Current Search: Wille, Luc T. (x)
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 Title
 Dynamical phase transitions in onedimensional, annealed cellular automata.
 Creator
 Blagoev, Krastan Blagoev., Florida Atlantic University, Wille, Luc T.
 Abstract/Description

A dynamical phase transition between a frozen and a chaotic state has been found in onedimensional lattice systems with annealed disorder. An exponential decay to a homogeneous state is observed below the transition point. Above the transition point damage spreading and damage decaying phases are observed. A time dependent order parameter is suggested for describing the observed behavior.
 Date Issued
 1992
 PURL
 http://purl.flvc.org/fcla/dt/14820
 Subject Headings
 Lattice theory, Thermodynamics, Statistical mechanics
 Format
 Document (PDF)
 Title
 Molecular dynamics simulation of singlewalled carbon nanotubes.
 Creator
 Cornwell, Charles F., Florida Atlantic University, Wille, Luc T.
 Abstract/Description

Classical trajectory molecular dynamics methods are used to investigate open ended free standing single wall carbon nanotubes ("SWT"). Total energy calculations performed using classical threebody interatomic potentials with periodic boundary conditions along the tube axis, showed that the minimum strain energy varied as 1/$R\sp2$ relative to an unstrained graphite sheet. We discuss the development of a parallel code to simulate shortranged empirical potentials such as those of Stillinger...
Show moreClassical trajectory molecular dynamics methods are used to investigate open ended free standing single wall carbon nanotubes ("SWT"). Total energy calculations performed using classical threebody interatomic potentials with periodic boundary conditions along the tube axis, showed that the minimum strain energy varied as 1/$R\sp2$ relative to an unstrained graphite sheet. We discuss the development of a parallel code to simulate shortranged empirical potentials such as those of Stillinger and Weber, Tersoff, and TersoffBrenner. We then use the Tersoff and TersoffBrenner potentials to examine SWT and the tube response to axial stretching and compression. Data collected are used to calculate Young's modulus for the tubes and to develop a simple formula that approximates Young's modulus over a range of tube radii. The investigation of the free standing SWT leads to a suggestion for the possible mechanism responsible for holding the tubes open during the growth process.
Show less  Date Issued
 1996
 PURL
 http://purl.flvc.org/fcla/dt/15269
 Subject Headings
 Carbon, Nanostructured materials, Simulation methods
 Format
 Document (PDF)
 Title
 Nonequilibrium transport phenomena in lowdimensional quantum systems.
 Creator
 Valtchinov, Vladimir Ivanov., Florida Atlantic University, Wille, Luc T.
 Abstract/Description

In this thesis we have introduced and extensively studied a model for describing some essential nonequilibrium transport properties of a quantum system with reduced dimensionality. The problem of finding some of the kinetic characteristics of such a model system is formulated as that of finding a solution of a tunneling Hamiltonian with a Hubbard term. To solve this Hamiltonian we first make use of the path integral formalism, generalized for systems far from equilibrium, to perform the...
Show moreIn this thesis we have introduced and extensively studied a model for describing some essential nonequilibrium transport properties of a quantum system with reduced dimensionality. The problem of finding some of the kinetic characteristics of such a model system is formulated as that of finding a solution of a tunneling Hamiltonian with a Hubbard term. To solve this Hamiltonian we first make use of the path integral formalism, generalized for systems far from equilibrium, to perform the quantumstatistical average. The spectral function for the electrons in the well is calculated for different relevant sets of parameters. The possible presence of a Kondo peak in the interacting density of states is discussed. We calculate the frequencydriven conductance and energy losses in the linear response approximation. Numerical simulations of the general expressions show that for a given set of parameters consistent with the particular physical situation of interest, a resonant behavior is obtained for both the conductance and energy absorption for external frequencies equal to the Coulomb repulsion energy E(C).
Show less  Date Issued
 1993
 PURL
 http://purl.flvc.org/fcla/dt/14938
 Subject Headings
 Statistical mechanics, Quantum theory, Green's functions, Equilibrium
 Format
 Document (PDF)
 Title
 Population dynamics in spatially explicit lattice epidemic models.
 Creator
 St. John, Shane C., Florida Atlantic University, Wille, Luc T.
 Abstract/Description

