Double Step Structure Research Articles

Experimental Study on the Improvement of Film Cooling Effectiveness of Various Modified Configurations Based on a Fan-Shaped Film Cooling Hole on an Endwall

Several studies have previously been conducted to improve the cooling performance of film cooling. However, most of the research has conducted experiments with film cooling holes on flat plates, and thus, the results of these studies do not encompass the influence of the complex mainstream behavior within the turbine passage on film cooling. In this study, three different film cooling hole configurations were installed on the endwall of a turbine linear cascade to measure adiabatic film cooling effectiveness and evaluate cooling performance. The film cooling holes compared in the experiment for film cooling effectiveness were a 7-7-7 fan-shaped hole (Baseline), a Baseline with a double-step structure at the hole exit (Staircase), and a Baseline with an additional expanded passage at the hole leading edge (Compound Expansion). A total of nine holes were manufactured on the turbine endwall to assess film cooling performance, as various factors, such as mainstream acceleration, secondary flow within the turbine passage, and so on, can influence film cooling. Adiabatic film cooling effectiveness was measured using the pressure-sensitive paint (PSP) technique. Mass flow ratios ranging from 0.25% to 1.25% of the mass flow rate of a single turbine passage were supplied to the plenum chamber within the test rig. As a result, all experimental results confirmed the impact of secondary flow within the turbine passage on film cooling. In the case of the Staircase, it exhibits an overall cooling trend similar to the Baseline. It shows small cooling performance degradation compared with Baseline due to lift-off, and its double-step structure laterally expanding results in better cooling performance at high mass flow ratio (MFR) conditions. For the Compound Expansion, at low MFR, the momentum of the coolant is lower compared with other configurations, leading to lower cooling performance due to the influence of secondary flow. However, at high MFR, the Compound Expansion provides wider protection compared with other hole geometries and shows high cooling performance.

Design and Simulation Electrothermal Double-Step Structure for Out-of-Plane Actuation

Design and Simulation Electrothermal Double-Step Structure for Out-of-Plane Actuation

Representation of an engineered double-step structure SOI-TFET with linear doped channel for electrical performance improvement: a 2D numerical simulation study

In this paper, a novel double-step (DS) structure tunnel field-effect transistor with a linear doping profile channel (DSS-LDC-TFET) is presented. The use of a step-shaped structure near the source/channel interface leads to the large tunneling junction area because the band-to-band tunneling of the carriers occurs perpendicularly along the conducting path in the channel. The step-shape of the channel/drain interface reduces the electric field distribution near the drain junction which helps to suppress the ambipolar behavior. Further, the DS structure of the body suppresses the ambipolar conduction due to increasing the effective length of channel area along the device. Therefore, the height of the steps in the proposed structure plays an important role in the device characteristics. The doping profile in the channel region is considered to be linear. The maximum value of the doping concentration is at the source side and linearly decreases to its minimum value along the x-axis. Numerical simulation results show that using the linear doping distribution at the channel improves device behavior through reducing the tunneling barrier width at the source/channel interface. The optimum length for the linear-doped part of the channel is selected to maximize the on-state current without degrading much the off-state current. Finally, the comparative study between DSS-LDC-TFET with the conventional silicon-on-insulator tunnel field-effect transistor is presented.

Optical properties of magnetically doped ultrathin topological insulator slabs

Starting from a three dimensional Hamiltonian, we study the optical properties of ultra-thin topological insulator slabs for which the coupling between Dirac fermions on opposite surfaces results in two degenerated gapped hyperbolic bands. The gap is a threshold for the optical absorption and translates in a peak in the imaginary part of the optical conductivity. An exchange field applied perpendicular to the slab splits the degenerated hyperbolic bands and a double step structure come out in the optical absorption, whereas a double peak structure appears in the imaginary part of the longitudinal optical conductivity. The exchange field breaks time-reversal symmetry and for exchange fields larger than the surfaces coupling gap, the zero frequency Hall conductivity is quantized to $e^2/h$. This result implies large values of the Kerr and Faraday rotation angles. In ultra-thin slabs, the absence of light multiple scattering and bulk conductivity, makes the Kerr and Faradays angles to remain rather large in a wide range of frequencies.

