The specific heat of the Coulomb glass is studied by numerical simulations. Both the lattice model with various strengths of disorder, and the random-position model are considered for the one- to three-dimensional cases. In order to extend the investigations down to very low temperatures where the many-valley structure of the configuration space is of great importance we use a hybrid-Metropolis procedure. This algorithm bridges the gap between Metropolis simulation and analytical statistical mechanics. The analysis of the simulation results shows that the correlation length of the relevant processes is rather small, and that multi-particle processes yield an essential contribution to the specific heat in all cases except the one-dimensional random-position model.

We focus on the central problem of discriminating between metallic and insulating behaviour in amorphous alloys formed between a semiconductor and a metal. For this, the logarithmic temperature derivative of the conductivity, w=dlnσ/dln T, has proved over recent years to be very helpful in determining the critical value xc of the metal content x for the metal–insulator transition (MIT). We show that, for various amorphous alloys, recent experimental results on w(T,x) are qualitatively inconsistent with the usual assumptions of continuity of the MIT at T=0 and of σ(T,xc) being proportional to a power of T. These results suggest that w(T,xc) tends to 0 as T→0, in which case the MIT should be discontinuous at T=0 (but only there), in agreement with Mott’s hypothesis of a finite minimum metallic conductivity.

We study the metal-insulator transition in two sets of amorphous Si_{1-x}Ni_x films. The sets were prepared by different, electron-beam-evaporation-based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission spectroscopy, and Rutherford back scattering. Investigating the logarithmic temperature derivative of the conductivity, w = d ln sigma / d ln T, we observe that, for insulating samples, w(T) shows a minimum increasing at both low and high T. Both the minimum value of w and the corresponding temperature seem to tend to zero as the transition is approached. The analysis of this feature of w(T,x) leads to the conclusion that the transition in Si_{1-x}Ni_x is very likely discontinuous at zero temperature in agreement with Mott's original views.

An analysis of high field hopping transport in a-Si1-yTay:H based on the effective temperature model is presented. Samples of a-Si1-yTay:H in sandwich configuration were prepared by sputtering in Ar/H-2 (5:1). High field measurements were made for temperatures T-M between 125 and 10 K with electric fields F from 1.0 x 10(5) to 7.5 x 10(7) Vm(-1). Experimental values of the effective temperature T-eff were obtained in conformity with the formula: sigma(T-eff; F congruent to 0) = sigma(T-M, F). Theoretical values of T-eff were calculated with the formula: T-eff(2) = T-M(2) + (0.6:eaF/k(B))(2). The analysis was carried out for two a-Si1-yTay:H samples: S5 and S6 with y = 0.0045 and 0.009, respectively. The results show a slight increase of the localisation length a with increasing both T-M and F. The values obtained for a (4.5 x 10(-10) m for the sample S5 and 3.7 x 10(-10) m for the sample S6) are compar able with those obtained from analysis of the de low field data ard are in partial agreement with those derived from the analysis of the ac low field data.

The paper presents resistivity characteristics of RuO2-based thick resistive films (temperature and magnetic field dependences), and analyzes them from the point of view of the possible conduction mechanism at low temperatures. It is shown that simple models based on tunnelling of charge carriers between conductive RuO2 grains and on variable range hopping of carriers between localized impurity states in the glass matrix iia thermal activation do not provide a satisfactory explanation for the electrical conductivity of the investigated thick film resistors. We suggest a new mechanism based on tunnelling of electrons through graded barriers between conductive particles which might explain the observed behaviour.

Scanning tunnelling microscope (STM) is a highly local probe of topology. It is also sensitive, however, to the three-dimensional electronic structure of the materials. We discuss how these features may be combined to allow the STM to be used for subsurface investigations. In particular, we discuss in detail the STM observations of quantum size effects (QSE). Supplementary techniques concerned with the Schottky barrier, connectivity and crystal orientation mapping are also discussed briefly.

We present conductivity data for a range of amorphous indium oxide samples and analyse the region of activated conductivity in an attempt to identify hopping processes. The results suggest that, in highly resistive samples, conduction is by variable-range hopping in a Coulomb gap, the localized states being deep in the gap and related to the disorder. In more conductive material, there appears to be a trend towards Mott hopping as the Fermi level rises towards the conduction band.

In January of this year the Secretaries of the GCE examining boards received from their Inter-Board Committee its final recommendations for a national common core in A-level physics. The events leading up to this were as follows. In December 1977 the Standing Conference on University Entrance (SCUE) published a consultative document entitled A University View on a Possible Minimal Core Syllabus for Sixth Form Physics. The report, which had been prepared in the context of the then current debate about the proposed two-level (N and F) examination structure, reflected the increasing concern in the institutions of higher education at the lack of common knowledge in physics among those who came to them having taken the subject at A-level. The report was widely circulated and discussed, and the desirability of having a common core was generally agreed by those concerned with science education. As a result of the welcome given to the 1977 SCUE document, the GCE boards set up an inter-board committee to explore the possibility of agreeing a common core for A-level physics. In the spring of 1980, after the Inter-Board Committee had begun work, the Secretary of State

Thermodynamics and Statistical Mechanics. By P.T. Landsberg (Oxford University Press: Oxford, 1979.) £9.75.

