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1
Baumann, Hannes, und David O. Conover. „Adaptation to climate change: contrasting patterns of thermal-reaction-norm evolution in Pacific versus Atlantic silversides“. Proceedings of the Royal Society B: Biological Sciences 278, Nr. 1716 (05.01.2011): 2265–73. http://dx.doi.org/10.1098/rspb.2010.2479.
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How organisms may adapt to rising global temperatures is uncertain, but concepts can emerge from studying adaptive physiological trait variations across existing spatial climate gradients. Many ectotherms, particularly fish, have evolved increasing genetic growth capacities with latitude (i.e. countergradient variation (CnGV) in growth), which are thought to be an adaptation primarily to strong gradients in seasonality. In contrast, evolutionary responses to gradients in mean temperature are often assumed to involve an alternative mode, ‘thermal adaptation’. We measured thermal growth reaction norms in Pacific silverside populations ( Atherinops affinis ) occurring across a weak latitudinal temperature gradient with invariant seasonality along the North American Pacific coast. Instead of thermal adaptation, we found novel evidence for CnGV in growth, suggesting that CnGV is a ubiquitous mode of reaction-norm evolution in ectotherms even in response to weak spatial and, by inference, temporal climate gradients. A novel, large-scale comparison between ecologically equivalent Pacific versus Atlantic silversides ( Menidia menidia ) revealed how closely growth CnGV patterns reflect their respective climate gradients. While steep growth reaction norms and increasing growth plasticity with latitude in M. menidia mimicked the strong, highly seasonal Atlantic coastal gradient, shallow reaction norms and much smaller, latitude-independent growth plasticity in A. affinis resembled the weak Pacific latitudinal temperature gradient.
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Thomas, Carl M., und David M. Schultz. „What are the Best Thermodynamic Quantity and Function to Define a Front in Gridded Model Output?“ Bulletin of the American Meteorological Society 100, Nr. 5 (Mai 2019): 873–95. http://dx.doi.org/10.1175/bams-d-18-0137.1.
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AbstractFronts can be computed from gridded datasets such as numerical model output and reanalyses, resulting in automated surface frontal charts and climatologies. Defining automated fronts requires quantities (e.g., potential temperature, equivalent potential temperature, wind shifts) and kinematic functions (e.g., gradient, thermal front parameter, and frontogenesis). Which are the most appropriate to use in different applications remains an open question. This question is investigated using two quantities (potential temperature and equivalent potential temperature) and three functions (magnitude of the horizontal gradient, thermal front parameter, and frontogenesis) from both the context of real-time surface analysis and climatologies from 38 years of reanalyses. The strengths of potential temperature to identify fronts are that it represents the thermal gradients and its direct association with the kinematics and dynamics of fronts. Although climatologies using potential temperature show features associated with extratropical cyclones in the storm tracks, climatologies using equivalent potential temperature include moisture gradients within air masses, most notably at low latitudes that are unrelated to the traditional definition of a front, but may be representative of a broader definition of an airmass boundary. These results help to explain previously published frontal climatologies featuring maxima of fronts in the subtropics and tropics. The best function depends upon the purpose of the analysis, but Petterssen frontogenesis is attractive, both for real-time analysis and long-term climatologies, in part because of its link to the kinematics and dynamics of fronts. Finally, this study challenges the conventional definition of a front as an airmass boundary and suggests that a new, dynamically based definition would be useful for some applications.
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Mohamed, Ashraf R., und Will Hansen. „Effect of Nonlinear Temperature Gradient on Curling Stress in Concrete Pavements“. Transportation Research Record: Journal of the Transportation Research Board 1568, Nr. 1 (Januar 1997): 65–71. http://dx.doi.org/10.3141/1568-08.
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Temperature and moisture gradients can lead to significant tensile stresses at the slab top and bottom. Current techniques for assessing the internal stresses due to such gradients are based on the assumption that temperature and moisture distributions through the slab thickness are linear. However, the actual distributions of such gradients have been found to be highly nonlinear. A new closed form solution technique for calculating the stresses in a pavement slab due to nonlinear gradients is introduced. The analysis is separated into two parts. In the first, an expression is presented for calculating the self-equilibrated stresses within a cross section due to internal restraint (i.e., satisfying equilibrium conditions and continuity of the strain field within the cross section). These stresses are independent of slab dimensions and boundary conditions. In the second, the stresses due to external restraint (i.e., self-weight and subgrade reaction) are calculated using an equivalent linear temperature gradient obtained from the first part and existing closed form solutions by Westergaard or Bradbury. The solution to this step includes slab length and boundary conditions. Total internal stresses due to nonlinear gradients are obtained by using the superposition principle. The methodology has been applied to field data from two studies in which the temperature profiles were recorded throughout a 24-hr period. Linear gradient solution methods cannot accurately predict the curling stresses in concrete pavements. This is especially pronounced during nighttime and early morning hours, during which nonlinear analysis predicts tensile stress in both the slab bottom and top before the application of any traffic loading.
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Huang, Zi Qian, und Qing Lian Xie. „Study on Thermal Stresses of Cylinder Liner’s Fabrication Using FEM Analysis“. Advanced Materials Research 189-193 (Februar 2011): 2058–61. http://dx.doi.org/10.4028/www.scientific.net/amr.189-193.2058.
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In the process of casing casting, great temperature gradient leads to contraction deformation of cylinder liner, which influences the quality of products. The thermal stresses caused by temperature gradient were analyzed by finite element method. The numerical results show that high equivalent Von Mises stress(242MPa) occurs in the surface zone of the cylinder liner as Cooling down to room temperature within pipe die ,also there is plastic deformation in the internal and external surface zone. Reducing the cooling speed, decreasing the temperature gradient and aging can reduce the influence of thermal stresses.
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Gao, Xiang, Ya Wei und Wei Huang. „Strain-based equivalent temperature gradient in concrete pavement and comparison with other quantification methods“. Road Materials and Pavement Design 18, Nr. 6 (17.08.2016): 1460–72. http://dx.doi.org/10.1080/14680629.2016.1218788.
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Billon, Noelle, Jean Marc Haudin, Camille Vallot und Charles Babin. „Stretch Blow Moulding of Mineral Filled PET“. Key Engineering Materials 504-506 (Februar 2012): 1099–104. http://dx.doi.org/10.4028/www.scientific.net/kem.504-506.1099.
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Injection Stretch Blow mouldng is a two step processing that was designed and optimized mainly using unfilled PET resins. This study focuses on stretch blow moulding of a PET filled with a few percent of sub micronic mineral fillers. Based on DSC, DMA, tensile tests as well as blowing on prototype machine main effects of fillers are analysed. It is demonstrated that fillers increases crystallization kinetics resulting in a reduction of the processing range. Difference in strain hardening induced by fillers makes it necessary to adjust blowing temperature. However main effect occurs during heating phase. Temperature within the perform is much less homogeneous than in PET making thermal gradient totally different if heating protocole is kept unchanged. Once heating is controlled to reach to equivalent thermal gradients as for PET blowing is possible and rather equivalent to that of pure PET.
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Domine, F., S. Morin, E. Brun, M. Lafaysse und C. M. Carmagnola. „Seasonal evolution of snow permeability under equi-temperature and temperature-gradient conditions“. Cryosphere 7, Nr. 6 (18.12.2013): 1915–29. http://dx.doi.org/10.5194/tc-7-1915-2013.
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Abstract. The permeability (K) of snow to air flow affects the transfer of energy, water vapor and chemical species between the snow and the atmosphere. Yet today little is known about the temporal evolution of snow permeability as a function of metamorphic regime. Furthermore, our ability to simulate snow permeability over the seasonal evolution of a snowpack has not been tested. Here we have measured the evolution of snow permeability in a subarctic snowpack subject to high temperature-gradient (TG) metamorphism. We have also measured the evolution of the same snowpack deposited over tables so that it evolved in the equi-temperature (ET) regime. Permeability varies in the range 31 × 10−10 (ET regime) to 650 × 10−10 m2 (TG regime). Permeability increases over time in TG conditions and decreases under ET conditions. Using measurements of density ρ and of specific surface area (SSA), from which the equivalent sphere radius r is determined, we show that the equation linking SSA, density ρ and permeability, K = 3.0 r2 e(−0.013 ρ) (with K in m2, r in m and ρ in kg m−3) obtained in a previous study adequately predicts permeability values. The detailed snowpack model Crocus is used to simulate the physical properties of the TG and ET snowpacks. For the most part, all variables are well reproduced. Simulated permeabilities are up to a factor of two greater than measurements for depth hoar layers, which we attribute to snow microstructure and its aerodynamic properties. Finally, the large difference in permeabilities between ET and TG metamorphic regimes will impact atmosphere-snow energy and mass exchanges. These effects deserve consideration in predicting the effect of climate change on snow properties and snow–atmosphere interactions.
