Depth-dependent acoustic features of diving sperm whales (Physeter macrocephalus) in the Gulf of Mexico

Three-dimensional dive trajectories of three sperm whales in the Gulf of Mexico have been obtained by measuring the relative arrival times and bearings of the animals' acoustic multipath reflections, using two elements of a towed hydrophone array deployed at an unknown depth and orientation. Within the first 6-12 min of the start of a dive, the intervals between successive "clicks" of all three whales corresponded closely with the two-way travel time of an acoustic pulse traveling vertically between the animals' position and the ocean bottom. The click spectra contained multiple peaks, including a faint band of energy originally centered near 10 kHz. As the animals descended over 500 m in depth, the center frequency of this band shifted to nearly 15 kHz, but subsequently remained near this value during the rest of the dive. This frequency shift is consistent with that expected from energy scattering from an ensemble of incompressible small-scale air-filled resonators, with diameters on the order of 4 mm. One possible candidate for such an ensemble is proposed to reside in the collapsed frontal sac of the animal. A comparison of the received levels for the bottom and direct multipath arrivals indicates that the whales' acoustic directivity must range between 10-30 dB in the 5-20-kHz region.     

Synthesis of the RuIV amido complex [TpRu(CO)(PPh3)(NHPh)][OTf]2 (Tp = hydridotris(pyrazolyl)borate; OTf = trifluoromethanesulfonate) and deprotonation to form an octahedral and d4 imido complex: computational study of RuIV-imido bonding

Deprotonation of [TpRu(CO)(PPh3)(NHPh)][OTf]2 yields the thermally unstable d4 imido complex [TpRu-(CO)(PPh3)(NPh)][OTf]; a computational study of the bonding of the imido complex provides a foundation for discussion of its instability in terms of pi-conflict.     

Isoapoptolidin: structure and activity of the ring-expanded isomer of apoptolidin

[formula: see text] Apoptolidin (1) is a novel oncolytic lead that induces apoptosis in transformed cell lines with exceptional selectivity. We report the isolation and characterization of a ring-expanded macrolide isomer of apoptolidin: isoapoptolidin (2). The solution conformation of isoapoptolidin is described. The rate of isomerization was measured under biologically relevant conditions and found to approach equilibrium within the time frame of most cell-based assays. Isoapoptolidin's ability to inhibit mitochondrial F0F1-ATPase is over 10-fold less than that of apoptolidin.     

Asymmetric total synthesis of dendrobatid alkaloid 251F

The dendrobatid alkaloid (-)-251F was synthesized. The key steps of the synthesis were (1) an asymmetric Diels-Alder reaction to establish four of the necessary stereocenters in the target, (2) a ring-opening/ring-closing metathesis reaction to establish a key [3.3.0] bicyclic intermediate, and (3) an intramolecular Schmidt reaction.     

Surface chemistry of silicon nanoclusters

We employ density functional and quantum Monte Carlo calculations to show that significant changes occur in the gap of fully hydrogenated nanoclusters when the surface contains passivants other than hydrogen, in particular atomic oxygen. In the case of oxygen, the gap reduction computed as a function of the nanocluster size provides a consistent interpretation of several recent experiments. Furthermore, we predict that other double bonded groups also significantly affect the optical gap, while single bonded groups have a minimal influence.     

Realistic Dirac leptogenesis

We present a model of leptogenesis that preserves lepton number. The model maintains the important feature of more traditional leptogenesis scenarios: The decaying particles that provide the CP violation necessary for baryogenesis also provide the explanation for the smallness of the neutrino Yukawa couplings. This model clearly demonstrates that, contrary to conventional wisdom, neutrinos need not be Majorana in nature in order to help explain the baryon asymmetry of the universe.     

Luminescence Properties of New Fused Benzothiophene Derivatives and Their Conductive Oligomers Structural and Solvent Effects

The structural and solvent effects on the electronic absorption and fluorescence spectra, and fluorescence quantum yields, of four new fused benzothiophene derivatives, including benzothieno[3,2b]-thiophene (BTT), benzothieno[3,2-b]benzothiophene (BTBT), 6-methoxy[1]benzothieno[3,2b]-thiophene (MeOBTT), and benzothieno[3,2-b]indole (BTI) were investigated at 295 K. The luminescence properties of the corresponding conductive oligomers, poly(BTT) and poly (MeOBTT), electrosynthesized in acetonitrile, were also studied. Satisfactory McRae, Suppan, and Kawski-Chamma-Viallet solvatochromic correlations were established for the four monomers in most solvents. A weak negative solvatochromic behavior was found for these compounds, indicating that their dipole moments are slightly lower in the excited singlet state than in the ground state. Kamlet-Abboud-Taft multiparametric correlations were also obtained for absorption and fluorescence wave numbers and quantum yields, demonstrating the existence of specific solute-solvent interactions. In the case of the oligomers, important red-shifts of the fluorescence emission maxima ( 90–110 nm) relative to the corresponding monomers were observed, which shows the extent of conjugated segments in the oligomer chains.     

Small-angle X-ray scattering study of liquid crystalline polycarbonates based on α-methyl stilbene mesogen and methylene-containing flexible spacer

Crystallization and melting behavior are studied by small-angle X-ray scattering (SAXS) for a series of recently synthesized monotropic liquid crystalline polycarbonates based on α-methyl stilbene mesogen and methylene flexible spacer. The one-dimensional electron density correlation function is used to obtain long period, crystal thickness, and linear crystallinity from the Lorentz-corrected SAXS intensity. Changes in these parameters during nonisothermal crystallization and melting are explained by a model of dual crystal populations. The primary crystals form first using the liquid crystalline phase as crystal nuclei, while smaller and less perfect crystals form later from the isotropic phase at low temperature. The results of the real-time SAXS study of isothermal crystallization also support the view that the nematic phase serves as crystal nuclei for fast crystallization. An odd-even effect in crystal thickness and linear crystallinity is observed in all the SAXS experiments mentioned above. The results of this study and our complementary wide-angle X-ray scattering (WAXS) investigation show clearly that the difference in the position of the neighboring carbonate dipoles on a chain affects structural organization both at the unit cell level and at the level of the crystal in these monotropic LCPs. © 1995 John Wiley & Sons, Inc.     

CHEMILUMINESCENCE QUENCHING TERMS

Abstract— A methodology for the determination of chemiluminescence quenching terms is given. By using the oxidation of tetrakis(dimethylamino)ethylene as an example, it is shown how the nature and magnitude of the quenching terms help to elucidate the reaction mechanism, or how ignoring them can lead to false impressions. It is shown that chemiluminescence quenching effects need not be the same as those for photoluminescence of the same electronically excited species.     

The TEM characterization of the lamellar structure of osteoporotic human trabecular bone

The lamellar structure of osteoporotic human trabecular bone was characterized experimentally by means of transmission electron microscopy (TEM). More specifically, the TEM was used to determine if trabecular bone exhibits similar lamellar structural motifs as cortical bone by analyzing unmineralized, mineralized and demineralized bone, and to study the influence of the osteocyte network on the lamellar structure of osteoporotic trabecular bone. Comparison with normal trabecular bone is included. This paper summarizes partial results of a larger study, which addressed the characterization of the hierarchical structure of normal versus osteoporotic human trabecular bone [Rubin, M.A., 2001. Multiscale characterization of the ultrastructure of trabecular bone in osteoporotic and normal humans and in two inbred strains of mice. MS Thesis, Georgia Institute of Technology.] at several structural scales.