Quantum mechanical studies of complex ferroelectric perovskites

NASA Astrophysics Data System (ADS)

Ramer, Nicholas John

In many electronic device applications, there is a need to interconvert electrical energy and other types of energy. Ferroelectric materials, which possess a voltage-dependent polarization, can enable this energy conversion process. Because of the broad interest in ferroelectric materials for these devices, there is a critical research effort, both experimental and theoretical, to understand these materials and aid in the development of materials with improved properties. This thesis presents detailed quantum mechanical investigations of the behavior of a complex ferroelectric perovskite under applied stress. In particular, we have chosen to study the solid solution PbZr1-xTix O3 (PZT). Since the study of ferroelectricity involves understanding both its structural and electronic signatures in materials, it has necessitated the development of a novel theoretical technique which improves the accuracy of the pseudopotentials used in our density functional theory calculations as well as a new method for constructing three-dimensional atomistic responses to small amounts of external stress. To examine the material's behavior under larger amounts of stress, we have studied the behavior of a composition of PZT lying near a structural phase boundary. On either side of the phase boundary, the material is characterized by a different polarization direction and may easily be switched between phases by applying external stress. In addition to stress-induced phase transitions, most ferroelectric materials also have composition dependent phase boundaries. Since different compositions of PZT would require increased computational effort, we have formulated an improved virtual crystal approach that makes tractable the study of the entire composition range. Using this method, we have been able to show for the first time via first-principles calculations, a composition dependent phase transition in a ferroelectric material. This thesis has accomplished three important goals: new theoretical methodology has been developed to enable accurate modeling of complex materials; application of these methods has been demonstrated for the study of ferroelectric oxides; and these investigations have revealed new insights into the relationships between stress, chemical composition, and ferroelectricity in oxides. This set of accomplishments enables the future study of even more complex perovskites and other multi-component systems.

Crash simulation of hybrid structures considering the stress and strain rate dependent material behavior of thermoplastic materials

NASA Astrophysics Data System (ADS)

Hopmann, Ch.; Schöngart, M.; Weber, M.; Klein, J.

2015-05-01

Thermoplastic materials are more and more used as a light weight replacement for metal, especially in the automotive industry. Since these materials do not provide the mechanical properties, which are required to manufacture supporting elements like an auto body or a cross bearer, plastics are combined with metals in so called hybrid structures. Normally, the plastics components are joined to the metal structures using different technologies like welding or screwing. Very often, the hybrid structures are made of flat metal parts, which are stiffened by a reinforcement structure made of thermoplastic materials. The loads on these structures are very often impulsive, for example in the crash situation of an automobile. Due to the large stiffness variation of metal and thermoplastic materials, complex states of stress and very high local strain rates occur in the contact zone under impact conditions. Since the mechanical behavior of thermoplastic materials is highly dependent on these types of load, the crash failure of metal plastic hybrid parts is very complex. The problem is that the normally used strain rate dependent elastic/plastic material models are not capable to simulate the mechanical behavior of thermoplastic materials depended on the state of stress. As part of a research project, a method to simulate the mechanical behavior of hybrid structures under impact conditions is developed at the IKV. For this purpose, a specimen for the measurement of mechanical properties dependet on the state of stress and a method for the strain rate depended characterization of thermoplastic materials were developed. In the second step impact testing is performed. A hybrid structure made from a metal sheet and a reinforcement structure of a Polybutylenterephthalat Polycarbonate blend is tested under impact conditions. The measured stress and strain rate depended material data are used to simulate the mechanical behavior of the hybrid structure under highly dynamic load with impact velocities up to 5 m/s. The mechanical behavior of the plastics structure is simulated using a quadratic yield surface, which takes the state of stress and the strain rate into account. The FE model is made from mid surface elements to reduce the computing time.

Using Ultrasonic Speckle Velocimetry to Detect Fluid Instabilities in a Surfactant Solution

NASA Astrophysics Data System (ADS)

Bice, Jason E.

Rheometry is a leading technology used to define material properties of multi-phase viscoelastic fluid-like materials, such as the shear modulus and viscosity. However, traditional rheometry relies on a mechanical response from a rotating or oscillating rotor of various geometries which does not allow for any spatial or temporal quantification of the material characteristics. Further, the setup operates under the assumption of a uniform and homogeneous flow. Thus, only qualitative deductions can be realized when a complex fluid displays inhomogeneous behavior, such as wall slip or shear banding. Due to this lack of capability, non-intrusive imaging is required to define and quantify behavior that occurs in a complex fluid under shear conditions. This thesis outlines the design, fabrication, and experimental examples of an adapted ultrasonic speckle velocimetry device, which enables spatial and temporal resolution of inhomogeneous fluid behavior using ultrasound acoustics. For the experimental example, a commercial surfactant mixture (hair shampoo) was tested to show the utility and precision that ultrasonic speckle velocimetry possesses.

Mesenchymal Stem Cell Fate: Applying Biomaterials for Control of Stem Cell Behavior

PubMed Central

Anderson, Hilary J.; Sahoo, Jugal Kishore; Ulijn, Rein V.; Dalby, Matthew J.

2016-01-01

The materials pipeline for biomaterials and tissue engineering applications is under continuous development. Specifically, there is great interest in the use of designed materials in the stem cell arena as materials can be used to manipulate the cells providing control of behavior. This is important as the ability to “engineer” complexity and subsequent in vitro growth of tissues and organs is a key objective for tissue engineers. This review will describe the nature of the materials strategies, both static and dynamic, and their influence specifically on mesenchymal stem cell fate. PMID:27242999

Dependence of behavioral performance on material category in an object grasping task with monkeys.

PubMed

Yokoi, Isao; Tachibana, Atsumichi; Minamimoto, Takafumi; Goda, Naokazu; Komatsu, Hidehiko

2018-05-02

Material perception is an essential part of our cognitive function that enables us to properly interact with our complex daily environment. One important aspect of material perception is its multimodal nature. When we see an object, we generally recognize its haptic properties as well as its visual properties. Consequently, one must examine behavior using real objects that are perceived both visually and haptically to fully understand the characteristics of material perception. As a first step, we examined whether there is any difference in the behavioral responses to different materials in monkeys trained to perform an object grasping task in which they saw and grasped rod-shaped real objects made of various materials. We found that the monkeys' behavior in the grasping task, measured based on the success rate and the pulling force, differed depending on the material category. Monkeys easily and correctly grasped objects of some materials, such as metal and glass, but failed to grasp objects of other materials. In particular, monkeys avoided grasping fur-covered objects. The differences in the behavioral responses to the material categories cannot be explained solely based on the degree of familiarity with the different materials. These results shed light on the organization of multimodal representation of materials, where their biological significance is an important factor. In addition, a monkey that avoided touching real fur-covered objects readily touched images of the same objects presented on a CRT display. This suggests employing real objects is important when studying behaviors related to material perception.

Multiscale Modeling and Process Optimization for Engineered Microstructural Complexity

DTIC Science & Technology

2007-10-26

R. C. Rogan, E. Üstündag, M. R. Daymond and V. Knoblauch Ferroelastic Behavior of PZT -Based Ferroelectric Ceramics , Materials Science Forum, 404...Bhattacharya, Materials Science Seminar, University of Southern California, 2003. 42. R.C. Rogan, Texture and Strain Analysis of PZT by In-Situ...Annual Meeting of the American Ceramic Society, St. Louis, MO; May 2002. 44. R. Rogan, Ferroelastic Behavior of PZT -Based Ferroelectric Ceramics , 6th

Insights into dynamic processes of cations in pyrochlores and other complex oxides

DOE PAGES

Uberuaga, Blas Pedro; Perriot, Romain

2015-08-26

Complex oxides are critical components of many key technologies, from solid oxide fuel cells and superionics to inert matrix fuels and nuclear waste forms. In many cases, understanding mass transport is important for predicting performance and, thus, extensive effort has been devoted to understanding mass transport in these materials. However, most work has focused on the behavior of oxygen while cation transport has received relatively little attention, even though cation diffusion is responsible for many phenomena, including sintering, radiation damage evolution, and deformation processes. Here, we use accelerated molecular dynamics simulations to examine the kinetics of cation defects in onemore » class of complex oxides, A₂B₂O₇ pyrochlore. In some pyrochlore chemistries, B cation defects are kinetically unstable, transforming to A cation defects and antisites at rates faster than they can diffuse. When this occurs, transport of B cations occurs through defect processes on the A sublattice. Further, these A cation defects, either interstitials or vacancies, can interact with antisite disorder, reordering the material locally, though this process is much more efficient for interstitials than vacancies. Whether this behavior occurs in a given pyrochlore depends on the A and B chemistry. Pyrochlores with a smaller ratio of cation radii exhibit this complex behavior, while those with larger ratios exhibit direct migration of B interstitials. Similar behavior has been reported in other complex oxides such as spinels and perovskites, suggesting that this coupling of transport between the A and B cation sublattices, while not universal, occurs in many complex oxide.« less

On the dynamic behavior of three readily available soft tissue simulants

NASA Astrophysics Data System (ADS)

Appleby-Thomas, G. J.; Hazell, P. J.; Wilgeroth, J. M.; Shepherd, C. J.; Wood, D. C.; Roberts, A.

2011-04-01

Plate-impact experiments have been employed to investigate the dynamic response of three readily available tissue simulants for ballistic purposes: gelatin, ballistic soap (both subdermal tissue simulants), and lard (adipose layers). All three materials exhibited linear Hugoniot equations-of-state in the US-uP plane. While gelatin behaved hydrodynamically under shock, soap and lard appeared to strengthen under increased loading. Interestingly, the simulants under test appeared to strengthen in a material-independent manner on shock arrival (tentatively attributed to a rearrangement of the amorphous molecular chains under loading). However, material-specific behavior was apparent behind the shock. This behavior appeared to correlate with microstructural complexity, suggesting a steric hindrance effect.

Micromechanical model for protein materials: From macromolecules to macroscopic fibers

NASA Astrophysics Data System (ADS)

Puglisi, G.; De Tommasi, D.; Pantano, M. F.; Pugno, N. M.; Saccomandi, G.

2017-10-01

We propose a model for the mechanical behavior of protein materials. Based on a limited number of experimental macromolecular parameters (persistence and contour length) we obtain the macroscopic behavior of keratin fibers (human, cow, and rabbit hair), taking into account the damage and residual stretches effects that are fundamental in many functions of life. We also show the capability of our approach to describe the main dissipation and permanent strain effects observed in the more complex spider silk fibers. The comparison between our results and the data obtained experimentally from cyclic tests demonstrates that our model is robust and is able to reproduce with a remarkable accuracy the experimental behavior of all protein materials we tested.

The behavior of a macroscopic granular material in vortex flow

NASA Astrophysics Data System (ADS)

Nishikawa, Asami

A granular material is defined as a collection of discrete particles such as powder and grain. Granular materials display a large number of complex behaviors. In this project, the behavior of macroscopic granular materials under tornado-like vortex airflow, with varying airflow velocity, was observed and studied. The experimental system was composed of a 9.20-cm inner diameter acrylic pipe with a metal mesh bottom holding the particles, a PVC duct, and an airflow source controlled by a variable auto-transformer, and a power-meter. A fixed fan blade was attached to the duct's inner wall to create a tornado-like vortex airflow from straight flow. As the airflow velocity was increased gradually, the behavior of a set of same-diameter granular materials was observed. The observed behaviors were classified into six phases based on the macroscopic mechanical dynamics. Through this project, we gained insights on the significant parameters for a computer simulation of a similar system by Heath Rice [5]. Comparing computationally and experimentally observed phase diagrams, we can see similar structure. The experimental observations showed the effect of initial arrangement of particles on the phase transitions.

Mathematical and numerical challenges in living biological materials

NASA Astrophysics Data System (ADS)

Forest, M. Gregory; Vasquez, Paula A.

2013-10-01

The proclaimed Century of Biology is rapidly leading to the realization of how starkly different and more complex biological materials are than the materials that underpinned the industrial and technological revolution. These differences arise, in part, because biological matter exhibits both viscous and elastic behavior. Moreover, this behavior varies across the frequency, wavelength and amplitude spectrum of forcing. This broadclass of responsesin biological matter requires multiple frequency-dependent functions to specify material behavior, instead of a discrete set of parameters that relate to either viscosity or elasticity. This complexity prevails even if the biological matter is assumed to be spatially homogeneous, which is rarely true. However, very little progress has been made on the characterization of heterogeneity and how to build that information into constitutive laws and predictive models. In addition, most biological matter is non-stationary, which motivates the term "living". Biomaterials typically are in an active state in order to perform certain functions, and they often are modified or replenished on the basis of external stimuli. It has become popular in materials engineering to try to duplicate some of the functionality of biomaterials, e.g., a lot of effort has gone into the design of self-assembling, self-healing and shape shifting materials. These distinguishing features of biomaterials require significantly more degrees of freedom than traditional composites and many of the molecular species and their roles in functionality have yet to be determined. A typical biological material includes small molecule biochemical species that react and diffuse within larger species. These large molecular weightspecies provide the primary structural and biophysical properties of the material. The small molecule binding and unbinding kinetics serves to modulate material properties, and typical small molecule production and release are governed by external stimuli (e.g., stress). The bottom line is that the mathematical and numerical tools of 20th Century materials science are often insufficient for describing biological materials and for predicting their behavior both in vitro and in vivo.

Zonal Articular Cartilage Possesses Complex Mechanical Behavior Spanning Multiple Length Scales: Dependence on Chemical Heterogeneity, Anisotropy, and Microstructure

NASA Astrophysics Data System (ADS)

Wahlquist, Joseph A.

This work focused on characterizing the mechanical behavior of biological material in physiologically relevant conditions and at sub millimeter length scales. Elucidating the time, length scale, and directionally dependent mechanical behavior of cartilage and other biological materials is critical to adequately recapitulate native mechanosensory cues for cells, create computational models that mimic native tissue behavior, and assess disease progression. This work focused on three broad aspects of characterizing the mechanical behavior of articular cartilage. First, we sought to reveal the causes of time-dependent deformation and variation of mechanical properties with distance from the articular surface. Second, we investigated size dependence of mechanical properties. Finally, we examined material anisotropy of both the calcified and uncalcified tissues of the osteochondral interface. This research provides insight into how articular cartilage serves to support physiologic loads and simultaneously sustain chondrocyte viability.

Acoustic behavior of a fibrous bulk material. [Kevlar 29 sound absorber

NASA Technical Reports Server (NTRS)

Hersh, A. S.; Walker, B.

1979-01-01

A semiempirical model is presented describing the acoustic behavior of Kevlar 29, a bulk absorbing material. The model is based on an approximate solution to the one-dimensional equations representing conservation of fluctuating mass, momentum and energy. By treating the material as a momentum sink, theoretical expressions of the material complex propagation constants and characteristic impedance were derived in terms of a single constant. Evaluating the constant at a single frequency for a particular specimen, excellent agreement between prediction and measurement was achieved for a large range of sound frequencies and material porosities and thicknesses. Results show that Kevlar 29 absorbs sound efficiently even at low frequencies. This is explained in terms of a frequency dependent material phase speed.

Algal Culture Material

ERIC Educational Resources Information Center

Baldock, R.

1971-01-01

Suggests suitable species of microscopic green algae for demonstrating diversity of form, increasing complexity in related species, the animal" and plant" characteristics of protists, and protist behavior. (AL)

A comparison of thermoelectric phenomena in diverse alloy systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, Bruce

1999-01-01

The study of thermoelectric phenomena in solids provides a wealth of opportunity for exploration of the complex interrelationships between structure, processing, and properties of materials. As thermoelectricity implies some type of coupled thermal and electrical behavior, it is expected that a basic understanding of transport behavior in materials is the goal of such a study. However, transport properties such as electrical resistivity and thermal diffusivity cannot be fully understood and interpreted without first developing an understanding of the material's preparation and its underlying structure. It is the objective of this dissertation to critically examine a number of diverse systems inmore » order to develop a broad perspective on how structure-processing-property relationships differ from system to system, and to discover the common parameters upon which any good thermoelectric material is based. The alloy systems examined in this work include silicon-germanium, zinc oxide, complex intermetallic compounds such as the half-Heusler MNiSn, where M = Ti, Zr, or Hf, and rare earth chalcogenides.« less

High pressure and multiferroics materials: a happy marriage

PubMed Central

Gilioli, Edmondo; Ehm, Lars

2014-01-01

The community of material scientists is strongly committed to the research area of multiferroic materials, both for the understanding of the complex mechanisms supporting the multiferroism and for the fabrication of new compounds, potentially suitable for technological applications. The use of high pressure is a powerful tool in synthesizing new multiferroic, in particular magneto-electric phases, where the pressure stabilization of otherwise unstable perovskite-based structural distortions may lead to promising novel metastable compounds. The in situ investigation of the high-pressure behavior of multiferroic materials has provided insight into the complex interplay between magnetic and electronic properties and the coupling to structural instabilities. PMID:25485138

Corrosion Issues for Ceramics in Gas Turbines

NASA Technical Reports Server (NTRS)

Jacobson, Nathan; Opila, Elizabeth; Nickel, Klaus G.

2004-01-01

The requirements for hot-gas-path materials in gas turbine engines are demanding. These materials must maintain high strength and creep resistance in a particularly aggressive environment. A typical gas turbine environment involves high temperatures, rapid gas flow rates, high pressures, and a complex mixture of aggressive gases. Over the past forty years, a wealth of information on the behavior of ceramic materials in heat engine environments has been obtained. In the first part of the talk we summarize the behavior of monolithic SiC and Si3N4. These materials show excellent baseline behavior in clean, oxygen environments. However the aggressive components in a heat engine environment such as water vapor and salt deposits can be quite degrading. In the second part of the talk we discuss SiC-based composites. The critical issue with these materials is oxidation of the fiber coating. We conclude with a brief discussion of future directions in ceramic corrosion research.

Chemical modeling of boron adsorption by humic materials using the constant capacitance model

USDA-ARS?s Scientific Manuscript database

The constant capacitance surface complexation model was used to describe B adsorption behavior on reference Aldrich humic acid, humic acids from various soil environments, and dissolved organic matter extracted from sewage effluents. The reactive surface functional groups on the humic materials wer...

Non-linear mechanical behavior of a sintered material for braking application using digital image correlation

NASA Astrophysics Data System (ADS)

Mann, Ruddy; Magnier, Vincent; Serrano-Munoz, Itziar; Brunel, Jean-Francois; Brunel, Florent; Dufrenoy, Philippe; Henrion, Michele

2017-12-01

Friction materials for braking applications are complex composites made of many components to ensure the various performances required (friction coefficient level, low wear, mechanical strength, thermal resistance, etc.). The material is developed empirically by a trial and error approach. With the solicitation, the material evolves and probably also its properties. In the literature, the mechanical behavior of such materials is generally considered as linear elastic and independent of the loading history. This paper describes a methodology to characterize the mechanical behavior of such a heterogeneous material in order to investigate its non-linear mechanical behavior. Results from mechanical tests are implemented into material laws for numerical simulations. Thanks to the instrumentation, some links with the microstructure can also be proposed. The material is made of a metallic matrix embedding graphite and ceramic particles and is manufactured by sintering. It is used for dry friction applications such as high-energy brake for trains, cars and motorcycles. Compression tests are done with digital image correlation to measure full-filled displacement. It allows to calculate strain fields with enough resolution to identify the material heterogeneity and the role of some of the components of the formulation. A behavior model of the material with plasticity and damage is proposed to simulate the non-linear mechanical behavior and is implemented in an FEM code. Results of mechanical test simulations are compared with two types of experiments showing good agreement. This method thus makes it possible to determine mechanical properties at a virgin state but is extensible for characterizing a material having been submitted to braking solicitations.

A Platform for Development of Mathematical Games on Silverlight

ERIC Educational Resources Information Center

Radakovic, Davorka; Herceg, Dorde

2013-01-01

Dynamic geometry software (DGS) is often used for development of interactive teaching materials in many subjects, not only mathematics. These interactive materials can contain hundreds of elements in order to represent complex objects, and script programs to control their behavior. We propose an approach for creating, importing and using…

Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

NASA Astrophysics Data System (ADS)

Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

2018-03-01

Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

NASA Astrophysics Data System (ADS)

Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

2018-02-01

Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

Behavior of Materials Under Conditions of Thermal Stress

NASA Technical Reports Server (NTRS)

Manson, S S

1954-01-01

A review is presented of available information on the behavior of brittle and ductile materials under conditions of thermal stress and thermal shock. For brittle materials, a simple formula relating physical properties to thermal-shock resistance is derived and used to determine the relative significance of two indices currently in use for rating materials. For ductile materials, thermal-shock resistance depends upon the complex interrelation among several metallurgical variables which seriously affect strength and ductility. These variables are briefly discussed and illustrated from literature sources. The importance of simulating operating conditions in tests for rating materials is especially to be emphasized because of the importance of testing conditions in metallurgy. A number of practical methods that have been used to minimize the deleterious effects of thermal stress and thermal shock are outlined.

Annealing study of poly(etheretherketone)

NASA Technical Reports Server (NTRS)

Cebe, Peggy

1988-01-01

Annealing of PEEK has been studied for two materials cold-crystallized from the rubbery amorphous state. The first material is a low molecular weight PEEK; the second is commercially available neat resin. Differential scanning calorimetry was used to monitor the melting behavior of annealed samples. The effect of thermal history on melting behavior is very complex and depends upon annealing temperature, residence time at the annealing temperature, and subsequent scanning rate. Thermal stability of both materials is improved by annealing, and for an annealing temperature near the melting point, the polymer can be stabilized against reorganization during the scan. Variations of density, degree of crystallinity, and X-ray long period were studied as a function of annealing temperature for the commercial material.

Mechanistic Studies in Friction and Wear of Bulk Materials

NASA Astrophysics Data System (ADS)

Sawyer, W. Gregory; Argibay, Nicolas; Burris, David L.; Krick, Brandon A.

2014-07-01

From the context of a contemporary understanding of the phenomenological origins of friction and wear of materials, we review insightful contributions from recent experimental investigations of three classes of materials that exhibit uniquely contrasting tribological behaviors: metals, polymers, and ionic solids. We focus on the past decade of research by the community to better understand the correlations between environment parameters, materials properties, and tribological behavior in systems of increasingly greater complexity utilizing novel synthesis and in situ experimental techniques. In addition to such review, and a half-century after seminal publications on the subject, we present recently acquired evidence linking anisotropy in friction response with anisotropy in wear behavior of crystalline ionic solids as a function of crystallographic orientation. Although the tribological behaviors of metals, polymers, and ionic solids differ widely, it is increasingly more evident that the mechanistic origins (such as fatigue, corrosion, abrasion, and adhesion) are essentially the same. However, we hope to present a clear and compelling argument favoring the prominent and irreplaceable role of in situ experimental techniques as a bridge between fundamental atomistic and molecular processes and emergent behaviors governing tribological contacts.

Studies on Stress-Strain Relationships of Polymeric Materials Used in Space Applications

NASA Technical Reports Server (NTRS)

Jana, Sadhan C.; Freed, Alan

2002-01-01

A two-year research plan was undertaken in association with Polymers Branch, NASA Glenn Research Center, to carry out experimental and modeling work relating stress and strain behavior of polymeric materials, especially elastomers and vulcanized rubber. An experimental system based on MTS (Mechanical Testing and Simulation) A/T-4 test facility environment has been developed for a broader range of polymeric materials in addition to a design of laser compatible temperature control chamber for online measurements of various strains. Necessary material processing has been accomplished including rubber compounding and thermoplastic elastomer processing via injection molding. A broad suite of testing methodologies has been identified to reveal the complex non-linear mechanical behaviors of rubbery materials when subjected to complex modes of deformation. This suite of tests required the conceptualization, design and development of new specimen geometries, test fixtures, and test systems including development of a new laser based technique to measure large multi-axial deformations. Test data has been generated for some of these new fixtures and has revealed some complex coupling effects generated during multi-axial deformations. In addition, fundamental research has been conducted concerning the foundation principles of rubber thermodynamics and resulting theories of rubber elasticity. Studies have been completed on morphological properties of several thermoplastic elastomers. Finally, a series of steps have been identified to further advance the goals of NASA's ongoing effort.

Characterization of craniofacial sutures using the finite element method.

PubMed

Maloul, Asmaa; Fialkov, Jeffrey; Wagner, Diane; Whyne, Cari M

2014-01-03

Characterizing the biomechanical behavior of sutures in the human craniofacial skeleton (CFS) is essential to understand the global impact of these articulations on load transmission, but is challenging due to the complexity of their interdigitated morphology, the multidirectional loading they are exposed to and the lack of well-defined suture material properties. This study aimed to quantify the impact of morphological features, direction of loading and suture material properties on the mechanical behavior of sutures and surrounding bone in the CFS. Thirty-six idealized finite element (FE) models were developed. One additional specimen-specific FE model was developed based on the morphology obtained from a µCT scan to represent the morphological complexity inherent in CFS sutures. Outcome variables of strain energy (SE) and von Mises stress (σvm) were evaluated to characterize the sutures' biomechanical behavior. Loading direction was found to impact the relationship between SE and interdigitation index and yielded varied patterns of σvm in both the suture and surrounding bone. Adding bone connectivity reduced suture strain energy and altered the σvm distribution. Incorporating transversely isotropic material properties was found to reduce SE, but had little impact on stress patterns. High-resolution µCT scanning of the suture revealed a complex morphology with areas of high and low interdigitations. The specimen specific suture model results were reflective of SE absorption and σvm distribution patterns consistent with the simplified FE results. Suture mechanical behavior is impacted by morphologic factors (interdigitation and connectivity), which may be optimized for regional loading within the CFS. © 2013 Elsevier Ltd. All rights reserved.

Challenges in the analysis of complex systems: introduction and overview

NASA Astrophysics Data System (ADS)

Hastings, Harold M.; Davidsen, Jörn; Leung, Henry

2017-12-01

One of the main challenges of modern physics is to provide a systematic understanding of systems far from equilibrium exhibiting emergent behavior. Prominent examples of such complex systems include, but are not limited to the cardiac electrical system, the brain, the power grid, social systems, material failure and earthquakes, and the climate system. Due to the technological advances over the last decade, the amount of observations and data available to characterize complex systems and their dynamics, as well as the capability to process that data, has increased substantially. The present issue discusses a cross section of the current research on complex systems, with a focus on novel experimental and data-driven approaches to complex systems that provide the necessary platform to model the behavior of such systems.

Shock Wave Propagation in Cementitious Materials at Micro/Meso Scales

NASA Astrophysics Data System (ADS)

Rajendran, Arunachalam

2015-06-01

The mechanical and constitutive response of materials like cement, and bio materials like fish scale and abalone shell is very complex due to heterogeneities that are inherently present in the nano and microstructures. The intrinsic constitutive behaviors are driven by the chemical composition and the molecular, micro, and meso structures. Therefore, it becomes important to identify the material genome as the building block for the material. For instance, in cementitious materials, the genome of C-S-H phase (the glue or the paste) that holds the various clinkers, such as the dicalcium silicate, tricalcium silicate, calcium ferroaluminates, and others is extremely complex. Often mechanical behaviors of C-S-H type materials are influenced by the chemistry and the structures at all nano to micro length scales. By explicitly modeling the molecular structures using appropriate potentials, it is then possible to compute the elastic tensor from molecular dynamics simulations using all atom method. The elastic tensors for the C-S-H gel and other clinkers are determined using the software suite ``Accelrys Materials Studio.'' A strain rate dependent, fracture mechanics based tensile damage model has been incorporated into ABAQUS finite element code to model spall evolution in the heterogeneous cementitious material with all constituents explicitly modeled through one micron element resolution. This paper presents results from nano/micro/meso scale analyses of shock wave propagation in a heterogeneous cementitious material using both molecular dynamic and finite element codes.

High pressure and Multiferroics materials. A happy marriage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilioli, Edmondo; Ehm, Lars

2014-10-31

We found that the community of material scientists is strongly committed to the research area of multiferroic materials, both for the understanding of the complex mechanisms supporting the multiferroism and for the fabrication of new compounds, potentially suitable for technological applications. The use of high pressure is a powerful tool in synthesizing new multiferroic, in particular magneto-electric phases, where the pressure stabilization of otherwise unstable perovskite-based structural distortions may lead to promising novel metastable compounds. Moreover, the in situ investigation of the high-pressure behavior of multiferroic materials has provided insight into the complex interplay between magnetic and electronic properties andmore » the coupling to structural instabilities.« less

Complexity in modeling of residual stresses and strains during polymerization of bone cement: effects of conversion, constraint, heat transfer, and viscoelastic property changes.

PubMed

Gilbert, Jeremy L

2006-12-15

Aseptic loosening of cemented joint prostheses remains a significant concern in orthopedic biomaterials. One possible contributor to cement loosening is the development of porosity, residual stresses, and local fracture of the cement that may arise from the in-situ polymerization of the cement. In-situ polymerization of acrylic bone cement is a complex set of interacting processes that involve polymerization reactions, heat generation and transfer, full or partial mechanical constraint, evolution of conversion- and temperature-dependent viscoelastic material properties, and thermal and conversion-driven changes in the density of the cement. Interactions between heat transfer and polymerization can lead to polymerization fronts moving through the material. Density changes during polymerization can, in the presence of mechanical constraint, lead to the development of locally high residual strain energy and residual stresses. This study models the interactions during bone cement polymerization and determines how residual stresses develop in cement and incorporates temperature and conversion-dependent viscoelastic behavior. The results show that the presence of polymerization fronts in bone cement result in locally high residual strain energies. A novel heredity integral approach is presented to track residual stresses incorporating conversion and temperature dependent material property changes. Finally, the relative contribution of thermal- and conversion-dependent strains to residual stresses is evaluated and it is found that the conversion-based strains are the major contributor to the overall behavior. This framework provides the basis for understanding the complex development of residual stresses and can be used as the basis for developing more complex models of cement behavior.

Modeling and Characterization of Cyclic Shape Memory Behaviors of the Binary Ni49.9Ti50.1 Material System

NASA Astrophysics Data System (ADS)

Saleeb, A. F.; Natsheh, S. H.; Owusu-Danquah, J. S.; Dhakal, B.

2017-05-01

In this work, we address two of the main challenges encountered in constitutive modeling of the thermomechanical behaviors of actuation-based shape memory alloys. Firstly, the complexity of behavior under cyclic thermomechanical loading is properly handled, particularly with regard to assessing the long-term dimensional stability. Secondly, we consider the marked differences in behavior distinguishing virgin-versus-trained SMA material. To this end, we utilize a set of experimental data comprehensive in scope to cover all the anticipated operational conditions for one and same SMA alloy, having a specific chemical composition with fixed heat treatment. More specifically, this includes twenty-four different tests from the recent SMA experimental literature for the Ni49.9Ti50.1 material having austenite finish temperature above 100 °C. Under all the different conditions investigated, the model results were found to be in very good agreement with the experimental measurements.

Crystallization features of normal alkanes in confined geometry.

PubMed

Su, Yunlan; Liu, Guoming; Xie, Baoquan; Fu, Dongsheng; Wang, Dujin

2014-01-21

How polymers crystallize can greatly affect their thermal and mechanical properties, which influence the practical applications of these materials. Polymeric materials, such as block copolymers, graft polymers, and polymer blends, have complex molecular structures. Due to the multiple hierarchical structures and different size domains in polymer systems, confined hard environments for polymer crystallization exist widely in these materials. The confined geometry is closely related to both the phase metastability and lifetime of polymer. This affects the phase miscibility, microphase separation, and crystallization behaviors and determines both the performance of polymer materials and how easily these materials can be processed. Furthermore, the size effect of metastable states needs to be clarified in polymers. However, scientists find it difficult to propose a quantitative formula to describe the transition dynamics of metastable states in these complex systems. Normal alkanes [CnH2n+2, n-alkanes], especially linear saturated hydrocarbons, can provide a well-defined model system for studying the complex crystallization behaviors of polymer materials, surfactants, and lipids. Therefore, a deeper investigation of normal alkane phase behavior in confinement will help scientists to understand the crystalline phase transition and ultimate properties of many polymeric materials, especially polyolefins. In this Account, we provide an in-depth look at the research concerning the confined crystallization behavior of n-alkanes and binary mixtures in microcapsules by our laboratory and others. Since 2006, our group has developed a technique for synthesizing nearly monodispersed n-alkane containing microcapsules with controllable size and surface porous morphology. We applied an in situ polymerization method, using melamine-formaldehyde resin as shell material and nonionic surfactants as emulsifiers. The solid shell of microcapsules can provide a stable three-dimensional (3-D) confining environment. We have studied multiple parameters of these microencapsulated n-alkanes, including surface freezing, metastability of the rotator phase, and the phase separation behaviors of n-alkane mixtures using differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD), and variable-temperature solid-state nuclear magnetic resonance (NMR). Our investigations revealed new direct evidence for the existence of surface freezing in microencapsulated n-alkanes. By examining the differences among chain packing and nucleation kinetics between bulk alkane solid solutions and their microencapsulated counterparts, we also discovered a mechanism responsible for the formation of a new metastable bulk phase. In addition, we found that confinement suppresses lamellar ordering and longitudinal diffusion, which play an important role in stabilizing the binary n-alkane solid solution in microcapsules. Our work also provided new insights into the phase separation of other mixed system, such as waxes, lipids, and polymer blends in confined geometry. These works provide a profound understanding of the relationship between molecular structure and material properties in the context of crystallization and therefore advance our ability to improve applications incorporating polymeric and molecular materials.

Exemplar for simulation challenges: Large-deformation micromechanics of Sylgard 184/glass microballoon syntactic foams.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Judith Alice; Long, Kevin Nicholas

2018-05-01

Sylgard® 184/Glass Microballoon (GMB) potting material is currently used in many NW systems. Analysts need a macroscale constitutive model that can predict material behavior under complex loading and damage evolution. To address this need, ongoing modeling and experimental efforts have focused on study of damage evolution in these materials. Micromechanical finite element simulations that resolve individual GMB and matrix components promote discovery and better understanding of the material behavior. With these simulations, we can study the role of the GMB volume fraction, time-dependent damage, behavior under confined vs. unconfined compression, and the effects of partial damage. These simulations are challengingmore » and push the boundaries of capability even with the high performance computing tools available at Sandia. We summarize the major challenges and the current state of this modeling effort, as an exemplar of micromechanical modeling needs that can motivate advances in future computing efforts.« less

Complexity and Anisotropy of Plastic Flow of α-Ti Probed by Acoustic Emission and Local Extensometry.

PubMed

Lebyodkin, Mikhail; Amouzou, Kékéli; Lebedkina, Tatiana; Richeton, Thiebaud; Roth, Amandine

2018-06-22

Current progress in the prediction of mechanical behavior of solids requires understanding of spatiotemporal complexity of plastic flow caused by self-organization of crystal defects. It may be particularly important in hexagonal materials because of their strong anisotropy and combination of different mechanisms of plasticity, such as dislocation glide and twinning. These materials often display complex behavior even on the macroscopic scale of deformation curves, e.g., a peculiar three-stage elastoplastic transition, the origin of which is a matter of debates. The present work is devoted to a multiscale study of plastic flow in α-Ti, based on simultaneous recording of deformation curves, 1D local strain field, and acoustic emission (AE). It is found that the average AE activity also reveals three-stage behavior, but in a qualitatively different way depending on the crystallographic orientation of the sample axis. On the finer scale, the statistical analysis of AE events and local strain rates testifies to an avalanche-like character of dislocation processes, reflected in power-law probability distribution functions. The results are discussed from the viewpoint of collective dislocation dynamics and are confronted to predictions of a recent micromechanical model of Ti strain hardening.

The mechanisms of plastic strain accommodation and post critical behavior of heterogeneous reactive composites subject to dynamic loading

NASA Astrophysics Data System (ADS)

Olney, Karl L.

The dynamic behavior of granular/porous and laminate reactive materials is of interest due to their practical applications; reactive structural components, reactive fragments, etc. The mesostructural properties control meso- and macro-scale dynamic behavior of these heterogeneous composites including the behavior during the post-critical stage of deformation. They heavily influence mechanisms of fragment generation and the in situ development of local hot spots, which act as sites of ignition in these materials. This dissertation concentrates on understanding the mechanisms of plastic strain accommodation in two representative reactive material systems with different heterogeneous mesostructrues: Aluminum-Tungsten granular/porous and Nickel-Aluminum laminate composites. The main focus is on the interpretation of results of the following dynamic experiments conducted at different strain and strain rates: drop weight tests, explosively expanded ring experiments, and explosively collapsed thick walled cylinder experiments. Due to the natural limitations in the evaluation of the mesoscale behavior of these materials experimentally and the large variation in the size scales between the mesostructural level and the sample, it is extremely difficult, if not impossible, to examine the mesoscale behavior in situ. Therefore, numerical simulations of the corresponding experiments are used as the main tool to explore material behavior at the mesoscale. Numerical models were developed to elucidate the mechanisms of plastic strain accommodation and post critical behavior in these heterogeneous composites subjected to dynamic loading. These simulations were able to reproduce the qualitative and quantitative features that were observable in the experiments and provided insight into the evolution of the mechanisms of plastic strain accommodation and post critical behavior in these materials with complex mesotructure. Additionally, these simulations provided a framework to examine the influence of various mesoscale properties such as the bonding of interfaces, the role of material properties, and the influence of mesoscale geometry. The results of this research are helpful in the design of material mesotructures conducive to the desirable behavior under dynamic loading.

Prediction of Thermal Transport Properties of Materials with Microstructural Complexity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Youping

This project aims at overcoming the major obstacle standing in the way of progress in dynamic multiscale simulation, which is the lack of a concurrent atomistic-continuum method that allows phonons, heat and defects to pass through the atomistic-continuum interface. The research has led to the development of a concurrent atomistic-continuum (CAC) methodology for multiscale simulations of materials microstructural, mechanical and thermal transport behavior. Its efficacy has been tested and demonstrated through simulations of dislocation dynamics and phonon transport coupled with microstructural evolution in a variety of materials and through providing visual evidences of the nature of phonon transport, such asmore » showing the propagation of heat pulses in single and polycrystalline solids is partially ballistic and partially diffusive. In addition to providing understanding on phonon scattering with phase interface and with grain boundaries, the research has contributed a multiscale simulation tool for understanding of the behavior of complex materials and has demonstrated the capability of the tool in simulating the dynamic, in situ experimental studies of nonequilibrium transient transport processes in material samples that are at length scales typically inaccessible by atomistically resolved methods.« less

4D Origami by Smart Embroidery.

PubMed

Stoychev, Georgi; Razavi, Mir Jalil; Wang, Xianqiao; Ionov, Leonid

2017-09-01

There exist many methods for processing of materials: extrusion, injection molding, fibers spinning, 3D printing, to name a few. In most cases, materials with a static, fixed shape are produced. However, numerous advanced applications require customized elements with reconfigurable shape. The few available techniques capable of overcoming this problem are expensive and/or time-consuming. Here, the use of one of the most ancient technologies for structuring, embroidering, is proposed to generate sophisticated patterns of active materials, and, in this way, to achieve complex actuation. By combining experiments and computational modeling, the fundamental rules that can predict the folding behavior of sheets with a variety of stitch-patterns are elucidated. It is demonstrated that theoretical mechanics analysis is only suitable to predict the behavior of the simplest experimental setups, whereas computer modeling gives better predictions for more complex cases. Finally, the applicability of the rules by designing basic origami structures and wrinkling substrates with controlled thermal insulation properties is shown. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dynamics in Complex Coacervates

NASA Astrophysics Data System (ADS)

Perry, Sarah

Understanding the dynamics of a material provides detailed information about the self-assembly, structure, and intermolecular interactions present in a material. While rheological methods have long been used for the characterization of complex coacervate-based materials, it remains a challenge to predict the dynamics for a new system of materials. Furthermore, most work reports only qualitative trends exist as to how parameters such as charge stoichiometry, ionic strength, and polymer chain length impact self-assembly and material dynamics, and there is little information on the effects of polymer architecture or the organization of charges within a polymer. We seek to link thermodynamic studies of coacervation phase behavior with material dynamics through a carefully-controlled, systematic study of coacervate linear viscoelasticity for different polymer chemistries. We couple various methods of characterizing the dynamics of polymer-based complex coacervates, including the time-salt superposition methods developed first by Spruijt and coworkers to establish a more mechanistic strategy for comparing the material dynamics and linear viscoelasticity of different systems. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for support of this research.

Rheological Behavior of a Novel Organic-Inorganic Hybrid: Micro/Nano-Tin Fluorophosphate Glass-Polycarbonate.

PubMed

Yang, Jing; Liu, Huiwen; Yu, Honglin; Zou, Xiaoxuan; Jing, Bo; Dai, Wenli

2016-03-01

The rheological behavior of a novel, binary organic-inorganic hybrid consisting of an ultra-low Tg tin fluorophosphate glass (Pglass) and polycarbonate (PC) was investigated using oscillatory rheometry. It was found that the complex viscosity of the hybrid showed Pglass content dependence. Under low Pglass content (10-30%), the complex viscosity of the hybrid was lower than that of pure PC. While the complex viscosity was dramatically increased and higher than that of pure PC with the content of Pglass above 30%. This phenomenon was particularly remarkable at low frequencies. Besides, with the addition of Pglass the hybrid material exhibited shear-thinning behavior and the shear-thinning characteristics became more obvious with the enhancement of the Pglass content, indicating the presence of nonlinear chemical and physical interactions between the hybrid components. Differential scanning calorimetry (DSC) measurements revealed that increasing the content of Pglass caused a decrease of the glass transition temperature (Tg) of the hybrids, suggesting that Pglass was acting as a macromolecular plasticizer for the PC. The microstructure of the Pglass in the hybrid material was characterized by scanning electron microscopy (SEM). The results showed that the Pglass were dispersed as micro- and nano-bead in the continuous phase of PC and the Pglass appeared aggregation partly with the increase of the Pglass content. This contribution was anticipated to be a guideline for the processing of this promising new class of hybrid materials.

A Viscoplastic Constitutive Theory for Monolithic Ceramic Materials. Series 1

NASA Technical Reports Server (NTRS)

Janosik, Lesley A.; Duffy, Stephen F.

1997-01-01

With increasing use of ceramic materials in high temperature structural applications such as advanced heat engine components, the need arises to accurately predict thermomechanical behavior. This paper, which is the first of two in a series, will focus on inelastic deformation behavior associated with these service conditions by providing an overview of a viscoplastic constitutive model that accounts for time-dependent hereditary material deformation (e.g., creep, stress relaxation, etc.) in monolithic structural ceramics. Early work in the field of metal plasticity indicated that inelastic deformations are essentially unaffected by hydrostatic stress. This is not the case, however, for ceramic-based material systems, unless the ceramic is fully dense. The theory presented here allows for fully dense material behavior as a limiting case. In addition, ceramic materials exhibit different time-dependent behavior in tension and compression. Thus, inelastic deformation models for ceramics must be constructed in a fashion that admits both sensitivity to hydrostatic stress and differing behavior in tension and compression. A number of constitutive theories for materials that exhibit sensitivity to the hydrostatic component of stress have been proposed that characterize deformation using time-independent classical plasticity as a foundation. However, none of these theories allow different behavior in tension and compression. In addition, these theories are somewhat lacking in that they are unable to capture creep, relaxation, and rate-sensitive phenomena exhibited by ceramic materials at high temperature. When subjected to elevated service temperatures, ceramic materials exhibit complex thermomechanical behavior that is inherently time-dependent, and hereditary in the sense that current behavior depends not only on current conditions, but also on thermo-mechanical history. The objective of this work is to present the formulation of a macroscopic continuum theory that captures these time-dependent phenomena. Specifically, the overview contained in this paper focuses on the multiaxial derivation of the constitutive model, and examines the scalar threshold function and its attending geometrical implications.

Physics and Chemistry of Earth Materials

NASA Astrophysics Data System (ADS)

Navrotsky, Alexandra

1994-11-01

Stressing the fundamental solid state behavior of minerals, and emphasizing both theory and experiment, this text surveys the physics and chemistry of earth materials. The author begins with a systematic tour of crystal chemistry of both simple and complex structures (with completely new structural drawings) and discusses how to obtain structural and thermodynamic information experimentally. Dr. Navrotsky also reviews the quantitative concepts of chemical bonding--band theory, molecular orbit and ionic models. She then covers physical properties and relates microscopic features to macroscopic thermodynamic behavior and treats high pressure phase transitions, amorphous materials and solid state reactions. The author concludes with a look at the interface between mineral physics and materials science. Highly illustrated throughout, this book fills the gap between undergraduate texts and specialized review volumes and is appropriate for students and researchers in earth science and materials science.

Calibration and Finite Element Implementation of an Energy-Based Material Model for Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Junker, Philipp; Hackl, Klaus

2016-09-01

Numerical simulations are a powerful tool to analyze the complex thermo-mechanically coupled material behavior of shape memory alloys during product engineering. The benefit of the simulations strongly depends on the quality of the underlying material model. In this contribution, we discuss a variational approach which is based solely on energetic considerations and demonstrate that unique calibration of such a model is sufficient to predict the material behavior at varying ambient temperature. In the beginning, we recall the necessary equations of the material model and explain the fundamental idea. Afterwards, we focus on the numerical implementation and provide all information that is needed for programing. Then, we show two different ways to calibrate the model and discuss the results. Furthermore, we show how this model is used during real-life industrial product engineering.

Binary Phase Behavior of Saturated-Unsaturated Mixed-Acid Triacylglycerols-A Review.

PubMed

Zhang, Lu; Ueno, Satoru; Sato, Kiyotaka

2018-06-01

Most natural lipids contain a complex mixture of individual triacylglycerols (TAGs). An in-depth knowledge of the mixing behavior of TAGs is necessary for the rational design and engineering of food materials. The binary phase diagram of TAGs is a simplified model that can be explored to help foster an understanding of the phase behavior of complex fats and oils. This article reviews recent research on the binary phase behavior of saturated-unsaturated mixed-acid TAGs, with special emphasis on the stearicunsaturated and palmitic-unsaturated diacid TAGs. The occurrence of polymorphic forms and mutual solubility of TAG mixtures are strongly related to the glycerol conformation of the saturated-oleic diacid TAGs; it appears to be most influenced by the chain-length mismatch in saturated-elaidic diacid TAGs. In addition, the polymorphism of pure enantiomers and racemic mixture of chiral TAGs was also reviewed, while the effect of chirality on mixing behavior was discussed.

An atom is known by the company it keeps: Content, representation and pedagogy within the epistemic revolution of the complexity sciences

NASA Astrophysics Data System (ADS)

Blikstein, Paulo

The goal of this dissertation is to explore relations between content, representation, and pedagogy, so as to understand the impact of the nascent field of complexity sciences on science, technology, engineering and mathematics (STEM) learning. Wilensky & Papert coined the term "structurations" to express the relationship between knowledge and its representational infrastructure. A change from one representational infrastructure to another they call a "restructuration." The complexity sciences have introduced a novel and powerful structuration: agent-based modeling. In contradistinction to traditional mathematical modeling, which relies on equational descriptions of macroscopic properties of systems, agent-based modeling focuses on a few archetypical micro-behaviors of "agents" to explain emergent macro-behaviors of the agent collective. Specifically, this dissertation is about a series of studies of undergraduate students' learning of materials science, in which two structurations are compared (equational and agent-based), consisting of both design research and empirical evaluation. I have designed MaterialSim, a constructionist suite of computer models, supporting materials and learning activities designed within the approach of agent-based modeling, and over four years conducted an empirical inves3 tigation of an undergraduate materials science course. The dissertation is comprised of three studies: Study 1 - diagnosis . I investigate current representational and pedagogical practices in engineering classrooms. Study 2 - laboratory studies. I investigate the cognition of students engaging in scientific inquiry through programming their own scientific models. Study 3 - classroom implementation. I investigate the characteristics, advantages, and trajectories of scientific content knowledge that is articulated in epistemic forms and representational infrastructures unique to complexity sciences, as well as the feasibility of the integration of constructionist, agent-based learning environments in engineering classrooms. Data sources include classroom observations, interviews, videotaped sessions of model-building, questionnaires, analysis of computer-generated logfiles, and quantitative and qualitative analysis of artifacts. Results shows that (1) current representational and pedagogical practices in engineering classrooms were not up to the challenge of the complex content being taught, (2) by building their own scientific models, students developed a deeper understanding of core scientific concepts, and learned how to better identify unifying principles and behaviors in materials science, and (3) programming computer models was feasible within a regular engineering classroom.

Aeropropulsion 1987. Session 2: Aeropropulsion Structures Research

NASA Technical Reports Server (NTRS)

1987-01-01

Aeropropulsion systems present unique problems to the structural engineer. The extremes in operating temperatures, rotational effects, and behaviors of advanced material systems combine into complexities that require advances in many scientific disciplines involved in structural analysis and design procedures. This session provides an overview of the complexities of aeropropulsion structures and the theoretical, computational, and experimental research conducted to achieve the needed advances.

Tuning bad metal and non-Fermi liquid behavior in a Mott material: Rare-earth nickelate thin films

PubMed Central

Mikheev, Evgeny; Hauser, Adam J.; Himmetoglu, Burak; Moreno, Nelson E.; Janotti, Anderson; Van de Walle, Chris G.; Stemmer, Susanne

2015-01-01

Resistances that exceed the Mott-Ioffe-Regel limit (known as bad metal behavior) and non-Fermi liquid behavior are ubiquitous features of the normal state of many strongly correlated materials. We establish the conditions that lead to bad metal and non-Fermi liquid phases in NdNiO3, which exhibits a prototype bandwidth-controlled metal-insulator transition. We show that resistance saturation is determined by the magnitude of Ni eg orbital splitting, which can be tuned by strain in epitaxial films, causing the appearance of bad metal behavior under certain conditions. The results shed light on the nature of a crossover to a non-Fermi liquid metal phase and provide a predictive criterion for Anderson localization. They elucidate a seemingly complex phase behavior as a function of film strain and confinement and provide guidelines for orbital engineering and novel devices. PMID:26601140

Crashworthiness analysis using advanced material models in DYNA3D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Logan, R.W.; Burger, M.J.; McMichael, L.D.

1993-10-22

As part of an electric vehicle consortium, LLNL and Kaiser Aluminum are conducting experimental and numerical studies on crashworthy aluminum spaceframe designs. They have jointly explored the effect of heat treat on crush behavior and duplicated the experimental behavior with finite-element simulations. The major technical contributions to the state of the art in numerical simulation arise from the development and use of advanced material model descriptions for LLNL`s DYNA3D code. Constitutive model enhancements in both flow and failure have been employed for conventional materials such as low-carbon steels, and also for lighter weight materials such as aluminum and fiber compositesmore » being considered for future vehicles. The constitutive model enhancements are developed as extensions from LLNL`s work in anisotropic flow and multiaxial failure modeling. Analysis quality as a function of level of simplification of material behavior and mesh is explored, as well as the penalty in computation cost that must be paid for using more complex models and meshes. The lightweight material modeling technology is being used at the vehicle component level to explore the safety implications of small neighborhood electric vehicles manufactured almost exclusively from these materials.« less

Installing Mechanics of Granular Materials (MGM) Experiment Test Cell

NASA Technical Reports Server (NTRS)

1996-01-01

Astronaut Carl Walz installs Mechanics of Granular Materials (MGM) test cell on STS-79. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/John Space Center

High-resolution 2-D Bragg diffraction reveal heterogeneous domain transformation behavior in a bulk relaxor ferroelectric

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pramanick, Abhijit, E-mail: apramani@cityu.edu.hk; Stoica, Alexandru D.; An, Ke

2016-08-29

In-situ measurement of fine-structure of neutron Bragg diffraction peaks from a relaxor single-crystal using a time-of-flight instrument reveals highly heterogeneous mesoscale domain transformation behavior under applied electric fields. It is observed that only ∼25% of domains undergo reorientation or phase transition contributing to large average strains, while at least 40% remain invariant and exhibit microstrains. Such insights could be central for designing new relaxor materials with better performance and longevity. The current experimental technique can also be applied to resolve complex mesoscale phenomena in other functional materials.

Symposium II: Mechanochemistry in Materials Science, MRS Fall Meeting, Nov 30-Dec 4, 2009, Boston, MA

DTIC Science & Technology

2010-09-02

Dynamic Mechanical Analysis (DMA). The fracture behavior of the mechanophore-linked polymer is also examined through the Double Cleavage Drilled ...multinary complex structures. Structural, microstructural, and chemical characterizations were explored by metrological tools to support this...simple hydrocarbons in order to quantitatively define structure-property relationships for reacting materials under shock compression. Embedded gauge

Dynamic behavior of geometrically complex hybrid composite samples in a Split-Hopkinson Pressure Bar system

NASA Astrophysics Data System (ADS)

Pouya, M.; Balasubramaniam, S.; Sharafiev, S.; F-X Wagner, M.

2018-06-01

The interfaces between layered materials play an important role for the overall mechanical behavior of hybrid composites, particularly during dynamic loading. Moreover, in complex-shaped composites, interfacial failure is strongly affected by the geometry and size of these contact interfaces. As preliminary work for the design of a novel sample geometry that allows to analyze wave reflection phenomena at the interfaces of such materials, a series of experiments using a Split-Hopkinson Pressure Bar technique was performed on five different sample geometries made of a monomaterial steel. A complementary explicit finite element model of the Split-Hopkinson Pressure Bar system was developed and the same sample geometries were studied numerically. The simulated input, reflected and transmitted elastic wave pulses were analyzed for the different sample geometries and were found to agree well with the experimental results. Additional simulations using different composite layers of steel and aluminum (with the same sample geometries) were performed to investigate the effect of material variation on the propagated wave pulses. The numerical results show that the reflected and transmitted wave pulses systematically depend on the sample geometry, and that elastic wave pulse propagation is affected by the properties of individual material layers.

Super Stable Ferroelectrics with High Curie Point.

PubMed

Gao, Zhipeng; Lu, Chengjia; Wang, Yuhang; Yang, Sinuo; Yu, Yuying; He, Hongliang

2016-04-07

Ferroelectric materials are of great importance in the sensing technology due to the piezoelectric properties. Thermal depoling behavior of ferroelectrics determines the upper temperature limit of their application. So far, there is no piezoelectric material working above 800 °C available. Here, we show Nd2Ti2O7 with a perovskite-like layered structure has good resistance to thermal depoling up to 1400 °C. Its stable behavior is because the material has only 180° ferroelectric domains, complex structure change at Curie point (Tc) and their sintering temperature is below their Tc, which avoided the internal stresses produced by the unit cell volume change at Tc. The phase transition at Tc shows a first order behavior which involving the tilting and rotation of the octahedron. The Curie - Weiss temperature is calculated, which might explain why the thermal depoling starts at about 1400 °C.

Super Stable Ferroelectrics with High Curie Point

PubMed Central

Gao, Zhipeng; Lu, Chengjia; Wang, Yuhang; Yang, Sinuo; Yu, Yuying; He, Hongliang

2016-01-01

Ferroelectric materials are of great importance in the sensing technology due to the piezoelectric properties. Thermal depoling behavior of ferroelectrics determines the upper temperature limit of their application. So far, there is no piezoelectric material working above 800 °C available. Here, we show Nd2Ti2O7 with a perovskite-like layered structure has good resistance to thermal depoling up to 1400 °C. Its stable behavior is because the material has only 180° ferroelectric domains, complex structure change at Curie point (Tc) and their sintering temperature is below their Tc, which avoided the internal stresses produced by the unit cell volume change at Tc. The phase transition at Tc shows a first order behavior which involving the tilting and rotation of the octahedron. The Curie – Weiss temperature is calculated, which might explain why the thermal depoling starts at about 1400 °C. PMID:27053338

Three-Dimensional High Fidelity Progressive Failure Damage Modeling of NCF Composites

NASA Technical Reports Server (NTRS)

Aitharaju, Venkat; Aashat, Satvir; Kia, Hamid G.; Satyanarayana, Arunkumar; Bogert, Philip B.

2017-01-01

Performance prediction of off-axis laminates is of significant interest in designing composite structures for energy absorption. Phenomenological models available in most of the commercial programs, where the fiber and resin properties are smeared, are very efficient for large scale structural analysis, but lack the ability to model the complex nonlinear behavior of the resin and fail to capture the complex load transfer mechanisms between the fiber and the resin matrix. On the other hand, high fidelity mesoscale models, where the fiber tows and matrix regions are explicitly modeled, have the ability to account for the complex behavior in each of the constituents of the composite. However, creating a finite element model of a larger scale composite component could be very time consuming and computationally very expensive. In the present study, a three-dimensional mesoscale model of non-crimp composite laminates was developed for various laminate schemes. The resin material was modeled as an elastic-plastic material with nonlinear hardening. The fiber tows were modeled with an orthotropic material model with brittle failure. In parallel, new stress based failure criteria combined with several damage evolution laws for matrix stresses were proposed for a phenomenological model. The results from both the mesoscale and phenomenological models were compared with the experiments for a variety of off-axis laminates.

Modeling lahar behavior and hazards

USGS Publications Warehouse

Manville, Vernon; Major, Jon J.; Fagents, Sarah A.

2013-01-01

Lahars are highly mobile mixtures of water and sediment of volcanic origin that are capable of traveling tens to > 100 km at speeds exceeding tens of km hr-1. Such flows are among the most serious ground-based hazards at many volcanoes because of their sudden onset, rapid advance rates, long runout distances, high energy, ability to transport large volumes of material, and tendency to flow along existing river channels where populations and infrastructure are commonly concentrated. They can grow in volume and peak discharge through erosion and incorporation of external sediment and/or water, inundate broad areas, and leave deposits many meters thick. Furthermore, lahars can recur for many years to decades after an initial volcanic eruption, as fresh pyroclastic material is eroded and redeposited during rainfall events, resulting in a spatially and temporally evolving hazard. Improving understanding of the behavior of these complex, gravitationally driven, multi-phase flows is key to mitigating the threat to communities at lahar-prone volcanoes. However, their complexity and evolving nature pose significant challenges to developing the models of flow behavior required for delineating their hazards and hazard zones.

[Research on the aging of all-ceramics restoration materials].

PubMed

Zhang, Dongjiao; Chen, Xinmin

2011-10-01

All-ceramic crowns and bridges have been widely used for dental restorations owing to their excellent functionality, aesthetics and biocompatibility. However, the premature clinical failure of all-ceramic crowns and bridges may easily occur when they are subjected to the complex environment of oral cavity. In the oral environment, all-ceramic materials are prone to aging. Aging can lead all-ceramic materials to change color, to lower bending strength, and to reduce anti-fracture toughness. There are many factors affecting the aging of the all-ceramic materials, for example, the grain size, the type of stabilizer, the residual stress and the water environment. In order to analyze the aging behavior, to optimize the design of all-ceramic crowns and bridges, and to evaluate the reliability and durability, we review in this paper recent research progress of aging behavior for all-ceramics restoration materials.

Acoustic emission monitoring of polymer composite materials

NASA Technical Reports Server (NTRS)

Bardenheier, R.

1981-01-01

The techniques of acoustic emission monitoring of polymer composite materials is described. It is highly sensitive, quasi-nondestructive testing method that indicates the origin and behavior of flaws in such materials when submitted to different load exposures. With the use of sophisticated signal analysis methods it is possible the distinguish between different types of failure mechanisms, such as fiber fracture delamination or fiber pull-out. Imperfections can be detected while monitoring complex composite structures by acoustic emission measurements.

Thermomechanical Properties and Glass Dynamics of Polymer-Tethered Colloidal Particles and Films.

PubMed

Cang, Yu; Reuss, Anna N; Lee, Jaejun; Yan, Jiajun; Zhang, Jianan; Alonso-Redondo, Elena; Sainidou, Rebecca; Rembert, Pascal; Matyjaszewski, Krzysztof; Bockstaller, Michael R; Fytas, George

2017-11-14

Polymer-tethered colloidal particles (aka "particle brush materials") have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush-brush interactions as well as global chain relaxation sensitively depend on grafting density; i.e., more polymer-like behavior is observed in sparse brush systems. This is interpreted to be a consequence of more extensive chain entanglement. In contrast, the local relaxation of films does not depend on grafting density. The results highlight that relaxation processes in particle brush-based materials span a wider range of time and length scales as compared to linear chain polymers. Differentiation between relaxation on local and global scale is necessary to reveal the influence of molecular structure and connectivity on the aging behavior of these complex systems.

Computer modeling of the mechanical behavior of composites -- Interfacial cracks in fiber-reinforced materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmauder, S.; Haake, S.; Mueller, W.H.

Computer modeling of materials and especially modeling the mechanical behavior of composites became increasingly popular in the past few years. Among them are examples of micromechanical modeling of real structures as well as idealized model structures of linear elastic and elasto-plastic material response. In this paper, Erdogan`s Integral Equation Method (IEM) is chosen as an example for a powerful method providing principle insight into elastic fracture mechanical situations. IEM or, alternatively, complex function techniques sometimes even allow for deriving analytical solutions such as in the case of a circumferential crack along a fiber/matrix interface. The analytical formulae of this interfacemore » crack will be analyzed numerically and typical results will be presented graphically.« less

A numerical and experimental study of temperature effects on deformation behavior of carbon steels at high strain rates

NASA Astrophysics Data System (ADS)

Pouya, M.; Winter, S.; Fritsch, S.; F-X Wagner, M.

2017-03-01

Both in research and in the light of industrial applications, there is a growing interest in methods to characterize the mechanical behavior of materials at high strain rates. This is particularly true for steels (the most important structural materials), where often the strain rate-dependent material behavior also needs to be characterized in a wide temperature range. In this study, we use the Finite Element Method (FEM), first, to model the compressive deformation behavior of carbon steels under quasi-static loading conditions. The results are then compared to experimental data (for a simple C75 steel) at room temperature, and up to testing temperatures of 1000 °C. Second, an explicit FEM model that captures wave propagation phenomena during dynamic loading is developed to closely reflect the complex loading conditions in a Split-Hopkinson Pressure Bar (SHPB) - an experimental setup that allows loading of compression samples with strain rates up to 104 s-1 The dynamic simulations provide a useful basis for an accurate analysis of dynamically measured experimental data, which considers reflected elastic waves. By combining numerical and experimental investigations, we derive material parameters that capture the strain rate- and temperature-dependent behavior of the C75 steel from room temperature to 1000 °C, and from quasi-static to dynamic loading.

The adhesion and hysteresis effect in friction skin with artificial materials

NASA Astrophysics Data System (ADS)

Subhi, K. A.; Tudor, A.; Hussein, E. K.; Wahad, H. S.

2017-02-01

Human skin is a soft biomaterial with a complex anatomical structure and it has a complex material behavior during the mechanical contact with objects and surfaces. The friction adhesion component is defined by means of the theories of Johnson-Kendall-Roberts (JKR), Derjaguin-Muller-Toporov (DMT) and Maugis - Dugdale (MD). We shall consider the human skin entering into contact with a rigid surface. The deformation (hysteresis) component of the skin friction is evaluated with Voigt rheological model for the spherical contact, with the original model, developed in MATHCAD software. The adhesive component of the skin friction is greater than the hysteresis component for all friction parameters (load, velocity, the strength of interface between skin and the artificial material).

Films, Needles, and Particles: A Comparative Study on the Ferroic Properties of Complex Oxides Nano-Structured in One, Two, and Three Dimensions

DTIC Science & Technology

2014-03-01

materials (2). .......................................................2 Figure 2. Theoretical SPE phase region in Temperature vs. Size for PbZr0.6Ti0.4O3...ferroelasticity, ferromagnetism , and ferrotoroidicity (whose existence has not yet been proven by physical observation). A multiferroic material exhibits more... materials all belong to the class of primary ferroics. As such, we can expect analogous behavior in certain physical properties across this class of

Comparative evaluation of ibuprofen/beta-cyclodextrin complexes obtained by supercritical carbon dioxide and other conventional methods.

PubMed

Hussein, Khaled; Türk, Michael; Wahl, Martin A

2007-03-01

The preparation of drug/cyclodextrin complexes is a suitable method to improve the dissolution of poor soluble drugs. The efficacy of the Controlled Particle Deposition (CPD) as a new developed method to prepare these complexes in a single stage process using supercritical carbon dioxide is therefore compared with other conventional methods. Ibuprofen/beta-cyclodextrin complexes were prepared with different techniques and characterized using FTIR-ATR spectroscopy, powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). In addition, the influences of the processing technique on the drug content (HPLC) and the dissolution behavior were studied. Employing the CPD-process resulted in a drug content of 2.8+/-0.22 wt.% in the carrier. The material obtained by CPD showed an improved dissolution rate of ibuprofen at pH 5 compared with the pure drug and its physical mixture with beta-cyclodextrin. In addition CPD material displays the highest dissolution (93.5+/- 2.89% after 75 min) compared to material obtained by co-precipitation (61.3 +/-0.52%) or freeze-drying (90.6 +/-2.54%). This study presents the CPD-technique as a well suitable method to prepare a drug/beta-cyclodextrin complex with improved drug dissolution compared to the pure drug and materials obtained by other methods.

Multidisciplinary tailoring of hot composite structures

NASA Technical Reports Server (NTRS)

Singhal, Surendra N.; Chamis, Christos C.

1993-01-01

A computational simulation procedure is described for multidisciplinary analysis and tailoring of layered multi-material hot composite engine structural components subjected to simultaneous multiple discipline-specific thermal, structural, vibration, and acoustic loads. The effect of aggressive environments is also simulated. The simulation is based on a three-dimensional finite element analysis technique in conjunction with structural mechanics codes, thermal/acoustic analysis methods, and tailoring procedures. The integrated multidisciplinary simulation procedure is general-purpose including the coupled effects of nonlinearities in structure geometry, material, loading, and environmental complexities. The composite material behavior is assessed at all composite scales, i.e., laminate/ply/constituents (fiber/matrix), via a nonlinear material characterization hygro-thermo-mechanical model. Sample tailoring cases exhibiting nonlinear material/loading/environmental behavior of aircraft engine fan blades, are presented. The various multidisciplinary loads lead to different tailored designs, even those competing with each other, as in the case of minimum material cost versus minimum structure weight and in the case of minimum vibration frequency versus minimum acoustic noise.

