Laboratory measurements of the physics of auroral electron acceleration by Alfvén waves.

While the aurora has attracted attention for millennia, important questions remain unanswered. Foremost is how auroral electrons are accelerated before colliding with the ionosphere and producing auroral light. Powerful Alfvén waves are often found traveling Earthward above auroras with sufficient energy to generate auroras, but there has been no direct measurement of the processes by which Alfvén waves transfer their energy to auroral electrons. Here, we show laboratory measurements of the resonant transfer of energy from Alfvén waves to electrons under conditions relevant to the auroral zone. Experiments are performed by launching Alfvén waves and simultaneously recording the electron velocity distribution. Numerical simulations and analytical theory support that the measured energy transfer process produces accelerated electrons capable of reaching auroral energies. The experiments, theory, and simulations demonstrate a clear causal relationship between Alfvén waves and accelerated electrons that directly cause auroras.

Observation of an Alfvén Wave Parametric Instability in a Laboratory Plasma.

A shear Alfvén wave parametric instability is observed for the first time in the laboratory. When a single finite ω/Ω_{i} kinetic Alfvén wave (KAW) is launched in the Large Plasma Device above a threshold amplitude, three daughter modes are produced. These daughter modes have frequencies and parallel wave numbers that are consistent with copropagating KAW sidebands and a low frequency nonresonant mode. The observed process is parametric in nature, with the frequency of the daughter modes varying as a function of pump wave amplitude. The daughter modes are spatially localized on a gradient of the pump wave magnetic field amplitude in the plane perpendicular to the background field, suggesting that perpendicular nonlinear forces (and therefore k_{⊥} of the pump wave) play an important role in the instability process. Despite this, modulational instability theory with k_{⊥}=0 has several features in common with the observed nonresonant mode and Alfvén wave sidebands.

Nonlinear excitation of acoustic modes by large-amplitude Alfvén waves in a laboratory plasma.

The nonlinear three-wave interaction process at the heart of the parametric decay process is studied by launching counterpropagating Alfvén waves from antennas placed at either end of the Large Plasma Device. A resonance in the beat wave response produced by the two launched Alfvén waves is observed and is identified as a damped ion acoustic mode based on the measured dispersion relation. Other properties of the interaction including the spatial profile of the beat mode and response amplitude are also consistent with theoretical predictions for a three-wave interaction driven by a nonlinear ponderomotive force.

Quantitative study of guide-field effects on Hall reconnection in a laboratory plasma.

The effect of guide field on magnetic reconnection is quantitatively studied by systematically varying an applied guide field in the Magnetic Reconnection Experiment (MRX). The quadrupole field, a signature of two-fluid reconnection at zero guide field, is altered by a finite guide field. It is shown that the reconnection rate is significantly reduced with increasing guide field, and this dependence is explained by a combination of local and global physics: locally, the in-plane Hall currents are reduced, while globally guide field compression produces an increased pressure both within and downstream of the reconnection region.

Primary cerebral fibrosarcoma in a child.

OBJECTIVE: To describe the case of a primary cerebral fibrosarcoma in a child. CLINICAL CASE: A 6-year-old boy presented with a history of headache, drowsiness, vomiting and seizures. He was referred to our institution and died shortly upon arrival to the ER. The autopsy revealed a large left frontoparietal mass with histopathologic features characteristic of fibrosarcoma. Immunohistochemical and ultrastructural studies allowed the exclusion of other mimickers such as meningiomas, and neoplasms of glial or neuronal origin. No other growths were found in the CNS or in other parts of the body. CONCLUSIONS: Brain fibrosarcoma is an exceedingly uncommon tumor. Only 41 cases have been reported to date. The diagnosis of fibrosarcoma must be based on the identification of a predominant herringbone architectural pattern, and immunohistochemical features, although the latter are of limited diagnostic value, its importance being that they facilitate the exclusion of other entities considered in the differential diagnosis.

Penile cancer associated with so-called low-risk human papilloma virus. Report of five cases from rural Venezuela.

Penile cancer is uncommon in western countries. It has been related to human papilloma virus (HPV) types 16 and 18. We describe five cases of carcinoma of the penis in men from a rural Venezuelan town that were related to HPV types 6, 11, 53, which represent a rather low risk for cancer.

Right lower quadrant pain in children caused by omental infarction.

BACKGROUND: Omental infarction is a rare cause of abdominal pain, with fewer than 300 cases reported in the literature. Only 15% of reported cases occur in the pediatric population. We present our experience with 18 children diagnosed with omental infarction admitted to Texas Children's Hospital over a 15-year period. STUDY DESIGN: A retrospective review of clinical records, diagnostic images, and pathologic findings was carried out for all children diagnosed with isolated omental infarction from 1986 to 2000 in order to analyze presenting signs and symptoms, preoperative imaging, surgical management, and postoperative outcomes. RESULTS: Eighteen children were treated for isolated omental infarction. There were 12 boys and 6 girls with an average age of 7.5 years (range 2 to 13). All patients presented with acute onset of right lower quadrant pain. Only 5 of 18 (24%) had associated gastrointestinal symptoms. The average temperature at presentation was 99.4 degrees F (+/- 0.78). The average white blood cell count was 11.4 (+/- 4.4). Fourteen patients had ultrasonographys performed preoperatively: 6 of 14 incorrectly diagnosed appendicitis, 4 of 14 were nondiagnostic and 4 of 14 correctly diagnosed omental infarction. Two of 18 patients underwent computed tomography scans, which were diagnostic for omental infarction. Resection of the infarcted omentum was performed in all patients and appendectomy in 16 of 18. Thirteen patients underwent an open procedure, 5 were performed laparoscopically. There were no postoperative complications. All patients had resolution of pain postoperatively and were discharged an average of 3.0 (+/- 0.9) days after admission. CONCLUSIONS: Omental infarction is an uncommon cause of right lower quadrant pain in children and is often diagnosed as appendicitis preoperatively. Ultrasonography and computed tomography can be diagnostic. Surgical resection of the infarcted omentum results in immediate resolution of pain with no morbidity.

