433 research outputs found
Effect of interchain separation on the photoinduced absorption spectra of polycarbazolyldiacetylenes
The photoinduced absorption spectra of a novel polycarbazolyldiacetylene with long aliphatic chains on the carbazolyl side groups are measured and compared with those of the unsubstituted polyDCHD. The two polymers in the blue form exhibit very similar electronic absorption spectra and Raman frequencies. This fact indicates that the conjugation length of the polydiacetylene backbone is not too affected by the long substituents. In contrast, the near steady-state photoinduced absorption spectra show that different photogeneration mechanisms are involved in the two polymers. This result can be ascribed to the role played by the interchain distance in the dynamics of the relaxation processes in polydiacetylenes
Long-lived photoexcited states in polydiacetylenes with different molecular and supramolecular organization
With the aim of determining the importance of the molecular and supramolecular organization on the excited states of polydiacetylenes, we have studied the photoinduced absorption spectra of the red form of poly[1,6-bis(3,6-didodecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-S) and the results compared with those of the blue form of the same polymer. An interpretation of the data is given in terms of both the conjugation length and the interbackbone separation also in relation to the photoinduced absorption spectra of both blue and red forms of poly[1,6-bis(N-carbazolyl)-2,4-hexadiyne] (polyDCHD), which does not carry the alkyl substituents on the carbazolyl side groups. Information on the above properties is derived from the analysis of the absorption and Raman spectra of this class of polydiacetylenes
Monitoring water masers in star-forming regions
An overview is given of the analysis of more than a decade of H2O maser data
from our monitoring program. We find the maser emission to generally depend on
the luminosity of the YSO as well as on the geometry of the SFR. There appears
to be a threshold luminosity of a few times 10**4 Lsol above and below which we
find different maser characteristics.Comment: 9 pages, 1 table, 11 figures. Accepted for publ. in Ap&SpSci.
Refereed contribution to "Dense Molecular Gas around Protostars and in
Galactic Nuclei", European Workshop 2004 on Astronomical Molecules. Eds. Y.
Hagiwara, W.A. Baan, H.J. van Langeveld
Transmission curves and effective refraction indices of MKO near infrared consortium filters at cryogenic temperatures
We report transmission measurements at cryogenic temperatures for 4 broad-band filters of the Mauna Kea Observatories (MKO) near-infrared filter set and 5 narrow-band filters. The spectral scans were collected using the multi-mode IR instrument of the TNG telescope (NICS) in which these filters are permanently mounted and commonly used for astronomical observations. We determined the transmission curves at a temperature of 78K and found no significant red-leak up to 2.6 microns, the data are available in electronic form on the TNG web page. We also estimated the variation of the wavelength response with the incidence angle and found it compatible with an effective refractive index of about 2
A project for polarimetric observations in single dish with Medicina and Noto 32 m antennas
A project with multidisciplinary characteristics, aimed to implement the possibility of polarimetric measurements in single dish at the VLBI stations of Medicina and Noto, is presented. The project will open a new window on many
astrophysical items that may be approached using the already existing instrumentation and facilities of the two Italian radioastronomical stations. We report here some scientific backgrounds, together with some technical evaluations, on which the feasibility of the project is based
High refractive index inverse vulcanized polymers for organic photonic crystals
Photonic technologies are nowadays dominated by highly performing inorganic structures that are commonly fabricated via lithography or epitaxial growths. Unfortunately, the fabrication of these systems is costly, time consuming, and does not allow for the growth of large photonic structures. All-polymer photonic crystals could overcome this limitation thanks to easy solubility and melt processing. On the other hand, macromolecules often do not offer a dielectric contrast large enough to approach the performances of their inorganic counterparts. In this work, we demonstrate a new approach to achieve high dielectric contrast distributed Bragg reflectors with a photonic band gap that is tunable in a very broad spectral region. A highly transparent medium was developed through a blend of a commercial polymer with a high refractive index inverse vulcanized polymer that is rich in sulfur, where the large polarizability of the S–S bond provides refractive index values that are unconceivable with common non-conjugated polymers. This approach paves the way to the recycling of sulfur byproducts for new high added-value nanostructures
