•Fluoride removal from drinking water by electrocoagulation using aluminum anodes.•SEM, EDA-X and FTIR analyses confirmed the presence of fluoride in the flocs.•Electrocoagulation led to fluoride ...removal from 10 to 1mgL−1 with 0.37kWhm−3.•At currents of 4–6mAcm−2 and flow rates of 0.91–1.82cms−1 F− removal is favored.•At j>7mAcm−2 massive generation of electrolytic gases disfavored F− removal.
This investigation is about fluoride removal from synthetic drinking water (10mgL−1 F− in 0.5gL−1 Na2SO4 and 1.5mgL−1 ClO− at pH 7.7 and conductivity 410μScm−1), by electrocoagulation (EC) using aluminum as the sacrificial anode in a continuous filter press reactor coupled to a flocculator and clarifier (sludge settler). The influence of current density (j) and linear flow velocity in the EC reactor (ur) on the fluoride removal efficiency was analyzed. The EC tests that satisfy the WHO norm for fluoride (CF⩽1.5mgL−1) were obtained at 0.91⩽ur⩽1.82cms−1 and 5⩽j⩽7mAcm−2, giving aluminum doses between 19.28⩽CAl(III)⩽52.67mgL−1. Scanning Electron Microscopy (SEM), Energy Dispersive Analysis of X-rays (EDA-X) and Fourier Transform Infrared Spectroscopy (FTIR) analyses were performed to confirm the presence of fluoride in the flocs. The best EC tests in terms of energy consumption was obtained at 5mAcm−2, with a mean linear flow velocity in the EC reactor of 1.82cms−1, which gives an energy consumption of 0.37kWhm−3, during the removal of fluoride from 10 to 1mgL−1. EC at j>7mAcm−2 did not improve the EC process any further owing to massive generation of electrolytic gases which promote the breaking of the flocs.
We present a carefully selected sub-sample of Swift long gamma-ray bursts (GRBs) that is complete in redshift. The sample is constructed by considering only bursts with favorable observing conditions ...for ground-based follow-up searches, which are bright in the 15-150 keV Swift/BAT band, i.e., with 1-s peak photon fluxes in excess to 2.6 photons s super(-1) cm super(-2). The sample is composed of 58 bursts, 52 of them with redshift for a completeness level of 90%, while another two have a redshift constraint, reaching a completeness level of 95%. For only three bursts we have no constraint on the redshift. The high level of redshift completeness allows us for the first time to constrain the GRB luminosity function and its evolution with cosmic times in an unbiased way. We find that strong evolution in luminosity ( delta sub()l = 2.3 + or - 0.6) or in density ( delta sub()d = 1.7 + or - 0.5) is required in order to account for the observations. The derived redshift distributions in the two scenarios are consistent with each other, in spite of their different intrinsic redshift distributions. This calls for other indicators to distinguish among different evolution models. Complete samples are at the base of any population studies. In future works we will use this unique sample of Swift bright GRBs to study the properties of the population of long GRBs.
The Gamma-ray Burst Monitor (GBM) on board Fermi allows us to study the spectra of gamma-ray bursts (GRBs) over an unprecedented wide energy range (8 keV-35 MeV). We compare the spectral properties ...of short and long GRBs detected by the GBM (up to 2010 March) with those of GRBs detected by the Burst And Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO). GBM and BATSE long bursts have similar distributions of fluence (F), E
obs
peak and peak flux (P) but GBM bursts have a slightly harder low-energy spectral index α with respect to BATSE GRBs. GBM and BATSE short bursts have similar distributions of fluence, α and peak flux, with GBM bursts having slightly larger E
obs
peak. We discuss these properties in light of the correlations found between E
obs
peak and the fluence and the peak flux. GBM bursts confirm that these correlations are not determined by instrumental selection effects. Indeed, GBM bursts extend the E
obs
peak-F and E
obs
peak-P correlations both in fluence/peak flux and in peak energy. No GBM long burst with E
obs
peak exceeding a few MeV is found, despite the possibility of detecting it. Similarly to what is found with BATSE, there are 3 per cent of GBM long bursts (and almost all short ones) that are outliers at more than 3σ of the E
peak-E
iso correlation. In contrast, there is no outlier of the E
peak-L
iso correlation, for both long and short GBM bursts.
