A Research of Nonreciprocal Transmission of Graphene Defect

In this paper, modified transmission matrix method is used to construct one-dimensional multilayer composite membrane structure doped with graphene defect. The optimal construction can be found to realize reciprocity transmission by comparing the influence of the time inversion-symmetry and space inversion-symmetry doped on nonreciprocal transmission. The simulation results show that it cannot ensure the nonreciprocal transmission with rotatory material only. Nonreciprocal transmission should be designed through the structure damage of the space inversion-symmetry to realize it. The structure absorption peak position will move to the direction of the wavelength increase along with the increase of thickness of rotation media. The structure shows the approximate perfect absorption characteristics.     

Transverse Magneto-Optical Kerr Effect in Strongly Coupled Plasmon Gratings

Enhancement of magneto-optical response by coupling of propagating with localized plasmons in a structure based on silver and bismuth-substituted ferrite garnet has been numerically studied. It is shown that the absolute value of the magneto-optical response in the examined structure reaches a high value of 0.04, and the structure has a reflection coefficient sufficiently high for a number of practical applications. The strong coupling between localized and propagating plasmons, which caused the significant enhancement of the magneto-optical response, was manifested in the reflection spectrum of the structure in the form of an asymmetric Fano-like resonance. The proposed structure, intended for operation in the near infrared range, is a promising one for solving various problems in magnonics and bionanophotonics.     

Development of an Exactly Solvable Model of Resonance Tunneling of Electromagnetic Waves through Gradient Barriers in a Nonuniform Magnetoactive Plasma

An exactly solvable one-dimensional model describing resonance tunneling (reflectionless transmission) of a transverse electromagnetic wave through wide layers of magnetoactive plasma is developed on the basis of the Helmholtz equation. The plasma layers include a set of spatially localized density structures the amplitudes and thicknesses of which are such that approximate methods are inapplicable for their analysis. The profiles of the plasma density structures strongly depend on the choice of the free parameters of the problem that determine the amplitudes of plasma density modulation, characteristic scale lengths of the density structures, their number, and the total thickness of the nonuniform plasma layer. The plasma layers can also include a set of random inhomogeneities. The propagation of electromagnetic waves through such complicated plasma inhomogeneities is analyzed numerically within the proposed exactly solvable model. According to calculations, there are a wide set of inhomogeneous structures for which an electromagnetic wave incident from vacuum can propagate through the plasma layer without reflection, i.e., the complete tunneling of thick plasma barriers takes place. The model also allows one to exactly solve a one-dimensional problem on the nonlinear transillumination of a nonuniform plasma layer in the presence of cubic nonlinearity. It is important that, due to nonlinearity, the thicknesses of the evanescent plasma regions can decrease substantially and, at a sufficiently strong nonlinearity, such regions will disappear completely. The problem of resonance tunneling of electromagnetic radiation through gradient wave barriers is of interest for various applications, such as efficient heating of dense plasma by electromagnetic radiation and transmission of electromagnetic signals from a source located in the near-Earth plasma or deep in the plasma of an astrophysical object through the surrounding evanescent regions.     

Plasmonics Resonance Enhance Magneto-Optical Effects Through Metallic Sub-wavelength Grating with Bismuth Iron Garnet Slab

We theoretically investigated an enhancement of the magneto-optical Faraday rotations along with large transmittance in two multilayer structures. The shifts of the Faraday rotation peaks are more obvious than the transmittance peaks when the grating period is changed, which is beneficial to acquire the large Faraday rotation and transmittance. The Faraday rotation of tri-layer system is five times larger than the bilayer system, and the Faraday resonance peak can be mediated by changing the refractive index or thickness of the additional nonmagnetic dielectric layer (NDL) layer. These results are important for applications in highly integrated optoelectronic and magneto-optical devices.     

