2,926 research outputs found
Satellites of Simulated Galaxies: survival, merging, and their relation to the dark and stellar halos
We study the population of satellite galaxies formed in a suite of
N-body/gasdynamical simulations of galaxy formation in a LCDM universe. We find
little spatial or kinematic bias between the dark matter and the satellite
population. The velocity dispersion of the satellites is a good indicator of
the virial velocity of the halo: \sigma_{sat}/V_{vir}=0.9 +/- 0.2. Applied to
the Milky Way and M31 this gives V_{vir}^{MW}=109 +/- 22$ km/s and
V_{vir}^{M31} = 138 +/- 35 km/s, respectively, substantially lower than the
rotation speed of their disk components. The detailed kinematics of simulated
satellites and dark matter are also in good agreement. By contrast, the stellar
halo of the simulated galaxies is kinematically and spatially distinct from the
population of surviving satellites. This is because the survival of a satellite
depends on mass and on time of accretion; surviving satellites are biased
toward low-mass systems that have been recently accreted by the galaxy. Our
results support recent proposals for the origin of the systematic differences
between stars in the Galactic halo and in Galactic satellites: the elusive
``building blocks'' of the Milky Way stellar halo were on average more massive,
and were accreted (and disrupted) earlier than the population of dwarfs that
has survived self-bound until the present.Comment: 13 pages, 11 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Cosmic M\'enage \`a Trois: The Origin of Satellite Galaxies On Extreme Orbits
We examine the orbits of satellite galaxies identified in a suite of
N-body/gasdynamical simulations of the formation of galaxies in a LCDM
universe. Most satellites follow conventional orbits; after turning around,
they accrete into their host halo and settle on orbits whose apocentric radii
are steadily eroded by dynamical friction. However, a number of outliers are
also present, we find that ~1/3 of satellites identified at are on
unorthodox orbits, with apocenters that exceed their turnaround radii. This
population of satellites on extreme orbits consists typically of the faint
member of a satellite pair that has been ejected onto a highly-energetic orbit
during its first approach to the primary. Since the concurrent accretion of
multiple satellite systems is a defining feature of hierarchical models of
galaxy formation, we speculate that this three-body ejection mechanism may be
the origin of (i) some of the newly discovered high-speed satellites around M31
(such as Andromeda XIV); (ii) some of the distant fast-receding Local Group
members, such as Leo I; and (iii) the oddly isolated dwarf spheroidals Cetus
and Tucana in the outskirts of the Local Group. Our results suggest that care
must be exercised when using the orbits of the most weakly bound satellites to
place constraints on the total mass of the Local Group.Comment: 10 pages, 6 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
A novel printed 3-electrode system for the electrochemical detection of sulfadiazine
We thank the financial support of 3C´s – Cellulose and Cork in the Control of antibiotics in
aquaculture (PTDC/AAG-TEC/5400/2014 and POCI-01-0145-FEDER-016637), to FEDER, through COMPETE2020,
POCI, and FCT (Fundação para a Ciência e a Tecnologia I.P.).info:eu-repo/semantics/publishedVersio
Electrochemistry combined-surface plasmon resonance biosensors: A review
Over the years, most of the literature reported applications of electrochemical and surface plasmon resonance (SPR) immunoassays for biosensing but, so far, the combination of the two methods in the same sensing spot for analytical purposes is much less explored and discussed. The aim of this Review is to highlight the great potential of electrochemistry combined-SPR (eSPR) as analytical tool for screening chemically and biologically relevant (bio)molecules by combining the unique features of SPR integrated with electrochemical readout. In the first part of the Review, we describe the urgent need of innovative methods for screening clinical biological markers (General Introduction), briefly discuss general concepts of SPR and electrochemical sensing (Concepts behind eSPR biosensors) and highlight the hyphenation of two methods to developed combined biosensing