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1
Mechem, David B., e Yefim L. Kogan. "A Bulk Parameterization of Giant CCN". Journal of the Atmospheric Sciences 65, n. 7 (1 luglio 2008): 2458–66. http://dx.doi.org/10.1175/2007jas2502.1.
Testo completoAbstract (sommario):
Abstract A parameterization for giant cloud condensation nuclei (GCCN), suitable for use in bulk microphysical models, has been developed that uses precise representations of the condensational growth of aerosol particles in the subcloud layer. The formulation employs an observationally based GCCN distribution function and directly observable parameters of GCCN, such as concentration and the shape of the aerosol spectra. The parameterization couples naturally to parameterizations of sea salt flux from the ocean surface. The behavior of the GCCN parameterization in a large eddy simulation (LES) framework is consistent with simulations employing explicit, size-resolving microphysical methods. The parameterization properly represents the sensitivity of cloud, drizzle, turbulence, and radiative properties to changes in GCCN concentration for polluted and clean background CCN environments.
2
Ming, Yi, V. Ramaswamy, Leo J. Donner e Vaughan T. J. Phillips. "A New Parameterization of Cloud Droplet Activation Applicable to General Circulation Models". Journal of the Atmospheric Sciences 63, n. 4 (1 aprile 2006): 1348–56. http://dx.doi.org/10.1175/jas3686.1.
Testo completoAbstract (sommario):
Abstract A new parameterization is proposed to link the droplet number concentration to the size distribution and chemical composition of aerosol and updraft velocity. Except for an empirical assumption of droplet growth, the parameterization is formulated almost entirely on first principles to allow for satisfactory performance under a variety of conditions. For a series of updraft velocity ranging from 0.03 to 10.0 m s−1, the droplet number concentrations predicted with the parameterization are in good agreement with the detailed parcel model simulations with an average error of −4 ± 26% (one standard deviation). The accuracy is comparable to or better than some existing parameterizations. The parameterization is able to account for the effects of droplet surface tension and mass accommodation coefficient on activation without adjusting the empirical parameter. These desirable attributes make the parameterization suitable for being used in the prognostic determination of the cloud droplet number concentration in general circulation models (GCMs).
3
Sun, Difu, Junqiang Song, Xiaoyong Li, Kaijun Ren e Hongze Leng. "A Novel Sea Surface Roughness Parameterization Based on Wave State and Sea Foam". Journal of Marine Science and Engineering 9, n. 3 (25 febbraio 2021): 246. http://dx.doi.org/10.3390/jmse9030246.
Testo completoAbstract (sommario):
A wave state related sea surface roughness parameterization scheme that takes into account the impact of sea foam is proposed in this study. Using eight observational datasets, the performances of two most widely used wave state related parameterizations are examined under various wave conditions. Based on the different performances of two wave state related parameterizations under different wave state, and by introducing the effect of sea foam, a new sea surface roughness parameterization suitable for low to extreme wind conditions is proposed. The behaviors of drag coefficient predicted by the proposed parameterization match the field and laboratory measurements well. It is shown that the drag coefficient increases with the increasing wind speed under low and moderate wind speed conditions, and then decreases with increasing wind speed, due to the effect of sea foam under high wind speed conditions. The maximum values of the drag coefficient are reached when the 10 m wind speeds are in the range of 30–35 m/s.
4
Alexias, Pavlos, e Kyriakos C. Giannakoglou. "Shape Optimization of a Two-Fluid Mixing Device Using Continuous Adjoint". Fluids 5, n. 1 (8 gennaio 2020): 11. http://dx.doi.org/10.3390/fluids5010011.
Testo completoAbstract (sommario):
In this paper, the continuous adjoint method is used for the optimization of a static mixing device. The CFD model used is suitable for the flow simulation of the two miscible fluids that enter the device. The formulation of the adjoint equations, which allow the computation of the sensitivity derivatives is briefly demonstrated. A detailed analysis of the geometry parameterization is presented and a set of different parameterization scenarios are investigated. In detail, two different parameterizations are combined into a two-stage optimization algorithm which targets maximum mixture uniformity at the exit of the mixer and minimum total pressure losses. All parameterizations are in conformity with specific manufacturability constraints of the final shape. The non-dominated front of optimal solutions is obtained by using the weighted sum of the two objective functions and executing a set of optimization runs. The effectiveness of the proposed synthetic parameterization schemes is assessed and discussed in detail. Finally, a reduced length mixer is optimized to study the impact of the length of the tube on the device’s performance.
5
Madi, Raneem, Gerrit Huibert de Rooij, Henrike Mielenz e Juliane Mai. "Parametric soil water retention models: a critical evaluation of expressions for the full moisture range". Hydrology and Earth System Sciences 22, n. 2 (12 febbraio 2018): 1193–219. http://dx.doi.org/10.5194/hess-22-1193-2018.
Testo completoAbstract (sommario):
Abstract. Few parametric expressions for the soil water retention curve are suitable for dry conditions. Furthermore, expressions for the soil hydraulic conductivity curves associated with parametric retention functions can behave unrealistically near saturation. We developed a general criterion for water retention parameterizations that ensures physically plausible conductivity curves. Only 3 of the 18 tested parameterizations met this criterion without restrictions on the parameters of a popular conductivity curve parameterization. A fourth required one parameter to be fixed. We estimated parameters by shuffled complex evolution (SCE) with the objective function tailored to various observation methods used to obtain retention curve data. We fitted the four parameterizations with physically plausible conductivities as well as the most widely used parameterization. The performance of the resulting 12 combinations of retention and conductivity curves was assessed in a numerical study with 751 days of semiarid atmospheric forcing applied to unvegetated, uniform, 1 m freely draining columns for four textures. Choosing different parameterizations had a minor effect on evaporation, but cumulative bottom fluxes varied by up to an order of magnitude between them. This highlights the need for a careful selection of the soil hydraulic parameterization that ideally does not only rely on goodness of fit to static soil water retention data but also on hydraulic conductivity measurements. Parameter fits for 21 soils showed that extrapolations into the dry range of the retention curve often became physically more realistic when the parameterization had a logarithmic dry branch, particularly in fine-textured soils where high residual water contents would otherwise be fitted.
6
Hernández-Rivera, Efraín, Souma Chowdhury, Shawn P. Coleman, Payam Ghassemi e Mark A. Tschopp. "Integrating exploratory data analytics into ReaxFF parameterization". MRS Communications 8, n. 03 (settembre 2018): 1300–1310. http://dx.doi.org/10.1557/mrc.2018.155.
Testo completoAbstract (sommario):
We present a systematic approach to refine hyperdimensional interatomic potentials, which is showcased on the ReaxFF formulation. The objective of this research is to utilize the relationship between interatomic potential input variables and objective responses (e.g., cohesive energy) to identify and explore suitable parameterizations for the boron carbide (B–C) system. Through statistical data analytics, ReaxFF's parametric complexity was overcome via dimensional reduction (55 parameters) while retaining enough degrees of freedom to capture most of the variability in responses. Two potentials were identified which improved on an existing parameterization for the objective set if interest, showcasing the framework's capabilities.
7
Ratkowsky, D. A. "A suitable parameterization of the Michaelis-Menten enzyme reaction". Biochemical Journal 240, n. 2 (1 dicembre 1986): 357–60. http://dx.doi.org/10.1042/bj2400357.
