Scale Of Several Hundreds Research Articles

Numerical modelling of the suspended particulate matter dynamics in a regulated river network

Understanding and predicting the propagation, deposition and resuspension of suspended particulate matter (SPM) in river networks is important for managing water resources, ecological habitat, pollution, navigation, hydropower generation, reservoir sedimentation, etc. Observational data are scarce and costly, and there is little feedback on the efficiency of numerical simulation tools for compensating the lack of data on a river scale of several hundreds of kilometers. This paper aims at exploring the use of a one-dimensional (1-D) hydrodynamical model for understanding the source and fate of SPM during complex events. The numerical model was applied to the May–June 2008 flood in the Lower Rhône River, France. This event was a combination of floods of the Isère (including dam flushing operations in the Lower Isère River) and Durance tributaries over a two-week period. The simulation code was used to model the SPM fluxes at a high spatial and temporal resolution using a multi-class approach. Approximately half of the 4.9 Mt of SPM measured at the outlet at Beaucaire were found to come from the Isère River and the other half from the Durance River, whereas previous studies estimated that most of the SPM flux at the outlet came from the Durance River. The amount of SPM trapped within the river network, mainly behind the first hydropower structure downstream of the Isère confluence, was estimated to be 3.7 Mt due to the deposition of the coarsest particles. Such a model proved to be able to compute the interaction of various grain size classes with dams and other structures. In turn, the quality of the results of SPM fluxes and deposition is highly sensitive to particle parameters, especially grain size distribution, and to the operational rules of reservoirs.

Visualization of traps at SiO2/SiC interfaces near the conduction band by local deep level transient spectroscopy at low temperatures

Local deep level transient spectroscopy (local-DLTS) at low temperatures is performed to investigate microscopic distributions of traps at SiO2/SiC interfaces near the conduction band. We find that the distributions of the density of interface states (Dit) with the energy depth of 0.20 eV from the conduction band edge show nonuniform contrasts with the scale of several hundreds of nanometers. We also apply local-DLTS to reveal the contribution of Dit to the nonuniform contrasts observed in scanning nonlinear dielectric microscopy (SNDM) images of SiO2/SiC samples. We analyze the cross-correlation between SNDM and Dit images obtained by simultaneous measurement with SNDM and local-DLTS, respectively. The patterns observed in the SNDM and Dit images simultaneously obtained at 150 K show a weak negative correlation, suggesting that nonuniform distributions of Dit contribute to the formation of inhomogeneous contrasts in the SNDM images.

Improvement of Local Deep Level Transient Spectroscopy for Microscopic Evaluation of SiO<sub>2</sub>/4H-SiC Interfaces

We demonstrate our new local deep level spectroscopy system improved for more accurate analysis of trap states at SiO2/4H-SiC interfaces. Full waveforms of the local capacitance transient with the amplitude of attofarads and the time scale of microseconds were obtained and quantitatively analyzed. The local energy distribution of interface state density in the energy range of EC − Eit = 0.31–0.38 eV was obtained. Two-dimensional mapping of the interface states showed inhomogeneous contrasts with the lateral spatial scale of several hundreds of nanometers, suggesting that the physical origin of the trap states at SiO2/SiC interfaces is likely to be microscopically clustered.

Chemobacterial Synthesis of a Sialyl-Tn Cyclopeptide Vaccine Candidate.

A conjugatable form of the tumour-associated carbohydrate antigen sialyl-Tn (Neu5Ac-α-2,6-GalNAc) was efficiently produced in Escherichia coli. Metabolically engineered E. coli strains overexpressing the 6-sialyltransferase gene of Photobacterium sp. and CMP-Neu5Ac synthetase genes of Neisseria meningitidis were cultivated at high density in the presence of GalNAc-α-propargyl as the exogenous acceptor. The target disaccharides, which were produced on the scale of several hundreds of milligrams, were then conjugated by using copper(I)-catalysed azide-alkyne cycloaddition click chemistry to a fully synthetic and immunogenic scaffold with the aim to create a candidate anticancer vaccine. Four sialyl-Tn epitopes were introduced on the upper face of an azido-functionalised multivalent cyclopeptide scaffold, the lower face of which was previously modified by an immunogenic polypeptide, PADRE. The ability of the resulting glycoconjugate to interact with oncofoetal sialyl-Tn monoclonal antibodies was confirmed in ELISA assays.

