The absorption spectrum of 12C2H2 between 12800 and 18500cm−1 II. Rotational analysis

The rotational structure of the vibrational bands of ¹²C₂H₂ is investigated in three spectral energy regions not previously systematically explored at high resolution, 12800–13500 cm^?1, 14000–15200 cm^?1 and 16500–18360 cm^?1, on the basis of new spectral data recorded by intracavity laser absorption spectroscopy. The rotational analysis of 17 new absorption bands arising from the ground state is reported (11 Σ_u ⁺ ? Σ_g ⁺ bands and 6Π_u ? Σ_g ⁺ bands). Four bands in the range studied show strong perturbations affecting both the line positions and intensities. Their detailed analysis is performed in order to determine the nature of the coupling schemes, the vibrational species and the rotational constants of the perturber states. Altogether, the vibration-rotation parameters of 21 newly observed vibrational states are derived.     

The effect of oil on the performance of heat pumps and refrigerators—II. Experimental results

The results of a prolonged investigation of the influence of the lubricating oil Shell Clavus 68 on the performance of an R12-based refrigeration-heat pump system are presented. The strategy is discussed for deciding if a given series of data collected at 10s intervals adequately represents the chosen experimental conditions and results are presented under both transient and steady state conditions. The effects of oil on evaporator capacity, coefficient of performance, heat transfer rates, evaporator outlet superheat stability, refrigerant mass flow rate, evaporator pressure drop and compressor discharge temperature are discussed, and the experimental results are compared with a theoretical analysis. Finally, it is shown that under certain (albeit unlikely) conditions, it is possible for both the evaporator and condensor to act as heat rejectors.     

The power and limits of the Judd—Ofelt theory: a case of Pr3+ and Tm3+ acetates and dipicolinates

Electronic absorption spectra of crystals and solutions of praseodymium and thulium acetates and dipicolinates are reported. The influence of spectral properties of both ligands on intensities of the f—f transitions in the crystals studied is discussed. In the near-IR region, overtone vibrations of ligands are strongly coupled with the f—f transitions, particularly with the hypersensitive ones. In the UV spectral range, absorption bands of the π → π?, n → π? and possible charge transfer of metal ? ligand transitions affect f—f transitions and should also be taken into account. The phenomenological Judd—Ofelt parameters evaluated for praseodymium complexes in solution and crystals are meaningless, because no set of intensities unbiased by ligand transitions and/or neighbouring f-d configurations is available. For Tm³⁺ compounds the Judd-Ofelt analysis has given quite good results, however no significant influence of the metal ion environment changes on the Ωλ parameters can be observed.     

Resonance line transfer and transport of excited atoms—II. Self-consistent solutions (1)

This second part of our study of non-LTE line transfer with convective transport of excited atoms presents self-consistent solutions of the radiative transfer equation and the kinetic equation of the excited two-level atoms, for the limiting case of no elastic velocity-changing collisions of the excited atoms. Pure Doppler broadening of the spectral line is assumed. We investigate reflecting and destroying boundaries for the excited atoms, while the boundary condition for the photons corresponds to free photon escape from the system. Our numerical procedure for solving the two coupled kinetic equations for the excited atoms and the photons is an iterative method using variable Eddington factors, and is described in detail. We present a simple model that considers the gas of excited atoms and the radiation field as two interacting fluids, which yields a straightforward interpretation of the various scale lengths encountered in the numerical results for the hydrodynamic properties (density, flux density, mean velocity) of the gas of excited atoms.     

The primary and secondary acceptors in bacterial photosynthesis: II. The structure of the Fe2+-Q− complex

