90 research outputs found
Practical fast gate rate InGaAs/InP single-photon avalanche photodiodes
We present a practical and easy-to-implement method for high-speed near
infrared single-photon detection based on InGaAs/InP single-photon avalanche
photodiodes (SPADs), combining aspects of both sine gating and
self-differencing techniques. At a gating frequency of 921 MHz and temperature
of -30 C we achieve: a detection efficiency of 9.3 %, a dark count
probability of 2.8 ns, while the afterpulse probability
is 1.6 ns, with a 10 ns "count-off time" setting. In
principle, the maximum count rate of the SPAD can approach 100 MHz, which can
significantly improve the performance for diverse applications.Comment: 3 pages and a few lines, 5 figures, 1 table. Accepted by Applied
Physics Letter
Free Running Single Photon Detection based on a negative feedback InGaAs APD
InGaAs/InP-based semiconductor avalanche photodiode are usually employed for
single-photon counting at telecom wavelength. However they are affected by
afterpulsing which limits the diode performance. Recently, Princeton Lightwave
has commercialised a diode integrating monolithically a feedback resistor. This
solution effectively quenches the avalanche and drastically reduces
afterpulsing. Here, we report the development and characterization of a
detector module based on this diode, implementing an active hold-off circuit
which further reduces the afterpulsing and notably improves the detector
performances. We demonstrate free-running operation with 600 Hz dark count rate
at 10% detection efficiency. We also improved the standard double-window
technique for the afterpulsing characterization. Our algorithm implemented by a
FPGA allows to put the APD in a well-defined initial condition and to measure
the impact of the higher order afterpulses.Comment: 18 pages, 15 figures. Submitted to Journal of Modern Optic
Tracker fields from nonminimally coupled theory
We extend the concept of quintessence to a flat nonminimally coupled scalar -
tensor theories of gravity. By means of Noether's symmetries for the
cosmological pointlike Lagrangian L, it is possible to exhibit exact solutions
for a class of models depending on a free parameter s. This parameter comes out
in the relationship existing between the coupling F(\phi) and the potential
V(\phi) because of such a symmetry for L. When inverse power law potentials are
taken in account, a whole family of exact solutions parametrized by such an s
is proposed as a class of tracker fields, and some considerations are made
about them.Comment: 17 pages, submitted to Physical Review
Adopting sustainability competence-based education in academic disciplines : Insights from 13 higher education institutions
Higher Education Institutions (HEIs) have been incorporating sustainability into education and curricula, where recent research has focussed on sustainability competences, pedagogical approaches, and how to connect them, generally on a single HEI. The process of integrating sustainability into education based on curricula assessment has been explained using adoption of innovations; and has the potential to explain the process of developing competences through pedagogical approaches. The aim of this paper is to investigate this process at academic discipline level. An online survey was developed to investigate teaching sustainability competences in 13 HEIs, from which 678 responses from educators were obtained. The competences and pedagogical approaches from the responses were ranked, and then the connections between the competences and pedagogical approaches per discipline were analysed using a correlations-based framework, from which three disciplines groups were created. The groups were categorised using diffusion of innovations theory, which indicated that some disciplines are more innovative than others in adopting sustainability competence-based teaching. The results are used to propose two frameworks to better understand the adoption of sustainability competence-based teaching: (a) the D-RAPID framework; and (b) the Disciplinary Multi-dimensional Sustainability Influence Change for Academia (D-MuSICA) memework. The adoption of sustainability competence-base education must expand from a single HEI perspective to a disciplinary collaborative one spanning many HEIs, where academic disciplines should learn from each other's insights and mistakes and provide students with more transdisciplinary skillsets to make societies more sustainable.Peer reviewe
Improving sustainability teaching by grouping and interrelating pedagogical approaches and sustainability competences: evidence from 15 worldwide higher education institutions
There has been increasing research on pedagogical approaches, sustainability competences, and how to connect them in Higher Education Institutions (HEIs). This paper's