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Domine, F., S. Morin, E. Brun und M. Lafaysse. „Seasonal evolution of snow permeability under equi-temperature and temperature-gradient conditions“. Cryosphere Discussions 7, Nr. 3 (17.06.2013): 2725–59. http://dx.doi.org/10.5194/tcd-7-2725-2013.
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Abstract. The permeability K of snow to air flow affects the transfer of energy, water vapor and chemical species between the snow and the atmosphere. Yet today little is known of the temporal evolution of snow permeability as a function of metamorphic regime. Furthermore, our ability to simulate snow permeability over the seasonal evolution of a snowpack has not been tested. Here we have measured the evolution of snow permeability in a subarctic snowpack subject to high temperature-gradient (TG) metamorphism. We have also measured the evolution of the same snowpack deposited over tables so that it evolved in the equi-temperature (ET) regime. Permeability varies in the range 31 × 10–10 (ET regime) to 650 × 10–10 m2 (TG regime). Permeability increases over time in TG conditions and decreases under ET conditions. Using measurements of density ρ and of specific surface area (SSA), from which the equivalent sphere radius r is determined, we show that the equation linking SSA, density ρ and permeability, K = 3.0 r2 e(–0.013 ρ) (with K in m2, r in m and ρ in kg m−3) obtained in a previous study adequately predicts permeability values. The detailed snowpack model Crocus is used to simulate the physical properties of the TG and ET snowpacks. For the most part, all variables are well reproduced. Simulated permeabilities are up to a factor of two greater than measurements for depth hoar layers, which we attribute to snow microstructure, as the aerodynamic properties of hollow depth hoar crystals are different from those of spheres. Finally, the large difference in permeabilities between ET and TG metamorphic regimes will impact atmosphere-snow energy and mass exchanges and these effects deserve consideration in predicting the effect of climate change on snow properties and snow-atmosphere interactions.
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Riley, Jeffrey B., Scott B. Hardin, Brad A. Winn und Michael B. Hurdle. „In vitro comparison of cavoatrial (dual stage) cannulae for use during cardiopulmonary bypass“. Perfusion 1, Nr. 3 (Juli 1986): 197–204. http://dx.doi.org/10.1177/026765918600100308.
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An in vitro normothermic, human blood test circuit was constructed to test four cavoatrial (dual stage) cannulae, their right atrial baskets and IVC tips for venous return flow versus siphon drainage gradient. Simulated patient CVP and ECC oxygenator/venous reservoir inlet resistance were held constant at 10 mmHg and 15 mmHg respectively as siphon gradient was varied from 0 centimetres (cm) to -40 cm of blood. At the same siphon gradients between -10 and -40 cm, the Research Medical, Inc. (RMI) VV 3651 L, its right atrial (RA) basket, and IVC tip yielded significantly greater flows than the Sarns Inc. 12340, CR Bard, Inc. 1969, and the RMI VV 3651 B cannula, except the RMI VV 3651 B RA basket was equivalent to the VV 3651 L basket. The 12340 and 1969 baskets were equivalent. The 1969 IVC tip was superior to the 12340 tip. The mechanism for CPB venous collapse and flutter, its treatment, and the importance of monitoring myocardial temperature, as well as assuring great vein and cardiac decompression during cavoatrial cannulation and aortic cross clamping are outlined.
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Yu, Peng, Ruiqing Li, Dapeng Bie, Xiancai Liu, Xiaomin Yao und Yahui Duan. „Precise Simulation of Heat-Flow Coupling of Pipe Cooling in Mass Concrete“. Materials 14, Nr. 18 (08.09.2021): 5142. http://dx.doi.org/10.3390/ma14185142.
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For a long time, temperature control and crack prevention of mass concrete is a difficult job in engineering. For temperature control and crack prevention, the most effective and common-used method is to embed cooling pipe in mass concrete. At present, there still exists some challenges in the precise simulation of pipe cooling in mass concrete, which is a complex heat-flow coupling problem. Numerical simulation is faced with the problem of over-simplification and inaccuracy. In this study, precise simulation of heat-flow coupling of pipe cooling in mass concrete is carried out based on finite element software COMSOL Multiphysics 5.4. Simulation results are comprehensively verified with results from theoretical solutions and equivalent algorithms, which prove the correctness and feasibility of precise simulation. Compared with an equivalent algorithm, precise simulation of pipe cooling in mass concrete can characterize the sharp temperature gradient around cooling pipe and the temperature rise of cooling water along pipeline more realistically. In addition, the cooling effects and local temperature gradient under different water flow (0.60 m3/h, 1.20 m3/h, and 1.80 m3/h) and water temperature (5 °C, 10 °C, and 15 °C) are comprehensively studied and related engineering suggestions are given.
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Lee, Jon. „Large-Amplitude Plate Vibration in an Elevated Thermal Environment“. Applied Mechanics Reviews 46, Nr. 11S (01.11.1993): S242—S254. http://dx.doi.org/10.1115/1.3122643.
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At elevated temperatures the dynamics of vibrating plate (or shell) must include the three thermal effects: (i) the global expansion by uniform plate temperature, (ii) the local expansion by temperature variation over the plate, and (iii) the thermal moment induced by temperature gradient across the plate thickness. For the single-mode prototype model of Galerkin representation, (i) and (ii) give rise to the combined stiffness that is responsible for thermal buckling, whereas (iii) contributes to the combined forcing of acoustic and thermal excitations. For the high-temperature sonic fatigue test facility at the Wright Lab, the present study is devoted to the mean square estimates on transverse displacement and normal stress/strain by the equivalent linearization technique.
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Chen, Chi, Xia Wang, Zepeng Lv, Kai Wu und Chuanhui Cheng. „An equivalent investigation of space charge for plane samples and coaxial cables under a temperature gradient“. IEEE Transactions on Dielectrics and Electrical Insulation 27, Nr. 4 (August 2020): 1256–64. http://dx.doi.org/10.1109/tdei.2020.008676.
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13
Sneddon, Jennifer C. „The effect of treadmill slope on the relationship between heart rate and energy expenditure in cattle walking on treadmills“. Journal of Agricultural Science 106, Nr. 3 (Juni 1986): 433–36. http://dx.doi.org/10.1017/s0021859600063292.
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SummaryTwo steers (Bos indicus and Bos indicus x Bos taurus) were acclimatized to an ambient temperature of 30 °C before working at this temperature on two treadmills (gradients 0 and 6°) for 2 h (one on each treadmill) whilst carrying a load equivalent to 10% of body weight. The study was then repeated at an ambient temperature of 15 °C. The effect of variation between animals, ambient temperature and rate of energy expenditure were tested on the linear regression model EEw = A PHR + B (where EEw is the energy expenditure (w/kg0·75) and PHR is the percentage increase of working heart rate over resting heart rate).Animal and ambient temperature had no significant effect on the model. The gradient of the regression line was significantly greater (P < 0·01) when the animals were expending energy at the higher rate (about 30 W/kg live weight0·75) than when they were expending energy at the lower rate (about 14 W/kg live weight0·75).
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Skinner, Patrick S., Christopher C. Weiss, John L. Schroeder, Louis J. Wicker und Michael I. Biggerstaff. „Observations of the Surface Boundary Structure within the 23 May 2007 Perryton, Texas, Supercell“. Monthly Weather Review 139, Nr. 12 (01.12.2011): 3730–49. http://dx.doi.org/10.1175/mwr-d-10-05078.1.
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Abstract In situ data collected within a weakly tornadic, high-precipitation supercell occurring on 23 May 2007 near Perryton, Texas, are presented. Data were collected using a recently developed fleet of 22 durable, rapidly deployable probes dubbed “StickNet” as well as four mobile mesonet probes. Kinematic and thermodynamic observations of boundaries within the supercell are described in tandem with an analysis of data from the Shared Mobile Atmospheric Research and Teaching Radar. Observations within the rear-flank downdraft of the storm exhibit large deficits of both virtual potential temperature and equivalent potential temperature, with a secondary rear-flank downdraft gust front trailing the mesocyclone. A primarily thermodynamic boundary resided across the forward-flank reflectivity gradient of the supercell. This boundary is characterized by small deficits in virtual potential temperature coupled with positive perturbations of equivalent potential temperature. The opposing thermodynamic perturbations appear to be representative of modified storm inflow, with a flux of water vapor responsible for the positive perturbations of the equivalent potential temperature. Air parcels exhibiting negative perturbations of virtual potential temperature and positive perturbations of equivalent potential temperature have the ability to be a source of both baroclinically generated streamwise horizontal vorticity and greater potential buoyancy if ingested by the low-level mesocyclone.