The primary processes of bacterial photosynthesis take place in a membrane-bound protein called the reaction center (RC). The process involves light-induced electron transfer from a primary electron donor to a sequence of electron acceptors. The terminal acceptors, operating sequentially, are two ubiquinones, Q_A and Q_B, that couple magnetically to a high-spin (S = 2) Fe²⁺ forming an Fe²⁺-Q^? complex. We have used a variety of techniques to investigate the electronic as well as some features of the spatial structure of the Fe²⁺-Q^? complex in RCs fromRb. sphaeroides. These include: (a) static magnetization measurements in the temperature range of 0.7 to 190 K and magnetic fields up to 8 kG, (b) EPR spectroscopy at helium temperatures at 1.2, 9, and 35 GHz, (c) Mössbauer spectroscopy and (d) extended X-ray fine structure (EXAFS) determinations. The results of these measurements showed that Fe²⁺ resides in an asymmetric ligand field environment forming 6 ligands with a combination of oxygens and nitrogens. From the EXAFS results the distances of the Fe²⁺ to the first and third coordination shells were determined. These spatial features were subsequently corroborated by the X-ray structure of the RC, which showed the environment of the Fe to be a distorted octahedron, the base plane of which is formed by three N_?’s of histidines and one carbonyl oxygen; the apex is formed by a fourth N_? and a second carbonyl oxygen. The distances from the Fe²⁺ to the first and third shell were in good agreement with the values obtained from EXAFS. The most detailed information of the electronic structure of the Fe²⁺-Q^? complex was obtained from the EPR spectra using the spin Hamiltonian formalism. The following spin-Hamiltonian parameters were obtained: for the crystalline field parameters,D = 7.60 K,E/D = 0.25; for the electronicg-values, g_{Fe, x} = 2.16, g_{Fe, y} = 2.27, g_{Fe, z} = 2.04 and for the antiferromagnetic exchange interaction,J _x = ?0.13 K,J _y = ?0.58 K,J _z = ?0.58 K. The use of the spin Hamiltonian was validated by comparing the results obtained from it with those obtained from an exact numerical solution of the 25 lowest energy levels of the orbital Hamiltonian. Possible roles that Fe²⁺ may play in the function of the RC are discussed. They include a structural role in which Fe²⁺ liganded to four histidine nitrogens imparts a rigid structure to a four α-helix bundle and a role in the electron transfer kinetics, most notably from the intermediate acceptor I^? (bacteriopheophytin) to Q_A. Replacement of Fe²⁺ by diamagnetic Zn²⁺ retained all observed native characteristics of the RC.     

Absorption properties of infrared active gases at high pressures—II. N2O and CO

Absorptions of the near infrared N₂O and CO bands were measured at high pressures. The band intensities were found to be 0.153 ± 0.002, 1.14 ± 0.01, 1.67 ± 0.01,0.035 ± 0.002, 3.25 ± 0.02 and 49.9 ± 0.3 cm^-1/(atm-cm)_STP for the 2.0, 2.1, 2.3, 2.5, 2.6 and 2.9 μm N₂O bands, respectively, and 2.07 ± 0.02 cm^-1/(atm-cm)_STP for the first overtone CO band. It was also found for both molecules that the spectra measured under large absorber amounts are smaller in the band wings than those calculated from the Lorentzian line profile. This discrepancy is discussed in terms of non-Lorentzian behavior of the line profile.     

The deformation texture of β-tin II. Rolling texture

Measurements were made of the rolling texture of -tin which is produced by rolling the sample at a temperature of 20 °C and in the temperature interval –80°C–60 °C and –180 °C–110 °C.     

On the performance of advanced absorption heat transformers—II. The double absorption configuration

An innovative heat transformer can be derived from the TSHT discussed in Part I. Its configuration is essentially based on a serial arrangement of the two absorbers (“double absorption heat transformer”, DAHT) and allows a drastic reduction of the number of items necessary for the TSHT.The performance of a DAHT operated with the water-sulphuric acid system was computed by means of a lumped-parameter mathematical model and expressed in terms of the four indexes of performance previously used for the TSHT examined in Part I. The results show that the DAHT reaches its optimum performance at values of gross temperature lift intermediate between those optimal for the SSHT and the TSHT, respectively.     

