Double Barrier System Research Articles

PH-responsive chitosan hollow microspheres pro-flavor based on interfacial Schiff-base bonding for controlled release of cinnamaldehyde

The strong volatility and instability of cinnamaldehyde (CA) limits its application in food and flavor industry. Combining physical encapsulation techniques and chemical bonding methods is a novel strategy to overcome this challenge. Herein, a cinnamaldehyde-chitosan hollow microsphere pro-flavor (CHMP) was developed through interfacial Schiff-base bonding reaction with an average size of 220∼800 nm. Hydrophilic macromolecules of glycol chitosan (GC) are fixed at the oil/water interface via numerous hydrophobic small molecules of CA, forming the CHMP with a positively charged surface and lipophilic cavity. Thus, physical and chemical double-barrier CA delivery system was fabricated in which CA molecules were chemically linked to GC and at the same time embedded in the particles’ core. This structure endows CHMP excellent stability and pH-responsive release abilities. After 48 d of open storage at room temperature, the retention rate of CA in CHMP powder was above 85%. CA release from CHMP exhibited a sustained release rate at neutral pH and a fast release under acidic condition. CHMP also retained excellent sensory profile and exhibited durable antibacterial performance against both Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). Therefore, rather than most of the traditional methods, this CHMP may open a new path for CA controlled release, widening their applications with multifunctionalities.

Exact prime density reproduced through resonant tunneling across a double barrier system

A solid-state experiment based on quantum tunneling is proposed to reproduce the natural numbers and prime numbers as resonant tunneling energies in a double barrier system (DBS). For getting the prime numbers as eigenvalues the well potential is considered as the superposition of a smooth potential which is estimated using a semi-classical approach and a weak local fluctuating potential. We use the transfer matrix approach and finite element method by taking only the smooth part of the potential to obtain resonant energies which reproduces the local average prime density and the local average prime gap exactly. The methodology when applied to a quadratic potential of the well, produces whole numbers as eigenvalues except for a constant zero-point energy —the energy levels of a simple harmonic oscillator.

Transport properties of the resonant tunneling structures based on the pseudospin-1 Dirac–Weyl fermions

Transmission, conductivity, and shot noise are investigated in multi-barrier resonant tunneling structures based on the pseudospin-1 Dirac–Weyl model. Super Klein tunneling, perfect transmission plateau, and resonant tunneling collectively contribute to the transport properties. While resonant tunneling occurs when the energy of the passing quasiparticle coincides with the discrete quasibound energy level of the multi-barrier structure and is widely observed in parabolic and Dirac-cone-shape dispersive materials, super Klein tunneling and perfect transmission plateau are unique in pseudospin-1 systems and barrier-structure independent. As a result, the conductivity and shot noise in pseudospin-1 resonant-tunneling multi-barrier structures demonstrate remarkably different properties from their counterparts of both parabolic-dispersion semiconductors and pseudospin-1/2 Dirac–Weyl materials, typically graphene. It is found that the zero conductivity minimum remains for multi-barrier structures and the relative shot noise indicated by the Fano factor in the three-barrier system is larger than that in the double-barrier system when the Klein tunneling effect weakens.

2-D tunneling structures and increased peak to valley current ratio in double barrier quantum systems under perpendicular electric and magnetic bias

Tunneling across an electrically biased double barrier system (with potential V along the z-axis) in a transverse magnetic field B (along the x-axis) is studied. The magnetic field-induced coupling of the transverse momentum (ky) with the z-direction motion of the electron selects the minimum value of ky depending on the incident energy εz below which the wave becomes evanescent in nature and is restricted from participating in the tunneling process. With the increase in B, resonant tunneling across the DBS occurs for an increasing range of resonant energy εzr albeit at a particular transverse momentum kyr for each εzr. Thus, the one-dimensional resonant tunneling feature at the quasi-resonant energy εzr0 for the entire spectrum of ky in absence of the magnetic field changes to a two-dimensional resonance structure in the εy and εz plane with the application of the magnetic field. The lower and upper bound of εzr and the corresponding limits on kyr for resonant tunneling based on B and V is spelt out. A formula for current density based on these observations is developed and the current–voltage relation for the DBS in presence of the transverse magnetic field is studied. With the application of the magnetic field the Peak to Valley current ratio (PVCR) calculated on the basis of tunneling current increases by many folds. The effect of Zeeman splitting due to interaction of spin moment of conduction electrons with magnetic field on the tunnel current is discussed.