Testo completoAbstract (sommario):
It is shown here that a suitable form for estimation and inference using the Michaelis-Menten [(1913) Biochem Z. 49, 333-369] model for simple enzymic reactions is one in which the two parameters appear in the denominator of the equation. In this form, convergence to the least-squares estimates using the Gauss-Newton method [see Kennedy & Gentle (1980) Statistical Computing, Marcel Dekker, New York] is virtually ensured, or, as the model in this form is a member of the class of ‘generalized linear models’, it may be fitted by packages such as those of Rothamsted Experimental Station [(1977) GENSTAT (A General Statistical Program), Rothamsted Experimental Station, Harpenden] and the Numerical Algorithms Group [(1978) GLIM (Generalised Linear Interactive Modeling), Numerical Algorithms Group, Oxford]. Furthermore, the parameters-in-denominator principle is readily extended to more complicated catalytic models. With all parameters in the denominator, the least-squares estimators are close to being unbiased and normally distributed, whereas severe bias and non-normality may result from use of the standard formulations.
8
Njuki, Sammy M., Chris M. Mannaerts e Zhongbo Su. "Accounting for Turbulence-Induced Canopy Heat Transfer in the Simulation of Sensible Heat Flux in SEBS Model". Remote Sensing 15, n. 6 (14 marzo 2023): 1578. http://dx.doi.org/10.3390/rs15061578.
Testo completoAbstract (sommario):
Surface turbulent heat fluxes are crucial for monitoring drought, heat waves, urban heat islands, agricultural water management, and other hydrological applications. Energy Balance Models (EBMs) are widely used to simulate surface heat fluxes from a combination of remote sensing-derived variables and meteorological data. Single-source EBMs, in particular, are preferred in mapping surface turbulent heat fluxes due to their relative simplicity. However, most single-source EBMs suffer from uncertainties inherent to the parameter kB−1, which is used to account for differences in the source of heat and the sink of momentum when representing aerodynamic resistance in single-source EBMs. For instance, the parameterization of kB−1 in the commonly used single-source Surface Energy Balance System (SEBS) model uses a constant value of the foliage heat transfer coefficient (Ct), in the parameterization of the vegetation component of kB−1 (kBv−1). Thus, SEBS ignores the effect of turbulence on canopy heat transfer. As a result, SEBS has been found to greatly underestimate sensible heat flux in tall forest canopies, where turbulence is a key contributor to canopy heat transfer. This study presents a revised parameterization of kBv−1 for the SEBS model. A physically based formulation of Ct, which considers the effect of turbulence on Ct, is used in deriving the revised parameterization. Simulation results across 15 eddy covariance (EC) flux tower sites show that the revised parameterization significantly reduces the underestimation of sensible heat flux compared to the original parameterization under tall forest canopies. The revised parameterization is relatively simple and does not require additional information on canopy structure compared to some more complex parameterizations proposed in the literature. As such, the revised parameterization is suitable for mapping surface turbulent heat fluxes, especially under tall forest canopies.
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Gholami, Yaser, Romain Brossier, Stéphane Operto, Alessandra Ribodetti e Jean Virieux. "Which parameterization is suitable for acoustic vertical transverse isotropic full waveform inversion? Part 1: Sensitivity and trade-off analysis". GEOPHYSICS 78, n. 2 (1 marzo 2013): R81—R105. http://dx.doi.org/10.1190/geo2012-0204.1.
Testo completoAbstract (sommario):
In most geologic environments, accounting for anisotropy is necessary to perform acoustic full waveform inversion (FWI) of wide-azimuth and wide-aperture seismic data because of the potential dependence of wave speeds on the direction of the wave propagation. In the framework of multiparameter FWI, the subsurface parameterization controls the influence of the different parameter classes on the modeled seismic data as a function of the scattering angle and hence the resolution with which the parameters can be reconstructed and the potential trade-off between different parameters. We have evaluated a numerical procedure based on computation of the scattering patterns of the different parameters to assess the sensitivity of the seismic data to different parameterizations of vertical transverse isotropic media in the acoustic approximation. Among the different categories we have tested, a monoparametric FWI was found for imaging one wave speed with a broad wavenumber content, keeping the Thomsen parameters fixed, which have a small influence on the data relative to the wave speed. This raises the question of the initial information required in the background models of the Thomsen parameters to perform reliable monoparameter FWI. Alternatively, simultaneously inverting the horizontal and vertical wave speeds introduces limited trade-off effects because these wave speeds have significant influence on the data for distinct ranges of scattering angles, while the influence of the Thomsen parameter [Formula: see text] remains weak. With such parameterization, the short-to-intermediate wavelengths of the vertical velocity are updated from the short-to-intermediate scattering angles, while the long-to-intermediate wavelengths of the horizontal velocity are updated from the wide-to-intermediate scattering angles. We concluded that the choice of the subsurface parameterization can be driven by the acquisition geometry, which controls the scattering-angle coverage and hence the resolving power of FWI, and by the accuracy of the available initial FWI models.
10
Boutle, I. A., J. E. J. Eyre e A. P. Lock. "Seamless Stratocumulus Simulation across the Turbulent Gray Zone". Monthly Weather Review 142, n. 4 (27 marzo 2014): 1655–68. http://dx.doi.org/10.1175/mwr-d-13-00229.1.
Testo completoAbstract (sommario):
Abstract A pragmatic approach for representing partially resolved turbulence in numerical weather prediction models is introduced and tested. The method blends a conventional boundary layer parameterization, suitable for large grid lengths, with a subgrid turbulence scheme suitable for large-eddy simulation. The key parameter for blending the schemes is the ratio of grid length to boundary layer depth. The new parameterization is combined with a scale-aware microphysical parameterization and tested on a case study forecast of stratocumulus evolution. Simulations at a range of model grid lengths between 1 km and 100 m are compared to aircraft observations. The improved microphysical representation removes the correlation between precipitation rate and model grid length, while the new turbulence parameterization improves the transition from unresolved to resolved turbulence as grid length is reduced.
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Masmoudi, Nabil, e Tariq Alkhalifah. "A new parameterization for waveform inversion in acoustic orthorhombic media". GEOPHYSICS 81, n. 4 (luglio 2016): R157—R171. http://dx.doi.org/10.1190/geo2015-0635.1.
Testo completoAbstract (sommario):
Orthorhombic anisotropic model inversion is extra challenging because of the multiple parameter nature of the inversion problem. The high number of parameters required to describe the medium exerts considerable trade-off and additional nonlinearity to a full-waveform inversion (FWI) application. Choosing a suitable set of parameters to describe the model and designing an effective inversion strategy can help in mitigating this problem. Using the Born approximation, which is the central ingredient of the FWI update process, we have derived radiation patterns for the different acoustic orthorhombic parameterizations. Analyzing the angular dependence of scattering (radiation patterns) of the parameters of different parameterizations starting with the often used Thomsen-Tsvankin parameterization, we have assessed the potential trade-off between the parameters and the resolution in describing the data and inverting for the parameters. The analysis led us to introduce new parameters [Formula: see text], [Formula: see text], and [Formula: see text], which have azimuthally dependent radiation patterns, but keep the scattering potential of the transversely isotropic parameters stationary with azimuth (azimuth independent). The novel parameters [Formula: see text], [Formula: see text], and [Formula: see text] are dimensionless and represent a measure of deviation between the vertical planes in orthorhombic anisotropy. Therefore, these deviation parameters offer a new parameterization style for an acoustic orthorhombic medium described by six parameters: three vertical transversely isotropic (VTI) parameters, two deviation parameters, and one parameter describing the anisotropy in the horizontal symmetry plane. The main feature of any parameterization based on the deviation parameters, is the azimuthal independency of the modeled data with respect to the VTI parameters, which allowed us to propose practical inversion strategies based on our experience with the VTI parameters. This feature of the new parameterization style holds for even the long-wavelength components of the model constrained by traveltimes.
12
Liu, Chun Li, Hai Long Chen, Lei Shao, Jun Ting Wang e Cheng Ji You. "Parameterizations and Parameters Relations of Stable Distribution". Applied Mechanics and Materials 543-547 (marzo 2014): 1721–27. http://dx.doi.org/10.4028/www.scientific.net/amm.543-547.1721.
