Operative Candidates Research Articles

FPGA-Based Space Vector Modulation of an Indirect Matrix Converter

The insertion of powers sources onto the grid require an energy processing stage between generator and electrical grid, which adapts amplitude and frequency levels for alternating current (AC) quantities. The Indirect Matrix Converter is a candidate for such operation, although one of the greatest challenges of the topology lies in a way to command the switches while controlling the structure power-flow, as well as the synchronism between source–converter and converter–grid. Hence this paper presents a different view on the converter modelling and proposes a FPGA-based method to perform the Space Vector Modulation (SVM) and synchronism algorithms minimizing the resource consumption, focusing on digital processing algorithms and resource sharing to reduce resource consumption and the number of multipliers employed, ideal for implementation in low-cost FPGAs. Experimental results are shown using a prototype, demonstrating the efficacy of the implementation and verifying the converter behaviour.

Broadband infrared reflective surfaces using doped and stacked polar dielectric layers

Polar dielectrics, such as SiC, are excellent candidates for operation in extreme environments due to their excellent mechanical and thermal properties. In addition, they can achieve good IR reflection in the Reststrahlen band. However, these materials have relatively narrow spectral bandwidth for reflection, especially considering that the broadband illumination sources in extreme environments. In this study, we investigated the broadband reflection properties of polar dielectrics by engineering the Reststrahlen band through doping and stacked layers. Our results indicate that by doping polar dielectrics, spectral reflection bandwidth can be significantly broadened. In addition, we demonstrate that by stacking different polar dielectric layers, the reflection spectrum of different materials can be overlapped, and thereby, significantly broader spectrum is obtained.

Magnetic resonance with diffusion-weighted imaging improves assessment of focal liver lesions in patients with potentially resectable pancreatic cancer on CT.

To investigate added value of MRI to preoperative staging MDCT for evaluation of focal liver lesions (FLLs) in potentially resectable pancreatic ductal adenocarcinomas (PDACs). In patients with potentially resectable PDACs after staging MDCT (n=167), characteristics of FLLs were scored as benign, indeterminate or metastases on an MDCT set and combined MDCT and MRI set by two readers, independently. Size of hepatic lesions was measured and detection rate of hepatic metastasis unsuspected by MDCT and diagnostic yield of MRI for FLLs were assessed. Reader-averaged figure-of-merit (FOM) of the combined set was significantly higher than that of MDCT alone (0.94 vs. 0.86, p=.028). In the negative-on-CT group, the diagnostic yield of MRI was 1.5-2.3% (2/133 and 3/133 for readers 1 and 2, respectively). In the indeterminate-on-CT group, MRI yield was 10.5-13.6% (2/19 and 3/22) and in patients with suspicious-metastasis-on-CT, 8.3-26.7% (1/12 and 4/15). All lesions with false-positive and false-negative CT findings were ≤1 cm. In potentially resectable PDACs, addition of MRI with DWI can provide significantly better diagnostic performance in characterization of focal liver lesions, especially for small-sized (≤ 1 cm) MDCT-indeterminate or suspicious metastasis lesions, aiding in determination of appropriate operation candidates. • Addition of MRI provides better diagnostic performance in characterization of liver lesions. • Combined interpretation of MRI and MDCT provided less frequent indeterminate liver lesions. • Diagnostic yield of MRI was high in CT-indeterminate or suspicious metastatic lesions. • Operation candidates can be determined with greater confidence in potentially resectable PDACs.

Femoral Neck Stress Injuries: Analysis of 156 Cases in a U.S. Military Population and Proposal of a New MRI Classification System.

