772 research outputs found
Acid catalyzed synthesis of dimethyl isosorbide via dimethyl carbonate chemistry
Dimethyl isosorbide (DMI) is a bio-based solvent that can be used as green alternative for conventional dipolar
media (dimethyl sulfoxide, dimethylformamide, and dimethylacetamide). The main synthetic procedures to DMI
reported in the literature are based on the methylation of isosorbide employing different alkylating agents
including toxic halogen compounds such as alkyl halides. A more sustainable alternative would be to employ
dimethyl carbonate (DMC), a well-known green reagent and solvent, considered one of the most promising
methylating agents for its good biodegradability and low toxicity. Indeed, in recent years, DMC-promoted
methylation of isosorbide has been extensively exploited although mostly in the presence of a base or an
amphoteric catalyst. In this work, we report for the first time a comprehensive investigation on the synthesis of
DMI via DMC chemistry promoted by heterogeneous acid catalyst (Amberlyst-36 and Purolite CT275DR). Re-
action conditions were optimized and then applied for the methylation of isosorbide and its epimers, isoidide and
isomannide. Considerations on the related reaction mechanism were reported highlighting the difference in the
preferred reaction pathways among this new synthetic approach and the previously reported base-catalyzed
procedures
CLAM, a continuous line alignment and monitoring method for RICH mirrors
A method is proposed for the angular alignment of RICH mirrors and for its monitoring, in particular for the COMPASS RICH-1 mirror system. Observing (by means of four cameras) apparent discontinuities in the images of continuous linear objects reflected by the mirrors surface, a relative misalignment of adjacent mirrors can be deduced and then corrected. The method can attain a sensitivity of at least 0.1 mrad, and can also be applied on-line to keep under control the stability of the mirrors during data taking
A map-matching algorithm dealing with sparse cellular fingerprint observations
The widespread availability of mobile communication makes mobile devices a resource for the collection of data about mobile infrastructures and user mobility. In these contexts, the problem of reconstructing the most likely trajectory of a device on the road network on the basis of the sequence of observed locations (map-matching problem) turns out to be particularly relevant. Different contributions have demonstrated that the reconstruction of the trajectory of a device with good accuracy is technically feasible even when only a sparse set of GNSS positions is available. In this paper, we face the problem of coping with sparse sequences of cellular fingerprints. Compared to GNSS positions, cellular fingerprints provide coarser spatial information, but they work even when a device is missing GNSS positions or is operating in an energy saving mode. We devise a new map-matching algorithm, that exploits the well-known Hidden Markov Model and Random Forests to successfully deal with noisy and sparse cellular observations. The performance of the proposed solution has been tested over a medium-sized Italian city urban environment by varying both the sampling of the observations and the density of the fingerprint map as well as by including some GPS positions into the sequence of fingerprint observations
RHIP, a Radio-controlled High-Voltage Insulated Picoammeter and its usage in studying ion backflow in MPGD-based photon detectors
A picoammeter system has been developed and engineering. It consists in a
current-voltage converter, based on an operational amplifier with very low
input current, a high precision ADC, a radio controlled data acquisition unit
and the computer-based control, visualization and storage. The precision is of
the order of a tenth of picoampers and it can measure currents between
electrodes at potentials up to 8 kV. The system is battery powered and a number
of strategies have been implemented to limit the power consumption. The system
is designed for multichannel applications, up to 256 parallel channels. The
overall implementation is cost-effective to make the availability of
multichannel setups easily affordable. The design, implementation and
performance of the picoammeter system are described in detail as well as a an
application: the measurement of ion backflow in MPGD-based photon detectors.Comment: 5th International Conference on Micro-Pattern Gas Detectors
(MPGD2017), presentation by Silvia Dalla Torr
Development of large area resistive electrodes for ATLAS NSW Micromegas
Micromegas with resistive anodes will be used for the NSW upgrades of the ATLAS experiment at LHC. Resistive electrodes are used in MPGD devices to prevent sparks in high-rate operation. Large-area resistive electrodes for Micromegas have been developed using two different technologies: screen printing and carbon sputtering. The maximum resistive foil size is 45 Ă— 220 cm with a printed pattern of 425-ÎĽm pitch strips. These technologies are also suitable for mass production. Prototypes of a production model series have been successfully produced. In this paper, we report the development, the production status, and the test results of resistive Micromegas
Remote alignment of large mirror array for RICH detectors
Image focusing in large RICH detectors is obtained by composite systems of mirror elements. Monitoring and adjusting the alignment of the mirror elements during data taking are important handles to improve the detector resolution. Mirror adjustment via piezoelectric actuators can combine unprecedented accuracy and match some fundamental requirements: the detector material budget can be kept low and the high purity of the gas radiator can be preserved, a prerequisite when UV photons are detected. A system based on this principle, well suited for COMPASS RICH-1 mirrors, is proposed
Study of MicroPattern Gaseous detectors with novel nanodiamond based photocathodes for single photon detection in EIC RICH
Identification of high momentum hadrons at the future EIC is crucial, gaseous
RICH detectors are therefore viable option. Compact collider setups impose to
construct RICHes with small radiator length, hence significantly limiting the
number of detected photons. More photons can be detected in the far UV region,
using a windowless RICH approach. QE of CsI degrades under strong irradiation
and air contamination. Nanodiamond based photocathodes (PCs) are being
developed as an alternative to CsI. Recent development of layers of
hydrogenated nanodiamond powders as an alternative photosensitive material and
their performance, when coupled to the THick Gaseous Electron Multipliers
(THGEM)-based detectors, are the objects of an ongoing R\&D. We report about
the initial phase of our studies.Comment: 3 pages, 5 figures, RICH2018 conference proceedin
Rise and fall of hidden string order of lattice bosons
We investigate the ground state properties of a newly discovered phase of one
dimensional lattice bosons with extended interactions (see E. G. Dalla Torre et
al., Phys. Rev. Lett. \textbf{97}, 260401 (2006)). The new phase, termed the
Haldane Insulator (HI) in analogy with the gapped phase of spin-1 chains, is
characterized by a non local order parameter, which can only be written as an
infinite string in terms of the bosonic densities. We show that the string
order can nevertheless be probed with physical fields that couple locally, via
the effect those fields have on the quantum phase transitions separating the
exotic phase from the conventional Mott and density wave phases. Using a field
theoretical analysis we show that a perturbation which breaks lattice inversion
symmetry gaps the critical point separating the Mott and Haldane phases and
eliminates the sharp distinction between them. This is remarkable given that
neither of these phases involves broken inversion symmetry. We also investigate
the evolution of the phase diagram with the tunable coupling between parallel
chains in an optical lattice setup. We find that inter-chain tunneling destroys
the direct phase transition between the Mott and Haldane insulators by
establishing an intermediate superfluid phase. On the other hand coupling the
chains only by weak repulsive interactions does not modify the structure of the
phase diagram. The theoretical predictions are confirmed with numerical
calculations using the Density Matrix Renormalization Group (DMRG).Comment: 15 pages, 8 figures. Minor corrections, published versio
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