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1.
Summary Thermal diffusivity is obtained with an accuracy of ∼ 1% by means of a new simple method, in which two parallel disks (of
chromel and alumel, respectively) surround the middle section of a cylindrical specimen of conducting material. The disks
act in the clamped zone as the hot juction of a thermocouple and, at the same time, as a heat source for the specimen, subjected
to a laminar air flow. A second thermocouple placed at the base of the cylinder accomplishes acquisition of another set of
experimental data from which the thermal diffusivity and the surface heat loss coefficient can be determined. Preliminary
measurements on aluminium 99.999% consistent with literature data have been reported.
Work supported by the Ministero della Pubblica Istruzione of the Italian Goverment. 相似文献
2.
Summary We show that an extrinsic semiconductor (n-type), containing a deep level from impurity centres, may produce stochastic self-oscillations in the electron density and
in the electric field, under intense illumination which ionizes the deep traps and heats the electrons. The feedback mechanism
is the dependence of the capture coefficient of the deep centres on the electron temperature and the dependence of the deep
energy level on electron temperature and concentration. The conditions for the occurrence of periodic and stochastic self-oscillations
are explicitly given.
Riassunto Si mostra che in un semiconduttore estrinseco (di tipon), contenente impurezze con un livello profondo, si possono produrre auto-oscillazioni stocastiche nella densità di elettroni in modo da ionizzare le impurezze e riscaldare gli elettroni. Il meccanismo responsabile è la dipendenza della sezione di cattura degli elettroni nel livello profondo della temperatura degli elettroni e la dipendenza dell’energia del livello dalla temperatura degli elettroni e dalla loro densitá. Si danno le esplicite condizioni per l’insorgere di auto-oscillazioni periodiche e stocastiche.
Резюме Мы показываем, что собственный полупроводник (n-типа), содержащий глубокий уровень, связанный с примесными центрами, может производить стохастические автоколебания в электронной плотности и в электрическом поле при интенсивном облучении, которое ионизует глубокие ловушки и нагревает электроны. Этот механизм обратной связи представляет зависимость коэффициента захвата для глубоких центров от электронной температуры и зависимость глубокого энергетического уровня от температуры и концентрации электронов. В явном виде приводятся условия для возникновения периодических и стохастических автоколебаний.相似文献
3.
Y. N. Pokotilovski 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):105-107
A possible experiment is discussed, for the observation of Anderson localization of the neutron. The localized state may be
formed in the process of inelastic downscattering of thermal or cold neutrons in a highly disordered substance with low neutron
capture and upscattering cross sections. The lifetime of trapped (localized) neutrons in the sample is measured by counting
the upscattered neutrons with a neutron counter surrounding the sample. Estimations of experimental parameters relevant to
such an experiment are given.
Received: 12 May 1997 / Revised: 12 September 1997 / Accepted: 16 September 1997 相似文献
4.
K. Ramesh S. Asokan K.S. Sangunni E.S.R. Gopal 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):207-212
Differential Scanning Calorimetric (DSC) studies on AgxGe15Te85-x glasses have been undertaken over a wide range of compositions, to understand the effect of topological thresholds on thermal
properties. It is found that the compositional dependence of glass transition temperature (T
g
), crystallization temperature (T
c
), activation energy for crystallization and thermal stability show anomalies at the rigidity percolation threshold. Unusual variations also observed in different thermal properties at
the composition x = 20, clearly establishes the occurrence of chemical threshold in these glasses.
Received: 27 January 1998 / Revised: 12 June 1998 / Accepted: 3 July 1998 相似文献
5.
H. Narnhofer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):351-356
It is shown using Vlasov dynamics that the density distribution corresponding to a mean field Bose condensate in an external
time dependent potential is adiabatically stable whereas density distributions corresponding to finite temperature are not.
Received: 27 February 1998 / Revised: 20 April 1998 / Accepted: 23 April 1998 相似文献
6.
Summary An iron meteorite has been studied by backscattering M?ssbauer spectroscopy. The internal magnetic field is found to exceed
significantly that of pure iron. 相似文献
7.
C. Basu 《Il Nuovo Cimento D》1992,14(9):947-953
Summary A simple method has been suggested to estimate the acoustic characteristics of porous structure from a hybrid model—a hybridisation
of Biot's phenomenological model and the microscopic multiple-scattering theory which introduces the idea of an effective
tortuosity. Without using any adjustable parameter this model may be used to provide rough estimates of the tortuosity, the
fast, the shear and the slow sound speeds. The predictions are compared with observation on water-saturated glass bead samples.
