Function Of Time Research Articles

Spectrally filtered time domain study of coherent phonons in semimetals

We have investigated the spectrally resolved coherent phononoscillation in semimetals of Sb and Bi. The oscillation initial phase isπ-shifted for the high- and low-frequency components of the probe pulse, indicating that notonly the integrated intensity, but also the spectral content of the probe, are a function oftime delay. This means that the coherent phonon, corresponding to nuclear motion, is awavepacket localized in different regions of the phase space. Furthermore, the spectralfiltering results in the appearance of the signal for negative delay time with thesimultaneous disappearance of the coherent artefact. We conjecture that all these findingsare the indication of the non-classical nature of coherent phonons that has beenearlier inferred from squeezing and revivals of the lattice mode in semimetals.

Effects of pH and Alum Concentrations on TiO2 Capture on Cellulose Fibers during Co-Filtration

Much research has been carried out to correlate the surface charges to particle capture in papermaking and filtration industries. Most of the previous works model the co-filtration process of simultaneous fibrous mat formation and filler particle capture as a sequential combination of cake and depth filtration. Very few works have quantified the surface charge and related it to the filtration behavior. The objective of this work is to model the co-filtration process through multiphase transport theory, coupled with the postulated constitutive equations and explain the dominant particle capture mechanism under different water chemistry conditions. The model proposed here is compared with experimental data from a co-filtration process of raw paper formation using cellulose fibers, Tio2particles as the fillers, and alum as the salt additive. The zeta potentials, i. e , effective surface charges, of cellulose fibers and TiO2 particles under different conditions were measured prior to filtration experiments. The pH, salt and particle concentrations were varied in bench and pilot filtration experiments. The results of filtration experiments show a significant effect of material surface charges on particle capture efficiency. The filtration efficiency increased between 30%to over 50%by adding the salt to the slurries. The model equations with constitutive functions were numerically solved and the capture coefficients were optimized using a genetic algorithm to best fit the experimental data. AFPRTRAM program was written to handle the moving boundary condition (function of time) of co-filtration process. A dimensionless zeta potential function was defined to relate the zeta potentials of both the fibers and the filler particles and incorporated into the particle capture relation. The capture relation separates the particle capture due to electrostatic attraction from other capture mechanisms. The model results show electrostatic attraction between fibers and fillers to be the dominant particle capture mechanism when salt is added to the slurry.

Kinetic Investigation of Consecutive-Parallel Reactions in the Non-Catalytic Process of Ethylene Oxide Hydrolysis

A large class of consecutive-parallel addition reactions with a large number of steps has been considered. The system of differential equations describing the kinetics of consecutive-parallel reactions in the non-catalytic process of ethylene oxide hydrolysis has been investigated. By a series of assumptions it is possible to obtain the analytical solution for the distribution of reaction products at non-zero initial conditions. The analytical solution of differential equations as a function of time has been obtained. The comparison between the solutions of the kinetics model with the reported experimental data has shown its sufficient adequacy.

Strain-Rate Effects on Unidirectional Carbon-Fiber Composites

Strain-rate effects on mode I fracture of unidirectional carbon-e ber tow composites corresponding to crack propagation parallel to the e ber tow direction was investigated. Precracked unidirectional stitched carbon-e ber specimensweresubjected to a staticandlow-velocity-impactthree-pointbend test.Thecrack position asa function oftime and hencethecrack-propagation velocity were measured with thehelp ofspecial crack-propagation gauges and a high-resolution digital camera. Load vs load point displacement was measured for every test. The effect of strain rate on fracture energy was characterized. The Iosipescu shear test under static and low-velocity-impact loading conditions wasused to characterizetherate-dependent shearresponse ofthematerial. In addition, tension and compression responses were characterized using American Society for Testing and Materials standard test cone gurations. It is found that the mode I fracture energy decreases with an increase in the rate of loading. with the failure event. The resin used for the tubes is slightly rate sensitive; however,thisindicatesthat theresin isstiffer and stronger under dynamic conditions. Yet, the dynamically crushed tubes con- sistently absorblessenergythan thestatically crushedtubes,always atalowermeanplateauload.Thus,itappearsthattheratesensitivity of the fracture events warrant a careful examination. The basic building block of braided composite plaques are e ber tows that are braided into different microstructural architectures prior to being infused with resin. Different types of braided archi- tectures are summarized in the text. 1 Prior to studying the fracture propertiesofthebraidedplaques (thebraidedplaquescontainacom- plex internal microstructure ), it is prudent to understand the various fracturemechanisms andfractureproperties of thetows themselves. Fundamental issues related to mode I, mode II, and mixed mode fracture of stitched tow-reinforced composites need investigation. The mode I, mode II, and mixed mode fracture energies are fun- damental properties of a e ber-reinforced composite. Consequently, measurement of these fracture energies is necessary for properly characterizing the response and failure of structures made of these composites. In this paper we present the results of an experimental study that examined the mode I fracture of unidirectional carbon- e ber tow composites with crack propagation along the e ber tow direction. The present investigation of crack growth is limited to low ve- locity impact (LVI) conditions. Under these conditions the dy- namic stress e eld produced by the impact loading subsides, and this transient e eld occurs at the very early stages of loading. In the present experiments the maximum impactor velocity is 4.6 m/s, re- sulting in maximum crack-propagation velocities on the order of 350 m/s. These velocities are a small fraction of the shear wave speed (1540 m/s) and Rayleigh wave speed of the material. Con- sequently, dynamic effects can be neglected. Researchers 7i11 have conducted an extensive experimental and numerical investigation of dynamic crack propagation in unidirectional continuous e ber (prepreg)-laminated composites. The present study examines con- tinuous e ber (e ber tows) unidirectional composites under LVI con- ditions.