Chitosan Hydrogels with Embedded Thermo- and pH-Responsive Microgels as a Potential Carrier for Controlled Release of Drugs.

We report a promising strategy based on chitosan (CS) hydrogels and dual temperature- and pH-responsive poly(N-isopropylacrylamide-co-methacrylic acid) (PNIPAM-co-MAA) microgels to facilitate release of a model drug, moxifloxacin (MFX). In this protocol, first, the microgels were prepared using a free radical copolymerization method, and subsequently, these carboxyl-group-rich soft particles were incorporated inside the hydrogel matrix using an EDC-NHS amidation method. Interestingly, the resulting microgel-embedded hydrogel composites (MG-HG) acting as a double barrier system largely reduced the drug release rate and prolonged the delivery time for up to 68 h, which was significantly longer than that obtained using microgels or hydrogels alone (20 h). On account of the dual-responsive features of the embedded microgels and the variation of water-solubility of drug molecules as a function of pH, MFX could be released in a controllable manner by regulating the temperature and pH of the delivery medium. The release kinetics followed a Korsmeyer-Peppas model, and the drug delivery mechanism was described by Fickian diffusion. Both the gel precursors and the hydrogel composites exhibited low cytotoxicity against mammalian cell lines (HeLa and HEK-293) and no deleterious hemolytic activity up to a certain higher concentration, indicating excellent biocompatibility of the materials. Thus, the unprecedented combination of modularity of physical properties caused by soft particle entrapment, unique macromolecular architecture, biocompatibility, and the general utility of the stimuli-responsive polymers offers a great promise to use these composite materials in drug delivery applications.

Study of Electronic and Transport Properties in Double-Barrier Resonant Tunneling Systems.

Resonant tunneling devices are still under study today due to their multiple applications in optoelectronics or logic circuits. In this work, we review an out-of-equilibrium GaAs/AlGaAs double-barrier resonant tunneling diode system, including the effect of donor density and external potentials in a self-consistent way. The calculation method uses the finite-element approach and the Landauer formalism. Quasi-stationary states, transmission probability, current density, cut-off frequency, and conductance are discussed considering variations in the donor density and the width of the central well. For all arrangements, the appearance of negative differential resistance (NDR) is evident, which is a fundamental characteristic of practical applications in devices. Finally, a comparison of the simulation with an experimental double-barrier system based on InGaAs with AlAs barriers reported in the literature has been obtained, evidencing the position and magnitude of the resonance peak in the current correctly.

Quantum transport in p-type narrow channel with DC-biased double finger gate

The quantum transport in a p-type narrow channel device with a DC-biased double finger gate is investigated using a Luttinger four-band Hamiltonian and a propagation matrix approach. The results show that when the potential energy modulation effect produced by the finger gate is large, the quantum transport shows a resonance behavior indicative of large barriers in a double-barrier system. A simple analytical method based on an ideal resonant square quantum well approximation is used to predict the energies of the resonance peaks contributed by the light and heavy holes. The results show that the first conductance peak is formed at 2e2/h and is contributed by the heavy holes. A second conductance resonance peak is formed at 3e2/h due to the semi-reflection of the heavy holes and resonant transmission of the light holes. Finally, a third conductance resonance peak is formed at 4e2/h as a result of the concurrent resonant transmission of the light holes and heavy holes.

DFT-NEGF Study of Electron Transfer Property in Graphene Nanoribbon Double Barrier System

Current-voltage (I – V) characteristics in armchair graphene nanoribbon (AGNR) double barrier systems (DBSs) are investigated by the density functional theory (DFT) and the non-equilibrium Green’s function (NEGF) methods. The hexagonal boron nitride (h-BN) which has an analogous structure with a graphene shows wide bandgap and becomes an electrical barrier in DBSs. The heterojunction structure of AGNR and two h-BNs with one six-membered ring width has properties as a resonant tunnelling device. Due to the resonance, sharp peaks are formed in the transmission function around the Fermi energy EF . Our previous studies have explained the origins of some peaks by solving the one-dimensional Dirac equation for massless particles. Here, by using the two-dimensional Dirac equation, we show that the remaining sharp peaks depend on the transverse nodal pattern of the wavefunction as well as the anisotropy of the Fermi velocity. Moreover, in the I – V characteristics, a flat part is formed without the negative differential resistance appearing. By partial density of state (PDOS) analysis, we reveal that the flat part in the current is caused by the fact that the peak positions in the resonance region are stable against the bias voltage.

