Probable Orientation Research Articles

Functional morphology of Cretaceous helically-coiled ammonite shells

Torticonic (helically-coiled) ammonoids have been most commonly interpreted as vagile, benthonic forms. Their mode of coiling, however, places the siphuncle in a functionally dorsolateral, rather than ventral position on the shell whorl due to: 1) their probable apex-upward shell orientation during life, and 2) size asymmetry of the lateral sutural saddles due to helical coiling, associated with upward siphuncle displacement. The resultant positioning of the siphuncle produces cameral liquid de-coupling soon after initiation of cameral liquid removal (emptying of liquid from a newly formed chamber within the phragmocone). Since in Recent chambered cephalopods cameral liquid de-coupling increases efficiency of vertical migration, a similar mode of life was indicated for the torticonic ammonites.

31P NMR chemical shielding tensors of α-Ca2P2O7

The 31P NMR chemical shielding tensors were measured in a crystal of α-Ca2P2O7; the principal values, relative to 85% H3PO4, were found to be −42, 32, 65 ppm for P(1) and −48, 44, 67 ppm for P(2) with an average relative standard deviation of 7%. The most probable orientations of the tensors in the molecule were determined, and in both cases the most downfield component of the shielding tensor is along the P–O(P) bond direction; this orientation is correlated with the electronic distribution around the phosphorous nuclei. The high resolution spectra used in determing the shielding tensors were taken using the multiple pulse WAHUHA technique which removes homonuclear dipolar interactions in solids [J. S. Waugh, L. M. Huber, and U. Haeberlin, Phys. Rev. Lett. 20, 180 (1968)]. The linewidths were reduced from 1 KHz to 100 Hz by this technique. Details of the spectrometer design and the tuneup procedure for the WAHUHA experiment are also given.

Monolayers and multilayers of anthraquinone derivatives containing long alkyl chains

Monolayers of seven anthraquinone derivatives containing one or two stearylamino-groups at different positions of the ring system, spread at the air/water interface, have been studied by pressure-area isotherms and qualitative tests for rheological behaviors. Further, preparation of multilayers of these anthraquinone derivatives on solid surfaces has been examined, using two techniques of the vertical dipping and the horizontal lifting methods, and the thickness per single layer was measured by the optical method. From a consideration of molecular models, probable orientations of the anthraquinone ring in these films are discussed. It has been concluded that different types of orientation of the anthraquinone nuclei can be realized in the surface films of these long-chain dyes, depending on the chemical modifications, such as variation in the numbers and relative positions of the long substituent groups, and also on the physical conditions for deposition, such as surface pressures. It is suggested that the multilayers of these anthraquinone derivatives with long alkyl chains may provide a model of much interest for the spectroscopic researches on dye aggregates.

Convective Plumes in the Planetary Boundary Layer, Investigated with an Acoustic Echo Sounder

Abstract The turbulent temperature structure and winds in thermal convective plumes over prairie grassland have been investigated with an acoustic echo sounder system. Three spaced acoustic antennas, with two inclined at 45° elevation, were used to provide plume shape information and Doppler-derived total wind-vector patterns between heights of 70 and 500 m. Supporting in situ measurements were made on a 15 m tower, with a tethered balloon-supported Boundary Layer Profiler, and from a light aircraft. The most probable orientation of the plumes was nearly vertical, but frequent upwind and downwind tilts were also observed. Maximum positive vertical velocities in the plumes at midday were near 2 m s−1, while maximum downward currents were one-half this value. Acoustic echoes from regions above the mixed layer, corresponding in height to an elevated temperature inversion, correlate well with regions of maximum wind shear.

Interpretation of experimental M�ssbauer quadrupole splittings of iron pentacyanide complexes using molecular orbital theory

Semiempirical self-consistent-field molecular-orbital calculations are carried out for six iron-pentacyanide complexes and are used to interpret their experimental Mossbauer quadrupole splittings. Probable orientations are identified for the C6H 5 − and NO 2 − groups in Fe(CN)5NOC6H 5 −3 and Fe(CN)5NO 2 −4 . Calculations on Fe(CN)5NO−2 and Fe(CN)5NO−3 can simultaneously be brought into agreement with experiment by reparametrization to make the NO group more positively charged. All the calculations indicate the importance of including all the Fe 3d and 4p orbitals in the calculations and of considering neighboring-atom effects.