Evaluating Flight Crew Operator Manual Documentation

NASA Technical Reports Server (NTRS)

Sherry, Lance; Feary, Michael

1998-01-01

Aviation and cognitive science researchers have identified situations in which the pilot s expectations for the behavior of the avionics are not matched by the actual behavior of the avionics. Researchers have attributed these "automation surprises" to the complexity of the avionics mode logic, the absence of complete training, limitations in cockpit displays, and ad-hoc conceptual models of the avionics. Complete canonical rule-based descriptions of the behavior of the autopilot provide the basis for understanding the perceived complexity of the autopilots, the differences between the pilot s and autopilot s conceptual models, and the limitations in training materials and cockpit displays. This paper compares the behavior of the autopilot Vertical Speed/Flight Path Angle (VS-FPA) mode as described in the Flight Crew Operators Manual (FCOM) and the actual behavior of the VS-FPA mode defined in the autopilot software. This example demonstrates the use of the Operational Procedure Model (OPM) as a method for using the requirements specification for the design of the software logic as information requirements for training.

(International seminar on the inelastic behavior of solids: Models and utilization)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruggles, M.B.

The traveler attended the International Seminar on the Inelastic Behavior of Solids: Models and Utilization, and presented an invited paper. Development and validation of constitutive models for complex loading and environmental conditions was the principal subject of the seminar. Session 1. Constitutive Models: Theoretical Development, Analysis and Comparison, and Session 2. Constitutive Models: Experimental Identification and Use, were of particular interest to the ORNL constitutive equations development effort. The traveler also visited the Applied Mechanics Laboratory at the University of Franche-Comte in Besancon and the Laboratory of Mechanics and Technology at the ENSET/Paris University 6 in Cachan. In both laboratoriesmore » the traveler held discussions regarding inelastic material behavior at room and elevated temperatures, exploratory testing and modeling, and materials testing equipment and techniques.« less

Thermal behavior of glassy phase stabilized ammonium nitrate (PSAN) thin films

DOE PAGES

Yeager, J. D.; Chellappa, R.; Singh, S.; ...

2015-06-01

Ammonium nitrate (AN) is a high interest material because of its wide usage in propellants and explosives but can be difficult to handle from a formulation standpoint. It is soluble in many common solvents and has complex phase behavior. Here, we formulate phase stabilized AN (PSAN) films in a polymer matrix and characterize thermal and phase behavior using neutron reflectometry and ellipsometry. Our PSAN films are generally stable up to 160 °C, though we observe small material loss between 60 and 100 °C, which we attribute to solvent interactions with the PSAN. Crystallization of AN from supersaturated polymer is mostmore » common at thicker regions of the film, suggesting a critical nucleation thickness for the AN which can be avoided by making very thin films.« less

Silver and gold nanoparticle separation using asymmetrical flow-field flow fractionation: Influence of run conditions and of particle and membrane charges.

PubMed

Meisterjahn, Boris; Wagner, Stephan; von der Kammer, Frank; Hennecke, Dieter; Hofmann, Thilo

2016-04-01

Flow-Field Flow Fractionation (Flow-FFF), coupled with online detection systems is one of the most promising tools available for the separation and quantification of engineered nanoparticles (ENPs) in complex matrices. To correctly relate the retention of nanoparticles in the Flow-FFF-channel to the particle size, ideal separation conditions must be met. This requires optimization of the parameters that influence the separation behavior. The aim of this study was therefore to systematically investigate and evaluate the influence of parameters such as the carrier liquid, the cross flow, and the membrane material, on the separation behavior of two metallic ENPs. For this purpose the retention, recovery, and separation efficiency of sterically stabilized silver nanoparticles (AgNPs) and electrostatically stabilized gold nanoparticles (AuNPs), which represent two materials widely used in investigations on environmental fate and ecotoxicology, were investigated against a parameter matrix of three different cross-flow densities, four representative carrier solutions, and two membrane materials. The use of a complex mixture of buffers, ionic and non-ionic surfactants (FL-70 solution) together with a medium cross-flow density provided an acceptable compromise in peak quality and recovery for both types of ENPs. However, these separation conditions do not represent a perfect match for both particle types at the same time (maximized recovery at maximized retention). It could be shown that the behavior of particles within Flow-FFF channels cannot be predicted or explained purely in terms of electrostatic interactions. Particles were irreversibly lost under conditions where the measured zeta potentials suggested that there should have been sufficient electrostatic repulsion to ensure stabilization of the particles in the Flow-FFF channel resulting in good recoveries. The wide variations that we observed in ENP behavior under different conditions, together with the different behavior that has been reported in published literature for the same NPs under similar conditions, indicate a need for improvement in the membrane materials used for Flow-FFF analysis of NPs. This research has shown that careful adjustment of separation conditions can result in acceptable, but not ideal, separation conditions for two fundamentally different stabilized materials, and that it may not be possible to separate a set of different particles under ideal conditions for each particle type. This therefore needs to be taking into account in method development and when interpreting FFF results from complex samples. Copyright © 2016 Elsevier B.V. All rights reserved.

The Usability of Rock-Like Materials for Numerical Studies on Rocks

NASA Astrophysics Data System (ADS)

Zengin, Enes; Abiddin Erguler, Zeynal

2017-04-01

The approaches of synthetic rock material and mass are widely used by many researchers for understanding the failure behavior of different rocks. In order to model the failure behavior of rock material, researchers take advantageous of different techniques and software. But, the majority of all these instruments are based on distinct element method (DEM). For modeling the failure behavior of rocks, and so to create a fundamental synthetic rock material model, it is required to perform related laboratory experiments for providing strength parameters. In modelling studies, model calibration processes are performed by using parameters of intact rocks such as porosity, grain size, modulus of elasticity and Poisson ratio. In some cases, it can be difficult or even impossible to acquire representative rock samples for laboratory experiments from heavily jointed rock masses and vuggy rocks. Considering this limitation, in this study, it was aimed to investigate the applicability of rock-like material (e.g. concrete) to understand and model the failure behavior of rock materials having complex inherent structures. For this purpose, concrete samples having a mixture of %65 cement dust and %35 water were utilized. Accordingly, intact concrete samples representing rocks were prepared in laboratory conditions and their physical properties such as porosity, pore size and density etc. were determined. In addition, to acquire the mechanical parameters of concrete samples, uniaxial compressive strength (UCS) tests were also performed by simultaneously measuring strain during testing. The measured physical and mechanical properties of these extracted concrete samples were used to create synthetic material and then uniaxial compressive tests were modeled and performed by using two dimensional discontinuum program known as Particle Flow Code (PFC2D). After modeling studies in PFC2D, approximately similar failure mechanism and testing results were achieved from both experimental and artificial simulations. The results obtained from these laboratory tests and modelling studies were compared with the other researcher's studies in respect to failure mechanism of different type of rocks. It can be concluded that there is similar failure mechanism between concrete and rock materials. Therefore, the results obtained from concrete samples that would be prepared at different porosity and pore sizes can be used in future studies in selection micro-mechanical and physical properties to constitute synthetic rock materials for understanding failure mechanism of rocks having complex inherent structures such as vuggy rocks or heavily jointed rock masses.

Assessing the Validity of the Simplified Potential Energy Clock Model for Modeling Glass-Ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jamison, Ryan Dale; Grillet, Anne M.; Stavig, Mark E.

Glass-ceramic seals may be the future of hermetic connectors at Sandia National Laboratories. They have been shown capable of surviving higher temperatures and pressures than amorphous glass seals. More advanced finite-element material models are required to enable model-based design and provide evidence that the hermetic connectors can meet design requirements. Glass-ceramics are composite materials with both crystalline and amorphous phases. The latter gives rise to (non-linearly) viscoelastic behavior. Given their complex microstructures, glass-ceramics may be thermorheologically complex, a behavior outside the scope of currently implemented constitutive models at Sandia. However, it was desired to assess if the Simplified Potential Energymore » Clock (SPEC) model is capable of capturing the material response. Available data for SL 16.8 glass-ceramic was used to calibrate the SPEC model. Model accuracy was assessed by comparing model predictions with shear moduli temperature dependence and high temperature 3-point bend creep data. It is shown that the model can predict the temperature dependence of the shear moduli and 3- point bend creep data. Analysis of the results is presented. Suggestions for future experiments and model development are presented. Though further calibration is likely necessary, SPEC has been shown capable of modeling glass-ceramic behavior in the glass transition region but requires further analysis below the transition region.« less

3D Printing of Materials with Tunable Failure via Bioinspired Mechanical Gradients.

PubMed

Kokkinis, Dimitri; Bouville, Florian; Studart, André R

2018-05-01

Mechanical gradients are useful to reduce strain mismatches in heterogeneous materials and thus prevent premature failure of devices in a wide range of applications. While complex graded designs are a hallmark of biological materials, gradients in manmade materials are often limited to 1D profiles due to the lack of adequate fabrication tools. Here, a multimaterial 3D-printing platform is developed to fabricate elastomer gradients spanning three orders of magnitude in elastic modulus and used to investigate the role of various bioinspired gradient designs on the local and global mechanical behavior of synthetic materials. The digital image correlation data and finite element modeling indicate that gradients can be effectively used to manipulate the stress state and thus circumvent the weakening effect of defect-rich interfaces or program the failure behavior of heterogeneous materials. Implementing this concept in materials with bioinspired designs can potentially lead to defect-tolerant structures and to materials whose tunable failure facilitates repair of biomedical implants, stretchable electronics, or soft robotics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanics of Granular Materials (MGM) Test Cell

NASA Technical Reports Server (NTRS)

1998-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is shown approximately 20 and 60 minutes after the start of an experiment on STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Mechanics of Granular Materials Test Cell

NASA Technical Reports Server (NTRS)

1998-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is shown from all three sides by its video camera during STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Non-Newtonian behavior observed via dynamic rheology for various particle types in energetic materials and simulant composites

NASA Astrophysics Data System (ADS)

Choi, Jong Han; Lee, Sangmook; Lee, Jae Wook

2017-02-01

The rheological properties of polymer composites highly filled with different filler materials were examined using a stress-controlled rheometer with a parallel-plate configuration, for particle characterization of the filler materials in plastic (polymer) bonded explosive (PBX). Ethylene vinyl acetate (EVA) with dioctyl adipate (DOA) was used as the matrix phase, which was shown to exhibit Newtonian-like behavior. The dispersed phase consisted of one of two energetic materials, i.e., explosive cyclotrimethylene trinitramine (RDX) or cyclotetramethylene tetranitramine (HMX), or a simulant (Dechlorane) in a bimodal size distribution. Before the test, preshearing was conducted to identify the initial condition of each sample. All examined filled polymer specimens exhibited yield stress and shear-thinning behavior over the investigated frequency range. The complex viscosity dependence on the dynamic oscillation frequency was also fitted using an appropriate rheological model, suggesting the model parameters. Furthermore, the temperature dependency of the different filler particle types was determined for different filler volume fractions. These comparative studies revealed the influence of the particle characteristics on the rheological properties of the filled polymer.

The Effect of Salt on the Complex Coacervation of Vinyl Polyelectrolytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perry, Sarah; Li, Yue; Priftis, Dimitrios

2014-06-01

Complex coacervation is an electrostatically-driven phase separation phenomenon that is utilized in a wide range of everyday applications and is of great interest for the creation of self-assembled materials. Here, we utilized turbidity to characterize the effect of salt type on coacervate formation using two vinyl polyelectrolytes, poly(acrylic acid sodium salt) (pAA) and poly(allylamine hydrochloride) (pAH), as simple models for industrial and biological coacervates. We confirmed the dominant role of salt valence on the extent of coacervate formation, while demonstrating the presence of significant secondary effects, which can be described by Hofmeister-like behavior. These results revealed the importance of ion-specificmore » interactions, which are crucial for the informed design of coacervate-based materials for use in complex ionic environments, and can enable more detailed theoretical investigations on the role of subtle electrostatic and thermodynamic effects in complex coacervation.« less

Investigate the complex process in particle-fluid based surface generation technology using reactive molecular dynamics method

NASA Astrophysics Data System (ADS)

Han, Xuesong; Li, Haiyan; Zhao, Fu

2017-07-01

Particle-fluid based surface generation process has already become one of the most important materials processing technology for many advanced materials such as optical crystal, ceramics and so on. Most of the particle-fluid based surface generation technology involves two key process: chemical reaction which is responsible for surface softening; physical behavior which is responsible for materials removal/deformation. Presently, researchers cannot give a reasonable explanation about the complex process in the particle-fluid based surface generation technology because of the small temporal-spatial scale and the concurrent influence of physical-chemical process. Molecular dynamics (MD) method has already been proved to be a promising approach for constructing effective model of atomic scale phenomenon and can serve as a predicting simulation tool in analyzing the complex surface generation mechanism and is employed in this research to study the essence of surface generation. The deformation and piles of water molecule is induced with the feeding of abrasive particle which justifies the property mutation of water at nanometer scale. There are little silica molecule aggregation or materials removal because the water-layer greatly reduce the strength of mechanical interaction between particle and materials surface and minimize the stress concentration. Furthermore, chemical effect is also observed at the interface: stable chemical bond is generated between water and silica which lead to the formation of silconl and the reaction rate changes with the amount of water molecules in the local environment. Novel ring structure is observed in the silica surface and it is justified to be favored of chemical reaction with water molecule. The siloxane bond formation process quickly strengthened across the interface with the feeding of abrasive particle because of the compressive stress resulted by the impacting behavior.

Thermomechanical deformation testing and modeling in the presence of metallurgical instabilities. M.S. Thesis - Akron Univ. Final Report

NASA Technical Reports Server (NTRS)

Castelli, Michael G.

1990-01-01

A number of viscoplastic constitutive models were developed to describe deformation behavior under complex combinations of thermal and mechanical loading. Questions remain, however, regarding the validity of procedures used to characterize these models for specific structural alloys. One area of concern is that the majority of experimental data available for this purpose are determined under isothermal conditions. This experimental study is aimed at determining whether viscoplastic constitutive theories characterized using an isothermal data base can adequately model material response under the complex thermomechanical loading conditions typical of power generation service. The approach adopted was to conduct a series of carefully controlled thermomechanical experiments on a nickel-based superalloy, Hastelloy Alloy X. Previous investigations had shown that this material experiences metallurgical instabilities leading to complex hardening behavior, termed dynamic strain aging. Investigating this phenomenon under full thermomechanical conditions leads to a number of challenging experimental difficulties which up to the present work were unresolved. To correct this situation, a number of advances were made in thermomechanical testing techniques. Advanced methods for dynamic temperature gradient control, phasing control and thermal strain compensation were developed and incorporated into real time test control software. These advances allowed the thermomechanical data to be analyzed with minimal experimental uncertainty. The thermomechanical results were evaluated on both a phenomenological and microstructural basis. Phenomenological results revealed that the thermomechanical hardening trends were not bounded by those displayed under isothermal conditions. For the case of Hastelloy Alloy X (and similar dynamic strain aging materials), this strongly suggests that some form of thermomechanical testing is necessary when characterizing a thermoviscoplastic deformation model. Transmission electron microscopy was used to study the microstructural physics, and analyze the unique phenomenological behavior.

Micro-scale investigation on the quasi-static behavior of granular material

NASA Astrophysics Data System (ADS)

Li, Xia

Granular material exhibits complex responses when subjected to various external loading. Fundamental mechanisms have not been well established so far, including that about the critical state, one of the most important concepts in the modern soil mechanics. With the recognition that granular material is discrete in nature, the basic understanding can only be obtained from the particle scale. The complexity in granular material behavior lies in the fact that the macroscopic behavior of granular material is determined by not only the interactions operating at contacts, but also how the particles become arranged in space to form an internal structure. This research is aimed to microscopically investigate the influence of the internal structure and the fundamental mechanism about the critical state. In view of the extensive laboratory test data already available in the literature, a numerical simulation method, DEM, is employed as the tool to conduct particle-scale investigations. The contact model for two in-contact circular disks is derived theoretically from the elasticity theory, and the result is a linear contact model with constant stiffness and lateral sliding. Based on the contact model, a systematic series of numerical tests has been implemented, and the results can successfully reproduce the main characteristics in the behavior of natural granular material, under various loading conditions. The macro-micro relationship is the link between the investigations at the two worlds. The key point is to describe the internal structure with the two dual cell systems, a particle cell system and a void cell system. Based on these two systems, the stress and strain in a uniform field are equivalently expressed in terms of the contact forces/relative displacements, and the micro-geometrical variables. With the microstructural definition of the stress tensor, the stress state of granular material is studied microscopically. The stress-fabric-force relation is derived, based on the variables describing the statistics of the contact forces and the contact vectors. By studying the evolution of the micro-quantities during shearing, how the internal structure affects the macro stress state under different loading condition is revealed. With the assumption that the influence of the local variance in stress is ignorable, the response of granular material can be investigated based on the void cell system. Starting from the behavior of a single void cell, the evolutions of the internal structure and its influence on the response of granular material are explained. The stress ratio and the dilatancy behavior of granular material are investigated. The influences of the void ratio, the mean normal stress and the drainage condition are discussed. The fundamental mechanism of the critical state is studied in the framework of thermodynamics with properly considering the influence of the internal structure. The normalized stress ratio tensor at critical state is associated with the critical void cell anisotropy, corresponding to the maximal energy dissipation. The (e, p) relationship at critical state is associated with the critical combination of the void cell size and the contact interactions, corresponding to the minimal free energy. The investigation on the influence of the internal structure anisotropy on the granular material behavior and the critical state is carried out. The results show that at small strain levels, the behavior of granular material is mainly affected by the initial fabric. As shearing continuous, the internal structure of granular material is gradually changed. The granular material approaches the critical state, which is irrespective with the initial internal structure. The critical state of granular material is not unique. With different loading modes, the critical state of granular material, including both the critical stress ratio and the critical (e, p) relations, are found to be different. A fabric tensor is defined based on the characteristics of the void cells. The laboratory method to quantify the fabric anisotropy is proposed by deviatoric shearing. 3D numerical simulations have been carried out to investigate the influence of the loading mode, which is found to be an important factor in the large strain behavior of granular material. With the obtained microscopic understanding, the influence of contact model on granular material behavior is investigated. A method to quantify the fabric anisotropy is proposed. And a simple discussion on the state variable used in the elasto-plastic constitutive model is given.

Thermal - Hydraulic Behavior of Unsaturated Bentonite and Sand-Bentonite Material as Seal for Nuclear Waste Repository: Numerical Simulation of Column Experiments

NASA Astrophysics Data System (ADS)

Ballarini, E.; Graupner, B.; Bauer, S.

2015-12-01

For deep geological repositories of high-level radioactive waste (HLRW), bentonite and sand bentonite mixtures are investigated as buffer materials to form a a sealing layer. This sealing layer surrounds the canisters and experiences an initial drying due to the heat produced by HLRW and a successive re-saturation with fluid from the host rock. These complex thermal, hydraulic and mechanical processes interact and were investigated in laboratory column experiments using MX-80 clay pellets as well as a mixture of 35% sand and 65% bentonite. The aim of this study is to both understand the individual processes taking place in the buffer materials and to identify the key physical parameters that determine the material behavior under heating and hydrating conditions. For this end, detailed and process-oriented numerical modelling was applied to the experiments, simulating heat transport, multiphase flow and mechanical effects from swelling. For both columns, the same set of parameters was assigned to the experimental set-up (i.e. insulation, heater and hydration system), while the parameters of the buffer material were adapted during model calibration. A good fit between model results and data was achieved for temperature, relative humidity, water intake and swelling pressure, thus explaining the material behavior. The key variables identified by the model are the permeability and relative permeability, the water retention curve and the thermal conductivity of the buffer material. The different hydraulic and thermal behavior of the two buffer materials observed in the laboratory observations was well reproduced by the numerical model.

Impedance spectroscopy and electric modulus behavior of Molybdenum doped Cobalt-Zinc ferrite

NASA Astrophysics Data System (ADS)

Pradhan, A. K.; Nath, T. K.; Saha, S.

2017-07-01

The complex impedance spectroscopy and the electric modulus of Mo doped Cobalt-Zinc inverse spinel ferrite has been investigated in detail. The conventional ceramic technique has been used to prepare the CZMO. The HRXRD technique has been used to study the structural analysis which confirms the inverse spinel structure of the material and also suggest the material have Fd3m space group. The complex impedance spectroscopic data and the electric modulus formalism have been used to understand the dielectric relaxation and conduction process. The contribution of grain and grain boundary in the electrical conduction process of CZMO has been confirmed from the Cole-Cole plot. The activation energy is calculated from both the IS (Impedance Spectroscopy) and electric modulus formalism and found to be nearly same for the materials.

Machanics of Granular Materials (MGM) Investigator

NASA Technical Reports Server (NTRS)

2000-01-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment include Khalid Alshibli, project scientist at NASA's Marshall Space Flight Center (MSFC). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: MSFC).

Microgravity

NASA Image and Video Library

1998-01-25

Astronaut James Reilly uses a laptop computer monitor the Mechanics of Granular Materials (MGM) experiment during STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Microgravity

NASA Image and Video Library

1996-09-18

Astronaut Carl Walz installs Mechanics of Granular Materials (MGM) test cell on STS-79. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/John Space Center

Time-domain damping models in structural acoustics using digital filtering

NASA Astrophysics Data System (ADS)

Parret-Fréaud, Augustin; Cotté, Benjamin; Chaigne, Antoine

2016-02-01

This paper describes a new approach in order to formulate well-posed time-domain damping models able to represent various frequency domain profiles of damping properties. The novelty of this approach is to represent the behavior law of a given material directly in a discrete-time framework as a digital filter, which is synthesized for each material from a discrete set of frequency-domain data such as complex modulus through an optimization process. A key point is the addition of specific constraints to this process in order to guarantee stability, causality and verification of thermodynamics second law when transposing the resulting discrete-time behavior law into the time domain. Thus, this method offers a framework which is particularly suitable for time-domain simulations in structural dynamics and acoustics for a wide range of materials (polymers, wood, foam, etc.), allowing to control and even reduce the distortion effects induced by time-discretization schemes on the frequency response of continuous-time behavior laws.

Numerically stable finite difference simulation for ultrasonic NDE in anisotropic composites

NASA Astrophysics Data System (ADS)

Leckey, Cara A. C.; Quintanilla, Francisco Hernando; Cole, Christina M.

2018-04-01

Simulation tools can enable optimized inspection of advanced materials and complex geometry structures. Recent work at NASA Langley is focused on the development of custom simulation tools for modeling ultrasonic wave behavior in composite materials. Prior work focused on the use of a standard staggered grid finite difference type of mathematical approach, by implementing a three-dimensional (3D) anisotropic Elastodynamic Finite Integration Technique (EFIT) code. However, observations showed that the anisotropic EFIT method displays numerically unstable behavior at the locations of stress-free boundaries for some cases of anisotropic materials. This paper gives examples of the numerical instabilities observed for EFIT and discusses the source of instability. As an alternative to EFIT, the 3D Lebedev Finite Difference (LFD) method has been implemented. The paper briefly describes the LFD approach and shows examples of stable behavior in the presence of stress-free boundaries for a monoclinic anisotropy case. The LFD results are also compared to experimental results and dispersion curves.

Installing Mechanics of Granular Materials (MGM) experiment Test Cell

NASA Technical Reports Server (NTRS)

1996-01-01

Astronaut Jay Apt installs Mechanics of Granular Materials (MGM0 test cell on STS-79. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: NASA/John Space Center).

Mechanics of Granular Materials labeled hardware

NASA Technical Reports Server (NTRS)

2000-01-01

Mechanics of Granular Materials (MGM) flight hardware takes two twin double locker assemblies in the Space Shuttle middeck or the Spacehab module. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: NASA/MSFC).

Interconversion of dynamic modulus to creep compliance and relaxation modulus : numerical modeling and laboratory validation - final report.

DOT National Transportation Integrated Search

2016-09-01

Viscoelastic material functions such as time domain functions, such as, relaxation modulus and creep compliance, : or frequency domain function, such as, complex modulus can be used to characterize the linear viscoelastic behavior : of asphalt concre...

Artifacts as Authoritative Actors in Educational Reform

ERIC Educational Resources Information Center

März, Virginie; Kelchtermans, Geert; Vermeir, Karen

2017-01-01

Educational reforms are often translated in and implemented through artifacts. Although research has frequently treated artifacts as merely functional, more recent work acknowledges the complex relationship between material artifacts and human/organizational behavior. This article aims at disentangling this relationship in order to deepen our…

Measurement of Sticky Point Temperature of Coffee Powder with a Rheometer

USDA-ARS?s Scientific Manuscript database

Sticky point temperature (Ts) measurement for hygroscopic food and biomaterial powders is traditionally performed with complex glass instruments. This property is used to characterize material stickiness, which substantially affects the flow and physical behavior of powders. In this research study w...

Capturing the Complexity of Additively Manufactured Microstructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Livescu, Veronica; Bronkhorst, Curt Allan; Vander Wiel, Scott Alan

2016-05-12

The underlying mechanisms and kinetics controlling damage nucleation and growth as a function of material microstructure and loading paths are discussed. These experiments indicate that structural features such as grain boundaries, grain size distribution, grain morphology crystallographic texture are all factors that influence mechanical behavior.

Design Considerations for Developing Biodegradable Magnesium Implants

NASA Astrophysics Data System (ADS)

Brar, Harpreet S.; Keselowsky, Benjamin G.; Sarntinoranont, Malisa; Manuel, Michele V.

The integration of biodegradable and bioabsorbable magnesium implants into the human body is a complex undertaking that faces major challenges. The complexity arises from the fact that biomaterials must meet both engineering and physiological requirements to ensure the desired properties. Historically, efforts have been focused on the behavior of commercial magnesium alloys in biological environments and their resultant effect on cell-mediated processes. Developing causal relationships between alloy chemistry and micro structure, and its effect on cellular behavior can be a difficult and time intensive process. A systems design approach driven by thermodynamics has the power to provide significant contributions in developing the next generation of magnesium alloy implants with controlled degradability, biocompatibility, and optimized mechanical properties, at reduced time and cost. This approach couples experimental research with theory and mechanistic modeling for the accelerated development of materials. The aim of this article is to enumerate this strategy, design considerations and hurdles for developing new magnesium alloys for use as biodegradable implant materials [1].

Sensitivity of corneal biomechanical and optical behavior to material parameters using design of experiments method.

PubMed

Xu, Mengchen; Lerner, Amy L; Funkenbusch, Paul D; Richhariya, Ashutosh; Yoon, Geunyoung

2018-02-01

The optical performance of the human cornea under intraocular pressure (IOP) is the result of complex material properties and their interactions. The measurement of the numerous material parameters that define this material behavior may be key in the refinement of patient-specific models. The goal of this study was to investigate the relative contribution of these parameters to the biomechanical and optical responses of human cornea predicted by a widely accepted anisotropic hyperelastic finite element model, with regional variations in the alignment of fibers. Design of experiments methods were used to quantify the relative importance of material properties including matrix stiffness, fiber stiffness, fiber nonlinearity and fiber dispersion under physiological IOP. Our sensitivity results showed that corneal apical displacement was influenced nearly evenly by matrix stiffness, fiber stiffness and nonlinearity. However, the variations in corneal optical aberrations (refractive power and spherical aberration) were primarily dependent on the value of the matrix stiffness. The optical aberrations predicted by variations in this material parameter were sufficiently large to predict clinically important changes in retinal image quality. Therefore, well-characterized individual variations in matrix stiffness could be critical in cornea modeling in order to reliably predict optical behavior under different IOPs or after corneal surgery.

Determination of elastomeric foam parameters for simulations of complex loading.

PubMed

Petre, M T; Erdemir, A; Cavanagh, P R

2006-08-01

Finite element (FE) analysis has shown promise for the evaluation of elastomeric foam personal protection devices. Although appropriate representation of foam materials is necessary in order to obtain realistic simulation results, material definitions used in the literature vary widely and often fail to account for the multi-mode loading experienced by these devices. This study aims to provide a library of elastomeric foam material parameters that can be used in FE simulations of complex loading scenarios. Twelve foam materials used in footwear were tested in uni-axial compression, simple shear and volumetric compression. For each material, parameters for a common compressible hyperelastic material model used in FE analysis were determined using: (a) compression; (b) compression and shear data; and (c) data from all three tests. Material parameters and Drucker stability limits for the best fits are provided with their associated errors. The material model was able to reproduce deformation modes for which data was provided during parameter determination but was unable to predict behavior in other deformation modes. Simulation results were found to be highly dependent on the extent of the test data used to determine the parameters in the material definition. This finding calls into question the many published results of simulations of complex loading that use foam material parameters obtained from a single mode of testing. The library of foam parameters developed here presents associated errors in three deformation modes that should provide for a more informed selection of material parameters.

Nanomechanics of silk: the fundamentals of a strong, tough and versatile material

NASA Astrophysics Data System (ADS)

Su, Isabelle; Buehler, Markus J.

2016-07-01

Spider silk is a remarkable material that provides a template for upscaling molecular properties to the macroscale. In this article we review fundamental aspects of the mechanisms behind these behaviors, discuss the molecular makeup, chemical designs, and how these integrate in a complex arrangement to form webs, cocoons and other material architectures. Moreover, this review paper explores the unique ability of silk to tolerate various kinds of defects, in a way enabling this material platform to serve as one of the most resilient materials in nature. We conclude the discussion with a summary of key scaling laws, an attempt model and define hierarchical length-scales, and the translation to synthetic materials.

Nanomechanics of silk: the fundamentals of a strong, tough and versatile material.

PubMed

Su, Isabelle; Buehler, Markus J

2016-07-29

Spider silk is a remarkable material that provides a template for upscaling molecular properties to the macroscale. In this article we review fundamental aspects of the mechanisms behind these behaviors, discuss the molecular makeup, chemical designs, and how these integrate in a complex arrangement to form webs, cocoons and other material architectures. Moreover, this review paper explores the unique ability of silk to tolerate various kinds of defects, in a way enabling this material platform to serve as one of the most resilient materials in nature. We conclude the discussion with a summary of key scaling laws, an attempt model and define hierarchical length-scales, and the translation to synthetic materials.

Battery designs with high capacity anode materials and cathode materials

DOEpatents

Masarapu, Charan; Anguchamy, Yogesh Kumar; Han, Yongbong; Deng, Haixia; Kumar, Sujeet; Lopez, Herman A.

2017-10-03

Improved high energy capacity designs for lithium ion batteries are described that take advantage of the properties of high specific capacity anode active compositions and high specific capacity cathode active compositions. In particular, specific electrode designs provide for achieving very high energy densities. Furthermore, the complex behavior of the active materials is used advantageously in a radical electrode balancing design that significantly reduced wasted electrode capacity in either electrode when cycling under realistic conditions of moderate to high discharge rates and/or over a reduced depth of discharge.

Thermoviscoplastic nonlinear constitutive relationships for structural analysis of high temperature metal matrix composites

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Hopkins, D. A.

1985-01-01

A set of thermoviscoplastic nonlinear constitutive relationships (1VP-NCR) is presented. The set was developed for application to high temperature metal matrix composites (HT-MMC) and is applicable to thermal and mechanical properties. Formulation of the TVP-NCR is based at the micromechanics level. The TVP-NCR are of simple form and readily integrated into nonlinear composite structural analysis. It is shown that the set of TVP-NCR is computationally effective. The set directly predicts complex materials behavior at all levels of the composite simulation, from the constituent materials, through the several levels of composite mechanics, and up to the global response of complex HT-MMC structural components.

Insights to regenerate materials: learning from nature

NASA Astrophysics Data System (ADS)

García-Aznar, J. M.; Valero, C.; Gómez-Benito, M. J.; Javierre, E.

2016-08-01

Self-healing materials, both biological and engineered, integrate the ability to repair themselves and recover their functionality using the resources inherently available to them. Although significant advances have been made, in recent years, for the design of different concepts of self-healing materials, this work aims to provide some insights into how living materials are able to regenerate or heal when a fracture or injury occurs. The main sensors that regulate this adaptive and regenerative behavior are the cells. These are able to sense the mechanical alterations in their surroundings and regulate their activity in order to remove dead tissue and/or create new tissue. Therefore, understanding how cells are able to regenerate tissues under complex and multiphysics conditions can define the biomimetics guidelines to heal through inert or traditional engineering materials. In this work, we present a combination of experiments and different kinds of multiscale and multiphysics models in order to understand how mechanics regulate some mechanisms at cell and tissue level. This combination of results aims to gain insight into the development of novel strategies for self-healing materials, mimicking the behavior induced by cells and biological tissues.

Humane Education: Resource Guide. A Guide for Elementary School Teachers.

ERIC Educational Resources Information Center

New York City Board of Education, Brooklyn, NY. Div. of Curriculum and Instruction.

Humane education promotes responsible behavior and improves the quality of life for animals and humans. Teaching the humane treatment of animals is a complex, philosophical, and values-oriented subject. Lessons for each grade level have performance objectives, materials, and activities. Student activity sheets are provided for follow-up…

Mechanics of Granular Materials (MGM0 Flight Hardware in Bench Test

NASA Technical Reports Server (NTRS)

2000-01-01

Engineering bench system hardware for the Mechanics of Granular Materials (MGM) experiment is tested on a lab bench at the University of Colorado in Boulder. This is done in a horizontal arrangement to reduce pressure differences so the tests more closely resemble behavior in the microgravity of space. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Calculation of thermomechanical fatigue life based on isothermal behavior

NASA Technical Reports Server (NTRS)

Halford, Gary R.; Saltsman, James F.

1987-01-01

The isothermal and thermomechanical fatigue (TMF) crack initiation response of a hypothetical material was analyzed. Expected thermomechanical behavior was evaluated numerically based on simple, isothermal, cyclic stress-strain - time characteristics and on strainrange versus cyclic life relations that have been assigned to the material. The attempt was made to establish basic minimum requirements for the development of a physically accurate TMF life-prediction model. A worthy method must be able to deal with the simplest of conditions: that is, those for which thermal cycling, per se, introduces no damage mechanisms other than those found in isothermal behavior. Under these assumed conditions, the TMF life should be obtained uniquely from known isothermal behavior. The ramifications of making more complex assumptions will be dealt with in future studies. Although analyses are only in their early stages, considerable insight has been gained in understanding the characteristics of several existing high-temperature life-prediction methods. The present work indicates that the most viable damage parameter is based on the inelastic strainrange.

A Unified Approach for Modeling Inelastic Behavior of Structural Metals under Complex Cyclic Loadings.

DTIC Science & Technology

1977-05-01

this report are not to be used for advertising , publication, or promotional purposes. Citat ion of trade names does not constitute an off icial... Vs . Real Materials 3 PLASTIC HYSTERESIS PHENOMENA 12 Observed Transient Phenomena Analysis of Hysteresis Loops Observed Typical Yie ld Range...strain or stress amp litude). Fitr examp le , if varm m uus sited hyshet esis loops produced by the model a me super- Memory Modei Vs . Real Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ceder, Gerbrand

Novel materials are often the enabler for new energy technologies. In ab-initio computational materials science, method are developed to predict the behavior of materials starting from the laws of physics, so that properties can be predicted before compounds have to be synthesized and tested. As such, a virtual materials laboratory can be constructed, saving time and money. The objectives of this program were to develop first-principles theory to predict the structure and thermodynamic stability of materials. Since its inception the program focused on the development of the cluster expansion to deal with the increased complexity of complex oxides. This researchmore » led to the incorporation of vibrational degrees of freedom in ab-initio thermodynamics, developed methods for multi-component cluster expansions, included the explicit configurational degrees of freedom of localized electrons, developed the formalism for stability in aqueous environments, and culminated in the first ever approach to produce exact ground state predictions of the cluster expansion. Many of these methods have been disseminated to the larger theory community through the Materials Project, pymatgen software, or individual codes. We summarize three of the main accomplishments.« less

Biomechanical validation of an artificial tooth–periodontal ligament–bone complex for in vitro orthodontic load measurement

PubMed Central

Xia, Zeyang; Chen, Jie

2014-01-01

Objectives To develop an artificial tooth–periodontal ligament (PDL)–bone complex (ATPBC) that simulates clinical crown displacement. Material and Methods An ATPBC was created. It had a socket hosting a tooth with a thin layer of silicon mixture in between for simulating the PDL. The complex was attached to a device that allows applying a controlled force to the crown and measuring the resulting crown displacement. Crown displacements were compared to previously published data for validation. Results The ATPBC that had a PDL made of two types of silicones, 50% gasket sealant No. 2 and 50% RTV 587 silicone, with a thickness of 0.3 mm, simulated the PDL well. The mechanical behaviors (1) force-displacement relationship, (2) stress relaxation, (3) creep, and (4) hysteresis were validated by the published results. Conclusion The ATPBC simulated the crown displacement behavior reported from biological studies well. PMID:22970752

A Hybrid Methacrylate-Sodium Carboxymethylcellulose Interpolyelectrolyte Complex: Rheometry and in Silico Disposition for Controlled Drug Release

PubMed Central

Ngwuluka, Ndidi Chinyelu; Choonara, Yahya Essop; Kumar, Pradeep; Modi, Girish; du Toit, Lisa Claire; Pillay, Viness

2013-01-01

The rheological behavioral changes that occurred during the synthesis of an interpolyelectrolyte complex (IPEC) of methacrylate copolymer and sodium carboxymethylcellulose were assessed. These changes were compared with the rheological behavior of the individual polymers employing basic viscosity, yield stress, stress sweep, frequency sweep, temperature ramp as well as creep and recovery testing. The rheological studies demonstrated that the end-product of the complexation of low viscous methacrylate copolymer and entangled solution of sodium carboxymethylcellulose generated a polymer, which exhibited a solid-like behavior with a three-dimensional network. Additionally, the rheological profile of the sodium carboxymethylcellulose and methacrylate copolymer with respect to the effect of various concentrations of acetic acid on the synthesis of the IPEC was elucidated using molecular mechanics energy relationships (MMER) by exploring the spatial disposition of carboxymethylcellulose and methacrylate copolymer with respect to each other and acetic acid. The computational results corroborated well with the experimental in vitro drug release data. Results have shown that the IPEC may be suitable polymeric material for achieving controlled zero-order drug delivery. PMID:28788332

Mechanics of Granular Materials (MGM) Test Cell

NASA Technical Reports Server (NTRS)

2000-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the compressed sand column with the protective water jacket removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Mechanics of Granular Materials (MGM) Cell

NASA Technical Reports Server (NTRS)

1996-01-01

One of three Mechanics of Granular Materials (MGM) test cells after flight on STS-79 and before impregnation with resin. Note that the sand column has bulged in the middle, and that the top of the column is several inches lower than the top of the plastic enclosure. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Mechanics of Granular Materials (MGM) Test Cell

NASA Technical Reports Server (NTRS)

2000-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the top of the sand column with the metal platten removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Wormlike micelle formation by acylglutamic acid with alkylamines.

PubMed

Sakai, Kenichi; Nomura, Kazuyuki; Shrestha, Rekha Goswami; Endo, Takeshi; Sakamoto, Kazutami; Sakai, Hideki; Abe, Masahiko

2012-12-21

Rheological properties of alkyl dicarboxylic acid-alkylamine complex systems have been characterized. The complex materials employed in this study consist of an amino acid-based surfactant (dodecanoylglutamic acid, C12Glu) and a tertiary alkylamine (dodecyldimethylamine, C12DMA) or a secondary alkylamine (dodecylmethylamine, C12MA). (1)H NMR and mass spectroscopic data have suggested that C12Glu forms a stoichiometric 1:1 complex with C12DMA and C12MA. Rheological measurements have suggested that the complex systems yield viscoelastic wormlike micellar solutions and the rheological behavior is strongly dependent on the aqueous solution pH. This pH-dependent behavior results from the structural transformation of the wormlike micelles to occur in the narrow pH range 5.5-6.2 (in the case of C12Glu-C12DMA system); i.e., positive curved aggregates such as spherical or rodlike micelles tend to be formed at high pH values. Our current study offers a unique way to obtain viscoelastic wormlike micellar solutions by means of alkyl dicarboxylic acid-alkylamine complex as gemini-like amphiphiles.

Computational characterization of ordered nanostructured surfaces

NASA Astrophysics Data System (ADS)

Mohieddin Abukhdeir, Nasser

2016-08-01

A vital and challenging task for materials researchers is to determine relationships between material characteristics and desired properties. While the measurement and assessment of material properties can be complex, quantitatively characterizing their structure is frequently a more challenging task. This issue is magnified for materials researchers in the areas of nanoscience and nanotechnology, where material structure is further complicated by phenomena such as self-assembly, collective behavior, and measurement uncertainty. Recent progress has been made in this area for both self-assembled and nanostructured surfaces due to increasing accessibility of imaging techniques at the nanoscale. In this context, recent advances in nanomaterial surface structure characterization are reviewed including the development of new theory and image processing methods.

Linear analysis using secants for materials with temperature dependent nonlinear elastic modulus and thermal expansion properties

NASA Astrophysics Data System (ADS)

Pepi, John W.

2017-08-01

Thermally induced stress is readily calculated for linear elastic material properties using Hooke's law in which, for situations where expansion is constrained, stress is proportional to the product of the material elastic modulus and its thermal strain. When material behavior is nonlinear, one needs to make use of nonlinear theory. However, we can avoid that complexity in some situations. For situations in which both elastic modulus and coefficient of thermal expansion vary with temperature, solutions can be formulated using secant properties. A theoretical approach is thus presented to calculate stresses for nonlinear, neo-Hookean, materials. This is important for high acuity optical systems undergoing large temperature extremes.

Biology of Nanobots

NASA Astrophysics Data System (ADS)

Duan, Wentao; Pavlick, Ryan; Sen, Ayusman

2013-12-01

One of the more interesting recent discoveries has been the ability to design nano/microbots which catalytically harness the chemical energy in their environment to move autonomously. Their potential applications include delivery of materials, self-assembly of superstructures, and roving sensors. One emergent area of research is the study of their collective behavior and how they emulate living systems. The aim of this chapter is to describe the "biology" of nanobots, summarizing the fundamentals physics behind their motion and how the bots interact with each other to initiate complex emergent behavior.

Network-induced oscillatory behavior in material flow networks and irregular business cycles

NASA Astrophysics Data System (ADS)

Helbing, Dirk; Lämmer, Stefen; Witt, Ulrich; Brenner, Thomas

2004-11-01

Network theory is rapidly changing our understanding of complex systems, but the relevance of topological features for the dynamic behavior of metabolic networks, food webs, production systems, information networks, or cascade failures of power grids remains to be explored. Based on a simple model of supply networks, we offer an interpretation of instabilities and oscillations observed in biological, ecological, economic, and engineering systems. We find that most supply networks display damped oscillations, even when their units—and linear chains of these units—behave in a nonoscillatory way. Moreover, networks of damped oscillators tend to produce growing oscillations. This surprising behavior offers, for example, a different interpretation of business cycles and of oscillating or pulsating processes. The network structure of material flows itself turns out to be a source of instability, and cyclical variations are an inherent feature of decentralized adjustments.

Debris-carrying camouflage among diverse lineages of Cretaceous insects.

PubMed

Wang, Bo; Xia, Fangyuan; Engel, Michael S; Perrichot, Vincent; Shi, Gongle; Zhang, Haichun; Chen, Jun; Jarzembowski, Edmund A; Wappler, Torsten; Rust, Jes

2016-06-01

Insects have evolved diverse methods of camouflage that have played an important role in their evolutionary success. Debris-carrying, a behavior of actively harvesting and carrying exogenous materials, is among the most fascinating and complex behaviors because it requires not only an ability to recognize, collect, and carry materials but also evolutionary adaptations in related morphological characteristics. However, the fossil record of such behavior is extremely scarce, and only a single Mesozoic example from Spanish amber has been recorded; therefore, little is known about the early evolution of this complicated behavior and its underlying anatomy. We report a diverse insect assemblage of exceptionally preserved debris carriers from Cretaceous Burmese, French, and Lebanese ambers, including the earliest known chrysopoid larvae (green lacewings), myrmeleontoid larvae (split-footed lacewings and owlflies), and reduviids (assassin bugs). These ancient insects used a variety of debris material, including insect exoskeletons, sand grains, soil dust, leaf trichomes of gleicheniacean ferns, wood fibers, and other vegetal debris. They convergently evolved their debris-carrying behavior through multiple pathways, which expressed a high degree of evolutionary plasticity. We demonstrate that the behavioral repertoire, which is associated with considerable morphological adaptations, was already widespread among insects by at least the Mid-Cretaceous. Together with the previously known Spanish specimen, these fossils are the oldest direct evidence of camouflaging behavior in the fossil record. Our findings provide a novel insight into early evolution of camouflage in insects and ancient ecological associations among plants and insects.

Iron chalcogenide superconductors at high magnetic fields

PubMed Central

Lei, Hechang; Wang, Kefeng; Hu, Rongwei; Ryu, Hyejin; Abeykoon, Milinda; Bozin, Emil S; Petrovic, Cedomir

2012-01-01

Iron chalcogenide superconductors have become one of the most investigated superconducting materials in recent years due to high upper critical fields, competing interactions and complex electronic and magnetic phase diagrams. The structural complexity, defects and atomic site occupancies significantly affect the normal and superconducting states in these compounds. In this work we review the vortex behavior, critical current density and high magnetic field pair-breaking mechanism in iron chalcogenide superconductors. We also point to relevant structural features and normal-state properties. PMID:27877518

Optimization of Microporous Carbon Structures for Lithium-Sulfur Battery Applications in Carbonate-Based Electrolyte.

PubMed

Hu, Lei; Lu, Yue; Li, Xiaona; Liang, Jianwen; Huang, Tao; Zhu, Yongchun; Qian, Yitai

2017-03-01

Developing appropriate sulfur cathode materials in carbonate-based electrolyte is an important research subject for lithium-sulfur batteries. Although several microporous carbon materials as host for sulfur reveal the effect, methods for producing microporous carbon are neither easy nor well controllable. Moreover, due to the complexity and limitation of microporous carbon in their fabrication process, there has been rare investigation of influence on electrochemical behavior in the carbonate-based electrolyte for lithium-sulfur batteries by tuning different micropore size(0-2 nm) of carbon host. Here, we demonstrate an immediate carbonization process, self-activation strategy, which can produce microporous carbon for a sulfur host from alkali-complexes. Besides, by changing different alkali-ion in the previous complex, the obtained microporous carbon exhibits a major portion of ultramicropore (<0.7 nm, from 54.9% to 25.8%) and it is demonstrated that the micropore structure of the host material plays a vital role in confining sulfur molecule. When evaluated as cathode materials in a carbonate-based electrolyte for Li-S batteries, such microporous carbon/sulfur composite can provide high reversible capacity, cycling stability and good rate capability. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interface Reactions and Synthetic Reaction of Composite Systems

PubMed Central

Park, Joon Sik; Kim, Jeong Min

2010-01-01

Interface reactions in composite systems often determine their overall properties, since product phases usually formed at interfaces during composite fabrication processing make up a large portion of the composites. Since most composite materials represent a ternary or higher order materials system, many studies have focused on analyses of diffusion phenomena and kinetics in multicomponent systems. However, the understanding of the kinetic behavior increases the complexity, since the kinetics of each component during interdiffusion reactions need to be defined for interpreting composite behaviors. From this standpoint, it is important to clarify the interface reactions for producing compatible interfaces with desired product phases. A thermodynamic evaluation such as a chemical potential of involving components can provide an understanding of the diffusion reactions, which govern diffusion pathways and product phase formation. A strategic approach for designing compatible interfaces is discussed in terms of chemical potential diagrams and interface morphology, with some material examples.

Adaptive and Resilient Soft Tensegrity Robots.

PubMed

Rieffel, John; Mouret, Jean-Baptiste

2018-04-17

Living organisms intertwine soft (e.g., muscle) and hard (e.g., bones) materials, giving them an intrinsic flexibility and resiliency often lacking in conventional rigid robots. The emerging field of soft robotics seeks to harness these same properties to create resilient machines. The nature of soft materials, however, presents considerable challenges to aspects of design, construction, and control-and up until now, the vast majority of gaits for soft robots have been hand-designed through empirical trial-and-error. This article describes an easy-to-assemble tensegrity-based soft robot capable of highly dynamic locomotive gaits and demonstrating structural and behavioral resilience in the face of physical damage. Enabling this is the use of a machine learning algorithm able to discover effective gaits with a minimal number of physical trials. These results lend further credence to soft-robotic approaches that seek to harness the interaction of complex material dynamics to generate a wealth of dynamical behaviors.

Microgravity

NASA Image and Video Library

2000-05-05

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the top of the sand column with the metal platten removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Microgravity

NASA Image and Video Library

2000-05-05

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the compressed sand column with the protective water jacket removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Microgravity

NASA Image and Video Library

1998-01-25

A test cell for Mechanics of Granular Materials (MGM) experiment is shown approximately 20 and 60 minutes after the start of an experiment on STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Mechanics of Granular Materials (MGM) Investigators

NASA Technical Reports Server (NTRS)

2000-01-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment at the University of Colorado at Boulder include Tawnya Ferbiak (software engineer), Susan Batiste (research assistant), and Christina Winkler (graduate research assistant). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Mechanic of Granular Materials (MGM) Investigator

NASA Technical Reports Server (NTRS)

2000-01-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment are Mark Lankton (Program Manager at University Colorado at Boulder), Susan Batiste (research assistance, UCB), and Stein Sture (principal investigator). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Dynamics of Charged Species in Ionic-Neutral Block Copolymer and Surfactant Complexes [Structural Relaxation and Dynamics of Ionic-Neutral Block Copolymer Surfactant Complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borreguero, Jose M.; Pincus, Philip A.; Sumpter, Bobby G.

Structure–property relationships of ionic block copolymer (BCP) surfactant complexes are critical toward the progress of favorable engineering design of efficient charge-transport materials. In this paper, molecular dynamics simulations are used to understand the dynamics of charged-neutral BCP and surfactant complexes. The dynamics are examined for two different systems: charged-neutral double-hydrophilic and hydrophobic–hydrophilic block copolymers with oppositely charged surfactant moieties. The dynamics of the surfactant head, tails, and charges are studied for five different BCP volume fractions. We observe that the dynamics of the different species solely depend on the balance between electrostatic and entropic interactions between the charged species andmore » the neutral monomers. The favorable hydrophobic–hydrophobic interactions and the unfavorable hydrophobic–hydrophilic interactions determine the mobilities of the monomers. The dynamical properties of the charge species influence complex formation. Structural relaxations exhibit length-scale dependent behavior, with slower relaxation at the radius of gyration length-scale and faster relaxation at the segmental length-scale, consistent with previous results. The dynamical analysis correlates ion-exchange kinetics to the self-assembly behavior of the complexes.« less

Dynamics of Charged Species in Ionic-Neutral Block Copolymer and Surfactant Complexes [Structural Relaxation and Dynamics of Ionic-Neutral Block Copolymer Surfactant Complexes

DOE PAGES

Borreguero, Jose M.; Pincus, Philip A.; Sumpter, Bobby G.; ...

2017-06-21

Structure–property relationships of ionic block copolymer (BCP) surfactant complexes are critical toward the progress of favorable engineering design of efficient charge-transport materials. In this paper, molecular dynamics simulations are used to understand the dynamics of charged-neutral BCP and surfactant complexes. The dynamics are examined for two different systems: charged-neutral double-hydrophilic and hydrophobic–hydrophilic block copolymers with oppositely charged surfactant moieties. The dynamics of the surfactant head, tails, and charges are studied for five different BCP volume fractions. We observe that the dynamics of the different species solely depend on the balance between electrostatic and entropic interactions between the charged species andmore » the neutral monomers. The favorable hydrophobic–hydrophobic interactions and the unfavorable hydrophobic–hydrophilic interactions determine the mobilities of the monomers. The dynamical properties of the charge species influence complex formation. Structural relaxations exhibit length-scale dependent behavior, with slower relaxation at the radius of gyration length-scale and faster relaxation at the segmental length-scale, consistent with previous results. The dynamical analysis correlates ion-exchange kinetics to the self-assembly behavior of the complexes.« less

Modeling the dynamic crush of impact mitigating materials

NASA Astrophysics Data System (ADS)

Logan, R. W.; McMichael, L. D.

1995-05-01

Crushable materials are commonly utilized in the design of structural components to absorb energy and mitigate shock during the dynamic impact of a complex structure, such as an automobile chassis or drum-type shipping container. The development and application of several finite-element material models which have been developed at various times at LLNL for DYNA3D are discussed. Between the models, they are able to account for several of the predominant mechanisms which typically influence the dynamic mechanical behavior of crushable materials. One issue we addressed was that no single existing model would account for the entire gambit of constitutive features which are important for crushable materials. Thus, we describe the implementation and use of an additional material model which attempts to provide a more comprehensive model of the mechanics of crushable material behavior. This model combines features of the pre-existing DYNA models and incorporates some new features as well in an invariant large-strain formulation. In addition to examining the behavior of a unit cell in uniaxial compression, two cases were chosen to evaluate the capabilities and accuracy of the various material models in DYNA. In the first case, a model for foam filled box beams was developed and compared to test data from a four-point bend test. The model was subsequently used to study its effectiveness in energy absorption in an aluminum extrusion, spaceframe, vehicle chassis. The second case examined the response of the AT-400A shipping container and the performance of the overpack material during accident environments selected from 10CFR71 and IAEA regulations.

Fused deposition of ceramics: A comprehensive experimental, analytical and computational study of material behavior, fabrication process and equipment design

NASA Astrophysics Data System (ADS)

Bellini, Anna

Customer-driven product customization and continued demand for cost and time savings have generated a renewed interest in agile manufacturing based on improvements on Rapid Prototyping (RP) technologies. The advantages of RP technologies are: (1) ability to shorten the product design and development time, (2) suitability for automation and decrease in the level of human intervention, (3) ability to build many geometrically complex shapes. A shift from "prototyping" to "manufacturing" necessitates the following improvements: (1) Flexibility in choice of materials; (2) Part integrity and built-in characteristics to meet performance requirements; (3) Dimensional stability and tolerances; (4) Improved surface finish. A project funded by ONR has been undertaken to develop an agile manufacturing technology for fabrication of ceramic and multi-component parts to meet various needs of the Navy, such as transducers, etc. The project is based on adaptation of a layered manufacturing concept since the program required that the new technology be developed based on a commercially available RP technology. Among various RP technologies available today, Fused Deposition Modeling (FDM) has been identified as the focus of this research because of its potential versatility in the choice of materials and deposition configuration. This innovative approach allows for designing and implementing highly complex internal architectures into parts through deposition of different materials in a variety of configurations in such a way that the finished product exhibit characteristics to meet the performance requirements. This implies that, in principle, one can tailor-make the assemble of materials and structures as per specifications of an optimum design. The program objectives can be achieved only through accurate process modeling and modeling of material behavior. Oftentimes, process modeling is based on some type of computational approach where as modeling of material behavior is based on extensive experimental investigations. Studies are conducted in the following categories: (1) Flow modeling during extrusion and deposition; (2) Thermal modeling; (3) Flow control during deposition; (4) Product characterization and property determination for dimensional analysis; (5) Development of a novel technology based on a mini-extrusion system. Studies in each of these stages have involved experimental as well as analytical approaches to develop a comprehensive modeling.

Structure and Function of Iron-Loaded Synthetic Melanin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yiwen; Xie, Yijun; Wang, Zhao

We describe a synthetic method for increasing and controlling the iron loading of synthetic melanin nanoparticles and use the resulting materials to perform a systematic quantitative investigation on their structure- property relationship. A comprehensive analysis by magnetometry, electron paramagnetic resonance, and nuclear magnetic relaxation dispersion reveals the complexities of their magnetic behavior and how these intraparticle magnetic interactions manifest in useful material properties such as their performance as MRI contrast agents. This analysis allows predictions of the optimal iron loading through a quantitative modeling of antiferromagnetic coupling that arises from proximal iron ions. This study provides a detailed understanding ofmore » this complex class of synthetic biomaterials and gives insight into interactions and structures prevalent in naturally occurring melanins.« less

Multiferroic behavior in CdCr2X4(X=S,Se)

NASA Astrophysics Data System (ADS)

Hemberger, J.; Lunkenheimer, P.; Fichtl, R.; Weber, S.; Tsurkan, V.; Loidl, A.

2006-05-01

The recently discovered multiferroic material CdCr2S4 shows a coexistence of ferromagnetism and relaxor ferroelectricity together with a colossal magnetocapacitive effect. The complex dielectric permittivity of this compound and of the structurally related CdCr2Se4 was studied by means of broadband dielectric spectroscopy using different electrode materials. The observed magnetocapacitive coupling at the magnetic transition is driven by enormous changes of the relaxation dynamics induced by the development of magnetic order.

Material Models and Properties in the Finite Element Analysis of Knee Ligaments: A Literature Review

PubMed Central

Galbusera, Fabio; Freutel, Maren; Dürselen, Lutz; D’Aiuto, Marta; Croce, Davide; Villa, Tomaso; Sansone, Valerio; Innocenti, Bernardo

2014-01-01

Knee ligaments are elastic bands of soft tissue with a complex microstructure and biomechanics, which are critical to determine the kinematics as well as the stress bearing behavior of the knee joint. Their correct implementation in terms of material models and properties is therefore necessary in the development of finite element models of the knee, which has been performed for decades for the investigation of both its basic biomechanics and the development of replacement implants and repair strategies for degenerative and traumatic pathologies. Indeed, a wide range of element types and material models has been used to represent knee ligaments, ranging from elastic unidimensional elements to complex hyperelastic three-dimensional structures with anatomically realistic shapes. This paper systematically reviews literature studies, which described finite element models of the knee, and summarizes the approaches, which have been used to model the ligaments highlighting their strengths and weaknesses. PMID:25478560

Nanoscale Structure and Interaction of Compact Assemblies of Carbon Nano-Materials

NASA Astrophysics Data System (ADS)

Timsina, Raju; Qiu, Xiangyun

Carbon-based nano-materials (CNM) are a diverse family of multi-functional materials under research and development world wide. Our work is further motivated by the predictive power of the physical understanding of the underlying structure-interaction-function relationships. Here we present results form recent studies of the condensed phases of several model CNMs in complexation with biologically derived molecules. Specifically, we employ X-ray diffraction (XRD) to determine nanoscale structures and use the osmotic stress method to quantify their interactions. The systems under investigation are dsDNA-dispersed carbon nanotubes (dsDNA-CNT), bile-salt-dispersed carbon nanotubes, and surfactant-assisted assemblies of graphene oxides. We found that salt and molecular crowding are both effective in condensing CNMs but the resultant structures show disparate phase behaviors. The molecular interactions driving the condensation/assembly sensitively depend on the nature of CNM complex surface chemistry and range from hydrophobic to electrostatic to entropic forces.

Semisolid Metal Processing Consortium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Apelian,Diran

Mathematical modeling and simulations of semisolid filling processes remains a critical issue in understanding and optimizing the process. Semisolid slurries are non-Newtonian materials that exhibit complex rheological behavior. There the way these slurries flow in cavities is very different from the way liquid in classical casting fills cavities. Actually filling in semisolid processing is often counter intuitive

Thermomechanical Properties and Glass Dynamics of Polymer-Tethered Colloidal Particles and Films

PubMed Central

2017-01-01

Polymer-tethered colloidal particles (aka “particle brush materials”) have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush–brush interactions as well as global chain relaxation sensitively depend on grafting density; i.e., more polymer-like behavior is observed in sparse brush systems. This is interpreted to be a consequence of more extensive chain entanglement. In contrast, the local relaxation of films does not depend on grafting density. The results highlight that relaxation processes in particle brush-based materials span a wider range of time and length scales as compared to linear chain polymers. Differentiation between relaxation on local and global scale is necessary to reveal the influence of molecular structure and connectivity on the aging behavior of these complex systems. PMID:29755139

Revealing the Origins of Mechanically Induced Fluorescence Changes in Organic Molecular Crystals.

PubMed

Wilbraham, Liam; Louis, Marine; Alberga, Domenico; Brosseau, Arnaud; Guillot, Régis; Ito, Fuyuki; Labat, Frédéric; Métivier, Rémi; Allain, Clémence; Ciofini, Ilaria

2018-05-29

Mechanofluorochromic molecular materials display a change in fluorescence color through mechanical stress. Complex structure-property relationships in both the crystalline and amorphous phases of these materials govern both the presence and strength of this behavior, which is usually deemed the result of a mechanically induced phase transition. However, the precise nature of the emitting species in each phase is often a matter of speculation, resulting from experimental data that are difficult to interpret, and a lack of an acceptable theoretical model capable of capturing complex environmental effects. With a combined strategy using sophisticated experimental techniques and a new theoretical approach, here the varied mechanofluorochromic behavior of a series of difluoroboron diketonates is shown to be driven by the formation of low-energy exciton traps in the amorphous phase, with a limited number of traps giving rise to the full change in fluorescence color. The results highlight intrinsic structural links between crystalline and amorphous phases, and how these may be exploited for further development of powerful mechanofluorochromic assemblies, in line with modern crystal engineering approaches. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optimizing the chances of success in the search for epigenetic biomarkers: Embracing genetic variation.

PubMed

Philibert, Robert; Glatt, Stephen J

2017-09-01

The emphasis on clinical translation in biomedical research continues to grow. This focus has been particularly notable in those investigators using epigenetic approaches to decipher the biology of complex behavioral disorders. As a result of these efforts, reproducible findings for several disorders, such as smoking, have been generated, giving rise to hopes that biomarkers for other behavioral illnesses would be forthcoming. Unfortunately, that biomedical cornucopia has not yet materialized. In this editorial, we review progress to date and discuss barriers to generating epigenetic biomarkers for complex behavioral disorders. We highlight the need to incorporate information on genetic variation and develop more powerful bioinformatics tools in order to optimize the likelihood of success. We emphasize that searches should focus on clearly defined, readily distinguishable behavioral constructs and suggest that some well-intentioned methods, such as correction for cellular heterogeneity, may actually impede the identification of clinically relevant biomarkers in peripheral blood. Finally, we describe how the understanding created by the development of these biomarkers may lead to more valid animal models of neuropsychiatric illness. We conclude that the prospects for epigenetic biomarkers for complex disorders are bright, but emphasize that the journey to the clinical implementation of these findings will be a slow, iterative process. © 2017 Wiley Periodicals, Inc.

Deformation partitioning provides insight into elastic, plastic, and viscous contributions to bone material behavior.

PubMed

Ferguson, V L

2009-08-01

The relative contributions of elastic, plastic, and viscous material behavior are poorly described by the separate extraction and analysis of the plane strain modulus, E('), the contact hardness, H(c) (a hybrid parameter encompassing both elastic and plastic behavior), and various viscoelastic material constants. A multiple element mechanical model enables the partitioning of a single indentation response into its fundamental elastic, plastic, and viscous deformation components. The objective of this study was to apply deformation partitioning to explore the role of hydration, tissue type, and degree of mineralization in bone and calcified cartilage. Wet, ethanol-dehydrated, and PMMA-embedded equine cortical bone samples and PMMA-embedded human femoral head tissues were analyzed for contributions of elastic, plastic and viscous deformation to the overall nanoindentation response at each site. While the alteration of hydration state had little effect on any measure of deformation, unembedded tissues demonstrated significantly greater measures of resistance to plastic deformation than PMMA-embedded tissues. The PMMA appeared to mechanically stabilize the tissues and prevent extensive permanent deformation within the bone material. Increasing mineral volume fraction correlated with positive changes in E('), H(c), and resistance to plastic deformation, H; however, the partitioned deformation components were generally unaffected by mineralization. The contribution of viscous deformation was minimal and may only play a significant role in poorly mineralized tissues. Deformation partitioning enables a detailed interpretation of the elastic, plastic, and viscous contributions to the nanomechanical behavior of mineralized tissues that is not possible when examining modulus and contact hardness alone. Varying experimental or biological factors, such as hydration or mineralization level, enables the understanding of potential mechanisms for specific mechanical behavior patterns that would otherwise be hidden within a more complex set of material property parameters.

Technique for measurement of characteristic impedance and propagation constant for porous materials

NASA Astrophysics Data System (ADS)

Jung, Ki Won; Atchley, Anthony A.

2005-09-01

Knowledge of acoustic properties such as characteristic impedance and complex propagation constant is useful to characterize the acoustic behaviors of porous materials. Song and Bolton's four-microphone method [J. Acoust. Soc. Am. 107, 1131-1152 (2000)] is one of the most widely employed techniques. In this method two microphones are used to determine the complex pressure amplitudes for each side of a sample. Muehleisen and Beamer [J. Acoust. Soc. Am. 117, 536-544 (2005)] improved upon a four-microphone method by interchanging microphones to reduce errors due to uncertainties in microphone response. In this paper, a multiple microphone technique is investigated to reconstruct the pressure field inside an impedance tube. Measurements of the acoustic properties of a material having square cross-section pores is used to check the validity of the technique. The values of characteristic impedance and complex propagation constant extracted from the reconstruction agree well with predicted values. Furthermore, this technique is used in investigating the acoustic properties of reticulated vitreous carbon (RVC) in the range of 250-1100 Hz.

Multi-Dimensional Simulation of LWR Fuel Behavior in the BISON Fuel Performance Code

NASA Astrophysics Data System (ADS)

Williamson, R. L.; Capps, N. A.; Liu, W.; Rashid, Y. R.; Wirth, B. D.

2016-11-01

Nuclear fuel operates in an extreme environment that induces complex multiphysics phenomena occurring over distances ranging from inter-atomic spacing to meters, and times scales ranging from microseconds to years. To simulate this behavior requires a wide variety of material models that are often complex and nonlinear. The recently developed BISON code represents a powerful fuel performance simulation tool based on its material and physical behavior capabilities, finite-element versatility of spatial representation, and use of parallel computing. The code can operate in full three dimensional (3D) mode, as well as in reduced two dimensional (2D) modes, e.g., axisymmetric radial-axial ( R- Z) or plane radial-circumferential ( R- θ), to suit the application and to allow treatment of global and local effects. A BISON case study was used to illustrate analysis of Pellet Clad Mechanical Interaction failures from manufacturing defects using combined 2D and 3D analyses. The analysis involved commercial fuel rods and demonstrated successful computation of metrics of interest to fuel failures, including cladding peak hoop stress and strain energy density. In comparison with a failure threshold derived from power ramp tests, results corroborate industry analyses of the root cause of the pellet-clad interaction failures and illustrate the importance of modeling 3D local effects around fuel pellet defects, which can produce complex effects including cold spots in the cladding, stress concentrations, and hot spots in the fuel that can lead to enhanced cladding degradation such as hydriding, oxidation, CRUD formation, and stress corrosion cracking.

Multi-Dimensional Simulation of LWR Fuel Behavior in the BISON Fuel Performance Code

DOE PAGES

Williamson, R. L.; Capps, N. A.; Liu, W.; ...

