Low Specific Mass Research Articles

Effect of Feedstock Powders on the Microstructural and Electrical Characteristics of 8 mol% Yttria-Stabilized Zirconia Plasma-Sprayed Coatings

Plasma-sprayed coatings of 8 mol% yttria-stabilized zirconia (YSZ) were fabricated using the feedstock powders obtained from co-precipitation (PPT) and spray-drying (SD) processes. Particle size and the specific mass (SM) of the feedstock powder were found to be the critical parameters that influence the microstructural and electrical properties of the coatings. While dense and larger particle-sized PPT powder resulted in a porous microstructure, dense coatings were obtained for SD powders with relatively lower SM. Electrical conductivity values of SD-coatings were found to be 30% higher than that of PPT-coatings. Electrical conductivity values of plasma-sprayed PPT-coatings improved significantly on decreasing the particles size. However, the size effect was only subtle in the case of SD coatings. PPT-coatings fabricated from smaller particle-sized powders had the necessary electrical conductivities appropriate for solid oxide fuel cell electrolyte applications.

A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes

The present study explores the versatility of solution combustion method for preparing powders of varying characteristics suitable for intermediate temperature solid oxide fuel cell (IT-SOFC) fabrication. The promising electrolyte material for IT-SOFC, Gd0.2Ce0.8O2−δ (GDC), is considered for the present investigation. GDC powders consisting of sub-micron sized particles (<250 nm) and micron sized (>20 μm) particles are produced by varying the fuel used in the combustion reaction. Highly sinteractive nano-GDC powders prepared using oxalyl dihydrazide as a fuel results in dense pellets with high conductivity (3 × 10−4 Scm−1 at 400 °C). This powder also results in a stable suspension suitable for wet powder spraying and electrophoretic deposition. Powders with larger particle size (>20 μm) prepared by solution combustion method using mixture of fuels, exhibits necessary flowability for atmospheric plasma spraying (APS). GDC coatings fabricated by APS using flowable powders are dense with superior adhesion between the splats. Good adhesion between the splats in the APS coatings is attributed to the higher level of melting of the combustion synthesized particles in the plasma flame owing to their low specific mass.

The influence of acrylate triblock copolymer embedded in matrix on composite structures’ responses to low-velocity impacts

In passive safety structures the use of composite materials has increased significantly recently due to their low specific mass and high energy absorption capacities. The purpose of this experimental study is to describe the macroscopic behaviors of different Kevlar woven composite materials with different kinds of matrix (pure and with acrylate based block copolymer additives: Nanostrength®) under low-velocity impact. Tests were performed with a drop weight tower on square plates (100 × 100 mm 2) clamped by means of a circular fixture. Images were recorded during impact by a high-speed video camera fixed underneath the plate. It was found that Kevlar epoxy composite material with Nanostrength M52N has the best resistance to perforation. The second purpose is to study the influence of physicochemical parameters (fibers ratio, percentage of M52N, micro-porosity) on the behavior of the selected composite material. Based on correlation between pictures, displacement, and loading histories, two criteria are defined to quantify the energy absorption capability of the composite material just before the fibers’ failure and after perforation of the plate. A high-fiber weight improves performance regarding criteria and also improves the efficiency of the block copolymer present in the epoxy matrix.

Dynamic Simulation of a Space Reactor System with Closed Brayton Cycle Loops

A dynamic simulation model for space reactor power systems with multiple closed Brayton cycle loops for energy conversion is developed and demonstrated for a startup transient. The simulated power system employs a submersion-subcritical safe space S ^ 4 reactor with a negative temperature reactivity feedback and has no single-point failures in reactor cooling and energy conversion. The S ^ 4 reactor core is divided into three hydraulically independent sectors, and each sector has a separate closed Brayton cycle loop that is thermal-hydraulically coupled to a circulating liquid NaK-78 secondary loop with two water heat pipe heat rejection radiator panels. Each closed Brayton cycle loop has a Brayton rotating unit designed and optimized for high thermal efficiency and low specific mass (1.16 kg/kW e ). The reactor coolant and the closed Brayton cycle working fluid is a He-Xe binary gas mixture with a molecular weight of 40 g/mol. Results are presented for a startup transient of the S ^ 4 closed Brayton cycle power system to full-power operation at a reactor thermal power 471 kW th , a Brayton rotating unit shaft speed of 45 krpm, and turbine and compressor inlet temperatures of 1149 and 400 K, respectively. At these conditions, the nominal electrical power and thermal efficiency of the power system are 130.8 kW e and 27.8%.

