Search results

The main purpose of this study is to develop a systematic method that can minimize joint clearance for non‐assembly mechanism fabrication using a layer‐based fabrication technology.

Joint clearance is one of the key factors affecting a mechanism's performance. Hertz theory is adopted to analyze the joint clearance‐penetration displacement relationship and the impact force‐displacement relationship. This analysis has indicated the importance of reducing joint clearance. To reduce joint clearance in layer‐based fabrication, a drum‐shaped roller is proposed for pin joint design in non‐assembly mechanism fabrication. Compared to cylindrical pin joint design, a drum‐shaped roller joint results in less impact force in mechanism operation. Furthermore, the joint clearance can also be drastically reduced.

Large joint clearance could introduce instability into the dynamic behaviour of a mechanism. By applying a drum‐shaped roller, the instability could apparently be alleviated. This has been demonstrated by both simulation and fabrication of a number of mechanisms with and without drum‐shaped pin joints.

Since the proposed joint design can reduce the joint clearance in rapid fabrication of non‐assembly mechanisms, it is possible to expand layer‐based rapid fabrication techniques for more mechanism design applications.

Layer‐based fabrication technologies have two distinct advantages: building parts without geometry restriction; and building sub‐systems (static or mobile) without the need for assembly. Only very few previous studies have investigated the applications that can benefit from the second advantage due to the limited accuracy of layer‐based technologies in making joints of a mechanism. Through the proposed drum‐shaped roller pin joint design together with the proposed joint design guidelines, joint clearance can be reduced significantly. Thus, sub‐systems or mechanisms built using layer‐based technologies could have accuracy close to the design specification. This will expand the application of layer‐based technologies to more mechanism or mobile mechanical system studies.

The existence of clearance in joints of positioning mechanism is inevitable and the movements of the real mechanism are deflected from the ideal mechanism due to the clearances. The purpose of this paper is to investigate the effects of clearance on the dynamic characteristics of dual-axis positioning mechanism of a satellite antenna.

The dynamics analysis of dual-axis positioning mechanism with clearance are investigated using a computational approach based on virtual prototyping technology. The contact model in joint clearance is established by using a hybrid nonlinear continuous contact force model and the friction effect is considered by using a modified Coulomb friction model. Then the numerical simulation of dual-axis positioning mechanism with joint clearance is carried out and four case studies are implemented for different clearance sizes.

Clearance leads to degradation of the dynamic performance of the system. The existence of clearance causes impact dynamic loads, and influences the motion accuracy and stability of the dual-axis positioning mechanism. Larger clearance induces higher frequency shakes and larger shake amplitudes, which will deteriorate positioning accuracy.

Providing an effective and practical method to analyze dynamic characteristics of dual-axis positioning mechanism of satellite antenna with joint clearance and describing the dynamic characteristics of the dual-axis positioning system more realistically, which improves the engineering application.

The paper is the basis of mechanism design, precision analysis and robust control system design of dual-axis positioning mechanism of satellite antenna.

The study aims to examine the effect of detective experience on the likelihood of clearing a homicide, while controlling for additional extralegal and case/investigative characteristics.

This study uses homicide and policing data collected from case files in a mid-sized US city. Detective experience is measured in multiple ways. Analytical models include extralegal variables, case characteristics, and proxies of investigative quality as controls. The study uses logistic regression with a dichotomous clearance outcome.

The results suggest a robust and significant inverse relationship between the years spent as a homicide detective and the likelihood of case closure. However, years of experience with the department overall has a significant and positive relationship to clearance. Investigation-related variables and case characteristics contribute more to model explanatory power than extralegal factors.

The potential role of experience has not been fully explored, with contradictory findings over time. This work builds on previous research to highlight the potential role of experience in clearing cases, while questioning previous assumptions tied to the belief that more experience improves investigative outcomes.

For the automatic drilling and riveting in panel assembly, gaps between the skin and strangers are inevitable and undesirable. At present, the determination of pre-joining schemes relies on workers’ experience, introducing excessive number and inappropriate locations of pre-joining. This paper aims to present a new method for the evaluation of residual clearances after pre-joining and the pre-joining scheme optimization, providing operation guidance for the workers in panel assembly workshop.

In this paper, an equivalent gap assembly model for pre-joining is proposed on the basis of the mechanism of variation. This model retains the essential elastic behavior of the key features during the pre-joining operation and calculates the residual clearances in the view of the potential energy. Subsequently, this method is embedded into a Pareto optimality-based genetic algorithm, and the optimal pre-joining schemes are achieved with the consideration of the total residual clearances and the permissive tolerances.

The equivalent gap assembly model has the capability to predict an acceptable degree of accuracy of the residual clearances and achieve the optimized pre-joining schemes with less number of pre-joining at the same level of residual clearances.

The optimized pre-joining schemes are given in the form of Pareto optimality set, and workers can select suitable results according to their inclination to the quality and efficiency.

The paper is the first to propose the equivalent gap assembly model for the pre-joining operation, which provides for the simplification of the calculation of residual clearances based on the constrained variation principles.