2016-09-27

Nuclear fuel operates in an extreme environment that induces complex multiphysics phenomena occurring over distances ranging from inter-atomic spacing to meters, and times scales ranging from microseconds to years. To simulate this behavior requires a wide variety of material models that are often complex and nonlinear. The recently developed BISON code represents a powerful fuel performance simulation tool based on its material and physical behavior capabilities, finite-element versatility of spatial representation, and use of parallel computing. The code can operate in full three dimensional (3D) mode, as well as in reduced two dimensional (2D) modes, e.g., axisymmetric radial-axial (R-Z) ormore » plane radial-circumferential (R-θ), to suit the application and to allow treatment of global and local effects. A BISON case study was used in this paper to illustrate analysis of Pellet Clad Mechanical Interaction failures from manufacturing defects using combined 2D and 3D analyses. The analysis involved commercial fuel rods and demonstrated successful computation of metrics of interest to fuel failures, including cladding peak hoop stress and strain energy density. Finally, in comparison with a failure threshold derived from power ramp tests, results corroborate industry analyses of the root cause of the pellet-clad interaction failures and illustrate the importance of modeling 3D local effects around fuel pellet defects, which can produce complex effects including cold spots in the cladding, stress concentrations, and hot spots in the fuel that can lead to enhanced cladding degradation such as hydriding, oxidation, CRUD formation, and stress corrosion cracking.« less

Nitrogen-Rich Energetic Metal-Organic Framework: Synthesis, Structure, Properties, and Thermal Behaviors of Pb(II) Complex Based on N,N-Bis(1H-tetrazole-5-yl)-Amine

PubMed Central

Liu, Qiangqiang; Jin, Bo; Zhang, Qingchun; Shang, Yu; Guo, Zhicheng; Tan, Bisheng; Peng, Rufang

2016-01-01

The focus of energetic materials is on searching for a high-energy, high-density, insensitive material. Previous investigations have shown that 3D energetic metal–organic frameworks (E-MOFs) have great potential and advantages in this field. A nitrogen-rich E-MOF, Pb(bta)·2H2O [N% = 31.98%, H2bta = N,N-Bis(1H-tetrazole-5-yl)-amine], was prepared through a one-step hydrothermal reaction in this study. Its crystal structure was determined through single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, and elemental analysis. The complex has high heat denotation (16.142 kJ·cm−3), high density (3.250 g·cm−3), and good thermostability (Tdec = 614.9 K, 5 K·min−1). The detonation pressure and velocity obtained through theoretical calculations were 43.47 GPa and 8.963 km·s−1, respectively. The sensitivity test showed that the complex is an impact-insensitive material (IS > 40 J). The thermal decomposition process and kinetic parameters of the complex were also investigated through thermogravimetry and differential scanning calorimetry. Non-isothermal kinetic parameters were calculated through the methods of Kissinger and Ozawa-Doyle. Results highlighted the nitrogen-rich MOF as a potential energetic material. PMID:28773805

The high temperature creep behavior of oxides and oxide fibers

NASA Technical Reports Server (NTRS)

Jones, Linda E.; Tressler, Richard E.

1991-01-01

A thorough review of the literature was conducted on the high-temperature creep behavior of single and polycrystalline oxides which potentially could serve as fiber reinforcements in ceramics or metal matrix applications. Sapphire when oriented with the basal plane perpendicular to the fiber axis (c-axis oriented) is highly creep resistant at temperatures in excess of 1600 C and applied loads of 100 MPa and higher. Pyramidal slip is preferentially activated in sapphire under these conditions and steady-state creep rates in the range of 10(exp -7) to 10 (exp -8)/s were reported. Data on the creep resistance of polycrystalline beryllia suggest that C-axiz oriented single crystal beryllia may be a viable candidate as a fiber reinforcement material; however, the issure of fabricability and moisture sensitivity must be addressed for this material. Yttrium aluminum garnet (YAG) also appears to be a fiber candidate material having a high resistance to creep which is due to it's complex crystal structure and high Peierl resistance. The high creep resistance of garnet suggests that there may be other complex ternary oxides such as single crystal mullite which may also be candidate materials for fiber reinforcements. Finally, CVD and single crystal SiC, although not oxides, do possess a high resistance to creep in the temperature range between 1550 and 1850 C and under stresses of 110 to 220 MPa. From a review of the literature, it appears that for high creep resistant applications sapphire, silicon carbide, yttrium aluminum garnet, mullite, and beryllia are desirable candidate materials which require further investigation.

New developments in tribomechanical modeling of automotive sheet steel forming

NASA Astrophysics Data System (ADS)

Khandeparkar, Tushar; Chezan, Toni; van Beeck, Jeroen

2018-05-01

Forming of automotive sheet metal body panels is a complex process influenced by both the material properties and contact conditions in the forming tooling. Material properties are described by the material constitutive behavior and the material flow into the forming die can be described by the tribological system. This paper investigates the prediction accuracy of the forming process using the Tata Steel state of the art description of the material constitutive behavior in combination with different friction models. A cross-die experiment is used to investigate the accuracy of local deformation modes typically seen in automotive sheet metal forming operations. Results of advanced friction models as well as the classical Coulomb friction description are compared to the experimentally measured strain distribution and material draw-in. Two hot-dip galvanized coated steel forming grades were used for the investigations. The results show that the accuracy of the simulation is not guaranteed by the advanced friction models for the entire investigated blank holder force range, both globally and locally. A measurable difference between the calculated and measured local strains is seen for both studied models even in the case where the global indicator, i.e. the draw-in, is well predicted.

Mechanical characterization of a short fiber-reinforced polymer at room temperature: experimental setups evaluated by an optical measurement system

NASA Astrophysics Data System (ADS)

Röhrig, C.; Scheffer, T.; Diebels, S.

2017-09-01

Composite materials are of great interest for industrial applications because of their outstanding properties. Each composite material has its own characteristics due to the large number of possible combinations of matrix and filler. As a result of their compounding, composites usually show a complex material behavior. This work is focused on the experimental testing of a short fiber-reinforced thermoplastic composite at room temperature. The characteristic behavior of this material class is often based on a superposition of typical material effects. The predicted characteristic material properties such as elasto-plasticity, damage and anisotropy of the investigated material are obtained from results of cyclic uniaxial tensile tests at constant strain rate. Concerning the manufacturing process as well as industrial applications, the experimental investigations are extended to multiaxial loading situations. Therefore, the composite material is examined with a setup close to a deep-drawing process, the Nakajima test (Nakazima et al. in Study on the formability of steel sheets. Yawate Technical Report No. 264, pp 8517-8530, 1968). The evaluation of the experimental investigations is provided by an optical analysis system using a digital image correlation software. Finally, based on the results of the uniaxial tensile tests, a one-dimensional macroscopic model is introduced and first results of the simulation are provided.

Tilts, dopants, vacancies and non-stoichiometry: Understanding and designing the properties of complex solid oxide perovskites from first principles

NASA Astrophysics Data System (ADS)

Bennett, Joseph W.

Perovskite oxides of formula ABO3 have a wide range of structural, electrical and mechanical properties, making them vital materials for many applications, such as catalysis, ultrasound machines and communication devices. Perovskite solid solutions with high piezoelectric response, such as ferroelectrics, are of particular interest as they can be employed as sensors in SONAR devices. Ferroelectric materials are unique in that their chemical and electrical properties can be non-invasively and reversibly changed, by switching the bulk polarization. This makes ferroelectrics useful for applications in non-volatile random access memory (NVRAM) devices. Perovskite solid solutions with a lower piezoelectric response than ferroelectrics are important for communication technology, as they function well as electroceramic capacitors. Also of interest is how these materials act as a component in a solid oxide fuel cell, as they can function as an efficient source of energy. Altering the chemical composition of these solid oxide materials offers an opportunity to change the desired properties of the final ceramic, adding a degree of flexibility that is advantageous for a variety of applications. These solid oxides are complex, sometimes disordered systems that are a challenge to study experimentally. However, as it is their complexity which produces favorable properties, highly accurate modeling which captures the essential features of the disordered structure is necessary to explain the behavior of current materials and predict favorable compositions for new materials. Methodological improvements and faster computer speeds have made first-principles and atomistic calculations a viable tool for understanding these complex systems. Offering a combination of accuracy and computational speed, the density functional theory (DFT) approach can reveal details about the microscopic structure and interactions of complex systems. Using DFT and a combination of principles from both inorganic chemistry and materials science, I have been able to gain insights into solid oxide perovskite-based systems.

Numerical study of impact erosion of multiple solid particle

NASA Astrophysics Data System (ADS)

Zheng, Chao; Liu, Yonghong; Chen, Cheng; Qin, Jie; Ji, Renjie; Cai, Baoping

2017-11-01

Material erosion caused by continuous particle impingement during hydraulic fracturing results in significant economic loss and increased production risks. The erosion process is complex and has not been clearly explained through physical experiments. To address this problem, a multiple particle model in a 3D configuration was proposed to investigate the dynamic erosion process. This approach can significantly reduce experiment costs. The numerical model considered material damping and elastic-plastic material behavior of target material. The effects of impact parameters on erosion characteristics, such as plastic deformation, contact time, and energy loss rate, were investigated. Based on comprehensive studies, the dynamic erosion mechanism and geometry evolution of eroded crater was obtained. These findings can provide a detailed erosion process of target material and insights into the material erosion caused by multiple particle impingement.

Effect of Charge Patterning on the Phase Behavior of Polymer Coacervates for Charge Driven Self Assembly

NASA Astrophysics Data System (ADS)

Radhakrishna, Mithun; Sing, Charles E.

Oppositely charged polymers can undergo associative liquid-liquid phase separation when mixed under suitable conditions of ionic strength, temperature and pH to form what are known as `polymeric complex coacervates'. Polymer coacervates find use in diverse array of applications like microencapsulation, drug delivery, membrane filtration and underwater adhesives. The similarity between complex coacervate environments and those in biological systems has also found relevance in areas of bio-mimicry. Our previous works have demonstrated how local charge correlations and molecular connectivity can drastically affect the phase behavior of coacervates. The precise location of charges along the chain therefore dramatically influences the local charge correlations, which consequently influences the phase behavior of coacervates. We investigate the effect of charge patterning along the polymer chain on the phase behavior of coacervates in the framework of the Restricted Primitive Model using Gibbs Ensemble Monte Carlo simulations. Our results show that charge patterning dramatically changes the phase behavior of polymer coacervates, which contrasts with the predictions of the classical Voorn-Overbeek theory. This provides the basis for designing new materials through charge driven self assembly by controlling the positioning of the charged monomers along the chain.

A general computation model based on inverse analysis principle used for rheological analysis of W/O rapeseed and soybean oil emulsions

NASA Astrophysics Data System (ADS)

Vintila, Iuliana; Gavrus, Adinel

2017-10-01

The present research paper proposes the validation of a rigorous computation model used as a numerical tool to identify rheological behavior of complex emulsions W/O. Considering a three-dimensional description of a general viscoplastic flow it is detailed the thermo-mechanical equations used to identify fluid or soft material's rheological laws starting from global experimental measurements. Analyses are conducted for complex emulsions W/O having generally a Bingham behavior using the shear stress - strain rate dependency based on a power law and using an improved analytical model. Experimental results are investigated in case of rheological behavior for crude and refined rapeseed/soybean oils and four types of corresponding W/O emulsions using different physical-chemical composition. The rheological behavior model was correlated with the thermo-mechanical analysis of a plane-plane rheometer, oil content, chemical composition, particle size and emulsifier's concentration. The parameters of rheological laws describing the industrial oils and the W/O concentrated emulsions behavior were computed from estimated shear stresses using a non-linear regression technique and from experimental torques using the inverse analysis tool designed by A. Gavrus (1992-2000).

Nonlinear oscillatory rheology and structure of wormlike micellar solutions and colloidal suspensions

NASA Astrophysics Data System (ADS)

Gurnon, Amanda Kate

The complex, nonlinear flow behavior of soft materials transcends industrial applications, smart material design and non-equilibrium thermodynamics. A long-standing, fundamental challenge in soft-matter science is establishing a quantitative connection between the deformation field, local microstructure and macroscopic dynamic flow properties i.e., the rheology. Soft materials are widely used in consumer products and industrial processes including energy recovery, surfactants for personal healthcare (e.g. soap and shampoo), coatings, plastics, drug delivery, medical devices and therapeutics. Oftentimes, these materials are processed by, used during, or exposed to non-equilibrium conditions for which the transient response of the complex fluid is critical. As such, designing new dynamic experiments is imperative to testing these materials and further developing micromechanical models to predict their transient response. Two of the most common classes of these soft materials stand as the focus of the present research; they are: solutions of polymer-like micelles (PLM or also known as wormlike micelles, WLM) and concentrated colloidal suspensions. In addition to their varied applications these two different classes of soft materials are also governed by different physics. In contrast, to the shear thinning behavior of the WLMs at high shear rates, the near hard-sphere colloidal suspensions are known to display increases, sometimes quite substantial, in viscosity (known as shear thickening). The stress response of these complex fluids derive from the shear-induced microstructure, thus measurements of the microstructure under flow are critical for understanding the mechanisms underlying the complex, nonlinear rheology of these complex fluids. A popular micromechanical model is reframed from its original derivation for predicting steady shear rheology of polymers and WLMs to be applicable to weakly nonlinear oscillatory shear flow. The validity, utility and limits of this constitutive model are tested by comparison with experiments on model WLM solutions. Further comparisons to the nonlinear oscillatory shear responses measured from colloidal suspensions establishes this analysis as a promising, quantitative method for understanding the underlying mechanisms responsible for the nonlinear dynamic response of complex fluids. A new experimental technique is developed to measure the microstructure of complex fluids during steady and transient shear flow using small-angle neutron scattering (SANS). The Flow-SANS experimental method is now available to the broader user communities at the NIST Center for Neutron Research, Gaithersburg, MD and the Institut Laue-Langevin, Grenoble, France. Using this new method, a model shear banding WLM solution is interrogated under steady and oscillatory shear. For the first time, the flow-SANS methods identify new metastable states for shear banding WLM solutions, thus establishing the method as capable of probing new states not accessible using traditional steady or linear oscillatory shear methods. The flow-induced three-dimensional microstructure of a colloidal suspension under steady and dynamic oscillatory shear is also measured using these rheo- and flow-SANS methods. A new structure state is identified in the shear thickening regime that proves critical for defining the "hydrocluster" microstructure state of the suspension that is responsible for shear thickening. For both the suspensions and the WLM solutions, stress-SANS rules with the measured microstructures define the individual stress components arising separately from conservative and hydrodynamic forces and these are compared with the macroscopic rheology. Analysis of these results defines the crucial length- and time-scales of the transient microstructure response. The novel dynamic microstructural measurements presented in this dissertation provide new insights into the complexities of shear thickening and shear banding flow phenomena, which are effects observed more broadly across many different types of soft materials. Consequently, the microstructure-rheology property relationships developed for these two classes of complex fluids will aid in the testing and advancement of micromechanical constitutive model development, smart material design, industrial processing and fundamental non-equilibrium thermodynamic research of a broad range of soft materials.

In situ TEM of radiation effects in complex ceramics.

PubMed

Lian, Jie; Wang, L M; Sun, Kai; Ewing, Rodney C

2009-03-01

In situ transmission electron microscopy (TEM) has been extensively applied to study radiation effects in a wide variety of materials, such as metals, ceramics and semiconductors and is an indispensable tool in obtaining a fundamental understanding of energetic beam-matter interactions, damage events, and materials' behavior under intense radiation environments. In this article, in situ TEM observations of radiation effects in complex ceramics (e.g., oxides, silicates, and phosphates) subjected to energetic ion and electron irradiations have been summarized with a focus on irradiation-induced microstructural evolution, changes in microchemistry, and the formation of nanostructures. New results for in situ TEM observation of radiation effects in pyrochlore, A(2)B(2)O(7), and zircon, ZrSiO(4), subjected to multiple beam irradiations are presented, and the effects of simultaneous irradiations of alpha-decay and beta-decay on the microstructural evolution of potential nuclear waste forms are discussed. Furthermore, in situ TEM results of radiation effects in a sodium borosilicate glass subjected to electron-beam exposure are introduced to highlight the important applications of advanced analytical TEM techniques, including Z-contrast imaging, energy filtered TEM (EFTEM), and electron energy loss spectroscopy (EELS), in studying radiation effects in materials microstructural evolution and microchemical changes. By combining ex situ TEM and advanced analytical TEM techniques with in situ TEM observations under energetic beam irradiations, one can obtain invaluable information on the phase stability and response behaviors of materials under a wide range of irradiation conditions. (c) 2009 Wiley-Liss, Inc.

Linking Microstructural Changes to Bulk Behavior in Shear Disordered Matter

NASA Astrophysics Data System (ADS)

Blair, Daniel

Soft and biological materials often exhibit disordered and heterogeneous microstructure. In most cases, the transmission and distribution of stresses through these complex materials reflects their inherent heterogeneity. Through the combination of rheology and 4D imaging we can directly alter and quantify the connection between microstructure and local stresses. We subject soft and biological materials to precise shear deformations while measuring real space information about the distribution and redistribution of the applied stress.In this talk, I will focus on the flow behavior of two distinct but related disordered materials; a flowing compressed emulsion above its yield stress and a strained collagen network. In the emulsion system, I will present experimental and computational results on the dynamical response, at the level of individual droplets, that directly links the particle motion and deformation to the rheology. I will also present results that utilize boundary stress microscopy to quantify the spatial distribution of surface stresses that arise from sheared in-vitro collagen networks. I will outline our main conclusions which is that the strain stiffening behavior observed in collagen networks can be parameterized by a single characteristic strain and associated stress. This characteristic rheological signature seems to describe both the strain stiffening regime and network yielding. NSF DMR: 0847490.

Ottawa Sand for Mechanics of Granular Materials (MGM) Experiment

NASA Technical Reports Server (NTRS)

2000-01-01

What appear to be boulders fresh from a tumble down a mountain are really grains of Ottawa sand, a standard material used in civil engineering tests and also used in the Mechanics of Granular Materials (MGM) experiment. The craggy surface shows how sand grans have faces that can cause friction as they roll and slide against each other, or even causing sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM uses the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. These images are from an Electron Spectroscopy for Chemical Analysis (ESCA) study conducted by Dr. Binayak Panda of IITRI for Marshall Space Flight Center (MSFC). (Credit: NASA/MSFC)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borreguero, Jose M.; Pincus, Philip A.; Sumpter, Bobby G.

Structure–property relationships of ionic block copolymer (BCP) surfactant complexes are critical toward the progress of favorable engineering design of efficient charge-transport materials. In this paper, molecular dynamics simulations are used to understand the dynamics of charged-neutral BCP and surfactant complexes. The dynamics are examined for two different systems: charged-neutral double-hydrophilic and hydrophobic–hydrophilic block copolymers with oppositely charged surfactant moieties. The dynamics of the surfactant head, tails, and charges are studied for five different BCP volume fractions. We observe that the dynamics of the different species solely depend on the balance between electrostatic and entropic interactions between the charged species andmore » the neutral monomers. The favorable hydrophobic–hydrophobic interactions and the unfavorable hydrophobic–hydrophilic interactions determine the mobilities of the monomers. The dynamical properties of the charge species influence complex formation. Structural relaxations exhibit length-scale dependent behavior, with slower relaxation at the radius of gyration length-scale and faster relaxation at the segmental length-scale, consistent with previous results. The dynamical analysis correlates ion-exchange kinetics to the self-assembly behavior of the complexes.« less

Spin-ice behavior of three-dimensional inverse opal-like magnetic structures: Micromagnetic simulations

NASA Astrophysics Data System (ADS)

Dubitskiy, I. S.; Syromyatnikov, A. V.; Grigoryeva, N. A.; Mistonov, A. A.; Sapoletova, N. A.; Grigoriev, S. V.

2017-11-01

We perform micromagnetic simulations of the magnetization distribution in inverse opal-like structures (IOLS) made from ferromagnetic materials (nickel and cobalt). It is shown that the unit cell of these complex structures, whose characteristic length is approximately 700 nm, can be divided into a set of structural elements some of which behave like Ising-like objects. A spin-ice behavior of IOLS is observed in a broad range of external magnetic fields. Numerical results describe successfully the experimental hysteresis curves of the magnetization in Ni- and Co-based IOLS. We conclude that ferromagnetic IOLS can be considered as the first realization of three-dimensional artificial spin ice. The problem is discussed of optimal geometrical properties and material characteristics of IOLS for the spin-ice rule fulfillment.

Modeling of Damage Initiation and Progression in a SiC/SiC Woven Ceramic Matrix Composite

NASA Technical Reports Server (NTRS)

Mital, Subodh K.; Goldberg, Robert K.; Bonacuse, Peter J.

2012-01-01

The goal of an ongoing project at NASA Glenn is to investigate the effects of the complex microstructure of a woven ceramic matrix composite and its variability on the effective properties and the durability of the material. Detailed analysis of these complex microstructures may provide clues for the material scientists who `design the material? or to structural analysts and designers who `design with the material? regarding damage initiation and damage propagation. A model material system, specifically a five-harness satin weave architecture CVI SiC/SiC composite composed of Sylramic-iBN fibers and a SiC matrix, has been analyzed. Specimens of the material were serially sectioned and polished to capture the detailed images of fiber tows, matrix and porosity. Open source analysis tools were used to isolate various constituents and finite elements models were then generated from simplified models of those images. Detailed finite element analyses were performed that examine how the variability in the local microstructure affected the macroscopic behavior as well as the local damage initiation and progression. Results indicate that the locations where damage initiated and propagated is linked to specific microstructural features.

Evaluation of Environmentally Acceptable Lubricants (EALS) for Dams Managed by the U.S. Army Corps of Engineers

DTIC Science & Technology

2015-08-01

power, and seal against dirt, dust, and water. Lubricants work by serving as a lower viscosity material between moving surfaces. The wearing surfaces...aluminum, clay , polyurea, sodium, and calcium are most common. Complex thickeners can be composed of metal soaps mixed with low-molecular-weight organic...Polyalkyl DAE N Polyest Rape Seed Viscosity Temperature Behavior (VI) 4 2 2 2 2 2 Low Temperature Behavior (Pourpoint) 5 1 3 1 2 3 Liquid Range 4 2 3 1 2 3

SCScore: Synthetic Complexity Learned from a Reaction Corpus.

PubMed

Coley, Connor W; Rogers, Luke; Green, William H; Jensen, Klavs F

2018-02-26

Several definitions of molecular complexity exist to facilitate prioritization of lead compounds, to identify diversity-inducing and complexifying reactions, and to guide retrosynthetic searches. In this work, we focus on synthetic complexity and reformalize its definition to correlate with the expected number of reaction steps required to produce a target molecule, with implicit knowledge about what compounds are reasonable starting materials. We train a neural network model on 12 million reactions from the Reaxys database to impose a pairwise inequality constraint enforcing the premise of this definition: that on average, the products of published chemical reactions should be more synthetically complex than their corresponding reactants. The learned metric (SCScore) exhibits highly desirable nonlinear behavior, particularly in recognizing increases in synthetic complexity throughout a number of linear synthetic routes.

The Intersection of Culture and Behavior in Social Studies Classrooms

ERIC Educational Resources Information Center

Schlein, Candace; Taft, Raol J.; Ramsay, Crystal M.

2016-01-01

Social studies is a school subject that aims to enmesh local and global concerns and ways of understanding the world. It is a complex task to position local concerns and perspectives within an intercultural vantage. In turn, this objective for teaching and learning also presumes that students interact with social studies material from fixed and…

The Play Behavior and Play Materials of Blind and Sighted Infants and Preschoolers.

ERIC Educational Resources Information Center

Troster, H.; Brambring, M.

1994-01-01

Analysis of questionnaires completed by parents of 91 young blind children and 74 matched sighted children indicated that sighted children engaged in more complex levels of play at an earlier age; blind children interacted less frequently with other children than did sighted children; blind children preferred tactile-auditory games and toys; and…

Optical Computing Based on Neuronal Models

DTIC Science & Technology

1988-05-01

walking, and cognition are far too complex for existing sequential digital computers. Therefore new architectures, hardware, and algorithms modeled...collective behavior, and iterative processing into optical processing and artificial neurodynamical systems. Another intriguing promise of neural nets is...with architectures, implementations, and programming; and material research s -7- called for. Our future research in neurodynamics will continue to

Amperometric Enzyme Electrodes

DTIC Science & Technology

1989-12-01

form of carbon (glascy carbon , graphite, reticulated vitreous carbon , carbon paste, fiber or foil). Carbon is favored for enzyme immoblization...the surface for covalent bonding. The most frequently used electrode material, glassy carbon , often displays complex behavior. Although attempts have...Mixed Carbon Paste Electrode with an Immobilized Layer of D-Gluconate Dehydrogenase from Bacteral Membranes," Agric. Biol. Chelm., 51 (1987), 747-754

Sandia Dynamic Materials Program Strategic Plan.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flicker, Dawn Gustine; Benage, John F.; Desjarlais, Michael P.

2017-05-01

Materials in nuclear and conventional weapons can reach multi-megabar pressures and 1000s of degree temperatures on timescales ranging from microseconds to nanoseconds. Understanding the response of complex materials under these conditions is important for designing and assessing changes to nuclear weapons. In the next few decades, a major concern will be evaluating the behavior of aging materials and remanufactured components. The science to enable the program to underwrite decisions quickly and confidently on use, remanufacturing, and replacement of these materials will be critical to NNSA’s new Stockpile Responsiveness Program. Material response is also important for assessing the risks posed bymore » adversaries or proliferants. Dynamic materials research, which refers to the use of high-speed experiments to produce extreme conditions in matter, is an important part of NNSA’s Stockpile Stewardship Program.« less

Emergent 1d Ising Behavior in AN Elementary Cellular Automaton Model

NASA Astrophysics Data System (ADS)

Kassebaum, Paul G.; Iannacchione, Germano S.

The fundamental nature of an evolving one-dimensional (1D) Ising model is investigated with an elementary cellular automaton (CA) simulation. The emergent CA simulation employs an ensemble of cells in one spatial dimension, each cell capable of two microstates interacting with simple nearest-neighbor rules and incorporating an external field. The behavior of the CA model provides insight into the dynamics of coupled two-state systems not expressible by exact analytical solutions. For instance, state progression graphs show the causal dynamics of a system through time in relation to the system's entropy. Unique graphical analysis techniques are introduced through difference patterns, diffusion patterns, and state progression graphs of the 1D ensemble visualizing the evolution. All analyses are consistent with the known behavior of the 1D Ising system. The CA simulation and new pattern recognition techniques are scalable (in both dimension, complexity, and size) and have many potential applications such as complex design of materials, control of agent systems, and evolutionary mechanism design.

Doping as a means to probe the potential dependence of dopamine adsorption on carbon-based surfaces: A first-principles study

NASA Astrophysics Data System (ADS)

Aarva, Anja; Laurila, Tomi; Caro, Miguel A.

2017-06-01

In this work, we study the adsorption characteristics of dopamine (DA), ascorbic acid (AA), and dopaminequinone (DAox) on carbonaceous electrodes. Our goal is to obtain a better understanding of the adsorption behavior of these analytes in order to promote the development of new carbon-based electrode materials for sensitive and selective detection of dopamine in vivo. Here we employ density functional theory-based simulations to reach a level of detail that cannot be achieved experimentally. To get a broader understanding of carbonaceous surfaces with different morphological characteristics, we compare three materials: graphene, diamond, and amorphous carbon (a-C). Effects of solvation on adsorption characteristics are taken into account via a continuum solvent model. Potential changes that take place during electrochemical measurements, such as cyclic voltammetry, can also alter the adsorption behavior. In this study, we have utilized doping as an indirect method to simulate these changes by shifting the work function of the electrode material. We demonstrate that sp2- and sp3-rich materials, as well as a-C, respond markedly different to doping. Also the adsorption behavior of the molecules studied here differs depending on the surface material and the change in the surface potential. In all cases, adsorption is spontaneous, but covalent bonding is not detected in vacuum. The aqueous medium has a large effect on the adsorption behavior of DAox, which reaches its highest adsorption energy on diamond when the potential is shifted to more negative values. In all cases, inclusion of the solvent enhances the charge transfer between the slab and DAox. Largest differences in adsorption energy between DA and AA are obtained on graphene. Gaining better understanding of the behavior of the different forms of carbon when used as electrode materials provides a means to rationalize the observed complex phenomena taking place at the electrodes during electrochemical oxidation/reduction of these biomolecules.

Extracting physics through deep data analysis

DOE PAGES

Strelcov, Evgheni; Belianinov, Alex; Sumpter, Bobby G.; ...

2014-10-31

In recent decades humankind has become very apt at generating and recording enormous amounts of data, ranging from tweets and selfies on social networks, to financial transactions in banks and stores. The scientific community has not shunned this popular trend and now routinely produces hundreds of petabytes of data per year [1]. This is because materials and phenomena in the world around us exist in an interweaved, entangled form, which gives rise to the complexity of the Universe and determines the size and complexity of the data that describes it. Science and technology endeavor to unravel this convolution and extractmore » pure components from the mixtures, be it in ore mining and metal smelting or separation of thermal conductivity into the electronic and phononic contributions. Decomposition of complex behavior is the key to understanding manifestations of Nature. However, tools to carry out this task are not readily available, and therefore, intricate systems often remain well-characterized experimentally, but still not well understood due to intricacy of the collected data. Lastly, in materials science, understanding and ultimately designing new materials with complex properties will require the ability to integrate and analyze data from multiple instruments, including computational models, designed to probe complementary ranges of space, time, and energy.« less

Phenotyping the quality of complex medium components by simple online-monitored shake flask experiments.

PubMed

Diederichs, Sylvia; Korona, Anna; Staaden, Antje; Kroutil, Wolfgang; Honda, Kohsuke; Ohtake, Hisao; Büchs, Jochen

2014-11-07

Media containing yeast extracts and other complex raw materials are widely used for the cultivation of microorganisms. However, variations in the specific nutrient composition can occur, due to differences in the complex raw material ingredients and in the production of these components. These lot-to-lot variations can affect growth rate, product yield and product quality in laboratory investigations and biopharmaceutical production processes. In the FDA's Process Analytical Technology (PAT) initiative, the control and assessment of the quality of critical raw materials is one key aspect to maintain product quality and consistency. In this study, the Respiration Activity Monitoring System (RAMOS) was used to evaluate the impact of different yeast extracts and commercial complex auto-induction medium lots on metabolic activity and product yield of four recombinant Escherichia coli variants encoding different enzymes. Under non-induced conditions, the oxygen transfer rate (OTR) of E. coli was not affected by a variation of the supplemented yeast extract lot. The comparison of E. coli cultivations under induced conditions exhibited tremendous differences in OTR profiles and volumetric activity for all investigated yeast extract lots of different suppliers as well as lots of the same supplier independent of the E. coli variant. Cultivation in the commercial auto-induction medium lots revealed the same reproducible variations. In cultivations with parallel offline analysis, the highest volumetric activity was found at different cultivation times. Only by online monitoring of the cultures, a distinct cultivation phase (e.g. glycerol depletion) could be detected and chosen for comparable and reproducible offline analysis of the yield of functional product. This work proves that cultivations conducted in complex media may be prone to significant variation in final product quality and quantity if the quality of the raw material for medium preparation is not thoroughly checked. In this study, the RAMOS technique enabled a reliable and reproducible screening and phenotyping of complex raw material lots by online measurement of the respiration activity. Consequently, complex raw material lots can efficiently be assessed if the distinct effects on culture behavior and final product quality and quantity are visualized.

Synthesis, crystal growth, structural, thermal and optical properties of naphthalene picrate an organic NLO material.

PubMed

Chandramohan, A; Bharathikannan, R; Kandavelu, V; Chandrasekaran, J; Kandhaswamy, M A

2008-12-01

Crystalline substance of naphthalene picrate (NP) was synthesized and single crystals were grown using slow evaporation solution growth technique. The solubility of the naphthalene picrate complex was estimated using different solvents such as chloroform and benzene. The material was characterized by elemental analysis, powder X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and fourier transform-infrared (FT-IR) techniques. The electronic absorption was studied through UV-vis spectrophotometer. Thermal behavior and stability of the crystal were studied using thermogravimetric (TG) and differential thermal analysis (DTA) techniques. The second harmonic generation (SHG) of the material was confirmed using Nd:YAG laser.

Complex rheological properties of a water-soluble extract from the fronds of the black tree fern, Cyathea medullaris.

PubMed

Goh, Kelvin K T; Matia-Merino, Lara; Hall, Christopher E; Moughan, Paul J; Singh, Harjinder

2007-11-01

A water-soluble extract was obtained from the fronds of a New Zealand native black tree fern (Cyathea medullaris or Mamaku in Māori). The extract exhibited complex rheological behavior. Newtonian, shear-thinning, shear-thickening, thixotropic, antithixotropic, and viscoelastic behaviors were observed depending on polymer concentration, shear rate, and shear history. The extract also displayed rod-climbing and self-siphoning properties typical of viscoelastic fluids. Such complex rheological properties have been reported in synthetic or chemically modified polymers but are less frequent in unmodified biopolymers. Although Mamaku extract obtained from the pith of the fern has been traditionally used by the Māori in New Zealand for treating wounds and diarrhea among other ailments, this material has never been characterized before. This study reports on the chemical composition of the extract and on its viscoelastic properties through rotational and oscillatory rheological measurements. Explanations of the mechanism behind the rheological properties were based on transient network models for associating polymers.

Microgravity

NASA Image and Video Library

1996-09-18

Astronaut Jay Apt installs Mechanics of Granular Materials (MGM0 test cell on STS-79. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: NASA/John Space Center).

Microgravity

NASA Image and Video Library

2000-07-01

Mechanics of Granular Materials (MGM) flight hardware takes two twin double locker assemblies in the Space Shuttle middeck or the Spacehab module. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: NASA/MSFC).

Microgravity

NASA Image and Video Library

2000-07-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment include Khalid Alshibli, project scientist at NASA's Marshall Space Flight Center (MSFC). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: MSFC).

The microstructure of capsule containing self-healing materials: A micro-computed tomography study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Stappen, Jeroen, E-mail: Jeroen.Vanstappen@uge

Autonomic self-healing materials are materials with built-in (micro-) capsules or vessels, which upon fracturing release healing agents in order to recover the material's physical and mechanical properties. In order to better understand and engineer these materials, a thorough characterization of the material's microstructural behavior is essential and often overlooked. In this context, micro-computed tomography (μCT) can be used to investigate the three dimensional distribution and (de)bonding of (micro-) capsules in their native state in a polymer system with self-healing properties. Furthermore, in-situ μCT experiments in a self-healing polymer and a self-healing concrete system can elucidate the breakage and leakage behaviormore » of (micro-) capsules at the micrometer scale. While challenges related to image resolution and contrast complicate the characterization in specific cases, non-destructive 3D imaging with μCT is shown to contribute to the understanding of the link between the microstructure and the self-healing behavior of these complex materials. - Highlights: • μCT imaging allows for the analysis of microcapsule distribution patterns in self-healing materials. • μCT allows for qualitative and quantitative measurements of healing agent release from carriers in self-healing materials. • Experimental set-ups can be optimized by changing chemical compounds in the system to ensure maximum quality imaging.« less

Electro-Chemical Behavior of Low Carbon Steel Under H2S Influence

NASA Astrophysics Data System (ADS)

Zaharia, M. G.; Stanciu, S.; Cimpoesu, R.; Nejneru, C.; Savin, C.; Manole, V.; Cimpoeșu, N.

2017-06-01

Abstract A commercial low carbon steel material (P265GH) with application at industrial scale for natural gas delivery and transportation systems was analyzed in H2S atmosphere. The article proposed a new experimental cell in order to establish the behavior of the material in sulfur contaminated environment. In most of the industrial processes for gas purification the corrosion rate is speed up by the presence of S (sulfur) especially as ions or species like H2S. The H2S (hydrogen sulfide) is, beside a very toxic compound, a very active element in the acceleration of metallic materials deterioration especially in complex solicitations like pressure and temperature in the same time. For experiments we used a three electrodes cell with Na2SO4 + Na2S solution at pH 3 at room temperature (∼ 25 °C) to realize EIS (electrochemical impedance spectroscopy) and potentio-dynamic polarization experiments. Scanning electron microscopy and X-ray dispersive energy spectroscopy were used to characterize the metallic material surface exposed to experimental environment.

Microgravity

NASA Image and Video Library

1996-09-18

One of three Mechanics of Granular Materials (MGM) test cells after flight on STS-79 and before impregnation with resin. Note that the sand column has bulged in the middle, and that the top of the column is several inches lower than the top of the plastic enclosure. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Microgravity

NASA Image and Video Library

2000-07-01

What appear to be boulders fresh from a tumble down a mountain are really grains of Ottawa sand, a standard material used in civil engineering tests and also used in the Mechanics of Granular Materials (MGM) experiment. The craggy surface shows how sand grans have faces that can cause friction as they roll and slide against each other, or even causing sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM uses the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. These images are from an Electron Spectroscopy for Chemical Analysis (ESCA) study conducted by Dr. Binayak Panda of IITRI for Marshall Space Flight Center (MSFC). (Credit: NASA/MSFC)

Electrospun microcrimped fibers with nonlinear mechanical properties enhance ligament fibroblast phenotype.

PubMed

Grace Chao, Pen-hsiu; Hsu, Hsiang-Yi; Tseng, Hsiao-Yun

2014-09-01

Fiber structure and order greatly impact the mechanical behavior of fibrous materials. In biological tissues, the nonlinear mechanics of fibrous scaffolds contribute to the functionality of the material. The nonlinear mechanical properties of the wavy structure (crimp) in collagen allow tissue flexibility while preventing over-extension. A number of approaches have tried to recreate this complex mechanical functionality. We generated microcrimped fibers by briefly heating electrospun parallel fibers over the glass transition temperature or by ethanol treatment. The crimp structure is similar to those of collagen fibers found in native aorta, intestines, or ligaments. Using poly-L-lactic acid fibers, we demonstrated that the bulk materials exhibit changed stress-strain behaviors with a significant increase in the toe region in correlation to the degree of crimp, similar to those observed in collagenous tissues. In addition to mimicking the stress-strain behavior of biological tissues, the microcrimped fibers are instructive in cell morphology and promote ligament phenotypic gene expression. This effect can be further enhanced by dynamic tensile loading, a physiological perturbation in vivo. This rapid and economical approach for microcrimped fiber production provides an accessible platform to study structure-function relationships and a novel functional scaffold for tissue engineering and cell mechanobiology studies.

Comparison of Crack Initiation, Propagation and Coalescence Behavior of Concrete and Rock Materials

NASA Astrophysics Data System (ADS)

Zengin, Enes; Abiddin Erguler, Zeynal

2017-04-01

There are many previously studies carried out to identify crack initiation, propagation and coalescence behavior of different type of rocks. Most of these studies aimed to understand and predict the probable instabilities on different engineering structures such as mining galleries or tunnels. For this purpose, in these studies relatively smaller natural rock and synthetic rock-like models were prepared and then the required laboratory tests were performed to obtain their strength parameters. By using results provided from these models, researchers predicted the rock mass behavior under different conditions. However, in the most of these studies, rock materials and models were considered as contains none or very few discontinuities and structural flaws. It is well known that rock masses naturally are extremely complex with respect to their discontinuities conditions and thus it is sometimes very difficult to understand and model their physical and mechanical behavior. In addition, some vuggy rock materials such as basalts and limestones also contain voids and gaps having various geometric properties. Providing that the failure behavior of these type of rocks controlled by the crack initiation, propagation and coalescence formed from their natural voids and gaps, the effect of these voids and gaps over failure behavior of rocks should be investigated. Intact rocks are generally preferred due to relatively easy side of their homogeneous characteristics in numerical modelling phases. However, it is very hard to extract intact samples from vuggy rocks because of their complex pore sizes and distributions. In this study, the feasibility of concrete samples to model and mimic the failure behavior vuggy rocks was investigated. For this purpose, concrete samples were prepared at a mixture of %65 cement dust and %35 water and their physical and mechanical properties were determined by laboratory experiments. The obtained physical and mechanical properties were used to constitute numerical models, and then uniaxial compressive strength (UCS) tests were performed on these models by using a commercial software called as Particle Flow Code (PFC2D). When the crack behavior of concrete samples obtained from both laboratory tests and numerical models are compared with the results of previous studies, a significant similarity was found. As a result, due to the observed similarity crack behavior between concretes and rocks, it can be concluded that intact concrete samples can be used for modelling purposes to understand the effect of voids and gaps on failure characteristics of vuggy rocks.

A novel gel based on an ionic complex from a dendronized polymer and ciprofloxacin: Evaluation of its use for controlled topical drug release.

PubMed

García, Mónica C; Cuggino, Julio C; Rosset, Clarisa I; Páez, Paulina L; Strumia, Miriam C; Manzo, Ruben H; Alovero, Fabiana L; Alvarez Igarzabal, Cecilia I; Jimenez-Kairuz, Alvaro F

2016-12-01

The development and characterization of a novel, gel-type material based on a dendronized polymer (DP) loaded with ciprofloxacin (CIP), and the evaluation of its possible use for controlled drug release, are presented in this work. DP showed biocompatible and non-toxic behaviors in cultured cells, both of which are considered optimal properties for the design of a final material for biomedical applications. These results were encouraging for the use of the polymer loaded with CIP (as a drug model), under gel form, in the development of a new controlled-release system to be evaluated for topical administration. First, DP-CIP ionic complexes were obtained by an acid-base reaction using the high density of carboxylic acid groups of the DP and the amine groups of the CIP. The complexes obtained in the solid state were broadly characterized using FTIR spectroscopy, XRP diffraction, DSC-TG analysis and optical microscopy techniques. Gels based on the DP-CIP complexes were easily prepared and presented excellent mechanical behaviors. In addition, optimal properties for application on mucosal membranes and skin were achieved due to their high biocompatibility and acute skin non-irritation. Slow and sustained release of CIP toward simulated physiological fluids was observed in the assays (in vitro), attributed to ion exchange phenomenon and to the drug reservoir effect. An in vitro bacterial growth inhibition assay showed significant CIP activity, corresponding to 38 and 58% of that exhibited by a CIP hydrochloride solution at similar CIP concentrations, against Staphylococcus aureus and Pseudomonas aeruginosa, respectively. However, CIP delivery was appropriate, both in terms of magnitude and velocity to allow for a bactericidal effect. In conclusion, the final product showed promising behavior, which could be exploited for the treatment of topical and mucosal opportunistic infections in human or veterinary applications. Copyright © 2016 Elsevier B.V. All rights reserved.

The Fremont complex: A behavioral perspective

USGS Publications Warehouse

Madsen, D.B.; Simms, S.R.

1998-01-01

The Fremont complex is composed of farmers and foragers who occupied the Colorado Plateau and Great Basin region of western North America from about 2100 to 500 years ago. These people included both immigrants and indigenes who shared some material culture and symbolic attributes, but also varied in ways not captured by definitions of the Fremont as a shared cultural tradition. The complex reflects a mosaic of behaviors including full-time farmers, full-time foragers, part-time farmer/foragers who seasonally switched modes of production, farmers who switched to full-time foraging, and foragers who switched to full-time farming. Farming defines the Fremont, but only in the sense that it altered the matrix in which both farmers and foragers lived, a matrix which provided a variety of behavioral options to people pursuing an array of adaptive strategies. The mix of symbiotic and competitive relationships among farmers and between farmers and foragers presents challenges to detection in the archaeological record. Greater clarity results from use of a behavioral model which recognizes differing contexts of selection favoring one adaptive strategy over another. The Fremont is a case where the transition from foraging to farming is followed by a millennium of adaptive diversity and terminates with the abandonment of farming. As such, it serves as a potential comparison to other cases in the world during the early phases of the food producing transition.

Electromagnetic game modeling through Tensor Analysis of Networks and Game Theory

NASA Astrophysics Data System (ADS)

Maurice, Olivier; Reineix, Alain; Lalléchère, Sébastien

2014-10-01

A complex system involves events coming from natural behaviors. Whatever is the complicated face of machines, they are still far from the complexity of natural systems. Currently, economy is one of the rare science trying to find out some ways to model human behavior. These attempts involve game theory and psychology. Our purpose is to develop a formalism able to take in charge both game and hardware modeling. We first present the Tensorial Analysis of Networks, used for the material part of the system. Then, we detail the mathematical objects defined in order to describe the evolution of the system and its gaming side. To illustrate the discussion we consider the case of a drone whose electronic can be disturbed by a radar field, but this drone must fly as near as possible close to this radar.

New gelling systems to fabricate complex-shaped transparent ceramics

NASA Astrophysics Data System (ADS)

Yang, Yan; Wu, Yiquan

2013-06-01

The aim of this work was to prepare transparent ceramics with large size and complex-shapes by a new water-soluble gelling agent poly(isobutylene-alt-maleic anhydride). Alumina was used as an example of the application of the new gelling system. A stable suspension with 38vol% was prepared by ball milling. Trapped bubbles were removed before casting to obtain homogenous green bodies. The microstructure and particle distribution of alumina raw material were tested. The thermal behavior of the alumina green body was investigated, which exhibited low weight loss when compared with other gelling processes. The influence of solid loading and gelling agent addition were studied on the basis of rheological behavior of the suspension. The microstructures of alumina powders, green bodies before and after de-bindering process, were compared to understand the gelling condition between alumina particles and gelling agent.

The photoelectronic behaviors of MoO3-loaded ZrO2/carbon cluster nanocomposite materials

NASA Astrophysics Data System (ADS)

Matsui, H.; Ishiko, A.; Karuppuchamy, S.; Hassan, M. A.; Yoshihara, M.

2012-03-01

A novel nano-sized ZrO2/carbon cluster composite materials (Ic's) were successfully obtained by the calcination of ZrCl4/starch complexes I's under an argon atmosphere. Pt- and/or MoO3-loaded ZrO2/carbon clusters composite materials were also prepared by doping Pt and/or MoO3 particles on the surface of Ic's. The surface characterization of the composite materials was carried out using transmission electron microscopy (TEM). The TEM observation of the materials showed the presence of particles with the diameters of a few nanometers, possibly Pt particles, and of 50-100 nm, possibly MoO3 particles, in the matrix. Pt- and/or MoO3-loaded ZrO2/carbon cluster composite materials show the efficient photocatalytic activity under visible light irradiation.

Prelude: The renaissance of electrocatalysis

DOE PAGES

Shao, Yuyan; Markovic, Nenad M.

2016-09-16

Recent improvements in the fundamental understanding of the behavior of electrochemical interfaces in aqueous electrolytes have begun a revolution in the field of electrocatalysis, enabling the design of interfaces tailored to the efficient breaking and making of specific chemical bonds, as well as providing insight into the redistribution of the electrons that are associated with these transformations. We intentionally emphasize the importance of electrochemical interfaces, rather than electrode materials, because contemporary electrocatalysis goes well beyond the design and synthesis of materials. Rather, it has become the science of electrode processes, where the reaction rates have a strong dependence on themore » nature of both the electrode material as well as the electrolyte, i.e., solvated ions in the vicinity (~0.3 nm) of the electrode. Lastly, although understanding the role of electrolyte components introduces an additional level of complexity, this very same complexity has led to a new wave of discovery and will provide the knowledge required to move beyond the current generation of materials and electrolytes and shape the future of alternative energy sources that are key to delivering energy security and protecting the environment.« less

Electrospun curcumin-loaded cellulose acetate/polyvinylpyrrolidone fibrous materials with complex architecture and antibacterial activity.

PubMed

Tsekova, Petya B; Spasova, Mariya G; Manolova, Nevena E; Markova, Nadya D; Rashkov, Iliya B

2017-04-01

Novel fibrous materials from cellulose acetate (CA) and polyvinylpyrrolidone (PVP) containing curcumin (Curc) with original design were prepared by one-pot electrospinning or dual spinneret electrospinning. The electrospun materials were characterized by scanning electron microscopy (SEM), fluorescence microscopy, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), differential scanning calorimetry (DSC), water contact angle measurements, and microbiological tests. It was found that the incorporation of Curc into the CA and PVP solutions resulted in an increase of the solution viscosity and obtaining fibers with larger diameters (ca. 1.5μm) compared to the neat CA (ca. 800nm) and PVP fibers (ca. 500nm). The incorporation of PVP resulted in increased hydrophilicity of the fibers and in faster Curc release. Curc was found in the amorphous state in the Curc-containing fibers and these mats exhibited antibacterial activity against Staphylococcus aureus (S. aureus). The results suggest that, due to their complex architecture, the obtained new antibacterial materials are suitable for wound dressing applications, which necessitate diverse release behaviors of the bioactive compound. Copyright © 2016 Elsevier B.V. All rights reserved.

Dynamic Modeling of ALS Systems

NASA Technical Reports Server (NTRS)

Jones, Harry

2002-01-01

The purpose of dynamic modeling and simulation of Advanced Life Support (ALS) systems is to help design them. Static steady state systems analysis provides basic information and is necessary to guide dynamic modeling, but static analysis is not sufficient to design and compare systems. ALS systems must respond to external input variations and internal off-nominal behavior. Buffer sizing, resupply scheduling, failure response, and control system design are aspects of dynamic system design. We develop two dynamic mass flow models and use them in simulations to evaluate systems issues, optimize designs, and make system design trades. One model is of nitrogen leakage in the space station, the other is of a waste processor failure in a regenerative life support system. Most systems analyses are concerned with optimizing the cost/benefit of a system at its nominal steady-state operating point. ALS analysis must go beyond the static steady state to include dynamic system design. All life support systems exhibit behavior that varies over time. ALS systems must respond to equipment operating cycles, repair schedules, and occasional off-nominal behavior or malfunctions. Biological components, such as bioreactors, composters, and food plant growth chambers, usually have operating cycles or other complex time behavior. Buffer sizes, material stocks, and resupply rates determine dynamic system behavior and directly affect system mass and cost. Dynamic simulation is needed to avoid the extremes of costly over-design of buffers and material reserves or system failure due to insufficient buffers and lack of stored material.

Research on mechanical and sensoric set-up for high strain rate testing of high performance fibers

NASA Astrophysics Data System (ADS)

Unger, R.; Schegner, P.; Nocke, A.; Cherif, C.

2017-10-01

Within this research project, the tensile behavior of high performance fibers, such as carbon fibers, is investigated under high velocity loads. This contribution (paper) focuses on the clamp set-up of two testing machines. Based on a kinematic model, weight optimized clamps are designed and evaluated. By analyzing the complex dynamic behavior of conventional high velocity testing machines, it has been shown that the impact typically exhibits an elastic characteristic. This leads to barely predictable breaking speeds and will not work at higher speeds when acceleration force exceeds material specifications. Therefore, a plastic impact behavior has to be achieved, even at lower testing speeds. This type of impact behavior at lower speeds can be realized by means of some minor test set-up adaptions.

Probing dynamics and pinning of single vortices in superconductors at nanometer scales.

PubMed

Embon, L; Anahory, Y; Suhov, A; Halbertal, D; Cuppens, J; Yakovenko, A; Uri, A; Myasoedov, Y; Rappaport, M L; Huber, M E; Gurevich, A; Zeldov, E

2015-01-07

The dynamics of quantized magnetic vortices and their pinning by materials defects determine electromagnetic properties of superconductors, particularly their ability to carry non-dissipative currents. Despite recent advances in the understanding of the complex physics of vortex matter, the behavior of vortices driven by current through a multi-scale potential of the actual materials defects is still not well understood, mostly due to the scarcity of appropriate experimental tools capable of tracing vortex trajectories on nanometer scales. Using a novel scanning superconducting quantum interference microscope we report here an investigation of controlled dynamics of vortices in lead films with sub-Angstrom spatial resolution and unprecedented sensitivity. We measured, for the first time, the fundamental dependence of the elementary pinning force of multiple defects on the vortex displacement, revealing a far more complex behavior than has previously been recognized, including striking spring softening and broken-spring depinning, as well as spontaneous hysteretic switching between cellular vortex trajectories. Our results indicate the importance of thermal fluctuations even at 4.2 K and of the vital role of ripples in the pinning potential, giving new insights into the mechanisms of magnetic relaxation and electromagnetic response of superconductors.

Probing dynamics and pinning of single vortices in superconductors at nanometer scales

NASA Astrophysics Data System (ADS)

Embon, L.; Anahory, Y.; Suhov, A.; Halbertal, D.; Cuppens, J.; Yakovenko, A.; Uri, A.; Myasoedov, Y.; Rappaport, M. L.; Huber, M. E.; Gurevich, A.; Zeldov, E.

2015-01-01

The dynamics of quantized magnetic vortices and their pinning by materials defects determine electromagnetic properties of superconductors, particularly their ability to carry non-dissipative currents. Despite recent advances in the understanding of the complex physics of vortex matter, the behavior of vortices driven by current through a multi-scale potential of the actual materials defects is still not well understood, mostly due to the scarcity of appropriate experimental tools capable of tracing vortex trajectories on nanometer scales. Using a novel scanning superconducting quantum interference microscope we report here an investigation of controlled dynamics of vortices in lead films with sub-Angstrom spatial resolution and unprecedented sensitivity. We measured, for the first time, the fundamental dependence of the elementary pinning force of multiple defects on the vortex displacement, revealing a far more complex behavior than has previously been recognized, including striking spring softening and broken-spring depinning, as well as spontaneous hysteretic switching between cellular vortex trajectories. Our results indicate the importance of thermal fluctuations even at 4.2 K and of the vital role of ripples in the pinning potential, giving new insights into the mechanisms of magnetic relaxation and electromagnetic response of superconductors.

Tribological and Mechanical Behaviors of Polyamide 6/Glass Fiber Composite Filled with Various Solid Lubricants

PubMed Central

Li, Duxin; Xie, Ying; Li, Wenjuan; You, Yilan; Deng, Xin

2013-01-01

The effects of polytetrafluoroethylene (PTFE), graphite, ultrahigh molecular weight polyethylene (UHMWPE), and their compounds on mechanical and tribological properties of glass-fiber-reinforced polyamide 6 (PA6/GF) were studied. The polymeric materials were blended using twin-screw extruder and subsequently injection molded for test samples. Mechanical properties were investigated in terms of hardness, tensile strength, and impact strength. Friction and wear experiments were run under ambient conditions at a rotating speed of 200 rpm and load of 100 N. The morphologies of the worn surfaces were also observed with scanning electron microscope. The results showed that graphite could increase the tensile strength of PA6/GF-15 composite, but the material became soft. Graphite/UHMWPE complex solid lubricants were effective in increasing the already high impact strength of PA6/GF-15 composite. 5% PTFE gave the maximum reduction in the coefficient of friction. However, PTFE/UHMWPE complex solid lubricants were the best choice for improving both friction and wear behaviors due to the lower friction coefficient and mass wear rate. Moreover, the worn surface of PA6 composites revealed that adhesive wear, abrasive wear, and fatigue wear occurred in this study. PMID:23766687

Molecular structure and biological studies on Cr(III), Mn(II) and Fe(III) complexes of heterocyclic carbohydrazone ligand.

PubMed

Abu El-Reash, G M; El-Gammal, O A; Radwan, A H

2014-01-01

The chelating behavior of the ligand (H2APC) based on carbohydrazone core modified with pyridine end towards Cr(III), Mn(II) and Fe(III) ions have been examined. The (1)H NMR and IR data for H2APC revealed the presence of two stereoisomers syn and anti in both solid state and in solution in addition to the tautomeric versatility based on the flexible nature of the hydrazone linkage leading to varied coordination modes. The spectroscopic data confirmed that the ligand behaves as a monobasic tridentate in Cr(III) and Fe(III) complexes and as neutral tetradentate in Mn(II) complex. The electronic spectra as well as the magnetic measurements confirmed the octahedral geometry for all complexes. The bond length and angles were evaluated by DFT method using material studio program for all complexes. The thermal behavior and the kinetic parameters of degradation were determined using Coats-Redfern and Horowitz-Metzger methods. The antioxidant (DDPH and ABTS methods), anti-hemolytic and cytotoxic activities of the compounds have been screened. Cr(III) complex and H2APC showed the highest antioxidant activity using ABTS and DPPH methods. With respect to in vitro Ehrlich ascites assay, H2APC exhibited the potent activity followed by Fe(III) and Cr(III)complexes. Copyright © 2013 Elsevier B.V. All rights reserved.

Fast Physically Accurate Rendering of Multimodal Signatures of Distributed Fracture in Heterogeneous Materials.

PubMed

Visell, Yon

2015-04-01

This paper proposes a fast, physically accurate method for synthesizing multimodal, acoustic and haptic, signatures of distributed fracture in quasi-brittle heterogeneous materials, such as wood, granular media, or other fiber composites. Fracture processes in these materials are challenging to simulate with existing methods, due to the prevalence of large numbers of disordered, quasi-random spatial degrees of freedom, representing the complex physical state of a sample over the geometric volume of interest. Here, I develop an algorithm for simulating such processes, building on a class of statistical lattice models of fracture that have been widely investigated in the physics literature. This algorithm is enabled through a recently published mathematical construction based on the inverse transform method of random number sampling. It yields a purely time domain stochastic jump process representing stress fluctuations in the medium. The latter can be readily extended by a mean field approximation that captures the averaged constitutive (stress-strain) behavior of the material. Numerical simulations and interactive examples demonstrate the ability of these algorithms to generate physically plausible acoustic and haptic signatures of fracture in complex, natural materials interactively at audio sampling rates.

Role of chemically and thermally induced crystal lattice distortion in enhancing the Seebeck coefficient in complex tellurides

DOE PAGES

Levin, E. M.; Iowa State Univ., Ames, IA; Kramer, M. J.; ...

2016-07-14

Composition and crystal structure of complex materials can significantly change the Seebeck effect, i.e., heat to electrical energy conversion, which is utilized in thermoelectric materials. Despite decades of studies of various thermoelectric materials and their application, the fundamental understanding of this effect still is limited. One of the most efficient groups of thermoelectric materials is based on GeTe, where Ge is replaced by [Ag + Sb], i.e., Ag xSb xGe 50-2xTe 50 alloys, traditionally shown as (GeTe) m(AgSbTe 2) 100-m (TAGS-m series). Here, in this article, we report on the discovery of two unique phenomena in TAGS materials attributed tomore » the effects from [Ag + Sb] atoms: (i) a linear relation between the Seebeck coefficient and rhombohedral lattice distortion, and (ii) resonance-like temperature-induced behavior of the contribution to the Seebeck coefficient produced by [Ag + Sb] atoms. Finally, our findings show that heat to electrical energy conversion strongly depends on the temperature- and compositionally-induced rhombohedral to cubic transformation where [Ag + Sb] atoms play a crucial mediating role.« less

Does formal complexity reflect cognitive complexity? Investigating aspects of the Chomsky Hierarchy in an artificial language learning study.

PubMed

Öttl, Birgit; Jäger, Gerhard; Kaup, Barbara

2015-01-01

This study investigated whether formal complexity, as described by the Chomsky Hierarchy, corresponds to cognitive complexity during language learning. According to the Chomsky Hierarchy, nested dependencies (context-free) are less complex than cross-serial dependencies (mildly context-sensitive). In two artificial grammar learning (AGL) experiments participants were presented with a language containing either nested or cross-serial dependencies. A learning effect for both types of dependencies could be observed, but no difference between dependency types emerged. These behavioral findings do not seem to reflect complexity differences as described in the Chomsky Hierarchy. This study extends previous findings in demonstrating learning effects for nested and cross-serial dependencies with more natural stimulus materials in a classical AGL paradigm after only one hour of exposure. The current findings can be taken as a starting point for further exploring the degree to which the Chomsky Hierarchy reflects cognitive processes.

Does Formal Complexity Reflect Cognitive Complexity? Investigating Aspects of the Chomsky Hierarchy in an Artificial Language Learning Study

PubMed Central

Öttl, Birgit; Jäger, Gerhard; Kaup, Barbara

2015-01-01

This study investigated whether formal complexity, as described by the Chomsky Hierarchy, corresponds to cognitive complexity during language learning. According to the Chomsky Hierarchy, nested dependencies (context-free) are less complex than cross-serial dependencies (mildly context-sensitive). In two artificial grammar learning (AGL) experiments participants were presented with a language containing either nested or cross-serial dependencies. A learning effect for both types of dependencies could be observed, but no difference between dependency types emerged. These behavioral findings do not seem to reflect complexity differences as described in the Chomsky Hierarchy. This study extends previous findings in demonstrating learning effects for nested and cross-serial dependencies with more natural stimulus materials in a classical AGL paradigm after only one hour of exposure. The current findings can be taken as a starting point for further exploring the degree to which the Chomsky Hierarchy reflects cognitive processes. PMID:25885790

Electro-Statically Stricted Polymers (ESSP)

NASA Technical Reports Server (NTRS)

Liu, C.; Bar-Cohen, Y.; Leary, S.

1999-01-01

Miniature, lightweight, miser actuators that operate similar to biological muscles can be used to develop robotic devices with unmatched capabilities and impact many technology areas. Electroactive polymers (EAP) offer the potential to producing such actuators and their main attractive feature is their ability to induce relatively large bending or longitudinal strain. EAP actuators can change the paradigm about the complexity of robots, where robotic components such as motors, gears, bearings, and others can be eliminated with simple drive mechanisms. Generally, these materials produce a relatively low force and the applications that can be considered at the current state of the art are relatively limited. While improved material are being developed there is a need for methods to develop longitudinal actuators that can contract similar to muscles. In this study, the authors began investigating the electromechanical behavior of polymers in reaction to a complex configuration of electric fields. A computer model was used to simulate the electromechanical response. Efforts were made to develop both the material basis as well as the electromechanical modeling of the actuator.

Microfabrication of hierarchical structures for engineered mechanical materials

NASA Astrophysics Data System (ADS)

Vera Canudas, Marc

Materials found in nature present, in some cases, unique properties from their constituents that are of great interest in engineered materials for applications ranging from structural materials for the construction of bridges, canals and buildings to the fabrication of new lightweight composites for airplane and automotive bodies, to protective thin film coatings, amongst other fields. Research in the growing field of biomimetic materials indicates that the micro-architectures present in natural materials are critical to their macroscopic mechanical properties. A better understanding of the effect that structure and hierarchy across scales have on the material properties will enable engineered materials with enhanced properties. At the moment, very few theoretical models predict mechanical properties of simple materials based on their microstructures. Moreover these models are based on observations from complex biological systems. One way to overcome this challenge is through the use of microfabrication techniques to design and fabricate simple materials, more appropriate for the study of hierarchical organizations and microstructured materials. Arrays of structures with controlled geometry and dimension can be designed and fabricated at different length scales, ranging from a few hundred nanometers to centimeters, in order to mimic similar systems found in nature. In this thesis, materials have been fabricated in order to gain fundamental insight into the complex hierarchical materials found in nature and to engineer novel materials with enhanced mechanical properties. The materials fabricated here were mechanically characterized and compared to simple mechanics models to describe their behavior with the goal of applying the knowledge acquired to the design and synthesis of future engineered materials with novel properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siranosian, Antranik Antonio; Schembri, Philip Edward; Luscher, Darby Jon

The Los Alamos National Laboratory's Weapon Systems Engineering division's Advanced Engineering Analysis group employs material constitutive models of composites for use in simulations of components and assemblies of interest. Experimental characterization, modeling and prediction of the macro-scale (i.e. continuum) behaviors of these composite materials is generally difficult because they exhibit nonlinear behaviors on the meso- (e.g. micro-) and macro-scales. Furthermore, it can be difficult to measure and model the mechanical responses of the individual constituents and constituent interactions in the composites of interest. Current efforts to model such composite materials rely on semi-empirical models in which meso-scale properties are inferredmore » from continuum level testing and modeling. The proposed approach involves removing the difficulties of interrogating and characterizing micro-scale behaviors by scaling-up the problem to work with macro-scale composites, with the intention of developing testing and modeling capabilities that will be applicable to the mesoscale. This approach assumes that the physical mechanisms governing the responses of the composites on the meso-scale are reproducible on the macro-scale. Working on the macro-scale simplifies the quantification of composite constituents and constituent interactions so that efforts can be focused on developing material models and the testing techniques needed for calibration and validation. Other benefits to working with macro-scale composites include the ability to engineer and manufacture—potentially using additive manufacturing techniques—composites that will support the application of advanced measurement techniques such as digital volume correlation and three-dimensional computed tomography imaging, which would aid in observing and quantifying complex behaviors that are exhibited in the macro-scale composites of interest. Ultimately, the goal of this new approach is to develop a meso-scale composite modeling framework, applicable to many composite materials, and the corresponding macroscale testing and test data interrogation techniques to support model calibration.« less

Open problems in active chaotic flows: Competition between chaos and order in granular materials.

PubMed

Ottino, J. M.; Khakhar, D. V.

2002-06-01

There are many systems where interaction among the elementary building blocks-no matter how well understood-does not even give a glimpse of the behavior of the global system itself. Characteristic for these systems is the ability to display structure without any external organizing principle being applied. They self-organize as a consequence of synthesis and collective phenomena and the behavior cannot be understood in terms of the systems' constitutive elements alone. A simple example is flowing granular materials, i.e., systems composed of particles or grains. How the grains interact with each other is reasonably well understood; as to how particles move, the governing law is Newton's second law. There are no surprises at this level. However, when the particles are many and the material is vibrated or tumbled, surprising behavior emerges. Systems self-organize in complex patterns that cannot be deduced from the behavior of the particles alone. Self-organization is often the result of competing effects; flowing granular matter displays both mixing and segregation. Small differences in either size or density lead to flow-induced segregation and order; similar to fluids, noncohesive granular materials can display chaotic mixing and disorder. Competition gives rise to a wealth of experimental outcomes. Equilibrium structures, obtained experimentally in quasi-two-dimensional systems, display organization in the presence of disorder, and are captured by a continuum flow model incorporating collisional diffusion and density-driven segregation. Several open issues remain to be addressed. These include analysis of segregating chaotic systems from a dynamical systems viewpoint, and understanding three-dimensional systems and wet granular systems (slurries). General aspects of the competition between chaos-enhanced mixing and properties-induced de-mixing go beyond granular materials and may offer a paradigm for other kinds of physical systems. (c) 2002 American Institute of Physics.

Nb-Base FS-85 Alloy as a Candidate Structural Material for Space Reactor Applications: Effects of Thermal Aging

NASA Astrophysics Data System (ADS)

Leonard, Keith J.; Busby, Jeremy T.; Hoelzer, David T.; Zinkle, Steven J.

