552 research outputs found
F-2(D(3)) measurements at ZEUS
No full textResults on the diffractive structure function F-2(D(3)) in deep inelastic neutral current positron-proton scattering (DIS) have been obtained by the ZEUS collaboration using two different methods. Diffractive interactions are selected by either requiring a small, not exponentially suppressed invariant hadronic mass M-X in the main detector or by detecting a fast proton in the ZEUS leading proton spectrometer (LPS). The results of the two methods are compared
Measurement of D*+- production and the charm contribution to F(2) in deep inelastic scattering at HERA
No full textThe production of D*(+/-)(2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb(-1). The decay channels D*(+) → D(0)pi(+) (+ c.c.), with D-0 → K(-)pi(+) or D-0 → K(- )pi(-)pi(+)pi(+), have been used to identify the D mesons. The e(+)p cross section for inclusive D*(+/-) production with 1 lt Q(2) lt 600 GeV2 and 0.02 lt y lt 0.7 is 8.31+/- 0.31(stat.)(+0.30)(-0.50) (syst.) nb in the kinematic region 1.5 lt pT(D*(+/-)) lt 15GeV and \eta(D*(+/-))\ lt 1.5. Differential cross sections are consistent with a next-to- leading-order perturbative-QCD calculation when using charm- fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in pr(D*(+/-)) and eta(D*(+/-)) in order to determine the charm contribution, F-2(c (c) over bar)(x,Q(2)), to the proton structllre function. The ratio F-2(c (c) over bar)/F-2 rises from similar or equal to 10% at Q(2) similar or equal to 1.8 GeV2 to similar or equal to 30% at Q(2) similar or equal to 130 GeV2 for x values in the rarlge 10(-4) to 10(-3)
Measurement of the proton structure function F-2 at low x and low Q(2) at HERA
No full textWe report on a measurement of the proton structure function F 2 in the range 3.5×10-5≤x≤4×10-3 and 1.5 GeV2≤Q 2≤15GeV2 at the ep collider HERA operating at a centre-of-mass energy of √s=300GeV. The rise of F 2 with decreasing x observed in the previous HERA measurements persists in this lower x and Q 2 range. The Q 2 evolution of F 2, even at the lowest Q 2 and x measured, is consistent with perturbative QCD. © 1996 Springer-Verlag
ZEUS results on the measurement and phenomenology of F(2) at low x and low Q**2
No full textMeasurements of the proton structure function F<sub>2</sub> for 0.6 < Q<sup>2</sup> < 17 GeV<sup>2</sup> and 1.2x10<sup>−5</sup> < x < 1.9x10<sup>−3</sup> from ZEUS 1995 shifted vertex data are presented. From ZEUS F<sub>2</sub> data the slopes <i>d</i>F<sub>2</sub>=<i>d</i> ln Q<sup>2</sup> at fixed <i>x</i> and <i>d</i> ln F<sub>2</sub>=<i>d</i> ln(1/<i>x</i>) for <i>x</i> < 0.01 at fixed Q<sup>2</sup> are derived. For the latter, E665 data are also used. The transition region in Q<sup>2</sup> is explored using the simplest non-perturbative models and NLO QCD. The data at very low Q<sup>2</sup> ≤ 0.65 GeV<sup>2</sup> are described successfully by a combination of generalised vector meson dominance and Regge theory. From a NLO QCD fit to ZEUS data the gluon density in the proton is extracted in the range 3x10<sup>−5</sup> < <i>x</i> < 0.7. Data from NMC and BCDMS constrain the fit at large <i>x</i>. Assuming the NLO QCD description to be valid down to Q<sup>2</sup> ∼ 1 GeV<sup>2</sup>, it is found that the <i>qq</i> sea distribution is still rising at small <i>x</i> and the lowest Q<sup>2</sup> values whereas the gluon distribution is strongly suppressed
Simulation of a Silicon Pore Optic mirror module diffraction pattern: the case of a light source at finite distance
No full textPerformance testing of a large-format reflection grating prototype for a suborbital rocket payload
