Fundamental Physical Models Research Articles

THM-coupled finite element analysis of frozen soil: formulation and application

A fully coupled thermo-hydro-mechanical (THM) finite element (FE) formulation is presented that considers freezing and thawing in water-saturated soils. The formulation considers each thermal, hydraulic and mechanical process, and their various interactions, through fundamental physical laws and models. By employing a combination of ice pressure, liquid pressure and total stress as state variables, a new mechanical model has been developed that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework. Important frozen soil features such as temperature and porosity dependence of shear strength are captured inherently by the model. Potential applications to geotechnics include analysis of frost heave, foundation stability or mass movements in cold regions. The model's performance is demonstrated with reference to the in situ pipeline frost heave tests conducted by Slusarchuk et al. Detailed consideration is given to FE mesh design, the influence of hydraulic parameters, and the treatment of air/ground interface boundary conditions. The THM simulation is shown to reproduce, with fair accuracy, the observed pipeline heave and the porosity growth driven by water migration.

Design for manufacturability for fabless manufactuers

When a company designs and sells ICs but outsources their manufacture, design for manufacturability poses special challenges. It is clear that these DfM solutions are very complex and require a series of fundamental new physical models and design practices. Practical deployment of DfM solutions requires development of an entire incremental infrastructure on both the process and design sides of the technology integration spectrum. Optimizing the various DfM methods involves complex, multi-faceted tradeoffs that are ultimately dependent on target technology and various product attributes. DfM is definitely not a one-size-fits-all panacea for all of the process manufacturability and variability challenges. Complete and successful DfM deployment is a true ecosystem that requires multiple tools using multiple models, potentially calibrated to multiple levels of accuracy, inserted at multiple points in the design flow.

Towards sustainable nuclear energy: Putting nuclear physics to work

We have developed a new method to propagate the uncertainties of fundamental nuclear physics models and parameters to the design and performance parameters of future, clean nuclear energy systems. Using Monte Carlo simulation, it is for the first time possible to couple these two fields at the extremes of nuclear science without any loss of information in between. With the help of a large database of nuclear reaction measurements, we have determined the uncertainties of theoretical nuclear reaction models such as the optical, compound nucleus, pre-equilibrium and fission models. A similar assessment is done for the parameters that describe the resolved resonance range. Integrating this into one simulation program enables us to describe all open channels in a nuclear reaction, including a complete handling of uncertainties. Moreover, in one and the same process, values and uncertainties of nuclear reactor parameters are computed. This bypasses all the intermediate steps which have been used so far in nuclear data and reactor physics. Two important results emerge from this work: (a) we are able to quantify the required quality of theoretical nuclear reaction models directly from the reactor design requirements and (b) our method leads to a deviation from the commonly assumed normal distribution for uncertainties of safety related reactor parameters, and this should be taken into account for future nuclear energy development. In particular, calculated k eff distributions show a high-value tail for fast reactor spectra.

No free energy lunch

Prediction of a protein's affinity for a ligand has been improved through fundamental physical modeling.

Global Modeling of Magnetized Capacitive Discharges

Capacitive reactors for semiconductor processing must simultaneously balance many physical phenomena with engineering constraints to achieve the desired processing properties. Important phenomena include electromagnetic RF propagation, gas ionization, plasma heating, plasma transport, and nonlinear sheath effects. Constraints are driven by process uniformity, radical production, thermal control, and reactor-component lifetime. These phenomena and constraints are often modeled in isolation; however, in a real system, they can interact in ways that are not easily foreseen. It is highly desirable to have global models that can provide relatively quick feedback for the proposed modifications to these systems. While an approach based on fundamental physics models is highly desirable whenever possible, the system can quickly become too complicated for quick design evaluations. In this paper, we explore the interaction between several processes by combining fundamental physics models when reasonable, with simplified, heuristic, or even empirical models for processes that are difficult to model from first principles. The goal is to understand the interaction between these processes in a global system without becoming overly encumbered by details in the individual components of the model. We study the effects of static magnetic field on plasma transport and electromagnetic effects arising at high RF frequency. We also change the RF-coupled power and ionization efficiency in a simplified 2-D model geometry to contrast the various effects. We find that discharges with very high frequency and high plasma density can exhibit localized nulls in the RF fields caused by electromagnetic-propagation effects in the sheath region. We find that relatively low static magnetic fields can modify the radial-plasma density profiles. Good agreement is found between the radial-plasma profiles given by the model and those measured in an experiment where the currents in two concentric coils near the plasma are the only variables.