2009-04-01

The proposed uses of fission reactors for manned or deep space missions have typically relied on the potential use of refractory metal alloys as structural materials. Throughout the history of these programs, a leading candidate has been Nb-1Zr, due to its good fabrication and welding characteristics. However, the less-than-optimal creep resistance of this alloy has encouraged interest in the more complex FS-85 (Nb-28Ta-10W-1Zr) alloy. Despite this interest, only a relatively small database exists for the properties of FS-85. Database gaps include the potential microstructural instabilities that can lead to mechanical property degradation. In this work, changes in the microstructure and mechanical properties of FS-85 were investigated following 1100 hours of thermal aging at 1098, 1248, and 1398 K. The changes in electrical resistivity, hardness, and tensile properties between the as-annealed and aged materials are compared. Evaluation of the microstructural changes was performed through optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The development of intragranular and grain-boundary precipitation of Zr-rich compounds as a function of aging temperature was followed. Brittle tensile behavior was measured in the material aged at 1248 K, while ductile behavior occurred in samples aged above and below this temperature. The effect of temperature on the under- and overaging of the grain-boundary particles is believed to have contributed to the mechanical property behavior of the aged materials.

Cyclic Oxidation Testing and Modelling: A NASA Lewis Perspective

NASA Technical Reports Server (NTRS)

Smialek, J. L.; Nesbitt, J. A.; Barrett, C. A.; Lowell, C. E.

2000-01-01

The Materials Division of the NASA Lewis Research Center has been heavily involved in the cyclic oxidation of high temperature materials for 30 years. Cyclic furnace and burner rig apparati have been developed, refined, and replicated to provide a large scale facility capable of evaluating many materials by a standard technique. Material behavior is characterized by weight change data obtained throughout the test, which has been modelled in a step-wise process of scale growth and spallation. This model and a coupled diffusion model have successfully described cyclic behavior for a number of systems and have provided insights regarding life prediction and variations in the spalling process. Performance ranking and mechanistic studies are discussed primarily for superalloys and coating alloys. Similar cyclic oxidation studies have been performed on steels, intermetallic compounds, thermal barrier coatings, ceramics, and ceramic composites. The most common oxidation test was performed in air at temperatures ranging from 800 deg. to 1600 C, for times up to 10000 h, and for cycle durations of 0.1 to 1000 h. Less controlled, but important, test parameters are the cooling temperature and humidity level. Heating and cooling rates are not likely to affect scale spallation. Broad experience has usually allowed for considerable focus and simplification of these test parameters, while still revealing the principal aspects of material behavior and performance. Extensive testing has been performed to statistically model the compositional effects of experimental alloys and to construct a comprehensive database of complex commercial alloys.

Numerical investigation of shape domain effect to its elasticity and surface energy using adaptive finite element method

NASA Astrophysics Data System (ADS)

Alfat, Sayahdin; Kimura, Masato; Firihu, Muhammad Zamrun; Rahmat

2018-05-01

In engineering area, investigation of shape effect in elastic materials was very important. It can lead changing elasticity and surface energy, and also increase of crack propagation in the material. A two-dimensional mathematical model was developed to investigation of elasticity and surface energy in elastic material by Adaptive Finite Element Method. Besides that, behavior of crack propagation has observed for every those materials. The government equations were based on a phase field approach in crack propagation model that developed by Takaishi-Kimura. This research has varied four shape domains where physical properties of materials were same (Young's modulus E = 70 GPa and Poisson's ratio ν = 0.334). Investigation assumptions were; (1) homogeneous and isotropic material, (2) there was not initial cracking at t = 0, (3) initial displacement was zero [u1, u2] = 0) at initial condition (t = 0), and (4) length of time simulation t = 5 with interval Δt = 0.005. Mode I/II or mixed mode crack propagation has been used for the numerical investigation. Results of this studies were very good and accurate to show changing energy and behavior of crack propagation. In the future time, this research can be developed to complex phenomena and domain. Furthermore, shape optimization can be investigation by the model.

STUDY OF BIFERROIC PROPERTIES IN THE La0.37Ca0.17Ba0.43Mn0.52Ti0.44Zr0.04O3 COMPLEX PEROVSKITE

NASA Astrophysics Data System (ADS)

Cardona-Vásquez, J. A.; Gómez, M. E.; Landínez-Téllez, D. A.; Roa-Rojas, J.

2013-10-01

In this paper, details of synthesis and structural, morphological, electrical, and magnetic characterization of the new La0.37Ca0.17Ba0.43Mn0.52Ti0.44Zr0.04O3 multiferroic complex perovskite are reported. Mixtures with 50% mass of ferromagnetic lanthanum calcium manganite La0.67Ca0.33MnO3 and ferroelectric barium-lanthanum zirconate titanate Ba0.9La0.067Ti0.91Zr0.09 O3 were prepared by the solid state reaction technique. Patterns of X-ray diffraction showed that the materials have reacted resulting in a new perovskite-like structure with tetragonal symmetry, space group P4mm(#99). The structure of the material was refined using the Rietveld method through the GSAS code. ZFC and FC magnetization curves show the occurrence of two phase transitions at 42.25 K and 203.9 K which have been associated with two different magnetic regimes. Hysteresis curves measured confirm that the relationship between the applied field and the magnetization does not evidence a linear behavior. These curves also show that in the low temperature regime the magnetic memory of the material is greater than in the high temperature region. AC impedance as a function of temperature measurements show the same two regions observed in the magnetization curves. The ferroelectric behavior with relative permittivity of 153.12 is observed by polarization curves performed at room temperature in the synthesized materials.

Analysis of the Lankford coefficient evolution at different strain rates for AA6016-T4, DP800 and DC06

NASA Astrophysics Data System (ADS)

Lenzen, Matthias; Merklein, Marion

2017-10-01

In the automotive sector, a major challenge is the deep-drawing of modern lightweight sheet metals with limited formability. Thus, conventional material models lack in accuracy due to the complex material behavior. A current field of research takes into account the evolution of the Lankford coefficient. Today, changes in anisotropy under increasing degree of deformation are not considered. Only a consolidated average value of the Lankford coefficient is included in conventional material models. This leads to an increasing error in prediction of the flow behavior and therefore to an inaccurate prognosis of the forming behavior. To increase the accuracy of the prediction quality, the strain dependent Lankford coefficient should be respected, because the R-value has a direct effect on the contour of the associated flow rule. Further, the investigated materials show a more or less extinct rate dependency of the yield stress. For this reason, the rate dependency of the Lankford coefficient during uniaxial tension is focused within this contribution. To quantify the influence of strain rate on the Lankford coefficient, tensile tests are performed for three commonly used materials, the aluminum alloy AA6016-T4, the advanced high strength steel DP800 and the deep drawing steel DC06 at three different strain rates. The strain measurement is carried out by an optical strain measurement system. An evolution of the Lankford coefficient was observed for all investigated materials. Also, an influence of the deformation velocity on the anisotropy could be detected.

Testing equivalence of mediating models of income, parenting, and school readiness for white, black, and Hispanic children in a national sample.

PubMed

Raver, C Cybele; Gershoff, Elizabeth T; Aber, J Lawrence

2007-01-01

This paper examines complex models of the associations between family income, material hardship, parenting, and school readiness among White, Black, and Hispanic 6-year-olds, using the Early Childhood Longitudinal Study-Kindergarten Cohort (ECLS-K). It is critical to test the universality of such complex models, particularly given their implications for intervention, prevention, and public policy. Therefore this study asks: Do measures and models of low income and early school readiness indicators fit differently or similarly for White, Black, and Hispanic children? Measurement equivalence of material hardship, parent stress, parenting behaviors, child cognitive skills, and child social competence is first tested. Model equivalence is then tested by examining whether category membership in a race/ethnic group moderates associations between predictors and young children's school readiness.

Testing Equivalence of Mediating Models of Income, Parenting, and School Readiness for White, Black, and Hispanic Children in a National Sample

PubMed Central

Raver, C. Cybele; Gershoff, Elizabeth T.; Aber, J. Lawrence

2010-01-01

This paper examines complex models of the associations between family income, material hardship, parenting, and school readiness among White, Black, and Hispanic 6-year-olds, using the Early Childhood Longitudinal Study – Kindergarten Cohort (ECLS – K). It is critical to test the universality of such complex models, particularly given their implications for intervention, prevention, and public policy. Therefore this study asks: Do measures and models of low income and early school readiness indicators fit differently or similarly for White, Black, and Hispanic children? Measurement equivalence of material hardship, parent stress, parenting behaviors, child cognitive skills, and child social competence is first tested. Model equivalence is then tested by examining whether category membership in a race/ethnic group moderates associations between predictors and young children’s school readiness. PMID:17328695

Finite Dimensional Approximations for Continuum Multiscale Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berlyand, Leonid

2017-01-24

The completed research project concerns the development of novel computational techniques for modeling nonlinear multiscale physical and biological phenomena. Specifically, it addresses the theoretical development and applications of the homogenization theory (coarse graining) approach to calculation of the effective properties of highly heterogenous biological and bio-inspired materials with many spatial scales and nonlinear behavior. This theory studies properties of strongly heterogeneous media in problems arising in materials science, geoscience, biology, etc. Modeling of such media raises fundamental mathematical questions, primarily in partial differential equations (PDEs) and calculus of variations, the subject of the PI’s research. The focus of completed researchmore » was on mathematical models of biological and bio-inspired materials with the common theme of multiscale analysis and coarse grain computational techniques. Biological and bio-inspired materials offer the unique ability to create environmentally clean functional materials used for energy conversion and storage. These materials are intrinsically complex, with hierarchical organization occurring on many nested length and time scales. The potential to rationally design and tailor the properties of these materials for broad energy applications has been hampered by the lack of computational techniques, which are able to bridge from the molecular to the macroscopic scale. The project addressed the challenge of computational treatments of such complex materials by the development of a synergistic approach that combines innovative multiscale modeling/analysis techniques with high performance computing.« less

Mechanics of Granular Materials (MGM) Flight Hardware

NASA Technical Reports Server (NTRS)

1997-01-01

A test cell for the Mechanics of Granular Materials (MGM) experiment is shown in its on-orbit configuration in Spacehab during preparations for STS-89. The twin locker to the left contains the hydraulic system to operate the experiment. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Note: Because the image on the screen was muted in the original image, its brightness and contrast are boosted in this rendering to make the test cell more visible. Credit: NASA/Marshall Space Flight Center (MSFC)

Equation of State and Shock-Driven Decomposition of 'Soft' Materials

DOE PAGES

Coe, Joshua Damon; Dattelbaum, Dana Mcgraw

2017-12-01

Equation of state (EOS) efforts at National Nuclear Security Administration (NNSA) national laboratories tend to focus heavily on metals, and rightly so given their obvious primacy in nuclear weapons. Our focus here, however, is on the EOS of 'soft' matter such as polymers and their derived foams, which present a number of challenges distinct from those of other material classes. This brief description will cover only one aspect of polymer EOS modeling: treatment of shock-driven decomposition. Here, these interesting (and sometimes neglected) materials exhibit a number of other challenging features— glass transitions, complex thermal behavior, response that is both viscousmore » and elastic—each warranting additional discussions of their own.« less

Energy absorption capability and crashworthiness of composite material structures: A review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carruthers, J.J.; Kettle, A.P.; Robinson, A.M.

1998-10-01

The controlled brittle failure of thermosetting fiber-reinforced polymer composites can provide a very efficient energy absorption mechanism. Consequently, the use of these materials in crashworthy vehicle designs has been the subject of considerable interest. In this respect, their more widespread application has been limited by the complexity of their collapse behavior. This article reviews the current level of understanding i this field, including the correlations between failure mode and energy absorption, the principal material, geometric, and physical parameters relevant to crashworthy design and methods of predicting the energy absorption capability of polymer composites. Areas which require further investigation are identified.more » This review article contains 70 references.« less

Equation of State and Shock-Driven Decomposition of 'Soft' Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coe, Joshua Damon; Dattelbaum, Dana Mcgraw

Equation of state (EOS) efforts at National Nuclear Security Administration (NNSA) national laboratories tend to focus heavily on metals, and rightly so given their obvious primacy in nuclear weapons. Our focus here, however, is on the EOS of 'soft' matter such as polymers and their derived foams, which present a number of challenges distinct from those of other material classes. This brief description will cover only one aspect of polymer EOS modeling: treatment of shock-driven decomposition. Here, these interesting (and sometimes neglected) materials exhibit a number of other challenging features— glass transitions, complex thermal behavior, response that is both viscousmore » and elastic—each warranting additional discussions of their own.« less

Shock interactions with heterogeneous energetic materials

NASA Astrophysics Data System (ADS)

Yarrington, Cole D.; Wixom, Ryan R.; Damm, David L.

2018-03-01

The complex physical phenomenon of shock wave interaction with material heterogeneities has significant importance and nevertheless remains little understood. In many materials, the observed macroscale response to shock loading is governed by characteristics of the microstructure. Yet, the majority of computational studies aimed at predicting phenomena affected by these processes, such as the initiation and propagation of detonation waves in explosives or shock propagation in geological materials, employ continuum material and reactive burn model treatment. In an effort to highlight the grain-scale processes that underlie the observable effects in an energetic system, a grain-scale model for hexanitrostilbene (HNS) has been developed. The measured microstructures were used to produce synthetic computational representations of the pore structure, and a density functional theory molecular dynamics derived equation of state (EOS) was used for the fully dense HNS matrix. The explicit inclusion of the microstructure along with a fully dense EOS resulted in close agreement with historical shock compression experiments. More recent experiments on the dynamic reaction threshold were also reproduced by inclusion of a global kinetics model. The complete model was shown to reproduce accurately the expected response of this heterogeneous material to shock loading. Mesoscale simulations were shown to provide a clear insight into the nature of threshold behavior and are a way to understand complex physical phenomena.

Shock interactions with heterogeneous energetic materials

DOE PAGES

Yarrington, Cole D.; Wixom, Ryan R.; Damm, David L.

2018-03-14

The complex physical phenomenon of shock wave interaction with material heterogeneities has significant importance and nevertheless remains little understood. In many materials, the observed macroscale response to shock loading is governed by characteristics of the microstructure. Yet the majority of computational studies aimed at predicting phenomena affected by these processes, such as initiation and propagation of detonation waves in explosives, or shock propagation in geological materials, employ continuum material and reactive burn model treatment. In an effort to highlight the grain-scale processes that underlie the observable effects in an energetic system, a grain-scale model for hexanitrostilbene (HNS) has been developed.more » Measured microstructures were used to produce synthetic computational representations of the pore structure, and a density functional theory molecular dynamics (DFT-MD) derived equation of state (EOS) was used for the fully dense HNS matrix. The explicit inclusion of microstructure along with a fully-dense EOS resulted in close agreement with historical shock compression experiments. More recent experiments on dynamic reaction threshold were also reproduced by inclusion of a global kinetics model. The complete model was shown to reproduce accurately the expected response of this heterogeneous material to shock loading. Mesoscale simulations were shown to provide clear insight into the nature of threshold behavior, and are a way to understand complex physical phenomena.« less

An Analysis of the Macroscopic Tensile Behavior of a Nonlinear Nylon Reinforced Elastomeric Composite System Using MAC/GMC

NASA Technical Reports Server (NTRS)

Assaad, Mahmoud; Arnold, Steven M.

1999-01-01

A special class of composite laminates composed of soft rubbery matrices and stiff reinforcements made of steel wires or synthetic fibers is examined, where each constituent behaves in a nonlinear fashion even in the small strain domain. Composite laminates made of piles stacked at alternating small orientation angles with respect to the applied axial strain are primarily dominated by the nonlinear behavior of the reinforcing fibers. However; composites with large ply orientations or those perpendicular to the loading axis, will approximate the behavior of the matrix phase and respond in even a more complex fashion for arbitrarily stacked piles. The geometric nonlinearity due to small cord rotations during loading was deemed here to have a second order effect and consequently dropped from any consideration. The user subroutine USRMAT within the Micromechanics Analysis Code with the Generalized Method of Cells (MAC/GMC), was utilized to introduce the constituent material nonlinear behavior. Stress-strain behavior at the macro level was experimentally generated for single and multi ply composites comprised of continuous Nylon-66 reinforcements embedded in a carbon black loaded rubbery matrix. Comparisons between the predicted macro composite behavior and experimental results are excellent when material nonlinearity is included in the analysis. In this paper, a brief review of GMC is provided, along with a description of the nonlinear behavior of the constituents and associated constituent constitutive relations, and the improved macro (or composite) behavior predictions are documented and illustrated.

Understanding the role of the OneLove campaign in facilitating drivers of social and behavioral change in southern Africa: a qualitative evaluation.

PubMed

Jana, Michael; Letsela, Lebohang; Scheepers, Esca; Weiner, Renay

2015-01-01

In the wake of the HIV and AIDS pandemic, health communication has played an important role in social and behavior change in HIV prevention and treatment efforts. Despite this significant role, it is not always clear how health communication influences individuals and communities to facilitate social and behavior change. Guided predominantly by Lewin's theory of change in the context of complexity thinking, and supported by qualitative evidence from Soul City Institute's midterm evaluation of the OneLove multimedia campaign in 9 southern African countries, this article illustrates how carefully designed health edutainment communication materials facilitate drivers of social and behavior change. Thus, researched and theory-based health communication aimed at behavior and social change remains an important pillar in HIV prevention and treatment, where personal and social agency remain key.

Exploring the significance of structural hierarchy in material systems-A review

NASA Astrophysics Data System (ADS)

Pan, Ning

2014-06-01

Structural hierarchy and heterogeneity are inherent features in biological materials, but their significance in affecting the system behaviors is yet to be fully understood. In Sec. I, this article first identifies the major characteristics that manifest, or are resulted from, such hierarchy and heterogeneity in materials. Then in Sec. II, it presents several typical natural material systems including wood, bone, and others from animals to illustrate the proposed views. The paper also discusses a man-made smart material, textiles, to demonstrate that textiles are hierarchal, multifunctional, highly complex, and arguably the engineered material closest on a par with biological materials in complexity, and, more importantly, we can still learn quite a few new things from them in development of novel materials. In Sec. III, the paper summarizes several general approaches in developing a hierarchal material system at various scales, including structure thinning and splitting, laminating and layering, spatial and angular orientation, heterogenization and hybridization, and analyzes the advantages associated with them. It also stresses the adverse consequences once the existing structural hierarchy breaks down due to various mutations in biological systems. It discusses, in particular, the influences of moisture and air on material properties, given the near ubiquitousness of both air and water in materials. It next deals with in Sec. IV, some theoretical issues in material research including packing and ordering, the bi-modular mechanics, the behavior non-affinities due to disparity in hierarchal levels, the importance of system dimensionality in a hierarchal material system, and more philosophically, the issues of Nature's wisdom versus Intelligent Design. Section V then offers some concluding remarks, including a recap of the major issues covered in this article, and some general conclusions derived from the analyses and discussions. The main purpose of this paper is to make an effort to explore, identify, derive, or theorize some generic principles based on the existing results, not to offer another comprehensive review of current research activities in the fields for that there already exist some excellent ones. This paper examines the related topics with several approaches to not only reveal the underlying geometrical and physical mechanisms but also to emphasize the ways in which such mechanisms may be applied to developing engineered material systems with novel properties.

Effects of Task Complexity on L2 Writing Behaviors and Linguistic Complexity

ERIC Educational Resources Information Center

Révész, Andrea; Kourtali, Nektaria-Efstathia; Mazgutova, Diana

2017-01-01

This study investigated whether task complexity influences second language (L2) writers' fluency, pausing, and revision behaviors and the cognitive processes underlying these behaviors; whether task complexity affects linguistic complexity of written output; and whether relationships between writing behaviors and linguistic complexity are…

Ductile and brittle transition behavior of titanium alloys in ultra-precision machining.

PubMed

Yip, W S; To, S

2018-03-02

Titanium alloys are extensively applied in biomedical industries due to their excellent material properties. However, they are recognized as difficult to cut materials due to their low thermal conductivity, which induces a complexity to their deformation mechanisms and restricts precise productions. This paper presents a new observation about the removal regime of titanium alloys. The experimental results, including the chip formation, thrust force signal and surface profile, showed that there was a critical cutting distance to achieve better surface integrity of machined surface. The machined areas with better surface roughness were located before the clear transition point, defining as the ductile to brittle transition. The machined area at the brittle region displayed the fracture deformation which showed cracks on the surface edge. The relationship between depth of cut and the ductile to brittle transaction behavior of titanium alloys in ultra-precision machining(UPM) was also revealed in this study, it showed that the ductile to brittle transaction behavior of titanium alloys occurred mainly at relatively small depth of cut. The study firstly defines the ductile to brittle transition behavior of titanium alloys in UPM, contributing the information of ductile machining as an optimal machining condition for precise productions of titanium alloys.

Experimental characterization and microstructure linked modeling of mechanical behavior of ultra-thin aluminum foils used in packaging

NASA Astrophysics Data System (ADS)

Tabourot, Laurent; Charleux, Ludovic; Balland, Pascale; Sène, Ndèye Awa; Andreasson, Eskil

2018-05-01

This paper is based on the hypothesis that introducing distribution of mechanical properties is beneficial for modeling all kinds of mechanical behavior, even of ordinary metallic materials. To bring proof of its admissibility, it has to be first shown that modeling based on this assertion is able to efficiently describe standard mechanical behavior of materials. Searching for typical study case, it has been assessed that at a low scale, yield stresses could be strongly distributed in ultrathin aluminum foils used in packaging industry, offering opportunities to identifying their distribution and showing its role on the mechanical properties. Considering initially reduced modeling allow to establish a valuable connection between the hardening curve and the distribution of local yield stresses. This serves for finding initial value of distribution parameters in a more sophisticated identification procedure. With finally limited number of representative classes of local yield stresses, concretely 3 is enough, it is shown that a 3D finite element simulation involving limited numbers of elements returns realistic behavior of an ultrathin aluminum foil exerted to tensile test, in reference to experimental results. This gives way to large possibilities in modeling in order to give back complex experimental evidence.

Microgravity

NASA Image and Video Library

2000-07-01

Engineering bench system hardware for the Mechanics of Granular Materials (MGM) experiment is tested on a lab bench at the University of Colorado in Boulder. This is done in a horizontal arrangement to reduce pressure differences so the tests more closely resemble behavior in the microgravity of space. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Multimaterial 4D Printing with Tailorable Shape Memory Polymers

PubMed Central

Ge, Qi; Sakhaei, Amir Hosein; Lee, Howon; Dunn, Conner K.; Fang, Nicholas X.; Dunn, Martin L.

2016-01-01

We present a new 4D printing approach that can create high resolution (up to a few microns), multimaterial shape memory polymer (SMP) architectures. The approach is based on high resolution projection microstereolithography (PμSL) and uses a family of photo-curable methacrylate based copolymer networks. We designed the constituents and compositions to exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior. We used a high resolution, high contrast digital micro display to ensure high resolution of photo-curing methacrylate based SMPs that requires higher exposure energy than more common acrylate based polymers. An automated material exchange process enables the manufacture of 3D composite architectures from multiple photo-curable SMPs. In order to understand the behavior of the 3D composite microarchitectures, we carry out high fidelity computational simulations of their complex nonlinear, time-dependent behavior and study important design considerations including local deformation, shape fixity and free recovery rate. Simulations are in good agreement with experiments for a series of single and multimaterial components and can be used to facilitate the design of SMP 3D structures. PMID:27499417

Thin film of polyelectrolyte complex nanoparticles for protein sensing

NASA Astrophysics Data System (ADS)

Talukdar, Hrishikesh; Kundu, Sarathi

2018-04-01

Polyelectrolyte complex nanoparticles (PEC NPs) are prepared using two polyelectrolytes poly(Na-4-styrene sulphonate) (PSS) and poly(diallyldimethylammoniumchloride) (PDADMAC) at a molar mixing ratio of n-/n+ ≈ 0.67 by consecutive centrifugation. PEC NPs formation is investigated through dynamic light scattering (DLS) and atomic force microscopy (AFM). Optical behaviors of PEC NPs in thin film confirmation are studied using UV-Vis and photoluminescence spectroscopy. Although absorption peaks of PSS occurs at the same position before and after the formation of PEC NPs but emission peaks are found at ≈ 278 and 305 nm whereas for pure PSS emission peaks exist at ≈ 295 and 365 nm. Hence, thin film of PEC NPs can be applied as very sensitive material for protein sensing since absorption of protein is occurred at ≈ 278 nm. Protein sensing behavior of such PEC NPs thin film is studied using photoluminescence spectroscopy.

Fracture mechanics of cellular glass

NASA Technical Reports Server (NTRS)

Zwissler, J. G.; Adams, M. A.

1981-01-01

The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solr concentrator reflecting panels) are discussed. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials were developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region 1 may be slower, by orders of magnitude, than that found in dense glasses.

Viscosity characteristics of selected volcanic rock melts

NASA Astrophysics Data System (ADS)

Hobiger, Manuel; Sonder, Ingo; Büttner, Ralf; Zimanowski, Bernd

2011-02-01

A basic experimental study of the behavior of magma rheology was carried out on remelted volcanic rocks using wide gap viscometry. The complex composition of magmatic melts leads to complicated rheologic behavior which cannot be described with one simple model. Therefore, measurement procedures which are able to quantify non-Newtonian behavior have to be employed. Furthermore, the experimental apparatus must be able to deal with inhomogeneities of magmatic melts. We measured the viscosity of a set of materials representing a broad range of volcanic processes. For the lower viscous melts (low-silica compositions), non-Newtonian behavior is observed, whereas the high-silica melts show Newtonian behavior in the measured temperature and shear rate range (T = 1423 K - 1623 K, γ˙ = 10 - 2 s - 1 - 20 s - 1 ). The non-Newtonian materials show power-law behavior. The measured viscosities η and power-law indexes m lie in the intervals 8 Pa s ≤ η ≤ 210 3 Pa s, 0.71 ≤ m ≤ 1.0 (Grímsvötn basalt), 0.9 Pa s ≤ η ≤ 350 Pa s, 0.61 ≤ m ≤ 0.93 (Hohenstoffeln olivine-melilitite), and 8 Pa s ≤ η ≤ 1.510 4 Pa s, 0.55 ≤ m ≤ 1.0 (Sommata basalt). Measured viscosities of the Newtonian high-silica melts lie in the range 10 4 Pa s ≤ η ≤ 310 5 Pa s.

Computer-Aided Design/Computer-Assisted Manufacture Monolithic Restorations for Severely Worn Dentition: A Case History Report.

PubMed

Abou-Ayash, Samir; Boldt, Johannes; Vuck, Alexander

Full-arch rehabilitation of patients with severe tooth wear due to parafunctional behavior is a challenge for dentists and dental technicians, especially when a highly esthetic outcome is desired. A variety of different treatment options and prosthetic materials are available for such a clinical undertaking. The ongoing progress of computer-aided design/computer-assisted manufacture technologies in combination with all-ceramic materials provides a predictable workflow for these complex cases. This case history report describes a comprehensive, step-by-step treatment protocol leading to an optimally predictable treatment outcome for an esthetically compromised patient.

Procedures for determining MATMOD-4V material constants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lowe, T.C.

1993-11-01

The MATMOD-4V constitutive relations were developed from the original MATMOD model to extend the range of nonelastic deformation behaviors represented to include transient phenomena such as strain softening. Improvements in MATMOD-4V increased the number of independent material constants and the difficulty in determining their values. Though the constitutive relations are conceptually simple, their form and procedures for obtaining their constants can be complex. This paper reviews in detail the experiments, numerical procedures, and assumptions that have been used to determine a complete set of MATMOD-4V constants for high purity aluminum.

Creep and Environmental Durability of EBC/CMCs Under Imposed Thermal Gradient Conditions

NASA Technical Reports Server (NTRS)

Appleby, Matthew; Morscher, Gregory N.; Zhu, Dongming

2013-01-01

Interest in SiC fiber-reinforced SiC ceramic matrix composite (CMC) environmental barrier coating (EBC) systems for use in high temperature structural applications has prompted the need for characterization of material strength and creep performance under complex aerospace turbine engine environments. Stress-rupture tests have been performed on SiC/SiC composites systems, with varying fiber types and coating schemes to demonstrate material behavior under isothermal conditions. Further testing was conducted under exposure to thermal stress gradients to determine the effect on creep resistance and material durability. In order to understand the associated damage mechanisms, emphasis is placed on experimental techniques as well as implementation of non-destructive evaluation; including electrical resistivity monitoring. The influence of environmental and loading conditions on life-limiting material properties is shown.

Thermo-mechanical behavior of power electronic packaging assemblies: From characterization to predictive simulation of lifetimes

NASA Astrophysics Data System (ADS)

Dalverny, O.; Alexis, J.

2018-02-01

This article deals with thermo-mechanical behavior of power electronic modules used in several transportation applications as railway, aeronautic or automotive systems. Due to a multi-layered structures, involving different materials with a large variation of coefficient of thermal expansion, temperature variations originated from active or passive cycling (respectively from die dissipation or environmental constraint) induces strain and stresses field variations, giving fatigue phenomenon of the system. The analysis of the behavior of these systems and their dimensioning require the implementation of complex modeling strategies by both the multi-physical and the multi-scale character of the power modules. In this paper we present some solutions for studying the thermomechanical behavior of brazed assemblies as well as taking into account the interfaces represented by the numerous metallizations involved in the process assembly.

Molecular Effects on Coacervate-Driven Block Copolymer Self Assembly

NASA Astrophysics Data System (ADS)

Lytle, Tyer; Radhakrishna, Mithun; Sing, Charles

Two oppositely charged polymers can undergo associative phase separation in a salt solution in a process known as \\x98complex coacervation. Recent work has used this as a motif to control the self-assembly behavior of a mixture of oppositely-charged block copolymers which form nanoscale structures. The materials formed from these complex coacervate-block copolymers (BCPs) have potential use as drug delivery systems, gels, and sensors. We have developed a hybrid Monte Carlo-Single Chain in a Mean Field (MC-SCMF) simulation method that is able to determine morphological phase diagrams for BCPs. This technique is an efficient way to calculate morphological phase diagrams and provides a clear link between molecular level features and self-assembly behaviors. Morphological phase diagrams showing the effects of polymer concentration, salt concentration, chain length, and charge-block fraction at large charge densities on self-assembly behavior have been determined. An unexpected phase transition from disorder to hexagonal packing at large salt concentrations has been observed for charge-block fractions equal to and larger than 0.5. This is attributed to the salt filling space stabilizing the morphology of the BCP.

Study of Maxwell–Wagner (M–W) relaxation behavior and hysteresis observed in bismuth titanate layered structure obtained by solution combustion synthesis using dextrose as fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subohi, Oroosa, E-mail: oroosa@gmail.com; Shastri, Lokesh; Kumar, G.S.

2014-01-01

Graphical abstract: X-ray diffraction studies show that phase formation and crystallinity was reached only after calcinations at 800 °C. Dielectric constant versus temperature curve shows ferroelectric to paraelectric transition temperature (T{sub c}) to be 650 °C. Complex impedance curves show deviation from Debye behavior. The material shows a thin PE Loop with low remnant polarization due to high conductivity in the as prepared sample. - Highlights: • Bi{sub 4}Ti{sub 3}O{sub 12} is synthesized using solution combustion technique with dextrose as fuel. • Dextrose has high reducing capacity (+24) and generates more no. of moles of gases. • Impedance studies showmore » that the sample follows Maxwell–Wagner relaxation behavior. • Shows lower remnant polarization due to higher c-axis ratio. - Abstract: Structural, dielectric and ferroelectric properties of bismuth titanate (Bi{sub 4}Ti{sub 3}O{sub 12}) obtained by solution combustion technique using dextrose as fuel is studied extensively in this paper. Dextrose is used as fuel as it has high reducing valancy and generates more number of moles of gases during the reaction. X-ray diffraction studies show that phase formation and crystallinity was reached only after calcinations at 800 °C. Dielectric constant versus temperature curve shows ferroelectric to paraelectric transition temperature (T{sub c}) to be 650 °C. The dielectric loss is very less (tan δ < 1) at lower temperatures but increases around T{sub c} due to structural changes in the sample. Complex impedance curves show deviation from Debye behavior. The material shows a thin PE Loop with low remnant polarization due to high conductivity in the as prepared sample.« less

Bioinspired peony-like beta-Ni(OH)2 nanostructures with enhanced electrochemical activity and superhydrophobicity.

PubMed

Cao, Huaqiang; Zheng, He; Liu, Kaiyu; Warner, Jamie H

2010-02-01

Constructing complex nanostructures has become increasingly important in the development of hydrogen storage, self-cleaning materials, and the formation of chiral branched nanowires. Several approaches have been developed to generate complex nanostructures, which have led to novel applications. Combining biology and nanotechnology through the utilization of biomolecules to chemically template the growth of complex nanostructures during synthesis has aroused great interest. Herein, we use a biomolecule-assisted hydrothermal method to synthesize beta-phase Ni(OH)(2) peony-like complex nanostructures with second-order structure nanoplate structure. The novel beta-Ni(OH)(2) nanostructures exhibit high-power Ni/MH battery performance, close to the theoretical capacity of Ni(OH)(2), as well as controlled wetting behavior. We demonstrate that this bioinspired route to generate a complex nanostructure has applications in environmental protection and green secondary cells. This approach opens up opportunities for the synthesis and potential applications of new kinds of nanostructures.

Long Term Degradation of Resin for High Temperature Composites

NASA Technical Reports Server (NTRS)

Patekar, Kaustubh A.

2000-01-01

The durability of polymer matrix composites exposed to harsh environments is a major concern. Surface degradation and damage are observed in polyimide composites used in air at 125 to 300 C. It is believed that diffusion of oxygen into the material and oxidative chemical reactions in the matrix are responsible. Previous work has characterized and modeled diffusion behavior, and thermogravimetric analyses (TGAs) have been carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. However, the model developed using these data was not able to capture behavior seen in isothermal tests, especially those of long duration. A test program that focuses on lower temperatures and makes use of isothermal tests was undertaken to achieve a better understanding of the degradation reactions under use conditions. A new low-cost technique was developed to collect chemical degradation data for isothermal tests lasting over 200 hr in the temperature range 125 to 300 C. Results indicate complex behavior not captured by the previous TGA tests, including the presence of weight-adding reactions. Weight gain reactions dominated in the 125 to 225 C temperature range, while weight loss reactions dominated beyond 225 C. The data obtained from isothermal tests was used to develop a new model of the material behavior. This model was able to fully capture the behavior seen in the tests up to 275 C. Correlation of the current model with both isothermal data at 300 C and high rate TGA test data is mediocre. At 300 C and above, the reaction mechanisms appear to change. Attempts (which failed) to measure non-oxidative degradation indicate that oxidative reactions dominate the degradation at low temperatures. Based on this work, long term isothermal testing in an oxidative atmosphere is recommended for studying the degradation behavior of this class of materials.

Synthesis, spectroscopic, fluorescence properties and biological evaluation of novel Pd(II) and Cd(II) complexes of NOON tetradentate Schiff bases.

PubMed

Ali, Omyma A M

2014-01-01

The solid complexes of Pd(II) and Cd(II) with N,N/bis(salicylaldehyde)4,5-dimethyl-1,2-phenylenediamine (H2L(1)), and N,N/bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H2L(2)) have been synthesized and characterized by several techniques using elemental analysis (CHN), FT-IR, (1)H NMR, UV-Vis spectra and thermal analysis. Elemental analysis data proved 1:1 stoichiometry for the reported complexes while spectroscopic data indicated square planar and octahedral geometries for Pd(II) and Cd(II) complexes, respectively. The prepared ligands, Pd(II) and Cd(II) complexes exhibited intraligand (π-π(∗)) fluorescence and can potentially serve as photoactive materials. Thermal behavior of the complexes was studied and kinetic parameters were determined by Coats-Redfern method. Both the ligands and their complexes have been screened for antimicrobial activities. Copyright © 2013 Elsevier B.V. All rights reserved.

Healable supramolecular polymers as organic metals.

PubMed

Armao, Joseph J; Maaloum, Mounir; Ellis, Thomas; Fuks, Gad; Rawiso, Michel; Moulin, Emilie; Giuseppone, Nicolas

2014-08-13

Organic materials exhibiting metallic behavior are promising for numerous applications ranging from printed nanocircuits to large area electronics. However, the optimization of electronic conduction in organic metals such as charge-transfer salts or doped conjugated polymers requires high crystallinity, which is detrimental to their processability. To overcome this problem, the combination of the electronic properties of metal-like materials with the mechanical properties of soft self-assembled systems is attractive but necessitates the absence of structural defects in a regular lattice. Here we describe a one-dimensional supramolecular polymer in which photoinduced through-space charge-transfer complexes lead to highly coherent domains with delocalized electronic states displaying metallic behavior. We also reveal that diffusion of supramolecular polarons in the nanowires repairs structural defects thereby improving their conduction. The ability to access metallic properties from mendable self-assemblies extends the current understanding of both fields and opens a wide range of processing techniques for applications in organic electronics.

Fatigue of Nitinol: The state-of-the-art and ongoing challenges.

PubMed

Mahtabi, M J; Shamsaei, Nima; Mitchell, M R

2015-10-01

Nitinol, a nearly equiatomic alloy of nickel and titanium, has been considered for a wide range of applications including medical and dental devices and implants as well as aerospace and automotive components and structures. The realistic loading condition in many of these applications is cyclic; therefore, fatigue is often the main failure mode for such components and structures. The fatigue behavior of Nitinol involves many more complexities compared with traditional metal alloys arising from its uniqueness in material properties such as superelasticity and shape memory effects. In this paper, a review of the present state-of-the-art on the fatigue behavior of superelastic Nitinol is presented. Various aspects of fatigue of Nitinol are discussed and microstructural effects are explained. Effects of material preparation and testing conditions are also reviewed. Finally, several conclusions are made and recommendations for future works are offered. Copyright © 2015 Elsevier Ltd. All rights reserved.

Thin Hydrogel Films for Optical Biosensor Applications

PubMed Central

Mateescu, Anca; Wang, Yi; Dostalek, Jakub; Jonas, Ulrich

2012-01-01

Hydrogel materials consisting of water-swollen polymer networks exhibit a large number of specific properties highly attractive for a variety of optical biosensor applications. This properties profile embraces the aqueous swelling medium as the basis of biocompatibility, non-fouling behavior, and being not cell toxic, while providing high optical quality and transparency. The present review focuses on some of the most interesting aspects of surface-attached hydrogel films as active binding matrices in optical biosensors based on surface plasmon resonance and optical waveguide mode spectroscopy. In particular, the chemical nature, specific properties, and applications of such hydrogel surface architectures for highly sensitive affinity biosensors based on evanescent wave optics are discussed. The specific class of responsive hydrogel systems, which can change their physical state in response to externally applied stimuli, have found large interest as sophisticated materials that provide a complex behavior to hydrogel-based sensing devices. PMID:24957962

Multifaceted Modularity: A Key for Stepwise Building of Hierarchical Complexity in Actinide Metal–Organic Frameworks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolgopolova, Ekaterina A.; Ejegbavwo, Otega A.; Martin, Corey R.

Growing necessity for efficient nuclear waste management is a driving force for development of alternative architectures towards fundamental understanding of mechanisms involved in actinide integration inside extended structures. In this manuscript, metal-organic frameworks (MOFs) were investigated as a model system for engineering radionuclide containing materials through utilization of unprecedented MOF modularity, which cannot be replicated in any other type of materials. Through the implementation of recent synthetic advances in the MOF field, hierarchical complexity of An-materials were built stepwise, which was only feasible due to preparation of the first examples of actinide-based frameworks with “unsaturated” metal nodes. The first successfulmore » attempts of solid-state metathesis and metal node extension in An-MOFs are reported, and the results of the former approach revealed drastic differences in chemical behavior of extended structures versus molecular species. Successful utilization of MOF modularity also allowed us to structurally characterize the first example of bimetallic An-An nodes. To the best of our knowledge, through combination of solid-state metathesis, guest incorporation, and capping linker installation, we were able to achieve the highest Th wt% in mono- and bi-actinide frameworks with minimal structural density. Overall, combination of a multistep synthetic approach with homogeneous actinide distribution and moderate solvothermal conditions could make MOFs an exceptionally powerful tool to address fundamental questions responsible for chemical behavior of An-based extended structures, and therefore, shed light on possible optimization of nuclear waste administration.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehrez, Loujaine; Ghanem, Roger; Aitharaju, Venkat

Design of non-crimp fabric (NCF) composites entails major challenges pertaining to (1) the complex fine-scale morphology of the constituents, (2) the manufacturing-produced inconsistency of this morphology spatially, and thus (3) the ability to build reliable, robust, and efficient computational surrogate models to account for this complex nature. Traditional approaches to construct computational surrogate models have been to average over the fluctuations of the material properties at different scale lengths. This fails to account for the fine-scale features and fluctuations in morphology, material properties of the constituents, as well as fine-scale phenomena such as damage and cracks. In addition, it failsmore » to accurately predict the scatter in macroscopic properties, which is vital to the design process and behavior prediction. In this work, funded in part by the Department of Energy, we present an approach for addressing these challenges by relying on polynomial chaos representations of both input parameters and material properties at different scales. Moreover, we emphasize the efficiency and robustness of integrating the polynomial chaos expansion with multiscale tools to perform multiscale assimilation, characterization, propagation, and prediction, all of which are necessary to construct the data-driven surrogate models required to design under the uncertainty of composites. These data-driven constructions provide an accurate map from parameters (and their uncertainties) at all scales and the system-level behavior relevant for design. While this perspective is quite general and applicable to all multiscale systems, NCF composites present a particular hierarchy of scales that permits the efficient implementation of these concepts.« less

Multifaceted Modularity: A Key for Stepwise Building of Hierarchical Complexity in Actinide Metal-Organic Frameworks.

PubMed

Dolgopolova, Ekaterina A; Ejegbavwo, Otega A; Martin, Corey R; Smith, Mark D; Setyawan, Wahyu; Karakalos, Stavros G; Henager, Charles H; Zur Loye, Hans-Conrad; Shustova, Natalia B

2017-11-22

Growing necessity for efficient nuclear waste management is a driving force for development of alternative architectures toward fundamental understanding of mechanisms involved in actinide (An) integration inside extended structures. In this manuscript, metal-organic frameworks (MOFs) were investigated as a model system for engineering radionuclide containing materials through utilization of unprecedented MOF modularity, which cannot be replicated in any other type of materials. Through the implementation of recent synthetic advances in the MOF field, hierarchical complexity of An-materials was built stepwise, which was only feasible due to preparation of the first examples of actinide-based frameworks with "unsaturated" metal nodes. The first successful attempts of solid-state metathesis and metal node extension in An-MOFs are reported, and the results of the former approach revealed drastic differences in chemical behavior of extended structures versus molecular species. Successful utilization of MOF modularity also allowed us to structurally characterize the first example of bimetallic An-An nodes. To the best of our knowledge, through combination of solid-state metathesis, guest incorporation, and capping linker installation, we were able to achieve the highest Th wt % in mono- and biactinide frameworks with minimal structural density. Overall, the combination of a multistep synthetic approach with homogeneous actinide distribution and moderate solvothermal conditions could make MOFs an exceptionally powerful tool to address fundamental questions responsible for chemical behavior of An-based extended structures and, therefore, shed light on possible optimization of nuclear waste administration.

Microgravity

NASA Image and Video Library

1997-09-09

A test cell for the Mechanics of Granular Materials (MGM) experiment is shown in its on-orbit configuration in Spacehab during preparations for STS-89. The twin locker to the left contains the hydraulic system to operate the experiment. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Note: Because the image on the screen was muted in the original image, its brightness and contrast are boosted in this rendering to make the test cell more visible. Credit: NASA/Marshall Space Flight Center (MSFC)

Analysis of the relation between the cellulose, hemicellulose and lignin content and the thermal behavior of residual biomass from olive trees.

PubMed

Garcia-Maraver, A; Salvachúa, D; Martínez, M J; Diaz, L F; Zamorano, M

2013-11-01

The heterogeneity of biomass makes it difficult if not impossible to make sweeping generalizations concerning thermochemical treatment systems and the optimal equipment to be used in them. Chemical differences in the structural components of the biomass (cellulose, hemicellulose, and lignin) have a direct impact on its chemical reactivity. The aim of this research was to study the influence of the organic components of the raw material from olive trees (leaves, pruning residues, and wood) in the combustion behavior of this biomass, as well as to find the component responsible for the higher ash content of olive leaves. Accordingly, the study used a thermogravimetric analyzer to monitor the different states and complex transitions that occurred in the biomass as the temperature varied. The decomposition rates of the different samples were analyzed in order to establish a link between each combustion phase and the composition of the raw materials. Two methods were used to determine the hemicellulose and cellulose contents of biomass from olive trees. Significant differences among the results obtained by the different methods were observed, as well as important variations regarding the chemical composition and consequently the thermal behavior of the raw materials tested. Copyright © 2013 Elsevier Ltd. All rights reserved.

An analysis of health promotion materials for Dutch truck drivers: Off target and too complex?

PubMed

Boeijinga, Anniek; Hoeken, Hans; Sanders, José

2017-01-01

Despite various health promotion initiatives, unfavorable figures regarding Dutch truck drivers' eating behaviors, exercise behaviors, and absenteeism have not improved. The aim was to obtain a better understanding of the low level of effectiveness of current health interventions for Dutch truck drivers by examining to what extent these are tailored to the target group's particular mindset (focus of content) and health literacy skills (presentation of content). The article analyzes 21 health promotion materials for Dutch truck drivers using a two-step approach: (a) an analysis of the materials' focus, guided by the Health Action Process Approach; and (b) an argumentation analysis, guided by pragma-dialectics. The corpus analysis revealed: (a) a predominant focus on the motivation phase; and (b) in line with the aim of motivating the target group, a consistent use of pragmatic arguments, which were typically presented in an implicit way. The results indicate that existing health promotion materials for Dutch truck drivers are not sufficiently tailored to the target group's mindset and health literacy skills. Recommendations are offered to develop more tailored/effective health interventions targeting this high-risk, underserved occupational group.

Nonlinear dynamics and instability of aqueous dissolution of silicate glasses and minerals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yifeng; Jove-Colon, Carlos F.; Kuhlman, Kristopher L.

2016-07-22

Aqueous dissolution of silicate glasses and minerals plays a critical role in global biogeochemical cycles and climate evolution. The reactivity of these materials is also important to numerous engineering applications including nuclear waste disposal. The dissolution process has long been considered to be controlled by a leached surface layer in which cations in the silicate framework are gradually leached out and replaced by protons from the solution. This view has recently been challenged by observations of extremely sharp corrosion fronts and oscillatory zonings in altered rims of the materials, suggesting that corrosion of these materials may proceed directly through congruentmore » dissolution followed by secondary mineral precipitation. Here we show that complex silicate material dissolution behaviors can emerge from a simple positive feedback between dissolution-induced cation release and cation-enhanced dissolution kinetics. This self-accelerating mechanism enables a systematic prediction of the occurrence of sharp dissolution fronts (vs. leached surface layers), oscillatory dissolution behaviors and multiple stages of glass dissolution (in particular the alteration resumption at a late stage of a corrosion process). In conclusion, our work provides a new perspective for predicting long-term silicate weathering rates in actual geochemical systems and developing durable silicate materials for various engineering applications.« less

Tribology of Polymer Matrix Composites (PMCs) Fabricated by Additive Manufacturing (AM)

NASA Technical Reports Server (NTRS)

Gupta, S.; Dunnigan, R.; Salem, A.; Kuentz, L.; Halbig, M. C.; Singh, M.

2016-01-01

The integral process of depositing thin layers of material, one after another, until the designed component is created is collectively referred to as Additive Manufacturing (AM). Fused deposition process (FDP) is a type of AM where feedstock is extruded into filaments which then are deposited by 3D printing, and the solidification occurs during cooling of the melt. Currently, complex structures are being fabricated by commercial and open source desktop 3D printers. Recently, metal powder containing composite filaments based on polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) have emerged, which could be utilized for multifunctional applications. For further deployment in the field, especially for aerospace and ground-based applications, it is critical to understand the tribological behavior of 3D printed materials. In this presentation, we will report the tribological behavior of different polymer matrix composites fabricated by fused deposition process. These results will be compared with the base polymer systems. During this study, the tribological behavior of all the samples will be evaluated with tab-on-disc method and compared for different metallic powder reinforcements.

Microgravity

NASA Image and Video Library

2000-07-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment are Mark Lankton (Program Manager at University Colorado at Boulder), Susan Batiste (research assistance, UCB), and Stein Sture (principal investigator). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Primary role of the electrostatic contributions in a rational growth of hysteresis loop in spin-crossover Fe(II) complexes.

PubMed

Kepenekian, Mikaël; Le Guennic, Boris; Robert, Vincent

2009-08-19

We report a comprehensive analysis of the hysteresis behavior in a series of well-characterized spin-crossover Fe(II) materials. On the basis of the available X-ray data and multireference CASSCF (complete active space self-consistent field) calculations, we show that the growth of the hysteresis loop is controlled by electrostatic contributions. These environment effects turn out to be deeply modified as the crystal structure changes along the spin transition. Our theoretical inspection demonstrates the synergy between weak bonds and electrostatic interactions in the growth of hysteresis behavior. Quantitatively, it is suggested that the electrostatic contributions significantly enhance the cooperativity factor while weak bonds are determinant in the structuration of the 3D networks. Our picture does not rely on any parametrization but uses the microscopic information to derive an expression for the cooperativity parameter. The calculated values are in very good agreement with the experimental observations. Such inspection can thus be carried out to anticipate the hysteresis behavior of this intriguing class of materials.

Microgravity

NASA Image and Video Library

2000-07-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment at the University of Colorado at Boulder include Tawnya Ferbiak (software engineer), Susan Batiste (research assistant), and Christina Winkler (graduate research assistant). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

FATIGUE OF BIOMATERIALS: HARD TISSUES

PubMed Central

Arola, D.; Bajaj, D.; Ivancik, J.; Majd, H.; Zhang, D.

2009-01-01

The fatigue and fracture behavior of hard tissues are topics of considerable interest today. This special group of organic materials comprises the highly mineralized and load-bearing tissues of the human body, and includes bone, cementum, dentin and enamel. An understanding of their fatigue behavior and the influence of loading conditions and physiological factors (e.g. aging and disease) on the mechanisms of degradation are essential for achieving lifelong health. But there is much more to this topic than the immediate medical issues. There are many challenges to characterizing the fatigue behavior of hard tissues, much of which is attributed to size constraints and the complexity of their microstructure. The relative importance of the constituents on the type and distribution of defects, rate of coalescence, and their contributions to the initiation and growth of cracks, are formidable topics that have not reached maturity. Hard tissues also provide a medium for learning and a source of inspiration in the design of new microstructures for engineering materials. This article briefly reviews fatigue of hard tissues with shared emphasis on current understanding, the challenges and the unanswered questions. PMID:20563239

Deep Drawing Simulations With Different Polycrystalline Models

NASA Astrophysics Data System (ADS)

Duchêne, Laurent; de Montleau, Pierre; Bouvier, Salima; Habraken, Anne Marie

2004-06-01

The goal of this research is to study the anisotropic material behavior during forming processes, represented by both complex yield loci and kinematic-isotropic hardening models. A first part of this paper describes the main concepts of the `Stress-strain interpolation' model that has been implemented in the non-linear finite element code Lagamine. This model consists of a local description of the yield locus based on the texture of the material through the full constraints Taylor's model. The texture evolution due to plastic deformations is computed throughout the FEM simulations. This `local yield locus' approach was initially linked to the classical isotropic Swift hardening law. Recently, a more complex hardening model was implemented: the physically-based microstructural model of Teodosiu. It takes into account intergranular heterogeneity due to the evolution of dislocation structures, that affects isotropic and kinematic hardening. The influence of the hardening model is compared to the influence of the texture evolution thanks to deep drawing simulations.

Analysis of Long-Range Interaction in Lithium-Ion Battery Electrodes

DOE PAGES

Mistry, Aashutosh; Juarez-Robles, Daniel; Stein, Malcolm; ...

2016-12-01

The lithium-ion battery (LIB) electrode represents a complex porous composite, consisting of multiple phases including active material (AM), conductive additive, and polymeric binder. This study proposes a mesoscale model to probe the effects of the cathode composition, e.g., the ratio of active material, conductive additive, and binder content, on the electrochemical properties and performance. The results reveal a complex nonmonotonic behavior in the effective electrical conductivity as the amount of conductive additive is increased. Insufficient electronic conductivity of the electrode limits the cell operation to lower currents. Once sufficient electron conduction (i.e., percolation) is achieved, the rate performance can bemore » a strong function of ion-blockage effect and pore phase transport resistance. In conclusion, even for the same porosity, different arrangements of the solid phases may lead to notable difference in the cell performance, which highlights the need for accurate microstructural characterization and composite electrode preparation strategies.« less

Analysis of Long-Range Interaction in Lithium-Ion Battery Electrodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mistry, Aashutosh; Juarez-Robles, Daniel; Stein, Malcolm

The lithium-ion battery (LIB) electrode represents a complex porous composite, consisting of multiple phases including active material (AM), conductive additive, and polymeric binder. This study proposes a mesoscale model to probe the effects of the cathode composition, e.g., the ratio of active material, conductive additive, and binder content, on the electrochemical properties and performance. The results reveal a complex nonmonotonic behavior in the effective electrical conductivity as the amount of conductive additive is increased. Insufficient electronic conductivity of the electrode limits the cell operation to lower currents. Once sufficient electron conduction (i.e., percolation) is achieved, the rate performance can bemore » a strong function of ion-blockage effect and pore phase transport resistance. In conclusion, even for the same porosity, different arrangements of the solid phases may lead to notable difference in the cell performance, which highlights the need for accurate microstructural characterization and composite electrode preparation strategies.« less

Controlled Detonation Dynamics in Additively Manufactured High Explosives

NASA Astrophysics Data System (ADS)

Schmalzer, Andrew; Tappan, Bryce; Bowden, Patrick; Manner, Virginia; Clements, Brad; Menikoff, Ralph; Ionita, Axinte; Branch, Brittany; Dattelbaum, Dana; Espy, Michelle; Patterson, Brian; Wu, Ruilian; Mueller, Alexander

2017-06-01

The effect of structure in explosives has long been a subject of interest to explosives engineers and scientists. Through structure, detonation dynamics in explosives can be manipulated, introducing a new level of safety and directed performance into these previously difficult to control materials. New advances in additive manufacturing (AM) allow the deliberate introduction of exact internal structures at dimensions approaching the mesoscale of these energetic materials. We show through simulation and experiment that this structure can be used to control detonation behavior by manipulating complex shockwave interactions. We use high-speed video and shorting mag-wires to determine the detonation velocity in AM generated explosive structures, demonstrating, for the first time, a method of controlling the directional propagation of reactive flow through the controlled introduction of structure within a high explosive. With ongoing improvement in the AM methods available coupled with guidance through modeling and simulations, more complex interactions are being explored. LANL LDRD Office.

Cellular complexity captured in durable silica biocomposites

PubMed Central

Kaehr, Bryan; Townson, Jason L.; Kalinich, Robin M.; Awad, Yasmine H.; Swartzentruber, B. S.; Dunphy, Darren R.; Brinker, C. Jeffrey

2012-01-01

Tissue-derived cultured cells exhibit a remarkable range of morphological features in vitro, depending on phenotypic expression and environmental interactions. Translation of these cellular architectures into inorganic materials would provide routes to generate hierarchical nanomaterials with stabilized structures and functions. Here, we describe the fabrication of cell/silica composites (CSCs) and their conversion to silica replicas using mammalian cells as scaffolds to direct complex structure formation. Under mildly acidic solution conditions, silica deposition is restricted to the molecularly crowded cellular template. Inter- and intracellular heterogeneity from the nano- to macroscale is captured and dimensionally preserved in CSCs following drying and subjection to extreme temperatures allowing, for instance, size and shape preserving pyrolysis of cellular architectures to form conductive carbon replicas. The structural and behavioral malleability of the starting material (cultured cells) provides opportunities to develop robust and economical biocomposites with programmed structures and functions. PMID:23045634

Assessment of tbe Performance of Ablative Insulators Under Realistic Solid Rocket Motor Operating Conditions (a Doctoral Dissertation)

NASA Technical Reports Server (NTRS)

Martin, Heath Thomas

2013-01-01

Ablative insulators are used in the interior surfaces of solid rocket motors to prevent the mechanical structure of the rocket from failing due to intense heating by the high-temperature solid-propellant combustion products. The complexity of the ablation process underscores the need for ablative material response data procured from a realistic solid rocket motor environment, where all of the potential contributions to material degradation are present and in their appropriate proportions. For this purpose, the present study examines ablative material behavior in a laboratory-scale solid rocket motor. The test apparatus includes a planar, two-dimensional flow channel in which flat ablative material samples are installed downstream of an aluminized solid propellant grain and imaged via real-time X-ray radiography. In this way, the in-situ transient thermal response of an ablator to all of the thermal, chemical, and mechanical erosion mechanisms present in a solid rocket environment can be observed and recorded. The ablative material is instrumented with multiple micro-thermocouples, so that in-depth temperature histories are known. Both total heat flux and thermal radiation flux gauges have been designed, fabricated, and tested to characterize the thermal environment to which the ablative material samples are exposed. These tests not only allow different ablative materials to be compared in a realistic solid rocket motor environment but also improve the understanding of the mechanisms that influence the erosion behavior of a given ablative material.

Graphene Oxide: An All-in-One Processing Additive for 3D Printing.

PubMed

García-Tuñón, Esther; Feilden, Ezra; Zheng, Han; D'Elia, Eleonora; Leong, Alan; Saiz, Eduardo

2017-09-27

Many 3D printing technologies are based on the development of inks and pastes to build objects through droplet or filament deposition (the latter also known as continuous extrusion, robocasting, or direct ink writing). Controlling and tuning rheological behavior is key for successful manufacturing using these techniques. Different formulations have been proposed, but the search continues for approaches that are clean, flexible, robust and that can be adapted to a wide range of materials. Here, we show how graphene oxide (GO) enables the formulation of water-based pastes to print a wide variety of materials (polymers, ceramics, and steel) using robocasting. This work combines flow and oscillatory rheology to provide further insights into the rheological behavior of suspensions combining GO with other materials. Graphene oxide can be used to manipulate the viscoelastic response, enabling the formulation of pastes with excellent printing behavior that combine shear thinning flow and a fast recovery of their elastic properties. These inks do not contain other additives, only GO and the material of interest. As a proof of concept, we demonstrate the 3D printing of additive-free graphene oxide structures as well as polymers, ceramics, and steel. Due to its amphiphilic nature and 2D structure, graphene oxide plays multiple roles, behaving as a dispersant, viscosifier, and binder. It stabilizes suspensions of different powders, modifies the flow and viscoelasticity of materials with different chemistries, particle sizes and shapes, and binds the particles together, providing green strength for manual handling. This approach enables printing complex 3D ceramic structures using robocasting with similar properties to alternative formulations, thus demonstrating the potential of using 2D colloids in materials manufacturing.

ICME for Crashworthiness of TWIP Steels: From Ab Initio to the Crash Performance

NASA Astrophysics Data System (ADS)

Güvenç, O.; Roters, F.; Hickel, T.; Bambach, M.

2015-01-01

During the last decade, integrated computational materials engineering (ICME) emerged as a field which aims to promote synergetic usage of formerly isolated simulation models, data and knowledge in materials science and engineering, in order to solve complex engineering problems. In our work, we applied the ICME approach to a crash box, a common automobile component crucial to passenger safety. A newly developed high manganese steel was selected as the material of the component and its crashworthiness was assessed by simulated and real drop tower tests. The crashworthiness of twinning-induced plasticity (TWIP) steel is intrinsically related to the strain hardening behavior caused by the combination of dislocation glide and deformation twinning. The relative contributions of those to the overall hardening behavior depend on the stacking fault energy (SFE) of the selected material. Both the deformation twinning mechanism and the stacking fault energy are individually well-researched topics, but especially for high-manganese steels, the determination of the stacking-fault energy and the occurrence of deformation twinning as a function of the SFE are crucial to understand the strain hardening behavior. We applied ab initio methods to calculate the stacking fault energy of the selected steel composition as an input to a recently developed strain hardening model which models deformation twinning based on the SFE-dependent dislocation mechanisms. This physically based material model is then applied to simulate a drop tower test in order to calculate the energy absorption capacity of the designed component. The results are in good agreement with experiments. The model chain links the crash performance to the SFE and hence to the chemical composition, which paves the way for computational materials design for crashworthiness.

Indentation mapping revealed poroelastic, but not viscoelastic, properties spanning native zonal articular cartilage.

PubMed

Wahlquist, Joseph A; DelRio, Frank W; Randolph, Mark A; Aziz, Aaron H; Heveran, Chelsea M; Bryant, Stephanie J; Neu, Corey P; Ferguson, Virginia L

2017-12-01

Osteoarthrosis is a debilitating disease affecting millions, yet engineering materials for cartilage regeneration has proven difficult because of the complex microstructure of this tissue. Articular cartilage, like many biological tissues, produces a time-dependent response to mechanical load that is critical to cell's physiological function in part due to solid and fluid phase interactions and property variations across multiple length scales. Recreating the time-dependent strain and fluid flow may be critical for successfully engineering replacement tissues but thus far has largely been neglected. Here, microindentation is used to accomplish three objectives: (1) quantify a material's time-dependent mechanical response, (2) map material properties at a cellular relevant length scale throughout zonal articular cartilage and (3) elucidate the underlying viscoelastic, poroelastic, and nonlinear poroelastic causes of deformation in articular cartilage. Untreated and trypsin-treated cartilage was sectioned perpendicular to the articular surface and indentation was used to evaluate properties throughout zonal cartilage on the cut surface. The experimental results demonstrated that within all cartilage zones, the mechanical response was well represented by a model assuming nonlinear biphasic behavior and did not follow conventional viscoelastic or linear poroelastic models. Additionally, 10% (w/w) agarose was tested and, as anticipated, behaved as a linear poroelastic material. The approach outlined here provides a method, applicable to many tissues and biomaterials, which reveals and quantifies the underlying causes of time-dependent deformation, elucidates key aspects of material structure and function, and that can be used to provide important inputs for computational models and targets for tissue engineering. Elucidating the time-dependent mechanical behavior of cartilage, and other biological materials, is critical to adequately recapitulate native mechanosensory cues for cells. We used microindentation to map the time-dependent properties of untreated and trypsin treated cartilage throughout each cartilage zone. Unlike conventional approaches that combine viscoelastic and poroelastic behaviors into a single framework, we deconvoluted the mechanical response into separate contributions to time-dependent behavior. Poroelastic effects in all cartilage zones dominated the time-dependent behavior of articular cartilage, and a model that incorporates tension-compression nonlinearity best represented cartilage mechanical behavior. These results can be used to assess the success of regeneration and repair approaches, as design targets for tissue engineering, and for development of accurate computational models. Copyright © 2017 Acta Materialia Inc. All rights reserved.

Structure-property-glass transition relationships in non-isocyanate polyurethanes investigated by dynamic nanoindentation

NASA Astrophysics Data System (ADS)

Weyand, Stephan; Blattmann, Hannes; Schimpf, Vitalij; Mülhaupt, Rolf; Schwaiger, Ruth

2016-07-01

Newly developed green-chemistry approaches towards the synthesis of non-isocyanate polyurethane (NIPU) systems represent a promising alternative to polyurethanes (PU) eliminating the need for harmful ingredients. A series of NIPU systems were studied using different nanoindentation techniques in order to understand the influence of molecular parameters on the mechanical behavior. Nanoindentation revealed a unique characteristic feature of those materials, i.e. stiffening with increasing deformation. It is argued that the origin of this observed stiffening is a consequence of the thermodynamic state of the polymer network, the molecular characteristics of the chemical building blocks and resulting anisotropic elastic response of the network structure. Flat-punch nanoindentation was applied in order to characterize the constitutive viscoelastic nature of the materials. The complex modulus shows distinct changes as a function of the NIPU network topology illustrating the influence of the chemical building blocks. The reproducibility of the data indicates that the materials are homogeneous over the volumes sampled by nanoindentation. Our study demonstrates that nanoindentation is very well-suited to investigate the molecular characteristics of NIPU materials that cannot be quantified in conventional experiments. Moreover, the technique provides insight into the functional significance of complex molecular architectures thereby supporting the development of NIPU materials with tailored properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yarrington, Cole D.; Wixom, Ryan R.; Damm, David L.

The complex physical phenomenon of shock wave interaction with material heterogeneities has significant importance and nevertheless remains little understood. In many materials, the observed macroscale response to shock loading is governed by characteristics of the microstructure. Yet the majority of computational studies aimed at predicting phenomena affected by these processes, such as initiation and propagation of detonation waves in explosives, or shock propagation in geological materials, employ continuum material and reactive burn model treatment. In an effort to highlight the grain-scale processes that underlie the observable effects in an energetic system, a grain-scale model for hexanitrostilbene (HNS) has been developed.more » Measured microstructures were used to produce synthetic computational representations of the pore structure, and a density functional theory molecular dynamics (DFT-MD) derived equation of state (EOS) was used for the fully dense HNS matrix. The explicit inclusion of microstructure along with a fully-dense EOS resulted in close agreement with historical shock compression experiments. More recent experiments on dynamic reaction threshold were also reproduced by inclusion of a global kinetics model. The complete model was shown to reproduce accurately the expected response of this heterogeneous material to shock loading. Mesoscale simulations were shown to provide clear insight into the nature of threshold behavior, and are a way to understand complex physical phenomena.« less

Integrated Micro/nanoengineered Functional Biomaterials for Cell Mechanics and Mechanobiology: A Materials Perspective

PubMed Central

Shao, Yue

2014-01-01

The rapid development of micro/nanoengineered functional biomaterials in the last two decades has empowered materials scientists and bioengineers to precisely control different aspects of the in vitro cell microenvironment. Following a philosophy of reductionism, many studies using synthetic functional biomaterials have revealed instructive roles of individual extracellular biophysical and biochemical cues in regulating cellular behaviors. Development of integrated micro/nanoengineered functional biomaterials to study complex and emergent biological phenomena has also thrived rapidly in recent years, revealing adaptive and integrated cellular behaviors closely relevant to human physiological and pathological conditions. Working at the interface between materials science and engineering, biology, and medicine, we are now at the beginning of a great exploration using micro/nanoengineered functional biomaterials for both fundamental biology study and clinical and biomedical applications such as regenerative medicine and drug screening. In this review, we present an overview of state of the art micro/nanoengineered functional biomaterials that can control precisely individual aspects of cell-microenvironment interactions and highlight them as well-controlled platforms for mechanistic studies of mechano-sensitive and -responsive cellular behaviors and integrative biology research. We also discuss the recent exciting trend where micro/nanoengineered biomaterials are integrated into miniaturized biological and biomimetic systems for dynamic multiparametric microenvironmental control of emergent and integrated cellular behaviors. The impact of integrated micro/nanoengineered functional biomaterials for future in vitro studies of regenerative medicine, cell biology, as well as human development and disease models are discussed. PMID:24339188

Environmental Enrichment of Laboratory Rodents: The Answer Depends on the Question

DTIC Science & Technology

2011-01-01

that offer enhanced sensory , motor, and cognitive stimulation of brain neuronal systems in comparison with standard caging13 and, alternatively, as...benefit the animal in a signifi- cant way in terms of stimulation of positive species-typical behaviors and/or prevention of abnormal or undesirable...naturalistic nesting materials, as compared with less natural substitutes, al- lows laboratory mice to construct complex dome-shaped, multi - layered nests

From supramolecular polymers to multi-component biomaterials.

