Polarization Characteristics of High-Birefringence Photonic Crystal Fiber Selectively Coated with Silver Layers

The polarization characteristics of high-birefringence photonic crystal fiber (HB-PCF) selectively coated with silver layers are numerically investigated using the full-vector finite element method (FEM). The fundamental mode coupling properties and polarization splitting effect are discussed in detail. Results show that the resonance wavelength, resonance strength, and splitting distance between two polarized modes can be adjusted significantly by changing the fiber structure, the diameter of silver rings, and the thickness of silver layers. A single-polarization filter at 1310 nm bands is proposed with the corresponding loss 500 dB/cm and full width half maximum (FWHM) only 23 nm. This work is very helpful for further studies in polarization-dependent wavelength-selective applications or other fiber-based plasmonic devices.

     

Nanofocusing of Surface Plasmon Polaritons on Metal-Coated Fiber Tip Under Internal Excitation of Radial Vector Beam

We theoretically present the nanofocusing of the metal-coated fiber tip under internal excitation of the radial vector beam within visible band based on the finite difference time domain (FDTD) analysis. The electric field intensity enhancement factor of the localized surface plasmons (LSP) mode at the tip apex is quantitatively shown in relation with incident wavelength, coating material, conical angle of tip, and coating film thickness/length. Specially, the evolution of fiber radial vector mode to surface mode with respect to the radius of metal-coated fiber tip is calculated under typical excitation wavelengths of 633 nm and 785 nm. Furthermore, the reason of the tip eliminating far-field background signal is explained, and the transverse electric field distributions of LSP mode and the tip-substrate coupling are also given at the optimal excitation wavelength. These calculation results will be a good reference for the fabrication of metal-coated fiber tips and for the experimental design of the tip-enhanced spectroscopy (TES) system.

     

Application of a Plasmonic Biosensor for Detection of Human-Liver Tissues

A recently published plasmonic biosensor based on birefringent solid-core microstructured optical fiber is applied for detection of five types of human-liver tissues (normal N, metastatic MET, non-cancerous metastatic (NMET), hepatocellular carcinoma (HCC), and non-cancerous hepatocellular carcinoma (NHCC)). The birefringent behavior is obtained by removing five central air holes of a two-ring hexagonal lattice of holes in a gold covered silica fiber with the liver layer surrounding the fiber. The loss spectra show two resonant peaks corresponding to the phase matching points. To distinguish between normal and malignant liver tissues, we compare the relevant parameter for the type I and II core modes. Thus, for a decrease of the real part of the refractive index from 1.373431 (human-liver N) to 1.354602 (human-liver MET), the resonance spectral width δλ _0.5 is increased from 44.3 to 54.2 nm for the core mode II. In addition, the amplitude sensitivity S _A is decreased from 158.6 to 88.4 RIU⁻¹ for the same core mode. The advantages of another recently proposed plasmonic sensor based on a Bragg fiber are the larger values of the transmission loss, maximum value of the amplitude sensitivity, figure of merit, power fraction in a normal liver layer, and power fraction in the gold layer as compared with that for a microstructured fiber when applied for detection of a normal liver tissue. Another advantage of the Bragg fiber is related to the smaller value of the difference between maximal amplitude sensitivity and resonant wavelengths.

     

Dynamics of Type IV Pili Is Controlled by Switching Between Multiple States

Type IV pili are major bacterial virulence factors supporting adhesion, surface motility, and gene transfer. The polymeric pilus fiber is a highly dynamic molecular machine that switches between elongation and retraction. We used laser tweezers to investigate the dynamics of individual pili of Neisseria gonorrheae at clamped forces between 8 pN and 100 pN and at varying concentration of the retraction ATPase PilT. The elongation probability of individual pili increased with increasing mechanical force. Directional switching occurred on two distinct timescales, and regular stepping was absent on a scale > 3 nm. We found that the retraction velocity is bimodal and that the bimodality depends on force and on the concentration of PilT proteins. We conclude that the pilus motor is a multistate system with at least one polymerization mode and two depolymerization modes with the dynamics fine-tuned by force and PilT concentration.     

