Single Barrier Research Articles

Wave attenuation by multiple thin vertical porous walls in water of uniform finite depth

The analysis for wave attenuation by multiple thin porous walls submerged in water of uniform finite depth is carried out under the acceptance of linear theory of water waves. Two different types of barrier configurations are considered, namely partially immersed walls and bottom-standing walls. A set of coupled Fredholm-type integral equations are obtained for the boundary value problem by employing Havelock's inversion formulae and continuity of water wave potential across the gap below or above the walls. The methodology adopted to solve these integral equations is multi-term Galerkin's approximation with Chebychev's polynomials as a set of basis functions multiplied by suitable weights. Also, the square-root singularity of fluid velocity at the edge of the porous walls is precisely handled. The numerical results are depicted for reflection and transmission coefficients, dissipation of wave energy and dynamic wave force against wavenumber for different parametric values involving in the barrier configurations. This theory demonstrates that the dynamic wave forces exerted on the porous walls are reduced significantly as the magnitude of the porous effect parameter is increased. The present study is ratified with the existing results in the literature of water waves for a single as well as double rigid barriers and single porous barrier.

Anisotropic thermionic response of Weyl semimetals with application in thermionic cooling

We demonstrate that Weyl semimetals can exhibit intriguing thermionic properties. The emission current varies significantly in systems with different Weyl point separation, the key topological parameter of such materials. The emission is highly anisotropic along directions parallel and perpendicular to the Weyl point separation. For large separations, emission is higher along the perpendicular direction. However, for smaller separations, there exists a changeover temperature at which the dominant emission direction changes from parallel to perpendicular when increasing temperature. The optimal cooling efficiency of a single barrier device can approach 80% of the theoretical limit in the perpendicular direction, 5% greater than a conventional parabolic material. Our results suggest that this class of material has potential applications in thermionic cooling and power generation.

Flow field generated by a dielectric barrier discharge plasma actuator in quiescent air at initiation stage

A single Dielectric Barrier Discharge (DBD) plasma actuator driven by Alternating Current (AC) power, capable of inducing a starting vortex and a wall jet in quiescent air, is suited for low-Reynolds-number flow control. However, the starting vortex and the wall jet are usually observed after the plasma actuator has been operated for dozens of and hundreds of cycles of the voltage, respectively. The detail of the induced flow field at the initiation stage of the plasma actuator has rarely been addressed. At the initiation stage, a thin jet that provides the impetus for the entrainment of the induced flow at the beginning of the plasma actuation is first observed by using a high-accuracy phase-lock Schlieren technique and a high-speed Particle Image Velocimetry (PIV) system. This is the initial form of the momentum transfer from the plasma to the fluid. Then, an arched type jet is created by the plasma actuator. In addition, the whole development process of the induced flow field from the starting point of the thin jet to the quasi-steady stage of wall jet is presented for providing a comprehensive understanding of the plasma actuator and proposing a relevant enhancement of the numerical simulation model.

Testiranje biološke učinkovitosti feromona i klopki za ulov mediteranskog potkornjaka Orthotomicus erosus (Coleoptera, Curculionidae)

In the Aleppo pine forests at the Croatian Mediterranean in 2017, a Mediterranean bark beetle (Orthotomicus erosus) appeared in population densities that had not been recorded before and until then was not considered a significant pest in that area. Natural enemies are not able to follow a sudden increase of the bark beetle population, which results in rapid increase of drying trees. As a part of the suppression of the Mediterranean bark beetle in 2018, pheromone traps have been installed in Croatia for monitoring purposes. Although there are multiple options for applying different types of traps and pheromone preparations for the Mediterranean bark beetle, so far the differences in catches of different types of traps and their selectivity have not been investigated. In 2019, 40 pheromone traps were placed in the Forest Park ​​Marjan (Split) on 196 ha of forest area. A pairs of pheromone preparations Pheroprax and Erosowit were compared, a system of three traps (Triplet) with a single flight barrier trap as well as the modified wet flight barrier trap with a regular flight barrier trap. In addition to the average number of catches in pheromone traps, particular attention was given to selectivity. Two predator species Tanasimus formicarius and Temnochila caerulea were found in traps, with T. formicarius in insignificant quantities relative to T. caerulea. The results indicate that Erosowit exhibits significantly higher catches compared to Pheroprax and is significantly more selective. Pheroprax has a very high catches of T. caerulea predators and is not recommended for practical use. The Triplet had only slightly better catches compared to the single flight barrier trap, but also showed slightly better selectivity. The Triplet did not show the expected effect due to the amount of the catch, which was slightly higher than in the single trap, but not significantly in order to recommend their use. The wet flight barrier trap turned out not to be satisfactory as it does not produce significantly higher catches than a regular flight barrier trap, and is twice less selective. Given the additional costs (trap adaptation, fluid that needs to be changed, slower collection), this trap type is not recommended for use. Comparing the results of the catch in 2019, the number of bark beetles was found to be almost 5 times lower than in 2018.

