Gaussian simulation. 5_Variogram_interpolation_comparison.


See geometric_conj*, gauss_conj and conjugate_gauss_beams. Apr 19, 2022 · Sequential Gaussian simulation is a computer-based technique for the generation of realizations z(x) from a multi-Gaussian random function Z(x) defined on a finite point set D, generally discretizing into N voxels a one-, two-, or three-dimensional area of interest. The asymmetry is still preserved in the simulations, with supratidal facies always on top of the intertidal facies and the intertidal facies on top of the Aug 5, 2017 · Sequential Gaussian simulation was considered and 100 realizations were generated. For geo-domains that do not exhibit greater complexity in their spatial distribution and contact relationships (typically of sequential contact relationships), the truncated Gaussian simulation, first proposed by Matheron et al. It models beam propagation using geometrical ray trace. The Gaussian Geostatistical Simulations tool accepts any simple kriging model. We build two gaussian fields, and then we apply the transformations described in Eq. The paper presents the formal methodology used for Watch quantum "particles" tunnel through barriers. GRFS more accurately reproduces distributions. Dec 1, 2003 · A non-Gaussian simulation algorithm proposed by Masters and Gurley (2003) in conjunction with the ILI data is applied to generate realizations of corrosion anomalies and then merge them into a Jan 5, 2017 · Last updated on: 05 January 2017. " FRED (A Framework for Mar 11, 2022 · Last updated on: 11 March 2022. Gaussian source center of focus. We can be over-confident in our statistics: "hey look: the mean is 12. 6_interpolation_with_anisotropy. Existing methods, however, heavily rely on pre-computed poses and Gaussian initialization by Structure from Motion (SfM) algorithms or expensive sensors. The errors are either scalar, such as vertical errors, or multivariate, such as , , and errors. This is possible by adjusting the center of focus from "beam options" tab in source properties as is discussed further in this page. 4). The so-called Gaussian Random Function simulation (GRFS) differs substantially from the Sequential Gaussian simulation (SGS) from GSLIB. Mar 1, 2023 · The combination of Sequential Gaussian Simulation (SGS) and co-kriging with the seismic acoustic impedance inversion (AI) cube have been used to construct the final model of the compressional velocity cube in the entire South Azadegan Field area for the first time. A plane wave, on the other hand, is the extreme case where the angular spectrum function is a delta function. Nov 3, 2023 · The simulation results showed how much the beam is distorted at the output of the imaging system depending on the size of the obstacle and its distance from the propagation axis. 010. Gaussian 16 is licensed for a wide variety of computer systems. If you are not redirected automatically, follow this link. . The sequential Gaussian simulation (SGS) is a stochastic approach for producing equiprobable realizations (maps) of spatial distribution of a variable on a grid by means of kriging methodology. This last method yields a lesser computational effort, but which is not effective for random fields. The simulation of Gaussian random fields is important in the study of spatially distributed data, both as a means of investigating the properties of proposed models of spatial variation and as a way of constructing goodness-of-fit tests by the Monte Carlo method. PEGASUS allows the composition of new scenes by merging the respective underlying Sep 1, 2018 · The detailed procedure of performing LSA, combined with sequential Gaussian simulation, is then described in subsection 2. Figures below demonstrate how the center of focus for a Gaussian beam can be adjusted to any desired coordinates in the simulation. 4 , where we see that the local Gaussian correlation for the Student t-copula becomes more constant as the level of dependence Additionally, Gaussian beams’ unique focusing properties make them indispensable in applications such as laser cutting, material processing, and medical procedures. 7. 1c), and the latter employs two or more Gaussian random fields (Fig. Broadband sources can be used to perform simulations in which wideband frequency data is required – for instance, from 200 to 1000 THz. Similarly, a rotating Laguerre–Gaussian beam with a superimposed “triangle” shadow image propagates through the second system. The specific realizations typically correspond to geospatial errors or perturbations over a horizontal plane or grid. [G16 Rev. Similarly, a white noise signal generated from a Uniform distribution is called Uniform White Noise. Jul 5, 2021 · The literature for copulas is mathematically formidable, but this article provides an intuitive introduction to copulas by describing the geometry of the transformations that are involved