Active peristaltic movements and fluid production of the mouse oviduct: their roles in fluid and sperm transport and fertilization†

To study how the oviduct behaves in relation to fluid secretion and sperm transport, ovary–oviduct–uterus complexes of the mouse were installed in a fluid-circulating chamber without disturbing the blood circulation or parasympathetic innervation. Injection of a bolus of Indian ink into the lower isthmus revealed very active adovarian peristalsis of the isthmus, which was most prominent during the periovulatory period. Oviduct fluid, secreted by the entire length of the isthmus, was rapidly transported to the ampulla and ovarian bursa before draining into the peritoneal cavity. The upper isthmus, in particular the isthmic–ampullary junction, was responsible for this adovarian fluid flow. Peristalsis of the oviduct, undisturbed flow of oviduct fluid from the isthmus to the peritoneal cavity, and the spermatozoon's own motility all contribute to efficient sperm ascent and to fertilization within the oviduct. Therefore, chemotaxis, rheotaxis, and thermotaxis of spermatozoa toward oocyte–cumulus complexes in the ampulla are all unlikely mechanisms for explaining sperm–oocyte contact and successful fertilization, given the rapid adovarian flow of oviduct fluid in this species.

A 3D Compressible Flow Model for Weak Rotating Waves in Vaneless Diffusers—Part I: The Model and Mach Number Effects

A three-dimensional compressible flow model is presented to study the occurrence of weak rotating waves in vaneless diffusers of centrifugal compressors. The diffuser considered has two parallel walls, and the undisturbed flow is assumed to be circumferentially uniform, isentropic, and to have no axial velocity. Linearized 3D compressible Euler equations were casted on a rotating coordinate system traveling at the same angular speed as the wave cells. A uniform static pressure at the outlet of the diffuser was imposed. Complex functions of the solutions to the equations were obtained by a second-order finite difference method and the singular value decomposition technique. The influences of the inlet Mach number of undisturbed flow, inlet spanwise distribution of undisturbed radial velocity, and diffuser radius ratio on the rotating waves were studied and results show that (1) the critical flow angle and rotating wave speed are both affected by the Mach number. However, the angle only increases slightly with the Mach number while the wave speed increases rapidly with the Mach number; (2) inlet distribution has minor influences on diffuser instability but the wave speed increases with the inlet distortion; (3) diffuser instability increases rapidly and the wave speed decreases quickly with the diffuser radius ratio; and (4) backward traveling rotating wave may occur if diffuser is sufficiently long and the inlet Mach number is sufficiently small.

Thrombus Initiation With Subsequent Growth Measured for Physiological Shear and High Pathological Shear

Arterial thrombosis is often found near an atheroma in atherosclerotic disease, which can lead to acute myocardial infarction, i.e. a heart attack. Thrombus typically grows in regions of exposed subendothelium, which can exist when the plaque cap of the atheroma ruptures or erodes. The subendothelium creates an adherent surface to platelets and other thrombus constituents. Furthermore, an atheroma alters the normal physiological hemodynamics, which has been reported to correspond to local thrombus growth, despite equally adherent surfaces in undisturbed flow regions [1,2]. However, there has been some disagreement about which hemodynamics, specifically shear, may play the most influential role of localizing thrombus. Low shear and high shear have both resulted in thrombus growth [1,2]. Shear in the region of an atheroma can get over 100,000 s−1 [3].

Selected results of a model validation exercise

The concentration fields calculated with three Gaussian models and one Lagrangian dispersion model are validated against a set of SF6 concentration data provided by the German environmental programme BWPLUS. The source was a pig fattening unit in fairly flat terrain. The results reveal that, in flat terrain with steady undisturbed flow, the use of Gauss models is still justified, whereas Lagrangian models should be used whenever the flow is modified by obstacles or topography.

