4,766 research outputs found
Evaporation waves in superheated dodecane
We have observed propagating adiabatic evaporation waves in superheated liquid dodecane, C_(12)H_(26). Experiments were performed with a rapid decompression apparatus at initial temperatures of 180–300°C. Saturated dodecane in a tube was suddenly depressurized by rupturing a diaphragm. Motion pictures and still photographic images, and pressure and temperature data were obtained during the evaporation event that followed depressurization. Usually, a front or wave of evaporation started at the liquid free surface and propagated into the undisturbed regions of the metastable liquid. The evaporation wave front moved with a steady mean velocity but the front itself was unstable and fluctuating in character. At low superheats, no waves were observed until a threshold superheat was exceeded. At moderate superheats, subsonic downstream states were observed. At higher superheats, the downstream flow was choked, corresponding to a Chapman–Jouguet condition. At the most extreme superheat tested, a vapour content of over 90% was estimated from the measured data, indicating a nearly complete evaporation wave. Our results are interpreted by modelling the evaporation wave as a discontinuity, or jump, between a superheated liquid state and a two-phase liquid–vapour downstream state. Reasonable agreement is found between the model and observations; however, there is a fundamental indeterminacy that prevents the prediction of the observed wave speeds
Impulsive Heating of Solar Flare Ribbons Above 10 MK
The chromospheric response to the input of flare energy is marked by extended
extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are
usually explained as the result of heating and bremsstrahlung emission from
accelerated electrons colliding in the dense chromospheric plasma. We present
evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon
flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class
event using data from Atmospheric Imaging Assembly (AIA) on board of Solar
Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and
differential emission measure of the flaring regions and investigate the
evolution of the plasma in the flaring ribbons. The ribbons were visible at all
SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 \AA\ filters,
sensitive to temperatures of 8 MK and 12 MK. Time evolution of the emission
measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak
time. The presence of hot plasma in the lower atmosphere is further confirmed
by RHESSI imaging spectroscopy analysis, which shows resolved sources at 11-13
MK associated with at least one ribbon. We found that collisional beam heating
can only marginally explain the necessary power to heat the 10 MK plasma at the
ribbons.Comment: 21 pages, 15 figure
A Route Implementation Model for Military Tourism: Looking Back, Moving Forward
Military tourism has been growing in Portugal in recent years with numerous initiatives to
enhance and promote the country’s military and historical heritage. In the academic context, studies
have emerged to consolidate the segment in the tourism activity. In this framework, INSIGNIA was
born, a project aimed at monitoring, evaluating and optimizing the Military Tourism Route. The
implementation of the route and the network-based strategies chosen to structure the supply have
been monitored to register key insights gathered through this model of heritage asset intervention
and tourism development. This paper proposes a reflective overview of the implementation and
monitoring processes, a lookback at the work conducted. Firstly, proposes a reflection on the
implementation process, tracing its genesis in response to the conjunctures of the structuring of
tourism supply and the consolidation of the concept itself. It seeks to reflect on the specific choices
and services developed during the implementation process. Based on this lookback, the authors
then propose a replicable model to guide these implementation processes. Using the monitoring
experience of this study as a reference point, the model suggests possible metrics, as well as proposals
for the collection and analysis of data relevant to its wider application.info:eu-repo/semantics/publishedVersio
The effects of metabolite molecules produced by drinking water-isolated bacteria on their single and multispecies biofilms
The elucidation of the mechanisms by which diverse species survive and interact in drinking water (DW) biofilm communities may allow the identification of new biofilm control strategies. The purpose of the present study was to investigate the effects of metabolite molecules produced by bacteria isolated from DW on biofilm formation. Six opportunistic bacteria, viz. Acinetobacter calcoaceticus, Burkholderia cepacia, Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata and Staphylococcus sp. isolated from a drinking water distribution systems (DWDS) were used to form single and multispecies biofilms in the presence and absence of crude cell-free supernatants produced by the partner bacteria. Biofilms were characterized in terms of mass and metabolic activity. Additionally, several physiological aspects regulating interspecies interactions (sessile growth rates, antimicrobial activity of cell-free supernatants, and production of iron chelators) were studied to identify bacterial species with biocontrol potential in DWDS. Biofilms of Methylobacterium sp. had the highest growth rate and M. mucogenicum biofilms the lowest. Only B. cepacia was able to produce extracellular iron-chelating molecules. A. calcoaceticus, B. cepacia, Methylobacterium sp. and M. mucogenicum biofilms were strongly inhibited by crude cell-free supernatants from the other bacteria. The crude cell-free supernatants of M. mucogenicum and S. capsulata demonstrated a high potential for inhibiting the growth of counterpart biofilms. Multispecies biofilm formation was strongly inhibited in the absence of A. calcoaceticus. Only crude cell-free supernatants produced by B. cepacia and A. calcoaceticus had no inhibitory effects on multispecies biofilm formation, while metabolite molecules of M. mucogenicum showed the most
