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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 136 (1987), S. 259-279 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In anisotropic plasmas, the radiative power emitted and the power observed per unit solid angle should be calculated along the direction of the group velocityv g . The two power functions referred differ by a product of two factors: one is the group Doppler factor and the other is the ‘squeezing effect’ of the radiative energy due to the dependence ofv g on direction. In this paper, the group Doppler factor is derived using two different methods, and the relevant physical concepts are analyzed in details. A number of numerical examples pertaining to astrophysical situations are presented, to illustrate the significance of the group Doppler effect with respect to the ‘wave Doppler effect’ which is valid in isotropic media.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 10 (1988), S. 247-276 
    ISSN: 0392-6737
    Keywords: Boson degeneracy and superfluidity of helium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Impiegando la teoria della matriceU nella forma presente, abbiamo presentato una teoria microscopica di un sistema interagente diN bosoni a temperatura non nulla. L'hamiltoniana include un termine che descrive l'influenza esterna, un termine per un'interazione a 2 particelle e une che riguarda l'interazione di tipo dipolare. Per studiare lo stato fondamentale dell'4He liquido s'include solo l'interazione a 2 particelle. Basandoci su dati di scattering, abbiamo dedotto la funzione potenziale a 2 particelle. Con quella, calcoliamo numericamente la distribuzione dell'impulso aT=1.1K per diversi gruppi di parametri. Si mostra che le curve teoriche sono in buon accordo con i risultati osservati. Le corrispondenti curve del fattore di struttura del liquido si adattano benissimo ai dati misurati e il risultato migliore per l'energia dello stato fondamentale è − 7.12K.
    Abstract: Резюме Используь теориюU-матрицы, мы предлагаем микроскопическую теорию взаимодеюствующейN-бозонной системы при ненулевых температурах. Гамильтониан включает член, описывающий внешнее влияние, член двух-частичного взаимодействия и член, относящийся к дипольному типу взаимодействия. При исследовании основного состояния шидкого4He учитяватся только двух-частичное взаимодействие. Основываясь на данных по рассеянию, мы выводим двух-частичную потенциальную функцию. Мы численно определяем распределение по импульсам приT=1.1K для некоторых систем параметров. Показывается, что теоретические кривые согласуются с наблюденными результатами. Соответст вующий структурный фактор зидкости хорошо согласуется с экспериментальными данными. Полученная величина энергии основного состояния составляет −7.12 K.
    Notes: Summary Employing theU-matrix theory in the present form we have presented a microscopic theory of an interactingN-boson system at nonzero temperature. The Hamiltonian includes a term describing the external influence, a term for a two-particle interaction and one pertaining to the dipole-type interaction. To study the ground state of liquid4He, only the two-particle interaction is included. Based on scattering data, we have deduced the two-particle potential function. With that we calculate numerically the momentum atT=1.1 K for several sets of parameters. It is shown that the theoretical curves agree well with the observed results. The corresponding liquid-structure-factor curves fit the measured data very well and the best result for the ground-state energy is −7.12K.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 10 (1988), S. 915-932 
    ISSN: 0392-6737
    Keywords: Quantum effects on the structure and dynamics of nondegenerate fluids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto In questo lavoro si applica la teoria della matriceU per dedurre un'espressione esplicita per lo spettro d'energia di eccitazione dell'4He liquido. Usando un modello per il potenziale chimico efficace per l'4He si è in grado di produrre uno spettro di eccitazione molto simile a quello osservato. L'inverso della massa efficace, cioè 1/m *, è ottenuto in funzione del momentok. Si trova che il rapporto tra massa efficace e la massa dell'atomo di elio ak=2.0 Å−1, cioè vicino alla profondità del rotore, èm * (k=2.0 Å−1)/m He= =0.18298, mentre quello ak=1.0 Å−1 èm * (k=1.0 Å−1)/m he=−0.17103. Il risultato teorico dello spettro di eccitazione è coerente con i dati sperimentali.
    Abstract: Резюме В этой статье мы применяем теориюU-матрицы для вывода явного выражения для энергетического спектра возбуждений Зидкого4He. Используя модель для эффективного химического потенциала для4He, мы воспроизводим спектр возбуждений который оказывается очень близким к зкспериментально наблюдаемому. Вычисляется обратная величина эффективной массы, т.е. 1/m *, как функция импульсаk. Получено отношение эффективной массы к массе атома гелия приk=2.0 Å−1, которое составляетm * (k=2.0 Å−1)/m He=0.18298, тогда как это отношение приk=1.0 Å−1 равноm * (k=1.0 Å−1)/m He=−0.17103. Теоретический результат для спектра возбужений согласуется с имеющимися экспериментальными данными.
    Notes: Summary In this paper, we apply theU-matrix theory to derive an explicit expression for the excitation energy spectrum of liquid4He. Using a model for the effective chemical potential for4He, we are able to produce an excitation spectrum which is very close to the observed one. The inverse of the effective mass,i.e. 1/m *, is obtained as a function of momentumk. The ratio between the effective mass and the mass of helium atom atk=2.0 Å−1,i.e. near the roton depth, is found to bem *(k=2.0 Å−1)/m He=0.18298, while the ratio atk=1.0 Å−1 ism *(k=1.0 Å−1)/m He=−0.17103. The theoretical result of the excitation spectrum is consistent with observational data.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 153 (1989), S. 229-251 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Following our series of works on anisotropic radiation, we analyze the Čerenkov condition in magnetized plasmas in this paper. We have discovered that the usual Čerenkov condition cos θ=1/nβ‖ isnot satisfied at a far field point in anisotropic media, implying that when a charge is moving in a magnetized plasma, a linear shock wave front does not form. Thus we can calculate the power received at a far field per unit time in such a medium — this quantity could not be evaluated according to previous theory. Numerical examples are presented to show various relevant characteristics of Čerenkov radiation in model plasmas.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 139 (1987), S. 311-320 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using a differential geometry approach, we have found two sets of new solutions to Einstein's equation of gravity in the presence of a spherically-symmetrical gravitational background, like the Earth. The transverse and longitudinal components of the metric tensor representing the gravity waves are all soliton solutions, propagating towards the origin of the Earth. If we consider the situation where the static background field is absent, the solutions still remain soliton-like in nature. The difference between our result and Einstein's is attributed to the two approximations taken previously — weak field and ‘harmonic condition’.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 137 (1987), S. 33-62 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We analyze the special features of cyclotron radiation in four different modes radiated by a mildly relativistic electron current in an anisotropic plasma, taking into consideration that the radiation is transmitted along the group velocity, rather than the wave normal direction. A systematic series of numerical analysis is carried out, to demonstrate the characteristics of the focussing effect and Doppler effect of the radiation, arising from anisotropy. The parameters used pertain to plasmas and radiators of the types encountered in the terrestrial upper atmosphere and the solar corona.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 151 (1989), S. 293-306 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Following up our previous analysis of cyclotron radiation in anisotropic plasmas, we derived expression for the power received at a far field point per unit frequency range along the group velocity direction dP(ξ, α)/dξ. We then carry out a series of numerical analysis presenting the spectral features rather than directional features of cyclotron radiation. In particular, we analyse the power received per unit solid angle per unit frequency range d2 P(ξ, α)/(dΦ dξ). It is expected the analysis result presented here can be compared directly with observation for parameters pertaining to astrophysical plasmas in stellar and terrestrial atmospheres.
    Type of Medium: Electronic Resource
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