Presented is a computational implementation simulating the propagation of an infectious disease through a host population extended over a 2dimensional square lattice. The model incorporates the effects of spatial distribution allowing for an analysis of the persistence and dynamics of the disease. Computational issues are discussed along with the results of the simulations. The simulations show that there is a threshold or critical population density. Below the critical density the disease...
Show morePresented is a computational implementation simulating the propagation of an infectious disease through a host population extended over a 2dimensional square lattice. The model incorporates the effects of spatial distribution allowing for an analysis of the persistence and dynamics of the disease. Computational issues are discussed along with the results of the simulations. The simulations show that there is a threshold or critical population density. Below the critical density the disease dies out and above it, the disease persists endemically. Population mixing affects the disease's ability to persist and, hence, the critical density. Higher degrees of mixing improve a disease's ability to persist. The model is then studied analytically in the meanfield point approximation limit. Higher meanfield approximations, which better account for the spatial inhomogeneities of the spatially discrete computational model, are also considered.
Show less  Date Issued
 1997
 PURL
 http://purl.flvc.org/fcla/dt/15419
 Subject Headings
 EpidemicsComputer simulation, Population density, Population
 Format
 Document (PDF)
 Title
 Largescale molecular dynamics simulations of semiconductor nanostructures.
 Creator
 Cornwell, Charles F., Florida Atlantic University, Wille, Luc T.
 Abstract/Description

Classical trajectory molecular dynamics methods are used to investigate the critical strain of singlewalled carbon nanotubes ("SWT") and the strength and extent of the interactions between 3D Ge structures on the surface of Si(001). The discrete model is capable of giving some insight into the critical strain of the SWT's beyond the limits of the continuous model and allow us to investigate the effects of lattice distortion due to the placement of Ge structures on the surface of a Si...
Show moreClassical trajectory molecular dynamics methods are used to investigate the critical strain of singlewalled carbon nanotubes ("SWT") and the strength and extent of the interactions between 3D Ge structures on the surface of Si(001). The discrete model is capable of giving some insight into the critical strain of the SWT's beyond the limits of the continuous model and allow us to investigate the effects of lattice distortion due to the placement of Ge structures on the surface of a Si substrate. Total energy calculations performed using classical threebody interatomic potentials with appropriate boundary conditions for each case are used to investigate the two systems. We discuss the development of a parallel code to simulate shortranged empirical potentials such as those of Stillinger and Weber, Tersoff, and TersoffBrenner. We then use the Tersoff potential to model C and Si/Ge system. Data collected are used to examine the behavior of the two systems.
Show less  Date Issued
 1999
 PURL
 http://purl.flvc.org/fcla/dt/12614
 Subject Headings
 Molecular dynamicsComputer simulation, Nanostructured materials, Semiconductors
 Format
 Document (PDF)
 Title
 The role of seed dispersal in mediating competition between two temperate understory plant populations, Cornus florida and Lindera benzoin, in a Pennsylvania state park.
 Creator
 Vejdani, Vivianne, Florida Atlantic University, Wille, Luc T.
 Abstract/Description

This study examines the demographic status of two cooccurring plant populations, Cornus florida and Lindera benzoin, with a stage matrix population projection model, and the potential for a competitive advantage in endozoochorous seed dispersal for L. benzoin in the quantity of seeds dispersed, the quality of seed dispersal, or a combination of the two. A plant pathology analysis indicates that the C. florida population has been impacted by the fungal pathogen Discula destructiva . The...
Show moreThis study examines the demographic status of two cooccurring plant populations, Cornus florida and Lindera benzoin, with a stage matrix population projection model, and the potential for a competitive advantage in endozoochorous seed dispersal for L. benzoin in the quantity of seeds dispersed, the quality of seed dispersal, or a combination of the two. A plant pathology analysis indicates that the C. florida population has been impacted by the fungal pathogen Discula destructiva . The population model predicts a decline in the C. florida population and an increase in the L. benzoin population. Seed removal experiments revealed that significantly more seeds of L. benzoin were removed by insects, presumably ants. This could represent an important advantage for L. benzoin in the quality of seed dispersal. However, L. benzoin is likely also benefiting by the increase in colonization opportunities that are provided as individuals of C. florida succumb to D. destructiva.
Show less  Date Issued
 2006
 PURL
 http://purl.flvc.org/fcla/dt/13398
 Subject Headings
 Plant populationsPennsylvania, Insectplant relationshipsPennsylvania, InsectsEcology
 Format
 Document (PDF)
 Title
 Spatiotemporal dynamics in the SEIRS epidemic model.
 Creator
 Mei, Lei, Florida Atlantic University, Wille, Luc T.
 Abstract/Description

