22 research outputs found
Algorithms for passive dynamical modeling and passive circuit realizations
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 163-174).The design of modern electronic systems is based on extensive numerical simulations, aimed at predicting the overall system performance and compliance since early design stages. Such simulations rely on accurate dynamical models. Linear passive components are described by their frequency response in the form of admittance, impedance or scattering parameters which are obtained by physical measurements or electromagnetic field simulations. Numerical dynamical models for these components are constructed by a fitting to frequency response samples. In order to guarantee stable system level simulations, the dynamical models of the passive components need to preserve the passivity property (or inability to generate power), in addition to being causal and stable. A direct formulation results into a non-convex nonlinear optimization problem which is difficult to solve. In this thesis, we propose multiple algorithms that fit linear passive multiport dynamical models to given frequency response samples. The algorithms are based on convex relaxations of the original non-convex problem. The proposed techniques improve accuracy and computational complexity compared to the existing approaches. Compared to sub-optimal schemes based on singular value or Hamiltonian eigenvalue perturbation, we are able to guarantee convergence to the optimal solution within the given relaxation. Compared to convex formulations based on direct Bounded-Real (or Positive-Real) Lemma constraints, we are able to reduce both memory and time requirements by orders of magnitude. We show how these models can be extended to include geometrical and design parameters. We have applied our passive modeling algorithms and developed new strategies to realize passive multiport circuits to decouple multichannel radio frequency (RF) arrays, specifically for magnetic resonance imaging (MRI) applications. In a coupled parallel transmit array, because of the coupling, the power delivered to a channel is partially distributed to other channels and is dissipated in the circulators. This dissipated power causes a significant reduction in the power efficiency of the overall system. In this work, we propose an automated eigen-decomposition based approach to designing a passive decoupling matrix interfaced between the RF amplifiers and the coils. The decoupling matrix, implemented via hybrid couplers and reactive elements, is optimized to ensure that all forward power is delivered to the load. The results show that our decoupling matrix achieves nearly ideal decoupling. The methods presented in this work scale to any arbitrary number of channels and can be readily applied to other coupled systems such as antenna arrays.by Zohaib Mahmood.Ph. D
Fiber post: Physics, chemistry, adhesive properties, and its implications on root canal retreatment
No full textThis chapter covers a comprehensive knowledge about the variety of fiber-reinforced post systems and its implication on the root canal retreatment. When successful outcomes of endodontic treatment are considered, the selection of restorative material becomes a necessity. The objectives of this chapter are to deliver an understanding of chemistry, physics, and adhesive properties of fiber-reinforced posts, including carbon/glass/quartz and prefabricated fiber posts. Although the implications of fiber post on root canal retreatment possess some difficulties, such as post removal, etc.; it is still recommended over other post systems because of their physical and chemical characteristics which include the ideal modulus of elasticity, flexure strength similar to that of dentine; and their ever-evolving adhesive properties. Therefore, it qualifies as a “worthy choice” in endodontic practice when the procedure of retreatment is performed with clinical expertise. Furthermore, advancements in fiber posts system may help prevent the current and the remaining shortcomings
Determinants of Energy Inflation in Pakistan: An Empirical Analysis
No full textEnergy inflation has remained a significant topic in
macroeconomic policy for the past few decades. This is due to several
reasons pertaining to both demand and supply sides. In addition, the
history of energy prices has also been characterised by extreme
volatilities, Hamilton (2008). This makes forecasting and modelling of
energy prices difficult, nevertheless it is important to model and
forecast energy prices in all economies. In this paper we have tried to
identify the determinants of energy inflation in Pakistan. Energy
products are a critical component in any economy, serving as a core
input, particularly in manufacturing industries. Moreover, the demand
for energy and fuel comes from households fuelling cars and kitchens for
which other alternatives are not easily available. This renders the
demand inelastic compared to any other good [Edelstein and Kilian
(2009)], making economies vulnerable to supply and price shocks. The
energy price inflation therefore through cost push inflation and
demand-pull inflation has a major impact on core inflation itself,
thereby playing a significant role in macroeconomic health of a country.
