Light In Medium Research Articles

Mode-Symmetry-Assisted Optical Pulling by Bound States in the Continuum.

Aside from optical pushing and trapping that have been implemented successfully, the transportation of objects backward to the source by the optical pulling forces (OPFs) has attracted tremendous attention, which was usually achieved by increasing the forward momentum of light. However, the limited momentum transfer between light and object greatly constrains the amplitudes of OPFs. Here, we present a mechanism to generate strong interactions between object and background through the bound states in the continuums, which can generate large OPFs without increasing the forward momentum of light. The underlying physics is the extraction of momentum from the designed background lattice units assisted by mode symmetry. This work paves the way for extraordinary optical manipulations and shows great potential for exploring the momenta of light in media.

Fermat Principle, Ramsey Theory and Metamaterials.

Reinterpretation of the Fermat principle governing the propagation of light in media within the Ramsey theory is suggested. Complete bi-colored graphs corresponding to light propagation in media are considered. The vertices of the graphs correspond to the points in real physical space in which the light sources or sensors are placed. Red links in the graphs correspond to the actual optical paths, emerging from the Fermat principle. A variety of optical events, such as refraction and reflection, may be involved in light propagation. Green links, in turn, denote the trial/virtual optical paths, which actually do not occur. The Ramsey theorem states that within the graph containing six points, inevitably, the actual or virtual optical cycle will be present. The implementation of the Ramsey theorem with regard to light propagation in metamaterials is discussed. The Fermat principle states that in metamaterials, a light ray, in going from point S to point P, must traverse an optical path length L that is stationary with respect to variations of this path. Thus, bi-colored graphs consisting of links corresponding to maxima or minima of the optical paths become possible. The graphs, comprising six vertices, will inevitably demonstrate optical cycles consisting of the mono-colored links corresponding to the maxima or minima of the optical path. The notion of the "inverse graph" is introduced and discussed. The total number of triangles in the "direct" (source) and "inverse" Ramsey optical graphs is the same. The applications of "Ramsey optics" are discussed, and an optical interpretation of the infinite Ramsey theorem is suggested.

A Numerical Code for a Wide Range of Compressible Flows on Hybrid Computational Architectures

The major points in the development of the parallel multiplatform multipurpose numerical code solving the full unsteady Navier–Stokes equations are presented. The developed code is primarily designed for running on multi-GPU computational devices but can also be used on traditional multicore CPUs and even on manycore processors such as Intel Xeon Phi. Physical models include calorically perfect inert gas, single- and multi-temperature approaches for chemically reactive flows and an Euler–Euler model for gas-particle suspensions. Main details of the implementation are described. Shock capturing TVD and WENO schemes in general curvilinear coordinates are used for spatial approximation. Explicit, semi-implicit and fully implicit schemes are employed for advancing solution in time. The code is written in C++ with CUDA API and opensource libraries, such as MPI, zlib and VTK. A few examples of numerical simulations are briefly described to provide general idea of the numerical code capabilities. They include a supersonic flow past a wedge, a jet exhausting from a square nozzle, a heavy gas bubble descending in a lighter medium and a heterogeneous detonation in gas-particle suspension.

Consumption of Galactose by Trypanosoma cruzi Epimastigotes Generates Resistance against Oxidative Stress.

In this study, we demonstrate that Trypanosoma cruzi epimastigotes previously grown in LIT medium supplemented with 20 mM galactose and exposed to sub-lethal concentrations of hydrogen peroxide (100 μM) showed two-fold and five-fold viability when compared to epimastigotes grown in LIT medium supplemented with two different glucose concentrations (20 mM and 1.5 mM), respectively. Similar results were obtained when exposing epimastigotes from all treatments to methylene blue 30 μM. Additionally, through differential centrifugation and the selective permeabilization of cellular membranes with digitonin, we found that phosphoglucomutase activity (a key enzyme in galactose metabolism) occurs predominantly within the cytosolic compartment. Furthermore, after partially permeabilizing epimastigotes with digitonin (0.025 mg × mg−1 of protein), intact glycosomes treated with 20 mM galactose released a higher hexose phosphate concentration to the cytosol in the form of glucose-1-phosphate, when compared to intact glycosomes treated with 20 mM glucose, which predominantly released glucose-6-phosphate. These results shine a light on T. cruzi’s galactose metabolism and its interplay with mechanisms that enable resistance to oxidative stress.

