#### Sample records for model theoretical aspects

1. Theoretical aspects of an electricity marginal cost model

SciTech Connect

Oyama, T.

1986-01-01

A separable programming model has been built to estimate electricity marginal costs. The model can be solved by applying linear programming techniques, hence marginal costs are obtained from shadow prices of model's optimal solution. In order to obtain more accurate and more detailed composition of electricity marginal costs, shadow prices are mathematically explained rigorously from model's structural points of view. Theoretical aspects of our electricity marginal cost model are investigated by applying theory of linear programming. Furthermore, various types of mathematical expression are also shown with their interpretation in the real power system.

2. Theoretical aspects of an electricity marginal cost model

SciTech Connect

Oyama, T.

1987-05-01

A separable programming model has been built to estimate electricity marginal costs. The model can be solved by applying linear programming techniques, hence marginal costs are obtained from shadow prices of model's optimal solution. In order to obtain more accurate and more detailed composition of electricity marginal costs, shadow prices are mathematically explained rigorously from model's structural points of view. Theoretical aspects of our electricity marginal cost model are investigated by applying theory of linear programming. Furthermore, various types of mathematical expression are also shown with their interpretation in the real power system.

3. The theoretical aspects of UrQMD & AMPT models

Saini, Abhilasha; Bhardwaj, Sudhir

2016-05-01

The field of high energy physics is very challenging in carrying out theories and experiments to unlock the secrets of heavy ion collisions and still not cracked and solved completely. There are many theoretical queries; some may be due to the inherent causes like the non-perturbative nature of QCD in the strong coupling limit, also due to the multi-particle production and evolution during the heavy ion collisions which increase the complexity of the phenomena. So for the purpose of understanding the phenomena, variety of theories and ideas are developed which are usually implied in the form of Monte-Carlo codes. The UrQMD model and the AMPT model are discussed here in detail. These methods are useful in modeling the nuclear collisions.

4. Information theoretic aspects of the two-dimensional Ising model.

PubMed

Lau, Hon Wai; Grassberger, Peter

2013-02-01

We present numerical results for various information theoretic properties of the square lattice Ising model. First, using a bond propagation algorithm, we find the difference 2H(L)(w)-H(2L)(w) between entropies on cylinders of finite lengths L and 2L with open end cap boundaries, in the limit L→∞. This essentially quantifies how the finite length correction for the entropy scales with the cylinder circumference w. Secondly, using the transfer matrix, we obtain precise estimates for the information needed to specify the spin state on a ring encircling an infinitely long cylinder. Combining both results, we obtain the mutual information between the two halves of a cylinder (the "excess entropy" for the cylinder), where we confirm with higher precision but for smaller systems the results recently obtained by Wilms et al., and we show that the mutual information between the two halves of the ring diverges at the critical point logarithmically with w. Finally, we use the second result together with Monte Carlo simulations to show that also the excess entropy of a straight line of n spins in an infinite lattice diverges at criticality logarithmically with n. We conjecture that such logarithmic divergence happens generically for any one-dimensional subset of sites at any two-dimensional second-order phase transition. Comparing straight lines on square and triangular lattices with square loops and with lines of thickness 2, we discuss questions of universality. PMID:23496480

5. Information theoretic aspects of the two-dimensional Ising model

Lau, Hon Wai; Grassberger, Peter

2013-02-01

We present numerical results for various information theoretic properties of the square lattice Ising model. First, using a bond propagation algorithm, we find the difference 2HL(w)-H2L(w) between entropies on cylinders of finite lengths L and 2L with open end cap boundaries, in the limit L→∞. This essentially quantifies how the finite length correction for the entropy scales with the cylinder circumference w. Secondly, using the transfer matrix, we obtain precise estimates for the information needed to specify the spin state on a ring encircling an infinitely long cylinder. Combining both results, we obtain the mutual information between the two halves of a cylinder (the “excess entropy” for the cylinder), where we confirm with higher precision but for smaller systems the results recently obtained by Wilms , and we show that the mutual information between the two halves of the ring diverges at the critical point logarithmically with w. Finally, we use the second result together with Monte Carlo simulations to show that also the excess entropy of a straight line of n spins in an infinite lattice diverges at criticality logarithmically with n. We conjecture that such logarithmic divergence happens generically for any one-dimensional subset of sites at any two-dimensional second-order phase transition. Comparing straight lines on square and triangular lattices with square loops and with lines of thickness 2, we discuss questions of universality.

6. Some theoretical and computational aspects of a simplified subchannel model

SciTech Connect

Neil, C.H.

1983-01-01

Some recently obtained results are presented concerning the qualitative behavior of solutions to equations governing a simplified subchannel model for reactor hydrodynamics. The model describes time-independent flow of an incompressible fluid in two parallel, interconnected channels, subject to axial and lateral pressure drops defined by a Darcy friction factor. The phase portrait for the system of ordinary differential equations is presented, a solution to a boundary-value problem describing flow blockage is discussed, and the effect of the qualitative behavior of solutions on their numerical approximation is examined. The study was undertaken to determine the cause of numerical difficulty in approximating solutions to problems.

7. Theoretical aspects and practical implications of the heuristic drift SOL model

Goldston, R. J.

2015-08-01

The heuristic drift (HD) model for the tokamak power scrape-off layer width provides remarkable agreement in both absolute magnitude and scalings with the measured width of the exponential component of the heat flux at divertors targets, in low gas-puff H-Mode tokamaks. This motivates further exploration of its theoretical aspects and practical implications. The HD model requires a small non-ambipolar electron particle diffusivity ∼10-2 m2/s. It also implies large parallel heat flux in ITER and suggests that more radical approaches will be needed to handle the ∼20 GW/m2 parallel heat flux expected in Demo. Remarkably, the HD model is also in good agreement with recent near-SOL heat flux profiles measured in a number of limiter L-Mode experiments, implying ubiquity of the underlying mechanism. Finally, the HD model suggests that the H-Mode and more generally Greenwald density limit may be caused by MHD instability in the SOL, rather than originating in the core plasma or pedestal. If the SOL width in stellarators is set by magnetic topology rather than by drifts, this would be consistent with the absence of the Greenwald density limit in stellarators.

8. Some Theoretical Aspects for Elastic Wave Modeling in a Recently Developed Spectral Element Method

Wang, X. M.; Seriani, G.; Lin, W. J.

2006-10-01

A spectral element method has been recently developed for solving elastodynamic problems. The numerical solutions are obtained by using the weak formulation of the elastodynamic equation for heterogeneous media and by the Galerkin approach applied to a partition, in small subdomains, of the original physical domain under investigation. In the present work some mathematical aspects of the method and of the associated algorithm implementation are systematically investigated. Two kinds of orthogonal basis functions, constructed with Legendre and Chebyshev polynomials, and their related Gauss-Lobbatto collocation points, used in reference element quadrature, are introduced. The related analytical integration formulas are obtained. The standard error estimations and expansion convergence are discussed. In order to improve the computation accuracy and efficiency, an element-by-element pre-conditioned conjugate gradient linear solver in the space domain and a staggered predictor/multi-corrector algorithm in the time integration are used for strong heterogeneous elastic media. As a consequence neither the global matrices, nor the effective force vector is assembled. When analytical formula are used for the element quadrature, there is even no need for forming element matrix in order to further save memory without loosing much in computational efficiency. The element-by-element algorithm uses an optimal tensor product scheme which makes spectral element methods much more efficient than finite-element methods from the point of view of both memory storage and computational time requirements. This work is divided into two parts. The second part will give the algorithm implementation, numerical accuracy and efficiency analyses, and then the modelling example comparison of the proposed spectral element method with a conventional finite-element method and a staggered pseudo-spectral method that is to be reported in the other work.

9. Theoretic aspects of the identification of the parameters in the optimal control model

NASA Technical Reports Server (NTRS)

Vanwijk, R. A.; Kok, J. J.

1977-01-01

The identification of the parameters of the optimal control model from input-output data of the human operator is considered. Accepting the basic structure of the model as a cascade of a full-order observer and a feedback law, and suppressing the inherent optimality of the human controller, the parameters to be identified are the feedback matrix, the observer gain matrix, and the intensity matrices of the observation noise and the motor noise. The identification of the parameters is a statistical problem, because the system and output are corrupted by noise, and therefore the solution must be based on the statistics (probability density function) of the input and output data of the human operator. However, based on the statistics of the input-output data of the human operator, no distinction can be made between the observation and the motor noise, which shows that the model suffers from overparameterization.

10. Theoretical aspects of light meson spectroscopy

SciTech Connect

Barnes, T. |

1995-12-31

In this pedagogical review the authors discuss the theoretical understanding of light hadron spectroscopy in terms of QCD and the quark model. They begin with a summary of the known and surmised properties of QCD and confinement. Following this they review the nonrelativistic quark potential model for q{anti q} mesons and discuss the quarkonium spectrum and methods for identifying q{anti q} states. Finally, they review theoretical expectations for non-q{anti q} states (glueballs, hybrids and multiquark systems) and the status of experimental candidates for these states.

11. Large Aspect Ratio Roll Vortices (10 km Wavelength) In Tropical Cyclone Boundary Layers: SAR Evidence and Theoretical Modeling

Foster, Ralph; Patoux, Jerome; Horstmann, Jochen; Wackerman, Chris; Graber, Hans

2013-04-01

Analysis of synthetic aperture radar (SAR) images of the sea surface underneath tropical cyclones shows clear evidence of organized bands of surface wind convergence and wind stress curl. These patterns are consistent with the effects of planetary boundary roll vortices, except the observed wavelengths are O(10 km), which implies the rolls have aspect ratios (wavelength/PBL depth) many times what has been commonly observed in hurricane boundary layers (typically 2.5). The tropical cyclone boundary layer is a very favorable environment for the formation of roll vortices and observations show that O(1-3 km) wavelength rolls are a very common feature. We present an extension of the Foster (2005) nonlinear theory for hurricane PBL roll formation that posits a nonlinear, wave-wave, upscale energy transfer mechanism for the formation of large aspect ratio rolls. These large-aspect ratio rolls induce a circulation that extends from the sea-surface into the storm interior above the boundary layer and modulates the smaller rolls. Implications for improving SAR surface wind retrievals, hurricane boundary layer parameterization and surface fluxes are presented.

12. J. J. Sakurai Prize for Theoretical Particle Physics Lecture: Some QCD aspects of physics beyond the standard model

Sjostrand, Torbjorn

2012-03-01

The nature of observable events at the LHC is mainly determined by QCD physics, i.e. strong interactions. The search for new physics obviously implies a desire to go beyond QCD. Nevertheless, also in cases where non-QCD processes are studied, new aspects of QCD physics may enter the back door. We here give three examples: decays with R-parity violation in SUSY, the formation of long-lived R-hadrons in SUSY, and parton showers and hadronization in Hidden Valley scenarios. These three possibilities have been implemented in the general-purpose PYTHIA event generator, so that detailed studies of consequences can be performed.

13. Theoretical aspects of the biological catch bond.

PubMed

Prezhdo, Oleg V; Pereverzev, Yuriy V

2009-06-16

The biological catch bond is fascinating and counterintuitive. When an external force is applied to a catch bond, either in vivo or in vitro, the bond resists breaking and becomes stronger instead. In contrast, ordinary slip bonds, which represent the vast majority of biological and chemical bonds, dissociate faster when subjected to a force. Catch-bond behavior was first predicted theoretically 20 years ago and has recently been experimentally observed in a number of protein receptor-ligand complexes. In this Account, we review the simplest physical-chemical models that lead to analytic expressions for bond lifetime, the concise universal representations of experimental data, and the explicit requirements for catch binding. The phenomenon has many manifestations: increased lifetime with growing constant force is its defining characteristic. If force increases with time, as in jump-ramp experiments, catch binding creates an additional maximum in the probability density of bond rupture force. The new maximum occurs at smaller forces than the slip-binding maximum, merging with the latter at a certain ramp rate in a process resembling a phase transition. If force is applied periodically, as in blood flows, catch-bond properties strongly depend on force frequency. Catch binding results from a complex landscape of receptor-ligand interactions. Bond lifetime can increase if force (i) prevents dissociation through the native pathway and drives the system over a higher energy barrier or (ii) alters protein conformations in a way that strengthens receptor-ligand binding. The bond deformations can be associated with allostery; force-induced conformational changes at one end of the protein propagate to the binding site at the other end. Surrounding water creates further exciting effects. Protein-water tension provides an additional barrier that can be responsible for significant drops in bond lifetimes observed at low forces relative to zero force. This strong dependence of

14. Theoretical aspects and modelling of cellular decision making, cell killing and information-processing in photodynamic therapy of cancer

PubMed Central

2013-01-01

Background The aim of this report is to provide a mathematical model of the mechanism for making binary fate decisions about cell death or survival, during and after Photodynamic Therapy (PDT) treatment, and to supply the logical design for this decision mechanism as an application of rate distortion theory to the biochemical processing of information by the physical system of a cell. Methods Based on system biology models of the molecular interactions involved in the PDT processes previously established, and regarding a cellular decision-making system as a noisy communication channel, we use rate distortion theory to design a time dependent Blahut-Arimoto algorithm where the input is a stimulus vector composed of the time dependent concentrations of three PDT related cell death signaling molecules and the output is a cell fate decision. The molecular concentrations are determined by a group of rate equations. The basic steps are: initialize the probability of the cell fate decision, compute the conditional probability distribution that minimizes the mutual information between input and output, compute the cell probability of cell fate decision that minimizes the mutual information and repeat the last two steps until the probabilities converge. Advance to the next discrete time point and repeat the process. Results Based on the model from communication theory described in this work, and assuming that the activation of the death signal processing occurs when any of the molecular stimulants increases higher than a predefined threshold (50% of the maximum concentrations), for 1800s of treatment, the cell undergoes necrosis within the first 30 minutes with probability range 90.0%-99.99% and in the case of repair/survival, it goes through apoptosis within 3-4 hours with probability range 90.00%-99.00%. Although, there is no experimental validation of the model at this moment, it reproduces some patterns of survival ratios of predicted experimental data. Conclusions

15. Acting Out; Theoretical and Clinical Aspects.

ERIC Educational Resources Information Center

Abt, Lawrence Edwin, Ed.; Weissman, Stuart L.

The beneficial and harmful effects of acting out are studied in a series of short essays by numerous authors. Included are four articles on the theoretical and dynamic considerations of acting out, along with five clinical manifestations of acting out involving suicide and criminality in adolescents and adults. Special forms of harmful acting out…

16. Theoretical and computational aspects of seismic tomography

Alekseev, A. S.; Lavrentiev, M. M.; Romanov, V. G.; Romanov, M. E.

1990-12-01

This paper reviews aspects related to applications of seismic wave kinematics for the reconstruction of internal characteristics of an elastic medium. It presents the results of studying the inverse kinematic seismic problem and its linear analogue — problems of integral geometry, obtained in recent decades with an emphasis on the work done by Soviet scientists. Computational techniques of solving these problems are discussed. This review should be of interest to geophysicists studying the oceans, atmosphere and ionosphere as well as those studying the solid part of the Earth.

17. Theoretical aspects of fibre laser cutting

Mahrle, A.; Beyer, E.

2009-09-01

Fibre lasers offer distinct advantages over established laser systems with respect to power efficiency, beam guidance and beam quality. Consequently, the potential of these new laser beam sources will be increasingly exploited for laser cutting applications that are conventionally carried out with CO2 lasers. However, theoretical estimates of the effective absorptivity at the cut front suggest that the shorter wavelength of the fibre laser in combination with its high focusability seems to be primarily advantageous for thin sheet metal cutting whereas the CO2 laser is probably still capable of cutting thicker materials more efficiently. This surprising result is a consequence of the absorptivity behaviour of metals that shows essential quantitative differences for the corresponding wavelengths of both laser sources as a function of the angle of incidence between the laser beam and the material to be cut. In evaluation of the revealed dependences, solution strategies for an improvement of the efficiency of fibre laser cutting of thicker metal sheets are suggested.

18. Brain stimulation using electromagnetic sources: theoretical aspects.

PubMed Central

Heller, L; van Hulsteyn, D B

1992-01-01

We prove that, at the frequencies generally proposed for extracranial stimulation of the brain, it is not possible, using any superposition of external current sources, to produce a three-dimensional local maximum of the electric field strength inside the brain. The maximum always occurs on a boundary where the conductivity jumps in value. Nevertheless, it may be possible to achieve greater two-dimensional focusing and shaping of the electric field than is currently available. Towards this goal we have used the reciprocity theorem to present a uniform treatment of the electric field inside a conducting medium produced by a variety of sources: an external magnetic dipole (current loop), an external electric dipole (linear antenna), and surface and depth electrodes. This formulation makes use of the lead fields from magneto- and electroencephalography. For the special case of a system with spherically symmetric conductivity, we derive a simple analytic formula for the electric field due to an external magnetic dipole. This formula is independent of the conductivity profile and therefore embraces spherical models with any number of shells. This explains the "insensitivity" to the skull's conductivity that has been described in numerical studies. We also present analytic formulas for the electric field due to an electric dipole, and also surface and depth electrodes, for the case of a sphere of constant conductivity. PMID:1420862

19. Teacher Selection: Legal, Practical, and Theoretical Aspects. UCEA Monograph Series.

ERIC Educational Resources Information Center

Young, I. Philip; Ryerson, Dean

This monograph, structured for administrative use in analyzing and building systems for selecting teachers, outlines the legal, applied, and theoretical issues of teacher selection. This overview is presented in five sections. "Legal Aspects of Teacher Selection" examines individual rights and employer reactions in relation to federal and state…

20. 3D barcodes: theoretical aspects and practical implementation

Gladstein, David; Kakarala, Ramakrishna; Baharav, Zachi

2015-02-01

This paper introduces the concept of three dimensional (3D) barcodes. A 3D barcode is composed of an array of 3D cells, called modules, and each can be either filled or empty, corresponding to two possible values of a bit. These barcodes have great theoretical promise thanks to their very large information capacity, which grows as the cube of the linear size of the barcode, and in addition are becoming practically manufacturable thanks to the ubiquitous use of 3D printers. In order to make these 3D barcodes practical for consumers, it is important to keep the decoding simple using commonly available means like smartphones. We therefore limit ourselves to decoding mechanisms based only on three projections of the barcode, which imply specific constraints on the barcode itself. The three projections produce the marginal sums of the 3D cube, which are the counts of filled-in modules along each Cartesian axis. In this paper we present some of the theoretical aspects of the 2D and 3D cases, and describe the resulting complexity of the 3D case. We then describe a method to reduce these complexities into a practical application. The method features an asymmetric coding scheme, where the decoder is much simpler than the encoder. We close by demonstrating 3D barcodes we created and their usability.

1. K-theoretic aspects of string theory dualities

Mendez-Diez, Stefan Milo

String theory is a a physical field theory in which point particles are replaced by 1-manifolds propagating in time, called strings. The 2-manifold representing the time evolution of a string is called the string worldsheet. Strings can be either closed (meaning their worldsheets are closed surfaces) or open (meaning their worldsheets have boundary). A D-brane is a submanifold of the spacetime manifold on which string endpoints are constrained to lie. There are five different string theories that have supersymmetry, and they are all related by various dualities. This dissertation will review how D-branes are classified by K-theory. We will then explore the K-theoretic aspects of a hypothesized duality between the type I theory compactified on a 4-torus and the type IIA theory compactified on a K3 surface, by looking at a certain blow down of the singular limit of K3. This dissertation concludes by classifying D-branes on the type II orientifold Tn/Z2 when the Z2 action is multiplication by -1 and the H-flux is trivial. We find that classifying D-branes on the singular limit of K3, T4/Z2 by equivariant K-theory agrees with the classification of D-branes on a smooth K3 surface by ordinary K-theory.

2. Theoretical aspects of solid hydrogen halides under pressure

Jansen, Robert W.; Bertoncini, Rita; Pinnick, David A.; Katz, Allen I.; Hanson, R. C.; Sankey, Otto F.; O'keeffe, Michael

1987-06-01

The electronic and dynamic properties of the solid phases of HF, HCl, and HBr under pressure are studied theoretically. A simple model is constructed so that the pressure-dependent properties of these systems and possibly other hydrogen-bonded systems can be studied in terms of a few parameters. The model predicts quite simply the pressure dependence of the stretching-mode frequency and the nature of the phase transition from the molecular hydrogen-bonded phase to a new symmetrical hydrogen-bonded (nonmolecular) phase. Quantum effects due to the light hydrogen atom are taken into account within a many-body Hartree approximation. New experimental data on the pressure dependence of the symmetric-stretching-mode frequency in HF is presented. The possibility of soliton formation is discussed and it is shown how pressure may act as a unique tuner to adjust the energetics of these nonlinear excitations. In addition, we report the results of our ab initio calculations of the total energy of ringlike structures of HF and the first ab initio pseudopotential calculation of the band structure and total energy of solid HBr. The calculations for HF are within the Hartree-Fock approximation, while those of solid HBr are within the local-density approximation and have been simplified by considering a linear instead of a zigzag geometry. The use of the local-density approximation for hydrogen is also discussed.

3. Theoretical Foundation for Weld Modeling

NASA Technical Reports Server (NTRS)

Traugott, S.

1986-01-01

Differential equations describe physics of tungsten/inert-gas and plasma-arc welding in aluminum. Report collects and describes necessary theoretical foundation upon which numerical welding model is constructed for tungsten/inert gas or plasma-arc welding in aluminum without keyhole. Governing partial differential equations for flow of heat, metal, and current given, together with boundary conditions relevant to welding process. Numerical estimates for relative importance of various phenomena and required properties of 2219 aluminum included

4. Theoretical Models of Generalized Quasispecies.

PubMed

Wagner, Nathaniel; Atsmon-Raz, Yoav; Ashkenasy, Gonen

2016-01-01

Theoretical modeling of quasispecies has progressed in several directions. In this chapter, we review the works of Emmanuel Tannenbaum, who, together with Eugene Shakhnovich at Harvard University and later with colleagues and students at Ben-Gurion University in Beersheva, implemented one of the more useful approaches, by progressively setting up various formulations for the quasispecies model and solving them analytically. Our review will focus on these papers that have explored new models, assumed the relevant mathematical approximations, and proceeded to analytically solve for the steady-state solutions and run stochastic simulations . When applicable, these models were related to real-life problems and situations, including changing environments, presence of chemical mutagens, evolution of cancer and tumor cells , mutations in Escherichia coli, stem cells , chromosomal instability (CIN), propagation of antibiotic drug resistance , dynamics of bacteria with plasmids , DNA proofreading mechanisms, and more. PMID:26373410

5. Aspect-Oriented Design with Reusable Aspect Models

Kienzle, Jörg; Al Abed, Wisam; Fleurey, Franck; Jézéquel, Jean-Marc; Klein, Jacques

The idea behind Aspect-Oriented Modeling (AOM) is to apply aspect-oriented techniques to (software) models with the aim of modularizing crosscutting concerns. This can be done within different modeling notations, at different levels of abstraction, and at different moments during the software development process. This paper demonstrates the applicability of AOM during the software design phase by presenting parts of an aspect-oriented design of a crisis management system. The design solution proposed in this paper is based on the Reusable Aspect Models (RAM) approach, which allows a modeler to express the structure and behavior of a complex system using class, state and sequence diagrams encapsulated in several aspect models. The paper describes how the model of the "create mission" functionality of the server backend can be decomposed into 23 inter-dependent aspect models. The presentation of the design is followed by a discussion on the lessons learned from the case study. Next, RAM is compared to 8 other AOM approaches according to 6 criteria: language, concern composition, asymmetric and symmetric composition, maturity, and tool support. To conclude the paper, a discussion section points out the features of RAM that specifically support reuse.

Smith, F. T.

1984-06-01

The paper describes recent developments as well as basic aspects, for the rational theory of steady and unsteady separation. Steady two-dimensional separation is broadly accounted for but difficulties in describing large-scale eddy closure are emphasized. Steady three-dimensional separation theory is still in its early stages. Unsteady separation is linked closely with instabilities, e.g. in the boundary layer and separating shear layer, and with dynamic stall.

7. Managing interdisciplinary health research--theoretical and practical aspects.

PubMed

Aagaard-Hansen, Jens; Ouma, John Henry

2002-01-01

Interdisciplinary health research can offer valuable evidence for health care managers. However, there are specific challenges regarding the management of such projects. Based on 7 years of experience from a project in western Kenya, the authors point to the need for a sufficient time horizon, a high level of communication, equity between the disciplines and the identification of appropriate evaluation criteria as issues to be considered. The theoretical framework of Rosenfield was modified to comply with the complexities of field management. PMID:12298143

8. Molecular switches in carbon-rich organometallic compounds: Theoretical aspects

Costuas, Karine

2015-01-01

Organometallic complexes associated with an appropriate choice of ancillary ligands reveal to have a wide range of physical properties leading to promising applications when incorporated in nano-size devices. The challenge is to design innovative multifunctional compounds based on redox active carbon-rich organometallics associated with spin carriers and/or photochromic units. A multidisciplinary approach in this area has proved to be efficient in a series a systems combining carbon-rich bridging ligands and redox metallic moieties. In this domain, the role of theoretical investigations based on quantum mechanics tools have a crucial role in rationalizing and in helping designing systems possessing target properties.

9. Molecular switches in carbon-rich organometallic compounds: Theoretical aspects

SciTech Connect

Costuas, Karine

2015-01-22

Organometallic complexes associated with an appropriate choice of ancillary ligands reveal to have a wide range of physical properties leading to promising applications when incorporated in nano-size devices. The challenge is to design innovative multifunctional compounds based on redox active carbon-rich organometallics associated with spin carriers and/or photochromic units. A multidisciplinary approach in this area has proved to be efficient in a series a systems combining carbon-rich bridging ligands and redox metallic moieties. In this domain, the role of theoretical investigations based on quantum mechanics tools have a crucial role in rationalizing and in helping designing systems possessing target properties.

10. Theoretical aspects of product formation from the NCO + NO reaction

SciTech Connect

Lin, M.C.; He, Y. ); Melius, C.F. )

1993-09-09

The reaction of NCO with NO, an important elementary process involved in the reduction of NO[sub x] by HNCO, has been studied theoretically using the BAC-MP4 technique in conjunction with RRKM calculations. The computed molecular structures and thermochemical data for various intermediates and transition states suggest that the reaction takes place primarily via the singlet, ground electronic state OCNNO molecule according to the following mechanism; (step a) NCO + NO [leftrightarrow] [sup 1]OCNNO [yields] N[sub 2]O + CO; (step b) NCO + NO [leftrightarrow] [sup 1]OCNNO [yields] c-OCNNO[minus] N[sub 2] + CO[sub 2]. The formation of N[sub 2]O + CO occurs by the fragmentation of the singlet OCNNO intermediate step (a), whereas the production of N[sub 2] + CO[sub 2] by cyclization-fragmentation occurs via step b. The tight transition states leading to the formation of these products, coupled with the loose entrance channel, give rise to the experimentally observed strong negative temperature dependence which can be quantitatively accounted for by the results of RRKM calculations based on the BAC-MP4 data. The experimentally measured product branching ratio for channels a and b could be accounted for theoretically by lowering the calculated energy barrier for step a by 3.6 kcal/mol, corresponding to about 15% of the barrier height. 22 refs., 3 figs., 5 tabs.

11. Theoretical model of ``fuzz'' growth

Krasheninnikov, Sergei; Smirnov, Roman

2012-10-01

Recent more detailed experiments on tungsten irradiation with low energy helium plasma, relevant to the near-wall plasma conditions in magnetic fusion reactor like ITER, demonstrated (e.g. see Ref. 1) a very dramatic change in both surface morphology and near surface material structure of the samples. In particular, it was shown that a long (mm-scale) and thin (nm-scale) fiber-like structures filled with nano-bubbles, so-called ``fuzz,'' start to grow. In this work theoretical model of ``fuzz'' growth [2] describing the main features observed in experiments is presented. This model, based on the assumption of enhancement of creep of tungsten containing significant fraction of helium atoms and clusters. The results of the MD simulations [3] support this idea and demonstrate a strong reduction of the yield strength for all temperature range. They also show that the ``flow'' of tungsten strongly facilitates coagulation of helium clusters and the formation of nano-bubbles.[4pt] [1] M. J. Baldwin, et al., J. Nucl. Mater. 390-391 (2009) 885;[0pt] [2] S. I. Krasheninnikov, Physica Scripta T145 (2011) 014040;[0pt] [3] R. D. Smirnov and S. I. Krasheninnikov, submitted to J. Nucl. Materials.

12. Computational and theoretical aspects of biomolecular structure and dynamics

SciTech Connect

Garcia, A.E.; Berendzen, J.; Catasti, P., Chen, X.

1996-09-01

This is the final report for a project that sought to evaluate and develop theoretical, and computational bases for designing, performing, and analyzing experimental studies in structural biology. Simulations of large biomolecular systems in solution, hydrophobic interactions, and quantum chemical calculations for large systems have been performed. We have developed a code that implements the Fast Multipole Algorithm (FMA) that scales linearly in the number of particles simulated in a large system. New methods have been developed for the analysis of multidimensional NMR data in order to obtain high resolution atomic structures. These methods have been applied to the study of DNA sequences in the human centromere, sequences linked to genetic diseases, and the dynamics and structure of myoglobin.

13. Theoretical aspects of science with radioactive nuclear beams.

Dobaczewski, J.; Nazarewicz, W.

1998-09-01

Physics of radioactive nuclear beams is one of the main frontiers of nuclear science today. Experimentally, thanks to technological developments, we are on the verge of invading the territory of extreme N/Z ratios in an unprecedented way. Theoretically, nuclear exotica represent a formidable challenge for the nuclear many-body theories and their power to predict nuclear properties in nuclear terra incognita. It is important to remember that the lesson learned by going to the limits of the nuclear binding is also important for 'normal' nuclei from the neighbourhood of the beta stability valley. And, of course, radioactive nuclei are crucial astrophysically; they pave the highway along which the nuclear material is transported up in the proton and neutron numbers during the complicated synthesis process in stars.

14. Theoretical and Observational Aspects of Expanding H I Shells

Cazzolato, François; Pineault, Serge

2005-06-01

We have modeled H I shells expanding into a homogeneous medium in order to explain some of their observational peculiarities. Such peculiarities include difficult-to-observe caps, the presence of stationary rings, expansion velocity determination problems, inaccurate mass measurements, and a systematic discrepancy between H I missing masses and shell masses. Velocity dispersion within the shell, in the form of either thermal or turbulent motions, has been found to be the likely major cause for the absence of observable caps and the presence of stationary rings, hence explaining the apparent lack of ring transition. We discuss different methods generally used to calculate H I shell masses and show that, if one does not take into account the varying shape of the H I background local to the shell, shell masses are likely to be underestimated by a significant factor whose value depends on the relative shell thickness and the ratio of the dispersion to the expansion velocity.

15. Classical and Quantum Conditioning:. Mathematical and Information Theoretical Aspects

Accardi, Luigi

2010-01-01

The different notions of stochastic independences, introduced in quantum probability open new fascinating possibilities to deepen our intuition on what a composite system. In the present note we propose a general mathematical definition of composite system which emphasizes the fact that the naive idea, that a physical system is composed of a multiplicity of sub-systems, can be substantiated by a multiplicity of inequivalent mathematical models. This wealth of possibilities can considerably enrich the present approach to the theory of open systems, with potential implications for the theory of measurement and the theory of complex systems, such as biological or economical ones. The standard approach to composite system strongly privileges the tensor product construction and the corresponding notion of stochastic independence. But there are a multiplicity of other possibilities whose mathematical and physical investigation is only at the beginning. In particular, to any notion of statistical independence it is canonically associated a corresponding notion of entanglement.

16. Theoretical Aspects of Magnetic Fields for Gamma Ray Bursts

Hanami, Hitoshi

We propose magnetic cannon ball mechanism in which the collapse of a magnetosphere onto a black hole can generate strong outward Poynting flux which drives a baryon-free fireball called the magnetic cannon ball. In the early stage, the magnetic fields in the cannon ball can prepare the explanation for the cycrotoron absorptions observed by GINGA. The magnetic cannon ball can drive, in general, a relativistic outflow which interacts with the interstellar matter and forms a shock. The magnetic field in the shock approximately equal to 104 G can induce the synchrotron radiations with peaks at approximately equal to 10^2 keV observed. This magnetic field in the cannon ball can also confine the high energy protons (gamma_p > 30) which are required for delayed photons (>25 GeV) following a burst on 1994 February 17. Accretion induced collapse of a white dwarf of > 109 G, merger of a close binary and failed type Ib supernovae are possible scenarios even without the rotation of the central object. This mechanism works at the final phase of gravitational collapse even after a neutrino driven fireball proposed in most scenarios for gamma ray bursts. Twice bursts, which consist of primary neutrino driven fireball and secondary magnetic cannon ball can be induced sometime, can be explained in this model. It suggests that the magnetic cannon ball works some parts in multiple populations and delayed or multiple burst events. The final remnant in the model should be a black hole. It implies that any gamma ray bursts can have no optical counter part if they do not have a companion in a binary.

17. Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization

Mentink-Vigier, Frederic; Akbey, Ümit; Oschkinat, Hartmut; Vega, Shimon; Feintuch, Akiva

2015-09-01

Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160 K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea -eb - n } during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle

18. Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization.

PubMed

Mentink-Vigier, Frederic; Akbey, Ümit; Oschkinat, Hartmut; Vega, Shimon; Feintuch, Akiva

2015-09-01

Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea-eb-n} during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle. This

19. Explaining Facial Imitation: A Theoretical Model

PubMed Central

Meltzoff, Andrew N.; Moore, M. Keith

2013-01-01

A long-standing puzzle in developmental psychology is how infants imitate gestures they cannot see themselves perform (facial gestures). Two critical issues are: (a) the metric infants use to detect cross-modal equivalences in human acts and (b) the process by which they correct their imitative errors. We address these issues in a detailed model of the mechanisms underlying facial imitation. The model can be extended to encompass other types of imitation. The model capitalizes on three new theoretical concepts. First, organ identification is the means by which infants relate parts of their own bodies to corresponding ones of the adult’s. Second, body babbling (infants’ movement practice gained through self-generated activity) provides experience mapping movements to the resulting body configurations. Third, organ relations provide the metric by which infant and adult acts are perceived in commensurate terms. In imitating, infants attempt to match the organ relations they see exhibited by the adults with those they feel themselves make. We show how development restructures the meaning and function of early imitation. We argue that important aspects of later social cognition are rooted in the initial cross-modal equivalence between self and other found in newborns. PMID:24634574

20. Empirical and theoretical models of terrestrial trapped radiation

SciTech Connect

Panasyuk, M.I.

1996-07-01

A survey of current Skobeltsyn Institute of Nuclear Physics, Moscow State University (INP MSU) empirical and theoretical models of particles (electrons, protons and heavier irons) of the Earth{close_quote}s radiation belts developed to date is presented. Results of intercomparison of the different models as well as comparison with experimental data are reported. Aspects of further development of radiation condition modelling in near-Earth space are discussed. {copyright} {ital 1996 American Institute of Physics.}

1. APPRENTICESHIP--A THEORETICAL MODEL.

ERIC Educational Resources Information Center

DUFTY, NORMAN F.

AN INQUIRY INTO RECRUITMENT OF APPRENTICES TO SKILLED TRADES IN WESTERN AUSTRALIA INDICATED LITTLE CORRELATION BETWEEN THE NUMBER OF NEW APPRENTICES AND THE LEVEL OF INDUSTRIAL EMPLOYMENT OR THE TOTAL NUMBER OF APPRENTICES. THIS ARTICLE ATTEMPTS TO OUTLINE A MATHEMATICAL MODEL OF AN APPRENTICESHIP SYSTEM AND DISCUSS ITS IMPLICATIONS. THE MODEL, A…

2. Theoretical Modelling of Hot Stars

Najarro, F.; Hillier, D. J.; Figer, D. F.; Geballe, T. R.

1999-06-01

Recent progress towards model atmospheres for hot stars is discussed. A new generation of NLTE wind blanketed models, together with high S/N spectra of the hot star population in the central parsec, which are currently being obtained, will allow metal abundance determinations (Fe, Si, Mg, Na, etc). Metallicity studies of hot stars in the IR will provide major constraints not only on the theory of evolution of massive stars but also on our efforts to solve the puzzle of the central parsecs of the Galaxy. Preliminary results suggest that the metallicity of the Pistol Star is 3 times solar, thus indicating strong chemical enrichment of the gas in the Galactic Center.

3. Theoretical Modeling of Interstellar Chemistry

NASA Technical Reports Server (NTRS)

Charnley, Steven

2009-01-01

The chemistry of complex interstellar organic molecules will be described. Gas phase processes that may build large carbon-chain species in cold molecular clouds will be summarized. Catalytic reactions on grain surfaces can lead to a large variety of organic species, and models of molecule formation by atom additions to multiply-bonded molecules will be presented. The subsequent desorption of these mixed molecular ices can initiate a distinctive organic chemistry in hot molecular cores. The general ion-molecule pathways leading to even larger organics will be outlined. The predictions of this theory will be compared with observations to show how possible organic formation pathways in the interstellar medium may be constrained. In particular, the success of the theory in explaining trends in the known interstellar organics, in predicting recently-detected interstellar molecules, and, just as importantly, non-detections, will be discussed.

4. Theoretical models of helicopter rotor noise

NASA Technical Reports Server (NTRS)

Hawkings, D. L.

1978-01-01

For low speed rotors, it is shown that unsteady load models are only partially successful in predicting experimental levels. A theoretical model is presented which leads to the concept of unsteady thickness noise. This gives better agreement with test results. For high speed rotors, it is argued that present models are incomplete and that other mechanisms are at work. Some possibilities are briefly discussed.

5. Aspects of skeletal muscle modelling.

PubMed Central

Epstein, Marcelo; Herzog, Walter

2003-01-01

The modelling of skeletal muscle raises a number of philosophical questions, particularly in the realm of the relationship between different possible levels of representation and explanation. After a brief incursion into this area, a list of desiderata is proposed as a guiding principle for the construction of a viable model, including: comprehensiveness, soundness, experimental consistency, predictive ability and refinability. Each of these principles is illustrated by means of simple examples. The presence of internal constraints, such as incompressibility, may lead to counterintuitive results. A one-panel example is exploited to advocate the use of the principle of virtual work as the ideal tool to deal with these situations. The question of stability in the descending limb of the force-length relation is addressed and a purely mechanical analogue is suggested. New experimental results confirm the assumption that fibre stiffness is positive even in the descending limb. The indeterminacy of the force-sharing problem is traditionally resolved by optimizing a, presumably, physically meaningful target function. After presenting some new results in this area, based on a separation theorem, it is suggested that a more fundamental approach to the problem is the abandoning of optimization criteria in favour of an explicit implementation of activation criteria. PMID:14561335

6. Revealing membrane potential by advanced impedance spectroscopy: theoretical and experimental aspects

Gheorghiu, M.; Bratu, D.; Olaru, A.; Polonschii, C.; Gheorghiu, E.

2013-04-01

In spite of recent advancement of novel optical and electrical techniques, availability of non-invasive, label-free methods to assess membrane potential of living cells is still an open issue. The theory linking membrane potential to the low frequency α dispersion exhibited by suspensions of spherical shelled particles (presenting a net charge distribution on the inner side of the shell) has been pioneered in our previous studies with emphasis on the permittivity spectra. We now report on both theoretical and experimental aspects showing that whereas α dispersion is related to a rather large variation exhibited by the permittivity spectrum the decrement presented by impedance magnitude spectrum is either extremely small, or occurs (for large cells) at very low frequencies (~mHz) explaining the lack of experimental bioimpedance data on the matter. Based on the microscopic model we indicate that an appropriate design of the experiment may enable access to membrane potential as well as to other relevant parameters when investigating living cells and charged lipid vesicles. We discuss the effect on the low frequency of permittivity and impedance spectra of: I. Parameters pertaining to cell membrane i.e. (i) membrane potential, (ii) size of the cells/vesicles, (iii) conductivity; II. Conductivity of the outer medium. A novel measuring set-up has recently been developed within the International Centre of Biodynamics allowing for sensitive low frequency (~10mHz) four point (bio)impedance assays. Its capability to test theoretical predictions is reported as well. The far reaching implications of this study applicability for life sciences (noninvasive access to the dynamics of relevant cell parameters) as well as for biosensing applications, e.g. assess the cytotoxicity of a wide range of stimuli, will be outlined.

7. Dimensions of Black Suicide: A Theoretical Model.

ERIC Educational Resources Information Center

Davis, Robert; Short, James F., Jr.

This paper develops a theoretical model of sucide, based on the theory of "external restraints" proposed by previous researchers, A.F. Henry and J.F. Short, Jr., and applies the model to a study of black suicides in Orleans Parish, Louisiana. The focus of the study is on the complexity of relationships between dimensions of black suicide and the…

8. Theoretical analysis of the electrical aspects of the basic electro-impulse problem in aircraft de-icing applications

NASA Technical Reports Server (NTRS)

Henderson, R. A.; Schrag, R. L.

1986-01-01

A summary of modeling the electrical system aspects of a coil and metal target configuration resembling a practical electro-impulse deicing (EIDI) installation, and a simple circuit for providing energy to the coil, was presented. The model was developed in sufficient theoretical detail to allow the generation of computer algorithms for the current in the coil, the magnetic induction on both surfaces of the target, the force between the coil and target, and the impulse delivered to the target. These algorithms were applied to a specific prototype EIDI test system for which the current, magnetic fields near the target surfaces, and impulse were previously measured.

9. Hybrid quantum teleportation: A theoretical model

SciTech Connect

Takeda, Shuntaro; Mizuta, Takahiro; Fuwa, Maria; Yoshikawa, Jun-ichi; Yonezawa, Hidehiro; Furusawa, Akira

2014-12-04

Hybrid quantum teleportation – continuous-variable teleportation of qubits – is a promising approach for deterministically teleporting photonic qubits. We propose how to implement it with current technology. Our theoretical model shows that faithful qubit transfer can be achieved for this teleportation by choosing an optimal gain for the teleporter’s classical channel.

10. Hybrid rocket engine, theoretical model and experiment

Chelaru, Teodor-Viorel; Mingireanu, Florin

2011-06-01

The purpose of this paper is to build a theoretical model for the hybrid rocket engine/motor and to validate it using experimental results. The work approaches the main problems of the hybrid motor: the scalability, the stability/controllability of the operating parameters and the increasing of the solid fuel regression rate. At first, we focus on theoretical models for hybrid rocket motor and compare the results with already available experimental data from various research groups. A primary computation model is presented together with results from a numerical algorithm based on a computational model. We present theoretical predictions for several commercial hybrid rocket motors, having different scales and compare them with experimental measurements of those hybrid rocket motors. Next the paper focuses on tribrid rocket motor concept, which by supplementary liquid fuel injection can improve the thrust controllability. A complementary computation model is also presented to estimate regression rate increase of solid fuel doped with oxidizer. Finally, the stability of the hybrid rocket motor is investigated using Liapunov theory. Stability coefficients obtained are dependent on burning parameters while the stability and command matrixes are identified. The paper presents thoroughly the input data of the model, which ensures the reproducibility of the numerical results by independent researchers.

11. Theoretical models of neural circuit development.

PubMed

Simpson, Hugh D; Mortimer, Duncan; Goodhill, Geoffrey J

2009-01-01

Proper wiring up of the nervous system is critical to the development of organisms capable of complex and adaptable behaviors. Besides the many experimental advances in determining the cellular and molecular machinery that carries out this remarkable task precisely and robustly, theoretical approaches have also proven to be useful tools in analyzing this machinery. A quantitative understanding of these processes can allow us to make predictions, test hypotheses, and appraise established concepts in a new light. Three areas that have been fruitful in this regard are axon guidance, retinotectal mapping, and activity-dependent development. This chapter reviews some of the contributions made by mathematical modeling in these areas, illustrated by important examples of models in each section. For axon guidance, we discuss models of how growth cones respond to their environment, and how this environment can place constraints on growth cone behavior. Retinotectal mapping looks at computational models for how topography can be generated in populations of neurons based on molecular gradients and other mechanisms such as competition. In activity-dependent development, we discuss theoretical approaches largely based on Hebbian synaptic plasticity rules, and how they can generate maps in the visual cortex very similar to those seen in vivo. We show how theoretical approaches have substantially contributed to the advancement of developmental neuroscience, and discuss future directions for mathematical modeling in the field. PMID:19427515

12. Simple theoretical models for composite rotor blades

NASA Technical Reports Server (NTRS)

Valisetty, R. R.; Rehfield, L. W.

1984-01-01

The development of theoretical rotor blade structural models for designs based upon composite construction is discussed. Care was exercised to include a member of nonclassical effects that previous experience indicated would be potentially important to account for. A model, representative of the size of a main rotor blade, is analyzed in order to assess the importance of various influences. The findings of this model study suggest that for the slenderness and closed cell construction considered, the refinements are of little importance and a classical type theory is adequate. The potential of elastic tailoring is dramatically demonstrated, so the generality of arbitrary ply layup in the cell wall is needed to exploit this opportunity.

13. Theoretical modeling for the stereo mission

Aschwanden, Markus J.; Burlaga, L. F.; Kaiser, M. L.; Ng, C. K.; Reames, D. V.; Reiner, M. J.; Gombosi, T. I.; Lugaz, N.; Manchester, W.; Roussev, I. I.; Zurbuchen, T. H.; Farrugia, C. J.; Galvin, A. B.; Lee, M. A.; Linker, J. A.; Mikić, Z.; Riley, P.; Alexander, D.; Sandman, A. W.; Cook, J. W.; Howard, R. A.; Odstrčil, D.; Pizzo, V. J.; Kóta, J.; Liewer, P. C.; Luhmann, J. G.; Inhester, B.; Schwenn, R. W.; Solanki, S. K.; Vasyliunas, V. M.; Wiegelmann, T.; Blush, L.; Bochsler, P.; Cairns, I. H.; Robinson, P. A.; Bothmer, V.; Kecskemety, K.; Llebaria, A.; Maksimovic, M.; Scholer, M.; Wimmer-Schweingruber, R. F.

2008-04-01

We summarize the theory and modeling efforts for the STEREO mission, which will be used to interpret the data of both the remote-sensing (SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The modeling includes the coronal plasma, in both open and closed magnetic structures, and the solar wind and its expansion outwards from the Sun, which defines the heliosphere. Particular emphasis is given to modeling of dynamic phenomena associated with the initiation and propagation of coronal mass ejections (CMEs). The modeling of the CME initiation includes magnetic shearing, kink instability, filament eruption, and magnetic reconnection in the flaring lower corona. The modeling of CME propagation entails interplanetary shocks, interplanetary particle beams, solar energetic particles (SEPs), geoeffective connections, and space weather. This review describes mostly existing models of groups that have committed their work to the STEREO mission, but is by no means exhaustive or comprehensive regarding alternative theoretical approaches.

14. Propagation studies using a theoretical ionosphere model

NASA Technical Reports Server (NTRS)

Lee, M.

1973-01-01

The mid-latitude ionospheric and neutral atmospheric models are coupled with an advanced three dimensional ray tracing program to see what success would be obtained in predicting the wave propagation conditions and to study to what extent the use of theoretical ionospheric models is practical. The Penn State MK 1 ionospheric model, the Mitra-Rowe D region model, and the Groves' neutral atmospheric model are used throughout this work to represent the real electron densities and collision frequencies. The Faraday rotation and differential Doppler velocities from satellites, the propagation modes for long distance high frequency propagation, the group delays for each mode, the ionospheric absorption, and the spatial loss are all predicted.

15. Theoretical models for polarimetric radar clutter

NASA Technical Reports Server (NTRS)

Borgeaud, M.; Shin, R. T.; Kong, J. A.

1987-01-01

The Mueller matrix and polarization covariance matrix are described for polarimetric radar systems. The clutter is modeled by a layer of random permittivity, described by a three-dimensional correlation function, with variance, and horizontal and vertical correlation lengths. This model is applied, using the wave theory with Born approximations carried to the second order, to find the backscattering elements of the polarimetric matrices. It is found that 8 out of 16 elements of the Mueller matrix are identically zero, corresponding to a covariance matrix with four zero elements. Theoretical predictions are matched with experimental data for vegetation fields.

16. Research Developments in Li-Paczyński Novae (I): Theoretical Aspect

Shan-qin, Wang; Zi-gao, Dai; Xue-feng, Wu

2016-04-01

The neutron-rich matter ejected by compact object mergers (neutron star-neutron star merger and neutron star-black hole merger) provides one of the most important environments for the syntheses of r-process elements. In recent seventeen years, theoretical studies suggested that the energy produced during the decay of r-process elements will form optical/near infrared (NIR) radiations after thermalization. This type of optical/NIR transients are called Li-Paczyński novae, or LP-novae for short. Since the typical peak brightness of LP-novae is ∼1000 times brighter than that of a typical nova, they are also called Kilonovae. Besides, both theoretical and observational studies have showed, directly or indirectly, that under certain conditions, the compact object mergers can produce the gamma-ray bursts with a rather short duration of T90 ≤ 2s (SGRBs for short), and most SGRBs may come from compact object mergers. After the identification of SGRB afterglows, dedicated searches of the LP-novae associated with SGRBs have been taken. In this review we present the theoretical progress of LP-novae in recent seventeen years, and the observational aspect will appear in a upcoming paper.

17. Theoretical models for supercritical fluid extraction.

PubMed

Huang, Zhen; Shi, Xiao-Han; Jiang, Wei-Juan

2012-08-10

For the proper design of supercritical fluid extraction processes, it is essential to have a sound knowledge of the mass transfer mechanism of the extraction process and the appropriate mathematical representation. In this paper, the advances and applications of kinetic models for describing supercritical fluid extraction from various solid matrices have been presented. The theoretical models overviewed here include the hot ball diffusion, broken and intact cell, shrinking core and some relatively simple models. Mathematical representations of these models have been in detail interpreted as well as their assumptions, parameter identifications and application examples. Extraction process of the analyte solute from the solid matrix by means of supercritical fluid includes the dissolution of the analyte from the solid, the analyte diffusion in the matrix and its transport to the bulk supercritical fluid. Mechanisms involved in a mass transfer model are discussed in terms of external mass transfer resistance, internal mass transfer resistance, solute-solid interactions and axial dispersion. The correlations of the external mass transfer coefficient and axial dispersion coefficient with certain dimensionless numbers are also discussed. Among these models, the broken and intact cell model seems to be the most relevant mathematical model as it is able to provide realistic description of the plant material structure for better understanding the mass-transfer kinetics and thus it has been widely employed for modeling supercritical fluid extraction of natural matters. PMID:22560346

NASA Technical Reports Server (NTRS)

Morey-Holton, Emily R.; Globus, Ruth K.

2002-01-01

Since its inception at the National Aeronautics and Space Administration (NASA) Ames Research Center in the mid-1970s, many laboratories around the world have used the rat hindlimb unloading model to simulate weightlessness and to study various aspects of musculoskeletal loading. In this model, the hindlimbs of rodents are elevated to produce a 30 degrees head-down tilt, which results in a cephalad fluid shift and avoids weightbearing by the hindquarters. Although several reviews have described scientific results obtained with this model, this is the first review to focus on the technical aspects of hindlimb unloading. This review includes a history of the technique, a brief comparison with spaceflight data, technical details, extension of the model to mice, and other important technical considerations (e.g., housing, room temperature, unloading angle, the potential need for multiple control groups, age, body weight, the use of the forelimb tissues as internal controls, and when to remove animals from experiments). This paper is intended as a reference for researchers, reviewers of manuscripts, and institutional animal care and use committees. Over 800 references, related to the hindlimb unloading model, can be accessed via the electronic version of this article.

19. A Theoretical Model of Water and Trade

Dang, Q.; Konar, M.; Reimer, J.; Di Baldassarre, G.; Lin, X.; Zeng, R.

2015-12-01

Water is an essential factor of agricultural production. Agriculture, in turn, is globalized through the trade of food commodities. In this paper, we develop a theoretical model of a small open economy that explicitly incorporates water resources. The model emphasizes three tradeoffs involving water decision-making that are important yet not always considered within the existing literature. One tradeoff focuses on competition for water among different sectors when there is a shock to one of the sectors only, such as trade liberalization and consequent higher demand for the product. A second tradeoff concerns the possibility that there may or may not be substitutes for water, such as increased use of sophisticated irrigation technology as a means to increase crop output in the absence of higher water availability. A third tradeoff explores the possibility that the rest of the world can be a source of supply or demand for a country's water-using products. A number of propositions are proven. For example, while trade liberalization tends to increase water use, increased pressure on water supplies can be moderated by way of a tax that is derivable with observable economic phenomena. Another example is that increased riskiness of water availability tends to cause water users to use less water than would be the case under profit maximization. These theoretical model results generate hypotheses that can be tested empirically in future work.

20. Requirements for theoretical models of outflows

NASA Technical Reports Server (NTRS)

Linsky, Jeffrey L.

1988-01-01

Recent observational and theoretical investigations of astrophysical mass outflows are reviewed, with a focus on the basic physical principles. Specific limitations on the observational data and their interpretation are listed and discussed. Modeling problems considered include the role of the critical point in determining the mass-loss rate and terminal velocity, the physical processes controlling density at the critical point, the possible coexistence of multiple mass-loss mechanisms, time scales, instabilities and phase changes, multiphase atmospheres and winds, the definition of geometries, the role of the environment, explosive transient events, stochastic phenomena, mode-mode coupling and damping processes, departures from ionization equilibrium, and nonthermal phenomena.

1. A theoretical model of water and trade

Dang, Qian; Konar, Megan; Reimer, Jeffrey J.; Di Baldassarre, Giuliano; Lin, Xiaowen; Zeng, Ruijie

2016-03-01

Water is an essential input for agricultural production. Agriculture, in turn, is globalized through the trade of agricultural commodities. In this paper, we develop a theoretical model that emphasizes four tradeoffs involving water-use decision-making that are important yet not always considered in a consistent framework. One tradeoff focuses on competition for water among different economic sectors. A second tradeoff examines the possibility that certain types of agricultural investments can offset water use. A third tradeoff explores the possibility that the rest of the world can be a source of supply or demand for a country's water-using commodities. The fourth tradeoff concerns how variability in water supplies influences farmer decision-making. We show conditions under which trade liberalization affect water use. Two policy scenarios to reduce water use are evaluated. First, we derive a target tax that reduces water use without offsetting the gains from trade liberalization, although important tradeoffs exist between economic performance and resource use. Second, we show how subsidization of water-saving technologies can allow producers to use less water without reducing agricultural production, making such subsidization an indirect means of influencing water use decision-making. Finally, we outline conditions under which riskiness of water availability affects water use. These theoretical model results generate hypotheses that can be tested empirically in future work.

2. Theoretical Models of the Galactic Bulge

Shen, Juntai; Li, Zhao-Yu

Near infrared images from the COBE satellite presented the first clear evidence that our Milky Way galaxy contains a boxy shaped bulge. Recent years have witnessed a gradual paradigm shift in the formation and evolution of the Galactic bulge. Bulges were commonly believed to form in the dynamical violence of galaxy mergers. However, it has become increasingly clear that the main body of the Milky Way bulge is not a classical bulge made by previous major mergers, instead it appears to be a bar seen somewhat end-on. The Milky Way bar can form naturally from a precursor disc and thicken vertically by the internal firehose/buckling instability, giving rise to the boxy appearance. This picture is supported by many lines of evidence, including the asymmetric parallelogram shape, the strong cylindrical rotation (i.e., nearly constant rotation regardless of the height above the disc plane), the existence of an intriguing X-shaped structure in the bulge, and perhaps the metallicity gradients. We review the major theoretical models and techniques to understand the Milky Way bulge. Despite the progresses in recent theoretical attempts, a complete bulge formation model that explains the full kinematics and metallicity distribution is still not fully understood. Upcoming large surveys are expected to shed new light on the formation history of the Galactic bulge.

3. Modeling generic aspects of ideal fibril formation

Michel, D.

2016-01-01

Many different proteins self-aggregate into insoluble fibrils growing apically by reversible addition of elementary building blocks. But beyond this common principle, the modalities of fibril formation are very disparate, with various intermediate forms which can be reshuffled by minor modifications of physico-chemical conditions or amino-acid sequences. To bypass this complexity, the multifaceted phenomenon of fibril formation is reduced here to its most elementary principles defined for a linear prototype of fibril. Selected generic features, including nucleation, elongation, and conformational recruitment, are modeled using minimalist hypotheses and tools, by separating equilibrium from kinetic aspects and in vitro from in vivo conditions. These reductionist approaches allow to bring out known and new rudiments, including the kinetic and equilibrium effects of nucleation, the dual influence of elongation on nucleation, the kinetic limitations on nucleation and fibril numbers, and the accumulation of complexes in vivo by rescue from degradation. Overlooked aspects of these processes are also pointed: the exponential distribution of fibril lengths can be recovered using various models because it is attributable to randomness only. It is also suggested that the same term "critical concentration" is used for different things, involved in either nucleation or elongation.

4. Modeling generic aspects of ideal fibril formation.

PubMed

Michel, D

2016-01-21

Many different proteins self-aggregate into insoluble fibrils growing apically by reversible addition of elementary building blocks. But beyond this common principle, the modalities of fibril formation are very disparate, with various intermediate forms which can be reshuffled by minor modifications of physico-chemical conditions or amino-acid sequences. To bypass this complexity, the multifaceted phenomenon of fibril formation is reduced here to its most elementary principles defined for a linear prototype of fibril. Selected generic features, including nucleation, elongation, and conformational recruitment, are modeled using minimalist hypotheses and tools, by separating equilibrium from kinetic aspects and in vitro from in vivo conditions. These reductionist approaches allow to bring out known and new rudiments, including the kinetic and equilibrium effects of nucleation, the dual influence of elongation on nucleation, the kinetic limitations on nucleation and fibril numbers, and the accumulation of complexes in vivo by rescue from degradation. Overlooked aspects of these processes are also pointed: the exponential distribution of fibril lengths can be recovered using various models because it is attributable to randomness only. It is also suggested that the same term "critical concentration" is used for different things, involved in either nucleation or elongation. PMID:26801045

5. A Theoretical Model of Water and Trade

Dang, Qian; Zeng, Ruije; Ling, Xiaowen; Di Baldassarre, Giuliano; Konar, Megan

2014-05-01

Water is an essential factor of agricultural production. Agriculture, in turn, is globalized through the trade of food commodities. There is an extensive literature detailing the direct and local relationships between water and agricultural production. Here, we expand upon this important literature to understand how the globalized food economy interacts with water resources. In particular, we seek to understand the following questions: What is the impact of agricultural trade on water resources? How do water resources impact agricultural trade? Thus, we aim to explore the bidirectional feedbacks between water resources and food trade, using a socio-hydrologic framework. To do this, we develop a theoretical model of international trade that explicitly incorporates water resources.

6. Models in Educational Administration: Revisiting Willower's "Theoretically Oriented" Critique

ERIC Educational Resources Information Center

Newton, Paul; Burgess, David; Burns, David P.

