Topographical and mechanical characterization of living eukaryotic cells on opaque substrates: development of a general procedure and its application to the study of non-adherent lymphocytes

The mechanical behavior of living murine T-lymphocytes was assessed by atomic force microscopy (AFM). A robust experimental procedure was developed to overcome some features of lymphocytes, in particular their spherical shape and non-adherent character. The procedure included the immobilization of the lymphocytes on amine-functionalized substrates, the use of hydrodynamic effects on the deflection of the AFM cantilever to monitor the approaching, and the use of the jumping mode for obtaining the images. Indentation curves were analyzed according to Hertz's model for contact mechanics. The calculated values of the elastic modulus are consistent both when considering the results obtained from a single lymphocyte and when comparing the curves recorded from cells of different specimen

Sorption and thermodynamic properties of juvenile Pinus sylvestris L. wood after 103 years of submersion

The hygroscopicity and thermodynamic properties of juvenile Pinus sylvestris L. wood taken from the submerged piles of a bridge built in 1903 over the Jiloca River, in Spain, were compared with the corresponding values of juvenile wood of the same species from recently cut trees. The 35°C and 50°C isotherms were plotted and subsequently fitted using the Guggenheim-Anderson-Boer-Dent method, and the isosteric heat of sorption was obtained through the integration method of the Clausius-Clapeyron equation. The isotherms were compared by means of the hysteresis coefficients. Infrared spectra were recorded to study the chemical modifications, and the crystal structure of the cellulose was studied by X-ray diffractograms. The submersion in water resulted in hemicellulose degradation and a decrease in the crystallinity index and the crystallite length, accompanied by a corresponding increase in the proportion of amorphous zones. Owing to this, the equilibrium moisture contents of the water logged wood are higher than in the recent wood, both in adsorption and in desorption. In terms of the thermodynamic properties, the bond energy is higher in the recent wood than in the water logged wood. © 2008 by Walter de Gruyter

Local pressures in Zn chalcogenide polymorphs

Using the rich polymorphism of ZnX (X: S, Se, Te) compounds, we show how local pressures can be unequivocally determined from i) first-principles total energy calculations, and ii) atomic volumes derived by means of topological analysis of crystalline electron densities. An analogy between atoms and mechanical resistors is put forward since these local pressures lead to the inverse of the thermodynamic pressure once their respective inverses are added up. Accordingly, we define the atomic-like mechanical conductance as a measure of the atomic volume reduction for energy unit under pressure, and prove that, in agreement with chemical hardness expectations, Zn has lower values than S, Se, and Te in all the polymorphs of the chalcogenide crystal family

Effect of growth conditions on wood density of Spanish Pinus nigra

The natural forests of Laricio Pine (Pinus nigra Subsp. salzmannii) cover in Spain an area of 353,000 ha, producing annually 310,000 m3 of roundwood. This species is considered as the fourth, most important Spanish conifer, being its timber frequently used in construction. The natural area of distribution of Laricio pine in Spain is officially divided into ten different regions of provenance, being only four of them considered as productive. The present study on the influence of growth conditions on extracted wood basic density (EBD) is carried out on 89 P. nigra trees, sampled from the two most productive Spanish regions of provenance (R.7 and R.8) in seven different sites. Cross-sectional disks were cut at 3 m (in 89 trees) and every 3 m height (in 18 trees) from the butt up to 15 m. For assessing the pattern of radial variation of the properties, 20×20×20 mm3 wood samples were taken radially from every cross-sectional disk. In every 20×20×20 mm 3 wood sample, age and distance to the pith of the central annual ring was recorded, together with the average growth rate. Extractive content and EBD were measured in every sample. The results lead to the conclusion that there is not a significant relationship between EBD and provenance or growth rate. On the contrary, a significant relationship has been found between EBD and site quality or cambial age. The results also demonstrate that in a tree EBD tends to diminish from the base to the top and from the pith outwards. The main result of the present study is related with the observation that for the same cambial age, annual ring width has no significant influence on EBD, confirming that its utility as a predictor of the quality of timber is highly questionable, at least if the ring curvature is not considered

Curves for the estimation of the moisture content of ten hardwoods by means of electrical resistance measurements

Accuracy in moisture content measurement is of great importance in the assurance of wood product quality and is necessary to meet administrative and normative requirements. Improving the accuracy of resistance-type moisture meters, and meeting the normative demands of their annual calibration, requires the use of optimised curves relating electrical resistance to moisture content for the most commercially important wood types. The Samuelsson model, adjusted by linear regression techniques, was used to describe the relationship between the electrical resistance and moisture content of seven boreal and three tropical hardwoods available on the Spanish market. The curves produced can be used to predict the moisture contents of these hardwoods via the measurement of their electrical resistance with an error of just ± 1.0%. These curves should also prove of great use in the calibration of wood resistance-type moisture meters

Pressure-induced magnetic switching and linkage isomerism in K0.4Fe4[Cr(CN)6]2.8 •16H2O: X-ray Absorption and Magnetic Circular Dichroism Studies

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 ·16H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (TC) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching TC ) 7.5 K at 1200 MPa. Pressure-dependent Raman and Mo¨ssbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some CrIII-CtN-FeII linkages to the CrIII-NtC-FeII form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% CrIII-NtC-FeII linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process