in the simulation process. Replication plays an important role in that context, however previous methods leveraging replicates have either ignored the computational savings that come from such design, or have short-cut full likelihood In mathematics, a Gaussian function, often simply referred to as a Gaussian, is a function of the base form = ⁡ and with parametric extension = ⁡ (()) for arbitrary real constants a, b and non-zero c. nx, xmn, xsiz: definition of the grid system (x axis). This study presents a simple and efficient method for the simulation of multivariate stationary non-Gaussian process. This paper aims to review state-of-the-art of Gaussian random field generation methods, their applications in scientific and engineering issues of interest, and open-source software/packages for Nov 1, 1995 · It is shown that it is possible to calculate the square root of many two- and three dimensional covariance operators analytically so that the method of moving averages can be applied directly to the problem of multidimensional simulation. Graph functions, plot points, visualize algebraic equations, add sliders, animate graphs, and more. Comparison between the histograms show that the histogram reproduction is slightly better for the SGS algorithm, although the population reproductions are the same for both SGS and DSS results, and the DSS algorithm reproduce the mean of input data closer to themean of well data compared to that of the S GS algorithm. 3. In the simulation of optical designs, Gaussian beam modeling serves as a valuable starting point. Quick Links. SGS is one of the most used simulation algorithms because Standard sources consist of a Gaussian pulse at a fixed optical carrier, while the broadband sources consist of a Gaussian pulse with an optical carrier which varies across the pulse envelope. [27] extended an iterative method for unconditional non-Gaussian simulation proposed by Yamazaki and Shinozuka [20] to conditional simulation. 1. Basis Sets; Density Functional (DFT) Methods; Solvents List SCRF OpticStudio sequential mode provides three tools to model Gaussian beam propagation: Ray-based approach. Paraxial Gaussian Beam. One Oct 1, 2023 · Secondly, sequential Gaussian co-simulation was applied to improve the simulation results of the tectono-geochemical anomaly by introducing the ore-controlling structure system. The simulation displays a region with non-zero electric field. The videos in this series are for intermediate to advanced users of Gaussian and GaussView. Oct 1, 2015 · In the current paper the HPM is used as the basis for the development of an efficient non-Gaussian multivariate simulation method. In this Demonstration the initial beam waist is 100m. Gaussian random fields (GRF) - following a method based on (block) circulant embedding of the covariance matrix and Fast Fourier Transform (FFT) other classical geostatistical tools (two-point statistics analysis (covariance, variogram, connectivity) / simulation (SGS, SIS) / estimation (kriging)) pluri-Gaussian simulation (PGS) Sep 1, 2016 · Although the truncated pluri-Gaussian simulation method can generate complex layouts which cope with most of the sedimentary deposits, the outcomes always present a symmetrical pattern. A normal score back transformation was considered to bring all realizations back to the original units. 1e and f) is used to turn these Gaussian values into geo-domains. In this paper, an alternative model is presented, in which the Gaussian field is decomposed into a random mean, constant over space but Feb 18, 2024 · 2. ipynb - A demonstration of kriging and SGS with different variogram models. The Gaussian function has a 1/e 2 diameter (2w as used in the text) about 1. . C. Aug 28, 2021 · The rationale behind the truncation Gaussian and plurigaussian simulation is that the former considers one Gaussian random field (Fig. The focal lengths of lens 1 and lens 2 are 50mm and 100mm respectively. Gaussian PDF only depends on its 1st-order and 2nd-order moments. It also simulates conditional random fields for univariate and multivariat, spatial and spatio-temporal Gaussian random fields Here, only the simulation of Gaussian random fields is described. The method utilizes the well-known concept of translating Gaussian to non-Gaussian process with the desired Marginal Probability Density Functions (MPDFs) and Correlation Function Matrix (CFM) or equivalently Power Spectral Density Matrix (PSDM). Each one focuses on a specific Gaussian capability and the GaussView features that support it. Several methods for Gaussian simulation smoothing exist, most of which are based on the Kalman filter. Gaussian geostatistical simulation (GGS), more specifically, is suitable for continuous data and assumes that the data, or a transformation of the data, has a normal (Gaussian) distribution. Jun 1, 2024 · In the pluri-Gaussian simulation framework, we model the geostatistical properties of the Gaussian fields as follows, the first Gaussian field denoted Y 1, anisotropic with a long correlation range of 70 grid cells, short correlation range of 10 grid cells and principal direction horizontal. Secondly, the simulated Gaussian values are used in a conditional sequential Gaussian simulation process in order to populate with values the remaining grid cells. This was a quick summary of the underlying theory for nonparaxial Gaussian beams. 