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Zhou, Yushu, Liping Liu und Guo Deng. „Comparisons of the Generalized Potential Temperature in Moist Atmosphere with the Equivalent Potential Temperature in Saturated Moist Atmosphere“. Advances in Meteorology 2009 (2009): 1–9. http://dx.doi.org/10.1155/2009/105265.
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The real tropospheric atmosphere is neither absolutely dry nor completely saturated. It is in general moist but not saturated. Here the generalized potential temperature (GPT) was introduced to describe this humid feature of real moist atmosphere. GPT's conservation property in moist adiabatic process was discussed and proved. Comparisons of GPT in moist atmosphere with the equivalent potential temperature (EPT) in saturated moist atmosphere were made by analyzing three torrential rain cases occurring over Jianghuai Valleys in 2003, the north China in 2004, and with the typhoon Fung-Wong in 2008, respectively. Results showed that the relative humidity is not up to 100% even in torrential rain systems, the saturated condition for EPT is not always held, and thus GPT can describe the moisture concentration and moisture gradient better than EPT. The GPT's definition includes the process that the air changes from dry to moist, then up to saturated. Therefore, potential temperature (PT) and EPT can be considered as its two special status. Similar as PT and EPT, GPT can be used to study atmospheric dynamic and thermodynamic processes more generally because of its conservation property in moist adiabatic process.
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Shu, Xuedao, Zewei Cen, Yu Wang, Zixuan Li und Ying Zhu. „Exploring Strong Spinning Formation Mechanisms of GH3030 Superalloy Tapered Rotary Part with Wall Thickness Gradient“. Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 37, Nr. 4 (August 2019): 785–93. http://dx.doi.org/10.1051/jnwpu/20193740785.
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In order to effectively control the deformation of tapered spinning parts with gradually changing wall thickness, the precise forming of such sheet metal casing parts can be realized. This paper uses experiments to establish the true stress-strain curve equations of GH3030 superalloy at normal temperature. Based on the equations, it establishes the finite element model of the strong spinning forming of a GH3030 superalloy tapered rotary part with wall thickness gradient. The equivalent stress field for the strong spinning forming is used to combine the finite element simulation with experiments. The strong spinning forming is simulated, and the distribution characteristics of the equivalent stress field and the equivalent strain field for the strong spinning forming are analyzed in some detail, and their distribution law is obtained. The strong spinning forming mechanisms for the GH3030 superalloy tapered rotary part with wall thickness gradient is clarified. The experimental and simulation results are verified with the conical flange plane degree.
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Liang, Peixin, Yulong Pei, Feng Chai und Shukang Cheng. „Equivalent stator slot model of temperature field for high torque-density permanent magnet synchronous in-wheel motors accounting for winding type“. COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 35, Nr. 2 (07.03.2016): 713–27. http://dx.doi.org/10.1108/compel-02-2015-0040.
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Purpose – For high torque-density permanent magnet synchronous in-wheel motor, service life and electromagnetic performance are related directly to winding temperature. The purpose of this paper is to investigate the equivalent stator slot model to calculate the temperature of winding accurately. Design/methodology/approach – This paper analyzes the the law of heat flux transfer in slot, which points the main influence factors of equivalent stator slot model. Thermal network model is used to investigate the drawbacks of conventional equivalent model. Based on the law of heat transfer in stator slot, a new layered winding model is put forward. According to winding type and property of impregnations, detailed method and equivalent principle of the new model are presented. The accuracy of this new method has been verified experimentally. Findings – An accurate equivalent stator slot model should be built according to the low of heat transfer. According to theory analysis, the drawbacks of conventional equivalent stator slot model are pointed: it cannot reflect the temperature gradient of winding; the maximum and the average temperature of winding are much higher than actual value. For the new layered model, equivalent principle is related to winding type and property of impregnations, which makes the new model widely used. Originality/value – This paper presents a new layered model, and shows detailed method, which is more meaningful for designers. The new layered model takes winding type and property of impregnations into account, which makes the new model widely used. It is verified experimentally that layered model is applicable to not only steady-state temperature field but also transient temperature field.
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Tang, Siwen, Rui Wang, Pengfei Liu, Qiulin Niu, Guoqing Yang, Wenhui Liu und Deshun Liu. „Preparation of WC-TiC-Ni3Al-CaF2 functionally graded self-lubricating tool material by microwave sintering and its cutting performance“. High Temperature Materials and Processes 39, Nr. 1 (28.02.2020): 45–53. http://dx.doi.org/10.1515/htmp-2020-0004.
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AbstractWith the concern of the environment, green dry cutting technology is getting more and more attention and self-lubricating tool technology plays an important role in dry cutting. Due to the demand for high temperature performance of tools during dry cutting process, cemented carbide with Ni3Al as the binder phase has received extensive attention due to its excellent high temperature strength and high temperature oxidation resistance. In this paper, WC-TiC-Ni3Al-CaF2 graded self-lubricating material and tools were prepared by microwave heating method, and its microstructure, mechanical properties and cutting performance were studied. Results show that gradient self-lubricating material can be quickly prepared by microwave heating technology, and the strength is equivalent to that of conventional heating technology. CaF2 not only plays a role in self-lubrication, but also refines the grain of the material. A reasonable gradient design can improve the mechanical properties of the material. When the gradient distribution exponent is n1 = 2, the material has high mechanical properties. Cutting experiments show that the WC-TiC-Ni3Al-CaF2 functional gradient self-lubricating tool has better cutting performance than the homogeneous WC-TiC-Ni3Al hard alloys.
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Fischer, H., D. Wagenbach, M. Laternser und W. Haeberli. „Glacio-meteorological and isotopic studies along the EGIG line, central Greenland“. Journal of Glaciology 41, Nr. 139 (1995): 515–27. http://dx.doi.org/10.1017/s0022143000034857.
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AbstractThe geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements m 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from -31.6°C at Dome GRIP (3230 m a.s.l.) to -11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.sl.) and -18°C at T05 (near the western ice margin at 1900 m a.s.l.). The temperature/altitude gradient changes from -0.7°C (100 m)−1in the ice divide region to -1.1 °C (100 m)−1in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is -0.7° C lat−1The average annual accumulation decreases significantly from the west (~47 cm a−1water equivalent at T05) towards the ice divide (20–25 cm a−1water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (−23–17 cm a−1water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ18O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂18O/∂Tm= 0.69%ₒ °C–1Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.
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Fischer, H., D. Wagenbach, M. Laternser und W. Haeberli. „Glacio-meteorological and isotopic studies along the EGIG line, central Greenland“. Journal of Glaciology 41, Nr. 139 (1995): 515–27. http://dx.doi.org/10.3189/s0022143000034857.
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AbstractThe geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements m 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from -31.6°C at Dome GRIP (3230 m a.s.l.) to -11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.sl.) and -18°C at T05 (near the western ice margin at 1900 m a.s.l.). The temperature/altitude gradient changes from -0.7°C (100 m)−1 in the ice divide region to -1.1 °C (100 m)−1 in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is -0.7° C lat−1 The average annual accumulation decreases significantly from the west (~47 cm a−1 water equivalent at T05) towards the ice divide (20–25 cm a−1 water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (−23–17 cm a−1 water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ18O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂18O/∂Tm = 0.69%ₒ °C–1 Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.
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Ni, Feng, Shi Zhong Wei und Rui Long. „Analytical Solution on the Relation of Technique Parameters for Continuous Casting with Heated Mould“. Advanced Materials Research 337 (September 2011): 225–31. http://dx.doi.org/10.4028/www.scientific.net/amr.337.225.
