1,355,688 research outputs found
Active feedback cooling of a SiN membrane resonator by electrostatic actuation
No full textFeedback-based control techniques are useful tools in precision measurements as they allow us to actively shape the mechanical response of high quality factor oscillators used in force detection measurements. In this paper, we implement a feedback technique on a high-stress low-loss SiN membrane resonator, exploiting the charges trapped on the dielectric membrane. A properly delayed feedback force (dissipative feedback) enables the narrowing of the thermomechanical displacement variance in a similar manner to the cooling of the normal mechanical mode down to an effective temperature Teff. In the experiment reported here, we started from room temperature and gradually increasing the feedback gain, we were able to cool down the first normal mode of the resonator to a minimum temperature of about 124mK. This limit is imposed by our experimental setup and, in particular, by the injection of the read-out noise into the feedback. We discuss the implementation details and possible improvements to the technique.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and MaterialsEKL Equipmen
Component separation for all-sky CMB temperature maps
No full textThe work described in this Thesis is related to the PLANCK mission, scheduled for launch in 2008, which will observe the microwave sky with unprecedent resolution and sensitivity. The PLANCK collaboration involves hundreds of scientists and profits from the contributions of research groups in many countries. Among them, an Italian collaboration has a key role on component separation. This is a crucial step of the data reduction process, aimed at disentangling the Cosmic Microwave Background (CMB) and all the astrophysical components which are mixed in the nine observational channels of PLANCK The most important diffuse components are, besides the CMB, synchrotron, free-free and thermal dust emissions due to our own Galaxy. Moreover, the PLANCK maps will contain radio and infrared extragalactic sources as well as the Sunyaev-Zel'dovich effects from clusters of galaxies. All the components which mix with the CMB are referred to as ``foregrounds'', as they are placed between the CMB and the observer.
The main goal of component separation is to provide a map of the CMB, from which the relevant cosmological information will be derived, clean from foreground contamination. On the other hand, maps of astrophysical components are of great interest per se. The accuracy of the component separation process will ultimately set that of the final results PLANCK will provide.
Our work was mainly focused on the development and testing of a new method for the separation of diffuse foregrounds, the Correlated Component Analysis (CCA), proposed by Bedini et al. (2005). This technique exploits second-order statistics to estimate the ``mixing matrix'', which contains the frequency behavior of the components mixed in the data. It is necessary to adopt a model for such components, i.e. to parametrize their frequency scaling in a suitable way. Our approach is to estimate the mixing matrix separately in different regions of the sky, where the spectral dependencies of foregrounds can be assumed to be constant.
Once the mixing matrix is known, several methods are available to perform component separation, such as Wiener Filtering (WF), Maximum Entropy Method (MEM) or other Bayesian inversion techniques.
After having suitably implemented the CCA method, we tested its performances on simulated PLANCK data.
In Bonaldi et al. (2006) we applied the method to different sets of simulated PLANCK channels and estimated the errors on the mixing matrix with a Monte Carlo approach. The simulations included realistic diffuse foregrounds, with spatially varying spectral properties, and Gaussian noise at the nominal level for the PLANCK satellite.
This test showed that the method is efficient and that the errors on the mixing matrix estimation produce a minor contribution to the errors on the CMB power spectrum.
We then partecipated in a blind comparative test of component separation methods coordinated by the PLANCK working group on ``component separation''.
The test used a more sophisticated simulation of PLANCK data, which included, besides diffuse foreground emissions, also point sources and extragalactic background and a more realistic treatment of the noise. On these data, we tested CCA combined with harmonic Wiener Filtering. We focused on the reconstruction of the CMB map and on the power spectrum estimation, and obtained in both cases very good results, highly competitive with those provided with the best methods developed so far. We also got satisfactory reconstructions of Galactic dust emission, which is the dominant foreground in the highest resolution (high frequency) PLANCK channels.
