3,791 research outputs found
Hidden Semi Markov Models for Multiple Observation Sequences: The mhsmm Package for R
No full textThis paper describes the R package mhsmm which implements estimation and prediction methods for hidden Markov and semi-Markov models for multiple observation sequences. Such techniques are of interest when observed data is thought to be dependent on some unobserved (or hidden) state. Hidden Markov models only allow a geometrically distributed sojourn time in a given state, while hidden semi-Markov models extend this by allowing an arbitrary sojourn distribution. We demonstrate the software with simulation examples and an application involving the modelling of the ovarian cycle of dairy cows.
Use of Lawn Chemicals in the Twin Cities
No full textCreason, Jared R.; Runge, C. Ford. (1992). Use of Lawn Chemicals in the Twin Cities. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/219500
The nonlinear future stability of the FLRW family of solutions to the Euler–Einstein system with a positive cosmological constant
No full textOriginal manuscript January 24, 2012In this article, we study small perturbations of the family of Friedmann–Lemaître–Robertson–Walker cosmological background solutions to the 1 + 3 dimensional Euler–Einstein system with a positive cosmological constant. These background solutions describe an initially uniform quiet fluid of positive energy density evolving in a spacetime undergoing accelerated expansion. Our nonlinear analysis shows that under the equation of state p=c[2 over s]ρ, 0 < c[2 over s] < 1/3 , the background solutions are globally future-stable. In particular, we prove that the perturbed spacetime solutions, which have the topological structure [0,∞) × T[superscript 3], are future-causally geodesically complete. These results are extensions of previous results derived by the author in a collaboration with I. Rodnianski, in which the fluid was assumed to be irrotational. Our novel analysis of a fluid with non-zero vorticity is based on the use of suitably defined energy currents.National Science Foundation (U.S.). All-Institutes Postdoctoral Fellowship (Mathematical Sciences Research Institute (Berkeley, Calif.) Grant DMS-0441170
The Stabilizing Effect of Spacetime Expansion on Relativistic Fluids With Sharp Results for the Radiation Equation of State
No full textAuthor's final manuscript January 10, 2012In this article, we study the 1 + 3-dimensional relativistic Euler equations on a pre-specified conformally flat expanding spacetime background with spatial slices that are diffeomorphic to R[superscript 3]. R 3 . We assume that the fluid verifies the equation of state p = c[2 over s]ρ, p = c s 2 ρ, where 0 ≤ c[subscript s] ≤ √1/3 0 ≤ c s ≤ 1/3 is the speed of sound. We also assume that the reciprocal of the scale factor associated with the expanding spacetime metric verifies a c[subscript s]−dependent time-integrability condition. Under these assumptions, we use the vector field energy method to prove that an explicit family of physically motivated, spatially homogeneous, and spatially isotropic fluid solutions are globally future-stable under small perturbations of their initial conditions. The explicit solutions corresponding to each scale factor are analogs of the well-known spatially flat Friedmann–Lemaitre–Robertson–Walker family. Our nonlinear analysis, which exploits dissipative terms generated by the expansion, shows that the perturbed solutions exist for all future times and remain close to the explicit solutions. This work is an extension of previous results, which showed that an analogous stability result holds when the spacetime is exponentially expanding. In the case of the radiation equation of state p = (1/3)ρ, we also show that if the time-integrability condition for the reciprocal of the scale factor fails to hold, then the explicit fluid solutions are unstable. More precisely, we show the existence of an open family of initial data such that (i) it contains arbitrarily small smooth perturbations of the explicit solutions’ data and (ii) the corresponding perturbed solutions necessarily form shocks in finite time. The shock formation proof is based on the conformal invariance of the relativistic Euler equations when c[2 over s] =1/3, c s 2 = 1/3, which allows for a reduction to a well-known result of Christodoulou.National Science Foundation (U.S.) (Grant DMS-1162211)Solomon Buchsbaum Research FundNational Science Foundation (U.S.). All-Institutes Postdoctoral Fellowship (Mathematical Sciences Research Institute (Berkeley, Calif.) Grant DMS-0441170
Comparing applied general equilibrium and econometric estimates of the effect of an environmental policy shock
No full textThis file explains the programs and datasets used in the following paper:
Jared C. Carbone, Nicolas Rivers, Akio Yamazaki, and Hidemichi Yonezawa
"Comparing applied general equilibrium and econometric estimates of the
effect of an environmental policy shock," forthcoming in Journal of the
Association of Environmental and Resource Economists.
