Compartment Walls Research Articles

POPULATION DYNAMICS AND LIFE HISTORY OFCREPIDULA CONVEXASAY (GASTROPODA: PROSOBRANCHIA) IN DELAWARE BAY

1. The reproductive biology and population dynamics of two substrate forms Crepidula convexa were investigated. The species is a protandric hemaphrodite with direct development.2. The egg mass differs from other species in the genus in that the capsules comprising it are compartmentalized in early development. Later, the compartment walls break down and there is a decrease in the number of embryos, suggesting the existence of "embryonic cannibalism." Size-specific fecundity of the Deleware Bay population appears higher than published data for a Woods Hole population.3. There is rarely more than one male associated with a female and the ratio of males to females is low.4. Life span is at least two seasons. At the beginning of June, when reproduction is maximal, the population is predominantly female. The resulting influx of juveniles shifts the sexual composition of the population in such a way that males dominate by August. The transformation of these males to females during the winter gradually shifts the sexual composition so that females again predominate by Spring.5. Crepidula convexa living on Pagurus form a dwarf population which differs from cultch animals in morphology, mating behavior, breeding cycle and maturation rate. These differences are attributed to limitations of substrate. Exchange of individuals between subpopulations is facilitated by phoresis on hermit crabs.6. The high mobility of young C. convexa, which makes phoresis possible, is considered to be the key factor in the success of this species in the colonization of virgin substrates, thus facilitating dispersal in the absence of a larval stage. The capacity of males to fertilize more than one female is also a function of this mobility and is probably the major factor in maintaining a sex ratio (males < females) which favors maximal reproduction.

Testing blocks of refractory concrete in the walls of soaking pits

The use of refractory concrete in recuperative soaking pits is quite feasible. The use of block structures of refractory concrete cuts repair time by half and increases the efficiency during repairs 10 times. It is favorable to continue the work on testing these concretes in the walls of slabbing pits. It is necessary to build the compartment walls entirely from blocks of one composition. This composition is one based on Portland cement with finely milled chromite and forsterite aggregate.

A Proposed Method of Solution of the Oscillation of Ship containing the Movable Weight

In this report the authors have offered the equations of motion and a method of their solution about the oscillation of a ship containing a large amount of liquid cargo which is liable to movement but restrained the free motion with the rolling ship, making use of the theory of the physical double pendulum, and compared a calculated example with the experiment (in case where the centre of gravity of the movable weight lies below the axis of rotation). The results show that : (1) Owing to the restriction of movement of the weight, the righting moments are considerably non-linealized. This non-linearity shifts the peak of the resonance curve to higher frequency than that in the case where the restiction is removed, but much reduction of the peak amplitude can not necessarily be expected. (2) The impulsive force due to the collision of the moving weight to the stopper (the dash of the ilquid cargo to the compartment wall in the actual cases of ships) acts as the quenching moment, thus reduces the amplitudes of oscillations.