Interactive effects of water and nitrogen addition on soil microbial communities in a semiarid steppe

Aims Better understanding of microbial compositional and physiological acclimation mechanisms is critical for predicting terrestrial ecosystem responses to global change. The aim is to assess variations in soil microbial communities under future scenarios of changing precipitation and N deposition in a semiarid grassland of northern China.Methods In order to explicitly estimate microbial responses, a field experiment with water and N addition was established in April 2005 and continuously conducted for 4 years. Specifically, soil microbial community composition and microbial C utilization potential were determined by phospholipid fatty acid (PLFA) and community-level physiological profiles, respectively.Important findings Water addition had no effects on the PLFA concentrations of gram-positive (GP) and negative bacteria (GN), total bacteria and fungi. However, N addition caused significant reductions in the PLFA concentrations of GP, GN, total bacteria and fungi and thus decreased total PLFA of microbial communities. Moreover, there were interactive effects of water and N addition on GN/GP and the ratio of fungal to bacterial PLFA (F/B). In addition, synergistic effects were found between water and nitrogen in affecting microbial C utilization potentials, which implies that microbial C utilization potentials tend to be enhanced when both N and water availability are sufficient. Overall, the microbial responses to water and N addition support our hypothesis that water and N addition may be combined together to affect microbial communities in the semiarid grassland.     

中药薤白的研究进展

从生药来源、化学成分、药理活性及临床应用等几个方面对中药薤白的研究进展进行了综述,为该药的进一步研究及开发提供了参考。     

Interstitial fluid flow within bone canaliculi and electro-chemo-mechanical features of the canalicular milieu

Canalicular fluid flow is acknowledged to play a major role in bone functioning, allowing bone cells’ metabolism and activity and providing an efficient way for cell-to-cell communication. Bone canaliculi are small canals running through the bone solid matrix, hosting osteocyte’s dendrites, and saturated by an interstitial fluid rich in ions. Because of the small size of these canals (few hundred nanometers in diameter), fluid flow is coupled with electrochemical phenomena. In our previous works, we developed a multi-scale model accounting for coupled hydraulic and chemical transport in the canalicular network. Unfortunately, most of the physical and geometrical information required by the model is hardly accessible by nowadays experimental techniques. The goal of this study was to numerically assess the influence of the physical and material parameters involved in the canalicular fluid flow. The focus was set on the electro-chemo-mechanical features of the canalicular milieu, hopefully covering any in vivo scenario. Two main results were obtained. First, the most relevant parameters affecting the canalicular fluid flow were identified and their effects quantified. Second, these findings were given a larger scope to cover also scenarios not considered in this study. Therefore, this study gives insight into the potential interactions between electrochemistry and mechanics in bone and provides the rational for further theoretical and experimental investigations.     

The effects of different crossing-linking conditions of genipin on type I collagen scaffolds: an in vitro evaluation

The purpose of this paper is to analyze the properties of fabricating rat tail type I collagen scaffolds cross-linked with genipin under different conditions. The porous genipin cross-linked scaffolds are obtained through a two step freeze-drying process. To find out the optimal cross-link condition, we used different genipin concentrations and various cross-linked temperatures to prepare the scaffolds in this study. The morphologies of the scaffolds were characterized by scanning electron microscope, and the mechanical properties of the scaffolds were evaluated under dynamic compression. Additionally, the cross-linking degree was assessed by ninhydrin assay. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, the tests were also carried out by immersion of the scaffolds in a PBS solution or digestion in a type I collagenase respectively. The morphologies of the non-cross-linked scaffolds presented a lattice-like structure while the cross-linked ones displayed a sheet-like framework. The morphology of the genipin cross-linked scaffolds could be significantly changed by either increasing genipin concentration or the temperature. The swelling ratio of each cross-linked scaffold was much lower than that of the control (non-cross-linked).The ninhydrin assay demonstrated that the higher temperature and genipin concentration could obviously increase the cross-linking efficiency. The in vitro degradation studies indicated that genipin cross-linking can effectively elevate the biostability of the scaffolds. The biocompatibility and cytotoxicity of the scaffolds was evaluated by culturing rat chondrocytes on the scaffold in vitro and by MTT. The results of MTT and the fact that the chondrocytes adhered well to the scaffolds demonstrated that genipin cross-linked scaffolds possessed an excellent biocompatibility and low cytotoxicity. Based on these results, 0.3 % genipin concentrations and 37 °C cross-linked temperatures are recommended.     

