Super-resolution imaging in live Caulobacter crescentus cells using photoswitchable EYFP

The commonly used, monomeric EYFP enabled imaging of intracellular protein structures beyond the optical resolution limit ('super-resolution' imaging) in living cells. By combining photoinduced activation of single EYFP fusions and time-lapse imaging, we obtained sub-40 nm resolution images of the filamentous superstructure of the bacterial actin protein MreB in live Caulobacter crescentus cells. These studies demonstrated that EYFP is a useful emitter for in vivo super-resolution imaging.     

Radiotoxicity of an 125I-labeled DNA intercalator in mammalian cells

To explore the effect of the Auger electron emitter 125I attached to a DNA intercalator, we have synthesized 125I- and 127I-labeled 3-acetamido-5-iodoproflavine (AIP) and have examined the uptake, intracellular distribution, and radiotoxicity of A125IP in Chinese hamster V79 cells. After incubation with AIP, the nuclei of V79 cells become fluorescent. Uptake of A125IP is directly proportional to its extracellular radioactive concentration and reaches a plateau at about 10 h. Of the cell-associated radioactivity, 60% is retained by the cells after extensive washing. When the survival of V79 cells is plotted as a function of radioactive cell content, the curve has no shoulder with a mean lethal dose (DN) of about 1.3 Gy to the cell nucleus. Because the DN of these cells when irradiated with 250 kVp X rays is 5.8 Gy, the relative biological effectiveness (RBE) of A125IP is about 4.5. The dependence of the RBE values on the localization of the Auger emitter is discussed on the basis of our extended studies on the same cell line.     

Boundary conditions on the plasma emitter surface in the presence of a particle counter flow: I. Ion emitter

Emission of positively charged ions from a plasma emitter irradiated by a counterpropagating electron beam is studied theoretically. A bipolar diode with a plasma emitter in which the ion temperature is lower than the electron temperature and the counter electron flow is extracted from the ion collector is calculated in the one-dimensional model. An analog of Bohm’s criterion for ion emission in the presence of a counterpropagating electron beam is derived. The limiting density of the counterpropagating beam in a bipolar diode operating in the space-charge-limited-emission regime is calculated. The full set of boundary conditions on the plasma emitter surface that are required for operation of the high-current optics module in numerical codes used to simulate charged particle sources is formulated.     

Investment in attending to cues and the evolution of amplifiers

Signals and cues are extensively used in social interactions across diverse communication systems. Here, we extend an existing theoretical framework to explore investment by emitters and perceivers in the fidelity with which cues and signals associated with the former are detected by the latter. Traits of the emitter that improve cue or signal fidelity without adding information are termed ‘amplifiers’. We assume that each party can invest in improving fidelity but that it is increasingly costly the more fidelity is improved. Our model predicts that evolution of amplifier traits of a pre‐existing cue occurs over a broader range of circumstances than evolution of signalling in situations where the emitter offered no pre‐existing cue to the perceiver. It further predicts that the greater the intrinsic informational value of a cue, the more likely it is that the perceiver (and not the emitter) will invest in the fidelity of detecting that cue. A consequence of this predicted asymmetry is that true communication with reciprocal adaptations in emitters and perceivers to improve signal fidelity is likely to occur predominantly for traits of intermediate reliability. The corollary is that uncertainty of the perceiver will then be a key feature of communication. Uncertainty can arise because perceivers misinterpret signals or do not perceive them correctly, but here we argue that uncertainty is more fundamentally at the root of communication because traits that are intrinsically highly informative will induce only the perceiver and not the emitter to invest in improved fidelity of perception of that trait.     

Pareto Optimal Spectrally Selective Emitters for Thermophotovoltaics via Weak Absorber Critical Coupling

Tailoring the emission spectra of a thermophotovoltaic (TPV) emitter away from that of a blackbody has the potential to minimize transmission and thermalization loss in a photovoltaic receiver. Selective TPV emitters can lead to solar energy conversion with efficiency greater than the Shockley–Queisser limit and can facilitate the generation of useful energy from waste heat. A new design is introduced to radically tune thermal emission that leverages the interplay between two resonant phenomena in simple planar nanostructures—absorption in weakly absorbing nanofilms and reflection in multilayer dielectric stacks. A virtual screening approach is employed to identify promising structures for a selective thermal emitter from a search space of millions, several of which approach the ideal values of a step‐function selective thermal emitter. One of these structures is experimentally fabricated and evaluated, which includes a weakly absorbing alloy with tailored optical properties fabricated by atomic layer deposition (ALD). The versatility of the design and fabrication approach result in an emitter with excellent spectral density (0.8 W cm^?2 sr^?1) and spectral efficiency (46.8%) at 1373 K. Future experimental challenges to a more accurate realization of the optimal structures calculated are also considered.     

