Center Of Gap Research Articles

Effects of Forest Gaps on Forest Floor Microbial Community Composition in Pinus tabulaeformis Forests in a Rocky Mountain Area, Beijing, China

Forest gaps induce environmental heterogeneity, but their effects on the local forest floor microbial communities are not fully understood. This research investigated the impact of forest gap positions on the forest floor microbial community composition to provide baseline information for projects to accelerate nutrient cycling and forest regeneration and enhance ecosystem services. A one-year-old forest gap and an area of 40–50 m2 in Pinus tabulaeformis plantations were selected in the Beijing mountainous area. Forest floor samples were collected from the following positions: gap center, gap border, and adjacent closed canopy. Our study demonstrated that gap positions significantly influenced the forest floor microbial community composition. The Gram-positive bacteria, Gram-negative bacteria, and total bacteria, as well as the fungi, were significantly greater in the forest gap center and gap border compared to those in the closed canopy, and the dissolved organic carbon, readily oxidized organic carbon, ammonia nitrogen, and nitrate nitrogen followed the same trend. Compared with those of the closed canopy, the Gram-positive bacteria, Gram-negative bacteria, total bacteria, and fungi in the gap center were markedly greater by 23%, 25%, 22%, and 24% and by 14%, 14%, 11%, and 16% in the gap border, respectively (p < 0.05). Redundancy analysis demonstrated that shifts in the litter microbial community composition were predominantly predicted by litter moisture and β-1,4-glucosidase. In addition, we discovered that the microbial community composition was greater in the undecomposed forest layer than that in the semi-decomposed layer. In summary, gap positions and forest floor layers have a significant impact on microbial community composition. Nevertheless, additional long-term investigations are needed. Our study provides a reference for the promotion of nutrient cycling to guide future ecological management.

A comparative study of the effects of photovoltaic power plants in desert and lake on the microclimate

The utility-scale deployment of photovoltaic (PV) power plants is critical for achieving carbon peaking and carbon neutrality goals and mitigating climate change. However, the impact of a PV power plant project on the microclimate is unclear for different underlying surfaces. Therefore, PV power plants in deserts and lakes were selected to assess and compare the impact of PV array deployment on the environment by the observation. The results indicate that the PV array affected the wind pattern, the wind direction makes simple (from 10 m to 2 m), and wind speed in the PV site under two types of underlying surfaces was less than the reference site. For the PV power plant in desert, the delta (PV - REF) is increased from 0.12 m s−1 at 10 m to 0.27 m s−1 at 2 m. The counterpart in the lake is increased from 0.14 m s−1 at 10 m to 0.55 m s−1 at 2 m. However, the PV arrays had no effect on the air temperature at the center of the PV array gap. The difference in air temperature for two observation sites under two type of underlying surfaces was less than the resolution of instrument MaxiMet (0.1 °C). Instead, the heat from the PV panels is transmitted down to the land surface, causing a temperature effect in the desert and lakes. For the PV power plant in land, the arrays have heating effect on air temperature (The air temperature was 33.43 °C in the PV_land site, and 28.03 °C in the REF_land site in July, respectively). But the arrays have cooling effect on air temperature for the PV power plant in lake in the same month (PV_lake site, 28.58 °C; REF_lake site, 29.97 °C). Furthermore, evaporation is lower in the PV power plant owing to the physical shielding of PV arrays (For the land, the peak of hour evaporation (PV_land – REF_land) was 0.12 mm; for the lake, the peak of hour evaporation (PV_lake – REF_lake) was 0.32 mm). This study provides new evidence of the microclimate impact of photovoltaic array deployment on different underlying surfaces.

The response of seedlings and saplings to canopy structure and light in different gaps in a spruce-fir mixed stand in Changbai Mountains, China

