Channel Mode Research Articles

The Trust Relay QKD Network Communication Research

Because of its good network effect, expandability, technology easy to implement, the trust relay Quantum Key Distribution (QKD) network become future secure communication network preferred scheme. The classification and current status of the QKD network was introduced firstly; then the network model of trust relay network, network channel and key relay mode were put forward. Finally, the decisive parameters which affect the trust relay QKD networks effectiveness and performance were proposed. The simulation results confirm that the trust relay QKD network was used for secure communication is reliable.

Separation of neutral and charge modes in one-dimensional chiral edge channels

Coulomb interactions have a major role in one-dimensional electronic transport. They modify the nature of the elementary excitations from Landau quasiparticles in higher dimensions to collective excitations in one dimension. Here we report the direct observation of the collective neutral and charge modes of the two chiral co-propagating edge channels of opposite spins of the quantum Hall effect at filling factor 2. Generating a charge density wave at frequency f in the outer channel, we measure the current induced by inter-channel Coulomb interaction in the inner channel after a 3-μm propagation length. Varying the driving frequency from 0.7 to 11 GHz, we observe damped oscillations in the induced current that result from the phase shift between the fast charge and slow neutral eigenmodes. We measure the dispersion relation and dissipation of the neutral mode from which we deduce quantitative information on the interaction range and parameters.

Silicon mode (de)multiplexer enabling high capacity photonic networks-on-chip with a single-wavelength-carrier light

A small silicon mode (de)multiplexer with cascaded asymmetrical directional couplers is demonstrated experimentally. As an example, a four channel mode (de)multiplexer is designed and realized for TM polarization. The fabricated mode (de)multiplexer has a low excess loss (<1 dB) as well as low crosstalk (≤23 dB) over a broad wavelength range (~20 nm). More channels can be achieved with two sets of orthogonal-polarization modes (e.g., 2N=8) multiplexed when desired.

Serotonergic Drugs for Depression and Beyond

The current generation of antidepressant drugs acts predominantly by targeting the serotonin transporter (SERT). The original trend to do this selectively (e.g., with SSRIs or selective serotonin reuptake inhibitors) has given way to combining various additional pharmacologic mechanisms with SERT inhibition, including dual actions by single drugs (e.g., SNRIs or serotonin norepinephrine reuptake inhibitors), or by augmenting SSRIs with a second drug of a different mechanism (e.g., bupropion with dopamine and norepinephrine reuptake inhibition; trazodone with 5HT2A antagonism; mirtazapine with 5HT2A/5HT2C/5HT3/alpha2 antagonism; buspirone or some atypical antipsychotics with 5HT1A partial agonism; other atypical antipsychotics with 5HT2C/5HT7 antagonism and other mechanisms). Novel drugs in development include those that combine multiple simultaneous pharmacologic mechanisms in addition to SERT inhibition within the same molecule, such as vilazodone (combining 5HT1A partial agonism with SERT inhibition), triple reuptake inhibitors (combining norepinephrine and dopamine reuptake inhibition with SERT inhibition), and vortioxetine, a multimodal antidepressant combining actions at the G protein receptor mode (5HT1A and 5HT1B partial agonism and 5HT7 antagonism), at the ion channel mode (5HT3 antagonism) as well as the neurotransmitter transporter mode (SERT inhibition). These various strategies that build upon SERT inhibition provide promise for novel therapeutic approaches to depression, including the possibility of targeting residual symptoms not well treated by SERT inhibition alone, and reducing side effects, such as sexual dysfunction.

Computational Studies of Marine Toxins Targeting Ion Channels

Toxins from marine animals offer novel drug leads for treatment of diseases involving ion channels. Computational methods could be very helpful in this endeavour in several ways, e.g., (i) constructing accurate models of the channel-toxin complexes using docking and molecular dynamics (MD) simulations; (ii) determining the binding free energies of toxins from umbrella sampling MD simulations; (iii) predicting the effect of mutations from free energy MD simulations. Using these methods, one can design new analogs of toxins with improved affinity and selectivity properties. Here we present a review of the computational methods and discuss their applications to marine toxins targeting potassium and sodium channels. Detailed examples from the potassium channel toxins—ShK from sea anemone and κ-conotoxin PVIIA—are provided to demonstrate capabilities of the computational methods to give accurate descriptions of the channel-toxin complexes and the energetics of their binding. An example is also given from sodium channel toxins (µ-conotoxin GIIIA) to illustrate the differences between the toxin binding modes in potassium and sodium channels.

