This paper proposes the application of unsymmetric multifrontal method to solve the differential algebraic equations (DAE) encountered in the power system dynamic simulation. The proposed method ...achieves great computational efficiency as compared to the conventional Gaussian elimination methods and other linear sparse solvers due to the inherent parallel hierarchy present in the multifrontal methods. Multifrontal methods transform or reorganize the task of factorizing a large sparse matrix into a sequence of partial factorization of smaller dense frontal matrices which utilize the efficient Basic linear algebra subprograms 3 (BLAS 3) for dense matrix kernels. The proposed method is compared with the full Gaussian elimination methods and other direct sparse solvers on test systems and the results are reported.
Background
Bariatric surgery presently is the best possible intervention for treatment of severe obesity and its related conditions. This study presents retrospective data on the pregnancy outcomes ...of Indian patients who underwent bariatric surgery before conception.
Methodology
This is a single-centre retrospective, observational study. Data on demographics, pre-surgery weight, body mass index (BMI), types of bariatric surgery, weight at conception, weight gain during pregnancy, type of delivery and the health of the baby were collected and analysed to study the weight loss pattern and pregnancy outcomes in female patients of childbearing potential.
Results
The study included 34 women of childbearing potential (BMI>30 kg/m
2
) who underwent bariatric surgery. The study population was followed up from the time of surgery until 1-year post-delivery of the baby. The mean weight gain during the pregnancy was 14.9±5.4 kg. Twenty-three underwent LSCS, and the rest had normal delivery with mean baby weight of 2.5±0.4 kg. Six babies required neonatal intensive care. In our series, only 4 of 35 cohorts that are only 11% had substantial weight retention (range 5–13 kg) at the end of 12 months which is significantly lower than the normal cohorts who did not undergo bariatric surgery.
Conclusion
Bariatric surgery improves fertility with safe pregnancy and its outcomes in terms of preeclampsia, eclampsia, gestational diabetes, premature rupture of the membranes (PROM), postpartum haemorrhage (PPH) and puerperal sepsis in women with childbearing potential and safe for offspring in terms of shoulder dystocia, macrosomia, birth asphyxia and perinatal mortality. However, they should be well aware of the risks associated with bariatric surgery especially the mal-absorptive procedures.
Graphical abstract
Background
Gastroesophageal reflux disease (GERD) affects two thirds of the American population. Obesity is also a disease that affects two thirds of the population. The pathophysiology of reflux ...disease is reasonably understood, however, the degree to which obesity affects this disease remains poorly defined. Therefore the approach to GERD in the obese patient requires special attention and its own algorithm.
Methods
A literature search was conducted to consolidate the current available literature on GERD and its management in the obese. In addition, the authors reviewed the literature and present expert opinion on controversial topics.
Results
It is well established that GERD is increased in obesity and the pathophysiology is reviewed. Management options for GERD are discussed, with a focus on the obese population. Management strategies including fundoplication and gastric bypass are discussed. In addition, bariatric surgery in the setting of GERD is also reviewed.
Conclusions
Currently this is an extremely controversial topic and this white paper presents a strong review of the literature to help guide the management of this challenging disease in this population. Expert recommendations are given throughout the paper based upon the current available data.
Cutaneous myxoma (CM) is an uncommon benign neoplasm of skin, which may be sporadic or arise in association with syndromes such as Carney complex. There has been only one large case series describing ...CM. We report 54 additional cases of CM; patients had a mean age of 55 years (range = 7–91), with a female-to-male ratio of 1.3. Most occurred on the trunk (n = 19), with the back being the most common site. The remainder presented on the lower extremity (n = 18), head and neck (n = 10), and arm (n = 7). Histopathologically, they were relatively circumscribed, nodular, and centered in the dermis. All had abundant myxoid stroma, a thin, arborizing vascular network, and spindled to stellate cells with no to mild atypia without mitotic activity. Follicular induction, stromal neutrophils, and intranuclear inclusions were present in 35%, 25%, and 61% of cases, respectively. Collagen trapping, splitting of collagen fibers, and encircling of hair follicles or eccrine glands were encountered in a subset. Thirty-nine cases were treated with shave excision, whereas 12 cases underwent wide local excision. Follow-up data were available for 28 of 54 cases (mean = 50 months). Only one case recurred at 36 months. This study suggests CM has a lower risk of local recurrence than previously reported.
•Cutaneous myxoma is a benign myxoid neoplasm of skin•This is the largest clinicopathologic study of cutaneous myxoma till date.•We compared the clinicopathologic features of the cases in our series with the features described in the previous studies and also with a pooled data group of case reports of cutaneous myxoma between 1996-2020.•This study revealed a lower local recurrence rate in cutaneous myxoma compared to previous studies.
We sought to determine the impact of the addition of Dor fundoplication on the incidence of postoperative gastroesophageal reflux (GER) after Heller myotomy.
Based only on case series, many surgeons ...believe that an antireflux procedure should be added to the Heller myotomy. However, no prospective randomized data support this approach.
In this prospective, randomized, double-blind, institutional review board-approved clinical trial, patients with achalasia were assigned to undergo Heller myotomy or Heller myotomy plus Dor fundoplication. Patients were studied via 24-hour pH study and manometry at 6 months postoperatively. Pathologic GER was defined as distal esophageal time acid exposure time greater than 4.2% per 24-hour period. The outcome variables were analyzed on an intention-to-treat basis.
