Dissolving-grade birch pulps produced under various prehydrolysis intensities: quality,structure and applications

Aqueous-phase prehydrolysis followed by alkaline pulping is a viable process to produce wood-based dissolving pulps. However, detailed characterisation of the achievable pulp quality, performance and cellulose structure is yet lacking. In this study, the production of hemicellulose-lean birch soda-anthraquinone pulps after prehydrolysis under various intensities was investigated. Increasing prehydrolysis intensity resulted in pulps of higher purity but lower cellulose yield and degree of polymerisation. Higher cellulose yield by using sodium borohydride during pulping was achieved at the expense of reducing pulp purity. Cellulose crystallinity was similar in all pulps indicating simultaneous degradation of both crystalline and amorphous cellulose regions. Reinforced prehydrolysis seemingly increased the cellulose crystal size and the interfibrillar distances. Moderate intensity prehydrolysis (170 °C) resulted in a pulp well suited for viscose application, whereas reinforced prehydrolysis favoured the production of acceptable cellulose triacetate dope. The performance of the pulps in viscose and acetate applications was strongly related to the chemical and structural properties.     

An occupation time identity for reflecting Brownian motion with drift

Summary This note is about an occupation time identity derived in [14] for reflecting Brownian motion with drift ]]>]]>]]>]]>]]>]]>]]>]]>]]>]]>]]>]]>]]>-\mu<0,$ RBM($-\mu$), for short. The identity says that for RBM($-\mu$) in stationary state ]]>(I^{+}_t, I^{-}_t) \rr (t-G_t,D_t-t),\qquad t\in \mathbb{R},$$ where $G_t$ and $D_t$ denote the starting time and the ending time, respectively, of an excursion from 0 to 0 (straddling $t$) and $I^{+}_t$ and $I^{-}_t$ are the occupation times above and below, respectively, of the observed level at time $t$ during the excursion. Due to stationarity, the common distribution does not depend on $t.$ In fact, it is proved in [9] that the identity is true, under some assumptions, for all recurrent diffusions and stationary processes. In the null recurrent diffusion case the common distribution is not, of course, a probability distribution. The aim of this note is to increase understanding of the identity by studying the RBM($-\mu$) case via Ray--Knight theorems.     

Measurement of the binding of DNA to liposomes by resonance energy transfer

A rapid and simple semiquantitative method for monitoring the attachment of DNA to liposomes is described. This technique is based on the measurement of resonance energy transfer between a membrane-embedded fluorescent pyrene lipid donor and DNA labeled with adriamycin as an acceptor.     

Boroxol Rings in Liquid and Vitreous B2O3 from First Principles

We investigate the structural and vibrational properties of glassy B2O3 using first-principles molecular dynamics simulations. In particular, we determine the boroxol rings fraction f for which there is still no consensus in the literature. Two numerical models containing either a low or a high level of boroxol rings are tested against a gamut of experimental probes (static structure factor, Raman, 11B and 17O NMR data). We show that only the boroxol-rich model (f=75%) can reproduce the full set of observables. Total-energy calculations show that at the glass density, boroxol-rich structures are favored by about 6 kcal/(mol boroxol). Finally, the liquid state is explored in the 2,000-4,000 K range and a reduction of f to 10%-20% is obtained.     

Normalized amplitude quotient for parametrization of the glottal flow

Normalized amplitude quotient (NAQ) is presented as a method to parametrize the glottal closing phase using two amplitude-domain measurements from waveforms estimated by inverse filtering. In this technique, the ratio between the amplitude of the ac flow and the negative peak amplitude of the flow derivative is first computed using the concept of equivalent rectangular pulse, a hypothetical signal located at the instant of the main excitation of the vocal tract. This ratio is then normalized with respect to the length of the fundamental period. Comparison between NAQ and its counterpart among the conventional time-domain parameters, the closing quotient, shows that the proposed parameter is more robust against distortion such as measurement noise that make the extraction of conventional time-based parameters of the glottal flow problematic. Experiments with breathy, normal, and pressed vowels indicate that NAQ is also able to separate the type of phonation effectively.     