UPPER FIRST-EXIT TIMES OF COMPOUND POISSON PROCESSES REVISITED

For a compound Poisson process (CPP) with only positive jumps, an elegant formula connects the density of the hitting time for a lower straight line with that of the process itself at time t, h(x; t), considered as a function of time and position jointly. We prove an analogous (albeit more complicated) result for the first time the CPP crosses an upper straight line. We also consider the conditional density of the CPP at time t, given that the upper line has not been reached before t. Finally, it is shown how to compute certain moment integrals of h.

Compositional changes of a brushite hydraulic cement after implantation in sheep

A hydraulic calcium phosphate cement having dicalcium phosphate dihydrate (DCPD) as end-product of the setting reaction was implanted in a cylindrical defect in the diaphysis of sheep for up to 6 months. The composition of the cement was investigated as a function of time. After setting, the cement composition consisted essentially of a mixture of DCPD and beta-tricalcium phosphate (beta-TCP). In the first few weeks of implantation, the edges of the cement samples became depleted in DCPD, suggesting a selective dissolution of DCPD, possibly due to low pH conditions. The cement resorption at this stage was high. After 8 weeks, the resorption rate slowed down. Simultaneously, a change of the color and density of the cement center was observed. These changes were due to the conversion of DCPD into a poorly crystalline apatite. Precipitation started after 6-8 weeks and progressed rapidly. At 9 weeks, the colored central zone reached its maximal size. The fraction of beta-TCP in the cement was constant at all time. Therefore, this study demonstrates that the resorption rate of DCPD cement is more pronounced as long as DCPD is not transformed in vivo.

Dependence of inertial measurements ofdistance on accelerometer noise

An investigation is made into the errors in estimatedposition that are caused by noise and drift effects instationary accelerometers. An analytical study is made into theeffects of biases in the accelerometer data and the effects ofchanging the cut-off frequency in the anti-aliasing filter. Theroot mean square errors in position are calculated as a functionof time and sampling frequency. A comparison is made between thetheoretical results and experimental data taken from twocommercial accelerometers. Recommendations are made regardingthe calibration of accelerometers prior to their use inpractical situations.

In vivo generation of hybrids between different species of RNA phages.

Hybrids between different species or genera of the single-stranded RNA coliphages have not been found in nature. Here, it has been shown that viable hybrids between different phage species can easily be generated in the laboratory by in vivo recombination. cDNA of species I phage MS2 located on a plasmid and lacking part of its 5' untranslated leader (5' UTR) was complemented with another plasmid carrying the 5' half of the genome of fr, a species I phage, or of KU1, a species II representative with low sequence similarity. When the two plasmids were present in the same cell there was spontaneous production of hybrid phages. Interestingly, these hybrids did not arise by a double or single crossover that would replace the missing MS2 sequences with those of fr or KU1. Rather, hybrids arose by attaching the complete 5' UTR of fr or KU1 to the 5' terminus of the defective MS2 phage. Several elements of the 5' UTR then occurred twice, one from KU1 (or fr) and the other from MS2. These redundant elements are in most cases deleted upon evolution of the hybrids. As a result, the 5' UTR of KU1 (or fr) then replaced that of MS2. It was earlier shown that this 5' UTR could assume two alternating structures that facilitated transient translation of the proximal maturation gene. Apparently, this timer function of the 5' UTR was exchangeable and could function independently of the rest of the genome. When hybrids were competed against wild-type, they were quickly outgrown, probably explaining their absence from natural isolates.

