Mechanical and structural properties of native and alkali-treated bacterial cellulose produced by Gluconacetobacter xylinus strain ATCC 53524

Mechanical properties of hydrated bacterial cellulose have been tested as a function of fermentation time and following the alkali treatment required for sterilisation prior to biomedical applications. Bacterial cellulose behaves as a viscoelastic material, with brittle failure reached at approximately 20% strain and 1.5 MPa stress under uniaxial tension. Treatment with 0.1 M NaOH resulted in minimal effects on the mechanical properties of bacterial cellulose. Fermentation time had a large effect on both bacterial numbers and cellulose yield but only minor effects on mechanical properties, showing that the fermentation system is a robust method for producing cellulose with predictable materials properties. The failure zone in uniaxial tension was shown to be associated with large-scale fibre alignment, consistent with this being the major determinant of mechanical properties. Under uniaxial tension, elastic moduli and failure stresses are an order of magnitude lower than those obtained under biaxial tension, consistent with the fibre alignment mechanism which is not available under biaxial tension.     

Investigation of the validity of the kinetic plot method to predict the performance of coupled column systems operated at very high pressures under different thermal conditions

The present study investigates how strong the kinetic plot method is influenced by the changes in plate height, retention factor and apparent column permeability that arise under conditions of very high pressure. More precisely, the study investigates how well a set of performance measurements conducted on a single short column can be used to predict the performance of a long sequence of coupled columns. This has been investigated for the two practically most relevant thermal conditions, i.e., that of a forced-air oven and that of a still-air oven. Measuring column performance data for acetophenone and benzene on a series of coupled 3.5 μm columns that could be operated up to 1000 bar, it was found that the kinetic plot method provides accurate predictions of time versus efficiency for the still-air oven systems, over the entire range of investigated pressures and column lengths (up to 60 cm), provided k′ and K_v0 are evaluated at the maximal pressure. For the forced-air oven which leads to worse performances than the still-air oven, the kinetic plot prediction is less accurate, partly because the thermal conditions (near-isothermal) tend to vary if the number of coupled columns increases. The fact that the thermal conditions of the column wall might vary with the column length is an additional complexity making very-high pressure separations less predictable and harder to interpret and model.     

Oxygen-induced changes in longitudinal relaxation times in skeletal muscle

The objective was to measure the effect of 100% oxygen inhalation on T1 relaxation times in skeletal muscle. Healthy volunteers were scanned using three different MRI protocols while breathing medical air and 100% oxygen. Measurements of T1 were made from regions of interest (ROIs) within various skeletal muscle groups. Dynamic data of subjects breathing a sequence of air-oxygen-air allowed the calculation of characteristic wash-in and -out times for dissolved oxygen in muscle. Contrary to previous findings, a statistically significant decrease in T1 in skeletal muscle was observed due to oxygen inhalation. We report approximate baseline characteristic values for the response of skeletal muscle to oxygen inhalation. This measurement may provide new biomarkers for evaluation of oxygen delivery and consumption in normal and diseased skeletal muscle.     

On the existence of approximate identities in ideals of group algebras

A short proof is given of the theorem by Wik, who, in 1965, showed that the nowhere-dense strong Ditkin subsets ofT, the circle group, are finite.     

On the subspaces ofL p (p>2) spanned by sequences of independent random variables

Let 2<p<∞. The Banach space spanned by a sequence of independent random variables inL ^p , each of mean zero, is shown to be isomorphic tol ²,l ^p ,l ²⊕l ^p , or a new spaceX _p , and the linear topological properties ofX _p are investigated. It is proved thatX _p is isomorphic to a complemented subspace ofL ^p and another uncomplemented subspace ofL ^p , whence there exists an uncomplemented subspace ofl ^p isomorphic tol ^p . It is also proved thatX _p is not isomorphic to the previously knownℒ _p spaces. The work for this research was partially supported by the National Science Foundation GP-12997.     

A novel bicyclic phosphonium ylide from the reaction of a 1,2-dihydrophosphorin with dimethyl acetylenedicarboxylate.