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The technique of continuous casting with heated mould is a kind of near-net-shape processing technology, which combines unidirectional solidification with continuous casting and has been used widely for new material development and processing. A steady-state heat-transfer model was suggested for pure metal case. Some of modeling parameters, such as equivalent specific conductance and equivalent heat-transfer coefficient, etc, had been defined. The analytic solution of temperature profile along the axis of casting rod was obtained for solid-liquid interface to be as origin of position coordinate, by which the relations had been solved among mould temperature, casting speed, solid-liquid interface position, equivalent specific conductance between mould and metal, equivalent heat-transfer coefficient of cooling of cast rod, temperature gradient and cooling rate of melt in front of solid-liquid interface. As an example, the coordinate relations of solid-liquid interface position, mould temperature and casting speed were calculated and compared with experimental results in the case of pure copper. The calculation results conformed very well to the experimental ones. And it was indicated that the cooling rate of melt in front of solid-liquid interface had a nonlinear relation with casting speed during steady continuous casting process.
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Zhang, Hai Yang, Wei Bing Zhu, Gang Zhou und Xu Hao. „Study on the Thermal Stress Couple Field of Nuclear Power Pump Mechanical Seal Based on ADINA“. Advanced Materials Research 971-973 (Juni 2014): 1160–64. http://dx.doi.org/10.4028/www.scientific.net/amr.971-973.1160.
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In this paper, a two-dimensional axisymmetric thermal stress coupling model of mechanical seal’s rotator and stator components was established by ADINA, simplification and appropriate boundary constrained condition of stator and rotator was obtained by analyzing the contact state among the seal rings. It’s shown that the contact surface is equivalent to a resource of constant thermal, temperature of contact surface rises step by step and the location of the maximum temperature getting close to the midpoint within the contact surface according to the sliding time, the temperature gradient decrease along the worksheet so that the temperature decrease accordingly in a parabolic isogram.
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Sha, Yun Dong, Hao Yuan Wang und Huan Yu. „Nonlinear Response of Carbon-Carbon Laminated Panels to Random Acoustic Excitation under a Gradient Temperature Field“. Applied Mechanics and Materials 696 (November 2014): 23–29. http://dx.doi.org/10.4028/www.scientific.net/amm.696.23.
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Future missions for aircraft will expose structures to severe thermal and acoustic loads. Efficient analysis methods for predicting nonlinear random response and fatigue life are urgently important. This paper presents a finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels under temperature gradients and Guassian excitations. The temperature distribution over the plate follows double sine curve. A finite element formulation combined with the equivalent linearization approach and normal mode method is established. The global system of equations is reduced to a set of nonlinear, coupled modal equations. Examples are given for an orthotropic C/C composite laminated panel at various combinations of temperatures gradients and sound pressure levels. Numerical results include RMS values of maximum deflection, time histories of deflection response and stress response, power spectrum densities, probability distribution functions and higher statistical moments. Numerical results verified all three types of panel motions for a simply supported orthotropic laminated plate: small-deflection random vibration about the initial equilibrium positions, snap-through motions between the two buckled positions, and nonlinear random response about new equilibrium positions after post-buckling. Numerical results will provide the important reference basis to aero engine structural integrity design and improving the structure dynamic strength and working life.
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Gammoudi, Rabiaa, Houda Brahmi und Rachid Dhifaoui. „Estimation of Climatic Parameters of a PV System Based on Gradient Method“. Complexity 2019 (18.02.2019): 1–10. http://dx.doi.org/10.1155/2019/7385927.
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The behavior of a photovoltaic generator is generally described by its current-voltage characteristic whose appearance depends on the climatic conditions (temperature and solar radiation). The aim of this work is to show the possibility of identifying the values of these two parameters from an experimental curve Ipv (Vpv) using numerical method. Subsequently, we will also estimate the series and shunt resistors of the equivalent scheme of a PVG. This estimate is certainly beneficial to properly evaluate its energy balance. The integration of these resistances allows us to obtain a new model. In this work, we will propose a mathematical calculation strategy to ensure the estimation of all the parameters.
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Wang, Xi, Jiao Zhong und Hao Ke. „Effect of Pipe Length on the Temperature Field for 9% Cr Heat-Resistant Steel Pipes in Local Post Weld Heat Treatment“. Materials Science Forum 953 (Mai 2019): 32–38. http://dx.doi.org/10.4028/www.scientific.net/msf.953.32.
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ANSYS was used to establish the calculation model of the temperature field for 9% Cr heat-resistant steel pipes in local post-weld heat treatment (PWHT). And the computation model has been validated experimentally. Based on the numerical model, the temperature field distribution was simulated for different pipe lengths in local PWHT, and effects of pipe length on the temperature distribution of heat treatment was further studied. Results show that increase of pipe length has little influence on equivalent temperature measurement point, soak band (SB) width of outer wall and axial temperature gradient, while it causes temperature difference between outer and inner wall to increase and soak band width to reduce significantly in inner wall. And when pipe length increases to a certain extent, the temperature field tends to be stable gradually.
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Perpar, Matjaž, und Zlatko Rek. „The Ability of a Soil Temperature Gradient-Based Methodology to Detect Leaks from Pipelines in Buried District Heating Channels“. Energies 14, Nr. 18 (10.09.2021): 5712. http://dx.doi.org/10.3390/en14185712.
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We carried out several numerical experiments to analyze how different boundary conditions affect the ability to detect small pipeline leaks. Our method is based on determining the soil temperature gradient above a buried district heating channel. The equivalent thermal conductivity of a wet insulation (λeq) value of 0.5 W/(m·K) was used to mimic a small water leakage. To evaluate the heat loss through the channel cross section, the heat conduction model was used for the pipe insulation, the concrete, and the soil, while the convection model was considered within the channel. The following effects were used to simulate different operating conditions: heat convection at the soil surface, leakage only from the supply or return pipe, soil height above the channel, soil thermal conductivity, and pipe diameter. With the exception of leakage only from the return pipe and low soil thermal conductivity 0.4 W/(m·K), the results showed a doubling of the soil temperature gradient when compared with the no-leakage case. This fact undoubtedly confirms the potential of the method, which is particularly suitable for leak detection in old pipelines that have priority for renovation. A key added value of this research is that the soil temperature gradient-based leak detection technique was found useful in most foreseeable DH operating situations.
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Jiang, Lian-Yun, Tao Zhen, Guo Yuan, Jin-Bo Huang, Yao-Yu Wei, Heng Li und Ping Wang. „The mechanical parameters modeling of heavy steel plate snake/gradient temperature rolling with the same roll diameters“. Metallurgical Research & Technology 117, Nr. 3 (2020): 301. http://dx.doi.org/10.1051/metal/2020019.
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The grains in the center of the heavy steel plate can be refined by the snake/gradient temperature rolling, and the deformation penetration, the microstructure, and the properties of the steel plate will be improved. The existing rolling mechanical models are not suitable for the snake/gradient temperature rolling, so it is necessary to establish the mechanical parameters model of the snake/gradient temperature rolling to instruct production. The yield criterion of rolled material was modified based on the idea of equivalent flow stress. The element stress analyses were carried out based on the uniform normal stress and nonuniform shear stress in the vertical sides of each slab. Then the equilibrium equation of the unit pressure based on the slab method was established on this basis. The deformation region was divided into three layers (the top layer, the bottom layer, and the central layer) and maximum four zones (back slip zone, front slip zone, cross shear zone, and reverse deflection zone) according to the temperature distribution and position of the neutral point, and then the 12 zones were formed during the snake/gradient temperature rolling. The boundary conditions of the existence of the back slip zone, the front slip zone, and the cross shear zone were established according to the relationship between the threading angle and the neutral angle. The accurate mechanical parameters model of the rolling force and rolling torque of the snake/gradient temperature rolling with the same roll diameters was set up on this basis. The ANSYS software has been used in the rolling process simulation by many scholars, and the calculating precision has been verified. So the rolling processes were simulated by the ANSYS software to validate the model precision. The results show that the maximum relative deviation of the rolling force analytic model is less than 7% compared with the numerical method, and the maximum relative deviation of the rolling torque analytic model is less than 11% compared with the measured results. The mechanical parameters model can accurately predict the rolling force and rolling torque during the snake/gradient temperature rolling with the same roll diameters, so as to provide a theoretical basis for the design of rolling mill and the setup of the process parameters.
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Lentz, Steven J. „The Mean Along-Isobath Heat and Salt Balances over the Middle Atlantic Bight Continental Shelf“. Journal of Physical Oceanography 40, Nr. 5 (01.05.2010): 934–48. http://dx.doi.org/10.1175/2009jpo4214.1.