Optical Transmission in Arrayed Asymmetric Multilayered Ultra-Thin Metal Stripes

An arrayed structure of asymmetric multilayered ultra-thin metal stripes is proposed to achieve a narrow transmission peak in an ultra-broad transmission valley, which is formed due to the destructive multiple-interference tunneling existed in an ultra-thin metal and dielectric multilayers. The transmission peak is influenced by two resonant modes. One is the coupled gap surface plasmon (cg-SP) resonance mode confined in entire multilayered ridges, the other is the modified gap surface plasmon (g-SP) mode within metal-dielectric layers. Furthermore, the transmission mode and the stopband are tunable in a wide range through designing the dimension parameters. The proposed plasmonic structure is promising for wideband filters.     

Backbone resonance assignment and order tensor estimation using residual dipolar couplings

An NMR investigation of proteins with known X-ray structures is of interest in a number of endeavors. Performing these studies through nuclear magnetic resonance (NMR) requires the costly step of resonance assignment. The prevalent assignment strategy does not make use of existing structural information and requires uniform isotope labeling. Here we present a rapid and cost-effective method of assigning NMR data to an existing structure—either an X-ray or computationally modeled structure. The presented method, Exhaustively Permuted Assignment of RDCs (EPAR), utilizes unassigned residual dipolar coupling (RDC) data that can easily be obtained by NMR spectroscopy. The algorithm uses only the backbone N–H RDCs from multiple alignment media along with the amino acid type of the RDCs. It is inspired by previous work from Zweckstetter and provides several extensions. We present results on 13 synthetic and experimental datasets from 8 different structures, including two homodimers. Using just two alignment media, EPAR achieves an average assignment accuracy greater than 80%. With three media, the average accuracy is higher than 94%. The algorithm also outputs a prediction of the assignment accuracy, which has a correlation of 0.77 to the true accuracy. This prediction score can be used to establish the needed confidence in assignment accuracy.     

Optical Transmission Through Multilayered Ultra-Thin Metal Gratings

Optical transmission properties of multilayered ultra-thin metal gratings are numerically studied. The transmission spectrum has a broad stop-band with extremely low transmittance compared to that of a single-layer one for TM polarization. The stop-band is shown to be formed by multiple-interference tunneling and various plasmon resonance processes in ultra-thin-metal and dielectric multilayers. That is on the transmission background of non-apertured metal/dielectric multilayer structures that have low transmission in the long-wavelength range due to destructive multiple-interference tunneling, the transmission is further suppressed in the stop-band by plasmon resonances in the top metal/dielectric layers, e.g., the anti-symmetric bound surface plasmon mode in the ultra-thin metal layer and the gap surface plasmon mode in the metal-sandwiched dielectric layer. High transmission beyond the stop-band is due to coupled gap surface plasmon mode in the entire multilayer structures. Applications of the optical properties of the multilayered ultra-thin metal gratings are suggested for optical filtering (wavelength or polarization selective).     

Periodic coupling strength-dependent multiple coherence resonance by time delay in Newman–Watts neuronal networks

Recently, multiple coherence resonance induced by time delay has been observed in neuronal networks with constant coupling strength. In this paper, by employing Newman–Watts Hodgkin–Huxley neuron networks with time-periodic coupling strength, we study how the temporal coherence of spiking behavior and coherence resonance by time delay change when the frequency of periodic coupling strength is varied. It is found that delay induced coherence resonance is dependent on periodic coupling strength and increases when the frequency of periodic coupling strength increases. Periodic coupling strength can also induce multiple coherence resonance, and the coherence resonance occurs when the frequency of periodic coupling strength is approximately multiple of the spiking frequency. These results show that for periodic coupling strength time delay can more frequently optimize the temporal coherence of spiking activity, and periodic coupling strength can repetitively optimize the temporal coherence of spiking activity as well. Frequency locking may be the mechanism for multiple coherence resonance induced by periodic coupling strength. These findings imply that periodic coupling strength is more efficient for enhancing the temporal coherence of spiking activity of neuronal networks, and thus it could play a more important role in improving the time precision of information processing and transmission in neural networks.     

