Oscillator strength of electron-type color centers in KCl single crystals irradiated with electrons and protons

The absorption spectra of KCl single crystals irradiated with electrons and protons at energies of 15 and 100 keV and a particle flux ranging from 5×10¹² to 10¹⁵ cm^?2 are investigated. The absorption bands attributed to simple (F, F _a, K) and complex (M, R ₂, R ₄, N) color centers are identified in the spectra. The correlation dependences of the absorption coefficients for M, R ₂, and R ₄ centers on the absorption coefficient of F centers and the correlation dependences of the absorption coefficients for R ₂ and R ₄ centers on the absorption coefficient of M centers are established. The oscillator strengths are calculated for M, R ₂, and R ₄ color centers.     

Magnetic and microwave absorbing properties of magnetite-thermoplastic natural rubber nanocomposites

Magnetic and microwave absorbing properties of thermoplastic natural rubber (TPNR) filled magnetite (Fe₃O₄) nanocomposites were investigated. The TPNR matrix was prepared from polypropylene (PP), natural rubber (NR) and liquid natural rubber (LNR) in the ratio of 70:20:10 with the LNR as the compatibilizer. TPNR-Fe₃O₄ nanocomposites with 4-12 wt% Fe₃O₄ as filler were prepared via a Thermo Haake internal mixer using a melt-blending method. XRD reveals the presence of cubic spinel structure of Fe₃O₄ with the lattice parameter of a=8.395 Å. TEM micrograph shows that the Fe₃O₄ nanoparticles are almost spherical with the size ranging 20-50 nm. The values of saturation magnetization (M_S), remanence (M_R), initial magnetic susceptibility (χ_i) and initial permeability (μ_i) increase, while the coercivity (H_C) decreases with increasing filler content for all compositions. For nanocomposites, the values of the real (ε_r′) and imaginary permittivity (ε_r′′) and imaginary permeability (μ_r′′) increase, while the value of real permeability (μ_r′) decreases as the filler content increases. The absorption or minimum reflection loss (R_L) continuously increases and the dip shifts to a lower frequency region with the increasing of both filler content in nanocomposites and the sample thickness. The R_L is −25.51 dB at 12.65 GHz and the absorbing bandwidth in which the R_L is less than −10 dB is 2.7 GHz when the filler content is 12 wt% at 9 mm sample thickness.     

Graviton and scalar propagations on AdS<Subscript>4</Subscript> space in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) gravities

We investigate propagations of graviton and additional scalar on four-dimensional anti-de Sitter (AdS₄) space using f(R) gravity models with external sources. It is shown that there is the van Dam–Veltman–Zakharov (vDVZ) discontinuity in f(R) gravity models because f(R) gravity implies GR with additional scalar. This clearly indicates a difference between general relativity and f(R) gravity.     

Affine extensions of supersymmetry: The finite case

We examine the graded Poincaré (GP) Lie algebra of supersymmetry with a view to constructing possible affine extensions of the algebra, i.e. extensions of the GP algebra which contain as a subalgebra the Lie algebra $\text{ga}\text{(4,}\text{R}\text{)}$. We restrict our attention in this paper to an examination of the finite extensions. We demonstrate explicitly that if we adjoin only a symmetric tensor generator to the GP algebra, then such a generator cannot generate all the deformations, in particular the shear, of the general affine group GA(4, $\text{R}$). Similarly, we show that adjoining the supersymmetry generator to $\text{ga}\text{(4,}\text{R}\text{)}$ cannot lead to closure of the resulting algebra, even in the trivial case. We further demonstrate that the GLA $\text{ga}\text{(}\text{4}\text{4}\text{,}\text{R}\text{)}$ does not contain the Lie algebra $\text{ga}\text{(4,}\text{R}\text{)}$ represented over the entire superspace upon which $\text{ga}\text{(}\text{4}\text{4}\text{,}\text{R}\text{)}$ is defined.     