Affects of applied stresses on the isothermal and cyclic high-temperature oxidation behavior of superalloys

In this investigation, the affect of applied tensile stresses on the isothermal and cyclic oxidation behavior of nickel-based superalloys was studied. The influence of applied stresses was investigated through measurements of specific mass change, oxide morphology and thickness, degree and depth of internal oxidation, and compositional changes in and around the oxide scales. It was determined that an applied tensile stress generally led to larger Cr/Ni ratios in the oxide scales, greater overall chromium depletion values directly under the oxide scales, lower specific mass change values, and thinner oxide scales. These affects are attributed to a greater concentration of dislocations, defects, etc. in the materials caused by the applied stress. These defects act as fast diffusion paths for the Cr atoms to diffuse to the surface, and thus, cause a reduction in the duration of the less protective transient oxidation period, and promote a faster formation of the protective Cr 2O 3 layer.

Relação entre a condutividade térmica e parâmetros físicos dos gnaisses Casablanca, Juparaná Delicato e Giallo Falésia (Ceará-Brasil)

This work presents and discusses the relationship among the thermal conductivity (κ), the physical parameters and the petrographic aspects of the Casablanca, Delicato and Falésia gneisses. In general, the outcomes of thermal conductivity, although affected by local influences from the mineralogy, they reflect the general physical characteristics of each different rock. In this case, the discrepant physical characteristics influence significantly the results, including the thermal conductivity. The results show that the lower values of thermical conductivity (κ) from the Falésia gneiss are compatible with the results of its physical índex, since the level of conductivity will be inverse to the rock porosity level (high conductivity, low rock porosity), or direct to the specific mass (low conductivity, low specific mass). The Delicato gneiss presents higher values of ultrasonic speed on its natural state, denoting a higher cohesion of this rock in comparison to the others. The lower values were stated to the Falesia gneiss, and are controlled by the micaceous levels, fissures and change intensity in the feldspars. The Falesia gneiss showed the higher values of thermical dilatation, improved by the expressive amount of biotite and by the susceptibility of this mineral to thermal fatigue. The three samples have a behavior similar to that of rocks of medium to high thermal conductivity, with mean values ranging from 3,19 W/mºK (Casablanca gneiss) to 3,64W/mºK (Delicato gneiss). The Falesia gneiss shows the lower mean value (2,99W/mºK), as consequence of the presence of fissures and higher intensity of mineral alteration. Conclusively, the results of thermal conductivity ratify and answer in a consistent way the tests and physical and technological results serving as a tool to petrophysical characterization.

Behavior of composite and polycarbonate plate under impact

The use of filled composite materials in passive safety structure has significantly increased recently because of their low specific mass, stiffness and energy absorption capacities. However those new light weight materials are supposed to exhibit equal or higher performances than classical ones. Therefore interesting applications by using those materials can be thought about like in the manufacturing of aeronautical helmets.

High-Power Brayton Rotating Unit for Reactor and Solar Dynamic Power Systems

The University of New Mexico Brayton Rotating Unit-3 (UNM-BRU-3), designed for 40 g/mole He-Xe working fluid, is optimized for shaft speed of 45 krpm, turbine and compressor inlet temperatures of 1149 and 400 K, and thermal power input of 157 k W th . At these conditions, the electrical power and thermal efficiency are 54.2 k W e and 34.5%, the compressor exit pressure is 1.044 MPa, the He-Xe flow rate is 1.54 kg/s, and the corresponding specific mass is 0.98 kg/kW e . Investigated are the effects of decreasing the turbine inlet temperature to 900 K and the thermal power input to 40 k W th and varying the shaft speed from 30 to 55 krpm. At 900 K turbine inlet temperature, thermal power input of 157 k W th , and shaft rotation speed of 45 krpm, the UNM-BRU-3 has a thermal efficiency of 22.8% and generates 34.2 k W e at a compressor exit pressure of 1.3 MPa and He-Xe flow rate of 2.07 k g/s; but the specific mass of the unit increases to ∼1.55 kg/k W e . The unit performance at 900 K is attractive for early deployment of space reactor and solar dynamics power systems with stainless steel structure, thus minimizing development cost and enhancing operation reliability and life. The low specific mass of UNM-BRU-3 will reduce the total mass and launch cost of these systems.

