High-magnetic-confinement mode in partially magnetized E×B plasmas.

The suppression of the gradient-drift driven instability and the transition to the high-magnetic-confinement mode are experimentally observed in a cylindrical partially magnetized E×B plasma using an additional biasable electrode installed at the radial edge. When a positive voltage is applied to the electrode, an electron-loss channel forms in its direction, breaking the spatially symmetric nonambipolar flow. Finally, in the steady state, the plasma density tends to peak in the plasma core, approaching plasma densities that are four times larger than those observed in the case where the instability is the strongest. A high-magnetic-confinement mode with a reduced edge-to-center density ratio of 0.16 is observed, which demonstrates that the saturation of magnetic confinement due to the gradient-drift driven instability can be prevented by an asymmetric nonambipolar flow.

Exploring the nonextensive thermodynamics of partially ionized gas in magnetic field.

Contrary to classical thermodynamics, which deals with systems in thermal equilibrium, partially ionized gases generally do not reach thermal equilibrium. Nonextensive statistical mechanics has helped extend classical thermodynamics to nonequilibrium ionized gas. However, the fundamental question on whether the statistics of non-Maxwellian electrons satisfy the laws of thermodynamics has not been resolved. Here, we verify the thermodynamic laws of reversible and adiabatic processes for a magnetically expanding ionized gas. Together with the experimental evidence of the non-Maxwellian electron distribution, the κ distribution, which measures the thermal equilibrium states, shows the Tsallis entropy to be nearly constant and the polytropic index to be close to adiabatic values along a divergent magnetic field. These results verify that the collisionless magnetic expansion of a nonequilibrium plasma is reversible and adiabatic, and an isentropic process is the origin of the high-energy tail of the energy distribution far downstream.

Electron cyclotron resonance heating by magnetic filter field in a negative hydrogen ion source.

The influence of magnetic filter field on plasma properties in the heating region has been investigated in a planar-type inductively coupled radio-frequency (RF) H(-) ion source. Besides filtering high energy electrons near the extraction region, the magnetic filter field is clearly observed to increase the electron temperature in the heating region at low pressure discharge. With increasing the operating pressure, enhancement of electron temperature in the heating region is reduced. The possibility of electron cyclotron resonance (ECR) heating in the heating region due to stray magnetic field generated by a filter magnet located at the extraction region is examined. It is found that ECR heating by RF wave field in the discharge region, where the strength of an axial magnetic field is approximately ∼4.8 G, can effectively heat low energy electrons. Depletion of low energy electrons in the electron energy distribution function measured at the heating region supports the occurrence of ECR heating. The present study suggests that addition of axial magnetic field as small as several G by an external electromagnet or permanent magnets can greatly increase the generation of highly ro-vibrationally excited hydrogen molecules in the heating region, thus improving the performance of H(-) ion generation in volume-produced negative hydrogen ion sources.

Optimization of plasma parameters with magnetic filter field and pressure to maximize H⁻ ion density in a negative hydrogen ion source.

Transverse magnetic filter field as well as operating pressure is considered to be an important control knob to enhance negative hydrogen ion production via plasma parameter optimization in volume-produced negative hydrogen ion sources. Stronger filter field to reduce electron temperature sufficiently in the extraction region is favorable, but generally known to be limited by electron density drop near the extraction region. In this study, unexpected electron density increase instead of density drop is observed in front of the extraction region when the applied transverse filter field increases monotonically toward the extraction aperture. Measurements of plasma parameters with a movable Langmuir probe indicate that the increased electron density may be caused by low energy electron accumulation in the filter region decreasing perpendicular diffusion coefficients across the increasing filter field. Negative hydrogen ion populations are estimated from the measured profiles of electron temperatures and densities and confirmed to be consistent with laser photo-detachment measurements of the H(-) populations for various filter field strengths and pressures. Enhanced H(-) population near the extraction region due to the increased low energy electrons in the filter region may be utilized to increase negative hydrogen beam currents by moving the extraction position accordingly. This new finding can be used to design efficient H(-) sources with an optimal filtering system by maximizing high energy electron filtering while keeping low energy electrons available in the extraction region.

Intraoperative electrophysiological monitoring during posterior craniocervical distraction and realignment for congenital craniocervical anomaly.

