Kaon photoproduction: background contributions, form factors and missing resonances

The photoproduction p(gamma, K+)Lambda process is studied within a field-theoretic approach. It is shown that the background contributions constitute an important part of the reaction dynamics. We compare predictions obtained with three plausible techniques for dealing with these background contributions. It appears that the extracted resonance parameters drastically depend on the applied technique. We investigate the implications of the corrections to the functional form of the hadronic form factor in the contact term, recently suggested by Davidson and Workman (Phys. Rev. C 63, 025210). The role of background contributions and hadronic form factors for the identification of the quantum numbers of ``missing'' resonances is discussed.Comment: 11 pages, 7 eps figures, submitted to Phys. Rev.

Polarization degrees of freedom in photoinduced two-nucleon knockout from finite nuclei

The polarization degrees of freedom in photoinduced two-nucleon knockout from finite nuclei are studied. It is pointed out that they open good perspectives to study the dynamics of dinucleons in the medium in detail. The ($\gamma,pp$) and ($\gamma,pn$) angular cross sections, photon asymmetries and outgoing nucleon polarizations are calculated for the target nuclei $^{16}$O and $^{12}$C and photonenergies ranging from 100 up to 500 MeV. It is investigated to which degree the two-nucleon emission reaction is dominated by photoabsorption on $^3S_1(T=0)$ proton-neutron and $^1S_0(T=1)$ proton-proton pairs in the nuclear medium. The calculations demonstrate that dominance of $S$ wave photoabsorption in the ($\gamma,pn$) channel does not necessarily imply that the reaction mechanism is similar to what is observed in deuteron photodisintegration.Comment: 27 pages, REVTeX 3.0 with epsf.sty, 11 figures in EPS forma

Divergent Roles of Clock Genes in Retinal and Suprachiasmatic Nucleus Circadian Oscillators

The retina is both a sensory organ and a self-sustained circadian clock. Gene targeting studies have revealed that mammalian circadian clocks generate molecular circadian rhythms through coupled transcription/translation feedback loops which involve 6 core clock genes, namely Period (Per) 1 and 2, Cryptochrome (Cry) 1 and 2, Clock, and Bmal1 and that the roles of individual clock genes in rhythms generation are tissue-specific. However, the mechanisms of molecular circadian rhythms in the mammalian retina are incompletely understood and the extent to which retinal neural clocks share mechanisms with the suprachiasmatic nucleus (SCN), the central neural clock, is unclear. In the present study, we examined the rhythmic amplitude and period of real-time bioluminescence rhythms in explants of retina from Per1-, Per2-, Per3-, Cry1-, Cry2-, and Clock-deficient mice that carried transgenic PERIOD2::LUCIFERASE (PER2::LUC) or Period1::luciferase (Per1::luc) circadian reporters. Per1-, Cry1- and Clock-deficient retinal and SCN explants showed weakened or disrupted rhythms, with stronger effects in retina compared to SCN. Per2, Per3, and Cry2 were individually dispensable for sustained rhythms in both tissues. Retinal and SCN explants from double knockouts of Cry1 and Cry2 were arrhythmic. Gene effects on period were divergent with reduction in the number of Per1 alleles shortening circadian period in retina, but lengthening it in SCN, and knockout of Per3 substantially shortening retinal clock period, but leaving SCN unaffected. Thus, the retinal neural clock has a unique pattern of clock gene dependence at the tissue level that it is similar in pattern, but more severe in degree, than the SCN neural clock, with divergent clock gene regulation of rhythmic period

Constraint solving in uncertain and dynamic environments - a survey

International audienceThis article follows a tutorial, given by the authors on dynamic constraint solving at CP 2003 (Ninth International Conference on Principles and Practice of Constraint Programming) in Kinsale, Ireland. It aims at offering an overview of the main approaches and techniques that have been proposed in the domain of constraint satisfaction to deal with uncertain and dynamic environments

The rationale of opportunistic bilateral salpingectomies (OBS) during benign gynaecological and obstetric surgery : a consensus text of the Flemish Society of Obstetrics and Gynaecology (VVOG)

