Showing papers by "University of Milan published in 1971"

Kinetic models for gas-surface interactions

Abstract: The problem of a mathematical description of the relation between the distribution functions of impinging and emerging molecules at a solid wall is considered. Under suitable assumptions, of a rather general nature, certain properties of the acceptable models are set forth. These properties are then used to prove certain basic inequalities (including the one necessary to prove the H-theorem in presence of physical walls) as. well as constructing a specific model containing two disposable parameters. Preliminary comparisons of this model with experiment seem satisfactory.

Quantum Statistical Theory of Superradiance. II

Abstract: We discuss the solution of the "superradiance master equation" derived in a preceding paper. During the first few photon transient times the cooperative atomic decay goes through a non-adiabatic oscillatory regime. For later times the decay takes place monotonically in time with the electromagnetic field following it adiabatically. The emitted light pulse has different statistical properties for an incoherently and a coherently prepared "superradiant" atomic initial state. The former case is characterized by large quantum fluctuations and strong atom-atom and atom-field correlations. In the latter case quantum fluctuations are small and the system behaves essentially classically. By also solving for a class of coherently prepared intermediate initial states we show that large quantum fluctuations occur only if the initial total occupancy of the excited state differs from the total number of atoms at most by a number of order unity.

Immunoglobulins as cell receptors.

Abstract: It is conceivable that immunoglobulin molecules in a suitable position on the external membrane of immunocytes may play the role of cell receptors. Through an interaction of these antibody molecules with the corresponding antigens, the cells might be triggered to proliferation and/or differentiation. This might be a crucial role played by membrane-bound immunoglobulins in the immune response, and it is therefore of considerable interest to study the presence, distribution and specificity of immunoglobulin molecules on the membrane of lymphoid cells. The first demonstration of the presence of immunoglobulin determinants on the membrane of lymphocytes has been provided by the blast transformation of these cells after contact with antiimmunoglobulin or antiallotype antisera.' More direct demonstration has been provided by the immunocytoadherence with marker erythrocytes sensitized with immunoglobulins or with radiolabeled antiimmunoglobulin an t ib~dies .~ Recently, a direct visualization of surface immunoglobulins on lymphocyte membrane has been achieved by immunofluorescence.4-8 The purpose of this paper is to report briefly further experiments on the immunoglobulins on the membrane of human or rabbit lymphocytes, and also give a preliminary account of immunoglobulins which are demonstrable on the membrane of some cells of the plasma cell series. Particularly interesting in the latter case is the comparison of the membrane immunoglobulins with the immunoglobulins present in the cytoplasm. These studies have been performed by means of immunofluorescence, utilizing appropriate double-staining procedures in two steps to study the surface and intracytoplasmic immunoglobulins of the same cells, in conjunction with optimal instruments which allow selective visualization of fluorescein or rhodamine.7

Lymphocytes in human immunodeficiency states: a study of membrane-associated immunoglobulins.

Abstract: The peripheral blood lymphocytes from fourteen patients with various types of immunodeficiency states were studied with respect to surface immunoglobulins by the fluorescent antibody technique. The results obtained ranged from a complete absence of immunoglobulin-bearing lymphocytes in certain patients to normal levels in others. Serial determinations in each patient gave similar results. Three male children with the X-linked form of the disease and very low serum immunoglobulins had no lymphocytes that stained for immunoglobulins. However, two brothers and a third boy who presumably also had this type of disease, had immunoglobulin-bearing lymphocytes in the low normal range. Of special interest was an adult female patient with a thymoma who showed no such lymphocytes. Patients with the common variable type of immunodeficiency all had some staining lymphocytes numbering from a very few to within the normal range. The findings indicate that this approach provides important information regarding the basic defects in certain of these patients, and various hypotheses are proposed.

Chromosome changes and their evolution in subjects with past exposure to benzene.

Abstract: Chromosome studies of peripheral blood lymphocytes in 25 subjects who had recovered from benzene hemopathy, in four subjects with bone marrow toxicity from benzene, and in three subjects who had recovered from acute benzene poisoning revealed significantly increased rates of “unstable” and “stable” chromosome aberrations which, In most cases, were still present several years after cessation of exposure to the toxic agent and recovery from the poisoning. The follow-up cytogenetic studies showed a tendency toward a decrease in unstable chromosome changes and, generally, a persistence or an increase in stable changes. Bn some cases there was evidence of abnormal clone formation in peripheral blood lymphocytes. Chromosomes of the G group seemed to be involved in stable changes with a frequency higher than expected.

