Search

We have measured elastic pion-proton scattering in a 50 GeV/ c π − beam at the 76 GeV proton synchrotron in Serpukhov. Data are presented for four-momenta transfer squared in the range 0.03 t c ) 2 .

The pion radius has been measured by direct scattering of 50 GeV negative pions from stationary electrons in a hydrogen target. We find the square of the radius to be 〈 r π 2 〉 = (0.61 ± 0.15) fm 2 .

The recent reported evidence for the existence of the Λ6Li hypernucleus is questioned. No example of the (π−1H1H4He) decay mode of this hypernucleus was found in a sample of 7000 mesonically decaying hypernuclei.

The results of an experimental study of the binding energies of light hypernuclei are presented, based on a sample of 2008 uniquely identified π − mesonic decays. The problems of the calibration procedure and the selection criteria are discussed. Various aspects of the Λ -N interaction are reviewed in the light of these new results.

White-spored mutants ofAscobolus immersuswere used to study postmeiotic segregation within a gene. It was found that in two-point crosses between mutants showing postmeiotic segregation, polarization in recombinant asci resulting from this type of segregation resembled that in normal (even-type) conversion. However, the ratio of recombinant asci with even segregation (6:2 asci) to those with odd segregation (7:1 asci) was much higher than might have been expected on the basis of the frequencies of various recombinant asci found in crosses between the same mutants and the wild-type strain. It seems that none of the current models of recombination gives a satisfactory explanation of the results obtained.

About 200 hammer tracks from the 24-GeV proton interactions with heavy emulsion nuclei were collected. After a careful analysis of possible biases the total emission frequency of 8Li fragments for Nh8 stars was found to be (2.49±0.24)%. The emission frequency for different Nh intervals was investigated. An additional sample of N h ≧ 27 interactions of 9-GeV protons was also collected, and the emission frequency of 8Li fragments for these stars was found.

About 200 hammer tracks from primary 9 GeV proton interactions with heavy emulsion nuclei were collected. Using a width measurement method and correcting the results for the inclined tracks we were able to separate the boron fragments from lithium fragments in 90–95% of all the events. A careful analysis of possible biases has been made in a sample of some 100 hammer tracks not limited in inclination. The energy spectrum of α particles from 8 Li decay was found and compared with other theoretical and experimental results. The full kinematical analysis of 9 Li decay and critical analysis of measurement data made it possible to draw conclusions concerning the method of identification and the relative frequency of emission of these fragments. The absolute frequency of emission of 8 Li fragments for different N h intervals was estimated.

A full account of the work concerning 445 hammer tracks collected from 9 GeV and 24 GeV proton interactions with heavy emulsion nuclei is presented. The conditions of the routine work on hammer tracks are established. The frequency of emission of 8 Li fragments for different N h intervals was estimated. Taking into account the effect of the motion of the nucleus the velocity fluctuations and nuclear recoil resulting from the fragment emission, the angular distribution and the energy spectrum were compared with the results of evaporation theory. The values of the parameters T , V and β, representing the temperature, Coulomb barrier and average velocity of the emitting nucleus, were estimated on different assumptions. A high value of T and a low value of V were obtained.

The results of a search for the presence of sharp resonances in systems of four nucleons produced as a result of various π ± mesonic decay modes of the hypernuclei ∧ 4 H and ∧ 4 He are presented.

The results of a study of the decay of the Λ8Li and Λ12B hypernuclei are presented. The Λ 8 Li →π − + 8 Be ∗ →π − + 4 He + 4 He and Λ 12 B →π − + 12 C ∗ →π − + 4 He + 4 He + 4 He modes have been investigated in detail. New information on the decay mechanism of the 16.11 MeV state of 12C has been obtained.

Further examples of the π− mesonic decay of Λ 7 Be , Λ 10 B and Λ 11 B hypernuclei are reported. The binding energy values obtained in this work are combined with previous results.

From the observation of 11 examples of the π − mesonic decay of Λ 13 C the binding energy of this hypernucleus is found to be 11.39 ± 0.15 MeV.

The results of a search for final-state interactions between the decay products of some light hypernuclei are presented. The following π− mesonic decays have been considered: Λ 3 H → π − + 1 H , Λ 4 H → π − + 1 H + 3 H , Λ 4 He → π − + 1 H + 3 He , Λ 5 He → π − + 1 H + 4 He , Λ 7 Li → π − + 3 He + 4 He , Λ 7 Li → π − + 1 H + 2 H + 4 He , Λ 7 Li → π − + 1 H + 6 Li , Λ 8 Li → π − + 4 He + 4 He , Λ 9 Li → π − + 4 He + 4 He + n , Λ 9 Be → π − + 1 H + 4 He + 4 He and Λ 12 B → π − + 4 He + 4 He + 4 He .

Eight methionine loci inAspergillus nidulans were found. Their metabolic blocks and localization were determined. The spontaneous reversion rates for different methionine loci were studied. The revertants were all of suppressor type unlinked or loosely linked with methionine loci. There are at least 8 different suppressor loci. The suppressor mutations are recessive or partly dominant and many of them are quite unspecific, acting on all methionine loci even on those with different metabolic blocks.

