Compact Density Research Articles

Theoretical modeling of nonlinear optical properties in spheroidal CdTe/ZnTe core/shell quantum dot embedded in various dielectric matrices

The theoretical investigation of the electronic and nonlinear optical properties in spheroid-shaped CdTe/ZnTe core/shell quantum dots (CSQDs) embedded into two commonly adopted dielectric matrices (PVA, SiO2) is done in the framework of the Effective Mass Approximation (EMA). The discrete intra-band confined energy levels and their matching wave functions were calculated by solving the stationary Schrödinger equation taking into account the Compact Density Matrix (CDM) approach. The effect of the dielectric mismatch between the system and the capped matrix has been studied and discussed. Our numerical results revealed that the third-order nonlinear (TON) optical susceptibility χ3 is strongly influenced by the geometrical parameters and the dielectric environment.

Dust- and inclination-corrected star formation and interstellar medium scaling relations in nearby galaxies

ABSTRACT Following from our recent work, we present a detailed analysis of star formation and interstellar medium (ISM) scaling relations, done on a representative sample of nearby galaxies. H α images are analysed in order to derive the integrated galaxy luminosity, known as a more instantaneous and accurate star formation rate (SFR) tracer, and the required photometric and structural parameters. Dust- and inclination-corrected H α luminosities, SFRs, and related quantities are determined using a self-consistent method based on previous work prescriptions, which does not require the assumption of a dust attenuation curve and use of Balmer decrements (or other hydrogen recombination lines) to estimate the dust attenuation, with the advantage of determining dust opacities and dust masses along the way. We investigate the extent to which the dust and inclination effects bias the specific parameters of these relations, the scatter and degree of correlation, and which relations are fundamental or are just a consequence of others. Most of our results are consistent with errors with other similar studies, while others come in opposition or are inconclusive. By comparing the B-band optical and H α (star-forming) discs scale lengths, we found on average the star formation distribution to be more extended than the stellar continuum emission one (the ratio being 1.10), this difference increasing with stellar mass. Similarly, more massive galaxies have a more compact stellar emission surface density than the star formation one (average ratio of 0.77). The method proposed can be applied in larger scale studies of star formation and ISM evolution, for normal low- to intermediate-redshift galaxies.

Effects of milling time and sintering temperature on the mechanical properties of 8 wt% WC/AlCoCrFeNiTi0.5 high entropy alloy matrix composite

The present study investigates the effect of milling time, and sintering temperature on the microstructure and mechanical properties of the spark plasma sintered 8 wt% WC/AlCoCrFeNiTi0.5 high entropy alloys matrix composite (HEAC). The results show that the grain size is decreased first and then increased with an increase of milling time. The refined grain along with the homogeneous distribution of reinforcements is observed when milling for 15 h. It also shows both of relative density and compression strength of compacts are increased first and then decreased with an increase of sintering temperature. A highest relative density of 99.89 % and a fracture strength of 2683 MPa are obtained at 1150 °C. Another, sintering leads to crystal structure transition from BCC to FCC for the solid solution phase. The formation of (Fe, Co)6W6C complex carbide as a main strengthening phase is conducive to the enhancement of hardness. The strengthening mechanism is mainly attributed to dislocation strengthening and Orowan mechanism.

Investigation of nonlinear optical rectification within multilayer wurtzite InGaN/GaN cylindrical quantum dots under the impact of temperature and pressure

We have looked numerically at variations of the nonlinear optical rectification (NOR) for an impurity donor localized in a wurtzite Inx0Ga1−x0N/GaN multilayer cylindrical quantum dots (MLCQDs), which is under the effect of hydrostatic pressure and temperature. Using the effective mass approximation, the compact density matrix formalism, we have solved the Schrödinger equation by the finite element method (FEniCS Project) . Firstly, we consider the impact of altering the polarization direction of the incident electromagnetic radiation. Specifically, we explore two distinct scenarios: axial, along the growth axis of the structure, and circular, across the cross-section of the cylinder. From our investigation, we found that the nonlinear optical rectification is determined by two main parameters: the transition energy, which is mainly related to quantum confinement, and the geometrical factor that depends on the distribution of the electron wave functions. The NOR experiences a blueshift with an increase in hydrostatic pressure or indium composition, and a redshift with an increase in temperature or quantum dot radius, where the impurity is located in the center of the upper QD. Furthermore, the results show that the amplitude and resonance peak position of NOR are significantly influenced by varying the impurity’s position and the barrier width.

