Search results

The purpose of this paper is to investigate the effect of different soldering temperatures on the performance of chip-on-board (COB) light sources during vacuum reflow soldering.

First, the influence of the void ratio of the COB light source on the steady-state voltage, luminous flux, luminous efficiency and junction temperature has been explored at soldering temperatures of 250°C, 260°C, 270°C, 280°C and 290°C. The COB chip has also been tested for practical application and aging.

The results show that when the soldering temperature is 270°C, the void ratio of the soldering layer is only 5.1%, the junction temperature of the chip is only 76.52°C, and the luminous flux and luminous efficiency are the highest, and it has been observed that the luminous efficiency and average junction temperature of the chip are 107 lm/W and 72.3°C, respectively, which meets the requirements of street lights. After aging for 1,080 h, the light attenuation is 84.64% of the initial value, which indicates that it has higher reliability and longer life.

It can provide reference data for readers and people in this field and can be directly applied to practical engineering.

This study aims to study the mechanical, photoelectric, and thermal reliability of SAC307 solder joints with Ni-decorated MWCNTs for flip-chip light-emitting diode (LED) package component during aging. By adding nanoparticles (Ni-multi-walled carbon nanotubes [MWCNTs]) to the solder paste, the shear strength and fatigue resistance of the brazed joint can be improved. However, the aging properties of Ni-modified MWCNTs composite solder joints have not been deeply studied. In this research, the mechanical, photoelectric and thermal reliability of SAC307 packaged flip-chip LEDs with Ni-MWCNTs added during aging were studied.

Compared with SAC solder alloys, the effects of different contents (0, 0.05, 0.1 and 0.2 Wt.%) of Ni-MWCNTs on the photoelectric and thermal properties of composite solder joints were examined. To study the aging characteristics of composite solder joints, the solder joints were aged at 85°C/85% relative humidity.

The addition of an appropriate amount of reinforcing agent Ni-MWCNTs reduces the density of the composite solder to 96% of the theoretical value of the SAC solder alloy. In addition, the microhardness increases and the wetting angle decreases. Two different phase compositions were observed in the solder joints with Ni-MWCNTs reinforcement: Cu₃Sn and (Cu, Ni)₆Sn₅. The solder joints of SAC307-0.1Ni-MWCNTs exhibit the highest luminous flux and luminous efficiency of flip-chip LED filaments, the lowest steady-state voltage and junction temperature. And with the extension of the aging time, its aging stability is the best. In short, when the addition amount of Ni-MWCNTs is 0.1 Wt.%, the solder joints exhibit the best wettability and the thinnest intermetallic compound layer. And the shear strength of the tested solder joints is the best, and the void ratio is the lowest. At this time, the enhancement effect of Ni-MWCNTs on the composite solder has been best demonstrated.

The content range of enhancer Ni-MWCNTs needs to be further reduced.

The authors have improved the performance of Ni-modified MWCNTs composite solder joints.

Composite solder with high performance has great practical application significance for improving the reliability and life of the whole device.

Law enforcement is a dangerous profession not only due to assaults, accidents and homicides but also due to health risks. This study examined trends in the national frequency and rate of law enforcement job-related illness deaths in the United States over a 22-year period (1997–2018).

Data were obtained from the National Law Enforcement Officers Memorial Fund (NLEOMF) on death frequencies related to health issues at work. Death rates were based on the total number of police officers in the United States [rate = (frequency/population at risk) × 100,000]. Trends were examined using standardized regression.

A total of 646 deaths were attributed to job-related illness. There was a significant upward trend in overall job-related illness deaths (frequency analyses: β = 0.88, p < 0.0001; rate analyses: β = 0.82, p ≤ 0.0001) mainly driven by a significant increase in 911 cancer deaths (frequency analyses: β = 0.88, p < 0.0001; rate analyses: β = 0.88, p ≤ 0.0001). Nearly 82 percent of circulatory deaths were from a heart attack, with an average death age of 46.5 years.

