Internal heavy atom effect on the radiative and non-radiative rate constants in xanthene dyes

Flourescence quantum yield (ø_f), phosphorescence and fluorescence quantum yield ratio (ø_p/ø_f) and the observed triplet decay time (τ_po) of fluorescein and its halogen derivatives have been measured. On halogen substitution an increase in ø_p/ø_f and a decrease in ø_f and τ_po is observed in the sequence of Cl, Br, and I. The increase in ø_p/ø_f is not in the same proportion as the decrease in τ_po. Although ø_p/ø_f is higher for cations than for dianions, it increases more for dianions on halogen substitution. However, the increase in 1/τ_po is about 10³ times more for cations than for dianions. The radiative and non-radiative rate constants viz., k_is, k_p and k_qp have been calculated. On halogen substitution k_f remains almost constant, whereas an increase in k_p, k_is and k_qp is observed. For dianions the increase occurs in the order k_qp> k_is> k_p while for cations the order is k_qp> k_p> k_is. The deuterium solvent effect on triplet decay time and intensity is also observed.     

Inverse scattering problem for internal waves with finite fluid depth

In this paper, we derive the Bäcklund transformation, an infinite set of conservation laws and the inverse scattering transform of nonlinear equation that describes the internal waves of fluids with finite depth, ø_t + 2øø_x + (C/S)ø_xx = 0, which has been shown before to have N-soliton solutions.     

Kinetic perturbation theory for dilute gases

We prove, for two classes of smooth, repulsive interparticle potentials ø(r) = ø₀(r) + δø₁(r), that the collision integ rals of the linearized Boltzmann equation are analytic functions of λ in the neighborhood of λ = 0. It then follows, for example, that the first Enskog approximation for the transport coefficients can be represented by a power series in λ.     

Observation of double ø-meson production in 100 and 175 GeV π−-Be interactions

Inclusive øø production has been studied in π^?-Be interactions for 100 and 175 GeV incident momentum. An upper limit of 72 nb has been set for $\text{σ(π}{}^{\mathrm{?}}\text{Be → η}{}_{\mathrm{<mtext>c</mtext>}}\text{(2980) +}\text{X}\text{)}\text{s}\text{?}\text{BR}\text{(η}{}_{\mathrm{<mtext>c</mtext>}}\text{→ øø) at 175 GeV}$. At both momenta the number of øø events is larger than expected for uncorrelated ø pairs. A narrow width enhancement is observed at M_øø≈2100 MeV with a 4 standard deviation significance.     

Functional integral representations of partition function without limiting procedure. Techniques of calculation of moments

A definition of the Feynman path integral which does not rest on a limiting procedure based on time-slicing has been given by DeWitt-Morette. We present in this paper a discussion of real Gaussian measures and formulate expressions for the quantum statistical partition function directly in terms of measures of integration on the topological vector space ø₀ of continuous functions defined on the time intervalT = (t _a ,t _b ), such thatx(t _a ,t _b )=0 for allx ? ø₀. We give a definition of a measure for the space ø₀ equivalent to the path integral based on the Uhlenbeck-Ornstein probability distribution. We give expressions for the partition function using the Wiener-Feynman measure and the Uhlenbeck-Ornstein measure. As an exercise in the use of the new techniques, we present calculations of moments of potential functions. The techniques will enable one to solve in a rigorous manner practical problems in quantum statistical mechanics.     

Random fields in the diluted Ising system Fe1−xMgxCl2

We discuss how random fields (RFs) are generated in uniaxial random antiferromagnets by applied fields and report a systematic specific heat study on the three-dimensional (3-D) system Fe_1?xMg_xCl₂ to demonstrate their effects. The RF crossover exponent ø is determined by measuring the shape of the phase boundary in the TH plane and we obtain ø=1.26 ± 0.10, in agreement with theoretical prediction. Drastic changes in the shape of the specific anomaly are observed. We argue that they are due to the temperature dependence of the random fields.     

Magneto-optical activity at the structural phase transition in paramagnetic KMnF3

The magneto-optical Verdet constant ø has been measured in the paramagnetic phase of KMnF₃ and particularly in the neighbourhood of the cubic-tetragonal phase transition driven by the softening of zone boundary modes. ø is positive and displays a sizeable decrease on cooling, thus indicating the presence of a temperature dependent paramagnetic contribution that, in view of the ⁶S ground state of the Mn²⁺ ion, is attributed to the role of spin-orbit interaction. In a temperature range of about 20K around T_c = 186K, a cusp-shaped anomaly of ø is observed. From the dependence on the wavelength, and by taking into account also EPR linewidth and g measurements and optical absorption spectra, an analysis of the possible mechanisms for the cusp-shaped anomaly is given. It is argued that the enhancement of the critical rotational fluctuations of the MnF₆ octahedra can be responsible for this effect.     

