Ablation Rates (ablation + rate)

Distribution by Scientific Domains


Selected Abstracts


Surface Heat Balance and Spatially Distributed Ablation Modelling at Koryto Glacier, Kamchatka Peninsula, Russia

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2004
Keiko Konya
Abstract To investigate the characteristics of ablation at Koryto Glacier, a mountain glacier under maritime climate in Kamchatka Peninsula, Russia, we made field observations from August to early September 2000. At a site near the equilibrium line, the 31-day average net radiation, sensible heat flux, and latent heat flux were 43, 59 and 31 W,2, respectively. We developed a new distributed ablation model, which only needs measurements of air temperature and global radiation at one site. Hourly ablation rates at this site obtained by the energy balance method are related to measured air temperature and global radiation by linear multiple regression. A different set of multiple regression coefficients is fitted for snow and ice surfaces. Better estimates of ablation rate can be obtained by this approach than by other temperature index models. These equations are then applied to each grid cell of a digital elevation model to estimate spatially distributed hourly melt. Air temperature is extrapolated using a constant temperature lapse rate and global radiation is distributed considering topographic effects. The model enables us to calculate the hourly spatial distribution of ablation rates within the glacier area and could well provide a realistic simulation of ablation over the whole glacier. [source]


Laser,target interaction during high-power pulsed laser deposition of superconducting thin films

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007
Ranran Fang
Abstract We present a theoretical model to describe the high-power nanosecond pulsed laser ablation of multi-elemental oxide superconductors by considering both the vaporization effect and the plasma shielding effect. Using as an example a YBa2Cu3O7 target, the numerical solutions are obtained by solving the heat flow equations using a finite difference method. We obtain the time dependence of temperature, the transmitted intensity and the ablation rate of the target. The numerical results agree well with the experimental data and are much better than without considering the effects of vaporization and plasma shielding, which indicates that the two effects in high-power nanosecond laser ablation of superconductors must not be neglected. The present model will be helpful for the investigation of superconducting thin films prepared by pulsed laser deposition. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Rotoresect for bloodless transurethral resection of the prostate: a 4-year follow-up

BJU INTERNATIONAL, Issue 1 2003
M.S. Michel
OBJECTIVE To report the results and long-term follow-up of transurethral resection of the prostate (TURP) with a new resection device, the Rotoresect (Karl Storz, Tuttlingen, Germany). PATIENTS AND METHODS Most endoscopic resection techniques for benign prostatic tissue aim for high ablation rates and minimal bleeding. Available resection electrodes are effective, but cause high blood loss (loop electrode), or less bleeding but poorer ablation rates (electrovaporization). To resolve these conflicts the Rotoresect was developed in 1995; it consists of a specially designed rotating resection electrode, driven by a micromotor, and a high-frequency current to enable simultaneous coagulation, vaporization and mechanical tissue removal during resection. To date, 84 patients with benign prostatic hyperplasia have had their prostate resected with this device (mean prostate size 46.0, sd 18.4 mL) and have been assessed for up to 4 years. RESULTS During resection there was very little bleeding, with no significant changes in haemoglobin or sodium levels. The mean (sd) duration of catheterization was 1.4 (1.1) days; the urinary peak flow rate was improved from 9.7 (3.2) to 24.2 (8.23) mL/s and the residual urine volume reduced from 187.3 (109.6) to 22.7 (19.5) mL. The International Prostate Symptom Score and quality-of-life index were both improved, from 24.0 (7.5) to 4.1 (2.7), and 4.2 (3.2) to 0.8 (0.9), respectively. Overall the results were stable during the 4 years of follow-up. CONCLUSION The Rotoresect combines the advantages of standard resection (high ablation rate) by actively rotating the resection electrode, and the haemostatic effect of electrovaporization (minimal blood loss) by simultaneous tissue coagulation and vaporization. [source]


Ecohydrological controls on snowmelt partitioning in mixed-conifer sub-alpine forests

