bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal and inter‐annual variability of the net ecosystem CO2 exchange of a temperate mountain grassland: Effects of weather and management
Authors: Wohlfahrt Georg , Hammerle Albin , Haslwanter Alois , Bahn Michael , Tappeiner Ulrike , Cernusca Alexander
Published: April 2008

The role and relative importance of weather and cutting for the seasonal and inter‐annual variability of the net ecosystem CO2 exchange (NEE) of a temperate mountain grassland was investigated. Eddy covariance CO2 flux data and associated measurements of the green plant area index and the major environmental driving forces acquired during 2001–2006 at the study site Neustift (Austria) were analyzed. Driven by three cutting events per year which kept the investigated grassland in a stage of vigorous growth, the seasonal variability of NEE was primarily modulated by gross primary productivity (GPP). The role of environmental parameters in modulating the seasonal variability of NEE was obscured by the strong response of GPP to changes in the amount of green plant area, as well as the cutting‐mediated decoupling of phenological development and the seasonal course of environmental drivers. None of the environmental and management metrics examined was able to explain the inter‐annual variability of annual NEE. This is thought to result from (1) a high covariance between GPP and ecosystem respiration (Reco) at the annual timescale which results in a comparatively small inter‐annual variation of NEE, (2) compensating effects between carbon exchange during and outside the management period, and (3) changes in the biotic response to rather than the environmental variables per se. GPP was more important in modulating inter‐annual variations in NEE in spring and before the first and second cut, while Reco explained a larger fraction of the inter‐annual variability of NEE during the remaining periods, in particular the post‐cut periods.
Direct measurement of biosphere‐atmosphere isotopic CO2 exchange using the eddy covariance technique
Authors: Griffis T. J. , Sargent S. D. , Baker J. M. , Lee X. , Tanner B. D. , Greene J. , Swiatek E. , Billmark K.
Published: April 2008

Quantifying isotopic CO2 exchange between the biosphere and atmosphere presents a significant measurement challenge, but has the potential to provide important constraints on local, regional, and global carbon cycling. Past approaches have indirectly estimated isotopic CO2 exchange using relaxed eddy accumulation, the flask‐based isoflux method, and flux‐gradient techniques. Eddy covariance (EC) is an attractive method because it has the fewest theoretical assumptions and the potential to give a direct measure of isotopic CO2 flux, but it requires a highly sensitive and relatively fast response instrument. To date, no such field measurements have been reported. Here we describe the use of a closed‐path tunable diode laser absorption spectroscopy and eddy covariance (EC‐TDL) system for isotopic (C16O2, 13CO2, C18O16O) flux measurements. Results are presented from an intensive field experiment conducted over a soybean canopy from 18 July to 20 September 2006. This experiment represents a rigorous field test of the EC‐TDL technique because the transport was dominated by relatively high frequency eddies. Net ecosystem CO2 exchange (FN) measured with the EC‐TDL system showed strong correlation (r2 = 0.99) in the half‐hourly fluxes with an EC open‐path infrared gas analyzer (EC‐IRGA) over the 60‐d period. Net CO2 flux measured with the EC‐IRGA and EC‐TDL systems agreed to within 9%. Flux loss associated with diminished frequency response beyond 1 Hz for the EC‐TDL system was approximately 8% during daytime windy (>4 m s−1) conditions. There was no significant evidence of a kinetic‐type fractionation effect related to a phase shift among isotopologues due to tube attenuation. Investigation of isotopic spectral similarity in the flux ratio (δNx) for both 13CO2 and C18O16O transport showed that δNx was relatively independent of eddy scale for this ecosystem type. Flux loss, therefore, did not significantly bias δNx. There was excellent agreement between isofluxes (Fδx) measured using the flux‐gradient and eddy covariance methods. Application of the EC‐TDL technique over rougher surfaces or below canopy, where the flux‐gradient approach is difficult to apply, appears promising for obtaining continuous long‐term measurements of isotopic CO2 exchange.
Hydrothermal processes at Gusev Crater: An evaluation of Paso Robles class soils
Authors: Yen A. S. , Morris R. V. , Clark B. C. , Gellert R. , Knudson A. T. , Squyres S. , Mittlefehldt D. W. , Ming D. W. , Arvidson R. , McCoy T. , Schmidt M. , Hurowitz J. , Li R. , Johnson J. R.
Published: April 2008

The Mars Exploration Rover Spirit analyzed multiple occurrences of sulfur‐rich, light‐toned soils along its traverse within Gusev Crater. These hydrated deposits are not readily apparent in images of undisturbed soil but are present at shallow depths and were exposed by the actions of the rover wheels. Referred to as “Paso Robles” class soils, they are dominated by ferric iron sulfates, silica, and Mg‐sulfates. Ca‐sulfates, Ca‐phosphates, and other minor phases are also indicated in certain specific samples. The chemical compositions are highly variable over both centimeter‐scale distances and between the widely separated exposures, but they clearly reflect the elemental signatures of nearby rocks. The quantity of typical basaltic soil mixed into the light‐toned materials prior to excavation by the rover wheels is minimal, suggesting negligible reworking of the deposits after their initial formation. The mineralogy, geochemistry, variability, association with local compositions, and geologic setting of the deposits suggest that Paso Robles class soils likely formed as hydrothermal and fumarolic condensates derived from magma degassing and/or oxidative alteration of crustal iron sulfide deposits. Their occurrence as unconsolidated, near‐surface soils permits, though does not require, an age that is significantly younger than that of the surrounding rocks.
Magnetic field measuring system and current retrieval in artificially triggering lightning experiment
Authors: Yang Jing , Qie Xiushu , Zhang Guangshu , Wang Huaibin
Published: April 2008

