Limits of the plane wave approximation in the measurement of molecular properties

Rescattering electrons offer great potential as probes of molecular properties on ultrafast timescales. The most famous example is molecular tomography, in which high harmonic spectra of oriented molecules are mapped to "tomographic images" of the relevant molecular orbitals. The accuracy of such reconstructions can be greatly affected by the distortion of scattering wave functions from their asymptotic forms due to interactions with the parent ion. We investigate the validity of the commonly used plane wave approximation in molecular tomography, showing how such distortions affect the resulting orbital reconstructions.     

Separation of substituted fullerenes using non-aqueous reversed-phase liquid chromatography-mass spectrometry

A simple non-aqueous reversed-phase separation HPLC-MS method has been developed to allow for the rapid screening and separation of fullerenes and substituted fullerenes. This procedure provides confirmation that the proposed substitution methodology for the fullerene is not only successful but that multiple substitution products are obtained. The methodology is being expanded to analyze other substituted fullerene product mixtures.     

The Dedekind MacNeille site completion of a meet semilattice

The cuts of the classical Dedekind-MacNeille completion DM(S) of a meet semilattice S give rise to a natural cut coverage in the down-set frame \({\mathcal{D}S}\): down-set D covers element s if s lies below all upper bounds of D. This, in turn, leads to what we call the Dedekind-MacNeille frame extension DMF(S). The meet semilattices S for which DM(S) = DMF(S), which we refer to as proHeyting semilattices, can be specified by a simple formula, and we provide a number of equivalent characterizations. A sample result is that DM(S) = DMF(S) iff DM(S) is a Heyting algebra iff DM(S) coincides with the Bruns-Lakser injective envelope.     

XPS study on the use of 3-aminopropyltriethoxysilane to bond chitosan to a titanium surface

Chitosan, a biopolymer found in the exoskeletons of shellfish, has been shown to be antibacterial, biodegradable, osteoconductive, and has the ability to promote organized bone formation. These properties make chitosan an ideal material for use as a bioactive coating on medical implant materials. In this study, coatings made from 86.4% de-acetylated chitosan were bound to implant-quality titanium. The chitosan films were bound through a three-step process that involved the deposition of 3-aminopropyltriethoxysilane (APTES) in toluene, followed by a reaction between the amine end of APTES with gluteraldehyde, and finally, a reaction between the aldehyde end of gluteraldehyde and chitosan. Two different metal treatments were examined to determine if major differences in the ability to bind chitosan could be seen. X-ray photoelectron spectroscopy (XPS) was used to examine the surface of the titanium metal and to study the individual reaction steps. The changes to the titanium surface were consistent with the anticipated reaction steps, with significant changes in the amounts of nitrogen, silicon, and titanium that were present. It was demonstrated that more APTES was bound to the piranha-treated titanium surface as compared to the passivated titanium surface, based on the amounts of titanium, carbon, nitrogen, and silicon that were present. The metal treatments did not affect the chemistry of the chitosan films. Using toluene to bond APTES on titanium surfaces, rather than aqueous solutions, prevented the formation of unwanted polysiloxanes and increased the amount of silane on the surface for forming bonds to the chitosan films. Qualitatively, the films were more strongly attached to the titanium surfaces after using toluene, which could withstand the ultrahigh vacuum environment of XPS, as compared to the aqueous solutions, which were removed from the titanium surface when exposed to the ultrahigh vacuum environment of XPS.     

Comments on the article "On evaluating molecular-docking methods for pose prediction and enrichment factors"

The recent article "On Evaluating Molecular-Docking Methods for Pose Prediction and Enrichment Factors" (Chen H. et al. J. Chem. Inf. Model. 2006, 46, 401-415) contains a series of comments on a similar study we published in Proteins in 2004 (Perola et al. Proteins 2004, 56, 235-249). We believe that some of these comments are misleading, and we feel that an adequate response is in order.     

Effect of a triaxial nuclear shape on proton tunneling: the decay and structure of 145Tm

Gamma rays deexciting states in the proton emitter 145Tm were observed using the recoil-decay tagging method. The 145Tm ground-state rotational band was found to exhibit the properties expected for an h{11/2} proton decoupled band. In addition, coincidences between protons feeding the 2{+} state in 144Er and the 2{+}-->0{+} gamma-ray transition were detected, the first measurement of this kind, leading to a more precise value for the 2{+} excitation energy of 329(1) keV. Calculations with the particle-rotor model and the core quasiparticle coupling model indicate that the properties of the pi{11/2} band and the proton-decay rates in 145Tm are consistent with the presence of triaxiality with an asymmetry parameter gamma approximately 20 degrees .     