Study on the Implementation of Quality Assurance Aspect on High-Temperature Gas Cooled Reactor (HTGR)

High-Temperature Gas Cooled Reactor (HTGR) Power Reactors have a layered safety system with the concept of a double barrier system. However, quality assurance is required to ensure the fulfillment of technological analysis weightings on power chamber materials, power ratings, fabrication components of High- Temperature Gas Cooled Reactor (HTGR) fuel elements, primary and secondary coolant pressures to meet customer requirements and be carried out continuously systematic and objective. This study analyzes the application of quality assurance, safety, security, the correctness of test/calibration results, increasing competitiveness, consumer protection and building trust (brand image) in the use of HTGR reactors to provide a reliable level of safety and security. The study method used is based on the literature review. The output of this study is the document of the HTGR reactor quality assurance systems to fulfill the IAEA-TECDOC-1645 requirements according to safety and standardization in frameworks design, material, fuel, and physical properties of the quality management systems. HTGR reactor has technical qualification, good performance of HTGR fuel, safety and accident analysis source term analysis, control of multi-modular HTGR and related human factor analysis, also optimizing radiation protection of HTGR

Implication of TeO2 and SeO2 as well matrices and GeGa-AsAl for quantum dot reservoir in tunneling assists detection of gamma ray and fermions from space

Abstract Indirect tunneling device serves implicative technique in sensing technology. Navigation through space telescopes and Detection of gamma radiation leakage in nuclear plant, sensing of Gamma radiation while navigating in space astronomy with an effective tool is the requisite issue for nuclear and space physics. Implication of quantum dot reservoir with selective metals like oxides of Se, Te, and Si, Al as double barrier system in Indirect tunneling device makes it possible by theoretical agreement on base of Klein paradox equation and Dirac equation support Josephson Current effect in evaluating magnetic field due to radiant charged particles like fermions and gamma particles. Rise and fluctuations of voltage vide I-J and IV characteristic due to interactive particles (massive or mass less) under constant potential barrier set up in the indirect tunneling diagnose phonons.

Blood-brain barrier genetic disruption leads to protective barrier formation at the Glia Limitans.

Inflammation of the central nervous system (CNS) induces endothelial blood-brain barrier (BBB) opening as well as the formation of a tight junction barrier between reactive astrocytes at the Glia Limitans. We hypothesized that the CNS parenchyma may acquire protection from the reactive astrocytic Glia Limitans not only during neuroinflammation but also when BBB integrity is compromised in the resting state. Previous studies found that astrocyte-derived Sonic hedgehog (SHH) stabilizes the BBB during CNS inflammatory disease, while endothelial-derived desert hedgehog (DHH) is expressed at the BBB under resting conditions. Here, we investigated the effects of endothelial Dhh on the integrity of the BBB and Glia Limitans. We first characterized DHH expression within endothelial cells at the BBB, then demonstrated that DHH is down-regulated during experimental autoimmune encephalomyelitis (EAE). Using a mouse model in which endothelial Dhh is inducibly deleted, we found that endothelial Dhh both opens the BBB via the modulation of forkhead box O1 (FoxO1) transcriptional activity and induces a tight junctional barrier at the Glia Limitans. We confirmed the relevance of this glial barrier system in human multiple sclerosis active lesions. These results provide evidence for the novel concept of "chronic neuroinflammatory tolerance" in which BBB opening in the resting state is sufficient to stimulate a protective barrier at the Glia Limitans that limits the severity of subsequent neuroinflammatory disease. In summary, genetic disruption of the BBB generates endothelial signals that drive the formation under resting conditions of a secondary barrier at the Glia Limitans with protective effects against subsequent CNS inflammation. The concept of a reciprocally regulated CNS double barrier system has implications for treatment strategies in both the acute and chronic phases of multiple sclerosis pathophysiology.