PubMed

Goor, Olga J G M; Hendrikse, Simone I S; Dankers, Patricia Y W; Meijer, E W

2017-10-30

The most striking and general property of the biological fibrous architectures in the extracellular matrix (ECM) is the strong and directional interaction between biologically active protein subunits. These fibers display rich dynamic behavior without losing their architectural integrity. The complexity of the ECM taking care of many essential properties has inspired synthetic chemists to mimic these properties in artificial one-dimensional fibrous structures with the aim to arrive at multi-component biomaterials. Due to the dynamic character required for interaction with natural tissue, supramolecular biomaterials are promising candidates for regenerative medicine. Depending on the application area, and thereby the design criteria of these multi-component fibrous biomaterials, they are used as elastomeric materials or hydrogel systems. Elastomeric materials are designed to have load bearing properties whereas hydrogels are proposed to support in vitro cell culture. Although the chemical structures and systems designed and studied today are rather simple compared to the complexity of the ECM, the first examples of these functional supramolecular biomaterials reaching the clinic have been reported. The basic concept of many of these supramolecular biomaterials is based on their ability to adapt to cell behavior as a result of dynamic non-covalent interactions. In this review, we show the translation of one-dimensional supramolecular polymers into multi-component functional biomaterials for regenerative medicine applications.

Preparation and characterization of triple shape memory composite foams.

PubMed

Nejad, Hossein Birjandi; Baker, Richard M; Mather, Patrick T

2014-10-28

Foams prepared from shape memory polymers (SMPs) offer the potential for low density materials that can be triggered to deploy with a large volume change, unlike their solid counterparts that do so at near-constant volume. While examples of shape memory foams have been reported in the past, they have been limited to dual SMPs: those polymers featuring one switching transition between an arbitrarily programmed shape and a single permanent shape established by constituent crosslinks. Meanwhile, advances by SMP researchers have led to several approaches toward triple- or multi-shape polymers that feature more than one switching phase and thus a multitude of temporary shapes allowing for a complex sequence of shape deployments. Here, we report the design, preparation, and characterization of a triple shape memory polymeric foam that is open cell in nature and features a two phase, crosslinked SMP with a glass transition temperature of one phase at a temperature lower than a melting transition of the second phase. The soft materials were observed to feature high fidelity, repeatable triple shape behavior, characterized in compression and demonstrated for complex deployment by fixing a combination of foam compression and bending. We further explored the wettability of the foams, revealing composition-dependent behavior favorable for future work in biomedical investigations.

Modeling the behaviour of shape memory materials under large deformations

NASA Astrophysics Data System (ADS)

Rogovoy, A. A.; Stolbova, O. S.

2017-06-01

In this study, the models describing the behavior of shape memory alloys, ferromagnetic materials and polymers have been constructed, using a formalized approach to develop the constitutive equations for complex media under large deformations. The kinematic and constitutive equations, satisfying the principles of thermodynamics and objectivity, have been derived. The application of the Galerkin procedure to the systems of equations of solid mechanics allowed us to obtain the Lagrange variational equation and variational formulation of the magnetostatics problems. These relations have been tested in the context of the problems of finite deformation in shape memory alloys and ferromagnetic materials during forward and reverse martensitic transformations and in shape memory polymers during forward and reverse relaxation transitions from a highly elastic to a glassy state.

Leach-proof magnetic thrombolytic nanoparticles and coatings of enhanced activity

NASA Astrophysics Data System (ADS)

Drozdov, Andrey S.; Vinogradov, Vasiliy V.; Dudanov, Ivan P.; Vinogradov, Vladimir V.

2016-06-01

Despite the fact that magnetic thrombolytic composites is an emerging area, all known so far systems are based on the similar mechanism of action: thrombolytic enzyme releases from the magnetic carrier leaving non-active matrix, thus making the whole system active only for a limited period of time. Such systems often have very complex structure organization and composition, consisting of materials not approved for parenteral injection, making them poor candidates for real clinical trials and implementation. Here we report, for the first time, the production of thrombolytic magnetic composite material with non-releasing behavior and prolonged action. Obtained composite shows good thrombolytic activity, consists of fully biocompatible materials and could be applied as infinitely active thrombolytic coatings or magnetically-targetable thrombolytic agents.

The photometric functions of Phobos and Deimos. II - Surface photometry of Deimos

NASA Technical Reports Server (NTRS)

Noland, M.; Veverka, J.

1977-01-01

Mariner 9 television pictures of Deimos are used to study the uniformity of a certain photometric scattering parameter over the surface of the satellite. It is shown that the photometric data considered satisfy the reciprocity principle and that the Hapke-Irvine scattering law is adequate for describing the surface. Phase functions for Deimos are obtained from scans along the photometric equator, and the photometric behavior of the brightest and darkest areas on the satellite's disk is examined. The results indicate that the surface of Deimos is covered uniformly by a dark and texturally complex material whose photometric behavior is well-represented by the Hapke-Irvine law, that the intrinsic phase coefficient of this material is about 0.017 mag/deg over the phase-angle range from 20 to 80 deg, and that slightly brighter material is present near some craters. Since enhanced brightening was not observed at the specular point of the photometric equator in any of the pictures studied, it is concluded that large exposures of solid rock are absent from the Mars-facing side of Deimos.

Determination of the magnetization scaling exponent for single-crystal La0.8Sr0.2MnO3 by broadband microwave surface impedance measurements

NASA Astrophysics Data System (ADS)

Schwartz, Andrew; Scheffler, Marc; Anlage, Steven M.

2000-01-01

Employing a broadband microwave reflection configuration, we have measured the complex surface impedance, ZS(ω,T), of single-crystal La0.8Sr0.2MnO3, as a function of frequency (0.045-45 GHz) and temperature (250-325 K). Through the dependence of the microwave surface impedance on the magnetic permeability, μ⁁(ω,T), we have studied the local magnetic behavior of this material, and have extracted the spontaneous magnetization, M0(T), in zero applied field. The broadband nature of these measurements and the fact that no external field is applied to the material provide a unique opportunity to analyze the critical behavior of the spontaneous magnetization at temperatures very close to the ferromagnetic phase transition. We find a Curie temperature TC=305.5+/-0.5 K and scaling exponent β=0.45+/-0.05, in agreement with the prediction of mean-field theory. We also discuss other recent determinations of the magnetization critical exponent in this and similar materials and show why our results are more definitive.

Multiphase magnetic systems: Measurement and simulation

NASA Astrophysics Data System (ADS)

Cao, Yue; Ahmadzadeh, Mostafa; Xu, Ke; Dodrill, Brad; McCloy, John S.

2018-01-01

Multiphase magnetic systems are common in nature and are increasingly being recognized in technical applications. One characterization method which has shown great promise for determining separate and collective effects of multiphase magnetic systems is first order reversal curves (FORCs). Several examples are given of FORC patterns which provide distinguishing evidence of multiple phases. In parallel, a visualization method for understanding multiphase magnetic interaction is given, which allocates Preisach magnetic elements as an input "Preisach hysteron distribution pattern" to enable simulation of different "wasp-waisted" magnetic behaviors. These simulated systems allow reproduction of different major hysteresis loops and FORC patterns of real systems and parameterized theoretical systems. The experimental FORC measurements and FORC diagrams of four commercially obtained magnetic materials, particularly those sold as nanopowders, show that these materials are often not phase pure. They exhibit complex hysteresis behaviors that are not predictable based on relative phase fraction obtained by characterization methods such as diffraction. These multiphase materials, consisting of various fractions of BaFe12O19, ɛ-Fe2O3, and γ-Fe2O3, are discussed.

Two phase modeling of the influence of plastic strain on the magnetic and magnetostrictive behaviors of ferromagnetic materials

NASA Astrophysics Data System (ADS)

Hubert, Olivier; Lazreg, Said

2017-02-01

A growing interest of automotive industry in the use of high performance steels is observed. These materials are obtained thanks to complex manufacturing processes whose parameters fluctuations lead to strong variations of microstructure and mechanical properties. The on-line magnetic non-destructive monitoring is a relevant response to this problem but it requires fast models sensitive to different parameters of the forming process. The plastic deformation is one of these important parameters. Indeed, ferromagnetic materials are known to be sensitive to stress application and especially to plastic strains. In this paper, a macroscopic approach using the kinematic hardening is proposed to model this behavior, considering a plastic strained material as a two phase system. Relationship between kinematic hardening and residual stress is defined in this framework. Since stress fields are multiaxial, an uniaxial equivalent stress is calculated and introduced inside the so-called magneto-mechanical multidomain modeling to represent the effect of plastic strain. The modeling approach is complemented by many experiments involving magnetic and magnetostrictive measurements. They are carried out with or without applied stress, using a dual-phase steel deformed at different levels. The main interest of this material is that the mechanically hard phase, soft phase and the kinematic hardening can be clearly identified thanks to simple experiments. It is shown how this model can be extended to single phase materials.

Chairside CAD/CAM materials. Part 1: Measurement of elastic constants and microstructural characterization.

PubMed

Belli, Renan; Wendler, Michael; de Ligny, Dominique; Cicconi, Maria Rita; Petschelt, Anselm; Peterlik, Herwig; Lohbauer, Ulrich

2017-01-01

A deeper understanding of the mechanical behavior of dental restorative materials requires an insight into the materials elastic constants and microstructure. Here we aim to use complementary methodologies to thoroughly characterize chairside CAD/CAM materials and discuss the benefits and limitations of different analytical strategies. Eight commercial CAM/CAM materials, ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Elastic constants were evaluated using three methods: Resonant Ultrasound Spectroscopy (RUS), Resonant Beam Technique (RBT) and Ultrasonic Pulse-Echo (PE). The microstructures were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Raman Spectroscopy and X-ray Diffraction (XRD). Young's modulus (E), Shear modulus (G), Bulk modulus (B) and Poisson's ratio (ν) were obtained for each material. E and ν reached values ranging from 10.9 (Lava Ultimate) to 201.4 (e.max ZirCAD) and 0.173 (Empress CAD) to 0.47 (Lava Ultimate), respectively. RUS showed to be the most complex and reliable method, while the PE method the easiest to perform but most unreliable. All dynamic methods have shown limitations in measuring the elastic constants of materials showing high damping behavior (hybrid materials). SEM images, Raman spectra and XRD patterns were made available for each material, showing to be complementary tools in the characterization of their crystal phases. Here different methodologies are compared for the measurement of elastic constants and microstructural characterization of CAD/CAM restorative materials. The elastic properties and crystal phases of eight materials are herein fully characterized. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Emulsion Inks for 3D Printing of High Porosity Materials.

PubMed

Sears, Nicholas A; Dhavalikar, Prachi S; Cosgriff-Hernandez, Elizabeth M

2016-08-01

Photocurable emulsion inks for use with solid freeform fabrication (SFF) to generate constructs with hierarchical porosity are presented. A high internal phase emulsion (HIPE) templating technique was utilized to prepare water-in-oil emulsions from a hydrophobic photopolymer, surfactant, and water. These HIPEs displayed strong shear thinning behavior that permitted layer-by-layer deposition into complex shapes and adequately high viscosity at low shear for shape retention after extrusion. Each layer was actively polymerized with an ultraviolet cure-on-dispense (CoD) technique and compositions with sufficient viscosity were able to produce tall, complex scaffolds with an internal lattice structure and microscale porosity. Evaluation of the rheological and cure properties indicated that the viscosity and cure rate both played an important role in print fidelity. These 3D printed polyHIPE constructs benefit from the tunable pore structure of emulsion templated material and the designed architecture of 3D printing. As such, these emulsion inks can be used to create ultra high porosity constructs with complex geometries and internal lattice structures not possible with traditional manufacturing techniques. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Printing-Centric Approach to the Electrostatic Modification of Polymer/Clay Composites for use in 3D Direct-Ink Writing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rauzan, Brittany; Lehman, Sean; McCracken, Josell

Polymer/clay composite inks are exceptionally useful materials for fabrication processes based on 3D direct-ink writing, however, there remains an insufficient understanding of how their physiochemical dynamics impact printability. Using a model system, N-isopropylacrylamide/Laponite, the electrostatic interactions between Laponite platelets are modified to tune critical rheological properties in order to improve printability. Rheological measurements and X-ray scattering experiments are carried out to monitor the nano/micro-structural dynamics and complex physicochemical interactions of Laponite as it impacts complex modulus in the linear region, flow behavior, thixotropy, and yield stress of the composite ink. Modification of the electrostatic interactions between platelets reduces the yieldmore » stress of the material, while maintaining a complex microstructure that allows for sufficient recovery times upon removal of stress to form stable, and thus printable, filaments. A printing-centric approach is established based on a fundamental understanding of electrostatic inter-particle interactions, harnessing the innate microstructure of Laponite in 3D direct-ink writing of composites.« less

Coupled numerical modeling of gas hydrates bearing sediments from laboratory to field-scale conditions

NASA Astrophysics Data System (ADS)

Sanchez, M. J.; Santamarina, C.; Gai, X., Sr.; Teymouri, M., Sr.

2017-12-01

Stability and behavior of Hydrate Bearing Sediments (HBS) are characterized by the metastable character of the gas hydrate structure which strongly depends on thermo-hydro-chemo-mechanical (THCM) actions. Hydrate formation, dissociation and methane production from hydrate bearing sediments are coupled THCM processes that involve, amongst other, exothermic formation and endothermic dissociation of hydrate and ice phases, mixed fluid flow and large changes in fluid pressure. The analysis of available data from past field and laboratory experiments, and the optimization of future field production studies require a formal and robust numerical framework able to capture the very complex behavior of this type of soil. A comprehensive fully coupled THCM formulation has been developed and implemented into a finite element code to tackle problems involving gas hydrates sediments. Special attention is paid to the geomechanical behavior of HBS, and particularly to their response upon hydrate dissociation under loading. The numerical framework has been validated against recent experiments conducted under controlled conditions in the laboratory that challenge the proposed approach and highlight the complex interaction among THCM processes in HBS. The performance of the models in these case studies is highly satisfactory. Finally, the numerical code is applied to analyze the behavior of gas hydrate soils under field-scale conditions exploring different features of material behavior under possible reservoir conditions.

Characterization and biological studies on Co(II), Ni(II) and Cu(II) complexes of carbohydrazones ending by pyridyl ring.

PubMed

Abu El-Reash, G M; El-Gammal, O A; Ghazy, S E; Radwan, A H

2013-03-01

The chelating behavior of ligands based on carbohydrazone core modified with pyridine end towards Co(II), Ni(II) and Cu(II) ions have been examined. The ligands derived from the condensation of carbohydrazide with 2-acetylpyridine (H(2)APC) and 4-acetylpyridine (H(2)APEC). The (1)H NMR, IR data and the binding energy calculations of H(2)APC revealed the presence of two stereoisomers syn and anti in the solid state and in the solution. The (1)H NMR, IR data and the binding energy calculations confirmed the presence of H(2)APEC in one keto form only in the solid state and in the solution. The spectroscopic data confirmed that H(2)APC behaves as a monobasic pentadentate in Co(II) and Cu(II) complexes and as mononegative tetradentate in Ni(II) complex. On the other hand, H(2)APEC acts as a mononegative tridentate in Co(II) complex, neutral tridentate in Ni(II) complex and neutral bidentate in Cu(II) complex. The electronic spectra and the magnetic measurements of complexes as well as the ESR of the copper complexes suggested the octahedral geometry. The bond length and bond angles were evaluated by DFT method using material studio program. The thermal behavior and the kinetic parameters of degradation were determined using Coats-Redfern and Horowitz-Metzger methods. The antioxidant (DDPH and ABTS methods), anti-hemolytic and in vitro Ehrlich ascites of the compounds have been screened. Copyright © 2012 Elsevier B.V. All rights reserved.

Multi-functional bis(alkynyl)gold(iii) N⁁C complexes with distinct mechanochromic luminescence and electroluminescence properties† †Electronic supplementary information (ESI) available: CCDC 1552808. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc02410j

PubMed Central

Wong, Ben Yiu-Wing; Wong, Hok-Lai; Wong, Yi-Chun; Au, Vonika Ka-Man

2017-01-01

A new class of donor–acceptor type luminescent bis(alkynyl)gold(iii) N⁁C complexes has been synthesized and characterized. These gold(iii) complexes not only exhibit high photoluminescence quantum yields of up to 0.81, but also interesting mechanochromic luminescence behaviors that are reversible. Upon grinding, a dramatic luminescence color change from green to red can be observed in solid samples of the gold(iii) complexes, and the mechanochromic luminescence can be readily tuned via a judicious selection of substituents on the pyridine ring. In addition, solution-processable OLEDs based on this class of complexes with EQE values of up to 4.0% have been realized, representing the first demonstration of bis(alkynyl)gold(iii) N⁁C complexes as emissive materials in solution-processable OLEDs. PMID:29147519

Results of studying creep and long-term strength of metals at the Institute of Mechanics at the Lomonosov Moscow State University (To Yu. N. Rabotnov's Anniversary)

NASA Astrophysics Data System (ADS)

Lokoshchenko, A. M.

2014-01-01

Basic results of experimental and theoretical research of creep processes and long-term strength of metals obtained by researchers of the Institute of Mechanics at the Lomonosov Moscow State University are presented. These results further develop and refine the kinetic theory of creep and long-duration strength proposed by Yu. N. Rabotnov. Some problems arising in formulating various types of kinetic equations and describing experimental data for materials that can be considered as statically homogeneous materials (in studying the process of deformation and rupture of such materials, there is no need to study the evolution of individual cracks) are considered. The main specific features of metal creep models at constant and variable stresses, in uniaxial and complex stress states, and with allowance for one or two damage parameters are described. Criterial and kinetic approaches used to determine long-term strength under conditions of a complex stress state are considered. Methods of modeling the metal behavior in an aggressive medium are described. A possibility of using these models for solving engineering problems is demonstrated.

Mechanisms of cooperation in cancer nanomedicine: towards systems nanotechnology.

PubMed

Hauert, Sabine; Bhatia, Sangeeta N

2014-09-01

Nanoparticles are designed to deliver therapeutics and diagnostics selectively to tumors. Their size, shape, charge, material, coating, and cargo determine their individual functionalities. A systems approach could help predict the behavior of trillions of nanoparticles interacting in complex tumor environments. Engineering these nanosystems may lead to biomimetic strategies where interactions between nanoparticles and their environment give rise to cooperative behaviors typically seen in natural self-organized systems. Examples include nanoparticles that communicate the location of a tumor to amplify tumor homing or self-assemble and disassemble to optimize nanoparticle transport. The challenge is to discover which nanoparticle designs lead to a desired system behavior. To this end, novel nanomaterials, deep understanding of biology, and computational tools are emerging as the next frontier. Copyright © 2014 Elsevier Ltd. All rights reserved.

Anisotropic mechanical behavior of an injection molded short fiber reinforced thermoplastic

NASA Astrophysics Data System (ADS)

Lopez, Delphine; Thuillier, Sandrine; Bessières, Nicolas; Grohens, Yves

2016-10-01

A short fiber reinforced thermoplastic was injected into a rectangular mold, in order to prepare samples to characterize the mechanical behavior of the material. The injection process was simulated with Moldflow and a cutting pattern was deduced from the predicted fiber orientation, leading to samples with several well-defined orientations with respect to the injection direction. Monotonic tensile tests up to rupture, as well as complex cycles made of loading steps followed by relaxation steps at different strain levels were performed, in order to check the reproducibility for a given orientation. Moreover, the fiber orientation in the central part of the tensile samples was also analyzed with X-ray tomography. The results show that the mechanical behavior for each orientation (among 6) was rather reproducible, thus validating the cutting pattern.

3D Printed Silicones with Shape Memory

DOE PAGES

Wu, Amanda S.; Small IV, Ward; Bryson, Taylor M.; ...

2017-07-05

Direct ink writing enables the layer-by-layer manufacture of ordered, porous structures whose mechanical behavior is driven by architecture and material properties. Here, we incorporate two different gas filled microsphere pore formers to evaluate the effect of shell stiffness and T g on compressive behavior and compression set in siloxane matrix printed structures. The lower T g microsphere structures exhibit substantial compression set when heated near and above T g, with full structural recovery upon reheating without constraint. By contrast, the higher T g microsphere structures exhibit reduced compression set with no recovery upon reheating. Aside from their role in tuningmore » the mechanical behavior of direct ink write structures, polymer microspheres are good candidates for shape memory elastomers requiring structural complexity, with potential applications toward tandem shape memory polymers.« less

3D Printed Silicones with Shape Memory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Amanda S.; Small IV, Ward; Bryson, Taylor M.

Direct ink writing enables the layer-by-layer manufacture of ordered, porous structures whose mechanical behavior is driven by architecture and material properties. Here, we incorporate two different gas filled microsphere pore formers to evaluate the effect of shell stiffness and T g on compressive behavior and compression set in siloxane matrix printed structures. The lower T g microsphere structures exhibit substantial compression set when heated near and above T g, with full structural recovery upon reheating without constraint. By contrast, the higher T g microsphere structures exhibit reduced compression set with no recovery upon reheating. Aside from their role in tuningmore » the mechanical behavior of direct ink write structures, polymer microspheres are good candidates for shape memory elastomers requiring structural complexity, with potential applications toward tandem shape memory polymers.« less

Adapting Dialectical Behavior Therapy for the Treatment of Dissociative Identity Disorder.

PubMed

Foote, Brad; Van Orden, Kim

2016-12-31

Dialectical Behavior Therapy (DBT), created by Marsha Linehan, has been shown to be an effective therapy for the treatment of borderline personality disorder (BPD) and for suicidal and self-harming behavior. Dissociative identity disorder (DID) is a complex post-traumatic disorder which is highly comorbid with BPD, shares a number of clinical features with BPD, and which like BPD features a high degree of suicidality. The DID treatment literature emphasizes the importance of a staged approach, beginning with the creation of a safe therapeutic frame prior to addressing traumatic material; DBT is also a staged treatment, in which behavioral and safety issues are addressed in Stage 1, and trauma work reserved for Stage 2. The authors describe adapting DBT, and especially its techniques for Stage 1 safety work, for work with DID patients. Basic theoretical principles are described and illustrated with a case example.

Adapting Dialectical Behavior Therapy for the Treatment of Dissociative Identity Disorder

PubMed Central

Foote, Brad; Van Orden, Kim

2017-01-01

Dialectical Behavior Therapy, created by Marsha Linehan, has been shown to be an effective therapy for the treatment of borderline personality disorder (BPD) and for suicidal and self-harming behavior. Dissociative identity disorder (DID) is a complex post-traumatic disorder which is highly comorbid with BPD, shares a number of clinical features with BPD, and which like BPD features a high degree of suicidality. The DID treatment literature emphasizes the importance of a staged approach, beginning with the creation of a safe therapeutic frame prior to addressing traumatic material; DBT is also a staged treatment, where behavioral and safety issues are addressed in Stage 1 and trauma work reserved for Stage 2. The authors describe adapting DBT, and especially its techniques for Stage 1 safety work, for work with DID patients. Basic theoretical principles are described and illustrated with a case example. PMID:28068498

Colloidal characterization of silicon nitride and silicon carbide

NASA Technical Reports Server (NTRS)

Feke, Donald L.

1986-01-01

The colloidal behavior of aqueous ceramic slips strongly affects the forming and sintering behavior and the ultimate mechanical strength of the final ceramic product. The colloidal behavior of these materials, which is dominated by electrical interactions between the particles, is complex due to the strong interaction of the solids with the processing fluids. A surface titration methodology, modified to account for this interaction, was developed and used to provide fundamental insights into the interfacial chemistry of these systems. Various powder pretreatment strategies were explored to differentiate between true surface chemistry and artifacts due to exposure history. The colloidal behavior of both silicon nitride and carbide is dominated by silanol groups on the powder surfaces. However, the colloid chemistry of silicon nitride is apparently influenced by an additional amine group. With the proper powder treatments, silicon nitride and carbide powder can be made to appear colloidally equivalent. The impact of these results on processing control will be discussed.

Simulation of Mechanical Behavior and Damage of a Large Composite Wind Turbine Blade under Critical Loads

NASA Astrophysics Data System (ADS)

Tarfaoui, M.; Nachtane, M.; Khadimallah, H.; Saifaoui, D.

2018-04-01

Issues such as energy generation/transmission and greenhouse gas emissions are the two energy problems we face today. In this context, renewable energy sources are a necessary part of the solution essentially winds power, which is one of the most profitable sources of competition with new fossil energy facilities. This paper present the simulation of mechanical behavior and damage of a 48 m composite wind turbine blade under critical wind loads. The finite element analysis was performed by using ABAQUS code to predict the most critical damage behavior and to apprehend and obtain knowledge of the complex structural behavior of wind turbine blades. The approach developed based on the nonlinear FE analysis using mean values for the material properties and the failure criteria of Tsai-Hill to predict failure modes in large structures and to identify the sensitive zones.

Drug Release Kinetics and Transport Mechanisms of Non-degradable and Degradable Polymeric Delivery Systems

PubMed Central

Fu, Yao; Kao, Weiyuan John

2010-01-01

Importance of the field The advancement in material design and engineering has led to the rapid development of novel materials with increasing complexity and functions. Both non-degradable and degradable polymers have found wide applications in the controlled delivery field. Studies on drug release kinetics provide important information into the function of material systems. To elucidate the detailed transport mechanism and the structure-function relationship of a material system, it is critical to bridge the gap between the macroscopic data and the transport behavior at the molecular level. Areas covered in this review The structure and function information of selected non-degradable and degradable polymers have been collected and summarized from literatures published after 1990s. The release kinetics of selected drug compounds from various material systems will be discussed in case studies. Recent progresses in the mathematical models based on different transport mechanisms will be highlighted. What the reader will gain This article aims to provide an overview of structure-function relationships of selected non-degradable and degradable polymers as drug delivery matrices. Take home message Understanding the structure-function relationship of the material system is key to the successful design of a delivery system for a particular application. Moreover, developing complex polymeric matrices requires more robust mathematical models to elucidate the solute transport mechanisms. PMID:20331353

Novel characterization method for fibrous materials using non-contact acoustics: material properties revealed by ultrasonic perturbations.

PubMed

Periyaswamy, Thamizhisai; Balasubramanian, Karthikeyan; Pastore, Christopher

2015-02-01

Fibrous materials are unique hierarchical complex structures exhibiting a range of mechanical, thermal, optical and electrical properties. The inherent discontinuity at micro and macro levels, heterogeneity and multi-scale porosity differentiates fibrous materials from other engineering materials that are typically continuum in nature. These structural complexities greatly influence the techniques and modalities that can be applied to characterize fibrous materials. Typically, the material response to an applied external force is measured and used as a characteristic number of the specimen. In general, a range of equipment is in use to obtain these numbers to signify the material properties. Nevertheless, obtaining these numbers for materials like fiber ensembles is often time consuming, destructive, and requires multiple modalities. It is hypothesized that the material response to an applied acoustic frequency would provide a robust alternative characterization mode for rapid and non-destructive material analysis. This research proposes applying air-coupled ultrasonic acoustics to characterize fibrous materials. Ultrasonic frequency waves transmitted through fibrous assemblies were feature extracted to understand the correlation between the applied frequency and the material properties. Mechanical and thermal characteristics were analyzed using ultrasonic features such as time of flight, signal velocity, power and the rate of attenuation of signal amplitude. Subsequently, these temporal and spectral characteristics were mapped with the standard low-stress mechanical and thermal properties via an empirical artificial intelligence engine. A high correlation of >0.92 (S.D. 0.06) was observed between the ultrasonic features and the standard measurements. The proposed ultrasonic technique can be used toward rapid characterization of dynamic behavior of flexible fibrous assemblies. Copyright © 2014 Elsevier B.V. All rights reserved.

Dynamic Fracture Behavior of Plastic-Bonded Explosives

NASA Astrophysics Data System (ADS)

Fu, Hua; Li, Jun-Ling; Tan, Duo-Wang; Ifp, Caep Team

2011-06-01

Plastic-Bonded Explosives (PBX) are used as important energetic materials in nuclear or conventional weapons. Arms Warhead in the service process and the ballistic phase, may experience complex process such as long pulse and higher loading, compresson, tension and reciprocating compression - tension, friction with the projectile shell, which would lead to explosive deformation and fracture.And the dynamic deformation and fracture behavior of PBX subsequently affect reaction characteristics and initiation mechanism in explosives, then having influence on explosives safety. The dynamic fracure behavior of PBX are generally complex and not well studied or understood. In this paper, the dynamic fracture of explosives are conducted using a Kolsky bar. The Brazilian test, also known as a indirect tensile test or splitting test, is chosen as the test method. Tensile strength under different strain rates are obtained using quartz crystal embedded in rod end. The dynamic deformation and fracture process are captured in real-time by high-speed digital camera, and the displacement and strain fields distribution before specimen fracture are obtained by digital correlation method. Considering the non-uniform microstructure of explosives,the dynamic fracture behavior of explosive are simulated by discrete element method, the simulation results can reproduce the deformation and fracture process in Brazilian test using a maximum tensile strain criterion.

Thermomechanical behavior of shape memory elastomeric composites

NASA Astrophysics Data System (ADS)

Ge, Qi; Luo, Xiaofan; Rodriguez, Erika D.; Zhang, Xiao; Mather, Patrick T.; Dunn, Martin L.; Qi, H. Jerry

2012-01-01

Shape memory polymers (SMPs) can fix a temporary shape and recover their permanent shape in response to environmental stimuli such as heat, electricity, or irradiation. Most thermally activated SMPs use the macromolecular chain mobility change around the glass transition temperature ( Tg) to achieve the shape memory (SM) effects. During this process, the stiffness of the material typically changes by three orders of magnitude. Recently, a composite materials approach was developed to achieve thermally activated shape memory effect where the material exhibits elastomeric response in both the temporary and the recovered configurations. These shape memory elastomeric composites (SMECs) consist of an elastomeric matrix reinforced by a semicrystalline polymer fiber network. The matrix provides background rubber elasticity while the fiber network can transform between solid crystals and melt phases over the operative temperature range. As such it serves as a reversible "switching phase" that enables shape fixing and recovery. Shape memory elastomeric composites provide a new paradigm for the development of a wide array of active polymer composites that utilize the melt-crystal transition to achieve the shape memory effect. This potentially allows for material systems with much simpler chemistries than most shape memory polymers and thus can facilitate more rapid material development and insertion. It is therefore important to understand the thermomechanical behavior and to develop corresponding material models. In this paper, a 3D finite-deformation constitutive modeling framework was developed to describe the thermomechanical behavior of SMEC. The model is phenomenological, although inspired by micromechanical considerations of load transfer between the matrix and fiber phases of a composite system. It treats the matrix as an elastomer and the fibers as a complex solid that itself is an aggregate of melt and crystal phases that evolve from one to the other during a temperature change. As such, the composite consists of an elastomer reinforced by a soft liquid at high temperature and a stiff solid at low temperature. The model includes a kinetic description of the non-isothermal crystallization and melting of the fibers during a temperature change. As the fibers transform from melt to crystal during cooling it is assumed that new crystals are formed in an undeformed state, which requires careful tracking of the kinematics of the evolving phases which comes at a significant computational cost. In order to improve the computational efficiency, an effective phase model (EPM) is adopted to treat the evolving crystal phases as an effective medium. A suite of careful thermomechanical experiments with a SMEC was carried out to calibrate various model parameters, and then to demonstrate the ability of the model to accurately capture the shape memory behavior of the SMEC system during complex thermomechanical loading scenarios. The model also identifies the effects of microstructural design parameters such as the fiber volume fraction.

Constitutive model for porous materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weston, A.M.; Lee, E.L.

1982-01-01

A simple pressure versus porosity compaction model is developed to calculate the response of granular porous bed materials to shock impact. The model provides a scheme for calculating compaction behavior when relatively limited material data are available. While the model was developed to study porous explosives and propellants, it has been applied to a much wider range of materials. The early development of porous material models, such as that of Hermann, required empirical dynamic compaction data. Erkman and Edwards successfully applied the early theory to unreacted porous high explosives using a Gruneisen equation of state without yield behavior and withoutmore » trapped gas in the pores. Butcher included viscoelastic rate dependance in pore collapse. The theoretical treatment of Carroll and Holt is centered on the collapse of a circular pore and includes radial inertia terms and a complex set of stress, strain and strain rate constitutive parameters. Unfortunately data required for these parameters are generally not available. The model described here is also centered on the collapse of a circular pore, but utilizes a simpler elastic-plastic static equilibrium pore collapse mechanism without strain rate dependence, or radial inertia terms. It does include trapped gas inside the pore, a solid material flow stress that creates both a yield point and a variation in solid material pressure with radius. The solid is described by a Mie-Gruneisen type EOS. Comparisons show that this model will accurately estimate major mechanical features which have been observed in compaction experiments.« less

Dilation Behavior of Thermal Spray Coatings

NASA Astrophysics Data System (ADS)

Bejarano Lopez, Miryan Lorena

Thermal Spray (TS) is a very versatile manufacturing process to deposit thick coatings on a variety of substrates. Coatings are used in protective (i.e. wear, chemical attack, high temperature, etc.) and functional (i.e. sensors) applications. TS coatings have a unique lamellar microstructure as a result of the overlapping of millions of molten and partially-molten particles. During processing, high deformation by impact, high temperature, and rapid solidification lead to a complex hierarchical material system that contains a high amount of microstructural defects. The presence of defects in the microstructure contribute to differences in property values in comparison to bulk materials. Thermal stresses and residual strains arise from processing, thermal gradients and thermal exposure. Evaluation of thermal properties, in this case, the coefficient of thermal expansion (CTE) is of vital importance to enhance coating performance. In this dissertation, expansion measurements of various metals, alloys, ceramics, and cermet coatings; were carried out using various techniques (push rod dilatometry, x-ray diffraction XRD, digital image correlation DIC, and curvature method) to determine the dilation behavior at the atomic, micro- and macro-scale levels. The main results were. 1) Mathematical models (Turner and Kerner) used for composite materials, successfully predicted the CTE property of a TS coating where the primary phase is the coating material and the secondary phases can be oxides, precipitates, etc. (formed as a byproduct of the spraying process). CTE was found not to be affected by porosity. 2) Despite the anisotropic behavior characteristic of TS coatings, the experimental results shown that CTE results to be reasonable isotropic within the scope of this study. 3) The curvature method was found to be an alternative technique to obtain the CTE, as well as the Young's modulus of coating in a bi-material strip, with good approximation. 4) An anomalous expansion behavior during the first heating exposure was exhibited by all coatings. The effect was named here, as "thermal shakedown", and is magnified in metals and alloys. 5) Non-isothermal rapid annealing of defects was correlated to this first irreversible contraction or expansion behavior. Although observed in most thermal spray materials, two material systems, pure Al and Ni-5Al were evaluated in-depth to quantify the mechanisms contributing to this behavior: vacancy formation, dislocation annealing, grain boundaries annihilation, residual stress relief, inelastic mechanical effects, etc. Correct determination of CTE values are important for design to assure integrity and functionality of coatings. Considerations of appropriate measurements are described in this dissertation.

Application of Probabilistic Analysis to Aircraft Impact Dynamics

NASA Technical Reports Server (NTRS)

Lyle, Karen H.; Padula, Sharon L.; Stockwell, Alan E.

2003-01-01

Full-scale aircraft crash simulations performed with nonlinear, transient dynamic, finite element codes can incorporate structural complexities such as: geometrically accurate models; human occupant models; and advanced material models to include nonlinear stressstrain behaviors, laminated composites, and material failure. Validation of these crash simulations is difficult due to a lack of sufficient information to adequately determine the uncertainty in the experimental data and the appropriateness of modeling assumptions. This paper evaluates probabilistic approaches to quantify the uncertainty in the simulated responses. Several criteria are used to determine that a response surface method is the most appropriate probabilistic approach. The work is extended to compare optimization results with and without probabilistic constraints.

Failure criterion for materials with spatially correlated mechanical properties

NASA Astrophysics Data System (ADS)

Faillettaz, J.; Or, D.

2015-03-01

The role of spatially correlated mechanical elements in the failure behavior of heterogeneous materials represented by fiber bundle models (FBMs) was evaluated systematically for different load redistribution rules. Increasing the range of spatial correlation for FBMs with local load sharing is marked by a transition from ductilelike failure characteristics into brittlelike failure. The study identified a global failure criterion based on macroscopic properties (external load and cumulative damage) that is independent of spatial correlation or load redistribution rules. This general metric could be applied to assess the mechanical stability of complex and heterogeneous systems and thus provide an important component for early warning of a class of geophysical ruptures.

Multistate and phase change selection in constitutional multivalent systems.

PubMed

Barboiu, Mihail

2012-01-01

Molecular architectures and materials can be constitutionally self-sorted in the presence of different biomolecular targets or external physical stimuli or chemical effectors, thus responding to an external selection pressure. The high selectivity and specificity of different bioreceptors or self-correlated internal interactions may be used to describe the complex constitutional behaviors through multistate component selection from a dynamic library. The self-selection may result in the dynamic amplification of self-optimized architectures during the phase change process. The sol-gel resolution of dynamic molecular/supramolecular libraries leads to higher self-organized constitutional hybrid materials, in which organic (supramolecular)/inorganic domains are reversibily connected.

A numerical and experimental study on optimal design of multi-DOF viscoelastic supports for passive vibration control in rotating machinery

NASA Astrophysics Data System (ADS)

Ribeiro, Eduardo Afonso; Lopes, Eduardo Márcio de Oliveira; Bavastri, Carlos Alberto

2017-12-01

Viscoelastic materials have played an important role in passive vibration control. Nevertheless, the use of such materials in supports of rotating machines, aiming at controlling vibration, is more recent, mainly when these supports present additional complexities like multiple degrees of freedom and require accurate models to predict the dynamic behavior of viscoelastic materials working in a broad band of frequencies and temperatures. Previously, the authors propose a methodology for an optimal design of viscoelastic supports (VES) for vibration suppression in rotordynamics, which improves the dynamic prediction accuracy, the speed calculation, and the modeling of VES as complex structures. However, a comprehensive numerical study of the dynamics of rotor-VES systems, regarding the types and combinations of translational and rotational degrees of freedom (DOFs), accompanied by the corresponding experimental validation, is still lacking. This paper presents such a study considering different types and combinations of DOFs in addition to the simulation of their number of additional masses/inertias, as well as the kind and association of the applied viscoelastic materials (VEMs). The results - regarding unbalance frequency response, transmissibility and displacement due to static loads - lead to: 1) considering VES as complex structures which allow improving the efficacy in passive vibration control; 2) acknowledging the best configuration concerning DOFs and VEM choice and association for a practical application concerning passive vibration control and load resistance. The specific outcomes of the conducted experimental validation attest the accuracy of the proposed methodology.

Dopamine Modulates Egalitarian Behavior In Humans

PubMed Central

Sáez, Ignacio; Zhu, Lusha; Set, Eric; Kayser, Andrew; Hsu, Ming

2015-01-01

SUMMARY Egalitarian motives form a powerful force in promoting prosocial behavior and enabling large-scale cooperation in the human species [1]. At the neural level, there is substantial, albeit correlational, evidence suggesting a link between dopamine and such behavior [2, 3]. However, important questions remain about the specific role of dopamine in setting or modulating behavioral sensitivity to prosocial concerns. Here, using a combination of pharmacological tools and economic games, we provide critical evidence for a causal involvement of dopamine in human egalitarian tendencies. Specifically, using the brain-penetrant catechol-O-methyl transferase (COMT) inhibitor tolcapone [4, 5], we investigated the causal relationship between dopaminergic mechanisms and two prosocial concerns at the core of a number of widely used economic games: (i) the extent to which individuals directly value the material payoffs of others, i.e., generosity, and (ii) the extent to which they are averse to differences between their own payoffs and those of others, i.e., inequity. We found that dopaminergic augmentation via COMT inhibition increased egalitarian tendencies in participants who played an extended version of the dictator game [6]. Strikingly, computational modeling of choice behavior [7] revealed that tolcapone exerted selective effects on inequity aversion, and not on other computational components such as the extent to which individuals directly value the material payoffs of others. Together, these data shed light on the causal relationship between neurochemical systems and human prosocial behavior, and have potential implications for our understanding of the complex array of social impairments accompanying neuropsychiatric disorders involving dopaminergic dysregulation. PMID:25802148

Aging, memory, and nonhierarchical energy landscape of spin jam

NASA Astrophysics Data System (ADS)

Samarakoon, Anjana; Sato, Taku J.; Chen, Tianran; Chern, Gai-Wei; Yang, Junjie; Klich, Israel; Sinclair, Ryan; Zhou, Haidong; Lee, Seung-Hun

2016-10-01

The notion of complex energy landscape underpins the intriguing dynamical behaviors in many complex systems ranging from polymers, to brain activity, to social networks and glass transitions. The spin glass state found in dilute magnetic alloys has been an exceptionally convenient laboratory frame for studying complex dynamics resulting from a hierarchical energy landscape with rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo simulation study, that densely populated frustrated magnets in a spin jam state exhibit much weaker memory effects than spin glasses, and the characteristic properties can be reproduced by a nonhierarchical landscape with a wide and nearly flat but rough bottom. Our results illustrate that the memory effects can be used to probe different slow dynamics of glassy materials, hence opening a window to explore their distinct energy landscapes.

Investigations on the magnetization behavior of magnetic composite particles

NASA Astrophysics Data System (ADS)

Eichholz, Christian; Knoll, Johannes; Lerche, Dietmar; Nirschl, Hermann

2014-11-01

In life sciences the application of surface functionalized magnetic composite particles is establishing in diagnostics and in downstream processing of modern biotechnology. These magnetic composite particles consist of non-magnetic material, e.g. polystyrene, which serves as a matrix for the second magnetic component, usually colloidal magnetite. Because of the multitude of magnetic cores these magnetic beads show a complex magnetization behavior which cannot be described with the available approaches for homogeneous magnetic material. Therefore, in this work a new model for the magnetization behavior of magnetic composite particles is developed. By introducing an effective magnetization and considering an overall demagnetization factor the deviation of the demagnetization of homogeneously magnetized particles is taken into account. Calculated and experimental results show a good agreement which allows for the verification of the adapted model of particle magnetization. Besides, a newly developed magnetic analyzing centrifuge is used for the characterization of magnetic composite particle systems. The experimental results, also used for the model verification, give both, information about the magnetic properties and the interaction behavior of particle systems. By adding further components to the particle solution, such as salts or proteins, industrial relevant systems can be reconstructed. The analyzing tool can be used to adapt industrial processes without time-consuming preliminary tests with large samples in the process equipments.

Increasing honesty in humans with noninvasive brain stimulation

PubMed Central

Maréchal, Michel André; Cohn, Alain; Ugazio, Giuseppe

2017-01-01

Honesty plays a key role in social and economic interactions and is crucial for societal functioning. However, breaches of honesty are pervasive and cause significant societal and economic problems that can affect entire nations. Despite its importance, remarkably little is known about the neurobiological mechanisms supporting honest behavior. We demonstrate that honesty can be increased in humans with transcranial direct current stimulation (tDCS) over the right dorsolateral prefrontal cortex. Participants (n = 145) completed a die-rolling task where they could misreport their outcomes to increase their earnings, thereby pitting honest behavior against personal financial gain. Cheating was substantial in a control condition but decreased dramatically when neural excitability was enhanced with tDCS. This increase in honesty could not be explained by changes in material self-interest or moral beliefs and was dissociated from participants’ impulsivity, willingness to take risks, and mood. A follow-up experiment (n = 156) showed that tDCS only reduced cheating when dishonest behavior benefited the participants themselves rather than another person, suggesting that the stimulated neural process specifically resolves conflicts between honesty and material self-interest. Our results demonstrate that honesty can be strengthened by noninvasive interventions and concur with theories proposing that the human brain has evolved mechanisms dedicated to control complex social behaviors. PMID:28396395

Temperature-dependent IR spectroscopic and structural study of 18-crown-6 chelating ligand in the complexation with sodium surfactant salts and potassium picrate.

PubMed

Mihelj, Tea; Tomašić, Vlasta; Biliškov, Nikola; Liu, Feng

2014-04-24

18-crown-6 ether (18C6) complexes with the following anionic surfactants: sodium n-dodecylsulfate (18C6-NaDS), sodium 4-(1-pentylheptyl)benzenesulfonate (18C6-NaDBS); and potassium picrate (18C6-KP) were synthesized and studied in terms of their thermal and structural properties. Physico-chemical properties of new solid 1:1 coordination complexes were characterized by infrared (IR) spectroscopy, thermogravimetry and differential thermal analysis, differential scanning calorimetry, X-ray diffraction and microscopic observations. The strength of coordination between Na(+) and oxygen atoms of 18C6 ligand does not depend on anionic part of the surfactant, as established by thermodynamical parameters obtained by temperature-dependent IR spectroscopy. Each of these complexes exhibit different kinds of endothermic transitions in heating scan. Diffraction maxima obtained by SAXS and WAXS, refer the behavior of the compounds 18C6-NaDS and 18C6-NaDBS as smectic liquid crystalline. Distortion of 18C6-NaDS and 18C6-KP complexes occurs in two steps. Temperature of the decomplexation of solid crystal complex 18C6-KP is considerably higher than of mesophase complexes, 18C6-NaDS, and 18C6-NaDBS. The structural and liquid crystalline properties of novel 18-crown-ether complexes are function of anionic molecule geometry, type of chosen cation (Na(+), K(+)), as well as architecture of self-organized aggregates. A good combination of crown ether unit and amphiphile may provide a possibility for preparing new functionalized materials, opening the research field of ion complexation and of host-guest type behavior. Copyright © 2013 Elsevier B.V. All rights reserved.

Physically elastic analysis of a cylindrical ring as a unit cell of a complete composite under applied stress in the complex plane using cubic polynomials

NASA Astrophysics Data System (ADS)

Monfared, Vahid

2018-03-01

Elastic analysis is analytically presented to predict the behaviors of the stress and displacement components in the cylindrical ring as a unit cell of a complete composite under applied stress in the complex plane using cubic polynomials. This analysis is based on the complex computation of the stress functions in the complex plane and polar coordinates. Also, suitable boundary conditions are considered and assumed to analyze along with the equilibrium equations and bi-harmonic equation. This method has some important applications in many fields of engineering such as mechanical, civil and material engineering generally. One of the applications of this research work is in composite design and designing the cylindrical devices under various loadings. Finally, it is founded that the convergence and accuracy of the results are suitable and acceptable through comparing the results.

Rheological principles of development hetero-modulus and hetero-viscous complex materials with extreme dynamic strength

NASA Astrophysics Data System (ADS)

Gömze, L. A.; Gömze, L. N.

2017-02-01

Materials with different crystalline and morphological compositions have different chemical, physical, mechanical and rheological properties, including wear protection, melting temperature, module of elasticity and viscosity. Examining the material structures and behaviors of differentceramic bodies and CMCs under high speed collisions in several years the authors have understood the advantages of hetero-modulus and hetero-viscous complex material systems to absorb and dissipate the kinetic energy of objects during high speed collisions. Applying the rheo-mechanical principles the authors successfully developed a new family of hetero-modulus and hetero-viscous alumina matrix composite materials with extreme mechanical properties including dynamic strength. These new corundum-matrix composite materials reinforced with Si2ON 2, Si3N4 , SiAlON and AlN submicron and nanoparticles have excellent dynamic strength during collisions with high density metallic bodies with speeds about 1000 m/sec or more. At the same time in the alumina matrix composites can be observed a phase transformation of submicron and nanoparticles of alpha and beta silicone-nitride crystals into cubicc-Si3N4 diamond-like particles can be observed, when the high speed collision processes are taken place in vacuum or oxygen-free atmosphere. Using the rheological principles and the energy engorgement by fractures, heating and melting of components the authors successfully developed several new hetero-modulus, hetero-viscous and hetero-plastic complex materials. These materials generally are based on ceramic matrixes and components having different melting temperatures and modules of elasticity from low values like carbon and light metals (Mg, Al, Ti, Si) up to very high values like boride, nitride and carbide ceramics. Analytical methods applied in this research were scanning electron microscopy, X-ray diffractions and energy dispersive spectrometry. Digital image analysis was applied to microscopy results to enhance the results of transformations.

Thermal degradation of Lewis acid complexed LDPE films

NASA Astrophysics Data System (ADS)

Sreelatha, K.; Predeep, P.

2017-06-01

The study highlights the thermal behavior of the semiconducting LDPE films synthesized by SbCl5 doping. The structural peculiarities and the responses of the structure to energetic modifications are studied. TGA and DTG curves are used to determine the thermal stability of the material. Degradation kinetics is elucidated. Activation energy and the entropy of activation for the degradation of the samples are calculated using Coats-Redfern plots and the samples show appreciable thermal stability.

Recent advances in the deformation processing of titanium alloys

NASA Astrophysics Data System (ADS)

Tamirisakandala, S.; Bhat, R. B.; Vedam, B. V.

2003-12-01

Titanium (Ti) alloys are special-purpose materials used for several critical applications in aerospace as well as non-aerospace industries, and extensive deformation processing is necessary to shape-form these materials, which poses many challenges due to the microstructural complexities. Some of the recent developments in the deformation processing of Ti alloys and usefulness of integrating the material behavior information with simulation schemes while designing and optimizing manufacturing process schedules are discussed in this paper. Discussions are primarily focused on the most important alloy, Ti-6Al-4V and on developing a clear understanding on the influence of key parameters (e.g., oxygen content, starting microstructure, temperature, and strain rate) on the deformation behavior during hot working. These studies are very useful not only for obtaining controlled microstructures but also to design complex multi-step processing sequences to produce defect-free components. Strain-induced porosity (SIP) has been a serious problem during titanium alloy processing, and improved scientific understanding helps in seeking elegant solutions to avoid SIP. A novel high-speed processing technique for microstructural conversion in titanium has been described, which provides several benefits over the conventional slow-speed practices. The hot working behavior of some of the affordable α+β and β titanium alloys being developed recently—namely, Ti-5.5Al-1Fe, Ti-10V-2Fe-3Al, Ti-6.8Mo-4.5Fe-1.5Al, and Ti-10V-4.5Fe-1.5Al—has been analyzed, and the usefulness of the processing maps in optimizing the process parameters and design of hot working schedules in these alloys is demonstrated. Titanium alloys modified with small additions of boron are emerging as potential candidates for replacing structural components requiring high specific strength and stiffness. Efforts to understand the microstructural mechanisms during deformation processing of Ti-B alloys and the issues associated with their processing are discussed.

Complex adaptive behavior and dexterous action

PubMed Central

Harrison, Steven J.; Stergiou, Nicholas

2016-01-01

Dexterous action, as conceptualized by Bernstein in his influential ecological analysis of human behavior, is revealed in the ability to flexibly generate behaviors that are adaptively tailored to the demands of the context in which they are embedded. Conceived as complex adaptive behavior, dexterity depends upon the qualities of robustness and degeneracy, and is supported by the functional complexity of the agent-environment system. Using Bernstein’s and Gibson’s ecological analyses of behavior situated in natural environments as conceptual touchstones, we consider the hypothesis that complex adaptive behavior capitalizes upon general principles of self-organization. Here, we outline a perspective in which the complex interactivity of nervous-system, body, and environment is revealed as an essential resource for adaptive behavior. From this perspective, we consider the implications for interpreting the functionality and dysfunctionality of human behavior. This paper demonstrates that, optimal variability, the topic of this special issue, is a logical consequence of interpreting the functionality of human behavior as complex adaptive behavior. PMID:26375932

Scaled experiments to determine the role of density on granular flows behavior: preliminary results

NASA Astrophysics Data System (ADS)

Rodriguez Sedano, L. A.; Sarocchi, D.; Borselli, L.; Segura, O.

2013-12-01

Geological granular flows are very complex, gravity driven phenomena which can show different behaviors depending on its origin and the characteristics of the constituent material. Due to their dangerous nature, and multiple scientific and technological applications, these phenomena has being studied deeply in order to have a better comprehension, however, after more than one century of scientific research it remains as an open topic with more questions than answers. One of the aspects that still need exhaustive research is the effect of clast density on the flowing granular material, as pointed out by previous laboratory and field studies. There are anyway few studies which have tried to explain the role of bulk density, as well the density of different phases, as it increasing or decreasing on the kinematic and the rheological characteristics of geological granular flows. The content of low density juvenile material seems to condition the processes of transformations of debris flows to more diluted phases, as well the transport and emplacing mechanisms. It is well known that the content of clay in debris flows has great influence on its behavior, physical processes and the deposits characteristics for this reason lahars has being subdivided in base of this parameter. Our hypothesis is that, in like manner, the presence of low density material inside the granular flows (dry and wet) could conditioning its physical characteristics and its behavior. In order to put this to the test, we made some laboratory experiments using a five meter long and 0.3 m wide experimental flume equipped with a wide range of sensors and laser barriers to precisely measure the rheological properties and kinematic of the sliding avalanches. A special effort was devoted to determine a threshold or critical level in the amount of low density material at which the avalanche behavior suffer appreciable changes. The obtained preliminary results confirm our hypothesis and encouraged to perform further experiments. Such studies are important because they could provide useful information for developing analog models that take into account this important physical property.

New Platforms for Characterization of Biological Material Failure and Resilience Properties

NASA Astrophysics Data System (ADS)

Brown, Katherine; Butler, Benjamin J.; Nguyen, Thuy-Tien N.; Sorry, David; Williams, Alun; Proud, William G.

2017-06-01

Obtaining information about the material responses of viscoelastic soft matter, such as polymers and foams has, required adaptation of techniques traditionally used with hard condensed matter. More recently it has been recognized that understanding the strain-rate behavior of natural and synthetic soft biological materials poses even greater challenges for materials research due their heterogeneous composition and structural complexity. Expanding fundamental knowledge about how these classes of biomaterials function under different loading regimes is of considerable interest in both fundamental and applied research. A comparative overview of methods, developed in our laboratory or elsewhere, for determining material responses of cells and soft tissues over a wide range of strain rates (quasi-static to blast loading) will be presented. Examples will illustrate how data are obtained for studying material responses of cells and tissues. Strengths and weaknesses of current approaches will be discussed, with particular emphasis on challenges associated with the development of realistic experimental and computational models for trauma and other disease indications.

Developing a Magnetic Resonance Imaging measurement of the forces within 3D granular materials under external loads

NASA Astrophysics Data System (ADS)

Elrington, Stefan; Bertrand, Thibault; Frey, Merideth; Shattuck, Mark; O'Hern, Corey; Barrett, Sean

2014-03-01

Granular materials are comprised of an ensemble of discrete macroscopic grains that interact with each other via highly dissipative forces. These materials are ubiquitous in our everyday life ranging in scale from the granular media that forms the Earth's crust to that used in agricultural and pharmaceutical industries. Granular materials exhibit complex behaviors that are poorly understood and cannot be easily described by statistical mechanics. Under external loads individual grains are jammed into place by a network of force chains. These networks have been imaged in quasi two-dimensional and on the outer surface of three-dimensional granular materials. Our goal is to use magnetic resonance imaging (MRI) to detect contact forces deep within three-dimensional granular materials, using hydrogen-1 relaxation times as a reporter for changes in local stress and strain. To this end, we use a novel pulse sequence to narrow the line width of hydrogen-1 in rubber. Here we present our progress to date, and prospects for future improvements.

Arsenic removal via ZVI in a hybrid spouted vessel/fixed bed filter system

PubMed Central

Calo, Joseph M.; Madhavan, Lakshmi; Kirchner, Johannes; Bain, Euan J.

2012-01-01

The description and operation of a novel, hybrid spouted vessel/fixed bed filter system for the removal of arsenic from water are presented. The system utilizes zero-valent iron (ZVI) particles circulating in a spouted vessel that continuously generates active colloidal iron corrosion products via the “self-polishing” action between ZVI source particles rolling in the moving bed that forms on the conical bottom of the spouted vessel. This action also serves as a “surface renewal” mechanism for the particles that provides for maximum utilization of the ZVI material. (Results of batch experiments conducted to examine this mechanism are also presented.) The colloidal material produced in this fashion is continuously captured and concentrated in a fixed bed filter located within the spouted vessel reservoir wherein arsenic complexation occurs. It is demonstrated that this system is very effective for arsenic removal in the microgram per liter arsenic concentration (i.e., drinking water treatment) range, reducing 100 μg/L of arsenic to below detectable levels (≪10 μg/L) in less than an hour. A mechanistic analysis of arsenic behavior in the system is presented, identifying the principal components of the population of active colloidal material for arsenic removal that explains the experimental observations and working principles of the system. It is concluded that the apparent kinetic behavior of arsenic in systems where colloidal (i.e., micro/nano) iron corrosion products are dominant can be complex and may not be explained by simple first or zeroth order kinetics. PMID:22539917

A model for complex flows of soft glassy materials with application to flows through fixed fiber beds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarkar, Arijit; Koch, Donald L., E-mail: dlk15@cornell.edu

2015-11-15

The soft glassy rheology (SGR) model has successfully described the time dependent simple shear rheology of a broad class of complex fluids including foams, concentrated emulsions, colloidal glasses, and solvent-free nanoparticle-organic hybrid materials (NOHMs). The model considers a distribution of mesoscopic fluid elements that hop from trap to trap at a rate which is enhanced by the work done to strain the fluid element. While an SGR fluid has a broad exponential distribution of trap energies, the rheology of NOHMs is better described by a narrower energy distribution and we consider both types of trap energy distributions in this study.more » We introduce a tensorial version of these models with a hopping rate that depends on the orientation of the element relative to the mean stress field, allowing a range of relative strengths of the extensional and simple shear responses of the fluid. As an application of these models we consider the flow of a soft glassy material through a dilute fixed bed of fibers. The dilute fixed bed exhibits a range of local linear flows which alternate in a chaotic manner with time in a Lagrangian reference frame. It is amenable to an analytical treatment and has been used to characterize the strong flow response of many complex fluids including fiber suspensions, dilute polymer solutions and emulsions. We show that the accumulated strain in the fluid elements has an abrupt nonlinear growth at a Deborah number of order one in a manner similar to that observed for polymer solutions. The exponential dependence of the hopping rate on strain leads to a fluid element deformation that grows logarithmically with Deborah number at high Deborah numbers. SGR fluids having a broad range of trap energies flowing through fixed beds can exhibit a range of rheological behaviors at small Deborah numbers ranging from a yield stress, to a power law response and finally to Newtonian behavior.« less

Magnetism in Complex Oxide Heterostructures Determined with Neutron Scattering

NASA Astrophysics Data System (ADS)

Te Velthuis, Suzanne G. E.

2009-03-01

With the creation of high quality superlattices consisting of complex oxide materials novel materials exhibiting a wide range of interesting phenomena are emerging. Due to the diverse physical properties of complex oxides, (e.g., ferromagnetism, antiferromagnetism, superconductivity), some of which can be varied by doping, the versatility in their applications is large. The physical properties in these new materials, often is tied to the behavior at the interfaces between the different components of the superlattice, and therefore requires detailed knowledge of the relationship between the chemical and electronic composition. Polarized neutron reflectometry (PNR) provides access to the depth-dependent magnitude and orientation of the magnetization and can therefore link the magnetic to the electronic and chemical properties, especially close to these interfaces. Several examples of our work will be presented, including that on La0.7Ca0.3MnO3/ YBa2Cu3O7-δ/ La0.7Ca0.3MnO3 trilayers which exhibit the inverse superconducting spin switch behavior, and where suppression of the magnetization close to the interface, as well as a varying anisotropy axis have been determined [1]. Another example is work on digitally layered analogs of La1-xSrxMnO3, where PNR reveals an asymmetric distribution of the magnetization across the two components (antiferromagnetic) LaMnO3and SrMnO3, which has been linked to structural properties at the interfaces [2]. [4pt] [1] V. Peña, Z. Sefrioui, D. Arias, C. Leon, J. Santamaria, J. L. Martinez, S. G. E. te Velthuis, A. Hoffmann, Phys. Rev. Lett. 94 (2005) 057002. [0pt] [2] S. J. May, A. B. Shah, S. G. E. te Velthuis, M. R. Fitzsimmons, J. M. Zuo, X. Zhai, J. N. Eckstein, S. D. Bader, and A. Bhattacharya, Phys. Rev. B 77 (2008) 174409.

Instruction-specific brain activations during episodic encoding. a generalized level of processing effect.

PubMed

Petersson, Karl Magnus; Sandblom, Johan; Elfgren, Christina; Ingvar, Martin

2003-11-01

In a within-subject design we investigated the levels-of-processing (LOP) effect using visual material in a behavioral and a corresponding PET study. In the behavioral study we characterize a generalized LOP effect, using pleasantness and graphical quality judgments in the encoding situation, with two types of visual material, figurative and nonfigurative line drawings. In the PET study we investigate the related pattern of brain activations along these two dimensions. The behavioral results indicate that instruction and material contribute independently to the level of recognition performance. Therefore the LOP effect appears to stem both from the relative relevance of the stimuli (encoding opportunity) and an altered processing of stimuli brought about by the explicit instruction (encoding mode). In the PET study, encoding of visual material under the pleasantness (deep) instruction yielded left lateralized frontoparietal and anterior temporal activations while surface-based perceptually oriented processing (shallow instruction) yielded right lateralized frontoparietal, posterior temporal, and occipitotemporal activations. The result that deep encoding was related to the left prefrontal cortex while shallow encoding was related to the right prefrontal cortex, holding the material constant, is not consistent with the HERA model. In addition, we suggest that the anterior medial superior frontal region is related to aspects of self-referential semantic processing and that the inferior parts of the anterior cingulate as well as the medial orbitofrontal cortex is related to affective processing, in this case pleasantness evaluation of the stimuli regardless of explicit semantic content. Finally, the left medial temporal lobe appears more actively engaged by elaborate meaning-based processing and the complex response pattern observed in different subregions of the MTL lends support to the suggestion that this region is functionally segregated.

Applicability of the lattice Boltzmann method to determine the ohmic resistance in equivalent resistor connections

NASA Astrophysics Data System (ADS)

Espinoza-Andaluz, Mayken; Barzola, Julio; Guarochico-Moreira, Víctor H.; Andersson, Martin

2017-12-01

Knowing the ohmic resistance in the materials allow to know in advance its electrical behavior when a potential difference is applied, and therefore the prediction of the electrical performance can be achieved in a most certain manner. Although the Lattice Boltzmann method (LBM) has been applied to solve several physical phenomena in complex geometries, it has only been used to describe the fluid phase, but applicability studies of LBM on the solid-electric-conducting material have not been carried out yet. The purpose of this paper is to demonstrate the accuracy of calculating the equivalent resistor connections using LBM. Several series and parallel resistor connections are effected. All the computations are carried out with 3D models, and the domain materials are designed by the authors.

Identifying local characteristic lengths governing sound wave properties in solid foams

NASA Astrophysics Data System (ADS)

Tan Hoang, Minh; Perrot, Camille

2013-02-01

Identifying microscopic geometric properties and fluid flow through opened-cell and partially closed-cell solid structures is a challenge for material science, in particular, for the design of porous media used as sound absorbers in building and transportation industries. We revisit recent literature data to identify the local characteristic lengths dominating the transport properties and sound absorbing behavior of polyurethane foam samples by performing numerical homogenization simulations. To determine the characteristic sizes of the model, we need porosity and permeability measurements in conjunction with ligament lengths estimates from available scanning electron microscope images. We demonstrate that this description of the porous material, consistent with the critical path picture following from the percolation arguments, is widely applicable. This is an important step towards tuning sound proofing properties of complex materials.

Toward superconducting critical current by design

DOE PAGES

Sadovskyy, Ivan A.; Jia, Ying; Leroux, Maxime; ...

2016-03-31

The interaction of vortex matter with defects in applied superconductors directly determines their current carrying capacity. Defects range from chemically grown nanostructures and crystalline imperfections to the layered structure of the material itself. The vortex-defect interactions are non-additive in general, leading to complex dynamic behavior that has proven difficult to capture in analytical models. With recent rapid progress in computational powers, a new paradigm has emerged that aims at simulation assisted design of defect structures with predictable ‘critical-current-by-design’: analogous to the materials genome concept of predicting stable materials structures of interest. We demonstrate the feasibility of this paradigm by combiningmore » large-scale time-dependent Ginzburg-Landau numerical simulations with experiments on commercial high temperature superconductor (HTS) containing well-controlled correlated defects.« less

Evaluation of two strategies for heart health promotion by direct mail in a low-income urban community.

PubMed

O'Loughlin, J; Paradis, G; Meshefedjian, G

1997-01-01

The objective of this study was to evaluate the reach of mass mailings of heart health education print materials in a low-income, urban community. Materials included a monthly newsletter and a self-help behavior change kit, both distributed to all 12,789 households in the study community. Recall, use, and self-reported impact of the materials were measured in a cross-sectional survey of a random sample of 345 adults conducted 2 weeks after distribution of the kit and 18 months after delivery of the first newsletter. Over one-third of the subjects (38.6%) recalled the newsletter and 27.9% had read one or more newsletters; 21.7% recalled the kit and 10.8% had read it. Few subjects had read both materials. Female gender and older age were independent correlates of having seen and read the newsletters. Older age, being widowed/separated/divorced, and infrequent physical activity were correlates of having seen and read the kit. Although the newsletter and kit formats might appeal to different segments of the population, mass mailings of heart health education print materials in a low-income urban community can reach large numbers of individuals. The cost effectiveness of repeated mailings of short, simple newsletters might be higher than a single mailing of a more complex behavior change kit.