Testo completoAbstract (sommario):
For the problem of various non-Gaussian signals and noises have distinct spiky and impulsive characteristics in practice, which cannot be solved by Gaussian distribution, we focus on the Alpha stable distribution. This paper firstly sets forth the representation of standard parameterization, and gives some properties in this parameterization. Secondly, define a representation of the parameterization for the purpose of being suitable for numerical calculation and modeling, clears the meaning of each parameter, finds relations between parameters in these representations. Finally, analyze and prove the properties equally apply in this parameterization.
13
Plant, R. S., e G. C. Craig. "A Stochastic Parameterization for Deep Convection Based on Equilibrium Statistics". Journal of the Atmospheric Sciences 65, n. 1 (1 gennaio 2008): 87–105. http://dx.doi.org/10.1175/2007jas2263.1.
Testo completoAbstract (sommario):
Abstract A stochastic parameterization scheme for deep convection is described, suitable for use in both climate and NWP models. Theoretical arguments and the results of cloud-resolving models are discussed in order to motivate the form of the scheme. In the deterministic limit, it tends to a spectrum of entraining/detraining plumes and is similar to other current parameterizations. The stochastic variability describes the local fluctuations about a large-scale equilibrium state. Plumes are drawn at random from a probability distribution function (PDF) that defines the chance of finding a plume of given cloud-base mass flux within each model grid box. The normalization of the PDF is given by the ensemble-mean mass flux, and this is computed with a CAPE closure method. The characteristics of each plume produced are determined using an adaptation of the plume model from the Kain–Fritsch parameterization. Initial tests in the single-column version of the Unified Model verify that the scheme is effective in producing the desired distributions of convective variability without adversely affecting the mean state.
14
Ahasan, M. N., M. A. M. Chowdhury e D. A. Quadir. "SENSITIVITY TEST OF PARAMETERIZATION SCHEMES OF MM5 MODEL FOR PREDICTION OF THE HIGH IMPACT RAINFALL EVENTS OVER BANGLADESH". Journal of Mechanical Engineering 44, n. 1 (13 luglio 2014): 33–42. http://dx.doi.org/10.3329/jme.v44i1.19496.
Testo completoAbstract (sommario):
The sensitivity test of parameterization schemes for prediction of summer monsoon high impact rainfallevents (HIRE) over Bangladesh has been performed using the Fifth-Generation PSU/NCAR Mesoscale Model(MM5) conducting six historical HIRE cases. The MM5 model was run on triple-nested domains at 45, 15, 5 kmhorizontal resolutions using Anthes-Kuo (AK), Grell (Gr), Kain-Fritsch (KF), Betts-Miller (BM) andKain-Fritsch2 (KF2) cumulus parameterization schemes (CPS) with Medium Range Forecast (MRF) andBlackadar planetary boundary layer (PBL).The model predicted rainfall was compared both spatially andquantitatively with Tropical Rainfall Measuring Mission (TRMM) rainfall. While parameterization options ofMM5 model have been investigated spatially for Bangladesh, Anthes-Kuo CPS with both MRF and BlackadarPBL (AKM & AKB) options of MM5 have found suitable. Quantitatively, Anthes-Kuo CPS with MRF PBL (AKM)option has calculated the better average rainfall over Bangladesh. By this way, AKM has found suitable in bothspatial and quantitaive comparisons. Thus, Anthes-Kuo CPS with MRF PBL (AKM) has considered as the bestMM5 option for prediction of summer monsoon HIRE cases over Bangladesh.The sensitivity test of parameterization schemes for prediction of summer monsoon high impact rainfall events (HIRE) over Bangladesh has been performed using the Fifth-Generation PSU/NCAR Mesoscale Model (MM5) conducting six historical HIRE cases. The MM5 model was run on triple-nested domains at 45, 15, 5 km horizontal resolutions using Anthes-Kuo (AK), Grell (Gr), Kain-Fritsch (KF), Betts-Miller (BM) and Kain-Fritsch2 (KF2) cumulus parameterization schemes (CPS) with Medium Range Forecast (MRF) and Blackadar planetary boundary layer (PBL).The model predicted rainfall was compared both spatially and quantitatively with Tropical Rainfall Measuring Mission (TRMM) rainfall. While parameterization options of MM5 model have been investigated spatially for Bangladesh, Anthes-Kuo CPS with both MRF and Blackadar PBL (AKM & AKB) options of MM5 have found suitable. Quantitatively, Anthes-Kuo CPS with MRF PBL (AKM) option has calculated the better average rainfall over Bangladesh. By this way, AKM has found suitable in both spatial and quantitaive comparisons. Thus, Anthes-Kuo CPS with MRF PBL (AKM) has considered as the best MM5 option for prediction of summer monsoon HIRE cases over Bangladesh. DOI: http://dx.doi.org/10.3329/jme.v44i1.19496
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Larson, V. E., e D. P. Schanen. "The Subgrid Importance Latin Hypercube Sampler (SILHS): a multivariate subcolumn generator". Geoscientific Model Development 6, n. 5 (29 ottobre 2013): 1813–29. http://dx.doi.org/10.5194/gmd-6-1813-2013.
Testo completoAbstract (sommario):
Abstract. Coarse-resolution climate and weather forecast models cannot accurately parameterize small-scale, nonlinear processes without accounting for subgrid-scale variability. To do so, some models integrate over the subgrid variability analytically. Although analytic integration methods are attractive, they can be used only with physical parameterizations that have a sufficiently simple functional form. Instead, this paper introduces a method to integrate subgrid variability using a type of Monte Carlo integration. The method generates subcolumns with suitable vertical correlations and feeds them into a microphysics parameterization. The subcolumn methodology requires little change to the parameterization source code and can be used with a wide variety of physical parameterizations. Our subcolumn generator is multivariate, which is important for physical processes that involve two or more hydrometeor species, such as accretion of cloud droplets by rain drops. In order to reduce sampling noise in the integrations, our subcolumn generator employs two variance-reduction methods, namely importance and stratified (Latin hypercube) sampling. For this reason, we name the subcolumn generator the Subgrid Importance Latin Hypercube Sampler (SILHS). This paper tests SILHS in interactive, single-column simulations of a marine stratocumulus case and a shallow cumulus case. The paper then compares simulations that use SILHS with those that use analytic integration. Although the SILHS solutions exhibit considerable noise from time step to time step, the noise is greatly damped in most of the time-averaged profiles.
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Puig, Lluis. "Parameterization of Irreducible Characters for p-Solvable Groups". Algebra Colloquium 19, n. 01 (marzo 2012): 1–40. http://dx.doi.org/10.1142/s1005386712000028.
Testo completoAbstract (sommario):
The weights for a finite group G with respect to a prime number p were introduced by Jon Alperin, in order to formulate his celebrated conjecture. In 1992, Everett Dade formulated a refinement of Alperin's conjecture involving ordinary irreducible characters — with their defect — and, in 2000, Geoffrey Robinson proved that the new conjecture holds for p-solvable groups. But this refinement is formulated in terms of a vanishing alternating sum, without giving any possible refinement for the weights. In this note we show that, in the case of the p-solvable finite groups, the method developed in a previous paper can be suitably refined to provide, up to the choice of a polarization ω, a natural bijection — namely compatible with the action of the group of outer automorphisms of G — between the sets of absolutely irreducible characters of G and of G-conjugacy classes of suitable inductive weights, preserving blocks and defects.
17
Singh, Pankaj, e Nidhi Gaba. "Comparative Analysis of Different Control Schemes in Delta Domain Using Time Moments". International Journal of Advance Research and Innovation 3, n. 1 (2015): 84–89. http://dx.doi.org/10.51976/ijari.311515.
