Magnetic orientation of carbon nanotubes at temperatures of 231 K and 314 K

Carbon nanotubes were placed in magnetic fields of  80.0 kOe at temperatures of 231 K and 314 K. Scanning electron microscopy showed that nanotubes were oriented with the tube axis parallel to the fields. It was also observed that the probability of the orientation became higher, when the temperature was raised from 231 K to 314 K. The anisotropy in the susceptibilities parallel X∥ and perpendicular X _⊥ to the tube axis is suggested to increase with rise in temperature: X∥ ? X⊥ = (4 ± 2) × 10^?6 emu mol^?1 (per mol of carbon atoms) at 231 K and X∥ ? X⊥ = (45 ± 27) × 10^?6 emu mol^?1 at 314 K.     

Supertransferred hyperfine structure in EPR of V4+ ion in Ca3In2Ge3O12 garnet

Interaction of an unpaired electron of the tetrahedral V⁴⁺ ion in Ca₃In₂Ge₃O₁₂ garnet with the four nearest In nuclei gives rise to clearly resolved structure of EPR spectra. We report the observation and analysis of these spectra at three frequencies and at temperature 77 K. The temperature dependence between liquid helium and the room temperatures was also studied. Parameters of the spin Hamiltonian are g_∥=1·8735; g_⊥=1·9825; ∣ ¦A∥|=150·4×10^?4cm^?1; ¦ A_⊥¦ = 36·7 × 10^?4 cm^?1. The supertransferred hyperfine interaction was found to be isotropic, absolute value of the corresponding parameter a is 22·1 × 10^?4 cm^?1.     

Effects of anisotropy,order parameter,and viscosity on translational self-diffusion in nematic liquid crystals

A theory developed for the translational diffusion in nematic liquids crystals shows a dependence on the viscosities, order parameter, and molecular structure. Theoretical results for self-diffusion in p-azoxyanisole at 125°C are D^{∥ = 4.3 × 10?6, D⊥ = 3.1 × 10?6 c2/s}, andD^∥/D^⊥ = 1.4.     

Electron paramagnetic resonance of Dy3+ in cubic ZnSe and Tm3+ in hexagonal CdS single crystals

Electron paramagnetic resonance has been observed for Dy³⁺ in ZnSe and Tm³⁺ in CdS. For Dy³⁺ doped ZnSe, an isotropic spectrum was observed having well resolved hyperfine lines due to ¹⁶¹Dy and ¹⁶³Dy. The g value obtained was 6.577 ± 0.002 and ¹⁶¹A was 191 ± 1 × 10⁴ cm^?1 and ¹⁶³A was 265 ± 3 × 10^?4 cm^?1. The agreement of the observed g value to g(τ₆) = 6.667 and the point-charge calculations suggest that Dy³⁺ occupies an interstitial (II) site with no local charge compensation. For Tm³⁺ doped in hexagonal CdS, an axial spectrum consistent with g_⊥ = 0, g_∥ = 10.722 ± 0.007, D = 2.57 GHz (crystal field splitting) and ¹⁶⁹A = 1207 ± 5 × 10^?4cm^?1. The large g_∥ value indicates that the Tm ion exits in the trivalent state. This is in reasonable agreement with previous reports of the non-Kramer's state of Tm³⁺.     

The cross section of14N(n,p)14C at stellar energies and its role as a neutron poison forS-process nucleosynthesis

The absolute average cross section 〈σ〉 of the¹⁴N(n, p)¹⁴C reaction has been measured using neutron spectra that closely resemble Maxwell-Boltzmann distributions with thermal energies of kT=25.0 and 52.4 keV: 〈σ〉=0.81±0.05 and 0.52±0.06 mb, respectively. The resulting reaction rates are nearly the same at T₉=0.29 and 0.61, and their average, N_A〈συ〉=(1.3±0.1)×105 cm³ s^?1 mol^?1, is about a factor of three smaller than the previously adopted values obtained by extrapolation between thermal and higher-energy data. Thus, the¹⁴N(n, p)¹⁴C reaction plays a correspondingly smaller role as a neutron poison fors-process nucleosynthesis.     

Non-perturbative QCD effects explain the ΔI = 12 rule in the chiral limit

It is shown that in the chiral limit, the enhancement of the $\text{ΔI=}\text{1}\text{2}$ transitions for mesons is explained by the large size of non-perturbative QCD matrix elements. For $\text{〈}\text{s}\text{s〉 = 〈}\text{u}\text{u〉}$ we obtain ∣M(K_S⁰ → 2π⁰) ∣ =(5.2±0.6) × 10^?7m_K in excellent agreement with experiment.     