Vibro-acoustic analysis of parallel barriers integrated with flexible panels

In urban communities, parallel barriers are commonly erected for controlling environmental noise such as traffic and construction noise. However, owing to the multiple reflections between the parallel barriers, their performance may be worse than that of a single barrier. To improve the performance of parallel barriers, a small piece of flush-mounted panel backed by a slender cavity in an otherwise rigid wall of barriers is proposed. With the excitation of the incident wave from a sound source inside the parallel barriers, the flexible panel vibrates, and sound is radiated out to undergo acoustic interference with the sound field bounded by the parallel barriers. Consequently, the sound energy in this space and diffraction at the barrier top edge are reduced over a broad band in the low-frequency regime. A theoretical model for tackling the vibro-acoustic coupling between the sound field of the open cavity and the vibrating panel is established to investigate the noise reduction mechanism in the shadow zone. With optimal structural properties of the panel, an additional averaged insertion loss of approximately 5 dB can be achieved at 80–1000 Hz. The theorical results, which are experimentally validated, pave the way for the potential applications of the flexible panel devices (FPDs) for improving the noise reduction of parallel barriers.

Traffic Noise Mitigation Using Single and Double Barrier Caps of Different Shapes for an Extended Frequency Range

The primary function of noise barriers is to shield inhabitants of affected areas from excessive noise generated by road traffic. To enhance the performance of noise barriers while simultaneously adhering to height restrictions, the attachment of structures (caps) of different shapes to the tops of conventional screens can be considered. These caps can significantly impact the diffracted sound energy, thereby increasing the desired global acoustic losses. This work presents a comprehensive study of the acoustic performance of noise barriers with single and double attached caps of different shapes through a calculation of their insertion losses (IL). This study comprehensively addresses and compares different types, sizes, combinations, and numbers of noise barrier caps for different scenarios (including sloping and absorbent grounds) and sources (“car” and “ambulance”) for an extended frequency band up to 10 kHz. To the best of the authors’ knowledge, this is a range that has not previously been analyzed. A variety of different cap shapes were considered including cylinders, rectangles, trapezoids, and Y/T-shaped forms. To calculate the IL, an innovative and fast uniform theory of diffraction (UTD)-based method developed by the authors was applied in all simulations. The results showed that the Y-shaped single and double barrier caps were, in general, the most effective at increasing IL without raising the height of the barrier, thereby successfully managing the aesthetic impact. The results also showed how the consideration of sloping and absorbent floors could also contribute to improved noise abatement.

Magnetic field tuning of low-energy spin dynamics in the single-atomic magnet Li2(Li1−xFex)N

We present a systematic ${}^{57}\mathrm{Fe}$ M\"ossbauer study on highly diluted Fe centers in ${\mathrm{Li}}_{2}({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})\mathrm{N}$ single crystals as a function of temperature and magnetic field applied transverse and longitudinal with respect to the single-ion anisotropy axis. Below 30 K, the Fe centers exhibit a giant magnetic hyperfine field of ${\overline{B}}_{A}=70.25(2)\phantom{\rule{4pt}{0ex}}\mathrm{T}$ parallel to the axis of strongest electric field gradient ${\overline{V}}_{zz}=\ensuremath{-}154.0(1)\phantom{\rule{4pt}{0ex}}\mathrm{V}/{\AA{}}^{2}$. Fluctuations of the magnetic hyperfine field are observed between 50 and 300 K and described by the Blume two-level relaxation model. From the temperature dependence of the fluctuation rate, an Orbach spin-lattice relaxation process is deduced. An Arrhenius analysis yields a single thermal activation barrier of ${\overline{E}}_{A}=570(6)\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and an attempt frequency ${\overline{\ensuremath{\nu}}}_{0}=309(10)\phantom{\rule{4pt}{0ex}}\mathrm{GHz}$. M\"ossbauer spectroscopy studies with applied transverse magnetic fields up to 5 T reveal a large increase of the fluctuation rate by more than one order of magnitude. In longitudinal magnetic fields, a splitting of the fluctuation rate into two branches is observed consistent with a Zeeman induced modification of the energy levels. The experimental observations are qualitatively reproduced by a single-ion effective spin Hamiltonian analysis assuming a ${\mathrm{Fe}}^{1+}\phantom{\rule{4pt}{0ex}}{d}^{7}$ charge state with the unquenched orbital moment and a $J=7/2$ ground state. It is demonstrated that a weak axial single-ion anisotropy $D$ of the order of a few Kelvin can cause a two orders of magnitude larger energy barrier for longitudinal spin fluctuations.

