scholarly journals Pseudomomentum: origins and consequences

2021 ◽  
Vol 72 (3) ◽  
Author(s):  
H. Singh ◽  
J. A. Hanna
Keyword(s):  
General Framework ◽  
Rotational Inertia ◽  
J Integral ◽  
Balance Laws ◽  
Jump Conditions ◽  
Propulsive Force ◽  
Bending Energy ◽  
Ideal Fluids ◽  
Simultaneous Variation

AbstractThe balance of pseudomomentum is discussed and applied to simple elasticity, ideal fluids, and the mechanics of inextensible rods and sheets. A general framework is presented in which the simultaneous variation of an action with respect to position, time, and material labels yields bulk balance laws and jump conditions for momentum, energy, and pseudomomentum. The example of simple elasticity of space-filling solids is treated at length. The pseudomomentum balance in ideal fluids is shown to imply conservation of vorticity, circulation, and helicity, and a mathematical similarity is noted between the evaluation of circulation along a material loop and the J-integral of fracture mechanics. Integration of the pseudomomentum balance, making use of a prescription for singular sources derived by analogy with the continuous form of the balance, directly provides the propulsive force driving passive reconfiguration or locomotion of confined, inhomogeneous elastic rods. The conserved angular momentum and pseudomomentum are identified in the classification of conical sheets with rotational inertia or bending energy.

scholarly journals A novel framework for classification of selection mechanisms in epidemiological research

2019 ◽  
Author(s):  
Jonas Bjork ◽  
Anton Nilsson ◽  
Carl Bonander ◽  
Ulf Strömberg
Keyword(s):  
General Framework ◽  
Empirical Studies ◽  
Population Level ◽  
Epidemiological Studies ◽  
Three Dimensions ◽  
Epidemiological Research ◽  
Selection Processes ◽  
Selection Mechanisms

Abstract Background: Non-participation, losses to follow up and other types of study-specific selection mechanisms can be serious concerns in epidemiological studies. There are also selection processes that result in non-random groupings and changes in the composition of populations. These are continuously on-going irrespectively of whether they are subject to sampling in empirical studies. Such population selections are often overlooked, but may lead to lack of comparability of exposed and unexposed populations or decrease study validity in other ways. The overall aim of this study was to develop a simple but general framework for classifying various types of selection mechanisms of relevance for epidemiological research. Methods: We classify selection mechanisms in three dimensions: i) selection at the population level vs. selection that is study-specific, ii) type of mechanism (selection causing exposure vs. selection in population at risk), iii) timing of the selection (pre-exposure, during exposure or post-outcome). Results: Examples from the epidemiological literature of selection mechanisms are discussed and classified according to the three dimensions of the proposed framework. Conclusions: Increased mechanistic understanding of when, how, and why confusion of effects can occur because of selection is an important step towards improved validity of epidemiological research.

Definitions of solutions to the IBVP for multi-dimensional scalar balance laws

2018 ◽  
Vol 15 (02) ◽  
pp. 349-374 ◽  
Author(s):  
Elena Rossi
Keyword(s):  
Boundary Value Problem ◽  
Boundary Conditions ◽  
General Framework ◽  
Boundary Value ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Balance Laws ◽  
Initial Boundary Value

We consider four definitions of solution to the initial-boundary value problem (IBVP) for a scalar balance laws in several space dimensions. These definitions are extended to the same most general framework and then compared. The first aim of this paper is to detail differences and analogies among them. We focus then on the ways the boundary conditions are fulfilled according to each definition, providing also connections among these various modes. The main result is the proof of the equivalence among the presented definitions of solution.

scholarly journals Hypersurface Constrained Elasticae in Lorentzian Space Forms

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Óscar J. Garay ◽  
Álvaro Pámpano ◽  
Changhwa Woo
Keyword(s):  
Space Form ◽  
Energy Functional ◽  
Bending Energy ◽  
Space Forms ◽  
Lorentzian Space ◽  
Totally Geodesic ◽  
Critical Curves ◽  
Different Types ◽  
Lorentzian Space Forms

We study geodesics in hypersurfaces of a Lorentzian space formM1n+1(c), which are critical curves of theM1n+1(c)-bending energy functional, for variations constrained to lie on the hypersurface. We characterize critical geodesics showing that they live fully immersed in a totally geodesicM13(c)and that they must be of three different types. Finally, we consider the classification of surfaces in the Minkowski 3-space foliated by critical geodesics.

