Dielectric and thermoelastic properties of alkaline-earth fluoride crystals

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.

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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.

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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.

     

On Hurter-Driffield characteristics and optical storage in mixed crystals of alkali halides

Hurter-Driffield characteristic curves and the quality of stored and retrieved information in coloured mixed crystals of alkali halides are presented.     

Study of photo-elastic behaviour of mixed alkali halides

The present paper deals with the analysis of strain optical constants of the mixed alkali halide crystals.     

Experimental validation of a simulation code to describe the building thermal behaviour

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.

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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.

     

On some measurements of the propagation properties of thermal waves in the Nb-H and Ta-H systems

Summary By means of an experimental technique based on a nonsteady-state method,i.e. on the propagation of thermal waves, we have measured at room temperature for oscillation frequencies between 6 and 30 mHz the thermal diffusivity, the lateral thermal-loss coefficient and the ?fractional heat loss? in Nb and Ta wires as a function of hydrogen doping. The appearance of hydride formation and precipitation notably changes the behaviour of these quantities. From these measurements it was also possible to calculate the propagation velocity and attenuation coefficient of thermal waves. It was found that the increase of the hydrogen concentration in the solid solution produces a gradual decrease in the velocity and increase in the attenuation coefficient until the solubility limit is reached. For larger hydrogen concentrations, the velocity showed a tendency to increase towards the value of the pure metal, while the attenuation coefficient decreased below the value of the pure metal. These results as a whole appear quite promising for studying the properties of hydrogenated systems. This work was supported by the Gruppo Nazionale di Struttura della Materia of the Consiglio Nazionale delle Ricerche and by the Centro Interuniversitario di Struttura della Materia of the M.P.I., Roma (Italia).     

On the possibility of nonequilibrium high-temperature superconductivity in PdH and PdD

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.     

A ring-source method to measure the thermal diffusivity of a conducting specimen in forced air flow: Study on aluminium

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.     

Investigation on the chirality of positrons from22Na decay and their asymmetrical interactions with D-, L- and DL-alanines

Summary An investigation on the chirality of the positrons from²²Na and on their asymmetrical interactions with D-, L-, and DL-alanines was carried out. By using nuclear gamma-spectroscopy, the asymmetrical interaction was proved to be induced with a distinguishably asymmetrical effect.

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Riassunto è stata studiata l'interazione di positroni polarizzati con aminoacidi, D- L- e DL-alanine. Mediante misure di spettrometria nucleare gamma, si dimostra che l'interazione è asimmetrica e l'entità di tale effetto asimmetrico viene quantificata.

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Резюме Исследуются киральнсоть позитронов из распада²²Na и их асимметричные взаимодействия с D-, L- и DL-аланинами. Используя ядерную гаммаспектроскопию, доказывается, что асимметричное взаимодействие индуцирует асимметричный зффект.

     

The Born repulsive parameters and dielectric behaviour of alkali halides

The dependence of the Born repulsive parameters of alkali halides on elastic and dielectric data has been discussed. The values of hardness parameter in alkali halides have been recalculated using the revised values of van der Waals energies. It is observed that the two sets of hardness parameter corresponding to elastic and dielectric data differ from each other but become compatible if an effective charge parameter for the ions is introduced. Its usefulness has been demonstrated by calculating the strain derivative of static dielectric constant of alkali halides.     

Effective tortuosity and different acoustic waves in porous media

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.     

Air ions as possible environmental monitors

Summary Measurements in air of both positive and negative ions ((0.001÷0.003) μm diameter) concentrations were made on a monthly basis in the following different sites: a mountain top and a natural Gallery of the Gran Sasso laboratory. From the analysis of preliminary data, these concentration values seem to be strictly dependent upon the environmental characteristics and might be used as environmental monitors.     

Feasibility of model ecosystems

Summary We introduce a structure with preferential trophic channels in a two-level Lotka-Volterra model. We discuss the dependence of feasibility on the number of species and on other properties of the system.

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Riassunto S'introduce una struttura con canali trofici preferenziali in un modello di Lotka-Volterra a due livelli. Si discute la dipendenza della realizzabilità del modello dal numero di specie e da altre proprietà del sistema.

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Резюме В двухуровневую модель Лотки-Вольтерра вводится структура с предпочтительными трофическими каналами. Мы обсуждаем влияние числа видов и других свойств системы на реализуемость модели.

     

Saturation of the image potential at the metallic surfaces

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.

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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.

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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.

     

Applications of laser for ceramic alloying on metallic surfaces

Summary Ceramic and metallic materials were alloyed and cladded on a C40 steel by means of a CO₂ laser heat source. The main objectives of the research were to obtain a surface modification of the C40 steel in order to increase its wear resistance and to develop a repeatable coating process of potential industrial application. In the following sections, the laser coating process (including experimental equipment and working parameters) and the most important metallurgical results are described.     

The sign of interband interaction and stability of the superconducting ground state in the multiband model

Summary It is stressed that the stability of the superconducting ground state in the two-band model is guaranteed for both signs of the leading interband interactionW. Thereby the requirement for the energy minimum fixed the phase differences of two order parameters as |ϕ₁-ϕ₂|=0,2π, … ifW<0 and |ϕ₁-ϕ₂|=π 3π, … ifW>0, and this difference is reflected in the ground-state wave function.     

Stability of the α-RbCu4Cl3I2 solid-electrolyte cell

Summary The performance of the solid-state galvanic cells with α-RbCu₄Cl₃I₂ as the solid electrolyte has been investigated. The role of moisture in the decomposition of α-RbCu₄Cl₃I₂ has been studied, too. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

On the influence of superconductivity on the phonon frequencies in a two-band model

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.     

Eu掺杂TbMnO3多晶材料的介电性质

采用固相反应法制备了Tb_0.8Eu_0.2MnO₃多晶材料.对样品的X射线衍射（XRD）分析表明Eu³⁺固溶于TbMnO₃中.测量了样品在低温(100 K ≤T≤ 300 K)和低频下(200 Hz≤f≤100 kHz)的复介电性质.在此温度区间内发现了两个介电弛豫峰.经分析认为低温峰（T≈170 K）起源于局域载流子漂移引起的偶极子极化效应,而高温峰（T≈290 K）则是由离子电导产生的边界和界面层的电容效应引起的.电阻率的测量显示在低温下（T≈230 K）存在明显的导电机制转变. 关键词： 多铁性材料 掺杂 介电性质     

The role of davydov solitons in the molecular chains with cubic anharmonicity in the electron transfer from the donor to the acceptor molecule

Summary This paper is concerned with the study of electron transfer from a donor molecule (D) to an acceptor molecule (A) along a one-dimensional molecular chain to which D and A are joined. It is shown that, in the case when the chain vibrations are with cubic anharmonicity, the probability of electron transfer has analogous form as well as in a previous paper.

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Riassunto Questo lavoro tratta lo studio del trasferimento degli elettroni da una molecola donatrice (D) a una molecola ricevente (A) lungo una catena molecolare unidimensionale alla quale sono unite D e A. Si mostra che, nel caso in cui le vibrazioni della catena avvengano con anarmonicità cubica, la probabilità di trasferimento elettronico ha forma analoga a quella trattata in precedenza.

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Резюме В этой статье исследуется перенос электрона от донорной молекулы (D) к акцепторной молекуле (А) вдоль одномерной молекулярной цепочки, в которой объединены молекулы D и А. Показывается, что в случае, когда колебания цепочки обладают кубческой ангармоничностью, то вероятность переноса электрона имеет аналогичную форму, также как и в предыдущей статье.