Theory of the optical properties of phonon systems with disordered force constants, with application to NH 4Cl

A theory of systems with substitutional disorder is presented. The theory treats off-diagonal disorder and is thus suitable for application to systems with disordered force constants. An example of such a system, to which particular consideration is given, is NH 4Cl, which has a disordered phase in which the force constants between NH 4 + ions are disordered because there are two equally probable orientations of an NH 4 + ion within a unit cell. The effect of disorder, in particular the breakdown of k-conservation, on the optical properties of such systems is studied via a calculation of the single-particle Green's function. Both the optical absorption and Raman cross section are shown to be related to the self-energy of this Green's function, and expressions for these quantities are obtained which are exact to second order in the ratio of order-dependent to non order-dependent force constants. The major qualitative features of the expression for the Raman cross section are found to be in good agreement with existing Raman scattering data on NH 4Cl.

Strength of Fiber-Reinforced Concrete

The results of experimental and analytical studies on the characteristics of concrete reinforced with uniformly distributed short wire pieces are presented. The experimental program includes tests on workability, modulus of rupture strength, and compressive strength of 75 batches of concrete; the major variables are water-cement ratio, percentage of steel, and gage and length of wire pieces. Despite the slight loss of workability, preparation of good wire reinforced concrete is quite feasible. Effective wire spacing has been formulated taking into consideration the bond deficiency and probable orientation of the wire pieces both within the interior concrete and near the exterior faces of the specimen. Based on experimental results, a correlation has been obtained between effective wire spacing and tensile strength ratio.

Intensities in polarized light: near ultraviolet absorption spectrum of 1,2,4,5 tetramethylbenzene

The absorption anisotropy of 1,2,4,5 tetramethylbenzene crystals in the region 33 000–40 500 cm–1 is investigated at room and liquid nitrogen temperature. The f-values for both directions of propagation of the light vector in the (001) face were measured and corrected for reflectivity losses. Frequency shifts of the absorption peaks and changes in f-values with temperature are discussed. Comparison of crystal absorption with oriented gas intensities leads to the conclusion that the transition is long-axis polarized. The assignment is discussed in relation to a calculation on crystal shift and Davydov splitting. The probable orientation and magnitude of the transition moment, induced by the crystal field in the unit cell, is indicated.

Visible Spectra of Argon Matrix Isolated Phthalocyanines: Pair Interactions

The 5000–8000-Å transmission spectra of H2PC and CuPC embedded in an argon matrix at 5°K at molar ratios of 4000:1 are very similar to their spectra in liquid solution. The predominant CuPC species in the matrix are isolated molecules, but a strong sideband in more concentrated mixtures (1000 Ar:1 CuPC) is attributed to interacting pairs. Coupling of transition dipoles was invoked to correlate the observed spectrum with several CuPC “dimer” configurations. Computer calculations based upon nonbonded atom–atom potentials were conducted to find the most probable relative orientations of two neighboring solute CuPC molecules. H2PC does not appear to show the effects of pairs even in extremely dilute solutions. A strong doublet which is very similar to that in liquid solution persists in the matrix.

Temperature-Dependent Optical Activity Due to Quantized Molecular Rotation and Optical Rotation by Oriented Molecules

Classical works on optical rotation have dealt with random systems for which all molecular orientations are equally probable. We have considered here optical rotation by quantum mechanically rotating molecules. The contributions to optical rotation from the individual rotational levels of a symmetric- and a spherical-top molecule have been derived. These may be asymmetric molecules belonging to the C3, D3, or T point group. The contributions are weighed by the Boltzmann distribution over the rotational levels, thus giving rise to temperature dependence. Such dependence will be significant at low temperatures. It is shown that, the same as for classical random systems, the optical rotation by quantized rotors comes from the interference of an electric multipole of a given rank with a magnetic multipole of the same rank. However, because of the dependence on the rotational energy level K, for the rotation of infrared “light” which is close to the frequency of a rotational transition, the optical rotation may arise purely from the quantized rotation of symmetric-top molecules that are not necessarily asymmetric. The difference in behavior between a symmetric-top molecule with rotational angular momentum K and a linear molecule with electronic angular momentum Λ is discussed. In the limit of equally probable orientations and in the dipole approximation, it is shown that the results for quantized rotors reduce to the classical expression of optical rotation. Whereas for rotating molecules optical rotation normally requires asymmetry and interference between one electric and one magnetic multipole of the same rank, for oriented molecules, optical rotation may come purely from molecular arrangement requiring no asymmetry of the individual molecule, and may come from arbitrary interference mechanisms. We have considered the optical rotation by molecules uniformly oriented in solid matrices or in weakly interacting molecular crystals. We have derived the optical rotation from the following interference mechanisms: electric dipole–electric dipole (E1E1), electric dipole–magnetic dipole (E1M1), electric dipole–electric quadrupole (E1E2), magnetic dipole–magnetic dipole (M1M1). The angles of rotation have been expressed in terms of the Euler angles of orientation of the individual molecule with respect to the incident polarized light and in terms of the scattering tensor matrix elements over the molecular states. The conventional rotatory strength proportional to the matrix element of the pseudoscalar, R·M, was shown to come from the orientation-independent term in the E1M1 interference mechanism. The possible contributions, of these various mechanisms and various scattering tensors, to optical rotation by oriented molecules belonging to a few simple groups are illustrated in tabular form.