Tracing the allomerization pathways of chlorophylls by (18)O-labeling and mass spectrometry

The Willst?tter allomerization reaction of chlorophylls (Chl) has posed a difficult problem in Chl and photosynthesis research over the past 90 years. Here, we present strong additional evidence, based on (18)O-labeling and mass spectrometry, for the previously published free-radical allomerization (FRA) mechanism (Hynninen, Z. Naturforsch. 1981, 36b, 1010-1016). This mechanism is also complemented now by describing two alternative pathways for the formation of 13(2)(S/R)-hydroxy-Chl a. The results from the (18,18)O(2)-experiments suggest that the predominant route for the formation of the 13(2)(S/R)-hydroxy-Chl a under essentially anhydrous conditions (anhydrous Chl and thoroughly dried methanol) is the homolytic cleavage of the C-13(2)-hydroperoxide intermediate. However, if Chl dihydrate and undried methanol are used in the reaction mixture, the direct route from the Chl C-13(2) radical to 13(2)(S/R)-hydroxy-Chl a can be predicted to become significant. The results from the (18,18)O(2)-allomerization experiments described in this paper also verified that the 13(2)(S/R)-methoxy-lactone derivatives and the 15-glyoxylic acid derivative of Chl a incorporated each a single (18)O-atom, whereas 13(2)(R/S)-methoxy-Chl a remained unlabeled. Consequently, these allomers are formed via the pathways previously suggested in the original FRA mechanism. The possible factors contributing to the control of the allomerization reactions are considered. Finally, the relationship between the allomerization reactions of Chl a and those of Chl b and BChl a is briefly discussed.     

Ionisation and appearance potentials in the evaluation of nonbonded interactions—IV: Conformational effects in methyl-substituted 1,3-oxathianes

The ionization and appearance potentials for the molecular and [M ? Me]⁺ ions of several stereoisomeric methyl-1,3-oxathianes were measured. The differences between the ionisation and/or appearance potentials are shown to correlate well with the conformational energy differences in question.     

Thermal phase behavior of DMPG: the exclusion of continuous network and dense aggregates

1,2-Dimyristoyl-sn-glycero-3-phospho-rac-glycerol has been suggested to form at intermediate temperatures and at high concentrations in low-salt solutions as a continuous sponge phase (Heimburg, T.; Biltonen, R. L. Biochemistry 1994, 33, 9477-9488). In the present study, the changes in signals seen for a range of fluorescent probes during phase transformations of this phospholipid indicate continuous melting and a change in lipid packing, in accordance with previous reports. However, in accordance with Lamy-Freund and Riske (Lamy-Freund, M. T.; Riske, K. A. Chem. Phys. Lipids 2003, 122, 19-32), no enhancement of lipid mixing within the putative sponge phase region was seen, suggesting a lack of a connected lipid surface. Accordingly, a typical sponge phase cannot account for the properties of the intermediate phase. The low scattering intensities of the latter have also been taken as evidence for disaggregation. While dynamic light scattering and data for membranes containing poly(ethylene glycol)-ylated lipids could lend credence to disaggregation, the most likely explanation for the scattering data would appear to be a shape transition without significant changes in neither vesicle aggregation nor bilayer connectivity. An abrupt change in light scattering and signals from some of the fluorescent probes used reveals a new transition at Tt approximately 43 degrees C, with the formation of a more ordered interface.     

On First Range Times of Linear Diffusions

In this paper we consider first range times (with randomised range level) of a linear diffusion on R. Inspired by the observation that the exponentially randomised range time has the same law as a similarly randomised first exit time from an interval, we study a large family of non-negative 2-dimensional random variables (X,X′) with this property. The defining feature of the family is F^c(x,y)=F^c(x+y,0), ∀ x ≥ 0, y ≥ 0, where F^c(x,y):=P (X > x, X′ > y) We also explain the Markovian structure of the Brownian local time process when stopped at an exponentially randomised first range time. It is seen that squared Bessel processes with drift are serving hereby as a Markovian element.