2010-01-01

Three decades ago, Willower (1975) argued that much of what we take to be theory in educational administration is in fact only theoretically oriented. If we accept Willower's assessment of the field as true, what implications does this statement hold for the academic study and practical application of the theoretically oriented aspects of our…

7. Modeling aspects of the surface reconstruction problem

Toth, Charles K.; Melykuti, Gabor

1994-08-01

The ultimate goal of digital photogrammetry is to automatically produce digital maps which may in turn form the basis of GIS. Virtually all work in surface reconstruction deals with various kinds of approximations and constraints that are applied. In this paper we extend these concepts in various ways. For one, matching is performed in object space. Thus, matching and densification (modeling) is performed in the same reference system. Another extension concerns the solution of the second sub-problem. Rather than simply densifying (interpolating) the surface, we propose to model it. This combined top-down and bottom-up approach is performed in scale space, whereby the model is refined until compatibility between the data and expectations is reached. The paper focuses on the modeling aspects of the surface reconstruction problem. Obviously, the top-down and bottom-up model descriptions ought to be in a form which allows the generation and verification of hypotheses. Another crucial question is the degree of a priori scene knowledge necessary to constrain the solution space.

8. Information-Theoretic Perspectives on Geophysical Models

Nearing, Grey

2016-04-01

practice of science (except by Gong et al., 2013, whose fundamental insight is the basis for this talk), and here I offer two examples of practical methods that scientists might use to approximately measure ontological information. I place this practical discussion in the context of several recent and high-profile experiments that have found that simple out-of-sample statistical models typically (vastly) outperform our most sophisticated terrestrial hydrology models. I offer some perspective on several open questions about how to use these findings to improve our models and understanding of these systems. Cartwright, N. (1983) How the Laws of Physics Lie. New York, NY: Cambridge Univ Press. Clark, M. P., Kavetski, D. and Fenicia, F. (2011) 'Pursuing the method of multiple working hypotheses for hydrological modeling', Water Resources Research, 47(9). Cover, T. M. and Thomas, J. A. (1991) Elements of Information Theory. New York, NY: Wiley-Interscience. Cox, R. T. (1946) 'Probability, frequency and reasonable expectation', American Journal of Physics, 14, pp. 1-13. Csiszár, I. (1972) 'A Class of Measures of Informativity of Observation Channels', Periodica Mathematica Hungarica, 2(1), pp. 191-213. Davies, P. C. W. (1990) 'Why is the physical world so comprehensible', Complexity, entropy and the physics of information, pp. 61-70. Gong, W., Gupta, H. V., Yang, D., Sricharan, K. and Hero, A. O. (2013) 'Estimating Epistemic & Aleatory Uncertainties During Hydrologic Modeling: An Information Theoretic Approach', Water Resources Research, 49(4), pp. 2253-2273. Jaynes, E. T. (2003) Probability Theory: The Logic of Science. New York, NY: Cambridge University Press. Nearing, G. S. and Gupta, H. V. (2015) 'The quantity and quality of information in hydrologic models', Water Resources Research, 51(1), pp. 524-538. Popper, K. R. (2002) The Logic of Scientific Discovery. New York: Routledge. Van Horn, K. S. (2003) 'Constructing a logic of plausible inference: a guide to cox's theorem

9. Naturalness of unknown physics: Theoretical models and experimental signatures

Kilic, Can

In the last few decades collider experiments have not only spectacularly confirmed the predictions of the Standard Model but also have not revealed any direct evidence for new physics beyond the SM, which has led theorists to devise numerous models where the new physics couples weakly to the SM or is simply beyond the reach of past experiments. While phenomenologically viable, many such models appear finely tuned, even contrived. This work illustrates three attempts at coming up with explanations to fine-tunings we observe in the world around us, such as the gauge hierarchy problem or the cosmological constant problem, emphasizing both the theoretical aspects of model building as well as possible experimental signatures. First we investigate the "Little Higgs" mechanism and work on a specifical model, the "Minimal Moose" to highlight its impact on precision observables in the SM, and illustrate that it does not require implausible fine-tuning. Next we build a supersymmetric model, the "Fat Higgs", with an extended gauge structure which becomes confining. This model, aside from naturally preserving the unification of the SM gauge couplings at high energies, also makes it possible to evade the bounds on the lightest Higgs boson mass which are quite restrictive in minimal SUSY scenarios. Lastly we take a look at a possible resolution of the cosmological constant problem through the mechanism of "Ghost Condensation" and dwell on astrophysical observables from the Lorentz Violating sector in this model. We use current experimental data to constrain the coupling of this sector to the SM.

10. Theoretical and numerical aspects of fluid-saturated elasto-plastic soils

SciTech Connect

Ehlers, W.

1995-12-31

The theoretical and numerical treatment of fluid-saturated porous solid materials generally falls into the category of porous media models, which are described within the framework of the classical theory of mixtures extended by the concept of volume fractions (porous media theories). In particular, this concept allows for the description of saturated, unsaturated and empty porous matrix materials, thus offering a well-founded theoretical background for a lot of engineering problems occurring, for instance, in the fields of geomechanics (soil and rock mechanics as well as glacier and rock ice mechanics), oil producing industries, sintering technologies, biomechanics, etc. In the present contribution, theoretical and numerical studies are outlined to describe a two-phase material composed of an incompressible elasto-plastic soil matrix saturated by an incompressible viscous pore fluid. In this context, the phenomenon of phase incompressibility is well known as a microscopic effect not implying bulk incompressibility in the macro regime. This is seen from the fact that even if the material density functions of the individual constituents are constant during deformation, the corresponding bulk densities can still change through changes in the volume fractions. Within the framework of a pure mechanical theory, constitutive equations are given for both the solid and the fluid partial stress tensors and for the interaction force acting between the two materials. Concerning the porous soil matrix, the elastic properties are described by an elasticity law of Hookean type, while the plastic range is governed by a {open_quote}single surface{close_quote} yield function exhibiting a smooth and closed shape in the principal stress space together with a non-associated flow rule. The viscosity effects of the pore fluid are included in the fluid stress tensor and in the drag force.

11. A Review on the Wettability of Dental Implant Surfaces: Theoretical and Experimental Aspects

PubMed Central

Rupp, Frank; Gittens, Rolando A.; Scheideler, Lutz; Marmur, Abraham; Boyan, Barbara D.; Schwartz, Zvi; Geis-Gerstorfer, Jürgen

2014-01-01

The surface wettability of biomaterials determines the biological cascade of events at the biomaterial/host interface. Wettability is modulated by surface characteristics, such as surface chemistry and surface topography. However, the design of current implant surfaces focuses mainly on specific micro- and nanotopographical features and is still far from predicting the concomitant wetting behavior. There is an increasing interest in understanding the wetting mechanisms of implant surfaces and the role of wettability on the biological response at the implant/bone or implant/soft tissue interface. Fundamental knowledge related to the influence of surface roughness (i.e., a quantification of surface topography) on titanium and titanium alloy surface wettability, and the different associated wetting regimes, can improve our understanding of the role of wettability of rough implant surfaces on the biological outcome. Such an approach has been applied to biomaterial surfaces only in a limited way. Focusing on titanium dental and orthopaedic implants, the present study reviews the current knowledge on the wettability of biomaterial surfaces, encompassing basic and applied aspects that include measurement techniques, thermodynamic aspects of wetting, and models predicting topographical and roughness effects on the wetting behavior. PMID:24590162

12. Assessing a Theoretical Model on EFL College Students

ERIC Educational Resources Information Center

Chang, Yu-Ping

2011-01-01

This study aimed to (1) integrate relevant language learning models and theories, (2) construct a theoretical model of college students' English learning performance, and (3) assess the model fit between empirically observed data and the theoretical model proposed by the researchers of this study. Subjects of this study were 1,129 Taiwanese EFL…

13. Theoretical aspects of fluoride air contaminant formation in aluminium smelter potrooms.

PubMed

L'vov, Boris V; Polzik, Leonid K; Weinbruch, Stephan; Ellingsen, Dag G; Thomassen, Yngvar

2005-05-01

The amount of particulate fluorides evolved from aluminium electrolysis cells is not entirely accounted for by the fluorides entrained in the anode gas. The largest additional source of particulate fluoride formation is by direct evaporation of fluorides into the anode gas stream and subsequent condensation on the drops of electrolyte generated in the process of bubble burst. A theoretical model was used for the calculation of the main physical parameters responsible for the formation of particle nuclei when the hot anode-gas is mixed with ambient air. The results of these calculations are in agreement with experimental observations reported in the literature. In particular, the size distribution, composition and morphology of the nano-particles support the theory of a vapour condensation mechanism under conditions of extreme supersaturation, but further studies are necessary. PMID:15877162

14. Theoretical Models of Parental HIV Disclosure: A Critical Review

PubMed Central

Qiao, Shan; Li, Xiaoming; Stanton, Bonita

2012-01-01

This review critically examined three major theoretical models related to parental HIV disclosure (i.e., the Four-Phase Model, the Disclosure Decision Making Model, and the Disclosure Process Model), and the existing studies that could provide empirical support to these models or their components. For each model, we briefly reviewed its theoretical background, described its components and or mechanisms, and discussed its strengths and limitations. The existing empirical studies supported most theoretical components in these models. However, hypotheses related to the mechanisms proposed in the models have not yet tested due to a lack of empirical evidence. This review also synthesized alternative theoretical perspectives and new issues in disclosure research and clinical practice that may challenge the existing models. The current review underscores the importance of including components related to social and cultural contexts in theoretical frameworks, and calls for more adequately designed empirical studies in order to test and refine existing theories and to develop new ones. PMID:22866903

15. Theoretical and observational aspects of convection generated internal atmospheric gravity waves

Thokuluwa, Ramkumar

2012-07-01

Even though atmospheric gravity waves generated from convection contributes significantly to the middle atmospheric circulation and momentum balances, yet they have to be fully parameterized in general circulation models. The major constraint comes because of inadequacies in the exact measurement of four dimensional (including time) latent heating of the atmosphere occurring through condensation of water vapor. Satellite like TRMM measures the latent heating of the atmosphere but it is sparse in nature (both spatial and time) because of the continual shift in the azimuths of orbital plane of the satellite about the earth. Doppler weather radar is a good alternative in this sense but the poor signal to noise ratio of echoes with distance from the center of the radar and other simpler assumptions employed in deriving the latent heating, through using empirical relationship between the radar echoes and rain drop size distribution, rain rate and other precipitation characteristics, makes the estimation of latent heating of the atmospheric highly ambiguous. In such cases, it is essential to make comparative studies between theoretically estimated and observationally made convection generated gravity waves in the process of parameterizing the gravity waves. Here we report the theoretically estimated spectral characteristics of convection generated gravity waves and their comparison with observations made using Doppler weather radar (DWR) and MST radar (VHF, 53 MHz), which are located in the eastern coast of Southern India adjacent to the Bay of Bengal where tropical cyclones are forming. The determined latent heating of the atmosphere, using the DWR measurements, will be compared to that determined by the TRMM and other satellites. This determined heating will be utilized as inputs for the thermodynamics equations of high frequency gravity waves, the propagating nature of which can be determined using the MST radar at NARL, Gadanki. As this radar can give wind

16. Theoretical Models and QSRR in Retention Modeling of Eight Aminopyridines.

PubMed

Tumpa, Anja; Kalinić, Marko; Jovanović, Predrag; Erić, Slavica; Rakić, Tijana; Jančić-Stojanović, Biljana; Medenica, Mirjana

2016-03-01

In this article, retention modeling of eight aminopyridines (synthesized and characterized at the Faculty of Pharmacy) in reversed-phase high performance liquid chromatography (RP-HPLC) was performed. No data related to their retention in the RP-HPLC system were found. Knowing that, it was recognized as very important to describe their retention behavior. The influences of pH of the mobile phase and the organic modifier content on the retention factors were investigated. Two theoretical models for the dependence of retention factor of organic modifier content were tested. Then, the most reliable and accurate prediction of log k was created, testing multiple linear regression model-quantitative structure-retention relationships (MLR-QSRR) and support vector regression machine-quantitative structure-retention relationships (SVM-QSRR). Initially, 400 descriptors were calculated, but four of them (POM, log D, M-SZX/RZX and m-RPCG) were included in the models. SVM-QSRR performed significantly better than the MLR model. Apart from aminopyridines, four structurally similar substances (indapamide, gliclazide, sulfamethoxazole and furosemide) were followed in the same chromatographic system. They were used as external validation set for the QSRR model (it performed well within its applicability domain, which was defined using a bounding box approach). After having described retention of eight aminopyridines with both theoretical and QSRR models, further investigations in this field can be conducted. PMID:26590237

17. Theoretical Counseling Orientation: An Initial Aspect of Professional Orientation and Identity

ERIC Educational Resources Information Center

Jackson, James Lloyd, Jr.

2010-01-01

The literature on counselor development suggests that the development of a professional identity is a fundamental aspect of counselor training. The unique demands placed on counselors to integrate aspects of both personal and professional identity into the therapeutic process (Skovholt & Ronnestad, 1995) make development of a professional identity…

18. Field-theoretic simulations of directed self-assembly in cylindrical confinement: placement and rectification aspects

Laachi, Nabil; Iwama, Tatsuhiro; Delaney, Kris T.; Kim, Bongkeun; Bristol, Robert; Shykind, David; Weinheimer, Corey J.; Fredrickson, Glenn H.

2014-03-01

We have investigated the directed self-assembly (DSA) of cylinder-forming block copolymers inside cylindrical guiding templates. To complement and corroborate our experimental study, we use field-theoretic simulations to examine the fluctuations-induced variations in the size and position of the cylindrical microdomain that forms in the middle of the guiding hole. Our study goes beyond the usual mean-field approximation and self-consistent field theory simulations (SCFT) and incorporates the effects of thermal fluctuations in the description of the self-assembly process using complex Langevin (CL) dynamics. In both our experimental and modeling efforts, we focus on minor-block-attractive sidewalls and bottom substrates and neutral top surfaces and explore the properties of the formed cylinders, including fluctuations in the center position and the size of the domain, for various prepattern conditions. Our results indicate robust critical dimensions (CD) of the DSA cylinders relative to the incoming CD, with a sigma CD < 0.9nm. Likewise, we find that the DSA cylinders are accurately registered in the center of the guiding hole, with deviations in the hole-inhole distance on the order of ≍ 0.7-1nm, translating to errors in the hole-to-hole distance of ≍ 1-1.5nm.

19. Aspects of Particle Physics Beyond the Standard Model

Lu, Xiaochuan

This dissertation describes a few aspects of particles beyond the Standard Model, with a focus on the remaining questions after the discovery of a Standard Model-like Higgs boson. In specific, three topics are discussed in sequence: neutrino mass and baryon asymmetry, naturalness problem of Higgs mass, and placing constraints on theoretical models from precision measurements. First, the consequence of the neutrino mass anarchy on cosmology is studied. Attentions are paid in particular to the total mass of neutrinos and baryon asymmetry through leptogenesis. With the assumption of independence among mass matrix entries in addition to the basis independence, Gaussian measure is the only choice. On top of Gaussian measure, a simple approximate U(1) flavor symmetry makes leptogenesis highly successful. Correlations between the baryon asymmetry and the light-neutrino quantities are investigated. Also discussed are possible implications of recently suggested large total mass of neutrinos by the SDSS/BOSS data. Second, the Higgs mass implies fine-tuning for minimal theories of weak-scale supersymmetry (SUSY). Non-decoupling effects can boost the Higgs mass when new states interact with the Higgs, but new sources of SUSY breaking that accompany such extensions threaten naturalness. I will show that two singlets with a Dirac mass can increase the Higgs mass while maintaining naturalness in the presence of large SUSY breaking in the singlet sector. The modified Higgs phenomenology of this scenario, termed "Dirac NMSSM", is also studied. Finally, the sensitivities of future precision measurements in probing physics beyond the Standard Model are studied. A practical three-step procedure is presented for using the Standard Model effective field theory (SM EFT) to connect ultraviolet (UV) models of new physics with weak scale precision observables. With this procedure, one can interpret precision measurements as constraints on the UV model concerned. A detailed explanation is

20. Posttraumatic Stress Disorder: A Theoretical Model of the Hyperarousal Subtype

PubMed Central

Weston, Charles Stewart E.

2014-01-01

Posttraumatic stress disorder (PTSD) is a frequent and distressing mental disorder, about which much remains to be learned. It is a heterogeneous disorder; the hyperarousal subtype (about 70% of occurrences and simply termed PTSD in this paper) is the topic of this article, but the dissociative subtype (about 30% of occurrences and likely involving quite different brain mechanisms) is outside its scope. A theoretical model is presented that integrates neuroscience data on diverse brain regions known to be involved in PTSD, and extensive psychiatric findings on the disorder. Specifically, the amygdala is a multifunctional brain region that is crucial to PTSD, and processes peritraumatic hyperarousal on grounded cognition principles to produce hyperarousal symptoms. Amygdala activity also modulates hippocampal function, which is supported by a large body of evidence, and likewise amygdala activity modulates several brainstem regions, visual cortex, rostral anterior cingulate cortex (rACC), and medial orbitofrontal cortex (mOFC), to produce diverse startle, visual, memory, numbing, anger, and recklessness symptoms. Additional brain regions process other aspects of peritraumatic responses to produce further symptoms. These contentions are supported by neuroimaging, neuropsychological, neuroanatomical, physiological, cognitive, and behavioral evidence. Collectively, the model offers an account of how responses at the time of trauma are transformed into an extensive array of the 20 PTSD symptoms that are specified in the Diagnostic and Statistical Manual of Mental Disorders, Fifth edition. It elucidates the neural mechanisms of a specific form of psychopathology, and accords with the Research Domain Criteria framework. PMID:24772094

1. Empathy and Child Neglect: A Theoretical Model

ERIC Educational Resources Information Center

De Paul, Joaquin; Guibert, Maria

2008-01-01

Objective: To present an explanatory theory-based model of child neglect. This model does not address neglectful behaviors of parents with mental retardation, alcohol or drug abuse, or severe mental health problems. In this model parental behavior aimed to satisfy a child's need is considered a helping behavior and, as a consequence, child neglect…

2. A theoretical model to study melting of metals under pressure

Kholiya, Kuldeep; Chandra, Jeewan

2015-10-01

On the basis of the thermal equation-of-state a simple theoretical model is developed to study the pressure dependence of melting temperature. The model is then applied to compute the high pressure melting curve of 10 metals (Cu, Mg, Pb, Al, In, Cd, Zn, Au, Ag and Mn). It is found that the melting temperature is not linear with pressure and the slope dTm/dP of the melting curve decreases continuously with the increase in pressure. The results obtained with the present model are also compared with the previous theoretical and experimental data. A good agreement between theoretical and experimental result supports the validity of the present model.

3. Information-Theoretic Perspectives on Geophysical Models

Nearing, Grey

2016-04-01

To test any hypothesis about any dynamic system, it is necessary to build a model that places that hypothesis into the context of everything else that we know about the system: initial and boundary conditions and interactions between various governing processes (Hempel and Oppenheim, 1948, Cartwright, 1983). No hypothesis can be tested in isolation, and no hypothesis can be tested without a model (for a geoscience-related discussion see Clark et al., 2011). Science is (currently) fundamentally reductionist in the sense that we seek some small set of governing principles that can explain all phenomena in the universe, and such laws are ontological in the sense that they describe the object under investigation (Davies, 1990 gives several competing perspectives on this claim). However, since we cannot build perfect models of complex systems, any model that does not also contain an epistemological component (i.e., a statement, like a probability distribution, that refers directly to the quality of of the information from the model) is falsified immediately (in the sense of Popper, 2002) given only a small number of observations. Models necessarily contain both ontological and epistemological components, and what this means is that the purpose of any robust scientific method is to measure the amount and quality of information provided by models. I believe that any viable philosophy of science must be reducible to this statement. The first step toward a unified theory of scientific models (and therefore a complete philosophy of science) is a quantitative language that applies to both ontological and epistemological questions. Information theory is one such language: Cox' (1946) theorem (see Van Horn, 2003) tells us that probability theory is the (only) calculus that is consistent with Classical Logic (Jaynes, 2003; chapter 1), and information theory is simply the integration of convex transforms of probability ratios (integration reduces density functions to scalar

4. Theoretical Modeling of Amphiphilic Self-Assembly

Gunn, John Robert

1992-01-01

Mixtures of oil, water, and surfactant exhibit a number of complex phases and interesting properties. In an effort to provide a detailed statistical mechanical understanding of these systems, the following models have been developed. A microscopic model of lyotropic systems is presented in which amphiphile and water molecules are described by simple intermolecular potentials which correctly include important excluded volume effects and the relative energy scales in the system. A constant-temperature molecular dynamics study in which the divergence of the pressure tensor is constrained to zero is discussed. Preliminary calculations on the order parameters and dynamical observables of the model are reported. To explore the phase diagram further, a three -component lattice model with unit-vector orientations at the lattice sites is introduced. The model describes ternary mixtures of oil, water, and amphiphile, and in particular the microemulsion phase. The phase diagram of the model is derived using mean-field theory and simulation. It is shown that the results of Monte Carlo simulations of sufficiently large systems show remarkable agreement with experiment. In particular, the present model reproduces the mesoscopic order of the microemulsion phase. The structure of the microemulsion is understood in terms of the liquid -crystalline phases adjacent to it on the phase diagram, and the nature of the phase transitions that occur between them. The behaviour of the system when the ratio of oil to water is changed is investigated and the percolation threshold is described. The amphiphilic film is also discussed in the context of a simple surface model. We then present an algorithm for carrying out time-dependent canonical Monte Carlo simulations using this model. Sample calculations are carried out for the 2-dimensional Ising model for which the exact partition function is known. Our method reproduces the results of standard Monte Carlo simulations with comparable accuracy

5. THEORETICAL BASIS FOR MODELING ELEMENT CYCLING

EPA Science Inventory

A biophysical basis for modeling element cycling is described. The scheme consists of element cycles, organisms necessary to completely catalyze all the component reactions, and higher organisms as structurally complex systems and as subsystems of more complex ecosystems, all to ...

6. Electrochemical phase formation: classical and atomistic theoretical models.

PubMed

Milchev, Alexander

2016-08-01

The process of electrochemical phase formation at constant thermodynamic supersaturation is considered in terms of classical and atomistic nucleation theories. General theoretical expressions are derived for important thermodynamic and kinetic quantities commenting also upon the correlation between the existing theoretical models and experimental results. Progressive and instantaneous nucleation and growth of multiple clusters of the new phase are briefly considered, too. PMID:27108683

7. Theoretical outdoor noise propagation models: Application to practical predictions

Tuominen, H. T.; Lahti, T.

1982-02-01

The theoretical calculation approaches for outdoor noise propagation are reviewed. Possibilities for their application to practical engineering calculations are outlined. A calculation procedure, which is a combination and extension of several theoretical models, is described. Calculation examples are compared with the results of some propagation studies.

8. A Theoretical Framework for Physics Education Research: Modeling Student Thinking

ERIC Educational Resources Information Center

Redish, Edward F.

2004-01-01

Education is a goal-oriented field. But if we want to treat education scientifically so we can accumulate, evaluate, and refine what we learn, then we must develop a theoretical framework that is strongly rooted in objective observations and through which different theoretical models of student thinking can be compared. Much that is known in the…

9. Experiments to test theoretical models of the polarization of light by rough surfaces

NASA Technical Reports Server (NTRS)

Geake, J. E.; Geake, M.; Zellner, B. H.

1984-01-01

A number of attempts have been made to provide theoretical models of the physical processes involved in the polarization of light scattered by a rough surface, such as the regolith of an atmosphereless planet. Some laboratory experiments designed to test different aspects of these models are described. It is concluded that double Fresnel reflection is usually the dominant process in producing negative polarization, but that diffraction effects may play a significant part in double events involving small-scale surface features.

10. A theoretical model for airborne radars

Faubert, D.

1989-11-01

This work describes a general theory for the simulation of airborne (or spaceborne) radars. It can simulate many types of systems including Airborne Intercept and Airborne Early Warning radars, airborne missile approach warning systems etc. It computes the average Signal-to-Noise ratio at the output of the signal processor. In this manner, one obtains the average performance of the radar without having to use Monte Carlo techniques. The model has provision for a waveform without frequency modulation and one with linear frequency modulation. The waveform may also have frequency hopping for Electronic Counter Measures or for clutter suppression. The model can accommodate any type of encounter including air-to-air, air-to-ground (look-down) and rear attacks. It can simulate systems with multiple phase centers on receive for studying advanced clutter or jamming interference suppression techniques. An Airborne Intercept radar is investigated to demonstrate the validity and the capability of the model.

11. Theoretical models of synaptic short term plasticity

PubMed Central

Hennig, Matthias H.

2013-01-01

Short term plasticity is a highly abundant form of rapid, activity-dependent modulation of synaptic efficacy. A shared set of mechanisms can cause both depression and enhancement of the postsynaptic response at different synapses, with important consequences for information processing. Mathematical models have been extensively used to study the mechanisms and roles of short term plasticity. This review provides an overview of existing models and their biological basis, and of their main properties. Special attention will be given to slow processes such as calcium channel inactivation and the effect of activation of presynaptic autoreceptors. PMID:23626536

12. Theoretical Model for Nanoporous Carbon Supercapacitors

SciTech Connect

Sumpter, Bobby G; Meunier, Vincent; Huang, Jingsong

2008-01-01

The unprecedented anomalous increase in capacitance of nanoporous carbon supercapacitors at pore sizes smaller than 1 nm [Science 2006, 313, 1760.] challenges the long-held presumption that pores smaller than the size of solvated electrolyte ions do not contribute to energy storage. We propose a heuristic model to replace the commonly used model for an electric double-layer capacitor (EDLC) on the basis of an electric double-cylinder capacitor (EDCC) for mesopores (2 {50 nm pore size), which becomes an electric wire-in-cylinder capacitor (EWCC) for micropores (< 2 nm pore size). Our analysis of the available experimental data in the micropore regime is confirmed by 1st principles density functional theory calculations and reveals significant curvature effects for carbon capacitance. The EDCC (and/or EWCC) model allows the supercapacitor properties to be correlated with pore size, specific surface area, Debye length, electrolyte concentration and dielectric constant, and solute ion size. The new model not only explains the experimental data, but also offers a practical direction for the optimization of the properties of carbon supercapacitors through experiments.

13. Electronic and vibrational spectra of matrix isolated anthracene radical cations - Experimental and theoretical aspects

NASA Technical Reports Server (NTRS)

Szczepanski, Jan; Vala, Martin; Talbi, Dahbia; Parisel, Olivier; Ellinger, Yves

1993-01-01

The IR vibrational and visible/UV electronic absorption spectra of the anthracene cation, An(+), were studied experimentally, in argon matrices at 12 K, as well as theoretically, using ab initio calculations for the vibrational modes and enhanced semiempirical methods with configuration interaction for the electronic spectra. It was found that both approaches predicted well the observed photoelectron spectrum. The theoretical IR intensities showed some remarkable differences between neutral and ionized species (for example, the CH in-plane bending modes and CC in-plane stretching vibrations were predicted to increase by several orders of magnitude upon ionization). Likewise, estimated experimental IR intensities showed a significant increase in the cation band intensities over the neutrals. The implication of these findings for the hypothesis that polycyclic aromatic hydrocarbon cations are responsible for the unidentified IR emission bands from interstellar space is discussed.

14. [A framework for evaluating ethical issues of public health initiatives: practical aspects and theoretical implications].

PubMed

Petrini, Carlo

2015-01-01

The "Framework for the Ethical Conduct of Public Health Initiatives", developed by Public Health Ontario, is a practical guide for assessing the ethical implications of evidence-generating public health initiatives, whether research or non-research activities, involving people, their biological materials or their personal information. The Framework is useful not only to those responsible for determining the ethical acceptability of an initiative, but also to investigators planning new public health initiatives. It is informed by a theoretical approach that draws on widely shared bioethical principles. Two considerations emerge from both the theoretical framework and its practical application: the line between practice and research is often blurred; public health ethics and biomedical research ethics are based on the same common heritage of values. PMID:26241514

15. Theoretical Tinnitus Framework: A Neurofunctional Model

PubMed Central

Ghodratitoostani, Iman; Zana, Yossi; Delbem, Alexandre C. B.; Sani, Siamak S.; Ekhtiari, Hamed; Sanchez, Tanit G.

2016-01-01

Subjective tinnitus is the conscious (attended) awareness perception of sound in the absence of an external source and can be classified as an auditory phantom perception. Earlier literature establishes three distinct states of conscious perception as unattended, attended, and attended awareness conscious perception. The current tinnitus development models depend on the role of external events congruently paired with the causal physical events that precipitate the phantom perception. We propose a novel Neurofunctional Tinnitus Model to indicate that the conscious (attended) awareness perception of phantom sound is essential in activating the cognitive-emotional value. The cognitive-emotional value plays a crucial role in governing attention allocation as well as developing annoyance within tinnitus clinical distress. Structurally, the Neurofunctional Tinnitus Model includes the peripheral auditory system, the thalamus, the limbic system, brainstem, basal ganglia, striatum, and the auditory along with prefrontal cortices. Functionally, we assume the model includes presence of continuous or intermittent abnormal signals at the peripheral auditory system or midbrain auditory paths. Depending on the availability of attentional resources, the signals may or may not be perceived. The cognitive valuation process strengthens the lateral-inhibition and noise canceling mechanisms in the mid-brain, which leads to the cessation of sound perception and renders the signal evaluation irrelevant. However, the “sourceless” sound is eventually perceived and can be cognitively interpreted as suspicious or an indication of a disease in which the cortical top-down processes weaken the noise canceling effects. This results in an increase in cognitive and emotional negative reactions such as depression and anxiety. The negative or positive cognitive-emotional feedbacks within the top-down approach may have no relation to the previous experience of the patients. They can also be

16. Theoretical Tinnitus Framework: A Neurofunctional Model.

PubMed

Ghodratitoostani, Iman; Zana, Yossi; Delbem, Alexandre C B; Sani, Siamak S; Ekhtiari, Hamed; Sanchez, Tanit G

2016-01-01

Subjective tinnitus is the conscious (attended) awareness perception of sound in the absence of an external source and can be classified as an auditory phantom perception. Earlier literature establishes three distinct states of conscious perception as unattended, attended, and attended awareness conscious perception. The current tinnitus development models depend on the role of external events congruently paired with the causal physical events that precipitate the phantom perception. We propose a novel Neurofunctional Tinnitus Model to indicate that the conscious (attended) awareness perception of phantom sound is essential in activating the cognitive-emotional value. The cognitive-emotional value plays a crucial role in governing attention allocation as well as developing annoyance within tinnitus clinical distress. Structurally, the Neurofunctional Tinnitus Model includes the peripheral auditory system, the thalamus, the limbic system, brainstem, basal ganglia, striatum, and the auditory along with prefrontal cortices. Functionally, we assume the model includes presence of continuous or intermittent abnormal signals at the peripheral auditory system or midbrain auditory paths. Depending on the availability of attentional resources, the signals may or may not be perceived. The cognitive valuation process strengthens the lateral-inhibition and noise canceling mechanisms in the mid-brain, which leads to the cessation of sound perception and renders the signal evaluation irrelevant. However, the "sourceless" sound is eventually perceived and can be cognitively interpreted as suspicious or an indication of a disease in which the cortical top-down processes weaken the noise canceling effects. This results in an increase in cognitive and emotional negative reactions such as depression and anxiety. The negative or positive cognitive-emotional feedbacks within the top-down approach may have no relation to the previous experience of the patients. They can also be

17. Theoretical models of possible compact nucleosome structures.

PubMed

Besker, Neva; Anselmi, Claudio; De Santis, Pasquale

2005-04-01

Chromatin structure seems related to the DNA linker length. This paper presents a systematic search of the possible chromatin structure as a function of the linker lengths, starting from three different low-resolution molecular models of the nucleosome. Gay-Berne potential was used to evaluate the relative nucleosome packing energy. Results suggest that linker DNAs, which bridges and orientate nucleosomes, affect both the geometry and the rigidity of the global chromatin structure. PMID:15752596

18. A theoretical model for whole genome alignment.

PubMed

Belal, Nahla A; Heath, Lenwood S

2011-05-01

We present a graph-based model for representing two aligned genomic sequences. An alignment graph is a mixed graph consisting of two sets of vertices, each representing one of the input sequences, and three sets of edges. These edges allow the model to represent a number of evolutionary events. This model is used to perform sequence alignment at the level of nucleotides. We define a scoring function for alignment graphs. We show that minimizing the score is NP-complete. However, we present a dynamic programming algorithm that solves the minimization problem optimally for a certain class of alignments, called breakable arrangements. Algorithms for analyzing breakable arrangements are presented. We also present a greedy algorithm that is capable of representing reversals. We present a dynamic programming algorithm that optimally aligns two genomic sequences, when one of the input sequences is a breakable arrangement of the other. Comparing what we define as breakable arrangements to alignments generated by other algorithms, it is seen that many already aligned genomes fall into the category of being breakable. Moreover, the greedy algorithm is shown to represent reversals, besides rearrangements, mutations, and other evolutionary events. PMID:21210739

19. Theoretical and Computational Aspects of the Magnetic Confinement of Particles and Plasmas

Mehanian, Courosh

1987-09-01

This thesis covers various aspects of the magnetic confinement of particles and plasmas. It is composed of two separate problems which deal with two extreme limits of temperature. In the first problem, the setting is a device that is a candidate for a fusion reactor and thus represents a collection of ionized atoms at a very high temperature. The second problem concerns the magnetic confinement of a neutral hydrogen gas at a temperature low enough that a Bose-Einstein condensation occurs. The tilt stabilization of a spheromak by an energetic particle ring is analyzed. A comprehensive survey is made of numerically generated, hybrid equilibria which describe spheromak plasmas with an energetic ion ring component. Unlike the analytic treatments, neither the ion ring toroidal current nor the inverse aspect ration are required to be small. The tilt stability of the plasma is determined by calculating the torque due to the magnetic interaction with the ion-ring, assumed fixed. The tilt stability of the ring is determined by calculating the betatron frequencies of the ring particles. Bicycle-tire rings, since they flatten the separatix axially, provide the most stabilization of the plasma per unit ion ring current. On the other hand, axially elongated, toilet-paper-tube rings are themselves the most stable. These opposing trends indicate that the configuration with optimal stability is achieved near an ion ring aspect ratio of unity and for roughly equal plasma and fast particle currents. The confinement of an atomic hydrogen gas in the trap formed by a time-varying magnetic field is investigated. The trap uses the interaction of the magnetic field with the magnetic moments of the atoms, which are kept aligned by a strong uniform field. The effect of collisions is included via a Monte Carlo algorithm and it is found that the atoms can be confined when the frequency and the current of the coils producing the time-varying field are appropriately chosen.

20. Theoretical model for plasma opening switch

SciTech Connect

Baker, L.

1980-07-01

The theory of an explosive plasma switch is developed and compared with the experimental results of Pavlovskii and work at Sandia. A simple analytic model is developed, which predicts that such switches may achieve opening times of approximately 100 ns. When the switching time is limited by channel mixing it scales as t = C(m d/sub 0/)/sup 1/2/P/sub 0//sup 2/P/sub e//sup -5/2/ where m is the foil mass per unit area, d/sub 0/ the channel thickness and P/sub 0/ the channel pressure (at explosive breakout), P/sub e/ the explosive pressure, C a constant of order 10 for c.g.s. units. Thus faster switching times may be achieved by minimizing foil mass and channel pressure, or increasing explosive product pressure, with the scaling exponents as shown suggesting that changes in pressures would be more effective.

1. Theoretical modelling of epigenetically modified DNA sequences.

PubMed

Carvalho, Alexandra Teresa Pires; Gouveia, Maria Leonor; Raju Kanna, Charan; Wärmländer, Sebastian K T S; Platts, Jamie; Kamerlin, Shina Caroline Lynn

2015-01-01

We report herein a set of calculations designed to examine the effects of epigenetic modifications on the structure of DNA. The incorporation of methyl, hydroxymethyl, formyl and carboxy substituents at the 5-position of cytosine is shown to hardly affect the geometry of CG base pairs, but to result in rather larger changes to hydrogen-bond and stacking binding energies, as predicted by dispersion-corrected density functional theory (DFT) methods. The same modifications within double-stranded GCG and ACA trimers exhibit rather larger structural effects, when including the sugar-phosphate backbone as well as sodium counterions and implicit aqueous solvation. In particular, changes are observed in the buckle and propeller angles within base pairs and the slide and roll values of base pair steps, but these leave the overall helical shape of DNA essentially intact. The structures so obtained are useful as a benchmark of faster methods, including molecular mechanics (MM) and hybrid quantum mechanics/molecular mechanics (QM/MM) methods. We show that previously developed MM parameters satisfactorily reproduce the trimer structures, as do QM/MM calculations which treat bases with dispersion-corrected DFT and the sugar-phosphate backbone with AMBER. The latter are improved by inclusion of all six bases in the QM region, since a truncated model including only the central CG base pair in the QM region is considerably further from the DFT structure. This QM/MM method is then applied to a set of double-stranded DNA heptamers derived from a recent X-ray crystallographic study, whose size puts a DFT study beyond our current computational resources. These data show that still larger structural changes are observed than in base pairs or trimers, leading us to conclude that it is important to model epigenetic modifications within realistic molecular contexts. PMID:26448859

2. Theoretical aspects of light-element alloys under extremely high pressure

Feng, Ji

In this Dissertation, we present theoretical studies on the geometric and electronic structure of light-element alloys under high pressure. The first three Chapters are concerned with specific compounds, namely, SiH 4, CaLi2 and BexLi1- x, and associated structural and electronic phenomena, arising in our computational studies. In the fourth Chapter, we attempt to develop a unified view of the relationship between the electronic and geometric structure of light-element alloys under pressure, by focusing on the states near the Fermi level in these metals.

3. Electronic structure of Ni2TiAl: Theoretical aspects and Compton scattering measurement

Sahariya, Jagrati; Ahuja, B. L.

2012-11-01

In this paper, we report electron momentum density of Ni2TiAl alloy using an in-house 20 Ci 137Cs (661.65 keV) Compton spectrometer. The experimental data have been analyzed in terms of energy bands and density of states computed using linear combination of atomic orbitals (LCAO) method. In the LCAO computations, we have considered local density approximation, generalized gradient approximation and recently developed second order generalized gradient approximation within the frame work of density functional theory. Anisotropies in theoretical Compton profiles along [1 0 0], [1 1 0] and [1 1 1] directions are also explained in terms of energy bands.

4. Aspects of model selection in multivariate analyses

SciTech Connect

Picard, R.

1982-01-01

Analysis of data sets that involve large numbers of variables usually entails some type of model fitting and data reduction. In regression problems, a fitted model that is obtained by a selection process can be difficult to evaluate because of optimism induced by the choice mechanism. Problems in areas such as discriminant analysis, calibration, and the like often lead to similar difficulties. The preceeding sections reviewed some of the general ideas behind assessment of regression-type predictors and illustrated how they can be easily incorporated into a standard data analysis.

5. A numerical scheme and some theoretical aspects for the cylindrically and spherically symmetric sine-Gordon equations

Nguyen, Lu Trong Khiem

2016-07-01

A finite difference formula based on the predictor-corrector technique is presented to integrate the cylindrically and spherically symmetric sine-Gordon equations numerically. Based on various numerical observations, one property of the waves of kink type is conjectured and used to explain their returning effect. Several numerical experiments are carried out and they are in excellent agreement with the existing results. In addition, the corresponding modulation solution for the two-dimensional ring-shaped kink is extended to that in three-dimension. Both numerical and theoretical aspects are utilized to verify the reliability of the proposed numerical scheme and thus the analytical modulation solutions.

6. Neighbor intervention: a game-theoretic model.

PubMed

Mesterton-Gibbons, Mike; Sherratt, Tom N

2009-01-21

It has long been argued that a resident may benefit from helping its neighbor defend a territory against a challenger to avoid renegotiating its boundaries with a new and potentially stronger individual. We quantify this theory by exploring games involving challengers, residents and potential allies. In a simplified discrete game with zero variation of fighting strength, helping neighbors is part of an evolutionarily stable strategy (ESS) only if fighting costs are low relative to those of renegotiation. However, if relative fighting costs are high then an interventional ESS remains possible with finite variation of strength. Under these conditions, neighbors may help residents fight off intruders, but only when the resident does not stand a reliable chance of winning alone. We show that neighbor intervention is more likely with low home advantage to occupying a territory, strengths combining synergistically or low probability that an ally will be usurped, amongst other factors. Our parameterized model readily explains occasional intervention in the Australian fiddler crab, including why the ally tended to be larger than both the assisted neighbor and the intruder. Reciprocity is not necessary for this type of cooperation to persist, but also it is by no means inevitable in territorial species. PMID:18977365

7. A theoretical model of asymmetric wave ripples

PubMed Central

Blondeaux, P.; Foti, E.; Vittori, G.

2015-01-01

The time development of ripples under sea waves is investigated by means of the weakly nonlinear stability analysis of a flat sandy bottom subjected to the viscous oscillatory flow that is present in the boundary layer at the bottom of propagating sea waves. Second-order effects in the wave steepness are considered, to take into account the presence of the steady drift generated by the surface waves. Hence, the work of Vittori & Blondeaux (1990 J. Fluid Mech. 218, 19–39 (doi:10.1017/S002211209000091X)) is extended by considering steeper waves and/or less deep waters. As shown by the linear analysis of Blondeaux et al. (2000 Eur. J. Mech. B 19, 285–301 (doi:10.1016/S0997-7546(90)00106-I)), because of the presence of a steady velocity component in the direction of wave propagation, ripples migrate at a constant rate that depends on sediment and wave characteristics. The weakly nonlinear analysis shows that the ripple profile is no longer symmetric with respect to ripple crests and troughs and the symmetry index is computed as a function of the parameters of the problem. In particular, a relationship is determined between the symmetry index and the strength of the steady drift. A fair agreement between model results and laboratory data is obtained, albeit further data and analyses are necessary to determine the behaviour of vortex ripples and to be conclusive. PMID:25512587

8. A theoretical model of asymmetric wave ripples.

PubMed

Blondeaux, P; Foti, E; Vittori, G

2015-01-28

The time development of ripples under sea waves is investigated by means of the weakly nonlinear stability analysis of a flat sandy bottom subjected to the viscous oscillatory flow that is present in the boundary layer at the bottom of propagating sea waves. Second-order effects in the wave steepness are considered, to take into account the presence of the steady drift generated by the surface waves. Hence, the work of Vittori & Blondeaux (1990 J. Fluid Mech. 218, 19-39 (doi:10.1017/S002211209000091X)) is extended by considering steeper waves and/or less deep waters. As shown by the linear analysis of Blondeaux et al. (2000 Eur. J. Mech. B 19, 285-301 (doi:10.1016/S0997-7546(90)00106-I)), because of the presence of a steady velocity component in the direction of wave propagation, ripples migrate at a constant rate that depends on sediment and wave characteristics. The weakly nonlinear analysis shows that the ripple profile is no longer symmetric with respect to ripple crests and troughs and the symmetry index is computed as a function of the parameters of the problem. In particular, a relationship is determined between the symmetry index and the strength of the steady drift. A fair agreement between model results and laboratory data is obtained, albeit further data and analyses are necessary to determine the behaviour of vortex ripples and to be conclusive. PMID:25512587

9. Theoretical and numerical modelling of shocks in dusty plasmas

SciTech Connect

Eliasson, B.; Shukla, P.K.

2005-10-31

The formation of dust acoustic (DA) and dust ion-acoustic (DIA) shocks are are studied theoretically and numerically by means of simple-wave solutions and a comparison between fluid and kinetic model for DIA waves. A fluid model admits sharp discontinuities at the shock front while the kinetic model involves Landau-damping of the the shock front.

10. The Psychopathological Model of Mental Retardation: Theoretical and Therapeutic Considerations.

ERIC Educational Resources Information Center

La Malfa, Giampaolo; Campigli, Marco; Bertelli, Marco; Mangiapane, Antonio; Cabras, Pier Luigi

1997-01-01

Describes a new integrated bio-psycho-social model of etiology for mental retardation. Discusses the problems with current models and the ability of the "universe line" model to integrate data from different research areas, especially cognitive and psychopathologic indicators. Addresses implications of this theoretical approach. (Author/CR)

11. Dynamics in Higher Education Politics: A Theoretical Model

ERIC Educational Resources Information Center

Kauko, Jaakko

2013-01-01

This article presents a model for analysing dynamics in higher education politics (DHEP). Theoretically the model draws on the conceptual history of political contingency, agenda-setting theories and previous research on higher education dynamics. According to the model, socio-historical complexity can best be analysed along two dimensions: the…

12. Opposition Surge: Lab Studies and Theoretical Models

Nelson, R. M.; Hapke, B. W.; Smythe, W. D.; Hale, A. S.; Piatek, J. L.; Green, J.

The opposition effect, a non-linear intensity increase in the reflectance phase curve with decreasing phase angle, has long been observed in solar system bodies and in laboratory investigations of the angular scattering properties of particulate media[1]. It has been attributed to two processes. One, shadow hiding, is the elimination of shadows mutually cast between the regolith grains as the phase angle decreases[2]. The other is coherent constructive interference between rays of light traveling along identical but opposite paths in multiply scattering media (CBOE). [3,4,5,6]. We report the results of an investigation into the opposition surge of particulate materials of the same particle size and packing density but of differing reflectance. The measurements were made on the long arm goniometer at JPL. The phase angle studied varied from 0.05 to 5o. Samples of Al2O3, diamond, Si4C, and B4C were presented with linearly and circularly polarized light from a laser of wavelength 0.633 µm. The uncompressed, 22-24 µm samples differed widely in reflectance. Many published models of CBOE suggest that as the materials become more absorbing the shape of the phase curve should become more rounded near 0o [7,8 9, 10, 11,12,13]. We find that, regardless of reflectance, the phase curve exhibits increasing slope with decreasing phase angle down to the angular limit of our measurement. It becomes more sharply peaked and does not become rounded. Our measurements of powdered materials, including lunar regolith samples[14,15,16], do not agree with current models of coherent backscatter, which predict a rounding and truncation of the opposition effect peak near zero phase. This lack of rounding is consistent with the hypothesis that very long light paths contribute to the CBOE of particulate materials including planetary regoliths. This work was performed at NASA's JPL under a grant from NASA's Planetary Geology / Geophysics program. References: [1] T. Gehrels, Astrrophys. J. 123

13. Computational Aspects of N-Mixture Models

PubMed Central

Dennis, Emily B; Morgan, Byron JT; Ridout, Martin S

2015-01-01

The N-mixture model is widely used to estimate the abundance of a population in the presence of unknown detection probability from only a set of counts subject to spatial and temporal replication (Royle, 2004, Biometrics 60, 105–115). We explain and exploit the equivalence of N-mixture and multivariate Poisson and negative-binomial models, which provides powerful new approaches for fitting these models. We show that particularly when detection probability and the number of sampling occasions are small, infinite estimates of abundance can arise. We propose a sample covariance as a diagnostic for this event, and demonstrate its good performance in the Poisson case. Infinite estimates may be missed in practice, due to numerical optimization procedures terminating at arbitrarily large values. It is shown that the use of a bound, K, for an infinite summation in the N-mixture likelihood can result in underestimation of abundance, so that default values of K in computer packages should be avoided. Instead we propose a simple automatic way to choose K. The methods are illustrated by analysis of data on Hermann's tortoise Testudo hermanni. PMID:25314629

14. Ocean modelling aspects for drift applications

Stephane, L.; Pierre, D.

2010-12-01

Nowadays, many authorities in charge of rescue-at-sea operations lean on operational oceanography products to outline research perimeters. Moreover, current fields estimated with sophisticated ocean forecasting systems can be used as input data for oil spill/ adrift object fate models. This emphasises the necessity of an accurate sea state forecast, with a mastered level of reliability. This work focuses on several problems inherent to drift modeling, dealing in the first place with the efficiency of the oceanic current field representation. As we want to discriminate the relevance of a particular physical process or modeling option, the idea is to generate series of current fields of different characteristics and then qualify them in term of drift prediction efficiency. Benchmarked drift scenarios were set up from real surface drifters data, collected in the Mediterranean sea and off the coasts of Angola. The time and space scales that we are interested in are about 72 hr forecasts (typical timescale communicated in case of crisis), for distance errors that we hope about a few dozen of km around the forecast (acceptable for reconnaissance by aircrafts) For the ocean prediction, we used some regional oceanic configurations based on the NEMO 2.3 code, nested into Mercator 1/12° operational system. Drift forecasts were computed offline with Mothy (Météo France oil spill modeling system) and Ariane (B. Blanke, 1997), a Lagrangian diagnostic tool. We were particularly interested in the importance of the horizontal resolution, vertical mixing schemes, and any processes that may impact the surface layer. The aim of the study is to ultimately point at the most suitable set of parameters for drift forecast use inside operational oceanic systems. We are also motivated in assessing the relevancy of ensemble forecasts regarding determinist predictions. Several tests showed that mis-described observed trajectories can finally be modelled statistically by using uncertainties

15. Testing a Theoretical Model of Immigration Transition and Physical Activity.

PubMed

Chang, Sun Ju; Im, Eun-Ok

2015-01-01

The purposes of the study were to develop a theoretical model to explain the relationships between immigration transition and midlife women's physical activity and test the relationships among the major variables of the model. A theoretical model, which was developed based on transitions theory and the midlife women's attitudes toward physical activity theory, consists of 4 major variables, including length of stay in the United States, country of birth, level of acculturation, and midlife women's physical activity. To test the theoretical model, a secondary analysis with data from 127 Hispanic women and 123 non-Hispanic (NH) Asian women in a national Internet study was used. Among the major variables of the model, length of stay in the United States was negatively associated with physical activity in Hispanic women. Level of acculturation in NH Asian women was positively correlated with women's physical activity. Country of birth and level of acculturation were significant factors that influenced physical activity in both Hispanic and NH Asian women. The findings support the theoretical model that was developed to examine relationships between immigration transition and physical activity; it shows that immigration transition can play an essential role in influencing health behaviors of immigrant populations in the United States. The NH theoretical model can be widely used in nursing practice and research that focus on immigrant women and their health behaviors. Health care providers need to consider the influences of immigration transition to promote immigrant women's physical activity. PMID:26502554

16. Thermodynamical aspects of running vacuum models

Lima, J. A. S.; Basilakos, Spyros; Solà, Joan

2016-04-01

The thermal history of a large class of running vacuum models in which the effective cosmological term is described by a truncated power series of the Hubble rate, whose dominant term is Λ (H) ∝ H^{n+2}, is discussed in detail. Specifically, by assuming that the ultrarelativistic particles produced by the vacuum decay emerge into space-time in such a way that its energy density ρ _r ∝ T4, the temperature evolution law and the increasing entropy function are analytically calculated. For the whole class of vacuum models explored here we find that the primeval value of the comoving radiation entropy density (associated to effectively massless particles) starts from zero and evolves extremely fast until reaching a maximum near the end of the vacuum decay phase, where it saturates. The late-time conservation of the radiation entropy during the adiabatic FRW phase also guarantees that the whole class of running vacuum models predicts the same correct value of the present day entropy, S0 ˜ 10^{87}-10^{88} (in natural units), independently of the initial conditions. In addition, by assuming Gibbons-Hawking temperature as an initial condition, we find that the ratio between the late-time and primordial vacuum energy densities is in agreement with naive estimates from quantum field theory, namely, ρ _{Λ 0}/ρ _{Λ I} ˜ 10^{-123}. Such results are independent on the power n and suggests that the observed Universe may evolve smoothly between two extreme, unstable, non-singular de Sitter phases.

17. Surface activity of Janus particles adsorbed at fluid-fluid interfaces: Theoretical and experimental aspects.

PubMed

Fernandez-Rodriguez, Miguel Angel; Rodriguez-Valverde, Miguel Angel; Cabrerizo-Vilchez, Miguel Angel; Hidalgo-Alvarez, Roque

2016-07-01

Since de Gennes coined in 1992 the term Janus particle (JP), there has been a continued effort to develop this field. The purpose of this review is to present the most relevant theoretical and experimental results obtained so far on the surface activity of amphiphilic JPs at fluid interfaces. The surface activity of JPs at fluid-fluid interfaces can be experimentally determined using two different methods: the classical Langmuir balance or the pendant drop tensiometry. The second method requires much less amount of sample than the first one, but it has also some experimental limitations. In all cases collected here the JPs exhibited a higher surface or interfacial activity than the corresponding homogeneous particles. This reveals the significant advantage of JPs for the stabilization of emulsions and foams. PMID:26094083

18. Theoretical and applied aspects of night vision goggle resolution and visual acuity assessment

Task, H. Lee; Pinkus, Alan R.

2007-04-01

The image quality of night vision goggles is often expressed in terms of visual acuity, resolution or modulation transfer function. The primary reason for providing a measure of image quality is the underlying assumption that the image quality metric correlates with the level of visual performance that one could expect when using the device, for example, target detection or target recognition performance. This paper provides a theoretical analysis of the relationships between these three image quality metrics: visual acuity, resolution and modulation transfer function. Results from laboratory and field studies were used to relate these metrics to visual performance. These results can also be applied to non-image intensifier based imaging systems such as a helmet-mounted display coupled to an imaging sensor.

19. Theoretical and practical aspects of chemical functionalization of carbon nanofibers (CNFs): DFT calculations and adsorption study.

PubMed

Rokhina, Ekaterina V; Lahtinen, Manu; Makarova, Katerina; Jegatheesan, Veeriah; Virkutyte, Jurate

2012-06-01

The nitric acid-functionalized commercial carbon nanofibers (CNFs) were comprehensively studied by instrumental (XRD, BET, SEM, TGA) and theoretical (DFT calculations) methods. The detailed surface study revealed the variation in the characteristics of functionalized CNFs, such as a decreased (up to 34%) surface area and impacted structural, electronic and chemical properties. The effects of functional groups were studied by comparison with pristine nanofibers. The results showed that the C-C bond lengths of the modified CNFs varied significantly. Chemical functionalization altered the frontier orbitals of the pristine material, and therefore altered the nature of their interactions with other substances. Moreover, the pristine and modified CNFs were tested for the removal of phenol from aqueous solutions. It was observed that surface modification tuned the adsorption capacity of carbon nanofibers (up to 0.35 mmol g(-1)), whereas original fibers did not demonstrate any adsorption capacity of phenol. PMID:22209137

20. Aspect-Oriented Model-Driven Software Product Line Engineering

Groher, Iris; Voelter, Markus

Software product line engineering aims to reduce development time, effort, cost, and complexity by taking advantage of the commonality within a portfolio of similar products. The effectiveness of a software product line approach directly depends on how well feature variability within the portfolio is implemented and managed throughout the development lifecycle, from early analysis through maintenance and evolution. This article presents an approach that facilitates variability implementation, management, and tracing by integrating model-driven and aspect-oriented software development. Features are separated in models and composed of aspect-oriented composition techniques on model level. Model transformations support the transition from problem to solution space models. Aspect-oriented techniques enable the explicit expression and modularization of variability on model, template, and code level. The presented concepts are illustrated with a case study of a home automation system.

1. Theoretical models for the conformations and the protonation of triacetonamine.

PubMed

Navajas, C C; Montero, L A; La Serna, B

1990-12-01

In this paper we propose theoretical models for the conformations of triacetonamine and protonated triacetonamine (Vincubine, an anticancer chemotherapeutic agent) developed by quantum and molecular mechanics techniques. We discuss the theoretical factors which are involved in the stabilization of the conformations calculated by the MNDO, MM2 and COPEANE methods and show the relative percent abundance of each molecular shape. Graphic representations of the conformers are depicted. PMID:1965442

2. Theoretical Modeling of the Discharge-Pumped Xenon - Excimer Laser.

Zhu, Sheng-Bai

The present dissertation is dedicated to a theoretical study of the discharge pumped XeCl excimer laser. For a better description of our system, Two modelings which supplement each other from different angles have been successfully developed. The first one, a comprehensive kinetics model which can be applied to the detailed simulations of the temporal behavior of the discharge characteristics and laser performance, is constructed by a set of coupled first -order differential equations, such as the rate equations, the Boltzmann equation, the external electric circuit equations, the energy balance equation, and the equations of optical resonator. The starting and termination of the discharge are taken into deliberation for the first time, especially for the Blumlein case. Some 70 kinetic processes and 23 chemical species are included. Such a problem can only be numerically solved by means of an elaborate computer code. Another model, on the other hand, pays attention to the quasi-steady-state to facilitate parametric study. A group of rate coefficients for the kinetic processes involving free electrons are approximated by analytic expressions using numerical results compiled from computer code calculations. Explicit expressions of the number densities for all relevant chemical species are obtained. Among them, HCI(O), H, and Cl can never reach steady-state population. Time history of the concentrations for these species are computed instead. With the discussions about the effect of vibrational relaxation and state-to-state transfer in the upper energy level, and the discussions about the rotational structure, collisional broadening, and dissociation of the diatomic ground state, we have extensively investigated the spontaneous emission spectra, the small-signal gain, the non-saturable absorption, the steady-state laser output power, and various efficiencies. Saturation effects in laser oscillators and laser amplifiers are discussed as well. These topics relate to the

3. Theoretical aspects of energy range relations, stopping power and energy straggling of protons

Ulmer, W.

2007-07-01

The Bragg-Kleeman rule RCSDA=AE0p provides a connection between the initial energy E0 of a proton and the range RCSDA in a medium, if the continuous-slowing-down approximation (CSDA) is assumed. The rule results from a generalized (nonrelativistic) Langevin equation; its integration also yields information on the residual energy E(z) or dE(z)/dz of a proton at position z. A relativistic extension of the generalized Langevin equation leads to the formula RCSDA=A(E0+E02/2Mc2)p. Since the initial energy E0 of therapeutic protons satisfies E0≪2Mc2, relativistic contributions can be treated as correction terms. Besides this phenomenological aspect, a complete integration of Bethe-Bloch equation (BBE) is presented, which provides the determination of RCSDA, E(z), dE(z)/dz and works without any empirical parameters. The results of these different methods are compared with Monte Carlo calculations (GEANT4). Since the energy transfer from proton to the environmental atomic electrons regarded in the CSDA-framework has to account for local fluctuations, an analysis of the Gaussian convolution and the Landau-Vavilov distribution function is performed on the basis of quantum-statistical mechanics. The Landau tail can be described as a Hermite polynomial correction of a Gaussian convolution.

4. Theoretical Aspects of Minority Carrier Extraction in Unipolar Barrier Infrared Detectors

Ting, David Z.-Y.; Soibel, Alexander; Höglund, Linda; Gunapala, Sarath D.

2015-09-01

We have examined, theoretically, minority carrier collection in unipolar barrier infrared photodetectors. In barrier infrared detectors, for example the nBn, the unipolar barrier should block only majority carriers and allow unimpeded flow of minority carriers. However, an imperfect barrier would also block minority carriers, resulting in higher than expected turn-on bias. Minority carrier blocking can be caused by barrier doping or unintended band offset between the barrier and the absorber. The distinct manner in which these two mechanisms affect device performance were investigated. We found that introduction of an appropriate amount of barrier doping can reduce depletion dark current without increasing turn-on bias. We examined the effects of band structure on conductivity effective masses when the n-type absorber was a type-II superlattice (T2SL). We showed that for a long-wavelength infrared InAs/GaSb T2SL the vertical conductivity hole effective mass can be much smaller than that predicted by the simple band-edge effect mass picture, implying that the vertical hole mobility estimated from the band-edge effective mass can be unduly pessimistic.

5. Communication training for aircrews: A review of theoretical and pragmatic aspects of training program design

NASA Technical Reports Server (NTRS)

Linde, Charlotte; Goguen, Joseph; Devenish, Linda

1987-01-01

This study is the final report of a project studying methods of communications training applicable to both civilian and military aviation personnel, including multiperson teams or single pilot fixed wing or rotary wing aircraft. A review is provided of a number of theories proposed as relevant for producing training materials for improved communications. Criteria are given for evaluating the applicability of training programs to the aviation environment, and these criteria are applied to United Airlines' Resources Management Training, as well as to a number of commercially available general purpose training programs. The report considers in detail assertiveness training and grid management training, examining their theoretical background and attempts made to validate their effectiveness. It was found that there are substantive difficulties in assessing the effectiveness of both training programs, as well as problems with the theories underlying them. However, because the aviation environment offers unique advantages for studying the effectiveness of communications training, recommendations are made on the design of appropriate training programs and on procedures that might be used to validate them.