Transport and electrical properties of cryogenic thermoelectric FeSb2: the effect of isoelectronic and hole doping

Thermoelectric materials operating at cryogenic temperatures are in high demand for efficient cooling and power generation in applications ranging from superconductors to quantum computing. The narrow band-gap semiconductor FeSb2, known for its colossal Seebeck coefficient, holds promise for such applications, provided its thermal conductivity value can be reduced. This study investigates the impact of isoelectronic substitution (Bi) and hole doping (Pb) at the Sb site on the transport properties of FeSb2, with a particular focus on thermal conductivity (κ). Polycrystalline FeSb2 powder, along with Bi- and Pb-doped samples, were synthesized using a simple co-precipitation approach, followed by thermal treatment in an H2 atmosphere. XRD and SEM analysis confirms the formation of the desired phase pre- and post-consolidation using spark plasma sintering. The consolidation process resulted in a high compaction density and the formation of submicrometer-sized grains, as substantiated by electron backscattered diffraction analysis. Substituting 1% of Bi and Pb at the Sb site successfully suppressed the thermal conductivity (κ) from ∼15 W (m·K)−1 in pure FeSb2 to ∼10 and ∼8.7 W (m·K)−1, respectively. Importantly, resistivity measurements revealed a metal-to-insulator transition at around 6.5 K in undoped FeSb2 and isoelectronically Bi-substituted FeSb2, suggesting the existence of metallic surface states and provides valuable evidence for the perplexing topological behavior exhibited by FeSb2.

Insights into mechanics and electrochemistry evolution of SiO/graphite anode by a composite electrode model

Silicon-based materials are crucial for high-capacity anodes, but their volume expansion in batteries due to the presence of silicon requires further analysis and research. Silicon monoxide/Graphite (SiO/C) is a composite material that combines the volume expansion of silicon oxide material with the practical application of carbon material. Therefore, understanding its behavior during actual use is important, particularly in full batteries and in pairs with high-capacity LiNi0.8Co0.15Al0.05O2 (NCA) cathode. There are fewer studies on this topic, which highlights the need for research. Thus, in this work, SiO/C composite negative electrodes are prepared with different compaction densities (CDs) of 1.38, 1.52, and 1.62 g cm−3. Pouch cells are assembled with NCA positive electrode to investigate the changes in battery thickness and internal resistance under different CDs and state of charge (SOC), as well as the Coulombic efficiency and cyclic performance of batteries are also examined. Additionally, the capacity-voltage curves, expansion curves under different CDs and SOC, particle stress change, and lithium concentration distribution under different CDs are comprehensively simulated. Thus, the evolution of lithium concentration distribution and electrodes volumetric strain during charge and discharge are directly presented. The established model through matching experimental data provides a research basis for predicting the performance of SiO/C negative electrodes, especially its electrochemical and mechanical performance evolution in high‑nickel full batteries. This study has important implications for the development of high-performance silicon-based anodes in practical applications.

Conductive composite binder for recyclable LiFePO4 cathode

In order to solve the problem of poor conductivity of traditional LiFePO4 cathode binders, we developed sodium alginate-Congo red copolymers (SA-CR) as water-soluble electrically conductive and mechanically robust composite binder. Unlike most other electrically conductive polymer binders, the procedure is straightforward and low-cost to prepare SA-CR binder. Various SA -CR copolymers were prepared with different degree of compounding of CR to investigate the effect of CR on the electrochemical and physical properties of the prepared electrodes. The copolymer whose composition was filled with a mixture of SA and CR at a 3:1 mass ratio showed the best cell performance, due to the well-balanced electrical conductivity and mechanical properties. It exhibited a specific capacity of 118.8 mAh/g at the 100th cycle with 92.1 % capacity retention, significantly better than the 108.5 mAh/g of conventional acetylene black electrodes. CR as a conduction-promoting agent in water-soluble composite binder favors the formation of continuous and homogenous conducting bridges throughout the electrode and increases the compaction density of electrode by reducing the conducting agent content of acetylene black and thus the improvement of electrode performance is realized.

