Static characteristics of a continuous flow bioreactor containing antibiotic-resistant recombinant cells

The steady-state behavior of a continuous bioreactor containing antibiotic-resistant recombinant cells has been investigated. Only the plasmid-free cell is susceptible to and killed by antibiotics. A Monod form of specific death rate was found to simulate quite well the experimental death rates of various cells due to antibiotics. The stability characteristics, including bifurcation of the possible steady states, are examined. Appropriate numerical illustrations for the steady-state characteristics have been provided. Theoretically, two coexistence steady states (CO), three partial washout steady states (PW), and one total washout steady state (TW) are feasible, but only one CO, one PW, and one TW were realized. When antibiotic consumption is not extremely significant the CO can exist over one or two ranges of dilution rates depending upon the antibiotic concentration in the feed. The CO is globally stable. Whenever the PW and/or the TW exist(s) together with the CO they are unstable. Sensitivity analyses for several key kinetic parameters have been made. The rate at which the plasmid-bearing cells revert to the plasmid-free cells has the most significant effect on the antibiotic susceptibility of the system. Some simplified optimization calculations for maximum profit have been carried out.     

Global meta‐analysis reveals that invertebrate diversity is higher in permanent than in temporary lentic water bodies

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Application of the Lambert <Emphasis Type="Italic">W</Emphasis> function in mathematical problems of plasma physics

Examples of solutions to transcendental equations that arise in mathematical problems of plasma physics are considered. Earlier, such equations were solved only by approximate methods. The use of a new function—the Lambert W function—has made it possible to obtain explicit exact solutions that can help to refine the existing relevant theories. As examples, the following problems from different branches of plasma physics are considered: the equilibrium charge of a dust grain in a plasma, the structure of the Bohm sheath, the diameter of the separatrix in a Galathea-Belt system, the transverse structure of an electron beam in a plasma, the energy loss rate of a test charged particle in a plasma, and the structure of the Sagdeev pseudopotential for ion acoustic waves.     

Effects of assortative mating for pupa weight on genetic parameters of unselected Tribolium castaneum

Summary Effects of random (R) or positive assortative (A) mating for pupal weight (PW) on genetic parameters of pupation time (PT), pupal and larval weights (LW) were studied in unselected populations of Tribolium castaneum. Two groups, each with 50 males mated to 100 females in each of 5 replicates, were either R-mated or A-mated for 3 generations. Genetic parameters were estimated from covariances between sibs (R group) or by an iterative method (A group). Estimates of heritability in R and A groups were 0.30±0.12 and 0.39±0.02 (PW); 0.26±0.13 and 0.49±0.04 (LW); and 0.39±0.10 and 0.25±0.03 (PT). Estimates of genetic correlations in the R group were –0.21±0.23 (PW and LW); 0.45±0.10 (PW and PT); and –0.77±0.14 (LW and PT). Those in the A group were 0.27±0.10 (PW and LW); 0.15±0.14 (PW and PT); the genetic correlation between LW and PT was not estimable in this group. Within-family variances (grams squared) of PW by generation (1, 2, and 3) were, respectively: 0.048 (R) and 0.047 (A); 0.054 (R) and 0.041 (A); and 0.050 (R) and 0.046 (A). In agreement with theory, estimates of heritability of PW and LW were larger in the A group. Estimates of genetic correlations in the A group were inconsistent with expectations from theory. Assortative mating tended to decrease within-family variance of PW.     

Membrane potential and surface charge densities as possible generalized regulators of membrane protein activities

On the basis of experimental evidence accumulated in studies of coupling and other membranes a theoretical discussion of a “breathing” membrane structure dependent upon a changing transmembrane electrical (electrochemical) gradient is presented. In the case of certain membranes difference of electrical potentials across the membrane (Δψ) is considered as one of important driving forces for some membrane protein folding and/or the arrangement of subunits within some oligomeric proteins. Δψ changes may induce synchronous reversible energetically favourable transitions in the three-dimensional architecture of several spatially separated proteins of the biomembrane. A polyfunctional regulation of levels of activities of spatially separated membrane proteins may be achieved; in some cases alterations of Δψ and surface charge densities may fulfil function of a link in the chain of events triggering membrane-bound activities in response to external stimuli.     

