The crystallization kinetics and the resulting structure and morphology of polylactide (PLA) were investigated in the presence of carbon nanotubes (CNTs). Nanocomposite samples prepared by solution ...and melt mixing present homogeneous filler dispersion, as observed by scanning electron microscopy. Calorimetric characterization of the nonisothermal and isothermal crystallization behavior analyzed according to Avrami’s theory provides evidence of the significant impact of CNTs on the crystallization kinetics of the PLA matrix. The nucleating effect of the nanofillers is confirmed by Raman spectroscopy experiments. Indeed, during isothermal crystallization, the nanotube characteristic vibrations are strongly affected by the development of polymer crystalline phase. Additionally, CNTs increase the number of nucleation sites and thereby decrease the average spherolite size as observed by optical microscopy. The PLA crystal structure is not modified by the presence of CNTs, as probed by X-ray diffraction.
Blends of entirely biosourced polymers, namely polylactide (PLA) and polyamide11 (PA11), have been melt-compounded by twin-screw extrusion without the use of any compatibilizing agent. The ...crystallization and melting behavior, the morphology and mechanical properties of the melt-compounded binary blends have been investigated over the whole composition range. Albeit immiscibility prevails in all blends, the micronic and sub-micronic dispersion of the minor phase reveals a self-compatibilization behavior of the PLA/PA11 system as directly evidenced via scanning electron microscopy. For PLA compositions below 50%, PLA appears to be dispersed as globules in the PA11 matrix. With increasing PLA content beyond 50%, the blends exhibit co-continuous intertwined phases, then thread-like PA11 phase dispersed in a PLA matrix. For PLA composition greater than 80%, PA11 displays globular dispersion. In the case of PLA-rich blends, the crystallization of PA11 from the melt displayed a contribution of “homogeneous nucleation” corroborating the high degree of dispersion of the minor phase. However, the earlier crystallization of PA11 upon cooling did not promote that of PLA suggesting low interfacial free energy at the boundaries of the phase-separated domains,
i.e. roughly neutral interactions between the unlike species. The non-symmetric structural behavior of the blends over the whole composition range was found to influence the mechanical properties. If the elastic modulus of the blends roughly obeys an additive mixture law at room temperature (RT), this is not the case above the Tg of both PLA and PA11. More particularly in the PLA-rich range, the thread-like dispersion of the stiff PA11 component plays the role of
in situ fibrillar reinforcement of the soft PLA matrix. The strain at break and the yield stress also do not obey a simple mixture law, both at RT and above Tg. Perspectives of morphological and mechanical improvements of PLA/PA11 blends are discussed.
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This work deals with the study of the mesomorphic form or mesophase induced by tensile drawing from the amorphous state of a polylactide material containing 4 mol % of d-stereoisomer units. ...Investigations have been carried out over the draw temperature domain 45−90 °C, i.e. an interval spanning roughly ±20 °C about the glass transition temperature. In situ WAXS experiments during drawing, stress relaxation, and/or heating of stretched samples invariably showed the strain-induced occurrence of the mesophase as far as temperature did not exceed 70 °C. This seems to be the upper stability temperature of the mesophase identified in a previous study. DSC traces upon heating of drawn samples exhibit a post glass transition endothermic peak similar to the enthalpy relaxation phenomenon observed for aged polymers. The amplitude of this strain-induced endotherm proved to be strongly dependent on draw temperature and draw ratio. Draw ratio also appeared to strongly influence the temperature domain of cold crystallization. The quite different structural evolution of the drawn samples as a function of temperature, depending whether cold crystallization occurred close or far from the strain-induced endotherm, led us to the conclusion that this endotherm results from neither physical aging nor orientation relaxation but from “melting” of the mesophase. This proposal is thoroughly supported by the insensitivity of the endotherm enthalpy to the DSC scanning rate that gives evidence of a first order thermodynamic transition in contrast to the case of aging-induced endotherm. WAXS as a function of temperature on drawn samples annealed with free ends enabled to probe the persistence of chain orientation and the stability of the strain-induced structural changes in relation to drawing conditions.