A magnetic field measuring system with two rectangular loops perpendicular to each other is developed and used to detect the total horizontal magnetic field produced by lightning discharges. Two sets of antenna with low gain and high gain are designed separately in order to obtain both small and large signals. The system was tested experimentally in a high‐voltage laboratory, and the results show that the system is reliable, and the waveforms detected by the system are very similar to the source current. The corresponding maximum current that can be measured by the system with low gain antenna and high gain antenna locating at a distance of 60 m from a lightning channel, is about 84.4 kA and 37.7 kA, respectively. For artificially triggered lightning flashes the magnetic field waveforms detected at 60 m from the channel reflect quite well the channel base currents. Using Ampere's law of magnetostatics, the inferred currents from the magnetic fields for three artificially triggered lightning return strokes were 39.8 kA, 29.1 kA and 43 kA, respectively, which are close to the directly measured results of 41.6 kA, 29.6 kA and 38 kA at the base of the discharge channel. The system can be a useful tool in the research of close electromagnetic environment of lightning flashes.
Crustal rheology and seismicity in the Gibraltar Arc (western Mediterranean)
Authors: Fernández‐Ibáñez F. , Soto J. I.
Published: April 2008

On the basis of the lithospheric structure of the Gibraltar Arc (western Mediterranean), we constrain depth distribution of crustal seismicity and active tectonics by means of rheological modeling. Crustal yield strength and depth of the brittle‐ductile transition zone (BDT) mimic the curvature of the arc with maximum depths of 12–9 km whereas in the Betics and Rif, BDT shallows eastward (to 6–5 km depth), oblique to crustal thickening. Most of the crustal seismicity (>60%) is placed within the brittle crust, decaying exponentially in the ductile crust. Active faults observed in surface geology, control the present topography of the Betics, connect in depth with scattered seismic swarms, and merge into the BDT. This horizon is interpreted as a decoupling horizon that conditions the mode of present‐day deformation partitioning. Below the BDT, low‐strength domains enable crustal flow under central Betics promoting stress rotation and topographic uplift.
Ensemble 1‐Year predictions of Arctic sea ice for the spring and summer of 2008
Authors: Zhang Jinlun , Steele Mike , Lindsay Ron , Schweiger Axel , Morison James
Published: April 2008

Ensemble predictions of arctic sea ice in spring and summer 2008 have been carried out using an ice‐ocean model. The ensemble is constructed by using atmospheric forcing from 2001 to 2007 and the September 2007 ice and ocean conditions estimated by the model. The prediction results show that the record low ice cover and the unusually warm ocean surface waters in summer 2007 lead to a substantial reduction in ice thickness in 2008. Up to 1.2 m ice thickness reduction is predicted in a large area of the Canada Basin in both spring and summer of 2008, leading to extraordinarily thin ice in summer 2008. There is a 50% chance that both the Northern Sea Route and the Northwest Passage will be nearly ice free in September 2008. It is not likely there will be another precipitous decline in arctic sea ice extent such as seen in 2007, unless a new atmospheric forcing regime, significantly different from the recent past, occurs.
The contribution of cloud and radiation anomalies to the 2007 Arctic sea ice extent minimum
Authors: Kay Jennifer E. , L'Ecuyer Tristan , Gettelman Andrew , Stephens Graeme , O'Dell Chris
Published: April 2008

Reduced cloudiness and enhanced downwelling radiation are associated with the unprecedented 2007 Arctic sea ice loss. Over the Western Arctic Ocean, total summertime cloud cover estimated from spaceborne radar and lidar data decreased by 16% from 2006 to 2007. The clearer skies led to downwelling shortwave (longwave) radiative fluxes increases of +32 Wm−2 (−4 Wm−2) from 2006 to 2007. Over three months, simple calculations show that these radiation differences alone could enhance surface ice melt by 0.3 m, or warm the surface ocean by 2.4 K, which enhances basal ice melt. Increased air temperatures and decreased relative humidity associated with an anti‐cyclonic atmospheric circulation pattern explain the reduced cloudiness. Longer‐term observations show that the 2007 cloudiness is anomalous in the recent past, but is not unprecedented. Thus, in a warmer world with thinner ice, natural summertime circulation and cloud variability is an increasingly important control on sea ice extent minima.
Dust and sea surface temperature forcing of the 1930s “Dust Bowl” drought
Authors: Cook Benjamin I. , Miller Ron L. , Seager Richard
Published: April 2008