Theoretical analysis of the growth mode for thin metallic films on oxide substrates

We show how the growth mode of a thin metallic film on an insulating substrate can be predicted theoretically by combining thermodynamic considerations with ab initio calculations for ordered metal/insulator interfaces at low coverage. Our approach is illustrated by calculations for Ag film deposited on an MgO substrate. Ab initio calculations predict high mobility of adsorbed Ag atoms on MgO, even at low temperatures, which greatly aids their aggregation.

Sonographic appearance of omental infarction in children.

BACKGROUND: Omental infarction has been previously reported in the adult surgical and imaging literature; however, the imaging features of this entity in children have received little attention. OBJECTIVE: The purpose of our study was to identify the sonographic features of omental infarction in nine children who had preoperative sonography and surgically proven omental infarction. MATERIALS AND METHODS: Sonographic images were reviewed and correlated with clinical information obtained from the patients' medical records, including clinical presentation, operative notes, and pathology reports. RESULTS: In seven of the children, sonography demonstrated a focal area of moderately increased echogenicity in the omental fat in the right abdomen (a previously described finding in omental infarction). This was an isolated finding in four of these cases. In the three cases where this was not an isolated finding, the more complex sonographic appearance led to incorrect preoperative imaging diagnoses. This finding of increased echogenicity in the omental fat was not present in the two remaining patients. CONCLUSION: Our study confirms that foci of moderately increased echogenicity in the omentum of the right abdomen, a sonographic finding described in omental infarction in a large series in adults (and in a single prior case report in children), can be seen in children as well. However, although this is a relatively unique finding, it may be absent in some cases or may be seen in conjunction with other sonographic findings which may preclude the correct preoperative sonographic diagnosis.

Cholecystectomy via Kocher incision without peritoneal closure.

This investigation was carried out to evaluate the surgical wound outcome of patients who underwent cholecystectomy via Kocher incision, without peritoneal closure. Consecutive patients (n = 129) were randomized either to have the peritoneal closure (n = 66) or to have this step omitted (n = 63). Demographic data of the patients were similar in both groups. There were no significant differences in overall wound complication (p = 0.44), wound infection (p = 0.71), wound dehiscense (p = 0.96) and incisional hernia (p = 0.95). This study provides strong evidence that the avoidance of the peritoneal closure represents no adverse effect to the postoperative course of the patients.

Treatment guidelines for patients with thyroid nodules and well-differentiated thyroid cancer. American Thyroid Association.

A set of minimum clinical guidelines for use by primary care physicians in the evaluation and management of patients with thyroid nodules or thyroid cancer was developed by consensus by an 11-member Standards of Care Committee (the authors of the article) of the American Thyroid Association, New York, NY. The participants were selected by the committee chairman and by the president of the American Thyroid Association based on their clinical experience. The committee members represented different geographic areas within the United States, to reflect different practice patterns. The guidelines were developed based on the expert opinion of the committee participants, as well as on previously published information. Each committee participant was initially assigned to write a section of the document and to submit it to the committee chairman, who revised and assembled the sections into a complete draft document, which was then circulated among all committee members for further revision. Several of the committee members further revised and refined the document, which was then submitted to the entire membership of the American Thyroid Association for written comments and suggestions, many of which were incorporated into a final draft document, which was reviewed and approved by the Executive Council of the American Thyroid Association.

[Surgical treatment of congenital cysts of the liver]. / Tratamiento quirúrgico de los quistes congénitos del hígado.

We report 9 patients who were surgically treated for symptomatic congenital liver cysts. Median age at presentation was 51 years and all the cases were females. Symptoms and clinical findings included a painful mass in the upper right quadrant of the abdomen. Ultrasonography was used most frequently and was an accurate technique for diagnosing these lesions. The cysts were often located in the right hepatic lobe. Surgical technique included total excision (n = 6) and partial excision via fenestration (n = 3). Based in our limited experience we believe that fenestration constitutes the least aggressive approach with a high rate of symptom relief and should be considered as an alternative in the treatment of these lesions.

Renal venous thrombosis complicating acute myeloid leukemia with hyperleukocytosis.

PURPOSE: Leukemic hyperleukocytosis may cause organ- or life-threatening complications. Patients at highest risk appear to be those with acute myeloid leukemia (AML). Blast cell aggregation and thrombus formation in the microvasculature most commonly involves the central nervous system and the pulmonary circulation. We describe a child with AML and renal venous thrombosis (RVT), a previously unreported complication of hyperleukocytosis. PATIENTS AND METHODS: A 17-month-old boy had a white blood cell count of 103 X 10(9) cells/L and RVT (hematuria, arterial systolic hypertension, unilateral nephromegaly, poor renal venous blood flow) at diagnosis of acute myelomonocytic leukemia (AML, FAB M4). CONCLUSION: This case emphasizes the danger of hyperleukocytosis in AML and demonstrates that there may be other organ system dysfunction in addition to the well-described central nervous system and pulmonary complications. Renal venous thrombosis should be considered in the patient with leukemic hyperleukocytosis, hematuria, arterial hypertension, and appropriate radiographic findings. Aggressive cytoreductive measures should be pursued in such cases.