A Solar PV Based Multistage Grid Tie Inverter

The inherent advantage of fuel less and maintenance free energy production from solar photovoltaic makes it a very important source of energy. For harnessing power from the solar photovoltaic (PV) cell/array and to supply it to the utility grid, dc to ac inverters is needed. The conventional line commutated dc-to-ac inverter has square shaped line current which contains higher order harmonics whereas PWM based inverters employing IGBT/ MOSFET are less reliable and has low power handling capability. Moreover, a dc-to-dc converter is generally employed along with the inverter circuit to operate the solar PV array at maximum power point. It adds to the cost, which increases with the size of the system. This paper describes a multistage series converter topology for solar PV based grid tie inverter with low harmonic in line current and inbuilt maximum power point tracking (MPPT) features. The developed prototype has been experimentally tested and verified.Keywords: Multistage converter, Grid tie inverter, Maximum power point tracker (MPPT), Total harmonic distortion, photovoltaic system

Pulmonary talcosis 10 years after brief teenage exposure to cosmetic talcum powder.

Pulmonary talcosis is a rare but debilitating variant of pneumoconiosis often presenting with isolated non-specific symptoms of progressive exertional dyspnoea or cough. Occupational exposure to talc dust and intravenous drug abuse are well-recognised aetiological factors with only a few cases related to cosmetic talc exposure being reported to date. The authors report a case of a young woman in whom a mere 4 month ritual of inhaling cosmetic talcum powder led to full-blown pulmonary talcosis being diagnosed 10 years later. The importance of a taking a pertinent history relating to environmental exposures in all patients presenting with respiratory symptoms is re-established here

Comparison of Decompressive Craniectomy and Multi-Dural Stabs with Decompressive Craniectomy and Open-Dural Flap Method, in the Treatment of Acute Subdural Hematomas

Background: To compare the functional outcome between decompressive craniectomy and multi-dural stabs, with decompressive craniectomy and open-dural flap, in the removal of acute subdural hematomas . Methods : In this randomized controlled trial,  64 patients, with acute sub-dural hematomas were included.  Patients were divided into two groups on the basis of lottery method. All patients gave informed written consent. In group A, all patients were operated upon by multi-dural stab technique and in group B, patients were operated upon by open-dural flap technique. The objective degree of recovery in the patients treated by both craniectomy techniques was assessed by Glasgow Outcome Score (GOS), having maximum of 5 and minimum of 1 score. Favourable outcome was at points 4-5 and Un-favourable at 1-3 points, at 2 weeks. GOS attached as annexure A. Favourable outcome was assessed at 2 weeks according to GOS. Results : The mean age in group-A and group-B was 59.09 ± 9.39 years and 59.56 ± 9.98 years. Males constituted the main in both groups. Mean GOS in group A and in group B, was 3.06 ± 1.24 and 2.69 ± 0.82 respectively. Statistically mean GOS was same in this study groups, p-value 0.159, > 0.05. There were 37.5% patients in group A and 9.4% patients in group B who had favourable results, while in group A and group B, 62.5% and 90.60% patients had unfavourable results. Favourable results were statistically more in group A as compared to group B, p-value =0.008. Conclusion: Treatment of acute subdural hematoma by decompressive craniectomy with multi dural stabs technique has more favourable results (using GOS) than decompressive craniectomy with open-dural flap technique

Undetected common variable immune deficiency in a young adult of Pakistani descent.

Common variable immune deficiency (CVID) is a syndrome which is due to deficiency of humoral immune response resulting in increased susceptibility to infections We report a case of CVID in a 24-year-old male whopresented with a history of recurrent pneumonias

