2,674 research outputs found
Role of the extended lymphadenectomy in gastric cancer surgery: experience
Although curative resection is the treatment of choice for gastric
cancer, controversy exists about the adequate extent of lymph node dissection
when resection is performed. METHODS: We retrospectively assessed 85 patients who
underwent a limited lymphadenectomy (D1) and 71 who had an extended lymph node
dissection (D2) in a single institution between 1990 and 1998 (median follow-up,
37.3 months). Prognostic factors were assessed by Cox proportional hazard models
adjusted for potential confounders. RESULTS: We found no significant difference
in the length of hospital stay (median, 12.1 and 13.1 days), overall morbidity
(48.2% and 53.5%), or operative mortality (2.3% and 0%) between D1 and D2,
respectively. Five-year survival in the D2 group was longer (50.6%) than in the
D1 group (41.4%) for tumor stages (tumor-node-metastasis) >I. In multivariate
analysis, tumor-node-metastasis stage (hazard ratio for stages >I vs. 0-I, 11.6),
the ratio between invaded and removed lymph nodes, the presence of distant
metastases, Lauren classification, and the extent of lymphadenectomy (hazard
ratio for D1 vs. D2, 2.3; 95% confidence interval, 1.25-4.30) were the only
significant prognostic factors. CONCLUSIONS: Our experience shows that extended
(D2) lymph node dissection improves survival in patients with resected gastric
cancer
Totally Laparoscopic Roux-en-Y Duct-to-Mucosa Pancreaticojejunostomy After Middle Pancreatectomy A Consecutive Nine-case Series at a Single Institution
To present the results of a series of laparoscopic middle
pancreatectomies with roux-en-Y duct-to-mucosa pancreaticojejunostomy. SUMMARY OF
BACKGROUND DATA: Middle pancreatectomy makes it possible to preserve pancreatic
parenchyma in the resection of lesions that traditionally have been treated by
distal splenopancreatectomy or cephalic duodenopancreatectomy. The laparoscopic
approach could minimize the invasiveness of the procedure and enhance the
benefits of middle pancreatectomy. METHODS: From March 2005 to October 2007, 9
consecutive patients with benign or low malignant potential lesions in the
pancreatic neck or body underwent surgery. Laparoscopic middle pancreatectomy
with a roux-en-Y duct-to-mucosa pancreaticojejunostomy was planned on all of
them. In the first 2 patients, the pancreas was transected by endostapler; in the
last 7, the staple line was reinforced with absorbable polymer membrane. RESULTS:
The intervention was concluded laparoscopically in every case except 1
(laparoscopic-assisted) in which pancreaticojejunostomy was performed by means of
minilaparotomy. Mortality was 0% and perioperative morbidity was 33%, (fistula of
the cephalic stump in the first 2 patients (22%)). The pancreaticojejunostomy
fistula rate was 0%. The median postoperative hospital stay was 5 days (range,
3-41). In the last 7 patients, in which pancreas was transected with staple line
reinforcement material there were no stump fistulas; morbidity decreased to 14%
and the median hospital stay was 4 days (range, 3-30). CONCLUSIONS: Laparoscopic
middle pancreatectomy is feasible and safe. Duct-to-mucosa pancreaticojejunostomy
can be performed safely using this approach. The method of pancreatic transection
seems to be decisive in the incidence of cephalic stump fistulas
Editorial: Grid Connection of Converters in Renewable Applications
Energy generated from renewable sources is fed into the grid by means of electronic power converters. These can be supervised at system (grid) level to coordinate all productions points together with storages and loads. Regulations impose power supply quality requirements regarding harmonics, grid fault response and low voltage ride through (LVRT). The progress of distributed generation presents challenges to converters such as island mode operation, voltage and frequency regulation, simulation, etc. New collaborative solutions for “more smart” microgrids must be included to improve power quality, reliability, service quality and duty.
Wind turbines employing double-fed induction generators (DFIG) use two converters, one for the rotor side and one for the generator side. To improve the performance during severe grid failures, in Okedu and Barghash the advantages of using alternative configurations to the two-level converter, such as the parallel interleaved 2-level inverter, and the 3-level inverter, have been investigated. It has also been investigated to replace the classical dq-PLL with a new PLL, and to include a series dynamic braking resistor (SDBR) between the converters and the three-phase connections.