Simultaneous removal of toluene and styrene by non-thermal plasma-catalysis: Effect of VOCs interaction and system configuration

Toluene and styrene were two typical aromatic VOCs which were commonly used and coexistence in the exhaust gases from industrial manufacturing. Their simultaneous removal performances under non-thermal plasma (NTP) and NTP-catalysis were carried out and compared by a single stage coaxial dielectric barrier discharge (DBD) reactor. The effects of VOCs mixture, humidity, materials filling in the discharge zoon on the removal efficiency, COx selectivity, byproducts types and their emission levels were deeply investigated to explore the degradation mechanism and coexistence effect. Experimental results showed that the toluene removal was significantly inhibited when treated together with styrene under plasma treatment. But that of styrene was hardly affected at the same conditions. It was found that benzaldehyde as the primary organic byproducts from styrene consumed the oxidizing particles (O and . OH), limiting the conversion of toluene. The introduction of Cu-doped MnO2 materials significantly improved the VOCs removal performance with nearly 100% conversion to COx at a discharge power less than 30 W, as well as O3 generation from more than 1.2 mg L−1 by NTP to 1.6 × 10−3 mg L−1 by NTP-catalysis. With the help of in situ FT-IR, it was believed that catalysts not only accelerated the adsorption and degradation of pollutants but also utilized ozone to involve this process. At last, a plausible explanation on binary coexistence effect under different conditions had been suggested and discussed.

Development and Optimization of Single Filament Plasma Jets for Wastewater Decontamination

New efficient depollution techniques for water decontamination, purification and disinfection are being sought to replace those classic methods (chemical, filtration, ozonisation, photochemical reactions) that have deficiency for some substances. The use of plasma technologies, discharges in, or in contact with, wastewater are promising approaches for the decomposition of pollutants by highly oxidative radicals, charged particles, UV radiation, etc. produced by plasma. In the present study we report on the potential of radiofrequency single and multiple filamentary Dielectric Barrier Discharge (DBD) jets for the decolorization of methylene blue (MB) dye in water solutions. Optical emission spectroscopy (OES) investigations were performed for the characterization of plasma evolving in air, and in liquid. The decolorization process was monitored by absorption spectroscopy. We determined the decolorization time, according to a variety of external parameters. The key parameters for obtaining the maximum decolorization rate were identified as being the discharge tube diameter, tube nature (glass/ceramic), the injected power in the discharge, the type of reactive gas and the number of filamentary plasma jets.

Wave Interaction with Single and Twin Vertical and Sloped Slotted Walls

The interaction between waves and slotted vertical walls was experimentally studied in this research to examine the performance of the structure in terms of wave transmission, reflection, and energy dissipation. Single and twin slotted barriers of different slopes and porosities were tested under random wave conditions. A parametric analysis was performed to understand the effect of wall porosity and slope, the number of walls, and the incoming relative wave height and period on the structure performance. The main focus of the study was on wave transmission, which is the main parameter required for coastal engineering applications. The results show that reducing wall porosity from 30% to 10% decreases the wave transmission by a maximum of 35.38% and 38.86% for single and twin walls, respectively, increases the wave reflection up to 47.6%, and increases the energy dissipation by up to 23.7% on average for single walls. For twin-walls, the reduction in wall porosity decreases the wave transmission up to 26.3%, increases the wave reflection up to 40.5%, and the energy dissipation by 13.3%. The addition of a second wall is more efficient in reducing the transmission coefficient than the other wall parameters. The reflection and the energy dissipation coefficients are more affected by the wall porosity than the wall slope or the existence of a second wall. The results show that as the relative wave height increases from 0.1284 to 0.2593, the transmission coefficient decreases by 21.2%, the reflection coefficient decreases by 15.5%, and the energy dissipation coefficient increases by 18.4% on average. Both the transmission and the reflection coefficients increase as the relative wave length increases while the energy dissipation coefficient decreases. The variation in the three coefficients is more significant in deep water than in shallower water.

