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Time Resolution (time + resolution)
Selected AbstractsReinterpretable Imager: Towards Variable Post-Capture Space, Angle and Time Resolution in PhotographyCOMPUTER GRAPHICS FORUM, Issue 2 2010Amit Agrawal Abstract We describe a novel multiplexing approach to achieve tradeoffs in space, angle and time resolution in photography. We explore the problem of mapping useful subsets of time-varying 4D lightfields in a single snapshot. Our design is based on using a dynamic mask in the aperture and a static mask close to the sensor. The key idea is to exploit scene-specific redundancy along spatial, angular and temporal dimensions and to provide a programmable or variable resolution tradeoff among these dimensions. This allows a user to reinterpret the single captured photo as either a high spatial resolution image, a refocusable image stack or a video for different parts of the scene in post-processing. A lightfield camera or a video camera forces a-priori choice in space-angle-time resolution. We demonstrate a single prototype which provides flexible post-capture abilities not possible using either a single-shot lightfield camera or a multi-frame video camera. We show several novel results including digital refocusing on objects moving in depth and capturing multiple facial expressions in a single photo. [source] Potential biases in sampling design and interpretation of intra-tooth isotope analysisINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 1-2 2003M. BalasseArticle first published online: 30 JAN 200 Abstract An increasing number of studies dealing with environmental and dietary reconstruction involve measurement of intra-tooth variation of isotope ratios. The sampling procedure typically consists of collecting a sequence of horizontal bands perpendicular to the growth axis of the tooth. The objective is to obtain a temporal sequence of the changes recorded in dental tissues during tooth development. This paper examines some issues associated with this sampling strategy and consequences for interpretation of the data. Time resolution is influenced by the pattern and duration of enamel mineralization, in a way that might, however, depend on the species and the tooth analysed. Although it may be impossible to sample discrete amounts of time, a chronological order seems to be respected, which should be well enough when the objective is to detect changes in isotope ratios with time. Absolute data must be interpreted with caution. Such issues do not affect studies of inter-individual variability as long as the sampling procedure applied to the compared specimens is consistent. A new sampling strategy is tested on modern goat teeth, involving drilling in an oblique direction. The results obtained from obliquely drilled samples are very similar to those obtained from the horizontal sampling procedure. More work is still needed to determine the value of alternative sampling strategies. Copyright © 2003 John Wiley & Sons, Ltd. [source] Reinterpretable Imager: Towards Variable Post-Capture Space, Angle and Time Resolution in PhotographyCOMPUTER GRAPHICS FORUM, Issue 2 2010Amit Agrawal Abstract We describe a novel multiplexing approach to achieve tradeoffs in space, angle and time resolution in photography. We explore the problem of mapping useful subsets of time-varying 4D lightfields in a single snapshot. Our design is based on using a dynamic mask in the aperture and a static mask close to the sensor. The key idea is to exploit scene-specific redundancy along spatial, angular and temporal dimensions and to provide a programmable or variable resolution tradeoff among these dimensions. This allows a user to reinterpret the single captured photo as either a high spatial resolution image, a refocusable image stack or a video for different parts of the scene in post-processing. A lightfield camera or a video camera forces a-priori choice in space-angle-time resolution. We demonstrate a single prototype which provides flexible post-capture abilities not possible using either a single-shot lightfield camera or a multi-frame video camera. We show several novel results including digital refocusing on objects moving in depth and capturing multiple facial expressions in a single photo. [source] Tubular reabsorption and diabetes-induced glomerular hyperfiltrationACTA PHYSIOLOGICA, Issue 1 2010P. Persson Abstract Elevated glomerular filtration rate (GFR) is a common observation in early diabetes mellitus and closely correlates with the progression of diabetic nephropathy. Hyperfiltration has been explained to be the result of a reduced load of sodium and chloride passing macula densa, secondarily to an increased proximal reabsorption of glucose and sodium by the sodium-glucose co-transporters. This results in an inactivation of the tubuloglomerular feedback (TGF), leading to a reduced afferent arteriolar vasoconstriction and subsequently an increase in GFR. This hypothesis has recently been questioned due to the observation that adenosine A1 -receptor knockout mice, previously shown to lack a functional TGF mechanism, still display a pronounced hyperfiltration when diabetes is induced. Leyssac demonstrated in the 1960s (Acta Physiol Scand58, 1963:236) that GFR and proximal reabsorption can work independently of each other. Furthermore, by the use of micropuncture technique a reduced hydrostatic pressure in Bowman's space or in the proximal tubule of diabetic rats has been observed. A reduced pressure in Bowman's space will increase the pressure