Specific appearance of sympathetic cholinergic vasodilatation in muscles during conditioned movements.

Abstract: THE anticipation of movement might increase blood flow to the skeletal muscles, and it is usually assumed that this adaptive function is performed by the sympathetic cholinergic system1. This consists of a series of cerebral relays connecting the motor cortex, the hypothalamus, and the mesencephalic periaqueductal grey to sympathetic postganglionic neurones exerting an atropine-sensitive dilating action on the vasculature of skeletal muscles2,3. Although it has been demonstrated that the sympathetic cholinergic system can be conditioned4,5, there is no clear evidence of its relationship to movement, nor any basis for suggesting that its function is specific, limited to active muscles (as would be expected should it subserve muscle exercise2), or more diffuse and indiscriminate (as might be advantageous in emotional behaviour6). The study described here was designed to define more precisely whether the sympathetic cholinergic system can exert a specific and motor-related action.

Immunoglobulins on Lymphocyte Membranes

Abstract: Publisher Summary This chapter discusses the presence of immunoglobulins on lymphocyte membranes. The presence of immunoglobulin molecules firmly attached to the membrane of lymphocytes from different species has been demonstrated with a variety of methods. The proportion of immunoglobulin-positive lymphocytes varies according to the species and the source of lymphocytes; among peripheral blood lymphocytes, it was found that the immunoglobulin-positive cells were 10–30% in man and mice, whereas higher values, up to 60–70%, were found in the rabbit. In lymphoid organs, the percentage of immunoglobulin-positive cells is correlated with the expected population of B (bone marrow derived) lymphocytes and the thymus lymphocytes have been found to be immunoglobulin negative when tested by immunofluorescence in different species and at different ages ranging from fetus to adult.

The metabolism of biphenyl by Pseudomonas putida.

Abstract: La degradazione del bifenile da parte diPs. putida inizia con la formazione di un diolo cui si attribuisce la struttura di 2,3-diidro-2,3-diossibifenile, in quanto, per disidratazione a caldo con acido cloridrico, si trasforma in 2-ossibifenile e tracce di 3-ossibifenile. Il diolo viene ulteriormente degradato ad acido benzoico. Le cellule diPs. putida cresciute su bifenile sono simultaneamente indotte ad ossidare al Warburg il bifenile e l'acido benzoico, non il 3,4-diossibifenile e l'acido fenilpiruvico. Le stesse cellule contengono una metapirocatecasi costitutiva.

Brain recovery from essential fatty acid deficiency in developing rats.

Abstract: — Rats were supplied from before birth with an essential fatty acid (EFA) deficient, a control, or an EFA deficient-control combination diet for various periods up to 6 months It was found that EFA deficiency resulted in brain weights decreased in comparison with control values throughout development The brain weight/body weight relationship, however, expressed by Donaldson's equation was generally maintained in animals fed either totally deficient or control diets Animals deficient even during the brain's most actively growing period were able to recover completely on restoration of the control diet for a sufficiently long period Fatty acid alterations in brain ethanolamine phosphoglyceride (EPG) during EFA deficiency were extensive Acids of the ω6 family (18:2, 20:2, 20:3, 20:4, 22:3, 22:4 but not 22:5) were reduced from control figures In the w9 family 20:3 and 22:3 were especially elevated whereas 22:6 ω3 levels were similar to those of the controls, finally decreasing only after a lengthy period of EFA deprivation Mean unsaturation contents, as expressed by the proposed unsaturation index notation (Ulmol) agreed closely in EPG fatty acids of deficient and control rats at a particular age On substitution of the control for the deficient diet the ω6 family rebounded in a manner such that values for 20:4, 22:4, and 22:5 exceeded comparable figures in control animals Concomitantly the ω9 family receded below control levels, and ω3 acids remained or returned to normal This overadjustment in ω6 and ω9 families continued even after a prolonged period on the control diet

Lipid alterations and their reversion in the central nervous system of growing rats deficient in essential fatty acids