6. STED Nanoscopy with Time-Gated Detection: Theoretical and Experimental Aspects

PubMed Central

Vicidomini, Giuseppe; Schönle, Andreas; Ta, Haisen; Han, Kyu Young; Moneron, Gael; Eggeling, Christian; Hell, Stefan W.

2013-01-01

In a stimulated emission depletion (STED) microscope the region in which fluorescence markers can emit spontaneously shrinks with continued STED beam action after a singular excitation event. This fact has been recently used to substantially improve the effective spatial resolution in STED nanoscopy using time-gated detection, pulsed excitation and continuous wave (CW) STED beams. We present a theoretical framework and experimental data that characterize the time evolution of the effective point-spread-function of a STED microscope and illustrate the physical basis, the benefits, and the limitations of time-gated detection both for CW and pulsed STED lasers. While gating hardly improves the effective resolution in the all-pulsed modality, in the CW-STED modality gating strongly suppresses low spatial frequencies in the image. Gated CW-STED nanoscopy is in essence limited (only) by the reduction of the signal that is associated with gating. Time-gated detection also reduces/suppresses the influence of local variations of the fluorescence lifetime on STED microscopy resolution. PMID:23349884

7. Theoretical models for near forward light scattering by a Plasmodium falciparum infected red blood cell

Sharma, S. K.

2012-12-01

A number of experimental elastic light scattering studies have been performed in the past few years with the aim of developing automated in vivo tools for differentiating a healthy red blood cell from a Plasmodium falciparum infected cell. This paper examines some theoretical aspects of the problem. An attempt has been made to simulate the scattering patterns of healthy as well as infected individual red blood cells. Two models, namely, a homogeneous sphere model and a coated sphere model have been considered. The scattering patterns predicted by these models are examined. A possible method for discriminating infected red blood cells from healthy ones has been suggested.

8. Culture and Developmental Trajectories: A Discussion on Contemporary Theoretical Models

ERIC Educational Resources Information Center

de Carvalho, Rafael Vera Cruz; Seidl-de-Moura, Maria Lucia; Martins, Gabriela Dal Forno; Vieira, Mauro Luís

2014-01-01

This paper aims to describe, compare and discuss the theoretical models proposed by Patricia Greenfield, Çigdem Kagitçibasi and Heidi Keller. Their models have the common goal of understanding the developmental trajectories of self based on dimensions of autonomy and relatedness that are structured according to specific cultural and environmental…

9. A methodology for evacuation design for urban areas: theoretical aspects and experimentation

Russo, F.; Vitetta, A.

2009-04-01

This paper proposes an unifying approach for the simulation and design of a transportation system under conditions of incoming safety and/or security. Safety and security are concerned with threats generated by very different factors and which, in turn, generate emergency conditions, such as the 9/11, Madrid and London attacks, the Asian tsunami, and the Katrina hurricane; just considering the last five years. In transportation systems, when exogenous events happen and there is a sufficient interval time between the instant when the event happens and the instant when the event has effect on the population, it is possible to reduce the negative effects with the population evacuation. For this event in every case it is possible to prepare with short and long term the evacuation. For other event it is possible also to plan the real time evacuation inside the general risk methodology. The development of models for emergency conditions in transportation systems has not received much attention in the literature. The main findings in this area are limited to only a few public research centres and private companies. In general, there is no systematic analysis of the risk theory applied in the transportation system. Very often, in practice, the vulnerability and exposure in the transportation system are considered as similar variables, or in other worse cases the exposure variables are treated as vulnerability variables. Models and algorithms specified and calibrated in ordinary conditions cannot be directly applied in emergency conditions under the usual hypothesis considered. This paper is developed with the following main objectives: (a) to formalize the risk problem with clear diversification (for the consequences) in the definition of the vulnerability and exposure in a transportation system; thus the book offers improvements over consolidated quantitative risk analysis models, especially transportation risk analysis models (risk assessment); (b) to formalize a system

10. Cognitive Aspects of Change in Drawings: A Neo-Piagetian Theoretical Account

ERIC Educational Resources Information Center

Morra, Sergio

2005-01-01

This study reconsiders a series of drawing tasks (Goodnow, 1978) in which children have to modify their stereotypical drawing of the human figure to represent a person in movement. Another task, in which children have to differentiate the drawing of a kangaroo from that of a person, is also considered. According to a neo-Piagetian model of drawing…

11. Theoretical models on prediction of thermal property of nanofluids

Shalimba, Veikko; Skočilasová, Blanka

2014-08-01

This paper deals with theoretical models on prediction of thermo physical properties of iron nanoparticles in base fluid. A high performance of heat transfer fluid has a great influence on the size, weight and cost of heat transfer systems, therefore a high performance heat transfer fluid is very important in many industries. Over the last decades nanofluids have been developed. According to many researchers and publications on nanofluids it is evident that nanofluids are found to exhibit enhanced thermal properties i.e. thermal conductivity etc. Theoretical models for predicting enhanced thermal conductivity have been established. The underlying mechanisms for the enhancement are still debated and not fully understood. In this paper, theoretical analytical models on prediction of thermal conductivity of iron nano particle in base Jatropha oil are discussed. The work arises from the projects which were realized at UJEP, FPTM, department of Machines and Mechanics with cooperation with Polytechnic of Namibia, department of Mechanical Engineering.

12. Theoretical aspects of electroweak and other interactions in medium energy nuclear physics

1994-12-01

Significant progress has been made in the current project year in the development of chiral soliton model and its applications to the electroweak structure of the nucleon and the Delta (1232) resonance. Further progress also has been made in the application of the perturbative QCD (pQCD) and the study of physics beyond the standard model. The postdoctoral associate and the graduate student working towards his Ph.D. degree have both made good progress. The review panel of the DOE has rated this program as a 'strong, high priority' one. A total of fifteen research communications -- eight journal papers and, conference reports and seven other communications -- have been made during the project year so far.

13. Upscaling the diffusion equations in particulate media made of highly conductive particles. I. Theoretical aspects

Vassal, J.-P.; Orgéas, L.; Favier, D.; Auriault, J.-L.; Le Corre, S.

2008-01-01

Many analytical and numerical works have been devoted to the prediction of macroscopic effective transport properties in particulate media. Usually, structure and properties of macroscopic balance and constitutive equations are stated a priori. In this paper, the upscaling of the transient diffusion equations in concentrated particulate media with possible particle-particle interfacial barriers, highly conductive particles, poorly conductive matrix, and temperature-dependent physical properties is revisited using the homogenization method based on multiple scale asymptotic expansions. This method uses no a priori assumptions on the physics at the macroscale. For the considered physics and microstructures and depending on the order of magnitude of dimensionless Biot and Fourier numbers, it is shown that some situations cannot be homogenized. For other situations, three different macroscopic models are identified, depending on the quality of particle-particle contacts. They are one-phase media, following the standard heat equation and Fourier’s law. Calculations of the effective conductivity tensor and heat capacity are proved to be uncoupled. Linear and steady state continuous localization problems must be solved on representative elementary volumes to compute the effective conductivity tensors for the two first models. For the third model, i.e., for highly resistive contacts, the localization problem becomes simpler and discrete whatever the shape of particles. In paper II [Vassal , Phys. Rev. E 77, 011303 (2008)], diffusion through networks of slender, wavy, entangled, and oriented fibers is considered. Discrete localization problems can then be obtained for all models, as well as semianalytical or fully analytical expressions of the corresponding effective conductivity tensors.

14. Theoretical aspects of dynamic nuclear polarization in the solid state--spin temperature and thermal mixing.

PubMed

Hovav, Yonatan; Feintuch, Akiva; Vega, Shimon

2013-01-01

Dynamic nuclear polarization is a method which allows for a dramatic increase of the NMR signals due to polarization transfer between electrons and their neighboring nuclei, via microwave irradiation. These experiments have become popular in recent years due to the ability to create hyper-polarized chemically and biologically relevant molecules, in frozen glass forming mixtures containing free radicals. Three mechanisms have been proposed for the polarization transfer between electrons and their surrounding nuclei in such non-conducting samples: the solid effect and cross effect mechanisms, which are based on quantum mechanics and relaxation on small spin systems, and thermal mixing, which originates from the thermodynamic macroscopic notion of spin temperature. We have recently introduced a spin model, which is based on the density matrix formalism and includes relaxation, and applied it to study the solid effect and cross effect mechanisms on small spin systems. In this publication we use the same model to describe the thermal mixing mechanism, and the creation of spin temperature. This is obtained without relying on the spin temperature formalism. Simulations of small model systems are used on systems with homogeneously and inhomogeneously broadened EPR lines. For the case of a homogeneously broadened line we show that the nuclear enhancement results from the thermal mixing and solid effect mechanisms, and that spin temperatures are created in the system. In the inhomogeneous case the enhancements are attributed to the solid effect and cross effect mechanisms, but not thermal mixing. PMID:23160533

15. A control theoretic model for piloted approach to landing.

NASA Technical Reports Server (NTRS)

Kleinman, D. L.; Baron, S.

1972-01-01

Using manned vehicle systems analysis, a model for manual approach to landing is developed. This model is developed and applied in the specific context of a problem of analytical evaluation of a pictorial display for longitudinal control of glide path errors. This makes it possible to discuss the model in concrete terms, and the availability of experimental data provides opportunities for checking the theoretical results obtained.

16. [Pain and opioid dependency as multilevel network phenomenon : Theoretical and metatheoretical aspects].

PubMed

Tretter, F

2016-08-01

Methodological reflections on pain research and pain therapy focussing on addiction risks are addressed in this article. Starting from the incompleteness of objectification of the purely subjectively fully understandable phenomena of pain and addiction, the relevance of a comprehensive general psychology is underlined. It is shown that that reduction of pain and addiction to a mainly focally arguing neurobiology is only possible if both disciplines have a systemic concept of pain and addiction. With this aim, parallelized conceptual network models are presented. PMID:27422300

17. Theoretical aspects of the Edelstein effect for anisotropic two-dimensional electron gas and topological insulators

Johansson, Annika; Henk, Jürgen; Mertig, Ingrid

2016-05-01

A charge current driven through a two-dimensional electron gas (2DEG) with Rashba spin-orbit coupling generates a spatially homogeneous spin polarization perpendicular to the applied electric field. This phenomenon is the Aronov-Lyanda-Geller-Edelstein (ALGE) effect. For selected model systems, we consider the ALGE effect within the semiclassical Boltzmann transport theory. Its energy dependence is investigated, in particular the regime below the Dirac point of the 2DEG. In addition to an isotropic 2DEG, we analyze systems with anisotropic Fermi contours. We predict that the current-induced spin polarization vanishes if the Fermi contour passes through a Lifshitz transition. Further, we corroborate that topological insulators (TI) provide a very efficient charge-to-spin conversion.

18. Deficits of Affect Mentalization in Patients with Drug Addiction: Theoretical and Clinical Aspects

PubMed Central

Savov, Svetoslav; Atanassov, Nikola

2013-01-01

Traditionally treated with wariness, drug addictions have provoked a serious interest in psychodynamically oriented clinicians in recent decades. This paper discusses the development of contemporary psychodynamic conceptualizations of addictions, focusing specifically on mentalization-based theories. The concept of mentalization refers to a complex form of self-regulation which includes attribution of psychological meaning to one's own behavior and affective states, as well as those of the others. We hypothesize that drug-addicted patients have severe impairments in mentalizing, associated with developmental deficits, characteristic for the borderline personality disorder and psychosomatic conditions. Psychodynamic models of mentalization and their corresponding research operationalizations are reviewed, and implications for a contemporary understanding of drug addictions and psychotherapy are drawn. The authors propose that mentalization-oriented theories provide an adequate conceptualization, which is open to empirical testing and has clear and pragmatic guidelines for treatment. PMID:25969831

19. Computer simulations and theoretical aspects of the depletion interaction in protein-oligomer mixtures

Bončina, M.; Reščič, J.; Kalyuzhnyi, Yu. V.; Vlachy, V.

2007-07-01

The depletion interaction between proteins caused by addition of either uncharged or partially charged oligomers was studied using the canonical Monte Carlo simulation technique and the integral equation theory. A protein molecule was modeled in two different ways: either as (i) a hard sphere of diameter 30.0Å with net charge 0, or +5, or (ii) as a hard sphere with discrete charges (depending on the pH of solution) of diameter 45.4Å. The oligomers were pictured as tangentially jointed, uncharged, or partially charged, hard spheres. The ions of a simple electrolyte present in solution were represented by charged hard spheres distributed in the dielectric continuum. In this study we were particularly interested in changes of the protein-protein pair-distribution function, caused by addition of the oligomer component. In agreement with previous studies we found that addition of a nonadsorbing oligomer reduces the phase stability of solution, which is reflected in the shape of the protein-protein pair-distribution function. The value of this function in protein-protein contact increases with increasing oligomer concentration, and is larger for charged oligomers. The range of the depletion interaction and its strength also depend on the length (number of monomer units) of the oligomer chain. The integral equation theory, based on the Wertheim Ornstein-Zernike approach applied in this study, was found to be in fair agreement with Monte Carlo results only for very short oligomers. The computer simulations for a model mimicking the lysozyme molecule (ii) are in qualitative agreement with small-angle neutron experiments for lysozyme-dextran mixtures.

20. Theoretical and practical aspects in total uncemented hip arthroplasty by using short femoral stem prosthesis

PubMed Central

Moga, M; Pogarasteanu, ME; Barbilian, A

2015-01-01

Hip arthrosis, primary or secondary, is an osteoarthritic degenerative process that affects the hip joint. Primary hip arthrosis has an unknown etiology, and secondary hip arthrosis has well defined causes; of these causes, some are known to lead to arthrosis of the hip in the young age patient. The surgical treatment aims either to preserve the patient’s hip joint, or to replace the joint. The most commonly used procedure at this time is the total hip arthroplasty. The femoral component may have a short or a long stem. The short femoral stem prosthesis is usually impacted by using a unique technique and unique instruments, according to the manufacturer’s specifications. There are several models of short stem femoral prosthesis, but no matter which one is chosen, the surgical indication, the surgical technique and a well-conducted recovery program are important. The choosing of each arthroplastic implant must be made with care, taking into consideration the patient’s benefit, his expectations, and also the surgeon’s experience. PMID:26103643

1. Rotor-stator contact dynamics using a non-ideal drive—Theoretical and experimental aspects

Lahriri, Said; Weber, Hans I.; Santos, Ilmar F.; Hartmann, Henning

2012-09-01

The possible contact between rotor and stator is considered a serious malfunction that may lead to catastrophic failure. Rotor rub is seen as a secondary phenomenon caused by a primary source, i.e. sudden mass unbalance, instabilities generated by aerodynamic and hydrodynamic forces in seals and bearings among others. The contact event gives rise to normal and friction forces exerted on the rotor at impact events. The friction force plays a significant role by transferring some rotational energy of the rotor to lateral motion. A mathematical model has been developed to capture this for a conventional backup annular guide setup. It is reasonable to superpose an impact condition to the rub, where the rotor spin energy can be fully transformed into rotor lateral movements. Using a nonideal drive, i.e. an electric motor without any kind of velocity feedback control, it is even possible to stop the rotor spin under rubbing conditions. All the rotational energy will be transformed in a kind of "self-excited" rotor lateral vibration with repeated impacts against the housing. This paper studies the impact motion of a rotor impacting a conventional backup annular guide for the case of dry and lubricated inner surface of the guide. For the dry surface case, the experimental and numerical analysis shows that the rotational energy is fully transformed into lateral motion and the rotor spin is stopped. Based on this study this paper proposes a new unconventional backup bearing design in order to reduce the rub related severity in friction and center the rotor at impact events. The analysis shows that the rotor at impacts is forced to the center of the backup bearing and the lateral motion is mitigated. As a result of this, the rotor spin is kept constant.

2. The Theoretical Basis of the Effective School Improvement Model (ESI)

ERIC Educational Resources Information Center

Scheerens, Jaap; Demeuse, Marc

2005-01-01

This article describes the process of theoretical reflection that preceded the development and empirical verification of a model of "effective school improvement". The focus is on basic mechanisms that could be seen as underlying "getting things in motion" and change in education systems. Four mechanisms are distinguished: synoptic rational…

3. Healing from Childhood Sexual Abuse: A Theoretical Model

ERIC Educational Resources Information Center

Draucker, Claire Burke; Martsolf, Donna S.; Roller, Cynthia; Knapik, Gregory; Ross, Ratchneewan; Stidham, Andrea Warner

2011-01-01

Childhood sexual abuse is a prevalent social and health care problem. The processes by which individuals heal from childhood sexual abuse are not clearly understood. The purpose of this study was to develop a theoretical model to describe how adults heal from childhood sexual abuse. Community recruitment for an ongoing broader project on sexual…

4. Organizational Learning and Product Design Management: Towards a Theoretical Model.

ERIC Educational Resources Information Center

Chiva-Gomez, Ricardo; Camison-Zornoza, Cesar; Lapiedra-Alcami, Rafael

2003-01-01

Case studies of four Spanish ceramics companies were used to construct a theoretical model of 14 factors essential to organizational learning. One set of factors is related to the conceptual-analytical phase of the product design process and the other to the creative-technical phase. All factors contributed to efficient product design management…

5. Assessing Students' Understandings of Biological Models and their Use in Science to Evaluate a Theoretical Framework

Grünkorn, Juliane; Belzen, Annette Upmeier zu; Krüger, Dirk

2014-07-01

Research in the field of students' understandings of models and their use in science describes different frameworks concerning these understandings. Currently, there is no conjoint framework that combines these structures and so far, no investigation has focused on whether it reflects students' understandings sufficiently (empirical evaluation). Therefore, the purpose of this article is to present the results of an empirical evaluation of a conjoint theoretical framework. The theoretical framework integrates relevant research findings and comprises five aspects which are subdivided into three levels each: nature of models, multiple models, purpose of models, testing, and changing models. The study was conducted with a sample of 1,177 seventh to tenth graders (aged 11-19 years) using open-ended items. The data were analysed by identifying students' understandings of models (nature of models and multiple models) and their use in science (purpose of models, testing, and changing models), and comparing as well as assigning them to the content of the theoretical framework. A comprehensive category system of students' understandings was thus developed. Regarding the empirical evaluation, the students' understandings of the nature and the purpose of models were sufficiently described by the theoretical framework. Concerning the understandings of multiple, testing, and changing models, additional initial understandings (only one model possible, no testing of models, and no change of models) need to be considered. This conjoint and now empirically tested framework for students' understandings can provide a common basis for future science education research. Furthermore, evidence-based indications can be provided for teachers and their instructional practice.

6. A Generalized Information Theoretical Model for Quantum Secret Sharing

Bai, Chen-Ming; Li, Zhi-Hui; Xu, Ting-Ting; Li, Yong-Ming

2016-07-01

An information theoretical model for quantum secret sharing was introduced by H. Imai et al. (Quantum Inf. Comput. 5(1), 69-80 2005), which was analyzed by quantum information theory. In this paper, we analyze this information theoretical model using the properties of the quantum access structure. By the analysis we propose a generalized model definition for the quantum secret sharing schemes. In our model, there are more quantum access structures which can be realized by our generalized quantum secret sharing schemes than those of the previous one. In addition, we also analyse two kinds of important quantum access structures to illustrate the existence and rationality for the generalized quantum secret sharing schemes and consider the security of the scheme by simple examples.

7. Electromechanical properties of smart aggregate: theoretical modeling and experimental validation

Wang, Jianjun; Kong, Qingzhao; Shi, Zhifei; Song, Gangbing

2016-09-01

Smart aggregate (SA), as a piezoceramic-based multi-functional device, is formed by sandwiching two lead zirconate titanate (PZT) patches with copper shielding between a pair of solid-machined cylindrical marble blocks with epoxy. Previous researches have successfully demonstrated the capability and reliability of versatile SAs to monitor the structural health of concrete structures. However, the previous works concentrated mainly on the applications of SAs in structural health monitoring; no reasonable theoretical model of SAs was proposed. In this paper, electromechanical properties of SAs were investigated using a proposed theoretical model. Based on one dimensional linear theory of piezo-elasticity, the dynamic solutions of a SA subjected to an external harmonic voltage were solved. Further, the electric impedance of the SA was computed, and the resonance and anti-resonance frequencies were calculated based on derived equations. Numerical analysis was conducted to discuss the effects of the thickness of epoxy layer and the dimension of PZT patch on the fundamental resonance and anti-resonance frequencies as well as the corresponding electromechanical coupling factor. The dynamic solutions based on the proposed theoretical model were further experimentally verified with two SA samples. The fundamental resonance and anti-resonance frequencies of SAs show good agreements in both theoretical and experimental results. The presented analysis and results contribute to the overall understanding of SA properties and help to optimize the working frequencies of SAs in structural health monitoring of civil structures.

8. Using Spreadsheets to Teach Aspects of Biology Involving Mathematical Models

ERIC Educational Resources Information Center

Carlton, Kevin; Nicholls, Mike; Ponsonby, David

2004-01-01

Some aspects of biology, for example the Hardy-Weinberg simulation of population genetics or modelling heat flow in lizards, have an undeniable mathematical basis. Students can find the level of mathematical skill required to deal with such concepts to be an insurmountable hurdle to understanding. If not used effectively, spreadsheet models…

9. Aspects of the Cognitive Model of Physics Problem Solving.

ERIC Educational Resources Information Center

Brekke, Stewart E.

Various aspects of the cognitive model of physics problem solving are discussed in detail including relevant cues, encoding, memory, and input stimuli. The learning process involved in the recognition of familiar and non-familiar sensory stimuli is highlighted. Its four components include selection, acquisition, construction, and integration. The…

10. Chosen aspects of modeling and control of quadrotor platform

2012-11-01

This article is presenting the extended model of quadrotor platform together with a bespoken control system based on optimal approach. It highlights particular aspects of the derived model, such as inclusion of rotor gyroscopic effects and thrust generation based on momentum theory. The controller's behavior is tested by simulations. Comparisons with literature-available solutions to the problem of full quadrotor optimal control are made and important differences exposed. Conclusions are drawn and future work proposed.

11. Parallel Path Magnet Motor: Development of the Theoretical Model and Analysis of Experimental Results

Dirba, I.; Kleperis, J.

2011-01-01

Analytical and numerical modelling is performed for the linear actuator of a parallel path magnet motor. In the model based on finite-element analysis, the 3D problem is reduced to a 2D problem, which is sufficiently precise in a design aspect and allows modelling the principle of a parallel path motor. The paper also describes a relevant numerical model and gives comparison with experimental results. The numerical model includes all geometrical and physical characteristics of the motor components. The magnetic flux density and magnetic force are simulated using FEMM 4.2 software. An experimental model has also been developed and verified for the core of switchable magnetic flux linear actuator and motor. The results of experiments are compared with those of theoretical/analytical and numerical modelling.

12. Using thermal stress to model aspects of disease states.

PubMed

Wilson, Thad E; Klabunde, Richard E; Monahan, Kevin D

2014-07-01

Exposure to acute heat or cold stress elicits numerous physiological responses aimed at maintaining body temperatures. Interestingly, many of the physiological responses, mediated by the cardiovascular and autonomic nervous systems, resemble aspects of, or responses to, certain disease states. The purpose of this Perspective is to highlight some of these areas in order to explore how they may help us better understand the pathophysiology underlying aspects of certain disease states. The benefits of using this human thermal stress approach are that (1) no adjustments for inherent comparative differences in animals are needed, (2) non-medicated healthy humans with no underlying co-morbidities can be studied in place of complex patients, and (3) more mechanistic perturbations can be safely employed without endangering potentially vulnerable populations. Cold stress can be used to induce stable elevations in blood pressure. Cold stress may also be used to model conditions where increases in myocardial oxygen demand are not met by anticipated increases in coronary blood flow, as occurs in older adults. Lower-body negative pressure has the capacity to model aspects of shock, and the further addition of heat stress improves and expands this model because passive-heat exposure lowers systemic vascular resistance at a time when central blood volume and left-ventricular filling pressure are reduced. Heat stress can model aspects of heat syncope and orthostatic intolerance as heat stress decreases cerebral blood flow and alters the Frank-Starling mechanism resulting in larger decreases in stroke volume for a given change in left-ventricular filling pressure. Combined, thermal perturbations may provide in vivo paradigms that can be employed to gain insights into pathophysiological aspects of certain disease states. PMID:24956954

13. A sequential decision-theoretic model for medical diagnostic system.

PubMed

Li, Aiping; Jin, Songchang; Zhang, Lumin; Jia, Yan

2015-01-01

Although diagnostic expert systems using a knowledge base which models decision-making of traditional experts can provide important information to non-experts, they tend to duplicate the errors made by experts. Decision-Theoretic Model (DTM) is therefore very useful in expert system since they prevent experts from incorrect reasoning under uncertainty. For the diagnostic expert system, corresponding DTM and arithmetic are studied and a sequential diagnostic decision-theoretic model based on Bayesian Network is given. In the model, the alternative features are categorized into two classes (including diseases features and test features), then an arithmetic for prior of test is provided. The different features affect other features weights are also discussed. Bayesian Network is adopted to solve uncertainty presentation and propagation. The model can help knowledge engineers model the knowledge involved in sequential diagnosis and decide evidence alternative priority. A practical example of the models is also presented: at any time of the diagnostic process the expert is provided with a dynamically updated list of suggested tests in order to support him in the decision-making problem about which test to execute next. The results show it is better than the traditional diagnostic model which is based on experience. PMID:26410326

14. A theoretical model for lunar surface material thermal conductivity.

NASA Technical Reports Server (NTRS)

Khader, M. S.; Vachon, R. I.

1973-01-01

This paper presents a theoretical thermal conductivity model for the uppermost layer of lunar surface material under the lunar vacuum environment. The model assumes that the lunar soil can be simulated by spherical particles in contact with each other and that the effective thermal conductivity is a function of depth, temperature, porosity, particle dimension, and mechanical-thermal properties of the solid particles. Two modes of heat transport are considered, conduction and radiation - with emphasis on the contact resistance between particles. The model gives effective conductivity values that compare favorably with the experimental data from lunar surface samples obtained on Apollo 11 and 12 missions.

15. Modeling and Composing Scenario-Based Requirements with Aspects

NASA Technical Reports Server (NTRS)

Araujo, Joao; Whittle, Jon; Ki, Dae-Kyoo

2004-01-01

There has been significant recent interest, within the Aspect-Oriented Software Development (AOSD) community, in representing crosscutting concerns at various stages of the software lifecycle. However, most of these efforts have concentrated on the design and implementation phases. We focus in this paper on representing aspects during use case modeling. In particular, we focus on scenario-based requirements and show how to compose aspectual and non-aspectual scenarios so that they can be simulated as a whole. Non-aspectual scenarios are modeled as UML sequence diagram. Aspectual scenarios are modeled as Interaction Pattern Specifications (IPS). In order to simulate them, the scenarios are transformed into a set of executable state machines using an existing state machine synthesis algorithm. Previous work composed aspectual and non-aspectual scenarios at the sequence diagram level. In this paper, the composition is done at the state machine level.

16. Inhibition-based first-generation electrochemical biosensors: theoretical aspects and application to 2,4-dichlorophenoxy acetic acid detection.

PubMed

Bollella, Paolo; Fusco, Giovanni; Tortolini, Cristina; Sanzò, Gabriella; Antiochia, Riccarda; Favero, Gabriele; Mazzei, Franco

2016-05-01

In this work, several theoretical aspects involved in the first-generation inhibition-based electrochemical biosensor measurements have been discussed. In particular, we have developed a theoretical-methodological approach for the characterization of the kinetic interaction between alkaline phosphatase (AlP) and 2,4-dichlorophenoxy acetic acid (2,4-D) as representative inhibitor studied by means of cyclic voltammetry and amperometry. Based on these findings, a biosensor for the fast, simple, and inexpensive determination of 2,4-D has been developed. The enzyme has been immobilized on screen-printed electrodes (SPEs). To optimize the biosensor performances, several carbon-based SPEs, namely graphite (G), graphene (GP), and multiwalled carbon nanotubes (MWCNTs), have been evaluated. AlP was immobilized on the electrode surface by means of polyvinyl alcohol with styryl-pyridinium groups (PVA-SbQ) as cross-linking agent. In the presence of ascorbate 2-phosphate (A2P) as substrate, the herbicide has been determined, thanks to its inhibition activity towards the enzyme catalyzing the oxidation of A2P to ascorbic acid (AA). Under optimum experimental conditions, the best performance in terms of catalytic efficiency has been demonstrated by MWCNTs SPE-based biosensor. The inhibition biosensor shows a linearity range towards 2,4-D within 2.1-110 ppb, a LOD of 1 ppb, and acceptable repeatability and stability. This analysis method was applied to fortified lake water samples with recoveries above 90 %. The low cost of this device and its good analytical performances suggest its application for the screening and monitoring of 2,4-D in real matrices. Graphical Abstract ᅟ. PMID:26874693

17. An information-theoretic model for link prediction in complex networks

Zhu, Boyao; Xia, Yongxiang

2015-09-01

Various structural features of networks have been applied to develop link prediction methods. However, because different features highlight different aspects of network structural properties, it is very difficult to benefit from all of the features that might be available. In this paper, we investigate the role of network topology in predicting missing links from the perspective of information theory. In this way, the contributions of different structural features to link prediction are measured in terms of their values of information. Then, an information-theoretic model is proposed that is applicable to multiple structural features. Furthermore, we design a novel link prediction index, called Neighbor Set Information (NSI), based on the information-theoretic model. According to our experimental results, the NSI index performs well in real-world networks, compared with other typical proximity indices.

18. An information-theoretic model for link prediction in complex networks

PubMed Central

Zhu, Boyao; Xia, Yongxiang

2015-01-01

Various structural features of networks have been applied to develop link prediction methods. However, because different features highlight different aspects of network structural properties, it is very difficult to benefit from all of the features that might be available. In this paper, we investigate the role of network topology in predicting missing links from the perspective of information theory. In this way, the contributions of different structural features to link prediction are measured in terms of their values of information. Then, an information-theoretic model is proposed that is applicable to multiple structural features. Furthermore, we design a novel link prediction index, called Neighbor Set Information (NSI), based on the information-theoretic model. According to our experimental results, the NSI index performs well in real-world networks, compared with other typical proximity indices. PMID:26335758

19. Structure of plant photosystem I revealed by theoretical modeling.

PubMed

Jolley, Craig; Ben-Shem, Adam; Nelson, Nathan; Fromme, Petra

2005-09-30

Photosystem (PS) I is a large membrane protein complex vital for oxygenic photosynthesis, one of the most important biological processes on the planet. We present an "atomic" model of higher plant PSI, based on theoretical modeling using the recent 4.4 angstroms x-ray crystal structure of PSI from pea. Because of the lack of information on the amino acid side chains in the x-ray structural model and the high cofactor content in this system, novel modeling techniques were developed. Our model reveals some important structural features of plant PSI that were not visible in the crystal structure, and our model sheds light on the evolutionary relationship between plant and cyanobacterial PSI. PMID:15955818

20. Decision support models for solid waste management: Review and game-theoretic approaches

SciTech Connect

Karmperis, Athanasios C.; Aravossis, Konstantinos; Tatsiopoulos, Ilias P.; Sotirchos, Anastasios

2013-05-15

Highlights: ► The mainly used decision support frameworks for solid waste management are reviewed. ► The LCA, CBA and MCDM models are presented and their strengths, weaknesses, similarities and possible combinations are analyzed. ► The game-theoretic approach in a solid waste management context is presented. ► The waste management bargaining game is introduced as a specific decision support framework. ► Cooperative and non-cooperative game-theoretic approaches to decision support for solid waste management are discussed. - Abstract: This paper surveys decision support models that are commonly used in the solid waste management area. Most models are mainly developed within three decision support frameworks, which are the life-cycle assessment, the cost–benefit analysis and the multi-criteria decision-making. These frameworks are reviewed and their strengths and weaknesses as well as their critical issues are analyzed, while their possible combinations and extensions are also discussed. Furthermore, the paper presents how cooperative and non-cooperative game-theoretic approaches can be used for the purpose of modeling and analyzing decision-making in situations with multiple stakeholders. Specifically, since a waste management model is sustainable when considering not only environmental and economic but also social aspects, the waste management bargaining game is introduced as a specific decision support framework in which future models can be developed.

1. Selected aspects of modelling monetary transmission mechanism by BVAR model

Vaněk, Tomáš; Dobešová, Anna; Hampel, David

2013-10-01

In this paper we use the BVAR model with the specifically defined prior to evaluate data including high-lag dependencies. The results are compared to both restricted and common VAR model. The data depicts the monetary transmission mechanism in the Czech Republic and Slovakia from January 2002 to February 2013. The results point to the inadequacy of the common VAR model. The restricted VAR model and the BVAR model appear to be similar in the sense of impulse responses.

2. A theoretical model for smoking prevention studies in preteen children.

PubMed

McGahee, T W; Kemp, V; Tingen, M

2000-01-01

The age of the onset of smoking is on a continual decline, with the prime age of tobacco use initiation being 12-14 years. A weakness of the limited research conducted on smoking prevention programs designed for preteen children (ages 10-12) is a well-defined theoretical basis. A theoretical perspective is needed in order to make a meaningful transition from empirical analysis to application of knowledge. Bandura's Social Cognitive Theory (1977, 1986), the Theory of Reasoned Action (Ajzen & Fishbein, 1980), and other literature linking various concepts to smoking behaviors in preteens were used to develop a model that may be useful for smoking prevention studies in preteen children. PMID:12026266

3. Theoretical model for plasma expansion generated by hypervelocity impact

SciTech Connect

Ju, Yuanyuan; Zhang, Qingming Zhang, Dongjiang; Long, Renrong; Chen, Li; Huang, Fenglei; Gong, Zizheng

2014-09-15

The hypervelocity impact experiments of spherical LY12 aluminum projectile diameter of 6.4 mm on LY12 aluminum target thickness of 23 mm have been conducted using a two-stage light gas gun. The impact velocity of the projectile is 5.2, 5.7, and 6.3 km/s, respectively. The experimental results show that the plasma phase transition appears under the current experiment conditions, and the plasma expansion consists of accumulation, equilibrium, and attenuation. The plasma characteristic parameters decrease as the plasma expands outward and are proportional with the third power of the impact velocity, i.e., (T{sub e}, n{sub e}) ∝ v{sub p}{sup 3}. Based on the experimental results, a theoretical model on the plasma expansion is developed and the theoretical results are consistent with the experimental data.

4. Aspects and Strategies of Numerical Modelling of Underground Coal Fires

Wuttke, M. W.; Han, J.; Liu, G.; Kessels, W.; Schmidt, M.; Gusat, D.; Fischer, Chr.; Hirner, A.; Meyer, U.

2009-04-01

Numerical modelling of underground coal fires has become a valuable tool even for practical fire extinction work. The approaches, methods and finally codes that are used depend on the targets that are aimed at by the particular modelling task. The most general one is to fully understand the processes that sustain or suppress the fire. Another purpose is to produce realistic data for regions that are not accessible (e . g. underneath a burning coal seam) or couldn't be investigated (e.g due to limited resources) to estimate the complete energy budget of the fire. Last but not least one would like to forecast the fire dynamics to predict the future damage or to assess the effectivenees of extinction work. These purposes require the consideration of all aspects with respect to thermal, hydraulic, mechanical and chemical (THMC) processes. At the moment there is no single code that completely covers all these aspects with every degree of complexity. Within the Sino-German project "Innovative Technologies for Exploration, Extinction and Monitoring of Coal Fires in North China" we apply existing codes with different foci with respect to THMC processes and try to combine all codes to one comprehensive model. Besides the sophisticated academic modelling approach we also pursue the concept of "Onsite" modelling to enable fire fighting personnel to perform simplified modelling tasks even by means of web-based applications.

5. A Modified Theoretical Model of Intrinsic Hardness of Crystalline Solids

PubMed Central

Dai, Fu-Zhi; Zhou, Yanchun

2016-01-01

Super-hard materials have been extensively investigated due to their practical importance in numerous industrial applications. To stimulate the design and exploration of new super-hard materials, microscopic models that elucidate the fundamental factors controlling hardness are desirable. The present work modified the theoretical model of intrinsic hardness proposed by Gao. In the modification, we emphasize the critical role of appropriately decomposing a crystal to pseudo-binary crystals, which should be carried out based on the valence electron population of each bond. After modification, the model becomes self-consistent and predicts well the hardness values of many crystals, including crystals composed of complex chemical bonds. The modified model provides fundamental insights into the nature of hardness, which can facilitate the quest for intrinsic super-hard materials. PMID:27604165

6. A Modified Theoretical Model of Intrinsic Hardness of Crystalline Solids.

PubMed

Dai, Fu-Zhi; Zhou, Yanchun

2016-01-01

Super-hard materials have been extensively investigated due to their practical importance in numerous industrial applications. To stimulate the design and exploration of new super-hard materials, microscopic models that elucidate the fundamental factors controlling hardness are desirable. The present work modified the theoretical model of intrinsic hardness proposed by Gao. In the modification, we emphasize the critical role of appropriately decomposing a crystal to pseudo-binary crystals, which should be carried out based on the valence electron population of each bond. After modification, the model becomes self-consistent and predicts well the hardness values of many crystals, including crystals composed of complex chemical bonds. The modified model provides fundamental insights into the nature of hardness, which can facilitate the quest for intrinsic super-hard materials. PMID:27604165

7. Theoretical models for Mars and their seismic properties

NASA Technical Reports Server (NTRS)

Okal, E. A.; Anderson, D. L.

1978-01-01

Theoretical seismic properties of the planet Mars are investigated on the basis of the various models which have been proposed for the internal composition of the planet. The latest interpretation of gravity-field data, assuming a lower value of the moment of inertia, would require a less dense mantle and a larger core than previous models. If Mars is chondritic in composition, the most reasonable models are an incompletely differentiated H-chondrite or a mixture of H-chondrites and carbonaceous chondrites. Seismic profiles, travel times, and free oscillation periods are computed for various models, with the aim of establishing which seismic data is crucial for deciding among the alternatives. A detailed discussion is given of the seismic properties which could - in principle - help answer the questions of whether Mars' core is liquid or solid and whether Mars has a partially molten asthenosphere in its upper mantle.

8. Theoretical consideration of a microcontinuum model of graphene

Yang, Gang; Huang, Zaixing; Gao, Cun-Fa; Zhang, Bin

2016-05-01

A microcontinuum model of graphene is proposed based on micromorphic theory, in which the planar Bravais cell of graphene crystal is taken as the basal element of finite size. Governing equations including the macro-displacements and the micro-deformations of the basal element are modified and derived in global coordinates. Since independent freedom degrees of the basal element are closely related to the modes of phonon dispersions, the secular equations in micromorphic form are obtained by substituting the assumed harmonic wave equations into the governing equations, and simplified further according to the properties of phonon dispersion relations of two-dimensional (2D) crystals. Thus, the constitutive equations of the microcontinuum model are confirmed, in which the constitutive constants are determined by fitting the data of experimental and theoretical phonon dispersion relations in literature respectively. By employing the 2D microcontinuum model, we obtained sound velocities, Rayleigh velocity and elastic moduli of graphene, which show good agreements with available experimental or theoretical values, indicating that the current model would be another efficient and reliable methodology to study the mechanical behaviors of graphene.

9. Healing from Childhood Sexual Abuse: A Theoretical Model

PubMed Central

Draucker, Claire Burke; Martsolf, Donna S.; Roller, Cynthia; Knapik, Gregory; Ross, Ratchneewan; Stidham, Andrea Warner

2014-01-01

Childhood sexual abuse (CSA) is a prevalent social and healthcare problem. The processes by which individuals heal from CSA are not clearly understood. The purpose of this study was to develop a theoretical model to describe how adults heal from CSA. Community recruitment for an on-going, broader project on sexual violence throughout the lifespan, referred to as the Sexual Violence Study, yielded a subsample of 48 women and 47 men who had experienced CSA. During semi-structured, open-ended interviews, they were asked to describe their experiences with healing from CSA and other victimization throughout their lives. Constructivist grounded theory methods were used with these data to develop constructs and hypotheses about healing. For the Sexual Violence Study, frameworks were developed to describe the participants' life patterns, parenting experiences, disclosures about sexual violence, spirituality, and altruism. Several analytic techniques were used to synthesize the findings of these frameworks to develop an overarching theoretical model that describes healing from CSA. The model includes four stages of healing, five domains of functioning, and six enabling factors that facilitate movement from one stage to the next. The findings indicate that healing is a complex and dynamic trajectory. The model can be used to alert clinicians to a variety of processes and enabling factors that facilitate healing in several domains and to guide discussions on important issues related to healing from CSA. PMID:21812546

10. Game-Theoretic Models of Information Overload in Social Networks

Borgs, Christian; Chayes, Jennifer; Karrer, Brian; Meeder, Brendan; Ravi, R.; Reagans, Ray; Sayedi, Amin

We study the effect of information overload on user engagement in an asymmetric social network like Twitter. We introduce simple game-theoretic models that capture rate competition between celebrities producing updates in such networks where users non-strategically choose a subset of celebrities to follow based on the utility derived from high quality updates as well as disutility derived from having to wade through too many updates. Our two variants model the two behaviors of users dropping some potential connections (followership model) or leaving the network altogether (engagement model). We show that under a simple formulation of celebrity rate competition, there is no pure strategy Nash equilibrium under the first model. We then identify special cases in both models when pure rate equilibria exist for the celebrities: For the followership model, we show existence of a pure rate equilibrium when there is a global ranking of the celebrities in terms of the quality of their updates to users. This result also generalizes to the case when there is a partial order consistent with all the linear orders of the celebrities based on their qualities to the users. Furthermore, these equilibria can be computed in polynomial time. For the engagement model, pure rate equilibria exist when all users are interested in the same number of celebrities, or when they are interested in at most two. Finally, we also give a finite though inefficient procedure to determine if pure equilibria exist in the general case of the followership model.

11. Information-Theoretic Benchmarking of Land Surface Models

Nearing, Grey; Mocko, David; Kumar, Sujay; Peters-Lidard, Christa; Xia, Youlong

2016-04-01

Benchmarking is a type of model evaluation that compares model performance against a baseline metric that is derived, typically, from a different existing model. Statistical benchmarking was used to qualitatively show that land surface models do not fully utilize information in boundary conditions [1] several years before Gong et al [2] discovered the particular type of benchmark that makes it possible to *quantify* the amount of information lost by an incorrect or imperfect model structure. This theoretical development laid the foundation for a formal theory of model benchmarking [3]. We here extend that theory to separate uncertainty contributions from the three major components of dynamical systems models [4]: model structures, model parameters, and boundary conditions describe time-dependent details of each prediction scenario. The key to this new development is the use of large-sample [5] data sets that span multiple soil types, climates, and biomes, which allows us to segregate uncertainty due to parameters from the two other sources. The benefit of this approach for uncertainty quantification and segregation is that it does not rely on Bayesian priors (although it is strictly coherent with Bayes' theorem and with probability theory), and therefore the partitioning of uncertainty into different components is *not* dependent on any a priori assumptions. We apply this methodology to assess the information use efficiency of the four land surface models that comprise the North American Land Data Assimilation System (Noah, Mosaic, SAC-SMA, and VIC). Specifically, we looked at the ability of these models to estimate soil moisture and latent heat fluxes. We found that in the case of soil moisture, about 25% of net information loss was from boundary conditions, around 45% was from model parameters, and 30-40% was from the model structures. In the case of latent heat flux, boundary conditions contributed about 50% of net uncertainty, and model structures contributed

12. Theoretical models for coronary vascular biomechanics: progress & challenges.

PubMed

Waters, Sarah L; Alastruey, Jordi; Beard, Daniel A; Bovendeerd, Peter H M; Davies, Peter F; Jayaraman, Girija; Jensen, Oliver E; Lee, Jack; Parker, Kim H; Popel, Aleksander S; Secomb, Timothy W; Siebes, Maria; Sherwin, Spencer J; Shipley, Rebecca J; Smith, Nicolas P; van de Vosse, Frans N

2011-01-01

A key aim of the cardiac Physiome Project is to develop theoretical models to simulate the functional behaviour of the heart under physiological and pathophysiological conditions. Heart function is critically dependent on the delivery of an adequate blood supply to the myocardium via the coronary vasculature. Key to this critical function of the coronary vasculature is system dynamics that emerge via the interactions of the numerous constituent components at a range of spatial and temporal scales. Here, we focus on several components for which theoretical approaches can be applied, including vascular structure and mechanics, blood flow and mass transport, flow regulation, angiogenesis and vascular remodelling, and vascular cellular mechanics. For each component, we summarise the current state of the art in model development, and discuss areas requiring further research. We highlight the major challenges associated with integrating the component models to develop a computational tool that can ultimately be used to simulate the responses of the coronary vascular system to changing demands and to diseases and therapies. PMID:21040741

13. Theoretical models for coronary vascular biomechanics: Progress & challenges

PubMed Central

Waters, Sarah L.; Alastruey, Jordi; Beard, Daniel A.; Bovendeerd, Peter H.M.; Davies, Peter F.; Jayaraman, Girija; Jensen, Oliver E.; Lee, Jack; Parker, Kim H.; Popel, Aleksander S.; Secomb, Timothy W.; Siebes, Maria; Sherwin, Spencer J.; Shipley, Rebecca J.; Smith, Nicolas P.; van de Vosse, Frans N.

2013-01-01

A key aim of the cardiac Physiome Project is to develop theoretical models to simulate the functional behaviour of the heart under physiological and pathophysiological conditions. Heart function is critically dependent on the delivery of an adequate blood supply to the myocardium via the coronary vasculature. Key to this critical function of the coronary vasculature is system dynamics that emerge via the interactions of the numerous constituent components at a range of spatial and temporal scales. Here, we focus on several components for which theoretical approaches can be applied, including vascular structure and mechanics, blood flow and mass transport, flow regulation, angiogenesis and vascular remodelling, and vascular cellular mechanics. For each component, we summarise the current state of the art in model development, and discuss areas requiring further research. We highlight the major challenges associated with integrating the component models to develop a computational tool that can ultimately be used to simulate the responses of the coronary vascular system to changing demands and to diseases and therapies. PMID:21040741

14. Accuracy Analysis of a Box-wing Theoretical SRP Model

Wang, Xiaoya; Hu, Xiaogong; Zhao, Qunhe; Guo, Rui

2016-07-01

For Beidou satellite navigation system (BDS) a high accuracy SRP model is necessary for high precise applications especially with Global BDS establishment in future. The BDS accuracy for broadcast ephemeris need be improved. So, a box-wing theoretical SRP model with fine structure and adding conical shadow factor of earth and moon were established. We verified this SRP model by the GPS Block IIF satellites. The calculation was done with the data of PRN 1, 24, 25, 27 satellites. The results show that the physical SRP model for POD and forecast for GPS IIF satellite has higher accuracy with respect to Bern empirical model. The 3D-RMS of orbit is about 20 centimeters. The POD accuracy for both models is similar but the prediction accuracy with the physical SRP model is more than doubled. We tested 1-day 3-day and 7-day orbit prediction. The longer is the prediction arc length, the more significant is the improvement. The orbit prediction accuracy with the physical SRP model for 1-day, 3-day and 7-day arc length are 0.4m, 2.0m, 10.0m respectively. But they are 0.9m, 5.5m and 30m with Bern empirical model respectively. We apply this means to the BDS and give out a SRP model for Beidou satellites. Then we test and verify the model with Beidou data of one month only for test. Initial results show the model is good but needs more data for verification and improvement. The orbit residual RMS is similar to that with our empirical force model which only estimate the force for along track, across track direction and y-bias. But the orbit overlap and SLR observation evaluation show some improvement. The remaining empirical force is reduced significantly for present Beidou constellation.

15. Theoretical Modeling of Mechanical-Electrical Coupling of Carbon Nanotubes

SciTech Connect

Lu, Jun-Qiang; Jiang, Hanqiang

2008-01-01

Carbon nanotubes have been studied extensively due to their unique properties, ranging from electrical, mechanical, optical, to thermal properties. The coupling between the electrical and mechanical properties of carbon nanotubes has emerged as a new field, which raises both interesting fundamental problems and huge application potentials. In this article, we will review our recently work on the theoretical modeling on mechanical-electrical coupling of carbon nanotubes subject to various loading conditions, including tension/compression, torsion, and squashing. Some related work by other groups will be also mentioned.

16. Theoretical Models and Operational Frameworks in Public Health Ethics

PubMed Central

Petrini, Carlo

2010-01-01

The article is divided into three sections: (i) an overview of the main ethical models in public health (theoretical foundations); (ii) a summary of several published frameworks for public health ethics (practical frameworks); and (iii) a few general remarks. Rather than maintaining the superiority of one position over the others, the main aim of the article is to summarize the basic approaches proposed thus far concerning the development of public health ethics by describing and comparing the various ideas in the literature. With this in mind, an extensive list of references is provided. PMID:20195441

17. The Thomas–Fermi quark model: Non-relativistic aspects

SciTech Connect

Liu, Quan Wilcox, Walter

2014-02-15

The first numerical investigation of non-relativistic aspects of the Thomas–Fermi (TF) statistical multi-quark model is given. We begin with a review of the traditional TF model without an explicit spin interaction and find that the spin splittings are too small in this approach. An explicit spin interaction is then introduced which entails the definition of a generalized spin “flavor”. We investigate baryonic states in this approach which can be described with two inequivalent wave functions; such states can however apply to multiple degenerate flavors. We find that the model requires a spatial separation of quark flavors, even if completely degenerate. Although the TF model is designed to investigate the possibility of many-quark states, we find surprisingly that it may be used to fit the low energy spectrum of almost all ground state octet and decuplet baryons. The charge radii of such states are determined and compared with lattice calculations and other models. The low energy fit obtained allows us to extrapolate to the six-quark doubly strange H-dibaryon state, flavor symmetric strange states of higher quark content and possible six quark nucleon–nucleon resonances. The emphasis here is on the systematics revealed in this approach. We view our model as a versatile and convenient tool for quickly assessing the characteristics of new, possibly bound, particle states of higher quark number content. -- Highlights: • First application of the statistical Thomas–Fermi quark model to baryonic systems. • Novel aspects: spin as generalized flavor; spatial separation of quark flavor phases. • The model is statistical, but the low energy baryonic spectrum is successfully fit. • Numerical applications include the H-dibaryon, strange states and nucleon resonances. • The statistical point of view does not encourage the idea of bound many-quark baryons.

18. Theoretical and experimental impact of the bed aspect ratio on the axial dispersion coefficient of columns packed with 2.5 μm particles.

PubMed

Gritti, Fabrice; Guiochon, Georges

2012-11-01

The impact of the ratio of the column diameter to the average particle size (or bed aspect ratio) on the column performance was investigated from theoretical and experimental viewpoints. The experiments were conducted for two series of 100mm long columns, 2.1, 3.0, and 4.6mm in diameter, packed with 2.5 μm fully porous particles of Bridge Ethylene Hybrid (BEH) for one series and Charged Surface Hybrid (CSH) for the other. The heights equivalent to a theoretical plate (HETP) of two low molecular weight compounds, uracil (non-retained, k=0) and naphthalene (retained, k=2.5), were determined from the true moments of the recorded peak profiles. The results showed a systematic decrease of the column performance for uracil at high flow velocities with decreasing column inner diameter, in agreement with the theoretical predictions of the variation of the trans-column eddy dispersion HETP term with decreasing bed aspect ratio. This result is consistent with the increasing volume fraction of the wall region of the column, in which the average linear velocity of the mobile phase over a distance of 5 particle diameters from the column wall is about 10% larger than in the bulk center of the column (infinite diameter column). For the retained compound, the discrepancies are levelled out due to the longer average residence time and larger particle diffusivities of retained compounds, which allow a more efficient relaxation of the radial concentration gradients. Further improvements of the performance of the larger I.D. columns (3.0 and 4.6mm I.D.) may be achieved by decreasing the harmful effect of this trans-column velocity bias by injecting and/or collecting the sample molecules in a wide central zone of the column. For 2.1mm I.D. columns, this approach would prove useful only when HPLC instruments providing a lower extra-column band broadening contribution will become available. Finally, the further minimization of the trans-column eddy dispersion HETP term and the design of

19. NMR relaxation induced by iron oxide particles: testing theoretical models.

PubMed

Gossuin, Y; Orlando, T; Basini, M; Henrard, D; Lascialfari, A; Mattea, C; Stapf, S; Vuong, Q L

2016-04-15

Superparamagnetic iron oxide particles find their main application as contrast agents for cellular and molecular magnetic resonance imaging. The contrast they bring is due to the shortening of the transverse relaxation time T 2 of water protons. In order to understand their influence on proton relaxation, different theoretical relaxation models have been developed, each of them presenting a certain validity domain, which depends on the particle characteristics and proton dynamics. The validation of these models is crucial since they allow for predicting the ideal particle characteristics for obtaining the best contrast but also because the fitting of T 1 experimental data by the theory constitutes an interesting tool for the characterization of the nanoparticles. In this work, T 2 of suspensions of iron oxide particles in different solvents and at different temperatures, corresponding to different proton diffusion properties, were measured and were compared to the three main theoretical models (the motional averaging regime, the static dephasing regime, and the partial refocusing model) with good qualitative agreement. However, a real quantitative agreement was not observed, probably because of the complexity of these nanoparticulate systems. The Roch theory, developed in the motional averaging regime (MAR), was also successfully used to fit T 1 nuclear magnetic relaxation dispersion (NMRD) profiles, even outside the MAR validity range, and provided a good estimate of the particle size. On the other hand, the simultaneous fitting of T 1 and T 2 NMRD profiles by the theory was impossible, and this occurrence constitutes a clear limitation of the Roch model. Finally, the theory was shown to satisfactorily fit the deuterium T 1 NMRD profile of superparamagnetic particle suspensions in heavy water. PMID:26933908

20. NMR relaxation induced by iron oxide particles: testing theoretical models

Gossuin, Y.; Orlando, T.; Basini, M.; Henrard, D.; Lascialfari, A.; Mattea, C.; Stapf, S.; Vuong, Q. L.

2016-04-01

Superparamagnetic iron oxide particles find their main application as contrast agents for cellular and molecular magnetic resonance imaging. The contrast they bring is due to the shortening of the transverse relaxation time T 2 of water protons. In order to understand their influence on proton relaxation, different theoretical relaxation models have been developed, each of them presenting a certain validity domain, which depends on the particle characteristics and proton dynamics. The validation of these models is crucial since they allow for predicting the ideal particle characteristics for obtaining the best contrast but also because the fitting of T 1 experimental data by the theory constitutes an interesting tool for the characterization of the nanoparticles. In this work, T 2 of suspensions of iron oxide particles in different solvents and at different temperatures, corresponding to different proton diffusion properties, were measured and were compared to the three main theoretical models (the motional averaging regime, the static dephasing regime, and the partial refocusing model) with good qualitative agreement. However, a real quantitative agreement was not observed, probably because of the complexity of these nanoparticulate systems. The Roch theory, developed in the motional averaging regime (MAR), was also successfully used to fit T 1 nuclear magnetic relaxation dispersion (NMRD) profiles, even outside the MAR validity range, and provided a good estimate of the particle size. On the other hand, the simultaneous fitting of T 1 and T 2 NMRD profiles by the theory was impossible, and this occurrence constitutes a clear limitation of the Roch model. Finally, the theory was shown to satisfactorily fit the deuterium T 1 NMRD profile of superparamagnetic particle suspensions in heavy water.

1. Sampling artifact in volume weighted velocity measurement. I. Theoretical modeling

Zhang, Pengjie; Zheng, Yi; Jing, Yipeng

2015-02-01

Cosmology based on large scale peculiar velocity prefers volume weighted velocity statistics. However, measuring the volume weighted velocity statistics from inhomogeneously distributed galaxies (simulation particles/halos) suffers from an inevitable and significant sampling artifact. We study this sampling artifact in the velocity power spectrum measured by the nearest particle velocity assignment method by Zheng et al., [Phys. Rev. D 88, 103510 (2013).]. We derive the analytical expression of leading and higher order terms. We find that the sampling artifact suppresses the z =0 E -mode velocity power spectrum by ˜10 % at k =0.1 h /Mpc , for samples with number density 10-3 (Mpc /h )-3 . This suppression becomes larger for larger k and for sparser samples. We argue that this source of systematic errors in peculiar velocity cosmology, albeit severe, can be self-calibrated in the framework of our theoretical modelling. We also work out the sampling artifact in the density-velocity cross power spectrum measurement. A more robust evaluation of related statistics through simulations will be presented in a companion paper by Zheng et al., [Sampling artifact in volume weighted velocity measurement. II. Detection in simulations and comparison with theoretical modelling, arXiv:1409.6809.]. We also argue that similar sampling artifact exists in other velocity assignment methods and hence must be carefully corrected to avoid systematic bias in peculiar velocity cosmology.

2. Aspects of Mathematical Modelling of Pressure Retarded Osmosis

PubMed Central

Anissimov, Yuri G.

2016-01-01

In power generating terms, a pressure retarded osmosis (PRO) energy generating plant, on a river entering a sea or ocean, is equivalent to a hydroelectric dam with a height of about 60 meters. Therefore, PRO can add significantly to existing renewable power generation capacity if economical constrains of the method are resolved. PRO energy generation relies on a semipermeable membrane that is permeable to water and impermeable to salt. Mathematical modelling plays an important part in understanding flows of water and salt near and across semipermeable membranes and helps to optimize PRO energy generation. Therefore, the modelling can help realizing PRO energy generation potential. In this work, a few aspects of mathematical modelling of the PRO process are reviewed and discussed. PMID:26848696

3. Dynamical aspects in modeling long cantilevering workpieces in tool grinding

de Payrebrune, K. M.; Kröger, M.

2015-10-01

Tool grinding is a complex process in which temporal dynamics of workpiece and grinding wheel, and the material removal process itself, affect the quality of the workpiece. Many existing models already provide the option to study the dynamics of workpiece and grinding wheel or cutting forces and material removal processes, but mostly do not combine these aspects. Here, workpiece dynamics are studied in relation to its structural and geometrical changing properties during machining, and are used to simulate the vibrations and deformation of the workpiece during grinding. In combination with models for the grinding wheel and the material removal process, dependencies of the workpiece dynamics on the workpieces quality are studied and results from this hybrid model are in excellent agreement with empirical measurements. Furthermore, the results demonstrate the significant effects of deformations of the workpiece on its final geometry.

4. Aspects of Mathematical Modelling of Pressure Retarded Osmosis.

PubMed

Anissimov, Yuri G

2016-01-01

In power generating terms, a pressure retarded osmosis (PRO) energy generating plant, on a river entering a sea or ocean, is equivalent to a hydroelectric dam with a height of about 60 meters. Therefore, PRO can add significantly to existing renewable power generation capacity if economical constrains of the method are resolved. PRO energy generation relies on a semipermeable membrane that is permeable to water and impermeable to salt. Mathematical modelling plays an important part in understanding flows of water and salt near and across semipermeable membranes and helps to optimize PRO energy generation. Therefore, the modelling can help realizing PRO energy generation potential. In this work, a few aspects of mathematical modelling of the PRO process are reviewed and discussed. PMID:26848696

5. Inference of Mix from Experimental Data and Theoretical Mix Models

SciTech Connect

Welser-Sherrill, L.; Haynes, D. A.; Cooley, J. H.; Mancini, R. C.; Haan, S. W.; Golovkin, I. E.

