6,511 research outputs found
Shape of Deconstruction
We construct a six-dimensional Maxwell theory using a latticized extra space,
the continuum limit of which is a shifted torus recently discussed by Dienes.
This toy model exhibits the correspondence between continuum theory and
discrete theory, and give a geometrical insight to theory-space model building.Comment: 10 pages, 2 figures, RevTeX4. a citation adde
Kinetic response of ionospheric ions to onset of auroral electric fields
Examination of the exact analytic solution of a kinetic model of collisional interaction of ionospheric fions with atmospheric neutrals in the Bhatnagar-Gross-Krook approximation, shows that the onset of intense auroral electric fields in the topside ionosphere can produce the following kinetic effects: (1) heat the bulk ionospheric ions to approximately 2 eV, thus driving them up to higher altitudes where they can be subjected to collisionless plasma processes; (2) produce a nonMaxwellian superthermal tail in the distribution function; and (3) cause the ion distribution function to be anisotropic with respect to the magnetic field with the perpendicular average thermal energy exceeding the parallel thermal energy
Kondo Effect in Fermi Systems with a Gap: A Renormalization Group Study
We present the results of a Wilson Renormalization Group study of the
single-impurity Kondo and Anderson models in a system with a gap in the
conduction electron spectrum. The behavior of the impurity susceptibility and
the zero-frequency response function, are discussed in the
cases with and without particle-hole symmetry. In addition, for the asymmetric
Anderson model the correlation functions, , are computed.Comment: 10 pages, 10 figure
Theory of the Three-Group Evolutionary Minority Game
Based on the adiabatic theory for the evolutionary minority game (EMG) that
we proposed earlier[1], we perform a detail analysis of the EMG limited to
three groups of agents. We derive a formula for the critical point of the
transition from segregation (into opposing groups) to clustering (towards
cautious behaviors). Particular to the three-group EMG, the strategy switching
in the "extreme" group does not occur at every losing step and is strongly
intermittent. This leads to an correction to the critical value of the number
of agents at the transition, . Our expression for is in agreement
with the results obtained from our numerical simulations.Comment: 4 pages and 2 figure
Decompression of cavernous sinus meningioma for preservation and improvement of cranial nerve function
Journal ArticleMeningiomas are the most common tumors affecting the cavernous sinus (CS). Despite advances in microsurgery and radiosurgery, treatment of CS meningiomas remains difficult and controversial. As in cases of other meningiomas, the goal of treatment for CS meningioma is long-term growth control and preservation of neural function. Gross-total resection, the ideal treatment for meningioma, is not always possible to obtain in patients with CS meningiomas with an acceptable level of morbidity. Therefore, microsurgery and radiosurgery have recently been advocated as a combined therapy to achieve good control of tumor growth and favorable functional outcome. The authors describe a technique in which tumor volume can be reduced to a minimal residual amount, while preserving cranial nerve function. This enables the smallest field to be treated radiosurgically. The optic nerve is decompressed, and the tumor mass is reduced to provide at least a 5-mm interpositional distance between the optic nerve and the residual lesion. Direct decompression of the CS, with opening of the lateral and superior sinus walls, and piecemeal removal of the tumor in "safe" locations are performed to facilitate an improvement in cranial nerve function. The authors describe the use of this technique in a series of patients and demonstrate improvement of cranial nerve function in a subset of these patients
Posterior fossa brain tumors and arterial hypertension
ManuscriptHypertension caused by arterial compression of the rostral ventrolateral medulla is well described. Much less information is available on the association between neurogenic hypertension and posterior fossa brain tumors. To date, multiple reports have supported the impression that a small subpopulation of patients with posterior fossa tumors can present with arterial hypertension, and many of those patients achieved significant improvement of their hypertension after tumor resection and medullary decompression. To review the relationship between posterior fossa brain tumors and hypertension, we detail the history, basic science, and clinical reports along with an illustrative case regarding this topic
Resolution of an anterior-inferior cerebellar artery feeding aneurysm with the treatment of a transverse-sigmoid dural arteriovenous fistula
