Utilization Coefficient Research Articles

Combining discrete choice models and neural networks through embeddings: Formulation, interpretability and performance

This paper proposes a novel approach that combines theory- and data-driven choice models using Artificial Neural Networks (ANNs). In particular, we use continuous vector representations, called embeddings, for encoding categorical or discrete explanatory variables with a special focus on interpretability and model transparency. Although embedding representations within the logit framework have been conceptualized by Pereira (2019), their dimensions do not have an absolute definitive meaning, hence offering limited behavioral insights in this earlier work. The novelty of our work lies in enforcing interpretability to the embedding vectors by formally associating each of their dimensions to a choice alternative. Thus, our approach brings benefits much beyond a simple parsimonious representation improvement over dummy encoding, as it provides behaviorally meaningful outputs that can be used in travel demand analysis and policy decisions. Additionally, in contrast to previously suggested ANN-based Discrete Choice Models (DCMs) that either sacrifice interpretability for performance or are only partially interpretable, our main model (E-MNL) preserves interpretability of the utility coefficients for all the input variables despite being based on ANN principles. The proposed models are tested on two real world datasets and evaluated against benchmark and baseline models that use dummy-encoding. The results of the experiments indicate that our models deliver state-of-the-art predictive performance, outperforming existing ANN-based models while drastically reducing the number of required network parameters.

SELF-EDUCATION AND WAYS OF TEACHER COMPETENCE FORMATION

The main aim of the article is to explore the self-education and ways of teacher competence formation. In the context of rapid informational flow, a number of high requirements are imposed on school education in the era of scientific and technological progress.The school should not only equip the younger generation with scientific knowledge, but also instill in them the skills of independent acquisition of knowledge, free labor skills, intellectual work culture, independent thinking, self-education, better readiness for independent work. This is one of the important directions of modern education reform. Self-education is one of the very necessary rings in a united complex intellectual work. This type of activity, which includes elements of independent activity, was in the center of attention in all structures and stages of public life as a means of improving socio-political and vocational training and acquiring knowledge by a person, besides has always attracted people with progressive views and has been highly appreciated it basing on its" utility coefficient”. Very little attention was paid to the work on the organization and implementation of self-educational activities of specialists engaged in professional activities, it was not considered as a means corresponding to self-educational upbringing, personal development and self-control skills.It should be added that in pedagogy there is no complete concept on self-education and teacher competence.

Social determinants of health factors and palliative care services use among patients with metastatic breast cancer in Florida.

1102 Background: ASCO recommends palliative care (PC) as an adjunct to the oncologic standard of care for patients with metastatic cancer. However, current evidence on PC utilization in patients with breast cancer and its relationship with area-level social determinants of health (SDoH) factors is limited. Therefore, we examined the associations between county-level factors and PC utilization among patients with metastatic breast cancer (mBC) in Florida. Methods: We extracted patient-level data (n = 23,539 patients diagnosed with mBC between 2012 and 2021) from the OneFlorida+ Data Trust and linked it to county-level data (67 Florida counties) from the AHRQ-SDoH Database. PC utilization since cancer diagnosis was identified using ICD-9 code V66.7 or ICD-10 code Z51.5. We assessed differences in PC utilization with county-level SDoH factors (e.g., poverty rate, transportation resource, provider supply, racial segregation) using bivariate analysis. Multivariable Poisson regression, including significant factors from bivariate analysis, was used to compare the PC utilization for the SDoH factors. Results: Our study population's overall prevalence of PC utilization was 16.1%. PC utilization was higher for patients with mBC residing in counties with a higher proportion of residents living in poverty and with a greater supply of advanced practice providers (APP: NP, PA), general surgeons, and nursing homes. Patients with mBC in counties with higher proportions of residents who identified as immigrants, with limited English proficiency, without personal transportation, and having higher racial segregation had lower PC utilization. In adjusted analysis, the supply of APP (coefficient:0.12) and nursing homes (coefficient:0.09) was associated with increased PC utilization. Conversely, racial segregation (White vs. non-White) was associated with decreased PC utilization (coefficient: -0.07). Conclusions: PC utilization among patients with mBC was associated with several SDoH at the county level. Notably, low PC utilization was associated with racial residential segregation and fewer APPs and nursing homes. Further research is needed to identify mediators in these relationships to improve PC effectiveness for patients with mBC in Florida.

