scholarly journals Diffusion Cooling of Electrons in an A.C. Field

1997 ◽  
Vol 50 (3) ◽  
pp. 577 ◽  
Author(s):  
R. E. Robson
Keyword(s):  
Velocity Distribution Function ◽  
Field Studies ◽  
Mean Free Path ◽  
Point Of View ◽  
Zero Field ◽  
Theoretical Point ◽  
Cooling Effects ◽  
Set Up ◽  
Gas Chamber ◽  
Harmonic Representation

Boundaries affect the measured values of transport coeffcients in all drift tube experiments, to a greater or lesser extent, and nowhere is this more apparent than in the experiment first devised by Cavalleri (1969) and subsequently adapted by Crompton and coworkers in the 1970s. The phenomenon of ‘diffusion cooling’ is particularly striking and arises essentially from a penetration of the ‘boundary layer’ (of thickness of the order of the mean free path for energy exchange) throughout a significant portion of the gas chamber. Although this is something of an obstacle to extracting the classical diffusion coefficient from experimental data, it is of great interest in its own right from a theoretical point of view, and the Crompton et al. experiments motivated several theoretical treatments which successfully explained diffusion cooling, albeit for zero applied field and on the basis of the ‘two-term’ spherical harmonic representation of the velocity distribution function. The present paper puts these theories in the context of the modern, generalised eigenvalue theory, which may be used as a basis for describing all swarm experiments. In addition, the earlier zero-field studies are generalised to the extent that an a.c. heating field is included, as was the case for the original Cavalleri experimental set-up. This field is found to enhance diffusion cooling effects for a simple model cross section.

Recent progress in prominence seismology

2005 ◽  
Vol 364 (1839) ◽  
pp. 405-415 ◽  
Author(s):  
José Luis Ballester
Keyword(s):  
Small Amplitude ◽  
Point Of View ◽  
Future Research ◽  
Theoretical Point ◽  
Structure And Properties ◽  
Research Topics ◽  
Solar Prominences ◽  
Different Types ◽  
Set Up ◽  
Local Nature

Prominence seismology is a rapidly developing topic which seeks to infer the internal structure and properties of solar prominences from the study of their oscillations. An extense observational background about oscillations in quiescent solar prominences has been gathered during the last 70 years. These observations point out the existence of two different types of oscillations: flare-induced oscillations (winking filaments) which affect the whole prominence and are of large amplitude and small amplitude oscillations which seem to be of local nature. From the theoretical point of view, few models have been set up to explain the phenomenon of winking filaments while, on the contrary, for small amplitude oscillations a large number of models trying to explain the observed features have been proposed. Here, recent theoretical and observational developments on both types of oscillations are reviewed, and suggestions about future research topics which should provide us with a more in-depth knowledge of solar prominences are made.

scholarly journals Adaptive metabolic strategies in consumer-resource models

2018 ◽  
Author(s):  
Leonardo Pacciani-Mori ◽  
Andrea Giometto ◽  
Samir Suweis ◽  
Amos Maritan
Keyword(s):  
Molecular Mechanisms ◽  
Growth Curves ◽  
Point Of View ◽  
Exclusion Principle ◽  
Relative Fitness ◽  
Metabolic Adaptation ◽  
Theoretical Point ◽  
Set Up ◽  
Metabolic Strategies ◽  
Consumer Resource

AbstractBacteria are able to adapt to different environments by changing their “metabolic strategies”, i.e. the ways in which they uptake available resources from the environment. For example, in a celebrated experiment Jacques Monod showed that bacteria cultured in media containing two different sugars consume them sequentially, resulting in bi-phasic growth curves called “diauxic shifts”. From the theoretical point of view, microbial communities are commonly described using MacArthur’s consumer-resource model, which describes the population dynamics of species competing for a given set of resources. In this model, however, metabolic strategies are treated as constant parameters. Here, we introduce adaptive metabolic strategies in the framework of consumer-resource models, allowing the strategies to evolve to maximize each species’ relative fitness. By doing so, we are able to describe quantitatively, and without invoking any specific molecular mechanisms for the metabolism of the microbial species, growth curves of the baker’s yeastSaccharomyces cerevisiaemeasured in a controlled experimental set-up, with galactose as the primary carbon source. We also show that metabolic adaptation enables the community to self-organize, allowing species to coexist even in the presence of few resources, and to respond optimally to a time-dependent environment. A connection between the Competitive Exclusion Principle and the metabolic theory of ecology is also discussed.