As predicted by Ben Bernanke for the US in 2006, “in the long run energy
prices can reduce the productive capacity of US economy if high energy
costs make businesses less willing to invest new capital”. The nature of
the energy market itself creates a major gap between the oil consumers
and oil producers. Whilst demand is inelastic everywhere, supply is
limited and is difficult to increase, and confined to certain regions on
Earth. This is true particularly for two of the most common energy
types: oil and gasoline. The supply of oil is controlled by a few
countries, and supply shocks therefore lead to an immediate surge in
prices
Investigation of passive root flaps on HAWT: An experimental analysis of different configurations of root flaps on the performance of Horizontal Axis Wind Turbines
No full textPassive root flaps and in particular the Gurney flaps have been employed for improving aerodynamic characteristics for various applications since the 1970's. The effects of passive flaps on two dimensional airfoils have therefore been studied extensively, however, research on their application to Horizontal axis wind turbine blades (HAWT) is lacking and scarce. This research is a part of ongoing efforts at the Delft University of Technology to fill this missing gap. The blade of a HAWT is generally divided into three different regions for aerodynamic analyses. The region closest to the rotational axis is defined as the root region (r/R=0 - 0.3) . This region experiences the lowest rotational speeds and requires higher structural strength, resulting in a thick airfoil section. Although this section does not contribute significantly to the power generation of the whole turbine, the flow from this region does however effect the performance of the rest of the blade. Improving the aerodynamic flow characteristics of this region, therefore increases the performance of the whole turbine. For this research, passive (i.e. stationary) flaps were considered to enhance the flow at the root region and experimental analyses carried out at the Open Jet Facility (OJF) wind tunnel of TU Delft. An LM388 wind turbine blade (of Nordex N80 wind turbines) was used as a reference to create a scaled blade. The Analyses consisted of load (power and thrust) measurements and calculations for various flap configurations on a scaled wind turbine model. Furthermore, to understand how the flow is effected by the augmentation of flaps a Stereoscopic Particle Image Velocimetry (SPIV) was carried out for the most effective flap configuration and also no-flap configuration for the sake of comparison.Aerospace Engineering | Aerodynamics and Wind Energ
Wheat straw‐derived bio‐based hydroponic polyurethane foams for plant growth
No full textAgricultural waste is a renewable and sustainable resource that can be used as an alternative to petroleum for the production of chemicals and materials. In this study, liquefied wheat straw was used as bio-polyols to prepare bio-based hydroponic polyurethane (BHPU) foams. The effects of foam preparation variables, such as surfactants, catalysts, blowing agents and types of petroleum-based polyols (PPG 400 and/or VORANOL 280) on the properties of BHPU foam were investigated through single-factor experiments. Response surface methodology was applied to optimize the foam formula. The prepared BHPU foams with 40–50% (w/w) bio-polyols had an open cell content of 70–96%, a water absorption capacity of 594–1085% (w/w) and a water absorption time of 6–140 s. The potential of using the prepared BHPU foam as a plant growing medium was evaluated via mechanical testing, cell morphology, thermal stability, UV weathering testing and Phaseolus vulgaris (Linn.) cultivar Prelude and Glycine max (Linn.) Merr. seed germination tests. The wheat straw-derived BHPU foams demonstrated potential as a plant growth medium in horticulture
A preliminary exploration of ChatGPT’s potential in medical reasoning and patient care
No full textThis preliminary study evaluates ChatGPT-4o’s potential in enhancing medical reasoning and patient care by addressing a diverse set of thirty medical-related queries. The research investigates ChatGPT’s performance in generating reliable and contextually relevant medical responses, with a focus on general health and mental health considerations. Utilizing the Revised-IDEA (rIDEA) tool, responses were assessed based on interpretive summary, differential diagnosis, explanation of lead diagnosis, and alternative diagnoses, scored on a Likert scale from 0 to 10. High-quality documentation was determined by a cut-off score of ≥6. The study reveals ChatGPT-4o’s ability to provide accurate, clear, and comprehensive information on common medical issues such as the symptoms of the common cold versus the flu, heart attack diagnostics, treatment options for typhoid fever, and natural remedies for managing blood pressure. Additionally, it highlights ChatGPT-4o’s proficiency in mental health domains, identifying key risk factors for depression and suggesting effective mitigation strategies. The findings underscore ChatGPT-4o’s potential as a valuable tool for medical reasoning and patient care, while also emphasizing the need for validating AI-generated medical responses to ensure reliability and applicability in real-world healthcare settings
Existing interventions for the management of the Menstrual health and hygiene management for school-going and out-of-school adolescent girls in LMICs: A Scoping Review
No full textThe scoping review will be conducted to evaluate the existing interventions for the management of menstrual health and hygiene among the adolescent girls in Low and middle income countries
Perspective of Medical and Dental Undergraduates towards Complementary and Alternative Medicine
No full textABSTRACT
Background:
The prevalent use of complementary and alternative medicine (CAM) requires health professionals including doctors and dentists having the essential knowledge to have better recommend their patients. This has lead to an increased need for integration of CAM teaching at the undergraduate level. Thus, the purpose of the study was to assess the perspective of complementary and alternative medicine among Pakistani medical and dental undergraduates.