Environmental heterogeneity caused by the formation of forest gaps has important implications for the establishment and growth of forest regeneration, and different tree species with different shade tolerance at various stages of regeneration respond differently to the environment. In this study, we investigated 48 forest gaps and classified them into four classes based on their area, including small (< 20 m2), medium (20 m2 to 50 m2), large (50 m2 to 120 m2), and extra-large (> 120 m2). We conducted an analysis of the differences and variations in canopy structure (canopy openness and leaf area index (LAI)) and light environment (direct light, diffuse light, and total light) for different sizes of gaps and along the north–south axis of the gaps. Additionally, we conducted a preliminary study of how the seedlings and saplings of different tree species (Korean pine (Pinus koraiensis), Ezo spruce (Picea jezoensis), and Khingan fir (Abies nephrolepsis)) respond to environmental factors such as canopy structure and light within gaps. Gap size significantly influenced the direct and total light in northern (N, N1) portion of gaps, while for diffuse light, gap size demonstrated a notable effect along the north–south axis, except for the N. Maximum direct light did not occur at the center of gaps, but rather near the center of the gap and tended to the crown edge. In contrast, the maximum diffuse light occurred at the center of gap. When the forest gap area < 20 m2, the diffuse light dominated the northern part of the gaps. However, when the gap area > 20 m2, the northern part was dominated by direct light. The variation pattern of total light showed a level of consistency with that of direct light. A redundancy analysis (RDA) showed that the density of shade-tolerant fir seedlings and saplings, as well as spruce seedlings, were primarily positively correlated with the LAI, while the density of spruce saplings was negatively correlated with direct light. The density of heliophilous species Korean pine seedlings and saplings was strongly and weakly positively correlated with the direct light, respectively. The mean ground diameter and height of spruce and fir seedlings and saplings positively correlated with diffuse light, whereas the mean ground diameter and mean height of Korean pine seedlings and saplings strongly positively correlated with the canopy openness and direct light, respectively. These findings suggest that the gap size and location within gaps can compensate each other in silvicultural practices based on the creation of gaps. Knowledge of the ecological characteristics of the target species, enables the selection of appropriate relative positions to achieve more suitable light conditions for their growth.

Observation of a Topological Edge State Stabilized by Dissipation.

Robust states emerging at the boundary of a system constitute a hallmark for topological band structures. Other than in closed systems, topologically protected states can occur even in systems with a trivial band structure, if exposed to suitably modulated losses. Here, we study the dissipation-induced emergence of a topological band structure in a non-Hermitian one-dimensional lattice system, realized by arrays of plasmonic waveguides with tailored loss. We obtain direct evidence for a topological edge state that resides in the center of the band gap. By tuning dissipation and hopping, the formation and breakdown of an interface state between topologically distinct regions is demonstrated.

Extremely Large Polymer Light‐Emitting Electrochemical Cells with Concentric Circular Electrodes

AbstractPlanar polymer light‐emitting electrochemical cells (LECs) with concentric circle electrodes are demonstrated. With a fixed outer electrode radius of 6.8 mm, the inner electrode radius is varied from 1 to 3 mm. All cells can be activated with a 40 V bias at 360 K. The extremely large electrode gap size allows for time‐lapsed imaging of the in situ electrochemical p‐ and n‐doping processes. When the advancing p‐ and n‐doping fronts meet, a light‐emitting junction in the shape of a jagged ring is formed near the center of the electrode gap. Reversing bias polarity pushes the light‐emitting junction outward to near the negative electrode. It is possible to achieve a perfectly centered emitting junction by fine tuning the inner electrode radius. The sensitivity of junction position to relative electrode radius indicates the p‐ and n‐doping reactions are strongly coupled. The concentric circular electrode configuration offers a cross sectional view of an LEC‐based light‐emitting fiber. In any fiber shaped light‐emitting device, the inner and outer electrodes always differ in size. This electrode asymmetry should be considered and exploited to achieve optimal cell performance.