The dual (p,q)-Alexander-Conway Hopf algebras and the associated universal ℐ-matrix

The dually conjugate Hopf algebrasFun _p,q (R) andU _p,q (R) associated with the two-parametric (p,q)-Alexander-Conway solution (R) of the Yang-Baxter equation are studied. Using the Hopf duality construction, the full Hopf structure of the quasitriangular enveloping algebraU _p,q (R) is extracted. The universal ?-matrix forsFun _p,q (R) is derived. While expressing an arbitrary group element of the quantum group characterized by the noncommuting parameters in a representation independent way, the ?-matrix generalizes the familiar exponential relation between a Lie group and its Lie algebra. The universal ?-matrix and the FRT matrix generators,L ^(±), forU _p,q (R) are derived from the ?-matrix.     

An approach to radially symmetrical solutions of the sine-Gordon equation

The solution φ(r, t) of the radially symmetric sine-Gordon equation is considered in three and two spatial dimensions for initial curves, analogous to a 2π-kink, in the expanding and in the shrinking phase, for R(t)j? R(0). It is shown that the parameterization φ(r, t) = 4 arcian exp[γ(r?R(0)] + x(r, t), where R(t) describes the exact propagation of the maximum of φ,(r, t), is suitable. Using an appoximate differential equation, recently given for the propagation of the solitary ring wave, a rough analytic approximation for the correction function x(r = R(t), t) is found and tested numerically. A relationship between the fluctuations in x(r = R(t), t) and those in $\text{R}\text{?}\text{(t), t)}\text{and}\text{R(t)}$ explains why the solitary wave is almost stable. From x(r = R(t), t) and the supposition x(1, t) ≈ x(∞, t) ≈ 0 an assymetry in φ_r(r, t) with respect to r = R(t) is predicted. It also exhibits fluctuations corresponding to those in x(r = R(t), t). The condition for validity of this approximation apparently is also a limit for the stability of the solitary ring wave.     

Field of linear frames as a fundamental self-interacting system

We present some philosophical and physical arguments supporting the hypothesis that the most fundamental self-interacting field in an amorphous space-time is the field of linear frames, i.e. the quadruple of vector bosons. We construct a wide class of Lagrangian dynamical models invariant under the total group of diffeomorphisms and under the natural action of the proper linear group GL⁺ (4, R) on the tetrad field. There exist some links between these models and the Hamiltonian dynamical systems on GL⁺ (3, R) (the mechanics of affinely-rigid bodies [23] [27]). We present the general form of field equations, conservation laws and Bianchi identities. There exist some formal similarities between our Lagrangians and those used in non-linear electrodynamics, in particular in the Born–Infeld theory [21]. We also give a few rough remarks concerning models invariant under natural subgroups of GL⁺ (4, R), i.e. under SL(4, R) and SO(1, 3; R) (special linear group and Lorentz group). The latter class includes the conventional Einstein relativity and the more general metrical-parallelism models. It turns out that there are GL⁺ (4, R)-invariant Lagrangians which are structurally alike the conventional Einstein Lagrangian.We have not derived as yet either mathematical or physical consequences of the presented model. Nevertheless, it seems to follow from our discussion that, a priori, the GL⁺ (4, R)-invariant tetrad models could be competitive with the Einstein theory. The next thing to be done would be a careful mathematical analysis of these models and attempts to compare their consequences with those of the Einstein relativity and of other field theories.     

Magnetic hyperfine fields for Sn atoms in rare-earth intermetallides: huge deviation from proportionality between Bhf and Sz

The magnetic hyperfine fields for ¹¹⁹Sn impurity atoms, localized in Ga sites of ferromagnetic intermetallic compounds RGa (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm), were measured by the Mössbauer spectroscopy technique. At T=5 K, the hyperfine field value (B_hf) varies from 3.3 T in TmGa to 28.0 T in GdGa. Huge deviation from the proportionality between B_hf and the projection of the R³⁺ ion spin (S_z=(g−1)J) was found. As the atomic number of the R element increases, the B_hf/S_z ratio drastically decreases from 12.6 T for PrGa to 3.3 T for TmGa. This unexpected result can be explained by the strong dependency of B_hf value on the relationship between the Sn-R atomic separation (R_nn) and the radius of the magnetic 4f shell (R_4f). In the framework of this concept, the available experimental data for Sn atom in the rare-earth compounds with non-magnetic sp elements were considered. The data may be described by the universal dependency on the single parameter, λ=R_nn/R_4f.     

