On Maximal Frequent and Minimal Infrequent Sets in Binary Matrices

Given an m×n binary matrix A, a subset C of the columns is called t-frequent if there are at least t rows in A in which all entries belonging to C are non-zero. Let us denote by the number of maximal t-frequent sets of A, and let denote the number of those minimal column subsets of A which are not t-frequent (so called t-infrequent sets). We prove that the inequality (m–t+1) holds for any binary matrix A in which not all column subsets are t-frequent. This inequality is sharp, and allows for an incremental quasi-polynomial algorithm for generating all minimal t-infrequent sets. We also prove that the analogous generation problem for maximal t-frequent sets is NP-hard. Finally, we discuss the complexity of generating closed frequent sets and some other related problems.     

Intravascular blood coagulation in patients with acute destructive cholecystitis with paravesical infiltration

Data are submitted on changes in the system of regulation of the aggregate state of blood, that result in the development of the second stage of intravascular hemocoagulation syndrome in patients with destructive forms of cholecystitis presenting with paravesicular infiltration in the preoperative period. Disruptions in hemostasis remain after surgery, which fact attests to the need for working out efficient pathogenetically validated methods of correction thereof for the combined treatment of the pathology in question to be raised to a much higher level.     

Surgeons in the United States. Activities, output and income

In a national surgical manpower questionnaire survey, 76% of those MD and DO surgeons who were contactable returned questionnaires that included a log diary reporting details of their daily activities. Comparisons were made of allocation of professional time, number of operations performed, and net income of respondents by physician classification (including certification), specialty, practice arrangement, age, and census division. The mean professional workweek was estimated at 46 hours for all respondents. More than two thirds of the total professional time was spent in direct patient care; about half the surgeon's time was spent in the hospital, with nearly 20% in the operating room. The median annual work load of respondents was 170 operations. Their median annual net income was $45,700.     

The importance of the density of spleen cell suspensions in cultures for development of immune reactions

A relationship was revealed between the number of cells in the suspension of the splenic tissue taken for induction of primary immunization of the reaction outside the organism and the number of the plaque-forming cells (PFC) formed by the end of incubation. It was shown that with increase of the cell density in the culture in the bottom of the incubation flask there was a 10-100 fold decrease of the PFC response; as to the cell viability--it was not affected or decreased but slightly. This effect was observed in using sheep red blood cells and water-soluble antigen extracted from them as an antigen. The effect was independent of shortage of the antigen or of the nutrient substances; it was accompanied by a general reduction of the 3H-thymidine incorporation into cultured cells.     

Phase diagrams and the kinetics of phospholipid exchange for vesicles of different composition and radius

Interactions between dimyristoyl- and dipalmitoyl phosphatidylcholine vesicles have been studied by light scattering of dilute dispersions (concn less than or equal to 1 mg/ml). It was found that at 50 degrees C, the two types of vesicles exchange lipid molecules, irrespective of the initial radii of the pure vesicles. When the initial radii are different, the process leads eventually to vesicles of intermediate size. The reaction follows second order kinetics. At room temperature no reaction was observed. The phase diagrams for several lipid systems are discussed.