A Simple New Way To Account for Free Volume in Glassy Dynamics: Model-Free Estimation of the Close-Packed Volume from PVT Data

2021 ◽  
Author(s):  
Ronald P. White ◽  
Jane E. G. Lipson
Keyword(s):  
Free Volume ◽  
Dynamics Model ◽  
Glassy Dynamics ◽  
Model Free ◽  
Pvt Data ◽  
Packed Volume

scholarly journals Исследование формирования избыточного свободного объема в тройных стыках границ зерен при кристаллизации на примере никеля

2018 ◽  
Vol 60 (5) ◽  
pp. 846
Author(s):  
Г.М. Полетаев ◽  
Д.В. Новоселова ◽  
И.В. Зоря ◽  
М.Д. Старостенков
Keyword(s):  
Molecular Dynamics ◽  
Liquid Phase ◽  
Free Volume ◽  
Triple Junctions ◽  
Phase Volume ◽  
Extended State ◽  
Dynamics Model ◽  
Excess Free Volume ◽  
High Fraction

AbstractThe formation of an excess free volume in triple junctions during crystallization has been studied by the molecular dynamics model using nickel as an example. It is shown that an excess free volume that forms during nickel crystallization in triple junctions predominantly forms as a result of the fixation of the liquid phase volume when contacting three crystallization fronts that contains, after crystallization, a high fraction of the free volume. In some cases, as the free volume is concentrated in triple junctions, a comparatively small crystalline subgrain (from one to several nanometers in diameter) forms, and the subgrain has the orientation different from those of contacting grains and exists in the extended state.

A molecular dynamics model of melting and glass transition in an idealized two-dimensional material I

1989 ◽  
Vol 329 (1608) ◽  
pp. 549-573 ◽  
Keyword(s):  
Molecular Dynamics ◽  
Thermal Expansion ◽  
Glass Transition ◽  
Free Volume ◽  
Dimensional Structure ◽  
Valuable Insight ◽  
Two Dimensional ◽  
Discrete Elements ◽  
Dynamics Model ◽  
Topological Features

In a preparatory study of structural relaxations and plastic flow in a two-dimensional idealized atomic glass, the process of melting and quenching through a glass transition has been studied by computer simulation using a molecular dynamics model. In this model, the transition from a solid to a melt was observed to take place when liquid-like structural elements composed of dipoles of five- and seven-sided Voronoi polygons percolate through the two-dimensional structure of distorted hexagons in the form of strings. Such dipoles constitute discrete elements of excess free volume within which liquid like behaviour is established in the sense of reduced cohesion or local elastic moduli. Upon quenching the melt, the percolation condition of liquid-like regions is retained for under-cooled melts between the melting point and a glass transition temperature below which the percolation condition is broken and the thermal expansion is sharply reduced. The simulation that has used empirical pair potentials characteristic of Cu and Zr has substantially underpredicted the melting and glass transition temperatures and overpredicted the thermal expansion of C u x Zr 1-x type glasses. These defects of the model can be partly attributed to the two-dimensional nature of the material, which stores larger concentrations of free volume than a corresponding three-dimensional material. In spite of these quantitative shortcomings, the model gives valuable insight into the topological features of the local atomic configurations at melting and upon vitrification.

Free Volume and Density Gradients of Amorphous Polymer Surfaces As Determined by Use of a Pulsed Low-Energy Positron Lifetime Beam and PVT Data

2004 ◽  
Vol 37 (11) ◽  
pp. 4201-4210 ◽  
Author(s):  
John Algers ◽  
Ryoichi Suzuki ◽  
Toshiyuki Ohdaira ◽  
Frans H. J. Maurer
Keyword(s):  
Free Volume ◽  
Positron Lifetime ◽  
Amorphous Polymer ◽  
Low Energy ◽  
Polymer Surfaces ◽  
Density Gradients ◽  
Pvt Data

scholarly journals Topological free volume and quasi-glassy dynamics in the melt of ring polymers

Soft Matter ◽  
2018 ◽  
Vol 14 (36) ◽  
pp. 7507-7515 ◽  
Author(s):  
Takahiro Sakaue
Keyword(s):  
Free Volume ◽  
Glassy Dynamics ◽  
Ring Polymers

Motivated by recent observations that non-concatenated ring polymers in their dense solution exhibit a glass-like dynamics, we propose a free volume description of the motion of such rings based on the notion of topological volume.

scholarly journals Self-Tuning Insulin Adjustment Algorithm for Type 1 Diabetic Patients based on Multi-Doses Regime

2005 ◽  
Vol 2 (2) ◽  
pp. 61-71 ◽  
Author(s):  
D. U. Campos-Delgado ◽  
R. Femat ◽  
M. Hernández-Ordoñez ◽  
A. Gordillo-Moscoso
Keyword(s):  
Insulin Dosage ◽  
Diabetic Patients ◽  
Dynamics Model ◽  
Model Free ◽  
Self Tuning ◽  
On Line ◽  
Long Acting ◽  
Glucose Dynamics ◽  
Type 1 Diabetic Patients

A self-tuning algorithm is presented for on-line insulin dosage adjustment in type 1 diabetic patients (chronic stage). The algorithm suggested does not need information of the patient insulin–glucose dynamics (model-free). Three doses are programmed daily, where a combination of two types of insulin: rapid/short and intermediate/long acting is injected into the patient through a subcutaneous route. The doses adaptation is performed by reducing the error in the blood glucose level from euglycemics. In this way, a total of five doses are tuned per day: three rapid/short and two intermediate/long, where there is large penalty to avoid hypoglycemic scenarios. Closed-loop simulation results are illustrated using a detailed nonlinear model of the subcutaneous insulin–glucose dynamics in a type 1 diabetic patient with meal intake.