Visualization of trapped charges being ejected from organic thin-film transistor channels by Kelvin-probe force microscopy during gate voltage sweeps

Kelvin-probe force microscopy (KFM) has been widely used to evaluate the localized charge trap states in the organic thin-film transistor (OTFT) channels. However, applicability of the KFM has been limited to the trapped charges whose lifetime is typically longer than several minutes because of the temporal resolution of the KFM. Therefore, it has not long been employed for studying the dynamics of the trapped charges in the OTFTs. Here, we demonstrate a method to visualize the transient distribution of the trapped charge carriers in operating OTFTs. The method allows visualizing the dynamics of the trapped charges during the gate voltage sweeps on a time scale of several hundreds of milliseconds. The experimental results performed on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) OTFTs indicate that, immediately after a bias voltage applied to a device was turned off, the primary discharging of the channel region around the electrode edges started and it limited the ejection process of the remaining accumulated charges to the electrodes, resulting in an increased density of long-lived trapped charges in a region distant from the electrodes. The presented results suggest that the method is useful to study the electrical connections at the interface between the DNTT grains and electrodes, or those between the grains.

Multicomponent reactions II

The concept of multicomponent reactions (MCR) [1] has been around in organic chemistry since the very early days. Indeed, the first example known in literature, the Strecker synthesis of α-aminonitriles [2], has been developed into an industrial process for the production of methionine in an annual scale of several hundreds of thousand tons per year. In addition, a lot of syntheses of heterocycles from the early days are MCR, and these reaction sequences paved the way to a multitude of applications. Moreover, Ugi's groundbreaking developments in isonitrile-based chemistry and his conclusions demonstrated that MCR are not only highly practicable in the light of approaching the ideal synthesis [3–4] as one-pot methodologies, but rely on a reactivity based concept [5]. The perpetual generation of reactive functionalities and reactivity is the underlying general principle. Therefore, MCR are intriguing for industrial applications. But they are also challenging for academia, in particular for the minute and sophisticated fine-tuning of reactivity and selectivity, which is required to concatenate elementary steps to novel sequences. This Thematic Series on multicomponent reactions is a continuation of the previously released series two years ago [6] and again presents a snap shot of this highly dynamic field. With the traditional formats of letters, full papers, and reviews it spans the broad range of modern chemistry, including organocatalytic, organometallic, transition metal-catalyzed, radical reactions, condensation and isonitrile-based MCR. Biologically active compounds and photonic properties are addressed as well as mechanistic studies and models. The interested reader – whether an expert in the field or a newcomer – will find exciting reports from the current realm of MCR chemistry. As the guest editor of this Thematic Series I cordially thank all authors for their excellent contributions. I am also grateful to the staff of the Beilstein-Institut for their excellent and professional support. Thomas J. J. Muller Dusseldorf, December 2013

Transparent copolyester/organoclay nanocomposites prepared by in situ intercalation polymerization: Synthesis, characterization, and properties

In this study, amorphous poly(ethylene terephthalate-co-1,3/1,4-cyclohexylenedimethylene terephthalate) (PETG)/organoclay nanocomposites was synthesized by the in situ intercalation polymerization of terephthalic acid, ethylene glycol, 1,3/1,4-cyclohexanedimethanol, and organoclay. The organoclay was obtained by modifying sodium montmorillonite (clay) with hexadecyl triphenylphosphonium bromide. The thermal, mechanical, optical, and gas barrier properties of these PETG nanocomposites with various organoclay contents (0–3 wt%) were discussed. The differential scanning calorimetry and X-ray analyses revealed that all of the nanocomposites were amorphous. X-ray diffraction and transmission electron micrographs showed that the organoclay was well dispersed in the polymer matrix, although some parts of the agglomerated layers remained on the scale of several hundreds of nanometers. The thermal stability and the mechanical property of the nanocomposites increased with organoclay content. The optical transmittances of nanocomposites that contained 0.5, 1, and 3 wt% of organoclay were 86.8%, 84.4%, and 77.4%, respectively. The oxygen transmission rate of the nanocomposite that contained 3 wt% of organoclay was about 50% of the PETG base polymer. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers

Determination of the elastic/plastic transition of human enamel by nanoindentation

Objectives/Methods From a materials scientist's perspective, dental materials used for tooth repair should exhibit compatible mechanical properties. Fulfillment of this criterion is complicated by the fact that teeth have a hierarchical structure with changing mechanical behavior at different length scales. In this study, nanoindentation with an 8 μm spherical indenter was used to determine the elastic/plastic transition under contact loading for enamel. Results The indentation elastic/plastic transition of enamel at the length scale of several hundreds of hydroxyapatite crystallites, which are within one enamel rod, is revealed for the first time. The corresponding penetration depth at the determined indentation yield point of 1.6 GPa and 0.6% strain is only 7 nm. As a consequence of the small depth it is decisive for the experiment to calibrate the indenter tip radius in this loading regime. The elastic modulus of 123 GPa was evaluated directly by the Hertzian penetration and not by the unloading part of the indentation curve. Significance We believe these data are also a valuable contribution to understand the mechanical behavior of enamel and to develop nanoscale biomimetic materials.

Intrachain photoluminescence dynamics of a long oligothiophene at room temperature

The temperature dependence of the photoluminescence (PL) and absorption spectra of the 16-mer oligothiophene (16 T) extremely diluted in polypropylene (PP) has been investigated to clarify the PL dynamics at room temperature of quasi-isolated conjugated polymers. Both of the PL and absorption spectra of 16 T in PP are found to blueshift with increasing temperature, due to the thermal conformational change. The Stokes shift estimated by the difference of the 0–0 peak between the absorption and PL spectra is shown to increase with temperature. It is found that the time-resolved PL spectra at room temperature of 16 T in PP exhibit a larger transient redshift than those at 4 K. The increase of the Stokes shift is thus concluded to result from the enhanced transient redshift due to the conformational change. The magnitude of the Stokes shift increasing with temperature is shown to be reduced in the case of 12-mer oligothiophene diluted in PP compared to that of 16 T in PP. This leads us to conclude that the thermal inhomogeneity increases with elongating the chain length. It is also shown that the exciton migration occurs in the time scale of several hundreds of picoseconds and competes with decay of emission.

Poly(vinyl pyrrolidone‐co‐vinyl acetate)‐graft‐poly(ε‐caprolactone) as a compatibilizer for cellulose acetate/poly(ε‐caprolactone) blends

AbstractPoly(vinyl pyrrolidone‐co‐vinyl acetate)‐graft‐poly(ε‐caprolactone) (PVPVAc‐g‐PCL) was synthesized by radical copolymerization of N‐vinyl‐2‐pyrrolidone (VP)/vinyl acetate (VAc) comonomer and PCL macromonomer containing a reactive 2‐hydroxyethyl methacrylate terminal. The graft copolymer was designed in order to improve the interfacial adhesiveness of an immiscible blend system composed of cellulose acetate/poly(ε‐caprolactone) (CA/PCL). Adequate selections of preparation conditions led to successful acquisition of a series of graft copolymer samples with different values of molecular weight ( $M_{n}^{{\rm PVPVA} {{\rm c} - g - {\rm PCL}}}$), number of grafts (n), and segmental molecular weight of PVPVAc between adjacent grafts (Mn (between grafts)). Differential scanning calorimetry measurements gave a still immiscible indication for all of the ternary blends of CA/PCL/PVPVAc‐g‐PCL (72 : 18 : 10 in weight) that were prepared by using any of the copolymer samples as a compatibilizer. However, the incorporation enabled the CA/PCL (4 : 1) blend to be easily melt‐molded to give a visually homogeneous film sheet. This compatibilizing effect was found to be drastically enhanced when PVPVAc‐g‐PCLs of higher $M_{ n}^{{\rm PVPVA}{\rm c} - g - {\rm PCL}}$ and Mn (between grafts) and lower n were employed. Scanning electron microscopy revealed that a uniform dispersion of the respective ingredients in the ternary blends was attainable with an assurance of the mixing scale of several hundreds of nanometers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Electromagnetic brain imaging

