1,367 research outputs found

    Body MRI artifacts in clinical practice: a physicist\u27s and radiologist\u27s perspective.

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    The high information content of MRI exams brings with it unintended effects, which we call artifacts. The purpose of this review is to promote understanding of these artifacts, so they can be prevented or properly interpreted to optimize diagnostic effectiveness. We begin by addressing static magnetic field uniformity, which is essential for many techniques, such as fat saturation. Eddy currents, resulting from imperfect gradient pulses, are especially problematic for new techniques that depend on high performance gradient switching. Nonuniformity of the transmit radiofrequency system constitutes another source of artifacts, which are increasingly important as magnetic field strength increases. Defects in the receive portion of the radiofrequency system have become a more complex source of problems as the number of radiofrequency coils, and the sophistication of the analysis of their received signals, has increased. Unwanted signals and noise spikes have many causes, often manifesting as zipper or banding artifacts. These image alterations become particularly severe and complex when they are combined with aliasing effects. Aliasing is one of several phenomena addressed in our final section, on artifacts that derive from encoding the MR signals to produce images, also including those related to parallel imaging, chemical shift, motion, and image subtraction

    Spatial Information System in the Context of Developing Spatial Data Infrastructure

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    This study focuses on the spatial information system in the context of developing spatial data infrastructure, developing spatial data infrastructure in the context of this study is  a spatial data infrastructure whose operational capacity does not satisfy the standards befitting of a functional or operational spatial data infrastructure. The researcher assumes spatial information system as the sum of the spatial data and spatial information obtained from a geographic information system manipulation, synthesized to give spatial information system useful for information exchange and sharing in spatial data infrastructure. Qualitative review of relevant texts and web information were used for the subjective analysis of the information obtained. The result obtained revealed a glaring gap difference in the understanding, performance and readiness of spatial information among the three geospatial communities analyzed, indicative of the context in which spatial information is held for spatial data infrastructure performance. An attempt was made to proffer requirements necessary for spatial data infrastructure. Keywords: Spatial Information System, Developing SDI, Functional SDI, SDI Complianc

    Evaluating the impact of adopting 3d printing services on the retailers

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    As additive manufacturing technology becomes more responsive to consumers’ demand, one important question for the retailers is whether they should provide 3D printing services in their brick-and-mortar store in addition to the traditional off-the-shelf product? If so, what should be the retailers pricing scheme to achieve a higher profit? What should be the optimal inventory level of off-the-shelf products? What is the optimal capacity of 3D printers? In this study, stochastic models are examined to capture the joint optimal 3D product price and capacity of 3D printers to maximize retailer’s expected profit while considering consumer product choices. Moreover, a stochastic model is developed to capture joint optimal pre-made inventory level and 3D product price to maximize retailer’s expected profit considering 3D services are offered in the off-the-shelf stock-out situations as a one-way substitution. Utilizing the Markov Decision Process, a framework for queuing systems is developed to examine the performance of various production/inventory strategies that optimize the system’s performance. Here, four strategies are developed: (i) providing only off-the-shelf products, (ii) providing only 3D printed products, (iii) substituting the shortage of the off-the-shelf products by 3D printed products, and (iv) providing consumers the options of selecting either the off-the-shelf product or the customized product produced by additive manufacturing. In essence, this approach assists decision makers in both capacity planning and inventory management. For all models, analytical results and numerical examples are given in order to demonstrate managerial insights

    IMPACT OF PTSD ON HCV/HIV RISK-REDUCTION INTERVENTIONS AMONG INCARCERATED DRUG-USING WOMEN IN RURAL APPALACHIA

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    Justice-involved women in rural Appalachian Kentucky are a particularly vulnerable group in need of targeted risk-reduction interventions for hepatitis C virus (HCV) and human immunodeficiency virus (HIV). Compared to women in the general U.S. population, justice-involved women in rural Appalachia report dramatically higher rates of HCV/HIV risk behaviors (e.g., injection drug use and risky sex), interpersonal violence (IV; e.g., physical, sexual, or emotional abuse), and posttraumatic stress disorder (PTSD). IV and PTSD may exacerbate rural Appalachian women’s risk for contracting and transmitting HIV/HCV, indicating a need to approach HCV/HIV risk-reduction interventions from a trauma-informed perspective. Brief motivational interviewing and psychoeducation interventions have both demonstrated efficacy in decreasing HCV/HIV risk behaviors among incarcerated women, including those with IV histories. Yet, few studies have considered the impact of PTSD on the effectiveness of these interventions. Therefore, this study aimed to examine the impact of PTSD on the effectiveness of HCV/HIV risk-reduction interventions administered to incarcerated rural Appalachian women with IV histories. Participants included a sample of 320 IV-exposed women who were enrolled in the Women’s Intervention to Stop HIV and HCV study. Women were randomized to receive an enhanced motivational interviewing-based HCV/HIV intervention or a standard HCV/HIV psychoeducational intervention while they were incarcerated. Women were then followed at 3, 6, and 12 months after being released into the community. Our findings indicate women’s change in HCV/HIV risk behavior after being released from jail did not differ based on whether they received a brief psychoeducation alone or enhanced with motivational interviewing while incarcerated. Moreover, PTSD symptoms were not associated with women’s change in injection drug or sexual risk behavior after community re-entry. PTSD symptoms trended toward decreasing more during re-entry for women who received a motivational-interviewing enhanced intervention compared to women who received psychoeducation alone, although this should be interpreted with caution. An unexpected finding was that anxiety and depressive symptoms prior to and during incarceration were associated with different trajectories of change in sexual, but not injection drug, risk behavior post-release. Results from this study address the call for evidence-based HCV/HIV interventions to be evaluated through a trauma-informed perspective and can inform targeted prevention and intervention efforts aimed at reducing HCV/HIV risk behaviors among rural Appalachian women