2007-08-02

The mixing between fuel and shell materials in Inertial Confinement Fusion implosion cores is a topic of great interest. Mixing due to hydrodynamic instabilities can affect implosion dynamics and could also go so far as to prevent ignition. We have demonstrated that it is possible to extract information on mixing directly from experimental data using spectroscopic arguments. In order to compare this data-driven analysis to a theoretical framework, two independent mix models, Youngs' phenomenological model and the Haan saturation model, have been implemented in conjunction with a series of clean hydrodynamic simulations that model the experiments. The first tests of these methods were carried out based on a set of indirect drive implosions at the OMEGA laser. We now focus on direct drive experiments, and endeavor to approach the problem from another perspective. In the current work, we use Youngs' and Haan's mix models in conjunction with hydrodynamic simulations in order to design experimental platforms that exhibit measurably different levels of mix. Once the experiments are completed based on these designs, the results of a data-driven mix analysis will be compared to the levels of mix predicted by the simulations. In this way, we aim to increase our confidence in the methods used to extract mixing information from the experimental data, as well as to study sensitivities and the range of validity of the mix models.

6. Development of theoretical models of integrated millimeter wave antennas

NASA Technical Reports Server (NTRS)

Yngvesson, K. Sigfrid; Schaubert, Daniel H.

1991-01-01

Extensive radiation patterns for Linear Tapered Slot Antenna (LTSA) Single Elements are presented. The directivity of LTSA elements is predicted correctly by taking the cross polarized pattern into account. A moment method program predicts radiation patterns for air LTSAs with excellent agreement with experimental data. A moment method program was also developed for the task LTSA Array Modeling. Computations performed with this program are in excellent agreement with published results for dipole and monopole arrays, and with waveguide simulator experiments, for more complicated structures. Empirical modeling of LTSA arrays demonstrated that the maximum theoretical element gain can be obtained. Formulations were also developed for calculating the aperture efficiency of LTSA arrays used in reflector systems. It was shown that LTSA arrays used in multibeam systems have a considerable advantage in terms of higher packing density, compared with waveguide feeds. Conversion loss of 10 dB was demonstrated at 35 GHz.

7. A theoretical model of sheath fold morphology in simple shear

Reber, Jacqueline E.; Dabrowski, Marcin; Galland, Olivier; Schmid, Daniel W.

2013-04-01

Sheath folds are highly non-cylindrical structures often associated with shear zones. The geometry of sheath folds, especially cross-sections perpendicular to the stretching direction that display eye-patterns, have been used in the field to deduce kinematic information such as shear sense and bulk strain type. However, how sheath folds form and how they evolve with increasing strain is still a matter of debate. We investigate the formation of sheath folds around a weak inclusion acting as a slip surface in simple shear by means of an analytical model. We systematically vary the slip surface orientation and shape and evaluate the impact on the evolving eye-pattern. In addition we compare our results to existing classifications. Based on field observations it has been suggested that the shear sense of a shear zone can be determined by knowing the position of the center of an eye-pattern and the closing direction of the corresponding sheath fold. In our modeled sheath folds we can observe for a given strain that the center of the eye-structure is subject to change in height with respect to the upper edge of the outermost closed contour for different cross-sections perpendicular to the shear direction. This results in a large variability in layer thickness, questioning the usefulness of sheath folds as shear sense indicators. The location of the center of the eye structure, however, is largely invariant to the initial configurations of the slip surface as well as to strain. It has been suggested that the ratio of the aspect ratio of the innermost and outermost closed contour in eye-patterns could be linked to the bulk strain type based on filed observations. We apply this classification to our modeled sheath folds and we observe that the values of the aspect ratios of the closed contours within the eye-pattern are dependent on the strain and the cross-section location. The ratio (R') of the aspect ratios of the outermost closed contour (Ryz) and the innermost closed

8. Theoretical light curves for deflagration models of type Ia supernova

Blinnikov, S. I.; Röpke, F. K.; Sorokina, E. I.; Gieseler, M.; Reinecke, M.; Travaglio, C.; Hillebrandt, W.; Stritzinger, M.

2006-07-01

Aims.We present synthetic bolometric and broad-band UBVRI light curves of SNe Ia for four selected 3D deflagration models of thermonuclear supernovae. Methods: .The light curves are computed with the 1D hydro code stella, which models (multi-group time-dependent) non-equilibrium radiative transfer inside SN ejecta. Angle-averaged results from 3D hydrodynamical explosion simulations with the composition determined in a nucleosynthetic postprocessing step served as the input to the radiative transfer model. Results: .The predicted model {UBV} light curves do agree reasonably well with the observed ones for SNe Ia in the range of low to normal luminosities, although the underlying hydrodynamical explosion models produced only a modest amount of radioactive {}56Ni(i.e. 0.24-0.42 M⊙) and relatively low kinetic energy in the explosion (less than 0.7 × 1051 erg). The evolution of predicted B and V fluxes in the model with a {}56Nimass of 0.42 M⊙ follows the observed decline rate after the maximum very well, although the behavior of fluxes in other filters deviates somewhat from observations, and the bolometric decline rate is a bit slow. The material velocity at the photospheric level is on the order of 104 km s-1 for all models. Using our models, we check the validity of Arnett's rule, relating the peak luminosity to the power of the deposited radioactive heating, and we also check the accuracy of the procedure for extracting the {}56Nimass from the observed light curves. Conclusions: .We find that the comparison between theoretical light curves and observations provides a useful tool to validate SN Ia models. The steps necessary for improving the agreement between theory and observations are set out.

9. Modeling semantic aspects for cross-media image indexing.

PubMed

Monay, Florent; Gatica-Perez, Daniel

2007-10-01

To go beyond the query-by-example paradigm in image retrieval, there is a need for semantic indexing of large image collections for intuitive text-based image search. Different models have been proposed to learn the dependencies between the visual content of an image set and the associated text captions, then allowing for the automatic creation of semantic indices for unannotated images. The task, however, remains unsolved. In this paper, we present three alternatives to learn a Probabilistic Latent Semantic Analysis model (PLSA) for annotated images, and evaluate their respective performance for automatic image indexing. Under the PLSA assumptions, an image is modeled as a mixture of latent aspects that generates both image features and text captions, and we investigate three ways to learn the mixture of aspects. We also propose a more discriminative image representation than the traditional Blob histogram, concatenating quantized local color information and quantized local texture descriptors. The first learning procedure of a PLSA model for annotated images is a standard EM algorithm, which implicitly assumes that the visual and the textual modalities can be treated equivalently. The other two models are based on an asymmetric PLSA learning, allowing to constrain the definition of the latent space on the visual or on the textual modality. We demonstrate that the textual modality is more appropriate to learn a semantically meaningful latent space, which translates into improved annotation performance. A comparison of our learning algorithms with respect to recent methods on a standard dataset is presented, and a detailed evaluation of the performance shows the validity of our framework. PMID:17699924

10. Nonlinear Flutter Aspects of the Flexible HSCT Semispan Model

NASA Technical Reports Server (NTRS)

Hajj, Muhammad R.; Silva, Walter A.

2003-01-01

The nonlinear aspects that lead to the flutter of an High-Speed Civil Transport (HSCT) Flexible Semispan Model are analyzed. A hierarchy of spectral moments was used to determine the characteristics of the aerodynamic loading and structural strains and motions. The results show that the frequency of the bending motion of the wing varied significantly as the Mach number was increased between 0.90 and 0.97. Examination of the pressure coefficients in terms of mean value and fluctuations showed that the flow characteristics over the wing changed significantly around a Mach number of 0.97. A strong shock was identified near the trailing edge. Nonlinear analysis of the pressure fluctuations, under these conditions, showed nonlinear coupling involving low-frequency components at pressure locations where the mean value was at a local minimum. This shows that the aerodynamic forces acting on the model had nonlinearly coupled frequency components. The results presented here show how nonlinear analysis tools can be used to identify nonlinear aspects of the flutter phenomenon which are needed in the validation of nonlinear computational methodologies. Keywords: Nonlinear aeroelasticity, Flutter, Bispectrum.

11. Theoretical model for the wetting of a rough surface.

PubMed

Hay, K M; Dragila, M I; Liburdy, J

2008-09-15

Many applications would benefit from an understanding of the physical mechanism behind fluid movement on rough surfaces, including the movement of water or contaminants within an unsaturated rock fracture. Presented is a theoretical investigation of the effect of surface roughness on fluid spreading. It is known that surface roughness enhances the effects of hydrophobic or hydrophilic behavior, as well as allowing for faster spreading of a hydrophilic fluid. A model is presented based on the classification of the regimes of spreading that occur when fluid encounters a rough surface: microscopic precursor film, mesoscopic invasion of roughness and macroscopic reaction to external forces. A theoretical relationship is developed for the physical mechanisms that drive mesoscopic invasion, which is used to guide a discussion of the implications of the theory on spreading conditions. Development of the analytical equation is based on a balance between capillary forces and frictional resistive forces. Chemical heterogeneity is ignored. The effect of various methods for estimating viscous dissipation is compared to available data from fluid rise on roughness experiments. Methods that account more accurately for roughness shape better explain the data as they account for more surface friction; the best fit was found for a hydraulic diameter approximation. The analytical solution implies the existence of a critical contact angle that is a function of roughness geometry, below which fluid will spread and above which fluid will resist spreading. The resulting equation predicts movement of a liquid invasion front with a square root of time dependence, mathematically resembling a diffusive process. PMID:18586259

12. Some aspects of statistical modeling of human-error probability

SciTech Connect

Prairie, R. R.

1982-01-01

Human reliability analyses (HRA) are often performed as part of risk assessment and reliability projects. Recent events in nuclear power have shown the potential importance of the human element. There are several on-going efforts in the US and elsewhere with the purpose of modeling human error such that the human contribution can be incorporated into an overall risk assessment associated with one or more aspects of nuclear power. An effort that is described here uses the HRA (event tree) to quantify and model the human contribution to risk. As an example, risk analyses are being prepared on several nuclear power plants as part of the Interim Reliability Assessment Program (IREP). In this process the risk analyst selects the elements of his fault tree that could be contributed to by human error. He then solicits the HF analyst to do a HRA on this element.

13. NONHOMOGENEOUS TERMS IN THE UNSTEADY FLOW EQUATIONS: MODELING ASPECTS.

USGS Publications Warehouse

Lai, Chintu; Schaffranek, Raymond W.; Baltzer, Robert A.

1987-01-01

A study is in progress to identify the relative significance, effects, and benefits attributable to the use of one-dimensional, unsteady, open-channel, flow-simulation models employing a variety of nonhomogeneous terms in their equation formulations. Nonhomogeneous terms being analyzed include those representing bed slope, frictional resistance, nonprismatic channel geometry, lateral flow, and (surface) wind stress. After an initial theoretical discussion, the results of a set of numerical experiments are presented that demonstrate cause-and-effect relationships and intercomparisons achieved by neglect or improper treatment of important nonhomogeneous terms. Preliminary results of this study are discussed and presented in this paper, both in the form of qualitative considerations and quantitative tabular findings. These results are expected to yield a definitive set of guidelines and suggestions useful to model engineers.

14. Group theoretical modeling of thermal explosion with reactant consumption

Ibragimov, Ranis N.; Dameron, Michael

2012-09-01

Today engineering and science researchers routinely confront problems in mathematical modeling involving nonlinear differential equations. Many mathematical models formulated in terms of nonlinear differential equations can be successfully treated and solved by Lie group methods. Lie group analysis is especially valuable in investigating nonlinear differential equations, for its algorithms act as reliably as for linear cases. The aim of this article is to provide the group theoretical modeling of the symmetrical heating of an exothermally reacting medium with approximations to the body's temperature distribution similar to those made by Thomas [17] and Squire [15]. The quantitative results were found to be in a good agreement with Adler and Enig in [1], where the authors were comparing the integral curves corresponding to the critical conditions for the first-order reaction. Further development of the modeling by including the critical temperature is proposed. Overall, it is shown, in particular, that the application of Lie group analysis allows one to extend the previous analytic results for the first order reactions to nth order ones.

15. Theoretical model for calculation of helicity in solar active regions

Chatterjee, P.

We (Choudhuri, Chatterjee and Nandy, 2005) calculate helicities of solar active regions based on the idea of Choudhuri (2003) that poloidal flux lines get wrapped around a toroidal flux tube rising through the convection zone, thereby giving rise to the helicity. Rough estimates based on this idea compare favourably with the observed magnitude of helicity. We use our solar dynamo model based on the Babcock--Leighton α-effect to study how helicity varies with latitude and time. At the time of solar maximum, our theoretical model gives negative helicity in the northern hemisphere and positive helicity in the south, in accordance with observed hemispheric trends. However, we find that, during a short interval at the beginning of a cycle, helicities tend to be opposite of the preferred hemispheric trends. Next we (Chatterjee, Choudhuri and Petrovay 2006) use the above idea along with the sunspot decay model of Petrovay and Moreno-Insertis, (1997) to estimate the distribution of helicity inside a flux tube as it keeps collecting more azimuthal flux during its rise through the convection zone and as turbulent diffusion keeps acting on it. By varying parameters over reasonable ranges in our simple 1-d model, we find that the azimuthal flux penetrates the flux tube to some extent instead of being confined to a narrow sheath outside.

16. Modeling of rolling element bearing mechanics. Theoretical manual

NASA Technical Reports Server (NTRS)

Merchant, David H.; Greenhill, Lyn M.

1994-01-01

This report documents the theoretical basis for the Rolling Element Bearing Analysis System (REBANS) analysis code which determines the quasistatic response to external loads or displacement of three types of high-speed rolling element bearings: angular contact ball bearings; duplex angular contact ball bearings; and cylindrical roller bearings. The model includes the effects of bearing ring and support structure flexibility. It is comprised of two main programs: the Preprocessor for Bearing Analysis (PREBAN) which creates the input files for the main analysis program; and Flexibility Enhanced Rolling Element Bearing Analysis (FEREBA), the main analysis program. A companion report addresses the input instructions for and features of the computer codes. REBANS extends the capabilities of the SHABERTH (Shaft and Bearing Thermal Analysis) code to include race and housing flexibility, including such effects as dead band and preload springs.

17. Modeling an Application's Theoretical Minimum and Average Transactional Response Times

SciTech Connect

Paiz, Mary Rose

2015-04-01

The theoretical minimum transactional response time of an application serves as a ba- sis for the expected response time. The lower threshold for the minimum response time represents the minimum amount of time that the application should take to complete a transaction. Knowing the lower threshold is beneficial in detecting anomalies that are re- sults of unsuccessful transactions. On the converse, when an application's response time falls above an upper threshold, there is likely an anomaly in the application that is causing unusual performance issues in the transaction. This report explains how the non-stationary Generalized Extreme Value distribution is used to estimate the lower threshold of an ap- plication's daily minimum transactional response time. It also explains how the seasonal Autoregressive Integrated Moving Average time series model is used to estimate the upper threshold for an application's average transactional response time.

18. Theoretical model for forming limit diagram predictions without initial inhomogeneity

Gologanu, Mihai; Comsa, Dan Sorin; Banabic, Dorel

2013-05-01

We report on our attempts to build a theoretical model for determining forming limit diagrams (FLD) based on limit analysis that, contrary to the well-known Marciniak and Kuczynski (M-K) model, does not assume the initial existence of a region with material or geometrical inhomogeneity. We first give a new interpretation based on limit analysis for the onset of necking in the M-K model. Considering the initial thickness defect along a narrow band as postulated by the M-K model, we show that incipient necking is a transition in the plastic mechanism from one of plastic flow in both the sheet and the band to another one where the sheet becomes rigid and all plastic deformation is localized in the band. We then draw on some analogies between the onset of necking in a sheet and the onset of coalescence in a porous bulk body. In fact, the main advance in coalescence modeling has been based on a similar limit analysis with an important new ingredient: the evolution of the spatial distribution of voids, due to the plastic deformation, creating weaker regions with higher porosity surrounded by sound regions with no voids. The onset of coalescence is precisely the transition from a mechanism of plastic deformation in both regions to another one, where the sound regions are rigid. We apply this new ingredient to a necking model based on limit analysis, for the first quadrant of the FLD and a porous sheet. We use Gurson's model with some recent extensions to model the porous material. We follow both the evolution of a homogeneous sheet and the evolution of the distribution of voids. At each moment we test for a potential change of plastic mechanism, by comparing the stresses in the uniform region to those in a virtual band with a larger porosity. The main difference with the coalescence of voids in a bulk solid is that the plastic mechanism for a sheet admits a supplementary degree of freedom, namely the change in the thickness of the virtual band. For strain ratios close to

19. Modeling postpartum depression in rats: theoretic and methodological issues

PubMed Central

Ming, LI; Shinn-Yi, CHOU

2016-01-01

The postpartum period is when a host of changes occur at molecular, cellular, physiological and behavioral levels to prepare female humans for the challenge of maternity. Alteration or prevention of these normal adaptions is thought to contribute to disruptions of emotion regulation, motivation and cognitive abilities that underlie postpartum mental disorders, such as postpartum depression. Despite the high incidence of this disorder, and the detrimental consequences for both mother and child, its etiology and related neurobiological mechanisms remain poorly understood, partially due to the lack of appropriate animal models. In recent decades, there have been a number of attempts to model postpartum depression disorder in rats. In the present review, we first describe clinical symptoms of postpartum depression and discuss known risk factors, including both genetic and environmental factors. Thereafter, we discuss various rat models that have been developed to capture various aspects of this disorder and knowledge gained from such attempts. In doing so, we focus on the theories behind each attempt and the methods used to achieve their goals. Finally, we point out several understudied areas in this field and make suggestions for future directions. PMID:27469254

20. Modeling postpartum depression in rats: theoretic and methodological issues.

PubMed

Li, Ming; Chou, Shinn-Yi

2016-07-18

The postpartum period is when a host of changes occur at molecular, cellular, physiological and behavioral levels to prepare female humans for the challenge of maternity. Alteration or prevention of these normal adaptions is thought to contribute to disruptions of emotion regulation, motivation and cognitive abilities that underlie postpartum mental disorders, such as postpartum depression. Despite the high incidence of this disorder, and the detrimental consequences for both mother and child, its etiology and related neurobiological mechanisms remain poorly understood, partially due to the lack of appropriate animal models. In recent decades, there have been a number of attempts to model postpartum depression disorder in rats. In the present review, we first describe clinical symptoms of postpartum depression and discuss known risk factors, including both genetic and environmental factors. Thereafter, we discuss various rat models that have been developed to capture various aspects of this disorder and knowledge gained from such attempts. In doing so, we focus on the theories behind each attempt and the methods used to achieve their goals. Finally, we point out several understudied areas in this field and make suggestions for future directions. PMID:27469254

1. Students' Levels of Understanding Models and Modelling in Biology: Global or Aspect-Dependent?

Krell, Moritz; Upmeier zu Belzen, Annette; Krüger, Dirk

2014-02-01

It is argued that knowledge about models is an important part of a profound understanding of Nature of Science. Consequently, researchers have developed different `levels of understanding' to analyse students', teachers', or experts' comprehension of this topic. In some approaches, global levels of understanding have been developed which mirror the idea of an understanding of models and modelling as a whole. Opposed to this, some authors have developed levels of understanding for distinct aspects concerning models and modelling in science (i.e. aspect-dependent levels). This points to an important issue for science education research since global conceptualisations might lead to less differentiated assessments and interventions than aspect-dependent ones. To contribute to this issue, the article summarises conceptualisations of both global and aspect-dependent levels of understanding models and modelling that have been developed in science education. Further, students' understanding of the aspects nature of models, multiple models, purpose of models, testing models, and changing models has been assessed ( N = 1,180; 11 to 19 years old; secondary schools; Berlin, Germany). It is discussed to what extent the data support the notion of global or aspect-dependent levels of understanding models and modelling in science. The results suggest that students seem to have a complex and at least partly inconsistent pattern of understanding models. Furthermore, students with high nonverbal intelligence and good marks seem to have a comparatively more consistent and more elaborated understanding of models and modelling than weaker students. Recommendations for assessment in science education research and teaching practice are made.

2. Formulation and computational aspects of plasticity and damage models with application to quasi-brittle materials

SciTech Connect

Chen, Z.; Schreyer, H.L.

1995-09-01

The response of underground structures and transportation facilities under various external loadings and environments is critical for human safety as well as environmental protection. Since quasi-brittle materials such as concrete and rock are commonly used for underground construction, the constitutive modeling of these engineering materials, including post-limit behaviors, is one of the most important aspects in safety assessment. From experimental, theoretical, and computational points of view, this report considers the constitutive modeling of quasi-brittle materials in general and concentrates on concrete in particular. Based on the internal variable theory of thermodynamics, the general formulations of plasticity and damage models are given to simulate two distinct modes of microstructural changes, inelastic flow and degradation of material strength and stiffness, that identify the phenomenological nonlinear behaviors of quasi-brittle materials. The computational aspects of plasticity and damage models are explored with respect to their effects on structural analyses. Specific constitutive models are then developed in a systematic manner according to the degree of completeness. A comprehensive literature survey is made to provide the up-to-date information on prediction of structural failures, which can serve as a reference for future research.

3. Computational Graph Theoretical Model of the Zebrafish Sensorimotor Pathway

Peterson, Joshua M.; Stobb, Michael; Mazzag, Bori; Gahtan, Ethan

2011-11-01

Mapping the detailed connectivity patterns of neural circuits is a central goal of neuroscience and has been the focus of extensive current research [4, 3]. The best quantitative approach to analyze the acquired data is still unclear but graph theory has been used with success [3, 1]. We present a graph theoretical model with vertices and edges representing neurons and synaptic connections, respectively. Our system is the zebrafish posterior lateral line sensorimotor pathway. The goal of our analysis is to elucidate mechanisms of information processing in this neural pathway by comparing the mathematical properties of its graph to those of other, previously described graphs. We create a zebrafish model based on currently known anatomical data. The degree distributions and small-world measures of this model is compared to small-world, random and 3-compartment random graphs of the same size (with over 2500 nodes and 160,000 connections). We find that the zebrafish graph shows small-worldness similar to other neural networks and does not have a scale-free distribution of connections.

4. Phenomenological aspects of no-scale inflation models

SciTech Connect

Ellis, John; Garcia, Marcos A.G.; Nanopoulos, Dimitri V.; Olive, Keith A.

2015-10-01

We discuss phenomenological aspects of inflationary models wiith a no-scale supergravity Kähler potential motivated by compactified string models, in which the inflaton may be identified either as a Kähler modulus or an untwisted matter field, focusing on models that make predictions for the scalar spectral index n{sub s} and the tensor-to-scalar ratio r that are similar to the Starobinsky model. We discuss possible patterns of soft supersymmetry breaking, exhibiting examples of the pure no-scale type m{sub 0}=B{sub 0}=A{sub 0}=0, of the CMSSM type with universal A{sub 0} and m{sub 0}≠0 at a high scale, and of the mSUGRA type with A{sub 0}=B{sub 0}+m{sub 0} boundary conditions at the high input scale. These may be combined with a non-trivial gauge kinetic function that generates gaugino masses m{sub 1/2}≠0, or one may have a pure gravity mediation scenario where trilinear terms and gaugino masses are generated through anomalies. We also discuss inflaton decays and reheating, showing possible decay channels for the inflaton when it is either an untwisted matter field or a Kähler modulus. Reheating is very efficient if a matter field inflaton is directly coupled to MSSM fields, and both candidates lead to sufficient reheating in the presence of a non-trivial gauge kinetic function.

5. Modeling aspects of human memory for scientific study.

SciTech Connect

Caudell, Thomas P.; Watson, Patrick; McDaniel, Mark A.; Eichenbaum, Howard B.; Cohen, Neal J.; Vineyard, Craig Michael; Taylor, Shawn Ellis; Bernard, Michael Lewis; Morrow, James Dan; Verzi, Stephen J.

2009-10-01

Working with leading experts in the field of cognitive neuroscience and computational intelligence, SNL has developed a computational architecture that represents neurocognitive mechanisms associated with how humans remember experiences in their past. The architecture represents how knowledge is organized and updated through information from individual experiences (episodes) via the cortical-hippocampal declarative memory system. We compared the simulated behavioral characteristics with those of humans measured under well established experimental standards, controlling for unmodeled aspects of human processing, such as perception. We used this knowledge to create robust simulations of & human memory behaviors that should help move the scientific community closer to understanding how humans remember information. These behaviors were experimentally validated against actual human subjects, which was published. An important outcome of the validation process will be the joining of specific experimental testing procedures from the field of neuroscience with computational representations from the field of cognitive modeling and simulation.

6. Graph theoretic modeling of large-scale semantic networks.

PubMed

Bales, Michael E; Johnson, Stephen B

2006-08-01

During the past several years, social network analysis methods have been used to model many complex real-world phenomena, including social networks, transportation networks, and the Internet. Graph theoretic methods, based on an elegant representation of entities and relationships, have been used in computational biology to study biological networks; however they have not yet been adopted widely by the greater informatics community. The graphs produced are generally large, sparse, and complex, and share common global topological properties. In this review of research (1998-2005) on large-scale semantic networks, we used a tailored search strategy to identify articles involving both a graph theoretic perspective and semantic information. Thirty-one relevant articles were retrieved. The majority (28, 90.3%) involved an investigation of a real-world network. These included corpora, thesauri, dictionaries, large computer programs, biological neuronal networks, word association networks, and files on the Internet. Twenty-two of the 28 (78.6%) involved a graph comprised of words or phrases. Fifteen of the 28 (53.6%) mentioned evidence of small-world characteristics in the network investigated. Eleven (39.3%) reported a scale-free topology, which tends to have a similar appearance when examined at varying scales. The results of this review indicate that networks generated from natural language have topological properties common to other natural phenomena. It has not yet been determined whether artificial human-curated terminology systems in biomedicine share these properties. Large network analysis methods have potential application in a variety of areas of informatics, such as in development of controlled vocabularies and for characterizing a given domain. PMID:16442849

7. Electron Scale Solar Wind Turbulence: Cluster Observations and Theoretical Modeling

SciTech Connect

Sahraoui, F.; Goldstein, M. L.

2011-01-04

Turbulence at MagnetoHydroDynamics (MHD) scales of the solar wind has been studied for more than three decades, using data analyzes, theoretical and numerical modeling. However smaller scales have not been explored until very recently. Here, we review recent results on the first observation of cascade and dissipation of the solar wind turbulence at the electron scales. Thanks to the high resolution magnetic and electric field data of the Cluster spacecraft, we computed the spectra of turbulence up to {approx}100 Hz (in the spacecraft reference frame) and found two distinct breakpoints in the magnetic spectrum at 0.4 Hz and 35 Hz, which correspond, respectively, to the Doppler-shifted proton and electron gyroscales, f{sub {rho}p} and f{sub {rho}e}. Below f{sub {rho}p} the spectrum follows a Kolmogorov scaling f{sup -1.62}, typical of spectra observed at 1 AU. Above f{sub {rho}p} a second inertial range is formed with a scaling f{sup -2.3} down to f{sub {rho}e}. Above f{sub {rho}e} the spectrum has a steeper power law {approx}f{sup -4.1} down to the noise level of the instrument. Solving numerically the linear Maxwell-Vlasov equations combined with recent theoretical predictions of the Gyro-Kinetic theory, we show that the present results are fully consistent with a scenario of a quasi-two-dimensional cascade into Kinetic Alfven modes (KAW).

8. Improvements to Nuclear Data and Its Uncertainties by Theoretical Modeling

SciTech Connect

Danon, Yaron; Nazarewicz, Witold; Talou, Patrick

2013-02-18

This project addresses three important gaps in existing evaluated nuclear data libraries that represent a significant hindrance against highly advanced modeling and simulation capabilities for the Advanced Fuel Cycle Initiative (AFCI). This project will: Develop advanced theoretical tools to compute prompt fission neutrons and gamma-ray characteristics well beyond average spectra and multiplicity, and produce new evaluated files of U and Pu isotopes, along with some minor actinides; Perform state-of-the-art fission cross-section modeling and calculations using global and microscopic model input parameters, leading to truly predictive fission cross-sections capabilities. Consistent calculations for a suite of Pu isotopes will be performed; Implement innovative data assimilation tools, which will reflect the nuclear data evaluation process much more accurately, and lead to a new generation of uncertainty quantification files. New covariance matrices will be obtained for Pu isotopes and compared to existing ones. The deployment of a fleet of safe and efficient advanced reactors that minimize radiotoxic waste and are proliferation-resistant is a clear and ambitious goal of AFCI. While in the past the design, construction and operation of a reactor were supported through empirical trials, this new phase in nuclear energy production is expected to rely heavily on advanced modeling and simulation capabilities. To be truly successful, a program for advanced simulations of innovative reactors will have to develop advanced multi-physics capabilities, to be run on massively parallel super- computers, and to incorporate adequate and precise underlying physics. And all these areas have to be developed simultaneously to achieve those ambitious goals. Of particular interest are reliable fission cross-section uncertainty estimates (including important correlations) and evaluations of prompt fission neutrons and gamma-ray spectra and uncertainties.

9. A theoretical model for the Lorentz force particle analyzer

Moreau, René; Tao, Zhen; Wang, Xiaodong

2016-07-01

In a previous paper [X. Wang et al., J. Appl. Phys. 120, 014903 (2016)], several experimental devices have been presented, which demonstrate the efficiency of electromagnetic techniques for detecting and sizing electrically insulating particles entrained in the flow of a molten metal. In each case, a non-uniform magnetic field is applied across the flow of the electrically conducting liquid, thereby generating a braking Lorentz force on this moving medium and a reaction force on the magnet, which tends to be entrained in the flow direction. The purpose of this letter is to derive scaling laws for this Lorentz force from an elementary theoretical model. For simplicity, as in the experiments, the flowing liquid is modeled as a solid body moving with a uniform velocity U. The eddy currents in the moving domain are derived from the classic induction equation and Ohm's law, and expressions for the Lorentz force density j ×B and for its integral over the entire moving domain follow. The insulating particles that are eventually present and entrained with this body are then treated as small disturbances in a classic perturbation analysis, thereby leading to scaling laws for the pulses they generate in the Lorentz force. The purpose of this letter is both to illustrate the eddy currents without and with insulating particles in the electrically conducting liquid and to derive a key relation between the pulses in the Lorentz force and the main parameters (particle volume and dimensions of the region subjected to the magnetic field).

10. A game theoretic model of drug launch in India.

PubMed

2006-01-01

There is a popular belief that drug launch is delayed in developing countries like India because of delayed transfer of technology due to a 'post-launch' imitation threat through weak intellectual property rights (IPR). In fact, this belief has been a major reason for the imposition of the Trade Related Intellectual Property Rights regime under the WTO. This construct undermines the fact that in countries like India, with high reverse engineering capabilities, imitation can occur even before the formal technology transfer, and fails to recognize the first mover advantage in pharmaceutical markets. This paper argues that the first mover advantage is important and will vary across therapeutic areas, especially in developing countries with diverse levels of patient enlightenment and quality awareness. We construct a game theoretic model of incomplete information to examine the delay in drug launch in terms of costs and benefits of first move, assumed to be primarily a function of the therapeutic area of the new drug. Our model shows that drug launch will be delayed only for external (infective/communicable) diseases, while drugs for internal, non-communicable diseases (accounting for the overwhelming majority of new drug discovery) will be launched without delay. PMID:18634701

11. Theoretical model of prion propagation: a misfolded protein induces misfolding.

PubMed

Małolepsza, Edyta; Boniecki, Michal; Kolinski, Andrzej; Piela, Lucjan

2005-05-31

There is a hypothesis that dangerous diseases such as bovine spongiform encephalopathy, Creutzfeldt-Jakob, Alzheimer's, fatal familial insomnia, and several others are induced by propagation of wrong or misfolded conformations of some vital proteins. If for some reason the misfolded conformations were acquired by many such protein molecules it might lead to a "conformational" disease of the organism. Here, a theoretical model of the molecular mechanism of such a conformational disease is proposed, in which a metastable (or misfolded) form of a protein induces a similar misfolding of another protein molecule (conformational autocatalysis). First, a number of amino acid sequences composed of 32 aa have been designed that fold rapidly into a well defined native-like alpha-helical conformation. From a large number of such sequences a subset of 14 had a specific feature of their energy landscape, a well defined local energy minimum (higher than the global minimum for the alpha-helical fold) corresponding to beta-type structure. Only one of these 14 sequences exhibited a strong autocatalytic tendency to form a beta-sheet dimer capable of further propagation of protofibril-like structure. Simulations were done by using a reduced, although of high resolution, protein model and the replica exchange Monte Carlo sampling procedure. PMID:15911770

12. Theoretical model of prion propagation: A misfolded protein induces misfolding

PubMed Central

Małolepsza, Edyta; Boniecki, Michał; Kolinski, Andrzej; Piela, Lucjan

2005-01-01

There is a hypothesis that dangerous diseases such as bovine spongiform encephalopathy, Creutzfeldt-Jakob, Alzheimer's, fatal familial insomnia, and several others are induced by propagation of wrong or misfolded conformations of some vital proteins. If for some reason the misfolded conformations were acquired by many such protein molecules it might lead to a “conformational” disease of the organism. Here, a theoretical model of the molecular mechanism of such a conformational disease is proposed, in which a metastable (or misfolded) form of a protein induces a similar misfolding of another protein molecule (conformational autocatalysis). First, a number of amino acid sequences composed of 32 aa have been designed that fold rapidly into a well defined native-like α-helical conformation. From a large number of such sequences a subset of 14 had a specific feature of their energy landscape, a well defined local energy minimum (higher than the global minimum for the α-helical fold) corresponding to β-type structure. Only one of these 14 sequences exhibited a strong autocatalytic tendency to form a β-sheet dimer capable of further propagation of protofibril-like structure. Simulations were done by using a reduced, although of high resolution, protein model and the replica exchange Monte Carlo sampling procedure. PMID:15911770

13. The neural mediators of kindness-based meditation: a theoretical model.

PubMed

Mascaro, Jennifer S; Darcher, Alana; Negi, Lobsang T; Raison, Charles L

2015-01-01

Although kindness-based contemplative practices are increasingly employed by clinicians and cognitive researchers to enhance prosocial emotions, social cognitive skills, and well-being, and as a tool to understand the basic workings of the social mind, we lack a coherent theoretical model with which to test the mechanisms by which kindness-based meditation may alter the brain and body. Here, we link contemplative accounts of compassion and loving-kindness practices with research from social cognitive neuroscience and social psychology to generate predictions about how diverse practices may alter brain structure and function and related aspects of social cognition. Contingent on the nuances of the practice, kindness-based meditation may enhance the neural systems related to faster and more basic perceptual or motor simulation processes, simulation of another's affective body state, slower and higher-level perspective-taking, modulatory processes such as emotion regulation and self/other discrimination, and combinations thereof. This theoretical model will be discussed alongside best practices for testing such a model and potential implications and applications of future work. PMID:25729374

14. The neural mediators of kindness-based meditation: a theoretical model

PubMed Central

Mascaro, Jennifer S.; Darcher, Alana; Negi, Lobsang T.; Raison, Charles L.

2015-01-01

Although kindness-based contemplative practices are increasingly employed by clinicians and cognitive researchers to enhance prosocial emotions, social cognitive skills, and well-being, and as a tool to understand the basic workings of the social mind, we lack a coherent theoretical model with which to test the mechanisms by which kindness-based meditation may alter the brain and body. Here, we link contemplative accounts of compassion and loving-kindness practices with research from social cognitive neuroscience and social psychology to generate predictions about how diverse practices may alter brain structure and function and related aspects of social cognition. Contingent on the nuances of the practice, kindness-based meditation may enhance the neural systems related to faster and more basic perceptual or motor simulation processes, simulation of another’s affective body state, slower and higher-level perspective-taking, modulatory processes such as emotion regulation and self/other discrimination, and combinations thereof. This theoretical model will be discussed alongside best practices for testing such a model and potential implications and applications of future work. PMID:25729374

15. Empirical STORM-E Model. [I. Theoretical and Observational Basis

NASA Technical Reports Server (NTRS)

Mertens, Christopher J.; Xu, Xiaojing; Bilitza, Dieter; Mlynczak, Martin G.; Russell, James M., III

2013-01-01

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region peak electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) volume emission rates (VER) derived from the TIMED/SABER 4.3 lm channel limb radiance measurements. The storm-time response of the NO+(v) 4.3 lm VER is sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3 lm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part II of this series describes the explicit development of the empirical storm-time correction factor for E-region peak electron densities, and shows comparisons of E-region electron densities between STORM-E predictions and incoherent scatter radar measurements. In this paper, Part I of the series, the efficacy of using SABER-derived NO+(v) VER as a proxy for the E-region response to solar-geomagnetic disturbances is presented. Furthermore, a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3 lm limb emission measurements is given. Finally, an assessment of key uncertainties in retrieving NO+(v) VER is presented

16. Martian weathering processes: Terrestrial analog and theoretical modeling studies

2008-06-01

Understanding the role of water in the Martian near-surface, and its implications for possible habitable environments, is among the highest priorities of NASA's Mars Exploration Program. Characterization of alteration signatures in surface materials provides the best opportunity to assess the role of water on Mars. This dissertation investigates Martian alteration processes through analyses of Antarctic analogs and numerical modeling of mineral-fluid interactions. Analog work involved studying an Antarctic diabase, and associated soils, as Mars analogs to understand weathering processes in cold, dry environments. The soils are dominated by primary basaltic minerals, but also contain phyllosilicates, salts, iron oxides/oxyhydroxides, and zeolites. Soil clay minerals and zeolites, formed primarily during deuteric or hydrothermal alteration of the parent rock, were subsequently transferred to the soil by physical rock weathering. Authigenic soil iron oxides/oxyhydroxides and small amounts of poorly-ordered secondary silicates indicate some contributions from low-temperature aqueous weathering. Soil sulfates, which exhibit a sulfate- aerosol-derived mass-independent oxygen isotope signature, suggest contributions from acid aerosol-rock interactions. The complex alteration history of the Antarctic materials resulted in several similarities to Martian materials. The processes that affected the analogs, including deuteric/ hydrothermal clay formation, may be important in producing Martian surface materials. Theoretical modeling focused on investigating the alteration of Martian rocks under acidic conditions and using modeling results to interpret Martian observations. Kinetic modeling of the dissolution of plagioclase-pyroxene mineral mixtures under acidic conditions suggested that surfaces with high plagioclase/pyroxene, such as several northern regions, could have experienced some preferential dissolution of pyroxenes at a pH less than approximately 3-4. Modeling of the

17. Multiscale modeling of lithium ion batteries: thermal aspects

PubMed Central

Zausch, Jochen

2015-01-01

Summary The thermal behavior of lithium ion batteries has a huge impact on their lifetime and the initiation of degradation processes. The development of hot spots or large local overpotentials leading, e.g., to lithium metal deposition depends on material properties as well as on the nano- und microstructure of the electrodes. In recent years a theoretical structure emerges, which opens the possibility to establish a systematic modeling strategy from atomistic to continuum scale to capture and couple the relevant phenomena on each scale. We outline the building blocks for such a systematic approach and discuss in detail a rigorous approach for the continuum scale based on rational thermodynamics and homogenization theories. Our focus is on the development of a systematic thermodynamically consistent theory for thermal phenomena in batteries at the microstructure scale and at the cell scale. We discuss the importance of carefully defining the continuum fields for being able to compare seemingly different phenomenological theories and for obtaining rules to determine unknown parameters of the theory by experiments or lower-scale theories. The resulting continuum models for the microscopic and the cell scale are numerically solved in full 3D resolution. The complex very localized distributions of heat sources in a microstructure of a battery and the problems of mapping these localized sources on an averaged porous electrode model are discussed by comparing the detailed 3D microstructure-resolved simulations of the heat distribution with the result of the upscaled porous electrode model. It is shown, that not all heat sources that exist on the microstructure scale are represented in the averaged theory due to subtle cancellation effects of interface and bulk heat sources. Nevertheless, we find that in special cases the averaged thermal behavior can be captured very well by porous electrode theory. PMID:25977870

Sanjeev, B. S.; Patra, S. M.; Vishveshwara, S.

2001-01-01

A general strategy has been developed based on graph theoretical methods, for finding amino acid sequences that take up a desired conformation as the native state. This problem of inverse design has been addressed by assigning topological indices for the monomer sites (vertices) of the polymer on a 3×3×3 cubic lattice. This is a simple design strategy, which takes into account only the topology of the target protein and identifies the best sequence for a given composition. The procedure allows the design of a good sequence for a target native state by assigning weights for the vertices on a lattice site in a given conformation. It is seen across a variety of conformations that the predicted sequences perform well both in sequence and in conformation space, in identifying the target conformation as native state for a fixed composition of amino acids. Although the method is tested in the framework of the HP model [K. F. Lau and K. A. Dill, Macromolecules 22, 3986 (1989)] it can be used in any context if proper potential functions are available, since the procedure derives unique weights for all the sites (vertices, nodes) of the polymer chain of a chosen conformation (graph).

19. Thermophotonic heat pump—a theoretical model and numerical simulations

Oksanen, Jani; Tulkki, Jukka

2010-05-01

We have recently proposed a solid state heat pump based on photon mediated heat transfer between two large-area light emitting diodes coupled by the electromagnetic field and enclosed in a semiconductor structure with a nearly homogeneous refractive index. Ideally the thermophotonic heat pump (THP) allows heat transfer at Carnot efficiency but in reality there are several factors that limit the efficiency. The efficient operation of the THP is based on the following construction factors and operational characteristics: (1) broad area semiconductor diodes to enable operation at optimal carrier density and high efficiency, (2) recycling of the energy of the emitted photons, (3) elimination of photon extraction losses by integrating the emitting and the absorbing diodes within a single semiconductor structure, and (4) eliminating the reverse thermal conduction by a nanometer scale vacuum layer between the diodes. In this paper we develop a theoretical model for the THP and study the fundamental physical limitations and potential of the concept. The results show that even when the most important losses of the THPs are accounted for, the THP has potential to outperform the thermoelectric coolers especially for heat transfer across large temperature differences and possibly even to compete with conventional small scale compressor based heat pumps.

20. A Game-Theoretic Model of Marketing Skin Whiteners.

PubMed

Mendoza, Roger Lee

2015-01-01

Empirical studies consistently find that people in less developed countries tend to regard light or "white" skin, particularly among women, as more desirable or superior. This is a study about the marketing of skin whiteners in these countries, where over 80 percent of users are typically women. It proceeds from the following premises: a) Purely market or policy-oriented approaches toward the risks and harms of skin whitening are cost-inefficient; b) Psychosocial and informational factors breed uninformed and risky consumer choices that favor toxic skin whiteners; and c) Proliferation of toxic whiteners in a competitive buyer's market raises critical supplier accountability issues. Is intentional tort a rational outcome of uncooperative game equilibria? Can voluntary cooperation nonetheless evolve between buyers and sellers of skin whiteners? These twin questions are key to addressing the central paradox in this study: A robust and expanding buyer's market, where cheap whitening products abound at a high risk to personal and societal health and safety. Game-theoretic modeling of two-player and n-player strategic interactions is proposed in this study for both its explanatory and predictive value. Therein also lie its practical contributions to the economic literature on skin whitening. PMID:26565686

1. Network-theoretic approach to model vortex interactions

2014-11-01

We present a network-theoretic approach to describe a system of point vortices in two-dimensional flow. By considering the point vortices as nodes, a complete graph is constructed with edges connecting each vortex to every other vortex. The interactions between the vortices are captured by the graph edge weights. We employ sparsification techniques on these graph representations based on spectral theory to construct sparsified models of the overall vortical interactions. The edge weights are redistributed through spectral sparsification of the graph such that the sum of the interactions associated with each vortex is maintained constant. In addition, sparse configurations maintain similar spectral properties as the original setup. Through the reduction in the number of interactions, key vortex interactions can be highlighted. Identification of vortex structures based on graph sparsification is demonstrated with an example of clusters of point vortices. We also evaluate the computational performance of sparsification for large collection of point vortices. Work supported by US Army Research Office (W911NF-14-1-0386) and US Air Force Office of Scientific Research (YIP: FA9550-13-1-0183).

2. PREFACE: First International Congress of the International Association of Inverse Problems (IPIA): Applied Inverse Problems 2007: Theoretical and Computational Aspects

Uhlmann, Gunther

2008-07-01

This volume represents the proceedings of the fourth Applied Inverse Problems (AIP) international conference and the first congress of the Inverse Problems International Association (IPIA) which was held in Vancouver, Canada, June 25 29, 2007. The organizing committee was formed by Uri Ascher, University of British Columbia, Richard Froese, University of British Columbia, Gary Margrave, University of Calgary, and Gunther Uhlmann, University of Washington, chair. The conference was part of the activities of the Pacific Institute of Mathematical Sciences (PIMS) Collaborative Research Group on inverse problems (http://www.pims.math.ca/scientific/collaborative-research-groups/past-crgs). This event was also supported by grants from NSF and MITACS. Inverse Problems (IP) are problems where causes for a desired or an observed effect are to be determined. They lie at the heart of scientific inquiry and technological development. The enormous increase in computing power and the development of powerful algorithms have made it possible to apply the techniques of IP to real-world problems of growing complexity. Applications include a number of medical as well as other imaging techniques, location of oil and mineral deposits in the earth's substructure, creation of astrophysical images from telescope data, finding cracks and interfaces within materials, shape optimization, model identification in growth processes and, more recently, modelling in the life sciences. The series of Applied Inverse Problems (AIP) Conferences aims to provide a primary international forum for academic and industrial researchers working on all aspects of inverse problems, such as mathematical modelling, functional analytic methods, computational approaches, numerical algorithms etc. The steering committee of the AIP conferences consists of Heinz Engl (Johannes Kepler Universität, Austria), Joyce McLaughlin (RPI, USA), William Rundell (Texas A&M, USA), Erkki Somersalo (Helsinki University of Technology

3. PREFACE: First International Congress of the International Association of Inverse Problems (IPIA): Applied Inverse Problems 2007: Theoretical and Computational Aspects

Uhlmann, Gunther

2008-07-01

This volume represents the proceedings of the fourth Applied Inverse Problems (AIP) international conference and the first congress of the Inverse Problems International Association (IPIA) which was held in Vancouver, Canada, June 25 29, 2007. The organizing committee was formed by Uri Ascher, University of British Columbia, Richard Froese, University of British Columbia, Gary Margrave, University of Calgary, and Gunther Uhlmann, University of Washington, chair. The conference was part of the activities of the Pacific Institute of Mathematical Sciences (PIMS) Collaborative Research Group on inverse problems (http://www.pims.math.ca/scientific/collaborative-research-groups/past-crgs). This event was also supported by grants from NSF and MITACS. Inverse Problems (IP) are problems where causes for a desired or an observed effect are to be determined. They lie at the heart of scientific inquiry and technological development. The enormous increase in computing power and the development of powerful algorithms have made it possible to apply the techniques of IP to real-world problems of growing complexity. Applications include a number of medical as well as other imaging techniques, location of oil and mineral deposits in the earth's substructure, creation of astrophysical images from telescope data, finding cracks and interfaces within materials, shape optimization, model identification in growth processes and, more recently, modelling in the life sciences. The series of Applied Inverse Problems (AIP) Conferences aims to provide a primary international forum for academic and industrial researchers working on all aspects of inverse problems, such as mathematical modelling, functional analytic methods, computational approaches, numerical algorithms etc. The steering committee of the AIP conferences consists of Heinz Engl (Johannes Kepler Universität, Austria), Joyce McLaughlin (RPI, USA), William Rundell (Texas A&M, USA), Erkki Somersalo (Helsinki University of Technology

4. Theoretical model for electrophilic oxygen atom insertion into hydrocarbons

SciTech Connect

Bach, R.D.; Su, M.D. ); Andres, J.L. Wayne State Univ., Detroit, MI ); McDouall, J.J.W. )

1993-06-30

A theoretical model suggesting the mechanistic pathway for the oxidation of saturated-alkanes to their corresponding alcohols and ketones is described. Water oxide (H[sub 2]O-O) is employed as a model singlet oxygen atom donor. Molecular orbital calculations with the 6-31G basis set at the MP2, QCISD, QCISD(T), CASSCF, and MRCI levels of theory suggest that oxygen insertion by water oxide occurs by the interaction of an electrophilic oxygen atom with a doubly occupied hydrocarbon fragment orbital. The electrophilic oxygen approaches the hydrocarbon along the axis of the atomic carbon p orbital comprising a [pi]-[sub CH(2)] or [pi]-[sub CHCH(3)] fragment orbital to form a carbon-oxygen [sigma] bond. A concerted hydrogen migration to an adjacent oxygen lone pair of electrons affords the alcohol insertion product in a stereoselective fashion with predictable stereochemistry. Subsequent oxidation of the alcohol to a ketone (or aldehyde) occurs in a similar fashion and has a lower activation barrier. The calculated (MP4/6-31G*//MP2/6-31G*) activation barriers for oxygen atom insertion into the C-H bonds of methane, ethane, propane, butane, isobutane, and methanol are 10.7, 8.2, 3.9, 4.8, 4.5, and 3.3 kcal/mol, respectively. We use ab initio molecular orbital calculations in support of a frontier MO theory that provides a unique rationale for both the stereospecificity and the stereoselectivity of insertion of electrophilic oxygen and related electrophiles into the carbon-hydrogen bond. 13 refs., 7 figs., 2 tabs.

5. Information-Theoretic Latent Distribution Modeling: Distinguishing Discrete and Continuous Latent Variable Models

ERIC Educational Resources Information Center

Markon, Kristian E.; Krueger, Robert F.

2006-01-01

Distinguishing between discrete and continuous latent variable distributions has become increasingly important in numerous domains of behavioral science. Here, the authors explore an information-theoretic approach to latent distribution modeling, in which the ability of latent distribution models to represent statistical information in observed…

6. A New Theoretical Model of Big-Bang Evidence as a Consequence of Global Symmetry Breakdown

Avetissian, Ara K.

2007-08-01

Problems and hardships in identification and understanding of physical quintessence of several phenomena in Cosmology such are Big-Bang of tremendously dense and hot matter with Baryons' asymmetry, Hubble's expansion Law, Cosmic Microwave Radiation, Dark Energy and Dark Matter, obviously require alternative investigations of additional theoretical aspects and corresponding models of early Universe both for Radiation and Baryonic periods. According to this aspiration and taking into consideration results from Wilkinson Microwave Anisotropy Probe one postulate an assumption of possibility of baryons (may be also antibaryons!) Bose-Einstein condensation in the early Universe due to their Cooper-pairing. The thermodynamical equilibrium between extrahigh energy photons and Bose-condensed baryonic matter is consider and evaluate the macro-parameters of the possible hydrostatic stable baryonic configuration of Universal scale. A new theoretical model of Big-Bang evidence is predicted as a consequence of Global Symmetry breakdown from the Bose-Einstein statistics to Fermi-Dirac one when the matter pressure due to Pauli exclusion principle spasmodically increasing outside more than 2.5×10^5 times.

7. Theoretical study on the inverse modeling of deep body temperature measurement.

PubMed

Huang, Ming; Chen, Wenxi

2012-03-01

We evaluated the theoretical aspects of monitoring the deep body temperature distribution with the inverse modeling method. A two-dimensional model was built based on anatomical structure to simulate the human abdomen. By integrating biophysical and physiological information, the deep body temperature distribution was estimated from cutaneous surface temperature measurements using an inverse quasilinear method. Simulations were conducted with and without the heat effect of blood perfusion in the muscle and skin layers. The results of the simulations showed consistently that the noise characteristics and arrangement of the temperature sensors were the major factors affecting the accuracy of the inverse solution. With temperature sensors of 0.05 °C systematic error and an optimized 16-sensor arrangement, the inverse method could estimate the deep body temperature distribution with an average absolute error of less than 0.20 °C. The results of this theoretical study suggest that it is possible to reconstruct the deep body temperature distribution with the inverse method and that this approach merits further investigation. PMID:22370094

8. String Theoretic Toy Models of the Big Bang

Michelson, Jeremy

2006-03-01

Recently, examples of toy cosmologies have been found that are exact solutions of String Theory. These solutions have the feature that the theoretical framework permits reliable calculation arbitrarily close to the big bang singularity. Thus one can understand both the big bang, and late time physics. I will describe these toy cosmologies, and how they fit into String Theory's chains of equivalences between gravitational and nongravitational theories. These equivalences are the means by which one theoretically probes the big bang.

9. Testing Models: A Key Aspect to Promote Teaching Activities Related to Models and Modelling in Biology Lessons?

ERIC Educational Resources Information Center

Krell, Moritz; Krüger, Dirk

2016-01-01

This study investigated biology teachers' (N = 148) understanding of models and modelling (MoMo), their model-related teaching activities and relations between the two. A framework which distinguishes five aspects of MoMo in science ("nature of models," "multiple models," "purpose of models," "testing…

10. Study of modeling aspects of long period fiber grating using three-layer fiber geometry

Singh, Amit

2015-03-01

The author studied and demonstrated the various modeling aspects of long period fiber grating (LPFG) such as the core effective index, cladding effective index, coupling coefficient, coupled mode theory, and transmission spectrum of the LPFG using three-layer fiber geometry. Actually, there are two different techniques used for theoretical modeling of the long period fiber grating. The first technique was used by Vengsarkar et al who described the phenomenon of long-period fiber gratings, and the second technique was reported by Erdogan who revealed the inaccuracies and shortcomings of the original method, thereby providing an accurate and updated alternative. The main difference between these two different approaches lies in their fiber geometry. Venserkar et al used two-layer fiber geometry which is simple but employs weakly guided approximation, whereas Erdogan used three-layer fiber geometry which is complex but also the most accurate technique for theoretical study of the LPFG. The author further discussed about the behavior of the transmission spectrum by altering different grating parameters such as the grating length, ultraviolet (UV) induced-index change, and grating period to achieve the desired flexibility. The author simulated the various results with the help of MATLAB.

11. Mathematical modeling of synergetic aspects of machine building enterprise management

Kazakov, O. D.; Andriyanov, S. V.

2016-04-01

The multivariate method of determining the optimal values of leading key performance indicators of production divisions of machine-building enterprises in the aspect of synergetics has been worked out.

12. A theoretical model of grainsize evolution during deformation

Ricard, Y.; Bercovici, D.; Rozel, A.

2007-12-01

Lithospheric shear localization, as occurs in the formation of tectonic plate boundaries, is often associated with diminished grainsize (e.g., mylonites). Grainsize reduction is typically attributed to dynamic recrystallization; however, theoretical models of shear-localization arising from this hypothesis are problematic since (1) they require the simultaneous action of two exclusive creep mechanisms (diffusion and dislocation creep), and (2) the grain-growth ("healing") laws employed by these models are derived from static grain-growth or coarsening theory, although the shear-localization setting itself is far from static equilibrium. We present a new first-principles grained-continuum theory which accounts for both coarsening and damage-induced grainsize reduction. Damage per se is the generic process for generation of microcracks, defects, dislocations (including recrystallization), subgrains, nucleii and cataclastic breakdown of grains. The theory contains coupled statistical grain-scale and continuum macroscopic components. The grain-scale element of the theory prescribes both the evolution of the grainsize distribution, and a phenomenological grain-growth law derived from non-equilibrium thermodynamics; grain-growth thus incorporates the free energy differences between grains, including both grain-boundary surface energy (which controls coarsening) and the contribution of deformational work to these free energiesconservation and positivity of entropy production provide the phenomenological law for the statistical grain-growth law. We identify four potential mechanisms that affect the distribution of grainsize; two of them conserve the number of grains but change their relative masses and two of them change the number of grains by sticking them together or breaking them. In the limit of static equilibrium, only the two mechanisms that increase the average grainsize are allowed by the second law of thermodynamics. The first one is a diffusive mass transport

13. A theoretical microbial contamination model for a human Mars mission

Lupisella, Mark Lewis

Contamination from a human presence on Mars could significantly compromise the search for extraterrestrial life. In particular, the difficulties in controlling microbial contamination, the potential for terrestrial microbes to grow, evolve, compete, and modify the Martian environment, and the likely microbial nature of putative Martian life, make microbial contamination worthy of focus as we begin to plan for a human mission to Mars. This dissertation describes a relatively simple theoretical model that can be used to explore how microbial contamination from a human Mars mission might survive and grow in the Martian soil environment surrounding a habitat. A user interface has been developed to allow a general practitioner to choose values and functions for almost all parameters ranging from the number of astronauts to the half-saturation constants for microbial growth. Systematic deviations from a baseline set of parameter values are explored as potential plausible scenarios for the first human Mars missions. The total viable population and population density are the primary state variables of interest, but other variables such as the total number of births and total dead and viable microbes are also tracked. The general approach was to find the most plausible parameter value combinations that produced a population density of 1 microbe/cm3 or greater, a threshold that was used to categorize the more noteworthy populations for subsequent analysis. Preliminary assessments indicate that terrestrial microbial contamination resulting from leakage from a limited human mission (perhaps lasting up to 5 months) will not likely become a problematic population in the near-term as long as reasonable contamination control measures are implemented (for example, a habitat leak rate no greater than 1% per hour). However, there appear to be plausible, albeit unlikely, scenarios that could cause problematic populations, depending in part on (a) the initial survival fraction and

14. Theoretical connections between mathematical neuronal models corresponding to different expressions of noise.

PubMed

Dumont, Grégory; Henry, Jacques; Tarniceriu, Carmen Oana

2016-10-01

Identifying the right tools to express the stochastic aspects of neural activity has proven to be one of the biggest challenges in computational neuroscience. Even if there is no definitive answer to this issue, the most common procedure to express this randomness is the use of stochastic models. In accordance with the origin of variability, the sources of randomness are classified as intrinsic or extrinsic and give rise to distinct mathematical frameworks to track down the dynamics of the cell. While the external variability is generally treated by the use of a Wiener process in models such as the Integrate-and-Fire model, the internal variability is mostly expressed via a random firing process. In this paper, we investigate how those distinct expressions of variability can be related. To do so, we examine the probability density functions to the corresponding stochastic models and investigate in what way they can be mapped one to another via integral transforms. Our theoretical findings offer a new insight view into the particular categories of variability and it confirms that, despite their contrasting nature, the mathematical formalization of internal and external variability is strikingly similar. PMID:27334547

15. Presenting a Theoretical Model of Four Conceptions of Civic Education

ERIC Educational Resources Information Center

Cohen, Aviv

2010-01-01

This conceptual study will question the ways different epistemological conceptions of citizenship and education influence the characteristics of civic education. While offering a new theoretical framework, the different undercurrent conceptions that lay at the base of the civic education process shall be brought forth. With the use of the method…

16. Pathways in coal thermolysis: a theoretical and experimental study with model compounds

SciTech Connect

Ekpenyong, I.A.; Virk, P.S.

