Picosecond photophysical processes in iodoanthracenes

Picosecond photophysical processes in 2- and 9-iodoanthracene in cyclohexane at room temperature were studied by triplet-triplet transient absorption spectroscopy between 420-500 nanometers. For small amounts of excess vibronic energy in S(,1), intersystem crossing from the first excited singlet state into high triplet states T(,n) (n \u3e 1) with subsequent internal conversion to T(,1) or dissociation from the upper triplet manifold is suggested as a primary pathway for nonradiative relaxation. Rate constants for the processes were estimated using the results from previous fluorescence studies and the population risetime data for T(,1). Analyses of the photoproducts generated by excitation at two different wavelengths into the first excited singlet state reveal a vibronic level dependence of the photodissociation yield, indicating that photodissociation can proceed via at least two different mechanisms in the iodoanthracenes;Stimulated Raman processes and self-action effects are shownto be primarily responsible for the generation of a picosecondcontinuum when 532 nm picosecond pulses are focused into aCCl(,4) continuum cell. An experimental assessment of the artifactsintroduced by the angular distribution of continuum light on the;triplet-triplet absorption spectra of acridine is given and proceduresto minimize these effects are suggested; (\u271)DOE Report IS-T-1042. This work was performed under contract number W-7405-Eng-82 with the U.S. Department of Energy

The order-disorder transition of the (3x3)Sn/Ge(111) phase

Growing attention has been drawn in the past years to the \alpha-phase (1/3 monolayer) of Sn on Ge(111), which undergoes a transition from the low temperature (3x3) phase to the room temperature (\sqrt3 x \sqrt3)R30 one. On the basis of scanning tunnelling microscopy experiments, this transition was claimed to be the manifestation of a surface charge density wave (SCDW), i.e. a periodic redistribution of charge, possibly accompanied by a periodic lattice distortion, which determines a change of the surface symmetry. As further experiments with different techniques were being performed, increasing doubts were cast about the SCDW model. We have measured by He scattering the long range order of the 1/3 monolayer phase of Sn on the Ge(111) surface throughout the phase transition. The transition has been found of the order-disorder type with a critical temperature Tc=220 K. The expected 3-State Potts critical exponents are shown to be consistent with the observed power law dependence of the (3x3) order parameter and its correlation length close to Tc, thus excluding a charge density wave driven phase transition.Comment: 6 pages with 4 figures; updated reference

Ouabain-induced cytoplasmic vesicles and their role in cell volume maintenance

Cellular swelling is controlled by an active mechanism of cell volume regulation driven by a Na+/K+-dependent ATPase and by aquaporins which translocate water along the osmotic gradient. Na+/K+-pump may be blocked by ouabain, a digitalic derivative, by inhibition of ATP, or by drastic ion alterations of extracellular fluid. However, it has been observed that some tissues are still able to control their volume despite the presence of ouabain, suggesting the existence of other mechanisms of cell volume control. In 1977, by correlating electron microscopy observation with ion and water composition of liver slices incubated in differentmetabolic conditions in the presence or absence of ouabain, we observed that hepatocytes were able to control their volume extruding water and recovering ion composition in the presence of ouabain. In particular, hepatocytes were able to sequester ions and water in intracellular vesicles and then secrete themat the bile canaliculus pole.We named this “vesicularmechanismof cell volume control.” Afterward, thismechanism has been confirmed by us and other laboratories in several mammalian tissues.This review summarizes evidences regarding this mechanism, problems that are still pending, and questions that need to be answered. Finally, we shortly review the importance of cell volume control in some human pathological conditions

The pseudomorphic to bulk fcc phase transition of thin Ni films on Pd(100)

We have measured the transformation of pseudomorphic Ni films on Pd(100) into their bulk fcc phase as a function of the film thickness. We made use of x-ray diffraction and x-ray induced photoemission to study the evolution of the Ni film and its interface with the substrate. The growth of a pseudomorphic film with tetragonally strained face centered symmetry (fct) has been observed by out-of-plane x-ray diffraction up to a maximum thickness of 10 Ni layers (two of them intermixed with the substrate), where a new fcc bulk-like phase is formed. After the formation of the bulk-like Ni domains, we observed the pseudomorphic fct domains to disappear preserving the number of layers and their spacing. The phase transition thus proceeds via lateral growth of the bulk-like phase within the pseudomorphic one, i.e. the bulk-like fcc domains penetrate down to the substrate when formed. This large depth of the walls separating the domains of different phases is also indicated by the strong increase of the intermixing at the substrate-film interface, which starts at the onset of the transition and continues at even larger thickness. The bulk-like fcc phase is also slightly strained; its relaxation towards the orthomorphic lattice structure proceeds slowly with the film thickness, being not yet completed at the maximum thickness presently studied of 30 Angstrom (i.e. about 17 layers).Comment: 8 pages, 7 figure

Quantum size effects in the low temperature layer-by-layer growth of Pb on Ge(001)

