Time-dependent Light Research Articles

Early Stages of FUS Droplet Formation via Liquid-Liquid Phase Separation.

The phase behavior of complex biomolecular solutions may explain different cellular processes, including the organization of cells by membraneless organelles. The early stages of phase separation are crucial to understanding the underlying mechanism and identifying biomolecules that trigger or drive the transition. Here, we analyze the early events of liquid-liquid phase separation (LLPS) of FUS by multiangle time-resolved static and dynamic light scattering. LLPS was triggered by TEV-catalyzed cleavage of the MBP-tag from FUS-MBP. The light scattering measurements revealed the existence of at least two fractions of FUS-MBP aggregates already prior to the onset of LLPS. The orders of magnitude of the aggregate size in these two fractions are 10 and 100 nm, respectively. LLPS started after an induction period, which depended on the concentration of FUS-MBP. The data from time-dependent light scattering revealed a coalescence of droplets also denoted as a step growth process. A step growth process instead of nucleation and growth via monomer addition suggests that LLPS takes place within the spinodal rather than between the binodal and the spinodal.

Neural networks determination of material elastic constants and structures in nematic complex fluids

Supervised machine learning and artificial neural network approaches can allow for the determination of selected material parameters or structures from a measurable signal without knowing the exact mathematical relationship between them. Here, we demonstrate that material nematic elastic constants and the initial structural material configuration can be found using sequential neural networks applied to the transmmited time-dependent light intensity through the nematic liquid crystal (NLC) sample under crossed polarizers. Specifically, we simulate multiple times the relaxation of the NLC from a random (qeunched) initial state to the equilibirum for random values of elastic constants and, simultaneously, the transmittance of the sample for monochromatic polarized light. The obtained time-dependent light transmittances and the corresponding elastic constants form a training data set on which the neural network is trained, which allows for the determination of the elastic constants, as well as the initial state of the director. Finally, we demonstrate that the neural network trained on numerically generated examples can also be used to determine elastic constants from experimentally measured data, finding good agreement between experiments and neural network predictions.

Electromagnetic Signatures from Supermassive Binary Black Holes Approaching Merger

Abstract We present fully relativistic predictions for the electromagnetic emission produced by accretion disks surrounding spinning and nonspinning supermassive binary black holes on the verge of merging. We use the code Bothros to post-process data from 3D general relativistic magnetohydrodynamic simulations via ray-tracing calculations. These simulations model the dynamics of a circumbinary disk and the mini-disks that form around two equal-mass black holes orbiting each other at an initial separation of 20 gravitational radii, and evolve the system for more than 10 orbits in the inspiral regime. We model the emission as the sum of thermal blackbody radiation emitted by an optically thick accretion disk and a power-law spectrum extending to hard X-rays emitted by a hot optically thin corona. We generate time-dependent spectra, images, and light curves at various frequencies to investigate intrinsic periodic signals in the emission, as well as the effects of the black hole spin. We find that prograde black hole spin makes mini-disks brighter since the smaller innermost stable circular orbit angular momentum demands more dissipation before matter plunges to the horizon. However, compared to mini-disks in larger separation binaries with spinning black holes, our mini-disks are less luminous: unlike those systems, their mass accretion rate is lower than in the circumbinary disk, and they radiate with lower efficiency because their inflow times are shorter. Compared to a single black hole system matched in mass and accretion rate, these binaries have spectra noticeably weaker and softer in the UV. Finally, we discuss the implications of our findings for the potential observability of these systems.

Hydrogen peroxide disproportionation: time-resolved optical measurements of spectra, scattering and imaging combined with correlation analysis and simulations

We study how time-dependent optical measurements of spectra, scattering, and imaging can be used to add to the understanding of heterogeneous reactions, compared to work performed using tools developed for homogeneous reactions. Using hydrogen peroxide disproportionation by potassium permanganate as a model reaction, we measure the entire spectrum over reaction time, enabling a clear and useful correlation analysis and assignment of chemical species in heterogeneous conditions. We measure time-dependent dynamic light scattering to study oxygen nanobubble product formation kinetics and equilibrium. We perform macroscopic video-rate reaction imaging and information-theoretic analysis to characterize reaction and transport contributions to the observed signal. To illustrate the differences arising from measuring sample subsets vs the entire system, we integrate stochastic and macroscopic numerical simulations of reaction-diffusion to study homogeneous and heterogeneous reaction conditions. We hope the tools presented here may help understanding other chemical reactions in similar conditions.