Molecular Biology of an Alarm Clock: A Timer-Protein Involved in an Active Resumption of Embryogenesis in the Bombyx Silkworm.

A model is proposed that an ATPase called EA4 measures time for an active resumption of embryonic development at the end of Bombyx diapause. The timer function of EA4 comprises a built-in mechanism in the EA4 protein structure and it may undergo a series of conformational changes with time. The carbohydrate moiety of EA4 regulates the time measurement through its interaction with a peptide named PIN. PIN forms an equimolar complex with EA4 and presumably inhibits the conformational change of EA4 to hold the timer. Winter cold is a possible external time cue that induces the dissociation of the complex, which in turn results in the timer activation of EA4. We refer to EA4 as a time interval measuring enzyme, TIME.

Modified Capillary Suction Theory with Effects of Sedimentation for Rectangular Cells

Solid/liquid separation (SLS) is a fundamental operation in the chemical and allied Industries and urban wastewater treatment plants. Usually the first step in SLS involves slurry pretreatment for the purpose of increasing settling velocities and cake permeability. The Capillary Suction Apparatus (CSA) developed by Gale and Baskerville at Stevenage, UK in 1967 provides a simple, rapid, and inexpensive method for comparing the effects of different agents and dosages. Slurry is poured into a small open tube resting on a piece of filter paper. Filtrate is sucked out by capillary suction, and cake is formed at the bottom of the tube. The rate at which filtrate is sucked out depends on the resistance of the cake. By measuring the distance the filtrate traveling along the paper as a function of time, the cake resistance can be determined. One problem in CSA test is the effect of sedimentation which can not be neglected for a majority of flocculated slurries we have investigated. Most existing theory does not take the effect of sedimentation into account, and leads to overestimation of cake resistance. In this work, a modified capillary suction theory for rectangular cells including sedimentation is presented. Calculated values of resistance based on the new model indicated the existence of large errors in the former model which omitted sedimentation.

Estimation of the probability for exceeding a threshold concentration of furosemide at various intervals after intravenous administration in horses.

To estimate the probability for exceeding a threshold concentration of furosemide commonly used for regulatory purposes after IV administration of furosemide in horses. 12 mature healthy horses (6 Thoroughbreds and 6 Quarter Horses). Venous blood was collected from each horse prior to and 0.25, 0.5, 0.75, 1, 2, 3, 4, 4.5, 5, and 6 hours after administration of 250 or 500 mg of furosemide. Concentrations of furosemide were determined, using an ELISA. Concentration of furosemide was modeled as a function of time, accounting for inter- and intrahorse variabilities. On the basis of pharmacokinetic data, the probability for exceeding a concentration of 100 ng/ml as a function of time was determined, using a semiparametric smooth functional averaging method. A bootstrap approach was used to assess inherent variation in this estimated probability. The estimated probability of exceeding the threshold of 100 ng of furosemide/ml ranged from 11.6% at 4 hours to 2.2% at 5.5 hours after IV administration of 250 mg of furosemide/horse and 34.2% at 4 hours to 12.3% at 5.5 hours after IV administration of 500 mg of furosemide/horse. The probability of a horse being falsely identified in violation of regulatory concentrations was inversely associated with time and positively associated with dose. Interhorse variability with respect to pharmacokinetics of furosemide will result in misclassification of some horses as being in violation of regulatory concentrations.

STUDY ON THE TWIN DYNAMIC INTERFACES OF BULK TARGET IRRIDIATED BY PULSED LASER 

The ablating model of a bulk target irradiated by a pulse laser is set up.Using the simple energy balance considerations,the relationship of the ablating surface's location with the time is derived.By adiabatic approximation,the continuous-temperature condition and conservation of energy,we find out all the boundary conditions.By using the combination of analytical method and integral-approximation method,and solving the heat flow equation,the temperature distribution of soild and liquid phases' as functions of time and location are obtained,the interface of solid and liquid phase is also derived.In addition,the results are compared with other published data.Finally,most of the calculated results present are on excimer-laser irradiated target Al,although the calculations can be easily extended to laser irradiation of other targets.

