Browsing by Author "Chen, Jie"

Now showing 1 - 9 of 9
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    The Design of a Three-Degrees-of-Freedom Walking Machine.
    (1989) Tsai, L.W.; Chen, Jie; Azarm, Shapour; ISR
    The walking machine presented in this paper consists of six walking legs arranged in a triangular configuration. Each leg may have two modes of operation: an elliptical mode for walking on a flat plane and a circular mode for stair climbing. The six legs are mechanically coupled to a single drive motor through the use of chains and sprockets. the coupling is arranged in such a way that three of the six legs, one from each corner of the triangle, are always in phase while the other three are 180 degrees out of phase. When walking, three of the six legs are always on the ground propelling the machine forward, while the other three are in the air in an opposing position rotating forward. Turning is achieved through the use of a two degres-of-freedom mechanism. Through the use of a prismatic joint, the body of the machine can be lifted up-anddown, and through the use of a revolute pint, it can be rotated to any desirable orientation. The result is a simple, three degrees of freedom, walking machine that is capable of walking on a flat plane and performing some limited stair climbing. Because of the simple construction, the control system is also extremely simple and fast locomotion may be achieved for a small sacrifice of flexibility.
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    Gender Differences in Mental Health Outcomes before, during, and after the Great Recession
    (PLOS (Public Library of Science), 2015-05-13) Dagher, Rada K.; Chen, Jie; Thomas, Stephen B.
    We examined gender differences in mental health outcomes during and post-recession versus pre-recession. We utilized 2005-2006, 2008-2009, and 2010-2011 data from the Medical Expenditure Panel Survey. Females had lower odds of depression diagnoses during and post-recession and better mental health during the recession, but higher odds of anxiety diagnoses post-recession. Males had lower odds of depression diagnoses and better mental health during and post-recession and lower Kessler 6 scores post-recession. We conducted stratified analyses, which confirmed that the aforementioned findings were consistent across the four different regions of the U.S., by employment status, income and health care utilization. Importantly, we found that the higher odds of anxiety diagnoses among females after the recession were mainly prominent among specific subgroups of females: those who lived in the Northeast or the Midwest, the unemployed, and those with low household income. Gender differences in mental health in association with the economic recession highlight the importance of policymakers taking these differences into consideration when designing economic and social policies to address economic downturns. Future research should examine the reasons behind the decreased depression diagnoses among both genders, and whether they signify decreased mental healthcare utilization or increased social support and more time for exercise and leisure activities.
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    LINK BETWEEN DYNAMICS AND FUNCTION IN SINGLE AND MULTI-SUBUNIT ENZYMES
    (2010) Chen, Jie; Thirumalai, Devarajan; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Biopolymers, such as proteins and DNA, are polymers whose three-dimensional conformations dene their biological functions. Current emphasis on structures has greatly advanced our understanding of the functions of biopolymers. However, there is a need to understand the deeper link between biopolymer dynamics and function, because in water and under cellular conditions, everything that biopolymers do can be understood in terms of "the jigglings and wigglings of atoms". These motions arise from thermal noise in the solvent and due to intrinsic motion of the enzymes. In biological systems, the motions are often highly regulated to ensure that cellular processes are executed over the required time scales. For enzymes, which are essentially proteins that catalyze chemical reactions or generate mechanical work, conformational fuctuations are coupled at various stages through interactions with ligands during the catalytic cycle. We have studied two dierent enzymes, dihydrofolate reductase (DHFR), which catalyzes reduction of dihydrofolate to tetrahydrofolate, and RNA polymerase (RNAP from bacteria and Pol II from yeast), which is responsible for RNA synthesis using DNA as a template. In order to study the link between dynamics and function we have developed new methods and extended a variety of computational techniques. For DHFR, we use both evolutionary imprints (SCA) and structure-based perturbation method (SPM) to extract a network of residues that facilitate the transitions between two distinct conformational states (closed and occluded states). The transition kinetics and pathways connecting the closed and occluded states are described using Brownian dynamics (BD) simulation. We found the sliding motion of Met20 loop across helix 2 is involved in the forward and reverse transitions between the closed and occluded states. We also found that cross-linking M16-G121 inhibits both the forward and the reverse transitions. In addition, we showed the transition states of these transitions are broad and resemble high energy states. For RNAP, we focus on the conformational changes of RNAP and DNA in promoter melting process. Using BD, we show that DNA conformation changes in promoter melting occur in three steps. We also show that internal dynamics of RNAP is relevant to facilitate the bending of DNA. For Pol II, the structural transitions between two initiation conformational states and between initiation state and elongation state are studied using SPM and BD. We determine the structural units that regulate structural transitions and describe the transition kinetics. The combination of three dierent methods, SCA, SPM and BD, provide results that are in accord with many experiments. Moreover, our description of the detailed structural transitions in these enzymes lead to new insights and testable predictions in these extraordinarily important enzyme functions.
