Constant Peak Research Articles

Far-infrared emission from graphene on SiC by current injection

The far-infrared emission properties of epitaxial graphene on SiC obtained by current injection were investigated using an infrared camera and Fourier-transform infrared spectroscopy. The radiation directivity from the graphene emitter was observed in the directions perpendicular to the surface and edge of the sample. The emission energy density from the graphene edge was larger than that from the graphene surface in all directions. The maximum measured temperature change at 0.4 W for the edge emission was 76.1 K for a tilt angle of 50° and that for the surface emission was 54.1 K for 0°. A blackbody-like emission spectrum with a constant peak wavelength of 10.0 μm, regardless of the applied electrical power, was observed for both the surface and edge. A far-infrared light emitter was successfully realized using single-crystal graphene on SiC.

Low Reynolds Number Effects on the Separation and Wake of a Compressor Blade

Abstract This paper investigates the surface boundary layer and wake development of a compressor blade at a range of low Reynolds number from 45,000 to 120,000. Experiments in a miniature linear compressor cascade facility have been performed with detailed surface pressure measurements and flow visualization to track variations in the separation bubble size. These have been combined with high-resolution pneumatic pressure and hot-wire probe traverses in the downstream wake. High-fidelity direct numerical simulations have been completed on the same compressor blade section across the same range of operating conditions. The results show that large laminar separation bubbles exist on both blade surfaces. As Reynolds number increases, these separation bubbles shorten in length and reduce in thickness. Correspondingly, the downstream wake narrows, although the peak wake loss coefficient remains approximately constant. As the Reynolds number is increased from 45,000 to 120,000, the bubble length on the suction side reduced from 48% to 28% chord and on the pressure side reduced from 35% to 20% chord, while the loss coefficient reduced from 9% to 5%. The flow features are examined further within the high-fidelity computations, which reveal the dependence of the wake turbulence on the laminar separation bubbles. The separation bubbles are found to generate turbulent kinetic energy, which convects downstream to form the outer part of wake. As Re increases, a shorter bubble produces less turbulence in the outer part of the boundary layer leading to a narrower wake. However, the trailing edge separation is largely independent of Reynolds number, leading to the constant peak loss coefficient observed. The overall loss is shown to vary linearly with the total turbulence production, and this depends on the size of the separation bubbles. Overall, this research provides new insight into the connection between the blade surface flow field and the wake characteristics at low Reynolds number. The findings suggest that changes that minimize the extent of the blade separation bubbles could provide significant improvements to both the steady and unsteady properties of the wake.

An Experimental Study of In-Cylinder Heat Transfer from a Pressurized Motored Engine with Varying Peak Bulk Gas Temperatures

<div class="section abstract"><div class="htmlview paragraph">The variation of in-cylinder heat transfer with parameters such as engine speed, air-to-fuel ratio, coolant temperature and compression ratio were frequently studied in classical research. These experimentally-obtained relationships are important for improving in-cylinder heat transfer models, essential in developing CO<sub>2</sub> reducing strategies. In this publication, a 2.0 liter compression ignition engine was tested in the pressurized motored configuration. This developed experimental setup allowed testing of the engine at speeds ranging between 1400 rpm and 3000 rpm, with peak in-cylinder gas pressures from 40 bar to 100 bar. The engine was motored using different gas compositions chosen specifically to have ratios of specific heats of 1.40, 1.50, 1.60 and 1.67 at room temperature. This enabled motored testing with peak in-cylinder bulk gas temperatures ranging from 700 K to 1500 K. This wide variation of peak bulk gas temperature was achievable even at constant peak in-cylinder gas pressure, which gave the possibility of varying the thermal load of the engine independently from the gas pressure load. This experimental setup offered the repeatability and robustness of motored testing, with the benefit of a fired-representative gas pressure and thermal load. Throughout the test matrix, the engine was instrumented with eroding surface thermocouples at two locations in the cylinder head; at the cylinder central axis, and at the periphery in the squish region. The steady-state and transient components of heat flux were investigated separately, along with the average surface temperature and its swing. The transient component of heat flux was computed using the Impulse Response method, coupled with a two-dimensional finite element model of the eroding thermocouples, as presented in SAE 2021-24-0018. This method takes into account the two-dimensional nature of heat flux through the thermocouples and hence presents a more robust analysis than the more common one-dimensional treatment using the Fast-Fourier Transform method.</div></div>

Chronopotentiometric sensing of native, oligomeric, denatured and aggregated serum albumin at charged surfaces

In protein analysis, fast techniques applicable for preliminary tests of the protein structural changes are sought. We show that using constant current chronopotentiometric stripping peak H, small amounts of oligomeric, denatured and aggregated bovine serum albumin (BSA) can be easily distinguished from native form. Different behavior of native, denatured, and aggregated BSA could be explained by combination of their different adsorption at charged surface and accessibility of electroactive amino acid residues. Ability to discriminate between individual forms allows to use chronopotentiometric stripping for study of processes responsible for structural changes, such as freezing treatment.

