On the cohomological equation for nilflows

Let X be a vector field on a compact connected manifold M. An important question in dynamical systems is to know when a function g:M -> R is a coboundary for the flow generated by X, i.e. when there exists a function f: M->R such that Xf=g. In this article we investigate this question for nilflows on nilmanifolds. We show that there exists countably many independent Schwartz distributions D_n such that any sufficiently smooth function g is a coboundary iff it belongs to the kernel of all the distributions D_n.Comment: 27 page

Invariant Distributions for homogeneous flows

We prove that every homogeneous flow on a finite-volume homogeneous manifold has countably many independent invariant distributions unless it is conjugate to a linear flow on a torus. We also prove that the same conclusion holds for every affine transformation of a homogenous space which is not conjugate to a toral translation. As a part of the proof, we have that any smooth partially hyperbolic flow on any compact manifold has countably many distinct minimal sets, hence countably many distinct ergodic probability measures. As a consequence, the Katok and Greenfield-Wallach conjectures hold in all of the above cases.Comment: 43 page

Ad illustriss. et reuerendiss. dominum d. Odoardum Farnesium s.r.e. cardinalem amplissimum. Ioannis Flaminii cler. Namurcen. carmen natalitium

[8! c. ; 4º Arma del cardinal Farnese incisa sul front Segn.: [A!-B⁴ La c. B4v e' bianca

Plant-syrphid interactions in an urban farm matrix

Insect biodiversity is being lost at a staggering rate. One of the largest contributors of global insects declines is urban development and expansion (Maxwell et al., 2020). This is because natural and semi-natural landscapes are converted into areas dominated by built features and impervious ground cover, leading to habitat loss and degradation and ultimately, insect and pollinator extinction or replacement (McKinney, 2006). Urban agricultural sites are a growing component of cities to improve food security and reintroduce ‘green spaces’ that could potentially revitalise dull city centres that are otherwise depauperate in vegetation and biodiversity. However, it is still unclear how urban agriculture contributes to biodiversity and whether it beneficially impacts pollinator communities

Evaluation of performance at experimental buildings and real demonstration sites in BFIRST project: Theoretical and practical aspects for BIPV monitoring system

Monitoring is one of the main activity of BFIRST, Building-integrated FIbre-Reinforced Solar Technology, project, a 5 years funded European project, project reference number 29601, that started in April 2102 and deals with the design, development and demonstration of a portfolio of innovative photovoltaic products for building integration, based on cell encapsulation within fibre-reinforced composite materials. Automatic data acquisition systems are generally required for monitoring, performance evaluation and exchanging data of PV systems. Standard IEC 61724:1998 “Photovoltaic system performance monitoring –Guidelines for measurement, data exchange and analysis” provides a guideline that shall be followed in these cases. As far as Building Integrated Photovoltaics (BIPV) are considered, besides electrical parameters there is in addition the need to monitor the specific building performances. That is because a BIPV module operates as a multi-functional building construction material; it generates energy and serves as part of the building envelope. Since the building related performances are not included in the aforementioned IEC standard, a general guideline for monitoring was prepared within the project that has been used within the project at two levels: one at experimental sites mainly related to experimental single module testing and the other at demosite with real PV size plants

First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto- noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far

Low loss coatings for the VIRGO large mirrors

présentée par L. PinardThe goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances. Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization). The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performances, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction)

The Virgo 3 km interferometer for gravitational wave detection

Virgo, designed, constructed and developed by the French-Italian VIRGO collaboration located in Cascina (Pisa, Italy) and aiming to detect gravitational waves, is a ground-based power recycled Michelson interferometer, with 3 km long suspended Fabry-Perot cavities. The first Virgo scientific data-taking started in mid-May 2007, in coincidence with the corresponding LIGO detectors. The optical scheme of the interferometer and the various optical techniques used in the experiment, such as the laser source, control, alignment, stabilization and detection strategies are outlined. The future upgrades that are planned for Virgo from the optical point of view, especially concerning the evolution of the Virgo laser, are presented. Finally, the next generation of the gravitational wave detector (advanced Virgo) is introduced from the point of view of the laser system