Testo completoAbstract (sommario):
Traditionally, discrete-data sampled data systems are represented using shift-operator parameterization. Such parameterization was not suitable at high sampling rates. An alternative parameterization using the so-called delta operator maintains the close correspondence to its continues-time counterpart at fast sampling rates. This paper deals with the application of time moment estimation and adaptive control schemes. In the fast sampling limit, the delta operator model tends to the analog dynamic system model. This intrinsic property of the delta operator model unifies continues and discrete time control engineering. Comparative analysis results are showed the usefulness of the scheme.
18
Romakkaniemi, S., H. Kokkola e A. Laaksonen. "Parameterization of the nitric acid effect on CCN activation". Atmospheric Chemistry and Physics 5, n. 4 (16 marzo 2005): 879–85. http://dx.doi.org/10.5194/acp-5-879-2005.
Testo completoAbstract (sommario):
Abstract. In this paper we present a parameterization of the nitric acid effect on cloud droplet formation. The new parameterization is intended to be used in large scale models in order to obtain regional and global estimates of the effect of nitric acid on cloud drop concentrations and the radiative balance. The parameterization is based on numerical air parcel model simulations and can be applied for unimodal and bimodal lognormal aerosol particle size distributions in a large variety of different conditions. In addition to the aerosol particle distribution and gas-phase HNO3 concentration, the parameterization requires temperature, total pressure, updraft velocity, and the number concentration of cloud droplets formed at zero nitric acid concentration, as input parameters. The parameterization is also suitable for describing the effect of hydrochloric acid on the cloud drop concentrations, and in practice, the HNO3 and HCl concentrations can be summed up to yield the total effect. The comparison between the parameterization and the results from numerical air parcel model simulations show good consistency.
19
Burgess, M., M. E. Carrington e G. Kunstatter. "Covariant approach to equilibration in effective field theories". Canadian Journal of Physics 80, n. 2 (1 febbraio 2002): 97–107. http://dx.doi.org/10.1139/p01-136.
Testo completoAbstract (sommario):
The equilibration of two coupled reservoirs is studied using a Green function approach that is suitable for future development with the closed time path method. The problem is solved in two parameterizations, to demonstrate the nontrivial issues of parameterization in both the intermediate steps and the interpretation of physical quantities. We use a covariant approach to find self-consistent solutions for the statistical distributions as functions of time. We show that by formally introducing covariant connections, one can rescale a slowly varying nonequilibrium theory so that it appears to be an equilibrium one, for the purposes of calculation. We emphasize the importance of properly tracking variable redefinitions to correctly interpret physical quantities. PACS Nos.: 11.10-z, 03.70+k, 05.70ln
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Jakóbczak, Dariusz. "Curve Parameterization and Curvature via Method of Hurwitz-Radon Matrices". Image Processing & Communications 16, n. 1-2 (1 gennaio 2011): 49–56. http://dx.doi.org/10.2478/v10248-012-0005-3.
Testo completoAbstract (sommario):
Curve Parameterization and Curvature via Method of Hurwitz-Radon MatricesParametric representation of the curve is more appropriate in computer vision applications then explicit formy=f(x)or implicit representationf(x, y) = 0. Proposed method of Hurwitz-Radon Matrices (MHR) can be used in parameterization and interpolation of curves in the plane. Suitable parameterization leads to curvature calculations. Points with local maximum curvature are treated as feature points in object recognition and image analysis. This paper contains the way of curve parameterization and computing the curvature in the range of two successive interpolation nodes via MHR method. Proposed method is based on a family of Hurwitz-Radon (HR) matrices. The matrices are skew-symmetric and possess columns composed of orthogonal vectors. The operator of Hurwitz-Radon (OHR), built from these matrices, is described. It is shown how to create the orthogonal OHR and how to use it in a process of curve parameterization and curvature calculation.
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Wang, Shiyi, Jingwen Ren, Xianzhong Fang, Hongwei Lin, Gang Xu, Hujun Bao e Jin Huang. "IGA-suitable planar parameterization with patch structure simplification of closed-form polysquare". Computer Methods in Applied Mechanics and Engineering 392 (marzo 2022): 114678. http://dx.doi.org/10.1016/j.cma.2022.114678.
Testo completo
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Wang, Xu, e Weiyin Ma. "Smooth Analysis-Suitable Parameterization Based on a Weighted and Modified Liao Functional". Computer-Aided Design 140 (novembre 2021): 103079. http://dx.doi.org/10.1016/j.cad.2021.103079.
Testo completo
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Xu, Gang, Bernard Mourrain, Régis Duvigneau e André Galligo. "Analysis-suitable volume parameterization of multi-block computational domain in isogeometric applications". Computer-Aided Design 45, n. 2 (febbraio 2013): 395–404. http://dx.doi.org/10.1016/j.cad.2012.10.022.
Testo completo
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Romakkaniemi, S., H. Kokkola e A. Laaksonen. "Parameterization of the nitric acid effect on CCN activation". Atmospheric Chemistry and Physics Discussions 4, n. 6 (2 dicembre 2004): 7859–79. http://dx.doi.org/10.5194/acpd-4-7859-2004.
Testo completoAbstract (sommario):
Abstract. In this paper we present a parameterization of the nitric acid effect on cloud droplet formation. The new parameterization is intended to be used in large scale models in order to obtain regional and global estimates of the effect of nitric acid on cloud drop concentrations and the radiative balance. The parameterization is based on numerical air parcel model simulations and can be applied for unimodal and bimodal lognormal aerosol particle size distributions in a large variety of different conditions. In addition to the aerosol particle distribution and gas-phase HNO3 concentration, the parameterization requires temperature, total pressure, updraft velocity, and the number concentration of cloud droplets formed at zero nitric acid concentration, as input parameters. The parametrization is also suitable for describing the effect of hydrochloric acid on the cloud drop concentrations, and in practice, the HNO3 and HCl concentrations can be summed up to yield the total effect. The comparison between the parameterization and the results from numerical air parcel model simulations show good consistency.
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Ostrowski, Janusz, Leszek Łabędzki e Ewa Kanecka-Geszke. "Parameterization and cartographic presentation of water deficits of cultivated plants". International Agrophysics 29, n. 3 (1 luglio 2015): 341–51. http://dx.doi.org/10.1515/intag-2015-0041.
Testo completoAbstract (sommario):
Abstract The aim of the paper was to characterise and present cartographically water deficits of crop plants grown on different soils in Poland. The calculation of water deficits was carried out for 40 meteorological stations of the Institute of Meteorology and Water Management and the Institute of Technology and Life Sciences using meteorological data from the growing seasons 1970-2004 for most crops grown in Poland. Estimations were made for soils suitable for growing the selected crop plants. Water deficits were determined for a probability of exceedance of 20 and 50%. They served to create a relative database. Maps of water deficit were generated for each crop and for two probabilities. The estimated share of soil area suitable for growing the particular crops was calculated for water deficits greater than 40 mm. Water deficits of a given crop on soils suitable for growing at probabilities of their occurrence once in 5 years are also presented in the paper.
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Jenkins, Adrian, Keith W. Nicholls e Hugh F. J. Corr. "Observation and Parameterization of Ablation at the Base of Ronne Ice Shelf, Antarctica". Journal of Physical Oceanography 40, n. 10 (1 ottobre 2010): 2298–312. http://dx.doi.org/10.1175/2010jpo4317.1.
Testo completoAbstract (sommario):
Abstract Parameterizations of turbulent transfer through the oceanic boundary layer beneath an ice shelf are tested using direct measurements of basal ablation. Observations were made in the southwestern part of Ronne Ice Shelf, about 500 km from open water. The mean basal ablation rate was measured over a month-long and a year-long period using phase-sensitive radar to record the thinning of the ice shelf. Ocean temperatures were observed within about 25 m of the ice shelf base over the period of the radar observations, while the tidally dominated ocean currents were estimated from tidal analysis of collocated current observations from an earlier period. Ablation rates derived using these ocean data and a number of bulk parameterizations of turbulent transfer within the boundary layer are compared with the direct measurements. The ablation rates derived using a parameterization that explicitly includes the impact of ocean currents on the turbulent transfer of heat and salt match the observations to within 40%; with suitable tuning of the drag coefficient, the mismatch can be reduced below the level of the observational errors. Equally good agreement can be obtained with two slightly simpler, current-dependent parameterizations that use constant turbulent transfer coefficients, and the optimal values for the coefficients at this particular location on Ronne Ice Shelf are given.