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Abstract The mean heat and salt balances over the Middle Atlantic Bight continental shelf are investigated by testing the hypothesis that surface fluxes of heat or freshwater are balanced by along-isobath fluxes resulting from the mean, depth-averaged, along-isobath flow acting on the mean, depth-averaged, along-isobath temperature or salinity gradient. This hypothesized balance is equivalent in a Lagrangian frame to a column of water, for example, warming because of surface heating as it is advected southward along isobath by the mean flow. Mean depth-averaged temperatures increase from north to south along isobath at a rate of 2°C (1000 km)−1 at midshelf, which is consistent with the hypothesized balance and mean surface heat flux estimates from the 50-yr NCEP Reanalysis. However, mean surface heat flux estimates from the higher-resolution 20-yr Objectively Analyzed Air–Sea Fluxes (OAFlux) reanalysis are too small to balance the along-isobath heat flux divergence implying a cross-shelf heat flux convergence. It is unclear which surface heat flux estimate, NCEP or OAFlux, is more accurate. The cross-shelf heat flux convergence resulting from the mean cross-shelf circulation is too small to balance the along-isobath heat flux divergence. Mean depth-averaged salinities increase from north to south along isobath at a rate of 1 (psu) (1000 km)−1 at midshelf. Mean precipitation and evaporation rates nearly balance so that the net freshwater flux is too small by more than an order of magnitude to account for the observed along-isobath increase in salinity. The cross-shelf salt flux divergence resulting from the mean cross-shelf circulation has the wrong sign to balance the divergence in the along-isobath salt flux. These results imply there must be an onshore “eddy” salt flux resulting from the time-dependent current and salinity variability. The along-isobath temperature and salinity gradients compensate for each other so that the mean, depth-averaged, along-isobath density gradient is approximately zero. This suggests that there may be a feedback between the along-isobath density gradient and the onshore salt and heat fluxes that maintains the density gradient near zero.
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Wei, Shuhuan, Huijun Feng, Lingen Chen und Yanlin Ge. „Constructal Equivalent Thermal Resistance Minimization for Tau-Shaped Fin“. Entropy 22, Nr. 11 (25.10.2020): 1206. http://dx.doi.org/10.3390/e22111206.
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With the aid of constructal theory and entransy theory, a Tau-shaped fin (TAUSF) is investigated in this paper, and the widths of the bend end and elemental fins are assumed to be different. The construct of the TAUSF is optimized by the minimum equivalent thermal resistance (ETR) obtained by entransy dissipation rate. The constraints of total enveloping volume and fin material volume are considered. The results show that in the specified range of width ratio, the twice minimum ETR of the TAUSF can be yielded by an optimal width ratio and an optimal length ratio. In addition, comparing the optimal performance of the TAUSF with the counterpart of a T-shaped fin, the former sacrifices a small amount of heat transfer performance and its stiffness increases due to its structure with the bend end. The optimal structure of the TAUSF yielded from ETR minimization is conspicuously different with the counterpart yielded from maximum thermal resistance minimization. Comparing the thermal performances of the two optimal constructs, the ETR of the former optimal construct is declined by 10.58%, whereas the maximum thermal resistance is augmented by 5.22%. The former optimal construct can lead to the uniformity of temperature gradient and the reduction in thermal stress, and can guide the engineering designs of practical fins.
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Sève, Danielle De, Monique Bernier, Jean-Pierre Fortin und Anne Walker. „Preliminary analysis of snow microwave radiometry using the SSM/I passive-microwave data: the case of La Grande River watershed (Quebec)“. Annals of Glaciology 25 (1997): 353–61. http://dx.doi.org/10.3189/s0260305500014270.
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The general objective of this paper is to estimate the snow water equivalent (SWE) of the La Grande River watershed (northern Quebec), using passive-microwave data from the SSM/I sensor. Particular emphasis is placed on the analysis of SSM/I multitemporal variations.The analysis of a database containing observations for three winters shows that the brightness temperatures of the snow decrease as the SWE increases for shallow snow covers. However, when the SWE is >180–200 mm, the relationship reverses. This is directly linked to the fraction of large snow crystals in the snow cover, since these are responsible for most of the volume scattering. The snow emissivity is lower for shallow snow covers, since the higher temperature gradient is responsible for the quick formation of large snow crystals. For SWE >80–200 mm, the temperature gradient decreases and large crystal formation is minimal. Since volume scattering is lower, snow emissivity tends to increase. The observations confirm what was observed by Mätzler and others (1982) and Mätzler (1994).Two regression lines were used to estimate the SWE for the beginning and the end of winter. This approach appears to be better, since it takes into account the structure of snow cover. The results were used to derive representative maps of the SWE.
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Han, Li Zhi, Liang Liang Chen und Bo Tian. „Influence of Paving Condition on Longitudinal Cracking of Portland Cement Concrete Pavement“. Advanced Materials Research 857 (Dezember 2013): 204–11. http://dx.doi.org/10.4028/www.scientific.net/amr.857.204.
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The curling stresses of rigid pavement are the result of in-situ and built-in temperature gradient. A profound investigation on the reasons causing longitudinal cracking (LC) was conducted in this paper. Based on finite element method (FEM) analysis results obtained from ISLAB 2000, the wheel load stress generated by a single axle load that is applied along the transverse joints is considered to be the critical loading condition for longitudinal cracking. Nonlinear environmental stress due to the curling of Portland Cement Concrete (PCC) was analyzed using the numerical program developed in this study; the paving time within a day has a significant influence on the curling stresses at the top portion of PCC slab at the critical loading position for longitudinal cracking. Research in this paper proposed an analytical method to determine the influence of the paving condition (day time and night time) on the built-in setting gradient and its effect on the in-situ effective equivalent temperature differential.
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Liu, Zun Chao, Ke Wang, Tong Liu, Wei Feng Xu und Min Shan Liu. „Structural Analysis and Optimization of Transition Section of Convex Tube Sheet“. Applied Mechanics and Materials 853 (September 2016): 356–60. http://dx.doi.org/10.4028/www.scientific.net/amm.853.356.
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The convex tube sheet which is used in heat recovery boiler consists of three parts: the high temperature tube sheet, the low temperature tube sheet and the transition section.Three-dimensional finite element model of convex tube sheet in new type of heat recovery boiler is established in this paper. Using the ANSYS Workbench software, thermal stress of the convex tube sheet is analyzed. The temperature fields and thermal stress distribution of convex tube sheet are obtained, and its structure strength is checked. The effects of the high temperature tube sheet thickness, low temperature tube sheet thickness and transition section thickness on the maximum equivalent stress of the convex tube sheet are analyzed. The results show that: temperature of most parts of convex tube sheet is close to the tube side fluid temperature, and the large temperature gradient only existed in the thinner regions of shell side of convex tube sheet; temperature distribution shows obvious skin effect. At the transition section, the temperature along the thickness direction is more evenly distributed, with little change in temperature gradient; larger thermal stress mainly concentrated at tube layout area which close to the shell side of the high temperature tube sheet and the connecting parts of transition section and low temperature tube sheet in the tube side. Through checking the strength intensity, convex tube sheet structural strength meets the requirements.The transition section thickness are optimized. The optimum thickness of the transition section analyzed in this paper is 31mm.
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Wang, Zhi Qiang, und Xiao Bin Wu. „Discussion of Method for Computing Temperature Load during Operation Period on High Arch Dam“. Applied Mechanics and Materials 470 (Dezember 2013): 976–79. http://dx.doi.org/10.4028/www.scientific.net/amm.470.976.
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According to the existing arch dam design specification, the temperature load is obtained based on analytic solution of infinite long free plate, it only considers the average temperature and the equivalent linear temperature difference of dam section in operation period, the influence of non-linear temperature difference has not been considered. This kind of simplification has some approximation; especially it can not reflect spatial effect of larger temperature gradient changes in the upstream and downstream water level change area. This paper first takes the free plate as an example, has calculated the temperature field corresponding to analytical method, finite element method, standard method, explains the rationality of using written program to carry on finite element analysis. On this basis, take Xiluodu arch dam as an example, the dam temperature load and temperature stress has been analyzed by using finite element method and standard method, the difference between both has been discussed
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Hu, Jian, Xiaofu Xiong, Jing Chen, Wei Wang und Jian Wang. „Transient Temperature Calculation and Multi-Parameter Thermal Protection of Overhead Transmission Lines Based on an Equivalent Thermal Network“. Energies 12, Nr. 1 (26.12.2018): 67. http://dx.doi.org/10.3390/en12010067.
