The phase behavior of a cross-linked polymer blend made of two incompatible species, $A$ and $B$, of different chemical nature is analyzed. Besides a homogeneous phase, this system also exhibits two microphases and a phase of total segregation. The transition between the homogeneous and the microphase is continuous along a $λ$-line; a first-order phase boundaries separate the microphase and the disordered phase from the phase of complete segregation. The critical line meets the first-order phase boundaries at an end point. Scaling arguments indicate that, close to any end point, the equations for the first-order phase boundaries exhibit nonanaliticities associated with the singularities present at the thermodynamic functions near the critical line. Explicit expressions for the phase boundaries near the end point for a cross-linked polymer mixture are obtained and checked for singularities.
The Z-expansion theory of Atomic Structure is supplemented with the inclusion of the external screening concept, calculated from a simplified version of the works of M. Kregar, where the two-body potential energy operators are split into the sum of effective one-body operators. The use of Z- and N-dependent screening parameters instead of screening constants, gives a simplified Screened Hydrogenic Model which compares favourably with more sophisticated methods, specially for ionized atoms.
The magnetic properties of unoccupied electronic states in nonmagnetic metal films deposited on a clean ferromagnetic surface are studied by Inverse Photoemission excited by low-energy spin-polarised electrons. V and Pt ultrathin films grown on Fe(001) are considered as examples. Along with the Fe substrate majority- and minority-spin peaks, interface and overlayer-derived features are clearly identified in Pt/Fe(001). The spin polarisation dependence of the relative transitions indicates a ferromagnetic coupling between Pt and Fe. In V/Fe(001) no overlayer-induced transitions are detected. A strong attenuation of both majority- and minority-spin electrons passing through the V film is observed. This result is discussed in terms of the electron mean free path and its spin dependence in magnetic films.
Iron molybdenum phosphate glasses [xMoO3 · (0.6 -x)P2O5 · 0.4Li2O] :yFe2O3 with 0 ≤x ≤ 0.6 andy = 0.03 (mol%) prepared in ambient atmosphere using the melt quenching technique were studied by using DC electrical conductivity,57Fe Mössbauer and infrared spectroscopies. The DC conductivity depends on the MoO3 concentrationx. It was observed that, with increasingx, the ratio Fe2+ /(Fe3+ + Fe2+) and the DC conductivity increase. Infrared spectroscopy and X-ray powder diffraction indicate that a Li2 MoO4 crystalline phase is present for high MoO3 content samples (x = 0.5, 0.6).
We review the predictions of the replica approach both for the statics and for the off-equilibrium dynamics. We stress the importance of the Cugliandolo-Kurchan off-equilibrium fluctuation-dissipation relation in providing a bridge between the statics and the dynamics. We present numerical evidence for the correctness of these relations. This approach allows an experimental determination of the basic parameters of the replica theory.
The design criteria used in the development of IR station 13.3 at the Daresbury SRS are reviewed particularly in terms of its principle application to reflection-absorption infrared spectroscopy (RAIRS). An example of current performance is given in the form of a RAIR spectrum of chlorine atoms adsorbed on Ag(100). The application of the station to infrared microscopy is reviewed and IR spectra from a thin polymer laminate are used to compare performance with that using a conventional infrared source.
In this paper we present a method to study the folding structure of a simple model consisting of two kinds of monomers, hydrophobic and hydrophilic. This method has three main steps: an efficient simulation method to bring an open sequence of homopolymer to a folded state, the application of a painting method called (regular hull) to the folded globule and the refolding process of the obtained copolymer sequence. This study allows us to suggest a theoretical function of disorder distribution for copolymer sequences that give rise to a compacted and well micro-phase separated globule.
A room temperature X-ray photoelectron spectroscopy study of crystals of the Sn2P2S6 monoclinic II phase has been carried out. Both the core level and valence band regions have been investigated. The spectra show single peak structures for the Sn, P and S core levels. These results are consistent with some crystal structure analysis data according to which for the room temperature Sn2P2S6 monoclinic II phase no significant difference in the tin coordination is observed. As regards the valence band photoemission spectrum, three main regions have been recognized by comparing this spectrum with those corresponding to both other M2P2S6 compounds and some Sn dichalcogenides.
The deviations from linearity in the concentration dependence of lattice spacings in AgcPd1-c have been recently related to the topology changes shown by the Fermi Surface, or Electronic Topological Transitions (ETTs), of this alloy. Using an extension of the ETTs theory to finite-temperature and impurity scattering case, and in terms of a simple Rigid Band Model, we study such deviations and interpret them as the results of the filling of the hole pocket centered at theX point of the Brillouin Zone, remarking the role of the finiteness of the quasi-particle lifetime of the relevant states. We also show howab initio calculations based on the Coherent Potential Approximation underestimate these lifetimes.