Distribution of Crystal Orientation and Work Function in Tungsten Ribbons

Polycrystalline tungsten ribbons tend to recrystallize on extended outgassing to a preferred orientation near the 〈1̄10〉 zonal axis between the 〈001〉 to 〈112〉 directions, the most probable orientations being in the 〈115〉 to 〈113〉 directions. Work function measurements on nine different crystal planes between the 〈001〉 to 〈112〉 directions have been made and show variations from 4.34 to 4.72 eV. The area average value from 15 different ribbons is 4.46 eV but the variation between ribbons can be as high as 0.2 eV.

Deuteron Magnetic Resonance Study in Co(ND3)6Cl3

Abstract Deuteron quadrupole coupling tensors in Co(ND3)6Cl3 were determined at various temperatures. The observed quadrupole coupling shows that Co(ND3)63+ ions execute a rapid isotropic reorientation at high temperatures (above 320°K for one of the sites (the 4f sites) and above 190°K for another (the 2e sites), while at low temperatures (below 190°K for the 4f sites, and 170°K for the 2e sites), only a C3 axis reorientation of the ligand ND3 groups is present. The deuteron resonance spectra clearly show that Co(ND3)63+ ions in the 4f sites begin to reorient about one of the three C4 axes at intermediate temperatures (about 240°K). On the basis of the orientation of quadrupole tensors, probable orientations of Co(ND3)63+ ions in the 4f sites in the crystal are proposed. Additional measurements of the proton resonance on a single crystal of Co(NH3)6Cl3support the results obtained from the deuteron resonance. To obtain the reorientation rates and the activation energies of these reorientational motions, the deuteron resonance line width at the 4f sites is measured at various temperatures and at various crystal orientations. From the temperature dependence of the line width, the presence of two cations with slightly different rates at the 4f sites is suggested. However, because of the limits set by the various experimental conditions, reliable values of the reorientation rates and activation energies could not be obtained.

Antiferromagnetic Domains in RbMnF3

The indirect observation of domains in the cubic antiferromagnet RbMn${\mathrm{F}}_{3}$ through antiferromagnetic resonance is reported. Because of the cubic anisotropy of RbMn${\mathrm{F}}_{3}$, the equilibrium orientation of the magnetic sublattices is not in general unique, and the formation of antiferromagnetic domains may occur. The appearance of more than two branches in the antiferromagnetic resonance spectrum implies the existence of a multidomain structure. The probable orientations of domains, corresponding to local minima in the free energy, have been calculated for the case of a magnetic field applied along the [$11\overline{2}$] direction. Measurements were made on a single-crystal sample of RbMn${\mathrm{F}}_{3}$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K. For small values of applied field (2000 Oe), the mode spectrum in the $X$-band region consisted of six branches. There is good agreement between the computed frequencies for the domains as a function of applied field and the experimentally observed values. The agreement implies that domain rotation takes place. A pronounced hysteresis in the resonance absorption, measured as a function of applied field, for certain resonances has been observed. The hysteresis has been attributed to domain-wall motion.

Astronomical Orientations at Teotihuacán, A Case Study in Astro-Archaeology

AbstractThe streets of this Classic period city were laid out in a grid pattern. The axes of this grid were almost, but not exactly, perpendicular. There were a number of celestial bodies that in the period from A.D. 150 to A.D. 750 rose or set so as to markthe orientations of the streets. The Pleiades, Sirius, and the sun were the most probable orientation points. Two techniques which have been developed to test the more certain past existence of celestial references are described.

Intensities in polarized light: A1 g → B2 u transition in hexamethylbenzene

The absorption anisotropy of hexamethylbenzene crystal is investigated at room temperature for the transition occurring at 2400–2900 Å. The f-values in both directions of propagation of the light vector for faces [100] and [001] were measured. Reflectivity corrections and those due to molecular librations are discussed. The total f-value for the transition in the crystal is compared to that observed in the free molecule. The probable orientation of the transition moment induced by the crystal field in the unit cell is indicated.