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The overload degree of a transmission line is represented by currents in traditional overload protection, which cannot reflect its safety condition accurately. The sudden rise in transmission line current may lead to cascading tripping under traditional protection during power flow transfer in a power system. Therefore, timely and accurate analysis of the transient temperature rise of overhead transmission lines, revealing their overload endurance capability under the premise of ensuring safety, and coordination with power system controls can effectively eliminate overloading. This paper presents a transient temperature calculation method for overhead transmission lines based on an equivalent thermal network. This method can fully consider the temperature-dependent characteristics with material properties, convective heat resistance, and radiation heat and can accurately calculate the gradient distribution and response of the conductor cross-section temperature. The validity and accuracy of the proposed calculation method are verified by a test platform. In addition, a multi-parameter thermal protection strategy is proposed on the basis of the abovementioned calculation method. The protection can adequately explore the maximum overload capability of the line, and prevent from unnecessary tripping to avoid the expansion of accidents. Finally, the validity of the proposed protection is verified by the modified 29-bus system.
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Thompson, Helen, und Robert Langhans. „Air and Water Temperature Effects on Growth of Lettuce in a Hydroponic System“. HortScience 31, Nr. 4 (August 1996): 586b—586. http://dx.doi.org/10.21273/hortsci.31.4.586b.
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This research explored cool crop production in various climate zones using CEA facilities and hydroponics ponds to control growth rate and quality through root zone temperature control. The precise controls were used to vary air and water temperatures to study the temperature gradient between root and shoot zones. Effect of this gradient was measured by growth rates and final harvest dry weights. Lactuca sativa L. cv. Ostinata seedlings were germinated and grown 11 days in a growth chamber and moved to greenhouse ponds. Air temperatures chosen were 17, 24, and 31°C. These were constant for the 24 days that lettuce grew in the ponds with a 5°C decrease for 14 hours. during the night. Water temperatures of the three ponds in the greenhouse were set and maintained at 17, 24, and 31°C. Maximum final harvest weights were obtained at 24°C air/water 24°C. Final weights for the 17 and 31°C water setpoint were comparable at 24°C air. The 31 °C air /water inhibited quality and final dry weight, while 17 and 24°C water produced equivalent dry weights at 31°C air. At 31°C air heads were tighter at 17 than at 24°C, and loose at 31°C. At air 17 °C maximum weight was at 24°C water and minimum at 31°C water. At 17°C air, the 24°C water plants were of good quality, with thicker leaves but visibly smaller than the 31°C water crop. Significant differences in harvest dry weights were shown at each 7-day harvest beginning on day 14, due to both air and water setpoint factors and there was significant interaction between them.
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You, J., D. G. Tarboton und C. H. Luce. „Modeling the snow surface temperature with a one-layer energy balance snowmelt model“. Hydrology and Earth System Sciences Discussions 10, Nr. 12 (10.12.2013): 15071–118. http://dx.doi.org/10.5194/hessd-10-15071-2013.
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Abstract. \\label{sec:abstract} Snow surface temperature is a key control on energy exchanges at the snow surface, particularly net longwave radiation and turbulent energy fluxes. The snow surface temperature is in turn controlled by the balance between various external fluxes and the conductive heat flux, internal to the snowpack. Because of the strong insulating properties of snow, thermal gradients in snow packs are large and nonlinear, a fact that has led many to advocate multiple layer snowmelt models over single layer models. In an effort to keep snowmelt modeling simple and parsimonious, the Utah Energy Balance (UEB) snowmelt model used only one layer but allowed the snow surface temperature to be different from the snow average temperature by using an equilibrium gradient parameterization based on the surface energy balance. Although this procedure was considered an improvement over the ordinary single layer snowmelt models, it still resulted in discrepancies between modeled and measured snowpack energy contents. In this paper we examine the parameterization of snow surface temperature in single layer snowmelt models from the perspective of heat conduction into a semi-infinite medium. We evaluate the equilibrium gradient approach, the force-restore approach, and a modified force-restore approach. In addition, we evaluate a scheme for representing the penetration of a refreezing front in cold periods following melt. We also introduce a method to adjust effective conductivity to account for the presence of ground near to a shallow snow surface. These parameterizations were tested against data from the Central Sierra Snow Laboratory, CA, Utah State University experimental farm, UT, and Subnivean snow laboratory at Niwot Ridge, CO. These tests compare modeled and measured snow surface temperature, snow energy content, snow water equivalent, and snowmelt outflow. We found that with these refinements the model is able to better represent the snowpack energy balance and internal energy content while still retaining a parsimonious one layer format.
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Johnson, Leah, Craig M. Lee, Eric A. D’Asaro, Leif Thomas und Andrey Shcherbina. „Restratification at a California Current Upwelling Front. Part I: Observations“. Journal of Physical Oceanography 50, Nr. 5 (Mai 2020): 1455–72. http://dx.doi.org/10.1175/jpo-d-19-0203.1.
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AbstractA coordinated survey between a subsurface Lagrangian float and a ship-towed Triaxus profiler obtained detailed measurements of a restratifying surface intensified front (above 30 m) within the California Current System. The survey began as downfront winds incited mixing in the boundary layer. As winds relaxed and mixing subsided, the system entered a different dynamical regime as the front developed an overturning circulation with large vertical velocities that tilted isopycnals and stratified the upper ocean within a day. The horizontal buoyancy gradient was 1.5 × 10−6 s−2 and associated with vorticity, divergence, and strain that approached the Coriolis frequency. Estimates of vertical velocity from the Lagrangian float reached 1.2 × 10−3 m s−1. These horizontal gradients and vertical velocities were consistent with submesoscale dynamics that are distinct from the classic quasigeostrophic framework used to describe larger-scale flows. Vertical and horizontal gradients of velocity and buoyancy in the vicinity of the float revealed that sheared currents differentially advected the horizontal buoyancy gradient to increase vertical stratification. This was supported by analyses of temperature and salinity gradients that composed the horizontal and vertical stratification. Potential vorticity was conserved during restratification at 16 m, consistent with adiabatic processes. Conversely, potential vorticity near the surface (8 m) increased, highlighting the role of friction in modulating near-surface stratification. The observed increase in stratification due to these submesoscale processes was equivalent to a heat flux of 2000 W m−2, which is an order-of-magnitude larger than the average observed surface heat flux of 100 W m−2.
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Sève, Danielle De, Monique Bernier, Jean-Pierre Fortin und Anne Walker. „Preliminary analysis of snow microwave radiometry using the SSM/I passive-microwave data: the case of La Grande River watershed (Quebec)“. Annals of Glaciology 25 (1997): 353–61. http://dx.doi.org/10.1017/s0260305500014270.
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The general objective of this paper is to estimate the snow water equivalent (SWE) of the La Grande River watershed (northern Quebec), using passive-microwave data from the SSM/I sensor. Particular emphasis is placed on the analysis of SSM/I multitemporal variations.The analysis of a database containing observations for three winters shows that the brightness temperatures of the snow decrease as the SWE increases for shallow snow covers. However, when the SWE is >180–200 mm, the relationship reverses. This is directly linked to the fraction of large snow crystals in the snow cover, since these are responsible for most of the volume scattering. The snow emissivity is lower for shallow snow covers, since the higher temperature gradient is responsible for the quick formation of large snow crystals. For SWE >80–200 mm, the temperature gradient decreases and large crystal formation is minimal. Since volume scattering is lower, snow emissivity tends to increase. The observations confirm what was observed by Mätzler and others (1982) and Mätzler (1994).Two regression lines were used to estimate the SWE for the beginning and the end of winter. This approach appears to be better, since it takes into account the structure of snow cover. The results were used to derive representative maps of the SWE.
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Ma, Niu Jing. „Analysis of Thermal Effect on Girder with Side Main Rib Section“. Applied Mechanics and Materials 501-504 (Januar 2014): 495–500. http://dx.doi.org/10.4028/www.scientific.net/amm.501-504.495.
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According to the common girder with side main rib section of PC cable-stayed bridge with double cable planes, a computational model of two-dimension temperature field is presented. Temperature gradient of main rib, small longitudinal rib, top plate and flange plate was computed respectively, and then the stress and strain of each section are derived through plane cross-section assumption. For the cable-stayed bridge, member structure FEM is applied to compute node equivalent load and displacement, which resulted from both sunshine and seasonal thermal difference. Finally, a case study is analyzed, the results showed: computed and measured deflection of girder that result from thermal effect are very close, therefore, this method is feasible.