10 μm-Level TiNb2 O7 Secondary Particles for Fast-Charging Lithium-Ion Batteries.

TiNb2 O7 with Wadsley-Roth phase delivers double theoretical specific capacity and similar working potential in comparison to spinel Li4 Ti5 O12 , the commercial high-rate anode material, and thus can enable much higher energy density of lithium-ion batteries. However, the inter-particle resistance within the high-mass-loading TiNb2 O7 electrode would impede the capacity release for practical application, especially under fast-charging conditions. Herein, 10-20 μm-size carbon-coated TiNb2 O7 secondary particle (SP-TiNb2 O7 ) consisting of initial micro-scale TiNb2 O7 particles (MP-TiNb2 O7 ) was fabricated. The high crystallinity of active material could enable fast-charge diffusion and electrochemical reaction rate within particles, and the small number of stacking layers of SP-TiNb2 O7 could reduce the large inter-particle resistance that regular particle electrode often possess and achieve high compaction density of electrodes with high mass loading. The investigation on materials structure and electrochemical reaction kinetics verified the advances of the as-fabricated SP-TiNb2 O7 in achieving superior electrochemical performance. The SP-TiNb2 O7 exhibited high reversible capacity of 292.7 mAh g-1 in the potential range of 1-3 V (Li+ /Li) at 0.1 C, delivering high-capacity release of 94.3 %, and high capacity retention of 86 % at 0.5 C for 250 cycles in half cell configuration. Particularly, the advances of such an anode were verified in practical 5 Ah-level laminated full pouch cell. The as-assembled LiFePO4 ||TiNb2 O7 full cell exhibited a high capacity of 5.08 Ah at high charging rate of 6 C (77.9 % of that at 0.2 C of 6.52 Ah), as well as an ultralow capacity decay rate of 0.0352 % for 250 cycles at 1 C, suggesting the great potential for practical fast-charging lithium-ion batteries.

Linear and nonlinear electric and magneto-optical absorption coefficients and relative refractive index changes in WxMo1−xS2 monolayer: Role of tungsten contents

In this work, we study the electric and magneto-optical absorption coefficients (ACs) and relative refractive index changes (RRICs) in W[Formula: see text]Mo[Formula: see text]S2 ternary alloys under the control of tungsten contents using the compact density matrix approach. With the influence of external electric and magnetic fields, the results show that there are a series of resonant peaks for both intra-band and inter-band transitions. With an increase in W-concentration and electric and magnetic fields, the resonant peaks give a blue (red) shift and reduce (increase) their amplitudes. These results suggest a potential application of monolayer W[Formula: see text]Mo[Formula: see text]S2 in future nanoscale electronic and magneto-optical devices.

Coastal vulnerability assessment using electrical resistivity tomography in Padang Betuah, Central Bengkulu

<span>Abrasion disaster in the coastal area of Padang Betuah Beach has a high level of abrasion in Central Bengkulu. The local community utilizes abrasion in the coastal area as a tourist attraction and becomes local revenue in the research location. The location that becomes a tourist attraction is decreasing because the coastal area’s land has been abraded. After conducting research using the electrical resistivity tomography (ERT) method in 2D and 3D, it was found that claystone dominated the coastal area at the research location with a resistivity value of 16-200 Ωm at a depth of 15-20 m. The coastal area in Padang Betuah Beach is composed of clay shale rocks (207-220 Ωm), and the depth is 2-14.8 m. Clay shale rocks are not abraded in stones with resistivity values >250 Ωm. This is caused by clay shale, which has low porosity, so it has a compact rock density. Seawater is identified at a depth of 21-63 m with a resistivity value of 2</span><span lang="IN">.</span><span>225-10</span><span lang="IN">.</span><span>2 Ωm. The depth of seawater determined follows the average height of the cliffs in the research location. The abrasion process can be slowed down by making jetties, water breakers, and mangrove cultivation.</span>

How highly efficient power electronics transfers high electrocaloric material performance to heat pump systems