PURPOSE: Congenital craniocervical segmentation anomaly associated with malalignment of the odontoid process causes progressive spinal cord compression with myelopathy. Recent literatures have reported that ventral decompression could be achieved with posterior craniocervical realignment through posterior instrumented reduction. The purpose of the present study is to show the efficacy of intraoperative electrophysiological monitoring during craniocervical realignment through screws and rod system for congenital craniocervical segmentation anomaly. METHODS: Consecutive ten patients with a congenital craniocervical segmentation anomaly and myelopathy due to a malaligned odontoid process, who underwent posterior craniocervical realignment, were included. Klippel-Feil syndrome (KFS) was combined in four patients. Gait disturbance and motor weakness were the main presentation. Craniocervical realignment was achieved by intraoperative distraction through a rod and screw system. Intraoperative neuromonitoring was performed with transcranial motor-evoked potential (TcMEP) and somatosensory-evoked potential (SSEP). RESULTS: Significant change in TcMEP occurred in two patients with KFS during surgery, but the change was reversed with release of distraction. All patients were awakened without neurological deficit. Motor weakness and gait disturbance were normalized within 6 months in all patients. Postoperative computed tomography scan and/or magnetic resonance imaging showed that the reduction was complete in all patients. CONCLUSIONS: Craniocervical realignment through screws and rod system may be safe and efficacious surgical technique for the treatment of congenital craniocervical anomaly with the help of intraoperative neuromonitoring. However, distraction should be cautiously monitored, especially when Klippel-Feil syndrome is combined.

The use of a staged drainage seton for the treatment of anal fistulae or fistulous abscesses.

PURPOSE: The aim of this retrospective study was to evaluate the rate of recurrence and incontinence after the treatment of fistulae or fistulous abscesses by using the staged drainage seton method. METHODS: According to the condition, a drainage seton alone or a drainage seton combined with internal opening (IO) closure and relocation of the seton was used. After a period of time, the seton was changed with 3-0 nylon; then, after another period of time, the authors terminated the treatment by removing the 3-0 nylon. Telephone interviews were used for follow-up. The following were evaluated: the relationship between the type of fistula and recurrence; the relationship between the type of fistula and the period of treatment; the relationship between the recurrence and presence of abscess; the relationship between IO closure and recurrence; the relationship between the period of seton change and recurrence; reported continence for flatus, liquid stool, and solid stool. RESULTS: The recurrence rate of fistulae or suppuration was 6.5%, but for cases of horseshoe extension, the recurrence rate was 57.1%. The rate of recurrence was related to the type of fistula (P = 0.001). Incontinence developed in 3.8% of the cases. No statistically significant relationship was found between the rate of recurrence and the presence of an abscess or between the closure of the IO and the period of seton change or removal. CONCLUSION: In the treatment of anal fistulae or fistulous abscesses, the use of a staged drainage seton can reduce the rate of recurrence and incontinence.

Operative risk factors in gastric cancer surgery for elderly patients.

PURPOSE: Gastric cancer surgery is a common operation in East Asia, such as Korea and Japan, and there has been a significant increase in the need for this procedure due to the aging population. As a result, surgery for the treatment of gastric cancer for elderly patients is expected to increase. This study examined the effect of old age on gastric cancer surgery, and analyzed the operative risk factors for elderly patients. MATERIALS AND METHODS: From November 2008 to August 2010, 590 patients, who underwent a curative resection for gastric cancers, were enrolled. Patients who underwent palliative or emergency surgery were excluded. A retrospective analysis of the correlation between surgical outcomes and age was performed. The elderly were defined as patients who were over the age of 65 years. RESULTS: The mean age of all patients was 58.3 years, and complications occurred in 87 cases (14.7%). The most common complication was wound infection and severe complications requiring surgical, endoscopic, or radiologic intervention developed in 52 cases (8.8%). The rate of complications increased with increasing age of the patients. Univariate analysis revealed age, comorbidity, extent of resection, operation time, and combined resection to be associated with surgical complications. In particular, age over 75 years old, operation time, and comorbidity were predictive factors in multivariate analysis. In the elderly, only comorbidity was associated with surgical complications. CONCLUSIONS: The patients' age is the most important factor for predicting surgical complications. Surgeons should pay an attention to the performance of gastric cancer surgery on elderly patients. In particular, it must be performed carefully for elderly patients with a comorbidity.