gradient over the filtration barrier and can contribute to the development of diabetic hyperfiltration. When inhibiting proximal reabsorption with a carbonic anhydrase inhibitor, GFR decreases and proximal tubular pressure increases. Measuring intratubular pressure allows a sufficient time resolution to reveal that net filtration pressure decreases before TGF is activated which highlights the importance of intratubular pressure as a regulator of GFR. Taken together, these results imply that the reduced intratubular pressure observed in diabetes might be crucial for the development of glomerular hyperfiltration. [source] Fluctuating Helium Emission in Optically Thick Divertor PlasmasCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2008F. B. Rosmej Abstract Simulations of the helium radiative properties carried out with the recently developed multi-level meta-stable resolved collisional-radiative code SOPHIA discovered new unique emission lines to analyze optically thick divertor plasmas relevant for ITER. The comparison of their time dependent line emission obtained from the NAGDIS-II plasma simulator experiments with time dependent temperature probe measurements shows a strong correlation. This indicates that line intensity fluctuations can be transformed to the important quantities of density and temperature fluctuations. A transformation method based on integral line intensity ratios which can be recorded with high time resolution is discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Measurement of barbed ends, actin polymerization, and motility in live carcinoma cells after growth factor stimulation,CYTOSKELETON, Issue 4 2004Mike Lorenz Abstract Motility is associated with the ability to extend F-actin-rich protrusions and depends on free barbed ends as new actin polymerization sites. To understand the function and regulation of different proteins involved in the process of generating barbed ends, e.g., cofilin and Arp2/3, fixed cell approaches have been used to determine the relative barbed end concentration in cells. The major disadvantages of these approaches are permeabilization and fixation of cells. In this work, we describe a new live-cell time-lapse microscopy assay to determine the increase of barbed ends after cell stimulation that does not use permeabilization and provides a better time resolution. We established a metastatic carcinoma cell line (MTLn3) stably expressing GFP-,-actin at physiological levels. Stimulation of MTLn3 cells with epidermal growth factor (EGF) causes rapid and transient lamellipod protrusion along with an increase in actin polymerization at the leading edge, which can be followed in live cell experiments. By measuring the increase of F-actin at the leading edge vs. time, we were able to determine the relative increase of barbed ends after stimulation with a high temporal resolution. The F-actin as well as the barbed end concentration agrees well with published data for this cell line. Using this newly developed assay, a decrease in lamellipod extension and a large reduction of barbed ends was documented after microinjecting an anti-cofilin function blocking antibody. This assay has a high potential for applications where rapid changes in the dynamic filament population are to be measured. Cell Motil. Cytoskeleton 57:207,217, 2004. © 2004 Wiley-Liss, Inc. [source] Monitoring of Machining Processes Using Sensor Equipped Tools,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Ekkard Brinksmeier A different to conventional monitoring systems sensor equipped tools give the possibility to gain information about the process status directly from the contact zone between tool and component to be machined. For example this can be realized by the integration of small temperature sensors into grinding wheels. The transmitting of the process data is performed by a telemetric unit attached to the grinding wheel's core. In this paper, the development of a new thin film thermocouple sensor concept is described. The unique feature of this sensor is the continuous contacting of the thermocouple through the grinding process inherent wear which leads to smearing of the thermoelectric layers and thus forming the measuring junction of a thermocouple. The system was used in OD grinding processes aiming to detect grinding burn and process instabilities. By reducing the volume of the sensors a fast response and high time resolution can be obtained. By this way, observance of the key parameters of the practical operation as closely as possible to the cutting area is enabled and so observance of process efficiency and tool status independent from workpiece machining conditions can be realized. All sensors used are thermocouples of type K, a combination of Chromel (NiCr) and Alumel (NiAlMnSi) material. The maximum temperature to be measured by this sensor is about 1350,°C, which ensures the applicability in the grinding process. Telemetry components to amplify and send the thermovoltage signals are adjusted to this type of thermocouple. The ability of the set-up to detect thermal influences was demonstrated in grinding processes with a continuously increasing specific material removal rate. The approach serves to measure temperatures between fast sliding surfaces in harsh environments (fluids, high pressure, heat), similar to the grinding process. Therefore their application is not limited to tools but also applicable for other rotating components such as bearings, gears and shafts in powertrains. [source] Daytime variations of interleukin-1, in gingival crevicular fluidEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2008Angela Bergmann Interleukin-1, (IL-1,) is an important parameter in periodontal research because of its role in inflammation and bone resorption. One measure used to assess local IL-1, concentrations is analysis of its levels in gingival crevicular fluid (GCF). While studies on serum IL-1, concentrations indicate a circadian rhythm of this parameter, nothing is known about daytime variations of IL-1, in GCF. The present study thus aimed to analyse such variations. Daytime variations of GCF-IL-1, between 08:00 and 22:00 h were assessed, with a time resolution of 2 h, in 28 periodontally healthy subjects. The data showed a significant variation throughout the day, with the lowest concentrations and total amounts in the morning and the highest in the evening. The effect sizes of comparisons between morning and evening samples were medium to high and corresponded in magnitude to those reported in other published research comparing healthy sites and those affected by periodontitis. The smallest daytime variations were found to occur between 12:00 h and 18:00 h. It is concluded that daytime variations in GCF-IL-1, are large enough to be able to mimic or mask differences caused by clinical factors. [source] Surface deformation induced by present-day ice melting in SvalbardGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009H. P. Kierulf SUMMARY The vertical movement of the Earth's surface is the result of a number of internal processes in the solid Earth, tidal forces and mass redistribution in the atmosphere, oceans, terrestrial hydrosphere and cryosphere. Close to ice sheets and glaciers, the changes in the ice loads can induce large vertical motions at intraseasonal to secular timescales. The Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) antennas in Ny-Ålesund, Svalbard that started observations in 1991 and 1995, respectively, observe vertical uplift rates on the order of 8 ± 2 mm yr,1, which are considerably larger than those predicted by postglacial rebound (PGR) models (order 2 mm yr,1). The observations also indicate increased uplift rates starting some time in 2000. A local GPS campaign network that has been reoccupied annually since 1998, reveals a tilting away from the neighbouring glaciers. The Svalbard glaciers have been undergoing melting and retreat during the last century, with increased melting since about 2000. We compared the observed vertical motion to the motion predicted by loading models using a detailed ice model with annual time resolution as forcing. The model predictions correlate well with the observations both with respect to the interannual variations and the spatial pattern of long-term trends. The regression coefficients for predicted and observed interannual variations in height is 1.08 ± 0.38, whereas the regression coefficient for the predicted and observed spatial pattern turns out to be 1.26 ± 0.42. Estimates of the predicted secular trend in height due to PGR and present-day melting are on the order of 4.8 ± 0.3 mm yr,1 and thus smaller than the observed secular trend in height. This discrepancy between predictions and observations is likely caused by the sum of errors in the secular rates determined from observations (due to technique-dependent large-scale offsets) and incomplete or erroneous models (unaccounted tectonic vertical motion, errors in the ice load history, scale errors in the viscoelastic PGR models and the elastic models for present-day melting). [source] Evaluation of model complexity and space,time resolution on the prediction of long-term soil salinity dynamics, western San Joaquin Valley, CaliforniaHYDROLOGICAL PROCESSES, Issue 13 2006G. Schoups Abstract The numerical simulation of long-term large-scale (field to regional) variably saturated subsurface flow and transport remains a computational challenge, even with today's computing power. Therefore, it is appropriate to develop and use simplified models that focus on the main processes operating at the pertinent time and space scales, as long as the error introduced by the simpler model is small relative to the uncertainties associated with the spatial and temporal variation of boundary conditions and parameter values. This study investigates the effects of various model simplifications on the prediction of long-term soil salinity and salt transport in irrigated soils. Average root-zone salinity and cumulative annual drainage salt load were predicted for a 10-year period using a one-dimensional numerical flow and transport model (i.e. UNSATCHEM) that accounts for solute advection, dispersion and diffusion, and complex salt chemistry. The model uses daily values for rainfall, irrigation, and potential evapotranspiration rates. Model simulations consist of benchmark scenarios for different hypothetical cases that include shallow and deep water tables, different leaching fractions and soil gypsum content, and shallow groundwater salinity, with and without soil chemical reactions. These hypothetical benchmark simulations are compared with the results of various model simplifications that considered (i) annual average boundary conditions, (ii) coarser spatial discretization, and (iii) reducing the complexity of the salt-soil reaction system. Based on the 10-year simulation results, we conclude that salt transport modelling does not require daily boundary conditions, a fine spatial resolution, or complex salt chemistry. Instead, if the focus is on long-term salinity, then a simplified modelling approach can be