Real-time observations of microtubule dynamic instability in living cells

Individual microtubule dynamics were observed in real time in primary cultures of newt lung epithelium using video-enhanced differential interference contrast microscopy and digital image processing. The linear filaments observed in cells corresponded to microtubules based on three criteria: (a) small particles translocated along them; (b) the majority of them disappeared after incubation in nocodazole; (c) and the distribution observed by differential interference contrast correlated with anti-tubulin immunofluorescence staining of the same cell. Microtubules were most clearly observed at the leading edge of cells located at the periphery of the epithelial sheet. Microtubules exhibited dynamic instability behavior: individual microtubules existed in persistent phases of elongation or rapid shortening. Microtubules elongated at a velocity of 7.2 micron/min +/- 0.3 SEM (n = 42) and rapidly shortened at a velocity of 17.3 micron/min +/- 0.7 SEM (n = 35). The transitions between elongation and rapid shortening occurred abruptly and stochastically with a transition frequency of 0.014 s-1 for catastrophe and 0.044 s-1 for rescue. Approximately 70% of the rapidly shortening microtubules were rescued and resumed elongation within the 35 x 35 micron microscopic field. A portion of the microtubule population appeared differentially stable and did not display any measurable elongation or shortening during 10-15-min observations

Formation of Spaced Cleavage and Concurrent Mass Removal of Si02, Meguma Goup Metagreywackes, Goldenville, Nova Scotia

Increasing inequancy and decreasing fluctuation of long axes of quartz grains from lithons to cleavage zones in Heguna Group metagreywackes indicate an increase in strain. This strain increase is best ascribed to pervasive pressure solution in which quartz grains are trimmed to yield nearly rectangular sections in cleavage zones, as compared to their irregular outlines in lithons. Shortening calculated from a one-dimensional strain model reaches 60-7OZ in cleavage zones. Comparable values of shortening are calculated from modal analyses, and from chemical analyses of cleavages and lithons. The Implication of such shortening is that about ten percent of all the quartz in the original rock has been removed from the immediate system. This demands volumes of water about one order of magnitude greater than any likely content of connate water. The transport system was a dynamic one, involving most of the rock volume. RÉSUMÉ L'accroieseaent de l'inégalité et la baisse des fluctuations des longs axes des grains de quartz, des lithons jusqu'aux zones de clivage, dans les métagrauwackes du groupe Méguma, indique une haueae de tension. Cette hausse de tension est attribute à la solution de pression pénétrante dans laquelle les grains de quartz sont tallés et donnent des sections presque rectangulaires dans les zones de clivage, comparé à leur profile irrégulier dans les lithons. Le raccourcissement, calculi à partlr d'un modèle de pression unidimensionnel, atteint des valeurs entre 60 et 702 dans les zones de clivage. Des valeurs comparables du raccourcissement sont calculées à partlr d'analyses modales, et d'analyses chimiques des clivages et des lithons. L'implicatlon de ce raccourclssement est qu'environ dix pourcent de tout le quartz de la roche originaire, a été supérime du système immédiate Cela exige des volumes d'eau d'un ordre de grandeur plus important que n'importe quel système inné d'eau vraissembable. Ce système de transport était un système dynamique qui comprenait la majorité du volume des roches. [Traduit par le journal

On the numerical approximation of p-biharmonic and ∞-biharmonic functions

In [KP16] (arXiv:1605.07880) the authors introduced a second-order variational problem in L∞. The associated equation, coined the ∞-Bilaplacian, is a \emph{third order} fully nonlinear PDE given by Δ2∞u:=(Δu)3|D(Δu)|2=0. In this work we build a numerical method aimed at quantifying the nature of solutions to this problem which we call ∞-Biharmonic functions. For fixed p we design a mixed finite element scheme for the pre-limiting equation, the p-Bilaplacian Δ2pu:=Δ(|Δu|p−2Δu)=0. We prove convergence of the numerical solution to the weak solution of Δ2pu=0 and show that we are able to pass to the limit p→∞. We perform various tests aimed at understanding the nature of solutions of Δ2∞u and in 1-d we prove convergence of our discretisation to an appropriate weak solution concept of this problem, that of -solutions

Spicule morphology impacts stable silicon isotopic composition of sponge archives

The stable silicon isotopic composition of siliceous sponge skeletal elements, spicules, forms a potential proxy for past dissolved silicon (DSi) concentrations of bottom waters. Field-based studies have shown that there is a non-linear relationship between the concentration of ambient DSi and both the isotopic composition (denoted by δ30Si) of spicules and apparent isotopic fractionation by sponges during growth. There is considerable scatter in the calibration, with some studies highlighting variation within an individual sponge, and between individuals, in both monospecific and more diverse communities. Furthermore, some derived sponge forms, including hypersilicified and carnivorous sponges, appear to have anomalous isotopic fractionation, deviating significantly from other sponges. When reconstructing past DSi, it is only possible to differentiate spicules by their morphology, which in many cases will not be taxonomically diagnostic. However, there has yet to be a systematic study of core top and downcore δ30Si measurements from different spicule types. Here we address that gap using spicules extracted from two sediment cores taken at the summit of the Schulz Bank, a seamount located on the Arctic Mid-Ocean Ridge between the Norwegian and Greenland Seas. Mean isotopic compositions of downcore spicules of a given morphology were similar between nearby cores and mainly did not show any significant differences. Our results did reveal a systematic difference between spicule types extracted from a given sediment horizon, and a significant difference in the downcore mean compositions, between needle-like Oxea and other morphologies. These new findings imply that picking a single spicule type is best practice for palaeoceanographic applications of sponge archives, but the choice of Oxea spicules could bias these reconstructions towards high DSi concentrations