SЕNSORS BASED ON POLYCRYSTALLINE 3C-SiC: IMPACT OF BORON DOPING

As a chemically inert wide bandgap semiconductor material with high hardness and thermal conductivity, stable electrical characteristics, silicon carbide SiC is attractive for harsh environment electronics and sensors applications. The concept of harsh environment includes extremes of temperature, pressure, shock loads, radiation and chemical attacks those arise in aircraft and automotive engines, industrial gas turbines, during oil and gas exploration, etc.&#x0D; Lower growing temperatures of polycrystalline cubic silicon carbide, pc-3C-SiC, compared to monocrystalline allow to significantly reduce its cost and expand the possibilities of application. It follows from previous works that the thermal sensitivity of pc -3C-SiC can be significantly increased by doping with an acceptor impurity of boron during the growth of the material. The purpose of this work is to determine the properties of pc-3C-SiC doped with boron for the creation of photosensors and thermosensors, as well as thermal anemometers for extreme operating conditions.&#x0D; It is shown that pс-3C-SiC doping with a boron impurity in the growth process causes the formation of acceptor-type centers in the band gap and the appearance of features in the photosensitivity spectrum, which may be of practical interest for photovoltaics. For temperatures T &gt; 150K, the conductivity of the doped sample increases almost exponentially with an activation energy of 0.28 eV, which is close to the activation energy of the photoconductivity of the same sample. This indicates that the ionization process of equilibrium and non-equilibrium charge carriers occurs from the same impurity centers. Boron doping causes the appearance of a broad photoconductivity band with a maximum at 1.7 eV in the impurity absorption region of pc-3C-SiC, similar to the situation in single crystal 3C-SiC.&#x0D; It was determined that the temperature coefficient of resistance for boron-doped pc-3C-SiC is 3.0´10-2 K-1 at T=300K and 1.1´10-2 K-1 at T=700K, which is almost an order of magnitude higher than for thermocouples, as well as for metals from which anemometer threads are made. The discussion of the obtained results allows to associate the value of the activation energy E=0.28 eV with the level of shallow boron in pc-3C-SiC and to assume this center is a point defect containing a boron atom that replaces a silicon atom in the 3C-SiC lattice, i.e. BSi.&#x0D; Photosensors that can be used as solar cells in the near-IR range of 0.6 - 1.8 μm, and as photocells in the visible range of 0.4 - 0.6 μm are proposed. The ability of pc-3C-SiC to work in extreme operating conditions, as well as the low cost of device manufacturing technology based on it, compared to other SiC polytypes, allow it to be considered a suitable material for creating temperature sensors, thermo-anemometers and photosensors, as well as detectors for monitoring nuclear facilities.

Cylindrical liquid crystal micro-lens array based on interdigital electrodes

ABSTRACT Based on the traditional structure of in plane switching liquid crystal display, a cylindrical liquid crystal micro-lens array driven by interdigital electrodes is proposed, and its performance is studied. Firstly, the director distribution and relative phase difference distribution of liquid crystal molecules were calculated, which shows that this structure can be used to fabricate cylindrical liquid crystal micro-lens. Then, by comparing lenses of difference sizes, it is found that narrow electrodes should be selected for lens production, and the centre of the electrode gap should be selected as the central axis of a single liquid crystal micro-lens. Finally, a certain electrode structure is selected to explore its focal length, focusing quality and zoom time. The results show that the focal length of the liquid crystal micro-lens decreases gradually with the increase of the driving voltage. When the driving voltage is between 3 Vrms and 5.5 Vrms, the liquid crystal micro-lens has good focusing quality, and its corresponding focal length changes from 1.63 mm to 20.28 mm. Based on this structure, when the liquid crystal lens is driven by the above two voltages alternately, the time required for liquid crystal molecules to reach stability is 2.35 s and 3.87 s respectively.

3D printing of fiber composite sandwich metamaterial with spiral resonators for attenuation of low-frequency structural vibration

This paper proposes a fiber composite sandwich metamaterial as a stiff structure with a low-frequency band gap. The proposed structure is a locally resonant metamaterial that inhibits the propagation of elastic waves with spiral resonators. The dispersion curves and stiffness of the metamaterial were obtained using the finite element method. The numerical analysis results indicated that the proposed sandwich structure contributes not only to the improvement of the specific stiffness but also to the widening of the band gap. From observations of the band gap boundary modes, an analytical model was developed to derive the lower and upper bound frequencies of the band gap. A metamaterial sample manufactured by 3D printing exhibited a frequency range with low vibration transmissibility, which agreed with the results of the frequency response analysis. The specific bending stiffness and band gap center frequency of the proposed metamaterial were compared with those of existing plate-type metamaterials.

Linked disturbance in the temperate forest: Earthworms, deer, and canopy gaps.