scholarly journals On broadband jet–ring interaction noise and aerofoil turbulence-interaction noise predictions

2010 ◽  
Vol 653 ◽  
pp. 337-364 ◽  
Author(s):  
MICHEL ROGER
Keyword(s):  
Transfer Function ◽  
Mixing Layer ◽  
Point Of View ◽  
Turbulent Velocity ◽  
Aerodynamic Noise ◽  
Experimental Point ◽  
Far Field ◽  
Theoretical Point ◽  
Parallel Side ◽  
Set Up

The aerodynamic noise of a thin rigid annulus (referred to as the ring here) placed in the mixing layer of a subsonic circular jet is investigated in the paper, both theoretically and experimentally. From the experimental point of view, the jet–ring configuration is understood as an axisymmetric alternative to more usual ones involving a rectangular aerofoil held between parallel side plates, dedicated to the study of the noise due to the impingement of upstream turbulence. The main advantages of the circular geometry are a minimum background noise, the absence of tip effects and more specifically the account for all radiation angles from the surface in the far-field acoustic signature. The circular set-up is well suited for the study of pure broadband interaction noise only if the flow remains free of self-sustained oscillations. This is ensured by keeping a sufficient interaction distance between the nozzle and the ring, and by shaping serrations on the nozzle lip. From the theoretical point of view, an analytical model is derived as a straightforward extension of existing formulations. The induced unsteady lift forces on the ring are first inferred from a linearized unsteady aerodynamic theory and the far field is calculated in a second step by a radiation integral. This relates the far-field acoustic pressure power spectral density (PSD) to the two-wavenumber spectrum of the radial turbulent velocity at the ring location, by means of an aeroacoustic transfer function. The latter is shown asymptotically identical to the one detailed in the Appendix for a rectangular aerofoil, in the limit of relatively high frequencies. The analytical acoustic predictions are found to agree well with the measurements over an extended frequency range, provided that the model is fed with turbulent velocity input data measured by a hot-wire probe. Indirectly, this agreement validates the transfer function for a rectangular aerofoil at oblique radiation angles, which is not achievable in a set-up involving side plates and a rectangular nozzle.

Investigations on a Base Excited Rotor

2005 ◽  
Author(s):  
N. Driot ◽  
C. H. Lamarque ◽  
A. Berlioz
Keyword(s):  
Dynamic Behavior ◽  
Ritz Method ◽  
Multiple Scale ◽  
Point Of View ◽  
Theoretical Point ◽  
Coupled Equations ◽  
Lateral Displacements ◽  
Support Excitation ◽  
Set Up ◽  
Form Approach

In this study, the dynamic behavior of a flexible rotor system under support excitation (imposed displacements of its base) is analyzed. The effect of an excitation on lateral displacements is investigated from an experimental and a theoretical point of view. The study focuses on the behavior in bending. An experimental set-up is developed to observe the dynamic behavior that permits to measure the lateral displacements when the support of the system is submitted to a sinusoidal rotation. A mathematical model with two gyroscopic coupled equations is then derived using Rayleigh-Ritz method. The theoretical study is based on both the multiple scale method and the normal form approach. The experimental results are favorably compared with the analytical and numerical results.

Timber Auctions in the Context of the Modern Auction Theory

2007 ◽  
pp. 86-94
Author(s):  
A. Manakov
Keyword(s):  
Theoretical Analysis ◽  
Auction Theory ◽  
Point Of View ◽  
Theoretical Point ◽  
English Auction ◽  
Analysis And Evaluation

The article provides theoretical analysis and evaluation of the timber auctions reforms in Russia. The author shows that the mechanism of the "combined auctions", which functioned until recently, is more appropriate from the theoretical point of view (and from the point of view of the Russian practice) as compared to the officially approved format of the English auction.