Low-Frequency Motions of H2O Molecules in Crystals. II

Translational and librational motions of H2O molecules in a frequency region lying below 1000 cm−1 have been previously examined for various configurations using the inelastic scattering of low-energy neutrons (0.005 eV). In the present work, H2O motions are studied in cases where neither of the lone electron pairs on the oxygen of the H2O molecule is specifically directed (K2C2O4·H2O), where the lone pairs are directed toward two monovalent metal ions (KF·2 H2O), where the H2O molecule has a single orientation [Ba(ClO3)2·H2O] or two distinct, equally probable orientations (Li2SO4·H2O). The neutron spectrum of K2C2O4·H2O typically exhibits torsional peaks at 500, 605, and 700 cm−1 which shift by 1.35 in frequency upon deuteration. They are well separated from a sharp peak at 195 cm−1 which is assigned to the stretching motion of an H2O molecule H bonded to the oxalate ion and does not shift upon deuteration. The neutron spectra are discussed and compared with the results of proton magnetic resonance, Raman, and infrared measurements.

The structure of Coppinger's radical and its orientation within a cluster of a liquid crystal

The electron resonance spectrum of Coppinger's radical has been measured throughout the nematic range of p-azoxyanisole and above the nematic-isotropic transition point. Because the proton hyperfine tensors are not cylindrically symmetric about an axis perpendicular to the molecular plane it is possible to deduce not only the mole fraction of radical in the cluster but also its probable orientation within the cluster. Although the results have been interpreted within the framework of the swarm theory we could equally well have used the distortion hypothesis.

Crystallite Orientation in Materials Having Fiber Texture. II. A Study of Strained Samples of Crosslinked Polyethylene

Diffraction data obtained for a crosslinked polyethylene sample crystallized at fixed strain are utilized to demonstrate the practicality of the method of analysis for samples having fiber texture which was presented in a previous paper. Plane-normal distributions qi(ζi) reconstructed using data for twelve reflections reproduce the features of the measured distributions quite satisfactorily. The series termination error is only appreciable for planes having a sharply peaked distribution, and fortunately it then appears mainly as false oscillations of small amplitude in the low-density region, which do not distort the principal features of the distribution. As a test of the accuracy of plane-normal distributions constructed for unmeasured reflections, qi(ζi) was recalculated for the (200) plane with omission of the intensity data for this plane. Deviations from the experimental distribution are again trivial. Thus, the procedure permits one to calculate the plane-normal distributions for the (002) and (401) planes, for which experimental measurements are not feasible. The crystallite orientation distribution G(ξ, φ) is calculated using the diffraction data for twelve reflections. This may be presented as a contour map or, if plotted in stereographic projection, as the inverse pole figure diagram. The most probable crystallite orientation for this sample, having relative elongation α=4.58, inclines the a, b, and c axes from the fiber direction by 41°, 90°, and 49°, respectively. The series termination error does not displace the peak positions, but it creates small areas of negative density in the low-density region. It is demonstrated that data for four planes suffice to reveal the qualitative aspects of the crystallite distribution. The approximate relation used to estimate the standard deviation of the truncated series is tested and verified. Diffraction data were also obtained for three additional samples covering a range of elongation α from 2.20 to 6.67. The (h0l) plane-normals orient most strongly toward the fiber axis, the (h/l) ratio of the plane exhibiting the best alignment decreasing continuously as α is increased. The implication that the b axis tends to orient perpendicular to the fiber axis is verified by the plane-normal distribution, which becomes more sharply peaked about χ=90° as α is increased. The maximum in the a-axis distribution shifts from χ=0° to larger values of χ as α is increased, while the c-axis distribution undergoes a more complex transformation.

AN ANALYSIS OF DESMOSOME SHAPE, SIZE, AND ORIENTATION BY THE USE OF HISTOMETRIC AND DENSITOMETRIC METHODS WITH ELECTRON MICROSCOPY

The probable shape, size, and orientation of desmosomes of the cells comprising the secretory tubules in rat submaxillary gland was determined by statistical and algebraic methods applied to electron micrographs. It was concluded that these desmosomes are discrete ellipsoidal discs whose principal axes are in the order of 4100 and 2500 angstrom units, and that they are preferentially oriented with their long axis more or less parallel to the base-apex axis of the cell. Densitometric interpretation agrees with the statistically based reconstruction of desmosomal shape. By densitometric analysis it was also determined that the peak to peak distances between layers within these desmosomes are in essential agreement with other reported findings. The approach described may have general applications to problems in the analysis of submicroscopic morphology.

Calculation of the Energy of Vaporization of Perfluorocyclopentane from Intermolecular Forces

By assuming a probable representative orientation of perfluorocyclopentane molecules in the liquid state, the energy of vaporization has been calculated, using both the London-Margenau equation of dispersion forces and the Slater-Kirkwood formula. Using only the data from density and dispersion measurements, fair agreement was found to the value experimentally determined. It is seen on the basis of this calculation that the contribution of the dipole-quadrupole interaction to the London formula is important.