214 research outputs found
Energy harvesting towards self-powered iot devices
The internet of things (IoT) manages a large infrastructure of web-enabled smart devices, small devices that use embedded systems, such as processors, sensors, and communication hardware to collect, send, and elaborate on data acquired from their environment. Thus, from a practical point of view, such devices are composed of power-efficient storage, scalable, and lightweight nodes needing power and batteries to operate. From the above reason, it appears clear that energy harvesting plays an important role in increasing the efficiency and lifetime of IoT devices. Moreover, from acquiring energy by the surrounding operational environment, energy harvesting is important to make the IoT device network more sustainable from the environmental point of view. Different state-of-the-art energy harvesters based on mechanical, aeroelastic, wind, solar, radiofrequency, and pyroelectric mechanisms are discussed in this review article. To reduce the power consumption of the batteries, a vital role is played by power management integrated circuits (PMICs), which help to enhance the system's life span. Moreover, PMICs from different manufacturers that provide power management to IoT devices have been discussed in this paper. Furthermore, the energy harvesting networks can expose themselves to prominent security issues putting the secrecy of the system to risk. These possible attacks are also discussed in this review article
The Lyman Alpha Reference Sample. VIII. Characterizing Lyman-Alpha Scattering in Nearby Galaxies
We examine the dust geometry and Ly{\alpha} scattering in the galaxies of the
Lyman Alpha Reference Sample (LARS), a set of 14 nearby (0.02 < < 0.2)
Ly{\alpha} emitting and starbursting systems with Hubble Space Telescope
Ly{\alpha}, H{\alpha}, and H{\beta} imaging. We find that the global dust
properties determined by line ratios are consistent with other studies, with
some of the LARS galaxies exhibiting clumpy dust media while others of them
show significantly lower Ly{\alpha} emission compared to their Balmer
decrement. With the LARS imaging, we present Ly{\alpha}/H{\alpha} and
H{\alpha}/H{\beta} maps with spatial resolutions as low as 40 pc, and
use these data to show that in most galaxies, the dust geometry is best modeled
by three distinct regions: a central core where dust acts as a screen, an
annulus where dust is distributed in clumps, and an outer envelope where
Ly{\alpha} photons only scatter. We show that the dust that affects the escape
of Ly{\alpha} is more restricted to the galaxies' central regions, while the
larger Ly{\alpha} halos are generated by scattering at large radii. We present
an empirical modeling technique to quantify how much Ly{\alpha} scatters in the
halo, and find that this "characteristic" scattering distance correlates with
the measured size of the Ly{\alpha} halo. We note that there exists a slight
anti-correlation between the scattering distance of Ly{\alpha} and global dust
properties.Comment: 32 pages, 51 figures, accepted to Ap
Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at z>1
We identify an abundant population of extreme emission line galaxies (EELGs)
at redshift z~1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy
Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3
(HST/WFC3). 69 EELG candidates are selected by the large contribution of
exceptionally bright emission lines to their near-infrared broad-band
magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission
lines -- with rest-frame equivalent widths ~1000\AA -- in the four candidates
that have HST/WFC3 grism observations, we conclude that these objects are
galaxies with 10^8 Msol in stellar mass, undergoing an enormous starburst phase
with M_*/(dM_*/dt) of only ~15 Myr. These bursts may cause outflows that are
strong enough to produce cored dark matter profiles in low-mass galaxies. The
individual star formation rates and the co-moving number density (3.7x10^-4
Mpc^-3) can produce in ~4 Gyr much of the stellar mass density that is
presently contained in 10^8-10^9 Msol dwarf galaxies. Therefore, our
observations provide a strong indication that many or even most of the stars in
present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z>1.Comment: accepted for publication in ApJ; 10 pages; 6 figures; 1 tabl
New Determinations of the UV Luminosity Functions from z~9 to z~2 show a remarkable consistency with halo growth and a constant star formation efficiency
Here we provide the most comprehensive determinations of the rest-frame
LF available to date with HST at z~2, 3, 4, 5, 6, 7, 8, and 9. Essentially all
of the non-cluster extragalactic legacy fields are utilized, including the
Hubble Ultra Deep Field (HUDF), the Hubble Frontier Field parallel fields, and
all five CANDELS fields, for a total survey area of 1136 arcmin^2. Our
determinations include galaxies at z~2-3 leveraging the deep HDUV, UVUDF, and
ERS WFC3/UVIS observations available over a ~150 arcmin^2 area in the GOODS
North and GOODS South regions. All together, our collective samples include
>24,000 sources, >2.3x larger than previous selections with HST. 5766, 6332,