Electrostatic engineering of strained ferroelectric perovskites from first principles

NASA Astrophysics Data System (ADS)

Cazorla, Claudio; Stengel, Massimiliano

2015-12-01

Design of novel artificial materials based on ferroelectric perovskites relies on the basic principles of electrostatic coupling and in-plane lattice matching. These rules state that the out-of-plane component of the electric displacement field and the in-plane components of the strain are preserved across a layered superlattice, provided that certain growth conditions are respected. Intense research is currently directed at optimizing materials functionalities based on these guidelines, often with remarkable success. Such principles, however, are of limited practical use unless one disposes of reliable data on how a given material behaves under arbitrary electrical and mechanical boundary conditions. Here we demonstrate, by focusing on the prototypical ferroelectrics PbTiO3 and BiFeO3 as test cases, how such information can be calculated from first principles in a systematic and efficient way. In particular, we construct a series of two-dimensional maps that describe the behavior of either compound (e.g., concerning the ferroelectric polarization and antiferrodistortive instabilities) at any conceivable choice of the in-plane lattice parameter, a , and out-of-plane electric displacement, D . In addition to being of immediate practical applicability to superlattice design, our results bring new insight into the complex interplay of competing degrees of freedom in perovskite materials and reveal some notable instances where the behavior of these materials depart from what naively is expected.

Effect of Zinc Oxide Doping on Electroluminescence and Electrical Behavior of Metalloporphyrins-Doped Samarium Complex

NASA Astrophysics Data System (ADS)

Janghouri, Mohammad; Amini, Mostafa M.

2018-02-01

Samarium complex [(Sm(III)] as a new host material was used for preparation of red organic light-emitting diodes (OLEDs). Devices with configurations of indium-doped tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):(poly(styrenesulfonate) (PEDOT:PSS (50 nm)/polyvinyl carbazole (PVK):[zinc oxide (ZnO)] (50 nm)/[(Sm(III)]:[zinc(II) 2,3-tetrakis(dihydroxyphenyl)-porphyrin and Pt(II) 2,3-dimethoxyporphyrin] (60 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (15 nm)/Al (150 nm) have been fabricated and investigated. An electroplex occurring at the (PVK/Sm: Pt(II) 2,3-dimethoxyporphyrin) interface has been suggested when ZnO nanoparticles were doped in PVK. OLED studies have revealed that the photophysical characteristics and electrical behavior of devices with ZnO nanoparticles are much better than those of devices with pure PVK. The efficiency of devices based on [(Sm(III)] was superior than that of known aluminum tris(8-hydroxyquinoline) (Alq3) and also our earlier reports on red OLEDs under the same conditions.

Understanding and simulating the material behavior during multi-particle irradiations

PubMed Central

Mir, Anamul H.; Toulemonde, M.; Jegou, C.; Miro, S.; Serruys, Y.; Bouffard, S.; Peuget, S.

2016-01-01

A number of studies have suggested that the irradiation behavior and damage processes occurring during sequential and simultaneous particle irradiations can significantly differ. Currently, there is no definite answer as to why and when such differences are seen. Additionally, the conventional multi-particle irradiation facilities cannot correctly reproduce the complex irradiation scenarios experienced in a number of environments like space and nuclear reactors. Therefore, a better understanding of multi-particle irradiation problems and possible alternatives are needed. This study shows ionization induced thermal spike and defect recovery during sequential and simultaneous ion irradiation of amorphous silica. The simultaneous irradiation scenario is shown to be equivalent to multiple small sequential irradiation scenarios containing latent damage formation and recovery mechanisms. The results highlight the absence of any new damage mechanism and time-space correlation between various damage events during simultaneous irradiation of amorphous silica. This offers a new and convenient way to simulate and understand complex multi-particle irradiation problems. PMID:27466040

Steady-state hydrodynamic instabilities of active liquid crystals: hybrid lattice Boltzmann simulations.

PubMed

Marenduzzo, D; Orlandini, E; Cates, M E; Yeomans, J M

2007-09-01

We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of an active nematic liquid crystal sandwiched between confining walls with various anchoring conditions. We confirm the existence of a transition between a passive phase and an active phase, in which there is spontaneous flow in the steady state. This transition is attained for sufficiently "extensile" rods, in the case of flow-aligning liquid crystals, and for sufficiently "contractile" ones for flow-tumbling materials. In a quasi-one-dimensional geometry, deep in the active phase of flow-aligning materials, our simulations give evidence of hysteresis and history-dependent steady states, as well as of spontaneous banded flow. Flow-tumbling materials, in contrast, rearrange themselves so that only the two boundary layers flow in steady state. Two-dimensional simulations, with periodic boundary conditions, show additional instabilities, with the spontaneous flow appearing as patterns made up of "convection rolls." These results demonstrate a remarkable richness (including dependence on anchoring conditions) in the steady-state phase behavior of active materials, even in the absence of external forcing; they have no counterpart for passive nematics. Our HLB methodology, which combines lattice Boltzmann for momentum transport with a finite difference scheme for the order parameter dynamics, offers a robust and efficient method for probing the complex hydrodynamic behavior of active nematics.

Carboxylate and amino group coated silver nanoparticles as joining materials for copper-to-copper silver joints.

PubMed

Oestreicher, A; Röhrich, T; Lerch, M

2012-12-01

Organic silver complexes are introduced where silver is linked either with a carboxyl group or with an amino group. Upon heating, nanoparticles are generated if the respective ligands are long enough to act as stabilizing agents in the nanoparticulate regime. With decomposition and volatilization of the organic material, the sintering of silver occurs. The thermal characteristics of the carboxylates silver-n-octanoate, silver-n-decanoate, and AgOOC(CH2OCH2)2CH2OCH3 are compared with silver-n-alkylamines (n = 8, 9, and 12), and their thermal behavior is discussed based on thermogravimetry (TG) measurements. The consecutive stages of a metallization process are addressed based on the properties of AgOOC(CH2OCH2)2CH2OCH3, and the usable effects of the individual phases of this metal organic compound are analyzed by cross-sectional scanning electron microscope (SEM) images of silver joints. Selection criteria are addressed based on the thermal behavior. A mechanism for the joining process is proposed, considering formation and sintering of the nanoparticles. It was found that the bulk material can be used for low-temperature joining processes. Strong adherence to copper as a basic material can be achieved.

Dynamic and impact contact mechanics of geologic materials: Grain-scale experiments and modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cole, David M.; Hopkins, Mark A.; Ketcham, Stephen A.

2013-06-18

High fidelity treatments of the generation and propagation of seismic waves in naturally occurring granular materials is becoming more practical given recent advancements in our ability to model complex particle shapes and their mechanical interaction. Of particular interest are the grain-scale processes that are activated by impact events and the characteristics of force transmission through grain contacts. To address this issue, we have developed a physics based approach that involves laboratory experiments to quantify the dynamic contact and impact behavior of granular materials and incorporation of the observed behavior indiscrete element models. The dynamic experiments do not involve particle damagemore » and emphasis is placed on measured values of contact stiffness and frictional loss. The normal stiffness observed in dynamic contact experiments at low frequencies (e.g., 10 Hz) are shown to be in good agreement with quasistatic experiments on quartz sand. The results of impact experiments - which involve moderate to extensive levels of particle damage - are presented for several types of naturally occurring granular materials (several quartz sands, magnesite and calcium carbonate ooids). Implementation of the experimental findings in discrete element models is discussed and the results of impact simulations involving up to 5 Multiplication-Sign 105 grains are presented.« less

Vitronectin as a Micromanager of Cell Response in Material-Driven Fibronectin Nanonetworks.

PubMed

Cantini, Marco; Gomide, Karina; Moulisova, Vladimira; González-García, Cristina; Salmerón-Sánchez, Manuel

2017-09-01

Surface functionalization strategies of synthetic materials for regenerative medicine applications comprise the development of microenvironments that recapitulate the physical and biochemical cues of physiological extracellular matrices. In this context, material-driven fibronectin (FN) nanonetworks obtained from the adsorption of the protein on poly(ethyl acrylate) provide a robust system to control cell behavior, particularly to enhance differentiation. This study aims at augmenting the complexity of these fibrillar matrices by introducing vitronectin, a lower-molecular-weight multifunctional glycoprotein and main adhesive component of serum. A cooperative effect during co-adsorption of the proteins is observed, as the addition of vitronectin leads to increased fibronectin adsorption, improved fibril formation, and enhanced vitronectin exposure. The mobility of the protein at the material interface increases, and this, in turn, facilitates the reorganization of the adsorbed FN by cells. Furthermore, the interplay between interface mobility and engagement of vitronectin receptors controls the level of cell fusion and the degree of cell differentiation. Ultimately, this work reveals that substrate-induced protein interfaces resulting from the cooperative adsorption of fibronectin and vitronectin fine-tune cell behavior, as vitronectin micromanages the local properties of the microenvironment and consequently short-term cell response to the protein interface and higher order cellular functions such as differentiation.

Collective cell behavior on basement membranes floating in space

NASA Astrophysics Data System (ADS)

Ellison, Sarah; Bhattacharjee, Tapomoy; Morley, Cameron; Sawyer, W.; Angelini, Thomas

The basement membrane is an essential part of the polarity of endothelial and epithelial tissues. In tissue culture and organ-on-chip devices, monolayer polarity can be established by coating flat surfaces with extracellular matrix proteins and tuning the trans-substrate permeability. In epithelial 3D culture, spheroids spontaneously establish inside-out polarity, morphing into hollow shell-like structures called acini, generating their own basement membrane on the inner radius of the shell. However, 3D culture approaches generally lack the high degree of control provided by the 2D culture plate or organ-on-chip devices, making it difficult to create more faithful in vitro tissue models with complex surface curvature and morphology. Here we present a method for 3D printing complex basement membranes covered in cells. We 3D print collagen-I and Matrigel into a 3D growth medium made from jammed microgels. This soft, yielding material allows extracellular matrix to be formed as complex surfaces and shapes, floating in space. We then distribute MCF10A epithelial cells across the polymerized surface. We envision employing this strategy to study 3D collective cell behavior in numerous model tissue layers, beyond this simple epithelial model.

Multi-scale modeling of microstructure dependent intergranular brittle fracture using a quantitative phase-field based method

DOE PAGES

Chakraborty, Pritam; Zhang, Yongfeng; Tonks, Michael R.

2015-12-07

In this study, the fracture behavior of brittle materials is strongly influenced by their underlying microstructure that needs explicit consideration for accurate prediction of fracture properties and the associated scatter. In this work, a hierarchical multi-scale approach is pursued to model microstructure sensitive brittle fracture. A quantitative phase-field based fracture model is utilized to capture the complex crack growth behavior in the microstructure and the related parameters are calibrated from lower length scale atomistic simulations instead of engineering scale experimental data. The workability of this approach is demonstrated by performing porosity dependent intergranular fracture simulations in UO 2 and comparingmore » the predictions with experiments.« less

A comprehensive Reputation mechanism for ubiquitous healthcare environment exploiting cloud model.

PubMed

Athanasiou, Georgia; Lymberopoulos, Dimitrios

2016-08-01

Absence of trust foundations may outweigh benefits of ubiquitous and personalized mental healthcare supervision provided within a Ubiquitous Healthcare environment (UH). Trust is composed by patient's Personal Interaction Experience (PIE) and social entourage accumulated PIE, i.e. Reputation (R). In this paper, a cloud-based Reputation mechanism is proposed. Since PIE is the elementary trust information source, also an Updating mechanism of PIE, is introduced, in this paper. Cloud materialization of combined mechanisms provides adaptability to UH Providers' dynamic behavior, facilitates detection of milking behaviors and complex malicious attacks while meets the challenge of limited accuracy in case of data sparseness. The effectiveness of the proposed mechanisms is verified via simulation in MATLAB.

Multi-scale modeling of microstructure dependent intergranular brittle fracture using a quantitative phase-field based method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty, Pritam; Zhang, Yongfeng; Tonks, Michael R.

In this study, the fracture behavior of brittle materials is strongly influenced by their underlying microstructure that needs explicit consideration for accurate prediction of fracture properties and the associated scatter. In this work, a hierarchical multi-scale approach is pursued to model microstructure sensitive brittle fracture. A quantitative phase-field based fracture model is utilized to capture the complex crack growth behavior in the microstructure and the related parameters are calibrated from lower length scale atomistic simulations instead of engineering scale experimental data. The workability of this approach is demonstrated by performing porosity dependent intergranular fracture simulations in UO 2 and comparingmore » the predictions with experiments.« less

Aeroelastic characteristics of a rapid prototype multi-material wind tunnel model of a mechanically deployable aerodynamic decelerator

NASA Astrophysics Data System (ADS)

Raskin, Boris

Scaled wind tunnel models are necessary for the development of aircraft and spacecraft to simulate aerodynamic behavior. This allows for testing multiple iterations of a design before more expensive full-scale aircraft and spacecraft are built. However, the cost of building wind tunnel models can still be high because they normally require costly subtractive manufacturing processes, such as machining, which can be time consuming and laborious due to the complex surfaces of aerodynamic models. Rapid prototyping, commonly known as 3D printing, can be utilized to save on wind tunnel model manufacturing costs. A rapid prototype multi-material wind tunnel model was manufactured for this thesis to investigate the possibility of using PolyJet 3D printing to create a model that exhibits aeroelastic behavior. The model is of NASA's Adaptable Deployable entry and Placement (ADEPT) aerodynamic decelerator, used to decelerate a spacecraft during reentry into a planet's atmosphere. It is a 60° cone with a spherically blunted nose that consists of a 12 flexible panels supported by a rigid structure of nose, ribs, and rim. The novel rapid prototype multi-material model was instrumented and tested in two flow conditions. Quantitative comparisons were made of the average forces and dynamic forces on the model, demonstrating that the model matched expected behavior for average drag, but not Strouhal number, indicating that there was no aeroelastic behavior in this particular case. It was also noted that the dynamic properties (e.g., resonant frequency) associated with the mounting scheme are very important and may dominate the measured dynamic response.

Integrated micro/nanoengineered functional biomaterials for cell mechanics and mechanobiology: a materials perspective.

PubMed

Shao, Yue; Fu, Jianping

2014-03-12

The rapid development of micro/nanoengineered functional biomaterials in the last two decades has empowered materials scientists and bioengineers to precisely control different aspects of the in vitro cell microenvironment. Following a philosophy of reductionism, many studies using synthetic functional biomaterials have revealed instructive roles of individual extracellular biophysical and biochemical cues in regulating cellular behaviors. Development of integrated micro/nanoengineered functional biomaterials to study complex and emergent biological phenomena has also thrived rapidly in recent years, revealing adaptive and integrated cellular behaviors closely relevant to human physiological and pathological conditions. Working at the interface between materials science and engineering, biology, and medicine, we are now at the beginning of a great exploration using micro/nanoengineered functional biomaterials for both fundamental biology study and clinical and biomedical applications such as regenerative medicine and drug screening. In this review, an overview of state of the art micro/nanoengineered functional biomaterials that can control precisely individual aspects of cell-microenvironment interactions is presented and they are highlighted them as well-controlled platforms for mechanistic studies of mechano-sensitive and -responsive cellular behaviors and integrative biology research. The recent exciting trend where micro/nanoengineered biomaterials are integrated into miniaturized biological and biomimetic systems for dynamic multiparametric microenvironmental control of emergent and integrated cellular behaviors is also discussed. The impact of integrated micro/nanoengineered functional biomaterials for future in vitro studies of regenerative medicine, cell biology, as well as human development and disease models are discussed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

25th Anniversary Article: Ordered Polymer Structures for the Engineering of Photons and Phonons

PubMed Central

Lee, Jae-Hwang; Koh, Cheong Yang; Singer, Jonathan P; Jeon, Seog-Jin; Maldovan, Martin; Stein, Ori; Thomas, Edwin L

2014-01-01

The engineering of optical and acoustic material functionalities via construction of ordered local and global architectures on various length scales commensurate with and well below the characteristic length scales of photons and phonons in the material is an indispensable and powerful means to develop novel materials. In the current mature status of photonics, polymers hold a pivotal role in various application areas such as light-emission, sensing, energy, and displays, with exclusive advantages despite their relatively low dielectric constants. Moreover, in the nascent field of phononics, polymers are expected to be a superior material platform due to the ability for readily fabricated complex polymer structures possessing a wide range of mechanical behaviors, complete phononic bandgaps, and resonant architectures. In this review, polymer-centric photonic and phononic crystals and metamaterials are highlighted, and basic concepts, fabrication techniques, selected functional polymers, applications, and emerging ideas are introduced. PMID:24338738

Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

DOE PAGES

Moll, Philip J. W.; Helm, Toni; Zhang, Shang-Shun; ...

2017-08-21

Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics. By using magnetic fields with strengths comparable to the crystal field energy scale, we illustrate a strong field-induced anisotropy as a consequence of non-spherically symmetric spin interactions in the prototypical heavy fermion material CeIn3. We demonstrate the importance of magnetic anisotropy in modeling f-electron materials when the orbital charactermore » of the 4f wavefunction changes (e.g., with pressure or composition). Additionally, magnetic fields are shown to tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in f-based materials.« less

Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moll, Philip J. W.; Helm, Toni; Zhang, Shang-Shun

Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics. By using magnetic fields with strengths comparable to the crystal field energy scale, we illustrate a strong field-induced anisotropy as a consequence of non-spherically symmetric spin interactions in the prototypical heavy fermion material CeIn3. We demonstrate the importance of magnetic anisotropy in modeling f-electron materials when the orbital charactermore » of the 4f wavefunction changes (e.g., with pressure or composition). Additionally, magnetic fields are shown to tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in f-based materials.« less

Forward ultrasonic model validation using wavefield imaging methods

NASA Astrophysics Data System (ADS)

Blackshire, James L.

2018-04-01

The validation of forward ultrasonic wave propagation models in a complex titanium polycrystalline material system is accomplished using wavefield imaging methods. An innovative measurement approach is described that permits the visualization and quantitative evaluation of bulk elastic wave propagation and scattering behaviors in the titanium material for a typical focused immersion ultrasound measurement process. Results are provided for the determination and direct comparison of the ultrasonic beam's focal properties, mode-converted shear wave position and angle, and scattering and reflection from millimeter-sized microtexture regions (MTRs) within the titanium material. The approach and results are important with respect to understanding the root-cause backscatter signal responses generated in aerospace engine materials, where model-assisted methods are being used to understand the probabilistic nature of the backscatter signal content. Wavefield imaging methods are shown to be an effective means for corroborating and validating important forward model predictions in a direct manner using time- and spatially-resolved displacement field amplitude measurements.

Electronic inhomogeneity in a Kondo lattice

PubMed Central

Bauer, E. D.; Yang, Yi-feng; Capan, C.; Urbano, R. R.; Miclea, C. F.; Sakai, H.; Ronning, F.; Graf, M. J.; Balatsky, A. V.; Movshovich, R.; Bianchi, A. D.; Reyes, A. P.; Kuhns, P. L.; Thompson, J. D.; Fisk, Z.

2011-01-01

Inhomogeneous electronic states resulting from entangled spin, charge, and lattice degrees of freedom are hallmarks of strongly correlated electron materials; such behavior has been observed in many classes of d-electron materials, including the high-Tc copper-oxide superconductors, manganites, and most recently the iron–pnictide superconductors. The complexity generated by competing phases in these materials constitutes a considerable theoretical challenge—one that still defies a complete description. Here, we report a manifestation of electronic inhomogeneity in a strongly correlated f-electron system, using CeCoIn5 as an example. A thermodynamic analysis of its superconductivity, combined with nuclear quadrupole resonance measurements, shows that nonmagnetic impurities (Y, La, Yb, Th, Hg, and Sn) locally suppress unconventional superconductivity, generating an inhomogeneous electronic “Swiss cheese” due to disrupted periodicity of the Kondo lattice. Our analysis may be generalized to include related systems, suggesting that electronic inhomogeneity should be considered broadly in Kondo lattice materials.

Testing of New Materials and Computer Aided Optimization of Process Parameters and Clamping Device During Predevelopment of Laser Welding Processes

NASA Astrophysics Data System (ADS)

Weidinger, Peter; Günther, Kay; Fitzel, Martin; Logvinov, Ruslan; Ilin, Alexander; Ploshikhin, Vasily; Hugger, Florian; Mann, Vincent; Roth, Stephan; Schmidt, Michael

The necessity for weight reduction in motor vehicles in order to save fuel consumption pushes automotive suppliers to use materials of higher strength. Due to their excellent crash behavior high strength steels are increasingly applied in various structures. In this paper some predevelopment steps for a material change from a micro alloyed to dual phase and complex phase steels of a T-joint assembly are displayed. Initially the general weldability of the materials regarding pore formation, hardening in the heat affected zone and hot cracking susceptibility is discussed. After this basic investigation, the computer aided design optimization of a clamping device is shown, in which influences of the clamping jaw, the welding position and the clamping forces upon weld quality are presented. Finally experimental results of the welding process are displayed, which validate the numerical simulation.

Plasma Spraying of Ceramics with Particular Difficulties in Processing

NASA Astrophysics Data System (ADS)

Mauer, G.; Schlegel, N.; Guignard, A.; Jarligo, M. O.; Rezanka, S.; Hospach, A.; Vaßen, R.

2015-01-01

Emerging new applications and growing demands of plasma-sprayed coatings initiate the development of new materials. Regarding ceramics, often complex compositions are employed to achieve advanced material properties, e.g., high thermal stability, low thermal conductivity, high electronic and ionic conductivity as well as specific thermo-mechanical properties and microstructures. Such materials however, often involve particular difficulties in processing by plasma spraying. The inhomogeneous dissociation and evaporation behavior of individual constituents can lead to changes of the chemical composition and the formation of secondary phases in the deposited coatings. Hence, undesired effects on the coating characteristics are encountered. In this work, examples of such challenging materials are investigated, namely pyrochlores applied for thermal barrier coatings as well as perovskites for gas separation membranes. In particular, new plasma spray processes like suspension plasma spraying and plasma spray-physical vapor deposition are considered. In some cases, plasma diagnostics are applied to analyze the processing conditions.

Impossible Neanderthals? Making string, throwing projectiles and catching small game during Marine Isotope Stage 4 (Abri du Maras, France)

NASA Astrophysics Data System (ADS)

Hardy, Bruce L.; Moncel, Marie-Hélène; Daujeard, Camille; Fernandes, Paul; Béarez, Philippe; Desclaux, Emmanuel; Chacon Navarro, Maria Gema; Puaud, Simon; Gallotti, Rosalia

2013-12-01

Neanderthal behavior is often described in one of two contradictory ways: 1) Neanderthals were behaviorally inflexible and specialized in large game hunting or 2) Neanderthals exhibited a wide range of behaviors and exploited a wide range of resources including plants and small, fast game. Using stone tool residue analysis with supporting information from zooarchaeology, we provide evidence that at the Abri du Maras, Ardèche, France, Neanderthals were behaviorally flexible at the beginning of MIS 4. Here, Neanderthals exploited a wide range of resources including large mammals, fish, ducks, raptors, rabbits, mushrooms, plants, and wood. Twisted fibers on stone tools provide evidence of making string or cordage. Using a variety of lines of evidence, we show the presence of stone projectile tips, possibly used in complex projectile technology. This evidence shows a level of behavioral variability that is often denied to Neanderthals. Furthermore, it sheds light on perishable materials and resources that are not often recovered which should be considered more fully in reconstructions of Neanderthal behavior.

Debris flow rheology: Experimental analysis of fine-grained slurries

USGS Publications Warehouse

Major, Jon J.; Pierson, Thomas C.

1992-01-01

The rheology of slurries consisting of ≤2-mm sediment from a natural debris flow deposit was measured using a wide-gap concentric-cylinder viscometer. The influence of sediment concentration and size and distribution of grains on the bulk rheological behavior of the slurries was evaluated at concentrations ranging from 0.44 to 0.66. The slurries exhibit diverse rheological behavior. At shear rates above 5 s−1 the behavior approaches that of a Bingham material; below 5 s−1, sand exerts more influence and slurry behavior deviates from the Bingham idealization. Sand grain interactions dominate the mechanical behavior when sand concentration exceeds 0.2; transient fluctuations in measured torque, time-dependent decay of torque, and hysteresis effects are observed. Grain rubbing, interlocking, and collision cause changes in packing density, particle distribution, grain orientation, and formation and destruction of grain clusters, which may explain the observed behavior. Yield strength and plastic viscosity exhibit order-of-magnitude variation when sediment concentration changes as little as 2–4%. Owing to these complexities, it is unlikely that debris flows can be characterized by a single rheological model.

Study of critical behavior in concrete during curing by application of dynamic linear and nonlinear means.

PubMed

Lacouture, Jean-Christoph; Johnson, Paul A; Cohen-Tenoudji, Frederic

2003-03-01

The monitoring of both linear and nonlinear elastic properties of a high performance concrete during curing is presented by application of compressional and shear waves. To follow the linear elastic behavior, both compressional and shear waves are used in wide band pulse echo mode. Through the value of the complex reflection coefficient between the cell material (Lucite) and the concrete within the cell, the elastic moduli are calculated. Simultaneously, the transmission of a continuous compressional sine wave at progressively increasing drive levels permits us to calculate the nonlinear properties by extracting the harmonics amplitudes of the signal. Information regarding the chemical evolution of the concrete based upon the reaction of hydration of cement is obtained by monitoring the temperature inside the sample. These different types of measurements are linked together to interpret the critical behavior.

"Tangible as tissue": Arnold Gesell, infant behavior, and film analysis.

PubMed

Curtis, Scott

2011-09-01

From 1924 to 1948, developmental psychologist Arnold Gesell regularly used photographic and motion picture technologies to collect data on infant behavior. The film camera, he said, records behavior "in such coherent, authentic and measurable detail that ... the reaction patterns of infant and child become almost as tangible as tissue." This essay places his faith in the fidelity and tangibility of film, as well as his use of film as evidence, in the context of developmental psychology's professed need for legitimately scientific observational techniques. It also examines his use of these same films as educational material to promote his brand of scientific child rearing. But his analytic techniques - his methods of extracting data from the film frames - are the key to understanding the complex relationship between his theories of development and his chosen research technology.

Does evolution lead to maximizing behavior?

PubMed

Lehmann, Laurent; Alger, Ingela; Weibull, Jörgen

2015-07-01

A long-standing question in biology and economics is whether individual organisms evolve to behave as if they were striving to maximize some goal function. We here formalize this "as if" question in a patch-structured population in which individuals obtain material payoffs from (perhaps very complex multimove) social interactions. These material payoffs determine personal fitness and, ultimately, invasion fitness. We ask whether individuals in uninvadable population states will appear to be maximizing conventional goal functions (with population-structure coefficients exogenous to the individual's behavior), when what is really being maximized is invasion fitness at the genetic level. We reach two broad conclusions. First, no simple and general individual-centered goal function emerges from the analysis. This stems from the fact that invasion fitness is a gene-centered multigenerational measure of evolutionary success. Second, when selection is weak, all multigenerational effects of selection can be summarized in a neutral type-distribution quantifying identity-by-descent between individuals within patches. Individuals then behave as if they were striving to maximize a weighted sum of material payoffs (own and others). At an uninvadable state it is as if individuals would freely choose their actions and play a Nash equilibrium of a game with a goal function that combines self-interest (own material payoff), group interest (group material payoff if everyone does the same), and local rivalry (material payoff differences). © 2015 The Author(s). Evolution © 2015 The Society for the Study of Evolution.

Modeling the Role of Dislocation Substructure During Class M and Exponential Creep. Revised

NASA Technical Reports Server (NTRS)

Raj, S. V.; Iskovitz, Ilana Seiden; Freed, A. D.

1995-01-01

The different substructures that form in the power-law and exponential creep regimes for single phase crystalline materials under various conditions of stress, temperature and strain are reviewed. The microstructure is correlated both qualitatively and quantitatively with power-law and exponential creep as well as with steady state and non-steady state deformation behavior. These observations suggest that creep is influenced by a complex interaction between several elements of the microstructure, such as dislocations, cells and subgrains. The stability of the creep substructure is examined in both of these creep regimes during stress and temperature change experiments. These observations are rationalized on the basis of a phenomenological model, where normal primary creep is interpreted as a series of constant structure exponential creep rate-stress relationships. The implications of this viewpoint on the magnitude of the stress exponent and steady state behavior are discussed. A theory is developed to predict the macroscopic creep behavior of a single phase material using quantitative microstructural data. In this technique the thermally activated deformation mechanisms proposed by dislocation physics are interlinked with a previously developed multiphase, three-dimensional. dislocation substructure creep model. This procedure leads to several coupled differential equations interrelating macroscopic creep plasticity with microstructural evolution.

Microgravity

NASA Image and Video Library

1989-10-17

An automobile lies crushed under the third story of this apartment building in the Marina District after the Oct. 17, 1989, Loma Prieta earthquake. The ground levels are no longer visible because of structural failure and sinking due to liquefaction. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: J.K. Nakata, U.S. Geological Survey.

Housing Damage Following Earthquake

NASA Technical Reports Server (NTRS)

1989-01-01

An automobile lies crushed under the third story of this apartment building in the Marina District after the Oct. 17, 1989, Loma Prieta earthquake. The ground levels are no longer visible because of structural failure and sinking due to liquefaction. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: J.K. Nakata, U.S. Geological Survey.

Non-Fermi liquids in oxide heterostructures

NASA Astrophysics Data System (ADS)

Stemmer, Susanne; Allen, S. James

2018-06-01

Understanding the anomalous transport properties of strongly correlated materials is one of the most formidable challenges in condensed matter physics. For example, one encounters metal-insulator transitions, deviations from Landau Fermi liquid behavior, longitudinal and Hall scattering rate separation, a pseudogap phase, and bad metal behavior. These properties have been studied extensively in bulk materials, such as the unconventional superconductors and heavy fermion systems. Oxide heterostructures have recently emerged as new platforms to probe, control, and understand strong correlation phenomena. This article focuses on unconventional transport phenomena in oxide thin film systems. We use specific systems as examples, namely charge carriers in SrTiO3 layers and interfaces with SrTiO3, and strained rare earth nickelate thin films. While doped SrTiO3 layers appear to be a well behaved, though complex, electron gas or Fermi liquid, the rare earth nickelates are a highly correlated electron system that may be classified as a non-Fermi liquid. We discuss insights into the underlying physics that can be gained from studying the emergence of non-Fermi liquid behavior as a function of the heterostructure parameters. We also discuss the role of lattice symmetry and disorder in phenomena such as metal-insulator transitions in strongly correlated heterostructures.

Optimal Damping Behavior of a Composite Sandwich Beam Reinforced with Coated Fibers

NASA Astrophysics Data System (ADS)

Lurie, S.; Solyaev, Y.; Ustenko, A.

2018-04-01

In the present paper, the effective damping properties of a symmetric foam-core sandwich beam with composite face plates reinforced with coated fibers is studied. A glass fiber-epoxy composite with additional rubber-toughened epoxy coatings on the fibers is considered as the material of the face plates. A micromechanical analysis of the effective properties of the unidirectional lamina is conducted based on the generalized self-consistent method and the viscoelastic correspondence principle. The effective complex moduli of composite face plates with a symmetric angle-ply structure are evaluated based on classical lamination theory. A modified Mead-Markus model is utilized to evaluate the fundamental modal loss factor of a simply supported sandwich beam with a polyurethane core. The viscoelastic frequency-dependent behaviors of the core and face plate materials are both considered. The properties of the face plates are evaluated based on a micromechanical analysis and found to implicitly depend on frequency; thus, an iterative procedure is applied to find the natural frequencies of the lateral vibrations of the beam. The optimal values of the coating thickness, lamination angle and core thickness for the best multi-scale damping behavior of the beam are found.

Synthesis, Photoluminescence Behavior of Green Light Emitting Tb(III) Complexes and Mechanistic Investigation of Energy Transfer Process.

PubMed

Bala, Manju; Kumar, Satish; Devi, Rekha; Khatkar, Avni; Taxak, V B; Boora, Priti; Khatkar, S P

2018-06-04

A series of five new terbium(III) ion complexes with 4,4-difluoro-1-phenylbutane-1,3-dione (HDPBD) and anciliary ligands was synthesized. The composition and properties of complexes were analyzed by elemental analysis, IR, NMR, powder X-ray diffaraction, TG-DTG and photoluminescence spectroscopy. These complexes exhibited ligand sensitized green emission at 546 nm associated with 5 D 4  →  7 F 5 transitions of terbium ion in the emission spectra. The photoluminescence study manifested that the organic ligands act as antenna and facilitate the absorbed energy to emitting levels of Tb(III) ion efficiently. The enhanced luminescence intensity and decay time of ternary C2-C5 complexes observed due to synergistic effect of anciliary ligands. The CIE color coordinates of complexes came under the green region of chromaticity diagram. The mechanistic investigation of intramolecular energy transfer in the complexes was discussed in detail. These terbium(III) complexes can be thrivingly used as one of the green component in light emitting material and in display devices. Graphical Abstract Illustrate the sensitization process of the Tb ion and intramolecular energy transfer process in the Tb 3+ complex.

FIRST PRINCIPLES STUDY ON ELECTRONIC AND OPTICAL PROPERTIES OF Al-DOPED γ-Ge3N4

NASA Astrophysics Data System (ADS)

Ding, Y. C.; Xiang, A. P.; Zhu, X. H.; Luo, J.; Hu, X. F.

2012-12-01

First principles study of the structural, electronic and optical properties of Al-doped γ-Ge3N4 with different concentration has been reported using the pseudo-potential plane wave method within the generalized gradient approximation (GGA). The binding energy and the formation energy suggest that Aluminum (Al) impurities prefer to substitute Ge at octahedral sites. Different doping concentrations are considered and the corresponding density of states (DOS) are analyzed. Calculated DOS indicates that there are holes in the top of the valance band after doping, meaning a p-type doping. We study the complex dielectric function, the absorption coefficient, and the electron energy loss spectra. It is demonstrated that for the low Al concentration, the material exhibits the dielectric behavior and for the high Al concentration, the material has possibilities to exhibit some metallic behavior. The γ-Ge3N4 doped with Al has a much higher static dielectric constant than undoped γ-Ge3N4, implying its potential applications in electronics and optics.

The influence of dislocation and hydrogen on thermal helium desorption behavior in Fe9Cr alloys

NASA Astrophysics Data System (ADS)

Zhu, Te; Jin, Shuoxue; Gong, Yihao; Lu, Eryang; Song, Ligang; Xu, Qiu; Guo, Liping; Cao, Xingzhong; Wang, Baoyi

2017-11-01

Transmutation helium may causes serious embrittlement which is considered to be due to helium from clustering as a bubble in materials. Suppression of transmutation helium can be achieved by introducing trapping sites such as dislocations and impurities in materials. Here, effects of intentionally-induced dislocations and hydrogen on helium migrate and release behaviors were investigated using thermal desorption spectrometry (TDS) technique applied to well-annealed and cold-worked Fe9Cr alloys irradiated by energetic helium/hydrogen ions. Synchronous desorption of helium and hydrogen was observed, and the microstructure states during helium release at different temperatures were analyzed. High thermally stable HenD type complexes formed in cold-worked specimens, resulting in the retardation of helium migration and release. The existence of hydrogen will strongly affect the thermal helium desorption which could be reflected in the TDS spectrum. It was confirmed that hydrogen retained in the specimens can result in obvious delay of helium desorption.

Predicting Multicomponent Adsorption Isotherms in Open-Metal Site Materials Using Force Field Calculations Based on Energy Decomposed Density Functional Theory.

PubMed

Heinen, Jurn; Burtch, Nicholas C; Walton, Krista S; Fonseca Guerra, Célia; Dubbeldam, David

2016-12-12

For the design of adsorptive-separation units, knowledge is required of the multicomponent adsorption behavior. Ideal adsorbed solution theory (IAST) breaks down for olefin adsorption in open-metal site (OMS) materials due to non-ideal donor-acceptor interactions. Using a density-function-theory-based energy decomposition scheme, we develop a physically justifiable classical force field that incorporates the missing orbital interactions using an appropriate functional form. Our first-principles derived force field shows greatly improved quantitative agreement with the inflection points, initial uptake, saturation capacity, and enthalpies of adsorption obtained from our in-house adsorption experiments. While IAST fails to make accurate predictions, our improved force field model is able to correctly predict the multicomponent behavior. Our approach is also transferable to other OMS structures, allowing the accurate study of their separation performances for olefins/paraffins and further mixtures involving complex donor-acceptor interactions. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of microstructure on the coupled electromagnetic-thermo-mechanical response of cyclotrimethylenetrinitramine-estane energetic aggregates to infrared laser radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Judith A.; Zikry, M. A., E-mail: zikry@ncsu.edu

2015-09-28

The coupled electromagnetic (EM)-thermo-mechanical response of cyclotrimethylenetrinitramine-estane energetic aggregates under laser irradiation and high strain rate loads has been investigated for various aggregate sizes and binder volume fractions. The cyclotrimethylenetrinitramine (RDX) crystals are modeled with a dislocation density-based crystalline plasticity formulation and the estane binder is modeled with finite viscoelasticity through a nonlinear finite element approach that couples EM wave propagation with laser heat absorption, thermal conduction, and inelastic deformation. Material property and local behavior mismatch at the crystal-binder interfaces resulted in geometric scattering of the EM wave, electric field and laser heating localization, high stress gradients, dislocation density, andmore » crystalline shear slip accumulation. Viscous sliding in the binder was another energy dissipation mechanism that reduced stresses in aggregates with thicker binder ligaments and larger binder volume fractions. This investigation indicates the complex interactions between EM waves and mechanical behavior, for accurate predictions of laser irradiation of heterogeneous materials.« less

A first-principles study of He, Xe, Kr and O incorporation in thorium carbide

NASA Astrophysics Data System (ADS)

Pérez Daroca, D.; Llois, A. M.; Mosca, H. O.

2015-05-01

Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. Understanding the incorporation of fission products and oxygen is very important to predict the behavior of nuclear fuels. A first approach to this goal is the study of the incorporation energies and stability of these elements in the material. By means of first-principles calculations within the framework of density functional theory, we calculate the incorporation energies of He, Xe, Kr and O atoms in Th and C vacancy sites, in tetrahedral interstitials and in Schottky defects along the 〈1 1 1〉 and 〈1 0 0〉 directions. We also analyze atomic displacements, volume modifications and Bader charges. This kind of results for ThC, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically. This should deal as a starting point towards the study of the complex behavior of fission products in irradiated ThC.

Unraveling complex nonlinear elastic behaviors in rocks using dynamic acousto-elasticity

NASA Astrophysics Data System (ADS)

Riviere, J.; Guyer, R.; Renaud, G.; TenCate, J. A.; Johnson, P. A.

2012-12-01

In comparison with standard nonlinear ultrasonic methods like frequency mixing or resonance based measurements that allow one to extract average, bulk variations of modulus and attenuation versus strain level, dynamic acousto-elasticity (DAE) allows to obtain the elastic behavior over the entire dynamic cycle, detailing the full nonlinear behavior under tension and compression, including hysteresis and memory effects. This method consists of exciting a sample in Bulk-mode resonance at strains of 10-7 to 10-5 and simultaneously probing with a sequence of high frequency, low amplitude pulses. Time of flight and amplitudes of these pulses, respectively related to nonlinear elastic and dissipative parameters, can be plotted versus vibration strain level. Despite complex nonlinear signatures obtained for most rocks, it can be shown that for low strain amplitude (< 10-6), the nonlinear classical theory issued from a Taylor decomposition can explain the harmonic content. For higher strain, harmonic content becomes richer and the material exhibits more hysteretic behaviors, i.e. strain rate dependencies. Such observations have been made in the past (e.g., Pasqualini et al., JGR 2007), but not with the extreme detail of elasticity provided by DAE. Previous quasi-static measurements made in Berea sandstone (Claytor et al, GRL 2009), show that the hysteretic behavior disappears when the protocol is performed at a very low strain-rate (static limit). Therefore, future work will aim at linking quasi-static and dynamic observations, i.e. the frequency or strain-rate dependence, in order to understand underlying physical phenomena.

A STUDY OF BROADBAND FARADAY ROTATION AND POLARIZATION BEHAVIOR OVER 1.3–10 GHz IN 36 DISCRETE RADIO SOURCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, C. S.; Gaensler, B. M.; Feain, I. J., E-mail: craiga@physics.usyd.edu.au

We present a broadband polarization analysis of 36 discrete polarized radio sources over a very broad, densely sampled frequency band. Our sample was selected on the basis of polarization behavior apparent in narrowband archival data at 1.4 GHz: half the sample shows complicated frequency-dependent polarization behavior (i.e., Faraday complexity) at these frequencies, while half shows comparatively simple behavior (i.e., they appear Faraday simple ). We re-observed the sample using the Australia Telescope Compact Array in full polarization, with 6 GHz of densely sampled frequency coverage spanning 1.3–10 GHz. We have devised a general polarization modeling technique that allows us tomore » identify multiple polarized emission components in a source, and to characterize their properties. We detect Faraday complex behavior in almost every source in our sample. Several sources exhibit particularly remarkable polarization behavior. By comparing our new and archival data, we have identified temporal variability in the broadband integrated polarization spectra of some sources. In a number of cases, the characteristics of the polarized emission components, including the range of Faraday depths over which they emit, their temporal variability, spectral index, and the linear extent of the source, allow us to argue that the spectropolarimetric data encode information about the magneto-ionic environment of active galactic nuclei themselves. Furthermore, the data place direct constraints on the geometry and magneto-ionic structure of this material. We discuss the consequences of restricted frequency bands on the detection and interpretation of polarization structures, and the implications for upcoming spectropolarimetric surveys.« less

Technical evaluation report of the Specialists Meeting on Characterization of Low Cycle High Temperature Fatigue by the Strainrange Partitioning Method

NASA Technical Reports Server (NTRS)

Drapier, J. M.; Hirschberg, M. H.

1979-01-01

The ability of the Strainrange Partitioning Method SRP was evaluated to correlate the creep-fatigue behavior of gas turbine materials and to predict the creep fatigue life of laboratory specimens subjected to complex cycling conditions. A reference body of high temperature creep fatigue data which can be used in the evaluation of other SRP and low cycle high temperature fatigue predictive techniques was provided.

Aging, memory, and nonhierarchical energy landscape of spin jam

PubMed Central

Samarakoon, Anjana; Sato, Taku J.; Chen, Tianran; Chern, Gai-Wei; Yang, Junjie; Klich, Israel; Sinclair, Ryan; Zhou, Haidong; Lee, Seung-Hun

2016-01-01

The notion of complex energy landscape underpins the intriguing dynamical behaviors in many complex systems ranging from polymers, to brain activity, to social networks and glass transitions. The spin glass state found in dilute magnetic alloys has been an exceptionally convenient laboratory frame for studying complex dynamics resulting from a hierarchical energy landscape with rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo simulation study, that densely populated frustrated magnets in a spin jam state exhibit much weaker memory effects than spin glasses, and the characteristic properties can be reproduced by a nonhierarchical landscape with a wide and nearly flat but rough bottom. Our results illustrate that the memory effects can be used to probe different slow dynamics of glassy materials, hence opening a window to explore their distinct energy landscapes. PMID:27698141

A Thermoplasticity Model for Oil Shale

DOE PAGES

White, Joshua A.; Burnham, Alan K.; Camp, David W.

2016-03-31

Several regions of the world have abundant oil shale resources, but accessing this energy supply poses a number of challenges. One particular difficulty is the thermomechanical behavior of the material. When heated to sufficient temperatures, thermal conversion of kerogen to oil, gas, and other products takes place. This alteration of microstructure leads to a complex geomechanical response. In this work, we develop a thermoplasticity model for oil shale. The model is based on critical state plasticity, a framework often used for modeling clays and soft rocks. The model described here allows for both hardening due to mechanical deformation and softeningmore » due to thermal processes. In particular, the preconsolidation pressure—defining the onset of plastic volumetric compaction—is controlled by a state variable representing the kerogen content of the material. As kerogen is converted to other phases, the material weakens and plastic compaction begins. We calibrate and compare the proposed model to a suite of high-temperature uniaxial and triaxial experiments on core samples from a pilot in situ processing operation in the Green River Formation. In conclusion, we also describe avenues for future work to improve understanding and prediction of the geomechanical behavior of oil shale operations.« less

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nutt, S. R.; Widener, C. A.; Champagne, V. K.; Hrabe, R. H.

2017-08-01

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

X-Ray Diffraction on NIF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eggert, J H; Wark, J

2012-02-15

The National Ignition Facility (NIF) is currently a 192 beam, 1.6 MJ laser. NIF Ramp-Compression Experiments have already made the relevant exo-planet pressure range from 1 to 50 Mbar accessible. We Proposed to Study Carbon Phases by X-Ray Diffraction on NIF. Just a few years ago, ultra-high pressure phase diagrams for materials were very 'simple'. New experiments and theories point out surprising and decidedly complex behavior at the highest pressures considered. High pressures phases of aluminum are also predicted to be complex. Recent metadynamics survey of carbon proposed a dynamic pathway among multiple phases. We need to develop diagnostics andmore » techniques to explore this new regime of highly compressed matter science. X-Ray Diffraction - Understand the phase diagram/EOS/strength/texture of materials to 10's of Mbar. Strategy and physics goals: (1) Powder diffraction; (2) Begin with diamond; (3) Continue with metals etc.; (4) Explore phase diagrams; (5) Develop liquid diffraction; and (6) Reduce background/improve resolution.« less

Mineralized alginate hydrogels using marine carbonates for bone tissue engineering applications.

PubMed

Diaz-Rodriguez, P; Garcia-Triñanes, P; Echezarreta López, M M; Santoveña, A; Landin, M

2018-09-01

The search for an ideal bone tissue replacement has led to the development of new composite materials designed to simulate the complex inorganic/organic structure of bone. The present work is focused on the development of mineralized calcium alginate hydrogels by the addition of marine derived calcium carbonate biomineral particles. Following a novel approach, we were able to obtain calcium carbonate particles of high purity and complex micro and nanostructure dependent on the source material. Three different types of alginates were selected to develop inorganic/organic scaffolds in order to correlate alginate composition with scaffold properties and cell behavior. The incorporation of calcium carbonates into alginate networks was able to promote extracellular matrix mineralization and osteoblastic differentiation of mesenchymal stem cells when added at 7 mg/ml. We demonstrated that the selection of the alginate type and calcium carbonate origin is crucial to obtain adequate systems for bone tissue engineering as they modulate the mechanical properties and cell differentiation. Copyright © 2018 Elsevier Ltd. All rights reserved.

Considerations on thermic and mechanic processes that appear when 3D printing using ABS fused deposition modelling technology

NASA Astrophysics Data System (ADS)

Amza, Catalin Gheorghe; Niţoi, Dan Florin

2018-02-01

3D printers are of recent history, but with an extremely rapid evolution both in technology and hardware involved. At present excellent performances are reached in applications such as 3D printing of various Acrylonitrile butadiene styrene (ABS) plastic parts for house building using Fused Deposition Modelling technology. Nevertheless, the thermic and mechanic processes that appear when manufacturing such plastic components are quite complex. This aspect is very important, especially when one wants to optimize the manufacturing of parts with certain geometrical complexity. The Finite Element Analysis/Modelling (FEA/FEM) is among the few methods that can study the thermic transfer processes and shape modifications that can appear due to non-seamar behavior that takes place when the ABS plastic material is cooling down. The current papers present such an analysis when simulating the deposition of several strings of materials. A thermic analysis is made followed by a study of deformations that appear when the structure cools down.

Realistic micromechanical modeling and simulation of two-phase heterogeneous materials

NASA Astrophysics Data System (ADS)

Sreeranganathan, Arun

This dissertation research focuses on micromechanical modeling and simulations of two-phase heterogeneous materials exhibiting anisotropic and non-uniform microstructures with long-range spatial correlations. Completed work involves development of methodologies for realistic micromechanical analyses of materials using a combination of stereological techniques, two- and three-dimensional digital image processing, and finite element based modeling tools. The methodologies are developed via its applications to two technologically important material systems, namely, discontinuously reinforced aluminum composites containing silicon carbide particles as reinforcement, and boron modified titanium alloys containing in situ formed titanium boride whiskers. Microstructural attributes such as the shape, size, volume fraction, and spatial distribution of the reinforcement phase in these materials were incorporated in the models without any simplifying assumptions. Instrumented indentation was used to determine the constitutive properties of individual microstructural phases. Micromechanical analyses were performed using realistic 2D and 3D models and the results were compared with experimental data. Results indicated that 2D models fail to capture the deformation behavior of these materials and 3D analyses are required for realistic simulations. The effect of clustering of silicon carbide particles and associated porosity on the mechanical response of discontinuously reinforced aluminum composites was investigated using 3D models. Parametric studies were carried out using computer simulated microstructures incorporating realistic microstructural attributes. The intrinsic merit of this research is the development and integration of the required enabling techniques and methodologies for representation, modeling, and simulations of complex geometry of microstructures in two- and three-dimensional space facilitating better understanding of the effects of microstructural geometry on the mechanical behavior of materials.

Ionic liquid structure, dynamics, and electrosorption in carbon electrodes with bimodal pores and heterogeneous surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dyatkin, Boris; Osti, Naresh C.; Zhang, Yu

In this paper, we investigate the aggregation, diffusion, and resulting electrochemical behavior of ionic liquids inside carbon electrodes with complex pore architectures and surface chemistries. Carbide-derived carbons (CDCs) with bimodal porosities and defunctionalized or oxidized electrode surfaces served as model electrode materials. Our goal was to obtain a fundamental understanding of room-temperature ionic liquid ion orientation, mobility, and electrosorption behavior. Neat 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide confined in CDCs was studied using an integrated experimental and modeling approach, consisting of quasielastic neutron scattering, small-angle neutron scattering, X-ray pair distribution function analysis, and electrochemical measurements, which were combined with molecular dynamics simulations. Our analysismore » shows that surface oxygen groups increase the diffusion of confined electrolytes. Consequently, the ions become more than twice as mobile in oxygen-rich pores. Although greater self-diffusion of ions translates into higher electrochemical mobilities in oxidized pores, bulk-like behavior of ions dominates in the larger mesopores and increases the overall capacitance in defunctionalized pores. Experimental results highlight strong confinement and surface effects of carbon electrodes on electrolyte behavior, and molecular dynamics simulations yield insight into diffusion and capacitance differences in specific pore regions. Finally, we demonstrate the significance of surface defects on electrosorption dynamics of complex electrolytes in hierarchical pore architectures of supercapacitor electrodes.« less

Ionic liquid structure, dynamics, and electrosorption in carbon electrodes with bimodal pores and heterogeneous surfaces

DOE PAGES

Dyatkin, Boris; Osti, Naresh C.; Zhang, Yu; ...

2017-12-05

In this paper, we investigate the aggregation, diffusion, and resulting electrochemical behavior of ionic liquids inside carbon electrodes with complex pore architectures and surface chemistries. Carbide-derived carbons (CDCs) with bimodal porosities and defunctionalized or oxidized electrode surfaces served as model electrode materials. Our goal was to obtain a fundamental understanding of room-temperature ionic liquid ion orientation, mobility, and electrosorption behavior. Neat 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide confined in CDCs was studied using an integrated experimental and modeling approach, consisting of quasielastic neutron scattering, small-angle neutron scattering, X-ray pair distribution function analysis, and electrochemical measurements, which were combined with molecular dynamics simulations. Our analysismore » shows that surface oxygen groups increase the diffusion of confined electrolytes. Consequently, the ions become more than twice as mobile in oxygen-rich pores. Although greater self-diffusion of ions translates into higher electrochemical mobilities in oxidized pores, bulk-like behavior of ions dominates in the larger mesopores and increases the overall capacitance in defunctionalized pores. Experimental results highlight strong confinement and surface effects of carbon electrodes on electrolyte behavior, and molecular dynamics simulations yield insight into diffusion and capacitance differences in specific pore regions. Finally, we demonstrate the significance of surface defects on electrosorption dynamics of complex electrolytes in hierarchical pore architectures of supercapacitor electrodes.« less

Material flow data for numerical simulation of powder injection molding

NASA Astrophysics Data System (ADS)

Duretek, I.; Holzer, C.

2017-01-01

The powder injection molding (PIM) process is a cost efficient and important net-shape manufacturing process that is not completely understood. For the application of simulation programs for the powder injection molding process, apart from suitable physical models, exact material data and in particular knowledge of the flow behavior are essential in order to get precise numerical results. The flow processes of highly filled polymers are complex. Occurring effects are very hard to separate, like shear flow with yield stress, wall slip, elastic effects, etc. Furthermore, the occurrence of phase separation due to the multi-phase composition of compounds is quite probable. In this work, the flow behavior of a 316L stainless steel feedstock for powder injection molding was investigated. Additionally, the influence of pre-shearing on the flow behavior of PIM-feedstocks under practical conditions was examined and evaluated by a special PIM injection molding machine rheometer. In order to have a better understanding of key factors of PIM during the injection step, 3D non-isothermal numerical simulations were conducted with a commercial injection molding simulation software using experimental feedstock properties. The simulation results were compared with the experimental results. The mold filling studies amply illustrate the effect of mold temperature on the filling behavior during the mold filling stage. Moreover, the rheological measurements showed that at low shear rates no zero shear viscosity was observed, but instead the viscosity further increased strongly. This flow behavior could be described with the Cross-WLF approach with Herschel-Bulkley extension very well.

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes.

PubMed

Wong, Michael Y; Zysman-Colman, Eli

2017-06-01

The design of thermally activated delayed fluorescence (TADF) materials both as emitters and as hosts is an exploding area of research. The replacement of phosphorescent metal complexes with inexpensive organic compounds in electroluminescent (EL) devices that demonstrate comparable performance metrics is paradigm shifting, as these new materials offer the possibility of developing low-cost lighting and displays. Here, a comprehensive review of TADF materials is presented, with a focus on linking their optoelectronic behavior with the performance of the organic light-emitting diode (OLED) and related EL devices. TADF emitters are cross-compared within specific color ranges, with a focus on blue, green-yellow, orange-red, and white OLEDs. Organic small-molecule, dendrimer, polymer, and exciplex emitters are all discussed within this review, as is their use as host materials. Correlations are provided between the structure of the TADF materials and their optoelectronic properties. The success of TADF materials has ushered in the next generation of OLEDs. © 2017 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dopamine modulates egalitarian behavior in humans.

PubMed

Sáez, Ignacio; Zhu, Lusha; Set, Eric; Kayser, Andrew; Hsu, Ming

2015-03-30

Egalitarian motives form a powerful force in promoting prosocial behavior and enabling large-scale cooperation in the human species [1]. At the neural level, there is substantial, albeit correlational, evidence suggesting a link between dopamine and such behavior [2, 3]. However, important questions remain about the specific role of dopamine in setting or modulating behavioral sensitivity to prosocial concerns. Here, using a combination of pharmacological tools and economic games, we provide critical evidence for a causal involvement of dopamine in human egalitarian tendencies. Specifically, using the brain penetrant catechol-O-methyl transferase (COMT) inhibitor tolcapone [4, 5], we investigated the causal relationship between dopaminergic mechanisms and two prosocial concerns at the core of a number of widely used economic games: (1) the extent to which individuals directly value the material payoffs of others, i.e., generosity, and (2) the extent to which they are averse to differences between their own payoffs and those of others, i.e., inequity. We found that dopaminergic augmentation via COMT inhibition increased egalitarian tendencies in participants who played an extended version of the dictator game [6]. Strikingly, computational modeling of choice behavior [7] revealed that tolcapone exerted selective effects on inequity aversion, and not on other computational components such as the extent to which individuals directly value the material payoffs of others. Together, these data shed light on the causal relationship between neurochemical systems and human prosocial behavior and have potential implications for our understanding of the complex array of social impairments accompanying neuropsychiatric disorders involving dopaminergic dysregulation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Tracking Control of Hysteretic Piezoelectric Actuator using Adaptive Rate-Dependent Controller.

PubMed

Tan, U-Xuan; Latt, Win Tun; Widjaja, Ferdinan; Shee, Cheng Yap; Riviere, Cameron N; Ang, Wei Tech

2009-03-16

With the increasing popularity of actuators involving smart materials like piezoelectric, control of such materials becomes important. The existence of the inherent hysteretic behavior hinders the tracking accuracy of the actuators. To make matters worse, the hysteretic behavior changes with rate. One of the suggested ways is to have a feedforward controller to linearize the relationship between the input and output. Thus, the hysteretic behavior of the actuator must first be modeled by sensing the relationship between the input voltage and output displacement. Unfortunately, the hysteretic behavior is dependent on individual actuator and also environmental conditions like temperature. It is troublesome and costly to model the hysteresis regularly. In addition, the hysteretic behavior of the actuators also changes with age. Most literature model the actuator using a cascade of rate-independent hysteresis operators and a dynamical system. However, the inertial dynamics of the structure is not the only contributing factor. A complete model will be complex. Thus, based on the studies done on the phenomenological hysteretic behavior with rate, this paper proposes an adaptive rate-dependent feedforward controller with Prandtl-Ishlinskii (PI) hysteresis operators for piezoelectric actuators. This adaptive controller is achieved by adapting the coefficients to manipulate the weights of the play operators. Actual experiments are conducted to demonstrate the effectiveness of the adaptive controller. The main contribution of this paper is its ability to perform tracking control of non-periodic motion and is illustrated with the tracking control ability of a couple of different non-periodic waveforms which were created by passing random numbers through a low pass filter with a cutoff frequency of 20Hz.

Structure-property relationships of a biological mesocrystal in the adult sea urchin spine

PubMed Central

Seto, Jong; Ma, Yurong; Davis, Sean A.; Meldrum, Fiona; Gourrier, Aurelien; Kim, Yi-Yeoun; Schilde, Uwe; Sztucki, Michael; Burghammer, Manfred; Maltsev, Sergey; Jäger, Christian; Cölfen, Helmut

2012-01-01

Structuring over many length scales is a design strategy widely used in Nature to create materials with unique functional properties. We here present a comprehensive analysis of an adult sea urchin spine, and in revealing a complex, hierarchical structure, show how Nature fabricates a material which diffracts as a single crystal of calcite and yet fractures as a glassy material. Each spine comprises a highly oriented array of Mg-calcite nanocrystals in which amorphous regions and macromolecules are embedded. It is postulated that this mesocrystalline structure forms via the crystallization of a dense array of amorphous calcium carbonate (ACC) precursor particles. A residual surface layer of ACC and/or macromolecules remains around the nanoparticle units which creates the mesocrystal structure and contributes to the conchoidal fracture behavior. Nature’s demonstration of how crystallization of an amorphous precursor phase can create a crystalline material with remarkable properties therefore provides inspiration for a novel approach to the design and synthesis of synthetic composite materials. PMID:22343283

Size effects of 109° domain walls in rhombohedral barium titanate single crystals—A molecular statics analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Endres, Florian, E-mail: florian.endres@ltm.uni-erlangen.de; Steinmann, Paul, E-mail: paul.steinmann@ltm.uni-erlangen.de

2016-01-14

Ferroelectric functional materials are of great interest in science and technology due to their electromechanically coupled material properties. Therefore, ferroelectrics, such as barium titanate, are modeled and simulated at the continuum scale as well as at the atomistic scale. Due to recent advancements in related manufacturing technologies the modeling and simulation of smart materials at the nanometer length scale is getting more important not only to predict but also fundamentally understand the complex material behavior of such materials. In this study, we analyze the size effects of 109° nanodomain walls in ferroelectric barium titanate single crystals in the rhombohedral phasemore » using a recently proposed extended molecular statics algorithm. We study the impact of domain thicknesses on the spontaneous polarization, the coercive field, and the lattice constants. Moreover, we discuss how the electromechanical coupling of an applied electric field and the introduced strain in the converse piezoelectric effect is affected by the thickness of nanodomains.« less

Computational methods for coupling microstructural and micromechanical materials response simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

HOLM,ELIZABETH A.; BATTAILE,CORBETT C.; BUCHHEIT,THOMAS E.

2000-04-01

Computational materials simulations have traditionally focused on individual phenomena: grain growth, crack propagation, plastic flow, etc. However, real materials behavior results from a complex interplay between phenomena. In this project, the authors explored methods for coupling mesoscale simulations of microstructural evolution and micromechanical response. In one case, massively parallel (MP) simulations for grain evolution and microcracking in alumina stronglink materials were dynamically coupled. In the other, codes for domain coarsening and plastic deformation in CuSi braze alloys were iteratively linked. this program provided the first comparison of two promising ways to integrate mesoscale computer codes. Coupled microstructural/micromechanical codes were appliedmore » to experimentally observed microstructures for the first time. In addition to the coupled codes, this project developed a suite of new computational capabilities (PARGRAIN, GLAD, OOF, MPM, polycrystal plasticity, front tracking). The problem of plasticity length scale in continuum calculations was recognized and a solution strategy was developed. The simulations were experimentally validated on stockpile materials.« less

Structure-property relationships of a biological mesocrystal in the adult sea urchin spine.

PubMed

Seto, Jong; Ma, Yurong; Davis, Sean A; Meldrum, Fiona; Gourrier, Aurelien; Kim, Yi-Yeoun; Schilde, Uwe; Sztucki, Michael; Burghammer, Manfred; Maltsev, Sergey; Jäger, Christian; Cölfen, Helmut

2012-03-06

Structuring over many length scales is a design strategy widely used in Nature to create materials with unique functional properties. We here present a comprehensive analysis of an adult sea urchin spine, and in revealing a complex, hierarchical structure, show how Nature fabricates a material which diffracts as a single crystal of calcite and yet fractures as a glassy material. Each spine comprises a highly oriented array of Mg-calcite nanocrystals in which amorphous regions and macromolecules are embedded. It is postulated that this mesocrystalline structure forms via the crystallization of a dense array of amorphous calcium carbonate (ACC) precursor particles. A residual surface layer of ACC and/or macromolecules remains around the nanoparticle units which creates the mesocrystal structure and contributes to the conchoidal fracture behavior. Nature's demonstration of how crystallization of an amorphous precursor phase can create a crystalline material with remarkable properties therefore provides inspiration for a novel approach to the design and synthesis of synthetic composite materials.

Studies of Lubricating Materials in Vacuum

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Johnson, R. L.; Swikert, M. A.

1964-01-01

Lubricating materials for use in a vacuum environment have been the subject of a series of experimental investigations. Evaporation properties were evaluated for solid polymeric compositions. Friction and wear studies explored the behavior during sliding contact for series of polymeric compositions, binary alloys containing soft film-forming phases, complex alloys with film-forming materials, and a burnished MoS2 film. Friction and wear experiments were conducted at 10(exp-9)mm Hg with a 3/16-inch-radius-hemisphere rider specimen sliding on the flat surface of a rotating 2-1/2-inch-diameter disk specimen with materials that had low rates of evaporation. The influence of fillers in polytetrafluoroethylene (PTFE) on decomposition during vacuum friction studies was determined with a mass spectrometer. A real advantage in reducing decomposition and improving friction wear properties is gained by adding fillers (e.g., copper) that improve thermal conductivity through the composite materials. A polyimide and an epoxy-MoS2 composition material were found to have better friction and wear properties than PTFE compositions. A series of alloys (cast binary as well as more complex alloys) that contained microinclusions of potential film-forming material was studied. These materials replaced the normal surface oxides as they were worn away on sliding contact. Iron sulfide, nickel oxide, and tin are typical film-forming materials employed and were demonstrated to be effective in inhibiting surface welding and reducing friction. A burnished MoS2 film applied to type 440-C stainless steel in argon with a rotating soft wire brush had good endurance properties but somewhat higher friction than commercially available bonded films. An oil film applied to the burnished MoS2 markedly reduced its endurance life.

Surfactant mediated polyelectrolyte self-assembly

DOE PAGES

Goswami, Monojoy; Borreguero Calvo, Jose M.; Pincus, Phillip A.; ...

2015-11-25

Self-assembly and dynamics of polyelectrolyte (PE) surfactant complex (PES) is investigated using molecular dynamics simulations. The complexation is systematically studied for five different PE backbone charge densities. At a fixed surfactant concentration the PES complexation exhibits pearl-necklace to agglomerated double spherical structures with a PE chain decorating the surfactant micelles. The counterions do not condense on the complex, but are released in the medium with a random distribution. The relaxation dynamics for three different length scales, polymer chain, segmental and monomer, show distinct features of the charge and neutral species; the counterions are fastest followed by the PE chain andmore » surfactants. The surfactant heads and tails have the slowest relaxation due to their restricted movement inside the agglomerated structure. At the shortest length scale, all the charge and neutral species show similar relaxation dynamics confirming Rouse behavior at monomer length scales. Overall, the present study highlights the structure-property relationship for polymer-surfactant complexation. These results will help improve the understanding of PES complex and should aid in the design of better materials for future applications.« less

Polydopamine-based concentric nanoshells with programmable architectures and plasmonic properties.

PubMed

Choi, Chun Kit K; Zhuo, Xiaolu; Chiu, Yee Ting Elaine; Yang, Hongrong; Wang, Jianfang; Choi, Chung Hang Jonathan

2017-11-09

Nanoshells, classically comprising gold as the metallic component and silica as the dielectric material, are important for fundamental studies in nanoplasmonics. They also empower a myriad of applications, including sensing, energy harvesting, and cancer therapy. Yet, laborious preparation precludes the development of next-generation nanoshells with structural complexity, compositional diversity, and tailorable plasmonic behaviors. This work presents an efficient approach to the bottom-up assembly of concentric nanoshells. By employing polydopamine as the dielectric material and exploiting its intrinsic adhesiveness and pH-tunable surface charge, the growth of each shell only takes 3-4 hours at room temperature. A series of polydopamine-based concentric nanoshells with programmable nanogap thickness, elemental composition (gold and silver), and geometrical configuration (number of layers) is prepared, followed by extensive structural characterization. Four of the silver-containing nanostructures are newly reported. Systematic investigations into the plasmonic properties of concentric nanoshells as a function of their structural parameters further reveal multiple Fano resonances and local-field "hot spots", infrequently reported plasmonic features for individual nanostructures fabricated using bottom-up wet chemistry. These results establish materials design rules for engineering complex plasmon-based systems originating from the integration of multiple plasmonic elements into defined locations within a compact nanostructure.