used, using annually averaged boundary conditions, a coarse spatial discretization, and inclusion of soil chemistry that only accounts for cation exchange and gypsum dissolution,precipitation. We also demonstrate that prediction errors due to these model simplifications may be small, when compared with effects of parameter uncertainty on model predictions. The proposed model simplifications lead to larger time steps and reduced computer simulation times by a factor of 1000. Copyright © 2006 John Wiley & Sons, Ltd. [source] Dynamic Processes at Solid-liquid InterfacesIMAGING & MICROSCOPY (ELECTRONIC), Issue 1 2006Video-STM Images Nanoscale Dynamics Scanning tunnelling microscopy (STM) not only provides unsurpassed resolution, enabling real-space imaging of individual surface atoms, but also is capable to operate in a wide range of environments, ranging from ultrahigh vacuum to gases and liquids. The latter allows studies of processes at solidliquid interfaces with a time resolution that can be as low as some 10 msec. in modern instruments. This is sufficiently fast to study elementary transport processes at these interfaces, such as surface diffusion or crystal growth, directly on the atomic scale. [source] Humidity parameters from temperature: test of a simple methodology for European conditionsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2008Yvonne Andersson-Sköld Abstract Atmospheric water content is important for local and regional climate, and for chemical processes of soluble and solute species in the atmosphere. Further, vapour pressure deficit (D) is one of the key controls on the opening of stomata in plants and is thus an important force for evapotransporation, plant respiration and biomass production and for the uptake of harmful pollutants such as ozone through the stomata. Most meteorological stations typically measure both temperature and relative humidity (RH). However, even if recorded at finer time resolution, it is usually the daily or often monthly means of RH which are published in climate reports. Unfortunately, such data cannot be used to obtain the changes in RH or vapour pressure deficit over the day, as this depends strongly on the diurnal temperature variation during the day and not upon the mean temperature. Although RH typically changes significantly over the day, the ambient vapour pressure is often remarkably constant. Here a simple method to estimate diurnal vapour pressure is evaluated, based upon an assumed constant vapour pressure, and that recorded minimum temperatures approximate dew-point temperatures. With a knowledge of only temperature, we will show that day to day estimates of vapour pressure, humidity and especially D, can be made with reasonable accuracy. This methodology is tested using meteorological data from 32 sites covering a range of locations in Europe. Such a simple methodology may be used to extract approximate diurnal curves of vapour pressures from published meteorological data which contains only minimum temperatures for each day, or where humidity data are not available. Copyright © 2007 Royal Meteorological Society [source] A comparative in situ Rietveld refinement study: thermal decomposition and transformation of CoAl and CoZnAl layered double hydroxidesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Rune E. Johnsen Rietveld refinement based on in situ X-ray powder diffraction (XRPD) data was combined with thermogravimetric analysis (TGA) and mass spectrometry (MS) to study and compare the phase transformations, thermal stability, microstructural and structural changes of two cobalt-containing nitrate-based layered double hydroxides (LDHs) upon heating in a controlled inert atmosphere of nitrogen. The XRPD data were collected, using synchrotron X-ray radiation, with a time resolution of 107,s, which made it possible to carry out detailed structural studies of the initial layered double hydroxides as well as their decomposition products: spinel for a CoAl,NO3 LDH and spinel/zincite for a CoZnAl,NO3 LDH. Correlating these data with those from the TGA,MS analyses gives us information about the transformation mechanisms. Rietveld refinements of the two spinel phases reveal remarkable differences. The a axis of the spinel formed by decomposition of the CoAl,NO3 LDH increases almost linearly from approximately 598 to 1163,K, mainly due to the dominating thermal expansion, whereas the a axis of the spinel formed by decomposition of the CoZnAl,NO3 shows a more complex temperature dependency. Between approximately 698 and 1073,K, the a axis is almost constant due to pronounced chemical interaction with an additional amorphous phase and the zincite phase, whereas from 1073 up to 1163,K it increases linearly. Calculations, based on the results of the Rietveld refinements, of the size of the octahedral and tetrahedral coordination polyhedra in the spinel show that the octahedra shrink and the tetrahedra expand with increasing temperature. The unusual thermal behaviour of the octahedra is discussed and attributed to the low formation temperature of the cobalt aluminium spinel phase. Finally, the intensity of a low-angle scattering (LAS) signal observed in the XRPD patterns was correlated with the decomposition of the LDH, and determination of the specific surface areas gave the temperature-dependent BET surface areas. [source] Focusing capillary optics for use in solution small-angle X-ray scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2007Jessica S. Lamb Measurements of the global conformation of macromolecules can be carried