7240, 3449, 1066, 601, 246, and 33 sources are identified at z~2, 3, 4, 5, 6,
7, 8, and 9, respectively. Combining our results with an earlier z~10 LF
determination by Oesch+2018a, we quantify the evolution of the LF. Our
results indicate that there is (1) a smooth flattening of the faint-end slope
alpha from alpha~-2.4 at z~10 to -1.5 at z~2, (2) minimal evolution in the
characteristic luminosity M* at z>~2.5, and (3) a monotonic increase in the
normalization log_10 phi* from z~10 to z~2, which can be well described by a
simple second-order polynomial, consistent with an "accelerated" evolution
scenario. We find that each of these trends (from z~10 to z~2.5 at least) can
be readily explained on the basis of the evolution of the halo mass function
and a simple constant star formation efficiency model.Comment: 18 pages, 10 figures, 5 tables, in submission to ApJ, figures 9 and
10 show the main resul
Hubble Frontier Fields: a high-precision strong-lensing analysis of the massive galaxy cluster Abell 2744 usingâŒ180 multiple images
We present a high-precision mass model of galaxy cluster Abell 2744, based on a strong gravitational-lensing analysis of the Hubble Space Telescope Frontier Fields (HFF) imaging data, which now include both Advanced Camera for Surveys and Wide Field Camera 3 observations to the final depth. Taking advantage of the unprecedented depth of the visible and near-infrared data, we identify 34 new multiply imaged galaxies, bringing the total to 61, comprising 181 individual lensed images. In the process, we correct previous erroneous identifications and positions of multiple systems in the northern part of the cluster core. With the lenstool software and the new sets of multiple images, we model the cluster using two cluster-scale dark matter haloes plus galaxy-scale haloes for the cluster members. Our best-fitting model predicts image positions with an rms error of 0.79arcsec, which constitutes an improvement by almost a factor of 2 over previous parametric models of this cluster. We measure the total projected mass inside a 200kpc aperture as (2.162±0.005) Ă1014âMâ, thus reaching 1âperâcent level precision for the second time, following the recent HFF measurement of MACSJ0416.1â2403. Importantly, the higher quality of the mass model translates into an overall improvement by a factor of 4 of the derived magnification factor. Together with our previous HFF gravitational lensing analysis, this work demonstrates that the HFF data enables high-precision mass measurements for massive galaxy clusters and the derivation of robust magnification maps to probe the early Univers
Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a starburst-driven outflow
We present the detection of Ly-alpha, [OIII] and H-alpha emission associated
with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards
the quasar SDSS J113520-001053. This is the largest HI column density ever
measured along a QSO line of sight, though typical of what is seen in GRB-DLAs.
This absorption system also classifies as ultrastrong MgII system with
W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion
factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally
larger than) the mean values found in the general QSO-DLA population. The
[OIII]-Ha emitting region has a very small impact parameter with respect to the
QSO line of sight, b=0.1", and is unresolved. From the Ha line, we measure
SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More
strikingly, the blue and red Ly-a peaks arise from distinct regions extended
over a few kpc on either side of the star-forming region. We propose that this
is the consequence of Ly-a transfer in outflowing gas. The presence of
starburst-driven outflows is also in agreement with the large SFR together with
a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV
continuum luminosity of the galaxy, we estimate an age of at most a few 10^7
yr, again consistent with a recent starburst scenario. We interpret the data as
the observation of a young, gas rich, compact starburst galaxy, from which
material is expelled through collimated winds powered by the vigorous star
formation activity. We substantiate this picture by modelling the radiative
transfer of Ly-a photons in the galactic counterpart. Though our model (a
spherical galaxy with bipolar outflowing jets) is a simplistic representation
of the true gas distribution and velocity field, the agreement between the
observed and simulated properties is particularly good. [abridged]Comment: 15 pages, 18 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
Outbreak of Marburg hemorrhagic fever among miners in Kamwenge and Ibanda Districts, Uganda, 2007
Marburg hemorrhagic fever was detected among 4 miners in Ibanda District, Uganda, from June through September, 2007. Infection was likely acquired through exposure to bats or bat secretions in a mine in Kamwenge District, Uganda, and possibly human-to-human transmission between some patients. We describe the epidemiologic investigation and the health education response
A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation
We present Hubble Space Telescope Wide Field Camera 3 slitless grism