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Albert, M. F. M. A., M. D. Anguelova, A. M. M. Manders, M. Schaap e G. de Leeuw. "Parameterization of oceanic whitecap fraction based on satellite observations". Atmospheric Chemistry and Physics Discussions 15, n. 15 (6 agosto 2015): 21219–69. http://dx.doi.org/10.5194/acpd-15-21219-2015.
Testo completoAbstract (sommario):
Abstract. In this study the utility of satellite-based whitecap fraction (W) values for the prediction of sea spray aerosol (SSA) emission rates is explored. More specifically, the study is aimed at improving the accuracy of the sea spray source function (SSSF) derived by using the whitecap method through the reduction of the uncertainties in the parameterization of W by better accounting for its natural variability. The starting point is a dataset containing W data, together with matching environmental and statistical data, for 2006. Whitecap fraction W was estimated from observations of the ocean surface brightness temperature TB by satellite-borne radiometers at two frequencies (10 and 37 GHz). A global scale assessment of the data set to evaluate the wind speed dependence of W revealed a quadratic correlation between W and U10, as well as a relatively larger spread in the 37 GHz data set. The latter could be attributed to secondary factors affecting W in addition to U10. To better visualize these secondary factors, a regional scale assessment over different seasons was performed. This assessment indicates that the influence of secondary factors on W is for the largest part imbedded in the exponent of the wind speed dependence. Hence no further improvement can be expected by looking at effects of other factors on the variation in W explicitly. From the regional analysis, a new globally applicable quadratic W(U10) parameterization was derived. An intrinsic correlation between W and U10 that could have been introduced while estimating W from TB was determined, evaluated and presumed to lie within the error margins of the newly derived W(U10) parameterization. The satellite-based parameterization was compared to parameterizations from other studies and was applied in a SSSF to estimate the global SSA emission rate. The thus obtained SSA production for 2006 of 4.1 × 1012 kg is within previously reported estimates. While recent studies that account for parameters other than U10 explicitly could be suitable to improve predictions of SSA emissions, we promote our new W(U10) parameterization as an alternative approach that implicitly accounts for these different parameters and helps to improve SSA emission estimates equally well.
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Manukyan, Edgar, e Hansruedi Maurer. "Elastic vertically transversely isotropic full-waveform inversion using cross-gradient constraints — An application toward high-level radioactive waste repository monitoring". GEOPHYSICS 85, n. 4 (8 maggio 2020): R313—R323. http://dx.doi.org/10.1190/geo2019-0061.1.
Testo completoAbstract (sommario):
Anisotropic seismic full-waveform inversion (FWI) is a challenging task. In the case of 2D vertically transversely isotropic (VTI) media, there are five independent model parameters. This relatively large number of different parameter types imposes significant trade-off issues and makes the inversion parameterization a challenging task. The problem is less severe in a crosshole configuration, in which a wider angular coverage of the region of interest is available. There exist many suggestions for suitable inversion parameterizations. We have determined that, for a crosshole configuration, a relatively simple velocity-based parameterization provides a good FWI reconstruction of the subsurface. Furthermore, considerable improvements of the tomographic images can be achieved by supplying structural similarity constraints using cross gradients to the inversion problem. With two synthetic data sets, we determine that a structurally constrained VTI FWI workflow produces sharper subsurface images without adversely affecting the parameter trade-off issue. With a second synthetic experiment, we find that structurally constrained VTI FWI is robust to major differences in anomaly locations for different parameter types. We successfully applied the methodology to a crosshole data set acquired to image a downscaled version of a high-level radioactive waste repository. The resulting tomograms allowed a narrow highly fractured zone to be imaged.
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Phillips, Thomas J., Gerald L. Potter, David L. Williamson, Richard T. Cederwall, James S. Boyle, Michael Fiorino, Justin J. Hnilo, Jerry G. Olson, Shaocheng Xie e J. John Yio. "Evaluating Parameterizations in General Circulation Models: Climate Simulation Meets Weather Prediction". Bulletin of the American Meteorological Society 85, n. 12 (1 dicembre 2004): 1903–16. http://dx.doi.org/10.1175/bams-85-12-1903.
Testo completoAbstract (sommario):
To significantly improve the simulation of climate by general circulation models (GCMs), systematic errors in representations of relevant processes must first be identified, and then reduced. This endeavor demands that the GCM parameterizations of unresolved processes, in particular, should be tested over a wide range of time scales, not just in climate simulations. Thus, a numerical weather prediction (NWP) methodology for evaluating model parameterizations and gaining insights into their behavior may prove useful, provided that suitable adaptations are made for implementation in climate GCMs. This method entails the generation of short-range weather forecasts by a realistically initialized climate GCM, and the application of six hourly NWP analyses and observations of parameterized variables to evaluate these forecasts. The behavior of the parameterizations in such a weather-forecasting framework can provide insights on how these schemes might be improved, and modified parameterizations then can be tested in the same framework. To further this method for evaluating and analyzing parameterizations in climate GCMs, the U.S. Department of Energy is funding a joint venture of its Climate Change Prediction Program (CCPP) and Atmospheric Radiation Measurement (ARM) Program: the CCPP-ARM Parameterization Testbed (CAPT). This article elaborates the scientific rationale for CAPT, discusses technical aspects of its methodology, and presents examples of its implementation in a representative climate GCM.
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Keita, Setigui Aboubacar, Eric Girard, Jean-Christophe Raut, Maud Leriche, Jean-Pierre Blanchet, Jacques Pelon, Tatsuo Onishi e Ana Cirisan. "A new parameterization of ice heterogeneous nucleation coupled to aerosol chemistry in WRF-Chem model version 3.5.1: evaluation through ISDAC measurements". Geoscientific Model Development 13, n. 11 (25 novembre 2020): 5737–55. http://dx.doi.org/10.5194/gmd-13-5737-2020.
Testo completoAbstract (sommario):
Abstract. In the Arctic, during polar night and early spring, ice clouds are separated into two leading types of ice clouds (TICs): (1) TIC1 clouds characterized by a large concentration of very small crystals and TIC2 clouds characterized by a low concentration of large ice crystals. Using a suitable parameterization of heterogeneous ice nucleation is essential for properly representing ice clouds in meteorological and climate models and subsequently understanding their interactions with aerosols and radiation. Here, we describe a new parameterization for ice crystal formation by heterogeneous nucleation in water-subsaturated conditions coupled to aerosol chemistry in the Weather Research and Forecasting model coupled with chemistry (WRF-Chem). The parameterization is implemented in the Milbrandt and Yau (2005a, b) two-moment cloud microphysics scheme, and we assess how the WRF-Chem model responds to the run-time interaction between chemistry and the new parameterization. Well-documented reference cases provided us with in situ data from the spring 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) over Alaska. Our analysis reveals that the new parameterization clearly improves the representation of the ice water content (IWC) in polluted or unpolluted air masses and shows the poor performance of the reference parameterization in representing ice clouds with low IWC. The new parameterization is able to represent TIC1 and TIC2 microphysical characteristics at the top of the clouds, where heterogenous ice nucleation is most likely occurring, even with the known bias of simulated aerosols by WRF-Chem over the Arctic.
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Jourdain, Nicolas C., Xylar Asay-Davis, Tore Hattermann, Fiammetta Straneo, Hélène Seroussi, Christopher M. Little e Sophie Nowicki. "A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections". Cryosphere 14, n. 9 (17 settembre 2020): 3111–34. http://dx.doi.org/10.5194/tc-14-3111-2020.