    A Review on Optimal Operation of Distributed Network Embedded to Wind-Battery Storage System

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    Energy is a vital requirement for today's socio-economic welfare and development. But due to the continuous increase of the demand the conventional energy resources are depleting day by day and on the verge of extinction. Hence more renewable generation units are emphasised to integrate to the power network to supply the required demand. This incorporation of the distributed generation into the distributed network has the advantages of controllability, flexibility and tremendous potential if it can be exploited properly. However, due to their intermittent and unpredictable nature, there is a need for energy storages to ensure continuous operations, i.e., to meet the load all the time. There are many possible options for energy storage, but the most popular and technologically sound option is battery storage. Along with this battery storage system (BSS), a power conditioning system (PCS) has to be connected for generation of both active and reactive power from the BSS which in turn increases the overall installation cost of BSS. Moreover, the energy storage cost is a function of the storage device power, energy capacities and their specific costs depending on the chosen technology of optimization. Thus, profit from those renewable energy producers have to be maximized, and losses are to be minimized by using dynamic optimization techniques. But along with the advantages there comes the complexities due to the inclusion of distributed generation and the additional energy storages in the power system network. Moreover, it is highly critical to operate the vast system optimally. Hence there are lots of research had been done or are in process for finding the proper approach of optimization of the system. This paper presents a review of the current state of the optimization methods applied to renewable and sustainable energy source embedded with the Energy storage for maximization of the revenue obtained from the power trading to the network

    Doubly-fed induction generator used in wind energy

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    Wound-rotor induction generator has numerous advantages in wind power generation over other generators. One scheme for wound-rotor induction generator is realized when a converter cascade is used between the slip-ring terminals and the utility grid to control the rotor power. This configuration is called the doubly-fed induction generator (DFIG). In this work, a novel induction machine model is developed. This model includes the saturation in the main and leakage flux paths. It shows that the model which considers the saturation effects gives more realistic results. A new technique, which was developed for synchronous machines, was applied to experimentally measure the stator and rotor leakage inductance saturation characteristics on the induction machine. A vector control scheme is developed to control the rotor side voltage-source converter. Vector control allows decoupled or independent control of both active and reactive power of DFIG. These techniques are based on the theory of controlling the B- and q- axes components of voltage or current in different reference frames. In this work, the stator flux oriented rotor current control, with decoupled control of active and reactive power, is adopted. This scheme allows the independent control of the generated active and reactive power as well as the rotor speed to track the maximum wind power point. Conventionally, the controller type used in vector controllers is of the PI type with a fixed proportional and integral gain. In this work, different intelligent schemes by which the controller can change its behavior are proposed. The first scheme is an adaptive gain scheduler which utilizes different characteristics to generate the variation in the proportional and the integral gains. The second scheme is a fuzzy logic gain scheduler and the third is a neuro-fuzzy controller. The transient responses using the above mentioned schemes are compared analytically and experimentally. It has been found that although the fuzzy logic and neuro-fuzzy schemes are more complicated and have many parameters; this complication provides a higher degree of freedom in tuning the controller which is evident in giving much better system performance. Finally, the simulation results were experimentally verified by building the experimental setup and implementing the developed control schemes

    A Review on Optimal Operation of Distributed Network Embedded to Wind-Battery Storage System

    Get PDF
    Energy is a vital requirement for today’s socio-economic welfare and development. But due to the continuous increase of the demand the conventional energy resources are depleting day by day and on the verge of extinction. Hence more renewable generation units are emphasised to integrate to the power network to supply the required demand. This incorporation of the distributed generation into the distributed network has the advantages of controllability, flexibility and tremendous potential if it can be exploited properly. However, due to their intermittent and unpredictable nature, there is a need for energy storages to ensure continuous operations, i.e., to meet the load all the time. There are many possible options for energy storage, but the most popular and technologically sound option is battery storage. Along with this battery storage system (BSS), a power conditioning system (PCS) has to be connected for generation of both active and reactive power from the BSS which in turn increases the overall installation cost of BSS. Moreover, the energy storage cost is a function of the storage device power, energy capacities and their specific costs depending on the chosen technology of optimization. Thus, profit from those renewable energy producers have to be maximized, and losses are to be minimized by using dynamic optimization techniques. But along with the advantages there comes the complexities due to the inclusion of distributed generation and the additional energy storages in the power system network. Moreover, it is highly critical to operate the vast system optimally. Hence there are lots of research had been done or are in process for finding the proper approach of optimization of the system. This paper presents a review of the current state of the optimization methods applied to renewable and sustainable energy source embedded with the Energy storage for maximization of the revenue obtained from the power trading to the network
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