Methane partial oxidation reverse flow reactor scale up and optimization

Estimation of methane partial oxidation reciprocal flow filtration combustion reactor performance in the case of its scale up (flow rates G = 4, 40, 400 and 4000 Nm 3/h) as well as parametric study of the bigger scale reactor is performed numerically. It is shown that residence time growth with reactor scale up is compensated with maximum temperature decrease. Reduced aspect ratio reactors are considered for higher productivity systems. Parametric study performed for G = 400 Nm 3/h reduced aspect ratio reactor show: Φ = 2.7 equivalence ratio is optimal to maximize conversion ratio and H 2 output concentration; smaller porous media particle d 0 = 2–3 mm should be used for lower specific mass flow rates G m = 0.5–1 kg/m 2/s and bigger particles – for higher G m ; porosity variation m = 0.4–0.55 does not influence conversion ratio; kaowool insulation layer increase from 3 to 10 cm results in ∼1% growth of conversion ratio while further increase up to 50 cm provides less than 0.5% gain. The results may be utilized for bigger scale reactors design, optimization and exploitation.

Evaluation of Silicon Nitride Ceramic Cutting Tools with Diamond Coatings

There is a substantial increase on carbon-carbon composites use for engineering applications, considering its high temperature properties and low specific mass. However the machining costs are relatively high, and new cutting tools, mainly ceramics, must be developed to overcome such difficulty, aiming cost reductions. In this work, silicon nitride based ceramics has been prepared , by pressureless sintering of silicon nitride powders and appropriate amounts of Al2O3,Ce2O3, Y2O3 and AlN. Cutting tools were prepared from the sintered materials, with geometry according to ISO1832. Selected cutting tools were also diamond coated by a hot filament-assisted Chemical Vapor Deposition (HFCVD) diamond coating process. Carbon Fiber Reinforced Carbon (CFRP) composites machining was performed, to evaluate the diamond coating influence on machining performance. After the tests, the uncoated tools presented severe flank wear and shorter life than the diamond coated ceramic tools. This flank wear is caused by the abrasive carbon powder generated during the facing operation. On CVD diamond coated α-SiAlON ceramic tools, no flank wear was observed, and the cutting edge remained unmodified, even for severe test conditions, such as high cutting length and speed. Carbon particles, originated from the machined composite, do not promotes diamond film rupture, but instead, acts as lubricant film and reduces composite surface initial roughness.

The hydraulic separator Multidune: Preliminary tests on fluid-dynamic features and plastic separation feasibility

Recycling of plastic materials is a rapidly developing discipline because of environmental awareness, the need to conserve materials and energy, and the growing demand to increase the production economy. The main problem in plastics recovery and recycling is related to the variety of plastic wastes, even if selective collection occurs. Therefore, plastic materials can be recycled either as mixtures or as single types, separating the different typologies by their physical (size, specific mass, etc.) and/or chemical properties. However, separation of plastics in single typologies by traditional processes and devices is difficult due to their typical low variability in properties. This paper presents a new research development for recycling industry: the Multidune separator. This is a device constructed from a sequence of parallel semi-cylindrical tubes of transparent plastic welded together in a plane. The lower half is shifted laterally and then fixed relative to the upper half. Flow is then induced in the lateral direction normal to the axis of the tubes, creating a main flow channel and two recirculation zones. This apparatus creates a differential transport of particles of low specific mass, near to 1g/cm3, allowing their separation. The flow field in the Multidune separator is studied via Particle Tracking Velocimetry (PTV). Eulerian analysis of the data is performed to gather information about the fluid-dynamics features established by different hydraulic heads at the inlet of the Multidune. Preliminary tests on monomaterial samples have been performed, varying several operative parameters to determine the best set of values. Therefore, separation tests have been executed on composite samples, obtaining satisfactory results in terms of plastic separation feasibility.