Dissipative morphological characteristics of photo-responsive block copolymers driven by time-oscillatory irradiations: An in silico study

Dissipative or dynamic self-assembly has become one of the most important topics in the past twenty years. Under continuous energy input, the building blocks may form various dissipative structures in steady states, which will be destroyed when the energy input is stopped. Among the common forms of energy input, light is widely used for its high efficiency and adjustability. However, there is lack of study on the dissipative self-assembly of photo-responsive block copolymers under time-dependent light irradiations (especially in time-oscillatory light irradiations) as well as its design strategies. We performed non-equilibrium dissipative particle dynamics simulations of azobenzene-contained semiflexible block copolymers in melt and investigated important controlling factors that influence dissipative structures, including the volume ratio of blocks, the interaction between blocks, the oscillation period and the volume fraction of photo-responsive polymers in the system. We found that, when the oscillation period is much smaller than the diffusional timescale of block copolymer, dissipative steady structures will be formed. With the increase of oscillation period, oscillatory dissipative structures with periodic structural variation were formed based on dissipative steady structures. As oscillation period increased further, there would be no regular structure. Furthermore, the dissipative steady structures could be finely tuned by adjusting the volume fraction of photo-responsive chains in block copolymer melt. Our study provides a guidance for the design of azobenzene-contained block copolymers that can form dissipative structures in time-oscillatory irradiations and helps to predict the self-assembled morphologies.

Prognostic Impact of Serum Free Light Chain Ratio Normalization in Patients with Multiple Myeloma Treated within the GMMG-MM5 Trial.

Simple SummaryFor multiple myeloma (MM) patients with measurable disease, there is no recommendation to monitor serum free light chains during therapy. However, this could provide important information in terms of prognosis. We investigated the prognostic impact of serum free light chain ratio (FLCr) normalization in 590 patients with secretory MM during first-line treatment within the German-Speaking Myeloma Multicenter Group MM5 trial. We are able to show that there is an increasing percentage of patients who achieve FLCr normalization during therapy. Importantly, we demonstrate that FLCr normalization at any time before the start of maintenance is significantly associated with prolonged progression-free and overall survival in multivariable time-dependent Cox regression analyses. This suggests that FLCr normalization during therapy is an important and simple way to assess prognostic factor in MM and supports the serial measurement of serum free light chains during therapy, even in patients with secretory MM.We investigated the prognostic impact of time-dependent serum free light chain ratio (FLCr) normalization in 590 patients with secretory multiple myeloma (MM) during first-line treatment within the German-Speaking Myeloma Multicenter Group MM5 trial. Serum free light chains (sFLC) were assessed by the Freelite test at baseline, after induction, mobilization, autologous blood stem cell transplantation, consolidation and every three months during maintenance or follow up within two years after the start of maintenance. The proportion of patients with a normal or normalized FLCr increased from 3.6% at baseline to 23.2% after induction and 64.7% after consolidation. The achievement of FLCr normalization at any one time before the start of maintenance was associated with significantly prolonged progression-free survival (PFS) (p < 0.01, hazard ratio (HR) = 0.61, 95% confidence interval (95% CI) = 0.47–0.79) and overall survival (OS) (p = 0.02, HR = 0.67, 95% CI = 0.48–0.93) in multivariable time-dependent Cox regression analyses. Furthermore, reaching immune reconstitution, defined as the normalization of uninvolved immunoglobulins, before maintenance was associated with superior PFS (p = 0.04, HR = 0.77, 95% CI = 0.60–0.99) and OS (p = 0.01, HR = 0.59, 95% CI = 0.41–0.86). We conclude that FLCr normalization during therapy is an important favorable prognostic factor in MM. Therefore, we recommend serial measurements of sFLC during therapy until achieving FLCr normalization, even in patients with secretory MM.