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    Macromodeling for Mixed Signal Circuits
    (1992) Chen, Jie; Milor, L.; ISR
    Macromodels of functional blocks of VLSI circuits are used to reduce the computational effort involved in the detailed simulation of general-purpose circuits. However the macromodeling approaches in the literature have considerable limitations both in the type of circuits that can be modeled or the functions that can be simulated. In this paper we propose a method to generate macromodels for any kind of circuit and any kind of function that needs to be simulated, without restrictions. Furthermore our approach has a superior convergence properties, compared to the previous results in the literature. Therefore our method can get optimal macromodels in reasonable time and the models are accurate enough to be used for general circuit simulation.
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    The medical home functions of primary care practices that care for adults with psychological distress: a cross-sectional study
    (Springer Nature, 2019-01-09) Linman, Shawn; Benjenk, Ivy; Chen, Jie
    Primary care practices are changing the way that they provide care by increasing their medical home functionality. Medical home functionality can improve access to care and increase patient-centeredness, which is essential for persons with mental health issues. This study aims to explore the degree to which medical home functions have been implemented by primary care practices that care for adults with psychological distress. Analysis of the 2015 Medical Expenditure Panel Survey Household Component and Medical Organizations Survey. This unique data set links data from a nationally representative sample of US households to the practices in which they receive primary care. This study focused on adults aged 18 and above. As compared to adults without psychological distress, adults with psychological distress had significantly higher rates of chronic illness and poverty. Adults with psychological distress were more likely to receive care from practices that include advanced practitioners and are non-profit or hospital-based. Multivariate models that were adjusted for patient-level and practice-level characteristics indicated that adults with psychological distress are as likely to receive primary care from practices with medical home functionality, including case management, electronic health records, flexible scheduling, and PCMH certification, as adults without psychological distress. Practices that care for adults with mental health issues have not been left behind in the transition towards medical home models of primary care. Policy makers should continue to prioritize adults with mental health issues to receive primary care through this model of delivery due to this population’s great potential to benefit from improved access and care coordination.
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    Mission of Mercy emergency dental clinics: an opportunity to promote general and oral health
    (BioMed Central Public Health, 2018) Jackson, Devlon N.; Passmore, Susan; Fryer, Craig S.; Chen, Jie; Kleinman, Dushanka V.; Horowitz, Alice M.; Butler, James III; Garza, Mary A.; Quinn, Sandra C.; Thomas, Stephen B.
    Mission of Mercy (MOM) emergency dental clinics are a resource for populations lacking access to dental care. We designed a MOM event incorporating health equity components with established community partners who shared a common vision of addressing the oral health, physical health, and social service needs of Maryland and Washington, DC area residents. Although studies have explored associations between oral and chronic health conditions, few studies to our knowledge have examined the relationship between these conditions and receipt of dental services. Therefore, this study explored these associations and the opportunity for better care coordination.
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    Racial and ethnic disparities in use of psychotherapy: evidence from U.S. national survey data.
    (2010) Chen, Jie; Rizzo, John
    This study found little evidence of racial and ethnic disparities in access to psychotherapy services. Health care reforms affecting mental health coverage under Medicaid would significantly affect psychotherapy expenditure and use among Latinos and African Americans.
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    A Systematic Methodology for the Dynamic Analysis of Articulated Gear-Mechanisms
    (1990) Chen, Jie; Chen, Dar-Zen; Tsai, Lung-Wen; ISR
    This paper describes a systematic methodology for the dynamic analysis of a general class of articulated gear-mechanisms. The approach is based on recently published results related to the kinematic and dynamic analyses of such gear systems. We have shown that the Lagrange's equations of motion can be derived in terms of the minimum number of generalized coordinates in a systematic manner. We have also shown that constraint forces and torques can be evaluated systematically and efficiently, once the equations of motion have been solved. The procedure can be automated in a computer program.
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    Walking Robot: A Multidisciplinary Design Project for Undergraduate Students.
    (1988) Azarm, Shapour; Chen, Jie; Tsai, L.W.; ISR
    The advances in computer technology have made many forms of industrial automation possible. Machines that help to enable this automation are usually controlled by computers through software. The design of such machines will involve engineering professionals working together as an interdisciplinary team. For engineering students to gain some experience on this design practice, a project course in which the students designed and built a walking robot was offered at the College Park campus of the University of Maryland. A walking robot competition with a comprehensive rules package provided the design objective for the project. The competition rules, the organization of the project, and the actual account of the project in a particular year are presented in the paper.