A novel cryptosystem based on abstract automata and Latin cubes

2015 ◽  
Vol 52 (2) ◽  
pp. 221-232
Author(s):  
Pál Dömösi ◽  
Géza Horváth
Keyword(s):  
Block Cipher ◽  
Finite Automata ◽  
Theoretical Background ◽  
Point Of View ◽  
Theoretical Point ◽  
Transition Matrices ◽  
Encryption And Decryption ◽  
Secret Keys ◽  
Automata Network ◽  
Fully Functioning

In this paper we introduce a novel block cipher based on the composition of abstract finite automata and Latin cubes. For information encryption and decryption the apparatus uses the same secret keys, which consist of key-automata based on composition of abstract finite automata such that the transition matrices of the component automata form Latin cubes. The aim of the paper is to show the essence of our algorithms not only for specialists working in compositions of abstract automata but also for all researchers interested in cryptosystems. Therefore, automata theoretical background of our results is not emphasized. The introduced cryptosystem is important also from a theoretical point of view, because it is the first fully functioning block cipher based on automata network.

The Revolutionizing of the Revolution

2017 ◽  
Author(s):  
R. R. Palmer
Keyword(s):  
French Revolution ◽  
Point Of View ◽  
Strict Sense ◽  
French Government ◽  
Thing In Itself ◽  
Set Up ◽  
The Moment ◽  
The French Revolution ◽  
The Revolution

In 1792, the French Revolution became a thing in itself, an uncontrollable force that might eventually spend itself but which no one could direct or guide. The governments set up in Paris in the following years all faced the problem of holding together against forces more revolutionary than themselves. This chapter distinguishes two such forces for analytical purposes. There was a popular upheaval, an upsurge from below, sans-culottisme, which occurred only in France. Second, there was the “international” revolutionary agitation, which was not international in any strict sense, but only concurrent within the boundaries of various states as then organized. From the French point of view these were the “foreign” revolutionaries or sympathizers. The most radical of the “foreign” revolutionaries were seldom more than advanced political democrats. Repeatedly, however, from 1792 to 1799, these two forces tended to converge into one force in opposition to the French government of the moment.

Graffiti als Version und Subversion–Praxen kultureller Re-Regulierung und die Möglichkeit von Gratiforschung

2010 ◽  
Vol 55 (2) ◽  
pp. 11-25 ◽  
Author(s):  
Bernd Dollinger
Keyword(s):  
Social Life ◽  
Point Of View ◽  
Theoretical Point ◽  
Research Practice ◽  
Wird Eine ◽  
Multiple Perspectives

Der Beitrag geht von Versuchen aus, integrative Perspektiven einer überaus heterogenen Graffitiforschung zu bestimmen. In Auseinandersetzung insbesondere mit Bruno Latours Ansatz des »Iconoclash« wird eine kulturtheoretische Referenz bestimmt, die Graffiti als Version identifiziert, d. h. als semiotisch orientierte Veränderung räumlich situierter Ordnungs- und Regulierungspraxen. Ihnen kann, wenn auch nicht zwingend, eine subversive Qualität zukommen. Durch die Ausrichtung am Konzept einer Version wird beansprucht, Forderungen einer normativ weitgehend abstinenten, nicht-essentialistischen und für komplexe Fragen der Identitäts- und Raumpolitik offenen Forschungspraxis einzulösen.<br><br>The contribution attempts to integrate multiple perspectives of current largely heterogeneous graffiti scholarship. Referring to Bruno Latour’s concept »iconoclash«, we discuss graffiti from a cultural-theoretical point of view as a »version«. It appears as a semiotically oriented modification of spatially situated practices that regulate social life. Often, but not necessarily, these practices involve subversive qualities. The concept of »version« facilitates a non-normative and non-essentialist strategy of research. This enables an explorative research practice in which the complex matters of identity and space politics that are associated with graffiti can be addressed.