Connecting steady emission and very high energy flaring states in blazars: the case of Mrk 421

ABSTRACT Various attempts have been made in the literature at describing the origin and the physical mechanisms behind flaring events in blazars with radiative emission models, but detailed properties of multiwavelength (MWL) light curves still remain difficult to reproduce. We have developed a versatile radiative code, based on a time-dependent treatment of particle acceleration, escape, and radiative cooling, allowing us to test different scenarios to connect the continuous low-state emission self-consistently with that during flaring states. We consider flares as weak perturbations of the quiescent state and apply this description to the 2010 February MWL flare of Mrk 421, the brightest very high energy (VHE) flare ever detected from this archetypal blazar, focusing on interpretations with a minimum number of free parameters. A general criterion is obtained, which disfavours a one-zone model connecting low and high state under our assumptions. A two-zone model combining physically connected acceleration and emission regions yields a satisfactory interpretation of the available time-dependent MWL light curves and spectra of Mrk 421, although certain details remain difficult to reproduce. The two-zone scenario finally proposed for the complex quiescent and flaring VHE emitting region involves both Fermi-I and Fermi-II acceleration mechanisms, respectively, at the origin of the quiescent and flaring emission.

Dynamics of a Q-switched bismuth-doped fibre laser: simulation and comparison with experiment

Using an improved travelling wave model, we have numerically investigated the dynamics of a Q-switched bismuth-doped fibre laser. Comparison of simulation results with previously reported experimental data demonstrates good agreement of the multipeak lasing structure and the shape of the strongest pulses at various levels of pumping. We have assessed the effect of the main laser parameters on output laser characteristics and quantitatively evaluated the effects of the nonsaturable loss in the active fibre and amplified spontaneous emission on output power saturation. Based on analysis of time-dependent light intensity and gain distributions in the gain medium at different instants in time, we have formulated recommendations how to improve output laser characteristics.

In vitro inactivation effect of blue light emitting diode (LED) on Shiga-toxin-producing Escherichia coli (STEC)

The antimicrobial effects of blue LED were investigated on seven Shiga-toxin-producing Escherichia coli strains (STEC 7 serotypes) using two LED formats at 405 nm (Prototype A, bulb array emitting 22.77 ± 1.054 mW/cm2; Prototype B, strip array emitting 4.25 ± 0.25 mW/cm2). For both prototypes, cytotoxic effects were detected with time-dependent light dosages and antimicrobial activity of 405 nm blue LED was most effective on minimal medium agar and Luria-Bertani (LB) agar, less effective on cooked meat agar, and least effective on sheep blood agar. Inactivation kinetics of individual STEC strains were determined within a dosage of 163.96 ± 7.55 J/cm2, 5–7 log10 cfu reduction was observed in 7 log10 cfu/ml LB suspension test among seven strains and no viable cells were detected in 3 log10 cfu/ml LB suspension test for all seven tested strains. Difference in light susceptibility among the tested strains was observed between the two prototypes with O111 strain being the most sensitive strain. Multiple factors (e.g. nutrient availability, treatment time, distance, and temperature) could be associated with the antimicrobial effect of 405 nm blue light and need to be well considered when using the technology under different food processing scenarios.

UV Light Driven Photoelectric Properties of ZnO Film to Humidity.

UV light driven photoelectric properties of ZnO film to humidity were researched. ZnO film was prepared through the method of screen printing sustained on Al₂O₃ substrate. ZnO was characterized by XRD, FE-SEM and EDX. The time-dependent UV light driven photoelectric properties of ZnO were investigated by exposing it to different bias voltages and different relative humidity (20% RH, 40% RH, 60% RH and 80% RH). On one hand, the photoelectric properties of ZnO increased with the augmenting of bias voltage, which shows that a higher bias causes more separation of carriers. On the other hand, the photocurrent decreased with the increase in relative humidity, which shows that bigger humidity results in smaller photoelectric property. To discuss these results, corresponding possible illustrations for the photoelectric properties under different conditions were proposed.