Double step structure and meandering due to the many body interaction at GaN(0001) surface in N-rich conditions

Growth of gallium nitride on GaN(0001) surface is modeled by Monte Carlo method. Simulated growth is conducted in N-rich conditions, hence it is controlled by Ga atoms surface diffusion. It is shown that dominating four-body interactions of Ga atoms can cause step flow anisotropy. Kinetic Monte Carlo simulations show that parallel steps with periodic boundary conditions form double terrace structures, whereas initially V-shaped parallel step train initially bends and then every second step moves forward, building regular, stationary ordering as observed during metal organic vapor phase epitaxy or hydride vapor phase epitaxy growth of GaN layers. These two phenomena recover surface meandered pair step pattern observed, since 1953, on many semiconductor surfaces, such as SiC, Si, or GaN. Change in terrace width or step orientation particle diffusion jump barriers leads either to step meandering or surface roughening. Additionally it is shown that step behavior changes with the Schwoebel barrier height. Furthermore, simulations under conditions corresponding to very high external particle flux result in triangular islands grown at the terraces. All structures, emerging in the simulations, have their corresponding cases in the experimental results.

Propagation of a shock-related disturbance in the Earth's magnetosphere

[1] The Grand Unified Magnetosphere-Ionosphere Coupling Simulation, version 4, magnetohydrodynamic simulation of the interplanetary shock event on 9 November 2002 is used to determine the shock-associated disturbance propagation characteristics inside the Earth's magnetosphere. Interaction of an interplanetary fast forward shock with the magnetopause caused a shock-related disturbance inside the magnetosphere that propagated at a speed significantly higher than that in the solar wind or magnetosheath. The propagation direction of the disturbance was calculated from the Rankine-Hugoniot conditions, velocity and magnetic coplanarity, and minimum variance analysis and is shown to vary in different regions of the magnetosphere. Furthermore, the impulse disturbance wave mode changes as the plasma and field conditions change inside the magnetosphere. These results bring important new information about the propagation processes that is not directly obtainable from point measurements made by (even several) spacecraft. On the other hand, comparison of ionospheric observations from the IMAGE magnetometer chain with geosynchronous data allow us to also interpret the double step structure observed at dayside geosynchronous orbit, which is below the simulation resolution. This combination provides us with quite a complete view on shock propagation inside the magnetosphere.

Surface patterns due to step flow anisotropy formed in crystal growth process

The growth of gallium nitride on a GaN(0001) surface was conducted in an N-rich state for both metal organic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) methods and therefore it was controlled by surface diffusion of Ga adatoms. At these conditions two consecutive atomic steps on the GaN(0001) surface had one or two broken bonds. Consequently, their kinetic properties were different. According to the wurtzite symmetry, the step had a trigonal symmetry preserving the number of broken bonds for rotation by 2 π/3 and exchanging the step type for rotation by π/3. The simplest model was introduced which allowed the growth of a GaN crystal to be simulated at this surface, preserving the lattice symmetry, and taking into account the presence of one or two broken bonds for the consecutive step order and orientation. The Monte Carlo simulations of the model showed that, depending on the terrace width, the steps either tended to group in a double step structure, or, for wider terraces, formed wave-like structures (step meandering). The results of the Monte Carlo simulations exactly recovered the structures that were observed in the Atomic Force Microscopy images of a GaN surface grown by MOVPE.

