Showing papers in "Il Nuovo Cimento B in 1971"
2,597 citations
TL;DR: Neutral pion decay and galactic gamma radiation from demodulated cosmic ray spectrum, discussing neutral pion meson production was discussed in this article, where the authors also discussed the role of neutral pions in meson creation.
Abstract: Neutral pion decay and galactic gamma radiation from demodulated cosmic ray spectrum, discussing neutral pion meson production
45 citations
TL;DR: In this article, it is shown that the "averaging" method put forward by Bogoliubov, Mitropolsky and Kruskal can in many cases be replaced by a method constructing a formal transformation which brings the Hamiltonian into a normal form.
Abstract: This paper discusses perturbation theories in classical and quantum mechanics which avoid secular terms. It is shown that the «averaging» method put forward by Bogoliubov, Mitropolsky and Kruskal can in many cases be replaced by a method constructing a formal transformation which brings the Hamiltonian into a normal form. The transformation bears great resemblance to the Foldy-Wouthuysen transformation of the Dirac equation.
43 citations
TL;DR: In this paper, the generalized anharmonic oscillator p2 +x2 +βx8 was considered and the convergence of the Pade approximants was shown to converge faster than (2n)!.
Abstract: We consider the generalized anharmonic oscillatorp2 +x2 +βx8. This model is interesting because the coefficients of the perturbation expansions for the energy eigenvalues diverge faster than (2n) !. Evidence is found against the convergence of the Pade approximants. The approximation method based on the Borel summability exhibits the same features found for theβx4-perturbation. The numerical analysis suggests also the introduction of another summation method, whose approximants have the useful monotonicity properties of the Pade ones.
40 citations
TL;DR: In this article, it was shown that the otherwise metastable 2s level of muonic hydrogen will rapidly be depopulated by collisions with neighboring hydrogen atoms at reasonable hydrogen densities.
Abstract: We find that the otherwise metastable 2s level of muonic hydrogen will rapidly be depopulated by collisions with neighboring hydrogen atoms at reasonable hydrogen densities ; σ≃4a 0 2 This is because of the « Stark transitions » 2s ⇆ 2p that take place when the mesic atom passes through a hydrogen atom The conclusion fails for slow (ke < 03 eV) Μp atoms, but these are expected to be rare
22 citations
TL;DR: In this article, a simple cosmological model was proposed to explain the missing mass attributed to gravitational waves and dead, dark galaxies, which is described by a simple rate equation containing a characteristic frequency α.
Abstract: The strong bursts of gravitational waves detected by Weber, if confirmed, suggest the presence in the Galaxy of arelativistic cluster of collapsed bodies which «burns» its own gravitational potential energy and slowly decays into a dead, collapsed object. We discuss the possibility of this being a common feature throughout the universe and consider a simple cosmological model in which the «missing mass» is attributed mainly to gravitational waves and dead, dark galaxies. The production of the former is described by a simple rate equation containing a characteristic frequency α. Using the known value of the Hubble constantH and the present visible mass density we find, when the efficiency of the process is, say, 0.5, α≈8H; the corresponding gravitational brightness of an average galaxy turns out to agree with Weber's figure (assuming a wide-band spectrum) to within a factor 2. This model features an isotropic cosmological background of gravitational waves, with energy density about 50 times smaller than the energy arriving from the galactic nucleus.
22 citations
TL;DR: In this paper, a new kind of antenna has been developed for gravitational radiation, which consists of a disc operating in the radial mode of circular symmetry, and search has been carried out for a scalar component.
Abstract: A new kind of antenna has been developed for gravitational radiation. It consists of a disc operating in the radial mode of circular symmetry, and search has been carried out for a scalar component. The observed ratios of coincidence rates and the observed directivity are consistent with an absence of a scalar component from the observed radiation.
21 citations
IBM1
TL;DR: In this article, a theory of nonlinear inelastic light scattering in solids involving two incident photons, a phonon of frequency ω(in0), and the scattered photon of frequencyω3=ω1+ω2±ω0 is developed.
Abstract: Nonlinear light scattering from phonons opens up new possibilities in the study of ionic motion. A theory of nonlinear inelastic light scattering in solids involving two incident photons of frequencies ω(in1) and ω(in2), a phonon of frequency ω(in0), and the scattered photon of frequencyω3=ω1+ω2±ω0 is developed. When both the incident light waves are the same, it reduces to the intensity-dependent light scattering from phonons in crystals. It is shown that the cross-section for the nonlinear scattering is smaller by a factor |E(inL)|(su2)/{|E(ina)|}(su2) as compared to the corresponding linear scattering with only one incident photon, where |EL| is the amplitude of the electric field of the additional incident wave andEais of the order of (106÷107) e.s.u. at optical frequencies. A nonlinear polarizability theory for the scattering based on the linear polarizability theory of Born and Bradburn of the first-order linear Raman effect is also considered and shown to be equivalent to the general theory in the limit of zero phonon frequency. Symmetries of the scattering tensor and selection rules for long-wavelength nonpolar optical phonons are derived for all the cubic point groups. These selection rules are different from those for the first-order Raman effect and the intra-red absorption. The rate of photon production in the stimulated nonlinear process is discussed.
