Coexistence of ferro- and antiferromagnetic interactions in a metal-organic radical-based (6,3)-helical network with large channels

A metal-organic open-framework with an unprecedented (6,3)-helical topology, large channels and mixed ferro- and antiferromagnetic interactions has been synthesized using a three-connecting tricarboxylic polychlorotriphenylmethyl radical and Co(ii) ions.     

Two-quanta progressive saturation: pulsed NMR of 23Na in single crystal sodium nitrate

Progressive saturation effects due to induction of two-quanta transitions in the quadrupolar-split levels of a spit, 3/2, (²³Na) nucleus were studied by monitoring changes occuring in the 1/2 → ? 1/2 magnetization after applying trains of identical pulses at various radiofrequencies and repetition rates. The variety of single- and double-quantum (DO) interconnected population effects observed in the experiments is explained by incorporating solutions of the ordinary two-level Bloch equations with those of the two-quanta, three-level Bloch-like equations (including off-resonance conditions) derived recently by Gold and Hahn. Small displacements of nuclear levels under DQ irradiation (analogous to the optical ac Stark shift) the cause rf power-dependent DQ frequency shifts are predicted for all spins I> 1, and explicit expressions are derived. Additional effects due to state mixing and to population transfer by satellite excitation are presented, and the relevance of DQ saturation to the recently developed double-resonance interferometric spectroscopy is discussed.     

Transmission of Circular Polarized Waves Between Elevated Antenna

Transmission of circularly polarized signals between elevated antenna over lossy earth is discussed for a frequency of 100 MHz. By decomposing the circularly polarized signals into vertical and horizontal components and considering only direct and ground-reflected waves, it is shown that for fixed transmitting antenna height and horizontal separation, the field intensity at the receiving antenna varies sinusoidally with receiving antenna height. Reference curves of field strength versus height are included for typical tower heights, separations, and soil conditions. Comments on FCC power height curves are also included.     

Research Model for Time-Separation Integrated Communication

A new communication system concept which is an important step toward an all-digital telecommunication plant is discussed. A research model, called ESSEX (Experimental Solid State Exchange), which combines remote line concentration, time-separation switching and PCM transmission is introduced to demonstrate the concept. The model, which uses solid state devices, works at the speed of a full-size system.     

Factorization of Q(h(T)(x)) over a finite field,where Q(x) is irreducible and h(T)(x) is linear II

Let GF(q) be the finite field of order q, let Q(x) be an irreducible polynomial in GF(qⁱ)[x], and let H(x) = h(T)(x) be a linear polynomial in GF(q)[x]. We give the degrees of the irreducible factors of Q(H(x)) in GF(qⁱ)[x], and the number of irreducible factors of each degree. We consider the special cases when H(x) is a trace function, and when h(x) is cyclotomic. Finally, we give several examples.     

Brillouin scattering in the nematic and isotropic phases of a liquid crystal

Brillouin scattering is the liquid crystal 5CB has been measured and the hypersonic speed and attenuation determined. At the nematic-isotropic transition a small discontinuity in the hypersonic speed is found. The results are compared with available ultrasonic data.     

An Asymptotic Version of the Multigraph 1‐Factorization Conjecture

We give a self‐contained proof that for all positive integers r and all , there is an integer such that for all any regular multigraph of order 2n with multiplicity at most r and degree at least is 1‐factorizable. This generalizes results of Perkovi? and Reed (Discrete Math 165/166 (1997), 567–578) and Plantholt and Tipnis (J London Math Soc 44 (1991), 393–400).     

An X-ray Crystallographic Study of the Related Triazenes, 1,4-Di[(<Emphasis Type="Italic">E</Emphasis>)-2-(2-nitrophenyl)-1-diazenyl]piperazine and Methyl 4-{(E)-2-(4-methylpiperazino)-1-diazenyl}benzoate

