291 research outputs found
On the interplay between the slowdown of dynamics and the kinetics of aggregation: The case study of a reactive binary mixture
No full textModeling the kinetics of aggregation requires a proper strategy to take into account not only the reactivity of reagents but also the ability they have to diffuse. The lack of direct information about diffusion represents the most serious experimental obstacle to the use of diffusion-corrected mean-field equations, which is usually overcome by using information on the structural relaxation dynamics. A very accurate description of the entire kinetics of aggregation can be made by introducing a single time scale of diffusion, set by the structural relaxation time tau of the system according to similar to tau(xi), with xi a fractional exponent. Here, we apply this modeling to the case of a reactive binary mixture made of diglycidyl ether of bisphenol-A and 1,3-phenylenediamine, where the reaction proceeds along an autocatalyic (hydroxyl catalyzed) and a non-catalytic (impurity catalyzed) pathway and find that a very small value of the exponent xi = 0.27 +/- 0.03 is needed to reproduce all the data. Our results help revise some preconceived ideas: contrary to widely held assumptions, we find that (i) the time scale of diffusion neither increases proportionally to the structural relaxation time nor is related to tau by a power law with the same fractional exponent as that relating tau to conductivity; (ii) no direct connection exists between the transition to diffusion-control and the development of a gel network or formation of a glassy phase; and (iii) there is no significant difference in the enthalpy barrier for bond formation in the presence of hydroxyl or other than hydroxyl catalyst groups
Curare e curarsi nella marginalità: i risultati dell’Indagine su senza dimora, salute e accesso alle cure in Toscana
No full textStress-induced modification of the boson peak scaling behavior
No full textThe scaling behavior of the so-called boson peak in glass-formers and its relation to the elastic properties of the system remains a source of controversy. Here the boson peak in a binary reactive mixture is measured by Raman scattering (i) on cooling the unreacted mixture well below its glass-transition temperature and (ii) after quenching to very low temperature the mixture at different times during isothermal polymerization. We find that the scaling behavior of the boson peak with the properties of the elastic medium - as measured by the Debye frequency - holds for states in which the elastic moduli follow a generalized Cauchy-like relationship, and breaks down in coincidence with the departure from this relation. A possible explanation is given in terms of the development of long-range stresses in glasses. The present study provides new insight into the boson peak behavior and is able to reconcile the apparently conflicting results presented in literature
Dynamics of a glass-forming triepoxide studied by dielectric spectroscopy
No full textDielectric measurements of an epoxy resin, N, N-diglycidyl-4-glycidyloxyaniline, have been carried out in the supercooled and glassy phase over a broad frequency range (10(2)-6x10(9) Hz). The measurements reveal electrical transport due to ionic impurities as well as three different dipolar relaxations-in addition to the alpha- and beta-relaxation, a slower alpha'-relaxation is recognized, whose loss peak is disclosed after subtraction of the de conductivity contribution. The glass transition is found to affect markedly the secondary relaxation, whose strength and shape parameters change across Tg The major inference from the results concerns the existence of a transition in the dynamics, occurring some tens of degrees above Tg, in the vicinity of the temperature Ts where the peaks of the alpha- and beta-relaxations merge. Evidence in favour of such a transition is given by: (i) the change in the temperature dependence of the a-relaxation time; (ii) independently, the change in the temperature dependence of the de conductivity; (iii) the breakdown of the Debye-Stokes-Einsten model, replaced at lower temperatures by a fractional regime. Concerning the alpha'-process, it shows a Vogel-Fulcher behaviour with the same temperature To as the alpha-relaxation but, unlike this last, it is not involved in a splitting phenomenon with the beta-relaxation. Several hypotheses concerning the nature of the alpha'-process are explored
Indicators of quality of care for the Internal Medicine Departments: a review of the literature
No full textHigh-performance versatile setup for simultaneous Brillouin-Raman micro-spectroscopy
No full textThis is the author accepted manuscript. The final version is available from American Physical Society via the DOI in this record.Brillouin and Raman scattering spectroscopy are established techniques for the nondestructive contactless and label-free readout of mechanical, chemical and structural properties of condensed matter. Brillouin-Raman investigations currently require separate measurements and a site-matched approach to obtain complementary information from a sample.
Here we demonstrate a new concept of fully scanning multimodal micro-spectroscopy for simultaneous detection of Brillouin and Raman light scattering in an exceptionally wide spectral range, from fractions of GHz to hundreds of THz. It yields an unprecedented 150 dB contrast, which is especially important for the analysis of opaque or turbid media such as biomedical samples, and spatial resolution on a sub-cellular scale.