Deaths were not included if they failed to meet medical requirements of the NLEOMF. The data are descriptive, do not estimate risk and should be interpreted cautiously.

Police wellness programs may help to reduce the danger of deaths associated with job-related illness.

This is among the first studies to examine frequency and rate of police health–related deaths due to job exposures.

Wine tourism is gaining increasing popularity among Chinese tourists, making it necessary to thoroughly examine tourist behavior. While online reviews posted by wine tourists have been extensively studied from the perspectives of destinations and wineries, the perspective of the tourists themselves has been overlooked. To address this gap, this study aims to identify significant attributes intrinsic to the tourism experiences of Chinese wine tourists by adopting a text-mining approach from a tourist-centric perspective.

The authors use topic modeling to extract these attributes, calculate topic intensity to understand tourists’ attention distribution across these attributes and conduct topical sentiment analysis to evaluate tourists’ satisfaction levels with each attribute. The authors perform importance-performance analyses (IPAs) using topic intensity and sentiment scores. Furthermore, the authors conduct semistructured in-depth interviews with Chinese wine tourists to gain insights into the underlying reasons behind the key findings.

The study identifies eleven attributes for domestic wine tourists and seven attributes for outbound wine tourists. From the reviews of both domestic and outbound tourists, three common attributes have been identified: “scenic view”, “wine tasting and purchase” and “wine knowledge”.

According to the results of the IPAs, there is a pressing need for enhancements in the wine tasting and purchasing experience at domestic wine attractions. Additionally, managers of domestic wine attractions should continue to prioritize the positive aspects of the family trip experience and scenic views. On the other hand, for outbound wine attractions, it is crucial for managers to maintain their efforts in providing opportunities for wine knowledge acquisition, ensuring scenic views and upholding the reputation of wine regions.

First, this study breaks new ground by adopting a tourist-centric perspective to extract significant attributes from real wine tourism reviews. Second, the authors conduct a comparative analysis between Chinese wine tourists who travel domestically and those who travel abroad. The third novel aspect of this study is the application of IPA based on textual review data in the context of wine tourism. Fourth, by integrating topic modeling with qualitative interviews, the authors use a mixed-method approach to gain deeper insights into the experiences of Chinese wine tourists.

The study aims to provide a critical review of the origin, development and process of sentiment analysis (SA) and a demonstration for hospitality researchers and students on how to perform SA using a sample study.

A critical review and sample case demonstration approach was applied. The sample study used Leximancer to perform SA using TripAdvisor review data.

A critical evaluation of the most popular SA tools was provided, highlighting their advantages and disadvantages. A step-by-step demonstration with data provided makes it possible for readers to learn this technique at own pace.

By providing a critical review of SA supported with a demonstration case study, this study makes a timely contribution for broader awareness and understanding, as well as the application of SA in hospitality.

The authors investigated the impacts of differentiated transformational leadership (TFL), including team-focused TFL and individual-focused TFL, on team creativity through the mediating effect of team conflict, consisting of task conflict and relationship conflict.

The authors designed and conducted a close-to-reality experiment, enrolling 180 students and six professors from a large Chinese university. Student participants worked on a real marketing project and professor participants imitated the behaviors of transformational leaders. Using the computed values of team-focused TFL, individual-focused TFL, team creativity, task conflict and relationship conflict, the authors assessed the relationship among differentiated TFL, team creativity and team conflict.

Team-focused TFL has a significantly positive impact on team creativity through the mediating effect of task conflict, whereas individual-focused TFL has a significantly negative impact on team creativity through the mediating effect of relationship conflict.

From a new perspective of team conflict, the authors revealed the “black box” of the differentiated TFL–team creativity relationship. Moreover, other determinants were well controlled in the experiment, and thus, the authors effectively clarified the intervening mechanism of differentiated TFL on team creativity through the mediating effect of team conflict.