Third harmonic generation of a nonlinear laser Eigen mode of a self sustained plasma channel

AbstractThe third harmonic generation of a self organized nonlinear laser Eigen mode of a two-dimensional plasma channel with complete electron evacuation from the inner region is investigated. The nonlinearities arise through the ponderomotive force and relativistic mass variations, while the ions are taken to be immobile. The second harmonic ponderomotive force produces electron density oscillations that beat with the oscillatory velocity due to the laser Eigen mode to create a nonlinear current, driving the third harmonic. As a0 increases up to the threshold value amin, at which complete electron evacuation begins in the inner region, the third harmonic amplitude rises rapidly. Above the threshold, as a0 increases, the width of the inner region where there is no third harmonic current, increases and third harmonic amplitude rises less rapidly. The conversion efficiency is found to be in reasonable agreement with the experimental results.

A New Threshold Switching Scheme for a DVB-RCS Mobile Return Link in a Terrestrian Railway Scenario

The new standard for DVB-RCS includes guidelines for mobile user in the market of aircraft, maritime and terrestrial transportation. The standard proposed by ETSI suggests the possibility of using a continuous carrier operation mode in the return channel, beside the classical MF-TDMA mode for better adapting the satellite bandwidth to the new requests of mobile users. It can be important a mechanism for switching between these modalities, in order to exploit in a better way the satellite resources. In this paper a proposal of a novel switching mechanism is presented. Simulation campaigns are carried out in order to validate the proposal algorithm considering different user application distributions. Simulation results proof the goodness of the proposal and provide some guidelines to the satellite operators that want to adopt in their satellite system this hybrid mode called by ETSI standard “Basic Mode”.

Threshold Selection for Ultra-Wideband TOA Estimation based on Neural Networks

Because of the good penetration into many common materials and inherent fine resolution, Ultra-Wideband (UWB) signals are widely used in remote ranging and positioning applications. On the other hand, because of the high sampling rate, coherent Time of Arrival (TOA) estimation algorithms are not practical for low cost, low complexity UWB systems. In order to improve the precision of TOA estimation, an Energy Detection (ED) based non-coherent TOA estimation algorithm using Artificial Neural Networks (ANN) is presented which is based on the skewness after energy detection. The expected values of skewness and kurtosis with respect to the Signal to Noise Ratio (SNR) are investigated. It is shown that the skewness is more suitable for TOA estimation. The best threshold values for different SNRs are investigated and the effects of integration period and channel modes are examined. Comparisons with other ED based algorithms show that in CM1 and CM2 channels, the proposed algorithm provides higher precision and robustness in both high and low SNR environments.

Effects of intrasubband coupling on the scattering phases and density of states in a quantum wire

The properties of scattering phases and density of states in a quantum wire with an attractive scatterer are analyzed. We consider two bound states which couple to a scattering channel and give rise to two Fano resonances. It is shown that varying the parameters of the scatterer (such as its strength and position) produces significantly different effects on the phase behavior and density of states, depending on the subband they occur. These effects stem mainly from the difference between the coupling matrix elements of the two resonant levels with the propagating channel mode.

Q=0collective modes originating from the low-lying Hg-O band in superconducting HgBa2CuO4+δ

Motivated by the recent discovery of two Q\sim0 collective modes [Y. Li et al., Nature 468, 283 (2010); ibid Nat. Phys. 8, 404 (2012)] in the single-layer HgBa2CuO4+\delta, which are often taken as evidence of the orbital current origin of a pseudogap, we examine an alternative and assumption-free scenario constrained by first-principle calculations. We find that in addition to the common CuO2 band, a hybridized Hg-O state is present in the vicinity of the Fermi level, and that it contributes to the low-energy ground state of this system. We calculate the spin-excitation spectrum based on the random-phase-approximation in the superconducting state using a two band model and show that a collective mode in the multi-orbital channel arises at Q=0. This mode splits in energy, yet remains at Q\sim0 as the pseudogap develops breaking both translational and time-reversal symmetries in the spin-channel, and thus gap out the electrnic states. The observations of the dynamical mode and static moment in the pseudogap state are in good accord with experimental observations. A verifiable prediction of this proposal is the development of magnetic order also in the Hg-O layer. Detection of Hg-O band via optical study, or magnetic moment in the Hg-O layer will be tests of this calculation.

Searching for confined modes in graphene channels: The variable phase method

Using the variable phase method, we reformulate the Dirac equation governing the charge carriers in graphene into a nonlinear first-order differential equation from which we can treat both confined-state problems in electron waveguides and above-barrier scattering problems for arbitrary-shaped potential barriers and wells, decaying at large distances. We show that this method agrees with a known analytic result for a hyperbolic secant potential and go on to investigate the nature of more experimentally realizable electron waveguides, showing that, when the Fermi energy is set at the Dirac point, truly confined states are supported in pristine graphene. In contrast to exponentially-decaying potentials, we discover that the threshold potential strength at which the first confined state appears is vanishingly small for potentials decaying at large distances as a power law, but nonetheless further confined states are formed when the strength and spread of the potential reach a certain threshold.