Product analysis and mechanism of toluene degradation by low temperature plasma with single dielectric barrier discharge

A single dielectric barrier discharge (DBD) low-temperature plasma reactor was set up, and toluene was selected as the representative substance for volatile organic compounds (VOCs), to study the reaction products and degradation mechanism of VOCs degradation by low-temperature plasma. Different parameters effect on the concentration of O3 and NOx during the degradation of toluene were studied. The exhaust in the process of toluene degradation was continuously detected and analyzed, and the degradation mechanism of toluene was explored. The results showed that the concentration of O3 increased with the increase of the power density and discharge voltage of the plasma device. However, as the initial concentration of toluene increased, the concentration of O3 basically keep steady. The concentration of NOx in the by-products increased with the discharge voltage, power density, and initial concentration of toluene in the plasma device, and the concentration of NO2 was much higher than the concentration of NO. The degradation process of toluene was detected and analyzed. The results showed that the degradation mechanism of toluene by plasma includes high energy electron bombardment reaction, active radical reaction and ion molecule reaction. Among them, the effect of high-energy electrons on toluene degradation is the largest, followed by the effect of free radicals, in which oxygen radicals participated in the reaction mainly through the formation of C–O bond, CO bond, (CO)–O– bond and –OH radical, while nitrogen radicals participate in the reaction mainly through the formation of C–NH2, (CNH)- bond, CN bond and C–NO2 bond. The results can provide some data supports for the study of low-temperature plasma degradation of VOCs.

Adolescent Barriers to HIV Prevention Research: Are Parental Consent Requirements the Biggest Obstacle?

PurposeOne third of people newly living with HIV/AIDS are adolescents. Research on adolescent HIV prevention is critical owing to differences between adolescents and adults. Parental permission requirements are often considered a barrier to adolescent enrollment in research, but whether adolescents view this barrier as the most important one is unclear. MethodsAdolescents were approached in schools in KwaZulu-Natal, South Africa, and at a sexually transmitted infection clinic at the Children’s Hospital of Aurora, Colorado. Surveys with a hypothetical vignette about participation in a pre-exposure prophylaxis trial were conducted on smartphones or tablets with 75 adolescents at each site. We calculated descriptive statistics for all variables, using 2-sample tests for equality of proportions with continuity correction. Statistical significance was calculated at p < 0.05. Multivariate analyses were also conducted. ResultsMost adolescents thought side effects (77%) and parental consent requirements (69%) were very important barriers to research participation. When asked to rank barriers, adolescents did not agree on a single barrier as most important, but the largest group of adolescents ranked parental consent requirements as most important (29.5%). Parental consent was seen as more of a barrier for adolescents in South Africa than in the United States. Concerns about being experimented on or researchers’ mandatory reporting to authorities were ranked much lower. Finally, most (71%, n = 106) adolescents said they would want to extra support from another adult if parental permission was not required. ConclusionAdolescents consider both parental permission requirements and side effects important barriers to their enrollment in HIV prevention research. Legal reform and better communication strategies may help address these barriers.

Control of a Detonation Wave in a Channel with Obstacles Using Preliminary Gas Mixture Preparation

Using the detailed kinetic mechanism of chemical interaction, the effect of preliminary preparation of the stoichiometric hydrogen-air mixture (dissociation of a part of molecular hydrogen and oxygen on atomic gases) on the detonation wave characteristics is investigated numerically with the aim to control detonation combustion in plane channels with obstacles. It is found that the above-mentioned partial initial dissociation can be used to prevent quenching of detonation in channels with both a single obstacle and multiple barriers. It is revealed that the mixture, obtained as a result of preparation, differs from the initial hydrogen-air mixture by the qualitatively different type of detonation re-initiation after interaction with obstacles.

Enhancement of a horizontal axis wind turbine airfoil performance using single dielectric barrier discharge plasma actuator