No full textThe soft X-ray grating spectrometer on board the Off-plane Grating Rocket Experiment (OGRE) hopes to achieve the highest resolution soft X-ray spectrum of an astrophysical object when it is launched via suborbital rocket. Paramount to the success of the spectrometer are the performance of the >250 reflection gratings populating its reflection grating assembly. To test current grating fabrication capabilities, a grating prototype for the payload was fabricated via electron-beam lithography at The Pennsylvania State University’s Materials Research Institute and was subsequently tested for performance at Max Planck Institute for Extraterrestrial Physics’ PANTER X-ray Test Facility. Bayesian modeling of the resulting data via Markov chain Monte Carlo (MCMC) sampling indicated that the grating achieved the OGRE single-grating resolution requirement of Rsub>g(λ∕Δλ)>4500 at the 94% confidence level. The resulting Rsub>g posterior probability distribution suggests that this confidence level is likely a conservative estimate though, since only a finite Rsub>g parameter space was sampled and the model could not constrain the upper bound of Rsub>g to less than infinity. Raytrace simulations of the tested system found that the observed data can be reproduced with a grating performing at Rsub>g=∞. It is therefore postulated that the behavior of the obtained Rsub>g posterior probability distribution can be explained by a finite measurement limit of the system and not a finite limit on Rsub>g. Implications of these results and improvements to the test setup are discussed
Development of soft and hard X-ray optics for astronomy: progress report II and considerations on material properties for large diameter segmented optics of future missions
No full textDevelopment of soft and hard X-ray optics for astronomy: progress report II and considerations on material properties for large diameter segmented optics of future missions
No full textDominis estructurals i noves interaccions proteiques de l'enzim deubiquitinant USP25
No full text[cat] La present Tesi Doctoral es presenta com una agrupació de quatre publicacions que resumeixen el treball realitzat al Departament de Genètica de la Facultat de Biologia de la Universitat de Barcelona. El principal objectiu és la caracterització funcional de les regions estructurals de la isoforma muscular de l’enzim deubiquitinat USP25, inicialment definides amb eines bioinformàtiques. A més a més, es pretén fer un estudi de noves interaccions moleculars tipus proteïna-proteïna per la cerca de nous substrats o reguladors enzimàtics. La cèl·lula eucariota posseeix, entre altres, un sistema senyalitzador intracel·lular basat en una família de pèptids, el representant dels quals és la ubiquitina. Aquest sistema presenta diferents categories funcionals, entre elles, els enzims deubiquitinants, un centenar a l’espècie humana. Aquests enzims hidrolitzen l’enllaç que uneix la ubiquitina als seus precursors o substrats, mantenint així l’homeostasi d’aquest pèptid dins la cèl·lula. Una alteració de la seva funció pot portar diferents conseqüències depenent de la via metabòlica que es vegi afectada, doncs suposa una desregulació estequiomètrica dels substrats ubiquitinants respecte els no ubiquitinats. L’enzim deubiquitinant USP25 es va descriure en el grup d’investigació d’aquesta tesi durant la cerca de nous gens relacionats amb la síndrome de Down. Un cop caracteritzat funcionalment com una proteasa específica d’ubiquitina, els estudis d’expressió van mostrar l’existència de tres isoformes proteiques, una d’elles, USP25m, restringida al teixit muscular i cardíac. Tenint en compte que en el fenotip dels pacients amb síndrome de Down, entre altres trets, hi ha deficiència cardiovascular i atonia muscular, els esforços del grup es van centrar en la descripció i anàlisi d’aquesta isoforma. Els primers estudis van mostrar la seva situació citosòlica, l’expressió correlativa amb la diferenciació de cèl·lules musculars i la relació específica amb diverses proteines del sarcòmer. En el treball realitzat per la present Tesi Doctoral, s’han caracteritzat funcionalment diferents regions reguladores descrites a nivell bioinformàtic, així com també s’ha analitzat la seva implicació fisiológica a la funció d’USP25m. A més a més, mitjançant un estudi de cerca de nous interactors proteics, s’ha trobat una nova molècula que pertany a la mateixa via senyalitzadora i que es relaciona de manera específica amb USP25m, la lligasa d’ubiquititna MKRN1 (makorin 1) Mitjançant l’ús de diferents construccions amb delecions i mutacions puntuals de la proteïna que afecten a les regions d’interès, s’ha arribat a diferents