scholarly journals Temperature dependence of ice-on-rock friction at realistic glacier conditions

2017 ◽  
Vol 375 (2086) ◽  
pp. 20150348 ◽  
Author(s):  
C. McCarthy ◽  
H. Savage ◽  
M. Nettles
Keyword(s):  
Steady State ◽  
Temperature Dependence ◽  
Normal Stress ◽  
Velocity Dependence ◽  
Ice Streams ◽  
Experimental Conditions ◽  
Rock Friction ◽  
Load Point ◽  
Basal Sliding ◽  
Temperature Dependences

Using a new biaxial friction apparatus, we conducted experiments of ice-on-rock friction in order to better understand basal sliding of glaciers and ice streams. A series of velocity-stepping and slide–hold–slide tests were conducted to measure friction and healing at temperatures between −20°C and melting. Experimental conditions in this study are comparable to subglacial temperatures, sliding rates and effective pressures of Antarctic ice streams and other glaciers, with load-point velocities ranging from 0.5 to 100 µm s −1 and normal stress σ n  = 100 kPa. In this range of conditions, temperature dependences of both steady-state friction and frictional healing are considerable. The friction increases linearly with decreasing temperature (temperature weakening) from μ  = 0.52 at −20°C to μ  = 0.02 at melting. Frictional healing increases and velocity dependence shifts from velocity-strengthening to velocity-weakening behaviour with decreasing temperature. Our results indicate that the strength and stability of glaciers and ice streams may change considerably over the range of temperatures typically found at the ice–bed interface. This article is part of the themed issue ‘Microdynamics of ice’.

Temperature dependence of the resistance, impedance and capacitance of semitransparent PTB7-Th and PCBM sensor

2019 ◽  
Vol 33 (12) ◽  
pp. 1950110
Author(s):  
Muhammad Riaz ◽  
Khasan S. Karimov ◽  
Jameel-Un Nabi
Keyword(s):  
Light Intensity ◽  
Temperature Dependence ◽  
Temperature Sensor ◽  
Visual Control ◽  
Capacitance Measurement ◽  
Experimental Conditions ◽  
Temperature Resistance ◽  
Graphene Composite ◽  
Temperature Dependences ◽  
Resistance Coefficients

The temperature dependences of resistance, impedance and capacitance of semitransparent sensor having structure ITO/PTB7-Th:PC[Formula: see text]BM/Graphene composite (semisurface type) were investigated. The transparency of the sensor was 58–60%. The dependences of the resistance, impedance and capacitance at different frequencies 100 Hz, 1 kHz, 10 kHz, 100 kHz and 200 kHz and temperature in the range of 23.8–80[Formula: see text]C for the sensor were studied. It was observed that as the temperature increased from 23.8[Formula: see text]C to 80[Formula: see text]C, the resistance and impedance (at 1 kHz) of the samples decreased, on average, by a factor of 3.51 and 3.79, respectively. At same experimental conditions (1 kHz), the capacitances of the samples also decreased by a factor of 9.6. It was also noted that as frequency increased from 100 Hz to 200 kHz, the impedance of the sensor decreased by a factor of 21 and 12, at temperatures 24[Formula: see text]C and 58[Formula: see text]C, respectively. Under the same conditions, the capacitance decreased by a factor of 30 and 28, respectively. The temperature resistance coefficients were measured to be −1.31%/[Formula: see text]C, −1.30%/[Formula: see text]C, −1.27%/[Formula: see text]C, −0.84%/[Formula: see text]C, −0.72%/[Formula: see text]C and −0.33%/[Formula: see text]C for R, Z (100 Hz), Z (1 kHz), Z (10 kHz), Z (100 kHz) and Z (200 kHz), respectively. For capacitance measurement, the temperature capacitance coefficients were measured as −1.39%/[Formula: see text]C, −1.38%/[Formula: see text]C, −1.37%/[Formula: see text]C, −1.36%/[Formula: see text]C and −1.34%/[Formula: see text]C, respectively. The semitransparent PTB7-Th- and PC[Formula: see text]BM-based temperature sensor can be used for measurement of the temperature as a teaching aid in situations where visual control of illumination and light intensity is required.

scholarly journals Model Studies on Ice-Stream Surging

1989 ◽  
Vol 12 ◽  
pp. 132-137 ◽  
Author(s):  
U. Radok ◽  
B.J. McInnes ◽  
D. Jenssen ◽  
W.F. Budd
Keyword(s):  
Steady State ◽  
Sliding Mode ◽  
Ice Streams ◽  
Model Studies ◽  
Ice Stream ◽  
Grounding Line ◽  
Basal Sliding ◽  
Converging Flow ◽  
Basic Characteristics ◽  
Dependent Behaviour