There is a long history to detection of neural current flow via specific changes in the electromagnetic field that is measured outside the brain. Electroencephalography (EEG) has been extensively investigated and utilized for the last 80 years [Berger, 1929] and electrocorticography (ECoG) for 60 years [Jasper and Penfield, 1949]. Magnetoencephalography (MEG) was introduced 40 years ago [Cohen, 1968] and it has since experienced intense technical development and growing interest in various fields of neuroscience. Clinicians and basic scientists who have chosen to utilize these time-sensitive techniques have always appreciated their great potential and pertinence to questions in both the clinical domain and integrative neuroscience, while understanding their respective limitations. These electromagnetic techniques have recently fostered increasing interest from investigators who originally entered the field of human brain mapping via other modalities, particulary functional magnetic resonance imaging (fMRI). An aspiration to reach beyond the hemodynamic response and its limited time resolution is likely to be at the origin of such interest which has also manifested as notable investments in cutting-edge MEG and fMRI-compatible EEG systems. For example, the organization and internal mechanisms of brain-wide functional networks are considered by many investigators a tough problem of great interest that can ultimately not be addressed with the time scale of several hundreds of milliseconds that is accessible with blood oxygen level dependent (BOLD) effects. Consequently, the functional neuroimaging community now seems to increasingly encompass the relevance of timing—in a very broad sense—as a natural complement to spatial mapping, when seeking to characterize and understand human brain function and its disorders as well as the relationship between neural processes and behavior. Each new development in electromagnetic methods and the more recent interplay between electromagnetic and hemodynamic techniques has brought along new views, challenges and disputes that have, eventually, moved the field forward. EEG was initially collected with a relatively small number of electrodes and, for several decades, the focus was set primarily on the identification and chronometry of typical scalp waveforms or components, with only indirect concern of the areas in the brain the signals would originate from—although there has been an unwarranted tendency to associate changes in EEG signals (or event-related potentials, ERPs) at specific electrodes with activation of the brain areas directly underneath. Emergence of the MEG technique, particularly devices covering large areas of the scalp (cortex), resulted in a palpable tension between EEG and MEG users and developers, akin to the brawls witnessed in the hemodynamic imaging community between users of positron emission tomography (PET) and the proponents of the rapidly emerging fMRI technique. Early MEG investigators—mostly from physics laboratories sought to localize—from the outset, the neural sources of the surface signals and determine the temporal variation of their activation. The prominent spatiotemporal (or source localization) emphasis in MEG had strong foundations: the volume currents that are generated by the intracellular (primary) currents and circulate within the head tissues have markedly less influence on the surface magnetic fields (MEG) than surface electric potentials (EEG), as *Correspondence to: Riitta Salmelin, Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, FIN02015 TKK, Finland. E-mail: riitta@neuro.hut.fi

Spherical and acicular representation of hydrates in a micromechanical model for cement paste: prediction of early-age elasticity and strength

Early-age stiffness and strength evolution of cement paste is studied in the framework of continuum micromechanics. Based on the self-consistent scheme, elastic and strength properties are upscaled from the scale of several micrometers up to the scale of several hundreds or thousands of micrometers. Four material phases are considered: clinker, hydration products, water and air. We assign a spherical geometry to clinker grains and pores, while we investigate both spherical and acicular (needle-type) shapes as geometrical representation of the micrometer-sized hydration products. As regards macroscopic poromechanical boundary conditions, two extreme cases are considered: drained conditions and sealed conditions, respectively. These choices allow for studying the influence of (i) the morphological representation of hydrates, and of (ii) the bulk stiffness of water, on the micromechanical prediction of early-age behavior of cement paste, including setting and the hydration-dependent evolutions of both elastic stiffness and uniaxial compressive strength. The newly proposed strength model is based on a von Mises-type elastic limit criterion for individual hydrates. Corresponding deviatoric stress peaks within hydrates are estimated through quadratic stress averages. In this way, the micromechanical strength criterion is formulated in terms of macroscopic loading (stresses or strains, respectively). Model-predicted elasticity and strength evolutions are compared with data from experimental testing of cement pastes with water–cement ratios ranging from 0.35 to 0.60. Satisfactory agreement between model predictions and experiments allows for two conclusions: the morphology of hydrates significantly influences micromechanics-based elastic stiffness estimates of cement paste particularly at very early ages, whereas elastic properties of mature cement paste can be estimated reliably on the basis of both spherical or acicular shaped hydrates. The development of a reliable strength model, however, requires consideration of hydrates as non-spherical particles, no matter what age of cement paste is considered.

