196,093 research outputs found
Director reorientation due to dye photoabsorption
No full textThe addition of small quantities of an absorbing dye can modify the optical properties of liquid crystals, in particular by producing a photo-induced torque reorienting the director. Such an effect is modelled by including in the free energy the contribution of dye-solvent electrostatic interactions between the molecular charges and the solvent polarisation. The system evolution is described through the torque acting on the director and the diffusion equations for the orientational distributions of the dye in the ground and the excited states. In the presence of a time scale separation between molecular variables (orientation) and collective properties (director), an explicit relation is derived for the dye photo-induced torque, which appears to be compatible with the experimental findings
Data for: In silico multi-scale analysis of the effect of resorption cavities on peri-implant bone after undersized drilling technique.
No full textDatabase of micro- and macro-scale analysi
Data for: In silico multi-scale analysis of the effect of resorption cavities on peri-implant bone after undersized drilling technique.
No full textDatabase of micro- and macro-scale analysi
PLS for classification
No full textPartial Least Squares regression (PLS) is a multivariate technique developed to perform regression in the case of multivariate responses when multicollinearity, redundancy and noise affect the predictors. In spite of several efforts have been made to extend PLS to classification problems, this is still a current field of research. In the present study, a new technique called PLS for classification is introduced to solve the general G-class problem. It is developed within a self-consistent framework based on linear algebra and on the theory of compositional data. After the introduction of the notion of probability-data vector, the space of the predictors and that of the conditional probabilities are linked, and a well-defined least squares problem, whose solution specifies the relationship between probabilities and predictors, is solved by a suitable reformulation of PLS2. The method estimates directly the conditional probability of the class membership given the predictors. The score vectors are introduced only in a second step to improve model interpretation. The main properties of PLS for classification and its relationships with PLS-DA are discussed. One simulated and one real data sets are investigated to show how the method works in practice
Metabolomica basata su LC-MS-Approcci innovativi nella sicurezza degli integratori di origine vegetale
No full textProjection to latent structures with orthogonal constraints for metabolomics data
No full textMultivariate techniques based on projection methods such as Principal Component Analysis and Partial Least Squares (PLS) regression are widely applied in metabolomics. However, the effects of confounding factors and the presence of specific clusters in the data could force the projection to produce inefficient representations in the latent space, preventing the identification of the most relevant data variation. To overcome this issue, we introduce a general framework for projection methods, allowing an easy integration of orthogonal constraints, which help in reducing the effect of uninformative variations. In particular, the discussed algorithms address different scenarios. When known confounding factors can be explicitly encoded into a proper constraint matrix, orthogonally Constrained Principal Component Analysis (oCPCA) and orthogonally Constrained PLS2 (oCPLS2) can be used. Orthogonal PLS (OPLS) and post‐transformation of PLS2 (ptPLS2), instead, are suited to problems in which a constraint matrix cannot be defined. Finally, a data integration task is considered: Orthogonal two‐block PLS (O2PLS) and Orthogonal Wold's two‐block Mode A PLS (OPLS‐W2A) are used to identify the common variation between two data set
Molecular theory of dielectric relaxation in nematic dimers
No full textThis paper reports a theory for the dielectric relaxation of dimeric mesogenic molecules in a nematic liquid crystal phase. Liquid crystal dimers consist of two mesogenic groups linked by a flexible chain. Recent experimental studies [D. A. Dunmur, G. R. Luckhurst, M. R. de la Fuente, S. Diez, and M. A. Perez Jubindo, J. Chem. Phys. 115, 8681 (2001)] of the dielectric properties of polar liquid crystal dimers have found unexpected results for both the static (low frequency) and variable frequency dielectric response of these materials. The theory developed in this paper provides a quantitative model with which to understand the observed experimental results. The mean-square dipole moments of alpha, omega-bis[(4-cyanobiphenyl-4'-yl]alkanes in a nematic phase have been calculated using both the rotational isomeric state model and a full torsional potential for the carbon-carbon bonds of the flexible chain. The orienting effect of the nematic phase is taken into account by a parametrized potential of mean torque acting on the mesogenic groups and the segments in the flexible chain. Results of calculations using the full torsional potential are in excellent agreement with experimental