Plant defence responses to volatile alert signals are population‐specific

Herbivore‐induced volatiles are widespread in plants. They can serve as alert signals that enable neighbouring leaves and plants to pre‐emptively increase defences and avoid herbivory damage. However, our understanding of the factors mediating volatile organic compound (VOC) signal interpretation by receiver plants and the degree to which multiple herbivores affect VOC signals is still limited. Here we investigated whether plant responses to damage‐induced VOC signals were population specific. As a secondary goal, we tested for interference in signal production or reception when plants were subjected to multiple types of herbivore damage. We factorially crossed the population sources of paired Phaseolus lunatus plants (same versus different population sources) with a mechanical damage treatment to one member of the pair (i.e. the VOC emitter, damaged versus control), and we measured herbivore damage to the other plant (the VOC receiver) in the field. Prior to the experiment, both emitter and receiver plants were naturally colonized by aphids, enabling us to test the hypothesis that damage from sap‐feeding herbivores interferes with VOC communication by including emitter and receiver aphid abundances as covariates in our analyses. One week after mechanical leaf damage, we removed all the emitter plants from the field and conducted fortnightly surveys of leaf herbivory. We found evidence that receiver plants responded using population‐specific ‘dialects’ where only receivers from the same source population as the damaged emitters suffered less leaf damage upon exposure to the volatile signals. We also found that the abundance of aphids on both emitter and receiver plants did not alter this volatile signalling during both production and reception despite well‐documented defence crosstalk within individual plants that are simultaneously attacked by multiple herbivores. Overall, these results show that plant communication is highly sensitive to genetic relatedness between emitter and receiver plants and that communication is resilient to herbivore co‐infestation.     

Are cancer risks associated with exposures to ionising radiation from internal emitters greater than those in the Japanese A-bomb survivors?

After ingestion or inhalation of radionuclides, internal organs of the human body will be exposed to ionising radiation. Current risk estimates of radiation-associated cancer from internal emitters are largely based on extrapolation of risk from high-dose externally exposed groups. Concerns have been expressed that extrapolated risk estimates from internal emitters are greatly underestimated, by factors of ten or more, thus implying a severe underestimation of the true risks. Therefore, data on cancer mortality and incidence in a number of groups who received exposure predominantly from internal emitters are examined and excess relative risks per Sv are compared with comparable (age at exposure, time since exposure, gender) matched subsets of the Japanese atomic bomb survivor cohort. Risks are examined separately for low LET and high LET internal emitters. There are eight studies informative for the effects of internal low LET radiation exposure and 12 studies informative for the effects of internal high LET radiation. For 11 of the 20 cancer endpoints (subgroups of particular study cohorts) examined in the low LET internal emitter studies, the best estimate of the excess relative risk is greater than the corresponding estimate in the Japanese atomic bomb survivors and for the other nine it is less. For four of these 20 studies, the relative risk is significantly (2-sided P < 0.05) different from that in the Japanese atomic bomb survivors, in three cases greater than the atomic bomb survivor relative risk and in one case less. Considering only those six low LET studies/endpoints with 100 or more deaths or cases, for four out of six studies/endpoints the internal emitter risk is greater than that in the Japanese atomic bomb survivors. For seven of the 24 cancer endpoints examined in the high LET internal emitter studies the best estimate of the ERR in the internal emitter study is greater than the corresponding estimate in the Japanese atomic bomb survivors and for the other 17 it is less. For six studies, the relative risk is significantly (2-sided P < 0.05) different from that in the Japanese atomic bomb survivors, in one case greater than the atomic bomb survivor relative risk and in five cases less. Considering only those eight high LET studies/endpoints with 100 or more deaths or cases, for five out of eight studies/endpoints the internal emitter risk is greater than that in the Japanese atomic bomb survivors. These results suggest that excess relative risks in the internal emitter studies do not appreciably differ from those in the Japanese atomic bomb survivors. However, there are substantial uncertainties in estimates of risks in the internal emitter studies, particularly in relation to lung cancer associated with radon daughter (alpha particle) exposure, so a measure of caution should be exercised in these conclusions.     

