To exploit the promised benefits of engineered nanomaterials, it is necessary to improve our knowledge of their bioavailability and toxicity. The interactions between engineered nanomaterials and ...vascular plants are of particular concern, as plants closely interact with soil, water, and the atmosphere, and constitute one of the main routes of exposure for higher species, i.e. accumulation through the food chain. A review of the current literature shows contradictory evidence on the phytotoxicity of engineered nanomaterials. The mechanisms by which engineered nanomaterials penetrate plants are not well understood, and further research on their interactions with vascular plants is required to enable the field of phytotoxicology to keep pace with that of nanotechnology, the rapid evolution of which constantly produces new materials and applications that accelerate the environmental release of nanomaterials.
Porous burners for lean-burn applications Wood, Susie; Harris, Andrew T.
Progress in energy and combustion science,
10/2008, Letnik:
34, Številka:
5
Journal Article
Recenzirano
We review research on lean methane combustion in porous burners, with an emphasis on practical aspects of burner design and operation and the application of the technology to real-world problems. In ...particular we focus on ‘ultra-lean’ combustion, where the methane concentration is actually at or below the lean flammability limit for a free flame (5% methane by volume in air). Porous burners are an advanced combustion technology whereby a premixed fuel/air mixture burns within the cavities of a solid porous matrix. They are capable of burning low-calorific value fuels and very lean fuel/air mixtures that would not normally be flammable, potentially allowing the exploitation of what would otherwise be wasted energy resources. Possible lean-burn applications include the reburn of exhaust gases from existing combustion systems, and the mitigation of fugitive methane emissions. Porous burners operate on the principle that the solid porous matrix serves as a means of recirculating heat from the hot combustion products to the incoming reactants. This results in burning velocities higher than those for a free flame, as well as extended lean flammability limits. Burner performance is also characterised by low emissions of combustion related pollutants and stable operation over a wide range of fuel concentrations and flow rates. Stable combustion of methane/air mixtures below the conventional lean limit has been observed by a number of researchers; in one study the combustion of a mixture with a fuel concentration of only 1% was reported. A number of design considerations are important as regards optimising burner performance for lean-burn applications. Foremost among these is the selection of a suitable material for the porous matrix. Possibilities include packed beds of alumina spheres or saddles, and reticulated foams made of silicon carbide or high temperature metal alloys. Other potentially significant design issues include the length of the porous bed, the use of ‘multi-section’ designs where different porous materials are used in each section, the incorporation of external heat exchangers to supplement the heat recirculation provided by the porous matrix, and the ability to operate the burner at elevated pressures. There is an extensive body of research relating to porous burners, comprising experimental and numerical investigations. However the majority of previous studies have been directed towards the use of porous burners for radiant heating applications rather than for the combustion of low-calorific value fuels. Consequently there is a lack of reliable data relating specifically to ultra-lean combustion. We identify specific areas where further research is required to progress this field. These include the influence on burner performance of the design considerations listed above, the stability of the combustion process to fluctuations in fuel concentration and flow rate, the development of reliable models specifically for ultra-lean combustion in practical burners, and the investigation of issues relating to scale-up and commercial application.
The synthesis of biomimetic, micropatterned surface coatings with topographical and chemical features to capture water from a humid atmosphere is demonstrated. The coatings are prepared by dewetting ...thin polymer films to create materials consisting of raised hydrophilic bumps on a hydrophobic background. An enhanced rate of water condensation is measured on these surfaces under representative climatic conditions.
A facile synthesis method to produce nitrogen-doped graphene containing a high atomic percentage of pyridinic N and graphitic N via the thermal annealing of graphene oxide and uric acid is reported. ...The method yielded N-doped graphene nanosheets that had high surface areas and that contained 9.22 at% nitrogen, which was present in four bonding configurations with a high ratio of pyridinic N and graphitic N. The synthesized N-doped graphene showed excellent capacitance properties, which led to the fabrication of a stacked electrode supercapacitor cell of 2-electrode configuration with a specific capacitance of 230 F g −1 at a current density of 1 A g −1 and with a remarkably high energy density of 62.6 W h kg −1 in aqueous electrolyte. Additionally, this material showed superior properties as an electrocatalyst for both the oxygen-reduction reaction (ORR) and oxygen evolution reaction (OER), producing high current density primarily via the four-electron pathway for ORR at a current density of −4.3 mA cm −2 and OER activity of a generating current density of 10 mA cm −2 at 1.74 V vs. RHE in alkaline media. Hence, this dual-natured N-doped graphene could provide a platform for developing nanostructured graphene-based advanced energy storage and conversion devices.