Clinicopathologic significance of gastric adenocarcinoma with neuroendocrine features.

PURPOSE: Composite neuroendocrine-exocrine carcinomas are malignancies that have two distinct components residing within the same tumor: an adenocarcinomatous portion and a neuroendocrine portion. This is rare in gastric cancers; however, poorly differentiated adenocarcinomas can sometimes reveal evidence of neuroendocrine features (NEF) or be 'mixed endocrine and exocrine carcinomas'. This study aimed to review NEF in gastric adenocarcinoma and to evaluate its prognostic significance. MATERIALS AND METHODS: We selected 29 patients who were diagnosed with gastric adenocarcinoma with NEF and received gastrectomies at the Department of Surgery, Ajou University Hospital between January 2001 and December 2009. We analyzed the clinicopathologic features of gastric cancer with NEF and the prognosis associated with such tumors. RESULTS: THE PATHOLOGIC RESULT WITH RESPECT TO TNM STAGING OF THE GASTRIC CANCERS WITH NEF WERE AS FOLLOWS: 5 cases of T1, 5 cases of T2, 10 cases of T3, and 9 cases of T4. There were 7 cases of N0, 7 cases of N1, 8 cases of N2 and 7 cases of N3. The staging of patients with NEF was higher than that of patients without NEF. Especially tumor lymphovascular invasion rate was 82.8%. The overall survival of patients with gastric cancer characterized by NEF was 73.8 months. CONCLUSIONS: Positive NEF status might be correlated with clinicopathologic parameters such as a high stage and high frequency of regional lymph node metastasis.

Technical feasibility of robot-sewn anastomosis in robotic surgery for gastric cancer.

BACKGROUND: Although several studies have reported on the feasibility of robot-assisted gastric cancer surgery using the da Vinci surgical system, reconstruction techniques have depended on staplers or hand sewing through minilaparotomy. AIM: The aim of this study is to report on the feasibility of reconstruction methods using a robot-sewing technique in robotic surgery for treatment of gastric cancer. PATIENT AND METHODS: Between January and April 2010, 7 patients in whom gastric adenocarcinoma was diagnosed underwent robotic surgery including robot-sewn anastomosis. We demonstrated the surgical techniques with analysis of clinicopathologic characteristics and surgical outcomes. RESULTS: All robotic surgeries were performed without other laparoscopic instruments. Two Roux-en-Y reconstructions for two total gastrectomy, two Roux-en-Y reconstructions, and three gastroduodenostomies, for five subtotal gastrectomies, were successfully accomplished. Total median operation time was 205 minutes, and median reconstruction time was 69 minutes. One patient was readmitted for stasis in the remnant stomach but conservatively recovered. CONCLUSIONS: A robot-sewn anastomosis for reconstruction in robotic surgery for gastric cancer was feasible regardless of the reconstruction method.

Hepatic splenosis preoperatively diagnosed as hepatocellular carcinoma in a patient with chronic hepatitis B: a case report.

We report on a case of hepatic splenosis. A 32-yr-old man underwent a splenectomy due to trauma at the age of 6. He had been diagnosed as being a chronic hepatitis B-virus carrier 16 yr prior to the surgery. The dynamic computer tomography (CT) performed due to elevated serum alpha-fetoprotein (128 ng/mL) demonstrated two hepatic nodules, which were located near the liver capsule. A nodule in Segment IVa had a slight enhancement during both the arterial and portal phases, and another nodule in Segment VI showed a slight enhancement only in the portal phases. Dynamic magnetic resonance imaging (MRI) of the mass in Segment VI showed enhanced development in the arterial phases and slight hyperintensivity to the liver parenchyma in the portal phases. These imaging findings suggested a hypervascular tumor in the liver, which could be either focal nodular hyperplasia, adenoma, or hepatocellular carcinoma (HCC). Even though these lesions were diagnosed as HCC, some of the findings were not compatible with typical HCC. On dynamic CT and MRI, all lesions showed a slight arterial enhancement and did not show early venous washout. All lesions were located near the liver capsule. These findings, along with a history of splenectomy, suggested a diagnosis of hepatic splenosis.