Anisotropy of Ag Diffusion on Vicinal Si Surfaces

Photoemission electron microscopy (PEEM) is used to study Ag surface diffusion on vicinal Si surfaces. The diffusion field is represented by Iso-Coverage Zones around Ag islands during desorption. By analyzing the shape and radius of the Iso-Coverage Zone we can determine diffusion parameters. For anisotropic diffusion the zone has an elliptical shape and the aspect ratio gives a measure for the anisotropy. Using this technique, we study the degree of anisotropy of Ag diffusion on vicinal Si(001) and Si(111). With increasing miscut angles, starting from Si(001) as well as from Si(111), we find a gradually increasing anisotropy, caused by the higher step density. On higher index surfaces, like Si(119), Si(115) and Si(113), we find isotropic diffusion for surfaces with comparable dimer and (double) step structure as on Si(001)-4°, where diffusion is strongly anisotropic. [DOI: 10.1380/ejssnt.2010.372]

Enhancement of Rashba Spin–Orbit Interaction Due to Wave Function Engineering

We have demonstrated an enhancement of Rashba spin–orbit interaction (SOI) in In0.53Ga0.47As/In0.7Ga0.3As/In0.53Ga0.47As double-step structure in comparison with In0.53Ga0.47As normal quantum well. In the double-step structure, high electron probability density is located on the In0.53Ga0.47As/In0.7Ga0.3As heterointerface to enhance the interface contribution of Rashba SOI. The double-step structure is designed based on k⋅p formalism considering field and interface contributions separately. The Rashba parameter α calculated by the k⋅p formalism shows good agreement with the experimental value by analyzing weak antilocalization. The large carrier density dependence of α is due to the In0.53Ga0.47As/In0.7Ga0.3As heterointerface contribution as well as the energy-band bending in the In0.7Ga0.3As quantum well. The results of this study suggest that the precise control of interface and field contributions in Rashba SOI will make its application to semiconductor spintronics.

A novel nanoscale high breakdown voltage lateral bipolar junction transistor on silicon-on-insulator

A novel nanoscale lateral bipolar junction transistor (LBJT) on silicon-on-insulator (SOI) with buried oxide double step (BODS) structure is proposed. Numerical simulations demonstrate that the breakdown voltage of the proposed device is significantly higher than that of the conventional device. An increase of 150% in breakdown voltage has been obtained in the proposed device. The increase in the breakdown voltage is due to the creation of an additional electric field peak in the collector drift region, leading to greater uniformity in the horizontal component of the surface electric field and hence increases in the breakdown voltage.

Understanding and using near-misses properties through a double-step conceptual structure

Though in literature there has been an extensive demonstration of the strict relationship between the frequency of occurrence of near-misses and the number of major accidents, there is a clear evidence in the industrial practice of a lack of a common accepted definition and denotation of a near-miss and the absence of an explicit model for assessing their main properties and how to turn into knowledge the information gathered thereby. The paper tries to fill this gap by providing a denotation and classification model of near-misses which can be easily adopted in the managerial practice. The structure is composed of a model based on the set theory which enables to denote the different categories (error, incident, operational interruption, accident and near-miss), and a classification algorithm to properly define each category. This double-step structure helps in understanding of how to use the power of near-misses properties in order to implement a company-wide improvement program.

A novel thin-film power MOSFET with an asymmetrical buried oxide double step structure

A novel thin-film power MOSFET with an asymmetrical buried oxide double step structure

New thin-film power MOSFETs with a buried oxide double step structure

A new silicon-on-insulator (SOI) power MOSFET structure is proposed, in which buried oxide step structure (BOSS) is replaced by a buried oxide double step (BODS). Numerical simulations are performed to demonstrate that higher breakdown voltages are obtained resulting from a higher electric-field peak introduced near the BODS, and higher impurity concentration is depleted due to thin-film SOI than that in the conventional SOI and BOSS structure.

A CONCEPTUAL STRUCTURE FOR THE USE OF NEAR-MISSES PROPERTIES

Aim of the paper is to define a scientific structure to prove the reason why ***near-misses should be the joint between the safety department and the rest of the company. The structure is composed of a model based on the set theory which enables us to denote the categories “error”, “incident”, “mishap”, “accident” and “near-miss”, and a classification algorithm to exactly define each category. This double-step structure helps in the understanding of how to use the power of near-misses properties to implement a company-wide improvement program.