The author of this paper has agreed to not receive the proofs for correction. 相似文献
8.
Summary An extended three-body force shell model is developed and used to make an analysis of the volume dependence of low- and high-frequency
dielectric constants and thermoelastic Grüneisen parameters for CaF2, SrF2, BaF2 and PbF2 crystals. Lorentz-Lorenz and Clausius-Mossotti relations are modified in view of three-body interactions (TBI). Calculated
results yield better agreement with the experimental data as compared to those obtained by previous investigators.
Riassunto Si sviluppa un modello esteso a strati della forza a tre corpi e se ne fa uso per un'analisi della dipendenza dal volume delle costanti dielettriche a bassa e alta frequenza e dei parametri termoelastici di Grüneisen per cristalli di CaF2, SrF2, BaF2 e PbF2. Si modificano le relazioni di Lorentz-Lorenz e di Clausius-Mossotti in vista delle interazioni a tre corpi (TBI). I risultati calcolati sono in migliore accordo con i dati sperimentali di quelli ottenuti da precedenti studi.
Резюме Предлагается оболочечная модель для протяженной трех-частичной силы. эта модель используется для анализа обьемной зависимости при низких и высоких частотах диэлектрических постоянных и термо-упругих параметров Грюнайзена для кристаллов CaF2, SrF2, BaF2 и PbF2. Для трех-частичных взаимодействий модифицируются соотношения Лоренц-Лоренца и Клаузиуса-Москотти. Вычисленные результаты дают лучшее согласие с экспериментальными данными, чем результаты других авторов.相似文献
9.
S. N. Vaidya 《Il Nuovo Cimento D》1991,13(12):1449-1451
Summary The possibility of acoustic plasmons leading to nonequilibrium high-temperature superconductivity is considered in the system
Pd-H(D).
The author of this paper has agreed to not receive the proofs for correction. 相似文献
10.
Summary Room temperature trends have been measured in a small apartment in different climatic conditions. The results are compared
with those evaluated through a recently reported simulation procedure which treats the building analytically by network theory.
Riassunto Sono stati misurati gli andamenti della temperatura interna di un piccolo appartmento in varie condizioni meteorologiche. I valori cosí ottenuti sono stati confrontati con quelli previsti mediante un metodo di simulazione recentemente presentato in letteratura e che si basa su una trattazione analitica dell'edificio attraverso la teoria delle reti.相似文献
11.
M. Wilkinson B. Mehlig 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):397-398
We discuss the absorption of electromagnetic radiation in small conducting particles, in the case where the electron motion
is diffusive. We refine an earlier theory in which we calculated the absorption coefficient using an effective potential describing
the screened electric field. Our new theory incorporates the effects of non-locality in the electrical conductivity, and shows
how the two limiting behaviours of the effective potential at high and low frequencies can be derived from a unified theory.
Our results are in full agreement with our earlier calculation.
Received: 3 November 1997 / Accepted: 29 January 1998 相似文献
12.
F.H.L. Eßler V.E. Korepin F.T. Latrémolière 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):559-563
We consider finite temperature dynamical correlation functions in the interacting delta-function Bose gas. In the low-temperature
limit the asymptotic behaviour of correlation functions can be determined from conformal field theory. In the present work
we determine the deviations from conformal behaviour at low temperatures.
Received: 14 January 1998 / Accepted: 17 March 1998 相似文献
13.
Summary In the present paper an analysis of the dielectric behaviour and anharmonic contribution to the dielectric constants has been
made of KCl−KBr mixed ionic crystals. The temperature and volume derivatives of static (ε0), electronic (ε∞) dielectric constants and energy gap parameter (E
g) have been calculated using the Szigeti and Havinga and Bosman dielectric theories. The anharmonic contributions have been
estimated in terms of temperature derivatives of dielectric constants at constant volumes. The modified form of Clausius-Mossotti
theory of dielectric polarization has been used for the mixed crystal under study. The calculated quantities have been compared
with the available experimental data. A good agreement has been obtained.
To speed up publication, the authors of this paper have agreed to not receive the proofs for correction. 相似文献
14.
