147 research outputs found
Direct detection of spin polarization in photoinduced charge transfer through a chiral bridge
It is well assessed that the charge transport through a chiral potential barrier can result in spin-polarized charges. The possibility of driving this process through visible photons holds tremendous potential for several aspects of quantum information science, e.g., the optical control and readout of qubits. In this context, the direct observation of this phenomenon via spin-sensitive spectroscopies is of utmost importance to establish future guidelines to control photo-driven spin selectivity in chiral structures. Here, we provide direct proof that time-resolved electron paramagnetic resonance (EPR) can be used to detect long-lived spin polarization generated by photoinduced charge transfer through a chiral bridge. We propose a system comprising CdSe quantum dots (QDs), as a donor, and C60, as an acceptor, covalently linked through a saturated oligopeptide helical bridge (χ) with a rigid structure of ∼10 Å. Time-resolved EPR spectroscopy shows that the charge transfer in our system results in a C60 radical anion, whose spin polarization maximum is observed at longer times with respect to that of the photogenerated C60 triplet state. Notably, the theoretical modelling of the EPR spectra reveals that the observed features may be compatible with chirality-induced spin selectivity, but the electronic features of the QD do not allow the unambiguous identification of the CISS effect. Nevertheless, we identify which parameters need optimization for unambiguous detection and quantification of the phenomenon. This work lays the basis for the optical generation and direct manipulation of spin polarization induced by chirality
Rheological Tunability of Perovskite Precursor Solutions: From Spin Coating to Inkjet Printing Process
The high efficiencies (>22%) reached by perovskite-based optoelectronic devices in a very short period, demonstrates the great potential and tunability of this material. The current challenge lies in translating such efficiencies to commercially feasible forms produced through industrial fabrication methods. Herein, a novel first step towards the processability of starch-perovskite inks, developed in our previous work, is investigated, by using inkjet printing technology. The tunability of the viscosity of the starch-perovskite-based inks allows the selection of suitable concentrations to be used as printable inks. After exploration of several printing parameters, thick and opaque starch-perovskite nanocomposite films were obtained, showing interesting morphological and optical properties. The results obtained in this work underline the potential and versatility of our approach, opening the possibility to explore and optimize, in the future, further large-scale deposition methods towards fully printed and stable perovskite devices
Silicon resonant microcantilevers for absolute pressure measurement
This work is focused on the developing of silicon resonant microcantilevers for the measurement of the absolute pressure. The microcantilevers have been fabricated with a two-mask bulk micromachining process. The variation in resonance response of microcantilevers was investigated as a function of pressure 10−1-105 Pa, both in terms of resonance frequency and quality factor. A theoretical description of the resonating microstructure is given according to different molecular and viscous regimes. Also a brief discussion on the different quality factors contributions is presented. Theoretical and experimental data show a very satisfying agreement. The microstructure behavior demonstrates a certain sensitivity over a six decade range and the potential evolution of an absolute pressure sensor working in the same rang
Direct measurement of stellar angular diameters by the VERITAS Cherenkov Telescopes
The angular size of a star is a critical factor in determining its basic
properties. Direct measurement of stellar angular diameters is difficult: at
interstellar distances stars are generally too small to resolve by any
individual imaging telescope. This fundamental limitation can be overcome by
studying the diffraction pattern in the shadow cast when an asteroid occults a
star, but only when the photometric uncertainty is smaller than the noise added
by atmospheric scintillation. Atmospheric Cherenkov telescopes used for
particle astrophysics observations have not generally been exploited for
optical astronomy due to the modest optical quality of the mirror surface.
However, their large mirror area makes them well suited for such
high-time-resolution precision photometry measurements. Here we report two
occultations of stars observed by the VERITAS Cherenkov telescopes with
millisecond sampling, from which we are able to provide a direct measurement of
the occulted stars' angular diameter at the milliarcsecond scale.