Theory of Ordered Spaces¶II. The Local Differential Structure

In this paper we investigate the conditions under which the ordered spaces defined in [1] are locally diffeomorphic to ℝ ^N . In Sect.~1 we give an introduction and an overview of the results. In Sect. 2 we show that the axioms of [1] do not suffice to make light rays locally homeomorphic to ℝ. We introduce this structure via the new connectedness axiom 2.13, and work out some of its immediate consequences. In Sect. 3 we give the (somewhat involved) construction of timelike curves in a D-set, which are basic to everything that follows. They are used in Sect. 4 to prove (i) a nested interval theorem for ordered spaces; (ii) the contractibility of order intervals in D-sets; and (iii) that order intervals in D-sets are star-shaped. The notion of D-countability (meaning that a D-set has a countable base in the subspace topology) is introduced in Sect. 5. The Urysohn lemma shows that a D-countable ordered space is locally metrizable. If this space is also locally compact, then it has finite topological dimension N; these results are established in Sect. 6. The local differential structure now follows from known results: the embedding of such spaces in ℝ^{2 n +1}, and the result that an open star-shaped region in ℝ ⁿ is diffeomorphic to ℝ ⁿ . In conclusion, we exhibit these inclusions in Fig. 3, and suggest the possibility that Wigner's position on the “Unreasonable effectiveness of mathematics in the natural sciences” may be open to reasonable doubt. The axioms of [1] are given in the Appendix. Received: 26 November 1997 / Accepted: 10 February 1999     

The absorption spectrum of 12C2H2 IV. The regions 7600–9200 cm−1 and 10600–11500 cm−1

The absorption spectrum of ¹²C₂H₂ has been recorded by intracavity laser absorption spectroscopy (ICLAS) in the 10600–11 500 cm^?1 spectral region, where no absorption bands were previously reported. Fifteen bands starting from the vibrational ground state are observed and rotationally analysed. All corresponding excited vibrational levels were assigned using the polyad model, the so-called cluster model (El Idrissi, M.I., Liévin, J., Campargue, A., and Herman, M., 1999, J. chem. Phys., 110, 2074) which allows vibrational energies, rotational B_v constants and, to some respect, relative band intensities to be predicted. Additional data and constants are also provided in the range 7600–9200cm^?1, whenever improving the literature results, from spectra recorded previously at ULB using Fourier transform spectroscopy. The assignment procedure in the range recorded by ICLAS is detailed, leading to a deeper understanding of vibration-rotation and intensity features of the absorption bands within the frame of the cluster model.     

The physics of 2 ≠ 1 + 1

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distant particles. In an entangled EPR two-particle system, the value of the momentum (position) for neither single subsystem is determined. However, if one of the subsystems is measured to have a certain momentum (position), the other subsystem is determined to have a unique corresponding value, despite the distance between them. This peculiar behavior of an entangled quantum system has surprisingly been observed experimentally in two-photon temporal and spatial correlation measurements, such as “ghost” interference and “ghost” imaging. This article addresses the fundamental concerns behind these experimental observations and to explore the nonclassical nature of two-photon superposition by emphasizing the physics of 2 ≠ 1 + 1.     

Structures and energetics of BenGen (n = 1–5) and Be2nGen (n = 1–4) clusters

Cluster geometries and energies of Be_nGe_n (n = 1–5) and Be_2nGe_n (n = 1–4) have been examined in theoretical electronic structure calculations. Structure optimisations were carried out using DFT B3LYP/6-31G(2df) and the energies of the optimum geometries were ordered in QCISD(T) calculations. Be and Ge bond to each other and to other atoms of their own kind, creating a great variety of low-energy clusters in a variety of structural types. Comparisons of the germanide clusters with previously explored silicide and carbide structures reveal some structural similarities, but the germanides have much more in common with the beryllium silicides than with the carbides. However, germanide clusters show a greater tendency to form cage-like structures with potential in technological applications.     

Computational simulation of δ-Bi2O3. II. Charge migration

The fluorite phase of Bi₂O₃ has an extremely high ionic conductivity and although this is connected with the 75% average occupancy of the oxygen sites it is not due solely to isolated jumps of oxygen vacancies. Static lattice simulations depend on the existence of a structure based on a periodic lattice and it was shown in paper I that the Sillén structure, which involves a <111> superlattice of vacancies, is a satisfactory model for δ-Bi₂O₃. However, the Sillén structure is highly defective and includes a large number of <110> defects. Near-perfect Sillén domains, separated by changed boundaries, are shown not to have a particularly low energy, so that a domain mechanism of charge transport is unlikely. Instead, the charged defects in δ-Bi₂O₃ are vacancies and pseudo-interstitials (that is oxygen ions occupying normally-vacant sites in the <111> superlattice) associated with <110> defect chains. It is proposed that these defects have a high mobility due to two mechanisms of charge transport. One of these involves the transfer of charge carriers between collinear <110> defects; the other depends on the delocalization of charge that accompanies the addition of a vacancy or a pseudo-interstitial to a chain of <110> defects and is thus quite analogous to the mechanism of proton conduction in water.     

