Science.gov

Sample records for basic mechanical properties

  1. Determination of basic physical and mechanical properties of basaltic rocks from P-wave velocity

    NASA Astrophysics Data System (ADS)

    Karakuş, Askeri; Akatay, Mahmut

    2013-12-01

    Physical and mechanical properties of basaltic rocks used as main building material in historical buildings in Diyarbakir show great diversity depending on the place of origin. Especially, earthquake studies as well as restoration jobs and civil engineers and architects who work on building dynamics need to know basic material properties of basaltic rocks that are the main building material. In this study, the basalt samples obtained from 18 different locations of the Diyarbakir area were tested in order to estimate the main material properties of basalts used in historical buildings without collecting samples from them. Subsequently, statistical relationships between the nondestructive P-wave velocity and other properties of basalts were investigated. Consequently, highly correlated models (R2 = 0.717-0.890) were obtained between P-wave velocity and density, porosity, uniaxial compressive strength, Brazilian tensile strength, modulus of elasticity and Poisson's ratio.

  2. Nature's amazing biopolymer: basic mechanical and hydrological properties of soil affected by plant exudates

    NASA Astrophysics Data System (ADS)

    Naveed, Muhammad; Roose, Tiina; Raffan, Annette; George, Timothy; Bengough, Glyn; Brown, Lawrie; Keyes, Sam; Daly, Keith; Hallett, Paul

    2016-04-01

    Plant exudates are known to have a very large impact on soil physical properties through changes in mechanical and hydrological processes driven by long-chain polysaccharides and surface active compounds. Whilst these impacts are well known, the basic physical properties of these exudates have only been reported in a small number of studies. We present data for exudates obtained from barley roots and chia seeds, incorporating treatments examining biological decomposition of the exudates. When these exudates were added to a sandy loam soil, contact angle and drop penetration time increased exponentially with increasing exudate concentration. These wetting properties were strongly correlated with both exudate density and zero-shear viscosity, but not with exudate surface tension. Water holding capacity and water repellency of exudate mixed soil tremendously increased with exudate concentration, however they were significantly reduced on decomposition when measured after 14 days of incubation at 16C. Mechanical stability greatly increased with increasing exudate amendment to soils, which was assessed using a rheological amplitude sweep test near saturation, at -50 cm matric potential (field capacity) using indentation test, and at air-dry condition using the Brazilian test. This reflects that exudates not only attenuate plant water stress but also impart mechanical stability to the rhizosphere. These data are highly relevant to the understanding and modelling of rhizosphere development, which is the next phase of our research.

  3. Basic Engineer Equipment Mechanic.

    ERIC Educational Resources Information Center

    Marine Corps Inst., Washington, DC.

    This student guide, one of a series of correspondence training courses designed to improve the job performance of members of the Marine Corps, deals with the skills needed by basic engineer equipment mechanics. Addressed in the four individual units of the course are the following topics: mechanics and their tools (mechanics, hand tools, and power…

  4. Basic properties and variability

    NASA Technical Reports Server (NTRS)

    Querci, Francois R.

    1987-01-01

    Giant and supergiant M, S, and C stars are discussed in this survey of research. Basic properties as determined by spectra, chemical composition, photometry, or variability type are discussed. Space motions and space distributions of cool giants are described. Distribution of these stars in our galaxy and those nearby is discussed. Mira variables in particular are surveyed with emphasis on the following topics: (1) phase lag phenomenon; (2) Mira light curves; (3) variations in color indices; (4) determination of multiple periods; (5) correlations between quantities such as period length, light-curve shape, infrared (IR) excess, and visible and IR color diagram; (6) semiregular (SR) variables and different time scales in SR light variations; (7) irregular variable Lb and Lc stars; (8) different time-scale light variations; (9) hydrogen-deficient carbon (HdC) stars, in particular RCB stars; and (10) irreversible changes and rapid evolution in red variable stars.

  5. Basic Mechanisms of the Epilepsies.

    ERIC Educational Resources Information Center

    Jasper, Herbert H., Ed.; And Others

    A collection of highly technical scientific articles by international basic and clinical neuroscientists constitutes a review of their knowledge of the brain and nervous system, particularly the aspects related to loss of brain function control and its explosive discharges which cause epileptic seizures. Anatomy, biophysics, biochemistry, and…

  6. Basic Shop Fundamentals for the Mechanic.

    ERIC Educational Resources Information Center

    Younce, J. R.; And Others

    These self-study materials are a basic course for Marines working as mechanics. The course contains three study units. The first unit explains mechanics' hand tools and their proper care and usage. The second unit introduces the duties of the personnel at a basic level, describes the areas of a typical shop, and deals with shop operations and…

  7. Basic Mechanisms of Mitral Regurgitation

    PubMed Central

    Dal-Bianco, Jacob P.; Beaudoin, Jonathan

    2014-01-01

    Any structural or functional impairment of the mitral valve (MV) apparatus that exhausts MV tissue redundancy available for leaflet coaptation will result in mitral regurgitation (MR). The mechanism responsible for MV malcoaptation and MR can be dysfunction or structural change of the left ventricle, the papillary muscles, the chordae tendineae, the mitral annulus and the MV leaflets. The rationale for MV treatment depends on the MR mechanism and therefore it is essential to identify and understand normal and abnormal MV and MV apparatus function. PMID:25151282

  8. Auto Mechanics. Performance Objectives. Basic Course.

    ERIC Educational Resources Information Center

    Carter, Thomas G., Sr.

    Several intermediate performance objectives and corresponding criterion measures are listed for each of 14 terminal objectives for a basic automotive mechanics course. The materials were developed for a two-semester course (2 hours daily) designed to provide training in the basic fundamentals in diagnosis and repair including cooling system and…

  9. Diesel Mechanics. Performance Objectives. Basic Course.

    ERIC Educational Resources Information Center

    Tidwell, Joseph

    Several intermediate performance objectives and corresponding criterion measures are listed for each of 12 terminal objectives for a basic diesel mechanics course. The course is designed as a two-semester (2 hour daily) course for 10th graders interested in being diesel service and repair mechanics; it would serve as the first year of a 3-year…

  10. Basic mechanisms governing solar-cell efficiency

    NASA Technical Reports Server (NTRS)

    Lindholm, F. A.; Neugroschel, A.; Sah, C. T.

    1976-01-01

    The efficiency of a solar cell depends on the material parameters appearing in the set of differential equations that describe the transport, recombination, and generation of electrons and holes. This paper describes the many basic mechanisms occurring in semiconductors that can control these material parameters.

  11. Gasoline Engine Mechanics. Performance Objectives. Basic Course.

    ERIC Educational Resources Information Center

    Jones, Marion

    Several intermediate performance objectives and corresponding criterion measures are listed for each of five terminal objectives presented in this curriculum guide for a basic gasoline engine mechanics course at the secondary level. (For the intermediate course guide see CE 010 946.) The materials were developed for a two semester (2 hours daily)…

  12. Basic Automotive Mechanics. Florida Vocational Program Guide.

    ERIC Educational Resources Information Center

    University of South Florida, Tampa. Dept. of Adult and Vocational Education.

    This program guide identifies primary concerns in the organization, operation, and evaluation of a basic automotive mechanics program. It is designed for local school district and community college administrators, instructors, program advisory committees, and regional coordinating councils. The guide begins with the Dictionary of Occupational…

  13. Basic mechanisms for the new millennium

    SciTech Connect

    Dressendorfer, P.V.

    1998-09-01

    This part of the Short Course will review the basic mechanisms for radiation effects in semiconductor devices. All three areas of radiation damage will be considered -- total dose, displacement effects, and single event effects. Each of these areas will be discussed in turn. First an overview and background will be provided on the historical understanding of the damage mechanism. Then there will be a discussion of recent enhancements to the understanding of those mechanisms and an up-to-date picture provided of the current state of knowledge. Next the potential impact of each of these damage mechanisms on devices in emerging technologies and how the mechanisms may be used to understand device performance will be described, with an emphasis on those likely to be of importance in the new millennium. Finally some additional thoughts will be presented on how device scaling expected into the next century may impact radiation hardness.

  14. Basicity, Catalytic and Adsorptive Properties of Hydrotalcites

    NASA Astrophysics Data System (ADS)

    Figueras, Francois

    Solid bases have numerous potential applications, not only as catalyst for the manufacture of fine chemicals, in refining and petrochemistry, but also for adsorption and anion exchange. The present processes use liquid bases, typically alcoholic potash, and require neutralisation of the reaction medium at the end of the reaction, with production of salts. The substitution of these liquid bases by solids would provide cleaner and safer processes, due to the reduction of salts, and facilitate separation of the products and recycling of the catalyst. This chapter reviews the recent ideas on the modification of the basic properties of hydrotalcites by anion exchange and on the catalytic properties of solid bases as catalysts. Many examples of successful applications are given, with emphasis to industrial processes recently presented such as isomerisation of olefins. The basic properties of hydrotalcites can also be used to carry the exchange of toxic anions, humic acids or dyes, and have driven recent developments proposing HDT as drug carriers.

  15. The Basic Properties of PPLP for HTS DC Cable

    NASA Astrophysics Data System (ADS)

    Kim, W. J.; Kim, H. J.; Cho, J. W.; Kim, S. H.

    In order to develop high temperature superconducting (HTS) DC cable, it is important to understand the cooling system, high voltage insulation and materials at cryogenic temperature. Especially, the basic properties of insulating materials must be solved for the long life, reliability and compact of system. In this paper, we will discuss mainly on the electrical and the mechanical properties of polypropylene laminated paper (PPLP) in liquid nitrogen (LN2). The polarity effect of DC and impulse voltage, the volume resistivity and the space charge distribution and frost were studied. Furthermore, the mechanical properties such as tensile strength of PPLP at LN2 (77 K) and room temperature (300 K) were studied.

  16. Mechanical Properties of Polymers.

    ERIC Educational Resources Information Center

    Aklonis, J. J.

    1981-01-01

    Mechanical properties (stress-strain relationships) of polymers are reviewed, taking into account both time and temperature factors. Topics include modulus-temperature behavior of polymers, time dependence, time-temperature correspondence, and mechanical models. (JN)

  17. The basis and basics of mechanical ventilation.

    PubMed

    Bone, R C; Eubanks, D H

    1991-06-01

    The development of mechanical ventilators and the procedures for their application began with the simple foot pump developed by Fell O'Dwyer in 1888. Ventilators have progressed through three generations, beginning with intermittent positive pressure breathing units such as the Bird and Bennett device in the 1960s. These were followed by second-generation units--represented by the Bennett MA-2 ventilator--in the 1970s, and the third-generation microprocessor-controlled units of today. During this evolutionary process clinicians recognized Types I and II respiratory failure as being indicators for mechanical ventilatory support. More recently investigators have expanded, clarified, and clinically applied the physiology of the work of breathing (described by Julius Comroe and other pioneers) to muscle fatigue, requiring ventilatory support. A ventilator classification system can help the clinician understand how ventilators function and under what conditions they may fail to operate as desired. Pressure-support ventilation is an example of how industry has responded to a clinical need--that is, to unload the work of breathing. All positive pressure ventilators generate tidal volumes by using power sources such as medical gas cylinders, air compressors, electrically driven turbines, or piston driven motors. Positive end-expiratory pressures, synchronized intermittent mandatory ventilation, pressure support ventilation, pressure release ventilation, and mandatory minute ventilation, are examples of the special functions available on modern ventilators. Modern third-generation ventilators use microprocessors to control operational functions and monitors. Because these units have incorporated the experience learned from earlier ventilators, it is imperative that clinicians understand basic ventilator operation and application in order to most effectively prescribe and assess their use. PMID:2036934

  18. Radiative Torques: Analytical Model And Basic Properties

    NASA Astrophysics Data System (ADS)

    Hoang, Thiem; Lazarian, A.

    2007-05-01

    We attempt to get a physical insight into grain alignment processes by studying basic properties of radiative torques (RATs). For this purpose we consider a simple toy model of a helical grain that reproduces well the basic features of RATs. The model grain consists of a reflecting spheroidal body with a reflecting mirror attached at an angle to it. Being very simple, the model allows analytical description of RATs that act upon it. We show a good correspondence of RATs obtained for this model and those of irregular grains calculated by DDSCAT. Our analysis of the role of different torque components for grain alignment reveals that one of the three RAT components does not affect the alignment, but induces only for grain precession. The other two components provide a generic alignment with grain long axes perpendicular to the light radiation, if the radiation dominates the grain precession, and perpendicular to magnetic field, otherwise. The latter coincides with the famous predictions of the Davis-Greenstein process, but our model does not invoke paramagnetic relaxation. In addition, we find that a substantial part of grains subjected to RATs gets aligned with low angular momentum, which testifies, that most of the grains in diffuse interstellar medium do not rotate fast, i.e. rotate with thermal or even sub-thermal velocities. For the radiation-dominated environments, we find that the alignment can take place on the time scale much shorter than the time of gaseous damping of grain rotation.

  19. Basic properties of strongly code disjoint checkers

    NASA Astrophysics Data System (ADS)

    Nicolaidis, M.

    1990-09-01

    In order to ensure total self checking, checkers have been introduced by Carter and defined by Anderson to be totally self checking: that is they are code disjoint, self testing, and fault secure. Checkers which are only code disjoint and self testing are also discussed. Strongly code disjoint checkers are not fault secure. Some researchers feel that the fault secure property is indeed necessary. This lack of agreement about the basic concepts of checkers is an important drawback in further research on self checking checkers. The various arguments used in the debate are presented. Aspects of the problem over which there is the most disagreement are highlighted. Some important points concerning strongly code disjoint checkers are discussed.

  20. Mechanical Properties of Respiratory Muscles

    PubMed Central

    Sieck, Gary C.; Ferreira, Leonardo F.; Reid, Michael B.; Mantilla, Carlos B.

    2014-01-01

    Striated respiratory muscles are necessary for lung ventilation and to maintain the patency of the upper airway. The basic structural and functional properties of respiratory muscles are similar to those of other striated muscles (both skeletal and cardiac). The sarcomere is the fundamental organizational unit of striated muscles and sarcomeric proteins underlie the passive and active mechanical properties of muscle fibers. In this respect, the functional categorization of different fiber types provides a conceptual framework to understand the physiological properties of respiratory muscles. Within the sarcomere, the interaction between the thick and thin filaments at the level of cross-bridges provides the elementary unit of force generation and contraction. Key to an understanding of the unique functional differences across muscle fiber types are differences in cross-bridge recruitment and cycling that relate to the expression of different myosin heavy chain isoforms in the thick filament. The active mechanical properties of muscle fibers are characterized by the relationship between myoplasmic Ca2+ and cross-bridge recruitment, force generation and sarcomere length (also cross-bridge recruitment), external load and shortening velocity (cross-bridge cycling rate), and cross-bridge cycling rate and ATP consumption. Passive mechanical properties are also important reflecting viscoelastic elements within sarcomeres as well as the extracellular matrix. Conditions that affect respiratory muscle performance may have a range of underlying pathophysiological causes, but their manifestations will depend on their impact on these basic elemental structures. PMID:24265238

  1. Estimating Infiltration Parameters from Basic Soil Properties

    NASA Astrophysics Data System (ADS)

    van de Genachte, G.; Mallants, D.; Ramos, J.; Deckers, J. A.; Feyen, J.

    1996-05-01

    Infiltration data were collected on two rectangular grids with 25 sampling points each. Both experimental grids were located in tropical rain forest (Guyana), the first in an Arenosol area and the second in a Ferralsol field. Four different infiltration models were evaluated based on their performance in describing the infiltration data. The model parameters were estimated using non-linear optimization techniques. The infiltration behaviour in the Ferralsol was equally well described by the equations of Philip, Green-Ampt, Kostiakov and Horton. For the Arenosol, the equations of Philip, Green-Ampt and Horton were significantly better than the Kostiakov model. Basic soil properties such as textural composition (percentage sand, silt and clay), organic carbon content, dry bulk density, porosity, initial soil water content and root content were also determined for each sampling point of the two grids. The fitted infiltration parameters were then estimated based on other soil properties using multiple regression. Prior to the regression analysis, all predictor variables were transformed to normality. The regression analysis was performed using two information levels. The first information level contained only three texture fractions for the Ferralsol (sand, silt and clay) and four fractions for the Arenosol (coarse, medium and fine sand, and silt and clay). At the first information level the regression models explained up to 60% of the variability of some of the infiltration parameters for the Ferralsol field plot. At the second information level the complete textural analysis was used (nine fractions for the Ferralsol and six for the Arenosol). At the second information level a principal components analysis (PCA) was performed prior to the regression analysis to overcome the problem of multicollinearity among the predictor variables. Regression analysis was then carried out using the orthogonally transformed soil properties as the independent variables. Results for

  2. Radiative torques: analytical model and basic properties

    NASA Astrophysics Data System (ADS)

    Lazarian, A.; Hoang, Thiem

    2007-07-01

    We attempt to get a physical insight into grain alignment processes by studying basic properties of radiative torques (RATs). For this purpose we consider a simple toy model of a helical grain that reproduces well the basic features of RATs. The model grain consists of a spheroidal body with a mirror attached at an angle to it. Being very simple, the model allows analytical description of RATs that act upon it. We show a good correspondence of RATs obtained for this model and those of irregular grains calculated by DDSCAT. Our analysis of the role of different torque components for grain alignment reveals that one of the three RAT components does not affect the alignment, but induces only for grain precession. The other two components provide a generic alignment with grain long axes perpendicular to the radiation direction, if the radiation dominates the grain precession, and perpendicular to magnetic field, otherwise. The latter coincides with the famous predictions of the Davis-Greenstein process, but our model does not invoke paramagnetic relaxation. In fact, we identify a narrow range of angles between the radiation beam and the magnetic field, for which the alignment is opposite to the Davis-Greenstein predictions. This range is likely to vanish, however, in the presence of thermal wobbling of grains. In addition, we find that a substantial part of grains subjected to RATs gets aligned with low angular momentum, which testifies that most of the grains in diffuse interstellar medium do not rotate fast, that is, rotate with thermal or even subthermal velocities. This tendency of RATs to decrease grain angular velocity as a result of the RAT alignment decreases the degree of polarization, by decreasing the degree of internal alignment, that is, the alignment of angular momentum with the grain axes. For the radiation-dominated environments, we find that the alignment can take place on the time-scale much shorter than the time of gaseous damping of grain rotation

  3. Two basic Uncertainty Relations in Quantum Mechanics

    SciTech Connect

    Angelow, Andrey

    2011-04-07

    In the present article, we discuss two types of uncertainty relations in Quantum Mechanics-multiplicative and additive inequalities for two canonical observables. The multiplicative uncertainty relation was discovered by Heisenberg. Few years later (1930) Erwin Schroedinger has generalized and made it more precise than the original. The additive uncertainty relation is based on the three independent statistical moments in Quantum Mechanics-Cov(q,p), Var(q) and Var(p). We discuss the existing symmetry of both types of relations and applicability of the additive form for the estimation of the total error.

  4. Two basic Uncertainty Relations in Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Angelow, Andrey

    2011-04-01

    In the present article, we discuss two types of uncertainty relations in Quantum Mechanics-multiplicative and additive inequalities for two canonical observables. The multiplicative uncertainty relation was discovered by Heisenberg. Few years later (1930) Erwin Schrödinger has generalized and made it more precise than the original. The additive uncertainty relation is based on the three independent statistical moments in Quantum Mechanics-Cov(q,p), Var(q) and Var(p). We discuss the existing symmetry of both types of relations and applicability of the additive form for the estimation of the total error.

  5. Basic mechanics of laminated composite plates

    NASA Technical Reports Server (NTRS)

    Nettles, Alan T.

    1994-01-01

    The mechanics of laminated composite materials is presented in a clear manner with only essential derivations included. The constitutive equations in all of their forms are developed and then summarized in a separate section. The effects of hygrothermal effects are included. The prediction of the engineering constants for a laminate are derived. Strength of laminated composites is not covered.

  6. Basic mechanism for abrupt monsoon transitions

    PubMed Central

    Levermann, Anders; Schewe, Jacob; Petoukhov, Vladimir; Held, Hermann

    2009-01-01

    Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and might act as an internal amplifier, leading to abrupt changes in response to relatively weak external perturbations. Here we present a minimal conceptual model capturing this positive feedback. The basic equations, motivated by observed relations, yield a threshold behavior, robust with respect to addition of other physical processes. Below this threshold in net radiative influx, R c, no conventional monsoon can develop; above R c, two stable regimes exist. We identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition. This dynamic similitude may be helpful in understanding past and future variations in monsoon circulation. Within the restrictions of the model, we compute R c for current monsoon systems in India, China, the Bay of Bengal, West Africa, North America, and Australia, where moisture advection is the main driver of the circulation. PMID:19858472

  7. Basic failure mechanisms in advanced composites

    NASA Technical Reports Server (NTRS)

    Mullin, J. V.; Mazzio, V. F.; Mehan, R. L.

    1972-01-01

    Failure mechanisms in carbon-epoxy composites are identified as a basis for more reliable prediction of the performance of these materials. The approach involves both the study of local fracture events in model specimens containing small groups of filaments and fractographic examination of high fiber content engineering composites. Emphasis is placed on the correlation of model specimen observations with gross fracture modes. The effects of fiber surface treatment, resin modification and fiber content are studied and acoustic emission methods are applied. Some effort is devoted to analysis of the failure process in composite/metal specimens.

  8. "Basic MR Relaxation Mechanisms & Contrast Agent Design"

    PubMed Central

    De León-Rodríguez, Luis M.; Martins, André F.; Pinho, Marco; Rofsky, Neil; Sherry, A. Dean

    2015-01-01

    The diagnostic capabilities of magnetic resonance imaging (MRI) have undergone continuous and substantial evolution by virtue of hardware and software innovations and the development and implementation of exogenous contrast media. Thirty years since the first MRI contrast agent was approved for clinical use, a reliance on MR contrast media persists largely to improve image quality with higher contrast resolution and to provide additional functional characterization of normal and abnormal tissues. Further development of MR contrast media is an important component in the quest for continued augmentation of diagnostic capabilities. In this review we will detail the many important considerations when pursuing the design and use of MR contrast media. We will offer a perspective on the importance of chemical stability, particularly kinetic stability, and how this influences one's thinking about the safety of metal-ligand based contrast agents. We will discuss the mechanisms involved in magnetic resonance relaxation in the context of probe design strategies. A brief description of currently available contrast agents will be accompanied by an in-depth discussion that highlights promising MRI contrast agents in development for future clinical and research applications. Our intention is to give a diverse audience an improved understanding of the factors involved in developing new types of safe and highly efficient MR contrast agents and, at the same time, provide an appreciation of the insights into physiology and disease that newer types of responsive agents can provide. PMID:25975847

  9. Mechanical Properties of Cells

    NASA Technical Reports Server (NTRS)

    Bradley, Robert; Becerril, Joseph; Jeevarajan, Anthony

    2007-01-01

    Many physiologic and pathologic processes alter the biomechanical properties of the tissue they affect, and these changes may be manifest at the single cell level. The normal and abnormal mechanical properties of a given cell type can be established with the aid of an atomic force microscope (AFM), nonetheless, consistency in the area of the tip has been a mayor limitation of using the AFM for quantitative measurements of mechanical properties. This project attempts to overcome this limitation by using materials with a known elastic modulus, which resembles the one of the cell, to create force-deformation curves to calculate the area of indentation by means of Hooke s Law (sigma = E(epsilon)), which states that stress (sigma) is proportional to the strain (epsilon) where the constant of proportionality, E, is called the Young s modulus, also referred as the elastic modulus. Hook s Law can be rearranged to find the area of indentation (Area= Force/ E(epsilon)), where the indentation force is defined by the means of the added mass spring calibration method.

  10. Mechanical Properties of Aerogels

    NASA Technical Reports Server (NTRS)

    Parmenter, Kelly E.; Milstein, Frederick

    1995-01-01

    Aerogels are extremely low density solids that are characterized by a high porosity and pore sizes on the order of nanometers. Their low thermal conductivity and sometimes transparent appearance make them desirable for applications such as insulation in cryogenic vessels and between double paned glass in solar architecture. An understanding of the mechanical properties of aerogels is necessary before aerogels can be used in load bearing applications. In the present study, the mechanical behavior of various types of fiber-reinforced silica aerogels was investigated with hardness, compression, tension and shear tests. Particular attention was paid to the effects of processing parameters, testing conditions, storage environment, and age on the aerogels' mechanical response. The results indicate that the addition of fibers to the aerogel matrix generally resulted in softer, weaker materials with smaller elastic moduli. Furthermore, the testing environment significantly affected compression results. Tests in ethanol show an appreciable amount of scatter, and are not consistent with results for tests in air. In fact, the compression specimens appeared to crack and begin to dissolve upon exposure to the ethanol solution. This is consistent with the inherent hydrophobic nature of these aerogels. In addition, the aging process affected the aerogels' mechanical behavior by increasing their compressive strength and elastic moduli while decreasing their strain at fracture. However, desiccation of the specimens did not appreciably affect the mechanical properties, even though it reduced the aerogel density by removing trapped moisture. Finally, tension and shear test results indicate that the shear strength of the aerogels exceeds the tensile strength. This is consistent with the response of brittle materials. Future work should concentrate on mechanical testing at cryogenic temperatures, and should involve more extensive tensile tests. Moreover, before the mechanical response

  11. Magnetic dipole discharges. I. Basic properties

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.; Teodorescu-Soare, C. T.; Ionita, C.; Schrittwieser, R.

    2013-08-15

    A simple discharge is described which uses a permanent magnet as a cold cathode and the metallic chamber wall as an anode. The magnet's equator is biased strongly negative, which produces secondary electrons due to the impact of energetic ions. The emitted electrons are highly confined by the strong dipolar magnetic field and the negative potential in the equatorial plane of the magnet. The emitted electrons ionize near the sheath and produce further electrons, which drift across field lines to the anode while the nearly unmagnetized ions are accelerated back to the magnet. A steady state discharge is maintained at neutral pressures above 10{sup −3} mbar. This is the principle of magnetron discharges, which commonly use cylindrical and planar cathodes rather than magnetic dipoles as cathodes. The discharge properties have been investigated in steady state and pulsed mode. Different magnets and geometries have been employed. The role of a background plasma has been investigated. Various types of instabilities have been observed such as sheath oscillations, current-driven turbulence, relaxation instabilities due to ionization, and high frequency oscillations created by sputtering impulses, which are described in more detail in companion papers. The discharge has also been operated in reactive gases and shown to be useful for sputtering applications.

  12. Basic properties, growth and preparation methods of group IV heterostructures

    NASA Astrophysics Data System (ADS)

    Kasper, E.

    This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum heterostructures based on group IV semiconductors. It discusses basic properties, growth and preparation methods of group IV heterostructures, including epitaxial growth processes, lattice mismatch and its implication on critical thickness and interface structure, and virtual substrates and strain relaxation.

  13. Basic mechanisms for adverse cardiovascular events associated with air pollution

    PubMed Central

    Chin, Michael T.

    2015-01-01

    Air pollution is a significant cause of cardiovascular morbidity and mortality worldwide. Although the epidemiologic association between air pollution exposures and exacerbation of cardiovascular disease is well established, the mechanisms by which these exposures promote cardiovascular disease are incompletely understood. In this review I will give an overview of the components of air pollution, an overview of the cardiovascular effects of air pollution exposure and a review of the basic mechanisms that are activated by exposure to promote cardiovascular disease. PMID:25552258

  14. Basic Gasoline Engine Mechanics. Florida Vocational Program Guide.

    ERIC Educational Resources Information Center

    University of South Florida, Tampa. Dept. of Adult and Vocational Education.

    This packet contains a program guide and Career Merit Achievement Plan (Career MAP) for the implementation of a basic gasoline engine mechanics program in Florida secondary and postsecondary schools. The program guide describes the program content and structure, provides a program description, lists job titles under the program, and includes a…

  15. Automotive Chassis; Automotive Mechanics-Basic: 9043.02.

    ERIC Educational Resources Information Center

    Dade County Public Schools, Miami, FL.

    This automotive chassis course is designed to familiarize the beginning student of the history and development of the automobile with basic concepts common to the automobile industry, and general information that is required for successful advancement in the automotive mechanics field. It is one quinmester in a series of quinmester outlines…

  16. Dimensional psychiatry: mental disorders as dysfunctions of basic learning mechanisms.

    PubMed

    Heinz, Andreas; Schlagenhauf, Florian; Beck, Anne; Wackerhagen, Carolin

    2016-08-01

    It has been questioned that the more than 300 mental disorders currently listed in international disease classification systems all have a distinct neurobiological correlate. Here, we support the idea that basic dimensions of mental dysfunctions, such as alterations in reinforcement learning, can be identified, which interact with individual vulnerability and psychosocial stress factors and, thus, contribute to syndromes of distress across traditional nosological boundaries. We further suggest that computational modeling of learning behavior can help to identify specific alterations in reinforcement-based decision-making and their associated neurobiological correlates. For example, attribution of salience to drug-related cues associated with dopamine dysfunction in addiction can increase habitual decision-making via promotion of Pavlovian-to-instrumental transfer as indicated by computational modeling of the effect of Pavlovian-conditioned stimuli (here affectively positive or alcohol-related cues) on instrumental approach and avoidance behavior. In schizophrenia, reward prediction errors can be modeled computationally and associated with functional brain activation, thus revealing reduced encoding of such learning signals in the ventral striatum and compensatory activation in the frontal cortex. With respect to negative mood states, it has been shown that both reduced functional activation of the ventral striatum elicited by reward-predicting stimuli and stress-associated activation of the hypothalamic-pituitary-adrenal axis in interaction with reduced serotonin transporter availability and increased amygdala activation by aversive cues contribute to clinical depression; altogether these observations support the notion that basic learning mechanisms, such as Pavlovian and instrumental conditioning and Pavlovian-to-instrumental transfer, represent a basic dimension of mental disorders that can be mechanistically characterized using computational modeling and

  17. Dimensional psychiatry: mental disorders as dysfunctions of basic learning mechanisms.

    PubMed

    Heinz, Andreas; Schlagenhauf, Florian; Beck, Anne; Wackerhagen, Carolin

    2016-08-01

    It has been questioned that the more than 300 mental disorders currently listed in international disease classification systems all have a distinct neurobiological correlate. Here, we support the idea that basic dimensions of mental dysfunctions, such as alterations in reinforcement learning, can be identified, which interact with individual vulnerability and psychosocial stress factors and, thus, contribute to syndromes of distress across traditional nosological boundaries. We further suggest that computational modeling of learning behavior can help to identify specific alterations in reinforcement-based decision-making and their associated neurobiological correlates. For example, attribution of salience to drug-related cues associated with dopamine dysfunction in addiction can increase habitual decision-making via promotion of Pavlovian-to-instrumental transfer as indicated by computational modeling of the effect of Pavlovian-conditioned stimuli (here affectively positive or alcohol-related cues) on instrumental approach and avoidance behavior. In schizophrenia, reward prediction errors can be modeled computationally and associated with functional brain activation, thus revealing reduced encoding of such learning signals in the ventral striatum and compensatory activation in the frontal cortex. With respect to negative mood states, it has been shown that both reduced functional activation of the ventral striatum elicited by reward-predicting stimuli and stress-associated activation of the hypothalamic-pituitary-adrenal axis in interaction with reduced serotonin transporter availability and increased amygdala activation by aversive cues contribute to clinical depression; altogether these observations support the notion that basic learning mechanisms, such as Pavlovian and instrumental conditioning and Pavlovian-to-instrumental transfer, represent a basic dimension of mental disorders that can be mechanistically characterized using computational modeling and

  18. BASIC PROPERTIES OF REFERENCE CROSSPLY CARBON-FIBER COMPOSITE

    SciTech Connect

    Corum, J.M.

    2001-01-11

    This report provides basic in-air property data and correlations-tensile, compressive, shear, tensile fatigue, and tensile creep-for a reference carbon-fiber composite being characterized as a part of the Durability of Carbon-Fiber Composites Project at Oak Ridge National Laboratory. The overall goal of the project, which is sponsored by the Department of Energy's Office of Advanced Automotive Materials and is closely coordinated with the Advanced Composites Consortium, is to develop durability-based design guidance for polymeric composites for automotive structural applications. The composite addressed here is a {+-}45{degree} crossply consisting of continuous Thornel T300 fibers in a Baydur 420 IMR urethane matrix. Basic tensile, compressive, and shear properties are tabulated for the temperature range from {minus}40 to 120 C. Fatigue response at room-temperature and 120 C are presented, and creep and creep rupture at room temperature only are reported. In all cases, two fiber orientations--0/90{degree} and {+-}45{degree}--relative to the specimen axes are addressed. The properties and correlations presented are interim in nature. They are intended as a baseline for planning a full durability test program on this reference composite.

  19. Radiative Plasmas At The Edge And Their Basic Properties

    SciTech Connect

    Morozov, D. Kh.

    2006-11-30

    Plasma radiation plays the determining role in temperature balance, equilibrium and stability of plasmas at the edge of fusion devices. The differences in properties of radiative plasmas and pure hydrogen ones are significant. The sound branch is split into two branches, i.e. fast and slow sounds. They may be destabilize by radiation and stabilized by internal relative motion of species. The basic properties of radiative plasmas are discussed in the current presentation. Radiation of multi-electron impurity ions is significant, even if the impurity concentration is small. It depends strongly on the Impurity Distribution Over Ionization States (IDOIS). One can find many interesting effects taking into account the finite relaxation time of IDOIS and thermal forces. In particular, the anomalous sound damping due to the internal friction, decompression shocks, slow thermal waves, and self-sustained thermal oscillation are discussed in the current presentation. Opacity effects also are discussed in the current presentation.

  20. 41 CFR 102-75.10 - What basic real property disposal policy governs disposal agencies?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false What basic real property disposal policy governs disposal agencies? 102-75.10 Section 102-75.10 Public Contracts and Property... PROPERTY 75-REAL PROPERTY DISPOSAL General Provisions § 102-75.10 What basic real property disposal...

  1. Basic mechanisms controlling the sweeping efficiency of propagating current sheets

    NASA Astrophysics Data System (ADS)

    Berkery, J. W.; Choueiri, E. Y.

    2006-02-01

    The basic mechanisms controlling the sweeping efficiency of propagating current sheets are investigated through experiments and analytical modelling. The sweeping efficiency of a current sheet in a parallel plate gas-fed pulsed plasma accelerator is defined as the ratio of the current sheet mass to the total available propellant mass. Permeability of neutrals through the sheet, and leakage of mass out of the sheet and into a cathode wake, decrease the sweeping efficiency. The sweeping efficiency of current sheets in argon, neon, helium and hydrogen propellants at different initial pressures was determined through measurements of sheet velocity with high speed photography and of sheet mass with laser interferometry. The mechanism that controls the sweeping efficiency of propagating current sheets was found to be an interplay of two processes: the flux of mass entering the sheet and the leakage of mass at the cathode, with the former dependent on the degree of permeability and the latter dependent on the level of ion current as determined by the ion Hall parameter.

  2. Solvation of polymers as mutual association. II. Basic thermodynamic properties

    NASA Astrophysics Data System (ADS)

    Dudowicz, Jacek; Freed, Karl F.; Douglas, Jack F.

    2013-04-01

    The theory of equilibrium solvation of polymers B by a relatively low molar mass solvent A, developed in the simplest form in Paper I, is used to explore some essential trends in basic thermodynamic properties of solvated polymer solutions, such as the equilibrium concentrations of solvated polymers AiB and free solvent molecules A, the mass distribution φ _{{AiB}}(i) of solvated clusters, the extent of solvation of the polymer Φsolv, the solvation transition lines T_{solv}(φ _{{B}}o), the specific heat CV, the osmotic second virial coefficient B2, phase stability boundaries, and the critical temperatures associated with closed loop phase diagrams. We discuss the differences between the basic thermodynamic properties of solvated polymers and those derived previously for hierarchical mutual association processes involving the association of two different species A and B into AB complexes and the subsequent polymerization of these AB complexes into linear polymeric structures. The properties of solvated polymer solutions are also compared to those for solutions of polymers in a self-associating solvent. Closed loop phase diagrams for solvated polymer solutions arise in the theory from the competition between the associative and van der Waals interactions, a behavior also typical for dispersed molecular and nanoparticle species that strongly associate with the host fluid. Our analysis of the temperature dependence of the second osmotic virial coefficient reveals that the theory must be generalized to describe the association of multiple solvent molecules with each chain monomer, and this complex extension of the present model will be developed in subsequent papers aimed at a quantitative rather than qualitative treatment of solvated polymer solutions.

  3. FMR1 Premutation: Basic Mechanisms and Clinical Involvement.

    PubMed

    Milà, Montserrat; Rodriguez-Revenga, Laia; Matilla-Dueñas, Antoni

    2016-10-01

    The wide spectrum of clinical phenotypes associated with the FMR1 premutation affect more than two million people worldwide. The clinical implications have only been recognized recently despite this disorder constitutes a relevant health problem. The present issue of The Cerebellum is focused on the "2(nd) International Conference on the FMR1 Premutation: Basic Mechanisms and Clinical Involvement" held in Sitges, Barcelona (Spain), from September 30th to October 2nd, 2015. The conference was attended by professionals from different countries in Europe, the USA, Chile, Israel, Australia, and Indonesia and covered the latest clinical and molecular findings resulting from FMR1 premutation studies. Although the pathologies associated with the FMR1 premutation are considered as rare diseases, seventy abstracts were presented. This reflects the relevance of this topic in the medical community and the growing interest among professionals from other disciplines. The major topics discussed included why and how the mRNA toxicity due to a gain of function and non-canonical RAN are responsible for disorders associated with the premutation. Several presentations addressed the impact of these mechanisms in FXTAS and FXPOI, two clinical presentations caused by the FMR1 premutation. Interestingly, a deterioration of the DNA repair machinery was first proposed as the pathogenicity cause of premutation alleles. Communications related to FXTAS and FXPOI animal models were also presented. These models facilitate studies aimed to understand disease progression and early treatment interventions. Finally, there were presentations related to psychiatric, psychological, neurological, and radiological aspects. Interesting discussion on intermediate alleles and their involvement in clinical and reproductive aspects was generated. In this regards, genetic counselling is improved by taking into account the AGG interruptions and including information about the FMR1 premutation associated

  4. Food mechanical properties and dietary ecology.

    PubMed

    Berthaume, Michael A

    2016-01-01

    Interdisciplinary research has benefitted the fields of anthropology and engineering for decades: a classic example being the application of material science to the field of feeding biomechanics. However, after decades of research, discordances have developed in how mechanical properties are defined, measured, calculated, and used due to disharmonies between and within fields. This is highlighted by "toughness," or energy release rate, the comparison of incomparable tests (i.e., the scissors and wedge tests), and the comparison of incomparable metrics (i.e., the stress and displacement-limited indices). Furthermore, while material scientists report on a myriad of mechanical properties, it is common for feeding biomechanics studies to report on just one (energy release rate) or two (energy release rate and Young's modulus), which may or may not be the most appropriate for understanding feeding mechanics. Here, I review portions of materials science important to feeding biomechanists, discussing some of the basic assumptions, tests, and measurements. Next, I provide an overview of what is mechanically important during feeding, and discuss the application of mechanical property tests to feeding biomechanics. I also explain how 1) toughness measures gathered with the scissors, wedge, razor, and/or punch and die tests on non-linearly elastic brittle materials are not mechanical properties, 2) scissors and wedge tests are not comparable and 3) the stress and displacement-limited indices are not comparable. Finally, I discuss what data gathered thus far can be best used for, and discuss the future of the field, urging researchers to challenge underlying assumptions in currently used methods to gain a better understanding between primate masticatory morphology and diet.

  5. Oscillating plasma bubbles. I. Basic properties and instabilities

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

    Plasma bubbles are created in an ambient discharge plasma. A bubble is a plasma volume of typically spherical shape, which is separated from the ambient plasma by a negatively biased grid of high transparency. Ions and electrons from the ambient plasma flow into the bubble volume. In steady state the flow of particles and currents is divergence-free, which is established by the plasma potential inside the bubble. The grid has two sheaths, one facing the ambient plasma, the other the bubble plasma. The inner sheath is observed to become unstable, causing the plasma potential in the bubble to oscillate. The instability arises from an excess of ions and a deficiency of electrons. Its frequency is in the range of the ion plasma frequency but depends on all parameters which influence the charge density in the sheath. When the grid voltage is very negative, electrons cannot enter the outer sheath, and the inner sheath becomes a virtual anode which reflects ions such that the bubble interior is empty. When an electron source is placed into the bubble it can neutralize the ions and the bubble refills. Without plasma sources or sinks the bubble plasma is extremely sensitive to perturbations by probes. Modified current-voltage characteristics of Langmuir and emissive probes are demonstrated. A sequence of papers first describes the basic steady-state properties, then the time evolution of bubbles, the effects of electron sources in bubbles, and the role of the grid and bubble geometry. The physics of plasma bubbles is important to several fields of basic plasma physics such as sheaths, sheath instabilities, diagnostic probes, electrostatic confinement, and current and space charge neutralization of beams.

  6. Biological pattern formation: from basic mechanisms to complex structures

    NASA Astrophysics Data System (ADS)

    Koch, A. J.; Meinhardt, H.

    1994-10-01

    The reliable development of highly complex organisms is an intriguing and fascinating problem. The genetic material is, as a rule, the same in each cell of an organism. How then do cells, under the influence of their common genes, produce spatial patterns? Simple models are discussed that describe the generation of patterns out of an initially nearly homogeneous state. They are based on nonlinear interactions of at least two chemicals and on their diffusion. The concepts of local autocatalysis and of long-range inhibition play a fundamental role. Numerical simulations show that the models account for many basic biological observations such as the regeneration of a pattern after excision of tissue or the production of regular (or nearly regular) arrays of organs during (or after) completion of growth. Very complex patterns can be generated in a reproducible way by hierarchical coupling of several such elementary reactions. Applications to animal coats and to the generation of polygonally shaped patterns are provided. It is further shown how to generate a strictly periodic pattern of units that themselves exhibit a complex and polar fine structure. This is illustrated by two examples: the assembly of photoreceptor cells in the eye of Drosophila and the positioning of leaves and axillary buds in a growing shoot. In both cases, the substructures have to achieve an internal polarity under the influence of some primary pattern-forming system existing in the fly's eye or in the plant. The fact that similar models can describe essential steps in organisms as distantly related as animals and plants suggests that they reveal some universal mechanisms.

  7. Biological pattern formation: from basic mechanisms to complex structures

    SciTech Connect

    Koch, A.J.; Meinhardt, H. )

    1994-10-01

    The reliable development of highly complex organisms is an intriguing and fascinating problem. The genetic material is, as a rule, the same in each cell of an organism. How then do cells, under the influence of their common genes, produce spatial patterns Simple models are discussed that describe the generation of patterns out of an initially nearly homogeneous state. They are based on nonlinear interactions of at least two chemicals and on their diffusion. The concepts of local autocatalysis and of long-range inhibition play a fundamental role. Numerical simulations show that the models account for many basic biological observations such as the regeneration of a pattern after excision of tissue or the production of regular (or nearly regular) arrays of organs during (or after) completion of growth. Very complex patterns can be generated in a reproducible way by hierarchical coupling of several such elementary reactions. Applications to animal coats and to the generation of polygonally shaped patterns are provided. It is further shown how to generate a strictly periodic pattern of units that themselves exhibit a complex and polar fine structure. This is illustrated by two examples: the assembly of photoreceptor cells in the eye of [ital Drosophila] and the positioning of leaves and axillary buds in a growing shoot. In both cases, the substructures have to achieve an internal polarity under the influence of some primary pattern-forming system existing in the fly's eye or in the plant. The fact that similar models can describe essential steps in organisms as distantly related as animals and plants suggests that they reveal some universal mechanisms.

  8. Mechanical properties of warped membranes.

    PubMed

    Košmrlj, Andrej; Nelson, David R

    2013-07-01

    We explore how a frozen background metric affects the mechanical properties of planar membranes with a shear modulus. We focus on a special class of "warped membranes" with a preferred random height profile characterized by random Gaussian variables h(q) in Fourier space with zero mean and variance <|h(q)|(2)>~q(-d(h)) and show that in the linear response regime the mechanical properties depend dramatically on the system size L for d(h)≥2. Membranes with d(h)=4 could be produced by flash polymerization of lyotropic smectic liquid crystals. Via a self-consistent screening approximation we find that the renormalized bending rigidity increases as κ(R)~L((d(h)-2)/2) for membranes of size L, while the Young and shear moduli decrease according to Y(R),μ(R)~L(-(d(h)-2)/2) resulting in a universal Poisson ratio. Numerical results show good agreement with analytically determined exponents.

  9. Basic guide to the mechanisms of antiestrogen action.

    PubMed

    MacGregor, J I; Jordan, V C

    1998-06-01

    Forty years ago, Lerner and coworkers (1958) discovered the first nonsteroidal antiestrogen and Jensen (Jensen and Jacobson, 1960) identified a target for drug action, the ER. This knowledge opened the door for the clinical development of tamoxifen which we now know provides a survival advantage in both node-positive and node-negative patients with ER-positive disease (Early Breast Cancer Trialists Collaborative Group, 1992, 1998). The drug has been studied extensively, and the results have provided an invaluable insight into possible ancillary advantages of "antiestrogens", i.e., maintenance of bone density and the prevention of coronary heart disease, and possible disadvantages, i.e., rat liver carcinogenesis and an increased risk of endometrial cancer. Most importantly, the identification of the target site-specific actions of tamoxifen caused a paradigm shift in the prospective uses of antiestrogens from a direct exploitation of the antitumor properties to the broader application as a preventative for osteoporosis, but with the beneficial side effects of preventing breast and endometrial cancer. Raloxifene, a second-generation SERM, has all the properties in the laboratory that would encourage development as a safe preventative for osteoporosis (Jordan et al., 1997). As a result, raloxifene has been evaluated in more than 11,000 postmenopausal women and found to maintain bone density with significant decreases in breast cancer incidence and no increase in endometrial thickness. Raloxifene is now available as a preventative for osteoporosis in postmenopausal women. There is every reason to believe that a multifaceted agent like raloxifene will find widespread use, and there will be continuing interest by the pharmaceutical industry in the development of new agents with even broader applications. The extensive clinical effort is augmented by past molecular innovations in the laboratory and the future promise of new discoveries. The cloning and sequencing of the

  10. The Back to Basics Curriculum as a Social Control Mechanism.

    ERIC Educational Resources Information Center

    Vickery, Tom Rusk; Smith, Cynthia G.

    Based on a review of literature by proponents and opponents of the back to basics movements, the authors contend that the movement will contribute to the continued existence of a stratified society in which the school reproduces existing power relationships. A summary of the literature of proponents presents varying ideas of what constitutes…

  11. Woven TPS Mechanical Property Evaluation

    NASA Technical Reports Server (NTRS)

    Gonzales, Gregory Lewis; Kao, David Jan-Woei; Stackpoole, Margaret M.

    2013-01-01

    Woven Thermal Protection Systems (WTPS) is a relatively new program funded by the Office of the Chief Technologist (OCT). The WTPS approach to producing TPS architectures uses precisely engineered 3-D weaving techniques that allow tailoring material characteristics needed to meet specific mission requirements. A series of mechanical tests were performed to evaluate performance of different weave types, and get a better understanding of failure modes expected in these three-dimensional architectures. These properties will aid in material down selection and guide selection of the appropriate WTPS for a potential mission.

  12. Mechanical Property Data for Fiberboard

    SciTech Connect

    WILLIAM, daugherty

    2004-12-14

    The 9975 shipping package incorporates a cane fiberboard overpack for thermal insulation and impact resistance. Mechanical properties (tensile and compressive behavior) have been measured on cane fiberboard and a similar wood-based product following short-term conditioning in several temperature/humidity environments. Both products show similar trends, and vary in behavior with material orientation, temperature and humidity. A memory effect is also seen in that original strength values are only partially recovered following exposure to a degrading environment and return to ambient conditions.

  13. Information as a basic property of the universe.

    PubMed

    Stonier, T

    1996-01-01

    A theory is proposed which considers information to be a basic property of the universe the way matter and energy are. Operationally--just as energy is defined in terms of its capacity to perform work--so is information defined in terms of its capacity to organize a system. Pure energy can perform no 'useful' (entropy reducing) work without a concomitant input of information. Conversely, all expenditures of energy lead to a reorganization of the universe, hence to a change in its information status. Energy and information are interconvertible; physicists have been able to ignore the information parameter principally for two major reasons. First, historically, just as there was no need to define energy prior to the advent of increasingly complex, powered machinery and cannons (Galileo was a military engineer), so was there no need until the 20th Century to define information. It was the telephone engineers who first preoccupied themselves with developing a theory of information. The second reason is that physicists invented accounting devices such as potential energy and entropy to explain the apparent disappearance of energy yet maintain the law of the conservation of energy. The proposed theory would consider that what is conserved is the sum of information and energy. The mathematical relationship between information and entropy is provided by the equation: I = (Io)e-S/k while the conversion of energy into information involves the relationship: 1 J/degree K = 10(23) bits (approximately) Acceptance of the theory would require paradigm shifts in a number of interrelated areas.

  14. Mechanical Properties of Silicon Nanowires.

    PubMed

    Sohn, Young-Soo; Park, Jinsung; Yoon, Gwonchan; Song, Jiseok; Jee, Sang-Won; Lee, Jung-Ho; Na, Sungsoo; Kwon, Taeyun; Eom, Kilho

    2009-10-27

    Nanowires have been taken much attention as a nanoscale building block, which can perform the excellent mechanical function as an electromechanical device. Here, we have performed atomic force microscope (AFM)-based nanoindentation experiments of silicon nanowires in order to investigate the mechanical properties of silicon nanowires. It is shown that stiffness of nanowires is well described by Hertz theory and that elastic modulus of silicon nanowires with various diameters from ~100 to ~600 nm is close to that of bulk silicon. This implies that the elastic modulus of silicon nanowires is independent of their diameters if the diameter is larger than 100 nm. This supports that finite size effect (due to surface effect) does not play a role on elastic behavior of silicon nanowires with diameter of >100 nm.

  15. Mechanical Properties of Silicon Nanowires

    PubMed Central

    2010-01-01

    Nanowires have been taken much attention as a nanoscale building block, which can perform the excellent mechanical function as an electromechanical device. Here, we have performed atomic force microscope (AFM)-based nanoindentation experiments of silicon nanowires in order to investigate the mechanical properties of silicon nanowires. It is shown that stiffness of nanowires is well described by Hertz theory and that elastic modulus of silicon nanowires with various diameters from ~100 to ~600 nm is close to that of bulk silicon. This implies that the elastic modulus of silicon nanowires is independent of their diameters if the diameter is larger than 100 nm. This supports that finite size effect (due to surface effect) does not play a role on elastic behavior of silicon nanowires with diameter of >100 nm. PMID:20652130

  16. Mechanical Properties of Niobium Cavities

    SciTech Connect

    Ciovati, Gianluigi; Dhakal, Pashupati; Matalevich, Joseph R.; Myneni, Ganapati Rao

    2015-09-01

    The mechanical stability of bulk Nb cavity is an important aspect to be considered in relation to cavity material, geometry and treatments. Mechanical properties of Nb are typically obtained from uniaxial tensile tests of small samples. In this contribution we report the results of measurements of the resonant frequency and local strain along the contour of single-cell cavities made of ingot and fine-grain Nb of different purity subjected to increasing uniform differential pressure, up to 6 atm. Measurements have been done on cavities subjected to different heat treatments. Good agreement between finite element analysis simulations and experimental data in the elastic regime was obtained with a single set of values of Young’s modulus and Poisson’s ratio. The experimental results indicate that the yield strength of medium-purity ingot Nb cavities is higher than that of fine-grain, high-purity Nb.

  17. Mechanical properties of metal dihydrides

    DOE PAGES

    Schultz, Peter A.; Snow, Clark S.

    2016-02-04

    First-principles calculations are used to characterize the bulk elastic properties of cubic and tetragonal phase metal dihydrides,more » $$\\text{M}{{\\text{H}}_{2}}$$ {$$\\text{M}$$ = Sc, Y, Ti, Zr, Hf, lanthanides} to gain insight into the mechanical properties that govern the aging behavior of rare-earth di-tritides as the constituent 3H, tritium, decays into 3He. As tritium decays, helium is inserted in the lattice, the helium migrates and collects into bubbles, that then can ultimately create sufficient internal pressure to rupture the material. The elastic properties of the materials are needed to construct effective mesoscale models of the process of bubble growth and fracture. Dihydrides of the scandium column and most of the rare-earths crystalize into a cubic phase, while dihydrides from the next column, Ti, Zr, and Hf, distort instead into the tetragonal phase, indicating incipient instabilities in the phase and potentially significant changes in elastic properties. We report the computed elastic properties of these dihydrides, and also investigate the off-stoichiometric phases as He or vacancies accumulate. As helium builds up in the cubic phase, the shear moduli greatly soften, converting to the tetragonal phase. Conversely, the tetragonal phases convert very quickly to cubic with the removal of H from the lattice, while the cubic phases show little change with removal of H. Finally, the source and magnitude of the numerical and physical uncertainties in the modeling are analyzed and quantified to establish the level of confidence that can be placed in the computational results, and this quantified confidence is used to justify using the results to augment and even supplant experimental measurements.« less

  18. Mechanical properties of metal dihydrides

    NASA Astrophysics Data System (ADS)

    Schultz, Peter A.; Snow, Clark S.

