Axisymmetric bioconvection in a cylinder

In three-dimensional bioconvection, the regions of rising and sinking fluid are dissimilar. This geometrical effect is studied for axisymmetric bioconvection in a cylindrical cell with stress-free (i.e. normal velocity and tangential stress vanish) lateral and top boundaries, and rigid bottom boundary. Using the continuum model of Pedley et al. (1988, J. Fluid Mech.195, 223-237) for bioconvection in a suspension of swimming, gyrotactic microorganisms, the structure and stability of an axisymmetric plume in a deep chamber are investigated. The system is governed by the Navier-Stokes equations for an incompressible fluid coupled with a microorganism conservation equation. These equations are solved numerically using a conservative finite-difference scheme. Comparisons are made with two-dimensional bioconvection.     

Change in the rate of shell deposition and shell microstructure in response to shell borers in the abalone haliotis rubra

Variations in heart rate under social interactions in unrestrained hermit crabs were studied. Two insulated Stainless Steel hook wires were inserted into the pericardiac cavity and connected simultaneously to a graphic recorder and to an oscilloscope used as control of the preparations.

Cardiac arrest is shown when another hermit appears into the visual field of the recording subject, coincident with the characteristic Alert Pattern. This arrest is followed by bradycardia (Hesitation Pattern). When motor activity is displayed or perceived from the other crab, cardiac arrest occurs again, and the heart rate is irregular during agonistic motor activity. When the conflict is resolved, a weak tachycardia is observed.     

Determination of cardiac contractility in awake unsedated mice with a fluid-filled catheter

Today, cardiac contractility in mice is exclusively measured under anesthesia or in sedated animals because the catheters available are too rigid to be used in awake mice. We therefore developed a new catheter (Pebax 03) to measure cardiac contractility in conscious mice. In this study, we evaluated the accuracy and utility of this new catheter for assessment of cardiac contractility in anesthetized and conscious mice. With the use of a balloon-pop test, the Pebax catheter with an inner diameter of 0.3 mm was found to exhibit a high natural frequency, a low damping coefficient, and a flat frequency of up to 50.5 +/- 0.6 Hz. Under anesthesia (0.5% or 1.0% halothane), no difference was found in heart rate (HR), left ventricular (LV) systolic pressure (LVSP), the maximum rates of LV pressure rise and fall (LV dP/dt(max) and LV dP/dt(min), respectively), ejection time (ET), and isovolumic relaxation time constant (tau) when measured with either the 1.4-Fr Millar or Pebax 03 catheter. However, when HR, LVSP, LV dP/dt(max), and LV dP/dt(min) were recorded with the Pebax catheter in awake mice, values were significantly higher, and ET and tau were lower, than under anesthesia, suggesting a major impact of anesthesia on these parameters. The Pebax catheter was also used in a normotensive one-renin gene mouse model of cardiac hypertrophy induced by DOCA and salt. In this model, DOCA-salt induced a severe decrease in cardiac contractility in the absence of changes in blood pressure. These data demonstrate that cardiac contractility can be measured very accurately in conscious mice. This new device can be of great help in the investigation of cardiac function in normal and genetically engineered mice.     

Mechanism of a plastic phenotypic response: predator-induced shell thickening in the intertidal gastropod Littorina obtusata

Phenotypic plasticity has been the object of considerable interest over the past several decades, but in few cases are mechanisms underlying plastic responses well understood. For example, it is unclear whether predator-induced changes in gastropod shell morphology represent an active physiological response or a by-product of reduced feeding. We address this question by manipulating feeding and growth of intertidal snails, Littorina obtusata, using two approaches: (i) exposure to predation cues from green crabs Carcinus maenas and (ii) reduced food availability, and quantifying growth in shell length, shell mass, and body mass, as well as production of faecal material and shell micro-structural characteristics (mineralogy and organic fraction) after 96 days. We demonstrate that L. obtusata actively increases calcification rate in response to predation threat, and that this response entails energetic and developmental costs. That this induced response is not strictly tied to the animal's behaviour should enhance its evolutionary potential.     