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There are three folders:
bc_cge.zip
replication_table2_4_5_C1
replication_figures_table3
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CGE Approach
bc_cge.zip contains the CGE model and its results including the benchmark data in Table 1 and the results of the central scenario and sensitivity analysis in Figure 6, 7 and 8, and the further details about the CGE model's replication can be found in the readme.txt within the zip file.
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Econometric Approach
replication_table2_4_5_C1 contains the program and multiple datasets to generate Table 2, 4, 5, and C.1, explained in detail below.
Data
Original data is from Yamazaki (2017) -- comes from CANSIM
Our data is "Carbone_et_al.dta"
Program
Run Carbone_et_al_JAERE.do file for replication of Table 2, 4, 5, and C.1.
This do file also merge other datasets for more control variables, such as oil price, US unemployment rate, population, and trade index. The data on these variables are obtained from these sources listed below.
EIA oil price (crude oil -- WTI)
https://www.eia.gov/dnav/pet/pet_pri_spt_s1_a.htm
US unemployment from Labor Force Statistics from the Current Population Survey (LNS14000000)
https://data.bls.gov/timeseries/LNS14000000
Population data is from Statistics Canada's Table 17-10-0005-01 (formerly CANSIM 051-0001)
https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=1710000501
World trade index (Export volume relative to 1913)
https://ourworldindata.org/trade-and-globalization
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replication_figures_table3 contains programs and datasets required to generate all the figures and Table 3. R software is used to generate them.
TABLE3.R is for Table 3
FIGURE1.R is for Figure 1
FIGURE2.R is for Figure 2
FIGURE3.R is for Figure 3
FIGURE4_5.R is for Figure 4 and 5
FIGURE6_7.R is for Figure 6 and 7
FIGURE8.R is for Figure 8
FIGUREC1.R is for Figure C.1
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Questions regarding this file and any programs and datasets pertains to the econometric approach should be directed to Akio Yamazaki, [email protected]
On the questions of local and global well-posedness for the hyperbolic PDEs occurring in some relativistic theories of gravity and electromagnetism
No full textThe two hyperbolic systems of PDEs we consider in this work are the source-free Maxwell-Born-Infeld (MBI) field equations and the Euler-Nordstr??m system for gravitationally self-interacting fluids. The former system plays a central role in Kiessling's recently proposed self-consistent model of classical
electrodynamics with point charges, a model that does not suffer from the infinities found in the classical Maxwell-Maxwell model with point charges. The latter system is a scalar gravity caricature of the incredibly more complex Euler-Einstein system. The primary original contributions of the thesis can be summarized as follows:
1) We give a sharp non-local criterion for the formation of singularities in plane-symmetric solutions to the source-free MBI field equations. We also use a domain of dependence argument to show that 3-d initial data agreeing with certain plane-symmetric data on a large enough ball lead to solutions that form singularities in finite time. This work is an extension of a theorem of Brenier, who studied singularity formation in periodic plane-symmetric solutions.
2) We prove well-posedness for the Euler-Nordstr??m system with a cosmological constant k (EN_k) for initial data that are an H^N perturbation (not necessarily small) of a uniform, quiet fluid, for N [greater than]= 3. The method of proof relies on the framework of energy currents that has been recently developed by Christodoulou. We turn to this method out of necessity: two common frameworks for showing well-posedness in H^N, namely symmetric hyperbolicity and strict hyperbolicity, do not apply to the EN_k system, while Christodoulou's techniques apply to all hyperbolic systems derivable from a Lagrangian, of which the EN_k system is an example.