Liquid Metal Loop and Heat Pipe Radiator for Space Reactor Power Systems

This paper presents four radiator configurations that could be stowed in the launch bay of the DELTA-IV Heavy vehicle and have effective areas of 69.1 to 350 m 2 . The radiator for a space reactor power system with a lithium-cooled sectored compact reactor and thermoelectric converters has an effective area of 203 m 2 and lowest specific mass. The sectored compact reactor and thermoelectric converters system generates ∼114 kWe for 7-10 years. The radiator consists of six panels, each having a forward, fixed segment and two rear, deployable segments, and rejects heat into space using rubidium heat pipes with carbon-carbon armor and fins. The D-shaped heat pipes operate below 50 % of the prevailing sonic or capillary limit. The radiator operates at a constant pressure drop of 12 kPa and inlet and exit temperatures of 780 and 755 K. Investigated are the effects on the radiator's specific mass and lithium inventory of 1) tapering and changing width of coolant channels, 2) thermal-hydraulically coupling the panel segments in parallel, and 3) using perforated dividers between inlet- and exit-channels. The radiator with perforated dividers has a wet specific mass of 6.82 kg/m 2 , a liquid-lithium inventory of 179.3 liters, and a stowed height of 8 m.

DynMo-TE: Dynamic simulation model of space reactor power system with thermoelectric converters

A space reactor power system (SRPS) has been developed for avoidance of single point failures in reactor cooling and energy conversion. The sectored compact reactor (SCoRe) in this system is lithium-cooled and the reactor core is divided into six equal sectors with liquid metal heat pipes dividers. These reactor sectors are neutronically, but not thermal-hydraulically, coupled. Each sector has its own primary and secondary circulating lithium loops, which are thermally coupled both in a SiGe thermoelectric (TE) power conversion assembly (PCA) and a thermoelectric conversion assembly (TAC) that powers the electromagnetic pumps in the primary and secondary loops. Each secondary loop also has a separate, segmented radiator panel that is optimized for low specific mass and low liquid lithium inventory. The primary loops transport the thermal power generated in the reactor to six PCAs that nominally supply a total of 111.5 kW e to the load at 450 V DC. Each of the 12 primary and secondary loops has its own bellows-type accumulator that is designed to regulate the lithium pressures in the loops. A dynamic simulation model of this thermoelectric SRPS (DynMo-TE) has been developed and used to investigate the transient operation of the system during a startup from a fully-thawed condition at 600 K, to nominal steady-state operation at which the lithium coolant exits the reactor at only 1179 K. Also investigated is the load-following characteristic of the SCoRe-TE SRPS, following a change in the electrical load demand.

Studies on Low Specific Mass NFR/MHD Power Generation System for Space Applications

The aim of this study is to examine a magnetohydrodynamic (MHD) power generation system for the space applications using a nuclear fission reactor as the heat source. This MHD system uses He/Xe mixed gas as coolant instead of alkali-metal-seeded inert gas. The interrelation between the specific heat of the coolant and the mass flow rate was examined. When the specific heat decreases due to increase of the Xe fraction, the mass flow rate must increase to keep the output power and plant efficiency constant. A regenerator efficiency of 100% and reactor output temperature of 1800 K or higher should be chosen for the highest plant efficiency of 56% and lowest specific mass of 1.4 kg/kW. This highest plant efficiency and lowest specific mass were also expected by optimizing parameters for enthalpy extraction and radiator temperature. This means achieving high plant efficiency or low specific mass gives different values for enthalpy extraction and radiator temperature. With a higher net electrical output power, lower specific mass is obtained. This explains why the present space MHD power generation system is better than other conventional space power generation systems for the high MW-range output power.

Plasma Technologies for Reducing CO2 Emissions From Combustion Exhaust with Toxic Admixtures to Utilisable Products

The method reported here provides a contribution to CO2 and combustion exhaust utilisation. A multifunctional system for gas removal was tested on various sources of exhaust (internal combustion engine, brown coal boiler, bituminous pulverised coal boiler, gas boiler, glass oven, VOC sources) in full-scale or by-pass gas flow volumes. A spontaneously-pulsing, direct-current electric discharge operating in a corona geometry was used. The discharge has strongly shining channels migrating quickly along the stressed electrode. The synergetic effect of electric discharge and heterogeneous catalysis on the organometallic part of the product formed on the non-stressed electrode was responsible for the specific character of the products. The final product of the process is a powder with a fractal structure on the microscopic level with low specific mass and insoluble in water. The main component (95%) of the solid product is an amorphous condensate of amino acids with about 5% of organometallic compound with catalytic properties. The product was analysed using IR absorption spectrometry, microscopic photography, HPLC and thermogravimetry. The following amino acids were observed in the final product: alanine, serine, glycine, aspartic acid, lysine, arginine, methionine, histidine.

