A number of correlations for friction factor determinations in smooth pipes have been proposed in the past decades. The accuracy and applicability of these friction factor formulas should be examined. Based on this notion the paper is designed to provide a comparative study of friction factor correlations in smooth pipes for all flow regimes of Bingham fluids. Nine models were chosen. The comparisons of the selected equations with the existing experimental results, which are available in the literature, were expressed through MARE, MRE+ , MRE- , RMSE, Ѳ, and S. The statistical comparisons were also carried out using MSC and AIC. The analyses show that the Wilson-Thomas (1985) and Morrison (2013) models are best fit models to the experimental data for the Reynolds number up to 40000. Within this range, both models can be used alternately. But beyond this Re value the discrepancy of the Wilson-Thomas model is higher than the Morrison model. In view of the fact that the Morrison model requires fewer calculations and parameters as well as a single equation is used to compute the friction factor for all flow regimes, it is the authors’ advice to use this model for friction factor estimation for the flow of Bingham fluids in smooth pipes as an alternative to the Moody chart and other implicit formulae.
Fifty-day-old fry of tilapia hybrids (Oreochromis aureus x niloticus) were placed in aquaria containing sediment with oocysts of Eimeria (sensu lato) vanasi Landsberg et Paperna. In the first 29 h after exposure sporulated oocysts in the stomach and free sporozoites in the gut could be found in examined fish. By 7 to 56 h after exposure, sporozoites, with their characteristic crystalloid body, were detected in intraepithélial lymphocyte-like and other leucocyte-like cells, but never in the epithelial cells. Infected cells were confined to the epithelial layer and did not enter the lamina propria. Within this time, some of the sporo-zoitcs divided by endodyogeny, once or twice in succession, to form daughter sporozoites. The parent’s sporozoite crystalline body was divided between the offspring of the primary and secondary divisions.
Morphometric analyses are used to evaluate the taxonomic status of two sympatric variants of Gyrodactylus anisopharynx Popazoglo et Boeger, 2000 (forma ''large-pharynx'' and forma ''small-pharynx''). The parasites were collected from the Piraquara River and the Miringuava River, State of Paraná, Brazil, between February 2005 and May 2006. A total of 132 parasites were measured from two hosts, Corydoras ehrhardti Steindachner and Corydoras paleatus (Jenyns). Eleven morphological features of the haptoral sclerites and pharynx were measured and analysed by discriminant analysis and principal components analysis. The results indicate that the observed morphological variation cannot be associated to intraspecific variation or phenotypic plasticity (P < 0.0001). Consequently, the two variants previously allocated in G. anisopharynx represent two independent species. Since the holotype was defined as the variant ''large-pharynx'', Gyrodactylus corydori sp. n. is proposed to accommodate specimens previously reported as ''small-pharynx'' variant of G. anisopharynx. Morphometric analyses showed that the hook, the anchor, and the pharyngeal bulb are significantly distinct (P < 0.0001) between G. corydori sp. n. and G. anisopharynx (s.s.). The new species is characterized by having hooks with point moderately curved, robust convex heel, convex shelf, toe concave moderately pointed with depression; deep bar with two submedial, posterior projections; anchors with robust superficial root; superficial bar with two small anterolateral projections; and male copulatory organ armed with two rows of spinelets.
Syntrichia caninervis Mitt. is the dominant species in the moss crusts of the Gurbantunggut Desert, Northwestern China. We experimented with this species under controlled environmental conditions. Modulated chlorophyll (Chl) fluorescence was used to test the speed of recovery as evidenced by the time course of photosynthetic activity following remoistening. Transmission electron microscopy was used to explore the cytological characteristics of the leaf cells. Minimum and maximum fluorescence (F0 and FM) and photosynthetic yield (FV/FM) of photosystem II (PSII) recovered quickly when shoots were remoistened in the dark. This was especially the case of FV/FM; within the first minute of remoistening this reached 90% or more of the value attained after 30 min. These physiological changes were closely paralleled by cytological changes that indicated no damage to membranes or organelles. Correlation analysis showed that Chl fluorescence decreased both above and below a narrow moisture optimum. Our results underline the capability of S. caninervis to photosynthesize after remoistening. Utilizing precipitation events such as dew, fog, rain, and melting snow allows S. caninervis to survive and grow in a harsh desert environment. and J. Zhang ... [et al.].
We discuss here the question whether there exists an invariant subspace M for a contraction T in the class $A$ such that the spectrum of the restriction of T on M is the whole closed unit disc.
Theories of the origin of the Oort ctoud are examined in the light of recent observations of comets and of star-forming environments, and some popular hypotheses are found to meet with difficulties. In particular chemical and experimental evidence that comets grow in an extremely cold, quiescent environment is proving difficult to reconcile with recent CO and IR observations showing that the environment of a star-forming region is characterised by turbulent,
high-velocity flows and that young stars are prone to recurrent, violent outbursts. The aggregation around young stars of
planetesimals pre-existing in molecular ciouds avoids these problems. However formed, the Oort cloud is disturbed through
interactions with its galactic environment. A record of these past disturbances, episodic or regular, is in principle recoverable through impact cratering and other geological signatures, and these terrestrial records therefore provide a further new constraint on the structure and evolution of the Oort cloud. The concepts of
r 'dense inner cloud' or a 'solar companion star' are difficult to reconcile with the impact cratering history. The debris from the very largest comets are expected to play a dominant role in producing galactic modulations of such fundamental phenomena as the rise and fali of oceans, ice ages, geomagnetic reversals and the origin of life. A ~15 Myr galactic cycle in particular is predicted. Power spectrum analyses applied to cratering, vulcanism and geomagnetic reversal records for the last -200 Myr reveal the presence of a 16 ± 2 Myr cycle.