| 1. |
- Hökerberg, Yara Hahr Marques, et al.
(författare)
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Cross-cultural validity of the demand-control questionnaire : Swedish and Brazilian workers.
- 2014
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Ingår i: Revista de Saude Publica. - : FapUNIFESP (SciELO). - 0034-8910 .- 1518-8787. ; 48:3, s. 486-96
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE To evaluate the cross-cultural validity of the Demand-Control Questionnaire, comparing the original Swedish questionnaire with the Brazilian version. METHODS We compared data from 362 Swedish and 399 Brazilian health workers. Confirmatory and exploratory factor analyses were performed to test structural validity, using the robust weighted least squares mean and variance-adjusted (WLSMV) estimator. Construct validity, using hypotheses testing, was evaluated through the inspection of the mean score distribution of the scale dimensions according to sociodemographic and social support at work variables. RESULTS The confirmatory and exploratory factor analyses supported the instrument in three dimensions (for Swedish and Brazilians): psychological demands, skill discretion and decision authority. The best-fit model was achieved by including an error correlation between work fast and work intensely (psychological demands) and removing the item repetitive work (skill discretion). Hypotheses testing showed that workers with university degree had higher scores on skill discretion and decision authority and those with high levels of Social Support at Work had lower scores on psychological demands and higher scores on decision authority. CONCLUSIONS The results supported the equivalent dimensional structures across the two culturally different work contexts. Skill discretion and decision authority formed two distinct dimensions and the item repetitive work should be removed.
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| 2. |
- Hökerberg, Yara Hahr Marques, et al.
(författare)
-
Cross-cultural validity of the demand-control questionnaire: Swedish and Brazilian workers
- 2014
-
Ingår i: Revista de Saude Publica. - 0034-8910 .- 1518-8787. ; 48:3, s. 486-496
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVETo evaluate the cross-cultural validity of the Demand-Control Questionnaire, comparing the original Swedish questionnaire with the Brazilian version.METHODSWe compared data from 362 Swedish and 399 Brazilian health workers. Confirmatory and exploratory factor analyses were performed to test structural validity, using the robust weighted least squares mean and variance-adjusted (WLSMV) estimator. Construct validity, using hypotheses testing, was evaluated through the inspection of the mean score distribution of the scale dimensions according to sociodemographic and social support at work variables.RESULTSThe confirmatory and exploratory factor analyses supported the instrument in three dimensions (for Swedish and Brazilians): psychological demands, skill discretion and decision authority. The best-fit model was achieved by including an error correlation between work fast and work intensely (psychological demands) and removing the item repetitive work (skill discretion). Hypotheses testing showed that workers with university degree had higher scores on skill discretion and decision authority and those with high levels of Social Support at Work had lower scores on psychological demands and higher scores on decision authority.CONCLUSIONSThe results supported the equivalent dimensional structures across the two culturally different work contexts. Skill discretion and decision authority formed two distinct dimensions and the item repetitive work should be removed.
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| 3. |
- Ferreira Fernandes, Ricardo Manuel, et al.
(författare)
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Lateral Diffusion of Dispersing Molecules On Nanotubes As Probed by NMR
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:1, s. 582-589
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Tidskriftsartikel (refereegranskat)abstract
- Noncovalent dispersion of carbon nanotubes is essential to most applications but still poorly understood at the molecular level. The interaction of the dispersing molecule with the nanotube, wrapping or nonwrapping, still awaits consensus. Herein, we have studied by H-1 NMR diffusometry some features of molecular dynamics in the system of carbon nanotubes dispersed by triblock copolymer Pluronics F127 in water. The diffusional decays obtained at different diffusion times, Delta, are not single-exponential and have a complex Delta-dependent profile, ultimately implying that the polymer is observed in two states: free (in unimeric form) and nanotube-bound. Fitting a two-site exchange model to the data indicates that at any instant, only a small fraction of polymers are adsorbed on the nanotubes, with polydisperse residence times in the range of 100-400 ms. Most significantly, we further provide an estimate of D = (3-8) x 10(-12) m(2) s(-1) the coefficient of lateral diffusion of the polymer along the nanotube surface, which is an order of magnitude slower than the corresponding self-diffusion coefficient in water. The emerging picture is that of a nonwrapping mode for the polymer-nanotube interaction.
