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Article
Publication date: 4 October 2011

Yonghua Chen and Chen Zhezheng

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…

Abstract

Purpose

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.

Design/methodology/approach

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.

Findings

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.

Practical implications

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.

Originality/value

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.

Details

Rapid Prototyping Journal, vol. 17 no. 6
Type: Research Article
ISSN: 1355-2546

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Book part
Publication date: 6 September 2018

Wendy C. Regoeczi

Purpose – The goal of this chapter is to assess the state of evidence examining and explaining trends and patterns in homicide clearances.Design/methodology/approach …

Abstract

Purpose – The goal of this chapter is to assess the state of evidence examining and explaining trends and patterns in homicide clearances.

Design/methodology/approach – After reviewing the varying bodies of literature on homicide investigations and clearances, the author assesses the degree of support for the prevailing explanations of why some homicides are more likely to be solved than others. The author also use national data to evaluate several reasons for declining clearances.

Findings – Changes in the nature of homicide and deteriorating police–community relations are likely major contributors to declining clearance rates. The most consistent findings regarding patterns are the greater likelihood of clearance in homicides involving young children, contact weapons, residential locations, and killings not occurring in the course of another crime. Explanations relying on notions of victim devaluing generate the least support. There is considerable support for the legal factors approach and community-level explanations show promise. The findings regarding the role of forensic evidence are mixed. Smaller scale studies are beginning to help identify best practices for homicide investigations.

Originality/value – This chapter assesses several explanations for declining clearance rates and brings together divergent streams of research to summarize the current state of knowledge on homicide clearances, best practices in homicide investigations, and gaps to be filled by further studies.

Details

Homicide and Violent Crime
Type: Book
ISBN: 978-1-78714-876-5

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Article
Publication date: 15 November 2019

Eric M. Cooke and Yan Zhang

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…

Abstract

Purpose

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.

Design/methodology/approach

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.

Findings

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.

Originality/value

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.

Details

Policing: An International Journal, vol. 43 no. 2
Type: Research Article
ISSN: 1363-951X

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Article
Publication date: 10 March 2021

Lisa Barao, Anthony A. Braga, Brandon Turchan and Philip J. Cook

Clearance rates for nonfatal shootings, especially cases involving gang- and drug-related violence, are disturbingly low in many US cities. Using data from a previously…

Abstract

Purpose

Clearance rates for nonfatal shootings, especially cases involving gang- and drug-related violence, are disturbingly low in many US cities. Using data from a previously completed project in Boston, we explore the prospects for improving gang/drug nonfatal shooting cases by investing the same investigative effort found in similar gang/drug gun murder cases.

Design/methodology/approach

Our analyses primarily focus on a sample of 231 nonfatal shootings that occurred in Boston from 2010 to 2014. Logistic regressions are first used to analyze differences in the likelihood of case clearance for gang/drug nonfatal shooting cases relative to other nonfatal shooting cases. Independent samples t-tests are then used to compare the investigative characteristics of these two different kinds of nonfatal shootings. Next, independent samples t-tests are used to compare the investigation of gang/drug gun assaults relative to the investigation of very similar gang/drug gun homicides.

Findings

Results demonstrate that the odds of clearing gang/drug nonfatal shootings are 77.2% less likely relative to the odds of clearing nonfatal shootings resulting from other circumstances. This stark difference in clearance rates is not driven by diminished investigative effort, but investigative effort does matter. Relative to gang/drug gun assaults, gang/drug gun homicides have much higher clearance rates that are the result of greater investigative resources and effort that produces significantly more witnesses and evidence, and generate more forensic tests and follow-up investigative actions.

Originality/value

Gang- and drug-related violence generates a bulk of urban nonfatal shootings. Low clearance rates for nonfatal shootings undermine police efforts to hold offenders accountable, disrupt cycles of gun violence, and provide justice to victims. Police should make investments to improve investigative effort such as handling these cases with the same vigor as homicide cases.

Details

Policing: An International Journal, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1363-951X

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Article
Publication date: 3 June 2014

Zheng Feng Bai, Yang Zhao and Jun Chen

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…

Abstract

Purpose

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.

Design/methodology/approach

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.

Findings

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.

Practical implications

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.

Originality/value

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

Details

Multidiscipline Modeling in Materials and Structures, vol. 10 no. 1
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 5 September 2016

Di Yang, Weiwei Qu and Yinglin Ke

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…

Abstract

Purpose

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.