On the Inverse LQG Homing Problem Lefebvre, M.
Journal of contemporary mathematical analysis,
04/2022, Letnik:
57, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The problem of minimizing or maximizing the time spent by a controlled diffusion process in a given interval is known as LQG homing. The optimal control, when it is possible to obtain an explicit ...solution to such a problem, is often expressed as special functions. Here, the inverse problem is considered: we determine, under certain assumptions, the processes for which the optimal control is a simple power function. Moreover, the problem is extended to the case of jump-diffusion processes.
Introduction
Concerning NMR-based metabolomics, 1D spectra processing often requires an expert eye for disentangling the intertwined peaks.
Objectives
The objective of NMRProcFlow is to assist the ...expert in this task in the best way without requirement of programming skills.
Methods
NMRProcFlow was developed to be a graphical and interactive 1D NMR (
1
H &
13
C) spectra processing tool.
Results
NMRProcFlow (
http://nmrprocflow.org
), dedicated to metabolic fingerprinting and targeted metabolomics, covers all spectra processing steps including baseline correction, chemical shift calibration and alignment.
Conclusion
Biologists and NMR spectroscopists can easily interact and develop synergies by visualizing the NMR spectra along with their corresponding experimental-factor levels, thus setting a bridge between experimental design and subsequent statistical analyses.
This work deals with the
in situ and
ex situ WAXS study of the strain-induced structural changes in relation to the mechanical behavior of a semi-crystalline polylactide containing 4% of
d-stereomer ...units. The crystals isothermally generated at 120
°C were in the α form. The draw temperature was in the range 65
°C
<
T
d
<
90
°C,
i.e. just above
T
g. In this
T
d range isothermal crystallization was so slow that only strain-induced crystals could be generated during the time scale of the experiments. This allowed studying samples with various initial levels of crystallinity,
X
cr. For
X
cr
=
5%, the early occurrence of strain-hardening contrasted with the case of the amorphous material. This was due to the physical crosslinking of the macromolecular network by the crystallites that prevented chain relaxation since the onset of drawing. Strain-induced α′ crystals developed in parallel with the mesophase, the respective amount of the two phases being dependent on
T
d. For
X
cr
=
24%, the drawing behavior was that of a crosslinked and filled elastomer. Again, both strain-induced α′ crystals and mesophase occurred in various proportions in relation to
T
d. For
X
cr
=
40%, it was shown that the initial α crystals underwent partial destruction and subsequent reorganization into mesophase and/or α′ crystals. Whatever
T
d and
X
cr, the total amount of ordered phases,
i.e. crystal
+
mesophase, did not exceed the value of 40% that was the maximum accessible crystal content for the present material. A mechanism of plastic deformation involving twinning is proposed from the WAXS analysis of the crystalline texturing in the case
X
cr
=
40%. AFM observations as a function of strain corroborate the proposed deformation scheme.
▪
Synopsis
Objective
After pilot and preliminary studies aimed at identifying pertinent biochemical parameters, a multicenter clinical study was performed to evaluate the effect of pollution on human ...skin.
Methods
The clinical study was performed in collaboration with the ‘Centre Régional de lutte contre le cancer de Montpellier’ and the ‘National Institute of Public Health of Mexico’ on 96 subjects in Mexico City (exposed to pollution) and 93 subjects in Cuernavaca (less exposed to pollution). Both biochemical and clinical skin parameters were studied.
Results
The study demonstrated significant quantitative and qualitative modifications of parameters related to sebum excretion in Mexico City compared to Cuernavaca one: An increased level of sebum excretion rate, a lower level of vitamin E and squalene in sebum, an increase of lactic acid and a higher erythematous index on the face of the subjects. In the stratum corneum, a significant higher level of carbonylated proteins and a lower level of IL 1α were noticed, as well as a decrease of ATP concentration with a decrease of chymotrysin like activity, without modifications of corneodesmosin content and trypsin like activity. From a clinical point of view, a higher frequency of atopic and urticarial skins, a higher frequency of red dermographism, an important seborrheic status at the forehead level and a lower level of dandruffs were noted in Mexico City population. The analysis taking into account the sex does not modify the observed results.
