Drift Measurements Research Articles

Femtosecond resolution timing jitter correction on a TW scale Ti:sapphire laser system for FEL pump-probe experiments

Intense ultrashort pulse lasers are used for fs resolution pump-probe experiments more and more at large scale facilities, such as free electron lasers (FEL). Measurement of the arrival time of the laser pulses and stabilization to the machine or other sub-systems on the target, is crucial for high time-resolution measurements. In this work we report on a single shot, spectrally resolved, non-collinear cross-correlator with sub-fs resolution. With a feedback applied we keep the output of the TW class Ti:sapphire amplifier chain in time with the seed oscillator to ~3 fs RMS level for several hours. This is well below the typical pulse duration used at FELs and supports fs resolution pump-probe experiments. Short term jitter and long term timing drift measurements are presented. Applicability to other wavelengths and integration into the timing infrastructure of the FEL are also covered to show the full potential of the device.

Spatiotemporally resolved electrodynamic properties of a Sun‐aligned arc over Resolute Bay

AbstractCommon volume measurements by the Resolute Bay Incoherent Scatter Radar‐North (RISR‐N) and Optical Mesosphere and Thermosphere Imagers (OMTI) have been used to clarify the electrodynamic structure of a Sun‐aligned arc in the polar cap. The plasma parameters of the dusk‐to‐dawn drifting arc and surrounding ionosphere are extracted using the volumetric imaging capabilities of RISR‐N. Multipoint line‐of‐sight RISR‐N measurements of the plasma drift are inverted to construct a time sequence of the electric field and field‐aligned current system of the arc. Evidence of dramatic electrodynamic and plasma structuring of the polar cap ionosphere due to the arc is described. One notable feature of the arc is a meridionally extended plasma density depletion on its leading edge, located partially within a downward field‐aligned current region. The depletion is determined to be a by‐product of enhanced chemical recombination operating on a time scale of 15 min. A similarly shaped electric field structure of over 100 mV/m and line‐of‐sight ion temperatures nearing 3000 K were collocated with the depletion.

CTAB modification of MCM-49 zeolite containing HMI and its acylation of anisole

A series of MCM-49 zeolite catalysts containing different amounts of the hexamethyleneimine (HMI) template were calcined at different temperatures, and then modified with cetyltrimethylammonium bromide (CTAB). Changes in structural and acidic properties were investigated by XRD, N2 adsorption, NH3-TPD, adsorbed pyridine infrared and DRIFTS measurements, and 29Si and 27Al MAS NMR. There were cleaning off of amorphous particles and extraframework Al atoms inserted into the framework of the zeolite due to the CTAB modification. These two effects resulted in more framework Al in the CTAB modified samples than the untreated samples, and a higher Brönsted acid concentration, which was confirmed by the acylation of anisole with acetic anhydride. The catalytic roles of the acid sites located in the different pore systems in the zeolite were investigated. It was verified that the active sites after CTAB modification were mainly in the HMI-free regions.

Robust, Error-Tolerant Photometric Projector Compensation.

We propose a novel error tolerant optimization approach to generate a high-quality photometric compensated projection. The application of a non-linear color mapping function does not require radiometric pre-calibration of cameras or projectors. This characteristic improves the compensation quality compared with related linear methods if this approach is used with devices that apply complex color processing, such as single-chip digital light processing projectors. Our approach consists of a sparse sampling of the projector's color gamut and non-linear scattered data interpolation to generate the per-pixel mapping from the projector to camera colors in real time. To avoid out-of-gamut artifacts, the input image's luminance is automatically adjusted locally in an optional offline optimization step that maximizes the achievable contrast while preserving smooth input gradients without significant clipping errors. To minimize the appearance of color artifacts at high-frequency reflectance changes of the surface due to usually unavoidable slight projector vibrations and movement (drift), we show that a drift measurement and analysis step, when combined with per-pixel compensation image optimization, significantly decreases the visibility of such artifacts.