Despite the large body of theory concerning multiple disturbances, relatively few attempts have been made to test the theoretical assumptions of how and if disturbances interact. Of particular importance is whether disturbance events are linked, as this can influence the probability and intensity of ecological change. Disturbances are linked when one disturbance event increases or decreases the likelihood or extent of another. To this end, we used two long-term, multi-disturbance experiments in northern Wisconsin to determine whether earthworm invasion is linked to canopy gap creation and white-tailed deer browsing. These three disturbances are common and influential within North American temperate forests, making any interactions among them particularly important to understand. We expected both deer and canopy gaps to favor invasive earthworms, particularly species that live close to or on the soil surface. However, we found only partial support of our hypotheses, as both deer exclosures and canopy gaps decreased earthworms in each experiment. Further, earthworm density increased the most over time in areas far from the gap center and in areas with deer present. Deer exclosures primarily decreased Aporrectodea and Lumbricus species, while gaps decreased Dendrobaena and Lumbricus species. Our findings show that earthworm invasion is linked to deer presence and gap-creating disturbances, which provides new insight in multiple disturbance theory, aboveground-belowground dynamics, and temperate forest management.

Tree regeneration and spatial patterning among midtolerant tree species following gap-based harvesting in a temperate hardwood forest

IntroductionField experiments of gap-based harvest systems in temperate northern hardwood forests have provided inconsistent support for the theory that such regeneration approaches can improve regeneration success among increasingly underrepresented tree species intermediate in shade tolerance. We established a field experiment in Wisconsin, USA testing the long-term response of tree regeneration to group selection harvesting that created small (50 m2–D:H 0.32), medium (200 m2—D:H 0.64) and large (380 m2—D:H 0.88) gaps.Materials and methodsLight levels were modeled to test the assumption of resource heterogeneity within and across these gap sizes. Spatial statistics were used to assess whether the point patterns of saplings of several midtolerant tree species (Betula alleghaniensis, Carya cordiformis, Fraxinus spp.) mapped in harvest gaps provided evidence for partitioning across resource gradients 9 years post-harvest. Finally, we measured occurrence and height of all saplings within the harvest gaps to test the effects of gap size and deer exclusion fencing on the density and total height of shade-tolerant and midtolerant tree regeneration.Results and discussionLight levels progressively increased with gap size, varied by position within gaps, and provided significant evidence of resource heterogeneity. The complex light gradients formed both within and across the three gap sizes may partially explain the statistically significant clustering of Fraxinus spp. saplings in gap centers and north and east into the forested edge of medium and large gaps, C. cordiformis on the west sides of forested transitions surrounding large gaps, and B. alleghaniensis in the centers of large gaps. Densities of tolerant and midtolerant saplings were similar in medium and large gaps after nine growing seasons, though tolerant saplings averaged two meters taller across all three gap sizes. Our results show that gap-based silvicultural systems can create resource gradients that are sufficient to regenerate mixtures of species with high to intermediate tolerance of shade. However, prescriptions beyond harvesting and deer exclusion fencing may be necessary for the recruitment of midtolerant species to canopy positions.

Influence of multiple islands on the hysteresis and dynamics of a western boundary current perturbed by a mesoscale eddy at a gap

The hysteresis of a western boundary current (WBC) flowing across a gap and the dynamics of the mesoscale eddy–WBC interaction with the presence of two islands in the gap are studied using a 1.5-layer ocean model. The hysteresis of the WBC suggests that the two islands in the gap facilitate the WBC to intrude into the western basin by shedding eddies compared with the no-island case, but they promote the WBC to leap across the gap compared with the one-island case. The mesoscale eddies from the east of the gap can induce the critical-state WBC shifting from penetration to leap and vice versa. The dynamics revealed by the vorticity balance analysis shows that the increased (decreased) meridional advection of the WBC perturbed by the eddy forces the WBC to leap across (intrude into the western basin through) the gap. We also present the parameter space of the critical strength of the eddy with variable north–south locations inducing the critical WBC transition. For the WBC critical from the eddy-shedding to leaping regime, the regime shift is most sensitive to the anticyclonic eddy from the gap center and to the cyclonic eddy from the southern gap. It is least sensitive to the eddy downstream of the WBC. For the WBC critical from the leaping to eddy-shedding regime, the regime shift is most sensitive to the anticyclonic eddy upstream of the WBC and to the cyclonic eddy from the southern gap. The least sensitive eddy is from the northern gap.