Droughts over the central United States (US) are modulated by sea surface temperature (SST) variations in the eastern tropical Pacific. Many models, however, are unable to reproduce the severity and spatial pattern of the “Dust Bowl” drought of the 1930s with SST forcing alone. We force an atmosphere general circulation model with 1930s SSTs and model‐generated dust emission from the Great Plains region. The SSTs alone force a drought over the US similar to observations, but with a weaker precipitation anomaly that is centered too far south. Inclusion of dust radiative forcing, centered over the area of observed wind erosion, increases the intensity of the drought and shifts its center northward. While our conclusions are tempered by limited quantitative observations of the dust aerosol load and soil erosion during this period, our study suggests that unprecedented atmospheric dust loading over the continental US exacerbated the “Dust Bowl” drought.
The case for dynamic subsidence of the U.S. east coast since the Eocene
Authors: Spasojević Sonja , Liu Lijun , Gurnis Michael , Müller R. Dietmar
Published: April 2008

The dynamic subsidence of the United States east coast is addressed using the discrepancy between regional and global estimates of sea level, elevation of paleoshorelines, and adjoint models of mantle convection that assimilate plate motions and seismic tomography. The positions of Eocene and Miocene paleoshorelines are lower than predicted by global sea levels, suggesting at least 50 m, and possibly as much as 200 m of subsidence since the end of the Eocene. Dynamic models predict subsidence of the east coast since the end of Eocene, although the exact magnitude is uncertain. This subsidence has been occurring during an overall global sea‐level fall, with the eustatic change being larger than the dynamic subsidence; this results in a regional sea‐level fall in the absence of land subsidence. Dynamic subsidence is consistent with the difference between eustasy and regional sea level at the New Jersey coastal plain.
Dendritic cell behaviour in vivo: lessons learned from intravital two‐photon microscopy
Authors: Cavanagh Lois L , Weninger Wolfgang
Published: April 2008

Dendritic cells (DC) are central regulators of immune responses. Their functional characterization has, thus far, mainly relied on the analysis of ex vivo isolated cells or immunohistology, which provides information in a static manner. While these approaches have enabled an excellent understanding of the role of DC in antigen uptake, processing and presentation, there has been a clear need to investigate the behaviour of DC in the context of intact tissues in real time. This demand has recently been met by the availability of intravital two‐photon microscopy, which allows for the visualization of single cells deep within intact organs over time. Thus, during the past few years, exciting new data have been generated as to how DC behave within secondary lymphoid and peripheral tissues both under homoeostatic and inflammatory conditions. Here, we will review what two‐photon microscopy studies have taught us about the migration of DC in the interstitial space as well as their interactions with adaptive immune cells.
CD4+ T cells are required during priming but not the effector phase of antibody‐mediated IFN‐γ‐dependent protective immunity against pulmonary Francisella novicida infection
Authors: Powell Heather J , Cong Yu , Yu Jieh‐Juen , Guentzel M Neal , Berton Michael T , Klose Karl E , Murthy Ashlesh K , Arulanandam Bernard P
Published: April 2008

We have previously demonstrated the protective efficacy of intranasal vaccination with a defined Francisella tularensis subsp. novicida ΔiglC mutant (KKF24) against pulmonary F. novicida U112 challenge. In this study, we further characterized the mechanisms of KKF24‐induced immunity. Intranasally vaccinated KKF24 C57BL/6 major histocompatibility class (MHC) class II−/− mice produced minimal antigen‐specific interferon (IFN)‐γ and serum antibodies and were highly susceptible (0% survival) to F. novicida challenge, compared to MHC class I−/− or wild‐type mice (both 100% survival). Protective immunity could be transferred by immune serum into recipient wild type, but not IFN‐γ−/− mice. The protective effect of KKF24 vaccination against the respiratory F. novicida U112 challenge was not abrogated by anti‐CD4 neutralizing antibody treatment and was not conferred by adoptive transfer of KKF24‐specific CD4+ T cells. The protective effect of antibody was partially dependent upon Fc receptor‐mediated clearance. Taken together, our data indicate that CD4+ T cells are required for priming, but not during the effector phase, of anti‐KKF24 antibody‐mediated IFN‐γ‐dependent immunity against pulmonary F. novicida infection.
Leptin Predicts a Worsening of the Features of the Metabolic Syndrome Independently of Obesity
Authors: Franks Paul W. , Brage Soren , Luan Jian'An , Ekelund Ulf , Rahman Mushtaquar , Farooqi I. Sadaf , Halsall Ian , O'Rahilly Stephen , Wareham Nicholas J.
Published: April 2008

Objective: The term metabolic syndrome (MS) describes a cluster of cardiovascular risk factors including dyslipidemia, glucose intolerance, insulin resistance, and hypertension. Obesity increases the risk of MS, but as obesity is neither necessary nor sufficient to cause the syndrome, there is considerable interest in identifying obesity‐independent pathways. One such pathway may involve the actions of the adipokine leptin, which is associated cross‐sectionally with MS and prospectively with coronary heart disease and stroke, independently of obesity. Our goal was to test the hypothesis that leptin predicts the development of the features of MS independently of obesity.