out using small-angle X-ray scattering (SAXS). Glass focusing capillaries, manufactured at the Cornell High Energy Synchrotron Source (CHESS), have been successfully employed for SAXS measurements on the heme protein cytochrome c. These capillaries provide high X-ray flux into a spot size of tens of micrometres, permitting short exposures of small-volume samples. Such a capability is ideal for use in conjunction with microfluidic mixers, where time resolution may be determined by beam size and sample volumes are kept small to facilitate mixing and conserve material. [source] Deconvolution of femtosecond time-resolved spectroscopy data in multivariate curve resolution.JOURNAL OF CHEMOMETRICS, Issue 7-8 2010Application to the characterization of ultrafast photo-induced intramolecular proton transfer Abstract In femtosecond absorption spectroscopy, deconvolution of the measured kinetic traces is still an important issue as photochemical processes that may possess shorter characteristic times than the time resolution of the experiment are usually considered. In this work, we propose to perform deconvolution of the time-dependent concentration profiles extracted from multivariate curve resolution (MCR) applied to spectrokinetic data. The profiles are fitted with a model function including a description of the instrumental response function (IRF) of the experiment. The method combines the potential benefits of soft-modeling data analysis with the ones of hard-modeling for parameter estimation. The potential of the method is demonstrated first analyzing five synthetic data sets for which IRF of different widths are simulated. It is then successfully applied to resolve femtosecond UV-visible transient absorption spectroscopy data investigating the photodynamics of salicylidene aniline, a photochromic molecule of wide interest. Considering a time resolution of 150,fs for the IRF, a characteristic time of 45,fs is recovered for the first step of the photo-induced process which consists of an ultrafast intramolecular proton transfer. Our results also confirm the existence of an intermediate species with a characteristic time of 240,fs. Copyright © 2010 John Wiley & Sons, Ltd. [source] Spectra of wavelet scale coefficients from process acoustic measurements as input for PLS modelling of pulp quality,JOURNAL OF CHEMOMETRICS, Issue 8-10 2002Anders Björk Abstract Acoustic and vibration signals are captured by simple standard accelerometers. These can often be mounted directly on operative process equipment, creating a completely non-invasive measurement system. The signals from the accelerometer are then amplified, digitized by an analogue-to-digital converter and stored in some suitable format in a PC. The method most often used for signal processing of acoustic data has been to apply variants of fast Fourier transform (FFT) on sampled data to produce a frequency domain representation. An alternative way tried here is to use the fast wavelet transform (FWT) in combination with FFT. The FWT has the advantage that it produces time-resolved representations and, on each time scale, different features can be extracted. However, in this case, time resolution has no meaning, since the starting points for data acquisitions were not fixed. The wavelet step can be seen as a series of pre-filters and it is here followed by FFT on coefficients at each wavelet scale. The results are compared to those obtained after FFT on the complete time series. We have used spectra of wavelet scale coefficients in an attempt to model pulp quality with PLS. In this case the number of points in the resulting wavelet multiresolution spectrum (WT-MRS) can be limited to a low number, e.g. 255 compared to 1025 with direct FFT on the time series. In the PLS modelling step the advantage is that the first two components describe Y much better than when using the conventional approach, e.g. 72% explained Y variance compared to 40%. A second advantage is that the model requires fewer coefficients. Copyright © 2002 John Wiley & Sons, Ltd. [source] Differential Increase in Taurine Levels by Low-Dose Ethanol in the Dorsal and Ventral Striatum Revealed by Microdialysis With On-Line Capillary ElectrophoresisALCOHOLISM, Issue 7 2004A Smith Ethanol increases taurine efflux in the nucleus accumbens or ventral striatum (VS), a dopaminergic terminal region involved in positive reinforcement. However, this has been found only at ethanol doses above 1 g/kg intraperitoneally, which is higher than what most rats will self-administer. We used a sensitive on-line assay of microdialysate content to test whether lower doses of ethanol selectively increase taurine efflux in VS as opposed to other dopaminergic regions not involved in reinforcement (e.g., dorsal striatum; DS). Adult male rats with microdialysis probes in VS or DS were injected with ethanol (0, 0.5, 1, and 2 g/kg intraperitoneally), and the amino acid content of the dialysate was measured every 11 sec using capillary electrophoresis and laser-induced fluorescence detection. In VS, 0.5 g/kg ethanol significantly increased taurine levels by 20% for 10 min. A similar increase was seen after 1 g/kg ethanol, which lasted for about 20 min after injection. A two-phased taurine efflux was observed with the 2.0 g/kg dose, where taurine was increased by 2-fold after 5 min but it remained elevated by 30% for at least 60 min. In contrast, DS exhibited much smaller dose-related increases in taurine. Glycine, glutamate, serine, and ,-aminobutyric acid were not systematically affected by lower doses of