The objective of this study is to formulate a new MRI classification system for fatigue-type femoral neck stress injuries (FNSIs) that is based on patient management and return-to-duty (RTD) time. A retrospective review of 156 consecutive FNSIs in 127 U.S. Army soldiers over a 24-month period was performed. The width of marrow edema for low-grade FNSIs and the measurement of macroscopic fracture as a percentage of femoral neck width for high-grade FNSIs were recorded. RTD time was available for 90 soldiers. Nonparametric testing, univariate linear regression, and survival analysis on RTD time were used in conjunction with patient management criteria to develop a new FNSI MRI classification system. The FNSI incidence was 0.09%, and all FNSIs were compressive-sided injuries. RTD time was significantly longer for high-grade FNSIs versus low-grade FNSIs (p < 0.001). Our FNSI MRI classification system showed a significant difference in RTD time between grades 1 and 2 (p = 0.001-0.029), 1 and 3 (p < 0.001), and 1 and 4 (p = 0.001-0.01). There was no significant RTD time difference between the remaining grades. The rates of completing basic training (BT) and requiring medical discharge were significantly associated with the FNSI MRI grades (p = 0.038 and p = 0.001, respectively). The proposed FNSI MRI classification system provides a robust framework for patient management optimization by permitting differentiation between operative and nonoperative candidates, by allowing accurate prediction of RTD time, and by estimating the risk of not completing BT and requiring medical discharge from the military.

Successful creation of pancreatic cancer organoids by means of EUS-guided fine-needle biopsy sampling for personalized cancer treatment

Pancreatic cancer organoids are tumor models of individualized human pancreatic ductal adenocarcinoma (PDA), created from surgical specimens and used for personalized treatment strategies. Unfortunately, most patients with PDA are not operative candidates. Creation of human PDA organoids at the time of initial tumor diagnosis is therefore critical. Our aim was to assess the feasibility of creating human PDA organoids by EUS fine-needle biopsy (EUS-FNB) sampling in patients with PDA. In this prospective clinical trial in patients referred to evaluate a pancreatic mass, EUS-FNA was performed for initial onsite diagnosis. Two additional needle passes were performed with a 22-gauge FNB needle for organoid creation. Primary outcome was successful isolation of organoids within 2 weeks of EUS-FNB sampling (P0, no passages), confirmed by organoid morphology and positive genotyping. Thirty-seven patients with 38 PDA tumors were enrolled. Successful isolation of organoids (P0) was achieved in 33 of 38 tumors (87%). Establishment of PDA organoid lines for≥5 passages of growth (P5, five passages) was reached in 25 of 38 tumors (66%). In the single patient with successful P5 FNB sampling-derived and P5 surgically derived organoids, there was identical matching of specimens. There were no serious adverse events. Two patients developed bleeding at the EUS-FNB puncture site requiring hemostasis clips. Pancreatic cancer organoids can be successfully and rapidly created by means of EUS-FNB sampling using a 22-gauge needle at the time of initial diagnosis. Successful organoid generation is essential for precision medicine in patients with pancreatic cancer in whom most are not surgically resectable. (Clinical trial registration number: NCT03140592.).

Management of acute upper gastrointestinal bleeding

The medical management of patients with acute upper gastrointestinal bleeding includes both diagnostic and therapeutic procedures. Emergency or early endoscopy has greatly improved the diagnosis, but it has not yet changed the therapeutic approach very much. The main emphasis is still on close observation of the patients in order to give blood transfusions when necessary and to identify those who need urgent operation. Most patients stop bleeding spontaneously, but the frequency of rebleeding is high. Patients with continuous bleeding or rebleeding are candidates for emergency operation. Much effort has been made to prevent rebleeding because, if the patients can be operated on electively, the frequency of complications is lower and vagotomy may be preferable to resection. Several medical treatments including antacids, H2-receptor antagonists, pepsin inhibitors and specific antifibrinolytic agents have been tried, but their value is still sub judice. Curiously, methods of treatment that are clearly effective in healing peptic ulcers seem less effective in preventing rebleeding from eroded vessels within such ulcerations.

