1,039 research outputs found
Salinity gradient energy: Assessment of pressure retarded osmosis and osmotic heat engines for energy generation from low-grade heat sources
Development of clean energy technologies that maximize efficiency and minimize resource consumption is a necessary component for a clean and secure energy future. The osmotic heat engine (OHE) is a closed-loop, membrane based process that utilizes low-grade heat and salinity-gradient energy between two streams for electrical energy generation. The OHE couples pressure retarded osmosis (PRO), an osmotically driven membrane process, with membrane distillation (MD), a thermally driven membrane process. In PRO, water permeates via osmosis through a semi-permeable membrane from a low concentration feed stream into a higher concentration brine (draw solution). The permeate stream becomes pressurized on the high concentration side of the membrane and a mechanical device (e.g., turbine generator set) is used to convert the hydraulic pressure to electrical energy. The MD process utilizes low-grade heat to reconcentrate the diluted brine from the PRO process and to produce a deionized water stream; these streams are then resupplied to the PRO process in the OHE. High power-density (power generated per unit area of membrane) of the PRO membrane is essential to maximize the efficiency and minimize the capital and operating costs of the OHE. Likewise, high separation efficiency is needed in the MD process to effectively reconcentrate the diluted draw solution. Thus, robust PRO membranes that can support high pressure, have high water flux, low reverse salt flux, low structural parameter, and a good membrane support structure are essential. The MD process must also be able to withstand high operating temperatures (\u3e 60 ºC) and feed water concentrations, and have low pore wetting propensity. Additionally, the use of highly soluble ionic organic and inorganic draw solutions can increase PRO power densities while achieving high MD water fluxes, thus increasing efficiencies and decreasing costs of OHE.
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Rank-Ordering Statistics of Extreme Events: Application to the Distribution of Large Earthquakes
Rank-ordering statistics provides a perspective on the rare, largest elements
of a population, whereas the statistics of cumulative distributions are
dominated by the more numerous small events. The exponent of a power law
distribution can be determined with good accuracy by rank-ordering statistics
from the observation of only a few tens of the largest events. Using analytical
results and synthetic tests, we quantify the systematic and the random errors.
We also study the case of a distribution defined by two branches, each having
a power law distribution, one defined for the largest events and the other for
smaller events, with application to the World-Wide (Harvard) and Southern
California earthquake catalogs. In the case of the Harvard moment catalog, we
make more precise earlier claims of the existence of a transition of the
earthquake magnitude distribution between small and large earthquakes; the
-values are for large shallow earthquakes and for smaller shallow earthquakes. However, the cross-over
magnitude between the two distributions is ill-defined. The data available at
present do not provide a strong constraint on the cross-over which has a
probability of being between magnitudes and for shallow
earthquakes; this interval may be too conservatively estimated. Thus, any
influence of a universal geometry of rupture on the distribution of earthquakes
world-wide is ill-defined at best. We caution that there is no direct evidence
to confirm the hypothesis that the large-moment branch is indeed a power law.
In fact, a gamma distribution fits the entire suite of earthquake moments from
the smallest to the largest satisfactorily. There is no evidence that the
earthquakes of the Southern California catalog have a distribution with tw
Modes of random lasers
In conventional lasers, the optical cavity that confines the photons also determines essential characteristics of the lasing modes such as wavelength, emission pattern, directivity, and polarization. In random lasers, which do not have mirrors or a well-defined cavity, light is confined within the gain medium by means of multiple scattering. The sharp peaks in the emission spectra of semiconductor powders, first observed in 1999, has therefore lead to an intense debate about the nature of the lasing modes in these so-called lasers with resonant feedback. We review numerical and theoretical studies aimed at clarifying the nature of the lasing modes in disordered scattering systems with gain. The past decade has witnessed the emergence of the idea that even the low-Q resonances of such open systems could play a role similar to the cavity modes of a conventional laser and produce sharp lasing peaks. We focus here on the nearthreshold single-mode lasing regime where nonlinear effects associated with gain saturation and mode competition can be neglected.We discuss in particular the link between random laser modes near threshold and the resonances or quasi-bound (QB) states of the passive system without gain. For random lasers in the localized (strong scattering) regime, QB states and threshold lasing modes were found to be nearly identical within the scattering medium. These studies were later extended to the case of more lossy systems such as random systems in the diffusive regime, where it was observed that increasing the openness of such systems eventually resulted in measurable and increasing differences between quasi-bound states and lasing modes. Very recently, a theory able to treat lasers with arbitrarily complex and open cavities such as random lasers established that the threshold lasing modes are in fact distinct from QB states of the passive system and are better described in terms of a new class of states, the so-called constant-flux states. The correspondence between QB states and lasing modes is found to improve in the strong scattering limit, confirming the validity of initial work in the strong scattering limit. © 2010 Optical Society of America
Draft genome sequence of the commercial biocontrol strain Pantoea agglomerans P10c
We report here the draft genome sequence of the biocontrol strain Pantoea agglomerans P10c, composed of a draft chromosome and two plasmids: the 559-kb large Pantoea plasmid 1 (pPag3) and a 182-kb plasmid (pPag1). A genomic island containing pantocin A biosynthesis genes was identified
Emission of photon echoes in a strongly scattering medium
We observe the two- and three-pulse photon echo emission from a scattering
powder, obtained by grinding a Pr:YSiO rare earth doped single
crystal. We show that the collective emission is coherently constructed over
several grains. A well defined atomic coherence can therefore be created
between randomly placed particles. Observation of photon echo on powders as
opposed to bulk materials opens the way to faster material development. More
generally, time-domain resonant four-wave mixing offers an attractive approach
to investigate coherent propagation in scattering media
Strong Interactions in Multimode Random Lasers
Unlike conventional lasers, diffusive random lasers (DRLs) have no resonator
to trap light and no high-Q resonances to support lasing. Due to this lack of
sharp resonances the DRL has presented a challenge to conventional laser
theory. We present a theory able to treat the DRL rigorously, and provide
results on the lasing spectra, internal fields and output intensities of DRLs.