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| 4. |
- Laohaprapanon, Sawanya
(författare)
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Wastewater generated by the wooden floor industry : Treatability investigation applying individual and coupled technologies
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the last half-century a growing concern has taken place in the world regarding water shortage and public health associated to water pollution. Safe discharges of industrial effluents and water reuse within the industry have been encouraged and several initiatives have promoted the development of wastewater treatment technologies with the main focus on industrial sectors that generate large volumes of wastewater. On the other hand, searching for onsite technological options to treat small volumes of highly polluted wastewaters generated by industrial sectors that have no water in their production processes (i.e. wooden floor and furniture industry) has been neglected. To minimize and prevent environmental effects through innovative approaches, onsite treatment options for wastewater generated by cleaning/washing activities in a wooden floor industry in Sweden have been investigated. It was found that different wastewater streams generated after cleaning/washing of machinery and surfaces at different stages of the wooden floor production can pose negative effects to aquatic organisms. Since they are intermittently and manually generated, these wastewater streams have high variability both in volumes and chemical composition. During treatability studies, equalization/sedimentation process was found to be an important pre-treatment step responsible for reduction of chemical oxygen demand (COD) of about 19%. Sorption/filtration with activated carbon and anaerobic biological treatment were found to be technically feasible for both COD and formaldehyde removal. Wood fly ash (waste material with negligible cost) showed moderate sorption efficiency as compared to commercial activated carbon and leaching of secondary pollutants might prevent the use of this material unless pretreatment is carried out. In the anaerobic treatment process, the treatment efficiency of COD in an anaerobic baffled reactor (ABR) was decreased 50% when the C/N ratio dropped below 3. A successful treatment of the cleaning wastewater with soluble COD removal of about 83% and FA removal higher than 99% was achieved by the ABR operated with hydraulic retention time (HRT) of 5 days. Mole ratio of Mg:N:P and pH were key parameters for ammonium precipitation in the wastewater. At Mg:N:P of 1:1:1 or higher and pH of 8.0, the highest ammonium removal (83%) was achieved. Combinations of treatment processes (e.g. sorption and electrocoagulation or biological treatment and chemical precipitation) improved the quality of the final effluent. However, process optimization is still required in order to improve even more the quality of the final effluent and reduce operation and maintenance costs. From the water reuse/recycle perspective, the application of advanced oxidation in combination with the above-mentioned processes seems to be a promising approach.
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| 5. |
- Margulis-Goshen, Katrin, et al.
(författare)
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Formation of solid organic nanoparticles from a volatile catanionic microemulsion
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:19, s. 9359-9365
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Tidskriftsartikel (refereegranskat)abstract
- A novel volatile microemulsion formed by the catanionic surfactant hexadecyltrimethylammonium octylsulfonate (TA(16)So(8)), heptane and water has been explored as a template for producing nanoparticles of hydrophobic organic materials. Butylated hydroxytoluene (BHT) was employed as the model hydrophobic substance. First, the oil-in-water microemulsion was formed, containing TA16So8 as the single emulsifier and BHT dispersed in the volatile microphase. Microstructure characterization by self-diffusion NMR revealed that BHT was indeed incorporated into the oil droplets and that the mean diameter of the main droplet population was 30 nm, larger than in the BHT-free microemulsion. Next, a rapid solvent and water removal by freeze drying allowed converting the microemulsion droplets into nanoparticles in the form of a dry, fine powder. This powder was freely dispersible in water to yield a stable suspension of amorphous BHT particles with a mean size of 19 nm and zeta-potential of +37 mV. The solid nanoparticles in the aqueous dispersion were thus smaller than the initial microemulsion droplets. For comparison, a conventional o/w microemulsion composed of CTAB and sec-butanol was also tested as a template for BHT particle formation by the same process, and it was found that it yielded crystalline particles of micrometre size. On the basis of our results, we anticipate the catanionic microemulsion method to be an efficient one for producing size-controlled, water-dispersible nanoparticles of other hydrophobic organic materials.
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| 6. |
- Marques, Eduardo, et al.
(författare)
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Surfactant Self-Assembly
- 2013
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Ingår i: Encyclopedia of Colloid and Interface Science. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642206641 ; , s. 1202-1241
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Marques, Eduardo, et al.
(författare)
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Surfactants, Phase Behavior
- 2013
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Ingår i: Encyclopedia of Colloid and Interface Science. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642206641 ; , s. 1290-1333
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Silva, Bruno F. B., et al.