Methods:
A questionnaire based cross sectional survey was conducted among first to fifth year undergraduate medical and dental students at Sindh Medical College and Ziauddin University in Karachi, during April until May 2019, using a structured 13-item questionnaire. Descriptive statistics were calculated for baseline characteristics. Frequency and proportions were calculated for categorical variables using SPSS version 20.
Results:
The response rate was 100% (40.7% for males and 59.3% for females). The mean age of medical and dental students was 20.5±1.39 years. Almost three-fourth of students (75.1%) had the knowledgeof CAM. The most experienced CAM modality amongst all was Yoga (23.4%) and Homeopathy (20%). Nearly 69.4 % of students believed that CAM is beneficial for medical and dental healthcare and 44.1% students will recommend CAM to their patients in future. Almost 39% of students think that CAM should be included into undergraduate medical and dental curriculum.
Conclusion:
This study showed an encouraging interpretation of both medical and dental students regarding CAM knowledge and benefits. Majority of the students have optimistic attitude towards CAM practice in future and for the integration of CAM studies at undergraduate level
Bibliometric Review of Mental Health Research in Medical Colleges of Pakistan
No full textObjectives: Mental health is a less frequently explored area of medical research as both developing and developed countries lack competent human resources and funding for this purpose. Reviewing mental health research can help medical professionals appreciate the progress of understanding and identify problems in this area. This systematic review examined the status of mental health research carried out in medical education institutions and tertiary healthcare hospitals across Pakistan over the past 70 years. Methods: PubMed ® (National Library of Medicine, Bethesda, Maryland, USA), was searched for articles published between 1947 and 2017 related to mental health with an emphasis on the exclusive affiliation of the first author with a medical college in Pakistan. Results: A total of 118 articles were included in this study. The number of published research-based studies has increased steadily over the past years. However, there are indicators of a lack of quality research, such as no declaration of conflict of interest or the identification of a funding source and a general lack of publications in a journal with a high impact factor. Conclusion: The findings of this study have shown a steady improvement in the quantity and quality of mental health research conducted in Pakistani medical colleges/universities. However, a lack of funding, training and faculty induction policies may be hindering the establishment of a research culture and contributing to the slow progression of mental health research in Pakistan.Keywords: Medical Education; Mental Health; Research; Psychiatry in Literature; Pakistan
Prevalence and Predictors of Willingness and Attitudes towards Organ Donation among Medical and Non-Medical University Students in Karachi
No full textBackground: Even though organ transplants save thousands of lives globally, there exists a wide mismatch between an increasing demand for organ transplants and limited number of organ donors. The aim of the study was to assess the reasons and inspect differences between donors and non-donors in both students of medical and non-medical universities.
Methods: A cross-sectional study was conducted over a period of 6 months (May 2018-March 2021). Sample of 400 participants enrolled from three medical colleges, two business/social sciences institutions and one engineering university of Karachi. Categorical variables were compared using the Chi-squared test. Continuous variables were compared using a student t-test. Variables with a univariate p-value ≤ 0.10 were included in multiple logistic regression models. Adjusted odds ratio (OR) with 95% confidence interval were reported.
Results: With a very high response rate 383(96%) for knowledge about organ donation, a subdued response 201(52.3%) for willingness to donate. Most common source of knowledge regarding organ donation was social media 249(65%), followed by university 207(54%), family/friends 184(48%) and television 172(45%). Multiple logistic regression model identified being comfortable discussing organ donation as a positive predictor of willingness to donate (OR: 2.71, p=0.005), and the belief that organ donation disfigures the body as a negative predictor (OR: 0.40, p<0.001).
Conclusion: Attitude towards organ donation was not up to the mark among the participants (201/383=52.3%). Better knowledge may ultimately yield into the act of donation. Valuable measures should be taken to teach young people with significant information with the contribution of social media, institutions and families.
Keywords: Organ Donation; Donor Card; Organ Transplants; Ethics