ECOHYDROLOGY, Issue 2 2009
Noah P. Molotch
Abstract We used co-located observations of snow depth, soil temperature, and moisture and energy fluxes to monitor variability in snowmelt infiltration and vegetation water use at mixed-conifer sub-alpine forest sites in the Valles Caldera, New Mexico (3020 m) and on Niwot Ridge, Colorado (3050 m). At both sites, vegetation structure largely controlled the distribution of snow accumulation with 29% greater accumulation in open versus under-canopy locations. Snow ablation rates were diminished by 39% in under-canopy locations, indicating increases in vegetation density act to extend the duration of the snowmelt season. Similarly, differences in climate altered snow-season duration, snowmelt infiltration and evapotranspiration. Commencement of the growing season was coincident with melt-water input to the soil and lagged behind springtime increases in air temperature by 12 days on average, ranging from 2 to 33 days under warmer and colder conditions, respectively. Similarly, the timing of peak soil moisture was highly variable, lagging behind springtime increases in air temperature by 42 and 31 days on average at the Colorado and New Mexico sites, respectively. Latent heat flux and associated evaporative loss to the atmosphere was 28% greater for the year with earlier onset of snowmelt infiltration. Given the large and variable fraction of precipitation that was partitioned into water vapour loss, the combined effects of changes in vegetation structure, climate and associated changes to the timing and magnitude of snowmelt may have large effects on the partitioning of snowmelt into evapotranspiration, surface runoff and ground water recharge. Copyright © 2009 John Wiley & Sons, Ltd. [source]


THE RESPONSE OF PARTIALLY DEBRIS-COVERED VALLEY GLACIERS TO CLIMATE CHANGE: THE EXAMPLE OF THE PASTERZE GLACIER (AUSTRIA) IN THE PERIOD 1964 TO 2006

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2008
ANDREAS KELLERER-PIRKLBAUER
ABSTRACT. Long-term observations of partly debris-covered glaciers have allowed us to assess the impact of supra-glacial debris on volumetric changes. In this paper, the behaviour of the partially debris-covered, 3.6 km2 tongue of Pasterze Glacier (47°05,N, 12°44,E) was studied in the context of ongoing climate changes. The right part of the glacier tongue is covered by a continuous supra-glacial debris mantle with variable thicknesses (a few centimetres to about 1 m). For the period 1964,2000 three digital elevation models (1964, 1981, 2000) and related debris-cover distributions were analysed. These datasets were compared with long-term series of glaciological field data (displacement, elevation change, glacier terminus behaviour) from the 1960s to 2006. Differences between the debriscovered and the clean ice parts were emphasised. Results show that volumetric losses increased by 2.3 times between the periods 1964,1981 and 1981,2000 with significant regional variations at the glacier tongue. Such variations are controlled by the glacier emergence velocity pattern, existence and thickness of supra-glacial debris, direct solar radiation, counter-radiation from the valley sides and their changes over time. The downward-increasing debris thickness is counteracting to a compensational stage against the common decrease of ablation with elevation. A continuous debris cover not less than 15 cm in thickness reduces ablation rates by 30,35%. No relationship exists between glacier retreat rates and summer air temperatures. Substantial and varying differences of the two different terminus parts occurred. Our findings clearly underline the importance of supra-glacial debris on mass balance and glacier tongue morphology. [source]


Surface Heat Balance and Spatially Distributed Ablation Modelling at Koryto Glacier, Kamchatka Peninsula, Russia

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2004
Keiko Konya
Abstract To investigate the characteristics of ablation at Koryto Glacier, a mountain glacier under maritime climate in Kamchatka Peninsula, Russia, we made field observations from August to early September 2000. At a site near the equilibrium line, the 31-day average net radiation, sensible heat flux, and latent heat flux were 43, 59 and 31 W,2, respectively. We developed a new distributed ablation model, which only needs measurements of air temperature and global radiation at one site. Hourly ablation rates at this site obtained by the energy balance method are related to measured air temperature and global radiation by linear multiple regression. A different set of multiple regression coefficients is fitted for snow and ice surfaces. Better estimates of ablation rate can be obtained by this approach than by other temperature index models. These equations are then applied to each grid cell of a digital elevation model to estimate spatially distributed hourly melt. Air temperature is extrapolated using a constant temperature lapse rate and global radiation is distributed considering topographic effects. The model enables us to calculate the hourly spatial distribution of ablation rates within the glacier area and could well provide a realistic simulation of ablation over the whole glacier. [source]