Improving brace member seismic performance with amplified-deformation lever-armed dampers

This study focused on the development and validation of a novel brace design that incorporated a hinged truss member and a set of lever-armed damper (LAD), namely LAD-Brace, for structural performance enhancement. The lever-armed damper was designed with adequate rotation mechanism to generate amplified-deformation and uniform yield zones in the tapered energy dissipation plate for efficient energy dissipation. A series of cyclic loads and constant peak amplitude tests were conducted on LAD-Braces with various geometries in the energy dissipation plates. Analytical expressions for yield strength estimation were derived and effectively validated by the test results. Cyclic load test results showed that adequate strength, effective equivalent viscous damping and significant energy dissipation were simultaneously achieved which justified the design applicability for earthquake-resistant purposes. Investigation through constant peak amplitude tests revealed that LAD-Braces, when designed with adequate geometries, possessed further seismic resilience after experiencing major earthquake excitation, thus validated the proposed design effectiveness and robustness.

Study of Composition Variation on Dielectric and Impedance Spectra of Tetragonal-Rhombohedral System in (1-x)BZT-(x)BCT Composites

Abstract: In present work, (1-x)[BaZr0.2Ti0.8O3]-(x)[Ba0.7Ca0.3TiO3] (BZT-BCT) (where x = 0.50, 0.60 and 0.75) were fabricated by solid-state reaction technique. Structural, dielectric and impedance properties of the synthesized composites were investigated and discussed in detail. The X-ray diffraction technique shows that all the samples possessed a double-phase polycrystalline sample with a tetragonal-rhombohedral structure. Dielectric and impedance behavior were investigated in a wide range of temperatures (room temperature (RT) - 500˚C) and frequency (100 Hz ≤f ≤ 1 MHz). A broad dielectric constant peak was observed around the phase transition temperature.

Far-infrared emission from graphene on SiC by current injection

Abstract The far-infrared emission properties of epitaxial graphene on SiC obtained by current injection were investigated using an infrared camera and Fourier-transform infrared spectroscopy. The radiation directivity from the graphene emitter was observed in the directions perpendicular to the surface and edge of the sample. The emission energy density from the graphene edge was larger than that from the graphene surface in all directions. The maximum measured temperature change at 0.4 W for the edge emission was 76.1 K for a tilt angle of 50° and that for the surface emission was 54.1 K for 0°. A blackbody-like emission spectrum with a constant peak wavelength of 10.0 µm, regardless of the applied electrical power, was observed for both the surface and edge. A far-infrared light emitter was successfully realized using single-crystal graphene on SiC.

Estimation of the depth-domain seismic wavelet based on velocity substitution and a generalized seismic wavelet model

Depth-domain seismic wavelet estimation is the essential foundation for depth-imaged data inversion, which is increasingly used for hydrocarbon reservoir characterization in geophysical prospecting. The seismic wavelet in the depth domain stretches with increasing medium velocity and compresses with decreasing medium velocity. The commonly used convolutional model cannot be directly used to estimate depth-domain seismic wavelets due to velocity-dependent wavelet variations. We have developed a separate parameter estimation method for estimating depth-domain seismic wavelets from poststack depth-domain seismic and well-log data. Our method is based on the velocity substitution and depth-domain generalized seismic wavelet model defined by the fractional derivative and reference wavenumber. Velocity substitution allows wavelet estimation with the convolutional model in the constant-velocity depth domain. The depth-domain generalized seismic wavelet model allows for a simple workflow that estimates the depth-domain wavelet by estimating two wavelet model parameters. In addition, this simple workflow does not need to perform searches for the optimal regularization parameter and wavelet length, which are time-consuming in least-squares (LS)-based methods. The limited numerical search ranges of the two wavelet model parameters can easily be calculated using the constant phase and peak wavenumber of the depth-domain seismic data. Our method is verified using synthetic and real seismic data and further compared with LS-based methods. The results indicate that our method is effective and stable even for data with a low signal-to-noise ratio.