Complete spatiotemporal and polarization characterization of ultrafast vector beams

The use of structured ultrashort pulses with coupled spatiotemporal properties is emerging as a key tool for ultrafast manipulation. Ultrafast vector beams are opening exciting opportunities in different fields such as microscopy, time-resolved imaging, nonlinear optics, particle acceleration or attosecond science. Here, we implement a technique for the full characterization of structured time-dependent polarization light waveforms with spatiotemporal resolution, using a compact twofold spectral interferometer, based on in-line bulk interferometry and fibre-optic coupler assisted interferometry. We measure structured infrared femtosecond vector beams, including radially polarized beams and complex-shaped beams exhibiting both temporal and spatial evolving polarization. Our measurements confirm that light waveforms with polarization evolving at the micrometer and femtosecond scales can be achieved through the use of structured waveplates and polarization gates. This new scale of measurement achieved will open the way to predict, check and optimize applications of structured vector beams at the femtosecond and micrometer scales.

Modeling the orbital motion of Sgr A*’s near-infrared flares

Infrared observations of Sgr A* probe the region close to the event horizon of the black hole at the Galactic center. These observations can constrain the properties of low-luminosity accretion as well as that of the black hole itself. The GRAVITY instrument at the ESO VLTI has recently detected continuous circular relativistic motion during infrared flares which has been interpreted as orbital motion near the event horizon. Here we analyze the astrometric data from these flares, taking into account the effects of out-of-plane motion and orbital shear of material near the event horizon of the black hole. We have developed a new code to predict astrometric motion and flux variability from compact emission regions following particle orbits. Our code combines semi-analytic calculations of timelike geodesics that allow for out-of-plane or elliptical motions with ray tracing of photon trajectories to compute time-dependent images and light curves. We apply our code to the three flares observed with GRAVITY in 2018. We show that all flares are consistent with a hotspot orbiting at R ∼ 9 gravitational radii with an inclination of i ∼ 140°. The emitting region must be compact and less than ∼5 gravitational radii in diameter. We place a further limit on the out-of-plane motion during the flare.

Mechanism of Dissociation Kinetics in Polyelectrolyte Complex Micelles

Polyelectrolyte-based nanoscale self-assemblies, such as micelles, possess diverse desirable attributes such as the capability for sequestering and protecting biomacromolecules against inhospitable environments, responsiveness to external stimuli, and tunability of physical behavior. However, little is known on the mechanisms of dissociation when micelles encounter and respond to environmental changes. Using salt-jump, time-dependent light scattering, the pathway of dissociation is observed in polyelectrolyte complex micelles that have complex cores and neutral coronas. The micelle dissociation kinetics appear to be a three-stage process, in good agreement with the scattering data. Using kinetic models of amphiphilic block copolymer micelles in polyelectrolyte complexation-driven micelles, we derive an analytical expression for dissociation relaxation rates as a function of solvent temperature, salt concentration, and the length of the charged polymer blocks. The theoretical predictions are compatible with the experimental data from light scattering experiments. This study experimentally demonstrates the relaxation kinetics of polyelectrolyte complex micelle dissociation and illustrates the underlying mechanism governing the dissociation kinetics. It is anticipated that these findings can be generalized to other electrostatic interaction-driven self-assemblies to better understand the relationship among the kinetics of dissociation, constituent polymer properties, and environmental parameters.

Floquet engineering of optical lattices with spatial features and periodicity below the diffraction limit

Floquet engineering or coherent time-periodic driving of quantum systems has been successfully used to synthesize Hamiltonians with novel properties. In ultracold atomic systems, this has led to experimental realizations of artificial gauge fields, topological bandstructures, and observation of dynamical localization, to name a few. Here we present a Floquet-based framework to stroboscopically engineer Hamiltonians with spatial features and periodicity below the diffraction limit of light used to create them by time-averaging over various configurations of a 1D optical Kronig–Penney (KP) lattice. The KP potential is a lattice of narrow subwavelength barriers spaced by half the optical wavelength (λ/2) and arises from the nonlinear optical response of the atomic dark state. Stroboscopic control over the strength and position of this lattice requires time-dependent adiabatic manipulation of the dark-state spin composition. We investigate adiabaticity requirements and shape our time-dependent light fields to respect the requirements. We apply this framework to show that a λ/4-spaced lattice can be synthesized using realistic experimental parameters as an example, discuss mechanisms that limit lifetimes in these lattices, explore candidate systems and their limitations, and treat adiabatic loading into the ground band of these lattices.