Additional Cardiac Remodeling Induced by Intense Military Training in Competitive Athletes

Abstract Background: Cardiac remodeling depends on the intensity, duration, and training method. Objective: To evaluate if the training performed in a Portuguese military special operations troop increases cardiac remodeling in a sample of young individuals who previously practiced competitive sports. Methods: A prospective study involving 76 military candidates for military special operations, 45 of whom previously practiced at competitive level (> 10 hours per week). Of these military athletes, only 17 successfully completed the course. The evaluation was performed at 6 months intervals and included a complete clinical history, physical examination, vital signs, anthropometric data and echocardiographic evaluation. Statistical significance was considered when p < 0.05, with a 95% confidence interval. Results: At the end of the course, there was a decrease in the percentage of fat mass (19.1 ± 3.3% vs. 13.1 ± 3.5%; p < 0.01), an increase in the percentage of lean mass (41.3 ± 2.1% vs. 44.4 ± 1.8%; p < 0.01), and decreased systolic and diastolic blood pressure and heart rate. Regarding cardiac remodeling, there was an increase in left ventricular diastolic diameter (49.7 ± 3.2 mm vs. 52.8 ± 3.4 mm; p < 0.01), an increase trend in left atrial volume (27.3 ± 4.5 mL/m2 vs. 28.2 ± 4.1 mL/m2; p = 0.07) and increased left ventricular mass (93.1 ± 7.7 g/m2 vs. 100.2 ± 11.4 g/m2; p < 0.01). Functional variables also changed, with an increase in S' (15 (13-16) cm/s vs. 17 (16-18) cm/s; p < 0,01) and a decrease in left ventricular ejection fraction (60 ± 6% vs. 54 ± 6%; p < 0.01). Conclusion: Intense military physical training resulted in additional cardiac remodeling in athletes of competitive level, both structural and functional.

Clinico-Radiographic Discordance: An Evidence-Based Commentary on the Management of Degenerative Cervical Spinal Cord Compression in the Absence of Symptoms or With Only Mild Symptoms of Myelopathy.

Study Design:Narrative review with commentary.Objectives:The growing use of magnetic resonance imaging (MRI) often leaves clinicians faced with scenarios where imaging findings are inconsistent with the clinical picture. This is particularly relevant for degenerative cervical spinal cord compression (CSCC). In this article, we provide a focused narrative literature review to address whether (1) surgery should be offered to asymptomatic patients with CSCC and (2) should MRI spinal cord signal changes influence clinical decisions for a patient with mild myelopathy from CSCC?Methods:Illustrative cases are presented with expert commentary which is supplemented by a focused literature review.Results:The literature suggests that CSCC from degenerative pathology is a common incidental radiographic finding. For those without symptoms of myelopathy, the short-term risk of progression is low. There is a lack of evidence to support surgery for asymptomatic individuals with CSCC who have no risk factors for progression. For these patients, the authors suggest non-operative management that includes education on the symptoms of myelopathy, clinical follow-up within 6 to 12 months, and avoidance of high-risk activities. Conversely, symptomatic patients have a notable risk of progression. Surgical intervention improves neurological function and quality of life regardless of severity. The authors support surgery as an option for all patients with mild myelopathy who are appropriate operative candidates. Intramedullary signal change on MRI has not been shown to reliably predict progression.Conclusions:While MRI technologies are under evolution, we advise that surgical decisions for patients with CSCC should rely on clinical assessment and not imaging findings.

Factors Affecting the Surgical Outcome in Extradural Hematoma in Punjab Institute of Neurosciences, Lahore, Pakistan