scholarly journals Polyprotic Acids and beyond—An Algebraic Approach

Chemistry ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 454-508
Author(s):  
Harald Kalka
Keyword(s):  
Algebraic Approach ◽  
Mass Action ◽  
Base System ◽  
Balance Laws ◽  
Acid Base ◽  
Acidity Constants ◽  
Isoelectric Points ◽  
Buffer Capacities ◽  
Special Case

For an N-protic acid–base system, the set of nonlinear equations (i.e., mass action and balance laws) provides a simple analytical solution/formula for any integer N ≥ 1. The approach is applicable for the general case of zwitterionic acids HNA+Z (e.g., amino acids, NTA, and EDTA), which includes (i) the “ordinary acids” as a special case (Z = 0) and (ii) surface complexation. Examples are presented for N = 1 to 6. The high-N perspective allows classification of equivalence points (including isoionic and isoelectric points). Principally, there are two main approaches to N-protic acids: one from hydrochemistry and one “outside inorganic hydrochemistry”. They differ in many ways: the choice of the reference state (either HNA or A−N), the reaction type (dissociation or association), the type/nature of the acidity constants, and the structure of the formulas. Once the (nonlinear) conversion between the two approaches is established, we obtain a systematics of acidity constants (macroscopic, microscopic, cumulative, and Simms). Finally, from the viewpoint of statistical mechanics (canonical isothermal–isobaric ensemble), buffer capacities, buffer intensities, and higher pH derivatives are actually fluctuations in the form of variance, skewness, and kurtosis.

scholarly journals Between Self-awareness and Descent: Constructing Lithuanian Identity in Re-established Lithuania, 1988–1993

Lituanistica ◽  
2019 ◽  
Vol 65 (1) ◽  
Author(s):  
Darius Daukšas
Keyword(s):  
General Framework ◽  
Early Years ◽  
Self Awareness ◽  
Main Criterion ◽  
National Belonging ◽  
Core Element ◽  
The Core ◽  
The Republic ◽  
Definition Of

The early years of the independence of the Lithuanian state in the last decade of the twentieth century witnessed the construction of the nationhood through the evolving definition of “we” and “the other” in the nation. The Lithuanian diaspora took an active part in the discussions of defining one’s belonging to a nation. The core element in the discussion was the Law on Citizenship of the Republic Lithuania of 1991, which could be seen as a tool for classification of the population in defining an individual’s belonging to the nation. In this law, gradual clarification of the notion of the Lithuanian descent could be seen as inclusion of the diaspora in the category of ‘we’ in the general framework of the nationhood. The analysis of media articles of that period gives a vivid picture of the process of the construction of national belonging and reveals quite innovative interpretations of belonging proposed by the diaspora. Lithuanian émigrés questioned the established assumption in nationalist thinking that regarded the territory as the main precondition for belonging to a nation; instead, they suggested definitions of belonging based on common self-awareness, language, and the like, but their main criterion was the Lithuanian descent.

Fundamental Control for a Manta-Like Fish Robot

2015 ◽  
pp. 153-167
Author(s):  
Masaaki Ikeda ◽  
Keigo Watanabe ◽  
Isaku Nagai
Keyword(s):  
Fluid Dynamics ◽  
Numerical Simulations ◽  
Propulsive Force ◽  
Robot System ◽  
Fish Robot ◽  
Pectoral Fins ◽  
Constant Angle ◽  
Fin Rays

This chapter analyzes a propulsive force generated from pectoral fins for a manta-like fish robot, which is one of rajiform-type fish robot in a classification of swimming mechanism of fishes, from fluid dynamics aspects. The fishes of this type swim underwater with two pectoral fins. A diving method is proposed, assuming that some front fin rays are fixed with a constant angle. The usefulness of the method is demonstrated by numerical simulations and an experiment with an actual robot system.

Fundamental Control for a Manta-Like Fish Robot

2019 ◽  
pp. 929-943
Author(s):  
Masaaki Ikeda ◽  
Keigo Watanabe ◽  
Isaku Nagai
Keyword(s):  
Fluid Dynamics ◽  
Numerical Simulations ◽  
Propulsive Force ◽  
Robot System ◽  
Fish Robot ◽  
Pectoral Fins ◽  
Constant Angle ◽  
Fin Rays

This chapter analyzes a propulsive force generated from pectoral fins for a manta-like fish robot, which is one of rajiform-type fish robot in a classification of swimming mechanism of fishes, from fluid dynamics aspects. The fishes of this type swim underwater with two pectoral fins. A diving method is proposed, assuming that some front fin rays are fixed with a constant angle. The usefulness of the method is demonstrated by numerical simulations and an experiment with an actual robot system.

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