POTENTIALS OF FRANJO TUDMAN AIRPORT IN THE DEVELOPMENT OF INTERMODAL TRANSPORT

In the territory of the Republic of Croatia, not a single airport is connected to the railway infrastructure, which is a limiting factor for the further development of air cargo transport. The traffic network within the catchment area of Franjo Tudman Airport in Zagreb is not sufficiently interconnected, and therefore the implementation of the rules of the single market within the transport sectors is uneven. This paper aims to investigate the factors of intermodality of air transport and other modes of transport, focusing on cases of infrastructure integration in order to improve transport connectivity. The research analysed several airports where increase in cargo traffic was influenced by the expanding capacities and connectivity at the airport. By calculating the coefficient of utilisation of the intermodal surfaces of the reference airports, it was determined that the increase of these capacities does not necessarily lead to a significant increase in air cargo transport. However, due to estimates of the global growth of air cargo transport, an adequate and modernised infrastructure gives an advantage of better positioning in the transport market compared to those airports that do not have such resources. Based on the obtained results and increased investment to improve rail speeds and intermodal accessibility, the modular approach of expanding the infrastructure, through monitoring of cargo transport utilisation coefficient, is considered sustainable.

A novel continuously variable-speed offshore wind turbine with magnetorheological transmission for optimal power extraction

ABSTRACT The paper introduces a novel magnetorheological transmission (MT) type offshore wind turbine (OWT), which integrates the MT into the traditional-geared train to construct a controllable power split type continuously variable gear train for the OWT. The design and construction of the MT-OWT are proposed. The continuous regulation of the transmission speed of the drive train is achieved by controlling the current of the MT. Then, a generalized utilization coefficient of wind power is defined to describe the overall efficiency of the OWT. A cooperative control strategy is proposed to track the optimal power points and capture the optimal wind kinetic energy with the best energy transmission efficiency by adjusting the electromagnetic torque and the MT of the OWT. The feasibility of the MT-OWT is verified through simulations. The results indicate that the maximum loads in the proposed MT-OWT can be reduced to be around 70% of the GT-OWT when adequate control is applied. Also, the generalized utilization coefficient of wind power can be well maintained around the rated value of around 0.45 and the generator speed can be well maintained around the rated value of around 1000 rpm (105 rad/s) regardless of the variations of the wind speeds and the turbine rotor speeds when using the proposed MT-OWT as compared with conventional OWT.

A Magnus Wind Turbine Mathematical Model

Wind power units using the Magnus effect are an alternative to conventional blade units in regions having a too low or a high wind potential. A feature of their design is the use of rotating cylinders for producing torque on the wind wheel shaft. The aim of the study was to develop a mathematical model of such unit. Three models of the wind energy utilization coefficient were considered: analytical, regression and correlation. The models were subjected to an analysis, based on which conclusions about their applicability limits were drawn, and their main advantages and disadvantages were highlighted. An alternative simulation aerodynamic model was synthesized using the computational aerodynamics method. The developed model was verified by comparing the unit power output estimated by the simulation model with experimental data obtained on a real unit in the course of field tests. The study results have shown that the developed model based on computational aerodynamics features high accuracy and can be used to simulate a wind power unit based on the Magnus effect under variable wind conditions. In the future, the presented model can be used in the development of algorithms for detecting the maximum power point for this type of wind power units.