Vertical Fine Structures of Temperature and Water Vapor in the Free Atmosphere

More than 400 upper-air soundings at different geographical locations over the Japanese Islands for various seasons reveal that vertical fine structures of temperature and water vapor, having a venical scale of several hundreds of meters, commonly exist in the troposphere between 1 and 8 km MSL. The temperature and specific humidity fluctuations associated with the fine structures range between −0.4 and 0.4 K, and between −0.6 and 0.6 g kg−1, respectively. The specific humidity fluctuations are negatively correlated with the temperature fluctuations, and the positive (negative) peaks of the former are located right below the local maxima (minima) of buoyancy frequency. The existence of such fine structures of temperature and water vapor was also confirmed by an observation using simultaneously a radiosonde and a Raman lidar, which measures water vapor independently.

Photoinduced Bimolecular Electron Transfer Investigated by Femtosecond Time-Resolved Infrared Spectroscopy

Ultrafast infrared transient absorption spectroscopy is used to study the photoinduced bimolecular electron transfer reaction between perylene in the first singlet excited state and 1,4-dicyanobenzene in acetonitrile and dichloromethane. Following vibrational marker modes on both donor and acceptor sides in real time provides direct insight into the structural dynamics during the reaction. A band narrowing on a time scale of a few tens of picoseconds observed on the antisymmetric CN stretching vibration of the dicyanobenzene radical anion indicates that a substantial part of the excess energy is channeled into vibrational modes of the product, despite the fact that the reaction is weakly exergonic. An additional narrowing of the same band on a time scale of several hundreds of picoseconds observed in acetonitrile only is interpreted as a signature of the dissociation of the geminate ion pairs into free ions.

Chlorine-36 dating of deep groundwater from northern Sahara

Summary The “Continental Intercalaire” from Sahara is one of the largest confined aquifers in the world. In the northern part of the basin, the depth of the aquifer ranges between 400 and 1800 m and the main flow direction is from west to east. Chlorine-36 analyses were performed on groundwater samples mainly collected along this flowpath. They show a wide range of 36 Cl contents, from 8 to 99 × 10 −15 at at −1 expressed as 36 Cl/Cl atomic ratio. In order to evaluate the epigene production, measurements were also performed on chloride extracted by leaching from a soil profile, near the recharge zone. This showed that the contribution of epigene production remains limited. A range of 36 Cl/Cl ratios from 116 to 133 × 10 −15 was adopted for groundwater recharging the aquifer, including both meteoric production and epigene production. For most of the samples collected along the main flowpath, a significant decay effect was observed. An attempt of dating was made by using an equation that takes into account radioactive decay of the meteoric–epigene input, deep production and chloride dissolution within the aquifer. The calculated 36 Cl residence time varies from 16 to 500 ka for the minimum ages, and from 25 to 1200 ka for the maximum ages. An increase of residence time is observed up to about 500 km from the recharge zone. This corresponds to mean flow velocities of 0.2–0.5 m a −1 and to an average permeability of 1.1 ± 0.6 × 10 −5 m s −1 , at the scale of several hundreds of kilometres.

Unusual conformational effects in proton transfer kinetics of an excited photochromic Schiff base

The compound 4-methoxy-2,5-bis(phenyliminomethyl)-phenol representing a group of recently synthesized new photochromic Schiff bases, has been studied by transient absorption and time-resolved fluorescence measurements in femto- and picosecond time domains. Two different conformers of the keto tautomer, decaying with the time constants 480 and 110 ps, have been detected. The first one is created within 50 fs, and the second one – exceptionally slowly – with the time constant of about 10 ps. The fast route occurs in the planar system, and the slow one involves the rotation around the C C bond between the central phenyl ring and the phenylimino group, leading to the metastable photochromic form. For the first keto conformer the evidence of fast vibrational relaxation taking place on the time scale of several hundreds of femtoseconds is observed.

