Channel Expansion Research Articles

Investigating the acceptance and use of massive open online courses (MOOCs) for health informatics education

BackgroundThis study investigated the acceptance and use of massive open online courses (MOOCs) among health informatics educators and students in Saudi Arabian academic institutions. A theoretical model based on the unified theory of acceptance and use of technology (UTAUT), self-determination theory (SDT), and channel expansion theory (CET) was used to identify factors that affect MOOC adoption in health informatics education.MethodsA survey research design was employed, and cross-sectional data were collected from health informatics instructors and students in academic institutions in Saudi Arabia. A total of 145 completed responses were used in the final analysis of the data.ResultsThe findings indicated that performance and effort expectancy were important factors that could predict the acceptance and use of MOOCs among health informatics instructors and students. Additionally, perceived media richness affected the actual use of health informatics MOOCs among students and instructors in Saudi Arabian academic institutions. The results of this study show that autonomy, relatedness, and competence must be considered in the design of health informatics MOOCs.ConclusionsA combination of these models can effectively explain the adoption and use of MOOCs in emerging fields such as health informatics.

Analysis of Factors Affecting User Inclination to use Virtual Education Exhibitions in the Post Pandemic Covid-19 Era: Case Study in Indonesia

Social distancing policies during the COVID-19 period have opened a space for interventions in the use of digital technology that was previously rejected by the public. Currently, most of the community activities have been carried out online, including those related to education, such as hosting virtual exhibitions with an educational purpose. Virtual exhibitions (VE) are online exhibitions that display information on specific topics. However, to the best of our knowledge, research on VE in the educational context is still lacking. This study aims to identify the variables that affect users' intentions to attend the virtual exhibition frequently. The channel expansion theory, flow theory, technology acceptance model, and expectation confirmation theory serve as the foundation for the research model that is constructed. The model was tested using data from 321 respondents who had visited VE, then analyzed using Structural Equation Modeling (SEM) with the aid of the SmartPLS application version 3.3.3. The findings show that 11 factors significantly influence the intention to continue using VE, while the other 2 factors have no significant influence. Thus, perceived usefulness has a significant effect on satisfaction and continued use intention to use VE, but not on perceived enjoyment. Furthermore, the perceived ease of use of VE has a significant impact on perceived usefulness and perceived enjoyment. However, media richness does not significantly affect perceived enjoyment. It's just that media richness influences perceived ease of use significantly. Confirmation also has a significant impact on perceived enjoyment, perceived usefulness, and satisfaction. Perceived enjoyment has a significant effect on satisfaction and continued use intention, and satisfaction has a significant effect on continued use intention to use VE. The findings are useful for VE providers and developers in developing a transformation strategy to increase the intention to use VE in every educational exhibition.

Evolution of underwater shock wave in far-field regime of electrical wire explosion system over wide range of electric pulse energy

The parametric relationships between underwater shock waves (SWs) in far-field regime and electrically exploded wire under different charging voltages of a generator are investigated. Contributions of the vaporization and current restrike to the resulting SWs have been examined by means of electro-physical diagnostics, free-field pressure probe, and high-speed photography. In the experiment, a 6-μF pulse capacitor is adopted to provide a microsecond timescale pulsed current, exploding a 90/185-μm-diameter, 2-cm-long copper wire with the charging voltage ranging from 7.1 kV (stored energy ∼ 150 J) to 18.3 kV (∼1000 J). Experimental results indicate that as the increase of the charging voltage, the relationship between electro-physical and shock wave parameters shows a rather complex situation. When the charging voltage ranging from 7.1 kV (∼150 J) to 11.6 kV (∼400 J), the peak pressure of SWs (300 mm away from the explosion source) increases almost linearly from 1.16 ± 0.03 to 2.24 ± 0.05 MPa (90-μm wire), and 1.67 ± 0.17 to 2.87 ± 0.12 MPa (185-μm wire). Nevertheless, at a higher charging voltage between 11.6 kV (400 J) to 14.1 kV (600 J), the peak pressure stabilizes in a strange “plateau”. Until the residual energy after the explosion is sufficiently large (>600 J in this study) to induce a strong current restrike, the development of the plasma channel could further enhance the expansion of explosion products, as well as the intensity of measured SWs. In addition, high-speed photography has been applied for those explosions, providing the information of plasma channel expansion and initial SWs propagation.