The purpose of this study was to investigate the impact of artificial intelligence (AI) adoption on knowledge workers' innovative work behaviors (IWB), as well as the mediating role of stress appraisal and the moderating role of individual learning abilities.

This study analyzed the questionnaire results of 313 knowledge workers, and data analysis was conducted by using SPSS 25.0, SPSS 25.0 macro-PROCESS and AMOS 28.0.

This study found that AI adoption has a double-edged sword effect on knowledge workers' IWB. Specifically, AI adoption can promote IWB by enhancing knowledge workers' challenging stress appraisal, while inhibiting IWB by fostering their hindering stress appraisal. Moreover, individual learning ability significantly moderated the relationship between AI adoption and stress appraisal, which further influenced IWB.

This study integrates the conflicting findings of previous studies and proposes a comprehensive theoretical model based on the theory of cognitive appraisal of stress. This study enriches the research on AI in the field of knowledge management, especially extending the understanding of the relationship between AI adoption and knowledge workers’ IWB by unraveling the psychological mechanisms and behavior outcomes of users' technology usage. Additionally, we provide new insights and suggestions for organizations to seek the cooperation and support of employees in introducing new technologies or driving intelligent transformation.

This paper aims to propose a type of T-shaped two-axis force sensor for measuring the forces in x- and z-axes. The developed sensor has a simple structure and can be effectively assembled into compact devices.

A T-shaped plate, with both ends fixed on a base, is used as the substrate of the sensor. Eight strain gauges are placed in the root of the plate or near the sensor head, which can construct two full Wheatstone bridges on the upper and lower surfaces of the plate. When the x- or z-axes forces are applied to the sensor head, different deformation can be generated to the strain gauges. Therefore, the two Wheatstone bridges can be constructed with a different configuration for measuring the forces in x- or z-axes, respectively.

A prototype was designed and constructed and experiments were carried out to test the basic performance of the sensor. It has been verified that the developed sensor could measure the x- and z-axes forces independently with a high resolution of 2.5 and 5 mN, respectively.

Only one thin plate was used in the design, the forces in x- and z-axes could be measured independently and simultaneously, which made the sensor with a simple structure and compact size. Experiments were also verified that there was no crosstalk error occurred in one axis when the force was applied to the other axis.

This study aims to explore the effect of corrosion monitoring technology for ensuring concrete structure safety.

A new monitoring system scheme with unattended operation to evaluate the durability of concrete structures is presented, which includes four components, namely, a multi-function embedded sensor, a microprocessor data collecting module, a system data analysis and storage module, and a remote server module.

The system carries out monitoring of chloride ion concentration and pH in concrete, corrosion current density and of the self-corrosion potential of the reinforcing steel bar.

This system provides real-time, online, lossless monitoring for concrete structures.

The purpose of this paper is to suggest an implicit integration method for updating the constitutive relationships in the newly proposed anisotropic egg-shaped elastoplastic (AESE) model and to apply it in ABAQUS.

The implicit integration algorithm based on the Newton–Raphson method and the closest point projection scheme containing an elastic predictor and plastic corrector are implemented in the AESE model. Then, the integration code for this model is incorporated into the commercial finite element software ABAQUS through the user material subroutine (UMAT) interface to simulate undrained monotonic triaxial tests for various saturated soft clays under different consolidation conditions.

The comparison between the simulated results from ABAQUS and the experimental results demonstrates the satisfactory performance of this implicit integration algorithm in terms of effectiveness and robustness and the ability of the proposed model to predict the characteristics of soft clay.

The rotational hardening rule in the AESE model together with the implicit integration algorithm cannot be considered.

The singularity problem existing in most elastoplastic models is eliminated by the closed, smooth and flexible anisotropic egg-shaped yield surface form in the AESE model. In addition, this notion leads to an efficient implicit integration algorithm for updating the highly nonlinear constitutive equations for unsaturated soft clay.