Lichtausbeute von α-Teilchen in kristallinem und dampfförmigem Anthrazen

The light output,S _v by α-particles stopped in anthracene vapour has been measured as a function of vapour pressure (10–700 mm Hg) and temperature (250°C–385°C). The comparison of the results for an idealised vapour neglecting collisions with the light output,S _c, from anthracene crystals by α-particles impinging parallel to thec′-axis yields the unexpected results: S_v(8.78 MeV)/S_c(8.78 MeV)=0.46±0.05 andS _v(6.05 MeV)/S _c(6.05 MeV)=0.57±0.08. A simple model assuming quenching by collisions of the vapour molecules could explain the observed dependence of the light output on the vapour pressure at fixed temperature. The path lengthsR _v of α-particles in anthracene vapour were determined to be R_v(8.78 MeV)=(9.0±0.6) mg/cm²,R _v(6.05 MeV)=(4.9±0.6) mg/cm² and the ratio of the light output by the two different α-energiesS _v(8.78 MeV)/S _v(6.05 MeV)=1.42±0.2.     

Instanton-induced flavour mixing in mesons

The U_L(N_f)×U_R(N_f) chiral symmetric version of the Nambu-Jona-Lasinio model is extended by the 't Hooft determinant and bosonized for an arbitrary number of flavours N_f. The resulting effective meson lagrangian is explicitly calculated to leading order in the derivatives for three flavours. The 't Hooft determinant induces flavour mixing of the mesons with diagonal flavour content (π⁰, η, η′, and their scalar chiral partners δ⁰, S, ϵ) and pushes up the physical η′-mass. The η-η′ mixing angle is found to be −31°.     

Die Temperaturabhängigkeit der magnetischen Jordan-Nachwirkung von Nickel

The magnetic after effect of pure polycristalline nickel and of a single crystal was measured between ?196 and +340 °C by a Förster second harmonic magnetometer. The viscosity constantS _v is shown to be proportional toB(T)·H_c(T) with an increasing functionB(T) for specimens of different magnetic hardness. The temperature dependence S_v(T) atH _c is rather complex in comparison to the simpleT- or √T-behaviour of former theoretical models. The latter is observed only forT??100 °C, whileS _v is nearly independent ofT between ?100 and +300 °C, and drops abruptly to zero forT?300 °C.     

Hyperfine shifts for cesium in Argon at high density

An optical pumping experiment was performed to obtain precise hfs shifts for Cs in Argon. The shifts measured include a term quadratic in the densityρ and a large temperature coefficient. The coefficients of the expansionδv/v ₀=a ρ+bρ ₂ area(80 °C)=?29.8(6)x10^?9(Torr^?1(0°C))b(80 °C)=+11(2)x10^?14(Torr^?2(0 °C)). The shift grows more negative with increasing temperature by 0.37 (2)%/°C.     

Measurement of the relative probability of the decay φ → η′γ in the channel η′ → ηπ0π0, η → γγ

The process e ⁺ e ^? → η′γ, η′ → η π⁰π⁰, η → γγ is investigated by an SND detector in experiment on a VEPP-2M equipment with colliding electron-positron beams. The analysis of experimental data yields a value of B(? → η′γ)=(6.7 _?4.2 ^+5.0 ±1.5)×10^?5 for the decay probability. Taking into account a previous measurement of this quantity by an SND detector in the decay channel η′ → π⁺π^?η, one finally obtains B(?→η ′γ)=(6.7 _?2.4 ^+2.8 ±0.8)×10^?5.     

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). I. Effect of Cross‐Linking Process on the Viscoelastic Properties

Abstract

Thermal cross‐linking of poly(vinyl methyl ether) (PVME) in the absence of cross‐linking agent, was detected rheologically. The linear viscoelastic properties of PVME were found to be greatly changed by the onset of the cross‐linking process. The viscoelastic material functions, such as dynamic shear moduli, G′ and G″, complex shear viscosity, η*, and loss tangent, tan δ, were found to be sensitive to the structure changes during the cross‐linking process and the formation of a three‐dimensional polymer network. At the onset temperature of the cross‐linking process, an abrupt increase in G′, G″, and η* (several orders of magnitude) during dynamic temperature ramps (2°C/min heating rate) was observed with some frequency dependence. The temperature dependence of tan δ was found to be frequency independent at the gel‐point, T _gel, that is, the crossover in tan δ regardless of the value of frequency can be taken as an accurate method for determination of T _gel. The coincidence of G′ and G″ at the gel‐point cannot be considered a general method for evaluation of T _gel due to its high frequency dependence, that is, T _gel determined from the crossover of G′ and G″ in the dynamic temperature ramp at 1 rad/sec is about 20°C less than at 100 rad/sec. Furthermore, a dramatic increase in η₀ above the minimum (“v” shape) was observed at T = T _gel in agreement with the value obtained from tan δ vs. T (190°C). The time–temperature‐superposition principle was found to be valid only for temperatures lower than the T _gel (190°C); the principle failed at T ≥ 190°C. This was clearly seen in the low‐frequency region as a deviation from the terminal slope in the G′ curve. Similar behavior was observed in the modified Cole–Cole analyses (G″ vs. G′) that is, the curves start to deviate at 190°C.     