    2016-03-01

    First-principles calculations are used to characterize the bulk elastic properties of cubic and tetragonal phase metal dihydrides, \\text{M}{{\\text{H}}2} {\\text{M}   =  Sc, Y, Ti, Zr, Hf, lanthanides} to gain insight into the mechanical properties that govern the aging behavior of rare-earth di-tritides as the constituent 3H, tritium, decays into 3He. As tritium decays, helium is inserted in the lattice, the helium migrates and collects into bubbles, that then can ultimately create sufficient internal pressure to rupture the material. The elastic properties of the materials are needed to construct effective mesoscale models of the process of bubble growth and fracture. Dihydrides of the scandium column and most of the rare-earths crystalize into a cubic phase, while dihydrides from the next column, Ti, Zr, and Hf, distort instead into the tetragonal phase, indicating incipient instabilities in the phase and potentially significant changes in elastic properties. We report the computed elastic properties of these dihydrides, and also investigate the off-stoichiometric phases as He or vacancies accumulate. As helium builds up in the cubic phase, the shear moduli greatly soften, converting to the tetragonal phase. Conversely, the tetragonal phases convert very quickly to cubic with the removal of H from the lattice, while the cubic phases show little change with removal of H. The source and magnitude of the numerical and physical uncertainties in the modeling are analyzed and quantified to establish the level of confidence that can be placed in the computational results, and this quantified confidence is used to justify using the results to augment and even supplant experimental measurements.

  19. Multidimensional Generalized Functions in Aeroacoustics and Fluid Mechanics. Part 1; Basic Concepts and Operations

    NASA Technical Reports Server (NTRS)

    Farassat, Fereidoun; Myers, Michael K.

    2011-01-01

    This paper is the first part of a three part tutorial on multidimensional generalized functions (GFs) and their applications in aeroacoustics and fluid mechanics. The subject is highly fascinating and essential in many areas of science and, in particular, wave propagation problems. In this tutorial, we strive to present rigorously and clearly the basic concepts and the tools that are needed to use GFs in applications effectively and with ease. We give many examples to help the readers in understanding the mathematical ideas presented here. The first part of the tutorial is on the basic concepts of GFs. Here we define GFs, their properties and some common operations on them. We define the important concept of generalized differentiation and then give some interesting elementary and advanced examples on Green's functions and wave propagation problems. Here, the analytic power of GFs in applications is demonstrated with ease and elegance. Part 2 of this tutorial is on the diverse applications of generalized derivatives (GDs). Part 3 is on generalized Fourier transformations and some more advanced topics. One goal of writing this tutorial is to convince readers that, because of their powerful operational properties, GFs are absolutely essential and useful in engineering and physics, particularly in aeroacoustics and fluid mechanics.

  20. Switchable antimicrobial and antifouling hydrogels with enhanced mechanical properties.

    PubMed

    Cao, Bin; Tang, Qiong; Li, Linlin; Humble, Jayson; Wu, Haiyan; Liu, Lingyun; Cheng, Gang

    2013-08-01

    New switchable hydrogels are developed. Under acidic conditions, hydrogels undergo self-cyclization and can catch and kill bacteria. Under neutral/basic conditions, hydrogels undergo ring-opening and can release killed bacterial cells and resist protein adsorption and bacterial attachment. Smart hydrogels also show a dramatically improved mechanical property, which is highly desired for biomedical applications.

  1. Mechanical properties of electron vortices

    NASA Astrophysics Data System (ADS)

    Lloyd, S. M.; Babiker, M.; Yuan, J.

    2013-09-01

    It is shown how the quantum mechanical mass flux and the electromagnetic fields of an electron Bessel vortex mode generate its intrinsic linear momentum and angular momentum properties. Although the corresponding volume density vectors due to the mass flux contain transverse vector components, their volume integrals are shown by explicit analysis to yield null results. The total linear and angular momenta are thus purely axial vectors. There are additional contributions associated with the vortex electric and magnetic fields and these too are shown to be purely axial vectors. Order of magnitude estimates are made in the context of a suggested experiment on the rotation of an optically levitated nanoparticle subject to an electron vortex.

  2. Mechanical Properties of Nanocrystal Supercrystals

    SciTech Connect

    Tam, Enrico; Podsiadlo, Paul; Shevchenko, Elena; Ogletree, D. Frank; Delplancke-Ogletree, Marie-Paule; Ashby, Paul D.

    2009-12-30

    Colloidal nanocrystals attract significant interest due to their potential applications in electronic, magnetic, and optical devices. Nanocrystal supercrystals (NCSCs) are particularly appealing for their well ordered structure and homogeneity. The interactions between organic ligands that passivate the inorganic nanocrystal cores critically influence their self-organization into supercrystals, By investigating the mechanical properties of supercrystals, we can directly characterize the particle-particle interactions in a well-defined geometry, and gain insight into both the self-assembly process and the potential applications of nanocrystal supercrystals. Here we report nanoindentation studies of well ordered lead-sulfide (Pbs) nanocrystal supercrystals. Their modulus and hardness were found to be similar to soft polymers at 1.7 GPa and 70 MPa respectively and the fractures toughness was 39 KPa/m1/2, revealing the extremely brittle nature of these materials.

  3. Mechanical Properties of Primary Cilia

    NASA Astrophysics Data System (ADS)

    Battle, Christopher; Schmidt, Christoph F.

    2013-03-01

    Recent studies have shown that the primary cilium, long thought to be a vestigial cellular appendage with no function, is involved in a multitude of sensory functions. One example, interesting from both a biophysical and medical standpoint, is the primary cilium of kidney epithelial cells, which acts as a mechanosensitive flow sensor. Genetic defects in ciliary function can cause, e.g., polycystic kidney disease (PKD). The material properties of these non-motile, microtubule-based 9 +0 cilia, and the way they are anchored to the cell cytoskeleton, are important to know if one wants to understand the mechano-electrochemical response of these cells, which is mediated by their cilia. We have probed the mechanical properties, boundary conditions, and dynamics of the cilia of MDCK cells using optical traps and DIC/fluorescence microscopy. We found evidence for both elastic relaxation of the cilia themselves after bending and for compliance in the intracellular anchoring structures. Angular and positional fluctuations of the cilia reflect both thermal excitations and cellular driving forces.

  4. [Basic mechanisms: structure, function and metabolism of plasma lipoproteins].

    PubMed

    Errico, Teresa L; Chen, Xiangyu; Martin Campos, Jesús M; Julve, Josep; Escolà-Gil, Joan Carles; Blanco-Vaca, Francisco

    2013-01-01

    The aim of this work is to present basic information on the lipoprotein physiology. The protein fraction of lipoproteins consists of several apolipoproteins and enzymes whose functions are lipid transport and metabolism. Classification of lipoproteins is based on their density. Chylomicrons, VLDL, IDL, LDL and HDL can be isolated by ultracentrifugation. Both chylomicrons- and VLDL-triglycerides are transported from the intestine and liver, respectively, to the peripheral tissues. The metabolism of VLDL originates IDL and LDL. LDL is the main transporter of cholesterol to extrahepatic tissues. HDL mobilizes cholesterol from peripheral tissues to the liver where it is secreted to bile as free cholesterol or bile salts, a process termed reverse cholesterol transport. Lipoprotein metabolism can be regulated by nuclear receptors that regulate the expression of genes involved in triglyceride and apolipoprotein metabolism. PMID:23769508

  5. [Basic mechanisms: structure, function and metabolism of plasma lipoproteins].

    PubMed

    Errico, Teresa L; Chen, Xiangyu; Martin Campos, Jesús M; Julve, Josep; Escolà-Gil, Joan Carles; Blanco-Vaca, Francisco

    2013-01-01

    The aim of this work is to present basic information on the lipoprotein physiology. The protein fraction of lipoproteins consists of several apolipoproteins and enzymes whose functions are lipid transport and metabolism. Classification of lipoproteins is based on their density. Chylomicrons, VLDL, IDL, LDL and HDL can be isolated by ultracentrifugation. Both chylomicrons- and VLDL-triglycerides are transported from the intestine and liver, respectively, to the peripheral tissues. The metabolism of VLDL originates IDL and LDL. LDL is the main transporter of cholesterol to extrahepatic tissues. HDL mobilizes cholesterol from peripheral tissues to the liver where it is secreted to bile as free cholesterol or bile salts, a process termed reverse cholesterol transport. Lipoprotein metabolism can be regulated by nuclear receptors that regulate the expression of genes involved in triglyceride and apolipoprotein metabolism.

  6. Basics of mechanical ventilation for dogs and cats.

    PubMed

    Hopper, Kate; Powell, Lisa L

    2013-07-01

    Respiratory failure may occur due to hypoventilation or hypoxemia. Regardless of the cause, emergent anesthesia and intubation, accompanied by positive pressure ventilation, may be necessary and life saving. Long-term mechanical ventilation requires some specialized equipment and knowledge; however, short-term ventilation can be accomplished without the use of an intensive care unit ventilator, and can provide oxygen supplementation and carbon dioxide removal in critical patients. PMID:23747268

  7. 41 CFR 102-75.10 - What basic real property disposal policy governs disposal agencies?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 41 Public Contracts and Property Management 3 2011-01-01 2011-01-01 false What basic real property disposal policy governs disposal agencies? 102-75.10 Section 102-75.10 Public Contracts and Property Management Federal Property Management Regulations System (Continued) FEDERAL MANAGEMENT REGULATION...

  8. Reversible atomic processes as basic mechanisms of the glass transition

    PubMed Central

    Ye, Feng; Sprengel, Wolfgang; Wunderlich, Rainer K.; Fecht, Hans-Jörg; Schaefer, Hans-Eckhardt

    2007-01-01

    Reversible formation and disappearance of vacant spaces (vacancy-type defects) in bulk Zr57Cu15.4Ni12.6Nb5Al10 glass are directly evidenced by high-resolution, time-differential dilatometry studies. The vacancy kinetics are strongly temperature-dependent, with an effective migration enthalpy of HVM = 3.34 eV. This may explain the strong temperature dependence of glass properties such as viscosity. The results presented here are of general importance for understanding amorphous condensed matter and biomaterials and for the technical development of amorphous steels. PMID:17664428

  9. The Elusive Memristor: Properties of Basic Electrical Circuits

    ERIC Educational Resources Information Center

    Joglekar, Yogesh N.; Wolf, Stephen J.

    2009-01-01

    We present an introduction to and a tutorial on the properties of the recently discovered ideal circuit element, a memristor. By definition, a memristor M relates the charge "q" and the magnetic flux [phi] in a circuit and complements a resistor R, a capacitor C and an inductor L as an ingredient of ideal electrical circuits. The properties of…

  10. Intrahepatic Cholangiocarcinoma Progression: Prognostic Factors and Basic Mechanisms

    PubMed Central

    Sirica, Alphonse E.; Dumur, Catherine I.; Campbell, Deanna J. W.; Almenara, Jorge A.; Ogunwobi, Olorunseun O.; Dewitt, Jennifer L.

    2013-01-01

    In this review, we will examine various molecular biomarkers for their potential to serve as independent prognostic factors for predicting survival outcome in postoperative patients with progressive intrahepatic cholangiocarcinoma. Specific rodent models of intrahepatic cholangiocarcinoma that mimic relevant cellular, molecular, and clinical features of the human disease are also described, not only in terms of their usefulness in identifying molecular pathways and mechanisms linked to cholangiocarcinoma development and progression, but also for their potential value as preclinical platforms for suggesting and testing novel molecular strategies for cholangiocarcinoma therapy. Last, recent studies aimed at addressing the role of desmoplastic stroma in promoting intrahepatic cholangiocarcinoma progression are highlighted in an effort to underline the potential value of targeting tumor stromal components together with that of cholangiocarcinoma cells as a novel therapeutic option for this devastating cancer. PMID:19896103

  11. Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications.

    PubMed

    Lei, Xin Gen; Zhu, Jian-Hong; Cheng, Wen-Hsing; Bao, Yongping; Ho, Ye-Shih; Reddi, Amit R; Holmgren, Arne; Arnér, Elias S J

    2016-01-01

    Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

  12. Thermoelastic waves and ratcheting - basic mechanism of global tectonics

    NASA Astrophysics Data System (ADS)

    Kalenda, Pavel; Ostřihanský, Lubor; Wandrol, Ivo; Frydrýšek, Karel; Kopf, Tomáš; Neumann, Libor

    2013-04-01

    The deformation measurement of rock mass in the depth and mathematical modelling solved the old question of Wegeneŕs theory "What is the main engine for the lithosphere movement?". The solar energy, which reaches the Earth, is two orders higher than the energy of all earthquakes and volcanoes. Only a small part of the solar energy is accumulated in the rocks and the thermal wave created by the solar irradiation penetrates the subsurface layers. The thermal expansions of rocks give rise to excitation of the thermoelastic waves, which are observable in depths as well as in the whole lithosphere plate. The thermoelastic waves with diurnal and annual periods are well observable. The limit cases were modeled by the Simulation-Based Reliability Assessment (SBRA) method (probabilistic Monte Carlo approach). The upper limit corresponds with slow slip events, tremors, creep or earthquakes, the lower limit corresponds with opening of cracks and faults, which can be filled by ratchets. Such mechanism leads to the non-reversible expansions of rocks and spreading of the ocean floor.

  13. Basic mechanisms leading to focal emphysema in coal workers' pneumoconiosis

    SciTech Connect

    Rom, W.N. )

    1990-10-01

    Coal miners develop focal emphysema characterized by dilatation of second- and third-order respiratory bronchioles with coal mine dust-laden macrophages infiltrating the wall. A reticulin network with small amounts of collagen and atrophy of smooth muscle occurs. To evaluate the mechanisms of lung injury associated with this lesion, 17 long-term non- or ex-smoking West Virginia underground coal miners underwent bronchoalveolar lavage (BAL) and were compared to healthy nonsmoker and smoker controls. The coal miners had evidence of an alveolar macrophage-neutrophil alveolitis with a significant increase in neutrophils/microliter of epithelial lining fluid and an increased gallium lung scan index (206 +/- 26 units). Alveolar macrophages lavaged from coal miners spontaneously released exaggerated amounts of superoxide anion and hydrogen peroxide in vitro compared to nonsmoking controls. Coal workers had significantly elevated levels of neutrophil elastase in BAL fluid complexed with alpha 1-antitrypsin (P less than 0.01) and normal levels of alpha 1-antitrypsin. An accumulation of activated, dust-laden inflammatory cells with increased release of oxidants and elastase may contribute to the development of focal emphysema identified at postmortem in miners with coal workers' pneumoconiosis.

  14. Basic MR relaxation mechanisms and contrast agent design.

    PubMed

    De León-Rodríguez, Luis M; Martins, André F; Pinho, Marco C; Rofsky, Neil M; Sherry, A Dean

    2015-09-01

    The diagnostic capabilities of magnetic resonance imaging (MRI) have undergone continuous and substantial evolution by virtue of hardware and software innovations and the development and implementation of exogenous contrast media. Thirty years since the first MRI contrast agent was approved for clinical use, a reliance on MR contrast media persists, largely to improve image quality with higher contrast resolution and to provide additional functional characterization of normal and abnormal tissues. Further development of MR contrast media is an important component in the quest for continued augmentation of diagnostic capabilities. In this review we detail the many important considerations when pursuing the design and use of MR contrast media. We offer a perspective on the importance of chemical stability, particularly kinetic stability, and how this influences one's thinking about the safety of metal-ligand-based contrast agents. We discuss the mechanisms involved in MR relaxation in the context of probe design strategies. A brief description of currently available contrast agents is accompanied by an in-depth discussion that highlights promising MRI contrast agents in the development of future clinical and research applications. Our intention is to give a diverse audience an improved understanding of the factors involved in developing new types of safe and highly efficient MR contrast agents and, at the same time, provide an appreciation of the insights into physiology and disease that newer types of responsive agents can provide.

  15. [Epidemiology and basic pathogenetic mechanisms of environmental and iatrogenic diseases].

    PubMed

    Neumayr, A

    1983-09-01

    In the first part environmental diseases by air pollution, water contamination and dietary factors are discussed. The important role of the combustion of coal and petrol and the increasing confrontation with carcinogenic substances, especially with those originated by smoking of tobacco are stressed and underlined by epidemiologic dates. Other epidemiologic evidences are mentioned concerning the development of cardiovascular diseases, neoplastic diseases of the colon or liver diseases by dietetic factors. In the second part epidemiologic facts of drug induced reactions and iatrogenic cases of death in hospitalized and out-patients are reported. The main responsible pathogenetic factors for such events, prevailing in elder persons, are seen in the reduced hepatic metabolic capacity, the decreasing tubular or glomerular function of the kidneys and above all the different and often unpredictable drug interactions. The most important pathogenetic mechanisms for drug interactions are changes of drug binding to albumin or competitive disturbance of renal excretion and particularly alterations of the biotransformation processes as enzyme induction or enzyme inhibition. The clinical relevance of these theoretical considerations is demonstrated by some practical examples referring to the importance of a solid knowledge of the many possible interactions in drug therapy especially in elder patients.

  16. Stimulating immune responses to fight cancer: Basic biology and mechanisms.

    PubMed

    O'Byrne, Kenneth

    2015-04-01

    Chronic inflammation is now recognized as a major cause of malignant disease. In concert with various mechanisms (including DNA instability), hypoxia and activation of inflammatory bioactive lipid pathways and pro-inflammatory cytokines open the doorway to malignant transformation and proliferation, angiogenesis, and metastasis in many cancers. A balance between stimulatory and inhibitory signals regulates the immune response to cancer. These include inhibitory checkpoints that modulate the extent and duration of the immune response and may be activated by tumor cells. This contributes to immune resistance, especially against tumor antigen-specific T-cells. Targeting these checkpoints is an evolving approach to cancer immunotherapy, designed to foster an immune response. The current focus of these trials is on the programmed cell death protein 1 (PD-1) receptor and its ligands (PD-L1, PD-L2) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4). Researchers have developed anti-PD-1 and anti-PDL-1 antibodies that interfere with the ligands and receptor and allow the tumor cell to be recognized and attacked by tumor-infiltrating T-cells. These are currently being studied in lung cancer. Likewise, CTLA-4 inhibitors, which have had success treating advanced melanoma, are being studied in lung cancer with encouraging results.

  17. The elusive memristor: properties of basic electrical circuits

    NASA Astrophysics Data System (ADS)

    Joglekar, Yogesh N.; Wolf, Stephen J.

    2009-07-01

    We present an introduction to and a tutorial on the properties of the recently discovered ideal circuit element, a memristor. By definition, a memristor M relates the charge q and the magnetic flux phi in a circuit and complements a resistor R, a capacitor C and an inductor L as an ingredient of ideal electrical circuits. The properties of these three elements and their circuits are a part of the standard curricula. The existence of the memristor as the fourth ideal circuit element was predicted in 1971 based on symmetry arguments, but was clearly experimentally demonstrated just last year. We present the properties of a single memristor, memristors in series and parallel, as well as ideal memristor-capacitor (MC), memristor-inductor (ML) and memristor-capacitor-inductor (MCL) circuits. We find that the memristor has hysteretic current-voltage characteristics. We show that the ideal MC (ML) circuit undergoes non-exponential charge (current) decay with two time scales and that by switching the polarity of the capacitor, an ideal MCL circuit can be tuned from overdamped to underdamped. We present simple models which show that these unusual properties are closely related to the memristor's internal dynamics. This tutorial complements the pedagogy of ideal circuit elements (R, C and L) and the properties of their circuits, and is aimed at undergraduate physics and electrical engineering students.

  18. Cryogenic compressive properties of basic epoxy resin systems

    SciTech Connect

    Markley, F.W.; Hoffman, J.A.; Muniz, D.P.

    1985-09-01

    The compressive properties of short cylindrical samples of many different epoxy resin systems have been measured at ambient temperature and at 77/sup 0/K. These are pure resin systems of known chemistry, without the inorganic fillers or fibrous reinforcements needed in final cryogenic systems. Of course, chemically incorporated modifiers such as flexibilizing resins have been included. This data should make possible inferences about cryogenic properties from molecular structures and provide specific data useful to formulators and end users. Measurements on some other plastics such as PTFE, Polyimides, and UHMWPE have been made for comparison purposes.

  19. Enhancement of mechanical properties of 123 superconductors

    DOEpatents

    Balachandran, U.

    1995-04-25

    A composition and method are disclosed of preparing YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} superconductor. Addition of tin oxide containing compounds to YBCO superconductors results in substantial improvement of fracture toughness and other mechanical properties without affect on T{sub c}. About 5-20% additions give rise to substantially improved mechanical properties.

  20. Enhancement of mechanical properties of 123 superconductors

    DOEpatents

    Balachandran, Uthamalingam

    1995-01-01

    A composition and method of preparing YBa.sub.2 Cu.sub.3 O.sub.7-x superconductor. Addition of tin oxide containing compounds to YBCO superconductors results in substantial improvement of fracture toughness and other mechanical properties without affect on T.sub.c. About 5-20% additions give rise to substantially improved mechanical properties.

  1. Magnetic antenna excitation of whistler modes. I. Basic properties

    SciTech Connect

    Urrutia, J. M.; Stenzel, R. L.

    2014-12-15

    Properties of magnetic loop antennas for exciting electron whistler modes have been investigated in a large laboratory plasma. The parameter regime is that of large plasma frequency compared to the cyclotron frequency and signal frequency below half the cyclotron frequency. The antenna diameter is smaller than the wavelength. Different directions of the loop antenna relative to the background magnetic field have been measured for small amplitude waves. The differences in the topology of the wave magnetic field are shown from measurements of the three field components in three spatial directions. The helicity of the wave magnetic field and of the hodogram of the magnetic vector in space and time are clarified. The superposition of wave fields is used to investigate the properties of two antennas for small amplitude waves. Standing whistler waves are produced by propagating two wave packets in opposite directions. Directional radiation is obtained with two phased loops separated by a quarter wavelength. Rotating antenna fields, produced with phased orthogonal loops at the same location, do not produce directionality. The concept of superposition is extended in a Paper II to generate antenna arrays for whistlers. These produce nearly plane waves, whose propagation angle can be varied by the phase shifting the currents in the array elements. Focusing of whistlers is possible. These results are important for designing antennas on spacecraft or diagnosing and heating of laboratory plasmas.

  2. [A study of mechanical properties of orthodontic wires in tension].

    PubMed

    Konstantellos, B; Lagoudakis, M; Toutountzakis, N

    1990-12-01

    Orthodontic forces are applied to the teeth basically by means of different types of orthodontic wires. Knowledge of the mechanical properties of such wires are very helpful to the clinician in design and application of optimal force systems during orthodontic treatment. The basic mechanical properties were studied for 17 types of orthodontic wires (all rectangular and of the same size), in tension. Modulus of elasticity (E), yield strength (YS) and maximum elastic strain (Springback) (YS/E) were calculated for each type of wires. Stainless steel wires have demonstrated higher modulus of elasticity (and yield strength) in comparison with wires of nickel-titanium and beta titanium alloys. B-titanium wires showed higher modulus of elasticity than nickel-titanium ones. In addition stainless steel wires were found to have higher values for springback than cobalt-chromium ones and lower values (for the same variable) than nickel-titanium and B-titanium wires. PMID:2129597

  3. Transit time instabilities in an inverted fireball. I. Basic properties

    SciTech Connect

    Stenzel, R. L.; Gruenwald, J.; Fonda, B.; Ionita, C.; Schrittwieser, R.

    2011-01-15

    A new fireball configuration has been developed which produces vircator-like instabilities. Electrons are injected through a transparent anode into a spherical plasma volume. Strong high-frequency oscillations with period corresponding to the electron transit time through the sphere are observed. The frequency is below the electron plasma frequency, hence does not involve plasma eigenmodes. The sphere does not support electromagnetic eigenmodes at the instability frequency. However, the rf oscillations on the gridded anode create electron bunches which reinforce the grid oscillation after one transit time or rf period, which leads to an absolute instability. Various properties of the instability are demonstrated and differences to the sheath-plasma instability are pointed out, one of which is a relatively high conversion efficiency from dc to rf power. Nonlinear effects are described in a companion paper [R. L. Stenzel et al., Phys. Plasmas 18, 012105 (2011)].

  4. Transit time instabilities in an inverted fireball. I. Basic properties

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Gruenwald, J.; Fonda, B.; Ionita, C.; Schrittwieser, R.

    2011-01-01

    A new fireball configuration has been developed which produces vircator-like instabilities. Electrons are injected through a transparent anode into a spherical plasma volume. Strong high-frequency oscillations with period corresponding to the electron transit time through the sphere are observed. The frequency is below the electron plasma frequency, hence does not involve plasma eigenmodes. The sphere does not support electromagnetic eigenmodes at the instability frequency. However, the rf oscillations on the gridded anode create electron bunches which reinforce the grid oscillation after one transit time or rf period, which leads to an absolute instability. Various properties of the instability are demonstrated and differences to the sheath-plasma instability are pointed out, one of which is a relatively high conversion efficiency from dc to rf power. Nonlinear effects are described in a companion paper [R. L. Stenzel et al., Phys. Plasmas 18, 012105 (2011)].

  5. A homogeneous sample of binary galaxies: Basic observational properties

    NASA Technical Reports Server (NTRS)

    Karachentsev, I. D.

    1990-01-01

    A survey of optical characteristics for 585 binary systems, satisfying a condition of apparent isolation on the sky, is presented. Influences of various selection effects distorting the average parameters of the sample are noted. The pair components display mutual similarity over all the global properties: luminosity, diameter, morphological type, mass-to-luminosity ratio, angular momentum etc., which is not due only to selection effects. The observed correlations must be caused by common origin of pair members. Some features (nuclear activity, color index) could acquire similarity during synchronous evolution of double galaxies. Despite the observed isolation, the sample of double systems is seriously contaminated by accidental pairs, and also by members of groups and clusters. After removing false pairs estimates of orbital mass-to-luminosity ratio range from 0 to 30 f(solar), with the mean value (7.8 plus or minus 0.7) f(solar). Binary galaxies possess nearly circular orbits with a typical eccentrity e = 0.25, probably resulting from evolutionary selection driven by component mergers under dynamical friction. The double-galaxy population with space abundance 0.12 plus or minus 0.02 and characteristic merger timescale 0.2 H(exp -1) may significantly influence the rate of dynamical evolution of galaxies.

  6. Mechanical properties of C-5 epimerized alginates.

    PubMed

    Mørch, Y A; Holtan, S; Donati, I; Strand, B L; Skjåk-Braek, G

    2008-09-01

    There is an increased need for alginate materials with both enhanced and controllable mechanical properties in the fields of food, pharmaceutical and specialty applications. In the present work, well-characterized algal polymers and mannuronan were enzymatically modified using C-5 epimerases converting mannuronic acid residues to guluronic acid in the polymer chain. Composition and sequential structure of controls and epimerized alginates were analyzed by (1)H NMR spectroscopy. Mechanical properties of Ca-alginate gels were further examined giving Young's modulus, syneresis, rupture strength, and elasticity of the gels. Both mechanical strength and elasticity of hydrogels could be improved and manipulated by epimerization. In particular, alternating sequences were found to play an important role for the final mechanical properties of alginate gels, and interestingly, a pure polyalternating sample resulted in gels with extremely high syneresis and rupture strength. In conclusion, enzymatic modification was shown to be a valuable tool in modifying the mechanical properties of alginates in a highly specific manner.

  7. Mechanical properties of cells and ageing.

    PubMed

    Starodubtseva, Maria N

    2011-01-01

    Mechanical properties are fundamental properties of the cells and tissues of living organisms. The mechanical properties of a single cell as a biocomposite are determined by the interdependent combination of cellular components mechanical properties. Quantitative estimate of the cell mechanical properties depends on a cell state, method of measurement, and used theoretical model. Predominant tendency for the majority of cells with ageing is an increase of cell stiffness and a decrease of cell ability to undergo reversible large deformations. The mechanical signal transduction in old cells becomes less effective than that in young cells, and with ageing, the cells lose the ability of the rapid functional rearrangements of cellular skeleton. The article reviews the theoretical and experimental facts touching the age-related changes of the mechanical properties of cellular components and cells in the certain systems of an organism (the blood, the vascular system, the musculoskeletal system, the lens, and the epithelium). In fact, the cell mechanical parameters (including elastic modulii) can be useful as specific markers of cell ageing.

  8. Microstructure and mechanical properties of sheep horn.

    PubMed

    Zhu, Bing; Zhang, Ming; Zhao, Jian

    2016-07-01

    The sheep horn presents outstanding mechanical properties of impact resistance and energy absorption, which suits the need of the vehicle bumper design, but the mechanism behind this phenomenon is less investigated. The microstructure and mechanical properties of the sheep horn of Small Tailed Han Sheep (Ovis aries) living in northeast China were investigated in this article. The effect of sampling position and orientation of the sheep horn sheath on mechanical properties were researched by tensile and compression tests. Meanwhile, the surface morphology and microstructure of the sheep horn were observed using scanning electron microscopy (SEM). The formation mechanism of the mechanical properties of the sheep horn was investigated by biological coupling analysis. The analytical results indicated that the outstanding mechanical properties of the sheep horn are determined by configuration, structure, surface morphology and material coupling elements. These biological coupling elements make the sheep horn possess super characteristics of crashworthiness and energy absorption through the internal coupling mechanism. We suppose that these findings would make a difference in vehicle bumper design. Microsc. Res. Tech. 79:664-674, 2016. © 2016 Wiley Periodicals, Inc.

  9. Microstructure and mechanical properties of sheep horn.

    PubMed

    Zhu, Bing; Zhang, Ming; Zhao, Jian

    2016-07-01

    The sheep horn presents outstanding mechanical properties of impact resistance and energy absorption, which suits the need of the vehicle bumper design, but the mechanism behind this phenomenon is less investigated. The microstructure and mechanical properties of the sheep horn of Small Tailed Han Sheep (Ovis aries) living in northeast China were investigated in this article. The effect of sampling position and orientation of the sheep horn sheath on mechanical properties were researched by tensile and compression tests. Meanwhile, the surface morphology and microstructure of the sheep horn were observed using scanning electron microscopy (SEM). The formation mechanism of the mechanical properties of the sheep horn was investigated by biological coupling analysis. The analytical results indicated that the outstanding mechanical properties of the sheep horn are determined by configuration, structure, surface morphology and material coupling elements. These biological coupling elements make the sheep horn possess super characteristics of crashworthiness and energy absorption through the internal coupling mechanism. We suppose that these findings would make a difference in vehicle bumper design. Microsc. Res. Tech. 79:664-674, 2016. © 2016 Wiley Periodicals, Inc. PMID:27184115

  10. Mechanical deformation mechanisms and properties of amyloid fibrils.

    PubMed

    Choi, Bumjoon; Yoon, Gwonchan; Lee, Sang Woo; Eom, Kilho

    2015-01-14

    Amyloid fibrils have recently received attention due to their remarkable mechanical properties, which are highly correlated with their biological functions. We have studied the mechanical deformation mechanisms and properties of amyloid fibrils as a function of their length scales by using atomistic simulations. It is shown that the length of amyloid fibrils plays a role in their deformation and fracture mechanisms in such a way that the competition between shear and bending deformations is highly dependent on the fibril length, and that as the fibril length increases, so does the bending strength of the fibril while its shear strength decreases. The dependence of rupture force for amyloid fibrils on their length is elucidated using the Bell model, which suggests that the rupture force of the fibril is determined from the hydrogen bond rupture mechanism that critically depends on the fibril length. We have measured the toughness of amyloid fibrils, which is shown to depend on the fibril length. In particular, the toughness of the fibril with its length of ∼3 nm is estimated to be ∼30 kcal mol(-1) nm(-3), comparable to that of a spider silk crystal with its length of ∼2 nm. Moreover, we have shown the important effect of the pulling rate on the mechanical deformation mechanisms and properties of amyloid fibril. It is found that as the pulling rate increases, so does the contribution of the shear effect to the elastic deformation of the amyloid fibril with its length of <10 nm. However, we found that the deformation mechanism of the amyloid fibril with its length of >15 nm is almost independent of the pulling rate. Our study sheds light on the role of the length scale of amyloid fibrils and the pulling rate in their mechanical behaviors and properties, which may provide insights into how the excellent mechanical properties of protein fibrils can be determined. PMID:25426573

  11. Mechanical properties testing and results for thermal barrier coatings

    NASA Astrophysics Data System (ADS)

    Cruse, T. A.; Johnsen, B. P.; Nagy, A.

    1997-03-01

    Mechanical test data for thermal barrier coatings, including modulus, static strength, and fatigue strength data, are reviewed in support of the development of durability models for heat engine applica-tions. The materials include 7 and 8 wt % yttria partially stabilized zirconia (PSZ) as well as a cermet ma-terial (PSZ +10 wt % NiCoCrAlY). Both air plasma sprayed and electron beam physical vapor deposited coatings were tested. The data indicate the basic trends in the mechanical properties of the coatings over a wide range of isothermal conditions. Some of the trends are correlated with material density.

  12. Mechanical properties of low tantalum alloys

    NASA Technical Reports Server (NTRS)

    Kortovich, C. S.

    1982-01-01

    The mechanical property behavior of equiaxed cast B-1900 + Hf alloy as a function of tantalum content was studied. Tensile and stress rupture characterization was conducted on cast to size test bars containing tantalum at the 4.3% (standard level), 2.2% and 0% levels. Casting parameters were selected to duplicate conditions used to prepare test specimens for master metal heat qualification. The mechanical property results as well as results of microstructural/phase analysis of failed test bars are presented.

  13. [Polyurethane denture base material "Pentalur" and modified polyurethane compositions: comparative study of mechanical properties].

    PubMed

    Al'ter, Iu M; Tkachuk, A-M P; Poiurovskaia, I Ia; Sutugina, T F; Ogorodnikov, M Iu

    2013-01-01

    Results of laboratory tests of polyurethane based material "Pentalur" conducted to determine its mechanical properties proved the material to meet basic requirements for removable dentures materials. The introduction of simple poluethers with certain molecular weight as well as 1,4-butanediol allows varying polyurethane properties in a fairly wide range. This range of polyurethane mechanical properties along with good biocompatibility opens new possibilities in creation of removable dentures with improved functional properties as well as maxillofacial prosthesis.

  14. Some Mechanical Properties of Austempered Ductile Iron

    NASA Astrophysics Data System (ADS)

    Waanders, F. B.; Vorster, S. W.; Vorster, M. J.

    1998-12-01

    In the present investigation the influence of the microstructure, obtained after an austempering treatment in a "process window", on the mechanical properties of austempered ductile iron has been investigated. These properties include tensile strength, elongation and hardness. Conversion electron Mössbauer spectra (CEMS) were measured, after heat treatment.

  15. Mechanical and thermal properties of the Czech marbles

    NASA Astrophysics Data System (ADS)

    Čáchová, Monika; Koňáková, Dana; Vejmelková, Eva; Keppert, Martin; Černý, Robert

    2016-06-01

    The paper is dealing with selected parameters of four marbles with respect to their utilization as building materials. Stones from four function quarries in the Czech Republic were chosen and scopes of physical properties were determined. Basic physical, mechanical and thermal properties belong among studied characteristics. Bulk density of studied marbles is in average 2750 kg/m3, matrix density 2770 kg/m3, open porosity 0.7%. Pore structure show similar distributions. Mechanical properties show more differences; however minimal value of compressive strength was 66.5 MPa, while maximum was 174 MPa. Thermal conductivity of studied marbles was about 2.955 W/mK. Last measured characteristic was specific heat capacity; its average value was 609 J/kgK.

  16. Brillouin microspectroscopy of nanostructured biomaterials: photonics assisted tailoring mechanical properties

    NASA Astrophysics Data System (ADS)

    Meng, Zhaokai; Jaiswal, Manish K.; Chitrakar, Chandani; Thakur, Teena; Gaharwar, Akhilesh K.; Yakovlev, Vladislav V.

    2016-03-01

    Developing new biomaterials is essential for the next-generation of materials for bioenergy, bioelectronics, basic biology, medical diagnostics, cancer research, and regenerative medicine. Specifically, recent progress in nanotechnology has stimulated the development of multifunctional biomaterials for tissue engineering applications. The physical properties of nanocomposite biomaterials, including elasticity and viscosity, play key roles in controlling cell fate, which underlines therapeutic success. Conventional mechanical tests, including uniaxial compression and tension, dynamic mechanical analysis and shear rheology, require mechanical forces to be directly exerted onto the sample and therefore may not be suitable for in situ measurements or continuous monitoring of mechanical stiffness. In this study, we employ spontaneous Brillouin spectroscopy as a viscoelasticity-specific probing technique. We utilized a Brillouin spectrometer to characterize biomaterial's microscopic elasticity and correlated those with conventional mechanical tests (e.g., rheology).

  17. What the Sun Has Taught Us About Basic Properties of Matter

    SciTech Connect

    Basu, Sarbani

    2012-03-07

    The Sun is an immensely large object formed out of many tons of gas. Yet the Sun can help us learn about some of the basic properties of matter. The structure of the Sun is governed not only by macrophysics such as hydrostatic equilibrium, convective and radiative heat transport, but also by microphysics such as nuclear reaction rates and the equation of state of the material that forms the Sun. Knowledge of the detailed structure of the Sun can therefore help us constrain the basic properties of matter. Helioseismology, the study of solar pulsations, has given us the means to get a detailed picture of the solar interior. In this talk I shall discuss how helioseismology has allowed us to determine details of solar structure, and in turn allowing us to study basic properties of matter.

  18. Thigmomorphogenesis: on the mechanical properties of mechanically perturbed bean plants.

    PubMed

    Jaffe, M J; Telewski, F W; Cooke, P W

    1984-01-01

    The mechanical properties of control and mechanically perturbed (MP) bean stems (Phaseolus vulgaris L., cv. Cherokee wax) were compared. The rubbed plants were greatly hardened against mechanical rupture by previous MP. This hardening was due to a dramatic increase in the flexibility of the stems, but not in their stiffness. The MP-plants were able to bend more than 90 degree without breaking, whereas the control plants broke after just slight bending. A comparison with other work reveals that different species utilize different tactics for achieving similar resistance to rupture due to mechanical stress. PMID:11540788

  19. MoH 101: Basic Concepts in the Mechanics of Hearing

    NASA Astrophysics Data System (ADS)

    Bergevin, Christopher; Epp, Bastian; Meenderink, Sebastiaan W. F.

    2011-11-01

    We provide a synopsis of selected questions and answers from the second triennial Mechanics of Hearing 101 session held at the 11th International Mechanics of Hearing Workshop in Williamstown, Massachusetts. The MoH 101 session offers a non-intimidating forum for students, postdocs, and others new to the field to explore issues and ideas relevant to the Workshop. We have augmented the discussion content by giving some basic background and references.

  20. Teaching Basic Quantum Mechanics in Secondary School Using Concepts of Feynman Path Integrals Method

    ERIC Educational Resources Information Center

    Fanaro, Maria de los Angeles; Otero, Maria Rita; Arlego, Marcelo

    2012-01-01

    This paper discusses the teaching of basic quantum mechanics in high school. Rather than following the usual formalism, our approach is based on Feynman's path integral method. Our presentation makes use of simulation software and avoids sophisticated mathematical formalism. (Contains 3 figures.)

  1. Mechanical properties characterization and modeling of active polymer gels

    NASA Astrophysics Data System (ADS)

    Marra, Steven Paul

    Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as actuators and "artificial muscles." While much work has been done to study the behavior and properties of these gels, little information is available regarding the full constitutive description of the mechanical and actuation properties. This work focuses on developing a means of characterizing the mechanical properties of active polymer gels and describing how these properties evolve as the gel actuates. Poly(vinyl alcohol)-poly(acrylic acid) (PVA-PAA) gel was chosen as the model material for this work because it is relatively simple and safe to both fabricate and actuate. PVA-PAA gels are fabricated on-site using a solvent-casting technique. These gels expand when moved from acidic to basic solutions, and contract when moved from basic to acidic solutions. Citric acid and sodium bicarbonate were used as the testing solutions for this work. The mechanical properties of the gel were characterized by conducting uniaxial and biaxial tests on thin PVA-PAA gel films. A biaxial testing system has been developed which can measure stresses and deformations of these films in a variety of liquid environments. The experimental results on PVA-PAA gels show these materials to be relatively compliant, and slightly viscoelastic and compressible. These gels are also capable of large recoverable deformations in both acidic and basic environments. A thermodynamically consistent finite-elastic constitutive model was developed to describe the mechanical and actuation behaviors of active polymer gels. The mechanical properties of the gel are characterized by a free-energy function, and the model utilizes an evolving internal variable to describe the actuation

  2. Mechanical Properties of Crystalline Silicon Carbide Nanowires.

    PubMed

    Zhang, Huan; Ding, Weiqiang; Aidun, Daryush K

    2015-02-01

    In this paper, the mechanical properties of crystalline silicon carbide nanowires, synthesized with a catalyst-free chemical vapor deposition method, were characterized with nanoscale tensile testing and mechanical resonance testing methods inside a scanning electron microscope. Tensile testing of individual silicon carbide nanowire was performed to determine the tensile properties of the material including the tensile strength, failure strain and Young's modulus. The silicon carbide nanowires were also excited to mechanical resonance in the scanning electron microscope vacuum chamber using mechanical excitation and electrical excitation methods, and the corresponding resonance frequencies were used to determine the Young's modulus of the material according to the simple beam theory. The Young's modulus values from tensile tests were in good agreement with the ones obtained from the mechanical resonance tests.

  3. The mechanical properties of FeAl

    SciTech Connect

    Baker, I.; George, E.P.

    1996-12-31

    Only in the last few years has progress been made in obtaining reproducible mechanical properties data for FeAl. Two sets of observations are the foundation of this progress. The first is that the large vacancy concentrations that exist in FeAl at high temperature are easily retained at low temperature and that these strongly affect the low-temperature mechanical properties. The second is that RT ductility is adversely affected by water vapor. Purpose of this paper is not to present a comprehensive overview of the mechanical properties of FeAl but rather to highlight our understanding of key phenomena and to show how an understanding of the factors which control the yield strength and fracture behavior has followed the discovery of the above two effects. 87 refs, 9 figs.

  4. Physical and mechanical properties of hemp seed

    NASA Astrophysics Data System (ADS)

    Taheri-Garavand, A.; Nassiri, A.; Gharibzahedi, S.

    2012-04-01

    The current study was conducted to investigate the effect of moisture content on the post-harvest physical and mechanical properties of hemp seed in the range of 5.39 to 27.12% d.b. Results showed that the effect of moisture content on the most physical properties of the grain was significant (P<0.05). The results of mechanical tests demonstrated that the effect of loading rate on the mechanical properties of hemp seed was not significant. However, the moisture content effect on rupture force and energy was significant (P<0.01). The lowest value of rupture force was obtained at the highest loading rate (3mm min-1)and in the moisture content of 27.12% d.b. Moreover, the interaction effects of loading rate and moisture content on the rupture force and energy of hemp seed were significant (P<0.05).

  5. Stainless Steel Microstructure and Mechanical Properties Evaluation

    SciTech Connect

    Switzner, Nathan T

    2010-06-01

    A nitrogen strengthened 21-6-9 stainless steel plate was spinformed into hemispherical test shapes. A battery of laboratory tests was used to characterize the hemispheres. The laboratory tests show that near the pole (axis) of a spinformed hemisphere the yield strength is the lowest because this area endures the least “cold-work” strengthening, i.e., the least deformation. The characterization indicated that stress-relief annealing spinformed stainless steel hemispheres does not degrade mechanical properties. Stress-relief annealing reduces residual stresses while maintaining relatively high mechanical properties. Full annealing completely eliminates residual stresses, but reduces yield strength by about 30%.

  6. Mechanical Properties of Ingot Nb Cavities

    SciTech Connect

    Ciovati, Gianluigi; Dhakal, Pashupati; Kneisel, Peter; Mammosser, John; Matalevich, Joseph; Rao Myneni, Ganapati

    2014-07-01

    This contribution presents the results of measurements of the resonant frequency and of strain along the contour of a single-cell cavity made of ingot Nb subjected to increasing uniform differential pressure, up to 6 atm. The data were used to infer mechanical properties of this material after cavity fabrication, by comparison with the results from simulation calculations done with ANSYS. The objective is to provide useful information about the mechanical properties of ingot Nb cavities which can be used in the design phase of SRF cavities intended to be built with this material.

  7. 41 CFR 102-80.10 - What are the basic safety and environmental management policies for real property?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... safety and environmental management policies for real property? 102-80.10 Section 102-80.10 Public... MANAGEMENT REGULATION REAL PROPERTY 80-SAFETY AND ENVIRONMENTAL MANAGEMENT General Provisions § 102-80.10 What are the basic safety and environmental management policies for real property? The basic safety...

  8. 41 CFR 102-80.10 - What are the basic safety and environmental management policies for real property?

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... safety and environmental management policies for real property? 102-80.10 Section 102-80.10 Public... MANAGEMENT REGULATION REAL PROPERTY 80-SAFETY AND ENVIRONMENTAL MANAGEMENT General Provisions § 102-80.10 What are the basic safety and environmental management policies for real property? The basic safety...

  9. 41 CFR 102-80.10 - What are the basic safety and environmental management policies for real property?

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... safety and environmental management policies for real property? 102-80.10 Section 102-80.10 Public... MANAGEMENT REGULATION REAL PROPERTY 80-SAFETY AND ENVIRONMENTAL MANAGEMENT General Provisions § 102-80.10 What are the basic safety and environmental management policies for real property? The basic safety...

  10. 41 CFR 102-80.10 - What are the basic safety and environmental management policies for real property?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... safety and environmental management policies for real property? 102-80.10 Section 102-80.10 Public... MANAGEMENT REGULATION REAL PROPERTY 80-SAFETY AND ENVIRONMENTAL MANAGEMENT General Provisions § 102-80.10 What are the basic safety and environmental management policies for real property? The basic safety...

  11. 41 CFR 102-80.10 - What are the basic safety and environmental management policies for real property?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... safety and environmental management policies for real property? 102-80.10 Section 102-80.10 Public... MANAGEMENT REGULATION REAL PROPERTY 80-SAFETY AND ENVIRONMENTAL MANAGEMENT General Provisions § 102-80.10 What are the basic safety and environmental management policies for real property? The basic safety...

  12. Mechanical Properties Of Large Sodium Iodide Crystals

    NASA Technical Reports Server (NTRS)

    Lee, Henry M.

    1988-01-01

    Report presents data on mechanical properties of large crystals of thallium-doped sodium iodide. Five specimens in shape of circular flat plates subjected to mechanical tests. Presents test results for each specimen as plots of differential pressure versus center displacement and differential pressure versus stress at center. Also tabulates raw data. Test program also developed procedure for screening candidate crystals for gamma-ray sensor. Procedure eliminates potentially weak crystals before installed and ensures material yielding kept to minimum.

  13. Laminar Tendon Composites with Enhanced Mechanical Properties

    PubMed Central

    Alberti, Kyle A.; Sun, Jeong-Yun; Illeperuma, Widusha R.; Suo, Zhigang; Xu, Qiaobing

    2015-01-01

    Purpose A strong isotropic material that is both biocompatible and biodegradable is desired for many biomedical applications, including rotator cuff repair, tendon and ligament repair, vascular grafting, among others. Recently, we developed a technique, called “bioskiving” to create novel 2D and 3D constructs from decellularized tendon, using a combination of mechanical sectioning, and layered stacking and rolling. The unidirectionally aligned collagen nanofibers (derived from sections of decellularized tendon) offer good mechanical properties to the constructs compared with those fabricated from reconstituted collagen. Methods In this paper, we studied the effect that several variables have on the mechanical properties of structures fabricated from tendon slices, including crosslinking density and the orientation in which the fibers are stacked. Results We observed that following stacking and crosslinking, the strength of the constructs is significantly improved, with crosslinked sections having an ultimate tens ile strength over 20 times greater than non-crosslinked samples, and a modulus nearly 50 times higher. The mechanism of the mechanical failure mode of the tendon constructs with or without crosslinking was also investigated. Conclusions The strength and fiber organization, combined with the ability to introduce transversely isotropic mechanical properties makes the laminar tendon composites a biocompatiable material that may find future use in a number of biomedical and tissue engineering applications. PMID:25691802

  14. Osteoarthritis year in review 2014: mechanics--basic and clinical studies in osteoarthritis.

    PubMed

    Moyer, R F; Ratneswaran, A; Beier, F; Birmingham, T B

    2014-12-01

    The purpose of this review was to highlight recent research in mechanics and osteoarthritis (OA) by summarizing results from selected studies spanning basic and clinical research methods. Databases were searched from January 2013 through to March 2014. Working in pairs, reviewers selected 67 studies categorized into four themes--mechanobiology, ambulatory mechanics, biomechanical interventions and mechanical risk factors. Novel developments in mechanobiology included the identification of cell signaling pathways that mediated cellular responses to loading of articular cartilage. Studies in ambulatory mechanics included an increased focus on instrumented knee implants and progress in computational models, both emphasizing the importance of muscular contributions to load. Several proposed biomechanical interventions (e.g., shoe insoles and knee braces) produced variable changes in external knee joint moments during walking, while meta-analysis of randomized clinical trials did not support the use of lateral wedge insoles for decreasing pain. Results from high quality randomized trials suggested diet with or without exercise decreased indicators of knee joint load during walking, whereas similar effects from exercise alone were not detected with the measures used. Data from longitudinal cohorts suggested mechanical alignment was a risk factor for incidence and progression of OA, with the mechanism involving damage to the meniscus. In combination, the basic and clinical studies highlight the importance of considering multiple contributors to joint loading that can evoke both protective and damaging responses. Although challenges clearly exist, future studies should strive to integrate basic and clinical research methods to gain a greater understanding of the interactions among mechanical factors in OA and to develop improved preventive and therapeutic strategies.

  15. Probing cell mechanical properties with microfluidic devices

    NASA Astrophysics Data System (ADS)

    Rowat, Amy

    2012-02-01

    Exploiting flow on the micron-scale is emerging as a method to probe cell mechanical properties with 10-1000x advances in throughput over existing technologies. The mechanical properties of cells and the cell nucleus are implicated in a wide range of biological contexts: for example, the ability of white blood cells to deform is central to immune response; and malignant cells show decreased stiffness compared to benign cells. We recently developed a microfluidic device to probe cell and nucleus mechanical properties: cells are forced to deform through a narrow constrictions in response to an applied pressure; flowing cells through a series of constrictions enables us to probe the ability of hundreds of cells to deform and relax during flow. By tuning the constriction width so it is narrower than the width of the cell nucleus, we can specifically probe the effects of nuclear physical properties on whole cell deformability. We show that the nucleus is the rate-limiting step in cell passage: inducing a change in its shape to a multilobed structure results in cells that transit more quickly; increased levels of lamin A, a nuclear protein that is key for nuclear shape and mechanical stability, impairs the passage of cells through constrictions. We are currently developing a new class of microfluidic devices to simultaneously probe the deformability of hundreds of cell samples in parallel. Using the same soft lithography techniques, membranes are fabricated to have well-defined pore distribution, width, length, and tortuosity. We design the membranes to interface with a multiwell plate, enabling simultaneous measurement of hundreds of different samples. Given the wide spectrum of diseases where altered cell and nucleus mechanical properties are implicated, such a platform has great potential, for example, to screen cells based on their mechanical phenotype against a library of drugs.

  16. Air pollution and adverse cardiac remodeling: clinical effects and basic mechanisms.

    PubMed

    Liu, Yonggang; Goodson, Jamie M; Zhang, Bo; Chin, Michael T

    2015-01-01

    Exposure to air pollution has long been known to trigger cardiovascular events, primarily through activation of local and systemic inflammatory pathways that affect the vasculature. Detrimental effects of air pollution exposure on heart failure and cardiac remodeling have also been described in human populations. Recent studies in both human subjects and animal models have provided insights into the basic physiological, cellular and molecular mechanisms that play a role in adverse cardiac remodeling. This review will give a brief overview of the relationship between air pollution and cardiovascular disease, describe the clinical effects of air pollution exposure on cardiac remodeling, describe the basic mechanisms that affect remodeling as described in human and animal systems and will discuss future areas of investigation.

  17. Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced By Electron Beam Freeform Fabrication

    NASA Technical Reports Server (NTRS)

    Domack, Marcia S.; Taminger, Karen M. B.; Begley, Matthew

    2006-01-01

    The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

  18. Mechanical properties testing and results for thermal barrier coatings

    NASA Technical Reports Server (NTRS)

    Cruse, Thomas A.; Johnsen, B. P.; Nagy, Andrew

    1995-01-01

    The paper reports on several years of mechanical testing of thermal barrier coatings. The test results were generated to support the development of durability models for the coatings in heat engine applications. The test data that are reviewed include modulus, static strength, and fatigue strength data. The test methods and results are discussed, along with the significant difficulties inherent in mechanical testing of thermal barrier coating materials. The materials include 7 percent wt. and 8 percent wt. yttria, partially stabilized zirconia as well as a cermet material. Both low pressure plasma spray and electron-beam physical vapor deposited coatings were tested. The data indicate the basic trends in the mechanical properties of the coatings over a wide range of isothermal conditions. Some of the trends are correlated with material density.

  19. Mechanical properties testing and results for thermal barrier coatings

    SciTech Connect

    Cruse, T.A.; Johnsen, B.P.; Nagy, A.

    1995-10-01

    The paper reports on several years of mechanical testing of thermal barrier coatings. The test results were generated to support the development of durability models for the coatings in heat engine applications. The test data that are reviewed include modulus, static strength, and fatigue strength data. The test methods and results are discussed, along with the significant difficulties inherent in mechanical testing of thermal barrier coating materials. The materials include 7 percent wt. and 8 percent wt. yttria, partially stabilized zirconia as well as a cermet material. Both low pressure plasma spray and electron-beam physical vapor deposited coatings were tested. The data indicate the basic trends in the mechanical properties of the coatings over a wide range of isothermal conditions. Some of the trends are correlated with material density.