Shear capacity estimation of core steel tube reinforced PCCC column-beam interior joint under quasi-static load

In this study, the quasi-static tests were conducted on 13 core steel tube (CST) reinforced PVC-CFRP confined concrete (PCCC) column-beam interior joints. Distinct shear failure occurred in all joint specimens. The load-displacement hysteresis curves appeared pinching phenomenon, and the shape of hysteresis loops gradually deformed from shuttle to arch and finally changed to reverse S shape. The overall shape of hysteresis curves were relatively full, demonstrating that the joints had favorable seismic performances and energy dissipation capacity. The strain development law of materials in the joint area in the process of stress was clarified. The increment of joint stirrup ratio ([Formula: see text]), axial compression ratio ([Formula: see text]), column reinforcement ratio ([Formula: see text]) or beam reinforcement ratio ([Formula: see text]) improved the calculated shear capacity of the joints. The calculated shear capacity increased first and then decreased slightly as the diameter-thickness ratio of CST ([Formula: see text]) increased. In comparison, spacing of CFRP strip had little impact on the calculated shear capacity. Additionally, the concrete strength enhancement coefficient ([Formula: see text]) and joint stirrup utilization coefficient ([Formula: see text]) were introduced respectively to modify the shear capacity of concrete and joint stirrups, and a simplified formula for predicting the shear capacity of CST reinforced PCCC column-beam interior joints under quasi-static load was proposed. The predicted results agreed well with the test data.

Aerodynamic design of wind turbine blade with second derivative of thickness distribution as constraint

In order to make more use of wind energy, large-scale wind turbine blade size is the trend of development. With the increasing of blade length, the design and manufacture of the structure with the requirements of safety and economy are faced with great challenges. It is most sensitive to the blade manufacturer to reduce the composite lamination and production cost as long as the stress and strain level of the structure is satisfied. Therefore, the ideal thickness distribution requires not only the thickness monotonically decrease along the radial direction, but also the concavity and convexity of the thickness distribution function are required to be constant. Based on the in-house design code SurroOpt and the momentum-blade theory method, an optimization design platform for wind turbine blades was established. A 400kW wind turbine blade design was carried out with the aim of maximizing the output power and the constraint of the second derivative of the thickness distribution. The results show that the concave-convex characteristic of thickness distribution function has not changed, which is beneficial to the structural design. The designed blades have been manufactured and installed for operation. For the whole device, the maximum coefficient of wind energy utilization (including the loss of motor and machinery) reaches 0.42, which is 2.4% higher than 0.41 of the same kind of products.

Distribution Characteristics of Wind Speed Relative Volatility and Its Influence on Output Power

The stochastic fluctuations of wind speed and wind power curve modeling are complex tasks due to fluctuations in the difference between actual and theoretical power output, leading to a reduction in the accuracy of wind-power curve models. To address this issue, this paper proposes a normal distribution-modeling method based on relative volatility, which extracts the wind-speed variation patterns from the onsite SCADA (Supervisory Control And Data Acquisition) data, analyzes the correlation between wind-speed relative volatility and power relative volatility, and establishes a wind-power volatility-curve model to provide a basis for evaluating the efficiency of wind turbines. First, the definitions of relative volatility and probability vectors are provided, and a probability vector volatility-assessment function is designed to calculate the volatility-assessment index of the probability vector. Then, the relative volatility and probability vectors of wind speed are modeled, and features extracted from the onsite SCADA data, and characteristic parameters such as mean, standard deviation, and confidence interval of wind-speed relative volatility are statistically analyzed, as well as the wide-window coefficient, volatility-assessment index, attribute features (volatility center and volatility boundary), normal distribution features (mean and standard deviation) of the probability vectors of wind-speed relative volatility with different periods. The visualization descriptions of six typical probability vector distributions show that there is a correlation between the volatility assessment index of the probability vector based on relative volatility and the standard deviation of its distribution. Finally, the correlation between wind-speed relative volatility and power relative volatility is analyzed: in the maximum wind-energy tracking area, the derivative of power is linearly related to the derivative of wind speed, while in the constant power area, the derivative of the wind-energy utilization coefficient is linearly related to the derivative of wind speed. The conclusions obtained in this paper will provide a method reference for data processing to mine the parameter variation patterns and interrelationships of wind farm SCADA data and provide a basis for evaluating the power generation efficiency of wind turbines.