Outcome of Endoscopic Third Ventriculostomy

Background: To study the outcome of endoscopic third ventriculostomy (ETV)Methods: In this observational study an endoscopic third ventriculostomy was applied in patients who suffered from hydrocephaly. The diagnosis of hydrocephalus was determined by  physical, neurological and neuro-radiological criteria. Patients with obstructed hydrocephalus whether congenital or acquired, with a dilated 3rd ventricle were included. Linear incision was given 2cm anterior to the coronal suture in mid pupillary line. Right frontal burr hole is made. For ETV, burr hole is placed on a line joining the foramen of monro and inter-peduncular line. Floor of the thirdventricle was punctured close to or over the dorsum sellae. Membrane was dilated with balloon. Balloon was inflated and subsequently was taken out from puncture site. It ensured easy visibility of basilar artery and its perforators.Result: Age of patients ranged from 06 months to 24 years, with a mean age of 4 years . Fourteen patients had posterior fossa tumour’s with dilated third ventricle, sixty four patients had aqua ductal stenosis, two patients with CSF ascites as complication of ventriculo-peritoneal shunt, eleven patients had blocked lower end of ventriculoperitoneal shunt. Seven patients had CSF leak. Time taken to complete endoscopic third ventriculostomy was from 20 to 40 min as compared to 1 hour to 1.30 hours, taken in a VP shunt. Patients who had ETV performed had a mean hospital stay of 3 days, where as patients in whom a VP shunt was performed stayed in the ward for an average of 5 to 10 days, depending on how eventful the post op period was. The cost incurred to the VP shunt patient who remained admitted for an average of 5 days was between Rupees 16,000 to 25,000, ascompared to Rs: 2000 for the patient who underwent endoscopic third ventriculostomy.Conclusion: Patients of ETV, with less per operative time, had decreased length of stay. ETV also was less expensive to the patient and he did not have to buy the shunt apparatus with less rehospitalization rates, compared to patients who had undergone shunt

A Robust Multilevel Inverter Topology for Operation under Fault Conditions

Multilevel inverters (MLIs) are new demanding topologies that have low total harmonic distortion (THD) and low voltage stress across the switches make them ideal for medium and high-power applications. The authenticity of semiconductor devices is one of the main concerns for these MLIs to operate properly. With an increment in the number of switches in multilevel inverters, the pos-sibility of the fault also arises. Hence, a reliable 5- level inverter topology with fault-tolerant ability has been proposed. The proposed topology can withstand against of Open Circuit (OC) fault caused when any single switch fails. The proposed configuration is fault-tolerant and reliable as compared to the conventional multilevel inverters. Simulation of the proposed topology is done in MATLAB-Simulink and PLECS software packages, and the results obtained for normal (pre-fault), during the fault, and post-fault conditions are discussed. Experimental results also prove the proposed cell topology's robustness and effectiveness in tolerating OC faults across the switches. Furthermore, a thorough comparison is provided to demonstrate the superiority of the proposed topology in comparison to recently published topologies that have fault-tolerant featurespublishedVersio

A randomized, double-blind, placebo-controlled trial of oral montelukast in acute asthma exacerbation.

Background: Leukotriene receptor antagonists (LTRAs) are well established in the management of outpatient asthma. However, there is very little information as to their role in acute asthma exacerbations. We hypothesized that LTRAs may accelerate lung function recovery when given in an acute exacerbation. Methods: A randomized, double blind, placebo-controlled trial was conducted at the Aga Khan University Hospital to assess the efficacy of oral montelukast on patients of 16 years of age and above who were hospitalized with acute asthma exacerbation. The patients were given either montelukast or placebo along with standard therapy throughout the hospital stay for acute asthma. Improvements in lung function and duration of hospital stay were monitored. Results: 100 patients were randomized; their mean age was 52 years (SD +/− 18.50). The majority were females (79%) and non-smokers (89%). The mean hospital stay was 3.70 ± 1.93 days with 80% of patients discharged in 3 days. There was no significant difference in clinical symptoms, PEF over the course of hospital stay (p = 0.20 at day 2 and p = 0.47 at day 3) and discharge (p = 0.15), FEV1 at discharge (p = 0.29) or length of hospital stay (p = 0.90) between the two groups. No serious adverse effects were noted during the course of the study. Conclusion: Our study suggests that there is no benefit of addition of oral montelukast over conventional treatment in the management of acute asthma attack