Offline reinforcement learning with task hierarchies

In this work, we build upon the observation that offline reinforcement learning (RL) is synergistic with task hierarchies that decompose large Markov decision processes (MDPs). Task hierarchies can allow more efficient sample collection from large MDPs, while offline algorithms can learn better policies than the so-called “recursively optimal” or even hierarchically optimal policies learned by standard hierarchical RL algorithms. To enable this synergy, we study sample collection strategies for offline RL that are consistent with a provided task hierarchy while still providing good exploration of the state-action space. We show that naïve extensions of uniform random sampling do not work well in this case and design a strategy that has provably good convergence properties. We also augment the initial set of samples using additional information from the task hierarchy, such as state abstraction. We use the augmented set of samples to learn a policy offline. Given a capable offline RL algorithm, this policy is then guaranteed to have a value greater than or equal to the value of the hierarchically optimal policy. We evaluate our approach on several domains and show that samples generated using a task hierarchy with a suitable strategy allow significantly more sample-efficient convergence than standard offline RL. Further, our approach also shows more sample-efficient convergence to policies with value greater than or equal to hierarchically optimal policies found through an online hierarchical RL approach.     

Wear resistance of laser-deposited boride reinforced Ti-Nb–Zr–Ta alloy composites for orthopedic implants

The inherently poor wear resistance of titanium alloys limits their application as femoral heads in femoral (hip) implants. Reinforcing the soft matrix of titanium alloys (including new generation β-Ti alloys) with hard ceramic precipitates such as borides offers the possibility of substantially enhancing the wear resistance of these composites. The present study discusses the microstructure and wear resistance of laser-deposited boride reinforced composites based on Ti–Nb–Zr–Ta alloys. These composites have been deposited using the LENS™ process from a blend of elemental Ti, Nb, Zr, Ta, and boron powders and consist of complex borides dispersed in a matrix of β-Ti. The wear resistance of these composites has been compared with that of Ti–6Al–4V ELI, the current material of choice for orthopedic femoral implants, against two types of counterfaces, hard Si₃N₄ and softer SS440C stainless steel. Results suggest a substantial improvement in the wear resistance of the boride reinforced Ti–Nb–Zr–Ta alloys as compared with Ti–6Al–4V ELI against the softer counterface of SS440. The presence of an oxide layer on the surface of these alloys and composites also appears to have a substantial effect in terms of enhanced wear resistance.     

TiO2/Si nanowires hybrid system for efficient photocatalytic degradation of organic dye

Herein, titanium dioxide (TiO₂)-coated vertically aligned silicon nanowires (SiNWs/TiO₂) were fabricated and evaluated for photocatalytic degradation of organic dyes. Aligned SiNWs arrays were prepared by facile metal-assisted chemical-etching process with varying the etching time that was followed by TiO₂ nanoparticles coating using sputtering technique. The TiO₂ film crystallized in pure anatase phase with an average crystalline size of 50 nm, as was elucidated with X-ray diffraction studies. SEM analysis showed nanowires with varying lengths from 2.5 to 13.5 µm and confirmed the homogenous surface decoration with TiO₂. The homogeneous distribution of TiO₂ nanoparticles on nanowires was co-evidenced with Energy-Dispersive X-ray spectroscopy (EDX) and Raman spectra analysis. The developed SiNWs/TiO₂ was exploited for photocatalytic degradation of methylene blue; the role of hydrogen peroxide was also elucidated. The highest photocatalytic efficiency of 96% was achieved for SiNWs/TiO₂ with optimum nanowire length of 3.5 μm. The developed photocatalyst was found to be almost stable even after 190 days (~?5 months) and could be used as reusable and easily removable photocatalysts. The current study highlighted the SiNWs/TiO₂/H₂O₂ system as excellent candidate for water remediation applications.

     

Low-Temperature Magnetic Properties of Vanadium-Doped ZnO Nanoparticles

Low-temperature magnetic study of transition metal-doped ZnO nanoparticles tends to spring ambiguities of magnetic phases due to defect states, environment of doped ions, and anisotropy. Interestingly, vanadium doping in ZnO brings out versatile magnetic ordering which offers more room for basic understanding of the underlying mechanism. Vanadium-doped ZnO nanoparticles are prepared using a simple cost-effective approach of solution combustion method. Macroscopic and microscopic aspects of the samples have been unraveled using structural and morphological studies with the implications on the exhibited magnetic behavior. Development of antiferromagnetic, ferromagnetic, and ferrimagnetic interactions in the material illustrated by low-temperature magnetic measurements preludes the possible interplay of dopant-initiated defect correlation and morphological and interfacial secondary phases. The grain boundary reformation due to vanadium in the ZnO nanograins is exploited through a systematic correlation of structural and morphological studies in order to gain more insight into the portrayed magnetic signatures.     

Heat transport in epoxy networks: A molecular dynamics study

In this article, thermal behavior of an epoxy based thermoset polymer has been discussed using atomistic molecular dynamics simulations. The simulations were performed on crosslinked network of EPON-862 and curing agent-W (DETDA) using consistent valence force field (CVFF). Thermal conductivity was calculated using both equilibrium as well as non-equilibrium molecular dynamics approaches and the results were found to be in good agreement with experimental findings. Different contributions of heat flux vector towards thermal conductivity and their possible coupling are discussed in terms of various convective and virial contributions. In addition, discussion of power spectra analysis of velocity autocorrelation function for crosslinked network shows a broad distribution of low frequency vibrational modes suggesting distribution of relaxation times.     