神经元轴突生长的力生物学

神经系统作为一个复杂的体系,在其发育过程中轴突需要延伸较长的距离才能与下一级神经元或靶细胞形成突触。在这个复杂的移动过程中,神经元轴突在空间分布上形成了精确有序的结构。过去认为这种有序结构的形成主要由形态发生素的化学浓度梯度来指导,而最近的研究发现力学因素对调控轴突的延伸速度与方向发挥着重要的作用。因此,轴突的延伸本质上是一个力化学耦合过程。本文将结合自己过去的工作论述力学因素对轴突延伸的调控机制及相关的信号转导。这一领域的研究将为认识对神经系统疾病的发生以及神经再生提供重要的参考。     

樟子松树轮δ13C的年内变化特征及其对气候要素的响应

对大兴安岭北部两株樟子松(Pinus sylvestris var.mongolica)树轮样品的年内稳定碳同位素比率(δ13C)进行测定,结果表明:樟子松树轮年内δ13C值在不同生长阶段总体表现出每年生长季中期最高、早期次之、晚期最低的变化特征.δ13C的年内变化趋势在幼龄期至速生期变化剧烈,成熟期至衰老期相对平缓.从幼龄期至衰老期的整个生长阶段,同时期年内δ13C的变动幅度基本为晚材大于早材.幼龄期年内晚材的δ13C一直明显高于早材,而成熟期年内早晚材δ13C的差别逐渐减小,至衰老期年内晚材δ13C已低于早材且无显著差别.树轮δ13C的年内变化主要体现在生长季中后期,即早晚材之间的过渡段至晚材.年内不同时段的d13C序列与同时段的宽度去除生长趋势序列(去趋势序列)之间的相关性随生长季节的推移而逐渐降低.当年早材宽度与前一年晚材宽度显著正相关,当年早材δ13C序列与前一年晚材宽度和当年早材宽度的去趋势合并序列呈现较显著的负相关性,与前一年晚材δ13C序列或宽度去趋势序列之间均未表现出显著的相关性.分析结果表明:早材的形成很可能来源于前一年光合作用的产物,在利用树轮年内不同材质宽度或δ13C序列进行气候环境重建时需要考虑这一点.年内早材、过渡段和晚材三个时段的δ13C分别对应于4月下旬至6月中旬土壤湿度较大、温度上升较快的时期,6月下旬至7月中旬降水增加、温度达到最高而相对湿度降低的时期,以及7月下旬至9月中旬降水增加、温度下降而相对湿度较大的时期.     

Attraction and repulsion of spiral waves by inhomogeneity of conduction anisotropy—a model of spiral wave interaction with electrical remodeling of heart tissue

Various forms of heart disease are associated with remodeling of the heart muscle, which results in a perturbation of cell-to-cell electrical coupling. These perturbations may alter the trajectory of spiral wave drift in the heart muscle. We investigate the effect of spatially extended inhomogeneity of transverse cell coupling on the spiral wave trajectory using a simple active media model. The spiral wave was either attracted or repelled from the center of inhomogeneity as a function of cell excitability and gradient of the cell coupling. High levels of excitability resulted in an attraction of the wave to the center of inhomogeneity, whereas low levels resulted in an escape and termination of the spiral wave. The spiral wave drift velocity was related to the gradient of the coupling and the initial position of the wave. In a diseased heart, a region of altered transverse coupling corresponds with local gap junction remodeling that may be responsible for stabilization-destabilization of spiral waves and hence reflect potentially important targets in the treatment of heart arrhythmias.     