1982-01-01

Fundamental aspects of coal thermolysis were investigated, including how the chemical structures of aromatics, hydroaromatics, and alcohols affect their reactivities as hydrogen donors and acceptors in coal processing. The susceptibilities of substructural entities in coals to fragmentation via a number of thermal pericyclic and free radical mechanisms were probed, as were the factors governing relative reactivities within series of such coal model compounds. The theoretical part of the work applied perturbation molecular orbital (PMO) and frontier orbital theories, in conjunction with ..pi..- and pseudo-..pi.. MO's, to the study of model compound reactivity. This enabled prediction of reactivity patterns of H-donors, H-acceptors and coal-like structures as functions of their ..pi..- and sigma-bond configurations, including heteroatomic effects. Experimentally, the liquid phase reactions of the coal model compound PhOCH/sub 2/Ph (Benzyl phenyl ether, BPE) were detailed for the first time in each of four hydronaphthalene H-donor solvents in the temperature range 220/sup 0/ to 300/sup 0/C. The thermolysis of BPE exhibited a pronounced dependence on solvent structure, both with respect to product selectivities and reaction kinetics. BPE thermolysis pathways were delineated as involving (a) rearrangement, leading to isomerization, (b) hydrogenations, leading ultimately to PhOH and PhCH/sub 3/ products, and (c) addition reactions, engendering heavy products. Pathways (b) and (c) are competitive and, in each, self-reactions of BPE-derivatives vie against reactions between these and the donor solvent. Of the detailed free radical and pericyclic reaction mechanisms postulated, the latter rationalized many more facets of the BPE results than the former. The theoretical and experimental results were appraised against previous coal thermolysis literature.

17. Suggestion for a theoretical model for secondary-tertiary transition in mathematics

Clark, Megan; Lovric, Miroslav

2008-09-01

One of most notable features of existing body of research in transition seems to be the absence of a theoretical model. The suggestion we present in this paper—to view and understand the high school to university transition in mathematics as a modern-day rite of passage—is an attempt at defining such framework. Although dominantly reflecting North-American reality, we believe that the model could be found useful in other countries as well. Let us emphasize that our model is not new in the sense that it recognizes the transition as such. In this paper, we try to determine whether (and, if so, how) the notion of a rite of passage—which is a well-understood concept in anthropology, as well as in some other disciplines (e.g. culture shock in cultural studies)—can help us understand mathematics transition issues better. Can it help us systematize existing body of research, and enhance our understanding of transition in mathematics; does it point at something new? We believe so, and by elaborating some traditional aspects of rites of passage, we hope to provide a useful lens through which we can examine the process of transition in mathematics, and make suggestions for improved management of some transitional issues.

18. Theoretical Perspectives Concerning Positive Aspects of Caring for Elderly Persons with Dementia: Stress/Adaptation and Existentialism.

ERIC Educational Resources Information Center

Farran, Carol J.

1997-01-01

Uses an existentialist perspective to examine the current empirical stress/adaptation model that guides caregiving of persons with dementia. Compares and contrasts key elements, strengths, and limitations of each model and isolates areas of convergence/divergence in both perspectives. Identifies implications for future theory development,…

19. A Dual Aspect Process Model of Intensive Interaction

ERIC Educational Resources Information Center

Firth, Graham

2009-01-01

Intensive Interaction is an empirically researched approach to developing fundamental communication and sociability for people with severe and profound learning disabilities and/or autism. However, it is the author's contention that certain aspects of Intensive Interaction are not universally conceptualised in a uniform manner, and that there are…

20. Theoretical Aspects of Differential Scanning Calorimetry as a Tool for the Studies of Equilibrium Thermodynamics in Pharmaceutical Solid Phase Transitions.

PubMed

Faroongsarng, Damrongsak

2016-06-01

Although differential scanning calorimetry (DSC) is a non-equilibrium technique, it has been used to gain energetic information that involves phase equilibria. DSC has been widely used to characterize the equilibrium melting parameters of small organic pharmaceutical compounds. An understanding of how DSC measures an equilibrium event could make for a better interpretation of the results. The aim of this mini-review was to provide a theoretical insight into the DSC measurement to obtain the equilibrium thermodynamics of a phase transition especially the melting process. It was demonstrated that the heat quantity obtained from the DSC thermogram (ΔH) was related to the thermodynamic enthalpy of the phase transition (ΔH (P) ) via: ΔH = ΔH (P) /(1 + K (- 1)) where K was the equilibrium constant. In melting, the solid and liquefied phases presumably coexist resulting in a null Gibbs free energy that produces an infinitely larger K. Thus, ΔH could be interpreted as ΔH (P). Issues of DSC investigations on melting behavior of crystalline solids including polymorphism, degradation impurity due to heating in situ, and eutectic melting were discussed. In addition, DSC has been a tool for determination of the impurity based on an ideal solution of the melt that is one of the official methods used to establish the reference standard. PMID:27091667

1. Theoretical analysis of the electrical aspects of the basic electro-impulse problem in aircraft de-icing applications

NASA Technical Reports Server (NTRS)

Henderson, Robert A.; Schrag, Robert L.

1987-01-01

A method of modelling a system consisting of a cylindrical coil with its axis perpendicular to a metal plate of finite thickness, and a simple electrical circuit for producing a transient current in the coil, is discussed in the context of using such a system for de-icing aircraft surfaces. A transmission line model of the coil and metal plate is developed as the heart of the system model. It is shown that this transmission model is central to calculation of the coil impedance, the coil current, the magnetic fields established on the surfaces of the metal plate, and the resultant total force between the coil and the plate. FORTRAN algorithms were developed for numerical calculation of each of these quantities, and the algorithms were applied to an experimental prototype system in which these quantities had been measured. Good agreement is seen to exist between the predicted and measured results.

2. Development of Children's Creative Visual Imagination: A Theoretical Model and Enhancement Programmes

ERIC Educational Resources Information Center

Dziedziewicz, Dorota; Karwowski, Maciej

2015-01-01

This paper presents a new theoretical model of creative imagination and its applications in early education. The model sees creative imagination as composed of three inter-related components: vividness of images, their originality, and the level of transformation of imageries. We explore the theoretical and practical consequences of this new…

3. A theoretical model of phase changes of a klystron due to variation of operating parameters

NASA Technical Reports Server (NTRS)

Kupiszewski, A.

1980-01-01

A mathematical model for phase changes of the VA-876 CW klystron amplifier output is presented and variations of several operating parameters are considered. The theoretical approach to the problem is based upon a gridded gap modeling with inclusion of a second order correction term so that actual gap geometry is reflected in the formulation. Physical measurements are contrasted to theoretical calculations.

4. A Model of Resource Allocation in Public School Districts: A Theoretical and Empirical Analysis.

ERIC Educational Resources Information Center

Chambers, Jay G.

This paper formulates a comprehensive model of resource allocation in a local public school district. The theoretical framework specified could be applied equally well to any number of local public social service agencies. Section 1 develops the theoretical model describing the process of resource allocation. This involves the determination of the…

5. Adaptive finite elements with high aspect ratio for the computation of coalescence using a phase-field model

Burman, E.; Jacot, A.; Picasso, M.

2004-03-01

A multiphase-field model for the description of coalescence in a binary alloy is solved numerically using adaptive finite elements with high aspect ratio. The unknown of the multiphase-field model are the three phase fields (solid phase 1, solid phase 2, and liquid phase), a Lagrange multiplier and the concentration field. An Euler implicit scheme is used for time discretization, together with continuous, piecewise linear finite elements. At each time step, a linear system corresponding to the three phases plus the Lagrange multiplier has to be solved. Then, the linear system pertaining to concentration is solved. An adaptive finite element algorithm is proposed. In order to reduce the number of mesh vertices, the generated meshes contain elements with high aspect ratio. The refinement and coarsening criteria are based on an error indicator which has already been justified theoretically for simpler problems. Numerical results on two test cases show the efficiency of the method.

6. Iodine and disinfection: theoretical study on mode of action, efficiency, stability, and analytical aspects in the aqueous system.

PubMed

Gottardi, W

1999-05-01

deduce general qualities of aqueous iodine solutions, such as reactivity, stability, and analytical aspects, and to estimate major disinfection-orientated properties such as microbicidal activity, irritation, and incorporation effects. Though the calculations consider primarily preparations devoid of polymeric organic compounds capable of complexing iodine species, the results can be largely transferred to iodophoric preparations. PMID:10409102

7. Information-theoretic model comparison unifies saliency metrics

PubMed Central

Kümmerer, Matthias; Wallis, Thomas S. A.; Bethge, Matthias

2015-01-01

Learning the properties of an image associated with human gaze placement is important both for understanding how biological systems explore the environment and for computer vision applications. There is a large literature on quantitative eye movement models that seeks to predict fixations from images (sometimes termed “saliency” prediction). A major problem known to the field is that existing model comparison metrics give inconsistent results, causing confusion. We argue that the primary reason for these inconsistencies is because different metrics and models use different definitions of what a “saliency map” entails. For example, some metrics expect a model to account for image-independent central fixation bias whereas others will penalize a model that does. Here we bring saliency evaluation into the domain of information by framing fixation prediction models probabilistically and calculating information gain. We jointly optimize the scale, the center bias, and spatial blurring of all models within this framework. Evaluating existing metrics on these rephrased models produces almost perfect agreement in model rankings across the metrics. Model performance is separated from center bias and spatial blurring, avoiding the confounding of these factors in model comparison. We additionally provide a method to show where and how models fail to capture information in the fixations on the pixel level. These methods are readily extended to spatiotemporal models of fixation scanpaths, and we provide a software package to facilitate their use. PMID:26655340

8. Theoretical model-based quantitative optimisation of numerical modelling for eddy current NDT

Yu, Yating; Li, Xinhua; Simm, Anthony; Tian, Guiyun

2011-06-01

Eddy current (EC) nondestructive testing (NDT) is one of the most widely used NDT methods. Numerical modelling of NDT methods has been used as an important investigative approach alongside experimental and theoretical studies. This paper investigates the set-up of numerical modelling using finite-element method in terms of the optimal selection of element mesh size in different regions within the model based on theoretical analysis of EC NDT. The modelling set-up is refined and evaluated through numerical simulation, balancing both computation time and simulation accuracy. A case study in the optimisation of the modelling set-up of the EC NDT system with a cylindrical probe coil is carried out to verify the proposed optimisation approach. Here, the mesh size of the simulation model is set based on the geometries of the coil and the magnetic sensor, as well as on the skin depth in the sample; so the optimised modelling set-up can be useful even when the geometry of EC system, the excitation frequency or the pulsed width is changed in multi-frequency EC, sweep-frequency EC or system and pulsed EC. Furthermore, this optimisation approach can be used to improve the trade-off between accuracy and the computation time in other more complex EC NDT simulations.

9. College Students Solving Chemistry Problems: A Theoretical Model of Expertise

ERIC Educational Resources Information Center

Taasoobshirazi, Gita; Glynn, Shawn M.

2009-01-01

A model of expertise in chemistry problem solving was tested on undergraduate science majors enrolled in a chemistry course. The model was based on Anderson's "Adaptive Control of Thought-Rational" (ACT-R) theory. The model shows how conceptualization, self-efficacy, and strategy interact and contribute to the successful solution of quantitative,…

10. Building a Theoretical Model of Metacognitive Processes in Complex Modeling Activities: A Window into the Development of Students' Metacognitive Abilities

ERIC Educational Resources Information Center

Kim, Young Rae

2013-01-01

A theoretical model of metacognition in complex modeling activities has been developed based on existing frameworks, by synthesizing the re-conceptualization of metacognition at multiple levels by looking at the three sources that trigger metacognition. Using the theoretical model as a framework, this study was designed to explore how students'…

11. Theoretical modelling of the semiconductor-electrolyte interface

Schelling, Patrick Kenneth

We have developed tight-binding models of transition metal oxides. In contrast to many tight-binding models, these models include a description of electron-electron interactions. After parameterizing to bulk first-principles calculations, we demonstrated the transferability of the model by calculating atomic and electronic structure of rutile surfaces, which compared well with experiment and first-principles calculations. We also studied the structure of twist grain boundaries in rutile. Molecular dynamics simulations using the model were also carried out to describe polaron localization. We have also demonstrated that tight-binding models can be constructed to describe metallic systems. The computational cost tight-binding simulations was greatly reduced by incorporating O(N) electronic structure methods. We have also interpreted photoluminesence experiments on GaAs electrodes in contact with an electrolyte using drift-diffusion models. Electron transfer velocities were obtained by fitting to experimental results.

12. A graph theoretical perspective of a drug abuse epidemic model

Nyabadza, F.; Mukwembi, S.; Rodrigues, B. G.

2011-05-01

A drug use epidemic can be represented by a finite number of states and transition rules that govern the dynamics of drug use in each discrete time step. This paper investigates the spread of drug use in a community where some users are in treatment and others are not in treatment, citing South Africa as an example. In our analysis, we consider the neighbourhood prevalence of each individual, i.e., the proportion of the individual’s drug user contacts who are not in treatment amongst all of his or her contacts. We introduce parameters α∗, β∗ and γ∗, depending on the neighbourhood prevalence, which govern the spread of drug use. We examine how changes in α∗, β∗ and γ∗ affect the system dynamics. Simulations presented support the theoretical results.

13. Some Aspects of Mathematical Model of Collaborative Learning

ERIC Educational Resources Information Center

Nakamura, Yasuyuki; Yasutake, Koichi; Yamakawa, Osamu

2012-01-01

There are some mathematical learning models of collaborative learning, with which we can learn how students obtain knowledge and we expect to design effective education. We put together those models and classify into three categories; model by differential equations, so-called Ising spin and a stochastic process equation. Some of the models do not…

14. A Type-Theoretic Framework for Certified Model Transformations

Calegari, Daniel; Luna, Carlos; Szasz, Nora; Tasistro, Álvaro

We present a framework based on the Calculus of Inductive Constructions (CIC) and its associated tool the Coq proof assistant to allow certification of model transformations in the context of Model-Driven Engineering (MDE). The approached is based on a semi-automatic translation process from metamodels, models and transformations of the MDE technical space into types, propositions and functions of the CIC technical space. We describe this translation and illustrate its use in a standard case study.

15. Self-consistent Equilibrium Model of Low-aspect-ratio Toroidal Plasma with Energetic Beam Ions

SciTech Connect

E.V. Belova; N.N. Gorelenkov; C.Z. Cheng

2003-04-09

A theoretical model is developed which allows the self-consistent inclusion of the effects of energetic beam ions in equilibrium calculations of low-aspect-ratio toroidal devices. A two-component plasma is considered, where the energetic ions are treated using a kinetic Vlasov description, while a one-fluid magnetohydrodynamic description is used to represent the thermal plasma. The model allows for an anisotropic distribution function and a large Larmor radius of the beam ions. Numerical results are obtained for neutral-beam-heated plasmas in the National Spherical Torus Experiment (NSTX). Self-consistent equilibria with an anisotropic fast-ion distribution have been calculated for NSTX. It is shown for typical experimental parameters that the contribution of the energetic neutral-beam ions to the total current can be comparable to that of the background plasma, and that the kinetic modifications of the equilibrium can be significant. The range of validity of the finite-Larmor-radius expansion and of the reduced kinetic descriptions for the beam ions in NSTX is discussed. The calculated kinetic equilibria can be used for self-consistent numerical studies of beam-ion-driven instabilities in NSTX.

16. THEORETICAL MODEL OF SOILING OF SURFACES BY AIRBORNE PARTICLES

EPA Science Inventory

A model is developed which can be used to predict the change in reflectance from a surface as a function of time. Reflectance change is a measure of soiling caused by the deposition of particles on a surface. The major inputs to the model are the parameters to a bimodal distribut...

17. Experimental observations and theoretical models for beam-beam phenomena

SciTech Connect

Kheifets, S.

1981-03-01

The beam-beam interaction in storage rings exhibits all the characteristics of nonintegrable dynamical systems. Here one finds all kinds of resonances, closed orbits, stable and unstable fixed points, stochastic layers, chaotic behavior, diffusion, etc. The storage ring itself being an expensive device nevertheless while constructed and put into operation presents a good opportunity of experimentally studying the long-time behavior of both conservative (proton machines) and nonconservative (electron machines) dynamical systems - the number of bunch-bunch interactions routinely reaches values of 10/sup 10/-10/sup 11/ and could be increased by decreasing the beam current. At the same time the beam-beam interaction puts practical limits for the yield of the storage ring. This phenomenon not only determines the design value of main storage ring parameters (luminosity, space charge parameters, beam current), but also in fact prevents many of the existing storage rings from achieving design parameters. Hence, the problem has great practical importance along with its enormous theoretical interest. A brief overview of the problem is presented.

18. Psychosocial stress and prostate cancer: a theoretical model.

PubMed

Ellison, G L; Coker, A L; Hebert, J R; Sanderson, S M; Royal, C D; Weinrich, S P

2001-01-01

African-American men are more likely to develop and die from prostate cancer than are European-American men; yet, factors responsible for the racial disparity in incidence and mortality have not been elucidated. Socioeconomic disadvantage is more prevalent among African-American than among European-American men. Socioeconomic disadvantage can lead to psychosocial stress and may be linked to negative lifestyle behaviors. Regardless of socioeconomic position, African-American men routinely experience racism-induced stress. We propose a theoretical framework for an association between psychosocial stress and prostate cancer. Within the context of history and culture, we further propose that psychosocial stress may partially explain the variable incidence of prostate cancer between these diverse groups. Psychosocial stress may negatively impact the immune system leaving the individual susceptible to malignancies. Behavioral responses to psychosocial stress are amenable to change. If psychosocial stress is found to negatively impact prostate cancer risk, interventions may be designed to modify reactions to environmental demands. PMID:11572415

19. Theoretical Tools in Modeling Communication and Language Dynamics

Loreto, Vittorio

Statistical physics has proven to be a very fruitful framework to describe phenomena outside the realm of traditional physics. In social phenomena, the basic constituents are not particles but humans and every individual interacts with a limited number of peers, usually negligible compared to the total number of people in the system. In spite of that, human societies are characterized by stunning global regularities that naturally call for a statistical physics approach to social behavior, i.e., the attempt to understand regularities at large scale as collective effects of the interaction among single individuals, considered as relatively simple entities. This is the paradigm of Complex Systems: an assembly of many interacting (and simple) units whose collective behavior is not trivially deducible from the knowledge of the rules governing their mutual interactions. In this chapter we review the main theoretical concepts and tools that physics can borrow to socially-motivated problems. Despite their apparent diversity, most research lines in social dynamics are actually closely connected from the point of view of both the methodologies employed and, more importantly, of the general phenomenological questions, e.g., what are the fundamental interaction mechanisms leading to the emergence of consensus on an issue, a shared culture, a common language or a collective motion?

20. Some aspects of application of the two parameter SEU model

SciTech Connect

Miroshkin, V.V.; Tverskoy, M.G.

1995-12-01

Influence of the projectile type, pion production in nucleon-nucleon interaction inside nucleus and direction of the beam incidence on SEU cross section for INTEL 2164A microcircuit in framework of the two parameter model is investigated. Model parameters for devices, investigated recently are reported. Optimum proton energies for determination of model parameters are proposed.

1. Ion Implantation into Presolar Grains: A Theoretical Model

Verchovsky, A. B.; Wright, I. P.; Pillinger, C. T.

A numerical model for ion implantation into spherical grains in free space has been developed. It can be applied to single grains or collections of grains with known grain-size distributions. Ion-scattering effects were taken into account using results of computer simulations. Possible isotope and element fractionation of the implanted species was investigated using this model. The astrophysical significance of the model lies in the possible identification of energetically different components (such as noble gases) implanted into presolar grains (such as diamond and SiC) and in establishing implantation energies of the components.

2. Design and implementation of a calibrated hyperspectral small-animal imager: Practical and theoretical aspects of system optimization

Leavesley, Silas Josiah

Pre-clinical imaging has been an important development within the bioscience and pharmacology fields. A rapidly growing area within these fields is small animal fluorescence imaging, in which molecularly targeted fluorescent probes are used to non-invasively image internal events on a gross anatomical scale. Small-animal fluorescence imaging has transitioned from a research technique to pre-clinical technology very quickly, due to its molecular specificity, low cost, and relative ease of use. In addition, its potential uses in gene therapy and as a translational technology are becoming evident. This thesis outlines the development of an alternative modality for small animal/tissue imaging, using hyperspectral techniques to enable the collection of fluorescence images at different excitation and emission wavelengths. In specific, acousto-optical tunable filters (AOTFs) were used to construct emission-wavelength-scanning and excitation-wavelength-scanning small animal fluorescence imagers. Statistical, classification, and unmixing algorithms have been employed to extract specific fluorescent-dye information from hyperspectral image sets. In this work, we have designed and implemented hyperspectral imaging and analysis techniques to remove background autofluorescence from the desired fluorescence signal, resulting in highly specific and localized fluorescence. Therefore, in practice, it is possible to more accurately pin-point the location and size of diagnostic anatomical markers (e.g. tumors) labeled with fluorescent probes. Furthermore, multiple probes can be individually distinguished. In addition to imaging hardware and acquisition and analysis software, we have designed an optical tissue phantom for quality control and inter-system comparison. The phantom has been modeled using Monte Carlo techniques. The culmination of this work results in an understanding of the advantages and complexities in applying hyperspectral techniques to small animal fluorescence

3. Including effects of microstructure and anisotropy in theoretical models describing hysteresis of ferromagnetic materials

Hauser, H.; Melikhov, Y.; Jiles, D. C.

2007-10-01

Two recent theoretical hysteresis models (Jiles-Atherton model and energetic model) are examined with respect to their capability to describe the dependence of the magnetization on magnetic field, microstructure, and anisotropy. It is shown that the classical Rayleigh law for the behavior of magnetization at low fields and the Stoner-Wohlfarth theory of domain magnetization rotation in noninteracting magnetic single domain particles can be considered as limiting cases of a more general theoretical treatment of hysteresis in ferromagnetism.

4. Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis

PubMed Central

Buesser, B.; Gröhn, A.J.

2013-01-01

Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

5. Translational neurocardiology: preclinical models and cardioneural integrative aspects.

PubMed

Ardell, J L; Andresen, M C; Armour, J A; Billman, G E; Chen, P-S; Foreman, R D; Herring, N; O'Leary, D S; Sabbah, H N; Schultz, H D; Sunagawa, K; Zucker, I H

2016-07-15

Neuronal elements distributed throughout the cardiac nervous system, from the level of the insular cortex to the intrinsic cardiac nervous system, are in constant communication with one another to ensure that cardiac output matches the dynamic process of regional blood flow demand. Neural elements in their various 'levels' become differentially recruited in the transduction of sensory inputs arising from the heart, major vessels, other visceral organs and somatic structures to optimize neuronal coordination of regional cardiac function. This White Paper will review the relevant aspects of the structural and functional organization for autonomic control of the heart in normal conditions, how these systems remodel/adapt during cardiac disease, and finally how such knowledge can be leveraged in the evolving realm of autonomic regulation therapy for cardiac therapeutics. PMID:27098459

6. High-Energy Aspects of Solar Flares: Observations and Models

SciTech Connect

Liu, Wei; Guo, Fan

2015-07-21

The paper begins by describing the structure of the Sun, with emphasis on the corona. The Sun is a unique plasma laboratory, which can be probed by Sun-grazing comets, and is the driver of space weather. Energization and particle acceleration mechanisms in solar flares is presented; magnetic reconnection is key is understanding stochastic acceleration mechanisms. Then coupling between kinetic and fluid aspects is taken up; the next step is feedback of atmospheric response to the acceleration process – rapid quenching of acceleration. Future challenges include applications of stochastic acceleration to solar energetic particles (SEPs), Fermi γ-rays observations, fast-mode magnetosonic wave trains in a funnel-shaped wave guide associated with flare pulsations, and the new SMEX mission IRIS (Interface Region Imaging Spectrograph),

7. Theoretical model of impact damage in structural ceramics

NASA Technical Reports Server (NTRS)

Liaw, B. M.; Kobayashi, A. S.; Emery, A. G.

1984-01-01

This paper presents a mechanistically consistent model of impact damage based on elastic failures due to tensile and shear overloading. An elastic axisymmetric finite element model is used to determine the dynamic stresses generated by a single particle impact. Local failures in a finite element are assumed to occur when the primary/secondary principal stresses or the maximum shear stress reach critical tensile or shear stresses, respectively. The succession of failed elements thus models macrocrack growth. Sliding motions of cracks, which closed during unloading, are resisted by friction and the unrecovered deformation represents the 'plastic deformation' reported in the literature. The predicted ring cracks on the contact surface, as well as the cone cracks, median cracks, radial cracks, lateral cracks, and damage-induced porous zones in the interior of hot-pressed silicon nitride plates, matched those observed experimentally. The finite element model also predicted the uplifting of the free surface surrounding the impact site.

8. Phenomenological aspects of heterotic orbifold models at one loop

SciTech Connect

Birkedal-Hansen, A.; Binetruy, P.; Mambrini, Y.; Nelson, B.

2003-08-05

We provide a detailed study of the phenomenology of orbifold compactifications of the heterotic string within the context of supergravity effective theories. Our investigation focuses on those models where the soft Lagrangian is dominated by loop contributions to the various soft supersymmetry breaking parameters. Such models typically predict non-universal soft masses and are thus significantly different from minimal supergravity and other universal models. We consider the pattern of masses that are governed by these soft terms and investigate the implications of certain indirect constraints on supersymmetric models, such as flavor-changing neutral currents, the anomalous magnetic moment of the muon and the density of thermal relic neutralinos. These string-motivated models show novel behavior that interpolates between the phenomenology of unified supergravity models and models dominated by the superconformal anomaly.

9. Theoretical models for duct acoustic propagation and radiation

NASA Technical Reports Server (NTRS)

Eversman, Walter

1991-01-01

The development of computational methods in acoustics has led to the introduction of analysis and design procedures which model the turbofan inlet as a coupled system, simultaneously modeling propagation and radiation in the presence of realistic internal and external flows. Such models are generally large, require substantial computer speed and capacity, and can be expected to be used in the final design stages, with the simpler models being used in the early design iterations. Emphasis is given to practical modeling methods that have been applied to the acoustical design problem in turbofan engines. The mathematical model is established and the simplest case of propagation in a duct with hard walls is solved to introduce concepts and terminologies. An extensive overview is given of methods for the calculation of attenuation in uniform ducts with uniform flow and with shear flow. Subsequent sections deal with numerical techniques which provide an integrated representation of duct propagation and near- and far-field radiation for realistic geometries and flight conditions.

10. Learning models of PTSD: Theoretical accounts and psychobiological evidence.

PubMed

Lissek, Shmuel; van Meurs, Brian

2015-12-01

Learning abnormalities have long been centrally implicated in posttraumatic psychopathology. Indeed, of all anxiety disorders, PTSD may be most clearly attributable to discrete, aversive learning events. In PTSD, such learning is acquired during the traumatic encounter and is expressed as both conditioned fear to stimuli associated with the event and more general over-reactivity-or failure to adapt-to intense, novel, or fear-related stimuli. The relatively straightforward link between PTSD and these basic, evolutionarily old, learning processes of conditioning, sensitization, and habituation affords models of PTSD comprised of fundamental, experimentally tractable mechanisms of learning that have been well characterized across a variety of mammalian species including humans. Though such learning mechanisms have featured prominently in explanatory models of psychological maladjustment to trauma for at least 90years, much of the empirical testing of these models has occurred only in the past two decades. The current review delineates the variety of theories forming this longstanding tradition of learning-based models of PTSD, details empirical evidence for such models, attempts an integrative account of results from this literature, and specifies limitations of, and future directions for, studies testing learning models of PTSD. PMID:25462219

11. Design theoretic analysis of three system modeling frameworks.

SciTech Connect

McDonald, Michael James

2007-05-01

This paper analyzes three simulation architectures from the context of modeling scalability to address System of System (SoS) and Complex System problems. The paper first provides an overview of the SoS problem domain and reviews past work in analyzing model and general system complexity issues. It then identifies and explores the issues of vertical and horizontal integration as well as coupling and hierarchical decomposition as the system characteristics and metrics against which the tools are evaluated. In addition, it applies Nam Suh's Axiomatic Design theory as a construct for understanding coupling and its relationship to system feasibility. Next it describes the application of MATLAB, Swarm, and Umbra (three modeling and simulation approaches) to modeling swarms of Unmanned Flying Vehicle (UAV) agents in relation to the chosen characteristics and metrics. Finally, it draws general conclusions for analyzing model architectures that go beyond those analyzed. In particular, it identifies decomposition along phenomena of interaction and modular system composition as enabling features for modeling large heterogeneous complex systems.

12. Theoretical and computational models of biological ion channels

Roux, Benoit

2004-03-01

A theoretical framework for describing ion conduction through biological molecular pores is established and explored. The framework is based on a statistical mechanical formulation of the transmembrane potential (1) and of the equilibrium multi-ion potential of mean forces through selective ion channels (2). On the basis of these developments, it is possible to define computational schemes to address questions about the non-equilibrium flow of ions through ion channels. In the case of narrow channels (gramicidin or KcsA), it is possible to characterize the ion conduction in terms of the potential of mean force of the ions along the channel axis (i.e., integrating out the off-axis motions). This has been used for gramicidin (3) and for KcsA (4,5). In the case of wide pores (i.e., OmpF porin), this is no longer a good idea, but it is possible to use a continuum solvent approximations. In this case, a grand canonical monte carlo brownian dynamics algorithm was constructed for simulating the non-equilibrium flow of ions through wide pores. The results were compared with those from the Poisson-Nernst-Planck mean-field electrodiffusion theory (6-8). References; 1. B. Roux, Biophys. J. 73:2980-2989 (1997); 2. B. Roux, Biophys. J. 77, 139-153 (1999); 3. Allen, Andersen and Roux, PNAS (2004, in press); 4. Berneche and Roux. Nature, 414:73-77 (2001); 5. Berneche and Roux. PNAS, 100:8644-8648 (2003); 6. W. Im and S. Seefeld and B. Roux, Biophys. J. 79:788-801 (2000); 7. W. Im and B. Roux, J. Chem. Phys. 115:4850-4861 (2001); 8. W. Im and B. Roux, J. Mol. Biol. 322:851-869 (2002).

13. Ray-theoretical modeling of secondary microseism P-waves

Farra, V.; Stutzmann, E.; Gualtieri, L.; Schimmel, M.; Ardhuin, F.

2016-06-01

Secondary microseism sources are pressure fluctuations close to the ocean surface. They generate acoustic P-waves that propagate in water down to the ocean bottom where they are partly reflected, and partly transmitted into the crust to continue their propagation through the Earth. We present the theory for computing the displacement power spectral density of secondary microseism P-waves recorded by receivers in the far field. In the frequency domain, the P-wave displacement can be modeled as the product of (1) the pressure source, (2) the source site effect that accounts for the constructive interference of multiply reflected P-waves in the ocean, (3) the propagation from the ocean bottom to the stations, (4) the receiver site effect. Secondary microseism P-waves have weak amplitudes, but they can be investigated by beamforming analysis. We validate our approach by analyzing the seismic signals generated by Typhoon Ioke (2006) and recorded by the Southern California Seismic Network. Back projecting the beam onto the ocean surface enables to follow the source motion. The observed beam centroid is in the vicinity of the pressure source derived from the ocean wave model WAVEWATCH IIIR. The pressure source is then used for modeling the beam and a good agreement is obtained between measured and modeled beam amplitude variation over time. This modeling approach can be used to invert P-wave noise data and retrieve the source intensity and lateral extent.

14. Ray-theoretical modeling of secondary microseism P waves

Farra, V.; Stutzmann, E.; Gualtieri, L.; Schimmel, M.; Ardhuin, F.

2016-09-01

Secondary microseism sources are pressure fluctuations close to the ocean surface. They generate acoustic P waves that propagate in water down to the ocean bottom where they are partly reflected and partly transmitted into the crust to continue their propagation through the Earth. We present the theory for computing the displacement power spectral density of secondary microseism P waves recorded by receivers in the far field. In the frequency domain, the P-wave displacement can be modeled as the product of (1) the pressure source, (2) the source site effect that accounts for the constructive interference of multiply reflected P waves in the ocean, (3) the propagation from the ocean bottom to the stations and (4) the receiver site effect. Secondary microseism P waves have weak amplitudes, but they can be investigated by beamforming analysis. We validate our approach by analysing the seismic signals generated by typhoon Ioke (2006) and recorded by the Southern California Seismic Network. Backprojecting the beam onto the ocean surface enables to follow the source motion. The observed beam centroid is in the vicinity of the pressure source derived from the ocean wave model WAVEWATCH IIIR. The pressure source is then used for modeling the beam and a good agreement is obtained between measured and modeled beam amplitude variation over time. This modeling approach can be used to invert P-wave noise data and retrieve the source intensity and lateral extent.

15. Theoretical modeling of electron mobility in superfluid 4He

Aitken, Frédéric; Bonifaci, Nelly; von Haeften, Klaus; Eloranta, Jussi

2016-07-01

The Orsay-Trento bosonic density functional theory model is extended to include dissipation due to the viscous response of superfluid 4He present at finite temperatures. The viscous functional is derived from the Navier-Stokes equation by using the Madelung transformation and includes the contribution of interfacial viscous response present at the gas-liquid boundaries. This contribution was obtained by calibrating the model against the experimentally determined electron mobilities from 1.2 K to 2.1 K along the saturated vapor pressure line, where the viscous response is dominated by thermal rotons. The temperature dependence of ion mobility was calculated for several different solvation cavity sizes and the data are rationalized in the context of roton scattering and Stokes limited mobility models. Results are compared to the experimentally observed "exotic ion" data, which provides estimates for the corresponding bubble sizes in the liquid. Possible sources of such ions are briefly discussed.

16. Theoretical modeling of electron mobility in superfluid (4)He.

PubMed

Aitken, Frédéric; Bonifaci, Nelly; von Haeften, Klaus; Eloranta, Jussi

2016-07-28

The Orsay-Trento bosonic density functional theory model is extended to include dissipation due to the viscous response of superfluid (4)He present at finite temperatures. The viscous functional is derived from the Navier-Stokes equation by using the Madelung transformation and includes the contribution of interfacial viscous response present at the gas-liquid boundaries. This contribution was obtained by calibrating the model against the experimentally determined electron mobilities from 1.2 K to 2.1 K along the saturated vapor pressure line, where the viscous response is dominated by thermal rotons. The temperature dependence of ion mobility was calculated for several different solvation cavity sizes and the data are rationalized in the context of roton scattering and Stokes limited mobility models. Results are compared to the experimentally observed "exotic ion" data, which provides estimates for the corresponding bubble sizes in the liquid. Possible sources of such ions are briefly discussed. PMID:27475346

17. A control theoretic model of driver steering behavior

NASA Technical Reports Server (NTRS)

Donges, E.

1977-01-01

A quantitative description of driver steering behavior such as a mathematical model is presented. The steering task is divided into two levels: (1) the guidance level involving the perception of the instantaneous and future course of the forcing function provided by the forward view of the road, and the response to it in an anticipatory open-loop control mode; (2) the stabilization level whereby any occuring deviations from the forcing function are compensated for in a closed-loop control mode. This concept of the duality of the driver's steering activity led to a newly developed two-level model of driver steering behavior. Its parameters are identified on the basis of data measured in driving simulator experiments. The parameter estimates of both levels of the model show significant dependence on the experimental situation which can be characterized by variables such as vehicle speed and desired path curvature.

18. Flavor symmetry based MSSM: Theoretical models and phenomenological analysis

Babu, K. S.; Gogoladze, Ilia; Raza, Shabbar; Shafi, Qaisar

2014-09-01

We present a class of supersymmetric models in which symmetry considerations alone dictate the form of the soft SUSY breaking Lagrangian. We develop a class of minimal models, denoted as sMSSM—for flavor symmetry-based minimal supersymmetric standard model—that respect a grand unified symmetry such as SO(10) and a non-Abelian flavor symmetry H which suppresses SUSY-induced flavor violation. Explicit examples are constructed with the flavor symmetry being gauged SU(2)H and SO(3)H with the three families transforming as 2+1 and 3 representations, respectively. A simple solution is found in the case of SU(2)H for suppressing the flavor violating D-terms based on an exchange symmetry. Explicit models based on SO(3)H without the D-term problem are developed. In addition, models based on discrete non-Abelian flavor groups are presented which are automatically free from D-term issues. The permutation group S3 with a 2+1 family assignment, as well as the tetrahedral group A4 with a 3 assignment are studied. In all cases, a simple solution to the SUSY CP problem is found, based on spontaneous CP violation leading to a complex quark mixing matrix. We develop the phenomenology of the resulting sMSSM, which is controlled by seven soft SUSY breaking parameters for both the 2+1 assignment and the 3 assignment of fermion families. These models are special cases of the phenomenological MSSM (pMSSM), but with symmetry restrictions. We discuss the parameter space of sMSSM compatible with LHC searches, B-physics constraints and dark matter relic abundance. Fine-tuning in these models is relatively mild, since all SUSY particles can have masses below about 3 TeV.

19. Aspects of B physics

SciTech Connect

Gaillard, M.K.

1987-10-14

Various aspects of weak decays are commented on. Probing of the standard model and of phenomena beyond the standard model are discussed, followed by a theoretical view of B mesons and some experimental observations on B mesons. The point is made that any data on B decay would be interesting in that it would provide powerful new constraints in analyses of the standard model and extensions thereof. (LEW)

20. Aging and Interdependence: A Theoretical Model for Close Relationships.

ERIC Educational Resources Information Center

Blieszner, Rosemary

This paper demonstrates the utility of interdependence theory for understanding older persons' social relationships. Using friendship as an exemplary case, a model of expectations for and reactions to social exchanges is described. Exchanges which are perceived to be motivated by obligation are distinguished from those which are perceived to…

1. Testing Theoretical Models of Magnetic Damping Using an Air Track

ERIC Educational Resources Information Center

Vidaurre, Ana; Riera, Jaime; Monsoriu, Juan A.; Gimenez, Marcos H.

2008-01-01

Magnetic braking is a long-established application of Lenz's law. A rigorous analysis of the laws governing this problem involves solving Maxwell's equations in a time-dependent situation. Approximate models have been developed to describe different experimental results related to this phenomenon. In this paper we present a new method for the…

2. Interpreting Unfamiliar Graphs: A Generative, Activity Theoretic Model

ERIC Educational Resources Information Center

Roth, Wolff-Michael; Lee, Yew Jin

2004-01-01

Research on graphing presents its results as if knowing and understanding were something stored in peoples' minds independent of the situation that they find themselves in. Thus, there are no models that situate interview responses to graphing tasks. How, then, we question, are the interview texts produced? How do respondents begin and end…

3. [Theoretical model for rocky desertification control in karst area].

PubMed

Liang, Liang; Liu, Zhi-Xiao; Zhang, Dai-Gui; Deng, Kai-Dong; Zhang, You-Xiang

2007-03-01

Based on the basic principles of restoration ecology, the trigger-action model for rocky desertification control was proposed, i. e. , the ability that an ecosystem enables itself to develop was called dominant force, and the interfering factor resulting in the deviation of the climax of ecological succession from its preconcerted status was called trigger factor. The ultimate status of ecological succession was determined by the interaction of dominant force and trigger factor. Rocky desertification was the result of serious malignant triggers, and its control was the process of benign triggers in using the ecological restoration method of artificial designs to activate the natural designing ability of an ecosystem. The ecosystem of Karst rocky desertification in Fenghuang County with restoration measures was taken as a case to test the model, and the results showed that the restoration measures based on trigger-action model markedly improved the physical and chemical properties of soil and increased the diversity of plant. There was a benign trigger between the restoration measures and the Karst area. The rationality of the trigger-action model was primarily tested by the results in practice. PMID:17552199

4. SBS mitigation with 'two-tone' amplification: a theoretical model

Bronder, T. J.; Shay, T. M.; Dajani, I.; Gavrielides, A.; Robin, C. A.; Lu, C. A.

2008-02-01

A new technique for mitigating stimulated Brillouin scattering (SBS) effects in narrow-linewidth Yb-doped fiber amplifiers is demonstrated with a model that reduces to solving an 8×8 system of coupled nonlinear equations with the gain, SBS, and four-wave mixing (FMW) incorporated into the model. This technique uses two seed signals, or 'two-tones', with each tone reaching its SBS threshold almost independently and thus increasing the overall threshold for SBS in the fiber amplifier. The wavelength separation of these signals is also selected to avoid FWM, which in this case possesses the next lowest nonlinear effects threshold. This model predicts an output power increase of 86% (at SBS threshold with no signs of FWM) for a 'two-tone' amplifier with seed signals at 1064nm and 1068nm, compared to a conventional fiber amplifier with a single 1064nm seed. The model is also used to simulate an SBS-suppressing fiber amplifier to test the regime where FWM is the limiting factor. In this case, an optimum wavelength separation of 3nm to 10nm prevents FWM from reaching threshold. The optimum ratio of the input power for the two seed signals in 'two-tone' amplification is also tested. Future experimental verification of this 'two-tone' technique is discussed.

5. Multiaxial cyclic ratcheting in coiled tubing -- Part 1: Theoretical modeling

SciTech Connect

Rolovic, R.; Tipton, S.M.

2000-04-01

Coiled tubing is a long, continuous string of steel tubing that is used in the oil well drilling and servicing industry. Bending strains imposed on coiled tubing as it is deployed and retrieved from a well are considerably into the plastic regime and can be as high as 3%. Progressive growth of tubing diameter occurs when tubing is cyclically bent-straightened under constant internal pressure, regardless of the fact that the hoop stress imposed by typical pressure levels is well below the material's yield strength. A new incremental plasticity model is proposed in this study that can predict multiaxial cyclic ratcheting in coiled tubing more accurately than the conventional plasticity models. A new hardening rule is presented based on published experimental observations. The model also implements a new plastic modulus function. The predictions based on the new theory correlate well with experimental results presented in Part 2 of this paper. Some previously unexpected trends in coiled tubing deformation behavior were observed and correctly predicted using the proposed model.

6. Photoabsorption spectrum of helium trimer cation—Theoretical modeling

Kalus, René; Karlický, František; Lepetit, Bruno; Paidarová, Ivana; Gadea, Florent Xavier

2013-11-01

The photoabsorption spectrum of He_3^+ is calculated for two semiempirical models of intracluster interactions and compared with available experimental data reported in the middle UV range [H. Haberland and B. von Issendorff, J. Chem. Phys. 102, 8773 (1995)]. Nuclear delocalization effects are investigated via several approaches comprising quantum samplings using either exact or approximate (harmonic) nuclear wavefunctions, as well as classical samplings based on the Monte Carlo methodology. Good agreement with the experiment is achieved for the model by Knowles et al., [Mol. Phys. 85, 243 (1995); Knowles et al., Mol. Phys. 87, 827 (1996)] whereas the model by Calvo et al., [J. Chem. Phys. 135, 124308 (2011)] exhibits non-negligible deviations from the experiment. Predictions of far UV absorption spectrum of He_3^+, for which no experimental data are presently available, are reported for both models and compared to each other as well as to the photoabsorption spectrum of He_2^+. A simple semiempirical point-charge approximation for calculating transition probabilities is shown to perform well for He_3^+.

7. Photoabsorption spectrum of helium trimer cation--theoretical modeling.

PubMed

Kalus, René; Karlický, František; Lepetit, Bruno; Paidarová, Ivana; Gadea, Florent Xavier

2013-11-28

The photoabsorption spectrum of He3(+) is calculated for two semiempirical models of intracluster interactions and compared with available experimental data reported in the middle UV range [H. Haberland and B. von Issendorff, J. Chem. Phys. 102, 8773 (1995)]. Nuclear delocalization effects are investigated via several approaches comprising quantum samplings using either exact or approximate (harmonic) nuclear wavefunctions, as well as classical samplings based on the Monte Carlo methodology. Good agreement with the experiment is achieved for the model by Knowles et al., [Mol. Phys. 85, 243 (1995); Mol. Phys. 87, 827 (1996)] whereas the model by Calvo et al., [J. Chem. Phys. 135, 124308 (2011)] exhibits non-negligible deviations from the experiment. Predictions of far UV absorption spectrum of He3(+), for which no experimental data are presently available, are reported for both models and compared to each other as well as to the photoabsorption spectrum of He2(+). A simple semiempirical point-charge approximation for calculating transition probabilities is shown to perform well for He3(+). PMID:24289357

8. Photoabsorption spectrum of helium trimer cation—Theoretical modeling

SciTech Connect

Kalus, René; Karlický, František; Lepetit, Bruno; Paidarová, Ivana; Gadea, Florent Xavier

2013-11-28

The photoabsorption spectrum of He{sub 3}{sup +} is calculated for two semiempirical models of intracluster interactions and compared with available experimental data reported in the middle UV range [H. Haberland and B. von Issendorff, J. Chem. Phys. 102, 8773 (1995)]. Nuclear delocalization effects are investigated via several approaches comprising quantum samplings using either exact or approximate (harmonic) nuclear wavefunctions, as well as classical samplings based on the Monte Carlo methodology. Good agreement with the experiment is achieved for the model by Knowles et al., [Mol. Phys. 85, 243 (1995); Mol. Phys. 87, 827 (1996)] whereas the model by Calvo et al., [J. Chem. Phys. 135, 124308 (2011)] exhibits non-negligible deviations from the experiment. Predictions of far UV absorption spectrum of He{sub 3}{sup +}, for which no experimental data are presently available, are reported for both models and compared to each other as well as to the photoabsorption spectrum of He{sub 2}{sup +}. A simple semiempirical point-charge approximation for calculating transition probabilities is shown to perform well for He{sub 3}{sup +}.

9. Neurological Aspects of Dyslexia: Comment on the Balance Model.

ERIC Educational Resources Information Center

Hynd, George W.

1992-01-01

This article reviews Bakker's developmental neuropsychological model (the Balance Model) of reading development (EC 602 750), notes the need for validating research before employing these procedures in clinical practice, and raises some conceptual problems such as evidence that learning disability subtypes evolve over time. (Author/DB)

10. Toward a Theoretical Model of Employee Turnover: A Human Resource Development Perspective

ERIC Educational Resources Information Center

Peterson, Shari L.

2004-01-01

This article sets forth the Organizational Model of Employee Persistence, influenced by traditional turnover models and a student attrition model. The model was developed to clarify the impact of organizational practices on employee turnover from a human resource development (HRD) perspective and provide a theoretical foundation for research on…

11. The abelian confinement mechanism revisited: New aspects of the Georgi-Glashow model

Anber, Mohamed M.

2014-02-01

The confinement problem remains one of the most difficult problems in theoretical physics. An important step toward the solution of this problem is Polyakov's work on abelian confinement. The Georgi-Glashow model is a natural testing ground for this mechanism which has been surprising us by its richness and wide applicability. In this work, we shed light on two new aspects of this model in 2+1 D. First, we develop a many-body description of the effective degrees of freedom. Namely, we consider a non-relativistic gas of W-bosons in the background of monopole-instanton plasma. Many-body treatment is a standard toolkit in condensed matter physics. However, we add a new twist by supplying the monopole-instantons as external background field. Using this construction along with a mean-field approximation, we calculate the form of the potential between two electric probes as a function of their separation. This potential is expressed in terms of the Meijer-G function which interpolates between logarithmic and linear behavior at small and large distances, respectively. Second, we develop a systematic approach to integrate out the effect of the W-bosons at finite temperature in the range 0≤Tmodel. Using a heat kernel expansion that takes into account the non-trivial thermal holonomy, we show that the partition function describes a three-dimensional two-component Coulomb gas. We repeat our analysis using the many-body description which yields the same result and provides a check on our formalism. At temperatures close to the deconfinement temperature, the gas becomes essentially two-dimensional recovering the partition function of the dual sine-Gordon model that was considered in a previous work.

12. Theoretical transport modeling of Ohmic cold pulse experiments

Kinsey, J. E.; Waltz, R. E.; St. John, H. E.

1998-11-01

The response of several theory-based transport models in Ohmically heated tokamak discharges to rapid edge cooling due to trace impurity injection is studied. Results are presented for the Institute for Fusion Studies—Princeton Plasma Physics Laboratory (IFS/PPPL), gyro-Landau-fluid (GLF23), Multi-mode (MM), and the Itoh-Itoh-Fukuyama (IIF) transport models with an emphasis on results from the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Technol./Fusion 1, 479 (1981)]. It is found that critical gradient models containing a strong ion and electron temperature ratio dependence can exhibit behavior that is qualitatively consistent with experimental observation while depending solely on local parameters. The IFS/PPPL model yields the strongest response and demonstrates both rapid radial pulse propagation and a noticeable increase in the central electron temperature following a cold edge temperature pulse (amplitude reversal). Furthermore, the amplitude reversal effect is predicted to diminish with increasing electron density and auxiliary heating in agreement with experimental data. An Ohmic pulse heating effect due to rearrangement of the current profile is shown to contribute to the rise in the core electron temperature in TEXT, but not in the Joint European Tokamak (JET) [A. Tanga and the JET Team, in Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 65] and the Tokamak Fusion Test Reactor (TFTR) [R. J. Hawryluk, V. Arunsalam, M. G. Bell et al., in Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 51]. While this phenomenon is not necessarily a unique signature of a critical gradient, there is sufficient evidence suggesting that the apparent plasma response to edge cooling may not require any underlying nonlocal mechanism and may be explained within the context of the intrinsic properties of electrostatic drift

13. Formation of different types of compaction bands: Theoretical analysis and numerical models

Chemenda, A. I.

2010-12-01

anti-crack model. The band propagation distance is proportional to the initial (resulted from the bifurcation) band length that in turn is proportional to the hardening modulus and theoretically can reach infinity. The aspect of "numerical" bands is very similar to that of natural (geological as opposed to experimental) bands. They are thicker in the central band segment and are progressively thinning toward the ends. The microphysics of the observed difference between geological and experimental banding is discussed and related to the evolution (continuous versus discontinuous) of the hardening modulus with inelastic deformation.

14. A differential game theoretical analysis of mechanistic models for territoriality.

PubMed

Hamelin, Frédéric M; Lewis, Mark A

2010-11-01

In this paper, elements of differential game theory are used to analyze a spatially explicit home range model for interacting wolf packs when movement behavior is uncertain. The model consists of a system of partial differential equations whose parameters reflect the movement behavior of individuals within each pack and whose steady-state solutions describe the patterns of space-use associated to each pack. By controlling the behavioral parameters in a spatially-dynamic fashion, packs adjust their patterns of movement so as to find a Nash-optimal balance between spreading their territory and avoiding conflict with hostile neighbors. On the mathematical side, we show that solving a nonzero-sum differential game corresponds to finding a non-invasible function-valued trait. From the ecological standpoint, when movement behavior is uncertain, the resulting evolutionarily stable equilibrium gives rise to a buffer-zone, or a no-wolf's land where deer are known to find refuge. PMID:20033174

15. Theoretical model for morphogenesis and cell sorting in Dictyostelium discoideum

Umeda, T.; Inouye, K.

1999-02-01

The morphogenetic movement and cell sorting in cell aggregates from the mound stage to the migrating slug stage of the cellular slime mold Dictyostelium discoideum were studied using a mathematical model. The model postulates that the motive force generated by the cells is in equilibrium with the internal pressure and mechanical resistance. The moving boundary problem derived from the force balance equation and the continuity equation has stationary solutions in which the aggregate takes the shape of a spheroid (or an ellipse in two-dimensional space) with the pacemaker at one of its foci, moving at a constant speed. Numerical calculations in two-dimensional space showed that an irregularly shaped aggregate changes its shape to become an ellipse as it moves. Cell aggregates consisting of two cell types differing in motive force exhibit cell sorting and become elongated, suggesting the importance of prestalk/prespore differentiation in the morphogenesis of Dictyostelium.

16. On physical aspects of the Jiles-Atherton hysteresis models

Zirka, Sergey E.; Moroz, Yuriy I.; Harrison, Robert G.; Chwastek, Krzysztof

2012-08-01

The physical assumptions underlying the static and dynamic Jiles-Atherton (JA) hysteresis models are critically analyzed. It is shown that the energy-balance method used in deriving these models is actually closer to a balance of coenergies, thereby depriving the resulting JA phenomenology of physical meaning. The non-physical basis of its dynamic extension is demonstrated by a sharp contrast between hysteresis loops predicted by the model and those measured for grain-oriented steel under conditions of controlled sinusoidal flux density at frequencies of 50, 100, and 200 Hz.

17. Automata-theoretic models of mutation and alignment

SciTech Connect

Searls, D.B.; Murphy, K.P.

1995-12-31

Finite-state automata called transducers, which have both input and output, can be used to model simple mechanisms of biological mutation. We present a methodology whereby numerically-weighted versions of such specifications can be mechanically adapted to create string edit machines that are essentially equivalent to recurrence relations of the sort that characterize dynamic programming alignment algorithms. Based on this, we have developed a visual programming system for designing new alignment algorithms in a rapid-prototyping fashion.

18. A Theoretical Model for the Associative Nature of Conference Participation.

PubMed

Smiljanić, Jelena; Chatterjee, Arnab; Kauppinen, Tomi; Mitrović Dankulov, Marija

2016-01-01

Participation in conferences is an important part of every scientific career. Conferences provide an opportunity for a fast dissemination of latest results, discussion and exchange of ideas, and broadening of scientists' collaboration network. The decision to participate in a conference depends on several factors like the location, cost, popularity of keynote speakers, and the scientist's association with the community. Here we discuss and formulate the problem of discovering how a scientist's previous participation affects her/his future participations in the same conference series. We develop a stochastic model to examine scientists' participation patterns in conferences and compare our model with data from six conferences across various scientific fields and communities. Our model shows that the probability for a scientist to participate in a given conference series strongly depends on the balance between the number of participations and non-participations during his/her early connections with the community. An active participation in a conference series strengthens the scientist's association with that particular conference community and thus increases the probability of future participations. PMID:26859404

19. A dynamic game-theoretic model of parental care.

PubMed

Mcnamara, J M; Székely, T; Webb, J N; Houston, A I

2000-08-21

We present a model in which members of a mated pair decide whether to care for their offspring or desert them. There is a breeding season of finite length during which it is possible to produce and raise several batches of offspring. On deserting its offspring, an individual can search for a new mate. The probability of finding a mate depends on the number of individuals of each sex that are searching, which in turn depends upon the previous care and desertion decisions of all population members. We find the evolutionarily stable pattern of care over the breeding season. The feedback between behaviour and mating opportunity can result in a pattern of stable oscillations between different forms of care over the breeding season. Oscillations can also arise because the best thing for an individual to do at a particular time in the season depends on future behaviour of all population members. In the baseline model, a pair splits up after a breeding attempt, even if they both care for the offspring. In a version of the model in which a pair stays together if they both care, the feedback between behaviour and mating opportunity can lead to more than one evolutionarily stable form of care. PMID:10931755

20. A Theoretical Model for the Associative Nature of Conference Participation

PubMed Central

Smiljanić, Jelena; Chatterjee, Arnab; Kauppinen, Tomi; Mitrović Dankulov, Marija

2016-01-01

Participation in conferences is an important part of every scientific career. Conferences provide an opportunity for a fast dissemination of latest results, discussion and exchange of ideas, and broadening of scientists’ collaboration network. The decision to participate in a conference depends on several factors like the location, cost, popularity of keynote speakers, and the scientist’s association with the community. Here we discuss and formulate the problem of discovering how a scientist’s previous participation affects her/his future participations in the same conference series. We develop a stochastic model to examine scientists’ participation patterns in conferences and compare our model with data from six conferences across various scientific fields and communities. Our model shows that the probability for a scientist to participate in a given conference series strongly depends on the balance between the number of participations and non-participations during his/her early connections with the community. An active participation in a conference series strengthens the scientist’s association with that particular conference community and thus increases the probability of future participations. PMID:26859404

1. BL Herculis stars - Theoretical models for field variables

NASA Technical Reports Server (NTRS)

Carson, R.; Stothers, R.

1982-01-01

Type II Cepheids with periods between 1 and 3 days, commonly designated as Bl Herculis stars, have been modeled here with the aim of interpreting the wide variety of light curves observed among the field variables. Previously modeled globular cluster members are used as standard calibration objects. The major finding is that only a small range of luminosities is capable of generating a large variety of light curve types at a given period. For a mass of approximately 0.60 solar mass, the models are able to reproduce the observed mean luminosities, dispersion of mean luminosities, periods, light amplitudes, light asymmetries, and phases of secondary features in the light curves of known BL Her stars. It is possible that the metal-rich variables (which are found only in the field) have luminosities lower than those of most metal-poor variables. The present revised mass for BL Her, a metal-rich object, is not significantly different from the mean mass of the metal-poor variables.

2. Theoretical aspects of color vision

NASA Technical Reports Server (NTRS)

Wolbarsht, M. L.

1972-01-01

The three color receptors of Young-Helmholtz and the opponent colors type of information processing postulated by Hering are both present in the human visual system. This mixture accounts for both the phenomena of color matching or hue discrimination and such perceptual qualities of color as the division of the spectrum into color bands. The functioning of the cells in the visual system, especially within the retina, and the relation of this function to color perception are discussed.

3. Imitative Modeling as a Theoretical Base for Instructing Language-Disordered Children

ERIC Educational Resources Information Center

Courtright, John A.; Courtright, Illene C.

1976-01-01

A modification of A. Bandura's social learning theory (imitative modeling) was employed as a theoretical base for language instruction with eight language disordered children (5 to 10 years old). (Author/SBH)

4. Using Epidemiological Models and Genetic Selection to Identify Theoretical Opportunities to Reduce Disease Impact

Technology Transfer Automated Retrieval System (TEKTRAN)

Selection for disease resistance is a contemporary topic with developing approaches for genetic improvement. Merging the sciences of genetic selection and epidemiology is essential to identify selection schemes to enhance disease resistance. Epidemiological models can identify theoretical opportuni...

5. Theoretical models for the emergence of biomolecular homochirality

Walker, Sara Imari

Little is known about the emergence of life from nonliving precursors. A key missing-piece is the origin of homochirality: nearly all life is characterized by exclusively dextrorotary sugars and levorotary amino acids. The research presented in this thesis addresses the challenge of uncovering mechanisms for chiral symmetry breaking in a prebiotic environment and implications for the origin of life on Earth. Expanding on a well-known model for chiral selection through polymerization, and modeling the spatiotemporal dynamics starting from near-racemic initial conditions, it is demonstrated that the net chirality of molecular building blocks grows with the longest polymer in the reaction network (of length N) with critical behavior for the onset of chiral asymmetry determined by the value of N. This surprising result indicates that significant chiral asymmetry occurs only for systems which permit growth of long polymers. Expanding on this work, the effects of environmental disturbances on the evolution of chirality in prebiotic reaction-diffusion networks are studied via the implementation of a stochastic spatiotemporal Langevin equation. The results show that environmental interactions can have significant impact on the evolution of prebiotic chirality: the history of prebiotic chirality is therefore interwoven with the Earths early environmental history in a mechanism we call punctuated chirality. This result establishes that the onset of homochirality is not an isolated phenomenon: chiral selection must occur in tandem with the transition from chemistry to biology, otherwise the prebiotic soup is unstable to environmental events. Addressing the challenge of understanding the role of chirality in the transition from non-life to life, the diffusive slowdown of reaction networks induced, for example, through tidal cycles or evaporating pools, is modeled. The results of this study demonstrate that such diffusive slowdown leads to the stabilization of homochiral

6. GSTARS computer models and their applications, part I: theoretical development

USGS Publications Warehouse

Yang, C.T.; Simoes, F.J.M.