Modeling left ventricular dynamics with characteristic deformation modes

A computationally efficient method is described for simulating the dynamics of the left ventricle (LV) in three dimensions. LV motion is represented as a combination of a limited number of deformation modes, chosen to represent observed cardiac motions while conserving volume in the LV wall. The contribution of each mode to wall motion is determined by a corresponding time-dependent deformation variable. The principle of virtual work is applied to these deformation variables, yielding a system of ordinary differential equations for LV dynamics, including effects of muscle fiber orientations, active and passive stresses, and surface tractions. Passive stress is governed by a transversely isotropic elastic model. Active stress acts in the fiber direction and incorporates length–tension and force–velocity properties of cardiac muscle. Preload and afterload are represented by lumped vascular models. The variational equations and their numerical solutions are verified by comparison to analytic solutions of the strong form equations. Deformation modes are constructed using Fourier series with an arbitrary number of terms. Greater numbers of deformation modes increase deformable model resolution but at increased computational cost. Simulations of normal LV motion throughout the cardiac cycle are presented using models with 8, 23, or 46 deformation modes. Aggregate quantities that describe LV function vary little as the number of deformation modes is increased. Spatial distributions of stress and strain change as more deformation modes are included, but overall patterns are conserved. This approach yields three-dimensional simulations of the cardiac cycle on a clinically relevant time-scale.

     

Low temperature FTIR study of the Schiff base reprotonation during the M-to-bR backphotoreaction: Asp 85 reprotonates two distinct types of Schiff base species at different temperatures

We have applied low temperature difference FTIR spectroscopy to investigate intermediates produced from the M intermediate upon blue light excitation (<480 nm). In agreement with an earlier report by Balashov and Litvin (1981), who studied these intermediates with low temperature visible absorption spectrophotometry, we have observed at least three stages in this backphotoreaction. The initial photoproduct is stable at 100 K, and two products of subsequent thermal reactions are observed upon raising the temperature to 130 and 160 K, respectively.

The alterations in the C=N stretching mode of the Schiff base have been identified by isotopically labeling the retinal chromophore, and changes in C=O stretching modes of amino acid residues with acidic side chains have been investigated. Analysis of the C=N stretching mode shows that the Schiff base remains unprotonated after the photochemical reaction at 100 K. Moreover, there are two types of Schiff bases, presumably associated with different bR species, that become thermally reprotonated at 130 and 160 K, respectively. Bands associated with the C=O stretching modes suggest that Asp 85 rather than Asp 96 reprotonates the Schiff base during the M to bR backphotoreaction. This conclusion is consistent with earlier observations that the polarity of electrical signals during this photochemical back reaction is reversed as compared to the thermal regeneration of bR from M.

     

Experimental Study on Localized Surface Plasmon Mode Hybridization in the Near and Mid Infrared

We investigate plasmon excitations within a regular grating of double-layered gold/insulator nanoparticles in the infrared and visible spectral region. Provided a flat gold film as substrate, strong coupling between the localized surface plasmon modes and their image-like excitations in the metal is observed. The interaction results in a strong red shift of the plasmon mode as well as the splitting of the modes into levels of different angular momenta, often referred to as plasmon hybridization. The diameters of the nanoparticles are designed in a way that the splitting of the resonances occurs in the spectral region between 0.1 and 1 eV, thus being accessible using an infrared microscope. Moreover, we investigated the infrared absorption signal of gratings that contain two differently sized nanoparticles. The interaction between two autonomous localized surface plasmon excitations is investigated by analyzing their crossing behavior. In contrast to the interaction between localized surface plasmons and propagating plasmon excitations which results in pronounced anticrossing, the presented structures show no interaction between two autonomous localized surface plasmons. Finally, plasmon excitations of the nanostructured surfaces in the visible spectral region are demonstrated through photographs acquired at three different illumination angles. The change in color of the gratings demonstrates the complex interaction between propagating and localized surface plasmon modes.     