Composition and digestibility during ageing of consecutive leaves on the main stem of Italian ryegrass plants, growing undisturbed or regrowing after cutting

For modelling of grass digestibility throughout the growing season, the impact of cutting on individual leaves needs to be quantified. Therefore, a glasshouse experiment was carried out with Italian ryegrass (Lolium multiflorum Lam) grown from seed. Half of the plants were grown undisturbed until leaf stage 8, while the other half were cut at leaf stage 4, after which they were allowed to grow until leaf stage 9. The composition and digestibility characteristics of leaves 6, 7 and 8 on the main shoot of plants from both treatments were quantified. In the uncut plants, leaf blade length and mass and specific cell wall (CW) and organic matter (OM) mass (mg cm−2) was higher for consecutive leaves. During leaf ageing specific CW mass remained unchanged, while specific OM mass and CW digestibility declined, resulting in a decline of OM digestibility. CW digestibility of leaves decreased to c 78%, a value also found in an earlier experiment. The newly formed leaves after cutting had a reduced leaf size and specific leaf mass (SLM, mg DM cm−2). Leaf 6, that was damaged by cutting, showed a lower initial CW content and a rapid decline of specific CW and OM mass and of digestibility during ageing. Its low specific mass and digestibility of CW could have been related to cessation of CW synthesis during its growth after cutting, as was evidenced by the lower CW thickness of sclerenchyma cells. The later-formed leaves, 7 and 8, had digestibility characteristics similar to those of the uncut plants. Since leaf 6 hardly contributed to the total plant dry matter mass, the cut and the uncut plants differed only slightly in digestibility of the total leaf fraction. It can be concluded that cutting sets back leaf size and growth rate but has little effect on digestibility characteristics during ageing. © 1999 Society of Chemical Industry

Graft polymerization of methyl methacrylate onto short leather fibers

SummaryIn this work, the graft polymerization of methyl methacrylate (MMA) monomer ontoshort leather fibers (SLF) was investigated as a function of the monomer/leather fiber ratio.This chemical modification was made by aqueous emulsion polymerization initiated by aredox system. The effect of' the monomer concentration on the grafting parameters(deposited and grafted polymer, as well as grafting efficiency) were determined.Composites formulated with SLF without chemical modification have showed lower tensileand impact properties in comparison with composites formulated with treated fibers.However, the elongation at break values for both systems remained similar as the MMAcontent changed. The morphology of SLF grafted with MMA was examined by both opticallight microscopy (OLM) and scanning electron microscopy (SEM). Micrographs haveshown polymer deposition on individual fibers and bundles of SLF. They have alsorevealed that PMMA may interpenetrate the SLF network and be deposited in large andcoarse aggregates around individual fibers, but without occupation of the free space in thefiber net.IntroductionResidues and wastes of organic fibers are used as fillers or reinforcements inthermosets and thermoplastic polymers, such as polyethylene (PE), polypropylene (PP),polyvinyl chloride (PVC), polystyrene (PS), polymethyl metacrylate (PMMA), etc. Thecomposites formulated offer significant weight advantages, a combination of goodmechanical properties with a low specific mass, and provide the economic benefit of lowercost (1-5). Taking into account that organic fillers or fibers are derived from renewablenatural resources; most of them show a common limitation in applications. The limitation isa poor compatibility between the hydrophilic filler (high level of moisture absorption by thefiber) and the hydrophobic thermoplastic polymer. However, a large number of attemptshave been made to improve the adhesion between polymeric matrices and natural fiberssuch as coconut, wood, nutshell flour, hemp, jute, sisal, and cellulose (6-9). These attemptshave included modifying the chemistry of the fiber surface or the polymer matrix.Some investigations into chemical modification of leather fibers have beenconducted on leather products (10-11). The aims of these investigations were to producenew leather products, such as leather boards, while retaining the natural appearance ofleather. These investigations demonstrated that acrylic monomers, such as methylmethacrylate (MMA), butyl acrylate (BA) and others, can be grafted onto tanned oruntanned leather fibers with an improvement in the mechanical properties (12). However,this system (acrylic-leather) has special characteristics, not all the polymer generated isgrafted onto the leather fibers. Usually the efficiency of grafting reactions is a function of