2008-01-01

GSTARS is a series of computer models developed by the U.S. Bureau of Reclamation for alluvial river and reservoir sedimentation studies while the authors were employed by that agency. The first version of GSTARS was released in 1986 using Fortran IV for mainframe computers. GSTARS 2.0 was released in 1998 for personal computer application with most of the code in the original GSTARS revised, improved, and expanded using Fortran IV/77. GSTARS 2.1 is an improved and revised GSTARS 2.0 with graphical user interface. The unique features of all GSTARS models are the conjunctive use of the stream tube concept and of the minimum stream power theory. The application of minimum stream power theory allows the determination of optimum channel geometry with variable channel width and cross-sectional shape. The use of the stream tube concept enables the simulation of river hydraulics using one-dimensional numerical solutions to obtain a semi-two- dimensional presentation of the hydraulic conditions along and across an alluvial channel. According to the stream tube concept, no water or sediment particles can cross the walls of stream tubes, which is valid for many natural rivers. At and near sharp bends, however, sediment particles may cross the boundaries of stream tubes. GSTARS3, based on FORTRAN 90/95, addresses this phenomenon and further expands the capabilities of GSTARS 2.1 for cohesive and non-cohesive sediment transport in rivers and reservoirs. This paper presents the concepts, methods, and techniques used to develop the GSTARS series of computer models, especially GSTARS3. ?? 2008 International Research and Training Centre on Erosion and Sedimentation and the World Association for Sedimentation and Erosion Research.

7. Spermatozoa: models for studying regulatory aspects of energy metabolism.

PubMed

Kamp, G; Büsselmann, G; Lauterwein, J

1996-05-15

Spermatozoa are highly specialized cells, and they offer advantages for studying several basic aspects of metabolic control such as the role of adenosine triphosphate-(ATP)-homeostasis for cell function, the mechanisms of fatigue and metabolic depression, the metabolic channelling through the cytoplasm and the organization and regulation of glycolytic enzymes. Spermatozoa of four species with different reproductive modes are introduced and the first results are presented: Spermatozoa of the marine worm Arenicola marina are well adapted to external fertilization in sea water with fluctuating oxygen tension: they are motile for several hours in oxygen-free sea water, even when the ATP level is dramatically reduced. Anaerobic ATP production occurs by alanine, acetate and propionate fermentation probably by the same pathways known from somatic cells of this species. Under aerobic conditions the phosphagen system might function like a shuttle for energy-rich phosphate from mitochondria to the dynein-ATPases. Storage of turkey and carp spermatozoa for several hours without exogenous substrates and oxygen results in the degradation of phosphocreatine and ATP to inorganic phosphate and adenosine monophosphate (AMP), respectively. Despite low energy charges, stored spermatozoa of both species are capable of progressive movements. In carp spermatozoa fatigue of motility is not accompanied by the dramatic acidosis one discusses as an important effect in muscle fatigue. Energy metabolism of boar spermatozoa is typically based on glycolysis consuming extracellular carbohydrates and producing lactate and protons. The sperm seem to tolerate low intracellular pH (< 6.5). The lack of a phosphagen system (no energy shuttle from mitochondria to the distal dynein-ATPases) is probably compensated by a high glycolytic ATP-production in the mitochondria-free piece of the flagellum. PMID:8641386

8. A predictive theoretical model for electron tunneling pathways in proteins

NASA Technical Reports Server (NTRS)

Onuchic, Jose Nelson; Beratan, David N.

1990-01-01

A practical method is presented for calculating the dependence of electron transfer rates on details of the protein medium intervening between donor and acceptor. The method takes proper account of the relative energetics and mutual interactions of the donor, acceptor, and peptide groups. It also provides a quantitative search scheme for determining the important tunneling pathways (specific sequences of localized bonding and antibonding orbitals of the protein which dominate the donor-acceptor electronic coupling) in native and tailored proteins, a tool for designing new proteins with prescribed electron transfer rates, and a consistent description of observed electron transfer rates in existing redox labeled metalloproteins and small molecule model compounds.

9. Theoretical Modeling of Various Spectroscopies for Cuprates and Topological Insulators

Basak, Susmita

Spectroscopies resolved highly in momentum, energy and/or spatial dimensions are playing an important role in unraveling key properties of wide classes of novel materials. However, spectroscopies do not usually provide a direct map of the underlying electronic spectrum, but act as a complex 'filter' to produce a 'mapping' of the underlying energy levels, Fermi surfaces (FSs) and excitation spectra. The connection between the electronic spectrum and the measured spectra is described as a generalized 'matrix element effect'. The nature of the matrix element involved differs greatly between different spectroscopies. For example, in angle-resolved photoemission (ARPES) an incoming photon knocks out an electron from the sample and the energy and momentum of the photoemitted electron is measured. This is quite different from what happens in K-edge resonant inelastic X-ray scattering (RIXS), where an X-ray photon is scattered after inducing electronic transitions near the Fermi energy through an indirect second order process, or in Compton scattering where the incident X-ray photon is scattered inelastically from an electron transferring energy and momentum to the scattering electron. For any given spectroscopy, the matrix element is, in general, a complex function of the phase space of the experiment, e.g. energy/polarization of the incoming photon and the energy/momentum/spin of the photoemitted electron in the case of ARPES. The matrix element can enhance or suppress signals from specific states, or merge signals of groups of states, making a good understanding of the matrix element effects important for not only a robust interpretation of the spectra, but also for ascertaining optimal regions of the experimental phase space for zooming in on states of the greatest interest. In this thesis I discuss a comprehensive scheme for modeling various highly resolved spectroscopies of the cuprates and topological insulators (TIs) where effects of matrix element, crystal

10. Polarimetric Signatures of Sea Ice. Part 1; Theoretical Model

NASA Technical Reports Server (NTRS)

Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.

1995-01-01

Physical, structural, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarimetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures.

11. Polarimetric signatures of sea ice. 1: Theoretical model

NASA Technical Reports Server (NTRS)

Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.

1995-01-01

Physical, structral, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarmetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies to interpretation of sea ice polarimetric signatures.

12. Theoretical model of electroosmotic flow for capillary zone electrophoresis

SciTech Connect

Tavares, M.F.M.; McGuffin, V.L.

1995-10-15

A mathematical model of electroosmotic flow in capillary zone electrophoresis has been developed by taking into consideration of the ion-selective properties of silica surfaces. The electroosmotic velocity was experimentally determined, underboth constant voltage and constant current conditions, by using the resistance-monitoring method. A detailed study of electroosmotic flow characteristics in solutions of singly charged, strong electrolytes (NaCl, LiCl, KCl, NaBr, NaI, NaNO{sub 3}, and NaClO{sub 4}), as well as the phosphate buffer system, revealed a linear correlation between the {Zeta} potential and the logarithm of the cation activity. These results suggest that the capillary surface behaves as an ion-selective electrode. Consequently, the {Zeta} potential can be calculated as a function of the composition and pH of the solution with the corresponding modified Nernst equation for ion-selective electrodes. If the viscosity and dielectric constant of the solution are known, the electroosmotic velocity can then be accurately predicted by means of the Helmholtz-Smoluchowski equation. The proposed model has been successfully applied to phosphate buffer solutions in the range of pH from 4 to 10, containing sodium chloride from 5 to 15 mM, resulting in nearly 3% error in the estimation of the electroosmotic velocity. 53 refs., 8 figs., 2 tabs.

13. Random walk on lattices: Graph-theoretic approach to simulating long-range diffusion-attachment growth models

Limkumnerd, Surachate

2014-03-01

Interest in thin-film fabrication for industrial applications have driven both theoretical and computational aspects of modeling its growth. One of the earliest attempts toward understanding the morphological structure of a film's surface is through a class of solid-on-solid limited-mobility growth models such as the Family, Wolf-Villain, or Das Sarma-Tamborenea models, which have produced fascinating surface roughening behaviors. These models, however, restrict the motion of an incidence atom to be within the neighborhood of its landing site, which renders them inept for simulating long-distance surface diffusion such as that observed in thin-film growth using a molecular-beam epitaxy technique. Naive extension of these models by repeatedly applying the local diffusion rules for each hop to simulate large diffusion length can be computationally very costly when certain statistical aspects are demanded. We present a graph-theoretic approach to simulating a long-range diffusion-attachment growth model. Using the Markovian assumption and given a local diffusion bias, we derive the transition probabilities for a random walker to traverse from one lattice site to the others after a large, possibly infinite, number of steps. Only computation with linear-time complexity is required for the surface morphology calculation without other probabilistic measures. The formalism is applied, as illustrations, to simulate surface growth on a two-dimensional flat substrate and around a screw dislocation under the modified Wolf-Villain diffusion rule. A rectangular spiral ridge is observed in the latter case with a smooth front feature similar to that obtained from simulations using the well-known multiple registration technique. An algorithm for computing the inverse of a class of substochastic matrices is derived as a corollary.

14. Deterministic versus stochastic aspects of superexponential population growth models

Grosjean, Nicolas; Huillet, Thierry

2016-08-01

Deterministic population growth models with power-law rates can exhibit a large variety of growth behaviors, ranging from algebraic, exponential to hyperexponential (finite time explosion). In this setup, selfsimilarity considerations play a key role, together with two time substitutions. Two stochastic versions of such models are investigated, showing a much richer variety of behaviors. One is the Lamperti construction of selfsimilar positive stochastic processes based on the exponentiation of spectrally positive processes, followed by an appropriate time change. The other one is based on stable continuous-state branching processes, given by another Lamperti time substitution applied to stable spectrally positive processes.

15. Geometric Aspects of Force Controllability for a Swimming Model

SciTech Connect

Khapalov, A. Y.

2008-02-15

We study controllability properties (swimming capabilities) of a mathematical model of an abstract object which 'swims' in the 2-D Stokes fluid. Our goal is to investigate how the geometric shape of this object affects the forces acting upon it. Such problems are of interest in biology and engineering applications dealing with propulsion systems in fluids.

16. Insights on non-perturbative aspects of TMDs from models

SciTech Connect

H. Avakian, A. Efremov, P. Schweitzer, O. Teryaev, F. Yuan, P. Zavada

2009-12-01

Transverse momentum dependent parton distribution functions are a key ingredient in the description of spin and azimuthal asymmetries in deep-inelastic scattering processes. Recent results from non-perturbative calculations in effective approaches are reviewed, with focus on relations among different parton distribution functions in QCD and models.

17. Predictive Aspects of a Stochastic Model for Citation Processes.

ERIC Educational Resources Information Center

Glanzel, W.; Schubert, A.

1995-01-01

A statistical model for citation processes is presented as a particular version of a nonhomogenous birth process. The mean value function and special transition probabilities, which can readily be calculated on the basis of known and estimated parameters, give essential information on the change of citation impact in time. (10 references) (KRN)

18. Modeling Spatial and Temporal Aspects of Visual Backward Masking

ERIC Educational Resources Information Center

Hermens, Frouke; Luksys, Gediminas; Gerstner, Wulfram; Herzog, Michael H.; Ernst, Udo

2008-01-01

Visual backward masking is a versatile tool for understanding principles and limitations of visual information processing in the human brain. However, the mechanisms underlying masking are still poorly understood. In the current contribution, the authors show that a structurally simple mathematical model can explain many spatial and temporal…

19. A numerical modeling study of a Montana thunderstorm: 1. Model results versus observations involving nonelectrical aspects

Helsdon, John H.; Farley, Richard D.

1987-05-01

A recently developed Storm Electrification Model (SEM) has been used to simulate the July 19, 1981, Cooperative Convective Precipitation Experiment (CCOPE) case study cloud. This part of the investigation examines the comparison between the model results and the observations of the actual cloud with respect to its nonelectrical aspects. A timing equivalence is established between the simulation and observations based on an explosive growth phase which was both observed and modeled. This timing equivalence is used as a basis upon which the comparisons are made. The model appears to do a good job of reproducing (in both space and time) many of the observed characteristics of the cloud. These include: (1) the general cloud appearance; (2) cloud size; (3) cloud top rise rate; (4) rapid growth phase; (5) updraft structure; (6) first graupel appearance; (7) first radar echo; (8) qualitative radar range-height indicator evolution; (9) cloud decay; and (10) the location of hydrometers with respect to the updraft/-downdraft structure. Some features that are not accurately modeled are the cloud base height, the maximum liquid water content, and the time from first formation of precipitation until it reaches the ground. While the simulation is not perfect, the faithfulness of the model results to the observations is sufficient to give us confidence that the microphysical processes active in this storm are adequately represented in the model physics. Areas where model improvement is indicated are also discussed.

20. Theoretical conditions for the stationary reproduction of model protocells.

PubMed

Mavelli, Fabio; Ruiz-Mirazo, Kepa

2013-02-01

In previous works we have explored the dynamics of chemically reacting proto-cellular systems, under different experimental conditions and kinetic parameters, by means of our stochastic simulation platform 'ENVIRONMENT'. In this paper we, somehow, turn the question around: accepting some broad modeling assumptions, we investigate the conditions under which simple protocells will spontaneously settle into a stationary reproducing regime, characterized by a regular growth/division cycle and the maintenance of a certain standard size and chemical composition across generations. In the first part, starting from purely geometric considerations, the condition for stationary reproduction of a protocell will be expressed in terms of a growth control coefficient (γ). Then, an explicit relationship, the osmotic synchronization condition, will be analytically derived under a set of kinetic simplifications and taking into account the osmotic pressure balance operating across the protocell membrane. In the second part of the paper, this general condition that constrains different molecular/kinetic parameters and features of the system (reaction rates, permeability coefficients, metabolite concentrations, system volume) will be applied to different cases of self-producing vesicles, predicting the stationary protocell size or lifetime. Finally, in order to test the validity of our analytic results and predictions, the case study is contrasted with data obtained through both stochastic and deterministic computational algorithms. PMID:23233152

1. Thermodynamical Aspects of Modified Holographic Dark Energy Model

Li, Hui; Zhang, Yi

2014-07-01

We investigate the unified first law and the generalized second law in a modified holographic dark energy model. The thermodynamical analysis on the apparent horizon can work and the corresponding entropy formula is extracted from the systematic algorithm. The entropy correction term depends on the extra-dimension number of the brane as expected, but the interplay between the correction term and the extra dimensions is more complicated. With the unified first law of thermodynamics well-founded, the generalized second law of thermodynamics is discussed and it is found that the second law can be violated in certain circumstances. Particularly, if the number of the extra dimensions is larger than one, the generalized law of thermodynamics is always satisfied; otherwise, the validity of the second law can only be guaranteed with the Hubble radius greatly smaller than the crossover scale rc of the 5-dimensional DGP model.

2. A Measurement-Theoretic Analysis of the Fuzzy Logic Model of Perception.

ERIC Educational Resources Information Center

Crowther, Court S.; And Others

1995-01-01

The fuzzy logic model of perception (FLMP) is analyzed from a measurement-theoretic perspective. The choice rule of FLMP is shown to be equivalent to a version of the Rasch model. In fact, FLMP can be reparameterized as a simple two-category logit model. (SLD)

3. Modeling and design aspects of active caloric regenerators

Engelbrecht, Kurt

2015-03-01

A cooling device based on a solid caloric material using, for example, the elastocaloric, magnetocaloric, barocaloric or electrocaloric effect has the potential to replace vapor-compression based systems for a variety of applications. Any caloric device using a solid refrigerant may benefit from using a regenerative cycle to increase the operating temperature span. This presentation shows how all active caloric regenerators can be modeled using similar techniques and how they are related to passive regenerator performance. The advantages and disadvantages of using a regenerative cycle are also discussed. The issue of hysteresis in caloric materials is investigated from a system/thermodynamic standpoint and the effects on cooling power and efficiency are quantified using a numerical model of an active regenerator using model caloric materials with assumed properties. The implementation in a working device will be discussed for elastocaloric and magnetocaloric cooling devices. It is shown that demagnetization effects for magnetocaloric systems and stress concentration effects in elastocaloric system reduce the overall effect in the regenerator and care must be taken in regenerator design for both technologies. Other loss mechanisms outside the regenerator such as heat leaks are also discussed. Finally, experimental results for active magnetic regenerative cooler are given for a range of operating conditions. The most recently published device uses a regenerator consisting of Gd and three alloys of GdY and has demonstrated a COP over 3.

4. Variable aspect ratio method in the Xu-White model for shear-wave velocity estimation

Bai, Jun-Yu; Yue, Cheng-Qi; Liang, Yi-Qiang; Song, Zhi-Xiang; Ling, Su; Zhang, Yang; Wu, Wei

2013-06-01

Shear-wave velocity logs are useful for various seismic interpretation applications, including bright spot analyses, amplitude-versus-offset analyses and multicomponent seismic interpretations. This paper presents a method for predicting the shear-wave velocity of argillaceous sandstone from conventional log data and experimental data, based on Gassmann's equations and the Xu-White model. This variable aspect ratio method takes into account all the influences of the matrix nature, shale content, porosity size and pore geometry, and the properties of pore fluid of argillaceous sandstone, replacing the fixed aspect ratio assumption in the conventional Xu-White model. To achieve this, we first use the Xu-White model to derive the bulk and shear modulus of dry rock in a sand-clay mixture. Secondly, we use Gassmann's equations to calculate the fluid-saturated elastic properties, including compressional and shear-wave velocities. Finally, we use the variable aspect ratio method to estimate the shear-wave velocity. The numerical results indicate that the variable aspect ratio method provides an important improvement in the application of the Xu-White model for sand-clay mixtures and allows for a variable aspect ratio log to be introduced into the Xu-White model instead of the constant aspect ratio assumption. This method shows a significant improvement in predicting velocities over the conventional Xu-White model.

5. Modeling aspects of the dynamic response of heterogeneous materials

SciTech Connect

Ionita, Axinte; Clements, Brad; Mas, Eric

2009-01-01

In numerical simulations of engineering applications involving heterogeneous materials capturing the local response coming from a distribution of heterogeneities can lead to a very large model thus making simulations difficult. The use of homogenization techniques can reduce the size of the problem but will miss the local effects. Homogenization can also be difficult if the constituents obey different types of constitutive laws. Additional complications arise if inelastic deformation. In such cases a two-scale approach is prefened and tills work addresses these issues in the context of a two-scale Finite Element Method (FEM). Examples of using two-scale FEM approaches are presented.

6. The Grain Structure of Castings: Some Aspects of Modelling

NASA Technical Reports Server (NTRS)

Hellawell, A.

1995-01-01

The efficacy of the modelling of the solidification of castings is typically tested against observed cooling curves and the final grain structures and sizes. Without thermo solutal convection, equiaxed grain formation is promoted by introduction of heterogeneous substrates into the melt, as grain refiners. With efficient thermo solutal convection, dendrite fragments from the mushy zone can act as an intrinsic source of equiaxed grains and resort to grain refining additions is unnecessary. The mechanisms of dendrite fragmentation and transport of these fragments are briefly considered.

7. Modeling Hydrologic and Geochemical Aspects of Rapid Infiltration Basins

Akhavan, M.; Imhoff, P. T.; Andres, S.; Finsterle, S.; Gu, C.; Maggi, F.

2010-12-01

Land-based wastewater treatment is the controlled application of wastewater to soil to remove wastewater constituents. A Rapid Infiltration Basin (RIB) is a major land treatment technique where treated wastewater is infiltrated at high rates in shallow basins, with further treatment occurring in soil and the vadose zone before the water recharges groundwater. Because the influent wastewater is usually enriched in nitrogen compounds, there is particular concern that a RIB may contaminant groundwater or nearby surface waters if not designed and operated properly. RIBs are operated in repetitive cycles of flooding, infiltration, and drying. Key operational parameters include the ratio of wetting to drying time and the hydraulic loading rate, which affect pollutant residence time and water table rise in shallow groundwater systems. They also alter water saturation and air content in the vadose zone, which have an impact on denitrification. Optimum values of the wetting-drying cycle ratio and the hydraulic loading rate are expected to vary with the quality of applied wastewater, soil type, treatment objective, and climate. Soil development within the basins may have an important effect on RIB performance. In this study, numerical modeling is used to obtain optimum values for the wetting-drying cycle ratio and hydraulic loading rate for different soil types and environmental conditions. TOUGH2/ iTOUGH2, a general-purpose numerical simulation program for multi-phase fluid flow in porous media, is used for modeling fluid movement. Overland flow within RIBs is coupled with subsurface flow to investigate the influence of non-uniform application of wastewater on hydraulic performance. TOUGHREACT v1.1 is used for modeling nitrogen fate and transport. Flow simulations indicate that using a long flooding cycle results in more water spreading over the basin and higher vadose zone water saturations than more frequent short-duration flooding events. Results of modeling fate and

8. A beginner's guide to writing the nursing conceptual model-based theoretical rationale.

PubMed

Gigliotti, Eileen; Manister, Nancy N

2012-10-01

Writing the theoretical rationale for a study can be a daunting prospect for novice researchers. Nursing's conceptual models provide excellent frameworks for placement of study variables, but moving from the very abstract concepts of the nursing model to the less abstract concepts of the study variables is difficult. Similar to the five-paragraph essay used by writing teachers to assist beginning writers to construct a logical thesis, the authors of this column present guidelines that beginners can follow to construct their theoretical rationale. This guide can be used with any nursing conceptual model but Neuman's model was chosen here as the exemplar. PMID:23087334

9. Modeling Connectionist Networks: Categorical, Geometric Aspects (Towards ``Homomorphic Learning'')

Pfalzgraf, Jochen

2004-08-01

Work in interdisciplinary fields is very interesting and always a great challenge. We present work on applications of mathematical methods to modeling problems arising in the area of artificial neural networks (ANN). We concentrate on modeling network structures that are motivated and based on knowledge about net structures coming from neurophysiology. In past years such insights have been exploited already in computer based ANN-simulations which are well suited for industrial applications. In the analysis of network structures, considering assemblies of cells (neurons) in biological nets, from a geometric point of view one can indentify and interpret, locally, what is called a geometric configuration. Following notions from algebraic topology, we are speaking about simplicial configurations (e.g. triangular, tetrahedral configurations, etc.). It turns out that category theory, geometry, algebra (group theory), graph theory (more general, net theory) come together, in a natural interdisciplinary way. Simplices are of basic importance.The interpretation of a learning step as a morphism in categorical terms suggests the opening of a systematic theory of learning (we call it "Homomorphic Learning").

10. Semiotic aspects of control and modeling relations in complex systems

SciTech Connect

Joslyn, C.

1996-08-01

A conceptual analysis of the semiotic nature of control is provided with the goal of elucidating its nature in complex systems. Control is identified as a canonical form of semiotic relation of a system to its environment. As a form of constraint between a system and its environment, its necessary and sufficient conditions are established, and the stabilities resulting from control are distinguished from other forms of stability. These result from the presence of semantic coding relations, and thus the class of control systems is hypothesized to be equivalent to that of semiotic systems. Control systems are contrasted with models, which, while they have the same measurement functions as control systems, do not necessarily require semantic relations because of the lack of the requirement of an interpreter. A hybrid construction of models in control systems is detailed. Towards the goal of considering the nature of control in complex systems, the possible relations among collections of control systems are considered. Powers arguments on conflict among control systems and the possible nature of control in social systems are reviewed, and reconsidered based on our observations about hierarchical control. Finally, we discuss the necessary semantic functions which must be present in complex systems for control in this sense to be present at all.

11. Modeling socioeconomic and ecologic aspects of land-use change

SciTech Connect

Dale, V.H.; Pedlowski, M.A.; O'Neill, R.V.; Southworth, F.

1992-01-01

Land use change is one of the major factors affecting global environmental conditions. Prevalent types of land-use change include replacing forests with agriculture, mines or ranches; forest degradation from collection of firewood; and forest logging. A global effect of wide-scale deforestation is an increase in atmospheric carbon dioxide concentration, which may affect climate. Regional effects include loss of biodiversity and disruption of hydrologic regimes. Local effects include soil erosion, siltation and decreases in soil fertility, loss of extractive reserves, and disruption of indigenous people. Modeling land use change requires combining socioeconomic and ecological factors because socioeconomic forces frequently initiate land-use change and are affected by the subsequent ecological degradation. This paper describes a modeling system that integrates submodels of human colonization and impacts to estimate patterns and rates of deforestation under different immigration and land use scenarios. Immigration which follows road building or paving is a major factor in the rapid deforestation of previously inaccessible areas. Roads facilitate colonization, allow access for large machines, and provide transportation routes for mort of raw materials and produce.

12. The Impact of Personality on Training-Related Aspects of Motivation: Test of a Longitudinal Model

ERIC Educational Resources Information Center

Rowold, Jens

2007-01-01

A model that proposed dispositional influences on training-related aspects of motivation was developed. More specifically, the model predicted influences of the Big Five personality variables on motivation to learn and transfer motivation, while controlling for general attitudes toward training. The model was tested empirically, drawing on a…

13. The abelian confinement mechanism revisited: New aspects of the Georgi–Glashow model

SciTech Connect

Anber, Mohamed M.

2014-02-15

The confinement problem remains one of the most difficult problems in theoretical physics. An important step toward the solution of this problem is Polyakov’s work on abelian confinement. The Georgi–Glashow model is a natural testing ground for this mechanism which has been surprising us by its richness and wide applicability. In this work, we shed light on two new aspects of this model in 2+1 D. First, we develop a many-body description of the effective degrees of freedom. Namely, we consider a non-relativistic gas of W-bosons in the background of monopole–instanton plasma. Many-body treatment is a standard toolkit in condensed matter physics. However, we add a new twist by supplying the monopole–instantons as external background field. Using this construction along with a mean-field approximation, we calculate the form of the potential between two electric probes as a function of their separation. This potential is expressed in terms of the Meijer-G function which interpolates between logarithmic and linear behavior at small and large distances, respectively. Second, we develop a systematic approach to integrate out the effect of the W-bosons at finite temperature in the range 0≤Tmodel. Using a heat kernel expansion that takes into account the non-trivial thermal holonomy, we show that the partition function describes a three-dimensional two-component Coulomb gas. We repeat our analysis using the many-body description which yields the same result and provides a check on our formalism. At temperatures close to the deconfinement temperature, the gas becomes essentially two-dimensional recovering the partition function of the dual sine-Gordon model that was considered in a previous work. -- Highlights: • We consider the problem of abelian confinement in the Georgi–Glashow model from a new perspective. • We develop a many

14. Filling high aspect ratio trenches by superconformal chemical vapor deposition: Predictive modeling and experiment

Wang, Wenjiao B.; Abelson, John R.

2014-11-01

Complete filling of a deep recessed structure with a second material is a challenge in many areas of nanotechnology fabrication. A newly discovered superconformal coating method, applicable in chemical vapor deposition systems that utilize a precursor in combination with a co-reactant, can solve this problem. However, filling is a dynamic process in which the trench progressively narrows and the aspect ratio (AR) increases. This reduces species diffusion within the trench and may drive the component partial pressures out of the regime for superconformal coating. We therefore derive two theoretical models that can predict the possibility for filling. First, we recast the diffusion-reaction equation for the case of a sidewall with variable taper angle. This affords a definition of effective AR, which is larger than the nominal AR due to the reduced species transport. We then derive the coating profile, both for superconformal and for conformal coating. The critical (most difficult) step in the filling process occurs when the sidewalls merge at the bottom of the trench to form the V shape. Experimentally, for the Mg(DMADB)2/H2O system and a starting AR = 9, this model predicts that complete filling will not be possible, whereas experimentally we do obtain complete filling. We then hypothesize that glancing-angle, long-range transport of species may be responsible for the better than predicted filling. To account for the variable range of species transport, we construct a ballistic transport model. This incorporates the incident flux from outside the structure, cosine law re-emission from surfaces, and line-of-sight transport between internal surfaces. We cast the transport probability between all positions within the trench into a matrix that represents the redistribution of flux after one cycle of collisions. Matrix manipulation then affords a computationally efficient means to determine the steady-state flux distribution and growth rate for a given taper angle. The

15. Single Droplet on Micro Square-Post Patterned Surfaces – Theoretical Model and Numerical Simulation

PubMed Central

Zu, Y. Q.; Yan, Y. Y.

2016-01-01

In this study, the wetting behaviors of single droplet on a micro square-post patterned surface with different geometrical parameters are investigated theoretically and numerically. A theoretical model is proposed for the prediction of wetting transition from the Cassie to Wenzel regimes. In addition, due to the limitation of theoretical method, a numerical simulation is performed, which helps get a view of dynamic contact lines, detailed velocity fields, etc., even if the droplet size is comparable with the scale of the surface micro-structures. It is found that the numerical results of the liquid drop behaviours on the square-post patterned surface are in good agreement with the predicted values by the theoretical model. PMID:26775561

16. Nurses' self-relation--becoming theoretically competent: the SAUC model for confirming nursing.

PubMed

Gustafsson, Barbro; Willman, Ania M

2003-07-01

The purpose of this study was to acquire an understanding of how nurses' self-relation (view of themselves as nurses) was influenced in connection with implementation of a nursing theory, the sympathy-acceptance-understanding-competence model for confirming nursing. This model was developed by Gustafsson and Pörn. Twenty-two nurses' written statements evaluating mentoring during the six-month implementation process in elder care, were analyzed hermeneutically with the hypothetic-deductive method. An action-theoretic and confirmatory approach was used for facilitating theoretically specified hypotheses. The nurses increased their ability to describe nursing theoretically and gained a foundation of common nursing values. The results provided an understanding of how nurses' self-relation was strengthened by becoming theoretically competent. PMID:12876885

17. Experimental and Simulational Studies on the Theoretical Model of the Plasma Absorption Probe

Li, Bin; Li, Hong; Chen, Zhipeng; Xie, Jinlin; Feng, Guangyao; Liu, Wandong

2010-10-01

Plasma absorption probe (PAP) was developed for measuring the electron density in plasmas processing based on the surface-wave characteristics. In order to diagnose the plasma with lower density and higher pressure, a sensitive PAP was also developed. Both types of PAP were analyzed theoretically under the quasi-static approximation, which is highly problematic when a conductor exists in the resonance region of the probe. For this reason, a theoretical model for the PAP is presented in this paper. The model is derived from the electromagnetic wave equation. Its principle is then verified via experiments and numerical simulations. Both experimental and numerical results show that the electromagnetic theoretical model is valid as compared with the quasi-static model. Consequently, a new type of PAP, named as the electromagnetic PAP, is thus proposed for the measurement of electron density.

18. Simple control-theoretic models of human steering activity in visually guided vehicle control

NASA Technical Reports Server (NTRS)

Hess, Ronald A.

1991-01-01

A simple control theoretic model of human steering or control activity in the lateral-directional control of vehicles such as automobiles and rotorcraft is discussed. The term 'control theoretic' is used to emphasize the fact that the model is derived from a consideration of well-known control system design principles as opposed to psychological theories regarding egomotion, etc. The model is employed to emphasize the 'closed-loop' nature of tasks involving the visually guided control of vehicles upon, or in close proximity to, the earth and to hypothesize how changes in vehicle dynamics can significantly alter the nature of the visual cues which a human might use in such tasks.

19. Achievement Goals and Discrete Achievement Emotions: A Theoretical Model and Prospective Test

ERIC Educational Resources Information Center

Pekrun, Reinhard; Elliot, Andrew J.; Maier, Markus A.

2006-01-01

A theoretical model linking achievement goals to discrete achievement emotions is proposed. The model posits relations between the goals of the trichotomous achievement goal framework and 8 commonly experienced achievement emotions organized in a 2 (activity/outcome focus) x 2 (positive/negative valence) taxonomy. Two prospective studies tested…

20. A Theoretical Model for Thin Film Ferroelectric Coupled Microstripline Phase Shifters

NASA Technical Reports Server (NTRS)

Romanofsky, R. R.; Quereshi, A. H.

2000-01-01

Novel microwave phase shifters consisting of coupled microstriplines on thin ferroelectric films have been demonstrated recently. A theoretical model useful for predicting the propagation characteristics (insertion phase shift, dielectric loss, impedance, and bandwidth) is presented here. The model is based on a variational solution for line capacitance and coupled strip transmission line theory.

1. REGIONAL SCALE (1000 KM) MODEL OF PHOTOCHEMICAL AIR POLLUTION. PART 1. THEORETICAL FORMULATION

EPA Science Inventory

A theoretical framework for a multi-day 1000 km scale simulation model of photochemical oxidant is developed. It is structured in a highly modular form so that eventually the model can be applied through straightforward modifications to simulations of particulates, visibility and...

2. Game Object Model Version II: A Theoretical Framework for Educational Game Development

ERIC Educational Resources Information Center

Amory, Alan

2007-01-01

Complex computer and video games may provide a vehicle, based on appropriate theoretical concepts, to transform the educational landscape. Building on the original game object model (GOM) a new more detailed model is developed to support concepts that educational computer games should: be relevant, explorative, emotive, engaging, and include…

3. Undergraduate Engineering Students' Beliefs, Coping Strategies, and Academic Performance: An Evaluation of Theoretical Models

ERIC Educational Resources Information Center

Hsieh, Pei-Hsuan; Sullivan, Jeremy R.; Sass, Daniel A.; Guerra, Norma S.

2012-01-01

Research has identified factors associated with academic success by evaluating relations among psychological and academic variables, although few studies have examined theoretical models to understand the complex links. This study used structural equation modeling to investigate whether the relation between test anxiety and final course grades was…

4. Engaging Dialogue in Our Diverse Social Work Student Body: A Multilevel Theoretical Process Model

ERIC Educational Resources Information Center

Rozas, Lisa Werkmeister

2007-01-01

This article presents a theoretical process model for students engaging in dialogic learning about issues of race and anti-oppression. The model identifies conditions present in the dialogue process and demonstrates how these conditions, when coordinated with certain interventions and strategies, help to create particular outcomes for…

5. EPA (ENVIRONMENTAL PROTECTION AGENCY) COMPLEX TERRAIN MODEL: THEORETICAL BASIS AND PRELIMINARY EVALUATION

EPA Science Inventory

The theoretical basis, physical structure, and preliminary evaluation of the U.S. Environmental Protection Agency's Complex Terrain Dispersion Model (CTDM) are described. CTDM is a point-source plume model designed primarily to estimate windward-side surface concentrations on dis...

6. Effect of shape, size, and aspect ratio on nanoparticle penetration and distribution inside solid tissues using 3D spheroid models.

PubMed

Agarwal, Rachit; Jurney, Patrick; Raythatha, Mansi; Singh, Vikramjit; Sreenivasan, Sidlgata V; Shi, Li; Roy, Krishnendu

2015-10-28

Efficient penetration and uniform distribution of nanoparticles (NPs) inside solid tissues and tumors is paramount to their therapeutic and diagnostic success. While many studies have reported the effect of NP size and charge on intratissue distribution, role of shape, and aspect ratio on NP transport inside solid tissues remain unclear. Here experimental and theoretical studies are reported on how nanoscale geometry of Jet and Flash Imprint Lithography-fabricated, polyethylene-glycol-based anionic nanohydrogels affect their penetration and distribution inside 3D spheroids, a model representing the intervascular region of solid, tumor-like tissues. Unexpectedly, low aspect ratio cylindrical NPs (H/D ≈0.3; disk-like particles, 100 nm height, and 325 nm diameter) show maximal intratissue delivery (>50% increase in total cargo delivered) and more uniform penetration compared to nanorods or smaller NPs of the same shape. This is in contrast to spherical NPs where smaller NP size resulted in deeper, more uniform penetration. Our results provide fundamental new knowledge on NP transport inside solid tissues and further establish shape and aspect ratio as important design parameters in developing more efficient, better penetrating, nanocarriers for drug, or contrast-agent delivery. PMID:26376024

7. Exploring Environmental Factors in Nursing Workplaces That Promote Psychological Resilience: Constructing a Unified Theoretical Model

PubMed Central

Cusack, Lynette; Smith, Morgan; Hegney, Desley; Rees, Clare S.; Breen, Lauren J.; Witt, Regina R.; Rogers, Cath; Williams, Allison; Cross, Wendy; Cheung, Kin

2016-01-01

Building nurses' resilience to complex and stressful practice environments is necessary to keep skilled nurses in the workplace and ensuring safe patient care. A unified theoretical framework titled Health Services Workplace Environmental Resilience Model (HSWERM), is presented to explain the environmental factors in the workplace that promote nurses' resilience. The framework builds on a previously-published theoretical model of individual resilience, which identified the key constructs of psychological resilience as self-efficacy, coping and mindfulness, but did not examine environmental factors in the workplace that promote nurses' resilience. This unified theoretical framework was developed using a literary synthesis drawing on data from international studies and literature reviews on the nursing workforce in hospitals. The most frequent workplace environmental factors were identified, extracted and clustered in alignment with key constructs for psychological resilience. Six major organizational concepts emerged that related to a positive resilience-building workplace and formed the foundation of the theoretical model. Three concepts related to nursing staff support (professional, practice, personal) and three related to nursing staff development (professional, practice, personal) within the workplace environment. The unified theoretical model incorporates these concepts within the workplace context, linking to the nurse, and then impacting on personal resilience and workplace outcomes, and its use has the potential to increase staff retention and quality of patient care. PMID:27242567

8. Exploring Environmental Factors in Nursing Workplaces That Promote Psychological Resilience: Constructing a Unified Theoretical Model.

PubMed

Cusack, Lynette; Smith, Morgan; Hegney, Desley; Rees, Clare S; Breen, Lauren J; Witt, Regina R; Rogers, Cath; Williams, Allison; Cross, Wendy; Cheung, Kin

2016-01-01

Building nurses' resilience to complex and stressful practice environments is necessary to keep skilled nurses in the workplace and ensuring safe patient care. A unified theoretical framework titled Health Services Workplace Environmental Resilience Model (HSWERM), is presented to explain the environmental factors in the workplace that promote nurses' resilience. The framework builds on a previously-published theoretical model of individual resilience, which identified the key constructs of psychological resilience as self-efficacy, coping and mindfulness, but did not examine environmental factors in the workplace that promote nurses' resilience. This unified theoretical framework was developed using a literary synthesis drawing on data from international studies and literature reviews on the nursing workforce in hospitals. The most frequent workplace environmental factors were identified, extracted and clustered in alignment with key constructs for psychological resilience. Six major organizational concepts emerged that related to a positive resilience-building workplace and formed the foundation of the theoretical model. Three concepts related to nursing staff support (professional, practice, personal) and three related to nursing staff development (professional, practice, personal) within the workplace environment. The unified theoretical model incorporates these concepts within the workplace context, linking to the nurse, and then impacting on personal resilience and workplace outcomes, and its use has the potential to increase staff retention and quality of patient care. PMID:27242567

9. A simple theoretical model for ⁶³Ni betavoltaic battery.

PubMed

Zuo, Guoping; Zhou, Jianliang; Ke, Guotu

2013-12-01

A numerical simulation of the energy deposition distribution in semiconductors is performed for ⁶³Ni beta particles. Results show that the energy deposition distribution exhibits an approximate exponential decay law. A simple theoretical model is developed for ⁶³Ni betavoltaic battery based on the distribution characteristics. The correctness of the model is validated by two literature experiments. Results show that the theoretical short-circuit current agrees well with the experimental results, and the open-circuit voltage deviates from the experimental results in terms of the influence of the PN junction defects and the simplification of the source. The theoretical model can be applied to ⁶³Ni and ¹⁴⁷Pm betavoltaic batteries. PMID:23974307

10. Models and Messengers of Resilience: A Theoretical Model of College Students' Resilience, Regulatory Strategy Use, and Academic Achievement

ERIC Educational Resources Information Center

Johnson, Marcus L.; Taasoobshirazi, Gita; Kestler, Jessica L.; Cordova, Jackie R.

2015-01-01

We tested a theoretical model of college students' ratings of messengers of resilience and models of resilience, students' own perceived resilience, regulatory strategy use and achievement. A total of 116 undergraduates participated in this study. The results of a path analysis indicated that ratings of models of resilience had a direct effect on…

11. Some aspects of mathematical and chemical modeling of complex chemical processes

NASA Technical Reports Server (NTRS)

Nemes, I.; Botar, L.; Danoczy, E.; Vidoczy, T.; Gal, D.

1983-01-01

Some theoretical questions involved in the mathematical modeling of the kinetics of complex chemical process are discussed. The analysis is carried out for the homogeneous oxidation of ethylbenzene in the liquid phase. Particular attention is given to the determination of the general characteristics of chemical systems from an analysis of mathematical models developed on the basis of linear algebra.

12. On the theoretical model for vertical ozone density distributions in the mesosphere and upper stratosphere.

NASA Technical Reports Server (NTRS)

Shimazaki, T.; Wuebbles, D. J.

1973-01-01

Calculations based on an improved, time-dependent theoretical model for the vertical ozone density distribution in the upper atmosphere are shown to clarify the cause and determine the appearance precondition for the depression at the 70-85 km altitude region in the ozone density distribution suggested by several theoretical models and only sometimes experimentally observed. It is concluded that the depression develops at night through the effects of hydrogen-oxygen and nitrogen-oxygen reactions, as well as those of eddy diffusion transports.

13. Proof of concept of an artificial muscle: theoretical model, numerical model, and hardware experiment.

PubMed

Haeufle, D F B; Günther, M; Blickhan, R; Schmitt, S

2011-01-01

Recently, the hyperbolic Hill-type force-velocity relation was derived from basic physical components. It was shown that a contractile element CE consisting of a mechanical energy source (active element AE), a parallel damper element (PDE), and a serial element (SE) exhibits operating points with hyperbolic force-velocity dependency. In this paper, the contraction dynamics of this CE concept were analyzed in a numerical simulation of quick release experiments against different loads. A hyperbolic force-velocity relation was found. The results correspond to measurements of the contraction dynamics of a technical prototype. Deviations from the theoretical prediction could partly be explained by the low stiffness of the SE, which was modeled analog to the metal spring in the hardware prototype. The numerical model and hardware prototype together, are a proof of this CE concept and can be seen as a well-founded starting point for the development of Hill-type artificial muscles. This opens up new vistas for the technical realization of natural movements with rehabilitation devices. PMID:22275541

14. Aspect Ratio Model for Radiation-Tolerant Dummy Gate-Assisted n-MOSFET Layout.

PubMed

Lee, Min Su; Lee, Hee Chul

2014-01-01

In order to acquire radiation-tolerant characteristics in integrated circuits, a dummy gate-assisted n-type metal oxide semiconductor field effect transistor (DGA n-MOSFET) layout was adopted. The DGA n-MOSFET has a different channel shape compared with the standard n-MOSFET. The standard n-MOSFET has a rectangular channel shape, whereas the DGA n-MOSFET has an extended rectangular shape at the edge of the source and drain, which affects its aspect ratio. In order to increase its practical use, a new aspect ratio model is proposed for the DGA n-MOSFET and this model is evaluated through three-dimensional simulations and measurements of the fabricated devices. The proposed aspect ratio model for the DGA n-MOSFET exhibits good agreement with the simulation and measurement results. PMID:27350975

15. Aspect Ratio Model for Radiation-Tolerant Dummy Gate-Assisted n-MOSFET Layout

PubMed Central

Lee, Min Su; Lee, Hee Chul

2014-01-01

In order to acquire radiation-tolerant characteristics in integrated circuits, a dummy gate-assisted n-type metal oxide semiconductor field effect transistor (DGA n-MOSFET) layout was adopted. The DGA n-MOSFET has a different channel shape compared with the standard n-MOSFET. The standard n-MOSFET has a rectangular channel shape, whereas the DGA n-MOSFET has an extended rectangular shape at the edge of the source and drain, which affects its aspect ratio. In order to increase its practical use, a new aspect ratio model is proposed for the DGA n-MOSFET and this model is evaluated through three-dimensional simulations and measurements of the fabricated devices. The proposed aspect ratio model for the DGA n-MOSFET exhibits good agreement with the simulation and measurement results. PMID:27350975

16. Theoretical Modeling and Experimental High-Speed Imaging of Elongated Vocal Folds

PubMed Central

Zhang, Yu; Regner, Michael F.; Jiang, Jack J.

2014-01-01

In this paper, the role of vocal fold elongation in governing glottal movement dynamics was theoretically and experimentally investigated. A theoretical model was first proposed to incorporate vocal fold elongation into the two-mass model. This model predicted the direct and nondirect components of the glottal time series as a function of vocal fold elongation. Furthermore, high-speed digital imaging was applied in excised larynx experiments to visualize vocal fold vibrations with variable vocal fold elongation from –10% to 50% and subglottal pressures of 18- and 24-cm H2O. Comparison between theoretical model simulations and experimental observations showed good agreement. A relative maximum was seen in the nondirect component of glottal area, suggesting that an optimal elongation could maximize the vocal fold vibratory power. However, sufficiently large vocal fold elongations caused the nondirect component to approach zero and the direct component to approach a constant. These results showed that vocal fold elongation plays an important role in governing the dynamics of glottal area movement and validated the applicability of the proposed theoretical model and high-speed imaging to investigate laryngeal activity. PMID:21118763

17. Theoretical modeling and experimental high-speed imaging of elongated vocal folds.

PubMed

Zhang, Yu; Regner, Michael F; Jiang, Jack J

2011-10-01

In this paper, the role of vocal fold elongation in governing glottal movement dynamics was theoretically and experimentally investigated. A theoretical model was first proposed to incorporate vocal fold elongation into the two-mass model. This model predicted the direct and nondirect components of the glottal time series as a function of vocal fold elongation. Furthermore, high-speed digital imaging was applied in excised larynx experiments to visualize vocal fold vibrations with variable vocal fold elongation from -10% to 50% and subglottal pressures of 18- and 24-cm H(2)O. Comparison between theoretical model simulations and experimental observations showed good agreement. A relative maximum was seen in the nondirect component of glottal area, suggesting that an optimal elongation could maximize the vocal fold vibratory power. However, sufficiently large vocal fold elongations caused the nondirect component to approach zero and the direct component to approach a constant. These results showed that vocal fold elongation plays an important role in governing the dynamics of glottal area movement and validated the applicability of the proposed theoretical model and high-speed imaging to investigate laryngeal activity. PMID:21118763

18. Theoretical results on the tandem junction solar cell based on its Ebers-Moll transistor model

NASA Technical Reports Server (NTRS)

Goradia, C.; Vaughn, J.; Baraona, C. R.

1980-01-01

A one-dimensional theoretical model of the tandem junction solar cell (TJC) with base resistivity greater than about 1 ohm-cm and under low level injection has been derived. This model extends a previously published conceptual model which treats the TJC as an npn transistor. The model gives theoretical expressions for each of the Ebers-Moll type currents of the illuminated TJC and allows for the calculation of the spectral response, I(sc), V(oc), FF and eta under variation of one or more of the geometrical and material parameters and 1MeV electron fluence. Results of computer calculations based on this model are presented and discussed. These results indicate that for space applications, both a high beginning of life efficiency, greater than 15% AM0, and a high radiation tolerance can be achieved only with thin (less than 50 microns) TJC's with high base resistivity (greater than 10 ohm-cm).

19. How parents choose to use CAM: a systematic review of theoretical models

PubMed Central

Lorenc, Ava; Ilan-Clarke, Yael; Robinson, Nicola; Blair, Mitch

2009-01-01

Background Complementary and Alternative Medicine (CAM) is widely used throughout the UK and the Western world. CAM is commonly used for children and the decision-making process to use CAM is affected by numerous factors. Most research on CAM use lacks a theoretical framework and is largely based on bivariate statistics. The aim of this review was to identify a conceptual model which could be used to explain the decision-making process in parental choice of CAM. Methods A systematic search of the literature was carried out. A two-stage selection process with predetermined inclusion/exclusion criteria identified studies using a theoretical framework depicting the interaction of psychological factors involved in the CAM decision process. Papers were critically appraised and findings summarised. Results Twenty two studies using a theoretical model to predict CAM use were included in the final review; only one examined child use. Seven different models were identified. The most commonly used and successful model was Andersen's Sociobehavioural Model (SBM). Two papers proposed modifications to the SBM for CAM use. Six qualitative studies developed their own model. Conclusion The SBM modified for CAM use, which incorporates both psychological and pragmatic determinants, was identified as the best conceptual model of CAM use. This model provides a valuable framework for future research, and could be used to explain child CAM use. An understanding of the decision making process is crucial in promoting shared decision making between healthcare practitioners and parents and could inform service delivery, guidance and policy. PMID:19386106

20. A Physically Based Theoretical Model of Spore Deposition for Predicting Spread of Plant Diseases.

PubMed

Isard, Scott A; Chamecki, Marcelo

2016-03-01

A physically based theory for predicting spore deposition downwind from an area source of inoculum is presented. The modeling framework is based on theories of turbulence dispersion in the atmospheric boundary layer and applies only to spores that escape from plant canopies. A "disease resistance" coefficient is introduced to convert the theoretical spore deposition model into a simple tool for predicting disease spread at the field scale. Results from the model agree well with published measurements of Uromyces phaseoli spore deposition and measurements of wheat leaf rust disease severity. The theoretical model has the advantage over empirical models in that it can be used to assess the influence of source distribution and geometry, spore characteristics, and meteorological conditions on spore deposition and disease spread. The modeling framework is refined to predict the detailed two-dimensional spatial pattern of disease spread from an infection focus. Accounting for the time variations of wind speed and direction in the refined modeling procedure improves predictions, especially near the inoculum source, and enables application of the theoretical modeling framework to field experiment design. PMID:26595112

1. Operational and research aspects of a radio-controlled model flight test program

NASA Technical Reports Server (NTRS)

Budd, Gerald D.; Gilman, Ronald L.; Eichstedt, David

1993-01-01

The operational and research aspects of a subscale, radio-controlled model flight test program are presented. By using low-cost free-flying models, an approach was developed for obtaining research-quality vehicle performance and aerodynamic information. The advantages and limitations learned by applying this approach to a specific flight test program are described. The research quality of the data acquired shows that model flight testing is practical for obtaining consistent repeatable flight data.

2. Operational and research aspects of a radio-controlled model flight test program

NASA Technical Reports Server (NTRS)

Budd, Gerald D.; Gilman, Ronald L.; Eichstedt, David

1993-01-01

The operational and research aspects of a subscale, radio-controlled model flight test program are presented. By using low-cost free-flying models, an approach was developed for obtaining research-quality vehicle performance and aerodynamic information. The advantages and limitations learned by applying this approach to a specific flight test program are described. The research quality of the data acquired shows that model flight testing is practical for obtaining consistent and repeatable flight data.

3. Statistical aspects of carbon fiber risk assessment modeling. [fire accidents involving aircraft

NASA Technical Reports Server (NTRS)

Gross, D.; Miller, D. R.; Soland, R. M.

1980-01-01

The probabilistic and statistical aspects of the carbon fiber risk assessment modeling of fire accidents involving commercial aircraft are examined. Three major sources of uncertainty in the modeling effort are identified. These are: (1) imprecise knowledge in establishing the model; (2) parameter estimation; and (3)Monte Carlo sampling error. All three sources of uncertainty are treated and statistical procedures are utilized and/or developed to control them wherever possible.

4. Measured Model, Theoretical Model and Represented Model: the So-Called Arch of Drusus in Rome

Canciani, M.; Maestri, D.; Spadafora, G.; Manacorda, D.; Di Cola, V.

2011-09-01

The Arch of Drusus is a complex building, stratified over time. It isn't possible to advance only one hypothesis about its origin, but its several transformations may be given some interpretations. The difficulty lies in the coexistence of two structures, typologically and chronologically different, in a single monument: an original structure which can be related to a commemorative travertine arch sheathed in marble, dating back to the Imperial Age, which probably had three fornices and a later structure reused in the III century as an aque- duct arch and monumentalized again with the application of decorated architectural elements on the southern façade. In order to provide a graphic description as much accurate as possible from the metric-dimensional point of view and as much detailed as possible in all the elements which form the building, a new survey methodology has been tested. It uses different kinds of systems - instrumental, topographic and GPS, photogrammetric and direct traditional - which complement each other, in order to render a three-dimensional computerized reference model. The analysis process of the monument, made from what emerged from the archaeological analysis, thanks to the carrying out of dif- ferent navigable models, has been developed making, in the early stage, a represented model subsequently detailed on the basis of the incongruities detected in the survey.

5. E-Learning Systems Support of Collaborative Agreements: A Theoretical Model

ERIC Educational Resources Information Center

2012-01-01

This paper introduces a theoretical model for developing integrated degree programmes through e-learning systems as stipulated by a collaboration agreement signed by two universities. We have analysed several collaboration agreements between universities at the national, European, and transatlantic level as well as various e-learning frameworks. A…

6. Spiritual Wellness and Depression: Testing a Theoretical Model with Older Adolescents and Midlife Adults

ERIC Educational Resources Information Center

Briggs, Michele Kielty; Shoffner, Marie F.

2006-01-01

Overall spiritual wellness, as well as 4 individual components of spiritual wellness, has been theoretically and empirically linked with depression. Prior to this investigation, no study has examined the relationship between spiritual wellness and depression by using a 4-component measurement model of spiritual wellness. In this study of older…

7. Unconscious Determinants of Career Choice and Burnout: Theoretical Model and Counseling Strategy.

ERIC Educational Resources Information Center

Malach-Pines, Ayala; Yafe-Yanai, Oreniya

2001-01-01

Proposes a psychodynamic-existential perspective as a theoretical model that explains career burnout and serves as a basis for a counseling strategy. According to existential theory, the root of career burnout lies in people's need to find existential significance in their life and their sense that their work does not provide it. (Contains 40…

8. A Game-Theoretic Model of Grounding for Referential Communication Tasks

ERIC Educational Resources Information Center

Thompson, William

2009-01-01

Conversational grounding theory proposes that language use is a form of rational joint action, by which dialog participants systematically and collaboratively add to their common ground of shared knowledge and beliefs. Following recent work applying "game theory" to pragmatics, this thesis develops a game-theoretic model of grounding that…

9. Suggestion for a Theoretical Model for Secondary-Tertiary Transition in Mathematics

ERIC Educational Resources Information Center

Clark, Megan; Lovric, Miroslav

2008-01-01

One of most notable features of existing body of research in transition seems to be the absence of a theoretical model. The suggestion we present in this paper--to view and understand the high school to university transition in mathematics as a modern-day rite of passage--is an attempt at defining such framework. Although dominantly reflecting…

10. Validation of a Theoretical Model of Diagnostic Classroom Assessment: A Mixed Methods Study

ERIC Educational Resources Information Center

Koh, Nancy

2012-01-01

The purpose of the study was to validate a theoretical model of diagnostic, formative classroom assessment called, "Proximal Assessment for Learner Diagnosis" (PALD). To achieve its purpose, the study employed a two-stage, mixed-methods design. The study utilized multiple data sources from 11 elementary level mathematics teachers who…

11. Rethinking High School Principal Compensation Practices: An Analysis of Salaries in South Carolina and Theoretical Models

ERIC Educational Resources Information Center

Newman, Tim A.

2012-01-01

This study described the current state of principal salaries in South Carolina and compared the salaries of similar size schools by specific report card performance and demographic variables. Based on the findings, theoretical models were proposed, and comparisons were made with current salary data. School boards, human resource personnel and…

12. Falling Chains as Variable-Mass Systems: Theoretical Model and Experimental Analysis

ERIC Educational Resources Information Center

de Sousa, Celia A.; Gordo, Paulo M.; Costa, Pedro

2012-01-01

In this paper, we revisit, theoretically and experimentally, the fall of a folded U-chain and of a pile-chain. The model calculation implies the division of the whole system into two subsystems of variable mass, allowing us to explore the role of tensional contact forces at the boundary of the subsystems. This justifies, for instance, that the…

13. The Practice-Theory-Practice Model: The Establishment of the Theoretical Bases of a Case Study.

ERIC Educational Resources Information Center

Michael, Robert O.; Barbe, Richard H.

The Practice-Theory-Practice Model (PTPM), a method designed to infuse theoretical perspectives into case study materials and to serve as a guide for examining chance processes in institutions of higher education, is described. The PTPM considers the historical and experiential environment that acts upon an institution, its practices and its…

14. Models of the Bilingual Lexicon and Their Theoretical Implications for CLIL

ERIC Educational Resources Information Center

Heine, Lena

2014-01-01

Although many advances have been made in recent years concerning the theoretical dimensions of content and language integrated learning (CLIL), research still has to meet the necessity to come up with integrative models that adequately map the interrelation between content and language learning in CLIL contexts. This article will suggest that…

15. How Students Experience and Navigate Transitions in Undergraduate Medical Education: An Application of Bourdieu's Theoretical Model

ERIC Educational Resources Information Center

Balmer, Dorene F.; Richards, Boyd F.; Varpio, Lara

2015-01-01

Using Bourdieu's theoretical model as a lens for analysis, we sought to understand how students experience the undergraduate medical education (UME) milieu, focusing on how they navigate transitions from the preclinical phase, to the major clinical year (MCY), and to the preparation for residency phase. Twenty-two medical students participated in…

16. Factors that Contribute to Talented Performance: A Theoretical Model from a Chinese Perspective

ERIC Educational Resources Information Center

Wu, Echo H.

2005-01-01

This paper examines the Chinese literature on giftedness and talented performance (TP) and compares its dominant theoretical features with some influential models to be found in the North American literature. One significant feature to emerge from the Chinese literature is a deemphasis on giftedness as an innate ability and an emphasis on the…

17. A Study of the Model of Mastery as a Theoretical Framework for Coaching Teachers Writing Workshop

ERIC Educational Resources Information Center

Kimbrell, Jennifer L.

2010-01-01

The study investigated a coach's use of a theoretical framework called the Model of Mastery to assist three teachers in becoming self-regulated in the teaching of writing workshop by moving them through three settings: acquisition, consolidation, and consultation. The goal of the coach was to assist teachers in developing expertise in procedural,…

18. Characterization of Titan 3-D acoustic pressure spectra by least-squares fit to theoretical model

Hartnett, E. B.; Carleen, E.

1980-01-01

A theoretical model for the acoustic spectra of undeflected rocket plumes is fitted to computed spectra of a Titan III-D at varying times after ignition, by a least-squares method. Tests for the goodness of the fit are made.

19. Theoretical values of various parameters in the Gummel-Poon model of a bipolar junction transistor

NASA Technical Reports Server (NTRS)

Benumof, R.; Zoutendyk, J.

1986-01-01

Various parameters in the Gummel-Poon model of a bipolar junction transistor are expressed in terms of the basic structure of a transistor. A consistent theoretical approach is used which facilitates an understanding of the foundations and limitations of the derived formulas. The results enable one to predict how changes in the geometry and composition of a transistor would affect performance.

20. Conceptualizing a Theoretical Model for School-Centered Adolescent Physical Activity Intervention Research

ERIC Educational Resources Information Center

Chen, Ang; Hancock, Gregory R.

2006-01-01

Adolescent physical inactivity has risen to an alarming rate. Several theoretical frameworks (models) have been proposed and tested in school-based interventions. The results are mixed, indicating a similar weakness as that observed in community-based physical activity interventions (Baranowski, Lin, Wetter, Resnicow, & Hearn, 1997). The…

1. On the Grammar and Model-Theoretic Semantics of Children's Noun Phrases.

ERIC Educational Resources Information Center

Suppes, Patrick

The paper shows informally how model-theoretical semantics may be used by a computer to give a straight-forward analysis of the meaning of children's language. This approach to semantics grows out of the main thrust of work in mathematical logic. It is discussed in the framework of generative grammar and is based on the application of the…

2. Using VCL as an Aspect-Oriented Approach to Requirements Modelling

Amálio, Nuno; Kelsen, Pierre; Ma, Qin; Glodt, Christian

Software systems are becoming larger and more complex. By tackling the modularisation of crosscutting concerns, aspect orientation draws attention to modularity as a means to address the problems of scalability, complexity and evolution in software systems development. Aspect-oriented modelling (AOM) applies aspect-orientation to the construction of models. Most existing AOM approaches are designed without a formal semantics, and use multi-view partial descriptions of behaviour. This paper presents an AOM approach based on the Visual Contract Language (VCL): a visual language for abstract and precise modelling, designed with a formal semantics, and comprising a novel approach to visual behavioural modelling based on design by contract where behavioural descriptions are total. By applying VCL to a large case study of a car-crash crisis management system, the paper demonstrates how modularity of VCL's constructs, at different levels of granularity, help to tackle complexity. In particular, it shows how VCL's package construct and its associated composition mechanisms are key in supporting separation of concerns, coarse-grained problem decomposition and aspect-orientation. The case study's modelling solution has a clear and well-defined modular structure; the backbone of this structure is a collection of packages encapsulating local solutions to concerns.

