Self-association of sodium cholate in isotonic saline solutions

The self-association of dialyzed solutions of sodium cholate in isotonic saline solutions has been studied by vapor pressure osmometry and sedimentation equilibrium. These studies were carried out at 25, 31 and 37 degrees C. In all experiments the self-association could be described as a two-equilibrium constant, indefinite self-association in which odd species beyond monomer were absent. The plots of M1/Mna or M1/Mwa vs. c were quite smooth with no sharp breaks; this suggested that there were no critical phenomena. The temperature dependence of the self-association was quite small. Our results are in accord with other studies on sodium cholate which indicate that the self-association involves several species, and that it is not a monomer-n-mer self-association.     

Resonance Raman spectroelectrochemistry of bacteriochlorophyll and bacteriochlorophyll cation radical.

The newly developed technique of resonance Raman spectroelectrochemistry (RRSE) is applied to the study of the radical ion species involved in the primary photochemistry of photosynthesis. By means of controlled potential coulometry combined with resonance Raman spectroscopic detection, the vibrational spectrum of the bacteriochlorophyll $\text{a}$ cation radical (BChl⁺·) has been obtained and compared with the corresponding spectrum of the parent molecule. The cation radical spectrum is significantly different from the neutral spectrum both in band frequencies and intensities. These results suggest that RR vibrational spectra may provide a new means of identifying and kinetically monitoring radical ion formation both in photosynthetic model systems and $\text{in vivo}$.     

Evaluating between-plant interference in field trials for assessing potato genotypes for resistance to late blight

Field trials were done with four cultivars over 3 years to assess the extent to which the amount of late blight on the foliage of a potato plant could be influenced by that on a neighbouring plant of the same or a different cultivar. Drills containing the test plants were interspersed with those of spreader plants (cv. King Edward) which were artificially inoculated with Phytophthora infestans. The intensity of blight on the test plants was recorded on several occasions.
Resistant cultivars tended to be scored as less resistant in mixtures with other cultivars than in pure stands, and susceptible cultivars tended likewise to be scored as more resistant in mixed stands. However, standard analysis of variance indicated no systematic evidence of a significant effect due to neighbour cultivars, nor of interaction between cultivars and neighbour cultivars. In contrast, Kempton's (1982) neighbour model indicated a significant and positive interference coefficient (β) in each trial, which generally decreased over time. Predicted pure stand scores for each cultivar indicated that the adjustment was greatest for the most resistant and most susceptible cultivars. There was no advantage in using two-plant rather than one-plant plots in withstanding neighbour effects.     

Examples of non-trivial efficiency-balanced designs with b=v+1

This note provides examples of binary efficiency-balanced block designs with b=v+1, having no complete blocks, which are unequal-replicated and unequal-blocksized from a biometrical and agricultural standpoint.     

Are all species necessary to reveal ecologically important patterns?

While studying ecological patterns at large scales, ecologists are often unable to identify all collections, forcing them to either omit these unidentified records entirely, without knowing the effect of this, or pursue very costly and time‐consuming efforts for identifying them. These “indets” may be of critical importance, but as yet, their impact on the reliability of ecological analyses is poorly known. We investigated the consequence of omitting the unidentified records and provide an explanation for the results. We used three large‐scale independent datasets, (Guyana/ Suriname, French Guiana, Ecuador) each consisting of records having been identified to a valid species name (identified morpho‐species – IMS) and a number of unidentified records (unidentified morpho‐species – UMS). A subset was created for each dataset containing only the IMS, which was compared with the complete dataset containing all morpho‐species (AMS: = IMS + UMS) for the following analyses: species diversity (Fisher's alpha), similarity of species composition, Mantel test and ordination (NMDS). In addition, we also simulated an even larger number of unidentified records for all three datasets and analyzed the agreement between similarities again with these simulated datasets. For all analyses, results were extremely similar when using the complete datasets or the truncated subsets. IMS predicted ≥91% of the variation in AMS in all tests/analyses. Even when simulating a larger fraction of UMS, IMS predicted the results for AMS rather well. Using only IMS also out‐performed using higher taxon data (genus‐level identification) for similarity analyses. Finding a high congruence for all analyses when using IMS rather than AMS suggests that patterns of similarity and composition are very robust. In other words, having a large number of unidentified species in a dataset may not affect our conclusions as much as is often thought.     