In Bonaldi et al. (2007b) we tested the same strategy on real data i.e. the first three years of WMAP data. Our results are generally compatible with the result published by the WMAP team. We investigated the presence in the data of the so-called "microwave anomalous emission", an additional foreground component which could dominate in the lowest frequency WMAP channel (23 GHz). This component, revealed by cross correlations of microwave data with IR maps, appears to be correlated with thermal dust emission and has been interpreted as emission due to spinning dust grains (Draine & Lazarian 1998) or, alternatively, as synchrotron emission from dusty active star-forming regions (Hinshaw et al. 2006). We adopted various models for the frequency scaling of such component, whose properties are still poorly known.
We then applied several quality tests to the maps reconstructed for each model and selected a subset of models having a good compatibility with the data. We also managed to get the first, albeit preliminary, template of the anomalous emission over about 90% of the sky.
We then estimated how our imperfect knowledge of the foreground components affects the CMB power spectrum. To this end we compared the CMB power spectra obtained adopting different foreground models that passed our quality tests. A significant spread has been found for the largest scales, where anomalies of the WMAP power spectrum compared to the expectations from the best fit cosmological model have been reported. Taking into account modelization errors, we find no large scale power spectrum anomalies significant at > 1.5 sigma, except for the excess power at l=40,
which is significant at around the 4 sigma level.
A minor part of this Thesis was devoted to the study of the Sunyaev-Zel'dovich (SZ) effect, due to inverse Compton scattering of CMB photons by hot electrons in the astrophysical plasmas bound to the cosmic structures. PLANCK is expected to provide a big sample of galaxy clusters observed through the SZ effect. One exploitation of the PLANCK cluster sample is related to the study of the physics of the intra-cluster (IC) gas. In Bonaldi et al. (2007a) we investigated
the observable effects of different modeling of the physics of the IC gas.
Another research field related to the SZ effect concerns the study of the Large Scale Structure of the Universe. In Dolag et al. (2006) we analysed the SZ emission due to the so-called cosmic web, the network of filamentary structures which is now believed to connect galaxy clusters. The signal is too weak to be detected but its presence may bias the observed properties of galaxy clusters both in the X-ray band and in the microwaves
Beneficial plant-microbe interactions in agriculture: reducing lettuce basal drop by application of rhizosphere competent Streptomyces
No full textYield losses caused by phytopathogens are major challenges to agriculture all over the world. Biological control based on plant-microbe interactions provides economically viable, environmentally sound, and socially responsible plant protection strategies. The ability of microorganisms to suppress plant pathogens and to interact with their host are fundamental prerequisites of microbial assisted plant protection. Two Streptomyces strains isolated from surface sterile crop roots, Streptomyces exfoliatus FT05W and Streptomyces cyaneus ZEA17I, showed up to 75% in vitro mycelial growth inhibition of Sclerotinia sclerotiorum, the causal agent of lettuce drop (Sardi et al. 1992; Chen et al. in press). We labeled them with the enhanced green fluorescent protein (EGFP) marker to investigate Streptomyces’ ability to colonize the lettuce root system using confocal laser scanning microscopy (CLSM) (Bonaldi et al. 2015; Erlacher et al. 2015). The well-colonized lettuce seedlings by both strains showed Streptomyces’ capability to interact with the host from early stages of seed germination and root development. We also observed colonization by EGFP-labeled Streptomyces on two-week-old roots. Additionally, we quantified S. exfoliatus FT05W and S. cyaneus ZEA17I viability and persistence in the rhizosphere and surface sterilized lettuce root tissues. After six weeks of plant growth, we recovered 2 x 104 CFU/g dry weight (DW) from the rhizosphere and 2 x 105 CFU/g DW from the inner root tissues. Moreover, we studied the biological activity of the two strains against S. sclerotiorum in vivo. When they were applied to S. sclerotiorum inoculated substrate in growth chamber, S. exfoliatus FT05W and S. cyaneus ZEA17I reduced disease incidence significantly by 40% and 50%, respectively, compared to the control (P < 0.05). Differently, under field conditions, S. exfoliatus FT05W reduced disease incidence by 54% (P = 0.12), but we did not observe protection of lettuce plants against S. sclerotiorum by S. cyaneus ZEA17I. Further studies on the complex host-pathogen-antagonist interactions will provide additional knowledge to understand the modes of Streptomyces acting as promising biological control agents