Constrained Random Walk Models for Euro/Swiss Franc Exchange Rates: Theory and Empirics

We study the performance of the euro/Swiss franc exchange rate in the extraordinary period from September 6, 2011 and January 15, 2015 when the Swiss National Bank enforced a minimum exchange rate of 1.20 Swiss francs per euro. Within the general framework built on geometric Brownian motions (GBM), the first-order effect of such a steric constraint would enter a priori in the form of a repulsive entropic force associated with the paths crossing the barrier that are forbidden. It turns out that this naive theory is proved empirically to be completely mistaken. The clue is to realise that the random walk nature of financial prices results from the continuous anticipations of traders about future opportunities, whose aggregate actions translate into an approximate efficient market with almost no arbitrage opportunities. With the Swiss National Bank stated commitment to enforce the barrier, trader's anticipation of this action leads to a volatility of the exchange rate that depends on the distance to the barrier. This effect described by Krugman's model [P.R. Krugman. Target zones and exchange rate dynamics. The Quarterly Journal of Economics, 106(3):669-682, 1991] is supported by non-parametric measurements of the conditional drift and volatility from the data. To the best of our knowledge, our results are the first to provide empirical support for Krugman's model, likely due to the exceptional pressure on the euro/Swiss franc exchange rate that made the barrier effect particularly strong. Despite the obvious differences between brainless physical Brownian motions and complex financial Brownian motions resulting from the aggregated investments of anticipating agents, we show that the two systems can be described with the same mathematics after all. Using a recently proposed extended analogy in terms of a colloidal Brownian particle embedded in a fluid of molecules associated with the underlying order book, we derive that, close to the restricting boundary, the dynamics of both systems is described by a stochastic differential equation with a very small constant drift and a linear diffusion coefficient. As a side result, we present a simplified derivation of the linear hydrodynamic diffusion coefficient of a Brownian particle close to a wall.

Spray drift reduction techniques for vineyards in fragmented landscapes

In intensive agricultural systems spray drift is one of the major potential diffuse pollution pathways for pesticides and poses a risk to the environment. There is also increasing concern about potential exposure to bystanders and passers-by, especially in fragmented landscapes like the Italian pre-Alps, where orchards and vineyards are surrounded by residential houses. There is thus an urgent need to do field measurements of drift generated by air-blast sprayer in vineyards, and to develop measures for its reduction (mitigation).A field experiment with an “event method” was conducted in north-eastern Italy in no-wind conditions, in the hilly area famed for Prosecco wine production, using an air-blast sprayer in order to evaluate the potential spray drift from equipment and the effectiveness of some practical mitigation measures, either single or in combination. A definition of mitigation is proposed, and a method for the calculation of total effectiveness of a series of mitigation measures is applied to some what-if scenarios of interest.Results show that low-drift equipment reduced potential spray drift by 38% and that a fully developed vine curtain mitigated it by about 70%; when the last row was treated without air-assistance mitigation was about 74%; hedgerows were always very effective in providing mitigation of up to 98%.In conclusion, spray drift is not inevitable and can be markedly reduced using a few mitigation measures, most already available to farmers, that can be strongly recommended for environmental regulatory schemes and community-based participatory research.

Formation of polar ionospheric tongue of ionization during minor geomagnetic disturbed conditions

AbstractPrevious investigations of ionospheric storm‐enhanced density (SED) and tongue of ionization (TOI) focused mostly on the behavior of TOI during intense geomagnetic storms. Little attention has been paid to the spatial and temporal variations of TOI during weak to moderate geomagnetic disturbed conditions. In this paper we investigate the source and development of TOI during a moderate geomagnetic storm on 14 October 2012. Multi‐instrumental observations including GPS total electron content (TEC), Defense Meteorological Satellite Program (DMSP) in situ measured total ion concentration and ion drift velocity, SuperDARN measured polar ion convection patterns, and electron density profiles from the Poker Flat Incoherent Scatter Radar (PFISR) have been utilized in the current analysis. GPS TEC maps show salient TOI structures persisting for about 5 h over high latitudes of North America on 14 October 2012 in the later recovery phase of the storm when the magnitudes of IMF By and Bz were less than 5 nT. The PFISR electron density profiles indicate that the extra ionization for TEC enhancements mainly occurred in the topside ionosphere with no obvious changes in the bottomside ionosphere and vertical plasma drifts. Additionally, there were no signatures of penetration electric fields in the equatorial electrojet data and upward ion drifts at high latitudes. At the same time, strong subauroral polarization streams with ion drift speeds exceeding 2.5 km/s carried sunward fluxes and migrated toward lower latitudes for about 5° based on the DMSP cross‐track drift measurements. Based on those measurements, we postulate that the combined effects of initial build‐up of ionization at midlatitudes through daytime production of ionization and equatorward (or less poleward than normal daytime) neutral wind reducing downward diffusion along the inclined filed lines, and an expanded polar ion convection pattern and its associated horizontal plasma transport are important in the formation of the TOI.