19 citations
19 citations
TL;DR: In this article, a realistic model is presented to study the structure of the donor ground states in the semiconducting III-V compounds, and the lifting of the degeneracies is due to the intervalley interaction of the impurity potential between degenerate minima and also between minima at different energy.
Abstract: A realistic model is set up in order to study the structure of the donor ground states in the semiconducting III-V compounds. The model is also applied to Si and gives results in agreement with those of Baldereschi. The lifting of the degeneracies, which are present in the effective-mass approximation, is shown to be due to the intervalley interaction of the impurity potential between degenerate minima and also between minima at different energy. The impurity states in GaAs are studied in detail as function of the energy separation between thek = 0 minimum and the subsidiary ones located atk = (2π/a)(1, 0, 0) etc. States of the same symmetry originating from those minima strongly interact, according to the noncrossing rule, when the energy separation is small and this produces a strong shift of the impurity states and a mixing of the wave functions.
19 citations
TL;DR: In this paper, the energy loss rate of underrock muons of energy between 10 and 105 GeV is calculated using recent experimental information on the nuclear interactions and recent calculations on pair production and bremsstrahlung.
Abstract: The energy loss rate of underrock muons of energy between 10 and 105 GeV is calculated using recent experimental information on the nuclear interactions and recent calculations on pair production and bremsstrahlung. The effect of the range straggling is evaluated with an accurate Monte Carlo calculation and the intensity-depth curve at great depths is derived for different values of the index of the muon energy spectrum at sea level in the TeV region.
TL;DR: In this paper, a general method of finding first-order wave equations without subsidiary conditions for integer spin and finite mass is described, and examples of spin 0, 1, 2 and 3 are used to illustrate this method.
Abstract: A general method of finding first-order wave equations without subsidiary conditions for integer spin and finite mass is described. Spins 0, 1, 2 and 3 are examples that we use to illustrate this method.
TL;DR: In this paper, a formulation of a nonrelativistio scattering theory is given which is based exclusively on the asymptotic behaviour in time of expectation values of observables, and it is shown how this approach to scattering theory can supply a framework which incorporates scattering involving long-range potentials.
Abstract: A formulation of a time-dependent nonrelativistio scattering theory is given which is based exclusively on the asymptotic behaviour in time of expectation values of observables. This leads in a natural way to the concepts of « physical » asymptotic states and wave operators, which are generalizations of their conventional « strong » counterparts. Basic properties of these quantities and their relation to their « renormalized » counterparts are derived. It is shown how this approach to scattering theory can supply a framework which incorporates scattering involving long-range potentials.
TL;DR: In this paper, a description of the valence and conduction bands of SrTiO3 was obtained from the analysis of structure in the absorption tail, which is observed in the low-temperature spectra.
Abstract: Absorption and electroabsorption (EA) measurements allow a description of the valence and conduction bands of SrTiO3, in theΔ-direction. This type of information has been obtained from the analysis of structure in the absorption tail, which is observed in the low-temperature spectra. Urbach’s behavior appears above 160 °K and is experimentally followed up to 514 °K. Possible mechanisms for the evolution of the absorption tail with temperature are discussed.
TL;DR: In this article, the absorption coefficient for two-photon transitions in a magnetic field is given for the case of M 0-type singularities in second-order perturbation theory.
Abstract: The absorption coefficient for two-photon transitions in a magnetic field is given for the case ofM0-type singularities in second-order perturbation theory. States belonging to the two bands between which the transitions occur and states associated with other bands of the crystal are considered, as well as intermediate states. Correspondingly, two types of transitions, with selection rules Δn = ± 1 (inter-intra) and Δn = 0 (inter-inter), are shown to occur and explicit expressions for the transition probabilities are given. The selection rules are also discussed.
TL;DR: The gravitational field predicted by general relativity for a tachyon is in many ways similar to the shock wave produced by an object moving faster than the signal velocity in a medium as discussed by the authors.
Abstract: The gravitational field predicted by general relativity for a tachyon is in many ways similar to the shock wave produced by an object moving faster than the signal velocity in a medium. It is an intense wave and for a dense macroscopic tachyon it is capable of exciting Weber’s gravitational radiation detection apparatus across astronomical distances.