Detection of weak stochastic forces in a parametrically stabilized micro-optomechanical system
No full textMeasuring a weak force is an important task for micromechanical systems, both when using devices as sensitive detectors and, particularly, in experiments of quantum mechanics. The optimal strategy for resolving a weak stochastic signal force on a huge background (typically given by thermal noise) is a crucial and debated topic, and the stability of the mechanical resonance is a further, related critical issue. We introduce and analyze the parametric control of the optical spring, which allows us to stabilize the resonance and provides a phase reference for the oscillator motion, yet conserving a free evolution in one quadrature of the phase space. We also study quantitatively the characteristics of our micro-optomechanical system as detector of stochastic force for short measurement times (for quick, high-resolution monitoring) as well as for the longer-term observations that optimize the sensitivity. We compare a simple strategy based on the evaluation of the variance of the displacement which is a widely used technique) with an optimal Wiener-Kolmogorov data analysis. We show that, due to the parametric stabilization of the effective susceptibility, we can more efficiently implement Wiener filtering, and we investigate how this strategy improves the performance of our system. We finally demonstrate the possibility to resolve stochastic force variations well below 1% of the thermal noise.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
«Essere già oltre il domani» : caratteri e dinamiche del successo imprenditoriale di Lorenzo Bonaldi
No full textIl contributo ricostruisce la biografia imprenditoriale di Lorenzo Bonaldi (1915-2001) basandosi sia sui documenti acrhivistici della famiglia che sulle testimonianza orali di chi ha lavorato con lui. Ne emerge un'esistenza di un uomo che ha attraversato il Novecento da cima a fondo, sino all’alba del nuovo millennio. Nel 2000 festeggiava i 65 anni da imprenditore con il record assoluto di vendite di automibili (5704 veicoli) e un utile d’esercizio di quasi un miliardo e 400 milioni di lire. Di lì a poco si sarebbe conclusa l’avventura terrena del ragazzo venuto da Serina e fattosi da solo, animato dalla voglia di fare, da un sapere tecnico e dalla curiosità per tutto ciò che era la meccanica. Nell’Italia devastata dalla guerra e in cerca di riscatto, Bonaldi non sapeva ancora che sarebbe diventato il signor Volkswagen, ma era consapevole di essere già oltre il domani. Quella sua frase, ricordata da un collaboratore, è la felice sintesi di una esistenza e il segreto di una buona riuscita: si considerava in prestito al presente e la sua prospettiva era quella di andare oltre il quotidiano e il contingente, di traguardo in traguardo. Nel suo intimo resisteva l’eco di quel che di lui, fresco sposo, diceva la moglie, Carla Comana: "Era pieno di avvenire e il futuro gli doveva apparire come una specie di risarcimento". Quel suo essere oltre il domani è il concetto che sorregge la struttura del volume e infatti sta nel titolo, perché riassume il modello Bonaldi: crescita, innovazione, investimenti, quindi leadership, solidità finanziaria, longevità dell’azienda. Passando dalla ricostruzione postbellica al miracolo economico, dai due chock petroliferi degli anni ’70, al rilancio degli anni ’80 e alle difficoltà dei primi anni ’90 in un settore quello delle auto che, peraltro, ha i vincoli dei cicli incerti della geopolitica internazionale e dei mutamenti negli stili di vita. Prima le moto e poi le auto: non le auto estere in un mercato egemonizzato dalle case italiane, ma le auto straniere come si diceva con un termine negativo, con una lontananza da mantenere tale, in quella Italia ancora protezionistica. C’è stato un tempo in cui Bonaldi avrebbe potuto fare una scelta diversa, cambiare casa automobilistica in termini competitivi. Non ha fatto conti economici, ma ha soltanto ringraziato declinando l’offerta: e qui s’è