Electrocaloric heat pumps for cooling or heating are an emerging emission-free technology, which could replace vapor-compression systems, harmful refrigerants, and mechanical compressors by a solid-state solution with theoretically even higher coefficient of performance. Existing electrocaloric ceramics could reach around 85% of the Carnot-limit, and existing electrocaloric polymers could enable a compact and high power density system. However, the performance of published system demonstrators stays significantly below this performance, partly because of the external electronic charging loss (cyclic charging/discharging of electrocaloric capacitors). This work analyzes how the latest 99.74% ultra-efficient power electronics enables to maintain a high performance even at the system level. A first-principle analysis on material and system parameters also shows the effect of significantly different material properties of ceramics (PMN, PST) and PVDF-based polymers on system parameters. A system benchmark provides insight into system characteristics not covered by material analysis.Graphical abstract

Injection-on-Skin Granular Adhesive for Interactive Human-Machine Interface.

Realization of interactive human-machine interfaces (iHMI) is improved with development of soft tissue-like strain sensors beyond hard robotic exosuits, potentially allowing cognitive behavior therapy and physical rehabilitation for patients with brain disorders. Here, this study reports on a strain-sensitive granular adhesive inspired by the core-shell architectures of natural basil seeds for iHMI as well as human-metaverse interfacing. The granular adhesive sensor consists of easily fragmented hydropellets as a core and tissue-adhesive catecholamine layers as a shell, satisfying great on-skin injectability, ionic-electrical conductivity, and sensitive resistance changes through reversible yet robust cohesion among the hydropellets. Particularly, it is found that the ionic-electrical self-doping of the catecholamine shell on hydrosurfaces leads to a compact ion density of the materials. Based on these physical and electrical properties of the sensor, it is demonstrated that successful iHMI integration with a robot arm in both real and virtual environments enables robotic control by finger gesture and haptic feedback. This study expresses benefits of using granular hydrogel-based strain sensors for implementing on-skin writable bioelectronics and their bridging into the metaverse world.

Laser Doppler in Green Compact Density Inspection of Powder Metallurgy

The density of green compact in powder metallurgy (PM) is a critical characteristic to determine the strength and tenacity of the product. Due to the fragility and sensitivity to the humidity of green compact, detection method triggers by knocking or immersion cannot be applied. Current inspection method for green compact is to use a densitometer with Archimedes Principle, which has to immerse green compact into water. This action considers a destructive test due to the porosity of the PM product, and the oxidation reaction of metal particles inside products cannot be controlled. Since the current detection method is destructive, most of the inspection on forming process of PM only complies after setup of compaction machine. The next non-destructive test is executed after sintering, such as Acoustic emission testing (AE) and Magnetic Testing (MT), which require a solid object for knocking or liquid immersion. To reduce defective compaction flow into the manufacturing process, a Non-destructive test in forming process is a prerequisite. Laser Doppler Vibrometer (LDV) takes advantage of measuring without damaging the test object and obtaining characteristic spectrum signal from the sample for further analysis, which is preferable for green compact of PM. The LDV test setup included a Polytec PSV-400 scanning laser vibrometer with a crystal resonator attached to the test product to generate reference vibration. Integrate spectrum in the frequency range 0 - 5000 Hz was recorded from 30 points of an annular pattern. Comparison of the spectrum and statistical analysis from defective specimens demonstrate that velocity increases within a specific frequency, which is different from with normal samples. Increases in velocity refer to uneven density distribution with an absence of particles inside product decline. The study approves the possibility of density detection in green compact using an LDV. Further studies aim to construct a relational model of specimen and compaction machine and determine a fundamental database for Advance Process Control (APC) of forming process in PM.