Morphogenesis and mechanostabilization of complex natural and 3D printed shapes

PubMed Central

Tiwary, Chandra Sekhar; Kishore, Sharan; Sarkar, Suman; Mahapatra, Debiprosad Roy; Ajayan, Pulickel M.; Chattopadhyay, Kamanio

2015-01-01

The natural selection and the evolutionary optimization of complex shapes in nature are closely related to their functions. Mechanostabilization of shape of biological structure via morphogenesis has several beautiful examples. With the help of simple mechanics-based modeling and experiments, we show an important causality between natural shape selection as evolutionary outcome and the mechanostabilization of seashells. The effect of biological growth on the mechanostabilization process is identified with examples of two natural shapes of seashells, one having a diametrically converging localization of stresses and the other having a helicoidally concentric localization of stresses. We demonstrate how the evolved shape enables predictable protection of soft body parts of the species. The effect of bioavailability of natural material is found to be a secondary factor compared to shape selectivity, where material microstructure only acts as a constraint to evolutionary optimization. This is confirmed by comparing the mechanostabilization behavior of three-dimensionally printed synthetic polymer structural shapes with that of natural seashells consisting of ceramic and protein. This study also highlights interesting possibilities in achieving a new design of structures made of ordinary materials which have bio-inspired optimization objectives. PMID:26601170

Exploring the Electronic Landscape at Interfaces and Junctions in Semiconductor Nanowire Devices with Subsurface Local Probing of Carrier Dynamics

NASA Astrophysics Data System (ADS)

McGuckin, Terrence

The solid state devices that are pervasive in our society, are based on building blocks composed of interfaces between materials and junctions that manipulate how charge carriers behave in a device. As the dimensions of these devices are reduced to the nanoscale, surfaces and interfaces play a larger role in the behavior of carriers in devices and must be thoroughly investigated to understand not only the material properties but how these materials interact. Separating the effects of these different building blocks is a challenge, as most testing methods measure the performance of the whole device. Semiconductor nanowires represent an excellent test system to explore the limits of size and novel device structures. The behavior of charge carriers in semiconductor nanowire devices under operational conditions is investigated using local probing technique electron beam induced current (EBIC). The behavior of locally excited carriers are driven by the forces of drift, from electric fields within a device at junctions, surfaces, contacts and, applied voltage bias, and diffusion. This thesis presents the results of directly measuring these effects spatially with nanometer resolution, using EBIC in Ge, Si, and complex heterostructure GaAs/AlGaAs nanowire devices. Advancements to the EBIC technique, have pushed the resolution from tens of nanometers down to 1 to 2 nanometers. Depth profiling and tuning of the interaction volume allows for the separating the signal originating from the surface and the interior of the nanowire. Radial junctions and variations in bands can now be analyzed including core/shell hetero-structures. This local carrier probing reveals a number of surprising behaviors; Most notably, directly imaging the evolution of surface traps filling with electrons causing bandbending at the surface of Ge nanowires that leads to an enhancement in the charge separation of electrons and holes, and extracting different characteristic lengths from GaAs and AlGaAs in core/shell nanowires. For new and emerging solid state materials, understanding charge carrier dynamics is crucial to designing functional devices. Presented here are examples of the wide application of EBIC, and its variants, through imaging domains in ferroelectric materials, local electric fields and defects in 2D semiconductor material MoS2, and gradients in doping profiles of solar cells. Measuring the local behavior of carrier dynamics, EBIC has the potential to be a key metrology technique in correlative microscopy, enabling a deeper understanding of materials and how they interact within devices.

Numerical analysis of the creeping behavior of the S. Andrea di Perarolo secondary landslide (Italian Eastern Alps)

NASA Astrophysics Data System (ADS)

Cioli, C.; Genevois, R.; Iafelice, M.; Zorzi, L.

2012-04-01

The S. Andrea landslide is a complex secondary phenomenon characterized by continuous movements causing a very high hazard condition for the near Perarolo di Cadore village (Italian Eastern Alps). A significant amount of geological and geotechnical investigations has been carried out in the past allowing the detection of the basal sliding surface. In specific, the sliding surface coincides with the contact between the bedrock and the overlying mass of an old landslides, involving a volume of about 180.000 cubic meters. A numerical approach has been adopted to analyze the stability of slope. This method is able to simulate the formation and development of shear zones as areas of strain localization in the model. Indeed, the S. Andrea landslide has been, then, investigated using FLAC, a two-dimensional explicit finite difference program, particularly useful in case of slopes with complex geometry. In order to build up a suitable model, variation of geological, hydrogeological and geotechnical parameters have been identified from the interpretation of all available data. In a preliminary stage, a Mohr-Coulomb plasticity model has been adopted except for the bedrock, which was characterized by an isotropic elastic model. Groundwater flow condition has been performed evaluating the change in pore pressure coupled to the mechanical deformation calculation. Numerical results show that this model cannot simulate real displacement behavior of the slope mainly due to both the complex material behavior and lithological heterogeneity, and due to geotechnical spatial complexity of different soils and mechanical parameters. It has been assumed that it was necessary to improve the model in the light of a time dependent behavior of existing soils. An elastic-viscoplastic model has been then used to reproduce the observed creeping behavior, and only in viscoplastic region time effects have been considered. Discussion of results points out on: i) the evolution of the ``mechanical damage'' within the moving mass; ii) the identification of possible causes of the displacements recorded in the field; iii) the utility of the computational approach for the creeping response of the soil slopes under constant load conditions and for two dimensional applications.

Challenges at the Frontiers of Matter and Energy: Transformative Opportunities for Discovery Science

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hemminger, John C.; Sarrao, John; Crabtree, George

FIVE TRANSFORMATIVE OPPORTUNITIES FOR DISCOVERY SCIENCE As a result of this effort, it has become clear that the progress made to date on the five Grand Challenges has created a springboard for seizing five new Transformative Opportunities that have the potential to further transform key technologies involving matter and energy. These five new Transformative Opportunities and the evidence supporting them are discussed in this new report, “Challenges at the Frontiers of Matter and Energy: Transformative Opportunities for Discovery Science.” Mastering Hierarchical Architectures and Beyond-Equilibrium Matter Complex materials and chemical processes transmute matter and energy, for example from CO2 and watermore » to chemical fuel in photosynthesis, from visible light to electricity in solar cells and from electricity to light in light emitting diodes (LEDs) Such functionality requires complex assemblies of heterogeneous materials in hierarchical architectures that display time-dependent away-from-equilibrium behaviors. Much of the foundation of our understanding of such transformations however, is based on monolithic single- phase materials operating at or near thermodynamic equilibrium. The emergent functionalities enabling next-generation disruptive energy technologies require mastering the design, synthesis, and control of complex hierarchical materials employing dynamic far-from-equilibrium behavior. A key guide in this pursuit is nature, for biological systems prove the power of hierarchical assembly and far- from-equilibrium behavior. The challenges here are many: a description of the functionality of hierarchical assemblies in terms of their constituent parts, a blueprint of atomic and molecular positions for each constituent part, and a synthesis strategy for (a) placing the atoms and molecules in the proper positions for the component parts and (b) arranging the component parts into the required hierarchical structure. Targeted functionality will open the door to significant advances in the harvesting, transforming (e.g., reducing CO2, splitting water, and fixing nitrogen), storing, and use of energy to create new materials, manufacturing processes, and technologies—the lifeblood of human societies and economic growth. Beyond Ideal Materials and Systems: Understanding the Critical Roles of Heterogeneity, Interfaces, and Disorder Real materials, both natural ones and those we engineer, are usually a complex mixture of compositional and structural heterogeneities, interfaces, and disorder across all spatial and temporal scales. It is the fluctuations and disorderly states of these heterogeneities and interfaces that often determine the system’s properties and functionality. Much of our fundamental scientific knowledge is based on “ideal” systems, meaning materials that are observed in “frozen” states or represented by spatially or temporally averaged states. Too often, this approach has yielded overly simplistic models that hide important nuances and do not capture the complex behaviors of materials under realistic conditions. These behaviors drive vital chemical transformations such as catalysis, which initiates most industrial manufacturing processes, and friction and corrosion, the parasitic effects of which cost the U.S. economy billions of dollars annually. Expanding our scientific knowledge from the relative simplicity of ideal, perfectly ordered, or structurally averaged materials to the true complexity of real-world heterogeneities, interfaces, and disorder should enable us to realize enormous benefits in the materials and chemical sciences, which translates to the energy sciences, including solar and nuclear power, hydraulic fracturing, power conversion, airframes, and batteries. Harnessing Coherence in Light and Matter Quantum coherence in light and matter is a measure of the extent to which a wave field vibrates in unison with itself at neighboring points in space and time. Although this phenomenon is expressed at the atomic and electronic scales, it can dominate the macroscopic properties of materials and chemical reactions such as superconductivity and efficient photosynthesis. In recent years, enormous progress has been made in recognizing, manipulating, and exploiting quantum coherence. This progress has already elucidated the role that symmetry plays in protecting coherence in key materials, taught us how to use light to manipulate atoms and molecules, and provided us with increasingly sophisticated techniques for controlling and probing the charges and spins of quantum coherent systems. With the arrival of new sources of coherent light and electron beams, thanks in large part to investments by the U.S. Department of Energy’s Office of Basic Energy Sciences (BES), there is now an opportunity to engineer coherence in heterostructures that incorporate multiple types of materials and to control complex, multistep chemical transformations. This approach will pave the way for quantum information processing and next-generation photovoltaic cells and sensors. Revolutionary Advances in Models, Mathematics, Algorithms, Data, and Computing Science today is benefiting from a convergence of theoretical, mathematical, computational, and experimental capabilities that put us on the brink of greatly accelerating our ability to predict, synthesize, and control new materials and chemical processes, and to understand the complexities of matter across a range of scales. Imagine being able to chart a path through a vast sea of possible new materials to find a select few with desired properties. Instead of the time-honored forward approach, in which materials with desired properties are found through either trial-and-error experiments or lucky accidents, we have the opportunity to inversely design and create new materials that possess the properties we desire. The traditional approach has allowed us to make only a tiny fraction of all the materials that are theoretically possible. The inverse design approach, through the harmonious convergence of theoretical, mathematical, computational, and experimental capabilities, could usher in a virtual cornucopia of new materials with functionalities far beyond what nature can provide. Similarly, enhanced mathematical and computational capabilities significantly enhance our ability to extract physical and chemical insights from vastly larger data streams gathered during multimodal and multidimensional experiments using advanced characterization facilities. Exploiting Transformative Advances in Imaging Capabilities across Multiple Scales Historically, improvements in imaging capabilities have always resulted in improved understanding of scientific phenomena. A prime challenge today is finding ways to reconstruct raw data, obtained by probing and mapping matter across multiple scales, into analyzable images. BES investments in new and improved imaging facilities, most notably synchrotron x-ray sources, free-electron lasers, electron microscopes, and neutron sources, have greatly advanced our powers of observation, as have substantial improvements in laboratory- scale technologies. Furthermore, BES is now planning or actively discussing exciting new capabilities. Taken together, these advances in imaging capabilities provide an opportunity to expand our ability to observe and study matter from the 3D spatial perspectives of today to true “4D” spatially and temporally resolved maps of dynamics that allow quantitative predictions of time-dependent material properties and chemical processes. The knowledge gained will impact data storage, catalyst design, drug delivery, structural materials, and medical implants, to name just a few key technologies. ENABLING SUCCESS Seizing each of these five Transformative Opportunities, as well as accelerating further progress on Grand Challenge research, will require specific, targeted investments from BES in the areas of synthesis, meaning the ability to make the materials and architectures that are envisioned; instrumentation and tools, a category that includes theory and computation; and human capital, the most important asset for advancing the Grand Challenges and Transformative Opportunities. While “Challenges at the Frontiers of Matter and Energy: Transformative Opportunities for Discovery Science” could be viewed as a sequel to the original Grand Challenges report, it breaks much new ground in its assessment of the scientific landscape today versus the scientific landscape just a few years ago. In the original Grand Challenges report, it was noted that if the five Grand Challenges were met, our ability to direct matter and energy would be measured only by the limits of human imagination. This new report shows that, prodded by those challenges, the scientific community is positioned today to seize new opportunities whose impacts promise to be transformative for science and society, as well as dramatically accelerate progress in the pursuit of the original Grand Challenges.« less

Reaction modeling of drainage quality in the Duluth Complex, northern Minnesota, USA

USGS Publications Warehouse

Seal, Robert; Lapakko, Kim; Piatak, Nadine; Woodruff, Laurel G.

2015-01-01

Reaction modeling can be a valuable tool in predicting the long-term behavior of waste material if representative rate constants can be derived from long-term leaching tests or other approaches. Reaction modeling using the REACT program of the Geochemist’s Workbench was conducted to evaluate long-term drainage quality affected by disseminated Cu-Ni-(Co-)-PGM sulfide mineralization in the basal zone of the Duluth Complex where significant resources have been identified. Disseminated sulfide minerals, mostly pyrrhotite and Cu-Fe sulfides, are hosted by clinopyroxene-bearing troctolites. Carbonate minerals are scarce to non-existent. Long-term simulations of up to 20 years of weathering of tailings used two different sets of rate constants: one based on published laboratory single-mineral dissolution experiments, and one based on leaching experiments using bulk material from the Duluth Complex conducted by the Minnesota Department of Natural Resources (MNDNR). The simulations included only plagioclase, olivine, clinopyroxene, pyrrhotite, and water as starting phases. Dissolved oxygen concentrations were assumed to be in equilibrium with atmospheric oxygen. The simulations based on the published single-mineral rate constants predicted that pyrrhotite would be effectively exhausted in less than two years and pH would rise accordingly. In contrast, only 20 percent of the pyrrhotite was depleted after two years using the MNDNR rate constants. Predicted pyrrhotite depletion by the simulation based on the MNDNR rate constant matched well with published results of laboratory tests on tailings. Modeling long-term weathering of mine wastes also can provide important insights into secondary reactions that may influence the permeability of tailings and thereby affect weathering behavior. Both models predicted the precipitation of a variety of secondary phases including goethite, gibbsite, and clay (nontronite).

Is it the real deal? Perception of virtual characters versus humans: an affective cognitive neuroscience perspective

PubMed Central

de Borst, Aline W.; de Gelder, Beatrice

2015-01-01

Recent developments in neuroimaging research support the increased use of naturalistic stimulus material such as film, avatars, or androids. These stimuli allow for a better understanding of how the brain processes information in complex situations while maintaining experimental control. While avatars and androids are well suited to study human cognition, they should not be equated to human stimuli. For example, the uncanny valley hypothesis theorizes that artificial agents with high human-likeness may evoke feelings of eeriness in the human observer. Here we review if, when, and how the perception of human-like avatars and androids differs from the perception of humans and consider how this influences their utilization as stimulus material in social and affective neuroimaging studies. First, we discuss how the appearance of virtual characters affects perception. When stimuli are morphed across categories from non-human to human, the most ambiguous stimuli, rather than the most human-like stimuli, show prolonged classification times and increased eeriness. Human-like to human stimuli show a positive linear relationship with familiarity. Secondly, we show that expressions of emotions in human-like avatars can be perceived similarly to human emotions, with corresponding behavioral, physiological and neuronal activations, with exception of physical dissimilarities. Subsequently, we consider if and when one perceives differences in action representation by artificial agents versus humans. Motor resonance and predictive coding models may account for empirical findings, such as an interference effect on action for observed human-like, natural moving characters. However, the expansion of these models to explain more complex behavior, such as empathy, still needs to be investigated in more detail. Finally, we broaden our outlook to social interaction, where virtual reality stimuli can be utilized to imitate complex social situations. PMID:26029133

True-3D Strain Mapping for Assessment of Material Deformation by Synchrotron X-Ray Microtomography

NASA Astrophysics Data System (ADS)

Ahn, J. J.; Toda, H.; Niinomi, M.; Kobayashi, T.; Akahori, T.; Uesugi, K.

2005-04-01

Downsizing of products with complex shapes has been accelerated thanks to the rapid development of electrodevice manufacturing technology. Micro electromechanical systems (MEMS) are one of such typical examples. 3D strain measurement of such miniature products is needed to ensure their reliability. In the present study, as preliminary trial for it 3D tensile deformation behavior of a pure aluminum wire is examined using the synchrotron X-ray microtomography technique at Spring-8, Japan. Multipurpose in-situ tester is used to investigate real-time tensile deformation behavior of the Al wire. Tensile tests are carried out under strokes of 0, 0.005, 0.01 and 0.015mm. It measures 3D local deformation of a region of interest by tracking a relative movement of a pair of particles at each point. Local deformation behavior of the Al wire is identified to be different from macroscopic deformation behavior. It may be closely associated with underlying microstructure.

True-3D Strain Mapping for Assessment of Material Deformation by Synchrotron X-Ray Microtomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, J.J.; Toda, H.; Niinomi, M.

2005-04-09

Downsizing of products with complex shapes has been accelerated thanks to the rapid development of electrodevice manufacturing technology. Micro electromechanical systems (MEMS) are one of such typical examples. 3D strain measurement of such miniature products is needed to ensure their reliability. In the present study, as preliminary trial for it 3D tensile deformation behavior of a pure aluminum wire is examined using the synchrotron X-ray microtomography technique at Spring-8, Japan. Multipurpose in-situ tester is used to investigate real-time tensile deformation behavior of the Al wire. Tensile tests are carried out under strokes of 0, 0.005, 0.01 and 0.015mm. It measuresmore » 3D local deformation of a region of interest by tracking a relative movement of a pair of particles at each point. Local deformation behavior of the Al wire is identified to be different from macroscopic deformation behavior. It may be closely associated with underlying microstructure.« less

Fatigue properties of JIS H3300 C1220 copper for strain life prediction

NASA Astrophysics Data System (ADS)

Harun, Muhammad Faiz; Mohammad, Roslina

2018-05-01

The existing methods for estimating strain life parameters are dependent on the material's monotonic tensile properties. However, a few of these methods yield quite complicated expressions for calculating fatigue parameters, and are specific to certain groups of materials only. The Universal Slopes method, Modified Universal Slopes method, Uniform Material Law, the Hardness method, and Medians method are a few existing methods for predicting strain-life fatigue based on monotonic tensile material properties and hardness of material. In the present study, nine methods for estimating fatigue life and properties are applied on JIS H3300 C1220 copper to determine the best methods for strain life estimation of this ductile material. Experimental strain-life curves are compared to estimations obtained using each method. Muralidharan-Manson's Modified Universal Slopes method and Bäumel-Seeger's method for unalloyed and low-alloy steels are found to yield batter accuracy in estimating fatigue life with a deviation of less than 25%. However, the prediction of both methods only yield much better accuracy for a cycle of less than 1000 or for strain amplitudes of more than 1% and less than 6%. Manson's Original Universal Slopes method and Ong's Modified Four-Point Correlation method are found to predict the strain-life fatigue of copper with better accuracy for a high number of cycles of strain amplitudes of less than 1%. The differences between mechanical behavior during monotonic and cyclic loading and the complexity in deciding the coefficient in an equation are probably the reason for the lack of a reliable method for estimating fatigue behavior using the monotonic properties of a group of materials. It is therefore suggested that a differential approach and new expressions be developed to estimate the strain-life fatigue parameters for ductile materials such as copper.

Model of anisotropic nonlinearity in self-defocusing photorefractive media.

PubMed

Barsi, C; Fleischer, J W

2015-09-21

We develop a phenomenological model of anisotropy in self-defocusing photorefractive crystals. In addition to an independent term due to nonlinear susceptibility, we introduce a nonlinear, non-separable correction to the spectral diffraction operator. The model successfully describes the crossover between photovoltaic and photorefractive responses and the spatially dispersive shock wave behavior of a nonlinearly spreading Gaussian input beam. It should prove useful for characterizing internal charge dynamics in complex materials and for accurate image reconstruction through nonlinear media.

Fundamental Properties of Soils for Complex Dynamic Loadings: Dynamic Constitutive Modeling of Sandy Soils.

DTIC Science & Technology

1983-04-01

1.0 INTRODUCTION AND SCOPE 1 2.0 PROGRESS SUMMARY 3 2.1 Soil Element Model Development 3 2.2 U.S. Any Engineer Waterways Experiment Station (WES...LABORATORY BEHAVIOR OF SAND 8 3.1 Introduction 8 3.2 Material Description 8 3.3 Laboratory Tests Performed 9 3.4 Laboratory Test Results 14 4.0 MODELING THE... INTRODUCTION AND SCOPE The subject of this annual report is constitutive modeling of cohesionless soil, for both laboratory standard static test conditions

A return mapping algorithm for isotropic and anisotropic plasticity models using a line search method

DOE PAGES

Scherzinger, William M.

2016-05-01

The numerical integration of constitutive models in computational solid mechanics codes allows for the solution of boundary value problems involving complex material behavior. Metal plasticity models, in particular, have been instrumental in the development of these codes. Here, most plasticity models implemented in computational codes use an isotropic von Mises yield surface. The von Mises, of J 2, yield surface has a simple predictor-corrector algorithm - the radial return algorithm - to integrate the model.

Development and test of advanced composite components. Center Directors discretionary fund program

NASA Technical Reports Server (NTRS)

Faile, G.; Hollis, R.; Ledbetter, F.; Maldonado, J.; Sledd, J.; Stuckey, J.; Waggoner, G.; Engler, E.

1985-01-01

This report describes the design, analysis, fabrication, and test of a complex bathtub fitting. Graphite fibers in an epoxy matrix were utilized in manufacturing of 11 components representing four different design and layup concepts. Design allowables were developed for use in the final stress analysis. Strain gage measurements were taken throughout the static load test and correlation of test and analysis data were performed, yielding good understanding of the material behavior and instrumentation requirements for future applications.

Engineering artificial cells by combining HeLa-based cell-free expression and ultra-thin double emulsion template

PubMed Central

Ho, Kwun Yin; Murray, Victoria L.; Liu, Allen P.

2015-01-01

Generation of artificial cells provides the bridge needed to cover the gap between studying the complexity of biological processes in whole cells and studying these same processes in an in vitro reconstituted system. Artificial cells are defined as the encapsulation of biologically active material in a biological or synthetic membrane. Here, we describe a robust and general method to produce artificial cells for the purpose of mimicking one or more behaviors of a cell. A microfluidic double emulsion system is used to encapsulate a mammalian cell free expression system that is able to express membrane proteins into the bilayer or soluble proteins inside the vesicles. The development of a robust platform that allows the assembly of artificial cells is valuable in understanding subcellular functions and emergent behaviors in a more cell-like environment as well as for creating novel signaling pathways to achieve specific cellular behaviors. PMID:25997354

The Effect of Fiber Architecture on Matrix Cracking in Sic/sic Cmc's

NASA Technical Reports Server (NTRS)

Morscher, Gregory N.

2005-01-01

Applications incorporating silicon carbide fiber reinforced silicon carbide matrix composites (CMC's) will require a wide range of fiber architectures in order to fabricate complex shape. The stress-strain response of a given SiC/SiC system for different architectures and orientations will be required in order to design and effectively life-model future components. The mechanism for non-linear stress-strain behavior in CMC's is the formation and propagation of bridged-matrix cracks throughout the composite. A considerable amount of understanding has been achieved for the stress-dependent matrix cracking behavior of SiC fiber reinforced SiC matrix systems containing melt-infiltrated Si. This presentation will outline the effect of 2D and 3D architectures and orientation on stress-dependent matrix-cracking and how this information can be used to model material behavior and serve as the starting point foe mechanistic-based life-models.

Organizational ethics in managed behavioral health care: perspectives from executives and leaders.

PubMed

Sharar, David A; Huff, Stan; Ackerson, Barry

2003-01-01

Managed behavioral health care (MBHC) is frequently criticized on ethical grounds for the way it undermines classical ideals of professionalism in mental health and addiction treatment. There is an implied assumption that practitioners who are executives and leaders in MBHC companies have moved away from clinical ethics to the adoption of business and financial models. This qualitative study explores perceptions of organizational ethical issues from the point of view of leaders working in MBHC settings and how their perspectives contribute to our current schemas for analyzing the ethical complexities of MBHC. Twenty-seven participants from across the United States were interviewed using an interview guide that relied on open-ended questions and probes. Inquiry findings present four major themes and describe participant material in a way that enhances sensitivity and understanding to organizational ethics in MBHC and behavioral health services and research.

SMA texture and reorientation: simulations and neutron diffraction studies

NASA Astrophysics Data System (ADS)

Gao, Xiujie; Brown, Donald W.; Brinson, L. Catherine

2005-05-01

With increased usage of shape memory alloys (SMA) for applications in various fields, it is important to understand how the material behavior is affected by factors such as texture, stress state and loading history, especially for complex multiaxial loading states. Using the in-situ neutron diffraction loading facility (SMARTS diffractometer) and ex situ inverse pole figure measurement facility (HIPPO diffractometer) at the Los Alamos Neutron Science Center (LANCE), the macroscopic mechanical behavior and texture evolution of Nickel-Titanium (Nitinol) SMAs under sequential compression in alternating directions were studied. The simplified multivariant model developed at Northwestern University was then used to simulate the macroscopic behavior and the microstructural change of Nitinol under this sequential loading. Pole figures were obtained via post-processing of the multivariant results for volume fraction evolution and compared quantitatively well to the experimental results. The experimental results can also be used to test or verify other SMA constitutive models.

Effective material parameter retrieval of anisotropic elastic metamaterials with inherent nonlocality

NASA Astrophysics Data System (ADS)

Lee, Hyung Jin; Lee, Heung Son; Ma, Pyung Sik; Kim, Yoon Young

2016-09-01

In this paper, the scattering (S-) parameter retrieval method is presented specifically for anisotropic elastic metamaterials; so far, no retrieval has been accomplished when elastic metamaterials exhibit fully anisotropic behavior. Complex constitutive property and intrinsic scattering behavior of elastic metamaterials make their characterization far more complicated than that for acoustic and electromagnetic metamaterials. In particular, elastic metamaterials generally exhibit anisotropic scattering behavior due to higher scattering modes associated with shear deformation. They also exhibit nonlocal responses to some degrees, which originate from strong multiple scattering interactions even in the long wavelength limit. Accordingly, the conventional S-parameter retrieval methods cannot be directly used for elastic metamaterials, because they determine only the diagonal components in effective tensor property. Also, the conventional methods simply use the analytic inversion formulae for the material characterization so that inherent nonlocality cannot be taken into account. To establish a retrieval method applicable to anisotropic elastic metamaterials, we propose an alternative S-parameter method to deal with full anisotropy of elastic metamaterials. To retrieve the whole effective anisotropic parameter, we utilize not only normal but also oblique wave incidences. For the retrieval, we first retrieve the ratio of the effective stiffness tensor to effective density and then determine the effective density. The proposed retrieval method is validated by characterizing the effective material parameters of various types of non-resonant anisotropic metamaterials. It is found that the whole effective parameters are retrieved consistently regardless of used retrieval conditions in spite of inherent nonlocality.

Microgravity

NASA Image and Video Library

1998-01-01

On STS-89, three Mechanics of Granular Materials (MGM) test cells were subjected to five cycles of compression and relief (left) and three were subjected to shorter displacement cycles that simulate motion during an earthquake (right). In the compression/relief tests, the sand particles rearranged themselves and slightly re-expanded the column during relief. In the short displacement tests, the specimen's resistance to compression decreases, even though the displacement remains the same. The specimens were cycled up to 100 times or until the resistive force was less than 1% that of the previous cycle. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Graphs of Soil Mechanics Tests in Orbit

NASA Technical Reports Server (NTRS)

1998-01-01

On STS-89, three Mechanics of Granular Materials (MGM) test cells were subjected to five cycles of compression and relief (left) and three were subjected to shorter displacement cycles that simulate motion during an earthquake (right). In the compression/relief tests, the sand particles rearranged themselves and slightly re-expanded the column during relief. In the short displacement tests, the specimen's resistance to compression decreases, even though the displacement remains the same. The specimens were cycled up to 100 times or until the resistive force was less than 1% that of the previous cycle. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Adaptive Crack Modeling with Interface Solid Elements for Plain and Fiber Reinforced Concrete Structures.

PubMed

Zhan, Yijian; Meschke, Günther

2017-07-08

The effective analysis of the nonlinear behavior of cement-based engineering structures not only demands physically-reliable models, but also computationally-efficient algorithms. Based on a continuum interface element formulation that is suitable to capture complex cracking phenomena in concrete materials and structures, an adaptive mesh processing technique is proposed for computational simulations of plain and fiber-reinforced concrete structures to progressively disintegrate the initial finite element mesh and to add degenerated solid elements into the interfacial gaps. In comparison with the implementation where the entire mesh is processed prior to the computation, the proposed adaptive cracking model allows simulating the failure behavior of plain and fiber-reinforced concrete structures with remarkably reduced computational expense.

Adaptive Crack Modeling with Interface Solid Elements for Plain and Fiber Reinforced Concrete Structures

PubMed Central

Zhan, Yijian

2017-01-01

The effective analysis of the nonlinear behavior of cement-based engineering structures not only demands physically-reliable models, but also computationally-efficient algorithms. Based on a continuum interface element formulation that is suitable to capture complex cracking phenomena in concrete materials and structures, an adaptive mesh processing technique is proposed for computational simulations of plain and fiber-reinforced concrete structures to progressively disintegrate the initial finite element mesh and to add degenerated solid elements into the interfacial gaps. In comparison with the implementation where the entire mesh is processed prior to the computation, the proposed adaptive cracking model allows simulating the failure behavior of plain and fiber-reinforced concrete structures with remarkably reduced computational expense. PMID:28773130

Micro-mechanics of micro-composites

NASA Technical Reports Server (NTRS)

Donovan, Richard P.

1995-01-01

The Structural Dynamics branch at NASA LaRC is working on developing an active passive mount system for vibration control. Toward this end a system utilizing piezoelectric actuators is currently being utilized. There are limitations to the current system related to space applications under which it is desired to eliminate deformations in the actuators associated with thermal effects. In addition, a material that is readily formable into complex shapes and whose mechanical properties can be optimized with regards to vibration control would be highly desirable. Microcomposite material are currently under study to service these needs. Microcomposite materials are essentially materials in which particles on the scale of microns are bound together with a polyimide (LaRC Si) that has been developed at LaRC. In particular a micro-composite consisting of LaRC Si binder and piezoelectric ceramic particles shows promise in satisfying the needs of the active passive mount project. The LaRC/ Si microcomposite has a unique combination of piezoelectric properties combined with a near zero coefficient of thermal expansion and easy machinability. The goal of this ASEE project is to develop techniques to analytically determine important material properties necessary to characterize the dynamic properties of actuators and mounts made from the LaRC Si / ceramic microcomposite. In particular, a generalized method of cells micromechanics originally developed at NASA Lewis is employed to analyze the microstructural geometry of the microcomposites and predict the overall mechanical properties of the material. A testing program has been established to evaluate and refine the GMC approach to these materials. In addition, a theory of mixtures analysis is being developed that utilizes the GMC micromechanics information to analyze complex behavior of the microcomposite material which has a near zero CTE.

The hygroscopic behavior of plant fibers: a review.

PubMed

Célino, Amandine; Fréour, Sylvain; Jacquemin, Frédéric; Casari, Pascal

2013-01-01

Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper.

The hygroscopic behavior of plant fibers: a review

PubMed Central

Célino, Amandine; Fréour, Sylvain; Jacquemin, Frédéric; Casari, Pascal

2013-01-01

Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper. PMID:24790971

Structural Controls of the Friction Constitutive Properties of Carbonate-bearing Faults

NASA Astrophysics Data System (ADS)

Carpenter, B. M.; Collettini, C.; Scuderi, M.; Marone, C.

2012-12-01

The identification of hetereogenous and complex post-seismic slip for the 2009, Mw = 6.3, L'Aquila earthquake highlights the importance of fault zone structure and frictional behavior. Many of the Mw 6 to 7 earthquakes that occur on normal faults in the active Apennines, such as L'Aquila, nucleate at depths where the lithology is dominated by carbonate rocks. Due to the complex structure observed in exhumed faults (i.e. the presence of highly polished principal slip surfaces, cemented cataclasites, and phyllosilicate-bearing, foliated fault gouge) as well as the large spectrum of fault slip behaviors identified world wide, we designed a suite of experiments using intact and powdered samples to better constrain the possible slip behaviors of these carbonate bearing faults. We collected samples from the exposed Rocchetta Fault, a ~10km long, normal fault with approximately 600m of total offset. The exposed principal slip surface cuts through the Calcare Massiccio formation, which is present throughout central Italy at depths of earthquake nucleation. We collected intact specimens of the natural slip surface and cemented cataclasite, as well as fragments of both which were later pulverized. Furthermore, we collected an intact sample of the hanging wall cataclasite and footwall limestone that contained the principal slip surface. We performed friction experiments in a variety of different configurations (slip surface on slip surface, slip surface on powdered cataclasite, etc.) in order to investigate heterogeneity in frictional behavior as controlled by fault structure. We sheared saturated samples at a constant normal stress of 10 MPa at room temperature. Velocity-stepping tests were performed from 1 to 300 μm/s to identify the friction constitutive parameters of this fault material. Furthermore, a series slide-hold-slide tests were performed (holds of 3 to 1000 seconds) to measure the amount of frictional healing and determine the frictional healing rate. Results from experiments designed to reactivate slip between the principal slip surface and cemented cataclasite show a peak friction value of ~0.95 followed by a ~3 MPa stress drop as the fault surface fails. Our other results suggest that earthquakes will easily nucleate in areas of the fault where two slip surfaces are in contact and are likely to propagate in areas where pulverized fault gouge is in contact with the slip surface. Our data show that samples collected from a single fault can exhibit a large range of slip behaviors. Heterogeneous frictional behavior documented in the lab must be combined with field observations of complex fault structure and seismological observations of the different modes of fault slip to further our understanding of fault slip. Future work will consist of thin section and XRD analysis of all experimental material.

A new mixed-ligand copper(II) complex of (E)-N";-(2-hydroxybenzylidene) acetohydrazide: Synthesis, characterization, NLO behavior, DFT calculation and biological activities

NASA Astrophysics Data System (ADS)

Yousef Ebrahimipour, S.; Sheikhshoaie, Iran; Crochet, Aurelien; Khaleghi, Moj; Fromm, Katharina M.

2014-08-01

A tridentate hydrazone Schiff base ligand, (E)-N";-(2-hydroxybenzylidene)acetohydrazide [HL], and its mixed-ligand Cu(II) complex [CuL(phen)], have been synthesized and characterized by elemental analyses, FT-IR, molar conductivity, UV-Vis spectroscopy. The structure of the complex has been determined by X-ray diffraction. This complex has square pyramidal geometry and the positions around central atom are occupied with donor atoms of Schiff base ligand and two nitrogens of 1,10-phenanthroline. Computational studies of compounds were performed by using DFT calculations. The linear polarizabilities and first hyperpolarizabilities of the studied molecules indicate that these compounds can be good candidates of nonlinear optical materials. It is in accordance with experimental data. In addition, invitro antimicrobial results show that these compounds specially [CuL(phen)] have great potential of antibacterial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Listeria monocytogenes bacteria and antifungal activity against Candida Albicans in comparison to some standard drugs.

A model based bayesian solution for characterization of complex damage scenarios in aerospace composite structures.

PubMed

Reed, H; Leckey, Cara A C; Dick, A; Harvey, G; Dobson, J

2018-01-01

Ultrasonic damage detection and characterization is commonly used in nondestructive evaluation (NDE) of aerospace composite components. In recent years there has been an increased development of guided wave based methods. In real materials and structures, these dispersive waves result in complicated behavior in the presence of complex damage scenarios. Model-based characterization methods utilize accurate three dimensional finite element models (FEMs) of guided wave interaction with realistic damage scenarios to aid in defect identification and classification. This work describes an inverse solution for realistic composite damage characterization by comparing the wavenumber-frequency spectra of experimental and simulated ultrasonic inspections. The composite laminate material properties are first verified through a Bayesian solution (Markov chain Monte Carlo), enabling uncertainty quantification surrounding the characterization. A study is undertaken to assess the efficacy of the proposed damage model and comparative metrics between the experimental and simulated output. The FEM is then parameterized with a damage model capable of describing the typical complex damage created by impact events in composites. The damage is characterized through a transdimensional Markov chain Monte Carlo solution, enabling a flexible damage model capable of adapting to the complex damage geometry investigated here. The posterior probability distributions of the individual delamination petals as well as the overall envelope of the damage site are determined. Copyright © 2017 Elsevier B.V. All rights reserved.

Interactions of platinum metals and their complexes in biological systems.

PubMed Central

LeRoy, A F

1975-01-01

Platinum-metal oxidation catalysts are to be introduced in exhaust systems of many 1975 model-year automobiles in the U.S. to meet Clean Air Act standards. Small quantities of finely divided catalyst have been found issuing from prototype systems; platinum and palladium compounds may be found also. Although platinum exhibits a remarkable resistance to oxidation and chemical attack, it reacts chemically under some conditions producing coordination complex compounds. Palladium reacts more readily than platinum. Some platinum-metal complexes interact with biological systems as bacteriostatic, bacteriocidal, viricidal, and immunosuppressive agents. Workers chronically exposed to platinum complexes often develop asthma-like respiratory distress and skin reactions called platinosis. Platinum complexes used alone and in combination therapy with other drugs have recently emerged as effective agents in cancer chemotherapy. Understanding toxic and favorable interactions of metal species with living organisms requires basic information on quantities and chemical characteristics of complexes at trace concentrations in biological materials. Some basic chemical kinetic and thermodynamic data are presented to characterize the chemical behavior of the complex cis-[Pt(NH3)2Cl2] used therapeutically. A brief discussion of platinum at manogram levels in biological tissue is discussed. PMID:50943

Actuation of chitosan-aptamer nanobrush borders for pathogen sensing.

PubMed

Hills, Katherine D; Oliveira, Daniela A; Cavallaro, Nicholas D; Gomes, Carmen L; McLamore, Eric S

2018-03-26

We demonstrate a sensing mechanism for rapid detection of Listeria monocytogenes in food samples using the actuation of chitosan-aptamer nanobrush borders. The bio-inspired soft material and sensing strategy mimic natural symbiotic systems, where low levels of bacteria are selectively captured from complex matrices. To engineer this biomimetic system, we first develop reduced graphene oxide/nanoplatinum (rGO-nPt) electrodes, and characterize the fundamental electrochemical behavior in the presence and absence of chitosan nanobrushes during actuation (pH-stimulated osmotic swelling). We then characterize the electrochemical behavior of the nanobrush when receptors (antibodies or DNA aptamers) are conjugated to the surface. Finally, we test various techniques to determine the most efficient capture strategy based on nanobrush actuation, and then apply the biosensors in a food product. Maximum cell capture occurs when aptamers conjugated to the nanobrush bind cells in the extended conformation (pH < 6), followed by impedance measurement in the collapsed nanobrush conformation (pH > 6). The aptamer-nanobrush hybrid material was more efficient than the antibody-nanobrush material, which was likely due to the relatively high adsorption capacity for aptamers. The biomimetic material was used to develop a rapid test (17 min) for selectively detecting L. monocytogenes at concentrations ranging from 9 to 107 CFU mL-1 with no pre-concentration, and in the presence of other Gram-positive cells (Listeria innocua and Staphylococcus aureus). Use of this bio-inspired material is among the most efficient for L. monocytogenes sensing to date, and does not require sample pretreatment, making nanobrush borders a promising new material for rapid pathogen detection in food.

The Effect of Some Key Changes in the Chemistry of Water in Relation to Copper and Brass Corrosion Control

NASA Astrophysics Data System (ADS)

Gorovei, M. C.; Benea, L.

2018-06-01

Corrosion means the degradation of the metals or their alloys, under the action of chemical or electrochemical agents from the environment. The complex corrosion phenomenon has a destructive action, generating undesirable economic consequences: metals and labor losses, appreciable reduction in the lifetime of various metal constructions, insecurity in the operation of industrial machinery. Under the current conditions of accelerated growth in the production of material goods, one of the most important issues is the economy of raw materials and materials, energy and labor force. Copper, having a purity of over 99%, is used in the manufacture of gas and water pipes, roofing materials, utensils and ornamental objects. Brass is used in the manufacture of flexible tubes, pipes, coils, cartridges, various electrochemical parts, jewelry, etc. The aim of this research work was to evaluate the corrosion resistance of copper and brass in various solutions: with different chloride ions as 35 g/L NaCl, waste water and tap water. The corrosion behavior of copper and brass was analyzed by electrochemical methods, such as: open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Pure copper exhibits more noble potential values than its alloy (brass), according to the evolution of free potential in all tested solutions. After performing the electrochemical assays, ex-situ investigations, by optical microscopy, were made and the results confirm that the chloride ions affect the corrosion behavior of copper and brass. Corrosion of materials is a very important process to consider when choosing a material that has to operate in a specific environment.

Elucidating the effects of adsorbent flexibility on fluid adsorption using simple models and flat-histogram sampling methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, Vincent K., E-mail: vincent.shen@nist.gov; Siderius, Daniel W.

2014-06-28

Using flat-histogram Monte Carlo methods, we investigate the adsorptive behavior of the square-well fluid in two simple slit-pore-like models intended to capture fundamental characteristics of flexible adsorbent materials. Both models require as input thermodynamic information about the flexible adsorbent material itself. An important component of this work involves formulating the flexible pore models in the appropriate thermodynamic (statistical mechanical) ensembles, namely, the osmotic ensemble and a variant of the grand-canonical ensemble. Two-dimensional probability distributions, which are calculated using flat-histogram methods, provide the information necessary to determine adsorption thermodynamics. For example, we are able to determine precisely adsorption isotherms, (equilibrium) phasemore » transition conditions, limits of stability, and free energies for a number of different flexible adsorbent materials, distinguishable as different inputs into the models. While the models used in this work are relatively simple from a geometric perspective, they yield non-trivial adsorptive behavior, including adsorption-desorption hysteresis solely due to material flexibility and so-called “breathing” of the adsorbent. The observed effects can in turn be tied to the inherent properties of the bare adsorbent. Some of the effects are expected on physical grounds while others arise from a subtle balance of thermodynamic and mechanical driving forces. In addition, the computational strategy presented here can be easily applied to more complex models for flexible adsorbents.« less

Elucidating the effects of adsorbent flexibility on fluid adsorption using simple models and flat-histogram sampling methods

NASA Astrophysics Data System (ADS)

Shen, Vincent K.; Siderius, Daniel W.

2014-06-01

Using flat-histogram Monte Carlo methods, we investigate the adsorptive behavior of the square-well fluid in two simple slit-pore-like models intended to capture fundamental characteristics of flexible adsorbent materials. Both models require as input thermodynamic information about the flexible adsorbent material itself. An important component of this work involves formulating the flexible pore models in the appropriate thermodynamic (statistical mechanical) ensembles, namely, the osmotic ensemble and a variant of the grand-canonical ensemble. Two-dimensional probability distributions, which are calculated using flat-histogram methods, provide the information necessary to determine adsorption thermodynamics. For example, we are able to determine precisely adsorption isotherms, (equilibrium) phase transition conditions, limits of stability, and free energies for a number of different flexible adsorbent materials, distinguishable as different inputs into the models. While the models used in this work are relatively simple from a geometric perspective, they yield non-trivial adsorptive behavior, including adsorption-desorption hysteresis solely due to material flexibility and so-called "breathing" of the adsorbent. The observed effects can in turn be tied to the inherent properties of the bare adsorbent. Some of the effects are expected on physical grounds while others arise from a subtle balance of thermodynamic and mechanical driving forces. In addition, the computational strategy presented here can be easily applied to more complex models for flexible adsorbents.

Social Insects: A Model System for Network Dynamics

NASA Astrophysics Data System (ADS)

Charbonneau, Daniel; Blonder, Benjamin; Dornhaus, Anna

Social insect colonies (ants, bees, wasps, and termites) show sophisticated collective problem-solving in the face of variable constraints. Individuals exchange information and materials such as food. The resulting network structure and dynamics can inform us about the mechanisms by which the insects achieve particular collective behaviors and these can be transposed to man-made and social networks. We discuss how network analysis can answer important questions about social insects, such as how effective task allocation or information flow is realized. We put forward the idea that network analysis methods are under-utilized in social insect research, and that they can provide novel ways to view the complexity of collective behavior, particularly if network dynamics are taken into account. To illustrate this, we present an example of network tasks performed by ant workers, linked by instances of workers switching from one task to another. We show how temporal network analysis can propose and test new hypotheses on mechanisms of task allocation, and how adding temporal elements to static networks can drastically change results. We discuss the benefits of using social insects as models for complex systems in general. There are multiple opportunities emergent technologies and analysis methods in facilitating research on social insect network. The potential for interdisciplinary work could significantly advance diverse fields such as behavioral ecology, computer sciences, and engineering.

Large-scale structure of randomly jammed spheres

NASA Astrophysics Data System (ADS)

Ikeda, Atsushi; Berthier, Ludovic; Parisi, Giorgio

2017-05-01

We numerically analyze the density field of three-dimensional randomly jammed packings of monodisperse soft frictionless spherical particles, paying special attention to fluctuations occurring at large length scales. We study in detail the two-point static structure factor at low wave vectors in Fourier space. We also analyze the nature of the density field in real space by studying the large-distance behavior of the two-point pair correlation function, of density fluctuations in subsystems of increasing sizes, and of the direct correlation function. We show that such real space analysis can be greatly improved by introducing a coarse-grained density field to disentangle genuine large-scale correlations from purely local effects. Our results confirm that both Fourier and real space signatures of vanishing density fluctuations at large scale are absent, indicating that randomly jammed packings are not hyperuniform. In addition, we establish that the pair correlation function displays a surprisingly complex structure at large distances, which is however not compatible with the long-range negative correlation of hyperuniform systems but fully compatible with an analytic form for the structure factor. This implies that the direct correlation function is short ranged, as we also demonstrate directly. Our results reveal that density fluctuations in jammed packings do not follow the behavior expected for random hyperuniform materials, but display instead a more complex behavior.

Preface

NASA Astrophysics Data System (ADS)

Lexcellent, C.; Patoor, E.

2004-06-01

This international conference was held between the 18 and the 23th may 2003, in the "Villa Clythia" belonging to the CAES of the french "Comité National de la Recherche Scientifique CNRS" at Fréjus (France). The scope of this EMMC7 conference was about the use of smart materials which permits the conception of some adaptive systems for industrial applications. A special attention was devoted to active and passive controls of damping in structures. The use of this new class of materials (shape memory alloys, piezoelectric ceramics, TRIP steels, ferromagnetic shape memory alloys, ...) implies the development of numerical tools for computer assisted design process. Complexity of the involved material behaviour requires a deep understanding of strain mechanisms (martensitic phase transformation, reorientation process of domains), the use of accurate experimental techniques and advanced modelling approaches at various scale (micro, meso, macroscopic). In this purpose, it is necessary to use some coupled calculations connecting different fields of physics such as thermal, electromagnetism, electricity and mechanics of materials ones. The conference topic gave the opportunity of fruitful discussions between the mechanics of materials communauty and the specialists of damping or passive control. The scientific program contains nine oral sessions and one poster session. - Experimental characterization of the shape memory alloys thermomechanical behavior (two sessions) - Modeling of the shape memory alloy thermomechanical behavior (two sessions) - Ferromagnetic shape memory alloys behavior (one session) - Piezoelectric ceramics behavior (one session) - Transformation induced plasticity steel behavior (one session) - Hybrid structures including smart materials as sensor or actuator (one session) - Adaptive structure for vibration control (one session) - Poster session. The conference programm contains 50 lectures. 57 scientists were present and come from 14 different countries: 20 from France, 7 from Germany, 6 from Italy, 4 from Russia, 4 from Finland and 5 from USA ... This scientific programm allows all the participants interesting exchanges on "the state of art" about smart materials and adaptive systems. In the aim of its publication in the Proceedings of the EMMC7 Conference (EDP Sciences "Journal de Physique IV") each paper was expertised by two reviewers belonging to the International Scientific Committee and also other specialists. On that occasion, we will thank them for their very important contribution of the scientific level quality of the Proceedings. We will also thank: the sponsors of the Conference: Délégation Générale aux Armements (DGA), le Ministère de la Recherche, l'Université de Metz, l'ENSAM, le CNRS, l'Association Française de Mécanique et l'Institut des Microtechniques de Franche-Comté, the members of the organizing committee, the MECAMAT committee for trusting us, EDP Sciences for the Proceedings, The "Villa Clythia" team for his nice help in the material organization, ... and all the participants. The Co-chairmen Christian LEXCELLENT et Étienne PATOOR

Avalanches and plastic flow in crystal plasticity: an overview

NASA Astrophysics Data System (ADS)

Papanikolaou, Stefanos; Cui, Yinan; Ghoniem, Nasr

2018-01-01

Crystal plasticity is mediated through dislocations, which form knotted configurations in a complex energy landscape. Once they disentangle and move, they may also be impeded by permanent obstacles with finite energy barriers or frustrating long-range interactions. The outcome of such complexity is the emergence of dislocation avalanches as the basic mechanism of plastic flow in solids at the nanoscale. While the deformation behavior of bulk materials appears smooth, a predictive model should clearly be based upon the character of these dislocation avalanches and their associated strain bursts. We provide here a comprehensive overview of experimental observations, theoretical models and computational approaches that have been developed to unravel the multiple aspects of dislocation avalanche physics and the phenomena leading to strain bursts in crystal plasticity.

The cognitive impact of interactive design features for learning complex materials in medical education.

PubMed

Song, Hyuksoon S; Pusic, Martin; Nick, Michael W; Sarpel, Umut; Plass, Jan L; Kalet, Adina L

2014-02-01

To identify the most effective way for medical students to interact with a browser-based learning module on the symptoms and neurological underpinnings of stroke syndromes, this study manipulated the way in which subjects interacted with a graphical model of the brain and examined the impact of functional changes on learning outcomes. It was hypothesized that behavioral interactions that were behaviorally more engaging and which required deeper consideration of the model would result in heightened cognitive interaction and better learning than those whose manipulation required less deliberate behavioral and cognitive processing. One hundred forty four students were randomly assigned to four conditions whose model controls incorporated features that required different levels of behavioral and cognitive interaction: Movie (low behavioral/low cognitive, n = 40), Slider (high behavioral/low cognitive, n = 36), Click (low behavioral/high cognitive, n = 30), and Drag (high behavioral/high cognitive, n = 38). Analysis of Covariates (ANCOVA) showed that students who received the treatments associated with lower cognitive interactivity (Movie and Slider) performed better on a transfer task than those receiving the module associated with high cognitive interactivity (Click and Drag, partial eta squared = .03). In addition, the students in the high cognitive interactivity conditions spent significantly more time on the stroke locator activity than other conditions (partial eta squared = .36). The results suggest that interaction with controls that were tightly coupled with the model and whose manipulation required deliberate consideration of the model's features may have overtaxed subjects' cognitive resources. Cognitive effort that facilitated manipulation of content, though directed at the model, may have resulted in extraneous cognitive load, impeding subjects in recognizing the deeper, global relationships in the materials. Instructional designers must, therefore, keep in mind that the way in which functional affordances are integrated with the content can shape both behavioral and cognitive processing, and has significant cognitive load implications.

Thermomechanical Characterization and Modeling of Superelastic Shape Memory Alloy Beams and Frames

NASA Astrophysics Data System (ADS)

Watkins, Ryan

Of existing applications, the majority of shape memory alloy (SMA) devices consist of beam (orthodontic wire, eye glasses frames, catheter guide wires) and framed structures (cardiovascular stents, vena cava filters). Although uniaxial tension data is often sufficient to model basic beam behavior (which has been the main focus of the research community), the tension-compression asymmetry and complex phase transformation behavior of SMAs suggests more information is necessary to properly model higher complexity states of loading. In this work, SMA beams are experimentally characterized under general loading conditions (including tension, compression, pure bending, and buckling); furthermore, a model is developed with respect to general beam deformation based on the relevant phenomena observed in the experimental characterization. Stress induced phase transformation within superelastic SMA beams is shown to depend on not only the loading mode, but also kinematic constraints imposed by beam geometry (such as beam cross-section and length). In the cases of tension and pure bending, the structural behavior is unstable and corresponds to phase transformation localization and propagation. This unstable behavior is the result of a local level up--down--up stress/strain response in tension, which is measured here using a novel composite-based experimental technique. In addition to unstable phase transformation, intriguing post-buckling straightening is observed in short SMA columns during monotonic loading (termed unbuckling here). Based on this phenomenological understanding of SMA beam behavior, a trilinear based material law is developed in the context of a Shanley column model and is found to capture many of the relevant features of column buckling, including the experimentally observed unbuckling behavior. Due to the success of this model, it is generalized within the context of beam theory and, in conjunction with Bloch wave stability analysis, is used to model and design SMA honeycombs.

Determining the mechanical constitutive properties of metals as a function of strain rate and temperature: A combined experimental and modeling approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

I. M. Robertson; A. Beaudoin; J. Lambros

2004-01-05

OAK-135 Development and validation of constitutive models for polycrystalline materials subjected to high strain rate loading over a range of temperatures are needed to predict the response of engineering materials to in-service type conditions (foreign object damage, high-strain rate forging, high-speed sheet forming, deformation behavior during forming, response to extreme conditions, etc.). To account accurately for the complex effects that can occur during extreme and variable loading conditions, requires significant and detailed computational and modeling efforts. These efforts must be closely coupled with precise and targeted experimental measurements that not only verify the predictions of the models, but also providemore » input about the fundamental processes responsible for the macroscopic response. Achieving this coupling between modeling and experimentation is the guiding principle of this program. Specifically, this program seeks to bridge the length scale between discrete dislocation interactions with grain boundaries and continuum models for polycrystalline plasticity. Achieving this goal requires incorporating these complex dislocation-interface interactions into the well-defined behavior of single crystals. Despite the widespread study of metal plasticity, this aspect is not well understood for simple loading conditions, let alone extreme ones. Our experimental approach includes determining the high-strain rate response as a function of strain and temperature with post-mortem characterization of the microstructure, quasi-static testing of pre-deformed material, and direct observation of the dislocation behavior during reloading by using the in situ transmission electron microscope deformation technique. These experiments will provide the basis for development and validation of physically-based constitutive models, which will include dislocation-grain boundary interactions for polycrystalline systems. One aspect of the program will involve the dire ct observation of specific mechanisms of micro-plasticity, as these will indicate the boundary value problem that should be addressed. This focus on the pre-yield region in the quasi-static effort (the elasto-plastic transition) is also a tractable one from an experimental and modeling viewpoint. In addition, our approach will minimize the need to fit model parameters to experimental data to obtain convergence. These are critical steps to reach the primary objective of simulating and modeling material performance under extreme loading conditions. In this annual report, we describe the progress made in the first year of this program.« less

Electrochemically synthesized amorphous and crystalline nanowires: dissimilar nanomechanical behavior in comparison with homologous flat films

NASA Astrophysics Data System (ADS)

Zeeshan, M. A.; Esqué-de Los Ojos, D.; Castro-Hartmann, P.; Guerrero, M.; Nogués, J.; Suriñach, S.; Baró, M. D.; Nelson, B. J.; Pané, S.; Pellicer, E.; Sort, J.

2016-01-01

The effects of constrained sample dimensions on the mechanical behavior of crystalline materials have been extensively investigated. However, there is no clear understanding of these effects in nano-sized amorphous samples. Herein, nanoindentation together with finite element simulations are used to compare the properties of crystalline and glassy CoNi(Re)P electrodeposited nanowires (φ ~ 100 nm) with films (3 μm thick) of analogous composition and structure. The results reveal that amorphous nanowires exhibit a larger hardness, lower Young's modulus and higher plasticity index than glassy films. Conversely, the very large hardness and higher Young's modulus of crystalline nanowires are accompanied by a decrease in plasticity with respect to the homologous crystalline films. Remarkably, proper interpretation of the mechanical properties of the nanowires requires taking the curved geometry of the indented surface and sink-in effects into account. These findings are of high relevance for optimizing the performance of new, mechanically-robust, nanoscale materials for increasingly complex miniaturized devices.The effects of constrained sample dimensions on the mechanical behavior of crystalline materials have been extensively investigated. However, there is no clear understanding of these effects in nano-sized amorphous samples. Herein, nanoindentation together with finite element simulations are used to compare the properties of crystalline and glassy CoNi(Re)P electrodeposited nanowires (φ ~ 100 nm) with films (3 μm thick) of analogous composition and structure. The results reveal that amorphous nanowires exhibit a larger hardness, lower Young's modulus and higher plasticity index than glassy films. Conversely, the very large hardness and higher Young's modulus of crystalline nanowires are accompanied by a decrease in plasticity with respect to the homologous crystalline films. Remarkably, proper interpretation of the mechanical properties of the nanowires requires taking the curved geometry of the indented surface and sink-in effects into account. These findings are of high relevance for optimizing the performance of new, mechanically-robust, nanoscale materials for increasingly complex miniaturized devices. Electronic supplementary information (ESI) available: Additional details on experimental and analysis methods, additional results on crystalline CoNi(Re)P alloys and two movies to illustrate the stress distribution during deformation of the amorphous and crystalline nanowires. See DOI: 10.1039/c5nr04398k

Neon diffusion kinetics and implications for cosmogenic neon paleothermometry in feldspars

NASA Astrophysics Data System (ADS)

Tremblay, Marissa M.; Shuster, David L.; Balco, Greg; Cassata, William S.

2017-05-01

Observations of cosmogenic neon concentrations in feldspars can potentially be used to constrain the surface exposure duration or surface temperature history of geologic samples. The applicability of cosmogenic neon to either application depends on the temperature-dependent diffusivity of neon isotopes. In this work, we investigate the kinetics of neon diffusion in feldspars of different compositions and geologic origins through stepwise degassing experiments on single, proton-irradiated crystals. To understand the potential causes of complex diffusion behavior that is sometimes manifest as nonlinearity in Arrhenius plots, we compare our results to argon stepwise degassing experiments previously conducted on the same feldspars. Many of the feldspars we studied exhibit linear Arrhenius behavior for neon whereas argon degassing from the same feldspars did not. This suggests that nonlinear behavior in argon experiments is an artifact of structural changes during laboratory heating. However, other feldspars that we examined exhibit nonlinear Arrhenius behavior for neon diffusion at temperatures far below any known structural changes, which suggests that some preexisting material property is responsible for the complex behavior. In general, neon diffusion kinetics vary widely across the different feldspars studied, with estimated activation energies (Ea) ranging from 83.3 to 110.7 kJ/mol and apparent pre-exponential factors (D0) spanning three orders of magnitude from 2.4 × 10-3 to 8.9 × 10-1 cm2 s-1. As a consequence of this variability, the ability to reconstruct temperatures or exposure durations from cosmogenic neon abundances will depend on both the specific feldspar and the surface temperature conditions at the geologic site of interest.

Emergence of complex chemistry on an organic monolayer.

PubMed

Prins, Leonard J

2015-07-21

In many origin-of-life scenarios, inorganic materials, such as FeS or mineral clays, play an important role owing to their ability to concentrate and select small organic molecules on their surface and facilitate their chemical transformations into new molecules. However, considering that life is made up of organic matter, at a certain stage during the evolution the role of the inorganic material must have been taken over by organic molecules. How this exactly happened is unclear, and, indeed, a big gap separates the rudimentary level of organization involving inorganic materials and the complex organization of cells, which are the building blocks of life. Over the past years, we have extensively studied the interaction of small molecules with monolayer-protected gold nanoparticles (Au NPs) for the purpose of developing innovative sensing and catalytic systems. During the course of these studies, we realized that the functional role of this system is very similar to that typically attributed to inorganic surfaces in the early stages of life, with the important being difference that the functional properties (molecular recognition, catalysis, signaling, adaptation) originate entirely from the organic monolayer rather than the inorganic support. This led us to the proposition that this system may serve as a model that illustrates how the important role of inorganic surfaces in dictating chemical processes in the early stages of life may have been taken over by organic matter. Here, we reframe our previously obtained results in the context of the origin-of-life question. The following functional roles of Au NPs will be discussed: the ability to concentrate small molecules and create different local populations, the ability to catalyze the chemical transformation of bound molecules, and, finally, the ability to install rudimentary signaling pathways and display primitive adaptive behavior. In particular, we will show that many of the functional properties of the system originate from two features: the presence of metal ions that are complexed in the organic monolayer and the multivalent nature of the system. Complexed metal ions play an important role in determining the affinity and selectivity of the interaction with small molecules, but serve also as regulatory elements for determining how many molecules are bound simultaneously. Importantly, neighboring metal ion complexes also create catalytic pockets in which two metal ions cooperatively catalyze the cleavage of an RNA-model compound. The multivalent nature of the system permits multiple noncovalent interactions with small molecules that enhances the affinity, but is also at the basis of simple signal transduction pathways and adaptive behavior.

Progress in Characterizing Thermal Degradation of Ethylene-Propylene Rubber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fifield, Leonard S.; Huang, Qian; Childers, Matthew I.

Ethylene-propylene rubber (EPR) is one of the two most common nuclear cable insulation materials. A large fraction of EPR-insulated cables in use in the nuclear industry were manufactured by The Okonite Company. Okoguard® is the name of the medium voltage thermoset EPR manufactured by The Okonite Company. Okoguard® has been produced with silane-treated clay filler and the characteristic pink color since the 1970’s. EPR is complex material that undergoes simultaneous reactions during thermal aging including oxidative and thermal cleavage and oxidative and thermal crosslinking. This reaction complexity makes precise EPR service life prediction from accelerated aging using approaches designed formore » single discreet reactions such as the Arrhenius approach problematic. Performance data and activation energies for EPR aged at conditions closer to service conditions will improve EPR lifetime prediction. In this report pink Okoguard® EPR insulation material has been thermally aged at elevated temperatures. A variety of characterization techniques have been employed to track material changes with aging. It was noted that EPR aged significant departure in aging behavior seemed to occur at accelerated aging temperatures between 140°C and 150°C at around 20 days of exposure. This may be due to alternative degradation mechanisms being accessed at this higher temperature and reinforces the need to perform accelerated aging for Okoguard® EPR service life prediction at temperatures below 150°C.« less

Three dimensional (3D) microstructure-based finite element modeling of Al-SiC nanolaminates using focused ion beam (FIB) tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayer, Carl R.

Al-SiC nanolaminate composites show promise as high performance coating materials due to their combination of strength and toughness. Although a significant amount of modeling effort has been focused on materials with an idealized flat nanostructure, experimentally these materials exhibit complex undulating layer geometries. This work utilizes FIB tomography to characterize this nanostructure in 3D and finite element modeling to determine the effect that this complex structure has on the mechanical behavior of these materials. A sufficiently large volume was characterized such that a 1 × 2 μm micropillar could be generated from the dataset and compared directly to experimental results.more » The mechanical response from this nanostructure was then compared to pillar models using simplified structures with perfectly flat layers, layers with sinusoidal waviness, and layers with arc segment waviness. The arc segment based layer geometry showed the best agreement with the experimentally determined structure, indicating it would be the most appropriate geometry for future modeling efforts. - Highlights: •FIB tomography was used to determine the structure of an Al-SiC nanolaminate in 3D. •FEM was used to compare the deformation of the nanostructure to experimental results. •Idealized structures from literature were compared to the FIB determined structure. •Arc segment based structures approximated the FIB determined structure most closely.« less

Analysis of Graphite-Reinforced Cementitious Composites

NASA Technical Reports Server (NTRS)

Vaughan, R. E.

2002-01-01

Strategically embedding graphite meshes in a compliant cementitious matrix produces a composite material with relatively high tension and compressive properties as compared to steel-reinforced structures fabricated from a standard concrete mix. Although these composite systems are somewhat similar, the methods used to analyze steel-reinforced composites often fail to characterize the behavior of their more advanced graphite-reinforced counterparts. This Technical Memorandum describes some of the analytical methods being developed to determine the deflections and stresses in graphite-reinforced cementitious composites. It is initially demonstrated that the standard transform section method fails to provide accurate results when the elastic moduli ratio exceeds 20. An alternate approach is formulated by using the rule of mixtures to determine a set of effective material properties for the composite. Tensile tests are conducted on composite samples to verify this approach. When the effective material properties are used to characterize the deflections of composite beams subjected to pure bending, an excellent agreement is obtained. Laminated composite plate theory is investigated as a means for analyzing even more complex composites, consisting of multiple graphite layers oriented in different directions. In this case, composite beams are analyzed using the laminated composite plate theory with material properties established from tensile tests. Then, finite element modeling is used to verify the results. Considering the complexity of the samples, a very good agreement is obtained.

The Toxicological Geochemistry of Dusts, Soils, and Other Earth Materials: Insights From In Vitro Physiologically-based Geochemical Leach Tests

NASA Astrophysics Data System (ADS)

Plumlee, G. S.; Ziegler, T. L.; Lamothe, P.; Meeker, G. P.; Sutley, S.

2003-12-01

Exposure to mineral dusts, soils, and other earth materials results in chemical reactions between the materials and different body fluids that include, depending upon the exposure route, lung fluids, gastrointestinal fluids, and perspiration. In vitro physiologically-based geochemical leach tests provide useful insights into these chemical reactions and their potential toxicological implications. We have conducted such leach tests on a variety of earth materials, including asbestos, volcanic ash, dusts from dry lake beds, mine wastes, wastes left from the roasting of mercury ores, mineral processing wastes, coal dusts and coal fly ash, various soils, and complex dusts generated by the World Trade Center collapse. Size-fractionated samples of earth materials that have been well-characterized mineralogically and chemically are reacted at body temperature (37 C) for periods from 2 hours up to multiple days with various proportions of simulated lung, gastric, intestinal, and/or plasma-based fluids. Results indicate that different earth materials may have quite different solubility and dissolution behavior in vivo, depending upon a) the mineralogic makeup of the material, and b) the exposure route. For example, biodurable minerals such as asbestos and volcanic ash particles, whose health effects result because they dissolve very slowly in vivo, bleed off low levels of trace metals into the simulated lung fluids; these include metals such as Fe and Cr that are suspected by health scientists of contributing to the generation of reactive oxygen species and resulting DNA damage in vivo. In contrast, dry lake bed dusts and concrete-rich dusts are highly alkaline and bioreactive, and cause substantial pH increases and other chemical changes in the simulated body fluids. Many of the earth materials tested contain a variety of metals that can be quite soluble (bioaccessible), depending upon the material and the simulated body fluid composition. For example, due to their acidic pH and high chloride concentrations, simulated gastric fluids are most efficient at solubilizing metals such as Hg, Pb, Zn, and others that form strong chloride complexes; although these metals tend to partially reprecipitate in the near-neutral simulated intestinal fluids, complexes with organic ligands (i.e., amino and carboxylic acids) enhance their solubility. These metals are also quite soluble in near-neutral, protein-rich plasma-based fluids because they form strong complexes with the proteins. In contrast, metalloids that form oxyanion species (such as As, Cr, Mo, W) are commonly more soluble in near-neutral pH simulated lung fluids than in simulated gastric fluids.