按单叶叶面积估测法评估蒿柳（Salix viminalis L．）第一生长季整株叶面积

本文在蒿柳（ＳａｌｉｘｖｉｍｉｎａｌｉｓＬ．）单叶叶面积（ＡＬ）估测的基础上预测枝条水平上的叶面积．ＡＬ与叶特征度量叶长（Ｌ）、宽（Ｗ）、Ｌ２、Ｗ２、乘积（ＬＷ）,叶干重（ＷＬ）之间相关性分析表明,尽管大多数相关关系本质上为非线性,但线性（Ｙ＝ｂ×Ｘ）和非线性指数方程（Ｙ＝ｂ×Ｘｃ）均有较高的复相关系数ｒ２和较好的预测能力,且以ＬＷ最好。ＡＬ估测方程的建立必须考虑植物生长阶段、枝类型及叶片着生的相对高度的影响．椭圆和抛物面的组合能成功地拟合叶片形状,反映叶形变化和较准确的计算单叶面积．以主技基径Ｄ,枝长Ｈ,Ｄ２Ｈ以及主枝上的叶片数与基径的乘积（ＮＬ·Ｄ）为独立交量来估测主枝叶面积（Ａｐ）的非线性方程好于线性方程,但方程的估计精度因腋生枝的萌生而受影响．腋生枝数与主枝基径的乘积组合（ＮＳＳ·Ｄ）、腋生枝干重（ＷＳ）的非线性方程可用于估测胶生枝叶面积（Ａｓ）,枝水平上叶面积的估测方程都因植物生长阶段的不同而有差异．     

Biomechanical analysis of the Rolled (RLD) leaf phenotype of maize

The pleiotropic effects of the Rld1-O/+ mutation of Zea mays (Poaceae) on leaf phenotype include a suppression of normal transverse unrolling, a reversed top/bottom epidermal polarity, and an apparently straighter longitudinal shape. According to engineering shell theory, there might be mechanical coupling between transverse and longitudinal habit, i.e., the leaf rolling itself might produce the longitudinal straightening. We tested this possibility with quantitative curvature measurements and mechanical uncoupling experiments. The contributions of elastic bending under self weight, mechanical coupling, and rest state of leaf parts to the longitudinal and transverse habit were assessed in Rld1-O/+ mutants and a population of sibling +/+ segregants. Elastic bending and curvature coupling are shown to be relatively unimportant. The Rld1-O/+ mutation is shown to alter not only the unrolling process, but also the developmental longitudinal curving in the growing leaf, leading to a straighter midrib and a rolled lamina. The Rld1-O/+ mutant is thus a suitable model to study the relation between tissue polarity and differential curvature development in the maize leaf. Since on the abaxial side of the leaf, more abundant sclerenchyma is found in +/+ than in Rld1-O/+, a gradient in sclerification may contribute to the development of midrib curvature.     

Simulation of two-dimensional fully developed laminar flow for a magneto-hydrodynamic (MHD) pump

MHD micro-pumps circumvent the wear and fatigue caused by high pressure-drop across the check valves of mechanical micro-pumps in micro-fluidic systems. Early analyses of the fluid flow for MHD micro-pumps were mostly made possible by the Poiseuille flow theory; however, this conventional laminar approach cannot illustrate the effects of various channel sizes and shapes. This paper, therefore, presents a simplified MHD flow model based upon steady state, incompressible and fully developed laminar flow theory to investigate the characteristics of a MHD pump. Inside the pump, flowing along the channel is the electrically conducting fluid flowing driven by the Lorentz forces in the direction perpendicular to both dc magnetic field and applied electric currents. The Lorentz forces were converted into a hydrostatic pressure gradient in the momentum equations of the MHD channel flow model. The numerical simulations conducted with the explicit finite difference method show that the channel dimensions and the induced Lorentz forces have significant influences on the flow velocity profile. Furthermore, the simulation results agree well with the experimental results published by other researchers.     