TL;DR: In this paper, a modified least-squares method is introduced with intent to explore effective numerical techniques for many-body scattering calculations, illustrated by applications to the nonrelativistic potential scattering.
Abstract: A modified least-squares method is introduced with intent to explore effective numerical techniques for many-body scattering calculations. In the present paper the least-squares method is illustrated by applications to the nonrelativistic potential scattering. Numerical calculations are carried out for an attractive exponential potential.
TL;DR: In this article, large-amplitude oscillations of the magnetization in Ba2Zn2Fe12O22 (Zn 2Y) single crystals were obtained by irradiating the sample with a 60 Oe magnetic field at 96 MHz.
Abstract: Large-amplitude oscillations of the magnetization in Ba2Zn2Fe12O22 (Zn2Y) single crystals have been obtained by irradiating the sample with a 60 Oe magnetic field at 96 MHz. The induced oscillations of hyperfine magnetic fields at the57Fe nuclei have been observed through an appreciable collapse of the Mossbauer spectra. Our experimental technique allowed us to measure simultaneously the Mossbauer spectrum with and without a radiofrequency field. A discussion of the magnetization processes which take place in the specimen is also given from a direct observation of the signal induced in a measuring coil.
TL;DR: In this article, the authors examined the deflection of rays of gravitational radiation passing through, the interior of a diffuse, static, spherically symmetric distribution of matter along with the focusing of the radiation by this process.
Abstract: The deflection of rays of gravitational radiation passing through, the interior of a diffuse, static, spherically symmetric distribution of matter is examined along with the focusing of the radiation by this process. Rays passing very near the centre of the distribution are the most strongly focused and meet the optical axis near a fixed « focal point ». It is found, in general, that sources of a given strength must lie within a particular region of space in order for their radiation to have a given threshold intensity near the focal point. For geometrical point sources, the volume of this region is infinite, but for sources with a nonzero radius it becomes finite and depends on the radius. By estimating the volume needed to explain the frequency of detection of pulses of gravitational radiation by Weber, we can put an upper limit on the size of the sources if the focusing mechanism is to be significant. The resulting size is too small to correspond to any reasonable physical process.
TL;DR: In this paper, the Cayley algebra of octonions is used to extract the square root of the classical Hamiltonian, in place of the Dirac-Clifford algebra.
Abstract: The Cayley algebra or algebra of octonions is used to extract the square root of the classical Hamiltonian, in place of the Dirac-Clifford algebra. The resulting wave equation is linear and covariant and possesses a positive definite conserved probability density, and a Lagrangian. The wave function is an octonion, and may be represented as a pair of quaternions. The wave function then possesses an internal degree of freedom which corresponds to multiplication from theright by the Pauli matrices. Lorentz transformation of the wave function is effected byleft multiplication, which does not mix up isospin eigenstates. The wave equation seems appropriate for a dynamical description of an isospin doublet. The electromagnetic properties of the objects described by the wave function are those of a Dirac particle with the usual magnetic moment.
TL;DR: In this paper, the applicability of the Slater and of the Kohn and Sham approximations to the exchange has been investigated through the behavior of thed-bands of zinc and cadmium within the framework of the APW method.
Abstract: The applicability to crystals of the Slater and of the Kohn and Sham approximations to the exchange has been investigated through the behaviour of thed-bands of zinc and cadmium within the framework of the APW method. Both approximations were found to give correctly the features of the Fermi surface in both metals. However, the Slater approximation locates thed-bands very deeply. On the contrary in the Kohn and Sham approximation thed-bands appear as resonances of the muffin-tin potential, within the width of thes-like conduction band. Such a strong rising could possibly not be entirely attributed to inadequacy of the exchange approximations but, more probably, to the lack of dynamical correlation in the crystal potential.
TL;DR: The absolute thermoelectric powerS of chromium and chromium-silicon alloys containing 0.46, 0.90, 1.37,1.85, 2.74, 3.19 and 3.67 at. % was determined as a function of temperatureT between 50° and 350 °K as discussed by the authors.
Abstract: The absolute thermoelectric powerS of chromium and chromium-silicon alloys containing 0.46, 0.90, 1.37, 1.85, 2.74, 3.19 and 3.67, at. % silicon has been determined as a function of temperatureT between 50° and 350 °K. TheS vs. T curves exhibit large anomalies in this temperature range due to the transition from a paramagnetic to an antiferromagnetic state. These transitions in samples containing 1.37, 1.85 and 2.74 are essentially discontinuous and similar to that observed in the chromium-3.3 at. % iron sample at 248 °K, where it undergoes a transformation from a transverse spin-density wave state to a commensurate antiferromagnetic structure. It is suggested that a commensurate antiferromagnetic structure also exists in the chromiumsilicon system for silicon concentrations larger than 1 at. %.