A comparison of the excited-state processes of nearly symmetrical perylene quinones: hypocrellin A and hypomycin B

The excited-state photophysics of two naturally occurring nearly symmetrical perylene quinones are discussed: hypocrellin A and hypomycin B. Hypocrellin A has a hydroxyl group peri to a carbonyl group on either end of its long molecular axis in addition to a hydroxyl group on its seven-membered ring. On the other hand, hypomycin B is unique among this class of known naturally occurring perylene quinones in that it possesses only one hydroxyl group, which is peri to a carbonyl group. These quinones are investigated in different nonionic micellar environments. For hypocrellin A and hypomycin B, a micelle concentration 10 times in excess of that used for hypericin in a previous study, i.e. 100 times the critical micelle concentration, must be employed to obviate aggregation. Under such conditions, the p K a of the peri hydroxyl groups of hypocrellin A have been determined to be 8.9. The p K a of the protonated carbonyl groups could not be measured. A comparable value is estimated for hypomycin B. The differing solubilities and behaviors of hypericin and hypocrellin in micellar environments are briefly discussed in the context of their biological activity. The excited-state processes in hypocrellin A and hypomycin B are compared on a time scale of several hundreds of picoseconds. No deuterium isotope effect is observed for hypomycin B. This result is discussed in the light of the previous assignment of the primary photoprocess in hypocrellin A to hydrogen atom transfer.

Resonant IR Photon Induced Dissociation in Organic Molecules with Chain-like Substructures

A nonstatistical model for the resonant IR photon induced dissociation of organic molecules by IR photons is suggested. The model is based on the excimol theory for molecules which contain chains of identical diatomic dipole groups. IR photon radiation can induce resonantly collective vibrational excitations (excimols) in these molecular substructures. The accumulation of several excimols in the molecular chain causes a local heating of the molecule and its fragmentation on a time scale of several hundreds of femtoseconds. An analytical expression for the fragmentation probability is derived and analysed.

Time-slicing: A model for cerebellar function based on synchronization, reverberation, and time windows

We present a functional model of the cerebellum comprising cerebellar cortex, inferior olive, cerebellar and brain-stem nuclei. Detailed single-neuron modeling combined with large network simulations show that (i) Golgi cells can restrict granule cell spikes to narrow time windows, that (ii) rebound firing in cerebellar nuclei cells leads to a delayed reverberation of Purkinje cell activity within the network, and that (iii) the system is able to learn spatio-temporal patterns of neuronal activity. These results shed new light on several experimental observations and explain how the cerebellum can solve timing tasks on a time scale of several hundreds of milliseconds.

Dispersion and Reservoir Heterogeneity

Summary Macroscopic dispersion is the mixing, on the scale of several hundreds of grain diameters, at a point in a permeable medium that is free of boundary effects. Megascopic dispersion is the one-dimensional (1D) dispersion derived by averaging across an entire cross section. This work investigates how both dispersions vary with heterogeneity, aspect ratio, diffusion coefficient, and autocorrelation. The theoretical results are compared to existing field and laboratory data and to existing theories for limiting cases. The degree of autocorrelation in the medium determines whether or not megascopic dispersivity (dispersion coefficient divided by velocity) is uniquely defined. Large correlation distances (with respect to the medium dimensions) imply a dispersivity that grows with distance traveled. Small correlation distances imply a dispersivity that is eventually stabilized at some constant value. This value is related to the heterogeneity of the medium. On the field scale, diffusion is insignificant, but on a laboratory scale, it can stabilize the dispersivity even if the medium is correlated. Macroscopic dispersivity is sensitive to diffusion in both the laboratory and field scale. It is smaller than or equal to megascopic dispersivity, also in conformance with experimental data, and comparable to laboratory-measured dispersivity.