Dissipative soliton resonance and noise-like pulse generation of large normal dispersion Yb-doped fiber laser

In this paper, we experimentally demonstrate two types of dissipative soliton resonant (DSR) and noise-like pulse (NLP) in a mode-locked fiber laser using the nonlinear optical loop mirror (NOLM). By appropriately adjusting the polarization states, the switchable generation of DSR and NLP can be achieved from one mode-locked fiber laser. By adjusting the pump power, the pulse width of DSR increases gradually from 2.45 to 13.35 ns with a constant peak intensity, while the NLP just has a little increase, even splitting into two narrower pulses at higher pump power. Two types of DSR and NLP have the same pulse periods of 1.29 μs, corresponding to the cavity length of the fiber laser. The obtained results display the evolution process of DSR pulse and NLP in mode-locked fiber laser and have some application in optical sensing, spectral reflectometry, micromachining, and other relative domains.

Finite element analysis to enhance the efficiency of the secondary roof of double skin roofs (DSRs)

The significant side effect of rapid urbanization in developing cities is urban heat island (UHI), resulting in elevated ambient air temperatures. This causes a further increase in the indoor air temperature of a building bringing thermal discomfort to the inhabitants. It is a well-established fact that the significant electric consumption in buildings creates thermal comfort conditions for the inhabitants. Cool roofs are one of the promising passive technologies to curb the entry of heat flux into the buildings through ceilings, and a double skin roof (DSR) is a cool roof technique in which an air channel inhibits the heat flux entry. This paper presents an opinion to increase the efficiency of the secondary roof of a DSR by providing perforations and fins (extended surfaces) to it by way of a simulation using Ansys software, a finite element analysis software, and incorporating constant peak ambient boundary conditions on the roof for five hours to obtain the temperature distribution. The simulated results show that such a secondary roof design is 16.43 % more efficient in decreasing the temperature at its lower surface than the conventional one.

High voltage gain bi‐directional Z‐source inverters with dual‐loop feed‐forward peak DC‐link voltage compensation for fuel cell vehicles

High boost inverter is an essential part to interface the fuel cell stack and traction motor for fuel cell vehicles (FCVs). This paper proposes two novel high voltage gain bi-directional Quasi-ZSIs (QZSI) with new active switched inductor cells for FCVs application. The disadvantages of low voltage boost ratio, large start up current, unfavourable mode operations and unidirectional power flow in conventional Z-source inverter (ZSI) are eliminated. The proposed Z-source inverters are combined with active switched inductor cells to achieve a higher voltage gain and lower voltage stress over capacitors, which can be widely applied in energy storage systems. A small signal model is derived by dynamic analysis. In order to achieve a constant peak dc-link voltage, a dual-loop feed-forward peak dc-link voltage control strategy for the proposed QZSI is introduced in this paper. Simulation and experiment waveforms are presented to verify the theoretic analysis of the designed QZSIs and the proposed control strategy.

Regenerative terahertz quantum detectors

Because of the ultrafast and photon-driven nature of the transport in their active region, we demonstrate that quantum cascade lasers can be operated as resonantly amplified terahertz detectors with wide RF bandwidth. Tunable responsivities up to 50 V/W and noise equivalent powers down to 100 pW/Hz1/2 are demonstrated at 4.7 THz. Constant peak responsivities with respect to the detector temperature are observed up to 80 K. Thanks to the ≈ps intersub-band lifetime, electrical bandwidths larger than 20 GHz can be obtained, allowing the detection of optical beatnotes from quantum cascade THz frequency combs.

Hybrid test bench for high repetition rate radial shock wave measurement

Abstract Radial shock wave therapy is used for different therapeutic indications. In order to assess the effect on the treated tissue, it is important to know the sound field parameters. However, it is challenging to measure the pressure curves of ballistic devices, especially at high pulse repetition rates. In the new standard IEC 63045:2020 two possibilities for sound field measurements of non-focusing devices are described, a wet and a dry test bench. The whole sound field can be characterised using a wet test bench, but the process is cumbersome and cavitation is likely to occur at high pulse repetition rates. This effect is avoided using a dry test bench where the measurement position is limited to a single spot. Therefore, a hybrid test bench was developed combining the dry bench’s device mounting and coupling with a small water basin. The ballistic device was coupled to the basin filled with degassed ultrapure water using a latex membrane covered with ultrasound gel and the contact pressure was applied with a spring. A fibre optic probe hydrophone was used for the sound field measurements. The pressure curves of every 10th shot were measured on the beam axis in a distance of 1mm to the membrane. The device was analysed at 3.5 bar with different pulse repetition rates (1 Hz, 10 Hz, 20 Hz). The test setup enables an easy handling and reproducible results at all pulse repetition rates. The ballistic device provides constant peak pressures over different frequencies. The small water basin has the advantage that the water quality is easy to control and the measuring process is fast and uncomplicated. Cavitation suppression requires a clean water basin filled with degassed ultrapure water kept at a constant, low temperature. The hybrid test bench can be used to easily study shock wave parameters of ballistic devices at high repetition rates.