Forty-three patients were enrolled. There were no differences in the baseline characteristics between study groups. Pathologic GER occurred in 10 of 21 patients (47.6%) after Heller and in 2 of 22 patients (9.1%) after Heller plus Dor (P = 0.005). Heller plus Dor was associated with a significant reduction in the risk of GER (relative risk 0.11; 95% confidence interval 0.02-0.59; P = 0.01). Median distal esophageal acid exposure time was lower in the Heller plus Dor (0.4%; range, 0-16.7) compared with the Heller group (4.9%; range, 0.1-43.6; P = 0.001). No significant difference in surgical outcome between the 2 techniques with respect to postoperative lower-esophageal sphincter pressure or postoperative dysphagia score was observed.
Heller Myotomy plus Dor Fundoplication was superior to Heller myotomy alone in regard to the incidence of postoperative GER.
Background
Recent Research evidences from across the world indicate the usefulness of bariatric surgery in improving the immunological co-morbidities in patients with morbid obesity.
Aim
The aim of ...the study was to evaluate the outcome from bariatric surgery in patients presenting with diabetes mellitus and or morbid obesity with immunological co-morbidities.
Methods
It was a retrospective cross-sectional study. Study included patients with morbid obesity with immunological co-morbidities, and additional co- morbidity of type 2 diabetes mellitus in about one third of the cases, who had undergone bariatric surgery during the period 2014–2016 at our center. Patient demographics, preoperative data, and follow-up data were collected and analyzed. Patients were followed for assessing the outcome in terms of BMI and dependency on medications to evaluate the effectiveness of the procedure.
Results
The study included 23 patients (52% female and 48% male). Bariatric surgery was effective in all the patients (except one) in weight reduction. Significant reduction in weight and BMI was observed (
p
< 0.05). The recent follow-up of these patients showed that the mean BMI of the study group decreased significantly, 34.4% patients had attained normal BMI ≤ 25 kg/m
2
. Three-month follow-up indicated that 55.56% were not dependent on medications. At 1-year follow-up, 94.4% patients were without any dependency on immunosuppressive medications. Complications included a reversal of surgery and a case of mortality.
Conclusion
The results of our study have shown that immune-compromised patients can undergo bariatric surgery with good weight loss results and improvement in co-morbidities.
•Identification of coherent group of generators.•Rotor angle stability.•Lyapunov exponents.
Recent trends of deregulation and expansion in power systems have greatly increased their stress levels and ...hence, ensuring their safety has become a critical challenge. In the event of disturbances, detecting the groups of coherent generators is important to study the characteristics of the system. We propose VANTAGE, a Lyapunov exponents based technique for identification of coherent groups of generators in power systems. VANTAGE performs time domain simulation of contingencies and uses this data to analyze rotor angle stability. VANTAGE offers an efficient algorithmic procedure for identification of coherent groups of generators using Lyapunov exponents method (LEM). VANTAGE does not require a priori estimation of number of groups of coherent generators. We evaluate VANTAGE using a 39-bus system and a 13029-bus system. The results demonstrate the effectiveness of VANTAGE in correctly identifying the coherent groups of generators.
•Parallel contingency analysis.•High performance computing (HPC).•Dynamic load balancing.•Work-stealing scheduling.•Master–slave scheduling.
In this paper, we present SCALE, a hybrid message passing ...interface (MPI) and multithreading based work Stealing approach for massive Contingency AnaLysis in powEr systems. SCALE performs time domain simulation of power systems using efficient numerical algorithms and scales the approach for analyzing a large number of contingencies using MPI. For achieving dynamic load balancing, SCALE uses efficient implementation of the work stealing algorithm. SCALE uses a hybrid MPI and multithreading based implementation, where MPI is used for communication between different nodes (processors) and multithreading is used within each processor to facilitate implementation of non-blocking version of work-stealing algorithm. We have evaluated SCALE on a large, 13,029 bus system using thousands of contingencies. Also, we have compared the dynamic load balancing based scheduling approach of SCALE with a state-of-art scheduling approach, namely master–slave scheduling approach. The results show that SCALE is effective in analyzing a large number of contingencies and scales well to a large number of processors.
With increasing emphasis on analyzing N−k contingencies, use of parallel resources has become imperative. Parallelization imposes the requirement of load-balancing for achieving high resource usage ...efficiency. Conventional static allocation based scheduling techniques fail to achieve load balancing. To address this limitation, master-slave scheduling (MSS) has been used; however, in MSS, after task completion, slave processors wait for the next task to arrive leading to idle-wait. In the case of contention at master, the idle-wait could become significant and degrade the performance of the MSS algorithm.
We present a technique to combine the advantage of proactive task scheduling and stealing with the simplicity of MSS. We refer to it as PTMSS. In PTMSS, master proactively queues an extra task at the slave processor, such that on completion of a task, the next task is immediately started. Further, when master runs out of the tasks, it steals a queued task from one slave and allocates to another slave which has completed its tasks. Simulation experiments have been conducted on a large power system with 13,029 buses and thousands of contingencies have been analyzed. The results show that PTMSS performs better than conventional MSS and also offers significant computational gains over serial execution.
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