139 research outputs found
Hybrid storage system coupled with PV power plant for primary frequency control
Transitioning from fossil fuel classical generators to intermittent, non-synchronous sources like solar and wind presents a series of technical challenges to be overcome on large scale. A specific issue is related with the concept of inertia of the electrical system: the less the number of generators with rotating masses connected to the grid, the less the value of total inertia of the system. Solar driven generating units such as PV present no mechanical inertia, therefore their increase in the electricity generation mix decreases the total inertia of the system, which lower the overall reliability of the system. Logically, it is of fundamental importance to ensure that PV power plants are more and more capable to provide ancillary services to improve the stability of the grid, especially in terms of frequency. The need for faster frequency regulation and voltage control in the electrical system can be ensured effectively by energy storage systems. In the purpose of this study it is addressed the possibility of large battery systems to overcome the variability of the solar resource, and the forecasting error, resulting in higher profit for a PV plant operator. The methodology consists in the formulation and the resolution of a Non-Linear Programming (NLP) problem, implemented in GAMS, applied to a 9.4 MW PV power plant. The output of the simulation determines the parameters that characterize the optimal Hybrid Storage System, in order to increase the profit during one typical day of solar radiation (01 April), while participating actively in the PFC. The result of the investigation determines that the most profitable hybrid storage system to be coupled with the PVPP is formed by a 883 kWh Lithium Ion Battery and a 32 kWh High Speed Flywheel. The analysis is finally complemented with a realistic simulation in Simulink environment in which is developed and implemented a prototype of EM
Dust Enshrouded AGN Models for Hyperluminous High Redshift IR Galaxies
We investigate models for the power supply and broad-band spectral energy
distribution (SED) of hyperluminous IR galaxies, recently discovered at high
redshifts, in terms of the emission from an active nucleus embedded in a
torus-like dusty structure. We find consistent solutions in terms of a simple
torus model extended several hundreds of parsecs, with in the equatorial
plane of a few hundreds and a typical covering factor of over . Objects
as different as the prototype high-z galaxy \fd, the z=0.93 IR object \fq, \fz\
found in a high-z cooling flow, and the optically selected BAL "Cloverleaf"
quasar, are all fitted by the same solution, for decreasing values of the polar
angle to the line-of-sight and proper scaling of the luminosities. We suggest
that such luminous high-z IR objects are heavily buried quasars surrounded by
large amounts of dust with high covering factors and large optical depths.
Comparison with UVX QSOs suggests that they are observed during a transient
phase. Forthcoming observations in the far-IR will soon allow probing this
phase and its relationship with the -- possibly concomitant -- formation of the
nuclear black hole and of the host galaxy.Comment: 12 pages including 3 figures. To appear on APJ
User Value in Modern Payment Platforms: A Graph Approach
Payment platforms have signiïŹcantly evolved in recent years to keep pace with the proliferation of online and cashless payments. These platforms are increasingly aligned with online social networks, allowing users to interact with each other and transfer small amounts of money in a Peer-to-Peer fashion. This poses new challenges for analysing payment data, as traditional methods are only user-centric or business-centric and neglect the network users build during the interaction. This paper proposes a ïŹrst methodology for measuring user value in modern payment platforms. We combine quantitative user-centric metrics with an analysis of the graph created by usersâ activities and its topological features inspired by the evolution of opinions in social networks. We showcase our approach using a dataset from a large operational payment platform and show how it can support business decisions and marketing campaign design, e.g., by targeting speciïŹc users
NGC1600 - Cluster or Field Elliptical?