An atomic Fabry\u2013Perot interferometer using a pulsed interacting Bose\u2013Einstein condensate

We numerically demonstrate atomic Fabry–Perot resonances for a pulsed interacting Bose–Einstein condensate (BEC) source transmitting through double Gaussian barriers. These resonances are observable for an experimentally-feasible parameter choice, which we determined using a previously-developed analytical model for a plane matter-wave incident on a double rectangular barrier system. Through numerical simulations using the non-polynomial Schödinger equation—an effective one-dimensional Gross–Pitaevskii equation—we investigate the effect of atom number, scattering length, and BEC momentum width on the resonant transmission peaks. For ^{85}Rb atomic sources with the current experimentally-achievable momentum width of 0.02 hbar k_0 [k_0 = 2pi /(780~text {nm})], we show that reasonably high contrast Fabry–Perot resonant transmission peaks can be observed using (a) non-interacting BECs, (b) interacting BECs of 5 times 10^4 atoms with s-wave scattering lengths a_s=pm 0.1a_0 (a_0 is the Bohr radius), and (c) interacting BECs of 10^3 atoms with a_s=pm 1.0a_0. Our theoretical investigation impacts any future experimental realization of an atomic Fabry–Perot interferometer with an ultracold atomic source.

Enhancement of transparency in a double-barrier structure by the Fano antiresonance

We show that the presence of a side-attached state strongly modifies the transmission through a one-dimensional double-barrier system in the window of wavevectors around the Fano antiresonance. Specifically, the interplay between the Fano interference and the size quantization inside the structure gives rise to narrow resonant peaks in the transmission coefficient. The height of the peaks may become close to unity (perfect transmission) even for an asymmetric setup with strong barriers, where the transmission coefficient in the absence of the Fano state is strongly suppressed at all other wavevectors. Thus, the two types of the interference phenomena, each by itself leading to the suppression of the transmission, conspire in a peculiar way to produce the transparency enhancement.

Sensitivity analysis of influencing parameters on slit-type barrier performance against debris flow using 3D-based numerical approach

Extreme rainfall-induced debris flow can be catastrophic to an urban area, and installation of slit-type barriers can prevent such damage while minimizing negative impact on environments. However, the performance of slit-type barriers against debris flows remains poorly identified partly due to the innate complexity in interactions between debris flow and solid structure. This paper investigated the flow behaviors of debris affected by slit-type barriers using the computational fluid dynamics (CFD) method, in which the numerical model based on the volume of fluid method was verified using the physical modeling results. The sensitivity analysis was performed by building metamodels to determine the primary parameters influencing the barrier performance against debris flows among various variables, in which the effect of input properties and design parameters, particularly the soil concentration in fluidized debris, initial velocity and volume of debris, the barrier height, and the opening ratio, was evaluated from the perspectives of the flow energy reduction and debris trapping. The initial velocity and volume of debris were found to play a significant role in determining the debris flow characteristics. A decrease in the opening ratio in the channel primarily facilitated the energy reduction and trapping due to the reduced opening size. However, the barrier height exhibited a limited effect when the height was sufficiently high to block the debris flow volume. In addition, it was observed that the double barrier system effectively increased the energy reduction while keeping the benefit of open-type barrier. The developed simulation method and obtained results provide an effective tool and an insight that can contribute to an optimum design of the debris-flow barrier.

АНАЛИТИЧЕСКОЕ РЕШЕНИЕ ИНТЕГРАЛЬНОГО УРАВНЕНИЯ ШРЕДИНГЕРА

In this paper, the question about the use of wave dynamics for solving problems of membrane separation of helium isotopes in the gas state at cryogenic temperatures is considered. The dimensionless form of the stationary Schrödinger differential equation is obtained. Following that, the integral representation form of the wave function is written. This form, which is equivalent to the classical equation, is similar to the integral equation with a degenerate core; however, it contains a modulus of the argument with a shift along the real axis. Using the shift operator, the existing exponential function in the Schrödinger integral equation can be split into a differential operator and an exponential function of the argument module which does not contain a shift. The Fourier identity allows reducing the exponent of the modulus of the argument to a regular exponent. Next, based on the general property of a differential operator acting on an exponent, it is possible to calculate the spectral functions of the problem and write down the distribution for the wave function. This distribution is ultimately expressed through the spectra of the potential barrier. Thereafter, the structure and the spectrum of the composite barrier are considered. With the expression determining the reflection coefficient, it is found that the double-barrier system can have a resonant passage of one of the components in the sequence of distances between the layers of the membrane.

