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Reliable simulation of polymers on an atomistic length scale requires a realistic representation of the cured material. A molecular modelling method for the curing of epoxy systems is presented, which is developed with respect to efficiency while maintaining a well equilibrated system. The main criterion for bond formation is the distance between reactive groups and no specific reaction probability is prescribed. The molecular modelling is studied for three different mixing ratios with respect to the curing evolution of reactive groups and the final curing stage. For the first time, the evolution of reactive groups during the curing process predicted by the molecular modelling is validated with near-infrared spectroscopy data, showing a good agreement between simulation results and experimental measurements. With the proposed method, deeper insights into the curing mechanism of epoxy systems can be gained and it allows us to provide reliable input data for molecular dynamics simulations of material properties.

To analyze the experimentally observed failure process in nanoparticle/polymer nanocomposites, a variety of factors, including nonlocal characteristics of damage mechanism and nonlinear viscoelasticity, are required to be investigated. This work presents the development and numerical implementation of a finite deformation gradient-enhanced damage model for boehmite nanoparticle (BNP)/epoxy nanocomposites. The parameters identification of the nonlocal constitutive description is realized using a framework based on molecular simulations and experimental tests. In this context, molecular simulations are performed to parameterize the Argon model of viscoelasticity, while damage and nonlocal parameters are determined using experimental data obtained from compact-tension tests. The nonlocal constitutive model integrated into a nonlinear FE analysis is validated by comparing the numerical results of compact-tension tests of BNP/epoxy samples with experimental data. The experimental–numerical validation confirms the predictive capability of the modeling framework. The proposed procedure can be extended to other types of nanoparticle reinforced thermosetting polymers.

The accurate prediction of the complex material response of nanoparticle/epoxy nanocomposites for thermomechanical load cases is of great interest for engineering applications. In the present work, three main contributions with respect to multi-scale modelling of the viscoelastic damage behaviour of nanocomposites are presented. Firstly, a constitutive model for the viscoelastic damage behaviour at finite temperatures below the glass-transition temperature is proposed. The constitutive model captures the main characteristics of the material response including the non-linear hyperelasticity, softening behaviour and the effect of temperature. Secondly, the material model is calibrated using purely experimental results to evaluate the best capability of the model in reproducing the stress–strain response at different strain rates and temperatures. The calibrated model predicts the material behaviour across a range of nanoparticle weight fractions with good agreement with experimental results. Finally, a combined approach of experimental testing and molecular simulations is proposed to identify the parameters of the constitutive model. This study shows that the proposed simulation-based framework can be used to significantly reduce the number of experimental tests required for identification of material parameters without a significant loss of accuracy in the material response prediction. The predictive capability of the atomistically calibrated constitutive model is validated, with additional experimental results not used within the parameter identification, in terms of an accurate representation of the viscoelastic damage behaviour of nanoparticle/epoxy nanocomposites at finite temperatures. The present study underlines the capabilities of numerical molecular simulations intended for the characterisation of material properties with respect to physically based constitutive modelling and multi-scale approaches.

1. Robin Unger, MD (drrobinunger{at}yahoo.com) 1. New York, New York, USA ![][1] There was a recent chain of emails pertaining to graft storage during hair transplant surgery. The main issue reviewed included the optimal temperature for graft storage solution and, by extension

This chapter describes the technique of hair transplant surgery and touches upon some of the more contentious debates in the field. Two harvest techniques, follicular unit excision (FUE) and strip/elliptical harvest, are described, and the pros and cons of each are discussed briefly. The design of the surgery in the recipient area should mimic nature, creating the illusion of density by producing a grade of hair density using grafts with different numbers of hairs and different densities of recipient sites. The most significant limitation continues to be the available source of donor hair, although this supply can be somewhat expanded with the use of a combination of techniques. The latest developments in hair transplant surgery enable skilled and experienced surgeons to consistently produce undetectable results.

In the United States, thousands of hair transplantations are being done annually. Although majority of patients having hair transplants are still male, there is an increasing number of women who undergo the procedure for their hair loss. As the technique evolves, hair transplant surgeons are able to provide their patients with results that more or less mimic the “natural look.” Current techniques in hair transplant surgery can produce incredibly natural results. Originally, hair transplantation was used almost exclusively to treat male pattern baldness. However, with the introduction of follicular unit grafting and tiny 1–3 hair grafts, the indications have broadened. Hair transplantation can now be used to treat delicate areas of hair loss on the face, such as eyebrows, eyelashes, beards, and mustaches. Other indications include secondary scarring on the scalp from accidents, burns, and surgery. Although controversial, transplantation can even be used to treat some forms of primary cicatricial and inflammatory alopecias. The goal of this chapter is to make the hair specialist familiar with the growing opportunities for surgical improvement of the hair loss in their patients. We introduce the reader to the contemporary transplant procedures sharing also pearls from our personal experience.

1. Robin Unger, MD (drrobinunger{at}yahoo.com) 1. New York, New York, USA ![][1] The topic of this chat is the use of implanters in hair transplant surgery. FUE grafts are generally very skeletonized with limited protective tissue. Furthermore, the splaying follicles (which are

1. Robin Unger, MD (drrobinunger{at}yahoo.com) 1. New York, New York, USA ![][1] This latest cyberchat was partially excerpted from a WhatsApp group to which I belong. I will not mention names of those who commented and will share only comments by doctors who have agreed their

[Figure][1] This meeting was ably summarized in the last edition of the Forum , but here I am happy to provide some additional thoughts and impressions. When ISHRS President Arthur Tykocinski asked me to be the Scientific Chair of the 2019 World Congress, I was far too honored to say

The precise knowledge of the temperature-dependent non-linear viscoelastic material behaviour of polymers is of great importance for engineering applications. The present work is a contribution to meet the challenge of bridging the inherently different time scales of molecular dynamics (MD) and experiments by providing a consistent comparison and assessment of viscoelastic theories. For this reason, the physically motivated theories for viscoelasticity of Eyring and Argon as well as the Cooperative model are evaluated with regard to their predictive capability for the characterisation of the viscous behaviour over a broad range of temperatures and strain rates. MD simulations of tensile tests are performed and the effect of strain rate and temperature on the yield stress is examined. The distinctive feature of this study is to demonstrate that viscoelastic theories can be successfully calibrated using only MD results. For a comparison to experimental data, we conduct tensile tests at three different strain rates and at three temperatures in the glassy regime. Experimental validation confirms the predictive capability of the Argon model, which can provide an accurate formulation of epoxy viscoelasticity for physically motivated constitutive models. The present study not only underlines the ability of MD simulations for identifying and characterising physical phenomena on the molecular level, but also shows that molecular simulations can substitute experimental tests for the characterisation of the viscoelastic material behaviour of polymers.

1. Robin Unger, MD (drrobinunger{at}yahoo.com) 1. New York, New York, USA The 2018 Hollywood meeting was one of the best meetings I have attended, and it will be hard to follow – but we will do our very best! I’d like to thank our president, Dr. Arthur Tykocinski, the Executive Committee

1. Robin Unger, MD (drrobinunger{at}yahoo.com) 1. New York, New York, USA ![][1] > A very interesting discussion took place between those involved in an online dialogue. Damkerng Pathomvanich started the chat with a question regarding one of his patients: I have a 36-year-old