Ovarian cancer (OC), is a disease difficult to diagnose in an early stage implicating a poor prognosis. The 5-year overall survival in Belgium has not changed in the last 18 years and remains 44 %. There is no effective screening method (secondary prevention) to detect ovarian cancer at an early stage. Primary prevention of ovarian cancer came in the picture through the paradigm shift that the fallopian tube is often the origin of ovarian cancer and not the ovary itself. Opportunistic bilateral salpingectomy (OBS) during benign gynaecological and obstetric surgery might have the potential to reduce the risk of ovarian cancer by as much as 65 %. Bilateral risk-reducing salpingectomy during a benign procedure is feasible, safe, appears to have no impact on the ovarian function and seems to be cost effective. The key question is whether we should wait for a RCT or implement OBS directly in our daily practice. Guidelines regarding OBS within our societies are therefore urgently needed. Our recommendation is to inform all women without a child wish, undergoing a benign gynaecological or obstetrical surgical procedure about the pro’s and the con’s of OBS and advise a bilateral salpingectomy. Furthermore, there is an urgent need for a prospective registry of OBS. The present article is the consensus text of the Flemish Society of Obstetrics and Gynaecology (VVOG) regarding OBS

Complete Mitochondrial Genome and Phylogeny of Pleistocene MammothMammuthus primigenius

Phylogenetic relationships between the extinct woolly mammoth(Mammuthus primigenius), and the Asian(Elephas maximus) and African savanna(Loxodonta africana) elephants remain unresolved. Here, we report the sequence of the complete mitochondrial genome (16,842 base pairs) of a woolly mammoth extracted from permafrost-preserved remains from the Pleistocene epoch—the oldest mitochondrial genome sequence determined to date. We demonstrate that well-preserved mitochondrial genome fragments, as long as ~1,600–1700 base pairs, can be retrieved from pre-Holocene remains of an extinct species. Phylogenetic reconstruction of the Elephantinae clade suggests thatM. primigenius andE. maximus are sister species that diverged soon after their common ancestor split from theL. africana lineage. Low nucleotide diversity found between independently determined mitochondrial genomic sequences of woolly mammoths separated geographically and in time suggests that north-eastern Siberia was occupied by a relatively homogeneous population ofM. primigenius throughout the late Pleistocene

Collateral Health Issues Derived from the Covid-19 Pandemic.

At the end of 2019, a new coronavirus (Covid-19) outbreak occurred in Wuhan, China, and spread throughout the world despite efforts to contain the virus. At the end of January 2020, the General Director of the World Health Organization (WHO) declared a Public Health Emergency of International Concern, and by mid-May 2020, the worldwide number of known Covid-19 cases had surpassed 4.4 million including more than 300,000 deaths..

Nuclear transparency from quasielastic A(e,e'p) reactions uo to Q^2=8.1 (GeV/c)^2

The quasielastic (e,e$^\prime$p) reaction was studied on targets of deuterium, carbon, and iron up to a value of momentum transfer $Q^2$ of 8.1 (GeV/c)$^2$. A nuclear transparency was determined by comparing the data to calculations in the Plane-Wave Impulse Approximation. The dependence of the nuclear transparency on $Q^2$ and the mass number $A$ was investigated in a search for the onset of the Color Transparency phenomenon. We find no evidence for the onset of Color Transparency within our range of $Q^2$. A fit to the world's nuclear transparency data reflects the energy dependence of the free proton-nucleon cross section.Comment: 11 pages, 6 figure

Survey of A_LT' asymmetries in semi-exclusive electron scattering on He4 and C12

Single spin azimuthal asymmetries A_LT' were measured at Jefferson Lab using 2.2 and 4.4 GeV longitudinally polarized electrons incident on He4 and C12 targets in the CLAS detector. A_LT' is related to the imaginary part of the longitudinal-transverse interference and in quasifree nucleon knockout it provides an unambiguous signature for final state interactions (FSI). Experimental values of A_LT' were found to be below 5%, typically |A_LT'| < 3% for data with good statistical precision. Optical Model in Eikonal Approximation (OMEA) and Relativistic Multiple-Scattering Glauber Approximation (RMSGA) calculations are shown to be consistent with the measured asymmetries.Comment: 9 pages, 5 figure