Abstract: Essential fatty acid (EFA) deficiency modifies several biological parameters, i.e., growth, metabolic rate and water balance and induces functional changes in liver, kidney and lung tissues. The brain fatty acid changes reported in the literature are generally smaller than those observed in other tissues. However, EFA deficiency initiated in rats prior to birth and continued for a prolonged period of time results in decreased brain weight, brain lipid and phospholipid content and in considerable changes in polyunsaturated fatty acid distribution, especially in the ethanolamine phosphoglyceride fraction. The unsaturation level of this phospholipid is maintained at a constant level in spite of the fatty acid distribution changes. Brain lipid analyses, carried out at various time intervals in EFA deficient animals, indicate that brain weights are already reduced in 10-day-old deficient rats, that brain phospholipids decrease, especially in the males after three months, and that fatty acid distribution changes begin rather early. The latter consist of a decrease of tetraenes and increase of trienes and of the triene-tetraene ratios as early as at 10 days, a decrease of hexaenes after six months, and after six months, an increase of pentaenes, which are elevated at birth but usually disappear after three months of age. Similar changes are observed in myelin. The induced changes are not completely reversed upon return to normal diet.

Lactic acid production in supramaximal exercise

Abstract: On 12 subjects of different muscular fitness the rate of lactic acid appearance in blood, while performing the same supramaximal exercise has been determined, together with the maximal performance time and the maximal L.A. concentration in blood. The rate of increase of lactic acid is higher in the less fit than in the athletic subjects, to compensate for the lower oxygen consumption. In all subjects the appearance of L.A. in the blood is delayed: at the onset of the exercise other anaerobic processes (alactic) supply the energy required, and only when these are exhausted L.A. formation enters into play. The energy due to lactic acid corresponds to 37±3.5 ml of O2 per g of lactic acid increase in 1 l of blood, or 50 ml of O2 (or 250 cal) per g of L.A. produced from glycogen. The maximal amount of the lactacid debt is equivalent to about the maximum oxygen consumption in 1 min. A simple relation is found between the time of performance in supramaximal exercise and the maximum oxygen consumption.

Dextro-gamma-carboxymethyl-gamma-methyl-delta-alpha-butenolide. A 1,2-ring-fission product of 4-methylcatechol by Pseudomonas desmolyticum.

Abstract: 1. (+)-gamma-Carboxymethyl-gamma-methyl-Delta(alpha)-butenolide was isolated from resting-cell cultures of Pseudomonas desmolyticum incubated in the presence of 5-methylsalicylic acid. 2. The structure of this metabolite was deduced from physical and chemical evidence. 3. The isolated compound must be formed in an enzymic reaction since it shows optical activity. 4. The degradative pathway of 4-methylcatechol by Ps. desmolyticum is discussed.

Optical and transport properties of the magnetic semiconductor α‐RuCl3

Abstract: The optical and transport properties in the paramagnetic phase of α-RuCl3 are studied here for the first time. Values are reported for the dc conductivity of single crystals over the temperature range 110 to 500 °K in the two crystallographic directions, along and perpendicular to the optic c-axis: at 300 °K, ϱ∥c = 8 × 106 Ωcm and ϱ⟂c = 1.7 × 103 Ωcm. The activation energy for both directions is ≈ 0.1 eV below 300 °K and ≈ 0.5 eV for temperatures above 400 °K. Detailed absorption spectra in the energy range 0.1 to 4 eV, and in the temperature interval 80 to 300 °K, reveal three weak bands (α ≈ 103 cm−1) at ≈ 0.28, 0.53, and 0.75 eV, two stronger peaks (α ≈ 104 to 105 cm−1) at ≈ 1.18, 2.08 and a step at 3.10 eV (values at 80 °K). Reflectivity measurements in the energy range 1 to 9 eV show maxima which, at 300°K, are centred at ≈ 1.1, 1.9, and 3.10 eV and a marked reflection peak, at ≈ 5.10 eV, probably related to p(Cl) → s(Ru) band-to-band transitions. Ac photoconductivity spectra in the 0.6 to 2.8 eV region show structures closely related to the absorption bands in the same energy range. The different temperature dependence of the absorption and photocurrent spectra over the 80 to 300 °K interval is discussed. After an analysis of the transport data, the absorption spectrum up to 3 eV is discussed in terms of the Tanabe and Sugano diagram for a d5 configuration.

Ionic conductivity in lithium compounds

Abstract: The electrical and structural properties of lithium compounds which present predominantly ionic conductivity are reviewed and relationships between structure and electrical properties are, where possible, discussed. A few results on lithium silico-aluminate glasses are also reported.