ESR study of color centers in yttria stabilized zirconia

The ESR of single crystals of yttria stabilized zirconia (YSZ), containing color centers due to reduction in a flowing H₂ atmosphere, has been measured at room temperature. The spin density is about 3 × 10¹⁷ cm^?3 and the strong ESR line displays axial symmetry with principal values g₆ = 1.989, g_⊥ = 1.860.The behaviour of the ESR spectra when the magnetic field is rotated about the 〈1 0 0〉 and 〈1 1 0〉 directions shows that the centers have axial symmetry, the symmetry axis being along the 〈111〉 and equivalent directions. The derivative peak to peak envelope width is g-dependent and varies from 18 Gauss at g = 1.989 to 65 Gauss at g = 1.860. The results are interpretable in terms of an electron trapped at an oxygen vacancy adjacent to an yttrium ion.     

Iodine as a donor in CdS

Iodine doped single crystals of CdS were grown from the vapor phase. High temperature Hall effect measurements for the crystals equilibrated with Cd and S₂ vapors at temperatures between 700 and 1000°C gave the free electron concentration as a function of p_Cd or p_S2 and temperature. The results can be explained on the basis of a model in which the CdS is saturated with iodine at low p_Cd (=high p_S2) but unsaturated at high p_Cd.The solubility of iodine in CdS is given by c_t=1·73×10²²p_S2^?1/8 exp (?1·045 eV/kT) cm^?3 atm^?1/8=4·62×10¹⁹p_Cd^1/4 exp (?0·195 eV/kT) cm^?3 atm^1/4The formation of pairs (I_SV_Cd)′ from I_S^· and V_Cd″ is governed by the equilibrium constant K_{P(I, V)}=4 exp (≤1·1 eV/kT)If Cd diffusion occurs primarily by free vacancies, the Cd^* tracer self diffusion leads to a vacancy mobility of (1·2±0·5)×10^?5 cm² sec^?1 at 900°C, in agreement with results reported by Woodbury [12], but (7±3) times larger than reported by Kumar and Kroger [10].     

Direct observation of the torsional fundamental of gaseous C2F6 in the far infrared

The forbidden a_1u torsional vibration of C₂F₆ has been observed in far-infrared absorption at 67.5 cm^?1 with an integrated intensity of 0.20 ± 0.08 × 10^?2 cm^?2. The observed intensity is compared with that expected theoretically from Coriolis coupling of the torsion to the infarred-active a_2u and e_u vibrations. For certain force fields and choices of sign for the dipole moment derivatives the agreement is satisfactory. The potential barrier to internal rotation has been recomputed from the observed torsional frequency to be 1367 cm^?1. (3.91 kcal mole^?1). This value is compared with those of ethane and partially fluorinated ethanes.     

克里奇中间体CH2OO与CF3CF=CF2反应的动力学研究

本文使用OH激光诱导荧光方法研究了结构最简单的克里奇中间体CH₂OO和CF₃CF=CF₂的反应动力学. 在压强为10 Torr条件下,测量了温度在283,298,308和318 K的反应速率常数,分别为(1.45±0.14)×10^-13,(1.18±0.11)×10^-13,(1.11±0.08)×10^-13和(1.04±0.08)×10^-13 cm³·molecule^-1·s^-1. 根据阿伦尼乌斯方程,获得该反应的活化能为(-1.66±0.21) kcal/mol. 在6.3∽70 torr压力范围内,未观察到该反应的速率常数存在压力相关.     

Electron paramagnetic resonance of Dy3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Dy³⁺ ions in lead thiogallate PbGa₂S₄ single crystals have been presented. It has been shown that the ground state of these ions corresponds to the lowest Stark sublevel Γ₆ of the term ⁶ H _15/2. The spectra are well described by the axially symmetric spin Hamiltonian with the effective spin S = 1/2 with the factors g _‖ = 15.06 and g _⊥ = 2.47. The Dy³⁺ ions substitute Pb²⁺ ions in the crystal lattice of PbGa₂S₄. The observed hyperfine structure has allowed to unambiguously interpret the EPR spectra. The hyperfine interaction constants of two odd isotopes of dysprosium in lead thiogallate single crystals have been found to be A _‖ = 675 × 10^?4 cm^?1 and A _⊥ = 111 × 10^?4 cm^?1 for ¹⁶³Dy and A _‖ = 472 × 10^?4 cm^?1 and A _⊥ = 77 × 10^?4 cm^?1 for ¹⁶¹Dy.     

