Immersions into Sasakian space forms Loi, A.; Placini, G.; Zedda, M.
Mathematische Zeitschrift,
07/2024, Letnik:
307, Številka:
3
Journal Article
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We study immersions of Sasakian manifolds into finite and infinite dimensional Sasakian space forms. After proving Calabi’s rigidity results in the Sasakian setting, we characterise all homogeneous ...Sasakian manifolds which admit a (local) Sasakian immersion into a nonelliptic Sasakian space form. Moreover, we give a characterisation of homogeneous Sasakian manifolds which can be embedded into the standard sphere both in the compact and noncompact case.
Studies on occupational stress have shown that police officers are exposed to stressful events more often than other workers and this can result in impaired psychosocial well-being and physical ...health.
To measure the level of stress experienced, the consequences in terms of anxiety and the coping strategies adopted in a sample of police officers working in a large city in northern Italy.
We used the Police Stress Questionnaire and the Distress Thermometer to measure occupational stress, the State-Trait Anxiety Inventory to measure anxiety and the Brief COPE questionnaire to measure coping strategies.
Six hundred seventeen police officers completed the questionnaire, a response rate of 34%. Differences between genders, sectors and roles emerged, but overall the study population generally demonstrated good use of positive coping strategies. Women in all operational service roles were more vulnerable to both organizational and operational stressors than men (P < 0.001), while in the interior department, men were more vulnerable to organizational stressors (P < 0.05).
Our results suggest that for Italian police officers, training courses and support in dealing with occupational stress should take into account gender, role and type of work. Tailored training courses and support programmes could be useful and effective tools for preventing stress before it becomes chronic.
For portable fuel cell systems a multitude of applications have been presented over the past few years. Most of these applications were developed for indoor use, and not optimised for outdoor ...conditions. The key problem concerning this case is the cold start ability of the polymer electrolyte membrane fuel cell (PEMFC). This topic was first investigated by the automotive industry, which has the same requirements for alternative traction systems as for conventional combustion engines.
The technical challenge is the fact that produced water freezes to ice after shut-down of the PEMFC and during start-up when the temperature is below 0
°C.
To investigate the basic cold start behaviour isothermal, potentiostatic single cell experiments were performed and the results are presented.
The cold start behaviour is evaluated using the calculated cumulated charge transfer through the membrane which directly corresponds with the amount of produced water in the PEMFC. The charge transfer curves were mathematically fitted to obtain only three parameters describing the cold start-up with the cumulated charge transfer density and the results are analysed using the statistical software Cornerstone 4.0.
The results of the statistic regression analyses are used to establish a statistic-based prediction model of the cold start behaviour which describes the behaviour of the current density during the experiment. The regression shows that the initial start current mainly depends on the membrane humidity and the operation voltage. After the membrane humidity has reached its maximum, the current density drops down to zero. The current decay also depends on the constant gas flows of the reactant gases.
Ionic conductivity of the membrane and charge transfer resistance were investigated by a series of ac impedance spectra during potentiostatic operation of the single cell at freezing temperatures. Cyclic voltammetry and polarisation curves between cold start experiments show degradation effects by ice formation in the porous structures which lead to significant performance loss.
The start up behaviour of PEM fuel cells below 0
°C is one of the most challenging tasks to be solved before commercialisation. The automotive industry started to develop solutions to reduce the ...start up time of fuel cell systems in the middle of the nineties. The strategies varied from catalytic combustion of hydrogen on the electrode catalyst to fuel starvation or external stack heating via cooling loops to increase the stack temperature.
Beside the automotive sector the cold start ability is as well important for portable PEMFC applications for outdoor use. But here the cold start issue is even more complicated, as the fuel cell system should be operated as passive as possible.
Below 0
°C freezing of water inside the PEMFC could form ice layers in the electrode and in the gas diffusion layer. Therefore the cell reaction is limited or even inhibited. Product water during the start up builds additional barriers and leads to a strong decay of the output power at isothermal operating conditions.
In order to find out which operational and hardware parameters affect this decay, potentiostatic experiments on single cells were performed at isothermal conditions. These experiments comprise investigations of the influence of membrane thickness and different GDL types as well as the effect of gas flow rates and humidification levels of the membrane. As pre stage to physical based models, empirical based prediction models are used to gain a better understanding of the main influence parameters during cold start. The results are analysed using the statistical software Cornerstone 4.0.
The experience of single cell investigations are compared to start up behaviour of portable fuel cell stacks which are operated in a climate chamber at different ambient temperatures below 0
°C. Additional flow sharing problems in the fuel cell stack could be seen during cold start up experiments.