The relationship between excitation energy transfer, trapping and antenna size in Photosystem II

A systematic study of a range of particles, isolated from both higher plants and the cyanobacterium Synechocystis 6803, has investigated the effect of antenna size on energy transfer and trapping in Photosystem II. Time resolved fluorescence experiments have been employed to obtain the absolute singlet state concentrations as a function of time from each sample, rather than focusing on a multiexponential lifetime analysis of the data. Models that may be used to describe the multiexponential dynamics of energy and electron transfer in isolated reaction centre samples were investigated, to establish whether they could be extended to predict the experimentally observed trapping dynamics in open and closed core particles without the need to vary the reaction centre (`trapping engine?) parameters. It is demonstrated that macroscopic and microscopic reaction centre `trapping engine? models may be extended to describe the experimentally observed trapping dynamics in a range of particles with QA in a fully closed state. This suggests that the presence of the shallow trap and slow charge separation kinetics, observed in isolated D1/D2/cyt b559 reaction centres, are retained in larger particles. Fluorescence decays obtained from cores particles with QA in a fully open state were more difficult to reconcile using macroscopic models without changing the free energy between the excited singlet and primary radical pair states. A microscopic description of the trapping engine may however be used to provide an alternative representation of the dynamics in open core particles that does not require the original parameters employed in the reaction centre trapping engine model to be altered.

Biochemical and morphological characterization of sulfur-deprived and hydrogen-producing Chlamydomonas reinhardtii (green algae)

Sulfur-deprivation in green algae causes a reversible inhibition in the activity of the H2O-oxidizing PSII complex. Within 24 h of S-deprivation, rates of photosynthetic O2-evolution drop below those of O2-consumption by respiration. In consequence, sealed cultures of Chlamydomonas reinhardtii become anaerobic in the light, enzymes of the hydrogenase pathway are induced, followed by photosynthetic H2 gas production. Concomitant with such H2-production, cells consume significant amounts of internal starch and protein. Such catabolic activity may sustain, directly or indirectly, the H2-production process. Profile analysis of selected photosynthetic proteins showed a precipitous decline in the amount of Rubisco as a function of time in S-deprivation, a more gradual decline in the level of PSII and PSI proteins, and change in the composition of the LHC-II. It is concluded that, in the absence of Rubisco (t>48 h in S-deprivation), electrons derived upon a residual H2O-oxidation activity of PSII feed into the hydrogenase pathway, thereby contributing to the H2-production process. Increase in the level of the enzyme Fe-hydrogenase was noted during the initial stages of S-deprivation (0-80 h) followed by a decline in the level of this enzyme during longer (t>80 h) S-deprivation times. Microscopic observations showed distinct morphological changes in C. reinhardtii. Ellipsoid-shaped cells (normal photosynthesis) gave way to spherical and larger cell shapes during the initial stages of S-deprivation (0-24 h), followed by cell mass reductions at longer S-deprivation and H2-production times. These biochemical and morphological changes are discussed in terms of cellular physiology in the S-deprived and H2-producing Chlamydomonas reinhardtii.

Bioenergetic and metabolic processes for the survival of sulfur-deprived Dunaliella salina (Chlorophyta)

The work addressed bioenergetic, metabolic and physiological responses ofthe green alga Dunaliella salina to sulfur (S)-deprivation. Photo-autotrophically grown cells were suspended in a medium in which thesulfates were replaced by chloride salts. Growth characteristics, pigmentcontent, rates of photosynthesis and respiration, as well as endogenoussubstrate (starch and protein) accumulation were monitored as a functionof time under S-deprivation. Lack of S from the growth medium had adifferential effect on photosynthesis and respiration. The rate oflight-saturated photosynthesis declined semi-exponentially with time,whereas the activity of respiration remained fairly constant over a periodof up to 100 h in S-deprived medium. Cell division and `packed cell volumeincrease' declined in tandem with the decline in the rate of photosynthesis. There was gradual loss of chlorophyll from the cells and a concomitant lossof photochemically competent system-II reaction centers, whereas theconcentration of system-I remained largely unaffected under S-deprivation. Cells altered the partition of photosynthate between starch and protein sothat control steady-state starch/protein ratios in the light (0.1: 1, w: w)gradually increased up to about 1: 1 as a function of S-deprivation. SealedDunaliella salina cultures, in which the capacity of photosynthesisdeclined to levels lower than that of respiration, consumed dissolvedoxygen and became anaerobic in the light. These cultures, however, did notactivate the reversible `hydrogenase pathway' and did not produceH2 gas. Instead, under extended S-deprivation, cells maintained alow-level cycling of O2 and CO2 between photosynthesis andrespiration that resulted in no net exchange of gases. Such low-level cyclingof photosynthesis and respiration was sufficient to ensure the generation ofATP needed for survival of the organism under protracted S-deprivationconditions.

Fast kinetics of chromatin assembly revealed by single-molecule videomicroscopy and scanning force microscopy.

