PL Spectra and Hot Charge Carrier Phenomena in an Undoped GaAs/AlGaAs Tunnel-Coupled Quantum Well

In this research, we experimentally investigated the photoluminescence (PL) spectra of an undoped GaAs/Al0.36Ga0.64As Tunnel-Coupled Quantum Well (TCQW) at 300 K and 77 K. At 300 K, PL spectra were broadened at various laser intensities due to the characteristic quantum-confinement electron levels in the active region of the TCQW during pumping excitation. At 77 K, at selected excitation intensities, the high-energy tails in the PL spectra of the studied structure corresponded with hot electron temperatures as functions of the energy of emitted photons. The average scattering energy rate of hot electrons in the system was also studied at a lattice temperature of 77 K. The average scattering energy rate of hot electrons obtained from this experimental study was in agreement with the calculated theoretical value.

Acoustic Emission and Fractal Precursory Characteristics of Coals with Different Bursting Liabilities in Loading Failure Process

Aimed at investigating the differentiation of acoustic emission (AE) signals and fractal precursory characteristics between strong, weak, and no bursting liability coals under uniaxial compression, as well as improving the accuracy of rockburst monitoring and early warning by AE techniques, we experimentally studied the evolution law and differences of AE ring count rate, energy rate, and correlation dimension between different loaded bursting liability coals by the YAW4306 electric mechanical test system and CTA-1 AE monitor. Our experimental results indicated that the AE count and energy of coal samples with different bursting liabilities showed a similar evolution law of “sharp increase-calm-sharp increase” before their main rupture. The active points of AE signals emitted from coal with strong, weak, and no bursting liability appeared at about 85∼90%, 75∼78%, and 51∼55% of the peak stress, respectively. The stronger the bursting liability of coal, the shorter the duration of main rupture and postpeak failure stage, and the greater the AE energy rate in the main rupture. The AE counts of different coals had obvious fractal characteristics, and the AE correlation dimension values of strong and weak bursting liability coal samples presented the phenomenon of “fluctuating rise to a peak value-sharp drop-continuous decrease,” which can be used as a precursory information of coal failure.

Objective Evaluation of Therapeutic Effects of ADHD Medication by Analyzing Movements Using a Smart Chair with Piezoelectric Material

Attention-deficit hyperactivity disorder (ADHD) is the most common neuropsychiatric disorder in schoolchildren. Several methods are available to evaluate ADHD therapeutic effects, including the Swanson, Nolan, and Pelham (SNAP) questionnaire, the Vanderbilt ADHD Diagnostic Rating Scale, and the visual analog scale. However, these scales are subjective. In this study, a piezoelectric material was applied to a medical chair to objectively evaluate the therapeutic effect of ADHD medication before and after treatment. A total of 22 patients (18 boys and 4 girls) with ADHD were enrolled. During the appointment, the patients’ movements were recorded by the piezoelectric material before being analyzed. The variance, zero-crossing rate, and high energy rate of movements were used to analyze the signal in this study. The results showed the variance, zero-crossing rate, and high energy rate in patients with ADHD all decreased significantly after 1 month of methylphenidate use. Although the hyperactivity subscales of SNAP obtained from parents and teachers demonstrated significant decreases after 1 month of medication, the reduction rate of the three aforementioned measurements decreased more than hyperactivity subscales. This suggests that the use of a smart chair equipped with a piezoelectric material is an objective and useful method for evaluating the therapeutic effects of ADHD medication.

Liquid based diurnal thermal storage

A comprehensive study of using thermal energy storage (TES) tank was performed. In this report, the comprehensive literature review of various options of storing thermal energy in buildings was discussed. The objective of the project was to evaluate charging and discharging performance of a storage tank with and without phase change material (PCM) blocks. The general format of the energy balance for the storage tank considering losses, input energy, inlet and outlet mass flow rates, and PCM blocks was developed. Charging performance was analyzed by three different approaches. Initially, constant input thermal energy rate was considered to be delivered to the tank by different heat pumps from 4.5 kW to 9 kW heating capacity. Charging time, phase change process, and stored energy were analyzed under constant thermal energy rate input mode for charging process. Then, the effect of constant coil temperature on charging process was studied and results were compared to previous cases. Also, a solar assisted heat pump was implemented into the model to verify the effect of solar radiation on pre-heating the air for heat pump and how this process improves the overall charging progress of storage tank. Moreover, discharge procedure was discussed to evaluate various discharge modes based on different water draw flow rates. Based on this analyses developing a complete TRNSYS model of the tank is recommended in order to do whole building energy simulation.