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Li, Shiwei, Yongqing Yang, Qianhui Pu, Wangqing Wen und Aiguo Yan. „Thermo-Hydro-Mechanical Combined Effect Analysis Model for Early-Age Concrete Bridges and Its Application“. Advances in Civil Engineering 2020 (07.09.2020): 1–15. http://dx.doi.org/10.1155/2020/8864109.
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The early cracking of concrete beam bridges remains a concern in civil engineering. An analytical model considering the combined effect of thermo-hydro-mechanical processes forms the basis for assessing the cracking risk of girders during construction. Based on the equivalent hydration theory, the temperature and moisture conduction processes and the evolution of the mechanical properties of concrete were modeled as a function of the equivalent age. A coupling model for the temperature and moisture fields was established, and a theoretical framework for analyzing the thermo-hydro-mechanical combined effect was presented. Based on this, a numerical analysis method was proposed and implemented into ABAQUS; the results were validated with some typical tests. Finally, a long-span prestressed concrete (PC) box girder bridge with balanced cantilever construction was taken as an example, and the causes of web cracking and its impact degree were analyzed. The results show that the rate of moisture conduction is significantly lower than the rate of temperature conduction; even for thin-walled components, there exists a significant humidity gradient on the surface layer. The humidity-induced shrinkage and restraint of the precast members are the main causes of web cracking.
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Cheng, Wenjie, Zhikai Deng, Guangdong Cao, Ling Xiao, Huimin Qi und Ming Li. „Analytical solution to thermal stresses of high speed PM rotor considering thermal load and heat convection“. International Journal of Applied Electromagnetics and Mechanics 64, Nr. 1-4 (10.12.2020): 533–40. http://dx.doi.org/10.3233/jae-209361.
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Aiming at the high speed permanent magnet (PM) rotor with the heat source, this work investigates the analytic solution to the transient temperature field and thermal stress field of the rotor, considering the influence of the forced air cooling of rotor surface on the stress field. Firstly, dimensionless formulation of the transient heat conduction equation including interior heat source is derived, where the axially non-uniform heat convection coefficient and the temperature of main flow region are equivalent to their mean values. Secondly, the Fourier integral transform method is used to solve the dimensionless heat conduction equation. Then, the obtained temperature field is loaded into the analytical solution of strength, in which three types of stress sources such as interference fit, centrifugal force and temperature gradient are included. Finally, examples are carried out to verify the analytical solutions and relative results are discussed.
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Zhao, Chenwei, Zecan Tu und Junkui Mao. „Investigation of the Film-Cooling Performance of 2.5D Braided Ceramic Matrix Composite Plates with Preformed Hole“. Aerospace 8, Nr. 4 (19.04.2021): 116. http://dx.doi.org/10.3390/aerospace8040116.
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The film-cooling performance of a 2.5D braided ceramic matrix composite (CMC) plate with preformed holes was numerically studied. Four numerical models containing braided structures were established: one model with film-cooling holes preformed through fiber extrusion deformation (EP-Hole), one model with film-cooling holes directly woven through fibers (WP-Hole), and two models with directly drilled holes (DP-Hole1,2). Besides, the influence of the ratio between the equivalent thermal conductivities on the axial and radial directions of fiber Kr was investigated. The results show that the preformed holes have better performance in controlling the thermal gradient with the increase of Kr. The maximum thermal gradient around the DP-Hole is significantly higher than that of the WP-Hole and EP-Hole, and the maximum relative variation reaches 123.3%. With Kr increasing from 3.32 to 13.05, the overall cooling effectiveness on the hot-side wall decreases for all models, by about 10%. Compared with the traditional drill method, the new preformed film-cooling hole studied in this paper can reduce the temperature and the thermal gradient in the region around the holes.
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Pisso, I., K. S. Law, F. Fierli, P. H. Haynes, P. Hoor, E. Palazzi, F. Ravegnani und S. Viciani. „On the structure of the extra-tropical transition layer from in-situ observations“. Atmospheric Chemistry and Physics Discussions 12, Nr. 10 (25.10.2012): 28033–68. http://dx.doi.org/10.5194/acpd-12-28033-2012.
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Abstract. In-situ observations of atmospheric tracers from multiple measurement campaigns over the period 1994–2007 were combined to investigate the Extra-tropical Transition Layer (ExTL) region and the properties of large scale meridional transport. We used potential temperature, equivalent latitude and distance relative to the local dynamical tropopause as vertical coordinates to highlight the behaviour of trace gases in the tropopause region. Vertical coordinates based on constant PV surfaces allowed us to relate the dynamical definition of the tropopause with trace gases distributions and vertical gradients and hence analyse its latitudinal dependence and seasonal variability. Analysis of the available data provides a working definition of the upper limit of the ExTL based on the upper limit of the region of high vertical CO gradient in PV relative coordinates. A secondary local maximum in vertical O3 gradient can be used a proxy for the lower limit, although it is less clearly defined than that of CO. The sloping isopleths of CO and O3 mixing ratios and the CO mixing ratio gradient are consistent with isopleths in purely dynamical diagnostics such as χ30 d, the proportion of air masses in contact with the PBL within one month and underline the differences between the PV based and chemical tropopauses. The use of tropopause relative coordinates allows different seasons to be analysed together to produce climatological means. The weak dependence of dynamical diagnostics of transport on the absolute values of tracer concentrations makes them a suitable process-oriented tool to evaluate global chemical models and make Lagrangian comparisons.
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You, J., D. G. Tarboton und C. H. Luce. „Modeling the snow surface temperature with a one-layer energy balance snowmelt model“. Hydrology and Earth System Sciences 18, Nr. 12 (11.12.2014): 5061–76. http://dx.doi.org/10.5194/hess-18-5061-2014.
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Abstract. Snow surface temperature is a key control on and result of dynamically coupled energy exchanges at the snow surface. The snow surface temperature is the result of the balance between external forcing (incoming radiation) and energy exchanges above the surface that depend on surface temperature (outgoing longwave radiation and turbulent fluxes) and the transport of energy into the snow by conduction and meltwater influx. Because of the strong insulating properties of snow, thermal gradients in snow packs are large and nonlinear, a fact that has led many to advocate multiple layer snowmelt models over single layer models. In an effort to keep snowmelt modeling simple and parsimonious, the Utah Energy Balance (UEB) snowmelt model used only one layer but allowed the snow surface temperature to be different from the snow average temperature by using an equilibrium gradient parameterization based on the surface energy balance. Although this procedure was considered an improvement over the ordinary single layer snowmelt models, it still resulted in discrepancies between modeled and measured snowpack energy contents. In this paper we evaluate the equilibrium gradient approach, the force-restore approach, and a modified force-restore approach when they are integrated as part of a complete energy and mass balance snowmelt model. The force-restore and modified force-restore approaches have not been incorporated into the UEB in early versions, even though Luce and Tartoton have done work in calculating the energy components using these approaches. In addition, we evaluate a scheme for representing the penetration of a refreezing front in cold periods following melt. We introduce a method to adjust effective conductivity to account for the presence of ground near to a shallow snow surface. These parameterizations were tested against data from the Central Sierra Snow Laboratory, CA, Utah State University experimental farm, UT, and subnivean snow laboratory at Niwot Ridge, CO. These tests compare modeled and measured snow surface temperature, snow energy content, snow water equivalent, and snowmelt outflow. We found that with these refinements the model is able to better represent the snowpack energy balance and internal energy content while still retaining a parsimonious one layer format.
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Ou, Jiajie, und Lifu Li. „Application of the multi-field coupling enhanced heat transfer principle to the engine compartment design of clean gas bus“. Mechanical Sciences 11, Nr. 1 (17.06.2020): 205–20. http://dx.doi.org/10.5194/ms-11-205-2020.
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Abstract. Clean gas engines, such as liquefied petroleum gas (LPG) engines, have high thermal loads on parts under equivalent specific combustion. This study examines the multi-field coupling enhanced heat transfer principle and its applications to the engine compartment of a typical LPG city bus. The field synergy enhanced heat transfer principle (FSP) was applied in the radiator assembly area. The FSP model yielded an optimum velocity -temperature gradient matching field that would improve convective heat transfer in this area. To strengthen the convective heat transfer ability of the limited cooling air in the cabin, temperature field homogenization (TFH) in the core flow region of the engine block area was achieved. The TFH optimization model helped minimize the temperature gradient in the core flow region and maximize it at the heat transfer boundary, and the optimum vector field and flow path were obtained. More comprehensive changes to the structural design were made according to the multi-field coupling enhanced heat transfer principles. The simulation results showed that in the comprehensive structure, the heat transfer efficiency of the radiator increased by 14.66 %, the average temperature of the air passages in the engine block area decreased by 22.23 %, and the heat dissipation coefficient of the engine body and engine cover increased by 4.60 times and 3.49 times, respectively.