The influence of glacial cover on riverine silicon and iron exports in Chilean Patagonia

Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (0.45 mu m) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal-nanoparticulate and reactive sediment-bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional-scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems

A posteriori error estimates for the virtual element method

An a posteriori error analysis for the virtual element method (VEM) applied to general elliptic problems is presented. The resulting error estimator is of residual-type and applies on very general polygonal/polyhedral meshes. The estimator is fully computable as it relies only on quantities available from the VEM solution, namely its degrees of freedom and element-wise polynomial projection. Upper and lower bounds of the error estimator with respect to the VEM approximation error are proven. The error estimator is used to drive adaptive mesh refinement in a number of test problems. Mesh adaptation is particularly simple to implement since elements with consecutive co-planar edges/faces are allowed and, therefore, locally adapted meshes do not require any local mesh post-processing

Evaluation of energy and dietary intake estimates from a food frequency questionnaire using independent energy expenditure measurement and weighed food records

<p>Abstract</p> <p>Background</p> <p>We have developed a food frequency questionnaire (FFQ) for the assessment of habitual diet, with special focus on the intake of fruit, vegetables and other antioxidant-rich foods and beverages. The aim of the present study was to evaluate the relative validity of the intakes of energy, food and nutrients from the FFQ.</p> <p>Methods</p> <p>Energy intake was evaluated against independent measures of energy expenditure using the ActiReg^®system (motion detection), whereas 7-days weighed food records were used to study the relative validity of food and nutrient intake. The relationship between methods was investigated using correlation analyses and cross-classification of participants. The visual agreement between the methods was evaluated using Bland-Altman plots.</p> <p>Results</p> <p>We observed that the FFQ underestimated the energy intake by approximately 11% compared to the energy expenditure measured by the ActiReg^®. The correlation coefficient between energy intake and energy expenditure was 0.54 and 32% of the participants were defined as under-reporters. Compared to the weighed food records the percentages of energy from fat and added sugar from the FFQ were underestimated, whereas the percentage of energy from total carbohydrates and protein were slightly overestimated. The intake of foods rich in antioxidants did not vary significantly between the FFQ and weighed food records, with the exceptions of berries, coffee, tea and vegetables which were overestimated. Spearman's Rank Order Correlations between FFQ and weighed food records were 0.41 for berries, 0.58 for chocolate, 0.78 for coffee, 0.61 for fruit, 0.57 for fruit and berry juices, 0.40 for nuts, 0.74 for tea, 0.38 for vegetables and 0.70 for the intake of wine.</p> <p>Conclusions</p> <p>Our new FFQ provides a good estimate of the average energy intake and it obtains valid data on average intake of most antioxidant-rich foods and beverages. Our study also showed that the FFQs ability to rank participants according to intake of total antioxidants and most of the antioxidant-rich foods was good.</p

Association between urinary biomarkers of total sugars intake and measures of obesity in a cross-sectional study

Obesity is an important modifiable risk factor for chronic diseases. While there is increasing focus on the role of dietary sugars, there remains a paucity of data establishing the association between sugar intake and obesity in the general public. The objective of this study was to investigate associations of estimated sugar intake with odds for obesity in a representative sample of English adults. We used data from 434 participants of the 2005 Health Survey of England. Biomarkers for total sugar intake were measured in 24 h urine samples and used to estimate intake. Linear and logistic regression analyses were used to investigate associations between biomarker-based estimated intake and measures of obesity (body mass intake (BMI), waist circumference and waist-to-hip ratio) and obesity risk, respectively. Estimated sugar intake was significantly associated with BMI, waist circumference and waist-to-hip ratio; these associations remained significant after adjustment for estimated protein intake as a marker of non-sugar energy intake. Estimated sugar intake was also associated with increased odds for obesity based on BMI (OR 1.02; 95%CI 1.00-1.04 per 10g), waist-circumference (1.03; 1.01-1.05) and waist-to-hip ratio (1.04; 1.02-1.06); all OR estimates remained significant after adjusting for estimated protein intake. Our results strongly support positive associations between total sugar intake, measures of obesity and likelihood of being obese. It is the first time that such an association has been shown in a nationally-representative sample of the general population using a validated biomarker. This biomarker could be used to monitor the efficacy of public health interventions to reduce sugar intake