conclusions, entre elles, que USP25m és monoubiquitinat i té la capacitat d’autodeubiquitinar-se. La monoubiquitinació en regula la seva activitat enzimàtica i es proposa un mecanisme de regulació basat en la conjugació alternativa de SUMO (una altra molècula de la família de la ubiquitina) i ubiquitina, en el mateix residu aminoacídic, la lisina 99 (Lys99). Els dominis d’unió a ubiquitina regulen el reconeixement de substrat i afavoreixen la monoubiquitinació. USP25m oligomeritza dins la cèl·lula i es troba present en diferents formacions proteiques d’elevat pes molecular. S’ha comprovat la relació específica amb la nova lligasa MKRN1 i es suggereixen diferents escenaris moleculars on poden trobar-se inclosos els dos pèptids.[eng] The main aim of the present PhD work, titled “Structural domains and new protein interactions of the deubiquitinating enzyme USP25”, is the functional characterisation of the structural domains of the muscle isoform of USP25, USP25m, as well as the analysis of new protein‐protein interactions. The ubiquitin‐proteasome pathway is widely known as the preferential system to get ride of old or non‐functional proteins. Recently, it has become more apparent that this is not the only function. Ubiquitin (Ub) and all ubiquitin–like (UbLs) molecules acted as regulatory tags involved in different cellular events as subcellular localization, enzyme activation, DNA repair, etc. The intricate Ub‐signalling networks require a tight regulation of both conjugation and deconjugationprocesses, which are controlled by ubiquitin ligases and deubiquitinating enzymes (DUBs), respectively. USP25 is a DUB described while looking for novel genes involved in Down syndrome phenotype. First studies showed that it encoded three alternative protein isoforms, one of them, muscle specific. This muscle isoform, USP25m, is a cytosolic protein, upregulated during myogenesis that interacts in a specific manner with different sarcomeric proteins. Using an “in silico” approach, we were able to identify different structural domains, among them three ubiquitin binding domains (UBDs), and we aimed to characterise its role on USP25m function. By generating a collection of deletion and punctual mutants of the regions of interest, we conclude that USP25m is monoubiquitinated and that the UBDs modulate this modification. The preferential site for monoubiquitination is lysine 99 (K99), a residue that has been reported to undergo sumoylation (SUMO conjugation, being SUMO an UbL). According to our results, mutation of the K99 residue diminishes the deubiquitinating function, proposing a mechanistic model for USP25m regulation based on alternative conjugation of Ub and SUMO on the same residue, K99. Futhermore, while seeking new protein interactions of USP25m we identified Makorin Ring finger protein 1 (MKRN1), which belongs to an ubiquitin ligase family, as a putative interactor. We were capable of characterise its interaction and propose different cellular scenarios were they could interact
Measurement of the diffractive cross section in deep inelastic scattering using ZEUS 1994 data
No full textThe DIS diffractive cross section, d sigma(gamma*p-->XN)(diff)/dM(X), has been measured in the mass range M(X) XN)(diff) (M(X), W, Q(2))/dM(X) proportional to W(adiff) with a(diff) = 0.507 +/- 0.034(stat)(-0.046)(+0.155) (syst) corresponding to a t-averaged pomeron trajectory of (P) = 1.127 +/- 0.009(stat)(-0.012)(+0.039) (syst) which is larger than (P) observed in hadron-hadron scattering The W dependence of the diffractive cross section is found to be the same as that of the total cross section for scattering of virtual photons on protons. The data are consistent with the assumption that the diffractive structure function F(2)(D(3)) factorizes according to x(P)F(2)(D(3))(x(p), beta, Q(2)) = (x(0)/x(P))(n)F(2)(D(2)) (beta, Q(2)). They are also consistent with QCD based models which incorporate factorization breaking. The rise of x(P)F(2)(D(3)) with decreasing x(P) and the weak dependence of F(2)(D(2)) On Q(2) suggest a substantial contribution from partonic interactions
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