| 1. |
- Hermida-Ramon, Jose M., et al.
(författare)
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Structure and spectrum of the hydrated electron. A combined quantum chemical statistical mechanical simulation
- 2019
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Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 292:Oct
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Tidskriftsartikel (refereegranskat)abstract
- In the current work, in order to model a free electron solvated in water, we have implemented a method to represent the molecular charge distribution as a set of Slater-type functions within the framework of a QM/MM method called QMSTAT. Also, it has been introduced in this method a new approach to calculate the intermolecular induction energy in the presence of very strong electric fields. Unlike most previous potentials, our method uses the ab initio energies of the electron-water complex as reference to obtain the few fitted parameters that the model needs, instead of the ab initio potential of the electron. A Metropolis-Monte Carlo simulation of 15 million steps has been carried out in a system that consists of an electron solvated in 200 water molecules explicitly described. The obtained results predict a vertical electron detachment energy of 3.30 eV and a radius of gyration of 2.38 Å, which are in very good agreement with the experimental data of 3.27 ± 0.10 eV and 2.45 Å, respectively. We have also obtained the absorption spectrum of the hydrated electron from our simulation. The maximum of the spectrum agrees very well with the experimental result and the experimental width at half-maximum is only 0.11 eV wider than the calculated curve. The calculations predict the same blue tail as the experimental result but with a less smooth shape. Also, our results indicate that the transfer of intensity from the transition arriving to the highest of the three p states to transitions arriving to higher-lying states contributes to the intensity enhancement of the blue tail of the spectrum. Regarding the solvated structure of the free electron, we have found that if the basis center is used as the electron site to calculate the correlation functions, the results predict a structure where the electron places itself on top of a central water molecule surrounded by the remaining water molecules in a very organized and stable arrangement. However, if the maximum of the electron density is used as electron site the obtained picture shows an electron located in a very fluctuating cavity that collapses and reforms continuously.
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| 2. |
- Lundgren, A-M, et al.
(författare)
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Do adolescents who are night owls have a higher risk of dental caries? : A case-control study
- 2016
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Ingår i: International Journal of Dental Hygiene. - : Wiley. - 1601-5029 .- 1601-5037. ; 14:3, s. 220-225
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: The aim was to evaluate the association between circadian rhythm and the risk of caries in adolescents, as well as their dietary and toothbrushing habits.METHODS: A group of 196 adolescents (15 and 16 years old) were divided into two equal groups based on caries risk (case = high risk; and control = low risk). Before their dental examinations, they were asked to complete a questionnaire. The questionnaire included questions on circadian rhythm, dietary and oral self-care habits, and demographic variables. The participants were divided into three circadian types: evening types who are alert in the evening and tired in the morning; morning types who are the opposite; and neutral types who are neither particularly alert in the evening nor extremely tired in the morning.RESULTS: The most common sleep-cycle group type was neutral (50%). After this came evening types (37%) and finally morning types (13%). Morning and neutral types reported more frequently than evening types that they had breakfast every morning and brushed their teeth twice a day. More evening types were categorized as at high risk of caries. Circadian rhythm, breakfast habits and toothbrushing frequency were associated with a high risk of caries. The predicted probability of being at high risk of caries was almost four times higher for evening types than for morning types (OR 3.8; 95% CI 1.3-10.9).CONCLUSION: Adolescents who belonged to the evening circadian rhythm group brushed their teeth more seldom, ate breakfast less regularly and had a higher risk of caries than morning types. A patient's circadian rhythm should be considered when planning oral health education for adolescents with a high risk of caries.
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| 3. |
- Rolfö, Linda, et al.
(författare)
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Predictors of Preference for the Activity-based Flexible Office
- 2019
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Ingår i: Human Systems Engineering and Design. - Cham : Springer. - 9783030020521 - 9783030020538 ; 876, s. 547-553
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Konferensbidrag (refereegranskat)abstract
- Activity-based Flexible Offices (A-FOs) are implemented with varying degree of success. Employees relocate from cell or open-plan offices, from different organizational backgrounds, varying design and implementation processes, and have different types of work tasks. This study aims at investigating whether preference for the A-FO correlate with these preconditions. The results from Chi-square tests and Spearman’s non-parametric correlation of post-relocation questionnaires distributed to 11 A-FO sites, showed that a high preference for the A-FO correlated strongest with an A-FO preference prior to relocation, being a former open-plan office occupier and with frequent performance of innovation. Low preference for the A-FO correlated with frequent performance of concentration demanding tasks. Working with tasks with high confidentiality did not predict the preference ratings.
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| 4. |
- Öhrn, Anders, et al.
(författare)
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Method for Slater-Type Density Fitting for Intermolecular Electrostatic Interactions with Charge Overlap. I. the Model
- 2016
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 12:5, s. 2298-2311
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Tidskriftsartikel (refereegranskat)abstract
- The effects of charge overlap, or charge penetration, are neglected in most force fields and interaction terms in QM/MM methods. The effects are however significant at intermolecular distances near the van der Waals minimum. In the present study, we propose a method to evaluate the intermolecular Coloumb interaction using Slater-type functions, thus explicitly modeling the charge overlap. The computational cost of the method is low, which allows it to be used in large systems with most force fields as well as in QM/MM schemes. The charge distribution is modeled as a distributed multipole expansion up to quadrupole and Slater-type functions of angular momentum up to L = 1. The exponents of the Slater-type functions are obtained using a divide-and-conquer method to avoid the curse of dimensionality that otherwise is present for large nonlinear optimizations. A Levenberg-Marquardt algorithm is applied in the fitting process. A set of parameters is obtained for each molecule, and the process is fully automated. Calculations have been performed in the carbon monoxide and the water dimers to illustrate the model. Results show a very good accuracy of the model with relative errors in the electrostatic potential lower than 3% over all reasonable separations. At very short distances where the charge overlaps is the most significant, errors are lower than 8% and lower than 3.5% at distances near the van der Waals minimum.
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