Head injury is a leading cause of death in young age group. Extra Dural hematoma, a complication of head injury, is often fatal if not treated in time. The surgical outcome of EDH is dependent upon many variables including preoperative GCS, time between injury and surgery, associated intracranial injuries, anisocoria and hematoma volume. In order to reduce the mortality near to nil, it is essential to determine the magnitude of effect of affecting factors on surgical outcome which will also help us in preoperative counseling and prioritizing the operative candidates. This study was conducted determine the factors affecting surgical outcome of traumatic intracranial extradural Hematoma in Punjab Institute of Neurosciences/ Lahore general hospital, Lahore. It was a Cross sectional study conducted for 3 years from 28th May 2012 to 28th May 2015.The study was conducted on the patients admitted through emergency and diagnosed as Extramural hematoma. These patients underwent surgical evacuation of EDH on emergent basis and outcome was measured by Glasgow Outcome Scale (GOS) after 48 hours of surgery. Using GOS, good surgical outcome was observed in 80.9% (157 out of 194) patients. Preoperative GCS, anisocoria, hematoma volume, associated intracranial injuries and time between injury and surgery were the factors affecting the outcome significantly (p value=0.000) while age and sex of the patient had no significant effect. In Conclusion, good surgical outcome is associated with patients with solitary Extra Dural Hematoma of volume less than 60 ml, preoperative GCS more than 8, absence of anisocoria and undergoing surgical evacuation within 6 hours of injury. Nepal Journal of Neuroscience, Volume 14, Number 3, 2017, Page: 13-18

An approach to identify the optimal configurations and reconfiguration processes for design of reconfigurable machine tools

A reconfigurable machine tool (RMT) is a special machine that can deliver different machining functions through reconfiguration processes among its configurations during the machine utilisation stage. In this research, a new approach is developed to identify the optimal configurations and the reconfiguration processes for design of the RMTs. In this work, a generic design AND-OR tree is used to model different design solution candidates, their machine configurations and parameters of these configurations. A specific design solution is created from the generic design AND-OR tree through tree-based search and modelled by different machine configurations. For a reconfiguration process between two machine configurations, a generic process AND-OR graph is used to model reconfiguration operation candidates, sequential constraints among operations and operation parameters. A graph-based search is used to generate all feasible reconfiguration process candidates from the generic process AND-OR graph. The optimal design is identified by multi-level and multi-objective hybrid optimisation. A case study is developed to show how this new approach is used for the optimal design of a RMT.

Crystal growth, polarized spectroscopy and Judd-Ofelt analysis of Pr:YAlO3

Pr3+-doped YAlO3 (YAP) single crystal was successfully grown by the Czochralski (Cz) method. Polarized absorption and polarized fluorescence spectra were measured at the room temperature. The spectroscopic parameters based on the polarized absorption spectra were calculated by Judd-Ofelt (J-O) theory for the first time. The fluorescence lifetime of 3P0 energy level was fitted to be 19.16μs with the quantum efficiency of 95.8%. Through the analyzing of the spectroscopic properties, Pr:YAP crystal was demonstrated to be a promising candidate for solid state laser operation.

Investigation of impurity confinement in lower hybrid wave heated plasma on EAST tokamak

The transient perturbation method with metallic impurities such as iron (Fe, Z = 26) and copper (Cu, Z = 29) induced in plasma-material interaction (PMI) procedure is used to investigate the impurity confinement characters in lower hybrid wave (LHW) heated EAST sawtooth-free plasma. The dependence of metallic impurities confinement time on plasma parameters (e.g. plasma current, toroidal magnetic field, electron density and heating power) are investigated in ohmic and LHW heated plasma. It is shown that LHW heating plays an important role in the reduction of the impurity confinement time in L-mode discharges on EAST. The impurity confinement time scaling is given as on EAST, which is close to the observed scaling on Tore Supra and JET. Furthermore, the LHW heated high-enhanced-recycling (HER) H-mode discharges with ~25 kHz edge coherent modes (ECM), which have lower impurity confinement time and higher energy confinement time, provide promising candidates for high performance and steady state operation on EAST.

Chronic Thromboembolic Pulmonary Hypertension: Advances in Therapy.