Effects of Nitrogen and Light Intensity on the Astaxanthin Accumulation in Motile Cells of Haematococcus pluvialis

The dietary supplementation of Haematococcus pluvialis is a natural, safe, and sustainable method for fish pigmentation. However, astaxanthin-rich H. pluvialis cysts have a poor effect in pigmenting salmonid flesh due to their rigid and thick cell wall. H. pluvialis thin-walled motile cells have recently attracted attention due to their potential advantages in maintaining compound stability, easy digestion, enhancing the bioavailability of carotenoids, and reducing production costs. This study aimed to investigate the effect of various nitrogen concentrations and light intensities on astaxanthin production in motile cells. We first investigated the effect of four different concentrations of nitrogen on astaxanthin accumulation in motile cells. According to the results, the motile cells had the highest astaxanthin concentration and content under the 0 N condition. Then, we compared the differences in astaxanthin production in motile cells under three different light intensities under 0 N conditions. The results showed that after four days of treatment, the protoplasts of the motile cells in the medium light (ML) group and the high light (HL) group had distinct granularity. The cell mortality rate in the HL group reached more than 15%, which was significantly higher than that in the low light (LL) and ML groups, indicating that high light intensity was not suitable for inducing motile cells to accumulate astaxanthin. There were no significant differences between the LL and ML groups in astaxanthin content, motile cells percentage, and cell mortality rate. Considering these indicators, we recommended inducing motile cells to produce astaxanthin under low light conditions because it is more economical in terms of electricity consumption. This study added to the knowledge that nitrogen and light affects the accumulation of astaxanthin in H. pluvialis motile cells. The results would help determine the optimal nitrogen and light conditions in astaxanthin production from motile cells.

Insights of antiparasitic activity of sodium diethyldithiocarbamate against different strains of Trypanosoma cruzi

Chagas disease is caused by Trypanosoma cruzi and affects thousands of people. Drugs currently used in therapy are toxic and have therapeutic limitations. In addition, the genetic diversity of T. cruzi represents an important variable and challenge in treatment. Sodium diethyldithiocarbamate (DETC) is a compound with pharmacological versatility acting as metal chelators and ROS generation. Thus, the objective was to characterize the antiparasitic action of DETC against different strains and forms of T. cruzi and their mechanism. The different strains of T. cruzi were grown in LIT medium. To evaluate the antiparasitic activity of DETC, epimastigote and trypomastigote forms of T. cruzi were used by resazurin reduction methods and by counting. Different response patterns were obtained between the strains and an IC50 of DETC ranging from 9.44 ± 3,181 to 60.49 ± 7.62 µM. Cell cytotoxicity against 3T3 and RAW cell lines and evaluated by MTT, demonstrated that DETC in high concentration (2222.00 µM) presents low toxicity. Yet, DETC causes mitochondrial damage in T. cruzi, as well as disruption in parasite membrane. DETC has antiparasitic activity against different genotypes and forms of T. cruzi, therefore, representing a promising molecule as a drug for the treatment of Chagas disease.

New Theory of Light and Resolution of the Abraham-Minkowski Controversy

The Abraham-Minkowski controversy about the momentum of light in media has been debated for over a century and has been informed by many distinguished distributions, both theoretical and experimental. We show that both the Abraham and Minkowski forms of momentum are need to be modified according to the new theory of light. We prove that the total momentum of a photon in matter is the same as compared with that in free space by using the new relations between energy and mass of light with refractive index.