First observations of poleward large‐scale traveling ionospheric disturbances over the African sector during geomagnetic storm conditions

AbstractThis paper presents first observations of poleward traveling ionospheric disturbances (TIDs) during strong geomagnetic conditions over the African sector. By analyzing different data sets we have observed both positive and negative ionospheric responses during the storm period of 08–10 March 2012. Considering the African region as a whole, three longitudinal sectors were strategically selected to establish the entire regional response. On both sides of the geomagnetic equator, results show poleward shift in peak total electron content (TEC) enhancements/depletions at different times which are associated to large‐scale TIDs. The observed phenomena are linked to the global ionospheric response and electrodynamics. The understanding has been established using data from International GNSS Service receiver network, radio occultation electron density profiles, derived E×B drift measurements from magnetometer observations and regional ground‐based and satellite data. Contrary to other related studies, generated regional TEC perturbation maps were not enough to show obvious directions of the large‐scale TIDs due to insufficient data over the northern hemispheric part of the African sector. There appears to be a switch between positive and negative storm phases during the same storm period especially in the Southern Hemisphere part of the African region where “enough” data were available. However, a detailed analysis revealed that the positive storm phase corresponded to the expansion of the equatorial ionization anomaly (EIA) toward some parts of midlatitude regions (and possibly with the contribution from low‐latitude electrodynamics associated to equatorial electrojet), while the other part recorded a negative storm phase due to storm‐induced changes from the auroral origin. We have observed a simultaneous occurrence of both poleward and equatorward propagating TIDs over the African sector during the same geomagnetic storm period. Our results show that short‐lived large‐scale TIDs are possibly launched by the equatorial electrojet, while the EIA expansion contributes (through modulation) to the poleward propagation of the disturbances. Temporal variation of TEC perturbations on a storm day over the entire African sector showed the existence of large‐scale TIDs during the main and recovery phases which can travel poleward up to 20° latitude. The amplitudes of the TIDs have range ±2 total electron content unit, 1 TECU = 1016 el m−2, period of 2 h and virtual velocities of 250 ± 59–750 ± 95 m/s in midlatitude regions and up to 990 ± 65 m/s within the EIA region.

Dehydration of ethyl lactate over alkaline earth phosphates: Performances, effect of water on reaction pathways and active sites

In this work, alkaline earth phosphates have been prepared by co-precipitation and evaluated in gas phase dehydration of ethyl lactate to acrylic acid and ethyl acrylate. These solids, which were previously shown to be active for the dehydration of lactic acid, appeared more efficient. Indeed, it was shown that the decarbonylation/decarboxylation route leading to acetaldehyde was strongly inhibited compared to conversion of lactic acid and molar selectivity values to dehydration products reaching 87% were obtained. Furthermore, it was shown that the deactivation of the catalysts could strongly be slowed by addition of water vapor to the feed. The reaction pathways have been studied in the presence and absence of water and it was shown that acrylic acid was mainly formed by a simultaneous dehydration/hydrolysis reaction. The characterization of the catalysts surface from the results of XPS, cross polarization NMR, DRIFT and TEM showed the presence of a surface amorphous layer containing POH species. In situ DRIFT measurements have revealed that formation of POH groups was favored under water vapor and that these species interacted with reactants or reaction products at the reaction temperature.

Tuning the Chern number and Berry curvature with spin-orbit coupling and magnetic textures

We obtain the band structure of a particle moving in a magnetic spin texture, classified by its chirality and structure factor, in the presence of spin-orbit coupling. This rich interplay leads to a variety of novel topological phases characterized by the Berry curvature and their associated Chern numbers. We suggest methods of experimentally exploring these topological phases by Hall drift measurements of the Chern number and Berry phase interferometry to map the Berry curvature.

