122 research outputs found
Stellar population synthesis models between 2.5 and 5 {\mu}m based on the empirical IRTF stellar library
We present the first single-burst stellar population models in the infrared
wavelength range between 2.5 and 5 {\mu}m which are exclusively based on
empirical stellar spectra. Our models take as input 180 spectra from the
stellar IRTF (Infrared Telescope Facility) library. Our final single-burst
stellar population models are calculated based on two different sets of
isochrones and various types of initial mass functions of different slopes,
ages larger than 1 Gyr and metallicities between [Fe/H] = -0.70 and 0.26. They
are made available online to the scientific community on the MILES web page. We
analyse the behaviour of the Spitzer [3.6]-[4.5] colour calculated from our
single stellar population models and find only slight dependences on both
metallicity and age. When comparing to the colours of observed early-type
galaxies, we find a good agreement for older, more massive galaxies that
resemble a single-burst population. Younger, less massive and more metal-poor
galaxies show redder colours with respect to our models. This mismatch can be
explained by a more extended star formation history of these galaxies which
includes a metal-poor or/and young population. Moreover, the colours derived
from our models agree very well with most other models available in this
wavelength range. We confirm that the mass-to-light ratio determined in the
Spitzer [3.6] {\mu}m band changes much less as a function of both age and
metallicity than in the optical bands.Comment: 25 pages, 19 figures, published in MNRAS, models can be downloaded
from http://miles.iac.e
MILES extended: Stellar population synthesis models from the optical to the infrared
We present the first single-burst stellar population models which covers the
optical and the infrared wavelength range between 3500 and 50000 Angstrom and
which are exclusively based on empirical stellar spectra. To obtain these joint
models, we combined the extended MILES models in the optical with our new
infrared models that are based on the IRTF (Infrared Telescope Facility)
library. The latter are available only for a limited range in terms of both age
and metallicity. Our combined single-burst stellar population models were
calculated for ages larger than 1 Gyr, for metallicities between [Fe/H] = -0.40
and 0.26, for initial mass functions of various types and slopes, and on the
basis of two different sets of isochrones. They are available to the scientific
community on the MILES web page. We checked the internal consistency of our
models and compared their colour predictions to those of other models that are
available in the literature. Optical and near infrared colours that are
measured from our models are found to reproduce the colours well that were
observed for various samples of early-type galaxies. Our models will enable a
detailed analysis of the stellar populations of observed galaxies.Comment: 9 pages, 10 figures, published in A&
The puzzling interpretation of NIR indices: The case of NaI2.21
We present a detailed study of the Na I line strength index centered in the
-band at , {\AA} (NaI2.21 hereafter) relying on different samples of
early-type galaxies. Consistent with previous studies, we find that the
observed line strength indices cannot be fit by state-of-art scaled-solar
stellar population models, even using our newly developed models in the NIR.
The models clearly underestimate the large NaI2.21 values measured for most
early-type galaxies. However, we develop a Na-enhanced version of our newly
developed models in the NIR, which - together with the effect of a bottom-heavy
initial mass function - yield NaI2.21 indices in the range of the observations.
Therefore, we suggest a scenario in which the combined effect of [Na/Fe]
enhancement and a bottom-heavy initial mass function are mainly responsible for
the large NaI2.21 indices observed for most early-type galaxies. To a smaller
extent, also [C/Fe] enhancement might contribute to the large observed NaI2.21
values.Comment: 13 pages, 4 figures, accepted for publication in MNRA
The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence
We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6m photometry for > 2000
galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue
Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which
is populated by irregular and spiral galaxies, and is mainly driven by changes
in the formation timescale () and a degeneracy between and dust
reddening. The tightness of the GBS provides an unprecedented way of
identifying star-forming galaxies and objects that are just evolving to (or
from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS,
at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated
by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the
optical red sequence. We find no such dichotomy in terms of stellar mass
(measured by ), since both massive () blue and red sequence galaxies are identified. The type that is
proportionally more often found in the GGV are the S0-Sa's and most of these
are located in high-density environments. We discuss evolutionary models of
galaxies that show a rapid transition from the blue to the red sequence on
timescale of years.Comment: 7 pages, 4 figures, 1 table. Accepted for publication in ApJ
Belief Propagation for Min-Cost Network Flow: Convergence and Correctness
Distributed, iterative algorithms operating with minimal data structure while performing little computation per iteration are popularly known as message passing in the recent literature. Belief propagation (BP), a prototypical message-passing algorithm, has gained a lot of attention across disciplines, including communications, statistics, signal processing, and machine learning as an attractive, scalable, general-purpose heuristic for a wide class of optimization and statistical inference problems. Despite its empirical success, the theoretical understanding of BP is far from complete.