Testo completoAbstract (sommario):
Abstract. Climate model projections have previously been used to compute ice shelf basal melt rates in ice sheet models, but the strategies employed – e.g., ocean input, parameterization, calibration technique, and corrections – have varied widely and are often ad hoc. Here, a methodology is proposed for the calculation of circum-Antarctic basal melt rates for floating ice, based on climate models, that is suitable for ISMIP6, the Ice Sheet Model Intercomparison Project for CMIP6 (6th Coupled Model Intercomparison Project). The past and future evolution of ocean temperature and salinity is derived from a climate model by estimating anomalies with respect to the modern day, which are added to a present-day climatology constructed from existing observational datasets. Temperature and salinity are extrapolated to any position potentially occupied by a simulated ice shelf. A simple formulation is proposed for a basal melt parameterization in ISMIP6, constrained by the observed temperature climatology, with a quadratic dependency on either the nonlocal or local thermal forcing. Two calibration methods are proposed: (1) based on the mean Antarctic melt rate (MeanAnt) and (2) based on melt rates near Pine Island's deep grounding line (PIGL). Future Antarctic mean melt rates are an order of magnitude greater in PIGL than in MeanAnt. The PIGL calibration and the local parameterization result in more realistic melt rates near grounding lines. PIGL is also more consistent with observations of interannual melt rate variability underneath Pine Island and Dotson ice shelves. This work stresses the need for more physics and less calibration in the parameterizations and for more observations of hydrographic properties and melt rates at interannual and decadal timescales.
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Komori, Yoshio. "Suitable Algorithm Associated with a Parameterization for the Three-Parameter Log-Normal Distribution". Communications in Statistics - Simulation and Computation 44, n. 1 (28 luglio 2014): 239–46. http://dx.doi.org/10.1080/03610918.2013.773343.
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Franchito, S. H., V. Brahmananda Rao e R. Ramos da Silva. "A parameterization of radiative fluxes suitable for use in a statistical-dynamical model". Meteorology and Atmospheric Physics 69, n. 1-2 (marzo 1998): 23–38. http://dx.doi.org/10.1007/bf01025181.
Testo completo
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Gao, Jiajia, Yunyun Gao, Tao Ma, Ningtao Hou, Zhen Wei, Wei Guo, Rikun Huo e Zhijie Huo. "Bijective plannar parameterization based on a hyperelasticity analogy". Journal of Physics: Conference Series 2338, n. 1 (1 settembre 2022): 012004. http://dx.doi.org/10.1088/1742-6596/2338/1/012004.
Testo completoAbstract (sommario):
Abstract Isogeometric analysis (IGA) is a promising alternative for finite element analysis (FEA) with simplified design-through-analysis workflow. However, existing models in CAD software cannot be used directly for analysis. Parameterization of the input geometry is necessary to transform it into an analysis-suitable model. But it is non-trivial to produce smooth non-folding results. In this paper, we present a novel parameterization scheme based on the hyperelasticity analogy in solid mechanics. Compared with other state-of-the-art techniques, numerical examples prove that the proposed method guarantees bijective results with excellent smoothness.
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Kepert, Jeffrey D. "Choosing a Boundary Layer Parameterization for Tropical Cyclone Modeling". Monthly Weather Review 140, n. 5 (1 maggio 2012): 1427–45. http://dx.doi.org/10.1175/mwr-d-11-00217.1.
Testo completoAbstract (sommario):
Abstract The boundary layer in a tropical cyclone is in some respects unlike that elsewhere in the atmosphere. It is therefore necessary to evaluate boundary layer parameterizations for their suitability for use in tropical cyclone simulation. Previous work has shown substantial sensitivity to the choice of scheme and identified specific shortcomings in some schemes, but without recommending which schemes are most suitable. Here, several schemes, representative of those available in popular modeling systems, are reviewed and applied in a simplified modeling framework. Based on a comparison with observations and on theoretical grounds, one popular class of schemes is shown to be badly flawed in that it incorrectly predicts the near-surface wind profile, and therefore should not be used. Another is shown to be sensitive to diagnosis of the boundary layer depth, a difficult problem in the core of the tropical cyclone, and caution is advised. The Louis boundary layer scheme and a higher-order closure scheme are, so far as can be discerned, without major problems, and are recommended. The recommendations and discussion herein should help users make a more informed choice of boundary layer parameterization, and to better understand the results that they obtain.
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Yang, Junli, Jianglin Hu, Qiying Chen e Weijun Quan. "Parameterization of downward long-wave radiation based on long-term baseline surface radiation measurements in China". Atmospheric Chemistry and Physics 23, n. 7 (14 aprile 2023): 4419–30. http://dx.doi.org/10.5194/acp-23-4419-2023.
Testo completoAbstract (sommario):
Abstract. Downward long-wave radiation (DLR) affects energy exchange between the land surface and the atmosphere and plays an important role in weather forecasting, agricultural activities, and the development of climate models. Because DLR is seldom observed at conventional radiation stations, numerous empirical parameterizations have been presented to estimate DLR from screen-level meteorological variables. The reliability and representativeness of parameterization depend on the coefficients regressed from the simultaneous observations of DLR and meteorological variables. Only a few previous studies have attempted to build parameterizations over regions in China such as the Tibetan Plateau and East China. In this study, a long-term (2011–2022) hourly dataset of DLR and meteorological elements, obtained from seven stations of the China Baseline Surface Radiation Network, was used to recalculate the coefficients of the Brunt and Weng models and to develop a new model. Results showed that the mean bias error (MBE) and relative MBE (rMBE) between the measured clear-sky DLR and that estimated using the Brunt, Weng, and new models were −4.3, −5.1, and 3.7 W m−2 and −1.5 %, −1.8 %, and 1.3 %, respectively. The root mean square errors (RMSEs) were in the range of 13.8–14.3 W m−2, and the relative RMSEs (rRMSEs) were approximately 5.0 %. The MBEs (rMBEs) of the Brunt, Weng, and new models under all-sky conditions were −2.8 W m−2 (−1.0 %), −6.1 W m−2 (−2.1 %), and −1.5 W m−2 (−0.5 %), respectively. The RMSE (rRMSE) of the parameterization models in retrieving all-sky DLR was ∼ 17.5 W m−2 (∼ 6.1 %). Therefore, the models are considered suitable for retrieval of DLR over China.
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Masrom, Suraya, Abdullah Sani Abd Rahman, Nasiroh Omar e Suriani Rapa’ee. "PSO-GAScript: A Domain-specific Scripting Language for Meta-heuristics Algorithm". International Journal of Emerging Technology and Advanced Engineering 12, n. 7 (4 luglio 2022): 86–93. http://dx.doi.org/10.46338/ijetae0722_09.
Testo completoAbstract (sommario):
PSO-GAScript is a domain-specific scripting language designed to support easy and rapid implementation of meta-heuristics algorithms focused on Particle Swarm Optimization (PSO) and Genetic Algorithm (GA). The programming language has been developed to allow the hybridization of the two meta-heuristics algorithms. Hybridizations between PSO and GA are proven to be a comprehensive tool for solving different kinds of optimization problems. Moreover, the two algorithms have achieved a remarkable improvement from the adaptation of dynamic parameterization. Nevertheless, implementing the suitable hybrid algorithms is a considerably difficult, which in most cases is time consuming. To the best of our knowledge, the existing tools are not adequately designed to enable users to easily develop the meta-heuristics hybridization of PSO-GA with dynamic parameterizations. This paper presents the fundamental research methodology of domain-specific scripting language from the language design, constructs and evaluations focused on the case of PSO-GA hybridization and dynamic parameterizations. The PSO-GAScript are shown to easily use with minimal number of codes lines and concisely describe the meta-heuristics algorithms in a directly publishable form.
