Time-dependent Intensity Research Articles

Dynamic Colloidal Molecules Maneuvered by Light-Controlled Janus Micromotors.

In this work, we propose and demonstrate a dynamic colloidal molecule that is capable of moving autonomously and performing swift, reversible, and in-place assembly dissociation in a high accuracy by manipulating a TiO2/Pt Janus micromotor with light irradiation. Due to the efficient motion of the TiO2/Pt Janus motor and the light-switchable electrostatic interactions between the micromotor and colloidal particles, the colloidal particles can be captured and assembled one by one on the fly, subsequently forming into swimming colloidal molecules by mimicking space-filling models of simple molecules with central atoms. The as-demonstrated dynamic colloidal molecules have a configuration accurately controlled and stabilized by regulating the time-dependent intensity of UV light, which controls the stop-and-go motion of the colloidal molecules. The dynamic colloidal molecules are dissociated when the light irradiation is turned off due to the disappearance of light-switchable electrostatic interaction between the motor and the colloidal particles. The strategy for the assembly of dynamic colloidal molecules is applicable to various charged colloidal particles. The simulated optical properties of a dynamic colloidal molecule imply that the results here may provide a novel approach for in-place building functional microdevices, such as microlens arrays, in a swift and reversible manner.

Frictional Heating with Time-Dependent Specific Power of Friction

Abstract In this paper analytical solutions of the thermal problems of friction were received. The appropriate boundary-value problems of heat conduction were formulated and solved for a homogeneous semi–space (a brake disc) heated on its free surface by frictional heat fluxes with different and time-dependent intensities. Solutions were obtained in dimensionless form using Duhamel's theorem. Based on received solutions, evolution and spatial distribution of the dimensionless temperature were analyzed using numerical methods. The numerical results allowed to determine influence of the time distribution of friction power on the spatio-temporal temperature distribution in brake disc.

Tunable X-Band Optoelectronic Oscillators Based on External-Cavity Semiconductor Lasers

Laser diodes with optical feedback can exhibit periodic intensity oscillations at or near the relaxation-oscillation frequency. We demonstrate optoelectronic oscillators based on external-cavity semiconductor lasers in a periodic dynamical regime tunable over the entire X-band. Moreover, unlike standard optoelectronic oscillators, we need not employ the time-dependent optical intensity incident on a photodiode to generate the microwave signal, but rather have the option of generating the electrical microwave signal directly as a voltage $V(t)$ at the laser-diode injection terminals under constant current operation; no photodiode need be involved, thus circumventing optical-to-electrical conversion. We achieve a timing jitter of $\lesssim 10$ ps and a quality factor of $\gtrsim 2\times 10^5$ across the entire X-band, that ranges from 6.79 GHz to 11.48 GHz. Tuning is achieved by varying the injection current $J$.

Real-Time Analysis of Folding upon Binding of a Disordered Protein by Using Dissolution DNP NMR Spectroscopy.

The kinase inhibitory domain of the cell cycle regulatory protein p27Kip1 (p27) was nuclear spin hyperpolarized using dissolution dynamic nuclear polarization (D-DNP). While intrinsically disordered in isolation, p27 adopts secondary structural motifs, including an α-helical structure, upon binding to cyclin-dependent kinase 2 (Cdk2)/cyclin A. The sensitivity gains obtained with hyperpolarization enable the real-time observation of 13 C NMR signals during p27 folding upon binding to Cdk2/cyclin A on a time scale of several seconds. Time-dependent intensity changes are dependent on the extent of folding and binding, as manifested in differential spin relaxation. The analysis of signal decay rates suggests the existence of a partially folded p27 intermediate during the timescale of the D-DNP NMR experiment.