All-polymer methylammonium lead iodide perovskite microcavities
open8Thanks to a high photoluminescence quantum yield, large charge carrier diffusion, and ease of processing from solution, perovskite materials are becoming increasingly interesting for flexible optoelectronic devices. However, their deposition requires wide range solvents that are incompatible with many other flexible and solution-processable materials, including polymers. Here, we show that methylammonium lead iodide (MAPbI3) films can be directly synthesized on all-polymer microcavities via simple addition of a perfluorinated layer which protects the polymer photonic structure from the perovskite processing solvents. The new processing provides microcavities with a quality factor Q = 155, that is in agreement with calculations and the largest value reported so far for fully solution processed perovskite microcavities. Furthermore, the obtained microcavity shows strong spectral and angular redistribution of the the MAPbI3 photoluminescence spectrum, which shows a 3.5 fold enhanced intensity with respect to the detuned reference. The opportunity to control and modify the emission of a MAPbI3 film via a simple spun-cast polymer structure is of great interest in advanced optoelectronic applications requiring high colour purity or emission directionality.openLova, Paola; Giusto, Paolo; Di Stasio, Francesco; Manfredi, Giovanni; Paternò, Giuseppe M; Cortecchia, Daniele; Soci, Cesare; Comoretto, DavideLova, Paola; Giusto, Paolo; DI STASIO, Francesco; Manfredi, Giovanni; Paternò, Giuseppe M; Cortecchia, Daniele; Soci, Cesare; Comoretto, David
NIKEL: Electronics and data acquisition for kilopixels kinetic inductance camera
A prototype of digital frequency multiplexing electronics allowing the real
time monitoring of microwave kinetic inductance detector (MKIDs) arrays for
mm-wave astronomy has been developed. Thanks to the frequency multiplexing, it
can monitor simultaneously 400 pixels over a 500 MHz bandwidth and requires
only two coaxial cables for instrumenting such a large array. The chosen
solution and the performances achieved are presented in this paper.Comment: 21 pages, 14 figure
Improving healthy aging by monitoring patients’ lifestyle through a wearable device: results of a feasibility study
Exploring Brown Dwarf Disks in rho Oph
This paper discusses evidence for and properties of disks associated to brown
dwarfs in the star-forming region rho-Oph. We selected nine objects fr om the
ISOCAM survey of Bontemps et al. (2001) that have detections in the two
mid-infrared bands (6.7 and 14.3 um), relatively low extinction and low
luminosity. We present low-resolution near-infrared spectra in the J, H and K
bands, and determine for each source spectral type, extinction, effective
temperature a nd luminosity by comparing the spectra to those of field dwarfs
and to the most recent model stellar atmospheres. The results indicate that
eight objects have spectral types M6-M7.5, effective temperature of 2600-2700
K, one has a later spectral type (M8.5) and lower temperature (about 2400 K).
The derived extinctions range between Av~2 and 8 mag. The location of the
objects on the HR diagram, in spite of the uncertainties of the evolutionary
tracks for young objects of substellar mass, indicates that all the objects are
very young and have masses below about 0.08 Msun. The coolest object in our
sample has mass in the range 8-12 Mjup (0.008-0.012 Msun). In all cases, the
mid-infrared excess is consistent with the predictions of mode ls of disks
irradiated by the central object, showing that circumstellar disks are commonly
associated to young brown dwarfs and plan etary-mass objects. Finally, we
discuss possible variations of the disk geometry among different objects, as
well as the possibility of using these data to discriminate between various f
ormation scenarios.Comment: 15 pages, A&A in press, full resolution color figures for appendix A
and B are available at
http://www.arcetri.astro.it/~lt/preprints/preprints.htm
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