Summary The troposphere is the seat of powerful processes which originate separation of electric charges. Thunder clouds give rise
to a huge vertical separation of charges. But also known is a different electrification mechanism activated by wind, which
allows for horizontal separation of charges. In favourable conditions, when charges are displaced at long distances, image
charges appear in the ionspheric plasma and an upward electric field is originated which makes the ionosphere boundary unstable.
If this occurs, recombination of displaced charges involves ionosphere conductivity and gives rise to a downward electron
stream ejected from the bottom of the ionosphere. It may produce a peculiar airglow phenomenon, which consists of the emission
of light in a narrow region lying at stratospheric or mesospheric altitudes. This outcome of the electrification process just
mentioned shows a close connection with a special class of ?UFO? sightings, that is, those referred to by J. Hynek as ?nocturnal
light? and which consist of bright specks of light moving in the night sky. 相似文献
15.
V.N. Aseev A.I. Belesev A.I. Berlev E.V. Geraskin O.V. Kazachenko Yu.E. Kuznetsov V.M. Lobashev R.P. Ostroumov N.A. Titov S.V. Zadorozhny Yu.I. Zakharov J. Bonn B. Bornschein L. Bornschein E.W. Otten M. Przyrembel Ch. Weinheimer A. Saenz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):39-52
Measurements of the energy loss of fast electrons at an energy of 18 keV have been performed on molecules of hydrogen isotopes,
gaseous T
2
and frozen D
2
. Whereas in the case of gaseous T
2
the values of total inelastic cross-section ( cm2 for E
= 18.6 keV), average energy loss ( eV) and peak position of the energy loss spectra ( eV) agree well with the expectations, the corresponding values for quench condensed D
2
differ significantly from the ones for gaseous T
2
. We observe a significant lower total inelastic cross-section ( cm2, for E
= 18.6 keV) larger average energy loss ( eV) and higher peak position ( eV). These differences may be interpreted in terms of changes of the final state spectrum. A CI calculation for a D
2
cluster shows indeed a clear shift of the excited states in agreement with the observation.
Received 24 August 1999 相似文献
16.
N. Kristoffel 《Il Nuovo Cimento D》1994,16(2):149-153
Summary The influence of the onset of hole pairing onq=0 phonon frequency in a two-band model of high-T
c superconductivity is investigated. The estimated frequency shifts indicate a phonon softening with the lowering of temperature
and agree with the experimental magnitude. 相似文献
17.
Summary A quantum-mechanical calculation of the potential energy of a moving charged particle at the metal surface is presented for
a number of metals. We include both the plasmon dispersions and quantum recoil in obtaining our results. It is found that
both these effects are important in determining the value of the saturated potential.
Riassunto Si presenta un calcolo quantomeccanico dell’energia potenziale di una particella carica in movimento sulla superficie metallica, per un certo numero di metalli. Nell’ottenere i nostri risultati includiamo sia le dispersioni del plasma che il rinculo quantistico. Si trova che entrambi questi effetti sono importanti nel determinare il valore del potenziale saturo.
Реюме Для ряда металлов проводится квантовомезаническое вычислехие потехциалъной энергии движушейся заряженной частицы на металлической поверхности. Приi вычислениях учитывается дисперсия плаэмонов и квантовая отдача. Обнаружено, чмо эффеекта являются важными при определении определении величны насыщенного потенциала.相似文献
18.
19.
Summary The present paper provides a proposal to determine the configuration integral of non-ideal gas by the latent heat of phase
transition and the pressure coefficient. The integrated equation of the interaction potential is obtained. 相似文献
20.
Summary The heating energy required for the winter climatization of a small apartment has been measured; it results in good agreement
with the figures obtained by a recently reported simulation procedure. The comparison with the usually adopted calculation
code, which was taken as basis from the Italian standards, is discussed.
Riassunto è stata misurata l'energia necessaria a garantire, nel periodo invernale, il mantenimento di una data temperatura all'interno di un piccolo appartamento; si è confrontato il risultato cosí ottenuto con quello previsto mediante un programma di simulatzione recentemente descritto. Si discute il confronto tra questi risultati e le previsioni delle procedure di calcolo usualmente adottate, su cui si basa, ad esempio, la normativa italiana per questo settore.
Резюме Измеряется величина тепловой энергии, необходимой в зимний период для небольшой квартиры. Результаты хорошо согласуются с данными, полученными недавно с помощяю программы моделирования. Проводится сравнение полученных результатов с предсказаниями обычно применяемых вычислений, которые базируются на Итальянских стандартах.相似文献