Preferential triplet over singlet emission of Zn in laser-induced plasmas

An experimental study is performed on the time-dependent intensity variations of Zn emission focusing on the triplet (Zn I 481.0 nm) and singlet (Zn I 636.2 nm) emission lines induced under three experimental conditions. A single nanosecond (ns) Nd:YAG laser in standard laser-induced breakdown spectroscopy (LIBS) setup is employed for the investigation of direct shock wave-induced emission characteristics with N2 ambient gas at 0.4 kPa and the different effects of He ambient gas at 2 kPa. An additional two-laser system consisting of ns and picosecond (ps) lasers in an orthogonal setup is used to study the exclusive role of a He-assisted excitation (HAE) process for the generation of those two Zn emission lines. The results of this study consistently exhibit the dominant triplet emission over the singlet emission marked by initial maximum intensity ratios of 8 and 12 obtained from the experiments using a single-laser setup in N2 and He ambient gases, respectively, indicating the significant contribution of the HAE mechanism to the enhanced and longer lasting Zn emission in He gas. The experiment using the special two-laser setup further demonstrates the exclusive role of the HAE process in the Zn emission featuring an even markedly higher triplet/singlet intensity ratio of 22. Thus, the results of this study suggest the possibly more general nature of dominant triplet emission phenomena previously found in laser-induced He and Ca emission spectra.

Toward greener electrochemical synthesis of composition-tunable luminescent CdX-based (X = Te, Se, S) quantum dots for bioimaging cancer cells

A novel versatile and clean colloidal processing route was developed for synthesizing CdX (X=Te, Se or S) quantum dots (QDs) based on the simultaneous production of the respective precursors via cadmium sacrificial anode electrochemical methodology. The CdX QDs stabilized by 3-mercaptopropionic acid (MPA) were synthesized in one-pot electrochemical process using aqueous medium at room temperature with full reaction time of approximately 16min. The CdX quantum dots conjugates were extensively characterized by UV–vis, PL, FTIR, TEM-EDS, XRD, DLS, XPS, and Zeta potential, evidencing that very stable colloidal quantum dots were produced with uniform narrow-size distributions and average nanoparticle diameter of approximately 3.0nm and quantum yield (QY) of approximately 10%. The cell viability response of HeLa cells toward the CdX-MPA conjugates clearly demonstrated that they are non-toxic based on the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) mitochondrial metabolic activity assay for 24h of incubation with HeLa cervical cancer cells. Moreover, they showed effective fluorescent activity with time-dependent intensities for evaluating continuous endocytosis of cancer cells, thus, offering innumerous possibilities to be used as fluorescent nanoprobes for bioimaging and biosensing of cancer cells.

Investigating trade-offs between the operating cost and green house gas emissions from water distribution systems

For electricity grids with an increasing share of intermittent renewables, the power generation mix can have significant daily variations. This leads to time-dependent emission intensities and volatile electricity prices in the day-ahead and spot market tariffs that can be better utilised by energy intensive industries such as water supply utilities. A multi-objective optimisation method for scheduling the operation of pumps is investigated in this paper for the reduction of both electricity costs and greenhouse gas emissions for a benchmark water distribution system. A set of energy supply scenarios has been formulated based on future projections from National Grid plc (UK) in order to investigate the range of cost savings and emission reductions that could be possibly achieved. Pump scheduling options with fixed time-of-use and day ahead market tariffs are analysed in order to compare potential reduction tradeoffs for both electricity costs and greenhouse gas emissions using Pareto optimality. The presented analysis concludes that the explicit inclusion of greenhouse gas emission reductions in optimising the scheduling of pumps operation in water distribution systems could provide considerable benefits; however, more compelling fiscal and regulatory incentives are needed.

PHOTODISSOCIATION DYNAMICS OF SPATIALLY ALIGNED MOLECULES BY TIME-RESOLVED ELECTRON DIFFRACTION

The anisotropic ensembles of laser-excited molecules can be formed, for example, under the action of fs pulses of polarized laser radiation. It was theoretically predicted that the electron diffraction pattern from aligned molecules in the gas phase allows determining not only internuclear distances but also valence angles that is 3D molecular structure. In the current article, we propose the basic elements of the theory that can be employed for analyze of time-resolved electron diffraction (TRED) data obtained from oriented/aligned laser-excited molecules. This formalism is applicable to dissociative processes and to nuclear dynamics studies of photo dissociation studies. The theory is illustrated by modeling the diffraction intensities of photo generated dissociation of ICN molecules. The time-dependent intensities of the molecular scattering and the corresponding radial distribution functions of the internuclear distances at the processes of the photo dissociation of ICN were calculated.Based on model calculations presented in this article we conclude that TRED method provides the principal possibility of study of coherent dissociation dynamics for real scale of time which is essentially less than the electron pulse duration of 300 fs, which is achieved at present in a number of TRED experiments. The results obtained were compared with our previous modeling studies of randomly oriented and diatomic aligned molecular ensembles.Forcitation:Schafer L., Ischenko A.A., Zhabanov Yu.A., Otlyotov A.A., Girichev G.V. Photodissociation dynamics of spatially alig-ned molecules by time-resolved electron diffraction. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 3. P. 4-14.

