Semi-quantum approach to molecular dynamics simulation of thermal properties of low-dimensional nanostructures

We present a detailed description of semi-quantum molecular dynamics simulation of stochastic dynamics of a system of interacting particles. Within this approach, the dynamics of the system is described with the use of classical Newtonian equations of motion in which the effects of phonon quantum statistics are introduced through random Langevin-like forces with a specific power spectral density (the color noise). The color noise describes the interaction of the molecular system with the thermostat. We apply this technique to the simulation of thermal properties and heat transport in different low-dimensional nanostructures. We describe the determination of temperature in quantum lattice systems, to which the equipartition limit is not applied. We show that one can determine the temperature of such system from the measured power spectrum and temperature- and relaxation-rate-independent density of vibrational (phonon) states. We simulate the specific heat and heat transport in carbon nanotubes, as well as the heat transport in molecular nanoribbons with perfect (atomically smooth) and rough (porous) edges, and in nanoribbons with strongly anharmonic periodic interatomic potentials. We show that the effects of quantum statistics of phonons are essential for the carbon nanotube in the whole temperature range T<500K, in which the values of the specific heat and thermal conductivity of the nanotube are considerably less than that obtained within the description based on classical statistics of phonons.Comment: 19 pages, 15 figures, 2 table

Is higher physical fitness associated with better psychological health in young pediatric cancer survivors? A cross-sectional study from the iBoneFIT project

Objective To examine the associations of self-perceived and objectively-measured physical fitness with psychological well-being and distress indicators in young pediatric cancer survivors. Materials and Methods A total of 116 participants (12.1 ± 3.3 years, 56.9% boys) from the iBoneFIT project participated in this cross-sectional study. Objectively-measured physical fitness (muscular fitness) was obtained by handgrip strength and standing long jump tests for the upper and lower body, respectively. Self-perceived physical fitness was obtained by the International Fitness Scale (IFIS). Positive and negative affect were assessed by the positive affect schedule for children (PANAS-C), happiness by Subjective Happiness Scale (SHS), optimism by Life Orientation Test-Revised (LOT-R), self-esteem by the Rosenberg Self-Esteem Scale (RSE), anxiety by State–Trait Anxiety Inventory for Children (STAIC-R), and depression by Children Depression Inventory (CDI). Multiple linear regressions adjusted by key covariates were performed to analyze associations. Results No associations were found between objectively-measured muscular fitness and any of the psychological well-being and distress indicators (p > 0.05). Self-perceived overall fitness and flexibility were positively associated with positive affect (β ≥ 0.258, p < 0.05). Self-perceived cardiorespiratory fitness, speed/agility, and flexibility were negatively associated with depression (β ≥ −0.222, p < 0.05). Finally, self-perceived cardiorespiratory fitness was also negatively associated with anxiety and negative affect (β ≥ −0.264, p < 0.05). Conclusions Perceived physical fitness, but not objectively physical fitness, seems to be inversely related to psychological distress variables and to less extent positively related to psychological well-being. The findings from this study highlight the importance of promoting self-perceived fitness in the pediatric oncology population

Substrate strain and doping effects on the crystal structure of SrNb

Strontium titanate, SrTiO3 (STO), is an interesting material for both fundamental studies and technological applications. Modifications of the atomic and crystal structure by doping, e.g. replacing titanium with niobium atoms, and by strain, i.e. by growing STO on a different substrate such as lanthanum aluminate, LaAlO3 (LAO), have been proposed to tune the STO electronic, optical and transport properties for applications. Here we report the results of ab initio density-functional theory (DFT) simulations of both strain and Nb-doping effects, independently and joint, on the STO crystal structure. We found that the DFT energy differences among the three commonly observed STO crystal structures, Pm3̅m Pm3̄m , P4∕mmm, and I4∕mcm, are very small, <2.6 × 10−4 Ry, so that the ground-state cannot be determined unambiguously at this level of theory and physics. Our calculations show that an in-plane strain, at least at the level of only − 0.4% as observed in STO on LAO, does not lead to the expected increase in c toward tetragonal symmetry, where c is the length of the cell axis perpendicular to the plane. Instead, c also is reduced and the cubic symmetry tends to be restored. Nb doping, even at the maximum experimental level of 3.7%, does not have significant effects on lattice parameters. The latter result is confirmed also under the presence of strain, so we could not find any crossed effect of strain and doping

Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO2/Si3N4 multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si

Electroconductive poly(3,4‑ethylenedioxythiophene) (PEDOT) nanoparticle‑loaded silk fibroin biocomposite conduits for peripheral nerve regeneration