3) We insert the speed of light c as a parameter into the EN_k system (and designate the family of systems EN_k^c) in order to study the non-relativistic limit c to infinity. Taking the formal limit in the equations gives the Euler-Poisson system with a cosmological constant (EP_k). Using energy currents, we prove that for fixed initial data, as c goes to infinity, the solutions to the EN_k^c system converge uniformly on a spacetime slab [0,T] x R^3 to the solution of the EP_k system.Ph.D.Includes bibliographical references (p. 140-143)
The nonlinear future stability of the FLRW family of solutions to the irrotational Euler–Einstein system with a positive cosmological constant
No full textIn this article, we study small perturbations of the family of Friedmann-Lemaître-Robertson-Walker cosmological background solutions to the coupled Euler-Einstein system with a positive cosmological constant in 1+3 spacetime dimensions. The background solutions model an initially uniform quiet fluid of positive energy density evolving in a spacetime undergoing exponentially accelerated expansion. Our nonlinear analysis shows that under the equation of state p=c[superscript 2]ρ,0 < c[superscript 2] < 1/3, the background metric + fluid solutions are globally future-stable under small irrotational perturbations of their initial data. In particular, we prove that the perturbed spacetime solutions, which have the topological structure [0,∞)XT[superscript 3], are future causally geodesically complete. Our analysis is based on a combination of energy estimates and pointwise decay estimates for quasilinear wave equations featuring dissipative inhomogeneous terms. Our main new contribution is showing that when 0 < c[superscript 2] < 1/3, exponential spacetime expansion is strong enough to suppress the formation of fluid shocks. This contrasts against a well-known result of Christodoulou, who showed that in Minkowski spacetime, the corresponding constant-state irrotational fluid solutions are unstable
Celestial Bodies
No full textCelestial Bodies
Jared C. White
ABSTRACT
The following is a collection of original poetry written over a span of three years while attending the University of South Florida. The poetry is divided into five numbered sections, marking the major thematic divisions. Preceding the poetry is a critical introduction to the work that outlines the author\u27s developing thematic ideology
A methodology for the concurrent design of products and their assembly sequence
No full textThis thesis reports on the development of a Two-Tier methodology that provides
support for assembly sequence construction, validation and evaluation in parallel with
the design. This facilitates the production of products that are optimised for
assemblability. The proposed approach diverges significantly from many of the
sequence generation methods developed to date, which assume that assembly
planning starts at the conclusion of the design process. It is believed that the latter
approach misses an important opportunity to concurrently implement design and
sequence improvements that would result in products inherently suited to assembly.
The industrial assembly planning process was found to be completely different from
the automatic sequence generation approach. The Two-Tier methodology has its
foundations in this manual process, which uses a breadth-first, depth-second search. A
constraint-based method is used to interactively validate the sequence. In direct
contrast to traditional sequence generators, the hard and soft constraints are invoked
throughout the process. A novel approach to sequence evaluation allows the user to
quantitatively determine the suitability of the sequence at any time during the
construction process.
However, designers are rarely assembly experts and it is unreasonable to expect
practical sequences to be generated without assistance. Thus, a set of generic
assembly planning rules was identified from industrial surveys by the author. These
were collaboratively implemented into an Expert Assembler, which currently consists
of two mini advisors. Support is available to identify the most suitable base
component and the most appropriate component to add next.
The Two-Tier methodology has been implemented into a computer-based system
called SPADE (Sequence Planning And Design Environment). A four-layer model
holds the product data that underpins this implementation. The methodology and
SPADE have been successfully tested using representative case studies and the results
are reported as part of this thesis
The global future stability of the FLRW solutions to the Dust-Einstein system with a positive cosmological constant
No full textWe study small perturbations of the Friedman–Lemaître–Robertson–Walker (FLRW) solutions to the dust-Einstein system with a positive cosmological constant in the case that the space-like Cauchy hypersurfaces are diffeomorphic to 3. We show that the FLRW solutions are nonlinearly globally future-stable under small perturbations of their initial data. In our analysis, we construct harmonic-type coordinates such that the cosmological constant results in the presence of dissipative terms in the evolution equations. Our result extends those of [I. Rodnianski and J. Speck, The nonlinear future stability of the FLRW family of solutions to the irrotational Euler–Einstein system with a positive cosmological constant, J. Eur. Math. Soc. 15 (2013) 2369–2462; J. Speck, The nonlinear future stability of the FLRW family of solutions to the Euler–Einstein system with a positive cosmological constant, Selecta Math. 18 (2012) 633–715; C. Lübbe and J. A. Valiente Kroon, A conformal approach for the analysis of the nonlinear stability of pure radiation cosmologies, Ann. Phys. 328 (2013) 1–25], where analogous results were proved for the Euler–Einstein system under the equations of state [mathematical equation]. The dust-Einstein system is the case c[subscript s] = 0. The main difficulty that we overcome here is that the dust's energy density loses one degree of differentiability compared to the cases [mathematical equation] which introduces many obstacles for closing the estimates. To resolve this difficulty, we commute the equations with a well-chosen differential operator and derive elliptic estimates that complement the energy estimates of [I. Rodnianski and J. Speck, The nonlinear future stability of the FLRW family of solutions to the irrotational Euler–Einstein system with a positive cosmological constant, J. Eur. Math. Soc. 15 (2013) 2369–2462; J. Speck, The nonlinear future stability of the FLRW family of solutions to the Euler–Einstein system with a positive cosmological constant, Selecta Math. 18 (2012) 633–715]. Our results apply in particular to small perturbations of the vanishing dust state containing vacuum regions
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