Quadrupole interaction of117In in Zn metal

We have used the TDPAC method to measure the temperature dependence of the quadrupole interaction frequencyv _Q of¹¹⁷In in Zn lattice. The observedv _Q reduces from 187.4 (20) MHz at 77°K to 155.3 (20) MHz at 673°K. The variation ofv _Q is seen to be proportional toT ^3/2.     

O(mq/N) effects in the Ward identities approach to the pseudoscalar nonet

Anomalous Ward identities are investigated in the combined chiral and large-N limit of QCD, up to non-leading O(m_q/N) terms, taking into account chiral symmetry breaking effects in the η′ axial vector couplings. The bound θ > 16° for the η - η′ mixing angle is obtaned. Gasser and Leutwyler results on the O(m_q²) corrections to the η mass are used to determine the size of the O(m_q/N) terms, which are found to be reasonably small. Problems with the anomaly predictions for η, η′ → γγ are pointed out. Some aspects of the non-smoothness of the large-N expansion in presence of SU₃ breaking effects are clarified.     

Composition of oxide compounds supported on metal meshes when synthesizing catalysts for the oxidation of hydrocarbons

Samples of a woven mesh of metal wire (fechral) with supported aluminum hydroxide compounds are studied. Aluminum hydroxide is formed in its bayerite modification. Aluminum oxides are produced during calcination: η-Al₂O₃ at 600°C, and θ-Al₂O₃ at 900°C. Subsequent modification with silicon, cerium, lanthanum, tungsten, and calcination at the same temperature results in the formation of their oxides. Interaction between alumina and tungsten at 600°C, and alumina and lanthanum at 900°C, are observed.     

Cl35 NQR study of the structural phase transition in (CH3NH3)HgCl3

The Cl³⁵ nuclear quadrupole resonance spectra of (CH₃NH₃)HgCl₃ have been measured between -150°C and + 100°C. The spectra clearly show that a structural phase transition of first order takes place around T_c? 60°C. The transition may be related to a disordering of the CH₃NH₃ groups which are reorienting both above and below T_c. The positive temperature coefficient of the Cl NQR frequency, dv/dT may be also explained by the CH₃NH₃ motion.     

On the decomposition of the transition rhombohedral phase in the Al-30 wt.% Zn alloy

The decomposition of the transition rhombohedral α′_R-phase at the temperatures between 85 and 250 °C was investigated by transmission electron microscopy and by X-ray diffraction on single crystals. Below 161 °C the direct decomposition of α′_R-phase into the equilibrium hexagonal β-phase without the formation of the transition cubic α′-phase was found. Both transformation sequences α′_R → β and α/′_R→α′ → β were observed in the temperature range from 161 to 180 °C whereas only the previously known sequence α′_R → α′ → β was detected on ageing the alloy between 180 and 250 °C. The precipitation process at the temperatures from 161 to 180 °C is characterized by the decomposition of α′_R-phase into the equilibrium β-phase prior to the formation of the transition α′-phase and by the increased rate of decomposition of α′-precipitate. The observed transformation processes are related to the variation of strains at the partially coherent interface between α′_R-phase and α-matrix with the temperature in correlation with the metastable α′_R-phase boundary. These considerations allowed to estimate the relative stabilities of precipitated phases and their activation energies of formation and thus to discuss the decomposition mechanism of α′_R-phase at various temperatures.     

Emissivity and band-model parameters for infrared bands of nitrous oxide

Narrow band-model parameters S/d, γ_N/d and B have been obtained experimentally for the v₃, v₁ and 2v₂ bands of N₂O in the temperature range from 200°K to 500°K. The exponential-wide band-model parameters have been determined for all of the contributing bands and have been found to differ greatly from the values of Tien et al. Data of revised total gas emissivities are presented.     

