An improved modeling method to determine the model parameters of photovoltaic (PV) modules using differential evolution (DE)

To accurately model the PV module, it is crucial to include the effects of irradiance and temperature when computing the value of the model parameters. Considering the importance of this issue, this paper proposes an improved modeling approach using differential evolution (DE) method. Unlike other PV modeling techniques, this approach enables the computation of model parameters at any irradiance and temperature point using only the information provided by the manufacturer’s data sheet. The key to this improvement is the ability of DE to simultaneously compute all the model parameters at different irradiance and temperature. To validate the accuracy of the proposed model, three PV modules of different types (multi-crystalline, mono-crystalline and thin-film) are tested. The performance of the model is evaluated against the popular single diode model with series resistance Rs. It is found that the proposed model gives superior results for any irradiance and temperature variations. The modeling method is useful for PV simulator developers who require comprehensive and accurate model for the PV module

Conflict-free graph orientations with parity constraints

It is known that every multigraph with an even number of edges has an even orientation (i.e., all indegrees are even). We study parity constrained graph orientations under additional constraints. We consider two types of constraints for a multigraph G=(V,E): (1) an exact conflict constraint is an edge set C in E and a vertex v in V such that C should not equal the set of incoming edges at v; (2) a subset conflict constraint is an edge set C in E and a vertex v in V such that C should not be a subset of incoming edges at v. We show that it is NP-complete to decide whether G has an even orientation with exact or subset conflicts, for all conflict sets of size two or higher. We present efficient algorithms for computing parity constrained orientations with disjoint exact or subset conflict pairs.Comment: To appear, Sixth International Conference on Fun with Algorithms, June 4-6, 2012; 15 pages, 6 figure

Quantum Smearing in Hybrid Inflation with Chaotic Potentials

We study the impact of one-loop radiative corrections in a non-supersymmetric model of hybrid inflation with chaotic (polynomial-like) potential, $V_0 + \lambda_p \phi^p$. These corrections can arise from the possible couplings of inflaton with other fields which may play active role in the reheating process. The tree-level predictions of these models are shown to lie outside of the Planck's latest bounds on the scalar spectral index $n_s$ and the tensor to scalar ratio $r$. However, the radiatively corrected version of these models, $V_0 + \lambda_p \phi^p + A \phi^4 \ln \phi$, is fully consistent with the Planck's data. More specifically, fermionic radiative correction ($A<0$) reduces the tensor to scalar ratio significantly and a red-tilted spectral index $n_s<1$, consistent with Planck's data, is obtained even for sub-Planckian field-values.Comment: 14 pages, 25 figures (typos fixed

Depression and its associated risk factors in medical and surgical post graduate trainees at a teaching hospital: a cross sectional survey from a developing country

Objectives: To determine the frequency of depression among post graduate medical trainees in a teaching hospital of Pakistan and to explore the associated factors contributing to depression in them. Methods: It\u27s a cross-sectional study at the Aga Khan University Hospital, Karachi. It was done in June 2008 till August 2008. Zung Self-Rating Depression Scale was administered among 172 post graduate trainees. Self administered questionnaires were used to assess the associated demographic and work related risk factors. Adjusted odds ratios (OR) were calculated by logistic regression. Results: The survey response rate was 172(82.69%). Depression in the overall sample was 103(59.88%), of which 58(33.66%) were moderate to markedly depressed. Multiple logistic regression analysis revealed that working hours less than 76 hours (OR 3.71; CI=1.67, 8.23) and 76-90 hours (OR 3.15; CI= 1.42, 6.97) and none or occasional peer support (OR 2.05; CI=1.01, 4.18) were independent predictors for depression among the post graduate trainees. Conclusion: More than half of our sample population was depressed. Therefore, they should be encouraged to recognize and seek treatment. This study also indicates that less working hours and lack of peer support cause depression

A study protocol : using demand-side financing to meet the birth spacing needs of the underserved in Punjab Province in Pakistan

Background: High fertility rates, unwanted pregnancies, low modern contraceptive prevalence and a huge unmet need for contraception adversely affect women's health in Pakistan and this problem is compounded by limited access to reliable information and quality services regarding birth spacing especially in rural and underserved areas. This paper presents a study protocol that describes an evaluation of a demand-side financing (DSF) voucher approach which aims to increase the uptake of modern contraception among women of the lowest two wealth quintiles in Punjab Province, Pakistan. Methods/Design: This study will use quasi-experimental design with control arm and be implemented in: six government clinics from the Population Welfare Department; 24 social franchise facilities branded as `Suraj' (Sun), led by Marie Stopes Society (a local non-governmental organization); and 12 private sector clinics in Chakwal, Mianwali and Bhakkar districts. The study respondents will be interviewed at baseline and endline subject to voluntary acceptance and medical eligibility. In addition, health service data will record each client visit during the study period. Discussion: The study will examine the impact of vouchers in terms of increasing the uptake of modern contraception by engaging private and public sector service providers (mid-level and medical doctors). If found effective, this approach can be a viable solution to satisfying the current demand and meeting the unmet need for contraception, particularly among the poorest socio-economic group

An improved optimization technique for estimation of solar photovoltaic parameters

The nonlinear current vs voltage (I-V) characteristics of solar PV make its modelling difficult. Optimization techniques are the best tool for identifying the parameters of nonlinear models. Even though, there are different optimization techniques used for parameter estimation of solar PV, still the best optimized results are not achieved to date. In this paper, Wind Driven Optimization (WDO) technique is proposed as the new method for identifying the parameters of solar PV. The accuracy and convergence time of the proposed method is compared with results of Pattern Search (PS), Genetic Algorithm (GA), and Simulated Annealing (SA) for single diode and double diode models of solar PV. Furthermore, for performance validation, the parameters obtained through WDO are compared with hybrid Bee Pollinator Flower Pollination Algorithm (BPFPA), Flower Pollination Algorithm (FPA), Generalized Oppositional Teaching Learning Based Optimization (GOTLBO), Artificial Bee Swarm Optimization (ABSO), and Harmony Search (HS). The obtained results clearly reveal that WDO algorithm can provide accurate optimized values with less number of iterations at different environmental conditions. Therefore, the WDO can be recommended as the best optimization algorithm for parameter estimation of solar PV

Breaking bad news: exploring patient\u27s perspective and expectations

OBJECTIVE: To explore patient\u27s perspectives and expectations from physicians with respect to breaking of bad news. METHODS: A cross-sectional survey was carried out in the Community Health Centre of a tertiary care teaching hospital in Pakistan. All consenting individuals from 18 to 60 years of age were interviewed on the basis of a structured, pre-tested questionnaire. RESULTS: The response rate for this study was 91.3%. A total of 400 respondents completed the full interview. About 60% patients had a fairly accurate idea about the implications of the phrase bad news . A big proportion (44.1%) of people reported that bad news had been broken to them previously with incomplete details. From their personal experience, most respondents quoted disease diagnosis and chances of survival as most commonly encountered bad news. Diagnosis of cancer or its recurrence was stated as the most likely example of bad news (35.5%). A significant majority of respondents (40.5%) stated that it\u27s the patient\u27s absolute right to know bad news. A significant association for the relationship between both age as well as the gender of the respondents and type of emotional response expressed on hearing bad news (p = 0.000) was observed. CONCLUSION: This study documents the perceptions and expectations of patients from their physicians with regards to breaking of bad news. Most of the respondents wanted their doctors to be honest and upfront during the process