Photocatalytic processes are applicable in wastewater treatment, energy production, chemical synthesis, and greenhouse gas mitigation and thus have the potential to address both the consumption of ...nonrenewable fossil fuels and global warming, two of the greatest problems facing humankind. The ability to achieve these outcomes using only solar energy as an input is particularly attractive. However, the implementation of most photocatalytic processes at an effective scale requires the use of a photoreactor, a device which brings photons, a photocatalyst and reactants into contact, as well as collecting the reaction products. In this work, we review the state-of-the-art in solar photoreactor design and assess those systems which are most applicable for industrial-scale implementation. Designs for parabolic trough, compound parabolic, inclined plate, double skin sheet, rotating disk, water bell, fiber optic, and fixed/fluidized bed photoreactors are qualitatively discussed and compared. Compound parabolic photoreactors are most suited to near term applications at pilot-scale (>1000 L/day) due to their advantageous light collecting properties and well-known design methodology. Double-skin sheet photoreactors are also suited to near term applications; however, significantly less is known about their design and performance discrepancies between studies in the literature have been reported. Compared to other photoreactor designs, the significantly simplified design and low material cost of inclined plate photoreactors makes them particularly suitable for use in economically and logistically challenged areas where the volumes to be treated are small (<100 L/day). Fluidized bed photoreactors are highly efficient, but more research is needed into their design and operation for effective use with solar radiation. The other photoreactor designs reviewed are unlikely to see wide use due to, variously, high mechanical complexity, poor efficiency, and/or susceptibility to environmental conditions but may find limited use in specialized applications, e.g. in instances where it is advantageous to separate the light gathering and photocatalytic components of the photoreactor.
A new high-resolution Geophysical Fluid Dynamics Laboratory (GFDL) coupled model the High-Resolution Forecast-Oriented Low Ocean Resolution (FLOR) model (HiFLOR) has been developed and used to ...investigate potential skill in simulation and prediction of tropical cyclone (TC) activity. HiFLOR comprises high-resolution (∼25-km mesh) atmosphere and land components and a more moderate-resolution (∼100-km mesh) sea ice and ocean component. HiFLOR was developed from FLOR by decreasing the horizontal grid spacing of the atmospheric component from 50 to 25 km, while leaving most of the subgrid-scale physical parameterizations unchanged. Compared with FLOR, HiFLOR yields a more realistic simulation of the structure, global distribution, and seasonal and interannual variations of TCs, as well as a comparable simulation of storm-induced cold wakes and TC-genesis modulation induced by the Madden–Julian oscillation (MJO). Moreover, HiFLOR is able to simulate and predict extremely intense TCs (Saffir–Simpson hurricane categories 4 and 5) and their interannual variations, which represents the first time a global coupled model has been able to simulate such extremely intense TCs in a multicentury simulation, sea surface temperature restoring simulations, and retrospective seasonal predictions.
Various colloidal Ag nanoparticles that were synthesized by
M. sativa seed exudates in aqueous system under mild and non-photomediated conditions.
Display omitted
►
Medicago
sativa seed exudate is ...effective at reducing Ag salts to form and stabilize Ag(0) nanoparticles ► The particle size and shape can be modulated by varying Ag concentration, quantity of exudate, and pH ► The Ag particles were spherical, flower-like and triangular in shape, ranging from 5 to 108
nm in size ► Unpurified Ag nanoparticles have the capacity to inhibit the growth of certain bacteria.