Research Methods and Procedures: This study used a prospective population‐based cohort of 748 middle‐aged whites in whom baseline measures of leptin and repeated measurement of the subcomponents of the MS at 5 and 10 years were available. The features of the MS were characterized as five factors (obesity, dyslipidemia, elevated blood pressure, glucose intolerance, and insulin resistance), which were combined to create an MS summary score.

Results: Baseline leptin significantly predicted the development of obesity (p = 0.001) and, after adjustment for BMI, development of glucose intolerance (p = 0.016) and insulin resistance (p < 0.0001). Leptin levels did not independently predict a change in lipids or blood pressure. Leptin levels significantly predicted the development of the MS (p = 0.036), independently of baseline BMI.

Discussion: Leptin predicts the development of the MS independently of baseline obesity. This association is specifically related to the development of glucose intolerance and insulin resistance. The extent to which these relationships are explained through residual confounding by obesity remains to be determined.
Whiteflies on tomato crops in Portugal*
Authors: Lopes A.
Published: April 2008

In Portugal during the 1960/1980s, there was intensive development of vegetable crop production, in particular protected crops, of which tomato was the most important. The main producing regions now are Ribatejo e Oeste, Alentejo and Algarve. Tomato presents extensive phytosanitary problems, being host to a wide range of pests, including the whiteflies Trialeurodes vaporariorum, in protected crops, and Bemisia tabaci, in protected and field crops. Portugal has applied for the status of an EU ‘protected zone’ for this latter pest. As B. tabaci is an important vector of a large number of viruses, including tomato yellow leaf curl viruses (TYLCV), a monitoring programme of the tomato crop was implemented in Portugal. Preliminary data are presented concerning B. tabaci in the three main tomato‐growing regions of the country.
Situation de la maladie des feuilles jaunes en cuillère de la tomate (TYLCV) au Maroc*
Authors: Jebbour F. , Abaha L.
Published: April 2008

Durant la campagne 1996/1997, la maladie due au TYLCV a été signalée pour la première fois au Maroc dans la région d’El Jadida au nord‐ouest du pays, lors des prospections effectuées par le Service de la Protection des Végétaux. En 1998, la maladie s’est propagée dans d’autres régions productrices de tomate notamment Agadir au sud‐ouest et Berkane au nord‐est. Depuis l’apparition de la maladie, le Service de la Protection des Végétaux en concertation avec la profession a mis en place une stratégie de lutte contre cette maladie. Celle‐ci se base essentiellement sur le respect d’un certain nombre de mesures, visant à préserver les plantations de l’attaque par ce virus et éviter des attaques précoces susceptibles de compromettre la productivité de la culture de tomate. Parmi les actions de contrôle qui se font de manière régulière, il y a lieu de citer entre autres le renforcement des contrôles des pépinières pour la détection du virus et de la mouche blanche. En plus des actions prophylactiques, une assise réglementaire a étéélaborée. Elle consiste en l’interdiction de l’importation des solanacées (genre Lycopersicon) et l’organisation de la circulation à l’intérieur du pays des plants susceptibles de véhiculer le virus en question.
Tomato yellow leaf curl Sardinia virus and its vector Bemisia tabaci in Sicilia (Italy): present status and control possibilities*
Authors: Rapisarda C. , Tropea Garzia G.
Published: April 2008

Tomato yellow leaf curl Sardinia begomovirus (TYLCSV) appeared in Sicilia (IT) in 1988, creating great threats to agriculture and causing huge losses, especially in south‐eastern areas of the island, where protected tomato cultivation is widespread. Towards the mid‐1990s, a reduction occurred in the virus epidemics, probably due to new approaches which have been applied to rational control of its vector, the whitefly Bemisia tabaci. More recently, TYLCSV has increased again, creating great concern among local tomato producers and stimulating new research. Besides studies on natural enemies of the vector, aiming to investigate their role and distribution, the main current research lines in Sicilia concern the possibility of reducing both whitefly activity, using photoselective plastics as covers, and virus damage, by growing tolerant tomato genotypes.
Virus transmission studies and diagnostic detection of four begomovirus isolates in selected crop hosts and in Bemisia tabaci biotype B*
Authors: Morris J. , Harju V. , Cambridge J. , Boonham N. , Henry C.
Published: April 2008