Soft Tissue Modelling of Cardiac Fibres for Use in Coupled Mechano-Electric Simulations

The numerical solution of the coupled system of partial differential and ordinary differential equations that model the whole heart in three dimensions is a considerable computational challenge. As a consequence, it is not computationally practical—either in terms of memory or time—to repeat simulations on a finer computational mesh to ensure that convergence of the solution has been attained. In an attempt to avoid this problem while retaining mathematical rigour, we derive a one dimensional model of a cardiac fibre that takes account of elasticity properties in three structurally defined axes within the myocardial tissue. This model of a cardiac fibre is then coupled with an electrophysiological cell model and a model of cellular electromechanics to allow us to simulate the coupling of the electrical and mechanical activity of the heart. We demonstrate that currently used numerical methods for coupling electrical and mechanical activity do not work in this case, and identify appropriate numerical techniques that may be used when solving the governing equations. This allows us to perform a series of simulations that: (i) investigate the effect of some of the assumptions inherent in other models; and (ii) reproduce qualitatively some experimental observations.     

Interstitial fluid flow in the osteon with spatial gradients of mechanical properties: a finite element study

Bone remodelling is the process that maintains bone structure and strength through adaptation of bone tissue mechanical properties to applied loads. Bone can be modelled as a porous deformable material whose pores are filled with cells, organic material and interstitial fluid. Fluid flow is believed to play a role in the mechanotransduction of signals for bone remodelling. In this work, an osteon, the elementary unit of cortical bone, is idealized as a hollow cylinder made of a deformable porous matrix saturated with an interstitial fluid. We use Biot’s poroelasticity theory to model the mechanical behaviour of bone tissue taking into account transverse isotropic mechanical properties. A finite element poroelastic model is developed in the COMSOL Multiphysics software. Elasticity equations and Darcy’s law are implemented in this software; they are coupled through the introduction of an interaction term to obtain poroelasticity equations. Using numerical simulations, the investigation of the effect of spatial gradients of permeability or Poisson’s ratio is performed. Results are discussed for their implication on fluid flow in osteons: (i) a permeability gradient affects more the fluid pressure than the velocity profile; (ii) focusing on the fluid flow, the key element of loading is the strain rate; (iii) a Poisson’s ratio gradient affects both fluid pressure and fluid velocity. The influence of textural and mechanical properties of bone on mechanotransduction signals for bone remodelling is also discussed.     

Role of purinergic cotransmission in the sympathetic control of arterial pressure variability in conscious rats

Previous studies have shown that the sympathetically mediated oscillations of arterial pressure (AP), the so-called Mayer waves, are shifted from 0.4 to 0.6 Hz after acute alpha-adrenoceptor blockade in conscious rats. This raises the possibility that, under physiological conditions, Mayer waves are mediated by the conjoint action of norepinephrine and other sympathetic cotransmitters. To evaluate the possible role of the cotransmitter ATP in determining the frequency of Mayer waves, AP and renal sympathetic nerve activity (RSNA) were simultaneously recorded in 10 conscious rats with cardiac autonomic blockade before and after acute blockade of P2 receptors with pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid. P2 receptor blockade did not alter the mean level and overall variability of AP and RSNA but shifted peak coherence between AP and RSNA from 0.43 +/- 0.02 to 0.22 +/- 0.01 Hz. A model of the sympathetic limb of the arterial baroreceptor reflex was designed to simulate Mayer waves at 0.2 and 0.6 Hz, with norepinephrine and ATP, respectively, acting as the sole sympathetic cotransmitter. When both cotransmitters acted in concert, a single oscillation was observed at 0.4 Hz when the gain ratio of the adrenergic to the purinergic components was set at 15. The model thus accounted for an important role for ATP in determining Mayer wave frequency, but not in sustaining the mean level of AP or controlling its overall variability.     