Preparation and dielectric properties of co-contained unfilled tungsten bronze ceramics Ba4RCo0.5Nb9.5O30

In this study, Ba4RCo0.5Nb9.5O30 (R = La, Nd, Sm, Eu) (BRCN) ceramics were synthesized using a high-temperature solid-state reaction. The XRD refinement results show that ceramic samples are tetragonal tungsten bronze (TTB). As the radius of rare-earth ions decreases, the unit cell volume of BRCN ceramics decreases, and the radius difference between Ba2+ and R ions increase, which results in BO6 octahedral distortion and the Raman peaks shift to high frequency. In addition, as the radius of rare-earth ions decreases, the ionic displacements increase and thus the dielectric constant peak temperature goes up. The high-temperature impedance results show that there exists n-type electronic conduction in the samples. The remanent polarization of the P–E curve at low frequencies increases from 0.470 to 1.038 μC cm−2 as the rare-earth ion radius decreases.

Analysis and optimization of the piercing process in laser beam cutting by means of high-speed X-ray imaging

An in-process analysis of the piercing process at the beginning of a laser cut using high-speed X-ray imaging is presented for the first time. Sheets of stainless steel with thicknesses ranging from 10 mm to 30 mm were pierced by laser pulses at a wavelength of 1 μm with a peak power of 6 kW. With a constant pulse length and a constant peak power, a reduction of the piercing duration was achieved by increasing the pulse repetition rate, as long as the latter does not exceed a specific limit at which the sheet cannot be pierced successfully anymore. When the pulse repetition rate exceeds the thickness-specific limit, the growth of the piercing depths stagnates before the sheet is pierced through completely. Melt from the side walls starts to re-fill the bottom of the piercing hole and the diameter of the hole increases in the lower part. The time between the pulses is too short for the melt to move out of the hole. An optimization strategy is presented that results in a reduction of the piercing duration by 50%. • An in-process analysis of the piercing process at the beginning of a laser cut using high-speed X-ray imaging is presented. • An increase of the pulse repetition rate at constant pulse length and laser peak power leads to a reduction of the piercing duration. • When the pulse repetition rate exceeds the thickness-specific limit, the growth of the piercing depths stagnates. • An optimization strategy is presented that results in a reduction of the piercing duration by 50%.

Dynamic Influence of Near-Source Seismic Ground Motion on Underground Mine Working Stability Using Time-Frequency Analysis

Peak particle velocity parameter is very useful in assessing underground mine working stability. Its application is widespread and requires additional analysis of the dominant frequency of the seismic signal. In order to properly analyze the velocity amplitudes of strong ground motions generated from seismic sources, time-frequency properties of near-source seismic signals in underground mines should be quantified. Using numerical calculations, the continuous wavelet transform (CWT) of the recorded near-source seismic signals in three perpendicular directions was obtained to characterize its time-frequency properties. The properties of recorded strong ground motion velocity seismograms for two high energy seismic events and two blasts from two underground coal mines in Poland have been extracted with the use of continuous wavelet transform spectrograms showing the duration time of each frequency group. Assuming a constant peak particle velocity amplitude on the analyzed seismograms, the duration time of each frequency group starts to play a key role. The longer the duration time of the lower frequency group is on the CWT spectrogram, the more the damaging effect on underground mining excavations can be observed. Varying bandwidths of dominant frequencies in separate time intervals for the analyzed seismic signals have had significantly different influence on the potentially damaging effect on underground mining excavations.

Plate-height model of ion mobility-mass spectrometry: Part 2-Peak-to-peak resolution and peak capacity.