CO oxidation as a test reaction for strong metal–support interaction in nanostructured Pd/FeOx powder catalysts

A series of differently loaded palladium–iron catalysts was prepared by a controlled co-precipitation method of the nitrate precursors, in order to ensure homogeneous Pd particle size-distribution. After characterization of the pre-catalysts by various techniques, different controlled reduction conditions were applied to investigate the interactions within the Pd–iron system, containing reversible and irreversible processes like phase transformations, SMSI, sintering and alloying. Strong indications for the reversible surface decoration of the Pd nanoparticles with iron oxide species via strong metal–support interaction were found by the combined results of DRIFTS, CO-chemisorption, TEM and XPS measurements. This SMSI state was found to be unstable. It was observed independent of bulk phase or palladium particle size. Catalytic CO-oxidation was found to be a suitable test reaction for the study of the phenomenon: higher activity as well as oxidative deactivation of the SMSI state was observed by investigating the light-off behavior in repeated, temperature-programmed cycles as well as by isothermal measurements. The instability was found to be higher in case of higher Pd dispersion. In addition, bulk properties of the Pd–Fe system, like alloying, were investigated by detailed XRD measurements.

Restructuring of AuPd Nanoparticles Studied by a Combined XAFS/DRIFTS Approach

The use of AuPd nanoparticles in catalysis is widespread, with the activity being attributed to their precise structural properties. We demonstrate the restructuring of AuPd nanoparticles under CO oxidation conditions using a combined XAFS/DRIFTS approach. The fresh catalyst exhibits PdO islands at the surface of the nanoparticles, which are reduced under reaction conditions, a process observed via both DRIFTS and Pd K-edge XAFS measurements. From the EXAFS analysis alone the nanoparticles were observed to have a Au rich core with an outer region of intimately mixed Au and Pd atoms. This structure was found to remain mostly unaltered throughout reaction. However, the DRIFTS spectra showed that although Au was present on the surface during the initial stages of reaction the surface rearranged just before light-off, and contained only Pd atoms thereafter. This study highlights the advantage of this combined approach, where both the surface structure and local environment of the constituent metals can be probed simultaneously, allowing a complete picture of the restructuring of these bimetallic particles to be obtained under reaction conditions.

Impregnated Ni/ZrO2 and Pt/ZrO2 catalysts in dry reforming of methane: Activity tests in excess methane and mechanistic studies with labeled 13CO2

In the present work, 1%Ni/ZrO2, 3%Ni/ZrO2 and 1%Pt/ZrO2 catalysts prepared by impregnation with the concomitant addition of NaHCO3 were investigated and compared by structural investigations such as TEM, XRD, TPR, XPS and DRIFTS methods. Temperature programmed dry reforming (DRM) experiments were done (i) at atmospheric pressure in plug flow reactor and an in situ DRIFTS cell or (ii) under sub atmospheric pressure (∼50mbar) in a closed loop circulation system using labelled 13CO2 to trace the fate of carbon compounds. The calcined and reduced fresh catalysts contained nanoparticles in the range of 2–18nm. According to the TPR results, in 3%Ni/ZrO2 catalyst most of Ni is in strong interaction with the support. The presence of sodium was suggested to induce the appearance of strongly bound bridged CO sites during CO chemisorption in DRIFTS measurements for all samples and to cause BE shift in XPS spectrum of the highly dispersed Pt/ZrO2 only. In the catalytic tests in plug flow reactor the 3wt%Ni/ZrO2 sample turned to be the most active catalyst, but coke was deposited on its surface measured by the subsequent temperature programmed oxidation (TPO) measurements. In situ low temperature DRIFTS-DRM measurements suggested that stability of surface carbonates is less when dispersed electron-rich Pt nanoparticles are on the ZrO2 support, while more carbonates accumulate on Ni/ZrO2 samples. Based on our isotope labeled 13CO2+12CH4 experiments in circulation system, the same initial reaction pathways could be suggested for the Ni and Pt catalysts. The reactive surface carbon species from the two different sources (CH4 and CO2) were completely scrambled on 3wt%Ni/ZrO2 at 600°C, suggesting that common reaction intermediates do exist.

Stochastic modelling of shifts in allele frequencies reveals a strongly polygynous mating system in the re-introduced Asiatic wild ass.