Wind turbines must meet strict requirements, in terms of their behavior, in the event of grid failures, which are regulated by the LVRT regulations in each country. These regulations indicate, by means of voltage and time graphs, how long the wind turbines must remain connected depending on the depth of the faults. In addition, the limits of active and reactive power that can be exchanged during faults are established. The aim is to avoid cascading disconnections of wind turbines that would compromise the stability of the grid. In Okedu and Barghash, the effect of various elements in improving the behaviour of a DFIG against grid faults has been investigated. The first of these elements is the parameters of the IGBTs, concluding that the on-resistance has the greatest influence. The second is the use of a new PLL, and the third is the use of a SDBR during a grid failure. It was found that all of them could improve the performance of the generator in the event of a grid failure.
When a wind turbine uses a permanent magnet synchronous generator (PMSG), 100% of the energy generated passes through both converters. In Okedu and Barghash, the control systems of the generator-side and grid-side converters have been considered; several scenarios regarding the turn on resistance of the IGBTs have been considered, and their behaviour during grid faults has been analysed. Generator performance has also been studied with and without the use of a DC-DC converter for overvoltage protection.
The main generators used in wind turbines are DFIG and PMSG. In Okedu et al., a comparison of the behaviour of both wind turbines against grid faults has been carried out in various scenarios with different values of generator parameters.
The number of converters, associated with renewable generation, connected to the grid has increased significantly lately. This can affect the dynamic response, especially during disturbances, but it can also provide new grid support functionalities if information on the oscillation characteristics is available. Through the use of artificial intelligence, in Baltas et al. the abilities to predict and damp electromechanical oscillations have been improved.
With the constant increase in the number of wind turbines connected to the grid, it is very important to have the ability to maintain grid frequency control. In Okedu and Barghash, a work has been presented to stabilise the wind farm during periods of wind speed change by using capacitors connected via a DC-DC converter and a grid-connected DC-AC converter. It was concluded that higher values of the DC-DC converter time constant lead to better performances during load transients. A system including two steam turbines and two squirrel cage induction generators was used in the experiments.
Microgrids bring power generation closer to the places of consumption to reduce the saturation of distribution lines. They consist of renewable generation, energy storage and fossil fuel generation. They have three levels of control, where the primary level is the closest to the converters, and the tertiary level, the most external and slowest, performs general monitoring functions. The paper (Buraimoh et al.) focuses on the secondary control functions related to grid failure performance. It proposes a distributed control between inverters and is based on fast detection techniques (fast Delayed Signal Cancellation, DSC), with the objective of a fast control of active and reactive power. A robust transition method between fault mode and normal mode is proposed. Accurate coordination and power sharing between distributed energy resources is achieved.
Some energy conversion systems are so complex that they are very difficult to build and test in the laboratory. These include the study of high voltage direct current (HVDC) transmission when several modular multilevel converters (MMC) are involved together with DC grid failure protection elements. In Wang et al., a system including a simulated part (two digitally simulated MMC) and a physical part (two MMC) has been experimented with. The coupling between the two parts has been carried out by means of A/D and D/A converters and power amplifiers
Comparison Between Two Warm Ischemic Models in Experimental Liver Transplantation in Pigs
Experimental models of warm ischemia in liver transplantation have
been employed to study the mechanisms and treatment of ischemia reperfusion
injury. METHODS: We compared a control group without (group A, n = 10) versus two
models of warm ischemia of liver transplants in pigs: namely, occlusion of the
hepatic artery and portal vein for 30 minutes (group B, n = 23) and extraction of
the liver 60 minutes after cardiac arrest (group C, n = 5). Liver function tests,
coagulation studies, and liver biopsies were performed during the first 24 hours
post-liver transplant. RESULTS: Clamping of the hepatic vasculature in group B
produced a significant liver injury compared with the control group: elevation of
the ALT and an abnormal 1-hour post-revascularization biopsy similar to that
observed in the cardiac arrest group C. The transaminase levels were lower among
group A animals (P <.05). But the hepatic synthetic functions as reflected in the
protrombin time (PT) were not affected in group B versus group A. The alteration
in PT with respect to the initial value was similar among group A and group B
animals, which were significantly less than that in group C (P <.05).