Two Binding Modes of Netropsin are Involved in the Complex Formation with Poly(dA-dT)·Poly(dA-dT) and other Alternating DNA Duplex Polymers

Abstract

Using CD measurements we show that the interaction of netropsin to poly(dA-dT)·poly(dA-dT) involves two binding modes at low ionic strength. The first and second binding modes are distinguished by a defined shift of the CD maximum and the presence of characteristic isodichroic points in the long wavelength range from 313 nm to 325 nm. The first binding mode is independent of ionic strength and is primarily determined by specific interaction to dA·dT base pairs. Employing a netropsin derivative and different salt conditions it is demonstrated that ionic contacts are essential for the second binding mode. Other alternating duplexes and natural DNA also exhibit more or less a second step in the interaction with netropsin observable at high ratio of ligand per nucleotide. The second binding mode is absent for poly(dA)·poly(dT). The presence of a two-step binding mechanism is also demonstrated in the complex formation of poly(dA-dT)·poly(dA-dT) with the distamycin analog consisting of pentamethylpyrrolecarboxamide. While the binding mode I of netropsin is identical with its localization in the minor groove, for binding mode II we consider two alternative interpretations.     

Numerical Simulation of Extinction Spectra of Plasmonically Coupled Nanospheres Using Discrete Dipole Approximation: Influence of Compositional Asymmetry

We demonstrate plasmon coupling phenomenon between equivalent (homodimer) and non-equivalent (heterodimer) spherical shape noble metal nanoparticle (Ag, Au and Al). A systematic comparison of surface plasmon resonance (SPR) and extinction properties of various configurations (monomer, homodimer and heterodimer) has been investigated to observe the effect of compositional asymmetry. Numerical simulation has been done by using discrete dipole approximation method to study the optical properties of plasmonically coupled metal nanoparticles (MNPs). Plasmon coupling between similar nanoparticles allows only higher wavelength bonding plasmon mode while both the plasmon modes lower wavelength antibonding mode as well as higher wavelength bonding mode in the case of heterodimer. Au monomer of radius 50 nm shows resonance peak at 518 nm while plasmon coupling between Au-Au homodimer results in a spectral red shift around 609 nm. Au-Ag plasmonic heterodimer (radius 50 nm) reveals two resonant modes corresponding to higher energy antibonding mode (422 nm) as well as lower energy bonding mode (533 nm). Further, we have shown that interparticle edge-to-edge separation is the most significant parameter affecting the surface plasmon resonances of MNPs. As the inter particle separation decreases, resonance wavelength shows red spectral shift which is maximum for the touching condition. It is shown that plasmon coupling is a reliable strategy to tune the SPR.

     

Polarization Properties of Selectively Gold-filled Suspended Core Microstructured Optical Fibers

We study the polarization properties of suspended core microstructured optical fibers (SC-MOFs) with hexagonal lattice structure and high air-filling fraction having a single gold-filled hole along the horizontal axis. The interaction between the core-guided light and metal leads to surface plasmon resonance (SPR) at particular frequencies where the phase-matching condition is satisfied. We observe from the modal analysis that MOFs with high air-filling fraction offer the possibility of coupling of the fundamental mode with the first-order surface plasmon polariton (SPP) mode. With the increase in the suspension factor (SF), the fundamental mode couples with higher order SPP modes and the coupling strength also enhances. It also leads to an increase in modal birefringence. Reduction in beat length by an order of magnitude compared to the reported values is being reported for the first time to our knowledge. We have achieved the lowest beat length of 0.0105 mm at 1 μm wavelength for the structure having d/Λ = 0.85 and SF = 1.65. The results show that such plasmonic SC-MOFs may perform as efficient in-fiber polarizers and polarization filters.

     

Channel-like slippage modes in the human anion/proton exchanger ClC-4

The ClC family encompasses two classes of proteins with distinct transport functions: anion channels and transporters. ClC-type transporters usually mediate secondary active anion–proton exchange. However, under certain conditions they assume slippage mode behavior in which proton and anion transport are uncoupled, resulting in passive anion fluxes without associated proton movements. Here, we use patch clamp and intracellular pH recordings on transfected mammalian cells to characterize exchanger and slippage modes of human ClC-4, a member of the ClC transporter branch. We found that the two transport modes differ in transport mechanisms and transport rates. Nonstationary noise analysis revealed a unitary transport rate of 5 × 10⁵ s⁻¹ at +150 mV for the slippage mode, indicating that ClC-4 functions as channel in this mode. In the exchanger mode, unitary transport rates were 10-fold lower. Both ClC-4 transport modes exhibit voltage-dependent gating, indicating that there are active and non-active states for the exchanger as well as for the slippage mode. ClC-4 can assume both transport modes under all tested conditions, with exchanger/channel ratios determined by the external anion. We propose that binding of transported anions to non-active states causes transition from slippage into exchanger mode. Binding and unbinding of anions is very rapid, and slower transitions of liganded and non-liganded states into active conformations result in a stable distribution between the two transport modes. The proposed mechanism results in anion-dependent conversion of ClC-type exchanger into an anion channel with typical attributes of ClC anion channels.     