Analysis of a double step microstrip discontinuity using generalized transmission line equations

In this paper, a new analysis for a double step microstrip discontinuity is presented by using generalized transmission line equations . The new analysis is based on a new concept of a finite-length transmission line integrated with its double step discontinuity so that the double step discontinuity is regarded as a finite-length nonuniform transmission line and the generalized equations could be directly implemented. Since the generalized equation coefficients are determined by dynamic numerical methods and the coefficients are invariant with the line excitation and load, the equations are dynamic rather than TEM. The interested discoveries are that the generalized equations for the whole double step structure or a partial double step structure can give us the same results and the generalized equations have broadband frequency characteristics. For the double step structure used in this paper for the analysis, the S-parameters for a frequency band from 0.5 GHz to 10 GHz can be well calculated by using only two separately generalized equations at frequency of 3 GHz and 8 GHz.

Adsorbate-induced step-doubling reconstruction of a vicinal metal surface: oxygen on Rh {332}

Morphological transitions induced by oxygen on a stepped rhodium surface, Rh{332}, have been studied using LEED. The stable clean surface is made up of a series of six-atom-wide terraces separated by monatomic steps. At low coverages (θ ≈ 0.1 ML) oxygen induces a restructuring of the surface at temperatures in the range 430–510 K, with a doubling of step height and terrace width compared to the clean surface. With additional exposure to oxygen (θ ≈ 0.6 ML) the surface returns to the step structure of the clean sample. Both processes are reversible. A metastable double-step structure of the clean surface was produced by the catalytic removal of oxygen from the reconstructed surface with hydrogen at 360 K. The kinetics of these phase transitions has been investigated using LEED. Kinetic modelling provides a determination of kinetic parameters for the escape of rhodium atoms from single and double step edges. A reconstruction mechanism is presented, and the driving forces are discussed.

Anisotropy of superconducting properties of UPt3 close to Tc

Abstract Experiments have been performed on the unconventional superconductor UPt 3 close to T c . Topics that have been studied are: the double-step transition in the specific heat, the anisotropy in the enhanced conductivity above T c and the low field ac susceptibility. A double-step structure has been observed in χ(T) as well for the ac field parallel to the c-axis. The low field penetration depth λ varies with temperature as (T c -T) −β with β close to 1. These observations may be interpreted as a result of an interaction of the measuring current with vortices.

Experimental study by He diffraction (TEAS) of a vicinal silicon (100) surface: Si(1117)

The vicinal Si(100) surfaces shows a single-step or double-step reconstruction depending on the miscut angle of the surface. This phenomenon is now well known from LEED and STM studies. A critical miscut angle of the order of 3° can be deduced from the set of available data with the observation of the crystal at room temperature. In our He beam scattering experiment the Si(1117) face is investigated which corresponds to a miscut angle of 4.76°. In this way, a double-step reconstruction is guaranteed at room temperature. We follow the evolution of the surface structure as a function of temperature. A strong structural modification is found at 800 K, which is interpreted as a transition from the initial double-step structure to the single-step reconstruction. This observation is in good agreement with the prediction of a model presented by Alerhand and co-workers.

Photoionisation mass spectrometric study of acetylene in the VUV region

Photoionisation mass measurements on acetylene have been made between 1100 and 400 AA by using synchrotron radiation as a light source. Photoionisation efficiency curves are obtained for the molecular ion C2H2+ and also for fragment ions C2H+, C2+, CH2+ and CH+. To assign the structures of C2H2+, ab initio calculations have been performed for the excitation from the second (3 sigma g) and third (2 sigma u) occupied molecular orbitals. Two broad maxima at 930 and 810 AA between the first and second ionisation thresholds are assigned to the autoionisation from valence-type excited states. New Rydberg series (np pi u) converging to the second ionisation threshold were found. The appearance potentials of fragment ions by photoexcitation are given and discussed in terms of the heats of formation of molecular ions. For each of C2+ and CH+, two values of the appearance potential are obtained from a double-step structure. The maximum heat of formation of C2+ is estimated from the appearance potential to be 1980 kJ mole-1.