Analytic approximations for describing the interactionof charged particles with the emitter of a radioisotope current source

Approximate formulas for the modeling of the interaction of fast alpha particles and suprathermal electrons with solid-state plasmas of the emitter films in a secondary-electron-emission radioisotope current source are derived. The approximate formulas are used to estimate the characteristic interaction parameters, in particular, the effective stopping power of the composite material of the emitter, the ranges of alpha particles, the optimum thickness of the emitter, and the maximum possible number of binary current cells. The results obtained can be used to optimize the parameters of a prototype model of such a source and to analyze its current-voltage characteristic. They can also be applied in Monte Carlo modeling of the generation of suprathermal electrons by fast ion fluxes in a solid-state plasma and ion flux-induced fast nonequilibrium secondary electron emission from metallic and dielectric films.     

Identity of the emitter in the bacterial luciferase luminescence reaction: binding and fluorescence quantum yield studies of 5-decyl-4a-hydroxy-4a,5-dihydroriboflavin-5'-phosphate as a model

The excited state of 4a-hydroxy-4a,5-dihydroFMN has been postulated to be the emitter in the bacterial bioluminescence reaction. However, while the bioluminescence quantum yield of the luciferase emitter is about 0.16, chemiluminescence and fluorescence quantum yields of earlier flavin models mimicking the luciferase emitter were no more than 10(-5). To further examine the proposed chemical identity of the luciferase emitter, 5-decyl-4a-hydroxy-4a,5-dihydroFMN was prepared as a new flavin model. Both the wild-type Vibrio harveyi luciferase and a catalytically active alphaC106A mutant formed complexes with the flavin model at a 1:1 molar ratio with K(d) values at 2.4 and 1.2 microM, respectively. This flavin model inhibited the activity of both luciferases, suggesting that it was bound to the enzyme active center. While the free flavin model was itself only very weakly fluorescent, its binding to either luciferase species resulted in markedly enhanced fluorescence, peaking at 440 nm. The fluorescence quantum yields of 5-decyl-4a-hydroxy-4a,5-dihydroFMN bound to wild-type and alphaC106A luciferases were 0.08 and 0.05, respectively, which are about 50% of the respective emitter bioluminescence quantum yields of these two luciferases. The present findings clearly demonstrated that the luciferase active site was suitable for marked enhancement of fluorescence of 4a-hydroxyflavin and, hence, provides a strong support to the proposed identity of 4a-hydroxy-4a,5-dihydroFMN, in its exited state, as the luciferase emitter.     

Emission current formation in plasma electron emitters

A model of the plasma electron emitter is considered, in which the current redistribution over electrodes of the emitter gas-discharge structure and weak electric field formation in plasma are taken into account as functions of the emission current. The calculated and experimental dependences of the switching parameters, extraction efficiency, and strength of the electric field in plasma on the accelerating voltage and geometrical sizes of the emission channel are presented.     

Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.     

Nitrification inhibition in drip irrigation systems

The water flow pattern and distribution in drip irrigated soil are different than those for conventional irrigation systems, to an extent that could drastically effect reactions of nutrient ions in the soil.Ammonium applied through the irrigation system was not nitrified in the saturated zone below the emitter. Nitrification occurred in the unsaturated zone surrounding the central cylinder. Nitrate levels and number of nitrifying bacteria are low below the emitter and higher father away.The residual nitrogen in the soil was found to be higher than that found for conventional irrigation plots. It does seem that application of ammonical fertilizer through a drip irrigation system is potentially a controlled release fertilizer system.     

Wavelength-shifting molecular beacons

We describe wavelength-shifting molecular beacons, which are nucleic acid hybridization probes that fluoresce in a variety of different colors, yet are excited by a common monochromatic light source. The twin functions of absorption of energy from the excitation light and emission of that energy in the form of fluorescent light are assigned to two separate fluorophores in the same probe. These probes contain a harvester fluorophore that absorbs strongly in the wavelength range of the monochromatic light source, an emitter fluorophore of the desired emission color, and a nonfluorescent quencher. In the absence of complementary nucleic acid targets, the probes are dark, whereas in the presence of targets, they fluoresce-not in the emission range of the harvester fluorophore that absorbs the light, but rather in the emission range of the emitter fluorophore. This shift in emission spectrum is due to the transfer of the absorbed energy from the harvester fluorophore to the emitter fluorophore by fluorescence resonance energy transfer, and it only takes place in probes that are bound to targets. Wavelength-shifting molecular beacons are substantially brighter than conventional molecular beacons that contain a fluorophore that cannot efficiently absorb energy from the available monochromatic light source. We describe the spectral characteristics of wavelength-shifting molecular beacons, and we demonstrate how their use improves and simplifies multiplex genetic analyses.     

