Scattering from a single bubble near a roughened air-water interface: laboratory measurements and modeling

The problem of scattering from a single bubble located close to a slightly roughened, air-water interface is studied both theoretically and experimentally. Two well-controlled laboratory experiments were performed to investigate the effects of surface roughness on the scattering response of the bubble. In the first experiment, a bubble of radius 1200 microm was placed on a fine thread at a variable distance, d, from the mean-still-water level of the surface, which was roughened using a wind source. In the second experiment, a bubble of radius 800 microm was utilized, while the water surface was roughened using a plunger wave-making source. The waveheights and important characteristic length scales associated with each experiment were quantified using digital photography. The wind source produced waveheights that were represented by a Gaussian distribution, while the plunger source produced waveheights that were represented by a bimodal distribution. To model the acoustic measurements, an expression describing the four scattering paths, from source to bubble to receiver, was used. A random phase shift due to the surface roughness was added to the paths that interacted with the surface, and expectations of this phase shift were computed based on the analytical representations for the waveheight distribution. The data show good agreement with the simulations and the sensitivity of scattering from a subsurface bubble to small changes in waveheight is illustrated. The experiments highlight important parametric dependencies, which are summarized here, and the relation between monostatic and bistatic scattering is also discussed.     

Proteome analysis of conditioned medium from cultured adult hippocampal progenitors

It is known that proliferation and survival of neural stem/progenitor cells in vitro not only depend on exogenous factors, but also on autocrine factors secreted into the conditioned medium. It is also well known that the identification of bioactive proteins secreted into the conditioned medium poses a substantial challenge. Recently, neural stem/progenitor cells were shown to secrete a survival factor, cystatin C, into the conditioned medium. Here, we demonstrate an approach to identify other low molecular weight proteins in conditioned medium from cultured adult rat hippocampal progenitor cells. A combination of preparative two-dimensional gel electrophoresis (2-DE) and mass spectrometry was utilized in the analysis. We were able to identify a number of proteins, which include Rho-guanine nucleotide dissociation inhibitor 1, phosphatidylethanolamine binding protein (PEBP), also termed Raf-1 kinase interacting protein, polyubiquitin, immunophilin FK506 binding protein 12 (FKBP12) and cystatin C. The presence of PEBP and FKBP12 in conditioned medium was confirmed immunologically. All nestin-positive progenitor cells showed immunoreactivity for antibodies against PEBP and FKBP12. To our knowledge we are the first to use this preparative proteomic approach to search for stem cell factors in conditioned medium. The method could be used to identify novel bioactive proteins secreted by stem/progenitor cells in vitro. Identification of bioactive proteins in vitro is of potential importance for the understanding of the regulatory mechanisms of the cells in vivo.     

Inorganic coordination polymers. XII. Chromium(III) tris(phosphinates)

Cohesive films of a series of chromium(III) tris(phosphinates)[Cr(OPRR′O)(OPR″-R?O)(OPR^*R^**O)]_y in which the side groups on the phosphorus are alkyl, phenyl, and/or hydrogen groups have been prepared by reaction casting or by hot pressing. The preparative reaction appears to involve conversion of an aquahydroxo or hydroxo chromium(III) bis(phosphinate) to an intermediate hydroxo bis(phosphinate) containing coordinated phosphinic acid followed by an intrachain reaction leading to the tris(phosphinate). Tensile strengths of the chromium(III) tris(phosphinates) range from 100 to 5600 psi, elongations from less than 1 to 100%. Thermogravimetric data indicate that major decomposition occurs at temperatures from 200 to 435°C in air and from 410 to 510°C in nitrogen. Infrared spectra and physical properties are interpreted to support a structure for the chromium(III) tris(phosphinates) which is based on linear, triple-bridged chains. The presence of octyl or other long alkyl side groups on the phosphorus improves the physical properties, presumably by internal plasticization, but leads to decreased thermal stability.     

Synthesis of pyrrolidinone PNA: a novel conformationally restricted PNA analogue

To preorganize PNA for duplex formation, a new cyclic pyrrolidinone PNA analogue has been designed. In this analogue the aminoethylglycine backbone and the methylenecarbonyl linker are connected, introducing two chiral centers compared to PNA. The four stereoisomers of the adenine analogue were synthesized, and the hybridization properties of PNA decamers containing one analogue were measured against complementary DNA, RNA, and PNA strands. The (3S,5R) isomer was shown to have the highest affinity toward RNA, and to recognize RNA and PNA better than DNA. The (3S,5R) isomer was used to prepare a fully modified decamer which bound to rU10 with only a small decrease in Tm (delta Tm/mod = 1 degree C) relative to aminoethylglycine PNA.     

Exploring SmBr2-, SmI2-, and YbI2-mediated reactions assisted by microwave irradiation

The use of microwave heating in lanthanide(II) halide (LnX2 = SmBr2, SmI2, and YbI2) mediated reduction and coupling reactions has been investigated for a variety of functional groups including alpha,beta-unsaturated esters, aldehydes, ketones, imines, and alkyl halides. Good to quantitative transformations were obtained within a few minutes without the addition of any co-solvents, such as hexamethyl phosphoramide (HMPA). The redox potential of YbI2 in tetrahydrofuran (THF) has been determined as -1.02+/-0.05 V (versus Ag/AgNO3) by cyclic voltammetry. A large selectivity difference in various reactions was observed depending on the redox potential of the LnX2 reagent. The more powerful reductant, SmBr2, afforded mainly pinacol-coupling products of ketones whereas the weaker reductant YbI2 afforded mainly reduction products. The results indicate that the reducing power of LnX2 has a large impact on not only the pinacol coupling/reduction product ratio of ketones but also on other substrates in which there are competing coupling and reduction reactions. The use of in situ generated LnX2 has also been explored and proven useful in many of these reactions.     

Inclusive 2(3He,t) reaction at 2 GeV

The inclusive ²(³He,t) reaction has been studied at 2 GeV for energy transfers up to 500 MeV and scattering angles from 0.25⁰ up to 4⁰. Data are well reproduced by a model based on a coupled-channel approach for describing the NN and N( systems. The effect of final state interaction is important in the low energy part of the spectra. In the delta region, the cross-section is very sensitive to the effects of (-N interaction and (N M NN process. The latter has also a large influence well below the pion threshold. The calculation underestimates the experimental cross-section between the quasi-elastic and the delta peaks; this is possibly due to projectile excitation or purely mesonic exchange currents.     

Combinatorial Approach to the Hydrothermal Synthesis of Zeolites

One hundred or more solid-state syntheses can be conducted in parallel and employed for the combinatorial hydrothermal syntheses of zeolites by using a novel multiautoclave design. The operation of the multiautoclave was ascertained by the reinvestigation of the complete Na₂O-Al₂O₃-SiO₂ ternary system in a single experiment. In the picture on the right, the shaded areas on the left show the crystallization fields of the different phases obtained.     

Nodal structure of the electronic Wigner function of many-electron atoms and molecules

On the example of several atomic and small molecular systems, the regular behavior of nodal patterns in the electronic one-particle reduced Wigner function is demonstrated. An expression found earlier relates the nodal pattern solely to the dot-product of the position and the momentum vector, if both arguments are large. An argument analogous to the “bond-oscillatory principle” for momentum densities links the nuclear framework in a molecule to an additional oscillatory term in momenta parallel to bonds. It is shown that these are visible in the Wigner function in terms of characteristic nodes. © 1996 John Wiley & Sons, Inc.