The electronic properties of thin metallic films deviate from the corresponding bulk ones when the film thickness is comparable with the wavelength of the electrons at the Fermi level due to quantum size effects (QSE). QSE are expected to affect the film morphology and structure leading to the low temperature (LT) ``electronic growth'' of metals on semiconductors. In particular, layer-by-layer growth of Pb(111) films has been reported for deposition on Ge(001) below 130 K. An extremely flat morphology is preserved throughout deposition from four up to a dozen of monolayers. These flat films are shown to be metastable and to reorganize into large clusters uncovering the first Pb layer, pseudomorphic to the substrate, already at room temperature. Indications of QSE induced structural variations of the growing films have been reported for Pb growth on Ge(001), where the apparent height of the Pb(111) monatomic step was shown to change in an oscillatory fashion by He atom scattering (HAS) during layer-by-layer growth. The extent of the structural QSE has been obtained by a comparison of the HAS data with X-ray diffraction (XRD) and reflectivity experiments. Whereas step height variations as large as 20 % have been measured by HAS reflectivity, the displacement of the atomic planes from their bulk position, as measured by XRD, has been found to mainly affect the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are mainly due to a perpendicular displacement of the topmost layer charge density. The effect of the variable surface relaxation on the surface vibration has been studied by inelastic HAS to measure the acoustic dispersion of the low energy phonons.Comment: 28 pages (laTex,elsart) and 13 figures (eps); updated reference

The Planck Low Frequency Instrument

The Low Frequency Instrument (LFI) of the "Planck Surveyor" ESA mission will perform high-resolution imaging of the Cosmic Microwave Background anisotropies at four frequencies in the 30-100 GHz range. We review the LFI main scientific objectives, the current status of the instrument design and the on-going effort to develop software simulations of the LFI observations. In particular we discuss the design status of the PLANCK telescope, which is critical for reaching adequate effective angular resolution.Comment: 10 pages, Latex (use epsfig.sty); 4 Postscript figures; Astrophys. Lett & Comm, in press. Proc. of the Conference: "The Cosmic Microwave Background and the Planck Mission", Santander, Spain, 22-25 June 199

Ulipristal acetate before in vitro fertilization: Efficacy in infertile women with submucous fibroids

Background: The presence of submucous fibroids strongly impacts on IVF results, therefore, these patients should be considered for surgical or medical treatment. The aim of this study was to assess the role of Ulipristal acetate (UPA), a selective progesterone receptor modulator, in restoring uterine cavity deformation due to submucous fibroids, in infertile patients attempting an IVF treatment. The secondary study outcome was to evaluate the impact of preconception UPA treatment on rate of biochemical pregnancy, ongoing pregnancy, and live birth compared to a control group without fibroids. Methods: Infertile patients with submucosal fibroid (Type 1 and Type 2 according to FIGO classification) were enrolled in the study as fibroids group and received 1 to 3 treatment cycles of UPA, according to their response, as reflected by fibroid volume reduction and restoration of normal uterine cavity. Patients in control group were randomly selected from a general IVF cohort by a ratio of 2:1 with fibroids group, matched by age, BMI, type and cause of infertility and antral follicle count. The impact of UPA on fibroids volume reduction was evaluated. IVF outcome was compared between groups. Results: Twenty-six patients underwent UPA treatment revealed a mean volume reduction of their fibroids of 41%. A total of 15 (57.6%) biochemical pregnancy were obtained, resulting in 13 (50%) ongoing pregnancy and 9 (34.6%) healthy babies were already delivered. Similar results were obtained in control group. Conclusion: Restoration of normal uterine cavity by UPA treatment prior to IVF treatment avoids surgery and establishes a pregnancy rate comparable to a control group without fibroids

Exoelectron emission during oxidation of Cs films

During oxidation of thin Cs films, a nonadiabatic surface reaction manifests itself in the emission of electrons. This effect was investigated in detail by combining measurements of the current and of energy distributions of these exoelectrons with studies on the electronic properties of the surface by means of ultraviolet photoelectron spectroscopy and metastable deexcitation spectroscopy. Exoelectron emission occurs via Auger deexcitation of the empty state derived from the O2 affinity level. This process is confined to the stage Cs2O2→CsO2 in which resonance ionization of the affinity level of the impinging O2 molecule upon crossing the Fermi level EF is efficiently suppressed due to the absence of metallic states near EF. A kinetic model based on the successive steps involved in the oxidation of Cs is developed which describes qualitatively well all the experimental findings

Singlet-to-triplet conversion of metastable He atoms at alkali-metal overlayers

Energy distributions of electrons emitted from alkali-metal surfaces by impact of metastable He atoms reveal that there is a high probability for transformation of singlet atoms (excitation energy E*=20.6 eV) into triplet atoms (E*=19.8 eV) prior to deexcitation into the ground state. The conversion probability (as expressed by the ratio R of the intensities of valence-band emission due to triplet and singlet He* deexcitation, respectively) increases with increasing alkali-metal coverage on a Ru(0001) substrate, and in turn decreases with increasing oxygen exposure at a fixed alkali coverage. These findings indicate that R is a qualitative measure for the degree of ‘‘metallization’’ of the adlayer. R also increases with temperature due to broadening of the nearest-neighbor distribution whereby, on the average, a larger part of the adlayer becomes metalliclike. For Cs overlayers exhibiting work functions *− (1s12s2) formation as reflected by the R data as well as by the widths of the electron spectra

Sex of offspring influences metabolism during early transition period in dairy cows

Abstract. A study using 20 Holstein Friesian cows was conducted to investigate the influence of calf gender on metabolism during the transition period in dairy cattle. Blood samples were collected at three time points: 2–4 days prepartum (time 1), and 1 week and 2 weeks postpartum (time 2 and time 3 respectively). Serum samples obtained were analysed for total proteins, albumin, urea, glucose, non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHB). Depending on the sex of the offspring, cows were divided into two groups: Group 1 consisted of cows with heifer offspring (n = 12) and Group 2 consisted of cows with bull offspring (n = 8). A two-way repeated measures ANOVA and t tests for unpaired data were used to analyse the pattern of studied parameters and differences between the two groups. The results indicate differences in metabolic parameters between the two groups. These results highlight the importance of considering fetal sex as a factor that influences maternal metabolism during the early transition period in dairy cows