5_Variogram_interpolation_comparison. 1 Gaussian Random Fields. In recent years, great progress has been made in experiments on GBS 5 – 11. In modelling/simulation, white noise can be generated using an appropriate random generator. Apr 7, 2021 · Last updated on: 07 April 2021. Sequential simulation is the most widespread principle in geostatistical applications due to its straightforward nature (Emery, 2004). f ( x, μ, σ) = 1 σ 2 π e − ( x − μ) 2 2 σ 2. The output file will contain the results, cycling fastest on x then y then z then simulation by simulation. The conventions for the distances are as follows: focal There is a very simple method to simulate from the Gaussian copula which is based on the definitions of the multivariate normal distribution and the Gauss copula. exe must be in working directory) Spatial Model Resampling Jul 5, 2017 · Gaussian 16 is the latest version of the Gaussian series of electronic structure programs, used by chemists, chemical engineers, biochemists, physicists and other scientists worldwide. Although there are several families of copulas, this article focuses on the Gaussian copula, which is the simplest to understand. There are four buttons to select different Gaussian surfaces, in this case they are appear one dimensional. Oct 10, 2019 · Pre-modulation Gaussian low pass filter. Its bell-shaped curve is dependent on μ, the mean, and σ, the standard deviation ( σ 2 being the variance). Dec 16, 2020 · Last updated on: 16 December 2020. In that context, we are Jun 26, 2018 · For example, for a slow Gaussian beam, the angular spectrum is narrow. Elishakoff et al. exe must be in working directory) cosgsim_uncond - sequential Gaussian simulation, 2D unconditional wrapper for sgsim from GSLIB (GSLIB's sgsim. ipynb - A demonstration of kriging and SGS with anisotropy. 1c and d) that are simulated entire area under consideration, and then a truncation rule (Fig. See RayTransferMatrix, GeometricRay and BeamParameter. Aug 5, 2019 · Gaussian (normal) distribution is a basic continuous probability distribution in statistics, it plays a substantial role in scientific and engineering problems that related to stochastic phenomena. Simulated results, or so-called realizations, render spatial patterns consistent with the input data Gaussian accelerated molecular dynamics (GaMD) is a robust computational method for simultaneous unconstrained enhanced sampling and free energy calculations of biomolecules. The underlying Gaussian PSDM is identified using an explicit bidirectional relationship Sequential Gaussian Simulation (SGSIM) as a stochastic method has been developed to avoid the smoothing effect produced in deterministic methods by generating various stochastic realizations. By constructing a boost potential that follows Gaussian distribution, accurate reweighting of the GaMD simulations is achieved using cumulant expansion to the second order. Basis Sets; Density Functional (DFT) Methods; Solvents List SCRF Jan 1, 2014 · The method is based on the use of sequential Gaussian simulation to reproduce the spatial heterogeneity observed in studied attributes. Specific options have been designed to overcome this symmetry limitation and introduce an orientation in the facies organization. Gómez-Hernández and Cassiraga, 1994, Remy et al. Feb 1, 2012 · Geostatistical modeling of the gas emission zone and its in-place gas content for Pittsburgh-seam mines using sequential Gaussian simulation Int J Coal Geol . The importance of this method relates to the spatial distribution and determination of the fixed domains. This study proposes an Normal Distribution Simulator Get hands-on experience and develop an intuition for statistics. ) is available and includes the number of the facies types and the possible contacts (transition) the facies types. Sep 1, 2017 · The coupling of the truncated pluri-Gaussian simulation method with an ensemble based history matching method was first introduced by Liu and Oliver (2005), where the facies boundaries were automatically adjusted when the Gaussian random fields were updated with new measurements. The functions are intended to address the challenges of working with datasets with large crossover errors, non-linear trends, variability in measurement Nov 1, 2019 · Among many stochastic simulation algorithms available, sequential Gaussian simulation (SGS) is probably widely used due to improving running