Unitized Stiffened Composite Textile Panels: Manufacturing, Characterization, Experiments, and Analysis

NASA Astrophysics Data System (ADS)

Kosztowny, Cyrus Joseph Robert

Use of carbon fiber textiles in complex manufacturing methods creates new implementations of structural components by increasing performance, lowering manufacturing costs, and making composites overall more attractive across industry. Advantages of textile composites include high area output, ease of handling during the manufacturing process, lower production costs per material used resulting from automation, and provide post-manufacturing assembly mainstreaming because significantly more complex geometries such as stiffened shell structures can be manufactured with fewer pieces. One significant challenge with using stiffened composite structures is stiffener separation under compression. Axial compression loading conditions have frequently observed catastrophic structural failure due to stiffeners separating from the shell skin. Characterizing stiffener separation behavior is often costly computationally and experimentally. The objectives of this research are to demonstrate unitized stiffened textile composite panels can be manufactured to produce quality test specimens, that existing characterization techniques applied to state-of-the-art high-performance composites provide valuable information in modeling such structures, that the unitized structure concept successfully removes stiffener separation as a primary structural failure mode, and that modeling textile material failure modes are sufficient to accurately capture postbuckling and final failure responses of the stiffened structures. The stiffened panels in this study have taken the integrally stiffened concept to an extent such that the stiffeners and skin are manufactured at the same time, as one single piece, and from the same composite textile layers. Stiffener separation is shown to be removed as a primary structural failure mode for unitized stiffened composite textile panels loaded under axial compression well into the postbuckling regime. Instead of stiffener separation, a material damaging and failure model effectively captures local post-peak material response via incorporating a mesoscale model using a multiscaling framework with a smeared crack element-based failure model in the macroscale stiffened panel. Material damage behavior is characterized by simple experimental tests and incorporated into the post-peak stiffness degradation law in the smeared crack implementation. Computational modeling results are in overall excellent agreement compared to the experimental responses.

a Study of Dynamic Powder Consolidation Based on a Particle-Level Mathematical Model.

NASA Astrophysics Data System (ADS)

Williamson, Richard L.

A mathematical model is developed to investigate the effects of large amplitude shock waves on powder materials during dynamic consolidation. The model is constructed at the particle level, focusing on a region containing a few powder particles and the surrounding interstices. The general equations of continuum mechanics are solved over this region, using initial and boundary conditions appropriate for the consolidation process. Closure of the equation system is obtained using an analytical equation of state; relations are included to account for solid to liquid phase changes. An elastic, perfectly-plastic constitutive law, specifically modified to describe material behavior at high-strain-rates, is applied to the solid materials. To reduce complexity, the model is restricted to two dimensions, therefore individual particles are approximated as infinitely long cylinders rather than spheres. The equation system is solved using standard finite-difference numerical techniques. It is demonstrated that for typical consolidation conditions, energy diffusion mechanisms are insignificant during the rapid densification phase of consolidation. Using type 304 stainless steel powder material, the particle-level model is used to investigate the mechanisms responsible for particle surface heating and metallurgical bonding during consolidation. It is demonstrated that energy deposition near particle surfaces results both from rapid particle deformation during interstitial filling and large localized impacts occurring at the final instant of interstitial closure; particle interior regions remain at sufficiently low temperatures to avoid microstructural modification. Nonuniform metallurgical bonding is predicted around the particle periphery, ranging from complete fusion to mechanical abutment. Simulation results are used to investigate the detailed wave propagation phenomena at the particle level, providing an improved understanding of this complex behavior. A variety of parametric studies are conducted including investigations of the effects of stress wave amplitude and rise time, the role of interstitial gases during consolidation, and various geometric aspects including the importance of initial void fraction. The model is applied to a metal matrix composite system to investigate the consolidation of mixtures of differing materials; results of a two-dimensional experiment are included. Available experimental data are compared with simulation results. In general, very good agreement between simulation results and data is obtained.

Competition of density waves and quantum multicritical behavior in Dirac materials from functional renormalization

NASA Astrophysics Data System (ADS)

Classen, Laura; Herbut, Igor F.; Janssen, Lukas; Scherer, Michael M.

2016-03-01

We study the competition of spin- and charge-density waves and their quantum multicritical behavior for the semimetal-insulator transitions of low-dimensional Dirac fermions. Employing the effective Gross-Neveu-Yukawa theory with two order parameters as a model for graphene and a growing number of other two-dimensional Dirac materials allows us to describe the physics near the multicritical point at which the semimetallic and the spin- and charge-density-wave phases meet. With the help of a functional renormalization group approach, we are able to reveal a complex structure of fixed points, the stability properties of which decisively depend on the number of Dirac fermions Nf. We give estimates for the critical exponents and observe crucial quantitative corrections as compared to the previous first-order ɛ expansion. For small Nf, the universal behavior near the multicritical point is determined by the chiral Heisenberg universality class supplemented by a decoupled, purely bosonic, Ising sector. At large Nf, a novel fixed point with nontrivial couplings between all sectors becomes stable. At intermediate Nf, including the graphene case (Nf=2 ), no stable and physically admissible fixed point exists. Graphene's phase diagram in the vicinity of the intersection between the semimetal, antiferromagnetic, and staggered density phases should consequently be governed by a triple point exhibiting first-order transitions.

Road Damage Following Earthquake

NASA Technical Reports Server (NTRS)

1989-01-01

Ground shaking triggered liquefaction in a subsurface layer of water-saturated sand, producing differential lateral and vertical movement in a overlying carapace of unliquified sand and slit, which moved from right to left towards the Pajaro River. This mode of ground failure, termed lateral spreading, is a principal cause of liquefaction-related earthquake damage caused by the Oct. 17, 1989, Loma Prieta earthquake. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: S.D. Ellen, U.S. Geological Survey

Sand Volcano Following Earthquake

NASA Technical Reports Server (NTRS)

1989-01-01

Sand boil or sand volcano measuring 2 m (6.6 ft.) in length erupted in median of Interstate Highway 80 west of the Bay Bridge toll plaza when ground shaking transformed loose water-saturated deposit of subsurface sand into a sand-water slurry (liquefaction) in the October 17, 1989, Loma Prieta earthquake. Vented sand contains marine-shell fragments. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: J.C. Tinsley, U.S. Geological Survey)

Microgravity

NASA Image and Video Library

1989-10-17

Sand boil or sand volcano measuring 2 m (6.6 ft.) in length erupted in median of Interstate Highway 80 west of the Bay Bridge toll plaza when ground shaking transformed loose water-saturated deposit of subsurface sand into a sand-water slurry (liquefaction) in the October 17, 1989, Loma Prieta earthquake. Vented sand contains marine-shell fragments. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: J.C. Tinsley, U.S. Geological Survey)

Microgravity

NASA Image and Video Library

1989-10-17

Ground shaking triggered liquefaction in a subsurface layer of water-saturated sand, producing differential lateral and vertical movement in a overlying carapace of unliquified sand and slit, which moved from right to left towards the Pajaro River. This mode of ground failure, termed lateral spreading, is a principal cause of liquefaction-related earthquake damage caused by the Oct. 17, 1989, Loma Prieta earthquake. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: S.D. Ellen, U.S. Geological Survey

Ab-initio investigations for opto-electronic response of (Cd, Zn)Ga2Te4: Promising solar PV materials

NASA Astrophysics Data System (ADS)

Sahariya, Jagrati; Soni, Amit; Kumar, Pancham

2018-04-01

In this paper, the first principle calculations are performed to analyze the structural, electronic and optical behavior of promising solar materials (Cd,Zn)Ga2Te4. To perform these calculations we have used one of the most accurate Full Potential Linearized Augmented Plane Wave (FP-LAPW) method. The ground state properties of these compounds are confirmed over here after proper examination of energy and charge convergence using Perdew-Burke-Ernzerhof (PBE-sol) exchange correlation potential. The investigations performed such as energy band structure, Density of States (DOS), optical parameters like complex dielectric function and absorption co-efficient are discussed over here to understand the overall response of the chosen system.

Application of Probability Methods to Assess Crash Modeling Uncertainty

NASA Technical Reports Server (NTRS)

Lyle, Karen H.; Stockwell, Alan E.; Hardy, Robin C.

2003-01-01

Full-scale aircraft crash simulations performed with nonlinear, transient dynamic, finite element codes can incorporate structural complexities such as: geometrically accurate models; human occupant models; and advanced material models to include nonlinear stress-strain behaviors, and material failure. Validation of these crash simulations is difficult due to a lack of sufficient information to adequately determine the uncertainty in the experimental data and the appropriateness of modeling assumptions. This paper evaluates probabilistic approaches to quantify the effects of finite element modeling assumptions on the predicted responses. The vertical drop test of a Fokker F28 fuselage section will be the focus of this paper. The results of a probabilistic analysis using finite element simulations will be compared with experimental data.

Application of Probability Methods to Assess Crash Modeling Uncertainty

NASA Technical Reports Server (NTRS)

Lyle, Karen H.; Stockwell, Alan E.; Hardy, Robin C.

2007-01-01

Full-scale aircraft crash simulations performed with nonlinear, transient dynamic, finite element codes can incorporate structural complexities such as: geometrically accurate models; human occupant models; and advanced material models to include nonlinear stress-strain behaviors, and material failure. Validation of these crash simulations is difficult due to a lack of sufficient information to adequately determine the uncertainty in the experimental data and the appropriateness of modeling assumptions. This paper evaluates probabilistic approaches to quantify the effects of finite element modeling assumptions on the predicted responses. The vertical drop test of a Fokker F28 fuselage section will be the focus of this paper. The results of a probabilistic analysis using finite element simulations will be compared with experimental data.

Ultrafast studies of shock induced chemistry-scaling down the size by turning up the heat

NASA Astrophysics Data System (ADS)

McGrane, Shawn

2015-06-01

We will discuss recent progress in measuring time dependent shock induced chemistry on picosecond time scales. Data on the shock induced chemistry of liquids observed through picosecond interferometric and spectroscopic measurements will be reconciled with shock induced chemistry observed on orders of magnitude larger time and length scales from plate impact experiments reported in the literature. While some materials exhibit chemistry consistent with simple thermal models, other materials, like nitromethane, seem to have more complex behavior. More detailed measurements of chemistry and temperature across a broad range of shock conditions, and therefore time and length scales, will be needed to achieve a real understanding of shock induced chemistry, and we will discuss efforts and opportunities in this direction.

Oxygen vacancy ordering in transition-metal-oxide LaCoO3 films

NASA Astrophysics Data System (ADS)

Biskup, Neven; Salafranca, Juan; Mehta, Virat; Suzuki, Yuri; Pennycook, Stephen; Pantelides, Sokrates; Varela, Maria

2013-03-01

Oxygen vacancies in complex oxides affect the structure and the electronic and magnetic properties. Here we use atomically-resolved Z-contrast imaging, electron-energy-loss spectroscopy and densityfunctional calculations to demonstrate that ordered oxygen vacancies may act as the controlling degree of freedom for the structural, electronic, and magnetic properties of LaCoO3 thin films. We find that epitaxial strain is released through the formation of O vacancy superlattices. The O vacancies donate excess electrons to the Co d-states, resulting in ferromagnetic ordering. The appearance of Peierls-like minigaps followed by strain relaxation triggers a nonlinear rupture of the energy bands, which explains the observed insulating behavior. We conclude that oxygen vacancy ordering constitutes a degree of freedom that can be used to engineer novel behavior in complex-oxide films. Research at ORNL supported by U.S. DOE-BES, Materials Sciences and Engineering Div. and by ORNL's ShaRE User Program (DOE-BES), at UCM by the ERC Starting Inv. Award, at UC Berkeley and LBNL by BES-DMSE, at Vanderbilt by U.S DOE and the McMinn Endowment.

Fire behavior of halogen-free flame retardant electrical cables with the cone calorimeter.

PubMed

Meinier, Romain; Sonnier, Rodolphe; Zavaleta, Pascal; Suard, Sylvain; Ferry, Laurent

2018-01-15

Fires involving electrical cables are one of the main hazards in Nuclear Power Plants (NPPs). Cables are complex assemblies including several polymeric parts (insulation, bedding, sheath) constituting fuel sources. This study provides an in-depth characterization of the fire behavior of two halogen-free flame retardant cables used in NPPs using the cone calorimeter. The influence of two key parameters, namely the external heat flux and the spacing between cables, on the cable fire characteristics is especially investigated. The prominent role of the outer sheath material on the ignition and the burning at early times was highlighted. A parameter of utmost importance called transition heat flux, was identified and depends on the composition and the structure of the cable. Below this heat flux, the decomposition is limited and concerns only the sheath. Above it, fire hazard is greatly enhanced because most often non-flame retarded insulation part contributes to heat release. The influence of spacing appears complex, and depends on the considered fire property. Copyright © 2017 Elsevier B.V. All rights reserved.

Classification of electronically generated phantom targets by an Atlantic bottlenose dolphin (Tursiops truncatus).

PubMed

Aubauer, R; Au, W W; Nachtigall, P E; Pawloski, D A; DeLong, C M

2000-05-01

Animal behavior experiments require not only stimulus control of the animal's behavior, but also precise control of the stimulus itself. In discrimination experiments with real target presentation, the complex interdependence between the physical dimensions and the backscattering process of an object make it difficult to extract and control relevant echo parameters separately. In other phantom-echo experiments, the echoes were relatively simple and could only simulate certain properties of targets. The echo-simulation method utilized in this paper can be used to transform any animal echolocation sound into phantom echoes of high fidelity and complexity. The developed phantom-echo system is implemented on a digital signal-processing board and gives an experimenter fully programmable control over the echo-generating process and the echo structure itself. In this experiment, the capability of a dolphin to discriminate between acoustically simulated phantom replicas of targets and their real equivalents was tested. Phantom replicas were presented in a probe technique during a materials discrimination experiment. The animal accepted the phantom echoes and classified them in the same manner as it classified real targets.

Effects of environmental complexity and temporary captivity on foraging behavior of wild-caught meadow voles.

PubMed

Kozuch, Amaranta E; McPhee, M Elsbeth

2014-01-01

Increased housing of wild nonhuman animals in captivity for conservation, research, and rehabilitation has revealed the importance of systematically analyzing effects of the captive environment on behavior. This study focused on the effects of complexity and time held in captivity on foraging behaviors of wild-caught, adult meadow voles (Microtus pennsylvanicus). Forty-six individuals captured from a meadow outside Oshkosh, WI, were assigned to 1 of 4 captive treatment groups: simple/<50 days (SS), simple/>50 days, complex/<50 days, and complex/>50 days. Number of dish visits, proportion foraging, and frequency of nonforaging behaviors recorded during a 15-min foraging trial were measured for all subjects. Kruskal-Wallis and Mann-Whitney U Tests were conducted to analyze 4 different comparisons within this behavioral data. Overall, neither time in captivity or environmental complexity affected nonforaging behaviors. In contrast, foraging behaviors did change with treatment: Voles were less active at food dishes and visited control dishes more in treatment group SS than in the other treatment groups. In addition, sex-related differences in foraging behaviors were maintained when voles were exposed to environmental complexity. This article includes options for wildlife managers to adapt captive environments to meet the welfare and behavioral needs of translocated wild nonhuman mammals.

Deterministic Integration of Biological and Soft Materials onto 3D Microscale Cellular Frameworks

PubMed Central

McCracken, Joselle M.; Xu, Sheng; Badea, Adina; Jang, Kyung-In; Yan, Zheng; Wetzel, David J.; Nan, Kewang; Lin, Qing; Han, Mengdi; Anderson, Mikayla A.; Lee, Jung Woo; Wei, Zijun; Pharr, Matt; Wang, Renhan; Su, Jessica; Rubakhin, Stanislav S.; Sweedler, Jonathan V.

2018-01-01

Complex 3D organizations of materials represent ubiquitous structural motifs found in the most sophisticated forms of matter, the most notable of which are in life-sustaining hierarchical structures found in biology, but where simpler examples also exist as dense multilayered constructs in high-performance electronics. Each class of system evinces specific enabling forms of assembly to establish their functional organization at length scales not dissimilar to tissue-level constructs. This study describes materials and means of assembly that extend and join these disparate systems—schemes for the functional integration of soft and biological materials with synthetic 3D microscale, open frameworks that can leverage the most advanced forms of multilayer electronic technologies, including device-grade semiconductors such as monocrystalline silicon. Cellular migration behaviors, temporal dependencies of their growth, and contact guidance cues provided by the nonplanarity of these frameworks illustrate design criteria useful for their functional integration with living matter (e.g., NIH 3T3 fibroblast and primary rat dorsal root ganglion cell cultures). PMID:29552634

From organized high throughput data to phenomenological theory: The example of dielectric breakdown

NASA Astrophysics Data System (ADS)

Kim, Chiho; Pilania, Ghanshyam; Ramprasad, Rampi

Understanding the behavior (and failure) of dielectric insulators experiencing extreme electric fields is critical to the operation of present and emerging electrical and electronic devices. Despite its importance, the development of a predictive theory of dielectric breakdown has remained a challenge, owing to the complex multiscale nature of this process. Here, we focus on the intrinsic dielectric breakdown field of insulators--the theoretical limit of breakdown determined purely by the chemistry of the material, i.e., the elements the material is composed of, the atomic-level structure, and the bonding. Starting from a benchmark dataset (generated from laborious first principles computations) of the intrinsic dielectric breakdown field of a variety of model insulators, simple predictive phenomenological models of dielectric breakdown are distilled using advanced statistical or machine learning schemes, revealing key correlations and analytical relationships between the breakdown field and easily accessible material properties. The models are shown to be general, and can hence guide the screening and systematic identification of high electric field tolerant materials.

Characterized the pattern of the material deposition in the HL-2A tokamak

NASA Astrophysics Data System (ADS)

Cai, Laizhong; Wang, Jianbao; Wu, Ting; Zeng, Xiaoxiao; Hai, Ran; Ding, Hongbin

2017-03-01

Since the divertor geometry of a tokamak has a strong impact on the material erosion and deposition on the wall and HL-2A has a unique divertor configuration, it is necessary to investigate the material deposition pattern in HL-2A although a few results on other tokamaks have already been published. In this paper, tiles retrieved from the vessel are analyzed ex-situ by SIMS, SEM and laser-induced breakdown spectroscopy (LIBS). And deposition behind the lower divertor is in-situ measured by a quartz crystal microbalance (QMB). The deposition in HL-2A displays a complex pattern and clear localization characteristic. The thickness of the deposition layer varies in the range of 0-4μm. And in-situ diagnostic of QMB indicates that the average thickness of the deposition layer per pulse is over ten nanometers. In addition, the results imply that Si, Fe and D have different behaviors during the material deposition in HL-2A.

Quantifying the impact of material-model error on macroscale quantities-of-interest using multiscale a posteriori error-estimation techniques

DOE PAGES

Brown, Judith A.; Bishop, Joseph E.

2016-07-20

An a posteriori error-estimation framework is introduced to quantify and reduce modeling errors resulting from approximating complex mesoscale material behavior with a simpler macroscale model. Such errors may be prevalent when modeling welds and additively manufactured structures, where spatial variations and material textures may be present in the microstructure. We consider a case where a <100> fiber texture develops in the longitudinal scanning direction of a weld. Transversely isotropic elastic properties are obtained through homogenization of a microstructural model with this texture and are considered the reference weld properties within the error-estimation framework. Conversely, isotropic elastic properties are considered approximatemore » weld properties since they contain no representation of texture. Errors introduced by using isotropic material properties to represent a weld are assessed through a quantified error bound in the elastic regime. Lastly, an adaptive error reduction scheme is used to determine the optimal spatial variation of the isotropic weld properties to reduce the error bound.« less

High photoresponse of individual WS2 nanowire-nanoflake hybrid materials

NASA Astrophysics Data System (ADS)

Asres, Georgies Alene; Järvinen, Topias; Lorite, Gabriela S.; Mohl, Melinda; Pitkänen, Olli; Dombovari, Aron; Tóth, Geza; Spetz, Anita Lloyd; Vajtai, Robert; Ajayan, Pulickel M.; Lei, Sidong; Talapatra, Saikat; Kordas, Krisztian

2018-06-01

van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS2 nanowire-nanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to ˜0.4 AW-1 are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices.

Texture Development and Material Flow Behavior During Refill Friction Stir Spot Welding of AlMgSc

NASA Astrophysics Data System (ADS)

Shen, Junjun; Lage, Sara B. M.; Suhuddin, Uceu F. H.; Bolfarini, Claudemiro; dos Santos, Jorge F.

2018-01-01

The microstructural evolution during refill friction stir spot welding of an AlMgSc alloy was studied. The primary texture that developed in all regions, with the exception of the weld center, was determined to be 〈110〉 fibers and interpreted as a simple shear texture with the 〈110〉 direction aligned with the shear direction. The material flow is mainly driven by two components: the simple shear acting on the horizontal plane causing an inward-directed spiral flow and the extrusion acting on the vertical plane causing an upward-directed or downward-directed flow. Under such a complex material flow, the weld center, which is subjected to minimal local strain, is the least recrystallized. In addition to the geometric effects of strain and grain subdivision, thermally activated high-angle grain boundary migration, particularly continuous dynamic recrystallization, drives the formation of refined grains in the stirred zone.

Materials learning from life: concepts for active, adaptive and autonomous molecular systems.

PubMed

Merindol, Rémi; Walther, Andreas

2017-09-18

Bioinspired out-of-equilibrium systems will set the scene for the next generation of molecular materials with active, adaptive, autonomous, emergent and intelligent behavior. Indeed life provides the best demonstrations of complex and functional out-of-equilibrium systems: cells keep track of time, communicate, move, adapt, evolve and replicate continuously. Stirred by the understanding of biological principles, artificial out-of-equilibrium systems are emerging in many fields of soft matter science. Here we put in perspective the molecular mechanisms driving biological functions with the ones driving synthetic molecular systems. Focusing on principles that enable new levels of functionalities (temporal control, autonomous structures, motion and work generation, information processing) rather than on specific material classes, we outline key cross-disciplinary concepts that emerge in this challenging field. Ultimately, the goal is to inspire and support new generations of autonomous and adaptive molecular devices fueled by self-regulating chemistry.

Analysis of the connection of the timber-fiber concrete composite structure

NASA Astrophysics Data System (ADS)

Holý, Milan; Vráblík, Lukáš; Petřík, Vojtěch

2017-09-01

This paper deals with an implementation of the material parameters of the connection to complex models for analysis of the timber-fiber concrete composite structures. The aim of this article is to present a possible way of idealization of the continuous contact model that approximates the actual behavior of timber-fiber reinforced concrete structures. The presented model of the connection was derived from push-out shear tests. It was approved by use of the nonlinear numerical analysis, that it can be achieved a very good compliance between results of numerical simulations and results of the experiments by a suitable choice of the material parameters of the continuous contact. Finally, an application for an analytical calculation of timber-fiber concrete composite structures is developed for the practical use in engineering praxis. The input material parameters for the analytical model was received using data from experiments.

Selection considerations between ZERODUR® and silicon carbide for dimensionally-stable spaceborne optical telescopes in two-earth-orbits

NASA Astrophysics Data System (ADS)

Hull, Tony; Westerhoff, Thomas; Weidmann, Gunter

2015-09-01

A key consideration in defining a space telescope mission is definition of the optical materials. This selection defines both the performance of the system and system complexity and cost. Optimal material selection for system stability must consider the thermal environment and its variation. Via numerical simulations, we compare the thermal and structural-mechanical behavior of ZERODUR® and SiC as mirror substrates for telescope assemblies in space. SiC has significantly larger CTE values then ZERODUR®, but also its thermal diffusivity k/(ρcp) is larger, and that helps to homogenize thermal gradients in the mirror. Therefore it is not obvious at first glance which material performs with better dimensional stability under realistic unsteady, inhomogeneous thermal loads. We specifically examine the telescope response to transient, gradient driving, thermal environments representative of low- and high-earth- orbits.

Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa{sub 0.5}Sr{sub 0.5}CoO{sub 3}-(1−x)BiFeO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lohr, Javier H.; Saleta, Martín E.; Sánchez, Rodolfo D., E-mail: rodo@cab.cnea.gov.ar

Nanopowder of ferromagnetic La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) and multiferroic BiFeO{sub 3} (BFO) were synthesized by spray pyrolysis method. Different compositions of multiferroic xLSCO-(1−x)BFO composites were synthesized at 800 °C for 2 h. Scanning electron microscopy and energy dispersive spectroscopy elemental mapping were performed to study the morphology of composites. Ferri/ferromagnetic responses above T{sub C} (LSCO) are observed, which are associated with the interfaces LSCO/BFO. This interface presents a different behavior compared to the original perovskites, and the magnitude of the magnetization depends on x. Electrical DC conductivity as a function of temperature for LSCO nanopowder (x = 1) presents a different behaviormore » than that reported in bulk material. For x = 1 and 0.9, the model by Glazman and Matveev [Zh. Eksp. Teor. Fiz. 94, 332 (1988)] is proposed to describe the electrical conductivity. On the other hand, x = 0, 0.1, and 0.5 present a variable range hopping behavior. Complex impedance spectroscopy as a function of frequency indicates a pure resistive behavior for x ≥ 0.5 compositions, while a complex resistive-capacitive behavior is observed for low x values (0, 0.1). In these samples, low values of magnetoelectric coupling were measured with an AC lock-in technique.« less

Optothermal transport behavior in whispering gallery mode optical cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soltani, Soheil; Armani, Andrea M., E-mail: armani@usc.edu; Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089

Over the past century, whispering gallery mode optical cavities have enabled numerous advances in science and engineering, such as discoveries in quantum mechanics and non-linear optics, as well as the development of optical gyroscopes and add drop filters. One reason for their widespread appeal is their ability to confine light for long periods of time, resulting in high circulating intensities. However, when sufficiently large amounts of optical power are coupled into these cavities, they begin to experience optothermal or photothermal behavior, in which the optical energy is converted into heat. Above the optothermal threshold, the resonance behavior is no longermore » solely defined by electromagnetics. Previous work has primarily focused on the role of the optothermal coefficient of the material in this instability. However, the physics of this optothermal behavior is significantly more complex. In the present work, we develop a predictive theory based on a generalizable analytical expression in combination with a geometry-specific COMSOL Multiphysics finite element method model. The simulation couples the optical and thermal physics components, accounting for geometry variations as well as the temporal and spatial profile of the optical field. To experimentally verify our theoretical model, the optothermal thresholds of a series of silica toroidal resonant cavities are characterized at different wavelengths (visible through near-infrared) and using different device geometries. The silica toroid offers a particularly rigorous case study for the developed optothermal model because of its complex geometrical structure which provides multiple thermal transport paths.« less

Local mechanical and electromechanical properties of the P(VDF-TrFE)-graphene oxide thin films

NASA Astrophysics Data System (ADS)

Silibin, M. V.; Bystrov, V. S.; Karpinsky, D. V.; Nasani, N.; Goncalves, G.; Gavrilin, I. M.; Solnyshkin, A. V.; Marques, P. A. A. P.; Singh, Budhendra; Bdikin, I. K.

2017-11-01

Recently, many organic materials, including carbon materials such as carbon nanotubes (CNTs) and graphene (single-walled carbon sheet structure) were studied in order to improve their mechanical and electrical properties. In particular, copolymers of poly (vinylidene fluoride) and poly trifluoroethylene [P(VDF-TrFE)] are promising materials, which can be used as probes, sensors, actuators, etc. Composite thin film of the copolymer P(VDF-TrFE) with graphene oxide (GO) were prepared by spin coating. The obtained films were investigated using piezoresponse force microscopy (PFM). The switching behavior, piezoelectric response, dielectric permittivity and mechanical properties of the films were found to depend on the presence of GO. For understanding the mechanism of piezoresponse evolution of the composite we used models of PVDF chain, its behavior in electrical field and computed the data for piezoelectric coefficients using HyperChem software. The summarized models of graphene oxide based on graphene layer from 96 carbon atoms C: with oxygen and OH groups and with COOH groups arranged by hydrogen were used for PVDF/Graphene oxide complex: 1) with H-side (hydrogen atom) connected from PVDF to graphene oxide, 2) with F-side (fluorine atom) connected from PVDF graphene oxide and 3) Graphene Oxide/PVDF with both sides (sandwich type). Experimental results qualitatively correlate with those obtained in the calculations.

A cohesive-frictional force field (CFFF) for colloidal calcium-silicate-hydrates

NASA Astrophysics Data System (ADS)

Palkovic, Steven D.; Yip, Sidney; Büyüköztürk, Oral

2017-12-01

Calcium-silicate-hydrate (C-S-H) gel is a cohesive-frictional material that exhibits strength asymmetry in compression and tension and normal-stress dependency of the maximum shear strength. Experiments suggest the basic structural component of C-S-H is a colloidal particle with an internal layered structure. These colloids form heterogeneous assemblies with a complex pore network at the mesoscale. We propose a cohesive-frictional force field (CFFF) to describe the interactions in colloidal C-S-H materials that incorporates the strength anisotropy fundamental to the C-S-H molecular structure that has been omitted from recent mesoscale models. We parameterize the CFFF from reactive force field simulations of an internal interface that controls mechanical performance, describing the behavior of thousands of atoms through a single effective pair interaction. We apply the CFFF to study the mesoscale elastic and Mohr-Coulomb strength properties of C-S-H with varying polydispersity and packing density. Our results show that the consideration of cohesive-frictional interactions lead to an increase in stiffness, shear strength, and normal-stress dependency, while also changing the nature of local deformation processes. The CFFF and our coarse-graining approach provide an essential connection between nanoscale molecular interactions and macroscale continuum behavior for hydrated cementitious materials.

Concentration of stresses and strains in a notched cyclinder of a viscoplastic material under harmonic loading

NASA Astrophysics Data System (ADS)

Zhuk, Ya A.; Senchenkov, I. K.

1999-02-01

Certain aspects of the correct definitions of stress and strain concentration factors for elastic-viscoplastic solids under cyclic loading are discussed. Problems concerning the harmonic kinematic excitation of cylindrical specimens with a lateral V-notch are examined. The behavior of the material of a cylinder is modeled using generalized flow theory. An approximate model based on the concept of complex moduli is used for comparison. Invariant characteristics such as stress and strain intensities and maximum principal stress and strain are chosen as constitutive quantities for concentration-factor definitions. The behavior of time-varying factors is investigated. Concentration factors calculated in terms of the amplitudes of the constitutive quantities are used as representative characteristics over the cycle of vibration. The dependences of the concentration factors on the loads are also studied. The accuracy of Nueber's and Birger's formulas is evaluated. The solution of the problem in the approximate formulation agrees with its solution in the exact formulation. The possibilities of the approximate model for estimating low-cycle fatigue are evaluated.

Fabrication and Characterization of SMA Hybrid Composites

NASA Technical Reports Server (NTRS)

Turner, Travis L.; Lach, Cynthia L.; Cano, Robert J.

2001-01-01

Results from an effort to fabrication shape memory alloy hybrid composite (SMAHC) test specimens and characterize the material system are presented in this study. The SMAHC specimens are conventional composite structures with an embedded SMA constituent. The fabrication and characterization work was undertaken to better understand the mechanics of the material system, address fabrication issues cited in the literature, and provide specimens for experimental validation of a recently developed thermomechanical model for SMAHC structures. Processes and hardware developed for fabrication of the SMAHC specimens are described. Fabrication of a SMA14C laminate with quasi-isotropic lamination and ribbon-type Nitinol actuators embedded in the 0' layers is presented. Beam specimens are machined from the laminate and are the focus of recent work, but the processes and hardware are readily extensible to more practical structures. Results of thermomechanical property testing on the composite matrix and Nitinol ribbon are presented. Test results from the Nitinol include stress-strain behavior, modulus versus temperature. and constrained recovery stress versus temperature and thermal cycle. Complex thermomechanical behaviors of the Nitinol and composite matrix are demonstrated, which have significant implications for modeling of SMAHC structures.

The dependence of granular plasticity on particle shape

NASA Astrophysics Data System (ADS)

Murphy, Kieran; Jaeger, Heinrich

Granular materials plastically deform through reworking an intricate network of particle-particle contacts. Some particle rearrangements have only a fleeting effect before being forgotten while others set in motion global restructuring. How particle shape affects local interactions and how those, in turn, influence the nature of the aggregate's plasticity is far from clear, especially in three dimensions. Here we investigate the remarkably wide range of behaviors in the yielding regime, from quiescent flow to violent jerks, depending on particle shape. We study this complex dependence via uniaxial compression experiments on aggregates of 3D-printed particles, and complement stress-strain data with simultaneous x-ray videos and volumetric strain measurements. We find power law distributions of the slip magnitudes, and discuss their universality. Our data show that the multitude of small slips serves to gradually dilate the packing whereas the fewer large ones accompany significant compaction events. Our findings provide new insights into general features of granular materials during plastic deformation and highlight how small changes in particle shape can give rise to drastic differences in yielding behavior.

Antagonistic Enzymes in a Biocatalytic pH Feedback System Program Autonomous DNA Hydrogel Life Cycles.

PubMed

Heinen, Laura; Heuser, Thomas; Steinschulte, Alexander; Walther, Andreas

2017-08-09

Enzymes regulate complex functions and active behavior in natural systems and have shown increasing prospect for developing self-regulating soft matter systems. Striving for advanced autonomous hydrogel materials with fully programmable, self-regulated life cycles, we combine two enzymes with an antagonistic pH-modulating effect in a feedback-controlled biocatalytic reaction network (BRN) and couple it to pH-responsive DNA hydrogels to realize hydrogel systems with distinct preprogrammable lag times and lifetimes in closed systems. The BRN enables precise and orthogonal internal temporal control of the "ON" and "OFF" switching times of the temporary gel state by modulation of programmable, nonlinear pH changes. The time scales are tunable by variation of the enzyme concentrations and additional buffer substances. The resulting material system operates in full autonomy after injection of the chemical fuels driving the BRN. The concept may open new applications inherent to DNA hydrogels, for instance, autonomous shape memory behavior for soft robotics. We further foresee general applicability to achieve autonomous life cycles in other pH switchable systems.

COMPLEX CONDITIONAL CONTROL BY PIGEONS IN A CONTINUOUS VIRTUAL ENVIRONMENT

PubMed Central

Qadri, Muhammad A. J.; Reid, Sean; Cook, Robert G.

2016-01-01

We tested two pigeons in a continuously streaming digital environment. Using animation software that constantly presented a dynamic, three-dimensional (3D) environment, the animals were tested with a conditional object identification task. The correct object at a given time depended on the virtual context currently streaming in front of the pigeon. Pigeons were required to accurately peck correct target objects in the environment for food reward, while suppressing any pecks to intermixed distractor objects which delayed the next object’s presentation. Experiment 1 established that the pigeons’ discrimination of two objects could be controlled by the surface material of the digital terrain. Experiment 2 established that the pigeons’ discrimination of four objects could be conjunctively controlled by both the surface material and topography of the streaming environment. These experiments indicate that pigeons can simultaneously process and use at least two context cues from a streaming environment to control their identification behavior of passing objects. These results add to the promise of testing interactive digital environments with animals to advance our understanding of cognition and behavior. PMID:26781058

Fractal Theory and Field Cover Experiments: Implications for the Fractal Characteristics and Radon Diffusion Behavior of Soils and Rocks.

PubMed

Tan, Wanyu; Li, Yongmei; Tan, Kaixuan; Duan, Xianzhe; Liu, Dong; Liu, Zehua

2016-12-01

Radon diffusion and transport through different media is a complex process affected by many factors. In this study, the fractal theories and field covering experiments were used to study the fractal characteristics of particle size distribution (PSD) of six kinds of geotechnical materials (e.g., waste rock, sand, laterite, kaolin, mixture of sand and laterite, and mixture of waste rock and laterite) and their effects on radon diffusion. In addition, the radon diffusion coefficient and diffusion length were calculated. Moreover, new formulas for estimating diffusion coefficient and diffusion length functional of fractal dimension d of PSD were proposed. These results demonstrate the following points: (1) the fractal dimension d of the PSD can be used to characterize the property of soils and rocks in the studies of radon diffusion behavior; (2) the diffusion coefficient and diffusion length decrease with increasing fractal dimension of PSD; and (3) the effectiveness of final covers in reducing radon exhalation of uranium tailings impoundments can be evaluated on the basis of the fractal dimension of PSD of materials.

Microwave dielectric behavior of vegetation material

NASA Technical Reports Server (NTRS)

Elrayes, Mohamed A.; Ulaby, Fawwaz T.

1987-01-01

The microwave dielectric behavior of vegetation was examined through the development of theoretical models involving dielectric dispersion by both bound and free water and supported by extensive dielectric measurements conducted over a wide range of conditions. The experimental data were acquired using an open-ended coaxial probe that was developed for sensing the dielectric constant of thin layers of materials, such as leaves, from measurements of the complex reflection coefficient using a network analyzer. The probe system was successfully used to record the spectral variation of the dielectric constant over a wide frequency range extending from 0.5 to 20.4 GHz at numerous temperatures between -40 to +40 C. The vegetation samples were measured over a wide range of moisture conditions. To model the dielectric spectrum of the bound water component of the water included in vegetation, dielectric measurements were made for several sucrose-water solutions as analogs for the situation in vegetation. The results were used in conjunction with the experimental data for leaves to determine some of the constant coefficients in the theoretical models. Two models, both of which provide good fit to the data, are proposed.

Mathematical model of silicon smelting process basing on pelletized charge from technogenic raw materials

NASA Astrophysics Data System (ADS)

Nemchinova, N. V.; Tyutrin, A. A.; Salov, V. M.

2018-03-01

The silicon production process in the electric arc reduction furnaces (EAF) is studied using pelletized charge as an additive to the standard on the basis of the generated mathematical model. The results obtained due to the model will contribute to the analysis of the charge components behavior during melting with the achievement of optimum final parameters of the silicon production process. The authors proposed using technogenic waste as a raw material for the silicon production in a pelletized form using liquid glass and aluminum production dust from the electrostatic precipitators as a binder. The method of mathematical modeling with the help of the ‘Selector’ software package was used as a basis for the theoretical study. A model was simulated with the imitation of four furnace temperature zones and a crystalline silicon phase (25 °C). The main advantage of the created model is the ability to analyze the behavior of all burden materials (including pelletized charge) in the carbothermic process. The behavior analysis is based on the thermodynamic probability data of the burden materials interactions in the carbothermic process. The model accounts for 17 elements entering the furnace with raw materials, electrodes and air. The silicon melt, obtained by the modeling, contained 91.73 % wt. of the target product. The simulation results showed that in the use of the proposed combined charge, the recovery of silicon reached 69.248 %, which is in good agreement with practical data. The results of the crystalline silicon chemical composition modeling are compared with the real silicon samples of chemical analysis data, which showed the results of convergence. The efficiency of the mathematical modeling methods in the studying of the carbothermal silicon obtaining process with complex interphase transformations and the formation of numerous intermediate compounds using a pelletized charge as an additive to the traditional one is shown.

Synthesis and studies on Cu(II), Co(II), Ni(II) complexes of Knoevenagel β-diketone ligands.

PubMed

Sumathi, S; Tharmaraj, P; Sheela, C D; Anitha, C

2012-11-01

Transition metal complexes of various acetylacetone based ligands of the type ML [where M=Cu(II), Ni(II), Co(II); L=3-(aryl)-pentane-2,4-dione] have been synthesized. The structural features have been derived from their elemental analysis, magnetic susceptibility, molar conductance, IR, UV-Vis, (1)H NMR, Mass and ESR spectral studies. Conductivity measurements reveal that all the complexes are non-electrolytic in nature. Spectroscopic and other analytical data of the complexes suggest octahedral geometry for other metal(II) complexes. The redox behavior of the copper(II) complexes have been studied by cyclic voltammetry. The free ligands and their metal complexes have been screened for their in vitro biological activities against the bacteria Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus as well as the fungus Candida albicans by well diffusion method. The zone of inhibition value indicates that the most of the metal(II) complexes are found to possess increased activities compared to those of the free ligands. All synthesized compounds may serve as potential photoactive materials as indicated from their characteristic fluorescence properties. The second harmonic generation (SHG) efficiency of the ligands (L1-L3) was found to be considerable effect than that of urea and KDP (potassium dihydrogen phosphate). Copyright © 2012 Elsevier B.V. All rights reserved.

Synthesis and studies on Cu(II), Co(II), Ni(II) complexes of Knoevenagel β-diketone ligands

NASA Astrophysics Data System (ADS)

Sumathi, S.; Tharmaraj, P.; Sheela, C. D.; Anitha, C.

2012-11-01

Transition metal complexes of various acetylacetone based ligands of the type ML [where M = Cu(II), Ni(II), Co(II); L = 3-(aryl)-pentane-2,4-dione] have been synthesized. The structural features have been derived from their elemental analysis, magnetic susceptibility, molar conductance, IR, UV-Vis, 1H NMR, Mass and ESR spectral studies. Conductivity measurements reveal that all the complexes are non-electrolytic in nature. Spectroscopic and other analytical data of the complexes suggest octahedral geometry for other metal(II) complexes. The redox behavior of the copper(II) complexes have been studied by cyclic voltammetry. The free ligands and their metal complexes have been screened for their in vitro biological activities against the bacteria Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus as well as the fungus Candida albicans by well diffusion method. The zone of inhibition value indicates that the most of the metal(II) complexes are found to possess increased activities compared to those of the free ligands. All synthesized compounds may serve as potential photoactive materials as indicated from their characteristic fluorescence properties. The second harmonic generation (SHG) efficiency of the ligands (L1-L3) was found to be considerable effect than that of urea and KDP (potassium dihydrogen phosphate).

Experimental data showing the thermal behavior of a flat roof with phase change material.

PubMed

Tokuç, Ayça; Başaran, Tahsin; Yesügey, S Cengiz

2015-12-01

The selection and configuration of building materials for optimal energy efficiency in a building require some assumptions and models for the thermal behavior of the utilized materials. Although the models for many materials can be considered acceptable for simulation and calculation purposes, the work for modeling the real time behavior of phase change materials is still under development. The data given in this article shows the thermal behavior of a flat roof element with a phase change material (PCM) layer. The temperature and energy given to and taken from the building element are reported. In addition the solid-liquid behavior of the PCM is tracked through images. The resulting thermal behavior of the phase change material is discussed and simulated in [1] A. Tokuç, T. Başaran, S.C. Yesügey, An experimental and numerical investigation on the use of phase change materials in building elements: the case of a flat roof in Istanbul, Build. Energy, vol. 102, 2015, pp. 91-104.

A Case Study of the De Novo Evolution of a Complex Odometric Behavior in Digital Organisms

PubMed Central

Grabowski, Laura M.; Bryson, David M.; Dyer, Fred C.; Pennock, Robert T.; Ofria, Charles

2013-01-01

Investigating the evolution of animal behavior is difficult. The fossil record leaves few clues that would allow us to recapitulate the path that evolution took to build a complex behavior, and the large population sizes and long time scales required prevent us from re-evolving such behaviors in a laboratory setting. We present results of a study in which digital organisms–self-replicating computer programs that are subject to mutations and selection–evolved in different environments that required information about past experience for fitness-enhancing behavioral decisions. One population evolved a mechanism for step-counting, a surprisingly complex odometric behavior that was only indirectly related to enhancing fitness. We examine in detail the operation of the evolved mechanism and the evolutionary transitions that produced this striking example of a complex behavior. PMID:23577113

Meso-scopic Densification in Brittle Granular Materials

NASA Astrophysics Data System (ADS)

Neal, William; Appleby-Thomas, Gareth; Collins, Gareth

2013-06-01

Particulate materials are ideally suited to shock absorbing applications due to the large amounts of energy required to deform their inherently complex meso-structure. Significant effort is being made to improve macro-scale material models to represent these atypical materials. On the long road towards achieving this capability, an important milestone would be to understand how particle densification mechanisms are affected by loading rate. In brittle particulate materials, the majority of densification is caused by particle fracture. Macro-scale quasi-static and dynamic compaction curves have been measured that show good qualitative agreement. There are, however, some differences that appear to be dependent on the loading rate that require further investigation. This study aims to investigate the difference in grain-fracture behavior between the quasi-static and shock loading response of brittle glass microsphere beds using a combination of quasi-static and dynamic loading techniques. Results from pressure-density measurements, sample recovery, and meso-scale hydrocode models (iSALE, an in-house simulation package) are discussed to explain the differences in particle densification mechanisms between the two loading rate regimes. Gratefully funded by AWE.plc.

Carbon dots in zeolites: A new class of thermally activated delayed fluorescence materials with ultralong lifetimes

PubMed Central

Liu, Jiancong; Wang, Ning; Yu, Yue; Yan, Yan; Zhang, Hongyue; Li, Jiyang; Yu, Jihong

2017-01-01

Thermally activated delayed fluorescence (TADF) materials are inspiring intensive research in optoelectronic applications. To date, most of the TADF materials are limited to metal-organic complexes and organic molecules with lifetimes of several microseconds/milliseconds that are sensitive to oxygen. We report a facial and general “dots-in-zeolites” strategy to in situ confine carbon dots (CDs) in zeolitic matrices during hydrothermal/solvothermal crystallization to generate high-efficient TADF materials with ultralong lifetimes. The resultant CDs@zeolite composites exhibit high quantum yields up to 52.14% and ultralong lifetimes up to 350 ms at ambient temperature and atmosphere. This intriguing TADF phenomenon is due to the fact that nanoconfined space of zeolites can efficiently stabilize the triplet states of CDs, thus enabling the reverse intersystem crossing process for TADF. Meanwhile, zeolite frameworks can also hinder oxygen quenching to present TADF behavior at air atmosphere. This design concept introduces a new perspective to develop materials with unique TADF performance and various novel delayed fluorescence–based applications. PMID:28560347

Industrial based volume manufacturing of lightweight aluminium alloy panel components with high-strength and complex-shape for car body and chassis structures

NASA Astrophysics Data System (ADS)

Anyasodor, Gerald; Koroschetz, Christian

2017-09-01

To achieve the high volume manufacture of lightweight passenger cars at economic cost as required in the automotive industry, low density materials and new process route will be needed. While high strength aluminium alloy grades: AA7075 and AA6082 may provide the alternative material solution, hot stamping process used for high-strength and ultrahigh strength steels such as boron steel 22mnb5 can enable the volume manufacture of panel components with high-strength and complex-shape for car body and chassis structures. These aluminium alloy grades can be used to manufacture panel components with possible yield strengths ≥ 500 MPa. Due to the differences in material behaviors, hot stamping process of 22mnb5 cannot be directly applied to high strength aluminium alloy grades. Despite recorded successes in laboratories, researches and niche hot forming processes of high strength aluminium alloy grades, not much have been achieved for adequate and efficient volume manufacturing system applicable in the automotive industry. Due to lack of such system and based on expert knowledge in hot stamping production-line, AP&T presents in this paper a hot stamping processing route for high strength aluminium alloys been suitable for production-line development and volume manufacturing.

Structure and mechanics of aegagropilae fiber network.

PubMed

Verhille, Gautier; Moulinet, Sébastien; Vandenberghe, Nicolas; Adda-Bedia, Mokhtar; Le Gal, Patrice

2017-05-02

Fiber networks encompass a wide range of natural and manmade materials. The threads or filaments from which they are formed span a wide range of length scales: from nanometers, as in biological tissues and bundles of carbon nanotubes, to millimeters, as in paper and insulation materials. The mechanical and thermal behavior of these complex structures depends on both the individual response of the constituent fibers and the density and degree of entanglement of the network. A question of paramount importance is how to control the formation of a given fiber network to optimize a desired function. The study of fiber clustering of natural flocs could be useful for improving fabrication processes, such as in the paper and textile industries. Here, we use the example of aegagropilae that are the remains of a seagrass ( Posidonia oceanica ) found on Mediterranean beaches. First, we characterize different aspects of their structure and mechanical response, and second, we draw conclusions on their formation process. We show that these natural aggregates are formed in open sea by random aggregation and compaction of fibers held together by friction forces. Although formed in a natural environment, thus under relatively unconstrained conditions, the geometrical and mechanical properties of the resulting fiber aggregates are quite robust. This study opens perspectives for manufacturing complex fiber network materials.

Structural, optoelectronic, and thermoelectric properties of AZn13 (A=Na, K, Ca, Sr, Ba) compounds

NASA Astrophysics Data System (ADS)

Basit, Abdul; Murtaza, G.; Mahmood, Asif; Yar, Abdullah; Muhammad, S.

2016-08-01

We report the structural, electronic, optical, and thermoelectric properties of the five cubic alkali-earth transition-metals AZn13 (A-Na, K, Ca, Sr, Ba) using density functional theory. Structural properties, electronic structures and optical behaviors are calculated explicitly via highly accurate contemporary full potential-linearized augmented plane wave (FP-LAPW) method. The investigated ground state data of these materials is quite close to the experimental information. The modified Becke-Johnson (mBJ) predicts the intermetallic nature of AZn13 (A-Na, K, Ca, Sr, Ba) materials. The complex dielectric function of these intermetallic compounds has been calculated and the observed noticeable peaks are examined through mBJ. With the help of complex dielectric function, the other important optical parameters like reflectivities, conductivities and refractive indices of AZn13 (A-Na, K, Ca, Sr, Ba) have been calculated as a function of energy. The optical response suggests that AZn13 (A-Na, K, Ca, Sr, Ba) compounds can be used for the optoelectronic devices. Further, the thermoelectric properties have been calculated through BoltzTraP program, the calculated values for different thermoelectric parameters recommend that these AZn13 (A-Na, K, Ca, Sr, Ba) materials are the suitable candidates for thermoelectric applications.

Directing the phase behavior of polyelectrolyte complexes using chiral patterned peptides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pacalin, Naomi M.; Leon, Lorraine; Tirrell, Matthew

Polyelectrolyte complexes (PECs) have a broad range of promising applications as soft materials due to their self-assembly and diversity of structure and chemical composition. Peptide polymer PECs are highly biocompatible and biodegradable, making them particularly useful for encapsulation of food additives and flavors, micellar drug delivery, medical and underwater adhesives, fetal membrane patches, and scaffolds for cell growth in tissue engineering. While parameters affecting PEC formation and stability in regards to charge effects are well researched, little is known about the effects of van der Waals interactions, hydrogen bonding, and secondary structure in these materials. Peptide chirality provides a uniquemore » opportunity to manipulate PEC phase to modulate the amount of solid-like (precipitate) or liquid-like (coacervate) character by influencing hydrogen bonding interactions among peptide chains. In previous work, we showed that chiral peptides form solid complexes, while complexes with even one racemic peptide were fluid. This raised the interesting question of how long a homochiral sequence must be to result in solid phase formation. In this work, we designed chiral patterned peptides of polyglutamic acid and polylysine ranging from 50 to 90% L-chiral residues with increasing numbers of sequential L-chiral residues before a chirality change. These polymers were mixed together to form PECs. We observed that 8 or more sequential L-chiral residues are necessary to achieve both the appearance of a precipitate phase and sustained beta-sheets in the complex, as determined by optical imaging and FTIR Spectroscopy. Less homochiral content results in formation of a coacervate phase. Thus, we show that chiral sequence can be used to control the phase transition of PECs. Understanding how to manipulate PEC phase using chiral sequence as presented here may enable tuning of the material properties to achieve the desired mechanical strength for coatings and polymer brushes, or the most effective molecular release kinetics for drug delivery applications, for example.« less

Directing the phase behavior of polyelectrolyte complexes using chiral patterned peptides

NASA Astrophysics Data System (ADS)

Pacalin, Naomi M.; Leon, Lorraine; Tirrell, Matthew

2016-10-01

Polyelectrolyte complexes (PECs) have a broad range of promising applications as soft materials due to their self-assembly and diversity of structure and chemical composition. Peptide polymer PECs are highly biocompatible and biodegradable, making them particularly useful for encapsulation of food additives and flavors, micellar drug delivery, medical and underwater adhesives, fetal membrane patches, and scaffolds for cell growth in tissue engineering. While parameters affecting PEC formation and stability in regards to charge effects are well researched, little is known about the effects of van der Waals interactions, hydrogen bonding, and secondary structure in these materials. Peptide chirality provides a unique opportunity to manipulate PEC phase to modulate the amount of solid-like (precipitate) or liquid-like (coacervate) character by influencing hydrogen bonding interactions among peptide chains. In previous work, we showed that chiral peptides form solid complexes, while complexes with even one racemic peptide were fluid. This raised the interesting question of how long a homochiral sequence must be to result in solid phase formation. In this work, we designed chiral patterned peptides of polyglutamic acid and polylysine ranging from 50 to 90% L-chiral residues with increasing numbers of sequential L-chiral residues before a chirality change. These polymers were mixed together to form PECs. We observed that 8 or more sequential L-chiral residues are necessary to achieve both the appearance of a precipitate phase and sustained β-sheets in the complex, as determined by optical imaging and FTIR Spectroscopy. Less homochiral content results in formation of a coacervate phase. Thus, we show that chiral sequence can be used to control the phase transition of PECs. Understanding how to manipulate PEC phase using chiral sequence as presented here may enable tuning of the material properties to achieve the desired mechanical strength for coatings and polymer brushes, or the most effective molecular release kinetics for drug delivery applications, for example.

Seismic and Restoration Assessment of Monumental Masonry Structures

PubMed Central

Asteris, Panagiotis G.; Douvika, Maria G.; Apostolopoulou, Maria; Moropoulou, Antonia

2017-01-01

Masonry structures are complex systems that require detailed knowledge and information regarding their response under seismic excitations. Appropriate modelling of a masonry structure is a prerequisite for a reliable earthquake-resistant design and/or assessment. However, modelling a real structure with a robust quantitative (mathematical) representation is a very difficult, complex and computationally-demanding task. The paper herein presents a new stochastic computational framework for earthquake-resistant design of masonry structural systems. The proposed framework is based on the probabilistic behavior of crucial parameters, such as material strength and seismic characteristics, and utilizes fragility analysis based on different failure criteria for the masonry material. The application of the proposed methodology is illustrated in the case of a historical and monumental masonry structure, namely the assessment of the seismic vulnerability of the Kaisariani Monastery, a byzantine church that was built in Athens, Greece, at the end of the 11th to the beginning of the 12th century. Useful conclusions are drawn regarding the effectiveness of the intervention techniques used for the reduction of the vulnerability of the case-study structure, by means of comparison of the results obtained. PMID:28767073

Seismic and Restoration Assessment of Monumental Masonry Structures.

PubMed

Asteris, Panagiotis G; Douvika, Maria G; Apostolopoulou, Maria; Moropoulou, Antonia

2017-08-02

Masonry structures are complex systems that require detailed knowledge and information regarding their response under seismic excitations. Appropriate modelling of a masonry structure is a prerequisite for a reliable earthquake-resistant design and/or assessment. However, modelling a real structure with a robust quantitative (mathematical) representation is a very difficult, complex and computationally-demanding task. The paper herein presents a new stochastic computational framework for earthquake-resistant design of masonry structural systems. The proposed framework is based on the probabilistic behavior of crucial parameters, such as material strength and seismic characteristics, and utilizes fragility analysis based on different failure criteria for the masonry material. The application of the proposed methodology is illustrated in the case of a historical and monumental masonry structure, namely the assessment of the seismic vulnerability of the Kaisariani Monastery, a byzantine church that was built in Athens, Greece, at the end of the 11th to the beginning of the 12th century. Useful conclusions are drawn regarding the effectiveness of the intervention techniques used for the reduction of the vulnerability of the case-study structure, by means of comparison of the results obtained.

The Design of Large-Scale Complex Engineered Systems: Present Challenges and Future Promise

NASA Technical Reports Server (NTRS)

Bloebaum, Christina L.; McGowan, Anna-Maria Rivas

2012-01-01

Model-Based Systems Engineering techniques are used in the SE community to address the need for managing the development of complex systems. A key feature of the MBSE approach is the use of a model to capture the requirements, architecture, behavior, operating environment and other key aspects of the system. The focus on the model differentiates MBSE from traditional SE techniques that may have a document centric approach. In an effort to assess the benefit of utilizing MBSE on its flight projects, NASA Langley has implemented a pilot program to apply MBSE techniques during the early phase of the Materials International Space Station Experiment-X (MISSE-X). MISSE-X is a Technology Demonstration Mission being developed by the NASA Office of the Chief Technologist i . Designed to be installed on the exterior of the International Space Station (ISS), MISSE-X will host experiments that advance the technology readiness of materials and devices needed for future space exploration. As a follow-on to the highly successful series of previous MISSE experiments on ISS, MISSE-X benefits from a significant interest by the

Triblock copolyampholytes from 5-(N,N-dimethyl amino)isoprene styrene, and methacrylic acid: Synthesis and solution properties

NASA Astrophysics Data System (ADS)

Bieringer, R.; Abetz, V.; Müller, A. H. E.

ABC triblock copolymers of the type poly[5-(N,N-dimethyl amino)isoprene]-block-polystyrene-block-poly(tert-butyl methacrylate) (AiST) were synthesized and hydrolyzed to yield poly[5-(N,N-dimethyl amino)isoprene]-block-polystyrene-block-poly(methacrylic acid) (AiSA) triblock copolyampholytes. Due to a complex solubility behavior the solution properties of these materials had to be investigated in THF/water solvent mixtures. Potentiometric titrations of AiSA triblock copolyampholytes showed two inflection points with the A block being deprotonated prior to the Ai hydrochloride block thus forming a polyzwitterion at the isoelectric point (iep). The aggregation behavior was studied by dynamic light scattering (DLS) and freeze-fracture/transmission electron microscopy (TEM). Large vesicular structures with almost pH-independent radii were observed.

Effective search for stable segregation configurations at grain boundaries with data-mining techniques

NASA Astrophysics Data System (ADS)

Kiyohara, Shin; Mizoguchi, Teruyasu

2018-03-01

Grain boundary segregation of dopants plays a crucial role in materials properties. To investigate the dopant segregation behavior at the grain boundary, an enormous number of combinations have to be considered in the segregation of multiple dopants at the complex grain boundary structures. Here, two data mining techniques, the random-forests regression and the genetic algorithm, were applied to determine stable segregation sites at grain boundaries efficiently. Using the random-forests method, a predictive model was constructed from 2% of the segregation configurations and it has been shown that this model could determine the stable segregation configurations. Furthermore, the genetic algorithm also successfully determined the most stable segregation configuration with great efficiency. We demonstrate that these approaches are quite effective to investigate the dopant segregation behaviors at grain boundaries.

Effects of natural enrichment materials on stress, memory and exploratory behavior in mice.

PubMed

Acklin, Casey J; Gault, Ruth A

2015-07-01

Environmental enrichment is an essential component of laboratory animal housing that allows animals to engage in natural behaviors in an otherwise artificial setting. Previous research by the authors suggested that, compared with synthetic enrichment materials, natural materials were associated with lower stress levels in mice. Here, the authors compare the effects of different enrichment materials on stress, memory and exploratory behavior in Swiss Webster mice. Mice that were provided with natural enrichment materials had lower stress levels, better memory and greater exploratory behavior than did mice provided with synthetic enrichment materials or with no enrichment materials. These findings suggest that provision of natural enrichment materials can improve well-being of laboratory mice.

Reaction propagation test. Evaluation of the behavior of nonmetallic materials in hydrogen

NASA Technical Reports Server (NTRS)

Smith, I. D.

1972-01-01

Results of tests conducted to evaluate the behavior of nonmetallic materials in hydrogen are described. The reaction propagation test simulates the conditions resulting from the interaction of an electrical wire in an overload condition in contract with a material in the test medium. The test is designed to evaluate the behavior of a material subjected to an energy input (usually heat) sufficient to cause a reaction which propagates to consume larger quantities of the material. Ten nonmetallic materials were evaluated to establish baseline data on the behavior of nonmetallic materials in hydrogen and to characterize, on an initial basis, one mode of material failure considered to be a factor pertinent to the safe use of a material in hydrogen.

Physics-based Modeling of Material Behavior and Damage Initiation in Nanoengineered Composites

NASA Astrophysics Data System (ADS)

Subramanian, Nithya

Materials with unprecedented properties are necessary to make dramatic changes in current and future aerospace platforms. Hybrid materials and composites are increasingly being used in aircraft and spacecraft frames; however, future platforms will require an optimal design of novel materials that enable operation in a variety of environments and produce known/predicted damage mechanisms. Nanocomposites and nanoengineered composites with CNTs have the potential to make significant improvements in strength, stiffness, fracture toughness, flame retardancy and resistance to corrosion. Therefore, these materials have generated tremendous scientific and technical interest over the past decade and various architectures are being explored for applications to light-weight airframe structures. However, the success of such materials with significantly improved performance metrics requires careful control of the parameters during synthesis and processing. Their implementation is also limited due to the lack of complete understanding of the effects the nanoparticles impart to the bulk properties of composites. It is common for computational methods to be applied to explain phenomena measured or observed experimentally. Frequently, a given phenomenon or material property is only considered to be fully understood when the associated physics has been identified through accompanying calculations or simulations. The computationally and experimentally integrated research presented in this dissertation provides improved understanding of the mechanical behavior and response including damage and failure in CNT nanocomposites, enhancing confidence in their applications. The computations at the atomistic level helps to understand the underlying mechanochemistry and allow a systematic investigation of the complex CNT architectures and the material performance across a wide range of parameters. Simulation of the bond breakage phenomena and development of the interface to continuum scale damage captures the effects of applied loading and damage precursor and provides insight into the safety of nanoengineered composites under service loads. The validated modeling methodology is expected to be a step in the direction of computationally-assisted design and certification of novel materials, thus liberating the pace of their implementation in future applications.

Facilitating Behavior Change With Low-literacy Patient Education Materials

PubMed Central

Seligman, Hilary K.; Wallace, Andrea S.; DeWalt, Darren A.; Schillinger, Dean; Arnold, Connie L.; Shilliday, Betsy Bryant; Delgadillo, Adriana; Bengal, Nikki; Davis, Terry C.

2014-01-01

Objective To describe a process for developing low-literacy health education materials that increase knowledge and activate patients toward healthier behaviors. Methods We developed a theoretically informed process for developing educational materials. This process included convening a multidisciplinary creative team, soliciting stakeholder input, identifying key concepts to be communicated, mapping concepts to a behavioral theory, creating a supporting behavioral intervention, designing and refining materials, and assessing efficacy. Results We describe the use of this process to develop a diabetes self-management guide. Conclusions Developing low-literacy health education materials that will activate patients toward healthier behaviors requires attention to factors beyond reading level. PMID:17931139

Study of Adsorption and Desorption Performances of Zr-Based Metal-Organic Frameworks Using Paper Spray Mass Spectrometry.

PubMed

Wang, Xiaoting; Chen, Ying; Zheng, Yajun; Zhang, Zhiping

2017-07-08

The dynamic pore systems and high surface areas of flexible metal-organic framework materials make them excellent candidates to be used in different kinds of adsorption processes. However, the adsorption and desorption behaviors of therapeutic drugs on metal-organic frameworks in solution are not fully developed. Here, we systematically investigated the adsorption and desorption behaviors of a typical therapeutic drug, verapamil, over several Zr-based metal-organic frameworks [e.g., Zr-FUM, UiO-66(Zr), UiO-66(Zr)-NH₂ and UiO-66(Zr)-2COOH] as well as ZrO₂ in an acetonitrile solution by using paper spray mass spectrometry. In contrast to other materials, UiO-66(Zr)-2COOH demonstrated a superior adsorption performance to verapamil due to their strong acid-base and/or hydrogen-bond interactions, and the adsorption process fitted well with the pseudo-second-order kinetic model. As verapamil-adsorbed materials were used for desorption experiments, ZrO₂ demonstrated the most favorable desorption performance, whereas UiO-66(Zr)-2COOH yielded the poorest desorption capability. These Zr-based materials had also been coated at the surface with filter papers for the analysis of various drugs and proteins in the process of paper spray mass spectrometry. The results demonstrated that among the studied materials, ZrO₂-coated paper gave the most favorable desorption performance as a pure drug solution, whereas the paper from UiO-66(Zr) demonstrated the optimal capability in the analyses of therapeutic drugs in a complex matrix (e.g., blood) and a protein (e.g., myoglobin).

Finite Element Simulation of Compression Molding of Woven Fabric Carbon Fiber/Epoxy Composites: Part I Material Model Development

DOE PAGES

Li, Yang; Zhao, Qiangsheng; Mirdamadi, Mansour; ...

2016-01-06

Woven fabric carbon fiber/epoxy composites made through compression molding are one of the promising choices of material for the vehicle light-weighting strategy. Previous studies have shown that the processing conditions can have substantial influence on the performance of this type of the material. Therefore the optimization of the compression molding process is of great importance to the manufacturing practice. An efficient way to achieve the optimized design of this process would be through conducting finite element (FE) simulations of compression molding for woven fabric carbon fiber/epoxy composites. However, performing such simulation remains a challenging task for FE as multiple typesmore » of physics are involved during the compression molding process, including the epoxy resin curing and the complex mechanical behavior of woven fabric structure. In the present study, the FE simulation of the compression molding process of resin based woven fabric composites at continuum level is conducted, which is enabled by the implementation of an integrated material modeling methodology in LS-Dyna. Specifically, the chemo-thermo-mechanical problem of compression molding is solved through the coupling of three material models, i.e., one thermal model for temperature history in the resin, one mechanical model to update the curing-dependent properties of the resin and another mechanical model to simulate the behavior of the woven fabric composites. Preliminary simulations of the carbon fiber/epoxy woven fabric composites in LS-Dyna are presented as a demonstration, while validations and models with real part geometry are planned in the future work.« less

Analysis of Panel Data

NASA Astrophysics Data System (ADS)

Hsiao, Cheng

2003-02-01

Panel data models have become increasingly popular among applied researchers due to their heightened capacity for capturing the complexity of human behavior, as compared to cross-sectional or time series data models. This second edition represents a substantial revision of the highly successful first edition (1986). Recent advances in panel data research are presented in an accessible manner and are carefully integrated with the older material. The thorough discussion of theory and the judicious use of empirical examples make this book useful to graduate students and advanced researchers in economics, business, sociology and political science.