Rigorous model-based uncertainty quantification with application to terminal ballistics—Part II. Systems with uncontrollable inputs and large scatter

This Part II of this series is concerned with establishing the feasibility of an extended data-on-demand (XDoD) uncertainty quantification (UQ) protocol based on concentration-of-measure inequalities and martingale theory. Specific aims are to establish the feasibility of the protocol and its basic properties, including the tightness of the predictions afforded by the protocol. The assessment is based on an application to terminal ballistics and a specific system configuration consisting of 6061-T6 aluminum plates struck by spherical 440c stainless steel projectiles at ballistic impact speeds in the range of 2.4–2.8 km/s. The system's inputs are the plate thickness, plate obliquity and impact velocity. The perforation area is chosen as the sole performance measure of the system. The objective of the UQ analysis is to certify the lethality of the projectile, i.e., that the projectile perforates the plate with high probability over a prespecified range of impact velocities, plate thicknesses and plate obliquities. All tests were conducted at Caltech's Small Particle Hypervelocity Range (SPHIR), which houses a two-stage gas gun. A feature of this facility is that the impact velocity, while amenable to precise measurement, cannot be controlled precisely but varies randomly according to a known probability density function. In addition, due to a competition between petalling and plugging mechanisms for the material system under consideration, the measured perforation area exhibits considerable scatter. The analysis establishes the feasibility of the XDoD UQ protocol as a rigorous yet practical approach for model-based certification of complex systems characterized by uncontrollable inputs and noisy experimental data.     

A sequential extraction procedure for an insight into selenium speciation in garlic

A sequential extraction procedure was developed for the fractionation of different classes of selenium species present in garlic. The consecutive steps included leaching with water, extraction of cell-wall bound species after lysis with a mixture of cellulase, chitinase and β-glucanase completed by a proteolytic attack, extraction with HCl to liberate the residual organic bound species and finally, extractions with sulfite solution and CS₂ to complete the mass balance by the recovery of Se⁰ and Se²⁻, respectively. Selenium speciation in the aqueous fractions was probed by anion-exchange and ion-pairing reversed-phase HPLC-ICP MS after purification by preparative size-exclusion LC. It was found to be strongly affected by the sample redox conditions. The peak identity was matched with a mixture of 9 compounds expected to be present in allium plants; electrospray QTOF MS turned out to be unsuccessful. Selenite, selenate and selenomethionine were the dominating species present.     

Temperature dependence of viscosity–shear rate behavior in undiluted polystyrene

The time—temperature superposition principle is well-established for linear viscoelastic properties of polymer systems. It is generally supposed that the same principle carries over into nonlinear phenomena, such as the relationship between viscosity η and shear rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}. Guided by this principle and the forms of various molecular theories, one would expect that η—\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} data on the same polymer at different temperatures would superimpose when plotted as η/η0 versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}η0/ρT, η0 being the limiting viscosity at low shear rates, ρ the polymer density, and T the absolute temperature. Data on polystyrene melts, obtained in a plate-cone viscometer, appear systematically to violate this principle in the range 140–190°. Such anomalies are absent in concentrated solutions of polystyrene. The trends are similar to those reported by Plazek in the steady-state compliance of polystyrene melts near T_g, but they appear to persist to higher temperatures than the compliance anomaly.     

Electric field dependence of recombination kinetics in reaction centers of photosynthetic bacteria

Time-resolved charge recombination has been measured by reflectance/absorption spectroscopic analysis of Langmuir-Blodgett films of reaction centers of the photosynthetic bacterium, Rhodopseudomonas sphaeroides over a wide range of applied electric field strengths. The field dependence of the recombination kinetics has been deduced from the time-course of the reduction of the flash-oxidized bacteriochlorophyll dimer [(BChl)⁺₂] recorded at different applied field strengths. Measurements were performed under two different electric field biasing conditions: a constant bias and a high-frequency bipolar square-wave bias. The additional data obtained from bipolar biasing enabled the use of a new deconvolution method to obtain the field dependence of the rate constants from the experimental curves. The deconvolution shows that the rates for charge recombination from the flash-generated state back to the ground state (BChl)₂Q_A approximate exponential functions of the applied electric field. Correlation of the recombination kinetics data with photoinduced electrical response measurements on films with asymmetric up and down populations of reaction centers reveals that fields opposing charge separation result in faster rates of recombination. Although other possibilities are considered, the main source of the effect is believed to be a result of field-induced changes in the free energy gap between and (BChl)₂Q_A. The results presented here are compared to those obtained in experiments with solubilized reaction centers in which the free energy gap between and (BChl)₂Q_A has been changed by quinone replacement.     