speed and straightforward to implement simulation, and provide a practical tool for mapping spatial distribution of PTEs in soils. Gaussian 16 provides a wide-ranging suite of the most advanced modeling capabilities available. Gaussian Minimum Shift Keying (GMSK) is a modified MSK modulation technique, where the spectrum of MSK is manipulated by passing the rectangular shaped information pulses through a Gaussian LPF prior to the frequency modulation of the carrier. These realizations enable simulation-based performance Statistical Methods for Physical Science. AbstractThe square-root method provides a simple and computationally inexpensive way to generate multidimensional Gaussian random fields. Sequential Gaussian simulation. Let us assume that a prior description of the subsurface geology for a given reservoir obtained from different sources (seismic surveys, core interpretations, outcrops, etc. 01] Quick Links. In this paper, a novel translation model based on neural network is proposed to convert the target non-Gaussian power spectrum to the underlying Gaussian power spectrum for simulating non Feb 1, 2012 · Sequential Gaussian simulation (SGSIM) is a semivariogram-based simulation technique and a special case that takes advantage of convenient properties of Gaussian random functions (e. It is typically faster than SGS, with additional efficiencies due to its parallel architecture. The Gaussian distribution, (also known as the Normal distribution) is a probability distribution. Gaussian PDFs can model the distribution of many processes including some important classes of signals and noise. May 1, 2018 · Sequential Gaussian simulation was applied to both datasets, with the dissimilarity between a large number of realizations quantified using a Euclidean distance-based model and the relevant Use stationary underlying Gaussian random function Consider non-constant proportions / thresholds Conditioning to data: based on simulations of underlying Gaussian random functions Gaussian random functions can be conditioned to hard data Translate facies data into Gaussian values (Gibbs sampler) Possibility to handle hard and soft information 16 Introduction to Gaussian Random Function Simulation . 2, it must be true!" The second phase directly views the Gaussian ellipsoids as the simulatable particle discretization of the scene for MPM simulation. The module implements: Ray transfer matrices for geometrical and gaussian optics. ny, ymn, ysiz: definition of the grid system (y axis). Explore the properties of the wave functions that describe these particles. GStatSim is a Python package specifically designed for geostatistical interpolation and simulation. Oct 1, 2015 · Introduction. While kriging used to determine an estimation of the variable under study, simulation is generally performed to assess the uncertainty associated with the estimation of the mean value of the K-factor. For a fast Gaussian beam, the angular spectrum is wider, and vice versa. In the inset and indicate the beam waists of the beam after lens 1 and lens ;; Sep 13, 2007 · Conditioning realizations of stationary Gaussian random fields to a set of data is traditionally based on simple kriging. This Gaussian field models the spatial distribution This happened when H 0 was the Gaussian copula and H 1 was the t-copula with 4 degrees of freedom, and when H 0 was the t-copula with 4 degrees of freedom and H 1 was the Gaussian copula. In this study, using soil Pb collected from 2016 to 2019 in a mining city in China as case data, an ST sequential Gaussian simulation (STSGS) is proposed to reveal the ST distribution and variation in heavy metals in regional soils and their uncertainties. Oct 1, 2020 · Kriging and direct sequential Gaussian simulation. It is applied by Jan 4, 2024 · We introduce Physically Enhanced Gaussian Splatting Simulation System (PEGASUS) for 6DOF object pose dataset generation, a versatile dataset generator based on 3D Gaussian Splatting. Apr 1, 2024 · Introduction. Thirdly, the probability distribution of tectono-geochemical anomalies was quantified by uncertainty modeling technique. It is inspired by open source geostatistical resources such as GeostatsPy and SciKit-GStat. Jan 1, 2011 · Gaussian simulation smoothing is of particular interest, not only for the direct analysis of Gaussian linear models, but also for the indirect analysis of more general models. Agent-based simulation of disease spread in synthetic populations allows us to compare and contrast different effects across identical populations or to investigate the effect of interventions keeping every other factor constant between "digital twins. 2. Mar 8, 2017 · 4. Here, GaMD is demonstrated on three biomolecular model systems: alanine General workflow for Gaussian geostatistical simulation Simple kriging models for simulation. It provides state-of-the-art capabilities for electronic structure modeling. A flexible program is developed allowing practitioners to experiment with the techniques. 