Characterization and modeling of pattern dependencies and time evolution in plasma etching

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, June 2009."May 2008." Cataloged from PDF version of thesis.Includes bibliographical references (p. 43).A quantitative model capturing pattern dependent effects and time evolution of the etch rate in Deep Reactive Ion Etching (DRIE) is presented. DRIE is a key process for pattern formation in semiconductor fabrication. Non-uniformities are caused due to microloading and aspect ratio dependencies. The etch rate varies over time and lateral etch consumes some of the etching species. This thesis contributes a physical analysis for capturing and modeling microloading, aspect ratio dependencies, effects of lateral etch and time evolution of the etch rate. This methodology is applied to the study of etching variation on silicon wafers; the integrated model is able to predict pattern density and feature size dependent non-uniformities in trench depth and time evolution of the etch rate. Previous studies of variation in plasma etching have characterized microloading and aspect ratio dependent etching (ARDE) as distinct constant causes for etch non-uniformity. In contrast to these previous works, we present here a time-based methodology for vertical and lateral etch.by Ali Farahanchi.M.Eng

Dynamics of multibody systems with spherical clearance joints

This work deals with a methodology to assess the influence of the spherical clearance joints in spatial multibody systems. The methodology is based on the Cartesian coordinates, with the dynamics of the joint elements modeled as impacting bodies and controlled by contact forces. The impacts and contacts are described by a continuous contact force model that accounts for geometric and mechanical characteristics of the contacting surfaces. The contact force is evaluated as function of the elastic pseudo-penetration between the impacting bodies, coupled with a nonlinear viscous-elastic factor representing the energy dissipation during the impact process. A spatial four-bar mechanism is used as an illustrative example and some numerical results are presented, with the efficiency of the developed methodology discussed in the process of their presentation. The results obtained show that the inclusion of clearance joints in the modelization of spatial multibody systems significantly influences the prediction of components’ position and drastically increases the peaks in acceleration and reaction moments at the joints. Moreover, the system’s response clearly tends to be nonperiodic when a clearance joint is included in the simulation.Fundação para a Ciência e a Tecnologia (FCT)FEDER - Project POCTI/2001/ EME/3828

Clinical Results of Platelet-Rich Plasma in Frozen Shoulder

Background: Frozen shoulder is a common cause of shoulder pain and disability. Several treatments are utilized to reduce patients' pain and improve range of motion (ROM). Recent researches have been conducted on Platelet-rich plasma (PRP) injection. In this study, the clinical results of PRP injection for patients with frozen shoulder was assessed. Materials and Methods: Forty-four patients in phases I or II of frozen shoulder were treated with PRP. During the first session, two syringes of PRP were injected in the subacromial bursa and intra-articular space; this process was repeated after four weeks. In the second stage, PRP was injected only in the glenohumeral joint. Results: The average pre-treatment flexion was about 65°; abduction was 70°while external rotation was 22°. Also, baseline scores for VAS, DASH, and SF-12 Health Survey questionnaire were 8.4, 65.9 and 26, respectively. After 25 weeks follow-up, all patients showed significant improvement in shoulder ROM, pain, and function (p˂0.001). Patients reported 66.7% improvement in pain, 51.6% in DASH score, and 100% in SF-12 Health Survey questionnaire. They were also 65% satisfied with the treatment protocol. Conclusion: This case series study demonstrated clinically and statistically significant improvement in patients' pain and disability outcomes following PRP injection. These results provide support for PRP as a safe treatment protocol that decreases pain and increases upper limb function. In addition, it can also improve shoulder range of motion

The Prevalence and Mortality in COVID-19 Positive Patients with Hip Fracture: a Case-Series and Literature Review