Internationalization and digitalization: Their differing role on grocer and non-grocer retailer performance

This study investigates the interplay between two critical phenomena in retailing, i.e., internationalization and digitalization, while accounting for retail sector differences. On one hand, internationalization allows retailers to access a wider range of markets, and on the other, digital channel expansion enhances customer reach and convenience within international markets. More specifically, we examine the relationship between retailer internationalization and performance (I-P relationship), and how this relationship is contingent upon the idiosyncrasies of retail sectors (i.e., grocery vs. non-grocery), digitalization, and their combined effects. Building on the liability of foreignness perspective, we first argue that the I-P relationship is U-shaped, because internationalizing retailers initially incur greater costs in their international expansion owing to their unfamiliarity with foreign markets, but as their foreign presence increases, they benefit from greater market power, experience, and scale economies. Then, we contend that as grocers suffer from higher levels of liability of foreignness due to increased requirements for host country embeddedness, non-grocers benefit more from internationalization with any gains and losses further amplified by digitalization. Hypotheses are tested against a panel of the 234 largest international retailers in the world over a 21-year period (1997–2017) and findings support the conjectures.

Chirality-Assisted Phase Metasurface for Circular Polarization Preservation and Independent Hologram Imaging in Microwave Region

A chirality-assisted phase is introduced to innovatively impose separate phase profiles in two circular polarization (CP) preserving channels, namely, two co-polarized output components under left-handed and right-handed circularly polarized (LHCP and RHCP) illuminations. Such a scheme is physically implemented by a proposed multi-layered meta-atom that achieves chiral characteristics by inner twisting angles between adjacent functional elements. A proof-of-concept metasurface is constructed to realize separate holographic images in two polarization-preserved fields with different propagating distances, respectively. In order to achieve sufficient utilization of the two polarization-preserved components, a further approach that can suppress polarization conversion is proposed with a polyatomic unit composed of four separate chiral meta-atoms arranged in a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 2 array. A dual-holographic metasurface is designed to impose characters “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$</tex-math> </inline-formula> ” and “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> ” in two co-polarized fields with little energy distributed in corresponding cross-polarized fields. A prototype of the metasurface is fabricated and experimentally measured. The measurements agree well with theoretical predictions and full-wave simulations, showing in the co-polarized field a character “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$</tex-math> </inline-formula> ” under LHCP incidence and an “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> ” under LHCP incidence. The proposed mechanism provides a theoretical foundation for further CP channel expansion and modulations and has great potential in multifunctional antenna design and wireless communications.

Investigation of the flow and heat transfer performance of supercritical pressure hydrocarbon fuel in a novel rotating internal trapezoidal expansion channel

Hydrocarbon fuel is required to cool the rotating turbine blades in order to enable the hypersonic vehicle electricity supply turbine to withstand the impact of hot air. A novel internal trapezoidal expansion type hydrocarbon fuel rotating cooling channel is proposed for heat transfer enhancement of turbine blades. Numerical results show that among the expansion channels studied, the maximum value of thermal performance is obtained for the expansion angle 2° channel. The thermal performance of the channel corresponding to the expansion angle of 2° is maximally increased by 591.4% compared to the 0° channel. The factor of friction of the channel corresponding to the expansion angle of 2° is lowered maximally by 99.7% compared to the 0° channel. The channel thermal performance of the entrance temperature before the temperature of the critical state is improved by a maximum of 911.3% compared to the channel thermal performance of the entrance temperature after the temperature of the critical state. The internal trapezoidal expansion channels overcome the negative effect of the second channel velocity decrease caused by the increase in physical property of the fuel due to centrifugal force, and significantly enhance the second channel heat exchange capacity.