Assembly-level analysis on temperature coefficient of reactivity in a graphite-moderated fuel salt reactor fueled with low-enriched uranium

To provide a reliable and comprehensive data reference for core geometry design of graphite-moderated and low-enriched uranium fueled molten salt reactors, the influences of geometric parameters on the temperature coefficient of reactivity (TCR) at an assembly level were characterized. A four-factor formula was introduced to explain how different reactivity coefficients behave in terms of the fuel salt volume fraction and assembly size. The results show that the fuel salt temperature coefficient (FSTC) is always negative owing to a more negative fuel salt density coefficient in the over-moderated region or a more negative Doppler coefficient in the under-moderated region. Depending on the fuel salt channel spacing, the graphite moderator temperature coefficient (MTC) can be negative or positive. Furthermore, an assembly with a smaller fuel salt channel spacing is more likely to exhibit a negative MTC. As the fuel salt volume fraction increases, the negative FSTC first weakens and then increases, owing to the fuel salt density effect gradually weakening from negative to positive feedback and then decreasing. Meanwhile, the MTC weakens as the thermal utilization coefficient caused by the graphite temperature effect deteriorates. Thus, the negative TCR first weakens and then strengthens, mainly because of the change in the fuel salt density coefficient. As the assembly size increases, the magnitude of the FSTC decreases monotonously owing to a monotonously weakened fuel salt Doppler coefficient, whereas the MTC changes from gradually weakened negative feedback to gradually enhanced positive feedback. Then, the negative TCR weakens. Therefore, to achieve a proper negative TCR, particularly a negative MTC, an assembly with a smaller fuel salt channel spacing in the under-moderated region is strongly recommended.

Spatial-temporal distribution and accumulation characteristics of residual plastic film in cotton fields in arid oasis area and the effects on soil salt transport and crop growth

Plastic film residue pollutes farmland ecosystems and the natural environment though the plastic film employed in drip irrigation increases the utilization coefficient of irrigation water efficiency. Extensive studies have been conducted on soil pollution arising from residual films in northwest China, whereas the limits of the positive effect of plastic films on crop growth and the negative effect of residual plastic films remains unclear. To investigate the effects of residual films on soil salt transport and crop growth, the soil was collected from cotton fields under long-term film mulching and drip irrigation in arid oasis areas in this study to determine the distribution and accumulation of residual plastic films in the soil layers of an agricultural ecosystem. A plot experiment with eight residual film densities was performed in a cotton field at the experimental station, given the correlation between the film mulching year and residual film density. The effects of the residual film on soil salt migration and crop growth were elucidated through the observation of soil and cotton growth indicators, biomass, and yield. As indicated by the results, the density of residual mulching film in cotton fields under continuous mulching for five years exceeded the limit value of the determination standard (75 kg/ha). With the increase of the film mulching years, the residual film accumulated at a rate of 15.0 kg/ha annually, and it tended to migrate to the deep soil each year. The amount of the residual film of size < 4 cm2 was risen markedly, resulting in a problem of increasing fragmentation. Notably, the amount of the residual film was positively correlated with the variability in soil salinity. The growth index, biomass, and yield tended to be decreased with the increase of the mulching years. The yield reduction rate attributed to the residual film exceeded the yield increase arising from film mulching at the residual film density of 1210 kg·ha−1. This study takes on a critical significance to increasing the recycling efficiency of the residual films and ensure sustainable agricultural development in an oasis.

A new laser welding method of two transparent plastic parts based on reflector assisted method

It is a challenging work to joint two transparent plastic parts using traditional laser welding because the absorptivity of transparent plastic on short wavelength (800–1000 nm) laser energy is very low. During the laser welding of two transparent plastic parts, although laser absorber and long wavelength (1600–2000 nm) laser can obtain the high-strength weld joint, the problems of unattractive weld joint or pollution will occur when laser absorber is used, and the laser energy utilization coefficient is about 70% when long wavelength laser energy is used. To address this issue, this paper proposes a new production method for the absorber-free laser welding of two transparent plastic parts based on reflector assisted method. From three-dimensional thermal model, it can be found that the simulation data of the modified Gauss cylindrical body heat source show better agreement with the experimental result than those of Gauss surface heat source and Rotary-Gauss body heat source. In addition, for the same the weld joint width on the contact surface, the reflector assisted laser welding method can decrease the laser energy consumption by about 20%. Moreover, the maximum shear force of weld joint can be up to 1315 N. Under the same process parameters, the reflector assisted method can increase the shear strength of weld joint by 15.3%. Hence, the reflector assisted method has good application and promotion value in laser welding two transparent plastic parts.