Typically DRLs are highly multimode lasers, emitting light at a number of
wavelengths. We show that the modal interactions through the gain medium in
such lasers are extremely strong and lead to a uniformly spaced frequency
spectrum, in agreement with recent experimental observations.Comment: 13 pages, 4 figures. Supplementary information available at
arXiv:0805.449
N-Acyl Homoserine Lactones and Lux Solos Regulate Social Behaviour and Virulence of Pseudomonas syringae pv. actinidiae
The phyllosphere is a complex environment where microbes communicate through signalling molecules in a system, generally known as quorum sensing (QS). One of the most common QS systems in Gram-negative proteobacteria is based on the production of N-acyl homoserine lactones (AHLs) by a LuxI synthase and their perception by a LuxR sensor. Pseudomonas syringae pv. actinidiae (Psa), the aetiological agent of the bacterial canker of kiwifruit, colonises plant phyllosphere before penetrating via wounds and natural openings. Since Psa genome encodes three LuxR solos without a cognate LuxI, this bacterium may perceive diffusible signals, but it cannot produce AHLs, displaying a non-canonical QS system. The elucidation of the mechanisms underlying the perception of environmental cues in the phyllosphere by this pathogen and their influence on the onset of pathogenesis are of crucial importance for a long-lasting and sustainable management of the bacterial canker of kiwifruit. Here, we report the ability of Psa to sense its own population density and the presence of surrounding bacteria. Moreover, we show that Psa can perceive AHLs, indicating that AHL-producing neighbouring bacteria may regulate Psa virulence in the host. Our results suggest that the ecological environment is important in determining Psa fitness and pathogenic potential. This opens new perspectives in the use of more advanced biochemical and microbiological tools for the control of bacterial canker of kiwifruit
Comparative transcriptome analysis of the interaction between Actinidia chinensis var. chinensis and Pseudomonas syringae pv. Actinidiae in absence and presence of acibenzolar-S-methyl
Background: Since 2007, bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) has become a pandemic disease leading to important economic losses in every country where kiwifruit is widely cultivated. Options for controlling this disease are very limited and rely primarily on the use of bactericidal compounds, such as copper, and resistance inducers. Among the latter, the most widely studied is acibenzolar-S-methyl. To elucidate the early molecular reaction of kiwifruit plants (Actinidia chinensis var. chinensis) to Psa infection and acibenzolar-S-methyl treatment, a RNA seq analysis was performed at different phases of the infection process, from the epiphytic phase to the endophytic invasion on acibenzolar-S-methyl treated and on non-treated plants. The infection process was monitored in vivo by confocal laser scanning microscopy. Results: De novo assembly of kiwifruit transcriptome revealed a total of 39,607 transcripts, of which 3360 were differentially expressed during the infection process, primarily 3 h post inoculation. The study revealed the coordinated changes of important gene functional categories such as signaling, hormonal balance and transcriptional regulation. Among the transcription factor families, AP2/ERF, MYB, Myc, bHLH, GATA, NAC, WRKY and GRAS were found differentially expressed in response to Psa infection and acibenzolar-S-methyl treatment. Finally, in plants treated with acibenzolar-S-methyl, a number of gene functions related to plant resistance, such as PR proteins, were modulated, suggesting the set-up of a more effective defense response against the pathogen. Weighted-gene coexpression network analysis confirmed these results. Conclusions: Our work provides an in-depth description of the plant molecular reactions to Psa, it highlights the metabolic pathway related to acibenzolar-S-methyl-induced resistance and it contributes to the development of effective control strategies in open field
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