Ultrahigh Contrast One-Way Optical Transmission Through a Subwavelength Slit

We computationally demonstrate one-way optical transmission characteristics of a subwavelength slit. We comparatively study the effect in single layer and double layer metallic corrugations. We also investigate the effect of a dielectric spacer layer between double corrugations to control the volumetric coupling of plasmon and optical modes. We computationally show unidirectional transmission behavior with an ultrahigh contrast ratio of 53.4 dB at λ?=?1.56 μm. Volumetric coupling efficiency through the nanoslit strongly depends on the efficient excitation of both the surface plasmon resonance and metal–insulator–metal waveguide modes. We show that the behavior is tunable in a wide spectral range.     

A Three-Dimensional Plasmonic Nanostructure with Extraordinary Optical Transmission

We report a 3D plasmonic nanostructure having an extraordinary optical transmission due to localized surface plasmon (LSP) coupling between nanoholes and nanodisks. The nanostructure contains a free-standing gold nanohole array (NHA) film above a cavity and an array of nanodisks at the bottom of the cavity that is aligned with the NHA. For the device, the LSP-mediated resonance position was dependent on the hole and nanodisk diameter as well as the separation distance. Also, the effect of LSP coupling between each hole and corresponding nanodisk became negligible for cavities deeper than 200 nm as observed as a disappearance of the LSP resonance. The greatest LSP resonance transmission and the highest electric field intensity were observed for the structure with the shallowest cavity. In addition, the structure had high surface plasmon resonance sensitivity and may have potential for surface-enhanced Raman spectroscopy and optical trapping applications.     

Long-period gratings in photonic crystal fiber as an optofluidic label-free biosensor

Using long-period gratings (LPG) inscribed in photonic crystal fiber (PCF) and coupling this structure with an optically aligned flow cell, we have developed an optofluidic refractive index transduction platform for label-free biosensing. The LPG-PCF scheme possesses extremely high sensitivity to the change in refractive index induced by localized binding event in different solution media. A model immunoassay experiment was carried out inside the air channels of PCF by a series of surface modification steps in sequence that include adsorption of poly(allylamine hydrochloride) monolayer, immobilization of anti-rat bone sialoprotein monoclonal primary antibody, and binding interactions with non-specific goat anti-rabbit IgG (H+L) and specific secondary goat anti-mouse IgG (H+L) antibodies. These adsorption and binding events were monitored in situ using the LPG-PCF by measuring the shift of the core-to-cladding mode coupling resonance wavelength. Steady and significant resonance changes, about 0.75 nm per nanometer-thick adsorbed/bound bio-molecules, have been observed following the sequence of the surface events with monolayer sensitivity, suggesting the promising potential of LPG-PCF for biological sensing and evaluation.     

Transmission Control Property of a Nano-optical System Made by an Antenna over a Bowtie Aperture

In this paper, we report a characteristic transmission control property of a nano-optical system by introducing an antenna over the input opening of a bowtie aperture. The transmission process through the system is investigated quantitatively by the coupling and transmission efficiencies, and an optical switch effect is found as the antenna length varies. To understand the physical mechanism, we then investigate the electrical field distribution of the antenna over a rectangle aperture as a simplified model. It is discovered that the "on" state of the system is due to Fabry–Perot resonances in the horizontal cavity formed by antenna, dielectric layer, and metal film. On the other hand, a cutoff occurs for the characteristic rectangle length shorter than the diffraction limit to turn the device to the "off" state. Such a phenomenon can thus provide a promising candidate for application in manipulating light in large-scale optoelectronic device integration.     