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Essery, Richard. "Parameterization of fluxes over heterogeneous snow cover for GCMs". Annals of Glaciology 25 (1997): 38–41. http://dx.doi.org/10.3189/s0260305500013768.
Testo completoAbstract (sommario):
Fluxes of heat and moisture over heterogeneous snow cover are studied using a boundary-layer model. The performance of a “tile” model, suitable for calculating gridbox-average surface fluxes in a GCM, is assessed in comparison with the boundary-layer model. The impact of using a tile representation for heterogeneous snow cover in a single-column version of the Hadley Centre GCM is discussed.
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Essery, Richard. "Parameterization of fluxes over heterogeneous snow cover for GCMs". Annals of Glaciology 25 (1997): 38–41. http://dx.doi.org/10.1017/s0260305500013768.
Testo completoAbstract (sommario):
Fluxes of heat and moisture over heterogeneous snow cover are studied using a boundary-layer model. The performance of a “tile” model, suitable for calculating gridbox-average surface fluxes in a GCM, is assessed in comparison with the boundary-layer model. The impact of using a tile representation for heterogeneous snow cover in a single-column version of the Hadley Centre GCM is discussed.
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Xu, Gang, Bernard Mourrain, Régis Duvigneau e André Galligo. "Constructing analysis-suitable parameterization of computational domain from CAD boundary by variational harmonic method". Journal of Computational Physics 252 (novembre 2013): 275–89. http://dx.doi.org/10.1016/j.jcp.2013.06.029.
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Romero, R., E. L. Iglesias e L. Borrajo. "A Linear-RBF Multikernel SVM to Classify Big Text Corpora". BioMed Research International 2015 (2015): 1–14. http://dx.doi.org/10.1155/2015/878291.
Testo completoAbstract (sommario):
Support vector machine (SVM) is a powerful technique for classification. However, SVM is not suitable for classification of large datasets or text corpora, because the training complexity of SVMs is highly dependent on the input size. Recent developments in the literature on the SVM and other kernel methods emphasize the need to consider multiple kernels or parameterizations of kernels because they provide greater flexibility. This paper shows a multikernel SVM to manage highly dimensional data, providing an automatic parameterization with low computational cost and improving results against SVMs parameterized under a brute-force search. The model consists in spreading the dataset into cohesive term slices (clusters) to construct a defined structure (multikernel). The new approach is tested on different text corpora. Experimental results show that the new classifier has good accuracy compared with the classic SVM, while the training is significantly faster than several other SVM classifiers.
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Gálvez, Akemi, e Andrés Iglesias. "Firefly Algorithm for Polynomial Bézier Surface Parameterization". Journal of Applied Mathematics 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/237984.
Testo completoAbstract (sommario):
A classical issue in many applied fields is to obtain an approximating surface to a given set of data points. This problem arises in Computer-Aided Design and Manufacturing (CAD/CAM), virtual reality, medical imaging, computer graphics, computer animation, and many others. Very often, the preferred approximating surface is polynomial, usually described in parametric form. This leads to the problem of determining suitable parametric values for the data points, the so-called surface parameterization. In real-world settings, data points are generally irregularly sampled and subjected to measurement noise, leading to a very difficult nonlinear continuous optimization problem, unsolvable with standard optimization techniques. This paper solves the parameterization problem for polynomial Bézier surfaces by applying the firefly algorithm, a powerful nature-inspired metaheuristic algorithm introduced recently to address difficult optimization problems. The method has been successfully applied to some illustrative examples of open and closed surfaces, including shapes with singularities. Our results show that the method performs very well, being able to yield the best approximating surface with a high degree of accuracy.
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Chen, Yiyin, David Schlipf e Po Wen Cheng. "Parameterization of wind evolution using lidar". Wind Energy Science 6, n. 1 (12 gennaio 2021): 61–91. http://dx.doi.org/10.5194/wes-6-61-2021.
Testo completoAbstract (sommario):
Abstract. Wind evolution, i.e., the evolution of turbulence structures over time, has become an increasingly interesting topic in recent years, mainly due to the development of lidar-assisted wind turbine control, which requires accurate prediction of wind evolution to avoid unnecessary or even harmful control actions. Moreover, 4D stochastic wind field simulations can be made possible by integrating wind evolution into standard 3D simulations to provide a more realistic simulation environment for this control concept. Motivated by these factors, this research aims to investigate the potential of Gaussian process regression in the parameterization of wind evolution. Wind evolution is commonly quantified using magnitude-squared coherence of wind speed and is estimated with lidar data measured by two nacelle-mounted lidars in this research. A two-parameter wind evolution model modified from a previous study is used to model the estimated coherence. A statistical analysis is done for the wind evolution model parameters determined from the estimated coherence to provide some insights into the characteristics of wind evolution. Gaussian process regression models are trained with the wind evolution model parameters and different combinations of wind-field-related variables acquired from the lidars and a meteorological mast. The automatic relevance determination squared exponential kernel function is applied to select suitable variables for the models. The performance of the Gaussian process regression models is analyzed with respect to different variable combinations, and the selected variables are discussed to shed light on the correlation between wind evolution and these variables.
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Gholami, Yaser, Romain Brossier, Stéphane Operto, Vincent Prieux, Alessandra Ribodetti e Jean Virieux. "Which parameterization is suitable for acoustic vertical transverse isotropic full waveform inversion? Part 2: Synthetic and real data case studies from Valhall". GEOPHYSICS 78, n. 2 (1 marzo 2013): R107—R124. http://dx.doi.org/10.1190/geo2012-0203.1.
Testo completoAbstract (sommario):
It is necessary to account for anisotropy in full waveform inversion (FWI) of wide-azimuth and wide-aperture seismic data in most geologic environments, for correct depth positioning of reflectors, and for reliable estimations of wave speeds as a function of the direction of propagation. In this framework, choosing a suitable anisotropic subsurface parameterization is a central issue in monoparameter and multiparameter FWI. This is because this parameterization defines the influence of each physical parameter class on the data as a function of the scattering angle, and hence the resolution of the parameter reconstruction, and on the potential trade-off between different parameter classes. We apply monoparameter and multiparameter frequency-domain acoustic vertical transverse isotropic FWI to synthetic and real wide-aperture data, representative of the Valhall oil field. We first show that reliable monoparameter FWI can be performed to build a high-resolution velocity model (for the vertical, the horizontal, or normal move-out velocity), provided that the background models of two Thomsen parameters describe the long wavelengths of the subsurface sufficiently accurately. Alternatively, we show the feasibility of the joint reconstruction of two wave speeds (e.g., the vertical and horizontal wave speeds) with limited trade-off effects, while Thomsen parameter [Formula: see text] is kept fixed during the inversion. The influence of the wave speeds on the data for a limited range of scattering angles when combined each other can, however, significantly hamper the resolution with which the two wave speeds are imaged. These conclusions inferred from the application to the real data are fully consistent with those inferred from the theoretical parameterization analysis of acoustic vertical transverse isotropic FWI performed in the companion report.
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Guo, Xiaohao, Huijuan Lin, Jinyao Zhu e Fenfen Wei. "Parameterization of Entrainment Rate for Cumulus Clouds with WRF Simulation". Atmosphere 14, n. 8 (14 agosto 2023): 1285. http://dx.doi.org/10.3390/atmos14081285.