Background: The novel coronavirus has spread rapidly worldwide, with exceptionally high mortality in the elderly. Patients with hip fracture have an average age of 80 years, with an estimated 2.8 comorbidities per patient. This study aims to assess the impact of the COVID-19 pandemic on hip fracture care services and the associated mortality rate. Methods: PubMed, Medline, and Google Scholar databases were searched for relevant studies linked to mortality in COVID-19 patients who have undergone hip surgeries using the keywords “COVID-19” OR “SARS-cov-2” OR “Coronavirus Infections”; AND “Surgery” OR “Hip” OR “Fracture” OR “Orthopedics.” We included all patients with hip fractures but excluded pathological fractures and other non-traumatic hip pathologies 30 studies for the final review were selected according to the inclusion and exclusion criteria. Results: 30 studies were included in the review. The overall mortality was 10.52%. There was a significant difference in the mortality rate between patients with positive and negative tests and between the operative patients who tested positive and the operative patients who tested negative. Conclusions: COVID-19-infected elderly patients with hip fractures have a higher mortality rate than non-COVID-19 infected cases. Further studies are warranted to examine the morbidity and mortality rates in COVID-19-positive patients with hip fractures and investigate how these outcomes can be improved

Translational joints with clearance in rigid multibody systems

A computational methodology for dynamic description of rigid multibody systems with translational clearance joints is presented and discussed in this work. Over the last years, extensive work has been done to study the dynamic effect of the revolute joints with clearance in multibody systems, in contrast with the little work devoted to model translational joints with clearance. In a joint with translation clearance there are many possible ways to set the physical configuration between the slider and guide, namely: (i) no contact between the two elements, (ii) one corner of the slider in contact with the guide surface, (iii) two adjacent slider corners in contact with the guide surface, (iv) two opposite slider corners in contact with the guide surfaces. The proposed methodology takes into account these four different situations. The conditions for switching from one case to another depend on the system dynamics configuration. The existence of a clearance in a translational joint removes two kinematic constraints from a planar system and introduces two extra degrees of freedom in the system. Thus, a translational clearance joint does not constrain any degree of freedom of the mechanical system but it imposes some restrictions on the slider motion inside the guide limits. When the slider reaches the guide surfaces an impact occurs and the dynamic response of the joint is modeled by contact-impact forces. These forces are evaluated here with continuous contact force law together with a dissipative friction force model. The contact-impact forces are introduced into the system’s equations of motion as external generalized forces. The proposed methodology is applied to a planar multibody mechanical system with a translational clearance joint in order to demonstrate its features.Fundação para a Ciência e a Tecnologia (FCT

A parametric study on the dynamic response of planar multibody systems with multiple clearance joints

A general methodology for dynamic modeling and analysis of multibody systems with multiple clearance joints is presented and discussed in this paper. The joint components that constitute a real joint are modeled as colliding bodies, being their behavior influenced by geometric and physical properties of the contacting surfaces. A continuous contact force model, based on the elastic Hertz theory together with a dissipative term, is used to evaluate the intra-joint contact forces. Furthermore, the incorporation of the friction phenomenon, based on the classical Coulomb’s friction law, is also discussed. The suitable contact-impact force models are embedded into the dynamics of multibody systems methodologies. An elementary mechanical system is used to demonstrate the accuracy and efficiency of the presented approach, and to discuss the main assumptions and procedures adopted. Different test scenarios are considered with the purpose of performing a parametric study for quantifying the influence of the clearance size, input crank speed and number of clearance joints on the dynamic response of multibody systems with multiple clearance joints. Additionally, the total computation time consumed in each simulation is evaluated in order to test the computational accuracy and efficiency of the presented approach. From the main results obtained in this study, it can be drawn that clearance size and the operating conditions play a crucial role in predicting accurately the dynamic responses of multibody systems.Fundação para a Ciência e a Tecnologia (FCT

A review of friction models in interacting joints for durability design.

This paper presents a comprehensive review of friction modelling to provide an understanding of design for durability within interacting systems. Friction is a complex phenomenon and occurs at the interface of two components in relative motion. Over the last several decades, the effects of friction and its modelling techniques have been of significant interests in terms of industrial applications. There is however a need to develop a unified mathematical model for friction to inform design for durability within the context of varying operational conditions. Classical dynamic mechanisms model for the design of control systems has not incorporated friction phenomena due to non-linearity behaviour. Therefore, the tribological performance concurrently with the joint dynamics of a manipulator joint applied in hazardous environments needs to be fully analysed. Previously the dynamics and impact models used in mechanical joints with clearance have also been examined. The inclusion of reliability and durability during the design phase is very important for manipulators which are deployed in harsh environmental and operational conditions. The revolute joint is susceptible to failures such as in heavy manipulators these revolute joints can be represented by lubricated conformal sliding surfaces. The presence of pollutants such as debris and corrosive constituents has the potential to alter the contacting surfaces, would in turn affect the performance of revolute joints, and puts both reliability and durability of the systems at greater risks of failure. Key literature is identified and a review on the latest developments of the science of friction modelling is presented here. This review is based on a large volume of knowledge. Gaps in the relevant field have been identified to capitalise on for future developments. Therefore, this review will bring significant benefits to researchers, academics and industrial professionals