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Hoell, Andrew, Shraddhanand Shukla, Mathew Barlow, Forest Cannon, Colin Kelley und Chris Funk. „The Forcing of Monthly Precipitation Variability over Southwest Asia during the Boreal Cold Season“. Journal of Climate 28, Nr. 18 (11.09.2015): 7038–56. http://dx.doi.org/10.1175/jcli-d-14-00757.1.
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Abstract Southwest Asia, defined as the region containing the countries of Afghanistan, Iran, Iraq, and Pakistan, is water scarce and receives nearly 75% of its annual rainfall during the boreal cold season of November–April. The forcing of southwest Asia precipitation has been previously examined for the entire boreal cold season from the perspective of climate variability originating over the Atlantic and tropical Indo-Pacific Oceans. This study examines the intermonthly differences in precipitation variability over southwest Asia and the atmospheric conditions directly responsible in forcing monthly November–April precipitation. Seasonally averaged November–April precipitation over southwest Asia is significantly correlated with sea surface temperature (SST) patterns consistent with Pacific decadal variability (PDV), El Niño–Southern Oscillation (ENSO), and the long-term change of global SST (LT). In contrast, the precipitation variability during the individual months of November–April is unrelated and is correlated with SST signatures that include PDV, ENSO, and LT in different combinations. Despite strong intermonthly differences in precipitation variability during November–April over southwest Asia, similar atmospheric circulations, highlighted by a stationary equivalent barotropic Rossby wave centered over Iraq, force the monthly spatial distributions of precipitation. Tropospheric flow on the eastern side of the equivalent barotropic Rossby wave modifies the flux of moisture and advects the mean meridional temperature gradient, resulting in temperature advection that is balanced by vertical motions over southwest Asia. The forcing of monthly southwest Asia precipitation by equivalent barotropic Rossby waves is different from the forcing by baroclinic Rossby waves associated with tropically forced–only modes of climate variability.
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Plagge, Amanda, James B. Edson und Douglas Vandemark. „In Situ and Satellite Evaluation of Air–Sea Flux Variation near Ocean Temperature Gradients“. Journal of Climate 29, Nr. 4 (15.02.2016): 1583–602. http://dx.doi.org/10.1175/jcli-d-15-0489.1.
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Abstract Observations of ocean–atmosphere coupling across persistent mesoscale sea surface temperature (SST) gradients are used to examine the controls of atmospheric stability, pressure gradient force, and heat flux that are considered central to oft-observed coupling between wind and SST. Moored air–sea flux measurements near the Gulf Stream are combined with QuikSCAT satellite scatterometer equivalent neutral wind (ENW) data to assess correlations between SST, air–sea fluxes, pressure, and wind perturbations at scales of 10–100 days. The net effect of ocean fronts meandering past the site enabled buoy observation of SST impacts on wind, with coupling coefficients of 0.3–0.5 similar to past studies. Wind stress–SST and ENW–SST correlation coefficients are slightly higher, and roughly 20% of the ENW perturbation is attributed to stratification impacts predicted by Monin–Obukhov (MO) similarity theory. Significantly higher correlation is observed when relating wind or stress perturbations to buoyant heat flux variation. Atmospheric pressure perturbation with SST of order 0.5 hPa °C−1 is observed, as well as high negative correlation between wind and pressure variations. Length and time scales associated with the coupling indicate that peak correlations occur at 50–70 days and 300–500 km, consistent with mesoscale meander scales. Coupling coefficient values vary significantly depending on analysis time scale and exhibit a range near to recently observed interbasin variability. This variability is attributed to the extent of oceanic length scales permitted in the analysis. Together, results affirm the central role of SST-induced turbulent heat flux in controlling pressure field adjustments and thereby the wind perturbations over SST fronts.
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Fortuin, J. P. F., und J. Oerlemans. „Parameterization of the Annual Surface Temperature and Mass Balance of Antarctica“. Annals of Glaciology 14 (1990): 78–84. http://dx.doi.org/10.1017/s0260305500008302.
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This study entails the parameterization, by means of a linear multiple-regression analysis, of the annual surface temperature and mass balance of Antarctica. The analysis was performed for the entire ice cap as well as for three separate regions: ice shelves (elevation less than 200 m), the interior (elevation above 1500 m), and the escarpment region in between. It was found that temperature can be parameterized very well in terms of elevation and latitude. The latitudinal gradient on the ice shelves can be explained by the super-adiabatic lapse rate along the surface and latitudinal temperature gradient in the interior, assuming adiabatic descent of air in the inversion layer from the interior region towards the coast and an axisymmetric spreading over the ice shelves. The surface mass balance can be parameterized reliably only in the interior, where it has a strong positive correlation with the saturation vapour pressure of the free atmosphere, and a significant correlation with the shape of the dome. The convex shape of the dome contributes to the mass balance by inducing subsidence of the relatively moist air of the free atmosphere into the inversion layer. This results in precipitation, as radiative cooling in the inversion exceeds adiabatic warming. An estimate is made of the annual horizontal and vertical advective velocities in the free atmosphere above the interior, based on regression results and a physical analysis of the precipitation processes in this region. A temperature sensitivity analysis was performed for the current mass-balance distribution. For a 1 K. rise in surface temperature, the regression estimate of the increase in accumulation on the grounded ice sheet is equivalent to a rate of sea-level lowering of 0.2 mm a−1. This is about 30% less than estimates based on the current mass balance perturbated by the increase in saturation vapour pressure of the free atmosphere.
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Fortuin, J. P. F., und J. Oerlemans. „Parameterization of the Annual Surface Temperature and Mass Balance of Antarctica“. Annals of Glaciology 14 (1990): 78–84. http://dx.doi.org/10.3189/s0260305500008302.
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This study entails the parameterization, by means of a linear multiple-regression analysis, of the annual surface temperature and mass balance of Antarctica. The analysis was performed for the entire ice cap as well as for three separate regions: ice shelves (elevation less than 200 m), the interior (elevation above 1500 m), and the escarpment region in between. It was found that temperature can be parameterized very well in terms of elevation and latitude. The latitudinal gradient on the ice shelves can be explained by the super-adiabatic lapse rate along the surface and latitudinal temperature gradient in the interior, assuming adiabatic descent of air in the inversion layer from the interior region towards the coast and an axisymmetric spreading over the ice shelves. The surface mass balance can be parameterized reliably only in the interior, where it has a strong positive correlation with the saturation vapour pressure of the free atmosphere, and a significant correlation with the shape of the dome. The convex shape of the dome contributes to the mass balance by inducing subsidence of the relatively moist air of the free atmosphere into the inversion layer. This results in precipitation, as radiative cooling in the inversion exceeds adiabatic warming. An estimate is made of the annual horizontal and vertical advective velocities in the free atmosphere above the interior, based on regression results and a physical analysis of the precipitation processes in this region.A temperature sensitivity analysis was performed for the current mass-balance distribution. For a 1 K. rise in surface temperature, the regression estimate of the increase in accumulation on the grounded ice sheet is equivalent to a rate of sea-level lowering of 0.2 mm a−1. This is about 30% less than estimates based on the current mass balance perturbated by the increase in saturation vapour pressure of the free atmosphere.
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Arif, A. F. M., S. Z. Shuja und B. S. Yilbas. „Gas-assisted laser single-pulse heating: Study of thermal stresses“. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 215, Nr. 3 (01.03.2001): 291–306. http://dx.doi.org/10.1243/0954406011520724.
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Pulsed laser heating of metals causes an excessive temperature gradient across the heated zone, which in turn results in thermal stresses developing in the heated region. In the present study, gas-assisted pulsed laser heating of steel is simulated. The governing flow, energy and thermal stress equations are solved numerically. The low Reynolds number k-ε model is introduced to account for the turbulence. In the analysis, temporal variation in heating and stress development are considered. In order to examine the material response to the heating pulse, constant and variable properties of the workpiece are taken into account. It is found that the thermal stresses are highly concentrated in the surface region of the substrate. The radial component of the stress is compressive while the axial component is tensile. The maximum equivalent strain is of the order of 10−3. The maximum equivalent stress occurs below the surface along the z axis, where the radial intersection is the centre of the heated spot.