A simple and general derivation of approximate expressions for maximum metallic resistivity is given. Maximization of metallic resistance is then discussed, and it is argued that no system can remain electrically conducting with a resistance greater than about 20 kΩ as T → 0. Analysis of conditions necessary for observing maximum metallic resistance shows that it should be observable in practicable physical systems.

A new experimental technique, time domain spectroscopy (TDS) which enables the dielectric properties of materials to be measured over a wide range of frequencies is described. Results are presented of such measurements on amorphous germanium, prepared by thin film evaporation. The d.c. conductivity is shown to obey Mott's variable range hopping formula, whilst the a.c. conductivity has a frequency dependence of the form σ(ω)∝ω8, where 0.7

It is shown that the jew's harp excites the mouth cavity by producing short pulses when the lamella passes through the frame. A model is proposed for the mechanism by which the pulses are generated. When the mouth cavity is tuned to low frequencies, its natural resonance time is longer than the period between successive pulses and the harmonic series of the fundamental frequency of the lamella dominates the sound as the mouth tuning is changed. At high frequencies, the mouth cavity and ear respond to each successive pulse independently so that the dominant sensation of pitch coincides with the natural resonance frequency of the mouth and may be tuned continuously.

Results of theroretical and experimental investigations of the form of the transfer characteristics of phonon-coupled superconducting tunnel junctions are presented. In the ‘linear’ regime when quasiparticle densities are little deviated from their thermal values, the only outstanding feature is a gradient discontinuity which occurs when the generator voltage is large enough for quasiparticle relaxation processes to contribute to the density of detectable phonons. A fundamental theoretical treatment for this case gives an adequate qualitative description of observed structure and quantitative differences are tentatively attributed to inelastic scattering. Results in the ‘overinjection’ régime are much more complex. Some of the processes which may be expected to modify the spectrum of generated phonons and the detector response are discussed, and are shown to account qualitatively for the various features of the characteristics observed.

Samples of germanium in the doping range 1 × 1017 to 5 × 1017 cm−3 donors, with 25% compensation, have been investigated. The electrical receptivity-has been measured from 300 to below 0·2 K in most cases, and the Hall effect from 300 to 2·0 K. In all cases, activated conduction of some form is seen at low temperatures. This is interpreted in the more heavily doped samples as being initially due to activation to a mobility edge in the impurity band, going over to hopping (variable range) around the Fermi energy at very low temperatures as suggested by Mott. The behavior of the more lightly doped samples is consistent with the ideas of Mott and Davis on impurity conduction, each sample showing regions of different, constant activation energy even down to very low temperatures. The magnitude of the conductivities observed in the variable range hopping region is compared with the values suggested by theoretical considerations.

We report measurements of electrical conduction in thin films of amorphous carbon. The magnitude of the conductivity varies greatly from sample to sample. At low fields the current is always linear in voltage and shows the temperature dependence which is characteristic of the Mott hopping mechanism. At high fields conduction appears to be by the Poole-Frenkel mechanism with a range of trap depths and a large effective dielectric constant. In the case of conduction through thin carbon films the resistivity appears to become independent of temperature at very low temperatures, and for this we have no adequate explanation.

We have measured the lifetime of excitations in superconducting aluminium by two entirely different techniques. Several factors affecting the measured lifetimes are identified and an analysis of the experimental results shows them to be in agreement with theoretically calculated lifetimes.

Quarterly Journal of the Royal Meteorological SocietyVolume 86, Issue 368 p. 186-186 AddendumFree Access The fragmentation and electrification of very small droplets C. J. Adkins, C. J. Adkins Cavendish Laboratory, CambridgeSearch for more papers by this author C. J. Adkins, C. J. Adkins Cavendish Laboratory, CambridgeSearch for more papers by this author First published: April 1960 https://doi.org/10.1002/qj.49708636807Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume86, Issue368April 1960Pages 186-186 RelatedInformation

Measurements of the concentration of small ions near the ground showed that large numbers of «ions» of sign opposite to that of the potential gradient were produced in rain. A series of laboratory experiments designed to examine the processes involved, showed that the ions were produced by the disintegration of films of water when drops splash, and a determination was made of the dependence of the charge released by individual drops on the parameters involved.

AbstractIn certain atmospheric and geophysical studies it is desirable to have an accurate rate‐of‐rainfall recorder which can function for long periods unattended, which can respond within a few seconds to changes in rainfall and which can provide records of good time resolution. The instrument described in this paper was designed to meet these requirements.