KsKs resonances in deep inelastic scattering at HERA

Inclusive KsKs production in deep inelastic ep scattering at HERA has been studied with the ZEUS detector using an integrated luminosity of 120 pb-1. Two states are observed at masses of 1537{+9}{-8} MeV and 1726{+-7} MeV, as well as an enhancement around 1300 MeV. The state at 1537 MeV is consistent with the well established f'2(1525). The state at 1726 MeV may be the glueball candidate f0(1710). However, it's width of 38{+20}{-14} MeV is narrower than 125{+-10} MeV observed by previous experiments for the f0(1710).Comment: 5 pages, 3 figures, to appear in the proceedings of the 10th International Conference on Hadron Spectroscopy, Aschaffenburg (Germany), August 31 to September 6, 200

Hadron Spectroscopy at HERA

Inclusive photoproduction cross-sections of the neutral mesons eta, rho^0, f_0(980) and f_2(1270) have been measured by H1 and compared to the photoproduction of pi^+ in ep collisions at HERA. Also, inclusive KsKs production and evidence for a narrow baryonic state decaying to Ksp have been observed by ZEUS at HERA.Comment: 5 pages, 4 figures, to appear in the proceedings of the Lake Louise Winter Institute (LLWI 2004), Alberta, Canada, 15-21 February, 200

A proposal for a different chi-square function for Poisson distributions

We obtain an approximate Gaussian distribution from a Poisson distribution after doing a change of variable. A new chi-square function is obtained which can be used for parameter estimations and goodness-of-fit testing when adjusting curves to histograms. Since the new distribution is approximately Gaussian we can use it even when the bin contents are small. The corresponding chi-square function can be used for curve fitting. This chi-square function is simple to implement and presents a fast convergence of the parameters to the correct value, especially for the parameters associated with the width of the fitted curve. We present a Monte Carlo comparative study of the fitting method introduced here and two other methods for three types of curves: Gaussian, Breit-Wigner and Moyal, when each bin content obeys a Poisson distribution. It is also shown that the new method and the other two converge to the same result when the number of events increasesComment: 27 pages, 13 figure

How does the chromatin fiber deal with topological constraints?

In the nuclei of eukaryotic cells, DNA is packaged through several levels of compaction in an orderly retrievable way that enables the correct regulation of gene expression. The functional dynamics of this assembly involves the unwinding of the so-called 30 nm chromatin fiber and accordingly imposes strong topological constraints. We present a general method for computing both the twist and the writhe of any winding pattern. An explicit derivation is implemented for the chromatin fiber which provides the linking number of DNA in eukaryotic chromosomes. We show that there exists one and only one unwinding path which satisfies both topological and mechanical constraints that DNA has to deal with during condensation/decondensation processes.Comment: Presented in Nature "News and views in brief" Vol. 429 (13 May 2004). Movies available at http://www.lptl.jussieu.fr/recherche/operationE_fichiers/Page_figurePRL.htm

Pp65 antigenemia, plasma real-time PCR and DBS test in symptomatic and asymptomatic cytomegalovirus congenitally infected newborns

<p>Abstract</p> <p>Background</p> <p>Many congenitally cytomegalovirus-infected (cCMV) neonates are at risk for severe consequences, even if they are asymptomatic at birth. The assessment of the viral load in neonatal blood could help in identifying the babies at risk of sequelae.</p> <p>Methods</p> <p>In the present study, we elaborated the results obtained on blood samples collected in the first two weeks of life from 22 symptomatic and 48 asymptomatic newborns with cCMV diagnosed through urine testing. We evaluated the performances of two quantitative methods (pp65 antigenemia test and plasma Real-time PCR) and the semi-quantitative results of dried blood sample (DBS) test in the aim of identifying a valid method for measuring viral load.</p> <p>Results</p> <p>Plasma qPCR and DBS tests were positive in 100% of cases, antigenemia in 81%. Only the latter test gave quantitatively different results in symptomatic versus asymptomatic children. qPCR values of 10³copies/ml were found in 52% of newborn. "Strong" DBS test positivity cases had higher median values of both pp65 positive PBL and DNA copies/ml than cases with a "weak" positivity.</p> <p>Conclusions</p> <p>As expected antigenemia test was less sensitive than molecular tests and DBS test performed better on samples with higher rates of pp65 positive PBL and higher numbers of DNA copies/ml. The prognostic significance of the results of these tests will be evaluated on completion of the ongoing collection of follow-up data of these children.</p

Base sequence dependent sliding of proteins on DNA

The possibility that the sliding motion of proteins on DNA is influenced by the base sequence through a base pair reading interaction, is considered. Referring to the case of the T7 RNA-polymerase, we show that the protein should follow a noise-influenced sequence-dependent motion which deviate from the standard random walk usually assumed. The general validity and the implications of the results are discussed.Comment: 12 pages, 3 figure

Breathers in a system with helicity and dipole interaction

Recent papers that have studied variants of the Peyrard-Bishop model for DNA, have taken into account the long range interaction due to the dipole moments of the hydrogen bonds between base pairs. In these models the helicity of the double strand is not considered. In this particular paper we have performed an analysis of the influence of the helicity on the properties of static and moving breathers in a Klein--Gordon chain with dipole-dipole interaction. It has been found that the helicity enlarges the range of existence and stability of static breathers, although this effect is small for a typical helical structure of DNA. However the effect of the orientation of the dipole moments is considerably higher with transcendental consequences for the existence of mobile breathers.Comment: 4pages, 5 eps figure

Solitons in Yakushevich-like models of DNA dynamics with improved intrapair potential

The Yakushevich (Y) model provides a very simple pictures of DNA torsion dynamics, yet yields remarkably correct predictions on certain physical characteristics of the dynamics. In the standard Y model, the interaction between bases of a pair is modelled by a harmonic potential, which becomes anharmonic when described in terms of the rotation angles; here we substitute to this different types of improved potentials, providing a more physical description of the H-bond mediated interactions between the bases. We focus in particular on soliton solutions; the Y model predicts the correct size of the nonlinear excitations supposed to model the ``transcription bubbles'', and this is essentially unchanged with the improved potential. Other features of soliton dynamics, in particular curvature of soliton field configurations and the Peierls-Nabarro barrier, are instead significantly changed