopy Aharonov-Bohm (AB) interferometer on the surface of a topological insulator (TI) to probe the crossover from analogous weak antilocalization to weak localization phenomenon via the AB oscillations in spin-resolved local density of states (LDOS). Based on our analytical and numerical results, we show that with increasing the energy gap of TI surface states, the Φ0/2=hc/2e periodic AB oscillations in spin-resolved LDOS gradually transit into the Φ0 periodic oscillations.
Simultaneous observation of acoustic resonance phenomena at both surfaces of a plate coated with thin layers
Authors: Tohmyoh Hironori , Sunaga Tomoya , Suzuki Manabu
Published: March 2012

Acoustic resonance phenomena at the front and back surfaces of a plate coated with thin layers were successfully observed in the amplitude spectrum of the back surface echo. The amplitude ratio of spectra with and without layers takes its maximum and minimum values at the resonant frequencies of the front and back coatings and both frequencies can clearly be distinguished from each other. As an application, the thicknesses of the front and back coatings on a steel plate were measured simultaneously using their resonant frequencies, thus verifying the validity of the principle.
Tuning asymmetry parameter of Fano resonance of spoof surface plasmons by modes coupling
Authors: Cheng F. , Liu H. F. , Li B. H. , Han J. , Xiao H. , Han X. F. , Gu C. Z. , Qiu X. G.
Published: March 2012

We report a kind of subwavelength, compound hole arrays formed by two nested sub-lattices used to modulate the Fano resonance of spoof surface plasmons (SSPs). Experiments complemented with numerical simulations show that the asymmetry parameter (q) of the Fano line shape can be tuned artificially and continuously: the q value experiences a sign reversal and varies linearly with the variation of hole size. The coupling between different SSP modes of sub-lattices is suggested to be responsible for the tunability of Fano resonance in the compound hole arrays.
A nonequilibrium argon-oxygen planar plasma jet using a half-confined dielectric barrier duct in ambient air
Authors: Li Qing , Takana Hidemasa , Pu Yi-Kang , Nishiyama Hideya
Published: March 2012

A nonequilibrium argon plasma jet with oxygen addition, generated in a planar dielectric duct and issuing into ambient air with one edge stuck on a dielectric plane, is reported for the first time. This argon-oxygen plasma jet can be operated at low applied voltage as a filamentary discharge at atmospheric pressure. The addition of a small amount of oxygen results in the increase of produced ozone concentration and continuous emissions of centering at about 185 nm, 205 nm, 230 nm, and 253 nm. The synergistic generation of short wavelength ultraviolet emissions and active species is significantly important for plasma applications.