(författare)
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Aqueous phase behavior of salt-free catanionic surfactants: the influence of solubility mismatch on spontaneous curvature and balance of forces
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:1, s. 225-236
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the phase behavior and microstructure for a series of salt-free catanionic surfactants of the type Cm+Cn- with varied chain length mismatch (m not equal n), using light microscopy, DSC, turbidity, surface tension, SAXS and SANS. The compounds consist of alkyltrimethylammonium alkylsulfonates, denoted by TA(m)So(n). Depending on the asymmetry between both ions, three regimes can be identified: (i) weakly asymmetric; (ii) approximately symmetric; and (iii) highly asymmetric. For the TA(16)So(n) compounds, with n = 8 and 9 (weakly asymmetric), the surfactant forms a lamellar phase in water, however, with a striking miscibility gap. This miscibility gap is a consequence of the concentration dependent bilayer charge density. For n = 8, also a temperature-dependent vesicle-to-micelle transition at low surfactant concentration is observed. When the mismatch is low (n = 10) only a non-swelling lamellar phase is formed (approximately symmetric regime). For high mismatch, (n = 6 and 7) an extensive micellar phase is obtained - highly asymmetric regime. Conversely, for the TA(m)So(8) compounds, where m = 12 and 14, the unconventional lamellar miscibility gap and vesicle-micelle transition are again present. These findings are rationalized by considering the effect of film charge density-arising from the chain solubility difference-on the spontaneous curvature and balance of colloidal forces. The type of phase behavior reported here should be extensive to other families of salt-free catanionic amphiphiles, where an appropriate tuning of the solubility mismatch can allow the control of self-assembly.
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| 9. |
- Silva, Bruno F. B., et al.
(författare)
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Fusion and fission of catanionic bilayers
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:5, s. 1686-1689
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Tidskriftsartikel (refereegranskat)abstract
- We herein report the reversible formation of a planar lamellar phase as an intermediate structure in a vesicle-micelle transition induced by temperature, for a salt-free catanionic surfactant-water system. Turbidity, small-angle neutron scattering, dynamic light scattering and microscopy data altogether demonstrate that the vesicles formed by hexadecyltrimethylammonium octylsulfonate (TA(16)So(8)) in water fuse at high temperature into planar lamellae before transforming into elongated micelles. On cooling the micelles first nucleate into lamellae, and only then vesicles appear through lamellae fission. This behavior is both intriguing and counter-intuitive, since a monotonous dependence of the spontaneous curvature of the surfactant film on temperature should be expected.
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| 10. |
- Silva, Bruno F. B., et al.
(författare)
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Headgroup Effects on the Unusual Lamellar-Lamellar Coexistence and Vesicle-to-Micelle Transition of Salt-Free Catanionic Amphiphiles
- 2010
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Ingår i: Langmuir. - 0743-7463. ; 26:5, s. 3058-3066
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Tidskriftsartikel (refereegranskat)abstract
- Salt-free ion-paired catanionic amphiphiles of the C-m(+) C-n(-) type, with a high solubility mismatch (n >> m or m >> n) display a remarkable phase behavior in water. A temperature-driven vesicle-to-micelle transition in the dilute side together with a coexistence of two lamellar phases oil the concentrated side is one of the peculiar effects that have been reported for the hexadecyltrimethylammonium octylsulfonate surfactant, C16C8 or TA(16)So(8) (extensive to C14C8 and C12C8). In this work, with TA(16)So(8) as a reference, the cationic trimethylammonium (TA(+)) and pyridinium (P+) headgroups are combined with the anionic sulfate (S-) and sulfonate (So(-)) headgroups to yield other C16C8 compounds: hexadecyltrimethylammonium octylsulfate (TA(16)S(8)) 1-hexadecylpyridinium octylsulfonate (P(16)So(8)), and 1-hexadecylpyridinium octylsulfate (P(16)So(8)). We show that, if the asymmetry of the chain lengths is kept constant at C16C8 and the headgroup chemistry is changed, most of the unusual self-assembly properties are still observed, indicating that they are not system-specific but extensive to other combinations of headgroups and mainly dictated by the ion-pair solubility mismatch. Thus, all the compounds in water quite remarkably show a lamellar-lamellar phase coexistence and spontaneously form vesicles upon solubilization. Moreover, P(16)So(8) undergoes at temperature-driven vesicle-to-micelle transition that involves an intermediate planar lamellar state, similar to TA(16)So(8). Some interesting effects on the global phase behavior, however, do arise when the headgroups are changed, Geometric packing effects are shown to be important, but the differences in phase behavior seem to be mainly dictated by (i) the charge density of the headgroups, which tunes the solubility mismatch of the ion-pair, and (ii) specific interactions between headgroups, which affect the short-range repulsive force that controls the swelling of the concentrated lamellar phase,
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