ABSTRACT
We study the spectral evolution on second and subsecond time‐scales in 11 long and 12 short gamma‐ray bursts (GRBs) with peak flux >8.5 × 10−6 erg cm−2 s (8 keV–35 MeV) detected by the Fermi ...satellite. The peak flux correlates with the time‐averaged peak energy in both classes of bursts. The peak energy evolution, as a function of time, tracks the evolution of the flux on short time‐scales in both short and long GRBs. We do not find evidence of a hard‐to‐soft spectral evolution. While short GRBs have observed peak energies larger than few MeV during most of their evolution, long GRBs can start with a softer peak energy (of few hundreds keV) and become as hard as short ones (i.e. with Eobspeak larger than few MeV) at the peak of their light curve. Six GRBs in our sample have a measured redshift. In these few cases we find that their correlations between the rest frame Epeak and the luminosity Liso are less scattered than their correlations in the observer frame between the peak energy Eobspeak and the flux P. We find that the rest frame Epeak of long bursts can be as high or even larger than that of short GRBs and that short and long GRBs follow the same Epeak(t)–Liso(t) correlation, despite the fact that they likely have different progenitors.
In this paper, we compute rest-frame extinctions for the afterglows of a sample of Swift gamma-ray bursts (GRBs) complete in redshift. The selection criteria of the sample are based on observational ...high-energy parameters of the prompt emission and therefore our sample should not be biased against dusty sight-lines. It is therefore expected that our inferences hold for the general population of GRBs. Our main result is that the optical/near-infrared extinction of GRB afterglows in our sample does not follow a single distribution. 87 per cent of the events are absorbed by less than 2 mag, and 50 per cent suffer from less than 0.3-0.4 mag extinction. The remaining 13 per cent of the afterglows are highly absorbed. The true percentage of GRB afterglows showing high absorption could be even higher since a fair fraction of the events without reliable redshift measurement are probably part of this class. These events may be due to highly dusty molecular clouds/star-forming regions associated with the GRB progenitor or along the afterglow line of sight, and/or due to massive dusty host galaxies. No clear evolution in the dust extinction properties is evident within the redshift range of our sample, although the largest extinctions are at z ∼ 1.5-2, close to the expected peak of the star formation rate. Those events classified as dark are characterized, on average, by a higher extinction than typical events in the sample. A correlation between optical/near-infrared extinction and hydrogen-equivalent column density based on X-ray studies is shown, although the observed N
H appears to be well in excess compared to those observed in the Local Group. Dust extinction does not seem to correlate with GRB energetics or luminosity.
Macroscopic wear experiments were complemented by atomistic simulations to study the effect of nano- and micro-scale titanium dioxide particle lubricant additives on friction and wear. The size of ...the particles and initial roughness of the sliding surfaces were varied to characterize the interrelated effects of these two properties. Results from both experiments and simulations suggest that there is an optimal particle size that will minimize friction and wear for a given surface roughness. Analyses support a previously-proposed mechanism for particle-based additives in which the particles fill in valleys on the sliding surfaces. In this context, particles that are smaller than the characteristic roughness of the surfaces are most likely to perform this function.
•Wear experiments and atomistic simulations were used to study nano- and micro-scale particle additives.•The particle size and initial roughness of the sliding surfaces were varied.•Results suggest an optimal particle size can minimize friction and wear.•Findings support a mechanism in which particles fill in valleys on sliding surfaces.•The initial roughness of sliding surfaces can determine particle additive effectiveness.