With the goal of advancing the state of art of our understanding of BP, we study the performance of BP in the context of the capacitated minimum-cost network flow problem—a cornerstone in the development of the theory of polynomial-time algorithms for optimization problems and widely used in the practice of operations research. As the main result of this paper, we prove that BP converges to the optimal solution in pseudopolynomial time, provided that the optimal solution of the underlying network flow problem instance is unique and the problem parameters are integral. We further provide a simple modification of the BP to obtain a fully polynomial-time randomized approximation scheme (FPRAS) without requiring uniqueness of the optimal solution. This is the first instance where BP is proved to have fully polynomial running time. Our results thus provide a theoretical justification for the viability of BP as an attractive method to solve an important class of optimization problems.National Science Foundation (U.S.). Career Project (CNS 0546590)Natural Sciences and Engineering Research Council of Canada (NSERC). Postdoctoral FellowshipNational Science Foundation (U.S.). EMT Project (CCF 0829893)National Science Foundation (U.S.). (CMMI-0726733
New 3‐ethynylaryl coumarin‐based dyes for dssc applications: Synthesis, spectroscopic properties, and theoretical calculations
PTDC/QUI‐QOR/7450/2020 POCI‐01‐0145‐FEDER‐016387 UIDB/50006/2020 UIDP/50006/2020 RECI/BBB‐BQB/0230/2012 RECI/BBB‐BEP/0124/2012 2020.09047.BD PD/BD/135087/2017 PD/BD/145324/2019/ (G.M.) .A set of 3‐ethynylaryl coumarin dyes with mono, bithiophenes and the fused variant, thieno [3,2‐b] thiophene, as well as an alkylated benzotriazole unit were prepared and tested for dye‐sensitized solar cells (DSSCs). For comparison purposes, the variation of the substitution pattern at the coumarin unit was analyzed with the natural product 6,7‐dihydroxycoumarin (Esculetin) as well as 5,7‐dihydroxycomarin in the case of the bithiophene dye. Crucial steps for extension of the conjugated system involved Sonogashira reaction yielding highly fluorescent molecules. Spectroscopic characterization showed that the extension of conjugation via the alkynyl bridge resulted in a strong red‐shift of absorption and emission spectra (in solution) of approximately 73–79 nm and 52–89 nm, respectively, relative to 6,7‐dimethoxy‐4‐methylcoumarin (λabs = 341 nm and λem = 410 nm). Theoretical density functional theory (DFT) calculations show that the Lowest Unoccupied Molecular Orbital (LUMO) is mostly centered in the cyanoacrylic anchor unit, corroborating the high intramolecular charge transfer (ICT) character of the electronic transition. Photovoltaic performance evaluation reveals that the thieno [3,2‐b] thiophene unit present in dye 8 leads to the best sensitizer of the set, with a conversion efficiency (η = 2.00%), best VOC (367 mV) and second best Jsc (9.28 mA∙cm−2), surpassed only by dye 9b (Jsc = 10.19 mA∙cm−2). This high photocurrent value can be attributed to increased donor ability of the 5,7‐dimethoxy unit when compared to the 6,7 equivalent (9b).publishersversionpublishe
Embodied GHG emissions of buildings – The hidden challenge for effective climate change mitigation
Buildings are major sources of greenhouse gas (GHG) emissions and contributors to the climate crisis. To meet climate-change mitigation needs, one must go beyond operational energy consumption and related GHG emissions of buildings and address their full life cycle. This study investigates the global trends of GHG emissions arising across the life cycle of buildings by systematically compiling and analysing more than 650 life cycle assessment (LCA) case studies. The results, presented for different energy performance classes based on a final sample of 238 cases, show a clear reduction trend in life cycle GHG emissions due to improved operational energy performance. However, the analysis reveals an increase in relative and absolute contributions of so‐called ‘embodied’ GHG emissions, i.e., emissions arising from manufacturing and processing of building materials. While the average share of embodied GHG emissions from buildings following current energy performance regulations is approximately 20–25% of life cycle GHG emissions, this figure escalates to 45–50% for highly energy-efficient buildings and surpasses 90% in extreme cases. Furthermore, this study analyses GHG emissions at time of occurrence, highlighting the ‘carbon spike’ from building production. Relating the results to existing benchmarks for buildings’ GHG emissions in the Swiss SIA energy efficiency path shows that most cases exceed the target of 11.0 kgCOeq/ma. Considering global GHG reduction targets, these results emphasize the urgent need to reduce GHG emissions of buildings by optimizing both operational and embodied impacts. The analysis further confirmed a need for improving transparency and comparability of LCA studies
