Optical Fibres Contactless Sensor for Dynamic Testing of Lightweight Structures

With dynamic testing, engineers describe activities focused on the identification of some properties of vibrating structures. This step requires for the measurements of excitations and responses signals, applying appropriate sensors directly on the test article. These instruments modify the system's mass and stiffness distributions and eventually the eigen-properties of the structure. These errors become unacceptable especially when testing lightweight structures. This paper shows the results of some tests performed on a small compressor with the purpose of identifying the blades' natural frequencies and modes. It compares the acquisitions performed with standard accelerometers and two different contact-less systems using as exciters either a micro-hammer or a micro inertial shaker. The paper shows how the contact-less sensors provide good quality data and consistent results in the mode identification phase

Acoustic comfort depends on the psychological state of the individual

Recent studies have shown that comfort can be influenced more by psychological processes than from the characteristics of environmental stimulation. This is relevant for different industrial sectors, where comfort is defined only as a function of the intensity of external stimuli. In the present study, we measured physiological and psychological comfort during the exposure to four levels of acoustic noise [from 45 to 55 dB(A)] corresponding to different comfort classes inside a full-scale mock-up of a cruise ship cabin. We found an increase of psychological and physiological discomfort for higher noise intensities, but not for all the intensities defining the comfort classes. Furthermore, we found that negative psychological states determine a lower physiological sensitivity to acoustic noise variations compared to positive states. Our results show that, at normal/low intensities, psychological processes have a greater role in determining acoustic comfort when compared to the stimulus intensity. Practitioner Summary: This study shows that psychological factors can be more relevant in determining acoustic comfort inside a ship cabin than the intensity of acoustic stimulus itself. This finding suggests that the cruise industry should consider not only the engineering measurements when evaluating comfort on board, but also the passenger\u2019 psychological state. Abbreviations: AIC: akaike information criterion; CCT: colour correlated temperature; cd/m2: candela/square meters; df: degrees of freedom; F-test: Fisher's test; HF: high frequency; HR: heart rate; HRV: heart rate variability; HSV: hue saturation value; K: kelvin; LF: low frequency; LF/HF: low frequency to high frequency ratio; lme: linear mixed effects; ms: milliseconds; nu: normalized unit; p: p value; pNN50: percentage of adjacent pairs of normal to normal RR intervals differing by more than 50 milliseconds; r2: coefficient of determination; rc: concordance correlation coefficient; RMSSD: square root of the mean normal to normal RR interval; SD: standard deviation; SDNN: standard deviation of normal to normal RR intervals; SEM: standard error of the mean; t-test: student's tests; \u3c72: chi-square test

The DEAR experiment on DAΦNE

DEAR is one of the first experiments at the new DAΦNE Ø-factory at the Laboratori Nazionali di Frascati dell'INFN. The objective of the DEAR experiment is to perform a precision measurement of the strong interaction shifts and widths of the K-series lines in kaonic hydrogen and the first observation of the same quantities in kaonic deuterium. The aim is to obtain a precise determination of the isospin-dependent kaon-nucleon scattering lengths which will represent a breakthrough in KN low-energy phenomenology and will allow us to determine the kaon-nucleon sigma terms. The sigma terms give a direct measurement of chiral symmetry breaking and are connected to the strangeness content of the proton. First results on background measurements with the DEAR NTP setup installed on DAΦNE are reported

Σ−p\Sigma^- p emission rates in K−K^- absorptions at rest on 6^6Li, 7^7Li, 9^{9}Be, 13^{13}C and 16^{16}O

An experimental study of the $K^-_{stop}A\rightarrow \Sigma^- p A'$ reaction on $A=^6$Li, $^7$Li, $^9$Be, $^{13}$C and $^{16}$O $p$-shell nuclei is presented. The data were collected by the FINUDA spectrometer operating at the DA$\Phi$NE $\phi$-factory (LNF-INFN, Italy). Emission rates for the reaction in the mentioned nuclei are measured and compared with the few existing data. The spectra of several observables are discussed; indications of Quasi-Free absorptions by a $(np)$ pair embedded in the $A$ nucleus can be obtained from the study of the missing mass distributions.Comment: Version accepted by PR

Proton spectra from Non-Mesonic Weak Decay of p-shell Lambda-Hypernuclei and evidence for the two-nucleon induced process