A comprehensive survey of the analytical, numerical and experimental methodologies for dynamics of multibody mechanical systems with clearance or imperfect joints

"Available online 19 December 2017"A comprehensive survey of the literature of the most relevant analytical, numerical, and experimental approaches for the kinematic and dynamic analyses of multibody mechanical systems with clearance joints is presented in this review. Both dry and lubricated clearance joints are addressed here, and an effort is made to include a large number of research works in this particular field, which have been published since the 1960′s. First, the most frequently utilized methods for modeling planar and spatial multibody mechanical systems with clearance joints are analyzed, and compared. Other important phenomena commonly associated with clearance joint models, such as wear, non-smooth behavior, optimization and control, chaos, and uncertainty and links’ flexibility, are then discussed. The main assumptions procedures and conclusions for the different methodologies are also examined and compared. Finally, future developments and new applications of clearance joint modeling and analysis are highlighted.This research was supported in part by the China 111 Project (B16003) and the National Natural Science Foundation of China under Grants 11290151, 11472042 and 11221202. The work was also supported by the Portuguese Foundation for Science and Technology with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941.info:eu-repo/semantics/publishedVersio

The impact of strategic investment on success of capital-intensive ventures

Thesis: Ph. D. in Engineering Systems, Massachusetts Institute of Technology, School of Engineering, Institute for Data, Systems, and Society, 2017.Cataloged from PDF version of thesis.Includes bibliographical references (pages 408-417).Established companies in technology-enabled industries such as software, telecommunications, pharmaceuticals, and semiconductors, have used corporate venture capital as a lever to access and screen technological advances, and to drive innovation outside the traditional firm boundaries. Recent years have witnessed emergence of a new wave of corporate venture capital funds that increasingly interact and compete with traditional venture capital firms in the entrepreneurial ecosystem. The incremental benefits of financing a startup through corporate venture capital have been a subject of study by researchers across Economics, Finance, Strategy, and Innovation fields. First, this thesis examines entrepreneurs' rationale for raising capital from corporate investors. Through the analysis of an online survey conducted with startups based in the US and founded between 2010-15, we identify that startups that operate in capital-intensive industries, such as life sciences and manufacturing, raise capital from corporate investors in order to establish strategic partnership with corporates, significantly more than do startups in capital-light industries such as enterprise and consumer software. Second, through an empirical analysis of a panel of 8,190 startups founded in the US between 2000-10, this thesis shows that corporate venture capital is more beneficial to startups that operate in capital-intensive industries. Using a bi-variate probit model, this thesis shows that startups backed by corporate venture capital are more likely to be acquired or go public, and that the likelihood of an exit event increases as capital-intensity of the industry magnifies, as measured by the level of fixed assets on companies' balance sheets. In addition, we provide empirical evidence that participation of corporate venture capital in a financing round, helps a capital-intensive startup to raise further funding from reputable traditional venture capital firms. Third, this thesis presents empirical evidence that establishing strategic collaboration between capital-intensive startups and corporate parents of venture capital firms, in forms of joint research, product development, or commercialization, is a main source of value for startups. Using data gathered on 130 corporate news announcements on strategic collaborations, this thesis shows that capital-intensive startups backed by corporate venture capital, are significantly more likely to succeed when they establish strategic collaboration with corporate parents. The final contribution of this thesis is a formal assessment of traditional venture capital firms' investment behavior in presence of corporate investors. We present a game-theoretic model and identify the circumstances under which traditional venture capital firms benefit financially from corporate investors participation in financing a capital-intensive startup. By leveraging data gathered on 8,190 startups, we apply the game-theoretic model and Monte-Carlo method to simulate financial returns for a traditional venture capital firm investing a capital-intensive startup in the pharmaceutical industry.by Ali Farahanchi.Ph. D. in Engineering System