ethanol; however, 2 g/kg slowly decreased these amino acids in both brain regions during the hour after injection. These data implicate a possible role of taurine in the mechanism of action of ethanol in the VS. The high sensitivity and time resolution afforded by capillary electrophoresis and laser-induced fluorescence detection will be useful for detecting subtle changes of neuronally active amino acids levels due to low doses of ethanol. [source] CCD-based X-ray area detector for time-resolved diffraction experimentsJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2004Naoto Yagi A fast X-ray area detector for diffraction, scattering and imaging experiments at microsecond to millisecond time resolution has been developed. The key element of the detector is a fast (291,frames,s,1) framing camera with three CCDs. A prism forms identical images on the CCDs and the frame rate is increased three times by reading them alternately. In order to convert X-rays into visible light that is detectable with the CCDs, an X-ray image intensifier is used. The camera can also be used with a high-resolution X-ray detector. In both cases it was found to be important to use a phosphor with a short decay time to fully make use of the high-speed framing capability of the camera. Preliminary results of a fibre diffraction experiment on a skeletal muscle and coronary angiography are presented. [source] Time-resolved measurements of supersonic fuel sprays using synchrotron X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2000Christopher F. Powell A time-resolved radiographic technique has been developed for probing the fuel distribution close to the nozzle of a high-pressure single-hole diesel injector. The measurement was made using X-ray absorption of monochromatic synchrotron-generated radiation, allowing quantitative determination of the fuel distribution in this optically impenetrable region with a time resolution of better than 1,µs. These quantitative measurements constitute the most detailed near-nozzle study of a fuel spray to date. [source] Self-Propagating High-Temperature Synthesis of Ti3SiC2: II.JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Kinetics of Ultra-High-Speed Reactions from In Situ Neutron Diffraction In situ neutron diffraction data at 0.9-s time resolution during the self-propagating high-temperature synthesis of Ti3SiC2 from stoichiometric 3Ti+SiC+C mixtures have been further analyzed to give the phase quantities during all five stages of the identified reaction [(i) preheating, (ii) ,,, phase transformation in Ti, (iii) preignition reactions, (iv) intermediate phase formation, and (v) rapid nucleation and growth of Ti3SiC2]. The phase quantities thus determined have been used, in conjunction with temperatures estimated from lattice parameters and thermal expansion data, to determine the kinetic parameters for the nucleation and growth stage using a nonisothermal form of the Avrami kinetic equation. The analysis gave an Avrami exponent, n, close to 3 in agreement with nucleation and the observed two-dimensional growth of Ti3SiC2 crystals. An activation energy of ,45 kJ/mol was also estimated. [source] Effects of diagenesis on the astrochronological approach of defining stratigraphic boundaries in calcareous rhythmites: The Tortonian GSSPLETHAIA, Issue 4 2008HILDEGARD WESTPHAL Since the establishment of astrochronology, calcareous rhythmites are frequently used as the basis of high-resolution chronostratigraphy. In particular for the Neogene, calcareous rhythmites serve as stratotypes and for absolute dating of stratigraphic boundaries (Global Stratotype Sections and Points , GSSPs). However, the exact mechanisms responsible for the formation of the rhythmic intercalation of lithologies in such successions are complex and not easily reconstructed. To a large extent this is the effect of diagenetic modifications of the original sediment. Here, two examples of Neogene calcareous rhythmites are studied; the Monte dei Corvi section and the Monte Gibliscemi section. The first is the GSSP location of the Serravallian,Tortonian boundary, whereas the second is an auxiliary stratotype for the same boundary. During the past years, astrochronological approaches were applied to these successions to considerably increase time resolution compared to the elaborated biostratigraphic database. The present study focuses on micropetrographic, trace element and clay mineralogical methods in order to gain a better understanding of the genesis of the rhythmites. In the Monte Gibliscemi section, sediment parameters that are robust against diagenetic change clearly reflect primary differences, i.e. cyclical environmental changes. In contrast, no clear primary signal is determined for the Monte dei Corvi section on a couplet scale, leaving the origin of the rhythm ambiguous. This impedes the interpretation of the latter and the comparability between the two successions, and also compromises any bed-by-bed correlation between the two. The unclear origin of the rhythmites of Monte dei Corvi introduces uncertainty into the applicability of astrochronology to this succession. [source] In vivo qualitative assessments of articular cartilage in the rabbit knee with high-resolution MRI at 3 TMAGNETIC RESONANCE IN MEDICINE, Issue 3 2003Didier Laurent Abstract Proteoglycan (PG) loss and disruption of the collagen framework in cartilage are early events associated with osteoarthritis (OA). The feasibility of in vivo high-resolution MRI assessments probing both macromolecules was explored in articular