3. Requirements Modeling with the Aspect-oriented User Requirements Notation (AoURN): A Case Study

Mussbacher, Gunter; Amyot, Daniel; Araújo, João; Moreira, Ana

The User Requirements Notation (URN) is a recent ITU-T standard that supports requirements engineering activities. The Aspect-oriented URN (AoURN) adds aspect-oriented concepts to URN, creating a unified framework that allows for scenario-based, goal-oriented, and aspect-oriented modeling. AoURN is applied to the car crash crisis management system (CCCMS), modeling its functional and non-functional requirements (NFRs). AoURN generally models all use cases, NFRs, and stakeholders as individual concerns and provides general guidelines for concern identification. AoURN handles interactions between concerns, capturing their dependencies and conflicts as well as the resolutions. We present a qualitative comparison of aspect-oriented techniques for scenario-based and goal-oriented requirements engineering. An evaluation carried out based on the metrics adapted from literature and a task-based evaluation suggest that AoURN models are more scalable than URN models and exhibit better modularity, reusability, and maintainability.

4. A theoretical model for fault diagnosis of localized bearing defects under non-weight-dominant conditions

Han, Q. K.; Chu, F. L.

2015-07-01

Fault diagnosis of localized bearing defects under non-weight-dominant conditions is studied in this paper. A theoretical model with eight degrees of freedom is established, considering two transverse vibrations of the rotor and bearing raceway and one high-frequency resonant degree of freedom. Both the Hertzian contact between rolling elements and raceways, bearing clearance, unbalance force and self-weight of rotor are taken into account in the model. The localized defects in both inner and outer raceways are modeled as half sinusoidal waves. Then, the theoretical model is solved numerically and the vibrational responses are obtained. Through envelope analysis, the fault characteristic frequencies of inner/outer raceway defects for various conditions, including the weight-dominant condition and non-weight-dominant condition, are presented and compared with each other.

5. Generalized Constitutive-Based Theoretical and Empirical Models for Hot Working Behavior of Functionally Graded Steels

2013-07-01

Functionally graded steels with graded ferritic and austenitic regions including bainite and martensite intermediate layers produced by electroslag remelting have attracted much attention in recent years. In this article, an empirical model based on the Zener-Hollomon (Z-H) constitutive equation with generalized material constants is presented to investigate the effects of temperature and strain rate on the hot working behavior of functionally graded steels. Next, a theoretical model, generalized by strain compensation, is developed for the flow stress estimation of functionally graded steels under hot compression based on the phase mixture rule and boundary layer characteristics. The model is used for different strains and grading configurations. Specifically, the results for αβγMγ steels from empirical and theoretical models showed excellent agreement with those of experiments of other references within acceptable error.

6. Ocean color spectrum calculations. [theoretical models relating oceanographic parameters to upwelling radiances

NASA Technical Reports Server (NTRS)

Mccluney, W. R.

1974-01-01

The development is considered of procedures for measuring a number of subsurface oceanographic parameters using remotely sensed ocean color data. It is proposed that the first step in this effort should be the development of adequate theoretical models relating the desired oceanographic parameters to the upwelling radiances to be observed. A portion of a contributory theoretical model is shown to be described by a modified single scattering approach based upon a simple treatment of multiple scattering. The resulting quasi-single scattering model can be used to predict the upwelling distribution of spectral radiance emerging from the sea. The shape of the radiance spectrum predicted by this model for clear ocean water shows encouraging agreement with measurments made at the edge of the Sargasso Sea off Cape Hatteras.

7. Rational Design of Lanthanoid Single-Ion Magnets: Predictive Power of the Theoretical Models.

PubMed

Baldoví, José J; Duan, Yan; Morales, Roser; Gaita-Ariño, Alejandro; Ruiz, Eliseo; Coronado, Eugenio

2016-09-12

We report two new single-ion magnets (SIMs) of a family of oxydiacetate lanthanide complexes with D3 symmetry to test the predictive capabilities of complete active space ab initio methods (CASSCF and CASPT2) and the semiempirical radial effective charge (REC) model. Comparison of the theoretical predictions of the energy levels, wave functions and magnetic properties with detailed spectroscopic and magnetic characterisation is used to critically discuss the limitations of these theoretical approaches. The need for spectroscopic information for a reliable description of the properties of lanthanide SIMs is emphasised. PMID:27465352

8. Comparison of Theoretical Stresses and Deflections of Multicell Wings with Experimental Results Obtained from Plastic Models

NASA Technical Reports Server (NTRS)

Zender, George W

1956-01-01

The experimental deflections and stresses of six plastic multicell-wing models of unswept, delta, and swept plan form are presented and compared with previously published theoretical results obtained by the electrical analog method. The comparisons indicate that the theory is reliable except for the evaluation of stresses in the vicinity of the leading edge of delta wings and the leading and trailing edges of swept wings. The stresses in these regions are questionable, apparently because of simplifications employed in idealizing the actual structure for theoretical purposes and because of local effects of concentrated loads.

9. Cognitive-Existential Family Therapy: A Proposed Theoretical Integration Model for Pastoral Counselors.

PubMed

Saunders, James A

2015-03-01

Fundamental Christianity and psychology are frequently viewed as incompatible pursuits. However, proponents of the integrationist movement posit that pastoral counselors can utilize principles from psychology if they adopt the premise that all truth is God's truth. Assuming this perspective, Cognitive-Existential Family Therapy (CEFT) - a theoretical integration model compatible with Christian fundamentalism - is proposed. The philosophical assumptions and models of personality, health, and abnormality are explored. Additionally, the article provides an overview of the therapeutic process. PMID:26162205

10. Error control in the GCF: An information-theoretic model for error analysis and coding

NASA Technical Reports Server (NTRS)

1974-01-01

The structure of data-transmission errors within the Ground Communications Facility is analyzed in order to provide error control (both forward error correction and feedback retransmission) for improved communication. Emphasis is placed on constructing a theoretical model of errors and obtaining from it all the relevant statistics for error control. No specific coding strategy is analyzed, but references to the significance of certain error pattern distributions, as predicted by the model, to error correction are made.

11. Refinement and validation of two digital Microwave Landing System (MLS) theoretical models

NASA Technical Reports Server (NTRS)

Duff, W. G.; Guarino, C. R.

1975-01-01

Two digital microwave landing system theoretical models are considered which are generic models for the Doppler and scanning-beam frequency reference versions of the MLS. These models represent errors resulting from both system noise and discrete multipath. The data used for the validation effort were obtained from the Texas Instrument conventional scanning beam and the Hazeltine Doppler feasibility hardware versions of the MLS. Topics discussed include tape read software, time history plots, computation of power spectral density, smoothed power spectra, best-fit models, different equations for digital simulation, and discrete multipath errors.

12. Establishment and validation for the theoretical model of the vehicle airbag

Zhang, Junyuan; Jin, Yang; Xie, Lizhe; Chen, Chao

2015-05-01

The current design and optimization of the occupant restraint system (ORS) are based on numerous actual tests and mathematic simulations. These two methods are overly time-consuming and complex for the concept design phase of the ORS, though they're quite effective and accurate. Therefore, a fast and directive method of the design and optimization is needed in the concept design phase of the ORS. Since the airbag system is a crucial part of the ORS, in this paper, a theoretical model for the vehicle airbag is established in order to clarify the interaction between occupants and airbags, and further a fast design and optimization method of airbags in the concept design phase is made based on the proposed theoretical model. First, the theoretical expression of the simplified mechanical relationship between the airbag's design parameters and the occupant response is developed based on classical mechanics, then the momentum theorem and the ideal gas state equation are adopted to illustrate the relationship between airbag's design parameters and occupant response. By using MATLAB software, the iterative algorithm method and discrete variables are applied to the solution of the proposed theoretical model with a random input in a certain scope. And validations by MADYMO software prove the validity and accuracy of this theoretical model in two principal design parameters, the inflated gas mass and vent diameter, within a regular range. This research contributes to a deeper comprehension of the relation between occupants and airbags, further a fast design and optimization method for airbags' principal parameters in the concept design phase, and provides the range of the airbag's initial design parameters for the subsequent CAE simulations and actual tests.

13. Understanding Intention to Use Electronic Information Resources: A Theoretical Extension of the Technology Acceptance Model (TAM)

PubMed Central

Tao, Donghua

2008-01-01

This study extended the Technology Acceptance Model (TAM) by examining the roles of two aspects of e-resource characteristics, namely, information quality and system quality, in predicting public health students’ intention to use e-resources for completing research paper assignments. Both focus groups and a questionnaire were used to collect data. Descriptive analysis, data screening, and Structural Equation Modeling (SEM) techniques were used for data analysis. The study found that perceived usefulness played a major role in determining students’ intention to use e-resources. Perceived usefulness and perceived ease of use fully mediated the impact that information quality and system quality had on behavior intention. The research model enriches the existing technology acceptance literature by extending TAM. Representing two aspects of e-resource characteristics provides greater explanatory information for diagnosing problems of system design, development, and implementation. PMID:18999300

14. Theoretical modeling of the catch-slip bond transition in biological adhesion

Gunnerson, Kim; Pereverzev, Yuriy; Prezhdo, Oleg

2006-05-01

The mechanism by which leukocytes leave the blood stream and enter inflamed tissue is called extravasation. This process is facilitated by the ability of selectin proteins, produced by the endothelial cells of blood vessels, to form transient bonds with the leukocytes. In the case of P-selectin, the protein bonds with P-selectin glycoprotein ligands (PSGL-1) produced by the leukocyte. Recent atomic force microscopy and flow chamber analyses of the binding of P-selectin to PSGL-1 provide evidence for an unusual biphasic catch-bond/slip-bond behavior in response to the strength of exerted force. This biphasic process is not well-understood. There are several theoretical models for describing this phenomenon. These models use different profiles for potential energy landscapes and how they change under forces. We are exploring these changes using molecular dynamics. We will present a simple theoretical model as well as share some of our early MD results for describing this phenomenon.

15. Theoretical, experimental, and computational aspects of optical property determination of turbid media by using frequency-domain laser infrared photothermal radiometry.

PubMed

Nicolaides, L; Chen, Y; Mandelis, A; Vitkin, I A

2001-10-01

In this work, the optical and thermal properties of tissuelike materials are measured by using frequency-domain infrared photothermal radiometry. This technique is better suited for quantitative multiparameter optical measurements than the widely used pulsed-laser photothermal radiometry (PPTR) because of the availability of two independent signal channels, amplitude and phase, and the superior signal-to-noise ratio provided by synchronous lock-in detection. A rigorous three-dimensional (3-D) thermal-wave formulation with a 3-D diffuse and coherent photon-density-wave source is applied to data from model phantoms. The combined theoretical, experimental, and computational methodology shows good promise with regard to its analytical ability to measure optical properties of turbid media uniquely, as compared with PPTR, which exhibits uniqueness problems. From data sets obtained by using calibrated test phantoms, the reduced optical scattering and absorption coefficients were found to be within 20% and 10%, respectively, of the values independently derived by using Mie theory and spectrophotometric measurements. PMID:11583272

16. Theoretical base and numerical tools for modeling transitions between continuous and disperse multiphase motions

Zhang, Duan; Ma, Xia; Giguere, Paul

2009-11-01

Transitions between continuous and disperse multiphase motions happen commonly in nature and in our daily life. The phenomena include dissolving sugar cubes in a cup, formation of rain and hail, shattering a piece of glass. The capability of numerically simulating these phenomena is both important to industrial applications and to the understanding of nature. Relative to other aspects in this topic, theories for disperse multiphase flow is better developed despite many important issues still to be resolved. The theory for continuous multiphase flow is still in its infancy. The study of transition between continuous and disperse multiphase motion is at an even earlier stage of development. In this talk, we describe a possible theoretical framework based on the probability and statistical theory and a useful numerical method in simulating these phenomena. Deficiencies in the theory and in the numerical method are also discussed.

17. Clusters of DNA induced by ionizing radiation: formation of short DNA fragments. I. Theoretical modeling

NASA Technical Reports Server (NTRS)

Holley, W. R.; Chatterjee, A.

1996-01-01

We have developed a general theoretical model for the interaction of ionizing radiation with chromatin. Chromatin is modeled as a 30-nm-diameter solenoidal fiber comprised of 20 turns of nucleosomes, 6 nucleosomes per turn. Charged-particle tracks are modeled by partitioning the energy deposition between primary track core, resulting from glancing collisions with 100 eV or less per event, and delta rays due to knock-on collisions involving energy transfers >100 eV. A Monte Carlo simulation incorporates damages due to the following molecular mechanisms: (1) ionization of water molecules leading to the formation of OH, H, eaq, etc.; (2) OH attack on sugar molecules leading to strand breaks: (3) OH attack on bases; (4) direct ionization of the sugar molecules leading to strand breaks; (5) direct ionization of the bases. Our calculations predict significant clustering of damage both locally, over regions up to 40 bp and over regions extending to several kilobase pairs. A characteristic feature of the regional damage predicted by our model is the production of short fragments of DNA associated with multiple nearby strand breaks. The shapes of the spectra of DNA fragment lengths depend on the symmetries or approximate symmetries of the chromatin structure. Such fragments have subsequently been detected experimentally and are reported in an accompanying paper (B. Rydberg, Radiat, Res. 145, 200-209, 1996) after exposure to both high- and low-LET radiation. The overall measured yields agree well quantitatively with the theoretical predictions. Our theoretical results predict the existence of a strong peak at about 85 bp, which represents the revolution period about the nucleosome. Other peaks at multiples of about 1,000 bp correspond to the periodicity of the particular solenoid model of chromatin used in these calculations. Theoretical results in combination with experimental data on fragmentation spectra may help determine the consensus or average structure of the

18. Clusters of DNA induced by ionizing radiation: formation of short DNA fragments. I. Theoretical modeling.

PubMed

Holley, W R; Chatterjee, A

1996-02-01

We have developed a general theoretical model for the interaction of ionizing radiation with chromatin. Chromatin is modeled as a 30-nm-diameter solenoidal fiber comprised of 20 turns of nucleosomes, 6 nucleosomes per turn. Charged-particle tracks are modeled by partitioning the energy deposition between primary track core, resulting from glancing collisions with 100 eV or less per event, and delta rays due to knock-on collisions involving energy transfers >100 eV. A Monte Carlo simulation incorporates damages due to the following molecular mechanisms: (1) ionization of water molecules leading to the formation of OH, H, eaq, etc.; (2) OH attack on sugar molecules leading to strand breaks: (3) OH attack on bases; (4) direct ionization of the sugar molecules leading to strand breaks; (5) direct ionization of the bases. Our calculations predict significant clustering of damage both locally, over regions up to 40 bp and over regions extending to several kilobase pairs. A characteristic feature of the regional damage predicted by our model is the production of short fragments of DNA associated with multiple nearby strand breaks. The shapes of the spectra of DNA fragment lengths depend on the symmetries or approximate symmetries of the chromatin structure. Such fragments have subsequently been detected experimentally and are reported in an accompanying paper (B. Rydberg, Radiat, Res. 145, 200-209, 1996) after exposure to both high- and low-LET radiation. The overall measured yields agree well quantitatively with the theoretical predictions. Our theoretical results predict the existence of a strong peak at about 85 bp, which represents the revolution period about the nucleosome. Other peaks at multiples of about 1,000 bp correspond to the periodicity of the particular solenoid model of chromatin used in these calculations. Theoretical results in combination with experimental data on fragmentation spectra may help determine the consensus or average structure of the

19. Theoretical Modeling of Gpr Reflection from Vadose Zone in Silty Soils

Halabe, Udaya B.

2008-02-01

Ground Penetrating Radar (GPR) is routinely being used for subsurface investigations including detection of water table and contaminant flow pattern. Past laboratory studies on water table detection in silty soils has shown that GPR actually detects reflection from within the unsaturated capillary (vadose) zone, which is just above the water table. While this phenomenon has been observed from experimental studies, no attempt has been made so far to explain the theoretical basis for the occurrence of GPR reflection within the vadose zone above the water table and not at the level of the actual water table. Understanding this phenomenon from a theoretical stand point requires modeling of GPR reflection from the vadose zone where the moisture content varies with depth. This paper describes the theoretical model which includes discretization of the vadose zone into a number of thin layers with different moisture contents. The model also includes the dry soil above the vadose zone and the underlying fully saturated zone. The GPR waveforms are generated from this model by utilizing frequency domain synthesis algorithm which accounts for all the multiple reflections within the thin layers. These synthetic waveforms have been used to explain the phenomenon of GPR reflection from the vadose zone.

20. Theoretical model of the interaction of glycine with hydrogenated amorphous carbon (HAC).

PubMed

Timón, Vicente; Gálvez, Óscar; Maté, Belén; Tanarro, Isabel; Herrero, Víctor J; Escribano, Rafael

2015-11-21

A theoretical model of hydrogenated amorphous carbon (HAC) is developed and applied to study the interaction of glycine with HAC surfaces at astronomical temperatures. Two models with different H content are tried for the HAC surface. The theory is applied at the Density Functional Theory (DFT) level, including a semiempirical dispersion correlation potential, d-DFT or Grimme DFT-D2. The level of theory is tested on glycine adsorption on a Si(001) surface. Crystalline glycine is also studied in its two stable phases, α and β, and the metastable γ phase. For the adsorption on Si or HAC surfaces, molecular glycine is introduced in the neutral and zwitterionic forms, and the most stable configurations are searched. All theoretical predictions are checked against experimental observations. HAC films are prepared by plasma enhanced vapor deposition at room temperature. Glycine is deposited at 20 K into a high vacuum, cold temperature chamber, to simulate astronomical conditions. Adsorption takes place through the acidic group COO(-) and when several glycine molecules are present, they form H-bond chains among them. Comparison between experiments and predictions suggests that a possible way to improve the theoretical model would require the introduction of aliphatic chains or a polycyclic aromatic core. The lack of previous models to study the interaction of amino-acids with HAC surfaces provides a motivation for this work. PMID:26456640

1. Chemical and morphological gradient scaffolds to mimic hierarchically complex tissues: From theoretical modeling to their fabrication.

PubMed

Marrella, Alessandra; Aiello, Maurizio; Quarto, Rodolfo; Scaglione, Silvia

2016-10-01

Porous multiphase scaffolds have been proposed in different tissue engineering applications because of their potential to artificially recreate the heterogeneous structure of hierarchically complex tissues. Recently, graded scaffolds have been also realized, offering a continuum at the interface among different phases for an enhanced structural stability of the scaffold. However, their internal architecture is often obtained empirically and the architectural parameters rarely predetermined. The aim of this work is to offer a theoretical model as tool for the design and fabrication of functional and structural complex graded scaffolds with predicted morphological and chemical features, to overcome the time-consuming trial and error experimental method. This developed mathematical model uses laws of motions, Stokes equations, and viscosity laws to describe the dependence between centrifugation speed and fiber/particles sedimentation velocity over time, which finally affects the fiber packing, and thus the total porosity of the 3D scaffolds. The efficacy of the theoretical model was tested by realizing engineered graded grafts for osteochondral tissue engineering applications. The procedure, based on combined centrifugation and freeze-drying technique, was applied on both polycaprolactone (PCL) and collagen-type-I (COL) to test the versatility of the entire process. A functional gradient was combined to the morphological one by adding hydroxyapatite (HA) powders, to mimic the bone mineral phase. Results show that 3D bioactive morphologically and chemically graded grafts can be properly designed and realized in agreement with the theoretical model. Biotechnol. Bioeng. 2016;113: 2286-2297. © 2016 Wiley Periodicals, Inc. PMID:27093435

2. Abelian p-form (p = 1, 2, 3) gauge theories as the field theoretic models for the Hodge theory

Kumar, R.; Krishna, S.; Shukla, A.; Malik, R. P.

2014-09-01

Taking the simple examples of an Abelian 1-form gauge theory in two (1+1)-dimensions, a 2-form gauge theory in four (3+1)-dimensions and a 3-form gauge theory in six (5+1)-dimensions of space-time, we establish that such gauge theories respect, in addition to the gauge symmetry transformations that are generated by the first-class constraints of the theory, additional continuous symmetry transformations. We christen the latter symmetry transformations as the dual-gauge transformations. We generalize the above gauge and dual-gauge transformations to obtain the proper (anti-)BRST and (anti-)dual-BRST transformations for the Abelian 3-form gauge theory within the framework of BRST formalism. We concisely mention such symmetries for the 2D free Abelian 1-form and 4D free Abelian 2-form gauge theories and briefly discuss their topological aspects in our present endeavor. We conjecture that any arbitrary Abelian p-form gauge theory would respect the above cited additional symmetry in D = 2p(p = 1, 2, 3, …) dimensions of space-time. By exploiting the above inputs, we establish that the Abelian 3-form gauge theory, in six (5+1)-dimensions of space-time, is a perfect model for the Hodge theory whose discrete and continuous symmetry transformations provide the physical realizations of all aspects of the de Rham cohomological operators of differential geometry. As far as the physical utility of the above nilpotent symmetries is concerned, we demonstrate that the 2D Abelian 1-form gauge theory is a perfect model of a new class of topological theory and 4D Abelian 2-form as well as 6D Abelian 3-form gauge theories are the field theoretic models for the quasi-topological field theory.

3. A note on Black-Scholes pricing model for theoretical values of stock options

Edeki, S. O.; Ugbebor, O. O.; Owoloko, E. A.

2016-02-01

In this paper, we consider some conditions that transform the classical Black-Scholes Model for stock options valuation from its partial differential equation (PDE) form to an equivalent ordinary differential equation (ODE) form. In addition, we propose a relatively new semi-analytical method for the solution of the transformed Black-Scholes model. The obtained solutions via this method can be used to find the theoretical values of the stock options in relation to their fair prices. In considering the reliability and efficiency of the models, we test some cases and the results are in good agreement with the exact solution.

4. Field-theoretic model of inhomogeneous supramolecular polymer networks and gels

Mohan, Aruna; Elliot, Richard; Fredrickson, Glenn H.

2010-11-01

We present a field-theoretic model of the gelation transition in inhomogeneous reversibly bonding systems and demonstrate that our model reproduces the classical Flory-Stockmayer theory of gelation in the homogeneous limit. As an illustration of our model in the context of inhomogeneous gelation, we analyze the mean-field behavior of an equilibrium system of reacting trifunctional units in a good solvent confined within a slit bounded by parallel, repulsive walls. Our results indicate higher conversions and, consequently, higher concentrations of gel following the gelation transition near the center of the slit relative to the edges.

5. A theoretical model to predict tensile deformation behavior of balloon catheter.

PubMed

Todo, Mitsugu; Yoshiya, Keiji; Matsumoto, Takuya

2016-09-01

In this technical note, a simple theoretical model was proposed to express the tensile deformation and fracture of balloon catheter tested by the ISO standard using piece-wise linear force-displacement relations. The model was then validated by comparing with the tensile force-displacement behaviors of two types of typical balloon catheters clinically used worldwide. It was shown that the proposed model can effectively be used to express the tensile deformation behavior and easily be handled by physicians who are not familiar with mechanics of materials. PMID:27214691

6. Field-theoretic model of inhomogeneous supramolecular polymer networks and gels.

PubMed

Mohan, Aruna; Elliot, Richard; Fredrickson, Glenn H

2010-11-01

We present a field-theoretic model of the gelation transition in inhomogeneous reversibly bonding systems and demonstrate that our model reproduces the classical Flory-Stockmayer theory of gelation in the homogeneous limit. As an illustration of our model in the context of inhomogeneous gelation, we analyze the mean-field behavior of an equilibrium system of reacting trifunctional units in a good solvent confined within a slit bounded by parallel, repulsive walls. Our results indicate higher conversions and, consequently, higher concentrations of gel following the gelation transition near the center of the slit relative to the edges. PMID:21054065

7. [Nursing and the environmental question: proposal of a theoretical model for the professional practice].

PubMed

Ribeiro, M C; Bertolozzi, M R

1999-01-01

Considering the side effects of environmental changes over the population's health, a theoretical model is proposed in this study in order to incorporate ecologic matters into the nursing practices. The reference for this work is the eco-socialist-marxist theory. The model is based on the analysis of the capitalist economic process, its production technologies and consumption. It is known that this economic model generates ecoinequalities and anthropogenic impacts that rebound on the health-disease profile of the population. The nursing action, permeated by ecological awareness, can prevent and also combat ecoinequalities and destructive human actions on the environment. PMID:12138633

8. A Hebbian learning rule gives rise to mirror neurons and links them to control theoretic inverse models

PubMed Central

Hanuschkin, A.; Ganguli, S.; Hahnloser, R. H. R.

2013-01-01

Mirror neurons are neurons whose responses to the observation of a motor act resemble responses measured during production of that act. Computationally, mirror neurons have been viewed as evidence for the existence of internal inverse models. Such models, rooted within control theory, map-desired sensory targets onto the motor commands required to generate those targets. To jointly explore both the formation of mirrored responses and their functional contribution to inverse models, we develop a correlation-based theory of interactions between a sensory and a motor area. We show that a simple eligibility-weighted Hebbian learning rule, operating within a sensorimotor loop during motor explorations and stabilized by heterosynaptic competition, naturally gives rise to mirror neurons as well as control theoretic inverse models encoded in the synaptic weights from sensory to motor neurons. Crucially, we find that the correlational structure or stereotypy of the neural code underlying motor explorations determines the nature of the learned inverse model: random motor codes lead to causal inverses that map sensory activity patterns to their motor causes; such inverses are maximally useful, by allowing the imitation of arbitrary sensory target sequences. By contrast, stereotyped motor codes lead to less useful predictive inverses that map sensory activity to future motor actions. Our theory generalizes previous work on inverse models by showing that such models can be learned in a simple Hebbian framework without the need for error signals or backpropagation, and it makes new conceptual connections between the causal nature of inverse models, the statistical structure of motor variability, and the time-lag between sensory and motor responses of mirror neurons. Applied to bird song learning, our theory can account for puzzling aspects of the song system, including necessity of sensorimotor gating and selectivity of auditory responses to bird's own song (BOS) stimuli. PMID

9. Theoretical modeling of the plasma-assisted catalytic growth and field emission properties of graphene sheet

SciTech Connect

Sharma, Suresh C.; Gupta, Neha

2015-12-15

A theoretical modeling for the catalyst-assisted growth of graphene sheet in the presence of plasma has been investigated. It is observed that the plasma parameters can strongly affect the growth and field emission properties of graphene sheet. The model developed accounts for the charging rate of the graphene sheet; number density of electrons, ions, and neutral atoms; various elementary processes on the surface of the catalyst nanoparticle; surface diffusion and accretion of ions; and formation of carbon-clusters and large graphene islands. In our investigation, it is found that the thickness of the graphene sheet decreases with the plasma parameters, number density of hydrogen ions and RF power, and consequently, the field emission of electrons from the graphene sheet surface increases. The time evolution of the height of graphene sheet with ion density and sticking coefficient of carbon species has also been examined. Some of our theoretical results are in compliance with the experimental observations.

10. Comparison of selected theoretical models of bubble formation and experimental results

Rząsa, Mariusz R.

2014-06-01

Designers of all types of equipment applied in oxygenation and aeration need to get to know the mechanism behind the gas bubble formation. This paper presents a measurement method used for determination of parameters of bubbles forming at jet attachment from which the bubles are displaced upward. The measuring system is based on an optical tomograph containing five projections. An image from the tomograph contains shapes of the forming bubbles and determine their volumes and formation rate. Additionally, this paper presents selected theoretical models known from literature. The measurement results have been compared with simple theoretical models predictions. The paper also contains a study of the potential to apply the presented method for determination of bubble structures and observation of intermediate states.

11. Theoretical-computational modeling of photo-induced charge separation spectra and charge recombination kinetics in solution.

PubMed

Piacente, Giovanni; Amadei, Andrea; D'Abramo, Marco; Daidone, Isabella; Aschi, Massimiliano

2014-10-14

In this study we propose a theoretical-computational method, essentially based on molecular dynamics simulations and quantum-chemical calculations, for modelling the photo-induced charge separation (CS) and the subsequent charge recombination (CR) processes in solution. In particular we have reproduced the low-energy UV-Vis spectra of systems composed by an aromatic species (Ar = benzene or indene) and tetracyanoethylene (TCNE) in chloroform solution, dominated by the formation of the Ar(+)-TCNE(-) ion pair (IP) complex. The kinetics of the charge recombination process leading to the regeneration of Ar and TCNE has also been modelled. In both the cases the agreement with the experimental data is satisfactory. Although the presence of systematic deficiencies makes our approach unable to address some key aspects of the above processes (e.g. the ultrafast internal vibrational redistribution), it appears to be a rather promising tool for modelling the CS-CR process for atomic-molecular systems of very high complexity. The involvement of the triplet IP complex has also been discussed. PMID:25157909

12. A theoretical model for the cross spectra between pressure and temperature downstream of a combustor

NASA Technical Reports Server (NTRS)

Miles, J. H.; Krejsa, E. A.

1984-01-01

A theoretical model developed to calculate pressure-temperature cross spectra, pressure spectra, temperature spectra and pressure cross spectra in a ducted combustion system is presented. The model assumes the presence of a fluctuating-volumetric-heat-release-rate disk source and takes into account the spatial distribution of the steady-state volumetric-heat flux. Using the model, pressure, velocity, and temperature perturbation relationships can be obtained. The theoretical results show that, at a given air mass flow rate, the calculated pressure-temperature cross spectra phase angle at the combustor exit depends on the model selected for the steady-state volumetric-heat flux in the combustor. Using measurements of the phase angle, an appropriate source region model was selected. The model calculations are compared with the data. The comparison shows good agreement and indicates that with the use of this model the pressure-temperature cross spectra measurements provide useful information on the physical mechanisms active at the combustion noise source.

13. Control Theoretic Modeling and Generated Flow Patterns of a Fish-Tail Robot

Massey, Brian; Morgansen, Kristi; Dabiri, Dana

2003-11-01

Many real-world engineering problems involve understanding and manipulating fluid flows. One of the challenges to further progress in the area of active flow control is the lack of appropriate models that are amenable to control-theoretic studies and algorithm design and also incorporate reasonably realistic fluid dynamic effects. We focus here on modeling and model-verification of bio-inspired actuators (fish-fin type structures) used to control fluid dynamic artifacts that will affect speed, agility, and stealth of Underwater Autonomous Vehicles (UAVs). Vehicles using fish-tail type systems are more maneuverable, can turn in much shorter and more constrained spaces, have lower drag, are quieter and potentially more efficient than those using propellers. We will present control-theoretic models for a simple prototype coupled fluid and mechanical actuator where fluid effects are crudely modeled by assuming only lift, drag, and added mass, while neglecting boundary effects. These models will be tested with different control input parameters on an experimental fish-tail robot with the resulting flow captured with DPIV. Relations between the model, the control function choices, the obtained thrust and drag, and the corresponding flow patterns will be presented and discussed.

14. Analysis of a theoretical model for anisotropic enzyme membranes application to enzyme electrodes.

PubMed

Pedersen, H; Chotani, G K

1981-12-01

A theoretical model of diffusion and reaction in an anisotropic enzyme membrane is presented with particular emphasis on the application of such membranes in enzyme electrodes. The dynamic response of systems in which the kinetics are linear, which comprises the practical operating regime for enzyme electrodes in analysis, is investigated via an analytic solution of the governing differential equations. The response is presented as a function of a single dimensionless group, Μ, that is the membrane modulus. PMID:24233978

15. Dynamical gap generation in graphene nanoribbons: An effective relativistic field theoretical model

SciTech Connect

Chaves, A. J.; Paula, W. de; Frederico, T.; Lima, G. D.; Cordeiro, C. E.; Delfino, A.

2011-04-15

We show that the assumption of a nontrivial zero band gap for a graphene sheet within an effective relativistic field theoretical model description of interacting Dirac electrons on the surface of graphene describes the experimental band gap of graphene nanoribbons for a wide range of widths. The graphene band gap is dynamically generated, corresponding to a nontrivial gapless solution, found in the limit of an infinitely wide graphene ribbon. The nanoribbon band gap is determined by the experimental graphene work function.

16. Meta-Theoretical Contributions to the Constitution of a Model-Based Didactics of Science

Ariza, Yefrin; Lorenzano, Pablo; Adúriz-Bravo, Agustín

2016-07-01

There is nowadays consensus in the community of didactics of science (i.e. science education understood as an academic discipline) regarding the need to include the philosophy of science in didactical research, science teacher education, curriculum design, and the practice of science education in all educational levels. Some authors have identified an ever-increasing use of the concept of `theoretical model', stemming from the so-called semantic view of scientific theories. However, it can be recognised that, in didactics of science, there are over-simplified transpositions of the idea of model (and of other meta-theoretical ideas). In this sense, contemporary philosophy of science is often blurred or distorted in the science education literature. In this paper, we address the discussion around some meta-theoretical concepts that are introduced into didactics of science due to their perceived educational value. We argue for the existence of a `semantic family', and we characterise four different versions of semantic views existing within the family. In particular, we seek to contribute to establishing a model-based didactics of science mainly supported in this semantic family.

17. Theoretically Modeling the Ionospheric Response at Low Latitudes to the Great Storms in October, 2003

Anderson, D. N.; Anghel, A.; Eccles, V.; Valladares, C.; Chau, J.; Veliz, O.

2004-05-01

In the low latitude, ionospheric F region, the primary transport mechanism that determines the electron and ion density distributions is the magnitude of the daytime, upward ExB drift velocity. During the geomagnetic storms on Oct. 29 and 30, 2003, we have inferred these upward ExB drift velocities from ground-based magnetometer observations at Jicamarca and Piura, Peru as a function of local time (0700 - 1700LT). On both days these ExB drifts exceeded 80 m/sec which is about four times greater than the normal, quiet time value of 20 m/sec. We study the ionospheric response in the Peruvian longitude sector to these large upward drifts by theoretically-calculating electron and ion densities as a function of altitude, latitude and local time using the time-dependent Low-Latitude Ionospheric Sector model (LLIONS). This is a single sector ionosphere model capable of incorporating data-determined drivers. Initial results indicate that the large, upward ExB drift velocities on Oct. 29 produce equatorial anomaly crests in ionization at +/- 22° dip latitude rather than the usual +/- 16° dip latitude. We compare the theoretically-calculated results with a variety of ground-based and satellite observations for Oct. 28, 29, 30 and 31 and discuss the implications of these comparisons as they relate to the capabilities of current theoretical models and our ability to infer ionospheric drivers such as ExB drifts.

18. An Empirical Jet-Surface Interaction Noise Model with Temperature and Nozzle Aspect Ratio Effects

NASA Technical Reports Server (NTRS)

Brown, Cliff

2015-01-01

An empirical model for jet-surface interaction (JSI) noise produced by a round jet near a flat plate is described and the resulting model evaluated. The model covers unheated and hot jet conditions (1 less than or equal to jet total temperature ratio less than or equal to 2.7) in the subsonic range (0.5 less than or equal to M(sub a) less than or equal to 0.9), surface lengths 0.6 less than or equal to (axial distance from jet exit to surface trailing edge (inches)/nozzle exit diameter) less than or equal to 10, and surface standoff distances (0 less than or equal to (radial distance from jet lipline to surface (inches)/axial distance from jet exit to surface trailing edge (inches)) less than or equal to 1) using only second-order polynomials to provide predictable behavior. The JSI noise model is combined with an existing jet mixing noise model to produce exhaust noise predictions. Fit quality metrics and comparisons to between the predicted and experimental data indicate that the model is suitable for many system level studies. A first-order correction to the JSI source model that accounts for the effect of nozzle aspect ratio is also explored. This correction is based on changes to the potential core length and frequency scaling associated with rectangular nozzles up to 8:1 aspect ratio. However, more work is needed to refine these findings into a formal model.

19. Representing general theoretical concepts in structural equation models: The role of composite variables

USGS Publications Warehouse

Grace, J.B.; Bollen, K.A.

2008-01-01

Structural equation modeling (SEM) holds the promise of providing natural scientists the capacity to evaluate complex multivariate hypotheses about ecological systems. Building on its predecessors, path analysis and factor analysis, SEM allows for the incorporation of both observed and unobserved (latent) variables into theoretically-based probabilistic models. In this paper we discuss the interface between theory and data in SEM and the use of an additional variable type, the composite. In simple terms, composite variables specify the influences of collections of other variables and can be helpful in modeling heterogeneous concepts of the sort commonly of interest to ecologists. While long recognized as a potentially important element of SEM, composite variables have received very limited use, in part because of a lack of theoretical consideration, but also because of difficulties that arise in parameter estimation when using conventional solution procedures. In this paper we present a framework for discussing composites and demonstrate how the use of partially-reduced-form models can help to overcome some of the parameter estimation and evaluation problems associated with models containing composites. Diagnostic procedures for evaluating the most appropriate and effective use of composites are illustrated with an example from the ecological literature. It is argued that an ability to incorporate composite variables into structural equation models may be particularly valuable in the study of natural systems, where concepts are frequently multifaceted and the influence of suites of variables are often of interest. ?? Springer Science+Business Media, LLC 2007.

20. Simultaneous time-temperature-thickness superposition theoretical and statistical modelling of convective drying of guava.

PubMed

Kek, Siok Peng; Chin, Nyuk Ling; Yusof, Yus Aniza

2014-12-01

Modelling studies of guava drying and quality are presented using theoretical and statistical models by varying temperature from 55 to 75 °C and slice thickness from 3 to 9 mm. The quality of dried fruit was measured for its water activity, colour, vitamin C, and texture. The superposition technique with Midilli-Kucuk model showed efficiency in modelling the drying process with R (2)  = 0.9991. The second-order polynomial equations adequately described the quality of dried guava with regression coefficient, R (2)  > 0.7. Drying time was a good function of temperature and thickness (P < 0.001); water activity, colour and vitamin C showed strong dependence on temperature (P < 0.1); while texture was mainly influenced by its thickness (P < 0.005). The optimum drying temperature of 70 °C at slice thickness of 6 mm was determined using the desirability function method. Simultaneous modelling using the theoretical and statistical drying models provides information on water diffusion and evaporation with the drying responses and factors. PMID:25477628

1. Testing models for obliquely plunging lineations in transpression: a natural example and theoretical discussion

Czeck, Dyanna M.; Hudleston, Peter J.

2003-06-01

Theory predicts that stretching lineations in an ideal vertical transpressional zone should be either vertical or horizontal. Many field descriptions of transpressional zones, however, indicate a range of lineation orientations between these extremes. Several theoretical models have been developed to explain such departures from expected lineation orientation, and we discuss these in the context of a field example from the Archean Superior Province in the North American craton. Existing models are insufficient to explain obliquely plunging lineations in this example because: (1) obliquely plunging lineations cannot be accounted for by shear zone boundary effects imposed by a no-slip condition, (2) foliations and lineations vary independently, (3) the vorticity-normal section is subhorizontal, limiting possibilities for inclined simple shear, (4) high vorticity is needed for finite strains and lineations to match previously proposed triclinic models, but vorticity is relatively low, and (5) juxtaposed east and west plunging lineations are unlikely in the previously proposed triclinic models. Because existing theoretical models are not applicable to our field example, we contemplate a new model to explain obliquely plunging lineations within quasi homogeneous transpression.

2. Thermal conductivity of molten salt mixtures: Theoretical model supported by equilibrium molecular dynamics simulations.

PubMed

Gheribi, Aïmen E; Chartrand, Patrice

2016-02-28

A theoretical model for the description of thermal conductivity of molten salt mixtures as a function of composition and temperature is presented. The model is derived by considering the classical kinetic theory and requires, for its parametrization, only information on thermal conductivity of pure compounds. In this sense, the model is predictive. For most molten salt mixtures, no experimental data on thermal conductivity are available in the literature. This is a hindrance for many industrial applications (in particular for thermal energy storage technologies) as well as an obvious barrier for the validation of the theoretical model. To alleviate this lack of data, a series of equilibrium molecular dynamics (EMD) simulations has been performed on several molten chloride systems in order to determine their thermal conductivity in the entire range of composition at two different temperatures: 1200 K and 1300 K. The EMD simulations are first principles type, as the potentials used to describe the interactions have been parametrized on the basis of first principle electronic structure calculations. In addition to the molten chlorides system, the model predictions are also compared to a recent similar EMD study on molten fluorides and with the few reliable experimental data available in the literature. The accuracy of the proposed model is within the reported numerical and/or experimental errors. PMID:26931711

3. Theoretic Fit and Empirical Fit: The Performance of Maximum Likelihood versus Generalized Least Squares Estimation in Structural Equation Models.

ERIC Educational Resources Information Center

Olsson, Ulf Henning; Troye, Sigurd Villads; Howell, Roy D.

1999-01-01

Used simulation to compare the ability of maximum likelihood (ML) and generalized least-squares (GLS) estimation to provide theoretic fit in models that are parsimonious representations of a true model. The better empirical fit obtained for GLS, compared with ML, was obtained at the cost of lower theoretic fit. (Author/SLD)

4. Reality-Theoretical Models-Mathematics: A Ternary Perspective on Physics Lessons in Upper-Secondary School

ERIC Educational Resources Information Center

Hansson, Lena; Hansson, Örjan; Juter, Kristina; Redfors, Andreas

2015-01-01

This article discusses the role of mathematics during physics lessons in upper-secondary school. Mathematics is an inherent part of theoretical models in physics and makes powerful predictions of natural phenomena possible. Ability to use both theoretical models and mathematics is central in physics. This paper takes as a starting point that the…

5. A 3-dimensional in vitro model of epithelioid granulomas induced by high aspect ratio nanomaterials

PubMed Central

2011-01-01

Background The most common causes of granulomatous inflammation are persistent pathogens and poorly-degradable irritating materials. A characteristic pathological reaction to intratracheal instillation, pharyngeal aspiration, or inhalation of carbon nanotubes is formation of epithelioid granulomas accompanied by interstitial fibrosis in the lungs. In the mesothelium, a similar response is induced by high aspect ratio nanomaterials, including asbestos fibers, following intraperitoneal injection. This asbestos-like behaviour of some engineered nanomaterials is a concern for their potential adverse health effects in the lungs and mesothelium. We hypothesize that high aspect ratio nanomaterials will induce epithelioid granulomas in nonadherent macrophages in 3D cultures. Results Carbon black particles (Printex 90) and crocidolite asbestos fibers were used as well-characterized reference materials and compared with three commercial samples of multiwalled carbon nanotubes (MWCNTs). Doses were identified in 2D and 3D cultures in order to minimize acute toxicity and to reflect realistic occupational exposures in humans and in previous inhalation studies in rodents. Under serum-free conditions, exposure of nonadherent primary murine bone marrow-derived macrophages to 0.5 μg/ml (0.38 μg/cm2) of crocidolite asbestos fibers or MWCNTs, but not carbon black, induced macrophage differentiation into epithelioid cells and formation of stable aggregates with the characteristic morphology of granulomas. Formation of multinucleated giant cells was also induced by asbestos fibers or MWCNTs in this 3D in vitro model. After 7-14 days, macrophages exposed to high aspect ratio nanomaterials co-expressed proinflammatory (M1) as well as profibrotic (M2) phenotypic markers. Conclusions Induction of epithelioid granulomas appears to correlate with high aspect ratio and complex 3D structure of carbon nanotubes, not with their iron content or surface area. This model offers a time- and cost

6. Empirical, theoretical, and practical advantages of the HEXACO model of personality structure.

PubMed

Ashton, Michael C; Lee, Kibeom

2007-05-01

The authors argue that a new six-dimensional framework for personality structure--the HEXACO model--constitutes a viable alternative to the well-known Big Five or five-factor model. The new model is consistent with the cross-culturally replicated finding of a common six-dimensional structure containing the factors Honesty-Humility (H), Emotionality (E), eExtraversion (X), Agreeableness (A), Conscientiousness (C), and Openness to Experience (O). Also, the HEXACO model predicts several personality phenomena that are not explained within the B5/FFM, including the relations of personality factors with theoretical biologists' constructs of reciprocal and kin altruism and the patterns of sex differences in personality traits. In addition, the HEXACO model accommodates several personality variables that are poorly assimilated within the B5/FFM. PMID:18453460

7. Estimation of ozone with total ozone portable spectroradiometer instruments. I. Theoretical model and error analysis

Flynn, Lawrence E.; Labow, Gordon J.; Beach, Robert A.; Rawlins, Michael A.; Flittner, David E.

1996-10-01

Inexpensive devices to measure solar UV irradiance are available to monitor atmospheric ozone, for example, total ozone portable spectroradiometers (TOPS instruments). A procedure to convert these measurements into ozone estimates is examined. For well-characterized filters with 7-nm FWHM bandpasses, the method provides ozone values (from 304- and 310-nm channels) with less than 0.4 error attributable to inversion of the theoretical model. Analysis of sensitivity to model assumptions and parameters yields estimates of 3 bias in total ozone results with dependence on total ozone and path length. Unmodeled effects of atmospheric constituents and instrument components can result in additional 2 errors.

8. Theoretical modelling of the feedback stabilization of external MHD modes in toroidal geometry

Chance, M. S.; Chu, M. S.; Okabayashi, M.; Turnbull, A. D.

2002-03-01

A theoretical framework for understanding the feedback mechanism for stabilization of external MHD modes has been formulated. Efficient computational tools - the GATO stability code coupled with a substantially modified VACUUM code - have been developed to effectively design viable feedback systems against these modes. The analysis assumed a thin resistive shell and a feedback coil structure accurately modelled in θ and phi, albeit with only a single harmonic variation in phi. Time constants and induced currents in the enclosing resistive shell are calculated. An optimized configuration based on an idealized model has been computed for the DIII-D device. Up to 90% of the effectiveness of an ideal wall can be achieved.

9. Theoretical foundation, methods, and criteria for calibrating human vibration models using frequency response functions

PubMed Central

Dong, Ren G.; Welcome, Daniel E.; McDowell, Thomas W.; Wu, John Z.

2015-01-01

While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for model calibration, to help formulate the criteria for calibration validation, and to help appropriately select and apply calibration methods. In addition to established vibration theory, a novel theorem of mechanical vibration is also used to enhance the understanding of the mathematical and physical principles of the calibration. Based on this enhanced understanding, a set of criteria was proposed and used to systematically examine the calibration methods. Besides theoretical analyses, a numerical testing method is also used in the examination. This study identified the basic requirements for each calibration method to obtain a unique calibration solution. This study also confirmed that the solution becomes more robust if more than sufficient calibration references are provided. Practically, however, as more references are used, more inconsistencies can arise among the measured data for representing the biodynamic properties. To help account for the relative reliabilities of the references, a baseline weighting scheme is proposed. The analyses suggest that the best choice of calibration method depends on the modeling purpose, the model structure, and the availability and reliability of representative reference data. PMID:26740726

10. Theoretical foundation, methods, and criteria for calibrating human vibration models using frequency response functions

Dong, Ren G.; Welcome, Daniel E.; McDowell, Thomas W.; Wu, John Z.

2015-11-01

While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for model calibration, to help formulate the criteria for calibration validation, and to help appropriately select and apply calibration methods. In addition to established vibration theory, a novel theorem of mechanical vibration is also used to enhance the understanding of the mathematical and physical principles of the calibration. Based on this enhanced understanding, a set of criteria was proposed and used to systematically examine the calibration methods. Besides theoretical analyses, a numerical testing method is also used in the examination. This study identified the basic requirements for each calibration method to obtain a unique calibration solution. This study also confirmed that the solution becomes more robust if more than sufficient calibration references are provided. Practically, however, as more references are used, more inconsistencies can arise among the measured data for representing the biodynamic properties. To help account for the relative reliabilities of the references, a baseline weighting scheme is proposed. The analyses suggest that the best choice of calibration method depends on the modeling purpose, the model structure, and the availability and reliability of representative reference data.

11. Phenomenological and theoretical models of dark matter density profiles of galaxy clusters

Silva, Leandro Beraldo e.; Sodre, Laerte; Lima, Marcos

2015-08-01

We use the stacked gravitational lensing mass profile of four high-mass (M ≳ 1015 Msun) galaxy clusters around z ≈ 0.3 from Umetsu et al. to fit density profiles of phenomenological [Navarro-Frenk-White (NFW), Einasto, Sérsic, Stadel, Baltz-Marshall-Oguri (BMO) and Hernquist] and theoretical (non-singular Isothermal Sphere, DARKexp and Kang & He) models of the dark matter distribution. We account for large-scale structure effects, including a two-halo term in the analysis. We find that the BMO model provides the best fit to the data as measured by the reduced chi2. It is followed by the Stadel profile, the generalized NFW profile with a free inner slope and by the Einasto profile. The NFW model provides the best fit if we neglect the two-halo term, in agreement with results from Umetsu et al. Among the theoretical profiles, the DARKexp model with a single form parameter has the best performance, very close to that of the BMO profile. This may indicate a connection between this theoretical model and the phenomenology of dark matter haloes, shedding light on the dynamical basis of empirical profiles which emerge from numerical simulations. We also propose an association between the phase-space mixing level of a self-gravitating system and the indistinguishability of its constituents (stars or dark matter particles). This represents a refinement in the study of systems exhibiting incomplete violent relaxation. Within a combinatorial analysis similar to that of Lynden-Bell, we make use of this association to obtain a distribution function that deviates from the Maxwell-Boltzmann distribution, leading to a new non-singular density profile for the dark matter of halos in equilibrium.

12. Experimental verification of a theoretical model of an active cladding optical fiber fluorosensor

NASA Technical Reports Server (NTRS)

Albin, Sacharia; Briant, Alvin L.; Egalon, Claudio O.; Rogowski, Robert S.; Nankung, Juock S.

1993-01-01

Experiments were conducted to verify a theoretical model on the injection efficiency of sources in the cladding of an optical fiber. The theoretical results predicted an increase in the injection efficiency for higher differences in refractive indices between the core and cladding. The experimental apparatus used consisted of a glass rod 50 cm long, coated at one end with a thin film of fluorescent substance. The fluorescent substance was excited with side illumination, perpendicular to the rod axis, using a 476 nm Argon-ion laser. Part of the excited fluorescence was injected into the core and guided to a detector. The signal was measured for several different cladding refractive indices. The cladding consisted of sugar dissolved in water and the refractive index was changed by varying the sugar concentration in the solution. The results indicate that the power injected into the rod, due to evanescent wave injection, increases with the difference in refractive index which is in qualitative agreement with theory.

13. High density monolayers of plasmid protein on latex particles: experiments and theoretical modeling

2015-04-01

Monolayers obtained by adsorption of the plasmid protein KfrA on negatively charged polystyrene latex particles under diffusion-controlled conditions at pH 3.5 were interpreted in terms of the random sequential adsorption (RSA) model. A quantitative agreement of the theoretical results derived from these calculations with experimental data was attained for the ionic strength from 0.15 up to 10-2 M. This confirmed the adsorption mechanism of KfrA molecules on latex in the form of tetramers up to 10-2 M. On the other hand, for the ionic strength of 10-3 M the experimental coverage agreed with theoretical predictions under the assumption that screening of electrostatic interaction is enhanced by the presence of counterions and negatively charged polymer chains stemming from latex particles.

14. Theoretical spectral properties of PAHs: towards a detailed model of their photophysics in the ISM

Malloci, Giuliano; Mulas, Giacomo; Porceddu, Ignazio

2005-01-01

In the framework of density functional theory (DFT) we computed the spectral properties of a total of about 20 polycyclic aromatic hydrocarbons (PAHs) in different charge states. From our complete atlas of PAHs, ranging in size from naphthalene (C10H8) to dicoronylene (C48H20), we present here a sample of results concerning both ground state and excited state properties. Our theoretical results are in reasonable agreement with the available experimental data. This makes them particularly precious when the latter are not easily obtainable, as is often the case for the highly reactive radicals and ions of such species. In another paper (Mulas et al., same volume) we show that our theoretical results can be reliably used to model the behaviour of these molecules in astrophysical environments.

15. Crisis Management Systems: A Case Study for Aspect-Oriented Modeling

Kienzle, Jörg; Guelfi, Nicolas; Mustafiz, Sadaf

The intent of this document is to define a common case study for the aspect-oriented modeling research community. The domain of the case study is crisis management systems, i.e., systems that help in identifying, assessing, and handling a crisis situation by orchestrating the communication between all parties involved in handling the crisis, by allocating and managing resources, and by providing access to relevant crisis-related information to authorized users. This document contains informal requirements of crisis management systems (CMSs) in general, a feature model for a CMS product line, use case models for a car crash CMS (CCCMS), a domain model for the CCCMS, an informal physical architecture description of the CCCMS, as well as some design models of a possible object-oriented implementation of parts of the CCCMS backend. AOM researchers who want to demonstrate the power of their AOM approach or technique can hence apply the approach at the most appropriate level of abstraction.

16. A thematic analysis of theoretical models for translational science in nursing: mapping the field.

PubMed

Mitchell, Sandra A; Fisher, Cheryl A; Hastings, Clare E; Silverman, Leanne B; Wallen, Gwenyth R

2010-01-01

The quantity and diversity of conceptual models in translational science may complicate rather than advance the use of theory. This paper offers a comparative thematic analysis of the models available to inform knowledge development, transfer, and utilization. Literature searches identified 47 models for knowledge translation. Four thematic areas emerged: (1) evidence-based practice and knowledge transformation processes, (2) strategic change to promote adoption of new knowledge, (3) knowledge exchange and synthesis for application and inquiry, and (4) designing and interpreting dissemination research. This analysis distinguishes the contributions made by leaders and researchers at each phase in the process of discovery, development, and service delivery. It also informs the selection of models to guide activities in knowledge translation. A flexible theoretical stance is essential to simultaneously develop new knowledge and accelerate the translation of that knowledge into practice behaviors and programs of care that support optimal patient outcomes. PMID:21074646

17. Constraints on field theoretical models for variation of the fine structure constant

Steinhardt, Charles L.

2005-02-01

Recent theoretical ideas and observational claims suggest that the fine structure constant α may be variable. We examine a spectrum of models in which α is a function of a scalar field. Specifically, we consider three scenarios: oscillating α, monotonic time variation of α, and time-independent α that is spatially varying. We examine the constraints imposed upon these theories by cosmological observations, particle detector experiments, and “fifth force” experiments. These constraints are very strong on models involving oscillation but cannot compete with bounds from the Oklo subnuclear reactor on models with monotonic timelike variation of α. One particular model with spatial variation is consistent with all current experimental and observational measurements, including those from two seemingly conflicting measurements of the fine structure constant using the many multiplet method on absorption lines.

18. A Thematic Analysis of Theoretical Models for Translational Science in Nursing: Mapping the Field

PubMed Central

Mitchell, Sandra A.; Fisher, Cheryl A.; Hastings, Clare E.; Silverman, Leanne B.; Wallen, Gwenyth R.

2010-01-01

Background The quantity and diversity of conceptual models in translational science may complicate rather than advance the use of theory. Purpose This paper offers a comparative thematic analysis of the models available to inform knowledge development, transfer, and utilization. Method Literature searches identified 47 models for knowledge translation. Four thematic areas emerged: (1) evidence-based practice and knowledge transformation processes; (2) strategic change to promote adoption of new knowledge; (3) knowledge exchange and synthesis for application and inquiry; (4) designing and interpreting dissemination research. Discussion This analysis distinguishes the contributions made by leaders and researchers at each phase in the process of discovery, development, and service delivery. It also informs the selection of models to guide activities in knowledge translation. Conclusions A flexible theoretical stance is essential to simultaneously develop new knowledge and accelerate the translation of that knowledge into practice behaviors and programs of care that support optimal patient outcomes. PMID:21074646

19. 3-D Human body models in C.A.D. : Anthropometric Aspects

Renaud, C.; Steck, R.; Pineau, J. C.

1986-07-01

Modeling and simulation methods of man-machine systems are developed at the laboratory by interactive infography and C.A.D. technics. In order to better apprehend the morphological variability of populations we have enriched the 3-D model with a parametric function using classical anthropometric dimensions. We have selected reference, associate and complementary dimensions : lengths, breadths, circumferences and depths, which depend on operator's tasks and characteristics of workplaces. All anthropometric values come from the International Data Bank of Human Biometry of ERGODATA System. The utilization of the parametric function brings a quick and accurate description of morphology for theoretic subjects and can be used in C.A.D. analysis.

20. Theoretical Hill-type muscle and stability: numerical model and application.

PubMed

Schmitt, S; Günther, M; Rupp, T; Bayer, A; Häufle, D

2013-01-01

The construction of artificial muscles is one of the most challenging developments in today's biomedical science. The application of artificial muscles is focused both on the construction of orthotics and prosthetics for rehabilitation and prevention purposes and on building humanoid walking machines for robotics research. Research in biomechanics tries to explain the functioning and design of real biological muscles and therefore lays the fundament for the development of functional artificial muscles. Recently, the hyperbolic Hill-type force-velocity relation was derived from simple mechanical components. In this contribution, this theoretical yet biomechanical model is transferred to a numerical model and applied for presenting a proof-of-concept of a functional artificial muscle. Additionally, this validated theoretical model is used to determine force-velocity relations of different animal species that are based on the literature data from biological experiments. Moreover, it is shown that an antagonistic muscle actuator can help in stabilising a single inverted pendulum model in favour of a control approach using a linear torque generator. PMID:24319495

1. A comprehensive theoretical model for on-chip microring-based photonic fractional differentiators

PubMed Central

Jin, Boyuan; Yuan, Jinhui; Wang, Kuiru; Sang, Xinzhu; Yan, Binbin; Wu, Qiang; Li, Feng; Zhou, Xian; Zhou, Guiyao; Yu, Chongxiu; Lu, Chao; Yaw Tam, Hwa; Wai, P. K. A.

2015-01-01

Microring-based photonic fractional differentiators play an important role in the on-chip all-optical signal processing. Unfortunately, the previous works do not consider the time-reversal and the time delay characteristics of the microring-based fractional differentiator. They also do not include the effect of input pulse width on the output. In particular, it cannot explain why the microring-based differentiator with the differentiation order n > 1 has larger output deviation than that with n < 1, and why the microring-based differentiator cannot reproduce the three-peak output waveform of an ideal differentiator with n > 1. In this paper, a comprehensive theoretical model is proposed. The critically-coupled microring resonator is modeled as an ideal first-order differentiator, while the under-coupled and over-coupled resonators are modeled as the time-reversed ideal fractional differentiators. Traditionally, the over-coupled microring resonators are used to form the differentiators with 1 < n < 2. However, we demonstrate that smaller fitting error can be obtained if the over-coupled microring resonator is fitted by an ideal differentiator with n < 1. The time delay of the differentiator is also considered. Finally, the influences of some key factors on the output waveform and deviation are discussed. The proposed theoretical model is beneficial for the design and application of the microring-based fractional differentiators. PMID:26381934

2. Theoretical Hill-Type Muscle and Stability: Numerical Model and Application

PubMed Central

Schmitt, S.; Günther, M.; Rupp, T.; Bayer, A.; Häufle, D.

2013-01-01

The construction of artificial muscles is one of the most challenging developments in today's biomedical science. The application of artificial muscles is focused both on the construction of orthotics and prosthetics for rehabilitation and prevention purposes and on building humanoid walking machines for robotics research. Research in biomechanics tries to explain the functioning and design of real biological muscles and therefore lays the fundament for the development of functional artificial muscles. Recently, the hyperbolic Hill-type force-velocity relation was derived from simple mechanical components. In this contribution, this theoretical yet biomechanical model is transferred to a numerical model and applied for presenting a proof-of-concept of a functional artificial muscle. Additionally, this validated theoretical model is used to determine force-velocity relations of different animal species that are based on the literature data from biological experiments. Moreover, it is shown that an antagonistic muscle actuator can help in stabilising a single inverted pendulum model in favour of a control approach using a linear torque generator. PMID:24319495

3. The coupled effects of carbon and nitrogen on soil decomposition: A theoretical model

Darby, B.; Finzi, A.