In a previous work, we explored zone broadening and the achievable plate numbers in linear drift tube ion mobility-mass spectrometry through developing a plate-height model [1]. On the basis of these findings, the present theoretical study extends the model by exploring peak-to-peak resolution and peak capacity in ion mobility separations. The first part provides a critical overview of chromatography-influenced resolution equations, including refinement of existing formulae. Furthermore, we present exact resolution equations for drift tube ion mobility spectrometry based on first principles. Upon implementing simple modifications, these exact formulae could be readily extended to traveling wave ion mobility separations and to cases when ion mobility spectrometry is coupled to mass spectrometry. The second part focuses on peak capacity. The well-known assumptions of constant plate number and constant peak width form the basis of existing approximate solutions. To overcome their limitations, an exact peak capacity equation is derived for drift tube ion mobility spectrometry. This exact solution is rooted in a suitable physical model of peak broadening, accounting for the finite injection pulse and subsequent diffusional spreading. By borrowing concepts from the theoretical toolbox of chromatography, we believe that the present study will help in integrating ion mobility spectrometry into the unified language of separation science.

Cyclic tests of steel tee energy absorbers for precast exterior wall panels in steel building frames

This paper focuses on a new type of exterior wall system for steel building frames. The wall system consists of precast reinforced concrete wall panels that are bolted to the beams of a steel building frame and are equipped with the inter-panel steel tee energy absorbers. The precast wall panels and the steel tees are expected to remain elastic and absorb hysteretic energy under the frame inter-story drifts caused by earthquakes, respectively. To demonstrate the perceived benefits of the exterior wall system and investigate the behavior of the steel tee energy absorbers, a group of five specimens with each consisting of a steel frame, a pair of precast wall panels and a set of six steel tee energy absorbers were designed, constructed and tested. The test parameters varied among the specimens were the geometries of the steel tee energy absorbers and the technology adopted to develop them. The steel frame and the precast wall panels were re-used in all specimens. Each specimen was tested through a two-phase loading program which imposed the inter-story drift demands with progressively increasing and constant peak amplitudes, respectively. All the specimens sustained the maximum inter-story drift angle of 0.05 rad or larger and exhibited a stable energy dissipation response. The tests demonstrated the damage free response of the precast exterior wall panels as well as the replaceability of the steel tee energy absorbers. Based on an idealized curvature distribution in the webs of the steel tee energy absorbers, the classic beam theory, and the virtual work theory, this research established a simplified model for computing the strengths of the steel tee energy absorbers as well as their contribution to the lateral strength of the frame. The model was found to be able to provide acceptable predictions for the tested specimens and it is recommended for future design.

Lateral and Uplift Capacity of Pipeline Buried in Seabed of Homogeneous Clay

Buried offshore pipes are prone to upheaval and lateral buckling because of the high temperature and pressure of the materials being transported. An attempt has been made in the present study to evaluate uplift and lateral capacity of buried offshore pipes in a soft clay seabed using finite-element software. The numerical model used in the present study has been validated against results available in the literature. Finite-element analyses are carried out to study the upheaval and lateral buckling behavior of pipes for both the no-tension (NT) condition, i.e., when separation occurs between the pipe and soil, and the full-tension (FT) condition, i.e., when the soil beneath the pipe remains attached to the pipe. The variation of both uplift and lateral normalized capacity factors with soil cover depth ratio is presented for different combinations of soil strength and effective weight. Both uplift and lateral capacity factors have been found to increase and reach a constant peak value with increasing depth of soil cover. A transition from global and local failure mechanisms of a pipe is observed when the capacity factors attain their peak values at a limiting soil cover depth. The critical cases for the design of buried offshore pipe in homogeneous clay are established for both NT and FT conditions.

Investigation of ultra-lift Luo-converter with peak, average and hysteresis current-mode control

The Renewable energy system, electric vehicle, and telecommunication applications require relatively stable power converters with a high gain and enhanced noise immunity. A study of three different types of current-mode controllers for high-gain ultra-lift Luo-converter (ULC) is discussed in this paper. The stability of a constant frequency peak current-mode controller (PCM), an average current-mode controller (ACM) and a variable frequency hysteresis current-mode controller (HCM) are analyzed based on small-signal characteristics. Using mathematical modeling of the controllers, the closed-loop transfer functions such as control voltage to output voltage, current loop gain, inductor current to control voltage, and audio susceptibility are obtained. These transfer functions along with MATLAB simulation results for PCM, ACM and HCM controllers are compared. Then, the component losses of the ULC converter using PCM, ACM and HCM controllers are calculated and an efficiency comparison of different control techniques is done. Investigations of the voltage and current stresses of the switch and diodes are also carried out. Finally, a prototype is fabricated to validate the performance of the converter.