Excited state absorption in Mn2+ doped phosphate glass.

The possibility of obtaining laser action from Mn2+ doped glass has been investigated. The excited state absorption at the expected laser wavelength was measured and explains the unsuccessful attempts to obtain laser action

A Case History of Tehri Tunnels

Tehri Dam Project, a multipurpose river valley project, is being constructed in Garhwal, Himalaya. The project consists of a 260 m high earth and rock fill dam with a clay core, four diversion tunnels each of 11 m finish diameter, four head race tunnels each of 8.5 m finish diameter and two underground powerhouses cavities each measuring 180 m long, 49.5 m high and 21.5 m wide. The project is located near the district headquarters of Tehri in the state of Uttar Pradesh. The rock masses in the project area are fragile, tectonically active and geologically disturbed. The terrain is rugged and inaccessible and therefore precludes thorough geotechnical investigations for the design of the cavern. The diversion and the head race tunnels were therefore used to conduct geotechnical investigations with the purpose of collecting geotechnical data for the design of two caverns. Goodman Jack tests were used to estimate the modulus of deformation of the rock masses. Load cells and tape extensometers were used to monitor the support pressure and the tunnel closures. The modulus of deformation varied from 0.18 to 0.32 kg/cm.sq. X 105. Tunnel closures were about 0.3% of the tunnel size. The support pressure stabilized within three months of excavation and the measured support pressures varied between 0.16 and 1.14 kg/cm.sq. This geotechnical data indicate that the rock masses behaviour was elastic in nature and the cavern could be designed without much difficulties

Cavern Wall Support Requirements in a Hydro-Electric Project

Construction of a 23m wide, 57m high, and 210m long underground power house cavern is in progress as a part of the multi-purpose Sardar Sarovar Project in India. The rock mass around the cavern is basalt which is intruded by a number of dolerite dykes. In view of the high side walls of the cavern, and the presence of a 1 to 2m thick shear zone running across the cavern width, a comprehensive approach was worked out for estimation of the wall support requirements. The approach included estimation of the roof support requirements using the four available approaches, and comparison of these requirements with the roof support system actually provided, and established as safe and adequate by the instrumentation data of six years. A favourable comparison established the reliability of the approaches used, and the most reliable of these approaches, i.e., the Barton\u27s approach was then used with confidence for estimation of the wall support requirements

Case History of Maneri-Uttarkashi Power Tunnel

A 8.56 km long circular tunnel of 4.75 m diameter has been constructed under Maneri hydel project on the river Bhagirathi. The tunnel passes alternatively through quartzitic and metabasic rock formations of the young Himalayan terrain. Tunnel excavation was started from four faces, one at the upstream end at maneri, two from an intermediate adit at Heena, and one at the downstream end near Uttarkashi where a 80 MW surface powerhouse is located. In excavating the tunnel from different faces, the problems of tunnel face collapse with heavy ingress of water, cavity formations and large tunnel closures leading to buckling of steel ribs on account of squeezing ground conditions were encountered. In the paper the approach of these problems has been dealt in detail. The predicted values of support pressure obtained from Terzaghi, Barton et al and CMRS approaches have been compared with the observed values of support pressure. The CMRS approach shows promise for better results in both squeezing and the elastic ground conditions

Experiences of the Support Designs in the Two Large Underground Openings in India

Support requirements for two caverns arc worked out by empirical and the numerical approaches. The adequacy of the shotcrete-rock bolt support system is monitored by measuring the deformations of caverns walls and roof. The measurements are compared with the results obtained from the numerical approach. Brief geology, the supports, and the results of performance monitoring are presented in the paper

Squeezing Problems in Indian Tunnels

Case histories of three Indian tunnels indicate that squeezing conditions are created due to plastic flow of rock masses under the influence of high cover pressures. These examples emphasize that a tunnel experiencing squeezing conditions must be allowed to deform to optimize support costs and avoid delays. Allowance for desirable tunnel deformations must, therefore, be made while planning the size of excavation. Field data has shown that a flexible support system of compressible backfill and steel ribs may be used as an alternative to shotcrete support which is unpractical in Indian tunnels excavated largely by conventional methods. Instrumentation indicates that large broken zones are associated with late stabilization and that the coefficient of volumetric expansion of failed rock masses is significantly lower than believed so far. Comparison of measured rock pressures with those estimated from available methods shows that the elasto-plastic theory may provide reliable predictions provided that the strength parameters of rock masses are known precisely

Single Center Experience of Sirolimus Therapy in Head and Neck Low-flow Vascular Malformations

OBJECTIVE: Recently, studies have shown that sirolimus is clinically efficacious in the treatment of some low-flow vascular malformations (LFVM). This study aimed to assess the efficacy and safety of sirolimus in treating complex head and neck (H&N) LFVM that were challenging and/or refractory to standard treatment. METHODS: Each patient had baseline and 6-months assessments consisting of clinical history and examination, quality of life (QoL) questionnaires, laboratory investigations, MRI and medical photography. Patients were followed up 1-week and then 1-monthly for 6-months. Wilcoxon signed-rank test was used to compare pre-and 6-months treatment in all 8 domains of RAND 36-Item Short Form Health Survey (SF-36), hospital anxiety and depression scale (HADS), and visual analog score for pain (VAS-P). P < 0.05 was considered significant. RESULTS: Seven patients (median age 43 years, range 23-65 years) were recruited. Six patients completed the six-months course of therapy with 1 patient withdrawing due to intolerable side effects. All six patients reported reduction of swelling with and without other symptom improvement related to the vascular malformations while on treatment. However, at 1-month review after discontinuation of sirolimus, 5 patients reported return of initial symptoms. Overall, patients demonstrated an improvement in QoL six-months treatment but there was no statistical significance (P > 0.05) in all 8 domains of SF-36, HADS and VAS-P. Five patients demonstrated a minimum 10% decrease in lesion size six-months treatment (median 21%, range 13-40%). A Wilcoxon signed-rank test showed that sirolimus treatment did elicit a statistically significant change in lesion size in either direction (Z = -1.992, P = 0.046). The most common side effects found were dyslipidaemia (n-4) and mouth ulcers (n = 2). CONCLUSIONS: In our preliminary experience, sirolimus is effective and safe in treating patients with complex H&N LFVM. This provides an alternative treatment where standard treatment is challenging and/or refractory