Effect of the spin-orbit interaction of Ni2+ ions with a triplet orbital ground state on the magnetostriction of NiFe0.5Cr1.5O4 ferrite

The magnetization σ and the longitudinal (λ_∥) and transverse (λ_⊥) magnetostrictions of the NiFe_0.5Cr_1.5O₄ ferrite containing the tetrahedral ions Ni²⁺ with the triplet orbital ground state have been investigated for the first time at a temperature of 4.2 K in fields up to 55 kOe. It is revealed that the NiFe_0.5Cr_1.5O₄ ferrite exhibits an anomalously large magnetic anisotropy (H _c=12.5 kOe) and magnetostrictions (λ_∥≈?870×10^?6 and λ_⊥≈800×10^?6). In strong fields, the magnetostrictions λ_∥ and λ_⊥ are found to be anisotropic in character; i.e., the susceptibility Δλ_∥p and Δλ_⊥p. The conclusion is drawn that the studied compound is characterized by two paraprocesses: one paraprocess in the B sublattice has an exchange nature, and the second process in the A sublattice is due to the spin-orbit interaction of Ni _A ²⁺ ions.     

Interactions between metastable Xe atoms in the afterglow plasma

By measurements of the electron energy distribution function in a Xe afterglow plasma, the rate constants of the binary ionizing collisions between metastable Xe atoms were determined. The value of β₂₂ = (7.3 ± 1) × 10^?10cm³s^?1 satisfactorily agrees with the value for a van der Waals capture.     

Influence of pressure on the relative population of the two lowest vibrational levels of the C <Superscript>3</Superscript> Π<Subscript>u</Subscript> state of nitrogen for electron beam excitation

Continuous and pulsed 12 keV electron beams were used to excite nitrogen within a gas cell at pressures ranging from 10 to 1400 hPa. The pressure dependence of the ratio of photon fluxes for emission from vibrational levels v'=0 and 1 of the C ³Π _u state has been studied. The results confirm the presence of a collisional excitation mechanism populating v'=0, 1 in addition to electron impact excitation. Rate constants of (1.27 ±0.04)×10^-11 cm³s^-1 [ v'=0] and (2.68 ±0.08)×10^-11 cm³s^-1 [ v'=1] were measured for C ³Π _u quenching by ground state nitrogen. For electron beam conditions relative excitation efficiencies of 1:0.59:0.22 for vibrational levels 0, 1 and 2 were calculated. The recorded flux ratios are compared with the predictions given by a vibrational relaxation model.     

Transport and magnetic properties of multiwall carbon nanotubes before and after bromination

Bulk samples of oriented carbon nanotubes were prepared by electric arc evaporation of graphite in a helium environment. The temperature dependence of the conductivity σ(T), as well as the temperature and field dependences of the magnetic susceptibility χ(T, B) and magnetoresistance ρ(B, T), was measured for both the pristine and brominated samples. The pristine samples exhibit an anisotropy in the conductivity σ_∥(T)/σ_⊥>50, which disappears in the brominated samples. The χ(T, B) data were used to estimate the carrier concentration n ₀ in the samples: n _0ini ～3×10¹⁰ cm^?2 for the pristine sample, and n _0Br～10¹¹ cm^\t—2 for the brominated sample. Estimation of the total carrier concentration n=n _e+n _p from the data on ρ(B, T) yields n _ini=4×10¹⁷ cm^?3 (or 1.3×10¹⁰ cm^?2) and n _Br=2×10¹⁸ cm^?3 (or 6.7×10¹⁰ cm^?2). These estimates are in good agreement with one another and indicate an approximately fourfold increase in carrier concentration in samples after bromination.     

Tetravalent vanadium in CaF2 and SrF2 crystals: An EPR study

An EPR study of tetravalent vanadium centers created by room temperature X-irradiation in CaF₂ and SrF₂ is presented. The production efficiency of these centers is enhanced by previous annealing of the samples at 1000 K in air. The symmetry of V⁴⁺ ions is tetragonal and its EPR spectrum can be described by an axial spin Hamiltonian including a Zeeman and hyperfine term with $\text{S =}\text{1}\text{2}$ and $\text{I =}\text{7}\text{2}$ (corresponding to ⁵¹V nuclei). The following values for the spin Hamiltonian parameters are obtained g_∥ = 1.947 ± 0.002, g_⊥ = 1.935 ± 0.005, A_∥ = 500 ± 5 MHz, A_⊥ = 150 ± 10 MHz in the case of SrF₂ and g_∥ = 1.945 ± 0.002, A_∥ = 505 ± 5 MHz and A_⊥ < 200 MHz, in the case of CaF₂. A model for the center including an interstitial O^2? ion is tentatively proposed.     