Research on Water Resources Development and Utilization Based on Linear Regression and Multiple Nonlinear Regression

With the further development of industrialization and urbanization, China's water resources will be more severe. In order to study the synergy of the three red line targets, we predicted the total water consumption in 2030 by establishing the total water consumption model and using the linear regression prediction method. It is assumed that the water consumption of 10,000 yuan of industrial added value and the effective utilization coefficient of agricultural irrigation water all reached the red line value in 2030. Next, a multivariate nonlinear regression model of total water consumption is established, and the indirect substitution method is used to obtain the function of the internal relationship among the water consumption of 10,000 yuan GDP, the actual water consumption per mu of cultivated land for irrigation, and the water consumption of 10,000 yuan industrial added value, which includes time variables, and then the sensitivity analysis of the above functions are carried out. The following conclusions are drawn: China's overall water resources development and utilization should adopt the policy of improving the effective utilization coefficient of farmland irrigation water and reducing the industrial added value water consumption of 10,000 yuan as a supplement.

Effect of Air Inlet Spacing on Air Distribution and Ventilation Performance of Stratum Ventilation Using Multiple Parallel Jets

An appropriate layout of air terminals can improve the thermal comfort and air quality for room occupants. Stratum ventilation (SV) can efficiently provide thermal comfort and quality of inhaled air. However, investigations into the impact of the supply air inlet spacing on performance under SV are lacking. This study conducted experimental measurements and numerical simulations to analyze the effect of the supply inlet spacing on the air distribution and ventilation performance of the SV. Six theoretical axial velocity attenuation formulas were verified using experimental results. The effective draft temperature for SV (EDTS), air diffusion performance index (ADPI), the local mean age of air (LMAA), and energy utilization coefficient (EUC) were used as the evaluation indexes. The results indicated that the modified Abramovich formula was the most suitable for predicting the attenuation of the axial velocity of multiple parallel jets under SV. At an air supply spacing of 650 mm, the position near the central air supply inlet experienced a cold thermal environment with high air velocity and low air temperature; the positions on both sides of the room were warmer owing to insufficient airflow. The air distribution at these positions improved with increasing air inlet spacing, but some areas could not be covered by the supply airflow. The optimal value of ADPI corresponded to an air inlet spacing of 800 mm, whereas optimal LMAA and EUC corresponded to a spacing of 950 mm. Analysis of a multi-objective optimization method indicated that an air inlet spacing of 800 mm provided optimal overall performance.

Evaluation of the influence of the row of tillage implements on their work indicators

The purpose of the presented study is a quantitative assessment of the influence of the rows of tillage implements, using the example of steam cultivators, on their technological, operational and economic characteristics. An analysis of the data from the test reports of these implements showed that the most common three-row cultivators provided slightly worse performance than two- and four-row ones. At the same time, it was found that there is a direct relationship between the row and working width of cultivators. Two-row and four-row cultivators provided approximately equal quality of work in terms of such indicators as deviation from the specified cultivation depth (1.1-1.2 cm); degree of crumbling (91.7-92.2 %) and ridges (2.3 cm) of the field surface. The shift time utilization coefficient for two- and three-row implements (0.73-0.74) is noticeably lower than that for four-row implements (0.82), which can be indirectly explained by the fact that such implements are indeed less clogged with vegetation. remains and soil in comparison with analogues, however, it is not clear why such an effect is not observed when comparing two- and three-row tools. The specific fuel consumption of MTA with cultivators of different rows is approximately the same - 4.0 ... 4.1 kg / ha, i.e. from the energy point of view, the advantages of the multi-row tool layout are not obvious, which does not fully correspond to the earlier hypothesis about the lower clogging of multi-row tools. The material consumption of two-row guns (and hypothetically, the cost) is almost 1.1 times less than that of three-row ones, and almost 1.3 times less than four-row ones. At the same time, the increase in material consumption significantly exceeds the increase in the increase in the coefficient of use of the shift time. In general, the study conducted (on the example of steam cultivators) did not allow us to identify obvious advantages in terms of agrotechnical and energy indicators of the tendency to increase the rows of tillage implements, with the obvious disadvantage of this approach from a technical and economic point of view.