The SusceptibleExposedInfectedRecoveredSusceptible (SEIRS) spatial epidemic model is governed by nonlinear equations with several parameters related to birth and death, contact rate, disease latency, infectious period, and recycle rate. Both continuum results and lattice results show the existing of disease persistence and critical density. The upper limit of birth and death rate is observed, power spectrum with 1/f profile is discussed. Some other models, as limiting cases of the SEIRS...
Show moreThe SusceptibleExposedInfectedRecoveredSusceptible (SEIRS) spatial epidemic model is governed by nonlinear equations with several parameters related to birth and death, contact rate, disease latency, infectious period, and recycle rate. Both continuum results and lattice results show the existing of disease persistence and critical density. The upper limit of birth and death rate is observed, power spectrum with 1/f profile is discussed. Some other models, as limiting cases of the SEIRS model, are also studied. Lower limit of birth and death rate for the models without recycle rate has also obtained. Finally two general rules governing epidemic models are summarized. Visualization is available on our web site http://www.cse.fau.edu/~lmei/simulation.html
Show less  Date Issued
 1999
 PURL
 http://purl.flvc.org/fcla/dt/15633
 Subject Headings
 EpidemiologyMathematical models, Demography, EpidemicsComputer simulation
 Format
 Document (PDF)
 Title
 The influence of connectivity on the global dynamics of nonlinear oscillator ensembles.
 Creator
 Rogers, Jeffrey L., Florida Atlantic University, Wille, Luc T.
 Abstract/Description

In this thesis we have studied the global dynamics which spontaneously emerge in ensembles of interacting disparate nonlinear oscillators. Collective phenomena exhibited in these systems include synchronization, quasiperiodicity, chaos, and death. Exact analytical solutions are presented for two and three coupled oscillators with phase and amplitude variations. A phenomenon analogous to a phasetransition is found as a function of interactionrange in a onedimensional lattice: for coupling...
Show moreIn this thesis we have studied the global dynamics which spontaneously emerge in ensembles of interacting disparate nonlinear oscillators. Collective phenomena exhibited in these systems include synchronization, quasiperiodicity, chaos, and death. Exact analytical solutions are presented for two and three coupled oscillators with phase and amplitude variations. A phenomenon analogous to a phasetransition is found as a function of interactionrange in a onedimensional lattice: for coupling exponents larger than some critical value, alpha c, synchronization is shown to be impossible. Massively parallel computer simulations in conjunction with finitesize scaling were used to extrapolate to the infinitesize limit.
Show less  Date Issued
 1994
 PURL
 http://purl.flvc.org/fcla/dt/15031
 Subject Headings
 Nonlinear oscillators, Coupled mode theory, PhysicsData processing, Parallel processing (Electronic computers)
 Format
 Document (PDF)
 Title
 Statistical physics based heuristic clustering algorithms with an application to econophysics.
 Creator
 Baldwin, Lucia Liliana, Florida Atlantic University, Wille, Luc T.
 Abstract/Description

