scholarly journals Concepts of Nucleation in Polymer Crystallization

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 304
Author(s):  
Jun Xu ◽  
Günter Reiter ◽  
Rufina G. Alamo
Keyword(s):  
Polymer Crystallization ◽  
Vital Role ◽  
Polymer Chains ◽  
Polymer Materials ◽  
Crystal Nucleation ◽  
The Past ◽  
Open Questions ◽  
Lamellar Crystals ◽  
Kinetics Of ◽  
Complex Subject

Nucleation plays a vital role in polymer crystallization, in which chain connectivity and thus the multiple length and time scales make crystal nucleation of polymer chains an interesting but complex subject. Though the topic has been intensively studied in the past decades, there are still many open questions to answer. The final properties of semicrystalline polymer materials are affected by all of the following: the starting melt, paths of nucleation, organization of lamellar crystals and evolution of the final crystalline structures. In this viewpoint, we attempt to discuss some of the remaining open questions and corresponding concepts: non-equilibrated polymers, self-induced nucleation, microscopic kinetics of different processes, metastability of polymer lamellar crystals, hierarchical order and cooperativity involved in nucleation, etc. Addressing these open questions through a combination of novel concepts, new theories and advanced approaches provides a deeper understanding of the multifaceted process of crystal nucleation of polymers.

scholarly journals Use of PRP, PRF and CGF in Periodontal Regeneration and Facial Rejuvenation—A Narrative Review

Biology ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 317
Author(s):  
Eitan Mijiritsky ◽  
Haya Drora Assaf ◽  
Oren Peleg ◽  
Maayan Shacham ◽  
Loredana Cerroni ◽  
...  
Keyword(s):  
Growth Factors ◽  
Platelet Rich Plasma ◽  
Periodontal Regeneration ◽  
Clinical Work ◽  
Gingival Recession ◽  
Vital Role ◽  
Facial Rejuvenation ◽  
Cochrane Library ◽  
The Past ◽  
Autologous Platelet

Growth factors (GFs) play a vital role in cell proliferation, migration, differentiation and angiogenesis. Autologous platelet concentrates (APCs) which contain high levels of GFs make them especially suitable for periodontal regeneration and facial rejuvenation. The main generations of APCs presented are platelet-rich plasma (PRP), platelet-rich fibrin (PRF) and concentrated growth factor (CGF) techniques. The purpose of this review is to provide the clinician with an overview of APCs’ evolution over the past decade in order to give reliable and useful information to be used in clinical work. This review summarizes the most interesting and novel articles published between 1997 and 2020. Electronic and manual searches were conducted in the following databases: Pubmed, Scopus, Cochrane Library and Embase. The following keywords were used: growth factors, VEGF, TGF-b1, PRP, PRF, CGF and periodontal regeneration and/or facial rejuvenation. A total of 73 articles were finally included. The review then addresses the uses of the three different techniques in the two disciplines, as well as the advantages and limitations of each technique. Overall, PRP is mainly used in cases of hard and soft tissue procedures, while PRF is used in gingival recession and the treatment of furcation and intrabony defects; CGF is mainly used in bone regeneration.

scholarly journals Recent progress understanding pathophysiology and genesis of brain AVM—a narrative review

2021 ◽  
Author(s):  
Hans-Jakob Steiger
Keyword(s):  
Large Degree ◽  
Advanced Imaging ◽  
Genetic Origin ◽  
The Past ◽  
Open Questions ◽  
Brain Avm ◽  
Pubmed Search ◽  
Substantial Progress ◽  
The Individual ◽  
Arterial Aneurysms

AbstractConsiderable progress has been made over the past years to better understand the genetic nature and pathophysiology of brain AVM. For the actual review, a PubMed search was carried out regarding the embryology, inflammation, advanced imaging, and fluid dynamical modeling of brain AVM. Whole-genome sequencing clarified the genetic origin of sporadic and familial AVM to a large degree, although some open questions remain. Advanced MRI and DSA techniques allow for better segmentation of feeding arteries, nidus, and draining veins, as well as the deduction of hemodynamic parameters such as flow and pressure in the individual AVM compartments. Nonetheless, complete modeling of the intranidal flow structure by computed fluid dynamics (CFD) is not possible so far. Substantial progress has been made towards understanding the embryology of brain AVM. In contrast to arterial aneurysms, complete modeling of the intranidal flow and a thorough understanding of the mechanical properties of the AVM nidus are still lacking at the present time.