systems (Set-up configuration and eSPR principles). Firstly, we briefly give an overview of the setup for implementation of eSPR technique and discuss some relevant experimental conditions to perform the combined optical and electrochemical measurements. Then, the principles and fundamentals of eSPR biosensors are presented and described. We also present representative examples of eSPR biosensors in the literature (Applications of eSPR biosensors). In the second part, we review studies on how combined electrical and plasmonic detection contributed to the biosensing field, in particular, for the successful screening of clinically relevant biomolecules, namely proteins (Detection of proteins), nucleic acids (Detection of nucleic acids), small size chemical species (Detection of small molecules) and cells (Living-cell Analysis). Finally, we discuss the current limitations of eSPR biosensors performance and suggest possible ways to overcome these limitations (Limitations and optimization) and then we explore aspects about the development of the method and its applications and discuss areas of likely future growth (Conclusions and perspectives).This research had the financial support of FCT (Fundação para a Ciência e Tecnologia) and co-financed by the European Union (FEDER funds) under the Partnership Agreement PT2020, Research Grant Pest-C/QUI/UIDB/00081/2020 (CIQUP). J.A. Ribeiro (ref. SFRH/BPD/105395/2014) and C.M. Pereira (ref. SFRH/BSAB/150320/2019) acknowledge FCT under the QREN – POPH – Advanced Training, subsidized by
European Union and national MEC funds. The authors acknowledge the research project MyTag (ref. PTDC/EEI-EEE/4832/2021), funded by FCT, for financial support.info:eu-repo/semantics/publishedVersio
Development of an innovative flexible paper-based methanol fuel cell (PB-DMFC) sensing platform application to sarcosine detection
This work describes for the first time a paper-based direct methanol fuel cell platform (PB-DMFC) that functions as an energy source and biosensor, assembled on a simple paper substrate for point-of-care (POC) applications, targeting sarcosine as proof-of-concept. Specifically, a methanol fuel cell strip was developed from a square of Whatman paper, acting as substrate. The paper strip was treated with an impermeable agent (paraffin solution) and supported all fuel cell device components, including the electrolyte (Nafion®), anode electrode (carbon black Pt/Ru), cathode electrode (carbon black Pt), and current collectors (silver edges). All the described components formed a flexible single layer that operated in a completely passive mode by adding few microliters of a methanol solution on the anode side and by using atmospheric oxygen on the cathode side. The obtained platform had a stable electrical signal with an average OCV value of 0.45-0.55V and a maximum power density of 20-50µW/cm2, depending on the methanol concentration used (0.5M 2M). A sensing layer was built in situ on the anode electrode by electropolymerization of a solution of 3,4-ethylenedioxythiophene (EDOT) and pyrrole (Py) as monomers. The obtained PB-DMFC/biosensor was calibrated at room temperature in buffer and healthy human urine and showed linear responses from 1.0×10-7 to 1.0×10-3M with a detection limit of 6.6×10-8M. Selectivity studies evidenced signals changing within 1-10%, both in positive and negative directions. Results evidenced good reproducibility. Overall, the obtained results demonstrate a self-sufficient biosensor for the detection of sarcosine consisting of an innovative paper-based methanol fuel cell strip. This concept can open new horizons for massification of biosensors even in places with energy shortage.The authors acknowledge the financial support of EU-Horizon 2020 (Symbiotic, FET-Open, GA665046) and LPTC (Grant references: SFRH/BD/122954/2016; COVID/BD/151738/2021) acknowledges Fundação para a Ciência e Tecnologia (FCT) for financial support. This work was also financially supported by LA/P/0045/2020 (ALiCE), UIDB/00532/2020 and UIDP/00532/2020 (CEFT), funded by national funds through FCT/MCTES (PIDDAC).info:eu-repo/semantics/publishedVersio
Satellite Galaxies and Fossil Groups in the Millennium Simulation
We use a semianalytic galaxy catalogue constructed from the Millennium
Simulation to study the satellites of isolated galaxies in the LCDM cosmogony.