Regulation of photosystem I-light-harvesting complex I from a red alga Cyanidioschyzon merolae in response to light intensities.

Photosynthetic organisms use different means to regulate their photosynthetic activity in respond to different light conditions under which they grow. In this study, we analyzed changes in the photosystem I (PSI) light-harvesting complex I (LHCI) supercomplex from a red alga Cyanidioschyzon merolae, upon growing under three different light intensities, low light (LL), medium light (ML), and high light (HL). The results showed that the red algal PSI-LHCI is separated into two bands on blue-native PAGE, which are designated PSI-LHCI-A and PSI-LHCI-B, respectively, from cells grown under LL and ML. The former has a higher molecular weight and binds more Lhcr subunits than the latter. They are considered to correspond to the two types of PSI-LHCI identified by cryo-electron microscopic analysis recently, namely, the former with five Lhcrs and the latter with three Lhcrs. The amount of PSI-LHCI-A is higher in the LL-grown cells than that in the ML-grown cells. In the HL-grown cells, PSI-LHCI-A completely disappeared and only PSI-LHCI-B was observed. Furthermore, PSI core complexes without Lhcr attached also appeared in the HL cells. Fluorescence decay kinetics measurement showed that Lhcrs are functionally connected with the PSI core in both PSI-LHCI-A and PSI-LHCI-B obtained from LL and ML cells; however, Lhcrs in the PSI-LHCI-B fraction from the HL cells are not coupled with the PSI core. These results indicate that the red algal PSI not only regulates its antenna size but also adjusts the functional connection of Lhcrs with the PSI core in response to different light intensities.

Expansion of the strongly interacting superfluid Fermi gas: Symmetries and self-similar regimes

We consider an expansion of the strongly interacting superfluid Fermi gas in a vacuum, assuming absence of the trapping potential, in the so-called unitary regime (see, for instance, \cite{pitaevskii2008superfluid}) when the chemical potential $\mu \propto \hbar^2n^{2/3}/m$ where $n$ is the density of the Bose-Einstein condensate of Cooper pairs of fermionic atoms. In low temperatures, $T\to 0$, such expansion can be described in the framework of the Gross-Pitaevskii equation (GPE). Because of the chemical potential dependence on the density, $\sim n^{2/3}$, the GPE has additional symmetries, resulting in the existence of the virial theorem \cite% {vlasov1971averaged}, connecting the mean size of the gas cloud and its Hamiltonian. It leads asymptotically at $t\to\infty$ to the gas cloud expansion, linearly growing in time. We study such asymptotics, and reveal the perfect match between the quasi-classical self-similar solution and the asymptotic expansion of the non-interacting gas. This match is governed by the virial theorem, derived through utilizing the Talanov transformation \cite{talanov1970focusing}, which was first obtained for the stationary self-focusing of light in media with a cubic nonlinearity due to the Kerr effect. In the quasi-classical limit, the equations of motion coincide with 3D hydrodynamics for the perfect monoatomic gas with $\gamma=5/3$. Their self-similar solution describes, on the background of the gas expansion, the angular deformities of the gas shape in the framework of the Ermakov--Ray--Reid type system.

Two layer graphene heterostructures for waves slowing down: operator approach to waveguide problem

Slowing down the phase velocity of light in media has various applications. The generation of electromagnetic radiation using coherent Cherenkov mechanism is among them. Meanwhile, there is a need for compact terahertz radiation sources. Due to outstanding graphene properties, heterostructures consisting of alternating graphene/dielectric layers can operate as a medium for the generation of terahertz radiation. In the present paper, the slowing down and propagation coefficients for the modes supported in a two-layer graphene structure are studied. The study is conducted by means of the operator approach to wave propagation in stratified structures. The operator approach allows one to use coordinates-free notations and to consider consequently arbitrarily complex heterostructures (including anisotropic layers, for instance). The influence of interlayer distance and the value of graphene chemical potential on waves slowdown is determined. The obtained results open up prospects for creating a new type of terahertz radiation sources.