results for comparable systems. The probability density p(eq)(beta(A),beta(B)) for the orientation of the mesogenic groups (A,B) along the nematic director is also calculated. The resultant potential of mean torque is a surface characterized by four deep energy wells or sites equivalent to alignment of the terminal groups A and B approximately parallel and antiparallel to the director; of course, the reversal of the director leads to equivalent sites. This potential energy surface provides the basis for a kinetic model of dielectric relaxation in nematic dimers. Solution of the Fokker-Planck equation corresponding to this four-site model gives the time dependence of the site populations, and hence the time-correlation functions for the total dipole moment along the director. In this model the end-over-end rotation of the molecule, corresponding to simultaneous reversal of both mesogenic groups, is excluded because the activation energy is too large. Results are presented for a number of cases, in which a dipole is located on one or both of the mesogenic groups, and additionally where the groups differ in size. For the latter, under particular conditions, the correlation function exhibits a biexponential decay, which corresponds to two low frequency absorptions in the dielectric spectrum. This is exactly what has been observed for nonsymmetric nematic dimers having different groups terminating a flexible chain. Experimental results over a range of temperature for the nonsymmetric dimer alpha-[(4-cyanobiphenyl)-4'-yloxy]-omega-(4-decylanilinebenzylidene-4'-o xy)nonane can be fitted precisely to the theory, which provides new insight into the orientational and conformational dynamics of molecules in ordered liquid crystalline phases
Clinical effects of conventional and underprepared drilling preparation of the implant site based on bone density : A systematic review and meta-regression
No full textPURPOSE: There is no clinical consensus to determine the right balance between underpreparation and marginal bone level changes. The purpose of this systematic review and meta-regression was to investigate the influence of the type of drilling preparation of the implant site in relation to the bone mineral density on the clinical success, expressed in terms of the MBL and implant failure rate. STUDY SELECTION: A thorough search was performed using the digital databases MEDLINE PubMed, EMBASE, and Cochrane Central Register of Controlled Trials by entering research lines or various combinations of free words. The main keywords used were "dental implants", "bone density", and "torque". RESULTS: The mean bone resorption in the conventional preparation group was -0.43 (± 0.28) mm, whereas it was -0.80 (± 0.37) mm in the underprepared group. For the D1/D2/D3 bone group, the slope was significantly different from zero and linearity; the D4 bone group slope was not significantly different from zero and was almost parallel, although it was significantly different from linearity. The box and whiskers plot shows that the MBL in underprepared sites tended to be significantly higher with a higher variation than that in conventionally prepared sites. CONCLUSION: Within its limits, our meta-regression analysis showed that MBL is influenced by the type of drilling preparation and bone mineral density. In particular, a lower MBL was observed in the D1 bone with conventional preparation than with underpreparation. Moreover, a greater implant-to-osteotomy site mismatch was positively associated with greater MBLs in the bone densities of D1/D2/D3
Self-assembling in surfactant aggregates: An alternative way to the realization of fluorescence chemosensors for Cu(II) ions
No full textThe self-assembling of the proper subunits of fluorescence chemosensors within surfactant aggregates in water allows the easy design, realization, and testing of new effective sensing systems. It was shown that a proper ligand and a fluorescent dye, once transferred from bulk water into an inert surfactant aggregate, are kept in such a close proximity that communication between the binding site and the signaling unit effectively occurs, thus avoiding the need for a covalent connection between the sensor's two units. To further simplify the sensing system and get rid of the inert surfactant which somehow implies the dilution of the sensor's active components in the aggregate, we have synthesized a series of lipophilic ligands for Cu(II) based on dipeptides GlyLys and GlyGlu functionalized with n-alkyl chains of different lengths at the N-terminus. These ligands are soluble in water and can form homoaggregates in the absence and in the presence of Cu(II) ions. Lipophilic fluorophores, like 8-anilino-naphthalensulfonic acid or Rhodamine 6G, are effectively bound into the aggregate pseudophase, and the binding of Cu(II) ions to the dipeptide units causes a strong fluorescence quenching. The sensor system is very sensitive to Cu(II) (concentrations in the submicromolar range are detected), is promptly reversible, and no interference is observed due to the presence of many metal ions. The sensitivity of the systems improves by decreasing the ligand concentration and (up to a point) the ligand's cmc
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