Thermophysical properties of lead and lead–bismuth eutectic

Among different heavy liquid metals, lead (Pb) and lead–bismuth eutectic (Pb–Bi) are considered at present as the potential candidates for the liquid spallation targets of neutron sources and accelerated driven systems and for the coolant of new generation fast reactors due to their very good neutron and thermal features. Up to now, the published data on the properties of the lead alloys of interest are still limited and significant discrepancies exist between the values given by different sources. This work is a critical review of old and new data reported in the open literature on the main thermo-physical properties of the molten Pb and Pb–Bi: characteristic temperatures, latent heats of melting and evaporation, surface tension, density, heat capacity, viscosity, electric and thermal conductivity. In general, the reliability of data is satisfactory, however, a large uncertainty still exists in the saturation vapour pressure, sound velocity, heat capacity and thermal conductivity. The critical parameters of Pb and Pb–Bi are not well defined yet, and this hinder the development of the equations of state for these coolants. The correlations developed on the basis of the fundamental physical models and the ‘best fit’ approach are proposed for engineering estimations and design calculations.

The Universe is a Strange Place

This is a broad and in places unconventional overview of the strengths and shortcomings of our standard models of fundamental physics and of cosmology. The emphasis is on ideas that have accessible empirical consequences. It becomes clear that the frontiers of these subjects share much ground in common.

Optimal passive source localization in a fluctuating ocean waveguide based on an analytic model for the mean field and covariance

The ocean acts as an enormously complex channel for signal transmission. It is characterized by temporal fluctuations and spatial variabilities that often lead to significant randomization of the measured field. Signal processing techniques must be derived from fundamental physical models to attain statistical optimality in such an environment. Here we present such an analysis with a new analytic model [Ratilal and Makris, J. Acoust. Soc. Am. 114, 2428 (2003)] for the mean field and its covariance after propagation through a fluctuating ocean waveguide based on the first principles of waveguide scattering theory. The model is advantageous because it includes the primary physical effects of attenuation, dispersion, and coupling of modal energy due to multiple forward scattering in a convenient and intuitive form that is well suited to analytic manipulations. An example will be presented for passive source localization in range and depth in a fluctuating ocean waveguide by nonlinear matched field inversion. The necessary conditions on sample size and signal-to-noise ratio (SNR) for unbiased and minimum variance (optimal) estimates of source postion are then derived using asymptotic statistical inference theory [Naftali and Makris, J. Acoust. Soc. Am. 110, 1917–1930 (2001)]. Degradation in performance by environmental uncertainties are quantified within this statistical framework.

Simulation of City Fire

This study develops a physical model of city fire spreading. First, we developed a fundamental physical model of a city fire. Then we made a simulation program of a city fire based on the fundamental physical model. Using this model of city fire, risk of fire in urban area can be evaluated in detail.

Varying constants, black holes, and quantum gravity

Tentative observations and theoretical considerations have recently led to renewed interest in models of fundamental physics in which certain ``constants'' vary in time. Assuming fixed black hole mass and the standard form of the Bekenstein-Hawking entropy, Davies, Davis and Lineweaver have argued that the laws of black hole thermodynamics disfavor models in which the fundamental electric charge $e$ changes. I show that with these assumptions, similar considerations severely constrain ``varying speed of light'' models, unless we are prepared to abandon cherished assumptions about quantum gravity. Relaxation of these assumptions permits sensible theories of quantum gravity with ``varying constants,'' but also eliminates the thermodynamic constraints, though the black hole mass spectrum may still provide some restrictions on the range of allowable models.

