The mortality of selected groups of gasworkers has been observed over a period of eight years, and a comparison has been made of the mortality from different causes among different occupational groups. Men were included in the study if they had been employed by the industry for more than five years and were between 40 and 65 years of age when the observations began. All employees and pensioners of four area Gas Boards who met these conditions were initially included; but the number was subsequently reduced to 11,499 by excluding many of the occupations which did not involve entry into the carbonizing plants or involved this only irregularly. All but 0·4% of the men were followed successfully throughout the study. Mortality rates, standardized for age, were calculated for 10 diseases, or groups of diseases, for each of three broad occupational classes, i.e., those having heavy exposure in carbonizing plants (class A), intermittent exposure or exposure to conditions in other gas-producing plants (class B), and such exposure (class C). The results showed that the annual death rate was highest in class A (17·2 per 1,000), intermediate in class B (14·6 per 1,000), and lowest in class C (13·7 per 1,000), the corresponding mortallity for all men in England and Wales over the same period being slightly lower than the rate for class A (16·3 per 1,000). The differences between the three classes were largely accounted for by two diseases, cancer of the lung and bronchitis. For cancer of the lung the death rate (3·06 per 1,000) was 69% higher in class A than in class C; for bronchitis (2·89 per 1,000) it was 126% higher. For both diseases the mortality in class B was only slightly higher than in class C, and in both these categories the mortality was close to that observed in the country as a whole. Three other causes of death showed higher death rates in the exposed classes than in the unexposed or in the country as a whole, but the numbers of deaths attributed to them were very small. The death rate from cancer of the bladder in class A was four times that in class C, but the total number of deaths was only 14. Five deaths were attributed to pneumoconiosis, four of which occurred in bricklayers (class B). One death from cancer of the scrotum occurred in a retort house worker. For other causes of death the mortality rates were similar to or lower than the corresponding national rates. Examination of the data separately for each area Board showed that the excess mortality from lung cancer and chronic bronchitis in retort house workers persisted in each area. For two Boards the mortality from other causes was close to that recorded for other men living in the same region; in the other two Boards it was substantially lower. A comparison between the mortality of men who worked in horizontal retort houses and of those who worked in vertical houses suggested that the risk of lung cancer was greater in the horizontal houses and the risk of bronchitis was greater in the vertical houses, the differences being, however, not statistic...
MEWork with the drug is continuing, and, if our present results are confirmed, chlorthenoxazin should prove a most useful addition to the present range of mild analgesics.We are grateful to Messrs. For 41 men the coefficient of correlation between the two instruments was 0.81, and for 23 women 0.62. These can be compared with the coefficient of 0.86 obtained by Higgins (1957). The mean values of various categories for the two instruments are shown in the
A proper subsemigroup of a semigroup is maximal if it is not contained in any other proper subsemigroup. A maximal subsemigroup of a finite semigroup has one of a small number of forms, as described in a paper of Graham, Graham, and Rhodes. Determining which of these forms arise in a given finite semigroup is difficult, and no practical mechanism for doing so appears in the literature. We present an algorithm for computing the maximal subsemigroups of a finite semigroup S given knowledge of the Green's structure of S, and the ability to determine maximal subgroups of certain subgroups of S, namely its group H -classes.In the case of a finite semigroup S represented by a generating set X, in many examples, if it is practical to compute the Green's structure of S from X, then it is also practical to find the maximal subsemigroups of S using the algorithm we present. In such examples, the time taken to determine the Green's structure of S is comparable to that taken to find the maximal subsemigroups. The generating set X for S may consist, for example, of transformations, or partial permutations, of a finite set, or of matrices over a semiring. Algorithms for computing the Green's structure of S from X include the Froidure-Pin Algorithm, and an algorithm of the second author based on the Schreier-Sims algorithm for permutation groups. The worst case complexity of these algorithms is polynomial in |S|, which for, say, transformation semigroups is exponential in the number of points on which they act.Certain aspects of the problem of finding maximal subsemigroups reduce to other well-known computational problems, such as finding all maximal cliques in a graph and computing the maximal subgroups in a group.The algorithm presented comprises two parts. One part relates to computing the maximal subsemigroups of a special class of semigroups, known as Rees 0-matrix semigroups. The other part involves a careful analysis of certain graphs associated to the semigroup S, which, roughly speaking, capture the essential information about the action of S on its J -classes. arXiv:1606.05583v4 [math.CO] 6 Jul 2018 are L -related. Green's R-relation is defined dually to Green's L -relation; Green's H -relation is the meet, in the lattice of equivalence relations on S, of L and R. In any semigroup, xJ y if and only if the (2-sided) principal ideals generated by x and y are equal. However, in a finite semigroup J is the join of L and R. We will refer to the equivalence classes as K -classes where K is any of R, L , H , or J , and the K -class of x ∈ S will be denoted by K x . We write K S if it is necessary to explicitly refer to the semigroup on which the relation is defined. We denote the set of K -classes of a semigroup S by S/K .An idempotent is an element x ∈ S such that x 2 = x. We denote the set of idempotents in a semigroup S by E(S). A J -class of a finite semigroup is regular if it contains an idempotent, and a finite semigroup is called regular if each of its J -classes is regular. Containment of principal ideals induces a p...
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