This paper addresses the clearance of aggravated assaults (AAs). Specifically, the authors consider variations in these clearances over time for large agencies and test which crime, investigation and agency factors are associated with the likelihood of clearance by arrest or exceptional means. In doing this work, they seek to extend the understanding of how police can improve their investigations and ability to solve serious offenses.

Using case, investigative and organizational data collected from seven large police departments selected on the basis of their trajectory of index crime clearances, and measures of case characteristics, investigative effort and organizational best practices, this paper uses descriptive and inferential statistics to analyze AA investigations and case clearance.

Key findings include the following: trajectories of AA clearance vary across large agencies and covary with a measure of organizational best practices, and the relationship between investigative effort and case clearance can depend on organizational practices. The authors find that measures of investigative effort are either not related to case clearance or there is a negative association.

Now that police researchers have a better understanding of AAs and their investigations, they need to test how this knowledge can be used to improve the quality of police investigations. Tests, preferably multi-agency randomized control trials, of new investigative strategies and organizational practices are needed.

This research is original in that it uses a multi-agency sample and crime, investigation and organizational measures to understand AA clearance.

Business victimization is a serious and pervasive issue within the USA. According to recent estimates, roughly 2,058,194 businesses are victimized each year. Of those, approximately 33 percent of business victimization cases are solved. Taken together, it is important for research to examine factors that influence business victimization clearance. The purpose of this paper is to examine how broken windows enforcement, social disorganization, community and police organizational factors influence business robbery clearance using data from Houston, Texas over a two-year period from 2010 to 2012.

Using a hierarchical linear modeling strategy, the current study found no effect of broken windows tactics, social disorganization elements and various organizational, and community characteristics on business robbery clearance.

Significant effects were found for a number of incident and offense characteristics including gang involvement, business type, type of weapon used in the crime, the number of business entities in an area, and racial populous.

To date, few studies have examined factors that influence clearance rates for business robberies. Thus, the current study adds to and extends upon the literature in theoretically relevant ways by exploring how broken windows policing, social disorganization and various community/police organizational variables influence business robbery clearances in a large city.

Seaports play an immeasurable role in the advancement of international trade. They have been the common avenue for the transportation of goods and services from one continent to another, and it has also been the linking transport of one mode of transport to another. The study sought to assess the effect of paperless information technology (IT)-based custom clearance at Ghana Seaports on businesses and industrial supply chains in Ghana.

The study conducted a survey with a sample size of 200 trading firms in Ghana.

The study discovered that IT-based port clearance has positive impact on customer order fulfillment, transaction cost reduction and supply chain relationships.

With the aim of making Ghana the transportation hub of businesses in the sub region, the paperless custom clearance has the potential to reduce delays at the port and improve their supply chain.

This paper provides researchers with a contemporary perspective toward understanding the effect of paperless custom clearance on the supply chain of businesses in the West African sub region.

The paper discusses the assignment of security clearances to employees in a security conscious organisation. New approaches are suggested for solving two major problems. First, full implementation of the “need‐to‐know” principle is provided by the introduction of data access statements (DAS) as part of an employee’s job description. Second, for the problem of setting up border points between different security clearances, the paper introduces a fuzzy set model. This model helps to solve this problem, effectively connecting it with the cost of security.

Detective work is a mainstay of modern law enforcement, but its effectiveness has been much less evaluated than patrol work. To explore what is known about effective investigative practices and to identify evidence gaps, the authors assess the current state of empirical research on investigations.

The authors assess the empirical research about the effectiveness of criminal investigations and detective work in resolving cases and improving clearance rates.

The authors’ analysis of the literature produced 80 studies that focus on seven categories of investigations research, which include the impact that case and situational factors, demographic and neighborhood dynamics, organizational policies and practices, investigative effort, technology, patrol officers and community members have on case resolution. The authors’ assessment shows that evaluation research examining the effectiveness of various investigative activities is rare. However, the broader empirical literature indicates that a combination of organizational policies, investigative effort and certain technologies can be promising in improving investigative outcomes even in cases deemed less solvable.

From an evidence-based perspective, this review emphasizes the need for greater transparency, evaluation and accountability of investigative activities given the resources and importance afforded to criminal investigations.

This review is currently the most up-to-date review of the state of the research on what is known about effective investigative practices.

Although many studies have examined the correlates of homicide clearance rates, few analyses have examined the factors related to the clearance of burglary offenses. The purpose of this paper is to address several gaps in the literature to determine if burglary clearance rates are due to discretionary, non-discretionary, and/or neighborhood contextual factors.

Data are analyzed from more than 10,000 burglary incidents in Philadelphia from 2010 using multilevel models to simultaneously test for the influence of multiple perspectives of the factors of crime clearance.

The results indicate that variables representing broken windows enforcement, discretionary factors, and non-discretionary factors are related to the increased likelihood that burglaries are cleared, but processes associated with social disorganization within communities is not.

The findings contribute to the literature by showing that future examinations of the factors of burglary clearance should consider community contextual factors, and specifically, that broken windows police enforcement appears to be a more important predictor of burglary clearance than do factors related to social disorganization theory. As a result, it is suggested that law enforcement also consider their tactics regarding low-level offenses if they wish to address the clearance rate of burglaries.

This analysis is among the first to examine multiple perspectives of the factors of crime clearance on burglary incidents.