Laser deposited biocompatible Ca–P coatings on Ti–6Al–4V: Microstructural evolution and thermal modeling

A high intensity continuous wave diode pumped ytterbium laser source was used to deposit Ca–P coatings on a Ti–6Al–4V biocompatible alloy in order to generate a physically textured surface, enhancing osseointegration. Scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) studies were coupled with X-ray and micro diffraction work to determine the structure, composition, and phases present in various zones of a sample prepared across the coating/substrate interaction zone. Three-dimensional thermal modeling was also carried out to determine the cooling rate and maximum temperature experienced by different regions of the substrate. Combining these results provide us with valuable insights regarding the thermo-physical as well as chemical interactions that take place across the coating–substrate interface.     

A facile one-step synthesis of single crystalline hierarchical WO3 with enhanced activity for photoelectrochemical solar water oxidation

Hierarchical architectures consisting of one-dimensional (1D) nanostructures are of great interest for potential use in energy and environmental applications in recent years. In this work, hierarchical tungsten oxide (WO₃) has been synthesized via a straightforward, template-free, hydrothermal route from ammonium metatungstate hydrate and implemented in photoanode fabrication for solar water oxidation in photoelectrochemical cells and photocatalytic oxidation of organic pollutant. The flower-like WO₃ micro-patterns are constructed by self-organized nanoscale length 1D building blocks, which are single-crystalline in nature, grown along (001) direction and confirm an orthorhombic crystal phase. Time-dependent experiments have been conducted to demonstrate their morphology evolution. The hierarchical architecture based photoanodes produce higher photocurrent (2-fold high) than the nanoparticles based photoanodes from solar water oxidation. The photon to current conversion efficiency achieved with the hierarchical architectures is 45% at 400 nm. The enhanced activity can be attributed to improved charge-separation by superior charge transportation through single-crystalline 1D building blocks.     

Dairy biofilm: an investigation of the impact on the surface chemistry of two materials: silicone and stainless steel

Biofilms are the most common mode of bacterial growth in nature and the formation will occur on organic or inorganic solid surfaces in contact with a liquid. The aims of this study were, by combining numeration and sessile drop technique, (i) to characterize the structural dynamics of dairy biofilm growth and the physico chemical properties on silicone and stainless steel and (ii) to evaluate the impact of bio-adhesion on chemistry of surfaces at different times of contact (2, 7, 9 and 24?h). Significantly, greater biofilm volumes were observed after 48?h on two materials. Gram-positive bacteria and fungal population exhibited a significantly higher biofilm organization than gram-negative (43–64%). Elsewhere, after 48?h, results showed a slight difference on gram-negative adhered cells on stainless steel than silicone (2.6?×?10⁷?cfu/cm² and 4.7?×?10⁵?cfu/cm², respectively). Moreover, the physico chemical properties of the surfaces showed that the silicone and stainless steel have a hydrophobic character (Giwi?=??68.28?mJ/m² and ?57.6?mJ/m², respectively). Also, both the surfaces present a weak electron donor character (γ ^??=?2.2?mJ/m² and 4.1?mJ/m², respectively). The real-time investigation of the impact of dairy biofilm on the physico chemical properties of the materials has shown a decrease of hydrophobicity degree of the silicone surface that becomes hydrophilic (ΔGiwi?=?11.47?mJ/m²) after 7?h and the increase of electron donor character (γ ^??=?75.8?mJ/m²). Elsewhere, bio-adhesion on stainless steel was accompanied with a decrease of hydrophobicity degree of the surface, which becomes hydrophilic after 7?h of contact (ΔGiwi?=?6.62?mJ/m²) and the increase of the electron donor character (γ ^??=?44.8?mJ/m²). While, after 24?h of contact, results showed a decrease of the hydrophilicity degree and surface energy components of silicone and stainless steel that become hydrophobic (ΔGiwi?=??21.2?mJ/m² and ΔGiwi?=??56.51?mJ/m², respectively) and weak electron donor (γ ^??=?14.0 and 2.3?mJ/m², respectively).     

Pollution Control,Climate Change and Industrial Disasters

This paper reports research into the levels of awareness and engagement of Abrahamic communities regarding environmental sustainability in the State of Victoria, Australia. Seventeen faith groups were targeted for study at 22 locations throughout Victoria and metropolitan Melbourne; with 15 in-depth interviews completed. The study suggests that personal awareness does not always translate well into group action, resulting in conflicting positions within denominations on how to respond to environmental issues. Some denominations have funding and human resources to support environmental programs. Smaller groups struggle to maintain numbers, are trying to expand, or do not participate because of fundamentally different worldviews.     

Performance Improvement of Heterojunction Double Gate TFET with Gaussian Doping

Silicon - A new Ge/SiGe heterojunction double-gate tunnel field effect transistor (DGT) model with hetero dielectric gate and Gaussian doping drain region is investigated for the first time. The...