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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 11 (1989), S. 717-726 
    ISSN: 0392-6737
    Keywords: Hydrodynamic stability ; Convection and heat transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si dà una descrizione, in termini di un approccio di unoscillatore armonico, di moti in oscillazione crescente, per spinta idrostatica, cioè l'insorgenza di convezione oscillatoria in uno strato di fluido soggetto a vari vincoli termici e meccanici. Quando lo smorzamento si annulla, si definiscono i valori di soglia. Si sottolinea anche che l'oscillazione crescente è una conseguenza dell'accoppiamento sincrono delle forze che agiscono nel sistema.
    Abstract: Резюме В приближении гармонического осциллятора предлагается описание гидростатических устойчивых движений, т.е. возникновение осциияторной конвенции в слое жидкости, на который наложены различные тепловые и механические ограничения. При исчезающе малом затухании мы определяем пороговые значения. Мы также отмечаем, что устойчивость является следствием синхронной связи сил, действующих в системе.
    Notes: Summary A description of buoyancy-driven overstable motions,i.e. the onset of oscillatory convection in a fluid layer subjected to various thermal and mechanical constraints is given in terms of aharmonic-oscillator approach. At vanishing damping we define the threshold values. We also point out that overstability is a consequence of thesynchronous coupling of the forces acting in the system.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 11 (1989), S. 1057-1062 
    ISSN: 0392-6737
    Keywords: Hydrodynamic stability ; PACS 47.25.Qv ; Convection and heat transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si danno nuove previsioni teoriche che riguardano la sovrastabilità di fluidi viscoelastici nei termini del numero di Prandtl e del rapporto tra il rilassamento viscoelastico e i tempi di diffusione termica.
    Abstract: Резюме Предлагаются новые теоретические предсказания, касающиеся устойчивости упруговязких жидкостей. Предложенный подход основан на числе Прандтля и отношении времени упруговязкой релаксации к времени термодиффузии.
    Notes: Summary New theoretical predictions concerning overstability of viscoelastic fluids are given in terms of the Prandtl number and the ratio of viscoelastic relaxation to thermal diffusion times.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 570 (1989), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 4150-4156 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A complete theoretical treatment of the "mirage'' (optical beam deflection) technique has been performed for thermal diffusivity measurements in solids. Numerical calculations of the transverse deflection show there is a linear relation between the first noncentral zeros of the real part of this function and the inverse root frequency. The slope of this straight line is related to the thermal diffusivity through a factor (γ) which depends on the thermal and optical properties of the sample. We found γ=1 for transparent materials as well as for opaque thermally thin materials, whereas γ=1.44 for opaque thermally thick samples. We study further the experimental limits which make a sample to be considered as an opaque or transparent and as thermally thick or thin, and present a complete classification of solids according to their optical and thermal properties. The different behaviors observed may be related to the different geometry of thermal waves propagating through the media.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 26 (1985), S. 416-419 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: This paper presents a new method, that we call "the predictor jump,'' for driving to a faster solution of Laplace's equation. Some results obtained by applying this technique are compared with those that have been obtained by the traditional methods.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 27 (1986), S. 82-87 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The best conditions for the application of the predictor jump (PJ) method in the solution of the Laplace equation are discussed and some practical considerations for applying this new iterative technique are presented. The PJ method was remarked on in a previous article entitled "A new way for solving Laplace's problem (the predictor jump method)'' [J. M. Vega-Fernández, J. F. Duque-Carrillo, and J. J. Peña-Bernal, J. Math. Phys. 26, 416 (1985)].
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conjecture that magnetic helicity (linked flux) is conserved in magnetized plasmas for time scales that are short compared to the resistive diffusion time is experimentally tested in the CTX spheromak [Phys. Rev. Lett. 45, 1264 (1980); 51, 39 (1983); Nucl. Fusion 24, 267 (1984)]. Helicity is created electrostatically by current drawn from electrodes. The magnetized plasma then flows into a conducting flux conserver where the energy per helicity of the plasma is minimized and a spheromak is formed on a relaxation time scale of many Alfvén times. The magnetic field strength of the equilibrium is subsequently increased and sustained. The amount of helicity created by the magnetized coaxial plasma source, the helicity content of the spheromak equilibrium, and the resistive loss of the helicity are measured to determine the balance of helicity between source and spheromak with a ±16% uncertainty. In CTX the amount of energy that must be rapidly dissipated within the conducting boundary while conserving helicity in the process of sustaining the spheromak is experimentally controllable, and has varied from 1.8 times the spheromak magnetic energy to greater than 10 times. The relaxation, or minimization of the energy-to-helicity ratio, determines the gross structure (the normalized spatial profile) of the spheromak, while the conservation of helicity itself determines the magnitude and time dependence of the magnetic fields of the spheromak equilibrium. Helicity balance tests are done by individually varying the sign and magnitude of the source voltage and flux, and by observing sustainment of spheromaks with fields opposing those of the source. A threshold for helicity injection from the source is measured and related to the source and entrance region size. During times short compared to resistivediffusion time scales the helicity is shown to be conserved with a ±12% uncertainty using no free parameters. For longer times the resistive dissipation Its value is independently measured and appears to be related to the expected classical resistive decay. Absolutely calibrated bolometer measurements are consistent with excess source energy heating the spheromak plasma during the sustainment by electrostatic helicity injection.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1254-1270 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper extensive measurements of magnetic equilibrium and source parameters in the m=1 helicity source spheromak experiment are described (previously called the kinked z-pinch source [Comments Plasma Phys. Control Fusion 9, 161 (1985)]). In the cylindrical entrance region connecting the stabilized z-pinch helicity source to the spheromak flux conserver, the observed equilibrium configuration is the helical azimuthal m=1 state with no net axial flux. In the flux conserver, the equilibrium is a spheromak (m=0) state with an m=1 distortion. The magnetic equilibria observed are compared to theory. The performance of the source relative to coaxial helicity sources is also examined.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 1208-1216 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A mirror-confined hot-electron distribution is created using high-power, short-pulse electron-cyclotron resonance heating (ECRH) in a single, good curvature (magnetically stable) cell of a plasma-filled multiple mirror device. The hot electrons are observed to decouple good and bad curvature regions on the two sides of the hot-electron cell. An unstable magnetohydrodynamic (MHD)-like, rigid plasma motion to the walls occurs in the bad curvature region, with velocity comparable to that of a mode driven by the bad curvature alone. In some magnetic configurations the plasma restabilizes later in time. The hot-electron distribution decays stably, independent of the other processes. The initiation of the instability is correlated with the appearance in the hot-electron cell of a negative potential barrier. For the configurations in which plasma is restabilized, the restabilization is correlated with the decay of the potential barrier caused by ion trapping in the hot-electron cell. An electron beam time-of-flight probe has been used to measure the potential barrier and its decay. The experimental results are compared to a curvature-driven, trapped particle theory, including the effects of finite collisionality.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 3443-3446 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spheromaks are formed in a mesh flux conserver in the presence of an external dc bias magnetic field. The particle confinement is improved when the spheromak separatrix is put inside the metal mesh by the application of positive bias flux. The spheromaks remain stable to tilt instabilities with ratios of bias-to-spheromak flux of up to 47±7%.
    Type of Medium: Electronic Resource
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