I-V Characteristics of In-Plate Graphene Nanoribbon/h-BN Heterojunctions and Resonant Tunneling

We present here the first principle calculations of the electrical properties of in-plate heterojunctions of armchair graphene nanoribbon/h-BN(AGNR/h-BN)s. The calculations are carried out using SIESTA package, which is comprised of numerical codes of the density functional theory(DFT) and the non-equilibrium Green’s function(NEGF). Especially, adopting the conductive (3n-1)-family of AGNR((3n-1)-AGNR) makes the lead parts on both side of the model metallic. Two transverse arrays of h-BN, which is a wide-gap semiconductor, are embedded in the middle of (3n-1)-AGNR and act as a double barrier system.The quantum double barrier tunneling is found in the transmission functions(TF) and I-V characteristics of 8, 11, 14-AGNR/h-BN. The TF shows significantly spiky peaks in the neighborhood of the Fermi energy, and consequently, it results in step-sise I-V characteristics. Simple one-dimensional Dirac equation model for the double barrier system is also proposed to analyze numerical results. Our model reproduces most of the peaks of the transmission functions nearby the Fermi energy, as a result of quantum tunneling.

Cellulose-based injectable hydrogel composite for pH-responsive and controllable drug delivery

Cellulose-based biocompatible, tunable and injectable hydrogels embedded with pH-responsive diblock copolymer micelles were constructed to achieve localized drug delivery with prolonged, stimuli-driven and slow-release function. First, we prepared two types of modified carboxymethyl cellulose (CMC) including hydrazide-modified carboxymethyl cellulose (CMC-NH2) and oxidized carboxymethyl cellulose (CMC−CHO) with varying degrees of oxidation. Then, pH-responsive poly (ethylene oxide)-block-poly (2-(diisopropylamino) ethyl methacrylate) (PEO-b-PDPA) copolymers as micelle cores to carry hydrophobic substances were also synthesized through atom transfer radical polymerization (ATRP). An injectable hydrogel composite system was finally obtained by mixing CMC-NH2 and CMC−CHO polymer suspensions containing PEO-b-PDPA copolymer micelles through a Schiff base reaction. This newly-synthesized, tunable, cellulose-based double barrier system exhibits a pH-triggered, prolonged, and slow-release profile based on the release test using both Nile Red dye and doxorubicin. The hydrogel system also exhibited comparable storage moduli and tunable degradation properties.

I–V characteristics of graphene nanoribbon/h-BN heterojunctions and resonant tunneling

We present the first principle calculations of the electrical properties of graphene sheet/h-BN heterojunction (GS/h-BN) and 11-armchair graphene nanoribbon/h-BN heterojunction (11-AGNR/h-BN), which are carried out using the density functional theory (DFT) method and the non-equilibrium Green’s function (NEGF) technique. Since 11-AGNR belongs to the conductive (3n-1)-family of AGNR, both are metallic nanomaterials with two transverse arrays of h-BN, which is a wide-gap semi-conductor. The two h-BN arrays act as double barriers. The transmission functions (TF) and I– characteristics of GS/h-BN and 11-AGNR/h-BN are calculated by DFT and NEGF, and they show that quantum double barrier tunneling occurs. The TF becomes very spiky in both materials, and it leads to step-wise I– characteristics rather than negative resistance, which is the typical behavior of double barriers in semiconductors. The results of our first principle calculations are also compared with 1D Dirac equation model for the double barrier system. The model explains most of the peaks of the transmission functions nearby the Fermi energy quite well. They are due to quantum tunneling.

Molecularly imprinted polymer as drug delivery carrier in alginate dressing

Vancomycin was used as a template to obtain a molecularly imprinted polymer. The polymer imprinted with the antibiotic was encapsulated in alginate matrix to obtain a potential antibacterial wound dressing. The amount of vancomycin released in the first 24h after application of the double barrier system decreased with respect to that released from the polymer without the alginate from 87% to 47%. The antibiotic release process followed diffusion and swelling controlled mechanism (non-Fickian transport). The highest correlation coefficients were obtained for Higuchi kinetic model typical of polymer matrices or some transdermal systems. The system studied with vancomycin demonstrated antibacterial activity towards the bacteria strains selected. The diameters of inhibition zone were greater than for the reference samples. The system without the antibiotic had no effect on the growth of bacteria. The material studied has the properties of a dressing for a potential use in a long term wound healing.

Electronic transmission and dwell time on a double barrier system with an accelerating quantum well

Resonant tunneling quantum structures consist of asymmetric wells and barriers have been investigated to find their optimized geometrical parameters and potential profile by the numerical calculations. The results show that the widths and the depths of the asymmetric wells have a significant effect on the transmission coefficient and the dwell time. The properties exhibited in this work may establish guidance to the device applications.