cartilage of the rabbit knee. One-millimeter thick coronal images were obtained at 3 T with a 97 × 97 ,m2 pixel size. A 22% decrease in the magnetization transfer (MT) exchange rate along with an ,2-fold greater Gd(DTPA)2- -induced decrease in T1 relaxation time were measured in response to papain injection 1 day prior to the MRI session, indicative of an alteration of collagen integrity and PG depletion, respectively. A two-point method was tested as an alternative to the more time-consuming multipoint method typically used to measure T1 changes. Kinetics of Gd(DTPA)2- uptake were observed with a 10-min time resolution. The diffusive transport of Gd(DTPA)2- was characterized by a T1 decrease ,2-fold faster in papain-treated knees. These data suggest that kinetics of tracer diffusion may be used as an informative marker of PG loss, in addition to the amplitude of T1 variations. When applied to a relevant OA model, the combination of MT and Gd(DTPA)2- -MRI may help in identifying new active compounds during efficacy studies on cartilage protection. Magn Reson Med 50:541,549, 2003. © 2003 Wiley-Liss, Inc. [source] Time-resolved contrast-enhanced imaging with isotropic resolution and broad coverage using an undersampled 3D projection trajectoryMAGNETIC RESONANCE IN MEDICINE, Issue 2 2002Andrew V. Barger Abstract Time-resolved contrast-enhanced 3D MR angiography (MRA) methods have gained in popularity but are still limited by the tradeoff between spatial and temporal resolution. A method is presented that greatly reduces this tradeoff by employing undersampled 3D projection reconstruction trajectories. The variable density k -space sampling intrinsic to this sequence is combined with temporal k -space interpolation to provide time frames as short as 4 s. This time resolution reduces the need for exact contrast timing while also providing dynamic information. Spatial resolution is determined primarily by the projection readout resolution and is thus isotropic across the FOV, which is also isotropic. Although undersampling the outer regions of k -space introduces aliased energy into the image, which may compromise resolution, this is not a limiting factor in high-contrast applications such as MRA. Results from phantom and volunteer studies are presented demonstrating isotropic resolution, broad coverage with an isotropic field of view (FOV), minimal projection reconstruction artifacts, and temporal information. In one application, a single breath-hold exam covering the entire pulmonary vasculature generates high-resolution, isotropic imaging volumes depicting the bolus passage. Magn Reson Med 48:297,305, 2002. © 2002 Wiley-Liss, Inc. [source] Giant repeated ejections from GRS 1915+105MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000R. P. Fender We report simultaneous millimetre and infrared observations of a sequence of very large amplitude quasi-periodic oscillations from the black hole X-ray binary GRS 1915+105. These oscillations are near the end of a sequence of over 700 repeated events as observed at 15 GHz, and are simultaneous at the mm and infrared wavelengths to within our time resolution (4 min), consistent with the respective emitting regions being physically close near the base of the outflow. One infrared event appears to have no mm counterpart, perhaps owing to highly variable absorption. The overall radio,mm,infrared spectrum around the time of the observations does suggest some absorption at lower frequencies. We calculate the energy and mass-flow into the outflow for a number of different assumptions, and find that the time-averaged power required to produce the observed synchrotron emission cannot be much lower than 3×1038 erg s,1, and is likely to be much larger. This minimum power requirement is found regardless of whether the observed emission arises in discrete ejections or in an internal shock in a quasi-continuous flow. Depending on the similarity of the physical conditions in the two types of ejection, GRS 1915+105 may be supplying more power (and mass, if both have the same baryonic component) to the jet during periods of repeated oscillations than during the more obvious larger events. [source] An additional phase in PCr use during sustained isometric exercise at 30% MVC in the tibialis anterior muscleNMR IN BIOMEDICINE, Issue 4 2002C. J. Houtman Abstract The occurrence of an abrupt acceleration in phosphocreatine hydrolysis in the tibial anterior muscle during the last part of a sustained isometric exercise at 30% maximal voluntary contraction until fatigue is demonstrated in seven out of eight healthy subjects by applying in vivo31P NMR spectroscopy at 1.5,T field strength. This additional third phase in PCr hydrolysis, is preceded by a common biphasic pattern (first fast then slow) in PCr use. The NMR spectra, as localized by a surface coil and improved by proton irradiation, were collected at a time resolution of 16 s. Mean rates of PCr hydrolysis during exercise were ,0.44,±,0.19% s,1, ,0.07,±,0.04% s,1, and ,0.29,±,0.10% s,1 for the three successive phases. The increased rate of PCr hydrolysis, and also the loss of fine force control evident in the force records are consistent with increased involvement of large, fast-fatiguable units later in the contraction. Copyright © 2002 John Wiley & Sons, Ltd. [source] Second Harmonic Generation Spectroscopy as a Method for In Situ and Online Characterization of Particle Surface PropertiesPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2006Lars Schneider Abstract Non-linear optical spectroscopy is a recently