Three new approaches to the clustering of data sets are presented. They are heuristic methods and represent forms of unsupervised (nonparametric) clustering. Applied to an unknown set of data these methods automatically determine the number of clusters and their location using no a priori assumptions. All are based on analogies with different physical phenomena. The first technique, named the Percolation Clustering Algorithm, embodies a novel variation on the nearestneighbor algorithm...
Show moreThree new approaches to the clustering of data sets are presented. They are heuristic methods and represent forms of unsupervised (nonparametric) clustering. Applied to an unknown set of data these methods automatically determine the number of clusters and their location using no a priori assumptions. All are based on analogies with different physical phenomena. The first technique, named the Percolation Clustering Algorithm, embodies a novel variation on the nearestneighbor algorithm focusing on the connectivity between sample points. Exploiting the equivalence with a percolation process, this algorithm considers data points to be surrounded by expanding hyperspheres, which bond when they touch each other. Once a sequence of joined spheres spans an entire cluster, percolation occurs and the cluster size remains constant until it merges with a neighboring cluster. The second procedure, named Nucleation and Growth Clustering, exploits the analogy with nucleation and growth which occurs in island formation during epitaxial growth of solids. The original data points are nucleation centers, around which aggregation will occur. Additional "addata" that are introduced into the sample space, interact with the data points and stick if located within a threshold distance. These "addata" are used as a tool to facilitate the detection of clusters. The third method, named Discrete Deposition Clustering Algorithm, constrains deposition to occur on a grid, which has the advantage of computational efficiency as opposed to the continuous deposition used in the previous method. The original data form the vertexes of a sparse graph and the deposition sites are defined to be the middle points of this graphs edges. Addata are introduced on the deposition site and the system is allowed to evolve in a selforganizing regime. This allows the simulation of a phase transition and by monitoring the specific heat capacity of the system one can mark out a "natural" criterion for validating the partition. All of these techniques are competitive with existing algorithms and offer possible advantages for certain types of data distributions. A practical application is presented using the Percolation Clustering Algorithm to determine the taxonomy of the Dow Jones Industrial Average portfolio. The statistical properties of the correlation coefficients between DJIA components are studied along with the eigenvalues of the correlation matrix between the DJIA components.
Show less  Date Issued
 2003
 PURL
 http://purl.flvc.org/fcla/dt/12032
 Subject Headings
 Cluster analysis, Statistical physics, Percolation (Statistical physics), Algorithms
 Format
 Document (PDF)
 Title
 MODIFIED f(R) THEORY OF GRAVITY: AN ALTERNATIVE GRAVITY THEORY.
 Creator
 Saiedi, Hamidreza, Wille, Luc T., Florida Atlantic University, Department of Physics, Charles E. Schmidt College of Science
 Abstract/Description

Through the variational principle, we review the gravitational field equations in Einstein gravity and modified f(R) gravity theories. Metric and Palatini formalisms are two different approaches that are employed to obtain the field equations in the context of f(R) theory of gravity. In this framework, we attempt to investigate the energy conditions in FriedmannLemaitreRobertsonWalker (FLRW) metric using the Raychaudhuri equation. Then, we focus on wormhole geometries and their...
Show moreThrough the variational principle, we review the gravitational field equations in Einstein gravity and modified f(R) gravity theories. Metric and Palatini formalisms are two different approaches that are employed to obtain the field equations in the context of f(R) theory of gravity. In this framework, we attempt to investigate the energy conditions in FriedmannLemaitreRobertsonWalker (FLRW) metric using the Raychaudhuri equation. Then, we focus on wormhole geometries and their thermodynamics behavior in Palatini and metric versions of modified f(R) gravity, separately. To violate the null and the weak energy conditions, wormhole spacetimes need an exotic matter. It has been shown that in f(R) gravity the matter threading the wormholes serves the energy conditions, and it is the derivative terms of the higher order curvature that may be explained as a gravitational fluid, that supports these geometries. Therefore, in f(R) gravity theory it is not required to introduce exotic matter in order to have traversable wormholes. In the framework of metric and Palatini f(R) gravity, we investigate the thermodynamic properties of evolving wormholes. We obtain an expression for the variation of the total entropy to discuss the thermodynamic behavior of wormhole spacetimes. The investigation has been extended to the apparent and event horizons. Eventually, we apply the radius of these horizons to determine the validity of the generalized second law of thermodynamics. This law states that the rate of change of total entropy is positive.
Show less  Date Issued
 2022
 PURL
 http://purl.flvc.org/fau/fd/FA00013879
 Subject Headings
 Gravity, Gravitational fieldsMathematics, Wormholes (Physics)
 Format
 Document (PDF)
 Title
 A GEOMETRY OF ENTANGLEMENT.
 Creator
 Mostafanazhad, Shahabeddin Aslmarand, Wille, Luc T. Wille, Florida Atlantic University, Department of Physics, Charles E. Schmidt College of Science
 Abstract/Description