10. exe must be in working directory) Spatial Model Resampling Jul 1, 2023 · Simulation of non-Gaussian stochastic processes is of paramount importance to dynamic reliability assessment of structures driven by non-Gaussian loads. 3 Facies Asymmetrical Simulation with Pluri-Gaussian Model. If statistical polygons are provided, the output polygon feature class will be saved in the Output workspace, and it will have the same name as the input polygons, preceded by the Output simulation prefix. Many of the available methods for geostatistical modeling in a sequential Gaussian simulation framework are summarized. nsim: the number of simulations to generate. It models Gaussian beam and reports various beam data, including beam size and waist location as it propagates through a paraxial optical system. Gaussian Noise and Uniform Noise are frequently used in system modelling. , 2009). These videos may be viewed in any order. 2012 Feb 1;90-91:50-71. Computational models help decision makers understand epidemic dynamics to optimize public health interventions. doi: 10. 2011. It works by adding a harmonic boost potential to smooth biomolecular potential energy surface and reduce energy barriers. 1 Truncated Gaussian simulation. Jun 1, 2021 · Sequential Gaussian Simulation (SGSIM) as a stochastic method has been developed to avoid the smoothing effect produced in deterministic methods by generating various stochastic realizations. g. Basis Sets; Density Functional (DFT) Methods; Solvents List SCRF Explore math with our beautiful, free online graphing calculator. Gaussian boson sampling (GBS) is a variant of boson sampling (BS) that was originally proposed to demonstrate the quantum advantage 1 – 4. Peter Clifford, in Methods in Experimental Physics, 1994. The issue of insufficient samples hinders the effective training of reliable fault diagnosis models, impeding the industrial implementation of advanced intelligent methods. Aug 8, 2023 · Bayesian deep Gaussian processes (DGPs) outperform ordinary GPs as surrogate models of complex computer experiments when response surface dynamics are non-stationary, which is especially prevalent in aerospace simulations. One of the main issues of this technique is, however, an intensive computation related to the inverse operation in solving the Kriging system, which significantly limits its application when several Sep 1, 2019 · Sequential Gaussian simulation (SGS) A simulation is a possible realization of the contaminant contents on the field of interest, which reproduces the spatial variability of the studied phenomenon while respecting the histogram and the variogram of the measured contents (GeoSIPOL, 2005). This paper presents practical methods for the sequential generation or simulation of a Gaussian two-dimensional random field. Gaussian Sampling Probability Distributions The Normal Distribution Chi-Squared Distribution Results of Probability Theory Probability integral transform Simulation Monte Carlo Simulation via Rejection Sampling Concepts in HEP Extended Likelihood These polygons represent areas of interest for which summary statistics are calculated. 5. Jan 5, 2017 · Last updated on: 05 January 2017. In recent years, great progress has been made in Jul 12, 2024 · sgsim - sequential Gaussian simulation, 2D and 3D wrapper for sgsim from GSLIB (GSLIB's sgsim. Oct 12, 2011 · This Demonstration simulates Gaussian beam propagation and transformation by two lenses. 7 times the FWHM. Jun 26, 2024 · Dynamic Gaussian splatting has led to impressive scene reconstruction and image synthesis advances in novel views. In practice, this approach may be demanding as it does not account for the uncertainty in the spatial average of the random field. Jul 11, 2018 · We present a unified view of likelihood based Gaussian progress regression for simulation experiments exhibiting input-dependent noise. With different placement of the lenses the final beam waist (radius of the narrowest part) is different. 10 on three simulations (see Fig. However, simulation results are only valid if the input data (used to fit the semivariogram and to condition the realizations) is normally distributed. nz, zmn, zsiz: definition of the grid system (z axis). Jul 19, 2019 · Gaussian 16 & GaussView 6 Special Topics. Mar 8, 2017 · Firstly, at the observation grid cells, we generate pairs of Gaussian values such that those pairs yield correct facies observations in accordance with the truncation map. Environment and object representations can be easily obtained using commodity cameras to reconstruct with Gaussian Splatting. Apr 1, 2024 · Gaussian boson sampling (GBS) is a variant of boson sampling (BS) that was originally proposed to demonstrate the quantum advantage 1,2,3,4. Jun 1, 2006 · The closed loop FFT random shaker control