A self-surging glacier model (Budd and McInnes, 1974;Budd, 1975), in which basal sliding is parameterized in terms of energy per unit area dissipated by basal friction, TbVb, has been extended to model the steady-state and time-dependent behaviour of eight Antarctic ice streams. Their basic characteristics were established with the working hypothesis of steady-state mass balance for the ice sheet as a whole, using a 20 km grid digitization of the surface and bedrock-elevation contours inAntarctica: glaciological and geophysical folio(Drewry, 1983). When the viscosity of the ice is lowered to values that are somewhat unrealistic for the present Antarctic ice, all the model ice streams enter a pulsating fast-sliding mode of flow in which the velocity reaches several km/year for periods ranging from fractions οf a year to tens of years. Except for one ice stream (Slessor Glacier), no substantial surge-like advances were found, and even in that case no periodic surging regime developed. The pulses are tentatively attributed to processes at the grounding line, with the converging width-parameterization scheme in the surging velocity calculation as another complexity that is still being investigated. For the cyclic surging Medvezhi Glacier model (Budd and Mclnnes, 1978), it has been found that the model surges change to shorter pulses as the width-convergence rate is increased.It is concluded that the special regime and topography of ice streams — net accumulation increasing along the strongly converging flow and removal of the ice by calving rather than ablation — impede the onset of periodic surging. However, more sophisticated parameterizations of the basal hydraulics now in development may well show that ice-stream surges after all are possible.

scholarly journals Model Studies on Ice-Stream Surging

1989 ◽  
Vol 12 ◽  
pp. 132-137 ◽  
Author(s):  
U. Radok ◽  
B.J. McInnes ◽  
D. Jenssen ◽  
W.F. Budd
Keyword(s):  
Steady State ◽  
Sliding Mode ◽  
Ice Streams ◽  
Model Studies ◽  
Ice Stream ◽  
Grounding Line ◽  
Basal Sliding ◽  
Converging Flow ◽  
Basic Characteristics ◽  
Dependent Behaviour

A self-surging glacier model (Budd and McInnes, 1974; Budd, 1975), in which basal sliding is parameterized in terms of energy per unit area dissipated by basal friction, TbVb, has been extended to model the steady-state and time-dependent behaviour of eight Antarctic ice streams. Their basic characteristics were established with the working hypothesis of steady-state mass balance for the ice sheet as a whole, using a 20 km grid digitization of the surface and bedrock-elevation contours in Antarctica: glaciological and geophysical folio (Drewry, 1983). When the viscosity of the ice is lowered to values that are somewhat unrealistic for the present Antarctic ice, all the model ice streams enter a pulsating fast-sliding mode of flow in which the velocity reaches several km/year for periods ranging from fractions οf a year to tens of years. Except for one ice stream (Slessor Glacier), no substantial surge-like advances were found, and even in that case no periodic surging regime developed. The pulses are tentatively attributed to processes at the grounding line, with the converging width-parameterization scheme in the surging velocity calculation as another complexity that is still being investigated. For the cyclic surging Medvezhi Glacier model (Budd and Mclnnes, 1978), it has been found that the model surges change to shorter pulses as the width-convergence rate is increased. It is concluded that the special regime and topography of ice streams — net accumulation increasing along the strongly converging flow and removal of the ice by calving rather than ablation — impede the onset of periodic surging. However, more sophisticated parameterizations of the basal hydraulics now in development may well show that ice-stream surges after all are possible.

Temperature Dependences in the O + OH → O2 + H Reaction. Quasiclassical Trajectory Calculation

1993 ◽  
Vol 58 (2) ◽  
pp. 234-243 ◽  
Author(s):  
Viliam Klimo ◽  
Martina Bittererová ◽  
Stanislav Biskupič ◽  
Ján Urban ◽  
Miroslav Micov
Keyword(s):  
Temperature Dependence ◽  
Energy Surface ◽  
Analytical Form ◽  
Mean Values ◽  
Quantum Numbers ◽  
Mean Lifetime ◽  
Temperature Dependences ◽  
Quasiclassical Trajectory Calculation ◽  
The Mean ◽  
Combustion Processes

The reaction O + OH → O2 + H in conditions of combustion of hydrocarbons and polymers was modelled by using the method of quasiclassical trajectories. The potential energy surface was determined by the multiconfiguration interaction method and fitted with the analytical form of the extended LEPS function. Attention was paid to the mean values of the vibrational and rotational quantum numbers of O2 molecules and their temperature dependence. The temperature dependence of the mean lifetime of the OOH collision complex was also examined. The calculated rate constants were analyzed and compared with the experimental data over the temperature region of the combustion processes.

scholarly journals The steady-state visual evoked potential (SSVEP) reflects the activation of cortical object representations: evidence from semantic stimulus repetition