aim is to provide deeper insights into the system of pedagogical approaches and sustainability competences, as well as how these interrelate. A survey was developed to investigate sustainability teaching in 15 HEIs. The survey was sent to educators of
each HEI from which 668 responses were obtained. The responses were analysed in a
five-step process: (1) descriptive statistics; (2) Pearson correlations; (3) principal component analyses (PCAs) to detect groups; (4) Pearson correlations between the groups; and
(5) regressions. The first step provided the base to carry out the PCAs, from which three
groups for the pedagogical approaches (Universal, Social, and Environmental) and three
for the sustainability competences (Extrospective-social, Introspective-personal, and
Cogitative-processual) were obtained. The correlations between the groups showed that:
(1) the competences are closely interrelated; (2) the pedagogical approaches are somehow interrelated; and (3) the pedagogical approaches are somehow interrelated to the
competences. The regressions showed that the Universal and Social groups would be
most suitable to develop all the competences' groups. The Environmental group develops
only the cogitative-processual competences' group. The results served as bases to propose the Sustainability Teaching System (STS), which provides deeper insights into the
system of pedagogical approaches and sustainability competences by grouping them, as
well as showing directionality and strength. To improve sustainability teaching, it is necessary to understand the pedagogical approaches' groups and how they can develop the
competences' groups.info:eu-repo/semantics/publishedVersio
On exact solutions for quintessential (inflationary) cosmological models with exponential potentials
We first study dark energy models with a minimally-coupled scalar field and
exponential potentials, admitting exact solutions for the cosmological
equations: actually, it turns out that for this class of potentials the
Einstein field equations exhibit alternative Lagrangians, and are completely
integrable and separable (i.e. it is possible to integrate the system
analytically, at least by quadratures). We analyze such solutions, especially
discussing when they are compatible with a late time quintessential expansion
of the universe. As a further issue, we discuss how such quintessential scalar
fields can be connected to the inflationary phase, building up, for this class
of potentials, a quintessential inflationary scenario: actually, it turns out
that the transition from inflation toward late-time exponential quintessential
tail admits a kination period, which is an indispensable ingredient of this
kind of theoretical models. All such considerations have also been done by
including radiation into the model.Comment: Revtex4, 10 figure
Volcanism and climate change as drivers in Holocene depositional dynamic of Laguna del Maule (Andes of central Chile – 36° S)
Late Quaternary volcanic basins are active landscapes from which detailed archives of past climate and seismic and volcanic activity can be obtained. A multidisciplinary study performed on a transect of sediment cores was used to reconstruct the depositional evolution of the high-elevation Laguna del Maule (LdM) (36∘ S, 2180 m a.s.l., Chilean Andes). The recovered 5 m composite sediment sequence includes two thick turbidite units (LT1 and LT2) and numerous tephra layers (23 ash and 6 lapilli). We produced an age model based on nine new 14C AMS dates, existing 210Pb and 137Cs data, and the Quizapú ash horizon (1932 CE). According to this age model, the relatively drier Early Holocene was followed by a phase of increased productivity during the mid-Holocene and higher lake levels after 4.0 ka cal BP. Major hydroclimate transitions occurred at ca. 11, 8.0, 4.0 and 0.5 ka cal BP. Decreased summer insolation and winter precipitation due to a southward shift in the southern westerly winds and a strengthened Pacific Subtropical High could explain Early Holocene lower lake levels. Increased biological productivity during the mid-Holocene (∼8.0 to 6.0 ka cal BP) is coeval with a warm–dry phase described for much of southern South America. Periods of higher lake productivity are synchronous to a higher frequency of volcanic events. During the Late Holocene, the tephra layers show compositional changes suggesting a transition from silica-rich to silica-poor magmas at around 4.0 ka cal BP. This transition was synchronous with increased variability of sedimentary facies and geochemical proxies, indicating higher lake levels and increased moisture at LdM after 4.0 ka cal BP, most likely caused by the inception of current El Niño–Southern Oscillation and Pacific Decadal Oscillation (ENSO–PDO) dynamics in central Chile.Postprin
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