Effect of snowpack removal on energy balance, melt and runoff in a small supraglacial catchment

HYDROLOGICAL PROCESSES, Issue 14 2002
Ian C. Willis
Abstract Modelling melt and runoff from snow- and ice-covered catchments is important for water resource and hazard management and for the scientific study of glacier hydrology, dynamics and hydrochemistry. In this paper, a distributed, physically based model is used to determine the effects of the up-glacier retreat of the snowline on spatial and temporal patterns of melt and water routing across a small (0·11 km2) supraglacial catchment on Haut Glacier d'Arolla, Switzerland. The melt model uses energy-balance theory and accounts for the effects of slope angle, slope aspect and shading on the net radiation fluxes, and the effects of atmospheric stability on the turbulent fluxes. The water routing model uses simplified snow and open-channel hydrology theory and accounts for the delaying effects of vertical and horizontal water flow through snow and across ice. The performance of the melt model is tested against hourly measurements of ablation in the catchment. Calculated and measured ablation rates show a high correlation (r2 = 0·74) but some minor systematic discrepancies in the short term (hours). These probably result from the freezing of surface water at night, the melting of the frozen layer in the morning, and subsurface melting during the afternoon. The performance of the coupled melt/routing model is tested against hourly discharge variations measured in the supraglacial stream at the catchment outlet. Calculated and measured runoff variations show a high correlation (r2 = 0·62). Five periods of anomalously high measured discharge that were not predicted by the model were associated with moulin overflow events. The radiation and turbulent fluxes contribute c. 86% and c. 14% of the total melt energy respectively. These proportions do not change significantly as the surface turns from snow to ice, because increases in the outgoing shortwave radiation flux (owing to lower albedo) happen to be accompanied by decreases in the incoming shortwave radiation flux (owing to lower solar incidence angles) and increases in the turbulent fluxes (owing to higher air temperatures and vapour pressures). Model sensitivity experiments reveal that the net effect of snow pack removal is to increase daily mean discharges by c. 50%, increase daily maximum discharges by >300%, decrease daily minimum discharges by c. 100%, increase daily discharge amplitudes by >1000%, and decrease the lag between peak melt rates and peak discharges from c. 3 h to c. 50 min. These changes have important implications for the development of subglacial drainage systems. Copyright © 2002 John Wiley & Sons, Ltd. [source]


The influence of large-scale atmospheric circulation on the surface energy balance of the King George Island ice cap

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2001
Matthias Braun
Abstract During the austral summer 1997,1998 three automatic weather stations were operated at different altitudes on the sub-Antarctic ice cap of King George Island (South Shetland Islands). Snowmelt was derived from energy balance computations. Turbulent heat fluxes were calculated from meteorological measurements using the bulk aerodynamic approach, with net radiation being measured directly. Modelled ablation rates were compared with readings at ablation stakes and continuously measured snow height at a reference site. Snow depletion and daily snowmelt cycles could be well reproduced by the model. Generally, radiation balance provided the major energy input for snowmelt at all altitudes, whereas sensible heat flux was a second heat source only in lower elevations. The average latent heat flux was negligible over the entire measuring period. A strong altitudinal gradient of available energy for snowmelt was observed. Sensible heat flux as well as latent heat flux decreased with altitude. The measurements showed a strong dependence of surface energy fluxes and ablation rates on large-scale atmospheric conditions. Synoptic weather situations were analysed based on AVH RR infrared quicklook composite images and surface pressure charts. Maximum melt rates of up to 20 mm per day were recorded during a northwesterly advection event with meridional air mass transport. During this northwesterly advection, the contribution of turbulent heat fluxes to the energy available for snowmelt exceeded that of the radiation balance. For easterly and southerly flows, continentally toned, cold dry air masses dominated surface energy balance terms and did not significantly contribute to ablation. The link between synoptic situations and ablation is especially valuable, as observed climatic changes along the Antarctic Peninsula are attributed to changes in the atmospheric circulation. Therefore, the combination of energy balance calculations and the analysis of synoptic-scale weather patterns could improve the prediction of ablation rates for climate change scenarios. Copyright © 2001 Royal Meteorological Society [source]


