X‐ray mirrors with high focusing performances are commonly used in different sectors of science, such as X‐ray astronomy, medical imaging and synchrotron/free‐electron laser beamlines. While ...deformations of the mirror profile may cause degradation of the focus sharpness, a deliberate deformation of the mirror can be made to endow the focus with a desired size and distribution, via piezo actuators. The resulting profile can be characterized with suitable metrology tools and correlated with the expected optical quality via a wavefront propagation code or, sometimes, predicted using geometric optics. In the latter case and for the special class of profile deformations with monotonically increasing derivative, i.e. concave upwards, the point spread function (PSF) can even be predicted analytically. Moreover, under these assumptions, the relation can also be reversed: from the desired PSF the required profile deformation can be computed analytically, avoiding the use of trial‐and‐error search codes. However, the computation has been so far limited to geometric optics, which entailed some limitations: for example, mirror diffraction effects and the size of the coherent X‐ray source were not considered. In this paper, the beam‐shaping formalism in the framework of physical optics is reviewed, in the limit of small light wavelengths and in the case of Gaussian intensity wavefronts. Some examples of shaped profiles are also shown, aiming at turning a Gaussian intensity distribution into a top‐hat one, and checks of the shaping performances computing the at‐wavelength PSF by means of the WISE code are made.
A method to obtain the deformation profile to be imparted to an X‐ray mirror in order to turn a Gaussian intensity distribution into any assigned point spread function, and how to easily check the result using physical optics.
Context. The imaging sharpness of an X-ray telescope is chiefly determined by the optical quality of its focusing optics, which in turn mostly depends on the shape accuracy and the surface finishing ...of the grazing-incidence X-ray mirrors that compose the optical modules. To ensure the imaging performance during the mirror manufacturing, a fundamental step is predicting the mirror point spread function (PSF) from the metrology of its surface. Traditionally, the PSF computation in X-rays is assumed to be different depending on whether the surface defects are classified as figure errors or roughness. This classical approach, however, requires setting a boundary between these two asymptotic regimes, which is not known a priori. Aims. The aim of this work is to overcome this limit by providing analytical formulae that are valid at any light wavelength, for computing the PSF of an X-ray mirror shell from the measured longitudinal profiles and the roughness power spectral density, without distinguishing spectral ranges with different treatments. Methods. The method we adopted is based on the Huygens-Fresnel principle for computing the diffracted intensity from measured or modeled profiles. In particular, we have simplified the computation of the surface integral to only one dimension, owing to the grazing incidence that reduces the influence of the azimuthal errors by orders of magnitude. The method can be extended to optical systems with an arbitrary number of reflections – in particular the Wolter-I, which is frequently used in X-ray astronomy – and can be used in both near- and far-field approximation. Finally, it accounts simultaneously for profile, roughness, and aperture diffraction. Results. We describe the formalism with which one can self-consistently compute the PSF of grazing-incidence mirrors, and we show some PSF simulations including the UV band, where the aperture diffraction dominates the PSF, and hard X-rays where the X-ray scattering has a major impact on the PSF degradation. The results are validated with ray-tracing simulations, or by comparison with the analytical computation of the half-energy width based on the known scattering theory, where these approaches are applicable. Finally, we validate this by comparing the simulated PSF of a real Wolter-I mirror shell with the measured PSF in hard X-rays.
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•Fermentation of sheep cheese whey performed using exclusively indigenous biomass.•Carbohydrates were converted to lactate that was then degraded to VFAs and H2.•Different metabolites ...were produced depending on pH and fermentation time.•Maximum lactate yield (23 mmol/g TOCi) was attained at pH 6.0 after 45 h.•Maximum H2 yield (162 L/kg TOCi) was attained at pH 6.0 after 168 h.
Batch dark fermentation tests were performed on sheep cheese whey without inoculum addition at different operating pHs, relating the type and production yields of the observed gaseous and liquid by-products to the evolution of fermentation. Cheese whey fermentation evolved over time in two steps, involving an initial conversion of carbohydrates to lactic acid, followed by the degradation of this to soluble and gaseous products including short-chain fatty acids (mainly acetic, butyric and propionic acids) and hydrogen. The operating pH affected the production kinetics and yields, as well as the fermentation pathways. By varying the duration of the fermentation process, different cheese whey exploitation strategies may be applied and oriented to the main production of lactic acid, hydrogen or other organic acids.