High-performance supercapacitor electrode at commercial-level mass loading from N-enriched activated carbon derived from soybean dregs

N-enriched activated carbons (ACs) are prepared via a facile triple-doping technique route. The self-doping from the precursor of soybean dregs and additional introduction from egg white guarantee a high-level of N contents in the Hydrothermal carbonization (HTC) products (biochar). With a KOH-activation, relatively high surface area and easy-accessible ion channels are constructed. A post-doping from the subsequent ammonia-activation compensates the loss of the N contents during the KOH-activation. Relatively high surface area of 1518 m2/g and N atomic fraction of 4.311 % are achieved. Taking advantage of the compaction density of 0.68 g/cm3, electrodes with commercial-level mass loading of ∼10 mg/cm2 are fabricated with a moderate thickness of ∼0.15 mm. With symmetric supercapacitors (SCs) of commercial-level electrodes, high values are achieved of 357.1 F/g in gravimetric capacitance and 235.7 F/cm3 in volumetric capacitance at 0.5 A/g are achieved in 1 mol/L H2SO4. With 1 mol/L Et4NBF4 in acetonitrile (AN) as electrolyte, the gravimetric capacitance is 246.2 F/g and volumetric capacitance is 162.5 F/cm3. Moreover, a high energy density of 44.27 Wh/kg delivered at a high power of 2656 W/kg, good rate capability and excellent long-term cycling stability make the N-enriched ACs a competitive candidate for practical applications.

Electric field effect on the intersubband optical absorption of GeSn quantum wells with parabolically graded barriers

In this study, we propose a theoretical simulation of a Ge0.9Sn0.1 rectangular SQW with GeSn parabolically graded barriers (PGBs) in the terahertz (THz) region. The discrete intra-band confined energy levels and their matching wave functions were calculated by solving the stationary Schrödinger equation by the finite difference method taking into account the Compact Density Matrix approach under the framework of both the effective mass and the envelope wave function approximations. In this work, we studied the effect of the quantum square-well width on the intersubband transition and oscillator strength in a GeSn-strained-based Barrier-Well-Barrier GeSn/(Ge,α-Sn) PGBs to obtain the optimum quantum confinement of electrons. The electronic states and their wave functions in the conduction band were computed by solving the Schrödinger equation without and under the effect of an applied external electric field at room temperature. We then investigated the effect of the electric field on the optical absorption coefficient (OAC). Our numerical results show that for external fields (>15 kV/cm), an intersubband transitions (ISBTs) frequency band of 2–14 THz (8–58 meV) was obtained for the specific optimized parameters. These results should be beneficial to the design of devices based on GeSn QWs with PGB structures operating in the THz frequency range.

The effect of weathering on the variation of geotechnical properties of a granitic rock from Chile

The effect of rock weathering on geotechnical parameters can become substantial in geotechnical design. The weathering degree (WD) has usually been divided into five levels from fresh rock to completely weathered rock. In this study, the above five WDs are adopted to analyse the variation of several regularly used geotechnical properties. To that aim, a series of laboratory tests on a Chilean granitic rock in different stages of weathering was carried out. The results of the tests have been analysed by normalizing each geotechnical parameter with respect to the value obtained for slightly weathered samples instead of for fresh rock samples as is usually adopted. In this way, it was found that the unconfined compressive strength reduces steadily and considerably with each WD, as has been previously reported. Conversely, the modulus of deformation and P-wave velocity tend to stabilize the rate of reduction for highly and completely weathered rock samples, which does not agree with the trend and higher rate reductions found by other researchers. This stabilization reduction rate with WD was also found for compaction density, friction angle and Poisson's ratio.

Geothermal gradients in a high-organic content landfill

Geothermal gradients in a high-organic content landfill

Structure evolution and magnetization properties of FeSiBCCr amorphous alloys prepared by spark plasma sintering

FeSiBCCr bulk metallic glasses were prepared via spark plasma sintering, and the effects of holding time and heating rate on the structure and magnetization properties of powder compacts were investigated by SEM, TEM, XRD, DSC and VSM. The results show that when the holding time is increased from 10 min to 20 min, the internal porosity is reduced, and the amorphous fraction is decreased from 92.0 ± 1.7 % to 82.4 ± 4.3 % accompanied by the precipitation of fine nanocrystalline grains. When the holding time is increased to 30 min, the precipitation of the ferro-boron phase and growth of nanocrystalline grains lead to a significant deterioration of magnetization properties, although the compact density is significantly increased to 6.13±0.12 g/cm3. When the heating rate is increased from 20 K/min to 100 K/min, the activation energy of viscous flow is decreased and the compact density is improved due to the enhanced mass transfer. Moreover, the thermal stability of the amorphous material is also improved, effectively suppressing the grain coarsening and the precipitation of the ferro-boron phase. As a result, the saturation magnetic flux density is increased by 10 % and the coercivity is reduced by 83 %. The FeSiBCCr bulk metallic glasses prepared at a sintering temperature of 773 K, a heating rate of 100 K/min, and a holding time of 10 min contain an amorphous matrix with fine Fe2Si grains. And the compact has a density of 5.60±0.08 g/cm3, a saturation magnetic flux density of 1.03±0.03 T, and a coercivity of 15.9 ± 1.2 A/m, exhibiting promising magnetization properties and being expected to be used in medium and high frequency electronics.