  20. Isotropic microscale mechanical properties of coral skeletons

    PubMed Central

    Pasquini, Luca; Molinari, Alan; Fantazzini, Paola; Dauphen, Yannicke; Cuif, Jean-Pierre; Levy, Oren; Dubinsky, Zvy; Caroselli, Erik; Prada, Fiorella; Goffredo, Stefano; Di Giosia, Matteo; Reggi, Michela; Falini, Giuseppe

    2015-01-01

    Scleractinian corals are a major source of biogenic calcium carbonate, yet the relationship between their skeletal microstructure and mechanical properties has been scarcely studied. In this work, the skeletons of two coral species: solitary Balanophyllia europaea and colonial Stylophora pistillata, were investigated by nanoindentation. The hardness HIT and Young's modulus EIT were determined from the analysis of several load–depth data on two perpendicular sections of the skeletons: longitudinal (parallel to the main growth axis) and transverse. Within the experimental and statistical uncertainty, the average values of the mechanical parameters are independent on the section's orientation. The hydration state of the skeletons did not affect the mechanical properties. The measured values, EIT in the 76–77 GPa range, and HIT in the 4.9–5.1 GPa range, are close to the ones expected for polycrystalline pure aragonite. Notably, a small difference in HIT is observed between the species. Different from corals, single-crystal aragonite and the nacreous layer of the seashell Atrina rigida exhibit clearly orientation-dependent mechanical properties. The homogeneous and isotropic mechanical behaviour of the coral skeletons at the microscale is correlated with the microstructure, observed by electron microscopy and atomic force microscopy, and with the X-ray diffraction patterns of the longitudinal and transverse sections. PMID:25977958

  1. Mechanical properties of additively manufactured octagonal honeycombs.

    PubMed

    Hedayati, R; Sadighi, M; Mohammadi-Aghdam, M; Zadpoor, A A

    2016-12-01

    Honeycomb structures have found numerous applications as structural and biomedical materials due to their favourable properties such as low weight, high stiffness, and porosity. Application of additive manufacturing and 3D printing techniques allows for manufacturing of honeycombs with arbitrary shape and wall thickness, opening the way for optimizing the mechanical and physical properties for specific applications. In this study, the mechanical properties of honeycomb structures with a new geometry, called octagonal honeycomb, were investigated using analytical, numerical, and experimental approaches. An additive manufacturing technique, namely fused deposition modelling, was used to fabricate the honeycomb from polylactic acid (PLA). The honeycombs structures were then mechanically tested under compression and the mechanical properties of the structures were determined. In addition, the Euler-Bernoulli and Timoshenko beam theories were used for deriving analytical relationships for elastic modulus, yield stress, Poisson's ratio, and buckling stress of this new design of honeycomb structures. Finite element models were also created to analyse the mechanical behaviour of the honeycombs computationally. The analytical solutions obtained using Timoshenko beam theory were close to computational results in terms of elastic modulus, Poisson's ratio and yield stress, especially for relative densities smaller than 25%. The analytical solutions based on the Timoshenko analytical solution and the computational results were in good agreement with experimental observations. Finally, the elastic properties of the proposed honeycomb structure were compared to those of other honeycomb structures such as square, triangular, hexagonal, mixed, diamond, and Kagome. The octagonal honeycomb showed yield stress and elastic modulus values very close to those of regular hexagonal honeycombs and lower than the other considered honeycombs. PMID:27612831

  2. Mechanical properties of additively manufactured octagonal honeycombs.

    PubMed

    Hedayati, R; Sadighi, M; Mohammadi-Aghdam, M; Zadpoor, A A

    2016-12-01

    Honeycomb structures have found numerous applications as structural and biomedical materials due to their favourable properties such as low weight, high stiffness, and porosity. Application of additive manufacturing and 3D printing techniques allows for manufacturing of honeycombs with arbitrary shape and wall thickness, opening the way for optimizing the mechanical and physical properties for specific applications. In this study, the mechanical properties of honeycomb structures with a new geometry, called octagonal honeycomb, were investigated using analytical, numerical, and experimental approaches. An additive manufacturing technique, namely fused deposition modelling, was used to fabricate the honeycomb from polylactic acid (PLA). The honeycombs structures were then mechanically tested under compression and the mechanical properties of the structures were determined. In addition, the Euler-Bernoulli and Timoshenko beam theories were used for deriving analytical relationships for elastic modulus, yield stress, Poisson's ratio, and buckling stress of this new design of honeycomb structures. Finite element models were also created to analyse the mechanical behaviour of the honeycombs computationally. The analytical solutions obtained using Timoshenko beam theory were close to computational results in terms of elastic modulus, Poisson's ratio and yield stress, especially for relative densities smaller than 25%. The analytical solutions based on the Timoshenko analytical solution and the computational results were in good agreement with experimental observations. Finally, the elastic properties of the proposed honeycomb structure were compared to those of other honeycomb structures such as square, triangular, hexagonal, mixed, diamond, and Kagome. The octagonal honeycomb showed yield stress and elastic modulus values very close to those of regular hexagonal honeycombs and lower than the other considered honeycombs.

  3. Mechanical Properties of Polymer Nano-composites

    NASA Astrophysics Data System (ADS)

    Srivastava, Iti

    Thermoset polymer composites are increasingly important in high-performance engineering industries due to their light-weight and high specific strength, finding cutting-edge applications such as aircraft fuselage material and automobile parts. Epoxy is the most widely employed thermoset polymer, but is brittle due to extensive cross-linking and notch sensitivity, necessitating mechanical property studies especially fracture toughness and fatigue resistance, to ameliorate the low crack resistance. Towards this end, various nano and micro fillers have been used with epoxy to form composite materials. Particularly for nano-fillers, the 1-100 nm scale dimensions lead to fascinating mechanical properties, oftentimes proving superior to the epoxy matrix. The chemical nature, topology, mechanical properties and geometry of the nano-fillers have a profound influence on nano-composite behavior and hence are studied in the context of enhancing properties and understanding reinforcement mechanisms in polymer matrix nano-composites. Using carbon nanotubes (CNTs) as polymer filler, uniquely results in both increased stiffness as well as toughness, leading to extensive research on their applications. Though CNTs-polymer nano-composites offer better mechanical properties, at high stress amplitude their fatigue resistance is lost. In this work covalent functionalization of CNTs has been found to have a profound impact on mechanical properties of the CNT-epoxy nano-composite. Amine treated CNTs were found to give rise to effective fatigue resistance throughout the whole range of stress intensity factor, in addition to significantly enhancing fracture toughness, ductility, Young's modulus and average hardness of the nano-composite by factors of 57%, 60%, 30% and 45% respectively over the matrix as a result of diminished localized cross-linking. Graphene, a one-atom-thick sheet of atoms is a carbon allotrope, which has garnered significant attention of the scientific community and is

  4. The Acid Hydrolysis Mechanism of Acetals Catalyzed by a Supramolecular Assembly in Basic Solution

    SciTech Connect

    Pluth, Michael D.; Bergman, Robert G.; Raymond, Kenneth N.

    2008-09-24

    A self-assembled supramolecular host catalyzes the hydrolysis of acetals in basic aqueous solution. The mechanism of hydrolysis is consistent with the Michaelis-Menten kinetic model. Further investigation of the rate limiting step of the reaction revealed a negative entropy of activation ({Delta}S{double_dagger} = -9 cal mol{sup -1}K{sup -1}) and an inverse solvent isotope effect (k(H{sub 2}O)/k(D{sub 2}O) = 0.62). These data suggest that the mechanism of hydrolysis that takes place inside the assembly proceeds through an A-2 mechanism, in contrast to the A-1 mechanism operating in the uncatalyzed reaction. Comparison of the rates of acetal hydrolysis in the assembly with the rate of the reaction of unencapsulated substrates reveals rate accelerations of up to 980 over the background reaction for the substrate diethoxymethane.

  5. The Influence of Basic Physical Properties of Soil on its Electrical Resistivity Value under Loose and Dense Condition

    NASA Astrophysics Data System (ADS)

    Abidin, M. H. Z.; Ahmad, F.; Wijeyesekera, D. C.; Saad, R.

    2014-04-01

    Electrical resistivity technique has become a famous alternative tool in subsurface characterization. In the past, several interpretations of electrical resistivity results were unable to be delivered in a strong justification due to lack of appreciation of soil mechanics. Traditionally, interpreters will come out with different conclusion which commonly from qualitative point of view thus creating some uncertainty regarding the result reliability. Most engineers desire to apply any techniques in their project which are able to provide some clear justification with strong, reliable and meaningful results. In order to reduce the problem, this study presents the influence of basic physical properties of soil due to the electrical resistivity value under loose and dense condition. Two different conditions of soil embankment model were tested under electrical resistivity test and basic geotechnical test. It was found that the electrical resistivity value (ERV, ρ) was highly influenced by the variations of soil basic physical properties (BPP) with particular reference to moisture content (w), densities (ρbulk/dry), void ratio (e), porosity (η) and particle grain fraction (d) of soil. Strong relationship between ERV and BPP can be clearly presents such as ρ ∞ 1/w, ρ ∞ 1/ρbulk/dry, ρ ∞ e and ρ ∞ η. This study therefore contributes a means of ERV data interpretation using BPP in order to reduce ambiguity of ERV result and interpretation discussed among related persons such as geophysicist, engineers and geologist who applied these electrical resistivity techniques in subsurface profile assessment.

  6. Microstructure and Mechanical Properties of Porous Mullite

    NASA Astrophysics Data System (ADS)

    Hsiung, Chwan-Hai Harold

    Mullite (3 Al2O3 : 2 SiO2) is a technologically important ceramic due to its thermal stability, corrosion resistance, and mechanical robustness. One variant, porous acicular mullite (ACM), has a unique needle-like microstructure and is the material platform for The Dow Chemical Company's diesel particulate filter AERIFY(TM). The investigation described herein focuses on the microstructure-mechanical property relationships in acicular mullites as well as those with traditional porous microstructures with the goal of illuminating the critical factors in determining their modulus, strength, and toughness. Mullites with traditional pore morphologies were made to serve as references via slipcasting of a kaolinite-alumina-starch slurry. The starch was burned out to leave behind a pore network, and the calcined body was then reaction-sintered at 1600C to form mullite. The samples had porosities of approximately 60%. Pore size and shape were altered by using different starch templates, and pore size was found to influence the stiffness and toughness. The ACM microstructure was varied along three parameters: total porosity, pore size, and needle size. Total porosity was found to dominate the mechanical behavior of ACM, while increases in needle and pore size increased the toughness at lower porosities. ACM was found to have much improved (˜130%) mechanical properties relative to its non-acicular counterpart at the same porosity. A second set of investigations studied the role of the intergranular glassy phase which wets the needle intersections of ACM. Removal of the glassy phase via an HF etch reduced the mechanical properties by ˜30%, highlighting the intergranular phase's importance to the enhanced mechanical properties of ACM. The composition of the glassy phase was altered by doping the ACM precursor with magnesium and neodymium. Magnesium doping resulted in ACM with greatly reduced fracture strength and toughness. Studies showed that the mechanical properties of the

  7. Mechanical Properties of Fe-Ni Meteorites

    NASA Astrophysics Data System (ADS)

    Roberta, Mulford; El Dasher, B.

    2010-10-01

    Iron-nickel meteorites exhibit a unique lamellar microstructure, Widmanstatten patterns, consisting of small regions with steep-iron-nickel composition gradients.1,2 The microstructure arises as a result of extremely slow cooling in a planetary core or other large mass. Mechanical properties of these structures have been investigated using microindentation, x-ray fluorescence, and EBSD. Observation of local mechanical properties in these highly structured materials supplements bulk measurements, which can exhibit large variation in dynamic properties, even within a single sample. 3 Accurate mechanical properties for meteorites may enable better modeling of planetary cores, the likely origin of these objects. Appropriate values for strength are important in impact and crater modeling and in understanding the consequences of observed impacts on planetary crusts. Previous studies of the mechanical properties of a typical iron-nickel meteorite, a Diablo Canyon specimen, indicated that the strength of the composite was higher by almost an order of magnitude than values obtained from laboratory-prepared specimens.4 This was ascribed to the extreme work-hardening evident in the EBSD measurements. This particular specimen exhibited only residual Widmanstatten structures, and may have been heated and deformed during its traverse of the atmosphere. Additional specimens from the Canyon Diablo fall (type IAB, coarse octahedrite) and examples from the Muonionalusta meteorite and Gibeon fall ( both IVA, fine octahedrite), have been examined to establish a range of error on the previously measured yield, to determine the extent to which deformation upon re-entry contributes to yield, and to establish the degree to which the strength varies as a function of microstructure. 1. A. Christiansen, et.al., Physica Scripta, 29 94-96 (1984.) 2. Goldstein and Ogilvie, Geochim Cosmochim Acta, 29 893-925 (1965.) 3. M. D. Furnish, M.B. Boslough, G.T. Gray II, and J.L. Remo, Int. J. Impact Eng

  8. Mechanical Properties of Cellulose Microfiber Reinforced Polyolefin

    NASA Astrophysics Data System (ADS)

    Kobayashi, Satoshi; Yamada, Hiroyuki

    Cellulose microfiber (CeF) has been expected as a reinforcement of polymer because of its high modulus and strength and lower cost. In the present study, mechanical properties of CeF/polyolefin were investigated. Tensile modulus increased with increasing CeF content. On the other hand, tensile strength decreased. Fatigue properties were also investigated with acoustic emission measurement. Stiffness of the composites gradually decreased with loading. Drastic decrease in stiffness was observed just before the final fracture. Based on the Mori-Tanaka's theory, the method to calculate modulus of CeF were proposed to evaluate dispersion of CeF.

  9. AFM Investigation of mechanical properties of dentin

    SciTech Connect

    Cohen, Sidney R; Apter, Nathan; Jesse, Stephen; Kalinin, Sergei V; Barlam, David; Peretz, Adi Idit; Ziskind, Daniel; Wagner, H. Daniel

    2008-01-01

    Mechanical properties of peritubular dentin were investigated using scanning probe microscopy techniques, namely Nanoindentation and Band Excitation. Particular attention was directed to the possible existence of a gradient in these properties moving outward from the tubular lumen to the junction with the intertubular dentin. Finite element analysis showed that the influence of the boundaries is small relative to the effects observed. Thus, these results strongly support the concept of a lowering of modulus and hardness from the tubular exterior to its periphery, which appear to correlate with graded changes in the mineral content.

  10. Mechanical properties of crosslinked polymer coatings

    NASA Technical Reports Server (NTRS)

    Csernica, Jeffrey

    1994-01-01

    The objectives of this experiment are to: fabricate and test thin films to explore relations between a polymer's structure and its mechanical properties; expose students to testing methods for hardness and impact energy that are simple to perform and which have results that are easy to comprehend; show importance of polymer properties in materials that students frequently encounter; illustrate a system which displays a tradeoff between strength and impact resistance, the combination of which would need to be optimized for a particular application; and to expose students to coatings technology and testing.

  11. Investigation of Mechanical Properties and Interfacial Mechanics of Crystalline Nanomaterials

    NASA Astrophysics Data System (ADS)

    Qin, Qingquan

    Nanowires (NWs) and nanotubes (NTs) are critical building blocks of nanotechnologies. The operation and reliability of these nanomaterials based devices depend on their mechanical properties of the nanomaterials, which is therefore important to accurately measure the mechanical properties. Besides, the NW--substrate interfaces also play a critical role in both mechanical reliability and electrical performance of these nanodevices, especially when the size of the NW is small. In this thesis, we focus on the mechanical properties and interface mechanics of three important one dimensional (1D) nanomaterials: ZnO NWs, Ag NWs and Si NWs. For the size effect study, this thesis presents a systematic experimental investigation on the elastic and failure properties of ZnO NWs under different loading modes: tension and buckling. Both tensile modulus (from tension) and bending modulus (from buckling) were found to increase as the NW diameter decreased from 80 to 20 nm. The elastic modulus also shows loading mode dependent; the bending modulus increases more rapidly than the tensile modulus. The tension experiments showed that fracture strain and strength of ZnO NWs increase as the NW diameter decrease. A resonance testing setup was developed to measure elastic modulus of ZnO NWs to confirm the loading mode dependent effect. A systematic study was conducted on the effect of clamping on resonance frequency and thus measured Young's modulus of NWs via a combined experiment and simulation approach. A simple scaling law was provided as guidelines for future designs to accurate measure elastic modulus of a cantilevered NW using the resonance method. This thesis reports the first quantitative measurement of a full spectrum of mechanical properties of five-fold twinned Ag NWs including Young's modulus, yield strength and ultimate tensile strength. In situ tensile testing of Ag NWs with diameters between 34 and 130 nm was carried out inside a SEM. Young's modulus, yield strength and

  12. Mechanical properties of intra-ocular lenses

    NASA Astrophysics Data System (ADS)

    Ehrmann, Klaus; Kim, Eon; Parel, Jean-Marie

    2008-02-01

    Cataract surgery usually involves the replacement of the natural crystalline lens with a rigid or foldable intraocular lens to restore clear vision for the patient. While great efforts have been placed on optimising the shape and optical characteristics of IOLs, little is know about the mechanical properties of these devices and how they interact with the capsular bag once implanted. Mechanical properties measurements were performed on 8 of the most commonly implanted IOLs using a custom build micro tensometer. Measurement data will be presented for the stiffness of the haptic elements, the buckling resistance of foldable IOLs, the dynamic behaviour of the different lens materials and the axial compressibility. The biggest difference between the lens types was found between one-piece and 3-piece lenses with respect to the flexibility of the haptic elements

  13. Rhenium Mechanical Properties and Joining Technology

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.; Biaglow, James A.

    1996-01-01

    Iridium-coated rhenium (Ir/Re) provides thermal margin for high performance and long life radiation cooled rockets. Two issues that have arisen in the development of flight Ir/Re engines are the sparsity of rhenium (Re) mechanical property data (particularly at high temperatures) required for engineering design, and the inability to directly electron beam weld Re chambers to C103 nozzle skirts. To address these issues, a Re mechanical property database is being established and techniques for creating Re/C103 transition joints are being investigated. This paper discusses the tensile testing results of powder metallurgy Re samples at temperatures from 1370 to 2090 C. Also discussed is the evaluation of Re/C103 transition pieces joined by both, explosive and diffusion bonding. Finally, the evaluation of full size Re transition pieces, joined by inertia welding, as well as explosive and diffusion bonding, is detailed.

  14. Mechanical properties of silicones for MEMS

    NASA Astrophysics Data System (ADS)

    Schneider, F.; Fellner, T.; Wilde, J.; Wallrabe, U.

    2008-06-01

    This paper focuses on the mechanical properties of polydimethylsiloxane (PDMS) relevant for microelectromechanical system (MEMS) applications. In view of the limited amount of published data, we analyzed the two products most commonly used in MEMS, namely RTV 615 from Bayer Silicones and Sylgard 184 from Dow Corning. With regard to mechanical properties, we focused on the dependence of the elastic modulus on the thinner concentration, temperature and strain rate. In addition, creep and thermal aging were analyzed. We conclude that the isotropic and constant elastic modulus has strong dependence on the hardening conditions. At high hardening temperatures and long hardening time, RTV 615 displays an elastic modulus of 1.91 MPa and Sylgard 184 of 2.60 MPa in a range up to 40% strain.

  15. Mechanical Properties of Palm Fiber Mattress

    NASA Astrophysics Data System (ADS)

    Li, Yu-Qian; Wu, Jia-Yu; Gu, Hao-Wei; Chen, Zong-Yong; Shi, Xiao-Bing; Liao, Ting-Mao; An, Cheng; Yuan, Hong; Liu, Ren-Huai

    2016-05-01

    Palm fiber mattress is increasingly accepted by many families. This study aims at evaluating the mechanical properties of palm fiber mattress. Two experiments were conduct to investigate the Young's modulus of palm fiber mattress in three directions. In addition, finite element models were established to characterize palm fiber mattress under uniform distributed pressure. Finally, results from finite element analysis are presented to illustrate that the thick mattress will stick with human body curve perfectly, which can support vertebral column effectively.

  16. Thermodynamics and statistical mechanics. [thermodynamic properties of gases

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The basic thermodynamic properties of gases are reviewed and the relations between them are derived from the first and second laws. The elements of statistical mechanics are then formulated and the partition function is derived. The classical form of the partition function is used to obtain the Maxwell-Boltzmann distribution of kinetic energies in the gas phase and the equipartition of energy theorem is given in its most general form. The thermodynamic properties are all derived as functions of the partition function. Quantum statistics are reviewed briefly and the differences between the Boltzmann distribution function for classical particles and the Fermi-Dirac and Bose-Einstein distributions for quantum particles are discussed.

  17. Tensile mechanical properties of human forearm tendons.

    PubMed

    Weber, J F; Agur, A M R; Fattah, A Y; Gordon, K D; Oliver, M L

    2015-09-01

    Previous studies of the mechanical properties of tendons in the upper limb have used embalmed specimens or sub-optimal methods of measurement. The aim of this study was to determine the biomechanical properties of all tendons from five fresh frozen cadaveric forearms using updated methodology. The cross-sectional area of tendons was accurately measured using a laser reflectance system. Tensile testing was done in a precision servo-hydraulic device with cryo-clamp fixation. We determined that the cross-sectional area of some tendons is variable and directly influences the calculated material properties; visual estimation of this is unreliable. Data trends illustrate that digital extensor tendons possess the greatest tensile strength and a higher Young's modulus than other tendon types. PMID:25940499

  18. Tensile mechanical properties of human forearm tendons.

    PubMed

    Weber, J F; Agur, A M R; Fattah, A Y; Gordon, K D; Oliver, M L

    2015-09-01

    Previous studies of the mechanical properties of tendons in the upper limb have used embalmed specimens or sub-optimal methods of measurement. The aim of this study was to determine the biomechanical properties of all tendons from five fresh frozen cadaveric forearms using updated methodology. The cross-sectional area of tendons was accurately measured using a laser reflectance system. Tensile testing was done in a precision servo-hydraulic device with cryo-clamp fixation. We determined that the cross-sectional area of some tendons is variable and directly influences the calculated material properties; visual estimation of this is unreliable. Data trends illustrate that digital extensor tendons possess the greatest tensile strength and a higher Young's modulus than other tendon types.

  19. Determinants of the mechanical properties of bones

    NASA Technical Reports Server (NTRS)

    Martin, R. B.

    1991-01-01

    The mechanical properties of bones are governed by the same principles as those of man-made load-bearing structures, but the organism is able to adapt its bone structure to changes in skeletal loading. In this overview of the determinants of the strength and stiffness of bone, a continuum approach has been taken, in which the behavior of a macroscopic structure depends on its shape and size, and on the mechanical properties of the material within. The latter are assumed to depend on the composition (porosity and mineralization) and organization (trabecular or cortical bone architecture, collagen fiber orientation, fatigue damage) of the bone. The effects of each of these factors are reviewed. Also, the possible means of non-invasively estimating the strength or other mechanical properties of a bone are reviewed, including quantitative computed tomography, photon absorptiometry, and ultrasonic measurements. The best estimates of strength have been obtained with photon absorptiometry and computed tomography, which at best are capable of accounting for 90% of the strength variability in a simple in vitro test, but results from different laboratories have been highly variable.

  20. Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 1: Verification of basic methods

    NASA Technical Reports Server (NTRS)

    Chiang, T.; Tessarzik, J. M.; Badgley, R. H.

    1972-01-01

    The primary aim of this investigation was verification of basic methods which are to be used in cataloging elastomer dynamic properties (stiffness and damping) in terms of viscoelastic model constants. These constants may then be used to predict dynamic properties for general elastomer shapes and operating conditions, thereby permitting optimum application of elastomers as energy absorption and/or energy storage devices in the control of vibrations in a broad variety of applications. The efforts reported involved: (1) literature search; (2) the design, fabrication and use of a test rig for obtaining elastomer dynamic test data over a wide range of frequencies, amplitudes, and preloads; and (3) the reduction of the test data, by means of a selected three-element elastomer model and specialized curve fitting techniques, to material properties. Material constants thus obtained have been used to calculate stiffness and damping for comparison with measured test data. These comparisons are excellent for a number of test conditions and only fair to poor for others. The results confirm the validity of the basic approach of the overall program and the mechanics of the cataloging procedure, and at the same time suggest areas in which refinements should be made.

  1. Database of Mechanical Properties of Textile Composites

    NASA Technical Reports Server (NTRS)

    Delbrey, Jerry

    1996-01-01

    This report describes the approach followed to develop a database for mechanical properties of textile composites. The data in this database is assembled from NASA Advanced Composites Technology (ACT) programs and from data in the public domain. This database meets the data documentation requirements of MIL-HDBK-17, Section 8.1.2, which describes in detail the type and amount of information needed to completely document composite material properties. The database focuses on mechanical properties of textile composite. Properties are available for a range of parameters such as direction, fiber architecture, materials, environmental condition, and failure mode. The composite materials in the database contain innovative textile architectures such as the braided, woven, and knitted materials evaluated under the NASA ACT programs. In summary, the database contains results for approximately 3500 coupon level tests, for ten different fiber/resin combinations, and seven different textile architectures. It also includes a limited amount of prepreg tape composites data from ACT programs where side-by-side comparisons were made.

  2. Design considerations in mechanical face seals for improved performance. I - Basic configurations

    NASA Technical Reports Server (NTRS)

    Ludwig, L. P.; Greiner, H. F.

    1977-01-01

    Basic assembly configurations of the mechanical face seal are described and some advantages associated with each are listed. The various forms of seal components (the primary seal, secondary seal, etc.) are illustrated, and functions pointed out. The technique of seal pressure balancing and its application is described; and the concept of the PV factor, its different forms and limitations are discussed. Brief attention is given to seal lubrication since it is covered in detail in a companion paper. Finally, the operating conditions for various applications of low pressure seals (aircraft transmissions) are listed, and the seal failure mode of a particular application is discussed.

  3. Design considerations in mechanical face seals for improved performance. 1: Basic configurations

    NASA Technical Reports Server (NTRS)

    Ludwig, L. P.; Greiner, H. F.

    1977-01-01

    Basic assembly configurations of the mechanical face seal are described and some advantages associated with each are listed. The various forms of seal components are illustrated, and functions pointed out. The technique of seal pressure balancing and its application are described; and the concept of the PV factor, its different forms and limitations are discussed. Brief attention is given to seal lubrication since it is covered in detail in a companion paper. Finally, the operating conditions for various applications of low pressure seals (aircraft transmissions) are listed, and the seal failure mode of a particular application is discussed.

  4. Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced by Electron Beam Freeform Fabrication

    NASA Technical Reports Server (NTRS)

    Domack, Marcia S.; Tainger, Karen M.

    2006-01-01

    The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties demonstrated for electron beam deposited aluminum and titanium alloys are comparable to wrought products, although the microstructures of the deposits exhibit cast features. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. Tensile mechanical properties and microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains with interior dendritic structures, described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

  5. Basic properties of transformation remanent magnetization due to the Verwey transition of magnetite

    NASA Astrophysics Data System (ADS)

    Sato, M.; Mochizuki, N.; Tsunakawa, H.

    2010-12-01

    Recent explorations of Mars and Moon have observed many magnetic anomalies which probably recorded ancient magnetic fields. Many authors have pointed out a correlation between magnetic anomaly patterns and geological features, especially impact craters (e.g. Acuna et al., 1999; Mitchell et al., 2007). Although impact-origin magnetic signatures can give key information of the planetary dynamo evolution, details of shock remanent magnetization (SRM) acquisition mechanisms have not been revealed yet. One of the plausible mechanisms of SRM is transformation remanent magnetization (TrRM). Nagata et al. (1963) found that magnetite acquire remanence by heating through the Verwey transition in a magnetic field (inverse thermoremanent magnetization, ITRM). Ozima et al. (1963) measured field dependence of the intensity of ITRM which was produced by warming from 123 K to room temperature. Dunlop (2006, 2007) studied intensity and stability of TrRM as a function of grain size. However, there have been only a few systematic studies of TrRM concerning magnetic field record. Focusing on the Verwey transition, we have conducted TrRM experiments to examine basic magnetic properties of parallelism, proportionality and stability. In the experiment, natural rock samples containing multi-domain (MD) magnetite grains and crushed magnetite samples were used. They were cooled down from room temperature to a temperature lower than the Verwey transition temperature (Tv) and then warmed back to room temperature in a weak DC field or zero-filed. In the present study, three types of transformation remanences are defined: (1) transformation remanent magnetization (TrRM) which is acquired by cooling and warming in a constant DC field, (2) transformation warming remanent magnetization (TrWRM) which is acquired by cooling in zero field and warming in a DC field, and (3) transformation cooling remanent magnetization (TrCRM) which is acquired by cooling in a DC field and warming in zero field. We

  6. Two basic plastic joining methods are fusion, mechanical--Part 1. [Comparison of mechanical and fusion joints in pipeline construction

    SciTech Connect

    Gunther, K.M. )

    1993-09-01

    Two basics techniques currently accepted by gas distribution utility companies for joining polyethylene pipe underground are fusion methods and mechanical joining. The general philosophy of Washington Gas Light Co. is to use fusion methods as much as possible, and use mechanical joints for repair and final tie-ins where fusion methods are impractical or impossible to use. Fusion methods used by gas industry users of plastic pipe include: butt fusion; socket fusion; saddle fusion; electrofusion. Mechanical pipe joining techniques or procedures include: factory made mechanical joints such as meter risers and transition fittings; hydraulic compression couplings; bolted and screwed compression couplings; stab type compression couplings; interior seal couplings. Every joining method has strengths, weaknesses, pitfalls and ways they can fail in service. The key is making the best selection based on such factors as location, temperature, conditions, available equipment, training level of personnel on the job and cost. No one method will do it all or every company would be using that particular method. Part 1 focuses on strengths, weaknesses, pitfalls and failure possibilities of the four fusion methods. In the second part, attention will be given to the five mechanical techniques.

  7. Mechanical Properties Characterization at the Nanoscale

    NASA Astrophysics Data System (ADS)

    Fong, Hanson; Sopp, Jeffery; Sarikaya, Mehmet

    2001-05-01

    Nanoindentation is an unique technique that characterizes mechanical properties of materials down to the nanometer scale. With a force range from nanoNewtons to milliNewtons, unique properties of surface structures and thin films in the mesoscale can be routinely quantifieds. With technology continually pushing toward smaller feature size in electronic and mechanical devices as well as biomaterials applications, nanoindentation has become an invaluable method to measure these characteristic features. Here, we report its application in the study the biological hard tissues. For example, using engineered metallic indentation tips, the elastic properties of the 20 nm protein layer in the biocomposite of the abalone shell was measured. The elastic modulus was found to be exceptionally high compared to most synthetic polymers. With the combination of AFM imaging nanoindentation, we were able to measure the difference in deformation behavior at the mesoscale between normal and genetically altered mouse enamel. These measurements were complementary in determining the growth defects resulting from genetically modified enamel proteins. Details of these results and future prospects will be discussed.

  8. ERBB receptors: from oncogene discovery to basic science to mechanism-based cancer therapeutics.

    PubMed

    Arteaga, Carlos L; Engelman, Jeffrey A

    2014-03-17

    ERBB receptors were linked to human cancer pathogenesis approximately three decades ago. Biomedical investigators have since developed substantial understanding of the biology underlying the dependence of cancers on aberrant ERBB receptor signaling. An array of cancer-associated genetic alterations in ERBB receptors has also been identified. These findings have led to the discovery and development of mechanism-based therapies targeting ERBB receptors that have improved outcome for many cancer patients. In this Perspective, we discuss current paradigms of targeting ERBB receptors with cancer therapeutics and our understanding of mechanisms of action and resistance to these drugs. As current strategies still have limitations, we also discuss challenges and opportunities that lie ahead as basic scientists and clinical investigators work toward more breakthroughs.

  9. Anticommutation relations for fermionic fields derived from basic properties of the inner product

    NASA Astrophysics Data System (ADS)

    Wang, Wen-ge

    2016-07-01

    For fermionic fields with nonzero mass, it is shown that the spinor factor of the anticommutation relation between creation and annihilation operators can be justified in a natural way, based on basic properties of Lorentz-invariant inner product in Hilbert space. Furthermore, from the physical point that predictions for measurement results should take real and definite values, we examine the basic requirements for inner product and propose to make certain relaxation to them. Under the relaxed requirements, there exists an alternative way of introducing the anticommutation relation, independent of the mass. In a theory with the latter type of anticommutation relation, the ultraviolet divergence may become less serious than that met in ordinary theories.

  10. Design of monoliths through their mechanical properties.

    PubMed

    Podgornik, Aleš; Savnik, Aleš; Jančar, Janez; Krajnc, Nika Lendero

    2014-03-14

    Chromatographic monoliths have several interesting properties making them attractive supports for analytics but also for purification, especially of large biomolecules and bioassemblies. Although many of monolith features were thoroughly investigated, there is no data available to predict how monolith mechanical properties affect its chromatographic performance. In this work, we investigated the effect of porosity, pore size and chemical modification on methacrylate monolith compression modulus. While a linear correlation between pore size and compression modulus was found, the effect of porosity was highly exponential. Through these correlations it was concluded that chemical modification affects monolith porosity without changing the monolith skeleton integrity. Mathematical model to describe the change of monolith permeability as a function of monolith compression modulus was derived and successfully validated for monoliths of different geometries and pore sizes. It enables the prediction of pressure drop increase due to monolith compressibility for any monolith structural characteristics, such as geometry, porosity, pore size or mobile phase properties like viscosity or flow rate, based solely on the data of compression modulus and structural data of non-compressed monolith. Furthermore, it enables simple determination of monolith pore size at which monolith compressibility is the smallest and the most robust performance is expected. Data of monolith compression modulus in combination with developed mathematical model can therefore be used for the prediction of monolith permeability during its implementation but also to accelerate the design of novel chromatographic monoliths with desired hydrodynamic properties for particular application.

  11. PICA Variants with Improved Mechanical Properties

    NASA Technical Reports Server (NTRS)

    Thornton, Jeremy; Ghandehari, Ehson M.; Fan, Wenhong; Stackpoole, Margaret; Chavez-Garcia, Jose

    2011-01-01

    Phenolic Impregnated Carbon Ablator (PICA) is a member of the family of Lightweight Ceramic Ablators (LCAs) and was developed at NASA Ames Research Center as a thermal protection system (TPS) material for the Stardust mission probe that entered the Earth s atmosphere faster than any other probe or vehicle to date. PICA, carbon fiberform base and phenolic polymer, shows excellent thermal insulative properties at heating rates from about 250 W/sq cm to 1000 W/sq cm. The density of standard PICA - 0.26 g/cu cm to 0.28 g/cu cm - can be changed by changing the concentration of the phenolic resin. By adding polymers to the phenolic resin before curing it is possible to significantly improve the mechanical properties of PICA without significantly increasing the density.

  12. Electrical and Mechanical Properties of Graphene

    NASA Astrophysics Data System (ADS)

    Bao, Wenzhong

    Graphene is an exciting new atomically-thin two-dimensional (2D) system of carbon atoms organized in a hexagonal lattice structure. This "wonder material" has been extensively studied in the last few years since it's first isolation in 2004. Its rapid rise to popularity in scientific and technological communities can be attributed to a number of its exceptional properties. In this thesis I will present several topics including fabrication of graphene devices, electrical and mechanical properties of graphene. I will start with a brief introduction of electronic transport in nanosclae system including quantum Hall effect, followed by a discussion of fundamental electrical and mechanical properties of graphene. Next I will describe how graphene devices are produced: from the famous "mechnical exfoliation" to our innovative "scratching exfoliation" method, together with the traditional lithography fabrication for graphene devices. We also developed a lithography-free technique for making electrical contacts to suspended graphene devices. Most of the suspended devices presented in this thesis are fabricated by this technique. Graphene has remarkable electrical properties thanks to its crystal and band structures. In Chapter 3, I will first focus on proximity-induced superconductivity in graphene Josephson transistors. In this section we investigate electronic transport in single layer graphene coupled to superconducting electrodes. We observe significant suppression in the critical current I c and large variation in the product IcR n in comparison to theoretic prediction; both phenomena can be satisfactorily accounted for by premature switching in underdamped Josephson junctions. Another focus of our studies is quantum Hall effect and many body physics in graphene in suspended bilayer and trilayer graphene. We demonstrate that symmetry breaking of the first 3 Landau levels and fractional quantum Hall states are observed in both bilayer and trilayer suspended graphene

  13. High-Throughput Assessment of Cellular Mechanical Properties.

    PubMed

    Darling, Eric M; Di Carlo, Dino

    2015-01-01

    Traditionally, cell analysis has focused on using molecular biomarkers for basic research, cell preparation, and clinical diagnostics; however, new microtechnologies are enabling evaluation of the mechanical properties of cells at throughputs that make them amenable to widespread use. We review the current understanding of how the mechanical characteristics of cells relate to underlying molecular and architectural changes, describe how these changes evolve with cell-state and disease processes, and propose promising biomedical applications that will be facilitated by the increased throughput of mechanical testing: from diagnosing cancer and monitoring immune states to preparing cells for regenerative medicine. We provide background about techniques that laid the groundwork for the quantitative understanding of cell mechanics and discuss current efforts to develop robust techniques for rapid analysis that aim to implement mechanophenotyping as a routine tool in biomedicine. Looking forward, we describe additional milestones that will facilitate broad adoption, as well as new directions not only in mechanically assessing cells but also in perturbing them to passively engineer cell state.

  14. Mechanical properties of dried defatted spongy bone.

    PubMed

    Lindahl, O

    1976-02-01

    A study has been made of the compressive strength, compression at rupture, limit of proportionality, compression at the limit of proportionality and the modulus of elasticity of spongy bone from vertebrae and tibias. The specimens were obtained from autopsy subjects of both sexes aged 14 to 89 years. There was a qualitative deterioration of most of the strength parameters with age, and also differences between the sexes and between vertebrae and tibia. Spongy bone was found to have the unusual mechanical property that, despite rupture, its compressive strength often steadily increased; this was especially the case for vertebrae from young males.

  15. Mechanical properties of low dimensional materials

    NASA Astrophysics Data System (ADS)

    Saini, Deepika

    Recent advances in low dimensional materials (LDMs) have paved the way for unprecedented technological advancements. The drive to reduce the dimensions of electronics has compelled researchers to devise newer techniques to not only synthesize novel materials, but also tailor their properties. Although micro and nanomaterials have shown phenomenal electronic properties, their mechanical robustness and a thorough understanding of their structure-property relationship are critical for their use in practical applications. However, the challenges in probing these mechanical properties dramatically increase as their dimensions shrink, rendering the commonly used techniques inadequate. This dissertation focuses on developing techniques for accurate determination of elastic modulus of LDMs and their mechanical responses under tensile and shear stresses. Fibers with micron-sized diameters continuously undergo tensile and shear deformations through many phases of their processing and applications. Significant attention has been given to their tensile response and their structure-tensile properties relations are well understood, but the same cannot be said about their shear responses or the structure-shear properties. This is partly due to the lack of appropriate instruments that are capable of performing direct shear measurements. In an attempt to fill this void, this dissertation describes the design of an inexpensive tabletop instrument, referred to as the twister, which can measure the shear modulus (G) and other longitudinal shear properties of micron-sized individual fibers. An automated system applies a pre-determined twist to the fiber sample and measures the resulting torque using a sensitive optical detector. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers. Two industrially important fibers, IM7 carbon fiber and KevlarRTM 119, were found to have G = 17 and 2.4 GPa, respectively. In addition to measuring the shear

  16. Passive mechanical properties of ovine rumen tissue

    NASA Astrophysics Data System (ADS)

    Waite, Stephen J.; Cater, John E.; Walker, Cameron G.; Amirapu, Satya; Waghorn, Garry C.; Suresh, Vinod

    2016-05-01

    Mechanical and structural properties of ovine rumen tissue have been determined using uniaxial tensile testing of tissue from four animals at five rumen locations and two orientations. Animal and orientation did not have a significant effect on the stress-strain response, but there was a significant difference between rumen locations. Histological studies showed two orthogonal muscle layers in all regions except the reticulum, which has a more isotropic structure. A quasi-linear viscoelastic model was fitted to the relaxation stage for each region. Model predictions of the ramp stage had RMS errors of 13-24% and were within the range of the experimental data.

  17. Mechanical properties of phosphorene nanoribbons and oxides

    SciTech Connect

    Hao, Feng; Chen, Xi

    2015-12-21

    Mechanical properties of phosphorene nanoribbons and oxides are investigated by using density functional theory. It is found that the ideal strength of nanoribbon decreases in comparison with that of 2D phosphorene. The Young's modulus of armchair nanoribbon has a remarkable size effect because of the edge relaxations. The analysis of the stress-strain relation indicates that, owing to chemisorbed oxygen atoms, the ideal strength and Young's modulus of 2D phosphorene oxide are greatly reduced along the zigzag direction, especially upon high oxidation ratios. In addition, strain and oxidation have significant impacts on phonon dispersion.

  18. The mechanical properties of breast prostheses.

    PubMed

    Peters, W J

    1981-03-01

    The mechanical properties of inflatable and gel-filled breast prostheses were evaluated using the Instron Universal Testing Machine. Prosthesis strength characteristics were evaluated in terms of compression strength (rather than tensile strength) because of the relationship to closed capsulotomy. The compression breaking strength of prostheses ranged from 0.62 to 10.8 pounds per square inch. There was considerable variation among prostheses. Pressures exceeding these values have been recorded during closed compression capsulotomy. The clinical relevance of these results is discussed.

  19. Surveyor v: lunar surface mechanical properties.

    PubMed

    Christensen, E M; Choate, R; Jaffe, L D; Spencer, R L; Sperling, F B; Batterson, S A; Benson, H E; Hutton, R E; Jones, R H; Ko, H Y; Schmidt, F N; Scott, R F; Sutton, G H

    1967-11-01

    The mechanical properties of the lunar soil at the Surveyor V landing site seem to be generally consistent with values determined for soils at the landing sites of Surveyor I and III. These three maria sites are hundreds of kilometers apart. However, the static bearing capability may be somewhat lower than that at the previous landing sites (2 x 10(5) to 6 x 10(5) dynes per square centimeter or 3 to 8 pounds per square inch). The results of the erosion experiment, the spacecraft landing effects, and other observations indicate that the soil has significant amounts of fine-grained material and a measurable cohesion.

  20. Polyaniline: Factors affecting conductivity and mechanical properties

    SciTech Connect

    Scherr, E.M.

    1993-01-01

    The main objectives of this study were: (a) to study electronic and mechanical properties of films of the conducting polymer, polyaniline, in the doped and undoped emeraldine oxidation state, (b) to study how the electronic and mechanical properties were modified through mechanical stretch-orientation of the films, (c) to study the effect of water vapor on the conductivity of stretched protonic acid doped films, (d) to observe changes in tensile strength and Young's modulus when selected plasticizers were introduced into the films, (e) to observe, using UV/Vis spectroscopy, the effect that neutral salts in the doping media have on the doping level of thin, optically transparent films of polyaniline, (f) to use thin, optically transparent films to spectroscopically study (by UV/Vis) hysteresis in the doping and undoping behavior of polyaniline. The significant results and conclusions are: (a) mechanical stretch-orientation of polyaniline increased the tensile strength of emeraldine base films, (b) the conductivity of doped films of polyaniline was increased approximately two orders of magnitude by stretch-orientation (four-fold elongation) from [approximately]5 S/cm to [approximately]90 S/cm, (c) an increase in the relative percent crystallinity (by x-ray diffraction) upon stretch-orientation of emeraldine base films, (d) the removal of water vapor was found to decrease the conductivity of stretched emeraldine, (e) both tensile strength and Young's modulus are decreased by the introduction of plasticizers and [open quotes]dopant plasticizers[close quotes] into the films, (f) no loss in conductivity was observed due to the addition of plasticizers, (g) the presence of neutral salts in the doping media increased the doping level of thin films of polyaniline, (h) observed hysteresis upon doping and undoping thin polyaniline films is due to irreversible morphological changes that take place in polyaniline upon doping and undoping.

  1. Basic failure mechanisms in advanced composites. [composed of epoxy resins reinforced with carbon fibers

    NASA Technical Reports Server (NTRS)

    Mazzio, V. F.; Mehan, R. L.; Mullin, J. V.

    1973-01-01

    The fundamental failure mechanisms which result from the interaction of thermal cycling and mechanical loading of carbon-epoxy composites were studied. This work was confined to epoxy resin uniderictionally reinforced with HTS carbon fibers, and consists of first identifying local fiber, matrix and interface failure mechanisms using the model composite specimen containing a small number of fibers so that optical techniques can be used for characterization. After the local fracture process has been established for both mechanical loading and thermal cycling, engineering composite properties and gross fracture modes are then examined to determine how the local events contribute to real composite performance. Flexural strength in high fiber content specimens shows an increase in strength with increased thermal cycling. Similar behavior is noted for 25 v/o material up to 200 cycles; however, there is a drastic reduction after 200 cycles indicating a major loss of integrity probably through the accumulation of local cleavage cracks in the tensile region.

  2. Mechanical Properties of Nanoceramic Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Ojo, Ipidapo; Abunaemeh, Malek; Smith, Cydale; Muntele, Claudiu; Ila, Daryush

    2009-03-01

    Generation IV nuclear reactors will use the TRISO fuels, a type of micro fuel particle. It consists of a fuel kernel coated with four layers of isotropic material. One of the materials considered for these layers is silicon carbide ceramic. This lightweight material can maintain chemical and dimensional stability in adverse environments at very high temperatures up to 3000 C, and it is chemically inert. It is widely used as a semiconductor material in electronics because of its high thermo conductivity, high electric field break down strength, and high maximum current density, which makes it more desirable than silicon. Silicon carbide has a very low coefficient of thermal expansion and has no phase transition that would discontinue its thermal expansion. At the Center for Irradiation of Materials (C.I.M.) we are developing a new fabrication process for nanopowdered silicon carbide for TRISO fuel coating purposes. We also study the mechanical properties of the material produced. Among the different test being performed are particle induced X-ray emission (PIXE) an Rutherford backscattering spectroscopy (RBS). The mechanical properties of interest are hardness (measured by Vickers Hardness machine), toughness (measured by the Anstis equation, KIC= 1.6 x 10-2(E/H)^1/2(P/C0^3/2, where P=load, C0=crack length, E=Young's modulus and H=Vickers Hardness), tensile strength and flexural strength (measured by a three point bend test). Results will be presented during the meeting.

  3. Basic properties of the mixed oxides obtained by thermal decomposition of hydrotalcites containing different metallic compositions

    SciTech Connect

    Valente, J.S.; Figueras, F.; Gravelle, M.; Kumbhar, P.; Lopez, J.; Besse, J.P.

    2000-01-25

    Carbonated layered double hydroxides (LDHs) containing Al, Fe, or Cr in a Mg(OH){sub 2} matrix or Al dissolved in hydroxides of Mg, Cu, Ni, Co, or Zn are used as precursors of basic catalysts. Decarbonation is studied by thermal analysis. The average basic strength, evaluated by the decarbonation temperature, is related to the partial charge of oxygen in the LDHs obtained from the Sanderson theory of electronegativity. The enthalpy of adsorption of CO{sub 2} on the resulting mixed oxides is measured by calorimetry. A homogeneous surface is generally observed for CO{sub 2} adsorption, with initial heats of adsorption close to those reported for MgO. The number of sites determined by this method is proportional to the rate constants for {beta}-isophorone isomerization, suggesting that both techniques measure surface properties. The layered structure in which OH{sup {minus}} is the compensating anion can be re-formed by hydration. This process does not appreciably change the adsorption of CO{sub 2}; thus, oxygens and hydroxyls show similar basic strengths in this case.

  4. p-Chlorophenol adsorption on activated carbons with basic surface properties

    NASA Astrophysics Data System (ADS)

    Lorenc-Grabowska, Ewa; Gryglewicz, Grażyna; Machnikowski, Jacek

    2010-05-01

    The adsorption of p-chlorophenol (PCP) from aqueous solution on activated carbons (ACs) with basic surface properties has been studied. The ACs were prepared by two methods. The first method was based on the modification of a commercial CWZ AC by high temperature treatment in an atmosphere of ammonia, nitrogen and hydrogen. The second approach comprised the carbonization followed by activation of N-enriched polymers and coal tar pitch using CO 2 and steam as activation agent. The resultant ACs were characterized in terms of porous structure, elemental composition and surface chemistry (pH PZC, acid/base titration, XPS). The adsorption of PCP was carried out from an aqueous solution in static conditions. Equilibrium adsorption isotherm was of L2 type for polymer-based ACs, whereas L3-type isotherm was observed for CWZ ACs series. The Langmuir monolayer adsorption capacity was related to the porous structure and the amount of basic sites. A good correlation was found between the adsorption capacity and the volume of micropores with a width < 1.4 nm for polymer-based ACs. Higher nitrogen content, including that in basic form, did not correspond to the enhanced adsorption of PCP from aqueous solution. The competitive effect of water molecule adsorption on the PCP uptake is discussed.

  5. Basic Properties of Magnetic Shape-Memory Materials from First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Entel, Peter; Dannenberg, Antje; Siewert, Mario; Herper, Heike C.; Gruner, Markus E.; Comtesse, Denis; Elmers, Hans-Joachim; Kallmayer, Michael

    2012-08-01

    The mutual influence of phase transformations, magnetism, and electronic properties of magnetic-shape memory Heusler materials is a basic issue of electronic structure calculations based on density functional theory. In this article, we show that these calculations can be pursued to finite temperatures, which allows to derive on a first-principles basis the temperature versus composition phase diagram of the pseudo-binary Ni-Mn-(Ga, In, Sn, Sb) system. The free energy calculations show that the phonon contribution stabilizes the body-centered-cubic (bcc)-like austenite structure at elevated temperatures, whereas magnetism favors the low-temperature martensite phase with body-centered-tetragonal (bct) or rather face-centered-tetragonal (fct) structure. The calculations also allow to make predictions of magnetostructural and magnetic field induced properties of other (new) magnetic Heusler alloys not based on NiMn such as Co-Ni-(Ga-Zn) and Fe-Co-Ni-(Ga-Zn) intermetallic compounds.

  6. Mechanical properties of the beetle elytron, a biological composite material

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We determined the relationship between composition and mechanical properties of elytral (modified forewing) cuticle of the beetles Tribolium castaneum and Tenebrio molitor. Elytra of both species have similar mechanical properties at comparable stages of maturation (tanning). Shortly after adult ecl...

  7. Mechanical Properties of Nanoscopic Lipid Domains.

    PubMed

    Nickels, Jonathan D; Cheng, Xiaolin; Mostofian, Barmak; Stanley, Christopher; Lindner, Benjamin; Heberle, Frederick A; Perticaroli, Stefania; Feygenson, Mikhail; Egami, Takeshi; Standaert, Robert F; Smith, Jeremy C; Myles, Dean A A; Ohl, Michael; Katsaras, John

    2015-12-23

    The lipid raft hypothesis presents insights into how the cell membrane organizes proteins and lipids to accomplish its many vital functions. Yet basic questions remain about the physical mechanisms that lead to the formation, stability, and size of lipid rafts. As a result, much interest has been generated in the study of systems that contain similar lateral heterogeneities, or domains. In the current work we present an experimental approach that is capable of isolating the bending moduli of lipid domains. This is accomplished using neutron scattering and its unique sensitivity to the isotopes of hydrogen. Combining contrast matching approaches with inelastic neutron scattering, we isolate the bending modulus of ∼13 nm diameter domains residing in 60 nm unilamellar vesicles, whose lipid composition mimics the mammalian plasma membrane outer leaflet. Importantly, the bending modulus of the nanoscopic domains differs from the modulus of the continuous phase surrounding them. From additional structural measurements and all-atom simulations, we also determine that nanoscopic domains are in-register across the bilayer leaflets. Taken together, these results inform a number of theoretical models of domain/raft formation and highlight the fact that mismatches in bending modulus must be accounted for when explaining the emergence of lateral heterogeneities in lipid systems and biological membranes.

  8. Fundamental Entangling Operators in Quantum Mechanics and Their Properties

    NASA Astrophysics Data System (ADS)

    Dao-Ming, Lu

    2016-07-01

    For the first time, we introduce so-called fundamental entangling operators e^{iQ1 P2} and e^{iP1 Q2 } for composing bipartite entangled states of continuum variables, where Q i and P i ( i = 1, 2) are coordinate and momentum operator, respectively. We then analyze how these entangling operators naturally appear in the quantum image of classical quadratic coordinate transformation ( q 1, q 2) → ( A q 1 + B q 2, C q 1 + D q 2), where A D- B C = 1, which means even the basic coordinate transformation ( Q 1, Q 2) → ( A Q 1 + B Q 2, C Q 1 + D Q 2) involves entangling mechanism. We also analyse their Lie algebraic properties and use the integration technique within an ordered product of operators to show they are also one- and two- mode combinatorial squeezing operators.

  9. The Behaviour of Laboratory Soil Electrical Resistivity Value under Basic Soil Properties Influences

    NASA Astrophysics Data System (ADS)

    Hazreek, Z. A. M.; Aziman, M.; Azhar, A. T. S.; Chitral, W. D.; Fauziah, A.; Rosli, S.

    2015-01-01

    Electrical resistivity method (ERM) was a popular indirect geophysical tools adopted in engineering, environmental and archaeological studies. In the past, results of the electrical resistivity value (ERV) were always subjected to a long discussion and debate among the related parties such as an engineers, geophysicists and geologists due to its lack of clarification and evidences in quantitative point of view. Most of the results produced in the past was always been justified using qualitative ways which difficult to be accept by certain parties. In order to reduce the knowledge gap between those parties, this study has performed a laboratory experiment of soil box resistivity test which supported by an additional basic geotechnical test as referred to particle size distribution test (d), moisture content test (w), density test (ρbulk) and Atterberg limit test (LL, PL and PI). The test was performed to establish a series of electrical resistivity value with different quantity of water content for Clayey SILT and Silty SAND soil. It was found that the ERV of Silty SAND (600 - 7300 Ωm) was higher than Clayey SILT (13 - 7700 Ωm) due to the different quantity of basic soil properties value obtained from the basic geotechnical test. This study was successfully demonstrated that the fluctuation of ERV has greatly influenced by the variations of the soil physical properties (d, w, ρbulk, LL, PL and PI). Hence, the confidence level of ERV interpretation will be increasingly meaningful since it able to be proved by others parameter generated by laboratory direct test.