Oscillation-Induced Signal Transmission and Gating in Neural Circuits

Reliable signal transmission constitutes a key requirement for neural circuit function. The propagation of synchronous pulse packets through recurrent circuits is hypothesized to be one robust form of signal transmission and has been extensively studied in computational and theoretical works. Yet, although external or internally generated oscillations are ubiquitous across neural systems, their influence on such signal propagation is unclear. Here we systematically investigate the impact of oscillations on propagating synchrony. We find that for standard, additive couplings and a net excitatory effect of oscillations, robust propagation of synchrony is enabled in less prominent feed-forward structures than in systems without oscillations. In the presence of non-additive coupling (as mediated by fast dendritic spikes), even balanced oscillatory inputs may enable robust propagation. Here, emerging resonances create complex locking patterns between oscillations and spike synchrony. Interestingly, these resonances make the circuits capable of selecting specific pathways for signal transmission. Oscillations may thus promote reliable transmission and, in co-action with dendritic nonlinearities, provide a mechanism for information processing by selectively gating and routing of signals. Our results are of particular interest for the interpretation of sharp wave/ripple complexes in the hippocampus, where previously learned spike patterns are replayed in conjunction with global high-frequency oscillations. We suggest that the oscillations may serve to stabilize the replay.     

Modification of CETP function by changing its substrate preference: a new paradigm for CETP drug design

We previously determined that hamster cholesteryl ester transfer protein (CETP), unlike human CETP, promotes a novel one-way transfer of TG from VLDL to HDL, causing HDL to gain lipid. We hypothesize that this nonreciprocal lipid transfer activity arises from the usually high TG/cholesteryl ester (CE) substrate preference of hamster CETP. Consistent with this, we report here that ∼25% of the total lipid transfer promoted by the human Q199A CETP mutant, which prefers TG as substrate, is nonreciprocal transfer. Other human CETP mutants with TG/CE substrate preferences higher or lower than wild-type also possess nonreciprocal lipid transfer activity. Mutants with high TG/CE substrate preference promote the nonreciprocal lipid transfer of TG from VLDL to HDL, but mutants with low TG/CE substrate preference promote the nonreciprocal lipid transfer of CE, not TG, and this lipid flow is in the reverse direction (from HDL to VLDL). Anti-CETP TP2 antibody alters the TG/CE substrate preference of CETP and also changes the extent of nonreciprocal lipid transfer, showing the potential for externally acting agents to modify the transfer properties of CETP. Overall, these data show that the lipid transfer properties of CETP can be manipulated. Function-altering pharmaceuticals may offer a novel approach to modify CETP activity and achieve specific modifications in lipoprotein metabolism.     

All-Optical Strong Coupling Switches Based on a Coupled Meta-atom and MIM Nanocavity Configuration

Based on a coupled meta-atom and metal-nonlinear dielectric-metal nanocavity, nonlinear all-optical strong coupling switches are proposed and numerically investigated. In the absence of the external pumping light, the resonances of the meta-atom are continuously tuned across the one of the nanocavity by changing the size of the meta-atom. The meta-atomic electric dipole and quadrupole interaction with the plasmonic nanocavity is obtained. The characteristic anticrossing behaviors manifest the occurrence of the strong coupling. With the resonance of the meta-atom being tuned to the one of the nanocavity, we dynamically tune the coupled strength of the system by changing intensity (power) of the pumping light and realize the transition from the strong coupling regime to the weak one. This means that this system can be used as an on/off switch in which the strong coupling can be on/off with an external control light, and the on/off states correspond to strong/weak coupling regime, respectively. Such a strong coupling all-optical switching is of considerable interest for applications in nanoscale plasmonic circuits.     

Unidirectional Gene Conversion Associated with Two Insertions in NEUROSPORA CRASSA Mitochondrial DNA

The mitochondrial phenotype of [poky] and other extranuclear Neurospora mutants is known to predominate over that of wild type in heteroplasmons. In the present work, we have investigated the interaction between wild-type and [poky] mtDNAs using as many as four physical markers to distinguish the two types of mtDNAs. Two insertions, one of 1200 bp in Eco RI-5 and the other 50 bp in Eco RI-9, are identified as sites of high frequency, unidirectional gene conversion leading to their spread through mtDNA populations in heteroplasmons. However, the transmission of the [poky] mutation does not appear to be correlated with the transmission of either of these insertions or of other physical markers. The possibility that other loci of nonreciprocal recombination might be responsible for the "dominance" of Neurospora extranuclear mutants is discussed.     