Hot-Air-Assisted Radiofrequency Drying of Olive Pomace and Its Effect on the Quality of Olive Pomace Oil.

In this study, the drying of olive pomace in a hot-air-assisted radio frequency system (HA-RF) was conducted, and its effects on crude olive pomace oil quality were investigated. In this respect, the effects of radiofrequency electrode distance (90, 105 and 120 mm), sample thickness (2.5, 5, 7.5 and 10 cm) and compaction density (~0.45, ~0.60 and ~0.82 g/cm3) on drying rate have been evaluated. The best drying, with a higher drying efficiency, was obtained with 1 kg of sample weight and a 10 cm product thickness, ~0.45 g/cm3 compaction density and 105 mm electrode distance. Moreover, the results showed that the compaction density significantly affects the drying rate. The drying time was prolonged by approximately four times by increasing the compaction density from ~0.45 to ~0.82 g/cm3. The drying rate of olive pomace in HA-RF drying was compared with drying performed using hot air (HA) and radiofrequency (RF). The results revealed that HA-RF application reduced the drying time by almost 1.7 times compared to hot air drying and by about 2.7 times compared to radiofrequency. The peroxide value, free fatty acid content, p-anisidine value, polyaromatic hydrocarbon content, L*, a*, b*, chlorophyll and total carotenoid content of the oil extracted from the olive pomace dried under the best drying conditions were 1.09%, 12.2 meq O2/kg oil, 3.01, <1 ppb, 38.6, 7.5, 62.56, 105.25 mg pheophytin a/kg oil, 2.85 mg/kg oil, respectively. The drying of olive pomace in a hot-air-assisted radio frequency system could be an alternative way to ensure the safe and rapid drying of olive pomace.

Storage stability of a fluidized-bed agglomerated spray-dried strawberry powder mixture.

Background: Strawberry is a fruit with a high antioxidant capacity due to its richness in phenolic compounds that suffer a rapid post-harvest deterioration. Spray drying is an alternative to reduce losses; however, these powders present problems of instantanisation, making it necessary to implement agglomeration processes. During storage, powdered food products can undergo a series of changes in their amorphous state from a product initially in a vitreous state to a gummy state, where all properties are substantially modified due to the increased mobility of water in the matrix. Methods: The research objective was to evaluate the storage stability (6 months) of a fluidized bed agglomerated strawberry powder mixture at three temperatures (15, 25 and 25°C), a controlled environment at 65% relative moisture, and PET foil laminated film bags as packaging. Moisture, water activity, bulk and compacted density, Carr and Hausner indices, solubility, hygroscopicity, wettability, angle of repose, antioxidant capacities, total phenols, anthocyanins, vitamin C, color (CIE-Lab) and particle size were monitored. Results: ANOVA showed statistically significant differences (p<0.05) for all dependent variables concerning storage time; storage temperature had no significant effect on S, ABTS, DPPH and Hu. The time-temperature interaction during storage had no significant effect (p>0.05) on S, ABTS, DPPH, Hu and L. The agglomerate showed moisture and aw values that confer excellent stability against deterioration reactions; it retained good fluidity, low cohesiveness, and retentions above 50% for antioxidant capacity, 76% for total phenols, 39% for anthocyanins, and 40% for vitamin C; particle size was retained during the evaluation. The color was only affected in the 35°C treatment from the fifth month onwards. Conclusions: The study will serve as a tool for the determination of the shelf life of the chipboard once the critical values of the attributes selected as predictors of shelf life are defined.