  10. Effects of basic calponin on the flexural mechanics and stability of F-actin

    PubMed Central

    Jensen, Mikkel Herholdt; Watt, James; Hodgkinson, Julie; Gallant, Cynthia; Appel, Sarah; El-Mezgueldi, Mohammed; Angelini, Thomas E.; Morgan, Kathleen G.; Lehman, William; Moore, Jeffrey R.

    2012-01-01

    The cellular actin cytoskeleton plays a central role in the ability of cells to properly sense, propagate, and respond to external stresses and other mechanical stimuli. Calponin, an actin-binding protein found both in muscle and non-muscle cells, has been implicated in actin cytoskeletal organization and regulation. In this work, we studied the mechanical and structural interaction of actin with basic calponin, a differentiation marker in smooth muscle cells, on a single filament level. We imaged fluorescently labeled thermally fluctuating actin filaments and found that at moderate calponin binding densities, actin filaments were more flexible, evident as a reduction in persistence length from 8.0 μm to 5.8 μm. When calponin-decorated actin filaments were subjected to shear, we observed a marked reduction of filament lengths after decoration with calponin, which we argue was due to shear-induced filament rupture rather than depolymerization. This increased shear susceptibility was exacerbated with calponin concentration. Cryo-electron microscopy results confirmed previously published negative stain electron microscopy results and suggest alterations in actin involving actin subdomain 2. A weakening of F-actin intermolecular association is discussed as the underlying cause of the observed mechanical perturbations. PMID:22135101

  11. Basic properties of GaAs oxide generated by scanning probe microscope tip-induced nano-oxidation process

    NASA Astrophysics Data System (ADS)

    Okada, Yoshitaka; Iuchi, Yoshimasa; Kawabe, Mitsuo; Harris, James S.

    2000-07-01

    The basic properties of GaAs oxide generated by atomic force microscope (AFM) tip-induced nano-oxidation process have been investigated. The chemical analysis of the AFM tip-generated GaAs oxide was performed by using scanning microprobe x-ray photoelectron spectroscopy, and the main constituents of GaAs anodic oxide were determined to be Ga2O3 and As2O3. The electrical characterization showed that the electron transport across a GaAs oxide nanodot of ˜5.7 nm thickness, from a doped n+-Si tip into the n+-GaAs substrate follows the Fowler-Nordheim tunneling mechanism over a range of applied bias. Further, the tip-generated GaAs oxide nanodots were found to withstand moderate thermal treatments, but some volume reduction was observed.

  12. Environmental properties set cell mechanics and morphology

    NASA Astrophysics Data System (ADS)

    Janmey, Paul

    2012-02-01

    Many cell types are sensitive to mechanical signals that are produced either by application of exogenous force to their surfaces, or by the resistance that their surroundings place on forces generated by the cells themselves. Cell morphology, motility, proliferation, and protein expression all change in response to substrate stiffness. Changing the elastic moduli of substrates alters the formation of focal adhesions, the assembly of actin filaments into bundles, and the stability of intermediate filaments. The range of stiffness over which different primary cell types respond can vary over a wide range and generally reflects the elastic modulus of the tissue from which these cells were isolated. Mechanosensing depends on the type of adhesion receptor by which the cell binds, and therefore on both the molecular composition of the extracellular matrix and the nature of its link to the cytoskeleton. Many cell types can alter their own stiffness to match that of the substrate to which they adhere. The maximal elastic modulus that cells such as fibroblasts can attain is similar to that of crosslinked actin networks at the concentrations in the cell cortex. The precise mechanisms of mechanosensing are not well defined, but they presumably require an elastic connection between cell and substrate, mediated by transmembrane proteins. The viscoelastic properties of different extracellular matrices and cytoskeletal elements strongly influence the response of cells to mechanical signals, and the unusual non-linear elasticity of many biopolymer gels, characterized by strain-stiffening, leads to novel mechanisms by which cells alter their stiffness by engagement of molecular motors that produce internal stresses. Cell cortical elasticity is dominated by cytoskeletal polymer networks and can be modulated by internal tension. Simultaneous control of substrate stiffness and adhesive patterns suggests that stiffness sensing occurs on a length scale much larger than single molecular

  13. Mechanical properties of icosahedral virus capsids

    NASA Astrophysics Data System (ADS)

    Vliegenthart, G. A.; Gompper, G.

    2007-12-01

    Virus capsids are self-assembled protein shells in the size range of 10 to 100 nanometers. The shells of DNA-viruses have to sustain large internal pressures while encapsulating and protecting the viral DNA. We employ computer simulations to study the mechanical properties of crystalline shells with icosahedral symmetry that serve as a model for virus capsids. The shells are positioned on a substrate and deformed by a uni-axial force excerted by a small bead. We predict the elastic response for small deformations, and the buckling transitions at large deformations. Both are found to depend strongly on the number N of elementary building blocks (capsomers), and the Föppl-von Kármán number γ which characterizes the relative importance of shear and bending elasticity.

  14. Material modeling of biofilm mechanical properties.

    PubMed

    Laspidou, C S; Spyrou, L A; Aravas, N; Rittmann, B E

    2014-05-01

    A biofilm material model and a procedure for numerical integration are developed in this article. They enable calculation of a composite Young's modulus that varies in the biofilm and evolves with deformation. The biofilm-material model makes it possible to introduce a modeling example, produced by the Unified Multi-Component Cellular Automaton model, into the general-purpose finite-element code ABAQUS. Compressive, tensile, and shear loads are imposed, and the way the biofilm mechanical properties evolve is assessed. Results show that the local values of Young's modulus increase under compressive loading, since compression results in the voids "closing," thus making the material stiffer. For the opposite reason, biofilm stiffness decreases when tensile loads are imposed. Furthermore, the biofilm is more compliant in shear than in compression or tension due to the how the elastic shear modulus relates to Young's modulus. PMID:24560820

  15. Evaluation of mechanical properties of esthetic brackets

    PubMed Central

    Umezaki, Eisaku; Komazawa, Daigo; Otsuka, Yuichiro; Suda, Naoto

    2015-01-01

    Plastic brackets, as well as ceramic brackets, are used in various cases since they have excellent esthetics. However, their mechanical properties remain uncertain. The purpose of this study was to determine how deformation and stress distribution in esthetic brackets differ among materials under the same wire load. Using the digital image correlation method, we discovered the following: (1) the strain of the wings of plastic brackets is within 0.2% and that of ceramic and metal brackets is negligible, (2) polycarbonate brackets having a stainless steel slot show significantly smaller displacement than other plastic brackets, and (3) there is a significant difference between plastic brackets and ceramic and stainless steel brackets in terms of the displacement of the bracket wing. PMID:25755677

  16. The minimal nanowire: Mechanical properties of carbyne

    NASA Astrophysics Data System (ADS)

    Nair, A. K.; Cranford, S. W.; Buehler, M. J.

    2011-07-01

    Advances in molecular assembly are converging to an ultimate in atomistic precision —nanostructures built by single atoms. Recent experimental studies confirm that single chains of carbon atoms —carbyne— exist in stable polyyne structures and can be synthesized, representing the minimal possible nanowire. Here we report the mechanical properties of carbyne obtained by first-principles-based ReaxFF molecular simulation. A peak Young's modulus of 288 GPa is found with linear stiffnesses ranging from 64.6-5 N/m for lengths of 5-64 Å. We identify a size-dependent strength that ranges from 11 GPa (1.3 nN) for the shortest to a constant 8 GPa (0.9 nN) for longer carbyne chains. We demonstrate that carbyne chains exhibit extremely high vibrational frequencies close to 6 THz for the shortest chains, which are found to be highly length-dependent.

  17. The value of basic research insights into atrial fibrillation mechanisms as a guide to therapeutic innovation: a critical analysis.

    PubMed

    Heijman, Jordi; Algalarrondo, Vincent; Voigt, Niels; Melka, Jonathan; Wehrens, Xander H T; Dobrev, Dobromir; Nattel, Stanley

    2016-04-01

    Atrial fibrillation (AF) is an extremely common clinical problem associated with increased morbidity and mortality. Current antiarrhythmic options include pharmacological, ablation, and surgical therapies, and have significantly improved clinical outcomes. However, their efficacy remains suboptimal, and their use is limited by a variety of potentially serious adverse effects. There is a clear need for improved therapeutic options. Several decades of research have substantially expanded our understanding of the basic mechanisms of AF. Ectopic firing and re-entrant activity have been identified as the predominant mechanisms for arrhythmia initiation and maintenance. However, it has become clear that the clinical factors predisposing to AF and the cellular and molecular mechanisms involved are extremely complex. Moreover, all AF-promoting and maintaining mechanisms are dynamically regulated and subject to remodelling caused by both AF and cardiovascular disease. Accordingly, the initial presentation and clinical progression of AF patients are enormously heterogeneous. An understanding of arrhythmia mechanisms is widely assumed to be the basis of therapeutic innovation, but while this assumption seems self-evident, we are not aware of any papers that have critically examined the practical contributions of basic research into AF mechanisms to arrhythmia management. Here, we review recent insights into the basic mechanisms of AF, critically analyse the role of basic research insights in the development of presently used anti-AF therapeutic options and assess the potential value of contemporary experimental discoveries for future therapeutic innovation. Finally, we highlight some of the important challenges to the translation of basic science findings to clinical application.

  18. Rationally designing the mechanical properties of protein hydrogels

    NASA Astrophysics Data System (ADS)

    Cao, Yi

    Naturally occurring biomaterials possess diverse mechanical properties, which are critical to their unique biological functions. However, it remains challenging to rationally control the mechanical properties of synthetic biomaterials. Here we provide a bottom-up approach to rationally design the mechanical properties of protein-based hydrogels. We first use atomic fore microscope (AFM) based single-molecule force spectroscopy to characterize the mechanical stability of individual protein building blocks. We then rationally design the mechanical properties of hydrogels by selecting different combination of protein building blocks of known mechanical properties. As a proof-of-principle, we demonstrate the engineering of hydrogels of distinct extensibility and toughness. This simple combinatorial approach allows direct translation of the mechanical properties of proteins from the single molecule level to the macroscopic level and represents an important step towards rationally designing the mechanical properties of biomaterials.

  19. Biodegradable compounds: Rheological, mechanical and thermal properties

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Lucia, G.; Santella, M.; Malinconico, M.; Cerruti, P.; Pantani, R.

    2015-12-01

    Recently great attention from industry has been focused on biodegradable polyesters derived from renewable resources. In particular, PLA has attracted great interest due to its high strength and high modulus and a good biocompatibility, however its brittleness and low heat distortion temperature (HDT) restrict its wide application. On the other hand, Poly(butylene succinate) (PBS) is a biodegradable polymer with a low tensile modulus but characterized by a high flexibility, excellent impact strength, good thermal and chemical resistance. In this work the two aliphatic biodegradable polyesters PBS and PLA were selected with the aim to obtain a biodegradable material for the industry of plastic cups and plates. PBS was also blended with a thermoplastic starch. Talc was also added to the compounds because of its low cost and its effectiveness in increasing the modulus and the HDT of polymers. The compounds were obtained by melt compounding in a single screw extruder and the rheological, mechanical and thermal properties were investigated. The properties of the two compounds were compared and it was found that the values of the tensile modulus and elongation at break measured for the PBS/PLA/Talc compound make it interesting for the production of disposable plates and cups. In terms of thermal resistance the compounds have HDTs high enough to contain hot food or beverages. The PLA/PBS/Talc compound can be, then, considered as biodegradable substitute for polystyrene for the production of disposable plates and cups for hot food and beverages.

  20. Mechanical properties of different airway stents.

    PubMed

    Ratnovsky, Anat; Regev, Noa; Wald, Shaily; Kramer, Mordechai; Naftali, Sara

    2015-04-01

    Airway stents improve pulmonary function and quality of life in patients suffering from airway obstruction. The aim of this study was to compare main types of stents (silicone, balloon-dilated metal, self-expanding metal, and covered self-expanding metal) in terms of their mechanical properties and the radial forces they exert on the trachea. Mechanical measurements were carried out using a force gauge and specially designed adaptors fabricated in our lab. Numerical simulations were performed for eight different stent geometries, inserted into trachea models. The results show a clear correlation between stent diameter (oversizing) and the levels of stress it exerts on the trachea. Compared with uncovered metal stents, metal stents that are covered with less stiff material exert significantly less stress on the trachea while still maintaining strong contact with it. The use of such stents may reduce formation of mucosa necrosis and fistulas while still preventing stent migration. Silicone stents produce the lowest levels of stress, which may be due to weak contact between the stent and the trachea and can explain their propensity for migration. Unexpectedly, stents made of the same materials exerted different stresses due to differences in their structure. Stenosis significantly increases stress levels in all stents.

  1. Mechanical properties of DNA-like polymers

    PubMed Central

    Peters, Justin P.; Yelgaonkar, Shweta P.; Srivatsan, Seergazhi G.; Tor, Yitzhak; James Maher, L.

    2013-01-01

    The molecular structure of the DNA double helix has been known for 60 years, but we remain surprisingly ignorant of the balance of forces that determine its mechanical properties. The DNA double helix is among the stiffest of all biopolymers, but neither theory nor experiment has provided a coherent understanding of the relative roles of attractive base stacking forces and repulsive electrostatic forces creating this stiffness. To gain insight, we have created a family of double-helical DNA-like polymers where one of the four normal bases is replaced with various cationic, anionic or neutral analogs. We apply DNA ligase-catalyzed cyclization kinetics experiments to measure the bending and twisting flexibilities of these polymers under low salt conditions. Interestingly, we show that these modifications alter DNA bending stiffness by only 20%, but have much stronger (5-fold) effects on twist flexibility. We suggest that rather than modifying DNA stiffness through a mechanism easily interpretable as electrostatic, the more dominant effect of neutral and charged base modifications is their ability to drive transitions to helical conformations different from canonical B-form DNA. PMID:24013560

  2. Photopatterning the mechanical properties of polydimethylsiloxane films

    NASA Astrophysics Data System (ADS)

    Cotton, D. P. J.; Popel, A.; Graz, I. M.; Lacour, S. P.

    2011-03-01

    Silicone rubber films with graded and localized mechanical properties are prepared using two-part polydimethylsiloxane (PDMS) elastomer, photoinhibitor compounds and conventional photolithography. First the un-cross-linked PDMS is mixed with benzophenone. The resulting positive photosensitive material is then exposed through a mask to UV light from a conventional mask aligner. Cross-linking of the UV exposed elastomer is inhibited, leading to softer regions than the surrounding unexposed matrix. By empirically fitting the nonlinear, hyperelastic Mooney-Rivlin model to experimentally measured stress-strain curves we determine the equivalent tensile modulus (E) of the rubber film. We show the PDMS tensile modulus can then be adjusted in the 0.65-2.9 MPa range by decreasing the UV exposure dose (from 24 000 to 0 mJ cm-2). Further, using a patterned UV mask, we can locally define differential regions of tensile modulus within a single PDMS rubber film. We demonstrate that "hard islands" (E ≈ 2.9 MPa) of 100 μm minimum diameter can be patterned within a 100-μm-thick, single "soft" PDMS rubber membrane (E ≈ 0.65 MPa) cured at 150 °C for 24 h. Thin gold film conductors patterned directly onto the photopatterned PDMS are stretchable and withstand uniaxial cycling to tens of percent strain. The mechanically "pixellated" PDMS rubber film provides an improved substrate with built-in strain relief for stretchable electronics.

  3. Trabecular Bone Mechanical Properties and Fractal Dimension

    NASA Technical Reports Server (NTRS)

    Hogan, Harry A.

    1996-01-01

    Countermeasures for reducing bone loss and muscle atrophy due to extended exposure to the microgravity environment of space are continuing to be developed and improved. An important component of this effort is finite element modeling of the lower extremity and spinal column. These models will permit analysis and evaluation specific to each individual and thereby provide more efficient and effective exercise protocols. Inflight countermeasures and post-flight rehabilitation can then be customized and targeted on a case-by-case basis. Recent Summer Faculty Fellowship participants have focused upon finite element mesh generation, muscle force estimation, and fractal calculations of trabecular bone microstructure. Methods have been developed for generating the three-dimensional geometry of the femur from serial section magnetic resonance images (MRI). The use of MRI as an imaging modality avoids excessive exposure to radiation associated with X-ray based methods. These images can also detect trabecular bone microstructure and architecture. The goal of the current research is to determine the degree to which the fractal dimension of trabecular architecture can be used to predict the mechanical properties of trabecular bone tissue. The elastic modulus and the ultimate strength (or strain) can then be estimated from non-invasive, non-radiating imaging and incorporated into the finite element models to more accurately represent the bone tissue of each individual of interest. Trabecular bone specimens from the proximal tibia are being studied in this first phase of the work. Detailed protocols and procedures have been developed for carrying test specimens through all of the steps of a multi-faceted test program. The test program begins with MRI and X-ray imaging of the whole bones before excising a smaller workpiece from the proximal tibia region. High resolution MRI scans are then made and the piece further cut into slabs (roughly 1 cm thick). The slabs are X-rayed again

  4. Studies of Basic Electronic Properties of CdTe-Based Solar Cells and Their Evolution During Processing and Stress: Final Technical Report, 16 October 2001 - 31 August 2005

    SciTech Connect

    Kaydanov, V. I.; Ohno, T. R.

    2007-02-01

    This report describes basic issues behind CdTe/CdS cell performance and stability, such as the nature and electronic properties of impurities and defects that control the majority carrier concentration, mechanisms of dopant compensation, recombination processes, their nature and properties, migration and transformation of defects under various processing, stress, and operating conditions. We believe that a better basic understanding of the specific influence of grain boundaries, especially for fine-grain materials such as those making up CdTe-based cells, is now one of the most important issues we must address. We need to clarify the role of grain boundaries in forming the film electronic properties, as well as those of the p-n junction.

  5. Effect of Previous Agricultural Mechanics Training on Achievement in a Basic Metals and Welding Course at Iowa State University.

    ERIC Educational Resources Information Center

    Yoder, Benjamin Arthur

    The purposes of this study were to determine the effects of previous training in agricultural mechanics upon achievement of students enrolled in a college level agricultural mechanics course and to determine factors that affect performance in this course of basic metals and welding. Students enrolled in the course during the fall and winter…

  6. Finite-element analysis of the effect of basic hip movements on the mechanical stimulus within a proximal femur.

    PubMed

    Tovar-López, Francisco Javier; Domínguez-Hernández, Víctor Manuel; Diez-García, María Del Pilar; Araujo-Monsalvo, Víctor Manuel

    2014-07-01

    Osteoporosis is a serious and multifactorial disease. The number of people affected with osteoporosis is increasing due to the lengthening of life expectancy. Currently, unlike the genetic, nutritional and hormonal factors that have been the focus of most studies of osteoporosis, mechanical stimuli that potentially can produce an increase in bone strength have not been well studied. Studies suggest that the relationship between the health of the bone and mechanical stimuli occurs through bone adaptive remodeling, which is activated by means of the shear stress transmitted by the interstitial fluid flow. The present work consists of a finite element analysis of a femur to simulate the basic movements of the hip (flexion, extension, abduction, and adduction) to compare the shear stresses in a common zone of fracture and in the critical mechanical strength zones of the femoral head. A comparison of the distribution and magnitude of the shear stresses was performed to estimate the movement that could induce a more rapid adaptive bone remodeling. This study is the first step in the development of a physical therapy for a preventive rehabilitation that helps to prevent patients with low bone mineral density to avoid suffering osteoporosis hip fractures. The finite element model was constructed using a free-access three-dimensional standardized femur obtained from the Instituti Ortopedici Rizzoli, Bologna, Italy. The mechanical properties and the muscular forces were obtained from a specialized bibliography. We conclude that the movements that exhibit a higher mean value and a good shear stress distribution in the femoral neck are hip extension and abduction. PMID:25264795

  7. Finite-element analysis of the effect of basic hip movements on the mechanical stimulus within a proximal femur.

    PubMed

    Tovar-López, Francisco Javier; Domínguez-Hernández, Víctor Manuel; Diez-García, María Del Pilar; Araujo-Monsalvo, Víctor Manuel

    2014-07-01

    Osteoporosis is a serious and multifactorial disease. The number of people affected with osteoporosis is increasing due to the lengthening of life expectancy. Currently, unlike the genetic, nutritional and hormonal factors that have been the focus of most studies of osteoporosis, mechanical stimuli that potentially can produce an increase in bone strength have not been well studied. Studies suggest that the relationship between the health of the bone and mechanical stimuli occurs through bone adaptive remodeling, which is activated by means of the shear stress transmitted by the interstitial fluid flow. The present work consists of a finite element analysis of a femur to simulate the basic movements of the hip (flexion, extension, abduction, and adduction) to compare the shear stresses in a common zone of fracture and in the critical mechanical strength zones of the femoral head. A comparison of the distribution and magnitude of the shear stresses was performed to estimate the movement that could induce a more rapid adaptive bone remodeling. This study is the first step in the development of a physical therapy for a preventive rehabilitation that helps to prevent patients with low bone mineral density to avoid suffering osteoporosis hip fractures. The finite element model was constructed using a free-access three-dimensional standardized femur obtained from the Instituti Ortopedici Rizzoli, Bologna, Italy. The mechanical properties and the muscular forces were obtained from a specialized bibliography. We conclude that the movements that exhibit a higher mean value and a good shear stress distribution in the femoral neck are hip extension and abduction.

  8. An overview of zirconia dental implants: basic properties and clinical application of three cases.

    PubMed

    Bankoğlu Güngör, Merve; Aydın, Cemal; Yılmaz, Handan; Gül, Esma Başak

    2014-08-01

    Due to the possible aesthetic problems of titanium implants, the developments in ceramic implant materials are increasing. Natural tooth colored ceramic implants may be an alternative to overcome aesthetic problems. The purpose of this article is to give information about the basic properties of dental zirconia implants and present 3 cases treated with two-piece zirconia implants. Two-piece zirconia dental implants, 4.0 mm diameter and 11.5 mm in length, were inserted into maxillary incisor region. They were left for 6 months to osseointegrate. Panoramic and periapical radiographs were obtained and examined for bone-implant osseointegration. During the follow-up period the patients were satisfied with their prosthesis and no complication was observed.

  9. Mechanical properties of thermal protection system materials.

    SciTech Connect

    Hardy, Robert Douglas; Bronowski, David R.; Lee, Moo Yul; Hofer, John H.

    2005-06-01

    An experimental study was conducted to measure the mechanical properties of the Thermal Protection System (TPS) materials used for the Space Shuttle. Three types of TPS materials (LI-900, LI-2200, and FRCI-12) were tested in 'in-plane' and 'out-of-plane' orientations. Four types of quasi-static mechanical tests (uniaxial tension, uniaxial compression, uniaxial strain, and shear) were performed under low (10{sup -4} to 10{sup -3}/s) and intermediate (1 to 10/s) strain rate conditions. In addition, split Hopkinson pressure bar tests were conducted to obtain the strength of the materials under a relatively higher strain rate ({approx}10{sup 2} to 10{sup 3}/s) condition. In general, TPS materials have higher strength and higher Young's modulus when tested in 'in-plane' than in 'through-the-thickness' orientation under compressive (unconfined and confined) and tensile stress conditions. In both stress conditions, the strength of the material increases as the strain rate increases. The rate of increase in LI-900 is relatively small compared to those for the other two TPS materials tested in this study. But, the Young's modulus appears to be insensitive to the different strain rates applied. The FRCI-12 material, designed to replace the heavier LI-2200, showed higher strengths under tensile and shear stress conditions. But, under a compressive stress condition, LI-2200 showed higher strength than FRCI-12. As far as the modulus is concerned, LI-2200 has higher Young's modulus both in compression and in tension. The shear modulus of FRCI-12 and LI-2200 fell in the same range.

  10. Triadic closure as a basic generating mechanism of communities in complex networks

    NASA Astrophysics Data System (ADS)

    Bianconi, Ginestra; Darst, Richard K.; Iacovacci, Jacopo; Fortunato, Santo

    2014-10-01

    Most of the complex social, technological, and biological networks have a significant community structure. Therefore the community structure of complex networks has to be considered as a universal property, together with the much explored small-world and scale-free properties of these networks. Despite the large interest in characterizing the community structures of real networks, not enough attention has been devoted to the detection of universal mechanisms able to spontaneously generate networks with communities. Triadic closure is a natural mechanism to make new connections, especially in social networks. Here we show that models of network growth based on simple triadic closure naturally lead to the emergence of community structure, together with fat-tailed distributions of node degree and high clustering coefficients. Communities emerge from the initial stochastic heterogeneity in the concentration of links, followed by a cycle of growth and fragmentation. Communities are the more pronounced, the sparser the graph, and disappear for high values of link density and randomness in the attachment procedure. By introducing a fitness-based link attractivity for the nodes, we find a phase transition where communities disappear for high heterogeneity of the fitness distribution, but a different mesoscopic organization of the nodes emerges, with groups of nodes being shared between just a few superhubs, which attract most of the links of the system.

  11. Modeling absence seizure dynamics: implications for basic mechanisms and measurement of thalamocortical and corticothalamic latencies.

    PubMed

    Roberts, James A; Robinson, Peter A

    2008-07-01

    A successful physiologically based continuum model of the corticothalamic system is applied to determine the relative contributions of axonal and intrinsic cellular delays to the waveforms of absence seizures. The predicted period of the absence seizure depends linearly on model parameters describing thalamocortical, corticothalamic, intracortical, and synaptodendritic delays, and these dependences are linked to the seizure mechanism by showing how time intervals between peaks in the waveforms depend on the parameters. Counterintuitively, it is found that a peak in the local field potential recorded in the thalamic relay nuclei can precede the peak in the cortical field that drove it, without violating causality, but rendering naive interpretation of time intervals between peaks invalid. We argue that a thalamocortical loop mechanism for absence seizures is consistent with intrathalamic cellular properties being the leading determinant of the frequency of spike-wave discharges in rat genetic models, with the combination of network and cellular properties providing a natural explanation for the lower frequency of human absence seizures. Finally, our results imply that the seizure frequency is not determined by the fastest thalamocortical and corticothalamic fibers, but rather depends on an effective weighted conduction velocity of all pathways present.

  12. Mechanical properties and clinical applications of orthodontic wires.

    PubMed

    Kapila, S; Sachdeva, R

    1989-08-01

    This review article describes the mechanical properties and clinical applications of stainless steel, cobalt-chromium, nickel-titanium, beta-titanium, and multistranded wires. The consolidation of this literature will provide the clinician with the basic working knowledge on orthodontic wire characteristics and usage. Mechanical properties of these wires are generally assessed by tensile, bending, and torsional tests. Although wire characteristics determined by these tests do not necessarily reflect the behavior of the wires under clinical conditions, they provide a basis for comparison of these wires. The characteristics desirable in an orthodontic wire are a large springback, low stiffness, good formability, high stored energy, biocompatibility and environmental stability, low surface friction, and the capability to be welded or soldered to auxiliaries. Stainless steel wires have remained popular since their introduction to orthodontics because of their formability, biocompatibility and environmental stability, stiffness, resilience, and low cost. Cobalt-chromium (Co-Cr) wires can be manipulated in a softened state and then subjected to heat treatment. Heat treatment of Co-Cr wires results in a wire with properties similar to those of stainless steel. Nitinol wires have a good springback and low stiffness. This alloy, however, has poor formability and joinability. Beta-titanium wires provide a combination of adequate springback, average stiffness, good formability, and can be welded to auxiliaries. Multistranded wires have a high springback and low stiffness when compared with solid stainless steel wires. Optimal use of these orthodontic wires can be made by carefully selecting the appropriate wire type and size to meet the demands of a particular clinical situation. PMID:2667330

  13. Mechanical Properties of Nuclear Fuel Surrogates using Picosecond Laser Ultrasonics

    SciTech Connect

    David Hurley; Marat Khafizov; Farhad Farzbod; Eric Burgett

    2013-05-01

    Detailed understanding between microstructure evolution and mechanical properties is important for designing new high burnup nuclear fuels. In this presentation we discuss the use of picosecond ultrasonics to measure localize changes in mechanical properties of fuel surrogates. We develop measurement techniques that can be applied to investigate heterogeneous elastic properties caused by localize changes in chemistry, grain microstructure caused by recrystallization, and mechanical properties of small samples prepared using focused ion beam sample preparation. Emphasis is placed on understanding the relationship between microstructure and mechanical properties

  14. Extracting nanobelt mechanical properties from nanoindentation

    NASA Astrophysics Data System (ADS)

    Zhang, Yin

    2010-06-01

    A three-spring-in-series model is proposed for the nanobelt (NB) indentation test. Compared with the previous two-spring-in-series model, which considers the bending stiffness of atomic force microscope cantilever and the indenter/NB contact stiffness, this model adds a third spring of the NB/substrate contact stiffness. NB is highly flexural due to its large aspect ratio of length to thickness. The bending and lift-off of NB form a localized contact with substrate, which makes the Oliver-Pharr method [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)] and Sneddon method [I. N. Sneddon, Int. J. Eng. Sci. 3, 47 (1965)] inappropriate for NB indentation test. Because the NB/substrate deformation may have significant impact on the force-indentation depth data obtained in experiment, the two-spring-in-series model can lead to erroneous predictions on the NB mechanical properties. NB in indentation test can be susceptible to the adhesion influence because of its large surface area to volume ratio. NB/substrate contact and adhesion can have direct and significant impact on the interpretation of experimental data. Through the three-spring-in-series model, the influence of NB/substrate contact and adhesion is analyzed and methods of reducing such influence are also suggested.

  15. Mechanical properties of the aneurysmal aorta.

    PubMed

    MacSweeney, S T; Young, G; Greenhalgh, R M; Powell, J T

    1992-12-01

    The mechanical properties of the abdominal aorta were investigated non-invasively in 30 patients with aortic aneurysm and 11 with peripheral arterial disease. The distensibility of the aorta was measured using M-mode ultrasonography, permitting non-invasive assessment of the pressure--strain elastic modulus or aortic stiffness, Ep. The median Ep value increased from 4.0 N/cm2 in control subjects in their third decade of life (n = 10) to 10.4 N/cm2 in middle age (n = 11) to 14.0 N/cm2 in the elderly (n = 13). In the presence of a normal diameter, peripheral arterial disease with aortic atherosclerosis had little effect on aortic stiffness, median Ep being 16.0 N/cm2. Aneurysmal dilatation was associated with a significant increase in aortic stiffness, median Ep being 31.3 N/cm2 (P < 0.001). For aortas of normal diameter, Ep was at all ages dependent on mean arterial pressure. In patients with aortic aneurysms there was no clear relationship between Ep and mean arterial pressure or aortic diameter. Of the patients studied, 15 underwent aortic reconstruction; increasing aortic stiffness (log Ep) was associated with a decreased medial elastin content of the aortic biopsy (r = -0.63, P < 0.02). This study demonstrates the marked stiffness or inelasticity of dilated or aneurysmal vessels, part of which is attributable to the loss of elastin.

  16. Mechanical properties of carbon-implanted niobium

    SciTech Connect

    Zinkle, S.J. ); Huang, J.S. )

    1990-01-01

    Polycrystalline niobium specimens were implanted with either 200 keV carbon ions or a combination of 50, 100, and 200 keV carbon ions to peak concentrations of 0.6 to 50 at. {percent}. Microindentation techniques were used to measure the hardness and elastic modulus of the implanted layer. Both the hardness (H) and modulus (E) showed dramatic increases due to the carbon implantation. The measured peak hardness and modulus following uniform implantation with 16 at. {percent} C were 15{times} and 3{times} that of niobium, respectively, which is comparable to the literature values for NbC. The peak hardness and modulus for the implanted specimens were observed at an indent depth of {approximately}40 nm, which is about one-eighth of the depth of the implanted carbon layer. The decrease in the indentation mechanical properties at deeper indent depths is due to the interaction of long-ranging strain fields underneath the indenter with the niobium substrate. 17 refs., 6 figs.

  17. Mechanical properties of melamine-formaldehyde microcapsules.

    PubMed

    Sun, G; Zhang, Z

    2001-01-01

    The mechanical properties of melamine-formaldehyde (M-F) microcapsules were studied using a micromanipulation technique. Single microcapsules with diameters of 1-12 microm were compressed and held between two parallel planes, compressed and released, and compressed to burst at different speeds, whilst the force being imposed on the microcapsules and their deformation were measured simultaneously. This force increased as single microcapsules were compressed and then relaxed slightly as they were held. When the microcapsules were repeatedly compressed and released, a pseudo yield point was found for each microcapsule. Before the microcapsules were compressed to this point, the deformed microcapsules recovered to their original shape once the force was removed. However, when the deformation was beyond the 'yield point' there was profound hysteresis and the microcapsules showed plastic behaviour. As the microcapsules were compressed to burst at different speeds, ranging from 0.5-6.0 microm/s, it was found that their mean bursting forces did not change significantly. The deformations at the pseudo yield point and at bursting were also independent of the compression speed. On average, these melamine-formaldehyde microcapsules reached their 'yield point' at a deformation of about 19 +/- 1%, and burst at a deformation of 70 +/- 1%.

  18. Mechanical Properties of the Upper Airway

    PubMed Central

    Strohl, Kingman P.; Butler, James P.; Malhotra, Atul

    2013-01-01

    The importance of the upper airway (nose, pharynx, and larynx) in health and in the pathogenesis of sleep apnea, asthma, and other airway diseases, discussed elsewhere in the Comprehensive Physiology series, prompts this review of the biomechanical properties and functional aspects of the upper airway. There is a literature based on anatomic or structural descriptions in static circumstances, albeit studied in limited numbers of individuals in both health and disease. As for dynamic features, the literature is limited to studies of pressure and flow through all or parts of the upper airway and to the effects of muscle activation on such features; however, the links between structure and function through airway size, shape, and compliance remain a topic that is completely open for investigation, particularly through analyses using concepts of fluid and structural mechanics. Throughout are included both historically seminal references, as well as those serving as signposts or updated reviews. This article should be considered a resource for concepts needed for the application of biomechanical models of upper airway physiology, applicable to understanding the pathophysiology of disease and anticipated results of treatment interventions. PMID:23723026

  19. Kinetics and mechanism of hexavalent chromium removal by basic oxygen furnace slag.

    PubMed

    Han, Chong; Jiao, Yanan; Wu, Qianqian; Yang, Wangjin; Yang, He; Xue, Xiangxin

    2016-08-01

    Basic oxygen furnace slag (BOFS) has the potential to remove hexavalent chromium (Cr(VI)) from wastewater by a redox process due to the presence of minerals containing Fe(2+). The effects of the solution pH, initial Cr(VI) concentration, BOFS dosage, BOFS particle size, and temperature on the removal of Cr(VI) was investigated in detail through batch tests. The chemical and mineral compositions of fresh and reacted BOFS were characterized using scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) system and X-ray diffractometer (XRD). The results show that Cr(VI) in wastewater can be efficiently removed by Fe(2+) released from BOFS under appropriate acidic conditions. The removal of Cr(VI) by BOFS significantly depended on the parameters mentioned above. The reaction of Cr(VI) with BOFS followed the pseudo-second-order kinetic model. Fe(2+) responsible for Cr(VI) removal was primarily derived from the dissolution of FeO and Fe3O4 in BOFS. When H2SO4 was used to adjust the solution acidity, gypsum (CaSO4·2H2O) could be formed and become an armoring precipitate layer on the BOFS surface, hindering the release of Fe(2+) and the removal of Cr(VI). Finally, the main mechanism of Cr(VI) removal by BOFS was described using several consecutive reaction steps.

  20. Kinetics and mechanism of hexavalent chromium removal by basic oxygen furnace slag.

    PubMed

    Han, Chong; Jiao, Yanan; Wu, Qianqian; Yang, Wangjin; Yang, He; Xue, Xiangxin

    2016-08-01

    Basic oxygen furnace slag (BOFS) has the potential to remove hexavalent chromium (Cr(VI)) from wastewater by a redox process due to the presence of minerals containing Fe(2+). The effects of the solution pH, initial Cr(VI) concentration, BOFS dosage, BOFS particle size, and temperature on the removal of Cr(VI) was investigated in detail through batch tests. The chemical and mineral compositions of fresh and reacted BOFS were characterized using scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) system and X-ray diffractometer (XRD). The results show that Cr(VI) in wastewater can be efficiently removed by Fe(2+) released from BOFS under appropriate acidic conditions. The removal of Cr(VI) by BOFS significantly depended on the parameters mentioned above. The reaction of Cr(VI) with BOFS followed the pseudo-second-order kinetic model. Fe(2+) responsible for Cr(VI) removal was primarily derived from the dissolution of FeO and Fe3O4 in BOFS. When H2SO4 was used to adjust the solution acidity, gypsum (CaSO4·2H2O) could be formed and become an armoring precipitate layer on the BOFS surface, hindering the release of Fe(2+) and the removal of Cr(VI). Finally, the main mechanism of Cr(VI) removal by BOFS was described using several consecutive reaction steps. PMID:27521937

  1. Basic principles on selection and use of diagnostic tests: properties of diagnostic tests.

    PubMed

    Carneiro, A V

    2001-12-01

    In clinical practice, in order to design and implement a specific therapeutic plan, as well as communicating an appropriate prognosis, the doctor needs to establish a precise diagnosis of the condition. Sometimes all one needs is a clinical impression. More often, however, the definition of an accurate diagnosis will mandate the interpretation of specific diagnostic tests as well. The rational use of diagnostic tests in cardiology--whether laboratorial or imaging--should be based on three factors: 1) validity of results of studies on the test; 2) diagnostic properties of the test; and 3) applicability of the test in the clinical setting. The rational use and the correct interpretation of diagnostic tests are based on these three factors. In a previous article we presented the basic principles concerning the validity of the results from the study that defined the specific test, and what level of evidence that constitutes. In this article we present the diagnostic properties of tests (sensitivity, specificity, positive and negative predictive values, likelihood ratios, odds). Finally, in a forthcoming paper we will discuss the applicability of the test in clinical cardiological practice. PMID:11865687

  2. The auditory cortex of the bat Phyllostomus discolor: Localization and organization of basic response properties

    PubMed Central

    Hoffmann, Susanne; Firzlaff, Uwe; Radtke-Schuller, Susanne; Schwellnus, Britta; Schuller, Gerd

    2008-01-01

    Background The mammalian auditory cortex can be subdivided into various fields characterized by neurophysiological and neuroarchitectural properties and by connections with different nuclei of the thalamus. Besides the primary auditory cortex, echolocating bats have cortical fields for the processing of temporal and spectral features of the echolocation pulses. This paper reports on location, neuroarchitecture and basic functional organization of the auditory cortex of the microchiropteran bat Phyllostomus discolor (family: Phyllostomidae). Results The auditory cortical area of P. discolor is located at parieto-temporal portions of the neocortex. It covers a rostro-caudal range of about 4800 μm and a medio-lateral distance of about 7000 μm on the flattened cortical surface. The auditory cortices of ten adult P. discolor were electrophysiologically mapped in detail. Responses of 849 units (single neurons and neuronal clusters up to three neurons) to pure tone stimulation were recorded extracellularly. Cortical units were characterized and classified depending on their response properties such as best frequency, auditory threshold, first spike latency, response duration, width and shape of the frequency response area and binaural interactions. Based on neurophysiological and neuroanatomical criteria, the auditory cortex of P. discolor could be subdivided into anterior and posterior ventral fields and anterior and posterior dorsal fields. The representation of response properties within the different auditory cortical fields was analyzed in detail. The two ventral fields were distinguished by their tonotopic organization with opposing frequency gradients. The dorsal cortical fields were not tonotopically organized but contained neurons that were responsive to high frequencies only. Conclusion The auditory cortex of P. discolor resembles the auditory cortex of other phyllostomid bats in size and basic functional organization. The tonotopically organized posterior

  3. Basic mechanisms behind the effects of n-3 fatty acids on cardiovascular disease.

    PubMed

    Massaro, Marika; Scoditti, Egeria; Carluccio, Maria Annunziata; De Caterina, Raffaele

    2008-01-01

    The epidemiological association between high intakes of n-3 fatty acids (FA) and decreased morbidity and mortality from cardiovascular disease (CVD) can be explained by two main basic mechanisms: (a) an effect on atherothrombosis, and (b) an effect on cardiac arrhythmias. These mechanisms probably reflect different beneficial influences of n-3 FA on cardiovascular biology. Effects on atherothrombosis include the modulation of the expression of pro-atherogenic genes (e.g., endothelial leukocyte adhesion molecules, inflammatory cytokines and cyclooxygenase (COX)-2) and the hepatic synthesis of very low density lipoproteins (VLDL), and are slow in onset, requiring incorporation into cell membrane phospholipids, and usually doses in humans in the order of 3g/day or higher. Effects on cardiac arrhythmias include complex interactions with ion channels (sodium, potassium and calcium channels), typically requiring the presence of free FA in extracellular fluids and usually occurring with lower doses (around 1g/day) of nutritional or pharmacological intake. We have focused most of our research effort in unraveling the pathophysiological background of protection by n-3 FA from atherothrombosis. As the result of incorporation of n-3 FA in the sn-2 position predominantly of the phosphatidyl ethanolamine pool in the inner leaflet of the plasma membrane, n-3 FA appear on the one hand to increase the production of bioactive lipid mediators (protectins and resolvins) affecting cytokine-induced signal transduction; and on the other hand to directly interfere with the generation of reactive oxygen species (mostly hydrogen peroxide), directly responsible for the activation of the transcription factor nuclear factor (NF)-kappaB, which controls the expression of a variety of pro-inflammatory and pro-atherogenic genes, including those encoding for interleukin (IL)-1, IL-6, IL-8, tumor necrosis factor (TNF)alpha, vascular cell adhesion molecule-1 (VCAM-1), E-selectin, and COX-2. The

  4. Microstructure, mechanical properties, bio-corrosion properties and antibacterial properties of Ti-Ag sintered alloys.

    PubMed

    Chen, Mian; Zhang, Erlin; Zhang, Lan

    2016-05-01

    In this research, Ag element was selected as an antibacterial agent to develop an antibacterial Ti-Ag alloy by a powder metallurgy. The microstructure, phase constitution, mechanical properties, corrosion resistance and antibacterial properties of the Ti-Ag sintered alloys have been systematically studied by X-ray diffraction (XRD), scanning electron microscope (SEM), compressive test, electrochemical measurements and antibacterial test. The effects of the Ag powder size and the Ag content on the antibacterial property and mechanical property as well as the anticorrosion property have been investigated. The microstructure results have shown that Ti-Ag phase, residual pure Ag and Ti were the mainly phases in Ti-Ag(S75) sintered alloy while Ti2Ag was synthesized in Ti-Ag(S10) sintered alloy. The mechanical test indicated that Ti-Ag sintered alloy showed a much higher hardness and the compressive yield strength than cp-Ti but the mechanical properties were slightly reduced with the increase of Ag content. Electrochemical results showed that Ag powder size had a significant effect on the corrosion resistance of Ti-Ag sintered alloy. Ag content increased the corrosion resistance in a dose dependent way under a homogeneous microstructure. Antibacterial tests have demonstrated that antibacterial Ti-Ag alloy was successfully prepared. It was also shown that the Ag powder particle size and the Ag content influenced the antibacterial activity seriously. The reduction in the Ag powder size was benefit to the improvement in the antibacterial property and the Ag content has to be at least 3wt.% in order to obtain a strong and stable antibacterial activity against Staphylococcus aureus bacteria. The bacterial mechanism was thought to be related to the Ti2Ag and its distribution. PMID:26952433

  5. Microstructure, mechanical properties, bio-corrosion properties and antibacterial properties of Ti-Ag sintered alloys.

    PubMed

    Chen, Mian; Zhang, Erlin; Zhang, Lan

    2016-05-01

    In this research, Ag element was selected as an antibacterial agent to develop an antibacterial Ti-Ag alloy by a powder metallurgy. The microstructure, phase constitution, mechanical properties, corrosion resistance and antibacterial properties of the Ti-Ag sintered alloys have been systematically studied by X-ray diffraction (XRD), scanning electron microscope (SEM), compressive test, electrochemical measurements and antibacterial test. The effects of the Ag powder size and the Ag content on the antibacterial property and mechanical property as well as the anticorrosion property have been investigated. The microstructure results have shown that Ti-Ag phase, residual pure Ag and Ti were the mainly phases in Ti-Ag(S75) sintered alloy while Ti2Ag was synthesized in Ti-Ag(S10) sintered alloy. The mechanical test indicated that Ti-Ag sintered alloy showed a much higher hardness and the compressive yield strength than cp-Ti but the mechanical properties were slightly reduced with the increase of Ag content. Electrochemical results showed that Ag powder size had a significant effect on the corrosion resistance of Ti-Ag sintered alloy. Ag content increased the corrosion resistance in a dose dependent way under a homogeneous microstructure. Antibacterial tests have demonstrated that antibacterial Ti-Ag alloy was successfully prepared. It was also shown that the Ag powder particle size and the Ag content influenced the antibacterial activity seriously. The reduction in the Ag powder size was benefit to the improvement in the antibacterial property and the Ag content has to be at least 3wt.% in order to obtain a strong and stable antibacterial activity against Staphylococcus aureus bacteria. The bacterial mechanism was thought to be related to the Ti2Ag and its distribution.

  6. Ultrasonic nondestructive evaluation, microstructure, and mechanical property interrelations

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1984-01-01

    Ultrasonic techniques for mechanical property characterizations are reviewed and conceptual models are advanced for explaining and interpreting the empirically based results. At present, the technology is generally empirically based and is emerging from the research laboratory. Advancement of the technology will require establishment of theoretical foundations for the experimentally observed interrelations among ultrasonic measurements, mechanical properties, and microstructure. Conceptual models are applied to ultrasonic assessment of fracture toughness to illustrate an approach for predicting correlations found among ultrasonic measurements, microstructure, and mechanical properties.

  7. Real-time observations of mechanical stimulus-induced enhancements of mechanical properties in osteoblast cells.

    PubMed

    Zhang, Xu; Liu, Xiaoli; Sun, Jialun; He, Shuojie; Lee, Imshik; Pak, Hyuk Kyu

    2008-09-01

    Osteoblast, playing a key role in the pathophysiology of osteoporosis, is one of the mechanical stress sensitive cells. The effects of mechanical load-induced changes of mechanical properties in osteoblast cells were studied at real-time. Osteoblasts obtained from young Wistar rats were exposed to mechanical loads in different frequencies and resting intervals generated by atomic force microscopy (AFM) probe tip and simultaneously measured the changes of the mechanical properties by AFM. The enhancement of the mechanical properties was observed and quantified by the increment of the apparent Young's modulus, E*. The observed mechanical property depended on the frequency of applied tapping loads. For the resting interval is 50s, the mechanical load-induced enhancement of E*-values disappears. It seems that the enhanced mechanical property was recover able under no additional mechanical stimulus.

  8. Mechanical Properties of High Purity Niobium - Novel Measurements

    SciTech Connect

    Ganapati Myneni

    2003-09-01

    One of the procedures to improve the performance of superconducting niobium cavities is a heat treatment for several hours in an ultrahigh vacuum at temperatures between 800C and 1400C for hydrogen degassing or post-purification, respectively. However, it was recently observed with Spallation Neutron Source Project (SNS) prototype cavities, that a heat treatment at 800 C for even 1 hour degraded the mechanical properties of RRR niobium, in particular the yield strength. This lower strength resulted in cavity deformations during handling thus affecting both their resonant frequency and field profile. In addition to lowering the yield strength, it was observed in some lots of material that the Young's modulus was also apparently reduced by a factor of 2 as a result of the hydrogen outgassing at 800 C. Surprisingly, material received at other national laboratories exhibited similar anomalous behavior even without any heat treatments in vacuum. Based on these observations a multi-institutional collaborative basic research activity on high RRR niobium (determination of Nb yield strength as a function of grain size, work hardening, chemical composition, and heat treatment temperature) has been initiated by JLAB to gain a better understanding of the material properties affecting the mechanical behavior In this contribution, a brief review of the measurements at JLAB, at the Materials Science and Engineering Department of the University of Virginia, at the Analytical Chemistry and Metallurgy Divisions of the National Institute of Standard and Technology, Gaithersburg and in the Department of Physics, SUNY, Albany are presented. The measurements include yield strength, hardness, ultrasonic velocity, crystallographic structure, microstructure, determination of interstitial contents using internal friction; particular emphasis is placed on determining the hydrogen concentration in the niobium via Cold Neutron Prompt Gamma-Ray Activation Analysis and Neutron Incoherent

  9. The role of stochastic gene switching in determining the pharmacodynamics of certain drugs: basic mechanisms.

    PubMed

    Puszynski, Krzysztof; Gandolfi, Alberto; d'Onofrio, Alberto

    2016-08-01

    In this paper we analyze the impact of the stochastic fluctuation of genes between their ON and OFF states on the pharmacodynamics of a potentially large class of drugs. We focus on basic mechanisms underlying the onset of in vitro experimental dose-response curves, by investigating two elementary molecular circuits. Both circuits consist in the transcription of a gene and in the successive translation into the corresponding protein. Whereas in the first the activation/deactivation rates of the single gene copy are constant, in the second the protein, now a transcription factor, amplifies the deactivation rate, so introducing a negative feedback. The drug is assumed to enhance the elimination of the protein, and in both cases the success of therapy is assured by keeping the level of the given protein under a threshold for a fixed time. Our numerical simulations suggests that the gene switching plays a primary role in determining the sigmoidal shape of dose-response curves. Moreover, the simulations show interesting phenomena related to the magnitude of the average gene switching time and to the drug concentration. In particular, for slow gene switching a significant fraction of cells can respond also in the absence of drug or with drug concentrations insufficient for the response in a deterministic setting. For higher drug concentrations, the non-responding fraction exhibits a maximum at intermediate values of the gene switching rates. For fast gene switching, instead, the stochastic prediction follows the prediction of the deterministic approximation, with all the cells responding or non-responding according to the drug dose. PMID:27352096

  10. Mechanical Properties and Organic Carbon of Soil Aggregates in the Northern Appalachians

    SciTech Connect

    Blanco-Canqui, H.; Lal, Rattan; Owens, L. B.; Post, W. M.; Izaurralde, R Cesar C.

    2005-09-30

    The macroscale behavior of the soil depends on the mechanical properties of individual aggregates. The structural dynamics of the whole soil is defined by the architectural organization and attributes of ever-changing aggregates as the basic units of soil structure development. Aggregates influence root growth and seedling emergence (DeFreitas et al., 1996), soil moisture retention (SMR) and airflow (Watts and Dexter, 1997), and SOC sequestration and dynamics (Denef et al., 2004). Mechanical properties of aggregates are indicative of response of the soil system to tillage, compaction, and plant growth. The properties of aggregates may differ from those of the whole soil due to the dynamics of aggregate formation (Horn, 1990; Zhang, 1994). Understanding of mechanical properties of aggregates is cru- condicial to explain the macroscale functions of soil for plant growth (DeFreitas et al., 1996).

  11. Lattice model of linear telechelic polymer melts. II. Influence of chain stiffness on basic thermodynamic properties.

    PubMed

    Xu, Wen-Sheng; Freed, Karl F

    2015-07-14

    The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chain stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.

  12. Lattice model of linear telechelic polymer melts. II. Influence of chain stiffness on basic thermodynamic properties

    NASA Astrophysics Data System (ADS)

    Xu, Wen-Sheng; Freed, Karl F.

    2015-07-01

    The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chain stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.

  13. Lattice model of linear telechelic polymer melts. II. Influence of chain stiffness on basic thermodynamic properties

    SciTech Connect

    Xu, Wen-Sheng; Freed, Karl F.

    2015-07-14

    The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chain stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.