How Backward Poynting Flows Arise for Surface Plasmon Waves with Lossy Metals

We revisit the surface plasmon resonances established along a planar interface lying between a lossless dielectric and a lossy metal. By examining the orbital and spin parts of the Poynting vector, the mechanisms behind forward or backward flows are clearly illustrated. Consequently, we were able to construct more intuitive pictures of two-dimensional energy flows induced by the metallic losses. In addition, we recognized the importance of both asymmetry and symmetry hidden behind the familiar transverse-magnetic waves. Our numerical results are close to reality, since experimentally observed optical data of gold is employed for a lossy metal.

     

A Photonic Crystal Fiber Polarized Filter at 1.55 μm Based on Surface Plasmon Resonance

A single-polarization photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is proposed. Finite element method is employed in simulating the PCF with gold-coated. The resonance wavelength can be modulated by changing the thickness of gold layer. At the resonance wavelength 1.55 μm, the loss of y-polarized mode is much larger than the loss of x-polarized mode. When the fiber length is set to 2 mm, the value of extinction ratio reaches to −118.7 dB, the y-polarized mode is suppressed and only x-polarized mode can be guided. The fiber is applicable in the production of single-polarization filter. The PCF has a simple structure and a big error tolerance, it has a good practicability.

     

Detection of gaps in sinusoids by frog auditory nerve fibers: importance in AM coding

Physiological studies were carried out in the frog (Rana pipiens pipiens) eighth nerve to determine: (i) whether the modulation rate or the silent gap was the salient feature that set the upper limit of time-locking to pulsed amplitude-modulated (PAM) stimuli, (ii) the gap detection capacity of individual eighth nerve fibers. Time-locked responses of 79 eighth nerve fibers to PAM stimuli (at the fiber's characteristic frequency) showed that the synchronization coefficient was a low-pass function of the modulation rate. In response to PAM stimuli having different pulse durations, a fiber gave rise to non-overlapping modulation transfer functions. The upper cut-off frequency of time locking was higher when tonepulses in PAM stimuli had shorter duration. The fact that the cut-off frequency was different for the different PAM series suggested that the AM rate was neither the sole, nor the main, determinant for the decay in time-locking at high AM rates. Gap detection capacity was determined for 69 eighth nerve fibers by assessing fiber's spiking activities to paired tone-pulses during an OFF-window and an ON-window. It was found that the minimum detectable gap of eighth nerve fibers ranged from 0.5 to 10 ms with an average of 1.23–2.16 ms depending on the duration of paired tone pulses. For each fiber, the minimum detectable gap was longer when the duration of tone pulses comprising the twin-pulse stimuli was more than four times longer. When the synchronization coefficient was plotted against the silent gap between tones pulses in the PAM stimuli, the gap response functions of a fiber as derived from multiple PAM series were equivalent to gap response functions deriving from twin-pulse series suggesting that it was the silent gap which primarily determined the upper limit of time-locking to PAM stimuli.Abbreviations MTF modulation transfer function - PAM pulse amplitude modulated - SAM sinusoidally amplitude modulated - SC synchronization coefficient - TW time window     

Hi-Bi Photonic Crystal Fiber for Broadband Filter Realization Using Copper Microwires