scholarly journals A Response of Snow Cover to the Climate in the Northwest Himalaya (NWH) Using Satellite Products

2021 ◽  
Vol 13 (4) ◽  
pp. 655
Author(s):  
Animesh Choudhury ◽  
Avinash Chand Yadav ◽  
Stefania Bonafoni
Keyword(s):  
Snow Cover ◽  
Land Surface ◽  
Significant Negative Correlation ◽  
Shuttle Radar Topography Mission ◽  
Vital Role ◽  
Snow Cover Area ◽  
Study Region ◽  
Northwest Himalaya ◽  
The Past ◽  
Average Annual Temperature

The Himalayan region is one of the most crucial mountain systems across the globe, which has significant importance in terms of the largest depository of snow and glaciers for fresh water supply, river runoff, hydropower, rich biodiversity, climate, and many more socioeconomic developments. This region directly or indirectly affects millions of lives and their livelihoods but has been considered one of the most climatically sensitive parts of the world. This study investigates the spatiotemporal variation in maximum extent of snow cover area (SCA) and its response to temperature, precipitation, and elevation over the northwest Himalaya (NWH) during 2000–2019. The analysis uses Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra 8-day composite snow Cover product (MOD10A2), MODIS/Terra/V6 daily land surface temperature product (MOD11A1), Climate Hazards Infrared Precipitation with Station data (CHIRPS) precipitation product, and Shuttle Radar Topography Mission (SRTM) DEM product for the investigation. Modified Mann-Kendall (mMK) test and Spearman’s correlation methods were employed to examine the trends and the interrelationships between SCA and climatic parameters. Results indicate a significant increasing trend in annual mean SCA (663.88 km2/year) between 2000 and 2019. The seasonal and monthly analyses were also carried out for the study region. The Zone-wise analysis showed that the lower Himalaya (184.5 km2/year) and the middle Himalaya (232.1 km2/year) revealed significant increasing mean annual SCA trends. In contrast, the upper Himalaya showed no trend during the study period over the NWH region. Statistically significant negative correlation (−0.81) was observed between annual SCA and temperature, whereas a nonsignificant positive correlation (0.47) existed between annual SCA and precipitation in the past 20 years. It was also noticed that the SCA variability over the past 20 years has mainly been driven by temperature, whereas the influence of precipitation has been limited. A decline in average annual temperature (−0.039 °C/year) and a rise in precipitation (24.56 mm/year) was detected over the region. The results indicate that climate plays a vital role in controlling the SCA over the NWH region. The maximum and minimum snow cover frequency (SCF) was observed during the winter (74.42%) and monsoon (46.01%) season, respectively, while the average SCF was recorded to be 59.11% during the study period. Of the SCA, 54.81% had a SCF above 60% and could be considered as the perennial snow. The elevation-based analysis showed that 84% of the upper Himalaya (UH) experienced perennial snow, while the seasonal snow mostly dominated over the lower Himalaya (LH) and the middle Himalaya (MH).

scholarly journals Crystal nucleation and growth kinetics of NaF in photo-thermo-refractive glass

2013 ◽  
Vol 378 ◽  
pp. 115-120 ◽  
Author(s):  
I. Dyamant ◽  
A.S. Abyzov ◽  
V.M. Fokin ◽  
E.D. Zanotto ◽  
J. Lumeau ◽  
...  
Keyword(s):  
Growth Kinetics ◽  
Nucleation And Growth ◽  
Crystal Nucleation ◽  
Kinetics Of

At the Still Point of the Turning World: Freud's Reception of Winckelmann's Greece

2014 ◽  
Vol 16 (2) ◽  
pp. 137-152
Author(s):  
Sharon Kool
Keyword(s):  
Vital Role ◽  
Classical Literature ◽  
German Culture ◽  
Classical Greece ◽  
Cultural Ideal ◽  
The Past ◽  
Greco Roman ◽  
Late Nineteenth ◽  
With Memory ◽  
Of Greece