Virus transmission studies were conducted under glasshouse conditions using the vector Bemisia tabaci biotype B to determine how effectively isolates of the begomoviruses Tomato yellow leaf curl virus (TYLCV) and Tomato leaf curl Bangalore virus (ToLCBV) could be transmitted to phaseolus bean, capsicum and tomato test plants, the latter host used as a positive control for transmission. Diagnostic detection of viruses in these host crops and vector was also evaluated. Polymerase chain reaction (PCR) detection of TYLCV in bean cv. Wade and capsicum cv. Bellboy was achieved 4 weeks after fumigation in asymptomatic plants. Detection of TYLCV in tomato controls was achieved 2 weeks after fumigation with improved frequency of detection at 4 weeks. PCR was found to be a more sensitive method than triple‐antibody sandwich enzyme‐linked immunosorbent assay (TAS‐ELISA) for the detection of TYLCV isolates in all hosts. ToLCBV was detected by PCR and TAS‐ELISA in bean. TYLCV was also detected by PCR in the vector, with a novel internal positive control. This work was carried out to facilitate the development of a diagnostic protocol for the begomoviruses causing tomato yellow leaf curl under the EU SMT programme project –‘Diagnostic protocols for organisms harmful to plants’ (DIAGPRO).
Control of the Bemisia tabaci/Tomato yellow leaf curl virus complex on protected tomato crops in Algarve (Portugal)*
Authors: Arsénio A. F. , Neto E. , Ramos N. , Mangerico S. , Fortunato E. , Stigter L. , Fernandes J. E. , Lavadinho A. M. P. , Louro D.
Published: April 2008

The whitefly Bemisia tabaci has been a serious pest in protected tomato crops since 1995 in the south of Portugal (Algarve), causing severe losses mainly resulting from Tomato yellow leaf curl virus (TYLCV), first reported in the autumn/winter season. In order to manage and control the B. tabaci/TYLCV complex, experimental field trials were carried out between 1997 and 2000. Several control methods were tested, such as the application of white screen nets to windows and doors, chemical treatments against B. tabaci and the use of cucumber as a trap crop. The results show that the percentage of plants with TYLCV symptoms mainly reflects B. tabaci infestation level in the first 6 weeks. Screen net protection was the control method that clearly provided a low incidence of plants with TYLCV symptoms in the autumn/winter season. Additionally, insecticide treatments, made weekly in the first 6 weeks, may give improved protection. In the winter/spring season, the B. tabaci/TYLCV complex is a minor problem because of the low populations of B. tabaci and the climatic conditions. Information about the work in progress and results was given to growers through visits to the experimental fields and oral presentations.
Control of the Bemisia tabaci/Tomato yellow leaf curl virus complex in tomato nurseries in Portugal*
Authors: Ramos N. , Fernandes J. E. , Arsénio A. F. , Mangerico S. , Neto E.
Published: April 2008

According to EU and Portuguese law, inspection of horticultural nurseries is an important task for the Phytosanitary Inspection Services of the NPPO, which requires the introduction of some rules: official registration of producers and production of plant material of EC quality. Mainly as a result of the introduction of Tomato yellow leaf curl virus (TYLCV) in 1995, tight control of registered nurseries was implemented in Algarve in order to ensure the production of young horticultural plants of good varietal and phytosanitary quality. A survey system was established in order to contain pests by trying to eradicate them in nurseries. Nurseries were obliged to adopt new technologies, including for example the compulsory use of screen nets, the improvement of the existing glasshouses and the implementation of strict rules for access of people to these places. The Administration (MADRP/DRAALG) has provided financial support in order to have new nursery glasshouses (without increasing the area) suitable for the control of Bemisia tabaci and other pests which may be disease vectors. It should be stressed that about 50% of nursery production in Algarve is used in other regions of Portugal, considered as EU Protected Zones for B. tabaci.
Action Research: Solving Real-World Problems
Authors: Afify Mohamed Fawzy
Published: April 2008

This paper discusses action research (AR) as a research methodology. AR attempts to solve problems and bring about change. AR can be regarded as a marriage between ‘Theory’ and ‘Praxis’, requiring collaboration between researchers and practitioners. This paper reviews AR and some methodological issues associated with it. The status of AR in hospitality industry and some reported AR studies are examined.
Infrared analysis of CO ice particles in the aerosol phase
Authors: Dartois Emmanuel , Bauerecker Sigurd
Published: April 2008

Fourier transform infrared extinction spectra of a variety of CO ice aerosols, generated at low temperatures in a liquid helium cooled collisional-cooling cell, have been analyzed. Different operation modes of the cooling system were used for the generation of spherical and nonspherical CO nanoparticles at temperatures between 5 and 35K and with diameters between 10 and 1000nm. In contrast to the predominantly amorphous CO films described in the literature the presented CO particles are (poly)crystalline. A Mie inversion iterative scheme is presented and used to infer the optical constants of CO ice for the cases compact particles have been produced. The spectra of nonspherical CO aerosol particles are interpreted by modeling the extinction using the discrete dipole approximation procedure combined with the retrieved optical constants. A global positive matrix factorization scheme allows us to infer the dominant shapes in the observed particle distribution and can be used as a guide for further experiments. Near 25K a pronounced shape evolution of smaller particles from spherical toward longish structures was observed at low buffer-gas pressure over 400s.
Ultrafast photoinduced electron transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer
Authors: Mandal Ujjwal , Ghosh Subhadip , Dey Shantanu , Adhikari Aniruddha , Bhattacharyya Kankan
Published: April 2008

Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to coumarin dyes is studied in the micelle and the gel phase of a triblock copolymer, (PEO)20-(PPO)70-(PEO)20 (Pluronic P123) by picosecond and femtosecond emission spectroscopies. The rate of PET in a P123 micelle and gel is found to be nonexponential and faster than the slow components of solvation dynamics. In a P123 micelle and gel, PET occurs on multiple time scales ranging from a subpicosecond time scale to a few nanoseconds. In the gel phase, the highest rate constant (9.3×109M−1s−1) of ET for C152 is about two times higher than that (3.8×109M−1s−1) observed in micelle phase. The ultrafast components of electron transfer (ET) exhibits a bell shaped dependence with the free energy change which is similar to the Marcus inversion. Possible reasons for slower PET in P123 micelle compared to other micelles and relative to P123 gel are discussed.
Semidensities, second-class constraints, and conversion in anti-Poisson geometry
Authors: Bering K.
Published: April 2008

We consider Khudaverdian’s geometric version of a Batalin–Vilkovisky (BV) operator ΔE in the case of a degenerate anti-Poisson manifold. The characteristic feature of such an operator (aside from being a Grassmann-odd, nilpotent, second-order differential operator) is that it sends semidensities to semidensities. We find a local formula for the ΔE operator in arbitrary coordinates. As an important application of this setup, we consider the Dirac antibracket on an antisymplectic manifold with antisymplectic second-class constraints. We show that the entire Dirac construction, including the corresponding Dirac BV operator ΔED, exactly follows from conversion of the antisymplectic second-class constraints into first-class constraints on an extended manifold.
Theory of three-dimensional alignment by intense laser pulses
Authors: Artamonov Maxim , Seideman Tamar
Published: April 2008

We introduce a theoretical framework for study of three-dimensional alignment by moderately intense laser pulses and discuss it at an elementary level. Several features of formal interest are noted and clarified. Our approach is nonperturbative, treating the laser field within classical and the material system within quantum mechanics. The theory is implemented numerically using a basis set of rotational eigenstates, transforming the time-dependent Schrödinger equation to a set of coupled differential equations where all matrix elements are analytically soluble. The approach was applied over the past few years to explore different adiabatic and nonadiabatic three-dimensional alignment approaches in conjunction with experiments, but its formal details and numerical implementation were not reported in previous studies. Although we provide simple numerical examples to illustrate the content of the equations, our main goal is to complement previous reports through an introductory discussion of the underlying theory.
Ab initio spectroscopy and photoinduced cooling of the trans-stilbene molecule
Authors: Tatchen Jörg , Pollak Eli
Published: April 2008

We present a theoretical study of the S0→S1 and S0←S1 vibronic spectra for trans-stilbene. Franck–Condon spectra in the harmonic approximation are generated for the complete system with 72degrees of freedom by means of an analytic time-dependent approach accounting for Dushinsky rotations and thermal effects. The force fields are computed by means of density functional theory (DFT) and time-dependent DFT, on the one hand, and ab initio complete active space self-consistent field theory, on the other hand. The B3LYP functional shows that almost planar potential energy surface minima are found for the S0 and S1 state. Imposing C2h symmetry constraints, we obtain low-temperature high-resolution Franck–Condon spectra for both absorption and emission which are in reasonably good agreement with the experimental spectra measured by Syage et al. [J. Chem. Phys. 81, 4685 (1984)] in supersonic jets. Due to thermal population of low-energy modes, the room temperature absorption spectrum is very broad. An almost structureless band which extends over several thousand cm−1 is obtained from the present theory and agrees with the experimental absorption band shape. Finally, within the harmonic model, we study the effect of photoexcitation on the energy distribution in the excited S1 state. We find noticeable cooling of ≈20K within a frequency interval spanning from −400to200cm−1 around the 0-0 transition. This indicates that photoinduced cooling must be taken into account when considering the dynamics of the photoinduced isomerization of trans-stilbene. Moreover, this is not the final word, as anharmonicity of the low frequency modes must be taken into account to obtain a full picture which would explain both the energy dependence of the isomerization rates as well as the dependence on the pressure of an external buffer gas.
Exploring a free energy landscape by means of multidimensional infrared and terahertz spectroscopies
Authors: Suzuki Yohichi , Tanimura Yoshitaka
Published: April 2008

A model for the dipolar crystal system is employed to explore a role of free energy landscape (FEL), in which dipolar molecules are posted on two-dimensional lattice sites with two-state libratinal dynamics. All dipole-dipole interactions are included to have frustrated interactions among the dipoles. For the regular and distorted lattice cases, the FEL is calculated from the interaction energies and the total polarizations for all possible dipolar states at various temperatures. At high temperatures, the shape of the calculated FEL is smooth and parabolic, while it becomes bumpy at low temperatures exhibiting multiple local minima. To study dynamical aspects of the system, the single flip dynamics and the single-double mixed flips dynamics of dipoles are examined from a master equation approach. As the observables of linear absorption and two-dimensional (2D) infrared, far infrared, and terahertz spectroscopies, the first- and third-order response functions of polarization are calculated for different physical conditions characterized by the FEL. While the linear absorption signals decay in time in a similar manner regardless of the FEL profiles, the 2D signals exhibit prominent differences for those profiles. This indicates that we may differentiate the FEL profiles by changing two-time valuables in 2D spectroscopy. As illustrated in the single-double flips case, the FEL study by means of 2D spectroscopy, however, relies on the dynamics which is set independently from the FEL. The Smoluchowski equation is applied to examine the description of the collective dynamics on the microscopically calculated FEL. We found that the one-dimensional and 2D signals calculated from the Smoluchowski equation agree with those from master equation only at temperatures where the FEL becomes parabolic shape.
Twin optical traps for two-particle cross-correlation measurements: Eliminating cross-talk
Authors: Atakhorrami M. , Addas K. M. , Schmidt C. F.
Published: April 2008