Design/methodology/approach

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.

Findings

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.

Practical implications

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.

Originality/value

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.

Details

Assembly Automation, vol. 36 no. 4
Type: Research Article
ISSN: 0144-5154

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Article
Publication date: 1 December 2000

Lech J. Janczewski and Victor Portougal

The paper discusses the assignment of security clearances to employees in a security conscious organisation. New approaches are suggested for solving two major problems…

Abstract

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.

Details

Information Management & Computer Security, vol. 8 no. 5
Type: Research Article
ISSN: 0968-5227

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Article
Publication date: 11 November 2014

Brian Lockwood

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…

Abstract

Purpose

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.

Design/methodology/approach

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.

Findings

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.

Research limitations/implications

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.

Originality/value

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

Details

Policing: An International Journal of Police Strategies & Management, vol. 37 no. 4
Type: Research Article
ISSN: 1363-951X

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Article
Publication date: 1 February 1986

Tim Brindley and Gerry Stoker

It is now widely recognised that gradual renewal policies have failed to keep pace with the deterioration of the older housing stock. Commentators and critics are now…

Abstract

It is now widely recognised that gradual renewal policies have failed to keep pace with the deterioration of the older housing stock. Commentators and critics are now calling for an increase in clearance and redevelopment. A policy debate is developing around a range of technical, resource, social and political issues. While it is generally agreed that a return to the slum clearance programmes of the 1960s would be unacceptable the future direction of clearance policies is unsettled. The paper considers three broad approaches to clearance which reflect divergent assumptions and political positions.

Details

Property Management, vol. 4 no. 2
Type: Research Article
ISSN: 0263-7472

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Article
Publication date: 7 August 2017

Esmaeil Salahshoor and Saeed Ebrahimi

The purpose of this paper is to investigate the effect of joint clearance on the behavior of a needle driver mechanism (a slider-crank linkage) of a typical sewing machine…

Abstract

Purpose

The purpose of this paper is to investigate the effect of joint clearance on the behavior of a needle driver mechanism (a slider-crank linkage) of a typical sewing machine with an imperfect joint between the coupler and the slider (including needle).

Design/methodology/approach

In order to model the clearance, the momentum exchange approach is used. The Lankarani and Nikravesh’s continuous contact force model is used to model the contact force, and the modified Coulomb’s friction law represents the friction between sliding members. The penetration force applied on the needle by fabric is chosen based on an experimental data in the literature. The dynamic response is validated for the existing properties in the literature without considering the penetration force.

Findings

It is shown that the clearance joint made considerable effect on the dynamic response of the system. The rough changes of the needle acceleration and jerk are obvious. The base reaction force changed roughly and did not vary as smooth as that of the mechanism with ideal joint. So, clearance joint in the mechanism could lead to an undesirable vibration in the system. Furthermore, the crank driver must provide a non-smooth moment on the crank to keep the crank rotational velocity constant. Moreover, reducing the clearance size sufficiently could make the dynamic response closer to that of the mechanism with ideal joint. In addition, smoother crank moment could be required if the clearance size is reduced sufficiently. Furthermore, the rough change of the base reaction force which can represent the vibration caused by the mechanism on the fixed frame could be reduced if the clearance size is small enough.

Originality/value

Lockstitch sewing machine is one of the most common apparel industrial machines. The needle driver mechanism of a sewing machine could have an important role for proper stitch forming. On the other hand, clearances are inevitable in assemblage of mechanisms to allow the relative motion between the members. This clearance is due to machining tolerances, wear, material deformations, and imperfections, and it can worsen mechanism performance such as precision, dynamic behavior and vibration. Unfortunately, despite the importance of the dynamic behavior of the needle driver mechanism from practical point of view, very little publications have focused especially on the investigation of the effect of clearance joint on the dynamic behavior of the sewing machine which could lead to undesired vibration of the system and shorter lifetime as a result. In this paper, the dynamic behavior of the system including, needle velocity and acceleration, crank moment and base reaction force was compared with that of the ideal mechanism. Finally, the effect of clearance size on the dynamic behavior of the system was investigated.

Details

International Journal of Clothing Science and Technology, vol. 29 no. 4
Type: Research Article
ISSN: 0955-6222

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