Freud's theory is primarily concerned with memory, about the present contained within the past. It is also rooted to the past in another way; Freud's reception of the Greek classical tradition played a vital role in the genesis of his oeuvre. Winckelmann's revival of ‘Greece’ dominated German culture up to the late nineteenth and early twentieth century, yet besides the importance of Bildung in shaping Freud's early Gymnasium experience, his influence upon Freud is often neglected. While Freud's debt to German Hellenism is clearly demonstrated in his library of classical literature and his collection of Greco-Roman antiquities, the afterlife of Winckelmann's legacy is more subtly inscribed upon psychoanalysis. This paper focuses on Winckelmann's aesthetic reconstruction of classical Greece which made beauty, self-restraint and repression a cultural ideal to be imitated and admired. It is argued that hysteria provided one of the most powerful challenges to this ideal. Psychoanalysis can thus be seen as developing out of a milieu that was still overshadowed by Winckelmann's idealization of Greece. Further, it is argued that Winckelmann advanced a homoerotic tradition in German culture and the sedimentation of this tradition can be discerned in Freud's response to hysteria, his privileging of the masculine and his theory of bisexuality.

scholarly journals Fast-Scanning Chip-Calorimetry Measurement of Crystallization Kinetics of Poly(Glycolic Acid)

Polymers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 891
Author(s):  
Yongxuan Chen ◽  
Kefeng Xie ◽  
Yucheng He ◽  
Wenbing Hu
Keyword(s):  
Crystallization Kinetics ◽  
Temperature Region ◽  
Glycolic Acid ◽  
Crystal Nucleation ◽  
Side Group ◽  
Half Time ◽  
Temperature Range ◽  
Chip Calorimetry ◽  
Kinetics Of ◽  
Fast Scanning Chip Calorimetry

We report fast-scanning chip-calorimetry measurement of isothermal crystallization kinetics of poly(glycolic acid) (PGA) in a broad temperature range. We observed that PGA crystallization could be suppressed by cooling rates beyond -100 K s−1 and, after fast cooling, by heating rates beyond 50 K s-1. In addition, the parabolic curve of crystallization half-time versus crystallization temperature shows that PGA crystallizes the fastest at 130 °C with the minimum crystallization half-time of 4.28 s. We compared our results to those of poly(L-lactic acid) (PLLA) with nearby molecular weights previously reported by Androsch et al. We found that PGA crystallizes generally more quickly than PLLA. In comparison to PLLA, PGA has a much smaller hydrogen side group than the methyl side group in PLLA; therefore, crystal nucleation is favored by the higher molecular mobility of PGA in the low temperature region as well as by the denser molecular packing of PGA in the high temperature region, and the two factors together decide the higher crystallization rates of PGA in the whole temperature range.

Principles of exposure of polymer materials to heat, moisture and UV-radiation and study of their properties by full factorial experiment: A review

2021 ◽  
pp. 146-160
Author(s):  
A. B. Laptev ◽  
A. S. Nesterov ◽  
A. M. Vardanyan ◽  
A. M. Vardanyan
Keyword(s):  
Uv Radiation ◽  
Climatic Factors ◽  
Initial Period ◽  
Amorphous State ◽  
Surface Oxidation ◽  
Polymer Chains ◽  
Factorial Experiment ◽  
Polymer Materials ◽  
Full Factorial Experiment ◽  
Full Factorial

The work is dedicated to the effects of climatic factors on polyethylene terephthalate (PET) in terms of changes in the structure and interaction of polymer molecules. The kinetic concept of the strength of PET has been developed, and the factors influencing the strength have been considered. Effects of moisture, thermal oxidative destruction, and UV-radiation on the structure of PET have been investigated. Polymers’ properties predicting, durability and their computer modeling have been analyzed. A model of changes in PET properties under the influence of temperature, moisture and UV-radiation was constructed using the methods of a full factorial experiment. It has been shown that in the initial period of exposure, adsorption and diffusion of moisture, hydrolysis and surface oxidation occur; prolonged and constant exposure to UV-radiation break the bonds formed by moisture, then the C–C and C–O bonds in the PET molecule brake and new intermolecular bonds are formed. In the amorphous state of PET, the breaking of bonds in the polymer chain and the formation of bonds between two adjacent polymer chains, the formation of more densely packed nodes, the destruction of the polymer and its aging, are equally probable. Temperature has a secondary effect, facilitating both hydrolysis and oxidation and polymer degradation.

Kinetics of diffusion and sorption in aging processes of polymer materials (Review)

2021 ◽  
pp. 1-14
Author(s):  
A. A. Dalinkevich ◽  
◽  
L. V. Fomin ◽  
V. V. Melnikov ◽  
T. A. Nenasheva ◽  
...  
Keyword(s):  
Polymer Materials ◽  
Kinetics Of
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