The free volume in two untreated, pressure-densified, and CO2 gas exposed polymers from positron lifetime and pressure-volume-temperature experiments

e-Polymers ◽  
2007 ◽  
Vol 7 (1) ◽  
Author(s):  
Günter Dlubek ◽  
Jürgen Pionteck ◽  
Muhamad Qasim Shaikh ◽  
Liane Häußler ◽  
Stefan Thränert ◽  
...  
Keyword(s):  
Free Volume ◽  
Glassy State ◽  
Thermal Fluctuations ◽  
Bisphenol A Polycarbonate ◽  
Positron Annihilation Lifetime ◽  
Pvt Data ◽  
Order Of Magnitude ◽  
History Of ◽  
Ca 50 ◽  
Relative Change

AbstractChanges in the microstructure of the free volume and its temperature dependence in ethylene-norbornene copolymer and bisphenol-A polycarbonate due to densification under pressure and swelling with CO2 gas have been examined using positron annihilation lifetime spectroscopy (PALS) and pressurevolume- temperature (PVT) experiments. Employing the Simha-Somcynsky equation of state the specific hole free and occupied volumes were estimated. From the PALS spectra analyzed with the new routine LT9.0 the size distribution of subnanometre holes and its mean and mean dispersion were calculated. Above Tg, the dispersion mirrors the thermal fluctuations in the free volume. From comparison of PALS and PVT data the specific number of holes was estimated. It was found that the occupied volume has a constant and identical compressibility in the glassy and rubbery state. It shows no memory for the history of the glass and mirrors only the pressure and temperature during the measurement. The change in the total volume due to the pre-treatments of the polymers occurs exclusively in the hole free volume Vf and the relative change in Vf is one order of magnitude larger than in the total volume. PALS data show that the mean hole size and its dispersion in the glassy state is decreased due to densification and increased due to swelling. PVT data show that the volume changes are frozen in the polymer glasses and that, when heating the samples, the volume begins to recover at temperatures ca. 50 K in gas swollen and 20 K in densified polymers below Tg. The PALS data show a corresponding behaviour.

scholarly journals Imitation Learning from Observation

2019 ◽  
Vol 33 ◽  
pp. 9900-9901
Author(s):  
Faraz Torabi
Keyword(s):  
Autonomous Agents ◽  
Inverse Dynamics ◽  
Imitation Learning ◽  
State Transitions ◽  
Dynamics Model ◽  
State Action ◽  
Model Free ◽  
Relevant Today ◽  
Direct Knowledge ◽  
Full State

Humans and other animals have a natural ability to learn skills from observation, often simply from seeing the effects of these skills: without direct knowledge of the underlying actions being taken. For example, after observing an actor doing a jumping jack, a child can copy it despite not knowing anything about what's going on inside the actor's brain and nervous system. The main focus of this thesis is extending this ability to artificial autonomous agents, an endeavor recently referred to as "imitation learning from observation." Imitation learning from observation is especially relevant today due to the accessibility of many online videos that can be used as demonstrations for robots. Meanwhile, advances in deep learning have enabled us to solve increasingly complex control tasks mapping visual input to motor commands. This thesis contributes algorithms that learn control policies from state-only demonstration trajectories. Two types of algorithms are considered. The first type begins by recovering the missing action information from demonstrations and then leverages existing imitation learning algorithms on the full state-action trajectories. Our preliminary work has shown that learning an inverse dynamics model of the agent in a self-supervised fashion and then inferring the actions performed by the demonstrator enables sufficient action recovery for this purpose. The second type of algorithm uses model-free end-to-end learning. Our preliminary results indicate that iteratively optimizing a policy based on the closeness of the imitator's and expert's state transitions leads to a policy that closely mimics the demonstrator's trajectories.

scholarly journals MapGo: Model-Assisted Policy Optimization for Goal-Oriented Tasks

2021 ◽  
Author(s):  
Menghui Zhu ◽  
Minghuan Liu ◽  
Jian Shen ◽  
Zhicheng Zhang ◽  
Sheng Chen ◽  
...  
Keyword(s):  
Reinforcement Learning ◽  
Past Experience ◽  
Dynamics Model ◽  
Model Free ◽  
Framework Model ◽  
The Future ◽  
Sparsity Problem ◽  
Policy Optimization ◽  
Goal Inference

In Goal-oriented Reinforcement learning, relabeling the raw goals in past experience to provide agents with hindsight ability is a major solution to the reward sparsity problem. In this paper, to enhance the diversity of relabeled goals, we develop FGI (Foresight Goal Inference), a new relabeling strategy that relabels the goals by looking into the future with a learned dynamics model. Besides, to improve sample efficiency, we propose to use the dynamics model to generate simulated trajectories for policy training. By integrating these two improvements, we introduce the MapGo framework (Model-Assisted Policy optimization for Goal-oriented tasks). In our experiments, we first show the effectiveness of the FGI strategy compared with the hindsight one, and then show that the MapGo framework achieves higher sample efficiency when compared to model-free baselines on a set of complicated tasks.

scholarly journals Model-free volume and pressure cycled control of automatic bag valve mask ventilator

2021 ◽  
Vol 8 (3) ◽  
pp. 192-207
Author(s):  
Cong Toai Truong ◽  
◽  
Kim Hieu Huynh ◽  
Van Tu Duong ◽  
Huy Hung Nguyen ◽  
...  
Keyword(s):  
Free Volume ◽  
Model Free
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