Investigation of the Interaction of Modal and Chromatic Dispersion in VCSEL–MMF Channels

We develop a complete theoretical model to explain the interaction of modal and chromatic dispersion in optical channels based on vertical cavity surface emitting lasers and multimode fibers. We propose an original formalism to estimate the magnitude of this interaction on the channel bandwidth and mode partition noise power penalty within traditional communication system link models. Simulation results are experimentally validated.

Asymptotic Spectral Efficiency of Multiantenna Links in Wireless Networks With Limited Tx CSI

An asymptotic technique is presented for finding the spectral efficiency of multiantenna links in spatially distributed wireless networks where transmitters have channel-state-information (CSI) corresponding to their target receiver. Transmitters are assumed to transmit independent data streams on a limited number of channel modes which limits the rank of transmit covariance matrices. An approximation for the spectral efficiency in the interference-limited regime as a function of link-length, interferer density, number of antennas per receiver and transmitter, number of transmit streams, and path-loss exponent is derived. It is found that targeted-receiver CSI, which can be acquired with low overhead in duplex systems with reciprocity, can increase spectral efficiency several fold, particularly when link lengths are large, node density is high, or both. Additionally, the per-link spectral efficiency is found to be a function of the ratio of node density to the number of receiver antennas, and it can often be improved if nodes transmit using fewer streams. These results are validated for finite-sized systems by Monte-Carlo simulation and are asymptotic in the regime where the number of users and antennas per receiver approach infinity.

LOCAL TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS OF THE COLLISIONLESS MAGNETOROTATIONAL INSTABILITY

The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical accretion disks. In systems accreting at well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the rate of Coulomb collisions between particles is very small, making the disk evolve essentially as a collisionless plasma. We present a nonlinear study of the collisionless MRI using first-principles particle-in-cell (PIC) plasma simulations. In this initial study we focus on local two-dimensional (axisymmetric) simulations, deferring more realistic three-dimensional simulations to future work. For simulations with net vertical magnetic flux, the MRI continuously amplifies the magnetic field until the Alfv\'en velocity, v_A, is comparable to the speed of light, c (independent of the initial value of v_A/c). This is consistent with the lack of saturation of MRI channel modes in analogous axisymmetric MHD simulations. The amplification of the magnetic field by the MRI generates a significant pressure anisotropy in the plasma (with the perpendicular pressure being larger than the parallel pressure). We find that this pressure anisotropy in turn excites mirror modes and that the volume averaged pressure anisotropy remains near the threshold for mirror mode excitation. Particle energization is due to both reconnection and viscous heating associated with the pressure anisotropy. Reconnection produces a distinctive power-law component in the energy distribution function of the particles, indicating the likelihood of non-thermal ion and electron acceleration in collisionless accretion disks. This has important implications for interpreting the observed emission -- from the radio to the gamma-rays -- of systems such as Sgr A*.

Evaluation and optimization of multiple fluorophore analysis of a Pseudomonas aeruginosa biofilm

Conventional laser scanning microscopy for multiple fluorescent stains can be a useful tool if the problems of autofluorescence and cross-talk are eliminated. The technique of spectral imaging was employed to unmix five different fluorophores – ranging in emission from 435 to 665nm – applied to a Pseudomonas aeruginosa biofilm with overlapping spectra and which was not possible using traditional channel mode operation. Using lambda scanning and linear unmixing, the five fluorophores could be distinguished with regions of differentiation apparent.

Channeling of 20-35 MeV electrons in Si substrates of multilayer structures

Studying on X-rays generation by 20 – 33 MeV betatron electrons at its grazing incidence on a 56 ?m Si plate with 1.5 mm length along the electron beam are presented. The plate was prepared from the Si samples used as substrates to create the multilayers on their surfaces. The photos of the angular distributions of generated X-rays show its concentration along atomic axis [110] and atomic planes (110) and (111). That is due to electron channeling when electron moves along atomic axis or plane and radiates in a narrow cones along its directions. As a result, that forms the narrow spot and bands of intensity within the broad cone of ordinary bremsstrahlung. A capture of electrons in the channeling mode at large angles between crystallographic planes and electron beam takes place due to multiple scattering of electrons in the bulk of the crystalline plate. The orientation dependence of angular pattern and spectra of radiation in the intensity spot and bands were measured. Such a complicated "background" is necessary to take into account at studying the X-rays generated in the layered structures created on Si plates, which manifest itself also in the bands of intensity oriented along the layers.