A matter of size and shape: Microclimatic changes induced by experimental gap openings in a sessile oak–hornbeam forest

Forest management integrating nature conservation aspects into timber production focuses increasingly on small-scale interventions. However, the ecological consequences of gap cuttings remain ambiguous in oak-dominated forests. In the Pilis Gap Experiment, we analyze how combinations of different gap shapes (circular and elongated), and gap sizes (150 m2 and 300 m2) affect the microclimate and biota of a mature sessile oak-hornbeam forest in Hungary. We first report the changes in direct and diffuse light, soil moisture, daily air and soil temperatures, and relative air humidity in the experimental cuttings in the vegetation season directly following their implementation. Diffuse light had a central maximum and a concentric pattern. Direct light was distributed along a north-south gradient, with maxima in northern gap parts. Soil moisture was determined by gap shape: it increased significantly in the center of circular gaps, with multiple local maxima in the southern-central parts of large circular gaps. Its pattern was negatively related to direct light, and larger spatial variability was present in circular than in elongated gaps. The daily mean air temperatures at 1.3 m increased in all, especially in large gaps. Soil and ground-level temperatures remained largely unchanged, reflecting on light and soil moisture conditions affecting evaporative cooling. Relative humidity remained unaltered. Even though the opening of experimental gaps changed microclimatic conditions immediately, effect sizes remained moderate. Gap size and gap shape were both important determinants of microclimate responses: gap size markedly affected irradiation increase, gap shape determined soil moisture surplus, while soil and air temperatures, and air humidity depended on both components of the gap design. We conclude that 150–300 m2 sized management-created gaps can essentially maintain forest microclimate while theoretically providing enough light for oak regeneration; and that the manipulation of gap shape and gap size within this range are effective tools of adaptive management.

Influence of tree-fall gaps on directional seed dispersal by small mammals in Central Panama

Small mammals, particularly rodents, are often important seed-dispersal agents in Neotropical forests. Directional seed dispersal into tree-fall gaps may enhance seedling survival of light-demanding species and thus influence forest regeneration. To examine this proposition, we tracked seeds of a light-demanding palm (Attalea butyracea), with a focus on spiny rats (Proechimys semispinosus), the most-likely seed-removal agents. We established seed-removal stations at three distances relative to 28 gaps (gap center, gap edge, and intact forest 10 m from a gap edge) in a lowland forest in Central Panama. We placed five fresh fruits (with their seed) in semi-permeable exclosures to exclude larger mammals at each station and tracked the directions in which seeds were moved and deposited intact. More seeds were moved toward or into gaps when removed from gap center or edge stations; however, seeds dispersed from intact forest stations showed no such directionality. Small mammals may have dispersed seeds into and within tree-fall gaps because they favored caching seeds in areas that offered increased cover, which is typical of gaps, and consequently protection from predation. The lack of directional dispersal from intact forest stations may have been because spiny rats were able to find sufficient cover in the young intact forest that was closer than the gaps. In older forest, the contrast between intact forest and gaps may be greater, resulting in directed dispersal into gaps.

Intrinsic Defects and the Inducing Conduction Mechanism of Langasite-Type High-Temperature Piezoelectric Crystals.

Increasing the crystal resistivity is critically important for enhancing the signal-to-noise ratio and improving the sensing capability of high-temperature piezoelectric sensors based on langasite-type crystals. The resistivity of structural ordered langasite-type crystals is much higher compared to that of the disordered crystals. Here, we selected structural ordered Ca3TaGa3Si2O14 (CTGS) and disordered La3Ga5SiO14 (LGS) as representatives to investigate the microscopic conduction mechanism and further reveal the origin of the different resistivities of the ordered and disordered langasite-type crystals at elevated temperatures. By combining first-principles calculations and experimental investigations, we found that the different conductivity behaviors of the ordered and disordered crystals originate from different types of point defects formed in the crystal and their different contributions to the conductivity. For the disordered LGS crystal, the oxygen vacancies are apt to be formed at high temperatures, promoting the transition of valence electrons and yielding high conductivity. For the ordered CTGS crystal, the dominant TaGa antisite defects can introduce an electron-hole recombination center in the electronic band gap, significantly shortening the carrier lifetime and thus reducing the conductivity. This provides effective guidance to improve the resistivity performance of langasite-type crystals at high temperatures by optimizing the experimental conditions, such as oxygen atmosphere treatment, antisite defect modification, etc.