Low energy photoelectron spectroscopy of solids. Aspects of experimental methodology concerning metals and insulators

Both He(I) and He(II) ultraviolet photoelectron spectra (UPS) for metals (Ag, Au) and thin solid films of organic (anthracene) and inorganic compounds (LiF, LiCl, LiBr, LiI, NaF, NACl, Li₂SO₄, NaOH) are presented. The results of measurements on two different spectrometers have shown that both the bias voltage, V_b, applied to the solid sample, and the angle of incidence, Ø, of the photon beam with the sample are crucial to the accurate determination of the work function (metals) and binding energies (insulators). The true binding energy of a band in the UPS with respect to the vacuum level, E_b^vac, is defined as the minimum value of (hv - ΔE), where ΔE is the energy difference between the threshold of the SEED, E_T, and the band maximum. ΔE is maximized at low values of ø and of V_b. The intensity of photoelectron emission (signal) increases with both ø (2–30°) and V_b (5–20 V). It is recommended that the variation of ΔE with both ø and V_b should be observed in any determination of E_B^vac.     

Magnetization process in twisted uniaxial polycrystals

A single model has been developed to obtain the general features of the Matteucci, ME, and the inverse Wiedemann, IWE, effects. The model will be confined to polycrystalline tubes and thin wires whose uniaxial crystals are arbitrarily oriented. The domain arrangement is expressed as a function of applied twist in order to determine the remanent magnetization of the M_z-M_ø and M_ø-H_z hysteresis loops. Theory shows that, for certain values of the applied magnetic field, the ME and IWE decrease and vanish with torsion. The relation between the symmetry properties of the ME and IWE and the symmetry of the initial domain structure of the sample is discussed.     

Lichnerowicz-York equation and conformal deformations on maximal slicings in asymptotically flat space-times

The solvability of the Lichnerowicz-York equation is discussed on each sliceS _t=IR³ of a spacelike, asymptotically Euclidean maximal foliation {S _τ}. Following Cantor, the problem is reduced to a discussion of the properties of a smooth, time-dependent, family of conformal transformations,ø _t, relating the physical metrich _tofS _t to a metric ? _t =ø ⁴h_t, with vanishing scalar curvature. An estimate is provided for infø _t. This allows us to examine the properties of the scale geometry on eachS _twhen strong field regions are probed. It is shown that in such regions ? _t tends to become degenerate exponentially as a suitable average of the scalar curvature of (S _t, h _t ) increases. This is interpreted as representing the approach to a singular regime for (S _t, h _t ). An estimate is also provided for the lapse function-N _t defining {S _t}. This is found to be in agreement with a similar estimate suggested, on heuristic grounds, by Smarr and York. This latter result indicates that asymptotically flat maximal slicings in general (but not always) avoid reaching regions where the above singular regime is approached.     

Special-angle-of-incidence ellipsometry for uniaxial crystals: Part 1. Negative crystals

We introduce a new method to determine, by ellipsometry, the ordinary N_o and extraordinary N_e refractive indices of a uniaxial crystal, with its optic axis parallel to the surface. First, the type of the crystal; negative or positive, is determined. Second, N_o and N_e are determined using very simple expressions. The only measurement required is a special angle of incidence $\text{ø}$, which we define in this paper as the largest angle of incidence at which linearly polarized light as reflected linearly polarized, at two orientation angles ω. A detailed error analysis is presented considering errors of $\text{ø}$, ω, and the effect of the ambient refractive index n. The results prove the high accuracy of the method.     

Measurements of the inclusive pd breakup cross section at low and intermediate energies

Inclusive measurements of the D(p, p)pn reaction were made at incident proton energies of 248?MeV and 13?MeV, to investigate the global feature of the pd breakup reaction at intermediate and low energies. At 248?MeV, the cross section and analyzing power A _y were measured at four angles from 7° to 20°. The data largely disagree with Faddeev calculations even if 2π-exchange three-nucleon force (2π3NF) or Δ-isobar is included, and the disagreement increases at forward angles. At 13?MeV, the cross section was measured at eight angles from 10° to 70°. The data are well reproduced by a recent pd Faddeev calculation, and the effects of Δ-isobar at 13?MeV are very small.     

Nuclear spectroscopic studies of the 23.7 h 248Bk

Main features of the decay of the 23.7 h ²⁴⁸Bk have been determined by spectroscopy with scintillation and semiconductor detectors. The results are as follows: half-life 23.7 ± 0.2 h; branching is (30 ± 5)% to ²⁴⁸Cm (≈ 23% EC decay to 0⁺ ground state and ≈ 7% to first 2⁺ state) and (70 ± 5)%β^? decay to ²⁴⁸Cf(5 % to 592 keV K^π = 2^? state and (65 ± 5)% to the ground-state band). The β^? decay energy, Q_β^?, has been measured to be 860 ± 20 keV, and the electron capture decay energy, Q_EC, has been derived from closed cycle to be 705 ± 25 keV. The deduced logft values of β^? and EC transitions restrict the spin of the ²⁴⁸Bk ground state to 1, with configuration assignment $\text{{}\text{n}\text{[734]}\text{9}\text{2}{}^{\mathrm{?}}$; $\text{p}\text{[633]}\text{7}\text{2}{}^{\mathrm{+}}$. It has also been deduced that the long lived isomer lies 65 ± 40 keV abovethe 23.7h ²⁴⁸Bk ground state.     