The biogenic synthesis of metal nanomaterials offers an environmentally benign alternative to the traditional chemical synthesis routes. Colloidal silver (Ag) nanoparticles were synthesized by reacting aqueous AgNO
3 with
Medicago sativa seed exudates under non-photomediated conditions. Upon contact, rapid reduction of Ag
+ ions was observed in <1
min with Ag nanoparticle formation reaching 90% completion in <50
min. Effect of Ag concentration, quantity of exudate and pH on the particle size and shape were investigated. At Ag
+
=
0.01
M and 30
°C, largely spherical nanoparticles with diameters in the range of 5–51
nm were generated, while flower-like particle clusters (mean size
=
104
nm) were observed on treatment at higher Ag concentrations. Pre-dilution of the exudate induced the formation of single-crystalline Ag nanoplates, forming hexagonal particles and nanotriangles with edge lengths of 86–108
nm, while pH adjustment to 11 resulted in monodisperse Ag nanoparticles with an average size of 12
nm. Repeated centrifugation and redispersion enhanced the percentage of nanoplates from 10% to 75% in solution. The kinetics of nanoparticle formation were monitored using ultraviolet–visible spectroscopy and the Ag products were characterized using transmission electron microscopy, selected-area electron diffraction, scanning electron microscopy, X-ray powder diffraction, and atomic force microscopy. X-ray photoelectron spectroscopy was used to investigate the elements and chemical environment in the top layers of the as-synthesized Ag nanoparticles, while the metabolites in the exudate were analyzed using gas chromatography–mass spectroscopy. To our knowledge, this is the first account of
M. sativa seed exudate assisted synthesis and stabilization of biogenic Ag nanoparticles; the nanoplates are notably smaller and better faceted compared with those synthesized by vascular plant extracts previously reported. Stabilized films of exudate synthesized Ag nanoparticles were effective anti-bacterial agents.
In Policing the City , Harris seeks to explain the
transformation of criminal justice, particularly the transformation
of policing, between the 1780s and 1830s in the City of London. As
utilitarian ...legal reformers argued that criminal deterrence ought
to be based on certain and rational punishment rather than random
execution, they also had to control the discretionary authority of
enforcement. This meant in theory and practice the centralization
of policing in the 1830s, and the end of local policing, which was
seen as corrupt, inefficient, and unsuitable for rational criminal
justice. Revolutionary changes in policing began locally, however,
in the 1780s. Such local changes preceded and inspired national
reforms, and local policing up to the centralizing measures of the
1830s remained dynamic, responsive, and locally accountable right
until its demise. Anxiety about policing had as much to do with the
social origins of the police as it did about the origins of
criminality, and control over the discretionary authority of
watchmen and constables played a larger role in criminal justice
reform than the nature of crime. The national, metropolitan, and
City police reforms of the late 1830s were thus the culmination of
a contentious argument over the meanings of justice, efficiency,
and order, rather than its beginning. Harris's evidence reveals how
what we've come to think of as "modern" policing evolved out of
local practice and reflects shifts in wider debates about crime,
justice, and discretionary authority.
In Policing the City, Harris seeks to explain the transformation of criminal justice, particularly the transformation of policing, between the 1780s and 1830s in the City of London. As utilitarian ...legal reformers argued that criminal deterrence ought to be based on certain and rational punishment rather than random execution, they also had to control the discretionary authority of enforcement. This meant in theory and practice the centralization of policing in the 1830s, and the end of local policing, which was seen as corrupt, inefficient, and unsuitable for rational criminal justice. Revolutionary changes in policing began locally, however, in the 1780s. Such local changes preceded and inspired national reforms, and local policing up to the centralizing measures of the 1830s remained dynamic, responsive, and locally accountable right until its demise. Anxiety about policing had as much to do with the social origins of the police as it did about the origins of criminality, and control over the discretionary authority of watchmen and constables played a larger role in criminal justice reform than the nature of crime. The national, metropolitan, and City police reforms of the late 1830s were thus the culmination of a contentious argument over the meanings of justice, efficiency, and order, rather than its beginning. Harris's evidence reveals how what we've come to think of as “modern”policing evolved out of local practice and reflects shifts in wider debates about crime, justice, and discretionary authority.
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