History of Polymer Education-USA

Prior to 1940 there was little or no education directed toward polymer chemistry. With the contributions of Carothers and others that transformed the practice of polymers into a science-and the leadership of Herman Mark and others in formal graduate and postgraduate education-polymer education took root but rapid expansion and general acceptance by more traditionally oriented academic institutions was slowed by many barriers. Only since 1974 has there been a concerted effort to include education in the basic concepts of polymer chemistry into the undergraduate curriculum. Emphasis is on the development of polymer education in the United States.     

Structure determination of Na3DySi6O15 and crystal chemistry of zektzerite related compounds

The crystal structure of Na₃DySi₆O₁₅ has been solved and refined to an R₁=2.97% (wR₂=8.25%) for 1311 independent reflections. The compound was found to crystallize within the orthorhombic system with the space group Cmca (Z=8) and the lattice parameters: a=14.590(7) Å, b=17.813(4) Å, c=10.519(2) Å, V=2734.0 Å³, D_cal=3.11 g/cm³. The structure of Na₃DySi₆O₁₅ is a filled variant of the zektzerite with S like corrugated double chains of [SiO₄] tetrahedral, connected via Na⁺ and Dy³⁺ cations and running parallel to c-axis. The three-dimensional network results from the packing of these chains along [100] by skewering them in rods represented by the tunnels delimited by the S shape of the silicate chains. One of the main peculiar features of the Na₃DySi₆O₁₅ structure is the location of Na⁺ in tetrahedral sites with rather short Na-O bond lengths (2×2.243 and 2×2.262 Å).     

THE ENERGY ASPECT OF THE RECIPROCAL INTERACTIONS OF PAIRS OF TWO DIFFERENT VIBRATION MODES OF A CLAMPED ANNULAR PLATE

The standardized mutual active and reactive sound power of a clamped plate, representing the energy aspect of the reciprocal interactions of two different in vacuo modes, has been computed. It was assumed that the vibrations are axisymmetric, elastic and time harmonic, the plate's transverse deflection is small as compared with the plate's size, and that the vibration velocity is small as compared with the acoustic wavenumber generated. The Kirchhoff-Love theory of a perfectly elastic plate was used. The integral formulae for the mutual sound power were transformed into their Hankel representations which made possible their subsequent computation. A closed path integral was used to express the integral in its Hankel representation to compute the mutual active sound power. The asymptotic stationary phase method was used to compute the two magnitudes, i.e., the mutual active and reactive sound power. The results obtained are the asymptotic formulae valid for the acoustically fast waves. The oscillating as well as the non-oscillating terms have been identified in the formulae to make possible their further separate analysis. The availability of the asymptotic formulae makes possible some fast numerical computations of the mutual sound power. Moreover, the formulae presented herein, together with those for the individual modes known from the literature, make a complete basis for further computations of the total sound power of the plate's damped and forced vibrations in fluid.     

Synthesis,Single Crystal Growth and Crystal Structure of Ta7Cu10Ga34 – a 8 × 4 × 2 Super Structure of CsCl

Single crystals of Ta₇Cu₁₀Ga₃₄ were grown from the elements in a Cu/Ga melt. Ta₇Cu₁₀Ga₃₄ represents the first ternary compound of the system Ta/Cu/Ga. The crystal structure (Cmmm, oC102, Z = 2, a = 23.803(1), b = 12.2087(4), c = 5.7487(2) Å, 1291 refl. 78 parameters, R₁ = 0.037, wR₂ = 0.070). The crystal structure is characterized by rods of pentagonal prisms MGa₁₀, which are alternatingly occupied by Ta and Cu. Four of these rods are connected to columns running in direction (001). These columns are linked by cubic units TaGa₈, CuGa₈, and GaGa₈. According to the characteristic structural elements and the size of the unit cell Ta₇Cu₁₀Ga₃₄ represents a 8 × 4 × 2 super structure of CsCl or bcc. With respect to the underlying CsCl structure the formula can be written as [Ta₇Cu₁₀Ga₂□₁₃]Ga₃₂, i.e. a cubic primitive packing of 32 Ga atoms with Ta, Cu, and Ga in cubic voids and 13 vacancies. The pentagonal‐prismatic coordination of Ta and Cu can formally be obtained from the cubic primitive packing of Ga atoms by a 45° rotation of a part of the Ga₈ cubes. There is a close similarity to the binary compounds Ta₈Ga₄₁ and Ta_2–xGa_5+x. The first one is also related to a CsCl‐like structure, the latter one contains rods of pentagonal prisms, which form the same columns. There are also relations to the ternaries V₂Cu₃Ga₈ and V₁₁Cu₉Ga₄₆, whose cubic structures are more or less complex variants of CsCl.     

Binary boron-rich borides of magnesium: single-crystal investigations and properties of MgB(7) and the new boride Mg(∼5)B(44)

Single crystals of dark-red MgB(7) were grown from the elements in a Cu-melt. The crystal structure (Pearson symbol oI64; space group Imma; a = 10.478(2) ?, b = 5.977(1) ?, c = 8.125(2) ?, 2842 reflns, 48 params, R(1)(F) = 0.018, R(2)(I) = 0.034) consists of a hexagonal-primitive packing of B(12)-icosahedra and B(2)-units in trigonal-prismatic voids. According to the UV-vis spectra and band structure calculations MgB(7) is semiconducting with an optical gap of 1.9 eV. The long B-B distance of 2.278 ? within the B(2)-unit can be seen as a weak bonding interaction. The new Mg(～5)B(44) occurs beside the well-known MgB(12) as a byproduct. Small fragments of the black crystals are dark-yellow and transparent. The crystal structure (Pearson symbol tP196, space group P4(1)2(1)2, a = 10.380(2) ?, c = 14.391(3) ?, 4080 reflns, 251 params, R(1)(F) = 0.025, R(2)(I) = 0.037) is closely related to tetragonal boron-II (t-B(192)). It consists of B(12)-icosahedra and B(19+1)-units. With a charge of -6 for the B(19+1)-units and a Mg-content of ～20 Mg-atoms per unit cell the observed Mg content in Mg(～5)B(44) is quite close to the expected value derived from simple electron counting rules. All compositions were confirmed by EDXS. The microhardness was measured on single crystals for MgB(7) (H(V) = 2125, H(K) = 2004) and MgB(12) (H(V) = 2360, H(K) = 2459).     

Transverse magneto-optical Kerr effect of Fe at the 2p excitation threshold

The transverse magneto-optical Kerr effect (T-MOKE) was investigated for thin epitaxial Fe films grown on Ag(0 0 1) in the region of the 2p excitation threshold. The experimental reflectivity and asymmetry spectra are compared to those derived from the complex dielectric function tensor calculated by using the first-principles spin-polarized relativistic band theory. We found that the T-MOKE asymmetry in general is a mixture of both the real and imaginary parts of the off-diagonal element of the dielectric function tensor, depending sensitively on the relative magnitudes of real and imaginary parts of the diagonal element. For angles of incidence larger than about 5° the influence of the Ag-substrate is significant. The major features in experimental and calculated reflectivity and asymmetry spectra are in agreement.