Farm Mechanization and Women's Life Pattern: —Changing Time Allocation—

Abstract  Farm mechanization in Japan could be understood as a process brought a bout in the constellation of economic and political milieus of high economic growth. Labor productivity was raised to a degree unproportionate to the size of farming and yielded large amount of surplus labor power. This inherent contradiction became quite apparent after 1970. The expansion of non-farm labor market absorbed the surplus labor power. Thus part-time farming spreaded. changing the life pattern of farm families toward differentiation and individuation. A panel study at a rural community at the south-western part of HONSHU enables us to compare the time allocation of family members before and after mechanization. After mechanization. time allocation pattern differentiated by generation and sex. Younger members have gained private spheres outside farming. The older are left at farm, working in the fields. However, the time allocation data collected at a rural community at the northeastern part of HONSHU tells that the differentiation and individuation was slow due to the under-development of non-farm labor market.     

Competition and evolutionary stability of plants in a spatially structured habitat

We modelled the population dynamics of two types of plants with limited dispersal living in a lattice structured habitat. Each site of the square lattice model was either occupied by an individual or vacant. Each individual reproduced to its neighbors. We derived a criterion for the invasion of a rare type into a population composed of a resident type based on a pair-approximation method, in which the dynamics of both average densities and the nearest neighbor correlations were considered. Based on this invasibility criterion, we showed that, when there is a tradeoff between birth and death rates, the evolutionarily stable type is the one that has the highest ratio of birth rate to mortality. If these types are different species, they form segregated spatial patterns in the lattice model in which intraspecific competitive interactions occur more frequently than interspecific interactions. However, stable coexistence is not possible in the lattice model contrary to results from completely mixed population models. This clearly shows that the casual conclusion, based on traditional well mixed population models, that different species can coexist if intraspecific competition is stronger than interspecific competition, does not hold for spatially structured population models.     

Children with Keitai: When Mobile Phones Change from “Unnecessary” to “Necessary”

This paper focuses on children in Japan who begin using mobile phones (keitai) while in elementary school and will discuss aspects of parental–child relationships that involve keitai use. Firstly, this paper presents an overview of a Japanese society presently immersed in mobile media, focusing particularly on the spread of mobile media use to younger Japanese children. Data are presented from two research projects and analyzed to examine the cause of, and circumstances that lead to, child keitai use. Increasing social anxieties about safety and parental concern have reportedly led to increasing perception that keitai use is valuable in times of emergency, or in order to prevent crime, leading to a shift in attitudes towards children’s keitai use: that which was formerly considered “unnecessary” has now become “necessary”. However, the anxiety about safety is shared by almost all people and is therefore not itself a deciding factor regarding children’s keitai ownership. Keitai usage is, instead, prompted by several factors, some of which are not shared by children and parents. From this rift in reasoning emerges a game of tug-of-war over ownership and use between children and parents.

Extinction risk assessment of declining wild populations: The case of the southern Bluefin Tuna

We estimate the extinction probability of a large and decreasing population, the southern bluefin tuna. This tuna was listed as critically endangered by the World Conservation Union (IUCN) in 1996. However, the absolute population size is still large and the extinction probability within the next half century is negligible if the recent population decline rate does not increase in the future. IUCN’s criterion with respect to the population decline rate should be linked to the absolute population size, if this is estimated. Several methods estimating the probability of extinction conclude that the southern bluefin tuna population will be below 500 mature individuals within the next 100 years and may be listed as vulnerable. These analyses suggest that extinction risk assessment is useful for management action for taxa that still have large population and are rapidly decreasing.     

Impact factors of purse seine net and dip net fisheries on a chub mackerel population

There are two major kinds of fisheries for the chub mackerel in Japan. The purse seine net fishery exploits young and adult fish during the foraging season, while the dip net fishery exploits fish before and during the spawning season. To compare the damage to the chub mackerel stock caused by purse seine net and dip net fisheries, we introduced impact factors of the two kinds of fisheries on the two kinds of fisheries and estimated number of eggs spawned in 1982. We defined the impact factor as the ratio of the average reproductive value of individuals caught by each fishery to the reproductive value at maturity. The number of individuals caught by the purse seine net fishery was 66 times larger than the number caught by the dip net fishery, while the impact factor of the former was 84% of that of the latter. Thus, the total damage caused by the purse seine net fishery was much higher than the damage caused by the dip net fishery. We can evaluate the damage caused by mortality factors on endangered species using this method.     