  14. New radiochromic gel for 3D dosimetry based on Turnbull blue: basic properties.

    PubMed

    Solc, Jaroslav; Spevácek, Václav

    2009-09-01

    The recently developed new radiochromic gel dosimeter based on Turnbull blue dye formed by irradiation (the TBG dosimeter) does not exhibit dose pattern degradation due to diffusion effects as observed in the Fricke-gel dosimeter with xylenol orange incorporated into the gel matrix (the FXG dosimeter). The TBG dosimeter can be easily prepared and its optical properties enable evaluation of the gel's response using the cone-beam optical computed tomography technique. The preparation procedure is described in the paper along with the basic characteristics of the gel, including dose response, dose sensitivity, ageing under different storage conditions, diffusion rates of Turnbull blue and gel density. The measurement of diffusion is described in more detail. The same method was applied to the FXG dosimeter for direct comparison. It was found that the diffusion coefficient of the TBG dosimeter stored at 24 degrees C is less than 4 x 10(-3) mm(2) h(-1) (1sigma confidence level), compared to the value of 7.3 x 10(-1) mm(2) h(-1) (1sigma) of the FXG dosimeter measured at the same temperature. Although the TBG dosimeter is less sensitive than the FXG dosimeter, its diffusion coefficient is practically negligible and, therefore, it offers large potential as a three-dimensional dosimeter for applications encompassing sharp dose gradients such as high-dose-rate brachytherapy. PMID:19652291

  15. Mechanical properties of the passive sea urchin sperm flagellum.

    PubMed

    Pelle, Dominic W; Brokaw, Charles J; Lesich, Kathleen A; Lindemann, Charles B

    2009-09-01

    In this study we used Triton X-100 extracted sea urchin spermatozoa to investigate the mechanical behavior of the basic 9+2 axoneme. The dynein motors were disabled by vanadate so that the flagellum is rendered a passive structure. We find that when a proximal portion of the flagellum is bent with a glass microprobe, the remainder of the flagellum distal to the probe exhibits a bend in the opposite direction (a counterbend). The counterbend can be understood from the prevailing sliding doublet model of axoneme mechanics, but does require the existence of elastic linkages between the outer doublets. Analysis of the shapes of counterbends provides a consensus value of 0.03-0.08/microm(2) for the ratio of the interdoublet shear resistance (E(S)) to the bending resistance (E(B)) and we find that the ratio E(S)/E(B) is relatively conserved for both passive flagella and transiently quiescent live flagella. This ratio expresses a fundamental mechanical property of the eukaryotic axoneme. It defines the contributions to total bending resistance derived from bending the microtubules and from stretching the interdoublet linkages, respectively. Using this ratio, and computer simulations of earlier experiments that measured the total stiffness of the flagellum, we obtain estimates of approximately 1 x 10(8) pN nm(2)/rad for E(B) and 6 pN/rad for E(S), assuming that both elasticities are linear. Our results indicate that the behavior of the flagellum is close to that predicted by a linear model for shear elasticity. PMID:19536829

  16. On the Acquisition of Some Basic Word Spelling Mechanisms in a Deep (French) and a Shallow (Spanish) System

    ERIC Educational Resources Information Center

    Carrillo, Maria Soledad; Alegria, Jesus; Marin, Javier

    2013-01-01

    An experiment was carried out to compare the time course of the acquisition of two basic spelling mechanisms in Spanish, a shallow system, and French, a deep system. The first was lexical. It relies on the orthographic lexicon, a hypothetical structure containing the orthographic representations of words accessible for word spelling. To evaluate…

  17. Investigation of basic properties of fly ash from urban waste incinerators in China.

    PubMed

    Jiang, Jian-guo; Xu, Xin; Wang, Jun; Yang, Shi-jian; Zhang, Yan

    2007-01-01

    Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD). The leaching toxicity procedure and some factors influencing heavy metals distribution in fly ash were further investigated. Experimental results indicate that the fly ash structures are complex and its properties are variable. The results of XRF and SEM revealed that the major elements (>10000 mg/kg, listed in decreasing order of abundance) in fly ash are O, Ca, Cl, Si, S, K, Na, Al, Fe and Zn. These elements account for 93% to 97%, and the content of Cl ranges from 6.93% to 29.18 %, while that of SiO2 does from 4.48% to 24.84%. The minor elements (1000 to 10000 mg/kg) include Cr, Cu and Pb. Primary heavy metals in fly ash include Zn, Pb, Cr, Cu etc. According to standard leaching test, heavy metal leaching levels vary from 0 to 163.10 mg/L (Pb) and from 0.049 to 164.90 mg/L (Zn), mostly exceeding the Chinese Identification Standard for hazardous wastes. Morphology of fly ash is irregular, with both amorphous structures and polycrystalline aggregates. Further research showed that heavy metals were volatilized at a high furnace temperature, condensed when cooling down during the post-furnace system and captured at air pollution control systems. Generally, heavy metals are mainly present in the forms of aerosol particulates or tiny particulates enriched on surfaces of fly ash particles. The properties of fly ash are greatly influenced by the treatment capacities of incinerators or the variation of waste retention time in chamber. Fly ash from combustors of larger capacities generally has higher contents of volatile component and higher leaching toxicity, while those of smaller capacities often produce fly ash containing higher levels of nonvolatile components and has lower toxicity. The content of heavy metals and leaching toxicity maybe have no convincing

  18. Wave-Mechanical Properties of Stationary States.

    ERIC Educational Resources Information Center

    Holden, Alan

    This monograph is a review of the quantum mechanical concepts presented in two other monographs, "The Nature of Atoms" and "Bonds Between Atoms," by the same author. It is assumed the reader is familiar with these ideas. The monograph sketches only those aspects of quantum mechanics that are of most direct use in picturing and calculating the…

  19. Mechanical Properties of Degraded PMR-15 Resin

    NASA Technical Reports Server (NTRS)

    Tsuji, Luis C.; McManus, Hugh L.; Bowles, Kenneth J.

    1998-01-01

    Thermo-oxidative aging produces a non-uniform degradation state in PMR-15 resin. A surface layer, usually attributed to oxidative degradation, forms. This surface layer has different properties from the inner material. A set of material tests was designed to separate the properties of the oxidized surface layer from the properties of interior material. Test specimens were aged at 316 C in either air or nitrogen, for durations of up to 800 hours. The thickness of the oxidized surface layer in air aged specimens, and the shrinkage and Coefficient of Thermal Expansion (CTE) of nitrogen aged specimens were measured directly. Four-point-bend tests were performed to determine modulus of both the oxidized surface layer and the interior material. Bimaterial strip specimens consisting of oxidized surface material and unoxidized interior material were constructed and used to determine surface layer shrinkage and CTE. Results confirm that the surface layer and core materials have substantially different properties.

  20. Attractive mechanical properties of a lightweight highly sensitive bi layer thermistor: polycarbonate/organic molecular conductor

    NASA Astrophysics Data System (ADS)

    Laukhina, E.; Lebedev, V.; Rovira, C.; Laukhin, V.; Veciana, J.

    2016-03-01

    The paper covers some of the basic mechanical characteristics of a recently developed bi layer thermistor: polycarbonate/(001) oriented layer of organic molecular conductor α’-(BEDT-TTF)2IxBr3-x, were BEDT-TTF=bis(ethylenedithio)tetrathiafulvalen. The nano and macro mechanical properties have been studied in order to use this flexible, low cost thermistor in sensing applications by proper way. The nano-mechanical properties of the temperature sensitive semiconducting layer of α’-(BEDT-TTF)2IxBr3-x were tested using nanoindentation method. The value of Young's modulus in direction being perpendicular to the layer plan was found as 9.0 ±1.4 GPa. The macro mechanical properties of the thermistor were studied using a 5848 MicroTester. The tensile tests showed that basic mechanical characteristics of the thermistor are close to those of polycarbonate films. This indicates a good mechanical strength of the developed sensor. Therefore, the thermistor can be used in technologies that need to be instrumented with highly robustness lightweight low cost temperature sensors. The paper also reports synthetic details on fabricating temperature sensing e-textile. As the temperature control is becoming more and more important in biomedical technologies like healthcare monitoring, this work strongly contributes on the ongoing research on engineering sensitive conducting materials for biomedical applications.

  1. Mechanical and physical properties of plasma-sprayed stabilized zirconia

    NASA Technical Reports Server (NTRS)

    Siemers, P. A.; Mehan, R. L.

    1983-01-01

    Physical and mechanical properties were determined for plasma-sprayed MgO- or Y2O3-stabilized ZrO2 thermal barrier coatings. Properties were determined for the ceramic coating in both the freestanding condition and as-bonded to a metal substrate. The properties of the NiCrAlY bond coating were also investigated.

  2. Mechanical Properties of Degraded PMR-15 Resin

    NASA Technical Reports Server (NTRS)

    Tsuji, Luis C.

    2000-01-01

    Thermo-oxidative aging produces a nonuniform degradation state in PMR-15 resin. A surface layer, usually attributed to oxidative degradation, forms. This surface layer has different properties from the inner material. A set of material tests was designed to separate the properties of the oxidized surface layer from the properties of interior material. Test specimens were aged at 316 C in either air or nitrogen, for durations of up to 800 hr. The thickness of the oxidized surface layer in air aged specimens, and the shrinkage and coefficient of thermal expansion (CTE) of nitrogen aged specimens were measured directly. The nitrogen-aged specimens were assumed to have the same properties as the interior material in the air-aged specimens. Four-point-bend tests were performed to determine modulus of both the oxidized surface layer and the interior material. Bimaterial strip specimens consisting of oxidized surface material and unoxidized interior material were constructed and used to determine surface layer shrinkage and CTE. Results confirm that the surface layer and core materials have substantially different properties.

  3. Phonon spectrum, mechanical and thermophysical properties of thorium carbide

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    In this work, we study, by means of density functional perturbation theory and the pseudopotential method, mechanical and thermophysical properties of thorium carbide. These properties are derived from the lattice dynamics in the quasi-harmonic approximation. The phonon spectrum of ThC presented in this article, to the best authors' knowledge, have not been studied, neither experimentally, nor theoretically. We compare mechanical properties, volume thermal expansion and molar specific capacities with previous results and find a very good agreement.

  4. Polymer Basics: Classroom Activities Manipulating Paper Clips to Introduce the Structures and Properties of Polymers

    ERIC Educational Resources Information Center

    Umar, Yunusa

    2014-01-01

    A simple and effective hands-on classroom activity designed to illustrate basic polymer concepts is presented. In this activity, students build primary structures of homopolymers and different arrangements of monomers in copolymer using paper clips as monomers. The activity supports formation of a basic understanding of polymer structures,…

  5. Basic properties of sintering dust from iron and steel plant and potassium recovery.

    PubMed

    Zhan, Guang; Guo, Zhancheng

    2013-06-01

    With the production of crude steel, China produces several million tons of sintering dusts which contain a great deal of valuable metals such as, K, Na, Zn, Pb. If discharged directly without adequate treatment, these elements can lead to adverse effects on the environment. Therefore, it is very necessary to determine how to separate these elements from the dust before discharge. Several physical and chemical detection methods were used to study the basic properties of sintering dust. At the same time, preliminary experiments on the recovery of the potassium resources from the sintering dust were carried out. The mean particle size of the electrostatic precipitator (ESP) dust determined by a laser granulometer was 41.468 microm. Multi-point BET and single-point BET analysis showed that the surface area of the ESP dust was 2.697 m2/g. XRD measurements detected the following phases in the ESP dust: Fe2O3, Fe3O4, KCl and NaCl, and Fe2O3, Fe3O4 and SiO2 in the water-washed dust. SEM-EDS results proved that in the ESP dust, K mostly existed in the form of KCl particles without being coated. Leaching experiments showed that the KCl in the ESP dust could be separated and recovered by water leaching and fractional crystallization. Through the recovery experiments, the yield of K-Na vaporized crystalline salt was 18.56%, in which the mass fractions of KCl, NaCl, CaSO4 and K2SO4 were about 61.03%, 13.58%, 14.03% and 9.97%, respectively. This process is technically viable and considerable in economic benefit. There was almost no secondary pollution produced in the whole recovery process.

  6. Cold and warm atomic gas around the Perseus molecular cloud. I. Basic properties

    SciTech Connect

    Stanimirović, Snežana; Murray, Claire E.; Miller, Jesse; Lee, Min-Young

    2014-10-01

    Using the Arecibo Observatory, we have obtained neutral hydrogen (HI) absorption and emission spectral pairs in the direction of 26 background radio continuum sources in the vicinity of the Perseus molecular cloud. Strong absorption lines were detected in all cases, allowing us to estimate spin temperature (T{sub s} ) and optical depth for 107 individual Gaussian components along these lines of sight. Basic properties of individual H I clouds (spin temperature, optical depth, and the column density of the cold and warm neutral medium (CNM and WNM), respectively) in and around Perseus are very similar to those found for random interstellar lines of sight sampled by the Millennium H I survey. This suggests that the neutral gas found in and around molecular clouds is not atypical. However, lines of sight in the vicinity of Perseus have, on average, a higher total H I column density and the CNM fraction, suggesting an enhanced amount of cold H I relative to an average interstellar field. Our estimated optical depth and spin temperature are in stark contrast with the recent attempt at using Planck data to estimate properties of the optically thick H I. Only ∼15% of lines of sight in our study have a column density weighted average spin temperature lower than 50 K, in comparison with ≳ 85% of Planck's sky coverage. The observed CNM fraction is inversely proportional to the optical depth weighted average spin temperature, in excellent agreement with the recent numerical simulations by Kim et al. While the CNM fraction is, on average, higher around Perseus relative to a random interstellar field, it is generally low, between 10%-50%. This suggests that extended WNM envelopes around molecular clouds and/or significant mixing of CNM and WNM throughout molecular clouds are present and should be considered in the models of molecule and star formation. Our detailed comparison of H I absorption with CO emission spectra shows that only 3 of the 26 directions are clear

  7. Lunar soil properties and soil mechanics

    NASA Technical Reports Server (NTRS)

    Mitchell, J. K.; Houston, W. N.

    1974-01-01

    The long-range objectives were to develop methods of experimentation and analysis for the determination of the physical properties and engineering behavior of lunar surface materials under in situ environmental conditions. Data for this purpose were obtained from on-site manned investigations, orbiting and softlanded spacecraft, and terrestrial simulation studies. Knowledge of lunar surface material properties are reported for the development of models for several types of lunar studies and for the investigation of lunar processes. The results have direct engineering application for manned missions to the moon.

  8. The basic science of dermal fillers: past and present Part I: background and mechanisms of action.

    PubMed

    Gilbert, Erin; Hui, Andrea; Waldorf, Heidi A

    2012-09-01

    Dermal fillers have provided a safe and effective means for aesthetic soft tissue augmentation, and have experienced a dramatic increase in popularity during the past 10 years. Much focus has been placed upon filler technique and patient outcomes. However, there is a relative lack of literature reviewing the basic science of dermal fillers, which is vital to a physician's understanding of how each product behaves in vivo. Part I of this article reviews the basic science and evolution of both historical and contemporary dermal fillers; Part II examines their adverse effects. We endeavor to provide the physician with a practical approach to choosing products that maximize both aesthetic outcome and safety.

  9. Basic Psychological Skills Usage and Competitive Anxiety Responses: Perceived Underlying Mechanisms

    ERIC Educational Resources Information Center

    Wadey, Ross; Hanton, Sheldon

    2008-01-01

    This study examined the relationship between basic psychological skills usage (i.e., goal-setting, imagery, self-talk, and relaxation) and the intensity and directional dimensions of competitive anxiety. Semistructured interviews were used on a sample of 15 elite athletes (M age = 24.3 years, SD = 4.2) from a variety of team and individual sports.…

  10. Automotive Mechanics. COM-LINK. Competency Based Vocational Curricula with Basic Skills and Academic Linkages.

    ERIC Educational Resources Information Center

    Brown, Desmond

    This competency-based module uses the Ocean County (New Jersey) Vocational-Technical Schools curriculum-infused model for infusing basic skills instruction into vocational education. The model demonstrates the relationship of vocational skills to communication, mathematics, and science. The document begins with a philosophy statement; preface; a…

  11. Physical and mechanical properties of icebergs

    SciTech Connect

    Gammon, P.H.; Bobby, W.; Gagnon, R.E.; Russell, W.E.

    1983-05-01

    Physical and mechanical characteristics of iceberg ice were studied from samples collected near the shores of eastern Newfoundland. Although the physical characteristics show considerable diversity, iceberg ice has some common features and is generally porous, lacks significant concentrations of dissolved materials, contains internal cracks and has an irregular interlocking grain structure. A review of mechanical testing of ice was carried out and an experimental setup was devised to reduce effects of improper contact between specimen and loading apparatus. Uniaxial compressive strength for iceberg ice was determined and compared with that for lake ice. The strength of iceberg ice was higher than that of lake ice but Young's Modulus for lake ice was higher.

  12. Bone mechanical properties and changes with osteoporosis.

    PubMed

    Osterhoff, Georg; Morgan, Elise F; Shefelbine, Sandra J; Karim, Lamya; McNamara, Laoise M; Augat, Peter

    2016-06-01

    This review will define the role of collagen and within-bone heterogeneity and elaborate the importance of trabecular and cortical architecture with regard to their effect on the mechanical strength of bone. For each of these factors, the changes seen with osteoporosis and ageing will be described and how they can compromise strength and eventually lead to bone fragility. PMID:27338221

  13. Supramolecular Polymer Nanocomposites - Improvement of Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Hinricher, Jesse; Neikirk, Colin; Priestley, Rodney

    2015-03-01

    Supramolecular polymers differ from traditional polymers in that their repeat units are connected by hydrogen bonds that can reversibly break and form under various stimuli. They can be more easily recycled than conventional materials, and their highly temperature dependent viscosities result in reduced energy consumption and processing costs. Furthermore, judicious selection of supramolecular polymer architecture and functionality allows the design of advanced materials including shape memory and self-healing materials. Supramolecular polymers have yet to see widespread use because they can't support much weight due to their inherent mechanical weakness. In order to address this issue, the mechanical strength of supramolecular polymer nanocomposites based on ureidopyrmidinone (UPy) telechelic poly(caprolactone) doped with surface activated silica nanoparticles was investigated by tensile testing and dynamic mechanical analysis. The effects of varying amounts and types of nanofiller surface functionality were investigated to glean insight into the contributions of filler-filler and filler-matrix interactions to mechanical reinforcement in supramolecular polymer nanocomposites. MRSEC NSF DMR 0819860 (PI: Prof. N. Phuan Ong) REU Site Grant: NSF DMR-1156422 (PI: Prof. Mikko Haataja)

  14. Mechanical properties of alumina porcelain during heating

    NASA Astrophysics Data System (ADS)

    Šín, Peter; Podoba, Rudolf; ŠtubÅa, Igor; Trník, Anton

    2014-11-01

    The mechanical strength and Young's modulus of green alumina porcelain (50 wt. % of kaolin, 25 wt. % of Al2O3, and 25 wt. % of feldspar) were measured during heating up to 900 °C and 1100 °C, respectively. To this end, we used the three point-bending method and modulated force thermomechanical analysis (mf-TMA). The loss liberation - of the physically bound water (20 - 250 °C) strengthens the sample and Young's modulus increases its values significantly. The dehydroxylation that takes place in the range of 400 - 650 °C causes a slight decrease in Young's modulus. On the other hand, the mechanical strength slightly increases in this temperature range, although it has a sudden drop at 420 °C. Beyond the dehydroxylation range, above 650 °C, both Young's modulus and mechanical strength increase. Above 950 °C, a sharp increase of Young's modulus is caused by the solid-state sintering and the new structure created by the high-temperature reactions in metakaolinite.

  15. Mechanical Properties of Intermediate Filament Proteins.

    PubMed

    Charrier, Elisabeth E; Janmey, Paul A

    2016-01-01

    Purified intermediate filament (IF) proteins can be reassembled in vitro to produce polymers closely resembling those found in cells, and these filaments form viscoelastic gels. The cross-links holding IFs together in the network include specific bonds between polypeptides extending from the filament surface and ionic interactions mediated by divalent cations. IF networks exhibit striking nonlinear elasticity with stiffness, as quantified by shear modulus, increasing an order of magnitude as the networks are deformed to large strains resembling those that soft tissues undergo in vivo. Individual IFs can be stretched to more than two or three times their resting length without breaking. At least 10 different rheometric methods have been used to quantify the viscoelasticity of IF networks over a wide range of timescales and strain magnitudes. The mechanical roles of different classes of cytoplasmic IFs on mesenchymal and epithelial cells in culture have also been studied by an even wider range of microrheological methods. These studies have documented the effects on cell mechanics when IFs are genetically or pharmacologically disrupted or when normal or mutant IF proteins are exogenously expressed in cells. Consistent with in vitro rheology, the mechanical role of IFs is more apparent as cells are subjected to larger and more frequent deformations.

  16. Mechanical properties of intermediate filament proteins

    PubMed Central

    Charrier, Elisabeth E.; Janmey, Paul A.

    2016-01-01

    Purified intermediate filament proteins can be reassembled in vitro to produce polymers closely resembling those found in cells, and these filament form viscoelastic gels. The crosslinks holding IFs together in the network include specific bonds between polypeptides extending from the filament surface and ionic interactions mediated by divalent cations. IF networks exhibit striking non-linear elasticity with stiffness, as quantified by shear modulus, increasing an order of magnitude as the networks are deformed to large stains resembling those that soft tissues undergo in vivo. Individual Ifs can be stretched to more than 2 or 3 times their resting length without breaking. At least ten different rheometric methods have been used to quantify the viscoelasticity of IF networks over a wide range of timescales and strain magnitudes. The mechanical roles of different classes of IF on mesenchymal and epithelial cells in culture have also been studied by an even wider range of microrheological methods. These studies have documented the effects on cell mechanics when IFs are genetically or pharmacologically disrupted or when normal or mutant IF proteins are exogenously expressed in cells. Consistent with in vitro rheology, the mechanical role of IFs is more apparent as cells are subjected to larger and more frequent deformations. PMID:26795466

  17. Mechanical Properties of the Frog Sarcolemma

    PubMed Central

    Fields, R. Wayne

    1970-01-01

    The elastic properties of cylindrical segments of sarcolemma were studied in single striated fibers of the frog semitendinosus muscle. All measurements were made on membranes of retraction zones, cell segments from which the sarcoplasm had retracted. Quantitative morphological studies indicated that three deforming forces interact with the intrinsic elastic properties of the sarcolemma to determine membrane configuration in retraction zone segments. The three deforming forces, namely intrazone pressure, axial fiber loads, and radial stresses introduced by retracted cell contents, could all be experimentally removed, permitting determination of the “undeformed” configuration of the sarcolemma. Analysis of these results indicated that membrane of intact fibers at rest length is about four times as wide and two-thirds as long as undeformed membrane. Membrane geometry was also studied as a function of internal hydrostatic pressure and axial loading to permit calculation of the circumferential and longitudinal tension-strain (T-S) diagrams. The sarcolemma exhibited nonlinear T-S properties concave to the tension axis in both directions. Circumferential T-S slopes (measures of membrane stiffness) ranged from 1500 to greater than 50,000 dynes/cm over the range of deformations investigated, while longitudinal T-S slopes varied from 23,000 to 225,000 dynes/cm. Thus, the membrane is anisotropic, being much stiffer in the longitudinal direction. Certain ramifications of the present results are discussed in relation to previous biomechanical studies of the sarcolemma and of other tissues. ImagesFigure 2Figure 3Figure 4 PMID:5439320

  18. The mechanical and strength properties of diamond.

    PubMed

    Field, J E

    2012-12-01

    Diamond is an exciting material with many outstanding properties; see, for example Field J E (ed) 1979 The Properties of Diamond (London: Academic) and Field J E (ed) 1992 The Properties of Natural and Synthetic Diamond (London: Academic). It is pre-eminent as a gemstone, an industrial tool and as a material for solid state research. Since natural diamonds grew deep below the Earth's surface before their ejection to mineable levels, they also contain valuable information for geologists. The key to many of diamond's properties is the rigidity of its structure which explains, for example, its exceptional hardness and its high thermal conductivity. Since 1953, it has been possible to grow synthetic diamond. Before then, it was effectively only possible to have natural diamond, with a small number of these found in the vicinity of meteorite impacts. Techniques are now available to grow gem quality synthetic diamonds greater than 1 carat (0.2 g) using high temperatures and pressures (HTHP) similar to those found in nature. However, the costs are high, and the largest commercially available industrial diamonds are about 0.01 carat in weight or about 1 mm in linear dimension. The bulk of synthetic diamonds used industrially are 600 µm or less. Over 75% of diamond used for industrial purposes today is synthetic material. In recent years, there have been two significant developments. The first is the production of composites based on diamond; these materials have a significantly greater toughness than diamond while still maintaining very high hardness and reasonable thermal conductivity. The second is the production at low pressures by metastable growth using chemical vapour deposition techniques. Deposition onto non-diamond substrates was first demonstrated by Spitsyn et al 1981 J. Cryst. Growth 52 219-26 and confirmed by Matsumoto et al 1982 Japan J. Appl. Phys. 21 L183-5. These developments have added further to the versatility of diamond. Two other groups of

  19. Quantifying tissue mechanical properties using photoplethysmography

    SciTech Connect

    Akl, Tony; Wilson, Mark A.; Ericson, Milton Nance; Cote, Gerard L.

    2014-01-01

    Photoplethysmography (PPG) is a non-invasive optical method that can be used to detect blood volume changes in the microvascular bed of tissue. The PPG signal comprises two components; a pulsatile waveform (AC) attributed to changes in the interrogated blood volume with each heartbeat, and a slowly varying baseline (DC) combining low frequency fluctuations mainly due to respiration and sympathetic nervous system activity. In this report, we investigate the AC pulsatile waveform of the PPG pulse for ultimate use in extracting information regarding the biomechanical properties of tissue and vasculature. By analyzing the rise time of the pulse in the diastole period, we show that PPG is capable of measuring changes in the Young s Modulus of tissue mimicking phantoms with a resolution of 4 KPa in the range of 12 to 61 KPa. In addition, the shape of the pulse can potentially be used to diagnose vascular complications by differentiating upstream from downstream complications. A Windkessel model was used to model changes in the biomechanical properties of the circulation and to test the proposed concept. The modeling data confirmed the response seen in vitro and showed the same trends in the PPG rise and fall times with changes in compliance and vascular resistance.

  20. Mechanical property characterization of polymeric composites reinforced by continuous microfibers

    NASA Astrophysics Data System (ADS)

    Zubayar, Ali

    Innumerable experimental works have been conducted to study the effect of polymerization on the potential properties of the composites. Experimental techniques are employed to understand the effects of various fibers, their volume fractions and matrix properties in polymer composites. However, these experiments require fabrication of various composites which are time consuming and cost prohibitive. Advances in computational micromechanics allow us to study the various polymer based composites by using finite element simulations. The mechanical properties of continuous fiber composite strands are directional. In traditional continuous fiber laminated composites, all fibers lie in the same plane. This provides very desirable increases in the in-plane mechanical properties, but little in the transverse mechanical properties. The effect of different fiber/matrix combinations with various orientations is also available. Overall mechanical properties of different micro continuous fiber reinforced composites with orthogonal geometry are still unavailable in the contemporary research field. In this research, the mechanical properties of advanced polymeric composite reinforced by continuous micro fiber will be characterized based on analytical investigation and FE computational modeling. Initially, we have chosen IM7/PEEK, Carbon Fiber/Nylon 6, and Carbon Fiber/Epoxy as three different case study materials for analysis. To obtain the equivalent properties of the micro-hetero structures, a concept of micro-scale representative volume elements (RVEs) is introduced. Five types of micro scale RVEs (3 square and 2 hexagonal) containing a continuous micro fiber in the polymer matrix were designed. Uniaxial tensile, lateral expansion and transverse shear tests on each RVE were designed and conducted by the finite element computer modeling software ANSYS. The formulae based on elasticity theory were derived for extracting the equivalent mechanical properties (Young's moduli, shear

  1. Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing.

    PubMed

    Luecke, William E; Slotwinski, John A

    2014-01-01

    Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands.

  2. Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing

    PubMed Central

    Luecke, William E; Slotwinski, John A

    2014-01-01

    Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands. PMID:26601037

  3. Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing.

    PubMed

    Luecke, William E; Slotwinski, John A

    2014-01-01

    Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands. PMID:26601037

  4. Basic Properties of Plasma-Neutral Coupling in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Goodman, Michael

    2015-04-01

    Plasma-neutral coupling (PNC) in the solar atmosphere concerns the effects of collisions between charged and neutral species’. It is most important in the chromosphere, which is the weakly ionized, strongly magnetized region between the weakly ionized, weakly magnetized photosphere and the strongly ionized, strongly magnetized corona. The charged species’ are mainly electrons, protons, and singly charged heavy ions. The neutral species’ are mainly hydrogen and helium. The resistivity due to PNC can be several orders of magnitude larger than the Spitzer resistivity. This enhanced resistivity is confined to the chromosphere, and provides a highly efficient dissipation mechanism unique to the chromosphere. PNC may play an important role in many processes such as heating and acceleration of plasma; wave generation, propagation, and dissipation; magnetic reconnection; maintaining the near force-free state of the corona; and limiting mass flux into the corona. It might play a major role in chromospheric heating, and be responsible for the existence of the chromosphere as a relatively thin layer of plasma that emits a net radiative flux 10-100 times greater than that of the overlying corona. The required heating rate might be generated by Pedersen current dissipation triggered by the rapid increase of magnetization with height in the lower chromosphere, where most of the net radiative flux is emitted. Relatively cool regions of the chromosphere might be regions of minimal Pedersen current dissipation due to smaller magnetic field strength or perpendicular current density. This talk will discuss PNC from an MHD point of view, and focus on the basic parameters that determine its effectiveness. These parameters are ionization fraction, magnetization, and the electric field that drives current perpendicular to the magnetic field. By influencing this current and the electric field that drives it, PNC directly influences the rate at which energy is exchanged between the

  5. Porosity and mechanical properties of zirconium ceramics

    SciTech Connect

    Kalatur, Ekaterina Narikovich, Anton; Buyakova, Svetlana E-mail: kulkov@ispms.tsc.ru; Kulkov, Sergey E-mail: kulkov@ispms.tsc.ru

    2014-11-14

    The article studies the porous ceramics consisting of ultra-fine ZrO{sub 2} powders. The porosity of ceramic samples varied from 15% to 80%. The structure of the ceramic materials had a cellular configuration. The distinctive feature of all experimentally obtained strain diagrams is their nonlinearity at low deformations characterized by the parabolic law. It was shown that the observed nonlinear elasticity for low deformations shown in strain diagrams is due to the mechanical instability of cellular elements of the ceramic framework.

  6. Interfaces with Tunable Mechanical and Radiosensitizing Properties.

    PubMed

    Berg, Nora G; Pearce, Brady L; Snyder, Patrick J; Rohrbaugh, Nathaniel; Nolan, Michael W; Adhikari, Prajesh; Khan, Saad A; Ivanisevic, Albena

    2016-08-31

    We report the fabrication of a composite containing nanostructured GaOOH and Matrigel with tunable radiosensitizing and stiffness properties. Composite characterization was done with microscopy and rheology. The utility of the interface was tested in vitro using fibroblasts. Cell viability and reactive oxygen species assays quantified the effects of radiation dosages and GaOOH concentrations. Fibroblasts' viability decreased with increasing concentration of GaOOH and composite stiffness. During ionizing radiation experiments the presence of the scintillating GaOOH triggered a different cellular response. Reactive oxygen species data demonstrated that one can reduce the amount of radiation needed to modulate the behavior of cells on interfaces with different stiffness containing a radiosensitizing material. PMID:26882455

  7. Agricultural Mechanics. V-A-1 to V-E-1. Basic V.A.I.

    ERIC Educational Resources Information Center

    Texas A and M Univ., College Station. Vocational Instructional Services.

    This packet contains five units of informational materials and transparency masters with accompanying scripts, skill sheets, and safety tests for teacher and student use in an agricultural mechanics course in vocational agriculture. The first unit introduces the agricultural mechanics shop, covering the following topics: importance of agricultural…

  8. Primate dietary ecology in the context of food mechanical properties.

    PubMed

    Coiner-Collier, Susan; Scott, Robert S; Chalk-Wilayto, Janine; Cheyne, Susan M; Constantino, Paul; Dominy, Nathaniel J; Elgart, Alison A; Glowacka, Halszka; Loyola, Laura C; Ossi-Lupo, Kerry; Raguet-Schofield, Melissa; Talebi, Mauricio G; Sala, Enrico A; Sieradzy, Pawel; Taylor, Andrea B; Vinyard, Christopher J; Wright, Barth W; Yamashita, Nayuta; Lucas, Peter W; Vogel, Erin R

    2016-09-01

    Substantial variation exists in the mechanical properties of foods consumed by primate species. This variation is known to influence food selection and ingestion among non-human primates, yet no large-scale comparative study has examined the relationships between food mechanical properties and feeding strategies. Here, we present comparative data on the Young's modulus and fracture toughness of natural foods in the diets of 31 primate species. We use these data to examine the relationships between food mechanical properties and dietary quality, body mass, and feeding time. We also examine the relationship between food mechanical properties and categorical concepts of diet that are often used to infer food mechanical properties. We found that traditional dietary categories, such as folivory and frugivory, did not faithfully track food mechanical properties. Additionally, our estimate of dietary quality was not significantly correlated with either toughness or Young's modulus. We found a complex relationship among food mechanical properties, body mass, and feeding time, with a potential interaction between median toughness and body mass. The relationship between mean toughness and feeding time is straightforward: feeding time increases as toughness increases. However, when considering median toughness, the relationship with feeding time may depend upon body mass, such that smaller primates increase their feeding time in response to an increase in median dietary toughness, whereas larger primates may feed for shorter periods of time as toughness increases. Our results emphasize the need for additional studies quantifying the mechanical and chemical properties of primate diets so that they may be meaningfully compared to research on feeding behavior and jaw morphology.

  9. Primate dietary ecology in the context of food mechanical properties.

    PubMed

    Coiner-Collier, Susan; Scott, Robert S; Chalk-Wilayto, Janine; Cheyne, Susan M; Constantino, Paul; Dominy, Nathaniel J; Elgart, Alison A; Glowacka, Halszka; Loyola, Laura C; Ossi-Lupo, Kerry; Raguet-Schofield, Melissa; Talebi, Mauricio G; Sala, Enrico A; Sieradzy, Pawel; Taylor, Andrea B; Vinyard, Christopher J; Wright, Barth W; Yamashita, Nayuta; Lucas, Peter W; Vogel, Erin R

    2016-09-01

    Substantial variation exists in the mechanical properties of foods consumed by primate species. This variation is known to influence food selection and ingestion among non-human primates, yet no large-scale comparative study has examined the relationships between food mechanical properties and feeding strategies. Here, we present comparative data on the Young's modulus and fracture toughness of natural foods in the diets of 31 primate species. We use these data to examine the relationships between food mechanical properties and dietary quality, body mass, and feeding time. We also examine the relationship between food mechanical properties and categorical concepts of diet that are often used to infer food mechanical properties. We found that traditional dietary categories, such as folivory and frugivory, did not faithfully track food mechanical properties. Additionally, our estimate of dietary quality was not significantly correlated with either toughness or Young's modulus. We found a complex relationship among food mechanical properties, body mass, and feeding time, with a potential interaction between median toughness and body mass. The relationship between mean toughness and feeding time is straightforward: feeding time increases as toughness increases. However, when considering median toughness, the relationship with feeding time may depend upon body mass, such that smaller primates increase their feeding time in response to an increase in median dietary toughness, whereas larger primates may feed for shorter periods of time as toughness increases. Our results emphasize the need for additional studies quantifying the mechanical and chemical properties of primate diets so that they may be meaningfully compared to research on feeding behavior and jaw morphology. PMID:27542555

  10. Processing effects on the mechanical properties of tungsten heavy alloys

    NASA Technical Reports Server (NTRS)

    Kishi, Toshihito; German, R. M.

    1990-01-01

    Tungsten heavy alloys exhibit significant mechanical property sensitivities to the fabrication variables. These sensitivities are illustrated in this examination of vacuum sintering and the effects of composition, sintering temperature, and sintering time on the mechanical properties of tungsten heavy alloys. Measurements were conducted to assess the density, strength, hardness, and elongation dependencies. A detrimental aspect of vacuum sintering is matrix phase evaporation, although vacuum sintering does eliminate the need for postsintering heat treatments.

  11. Dynamic mechanical properties of an inlay composite.

    PubMed

    Dionysopoulos, P; Watts, D C

    1989-06-01

    A visible light-cured composite resin (Brilliant DI) has been studied over a wide range of temperature and frequency by a dynamic mechanical flexural method. The derived data of logarithmic modulus and loss tangent (tan delta) show considerable changes following a secondary-cure process applied to the material. This involved the application of heat and intense light with temperatures rising to 120 degrees C in 7 min. Following this oven-cure the resin phase exhibited enhanced stiffness with the activation-energy barrier for molecular motion at the glass-transition rising from 220 to 291 kJ/mol. This study clarifies the nature and extent of the internal molecular changes which may be produced in the fabrication of a composite inlay.

  12. Measuring the mechanical properties of molecular conformers

    NASA Astrophysics Data System (ADS)

    Jarvis, S. P.; Taylor, S.; Baran, J. D.; Champness, N. R.; Larsson, J. A.; Moriarty, P.

    2015-09-01

    Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules.

  13. Understanding and Tailoring the Mechanical Properties of LIGA Fabricated Materials

    SciTech Connect

    Buchheit, T.E.; Christenson, T.R.; Lavan, D.A.; Schmale, D.T.

    1999-01-25

    LIGA fabricated materials and components exhibit several processing issues affecting their metallurgical and mechanical properties, potentially limiting their usefulness for MEMS applications. For example, LIGA processing by metal electrodeposition is very sensitive to deposition conditions which causes significant processing lot variations of mechanical and metallurgical properties. Furthermore, the process produces a material with a highly textured lenticular rnicrostructural morphology suggesting an anisotropic material response. Understanding and controlling out-of-plane anisotropy is desirable for LIGA components designed for out-of-plane flexures. Previous work by the current authors focused on results from a miniature servo-hydraulic mechanical test frame constructed for characterizing LIGA materials. Those results demonstrated microstructural and mechanical properties dependencies with plating bath current density in LIGA fabricated nickel (LIGA Ni). This presentation builds on that work and fosters a methodology for controlling the properties of LIGA fabricated materials through processing. New results include measurement of mechanical properties of LIGA fabricated copper (LIGA Cu), out-of-plane and localized mechanical property measurements using compression testing and nanoindentation of LIGA Ni and LIGA Cu.

  14. Mechanical properties of nanotubes of polyelectrolyte multilayers

    NASA Astrophysics Data System (ADS)

    Cuenot, S.; Alem, H.; Louarn, G.; Demoustier-Champagne, S.; Jonas, A. M.

    2008-04-01

    The elastic properties of nanotubes fabricated by layer-by-layer (LbL) assembly of polyelectrolytes in the nanopores of polycarbonate track-etched membranes have been investigated by resonant contact Atomic Force Microscopy (AFM), for nanotube diameters in the range of 100 to 200nm. The elastic modulus of the nanotubes was computed from the resonance frequencies of a cantilever resting on freely suspended LbL nanotubes. An average value of 115MPa was found in air for Young's modulus of these nanostructures, well below the values reported for dry, flat multilayers, but in the range of values reported for water-swollen flat multilayers. These low values are most probably due to the lower degree of ionic cross-linking of LbL nanotubes and their consequently higher water content in air, resulting from the peculiar mode of growth of nanoconfined polyelectrolyte multilayers. The computation of the moment of inertia of the LbL nanostructures is only available in electronic form at 10.1140/epje/i2007-10291-3 and are accessible for authorised users.

  15. Analgesic Drugs Alter Connective Tissue Remodeling and Mechanical Properties.

    PubMed

    Carroll, Chad C

    2016-01-01

    Exercising individuals commonly consume analgesics, but these medications alter tendon and skeletal muscle connective tissue properties, possibly limiting a person from realizing the full benefits of exercise training. I detail the novel hypothesis that analgesic medications alter connective tissue structure and mechanical properties by modifying fibroblast production of growth factors and matrix enzymes, which are responsible for extracellular matrix remodeling.

  16. The CounterACT Research Network: basic mechanisms and practical applications.

    PubMed

    Jett, David A; Yeung, David T

    2010-07-01

    The National Institutes of Health has developed a comprehensive research program that includes research centers of excellence, individual research projects, small business projects, contracts, and interagency agreements to conduct basic, translational, and clinical research aimed at the discovery and/or identification of better medical countermeasures against chemical threat agents. Chemical threats include chemical warfare agents, toxic industrial and agricultural chemicals, and toxins and other chemicals that could be used intentionally as an act of terror or by large-scale accidents or natural disasters. The overarching goal of this research program is to enhance our medical response capabilities during an emergency. The program is named Countermeasures Against Chemical Threats (CounterACT). It supports translational research, applying ideas, insights, and discoveries generated through basic scientific inquiry to the treatment or prevention of mortality and morbidity caused by chemical threat agents. The categories of research supported under this program include creation and development of screening assays and animal models for therapy development, identification of candidate therapeutics, obtaining preliminary proof-of-principle data on the efficacy of candidate therapeutics, advanced efficacy and preclinical safety studies with appropriate animal models using Good Laboratory Practices (GLP), and clinical studies, including clinical trials with new drugs. Special consideration is given to research relevant to people who are particularly vulnerable, including the young, the elderly, and individuals with pre-existing medical conditions. PMID:20601628

  17. Prestressed F-actin networks cross-linked by hinged filamins replicate mechanical properties of cells

    NASA Astrophysics Data System (ADS)

    Gardel, M. L.; Nakamura, F.; Hartwig, J. H.; Crocker, J. C.; Stossel, T. P.; Weitz, D. A.

    2006-02-01

    We show that actin filaments, shortened to physiological lengths by gelsolin and cross-linked with recombinant human filamins (FLNs), exhibit dynamic elastic properties similar to those reported for live cells. To achieve elasticity values of comparable magnitude to those of cells, the in vitro network must be subjected to external prestress, which directly controls network elasticity. A molecular requirement for the strain-related behavior at physiological conditionsis a flexible hinge found in FLNa and some FLNb molecules. Basic physical properties of the in vitro filamin-F-actin network replicate the essential mechanical properties of living cells. This physical behavior could accommodate passive deformation and internal organelle trafficking at low strains yet resist externally or internally generated high shear forces. cytoskeleton | cell mechanics | nonlinear rheology

  18. Mechanical and Thermophysical Properties of Cerium Monopnictides

    NASA Astrophysics Data System (ADS)

    Bhalla, Vyoma; Singh, Devraj; Jain, S. K.

    2016-03-01

    The ultrasonic attenuation due to phonon-phonon interaction, thermoelastic relaxation and dislocation damping mechanisms has been investigated in cerium monopnictides CeX (X: N, P, As, Sb and Bi) for longitudinal and shear waves along {< }100{rangle }, {< }110{rangle } and {< }111{rangle } directions. The second- and third-order elastic constants of CeX have also been computed in the temperature range 0 K to 500 K using Coulomb and Born-Mayer potential upto second nearest neighbours. The computed values of these elastic constants have been applied to find out Young's moduli, bulk moduli, Breazeale's non-linearity parameters, Zener anisotropy, ultrasonic velocity, ultrasonic Grüneisen parameter, thermal relaxation time, acoustic coupling constants and ultrasonic attenuation. The fracture/toughness ratio is less than 1.75, which shows that the chosen materials are brittle in nature as found for other monopnictides. The drag coefficient acting on the motion of screw and edge dislocations due to shear and compressional phonon viscosities of the lattice have also been evaluated for both the longitudinal and shear waves. The thermoelastic loss and dislocation damping loss are negligible in comparison to loss due to Akhieser damping (phonon-phonon interaction). The obtained results for CeX are in qualitative agreement with other semi-metallic monopnictides.

  19. Porosity and mechanical properties of zirconium ceramics

    NASA Astrophysics Data System (ADS)

    Buyakova, S.; Sablina, T.; Kulkov, S.

    2015-11-01

    Has been studied a porous ceramics obtained from ultra-fine powders. Porous ceramic ZrO2(MgO), ZrO2(Y2O3) powder was prepared by pressing and subsequent sintering of compacts homologous temperatures ranging from 0.63 to 0.56 during the isothermal holding duration of 1 to 5 hours. The porosity of ceramic samples was from 15 to 80%. The structure of the ceramic materials produced from plasma-sprayed ZrO2 powder was represented as a system of cell and rod structure elements. Cellular structure formed by stacking hollow powder particles can be easily seen at the images of fracture surfaces of obtained ceramics. There were three types of pores in ceramics: large cellular hollow spaces, small interparticle pores which are not filled with powder particles and the smallest pores in the shells of cells. The cells generally did not have regular shapes. The size of the interior of the cells many times exceeded the thickness of the walls which was a single-layer packing of ZrO2 grains. A distinctive feature of all deformation diagrams obtained in the experiment was their nonlinearity at low deformations which was described by the parabolic law. It was shown that the observed nonlinear elasticity for low deformation on deformation diagrams is due to mechanical instability of the cellular elements in the ceramic carcass.

  20. Measuring the mechanical properties of molecular conformers

    PubMed Central

    Jarvis, S. P.; Taylor, S.; Baran, J. D.; Champness, N. R.; Larsson, J. A.; Moriarty, P.

    2015-01-01

    Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules. PMID:26388232

  1. Porosity and mechanical properties of zirconium ceramics

    SciTech Connect

    Buyakova, S. Kulkov, S.; Sablina, T.

    2015-11-17

    Has been studied a porous ceramics obtained from ultra-fine powders. Porous ceramic ZrO{sub 2}(MgO), ZrO{sub 2}(Y{sub 2}O{sub 3}) powder was prepared by pressing and subsequent sintering of compacts homologous temperatures ranging from 0.63 to 0.56 during the isothermal holding duration of 1 to 5 hours. The porosity of ceramic samples was from 15 to 80%. The structure of the ceramic materials produced from plasma-sprayed ZrO{sub 2} powder was represented as a system of cell and rod structure elements. Cellular structure formed by stacking hollow powder particles can be easily seen at the images of fracture surfaces of obtained ceramics. There were three types of pores in ceramics: large cellular hollow spaces, small interparticle pores which are not filled with powder particles and the smallest pores in the shells of cells. The cells generally did not have regular shapes. The size of the interior of the cells many times exceeded the thickness of the walls which was a single-layer packing of ZrO{sub 2} grains. A distinctive feature of all deformation diagrams obtained in the experiment was their nonlinearity at low deformations which was described by the parabolic law. It was shown that the observed nonlinear elasticity for low deformation on deformation diagrams is due to mechanical instability of the cellular elements in the ceramic carcass.

  2. Mechanical properties of lanthanum and yttrium chromites

    SciTech Connect

    Paulik, S.W.; Armstrong, T.R.

    1996-12-31

    In an operating high-temperature (1000{degrees}C) solid oxide fuel cell (SOFC), the interconnect separates the fuel (P(O{sub 2}){approx}10{sup -16} atm) and the oxidant (P(O2){approx}10{sup 0.2} atm), while being electrically conductive and connecting the cells in series. Such severe atmospheric and thermal demands greatly reduce the number of viable candidate materials. Only two materials, acceptor substituted lanthanum chromite and yttrium chromite, meet these severe requirements. In acceptor substituted chromites (Sr{sup 2+} or Ca{sup 2+} for La{sup 3+}), charge compensation is primarily electronic in oxidizing conditions (through the formation of Cr{sup 4+}). Under reducing conditions, ionic charge compensation becomes significant as the lattice becomes oxygen deficient. The formation of oxygen vacancies is accompanied by the reduction of Cr{sup 4+} ions to Cr{sup 3+} and a resultant lattice expansion. The lattice expansion observed in large chemical potential gradients is not desirable and has been found to result in greatly reduced mechanical strength.

  3. Fluid mechanical properties of flames in enclosures

    SciTech Connect

    Rotman, D.A.; Pindera, M.Z.; Oppenheim, A.K.

    1988-07-01

    In an enclosure where the reacting medium is initially at rest, the flame first generates a flowfield that then gets stretched, i.e., its front is pulled along the surface by the flowfield in which it then finds itself residing. A methodology developed for numerical modeling of such fields is described. Of key significance in this respect is the zero Mach number model/endash/a reasonable idealization in view of the relatively high temperature, and hence sound speed, that exists, concomitantly with a comparatively low particle velocity, in the confinement of a combustion chamber. According to this model, the density gradient in the field is nullified, while across the flame front it approaches infinity. One has thus two regimes: one of the unburned medium and the other of the burned gas, each of spatially uniform density, separated by a flame front interface. The latter is endowed with four properties, of which the first two are purely kinematic and the others dynamic in nature, namely: 1) it is advected at the local velocity of flow; 2) it self-advances at the normal burning speed, the eigenvalue of the system; 3) it acts as the velocity source due to the exothermicity of the combustion process; and 4) it acts as the vorticity source due to the baroclinic effect generated by the pressure gradient along its surface and the density gradient across it. A solution obtained for a flame propagating in an oblong rectangular enclosure demonstrates that the latter has a significant influence upon the formation of the well known tulip shape. 12 refs., 4 figs.

  4. Ground and excited state properties of high performance anthocyanidin dyes-sensitized solar cells in the basic solutions

    SciTech Connect

    Prima, Eka Cahya; Yuliarto, Brian; Suyatman; Dipojono, Hermawan Kresno

    2015-09-30

    The aglycones of anthocyanidin dyes were previously reported to form carbinol pseudobase, cis-chalcone, and trans-chalcone due to the basic levels. The further investigations of ground and excited state properties of the dyes were characterized using density functional theory with PCM(UFF)/B3LYP/6-31+G(d,p) level in the basic solutions. However, to the best of our knowledge, the theoretical investigation of their potential photosensitizers has never been reported before. In this paper, the theoretical photovoltaic properties sensitized by dyes have been successfully investigated including the electron injections, the ground and excited state oxidation potentials, the estimated open circuit voltages, and the light harvesting efficiencies. The results prove that the electronic properties represented by dyes’ LUMO-HOMO levels will affect to the photovoltaic performances. Cis-chalcone dye is the best anthocyanidin aglycone dye with the electron injection spontaneity of −1.208 eV, the theoretical open circuit voltage of 1.781 V, and light harvesting efficiency of 56.55% due to the best HOMO-LUMO levels. Moreover, the ethanol solvent slightly contributes to the better cell performance than the water solvent dye because of the better oxidation potential stabilization in the ground state as well as in the excited state. These results are in good agreement with the known experimental report that the aglycones of anthocyanidin dyes in basic solvent are the high potential photosensitizers for dye-sensitized solar cell.

  5. Ground and excited state properties of high performance anthocyanidin dyes-sensitized solar cells in the basic solutions

    NASA Astrophysics Data System (ADS)

    Prima, Eka Cahya; Yuliarto, Brian; Suyatman, Dipojono, Hermawan Kresno

    2015-09-01

    The aglycones of anthocyanidin dyes were previously reported to form carbinol pseudobase, cis-chalcone, and trans-chalcone due to the basic levels. The further investigations of ground and excited state properties of the dyes were characterized using density functional theory with PCM(UFF)/B3LYP/6-31+G(d,p) level in the basic solutions. However, to the best of our knowledge, the theoretical investigation of their potential photosensitizers has never been reported before. In this paper, the theoretical photovoltaic properties sensitized by dyes have been successfully investigated including the electron injections, the ground and excited state oxidation potentials, the estimated open circuit voltages, and the light harvesting efficiencies. The results prove that the electronic properties represented by dyes' LUMO-HOMO levels will affect to the photovoltaic performances. Cis-chalcone dye is the best anthocyanidin aglycone dye with the electron injection spontaneity of -1.208 eV, the theoretical open circuit voltage of 1.781 V, and light harvesting efficiency of 56.55% due to the best HOMO-LUMO levels. Moreover, the ethanol solvent slightly contributes to the better cell performance than the water solvent dye because of the better oxidation potential stabilization in the ground state as well as in the excited state. These results are in good agreement with the known experimental report that the aglycones of anthocyanidin dyes in basic solvent are the high potential photosensitizers for dye-sensitized solar cell.

  6. Meaning, Memory, and Multiplication: Integrating Patterns and Properties with Basic Facts

    ERIC Educational Resources Information Center

    Ploger, Don; Hecht, Steven

    2012-01-01

    Although learning mathematics certainly depends upon accurate understanding of the facts of multiplication, it requires much more. This study examines the relationship between a meaningful understanding of arithmetic operations and the mastery of basic facts. The study began with a joke about a mistaken mathematical fact. The children appreciated…

  7. Mechanical and biological properties of keratose biomaterials.

    PubMed

    de Guzman, Roche C; Merrill, Michelle R; Richter, Jillian R; Hamzi, Rawad I; Greengauz-Roberts, Olga K; Van Dyke, Mark E

    2011-11-01

    The oxidized form of extractable human hair keratin proteins, commonly referred to as keratose, is gaining interest as a biomaterial for multiple tissue engineering studies including those directed toward peripheral nerve, spinal cord, skin, and bone regeneration. Unlike its disulfide cross-linked counterpart, kerateine, keratose does not possess a covalently cross-linked network structure and consequently displays substantially different characteristics. In order to understand its mode(s) of action and potential for clinical translatability, detailed characterization of the composition, physical properties, and biological responses of keratose biomaterials are needed. Keratose was obtained from end-cut human hair fibers by peracetic acid treatment, followed by base extraction, and subsequent dialysis. Analysis of lyophilized keratose powder determined that it contains 99% proteins by mass with amino acid content similar to human hair cortex. Metallic elements were also found in minute quantities. Protein oxidation led to disulfide bond cleavage and drastic reduction of free thiols due to conversion of sulfhydryl to sulfonic acid, chain fragmentation, and amino acid modifications. Mass spectrometry identified the major protein constituents as a heterogeneous mixture of 15 hair keratins (type I: K31-35 and K37-39, and type II: K81-86) with small amounts of epithelial keratins which exist in monomeric, dimeric, multimeric, and even degraded forms. Re-hydration with PBS enabled molecular assembly into an elastic solid-like hydrogel. Highly-porous scaffolds formed by lyophilization of the gel had the compression behavior of a cellular foam material and reverted back to gel upon wetting. Cytotoxicity assays showed that the EC50 for various cell lines were attained at 8-10 mg/mL keratose, indicating the non-toxic nature of the material. Implantation in mouse subcutaneous tissue pockets demonstrated that keratose resorption follows a rectangular hyperbolic regression

  8. Dynamic monitoring of cell mechanical properties using profile microindentation

    NASA Astrophysics Data System (ADS)

    Guillou, L.; Babataheri, A.; Puech, P.-H.; Barakat, A. I.; Husson, J.

    2016-02-01

    We have developed a simple and relatively inexpensive system to visualize adherent cells in profile while measuring their mechanical properties using microindentation. The setup allows simultaneous control of cell microenvironment by introducing a micropipette for the delivery of soluble factors or other cell types. We validate this technique against atomic force microscopy measurements and, as a proof of concept, measure the viscoelastic properties of vascular endothelial cells in terms of an apparent stiffness and a dimensionless parameter that describes stress relaxation. Furthermore, we use this technique to monitor the time evolution of these mechanical properties as the cells’ actin is depolymerized using cytochalasin-D.

  9. Dynamic monitoring of cell mechanical properties using profile microindentation

    PubMed Central

    Guillou, L.; Babataheri, A.; Puech, P.-H.; Barakat, A. I.; Husson, J.