established technique used in the investigation of the properties of colloidal interfaces. Since it is an optical method it is non-invasive, can be applied in situ, and can provide real time resolution. Until recently, only a few papers concerning this method have been published, but these all show the great potential and the large field of applications of the technique. This paper gives an overview of the fundamentals of the technique and its possible applications. [source] Sub-5-fs Real-time Spectroscopy of Transition States in Bacteriorhodopsin During Retinal Isomerization,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2007Takayoshi Kobayashi By using a sub-5-fs visible laser pulse, we have made the first observation of the vibrational spectra of the transition state during trans-cis isomerization in the retinal chromophore of bacteriorhodopsin (bRS68). No instant isomerization of the retinal occurs in spite of electron promotion from the bonding ,-orbital to the anti-bonding ,*-orbital. The difference between the in-plane and out-of-plane vibrational frequencies (about 1150,1250 and 900,1000 cm,1, respectively) is reduced during the first time period. The vibrational spectra after this period became very broad and weak and are ascribed to a "silent state." The silent state lasts for 700,900 fs until the chromophore isomerizes to the cis -C13=C14 conformation. The frequency of the C=C stretching mode was modulated by the torsion mode of the C13=C14 double bond with a period of 200 fs. The modulation was clearly observed for four to five periods. Using the empirical equation for the relation between bond length and stretching frequency, we determined the transitional C=C bond length with about 0.01 Å accuracy during the torsion motion around the double bond with 1-fs time resolution. [source] Excitons in a perfect quasi-1D organic quantum wire, an isolated polydiacetylene chainPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008Laurent Legrand Abstract The exciton in single luminescent polydiacetylene (PDA) chains dispersed in their single crystal monomer matrix is studied. As reported these quantum wires have the properties of a perfect quasi-1D semiconducting system. The macroscopic spatial coherence of a single exciton state on a chain as a function of temperature is investigated using an interference experiment. The interference pattern contrast decreasing with increasing temperature is non zero up to 30 K. Experiments developed in order to observe the regime of formation of the stationary coherent exciton state are described. Within the time resolution of the experiment, it is concluded that the formation of this state is faster than ,5 picoseconds which confirms the assumption of a transient regime. Finally the first steps of the manipulation of phase locked excitonic wave-packets on a PDA wire are discussed. The experimental results measured in a weak exciton-photon coupling regime are compared to simulations obtained through the Bloch optical equations in the framework of a three-levels model. A direct estimate of the coherence time of the vibronic state photocreated in the present non resonant scheme is derived. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ultrafast intensity correlation measurements of quantum dot microcavity lasersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2009M. Aßmann Abstract We present an experimental technique, which allows us to determine the second order correlation function g(2) (t, t + ,) with picosecond time resolution. The method involves a streak camera which is modified such that a signal at fixed wavelength can be monitored after each pulsed laser excitation. From these measurements insight into the quantum optical properties of light emission from semiconductor nanostructures with dynamics on the sub-ns time scale can be taken. To demonstrate the possibilities of our setup, we present time resolved g(2) -measurements of quantum dot VCSEL micropillar emission. We show, that our measurement scheme enables us to determine the transition from predominantly spontaneous emission towards stimulated emission and the temporal evolution of the intensity correlation function. Additionally, we are also able to identify unexpected features like dynamical antibunching. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ion irradiation and reduction effect on the conductivity and optical absorption of heavily MgO-doped LiNbO3 single crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005V.F. Pichugin Abstract The confirmation of MgNb defects in heavily MgO doped LiNbO3 single crystals were investigated through optical absorption, electrical conductivity measurements, optical spectroscopy with nanosecond time resolution, and Raman spectroscopy technique. An increase in the MgO concentration up to 10 mole% provides an essential change of the luminescence of LiNbO3, the appearance of a supplementary optical absorption band at the 1.1 eV, an alteration of the Raman spectra caused by the formation of (MgNb) defects, a shift of the edge of the supplementary optical absorption due to ion irradiation toward the shorter wavelength region as the MgO concentration increases. The effect of Ar+ ions irradiation on the conduction of the MgO doped LiNbO3 samples was studied. The important role of reduction in modification of the conducting properties of the ion-irradiated crystals was established. The increase of the MgO concentration leads to a decrease of the reduction efficiency. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||