Growing food and biomass production at the global scale has determined a corresponding increase in the demand for and use of nutrients. In this study, the possibility of recovering nitrogen from ...agro-industrial digestate using bioelectrochemical systems was investigated: two microbial electrolysis cells (MECs) were fed with synthetic and real digestate (2.5 gNH
-N L
). Carbon felt and granular graphite were used as anodes in MEC-1 and MEC-2, respectively. As to synthetic wastewater, the optimal nitrogen load (NL) for MEC-1 and -2 was 1.25 and 0.75 gNH
-N d
, respectively. MEC-1 showed better performance in terms of NH
-N removal efficiency (39 ± 2.5%) and recovery rate (up to 70 gNH
-N m
d
), compared to MEC-2 (33 ± 4.7% and up to 30 gN m
d
, respectively). At the optimal hydraulic retention time, lower NH
-N removal efficiencies and recovery rates were observed when real digestate was fed to MEC-1 (29 ± 6.6% and 60 ± 13 gNH
-N m
d
, respectively) and MEC-2 (21 ± 7.9% and 10 ± 3.6 gNH
-N m
d
, respectively), likely due to the higher complexity of the influent. The average energy requirements were 3.6-3.7 kWh kgN
, comparable with values previously reported in the literature and lower than conventional ammonia recovery processes. Results are promising and may reduce the need for costly and polluting processes for nitrogen synthesis.
Hydrogen production from cheese whey through dark fermentation was investigated in this study in order to systematically analyse the effects of the operating pH. The effluents from pecorino cheese ...and mozzarella cheese production were the substrates used for the fermentation tests. Either CW only or a mixture of CW and heat-shocked activated sludge were used in mesophilic pH-controlled batch fermentation experiments. The results indicated that hydrogen production was strongly affected by multiple factors including the substrate characteristics, the addition of an inoculum as well as the pH. The process variables were found to affect to a varying extent numerous interrelated aspects of the fermentation process, including the hydrogen production potential, the type of fermentation pathways, as well as the process kinetics. The fermentation products varied largely with the operating conditions and mirrored the H sub(2) yield. Significant fermentative biohydrogen production was attained at pHs of 6.5-7.5, with the best performance in terms of H sub(2) generation potential (171.3 NL H sub(2)/kg TOC) being observed for CW from mozzarella cheese production, at a pH value of 6.0 with the heat-shocked inoculum.
Aims.The focusing performance of X-ray optics (conveniently expressed in terms of HEW, Half Energy Width) strongly depend on both mirrors deformations and photon scattering caused by the ...microroughness of reflecting surfaces. In particular, the contribution of X-ray Scattering (XRS) to the HEW of the optic is usually an increasing function $H(E)$ of the photon energy E. Therefore, in future hard X-ray imaging telescopes of the future (SIMBOL-X, NeXT, Constellation-X, XEUS), the X-ray scattering could be the dominant problem since they will operate also in the hard X-ray band (i.e. beyond 10 keV). In order to ensure the imaging quality at all energies, clear requirements have to be established in terms of reflecting surfaces microroughness. Methods.Several methods were proposed in the past years to estimate the scattering contribution to the HEW, dealing with the surface microroughness expressed in terms of its Power Spectral Density (PSD), on the basis of the well-established theory of X-ray scattering from rough surfaces. We faced that problem on the basis on the same theory, but we tried a new approach: the direct, analytical translation of a given surface roughness PSD into a $H(E)$ trend, and – vice versa – the direct translation of a $H(E)$ requirement into a surface PSD. This PSD represents the maximum tolerable microroughness level in order to meet the $H(E)$ requirement in the energy band of a given X-ray telescope. Results.We have thereby found a new, analytical and widely applicable formalism to compute the XRS contribution to the HEW from the surface PSD, provided that the PSD had been measured in a wide range of spatial frequencies. The inverse problem was also solved, allowing the immediate evaluation of the mirror surface PSD from a measured function $H(E)$. The same formalism allows establishing the maximum allowed PSD of the mirror in order to fulfill a given $H(E)$ requirement. Practical equations are firstly developed for the case of a single-reflection optic with a single-layer reflective coating, and then extended to an optical system with N identical reflections. The results are approximately valid also for multilayer-coated mirrors to be adopted in hard X-rays. These results will be extremely useful in order to establish the surface finishing requirements for the optics of future X-ray telescopes.