Valveless pumping in a fluid-filled closed elastic tube-system: one-dimensional theory with experimental validation

 An elastic rubber tube is connected with a stiffer rubber tube forming two halves of a torus and filled with water. Compressing one of the rubber tubes symmetrically and periodic at a point of asymmetry creates a remarkable unidirectional mean flow in the system. The size and the direction of the mean flow depend on the frequency of compression, the elasticity of the tubes, the compression ratio, and the type of compression with respect to time in a complicated manner. The system is modelled using a one-dimensional theory derived by averaging the Navier-Stokes equations ignoring higher order terms in a certain small quantity. The one-dimensional model is analysed partly analytically and partly numerically. A series of experiments on a physical realisation of the system are described. The theoretical findings and experimental results are compared; They show a remarkable agreement between the experiments and the predictions of the model. Frequencies at which the mean flow change direction are predicted numerically as well as analytically and the two results are compared. Received: 21 February 2002 / Revised version: 30 August 2002 / Published online: 17 January 2003 Key words or phrases: Flow – Elastic tubes – Valveless pumping – Navier-Stokes equations – Frequency dependent – One-dimensional model – Experimental validation     

Blue light induced response in the absence of free oxygen

The absence of oxygen had no effect on the photoinduced conidiationof Trichoderma, a system (unlike previously used systems) wherethe transient photoinduction and the prolonged respiratory oxygenrequirements are separable. The nature of the presumably ubiquitous blue-light absorbingpigment is not restricted to those requiring oxygen. ¹ Irene and David Schwartz Professor of Plant Genetics. (Received September 19, 1974; )     

A spike generator mechanism model simulates utricular afferents response to sinusoidal vibrations

Using a model of spike generator mechanism (SGM) with a variable threshold we simulate the responses of utricular afferents to sinusoidal vibrations. It reproduces the phase locking characteristics (bifurcations diagrams) and the stimulus frequency firing rate relationships of different types of utricular afferents. We estimate the model parameters selecting the values which best fit the experimental results and we compare them with those from basic mechanisms involved in utricular codification.     

Forced vibrations of a circular muscle ring

We consider the small radial displacement of a circular ring of cardiac muscle subjected to periodic forcing. The ring in question is that in the middle layer, at the transverse midsection, of the left ventricle. We show that the ring reacts in a periodic manner when forced in a periodic manner. This is accomplished by writing the differential equation for the ring and solving it for two cases-one for constant and one for variable ring thickness.     

Alveolar pressure in fluid-filled occluded lung segments during permeability edema

In a model of increased hydrostatic pressure pulmonary edema Parker et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 267-276, 1978) demonstrated that alveolar pressure in occluded fluid-filled lung segments was determined primarily by interstitial fluid pressure. Alveolar pressure was subatmospheric at base line and rose with time as hydrostatic pressure was increased and pulmonary edema developed. To further test the hypothesis that fluid-filled alveolar pressure is determined by interstitial pressure we produced permeability pulmonary edema-constant hydrostatic pressure. After intravenous injection of oleic acid in dogs (0.01 mg/kg) the alveolar pressure rose from -6.85 +/- 0.8 to +4.60 +/- 2.28 Torr (P less than 0.001) after 1 h and +6.68 +/- 2.67 Torr (P less than 0.01) after 3 h. This rise in alveolar fluid pressure coincided with the onset of pulmonary edema. Our experiments demonstrate that during permeability pulmonary edema with constant capillary hydrostatic pressures, as with hemodynamic edema, alveolar pressure of fluid-filled segments seems to be determined by interstitial pressures.     

Simulation of gravitational field variation on fluid-filled biological membranes

The knowledge of the behavior of biological organs in a gravitational field is important to understand the functioning of the human body in the aerospace environment. The disturbances in biological transport processes in microgravity have indicated adverse effects on humans engaged in space operations. The relationship between the deformations in the biological organs and the transport phenomena that take place in them has been long established and widely reported in biological sciences and engineering literature. A number of soft tissue organs such as brain, lungs, heart, kidney, bladder, stomach, and the circulatory system can be modeled as fluid-filled membranes. In this investigation, a mathematical model of a fluid-filled biological membrane is developed, and its deformation and spatial configuration in a variable gravitational field are calculated. The variation in the gravitational field in the range 1g to zero-g is simulated by partial submergence of the fluid-filled membrane which, by virtue of buoyancy, gains an effective density as if it is in a different gravitational field. The equations of motion are derived using the theory of large elastic deformations and numerically solved in conjunction with a constitutive equation suitably selected for the biological membrane.     

