Professor Jorge Ambrósio: A tribute on the occasion of his 65th birthday

It is a great pleasure and an immense honor to write this humble and personal tribute to Professor Jorge Ambrósio on the occasion of his 65th birthday. This report is very modest, since the authors cannot summarize all the work and impact of one of the most influential researchers in the field of multibody dynamics. Further, this narrative is quite personal in the measure that it reflects the authors’ knowledge acquired over the last decades of close interaction and cooperation with Jorge Ambrósio. Thus, this work presents his achievements at different levels, namely in what concerns the scientific research, the industrial influence, and the educational impact. Professor Jorge Ambrósio has been an extremely active and highly productive researcher in multibody dynamics, with more than 230 publications, which generated more than 6000 citations, and 45 of his publications receiving more than 45 citations, leading to an extraordinary h-index of 45 according to the Scopus database. This figure is absolutely extraordinary, since multibody dynamics is a relatively new discipline, where much lower author and paper citation rates are the norm compared to other scientific areas. In fact, Professor Jorge Ambrósio’s publications represent a remarkable and highly influential body of knowledge in the multibody dynamics community. In short, Professor Jorge Ambrósio is without any doubt one of the most prominent researcher and academic of his generation

A kriging model for dynamics of mechanical systems with revolute joint clearances

Over the past two decades, extensive work has been conducted on the dynamic effect of joint clearances in multibody mechanical systems. In contrast, little work has been devoted to optimizing the performance of these systems. In this study, the analysis of revolute joint clearance is formulated in terms of a Hertzian-based contact force model. For illustration, the classical slider-crank mechanism with a revolute clearance joint at the piston pin is presented and a simulation model is developed using the analysis/design software MSC.ADAMS. The clearance is modeled as a pin-in-a-hole surface-to-surface dry contact, with an appropriate contact force model between the joint and bearing surfaces. Different simulations are performed to demonstrate the influence of the joint clearance size and the input crank speed on the dynamic behavior of the system with the joint clearance. In the modeling and simulation of the experimental setup and in the followed parametric study with a slightly revised system, both the Hertzian normal contact force model and a Coulomb-type friction force model were utilized. The kinetic coefficient of friction was chosen as constant throughout the study. An innovative design-of-experiment (DOE)-based method for optimizing the performance of a mechanical system with the revolute joint clearance for different ranges of design parameters is then proposed. Based on the simulation model results from sample points, which are selected by a Latin hypercube sampling (LHS) method, a polynomial function Kriging meta-model is established instead of the actual simulation model. The reason for the development and use of the meta-model is to bypass computationally intensive simulations of a computer model for different design parameter values in place of a more efficient and cost-effective mathematical model. Finally, numerical results obtained from two application examples with different design parameters, including the joint clearance size, crank speed, and contact stiffness, are presented for the further analysis of the dynamics of the revolute clearance joint in a mechanical system. This allows for predicting the influence of design parameter changes, in order to minimize contact forces, accelerations, and power requirements due to the existence of joint clearance.Fundação para a Ciência e a Tecnologia (FCT

Drug Injection to Sites other than Arm: A Study of Iranian Heroin Injectors.

For almost all injecting drug users (IDUs), the first site of injection is the arm. Years after injection, IDUs may shift to using other sites for intravenous (IV) access. Although injection to sites other than the arm is associated with higher risks, literature is limited regarding this behavior. We aimed to determine the prevalence and associated factors of using IV access points other than the arm among a national sample of IDUs in Iran. Data came from the National Drug Dependence Survey, 2007, which had enrolled 863 IDUs with at least one daily injection. Data on socio-demographics, pattern of drug use, and injection-related behaviors were entered into a logistic regression to determine predictors of injection to sites other than the arm. From all participants, 54.8% reported current injection sites in areas other than the arm. The other injection sites were the femoral venous sinus (17.0%), followed by the groin (14.5%) and neck (11.5%). Logistic regression revealed that living alone [odds ratio (OR) = 1.789, 95% confidence interval (CI) = 1.218-2.629], being Sunni (OR = 3.475, 95% CI = 1.775-6.801), having higher family income (OR = 1.002, 95% CI = 1.001-1.003), higher age at first drug use (OR = 1.039, 95% CI = 1.009-1.069), longer injection duration (OR = 1.071, 95% CI = 1.041-1.102), and more injection frequency (OR = 1.255, 95% CI = 1.072-1.471) were associated with higher likelihood of using injection sites other than the arm. Using sites other than the arm for IV injection is linked to socio-demographics, drug use data, and injection-related characteristics that can be used by policy makers. This information can be used for harm reduction planning

Having Multiple Sexual Partners among Iranian Intra-Venous Drug Users

Background: Transmission of HIV from intra-venous drug users (IDUs) to the community occurs predominantly through high-risk sexual behaviors. Limited information exists regarding the high-risk sexual behaviors of IDUs in Iran. Aim. The aim of this study was to determine the prevalence and factors associated with having multiple sexual partners among Iranian IDUs. Methods. This is a national survey on drug-dependent adults. Participants were sampled from medical centers, prisons, and streets of capitals of 29 provinces in Iran, between May 2007 and February 2008. We analyzed data of 1,416 current IDUs. Socio-demographics and drug use characteristics were entered into a binary logistic regression model to determine predictors of having multiple sexual partners. Results. Having multiple sexual partners in the past or at the time of survey was reported by 56.4% of Iranian IDUs. Multivariate analysis showed that the likelihood of having multiple sexual partners in IDUs decreased by being married (odds ratio [OR], 0.38; P < .001) and increased by female gender (OR, 13.44; P = .02), having illegal income (OR, 1.72; P = .003), higher monthly family income (OR, 1.01; P = .003), pleasure, curiosity, and recreation as cause of first drug use (OR, 1.37; P = .04), ruins as usual place for injection (OR, 1.89; P = .001), and history of syringe sharing (OR, 1.50; P = .02). Conclusions. Having multiple sexual partners was reported by majority of Iranian IDUs, and this was linked to socio-demographics, initiation data, and other risk behaviors. This information should be considered in prevention efforts to reduce sexual transmission of HIV infection in Iran