Wind turbines are of the most promising devices to cut down carbon emissions. However, some phenomena that adversely affect their performance are inevitable. The aim of the present paper is to investigate flow separation prevention exploiting leading edge (LE) single dielectric barrier discharge plasma actuator (SDBD-PA) on an airfoil belonging to a section of a locally developed wind turbine. The numerical results of the surface pressure distribution over the airfoil were compared with the experimental measurements carried out by the authors on the same blade section, and good agreement was found between numerical and experimental data for both plasma-OFF and plasma-ON cases. An in-depth parametric numerical investigation was then carried out to provide a better understanding of the flow behavior affected by the activation of PA over the same airfoil at post stall angle of attacks (AOAs). According to the results, the frequency and voltage of actuation, AOA, and free stream velocity are shown to have strong impacts on separation delay and actuation effectiveness. In Reynolds number of 2.85 × 105, the maximum PA effectiveness takes place at 21° which is approximately 312%, 307%, and 256% corresponding to the PA location of LE, 0.02 chord, and 0.15 chord, respectively. Also, maximum velocity of the domain is increased three times of the free stream velocity on average for three investigated Reynolds numbers at the frequency and voltage of 12 kHz and 12 kV, respectively. Furthermore, the size of the wake area noticeably contracts due to the presence of the SDBD-PA. The results clearly indicate that the lift and drag coefficients as well as the lift-to-drag ratio fit a linear variation pattern with the frequency of actuation. The variation rate of the aforementioned parameters becomes steeper as the peak voltage of actuation increases. Highly nonlinear aerodynamic responses and significant interactions were demonstrated between the investigated parameters.

The innovative “NDBA” concrete safety barrier able to withstand two subsequent TB81 crash tests

The new NDBA concrete road safety barrier is characterized by an innovative anchorage system based on two “C” steel profiles incorporated into the terminal sections of each module and a vertical HEM 100 steel profile inserted for linking the barrier modules. Every single barrier module is fixed in the body of the road embankment and pavement layers by six IPE 80 steel beams (three for each side with a mutual distance of 2 m), each 78 cm long. The IPE 80 steel beams are placed into niches, in the lower part of the barrier.The new barrier has been analysed first by numerical simulations (LS-DYNA software) and afterwards by full-scale crash tests. One TB11 (light vehicle) and two successive TB 81 (heavy vehicle) full-scale crash tests have been performed on NDBA barrier of 72 m length. The second TB81 test was performed on a damaged barrier previously subjected to impact without it being repaired. The experiments were conducted at “CSI test centre” in Bollate, Milan (Italy).According to the EN 1317 regulation, the results have shown a containment level CL = 725 kj (H4b class), a measured maximum ASI = 1.26 (class B), a working width W = 0.74 m (class W2). The research proves that the NDBA barrier is able to withstand two subsequent heavy vehicle (38 t) impacts.In addition, the study demonstrates that the new barrier may guarantee more safety for light vehicle occupants (TB11 test) than a conventional steel safety barrier with equal containment level (H4b class).Therefore, in the near future, NDBA barrier may be installed on existing roads, especially where reduced working width (W2) is required or in motorways with high AADT values and heavy vehicle percentage.

Dynamical Transitions of Supercooled Water in Graphene Oxide Nanopores: Influence of Surface Hydrophilicity.

Molecular dynamics simulations are carried out to explore the dynamical crossover phenomenon in strongly confined and mildly supercooled water in graphene oxide nanopores. Since the extent of hydrophilicity can be varied on graphene oxide surfaces, they offer energetically heterogeneous environments that can potentially modulate the rotational and translational relaxation dynamics of confined water. The influence of the physicochemical nature of the graphene oxide surface on the dynamical transitions is investigated by varying the extent of hydrophobicity on the confining surfaces placed at an intersurface separation of 10 Å. Water forms two distinct layers in contact with the graphene oxide surface at this separation. All dynamical quantities show a typical slowing down as the temperature is lowered from 298 to 200 K; however, the nature of the transition is a distinct function of the surface type. Water confined between surfaces consisting of alternating hydrophilic and hydrophobic regions exhibit a strong-to-strong dynamical transition in the diffusion coefficients and rotational relaxation times at a crossover temperature of 237 K and show a fragile-to-strong transition in the α-relaxation time at 238 K. The observed crossover temperature is higher than the freezing point of the SPC/E water model used in this study, indicating that these dynamical transitions can occur with mild supercooling under strong confinement in the absence of bulk-like water. In contrast, water confined in a hydrophilic nanopore shows a single Arrhenius energy barrier over the entire temperature range. Our results indicate that in addition to confinement, the nature of the surface can play a critical role in determining the dynamical transitions for water upon supercooling.