A fracture mechanics study of the phase separating planar electrodes: Phase field modeling and analytical results

Abstract It is well known that phase separation could severely intensify mechanical degradation and expedite capacity fading in lithium-ion battery electrodes during electrochemical cycling. Experiments have frequently revealed that such degradation effects could be substantially mitigated via reducing the electrode feature size to the nanoscale. The purpose of this work is to present a fracture mechanics study of the phase separating planar electrodes. To this end, a phase field model is utilized to predict how phase separation affects evolution of the solute distribution and stress profile in a planar electrode. Behavior of the preexisting flaws in the electrode in response to the diffusion induced stresses is then examined via computing the time dependent stress intensity factor arising at the tip of flaws during both the insertion and extraction half-cycles. Further, adopting a sharp-interphase approximation of the system, a critical electrode thickness is derived below which the phase separating electrode becomes flaw tolerant. Numerical results of the phase field model are also compared against analytical predictions of the sharp-interphase model. The results are further discussed with reference to the available experiments in the literature. Finally, some of the limitations of the model are cautioned.

Optimal Stopping at Random Intervention Times

In decision problems, frictions as well as constraints play an increasingly important role. Especially, optimal timing problems can be affected by potentially “non-rational” behavior of the decision maker which is not incorporated in the standard theory. A relevant problem of this kind is the real option to abandon a project. Limited cognitive resources and external restrictions to option exercise may result in a suboptimal outcome. The term inattention can summarize such frictions and constraints. In this paper, we address this issue by proposing a Markovian model to value American-style contracts of agents who are temporarily inattentive. Exercise decisions maximizing the contract’s payoff are not admissible continuously but at random intervention times arriving with possibly state and time dependent intensities. An optimal stopping problem provides the contract value. It is converted to optimal control which, given sufficient regularity, induces a characterisation in terms of a partial integro differential equation. We consider three numerical approaches, forward improvement iteration, least squares Monte-Carlo and finite differences, each corresponding to one particular characterization of the contract value. Our adapted least squares Monte-Carlo method can treat complex and possibly multi-dimensional settings.

Spectrum-based and color-selective electrochemiluminescence immunoassay for determining human prostate specific antigen in near-infrared region

The conventional electrochemiluminescence (ECL) analyses were performed via detecting the time (or potential) dependent ECL intensity with the proceeding of ECL reaction. Herein, by spectrally recording all the photons generated in ECL process, a spectral ECL immunoassay was developed in near-infrared (NIR) region with human prostate specific antigen (PSA) as target and dual-stabilizers-capped CdTe nanocrystals (NCs) as tags. The CdTe NCs displayed efficient ECL around 780nm with the full width at half-maximum around 70nm in the immune-complexes, the maximum intensity on ECL spectrum profiles increased linearly with the logarithmic increased concentration of PSA from 20.0fg/mL to 100.0pg/mL, indicating a sensitive and color-selective ECL immunoassay in NIR region with improved anti-interference performance to biological autofluorescence and tissue absorption. The spectral ECL immunoassay in NIR region might provide an important technique support for developing color-selective ECL assay of different wavebands.

Detection-Identification of multiple unknown time-dependent point sources in a 2D transport equation: application to accidental pollution

We address the nonlinear inverse source problem of identifying multiple unknown time-dependent point sources occurring in a two-dimensional evolution advection–dispersion–reaction equation. Provided to be available within the monitored domain interfaces for recording the generated state and its flux crossing each suspected zone where a source could occur, we establish a constructive identifiability theorem based on an introduced dispersion-current function that yields uniqueness of the unknown elements defining all occurring sources. Then, the established theorem leads to develop a detection-identification method that goes throughout the monitored domain to detect in each suspected zone whether there exists or not an occurring source. Once a source is detected, the developed method determines lower and upper bounds of the mean value discharged by its unknown time-dependent intensity function. Thereafter, the method localizes the sought position of the detected source as the unique solution of an equation satisfied by the introduced dispersion-current function and identifies its unknown intensity function from solving an associated deconvolution problem. Ultimately, the unknown number of occurring sources is deduced as the sum of all detected-identified active sources. Some numerical experiments on a variant of the surface water BOD pollution model are presented.