Liquid based diurnal thermal storage

A comprehensive study of using thermal energy storage (TES) tank was performed. In this report, the comprehensive literature review of various options of storing thermal energy in buildings was discussed. The objective of the project was to evaluate charging and discharging performance of a storage tank with and without phase change material (PCM) blocks. The general format of the energy balance for the storage tank considering losses, input energy, inlet and outlet mass flow rates, and PCM blocks was developed. Charging performance was analyzed by three different approaches. Initially, constant input thermal energy rate was considered to be delivered to the tank by different heat pumps from 4.5 kW to 9 kW heating capacity. Charging time, phase change process, and stored energy were analyzed under constant thermal energy rate input mode for charging process. Then, the effect of constant coil temperature on charging process was studied and results were compared to previous cases. Also, a solar assisted heat pump was implemented into the model to verify the effect of solar radiation on pre-heating the air for heat pump and how this process improves the overall charging progress of storage tank. Moreover, discharge procedure was discussed to evaluate various discharge modes based on different water draw flow rates. Based on this analyses developing a complete TRNSYS model of the tank is recommended in order to do whole building energy simulation.

A MICROSTRUCTURE-BASED MECHANISTIC MODEL FOR BONE SAWING: PART 2 - ACOUSTIC ENERGY RATE PREDICTIONS

Part-2 of this paper is focused on modeling the acoustic emission (AE) energy rate as a function of the specific cortical bone microstructures (viz., osteon, interstitial matrix, lamellar bone, and woven bone) and the depth-of-cut encountered by the bone sawtooth. First, the AE signal characteristics from the sawing experiments (in Part-1) are related to the pure haversian and pure plexiform regions of the cut. Using the cutting force predictions from Part-1 as input, the AE energy rate is then modeled in terms of the energies dissipated in the shearing and ploughing zones encountered by the rounded cutting edge. For this calculation, the rounded edge geometry of the sawtooth is modeled as a combination of (i) shear-based cutting from a negative rake cutting tool; and (ii) ploughing deformation from a round-nose indenter. The spread seen in the AE energy rate is captured by modeling the variations in sawed surface height profile, tool cutting edge geometry, and porosity of the bone. The model calibration and validation protocols are similar to those used in Part-1. The validated AE model is useful for process planning both in terms of its ability to predict AE energy rate trends and cutting force variations, based on the differences in the underlying bone microstructures.

On the relationship between mechanical energy rate and heat dissipated rate during fatigue for a C45 steel depending on stress ratio

This work deals with the analysis in the frequency domain of the temperature signal and mechanical energy rate of C45 steel under two different fatigue stepwise loading series at stress ratios of 0.1 and -1. It was first investigated the energy distribution among the harmonic components of the signals to understand possible variations caused by a different stress ratio. In addition, the second amplitude harmonic (SAH) of heat dissipated and mechanical energy rates have been considered in the analysis and their relationship was investigated. It has been shown as it depends only on the material, hence it is valid whatever the kind of the test is without any assumption on the energy supplied to the material or material hysteresis loop stabilisation. The adopted approach allows the analysis of intrinsic dissipations by means of rapid, full-field and contactless techniques without any specific requirement on loading condition or temperature signal stabilisation.

Acoustic Emission Characteristics and Energy Evolution of Red Sandstone Samples under Cyclic Loading and Unloading

To explore the characteristics of rock deformation and failure under cyclic loading and unloading, the MTS815 rock mechanics test system and acoustic emission (AE) signal acquisition system were used to perform cyclic loading and unloading tests on red sandstone samples. The results showed that, compared with the uniaxial compression test, cyclic loading and unloading had a certain strengthening effect on the strength of the samples. The plastic deformation of the rock samples increased as the number of cycles increased. Based on AE signals, the cracking mode classification was analyzed on the basis of the average frequency and the rise angle of the waveforms. It was observed that the Felicity ratio gradually decreased with the increase in the stress level, which showed a cumulative damage effect. From the perspective of energy, the obvious increase of AE energy rate was mainly concentrated in the early and late stages of uniaxial compression, while the significant increase of dissipated energy rate occurred in the late stage of uniaxial compression. During the cyclic loading and unloading, most of the work done by external forces in the compaction stage and the elastic stage was converted into elastic strain energy, and dissipated energy began to gradually increase in the stage of stable fracture development. In addition, it was found that the damage evolution of the rock samples changed from slow to fast, and the dissipated energy ratio increased when failure was approaching.