Gleichzeitige Messung von Hyperfeinstruktur,Starkeffekt und Zeemaneffekt des85Rb19F mit einer Molekülstrahl-Resonanzapparatur

A molecular beam resonance apparatus with electric quadrupole lenses asA- andB-fields and with superimposed parallel electric and magnetic transition-fields was used. Molecules in different rotational statesJ, m _J are separated by theA-field. Spectra of molecules in different vibrational states are resolved by their different Starkeffect energies. By this means the following electric and magnetic properties of the molecule could be measured in the rotational stateJ=1 and vibrational statesv=0 and 1: The magnetic and electric dipole moment of the molecule, the scalar and the tensor nuclear dipole — dipole interactiond _s andd _T, the nuclear spinrotational interactionc _F andc _Rb, the nuclear quadrupole interactioneqQ, the nuclear magnetic moment μ_Rb, the anisotropy of the diamagnetic susceptibility ξ_⊥?ξ_∥, the anisotropy of the diamagnetic shielding of the external field by the electrons at the position of the nuclei σ_⊥?σ_∥. Using these quantities it was possible to calculate the quadrupole moment and a weighted quadrupole moment of the electronic charge distribution. The results are: (J=1,v=0) μ_el=8,5464 (17) debμ _J/J=?29,79(2)x10^?6 μ _B d _s/h=0,36(23) kHzd _T/h=0,69(22)kHzc _F/h=10,42(70) kHzc _Rb/h=0,479 (48) kHz.eqQ _Rb/h=?70,3410(26) MHzμ(1?σ_S)Rb=1,3474(5) μ_k (ξ⊥-ξ _∥)=12(6)×10^?30 erg/Gauß² (σ_⊥-σ∥)_Rb=?3,8(2,1)×10^?4 (σ⊥-σ _∥)_F=?2,6(3)×10^?4     

Gottfried Sum Rule in QCD Nonsinglet Analysis of DIS Fixed-Target Data

Deep-inelastic-scattering data from fixed-target experiments on the structure function F₂ were analyzed in the valence-quark approximation at the next-to-next-to-leading-order accuracy level in the strong-coupling constant. In this analysis, parton distributions were parametrized by employing information from the Gottfried sum rule. The strong-coupling constant was found to be α _s (M²_Z) = 0.1180 ± 0.0020 (total expt. error), which is in perfect agreement with the world-averaged value from an updated Particle Data Group (PDG) report, α^PDG _s (M²_Z) = 0.1181 ± 0.0011. Also, the value of 〈x〉_u?d = 0.187 ± 0.021 found for the second moment of the difference in the u- and d-quark distributions complies very well with the most recent lattice result 〈x〉^LATTICE_u?d = 0.208 ± 0.024.     

Die Diffusionskoeffizienten und mittleren freien Weglängen der geladenen und neutralen Radon-Folgeprodukte in Luft

The knowledge of the diffusion coefficients of radioactive atoms and ions in air is very important in a number of investigations on and computations of the attachment of radon decay products to aerosol particles. In this work measurements of the diffusion coefficients of neutral and charged²¹²Pb atoms are reported. The values found areD ₀=(7.6±0.4)·10^?2cm²s^?1 for neutral atomsD=(5.0±0.3)·10^?2cm²s^?1 for charged atoms The used method of measurement allowed to determine these constants 1–5 seconds after the formation aged²¹²Pb atoms, so that a “cluster” formation was improbable. The mean free path for neutral (λ₀=(4.9±0.3)·10^?6cm) and charged (λ=(3.2±0.2)· 10^?6cm) lead 212 atoms in air were computed from the measured diffusion coefficients. All obtained results were compared with values, calculated from theory.     

Remarks on the charged multiplicity of hadronic Z0(91) decays

The charged multiplicity distribution of hadronic decays of Z ⁰ from LEP and those of inclusive $e^{+}+e^{-}?ghtarrow h{?erline h} at E_{? cm}=14 {? to} 60 {? GeV}$ at E _cm = 14 to 61 GeV are analyzed using a Poisson-type distribution for photon statistics, due to Scully-Lamb. Its two parameters are expressed in terms of 〈n〉 and f ₂ = 〈n(n ? 1)〉 ? 〈n〉² of the data in order to perform no-free-parameter fits. It is found that f₂ behaves like $E_{? cm}^{a}$ with a = 2.01 ± 0.11, whereas C ₂ = 〈n ²〉/〈n〉² ～ E _cm with ΔC ₂/ΔE _cm = (1.81 ± 0.14)·10^?3.