653 research outputs found
VALUTAZIONE DELLE PROPRIETA’ MECCANICHE NEI MATERIALI IN ESERCIZIO CON PROVE DI LABORATORIO: LA FATICA TERMOMECCANICA
Le turbine a gas lavorano in condizioni operative estreme di temperatura e pressione per ottenere le massime prestazioni dell’impianto energetico. Tali requisiti possono risultare al limite delle condizioni di progettazione delle pale, dei cuscinetti e dei numerosi componenti presenti nella camera di combustione. Di conseguenza la loro vita in esercizio può risultare limitata, come verosimilmente risulta dalla frequenza delle fratture che tali componenti presentano rispetto alla minore incidenza verificabile in altre parti dell’impianto. I difetti, che insorgono in corrispondenza dello stadio delle pale della turbina esposto alla maggiore temperatura e pressione di lavoro, risultano attribuibili ai fenomeni di creep, di ossidazione e di danneggiamento per fatica. Inoltre non è ancora del tutto chiaro se queste azioni di danneggiamento agiscono in modo simultaneo o se alcune di esse risultano predominanti (come, quando e perché) rispetto ad altre che divengono meno influenti nel corso del danneggiamento per fatica termomeccanica (TMF). I materiali svolgono il ruolo fondamentale per l’incremento della vita in esercizio degli impianti. A tale proposito la via dell’innovazione è stata intrapresa con lo sviluppo di superleghe a base nickel ottenute per solidificazione direzionale (DS) o monocristalline (SX) e con l’impiego di rivestimenti ceramici che fanno da scudo termico al materiale sottoposto alle temperature preservando le superfici esposte dei componenti dall’ossidazione a caldo. Essi consentono di aumentare la temperatura di funzionamento degli impianti e, conseguentemente, di aumentarne il rendimento. Il vantaggio ottenuto dallo sviluppo dei nuovi materiali e dei rivestimenti va attentamente valutato mediante la messa a punto di nuove tecniche diagnostiche simulanti le condizioni di lavoro dei componenti e, in tale ambito, la fatica termomeccanica (TMF) ha dimostrato di essere un ottimo strumento diagnostico complementare di quello della fatica LCF, sinora più diffuso. Nella memoria sono descritte le procedure per l’esecuzione di prove TMF ed alcuni esempi di confronto tra TMF ed LCF per alcuni materiali innovativi impiegati in componenti turbogas
Search for dark Higgsstrahlung in e+ e- -> mu+ mu- and missing energy events with the KLOE experiment
We searched for evidence of a Higgsstrahlung process in a secluded sector,
leading to a final state with a dark photon U and a dark Higgs boson h', with
the KLOE detector at DAFNE. We investigated the case of h' lighter than U, with
U decaying into a muon pair and h' producing a missing energy signature. We
found no evidence of the process and set upper limits to its parameters in the
range 2m_mu<m_U<1000 MeV, m_h'<m_U.Comment: 16 pages, 7 figures, submitted to Physics Letters
Limit on the production of a new vector boson in , U with the KLOE experiment
The recent interest in a light gauge boson in the framework of an extra U(1)
symmetry motivates searches in the mass range below 1 GeV.
We present a search for such a particle, the dark photon, in , U based on 28 million
events collected at DANE
by the KLOE experiment. The production by initial-state radiation
compensates for a loss of sensitivity of previous KLOE , searches due to the small branching ratios in
the resonance region. We found no evidence for a signal and set a
limit at 90\% CL on the mixing strength between the photon and the dark photon,
, in the U mass range between and ~MeV. Above 700 MeV
this new limit is more stringent than previous ones.Comment: 6 pages, 9 figures, 1 table, submitted to Phys. Lett.
Measurement of the transition form factor with the KLOE detector
A measurement of the vector to pseudoscalar conversion decay with the KLOE experiment is presented. A sample of signal
events was selected from a data set of 1.7 fb of collisions at
collected at the DANE collider. These
events were used to obtain the first measurement of the transition form factor
and a new measurement of the branching ratio of the
decay: . The result improves
significantly on previous measurements and is in agreement with theoretical
predictions.Comment: 13 pages, 4 figures; matches published versio
Precision measurement of and determination of the contribution to the muon anomaly with the KLOE detector
We have measured the ratio
, with the KLOE detector at DANE for a total integrated
luminosity of 240 pb. From this ratio we obtain the cross section
. From the cross section we determine the
pion form factor and the two-pion contribution to the muon anomaly
for GeV, = . This result confirms the
current discrepancy between the Standard Model calculation and the experimental
measurement of the muon anomaly.Comment: 18 pages, 8 figures, minor text corrections, one table added, version
to appear on Physics Letters
Precision measurement of the Dalitz plot distribution with the KLOE detector
Using fb of data collected with
the KLOE detector at DANE, the Dalitz plot distribution for the decay is studied with the world's largest sample of events. The Dalitz plot density is parametrized as a polynomial
expansion up to cubic terms in the normalized dimensionless variables and
. The experiment is sensitive to all charge conjugation conserving terms of
the expansion, including a term. The statistical uncertainty of all
parameters is improved by a factor two with respect to earlier measurements.Comment: 11 pages, 9 figures, supplement: an ascii tabl
The Knee of the Cosmic Hydrogen and Helium Spectrum below 1 PeV Measured by ARGO-YBJ and a Cherenkov Telescope of LHAASO
The measurement of cosmic ray energy spectra, in particular for individual
species, is an essential approach in finding their origin. Locating the "knees"
of the spectra is an important part of the approach and has yet to be achieved.