70 vs 120 W thulium:yttrium-aluminium-garnet 2 µm continuous-wave laser for the treatment of benign prostatic hyperplasia: a systematic ex-vivo evaluation

BJU INTERNATIONAL, Issue 3 2010
Thorsten Bach
Study Type , Aetiology (case series) Level of Evidence 4 OBJECTIVE To evaluate the ablative and haemostatic properties of the recently introduced 120-W thulium:yttrium-aluminium-garnet (Tm-YAG) laser and to assess these results against those of the previously introduced 70-W Tm-YAG laser. MATERIALS AND METHODS The ex-vivo model of the isolated blood-perfused porcine kidney was used to determine the ablation capacity, haemostatic properties and coagulation depth of a 2 µm continuous-wave Tm-YAG laser. The energy was delivered using a 550-µm and an 800-µm bare-ended fibre. The results of the recently introduced 120-W Tm-YAG were compared to the established 70-W device. Kidney tissue was embedded for histological evaluation. After staining (haematoxylin and eosin, H&E; and NADH) of the specimen, the coagulation zone and depth of the necrotic tissue layer were measured. RESULTS With increased power output, the mean (sd) rate of vaporization of tissue increased, from 9.80 (3.03) g/10 min at 70 W to 16.41 (5.2) g/10 min at 120 W using the 550 µm fibre. The total amount of ablated tissue using the 800 µm fibre was lower than with the 550 µm fibre. With increasing power output the bleeding rate remained stable in either group. Tissue penetration remained shallow, even with increasing power output. In contrast to H&E staining, where the coagulation zone was measured, NADH staining showed an inner zone of necrotic tissue, again with no difference between the 70- and the 120-W Tm-YAG. CONCLUSION The 120-W Tm-YAG offers significantly higher ablation rates than the 70-W device, and despite the increased rate of ablation with the 120-W Tm-YAG, the bleeding rate and depth of tissue penetration were comparable to those using the 70-W device. [source]


Rotoresect for bloodless transurethral resection of the prostate: a 4-year follow-up

BJU INTERNATIONAL, Issue 1 2003
M.S. Michel
OBJECTIVE To report the results and long-term follow-up of transurethral resection of the prostate (TURP) with a new resection device, the Rotoresect (Karl Storz, Tuttlingen, Germany). PATIENTS AND METHODS Most endoscopic resection techniques for benign prostatic tissue aim for high ablation rates and minimal bleeding. Available resection electrodes are effective, but cause high blood loss (loop electrode), or less bleeding but poorer ablation rates (electrovaporization). To resolve these conflicts the Rotoresect was developed in 1995; it consists of a specially designed rotating resection electrode, driven by a micromotor, and a high-frequency current to enable simultaneous coagulation, vaporization and mechanical tissue removal during resection. To date, 84 patients with benign prostatic hyperplasia have had their prostate resected with this device (mean prostate size 46.0, sd 18.4 mL) and have been assessed for up to 4 years. RESULTS During resection there was very little bleeding, with no significant changes in haemoglobin or sodium levels. The mean (sd) duration of catheterization was 1.4 (1.1) days; the urinary peak flow rate was improved from 9.7 (3.2) to 24.2 (8.23) mL/s and the residual urine volume reduced from 187.3 (109.6) to 22.7 (19.5) mL. The International Prostate Symptom Score and quality-of-life index were both improved, from 24.0 (7.5) to 4.1 (2.7), and 4.2 (3.2) to 0.8 (0.9), respectively. Overall the results were stable during the 4 years of follow-up. CONCLUSION The Rotoresect combines the advantages of standard resection (high ablation rate) by actively rotating the resection electrode, and the haemostatic effect of electrovaporization (minimal blood loss) by simultaneous tissue coagulation and vaporization. [source]