We introduce a novel geometric approach to characterize entanglement relations in large quantum systems. Our approach is inspired by Schumacher’s singlet state triangle inequality, which used an entropicbased distance to capture the strange properties of entanglement using geometricbased inequalities. Schumacher uses classical entropy and can only describe the geometry of bipartite states. We extend his approach by using von Neumann entropy to create an entanglement monotone that can be...
Show moreWe introduce a novel geometric approach to characterize entanglement relations in large quantum systems. Our approach is inspired by Schumacher’s singlet state triangle inequality, which used an entropicbased distance to capture the strange properties of entanglement using geometricbased inequalities. Schumacher uses classical entropy and can only describe the geometry of bipartite states. We extend his approach by using von Neumann entropy to create an entanglement monotone that can be generalized for higher dimensional systems. We achieve this by utilizing recent definitions for entropic areas, volumes, and higher dimensional volumes for multipartite which we introduce in this thesis. This enables us to differentiate systems with high quantum correlation from systems with low quantum correlation and differentiate between different types of multipartite entanglement. It also enable us to describe some of the strange properties of quantum entanglement using simple geometrical inequalities. Our geometrization of entanglement provides new insight into quantum entanglement. Perhaps by constructing well motivated geometrical structures (e.g. relations among areas, volumes ...), a set of trivial geometrical inequalities can reveal some of the complex properties of higherdimensional entanglement in multipartite systems. We provide numerous illustrative applications of this approach.
Show less  Date Issued
 2022
 PURL
 http://purl.flvc.org/fau/fd/FA00013912
 Subject Headings
 Quantum systems, Geometry, Quantum entanglement
 Format
 Document (PDF)
 Title
 Numerical Investigation of Finite Kuramoto model with time dependent coupling strength.
 Creator
 Khatiwada, Dharma Raj, Wille, Luc T., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
 Abstract/Description

Synchronization of an ensemble of oscillators is a phenomenon present in systems of different fields, ranging from social and physical to biological and technological systems. The most successful approach to describe how synchrony emerges in these systems is given by the Kuramoto model. This model as it stands, however, assumes oscillators of fixed natural frequencies and a homogeneous alltoall coupling strength. The Kuramoto model has been analytically discussed to address the...
Show moreSynchronization of an ensemble of oscillators is a phenomenon present in systems of different fields, ranging from social and physical to biological and technological systems. The most successful approach to describe how synchrony emerges in these systems is given by the Kuramoto model. This model as it stands, however, assumes oscillators of fixed natural frequencies and a homogeneous alltoall coupling strength. The Kuramoto model has been analytically discussed to address the synchronization phenomena of coupled oscillators in the thermodynamic limit (N > ∞). However, there needs to be a modi cation to address the inevitable in uence of external fields on the pattern of various real life synchronization phenomena which, in general; involves a finite number of oscillators. This research introduces a time dependent coupling strength K(t) which is from the modulation of external elds in the form of, for example, a periodic impulse, in the nite oscillators assembly. A sinusoidal function with some arbitrary values of amplitude and frequency is added to the fixed coupling strength as a perturbation of external elds. Temporal evolution of order parameter r(t) and phase θ(t), both of which measure the degree of synchronization of an assembly of oscillators simultaneously, are compared between uniform and time dependent cases. Graphical comparison are made using a 2 oscillator system, a building block of any finite oscillators case. Also, similar comparisons are performed for a system of 32 oscillators which are chosen randomly as a representative of a nite number of oscillators (2 < N < ∞). A temporal variation of the relative phase angle θ(t) = θ2(t)  θ1(t) in 2 and 32 oscillators systems using uniform and time dependent cases is also a part of this research. This work also introduces a timedependent coupling strength in the form of a step function. The main objective of using such a function is to keep the synchronized behavior of the oscillators persistently. This behavior can be achieved with the perception that occasional boosting with higher coupling strength K(t) should be enough to sustain synchronous behavior of oscillators which, in general, are tuned with lower K(t).
Show less  Date Issued
 2018
 PURL
 http://purl.flvc.org/fau/fd/FA00013120
 Subject Headings
 Synchronization, Oscillations, Nonlinear oscillatorsMathematical models, Oscillator strengths, Frequency of oscillating systems
 Format
 Document (PDF)
 Title
 Massively parallel molecular dynamics simulation of crack initiation and growth in a coppernickel alloy.
 Creator
 Morrey, Willard C., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics, Wille, Luc T.
 Abstract/Description