Simultaneous estimation of mortality and dispersal rates of an artificially released population

Mark-recapture methods cannot estimate both mortality and dispersal rates of a wild population simultaneously. However, when an artificially cultured population is released into an area, the initial population size and the initial population distribution are usually known. If artificially cultured individuals are released with marks or distinguished from wild individuals or if no wild individual exists in the study area, we can estimate both the mortality and dispersal rates of the artificial population. The numbers of dispersed and dead individuals are estimated from the dispersal rate from the diffusion model and the total decreasing rate estimated from a mark-recapture data. We can estimate both the time-dependent and time-independent dispersal rates from the data. We choose the best fit model that has the smallest value of Akaike's Information Criteria. We also consider ‘concentric circles approximation” of spatial distribution, in which the cumulative and frequency distributions are analytically obtained.     

Model analysis of the effect of environmental fluctuation on the species replacement pattern of pelagic fishes under interspecific competition

Summary There are two factors affecting long-term fluctuation of planktotrophic pelagic fish: environmental fluctuation and interspecific competition. Long-term catch data of planktotrophic pelagic fishes in Japan suggest that the chub mackerel (species B) was replaced by the sardine (A), A was replaced by the anchovy, Pacific saury and horse mackerel (Group C), and species in group C were replaced by species B. If species A defeats B, B defeats C, and C defeats A in interspecific competitive ability, then the abundance of these three groups fluctuate forever and dominate in the same order. We call this cyclic advantage hypothesis for species replacement. In this model, environmental fluctuation affects the species replacement as a trigger. Environmental fluctuation does not determine the next dominant species but greatly affects when the next replacement occurs.     

Experimental study of assistant aids and new nursing method in nursing care work

This study seeks to evaluate the effect of regular and new nursing methods in nursing care work. Nursing care work often causes low back pain in nursing care worker. The principle of not lifting when transferring patients has been proposed as one way to prevent low back pain. This principle incorporates the use of the patient's strength and assistant aids. A sliding seats and transfer boards have been proposed as assistant aids for the transferring patients. It is necessary to evaluate the effectiveness of these assistant aids in preventing low back pain. Ten subjects performed two tasks in this experiment. Five were nursing experienced persons and five were the inexperienced. EMG results indicated that the new nursing method was less stressful than the methods. A questionnaire revealed that the new method was evaluated more highly than the regular method. Based on these results, we propose that a sliding seats and transfer boards be used in nursing care work.     

Alternative models for species replacement of pelagic fishes

Summary It is well known that the stock abundance of a pelagic fish usually fluctuates and a species of pelagic fish which was dominant in abundance is often taken over by another species. Several alternative models for species replacement among pelagic fishes are presented and analyzed: (A) environmental fluctuation, (B) strong density-dependent reproduction rate, (C) a two-species system with phase variation (density-dependent change of life history traits), (D) a two-species competition system with environmental fluctuation, (E) cyclic advantage relationship among three competitive species, and (F) a two-prey, one-predator system. Different model requires different number of species for the occurrence of species replacement. Three criteria to test each hypothesis from qualitative properties of species replacement are proposed. Possible management policies to decrease the amplitude of stock fluctuations are discussed. As a result, if the catching effort to mackerels which is rare now is large, or if the catching effort to the sardine is still large when it begins to decline in stock abundance, fisheries may be strong destabilizing effect on the stock abundance.     

Fourier analysis of irregularly spaced data on Rd

Summary.  The purpose of the paper is to propose a frequency domain approach for irregularly spaced data on R ^d . We extend the original definition of a periodogram for time series to that for irregularly spaced data and define non-parametric and parametric spectral density estimators in a way that is similar to the classical approach. Introduction of the mixed asymptotics, which are one of the asymptotics for irregularly spaced data, makes it possible to provide asymptotic theories to the spectral estimators. The asymptotic result for the parametric estimator is regarded as a natural extension of the classical result for regularly spaced data to that for irregularly spaced data. Empirical studies are also included to illustrate the frequency domain approach in comparisons with the existing spatial and frequency domain approaches.