Analysis of activation energy and conductivity in 1 MeV neutron irradiated silicon diodes

In a highly 1 MeV neutron-irradiated silicon (Si) diode, an ohmic current-voltage (I-V) behaviour is observed, with the ohmic region increasing with radiation fluence. Reverse current (minority carrier density) increasing more drastically than forward current (majority carrier density) explains the conductivity-type inversion of material-based devices from n-to p-type after irradiation. The reverse current activation energy decreases from 0.86 eV for unirradiated Si diodes to 0.54 eV for the highest irradiated diodes, confirming the material conductivity-type inversion. The activation energy is independent of the radiation fluence just below the Si intrinsic Fermi energy, showing that when the defects near the centre of the Si band gap dominate the conduction mechanism, diode properties are independent of incident radiation. Despite its detrimental effects, radiation can improve the stability of diode properties. The stability of the properties is important for the fabrication of sensors for current and future high-energy physics experiments. The improved stability is because of radiation-induced defect levels close to the centre of the band gap that behave as generation-recombination (g-r) centres in Si.

Ion transfer into solution-processed electrodes can significantly shift the p–n junction and emission efficiency of light-emitting electrochemical cells

A light-emitting electrochemical cell (LEC) comprises mobile ions in its active material, which enable for in situ formation of a p–n junction by electrochemical doping. The position of this emissive p–n junction in the interelectrode gap is important, because it determines whether the emission is affected by constructive or destructive interference. An appealing LEC feature is that the entire device can be fabricated by low-cost solution-based printing and coating. Here, we show, somewhat unexpectedly, that the replacement of conventional vacuum-deposited indium-tin-oxide (ITO) for the positive anode with solution-processed poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) can result in an increase in the peak light-emission output by 75%. We demonstrate that this emission increase is due to that the p–n junction shifts from a position of destructive interference in the center of the interelectrode gap with ITO to a position of constructive interference closer to the anode with PEDOT:PSS. We rationalize the anodic p–n junction shift by significant anion transfer into the soft and porous PEDOT:PSS electrode during LEC operation, which is prohibited for the ITO electrode because of its compact and hard nature. Our study, thus, contributes with important design criteria for the attainment of efficient light emission from solution-processed LEC devices.

Nonlinear Dynamics of a Hysteresis Western Boundary Current Perturbed by a Mesoscale Eddy at a Gap with an Island

Abstract We study a hysteresis western boundary current (WBC) flowing across a gap impinged by a mesoscale eddy, with an island of variable meridional size in the gap, using a 1.5-layer ocean model. The hysteresis curves suggest the island with a larger size facilitates the WBC intrusion by shedding the eddy more easily. Both anticyclonic and cyclonic eddies are able to induce the critical WBC transition from penetration regime to leap regime, and vice versa. The vorticity balance analysis indicates increased (decreased) meridional advection that induces the critical WBC shifting from the eddy shedding (leaping) regime to the leaping (eddy shedding) regime. The meridional size of the island significantly affects the critical WBC transition in terms of the critical strength of the mesoscale eddy. The regime shift from penetration to leap is most sensitive to the eddy upstream of the WBC for small islands and most sensitive to the southern anticyclonic eddy and northern cyclonic eddy for moderate and large islands. It is least sensitive to the central cyclonic eddy for small islands and to the cyclonic eddy upstream of the WBC for moderate and large islands and to the northern anticyclonic eddy regardless of island size. The regime shift from leap to penetration is most sensitive to the cyclonic eddy upstream of the WBC and to the northern anticyclonic eddy. It is least sensitive to the anticyclonic eddy from the south, and the least sensitive location of the cyclonic eddy shifts northward from the gap center as the island size increases.