Deploy Efficiency Driven k-Barrier Construction Scheme Based on Target Circle in Directional Sensor Network

With the increasing demand for security, building strong barrier coverage in directional sensor networks is important for effectively detecting un-authorized intrusions. In this paper, we propose an efficient scheme to form the strong barrier coverage by adding the mobile nodes one by one into the barrier. We first present the concept of target circle which determines the appropriate residence region and working direction of any candidate node to be added. Then we select the optimal relay sensor to be added into the current barrier based on its input-output ratio (barrier weight) which reflects the extension of barrier coverage. This strategy looses the demand of minimal required sensor nodes (maximal gain of each sensor) or maximal lifetime of one single barrier, leading to an augmentation of sensors to be used. Numerical simulation results show that, compared with the available schemes, the proposed method significantly reduces the minimal deploy density required to establish k-barrier, and increases the total service lifetime with a high deploy efficiency.

A low-water crossing impacts Northern Hog Sucker Hypentelium nigricans movement in an Ozark stream

Streams are complex systems that rely on connectivity to maintain natural ecological function. Low-water crossings are common in small-intermediate sized streams and can restrict longitudinal movement of fishes. The Current River in Missouri (USA) contains a single anthropogenic barrier to longitudinal connectivity: the Cedar Grove low-water crossing, which spans the main channel (10 culverts) and a side channel (4 culverts). In July 2017, we radio-tagged Northern Hog Sucker Hypentelium nigricans upstream (henceforth ‘above’; N = 24) and downstream (henceforth ‘below’; N = 26) of the crossing and followed their movements monthly for a year to assess fish passage and maximum displacement. Passage was limited to four below-tagged fish passing upstream of the crossing with one fish making an additional downstream and then upstream passage. Passage was more likely to occur during high flow. On average, below-tagged fish exhibited more than seven times greater maximum displacement (Mean (M) = 6.55 km, Standard Error (SE) = 2.91 km) than above-tagged fish (M = 0.92 km, SE = 0.33 km). The majority (71%) of fish exhibited stationary behavior (<1 km) compared to mobile behavior (>1 km). Among mobile individuals, maximum displacement was greatest away from the crossing, with above-tagged fish favoring upstream movements (100%) and below-tagged fish favoring downstream movements (67%). Our results suggest the crossing is a semi-permeable barrier in which fish passage primarily occurs during high flows. Alternatives to the low-water crossings at Cedar Grove should be considered to promote natural longitudinal movement of fishes. The side channel provides a potentially impactful and economically feasible management opportunity to act as a fish bypass channel on the Current River.

High Temperature Behavior of RuAl Thin Films on Piezoelectric CTGS and LGS Substrates.

This paper reports on a significant further improvement of the high temperature stability of RuAl thin films (110 nm) on the piezoelectric CaTaGaSiO (CTGS) and LaGaSiO (LGS) substrates. RuAl thin films with AlN or SiO cover layers and barriers to the substrate (each 20 nm), as well as a combination of both were prepared on thermally oxidized Si substrates, which serve as a reference for fundamental studies, and the piezoelectric CTGS, as well as LGS substrates. In some films, additional Al layers were added. To study their high temperature stability, the samples were annealed in air and in high vacuum up to 900 °C, and subsequently their cross-sections, phase formation, film chemistry, and electrical resistivity were analyzed. It was shown that on thermally oxidized Si substrates, all films were stable after annealing in air up to 800 °C and in high vacuum up to 900 °C. The high temperature stability of RuAl thin films on CTGS substrates was improved up to 900 °C in high vacuum by the application of a combined AlN/SiO barrier layer and up to 800 °C in air using a SiO barrier. On LGS, the films were only stable up to 600 °C in air; however, a single SiO barrier layer was sufficient to prevent oxidation during annealing at 900 °C in high vacuum.

Spin-Dependent Tunneling of Holes in Heterostructures Based on GaMnAs Semiconductor: Effects of Temperature and Quantum Size

In this paper, we investigated theoretically the spin-dependent transport of holes in heterostructures containing diluted magnetic semiconductor GaMnAs. Especially, we have addressed the transmission of holes through heterostructures based on single and double barriers within the mean field approximations. The diluted magnetic semiconductor acts as a barrier for spin-up holes and as a quantum well for spin-down ones. Our results show that the transmission depends on the temperature of the system and the number of the magnetic layers. For heterostructure with one magnetic layer, the spin-up transmission is suppressed for lower energies compared with the spin-down one. This suppressed transmission can be enhanced when we consider a heterostructure with additional magnetic layers. Furthermore, our findings indicate that the asymmetric heterostructure based on double magnetic layers presents a quite different transmission of holes compared with the symmetric one. These results can be useful to design and create spin filters based on magnetic and nonmagnetic semiconductors by tuning the temperature and the structural parameters.