    2016-01-01

    We have developed a simple and relatively inexpensive system to visualize adherent cells in profile while measuring their mechanical properties using microindentation. The setup allows simultaneous control of cell microenvironment by introducing a micropipette for the delivery of soluble factors or other cell types. We validate this technique against atomic force microscopy measurements and, as a proof of concept, measure the viscoelastic properties of vascular endothelial cells in terms of an apparent stiffness and a dimensionless parameter that describes stress relaxation. Furthermore, we use this technique to monitor the time evolution of these mechanical properties as the cells’ actin is depolymerized using cytochalasin-D. PMID:26857265

  10. Mechanical Properties of Continuous Fiber Reinforced Zirconium Diboride Matrix Composites

    NASA Technical Reports Server (NTRS)

    Stuffle, Kevin; Creegan, Peter; Nowell, Steven; Bull, Jeffrey D.; Rasky, Daniel J. (Technical Monitor)

    1995-01-01

    Continuous fiber reinforced zirconium diboride matrix composites, SCS-9a-(RBSiCZrB2)matrix, are being developed for leading edge, rocket nozzle and turbine engine applications. Recently, the composite materials have been characterized for tensile properties to 1250 C, the highest temperature tested. The tensile properties are fiber dominated as the matrix is microcracked on fabrication, but favorable failure characteristic are observed. Compression and shear mechanical testing results will be reported if completed. The effects of fiber volume fraction and matrix density on mechanical properties will be discussed. The target applications of the materials will be discussed. Specific testing being performed towards qualification for these applications will be included.

  11. Mechanical Properties and Durability of "Waterless Concrete"

    NASA Technical Reports Server (NTRS)

    Toutanji, Houssam; Grugel, Richard N.

    2008-01-01

    Waterless concrete consists of molten elementary sulfur and aggregate. The aggregates in lunar environment will be lunar rocks and soil. Sulfur is present on the Moon in Troilite soil (FeS) and by oxidation soil iron and sulfur can be produced. Iron can be used to reinforce the sulfur concrete. Sulfur concrete specimens were cycled between liquid nitrogen (approximately 191 C) and room temperature (approximately 21 C) to simulate exposure to a lunar environment. Cycled and control specimens were subsequently tested in compression at room temperatures (approximately 21 C) and approximately 101 C. Test results showed that due to temperature cycling, compressive strength of cycled specimens was 20% of those non-cycled. Microscopic examination of the fracture surfaces from the cycled samples showed clear de-bonding of the sulfur from the aggregate material whereas it was seen well bonded in those non-cycled. This reduction in strength can be attributed to the large differences in thermal coefficients of expansion of the materials constituting the concrete which promoted cracking. Similar sulfur concrete mixtures were strengthened with short and long glass fibers. The glass fibers from lunar regolith simulant was melted in a 25 cc Pt-Rh crucible in a Sybron Thermoline high temperature MoSi2 furnace at melting temperatures of 1450 to 1600 C for times of 30 min to 1 hour. Glass fibers were cast from the melt into graphite crucibles and were annealed for a couple of hours at 600 C. Glass fibers and small rods were pulled from the melt. The glass melt wets the ceramic rod and long continuous glass fibers were easily hand drawn. The glass fibers were immediately coated with a protective polymer to maintain the mechanical strength. The glass fibers were used to reinforce sulfur concrete plated to improve the flexural strength of the sulfur concrete. Prisms beams strengthened with glass fibers were tested in 4-point bending test. Beams strengthened with glass fiber showed to

  12. A novel mechanism for poisoning of metal oxide SCR catalysts: base-acid explanation correlated with redox properties.

    PubMed

    Chang, Huazhen; Li, Junhua; Su, Wenkang; Shao, Yuankai; Hao, Jiming

    2014-09-11

    A novel mechanism is proposed for the poisoning effect of acid gases and N2O formation on SCR catalysts involving base-acid properties correlated with redox ability of M-O or M-OH (M = Ce or V) of metal oxides and the strength of their basicity responsible for resistance to HCl and SO2 at medium and low temperatures.

  13. Lithophysal Rock Mass Mechanical Properties of the Repository Host Horizon

    SciTech Connect

    D. Rigby

    2004-11-10

    The purpose of this calculation is to develop estimates of key mechanical properties for the lithophysal rock masses of the Topopah Spring Tuff (Tpt) within the repository host horizon, including their uncertainties and spatial variability. The mechanical properties to be characterized include an elastic parameter, Young's modulus, and a strength parameter, uniaxial compressive strength. Since lithophysal porosity is used as a surrogate property to develop the distributions of the mechanical properties, an estimate of the distribution of lithophysal porosity is also developed. The resulting characterizations of rock parameters are important for supporting the subsurface design, developing the preclosure safety analysis, and assessing the postclosure performance of the repository (e.g., drift degradation and modeling of rockfall impacts on engineered barrier system components).

  14. A simple auxetic tubular structure with tuneable mechanical properties

    NASA Astrophysics Data System (ADS)

    Ren, Xin; Shen, Jianhu; Ghaedizadeh, Arash; Tian, Hongqi; Xie, Yi Min

    2016-06-01

    Auxetic materials and structures are increasingly used in various fields because of their unusual properties. Auxetic tubular structures have been fabricated and studied due to their potential to be adopted as oesophageal stents where only tensile auxetic performance is required. However, studies on compressive mechanical properties of auxetic tubular structures are limited in the current literature. In this paper, we developed a simple tubular structure which exhibits auxetic behaviour in both compression and tension. This was achieved by extending a design concept recently proposed by the authors for generating 3D metallic auxetic metamaterials. Both compressive and tensile mechanical properties of the auxetic tubular structure were investigated. It was found that the methodology for generating 3D auxetic metamaterials could be effectively used to create auxetic tubular structures as well. By properly adjusting certain parameters, the mechanical properties of the designed auxetic tubular structure could be easily tuned.

  15. Salt-leached silk scaffolds with tunable mechanical properties.

    PubMed

    Yao, Danyu; Dong, Sen; Lu, Qiang; Hu, Xiao; Kaplan, David L; Zhang, Bingbo; Zhu, Hesun

    2012-11-12

    Substrate mechanical properties have remarkable influences on cell behavior and tissue regeneration. Although salt-leached silk scaffolds have been used in tissue engineering, applications in softer tissue regeneration can be encumbered with excessive stiffness. In the present study, silk-bound water interactions were regulated by controlling processing to allow the preparation of salt-leached porous scaffolds with tunable mechanical properties. Increasing silk-bound water interactions resulted in reduced silk II (β-sheet crystal) formation during salt-leaching, which resulted in a modulus decrease in the scaffolds. The microstructures as well as degradation behavior were also changed, implying that this water control and salt-leaching approach can be used to achieve tunable mechanical properties. Considering the utility of silk in various fields of biomedicine, the results point to a new approach to generate silk scaffolds with controllable properties to better mimic soft tissues by combining scaffold preparation methods and silk self-assembly in aqueous solutions.

  16. Mechanical properties of carbon nanotube/polymer composites

    PubMed Central

    Arash, B.; Wang, Q.; Varadan, V. K.

    2014-01-01

    The remarkable mechanical properties of carbon nanotubes, such as high elastic modulus and tensile strength, make them the most ideal and promising reinforcements in substantially enhancing the mechanical properties of resulting polymer/carbon nanotube composites. It is acknowledged that the mechanical properties of the composites are significantly influenced by interfacial interactions between nanotubes and polymer matrices. The current challenge of the application of nanotubes in the composites is hence to determine the mechanical properties of the interfacial region, which is critical for improving and manufacturing the nanocomposites. In this work, a new method for evaluating the elastic properties of the interfacial region is developed by examining the fracture behavior of carbon nanotube reinforced poly (methyl methacrylate) (PMMA) matrix composites under tension using molecular dynamics simulations. The effects of the aspect ratio of carbon nanotube reinforcements on the elastic properties, i.e. Young's modulus and yield strength, of the interfacial region and the nanotube/polymer composites are investigated. The feasibility of a three-phase micromechanical model in predicting the elastic properties of the nanocomposites is also developed based on the understanding of the interfacial region. PMID:25270167

  17. Mechanical properties of carbon nanotubes and their polymer nanocomposites.

    PubMed

    Miyagawa, Hiroaki; Misra, Manjusri; Mohanty, Amar K

    2005-10-01

    More than 10 years have passed since carbon nanotubes (CNT) have been found during observations by transmission electron microscopy (TEM). Since then, one of the major applications of the CNT is the reinforcements of plastics in processing composite materials, because it was found by experiments that CNT possessed splendid mechanical properties. Various experimental methods are conducted in order to understand the mechanical properties of varieties of CNT and CNT-based composite materials. The systematized data of the past research results of CNT and their nanocomposites are extremely useful to improve processing and design criteria for new nanocomposites in further studies. Before the CNT observations, vapor grown carbon fibers (VGCF) were already utilized for composite applications, although there have been only few experimental data about the mechanical properties of VGCF. The structure of VGCF is similar to that of multi-wall carbon nanotubes (MWCNT), and the major benefit of VGCF is less commercial price. Therefore, this review article overviews the experimental results regarding the various mechanical properties of CNT, VGCF, and their polymer nanocomposites. The experimental methods and results to measure the elastic modulus and strength of CNT and VGCF are first discussed in this article. Secondly, the different surface chemical modifications for CNT and VGCF are reviewed, because the surface chemical modifications play an important role for polymer nanocomposite processing and properties. Thirdly, fracture and fatigue properties of CNT/polymer nanocomposites are reviewed, since these properties are important, especially when these new nanocomposite materials are applied for structural applications.

  18. Mechanical properties of carbon nanotube/polymer composites.

    PubMed

    Arash, B; Wang, Q; Varadan, V K

    2014-01-01

    The remarkable mechanical properties of carbon nanotubes, such as high elastic modulus and tensile strength, make them the most ideal and promising reinforcements in substantially enhancing the mechanical properties of resulting polymer/carbon nanotube composites. It is acknowledged that the mechanical properties of the composites are significantly influenced by interfacial interactions between nanotubes and polymer matrices. The current challenge of the application of nanotubes in the composites is hence to determine the mechanical properties of the interfacial region, which is critical for improving and manufacturing the nanocomposites. In this work, a new method for evaluating the elastic properties of the interfacial region is developed by examining the fracture behavior of carbon nanotube reinforced poly (methyl methacrylate) (PMMA) matrix composites under tension using molecular dynamics simulations. The effects of the aspect ratio of carbon nanotube reinforcements on the elastic properties, i.e. Young's modulus and yield strength, of the interfacial region and the nanotube/polymer composites are investigated. The feasibility of a three-phase micromechanical model in predicting the elastic properties of the nanocomposites is also developed based on the understanding of the interfacial region.

  19. Mechanical properties of carbon nanotube/polymer composites

    NASA Astrophysics Data System (ADS)

    Arash, B.; Wang, Q.; Varadan, V. K.

    2014-10-01

    The remarkable mechanical properties of carbon nanotubes, such as high elastic modulus and tensile strength, make them the most ideal and promising reinforcements in substantially enhancing the mechanical properties of resulting polymer/carbon nanotube composites. It is acknowledged that the mechanical properties of the composites are significantly influenced by interfacial interactions between nanotubes and polymer matrices. The current challenge of the application of nanotubes in the composites is hence to determine the mechanical properties of the interfacial region, which is critical for improving and manufacturing the nanocomposites. In this work, a new method for evaluating the elastic properties of the interfacial region is developed by examining the fracture behavior of carbon nanotube reinforced poly (methyl methacrylate) (PMMA) matrix composites under tension using molecular dynamics simulations. The effects of the aspect ratio of carbon nanotube reinforcements on the elastic properties, i.e. Young's modulus and yield strength, of the interfacial region and the nanotube/polymer composites are investigated. The feasibility of a three-phase micromechanical model in predicting the elastic properties of the nanocomposites is also developed based on the understanding of the interfacial region.

  20. Mechanical Properties Comparing Composite Fiber Length to Amalgam

    PubMed Central

    Petersen, Richard C.; Liu, Perng-Ru

    2016-01-01

    Photocure fiber-reinforced composites (FRCs) with varying chopped quartz-fiber lengths were incorporated into a dental photocure zirconia-silicate particulate-filled composite (PFC) for mechanical test comparisons with a popular commercial spherical-particle amalgam. FRC lengths included 0.5-mm, 1.0 mm, 2.0 mm, and 3.0 mm all at a constant 28.2 volume percent. Four-point fully articulated fixtures were used according to American Standards Test Methods with sample dimensions of 2×2×50 mm3 across a 40 mm span to provide sufficient Euler flexural bending and prevent top-load compressive shear error. Mechanical properties for flexural strength, modulus, yield strength, resilience, work of fracture, critical strain energy release, critical stress intensity factor, and strain were obtained for comparison. Fiber length subsequently correlated with increasing all mechanical properties, p < 1.1×10−5. Although the modulus was significantly statistically higher for amalgam than all composites, all FRCs and even the PFC had higher values than amalgam for all other mechanical properties. Because amalgams provide increased longevity during clinical use compared to the standard PFCs, modulus would appear to be a mechanical property that might sufficiently reduce margin interlaminar shear stress and strain-related microcracking that could reduce failure rates. Also, since FRCs were tested with all mechanical properties that statistically significantly increased over the PFC, new avenues for future development could be provided toward surpassing amalgam in clinical longevity. PMID:27642629

  1. Mechanical Properties Comparing Composite Fiber Length to Amalgam

    PubMed Central

    Petersen, Richard C.; Liu, Perng-Ru

    2016-01-01

    Photocure fiber-reinforced composites (FRCs) with varying chopped quartz-fiber lengths were incorporated into a dental photocure zirconia-silicate particulate-filled composite (PFC) for mechanical test comparisons with a popular commercial spherical-particle amalgam. FRC lengths included 0.5-mm, 1.0 mm, 2.0 mm, and 3.0 mm all at a constant 28.2 volume percent. Four-point fully articulated fixtures were used according to American Standards Test Methods with sample dimensions of 2×2×50 mm3 across a 40 mm span to provide sufficient Euler flexural bending and prevent top-load compressive shear error. Mechanical properties for flexural strength, modulus, yield strength, resilience, work of fracture, critical strain energy release, critical stress intensity factor, and strain were obtained for comparison. Fiber length subsequently correlated with increasing all mechanical properties, p < 1.1×10−5. Although the modulus was significantly statistically higher for amalgam than all composites, all FRCs and even the PFC had higher values than amalgam for all other mechanical properties. Because amalgams provide increased longevity during clinical use compared to the standard PFCs, modulus would appear to be a mechanical property that might sufficiently reduce margin interlaminar shear stress and strain-related microcracking that could reduce failure rates. Also, since FRCs were tested with all mechanical properties that statistically significantly increased over the PFC, new avenues for future development could be provided toward surpassing amalgam in clinical longevity.

  2. Coupling of mechanical and electronic properties of carbon nanotubes.

    PubMed

    Cristancho, Dahiyana; Benitez, Laura; Seminario, Jorge M

    2013-12-01

    Because of the potential importance of carbon nanotubes (CNT) in renewable energy and other fields, molecular orbital ab initio calculations are used to study the relation between mechanical and electronic properties of such structures. We estimate a modulus of elasticity of 1.3 TPa and find out that the mechanism of CNT structure deformation is dependent on their chirality. Armchair and chiral nanotubes have ductile deformation fracture while zigzag have both ductile and brittle; on the other hand armchair nanotubes fracture and form two caps while chiral nanotubes adopt a helical-structure conformation. In addition, the energy gap between occupied and unoccupied molecular orbitals increases when nanotubes are under plastic deformation. This strong coupling between mechanical and electrical properties can be used to tune CNT mechanically to specific electronic bandgaps, affecting directly their electromagnetic absorption properties.

  3. Mechanical properties of jennite: A theoretical and experimental study

    SciTech Connect

    Moon, Juhyuk; Yoon, Seyoon; Monteiro, Paulo J.M.

    2015-05-15

    The objective of this study is to determine the mechanical properties of jennite. To date, several hypotheses have been proposed to predict the structural properties of jennite. For the first time as reported herein, the isothermal bulk modulus of jennite was measured experimentally. Synchrotron-based high-pressure x-ray diffraction experiments were performed to observe the variation of lattice parameters under pressure. First-principles calculations were applied to compare with the experimental results and predict additional structural properties. Accurately measured isothermal bulk modulus herein (K{sub 0} = 64(2) GPa) and the statistical assessment on experimental and theoretical results suggest reliable mechanical properties of shear and Young's modulus, Poisson's ratio, and elastic tensor coefficients. Determination of these fundamental structural properties is the first step toward greater understanding of calcium–silicate–hydrate, as well as provides a sound foundation for forthcoming atomic level simulations.

  4. Sudden unexpected death in epilepsy: basic mechanisms and clinical implications for prevention.

    PubMed

    Dlouhy, Brian J; Gehlbach, Brian K; Richerson, George B

    2016-04-01

    Sudden unexpected death in epilepsy (SUDEP) is the most common cause of death in patients with intractable epilepsy. The substantial lifetime risk of SUDEP and the lack of a clear pathophysiological connection between epilepsy itself and sudden death have fuelled increased attention to this phenomenon. Understanding the mechanisms underlying SUDEP is paramount to developing preventative strategies. In this review, we discuss SUDEP population studies, case-control studies, witnessed and monitored cases, as well as human seizure cardiorespiratory findings related to SUDEP, and SUDEP animal models. We integrate these data to suggest the most probable mechanisms underlying SUDEP. Understanding the modifiable risk factors and pathophysiology allows us to discuss potential preventative strategies.

  5. Teaching the basics of autophagy and mitophagy to redox biologists--mechanisms and experimental approaches.

    PubMed

    Zhang, Jianhua

    2015-01-01

    Autophagy is a lysosomal mediated degradation activity providing an essential mechanism for recycling cellular constituents, and clearance of excess or damaged lipids, proteins and organelles. Autophagy involves more than 30 proteins and is regulated by nutrient availability, and various stress sensing signaling pathways. This article provides an overview of the mechanisms and regulation of autophagy, its role in health and diseases, and methods for its measurement. Hopefully this teaching review together with the graphic illustrations will be helpful for instructors teaching graduate students who are interested in grasping the concepts and major research areas and introducing recent developments in the field. PMID:25618581

  6. Teaching the basics of autophagy and mitophagy to redox biologists—Mechanisms and experimental approaches

    PubMed Central

    Zhang, Jianhua

    2015-01-01

    Autophagy is a lysosomal mediated degradation activity providing an essential mechanism for recycling cellular constituents, and clearance of excess or damaged lipids, proteins and organelles. Autophagy involves more than 30 proteins and is regulated by nutrient availability, and various stress sensing signaling pathways. This article provides an overview of the mechanisms and regulation of autophagy, its role in health and diseases, and methods for its measurement. Hopefully this teaching review together with the graphic illustrations will be helpful for instructors teaching graduate students who are interested in grasping the concepts and major research areas and introducing recent developments in the field. PMID:25618581

  7. Correlation of basic oil quality indices and electrical properties of model vegetable oil systems.

    PubMed

    Prevc, Tjaša; Cigić, Blaž; Vidrih, Rajko; Poklar Ulrih, Nataša; Šegatin, Nataša

    2013-11-27

    Model vegetable oil mixtures with significantly different basic oil quality indices (free fatty acid, iodine, and Totox values) were prepared by adding oleic acids, synthetic saturated triglycerides, or oxidized safflower oil ( Carthamus tinctorius ) to the oleic type of sunflower oil. Dielectric constants, dielectric loss factors, quality factors, and electrical conductivities of model lipids were determined at frequencies from 50 Hz to 2 MHz and at temperatures from 293.15 to 323.15 K. The dependence of these dielectric parameters on basic oil quality indices was investigated. Adding oleic acids to sunflower oil resulted in lower dielectric constants and conductivities and higher quality factors. Reduced iodine values resulted in increased dielectric constants and quality factors and decreased conductivities. Higher Totox values resulted in higher dielectric constants and conductivities at high frequencies and lower quality factors. Dielectric constants decreased linearly with temperature, whereas conductivities followed the Arrhenius law.

  8. A Dynamic Systems Model of Basic Developmental Mechanisms: Piaget, Vygotsky, and Beyond.

    ERIC Educational Resources Information Center

    van Geert, Paul

    1998-01-01

    A dynamic systems model is proposed on the basis of a general developmental mechanism adopted from the theories of J. Piaget and L. S. Vygotsky. In the model, action and experience have a distributed effect on the contents (skills, knowledge, rules, action patterns, etc.) along an abstract developmental distance dimension. (Author/SLD)

  9. Linking Basic Skills to Entry-Level Auto Mechanic & Auto Body Worker Tasks. Instructional Resources. Assessments.

    ERIC Educational Resources Information Center

    Benavidez, Charlotte; Miyatake, George

    This project first identified the duties and tasks required of an entry-level auto mechanic (AM) and an auto body worker (ABW), using a modified DACUM (Developing a Curriculum) occupational analysis process. In this process, a panel of local, expert workers determined the essential duties and tasks of their occupations. Next, the panel identified…

  10. Derivation of Performance Statements for the Automotive Mechanics Basic Trade Course: Research Documentation.

    ERIC Educational Resources Information Center

    Fox, A. P.; Kuhl, D. H.

    A project was conducted to derive a comprehensive list of the performances of a competence mechanic to satisfy the planning needs of automotive engineering lecturers, curriculum committees, researchers, course designers, and staff developers. A list of 127 tasks together with information about their relative importance and the frequency with which…

  11. Tipping Elements in Earth Systems Special Feature: Basic mechanism for abrupt monsoon transitions

    NASA Astrophysics Data System (ADS)

    Levermann, Anders; Schewe, Jacob; Petoukhov, Vladimir; Held, Hermann

    2009-12-01

    Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and might act as an internal amplifier, leading to abrupt changes in response to relatively weak external perturbations. Here we present a minimal conceptual model capturing this positive feedback. The basic equations, motivated by observed relations, yield a threshold behavior, robust with respect to addition of other physical processes. Below this threshold in net radiative influx, R c, no conventional monsoon can develop; above R c, two stable regimes exist. We identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition. This dynamic similitude may be helpful in understanding past and future variations in monsoon circulation. Within the restrictions of the model, we compute R c for current monsoon systems in India, China, the Bay of Bengal, West Africa, North America, and Australia, where moisture advection is the main driver of the circulation.

  12. Altered mechanical properties of the nucleus in disease.

    PubMed

    Lombardi, Maria Lucia; Lammerding, Jan

    2010-01-01

    In eukaryotic cells, the nucleus is the largest and most rigid organelle. Therefore, its physical properties contribute critically to the biomechanical behavior of cells, e.g., during amoeboid migration or perfusion through narrow capillaries. Furthermore, it has been speculated that nuclear deformations could directly allow cells to sense mechanical stress, e.g., by modulating the access of specific transcription factors to their binding sites. Defects in nuclear mechanics have also been reported in a variety of muscular dystrophies caused by mutations in nuclear envelope proteins, indicating an important role in the maintenance of cells in mechanically stressed tissue. These findings have prompted the growing field of nuclear mechanics to develop advanced experimental methods to study the physical properties of the nucleus as a function of nuclear structure and organization, and to understand its role in physiology and disease. These experimental techniques include micropipette aspiration, atomic force microscopy of isolated nuclei, cellular strain and compression experiments, and microneedle manipulation of intact cells. These experiments have provided important insights into the mechanical behavior of the nucleus under physiological conditions, the distinct mechanical contributions of the nuclear lamina and interior, and how mutations in nuclear envelope proteins associated with a variety of human diseases can cause distinct alterations in the physical properties of the nucleus and contribute to the disease mechanism. Here, we provide a brief overview of the most common experimental techniques and their application and discuss the implication of their results on our current understanding of nuclear mechanics.

  13. Metal Additive Manufacturing: A Review of Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Lewandowski, John J.; Seifi, Mohsen

    2016-07-01

    This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test orientation/build direction on properties, when available, are also provided, along with discussion of the potential source(s) (e.g., texture, microstructure changes, defects) of anisotropy in properties. Recommendations for additional work are also provided.

  14. Measurements and Characterizations of Mechanical Properties of Human Skins

    NASA Astrophysics Data System (ADS)

    Song, Han Wook; Park, Yon Kyu

    A skin is an indispensible organ for humans because it contributes to metabolism using its own biochemical functions and protects the human body from external stimuli. Recently, mechanical properties such as a thickness, a friction and an elastic coefficient have been used as a decision index in the skin physiology and in the skin care market due to the increased awareness of wellbeing issues. In addition, the use of mechanical properties is known to have good discrimination ability in the classification of human constitutions, which are used in the field of an alternative medicine. In this study, a system that measures mechanical properties such as a friction and an elastic coefficient is designed. The equipment consists of a load cell type (manufactured by the authors) for the measurements of a friction coefficient, a decompression tube for the measurement of an elastic coefficient. Using the proposed system, the mechanical properties of human skins from different constitutions were compared, and the relative repeatability error for measurements of mechanical properties was determined to be less than 2%. Combining the inspection results of medical doctors in the field of an alternative medicine, we could conclude that the proposed system might be applicable to a quantitative constitutional diagnosis between human constitutions within an acceptable level of uncertainty.

  15. Mechanical properties and in vitro degradation of bioresorbable knitted stents.

    PubMed

    Nuutinen, Juha-Pekka; Välimaa, Tero; Clerc, Claude; Törmälä, Pertti

    2002-01-01

    The aim of this study was to characterize the mechanical properties and in vitro degradation of bioresorbable knitted stents. Each stent was knitted using a single self-reinforced fibre made out of either PLLA or 96L/4D PLA or 80L/20G PLGA. The mechanical and physical properties of the fibres and stents were measured before and after gamma sterilization, as well as during in vitro degradation. The mechanical properties of the knitted stents made out of bioresorbable fibres were similar to those of commercially available metallic stents. The knitting geometry (loop height) had a marked effect on the mechanical properties of the stents. The rate of in vitro degradation in mechanical and physical properties for the PLLA and 96L/4D PLA stents was similar and significantly lower than that of the 80L/20G PLGA stents. The 80L/20G PLGA stents lost about 35% of their initial weight at 11 weeks. At this time, they had lost all their compression resistance strength. These data can be used as a guideline in planning further studies in vivo. PMID:12555898

  16. Deformation behavior and mechanical properties of amyloid protein nanowires.

    PubMed

    Solar, Max; Buehler, Markus J

    2013-03-01

    Amyloid fibrils are most often associated with their pathological role in diseases like Alzheimer's disease and Parkinson's disease, but they are now increasingly being considered for uses in functional engineering materials. They are among the stiffest protein fibers known but they are also rather brittle, and it is unclear how this combination of properties affects the behavior of amyloid structures at larger length scales, such as in films, wires or plaques. Using a coarse-grained model for amyloid fibrils, we study the mechanical response of amyloid nanowires and examine fundamental mechanical properties, including mechanisms of deformation and failure under tensile loading. We also explore the effect of varying the breaking strain and adhesion strength of the constituent amyloid fibrils on the properties of the larger structure. We find that deformation in the nanowires is controlled by a combination of fibril sliding and fibril failure and that there exists a transition from brittle to ductile behavior by either increasing the fibril failure strain or decreasing the strength of adhesion between fibrils. Furthermore, our results reveal that the mechanical properties of the nanowires are quite sensitive to changes in the properties of the individual fibrils, and the larger scale structures are found to be more mechanically robust than the constituent fibrils, for all cases considered. More broadly, this work demonstrates the promise of utilizing self-assembled biological building blocks in the development of hierarchical nanomaterials. PMID:23290516

  17. Dependence of the basic properties of meso-nitro-substituted derivatives of β-octaethylporphyrin on the nature of substituents

    NASA Astrophysics Data System (ADS)

    Pukhovskaya, S. G.; Ivanova, Yu. B.; Nam, Dao The; Vashurin, A. S.

    2014-10-01

    Spectrophotometric titration is used to study the basic properties of a series of porphyrins with a continuously increasing degree of macrocycle deformation resulting from the introduction of strong electron-withdrawing substituents: 2,3,7,8,12,13,17,18-octaethylporphyrin ( I), 5-nitro-2,3,7,8,12,13,17,18-octaethylporphyrin ( II), 5,15-dinitro-2,3,7,8,12,13,17,18-octaethylporphyrin ( III), 5,10,15-trinitro-2,3,7,8,12,13,17,18-octaethylporphyrin ( IV), and 5,10,15,20-tetranitro-2,3,7,8,12,13,17,18-octaethylporphyrin ( V). It is found that the values of log K b (total basicity constants) obtained for the investigated compounds consistently diminish with an increase in the number of meso-substituents: 11.85 ( I) > 10.45 ( II) > 10.31 ( III) > 10.23 ( IV) > 9.56 ( V). It is shown that two opposing factors, the steric and electronic effects of the substituents, change the basic properties of the above series of compounds.

  18. Basic knowledge on radiative and transport properties to begin in thermal plasmas modelling

    SciTech Connect

    Cressault, Y.

    2015-05-15

    This paper has for objectives to present the radiative and the transport properties for people beginning in thermal plasmas. The first section will briefly recall the equations defined in numerical models applied to thermal plasmas; the second section will particularly deal with the estimation of radiative losses; the third part will quickly present the thermodynamics properties; and the last part will concern the transport coefficients (thermal conductivity, viscosity and electrical conductivity of the gas or mixtures of gases). We shall conclude the paper with a discussion about the validity of these results the lack of data for some specific applications, and some perspectives concerning these properties for non-equilibrium thermal plasmas.

  19. Flux composition, microstructure and mechanical properties of HY-100 SAW weldments

    SciTech Connect

    Brothers, D.G.; Kettell, K.W.; Fox, A.G.

    1994-12-31

    The mechanical properties of submerged arc welds (SAW) on high strength steels are sensitive to weld-metal chemistry and thus the chemical composition of the welding consumables. Consumable chemistry determines the size, distribution, and composition of the nonmetallic inclusions present in the weld metal which together with cooling rate determines weld-metal microstructure and thus mechanical properties. Multirun submerged arc welds were made on HY-100 steel and all-weld variables were kept constant except the flux composition for which five different commercial fluxes were investigated. The basicity of each flux was calculated and correlated with weld-metal chemistry and it was found that lower basicity fluxes appeared to generate a higher oxygen activity in the weld-metal leading to more pronounced oxidation of carbon, manganese, and silicon and thus loss of weld-metal yield strength. Inclusion analyses showed the inclusion in the weld-metals to contain MnO, Al{sub 2}O{sub 3}, SiO{sub 2}, and TiO{sub 2}. These results suggest that the optimum flux for welding high-strength steels should have a high enough basicity and MnO content to avoid the loss of alloying elements from the weld metal due to high oxygen activity and to generate sufficient numbers of non-metallic inclusions to keep the DBTT low by forming significant amounts of acicular ferrite.

  20. Microstructural influences on the mechanical properties of solder

    SciTech Connect

    Morris, J.W. Jr.; Goldstein, J.L.F.; Mei, Z.

    1993-04-01

    Intent of this book is to review analytic methods for predicting behavior of solder joints, based on continuum mechanics. The solder is treated as a continuous, homogeneous body, or composite of such bodies, whose mechanical behavior is uniform and governed by simple constitutive equations. The microstructure of a solder joint influences its mechanical properties in 3 ways: it governs deformation and failure; common solders deform inhomogeneously; and common solders are microstructurally unstable. The variety of microstructures often found in solder joints are briefly reviewed, and some of the ways are discussed in which the microstructure influences the common types of high-temperature mechanical behavior. 25 figs, 40 refs.

  1. The HAND1 basic helix-loop-helix transcription factor regulates trophoblast differentiation via multiple mechanisms.

    PubMed

    Scott, I C; Anson-Cartwright, L; Riley, P; Reda, D; Cross, J C

    2000-01-01

    The basic helix-loop-helix (bHLH) transcription factor genes Hand1 and Mash2 are essential for placental development in mice. Hand1 promotes differentiation of trophoblast giant cells, whereas Mash2 is required for the maintenance of giant cell precursors, and its overexpression prevents giant cell differentiation. We found that Hand1 expression and Mash2 expression overlap in the ectoplacental cone and spongiotrophoblast, layers of the placenta that contain the giant cell precursors, indicating that the antagonistic activities of Hand1 and Mash2 must be coordinated. MASH2 and HAND1 both heterodimerize with E factors, bHLH proteins that are the DNA-binding partners for most class B bHLH factors and which are also expressed in the ectoplacental cone and spongiotrophoblast. In vitro, HAND1 could antagonize MASH2 function by competing for E-factor binding. However, the Hand1 mutant phenotype cannot be solely explained by ectopic activity of MASH2, as the Hand1 mutant phenotype was not altered by further mutation of Mash2. Interestingly, expression of E-factor genes (ITF2 and ALF1) was down-regulated in the trophoblast lineage prior to giant cell differentiation. Therefore, suppression of MASH2 function, required to allow giant cell differentiation, may occur in vivo by loss of its E-factor partner due to loss of its expression and/or competition from HAND1. In giant cells, where E-factor expression was not detected, HAND1 presumably associates with a different bHLH partner. This may account for the distinct functions of HAND1 in giant cells and their precursors. We conclude that development of the trophoblast lineage is regulated by the interacting functions of HAND1, MASH2, and their cofactors.

  2. Two basic properties of space representation in the brain: evidence from unilateral neglect.

    PubMed Central

    Bisiach, E; Capitani, E; Porta, E

    1985-01-01

    It is argued, on the grounds of earlier findings, that the neural substrate of egocentric space representation has analogue (non-symbolic) topo-topical properties. It is then argued from fresh evidence that space representation appears to be anchored to the sagittal midplane of the trunk and to the line of sight. A tentative reduction of the suggested properties of space representation to the neuro-physiological level is briefly outlined. Images PMID:3981171

  3. Method of predicting mechanical properties of decayed wood

    DOEpatents

    Kelley, Stephen S.

    2003-07-15

    A method for determining the mechanical properties of decayed wood that has been exposed to wood decay microorganisms, comprising: a) illuminating a surface of decayed wood that has been exposed to wood decay microorganisms with wavelengths from visible and near infrared (VIS-NIR) spectra; b) analyzing the surface of the decayed wood using a spectrometric method, the method generating a first spectral data of wavelengths in VIS-NIR spectra region; and c) using a multivariate analysis to predict mechanical properties of decayed wood by comparing the first spectral data with a calibration model, the calibration model comprising a second spectrometric method of spectral data of wavelengths in VIS-NIR spectra obtained from a reference decay wood, the second spectral data being correlated with a known mechanical property analytical result obtained from the reference decayed wood.

  4. Bioinspired Reductionistic Peptide Engineering for Exceptional Mechanical Properties.

    PubMed

    Avinash, M B; Raut, Devaraj; Mishra, Manish Kumar; Ramamurty, Upadrasta; Govindaraju, T

    2015-11-03

    A simple solution-processing and self-assembly approach that exploits the synergistic interactions between multiple hydrogen bonded networks and aromatic interactions was utilized to synthesize molecular crystals of cyclic dipeptides (CDPs), whose molecular weights (~0.2 kDa) are nearly three orders of magnitude smaller than that of natural structural proteins (50-300 kDa). Mechanical properties of these materials, measured using the nanoindentation technique, indicate that the stiffness and strength are comparable and sometimes better than those of natural fibres. The measured mechanical responses were rationalized by recourse to the crystallographic structural analysis and intermolecular interactions in the self-assembled single crystals. With this work we highlight the significance of developing small molecule based bioinspired design strategies to emulate biomechanical properties. A particular advantage of the successfully demonstrated reductionistic strategy of the present work is its amenability for realistic industrial scale manufacturing of designer biomaterials with desired mechanical properties.

  5. Bioinspired Reductionistic Peptide Engineering for Exceptional Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Avinash, M. B.; Raut, Devaraj; Mishra, Manish Kumar; Ramamurty, Upadrasta; Govindaraju, T.

    2015-11-01

    A simple solution-processing and self-assembly approach that exploits the synergistic interactions between multiple hydrogen bonded networks and aromatic interactions was utilized to synthesize molecular crystals of cyclic dipeptides (CDPs), whose molecular weights (~0.2 kDa) are nearly three orders of magnitude smaller than that of natural structural proteins (50-300 kDa). Mechanical properties of these materials, measured using the nanoindentation technique, indicate that the stiffness and strength are comparable and sometimes better than those of natural fibres. The measured mechanical responses were rationalized by recourse to the crystallographic structural analysis and intermolecular interactions in the self-assembled single crystals. With this work we highlight the significance of developing small molecule based bioinspired design strategies to emulate biomechanical properties. A particular advantage of the successfully demonstrated reductionistic strategy of the present work is its amenability for realistic industrial scale manufacturing of designer biomaterials with desired mechanical properties.

  6. Bioinspired Reductionistic Peptide Engineering for Exceptional Mechanical Properties

    PubMed Central

    Avinash, M. B.; Raut, Devaraj; Mishra, Manish Kumar; Ramamurty, Upadrasta; Govindaraju, T.

    2015-01-01

    A simple solution-processing and self-assembly approach that exploits the synergistic interactions between multiple hydrogen bonded networks and aromatic interactions was utilized to synthesize molecular crystals of cyclic dipeptides (CDPs), whose molecular weights (~0.2 kDa) are nearly three orders of magnitude smaller than that of natural structural proteins (50–300 kDa). Mechanical properties of these materials, measured using the nanoindentation technique, indicate that the stiffness and strength are comparable and sometimes better than those of natural fibres. The measured mechanical responses were rationalized by recourse to the crystallographic structural analysis and intermolecular interactions in the self-assembled single crystals. With this work we highlight the significance of developing small molecule based bioinspired design strategies to emulate biomechanical properties. A particular advantage of the successfully demonstrated reductionistic strategy of the present work is its amenability for realistic industrial scale manufacturing of designer biomaterials with desired mechanical properties. PMID:26525957

  7. Thin Films of Quasicrystals: Optical, Electronic, and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Symko, Orest G.

    1998-03-01

    In order to extend some of the unusual properties of quasicrystals toward practical applications and to study fundamental aspects of these properties, we have developed a technology for the deposition of high quality thin films of quasicrystals on a variety of substrates. Mechanical support for the thin films is provided by the substrate as bulk quasicrystals are brittle. We have applied the thin films to studies of their optical, electrical, and mechanical properties as well as to coatings of biomedical devices. An important characteristic of a quasicrystal is its pseudogap in the electronic density of states; it is determined directly from optical transmission measurements. Optical and mechanical characteristics of the thin films provide strong support for the cluster nature of quasicrystals and emphasize their importance for coatings. When used in biomedical devices, thin film quasicrystalline coatings show remarkable strength, low friction, and non-stick behavior. This work was in collaboration with W. Park, E. Abdel-Rahman, and T. Klein.

  8. Electronic and Mechanical Properties of Hydrogen Functionalized Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Yang, Liu; Han, Jie; Jaffe, Richard L.; Arnold, Jim (Technical Monitor)

    2001-01-01

    We examined the electronic and mechanical properties of hydrogen functionalized carbon nanotubes. The functionalization pattern covers two extreme groups. One group has randomly selected functionalization sites including one to twenty percent of the carbon atoms. The other group has regularly patterned functional sites parallel to the tube axis. Metallic, small-gap semiconducting and large-gap semiconducting carbon nanotubes are studied. The results reveal that the electronic properties of the tubes are very sensitive to the degree of functionalization, with even one percent functionalization being enough to render metallic tubes semiconducting. On the other hand, the mechanical properties, like tensile modulus, are much less sensitive to functionalization. For carbon nanotubes functionalized with specific patterns, the electric properties depends strongly on the nature of the functionalization pattern.

  9. Mechanical properties and fiber type composition of chronically inactive muscles

    NASA Technical Reports Server (NTRS)

    Roy, R. R.; Zhong, H.; Monti, R. J.; Vallance, K. A.; Kim, J. A.; Edgerton, V. R.

    2000-01-01

    A role for neuromuscular activity in the maintenance of skeletal muscle properties has been well established. However, the role of activity-independent factors is more difficult to evaluate. We have used the spinal cord isolation model to study the effects of chronic inactivity on the mechanical properties of the hindlimb musculature in cats and rats. This model maintains the connectivity between the motoneurons and the muscle fibers they innervate, but the muscle unit is electrically "silent". Consequently, the measured muscle properties are activity-independent and thus the advantage of using this model is that it provides a baseline level (zero activity) from which regulatory factors that affect muscle cell homeostasis can be defined. In the present paper, we will present a brief review of our findings using the spinal cord isolation model related to muscle mechanical and fiber type properties.

  10. Basic mechanism for biorientation of mitotic chromosomes is provided by the kinetochore geometry and indiscriminate turnover of kinetochore microtubules

    PubMed Central

    Zaytsev, Anatoly V.; Grishchuk, Ekaterina L.

    2015-01-01

    Accuracy of chromosome segregation relies on the ill-understood ability of mitotic kinetochores to biorient, whereupon each sister kinetochore forms microtubule (MT) attachments to only one spindle pole. Because initial MT attachments result from chance encounters with the kinetochores, biorientation must rely on specific mechanisms to avoid and resolve improper attachments. Here we use mathematical modeling to critically analyze the error-correction potential of a simplified biorientation mechanism, which involves the back-to-back arrangement of sister kinetochores and the marked instability of kinetochore–MT attachments. We show that a typical mammalian kinetochore operates in a near-optimal regime, in which the back-to-back kinetochore geometry and the indiscriminate kinetochore–MT turnover provide strong error-correction activity. In human cells, this mechanism alone can potentially enable normal segregation of 45 out of 46 chromosomes during one mitotic division, corresponding to a mis-segregation rate in the range of 10−1–10−2 per chromosome. This theoretical upper limit for chromosome segregation accuracy predicted with the basic mechanism is close to the mis-segregation rate in some cancer cells; however, it cannot explain the relatively low chromosome loss in diploid human cells, consistent with their reliance on additional mechanisms. PMID:26424798

  11. Basic Calcium Phosphate Crystals Activate c-fos Expression Through a Ras/ERK Dependent Signaling Mechanism

    PubMed Central

    Major, Michael L.; Cheung, Herman S.; Misra, Ravi P.

    2007-01-01

    Diseases caused by calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals occur frequently in osteoarthritic joints. Both crystals induce mitogenesis, metalloproteinase synthesis and secretion by fibroblasts and chondrocytes, promoting degradation of articular tissue. We investigated the mechanism by which BCP activates the c-fos proto-oncogene, which has been shown to activate various matrix metalloproteinases (MMPs). We demonstrate that BCP crystals induce c-fos expression primarily through a Ras/ERK dependent signaling mechanism targeting two highly conserved regulatory binding sites, the serum response element (SRE) and the cAMP response element (CRE). These results establish a calcium crystal induced, calcium/Calmodulin independent, signaling pathway in which BCP crystals activate Ras/MAPK, which can directly target an SRF-containing transcription factor complex, to induce fibroblasts to secrete metalloproteinases. PMID:17307136

  12. Flexible Composition: MEG Evidence for the Deployment of Basic Combinatorial Linguistic Mechanisms in Response to Task Demands

    PubMed Central

    Bemis, Douglas K.; Pylkkänen, Liina

    2013-01-01

    The present study investigates whether a minimal manipulation in task demands can induce core linguistic combinatorial mechanisms to extend beyond the bounds of normal grammatical phrases. Using magnetoencephalography, we measured neural activity evoked by the processing of adjective-noun phrases in canonical (red cup) and reversed order (cup red). During a task not requiring composition (verification against a color blob and shape outline), we observed significant combinatorial activity during canonical phrases only – as indexed by minimum norm source activity localized to the left anterior temporal lobe at 200–250 ms(cf. [1], [2]). When combinatorial task demands were introduced (by simply combining the blob and outline into a single colored shape) we observed significant combinatorial activity during reversed sequences as well. These results demonstrate the first direct evidence that basic linguistic combinatorial mechanisms can be deployed outside of normal grammatical expressions in response to task demands, independent of changes in lexical or attentional factors. PMID:24069253

  13. Hitting a Moving Target: Basic Mechanisms of Recovery from Acquired Developmental Brain Injury

    PubMed Central

    Giza, Christopher C.; Kolb, Bryan; Harris, Neil G.; Asarnow, Robert F.; Prins, Mayumi L.

    2009-01-01

    Acquired brain injuries represent a major cause of disability in the pediatric population. Understanding responses to developmental acquired brain injuries requires knowledge of the neurobiology of normal development, age-at-injury effects and experience-dependent neuroplasticity. In the developing brain, full recovery cannot be considered as a return to the premorbid baseline, since ongoing maturation means that cerebral functioning in normal individuals will continue to advance. Thus, the recovering immature brain has to ‘hit a moving target’ to achieve full functional recovery, defined as parity with age-matched uninjured peers. This review will discuss the consequences of developmental injuries such as focal lesions, diffuse hypoxia and traumatic brain injury (TBI). Underlying cellular and physiological mechanisms relevant to age-at-injury effects will be described in considerable detail, including but not limited to alterations in neurotransmission, connectivity/network functioning, the extracellular matrix, response to oxidative stress and changes in cerebral metabolism. Finally, mechanisms of experience-dependent plasticity will be reviewed in conjunction with their effects on neural repair and recovery. PMID:19956795

  14. Immunological analogy between allograft rejection, recurrent abortion and pre-eclampsia - the same basic mechanism?

    PubMed

    Wilczyński, Jacek R

    2006-07-01

    There are still controversies concerning the role of immunological mechanisms engaged both in recurrent abortions (RA) and pre-eclampsia (PE). According to some opinions, recurrent miscarriage is comparable to organ-specific autoimmune disease. Analysis of immune reactions shows that graft rejection shares many similar mechanisms with RA and PE. This fact allows us to conclude that rejection of transplanted alloantigenic organs and pregnancy loss have probably the same evolutionary origin. Subsets and functions of immunocompetent cells (T CD4, suppressor gammadeltaT, cytotoxic T CD8, Treg, Tr1, uterine NK cells), over-activation of innate immunity (activation of NK cytotoxic cells, macrophages, neutrophils and complement), changes of Th1/Th2 cytokine balance (IL-2, IL-12, IL-15, IL-18, IFNgamma, TNFalpha vs. IL-4, IL-10, TGFbeta), importance of HLA-G molecule, CD200/CD200R interaction, over-expression of adhesion molecules, fgl2 prothrombinase activation and stimulation of IDO and HO expression, all suggest that RA and PE are syndromes of fetal allograft rejection, and not organ-specific autoimmune diseases. According to that supposition, an analogy might exist between acute graft rejection and recurrent abortion, and between chronic graft rejection and pre-eclampsia. PMID:16829304

  15. Microstructures and Mechanical Properties of Irradiated Metals and Alloys

    SciTech Connect

    Zinkle, Steven J

    2008-01-01

    The effects of neutron irradiation on the microstructural evolution of metals and alloys are reviewed, with an emphasis on the roles of crystal structure, neutron dose and temperature. The corresponding effects of neutron irradiation on mechanical properties of metals and alloys are summarized, with particular attention on the phenomena of low temperature radiation hardening and embrittlement. The prospects of developing improved high-performance structural materials with high resistance to radiation-induced property degradation are briefly discussed.

  16. Rock Mechanical Properties from Logs Petrophysics : Concepts and Results

    NASA Astrophysics Data System (ADS)

    Gaillot, Philippe; Crawford, Brian; Alramahi, Bashar; Karner, Steve

    2010-05-01

    The objective of the "geomechanics from logs" (GML) research project is to develop model-driven predictive software for determining rock mechanical properties (specifically rock strength, compressibility and fracability) from other, more easily measured, rock properties (e.g. lithology, porosity, clay volume, velocity) routinely derived from nuclear, resistivity and acoustic logging tools. To this end, geomechanics from logs seeks to increase fundamental understanding of the primary geologic controls on rock mechanical properties and to translate this new insight into novel predictive tools. In detail, GML predictors rely on (i) the generation of relational rock mechanical properties databases incorporating QC'd core-based laboratory measurements (both in-house and high-precision published data); (ii) the use of established rock physics models (e.g. friable sand, contact cement models) to investigate theoretical relationships between geologic processes, reservoir environment, rock microstructure and elastic, bulk and transport petrophysical attributes/properties; (iii) the subdivision of database rocks into generic lithotypes (e.g. sand, shaly sand, sandy shale, shale) with common petrophysical attributes/properties; (iv) the use of multivariate statistics to generate lithotype-dependent empirical predictive relationships between mechanical properties and log-derived petrophysical attributes/properties; (v) the estimation of uncertainties associated with predictive function parameters; (vi) the application and validation of mechanical properties predictive tools to well-documented case studies (e.g. sand strength for perforation stability, rock compressibility for reservoir simulation) to test overall performance and quantify uncertainty in predictions. This paper presents the results of various rock strength, rock compressibility and rock fracability case studies conducted in wells of different stratigraphic age and depositional environment. Overall, GML (i

  17. Investigation of mechanical properties of cryogenically treated music wire.

    PubMed

    Heptonstall, A; Waller, M; Robertson, N A

    2015-08-01

    It has been reported that treating music wire (high carbon steel wire) by cooling to cryogenic temperatures can enhance its mechanical properties with particular reference to those properties important for musical performance. We use such wire for suspending many of the optics in Advanced LIGO, the upgrade to LIGO—the Laser Interferometric Gravitational-Wave Observatory. Two properties that particularly interest us are mechanical loss and breaking strength. A decrease in mechanical loss would directly reduce the thermal noise associated with the suspension, thus enhancing the noise performance of mirror suspensions within the detector. An increase in strength could allow thinner wire to be safely used, which would enhance the dilution factor of the suspension, again leading to lower suspension thermal noise. In this article, we describe the results of an investigation into some of the mechanical properties of music wire, comparing untreated wire with the same wire which has been cryogenically treated. For the samples we studied, we conclude that there is no significant difference in the properties of interest for application in gravitational wave detectors. PMID:26329213

  18. Mechanical properties of the brain-skull interface.

    PubMed

    Mazumder, Mohammad Mynuddin Gani; Miller, Karol; Bunt, Stuart; Mostayed, Ahmed; Joldes, Grand; Day, Robert; Hart, Robin; Wittek, Adam

    2013-01-01

    Knowledge of the mechanical properties of the brain-skull interface is important for surgery simulation and injury biomechanics. These properties are known only to a limited extent. In this study we conducted in situ indentation of the sheep brain, and proposed to derive the macroscopic mechanical properties of the brain-skull interface from the results of these experiments. To the best of our knowledge, this is the first ever analysis of this kind. When conducting in situ indentation of the brain, the reaction force on the indentor was measured. After the indentation, a cylindrical sample of the brain tissue was extracted and subjected to uniaxial compression test. A model of the brain indentation experiment was built in the Finite Element (FE) solver ABAQUS™. In the model, the mechanical properties of the brain tissue were assigned as obtained from the uniaxial compression test and the brain-skull interface was modeled as linear springs. The interface stiffness (defined as sum of stiffnesses of the springs divided by the interface area) was varied to obtain good agreement between the calculated and experimentally measured indentor force-displacement relationship. Such agreement was found to occur for the brain-skull interface stiffness of 11.45 Nmm⁻¹/mm². This allowed identification of the overall mechanical properties of the brain-skull interface. PMID:23951996

  19. Effects of humidity on the mechanical properties of gecko setae.

    PubMed

    Prowse, Michael S; Wilkinson, Matt; Puthoff, Jonathan B; Mayer, George; Autumn, Kellar

    2011-02-01

    We tested the hypothesis that an increase in relative humidity (RH) causes changes in the mechanical properties of the keratin of adhesive gecko foot hairs (setae). We measured the effect of RH on the tensile deformation properties, fracture, and dynamic mechanical response of single isolated tokay gecko setae and strips of the smooth lamellar epidermal layer. The mechanical properties of gecko setae were strongly affected by RH. The complex elastic modulus (measured at 5 Hz) of a single seta at 80% RH was 1.2 GPa, only 39% of the value when dry. An increase in RH reduced the stiffness and increased the strain to failure. The loss tangent increased significantly with humidity, suggesting that water absorption produces a transition to a more viscous type of deformation. The influence of RH on the properties of the smooth epidermal layer was comparable with that of isolated seta, with the exception of stress at rupture. These values were two to four times greater for the setae than for the smooth layer. The changes in mechanical properties of setal keratin were consistent with previously reported increases in contact forces, supporting the hypothesis that an increase in RH softens setal keratin, which increases adhesion and friction.

  20. Mechanical property quantification of endothelial cells using scanning acoustic microscopy

    NASA Astrophysics Data System (ADS)

    Shelke, A.; Brand, S.; Kundu, T.; Bereiter-Hahn, J.; Blase, C.

    2012-04-01

    The mechanical properties of cells reflect dynamic changes of cellular organization which occur during physiologic activities like cell movement, cell volume regulation or cell division. Thus the study of cell mechanical properties can yield important information for understanding these physiologic activities. Endothelial cells form the thin inner lining of blood vessels in the cardiovascular system and are thus exposed to shear stress as well as tensile stress caused by the pulsatile blood flow. Endothelial dysfunction might occur due to reduced resistance to mechanical stress and is an initial step in the development of cardiovascular disease like, e.g., atherosclerosis. Therefore we investigated the mechanical properties of primary human endothelial cells (HUVEC) of different age using scanning acoustic microscopy at 1.2 GHz. The HUVECs are classified as young (tD < 90 h) and old (tD > 90 h) cells depending upon the generation time for the population doubling of the culture (tD). Longitudinal sound velocity and geometrical properties of cells (thickness) were determined using the material signature curve V(z) method for variable culture condition along spatial coordinates. The plane wave technique with normal incidence is assumed to solve two-dimensional wave equation. The size of the cells is modeled using multilayered (solid-fluid) system. The propagation of transversal wave and surface acoustic wave are neglected in soft matter analysis. The biomechanical properties of HUVEC cells are quantified in an age dependent manner.

  1. Investigation of mechanical properties of cryogenically treated music wire

    NASA Astrophysics Data System (ADS)

    Heptonstall, A.; Waller, M.; Robertson, N. A.

    2015-08-01

    It has been reported that treating music wire (high carbon steel wire) by cooling to cryogenic temperatures can enhance its mechanical properties with particular reference to those properties important for musical performance. We use such wire for suspending many of the optics in Advanced LIGO, the upgrade to LIGO—the Laser Interferometric Gravitational-Wave Observatory. Two properties that particularly interest us are mechanical loss and breaking strength. A decrease in mechanical loss would directly reduce the thermal noise associated with the suspension, thus enhancing the noise performance of mirror suspensions within the detector. An increase in strength could allow thinner wire to be safely used, which would enhance the dilution factor of the suspension, again leading to lower suspension thermal noise. In this article, we describe the results of an investigation into some of the mechanical properties of music wire, comparing untreated wire with the same wire which has been cryogenically treated. For the samples we studied, we conclude that there is no significant difference in the properties of interest for application in gravitational wave detectors.

