Volume 16 / Fascículo 1-4
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ABSTRACT — The cycle animal values on the triangular and square site problems (extended by one more term) and the honeycomb bond cycle 1 animals are studied for their leading and confluent singularities as well as their multiplicities. 

ABSTRACT —Avariational approach to the dynamics of many-fermion systems appropriate to physical situations requiring a description in terms of mixed states has been developed. The formalism presented here leads in a straightforward way to a mean field theory for mixed states. In this framework, the well-known Hartree-Fock and RPA results for pure states are generalized to the case of mixtures.  

ABSTRACT — Using the Korff approximation for the first Townsend coefficient and the evolution of the charge with the anode voltage for a proportional counter geometry, effective molecular parameters were calculated for argon-isobutane mixtures with the following isobutane concentrations: 32, 39, 44, 48, 51, 56 and 60 percent.  

ABSTRACT — We report the effects of uniaxial stress perturbations on the H13 absorption lines in diamond. These lines are transitions to higher excited states of the well-known H3 optical centre. We show that, in common with other centres in diamond, the symmetry of the H3 centre is the same in each of its electronic states. 

ABSTRACT — The impact of the recent observational achievements of Space Astronomy together with new developments in the theories of star formation, stellar evolution and the origin of the Solar System led to a burst in research work on recently formed stars. 

ABSTRACT — The way the cyclotron absorption of gravitational waves varies with the cosmological red shift is analised.  

ABSTRACT — Observations of atmospheric ozone, including total and layered from the Dobson No. 13 spectrophotometer and direct sondings with the Brewer-Mast Ozonesonde are being made at Lisbon (38° 46’ N; 09° 09 W; 105 m msl.) covering almost three decades. In addition, as from December 1982 observations of the UV solar radiation at surface started at the same location, including the UV-B spectrum between 290nm and 330nm with the Berger’s Sunburning Ultraviolet Meter, as a contribution to radiation and ozone studies. 

ABSTRACT — We study degenerate four-wave mixing (DFWM) in a ruby crystal, theoretically and experimentally, in isotropic and anisotropic configurations. We show that thermal DFWM is negligible when compared with resonant DFWM and this one is not affected by self-focusing. Finally we present phase conjugate reconstruction of a microscopic object as an application of DFWM. 

ABSTRACT —It is shown that a simple circuit made of just an operational amplifier, a comparator with precision saturated output and two identical resistors can be used as the basic unit for fast, clockless, variable bit length ADC’s. An inexpensive version of this circuit is discussed. It is also shown how a modified circuit can be used as the basic unit for DAC’s. 

ABSTRACT — An approximate method, to calculate energy levels of quantum systems bound by a potential, is introduced which uses the virial theorem and an independent minimization procedure at each energy level. Results obtained are presented and discussed. 

ABSTRACT — The proton spin-lattice relaxation time T1 (T, « ) has been measured in the isotropic and columnar phases of hexaoctyloxytriphenilene 

BSTRACT — The development of an intermolecular potential energy function for carbon tetrafluoride is outlined, which is able, when used in conjunction with a perturbation theory, to accurately predict a variety of PVT properties over wide ranges of temperature and pressure (120-400 K, 0-110 MPa ). 

ABSTRACT — Using a corrected version of the method first developed by Shuttleworth, very precise calculations of surface energies for a large number of orientations of the surface in a monoatomic f.c.c. crystal have been undertaken. 

ABSTRACT — The description of the surface of a crystal in terms of terraces, ledges and kinks (TLK) is discussed , and equations are derived that determine the TLK content of the surface for any choice of terraces and ledges. The surface energy can be obtained as a sum of contributions of terraces, ledges and kinks. The form of the lattice sums that give these contributions in terms of a pairwise interaction potential is derived. 

ABSTRACT — X-ray diffraction data from two single crystals of VF2, obtained with two different wavelength radiations, ...

ABSTRACT — The paper reviews basic physical mechanisms underlying magnetoresistivity in normal and magnetic metals. It describes an experimental high accuracy system implemented in our laboratory and discusses some typical results of magnetoresistivy measurements in magnetic metals; brief comments on their interpretation are also presented. 

ABSTRACT —Astudy of pottery samples belonging to different periods is undertaken employing an energy dispersive high resolution X-ray fluorescence spectrometer and 30 mCi 238Pu source. 

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