Conclusion
The study demonstrated an important impact of polluted environmental conditions on skin quality, evidencing important modifications of superficial biochemical parameters. The cause/effects relationships of these modifications remain, however, to be further assessed by a complementary in vitro/in vivo approaches.
Résumé
Objectifs
L'effet de la pollution sur la peau humaine a été évalué en définissant au cours d'une étude pilote, suivie d'une étude préliminaire, les paramètres biochimiques superficiels impactés, et en conduisant une étude clinique multicentrique.
Méthodes
L’étude clinique a été conduite en collaboration avec le ‘Centre Régional de Lutte contre le Cancer de Montpellier’ et ‘l'Institut National de la Santé du Mexique’, sur 96 sujets de la ville de Mexico (Zone exposée à la pollution) et 93 sujets à Cuernavaca (zone moins exposée à la pollution). Des mesures biochimiques et des observations cliniques ont été effectuées.
Résultats
L’étude a démontré des modifications statistiquement significatives des paramètres liés à la production quantitative et qualitative de sébum dans la ville de Mexico comparativement à Cuernavaca : une augmentation de la vitesse d'excrétion du sébum, une concentration inférieure de vitamine E et de squalène dans le sébum, une augmentation de l'acide lactique et un index érythémateux supérieur sur le visage des sujets. Dans le stratum corneum, un niveau supérieur de protéines carbonylées, un niveau inférieur de IL1α, une diminution de la concentration en ATP ainsi qu'une diminution de l'activité ‘chymotrypsin like’ sans modification de la corneodesmosine ou de l'activité ‘Trypsin like’. Sur le plan clinique une fréquence plus élevée de peau atopique ou présentant des caractéristique d'urticaire, une plus grande fréquence de dermographisme et un niveau inférieur de pellicules ont été notés dans la ville de Mexico. L'analyse des résultats en prenant en compte l'influence du sexe ne modifie pas les conclusions tirées de l’étude.
Conclusion
L’étude démontre un impact important des conditions environnementales d'exposition sur la qualité de la peau en mettant en évidence d'importantes modifications des paramètres biochimiques superficiels de la peau. Les relations cause/effets de ces modifications restent cependant à être évaluées au cours de futures approches in vivo/in vitro.
The tensile behavior of nylon 6 films has been investigated in relation to water content. Modification of chain mobility in the amorphous phase via water plasticization appears to have a determining ...impact on the stress–strain response. More specifically, both yield stress value and hardening behavior over a large strain domain are strikingly equivalent for samples drawn at same Δ
T between draw temperature
T
d and main amorphous relaxation temperature
T
α. This apparent lack of thermal activation of crystal plasticity in the fibrillar transformation suggests that crystal block fragmentation proceeds via H-bond unzipping through water penetration at defective crystal interfaces.
Clear guidance for successive antidepressant pharmacological treatments for non-responders in major depression is not well established.
Based on the RAND/UCLA Appropriateness Method, the French ...Association for Biological Psychiatry and Neuropsychopharmacology and the fondation FondaMental developed expert consensus guidelines for the management of treatment-resistant depression. The expert guidelines combine scientific evidence and expert clinicians' opinions to produce recommendations for treatment-resistant depression. A written survey comprising 118 questions related to highly-detailed clinical presentations was completed on a risk-benefit scale ranging from 0 to 9 by 36 psychiatrist experts in the field of major depression and its treatments. Key-recommendations are provided by the scientific committee after data analysis and interpretation of the results of the survey.
The scope of these guidelines encompasses the assessment of pharmacological resistance and situations at risk of resistance, as well as the pharmacological and psychological strategies in major depression.
The expert consensus guidelines will contribute to facilitate treatment decisions for clinicians involved in the daily assessment and management of treatment-resistant depression across a number of common and complex clinical situations.
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