spectroscopy of 28 emission-line galaxies at z~2, in the GOODS-S region of the
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The
high sensitivity of these grism observations, with 1-sigma detections of
emission lines to f > 2.5x10^{-18} erg/s/cm^2, means that the galaxies in the
sample are typically ~7 times less massive (median M_* = 10^{9.5} M_sun) than
previously studied z~2 emission-line galaxies. Despite their lower mass, the
galaxies have OIII/Hb ratios which are very similar to previously studied z~2
galaxies and much higher than the typical emission-line ratios of local
galaxies. The WFC3 grism allows for unique studies of spatial gradients in
emission lines, and we stack the two-dimensional spectra of the galaxies for
this purpose. In the stacked data the OIII emission line is more spatially
concentrated than the Hb emission line with 98.1 confidence. We additionally
stack the X-ray data (all sources are individually undetected), and find that
the average L(OIII)/L(0.5-10 keV) ratio is intermediate between typical z~0
obscured active galaxies and star-forming galaxies. Together the compactness of
the stacked OIII spatial profile and the stacked X-ray data suggest that at
least some of these low-mass, low-metallicity galaxies harbor weak active
galactic nuclei.Comment: ApJ accepted. 8 pages, 6 figure
A predictive decision support system for coronavirus disease 2019 response management and medical logistic planning
Objective: Coronavirus disease 2019 demonstrated the inconsistencies in adequately responding to biological threats on a
global scale due to a lack of powerful tools for assessing various factors in the formation of the epidemic situation and
its forecasting. Decision support systems have a role in overcoming the challenges in health monitoring systems in light
of current or future epidemic outbreaks. This paper focuses on some applied examples of logistic planning, a key service
of the Earth Cognitive System for Coronavirus Disease 2019 project, here presented, evidencing the added value of artificial
intelligence algorithms towards predictive hypotheses in tackling health emergencies.
Methods: Earth Cognitive System for Coronavirus Disease 2019 is a decision support system designed to support healthcare
institutions in monitoring, management and forecasting activities through artificial intelligence, social media analytics, geo-
spatial analysis and satellite imaging. The monitoring, management and prediction of medical equipment logistic needs rely
on machine learning to predict the regional risk classification colour codes, the emergency rooms attendances, and the fore-
cast of regional medical supplies, synergically enhancing geospatial and temporal dimensions.
Results: The overall performance of the regional risk colour code classifier yielded a high value of the macro-average
F1-score (0.82) and an accuracy of 85%. The prediction of the emergency rooms attendances for the Lazio region yielded
a very low root mean square error (<11 patients) and a high positive correlation with the actual values for the major hos-
pitals of the Lazio region which admit about 90% of the regionâs patients. The prediction of the medicinal purchases for the
regions of Lazio and Piemonte has yielded a low root mean squared percentage error of 16%.
Conclusions: Accurate forecasting of the evolution of new cases and drug utilisation enables the resulting excess demand
throughout the supply chain to be managed more effectively. Forecasting during a pandemic becomes essential for effective
government decision-making, managing supply chain resources, and for informing tough policy decisions
Spectroscopic Confirmation of Three z-Dropout Galaxies at z = 6.844 - 7.213: Demographics of Lyman-Alpha Emission in z ~ 7 Galaxies
We present the results of our ultra-deep Keck/DEIMOS spectroscopy of
z-dropout galaxies in the SDF and GOODS-N. For 3 out of 11 objects, we detect
an emission line at ~ 1um with a signal-to-noise ratio of ~ 10. The lines show
asymmetric profiles with high weighted skewness values, consistent with being
Lya, yielding redshifts of z=7.213, 6.965, and 6.844. Specifically, we confirm
the z=7.213 object in two independent DEIMOS runs with different spectroscopic
configurations. The z=6.965 object is a known Lya emitter, IOK-1, for which our
improved spectrum at a higher resolution yields a robust skewness measurement.
The three z-dropouts have Lya fluxes of 3 x 10^-17 erg s^-1 cm^-2 and
rest-frame equivalent widths EW_0^Lya = 33-43A. Based on the largest
spectroscopic sample of 43 z-dropouts that is the combination of our and
previous data, we find that the fraction of Lya-emitting galaxies (EW_0^Lya >
25A) is low at z ~ 7; 17 +- 10% and 24 +- 12% for bright (Muv ~= -21) and faint
(Muv ~= -19.5) galaxies, respectively. The fractions of Lya-emitting galaxies
drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies
than for bright galaxies. These two pieces of evidence would indicate that the
neutral hydrogen fraction of the IGM increases from z ~ 6 to 7, and that the
reionization proceeds from high- to low-density environments, as suggested by
an inside-out reionization model.Comment: 15 pages, 9 figures, accepted for publication in Ap
- âŠ