Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Meaningful vocabulary practice in third grade reading,

Thesis (M.A.)--Boston Universit

The development and evaluation of exercises for meaningful responses in reading in grade two

Research chapter for this study will be found in Ash, Dorothea: "Development and evaluation of silent reading exercises in grade one" Thesis (M.A.)--Boston Universit

The development and evaluation of exercises in meaningful word practice in first grade,

Research chapter for this study will be found in Ash, Dorothea: "Development and evaluation of silent reading exercises in grade one" Thesis (M.A.)--Boston Universit

Knowledge-base black holes: the next (small) big thing?

Hydraulic EngineeringCivil Engineering and Geoscience

Real-time wavefront reconstruction from intensity measurements

We propose an efficient approximation to the nonlinear phase diversity method for wavefront reconstruction from intensity measurements. The new method, iterative linear phase diversity (ILPD), assumes that the residual phase aberration is small and makes use of a first order Taylor expansion of the point spread function (PSF) performed for an arbitrary (large) diversity in order to optimize the phase retrieval. For static aberrations, ILPD makes use of two images collected at each iteration of the algorithm. In each step, the residual phase aberrations are estimated by solving a linear least squares problem, followed by the use of a deformable mirror to correct for the aberrations. A further contribution of the paper is the extension of the static ILPD to the case of dynamic wavefront reconstruction for which a computationally efficient H2 controller is presented.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin

Can Clinical and Surgical Parameters Be Combined to Predict How Long It Will Take a Tibia Fracture to Heal? A Prospective Multicentre Observational Study: The FRACTING Study

Healing of tibia fractures occurs over a wide time range of months, with a number of risk factors contributing to prolonged healing. In this prospective, multicentre, observational study, we investigated the capability of FRACTING (tibia FRACTure prediction healING days) score, calculated soon after tibia fracture treatment, to predict healing time. Methods: The study included 363 patients. Information on patient health, fracture morphology, and surgical treatment adopted were combined to calculate the FRACTING score. Fractures were considered healed when the patient was able to fully weight-bear without pain. Results: 319 fractures (88%) healed within 12 months from treatment. Forty-four fractures healed after 12 months or underwent a second surgery. FRACTING score positively correlated with days to healing: r = 0.63 (p < 0.0001). Average score value was 7.3 ± 2.5; ROC analysis showed strong reliability of the score in separating patients healing before versus after 6 months: AUC = 0.823. Conclusions: This study shows that the FRACTING score can be employed both to predict months needed for fracture healing and to identify immediately after treatment patients at risk of prolonged healing. In patients with high score values, new pharmacological and nonpharmacological treatments to enhance osteogenesis could be tested selectively, which may finally result in reduced disability time and health cost savings

Tracking the evolution of hospice palliative care in Canada: A comparative case study analysis of seven provinces

<p>Abstract</p> <p>Background</p> <p>An aging population, rise in chronic illnesses, increase in life expectancy and shift towards care being provided at the community level are trends that are collectively creating an urgency to advance hospice palliative care (HPC) planning and provision in Canada. The purpose of this study was to analyze the evolution of HPC in seven provinces in Canada so as to inform such planning and provision elsewhere. We have endeavoured to undertake this research out of awareness that good future planning for health and social care, such as HPC, typically requires us to first look backwards before moving forward.</p> <p>Methods</p> <p>To identify key policy and practice events in HPC in Canada, as well as describe facilitators of and barriers to progress, a qualitative comparative case study design was used. Specifically, the evolution and development of HCP in 7 strategically selected provinces is compared. After choosing the case study provinces, the grey literature was searched to create a preliminary timeline for each that described the evolution of HPC beginning in 1970. Key informants (<it>n </it>= 42) were then interviewed to verify the content of each provincial timeline and to discuss barriers and facilitators to the development of HPC. Upon completion of the primary data collection, a face-to-face meeting of the research team was then held so as to conduct a comparative study analysis that focused on provincial commonalities and differences.</p> <p>Results</p> <p>Findings point to the fact that HPC continues to remain at the margins of the health care system. The development of HPC has encountered structural inheritances that have both sped up progress as well as slowed it down. These structural inheritances are: (1) foundational health policies (e.g., the Canada Health Act); (2) service structures and planning (e.g., the dominance of urban-focused initiatives); and (3) health system decisions (e.g., regionalization). As a response to these inheritances, circumventions of the established system of care were taken, often out of necessity. Three kinds of circumventions were identified from the data: (1) interventions to shift the system (e.g., the role of advocacy); (2) service innovations (e.g., educational initiatives); and (3) new alternative structures (e.g., the establishment of independent hospice organizations). Overall, the evolution of HPC across the case study provinces has been markedly slow, but steady and continuous.</p> <p>Conclusions</p> <p>HPC in Canada remains at the margins of the health care system. Its integration into the primary health care system may ensure dedicated and ongoing funding, enhanced access, quality and service responsiveness. Though demographics are expected to influence HPC demand in Canada, our study confirms that concerned citizens, advocacy organizations and local champions will continue to be the agents of change that make the necessary and lasting impacts on HPC in Canada.</p

A comparison of word analysis ability and spelling achievement of 562 sixth grade children

Thesis (M.A.)--Boston Universit