A study of the galaxy distribution in the field of the elliptical galaxy
NGC1600 has been undertaken. Although this galaxy is often classified as a
member of a loose group, all the neighbouring galaxies are much fainter and
could be taken as satellites of NGC1600. The number density profile of galaxies
in the field of this galaxy shows a decline with radius, with evidence of a
background at approximately 1.3 Mpc. The density and number density profile are
consistent with that found for other isolated early-type galaxies. NGC1600
appears as an extended source in X-rays, and the center of the X-ray emission
seems not to coincide with the center of the galaxy. The velocity distribution
of neighbouring galaxies has been measured from optical spectroscopic
observations and shows that the mean radial velocity is approximately 85 km/s
less than that of NGC1600, indicating that the centre of mass could lie outside
the galaxy. The velocity dispersion of the `group' is estimated at 429 km/s.
The inferred mass of the system is therefore of the order of 10^14 solar
masses, a value that corresponds to a large group. NGC1600 therefore shares
some similarities, but is not identical to, the `fossil clusters' detected in
X-ray surveys. Implications of this result for studies of isolated early-type
galaxies are briefly discussed.Comment: 8 pages, 5 figures and 2 table, accepted for publication in the Ap
Calcium supplementation for the prevention of colorectal adenomas: A systematic review and meta-analysis of randomized controlled trials
AIM: To determine the efficacy of calcium supplementation in reducing the recurrence of colorectal adenomas.
METHODS: We conducted a systematic review and meta-analysis of published studies. We searched PubMed, Scopus, the Cochrane Library, the WHO International Clinical Trials Registry Platform, and the ClinicalTrials.gov website, through December 2015. Randomized, placebo-controlled trials assessing supplemental calcium intake for the prevention of recurrence of adenomas were eligible for inclusion. Two reviewers independently selected studies based on predefined criteria, extracted data and outcomes (recurrence of colorectal adenomas, and advanced or âhigh-riskâ adenomas), and rated each trialâs risk-of-bias. Between-study heterogeneity was assessed, and pooled risk ratio (RR) estimates with their 95% confidence intervals (95%CI) were calculated using fixed- and random-effects models. To express the treatment effect in clinical terms, we calculated the number needed to treat (NNT) to prevent one adenoma recurrence. We also assessed the quality of evidence using GRADE.
RESULTS: Four randomized, placebo-controlled trials met the eligibility criteria and were included. Daily doses of elemental calcium ranged from 1200 to 2000 mg, while the duration of treatment and follow-up of participants ranged from 36 to 60 mo. Synthesis of intention-to-treat data, for participants who had undergone follow-up colonoscopies, indicated a modest protective effect of calcium in prevention of adenomas (fixed-effects, RR = 0.89, 95%CI: 0.82-0.96; random-effects, RR = 0.87, 95%CI: 0.77-0.98; high quality of evidence). The NNT was 20 (95%CI: 12-61) to prevent one colorectal adenoma recurrence within a period of 3 to 5 years. On the other hand, the association between calcium treatment and advanced adenomas did not reach statistical significance (fixed-effects, RR = 0.92, 95%CI: 0.75-1.13; random-effects, RR = 0.92, 95%CI: 0.71-1.18; moderate quality of evidence).
CONCLUSION: Our results suggest a modest chemopreventive effect of calcium supplements against recurrent colorectal adenomas over a period of 36 to 60 mo. Further research is warranted
Treatment with a Urokinase Receptor-derived Cyclized Peptide Improves Experimental Colitis by Preventing Monocyte Recruitment and Macrophage Polarization
Leukocyte migration across the blood barrier and into tissues represents a key process in the pathogenesis of inflammatory bowel diseases. The urokinase receptor (urokinase-type plasminogen activator receptor) is a master regulator of leukocyte recruitment. We recently found that cyclization of the urokinase-type plasminogen activator receptor-derived peptide Ser-Arg-Ser-Arg-Tyr [SRSRY] inhibits transendothelial migration of monocytes. Now, we have explored the effects of [SRSRY] administration during experimental colitis
A study of the galaxy redshift distribution toward the cosmic microwave background cold spot in the Corona Borealis supercluster
We present a study of the spatial and redshift distributions of Sloan Digital
Sky Survey (SDSS) galaxies toward the position of CrB-H, a very deep and
extended decrement in the Cosmic Microwave Background (CMB), located within the
Corona Borealis supercluster (CrB-SC). It was found in a survey with the Very
Small Array (VSA) interferometer at 33 GHz, with a peak negative brightness
temperature of -230 muK, and deviates 4.4-sigma from the Gaussian CMB
(G\'enova-Santos et al.). Observations with the Millimeter and Infrared Testa
Grigia Observatory (MITO) suggested that 25$^+21_-18% of this decrement may be
caused by the thermal Sunyaev-Zel'dovich (tSZ) effect (Battistelli et al.).