scholarly journals On Kaufmann's theory of the impact of the pianoforte hammer

1920 ◽  
Vol 97 (682) ◽  
pp. 99-110 ◽  
Keyword(s):  
Initial Conditions ◽  
Practical Importance ◽  
Prima Facie ◽  
Point Of View ◽  
Infinite Length ◽  
Modes Of Vibration ◽  
Rigorous Treatment ◽  
The Subject ◽  
Set Up ◽  
The Impact

The theory of the vibrations of the pianoforte string put forward by Kaufmann in a well-known paper has figured prominently in recent discussions on the acoustics of this instrument. It proceeds on lines radically different from those adopted by Helmholtz in his classical treatment of the subject. While recognising that the elasticity of the pianoforte hammer is not a negligible factor, Kaufmann set out to simplify the mathematical analysis by ignoring its effect altogether, and treating the hammer as a particle possessing only inertia without spring. The motion of the string following the impact of the hammer is found from the initial conditions and from the functional solutions of the equation of wave-propagation on the string. On this basis he gave a rigorous treatment of two cases: (1) a particle impinging on a stretched string of infinite length, and (2) a particle impinging on the centre of a finite string, neither of which cases is of much interest from an acoustical point of view. The case of practical importance treated by him is that in which a particle impinges on the string near one end. For this case, he gave only an approximate theory from which the duration of contact, the motion of the point struck, and the form of the vibration-curves for various points of the string could be found. There can be no doubt of the importance of Kaufmann’s work, and it naturally becomes necessary to extend and revise his theory in various directions. In several respects, the theory awaits fuller development, especially as regards the harmonic analysis of the modes of vibration set up by impact, and the detailed discussion of the influence of the elasticity of the hammer and of varying velocities of impact. Apart from these points, the question arises whether the approximate method used by Kaufmann is sufficiently accurate for practical purposes, and whether it may be regarded as applicable when, as in the pianoforte, the point struck is distant one-eighth or one-ninth of the length of the string from one end. Kaufmann’s treatment is practically based on the assumption that the part of the string between the end and the point struck remains straight as long as the hammer and string remain in contact. Primâ facie , it is clear that this assumption would introduce error when the part of the string under reference is an appreciable fraction of the whole. For the effect of the impact would obviously be to excite the vibrations of this portion of the string, which continue so long as the hammer is in contact, and would also influence the mode of vibration of the string as a whole when the hammer loses contact. A mathematical theory which is not subject to this error, and which is applicable for any position of the striking point, thus seems called for.

scholarly journals How Digital Inclusion Increase Opportunities for Young People: Case of NEETs from Bulgaria, Romania and Turkey

2021 ◽  
Vol 13 (14) ◽  
pp. 7894
Author(s):  
Gabriela Neagu ◽  
Muhammet Berigel ◽  
Vladislava Lendzhova
Keyword(s):  
Data Analysis ◽  
Rural Areas ◽  
Secondary Data ◽  
Point Of View ◽  
Multidimensional Analysis ◽  
Theoretical Point ◽  
Digital Inclusion ◽  
Virtual Mobility ◽  
Alternative Research ◽  
High Share

This paper examines the perspectives of rural NEETs in the information society. Our analysis focuses on the situation of three European countries—Bulgaria, Romania, and Turkey—characterized by a high share of rural areas and a population of NEETs. From a methodological point of view, we use alternative research methods (secondary data analysis) with statistical methods (simple linear regression). From a theoretical point of view, we will opt for a multidimensional analysis perspective: the theory of digital divide, digital inclusion, virtual mobility, etc. Through data analysis, we expect to obtain a more complete and detailed picture of the ICT situation in rural areas (level of digital skills, level of digital inclusion) to demonstrate the importance of ICT in optimizing virtual mobility for the living conditions of the population, especially the NEET population.

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