We developed code in MasPar Fortran (an extension of Fortran 90) to conduct molecular dynamics simulations on a MasPar MP1 massively parallel computer. The code is portable to other SingleInstruction MultipleData (SIMD) platforms with minor modifications. We used a two dimensional grid containing over 220,000 atoms to simulate a high strainrate fracture growth in CuNi alloys. The atoms are arranged in a triangular lattice corresponding to an fcc (111) surface and a LennardJones (LJ)...
Show moreWe developed code in MasPar Fortran (an extension of Fortran 90) to conduct molecular dynamics simulations on a MasPar MP1 massively parallel computer. The code is portable to other SingleInstruction MultipleData (SIMD) platforms with minor modifications. We used a two dimensional grid containing over 220,000 atoms to simulate a high strainrate fracture growth in CuNi alloys. The atoms are arranged in a triangular lattice corresponding to an fcc (111) surface and a LennardJones (LJ) potential with a spline cutoff is used for the interatomic potential. The location of the spline cutoff can be adjusted to simulate either brittle or ductile fracture. The atomic positions are spatially decomposed on each Processor Element, the data are shared with adjacent PEs, and atoms are transferred as they move. Free boundary conditions are used, and the appropriate techniques for applying strain and damping unwanted reflections are developed. We report variations in the critical applied strain with increasing temperature, and propose a novel method for characterizing the location of a crack tip. This method lends itself to algorithmic calculation and reporting by the fracture code. Our results represent the first microscopic analysis of fracture in an alloy system and extend recent work on pure metals. During the investigation, we introduced a Sigma 5 grain boundary (36.9) into the sample, with appropriate grainboundary segregation. We developed a technique for rapidly quenching the highenergy particles at an artificially constructed grain boundary. We demonstrate crack blunting at the grain boundary. We also report on flyer/target impact simulations in an alloy with an LJ interatomic potential.
Show less  Date Issued
 1996
 PURL
 http://purl.flvc.org/fcla/dt/12445
 Subject Headings
 Physics, Condensed Matter, Engineering, Materials Science
 Format
 Document (PDF)
 Title
 Microfluidic Electrical Impedance Spectroscopy for Blood Analysis.
 Creator
 Rikhtehgaran, Samaneh, Wille, Luc T., Du, E., Florida Atlantic University, Department of Physics, Charles E. Schmidt College of Science
 Abstract/Description

The study of the electrical properties of red blood cells (RBCs) plays a crucial role in advancing our understanding of human health. As RBCs age, they undergo changes that affect hemorheology and blood microcirculation, which have farreaching implications for disease research. Furthermore, the shortage of RBC storage units can be a major issue for patients, underscoring the importance of characterizing RBC aging with respect to cell densities. In individuals with abnormal hemoglobin disease...
Show moreThe study of the electrical properties of red blood cells (RBCs) plays a crucial role in advancing our understanding of human health. As RBCs age, they undergo changes that affect hemorheology and blood microcirculation, which have farreaching implications for disease research. Furthermore, the shortage of RBC storage units can be a major issue for patients, underscoring the importance of characterizing RBC aging with respect to cell densities. In individuals with abnormal hemoglobin disease, alterations in hemoglobin and its functionality can modify the volume and density of RBCs, making their study even more crucial. To this end, our aim is to investigate the impedance alterations of RBCs after distributing them into different layers based on their densities. We have developed a novel method for noninvasive, rapid, and realtime singlecell analysis of RBCs. Our approach involves the use of electrical impedance spectroscopy (EIS) to study the cells after performing cell fractionation. Our studies indicate an increasing trend for RBC resistance and a decreasing trend for the cell membrane as the density of the layer increases. Additionally, we have developed a method for extracting hemoglobin with high purity from fresh samples of RBCs. By passing lysed RBCs through ultrafiltration devices and removing debris and membranes, we were able to isolate hemoglobin. Using the EIS technique, we studied the alterations of impedance over a frequency range, obtaining valuable insight into the electrical properties of hemoglobin.
Show less  Date Issued
 2023
 PURL
 http://purl.flvc.org/fau/fd/FA00014223
 Subject Headings
 BloodAnalysis, ErythrocytesAging, Hemorheology, Electrical impedance spectroscopy, Microfluidics
 Format
 Document (PDF)