Comprehensive effects of exogenous salicylic acid and light on chlorophyll fluorescence parameters and photosynthetic oxygen evolution in Ulva prolifera

Ulva prolifera is one of the causative species of green tides. Salicylic acid (SA) alleviated the high-temperature damage by up-regulating a portion of antioxidant-related proteins, however, little is understood regarding the impacts of SA under high light in this species. In order to study the regulation effects of SA on U. prolifera under different light conditions, we grew this species under three SA concentrations (0, 2.5, 5.0 µg mL-1) and three light levels [high light (HL): 400 μmol(photon) m-2 s-1, medium light (ML): 160 μmol(photon) m-2 s-1, and low light (LL): 70 μmol(photon) m-2 s-1]. After 3 d, the growth, chlorophyll fluorescence parameters, photosynthetic oxygen rate production, and superoxide dismutase (SOD) activity of U. prolifera were investigated. We found that: (1) The relative growth rate (RGR) of U. prolifera increased with the increase of light, no matter if with or without SA; under the three light levels, the highest RGR was observed in the presence of 2.5 µg(SA) mL-1. (2) U. prolifera grown under HL conditions showed the highest values in nonphotochemical quenching and total content of cartenoids. (3) Under three light levels, the dark respiration rate, the net, maximal, and gross photosynthetic oxygen rate significantly decreased by SA. (4) The highest value of SOD activity was observed under LL in the presence of SA (5.0 µg mL-1). In conclusion, the effects of light on the physiology in U. prolifera could be mediated by SA in a concentration-dependent manner.

Utilization of proliferable extracellular amastigotes for transient gene expression, drug sensitivity assay, and CRISPR/Cas9-mediated gene knockout in Trypanosoma cruzi.

Trypanosoma cruzi has three distinct life cycle stages; epimastigote, trypomastigote, and amastigote. Amastigote is the replication stage in host mammalian cells, hence this stage of parasite has clinical significance in drug development research. Presence of extracellular amastigotes (EA) and their infection capability have been known for some decades. Here, we demonstrate that EA can be utilized as an axenic culture to aid in stage-specific study of T. cruzi. Amastigote-like property of axenic amastigote can be sustained in LIT medium at 37°C at least for 1 week, judging from their morphology, amastigote-specific UTR-regulated GFP expression, and stage-specific expression of selected endogenous genes. Inhibitory effect of benznidazole and nifurtimox on axenic amastigotes was comparable to that on intracellular amastigotes. Exogenous nucleic acids can be transfected into EA via conventional electroporation, and selective marker could be utilized for enrichment of transfectants. We also demonstrate that CRISPR/Cas9-mediated gene knockout can be performed in EA. Essentiality of the target gene can be evaluated by the growth capability of the knockout EA, either by continuation of axenic culturing or by host infection and following replication as intracellular amastigotes. By taking advantage of the accessibility and sturdiness of EA, we can potentially expand our experimental freedom in studying amastigote stage of T. cruzi.

Phase control algorithms and filamentation of ultrashort laser pulses in a scattering medium

The scattering nature of biological systems restricts the non-linear propagation of coherent light in media of biological interest. Using a spatial phase shaping technique, we optimize the filamentation of femtosecond laser pulses in an ethanol solution containing a fluorescent dye, while the laser beam has first traveled through 1 cm of scattering aqueous solution. Following three-photon absorption process, the fluorescence signal of the Coumarin 440 dye is used as a control parameter by genetic and partitioning algorithms. Applied to the incident wavefront, the partitioning algorithm successfully enhances the dye fluorescence signal in a medium with a scattering coefficient ( $$\mu _{\text {s}}$$ ) varying from 1.24 to $$3.71\hbox { cm}^{-1}$$ and gives rise to the production of a single laser filament several millimeters inside the observation cell that contains an ethanol solution. Interestingly, the optimal enhancement for the highest scattering medium is obtained with the partitioning algorithm at the lowest resolution. On the other hand, no significant enhancement is obtained when applying the genetic algorithm.