Dynamic Electrical-Mechanical Energy Coupling in Electrolyte-Mineral Systems

Electrical-mechanical and mechanical-electrical coupling phenomena have been observed in geo-materials. Underlying internal phenomena are not always clear. In this paper, we identify potential microscale processes on the bases of previously published research; fundamental physical principles and analytical models are included. Second, we notice important inconsistencies between theoretically predicted values or high-frequency laboratory data with respect to low-frequency field observations. To explore these differences, we conduct a laboratory experimental study that simulates field conditions, placing emphasis on low frequency coupling, that is, less than 10 kHz. Both, mechanical-electrical and electrical-mechanical effects are observed. Finally, hypotheses are presented in an attempt to explain observed differences.

Modeling, Monitoring and Control in High Quality Laser Cutting

Electrical discharge machining (EDM) and laser cutting are thermal separation processes widely used in shaping and contour cutting applications. However, there are gaps in understanding the dynamics of the process, especially issues related to cut quality. This work describes the advances in fundamental physical modeling and process monitoring of laser cutting, as well as time varying processes such as contour cutting. The onset of evaporation and the increase of capillary forces are the two physical phenomena relevant to the build-up of adherent dross. The dynamic model predicts a modulation frequency for the laser power that leads to almost complete suppression of adherent dross in contour cutting.

MODELING OF PH PROFILE IN PORE WATER BASED ON MASS TRANSPORT AND CHEMICAL EQUILIBRIUM THEORY

The authors present a computational system that can deal with pH fluctuations and the decomposition of cementitious materials exposed to various environmental actions. In order to evaluate the fall in pH due to carbon dioxide, material models are developed for the transport and equilibrium of carbon dioxide, ionization, ion equilibriums, and the carbonation reaction based on thermo-dynamic theory. The material properties of concrete are evaluated by considering the inter-relationships among hydration, moisture transport, and pore-structure development based on fundamental physical material models. The proposed system is able to reasonably predict the carbonation phenomena and pH profiles in concrete for arbitrary conditions.

Quantitative prediction of absorption maxima in the electronic spectra of unsaturated compounds: Extrapolation from fragments to molecules in quantum chemical calculations

Comparison of the positions of the long-wave bands in the electronic absorption spectra of expected reaction products calculated by quantum chemical methods with the corresponding experimental data yields important structural information. The role of quantum chemical calculations increases in the cases where the isolation of the products is impossible, as, e.g., with the oxidation products of diphenylamlne, its derivatives, and structural analogs. The modern all-valence semiempirical and ab initio methods for calculating the spectra (see the review in [1]) are often inadequate to quantitatively reproduce real wavelengths at the absorption maxima of the electronic spectra of complex compounds taking into account the medium effects [2]. In contrast to the above methods, the Pariser-Parr-Pople (PPP) method [3-5] does not allow the consideration of Rydberg states, transitions involving the sigma orbitals, spin-orbit interactions, etc. However, this method still remains in force and is treated as a fundamental physical model [6]. Moreover, it describes the z~---:r, excitations better than the CNDO/S approximation [7] does. The aim of this work is to study the possibility of predicting absorption maxima for unsaturated organic compounds by the PPP method with fitted parameters and classify the quantum chemical methods. The calculations were performed with an original program for IBM PC XT/AT with five lower unoccupied and five higher occupied molecular orbitals (MOs) involved in the single configuration interaction. For matrix diagonalization, the Householder method and the QL algorithm with an implicit shift [8] were used. The spatial parameters of molecules were borrowed from [9]. Even for relatively simple molecules (aniline, phenol, pyridine, etc.), the test calculations exhibit certain discrepancies with the experimental data (which is consistent with the data of [7]). For more complex chemical systems, these differences dramatically increase. To better reproduce the wavelengths at the absorption maxima of the electronic spectra of conjugated compounds, we used calibration of two-electron integrals y/q~ (whose estimation is the weakest point of the PPP method

Theoretical and numerical comparison between DMOS and trench technologies for insulated gate bipolar transistors