Discrimination of speaker sex and size when glottal-pulse rate and vocal-tract length are controlled

A recent study [Smith and Patterson, J. Acoust. Soc. Am. 118, 3177-3186 (2005)] demonstrated that both the glottal-pulse rate (GPR) and the vocal-tract length (VTL) of vowel sounds have a large effect on the perceived sex and age (or size) of a speaker. The vowels for all of the "different" speakers in that study were synthesized from recordings of the sustained vowels of one, adult male speaker. This paper presents a follow-up study in which a range of vowels were synthesized from recordings of four different speakers--an adult man, an adult woman, a young boy, and a young girl--to determine whether the sex and age of the original speaker would have an effect upon listeners' judgments of whether a vowel was spoken by a man, woman, boy, or girl, after they were equated for GPR and VTL. The sustained vowels of the four speakers were scaled to produce the same combinations of GPR and VTL, which covered the entire range normally encountered in every day life. The results show that listeners readily distinguish children from adults based on their sustained vowels but that they struggle to distinguish the sex of the speaker.     

Computations with viscoplastic and viscoelastoplastic fluids

This numerical study focuses on regularised Bingham-type and viscoelastoplastic fluids, performing simulations for 4:1:4 contraction?Cexpansion flow with a hybrid finite element?Cfinite volume subcell scheme. The work explores the viscoplastic regime, via the Bingham?CPapanastasiou model, and extends this into the viscoelastoplastic regime through the Papanastasiou?COldroyd model. Our findings reveal the significant impact that elevation has in yield stress parameters, and in sharpening of the stress singularity from that of the Oldroyd/Newtonian models to the ideal Bingham form. Such aspects are covered in field response via vortex behaviour, pressure-drops, stress field structures and yielded?Cunyielded zones. With rising yield stress parameters, vortex trends reflect suppression in both upstream and downstream vortices. Viscoelastoplasticity, with its additional elasticity properties, tends to disturb upstream?Cdownstream vortex symmetry balance, with knock-on effects according to solvent-fraction and level of elasticity. Yield fronts are traced with increasing yield stress influences, revealing locations where relatively unyielded material aggregates. Analysis of pressure drop data reveals significant increases in the viscoplastic Bingham?CPapanastasiou case, O (12%) above the equivalent Newtonian fluid, that are reduced to 8% total contribution increase in the viscoelastoplastic Papanastasiou?COldroyd case. This may be argued to be a consequence of strengthening in first normal stress effects.     

EPR Study of γ-Irradiated UHMWPE Doped with Vitamin E: Assessment of Thermal Effects on the Organic Radicals During Vitamin E Diffusion

Thermal effects on ultra-high-molecular-weight polyethylene (UHMWPE) residual radicals during the vitamin E diffusion process were studied in detail. Electron paramagnetic resonance (EPR) technique showed a significant reduction in concentrations of radiation-induced primary (alkyl (–CH₂– ^?CH–CH₂–), allyl (–CH₂–^?CH=CH–CH–CH₂–) and polyenyl (–^?CH–[CH=CH–] _m –) with m > 3) radicals for both control and vitamin E-doped samples. The concentrations of radiation-induced primary radicals (RIPRs) were found to decrease proportionally with the heat/diffusion time. While the EPR spectra of the control samples showed only polyethylene (PE) radicals, the spectra of vitamin E-doped samples were found to exhibit vitamin E radicals in addition to PE radicals. Of particular interest, the heat involved during vitamin E diffusion plays a significant role in reducing the radiation-induced primary radicals of UHMWPE. For 120 min of heat/diffusion time, the available quantity of primary radicals in control samples were found to be ~7.5 % of initial radicals. The leftover amounts of these primary radicals for vitamin E-doped samples were approximately ~10.0 %. In addition to this, EPR power saturation techniques were also used to assess the effects of initial heat/diffusion treatment on the oxygen-induced residual radicals (OIRRs): R₁ (–^?CH–[CH=CH–] _m –) with m > 3 and R₂ (^?OCH–[CH=CH–] _m –) with m = 2 or 3. It was found that the concentration of OIRRs also decreases proportionally with initial heat/diffusion time. The remaining amount of OIRRs relative to leftover RIPRs after heat/diffusion was found to be approximately 4.0 % in controls and was still found to be 10.0 % in vitamin E-doped UHMWPE. This may indicate that vitamin E slows down the oxidation processes, which may contribute to the strong oxidation resistance of vitamin E-doped UHMWPE.