Coherent multiple scattering of light in ( 2+1 ) dimensions

We formulate a multiple scattering theory of light in media spatially disordered along two directions and homogeneous along the third one, without making any paraxial approximation on the wave equation and fully treating the vector character of light. With this formalism, we calculate the distribution of transverse momenta of a beam as it evolves along the optical axis, and unveil a phenomenon not captured by the paraxial equation: a cross-over from a scalar to a vector regime, visible in the coherent backscattering peak as polarization gets randomized.

Covariant kinematics of light in media and a generalized Raychaudhuri equation

There is ongoing interest in adopting various tools and ideas from general relativity for optical applications and the study of light propagation through natural or engineered media. Here, the covariant kinematics of light propagating through arbitrary dielectric media in curved space-times are derived, allowing for analysis and tracing of congruences of light through media that may smoothly vary in character between vacuum, positively refracting, and negatively refracting; or null, timelike, and spacelike with respect to the background metric. The kinematics are then used to generalize the Raychaudhuri equation -- an important tool in general relativity that describes the focus of a congruence. These results will be useful for the analysis of optical devices, particularly those designed using transformation optics, and serve as theoretical tools to study generalized concepts in general relativity.

Molecular detection of Trypanosoma cruzi in acai pulp and sugarcane juice

Chagas disease, caused by Trypanosoma cruzi affects about 6–8 million people worldwide. Although transmission by triatomine insects has been controlled, other means of transmission maintain the infection. These forms of transmission are responsible for introducing Chagas disease in other non-endemic countries of the world. Thus, Chagas disease, nowadays is a worldwide health problem. In Brazil, acai pulp and sugarcane juice have been associated with Chagas disease outbreaks. The difficulties in isolation of the parasite from foods are hampering source tracking which could allow the confirmation of an implicated food commodity in these outbreak investigations. To address this scientific gap, we evaluated the performance of real-time PCR (qPCR) for detecting T. cruzi in acai pulp and sugarcane juice. All experiments were performed with acai pulp and sugarcane juice samples contaminated with different concentrations of T. cruzi. In assays with qPCR, the results showed that the ideal procedure for T. cruzi identification in acai pulp and sugarcane juice consisted of: i. centrifugation; ii. DNA extraction with a commercial kit for stool matrix; and iii. qPCR using a specific molecular marker for T. cruzi. The seeding in LIT medium of experimentally contaminated foods was effective in detecting the parasitic load by qPCR. The efficacy of qPCR was also verified testing food samples crushed with infected Triatomines. In conclusion, this methodology can be used to perform rapid diagnosis in outbreaks, facilitating measures in disease control.

Subcellular localization of glycolytic enzymes and characterization of intermediary metabolism of Trypanosoma rangeli

Trypanosoma rangeli is a hemoflagellate protist that infects wild and domestic mammals as well as humans in Central and South America. Although this parasite is not pathogenic for human, it is being studied because it shares with Trypanosoma cruzi, the etiological agent of Chagas' disease, biological characteristics, geographic distribution, vectors and vertebrate hosts. Several metabolic studies have been performed with T. cruzi epimastigotes, however little is known about the metabolism of T. rangeli. In this work we present the subcellular distribution of the T. rangeli enzymes responsible for the conversion of glucose to pyruvate, as determined by epifluorescense immunomicroscopy and subcellular fractionation involving either selective membrane permeabilization with digitonin or differential and isopycnic centrifugation. We found that in T. rangeli epimastigotes the first six enzymes of the glycolytic pathway, involved in the conversion of glucose to 1,3-bisphosphoglycerate are located within glycosomes, while the last four steps occur in the cytosol. In contrast with T. cruzi, where three isoenzymes (one cytosolic and two glycosomal) of phosphoglycerate kinase are expressed simultaneously, only one enzyme with this activity is detected in T. rangeli epimastigotes, in the cytosol. Consistent with this latter result, we found enzymes involved in auxiliary pathways to glycolysis needed to maintain adenine nucleotide and redox balances within glycosomes such as phosphoenolpyruvate carboxykinase, malate dehydrogenase, fumarate reductase, pyruvate phosphate dikinase and glycerol-3-phosphate dehydrogenase. Glucokinase, galactokinase and the first enzyme of the pentose-phosphate pathway, glucose-6-phosphate dehydrogenase, were also located inside glycosomes. Furthermore, we demonstrate that T. rangeli epimastigotes growing in LIT medium only consume glucose and do not excrete ammonium; moreover, they are unable to survive in partially-depleted glucose medium. The velocity of glucose consumption is about 40% higher than that of procyclic Trypanosoma brucei, and four times faster than by T. cruzi epimastigotes under the same culture conditions.