An accurate and comprehensive comparison between DMOS and Trench technologies for Insulated Gate Bipolar Transistors (IGBT) is presented. The study is performed using extensive two-dimensional numerical simulations and fundamental physical modeling. Various phenomena such as the influence of the channel density on the forward voltage drop and the effect of the channel mobility degradation on the on-state characteristics have been the object of controversial studies. The analysis performed here describes rigorously these phenomena and accounts for new physical effects such as the channel length modulation and PIN diode carrier dynamics. It is concluded that at relatively high voltage and high current densities (>100 A/cm/sup 2/) an optimally designed Trench IGBT results in significant theoretical advantages over its conventional DMOS variant, mainly due to an increased packing density, PIN diode effect, reduced latch-up current density and elimination of the JFET effect.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Plasma modelling for surface processing

Numerical modelling of plasma systems is proving an increasingly valuable tool in the understanding of fundamental processes in reactors for surface engineering applications. The present paper discusses some of the fundamental physical and mathematical models used to describe plasma behaviour and their range of validity and applicability to plasma reactors. A number of specific examples which illustrates the way in which these methods may be implemented to model plasmas in dc and rf diode reactors and plasma ‘ball’ microwave reactors are described, with comparison between numerical results, diagnostic measurements and experimental observations from the published literature.

Physical principles of the modeling of three-dimensional microwave and extremely high frequency integrated circuits

The fundamental principles, physical models, and design fundamentals of three-dimensional microwave integrated circuits are presented. The principles of mathematical modeling of transmission lines and basic elements are discussed. The topological approach to the description of the electromagnetic field in the elements of three-dimensional microwave integrated circuits is examined at the electrodynamic level. The structures of the base elements, functional units, and devices for processing signals from pickups as well as the physical and technological aspects of their fabrication based on three-dimensional microwave integrated circuits are examined.

Physics Modeling of Tokamak Transport, a Grand Challenge for Controlled Fusion

A challenge facing fusion is accurate prediction and understanding of plasma and heat confinement. Com puters and modeling techniques have advanced to where we can envision simulating real Tokamaks start ing from fundamental physics models. Charged parti cles in magnetic fields execute rapidly gyrating mo tions about the field. These orbits gradually drift where electric fields and magnetic nonuniformities exist. The gyrokinetic model averages out the rapid gyration and treats the plasma as a large number of drifting rings of charge and current; large numbers (approx. 106) of such rings are followed in their self-consistent electric and magnetic fields. Three-dimensional simulations of plasma and heat confinement for situations relevant to fusion give turbulence spectra and transport coeffi cients similar to experiments. Simpler particle models of plasma run on hypercubes achieves a high degree of parallelism (95%). With new parallel machines sub stantial gains in speed and memory can be expected; modeling of real Tokamaks should be possible.

The PPP‐CI scheme as a fundamental physical model

AbstractParametrized computational procedures and simplified physical models of molecular reality are often related to one another but are by no means the same thing. With special reference to work by Koutecky and by Cizek, Paldus et al., it is shown here that the PPP model rests on a simple but physically sound electrostatic picture of a molecular π system, and its intrinsic difference from an independent particle model is emphasized. As an illustration of the heuristic power which makes physical models powerful tools of theoretical research, ground state charge transfer GSCT, in situ molecular electronegativity, and the principle of electronegativity equalization are derived within the PPP‐CI scheme, no use being made of molecular orbitals, and the assumptions on which the CT theory rests are made explicit.

A physically based mobility model for MOSFET numerical simulation

A new modeling for the surface mobilities based on theoretical and experimental surface mobility studies has been implemented in the MINIMOS two-dimensional MOSFET current-voltage characterization program. The new model includes the following scattering mechanisms: surface and bulk acoustical and optical-intervalley phonons, bulk ionized impurities, oxide charges, surface roughness, dipoles or neutral surface states at the oxide-silicon interface, as well as hot-carrier mobility reduction in high longitudinal electric fields. The resultant combined mobility of this model is compared with Selberherr's mobility model, which he employed in the MINIMOS program. Selberherr's surface mobility is smaller at low fields than this, as well as other experimentally observed mobilities, However, a detailed comparison of the computed drain current-voltage characteristics of many devices showed excellent agreement between the Selberherr model and this model in the subthreshold range and a less than about 20-percent difference in the strong inversion range. The new model may be preferred since it has no adjustable parameters and all parameters were obtained by careful independent measurements on large-area and long-channel devices and data analyses based on fundamental physical models.