AbstractChronic thromboembolic pulmonary hypertension is a progressive disease characterized by obstruction of the pulmonary vascular bed by insufficient resolution of thromboemboli leading to increased pulmonary vascular resistance with resultant right heart dysfunction and poor long-term survival. Estimates of cumulative incidence after an acute pulmonary embolism range from 1 to 4% within 2 years of an initial event. Current recommendations focus on screening patients being evaluated for pulmonary hypertension with ventilation/perfusion scans and then considering them for potentially curative surgery consisting of a pulmonary endarterectomy. Outcomes at high-volume surgical centers continue to improve and overall perioperative mortality is close to 2 to 4% with excellent reported long-term survival. Unfortunately, adherence with guidelines remains poor and patients with this potentially remediable disease are being missed. In addition, a significant number of patients who are diagnosed are not felt to be operative candidates based on location of disease, hemodynamics, or comorbidities. Several new advances may improve outcomes for such patients who are not operative candidates or who have persistent pulmonary hypertension after surgery, including medical therapy and balloon pulmonary angioplasty. Further studies are needed to answer questions about how best to incorporate these advances into our overall treatment algorithm.

A Novel MRI-Based Classification System for Tibial Eminence Fractures in Pediatric Patients: An Improvement from Meyers and McKeever?

The most common system for classifying pediatric tibial spine fractures is based on X-Rays. We propose an MRI-based system. Our results show a moderate intra-rater and fair inter-rater reliability of the new system. In 1/3 of our cases, assessment using MRI substantially modified the treatment. This new system may be a helpful tool for planning the treatment of tibial spine fractures in children. The Meyers and McKeever Classification (MMC) is typically used to classify pediatric tibial spine fractures on plain radiographs. While MRI images can provide important information about the fractures, there is currently no system for classifying these fractures on MRI. The aims of this study were: (1) propose a new MRI-based system for classifying tibial spine fractures and (2) assess how often using an MRI-based system changes the treatment plan compared to the MMC, which is based on X-Rays. Our hypothesis is that an MRI-based system allows for more precise identification and treatment of tibial spine fractures. The new MRI-based system has three grades.-Grade I fractures are defined as non- or minimally-displaced fractures with < 2 mm of displacement.-Grade II fractures are posterior-hinged fractures with > 2 mm displacement of the anterior aspect of the fracture and < 2 mm displacement of the posterior aspect of the fragment.-Grade III fractures are displaced fractures (> 2 mm of displacement of the posterior aspect of the fragment), any tibial spine fracture that results in meniscal entrapment (where the meniscus or intra-meniscal ligament is underneath a fracture fragment), or any tibial spine fracture extending to the weight-bearing surface of the medial or lateral tibial plateau with > 2 mm of displacement. We considered three scenarios as “changes in treatment”: when use of the MRI-system (1) allowed raters to identify a fracture that had been graded as “no fracture” using X-Rays, (2) changed the treatment from non-operative to operative, and (3) changed the treatment from operative to non-operative. The number of cases that experienced a change was reported as raw counts and percentages. Four independent observers (one attending orthopaedic surgeon, one attending radiologist, a senior orthopaedic surgery resident, and a junior orthopaedic surgery resident) classified the images of 20 patients according to the MMC using plain X-Rays. Each observer graded images at two time points at least one week apart. Next, raters repeated their assessments on MRIs using the MRI-based system. The inter-rater and intra-rater reliability of each system was assessed (Stata 14.0 software). Based on the Altman threshold, there was moderate intra-rater correlation between the observers when using MRI-based classification (avg = 0.60; range = 0.45-0.75) and a fair inter-rater correlation (k = 0.33). Following the evaluation of MRIs with the new system, we observed “changes in treatment” in 33% (26 of 80) of grades after the first grading and 34% (27 of 80) after the second compared to the initial evaluation using X-Rays. In 11 grades (20%), MRI recognized previously unnoticed fractures; in 21 grades (40%), MRI assessment upgraded the lesion to operative treatment; in 21 grades (40%) formerly operative candidates were re-assigned to conservative treatment. There is moderate intra-rater and fair inter-rater reliability of the new system. In one third of the cases, assessment using MRI substantially modified the treatment recommendations. This MRI-based system may become a helpful tool for diagnosing and planning the treatment of tibial spine fractures in children.