Surface boundary conditions and angular dependence of the spin-wave resonance spectra

General surface boundary conditions with regard to the surface anisotropy energy E_s(iitv, ø) and changes of the static magnetization tM₀ in the presurface region layer have been formulated. On the example of uniaxial surface anosotropy the influence of these factors on the angular dependence of the SWR spectrum is briefly discussed.     

Measurement of fast neutron induced fission cross section of thorium using Lexan plastic track detector

Fission-track registration characteristics of Lexan solid state nuclear track detectors have been used to measure the fast neutron induced fission cross section of²³²Th. The fast neutrons (?14.2MeV) were produced with the help of an AN-400 model Van-de-Graaff accelerator at Banaras Hindu University laboratory using³H(²H,n)⁴He reaction and were used to irradiate the fissile target deposited on the plastic detector. The track densityT, registered on the plastic detector is related to the fission cross sectionσ _f, through the relationT=knσ _føt wheren is the number of fissile atoms per cm² in the deposit, ø is the neutron flux,k is fission track registration efficiency andt is the time of irradiation. The fission cross sectionσ _f of²³²Th, relative to the well measured fission cross section of²³⁸U, was found to be 0.36±0.04 barn.     

Nucleic acid conformation: Crystal and molecular structure of deoxyguanosine (5′) phosphate (disodium salt)—Agauche-trans (gt) conformation about the C(4′)-C(5′) bond and O(1′) puckering of the furanose ring

The crystal structure of deoxyguanosine (5′) phosphate, disodium salt, (5′-dGMP Na₂ 4H₂O) has been determined from three dimensional single crystal x-ray data collected by multiple film, equi-inclination, Weissenberg method using CuK_a radiation. The crystal belongs to the monoclinic space groupP2₁ witha=16.002±0.003 Å,b=10.730±0.003 Å,c=5.575±0.005 Å andβ=101.9°. The structure was solved by symbolic addition method using the program Multan, the reliability index being 0.090. The guanine base is in the usualanti conformation about the C (1′)-N (9) bond withx _CN=52.3°. The structure shows two unique conformational features not observed in any nucleotide structure reported so far. The deoxyribose moiety shows O (1′)endo puckering with respect to the best four atom plane defined by C(1′)-C(2′)-C(3′)-C(4′). The conformation about the C(4′)-C(5′) bond isgauche-trans with ø₀₀=62.5° and ø_oc=174.8°. This is the first nucleotide structure where agt conformer similar to that found in the Watson-Crick double helical DNA model has been experimentally observed. These two conformational features have also direct relevance to the concept of ‘a conformationally rigid nucleotide unit’ developed by Sundaralingam. The nine membered guanine ring is essentially planar. Bases of molecules related by a ‘c’ cell translation tend to overlap, the shortest distance being 3.51 Å between the atoms N (3) and C(8). One of the sodium atoms Na(1) has an octahedral coordination with four water oxygens and O(6) and O(3′) atoms occupying the corners at distances ranging from 2.35 Å to 2.55 Å.     

A chance for interaction in λø43+1, λ>0

By variational methods an approximate, nonperturbative, unique, renormalized, interacting effectice action λø⁴₃₊₁, λ>0, is obtained. It completes and corrects an earlier result for the effective potential. It opens a door towards interaction.     

Regge behavior under asymptotic freedom

By a new method, we show that the asymptotically free ø₆³ field theory has a point of accumulation of Regge poles but no fixed cut. It is plausible that nonabelian gauge theories have an analogous singularity at j = 1.     

Evidence for a high mass enhancement in K+K− photoproduction

The reaction γp → K⁺K^? p has been investigated with tagged photons in the energy range of 20 < E_γ < 70 GeV. A structure in the 1.7 GeV mass region is observed and interpreted in terms of a recurrence of the ø.     

Contribution of proton NMR relaxation to the investigation of molecular dynamics in columnar mesophases of discotic and polycatenar molecules

We present in this work a review concerning wide frequency rangeT ₁ proton NMR relaxation studies performed in compounds exhibiting columnar mesophases, namely the Col_ho mesophase in the case of a liquid crystal of discotic molecules and the ø_h mesophase in the case of a liquid crystal of biforked molecules. These NMR relaxation studies were performed combining conventional and fast field cycling NMR techniques in a frequency range between 100 Hz and 300 MHz. The possibility of probing such a large frequency range has provided a way to effectively distinguish the influence, on theT ₁ relaxation profiles, of the different molecular movements observed in this type of mesophases. In addition, we present a comparison between the molecular dynamics in columnar (ø_h) and lamellar (SmC) mesophases exhibited by the same biforked compound.