Enhanced continuous generation of non-Gaussianity through optomechanical modulation

We study the non-Gaussian character of quantum optomechanical systems evolving under the fully nonlinear optomechanical Hamiltonian. By using a measure of non-Gaussianity based on the relative entropy of an initially Gaussian state, we quantify the amount of non-Gaussianity induced by both a constant and time-dependent cubic light–matter coupling and study its general and asymptotic behaviour. We find analytical approximate expressions for the measure of non-Gaussianity and show that initial thermal phonon occupation of the mechanical element does not significantly impact the non-Gaussianity. More importantly, we also show that it is possible to continuously increase the amount of non-Gassuianity of the state by driving the light–matter coupling at the frequency of mechanical resonance, suggesting a viable mechanism for increasing the non-Gaussianity of optomechanical systems even in the presence of noise.

Cellular Responses of the Lichen Circinaria gyrosa in Mars-Like Conditions.

Lichens are extremely resistant organisms that colonize harsh climatic areas, some of them defined as “Mars-analog sites.” There still remain many unsolved questions as to how lichens survive under such extreme conditions. Several studies have been performed to test the resistance of various lichen species under space and in simulated Mars-like conditions. The results led to the proposal that Circinaria gyrosa (Lecanoromycetes, Ascomycota) is one of the most durable astrobiological model lichens. However, although C. gyrosa has been exposed to Mars-like environmental conditions while in a latent state, it has not been exposed in its physiologically active mode. We hypothesize that the astrobiological test system “Circinaria gyrosa,” could be able to be physiologically active and to survive under Mars-like conditions in a simulation chamber, based on previous studies performed at dessicated-dormant stage under simulated Mars-like conditions, that showed a complete recover of the PSII activity (Sánchez et al., 2012). Epifluorescence and confocal laser scanning microscopy (CLSM) showed that living algal cells were more abundant in samples exposed to niche conditions, which simulated the conditions in micro-fissures and micro-caves close to the surface that have limited scattered or time-dependent light exposure, than in samples exposed to full UV radiation. The medulla was not structurally affected, suggesting that the niche exposure conditions did not disturb the lichen thalli structure and morphology as revealed by field emission scanning electron microscopy (FESEM). In addition, changes in the lichen thalli chemical composition were determined by analytical pyrolysis. The chromatograms resulting from analytical pyrolysis at 500°C revealed that lichen samples exposed to niche conditions and full UV radiation consisted primarily of glycosidic compounds, lipids, and sterols, which are typical constituents of the cell walls. However, specific differences could be detected and used as markers of the UV-induced damage to the lichen membranes. Based on its viability responses after rehydration, our study shows that the test lichen survived the 30-day incubation in the Mars chamber particularly under niche conditions. However, the photobiont was not able to photosynthesize under the Mars-like conditions, which indicates that the surface of Mars is not a habitable place for C. gyrosa.

Investigating light curve modulation via kernel smoothing

Context.Recent studies have revealed a hitherto unknown complexity of Cepheid pulsations by discovering irregular modulated variability using photometry, radial velocities, and interferometry.Aims.We aim to perform a statistically rigorous search and characterization of such phenomena in continuous time, applying it to 53 classical Cepheids from the OGLE-III catalog.Methods.We have used local kernel regression to search for both period and amplitude modulations simultaneously in continuous time and to investigate their detectability. We determined confidence intervals using parametric and non-parametric bootstrap sampling to estimate significance, and investigated multi-periodicity using a modified pre-whitening approach that relies on time-dependent light curve parameters.Results.We find a wide variety of period and amplitude modulations and confirm that first overtone pulsators are less stable than fundamental mode Cepheids. Significant temporal variations in period are more frequently detected than those in amplitude. We find a range of modulation intensities, suggesting that both amplitude and period modulations are ubiquitous among Cepheids. Over the 12-year baseline offered by OGLE-III, we find that period changes are often nonlinear, sometimes cyclic, suggesting physical origins beyond secular evolution. Our method detects modulations (period and amplitude) more efficiently than conventional methods that are reliant on certain features in the Fourier spectrum, and pre-whitens time series more accurately than using constant light curve parameters, removing spurious secondary peaks effectively.Conclusions.Period and amplitude modulations appear to be ubiquitous among Cepheids. Current detectability is limited by observational cadence and photometric precision: detection of amplitude modulation below 3 mmag requires space-based facilities. Recent and ongoing space missions (K2, BRITE, MOST, CoRoT) as well as upcoming ones (TESS, PLATO) will significantly improve detectability of fast modulations, such as cycle-to-cycle variations, by providing high-cadence high-precision photometry. High-quality long-term ground-based photometric time series will remain crucial to study longer-term modulations and to disentangle random fluctuations from secular evolution.