2013-12-01

Soil organic matter (SOM) plays a crucial role in the carbon (C) cycle, holding 2.5 times more carbon than plant biomass. Ecosystem models predict that climate warming will stimulate decomposition of soil carbon stocks, in turn leading to positive feedbacks on warming. Recent empirical studies and modeling work has revealed the importance of microbial physiology and exoenzyme kinetics in driving SOM decomposition. Existing mathematical models describe the microbial processes and biophysics involved in the decomposition. However, although decomposition by nitrogen-degrading enzymes is included in some models, nitrogen (N) does not drive model behavior and there are no reaction kinetics associated with the depolymerization or uptake of N. Additionally, very few empirically measured kinetic values exist for N-degrading enzymes or the uptake of N by microbes. This study proposes a theoretical model of SOM decomposition based on the principles of exoenzyme kinetics and microbial biophysics that explicitly links C and N through microbial uptake and SOM decomposition kinetics and by placing stoichiometric constraints on microbial growth and exoenzyme production. After constructing the model framework, the model was then used to test soil-carbon responses to warming, and to explore the importance of N uptake and depolymerization kinetics in driving decomposition. The model predictions suggest that the response of kinetics to temperature are more important than microbial responses in determining decomposition rates. Additionally, variations in the kinetics of N depolymerization affected decomposition rates, whereas N uptake kinetics and their effect on enzyme production had almost no effect. The model outputs were also compared to a C-only model framework in order to assess the effects of N on model behavior. The incorporation of N into a SOM decomposition model produced different, and in some cases, contradictory results as compared to a C-only model. Overall, these

4. Theoretical model and experimental investigation of current density boundary condition for welding arc study

Boutaghane, A.; Bouhadef, K.; Valensi, F.; Pellerin, S.; Benkedda, Y.

2011-04-01

This paper presents results of theoretical and experimental investigation of the welding arc in Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) processes. A theoretical model consisting in simultaneous resolution of the set of conservation equations for mass, momentum, energy and current, Ohm's law and Maxwell equation is used to predict temperatures and current density distribution in argon welding arcs. A current density profile had to be assumed over the surface of the cathode as a boundary condition in order to make the theoretical calculations possible. In stationary GTAW process, this assumption leads to fair agreement with experimental results reported in literature with maximum arc temperatures of ~21 000 K. In contrast to the GTAW process, in GMAW process, the electrode is consumable and non-thermionic, and a realistic boundary condition of the current density is lacking. For establishing this crucial boundary condition which is the current density in the anode melting electrode, an original method is setup to enable the current density to be determined experimentally. High-speed camera (3000 images/s) is used to get geometrical dimensions of the welding wire used as anode. The total area of the melting anode covered by the arc plasma being determined, the current density at the anode surface can be calculated. For a 330 A arc, the current density at the melting anode surface is found to be of 5 × 107 A m-2 for a 1.2 mm diameter welding electrode.

5. Inverse Mathematical Model: Yet Another Aspect of Applications and Modeling in Undergraduate Mathematics for Prospective Teachers

ERIC Educational Resources Information Center

Peretz, Dvora

2005-01-01

This article conceptualises a real-like model of a mathematical model as an inverse model. The inverse model draws on the un-complexity of concrete real life operations in order to help students to add concrete meaning to mathematical algorithms. The inverse model is described in the context of a pedagogical perception, which grants students in…

6. Theoretically modeling the low-latitude, ionospheric response to large geomagnetic storms

Anderson, D.; Anghel, A.; Araujo, E.; Eccles, V.; Valladares, C.; Lin, C.

2006-10-01

In the low-latitude, ionospheric F region, the primary transport mechanism that determines the electron and ion density distributions is the magnitude of the daytime, upward E × B drift velocity. During large geomagnetic storms, penetration of high-latitude electric fields to low latitudes can often produce daytime, vertical E × B drift velocities in excess of 50 m/s. Employing a recently developed technique, we can infer these daytime, upward E × B drift velocities from ground-based magnetometer observations at Jicamarca and Piura, Peru, as a function of local time (0700-1700 LT). We study the ionospheric response in the Peruvian longitude sector to these large upward drifts by theoretically calculating electron and ion densities as a function of altitude, latitude, and local time using the time-dependent Low-Latitude Ionospheric Sector (LLIONS) model. This is a single-sector ionosphere model capable of incorporating data-determined drivers, such as E × B drift velocities. For this study, we choose three large storms in 2003 (29 and 30 October and 20 November) when daytime E × B drift velocities approached or exceeded 50 m/s. Initial results indicate that the large, upward E × B drift velocities on 29 October produced equatorial anomaly crests in ionization at ±20° dip latitude rather than the usual ±16° dip latitude. We compare the theoretically calculated results with a variety of ground-based and satellite observations for these three periods and discuss the implications of these comparisons as they relate to the capabilities of current theoretical models and our ability to infer ionospheric drivers such as E × B drifts (Anderson et al., 2002).

7. Elements of a flexible approach for conceptual hydrological modeling: 1. Motivation and theoretical development

Fenicia, Fabrizio; Kavetski, Dmitri; Savenije, Hubert H. G.

2011-11-01

This paper introduces a flexible framework for conceptual hydrological modeling, with two related objectives: (1) generalize and systematize the currently fragmented field of conceptual models and (2) provide a robust platform for understanding and modeling hydrological systems. In contrast to currently dominant "fixed" model applications, the flexible framework proposed here allows the hydrologist to hypothesize, build, and test different model structures using combinations of generic components. This is particularly useful for conceptual modeling at the catchment scale, where limitations in process understanding and data availability remain major research and operational challenges. The formulation of the model architecture and individual components to represent distinct aspects of catchment-scale function, such as storage, release, and transmission of water, is discussed. Several numerical strategies for implementing the model equations within a computationally robust framework are also presented. In the companion paper, the potential of the flexible framework is examined with respect to supporting more systematic and stringent hypothesis testing, for characterizing catchment diversity, and, more generally, for aiding progress toward more unified hydrological theory at the catchment scale.

8. Cohesive surface model for fracture based on a two-scale formulation: computational implementation aspects

Toro, S.; Sánchez, P. J.; Podestá, J. M.; Blanco, P. J.; Huespe, A. E.; Feijóo, R. A.

2016-07-01

The paper describes the computational aspects and numerical implementation of a two-scale cohesive surface methodology developed for analyzing fracture in heterogeneous materials with complex micro-structures. This approach can be categorized as a semi-concurrent model using the representative volume element concept. A variational multi-scale formulation of the methodology has been previously presented by the authors. Subsequently, the formulation has been generalized and improved in two aspects: (i) cohesive surfaces have been introduced at both scales of analysis, they are modeled with a strong discontinuity kinematics (new equations describing the insertion of the macro-scale strains, into the micro-scale and the posterior homogenization procedure have been considered); (ii) the computational procedure and numerical implementation have been adapted for this formulation. The first point has been presented elsewhere, and it is summarized here. Instead, the main objective of this paper is to address a rather detailed presentation of the second point. Finite element techniques for modeling cohesive surfaces at both scales of analysis (FE^2 approach) are described: (i) finite elements with embedded strong discontinuities are used for the macro-scale simulation, and (ii) continuum-type finite elements with high aspect ratios, mimicking cohesive surfaces, are adopted for simulating the failure mechanisms at the micro-scale. The methodology is validated through numerical simulation of a quasi-brittle concrete fracture problem. The proposed multi-scale model is capable of unveiling the mechanisms that lead from the material degradation phenomenon at the meso-structural level to the activation and propagation of cohesive surfaces at the structural scale.

9. Satellite, climatological, and theoretical inputs for modeling of the diurnal cycle of fire emissions

Hyer, E. J.; Reid, J. S.; Schmidt, C. C.; Giglio, L.; Prins, E.

2009-12-01

The diurnal cycle of fire activity is crucial for accurate simulation of atmospheric effects of fire emissions, especially at finer spatial and temporal scales. Estimating diurnal variability in emissions is also a critical problem for construction of emissions estimates from multiple sensors with variable coverage patterns. An optimal diurnal emissions estimate will use as much information as possible from satellite fire observations, compensate known biases in those observations, and use detailed theoretical models of the diurnal cycle to fill in missing information. As part of ongoing improvements to the Fire Location and Monitoring of Burning Emissions (FLAMBE) fire monitoring system, we evaluated several different methods of integrating observations with different temporal sampling. We used geostationary fire detections from WF_ABBA, fire detection data from MODIS, empirical diurnal cycles from TRMM, and simple theoretical diurnal curves based on surface heating. Our experiments integrated these data in different combinations to estimate the diurnal cycles of emissions for each location and time. Hourly emissions estimates derived using these methods were tested using an aerosol transport model. We present results of this comparison, and discuss the implications of our results for the broader problem of multi-sensor data fusion in fire emissions modeling.

10. Inclusion of persistence length-based secondary structure in replica field theoretic models of heteropolymer freezing

Weber, Jeffrey K.; Pande, Vijay S.

2013-09-01

The protein folding problem has long represented a "holy grail" in statistical physics due to its physical complexity and its relevance to many human diseases. While past theoretical work has yielded apt descriptions of protein folding landscapes, recent large-scale simulations have provided insights into protein folding that were impractical to obtain from early theories. In particular, the role that non-native contacts play in protein folding, and their relation to the existence of misfolded, β-sheet rich trap states on folding landscapes, has emerged as a topic of interest in the field. In this paper, we present a modified model of heteropolymer freezing that includes explicit secondary structural characteristics which allow observations of "intramolecular amyloid" states to be probed from a theoretical perspective. We introduce a variable persistence length-based energy penalty to a model Hamiltonian, and we illustrate how this modification alters the phase transitions present in the theory. We find, in particular, that inclusion of this variable persistence length increases both generic freezing and folding temperatures in the model, allowing both folding and glass transitions to occur in a more highly optimized fashion. We go on to discuss how these changes might relate to protein evolution, misfolding, and the emergence of intramolecular amyloid states.

11. Theoretical model for the evaporation loss of PM2.5 during filter sampling

Liu, Chun-Nan; Lin, Sih-Fan; Tsai, Chuen-Jinn; Wu, Yueh-Chuen; Chen, Chung-Fang

2015-05-01

The evaporation losses of PM2.5 particles in eight different size ranges corresponding to the 4th-10th stages and after filter of the MOUDI were calculated theoretically and then integrated to obtain the total PM2.5 evaporation loss. Results show that when PM2.5 particles are nearly neutral with pH in the range of 7-8, the evaporated concentrations predicted by the present model agree well with the experimental data with an average absolute difference of 20.2 ± 11.1%. When PM2.5 aerosols are acidic with pH less than 3.5, additional loss of nitrate and chloride can occur due to chemical interactions between collected particles and strong acids which are not considered in the present model. Under pH neutral conditions, the theoretical model was then used to examine the effect of PM2.5 concentration, gas-to-particle ratio, ambient temperature and relative humidity on the extent of evaporation loss. Results show that evaporated PM2.5 concentration increases with increasing temperature and decreasing relative humidity, PM2.5 concentration and gas-to-particle ratio.

12. The nature of voids - I. Watershed void finders and their connection with theoretical models

2015-12-01

The statistical study of voids in the matter distribution promises to be an important tool for precision cosmology, but there are known discrepancies between theoretical models of voids and the voids actually found in large simulations or galaxy surveys. The empirical properties of observed voids are also not well understood. In this paper, we study voids in an N-body simulation, using the ZOBOV watershed algorithm. As in other studies, we use sets of subsampled dark matter particles as tracers to identify voids, but we use the full-resolution simulation output to measure dark matter densities at the identified locations. Voids span a wide range of sizes and densities, but there is a clear trend towards larger voids containing deeper density minima, a trend which is expected for all watershed void finders. We also find that the tracer density at void locations is usually smaller than the true density, and that this relationship depends on the sampling density of tracers. We show that fits given in the literature fail to match the observed density profiles of voids. The average enclosed density contrast within watershed voids varies widely with both the size of the void and the minimum density within it, but is always far from the shell-crossing threshold expected from theoretical models. Voids with deeper density minima also show much broader density profiles. We discuss the implications of these results for the excursion set approach to modelling such voids.

13. A theoretical model of speed-dependent steering torque for rolling tyres

Wei, Yintao; Oertel, Christian; Liu, Yahui; Li, Xuebing

2016-04-01

It is well known that the tyre steering torque is highly dependent on the tyre rolling speed. In limited cases, i.e. parking manoeuvre, the steering torque approaches the maximum. With the increasing tyre speed, the steering torque decreased rapidly. Accurate modelling of the speed-dependent behaviour for the tyre steering torque is a key factor to calibrate the electric power steering (EPS) system and tune the handling performance of vehicles. However, no satisfactory theoretical model can be found in the existing literature to explain this phenomenon. This paper proposes a new theoretical framework to model this important tyre behaviour, which includes three key factors: (1) tyre three-dimensional transient rolling kinematics with turn-slip; (2) dynamical force and moment generation; and (3) the mixed Lagrange-Euler method for contact deformation solving. A nonlinear finite-element code has been developed to implement the proposed approach. It can be found that the main mechanism for the speed-dependent steering torque is due to turn-slip-related kinematics. This paper provides a theory to explain the complex mechanism of the tyre steering torque generation, which helps to understand the speed-dependent tyre steering torque, tyre road feeling and EPS calibration.

14. Theoretical analysis of electronic absorption spectra of vitamin B12 models

Andruniow, Tadeusz; Kozlowski, Pawel M.; Zgierski, Marek Z.

2001-10-01

Time-dependent density-functional theory (TD-DFT) is applied to analyze the electronic absorption spectra of vitamin B12. To accomplish this two model systems were considered: CN-[CoIII-corrin]-CN (dicyanocobinamide, DCC) and imidazole-[CoIII-corrin]-CN (cyanocobalamin, ImCC). For both models 30 lowest excited states were calculated together with transition dipole moments. When the results of TD-DFT calculations were directly compared with experiment it was found that the theoretical values systematically overestimate experimental data by approximately 0.5 eV. The uniform adjustment of the calculated transition energies allowed detailed analysis of electronic absorption spectra of vitamin B12 models. All absorption bands in spectral range 2.0-5.0 eV were readily assigned. In particular, TD-DFT calculations were able to explain the origin of the shift of the lowest absorption band caused by replacement of the-CN axial ligand by imidazole.

15. Effects of pump recycling technique on stimulated Brillouin scattering threshold: a theoretical model.

PubMed

Al-Asadi, H A; Al-Mansoori, M H; Ajiya, M; Hitam, S; Saripan, M I; Mahdi, M A

2010-10-11

We develop a theoretical model that can be used to predict stimulated Brillouin scattering (SBS) threshold in optical fibers that arises through the effect of Brillouin pump recycling technique. Obtained simulation results from our model are in close agreement with our experimental results. The developed model utilizes single mode optical fiber of different lengths as the Brillouin gain media. For 5-km long single mode fiber, the calculated threshold power for SBS is about 16 mW for conventional technique. This value is reduced to about 8 mW when the residual Brillouin pump is recycled at the end of the fiber. The decrement of SBS threshold is due to longer interaction lengths between Brillouin pump and Stokes wave. PMID:20941134

16. Theoretical modelling of physiologically stretched vessel in magnetisable stent assisted magnetic drug targetingapplication

2011-02-01

The magnetisable stent assisted magnetic targeted drug delivery system in a physiologically stretched vessel is considered theoretically. The changes in the mechanical behaviour of the vessel are analysed under the influence of mechanical forces generated by blood pressure. In this 2D mathematical model a ferromagnetic, coiled wire stent is implanted to aid collection of magnetic drug carrier particles in an elastic tube, which has similar mechanical properties to the blood vessel. A cyclic mechanical force is applied to the elastic tube to mimic the mechanical stress and strain of both the stent and vessel while in the body due to pulsatile blood circulation. The magnetic dipole-dipole and hydrodynamic interactions for multiple particles are included and agglomeration of particles is also modelled. The resulting collection efficiency of the mathematical model shows that the system performance can decrease by as much as 10% due to the effects of the pulsatile blood circulation.

17. B → K∗ ℓ + ℓ - decays at large recoil in the Standard Model: a theoretical reappraisal

Ciuchini, Marco; Fedele, Marco; Franco, Enrico; Mishima, Satoshi; Paul, Ayan; Silvestrini, Luca; Valli, Mauro

2016-06-01

We critically reassess the theoretical uncertainties in the Standard Model calculation of the B → K ∗ ℓ + ℓ - observables, focusing on the low q 2 region. We point out that even optimized observables are affected by sizable uncertainties, since hadronic contributions generated by current-current operators with charm are difficult to estimate, especially for q 2 ˜ 4 m c 2 ≃ 6.8 GeV2. We perform a detailed numerical analysis and present both predictions and results from the fit obtained using most recent data. We find that non-factorizable power corrections of the expected order of magnitude are sufficient to give a good description of current experimental data within the Standard Model. We discuss in detail the q 2 dependence of the corrections and their possible interpretation as shifts of the Standard Model Wilson coefficients.

18. Theoretical models of interstellar shocks. I - Radiative transfer and UV precursors

NASA Technical Reports Server (NTRS)

Shull, J. M.; Mckee, C. F.

1979-01-01

Theoretical models of interstellar radiative shocks are constructed, with special attention to the transfer of ionizing radiation. These models are 'self-consistent' in the sense that the emergent ionizing radiation (the UV precursor) is coupled with the ionization state of H, He, and the metals in the preshock gas. For shock velocities of at least 110 km/s the shocks generate sufficient UV radiation for complete preionization of H and He, the latter to He(+). At lower velocities the preionization can be much smaller, with important consequences for the cooling function, the shock structure, and the emission. For models with shock velocities of 40 to 130 km/s the intensities of the strongest emission lines in the UV, optical, and infrared are tabulated, as well as postshock column densities of metal ions potentially observable by UV absorption spectroscopy. Possible applications to supernova remnants and high-velocity interstellar gas are assessed.

19. Inference of ICF Implosion Core Mix using Experimental Data and Theoretical Mix Modeling

SciTech Connect

Welser-Sherrill, L; Haynes, D A; Mancini, R C; Cooley, J H; Tommasini, R; Golovkin, I E; Sherrill, M E; Haan, S W

2008-04-30

The mixing between fuel and shell materials in Inertial Confinement Fusion (ICF) implosion cores is a current topic of interest. The goal of this work was to design direct-drive ICF experiments which have varying levels of mix, and subsequently to extract information on mixing directly from the experimental data using spectroscopic techniques. The experimental design was accomplished using hydrodynamic simulations in conjunction with Haan's saturation model, which was used to predict the mix levels of candidate experimental configurations. These theoretical predictions were then compared to the mixing information which was extracted from the experimental data, and it was found that Haan's mix model performed well in predicting trends in the width of the mix layer. With these results, we have contributed to an assessment of the range of validity and predictive capability of the Haan saturation model, as well as increased our confidence in the methods used to extract mixing information from experimental data.

20. Inference of ICF implosion core mix using experimental data and theoretical mix modeling

SciTech Connect

Sherrill, Leslie Welser; Haynes, Donald A; Cooley, James H; Sherrill, Manolo E; Mancini, Roberto C; Tommasini, Riccardo; Golovkin, Igor E; Haan, Steven W

2009-01-01

The mixing between fuel and shell materials in Inertial Confinement Fusion (lCF) implosion cores is a current topic of interest. The goal of this work was to design direct-drive ICF experiments which have varying levels of mix, and subsequently to extract information on mixing directly from the experimental data using spectroscopic techniques. The experimental design was accomplished using hydrodynamic simulations in conjunction with Haan's saturation model, which was used to predict the mix levels of candidate experimental configurations. These theoretical predictions were then compared to the mixing information which was extracted from the experimental data, and it was found that Haan's mix model predicted trends in the width of the mix layer as a function of initial shell thickness. These results contribute to an assessment of the range of validity and predictive capability of the Haan saturation model, as well as increasing confidence in the methods used to extract mixing information from experimental data.

1. Theoretical shell-model signatures in heavy-ion, coherent pion production

NASA Technical Reports Server (NTRS)

Maung, Khin M.; Deutchman, P. A.; Buvel, R. L.

1992-01-01

A comprehensive summary of a many-body, microscopic, particle-hole formalism is presented that describes coherent, subthreshold, pion production in peripheral, heavy-ion collisions. The formalism uses a new separable model transition interaction that produces Delta-hole states in either the projectile or target nucleus. Shell-model states described by harmonic oscillator functions are used in the calculation of Delta formation and decay and Lorentz-contraction effects of the nucleus not at rest are included. An analytical expression to lowest multipole order for the differential cross section is examined. The sensitivity of the theoretical results to the shell-model states is determined with preliminary shape results compared with data. The effects of higher multipoles are examined with attention paid to the second-order multipole value.

2. The calculation of theoretical chromospheric models and the interpretation of solar spectra from rockets and spacecraft

NASA Technical Reports Server (NTRS)

Avrett, E. H.

1984-01-01

Models and spectra of sunspots were studied, because they are important to energy balance and variability discussions. Sunspot observations in the ultraviolet region 140 to 168 nn was obtained by the NRL High Resolution Telescope and Spectrograph. Extensive photometric observations of sunspot umbrae and prenumbrae in 10 chanels covering the wavelength region 387 to 3800 nm were made. Cool star opacities and model atmospheres were computed. The Sun is the first testcase, both to check the opacity calculations against the observed solar spectrum, and to check the purely theoretical model calculation against the observed solar energy distribution. Line lists were finally completed for all the molecules that are important in computing statistical opacities for energy balance and for radiative rate calculations in the Sun (except perhaps for sunspots). Because many of these bands are incompletely analyzed in the laboratory, the energy levels are not well enough known to predict wavelengths accurately for spectrum synthesis and for detailed comparison with the observations.

3. Microscopic theoretical model study of band gap opening in AA-stacked bi-layer graphene

Sahu, Sivabrata; Parashar, S. K. S.; Rout, G. C.

2016-05-01

We address here a tight-binding theoretical model calculation for AA-stacked bi-layer graphene taking into account of a biased potential between two layers to study the density of states and the band dispersion within the total Brillouin zone. We have calculated the electronic Green's function for electron operator corresponding to A and B sub lattices by Zubarev's Green's function technique from which the electronic density of states and the electron band energy dispersion are calculated. The numerically computed density of states and band energy dispersions are investigated by tuning the biased potential to exhibit the band gap by varying the different physical parameters.

4. [The professional differentiation in medical practice. A theoretical model of the process of changing].

PubMed

Zerón-Gutiérrez, Lydia Estela; Lifshitz, Alberto; Ramiro H, Manuel; Abreu-Hernández, Luis Felipe; Reyes-Lagunes, Isabel

2012-01-01

The structure of the change process on medical professionalization has not being studied enough. The physicians are made aware of the necessity of changing their medical practice in ways that also affect their personal life. A change involves the need to plan, evaluate possibilities and resources with efficacy and outline competencies. The aim is to contribute in the design of educational strategies that promote professional change and an understanding of change, as an evolution; we describe a theoretical-schematic model based on five consecutive ordained scopes: background, intentions, planning and making decisions, carrying out decisions and achieving the goal. PMID:23331751

5. Theoretical model study of dynamic ferromagnetic susceptibility in mono-layer graphene

Sahu, Sivabrata; Parashar, S. K. S.; Rout, G. C.

2016-04-01

We report here a microscopic theoretical study of dynamic ferromagnetic spin susceptibility of electrons for graphene systems, which deal with a tight-binding model Hamiltonian consisting of the hopping of electrons up to third-nearest-neighbors, impurity and substrate effects besides Coulomb interaction of electrons at A-and B- sub- lattices. The spin susceptibility involves four two-particle Green's functions, which are calculated by Zubarev's Green's function technique. The up and down electron occupancies at A and B sub-lattices are computed numerically and self-consistently. The temperature dependent susceptibility shows a pronounced peak at Curie temperature for critical Coulomb interaction Uc = 2.2t1.

6. Multimode cavity QED 2: Parameter dependence and limitations through theoretical modeling

Groszkowski, Peter; Leung, Nelson; Naik, Ravi; Chakram, Srivatsan; Schuster, David; Koch, Jens

Superconducting circuits are well-established as promising building blocks for future quantum information processing devices. While in recent years gate and readout fidelities have improved significantly, superconducting qubits can still benefit greatly from added intrinsic robustness and improved error resilience. In this talk, we present results for qubits based on the modes of a 1d resonator array, where qubit manipulation and readout are achieved by interaction with a parametrically driven superconducting transmon. Through theoretical modeling, we provide insight into mode addressability as well as crosstalk, and their dependence on the system's size in various parameter regimes.

7. Morphology of synthetic chrysoberyl and alexandrite crystals: Analysis of experimental data and theoretical modeling

Gromalova, N. A.; Eremin, N. N.; Dorokhova, G. I.; Urusov, V. S.

2012-07-01

A morphological analysis of chrysoberyl and alexandrite crystals obtained by flux crystallization has been performed. Seven morphological types of crystals are selected. The surface energies of the faces of chrysoberyl and alexandrite crystals and their isostructural analogs, BeCr2O4 and BeFe2O4, have been calculated by atomistic computer modeling using the Metadise program. A "combined" approach is proposed which takes into account both the structural geometry and the surface energy of the faces and thus provides better agreement between the theoretical and experimentally observed faceting of chrysoberyl and alexandrite crystals.

8. (A whistle-stop tour of) theoretical models of diffraction in DIS

McDermott, M. F.

1997-04-01

The purpose of this talk was to present a very brief overview of theoretical models of diffraction in deep inelastic scattering (DIS). In particular, predictions for the behaviour of the diffractive structure functions F2D, RD are presented. The measurement of these functions at both small and high values of the variable β and their evolution with Q2 is expected to reveal crucial information concerning the underlying dynamics. This talk is based on the more extensive review [1] which also discusses expectations for charm in diffraction and contains a more complete list of references.

9. B(s,d)→ℓ(+)ℓ(-) in the standard model with reduced theoretical uncertainty.

PubMed

Bobeth, Christoph; Gorbahn, Martin; Hermann, Thomas; Misiak, Mikołaj; Stamou, Emmanuel; Steinhauser, Matthias

2014-03-14

We combine our new results for the O(αem) and O(αs2) corrections to Bs,d→ℓ+ℓ-, and present updated branching ratio predictions for these decays in the standard model. Inclusion of the new corrections removes major theoretical uncertainties of perturbative origin that have just begun to dominate over the parametric ones. For the recently observed muonic decay of the Bs meson, our calculation gives B¯(Bs→μ+μ-)=(3.65±0.23)×10-9. PMID:24679279

10. Bs,d→ℓ+ℓ- in the Standard Model with Reduced Theoretical Uncertainty

Bobeth, Christoph; Gorbahn, Martin; Hermann, Thomas; Misiak, Mikołaj; Stamou, Emmanuel; Steinhauser, Matthias

2014-03-01

We combine our new results for the O(αem) and O(αs2) corrections to Bs,d→ℓ+ℓ-, and present updated branching ratio predictions for these decays in the standard model. Inclusion of the new corrections removes major theoretical uncertainties of perturbative origin that have just begun to dominate over the parametric ones. For the recently observed muonic decay of the Bs meson, our calculation gives B¯(Bs→μ+μ-)=(3.65±0.23)×10-9.

11. Theoretical models for cooperative steady-state ATPase activity of myosin subfragment-1 on regulated actin.

PubMed Central

Hill, T L; Eisenberg, E; Chalovich, J M

1981-01-01

Recent theoretical work on the cooperative equilibrium binding of myosin subfragment-1-ADP to regulated actin, as influenced by Ca2+, is extended here to the cooperative steady-state ATPase activity of myosin subfragment-1 on regulated actin. Exact solution of the general steady-state problem will require Monte Carlo calculations. Three interrelated special cases are discussed in some detail and sample computer (not Monte Carlo) solutions are given. The eventual objective is to apply these considerations to in vitro experimental data and to in vivo muscle models. PMID:6455170

12. Information-theoretic model selection and model averaging for closed-population capture-recapture studies

USGS Publications Warehouse

Stanley, T.R.; Burnham, K.P.

1998-01-01

Specification of an appropriate model is critical to valid stalistical inference. Given the "true model" for the data is unknown, the goal of model selection is to select a plausible approximating model that balances model bias and sampling variance. Model selection based on information criteria such as AIC or its variant AICc, or criteria like CAIC, has proven useful in a variety of contexts including the analysis of open-population capture-recapture data. These criteria have not been intensively evaluated for closed-population capture-recapture models, which are integer parameter models used to estimate population size (N), and there is concern that they will not perform well. To address this concern, we evaluated AIC, AICc, and CAIC model selection for closed-population capture-recapture models by empirically assessing the quality of inference for the population size parameter N. We found that AIC-, AICc-, and CAIC-selected models had smaller relative mean squared errors than randomly selected models, but that confidence interval coverage on N was poor unless unconditional variance estimates (which incorporate model uncertainty) were used to compute confidence intervals. Overall, AIC and AICc outperformed CAIC, and are preferred to CAIC for selection among the closed-population capture-recapture models we investigated. A model averaging approach to estimation, using AIC. AICc, or CAIC to estimate weights, was also investigated and proved superior to estimation using AIC-, AICc-, or CAIC-selected models. Our results suggested that, for model averaging, AIC or AICc. should be favored over CAIC for estimating weights.

13. Game Theoretic Modeling of Water Resources Allocation Under Hydro-Climatic Uncertainty

Brown, C.; Lall, U.; Siegfried, T.

2005-12-01

Typical hydrologic and economic modeling approaches rely on assumptions of climate stationarity and economic conditions of ideal markets and rational decision-makers. In this study, we incorporate hydroclimatic variability with a game theoretic approach to simulate and evaluate common water allocation paradigms. Game Theory may be particularly appropriate for modeling water allocation decisions. First, a game theoretic approach allows economic analysis in situations where price theory doesn't apply, which is typically the case in water resources where markets are thin, players are few, and rules of exchange are highly constrained by legal or cultural traditions. Previous studies confirm that game theory is applicable to water resources decision problems, yet applications and modeling based on these principles is only rarely observed in the literature. Second, there are numerous existing theoretical and empirical studies of specific games and human behavior that may be applied in the development of predictive water allocation models. With this framework, one can evaluate alternative orderings and rules regarding the fraction of available water that one is allowed to appropriate. Specific attributes of the players involved in water resources management complicate the determination of solutions to game theory models. While an analytical approach will be useful for providing general insights, the variety of preference structures of individual players in a realistic water scenario will likely require a simulation approach. We propose a simulation approach incorporating the rationality, self-interest and equilibrium concepts of game theory with an agent-based modeling framework that allows the distinct properties of each player to be expressed and allows the performance of the system to manifest the integrative effect of these factors. Underlying this framework, we apply a realistic representation of spatio-temporal hydrologic variability and incorporate the impact of

14. Theoretical model of aerodynamic forces at high speeds and angle of attack in a stratified flowfield of UF6

SciTech Connect

Harloff, G.J.

1985-09-01

A theoretical aerodynamic model of lift and drag forces on a flat plate at angle of attack and at hypersonic speeds is presented. Real gas effects and friction drag are accounted for. Theoretical results are presented as a function of the viscous interaction parameter. The performance for two geometries is presented. 3 refs., 8 figs., 4 tabs.

15. Toward a Theoretical Model of Decision-Making and Resistance to Change among Higher Education Online Course Designers

ERIC Educational Resources Information Center

Dodd, Bucky J.

2013-01-01

Online course design is an emerging practice in higher education, yet few theoretical models currently exist to explain or predict how the diffusion of innovations occurs in this space. This study used a descriptive, quantitative survey research design to examine theoretical relationships between decision-making style and resistance to change…

16. Experimental observation, theoretical models, and biomechanical inference in the study of mandibular form.

PubMed

Daegling, D J; Hylander, W L

2000-08-01

Experimental studies and mathematical models are disparate approaches for inferring the stress and strain environment in mammalian jaws. Experimental designs offer accurate, although limited, characterization of biomechanical behavior, while mathematical approaches (finite element modeling in particular) offer unparalleled precision in depiction of strain magnitudes, directions, and gradients throughout the mandible. Because the empirical (experimental) and theoretical (mathematical) perspectives differ in their initial assumptions and their proximate goals, the two methods can yield divergent conclusions about how masticatory stresses are distributed in the dentary. These different sources of inference may, therefore, tangibly influence subsequent biological interpretation. In vitro observation of bone strain in primate mandibles under controlled loading conditions offers a test of finite element model predictions. Two issues which have been addressed by both finite element models and experimental approaches are: (1) the distribution of torsional shear strains in anthropoid jaws and (2) the dissipation of bite forces in the human alveolar process. Not surprisingly, the experimental data and mathematical models agree on some issues, but on others exhibit discordance. Achieving congruence between these methods is critical if the nature of the relationship of masticatory stress to mandibular form is to be intelligently assessed. A case study of functional/mechanical significance of gnathic morphology in the hominid genus Paranthropus offers insight into the potential benefit of combining theoretical and experimental approaches. Certain finite element analyses claim to have identified a biomechanical problem unrecognized in previous comparative work, which, in essence, is that the enlarged transverse dimensions of the postcanine corpus may have a less important role in resisting torsional stresses than previously thought. Experimental data have identified

17. Theoretical model atmosphere spectra used for the calibration of infrared instruments

Decin, L.; Eriksson, K.

2007-09-01

Context: One of the key ingredients in establishing the relation between input signal and output flux from a spectrometer is accurate determination of the spectrophotometric calibration. In the case of spectrometers onboard satellites, the accuracy of this part of the calibration pedigree is ultimately linked to the accuracy of the set of reference spectral energy distributions (SEDs) that the spectrophotometric calibration is built on. Aims: In this paper, we deal with the spectrophotometric calibration of infrared (IR) spectrometers onboard satellites in the 2 to 200 μm wavelength range. We aim at comparing the different reference SEDs used for the IR spectrophotometric calibration. The emphasis is on the reference SEDs of stellar standards with spectral type later than A0, with special focus on the theoretical model atmosphere spectra. Methods: Using the MARCS model atmosphere code, spectral reference SEDs were constructed for a set of IR stellar standards (A dwarfs, solar analogs, G9-M0 giants). A detailed error analysis was performed to estimate proper uncertainties on the predicted flux values. Results: It is shown that the uncertainty on the predicted fluxes can be as high as 10%, but in case high-resolution observational optical or near-IR data are available, and IR excess can be excluded, the uncertainty on medium-resolution SEDs can be reduced to 1-2% in the near-IR, to ~3% in the mid-IR, and to ~5% in the far-IR. Moreover, it is argued that theoretical stellar atmosphere spectra are at the moment the best representations for the IR fluxes of cool stellar standards. Conclusions: When aiming at a determination of the spectrophotometric calibration of IR spectrometers better than 3%, effort should be put into constructing an appropriate set of stellar reference SEDs based on theoretical atmosphere spectra for some 15 standard stars with spectral types between A0 V and M0 III.

18. Ground Effects on the Longitudinal Characteristics of Two Models with Wings Having Low Aspect Ratio and Pointed Tips

NASA Technical Reports Server (NTRS)

Buell, Donald A; Tinling, Bruce E

1957-01-01

Wind-tunnel tests were conducted to determine the ground effects on a tailless model with a wing of aspect ratio 2 and infinite taper, and on a tailed model with a triangular wing of aspect ratio 3, with flaps. Control-surface hinge moments were measured on the tailless model. The results are compared with the predictions of the theory of Tani, et al.

19. Prefission Constriction of Golgi Tubular Carriers Driven by Local Lipid Metabolism: A Theoretical Model

PubMed Central

Shemesh, Tom; Luini, Alberto; Malhotra, Vivek; Burger, Koert N. J.; Kozlov, Michael M.

2003-01-01

Membrane transport within mammalian cells is mediated by small vesicular as well as large pleiomorphic transport carriers (TCs). A major step in the formation of TCs is the creation and subsequent narrowing of a membrane neck connecting the emerging carrier with the initial membrane. In the case of small vesicular TCs, neck formation may be directly induced by the coat proteins that cover the emerging vesicle. However, the mechanism underlying the creation and narrowing of a membrane neck in the generation of large TCs remains unknown. We present a theoretical model for neck formation based on the elastic model of membranes. Our calculations suggest a lipid-driven mechanism with a central role for diacylglycerol (DAG). The model is applied to a well-characterized in vitro system that reconstitutes TC formation from the Golgi complex, namely the pearling and fission of Golgi tubules induced by CtBP/BARS, a protein that catalyzes the conversion of lysophosphatidic acid into phosphatidic acid. In view of the importance of a PA-DAG cycle in the formation of Golgi TCs, we assume that the newly formed phosphatidic acid undergoes rapid dephosphorylation into DAG. DAG possesses a unique molecular shape characterized by an extremely large negative spontaneous curvature, and it redistributes rapidly between the membrane monolayers and along the membrane surface. Coupling between local membrane curvature and local lipid composition results, by mutual enhancement, in constrictions of the tubule into membrane necks, and a related inhomogeneous lateral partitioning of DAG. Our theoretical model predicts the exact dimensions of the constrictions observed in the pearling Golgi tubules. Moreover, the model is able to explain membrane neck formation by physiologically relevant mole fractions of DAG. PMID:14645071

20. Practical aspects of backward bifurcation in a mathematical model for tuberculosis.

PubMed

Gerberry, David J

2016-01-01

In this work, we examine practical aspects of backward bifurcation for a data-based model of tuberculosis that incorporates multiple features which have previously been shown to produce backward bifurcation (e.g. exogenous reinfection and imperfect vaccination) and new considerations such as the treatment of latent TB infection (LTBI) and the BCG vaccine's interference with detecting LTBI. Understanding the interplay between these multiple factors and backward bifurcation is particularly timely given that new diagnostic tests for LTBI detection could dramatically increase rates of both LTBI detection and vaccination in the coming decades. By establishing analytic thresholds for the existence of backward bifurcation, we identify those aspects of TB's complicated pathology that make backward bifurcation more or less likely to occur. We also examine the magnitude of the backward bifurcation produced by the model and its sensitivity to various model parameters. We find that backward bifurcation is unlikely to occur. While increased vaccine coverage and/or increased detection and treatment of LTBI can push the threshold for backward bifurcation into the region of biological plausibility, the resulting bifurcations may still be too small to have any noticeable epidemiological impact. PMID:26493359

1. Physical aspects of unitary evolution of Bianchi-I quantum cosmological model

Pal, Sridip

2016-02-01

In this study, we examine some physical aspects of unitary evolution of the Bianchi-I model. In particular, we investigate the behavior of the volume and the scale factor as a function of time for the Bianchi-I universe with ultra-relativistic fluid (α = 1). The expectation value of volume is shown not to hit any singularity. We elucidate on the anisotropic nature of the solution and physically interpret the wavefunction as a superposition of collapsing universe and expanding universe mimicking Hartle-Hawking type wavefunction. The same analysis has been done for α \

2. Developmental modeling effects on the quantitative and qualitative aspects of motor performance.

PubMed

McCullagh, P; Stiehl, J; Weiss, M R

1990-12-01

The purpose of the present experiment was to replicate and extend previous developmental modeling research by examining the qualitative as well as quantitative aspects of motor performance. Eighty females of two age groups (5-0 to 6-6 and 7-6 to 9-0 years) were randomly assigned to conditions within a 2 x 2 x 2 (Age x Model Type x Rehearsal) factorial design. Children received either verbal instructions only (no model) or a visual demonstration with experimenter-given verbal cues (verbal model) of a five-part dance skill sequence. Children were either prompted to verbally rehearse before skill execution or merely asked to reproduce the sequence without prompting. Both quantitative (order) and qualitative (form) performances were assessed. Results revealed a significant age main effect for both order and form performance, with older children performing better than younger children. A model type main effect was also found for both order and form performance. The verbal model condition produced better qualitative performance, whereas the no model condition resulted in better quantitative scores. These results are discussed in terms of differential coding strategies that may influence task components in modeling. PMID:2132893

3. Transport of fluorobenzoate tracers in a vegetated hydrologic control volume: 2. Theoretical inferences and modeling

Queloz, Pierre; Carraro, Luca; Benettin, Paolo; Botter, Gianluca; Rinaldo, Andrea; Bertuzzo, Enrico

2015-04-01

A theoretical analysis of transport in a controlled hydrologic volume, inclusive of two willow trees and forced by erratic water inputs, is carried out contrasting the experimental data described in a companion paper. The data refer to the hydrologic transport in a large lysimeter of different fluorobenzoic acids seen as tracers. Export of solute is modeled through a recently developed framework which accounts for nonstationary travel time distributions where we parameterize how output fluxes (namely, discharge and evapotranspiration) sample the available water ages in storage. The relevance of this work lies in the study of hydrologic drivers of the nonstationary character of residence and travel time distributions, whose definition and computation shape this theoretical transport study. Our results show that a large fraction of the different behaviors exhibited by the tracers may be charged to the variability of the hydrologic forcings experienced after the injection. Moreover, the results highlight the crucial, and often overlooked, role of evapotranspiration and plant uptake in determining the transport of water and solutes. This application also suggests that the ways evapotranspiration selects water with different ages in storage can be inferred through model calibration contrasting only tracer concentrations in the discharge. A view on upscaled transport volumes like hillslopes or catchments is maintained throughout the paper.

4. Theoretical modeling for radiofrequency ablation: state-of-the-art and challenges for the future

PubMed Central

Berjano, Enrique J

2006-01-01

Radiofrequency ablation is an interventional technique that in recent years has come to be employed in very different medical fields, such as the elimination of cardiac arrhythmias or the destruction of tumors in different locations. In order to investigate and develop new techniques, and also to improve those currently employed, theoretical models and computer simulations are a powerful tool since they provide vital information on the electrical and thermal behavior of ablation rapidly and at low cost. In the future they could even help to plan individual treatment for each patient. This review analyzes the state-of-the-art in theoretical modeling as applied to the study of radiofrequency ablation techniques. Firstly, it describes the most important issues involved in this methodology, including the experimental validation. Secondly, it points out the present limitations, especially those related to the lack of an accurate characterization of the biological tissues. After analyzing the current and future benefits of this technique it finally suggests future lines and trends in the research of this area. PMID:16620380

5. Theoretical modeling of single-molecule fluorescence with complicated photon statistics

Osad'ko, I. S.; Naumov, A. V.; Eremchev, I. Yu.; Vainer, Yu. G.; Kador, L.

2012-11-01

The use of techniques for analyzing the fluorescence photon statistics of a single molecule for modeling single-emitter dynamics is demonstrated. The photon distribution function measured in the fluorescence of a single tetra-tert-butylterrylene molecule embedded in polyisobutylene is used to devise a theoretical model for single emitters with complicated fluorescence photon statistics. Our analysis was carried out with the theoretical approach developed by Osad'ko and co-workers [J. Chem. Phys.JCPSA60021-960610.1063/1.3055287 130, 064904 (2009); J. Phys. Chem. C10.1021/jp1014093 114, 10349 (2010)] for photon distribution functions. Although the experimental data were obtained at cryogenic temperature where narrow zero-phonon lines are present, the method is based on a purely statistical approach and does not require spectrally resolved data. It can also be applied to the analysis of broad fluorescence bands as measured at room temperature. Therefore, the method has prospects for revealing the quantum dynamics of single biological objects and other single quantum emitters in ambient conditions.

6. Theoretical model of adaptive fiber tip positioner based on flexible hinges and levers

Zhi, Dong; Ma, Yan-xing; Wang, Xiao-lin; Zhou, Pu; Si, Lei

2015-10-01

In this manuscript, we establish a model and theoretically investigate the novel structure of AFTP designed by ourselves. We analyze each sub-structure of the new type of AFTP and firstly use the software of ANSYS to simulate the deformation of the flexible hinge under the external force. The result shows that the deformation of the flexible hinge is mainly from and almost linear to the middle part. Further, after considering the influence of the levers and piezoelectric actuators, we setup the theoretical model in which the displacement is only relative to the ratio of the lever R. With the optimal value of R, we can get the relative largest displacement of the end cap when the other parameters are confirmed. As the maximal voltage applied on the piezoelectric stacks actuators (PSA) is finite, the largest displacement of the end cap is restricted. Neglecting the influence of the effective friction force (Ff) of inner-system, the relationship between the largest displacement of the end cap and the ratio (R) is derived numerically. From the calculated results, we get the largest displacement is about 67 μm with R of 6.9. This work provides a reference for structure optimization of AFTP based on flexible hinges and levers.

7. A multiscale mechanism of drug release from polymeric matrices: confirmation through a nonlinear theoretical model.

PubMed

Bacaita, E S; Agop, M

2016-08-21

In this paper, we propose a new approach for the dynamics of drug delivery systems, assimilated to complex systems, an approach based on concepts like fractality, non-differentiability, and multiscale evolution. The main advantage of using these concepts is the possibility of eliminating the approximations used in the standard approach by replacing complexity with fractality, that imposes, in mathematical terms, the mandatory use of the non-differential character of defined physical quantities. The theoretical model presented, validated for other physical systems, demonstrates its functionality also for drug delivery systems, highlighting, in addition, new insights into the complexity of this system. The spatio-temporal scales of system evolution are characterized through the fractality degree, as a measure of the complexity of the phenomena occurring at each scale. Numerical analysis of the experiment showed that the overall drug release kinetics can be obtained by composing "smaller release kinetics" occurring at scales appropriate for each phase of the drug release mechanism, phases whose expansion depends on the system density. Moreover, the uncertainties in establishing the exact limits of the phases were removed by applying the principle of scale superposition, resulting in a global fractality degree corresponding to the entire release kinetics. Even if the theoretical model is perfectible by identifying constants specific to each delivery system, this paper is intended to be the beginning of an alternative approach to drug delivery mechanisms. PMID:27436760

8. A model-based analysis of a display for helicopter landing approach. [control theoretical model of human pilot

NASA Technical Reports Server (NTRS)

Hess, R. A.; Wheat, L. W.

1975-01-01

A control theoretic model of the human pilot was used to analyze a baseline electronic cockpit display in a helicopter landing approach task. The head down display was created on a stroke written cathode ray tube and the vehicle was a UH-1H helicopter. The landing approach task consisted of maintaining prescribed groundspeed and glideslope in the presence of random vertical and horizontal turbulence. The pilot model was also used to generate and evaluate display quickening laws designed to improve pilot vehicle performance. A simple fixed base simulation provided comparative tracking data.

9. Some aspects of the comparison of model and full-scale tests

NASA Technical Reports Server (NTRS)

Taylor, D W

1926-01-01

This paper was delivered before the Royal Aeronautical Society as the 1925 Wilbur Wright Memorial lecture. It treats the subject of scale effect from the standpoint of the engineer rather than the physicist, in that it shows what compromises are necessary to secure satisfactory engineering model test data and how these test data compare with full scale or with theoretical values. The paper consists essentially of three parts: (1) a brief exposition of the theory of dynamic similarity, (2) application of the theory to airplane model tests, illustrated by test data on airfoils from the National Advisory Committee for Aeronautics variable-density wind tunnel, and (3) application of the theory to propeller testing, illustrated by comparisons of model and full-scale results.

10. Novel approach for assessing uncertainty propagation via information-theoretic divergence metrics and multivariate Gaussian Copula modeling

Thelen, Brian J.; Rickerd, Chris J.; Burns, Joseph W.

2014-06-01

With all of the new remote sensing modalities available, with ever increasing capabilities, there is a constant desire to extend the current state of the art in physics-based feature extraction and to introduce new and innovative techniques that enable the exploitation within and across modalities, i.e., fusion. A key component of this process is finding the associated features from the various imaging modalities that provide key information in terms of exploitative fusion. Further, it is desired to have an automatic methodology for assessing the information in the features from the various imaging modalities, in the presence of uncertainty. In this paper we propose a novel approach for assessing, quantifying, and isolating the information in the features via a joint statistical modeling of the features with the Gaussian Copula framework. This framework allows for a very general modeling of distributions on each of the features while still modeling the conditional dependence between the features, and the final output is a relatively accurate estimate of the information-theoretic J-divergence metric, which is directly related to discriminability. A very useful aspect of this approach is that it can be used to assess which features are most informative, and what is the information content as a function of key uncertainties (e.g., geometry) and collection parameters (e.g., SNR and resolution). We show some results of applying the Gaussian Copula framework and estimating the J-Divergence on HRR data as generated from the AFRL public release data set known as the Backhoe Data Dome.

11. Dynamics of basaltic plumbing systems - a theoretical model of eruptive output and timescales

Blake, S.; Gunn, L. S.

2011-12-01

Eruptions of basaltic volcanoes are the culmination of magma transport processes within a plumbing system that extends from the mantle to the surface. We present a versatile model of this system and compare model output with the historical record of selected basaltic volcanoes. Components of the model system include a deep storage region from which magma escapes at a rate determined by magma buoyancy, viscosity, conduit dimensions and viscous collapse of ductile country rocks, and a shallow chamber from which dense magma erupts at a rate determined by viscosity, conduit dimensions and elastic relaxation of initially over-pressured magma and country rock. The volumes of the chambers are also important variables. Model systems built from these components connected to each other and/or the surface encapsulate the controls on eruption intensity and duration in several scenarios. Using appropriate ranges of input parameter values, Monte Carlo modelling generates synthetic distributions of eruption volume and duration whose characteristics are compared with the distributions derived from historic eruption data from various basaltic volcanoes. Our results provide probabilistic forecasts of eruption durations, theoretical models of the course of given eruptions, and insights on the contrasting behaviours of volcanoes fed from shallow upper crustal chambers or from chambers situated in the deep crust or mantle.

12. Accountability and pediatric physician-researchers: are theoretical models compatible with Canadian lived experience?

PubMed Central

2011-01-01

Physician-researchers are bound by professional obligations stemming from both the role of the physician and the role of the researcher. Currently, the dominant models for understanding the relationship between physician-researchers' clinical duties and research duties fit into three categories: the similarity position, the difference position and the middle ground. The law may be said to offer a fourth "model" that is independent from these three categories. These models frame the expectations placed upon physician-researchers by colleagues, regulators, patients and research participants. This paper examines the extent to which the data from semi-structured interviews with 30 physician-researchers at three major pediatric hospitals in Canada reflect these traditional models. It seeks to determine the extent to which existing models align with the described lived experience of the pediatric physician-researchers interviewed. Ultimately, we find that although some physician-researchers make references to something like the weak version of the similarity position, the pediatric-researchers interviewed in this study did not describe their dual roles in a way that tightly mirrors any of the existing theoretical frameworks. We thus conclude that either physician-researchers are in need of better training regarding the nature of the accountability relationships that flow from their dual roles or that models setting out these roles and relationships must be altered to better reflect what we can reasonably expect of physician-researchers in a real-world environment. PMID:21974866

13. How residency duration affects the outcome of a territorial contest: Complementary game-theoretic models.

PubMed

Mesterton-Gibbons, Mike; Sherratt, Tom N

2016-04-01

While the first individuals to discover and maintain territories are generally respected as owners, under some conditions there may be ambiguity as to who got there first. Here we attempt to understand the evolutionary consequences of this ambiguity by developing a pair of game-theoretic models in which we explicitly consider rival residency-based claims to ownership. Following earlier qualitative explanations for residency effects, we assume that either the value of the territory (Model A) or an interloper׳s self-belief that it is the owner (Model B) increases with duration of residency. Model A clearly demonstrates that if the value of a territory increases to a resident over time, so should its motivation to fight in terms of the effort it invests in fighting. Indeed, only a small increase in territory value with residency duration can be sufficient for longer established residents to win disputes, even without any arbitrary convention or other form of priority effect. Likewise, Model B shows that the observed increase in fighting persistence with residency duration can be readily explained as a consequence of increasing confidence on behalf of the interloper that it is the rightful owner. Collectively, the models help to explain some general findings long observed by empiricists, and shed light on the nature of conflicts that can arise when individuals do not have complete information about rival claims to ownership. PMID:26807804

14. Theoretical uncertainties due to AGN subgrid models in predictions of galaxy cluster observable properties

Yang, H.-Y. Karen; Sutter, P. M.; Ricker, Paul M.

2012-12-01

Cosmological constraints derived from galaxy clusters rely on accurate predictions of cluster observable properties, in which feedback from active galactic nuclei (AGN) is a critical component. In order to model the physical effects due to supermassive black holes (SMBH) on cosmological scales, subgrid modelling is required, and a variety of implementations have been developed in the literature. However, theoretical uncertainties due to model and parameter variations are not yet well understood, limiting the predictive power of simulations including AGN feedback. By performing a detailed parameter-sensitivity study in a single cluster using several commonly adopted AGN accretion and feedback models with FLASH, we quantify the model uncertainties in predictions of cluster integrated properties. We find that quantities that are more sensitive to gas density have larger uncertainties (˜20 per cent for Mgas and a factor of ˜2 for LX at R500), whereas TX, YSZ and YX are more robust (˜10-20 per cent at R500). To make predictions beyond this level of accuracy would require more constraints on the most relevant parameters: the accretion model, mechanical heating efficiency and size of feedback region. By studying the impact of AGN feedback on the scaling relations, we find that an anti-correlation exists between Mgas and TX, which is another reason why YSZ and YX are excellent mass proxies. This anti-correlation also implies that AGN feedback is likely to be an important source of intrinsic scatter in the Mgas-TX and LX-TX relations.

15. Toward a unifying model of identification with groups: integrating theoretical perspectives.

PubMed

Roccas, Sonia; Sagiv, Lilach; Schwartz, Shalom; Halevy, Nir; Eidelson, Roy

2008-08-01

Building on the contributions of diverse theoretical approaches, the authors present a multidimensional model of group identification. Integrating conceptions from the social identity perspective with those from research on individualism-collectivism, nationalism- patriotism, and identification with organizations, we propose four conceptually distinct modes of identification: importance (how much I view the group as part of who I am), commitment (how much I want to benefit the group), superiority (how much I view my group as superior to other groups), and deference (how much I honor, revere, and submit to the group's norms, symbols, and leaders). We present an instrument for assessing the four modes of identification and review initial empirical findings that validate the proposed model and show its utility in understanding antecedents and consequences of identification. PMID:18641386

16. Experimental and theoretical study of Pseudomonas putida transport in a three-dimensional model aquifer

Vasiliadou, I. A.; Katzourakis, V. E.; Syngouna, V. I.; Chrysikopoulos, C. V.

2012-04-01

This study is focused on the transport of Pseudomonas (P.) putida bacterial cells in a three-dimensional model aquifer. The pilot-scale aquifer consisted of a rectangular glass tank with internal dimensions: 120 cm length, 48 cm width, and 50 cm height, carefully packed with well-characterized quartz sand. The P. putida attachment onto the aquifer sand was determined with batch experiments, and was adequately described by a linear isotherm. Transport experiments with a conservative tracer and P. putida were conducted to characterize the aquifer and to investigate the bacterial behavior during transport in water saturated porous media. A three-dimensional, finite-difference numerical model for bacterial transport in saturated, homogeneous porous media was developed and was used to successfully fit the experimental data. Furthermore, theoretical interaction energy calculations suggested that the extended DLVO theory seems to predict bacteria attachment onto the aquifer sand better than the classical DLVO theory.

17. Angular anisotropy in valence photoionization of Na clusters: theoretical investigation using jellium model

Jänkälä, Kari

2013-03-01

Calculation of the behaviour of photoelectron angular anisotropy in valence ionization of initially neutral NaX (X = 34-58) clusters is provided. The calculations are carried out for 1p, 1d and 1g jellium orbitals as a function of photon energy. The adapted theoretical framework is spherical jellium model using Woods-Saxon potential, which is modified to account for the long-range Coulomb tail in the final state. We discuss on the observed dramatic variations of the angular anisotropy parameter β as a function incident photon energy. It is shown that the behaviour is connected to the oscillation of the valence photoionization cross sections, that is a specific interference property of such metallic clusters whose valence structure can be described using the jellium model. ISSPIC 16 - 16th International Symposium on Small Particles and Inorganic Clusters, edited by Kristiaan Temst, Margriet J. Van Bael, Ewald Janssens, H.-G. Boyen and Françoise Remacle.

18. Student Conceptual Level and Models of Teaching: Theoretical and Empirical Coordination of Two Models.

ERIC Educational Resources Information Center

Hunt, David E.; And Others

The Conceptual Level (CL) matching model describes the differential reaction of students varying in CL to educational environments varying in degree of structure. Models of teaching describe environments systematically varying in structure and therefore provide a specific basis for coordinated investigation of differential effects. The effects of…

19. Transport-theoretic model for the electron-proton-hydrogen atom aurora. I. Theory

SciTech Connect

Basu, B.; Jasperse, J.R; Strickland, D.J.

1993-12-01

The first self-consistent transport-theoretic model for the combined electron-proton-hydrogen atom aurora is presented. This is needed for accurate modeling of the diffuse aurora, particularly in the midnight sector, for which a statistical study indicates that the proton contribution to the total auroral energy flux is (on the average) about 20 to 25% of that of the electrons. As a result, the ionization yield as well as the yields of many emission features will be underestimated (on the average) by about the same percentage if the proton-hydrogen atom contributions are neglected. The model presented here can also be used to study a pure electron aurora or a pure proton-hydrogen atom aurora by choosing the appropriate boundary conditions, namely, by setting the incident flux of one or the other particle population equal to zero. In the latter case, the new feature of the present model is the rigorous transport-theoretic treatment of the contributions to ionization rates and to emission rates and yields from the secondary electrons produced by protons and hydrogen atoms. A coupled set of three linear transport equations is presented. Protons and hydrogen atoms are coupled only to each other through charge-changing (charge exchange and stripping) collisions, while the electrons are coupled to both protons and hydrogen atoms through the secondary electrons that they produce. Source functions for the secondary electrons produced by the three primary particle populations are compared and contrasted, and the numerical methods for solving the coupled transport equations are described. Finally, formulas for calculating pertinent aurora-related quantities from the particle fluxes are given. 66 refs., 9 figs., 2 tabs.

20. [Oxygen-dependent energy deficit as related to the problems of ontogenetic development disorders and human sociobiological adaptation (theoretical and applied aspects)].

PubMed

Ilyukhina, V A; Kataeva, G V; Korotkov, A D; Chernysheva, E M

2015-01-01

The review states and argues theoretical propositions on the pathogenetic role of pre- and perinatal hypoxic-ischemic brain damage in the formation of sustained oxygen-dependent energy deficit underlying in further ontogenesis the following neurobiological abnormalities: a) a decline in the level of health and compensatory-adaptive capacities of the organism, b) disorders of the psycho-speech development and adaptive behavior in children, c) early development of neuropsychic diseases, g) addition of other types of brain energy metabolism (including glucose metabolism) disorders in chronic polyetiologic diseases young and middle-aged individuals. We highlight and theoretically substantiate the integrated physiological parameters of the oxygen-dependent energy deficit types. We address the features of abnormalities in neuroreflectory and neurohumora regulatory mechanisms of the wakefulness level and its vegetative and hemodynamic provision in different types of energy deficit in children with DSMD, ADHD and school maladjustment. The use of the state-of-the-art neuroimaging techniques significantly increased the possibility of the disintegration of regulatory processes and cognitive functions in children with psycho-speech delays and in a wide range of chronic polyetiologic diseases. PMID:26027380