The effects of low level microwaves on the fluidity of photoreceptor cell membrane

Due to the extensive use of electromagnetic fields in everyday life, more information is required for the detection of mechanisms of interaction and the possible side effects of electromagnetic radiation on the structure and function of the organism.In this paper, we study the effects of low-power microwaves (2.45 GHz) on the membrane fluidity of rod photoreceptor cells. The retina is expected to be very sensitive to microwave irradiation due to the polar character of the photoreceptor cells [Biochim. Biophys. Acta 1273 (1995) 217] as well as to its high water content [Stud. Biophys. 81 (1981) 39].     

DOTA-bis(amide)]lanthanide complexes: NMR evidence for differences in water-molecule exchange rates for coordination isomers

Two derivatives of 1,4,7,10-tetraazacyclododecane with trans-acetate and trans-amide side-chain ligating groups have been prepared and their complexes with lanthanide cations examined by multinuclear NMR spectroscopy. These lanthanide complexes exist in aqueous solution as a mixture of slowly interconverting coordination isomers with 1H chemical shifts similar to those reported previously for the major (M) and minor (m) forms of the tetraacetate ([Ln(dota)]-) and tetraamide ([Ln(dtma)]3+) complexes. As in the [Ln(dota)]- and [Ln(dtma)]3+ complexes, the m/M ratio proved to be a sensitive function of lanthanide size and temperature. An analysis of 1H hyperfine shifts in spectra of the Yb3+ complexes revealed significant differences between the axial (D1) and non-axial (D2) components of the magnetic susceptibility tensor anisotropy in the m and M coordination isomers and the energetics of ring inversion and m <==> M isomerization as determined by two-dimensional exchange spectroscopy (EXSY). (17)O shift data for the Dy3+ complexes showed that both have one inner-sphere water molecule. A temperature-dependent (17)O NMR study of bulk water linewidths for solutions of the Gd3+ complexes provided direct evidence for differences in water exchange rates for the two coordination isomers. The bound-water lifetimes (tauM298) in the M and m isomers of the Gd3+ complexes ranged from 1.4-2.4 micros and 3-14 ns, respectively. This indicates that 1) the inner-sphere water lifetimes for the complexes with a single positive charge reported here are considerably shorter for both coordination isomers than the corresponding values for the [Gd(dtma)]3+ complex with three positive charges, and 2) the difference in water lifetimes for M and m isomers in these two series is magnified in the [Gd[dota-bis(amide)]] complexes. This feature highlights the remarkable role of both charge and molecular geometry in determining the exchange rate of the coordinated water.     

Epitaxial crystallization of polyesters on inorganic and organic substrates

A series of low-molecular-weight linear polyesters were epitaxially crystallized from dilute solution and the melt on a variety of organic and inorganic substrates. The rod-like polyester crystals which were formed assumed general orientations in alignment with substrate geometry. This yielded monodirectional orientation of these crystals on one of the organic substrates, and bidirectional orientation on the other surfaces. Heterogeneous nucleation on the organic substrates, trioxane and naphthalene, induced the growth of much larger epitaxial crystals than have previously been observed on inorganic substrates. Those polyesters, with a high percentage of methylene units per chain repeat, crystallized in an unusual polymorphic form when in contact with the organic substrates. Polymorphic transformation to the normal form was not possible under thermal treatment or with increased crystal thickness. The expected relationship between dipolar alignment in the polymer crystal and this polymorphism was established.