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M Cogan

Publications and source records attributed to M Cogan.

10 recordsLinked to original sources
PubMed1996

Partially Molten Middle Crust Beneath Southern Tibet: Synthesis of Project INDEPTH Results

INDEPTH geophysical and geological observations imply that a partially molten midcrustal layer exists beneath southern Tibet. This partially molten layer has been produced by crustal thickening and behaves as a fluid on the time scale of Himalayan deformation. It is confined on the south by the structurally imbricated Indian crust underlying the Tethyan and High Himalaya and is underlain, apparently, by a stiff Indian mantle lid. The results suggest that during Neogene time the underthrusting Indian crust has acted as a plunger, displacing the molten middle crust to the north while at the same time contributing to this layer by melting and ductile flow. Viewed broadly, the Neogene evolution of the Himalaya is essentially a record of the southward extrusion of the partially molten middle crust underlying southern Tibet.

Journal Article↗
PubMed1996

Bright Spots, Structure, and Magmatism in Southern Tibet from INDEPTH Seismic Reflection Profiling

INDEPTH seismic reflection profiling shows that the decollement beneath which Indian lithosphere underthrusts the Himalaya extends at least 225 kilometers north of the Himalayan deformation front to a depth of approximately 50 kilometers. Prominent reflections appear at depths of 15 to 18 kilometers near where the decollement reflector apparently terminates. These reflections extend north of the Zangbo suture to the Damxung graben of the Tibet Plateau. Some of these reflections have locally anomalous amplitudes (bright spots) and coincident negative polarities implying that they are produced by fluids in the crust. The presence of geothermal activity and high heat flow in the regions of these reflections and the tectonic setting suggest that the bright spots mark granitic magmas derived by partial melting of the tectonically thickened crust.

Journal Article↗
PubMed1994

[Cervical plexus block for carotid surgery. 313 consecutive operations].

OBJECTIVES: The optimal method for protecting the brain from ischaemia during carotid surgery is still a matter of debate. The aim of this study was to report our early results after carotid surgery performed with cervical plexus blockade in vigilant patients. METHODS: From 1987 to 1992, 313 consecutive operations were performed on the carotid bifurcation (217 males, 96 females; mean age 67 years; age range 41-87 years). Thirteen underwent bilateral operations at a 1 month interval. There were 118 (38%) asymptomatic patients with carotid narrowing greater than 80% and 195 (62%) symptomatic patients including 96 with temporary cerebral ischaemia, 12 with regressive ischaemic events, 37 with cerebral vascular events and 50 with non-hemispheric events. The contralateral carotid artery was occluded in 30 patients (9.5%). Deep cervical blockade of the C2-C3-C4 roots then superficial blockade was obtained with 0.5% bupivacaine. Operations were endartectomy (n = 301; 96%) including 59 (18.5%) with a prosthetic patch, venous grafts (n = 8; 2.5%) and direct reimplantations (n = 3; 0.9%). All neurological complications observed during the 30 days following operation were recorded. RESULTS: At occlusion, neurological events occurred in 40 patients (12.8%) and required the use of a temporary shunt. In patients with a contralateral occlusion such events occurred in 35.5% of the patients. No cases of myocardial infarction were observed and 1 patient died due to a neurological cause, giving a morbidity of 1.6% and a mortality of 0.3%. CONCLUSION: Cervical plexus blockade was shown to be a simple and effective method for carotid surgery allowing good myocardial haemodynamics and a reliable evaluation of tolerance to occlusion.

Adult↗
PubMedDate not supplied

Turnover and migration of meibomian gland cells in rats' eyelids.

PURPOSE: The object of this study is to determine the velocity and migration course of meibomian gland cells. MATERIALS AND METHODS: Twenty-seven adult rats weighing about 200 g were injected intraperitoneally with a single dose of 0.5 microCi [3H]-thymidine/g body weight. Three rats were sacrificed 1 h after injection and 3 rats each on days 3, 6, 9, 12, 15, 18, 21 and 28 after injection. The eyes and eyelids were removed in one piece, fixed in formalin, embedded in paraffin and cut into 5-micron-thick vertical sections along the pupillary-optic nerve axis. The sections were dipped in liquid autoradiographic emulsion, exposed for 3 weeks, and stained with HE. Meibomian glands were scanned in the lower eyelid of the left eye using an ocular micrometer grid. In each scan the basement membrane of each acinus served as a point of origin. Along the entire gland two parameters were noted for each nucleus with three grains or more: the distance from the basement membrane (Y) and grain count. RESULTS: This study demonstrates for the first time the exact timing and direction of meibomian gland cell migration. We have shown that the cells migrate from the basement membrane to the center of the acinus at an average rate of 0.62 +/- 0.11 micron/day. Cell generation time was an average of 4.1 days. CONCLUSIONS: The stem cells of meibomian glands lie at the circumference of each acinus. These cells migrate synchronously with a constant velocity towards the center of the acinus, and are secreted as sebaceous material.

Animals↗