The reaction of 1,2,5-triphenylphospholium fluorenylide with dimethyl acetylenedicarboxylate gives two 1:1 adducts, one of which is shown by X-ray analysis to have a novel 1-phosphabicyclo[3.2.1]octatriene structure.     

Relevance and Assessment of Molecular Diffusion Coefficients in Liquid Chromatography

Molecular diffusion plays an important role in high-performance liquid chromatography, especially in fundamental column performance studies. An accurate knowledge of the molecular diffusion coefficients (D _m) of compounds selected for column evaluation is therefore crucial. In this review, a general overview is presented of the advantages and drawbacks of correlation-based and experimental methods that can be employed to determine molecular diffusion coefficients. The former include the Wilke–Chang, Scheibel, Reddy–Doraiswamy, Lusis–Ratcliff and Hayduk–Laudie equations, and other empirical correlations based on the Wilke–Chang equation. It is discussed how the association factor (ψ) that is required in several of these correlations can be obtained from the solubility parameter (δ). Frequently used experimental methods include the light scattering, nuclear magnetic resonance, peak parking and Taylor–Aris method, and methods employing microfluidic devices. The principles of these experimental methods are elucidated in detail. Moreover, the influence of several parameters, such as solute characteristics, solvent viscosity, temperature and pressure on the molecular diffusion coefficient is described.     

A Highly Selective Mitochondria‐Targeting Fluorescent K+ Sensor

Regulation of intracellular potassium (K⁺) concentration plays a key role in metabolic processes. So far, only a few intracellular K⁺ sensors have been developed. The highly selective fluorescent K⁺ sensor KS6 for monitoring K⁺ ion dynamics in mitochondria was produced by coupling triphenylphosphonium, borondipyrromethene (BODIPY), and triazacryptand (TAC). KS6 shows a good response to K⁺ in the range 30–500 mM , a large dynamic range (F_max/F₀≈130), high brightness (?_f=14.4 % at 150 mM of K⁺), and insensitivity to both pH in the range 5.5–9.0 and other metal ions under physiological conditions. Colocalization tests of KS6 with MitoTracker Green confirmed its predominant localization in the mitochondria of HeLa and U87MG cells. K⁺ efflux/influx in the mitochondria was observed upon stimulation with ionophores, nigericin, or ionomycin. KS6 is thus a highly selective semiquantitative K⁺ sensor suitable for the study of mitochondrial potassium flux in live cells.     

Variation of long-lived free radicals responsible for the EPR native signal in bone of aged or diseased human females and ovariectomized adult rats

The purpose of this study was to gain insights into the variations seen in the electron paramagnetic resonance (EPR) spectroscopy of the native signals of teeth and bones used for retrospective dosimetry measurements. We determined that changes occur in the long-lived free radicals responsible for the native signal of cortical bone in aging or diseased human females and aged ovariectomized rats. This was done by measuring the magnitude of the broad (BC) and narrow (NC) components of the native EPR signal of bone following chemical extraction, aging, crushing and thermal annealing. Bone from the upper midshaft of femora of young (17-34 years old, n=5) and elderly (70-92 years old, n=18) females was examined. The results showed that the elderly women had significantly higher BC than the younger women (P<0.01). A similar interpretation was made of the data from an aging female rat osteoporosis model. The results for the NC signals were similar. Finally, dramatic decreases in both NC and BC signals were seen in HIV positive and uncontrolled diabetic (one each) patients indicating the need for studying this signal for a broad spectrum of metabolic disorders. Experiments were performed which strongly indicate that iron liganded with organic molecules is the source of the BC signal. Finally, the accuracy achieved in this study indicates that resolving the dosimetric signal (g=2.0018) should be improved by subtraction of the deconvoluted NC and BC signals from the original spectrum.     

One-Dimensional p-Adic Subanalytic Sets

In this paper we extend two theorems from [2] on p-adic subanalyticsets, where p is a fixed prime number, Q_p is the field of p-adicnumbers and Z_p is the ring of p-adic integers. One of thesetheorems [2, 3.32] says that each subanalytic subset of Z_p issemialgebraic. This is extended here as follows.