Bronchoscopic management of prolonged air leak.

Bronchopleural fistula (BPF) with prolonged air leak (PAL) is most often, though not always, a sequela of lung resection. When this complication occurs post-operatively, it is associated with substantial morbidity and mortality. Surgical closure of the defect is considered the definitive approach to controlling the source of the leak, but many patients with this condition are suboptimal operative candidates. Therefore there has been active interest for decades in the development of effective endoscopic management options. Successful use of numerous bronchoscopic techniques has been reported in the literature largely in the form of retrospective series and, at best, small prospective trials. In general, these modalities fall into one of two broad categories: implantation of a device or administration of a chemical agent. Closure rates are high in published reports, but the studies are limited by their small size and multiple sources of bias. The endoscopic procedure currently undergoing the most systematic investigation is the placement of endobronchial valves. The aim of this review is to present a concise discussion on the subject of PAL and summarize the described bronchoscopic approaches to its management.

Pressure-retarded osmosis with wastewater concentrate feed: Fouling process considerations

Pressure-retarded osmosis (PRO) has attracted worldwide attention for its potential applications in renewable osmotic energy harvesting, low energy seawater desalination, and industrial waste brine disposal. However, membrane fouling is one of the major issues limiting PRO performance with the use of a high-salinity draw solution and a low-value impaired feedwater. This study systematically investigated membrane fouling in the PRO process using a real wastewater retentate (a waste byproduct from wastewater reclamation plants) as the PRO feed. Organic fouling (e.g., by humic substances) and inorganic fouling (e.g., by calcium phosphate) were identified to be the major types of fouling, where the latter dominated the overall water-flux decline. The internal PRO membrane fouling was exacerbated by internal concentration polarization (ICP) and intermolecular interactions between the organic macromolecules and the scaling precursor ions (e.g., Ca2+). A limiting flux that was independent of the initial flux (i.e., applied pressure) was observed during the PRO fouling and was explained by a novel PRO limiting flux model. A membrane with a smaller structural parameter could achieve a higher limiting flux in PRO. A simple and effective pressure-assisted osmotic backwashing protocol was developed to clean the internally fouled membrane that could restore over 92% of the water flux within a short cleaning period (15mins). The PRO performance could also be significantly improved by decreasing the feedwater pH that mitigated alkaline scaling. Finally, performing the PRO membrane fouling test in the active-layer-facing-feed-solution (AL-FS) orientation revealed that the integral cellulose triacetate (CTA) membrane exhibited strong mechanical stability and anti-fouling tendency whereas the thin-film composite (TFC) membrane was not mechanically stable in this orientation. This study for the first time identified that an integral membrane instead of a TFC membrane is an excellent candidate for PRO operation in the AL-FS mode for fouling control.

MHD limits and plasma response in high-beta hybrid operations in ASDEX Upgrade

The improved H-mode scenario (or high β hybrid operations) is one of the main candidates for high-fusion performance tokamak operation that offers a potential steady-state scenario. In this case, the normalized pressure must be maximized and pressure-driven instabilities will limit the plasma performance. These instabilities could have either resistive ((m = 2, n = 1) and (3,2) neoclassical tearing modes (NTMs)) or ideal character (n = 1 ideal kink mode). In ASDEX Upgrade (AUG), the first limit for maximum achievable is set by the NTMs. The application of pre-emptive electron cyclotron current drive at the q = 2 and q = 1.5 resonant surfaces reduces this problem, so that higher values of can be reached. AUG experiments have shown that, in spite of the fact that hybrids are mainly limited by NTMs, the proximity to the no-wall limit leads to amplification of the external fields that strongly influence the plasma profiles. For example, rotation braking is observed throughout the plasma and peaks in the core. In this situation, even small external fields are amplified and their effect becomes visible. To quantify these effects, the plasma response to the magnetic fields produced by B-coils is measured as approaches the no-wall limit. These experiments and corresponding modeling allow the identification of the main limiting factors, which depend on the stabilizing influence of the conducting components facing the plasma surface, the existence of external actuators, and the kinetic interaction between the plasma and the marginally stable ideal modes. Analysis of the plasma reaction to external perturbations allowed us to identify optimal correction currents for compensating the intrinsic error field in the device. Such correction, together with the analysis of kinetic effects, will help to increase further in future experiments.