Fluorescence videomicroscopy and scanning force microscopy were used to follow, in real time, chromatin assembly on individual DNA molecules immersed in cell-free systems competent for physiological chromatin assembly. Within a few seconds, molecules are already compacted into a form exhibiting strong similarities to native chromatin fibers. In these extracts, the compaction rate is more than 100 times faster than expected from standard biochemical assays. Our data provide definite information on the forces involved (a few piconewtons) and on the reaction path. DNA compaction as a function of time revealed unique features of the assembly reaction in these extracts. They imply a sequential process with at least three steps, involving DNA wrapping as the final event. An absolute and quantitative measure of the kinetic parameters of the early steps in chromatin assembly under physiological conditions could thus be obtained.

Model of textural development of layered crystal aggregates

A two-dimensional computer model is developed to study the evolution of texture during the growth of layered mineral aggregates. The program computes the number, size and orientation (texture) of crystals forming the outer surface of the aggregate, as well as the evolution as a function of time. In particular, the analysis focuses on the influence of growth parameters such as the anisotropy of the growing crystal forms, the relative growth rate of the crystal faces, the nucleation density on the substrate surface, the flow direction of the mineralizing solution and the shape of the substrate. The simulation provides an explanation for the development of a preferential orientation in a polycrystalline material growing from randomly oriented nuclei. The calculated distribution of crystal orientations, and its evolution with time, is in agreement with textures observed in synthetic and natural polycrystalline aggregates.

Elderly dependence. Longitudinal approach to risk factors

The evolution of elderly dependence may be seen as a bunch of events sequences. This global approach by cohort, leads to a chain of conditionnal risks. Their scale is function of some main events and several variables which value is stable after 65 years old. Some of those main events are called endogeneous (steps of dependence evolution for example) because the probability of their occurrence grows with the occurrence of an earlier studied event and some others are called exogeneous (transformations of matrimonial status for example) because the probability of their occurrence is a priori independent of an earlier studied event. In that way, all exogeneous phenomenon is supposed to be risk factor to an endogeneous phenomenon, and several endogeneous phenomena are supposed to be risk factors to other endogeneous phenomena. The suggested system forms a dynamic resonance between risks scale and their realization, leading elderly to the largest dependence. The associated growth of vulnerability and dependence is patterned considering all cares which adequation is estimated with their ability to curb the autonomy loss process. Demographic analysis toolkits are a way to build a network of stacked probabilities tables which are functions of time flown since exogeneous or endogeneous studied events and potential cares have occured. The subdivision of cohorts along exogeneous variables which value is stable after 65 years old, gives them the best homogeneity attainable. The determination of datas required for this work is disputed considering the essential exactness, the delay before the first results, the continuously of observation and the costs of collection. Qualities of the different type of surveys conceivables (retrospective or prospective) and their sample base are examinated. Abilities of the use of large admistration data bases and the conditions for extrapolations beyond the population of aged registred in those files, are also considered. Then some criteria to form information systems about elderly dependence and its factors are suggested.

Réactions d'acylation sous irradiation micro-onde. II. Acylation d'éthers aromatiques

L'acylation d'éthers aromatiques a été réalisée sous irradiation micro-onde, dans des conditions efficaces (temps de réaction court et sans contrôle de la température) et en présence de divers catalyseurs, chlorures, oxydes (essentiellement dérivés du fer) ou triflates métalliques. Pour la benzoylation de l'anisole, la montée en tempéature en fonction du temps a été rapportée et reliée à l'efficacité des catalyseurs: les plus actifs d'entre eux conduisent aux gradients de température les plus forts. II a été montré que les micro-ondes ont une interaction spécifique avec l'arylcétone produite et particulièrement avec sa forme complexée au catalyseur. Toutefois, un effet non thermique des micro-ondes n'a été observé ni sur le rendement, ni sur les rapports d'isomères des différents produits. Acylation of aromatic ethers has been carried out under microwave irradiation, using rapid conditions (short reaction time and without temperature control) and in the presence of various catalysts, metallic chlorides, oxides (mainly iron derivatives), or triflates. For the benzoylation of anisole, the rise in temperature as a function of time is reported and connected to the efficiency of catalysts: the most active of them induce the largest temperature gradients. It is shown that microwaves have a specific interaction with the arylketone produced and especially with its catalyst-complexed form. However, a microwave nonthermal effect has not been observed, either for the yield or for the isomeric ratios of various products.

Changes in Infants' Cries as a Function of Time in a Cry Bout

Changes in Infants' Cries as a Function of Time in a Cry Bout