Tissue mineral density measured at the sub-millimetre scale can provide reliable statistics of elastic properties of bone matrix

Reliability of multiscale models of bone is related to the accuracy of the experimental information available on bone microstructure. X-ray-based imaging techniques allow to inspect bone structure and mineralization in vitro at the micrometre scale. However, spatial resolution achievable in vivo is much coarser and can produce blurry, uncertain information on bone microstructure. Working with uncertain data calls for new modelling paradigms able to propagate uncertainty through the scales. In this paper we investigate the effects of uncertain bone mineralization on the elastic coefficients of the bone matrix. To this aim, some stochastic concepts were developed and compared with one another in order to identify the best way to account for uncertain input data. These concepts step from a deterministic micromechanical model of bone matrix which was extended in order to account for uncertain bone composition. Uncertainty was introduced by assuming to know only mean value and dispersion of the parameters describing bone composition. Thus, these parameters were modelled as random variables and their distribution functions were obtained using the maximum entropy principle. Either the tissue mineral density (TMD) or the ensuing volume fractions of collagen and mineral were used to describe uncertain bone composition. Moreover, mean value and dispersion were estimated at the scales of either 10 or a few 100 \(\upmu \)m, representative of standard in vitro and in vivo spatial resolutions, respectively. Analysis of these modelling concepts suggests that TMD measured at the sub-millimetre scale can be used to obtain reliable statistical information about the elastic coefficients of bone matrix.     

Multi-objective workflow scheduling in cloud computing: trade-off between makespan and cost

Cluster Computing - Recently, modern businesses have started to transform into cloud computing platforms to deploy their workflow applications. However, scheduling workflow under resource...     

Assessing the effective elastic properties of the tendon-to-bone insertion: a multiscale modeling approach

Biomechanics and Modeling in Mechanobiology - The interphase joining tendon to bone plays the crucial role of integrating soft to hard tissues, by effectively transferring stresses across two...     

Purification of CBS 819.72 α-amylase by aqueous two-phase systems: Modelling using Response Surface Methodology

The partition and purification of α-amylase from a culture supernatant of Aspergillus oryzae CBS 819.72 was made in aqueous two-phase system (ATPS). According to bibliography and preliminary studies, the factors polyethylene glycol (PEG) molecular weight (M_PEG) and concentration (C_PEG), buffer type (BU) and concentration (C_BU), temperature (T), salt nature (SALT) and concentration (C_SALT), bioligand (BL) and concentration (C_BL) and pH were investigated using a Plackett–Burman design to identify the factors affecting separation. Taking into consideration a simultaneous increase in enzyme recovery (R_Y) and purification factor (P_F), the best performance of the system was obtained at 4 °C and pH 6 using PEG 8000 g/mol, citrate buffer, KCl and sucrose. Experimental Box–Behnken design together with the Response Surface Methodology (RSM) have been used to find optimum C_PEG, C_Citrate and C_SALT. Quadratic models were predicted for P_F and R_Y in the top phase and a better compromise between these two parameters can be found by superimposing the contour plots of P_F and R_Y for 8% citrate. A region in the experimental space can be defined where the purification factor is always higher than 3 with yields exceeding 65%.     

Independent scattering model and velocity dispersion in trabecular bone: comparison with a multiple scattering model

Speed of sound measurements are used clinically to assess bone strength. Trabecular bone is an attenuating composite material in which negative values of velocity dispersion have been measured; this behavior remaining poorly explained physically. The aim of this work is to describe the ultrasonic propagation in trabecular bone modeled by infinite cylinders immersed in a saturating matrix and to derive the physical determinants of velocity dispersion. An original homogenization model accounting for the coupling of independent scattering and absorption phenomena allows the computation of phase velocity and of dispersion while varying bone properties. The first step of the model consists in the computation of the attenuation coefficient at all frequencies. The second step of the model corresponds to the application of the general Kramers–Kr?nig relationship to derive the frequency dependence of phase velocity. The model predicts negative values of velocity dispersion in agreement with experimental results obtained in phantoms mimicking trabecular bone. In trabecular bone, only negative values of velocity dispersion are predicted by the model, which span within the range of values measured experimentally. However, the comparison of the present results with results obtained in Haiat et al. (J Acoust Soc Am 124:4047–4058, 2008) assuming multiple scattering indicates that accounting for multiple scattering phenomena leads to a better prediction of velocity dispersion in trabecular bone.