The acceleratory degradation of solids according to non-steady-state kinetics

The acceleratory degradation of solids represents an area of research where extreme care must be exercised to obtain reproducible data. Different preparations of the same substance often show great variation in degradation patterns. Many kinetic equations have been developed to describe the kinetics of acceleratory degradations. Most of them are empirical and apply only to certain phases of a degradation. The non-steady-state kinetics which were developed to describe the zip degradation of poly(vinyl chloride) will be shown to describe effectively the unusual degradation behavior of inorganic solids that follow an acceleratory pattern.     

Determination of structure of weak scatterers from holographic images

For a weak scatterer a three dimensional Fourier transform of the image formed by a generalized hologram is shown to yield directly the Fourier transform of the scattering potential evaluated on the Ewald sphere. The entire scattering potential can be approximately determined if the object is illuminated from all directions in a series of experiments and if the scattering potential is essentially bandlimited to within a sphere of radius 4π/λ.     

The nonlinear graviton: Superposition of plane waves

The nonlinear graviton construction of Penrose is given explicitly for the nonlinear superposition of a finite number of plane waves with arbitrary propagation directions, phase, and amplitude profiles. These are realized as generalizedH-spaces for which the asymptotic data are distributional and have singular support on a finite number of null generators ofI ⁺.     

Method of calibrating gel permeation chromatography with whole polymers

Column systems for gel permeation chromatography are usually calibrated by eluting a series of sharp polymer fractions of known molecular weights and by correlating their elution volumes with molecular size or weight. A different method for calibration is proposed in which only one polymer sample, with a broad, well-characterized molecular weight distribution, is used. The cumulative distribution and the integrated, normalized GPC chromatogram are successively superimposed, and molecular weights and corresponding elution volumes are correlated. It is found that calibration curves obtained in this manner show a definite curvature. A possible explanation and correction for this behavior is given, based on the concentration dependence of elution volumes.     

QCD asymptotics and kinematic thresholds in deep inelastic scattering

The Nachtmann moments of deep inelastic scattering structure functions are required by kinematics to contain a so far neglected threshold factor which is dependent on both n and q². Its presence significantly affects the “moment analysis” in the usual QCD phenomenology and it resolves the difficulties connected with improper threshold behavior of the “ξ-scaling” analysis of structure functions.     

Rheological properties of poly(2,6-dimethylphenylene oxide)—polystyrene blends

The viscoelastic (VE) response of freeze-dried blends of polystyrene (PS) and poly-(2,6-dimethyl phenylene oxide) (PPO) has been studied as a function of composition, frequency, and temperature to examine the degree of rheological compatibility. When blended together, the relaxation processes of both molecular species exhibit the same temperature dependence. However, the temperature dependence of the VE response is a function of composition. It is shown that this behavior can be predicted from the measured glass transition temperatures by assuming the additivity of the free volumes of the components. The properties of the blends are compared at equal free volumes. The effective segmental friction factor is found to be independent of composition while the modulus of the rubbery plateau increases with PPO concentration. This result is interpreted as a change in the entanglement molecular weight M_e of the blends. When the changes in M_e are considered, the relationship between the zero-shear viscosity η0 and the 3.4 power of the weight-average molecular weight, commonly found for high molecular weight homopolymers, predicts the compositional dependence of η0 for the PPO–PS blends. It is concluded that the PPO–PS system forms a rheologically compatible blend.     

DNA sequence-enabled reassembly of the green fluorescent protein

We describe a general methodology for the direct detection of DNA by the design of a split-protein system that reassembles to form an active complex only in the presence of a targeted DNA sequence. This approach, called SEquence Enabled Reassembly (SEER) of proteins, combines the ability to rationally dissect proteins to construct oligomerization-dependent protein reassembly systems and the availability of DNA binding Cys2-His2 zinc-finger motifs for the recognition of specific DNA sequences. We demonstrate the feasibility of the SEER approach utilizing the split green fluorescent protein appended to appropriate zinc fingers, such that chromophore formation is only catalyzed in the presence of DNA sequences that incorporate binding sites for both zinc fingers.     

Nonacid cleavable detergents applied to MALDI mass spectrometry profiling of whole cells

Although cleavable detergents were first synthesized a number of years ago, they have only recently been successfully applied to problems involving biological molecules. Recent reports have demonstrated that these compounds are useful for applications involving both 2D PAGE and mass spectrometry. However, most cleavable surfactants have utilized acid-labile functional groups to affect cleavage. In applications where extreme pH is required, acid cleavable detergents have limited usefulness. We report the synthesis of fluoride cleavable silane compounds and photolabile cinnamate esters as cleavable detergents having alternative cleavage chemistries than previously reported cleavable detergents. These compounds were applied to whole cell analysis using MALDI mass spectrometry, and it was demonstrated that their use results in an increase in the number of proteins analyzed by increasing protein solubility.     

Tensors,spinors, and functions on the unit sphere

A representation of tensors and spinors at a point of space-time as spin and conformally weighted functions on the unit sphere is derived. Methods for performing algebraic operations on tensors and spinors in this representation are discussed.Supported in part by grants Nos. GP-35773X1 and MPS74-18020 from the National Science Foundation.