Here we investigate whether the galaxy distribution could be tracing either a
previously unnoticed galaxy cluster or a Warm/Hot Intergalactic Medium (WHIM)
filament that could build up this tSZ effect.
We find that the projected density of galaxies outside Abell clusters and
with redshifts 0.05<z<0.12 at the position of CrB-H is the highest in the area
encompassed by the CrB-SC. Most of these galaxies are located around redshifts
z=0.07 and z=0.11, but no clear connection in the form of a filamentary
structure is appreciable in between. While the galaxy distribution at z=0.07 is
sparse, we find evidence at z=0.11 of a galaxy group or a low-mass galaxy
cluster. We estimate that this structure could produce a tSZ effect of ~ -18
muK. The remaining VSA signal of ~ -212 muK is still a significant 4.1-sigma
deviation from the Gaussian CMB. However, the MITO error bar allows for a
larger tSZ effect, which could be produced by galaxy clusters or superclusters
beyond the sensitivity of the SDSS. Contributions from other possible secondary
anisotropies associated with these structures are also discussed.Comment: 11 pages, 5 figures, 3 tables. Accepted in MNRA
Thick tori around AGN: the case for extended tori and consequences for their X-ray and IR emission
Two families of models of dusty tori in AGNs (moderately thick and extended
versus very thick and compact) are tested against available observations. The
confrontation suggests that the former class better explains the IR broad-band
spectra of both broad and narrow line AGNs, the anisotropy of the emission
deduced by comparing IR properties of Seyfert 1 and 2 nuclei, the results of IR
spectroscopy and those of high spatial resolution observations. There is
however clear evidence for a broad distribution of optical depths. We also
examine the relationship between IR and X-ray emission. The data support a view
in which the matter responsible for the X-ray absorption is mostly dust free,
lying inside the dust sublimation radius. The consequences of these results for
the hard X-ray background as well as IR counts and background are discussed.Comment: 33 pages, 9 Postscript figures, to appear in ApJ, September 199
Radio source calibration for the VSA and other CMB instruments at around 30 GHz
Accurate calibration of data is essential for the current generation of CMB
experiments. Using data from the Very Small Array (VSA), we describe procedures
which will lead to an accuracy of 1 percent or better for experiments such as
the VSA and CBI. Particular attention is paid to the stability of the receiver
systems, the quality of the site and frequent observations of reference
sources. At 30 GHz the careful correction for atmospheric emission and
absorption is shown to be essential for achieving 1 percent precision. The
sources for which a 1 percent relative flux density calibration was achieved
included Cas A, Cyg A, Tau A and NGC7027 and the planets Venus, Jupiter and
Saturn. A flux density, or brightness temperature in the case of the planets,
was derived at 33 GHz relative to Jupiter which was adopted as the fundamental
calibrator. A spectral index at ~30 GHz is given for each. Cas A,Tau A, NGC7027
and Venus were examined for variability. Cas A was found to be decreasing at
percent per year over the period March 2001 to August 2004.
In the same period Tau A was decreasing at percent per year. A
survey of the published data showed that the planetary nebula NGC7027 decreased
at percent per year over the period 1967 to 2003. Venus showed
an insignificant ( percent) variation with Venusian illumination.
The integrated polarization of Tau A at 33 GHz was found to be
percent at pa .}Comment: 13 pages, 15 figures, submitted to MNRA
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