Recreating human tissues and organs in the petri dish to establish models as tools in biomedical sciences has gained momentum. These models can provide insight into mechanisms of human physiology, ...disease onset, and progression, and improve drug target validation, as well as the development of new medical therapeutics. Transformative materials play an important role in this evolution, as they can be programmed to direct cell behavior and fate by controlling the activity of bioactive molecules and material properties. Using nature as an inspiration, scientists are creating materials that incorporate specific biological processes observed during human organogenesis and tissue regeneration. This article presents the reader with state‐of‐the‐art developments in the field of in vitro tissue engineering and the challenges related to the design, production, and translation of these transformative materials. Advances regarding (stem) cell sources, expansion, and differentiation, and how novel responsive materials, automated and large‐scale fabrication processes, culture conditions, in situ monitoring systems, and computer simulations are required to create functional human tissue models that are relevant and efficient for drug discovery, are described. This paper illustrates how these different technologies need to converge to generate in vitro life‐like human tissue models that provide a platform to answer health‐based scientific questions.
Transformative materials can be programmed to direct cell behavior and fate by controlling the activity of bioactive molecules and material properties. Using nature as an inspiration, scientists are developing novel materials to create in vitro tissue models that can provide insight into mechanisms of human physiology and disease, improve drug target validation, and facilitate the development of new medical therapeutics.
The jet opening angle θjet and the bulk Lorentz factor Γ0 are crucial parameters for the computation of the energetics of gamma-ray bursts (GRBs). From the ∼30 GRBs with measured θjet or Γ0 it is ...known that (i) the real energetic E
γ, obtained by correcting the isotropic equivalent energy E
iso for the collimation factor ∼ θ2
jet, is clustered around 1050-1051 erg and it is correlated with the peak energy E
p of the prompt emission and (ii) the comoving frame E′p and E′γ are clustered around typical values. Current estimates of Γ0 and θjet are based on incomplete data samples and their observed distributions could be subject to biases. Through a population synthesis code we investigate whether different assumed intrinsic distributions of Γ0 and θjet can reproduce a set of observational constraints. Assuming that all bursts have the same E′p and E′γ in the comoving frame, we find that Γ0 and θjet cannot be distributed as single power laws. The best agreement between our simulation and the available data is obtained assuming (a) log-normal distributions for θjet and Γ0 and (b) an intrinsic relation between the peak values of their distributions, i.e. θjet
2.5Γ0 = const. On average, larger values of Γ0 (i.e. the 'faster' bursts) correspond to smaller values of θjet (i.e. the 'narrower'). We predict that ∼6 per cent of the bursts that point to us should not show any jet break in their afterglow light curve since they have sin θjet < 1/Γ0. Finally, we estimate that the local rate of GRBs is ∼0.3 per cent of all local Type Ib/c supernova (SNIb/c) and ∼4.3 per cent of local hypernovae, i.e. SNIb/c with broad lines.
Gamma Ray Bursts (GRBs) are a powerful probe of the high-redshift Universe. We present a tool to estimate the detection rate of high-z GRBs by a generic detector with defined energy band and ...sensitivity. We base this on a population model that reproduces the observed properties of GRBs detected by Swift, Fermi and CGRO in the hard X-ray and γ-ray bands. We provide the expected cumulative distributions of the flux and fluence of simulated GRBs in different energy bands. We show that scintillator detectors, operating at relatively high energies (e.g. tens of keV to the MeV), can detect only the most luminous GRBs at high redshifts due to the link between the peak spectral energy and the luminosity (E
peak–L
iso) of GRBs. We show that the best strategy for catching the largest number of high-z bursts is to go softer (e.g. in the soft X-ray band) but with a very high sensitivity. For instance, an imaging soft X-ray detector operating in the 0.2–5 keV energy band reaching a sensitivity, corresponding to a fluence, of ∼10−8 erg cm−2 is expected to detect ≈40 GRBs yr−1 sr−1 at z ≥ 5 (≈3 GRBs yr−1 sr−1 at z ≥ 10). Once high-z GRBs are detected the principal issue is to secure their redshift. To this aim we estimate their NIR afterglow flux at relatively early times and evaluate the effectiveness of following them up and construct usable samples of events with any forthcoming GRB mission dedicated to explore the high-z Universe.
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