Halogen-substituted amides. VII—normal coordinate analysis of 2-fluoroacetamide and 2-iodoacetamide

A 30-parameter modified valence force field has been employed for a normal coordinate analysis of the in-plane vibrations of 2-fluoroacetamide and 2-iodoacetamide. The force constants have been refined using an overlay leastsquares technique. The potential energy distributions and eigen vectors have been used to make unambiguous vibrational assignments.     

Excitation of isomeric 1h 11/2 states in nuclear reactions induced by γ rays and neutrons and in beta decay

Isomeric ratios were measured for N=81 isotones (¹³⁵Xe, ¹³⁷Ba, ¹³⁹Ce, ¹⁴¹Nd, ¹⁴³Sm). In the experiment reported here, μ _ν ≤3±10^? J ^π=11/2^? isomers were excited in (n, γ) and (γ, n) reactions and in the β ⁺ decay of ¹³⁹Pr and ¹⁴¹Pm. In order to determine the reaction yields, use was made of the activation method involving measurement of the gamma-ray spectra of reaction products. It is found that, in the same reactions, isomeric ratios are different for isotones characterized by different atomic numbers Z. Isomeric ratios were calculated with the spectra of low-lying levels and radiative-transition probabilities established on the basis of the quasiparticle-phonon model. Good agreement between the experimental and calculated values of isomeric ratios is obtained for all isotopes invesigated here. The dependence of isomeric ratios on the atomic number Z of a nucleus is explained by the difference of reaction energies, which leads to different probabilities of excitation of activation levels through which the isomers being considered are populated.     

The Three Processes of Phase II – I Transformation of Isotactic Polybutene-1

The spontaneous transformation of the unstable tetragonal phase II to the stable twined hexagonal phase I of isotactic polybutene – 1 at room temperature and atmospheric pressure was shown to proceed by one of three different mechanisms with these mechanism being neutral (N), increasing (P) or decreasing (M) the phase transformation rate. The rate was shown to be influenced by environmental effects. The environment can increase or decrease the phase transformation rate and, to a smaller extent, influence the sample crystallinity and the amount of the residual, untransformed phase II. The transformation rate was principially affected by the segmental mobility, increased by solvents or decreased by some chemical compounds or groups (e.g.–CH₂-CH₂ – as a comonomer). The transformation rate of the M process starts after an induction period during which the transformation nuclei are blocked.     

The evaluation map in field theory,sigma-models and strings—II

In this paper, we examine specifically the rôle of the evaluation map in sigma-models and strings. We discuss the difference between sigma-models and field theory, as far as anomaly cancellation is concerned. The introduction of the Wess—Zumino terms in different sigma-models is considered. Anomalies in string theory are discussed, with special attention to the conformal anomalies and to the sigma-model anomalies for the imbedded (or immersed) world-sheet of the string. Conformal anomalies in two dimensions are connected to holomorphic and gravitational anomalies. In order to have the cancellation of the sigma-model anomalies of the string, certain topological conditions must be satisfied by the ambient manifold. The rôle of the evaluation map in the calculations of global anomalies is also discussed, both for field theories and for sigma-models. In particular global anomalies are connected with the differential characters of Cheeger and Simons. We show that the absence of global anomalies in sigma-models is guaranteed by the absence of torsion in suitable homology groups of the target space.On leave of absence from Dipartimento di Fisica dell'Università di Padova and Instituto Nazionale di Fisica Nucleare, Sezione di PadovaWork supported in part by: Ministero Pubblica Istruzione (research project on Geometry and Physics)On leave of absence from Department of Mathematics, University of North Carolina, Chapel Hill, N.C. 27514. From August 1 until December 20 at the School of Mathematics, Institute for Advanced Study Princeton NJ 08540, USA. Work supported in part by N.S.F.     

The elastic coupling between longitudinal and transversal vibrations оf isotropic rods II. Rods of circular cross-section

The new approximative method for calculating the frequencies of longitudinal vibrations of isotropic homogeneous rods described in part I. is used for rods of circular crosssection. Similarly to the rods of rectangular cross-section there does not exist any dead zone of frequencies.

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