Required coefficient of friction during turning at self-selected slow,normal, and fast walking speeds

This study investigated the relationship of required coefficient of friction to gait speed, obstacle height, and turning strategy as participants walked around obstacles of various heights. Ten healthy, young adults performed 90° turns around corner pylons of four different heights at their self selected normal, slow, and fast walking speeds using both step and spin turning strategies. Kinetic data was captured using force plates. Results showed peak required coefficient of friction (RCOF) at push off increased with increased speed (slow μ=0.38, normal μ=0.45, and fast μ=0.54). Obstacle height had no effect on RCOF values. The average peak RCOF for fast turning exceeded the OSHA safety guideline for static COF of μ>0.50, suggesting further research is needed into the minimum static COF to prevent slips and falls, especially around corners.     

Molecular simulation of cage occupancy and selectivity of binary THF–H2 sII hydrate

The hydrogen capacity of the binary THF–H₂ sII hydrate is determined by the cage occupancy and by the selectivity of guest molecules. Grand canonical Monte Carlo (GCMC) simulation is used to study the cage occupancy and selectivity of guest molecules from the equilibrium configuration of the binary sII hydrate. The cage framework is regarded as a rigid body and the number of guest molecules is varied to preserve the grand canonical ensemble. The occupancy and selectivity were investigated at a temperature of 270 K for pressures ranging from 0.1 to 200 MPa. It was found that most large cages select THF as guest molecules while small cages include only hydrogen molecules. Multiple occupancy of hydrogen, up to four molecules in large cages and two molecules in small cages, was found as the pressure increases. GCMC results show that the hydrogen capacity is approximately 1.1 wt% at 200 MPa.     

Fractal nature of protein surface roughness: a note on quantification of change of surface roughness in active sites,before and after binding

Year 2010 marked the 25th year since we came to know that roughness of a protein surface has fractal symmetry. Ever since the publication of Lewis and Rees' paper, hundreds of works from a spectrum of perspectives have established that fractal dimension (FD) can be considered as a reliable marker that describes roughness of protein surface objectively. In this article, we introduce readers to the fundamentals of fractals and present categorical biophysical and geometrical reasons as to why FD‐based constructs can describe protein surface roughness more accurately. We then review the commonality (and the lack of it) between numerous approaches that have attempted to investigate protein surface with fractal measures, before exploring the patterns in the results that they have produced. Apart from presenting the genealogy of approaches and results, we present an analysis that quantifies the difference in surface roughness in stretches of protein surface containing the active site, before and after binding to ligands, to underline the utility of FD‐based measures further. It has been found that surface stretches containing the active site, in general, undergo a significant increment in its roughness after binding. After presenting the entire repertoire of FD‐based surface roughness studies, we talk about two yet‐unexplored problems where application of FD‐based techniques can help in deciphering underlying patterns of surface interactions. Finally, we list the limitations of FD‐based constructs and put down several precautions that one must take while working with them. Copyright © 2013 John Wiley & Sons, Ltd.     

Temporal stability of urinary and plasma biomarkers of tobacco smoke exposure among cigarette smokers

Intraindividual variability of measurements of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), nicotine, cotinine, and r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene (PheT) over time is uncertain. From 70 habitual smokers’ plasma and urine sampled bimonthly for a year we analysed plasma for NNAL, cotinine and PheT, and urine for NNAL, cotinine and nicotine. We estimated the intraclass correlation coefficients (ρ_I) for each measurement. Plasma and creatinine-corrected urinary NNAL were stable (ρ_I ≥70%); plasma PheT and plasma and urinary total cotinine were fairly stable (ρ_I ≥50%), but urinary nicotine ρ_I ≈ 40% was not. Except for nicotine, single measurements from plasma or urine adequately represent individual mean exposure over time.     

Assessment of corneal viscoelasticity using elastic wave optical coherence elastography

The corneal viscoelasticity have great clinical significance, such as the early diagnosis of keratoconus. In this work, an analysis method which utilized the elastic wave velocity, frequency and energy attenuation to assess the corneal viscoelasticity is presented. Using phase‐resolved optical coherence tomography, the spatial‐temporal displacement map is derived. The phase velocity dispersion curve and center frequency are obtained by transforming the displacement map into the wavenumber‐frequency domain through the 2D fast Fourier transform (FFT). The shear modulus is calculated through Rayleigh wave equation using the phase velocity in the high frequency. The normalized energy distribution is plotted by transforming the displacement map into the spatial‐frequency domain through the 1D FFT. The energy attenuation coefficient is derived by exponential fitting to calculate the viscous modulus. Different concentrations of tissue‐mimicking phantoms and porcine corneas are imaged to validate this method, which demonstrates that the method has the capability to assess the corneal viscoelasticity.