Biomedical subjects

N Bianchi

Publications and source records attributed to N Bianchi.

At least 19 recordsLinked to original sources

PubMed2006

Double-hadron leptoproduction in the nuclear medium.

The first measurements of double-hadron production in deep-inelastic scattering within the nuclear medium were made with the HERMES spectrometer at DESY HERA using a 27.6 GeV positron beam. By comparing data for deuterium, nitrogen, krypton, and xenon nuclei, the influence of the nuclear medium on the ratio of double-hadron to single-hadron yields was investigated. Nuclear effects on the additional hadron are clearly observed, but with little or no difference among nitrogen, krypton, or xenon, and with smaller magnitude than effects seen on previously measured single-hadron multiplicities. The data are compared with models based on partonic energy loss or prehadronic scattering and with a model based on a purely absorptive treatment of the final-state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter.

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PubMed2006

Eta' photoproduction on the proton for photon energies from 1.527 to 2.227 GeV.

Differential cross sections for the reaction gamma p --> eta' p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data suggest for the first time the coupling of the eta'N channel to both the S11(1535) and P11(1710) resonances, known to couple strongly to the etaN channel in photoproduction on the proton, and the importance of J = 3/2 resonances in the process.

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PubMed2005

Measurement of the tensor structure function b1 of the deuteron.

The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.

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PubMed2005

Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target.

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.

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PubMed2005

Onset of asymptotic scaling in deuteron photodisintegration.

We investigate the transition from the nucleon-meson to the quark-gluon description of the strong interaction using the photon energy dependence of the d(gamma,p)n differential cross section for photon energies above 0.5 GeV and center-of-mass proton angles between 30 degrees and 150 degrees. A possible signature for this transition is the onset of cross-section s(-11) scaling with the total energy squared, s, at some proton transverse momentum P(T). The results show that the scaling has been reached for proton transverse momentum above about 1.1 GeV/c. This may indicate that the quark-gluon regime is reached above this momentum.

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PubMed2005

Bangladeshi medicinal plant extracts inhibiting molecular interactions between nuclear factors and target DNA sequences mimicking NF-kappaB binding sites.

Several medicinal plants can be employed to produce extracts exhibiting biological effects. The aim of this work was to verify the ability of extracts derived from different medicinal plants of Bangladesh in interfering with specific DNA-protein interactions. The rationale for this study is based on the observation that alteration of gene transcription represents a very promising approach to control the expression of selected genes and could be obtained using different molecules acting on the interactions between DNA and transcription factors (TFs). We have analysed the antiproliferative activity of extracts from the medicinal plants Hemidesmus indicus, Polyalthia longifolia, Aphanamixis polystachya, Moringa oleifera, Lagerstroemia speciosa, Paederia foetida, Cassia sophera, Hygrophila auriculata and Ocimum sanctum. Antiproliferative activity was assayed on different human cell lines, including erythroleukemia K562, B-lymphoid Raji, T-lymphoid Jurkat and erythroleukemia HEL cell lines. We employed the electrophoretic mobility shift assay (EMSA) as a suitable technique for the identification of plant extracts altering the binding between transcription factors and the specific DNA elements. We found that low concentrations of Hemidesmus indicus, Polyalthia longifolia, Moringa oleifera and Lagerstroemia speciosa, and very low concentrations of Aphanamixis polystachya extracts inhibit the interactions between nuclear factors and target DNA elements mimicking sequences recognized by the nuclear factor kappaB (NF-kappaB). On the contrary, high amount of extracts from Paederia foetida, Cassia sophera, Hygrophila auriculata or Ocimum sanctum were unable to inhibit NF-kappaB/DNA interactions. Extracts inhibiting both NF-kappaB binding activity and tumor cell growth might be a source for anti-tumor compounds, while extracts inhibiting NF-kappaB/DNA interactions with lower effects on cell growth, could be of interest in the search of compounds active in inflammatory diseases, for which inhibition of NF-kappaB binding activity without toxic effects should be obtained.

Antineoplastic Agents↗

PubMed2004

Proton source size measurements in the eA-->e'ppX reaction.

Two-proton correlations at small relative momentum q were studied in the eA(3He,4He,C,Fe)-->e(')ppX reaction at E(0)=4.46 GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on A and on the proton momentum. The size of the two-proton emission region for He was measured in eA reactions for the first time.

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PubMed2004

Two-nucleon momentum distributions measured in 3He(e,e'pp)n.

We have measured the 3He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for "fast" nucleons (p>250 MeV/c) peaks where two nucleons each have 20% or less, and the third nucleon has most of the transferred energy. These fast pp and pn pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair.

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PubMed2004

Observation of an exotic baryon with S=+1 in photoproduction from the proton.

The reaction gamma p-->pi(+)K(-)K(+)n was studied at Jefferson Laboratory using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S=+1 and mass M=1555+/-10 MeV/c(2) was observed in the nK(+) invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM=26 MeV/c(2)), and its statistical significance is (7.8+/-1.0)sigma. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by the chiral soliton model for the Theta(+) baryon. In addition, the pK(+) invariant mass distribution was analyzed in the reaction gamma p-->K(-)K(+)p with high statistics in search of doubly charged exotic baryon states. No resonance structures were found in this spectrum.