2020 ◽  
Author(s):  
Elise L. Radtke ◽  
Ulla Martens ◽  
Thomas Gruber
Keyword(s):  
Steady State ◽  
Object Representation ◽  
Sensory Information ◽  
Familiar Object ◽  
Object Representations ◽  
Stimulus Repetition ◽  
Experimental Conditions ◽  
Repetition Suppression ◽  
Task Irrelevant ◽  
Visual Evoked

AbstractWe applied high-density EEG to examine steady-state visual evoked potentials (SSVEPs) during a perceptual/semantic stimulus repetition design. SSVEPs are evoked oscillatory cortical responses at the same frequency as visual stimuli flickered at this frequency. In repetition designs, stimuli are presented twice with the repetition being task irrelevant. The cortical processing of the second stimulus is commonly characterized by decreased neuronal activity (repetition suppression). The behavioral consequences of stimulus repetition were examined in a companion reaction time pre-study using the same experimental design as the EEG study. During the first presentation of a stimulus, we confronted participants with drawings of familiar object images or object words, respectively. The second stimulus was either a repetition of the same object image (perceptual repetition; PR) or an image depicting the word presented during the first presentation (semantic repetition; SR)—all flickered at 15 Hz to elicit SSVEPs. The behavioral study revealed priming effects in both experimental conditions (PR and SR). In the EEG, PR was associated with repetition suppression of SSVEP amplitudes at left occipital and repetition enhancement at left temporal electrodes. In contrast, SR was associated with SSVEP suppression at left occipital and central electrodes originating in bilateral postcentral and occipital gyri, right middle frontal and right temporal gyrus. The conclusion of the presented study is twofold. First, SSVEP amplitudes do not only index perceptual aspects of incoming sensory information but also semantic aspects of cortical object representation. Second, our electrophysiological findings can be interpreted as neuronal underpinnings of perceptual and semantic priming.

The Urbach Rule for the Sodium- and Potassium-Halides

1974 ◽  
Vol 29 (1) ◽  
pp. 145-157 ◽  
Author(s):  
Tetsuhiko Tomiki ◽  
Takeo Miyata ◽  
Hirokazu Tsukamoto
Keyword(s):  
Temperature Dependence ◽  
Acoustic Phonon ◽  
Frequency Factor ◽  
Host Lattice ◽  
Exciton Peak ◽  
Urbach Rule ◽  
Temperature Dependences ◽  
Hole Band ◽  
Sodium And Potassium ◽  
Potassium Halides

Phenomenological and physical aspects of the intrinsic tail spectra of the alkalihalides are studied referring to the new results on the intrinsic tail spectra of KBr and KI and to the temperature dependences of the lowest-energy Γ-exciton peak of the sodium- and potassium-halides. Systematically analysing the temperature dependence of the steepness parameter σs (T) of the Urbach rule for these halides, it is found that the frequency factor has the value nearly equal to the acoustic phonon energy at X or L of each host lattice and the steepness constant σs0 becomes larger in passing from fluoride to iodide. This halogen dependence of σs0 is discussed in terms of the hole band-mass of the Γ8-level.

scholarly journals Participation of plasma membrane proteins in the formation of tight junction by cultured epithelial cells

1983 ◽  
Vol 96 (3) ◽  
pp. 693-702 ◽  
Author(s):  
EB Griepp ◽  
WJ Dolan ◽  
ES Robbins ◽  
DD Sabatini
Keyword(s):  
Protein Synthesis ◽  
Steady State ◽  
Tight Junction ◽  
Messenger Rna ◽  
Freeze Fracture ◽  
Epithelial Cell Line ◽  
Experimental Conditions ◽  
Tight Junction Formation ◽  
Junction Formation ◽  
Spinner Culture

Measurements of the transepithelial electrical resistance correlated with freeze-fracture observations have been used to study the process of tight junction formation under various experimental conditions in monolayers of the canine kidney epithelial cell line MDCK. Cells derived from previously confluent cultures and plated immediately after trypsin- EDTA dissociation develop a resistance that reaches its maximum value of several hundred ohms-cm(2) after approximately 24 h and falls to a steady-state value of 80-150 ohms- cm(2) by 48 h. The rise in resistance and the development of tight junctions can be completely and reversibly prevented by the addition of 10 μg/ml cycloheximide at the time of plating, but not when this inhibitor is added more than 10 h after planting. Thus tight junction formation consists of separable synthetic and assembly phases. These two phases can also be dissociated and the requirement for protein synthesis after plating eliminated if, following trypsinization, the cells are maintained in spinner culture for 24 h before plating. The requirement for protein synthesis is restored, however, if cells maintained in spinner culture are treated with trypsin before plating. Actinomycin D prevents development of resistance only in monolayers formed from cells derived from sparse rather than confluent cultures, but new mRNA synthesis is not required if cells obtained from sparse cultures are maintained for 24 h in spinner culture before plating. Once a steady-state resistance has been reached, its maintenance does not require either mRNA or protein synthesis; in fact, inhibition of protein synthesis causes a rise in the resistance over a 30-h period. Following treatments that disrupt the junctions in steady- state monolayers recovery of resistance also does not require protein synthesis. These observations suggest that proteins are involved in tight junction formation. Such proteins, which do not turn over rapidly under steady-state conditions, are destroyed by trypsinization and can be resynthesized in the absence of stable cell-cell or cell-substratum contact. Messenger RNA coding for proteins involved in tight junction formation is stable except when cells are sparsely plated, and can also be synthesized without intercellular contacts or cell-substratum attachment.