We report the first applications of this new multimodal method to a range of systems, from a single cell to the fast reaction kinetics of a curing process, and the mechano-chemical mapping of highly scattering biological samples.S. Corezzi acknowledges financial support from MIUR-PRIN (Project No. 2012J8X57P). S. Caponi acknowledges support from PAT (Provincia Autonoma di Trento) (GP/PAT/2012) “Grandi Progetti 2012” Project “MaDEleNA.” P. S., A. M., M. P. acknowledge financial support from Centro Nazionale Trapianti (Project: “Studio di cellule per uso clinico umano, con particolare riferimento a modelli cellulari (liposomi) e linee cellulari in interazione con crioconservanti e con materiali biocompatibili”). L. C. and S. Caponi acknowledge financial support from Consiglio Nazionale delle Ricerche-Istituto Officina dei Materiali. F. P. acnowledges support from the UK Engineering and Physical Sciences Research Council (Grant No. EP/M028739/1 (F. P.)). The authors acknowledge Jacopo Scarponi for valuable help in setting up the hardware and software system for simultaneous Raman and BLS measurements
Maternal-foetal attachment independently predicts the quality of maternal-infant bonding and post-partum psychopathology
No full textPurpose: The aim of this study was to evaluate the association of maternal antenatal attachment and post-partum psychopathology, maternal–infant bonding, while checking for antenatal psychopathology, for lifetime psychiatric diagnosis and for the known risk factors for peripartum depression. Methods: One hundred and six women recruited at the first month of pregnancy (T0) were evaluated with the structured interview for DSM-IV TR (SCID-I) to assess the presence of lifetime psychiatric diagnosis and with the Perinatal Depression Predictor Inventory-Revised (PDPI-R), the Edinburgh Postnatal Depression Scale (EPDS), and the State–Trait Anxiety Inventory (STAI). At the sixth month of pregnancy (T1) and at the first month post-partum (T2), all patients were evaluated with the PDPI-R, the EPDS, the STAI, at T1, with the Maternal Antenatal Attachment Scale (MAAS), and at T2 with the Maternal Postnatal Attachment Scale (MPAS). Results: Multivariate regression analyses showed that maternal–foetal attachment was the variable most significantly associated with postnatal symptoms of depression and anxiety and with quality of maternal-infant attachment. The logistic regression analyses showed that antenatal attachment may predict postnatal depressive and anxiety symptoms (respectively, OR: 0.83–IC [0.74 − 0.95], p =.005, OR: 0.88–IC [0.79 − 0.98], p =.02), and the quality of maternal postnatal attachment (OR: 1.17–IC [1.08 − 1.27], p <.001), also after taking into account the known risk factors for perinatal depression, the sociodemographic variables and lifetime psychiatric diagnosis. Conclusion: The quality of maternal–foetal bonding may independently predict the quality of maternal–infant attachment and post-partum depressive and anxiety symptoms. A comprehensive assessment of maternal risk factors for perinatal psychopathology during pregnancy should include the evaluation of antenatal attachment that could be modifiable by specific interventions promoting the quality of maternal bonding
VOC Air Pollution in Urban Areas – A Microscale Model experimentally validated
No full textPrevious theoretical and experimental studies (S. T. A.- Università di Pisa (DIMNP), 1998; Agostini E., M. Corezzi, I. Ciucci, M. Mazzini 2003; Agostini E., I. Ciucci, M. Mazzini, S. Strinati, 2003) even if partial, evidenced the problem of atmospheric pollution by Volatile Organic Compounds (VOC) in Livorno (Tuscany). This pollution is caused mainly by the presence of an important refinery, other industries and traffic. Other relevant VOC emission sources are linked to port activities and to numerous small companies using paints and solvents. Figure 1 shows the map of Livorno, situated on the Tyrrhenian sea. This is a simple site from the orography point of view, except for the southern zone where a promontory and a chain of hills impose a more complex pattern of air fluxes. The industrial zone is localized in the north of the map and the harbour activities along the coast (west area). It’s difficult to define a specific zone for the companies using solvents and paints, even though a grater concentration is present around the axis Viale Carducci – Piazza Repubblica – Via Grande.
The map outlines also the air pollution measurement stations managed by ARPAT (points) and the meteorological stations (crosses).
The simulation of the emission scenario, was done by using ISC3 (U. S. Environmental Protection Agency) code for treating diffuse sources and CALINE4 (California Department of Transportation) for those related to traffic on main roads.