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PubMed2004

Flavor decomposition of the sea-quark helicity distributions in the nucleon from semiinclusive deep inelastic scattering.

Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.

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PubMed2004

Peptide nucleic acids (PNA)-DNA chimeras targeting transcription factors as a tool to modify gene expression.

Peptide nucleic acids (PNAs)-DNA chimeras have been recently described as DNA mimics constituted of a part of PNA and of a part of DNA. We have demonstrated that double stranded molecules based on PNA-DNA chimeras bind to transcription factors in a sequence-dependent manner. Accordingly, these molecules can be used for transcription factor decoy (TFD) pharmacotherapy. Effects of double stranded PNA-DNA chimeras targeting NF-kappaB and Sp1 were determined on in vitro cultured human cells and were found to be comparable to those observed using double-stranded DNA decoys. The TFD molecules based on PNA-DNA chimeras can be further engineered by addition of short peptides facilitating cell penetration and nuclear localization. Therefore, these engineered molecules could be of great interest for in vivo experiments for non-viral gene therapy of a variety of diseases, including neoplastic and viral diseases, for which the TFD approach has been already demonstrated as a very useful strategy.

Apoptosis↗

PubMed2003

Observation of an exotic S = +1 baryon in exclusive photoproduction from the deuteron.

In an exclusive measurement of the reaction gammad-->K(+)K(-)pn, a narrow peak that can be attributed to an exotic baryon with strangeness S=+1 is seen in the K(+)n invariant mass spectrum. The peak is at 1.542+/-0.005 GeV/c(2) with a measured width of 0.021 GeV/c(2) FWHM, which is largely determined by experimental mass resolution. The statistical significance of the peak is (5.2+/-0.6)sigma. The mass and width of the observed peak are consistent with recent reports of a narrow S=+1 baryon by other experimental groups.

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PubMed2003

Measurement of the proton spin structure function g1(x,Q2) for Q2 from 0.15 to 1.6 GeV2 with CLAS.

Double-polarization asymmetries for inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH3 target in the CLAS detector. The polarized structure function g(1)(x,Q2) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q(2)=0.15-1.64 GeV2. The contributions to the first moment Gamma(1)(Q2)= integral g(1)(x,Q2) dx were determined up to Q(2)=1.2 GeV2. Using a parametrization for g(1) in the unmeasured low x regions, the complete first moment was estimated over this Q2 region. A rapid change in Gamma(1) is observed for Q2<1 GeV2, with a sign change near Q(2)=0.3 GeV2, indicating dominant contributions from the resonance region. At Q(2)=1.2 GeV2 our data are below the perturbative QCD evolved scaling value.

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PubMed2003

Measurement of ep-->e' ppi+ pi- and baryon resonance analysis.

The cross section for the reaction ep-->e(')ppi(+)pi(-) was measured in the resonance region for 1.4<W<2.1 GeV and 0.5<Q2<1.5 GeV(2)/c(2) using the CLAS detector at Jefferson Laboratory. The data show resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on N(*) and Delta states shows an evident discrepancy. A better description of the data is obtained either by a sizable change of the properties of the P13(1720) resonance or by introducing a new baryon state, not reported in published analyses.

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PubMed2003

First measurement of transferred polarization in the exclusive ep-->e'K+Lambda--> reaction.

The first measurements of the transferred polarization for the exclusive e-->p-->e(')K+Lambda--> reaction have been performed at Jefferson Laboratory using the CLAS spectrometer. A 2.567 GeV beam was used to measure the hyperon polarization over Q2 from 0.3 to 1.5 (GeV/c)(2), W from 1.6 to 2.15 GeV, and over the full K+ center-of-mass angular range. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. A nonrelativistic quark-model interpretation of our data suggests that the ssmacr; quark pair is produced with spins predominantly antialigned. Implications for the validity of the most widely used quark-pair creation operator are discussed.

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PubMed2003

Evidence for quark-hadron duality in the proton spin asymmetry A1.

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A1. Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q2 between 1.2 and 12 GeV2 and values of W2 between 1 and 4 GeV2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q2 above 1.6 GeV2.

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PubMed2003

Q2 dependence of nuclear transparency for exclusive rho0 production.

Exclusive coherent and incoherent electroproduction of the rho(0) meson from 1H and 14N targets has been studied at the HERMES experiment as a function of coherence length (l(c)), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon (-Q2). The ratio of 14N to 1H cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing l(c) for coherent (incoherent) rho(0) electroproduction. For fixed l(c), a rise of nuclear transparency with Q2 is observed for both coherent and incoherent rho(0) production, which is in agreement with theoretical calculations of color transparency.

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PubMed2003

Photoproduction of the omega meson on the proton at large momentum transfer.

The differential cross section, dsigma/dt, for omega meson exclusive photoproduction on the proton above the resonance region (2.6<W<2.9 GeV) was measured up to a momentum transfer -t=5 GeV2 using the CLAS detector at Jefferson Laboratory. The omega channel was identified by detecting a proton and pi(+) in the final state and using the missing mass technique. While the low momentum transfer region shows the typical diffractive pattern expected from Pomeron and Reggeon exchange, at large -t the differential cross section has a flat behavior. This feature can be explained by introducing quark interchange processes in addition to the QCD-inspired two-gluon exchange.

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