The genus Geum of the family Rosaceae consists of about 56 species widely spread over the world except in the tropics. All species are perenniial herbs growing in more or less mesic conditions. More than fifteen years' study of this genus by the present author have shown that this genus is a polyploid complex of which the various species represent different stages of evolution, and show interesting relationships. In spite of great morphological differentiation on different polyploid levels the crossability between different species is surprisingly high, permitting cytogenetic analysis of 1lumerous interspecific hybrids. Geumt presents many interesting general problems concernin-g the role of geographical and ecological isolation as well as hybridization and polyploidy in the process of speciation. Some of the more interestinlg results of published (Gajewski, 1948, 1949, 1950, 1952, 1953, 1955, 1957) as well as unpublished results will be presented here.

Es wird eine Blitzlichtphotolyseapparatur beschrieben, in der in einer Dunnschichtkuvette nach Einstrahlen von Blitzlicht die zeitliche Veranderung der optischen Adsorption und der DK beblitzter Losungen gleichzeitig gemessen werden konnen. Aus beiden Messungen kann das Dipolmoment eines kurzlebigen photochemisch erzeugten Transients bestimmt werden, wenn dessen optisches Absorptionsspektrum bekannt ist. Mit der Apparatur werden die Dipolmomente von cis-Benzalanilin und pp'-Dichlorbenzalanilin bestimmt. Durch Vergleich beider Werte laβt sich die Lage des Dipolmomentes im cis-Benzalanilin angeben. Zwei Moglichkeiten der theoretischen Berechnung dieses Dipolmomentes werden angegeben (Inkrementenmethode und SCF-Rechnung) und das Ergebnis dem experimentellen Befund gegenubergestellt. Die Quantenausbeute der photochemischen trans-cis-Isomerisation des Benzalanilins wird zu bestimmt The description of a flash-photolysis-apparature is given, which allows the simultaneous measurement of changes in the dielectric constant and optical density of flash-irridiated solutions. By the combination of both measurements the dipole moments of photochemically produced transients can be determined, provided the absorption-spectrum of the transient is known. With this apparature the dipole moments of cis-benzylideneaniline and cis-pp'-dichlorbenzylidenenaniline are measured: By comparison of both dipole moments the direction of the intrinsic dipole moment of cis-benzylidenenaniline is determined. By two theoretical methods (addition of increments and SCF-calculation) the dipole moment of cis-benzylideneaniline is calculated which compares well to the experimental value. The quantum-yield of the photochemical trans-cis-isomerization of benzylideneaniline is determined to be

Twenty examples of π+ mesonic decays of light hypernuclei have been found together with 7000 π− mesonic decays. The ratio R4 of π+ mesonic decays for the gL4 He hypernucleus has been computed from the results of this work and those of a previous experiment [1] and is found to lie between the values 5.4 ± 1.5%1.7% and 6.9 ± 1.8%2.1%. The π+ mesonic decays of other species of hypernuclei are briefly discussed.

Some 2780 ( π − 1 H 4 He ) and 15(π − 2 H 3 He ) decays of the Λ5He hypernucleus have been collected and analyzed. The energy spectra and the angular distribution of the decay products have been studied. An improved formulation of the theoretical model describing the ( π − 1 H 4 He ) decay has been made, allowing a detailed comparison between theory and experiment.

The results of a compilation of the binding energy values of light hypernuclei ( A ⩽ 16) obtained by the European K − Collaboration and the EFINS-North-western Collaboration are presented. The events were analysed by the same computer programme and uniform stringent selection criteria were applied.

185 hammer tracks from 9 GeV proton interactions with Pb nuclei were collected. After a careful study of possible errors the total emission frequency of Li8 fragments for stars with N h ≧7 was found to be 4.95±0.68%. The energy spectrum and angular distributions were also determined, and a comparison was made with the predictions of nuclear evaporation theory. The nuclear temperature T and barrier V were found to be equal: T = 14.9 MeV and V = 9.6 MeV. The data obtained are discussed.

Evidence for the existence of a particle-stable state of the 6 Λ He hypernucleus is presented.

Publisher Summary This chapter discusses synchronous zygote formation in yeasts. The sexual processes in haploid strains of opposite mating type ( a and α ) leading to zygote formation consist of many characteristic consecutive stages. Three main stages of the sexual cycle are courtship, cell fusion, and karyogamy. In each stage, characteristic genetic and biochemical processes occur that prepare the cells for the next sexual reaction. a and α cells are competent for sexual fusion only at an appropriate stage of the cell cycle; competent cells are unbudded and in a cycle position just before the initiation of DNA replication. The interaction among haploid cells of opposite mating type is mediated by hormonal substances released into the culture medium. It has also been suggested that α cells produce an α factor (peptidic in nature) that is released into the medium. This diffusible α factor inhibits the initiation of DNA replication in a cells. In this way synchronization of a cells is achieved; they stop budding and become competent for sexual fusion. In the chapter, general characteristic of the conjugation process are discussed. Basic principles for synchronous mass production of zygotes and method for poorly synchronized zygote formation for genetic analysis are discussed in the chapter.

The emission frequency of a fragment is strongly dependent on the excitation energy of the target nucleus. Hammer track fragments were used to investigate the higher values of the observed emission frequency of two fragments in one interaction. Seven pairs of Li/sup 8/ tracks were found, each pair was produced in one interaction; data are presented in tabular form. It was concluded that the emission of two heavy fragments can still be explained mainly as a chance coincidence. (L.N.N.)