Spectral Diffusion of Emissions of Excitons and Trions in Single CdSe/ZnS Nanocrystals: Charge Fluctuations in and around Nanocrystals

The temporal fluctuations in the photoluminescence (PL) spectra of single CdSe/ZnS nanocrystals (NCs) exhibiting PL blinking at room temperature as well as their dynamical properties were studied. In the case of large NCs, measuring the time-dependent PL intensities and lifetimes allowed us to separately characterize the degree of spectral diffusion (SD) of the exciton and trion (charged exciton) emissions. The SD properties, such as the polarizability and field fluctuation, were investigated quantitatively through comparisons with the results of numerical calculations based on a simple field fluctuation model. We found that trion emissions exhibit unique SD characteristics; i.e., their binding energies are positive and their polarizabilities are smaller than those of excitons. In addition, we observed that the exciton emissions exhibited size-dependent SD behaviors, reflecting the differences in the polarizabilities of the NCs with different sizes. Finally, the experimental data, including an analysis of...

Pulsed neutron time-dependent intensity modulation for quasi-elastic neutron scattering spectroscopy.

We propose a basic formula and demonstration for a high-resolution quasi-elastic neutron scattering (QENS) by combining the time-of-flight (TOF) method with Modulation of Intensity by Zero Effort (MIEZE) type neutron spin echo spectroscopy. The MIEZE technique has the potential to develop a unique approach to study on slow dynamics of condensed matter; however, the energy resolution is limited owing to the hypersensitivity of the MIEZE signal contrast to the echo condition, which is strongly affected by the alignment of the instruments and the sample. The narrow allowance of the optimal alignment is a major obstacle to the wide use of this technique. Combining the TOF method with MIEZE (TOF-MIEZE), the hypersensitivity of MIEZE signals is significantly alleviated with a short pulsed beam. This robustness is very useful to optimize experimental alignments and enables accurate measurements of QENS. The experimental results demonstrate the characteristic of the TOF-MIEZE technique and are well described by the formula presented in this study.

Estimation of the traffic intensity in a piecewise-stationary Mt/Gt/1 queue with probing

We use a probing strategy to estimate the time dependent traffic intensity in an Mt/Gt/1 queue, where the arrival rate and the general service-time distribution change from one time interval to another, and derive statistical properties of the proposed estimator. We present a method to detect a switch from a stationary interval to another using a sequence of probes to improve the estimation. At the end, we compare our results with two estimators proposed in the literature for the M/G/1 queue.

Session details: Special Issue on the Workshop on MAthematical performance Modeling and Analysis (MAMA 2016)

Session details: Special Issue on the Workshop on MAthematical performance Modeling and Analysis (MAMA 2016)

Doping dependence and electron–boson coupling in the ultrafast relaxation of hot electron populations in Ba(Fe1–xCox)2As2

Using femtosecond time- and angle-resolved photoemission spectroscopy we investigate the effect of electron doping on the electron dynamics in in a range of at temperatures slightly above the Néel temperature. By analyzing the time-dependent photoemission intensity of the pump laser excited population as a function of energy, we found that the relaxation times at are doping dependent and about 100 fs shorter at optimal doping than for overdoped and parent compounds. Analysis of the relaxation rates also reveals the presence of a pump fluence dependent step in the relaxation time at which we explain by coupling of the excited electronic system to a boson of this energy. We compare our results with static ARPES and transport measurements and find disagreement and agreement concerning the doping-dependence, respectively. We discuss the effect of the electron–boson coupling on the energy-dependent relaxation and assign the origin of the boson to a magnetic excitation.

Development and Application of Ultra-Performance Liquid Chromatography-TOF MS for Precision Large Scale Urinary Metabolic Phenotyping.