Photo-induced charge transfer. A critical test of the mechanism and range of biological electron transfer processes.

The vibronic coupling theory of electron tunneling between biomolecules requires that all such tunnelings involve vibronic coupling, finds temperature dependence to tunneling at finite temperatures, and predicts relatively short tunneling distances. This theory might be expected to apply to most electron transfers involved in the membrane-bound electron transfer reactions of photosynthesis and oxidative phosphorylation. This paper calculates the properties of a weak charge-transfer optical absorption band, whose predicted characteristics are a direct and simple consequence of the model that describes vibronically coupled tunneling. The new absorption band provides the basis for a critical experimental test of the constructs and parameters of the tunneling theory. If the tunneling theory is valid, the oscillator strength of such bands will be the most reliable measure of the tunneling matrix element and of the distance between the sites exchanging an electron.     

Present status and future directions of research in electron-transfer mediated by DNA

 This commentary article presents an overview of recent experimental results on DNA-mediated electron transfer (ET) from the perspective of semiclassical ET theory. The question concerning whether or not DNA can act as a wire is addressed. Much of the article focuses on a discussion of the decay of electronic coupling (β) between electron donors and acceptors with increasing donor/acceptor separation in DNA and in protein systems. In particular, the dependence of the electronic coupling itself (H _AB) on the energy gap between the tunneling energy of the reactants and the virtual ionic states of the DNA bridge is highlighted. The article concludes by suggesting that future experimental and theoretical work in this field should focus on the tunneling gap energies of the systems studied and that special attention should be paid to systems that are likely to be in the "small tunneling gap" regime. It is these systems that are expected to exhibit enhanced electronic couplings and consequently enhanced rates of long-distance ET. Received, accepted: 5 January 1998     

Suppressed Optical Transmission Through an Array of Ultrathin Interlayer Metal Slits

In contrast to the enhanced peak transmission in a subwavelength metal hole array structure (Ebbesen et al., Nature 391:667–669, 1998), here we theoretically investigate the spectral transmission through an array of identical metal slits with ultrathin interlayers and surprisingly find the depressed optical transmission for both infinite and finite array case. Notably, in the latter system, the narrowband dip transmission is evidently produced with the accompaniment of selective field enhancement and phase jumping across the structure. Analyses suggest that this phenomenon is intrinsically related to the penetrant coupling of intracavity surface plasmon polaritons together with the slit termination effect.     

Effective Coupling of Incident Light Through an Air Region into an S-Shape Plasmonic Ag Nanowire Waveguide with Relatively Long Propagation Length

Coupling of incident light through an air region into an S-shape silver (Ag) plasmonic nanowire waveguide (SSAPNW) is a highly difficult challenge of light guiding on the surface of metal nanowire. In this paper, we numerically analyze the coupling effect of an SSAPNW which is covered by a dielectric medium using a finite element method. The coupling effect can be modulated by adjusting the Ag nanowire diameter and the covering dielectric medium width and wavelength of incident light, and the propagation length of surface plasmon (SP) coupling can be maximized. Simulation results reveal that the field confinement can be significantly improved and the majority of the electric field can be carried on the surface of a bending Ag nanowire. The effect of electric field transport along an SSAPNW due to SP coupling and Fabry-Perot resonance is investigated for different dimensions and lengths. Accordingly, long propagation lengths of about 41.5 μm for 10?×?SSAPNW at an incident wavelength of 810 nm and longer propagation length can be achieved if more sections of an SSAPNW are used. Simulation results offer an efficient method for optimizing SP coupling into bending metal nanowire waveguides and promote the realization of highly integrated plasmonic devices.