rivisto il ragazzo di Serina dei primi passi, riconoscente verso chi lo aveva aiutato, e il saldarsi di tanti sentimenti, di una sinergia vissuta sulla reciproca stima. Proprio la leadership conquistata sul campo ha consentito all’imprenditore di dare identità e cittadinanza al settore delle vendite dell’auto, di definirlo nelle sue competenze e nella sua autonomia, portandolo così dentro i processi di modernizzazione dell’economia bergamasca. Bonaldi è stato molte cose: imprenditore agricolo, mecenate dell’arte, presidente di una scuola materna e di diverse società sportive, fra le quali la squadra di pallacanestro dell’Alpe. Territorio e comunità. Rappresentando in questo modo, e qui concludo, i tanti volti di una storia d’impresa e di un vissuto civile tutti bergamaschi: anzi, tipicamente bergamaschi
Frequency-noise cancellation in optomechanical systems for ponderomotive squeezing
No full textPonderomotive squeezing of the output light of an optical cavity has been recently observed in the megahertz range in two different cavity optomechanical devices. Quadrature squeezing becomes particularly useful at lower spectral frequencies, for example, in gravitational wave interferometers, despite being more sensitive to excess phase and frequency noise. Here we show a phase and frequency-noise cancellation mechanism due to destructive interference which can facilitate the production of ponderomotive squeezing in the kilohertz range and we demonstrate it experimentally in an optomechanical system formed by a Fabry-P´erot cavity with a micromechanical mirror.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Madonna col Bambino in trono e santi, detta Pala Bonaldi
No full textLa scheda analizza una delle più ammirate opere dipinte da Paolo Veronese, la pala Bonaldi, realizzata per l'altare della sagrestia della chiesa conventuale di San Zaccaria, a Venezia, investigandone la committenza e i riferimenti visivi
Improved bottom-up strategy to efficiently separate hypermodified histone eptides through ultra-HPLC separation on a bench top Orbitrap instrument
No full textHistone post-translational modifications (hPTMs) play a crucial role in modulating chromatin structure and enforcing specific functional states on the underlying genome. Through the design of ad hoc analytical methods, MS has contributed significantly in the dissection of hPTMs, exhibiting specific strengths in identifying novel marks and assessing their combinatorial interplay. However, the comprehensive analysis of all individual isoforms of some hypermodified histone regions remains highly challenging with conventional proteomics platforms. Since complex hPTM patterns have unique functional outcomes on the genes, the implementation of new MS-proteomics solutions can boost epigenetic research. Here, we assessed the effectiveness of a new analytical platform-which combines ultra high-performance LC (UHPLC) with high-resolutionMS/MS analysis-in dissecting hypermodified regions from macrophage core histones. We compared the resolving power of this configuration with a standard setup based on HPLC-MS/MS and focused on two case-study peptides, H3 (27-40) and H4 (4-17). We observed that the novel platform resolves a much larger set of distinct peptide isoforms; among them some were resolved for the first time. A comprehensive analysis of hPTMs from macrophages was then carried out at basal state and upon lipopolysaccharide induction, to profile their temporal change in bulk chromatin during the inflammatory response
EoR imaging with the SKA: the challenge of foreground removal
No full textAbstract21-cm observations of the Cosmic dawn (CD) and Epoch of Reionization (EoR) are one of the high priority science objectives for SKA Low. One of the most difficult aspects of the 21-cm measurement is the presence of foreground emission, due to our Galaxy and extragalactic sources, which is about four orders of magnitude brighter than the cosmological signal. While end-to-end simulations are being produced to investigate in details the foreground subtraction strategy, it is useful to complement this thorough but time-consuming approach with simpler, quicker ways to evaluate performance and identify possible critical steps. In this work, I present a forecast method, based on Bonaldi et al. (2015), Bonaldi & Ricciardi (2011), to understand the level of residual contamination after a component separation step, and its impact on our ability to investigate CD and EoR.</jats:p
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