Operation Optimization of Medium-Depth Ground Source Heat Pump (MD-GSHP) Systems Based on the Improved Particle Swarm Algorithm

In recent years, the medium-depth ground source heat pump (MD-GSHP) has become a promising and potential geothermal energy heating technology. This is due to the superior characteristics of buried pipes with a small diameter, the high energy efficiency of the heat pump, the insensitivity to the ground climate, and other conditions. Among currently available studies, both the variable operating conditions and the addition of thermal storage devices have rarely been considered. Despite this, the optimization methods applied to the medium-depth GSHP system are relatively simple. In this paper, an MD-GSHP system, including the thermal storage device with variable operating conditions, was fabricated. The operation strategies of the system were optimized by employing the improved particle swarm algorithm after applying the operating costs, the coefficient of performance of the system (COP) and the geothermal energy utilization coefficient to the objective functions, and the optimization results were compared and analyzed. The results show that the predictions of the optimized operating costs, the COP of the system, and the geothermal energy utilization coefficient were found to be CNY 279.27, 6.4420, and 0.8527, respectively. The effect of the COP on the optimization effect was opposite to that of operating costs, but analogous to that of the geothermal energy utilization coefficient.

Influence of inlet placement on the hydrodynamics of the dual-drain arc angle tank for fish growth

The aquaculture tank is an infrastructure for aquaculture, and the choice of its geometry, structural design of the inlet and outlet pipes and the placement position and other parameters are crucial to the influence of the hydrodynamic performance of the tank. In this paper, a numerical computational model of the hydrodynamics of a dual-channel rectangular circular-angle culture tank is established using the RNG k-ε turbulence model based on the Reynolds-averaged N-S equation (RANS) averaged over time. The three-dimensional simulation of the internal flow field of the breeding tank under the hydraulic drive mode of the dual inlet pipe structure was verified by comparing with the experimental results of the physical model, and the accuracy of the numerical model in simulating the flow characteristics in the rectangular circular-angle breeding tank was demonstrated. The model was further applied to study the effect of the relative inflow distance on the hydrodynamic characteristics inside the culture tank, and the energy effective utilization coefficient was proposed to measure the effective utilization of energy inside the culture tank system.The present study has shown that the relative inflow distance was an important parameter in the construction of the system flow field, the average velocity of aquaculture system (a = 0.05, P < 0.0001), the velocity distribution uniformity at the bottom of the tank as well as the kinetic energy gradient of flow field sublayer are significantly affected by which adjusting the relative inflow distance. The ratio parameter C/B in the range of 0.02–0.04 could effectively improve flow field characteristics of the system so as to get better hydrodynamic conditions for circulating aquaculture.

Design and Numerical Simulation of the Headworks in the Shizuishan Section of the Yellow River