A Novel Three-Loop Parallel Robot With Full Mobility: Kinematics, Singularity, Workspace, and Dexterity Analysis

A novel parallel robot, dubbed the SDelta, is the subject of this paper. SDelta is a simpler alternative to both the well-known Stewart–Gough platform (SGP) and current three-limb, full-mobility parallel robots, as it contains fewer components and all its motors are located on the base. This reduces the inertial load on the system, making it a good candidate for high-speed operations. SDelta features a symmetric structure; its forward-displacement analysis leads to a system of three quadratic equations in three unknowns, which admits up to eight solutions, or half the number of those admitted by the SGP. The kinematic analysis, undertaken with a geometrical method based on screw theory, leads to two Jacobian matrices, whose singularity conditions are investigated. Instead of using the determinant of a 6 × 6 matrix, we derive one simple expression that characterizes the singularity condition. This approach is also applicable to a large number of parallel robots whose six actuation wrench axes intersect pairwise, such as all three-limb parallel robots whose limbs include, each, a passive spherical joint. The workspace is analyzed via a geometric method, while the dexterity analysis is conducted via discretization. Both show that the given robot has the potential to offer both large workspace and good dexterity with a proper choice of design variables.

Centralized Regulation Scheme for a Parallel-Mode Switched-Capacitor Converter System With Simple Unit Commitment

Novel load regulation methods for switched-capacitor converter (SCC) system operating in parallel mode are proposed. SCCs are ready for integrated design which is ideal for mass production and also enables power conversion in compact footprint. At the same time, they are excellent candidates for parallel mode operation since the load current sharing among them is automatically allocated by the inherent droop characteristic, which is determined by the equivalent internal resistance. Instead of controlling the individual switching frequency of SCC units, this paper proposes a number of unit commitment schemes which regulate the output voltage by adjusting the number of activated SCC units. In addition to conventional discrete unit commitment, intermediate number of activated units is realized by employing pulse-dropping pulse width modulation. The proposed methods are verified by simulation and the experiment of a parallel SCC system consists of a number of double-mode zero-current switching SCC units.

Investigating the applicability and effects of hydraulic fracturing technology on well productivity in one of the Iranian gas condensate reservoirs

Hydraulic fracturing is an important method utilized to enhance oil and gas recovery from reservoirs, especially for low-permeability formations. It has been broadly used in gas reservoirs, especially tight formations. Gas condensate reservoirs (GCR) experience a noticeable loss of productivity after achieving dew point pressure and condensate drop out formation around the wellbore, and could be suitable candidates for hydraulic fracturing operations. The aim of this study is to determine the effect of hydraulic fracturing on well productivity of GCR. A single well reservoir model corresponding to the GCR in the South of Iran and another model with similar conditions for hydraulic fracturing were created and validated. Reservoir model simulation was performed using a commercial compositional simulator. Sensitivity analysis was performed on fracture geometry parameters including the fracture length and width, flow parameters such as positive coupling and inertia effect, and reservoir properties namely permeability and fluid condensate gas ratio (CGR). The results demonstrated that hydraulic fracturing in GCR, especially in this case study, noticeably increases the productivity and production plateau time as well as decreases condensate formation, which increasing the fracture length and width intensifies this effect. Moreover, the optimized fracture length was obtained. It was found that the negative inertia effect in low hydraulic fracture widths and positive coupling in high fracture widths are dominant. Hydraulic fracturing is most effective in low-permeability and high-CGR conditions. These results pave the hydraulic fracturing road not only from industrial viewpoint, but also as a guideline for field-scale projects.