Velocities of mixed dense-flow/powder-snow avalanches have been measured by means of pulsed Doppler radar and by continuous wave radar at the full scale avalanche test site Vallée de la Sionne. From ...the radar data, we derive velocities of the saltation layer and of the powder part of the avalanche. The results obtained by the two different radar measurement techniques are compared and also are checked against the velocity data obtained by opto-electronic velocity sensors installed at different heights on the 20 m high mast in the avalanche track and against videogrammetry velocity data. We demonstrate that the measurements are consistent and discuss how information about the avalanche structure can be derived from the measurements.
Single-use packaging articles made of expanded polystyrene (EPS) are currently used to serve and pack a variety of food and non-food products. Recently, there have been efforts to develop and ...commercialize materials from renewable resources such as starch to replace EPS. Starch based foams are, however, brittle and sensitive to water, and thus require expensive coating steps when exposure to cold or hot liquids is required. In this report, various modified starches and additives were tested in baked foam plate formulations to improve strength and water resistance properties in lieu of coating. Foam plates made from chemically modified starches had shorter baking times, lighter weights and higher elongations at break than unmodified starch. Plates made from genetically modified (waxy) starches and polyvinyl alcohol (PVOH) had elongations to break at low humidities, which were much higher than those made from normal starches and PVOH. Addition of softwood fibers increased starch foam plate strengths at low and high humidities. Addition of monostearyl citrate to starch batter formulations gave the best improvement in water resistance among the compounds tested. Baked foams made from potato amylopectin, PVOH, aspen fiber and monostearyl citrate appeared to have adequate flexibility and water resistance to function as clamshell-type hot sandwich containers.
The rheology of snow in large chute flows Kern, M.A.; Tiefenbacher, F.; McElwaine, J.N.
Cold regions science and technology,
10/2004, Letnik:
39, Številka:
2
Journal Article
Recenzirano
The velocity profile and basal shear force were measured for snow flowing down a chute 34 m long and 2.5 m wide. The flows were approximately steady by the end of the chute where measurements were ...taken and the angle was 32°. Measurements of the basal shear stress confirm approximate dynamic balance. The velocity profile was measured using optoelectronic sensors and showed a large slip velocity at the base, a shear layer of around 50 mm and an overlying plug-like flow of about 350 mm. The velocity profile is compatible with both a Herschel–Bulkley rheological model, which combines a constant critical stress with a power law dependence on the mean shear rate, and a Cross model where the effective viscosity varies between two limits. Estimates of the Reynolds number suggest that the flow is not turbulent. The measurements are used to estimate the distribution of energy dissipation and to show that its concentration near the base may locally melt the snow, and thus serve as an explanation for icy melt surfaces observed at the base of flowing avalanche tracks.
Baked starch foams were characterized by several physical methods in order to better understand the relationship between process parameters and starch foam structure. In this process, a thin-walled ...object such as a plate is formed by heating a starch batter inside a closed mould. Normal corn and potato starches are gelatinized by this treatment but some swollen granules remain. The foams have a dense outer skin and a less dense interior with large, mostly open cells. Overall foam density and strength increase with increasing starch concentration, molecular weight and amylose content. Foam flexibility tends to increase with decreasing density. Plates made from tuber starches such as potato have lower densities and higher flexibilities than those made from cereal starches such as corn. Starch foams are useful as disposable food packaging and serving articles which can be composted after use.
Physical modelling is an important tool for obtaining insight into the internal flow structure of gravity currents such as snow avalanches, or, more practically, for estimating the dimensions of ...avalanche defense structures. We present a large-scale experimental setup, which allows the generation of avalanche-like gravity currents of snow under reproducible experimental conditions. The Weissfluhjoch chute is 34 m long, 2.5 m wide and can be run with up to 25 m
3 of natural snow. We present two types of optical velocity measurement devices based on the correlation method. We discuss their applicability to snow flows and perform an error analysis of the observed flow velocities. Furthermore, preliminary results of velocity profile measurements in the snow flow are presented. We also describe the experimental determination of the total dynamic basal friction force exerted on the ground. An effective dynamic friction coefficient is calculated.