CONCLUSIONS: Occlusion of the hepatic artery and portal vein, a simple surgical
maneuver, causes moderate damage to a liver graft but less alteration of hepatic
synthetic function. Clamping of the hepatic vasculture obtains more long-term
survivors after OLT than cardiac arrest
Effect of treatment with tranexamic acid on complement activation and ischemia reperfusion in liver transplantation in pigs
Wersync: A WEB-BASED PLATFORM FOR DISTRIBUTED MEDIA SYNCHRONIZATION AND SOCIAL INTERACTION
This paper presents Wersync, which is an adaptive and accurate web-based platform that enables distributed media
synchronization and social interaction across remote users. By using Wersync, users can create or join on-going sessions
for concurrently consuming the same media content with other remote users in a synchronized manner. Besides, social
interaction is provided by sharing the navigation control commands and by integrating synchronized text chat
channels. Additionally, two social presence mechanisms have been added to stimulate the participation of external
users in on-going sessions on Wersync. By exclusively relying on standard web-based technologies, this platform
can guarantee cross-network, cross-platform and crossdevice support, which is a key point in the current heterogeneous media delivery ecosystem
Characterization and identification of field ectomycorrhizae of Boletus edulis and Cistus ladanifer
Field ectomycorrhizae sampled under Boletus edulis and Cistus ladanifer have been characterized and described in detail based on standard morphological and anatomical characters. The described ectomycorrhiza has traits typical of Boletales: whitish with three differentiated plectenchymatous layers in the mantle in plan view forming ring-like structures and rhizomorphs with highly differentiated hyphae. The inflated, smooth cystidia-like clavate end cells on the surface of the rhizomorphs and their slightly twisted external hyphae are additional characterizing features. The Hartig net occupies 1 1/2 rows of cortical cells, partly reaching the endodermis. Not all hyphae have clamps. The identification of the fungal symbiont as B. edulis was confirmed by ITS rDNA sequence comparison between mycorrhizas and sporocarps. The singularity of this symbiotic association, as well as its ecological and practical implications, are discussed
Surgery and radioembolization of liver tumors
Surgical resection is considered the curative treatment par excellence for patients with primary or
metastatic liver tumors. However, less than 40% of them are candidates for surgery, either due to nonmodifiable factors (comorbidities, age, liver dysfunction. . .), or to the invasion or proximity of the tumor
to the main vascular requirements, the lack of a future liver remnant (FLR) adequate to maintain postoperative liver function, or criteria oftumor size and number. In these lastfactors, hepatic radioembolization
has been shown to play a role as a presurgical tool, either by hypertrophy of the FLR or by reducing tumor
size that manages to reduce tumor staging (term known as downstaging ¨ ¨
). To these is added a third factor,
which is its ability to apply the test oftime, which makes it possible to identify those patients who present
progression of the disease in a short period of time (both locally and at distance), avoiding a unnecessary
surgery. This paper aims to review RE as a tool to facilitate liver surgery, both through the experience of
our center and the available scientific evidence.La resección quirúrgica se considera eltratamiento curativo por excelencia para los pacientes con tumores
hepáticos primarios o metastásicos. Sin embargo, menos del 40% de ellos son candidatos a cirugía, ya
sea por factores no modificables (comorbilidades, edad, disfunción hepática. . .), como por la invasión o
proximidad del tumor a los principales pedículos vasculares, la falta de un futuro remanente hepático
(FRH) adecuado para mantener una función hepática postoperatoria, o criterios de tamano˜ y numero
tumoral. En estos últimos factores, la radioembolización hepática ha mostrado tener un papel como
herramienta prequirúrgica, ya sea mediante la hipertrofia del FRH o mediante la reducción del tamano˜
tumoral que consigue disminuir la estadificación tumoral (término conocido como “downstaging”). A
estos se suma un tercer factor, que es su capacidad de aplicar el test del tiempo, que permite identificar
aquellos pacientes que presenten en un plazo corto de tiempo progresión de la enfermedad (tanto a
nivel local como a distancia), evitándoles una cirugía innecesaria. En este trabajo se pretende hacer una
revisión de la RE como herramienta facilitadora de la cirugía hepática, tanto a través de la experiencia de
nuestro centro como de la evidencia científica disponible
Sistemas de acceso venoso central (SAVC) en pacientes pediátricos. Experiencia de seis años
The need for an access to the venous system, in order to infuse chemotherapeutic treatments or parenteral nutrition, has increased the number of central venous access systems (CVAS) implanted in the past years. Between February 1985 and December 1990, 87 devices were implanted in 76 patients (from 11 months to 15 years of age), with a median function time of 349 days (range: 7 to 1887 days). The overall incidence of complications was 0.10 per 10 days of catheterization, with complication rates for infection and thrombosis of 0.02 and 0.03, respectively. Nineteen systems were removed because of complications and 11 because of completion of the treatment. Of the cases, 97.7% included a follow-up period. The present study confirms the advantages of these devices, with a long working life and a low complication rate, being a good alternative for chronically ill children requiring long-term and/or cyclic intravenous therapy
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