Fluorescence induction changes in bean leaves after heat treatment

The regularities in the alterations of chlorophyll a fluorescence induction curves of bean leaves after short (15 min) heating in the range of temperatures from 24 to 45°C were determined. A dramatic decrease in the relative f luorescence quenching (F_P–F_T)/F_T, as well as the F_v/_Fm ratio, were observed after heating at temperatures above 38°C, which indicates a decrease in the photochemical activity of photosystem II. The effect of an increase in the resistance of the photosynthetic apparatus to the temperature of 43°C after preheating at 37°C was demonstrated.     

Intensity and half-width measurements in the 1·525 μm band of acetylene

Line intensities at 150°K and 295°K, self-broadened half-widths at 171°K, 200°K, 250°K and 295°K, and hydrogen-broadened half-widths at 171°K, 200°K and 295°K have been measured in the ν₁+v₃ band of C₂H₂ at 1·525 μm. The absolute intensity of the band has been determined independently by employing the Wilson-Wells-Penner-Weber technique. Our best estimate for the absolute intensity of the band is S_v=7·82 ± 0·07 cm^?2 atm^?1 at 295°K. Line intensities calculated using this value of S_v are in good agreement with the measured intensities at the two extreme temperatures of 150°K and 295°K considered in the present study, thereby not suggesting any significant intensity anomalies. Line positions have been measured for the first time for this band for R(29)?P(25).     

Note on the Paper “Gibbs vs. Shannon Entropies” by Richard L. Liboff

In addition to the comparison of the Gibbs negentropy η_G = ∫ Π ln Π to the Shannon negentropy ηs = ∑ E_iΠ_i ln(E_iΠ_i), discussed in the cited paper, a comparison of the former to η_s′=η_s?∑E _i lnE _i the decrease in uncertainty, is of general interest from an information-theoretic standpoint. It is shown that η_G and η_s′ are similar in the situation in question. The additivity properties of η_G are briefly discussed.     

Hot́ hole anisotropic effect in silicon and germanium

Anisotropic effect of the hole drift velocity in silicon and germanium has been investigated with the time of flight technique by applying the electric field parallel to the <100 and <111 crystallographic axis. The measurements were performed for electric fields ranging from 10 to 3 × 10⁴V/cm and temperatures from 40 to 200°K. The results indicate that the anisotropic effect v_d<100/v_d<111 increases with decreasing temperature and increasing electric field, and reaches a saturation value at high electric fields (? 10⁴V/cm). The maximum anisotropic effect for Ge is 1.25 at 40°K and for Si is 1.2 at 45°K. A qualitative analysis of the experimental data indicates that the anisotropic effect is due to the warped heavy-valence-band shape.     

Measurement of hydrogen- and self-broadened half-widths of ammonia at 200 and 300°K

The hydrogen- and self-broadened half-widths have been measured for the (v₁+v₂)- and (v₂+v₃)-bands of ammonia at 300 and 207°K. Measurement of hydrogen-broadened widths has been restricted to J, K ?6, but that of self-broadened widths is done for a few lines outside that range. Assuming a power-law dependence of half-width on temperature given by γ(T)=γ(T₀)(T/T₀)^α, the average value of the index α for the lines measured is found to be 0·57 for hydrogen broadening.     

In situ electron microscopy investigations of solid-state synthesis in Al/Au thin bilayer films

In situ transmission electron microscopy investigations of solid-state synthesis in Al/Au thin bilayer films are conducted. The samples are heated in the column of a transmission electron microscope. The heating temperature is changed from room temperature to 300°C with a heating rate of up to 120°C min^?1. It is found that solid-phase synthesis starts at ≈100°C. At 140 ± 5°C, two crystal phases, Al₂Au (Fm3m) and AlAu₂ (I4/mmm), are simultaneously observed, while at 235 ± 5°C and higher (up to 300°C) only Al₂Au phase is detected.     

Temperature dependence of the soft acoustic shear modes in h.c.p. zirconium

Neutron measurements of the dispersion curve v(q) for [10·0] phonons polarized in [11·0] are presented for hexagonal close-packed Zr at 300°, 773°, and 1073°K. Given that the crystal transforms to b.c.c. at 1135°K and demonstrates a pronounced softening in the C₆₆ elastic constant, v(q) shows only a uniform lowering of the entire branch, consistent with the behavior of C₆₆(T) but fractionally smaller for large wave vectors. No anomalous phonon linewidths are observed.     

First measurement of the total width of the η′ (958) meson

In a high-resolution missing mass experiment the total width of the η′ (958) meson has been measured to be 0.28 ± 0.10 MeV. Using the known γγ branching ratio the value Γ(η′ → γγ) = 5.4 ± 2.1 keV is deduced. This is in good agreement with calculations based on fractional charge quarks and a pseudo-scalar mixing angle of 11°.