In this talk I will review some of the recent applications of the replica theory to glasses. I will firstly describe the basic assumptions and I will show that they can be considered as a precise reformulations of old ideas. The relation of this approach with the mode-coupling theory will be shortly discussed. I will present numerical simulations for binary mixtures. The results of these simulations point toward the correctness of the replica approach to glasses. I will describe the results of off-equilibrium simulations for large systems, in which the aging dynamics is studied.
Measurements of the transmittance of infrared radiation (v<500 cm-1) through cylindrical waveguides are presented and discussed. The experimental results are compared with numerical simulations, obtained through conventional ray tracing programs. Finally, we estimate the transmittance of a waveguide in the case of an infrared synchrotron radiation source. We apply our results to the case of the DAΦNE collider, where a synchrotron radiation beamline for the far infrared is under construction.
In this paper we try to give a unified picture of InxGa1-xAs/GaAs quantum systems (0 ≤x ≤ 1), as deduced primarily by optical measurements at 10 K. This has been made possible by the systematic investigation of photoluminescence and photoluminescence excitation of InGaAs/GaAs strained heterostructures differring for indium molar fraction and well width. The large number of samples used has allowed us to change in a controlled way the degree and source of disorder in the samples. The evolution from a two-dimensional growth, with formation of InGaAs and GaAs interconnected two-dimensional islands at the interfaces, to a three-dimensional growth, with self-aggregation of InGaAs dots, has been monitored, also with the help of structural measurements.
Capacitance-voltage measurements have been carried out onp-type ɛ-GaSe single crystal ∥c in the temperature range 300 to 360 K, with applied voltages of -1, 0 and +1 V. TheC-V measurements in this temperature range have shown a shift in capacitanceC and conductanceG to the higher values with an increase in temperature. The depletion layer widthW, the Debye length LD and the doping densityN α have been worked out and plots ofN α vs. W have shown a decrease inW with an increase in temperature. The plots of LD vs. N α vary as 1/N α 1/2 , which gives NαLD ⋍ 3.3 × 1011 charges/m2 for doping density of 1016m−3. The values ofG at different temperatures have been used to obtain the activation energies, which are found to be ΔE ⋍ 0.11 eV for -1 and +1 V applied voltages, and ΔE ⋍ 0.06 eV for zero volt.
The recently discovered plateau and rings in high-order multiphoton ionization apparently have their origin in rescattering. Similarly, rescattering is involved in higher-order harmonic generation. Using a simple one-dimensional model, it is shown that the phase-coherence in this rescattering process is of considerable importance.
Two-photon excitation spectra of intraconfigurational 4f7 transitions of Eu2+ in KMgF3 have been measured at temperatures ranging from 15 K up to 300 K. The results for the6P5/2 and6D9/2 excited multiplets are presented, which reveal the fully resolved Stark structure of the states and allow for a detailed study of the temperature dependence of the transition lineshapes. The temperature broadening and energy shift of the observed lines are discussed in terms of a vibrational phaserelaxation mechanism, which couples the electronic transitions to vibrational modes of the host lattice.
We report the observation of collision-induced spectra of calcium dimer in the 680–692 nm region. The spectra were recorded after resonant laser excitation of 4s4p 3 P 1 state of atomic calcium. Here the upper statea 3Σ u + is populated through collisions. The same spectra were reproduced in a low-current glow discharge in calcium vapor. The assignment of the observed spectral lines was carried out by applying the Dunham-type analysis and the spectra were assigned to thea 3Σ u + -X 1Σ g /+ transition of Ca2. The existence ofa 3Σ u + state withν 00 = 13850 ± 1 cm−1 andω e ∼ 37.6 cm−1 is confirmed.
High-resolution (0.04 cm-1 FTIR spectroscopy in the range 9-300 K is applied to study the stretching modes of16OH- and of its isotopic substitutions, as18OH,16OD and16OT, perturbed by neighbouring defects induced by Mg2+ and Ti3+ in LiF and NaF. The spectra are analysed in the framework of the Morse anharmonic oscillator model. The anharmonicity parameter (2–3 x 10-2) is evaluated either by considering the isotopic replicas or the first overtone transition. The former is found slightly higher than the latter, since the hydroxyl ion vibrates as a “nearly” free diatomic molecule. The very weak isotopic replica due to18O and D present in the samples as a result of the isotope natural abundance are detected as well.
Interferometric thermal diffusivity measurements and elastic constants obtained by ultrasonic techniques on Y3Fe5_ϰAlϰO12 (with ϰ 4 0, 0.4, 0.8, 1.1) ceramic samples are presented and discussed. The phonon mean free path is given as a function of ϰ using the Boltzmann transport equation.