Radiation Power of a Short High-Current Vacuum Arc at High Current Densities

The radiation of a vacuum arc was measured in the spectral region <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~\text {nm} \le \lambda \le 1100$ </tex-math></inline-formula> nm. The arc was initiated in the center of the cathode by breaking the current in the auxiliary circuit and was fed by the rectangular current pulse with a duration of 10 ms. The interelectrode gap was fixed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$h = 4$ </tex-math></inline-formula> mm, and the butt <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2r =30$ </tex-math></inline-formula> -mm CuCr30 electrodes were used. The arc was stabilized by an external uniform axial magnetic field (AMF). The radiation was coming out of the vacuum chamber through quartz ultraviolet (KU)-1 quartz window. The radiation detector was a silicon photodiode with a diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d =1.2$ </tex-math></inline-formula> mm. It was located on an axis intersecting the axis of symmetry of the discharge in the center of the interelectrode gap. The distance from the diode to the axis of symmetry was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L =1340$ </tex-math></inline-formula> mm. After amplification, the signal from the diode was recorded on an oscilloscope. The measurements were made in a range of currents from 10 to 25 kA in order to cover the modes with the anodic activity. It was found that under the conditions of these experiments, the anode activity begins to manifest itself at the end of the pulse, starting with currents exceeding 15 kA. As the current increases, the activity begins closer to the beginning of the pulse. Considering the type of the spectral sensitivity of the diode, two series of measurements were made—measurements without a filter and through a yellow filter ZhS-10 that cuts off radiation with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda \le400$ </tex-math></inline-formula> nm. The results obtained made it possible to analyze the dependence of the radiation power on the arc current. The results showed that at high current densities in the developed vacuum arc with anodic activity, a significant part of the power is transferred by radiation. At the end of a pulse with a current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 25$ </tex-math></inline-formula> kA, the radiation power is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {uv}}~\approx ~150$ </tex-math></inline-formula> kW, while in the discharge, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{a} ~\approx ~800$ </tex-math></inline-formula> kW is released. That is, at high current densities at the end of the pulse, the radiation power reaches almost 20% of the power released in the arc at this time. Estimates of lateral losses due to radiation are made.

Atomic and electronic properties of different types of SiC/SiO2 interfaces: First-principles calculations

The atomic and electronic properties of different types of SiC/SiO2 interfaces were investigated by using the first-principles method. Considering the four different terminal types on the SiO2 side and the two different crystal faces of 4H-SiC, we constructed eight different SiC/SiO2 interface models. Among the four different SiC/SiO2 interface structures with dangling bonds, the interface structures with Si dangling bonds will generate defect states at the center of the band gap and the conduction band edges, while the interface structures with C dangling bonds will create defect states at the valence band edges. The band alignment of four different SiC/SiO2 interface structures without dangling bonds indicates that the O-terminated interface structures have higher conduction band offsets than the Si-terminated interface structures. Besides, the O-terminated interface structures without dangling bonds have significantly higher interface separation work and are more favorable than the other interface structures, which can better resist leakage current and have the higher quality in SiC-based MOSFET applications.

Prediction of half-metallic gap formation and Fermi level position in Co-based Heusler alloy epitaxial thin films through anisotropic magnetoresistance effect

We have investigated the temperature $(T)$ dependence of the anisotropic magnetoresistance (AMR) effect of ${\mathrm{Co}}_{2}{\mathrm{FeGa}}_{0.5}{\mathrm{Ge}}_{0.5}$ (CFGG) epitaxial thin films having different compositions and atomic orders to examine the relation between AMR and the half-metallic electronic structure based on a developed theoretical model. The $T$ dependence of the resistance change (\ensuremath{\Delta}\ensuremath{\rho}) of the AMR normalized at 10 K is minimal in the CFGG films having a standard composition and high atomic order. In contrast, the films having a large atomic disorder due to the Co-rich composition exhibit a large reduction of \ensuremath{\Delta}\ensuremath{\rho} with $T$. Our theoretical model of AMR well explains this behavior; namely, the half-metallic ferromagnets having the Fermi level $({E}_{\mathrm{F}})$ around the center of the half-metallic gap are predicted to show a small $T$ dependence of \ensuremath{\Delta}\ensuremath{\rho} because of no/few localized $d\ensuremath{\downarrow}$ states at ${E}_{\mathrm{F}}$. On the contrary, a large change of \ensuremath{\Delta}\ensuremath{\rho} with $T$ is expected for the half-metallic materials having ${E}_{\mathrm{F}}$ close to gap edges or large in-gap states because of the contribution of thermally excited s-d scattering involving the $d\ensuremath{\downarrow}$ states. Moreover, we have also investigated the variation of \ensuremath{\Delta}\ensuremath{\rho} with $T$ for the thin films of various half-metallic Co-based Heusler alloys and found the behavior that agrees with our theoretical prediction. The present study proves that the formation of a half-metallic gap and the position of ${E}_{\mathrm{F}}$ in a half-metallic material are readily predictable from the $T$ dependence of \ensuremath{\Delta}\ensuremath{\rho} of the AMR effect, which can be a facile way for efficient screening of half-metallic materials.