大鼠脑片中细胞内游离钙动态变化的研究

目的：探索大鼠急性脑片中电刺激诱发的细胞内钙的动态变化规律。方法：采用表面灌流的急性脑片模型,结合电生理和激光共聚焦技术,利用细胞内钙荧光探针进行细胞内游离钙标记,观察电刺激诱发的脑片中神经细胞内游离钙的变化情况。结果：急性脑片组织中,钙标记染料的神经细胞内钙探针荧光强度,电刺激后出现显著增强,且具有波样特征,而Suramin明显抑制此反应,表现为钙探针荧光强度下降和钙反应时间出现延迟,两组之间差异具有统计学意义（P〈0．05）.结论：刺激诱发的大鼠急性脑片中瞬时动态钙信号变化具有一定的时空发生特征,且这种钙信号的时空变化过程可能与嘌呤能信号的作用有关。     

The influence of mechanical vibrations on human response in tall buildings with reference to Geomagnetic effects

It is stated that the indoor climate in high-rise buildings cannot be regarded as satisfactory in spite of the fact that it fulfils criteria of thermal, acoustic and light standards. Probably one of the factors which should not be omitted is the Geomagnetic field which affects (under specific conditions such as vibrations of a building) the persons occupying the inner space. Interim measurements to verify this idea were made in which the EEG of a man and the mechanical vibrations on the top of a 76.4 m. high building were sensed and recorded. Application of Fourier analysis resulted in spectral densities and a correlation was found between records of MV and EEG on the double frequency as fundamental frequency of MV of a building, confirming the suggested hypothesis. Amplitudes were not measured and only one measurement was undertaken which prevented any statistical evaluation of the significance of the phenomenon.     

Chilling response of plants: importance of galactolipase, free fatty acids and free radicals

The chilling response of plants is complex and based on the interplay of two important metabolic processes--lipolytic degradation of membrane lipids and a set of oxidative reactions leading to lipid peroxidation and membrane damage evoked in chilling-sensitive (CS) plants subjected to low temperature and light. The effects of chilling of detached leaves and intact plants differ and are often neglected during experiments. In closely-related species, the activity of several constitutive enzymes (i.e. superoxide dismutase, ascorbate peroxidase and glutathione reductase) appears to be higher in chilling-tolerant (CT) than in CS species; while in several native, closely-related CS species, lipid acyl hydrolase (galactolipase) activity is higher than in CT species. Moreover, in chilling-insensitive (CI) plants, galactolipase activity is very low and is neither activated by detachment of leaves nor under stress conditions in growing plants. Dark and low-temperature treatments of detached leaves of CS species and post-chilling recovery of growing plants in the light activate galactolipase, which is responsible for the release of free fatty acids (FFA), the main substrates of peroxidation by lipoxygenase and free radicals. In several CS species, increased galactolipase activity is an important factor contributing to chilling susceptibility. Thus, it seems likely that enhancement of chilling tolerance may be achieved by genetically suppressing galactolipase in order to reduce both the degradation of chloroplast lipids and the level of released FFA, and thereby avoiding the deleterious action of their peroxidation products on plant tissues.     

Young horse response on changing distance in free jumping combination

The aim of the present study was to verify the influence of distance between obstacles in combination for free jumping test on linear and temporal kinematic parameters of the jump. Investigated groups of halfbred stallions being prepared for 100 days performance test (two groups, 36 horses in total) were filmed on different distances between main doublebarre obstacle and last cross-pole in the jumping lane. Both groups of horses were filmed during their regular work in the same training centre 1 week before performance test. Jumping parameters were obtained on the same size of the obstacle. Data were analysed separately for both groups by analysis of variance. On the basis of the conducted study, it is possible to conclude that in the range of the most popular free jumping distance horses may use different jumping techniques to clear the jump. The shorter distances between last two obstacles in the jumping lane in the range of 6.8 to 7.1 m stimulate higher jumps; however, the reaction of horses was not exactly the same for all measured jumping parameters.