Study on mixing characteristics of multichamber static mixer

AbstractThis study presents a specialized mixer design for gas burners aimed at improving the efficiency of phase mixing while minimizing system resistance and energy consumption. The proposed design utilizes a multi‐cavity mixer employing both radial and axial mixing techniques, eliminating the need for additional power supply. Full premixed combustion of small gas‐fired industrial boiler has the function of “inhibiting” NOx emission from the source, and good mixing of fuel and combustion supporting air in the early stage is the primary prerequisite for realizing full premixed combustion denitration. In this article, a radial multichamber static mixer is designed following the characteristics of full premixed mixing in gas‐fired industrial boilers. The results demonstrate that the maximum pressure drop of the static mixer is 806 Pa; for gas and air branch pipes, the resistance coefficient f decreases rapidly with the increase in Reynolds number; when Re ≥ 1.2 × 103, the resistance coefficient in the air branch pipe decreases slowly; when Re ≥ 4.5 × 103, the resistance coefficient of gas branch pipe decreases slowly. Additionally, the maximum calculation error of symmetrical gas branch pipe is 9.1%. The static mixer's inlet exhibits a converted velocity of 24 m/s, and the outlet demonstrates an airflow velocity of 23.2 m/s. As a result, a kinetic energy loss of 6.5% is observed. The static mixing chamber makes the airflow rotate and causes different gases to shear and mix. The mixing channel has the function of correcting the airflow deviation, especially for the sudden expansion section. Generally, the two gases can be mixed evenly at the outlet of the mixer. The standard k‐e model and realizable k‐e model are employed to simulate the sudden expansion channel, and indicate that the standard k‐e has a wider range of influence. Further investigation is recommended to better comprehend and optimize this particular area of influence.

Research on the service quality of emergency medical language services during major unexpected public health events.

Emergency Medical Language Services (EMLS) have played a crucial role in the COVID-19 pandemic. Research on the quality and its influencing factors of EMLS is necessary. This study used the SERvice QUALity (SERVQUAL) model to determine factors affecting the quality of EMLS during the pandemic. An online questionnaire was completed by 206 participants who received the service in 2021-2022. Structural Equation Modeling (SEM) indicated that the service provider and service process significantly influenced the Service Results. In the service process, the evaluation of service content and responsiveness were highly correlated, and both factors significantly affected user satisfaction. In the service provider, tangibility and reliability were highly correlated. The key factors for user willingness to recommend the service were service content and tangibility. Based on the results of the data analysis, it can be inferred that EMLS should be improved and upgraded in terms of service organization, talent cultivation, and service channel expansion. To enhance service organization, an emergency medical language team should establish a close collaboration with local medical institutions and government departments, and an EMLS center should be established with the support of hospitals, government, or civil organizations.

Numerical simulation of the breakdown process of dielectric in high voltage pulse discharge

In order to study the breakdown process of the insulating medium of the needle-needle electrode under the action of high-voltage pulse discharge, the HV-LAB simulation software was used to study the discharge channel formed in the three kinds of insulating media, namely water, transformer oil, and air, and the three-dimensional model of the discharge breakdown insulating medium was designed. The process of discharge channel expansion, voltage, current, power, and energy loss in the discharge channel is analyzed. The results show that in the process of high-voltage pulse discharge breakdown of the insulating medium, the formation time of the discharge channel of transformer oil is long, the energy is accumulated, the number of discharge channels is less, the horizontal isopotential lines are dense, and the energy is concentrated. Under the same discharge conditions, the energy consumption of transformer oil in the process of high-voltage pulse discharge is the least. The results of this study can provide a reference for the selection of high-voltage crushing insulation medium.

Inherent Complexity and Early Warning of Zaozhuang Circular Economy System

Based on China’s green energy development strategy, this paper constructs a basic model of recycling and a channel expansion model for the circular economy foundation of Zaozhuang, Shandong Province, China. Through numerical simulation, it is found that each member of the supply chain should control the rate of price adjustment, otherwise it will cause market disruption. The model is controlled based on a chaos control method. Then, based on the fuzzy comprehensive evaluation method, an early warning system for the circular economy of Zaozhuang City is constructed. It is found that the economic development of Zaozhuang is a serious warning, resources are moderate warning, and the environment is not in an alarm state. In addition to paying attention to energy conservation and emission reduction of enterprises, the government should pay attention to creating awareness of energy conservation and emission reduction in society, and strengthen the technological investment in reducing pollutant emissions. This paper provides a strategic reference for the circular economy model in Zaozhuang, Shandong, China.

On the Performance of Sentinel-3 Altimetry over High Mountain and Cascade Reservoirs Basins: Case of the Lancang and Nu River Basins