The correlated motions of two micron-sized particles reflect the (micro-) rheological properties of a fluid and can be conveniently detected using two optical traps in combination with interferometric displacement detection. When the correlations become small, cross-talk between the two beams becomes important. We have used dual optical traps created by either two orthogonally polarized laser beams derived from one laser source, or by two independent lasers of different wavelengths for microrheology experiments. High numerical aperture lenses (objective and condenser) in the optical path can introduce depolarization, and polarizing beam splitters are not perfect, both of which can lead to optical cross-talk. We have characterized the cross-talk in our setup and demonstrate that the use of two independent laser eliminates cross-talk entirely.
A novel algorithm for creating coarse-grained, density dependent implicit solvent models
Authors: Allen Erik C. , Rutledge Gregory C.
Published: April 2008

Implicit solvent simulations are those in which solvent molecules are not explicitly simulated, and the solute-solute interaction potential is modified to compensate for the implicit solvent effect. Implicit solvation is well known in Brownian dynamics of dilute solutions but offers promise to speed up many other types of molecular simulations as well, including studies of proteins and colloids where the local density can vary considerably. This work examines implicit solvent potentials within a more general coarse-graining framework. While a pairwise potential between solute sites is relatively simple and ubiquitous, an additional parametrization based on the local solute concentration has the possibility to increase the accuracy of the simulations with only a marginal increase in computational cost. We describe here a method in which the radial distribution function and excess chemical potential of solute insertion for a system of Lennard–Jones particles are first measured in a fully explicit, all-particle simulation, and then reproduced across a range of solute particle densities in an implicit solvent simulation.
Multipathway dissociation dynamics of core-excited methyl chloride probed by high resolution electron spectroscopy and Auger-electron–ion coincidences
Authors: Miron Catalin , Morin Paul , Céolin Denis , Journel Loïc , Simon Marc
Published: April 2008

Core excitation triggers nuclear dynamics on the femtosecond time scale. A multiparametric electron/ion coincidence approach has been used to disentangle complex decay processes occurring at short (molecular) or long (atomic) time scales. Methyl chloride has been excited by scanning along the dissociative Cl2p→σ* resonance. The detailed chronology of the competing decay processes, leading to either the rearrangement product HCl+, or an ultrafast dissociation leading to Cl+, has been investigated. The observed Auger–Doppler shift has been analyzed for various orientations of the electron and fragment ion.
A first principles study on organic molecule encapsulated boron nitride nanotubes
Authors: He Wei , Li Zhenyu , Yang Jinlong , Hou J. G.
Published: April 2008

The electronic structures of boron nitride nanotubes (BNNTs) doped with organic molecules are investigated using density functional theory. An electrophilic molecule introduces acceptor states in the wide gap of BNNT close to the valence band edge, which makes the doped system a p-type semiconductor. However, with typical nucleophilic organic molecules encapsulation, only deep occupied molecular states but no shallow donor states are observed. There is a significant electron transfer from a BNNT to an electrophilic molecule, while the charge transfer between a nucleophilic molecule and a BNNT is negligible. When both electrophilic and nucleophilic molecules are encapsulated in the same BNNT, a large charge transfer between the two kinds of molecules occurs. The resulting small energy gap can strongly modify the transport and optical properties of the system.
Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals
Authors: Tang Jau
Published: April 2008

In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi–Pasta–Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit “breathing” standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (<70nm for aluminum and <200nm for gold), but becomes less dependent if further thickness increases. Coherent phonon excitation and propagation from the stressed bulk atoms due to impulsive forces as well as the linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.
Langmuir wave filamentation instability
Authors: Rose Harvey A. , Yin L.
Published: April 2008

A Langmuir wave (LW) model is constructed whose equilibria are consistent with stimulated Raman scatter optimization, with Hamiltonian dynamics, and with rotational invariance. Linear instability analysis includes terms to all orders in wave amplitude and fluctuation wavenumber expansions, δk. Resultant LW modulational instability is nonstandard: As the LW amplitude increases, the unstable δk range first expands and then shrinks to zero. Large amplitude wave model dynamics requires hyperdiffraction terms if kλD<0.45, lest artificially small length scales become unstable.
Precision sampling measurements using ac programmable Josephson voltage standards
Authors: Rüfenacht A. , Burroughs C. J. , Benz S. P.
Published: April 2008