The research work focuses the attention on the results of model validation by experimental data obtained along the roads of the studied area. The possibility to extend the application of this model to sites with similar orography and town-planning characteristics is also discussed in the aim of obtaining information about the level of atmospheric pollution on sites where there aren’t measurement stations
Cure modelling and monitoring of epoxy/amine resin systems
No full textThermoanalytical techniques and dielectric analysis were used in this study to describe
and characterise the cure processes occurring during the isothermal and dynamic cures
of four epoxy/amine resin systems.
The complexity of the cure reactions was illustrated by results from DSC and FTIR
experiments and was attributed to the variety of chemical reactions between the epoxy
and the amine groups. Several phenomenological and mechanistic cure kinetics models
were constructed, based on the cure reaction mechanisms, in order to simulate the
degree of conversion during the cure. A one-to-one relationship was established
between the degree of cure and the glass transition temperature of the curing resin,
which was finther used in the construction of chemoviscosity models and in a
simulation of the viscosity advancement during the cure.
A number of mathematical techniques were utilised to evaluate the parameters
involved in all the models, varying from simple linear regression methods to complex
non-linear least squared estimation procedures.
An in-situ dielectric monitoring technique was used in combination with the above
mentioned chemorheological models, to investigate the feasibility of a quantitative
correlation between the changes in the dielectric signal, the cure advancement and the
major physical transformations, namely gelation and vitrification. The imaginary
impedance response of the curing resin, as measured by the dielectric technique,
showed good agreement with the degree of conversion, depicting all the crucial
characteristics of the curing mechanism, such as autocatalysis and diflusion. The
endset of the cure reaction was also identified from the endset of the conductivity
changes and correlated to the vitrification time.
The analytical chemorheological models developed in this study to describe the cure
processes for some epoxy/amine resin systems, along with the dielectric monitoring
technique used, suggest that a real-time link between the above mentioned models and
the cure monitoring technique can be achieved. This would greatly enhance the
predictive capability of the technique and form the basis of a future feedback-loop
control system
Comparison of nanoindentation and Brillouin light scattering measurements on amorphous dielectrics and polymer thin films
No full textInternational audienceComparison of nanoindentation and Brillouin light scattering measurements on amorphous dielectrics and polymer thin films. Background, Motivation and Objective Microlenses for image sensors may consist of polymer films encapsulated by a dielectric layer. Difference in thermomechanical properties can cause adhesive or cohesive ruptures, impacting device reliability. Predictive failure simulations require accurate mechanical property data.This study investigates the elastic properties of two amorphous dielectric films (1.2 and 1.8 µm thick) and a 3 µm amorphous resin film using nanoindentation (NI) and Brillouin light scattering (BLS). Comparing reduced Young’s modulus from NI and BLS will assess if comparable mechanical properties are obtained despite technique limitations and different solicitation modes. Some studies show that NI yields higher reduced Young's modulus than BLS [1, 2], attributed to densification during NI tests or overestimation due to substrate influence. To reduce this effect a monolayer model is used here. Statement of Contribution/Methods NI tests are conducted using an MTS XP nanoindenter with the standard method [3]. To account for substrate influence, a monolayer model [4] is used. BLS measurements are performed using either the "p" or "s" polarization state of the incoming light and analyzing the polarization of the scattered light.To assess substrate impact on NI and BLS results, tests are performed on 1.2 and 1.8 µm dielectric films, along with a fused silica sample (a standard NI calibration material). Reduced Young’s modulus obtained from NI and BLS are then compared to evaluate their consistency across these testing conditions.Results/Discussion BLS measurements allows to detect Rayleigh surface wave but also shear horizontal and longitudinal guided modes, as well as longitudinal bulk wave in all samples. The isotropic assumption is valid for the resin film but shows noticeable deviations in the dielectrics.Despite technique limitations and different solicitation modes, NI and BLS measurements for the 1.8 µm dielectric film show good agreement, with a relative difference of less than 6%. This suggests the Bec model effectively accounts for substrate influence and that densification effects during NI tests are negligible for the studied thickness.For the 3 µm resin sample, the reduced Young's modulus measured by NI is 25% higher than obtained by BLS. It is attributed to the resin's viscoelastic behavior and the higher strain rate in BLS measurements. Despite different solicitation modes, BLS and NI yield comparable mechanical properties for the thin films studied. The importance of using a monolayer model in NI tests is highlighted, and dielectric densification is shown to be negligible. Further tests will be conducted on the 1.2 µm dielectric films and the fused silica sample to verify these findings
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