Satellite radar altimetry has been widely utilized in hydrological research, particularly with the advent of Sentinel-3, a Synthetic Aperture Radar (SAR) altimeter operating globally and equipped with an innovative onboard tracking system referred to as the open-loop tracking command (OLTC). Utilizing a pseudo-DEM (Digital Elevation Model), controlled through the OLTC, holds significant promise for the reliable observation of inland water bodies. Nevertheless, the complex geographical conditions in high mountain and reservoir river basins pose challenges in defining an appropriate pseudo-DEM for hydrological targets, potentially leading to reduced performance of Sentinel-3. This study aims to comprehensively evaluate the performance of Sentinel-3 by selecting the Lancang and Nu River basins in southwest China as a case study. These two rivers have a similar natural environment, but cascade reservoirs distinguish the Lancang River basin. By analyzing waveform energy from echoes of virtual stations (VSs) in both river basins (27 VSs in the Lancang River basin and 39 VSs in the Nu River basin), the performance of Sentinel-3 in different tracking modes and OLTC versions were compared. The results indicated that the detection rate of Sentinel-3A increased when transitioning from the closed-loop mode to the open-loop mode and with the implementation of newer OLTC versions (36.8% increased to 47.4%, 60.5%, and 63.2% in OLTC V5.0, V6.0, and V6.1, respectively). Similarly, the detection rate of Sentinel-3B rose from 64.3% (OLTC V2.0) to 71.4% and 75.0% in OLTC V3.0 and V3.1, respectively. Additionally, the cascade reservoir causing river channel expansion results in a better performance of Sentinel-3A in the Lancang River compared to the Nu River in the closed-loop mode (13.0% and 35.7%, respectively). Nevertheless, the considerable fluctuations in water surface caused by reservoir impoundment led to a wrong pseudo-DEM, resulting in poor performance of Sentinel-3 in reservoir regions before OLTC V6.0 was updated. The detection rate of low altitude, broad water surfaces (&gt;500 m) decreased from 100% in a closed-loop mode to 0% in an open-loop mode, but increased to 100% in OLTC V6.0 and V6.1, respectively. The detection rate of high altitude, narrow water surfaces (&lt;500 m) increased from 0% in a closed-loop mode to 40.9% in OLTC V6.1. Although the detection ability of Sentinel-3 is improving with the implementation of newer OLTC versions, the seasonal variations (usually more than 60 m) of water levels in reservoirs exceeded the size of the range window (60 m), rendering a complete measurement impossible.

Tax incentives and corporate internationalization performance: evidence from China’s accelerated depreciation policy

ABSTRACT Using data of China’s listed companies from 2010 to 2018, we investigate the effects of China’s accelerated depreciation (CACD) policy on corporate internationalization performance. The results show that CACD policy increases corporate incomes in foreign markets by 16.15% through the market expansion channel and the innovation incentive channel. The policy effect is more pronounced for firms with better corporate governance, more serious financial constraints, and weaker financial risks.

Stress wave analysis of high-voltage pulse discharge rock fragmentation based on plasma channel impedance model

High-voltage pulse discharge (HVPD) rock fragmentation controls a plasma channel forming inside the rock by adjusting the electrical parameters, electrode type, etc. In this work, an HVPD rock fragmentation test platform was built and the test waveforms were measured. Considering the effects of temperature, channel expansion and electromagnetic radiation, the impedance model of the plasma channel in the rock was established. The parameters and initial values of the model were determined by an iterative computational process. The model calculation results can reasonably characterize the development of the plasma channel in the rock and estimate the shock wave characteristics. Based on the plasma channel impedance model, the temporal and spatial distribution characteristics of the radial stress and tangential stress in the rock were calculated, and the rock fragmentation effect of the HVPD was analyzed.

A sparse convolution neural network accelerator with bandwidth-efficient data loopback structure

Convolutional neural network has become one of the mainstream algorithms of deep learning with high computational resource consumption. The model inferencing delay and power consumption can be effectively reduced by the sparsity-aware accelerator with low resource overhead and almost lossless accuracy. However, the computation fragmentation problem caused by sparse operations will greatly reduce convolution operation efficiency. In order to alleviate the above problems, an input channel expansion method is proposed to improve the resource utilization rate in this paper. Considering that bandwidth often becomes the bottleneck of accelerator performance, a bandwidth-efficient data loopback structure is designed to reduce data transmission between accelerator and off-chip memory. The proposed hardware architecture is implemented on Xilinx VC709. It contains up to 1024 multiplication and accumulation units, providing 409.6 GOP/s peak computing power. Its computation speed reaches 315.8 GOP/s in VGG-16 model, which is equivalent to 788 GOP/s of accelerator without sparse activation optimization. 54.2% of activation data transmission is canceled through data loopback bus, which eases the dependence on off-chip bandwidth. This flexible sparsity-aware accelerator architecture can be widely applied to deep convolutional neural networks for large-scale inferencing.