Structure of below-barrier and above-barrier energy bands and wave functions of a particle in the periodic potential of crystalline lattice

The knowledge of energy spectrum structure allows us to find the Bloch state wave functions. During the interaction of charged particles moving in a crystal, the wave functions represent the superposition of Bloch functions. The population of every Bloch state is characterized by Fourier-component squared. The analytical results received in the given work for periodic potential of a crystal lattice in the model of modified Pöschl-Teller's potential make a basis for studying the phenomena in a channeling mode of particles in crystals (the behaviour of particles at different depths of penetration into crystal, angular distributions of particles, both inside the crystal, and at its exited, etc.). The account of the zone structure of energetic spectrum of channeled electrons results in qualitative change of angular distributions of X-ray radiation under the Bragg angles. Therefore it is interesting within the framework of our approach to study the radiation, as well as an output of the nuclear reactions appearing in case of interaction of charged particles moving in a crystal.

Thermal Stability and Optimal Photoinduced Hydrophilicity of Mesoporous TiO2 Thin Films

Using the triblock copolymer Pluronic F127 (EO106PO70EO106) as the templating agent and Ti(OBun)4 as the titanium source, mesostructured TiO2 thin films were constructed through the sol–gel and evaporation-induced self-assembly method. The effect of the calcination temperature on the mesostructure and on the hydrophilicity of the obtained mesoporous TiO2 thin films was investigated. Small-angle and wide-angle X-ray diffractions, transmission electron microscopy, N2 adsorption–desorption, and contact angle measurements were used to characterize the as-synthesized TiO2 thin films. It was shown that the synthesized mesoporous TiO2 materials exhibited an excellent thermal stability and possessed pores with a diameter larger than 7 nm and a narrow pore-size distribution, and thick inorganic walls composed of nanocrystalline anatase. The calcination temperature affected the stability of the mesoporous structures. In the range of 450–600 °C, the mesoporous framework was stable and the pore size was from 7.3 to 7.8 nm. Above 600 °C, however, the structure collapsed partially. On the basis of the film structure, a four-coordinate channel mode was proposed and the collapse criterion for the mesoporous structure was established through thermodynamic calculation. The synthesized mesoporous TiO2 thin films showed excellent hydrophilicity without light illumination; for example, the film obtained after being treated at 600 °C had a contact angle of about 22.5°, whereas the sample treated at 500 °C (the particle and pore sizes were 10.2 and 7.5 nm, respectively) showed the optimal photoinduced hydrophilicity, with the contact angle of about 9.5°.

Performances of Amplify-and-Forward Cooperative Relay Networks with Different Topologies

When the sizes of terminals are limited, cooperative relay networks are recommended as promising virtual MIMO systems to improve the performances of wireless communication systems in literature. Accordingly, some comparisons on the performances of different systems are useful to guide the selection and deployment of cooperative relay systems in field applications. In this paper, we compare the outage probabilities of cooperative relay networks of different topologies (different numbers of antennas used at a transmitter and relays used in a system), as well as the outage probabilities of the MISO systems. We propose an aggregated channel mode, which combines the power gain obtained from the reduction of path loss through the deployment of relays, and the flat fading caused by multi-path propagation. During the evaluation of the performances of different systems, we apply information theory in the calculation of ergodic capacities and consider the requirement on wireless resources in the estimation of outage probabilities. Numerical simulation shows that (1) cooperative networks with multiple relays outperform those with multiple antennas; (2) only when the power gain is included, the performances of cooperative relay networks are comparable with their counterparts in direct transmission; (3) the performances are significantly affected by the locations of relays.

Phase encoding schemes for measurement-device-independent quantum key distribution with basis-dependent flaw

In this paper, we study the unconditional security of the so-called measurement device independent quantum key distribution (MDIQKD) with the basis-dependent flaw in the context of phase encoding schemes. We propose two schemes for the phase encoding, the first one employs a phase locking technique with the use of non-phase-randomized coherent pulses, and the second one uses conversion of standard BB84 phase encoding pulses into polarization modes. We prove the unconditional security of these schemes and we also simulate the key generation rate based on simple device models that accommodate imperfections. Our simulation results show the feasibility of these schemes with current technologies and highlight the importance of the state preparation with good fidelity between the density matrices in the two bases. Since the basis-dependent flaw is a problem not only for MDIQKD but also for standard QKD, our work highlights the importance of an accurate signal source in practical QKD systems. Note: We include the erratum of this paper in Appendix C. The correction does not affect the validity of the main conclusions reported in the paper, which is the importance of the state preparation in MDIQKD and the fact that our schemes can generate the key with the practical channel mode that we have assumed.