This is a resolution never achieved before with optical measurements and
represents an order of magnitude improvement over the equivalent lunar
occultation method. We compare the resulting stellar radius with empirically
derived estimates from temperature and brightness measurements, confirming the
latter can be biased for stars with ambiguous stellar classifications.Comment: Accepted for publication in Nature Astronom
Evidence for proton acceleration up to TeV energies based on VERITAS and Fermi-LAT observations of the Cas A SNR
We present a study of -ray emission from the core-collapse supernova
remnant Cas~A in the energy range from 0.1GeV to 10TeV. We used 65 hours of
VERITAS data to cover 200 GeV - 10 TeV, and 10.8 years of \textit{Fermi}-LAT
data to cover 0.1-500 GeV. The spectral analysis of \textit{Fermi}-LAT data
shows a significant spectral curvature around GeV that is
consistent with the expected spectrum from pion decay. Above this energy, the
joint spectrum from \textit{Fermi}-LAT and VERITAS deviates significantly from
a simple power-law, and is best described by a power-law with spectral index of
with a cut-off energy of TeV. These
results, along with radio, X-ray and -ray data, are interpreted in the
context of leptonic and hadronic models. Assuming a one-zone model, we exclude
a purely leptonic scenario and conclude that proton acceleration up to at least
6 TeV is required to explain the observed -ray spectrum. From modeling
of the entire multi-wavelength spectrum, a minimum magnetic field inside the
remnant of is deduced.Comment: 33 pages, 9 Figures, 6 Table
Common characteristics of open source software development and applicability for drug discovery: a systematic review
<p>Abstract</p> <p>Background</p> <p>Innovation through an open source model has proven to be successful for software development. This success has led many to speculate if open source can be applied to other industries with similar success. We attempt to provide an understanding of open source software development characteristics for researchers, business leaders and government officials who may be interested in utilizing open source innovation in other contexts and with an emphasis on drug discovery.</p> <p>Methods</p> <p>A systematic review was performed by searching relevant, multidisciplinary databases to extract empirical research regarding the common characteristics and barriers of initiating and maintaining an open source software development project.</p> <p>Results</p> <p>Common characteristics to open source software development pertinent to open source drug discovery were extracted. The characteristics were then grouped into the areas of participant attraction, management of volunteers, control mechanisms, legal framework and physical constraints. Lastly, their applicability to drug discovery was examined.</p> <p>Conclusions</p> <p>We believe that the open source model is viable for drug discovery, although it is unlikely that it will exactly follow the form used in software development. Hybrids will likely develop that suit the unique characteristics of drug discovery. We suggest potential motivations for organizations to join an open source drug discovery project. We also examine specific differences between software and medicines, specifically how the need for laboratories and physical goods will impact the model as well as the effect of patents.</p
An Archival Search for Neutron-Star Mergers in Gravitational Waves and Very-High-Energy Gamma Rays
The recent discovery of electromagnetic signals in coincidence with
neutron-star mergers has solidified the importance of multimessenger campaigns
in studying the most energetic astrophysical events. Pioneering multimessenger
observatories, such as LIGO/Virgo and IceCube, record many candidate signals
below the detection significance threshold. These sub-threshold event
candidates are promising targets for multimessenger studies, as the information
provided by them may, when combined with contemporaneous gamma-ray
observations, lead to significant detections. Here we describe a new method
that uses such candidates to search for transient events using archival
very-high-energy gamma-ray data from imaging atmospheric Cherenkov telescopes
(IACTs). We demonstrate the application of this method to sub-threshold binary
neutron star (BNS) merger candidates identified in Advanced LIGO's first
observing run. We identify eight hours of archival VERITAS observations
coincident with seven BNS merger candidates and search them for TeV emission.
No gamma-ray emission is detected; we calculate upper limits on the integral
flux and compare them to a short gamma-ray burst model. We anticipate this
search method to serve as a starting point for IACT searches with future
LIGO/Virgo data releases as well as in other sub-threshold studies for
multimessenger transients, such as IceCube neutrinos. Furthermore, it can be
deployed immediately with other current-generation IACTs, and has the potential
for real-time use that places minimal burden on experimental operations.
Lastly, this method may serve as a pilot for studies with the Cherenkov
Telescope Array, which has the potential to observe even larger fields of view
in its divergent pointing mode
Demonstration of stellar intensity interferometry with the four VERITAS telescopes
High angular resolution observations at optical wavelengths provide valuable
insights in stellar astrophysics, directly measuring fundamental stellar
parameters, and probing stellar atmospheres, circumstellar disks, elongation of
rapidly rotating stars, and pulsations of Cepheid variable stars. The angular
size of most stars are of order one milli-arcsecond or less, and to spatially
resolve stellar disks and features at this scale requires an optical
interferometer using an array of telescopes with baselines on the order of
hundreds of meters. We report on the successful implementation of a stellar
intensity interferometry system developed for the four VERITAS imaging
atmospheric-Cherenkov telescopes. The system was used to measure the angular
diameter of the two sub-mas stars Canis Majoris and Orionis
with a precision better than 5%. The system utilizes an off-line approach where
starlight intensity fluctuations recorded at each telescope are correlated
post-observation. The technique can be readily scaled onto tens to hundreds of
telescopes, providing a capability that has proven technically challenging to
current generation optical amplitude interferometry observatories. This work
demonstrates the feasibility of performing astrophysical measurements with
imaging atmospheric-Cherenkov telescope arrays as intensity interferometers and
the promise for integrating an intensity interferometry system within future
observatories such as the Cherenkov Telescope Array.Comment: Accepted for publication in Nature Astronomy (2020
VERITAS Discovery of VHE Emission from the Radio Galaxy 3C 264: A Multi-Wavelength Study
The radio source 3C 264, hosted by the giant elliptical galaxy NGC 3862, was
observed with VERITAS between February 2017 and May 2019. These deep
observations resulted in the discovery of very-high-energy (VHE; E GeV)
-ray emission from this active galaxy. An analysis of 57 hours of
quality-selected live time yields a detection at the position of the source,
corresponding to a statistical significance of 7.8 standard deviations above
background. The observed VHE flux is variable on monthly time scales, with an
elevated flux seen in 2018 observations. The VHE emission during this elevated
state is well-characterized by a power-law spectrum with a photon index and flux F( GeV) = ( cm s, or approximately 0.7%
of the Crab Nebula flux above the same threshold. 3C 264 () is the
most distant radio galaxy detected at VHE, and the elevated state is thought to
be similar to that of the famously outbursting jet in M 87. Consequently,
extensive contemporaneous multi-wavelength data were acquired in 2018 at the
time of the VHE high state. An analysis of these data, including VLBA, VLA,
HST, Chandra and Swift observations in addition to the VERITAS data, is
presented, along with a discussion of the resulting spectral energy
distribution.Comment: 19 pages, 11 figures, Accepted for publication in Astrophysical
Journa
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