Giuseppe Colombo

PRECISION MEASUREMENT OF THE SUN'S GRAVITATIONAL FIELD BY MEANS OF THE TWIN PROBE METHOD

An accurate measurement of the gravitational field of the Sun, needed for the verification of the theories of gravitation, requires the use of a geodesic test body. To eliminate the effect of non-gravitational forces (mainly the solar radiation pressure) we propose to use two twin space probes, whose surface has identical geometrical and optical properties, but with different mass. Their differential motion leads to the determination of the motion of an ideal geodesic point. We discuss in detail the various conditions which are needed to ensure the required degree of identity and submit as a possible solution two cylindrical probes, whose sides are covered by ‘cavities’ to make them absorbing, rotating at a fast rate around an axis orthogonal to the ecliptic plane. We discuss briefly also the accuracy in the determination of the parameters of the metric field of the Sun obtainable from range measurements.

Ricerche citologiche sull'oogenesi del Baco da seta (Bombyx mori L.) e considerazioni sull'oogenesi degli Insetti

Summary Bombyx mori L. has a polytrophic meroistic ovary. The follicles are formed by an oocyte and seven nurse cells. The oogenesis can be divide in three phases corresponding to the three periods of growth of the oocytes. The first period goes from the beginning of meiosis to pachytene; the second from pachytene up to the beginning of the yolk platelets formation; the third one is characterizided by storage of yolk platelets and ends with the egg matuturation. The second period of growth occurs mainly through the activity of the nurse cells. The nurse cells are, at first, undistinguishable from the oogonia, later they grow, polyploidize and produce, through a nucleus-nucleolar system, ribonucleo-proteins which flow in to the oocyte cytoplasm where protein synthesis occurs. Succesively the nurse cells degenerate, in the oocyte the formation of yolk platelets occurs and the third period of growth begins. The Casperssons theory on the system of protein synthesis may be applied to the second period of grow...

La diffcrenziazione delle gonadi negli embrioni della cavallette

Summary The differentiation of gonads in grasshopper embryos (Anacridium aegyptium L.) has been investigated from the beginning of abdominal lobe segmentation up to hatching. The germ cells are clearly seen at first in the dorsal part of the celomic sacs of abdomen, where they form the genital crest. Thereafter the germ cells migrate into the medial wall of somites to form the genital band. During the differentiation of the celomic sacs and before blastokinesis, a primordial not yet sex differentiated gonad obtains, which is formed by a dorsal cord of mesodermic cells and a ventral group of germ cells. The first differentiation is observed during and after blastokinesis, when the gonads reach their final position under the heart. The germ cells move into the dorsal mesodermic cells to form a gonad similar to that described by Nelsen (1934) in Melanoplus differentialis embryos, characterized by a dorsal mass of somatic cells, a central mass containing the germ cells and a ventral mass of mesodermic cells. ...

Tecnologia e Scienza Dello Spazio Nella Esplorazione di Venere

SuntoSi descrive schematicamente la missione compiuta dal Mariner II nell’ esplorazione del Pianeta Venere, per illustrare lo sviluppo raggiunto, in pochi anni, dalle tecnologia e scienza dello spazio.SummaryA brief outline of the mission of the spacecraft Mariner II in the exploration of the planet Venus is given for emphasizing the recent progress of the spacetechnology and spacescience.