To better understand the molecular mechanisms underpinning physiological variation in human populations, metabolic phenotyping approaches are increasingly being applied to studies involving hundreds and thousands of biofluid samples. Hyphenated ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) has become a fundamental tool for this purpose. However, the seemingly inevitable need to analyze large studies in multiple analytical batches for UPLC-MS analysis poses a challenge to data quality which has been recognized in the field. Herein, we describe in detail a fit-for-purpose UPLC-MS platform, method set, and sample analysis workflow, capable of sustained analysis on an industrial scale and allowing batch-free operation for large studies. Using complementary reversed-phase chromatography (RPC) and hydrophilic interaction liquid chromatography (HILIC) together with high resolution orthogonal acceleration time-of-flight mass spectrometry (oaTOF-MS), exceptional measurement precision is exemplified with independent epidemiological sample sets of approximately 650 and 1000 participant samples. Evaluation of molecular reference targets in repeated injections of pooled quality control (QC) samples distributed throughout each experiment demonstrates a mean retention time relative standard deviation (RSD) of <0.3% across all assays in both studies and a mean peak area RSD of <15% in the raw data. To more globally assess the quality of the profiling data, untargeted feature extraction was performed followed by data filtration according to feature intensity response to QC sample dilution. Analysis of the remaining features within the repeated QC sample measurements demonstrated median peak area RSD values of <20% for the RPC assays and <25% for the HILIC assays. These values represent the quality of the raw data, as no normalization or feature-specific intensity correction was applied. While the data in each experiment was acquired in a single continuous batch, instances of minor time-dependent intensity drift were observed, highlighting the utility of data correction techniques despite reducing the dependency on them for generating high quality data. These results demonstrate that the platform and methodology presented herein is fit-for-use in large scale metabolic phenotyping studies, challenging the assertion that such screening is inherently limited by batch effects. Details of the pipeline used to generate high quality raw data and mitigate the need for batch correction are provided.

Anti-plane interfacial crack with functionally graded coating: static and dynamic

The anti-plane displacement discontinuity method is applied to establish the Fredholm integral equation of the first kind for the orthotropic Functionally Graded Material (FGM) coatings subjected to static/dynamic shears. The shear modulus and mass density are assumed to vary exponentially through the thickness. The static and dynamic fundamental solutions with anti-plane displacement discontinuity are derived for orthotropic FGM coating by using Fourier transform method and Laplace transform method. It has been shown that the transformed fundamental solution with orthotropic coatings has the same order of hyper-singularity as in the static case, i.e. O(1/r2), and the Chebyshev polynomials of the second kind are used to solve the integral equations numerically. The time dependent stress intensity factors are obtained directly from the coefficients of the Chebyshev polynomials with the aid of Durbin’s Laplace transform inversion method. A comparative study of FGM versus homogeneous coating is conducted, and the dependence of the stress intensity factors in the coating/substrate system on the material property (orthotropic) and thickness of coating is examined. Two examples including the static/dynamic loads are given as benchmarks for the numerical methods and application in composite engineering.

Dynamic measurements and simulations of airborne picolitre-droplet coalescence in holographic optical tweezers.

We report studies of the coalescence of pairs of picolitre aerosol droplets manipulated with holographic optical tweezers, probing the shape relaxation dynamics following coalescence by simultaneously monitoring the intensity of elastic backscattered light (EBL) from the trapping laser beam (time resolution on the order of 100 ns) while recording high frame rate camera images (time resolution <10 μs). The goals of this work are to: resolve the dynamics of droplet coalescence in holographic optical traps; assign the origin of key features in the time-dependent EBL intensity; and validate the use of the EBL alone to precisely determine droplet surface tension and viscosity. For low viscosity droplets, two sequential processes are evident: binary coalescence first results from the overlap of the optical traps on the time scale of microseconds followed by the recapture of the composite droplet in an optical trap on the time scale of milliseconds. As droplet viscosity increases, the relaxation in droplet shape eventually occurs on the same time scale as recapture, resulting in a convoluted evolution of the EBL intensity that inhibits quantitative determination of the relaxation time scale. Droplet coalescence was simulated using a computational framework to validate both experimental approaches. The results indicate that time-dependent monitoring of droplet shape from the EBL intensity allows for robust determination of properties such as surface tension and viscosity. Finally, the potential of high frame rate imaging to examine the coalescence of dissimilar viscosity droplets is discussed.