This paper presents the results of an extensive set of laboratory experiments performed to design a demonstrative electrokinetic plant for extracting heavy metals from marine sediments dredged from ...the Livorno marine harbour. The investigated sediments displayed a high salinity, a high acid neutralization capacity, a low electrical resistivity (0.5Ωm), a high alkalinity (pH≈8) and a large fraction of fine particles. The target metals were Cd, Cr, Cu, Ni, Pb and Zn at relatively weak and inhomogeneous concentrations with high non-mobile fractions. After an accurate characterization, several screening and full electrokinetic tests were performed using cells of two different sizes, several conditioning agents (HNO3, HCl, H2SO4, citric acid, oxalic acid, ascorbic acid, EDTA), different applied current intensities and durations. The tests highlighted the need for long treatment times in order to obtain a significant pH reduction, with some appreciable metal removal being attained only after several weeks. The best results were obtained with strong acids used as the conditioning agents, with significant specific effects of each acid, including pronounced resistivity increase (from 0.5 up to 10Ωm) and a high electroosmotic flow (EOF) with H2SO4, or a reversed EOF (electroendosmosis), and minor resistivity changes with HNO3. The use of the obtained data to design a demonstrative plant is also presented in the paper, with considerations on operating parameters such as energy and reagent consumption, characteristics of plant components and required safety measures.
Ash generated by biomass combustion has been envisaged as a potential composting additive in order to address some of the most common critical issues concerning the composting process and final ...product quality. Nonetheless, a deeper awareness for the effective feasibility of such ash reuse option should be pursued. In this work, all the ash types produced at different sections of a typical biomass combustion plant (namely bottom, boiler and fly ash) were characterised with the scope of identifying the weaknesses and strengths of each residue in the light of their reuse as a composting additive. The results manifest that boiler and fly ash were very enriched in nutrients such as calcium, potassium, magnesium and phosphorus. They also had high porosity and water holding capacity. Because of these properties, they could act as a mineral additive and a physical amendment in composting. The pH values for boiler and fly ash were 12 and 13, respectively, so they could also act as a liming agent in composting of acidic substrates. The electrical conductivity was high (16 and 33 mS·cm−1, respectively) and could be harmful for plant growth. On the other hand, bottom ash had low salinity and alkalinity, but the physical properties and nutrient content were not of interest for composting. Heavy metals release was not a concern in all the ash types.
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•The amount of biomass combustion ash produced worldwide is rapidly increasing.•The lack of recovery option which are specific for biomass ash is acknowledged.•Characterisation is fundamental for evaluating any possible reuse option.•Biomass ash could be used as an additive in the organic waste composting.•Ash contains nutrients and micronutrients, has high pH, porosity and free airspace.
•A factorial study of biohydrogen production from food waste was conducted.•The influence of pH and ISR on fermentation was assessed.•Regression and response surface analyses were used to interpret ...the results.•Multiple fermentation pathways were likely to overlap during fermentation.•The maximum yield was 160 L H2/kg TOCFW at pH = 5.5 and ISR = 1.74 g VS/g TOC.
Factorial fermentation experiments on food waste (FW) inoculated with activated sludge (AS) were conducted to investigate the effects of pH and the inoculum-to-substrate ratio (ISR g VSAS/g TOCFW) on biohydrogen production. The two parameters affected the H2 yield, the fermentation rate and the biochemical pathways. The minimum and maximum yields were 41 L H2/kg TOCFW (pH = 7.5, ISR = 1.74) and 156–160 L H2/kg TOCFW (pH = 5.5, ISR = 0.58 and 1.74). The range of carbohydrates conversion into H2 was 0.37–1.45 mol H2/mol hexose, corresponding to 9.4–36.2% of the theoretical threshold. A second-order predictive model for H2 production identified an optimum region at low pHs and high ISRs, with a theoretical maximum of 168 L H2/kg TOCFW at pH = 5.5 and ISR = 1.74. The Spearman’s correlation method revealed several relationships between the variables, suggesting the potentially governing metabolic pathways, which turned out to involve both hydrogenogenic pathways and competing reactions.
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