A sheathless high precise particle separation chip integrated contraction–expansion channel and deterministic lateral displacement

Cell sorting plays an important role in medical and biological research. This study aimed to propose a novel approach combining a contraction–expansion array (CEA) channel and a deterministic lateral displacement (DLD) array to achieve high-throughput and high-precision particle separation of different sizes. The CEA channel could realize the focusing and preliminary sorting of particles with different sizes under the joint action of inertia force and Dean resistance. The separation purity and efficiency could be further improved by coupling triangular microcolumn DLD. The finite element simulation analysis was carried out using commercial software COMSOL Multiphysics 5.4. The flow field distribution and the particle movement trajectory under the CEA channel and DLD array were simulated, respectively. The simulation results showed that this structure could achieve high-throughput and high-precision particle separation of different sizes. Finally, the separation experiments showed that the separation efficiency of 5 µm polystyrene microspheres as the target particles was more than 99%, and the separation purity was 96.1% under a high flow velocity. The microfluidic chip had the advantages of low cost, simple preparation process, and label-free, sheathless characteristics, thus realizing high-efficiency, high-throughput particle separation of different sizes. In general, the proposed approach provided a new pathway for sheathless particle separation with high precision and high throughput.

Turbulence structure and bank erosion process in a dredged channel

AbstractRiverbank erosion has significant geomorphological as well as anthropogenic consequences. The geomorphological impacts include form changes such as lateral channel migration, meanders, channel expansion, etc. The anthropogenic effects include the threat to floodplain human habitation, agricultural land, and stability of instream hydraulic structures and buried pipelines. Channel dredging for the extraction of sand and gravel has seen a multi‐fold rise in the last few decades. Therefore, riverbank erosion response to channel mining gains importance in river basin management. Sandpits dredged in the riverbeds can significantly impact the downstream riverbank stability. In order to assess these impacts, we conducted a series of experiments at a laboratory scale in a recirculating water flume. Three riverbank slopes, 25° (gentle), 31° (equal to the angle of repose of the bank sediments), and 40° (steeper than the angle of repose), were tested along with a sandpit. Remarkable changes in the turbulence structure of riverbank flow were found due to the channel pit. Pit excavation directly impacts the fluvial erosion characteristics of the riverbank. Pit action increases the Reynolds shear stress fields in the near‐bank flow, which causes progressive fluvial erosion of the berm at the bank toe. The erosivity of the main channel flow in the riverbank also leads to channel degradation, which increases the exposed height of the bank slope. Pit dredging leads to the generation of stronger ejection bursts which provide a mechanism for berm sediment mobility and erosion. The hydro morphological response of the riverbank due to sand mining was analysed, and process understandings are presented in the paper.

A Sparsified Densely Connected Network with Separable Convolution for Finger-Vein Recognition

At present, ResNet and DenseNet have achieved significant performance gains in the field of finger-vein biometric recognition, which is partially attributed to the dominant design of cross-layer skip connection. In this manner, features from multiple layers can be effectively aggregated to provide sufficient discriminant representation. Nevertheless, an over-dense connection pattern may induce channel expansion of feature maps and excessive memory consumption. To address these issues, we proposed a low memory overhead and fairly lightweight network architecture for finger-vein recognition. The core components of the proposed network are a sequence of sparsified densely connected blocks with symmetric structure. In each block, a novel connection cropping strategy is adopted to balance the channel ratio of input/output feature maps. Beyond this, to facilitate smaller model volume and faster convergence, we substitute the standard convolutional kernels with separable convolutional kernels and introduce a robust loss metric that is defined on the geodesic distance of angular space. Our proposed sparsified densely connected network with separable convolution (hereinafter dubbed ‘SC-SDCN’) has been tested on two benchmark finger-vein datasets, including the Multimedia Lab of Chonbuk National University (MMCBNU)and Finger Vein of Universiti Sains Malaysia (FV-USM), and the advantages of our SC-SDCN can be evident from the experimental results. Specifically, an equal error rate (EER) of 0.01% and an accuracy of 99.98% are obtained on the MMCBNU dataset, and an EER of 0.45% and an accuracy of 99.74% are obtained on the FV-USM dataset.