Irrigation water for agriculture in Ningxia during the summer is primarily sourced from the Yellow River self-flow irrigation region. However, the water conveyance system in this region is significantly influenced by hydrodynamic factors, morphological factors, human factors, and the infrastructure used for social purposes, all of which directly impact the irrigation water utilization coefficient. In order to improve the irrigation water utilization coefficient, reduce suspended sediment deposition in the water conveyance channels, and mitigate negative effects on the water supply system, this study implemented a sediment diversion system at the channel head. This is expected to increase water usage efficiency to a certain degree. Using actual data on hydrodynamic factors from the Shizuishan section of the Yellow River in Ningxia, a two-dimensional numerical simulation was performed, and a two-dimensional hydrodynamic model and sediment model of the Shizuishan section of the Yellow River in Ningxia were developed using MIKE 21. The water conveyance method at the channel head was simulated under two different operating conditions. Results indicated that compared to operating condition 1, operating condition 2 had a beneficial effect on diverting and reducing sediment at the fish mouth of the channel head: the sediment accumulation thickness of one day in operating condition 1 was 0.16 m, 0.003 m, 0.15 m, and 0.21 m under actual flow, scenario 1, scenario 2, and scenario 3, respectively; whereas in operating condition 2, the sediment accumulation thickness of one day was 0.11 m, 0.001 m, 0.09 m, and 0.12 m under the same conditions, respectively. Additionally, as the computation period lengthened, the sediment accumulation thickness of operating condition 2 was significantly smaller than that of operating condition 1. In conclusion, operating condition 2 is superior for the design of the channel head in the Yellow River self-flow irrigation region.

Error analysis and realization of a phase-modulated diffraction grating used as a displacement sensor.

A grating-based interferometric cavity produces coherent diffraction light field in a compact size, serving as a promising candidate for displacement measurement by taking advantage of both high integration and high accuracy. Phase-modulated diffraction gratings (PMDGs) make use of a combination of diffractive optical elements, allowing for the diminishment of zeroth-order reflected beams and thus improving the energy utilization coefficient and sensitivity of grating-based displacement measurements. However, conventional PMDGs with submicron-scale features usually require demanding micromachining processes, posing a significant challenge to manufacturability. Involving a four-region PMDG, this paper establishes a hybrid error model including etching error and coating error, thus providing a quantitative analysis of the relation between the errors and optical responses. The hybrid error model and the designated process-tolerant grating are experimentally verified by micromachining and grating-based displacement measurements using an 850 nm laser, confirming the validity and effectiveness. It is found the PMDG achieves an energy utilization coefficient (the ratio of the peak-to-peak value of the ±1st order beams to the 0th-order beam) improvement of nearly 500% and a four-fold reduction in 0th-order beam intensity compared with the traditional amplitude grating. More importantly, this PMDG maintains very tolerant process requirements, and the etching error and coating error can be up to 0.5 µm and 0.6 µm, respectively. This offers attractive alternatives to the fabrication of PMDGs and grating-based devices with wide process compatibility. This work first systematically investigates the influence of fabrication errors and identifies the interplay between the errors and the optical response for PMDGs. The hybrid error model allows further avenues for the fabrication of diffraction elements with practical limitations of micromachining fabrication.

Comparative study of novel backfill coupled heat exchangers using different waste materials in underground stopes

Underground mines in China are rich in geothermal resources. Based on backfill mining technology, the collaborative development of deep mineral resources and geothermal resources can be realized. The key of this approach is to form artificial thermal reservoirs by heat storage backfill body and to extract geothermal energy as much as possible through the built-in pipe. It is important to investigate the backfill material and system parameter design to improve the heat storage and release performance of backfill body and enhance the extraction efficiency of geothermal energy in mine. In this paper, experimental and simulation studies of backfill coupled heat exchanger system with different backfill materials are carried out to make a comparative study. The backfill materials involved include traditional backfill material, natural flake graphite backfill material and paraffin RT28 backfill material. After comparing the heat storage and heat release behavior, liquid fraction variation and efficiency of different systems, the natural flake graphite backfill body which has better engineering value is selected to further conduct experiments to study the influence of surrounding rock temperature, initial temperature of backfill body and inlet water temperature on the thermal performance of the system. The results show that with the increase of surrounding rock temperature, initial temperature of backfill body, or the decrease of inlet water temperature, the total heat storage, heat release and energy utilization coefficient of the system all increase. When the initial temperature of backfill is 26 °C, surrounding rock temperature is 45 °C, inlet velocity and temperature are respectively 0.7 m/s and 18 °C, the energy utilization coefficient of the system is the highest, which is 81.4%. The research results are helpful to the design of heat storage backfill body and the improvement of thermal performance of the system.