Robust iterative method for nonlinear Helmholtz equation

A new iterative method is developed for solving the two-dimensional nonlinear Helmholtz equation which governs polarized light in media with the optical Kerr nonlinearity. In the strongly nonlinear regime, the nonlinear Helmholtz equation could have multiple solutions related to phenomena such as optical bistability and symmetry breaking. The new method exhibits a much more robust convergence behavior than existing iterative methods, such as frozen-nonlinearity iteration, Newton's method and damped Newton's method, and it can be used to find solutions when good initial guesses are unavailable. Numerical results are presented for the scattering of light by a nonlinear circular cylinder based on the exact nonlocal boundary condition and a pseudospectral method in the polar coordinate system.

Particle size and roasting on water sorption in conilon coffee during storage

The aim of this work was to evaluate alterations on the water sorption of coffee due to the effect of roast, grind and storage in two temperatures (10 and 30 oC) during 180 days. Crude grain coffee (Coffea canephora) with average initial moisture content of 12.61 % (d.b.) was used. Grain was roasted at two levels: medium light (ML) and moderately dark (MD). Afterwards, grain was processed in three different particle sizes: fine (0.59 mm), medium (0.84 mm) and coarse (1.19 mm), besides the whole coffee lot. Samples prepared were then stored in two temperatures (10 and 30 oC). These were analyzed during six months, at five distinct times (0, 30, 60, 120 and 180 days) regarding moisture content and water activity. Furthermore, mathematical modeling and thermodynamic properties acquisition of the coffee moisture adsorption process were accomplished. A split plot design was used, in which plots consisted of storage period and split-plots consisted of a 2 x 4 x 2 factorial (two roasting degrees, four particle sizes and two storage temperatures), with five repetitions.It was concluded thatparticle size did not significantly affectedmoisture content of coffee, independently of roast degree; Sigma-Copace model best represented hygroscopic equilibrium for sorption of roasted coffee; with moisture content reduction, an increase of differential enthalpy and entropy of sorption and Gibbs free energy occurs.

Study on 3-inch Hamamatsu photomultipliers

Several kinds of photomultipliers are widely used in astroparticle physics detectors to measure Cherenkov light in media like water or ice. In neutrino telescopes the key element of the detector is the optical module, which consists of one or more photodetectors inside a transparent pressure-resistant glass sphere. It serves as mechanical protection while ensuring good light transmission. The KM3NeT collaboration has developed an innovative design of an optical module composed by 31 photomultipliers (PMTs) of 3-inch diameter housed in a 17-inch glass shpere. The performance of the telescope is largely dependent on the presence on noise pulses present on the anode of the photomultipliers. A study was conducted of noise pulses of Hamamatsu 3-inch diameter photomultipliers measuring time and charge distributions of dark pulses, pre-pulses, delayed pulses and after-pulses, focusing in particular on analysis on multiple afterpulses. Effects of the Earth's magnetic field on 3-inch PMTs were also studied.