TL;DR: In this article, the angular, spectral and temporal properties of Cerenkov light produced in cosmic-ray extensive air showers (EAS) were investigated and a two-component model for the origin of the light was proposed, with production occurring not only at the electron maximum but also at greater atmospheric depths from unscattered, nearly "onaxis" particles, such as expected in the EAS core.
Abstract: New experimental studies of the angular, spectral and temporal properties of Cerenkov light produced in cosmic-ray extensive air showers (EAS) are reported. These data appear to be best explained by a two-component model for the origin of the Cerenkov light with production occurring not only (predominantly) at the electron maximum but also at greater atmospheric depths from unscattered, nearly «onaxis» particles, such as expected in the EAS core. Monte Carlo calculations to be published of EAS cores support this hypothesis. An individual EAS may thus be detected at its maximum of electromagnetic development and at its core simultaneously. New experiments employing these techniques are discussed and the important implications for the possible identification of the primary particle initiating the EAS detected are considered. Experiments are now in progress using the methods reported here to search for cosmic γ-ray sources as well as to study the primary cosmic-ray mass spectrum at energiesE0⋧1012eV.
TL;DR: In this paper, measurements of two-photon conductivity in ZnS(Cu) and CdS single crystals excited by aQ-switched ruby laser are reported.
Abstract: Measurements of two-photon conductivity in ZnS(Cu) and CdS single crystals excited by aQ-switched ruby laser are reported. The results show the typical quadratic dependence of two-photon processes. In CdS the photocurrent is originated by band-band transitions, while in ZnS(Cu) impurity states are involved. From a comparison between the experimental results and a theoretical analysis of the photo-current a determination of the nonlinear cross-section is obtained; this is in good agreement with two-photon absorption measurements.
TL;DR: In this article, the effects of the atomic motions on the stationarization of the electron speed distribution function in a gas in an electric field are studied, and particular attention is given to the cases in which the momentum transfer collision frequency between electrons and atoms is independent of their relative speed.
Abstract: The effects of the atomic motions on the stationarization of the electron speed distribution function in a gas in an electric field are studied. Particular attention is given to the cases in which 1) the momentum-transfer collision frequency between electrons and atoms is independent of their relative speed, 2) the background gas is xenon at the temperatureT= 300 ℴK.
TL;DR: In this article, a kinetic model for the interpretation of the monomolecular shape of T.S. signals has been proposed and the trap parameters have been obtained, which confirm the assumption that we are dealing with an anthracene molecular level.
Abstract: With T.S.C. measurements on anthracene crystals it is possible to obtain useful information on trapping levels. We have examined the trapping energy level withE = (0.75+-0.07) eV in anthracene crystals. A kinetic model for the interpretation of the monomolecular shape of T.S.C. signals has been proposed. The values of the trap parameters have been obtained. Such values confirm the assumption that we are dealing with an anthracene molecular level. We check that the energy level studied traps positive carriers and we obtain information on the distribution of carriers trapped near the illuminated surface of the anthracene crystal.
TL;DR: In this paper, the concept of spinors which transform according to the unimodular group is analyzed on the basis of Riemann-Cartan geometry, and conservation laws are derived by considering the invariance of the action function under infinitesimal co-ordinate and spin transformations.
Abstract: The concept of spinors which transform according to the unimodular group is analysed on the basis of Riemann-Cartan geometry. Using the principle of minimal coupling, we obtain a matter Lagrangian, which differs from the Lagrangian of the conventional theory of general relativity in that it is also a function of torsion. Conservation laws are derived by considering the invariance of the action function under infinitesimal co-ordinate and spin transformations. These conservation laws or identities lead to the definition of an asymmetric energy-momentum tensor, the antisymmetric part of which is related to the spin angular momentum. It is also shown that the force acting on the material system depends on the spin of the material and on the curvature.
TL;DR: In this paper, the conditions that a wave packet preserves its main characteristics during its motion in a crystal and that it scatters only after it has reached the impurity center are discussed.
Abstract: The conditions which ensure that a wave packet preserves its main characteristics during its motion in a crystal and that it scatters only after it has reached the impurity centre are discussed.
TL;DR: In this article, the decay time for the kernel of a generalized master equation and the evolution of macroscopic quantities of the measuring device were investigated. And they were found to justify the possibility of a macro-scopic description of the measurement apparatus, and a relevant hypothesis was found to be the separation of two characteristic times.
Abstract: A contribution is given to the attempts towards a solution of the measurement problem in quantum mechanics, in the spirit of some previous papers. In order to justify the possibility of a macroscopic description of the measuring apparatus, a relevant hypothesis is found to be the separation of two characteristic times: the decay time for the kernel of a generalized master equation and the characteristic time for the evolution of macroscopic quantities of the measuring device.