In general, quantum computer architectures which are based on the dynamical evolution of quantum states, also require the processing of classical information, obtained by measurements of the actual ...qubits that make up the computer. This classical processing involves fast, active adaptation of subsequent measurements and real-time error correction (feed-forward), so that quantum gates and algorithms can be executed in a deterministic and hence error-free fashion. This is also true in the linear optical regime, where the quantum information is stored in the polarization state of photons. The adaptation of the photon's polarization can be achieved in a very fast manner by employing electro-optical modulators, which change the polarization of a trespassing photon upon appliance of a high voltage. In this paper we discuss techniques for implementing fast, active feed-forward at the single photon level and we present their application in the context of photonic quantum computing. This includes the working principles and the characterization of the EOMs as well as a description of the switching logics, both of which allow quantum computation at an unprecedented speed.
Quantum entanglement is the main resource to endow the field of quantum information processing with powers that exceed those of classical communication and computation. In view of applications such ...as quantum cryptography or quantum teleportation, extension of quantum-entanglement-based protocols to global distances is of considerable practical interest. Here we experimentally demonstrate entanglement-based quantum key distribution over 144 km. One photon is measured locally at the Canary Island of La Palma, whereas the other is sent over an optical free-space link to Tenerife, where the Optical Ground Station of the European Space Agency acts as the receiver. This exceeds previous free-space experiments by more than an order of magnitude in distance, and is an essential step towards future satellite-based quantum communication and experimental tests on quantum physics in space. PUBLICATION ABSTRACT
Velocities inside avalanches have been calculated for many years by calculatingthe cross-correlation between opto-electronic sensors using a method pioneered by inlinecite Nishimura et al. and Dent ...et al. Their approachhas been widely adopted but there has been little discussion of the optimal designof such instruments and the best analysis techniques. This paper discusses some ofthe different sources of error that arise and how these can be mitigated. A statisticalframework that describes such instruments is developed and used to quantify the errors.PUBLICATION ABSTRACT
Recently, there have been efforts to manufacture single-use articles, such as fast food packaging and containers, from biodegradable materials. Starch-based foams have been developed to replace the ...expanded polystyrene foam packaging currently in use. Starch-based foams are water sensitive, and thus, their mechanical properties are susceptible to changes in relative humidity. In this report, aspen fiber was added to baked cornstarch foams to improve its mechanical properties. Foam trays were made with fiber content of the batter ranging from 2.5 to 45%. The starch–fiber composite foam trays were formed by heating a starch-based batter inside a closed mold. The trays were stored at different relative humidities (5, 20, 50, 81, and 93%) for 1 week prior to mechanical testing. Aspen fiber increased the baking time needed to make a complete tray. Batters containing greater than 15% fiber needed to be added in higher amounts to the mold to make complete trays. The strength of the foam trays increased as fiber content of the trays increased, until fiber content reached about 15%. Trays containing between 15 and 30% fibers had no significant difference in tray strength. Trays containing more than 30% fiber had lower tray strength. The lower tray strength was thought to be due to the lack of uniform fiber distribution at high fiber content. Displacement of the trays at break was also affected by fiber content. The effect of fiber on displacement at break was greatest at extreme relative humidities. At low humidity (5%), displacement at break went from 2.2 to 5.4
mm as fiber content increased from 2.5 to 40%. Displacement at break increased from 9 to 20
mm as the fiber content increased from 2.5 to 40% for trays stored at 93% relative humidity. Fiber content did not effect displacement at break for trays stored at moderate relative humidities. Fiber content of 15% was adequate to increase the tray strength. Greater amounts of fiber (up to 30%) can be added without detrimental affects to strength, but increasing fiber above 15% increased baking time and increased the amount of batter needed to make a complete tray.
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