New spectra from the FINUDA experiment of the Non Mesonic Weak Decay (NMWD) proton kinetic energy for 9(Lambda)Be, 11(Lambda)B, 12(Lambda)C, 13(Lambda)C, 15 (Lambda)N and 16(Lambda)O are presented and discussed along with the published data on 5(Lambda)He and 7(Lambda)Li. Exploiting the large mass number range and the low energy threshold (15 MeV) for the proton detection of FINUDA, an evaluation of both Final State Interactions (FSI) and the two nucleon induced NMWD contributions to the decay process has been done. Based on this evaluation, a linear dependence of FSI on the hypernuclear mass number A is found and for the two nucleon stimulated decay rate the experimental value of Gamma2/Gammap=0.43+-0.25 is determined for the first time. A value for the two nucleon stimulated decay rate to the total decay rate Gamma2/GammaNMWD=0.24+-0.10 is also extracted.Comment: 11 pages and 2 figure

A study of the proton spectra following the capture of K−K^- in 6^6Li and 12^{12}C with FINUDA

Momenta spectra of protons emitted following the capture of $K^-$ in $^6$Li and $^{12}$C have been measured with 1% resolution. The $^{12}$C spectrum is smooth whereas for $^6$Li a well defined peak appears at about 500 MeV/$c$. The first observation of a structure in this region was identified as a strange tribaryon or, possibly, a $\bar K$-nuclear state. The peak is correlated with a $\pi^-$ coming from $\Sigma^-$ decay in flight, selected by setting momenta larger than 275 MeV/$c$. The $\Sigma^-$ could be produced, together with a 500 MeV/$c$ proton, by the capture of a $K^-$ in a deuteron-cluster substructure of the $^6$Li nucleus. The capture rate for such a reaction is (1.62\pm 0.23_{stat} ^{+0.71}_{-0.44}(sys))%/K^-_{stop}, in agreement with the existing observations on $^4$He targets and with the hypothesis that the $^6$Li nucleus can be interpreted as a $(d+\alpha)$ cluster.Comment: 21 pages, 10 figures. Accepted for publication in NP

Production of Λ6^{6}_{\Lambda}H and Λ7^{7}_{\Lambda}H with the (Kstop−^{-}_{stop},π+\pi^+) reaction

The production of neutron rich $\Lambda$-hypernuclei via the ($K^-_stop$,$\pi^+$) reaction has been studied using data collected with the FINUDA spectrometer at the DA$\Phi$NE $\phi$-factory (LNF). The analysis of the inclusive $\pi^+$ momentum spectra is presented and an upper limit for the production of $^6_\Lambda$H and $^7_\Lambda$H from $^6$Li and $^7$Li, is assessed for the first time.Comment: 11 pages, 3 figures. Accepted for publication in PL

Hypernuclear spectroscopy with K−^- at rest on 7^7Li, 9^9Be, 13^{13}C and 16^{16}O

The FINUDA experiment collected data to study the production of hypernuclei on different nuclear targets. The hypernucleus formation occurred through the strangeness-exchange reaction K^-_{stop} + \; ^AZ \rightarrow \; ^A_{\Lambda}Z + \pi^-. From the analysis of the momentum of the emerging $\pi^-$, binding energies and formation probabilities of $^7_{\Lambda}$Li, $^9_{\Lambda}$Be, $^{13}_{\Lambda}$C and $^{16}_{\Lambda}$O have been measured and are here presented. The behavior of the formation probability as a function of the atomic mass number A is also discussed.Comment: Accepted for publication in PL

Probing For New Physics and Detecting non linear vacuum QED effects using gravitational wave interferometer antennas

Low energy non linear QED effects in vacuum have been predicted since 1936 and have been subject of research for many decades. Two main schemes have been proposed for such a 'first' detection: measurements of ellipticity acquired by a linearly polarized beam of light passing through a magnetic field and direct light-light scattering. The study of the propagation of light through an external field can also be used to probe for new physics such as the existence of axion-like particles and millicharged particles. Their existence in nature would cause the index of refraction of vacuum to be different from unity in the presence of an external field and dependent of the polarization direction of the light propagating. The major achievement of reaching the project sensitivities in gravitational wave interferometers such as LIGO an VIRGO has opened the possibility of using such instruments for the detection of QED corrections in electrodynamics and for probing new physics at very low energies. In this paper we discuss the difference between direct birefringence measurements and index of refraction measurements. We propose an almost parasitic implementation of an external magnetic field along the arms of the VIRGO interferometer and discuss the advantage of this choice in comparison to a previously proposed configuration based on shorter prototype interferometers which we believe is inadequate. Considering the design sensitivity in the strain, for the near future VIRGO+ interferometer, of $h<2\cdot10^{-23} \frac{1}{\sqrt{\rm Hz}}$ in the range 40 Hz $- 400$ Hz leads to a variable dipole magnet configuration at a frequency above 20 Hz such that $B^{2}D \ge 13000$ T$^{2}$m/$\sqrt{\rm Hz}$ for a `first' vacuum non linear QED detection