Optimum channel geometry for solar air heaters of conventional design and constant flow operation

The study presents a remarkably simple criterion for determining the channel optimum depth-to-length ratio ( D/ L) opt which effectively maximizes the useful energy from collectors that are designed to heat a fixed mass rate of air flow. The engineering accuracy of the analytically derived criterion has been corroborated over a wide range of ambient variables, design parameters and operating conditions. The results demonstrate clearly the decisive role of the ( D/ L) ratio in enhancing heater performance. A poor choice of this ratio can significantly affect the thermal conversion efficiency, especially for lower specific mass rates. In contrast, decreasing the ( D/ L) ratio beyond the optimal value leads to a slight enhancement in heater efficiency. Of significance is the finding that, by choosing ( D/ L) opt, we maximize also the air temperature rise. For variable flow operation, however, the ratio of D/ L=2.5×10 −3 is recommended as the optimal. Moreover, the reported results and discussions have provided valuable conceptual insights regarding generalization of the performance curves of conventional solar air heaters. It is found that the analytically determined channel depth parameter, in conjunction with the air specific mass rate, are quite successful in correlating the performance in general terms.

97/05092 Improved high temperature resistant SiC filter elements: Walch, A. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13th, (1), 349–356

High temperature resistant porous ceramics are of major importance in hot gas filtration to separate particles from process and flue gases in temperature ranges of 250 C to 850 C. DIA-SCHUMALITH{reg_sign} filter elements, produced by Schumacher Umwelt- und Trenntechnik GmbH, Crailsheim, Germany for over 10 years, are clay bonded, silicon carbide (SiC) filter elements which are used successfully in hot gas applications. DIA-SCHUMALITH fulfills the critical demands of utmost filtration efficiency, low cost, and long-term durability. These membrane coated, porous filter elements are exposed to complex and aggressive gas mixtures in oxidizing or reducing atmospheres at pressures up to 30 bar and as such require excellent material properties to survive. From an environmental point of view it is important to provide a filtration media which will ensure excellent filtration efficiency with particulate removal of <3 mg/m{sub N}{sup 3} (3 ppm) at low residual pressure drops and high specific mass flow rates to yield a reasonable low cost filtration system. Hot gas filtration, successfully used in advanced clean coal technologies such as PFBC and IGCC processes, allows much higher thermodynamic efficiencies. Other advantageous and successful applications of hot gas filters are the removal of ceramic powders, pigments or catalysts from processmore » gas streams, as well as flue gas filtration in pyrolysis processes and municipal waste incinerators. Technical requirements for high temperature resistance combined with long term durability and material reliability are constantly increasing. These requirements necessitate continuous material improvements as well as ongoing test procedure developments. The results of these material developments concerning thermal and mechanical properties will be presented in this paper.« less

The influence of superimposed-ice formation on the sensitivity of glacier mass balance to climate change

The formation of superimposed ice at the surface of high-Arctic glaciers is an important control on glacier mass balance, but one which is usually modelled in only a schematic fashion. A method is developed to predict the relationship between the thickness of superimposed ice formed and the mean annual air temperature (which approximates the ice temperature at 14 m depth). This relationship is used to investigate the dependence of the proportion of snowpack water equivalent which forms superimposed ice on changes in mean annual temperature and patterns of snow accumulation. Increased temperatures are likely to reduce the extent of the zone of superimposed-ice accumulation and the thickness of superimposed ice formed. This will have a negative effect on glacier mass balance. This is true even if warming occurs only in the winter months, since near-surface ice temperatures will respond to such warming. For John Evans Glacier, Ellesmere Island, Nunavut, Canada (79°40’ N, 74°00’ W), a 1°C rise in mean annual air temperature due solely to winter warming is predicted to reduce the specific mass balance of the glacier by 0.008 m a–1 as a result of decreased superimposed-ice formation. Although such a response is small in comparison to the changes which might result from summer warming, it is nonetheless significant given the very low specific mass balance of many high-Arctic glaciers.