Small populations are prone to loss of genetic variation and hence to a reduction in their evolutionary potential. Therefore, studying the mating system of small populations and its potential effects on genetic drift and genetic diversity is of high importance for their viability assessments. The traditional method for studying genetic mating systems is paternity analysis. Yet, as small populations are often rare and elusive, the genetic data required for paternity analysis are frequently unavailable. The endangered Asiatic wild ass (Equus hemionus), like all equids, displays a behaviourally polygynous mating system; however, the level of polygyny has never been measured genetically in wild equids. Combining noninvasive genetic data with stochastic modelling of shifts in allele frequencies, we developed an alternative approach to paternity analysis for studying the genetic mating system of the re-introduced Asiatic wild ass in the Negev Desert, Israel. We compared the shifts in allele frequencies (as a measure of genetic drift) that have occurred in the wild ass population since re-introduction onset to simulated scenarios under different proportions of mating males. We revealed a strongly polygynous mating system in which less than 25% of all males participate in the mating process each generation. This strongly polygynous mating system and its potential effect on the re-introduced population's genetic diversity could have significant consequences for the long-term persistence of the population in the Negev. The stochastic modelling approach and the use of allele-frequency shifts can be further applied to systems that are affected by genetic drift and for which genetic data are limited.

High Electron Mobility and Its Role in Charge Carrier Generation in Merocyanine/Fullerene Blends

Charge carrier generation and drift dynamics have been investigated in two types of dye:fullerene heterojunctions: vacuum-deposited merocyanine:C60 and solution-processed merocyanine:PC61BM blends by combining electric-field-induced fluorescence quenching and ultrafast time-resolved carrier drift measurements. We demonstrate that interfacial charge transfer (CT) states are strongly heterogeneous with energies dependent on the acceptor material and its domain sizes. Interfacial CT states on large C60 domains have low energies, while CT states on PC61BM domains have larger energies, which are weakly dependent on the domain sizes. We distinguish two interfacial CT state dissociation pathways: (i) ultrafast, weakly dependent on the electric field and (ii) slow field-assisted dissociation during entire CT state lifetime. We attribute process i to low-energy, weakly bound CT states on large fullerene domains and process ii to strongly bound CT states on small domains or single fullerene molecules. The electron mobility in films with 50% of C60 is several times higher than in the films with PC61BM and orders of magnitude higher than the hole mobility. We conclude that efficient carrier generation at low electric fields typical for operating solar cells relies on unperturbed motion of highly mobile electrons; thus, fast motion and extraction of electrons are crucial for efficient solar cells.

The equatorial electrojet during geomagnetic storms and substorms

AbstractThe climatology of the equatorial electrojet during periods of enhanced geomagnetic activity is examined using long‐term records of ground‐based magnetometers in the Indian and Peruvian regions. Equatorial electrojet perturbations due to geomagnetic storms and substorms are evaluated using the disturbance storm time (Dst) index and auroral electrojet (AE) index, respectively. The response of the equatorial electrojet to rapid changes in the AE index indicates effects of both prompt penetration electric field and disturbance dynamo electric field, consistent with previous studies based on F region equatorial vertical plasma drift measurements at Jicamarca. The average response of the equatorial electrojet to geomagnetic storms (Dst<−50 nT) reveals persistent disturbances during the recovery phase, which can last for approximately 24 h after the Dst index reaches its minimum value. This “after‐storm” effect is found to depend on the magnitude of the storm, solar EUV activity, season, and longitude.

Simultaneous drift, microsaccades, and ocular microtremor measurement from a single noncontact far-field optical sensor.

We report on the combined far-field measurement of the three involuntary eye movements, drift, microsaccades, and ocular microtremor (OMT), using a noncontact far-field optical method. We review the significance of the smallest and least measured, and thus least understood, of the three, OMT. Using modern digital imaging techniques, we perform detailed analysis, present experimental results, and examine the extracted parameters using a noncontact far-field sensor. For the first time, in vivo noncontact measurements of all fixational in-plane movements of the human eye are reported, which simultaneously provide both the horizontal (left-right) and vertical (up-down) displacement results.