procedure can be upgraded to non-Gaussian simulation by either a polynomial transformation of the Gaussain drive signals or by special phase selection in Apr 14, 2016 · The Advantages of Gaussian Model. Oct 14, 2019 · Gaussian 16 is the latest in the Gaussian series of programs. sgsim - sequential Gaussian simulation, 2D and 3D wrapper for sgsim from GSLIB (GSLIB's sgsim. Oct 1, 2021 · Besides, non-Gaussian stochastic process simulation is also a very interesting topic for more researches. Conjugation relations for geometrical and gaussian optics. Enabled by MPM solver for continuum mechanics and our novel kinematics for Gaussian kernels and spherical harmonics, the scene can undergo physics-aware deformations and maintain photo-realistic rendering quality Sep 1, 2018 · In this paper, a hybrid method named stochastic simulation-based LSA, combining sequential Gaussian simulation with grid-based LSA, is presented to address the two issues associated with common interpolation methods in grid-based LSA, namely smoothing effect and neglecting the uncertainty of values at unsampled locations. The main assumption behind GGS is that the data is stationary—the mean, variance, and spatial structure (semivariogram) do not change over the spatial May 9, 2020 · Sequential Gaussian simulation (SGS) The sequential Gaussian simulation algorithm is, by assumption, a multi-Gaussian stochastic function model and usually generates random data based on the entropy. This can be explained by Fig. coal. (), for simulating lithofacies in oil reservoirs, is an efficient stochastic modeling application. The authors used both the ensemble Kalman filter (EnKF) and the @article {zhong2024springgaus, title = {Reconstruction and Simulation of Elastic Objects with Spring-Mass 3D Gaussians}, author = {Zhong, Licheng and Yu, Hong-Xing and Wu, Jiajun and Li, Yunzhu}, journal = {European Conference on Computer Vision (ECCV)}, year = {2024}} Sep 1, 2017 · Section snippets The adaptive pluri-Gaussian simulation model. A wide-sense stationary Gaussian process is also a strict-sense stationary process and vice versa. Given a specific SNR point to simulate, we wish to generate a white Gaussian noise vector of appropriate strength and add it to the incoming signal. Basis Sets; Density Functional (DFT) Methods; Solvents List SCRF Gaussian Optics¶ Gaussian optics. At a position z along the beam (measured from the focus), the spot size parameter w is given by a hyperbolic relation: = + (), where = is called the Rayleigh range as further discussed below, and is the refractive index of the medium. Jun 15, 2015 · Consider the AWGN channel model given in Figure 1. In spatial distribution modeling kriging and simulation algorithms are generally used together. Compared with Gaussian stochastic processes, the value of the non-Gaussian stochastic process at certain instants of time requires more the probabilistic information, which leads the simulation of non-Gaussian stochastic processes more complex. 1016/j. For the first time, this paper addresses this issue by integrating self-supervised VO into our pose-free dynamic Gaussian Apr 1, 2024 · Nevertheless, the extension of conditional simulation to multivariate non-Gaussian processes has received limited attention to date. Nov 29, 2013 · This is called White Gaussian Noise (WGN) or Gaussian White Noise. Thus, the proposed method will enrich the methodologies for simulation of strongly non-Gaussian stochastic process [1], [3]. Figure 6 shows the back transformed results with the first three realizations and the average of all 100 realizations in original units. Basis Sets; Density Functional (DFT) Methods; Solvents List SCRF Apr 1, 2012 · Highlights Sequential Gaussian simulation is a robust and widely used algorithm and can be adapted for a variety of modeling techniques. Yet DGP surrogates have not been deployed for the canonical downstream task in that setting: reliability analysis through contour location (CL). Jan 23, 2014 · In this study, sequential Gaussian simulation was used to simulate the spatial distribution of soil nickel (Ni) in the top soils of a 31 km2 area within the urban-rural transition zone of Wuhan Jul 14, 2015 · A Gaussian accelerated molecular dynamics (GaMD) approach for simultaneous enhanced sampling and free energy calculation of biomolecules is presented. Aug 22, 2023 · 4_Sequential_Gaussian_Simulation. ipynb - An introduction to stochastic simulation. Jul 1, 2002 · The simulation method relies on the simulation of a Gaussian process, which can be simulated using either a spectral approach, or a Markovian approach. A typical Gaussian LPF, used in GMSK modulation standards, is Obtaining a substantial number of actual samples for rotating machinery in an industrial setting can be challenging, particularly when faulty samples are acquired under hazardous working conditions. dn zp cc ja qm yd sk xp ic vu