The enzymatic oxidation of Fe(II) by nitrate‐reducing bacteria was first suggested about two decades ago. It has since been found that most strains are mixotrophic and need an additional organic ...co‐substrate for complete and prolonged Fe(II) oxidation. Research during the last few years has tried to determine to what extent the observed Fe(II) oxidation is driven enzymatically, or abiotically by nitrite produced during heterotrophic denitrification. A recent study reported that nitrite was not able to oxidize Fe(II)‐EDTA abiotically, but the addition of the mixotrophic nitrate‐reducing Fe(II)‐oxidizer, Acidovorax sp. strain 2AN, led to Fe(II) oxidation (Chakraborty & Picardal, 2013). This, along with other results of that study, was used to argue that Fe(II) oxidation in strain 2AN was enzymatically catalyzed. However, the absence of abiotic Fe(II)‐EDTA oxidation by nitrite reported in that study contrasts with previously published data. We have repeated the abiotic and biotic experiments and observed rapid abiotic oxidation of Fe(II)‐EDTA by nitrite, resulting in the formation of Fe(III)‐EDTA and the green Fe(II)‐EDTA‐NO complex. Additionally, we found that cultivating the Acidovorax strains BoFeN1 and 2AN with 10 mm nitrate, 5 mm acetate, and approximately 10 mm Fe(II)‐EDTA resulted only in incomplete Fe(II)‐EDTA oxidation of 47–71%. Cultures of strain BoFeN1 turned green (due to the presence of Fe(II)‐EDTA‐NO) and the green color persisted over the course of the experiments, whereas strain 2AN was able to further oxidize the Fe(II)‐EDTA‐NO complex. Our work shows that the two used Acidovorax strains behave very differently in their ability to deal with toxic effects of Fe‐EDTA species and the further reduction of the Fe(II)‐EDTA‐NO nitrosyl complex. Although the enzymatic oxidation of Fe(II) cannot be ruled out, this study underlines the importance of nitrite in nitrate‐reducing Fe(II)‐ and Fe(II)‐EDTA‐oxidizing cultures and demonstrates that Fe(II)‐EDTA cannot be used to demonstrate unequivocally the enzymatic oxidation of Fe(II) by mixotrophic Fe(II)‐oxidizers.
Brown bear is a powerful, intelligent and robust beast that hides in the woods of Slovakia. Despite the bear's intense environmental, geographical and behavior research, a detailed analysis of its ...bone microstructure is still absent. Therefore, our study aims to analyse the effect of age, sex and body weight on bone parameters in compact bear bone. Qualitative histological observations of compact femoral bone show a high amount of dense Haversian bone tissue in brown bears confirming that this is a mammal with high locomotory capability. Only in 8-9 month old cub lack on the subperiosteal zone lines of arested growth. The histomorphometric analysis reported weak significant alternations in the sizes of Haversian canals. On the contrary, no significant differences in the osteons size were observed among groups. The correlation between osteon and Haversian canal diameters shows that all bears together have a little correlation (r = 0.284). In particular, the greater difference is between cub bears (r = 0.268) and all adult bears together (r = 0.394). Based on the results of our work, we can state that the different locomotor behavior could influence the differences between cubs and adults.
We study local rigidity and multiplicity of constant scalar curvature metrics in arbitrary products of compact manifolds. Using (equivariant) bifurcation theory we determine the existence of ...infinitely many metrics that are accumulation points of pairwise non-homothetic solutions of the Yamabe problem. Using local rigidity and some compactness results for solutions of the Yamabe problem, we also exhibit new examples of conformal classes (with positive Yamabe constant) for which uniqueness holds.
Reverse osmosis (RO) treatment has been found to be effective for a wide range of organics but generally small, polar, uncharged molecules such as
N
-nitrosodimethylamine (NDMA) can be poorly ...rejected. The rejection of seven
N
-nitrosoalkylamines with molecular masses in the range of 78–158
Da, including NDMA,
N
-nitrosodiethylamine (NDEA),
N
-nitrosomethylethylamine (NMEA),
N
-nitrosodipropylamine (NDPA),
N
-nitrosodibutylamine (NDBA),
N
-nitrosopyrrolidine (NPyr),
N
-nitrosopiperidine (NPip) by three commercial brackish-water reverse osmosis membranes was studied in flat-sheet cells under cross-flow conditions. The membranes used were ESPA3 (Hydranautics), LFC3 (Hydranautics) and BW-30 (Dow/Filmtec), commonly used in water reuse applications. The effects of varying ionic strength and pH, dip-coating membranes with PEBAX 1657, a hydrophilic polymer, and artificial fouling with alginate on nitrosamine rejection were quantified. Rejection in deionized (DI) water increased with molecular mass from 56 to 70% for NDMA, to 80–91% for NMEA, 89–97% for NPyr, 92–98% for NDEA, and to beyond the detection limits for NPip, NDPA and NDBA. For the nitrosamines with quantifiable transmission, linear correlations
(
r
2
>
0.97
)
were found between the number of methyl groups and the log(transmission), with factor 0.35 to 0.55 decreases in transmission per added methyl group. A PEBAX coating lowered the ESPA3 rejection of NDMA by 11% but increased the LFC3 and BW30 rejection by 6% and 15%, respectively. Artificially fouling ESPA3 membrane coupons with
170
g
/
m
2
alginate decreased the rejection of NDMA by 18%. A feed concentration of 100
mM NaCl decreased rejection of NDMA by 15% and acidifying the DI water feed to pH=3 decreased the rejection by 5%, whereas increasing the pH to 10 did not have a significant
(
p
<
0.05
)
effect.
Tryptase is a serin-protease produced and released by mast cells after IgE-mediated or non-IgE mediated stimuli. We here review the various aspects related to the molecular characteristics of the ...enzyme and its biological effects, the genetic basis of its production and the release kinetics. Recommendations for the clinical use of tryptase measurement developed by a task force of Società Italiana di Patologia Clinica e Medicina di Laboratorio and Associazione Allergologi Immunologi Italiani Territoriali e Ospedalieri are given on the best procedure for a correct definition of the reference values in relation to the inter-individual variability and to the correct determination of tryptase in blood and other biological liquids, in the diagnosis of anaphylaxis (from drugs, food, insect sting, or idiophatic), death from anaphylaxis (post mortem assessment) and cutaneous or clonal mastcell disorders.
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