Dynamic interactions between arterial pressure and sympathetic nerve activity: role of arterial baroreceptors

The role of arterial baroreceptors in controlling arterial pressure (AP) variability through changes in sympathetic nerve activity was examined in conscious rats. AP and renal sympathetic nerve activity (RSNA) were measured continuously during 1-h periods in freely behaving rats that had been subjected to sinoaortic baroreceptor denervation (SAD) or a sham operation 2 wk before study (n = 10 in each group). Fast Fourier transform analysis revealed that chronic SAD did not alter high-frequency (0.75-5 Hz) respiratory-related oscillations of mean AP (MAP) and RSNA, decreased by approximately 50% spectral power of both variables in the midfrequency band (MF, 0.27-0.74 Hz) containing the so-called Mayer waves, and induced an eightfold increase in MAP power without altering RSNA power in the low-frequency band (0.005-0.27 Hz). In both groups of rats, coherence between RSNA and MAP was maximal in the MF band and was usually weak at lower frequencies. In SAD rats, the transfer function from RSNA to MAP showed the characteristics of a second-order low-pass filter containing a fixed time delay ( approximately 0.5 s). These results indicate that arterial baroreceptors are not involved in production of respiratory-related oscillations of RSNA but play a major role in the genesis of synchronous oscillations of MAP and RSNA at the frequency of Mayer waves. The weak coupling between slow fluctuations of RSNA and MAP in sham-operated and SAD rats points to the interference of noise sources unrelated to RSNA affecting MAP and of noise sources unrelated to MAP affecting RSNA.     

On the fibre composite material models of disc annulus--comparison of predicted stresses

An axisymmetric finite element model of a body-disc-body unit has been developed and used to study the relative effects of two distinct direction-dependent material representations of the disc annulus on the predicted state of stresses in the disc. The annulus fibrosus is modelled either as nonhomogeneous fibre reinforced composite or alternatively as homogeneous orthotropic with transverse isotropy. In order to have identical states of displacements and hence strains, the unknown properties of the latter model are chosen to be equivalent with those of the former. The fibre slopes of 20 degrees, 30 degrees, and 40 degrees are considered in this study. The stresses in the annulus matrix in the circumferential planes parallel to the fibre layers are predicted to be significantly different depending on the annulus model used. In the nonhomogeneous model, the fibre membranes while under tensile forces, in turn, apply compression to the annulus matrix and, hence, decrease the annulus normal stresses in the above planes. Had the membranes carried compressive forces, a reverse trend would have resulted. The foregoing relative differences are dependent on the fibre orientation, and the magnitude of the tensile forces carried by the fibre layers. The latter also depends, amongst others, on the orientation of the fibres, decreasing as the fibre slope increases from 20 degrees to 30 degrees and 40 degrees. On the basis of the annulus micro-structure and the relative mechanical functions of its components, namely the annulus bulk and the collagenous fibre layers, it appears that nonhomogeneous fibre reinforced composite model of the disc annulus is more realistic resulting in a more accurate computation of stresses in the annulus fibrosus.     

Intrauterine growth retarded progeny of pregnant sows fed high protein:low carbohydrate diet is related to metabolic energy deficit