Photoluminescence Quenching in Quantum Emitter,Metallic Nanoparticle,and Graphene Hybrids

We have developed a theory for photoluminescence quenching and plasmonic properties in hybrid nanosystems made from three nanosystems such as a quantum emitters, metallic nanoparticles, and graphene. The metallic nanoparticles and graphene have surface plasmons which couple with probe photons and create surface plasmon polaritons. Therefore, the excitons in the quantum emitters interact with surface plasmon polaritons via the dipole-dipole interaction. Due to this interaction, energy is exchanged between the nanosystems. The second quantized formulation and the quantum density matrix method have been used to calculate photoluminescence and the radiative and non-radiative decay processes in the presence of dipole-dipole interaction. We have compared our theory with experiments of two and three nanosystems, and a good agreement between theory and experiments is achieved. It has been found that the photoluminescence quenching in hybrid systems not only occurs through the direct non-radiative energy transfer from the quantum emitter to the metal nanoparticle and to graphene but also occurs through the indirect non-radiative energy transfer from quantum emitter to the metal nanoparticle via graphene and from the quantum emitter to graphene via metal nanoparticle. These are interesting findings and they can be used to fabricate nanoswitches and nanosensors for medical applications.     

Proposed mechanism for the bacterial bioluminescence reaction involving a dioxirane intermediate

We propose here a verifiable mechanism for the bacterial bioluminescence reaction involving a dioxirane intermediate. Participation of the dioxirane predicts either formation of an excited carbonyl, rather than the flavin, as the primary excited state in the reaction, or, through a CIEEL mechanism, the C4a hydroxyflavin or the chromophore of a secondary emitter protein could become excited. We propose energy transfer from the primary excited state to the C4a hydroxyflavin in the absence of the lumazine protein or the yellow fluorescence protein, while in the presence of either of the secondary emitter proteins, excitation energy would be transferred to the second protein-bound chromophore. The mechanism is similar to other currently discussed mechanisms, except in the final steps leading to the primary excited state. The mechanism is consistent with the known details of the reactions of dioxiranes and of flavins and with recent studies of the secondary emitter proteins and bacterial luciferases.     

Monte Carlo modeling of the effects of injected short-, medium- and longer-range alpha-particle emitters on human marrow at various ages

The effects of injected short-, medium- and longer-range alpha-particle emitters ((149)Tb, (211)At/(211)Po and (213)Bi/(213)Po, respectively) on the total hemopoietic stem cell population of active normal bone marrow in humans of various ages has been estimated using Monte Carlo modeling. The fraction of the normal hemopoietic stem cells that are hit and survive has been calculated as a first step toward estimating the risk of development of therapy-induced leukemia. The fraction was lowest for the shorter-range alpha-particle emitter ((149)Tb) and highest for the longer-range alpha-particle emitter ((213)Bi/(213)Po), with the value for the medium-range alpha-particle emitter (211)At/(211)Po being intermediate between these. There was little variation in the data with the age of the subject within each alpha-particle emitter. This lack of age dependence provides reassurance that the fraction of cells hit in any subject of any age with normal marrow can be estimated by modeling newborn marrow (which requires little computing time) despite age-related differences in microarchitecture.     

Design,Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation ^1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors ⁹. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 ¹⁰.     

Plant volatile-induced aphid resistance in barley cultivars is related to cultivar age

Recent studies have shown that volatile chemical interaction between certain barley (Hordeum vulgare) cultivars can cause reduced host plant acceptance by the aphid Rhopalosiphum padi, and that certain cultivars can induce this effect while others can respond. In this study, we tested whether inducing and responding capabilities are linked to year of release in Swedish two-rowed spring barley. Eighteen cultivars released between 1897 and 1992 were tested in randomly selected subsets with pairwise combinations of volatile emitters and receivers. Significantly reduced aphid acceptance as a result of exposure to volatiles from plants of a different cultivar were found in 24% of the cultivar combinations. In general, older cultivars had a higher degree of aphid resistance after barley volatile treatment than did younger cultivars. The inducing effect of the emitter was also related to date of emitter cultivar release but the time relationship was reversed. Combinations with a younger volatile emitter and an older volatile receiver gave the strongest reduction in aphid acceptance of treated plants. Linear relationships between microsatellite diversity of emitting cultivars and their efficiency as inducers indicated that younger cultivars might have a more unique odour, whereas older cultivars may be more sensitive to induction.     

Energy efficiency of electron plasma emitters

Electron emission influence from gas-discharge plasma on plasma emitter energy parameters is considered. It is shown, that electron emission from plasma is accompanied by energy contribution redistribution in the gas-discharge from plasma emitter supplies sources—the gas-discharge power supply and the accelerating voltage power supply. Some modes of electron emission as a result can be realized: “a probe measurements mode,” “a transitive mode,” and “a full switching mode.”