Peripheral nerve injury (PNI) often clinically relies on the use of nerve grafts taken from the patient to establish a therapeutic effect, though secondary site of injury and morbidity have prompted the medical community to find alternative solutions. A new trend in the development of biomaterials arises in the form of electro-conductive biomaterials, especially for electrically active tissues such as the peripheral nerves. In this work, novel poly(3,4-ethylenedioxythiophene) PEDOT nanoparticles (PEDOT NPs) were synthetized via the mini-emulsion method and were combined with silk fibroin (SF) to create conduits for PNI repair. The synthesized PEDOT NPs-loaded SF conduits showed optimal properties for peripheral nerve substitution from the physico-chemical and biological point of view. They displayed excellent mechanical and conductivity performance with the tensile moduli reaching 6.61â ±â 0.55 MPa and the conduits reaching 5.4 · 10â 4 S cmâ 1, respectively. The conduits did not possess apatite-forming capacity, which were resistant to bending occlusions for angles up to 50° and to suturing. The developed conduits are promising as a novel biomaterial for applications in peripheral nerve regeneration; in vitro experiments showed that they did not allow BJ fibroblast infiltration, avoiding scar tissue formation in the lumen, and they did not show any toxic effect for Schwann cells.Open access funding provided by FCT|FCCN (b-on). This study received fnancial support from the Portuguese Foundation for Science and Technology under the distinction attributed to JMO (IF/01285/2015) and the project NanOptoNerv (ref. PTDC/NANMAT/29936/2017), the European Commission and FEDER program under the JUSTHera project (NORTE-01-0145-FEDER-000055) and the 0624_2IQBIONEURO_6_E project (Inter-regional cooperation program VA Spain-Portugal POCTEP 2014–2020), and the Irish Research Council under EPSPG/2020/78 and New Foundations Grant 2019

Controlling dielectrical properties of polymer blends through defined PEDOT nanostructures

[EN] The paper reports the crucial role of the morphology of poly(3,4-ethylenedioxythiophene) (PEDOT) nanostructures on the thermal and dielectric properties of polymer blends prepared thereof. PEDOT nanostructures with two different morphologies (nanoparticles and nanowires) were synthesized. The size for the nanoparticles was in the range 10 40 nm and the diameter of the nanowires was of ca. 200 nm. These nanostructures were blended with an insulating polymer matrix, poly(methyl methacrylate) (PMMA), to evaluate the dielectrical properties of the materials. The results of broadband dielèctric spectroscopy showed a strong correlation between the morphology of the nanostructure and the improvement of the electrical properties of the material.The authors acknowledge the financial support of the DGCYT through Grant MAT2015-63955-R. R. M. E. also acknowledges the financial support from the Spanish Ministry of Economy and Competitiveness through a Ramon y Cajal grant (grant No. RYC-2013-13451) and M. C. acknowledges the FPU program of the Spanish Ministry of Culture, Education and Sports.Sanchis Sánchez, MJ.; Redondo Foj, MB.; Carsí Rosique, M.; Ortiz Serna, MP.; Culebras, M.; Gomez, CM.; Cantarero, A.... (2016). Controlling dielectrical properties of polymer blends through defined PEDOT nanostructures. RSC Advances. 6(66):62024-62030. https://doi.org/10.1039/c6ra05597dS620246203066

Electroconductive poly(3,4‑ethylenedioxythiophene) (PEDOT) nanoparticle‑loaded silk fibroin biocomposite conduits for peripheral nerve regeneration

Peripheral nerve injury (PNI) often clinically relies on the use of nerve grafts taken from the patient to establish a therapeutic  efect, though secondary site of injury and morbidity have prompted the medical community to fnd alternative solutions. A  new trend in the development of biomaterials arises in the form of electro-conductive biomaterials, especially for electrically  active tissues such as the peripheral nerves. In this work, novel poly(3,4-ethylenedioxythiophene) PEDOT nanoparticles  (PEDOT NPs) were synthetized via the mini-emulsion method and were combined with silk fbroin (SF) to create conduits  for PNI repair. The synthesized PEDOT NPs-loaded SF conduits showed optimal properties for peripheral nerve substitution  from the physico-chemical and biological point of view. They displayed excellent mechanical and conductivity performance  with the tensile moduli reaching 6.61±0.55 MPa and the conduits reaching 5.4 · 10–4 S cm−1, respectively. The conduits did  not possess apatite-forming capacity, which were resistant to bending occlusions for angles up to 50° and to suturing. The  developed conduits are promising as a novel biomaterial for applications in peripheral nerve regeneration; in vitro experiments showed that they did not allow BJ fbroblast infltration, avoiding scar tissue formation in the lumen, and they did not  show any toxic effect for Schwann cells. </p