This paper presents a highly birefringence (Hi-Bi) photonic crystal fiber (PCF)-based single-polarization filter, which consists of copper microwires. Copper is chemically stable and the use of microwires is benefit to fabricate than any metal-coated PCF. The filter characteristics are inspected by the full-vector finite element method (FEM). The proposed filter can filter out y-polarized mode, while the x-polarized mode can be guided. The confinement loss of the y-polarized mode at the wavelength of 1.31 μm is achieved of 696.79 dB/cm, while the x-polarized loss is only 4.34 dB/cm. According to numerical results, 20 dB bandwidth of the proposed filter with a maximum value of crosstalk of 601.37 dB is achieved of 650 nm that range from 1.1 to 1.75 μm. Furthermore, the insertion loss of the guided mode (x-polarization) is as low as 0.142 dB for 1 mm of fiber length. Moreover, by optimizing the structural parameters, it has shown that the proposed filter can be effective at any wavelength at the optical communication window.

     

Spaser Based on Dark Quadrupolar Mode of a Single Metallic Nanodisk

A spaser based on dark quadrupolar mode of a single metallic nanodisk coated with a layer of gain media is studied theoretically. The absorption efficiency of the metallic structure, the gain efficiency of the gain media, and the scattering efficiency of the whole nanosystem are calculated separately. It is found that the ratio of the absorption and the scattering intensities (RAS) of the dark quadrupolar mode depends strongly on the gain coefficient, which increases from 0.8 to 4.39 with gain coefficient reaches the threshold, by contrast the bright dipolar mode keeps its RAS unchanged at 0.16. This is attributed to that the gain media mainly amplifies quadrupolar eigenmode composition of the dark quadrupolar mode, thus the scattering loss caused by dipolar eigenmode composition is under effective control, which changes the RAS and leads to super low-threshold spaser. Our works may benefit the achievement of spaser system with low scattering loss.

     

Allocation in recycling of composites - the case of life cycle assessment of products from carbon fiber composites

Purpose

Composites consist of at least two merged materials. Separation of these components for recycling is typically an energy-intensive process with potentially significant impacts on the components’ quality. The purpose of this article is to suggest how allocation for recycling of products manufactured from composites can be handled in life cycle assessment to accommodate for the recycling process and associated quality degradations of the different composite components, as well as to describe the challenges involved.

Method

Three prominent recycling allocation approaches were selected from the literature: the cut-off approach, the end-of-life recycling approach with quality-adjusted substitution, and the circular footprint formula. The allocation approaches were adapted to accommodate for allocation of impacts by conceptualizing the composite material recycling as a separation process with subsequent recycling of the recovered components, allowing for separate modeling of the quality changes in each individual component. The adapted allocation approaches were then applied in a case study assessing the cradle-to-grave climate impact and energy use of a fictitious product made from a composite material that in the end of life is recycled through grinding, pyrolysis, or by means of supercritical water treatment. Finally, the experiences and results from applying the allocation approaches were analyzed with regard to what incentives they provide and what challenges they come with.

Results and discussion

Using the approach of modeling the composite as at least two separate materials rather than one helped to clarify the incentives provided by each allocation approach. When the product is produced using primary materials, the cut-off approach gives no incentive to recycle, and the end-of-life recycling approach and the circular footprint formula give incentives to recycle and recover materials of high quality. Each of the allocation approaches come with inherent challenges, especially when knowledge is limited regarding future systems as in prospective studies. This challenge is most evident for the circular footprint formula, for example, with regard to the supply and demand balance.

Conclusions

We recommend modeling the composite materials in products as separate, individual materials. This proved useful for capturing changes in quality, trade-offs between recovering high quality materials and the environmental impact of the recycling system, and the incentives the different approaches provide. The cut-off and end-of-life approaches can both be used in prospective studies, whereas the circular footprint formula should be avoided as a third approach when no market for secondary material is established.

     

Strong and High-Precision Manipulation of Nanoparticle with Graphene-Coated Fiber Systems

Two kinds of graphene-coated fiber systems are proposed and studied for optical trapping. Their plasmonic modes in uniform environment and close to the substrate are studied in the finite element method. The optical forces exerted on dielectric nanoparticle by these systems are calculated by standalone waveguide approximation. It is found that for the dielectric particle with diameter of 1 nm, the maximal optical forces generated by certain modes are more than 10⁷ fN/W whereas their force ranges are only one to several nanometers. These results may have important applications in strong and high-precision optical tweezers.