Embodied GHG emissions of buildings - Critical reflection of benchmark comparison and in-depth analysis of drivers
In the face of the unfolding climate crisis, the role and importance of reducing Greenhouse gas (GHG) emissions from the building sector is increasing. This study investigates the global trends of GHG emissions occurring across the life cycle of buildings by systematically compiling life cycle assessment (LCA) studies and analysing more than 650 building cases. Based on the data extracted from these LCA studies, the influence of features related to LCA methodology and building design is analysed. Results show that embodied GHG emissions, which mainly arise from manufacturing and processing of building materials, are dominating life cycle emissions of new, advanced buildings. Analysis of GHG emissions at the time of occurrence, shows the upfront \u27carbon spike\u27 and emphasises the need to address and reduce the GHG \u27investment\u27 for new buildings. Comparing the results with existing life cycle-related benchmarks, we find only a small number of cases meeting the benchmark. Critically reflecting on the benchmark comparison, an in-depth analysis reveals different reasons for cases achieving the benchmark. While one would expect that different building design strategies and material choices lead to high or low embodied GHG emissions, the results mainly correlate with decisions related to LCA methodology, i.e. the scope of the assessments. The results emphasize the strong need for transparency in the reporting of LCA studies as well as need for consistency when applying environmental benchmarks. Furthermore, the paper opens up the discussion on the potential of utilizing big data and machine learning for analysis and prediction of environmental performance of buildings
Lack of gene-language correlation due to reciprocal female but directional male admixture in Austronesians and non-Austronesians of East Timor
Nusa Tenggara, including East Timor, located at the crossroad between Island Southeast Asia, Near Oceania, and Australia, are characterized by a complex cultural structure harbouring speakers from two different major linguistic groups of different geographic origins (Austronesian (AN) and non-Austronesian (NAN)). This provides suitable possibilities to study gene-language relationship; however, previous studies from other parts of Nusa Tenggara reported conflicting evidence about gene-language correlation in this region. Aiming to investigate gene-language relationships including sex-mediated aspects in East Timor, we analysed the paternally inherited non-recombining part of the Y chromosome (NRY) and the maternally inherited mitochondrial (mt) DNA in a representative collection of AN-and NAN-speaking groups. Y-SNP (single-nucleotide polymorphism) data were newly generated for 273 samples and combined with previously established Y-STR (short tandem repeat) data of the same samples, and with previously established mtDNA data of 290 different samples with, however, very similar representation of geographic and linguistic coverage of the country. We found NRY and mtDNA haplogroups of previously described putative East/Southeast Asian (E/SEA) and Near Oceanian (NO) origins in both AN and NAN speakers of East Timor, albeit in different proportions, suggesting reciprocal genetic admixture between both linguistic groups for females, but directional admixture for males. Our data underline the dual genetic origin of East Timorese in E/SEA and NO, and highlight that substantial genetic admixtur
An Experimental Biomimetic Platform for Artificial Olfaction
Artificial olfactory systems have been studied for the last two decades mainly from the point of view of the features of olfactory neuron receptor fields. Other fundamental olfaction properties have only been episodically considered in artificial systems. As a result, current artificial olfactory systems are mostly intended as instruments and are of poor benefit for biologists who may need tools to model and test olfactory models. Herewith, we show how a simple experimental approach can be used to account for several phenomena observed in olfaction
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