High and low protein diets fed to pregnant adolescent sows led to intrauterine growth retardation (IUGR). To explore underlying mechanisms, sow plasma metabolite and hormone concentrations were analyzed during different pregnancy stages and correlated with litter weight (LW) at birth, sow body weight and back fat thickness. Sows were fed diets with low (6.5%, LP), adequate (12.1%, AP), and high (30%, HP) protein levels, made isoenergetic by adjusted carbohydrate content. At -5, 24, 66, and 108 days post coitum (dpc) fasted blood was collected. At 92 dpc, diurnal metabolic profiles were determined. Fasted serum urea and plasma glucagon were higher due to the HP diet. High density lipoprotein cholesterol (HDLC), %HDLC and cortisol were reduced in HP compared with AP sows. Lowest concentrations were observed for serum urea and protein, plasma insulin-like growth factor-I, low density lipoprotein cholesterol, and progesterone in LP compared with AP and HP sows. Fasted plasma glucose, insulin and leptin concentrations were unchanged. Diurnal metabolic profiles showed lower glucose in HP sows whereas non-esterified fatty acids (NEFA) concentrations were higher in HP compared with AP and LP sows. In HP and LP sows, urea concentrations were 300% and 60% of AP sows, respectively. Plasma total cholesterol was higher in LP than in AP and HP sows. In AP sows, LW correlated positively with insulin and insulin/glucose and negatively with glucagon/insulin at 66 dpc, whereas in HP sows LW associated positively with NEFA. In conclusion, IUGR in sows fed high protein:low carbohydrate diet was probably due to glucose and energy deficit whereas in sows with low protein:high carbohydrate diet it was possibly a response to a deficit of indispensable amino acids which impaired lipoprotein metabolism and favored maternal lipid disposal.     

Transmembrane electric potential as a regulator of functional activity of biomembranes

The role of the transmembrane electric potential difference in producing structural tension of biological membranes is analysed. A suggestion is made that delta psi can optimize conditions of protein-protein interactions by ordering the membrane lipid. For energy-coupling membranes this makes it possible to explain the dependence of ATP synthesis on both electron transport and delta psi in terms of local bioenergetic coupling. The energized biomembrane is considered as a self-supporting structure, delta psi being a regulator of efficiency of molecular machines performing different membrane functions, including energization as well.     

Effect of a strong monochromatic electromagnetic wave with circular polarization on one-dimensional wake waves in plasma

A study is made of the excitation of wake waves by a one-dimensional bunch of charged particles in an electron plasma in the presence of an intense monochromatic pump wave with circular polarization. In the main state (in the absence of a bunch), the interaction between a pump wave and a plasma is described by the Maxwell equations and the nonlinear relativistic hydrodynamic equations for a cold plasma. The excitation of linear waves by a one-dimensional bunch is investigated against a cold plasma background. It is shown that, in a certain range of the parameter values of the bunch, pump wave, and plasma, the amplitude of the excited transverse waves grows as the energy of the bunch particles increases until the relativistic factor of the bunch reaches a certain threshold value above which the transverse wave amplitude becomes essentially independent of the bunch particle energy and grows as the intensity and frequency of the pump wave increase. The amplitude and wavelength of the longitudinal field, which is shown to depend weakly on the energy of the bunch particles, grows with increasing the pump wave intensity.     

Azimuthally asymmetric eigenmodes of a magnetized plasma cylinder around a dielectric rod in a circular waveguide

The electrodynamics of a circular waveguide with a dielectric rod surrounded by a magnetized plasma layer is considered. A general dispersion relation for azimuthally asymmetric perturbations is derived, and its solutions describing slow waves—specifically, electromagnetic and plasma modes, as well as (and primarily) hybrid waves that combine the properties of both mode types—are investigated numerically. For the fundamental waveguide mode of the system—the HE₁₁ mode—the parameters of the plasma layer are determined at which the mode cannot be subject to Cherenkov interaction with a relativistic electron beam at a given frequency. For both waveguide and plasma modes, the radial profiles of the longitudinal components of the electric field and Poynting vector, the fractions of RF power carried within the dielectric and plasma regions and vacuum gap, and the coupling impedance are calculated as functions of the parameters of the plasma layer. The evolution of the field structure during the formation of asymmetric hybrid waves is traced. The results of calculating the dispersion and coupling impedance are analyzed as applied to an antenna-amplifier—a relativistic traveling-wave tube operating on the HE₁₁ mode of the dielectric rod: specifically, the implementability of the concept in the presence of a plasma at the rod surface is estimated, and the possible role of azimuthally asymmetric and symmetric plasma modes is examined.