significant biocontrol potential.The authors acknowledge the financial support provided by the Portuguese Foundation for Science and Technology (SFRH/BD/31661/2006 - Lucia C. Simoes)
Intergeneric coaggregation among drinking water bacteria: evidence of a role for acinetobacter calcoaceticus as a bridging bacterium
Intergeneric coaggregation of drinking water bacteria was tested. Acinetobacter calcoaceticus was found not
only to autoaggregate but also to coaggregate with four of the five other isolates (Burkholderia cepacia,
Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata, and Staphylococcus sp.). In its
absence, no coaggregation was found. Interactions were lectin-saccharide mediated. The putative bridging
function of A. calcoaceticus was evidenced by multispecies biofilm studies, through a strain exclusion process.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/31661/2006; SFRH/BPD/20582/2004
Drinking water biofilm monitoring by Propella™ and flow cell bioreactors under different operating conditions
Monitoring of biofilm subjected to different process conditions was performed using two
distinct bioreactors, Propella™ and flow cell system. Biofilms were grown on polyvinyl
chloride (PVC) and stainless steel (SS) coupons under laminar (Reynolds number of 2000)
and turbulent (Reynolds number of 11000) flow. The parameters analyzed were culturable
cells, using R2A, and total bacteria, which were assessed using a DNA-binding stain coupled
with epifluorescence microscopy. The impact of the different operating conditions in the
studied parameters was established after the biofilms reached the steady-state. It was found
that the biofilm steady-state was achieved 3 d after the starting of operating conditions for
turbulent flow and for both bioreactors and adhesion surfaces. Under laminar flow it was only
achieved 6 d after. The number of total bacteria was invariably higher than the culturable
cells. The number of total and culturable bacteria in turbulent flow-generated biofilms were
similar in both bioreactors, regardless the adhesion surface tested. Under laminar flow, the
Propella™ bioreactor allowed the formation of steady-state biofilms with a higher number of
total and culturable bacteria than those from the flow cell system. Comparing the effect of the
flow regime on biofilm accumulation, only turbulent flow-generated biofilms formed on the
flow cell system had a higher amount of total and culturable bacteria than those formed
under laminar flow. In terms of adhesion surface effect on steady-state biofilms, a higher
number of total and culturable cells were found on PVC surfaces comparatively to SS when
biofilms were formed using the flow cell system. Biofilm formation on PVC and SS was
similar in the Propella™ system for both flow regimes.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/31661/200
Comparison of methods to assess biofilm disinfection and recovery by drinking water-isolated bacteria
Drinking water (DW) distribution systems are known to harbour biofilms even in the presence of disinfectants.
DW biofilms are constituted by microbial communities adapted to low nutrient concentrations and high chlorine
levels. Biofilm formation and resistance to disinfection have been recognized as important factors that contribute
to the survival and persistence of microbial contamination in DW.
The purpose of this work was the comparison of diverse methods to assess the disinfection of biofilms formed by
six DW-isolated opportunistic bacteria (Acinetobacter calcoaceticus, Burkholderia cepacia, Methylobacterium
sp., Mycobacterium mucogenicum, Sphingomonas capsulata and Staphylococcus sp.) by sodium hypochlorite
(SHC). Single and multi-species biofilms (composed of combinations of 6 and 5 bacteria) were developed in 96-
wells microtiter plates for 3 days, afterwards, were exposed to several independent SHC concentrations (0.1, 0.5,
1 and 10 mg/L) during 1 h. The potential of biofilms to recover was assessed 24 h after disinfection. The
disinfection efficacy and recovery were assessed in terms of variation in: biofilm mass (crystal violet staining);
metabolic activity (XTT staining); cultivability (CFUs) and viability (Live/Dead staining).
The results indicated that biomass removal increased with increasing SHC concentration, but total biofilm mass
removal was not achieved. The effects of SHC on the biofilm activity, cultivability and viability were also
concentration dependent. Total biofilm inactivation was achieved only for A. calcoaceticus biofilms and for
multi-species biofilms without A. calcoaceticus, when exposed to high SHC concentrations. Almost all multispecies
biofilms were more resistant to removal and inactivation than the single biofilms. Methylobacterium sp.
and A. calcoaceticus formed the most resistant and the most susceptible biofilms, respectively. On the other
hand, biofilm combination with the six DW bacteria was the most resistant to SHC and combination without A.
calcoaceticus was the least resistant, for all concentration tested. The several methods used to assess of biofilm
activity (metabolic activity, cultivability and viability) provided comparable results. However the viability results
provide the worst case scenario in terms of biofilm control analysis (higher number of viable cells for all the
SHC concentrations tested). The recovery results demonstrated that only biofilms without A.calcoaceticus were
not able to recover their biomass from the SHC treatments. Also, those biofilms had a decreased ability to
recover their metabolic activity, cultivability and viability. Conversely, multi-species biofilms without
Staphylococcus sp. had the highest ability to recover from disinfection. Biofilm mass and activity recovery were
not correlated for all the biofilms tested. However, the data of biofilm recovery in terms of metabolic activity,
cultivability and viability also provided comparable results
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