This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites)
allows the characterization, with minimal statistical uncertainty, of the
dynamical properties of satellite/primary galaxy systems in a LCDM universe. We
find that, overall, the satellite population traces the dark matter rather
well: its spatial distribution and kinematics may be approximated by an NFW
profile with a mildly anisotropic velocity distribution. Their spatial
distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg''
effect that reflects the misalignment between the major axis and angular
momentum of the host halo. The isolation criteria for our primaries picks not
only galaxies in sparse environments, but also a number of primaries at the
centre of ''fossil'' groups. We find that the abundance and luminosity function
of these unusual systems are in reasonable agreement with the few available
observational constraints. We recover the expected L_{host} \sigma_{sat}^3
relation for LCDM models for truly-isolated primaries. Less strict primary
selection, however, leads to substantial modification of the scaling relation.
Our analysis also highlights a number of difficulties afflicting studies that
rely on blind stacking of satellite systems to constrain the mean halo mass of
the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Autonomous biosensor for screening breast cancer biomarkers using passive Fuel Cells
Nádia S. Ferreira (Grant reference SFRH/BD/122955/2016) acknowledges Fundação para a Ciência e Tecnologia (FCT) for financial supportinfo:eu-repo/semantics/publishedVersio
A cellulose-based colour test-strip for equipment-free drug detection on-site: application to sulfadiazine in aquatic environment
This work develops a simple and innovative test-strip to monitor antibiotics in aquaculture facilities by an equipment-free approach. It consists of a low-cost disposable cellulose paper that was chemically modified to produce a colour change when in contact with a given antibiotic. In brief, the cellulose substrate was subject to oxidation with periodate, followed by amination with chitosan binding and modification with Cu(II). The test strip was then dipped in the target solution and the intensity of the colour generated therein revealed the concentration of antibiotic present for concentrations higher than 0.5 mM. The higher the concentration in sulfadiazine (SDZ), the more intense the pink colour formed in the final solution, which was also turbid due to the insolubility of the formed product. This colour intensity also varied linearly with the logarithm of the SDZ concentration (from 0.5 to 5 mM), when plotted against the sum of the RGB coordinates extracted from digital pictures. The linear equation of this response was represented by (R+G+B)=256.1 log(SDZ, mol/L)362.0, with an R-squared of 0.9913. The test-strip was stable for at least 15 days and was selective in the presence of tetracycline and difloxacin, while the response to other members of the sulfadiazine family requires prior evaluation. Overall, the test-strips developed herein are inexpensive and provide valuable (semi-) quantitative data for monitoring SDZ in waters, a most valuable approach to control and reduce the level of antibiotics in fish tanks, which in turn may reduce the costs of fish production and the environmental concerns linked to this practice. Moreover, the test strip uses a cellulose substrate that has little environmental impact upon discard.The authors acknowledge funding from project PTDC/AAGTEC/5400/2014, POCI-01-0145-FEDER-016637 funded by European through FEDER (European Funding or Regional Development) via COMPETE2020—POCI (operational program for internationalization and competitively) and by national funding through the National Foundation for Science and Technology, I.P.info:eu-repo/semantics/publishedVersio
Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms
In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 but Ba is
on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein
modes; yet only for the Eu and Sr systems is there a large dip in the thermal
conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here
we argue that it is the off-center displacement that is crucial for
understanding this unexplained difference in behavior. It enhances the coupling
between the "rattler" motion and the lattice phonons for the Eu and Sr systems,
and turns on/off another scattering mechanism (for 1K < T < 20K) produced by
the presence/absence of off-center sites. The random occupation of different
off-center sites produces a high density of symmetry-breaking defects which
scatters phonons. It may also be important for improving our understanding of
other glassy systems.Comment: 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened
arguments regarding need for additional phonon scattering mechanis
Driving nanozymes towards stereochemical recognition: application to biomolecules of interest in health
National Foundation for Science and Technology, I.P., FCT, with reference SFRH/BD/130107/2017info:eu-repo/semantics/publishedVersio
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