Hydraulic gradient and wave height control the success of estuary artificial entrance openings

Intermittently Open/Closed Estuaries (IOCEs) are dynamic, sensitive estuaries that periodically close as a function of competing marine and fluvial energies. Once closed, IOCEs are often artificially opened to relieve localised flooding. Artificial openings are generally effective as a short-term flood mitigation strategy, however, sometimes IOCEs can close immediately after excavation without draining the lagoon. In this situation, the opening does not achieve its management purpose and reimplementation is required – costing many thousands of dollars at a time and leading to adverse impacts on estuary biota. Using a dataset of 137 openings at 37 IOCEs globally, we show that the hydraulic gradient (or grade) at opening and offshore significant wave height determine whether an estuary will remain open and drain its lagoon. The hydraulic gradient represents the energy slope between the estuary and the ocean, and wave height determines the capacity of waves to infill the channel with sediment to counter offshore erosion. Artificial openings are only successful when IOCEs are opened with a hydraulic gradient steeper than 0.017 m/m (equivalent to a grade of 1:60) and when significant wave height is below 4.30 m. These findings highlight that the estuary water level alone is not a good predictor of opening success, despite it being widely used to decide when to implement artificial openings. Using near-continuous monitoring of geomorphic change at 28 artificial openings, we show that the hydraulic gradient (and grade) at the time of opening controls the rate of channel expansion, outflow velocity at the mouth, lagoon drainage rate, and the time to reach peak channel width and outflow velocities. The tidal stage at opening can be used to either speed up or slow down the rates of change, potentially reducing the occurrence of fish kills associated with rapid drainage. Although the decision to open an estuary is a complex balance between environmental, cultural, socio-economic, and practical factors, we present a simple and cost-effective way to predict if artificial openings will be successful. The thresholds of our study can be used to complement existing decision support tools, but as a standalone method, are best suited for emergency openings where draining the lagoon to reduce flooding is the main management priority.

Cooling of Heated Blocks with Triangular Guide Protrusions Simulating Printed Circuit Boards

There is no study that investigates triangular guide protrusions including their systematical geometrical changes together with the effects of channel height in the open literature in the context of the authors’ knowledge. Moreover, the number of laminar studies is less than turbulent studies, whereas low velocity or natural convection cases are still important, especially for small devices in small PCB passages. The objective of this study is to investigate numerically the effects of triangular guide protrusions for the enhancement of heat transfer from the blocks’ simulated electronic components in laminar flow conditions. Two-dimensional, incompressible, steady, and laminar flow analysis was performed to predict fluid flow and heat transfer characteristics for three heated blocks in a PCB (printed circuit board) passage with triangular guide protrusions mounted on the upper wall. The Galerkin finite element method of weighted residuals was used to discretize conservation equations. The effects of the channel expansion ratio and inlet velocity were investigated for five geometrical cases. If the size of the protrusions is increased, the existence of protrusions starts to affect the flow patterns on the lower wall. The size of the last protrusion controls the flow structure downstream of the last block. On the upper wall, after the last protrusion, a recirculation is formed and the length of the recirculation increases with an increasing Re number. Moreover, the reattachment length of recirculation after the last block increases with an increasing Reynolds number for a fixed expansion ratio. Expansion ratio and inflow conditions caused by blocks and protrusions have a great influence on the formation of secondary recirculation in addition to the Reynolds number. Heat transfer increases with increasing sizes of upper triangular protrusions. Maximum overall heat transfer enhancement is provided as 47.7% with the geometry of the maximum sized protrusions for the channel height of 3 h. In the case of 4 h, the maximum overall heat transfer enhancement is 24.21%. These enhancements in heat transfer that can be encountered in PCB cooling applications may help the PCB cooling designers.

SAPO-containing alumina CoMoNi-catalysts for hydrotreatment of heavy oil: Pore hierarchy as a key parameter for catalyst stabilization

This paper is devoted to the study of activity and lifetime of CoMoNi-catalyst containing one-dimensional SAPOs in heavy oil hydrotreatment. A special attention is paid to porous structure of SAPOs and catalyst supports. Porosity of supports is designed by two hard templates. Pore structure containing narrow and wide mesopores and macropores is referred as high-resolved pore hierarchy. In turn, pore structure containing narrow mesopores and macropores is referred as bimodal pore hierarchy. Zeolite-like SAPOs also differ in their own pore hierarchy and acidity. Catalysts have been characterized with XRD, nitrogen adsorption-desorption, Hg-intrusion, Raman and XP spectroscopies and SEM. Catalytic tests for 100 h for each catalysts have been shown that support pore hierarchy should be designed depending on pore hierarchy and morphology of zeolite-like material. In general, high-resolved pore hierarchy improves mass transfer, makes CoMoNi sites accessible and creates gradual pore channel expansion and, as a result, prevents deactivation of zeolite-like containing catalysts.