Abstract The crystal structures of methyl 4-{(E)-2-(4-methylpiperazino)-1-diazenyl}benzoate (2a) and 1,4-di[(E)-2-(2-nitrophenyl)-1-diazenyl]piperazine (3a) have been determined by single crystal X-ray diffraction analysis. The bis-triazene (3a) adopts an unusual pseudo-boat conformation in the piperazine ring, with a dihedral angle of 52.20(0.06)° between the two planes defined within the piperazine ring. The crystal structures of 2a and 3a are compared with the structure of the triazene (4) and the closely related bis-triazene (5). The piperazine ring of 2a adopts a typical chair conformation, whereas the piperazine ring of 3a adopts an unusual boat conformation. Crystal data: 2a C₁₃H₁₈N₄O₂, monoclinic, space group P2₁ /n, a = 13.849(3) ?, b = 6.577(1) ?, c = 14.904(3) ?, α = 90°, β = 96.098(3)°, γ = 90° and V = 1,349.8(4) ?³, for Z = 4. 3a C₁₆H₁₆N₈O₄, triclinic, space group P-1, a = 7.6066(6) ?, b = 8.3741(7) ?, c = 14.507(1) ?, α = 78.673(1)°, β = 81.877(1)°, γ = 73.445(1)° and V = 865.0(1) ?³, for Z = 2. Index abstract The crystal structures of methyl 4-{(E)-2-(4-methylpiperazino)-1-diazenyl}benzoate (2a) and 1,4-di[(E)-2-(2-nitrophenyl)-1-diazenyl]piperazine (3a) have been determined by single crystal X-ray diffraction analysis.     

Glass transition,thermal expansion and relaxation in B2O3 glass measured by time-resolved X-ray diffraction

In situ heating experiments using high-energy, high-intensity synchrotron radiation, can be successfully designed to study structural evolution with temperature of glassy materials. Coherent diffraction from glassy materials forms a succession of halos or diffraction maxima in reciprocal space and the variation with temperature, of the wave-vector Q_max or angular position of the first diffracted intensity I(Q_max) maximum below T_g can be used to determine the iso-structural volume expansion. In the present work we have obtained synchrotron X-ray diffraction patterns in transmission during in situ heating of a B₂O₃ glass. Samples were obtained by melting the B₂O₃ glass rods which were then air-cooled or liquid nitrogen-cooled. The evolution with temperature (and time) of the position of the first diffraction maximum of the diffraction pattern accurately reflected the thermal expansion coefficient and the relaxation behavior of the B₂O₃ glass. Such results allowed determination by diffraction of the glass transition temperature, T_g, at 580 K, as well as information on the structural relaxation during thermal annealing. The total volume changes due to relaxation were measured to be about 1.5 vol.% and 2.5 vol.%, for the air-cooled and the liquid nitrogen-cooled B₂O₃ glass, respectively.     

X-Band Pulsed ENDOR Study ofFe-Substituted Sodalite— The Effect of the Zero-Field Splitting

X-band (∼9.3 GHz) pulsed ENDOR measurements were carried out on⁵⁷Fe-substituted sodalite (FeSOD) which contains only one type of Fe(III) (S=) located at a framework site. The ENDOR spectrum recorded atg= 2 shows three doublets corresponding to the sixM_Smanifolds. The assignment of these signals was confirmed by hyperfine-selective and triple ENDOR experiments. The components of each of the doublets had different intensities, reflecting the different populations of the EPR energy levels at the measurement temperature, 1.8 K. ENDOR spectra were recorded at magnetic fields within the EPR powder pattern, and the field dependence observed showed an anisotropic behavior, unexpected from the isotropic character of the⁵⁷Fe(III) hyperfine coupling. This dependence was attributed to the high-order effects of the zero-field splitting (ZFS) interaction on the ENDOR frequencies. Three different theoretical approaches were used to account for the dependence of the ENDOR spectrum on the ZFS interaction. The first involves the exact diagonalization of the total spin Hamiltonian, the second uses third-order perturbation approximations, and the third employs an effective nuclear Hamiltonian for each of theM_Smanifolds. The simulations showed that the ENDOR signals of theM_S= ±5/2 (ν_±5/2) manifold are the least sensitive to the magnitude of the ZFS parameterDand are therefore the most appropriate for the determination ofa_iso. It is shown that at X band anda_isovalues of about 30 MHz, the perturbation approach is valid up toDvalues of 500 MHz if all three doublets are concerned. However, if only the ν_±5/2doublet is considered, then this approach is valid forD< 1000 MHz. The third approach was found inappropriate fora_isovalues of ∼30 MHz. Using the method of exact diagonalization together with orientation selectivity, the trends observed in the experimental spectra could be reproduced. The ENDOR spectra of the⁵⁷Fe-substituted zeolites ZSM5, L, and mazzite showed broad and ill-defined peaks since the ZFS of Fe(III) in these zeolites is significantly larger than that of FeSOD. Because this broadening is a high-order effect, it can be significantly reduced at higher spectrometer frequencies.