Effect of bi-layer ratio in ZnO/Al2O3 multilayers on microstructure and functional properties of ZnO nanocrystals embedded in Al2O3 matrix

Zinc oxide (ZnO) nanocrystals (NCs) embedded in alumina (Al₂O₃) matrix were produced via rapid thermal annealing (RTA) of pulsed laser deposited ZnO/Al₂O₃ multilayered nanostructures. The effect of the thickness ratio (R) between Al₂O₃ and ZnO in one bi-layer on the microstructure and functional properties of NCs has been investigated. Grazing incidence small angle X-ray scattering confirmed the formation of nanocrystals after RTA. Grazing incidence wide angle X-ray scattering studies revealed that ZnO NCs have a high crystalline quality with (100) as preferred orientation. Tensile strain of NCs decreases with increasing R and is correlated to the distribution of NCs. From Raman analysis, it is noticed that the phonon frequency of the E₂ mode, related to the ZnO wurtzite phase, in NCs is shifted towards that of bulk ZnO with increasing R. Photoluminescence studies revealed that the near edge peak position shifts from 382 nm to 371 nm as the ratio R changes from 1.5 to 4 and is attributed to the strain effect. The intensity of emission in the yellow–green region due to defects decreases significantly with increasing R. Current–voltage (I–V) characteristics of Al/ZnO NCs embedded in Al₂O₃/n-Si (100)/Al have shown a hysteresis behavior. The increasing width of the hysteresis with increasing R revealed that the origin of the hysteresis might be due to the existence of polar surface charges on well-separated NCs. The high-resistance and low-resistance states in I–V hysteresis curves seem to be governed by Fowler–Nordheim tunneling and Schottky emission mechanisms, respectively.     

Radial deformation and adhesion of carbon nanotube

The van der Waals (vdW) interactions of carbon nanotube (CNT)-substrate and CNT-CNT can cause strong adhesion. The adhesion can lead to radial deformation of CNTs, which is shown in both experiments and theoretical analysis. A scaling approach is used to predict the mechanical properties, vdW adhesion, and the elastic deformation of CNTs. It is found that the indentation of CNT is proportional to R _7/4 and h ^?3/2 in nanotube-substrate system and two same CNT system. Here, R and h are the radius and the wall thickness of CNT, respectively. The indentation ratio H ₁/H ₂ for CNT-CNT is proportional to (R ₁/R ₂)^3/2 and (h ₂/h ₁)^3/2.     

Effect of carrier concentration on the reflectivity spectrum of Ge and InSb

We have measured at 5 K the derivative spectra (1/R) dR/dE around the E₁ and E₁ + Δ₁ structures, of Ge and InSb with different impurity concentrations. In the more highly doped samples, the peaks are broadened and shifted slightly to lower frequencies. The change in the value of (1/R) dR/dE is much larger than recently predicted by Seraphin and Aspnes, based on the surface field effect. Different possibilities for the effect are discussed. Wavelength modulation measurements on samples with an applied surface electric field have shown no difference.     

Density-density correlations on a gelatin films surface

The spatial correlations on the surface of films obtained from aqueous solutions of gelatin during cooling from 320 to 293 K have been studied using electron microscopy. It has been shown that the total density fluctuation correlation function on the scale R > 4 nm can be represented in the form h(R) ～ R ^?n exp(?R/ζ), where the correlation radius ζ coincides with the hydrodynamic radius of a macromolecule. Unfolding of macromolecules in the coil → helix transformation leads to a decrease in the density and the fractal dimension of the physical network of pinnings of macromolecules and to variation in the index n of the power term in the function h(R) from n = 1 to 2, due to the transition from a continual type of disorder to a cellular type in a solid.     