scholarly journals Thermal controls on ice stream shear margins

2021 ◽  
pp. 1-15
Author(s):  
Pierce Hunter ◽  
Colin Meyer ◽  
Brent Minchew ◽  
Marianne Haseloff ◽  
Alan Rempel
Keyword(s):  
Steady State ◽  
Stream Velocity ◽  
Viscous Heating ◽  
Ice Streams ◽  
Temperature Dependent Viscosity ◽  
Stream Discharge ◽  
Ice Stream ◽  
Steady State Model ◽  
Slow Moving ◽  
Dependent Viscosity

Abstract Ice stream discharge responds to a balance between gravity, basal friction and lateral drag. Appreciable viscous heating occurs in shear margins between ice streams and adjacent slow-moving ice ridges, altering the temperature-dependent viscosity distribution that connects lateral drag to marginal strain rates and ice stream velocity. Warmer ice deforms more easily and accommodates faster flow, whereas cold ice supplied from ice ridges drives advective cooling that counteracts viscous heating. Here, we present a two-dimensional (three velocity component), steady-state model designed to explore the thermal controls on ice stream shear margins. We validate our treatment through comparison with observed velocities for Bindschadler Ice Stream and verify that calculated temperatures are consistent with results from previous studies. Sweeping through a parameter range that encompasses conditions representative of ice streams in Antarctica, we show that modeled steady-state velocity has a modest response to different choices in forcing up until temperate zones develop in the shear margins. When temperate zones are present, velocity is much more sensitive to changes in forcing. We identify key scalings for the emergence of temperate conditions in our idealized treatment that can be used to identify where thermo-mechanical feedbacks influence the evolution of the ice sheet.

scholarly journals Temperature uniformity in the CERN CLOUD chamber

2017 ◽  
Vol 10 (12) ◽  
pp. 5075-5088 ◽  
Author(s):  
António Dias ◽  
Sebastian Ehrhart ◽  
Alexander Vogel ◽  
Christina Williamson ◽  
João Almeida ◽  
...  
Keyword(s):  
Steady State ◽  
Air Temperature ◽  
Elevated Temperatures ◽  
Trace Gases ◽  
Vertical Direction ◽  
Cloud Chamber ◽  
Temperature Uniformity ◽  
Atmospheric Conditions ◽  
Cloud Droplets ◽  
Experimental Conditions

Abstract. The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN (European Council for Nuclear Research) investigates the nucleation and growth of aerosol particles under atmospheric conditions and their activation into cloud droplets. A key feature of the CLOUD experiment is precise control of the experimental parameters. Temperature uniformity and stability in the chamber are important since many of the processes under study are sensitive to temperature and also to contaminants that can be released from the stainless steel walls by upward temperature fluctuations. The air enclosed within the 26 m3 CLOUD chamber is equipped with several arrays (strings) of high precision, fast-response thermometers to measure its temperature. Here we present a study of the air temperature uniformity inside the CLOUD chamber under various experimental conditions. Measurements were performed under calibration conditions and run conditions, which are distinguished by the flow rate of fresh air and trace gases entering the chamber at 20 and up to 210 L min−1, respectively. During steady-state calibration runs between −70 and +20 °C, the air temperature uniformity is better than ±0.06 °C in the radial direction and ±0.1 °C in the vertical direction. Larger non-uniformities are present during experimental runs, depending on the temperature control of the make-up air and trace gases (since some trace gases require elevated temperatures until injection into the chamber). The temperature stability is ±0.04 °C over periods of several hours during either calibration or steady-state run conditions. During rapid adiabatic expansions to activate cloud droplets and ice particles, the chamber walls are up to 10 °C warmer than the enclosed air. This results in temperature differences of ±1.5 °C in the vertical direction and ±1 °C in the horizontal direction, while the air returns to its equilibrium temperature with a time constant of about 200 s.

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