We have performed a variety of precision measurements by comparing ac and dc waveforms generated by two independent ac programmable Josephson voltage standard (ACPJVS) systems. The objective of these experiments was to demonstrate the effectiveness of using a sampling digital voltmeter to measure small differences between Josephson waveforms for frequencies up to 3.6kHz. The low uncertainties that we obtained confirm the feasibility of using this differential sampling method for high accuracy comparisons between ACPJVS waveforms and signals from other sources.
A new quasiclassical method for modeling the high-resolution spectra of polyatomic systems
Authors: Kaprálová-Žďánská Petra R. , Hanák Filip , Lazebníček Jan
Published: April 2008

A new quasiclassical method for quantum autocorrelation functions based on the semiclassical limit in Wigner phase space has been derived. Unlike the existing quasiclassical method, the new method enables long-time simulations, thus making it possible to locate quantum spectral lines very precisely. The new method has been tested for a one-dimensional anharmonic oscillator fitted to the H2 molecule and for a six-dimensional calculation of the Ar2I van der Waals cluster in adiabatic approximation. The obtained results compare well with the benchmark quantum-mechanical calculations and are also roughly comparable to the experimental Ar2I− zero-kinetic-energy photoelectron spectrum, which is available in the literature.
Design and control of a nanoprecision XYΘ scanner
Authors: Choi Young-Man , Kim Jung Jae , Kim Jinwoo , Gweon Dae-Gab
Published: April 2008

This paper describes the design and control of a nanoprecision XYΘ scanner consisting of voice coil motors and air bearing guides. The proposed scanner can be installed on a conventional XY stage with long strokes to improve the positioning accuracy and settling performance. Major design considerations in developing a high precision scanner are sensor accuracy, actuator properties, structural stability, guide friction, and thermal expansion. Considering these factors, the proposed scanner is made of invar, which has a small thermal expansion coefficient and good structural stiffness. Four voice coil motors drive the scanner, which is suspended by four air bearing pads, in the x, y, and θ directions. The scanner’s position is measured by three laser interferometers which decouple the scanner from the conventional stage. The mirror blocks reflecting the laser beams are fixed using viscoelastic sheets, ensuring that the scanner has a well-damped structural mode. A time delay control algorithm is implemented on the real-time controller to control the scanner. The effectiveness of the proposed scanner is verified experimentally.
Pathways of polaron and bipolaron transport in DNA double strands
Authors: Wei J. H. , Liu X. J. , Berakdar J. , Yan YiJing
Published: April 2008

We investigate the pathways of polaron and bipolaron transports in DNA double strands with an extended Su–Schrieffer–Heeger model involving the effects of solvent polarization. We find that the long-range transport of polaron/bipolaron under high electric field at low temperature is the field-facilitated sequential tunneling through spatial-disordered potential barriers via multiple intrastrand and interstrand pathways. Although the interstrand pathways may be very active and effective in some DNA sequences, the intrastrand ones always dominate the charge transfer when the excess charge moves close to the final acceptor.
Modeling equilibrium concentrations of Bjerrum and molecular point defects and their complexes in ice Ih
Authors: de Koning Maurice , Antonelli Alex
Published: April 2008

We present a model for the determination of the thermal equilibrium concentrations of Bjerrum defects, molecular point defects, and their aggregates in ice Ih. First, using a procedure which minimizes the free energy of an ice crystal with respect to the numbers of defect species, we derive a set of equations for the equilibrium concentrations of free Bjerrum and point defects, as well their complexes. Using density-functional-theory calculations, we then evaluate the binding energies of Bjerrum-defect/vacancy and Bjerrum-defect/interstitial complexes. In contrast to the complexes which involve the molecular vacancy, the results suggest that the molecular interstitial binds preferentially to the D-type Bjerrum defect. Using both theoretical binding and formation free energies as well as the available experimental data, we find that the preferential binding and the substantial presence of the interstitial as the predominant point defect in ice Ih may lead to conditions in which the number of free D defects becomes considerably smaller than that of free L defects. Such a scenario could possibly be involved in the experimentally observed inactivity of D-type Bjerrum defects in the electrical properties of ice Ih.
Frozen natural orbital coupled-cluster theory: Forces and application to decomposition of nitroethane
Authors: Taube Andrew G. , Bartlett Rodney J.
Published: April 2008

The frozen natural orbital (FNO) coupled-cluster method increases the speed of coupled-cluster (CC) calculations by an order of magnitude with no consequential error along a potential energy surface. This method allows the virtual space of a correlated calculation to be reduced by about half, significantly reducing the time spent performing the coupled-cluster (CC) calculation. This paper reports the derivation and implementation of analytical gradients for FNO-CC, including all orbital relaxation for both noncanonical and semicanonical perturbed orbitals. These derivatives introduce several new orbital relaxation contributions to the CC density matrices. FNO-CCSD(T) and FNO-ΛCCSD(T) are applied to a test set of equilibrium structures, verifying that these methods are capable of reproducing geometries and vibrational frequencies accurately, as well as energies. Several decomposition pathways of nitroethane are investigated using CCSD(T) and ΛCCSD(T) with 60% of the FNO virtual orbitals in a cc-pVTZ basis, and find differences on the order of 5kcal∕mol with reordering of the transition state energies when compared to B3LYP 6-311+G(3df,2p).