Magnetic order and hyperfine interactions in RFe6Al6 (R = rare earth)

The systems RFe₆Al₆(R = Y, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) crystallize in the tetragonal body centered I4/mmm structure. In striking contrast to the magnetic behaviour of RFe₄Al₈ (weakly coupled R and Fe sublattices, complicated magnetic structure, low T_c ~ 130 K), in the RFe₆Al₆ systems all magnetic sublattices order simultaneously at a relatively high temperature. The magnetization curves start with low values at low temperatures and rise to very high values at T_max ~ 230 K and then drop to 0 at T_c ~ 330 K. All samples show strong hysteresis effects at temperatures just below T_max. Mossbauer studies of ⁵⁷Fe in the (f) and (j) sites and ¹⁵¹Eu, ¹⁵⁵Gd, ¹⁶¹Dy, ¹⁶⁶Er and ¹⁷⁰Yb in the (a) site yield all hyperfine interaction parameters and temperature dependence of the local magnetic moments. All Mossbauer and magnetization experimental results can be explained in a self consistent way with a simple molecular field model. The Fe in the (j) site plays the dominant role in its strong intrasublattice ferromagnetic exchange and its strong antiferromagnetic exchange with the rare earth site. The Fe in the (f) site have an antiferromagnetic intrasublattice exchange, they have a canted strcuture with the ferromagnetic component parallel to the (j) sublattice magnetization.     

Fluorescence lifetimes and radiative rate constants of alkanes at 25°C

Fluorescence lifetimes of 33 alkanes were measured at 25°C using a 0.7 ns pulse radiolysis system and the relationship between molecular structure, fluorescence lifetime (τ), quantum yield (Φ_f) and radiative rate constant (R = $\text{Φ}{}_{\mathrm{f}}\text{τ}$) is discussed. The τ's showed a large dependence on the molecular structure, however, the R-values were approximately constant for groups of alkanes: R = 1.3×10⁶s^?1 for n-alkanes, R ≈ 4×10⁶ s^?1 for aliphatic vicinally substituted dimethyl alkanes, R = 7×10⁶s^-1 for cyclohexane and alkylcyclohexanes, and R = 10×10⁶s^?1 for di- and trimethylcyclohexanes. The excited state lifetimes of some non-fluorescing alkanes were also determined from steady-state photolytic quenching data and found to be very low (? 0.3 ns).     

Near infrared transitions between Rydberg states of nitric oxide: The 4f-F2Δ band at 1.71 μm

Several near infrared transitions between highly excited Rydberg (R) states of nitric oxide have been recorded at high resolution (0.15 cm^?1) with a SISAM interferometer. The spectra all show a simple rotational structure, characteristic of R-R transitions. A full analysis has been performed of the previously unobserved 4f(v = 0) → F²Δ(v = 0) band at 1.71 μm. The band shows a peculiar structure, characteristic of Hund's Case (d) behaviour for one of the states. The relative branch intensities are calculated from first principles, and the agreement with the observed spectrum is excellent. This work shows the potential of interferometers for studying excited electronic states of simple molecules at high resolution.     

Spectroscopic investigations and luminescence spectra of Nd and Dy doped different phosphate glasses

Spectral properties of Nd³⁺ and Dy³⁺ ions in different phosphate glasses were studied and several spectroscopic parameters were reported. Covalency of rare-earth-oxygen bond was studied in these phosphate glass matrices with the variation of modifier in host glass matrix. Using Judd-Ofelt intensity parameters (Ω₂, Ω₄ and Ω₆), radiative transition probabilities (A) and radiative lifetimes (τ_R) of certain excited states of Nd³⁺ and Dy³⁺ ions are estimated in these glass matrices. From the magnitudes of branching ratios (β_R) and integrated absorption cross-sections (Σ), certain transitions of both the ions are identified for laser excitation. From the emission spectra, peak stimulated emission cross-sections (σ_P) are evaluated for the emission transitions observed in all these phosphate glass matrices for both Nd³⁺ and Dy³⁺ ions.     