  2. Transient dynamic mechanical properties of resilin-based elastomeric hydrogels

    PubMed Central

    Li, Linqing; Kiick, Kristi L.

    2014-01-01

    The outstanding high-frequency properties of emerging resilin-like polypeptides (RLPs) have motivated their development for vocal fold tissue regeneration and other applications. Recombinant RLP hydrogels show efficient gelation, tunable mechanical properties, and display excellent extensibility, but little has been reported about their transient mechanical properties. In this manuscript, we describe the transient mechanical behavior of new RLP hydrogels investigated via both sinusoidal oscillatory shear deformation and uniaxial tensile testing. Oscillatory stress relaxation and creep experiments confirm that RLP-based hydrogels display significantly reduced stress relaxation and improved strain recovery compared to PEG-based control hydrogels. Uniaxial tensile testing confirms the negligible hysteresis, reversible elasticity and superior resilience (up to 98%) of hydrated RLP hydrogels, with Young's modulus values that compare favorably with those previously reported for resilin and that mimic the tensile properties of the vocal fold ligament at low strain (<15%). These studies expand our understanding of the properties of these RLP materials under a variety of conditions, and confirm the unique applicability, for mechanically demanding tissue engineering applications, of a range of RLP hydrogels. PMID:24809044

  3. High basicity adsorbents from solid residue of cellulose and synthetic polymer co-pyrolysis for phenol removal: Kinetics and mechanism

    NASA Astrophysics Data System (ADS)

    Lorenc-Grabowska, Ewa; Rutkowski, Piotr

    2014-10-01

    The activated carbons (ACs) produced from solid residue of cellulose and synthetic polymer co-pyrolysis (CACs) and commercial activated carbon from coconut shell (GC) were used for phenol removal. The adsorption kinetics and mechanism were investigated. All studied activated carbons are predominantly microporous and are characterized by basic surface characteristics. Surface area SBET varies between 1235 and 1499 m2/g, whereas the pHPZC changes from 7.70 to 10.63. The bath adsorption of phenol (P) was carried out at ambient temperature. The equilibrium time and equilibrium sorption capacity were determined. It was found that the boundary layer effect is bigger in AC with high basic characteristics of the surface. The rate controlling step is the intraparticle diffusion in CACs only, whereas in ACs with higher amount of acidic functionalities the adsorbate-surface interaction influences the rate of kinetic as well. The equilibrium isotherms are L2 type for commercial AC and L4 for CACs. The CACs are characterized by very high adsorption capacity that vary between 312 and 417 mg/g. The main mechanism of phenol adsorption is micropore filling within pores smaller than 1.4 nm. In the absence of solvent effect further adsorption of phenol on CACs takes place. The enhanced adsorption is due to dispersive/repulsive interaction induced by oxygen functionalities.

  4. Hygrothermal ageing effect on mechanical properties of FRP laminates

    NASA Astrophysics Data System (ADS)

    Larbi, S.; Bensaada, R.; Bilek, A.; Djebali, S.

    2015-03-01

    The aim of this work is to study the effect of hygrothermal aging on mechanical properties of two composite materials (carbon fiber / epoxy and glass fiber E / vinylester). Two stratifications are studied for each material. Both materials are exposed to two different environments, the sea water and the deionized water at a temperature of 40°C. The kinetic of material absorption is plotted. We see an irreversible degradation of material caused by exposure time. The characterization of samples in the virgin state and the aged condition is achieved with three points bending tests. We can see significant loss of mechanical properties due to hygrothermal aging.

  5. Mechanical and Electrical Properties of Cryo-worked Cu

    NASA Astrophysics Data System (ADS)

    Bettinali, Livio; Tosti, Silvano; Pizzuto, Aldo

    2014-01-01

    For manufacturing the magnets of fusion machines pure copper of both high mechanical resistance and electrical conductivity is required. Though high purity copper guarantees high electrical conductivity, its mechanical properties may be not suitable for the applications in tokamaks. In this view, a new procedure developed for obtaining high purity copper with excellent mechanical strength is described in this work. Samples of oxygen free copper (OFC) have been worked by pressing in liquid nitrogen (77 K). It has been verified that the mechanical properties of the worked metal are strongly dependent on the strain rate. Very low strain rates permitted to attain values of tensile yield strength (550 MPa) significantly higher than those obtained by traditional cold-working at room temperature (450 MPa). The electrical conductivity of the cryo-worked Cu decreases with the tensile yield strength even though the hardest samples of tensile yield strength of 550 MPa exhibit still acceptable values of conductivity (about 94 % IACS at room temperature).

  6. Characterization of High Temperature Mechanical Properties Using Laser Ultrasound

    SciTech Connect

    David Hurley; Stephen Reese; Farhad Farzbod; Rory Kennedy

    2012-05-01

    Mechanical properties are controlled to a large degree by defect structures such as dislocations and grain boundaries. These microstructural features involve a perturbation of the perfect crystal lattice (i.e. strain fields). Viewed in this context, high frequency strain waves (i.e. ultrasound) provide a natural choice to study microstructure mediated mechanical properties. In this presentation we use laser ultrasound to probe mechanical properties of materials. This approach utilizes lasers to excite and detect ultrasonic waves, and as a consequence has unique advantages over other methods—it is noncontacting, requires no couplant or invasive sample preparation (other than that used in metallurgical analysis), and has the demonstrated capability to probe microstructure on a micron scale. Laser techniques are highly reproducible enabling sophisticated, microstructurally informed data analysis. Since light is being used for generation and detection of the ultrasonic wave, the specimen being examined is not mechanically coupled to the transducer. As a result, laser ultrasound can be carried out remotely, an especially attractive characteristic for in situ measurements in severe environments. Several examples involving laser ultrasound to measure mechanical properties in high temperature environments will be presented. Emphasis will be place on understanding the role of grain microstructure.

  7. Mechanical properties of carbon fiber composites for applications in space

    NASA Astrophysics Data System (ADS)

    Hana, P.; Inneman, A.; Daniel, V.; Sieger, L.; Petru, M.

    2015-01-01

    This article describes method of measurement mechanical properties of carbon fiber composites in space. New material structures are specifically designed for use on space satellites. Composite structures will be exposed to cosmic radiation in Earth orbit on board of a '2U CubeSat' satellite. Piezoelectric ceramic sensors are used for detection mechanical vibrations of composite test strip. A great deal of attention is paid to signal processing using 8-bit microcontroler. Fast Fourier Transformation is used. Fundamental harmonic frequencies and damping from on-board measurements will serve as the input data for terrestrial data processing. The other step of elaboration data is creation of the physical model for evaluating mechanical properties of Carbon composite - Piezoelectric ceramic system. Evaluation of anisotropic mechanical properties of piezoelectric ceramics is an interesting secondary outcome of the investigation. Extreme changes in temperature and the effect of cosmic rays will affect the mechanical properties and durability of the material used for the external construction of satellites. Comparative terrestrial measurements will be performed.

  8. Mechanical and tribological properties of ion beam-processed surfaces

    NASA Astrophysics Data System (ADS)

    Kodali, Padma

    A variety of surface modification and surface coating techniques are currently used in industry to modify the near-surface mechanical properties that influence the friction and wear behavior of metals, metallic alloys, ceramics, and polymers. Near-surface mechanical properties such as hardness and fracture toughness of a coating-substrate system can be tailored economically without changing the bulk properties of the system. The intent of this work was to broaden the applications of well-established surface modification techniques and to elucidate the various wear mechanisms that occur in sliding contact of ion-beam processed surfaces. The investigation included characterization and evaluation of coatings and modified surfaces synthesized by three surface engineering methods; namely, beam-line ion implantation, plasma-source ion implantation, and DC magnetron sputtering. Correlation among measured properties such as surface hardness, fracture toughness, and wear behavior was also examined. This dissertation focused on the following areas of research: (1) Investigating the mechanical and tribological properties of mixed implantation of carbon and nitrogen into single crystal silicon by beam-line implantation. (2) Characterizing the mechanical and tribological properties of diamond-like carbon (DLC) coatings processed by plasma source ion implantation. (3) Developing and evaluating metastable boron-carbon-nitrogen (BCN) compound coatings for mechanical and tribological properties. The surface hardness of a mixed carbon-nitrogen implant sample improved significantly compared to the unimplanted sample. However, the enhancement in the wear factor of this sample was found to be less significant than carbon-implanted samples. The presence of nitrogen might be responsible for the degraded wear behavior since nitrogen-implantation alone resulted in no improvement in the wear factor. Wear mechanisms that occurred in implanted and unimplanted surfaces tested against AIS152100

  9. Basic electrophysiological properties of spinal cord motoneurons during old age in the cat.

    PubMed

    Morales, F R; Boxer, P A; Fung, S J; Chase, M H

    1987-07-01

    1. The electrophysiological properties of alpha-motoneurons in old cats (14-15 yr) were compared with those of adult cats (1-3 yr). These properties were measured utilizing intracellular recording and stimulating techniques. 2. Unaltered in the old cat motoneurons were the membrane potential, action potential amplitude, and slopes of the initial segment (IS) and soma dendritic (SD) spikes, as well as the duration and amplitude of the action potential's afterhyperpolarization. 3. In contrast, the following changes in the electrophysiological properties of lumbar motoneurons were found in the old cats: a decrease in axonal conduction velocity, a shortening of the IS-SD delay, an increase in input resistance, and a decrease in rheobase. 4. In spite of these considerable changes in motoneuron properties in the old cat, normal correlations between different electrophysiological properties were maintained. The following key relationships, among others, were the same in adult and old cat motoneurons: membrane potential polarization versus action potential amplitude, duration of the afterhyperpolarization versus motor axon conduction velocity, and rheobase versus input conductance. 5. A review of the existing literature reveals that neither chronic spinal cord section nor deafferentation (13, 21) in adult animals produce the changes observed in old cats. Thus we consider it unlikely that a loss of synaptic contacts was responsible for the modifications in electrophysiological properties observed in old cat motoneurons. 6. We conclude that during old age there are significant changes in the soma-dendritic portion of cat motoneurons, as indicated by the modifications found in input resistance, rheobase, and IS-SD delay, as well as significant changes in their axons, as indicated by a decrease in conduction velocity. PMID:3612223

  10. Quadriceps Muscle Mechanical Simulator for Training of Vastus Medialis Obliquus and Vastus Lateralis Obliquus Mechanical Properties

    PubMed Central

    Irmak, Rafet; Irmak, Ahsen; Biçer, Gökhan

    2014-01-01

    Objectives: In classical anatomy quadriceps muscle has four heads. Clinical studies have demostrated 6 heads of this muscle. These heads were demostrated seperately not only by their functional properties,but also by innervation and kinesiological properties. In our previous study we have developed and demostrated electrophysiological properties of vastus medialis obliquus by an electronic patient simulator. The purpose of this study is to develop a mechanical simulator which can be used to demostrate mechanical properties of 6 heads of quadriceps muscle and the screw home mechanism. Methods: Quadriceps femoris muscle has 6 heads: rectus femoris, vastus intermedius, vastus medialis obliquus, vastus medialis longus, vastus lateralis obliquus and vastus lateralis longus. The fundamental mechanical properties of each head is seperated by insersio and angle of pull. Main design principle was to demostrate all heads with insersio and angle of pull properties. Second design principle was to demostrate the screw-home mechanism which is the result of difference in articular surfaces of medial and lateral of condyles of femur. Results: Final design of the simulator consists of three planes for demostration of angle of pull and pulling forces (patellar plane, proximal and distal planes) of each heads. On each plane channels were graved as origo and insersio for demostration of angle of pull. Distal plane was movable for demostration of pulling forces in different angels of knee flexion and extention. Also proximal plane was adjustable to demostrate different sitting and standing positions. Srew home mechanism was demostrated by specially designed hingle mechanism. Left and right side hingle mechanisms have different radii as femoral condyles and this difference can cause rotation in terminal extension as in the screw home mechanism. Conclusion: Vastus medialis obliquus, vastus lateralis obliquus and screw-home mechanism have clinical significance. We were not able to find

  11. Incretin-Based Therapies for Diabetic Complications: Basic Mechanisms and Clinical Evidence

    PubMed Central

    Kawanami, Daiji; Matoba, Keiichiro; Sango, Kazunori; Utsunomiya, Kazunori

    2016-01-01

    An increase in the rates of morbidity and mortality associated with diabetic complications is a global concern. Glycemic control is important to prevent the development and progression of diabetic complications. Various classes of anti-diabetic agents are currently available, and their pleiotropic effects on diabetic complications have been investigated. Incretin-based therapies such as dipeptidyl peptidase (DPP)-4 inhibitors and glucagon-like peptide-1 receptor agonists (GLP-1RA) are now widely used in the treatment of patients with type 2 diabetes. A series of experimental studies showed that incretin-based therapies have beneficial effects on diabetic complications, independent of their glucose-lowering abilities, which are mediated by anti-inflammatory and anti-oxidative stress properties. Based on these findings, clinical studies to assess the effects of DPP-4 inhibitors and GLP-1RA on diabetic microvascular and macrovascular complications have been performed. Several but not all studies have provided evidence to support the beneficial effects of incretin-based therapies on diabetic complications in patients with type 2 diabetes. We herein discuss the experimental and clinical evidence of incretin-based therapy for diabetic complications. PMID:27483245

  12. Basic properties of coals and other solids. Final report, September 1, 1989--August 30, 1992

    SciTech Connect

    Arnett, E.M.

    1992-12-31

    The previous project dissected the heats of interactions of a series of coals into components that represented Bronsted acidity, hydrogen-bonding acidity and dispersion force interactions through comparison with the simple prototype solid acids: sulfonic acid resin, silica, and graphitized carbon black respectively. The present grant has emphasized the interaction of basic components in the coal with strong Bronsted acids and boron trichloride, a very strong Lewis acid, with a brief examination of the interactions of the coals with phenols as weaker hydrogen-bonding acids. We have also compared several coals with liquids derived from them at Wilsonville and Exxon. Finally, we have examined the effect of citric acid washing on several coals.

  13. Limitations to maximum sprinting speed imposed by muscle mechanical properties.

    PubMed

    Miller, Ross H; Umberger, Brian R; Caldwell, Graham E

    2012-04-01

    It has been suggested that the force-velocity relationship of skeletal muscle plays a critical limiting role in the maximum speed at which humans can sprint. However, this theory has not been tested directly, and it is possible that other muscle mechanical properties play limiting roles as well. In this study, forward dynamics simulations of human sprinting were generated using a 2D musculoskeletal model actuated by Hill muscle models. The initial simulation results compared favorably to kinetic, kinematic, and electromyographic data recorded from sprinting humans. Muscle mechanical properties were then removed in isolation to quantify their effect on maximum sprinting speed. Removal of the force-velocity, excitation-activation, and force-length relationships increased the maximum speed by 15, 8, and 4%, respectively. Removal of the series elastic force-extension relationship decreased the maximum speed by 26%. Each relationship affected both stride length and stride frequency except for the force-length relationship, which mainly affected stride length. Removal of all muscular properties entirely (optimized joint torques) increased speed (+22%) to a greater extent than the removal of any single contractile property. The results indicate that the force-velocity relationship is indeed the most important contractile property of muscle regarding limits to maximum sprinting speed, but that other muscular properties also play important roles. Interactions between the various muscular properties should be considered when explaining limits to maximal human performance.

  14. [The effect of physical properties of chitosan on cell activity and on its mechanics property].

    PubMed

    Tian, Shengli; Ye, Zhiyi

    2012-12-01

    Chitosan is a natural biopolymer and is made up of D-glucosamine subunits linked by beta-(1,4) glycosidic bond. In recent years, the application of chitosan has attracted more and more attention because of its good biological function in cell biology. The properties of chitosan-based biomaterial are attributed to the physical properties and chemical composition of chitosan. The author of this paper summarized recent related studies and progresses of the influence of physical properties of chitosan on cell activity and cell mechanics property at home and abroad. The findings show that most studies mainly focused on the influence of chitosan and cell activity, while few were on cell mechanics property. The related studies of the influence of chitosan on cell will contribute to the explanation for the mechanism of the interaction between chitosan and cell, and provide the theoretical support for the further study.

  15. Measurement and Comparison of Mechanical Properties of Nitinol Stents

    NASA Astrophysics Data System (ADS)

    Hanus, Josef; Zahora, Jiri

    2005-01-01

    The self expandable Nitinol stents or stentgrafts are typically used for miniinvasive treatment of stenosis and aneurysms in the cardiovascular system. The minimal traumatisation of the patient, shorter time of hospitalization are typical advantages of these methods. More than ten years of experience has yielded also important information about the performance of stents in interaction with biological system and the possible problems related with it. The leakage or the shift of stent are some typical disadvantages, that can be related among other in the construction of the stent. The problem is that the mechanical properties, dimensions and the dynamical properties of the stent do not exactly correspond to the properties of the vessel or generally of tissue where this stent is introduced. The measurement, the description and the comparison of the relations between the mechanical properties of stents and tissues can be one of the possible ways to minimize these disadvantages. The developed original computer controlled measuring system allows the measurement of mechanical properties of stents, the measurement of strain-stress curves or simulation of interaction of the stent and vessel for exactly defined hemodynamic conditions. We measured and compared the mechanical parameters of different selfexpandable Nitinol stents, which differed in geometry (radius and length), in the type of construction (number of branches and rising of winding) and in the diameter of used wire. The results of measurements confirmed the theoretical assumptions that just the diameter of the Nitinol wire significantly influences the rigidity and the level of compressibility of the stent as well. A compromise must be found between the required rigidity of the stent and the minimal size of the delivery system. The exact description of the relation between the mechanical properties and geometry and construction of the stents enables to design the stent to fit the patient and it is expected that

  16. Definition and basic properties of one modification of computational schema for recognition algorithms

    SciTech Connect

    Okhtilev, M.Yu.

    1992-09-01

    This article presents one form of computational schema for recognition algorithms in the form of modified Petri nets. Associated concepts are introduced and a description is given of the fundamental properties of the proposed nets that make it possible to treat them as schema for programs for artificial intelligence systems. 13 refs., 4 figs.

  17. Characterization of mechanical and biochemical properties of developing embryonic tendon.

    PubMed

    Marturano, Joseph E; Arena, Jeffrey D; Schiller, Zachary A; Georgakoudi, Irene; Kuo, Catherine K

    2013-04-16

    Tendons have uniquely high tensile strength, critical to their function to transfer force from muscle to bone. When injured, their innate healing response results in aberrant matrix organization and functional properties. Efforts to regenerate tendon are challenged by limited understanding of its normal development. Consequently, there are few known markers to assess tendon formation and parameters to design tissue engineering scaffolds. We profiled mechanical and biological properties of embryonic tendon and demonstrated functional properties of developing tendon are not wholly reflected by protein expression and tissue morphology. Using force volume-atomic force microscopy, we found that nano- and microscale tendon elastic moduli increase nonlinearly and become increasingly spatially heterogeneous during embryonic development. When we analyzed potential biochemical contributors to modulus, we found statistically significant but weak correlation between elastic modulus and collagen content, and no correlation with DNA or glycosaminoglycan content, indicating there are additional contributors to mechanical properties. To investigate collagen cross-linking as a potential contributor, we inhibited lysyl oxidase-mediated collagen cross-linking, which significantly reduced tendon elastic modulus without affecting collagen morphology or DNA, glycosaminoglycan, and collagen content. This suggests that lysyl oxidase-mediated cross-linking plays a significant role in the development of embryonic tendon functional properties and demonstrates that changes in cross-links alter mechanical properties without affecting matrix content and organization. Taken together, these data demonstrate the importance of functional markers to assess tendon development and provide a profile of tenogenic mechanical properties that may be implemented in tissue engineering scaffold design to mechanoregulate new tendon regeneration.

  18. Basic Mechanisms of Therapeutic Resistance to Radiation and Chemotherapy in Lung Cancer

    PubMed Central

    Willers, Henning; Azzoli, Christopher G.; Santivasi, Wil L.; Xia, Fen

    2013-01-01

    In recent years, there have been multiple breakthroughs in our understanding of lung cancer biology. Despite significant advances in molecular targeted therapies DNA-damaging cytotoxic therapies will remain the mainstay of lung cancer management for the foreseeable future. Similar to the concept of personalized targeted therapies there is mounting evidence that perturbations in DNA repair pathways are common in lung cancers, altering the resistance of the affected tumors to many chemotherapeutics as well as radiation. Defects in DNA repair may be due to a multitude of mechanisms including gene mutations, epigenetic events, and alterations in signal transduction pathways such as EGFR and PI3K/AKT. Functional biomarkers that assess the subcellular localization of central repair proteins in response to DNA damage may prove useful for individualization of cytotoxic therapies including PARP inhibitors. A better mechanistic understanding of cellular sensitivity and resistance to DNA damaging agents should facilitate the development of novel, individualized treatment approaches. Absolute resistance to radiation therapy, however, does not exist. To some extent, radiation therapy will always have to remain unselective and indiscriminant to eradicate persistent, drug-resistant tumor stem cell pools. PMID:23708066

  19. [The basics on mechanical ventilation support in acute respiratory distress syndrome].

    PubMed

    Tomicic, V; Fuentealba, A; Martínez, E; Graf, J; Batista Borges, J

    2010-01-01

    Acute Respiratory Distress Syndrome (ARDS) is understood as an inflammation-induced disruption of the alveolar endothelial-epithelial barrier that results in increased permeability and surfactant dysfunction followed by alveolar flooding and collapse. ARDS management relies on mechanical ventilation. The current challenge is to determine the optimal ventilatory strategies that minimize ventilator-induced lung injury (VILI) while providing a reasonable gas exchange. The data support that a tidal volume between 6-8 ml/kg of predicted body weight providing a plateau pressure < 30 cmH₂O should be used. High positive end expiratory pressure (PEEP) has not reduced mortality, nevertheless secondary endpoints are improved. The rationale used for high PEEP argues that it prevents cyclic opening and closing of airspaces, probably the major culprit of development of VILI. Chest computed tomography has contributed to our understanding of anatomic-functional distribution patterns in ARDS. Electric impedance tomography is a technique that is radiation-free, but still under development, that allows dynamic monitoring of ventilation distribution at bedside.

  20. The role of HDL in plaque stabilization and regression: basic mechanisms and clinical implications.

    PubMed

    Feig, Jonathan E; Feig, Jessica L; Dangas, George D

    2016-11-01

    On the basis of studies that extend back to the early 1900s, regression and stabilization of atherosclerosis in humans has progressed from being a concept to one that is achievable. Successful attempts at regression generally applied robust measures to improve plasma lipoprotein profiles. Possible mechanisms responsible for lesion shrinkage include decreased retention of atherogenic apolipoprotein B within the arterial wall, efflux of cholesterol and other toxic lipids from plaques, emigration of lesional foam cells out of the arterial wall, and influx of healthy phagocytes that remove necrotic debris as well as other components of the plaque. Currently available clinical agents, however, still fail to stop most cardiovascular events. For years, HDL has been considered the 'good cholesterol.' Clinical intervention studies to causally link plasma HDL-C levels to decreased progression or to the regression of atherosclerotic plaques are relatively few because of the lack of therapeutic agents that can selectively and potently increase HDL-C. The negative results of studies that were carried out have led to uncertainty as to the role that HDL plays in atherosclerosis. It is becoming clearer, however, that HDL function rather than quantity is most crucial and, therefore, discovery of agents that enhance the quality of HDL should be the goal.

  1. Mechanical properties and barrier function of healthy human skin.

    PubMed

    Pedersen, Louise; Jemec, Gregor B E

    2006-01-01

    The aim of this study was to investigate the relationship between the mechanical properties and the epidermal barrier function of the skin in vivo. A suction cup device commonly used for measurement of skin mechanics was used to provide a defined stress to the skin using the ventral forearm in 16 healthy volunteers. The integrity of the barrier function was assessed by trans-epidermal water loss and skin capacitance. In the first part of the study, changes in barrier function were measured following the application of standardized strain to the skin barrier. In the second part of the study changes in skin mechanics were assessed following standardized barrier removal. The Wilcoxon signed rank test and Spearman's rank correlation were used for statistical analysis. Significant increases were established in trans-epidermal water loss (p < 0.01) with concomitant significant decreases in capacitance (p < 0.05) following 400 mbar and 600 mbar of suction, suggesting that the mechanical integrity of the skin barrier was disrupted. A significant increase in distensibility (p < 0.05) and hysteresis (p < 0.01) was found following stripping, relating the role of the skin barrier to the overall mechanical properties of the skin. This study showed that the water permeability of the epidermis was significantly affected by the application of mechanical stress to the skin and vice versa, the mechanical properties of the skin were altered when the barrier was compromised. These observations suggest that the mechanical strength of the skin barrier may play a role in the development of, for example, friction dermatitis and other skin diseases affected by mechanical stress.

  2. High-rate mechanical properties of energetic materials

    NASA Astrophysics Data System (ADS)

    Walley, S. M.; Siviour, C. R.; Drodge, D. R.; Williamson, D. M.

    2010-01-01

    Compared to the many thousands of studies that have been performed on the energy release mechanisms of high energy materials, relatively few studies have been performed (a few hundred) into their mechanical properties. Since it is increasingly desired to model the high rate deformation of such materials, it is of great importance to gather data on their response so that predictive constitutive models can be constructed. This paper reviews the state of the art concerning what is known about the mechanical response of high energy materials. Examples of such materials are polymer bonded explosives (used in munitions), propellants (used to propel rockets), and pyrotechnics (used to initiate munitions and also in flares).

  3. Exploration of mechanisms underlying the strain-rate-dependent mechanical property of single chondrocytes

    SciTech Connect

    Nguyen, Trung Dung; Gu, YuanTong

    2014-05-05

    Based on the characterization by Atomic Force Microscopy, we report that the mechanical property of single chondrocytes has dependency on the strain-rates. By comparing the mechanical deformation responses and the Young's moduli of living and fixed chondrocytes at four different strain-rates, we explore the deformation mechanisms underlying this dependency property. We found that the strain-rate-dependent mechanical property of living cells is governed by both of the cellular cytoskeleton and the intracellular fluid when the fixed chondrocytes are mainly governed by their intracellular fluid, which is called the consolidation-dependent deformation behavior. Finally, we report that the porohyperelastic constitutive material model which can capture the consolidation-dependent behavior of both living and fixed chondrocytes is a potential candidature to study living cell biomechanics.

  4. Mechanical Behavior of Agave Americana L. Fibres: Correlation Between Fine Structure and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Msahli, S.; Chaabouni, Y.; Sakli, F.; Drean, J. Y.

    In this study, results of a mechanical behavior study of fibres extracted from the agave Americana L. plant, the most abundant variety in Tunisia, are presented. These results deal with the principal and mechanical characteristics of these fibres which are the elongation at break, the elasticity modulus and the rupture facture. These results permitted to situate these fibres, compared to the other textile fibres, as materials that can be used in technical applications such as reinforcing composites or geotextile. In order to understand the mechanical properties of these fibres, a correlation study between the properties already cited and the fine structure was done. The obtained results showed that the mechanical properties of agave Americana L. fibres are closely related to the individual fibers deformations and to the natural matrix (lignin and gums) that links these elementary fibres.

  5. Mechanical and physical properties of modern boron fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1978-01-01

    The results of accurate measurements of the modern boron fiber's Young's modulus, flexural modulus, shear modulus, and Poisson's ratio are reported. Physical property data concerning fiber density, thermal expansion, and resistance obtained during the course of the mechanical studies are also given.

  6. Engineered disulfides improve mechanical properties of recombinant spider silk

    PubMed Central

    Grip, S; Johansson, J; Hedhammar, M

    2009-01-01

    Nature's high-performance polymer, spider silk, is composed of specific proteins, spidroins, which form solid fibers. So far, fibers made from recombinant spidroins have failed in replicating the extraordinary mechanical properties of the native material. A recombinant miniature spidroin consisting of four poly-Ala/Gly-rich tandem repeats and a nonrepetitive C-terminal domain (4RepCT) can be isolated in physiological buffers and undergoes self assembly into macrofibers. Herein, we have made a first attempt to improve the mechanical properties of 4RepCT fibers by selective introduction of AA → CC mutations and by letting the fibers form under physiologically relevant redox conditions. Introduction of AA → CC mutations in the first poly-Ala block in the miniature spidroin increases the stiffness and tensile strength without changes in ability to form fibers, or in fiber morphology. These improved mechanical properties correlate with degree of disulfide formation. AA → CC mutations in the forth poly-Ala block, however, lead to premature aggregation of the protein, possibly due to disulfide bonding with a conserved Cys in the C-terminal domain. Replacement of this Cys with a Ser, lowers thermal stability but does not interfere with dimerization, fiber morphology or tensile strength. These results show that mutagenesis of 4RepCT can reveal spidroin structure-activity relationships and generate recombinant fibers with improved mechanical properties. PMID:19388023

  7. Sterilizing elastomeric chains without losing mechanical properties. Is it possible?

    PubMed Central

    Pithon, Matheus Melo; Ferraz, Caio Souza; Rosa, Francine Cristina Silva; Rosa, Luciano Pereira

    2015-01-01

    OBJECTIVE: To investigate the effects of different sterilization/disinfection methods on the mechanical properties of orthodontic elastomeric chains. METHODS: Segments of elastomeric chains with 5 links each were sent for sterilization by cobalt 60 (Co60) (20 KGy) gamma ray technology. After the procedure, the elastomeric chains were contaminated with clinical samples of Streptococcus mutans. Subsequently, the elastomeric chains were submitted to sterilization/disinfection tests carried out by means of different methods, forming six study groups, as follows: Group 1 (control - without contamination), Group 2 (70°GL alcohol), Group 3 (autoclave), Group 4 (ultraviolet), Group 5 (peracetic acid) and Group 6 (glutaraldehyde). After sterilization/disinfection, the effectiveness of these methods, by Colony forming units per mL (CFU/mL), and the mechanical properties of the material were assessed. Student's t-test was used to assess the number of CFUs while ANOVA and Tukey's test were used to assess elastic strength. RESULTS: Ultraviolet treatment was not completely effective for sterilization. No loss of mechanical properties occurred with the use of the different sterilization methods (p > 0.05). CONCLUSION: Biological control of elastomeric chains does not affect their mechanical properties. PMID:26154462

  8. Mechanical Properties of Irradiated Polarization-Maintaining Optical Fibers

    NASA Technical Reports Server (NTRS)

    Moeti, L.; Moghazy, S.; Ally, A.; Barnes, S.; Watkins, L.; Cuddihy, E.

    1996-01-01

    Polarization-maintaining optical fibers, referred to as PANDA fibers, were subjected to Cobalt 60 radiation (300,000 Rad). The mechanical properties of the PANDA fibers were measured after exposure to gamma radiation and compared to non-irradiated PANDA fibers.

  9. Barrier and Mechanical Properties of Starch-Clay Nanocomposite Films

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The poor barrier and mechanical properties of biopolymer-based food packaging can potentially be enhanced by the use of layered silicates (nanoclay) to produce nanocomposites. In this study, starch-clay nano-composites were synthesized by a melt extrusion method. Natural (MMT) and organically modifi...

  10. Mechanical shear and tensile properties of selected biomass stems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Lignocellulosic biomass, such as big bluestem, corn stalk, intermediate wheat grass and switchgrass stem are abundant and dominant species in the Midwest region of US. There is a need to understand the mechanical properties for these crops for better handling and processing of the biomass feedstocks...

  11. Mechanical properties of hyaline and repair cartilage studied by nanoindentation.

    PubMed

    Franke, O; Durst, K; Maier, V; Göken, M; Birkholz, T; Schneider, H; Hennig, F; Gelse, K

    2007-11-01

    Articular cartilage is a highly organized tissue that is well adapted to the functional demands in joints but difficult to replicate via tissue engineering or regeneration. Its viscoelastic properties allow cartilage to adapt to both slow and rapid mechanical loading. Several cartilage repair strategies that aim to restore tissue and protect it from further degeneration have been introduced. The key to their success is the quality of the newly formed tissue. In this study, periosteal cells loaded on a scaffold were used to repair large partial-thickness cartilage defects in the knee joint of miniature pigs. The repair cartilage was analyzed 26 weeks after surgery and compared both morphologically and mechanically with healthy hyaline cartilage. Contact stiffness, reduced modulus and hardness as key mechanical properties were examined in vitro by nanoindentation in phosphate-buffered saline at room temperature. In addition, the influence of tissue fixation with paraformaldehyde on the biomechanical properties was investigated. Although the repair process resulted in the formation of a stable fibrocartilaginous tissue, its contact stiffness was lower than that of hyaline cartilage by a factor of 10. Fixation with paraformaldehyde significantly increased the stiffness of cartilaginous tissue by one order of magnitude, and therefore, should not be used when studying biomechanical properties of cartilage. Our study suggests a sensitive method for measuring the contact stiffness of articular cartilage and demonstrates the importance of mechanical analysis for proper evaluation of the success of cartilage repair strategies. PMID:17586107

  12. Enhanced Graphene Mechanical Properties through Ultrasmooth Copper Growth Substrates.

    PubMed

    Griep, Mark H; Sandoz-Rosado, Emil; Tumlin, Travis M; Wetzel, Eric

    2016-03-01

    The combination of extraordinary strength and stiffness in conjunction with exceptional electronic and thermal properties in lightweight two-dimensional materials has propelled graphene research toward a wide array of applications including flexible electronics and functional structural components. Tailoring graphene's properties toward a selected application requires precise control of the atomic layer growth process, transfer, and postprocessing procedures. To date, the mechanical properties of graphene are largely controlled through postprocess defect engineering techniques. In this work, we demonstrate the role of varied catalytic surface morphologies on the tailorability of subsequent graphene film quality and breaking strength, providing a mechanism to tailor the physical, electrical, and mechanical properties at the growth stage. A new surface planarization methodology that results in over a 99% reduction in Cu surface roughness allows for smoothness parameters beyond that reported to date in literature and clearly demonstrates the role of Cu smoothness toward a decrease in the formation of bilayer graphene defects, altered domain sizes, monolayer graphene sheet resistance values down to 120 Ω/□ and a 78% improvement in breaking strength. The combined electrical and mechanical enhancements achieved through this methodology allows for the direct growth of application quality flexible transparent conductive films with monolayer graphene. PMID:26882091

  13. Physical and mechanical properties of the lunar soil (a review)

    NASA Astrophysics Data System (ADS)

    Slyuta, E. N.

    2014-09-01

    We review the data on the physical and mechanical properties of the lunar soil that were acquired in the direct investigations on the lunar surface carried out in the manned and automatic missions and in the laboratory examination of the lunar samples returned to the Earth. In justice to the American manned program Apollo, we show that a large volume of the data on the properties of the lunar soil was also obtained in the Soviet automatic program Lunokhod and with the automatic space stations Luna-16, -20, and -24 that returned the lunar soil samples to the Earth. We consider all of the main physical and mechanical properties of the lunar soil, such as the granulometric composition, density and porosity, cohesion and adhesion, angle of internal friction, shear strength of loose soil, deformation characteristics (the deformation modulus and Poisson ratio), compressibility, and the bearing capacity, and show the change of some properties versus the depth. In most cases, the analytical dependence of the main parameters is presented, which is required in developing reliable engineering models of the lunar soil. The main physical and mechanical properties are listed in the summarizing table, and the currently available models and simulants of the lunar soil are reviewed.

  14. Hyperoxia alters the mechanical properties of alveolar epithelial cells.

    PubMed

    Roan, Esra; Wilhelm, Kristina; Bada, Alex; Makena, Patrudu S; Gorantla, Vijay K; Sinclair, Scott E; Waters, Christopher M

    2012-06-15

    Patients with severe acute lung injury are frequently administered high concentrations of oxygen (>50%) during mechanical ventilation. Long-term exposure to high levels of oxygen can cause lung injury in the absence of mechanical ventilation, but the combination of the two accelerates and increases injury. Hyperoxia causes injury to cells through the generation of excessive reactive oxygen species. However, the precise mechanisms that lead to epithelial injury and the reasons for increased injury caused by mechanical ventilation are not well understood. We hypothesized that alveolar epithelial cells (AECs) may be more susceptible to injury caused by mechanical ventilation if hyperoxia alters the mechanical properties of the cells causing them to resist deformation. To test this hypothesis, we used atomic force microscopy in the indentation mode to measure the mechanical properties of cultured AECs. Exposure of AECs to hyperoxia for 24 to 48 h caused a significant increase in the elastic modulus (a measure of resistance to deformation) of both primary rat type II AECs and a cell line of mouse AECs (MLE-12). Hyperoxia also caused remodeling of both actin and microtubules. The increase in elastic modulus was blocked by treatment with cytochalasin D. Using finite element analysis, we showed that the increase in elastic modulus can lead to increased stress near the cell perimeter in the presence of stretch. We then demonstrated that cyclic stretch of hyperoxia-treated cells caused significant cell detachment. Our results suggest that exposure to hyperoxia causes structural remodeling of AECs that leads to decreased cell deformability. PMID:22467640

  15. Synthesis, Structure, and Basic Magnetic and Thermoelectric Properties of the Light Lanthanide Aurobismuthides.

    PubMed

    Seibel, Elizabeth M; Xie, Weiwei; Gibson, Quinn D; Cava, Robert J

    2016-04-01

    We report the crystal structures and elementary properties of the new aurobismuthides La3Au3Bi4, Ce3Au3Bi4, Pr3Au3Bi4, Nd3Au3Bi4, Sm3Au3Bi4, and Gd3Au3Bi4. These ternary compounds are found only for the large lanthanides and crystallize in the cubic Y3Au3Sb4 structure type, which is a stuffed Th3P4-type derivative. The compounds are electron-precise, leading to semiconducting behavior, and display magnetic properties arising from localized lanthanide f states. Resistivity data, Seebeck coefficient measurements, and electronic structure calculations suggest that these phases are heavily doped, p-type semiconductors. Nd3Au3Bi4 and Sm3Au3Bi4 have Seebeck coefficients of 105 and 190 μV/K at 350 K, respectively, making them worthy of further thermoelectric studies.

  16. Basic Properties of the p38 Signaling Pathway in Response to Hyperosmotic Shock

    PubMed Central

    Ben Messaoud, Nabil; Katzarova, Ilina; López, José M.

    2015-01-01

    Some properties of signaling systems, like ultrasensitivity, hysteresis (a form of biochemical memory), and all-or-none responses at a single cell level, are important to understand the regulation of irreversible processes. Xenopus oocytes are a suitable cell model to study these properties. The p38 MAPK (mitogen-activated protein kinase) pathway is activated by different stress stimuli, including osmostress, and regulates multiple biological processes, from immune response to cell cycle. Recently, we have reported that activation of p38 and JNK regulate osmostress-induced apoptosis in Xenopus oocytes and that sustained activation of p38 accelerates cytochrome c release and caspase-3 activation. However, the signaling properties of p38 in response to hyperosmotic shock have not been studied. Here we show, using Xenopus oocytes as a cell model, that hyperosmotic shock activates the p38 signaling pathway with an ultrasensitive and bimodal response in a time-dependent manner, and with low hysteresis. At a single cell level, p38 activation is not well correlated with cytochrome c release 2 h after hyperosmotic shock, but a good correlation is observed at 4 h after treatment. Interestingly, cytochrome c microinjection induces p38 phosphorylation through caspase-3 activation, and caspase inhibition reduces p38 activation induced by osmostress, indicating that a positive feedback loop is engaged by hyperosmotic shock. To know the properties of the stress protein kinases activated by hyperosmotic shock will facilitate the design of computational models to predict cellular responses in human diseases caused by perturbations in fluid osmolarity. PMID:26335493

  17. Assessing the functional mechanical properties of bioengineered organs with emphasis on the lung.

    PubMed

    Suki, Béla

    2014-09-01

    Recently, an exciting new approach has emerged in regenerative medicine pushing the forefront of tissue engineering to create bioartificial organs. The basic idea is to create biological scaffolds made of extracellular matrix (ECM) that preserves the three-dimensional architecture of an entire organ. These scaffolds are then used as templates for functional tissue and organ reconstruction after re-seeding the structure with stem cells or appropriately differentiated cells. In order to make sure that these bioartificial organs will be able to function in the mechanical environment of the native tissue, it is imperative to fully characterize their mechanical properties and match them with those of the normal native organs. This mini-review briefly summarizes modern measurement techniques of mechanical function characterized mostly by the material or volumetric stiffness. Micro-scale and macro-scale techniques such as atomic force microscopy and the tissue strip stress-strain approach are discussed with emphasis on those that combine mechanical measurements with structural visualization. Proper micro-scale stiffness helps attachment and differentiation of cells in the bioartificial organ whereas macro-scale functionality is provided by the overall mechanical properties of the construct. Several approaches including failure mechanics are also described, which specifically probe the contributions of the main ECM components including collagen, elastin, and proteoglycans to organ level ECM function. Advantages, drawbacks, and possible pitfalls as well as interpretation of the data are given throughout. Finally, specific techniques to assess the functionality of the ECM of bioartificial lungs are separately discussed.

  18. Mechanical properties of liquid-filled shellac composite capsules.

    PubMed

    Leick, Sabine; Kott, Maureen; Degen, Patrick; Henning, Stefan; Päsler, Tobias; Suter, Dieter; Rehage, Heinz

    2011-02-21

    This paper describes the mechanical properties of thin-walled, liquid-filled composite capsules consisting of calcium pectinate and shellac. In a series of experiments we measured the deformation of these particles in a spinning drop apparatus. For different pH-values we studied the elastic properties of these particles and compared the obtained results with the mechanical response measured by squeezing capsule experiments. In analogy to these experiments, we also investigated liquid-filled unloaded calcium pectinate capsules without the addition of shellac. The deformation properties of these experiments and the surface Young moduli were in good agreement. Furthermore we investigated the liquid-filled calcium pectinate and the composite capsules by NMR microscopy. These experiments allowed investigations of the membrane thickness and the kinetics of membrane growing. Additional characterizations by stress controlled small amplitude surface shear experiments of similar composed gel layers provided coherent results for the surface Young modulus.

  19. Processing dependence of mechanical properties of metallic glass nanowires

    SciTech Connect

    Zhang, Qi; Li, Mo; Li, Qi-Kai

    2015-02-16

    Compared to their crystalline counterparts, nanowires made of metallic glass have not only superb properties but also remarkable processing ability. They can be processed easily and cheaply like plastics via a wide range of methods. To date, the underlying mechanisms of how these different processing routes affect the wires' properties as well as the atomic structure remains largely unknown. Here, by using atomistic modeling, we show that different processing methods can greatly influence the mechanical properties. The nanowires made via focused ion beam milling and embossing exhibit higher strength but localized plastic deformation, whereas that made by casting from liquid shows excellent ductility with homogeneous deformation but reduced strength. The different responses are reflected sensitively in the underlying atomic structure and packing density, some of which have been observed experimentally. The presence of the gradient of alloy concentration and surface effect will be discussed.

  20. Custom impression trays: Part I--Mechanical properties.

    PubMed

    Breeding, L C; Dixon, D L; Moseley, J P

    1994-01-01

    Dimensional stability of custom impression trays is an important factor in determining the degree of accuracy achieved in forming a master cast. Such trays must remain stable over time and must not exhibit permanent deformation when a completed impression is removed from the oral cavity. Measurement of the mechanical properties allows comparison between various tray materials and is useful in interpreting data on stresses incurred during removal of the completed impression. In Part I of this three-part series, the various mechanical properties of five tray resins: one autopolymerizing polymethyl methacrylate, one light-polymerizing, and three brands of thermoplastic resins were recorded and compared. The thermoplastic resins studied in this investigation exhibited lower measured values for the strength and elastic modulus properties than the light-polymerizing resin and the autopolymerizing polymethyl methacrylate resin studied.

  1. Custom impression trays: Part I--Mechanical properties.

    PubMed

    Breeding, L C; Dixon, D L; Moseley, J P

    1994-01-01

    Dimensional stability of custom impression trays is an important factor in determining the degree of accuracy achieved in forming a master cast. Such trays must remain stable over time and must not exhibit permanent deformation when a completed impression is removed from the oral cavity. Measurement of the mechanical properties allows comparison between various tray materials and is useful in interpreting data on stresses incurred during removal of the completed impression. In Part I of this three-part series, the various mechanical properties of five tray resins: one autopolymerizing polymethyl methacrylate, one light-polymerizing, and three brands of thermoplastic resins were recorded and compared. The thermoplastic resins studied in this investigation exhibited lower measured values for the strength and elastic modulus properties than the light-polymerizing resin and the autopolymerizing polymethyl methacrylate resin studied. PMID:8120842

  2. The influence of microstructure on the mechanical properties of solder

    SciTech Connect

    Morris, J.W. Jr.; Reynolds, H.L.

    1996-06-01

    Solder joints in microelectronics devices consist of low-melting solder compositions that wet and join metal contacts and are, ordinarily, used at high homologous temperatures in the as-solidified condition. Differences in solidification rate and substrate interactions have the consequence that even solder joints of similar compositions exhibit a wide range of microstructures. The variation in microstructure causes a variation in properties; in particular, the high-temperature creep properties that govern much of the mechanical behavior of the solder may differ significantly from joint to joint. The present paper reviews the varieties of microstructure that are found in common solder joints, and describes some of the ways in which microstructural changes affect mechanical properties and joint reliability.

  3. Determining the Mechanical Properties of Lattice Block Structures

    NASA Technical Reports Server (NTRS)

    Wilmoth, Nathan

    2013-01-01

    Lattice block structures and shape memory alloys possess several traits ideal for solving intriguing new engineering problems in industries such as aerospace, military, and transportation. Recent testing at the NASA Glenn Research Center has investigated the material properties of lattice block structures cast from a conventional aerospace titanium alloy as well as lattice block structures cast from nickel-titanium shape memory alloy. The lattice block structures for both materials were sectioned into smaller subelements for tension and compression testing. The results from the cast conventional titanium material showed that the expected mechanical properties were maintained. The shape memory alloy material was found to be extremely brittle from the casting process and only compression testing was completed. Future shape memory alloy lattice block structures will utilize an adjusted material composition that will provide a better quality casting. The testing effort resulted in baseline mechanical property data from the conventional titanium material for comparison to shape memory alloy materials once suitable castings are available.

  4. Mechanical and wear properties of PMMA/PVDF microfilled systems

    SciTech Connect

    Garcia, J.L.; Koelling, K.W.; Seghi, R.R.

    1996-12-31

    There is a clinical need in fixed prosthodontics for aesthetic materials that are biologically compatible. Polymethylmethacrylate (PMMA) has been used extensively in dental applications. Blends of PMMA and polyvinylidene fluoride (PVDF) are a new class of materials that might perform as aesthetic restorative materials. The fracture properties of PMMA have been intensively studied because it is an amorphous glass below 110{degrees}C, thus exhibiting brittle fracture under normal testing conditions below about 85{degrees}C. However, this brittle behavior leads to poor wear resistance. The properties of the matrix can be tailored by blending with PVDF. The blends are composed of homogeneous mixtures of the two polymers at the molecular level. Polyvinylidene fluoride molecules do not contribute to the mechanical yield behavior of the blend but do act as plasticizers. Improvements in the mechanical properties may be achieved by incorporating a filler into the polymer matrix.

  5. A review of mechanical and electromechanical properties of piezoelectric nanowires.

    PubMed

    Espinosa, Horacio D; Bernal, Rodrigo A; Minary-Jolandan, Majid

    2012-09-01

    Piezoelectric nanowires are promising building blocks in nanoelectronic, sensing, actuation and nanogenerator systems. In spite of great progress in synthesis methods, quantitative mechanical and electromechanical characterization of these nanostructures is still limited. In this article, the state-of-the art in experimental and computational studies of mechanical and electromechanical properties of piezoelectric nanowires is reviewed with an emphasis on size effects. The review covers existing characterization and analysis methods and summarizes data reported in the literature. It also provides an assessment of research needs and opportunities. Throughout the discussion, the importance of coupling experimental and computational studies is highlighted. This is crucial for obtaining unambiguous size effects of nanowire properties, which truly reflect the effect of scaling rather than a particular synthesis route. We show that such a combined approach is critical to establish synthesis-structure-property relations that will pave the way for optimal usage of piezoelectric nanowires. PMID:22581695

  6. Moisture effect on mechanical properties of polymeric composite materials

    NASA Astrophysics Data System (ADS)

    Airale, A. G.; Carello, M.; Ferraris, A.; Sisca, L.

    2016-05-01

    The influence of moisture on the mechanical properties of fibre-reinforced polymer matrix composites (PMCs) was investigated. Four materials had been take into account considering: both 2×2-Twill woven carbon fibre or glass fibre, thermosetting matrix (Epoxy Resin) or thermoplastic matrix (Polyphenylene Sulfide). The specimens were submitted for 1800 hours to a hygrothermic test to evaluate moisture absorption on the basis of the Fick's law and finally tested to verify the mechanical properties (ultimate tensile strength). The results showed that the absorbed moisture decreases those properties of composites which were dominated by the matrix or the interface, while was not detectable the influence of water on the considered fibre. An important result is that the diffusion coefficient is highest for glass/PPS and lowest for carbon/epoxy composite material. The results give useful suggestions for the design of vehicle components that are exposed to environmental conditions (rain, snow and humidity).

  7. Do Non-Collagenous Proteins Affect Skeletal Mechanical Properties?

    PubMed Central

    Morgan, Stacyann; Poundarik, Atharva A.; Vashishth, Deepak

    2015-01-01

    The remarkable mechanical behavior of bone is attributed to its complex nanocomposite structure that, in addition to mineral and collagen, comprises a variety of non-collagenous matrix proteins or NCPs. Traditionally, NCPs have been studied as signaling molecules in biological processes including bone formation, resorption and turnover. Limited attention has been given to their role in determining the mechanical properties of bone. Recent studies have highlighted that NCPs can indeed be lost or modified with aging, diseases and drug therapies. Homozygous and heterozygous mice models of key NCP provide a useful approach to determine the impact of NCPs on bone morphology as well as matrix quality, and to carry out detailed mechanical analysis for elucidating the pathway by which NCPs can affect the mechanical properties of bone. In this article, we present a systematic analysis of a large cohort of NCPs on bone’s structural and material hierarchy, and identify three principal pathways by which they determine bone’s mechanical properties. These pathways include alterations of bone morphological parameters crucial for bone’s structural competency, bone quality changes in key matrix parameters (mineral and collagen), and a direct role as load bearing structural proteins. PMID:26048282

  8. Multiscale Approach to Characterize Mechanical Properties of Tissue Engineered Skin.

    PubMed

    Tupin, S; Molimard, J; Cenizo, V; Hoc, T; Sohm, B; Zahouani, H

    2016-09-01

    Tissue engineered skin usually consist of a multi-layered visco-elastic material composed of a fibrillar matrix and cells. The complete mechanical characterization of these tissues has not yet been accomplished. The purpose of this study was to develop a multiscale approach to perform this characterization in order to link the development process of a cultured skin to the mechanical properties. As a proof-of-concept, tissue engineered skin samples were characterized at different stages of manufacturing (acellular matrix, reconstructed dermis and reconstructed skin) for two different aging models (using cells from an 18- and a 61-year-old man). To assess structural variations, bi-photonic confocal microscopy was used. To characterize mechanical properties at a macroscopic scale, a light-load micro-mechanical device that performs indentation and relaxation tests was designed. Finally, images of the internal network of the samples under stretching were acquired by combining confocal microscopy with a tensile device. Mechanical properties at microscopic scale were assessed. Results revealed that adding cells during manufacturing induced structural changes, which provided higher elastic modulus and viscosity. Moreover, senescence models exhibited lower elastic modulus and viscosity. This multiscale approach was efficient to characterize and compare skin equivalent samples and permitted the first experimental assessment of the Poisson's ratio for such tissues.

  9. Do Non-collagenous Proteins Affect Skeletal Mechanical Properties?

    PubMed

    Morgan, Stacyann; Poundarik, Atharva A; Vashishth, Deepak

    2015-09-01

    The remarkable mechanical behavior of bone is attributed to its complex nanocomposite structure that, in addition to mineral and collagen, comprises a variety of non-collagenous matrix proteins or NCPs. Traditionally, NCPs have been studied as signaling molecules in biological processes including bone formation, resorption, and turnover. Limited attention has been given to their role in determining the mechanical properties of bone. Recent studies have highlighted that NCPs can indeed be lost or modified with aging, diseases, and drug therapies. Homozygous and heterozygous mice models of key NCP provide a useful approach to determine the impact of NCPs on bone morphology as well as matrix quality, and to carry out detailed mechanical analysis for elucidating the pathway by which NCPs can affect the mechanical properties of bone. In this article, we present a systematic analysis of a large cohort of NCPs on bone's structural and material hierarchy, and identify three principal pathways by which they determine bone's mechanical properties. These pathways include alterations of bone morphological parameters crucial for bone's structural competency, bone quality changes in key matrix parameters (mineral and collagen), and a direct role as load-bearing structural proteins.

  10. Influence of sedimentary environments on mechanical properties of clastic rocks

    NASA Astrophysics Data System (ADS)

    Meng, Zhaoping; Zhang, Jincai; Peng, Suping

    2006-10-01

    The sedimentary environments are the intrinsic factor controlling the mechanical properties of clastic rocks. Examining the relationship between rock sedimentary environments and rock mechanical properties gives a better understanding of rock deformation and failure mechanisms. In this study, more than 55 samples in coal measures were taken from seven different lithologic formations in eastern China. Using the optical microscope the sedimentary characteristics, such as components of clastic rocks and sizes of clastic grains were quantitatively tested and analyzed. The corresponding mechanical parameters were tested using the servo-controlled testing system. Different lithologic attributes in the sedimentary rocks sampled different stress-strain behaviors and failure characteristics under different confining pressures, mainly due to different compositions and textures. Results demonstrate that clastic rocks have the linear best-fit for Mohr-Coulomb failure criterion. The elastic moduli in clastic rocks are highly dependent upon confining pressures, unlike hard rocks. The envelope lines of the mechanical properties versus the contents of quartz, detritus of the grain diameter of more than 0.03 mm, and grain size in clastic rocks are given. The compressive strength or elastic modulus and the grain diameter have a non-monotonic relation and demonstrate the “grain-diameter softening” effect.