Lead iodide as a buffer layer in UV-induced degradation of CH3NH3PbI3 films

Encapsulated CH3NH3PbI3 films, the 'work horse' of the organic–inorganic perovskite-based photovoltaics, grown by one step- and two step- deposition methods, were used to study the effect of the film preparation method on their photostability. Time dependent light absorption decay under exposure to concentrated sunlight was used to estimate the degradation of the films. Films deposited by one step showed a significant decrease in the CH3NH3PbI3 absorbance when illuminated through the substrate, while films obtained through two step deposition exhibited almost no photodegradation under similar sunlight exposure. On the other hand, both types of films degraded significantly when irradiated through the top encapsulation. Unreacted PbI2 present near the substrate is suggested to be responsible for enhancing the photostability of the films obtained by two step deposition. Here, remnant PbI2 works as a UV filter and reduces UV light-induced degradation. The results demonstrate the significance of the preparation method in determining photochemical stability of the perovskite films, due to favorable property of remnant PbI2 in the absorber as a UV-protective layer.

Time-dependent scattering of incident light of various wavelengths in ferrofluids under external magnetic field

Ferrofluids can exhibit the anisotropic thermodynamic properties under magnetic fields. The dynamic optical properties of ferrofluids in the presence of magnetic fields are of particular interest due to their potential application as various optical devices. Although time-dependent light scattering by ferrofluids have been extensively studied, the effect of wavelength of incident light have been rarely considered. Here, for the first time, we investigated both the time- and wavelength-dependent light scattering in water based ferrofluids containing Fe3O4 nanoparticles under an external magnetic field. The field-induced response behavior of the prepared ferrofluid samples was determined and verified first by thermal conductivity measurement and numerical simulation. Double-beam UV–Vis spectrophotometer was employed to record the temporal evolution of transmitted intensity of incident light of various wavelengths passing through the ferrofluid sample and propagating parallel to the applied field. As expected, the light intensity decreases to a certain value right after the field is turned on due to the thermal fluctuation induced disorder inside the flexible particle chains. Then the light intensity further decreases with time until the appearance of a minimum at time τ0 followed by an inversed increase before finally reaches equilibrium at a particular time. More importantly, the characteristic inversion time τ0 was found to follow a power law increase with the wavelength of incident light (τ0∼λα, where α=2.07). A quantitative explanation for the wavelength dependence of characteristic time was proposed based on the finite-difference time-domain (FDTD) method. The simulation results are in good agreement with our experimental observations. The time-dependent light scattering in ferrofluids under different incident wavelengths was rationalized by considering both the coarsening process of the particle chains and the occurrence of resonance within the magnetic scatterers. Our finding should be of value for the development of various light-tunable optical devices.

Estimating significance in observations of variable and transient gamma-ray sources

The standard method for estimating the statistical significance of a gamma-ray source detection is that introduced by Li & Ma (1983), Eq. (17). In observing sources with time-dependent light curves, one can improve on this method by including approximate a priori knowledge of the source temporal behavior. A maximum-likelihood-based approach is suggested that provides an improvement in sensitivity with respect to the Li & Ma technique. The method is demonstrated by applying it to Monte Carlo simulations of gamma-ray burst observations with parameters chosen to reproduce the performance of current generation imaging air Cherenkov telescopes (IACTs). One particular example of a simulated burst observation near the current-generation IACT detection threshold results in a sensitivity improvement of approximately 25% . It is also shown that this method can work with highly variable light curves without much computational complexity, and that the sensitivity gain is robust against uncertainties in the a priori-defined light curve.