Testo completoAbstract (sommario):
By using Weather Research and Forecasting Model (WRF) to simulate a southwest vortex precipitation process, this work studies the correlations between entrainment rate (λ) and dynamical parameters in the cloud and further fit λ. We relate the probability density distribution (PDF) to the parameterization of λ and find that the greater the probability, the larger the slope of the logarithmic liner function. The slope of the log-linear fitting function in fitting decreases for developing and enhancing cumulus clouds, which is related to the increase in updraft motion and the decrease in λ. Then, we group clouds according to cloud top heights and calculate average λ and dynamic parameters, and the results indicate that when only one dynamic parameter is used, vertical wind velocity (w) is more suitable than buoyancy (B) to be used to fit λ. The fitting functions combing one single parameter and more parameters by principal components regression are compared with two traditional schemes, and we found that λ obtained by our fitting schemes are between the two traditional schemes. Because the principal component regression method takes into account the interaction between more dynamic factors and entrainment, the fitting function, including w and B, is suitable to be applied to fit λ in the parameterization scheme for cumulus clouds.
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Ma, Li, Xiaoyu Li, Jing Liao, Xuan Wang, Qi Zhang, Jue Wang e Pedro V. Sander. "Neural Parameterization for Dynamic Human Head Editing". ACM Transactions on Graphics 41, n. 6 (30 novembre 2022): 1–15. http://dx.doi.org/10.1145/3550454.3555494.
Testo completoAbstract (sommario):
Implicit radiance functions emerged as a powerful scene representation for reconstructing and rendering photo-realistic views of a 3D scene. These representations, however, suffer from poor editability. On the other hand, explicit representations such as polygonal meshes allow easy editing but are not as suitable for reconstructing accurate details in dynamic human heads, such as fine facial features, hair, teeth, and eyes. In this work, we present Neural Parameterization (NeP), a hybrid representation that provides the advantages of both implicit and explicit methods. NeP is capable of photo-realistic rendering while allowing fine-grained editing of the scene geometry and appearance. We first disentangle the geometry and appearance by parameterizing the 3D geometry into 2D texture space. We enable geometric editability by introducing an explicit linear deformation blending layer. The deformation is controlled by a set of sparse key points, which can be explicitly and intuitively displaced to edit the geometry. For appearance, we develop a hybrid 2D texture consisting of an explicit texture map for easy editing and implicit view and time-dependent residuals to model temporal and view variations. We compare our method to several reconstruction and editing baselines. The results show that the NeP achieves almost the same level of rendering accuracy while maintaining high editability.
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Denkena, Berend, Benjamin Bergmann e H. Tobias Stiehl. "Anwenderfreundliche Prozessüberwachungssysteme/User-friendly Process Monitoring Systems". wt Werkstattstechnik online 110, n. 06 (2020): 435–39. http://dx.doi.org/10.37544/1436-4980-2020-06-75.
Testo completoAbstract (sommario):
Prozessüberwachungssysteme reduzieren Ausschuss und Stillstände. Allerdings schränken die prozessspezifische Parametrierung und das erforderliche Expertenwissen den wirtschaftlichen Einsatz der Systeme ein. Dieser Beitrag stellt nachvollziehbare und automatische Ansätze zur Auswahl geeigneter Signale, ihrer Verarbeitung und Bildung von Überwachungsgrenzen vor. Die Ergebnisse zeigen, dass die damit erreichte Überwachungsleistung vergleichbar mit einer Konfiguration durch geschultes Personal ist. Process monitoring systems reduce scrap, rework and downtime. However, process-specific parameterization and the required expert knowledge limit the economic use of the systems. This article presents approaches to the autonomous and comprehensible parameterization of systems covering the selection of suitable signals, their processing and the formation of monitoring limits. The results show that the achieved monitoring performance is comparable to a configuration by experts.
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Haghighatnasab, Mahnoosh, Mohammad Mirzaei, Ali R. Mohebalhojeh, Christoph Zülicke e Riwal Plougonven. "Application of the Compressible, Nonhydrostatic, Balanced Omega Equation in Estimating Diabatic Forcing for Parameterization of Inertia–Gravity Waves: Case Study of Moist Baroclinic Waves Using WRF". Journal of the Atmospheric Sciences 77, n. 1 (6 dicembre 2019): 113–29. http://dx.doi.org/10.1175/jas-d-19-0039.1.
Testo completoAbstract (sommario):
Abstract The parameterization of inertia–gravity waves (IGWs) is of considerable importance in general circulation models. Among the challenging issues faced in studies concerned with parameterization of IGWs is the estimation of diabatic forcing in a way independent of the physics parameterization schemes, in particular, convection. The requirement is to estimate the diabatic heating associated with balanced motion. This can be done by comparing estimates of balanced vertical motion with and without diabatic effects. The omega equation provides the natural method of estimating balanced vertical motion without diabatic effects, and several methods for including diabatic effects are compared. To this end, the assumption of spatial-scale separation between IGWs and balanced flows is combined with a suitable form of the balanced omega equation. To test the methods constructed for estimating diabatic heating, an idealized numerical simulation of the moist baroclinic waves is performed using the Weather Research and Forecasting (WRF) Model in a channel on the f plane. In overall agreement with the diabatic heating of the WRF Model, in the omega-equation-based estimates, the maxima of heating appear in the warm sector of the baroclinic wave and in the exit region of the upper-level jet. The omega-equation-based method with spatial smoothing for estimating balanced vertical motion is thus presented as the proper way to evaluate diabatic forcing for parameterization of IGWs.
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BASU, BK. "A model of the downdraft from convective clouds". MAUSAM 37, n. 2 (11 aprile 2022): 265–68. http://dx.doi.org/10.54302/mausam.v37i2.2363.
Testo completoAbstract (sommario):
A model of the downdraft from convective clouds has been proposed assuming evaporative cooling as the mechanism responsible for the downward motion. Effects of friction and liquid water content have also been taken into account through suitable parameterization and velocity and temperature of the downdraft at any level have been computed as the mass-weighted mean of contributions from all upper levels.
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Asmus, Christina, Peter Hoffmann, Joni-Pekka Pietikäinen, Jürgen Böhner e Diana Rechid. "Modeling and evaluating the effects of irrigation on land–atmosphere interaction in southwestern Europe with the regional climate model REMO2020–iMOVE using a newly developed parameterization". Geoscientific Model Development 16, n. 24 (19 dicembre 2023): 7311–37. http://dx.doi.org/10.5194/gmd-16-7311-2023.
Testo completoAbstract (sommario):
Abstract. Irrigation is a crucial land use practice to adapt agriculture to unsuitable climate and soil conditions. Aiming to improve the growth of plants, irrigation modifies the soil condition, which causes atmospheric effects and feedbacks through land–atmosphere interaction. These effects can be quantified with numerical climate models, as has been done in various studies. It could be shown that irrigation effects, such as air temperature reduction and humidity increase, are well understood and should not be neglected on local and regional scales. However, there is a lack of studies including the role of vegetation in the altered land–atmosphere interaction. With the increasing resolution of numerical climate models, these detailed processes have a chance to be better resolved and studied. This study aims to analyze the effects of irrigation on land–atmosphere interaction, including the effects and feedbacks of vegetation. We developed a new parameterization for irrigation, implemented it into the REgional climate MOdel (REMO2020), and coupled it with the interactive MOsaic-based VEgetation module (iMOVE). Following this new approach of a separate irrigated fraction, the parameterization is suitable as a subgrid parameterization for high-resolution studies and resolves irrigation effects on land, atmosphere, and vegetation. Further, the parameterization is designed with three different water application schemes in order to analyze different parameterization approaches and their influence on the representation of irrigation effects. We apply the irrigation parameterization for southwestern Europe including the Mediterranean region at a 0.11∘ horizontal resolution for hot extremes. The simulation results are evaluated in terms of the consistency of physical processes. We found direct effects of irrigation, like a changed surface energy balance with increased latent and decreased sensible heat fluxes, and a surface temperature reduction of more than −4 K as a mean during the growing season. Further, vegetation reacts to irrigation with direct effects, such as reduced water stress, but also with feedbacks, such as a delayed growing season caused by the reduction of the near-surface temperature. Furthermore, the results were compared to observational data, showing a significant bias reduction in the 2 m mean temperature when using the irrigation parameterization.