Al2O3-based passive NOx adsorbers for low temperature applications

NOx storage on Pt/Al2O3 and Pt/La-Al2O3 in the temperature range 80–160°C was investigated by means of microreactor and in situ DRIFTS experiments, to ascertain their suitability for passive NOx adsorber applications. Addition of 1wt% La to Al2O3 resulted in the creation of new NOx storage sites and improved NOx storage efficiency. However, according to TPD measurements, Pt/La-Al2O3 exhibited slightly lower NOx desorption efficiency below 250°C than Pt/Al2O3. During repeated NOx adsorption–desorption cycles, almost no benefit of La addition was observed after five cycles, due to the inability to regenerate the strong NOx storage sites associated with the La at 250°C. DRIFTS measurements indicated that during NOx-TPD, nitrites and weakly bound nitrate species were initially removed from the surface of Pt/Al2O3 and Pt/La-Al2O3. NOx desorption at higher temperatures (>250°C) was mainly associated with nitrate decomposition. DRIFTS measurements on Pt/Al2O3 revealed that NOx was mainly stored on the Al2O3 surface when oxidized Pt was present, although when a reductive re-treatment was applied NOx storage on reduced Pt sites became significant and total NOx storage efficiency was improved. However, compared to bare Al2O3, NOx desorption efficiency below 250°C significantly dropped when Pt was present, and was even lower after pre-reduction in H2. Overall, the Pt-Al without pre-reduction showed the highest amount of NOx desorption below 250°C.

Stability and activity of Pd-, Pt- and Pd–Pt catalysts supported on alumina for NO oxidation

The association of palladium and platinum supported on alumina was studied for diesel oxidation catalyst application. The effect of propene, water and their combination on NO oxidation activity was investigated in flow reactor over Pt/Al2O3, Pd/Al2O3 and two Pt–Pd/Al2O3 catalysts, prepared by co-impregnation and sequential impregnation of the metals. Contrary to Pd/Al2O3, activity improvement due to the repetition of activity test was observed on Pt/Al2O3 and both Pt–Pd/Al2O3. Metal sintering during activity test was revealed by CO chemisorption. The bimetallic catalysts reached their final stability and activity before Pt/Al2O3. The presence of water decreased the NO oxidation activity of all catalysts and the propene completely inhibited NO oxidation at low temperature until propene combustion occurred. The addition of palladium to Pt/Al2O3 was found very efficient to oxidize propene and therefore significantly limited the inhibition of NO oxidation by propene. A mechanism was proposed to explain the NO oxidation promotion lying behind the addition of Pd. DRIFT measurements and flow reactor experiments showed that propene was less stable and able to react with surface nitrates on Pd-containing catalyst at low temperature (175°C). On Pt/Al2O3, however, the propene consumption proceeded initially through selective catalytic reduction of NO, which took place at higher temperature (240°C). In this way, propene combustion and consequently NO oxidation occurred at lower temperature on bimetallic catalysts than on Pt/Al2O3.

Realization of Ru–C Eutectic Point for Evaluation of W–Re and IrRh/Ir Thermocouples

Tungsten–rhenium (W–Re) thermocouples are widely used in industry for measurements at high temperatures, up to \(2000\,^{\circ }\hbox {C}\). Since the electromotive force (emf) of a W–Re thermocouple is known to change during exposure at high temperatures, evaluation of the emf stability is essential for measuring temperature precisely and for realizing precise temperature control used to ensure the quality of products subject to annealing processes. To evaluate precisely the thermoelectric stability around \(2000\,^{\circ }\hbox {C}\), two Ru–C \((1953\,^{\circ }\hbox {C})\) cells (crucible and Ru–C eutectic alloy) were constructed in our laboratory. The key feature of the cells is that their dimensions are large to ensure there is sufficient immersion available to evaluate the homogeneity characteristics of the thermocouples. By using one of the Ru–C cells, the drift and inhomogeneity of Type C (tungsten–5 % rhenium vs tungsten–26 % rhenium) thermocouples during an exposure to high temperature around \(2000\,^{\circ }\hbox {C}\) were evaluated. Furthermore, to explore possible applications of the eutectic point to other types of high-temperature thermocouples, the drift of an IrRh/Ir thermocouple (iridium–40 % rhodium vs iridium) was also evaluated using another Ru–C cell. The tests with W–Re and IrRh/Ir thermocouples demonstrate that the newly developed Ru–C cells can be used to successfully realize melting plateaux repeatedly. This enables the long-term drift measurements essential for the evaluation and improvement of high-temperature thermocouples. The results obtained in this study will also be useful for evaluating the uncertainty of thermocouple calibrations at around \(2000\,^{\circ }\hbox {C}\).