Here we report a measurement of the mixed Hydrogen and Helium spectrum using
the combination of the ARGO-YBJ experiment and of a prototype Cherenkov
telescope for the LHAASO experiment. A knee feature at 640+/-87 TeV, with a
clear steepening of the spectrum, is observed. This gives fundamental inputs to
galactic cosmic ray acceleration models
Study of the diffuse gamma-ray emission from the Galactic plane with ARGO-YBJ
The events recorded by ARGO-YBJ in more than five years of data collection
have been analyzed to determine the diffuse gamma-ray emission in the Galactic
plane at Galactic longitudes 25{\deg} < l < 100{\deg} and Galactic latitudes .
The energy range covered by this analysis, from ~350 GeV to ~2 TeV, allows the
connection of the region explored by Fermi with the multi-TeV measurements
carried out by Milagro. Our analysis has been focused on two selected regions
of the Galactic plane, i.e., 40{\deg} < l < 100{\deg} and 65{\deg} < l <
85{\deg} (the Cygnus region), where Milagro observed an excess with respect to
the predictions of current models. Great care has been taken in order to mask
the most intense gamma-ray sources, including the TeV counterpart of the Cygnus
cocoon recently identified by ARGO-YBJ, and to remove residual contributions.
The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding
to the excess found by Milagro, and are consistent with the predictions of the
Fermi model for the diffuse Galactic emission. From the measured energy
distribution we derive spectral indices and the differential flux at 1 TeV of
the diffuse gamma-ray emission in the sky regions investigated.Comment: 11 pages, 6 figures, published in AP
KLOE results in kaon physics and prospects for KLOE-2
The phi-factory DAPHNE offers a possibility to select pure kaon beams,
charged and neutral ones. In particular, neutral kaons from phi->KS KL are
produced in pairs and the detection of a KS (KL) tags the presence of a KL
(KS). This allows to perform precise measurements of kaon properties by means
of KLOE detector. Another advantage of a phi-factory consists in fact that the
neutral kaon pairs are produced in a pure quantum state (J^(PC) = 1^(--)),
which allowsto investigate CP and CPT symmetries via quantum interference
effects, as well as the basic principles of quantum mechanics.A review of the
most recent results of the KLOE experiment at DAPHNE using pure kaon beams or
via quantum interferometry is presented together with prospects for kaon
physics at KLOE-2.Comment: 5 pages, 4 figures, From Phi To Psi 2011 conference, to be published
in Nuclear Physics B (Proceedings Supplements
Measurement of {\eta} meson production in {\gamma}{\gamma} interactions and {\Gamma}({\eta}-->{\gamma}{\gamma}) with the KLOE detector
We present a measurement of {\eta} meson production in photon-photon
interactions produced by electron-positron beams colliding with \sqrt{s}=1 GeV.
The measurement is done with the KLOE detector at the \phi-factory DA{\Phi}NE
with an integrated luminosity of 0.24 fb^{-1}. The e^+e^- --> e^+e^-{\eta}
cross section is measured without detecting the outgoing electron and positron,
selecting the decays {\eta}-->{\pi}^+{\pi}^-{\pi}^0 and
{\eta}-->{\pi}^0{\pi}^0{\pi}^0. The most relevant background is due to e^+e^-
--> {\eta}{\gamma} when the monochromatic photon escapes detection. The cross
section for this process is measured as {\sigma}(e^+e^- -->{\eta}{\gamma}) =
(856 \pm 8_{stat} \pm 16_{syst}) pb. The combined result for the e^+e^-
-->e^+e^-{\eta} cross section is {\sigma}(e^+e^- -->e^+e^-{\eta}) = (32.72 \pm
1.27_{stat} \pm 0.70_{syst}) pb. From this we derive the partial width
{\Gamma}({\eta}-->{\gamma}{\gamma}) = (520 \pm 20_{stat} \pm 13_{syst}) eV.
This is in agreement with the world average and is the most precise measurement
to date.Comment: Version accepted by JHE
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