ManuscriptThe authors describe a 27-year old man who developed an unruptured anterior-inferior cerebellar artery feeding aneurysm from a transverse-sigmoid dAVF and its subsequent resolution with the treatment of the dAVF. The patient, with a known history of left transverse and sigmoid sinus thrombosis, presented with pulse-synchronous tinnitus. Angiography revealed an extensive dAVF, with feeders from both the extracranial and intracranial circulations, involving the right transverse sinus, the torcula, and the left transverse/sigmoid sinuses. Multimodal endovascular and open surgical therapy was employed. Prior to a planned second-stage treatment for the left sigmoid sinus component, the dAVF improved significantly, but a small flow-related aneurysm developed on the left AICA feeding the petrous dural region in the interval. Resection of the involved sigmoid sinus resulted in resolution of the aneurysm. This is the first reported case of an unruptured feeding-artery aneurysm in an intracranial dAVF that resolved spontaneously with the treatment of the dAVF. Until more is known about its natural history, the decision on when and whether to treat an unruptured dAVF feedingartery aneurysm must be made on an individual basis
Carotid artery-sparing repair of a cavernous carotid artery pseudoaneurysm
Journal ArticleCarotid artery (CA) injury after transsphenoidal and endoscopic sinus surgery is a well-recognized but fortunately rare complication.1 It is associated with significant morbidity and mortality rates5 and is more common in cases of repeated surgery, cavernous sinus invasion, prior radiotherapy, and anatomical anomalies of the sphenoid and cavernous sinuses.4 It usually results in CA stenosis, occlusion, or pseudoaneurysm formation followed by serious complications, such as stroke and caroticocavernous fistulas.5 Direct surgical repair is difficult, and treatment may require parent vessel sacrifice and possibly vascular bypass.5 We describe the successful treatment of a cavernous? CA pseudoaneurysm with a novel CA-sparing approach. This 62-year-old woman with recurrent esthesioneuroblastoma underwent endoscopic tumor resection. A CA injury occurred intraoperatively. Hemostasis was rapidly achieved by packing the bleeding site with cottonoid and packing strip gauze within the sphenoid sinus. Postoperative angiography performed immediately after surgery revealed a 2-mm pseudoaneurysm at the anterior genu of the left cavernous internal CA (ICA) with minimal stenosis (Fig. 1 left). Eight days after the initial arterial injury, repeat angiography demonstrated persistence of the aneurysm. To repair the arterial defect and preserve the CA, an endovascular stent was placed across the puncture site to restore its normal caliber and to provide a buttressing surface for surgical repair by graft apposition (Fig. 1 right). Subsequently, with the aid of the operating microscope, a small piece of autologous fascia lata graft was placed directly over the arterial puncture site via a transnasal?transsphenoidal approach and bound using BioGlue (CryoLife, Inc., Kennesaw, GA), a two-component (bovine serum albumin and glutaraldehyde) surgical adhesive that is used as an adjunct to open surgical repair of large vessels, such as the aorta, femoral artery, and CA.2 The fascia lata graft was placed over the puncture site to patch the hole in the arterial wall directly because the pseudoaneurysm remained and was unchanged after stent placement alone, presumably because of the interstices of the stent
Giant fusiform aneurysm in an adolescent with PHACES syndrome treated with a high-flow external carotid artery-M3 bypass
Journal ArticleThe acronym PHACES describes a rare neurocutaneous syndrome that comprises posterior fossa malformations, facial hemangiomas, arterial anomalies, coarctation of the aorta and cardiac defects, eye abnormalities, and sternal defects. Facial hemangiomas constitute the hallmark of this disorder. Giant intracranial aneurysms have not been previously reported in the literature as manifestations of PHACES syndrome and can present difficult therapeutic challenges. The authors describe a unique case of a 13-year-old adolescent boy with an incomplete phenotypic expression of PHACES syndrome who harbored diffuse cerebral angiodysplasia and a giant fusiform internal carotid artery (ICA) aneurysm extending from the distal cavernous segment to the supraclinoid segment. The aneurysm was successfully treated with a high-flow saphenous vein graft bypass from the external carotid artery to the distal middle cerebral artery followed by proximal ICA occlusion. This case represents a unique vascular manifestation of PHACES syndrome that required a complex management strategy. The authors review the literature on this rare disorder and emphasize the importance of considering the diagnosis of PHACES syndrome in child with a facial hemangioma
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