On the separation of initial and final state effects in photoelectron spectroscopy using an extension of the auger-parameter concept

First, we show that the quantity Δβ(i) = ΔE_A(kii) + 2ΔE_B(i) — ΔE_B(k) is directly related to the final state relaxation contribution ΔE_R(i) of the binding energy shift ΔE_B(i). ΔE_A(kii) is the kinetic energy shift of the Auger transition which corresponds to the decay of a hole state with a hole in level k into a final state with two holes in level i. The shift parameter Δβ(i), which is based on information on two binding energies, is conceptually similar to Wagner's Auger parameter. To establish the relation between Δβ(i) and ΔR(i) one needs, however, less drastic approximations than in the case of Auger parameter shifts. The only approximation necessary is the assumption that ΔR(i) is determined by coulomb contributions.Secondly, we use Δβ (i) to analyse the experimental data of eighteen gaseous phosphorus-containing compounds obtained by Sodhi and Cavell¹. It is shown that ΔR(P_2p) is strongly related to changes in the polarizability of the ligands. The initial state effects derived from our study deviate from those expected on the basis of simple electronegativity considerations.     

Absence of magnetic field influences on the rate of Ni(CO)4 formation on Ni(100) under various surface conditions

Using UHV techniques and a flow system with continuous monitoring of the reaction rate, we have investigated the rate of Ni(CO)₄ formation, R, on Ni(100) in an external magnetic field up to 1000 G, under various surface conditions. No magnetic field effect ($\text{ΔR}\text{R}\text{< 0.01}$) has been found under any conditions (clean surface with or without roughness ;precoverage with C, S, Hg; temperatures up to 200°C; different B orientation; darkness or illumination).     

Use of fat suppression in R₂ relaxometry with MRI for the quantification of tissue iron overload in beta-thalassemic patients

Purpose

To assess the performance and results of R₂ relaxometry using a fat-suppressed (FS) multiecho sequence and compare these to conventional R₂ relaxometry in estimating tissue iron overload.

Materials and Methods

Relaxation rate values (R₂=1/T2) of the liver, spleen, pancreas and vertebral bone marrow (VBM) were estimated in 21 patients with β-thalassemia major, using a respiratory-triggered 16-echo Carr-Purcell-Meiboom-Gill (CPMG) spin-echo sequence before (R₂) and after (R₂ FS) the application of chemically selective fat suppression.

Results

Hepatic and splenic R₂ FS values correlated with respective R₂ values (r=0.98 and r=0.96, P<.001), whereas correlations between R₂ FS and R₂ values for pancreas and VBM were not statistically significant. Bland–Altman plots show disagreement between R₂ and R₂ FS values, particularly for pancreas and VBM. Hepatic, pancreatic and VBM R₂ FS values correlated with serum ferritin (r=0.88, P<.001; r=0.51, P<.003; and r=0.75, P<.002, respectively). Hepatic R₂ FS values correlated with splenic R₂ FS (r=0.77, P<.03), pancreatic R₂ FS (r=0.61, P<.006) and VBM R₂ FS values (r=0.70, P<.001), whereas pancreatic R₂ FS values correlated also with VMB R₂ FS values. On the contrary, among the R₂ values of the above tissues, obtained without fat suppression, only hepatic R₂ values correlated with serum ferritin, whereas no correlation was documented between hepatic and pancreatic or VBM R₂ values. The application of fat suppression did not improve breathing or flow artifacts.

Conclusion

Application of fat suppression in the standard CPMG sequence improved the capability of MRI in noninvasive quantification of iron, particularly in lipid-rich tissues, such as vertebral bone marrow (VBM) and pancreas.