Palaeoenvironmental reconstruction of the Oligocene Afales Basin, Ithaki island, western Greece

Assemblages of benthic foraminifera from one clastic succession in the Afales Basin (Ithaki Island, western Greece) were investigated to reconstruct palaeoenvironmental conditions during the Oligocene. The section consists of alternating hemipelagic marls and detrital deposits, designated as flysch-like beds, attributed to biostratigraphic Zones P20 and P21. Planktic percentages are mostly high (66–80%). Benthic foraminiferal assemblages comprise calcareous and agglutinated taxa (up to 15%). The prevalence of epifaunal foraminifera indicates good ventilation of the bottom water resulting from basin morphology, which enabled the undisturbed flow of water throughout the basin. Palaeodepth estimates imply bathyal deposition, from about 800 to 1200 m deep. The benthic foraminiferal fauna is of high diversity along the section, as is expected in deep marine environments. The abundances of the most common foraminiferal taxa (Cibicidoides spp., Oridorsalis umbonatus, Gyroidinoides spp., Stilostomella spp., Nodosariidae, Nuttallides umbonifera) are quite variable and imply generally oligotrophic to mesotrophic environmental conditions with variable organic flux.

The Influence of Multimode Transition Initiated by Periodic Wakes on the Profile Loss of a Linear Compressor Cascade

This paper presents results of boundary layer and loss measurements in a high speed cascade wind tunnel on a linear compressor cascade under the influence of unsteady, periodic wakes. The wakes of an upstream blade row were simulated by cylindrical bars moved by a belt mechanism upstream of the cascade. Extensive hot-film array, hot-wire and pressure measurements with variation of steady and unsteady inlet flow conditions have been performed for a better understanding of the transition and loss mechanisms on a blade row interacting with wakes. The incoming wakes are inducing early forced transition in the boundary layer followed in time by calmed regions. Due to its higher shear stress level and its fuller velocity profile, the calmed flow is able to suppress laminar separation bubbles and to delay transition in the region with undisturbed flow between wakes, playing a significant role in the loss generation process. At the investigated low Reynolds number, where the measurements for the steady flow case showed a well-developed laminar separation bubble, reductions of profile loss up to 20% were observed for the measured configuration. In the case of the high Reynolds number, where in undisturbed flow only a small separation bubble was detected, a profile loss rise up to 30% was measured. Beside a better understanding of unsteady flow physics the goal of these basic investigations of unsteady transition is to create a wide database for the improvement of transition modeling in unsteady CFD codes.

Dynamics of arthropod filiform hairs. III. Flow patterns related to air movement detection in a spider ( Cupiennius salei KEYS.)

In previous studies we related the mechanical properties of spider trichobothria to a generalized mathematical model of the movement of hair and air in filiform medium displacement receivers. We now present experiments aimed at understanding the complex stimulus fields the trichobothrial system is exposed to under natural conditions. Using the elicitation of prey capture as an indicator and a tethered humming fly as a stimulus source, it has been shown that the behaviourally effective range of the trichobothrial system in Cupiennius salei Keys, is approximately 20 cm in all horizontal directions. Additionally, the fly still elicits a suprathreshold deflection of trichobothria while distanced 50-70 cm from the spider prosoma. To gain insight into the fluid mechanics of the behaviourally effective situation we studied: first, undisturbed flow around the spider in a wind tunnel; second, background flow the spider is exposed to in the field; and third, flow produced by the tethered flying fly. 1. The motion of air around a complex geometrical structure like a spider is characterized by an uneven distribution of flow velocities over the spider body. With the flow approaching from the front, both the mean and r.m.s. values are higher above the legs than above the pro- and opisthosoma; the velocity in the wake behind the spider, however, is markedly decreased. The pattern of these gradients is more complicated when the spider’s horizontal orientation is changed with respect to the main flow direction. It introduces asymmetries, for exmple, increased vortical, unsteady flow on the leeward compared with the windward side. 2. Sitting on its dwelling plant and ambushing prey in its natural habitat, the background air flow around Cupiennius is characterized by low frequencies (< 10 Hz), a narrow frequency spectrum, and low velocities (typically below 0.1 m s -1 with less than 15% r.m.s. fluctuation). 3. The distinctive features of a biologically significant air flow (for example, that produced by the humming fly) seem to be a concentrated, i.e. directional unsteady, high speed flow of the order of 1 m s -1 , and a relatively broad frequency spectrum containing frequencies much higher than those of the background flow. For a spider, sitting on a solid substrate (a leaf of a bromeliad, for example), air speed just above the substrate increases and thus provides higher sensitivity when compared to a spider in a orb web, which is largely transparent to the airflow. The flow patterns stimulating the ensemble of the trichobothria contain directional cues in both the undisturbed flow and the flow due to prey cases.