  11. Mechanical Properties of Non-Accreting Neutron Star Crusts

    NASA Astrophysics Data System (ADS)

    Hoffman, Kelsey L.; Heyl, J. S.

    2013-01-01

    The mechanical properties of a neutron star crust, such as breaking strain and shear modulus, have implications for the detection of gravitational waves from a neutron star as well as bursts from Soft Gamma-ray Repeaters (SGRs). These properties are calculated here for three different crustal compositions for a non-accreting neutron star that results from three different cooling histories, as well as for a pure iron crust. A simple shear is simulated using molecular dynamics to the crustal compositions by deforming the simulation box. The breaking strain and shear modulus are found to be similar in the four cases, with a breaking strain of ˜0.1 and a shear modulus of ˜1030 dyne cm-2 at a density of ρ = 1014g cm-3 for simulations with an initially perfect BCC lattice. With these crustal properties and the observed properties of PSR J2124-3358 the predicted strain amplitude of gravitational waves for a maximally deformed crust is found to be greater than the observational upper limits from LIGO. This suggests that the neutron star crust in this case may not be maximally deformed or it may not have a perfect BCC lattice structure. The implications of the calculated crustal properties of bursts from SGRs are also explored. The mechanical properties found for a perfect BCC lattice structure find that crustal events alone can not be ruled out for triggering the energy in SGR bursts.

  12. Mechanical properties of non-accreting neutron star crusts

    NASA Astrophysics Data System (ADS)

    Hoffman, Kelsey; Heyl, Jeremy

    2012-11-01

    The mechanical properties of a neutron star crust, such as breaking strain and shear modulus, have implications for the detection of gravitational waves from a neutron star as well as bursts from soft Gamma-ray repeaters (SGRs). These properties are calculated here for three different crustal compositions for a non-accreting neutron star that results from three different cooling histories, as well as for a pure iron crust. A simple shear is simulated using molecular dynamics to the crustal compositions by deforming the simulation box. The breaking strain and shear modulus are found to be similar in the four cases, with a breaking strain of ˜0.1 and a shear modulus of ˜1030 dyne cm-2 at a density of ρ = 1014 g cm-3 for simulations with an initially perfect body-centred cubic (BCC) lattice. With these crustal properties and the observed properties of PSR J2124-3358, the predicted strain amplitude of gravitational waves for a maximally deformed crust is found to be greater than the observational upper limits from LIGO. This suggests that the neutron star crust in this case may not be maximally deformed or it may not have a perfect BCC lattice structure. The implications of the calculated crustal properties of bursts from SGRs are also explored. The mechanical properties found for a perfect BCC lattice structure find that crustal events alone cannot be ruled out for triggering the energy in SGR bursts.

  13. Ultrasonic evaluation of the physical and mechanical properties of granites.

    PubMed

    Vasconcelos, G; Lourenço, P B; Alves, C A S; Pamplona, J

    2008-09-01

    Masonry is the oldest building material that survived until today, being used all over the world and being present in the most impressive historical structures as an evidence of spirit of enterprise of ancient cultures. Conservation, rehabilitation and strengthening of the built heritage and protection of human lives are clear demands of modern societies. In this process, the use of nondestructive methods has become much common in the diagnosis of structural integrity of masonry elements. With respect to the evaluation of the stone condition, the ultrasonic pulse velocity is a simple and economical tool. Thus, the central issue of the present paper concerns the evaluation of the suitability of the ultrasonic pulse velocity method for describing the mechanical and physical properties of granites (range size between 0.1-4.0 mm and 0.3-16.5 mm) and for the assessment of its weathering state. The mechanical properties encompass the compressive and tensile strength and modulus of elasticity, and the physical properties include the density and porosity. For this purpose, measurements of the longitudinal ultrasonic pulse velocity with distinct natural frequency of the transducers were carried out on specimens with different size and shape. A discussion of the factors that induce variations on the ultrasonic velocity is also provided. Additionally, statistical correlations between ultrasonic pulse velocity and mechanical and physical properties of granites are presented and discussed. The major output of the work is the confirmation that ultrasonic pulse velocity can be effectively used as a simple and economical nondestructive method for a preliminary prediction of mechanical and physical properties, as well as a tool for the assessment of the weathering changes of granites that occur during the serviceable life. This is of much interest due to the usual difficulties in removing specimens for mechanical characterization. PMID:18471849

  14. Ultrasonic evaluation of the physical and mechanical properties of granites.

    PubMed

    Vasconcelos, G; Lourenço, P B; Alves, C A S; Pamplona, J

    2008-09-01

    Masonry is the oldest building material that survived until today, being used all over the world and being present in the most impressive historical structures as an evidence of spirit of enterprise of ancient cultures. Conservation, rehabilitation and strengthening of the built heritage and protection of human lives are clear demands of modern societies. In this process, the use of nondestructive methods has become much common in the diagnosis of structural integrity of masonry elements. With respect to the evaluation of the stone condition, the ultrasonic pulse velocity is a simple and economical tool. Thus, the central issue of the present paper concerns the evaluation of the suitability of the ultrasonic pulse velocity method for describing the mechanical and physical properties of granites (range size between 0.1-4.0 mm and 0.3-16.5 mm) and for the assessment of its weathering state. The mechanical properties encompass the compressive and tensile strength and modulus of elasticity, and the physical properties include the density and porosity. For this purpose, measurements of the longitudinal ultrasonic pulse velocity with distinct natural frequency of the transducers were carried out on specimens with different size and shape. A discussion of the factors that induce variations on the ultrasonic velocity is also provided. Additionally, statistical correlations between ultrasonic pulse velocity and mechanical and physical properties of granites are presented and discussed. The major output of the work is the confirmation that ultrasonic pulse velocity can be effectively used as a simple and economical nondestructive method for a preliminary prediction of mechanical and physical properties, as well as a tool for the assessment of the weathering changes of granites that occur during the serviceable life. This is of much interest due to the usual difficulties in removing specimens for mechanical characterization.

  15. Chirality-Mediated Mechanical and Structural Properties of Oligopeptide Hydrogels

    SciTech Connect

    Taraban, Marc B.; Feng, Yue; Hammouda, Boualem; Hyland, Laura L.; Yu, Y. Bruce

    2012-10-29

    The origin and the effects of homochirality in the biological world continuously stimulate numerous hypotheses and much debate. This work attempts to look at the biohomochirality issue from a different angle - the mechanical properties of the bulk biomaterial and their relation to nanoscale structures. Using a pair of oppositely charged peptides that co-assemble into hydrogels, we systematically investigated the effect of chirality on the mechanical properties of these hydrogels through different combinations of syndiotactic and isotactic peptides. It was found that homochirality confers mechanical advantage, resulting in a higher elastic modulus and strain yield value. Yet, heterochirality confers kinetic advantage, resulting in faster gelation. Structurally, both homochiral and heterochiral hydrogels are made of fibers interconnected by lappet-like webs, but the homochiral peptide fibers are thicker and denser. These results highlight the possible role of biohomochirality in the evolution and/or natural selection of biomaterials.

  16. Quantitative Characterization of Mechanical Property of Annealed Monolayer Colloidal Crystal.

    PubMed

    Zhang, Lijing; Wang, Weiqi; Zheng, Lu; Wang, Xiuyu; Yan, Qingfeng

    2016-01-19

    Quantitative characterization of the mechanical properties of a polystyrene (PS) monolayer colloidal crystal (MCC) annealed with solvent vapor has been performed for the first time by means of atomic force microscopy nanoindentation. The results showed that both the compressive and bending elastic modulus of PS MCC increased with the prolongation of annealing time from initial to 13 min. When the annealing time reached 15 min or even more, the PS MCC almost deformed to a planar film, and the elastic modulus of the PS MCC presented a drastic increase. These results provide a basis for tailoring the mechanical properties of a polymer colloidal monolayer via solvent vapor annealing. Such self-supported and high-mechanical-strength colloidal monolayers can be transferred to other surfaces for potential and promising applications in the bottom-up fabrication of highly ordered nanostructured materials such as nano dot arrays, photonic crystals, and many others.

  17. An Introduction to the Mechanical Properties of Ceramics

    NASA Astrophysics Data System (ADS)

    Green, David J.

    1998-09-01

    Over the past twenty-five years ceramics have become key materials in the development of many new technologies as scientists have been able to design these materials with new structures and properties. An understanding of the factors that influence their mechanical behavior and reliability is essential. This book will introduce the reader to current concepts in the field. It contains problems and exercises to help readers develop their skills. This is a comprehensive introduction to the mechanical properties of ceramics, and is designed primarily as a textbook for advanced undergraduates in materials science and engineering. It will also be of value as a supplementary text for more general courses and to industrial scientists and engineers involved in the development of ceramic-based products, materials selection and mechanical design.

  18. The influence of grain size on the mechanical properties ofsteel

    SciTech Connect

    Morris Jr., J.W.

    2001-05-01

    Many of the important mechanical properties of steel, including yield strength and hardness, the ductile-brittle transition temperature and susceptibility to environmental embrittlement can be improved by refining the grain size. The improvement can often be quantified in a constitutive relation that is an appropriate variant on the familiar Hall-Petch relation: the quantitative improvement in properties varies with d{sup -1/2}, where d is the grain size. Nonetheless, there is considerable uncertainty regarding the detailed mechanism of the grain size effect, and appropriate definition of ''grain size''. Each particular mechanism of strengthening and fracture suggests its own appropriate definition of the ''effective grain size'', and how it may be best controlled.

  19. Mechanical Properties of Materials with Nanometer Scale Microstructures

    SciTech Connect

    William D. Nix

    2004-10-31

    We have been engaged in research on the mechanical properties of materials with nanometer-scale microstructural dimensions. Our attention has been focused on studying the mechanical properties of thin films and interfaces and very small volumes of material. Because the dimensions of thin film samples are small (typically 1 mm in thickness, or less), specialized mechanical testing techniques based on nanoindentation, microbeam bending and dynamic vibration of micromachined structures have been developed and used. Here we report briefly on some of the results we have obtained over the past three years. We also give a summary of all of the dissertations, talks and publications completed on this grant during the past 15 years.

  20. Quantitative Characterization of Mechanical Property of Annealed Monolayer Colloidal Crystal.

    PubMed

    Zhang, Lijing; Wang, Weiqi; Zheng, Lu; Wang, Xiuyu; Yan, Qingfeng

    2016-01-19

    Quantitative characterization of the mechanical properties of a polystyrene (PS) monolayer colloidal crystal (MCC) annealed with solvent vapor has been performed for the first time by means of atomic force microscopy nanoindentation. The results showed that both the compressive and bending elastic modulus of PS MCC increased with the prolongation of annealing time from initial to 13 min. When the annealing time reached 15 min or even more, the PS MCC almost deformed to a planar film, and the elastic modulus of the PS MCC presented a drastic increase. These results provide a basis for tailoring the mechanical properties of a polymer colloidal monolayer via solvent vapor annealing. Such self-supported and high-mechanical-strength colloidal monolayers can be transferred to other surfaces for potential and promising applications in the bottom-up fabrication of highly ordered nanostructured materials such as nano dot arrays, photonic crystals, and many others. PMID:26700374

  1. Effect of the basic residue on the energetics, dynamics, and mechanisms of gas-phase fragmentation of protonated peptides.

    PubMed

    Laskin, Julia; Yang, Zhibo; Song, Tao; Lam, Corey; Chu, Ivan K

    2010-11-17

    The effect of the basic residue on the energetics, dynamics, and mechanisms of backbone fragmentation of protonated peptides was investigated. Time-resolved and collision energy-resolved surface-induced dissociation (SID) of singly protonated peptides with the N-terminal arginine residue and their analogues, in which arginine is replaced with less basic lysine and histidine residues, was examined using a specially configured Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS). SID experiments demonstrated different kinetics of formation of several primary product ions of peptides with and without arginine residue. The energetics and dynamics of these pathways were determined from Rice-Ramsperger-Kassel-Marcus (RRKM) modeling of the experimental data. Comparison between the kinetics and energetics of fragmentation of arginine-containing peptides and the corresponding methyl ester derivatives provides important information on the effect of dissociation pathways involving salt bridge (SB) intermediates on the observed fragmentation behavior. Because pathways involving SB intermediates are characterized by low threshold energies, they efficiently compete with classical oxazolone and imine/enol pathways of arginine-containing peptides on a long time scale of the FTICR instrument. In contrast, fragmentation of histidine- and lysine-containing peptides is largely determined by canonical pathways. Because SB pathways are characterized by negative activation entropies, fragmentation of arginine-containing peptides is kinetically hindered and observed at higher collision energies as compared to their lysine- and histidine-containing analogues.

  2. Structures and Mechanical Properties of Natural and Synthetic Diamonds

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1998-01-01

    A revolution in the diamond technology is in progress, as the low-pressure process becomes an industrial reality. It will soon be possible to take advantage of the demanding properties of diamond to develop a myriad of new applications, particularly for self-lubricating, wear-resistant, and superhard coatings. The production of large diamond films or sheets at low cost, a distinct possibility in the not-too-distant future, may drastically change tribology technology, particularly regarding solid lubricants and lubricating materials and systems. This paper reviews the structures and properties of natural and synthetic diamonds to gain a better understanding of the tribological properties of diamond and related materials. Atomic and crystal structure, impurities, mechanical properties, and indentation hardness of diamond are described.

  3. Crotamine, a small basic polypeptide myotoxin from rattlesnake venom with cell-penetrating properties.

    PubMed

    Rádis-Baptista, Gandhi; Kerkis, Irina

    2011-12-01

    Crotamine, a low molecular weight cationic polypeptide from the venom of the South American rattlesnake Crotalus durissus terrificus is a natural cell-penetrating peptide with functional versatility. The presence of nine lysine residues and three disulfide bonds renders crotamine highly compact, stable and positively charged. Topologically, crotamine adopts an ancient β-defensin fold that is found in diverse families of endogenous and venom polypeptides dedicated to host defense. Crotamine is unique among several classes of bioactive peptides because it possesses both cell penetrating and antimicrobial activities and selective biological action toward some cell types at a given cell cycle phase. Because it can rapidly and efficiently translocate into actively proliferating cells, crotamine is being investigated for labeling highly replicating cells and for use as a chemotherapeutic adjuvant. Peptides derived from crotamine, nucleolar targeting peptides (NrTPs), have been designed and are being studied. NrTPs retain some crotamine properties, such as efficient cellular uptake and preferential nuclear localization whereas they improve upon other properties. For example, NrTPs are smaller than crotamine, show higher preferential nucleolar localization, and better facilitate ZIP-code localization of therapeutic proteins. PMID:22204433

  4. Mechanical properties of several iron-nickel meteorites

    SciTech Connect

    Mulford, Roberta N; El - Dasher, Bassem

    2011-01-06

    Iron-nickel meteorites exhibit a unique lamellar microstructure, consisting of small regions with steep-iron-nickel composition gradients. The microstructure arises as a result of slow cooling in a planetary core or other large mass. The microstructure is further influenced by variable concentrations of other elements such as phosphorous which may have influenced cooling and phase separation. Mechanical properties of these composite structures have been investigated using Vickers and spherical indentation, x-ray fluorescence, and EBSD. Direct observation of mechanical properties in these highly structured materials provides a valuable supplement to bulk measurements, which frequently exhibit large variation in dynamic properties, even within a single sample. Previous studies of the mechanical properties of a typical iron-nickel meteorite, a Diablo Canyon specimen, indicated that the strength of the composite was higher by almost an order of magnitude than values obtained from laboratory-prepared specimens. This was ascribed to the extreme work-hardening evident in the EBSD measurements. Additional specimens from the Canyon Diablo fall (type IAB, coarse octahedrite) and several fine octahedrite meteorites, from the Muonionalusta meteorite (IVA) and Gibeon fall (IVA), have been examined to establish a range of error on the previously measured yield, to determine the extent to which deformation upon reentry contributes to yield, and to establish the degree to which the strength varies as a function of microstructure.

  5. Mechanical Properties of Nanostructured Materials Determined Through Molecular Modeling Techniques

    NASA Technical Reports Server (NTRS)

    Clancy, Thomas C.; Gates, Thomas S.

    2005-01-01

    The potential for gains in material properties over conventional materials has motivated an effort to develop novel nanostructured materials for aerospace applications. These novel materials typically consist of a polymer matrix reinforced with particles on the nanometer length scale. In this study, molecular modeling is used to construct fully atomistic models of a carbon nanotube embedded in an epoxy polymer matrix. Functionalization of the nanotube which consists of the introduction of direct chemical bonding between the polymer matrix and the nanotube, hence providing a load transfer mechanism, is systematically varied. The relative effectiveness of functionalization in a nanostructured material may depend on a variety of factors related to the details of the chemical bonding and the polymer structure at the nanotube-polymer interface. The objective of this modeling is to determine what influence the details of functionalization of the carbon nanotube with the polymer matrix has on the resulting mechanical properties. By considering a range of degree of functionalization, the structure-property relationships of these materials is examined and mechanical properties of these models are calculated using standard techniques.

  6. Mechanical properties of DyBaCuO superconducting bulks

    NASA Astrophysics Data System (ADS)

    Fujimoto, H.; Shimada, H.; Yoshizawa, S.

    2007-10-01

    Melt-processed REBaCuO (RE: rare earth) superconductors have a high Jc at 77 K and a high magnetic field, which are expected to be used for high field applications such as superconducting permanent magnets with liquid nitrogen refrigeration, flywheels, current leads and so on. Mechanical properties such as flexural strength, fracture toughness and ductility are very crucial as well as the superconducting properties: Tc, Jc, and Hirr for industrial applications of high-Tc oxide superconductors. However, oxide superconductors have the intrinsic brittleness of the perovskite structure, thus, the strength and the fracture toughness of REBaCuO superconductors have been reported to be low and anisotropic. Therefore, we should investigate and improve mechanical properties to achieve structural reliability for applications. Large single domain of melt-processed REBaCuO (Dy-123) superconductors with Dy2BaCuO5 (Dy-211) particles and Ag2O of 10 wt% was fabricated with a seeding and temperature gradient method in air. In this study, we discuss mechanical properties such as the hardness and the surface roughness, and the flexural strength of the RE-123 bulk, measured at RT. The results of Vickers hardness, surface roughness and the flexural strength showed very important information for evaluating characteristics of RE-123 bulks.

  7. Mechanical properties of Municipal Solid Waste by SDMT

    SciTech Connect

    Castelli, Francesco; Maugeri, Michele

    2014-02-15

    Highlights: • The adoption of the SDMT for the measurements of MSW properties is proposed. • A comparison between SDMT results and laboratory tests was carried out. • A good reliability has been found in deriving waste properties by SDMT. • Results seems to be promising for the friction angle and Young’s modulus evaluation. - Abstract: In the paper the results of a geotechnical investigation carried on Municipal Solid Waste (MSW) materials retrieved from the “Cozzo Vuturo” landfill in the Enna area (Sicily, Italy) are reported and analyzed. Mechanical properties were determined both by in situ and laboratory large-scale one dimensional compression tests. While among in situ tests, Dilatomer Marchetti Tests (DMT) is used widely in measuring soil properties, the adoption of the DMT for the measurements of MSW properties has not often been documented in literature. To validate its applicability for the estimation of MSW properties, a comparison between the seismic dilatometer (SDMT) results and the waste properties evaluated by laboratory tests was carried out. Parameters for “fresh” and “degraded waste” have been evaluated. These preliminary results seems to be promising as concerns the assessment of the friction angle of waste and the evaluation of the S-wave in terms of shear wave velocity. Further studies are certainly required to obtain more representative values of the elastic parameters according to the SDMT measurements.

  8. [Mechanical properties and biological evaluation of buffalo horn material].

    PubMed

    Zhang, Quanbin; Zhou, Qunfei; Shan, Guanghua; Cao, Ping; Huang, Yaoxiong; Ao, Ningjian

    2014-12-01

    Mechanical properties and biological evaluation of buffalo horn material were examined in this study. The effects of sampling position of buffalo horn on mechanical properties were investigated with uniaxial tension and micron indentation tests. Meanwhile, the variation of element contents in different parts of buffalo horn was determined with elemental analysis, and the microstructure of the horn was measured with scanning electron microscopy. In addition, biological evaluation of buffalo horn was studied with hemolytic test, erythrocyte morphology, platelet and erythrocyte count, and implantation into mouse. Results showed that the buffalo horn had good mechanical properties and mechanical characteristic values of it gradually increased along with the growth direction of the horn, which may be closely related to its microstructure and element content of C, N, and S in different parts of the buffalo horn. On the other hand, because the buffalo horn does not have toxicity, it therefore does not cause hemolysis of erythrocyte and has a good affinity with it. Buffalo horn has good histocompatibility but meanwhile it may induce the platelet adhesion and aggregation. Even so, it does not continue to rise to induce a large number of platelet to aggregate with resulting blood clotting. Therefore, the buffalo horn material has been proved to possess good blood compatibility according to the preliminary evaluation. PMID:25868248

  9. Mechanical properties of fibroblasts depend on level of cancer transformation.

    PubMed

    Efremov, Yu M; Lomakina, M E; Bagrov, D V; Makhnovskiy, P I; Alexandrova, A Y; Kirpichnikov, M P; Shaitan, K V

    2014-05-01

    Recently, it was revealed that tumor cells are significantly softer than normal cells. Although this phenomenon is well known, it is connected with many questions which are still unanswered. Among these questions are the molecular mechanisms which cause the change in stiffness and the correlation between cell mechanical properties and their metastatic potential. We studied mechanical properties of cells with different levels of cancer transformation. Transformed cells in three systems with different transformation types (monooncogenic N-RAS, viral and cells of tumor origin) were characterized according to their morphology, actin cytoskeleton and focal adhesion organization. Transformation led to reduction of cell spreading and thus decreasing the cell area, disorganization of actin cytoskeleton, lack of actin stress fibers and decline in the number and size of focal adhesions. These alterations manifested in a varying degree depending on type of transformation. Force spectroscopy by atomic force microscopy with spherical probes was carried out to measure the Young's modulus of cells. In all cases the Young's moduli were fitted well by log-normal distribution. All the transformed cell lines were found to be 40-80% softer than the corresponding normal ones. For the cell system with a low level of transformation the difference in stiffness was less pronounced than for the two other systems. This suggests that cell mechanical properties change upon transformation, and acquisition of invasive capabilities is accompanied by significant softening.

  10. Mechanical Properties of Nanoworm Assembled by DNA and Nanoparticle Conjugates.

    PubMed

    Zhou, Yihua; Sohrabi, Salman; Tan, Jifu; Liu, Yaling

    2016-06-01

    Recently, DNA-nanoparticle conjugates have been widely used as building blocks for assembling complex nanostructures, due to their programmable recognitions, high cellular uptake and enhanced binding capabilities. In this study, a nanoworm structure, which can be applied in fields of drug targeting, image probing and thermal therapies, has been assembled by DNA-nanoparticle conjugates. Subsequently, its mechanical properties have been investigated due to their importance on the structural stability, transport and circulations of the nanoworm. Stiffness and strengths of the nanoworm under different deformation types are studied by coarse-grained molecular dynamics simulations. Effects of temperature, DNA coating density and particle size on mechanical properties of nanoworms are also thoroughly investigated. Results show that both resistance and strength of the nanoworm are the weakest along the axial direction, indicating it is more prone to be ruptured by a stretching force. i addition, DNA strands are found to be more important than nanoparticles in determining mechanical properties of the nanoworm. Moreover, both strength and resistance in regardless of directions are proved to be enhanced by decreasing the temperature, raising the DNA coating density and enlarging the particle size. This study is capable of serving as guidance for designing nanoworms with optimal mechanical strengths for applications.

  11. Mechanical Properties of Nanoworm Assembled by DNA and Nanoparticle Conjugates.

    PubMed

    Zhou, Yihua; Sohrabi, Salman; Tan, Jifu; Liu, Yaling

    2016-06-01

    Recently, DNA-nanoparticle conjugates have been widely used as building blocks for assembling complex nanostructures, due to their programmable recognitions, high cellular uptake and enhanced binding capabilities. In this study, a nanoworm structure, which can be applied in fields of drug targeting, image probing and thermal therapies, has been assembled by DNA-nanoparticle conjugates. Subsequently, its mechanical properties have been investigated due to their importance on the structural stability, transport and circulations of the nanoworm. Stiffness and strengths of the nanoworm under different deformation types are studied by coarse-grained molecular dynamics simulations. Effects of temperature, DNA coating density and particle size on mechanical properties of nanoworms are also thoroughly investigated. Results show that both resistance and strength of the nanoworm are the weakest along the axial direction, indicating it is more prone to be ruptured by a stretching force. i addition, DNA strands are found to be more important than nanoparticles in determining mechanical properties of the nanoworm. Moreover, both strength and resistance in regardless of directions are proved to be enhanced by decreasing the temperature, raising the DNA coating density and enlarging the particle size. This study is capable of serving as guidance for designing nanoworms with optimal mechanical strengths for applications. PMID:27427583

  12. Mechanical Properties of Murine and Porcine Ocular Tissues in Compression

    PubMed Central

    Worthington, Kristan S.; Wiley, Luke A.; Bartlett, Alexandra M.; Stone, Edwin M.; Mullins, Robert F.; Salem, Aliasger K.; Guymon, C. Allan; Tucker, Budd A.

    2014-01-01

    Sub-retinal implantation of foreign materials is becoming an increasingly common feature of novel therapies for retinal dysfunction. The ultimate compatibility of implants depends not only on their in vitro chemical compatibility, but also on how well the mechanical properties of the material match those of the native tissue. In order to optimize the mechanical properties of retinal implants, the mechanical properties of the mammalian retina itself must be carefully characterized. In this study, the compressive moduli of eye tissues, especially the retina, were probed using a dynamic mechanical analysis instrument in static mode. The retinal compressive modulus was lower than that of the sclera or cornea, but higher than that of the RPE and choroid. Compressive modulus remained relatively stable with age. Conversely, apparent retinal softening occurred at an early age in mice with inherited retinal degeneration. Compressive modulus is an important consideration for the design of retinal implants. Polymer scaffolds with moduli that are substantially different than that of the native tissue in which they will ultimately reside will be less likely to aid in the differentiation and development of the appropriate cell types in vitro and will have reduced biocompatibility in vivo. PMID:24613781

  13. Loops determine the mechanical properties of mitotic chromosomes

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Heermann, Dieter W.

    2013-03-01

    In mitosis, chromosomes undergo a condensation into highly compacted, rod-like objects. Many models have been put forward for the higher-order organization of mitotic chromosomes including radial loop and hierarchical folding models. Additionally, mechanical properties of mitotic chromosomes under different conditions were measured. However, the internal organization of mitotic chromosomes still remains unclear. Here we present a polymer model for mitotic chromosomes and show how chromatin loops play a major role for their mechanical properties. The key assumption of the model is the ability of the chromatin fibre to dynamically form loops with the help of binding proteins. Our results show that looping leads to a tight compaction and significantly increases the bending rigidity of chromosomes. Moreover, our qualitative prediction of the force elongation behaviour is close to experimental findings. This indicates that the internal structure of mitotic chromosomes is based on self-organization of the chromatin fibre. We also demonstrate how number and size of loops have a strong influence on the mechanical properties. We suggest that changes in the mechanical characteristics of chromosomes can be explained by an altered internal loop structure. YZ gratefully appreciates funding by the German National Academic Foundation (Studienstiftung des deutschen Volkes) and support by the Heidelberg Graduate School for Mathematical and Computational Methods in the Sciences (HGS MathComp).

  14. Mechanical properties of murine and porcine ocular tissues in compression.

    PubMed

    Worthington, Kristan S; Wiley, Luke A; Bartlett, Alexandra M; Stone, Edwin M; Mullins, Robert F; Salem, Aliasger K; Guymon, C Allan; Tucker, Budd A

    2014-04-01

    Sub-retinal implantation of foreign materials is becoming an increasingly common feature of novel therapies for retinal dysfunction. The ultimate compatibility of implants depends not only on their in vitro chemical compatibility, but also on how well the mechanical properties of the material match those of the native tissue. In order to optimize the mechanical properties of retinal implants, the mechanical properties of the mammalian retina itself must be carefully characterized. In this study, the compressive moduli of eye tissues, especially the retina, were probed using a dynamic mechanical analysis instrument in static mode. The retinal compressive modulus was lower than that of the sclera or cornea, but higher than that of the RPE and choroid. Compressive modulus remained relatively stable with age. Conversely, apparent retinal softening occurred at an early age in mice with inherited retinal degeneration. Compressive modulus is an important consideration for the design of retinal implants. Polymer scaffolds with moduli that are substantially different than that of the native tissue in which they will ultimately reside will be less likely to aid in the differentiation and development of the appropriate cell types in vitro and will have reduced biocompatibility in vivo. PMID:24613781

  15. Classification and basic properties of contrast agents for magnetic resonance imaging.

    PubMed

    Geraldes, Carlos F G C; Laurent, Sophie

    2009-01-01

    A comprehensive classification of contrast agents currently used or under development for magnetic resonance imaging (MRI) is presented. Agents based on small chelates, macromolecular systems, iron oxides and other nanosystems, as well as responsive, chemical exchange saturation transfer (CEST) and hyperpolarization agents are covered in order to discuss the various possibilities of using MRI as a molecular imaging technique. The classification includes composition, magnetic properties, biodistribution and imaging applications. Chemical compositions of various classes of MRI contrast agents are tabulated, and their magnetic status including diamagnetic, paramagnetic and superparamagnetic are outlined. Classification according to biodistribution covers all types of MRI contrast agents including, among others, extracellular, blood pool, polymeric, particulate, responsive, oral, and organ specific (hepatobiliary, RES, lymph nodes, bone marrow and brain). Various targeting strategies of molecular, macromolecular and particulate carriers are also illustrated.

  16. Agar-Like Polysaccharide Produced by a Pseudomonas Species: Production and Basic Properties

    PubMed Central

    Kang, Kenneth S.; Veeder, George T.; Mirrasoul, Peter J.; Kaneko, Tatsuo; Cottrell, Ian W.

    1982-01-01

    A new species of Pseudomonas was isolated that produced copious amounts of an exocellular heteropolysaccharide (PS-60) after incubation for 3 days at 30°C in media containing 3% glucose as a carbon source. The polysaccharide was composed of approximately 46% glucose and 30% rhamnose and, in addition, contained 21% uronic acid and 3% O-acetyl. Upon deacetylation by a mild alkaline treatment, PS-60 produced a brittle, firm, and optically clear gel. This gelling property was thermoreversible. The PS-60 gel exhibited excellent heat stability that withstood autoclaving (i.e., 121°C for 15 min) for several cycles. The gel strength, melting point, and setting point of the polysaccharide were controlled primarily by the concentration of cations. PS-60 was not affected by a variety of enzymes. The results of tests involving various culture media and biochemical test media indicate that PS-60 is an excellent alternative gelling agent to agar. PMID:16346007

  17. Modulated IR radiometry for determining thermal properties and basic characteristics of titanium thin films

    SciTech Connect

    Apreutesei, Mihai; Lopes, Claudia; Vaz, Filipe; Macedo, Francisco; Borges, Joel

    2014-07-01

    Titanium thin films of different thicknesses were prepared by direct current magnetron sputtering to study modulated infrared (IR) radiometry as a tool for analyzing film thickness. Thickness was varied by regularly increasing the deposition time, keeping all the other deposition parameters constant. The influence of film thickness on morphological, structural, and electrical properties of the titanium coatings also was investigated. The experimental results revealed a systematic grain growth with increasing film thickness, along with enhanced film crystallinity, which led to increased electrical conductivity. Using the results obtained by modulated IR radiometry, the thickness of each thin film was calculated. These thickness values were then compared with the coating thickness measurements obtained by scanning electron microscopy. The values confirmed the reliability of modulated IR radiometry as an analysis tool for thin films and coatings, and for determining thicknesses in the micrometer range, in particular.

  18. Characterization of the mechanical properties of freestanding platinum thin films

    NASA Astrophysics Data System (ADS)

    Abbas, Khawar

    Many MEMS devices utilize nanocrystalline thin metallic films as mechanical structures, in particular, micro switching devices where these films are used as Ohmic contacts. But the elastic and plastic properties of these thin films (thickness < 1mum) are significantly different from those of the bulk material. At these scales the volume fraction of material defects such as: grain boundaries, dislocations and interstitials become quite significant and become a chief contributor to the physical and mechanical material properties. In order to effectively design MEMS devices it is important that these material properties are explored and mechanical behavior of the structure they form be characterized. Popular thin film materials used in MEMS devices are Aluminum (Al), Copper (Cu), Nickel (Ni) and Gold (Au). Platinum has traditionally gained acceptance into the MEMS industry because of its chemical inertness and high temperature stability. However the mechanical properties of platinum remains the least exploited. Platinum has a high Young's Modulus (164 GPa, for bulk) and high melting temperature (1768 °C) and therefore can be used as a 'thin film' structure (cantilever, a bridge or a membrane) in high temperature environments with high resistance to mechanical failure. The physical size of these thin film structure make it very difficult to handle them and employ traditional mechanical testing methodologies and techniques and therefore require custom test platforms. One such recently developed platform is presented in this dissertation. The test platform is comprised of a microfabricated cascaded thermal actuator system and test specimen. The cascaded thermal actuator system is capable of providing tens of microns of displacement and tens of milli-Newton forces simultaneously while applying a relatively low temperature gradient across the test specimen. The dimensions of the platform make its use possible in both the SEM/TEM environments and on a probe station under

  19. Woven glass fabric reinforced laminates based on polyolefin wastes: Thermal, mechanical and dynamic-mechanical properties

    NASA Astrophysics Data System (ADS)

    Russo, Pietro; Acierno, Domenico; Simeoli, Giorgio; Lopresto, Valentina

    2014-05-01

    Potentialities of polyolefin wastes in place of virgin polypropylene to produce composite laminates have been investigated. Plaques reinforced with a woven glass fabric were prepared by film-stacking technique and systematically analyzed in terms of thermal, mechanical and dynamic-mechanical properties. In case of PP matrices, the use of a typical compatibilizer to improve the adhesion at the interface has been considered. Thermal properties emphasized the chemical nature of plastic wastes. About mechanical properties, static tests showed an increase of flexural parameters for compatibilized systems due to the coupling effect between grafted maleic anhydride and silane groups on the surface of the glass fabric. These effects, maximized for composites based on car bumper wastes, is perfectly reflected in terms of storage modulus and damping ability of products as determined by single-cantilever bending dynamic tests.

  20. Mechanical properties and material characterization of polysialate structural composites

    NASA Astrophysics Data System (ADS)

    Foden, Andrew James

    One of the major concerns in using Fiber Reinforced Composites in applications that are subjected to fire is their resistance to high temperature. Some of the fabrics used in FRC, such as carbon, are fire resistant. However, almost all the resins used cannot withstand temperatures higher than 200°C. This dissertation deals with the development and use of a potassium aluminosilicate (GEOPOLYMER) resin that is inorganic and can sustain more than 1000°C. The results presented include the mechanical properties of the unreinforced polysialate matrix in tension, flexure, and compression as well as the strain capacities and surface energy. The mechanical properties of the matrix reinforced with several different fabrics were obtained in flexure, tension, compression and shear. The strength and stiffness of the composite was evaluated for each loading condition. Tests were conducted on unexposed samples as well as samples exposed to temperatures from 200 to 1000°C. Fatigue properties were determined using flexural loading. A study of the effect of several processing variables on the properties of the composite was undertaken to determine the optimum procedure for manufacturing composite plates. The processing variables studied were the curing temperature and pressure, and the post cure drying time required to remove any residual water. The optimum manufacturing conditions were determined using the void content, density, fiber volume fraction, and flexural strength. Analytical models are presented based on both micro and macro mechanical analysis of the composite. Classic laminate theory is used to evaluate the state of the composite as it is being loaded to determine the failure mechanisms. Several failure criteria theories are considered. The analysis is then used to explain the mechanical behavior of the composite that was observed during the experimental study.

  1. Mechanical and tribological properties of ion beam-processed surfaces

    SciTech Connect

    Kodali, P.

    1998-01-01

    The intent of this work was to broaden the applications of well-established surface modification techniques and to elucidate the various wear mechanisms that occur in sliding contact of ion-beam processed surfaces. The investigation included characterization and evaluation of coatings and modified surfaces synthesized by three surface engineering methods; namely, beam-line ion implantation, plasma-source ion implantation, and DC magnetron sputtering. Correlation among measured properties such as surface hardness, fracture toughness, and wear behavior was also examined. This dissertation focused on the following areas of research: (1) investigating the mechanical and tribological properties of mixed implantation of carbon and nitrogen into single crystal silicon by beam-line implantation; (2) characterizing the mechanical and tribological properties of diamond-like carbon (DLC) coatings processed by plasma source ion implantation; and (3) developing and evaluating metastable boron-carbon-nitrogen (BCN) compound coatings for mechanical and tribological properties. The surface hardness of a mixed carbon-nitrogen implant sample improved significantly compared to the unimplanted sample. However, the enhancement in the wear factor of this sample was found to be less significant than carbon-implanted samples. The presence of nitrogen might be responsible for the degraded wear behavior since nitrogen-implantation alone resulted in no improvement in the wear factor. DLC coatings have low friction, low wear factor, and high hardness. The fracture toughness of DLC coatings has been estimated for the first time. The wear mechanism in DLC coatings investigated with a ruby slider under a contact stress of 1 GPa was determined to be plastic deformation. The preliminary data on metastable BCN compound coatings indicated high friction, low wear factor, and high hardness.

  2. The mechanical and tribological properties of UHMWPE loaded ALN after mechanical activation for joint replacements.

    PubMed

    Gong, Kemeng; Qu, Shuxin; Liu, Yumei; Wang, Jing; Zhang, Yongchao; Jiang, Chongxi; Shen, Ru

    2016-08-01

    Ultra-high molecular weight polyethylene (UHMWPE) loaded with alendronate sodium (ALN) has tremendous potential as an orthopeadic biomaterial for joint replacements. However, poor mechanical and tribological properties of UHMWPE-ALN are still obstacle for further application. The purpose of this study was to investigate the effect and mechanism of mechanical activation on mechanical and tribological properties of 1wt% ALN-loaded UHMWPE (UHMWPE-ALN-ma). In this study, tensile test, small punch test and reciprocating sliding wear test were applied to characterize the mechanical and tribological properties of UHMWPE-ALN-ma. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize UHMWPE-ALN-ma. Tensile test and small punch test showed that Young׳s modulus, tensile strength and work-to-failure (WTF) of UHMWPE-ALN-ma increased significantly compared to those of UHMWPE-ALN. The friction coefficients and wear factors of UHMWPE-ALN-ma both decreased significantly compared to those of UHMWPE-ALN. Mechanical activation obviously reduced type 1 (void) and type 2 (the disconnected and dislocated machining marks) fusion defects of UHMWPE-ALN-ma, which were revealed by SEM images of freeze fracture surfaces after etching and lateral surfaces of specimens after extension to fracture, respectively. It was attributed to peeled-off layers and chain scission of molecular chains of UHMWPE particles after mechanical activation, which were revealed by SEM images and FTIR spectra of UHMWPE-ALN-ma and UHMWPE-ALN, respectively. Moreover, EDS spectra revealed the more homogeneous distribution of ALN in UHMWPE-ALN-ma compared to that of UHMWPE-ALN. The present results showed that mechanical activation was a potential strategy to improve mechanical and tribological properties of UHMWPE-ALN-ma as an orthopeadic biomaterial for joint replacements. PMID:27104932

  3. The mechanical and tribological properties of UHMWPE loaded ALN after mechanical activation for joint replacements.

    PubMed

    Gong, Kemeng; Qu, Shuxin; Liu, Yumei; Wang, Jing; Zhang, Yongchao; Jiang, Chongxi; Shen, Ru

    2016-08-01

    Ultra-high molecular weight polyethylene (UHMWPE) loaded with alendronate sodium (ALN) has tremendous potential as an orthopeadic biomaterial for joint replacements. However, poor mechanical and tribological properties of UHMWPE-ALN are still obstacle for further application. The purpose of this study was to investigate the effect and mechanism of mechanical activation on mechanical and tribological properties of 1wt% ALN-loaded UHMWPE (UHMWPE-ALN-ma). In this study, tensile test, small punch test and reciprocating sliding wear test were applied to characterize the mechanical and tribological properties of UHMWPE-ALN-ma. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize UHMWPE-ALN-ma. Tensile test and small punch test showed that Young׳s modulus, tensile strength and work-to-failure (WTF) of UHMWPE-ALN-ma increased significantly compared to those of UHMWPE-ALN. The friction coefficients and wear factors of UHMWPE-ALN-ma both decreased significantly compared to those of UHMWPE-ALN. Mechanical activation obviously reduced type 1 (void) and type 2 (the disconnected and dislocated machining marks) fusion defects of UHMWPE-ALN-ma, which were revealed by SEM images of freeze fracture surfaces after etching and lateral surfaces of specimens after extension to fracture, respectively. It was attributed to peeled-off layers and chain scission of molecular chains of UHMWPE particles after mechanical activation, which were revealed by SEM images and FTIR spectra of UHMWPE-ALN-ma and UHMWPE-ALN, respectively. Moreover, EDS spectra revealed the more homogeneous distribution of ALN in UHMWPE-ALN-ma compared to that of UHMWPE-ALN. The present results showed that mechanical activation was a potential strategy to improve mechanical and tribological properties of UHMWPE-ALN-ma as an orthopeadic biomaterial for joint replacements.

  4. Bubble growth and mechanical properties of tissue in decompression.

    PubMed

    Vann, R D; Clark, H G

    1975-09-01

    A survey of decompression literature leads to the conclusion that when tissue is subjected to gaseous supersaturation, pre-existing gas micronuclei grow into the gas bubbles which are routinely observed in decompression studies. These micronuclei may originate from mechanically induced tribonucleation or cavitation within joints. A new tissue model for decompression sickness based upon failure theory in rubber is proposed. The model shows theoretically that pre-existing sea-level nuclei can be stabilized at depth by elastic forces in tissue. These same elastic forces restrain the growth of nuclei when supersaturation occurs. Mechanical stress will lower the gaseous supersaturation required for growth of nuclei. Gaseous supersaturation, mechanical stress, and the elastic properties of various tissues interact to produce unbounded bubble growth leading to tissue lesions when combined gaseous and mechanical supersaturation exceeds a threshold value. The recommendation is made that the high levels of supersaturation generally used for the decompression of men be reduced.

  5. Brain mechanical property measurement using MRE with intrinsic activation

    NASA Astrophysics Data System (ADS)

    Weaver, John B.; Pattison, Adam J.; McGarry, Matthew D.; Perreard, Irina M.; Swienckowski, Jessica G.; Eskey, Clifford J.; Lollis, S. Scott; Paulsen, Keith D.

    2012-11-01

    Many pathologies alter the mechanical properties of tissue. Magnetic resonance elastography (MRE) has been developed to noninvasively characterize these quantities in vivo. Typically, small vibrations are induced in the tissue of interest with an external mechanical actuator. The resulting displacements are measured with phase contrast sequences and are then used to estimate the underlying mechanical property distribution. Several MRE studies have quantified brain tissue properties. However, the cranium and meninges, especially the dura, are very effective at damping externally applied vibrations from penetrating deeply into the brain. Here, we report a method, termed ‘intrinsic activation’, that eliminates the requirement for external vibrations by measuring the motion generated by natural blood vessel pulsation. A retrospectively gated phase contrast MR angiography sequence was used to record the tissue velocity at eight phases of the cardiac cycle. The velocities were numerically integrated via the Fourier transform to produce the harmonic displacements at each position within the brain. The displacements were then reconstructed into images of the shear modulus based on both linear elastic and poroelastic models. The mechanical properties produced fall within the range of brain tissue estimates reported in the literature and, equally important, the technique yielded highly reproducible results. The mean shear modulus was 8.1 kPa for linear elastic reconstructions and 2.4 kPa for poroelastic reconstructions where fluid pressure carries a portion of the stress. Gross structures of the brain were visualized, particularly in the poroelastic reconstructions. Intra-subject variability was significantly less than the inter-subject variability in a study of six asymptomatic individuals. Further, larger changes in mechanical properties were observed in individuals when examined over time than when the MRE procedures were repeated on the same day. Cardiac pulsation

  6. Micro-mechanical properties of bio-materials

    NASA Astrophysics Data System (ADS)

    Zakiev, V.; Markovsky, A.; Aznakayev, E.; Zakiev, I.; Gursky, E.

    2005-09-01

    Investigation of physical-mechanical characteristics of stomatologic materials (ceramics for crowns, silver amalgam, cements and materials on a polymeric basis) properties by the modern methods and correspondence their physical-mechanical properties to the physical-mechanical properties of native teeth is represented. The universal device "Micron-Gamma" is built for this purpose. This device allows investigate the physical-mechanical characteristics of stomatologic materials (an elastic modulus, micro-hardness, destruction energy, resistance to scratching) by the methods of continuous indentation, scanning and pricking. A new effective method as well as its device application for the investigation of surface layers of materials and their physical-mechanical properties by means of the constant indenting of an indenter is realized. This method is based on the automatic registration of loading (P) on the indenter with the simultaneous measurement of its indentation depth (h). The results of investigations are presented on a loading diagram P=f(h) and as a digital imaging on the PC. This diagram allows get not only more diverse characteristics in the real time regime but also gives new information about the stomatologic material properties. Therefore, we can to investigate the wide range of the physical-mechanical properties of stomatologic materials. "Micron-alpha" is digital detection device for light imaging applications. It enables to detect the very low material surface relief heights and restoration of surface micro topography by a sequence data processing of interferential data of partially coherent light also. "Micron-alpha" allows: to build 2D and 3D imaging of a material surface; to estimate the quantitatively characteristics of a material surface; to observe the imaging interferential pictures both in the white and in the monochromatic light; to carry out the investigation of blood cells, microbes and biological macromolecules profiles. The method allows

  7. Imaging-Based Methods for Non-invasive Assessment of Bone Properties Influenced by Mechanical Loading

    PubMed Central

    Lorbergs, Amanda L.

    2012-01-01

    ABSTRACT Purpose: To describe the most common in vivo imaging-based research tools used to assess bone properties that are influenced by mechanical loading associated with exercise, habitual physical activity, or disease states. Bone is a complex metabolically active tissue that adapts to changes in mechanical loading by altering the amount and spatial organization of mineral. Method: Using a narrative review design, the authors provide an overview of bone biology and biomechanics to emphasize the importance of bone size scale, porosity, and degree of mineralization when interpreting measures acquired using quantitative ultrasound (QUS), dual-energy X-ray absorptiometry (DXA), computed tomography (CT), magnetic resonance imaging (MRI), and finite element analysis (FEA). For each imaging modality, basic imaging principles, typical outcome measures associated with changes in mechanical loading, and salient features for physiotherapists are described. Main Results: While each imaging modality has strengths and limitations, currently CT-based methods are best suited for determining the effects of mechanical loading on bone properties—particularly in the peripheral skeleton. Conclusions: Regardless of the imaging technology used, the physiotherapist must carefully consider the assumptions of the imaging-based method, the clinical context, the nature of the change in mechanical loading, and the expected time course for change in bone properties. PMID:23449969

  8. Constitutive Modeling of the Mechanical Properties of Optical Fibers

    NASA Technical Reports Server (NTRS)

    Moeti, L.; Moghazy, S.; Veazie, D.; Cuddihy, E.

    1998-01-01

    Micromechanical modeling of the composite mechanical properties of optical fibers was conducted. Good agreement was obtained between the values of Young's modulus obtained by micromechanics modeling and those determined experimentally for a single mode optical fiber where the wave guide and the jacket are physically coupled. The modeling was also attempted on a polarization-maintaining optical fiber (PANDA) where the wave guide and the jacket are physically decoupled, and found not to applicable since the modeling required perfect bonding at the interface. The modeling utilized constituent physical properties such as the Young's modulus, Poisson's ratio, and shear modulus to establish bounds on the macroscopic behavior of the fiber.

  9. Study of mechanical properties of nanomaterials under high pressure

    NASA Astrophysics Data System (ADS)

    Sharma, Jyoti; Kaur, Namrat; Srivastava, A. K.

    2015-08-01

    In the present work, the study of physical properties and behaviour of nanomaterials i.e. n-γ- Al2O3and n-Si3C4 under high pressure is done. For this purpose Murnaghan equation of state is used. The applicability of Murnaghan equation of state is fully tested by calculating mechanical properties of nano materials i.e. volume compression (V/Vo), bulk modulus (KT) and relative isothermal compression coefficient (α(P)/α0) at different pressures. The present calculated values of compression curve for the cited nanomaterials come out to be in reasonable good agreement with the available experimental data.

  10. Workability and mechanical properties of alkali activated slag concrete

    SciTech Connect

    Collins, F.G.; Sanjayan, J.G.

    1999-03-01

    This paper reports the results of an investigation on concrete containing alkali activated slag (AAS) as the binder, with emphasis on achievement of reasonable workability and equivalent one-day strength to portland cement concrete at normal curing temperatures. Two types of activators were used: sodium hydroxide in combination with sodium carbonate and sodium silicate in combination with hydrated lime. The fresh concrete properties reported include slump and slump loss, air content, and bleed. Mechanical properties of AAS concrete, including compressive strength, elastic modulus, flexural strength, drying shrinkage, and creep are contrasted with those of portland cement concrete.

  11. Diversity and abundance: the basic properties of neuropeptide action in molluscs.

    PubMed

    Kiss, Tibor

    2011-05-15

    Neuropeptides, the most diverse group of signaling molecules, are responsible for regulating a variety of cellular and behavioral processes in all vertebrate and invertebrate animals. The role played by peptide signals in information processing is fundamentally different from that of conventional neurotransmitters. Neuropeptides may act as neurotransmitters or neuromodulators and are released at either synaptic or non-synaptic sites. Peptide signals control developmental processes, drive specific behaviors or contribute to the mechanisms of learning and memory storage. Co-transmission within or across peptide families, and between peptide and non-peptide signaling molecules, is common; this ensures the great versatility of their action. How these tasks are fulfilled when multiple neuropeptides are released has become an important topic for peptide research. Although our knowledge concerning the physiological and behavioral roles of most of the neuropeptides isolated from molluscs is incomplete, this article provides examples to address the complexity of peptide signaling.

  12. Electrical and dielectric properties of bovine trabecular bone - relationships with mechanical properties and mineral density

    NASA Astrophysics Data System (ADS)

    Sierpowska, J.; Töyräs, J.; Hakulinen, M. A.; Saarakkala, S.; Jurvelin, J. S.; Lappalainen, R.

    2003-03-01

    Interrelationships of trabecular bone electrical and dielectric properties with mechanical characteristics and density are poorly known. While electrical stimulation is used for healing fractures, better understanding of these relations has clinical importance. Furthermore, earlier studies have suggested that bone electrical and dielectric properties depend on the bone density and could, therefore, be used to predict bone strength. To clarify these issues, volumetric bone mineral density (BMDvol), electrical and dielectric as well as mechanical properties were determined from 40 cylindrical plugs of bovine trabecular bone. Phase angle, relative permittivity, loss factor and conductivity of wet bovine trabecular bone were correlated with Young's modulus, yield stress, ultimate strength, resilience and BMDvol. The reproducibility of in vitro electrical and dielectric measurements was excellent (standardized coefficient of variation less than 1%, for all parameters), especially at frequencies higher than 1 kHz. Correlations of electrical and dielectric parameters with the bone mechanical properties or density were frequency-dependent. The relative permittivity showed the strongest linear correlations with mechanical parameters (r > 0.547, p < 0.01, n = 40, at 50 kHz) and with BMDvol (r = 0.866, p < 0.01, n = 40, at 50 kHz). In general, linear correlations between relative permittivity and mechanical properties or BMDvol were highest at frequencies over 6 kHz. In addition, a significant site-dependent variation of electrical and dielectric characteristics, mechanical properties and BMDvol was revealed in bovine femur (p < 0.05, Kruskall-Wallis H-test). Based on the present results, we conclude that the measurement of electrical and dielectric properties provides quantitative information that is related to bone quantity and quality.

  13. Quantification of mechanical properties of human skin in vivo

    NASA Astrophysics Data System (ADS)

    Heinrich, Thorsten; Lunderstaedt, Reinhart A.

    2001-12-01

    Dermatologist as well as the cosmetical industry are interested in evaluating the mechanical properties of human skin. Many devices have been developed to measure skin's response to mechanical stress. In the presented paper a new approach to quantify the viscoelastic behavior of human skin on mechanical stress is proposed. Image processing techniques are used to detect the two-dimensional deformation of the skin in uniaxial tensile tests. The apparatus consists of a computer-controlled stepper motor drive mechanism to extend the skin, a load cell to measure displacement vector fields are calculated by a method based on local template matching and interpolation algorithms. From the displacement vector fields a strain tensor and the principal strain directions are evaluated. A model built up of springs and dashpots, is used to characterize the stress-strain-time relationships of skin and to obtain a set of parameters, which represent the instantaneous elasticity, the delayed elasticity and the viscosity of skin on loading. The results show the accuracy of the model. The method seems to be useful to investigate the influences of age, test area, cosmetics, etc. on the mechanical properties of human skin in vivo.

  14. Material properties and fracture mechanics in relation to ceramic machining

    SciTech Connect

    Griffith, L.V.

    1993-12-02

    Material removal rate, surface finish, and subsurface damage are largely governed by fracture mechanics and plastic deformation, when ceramics are machined using abrasive methods. A great deal of work was published on the fracture mechanics of ceramics in the late 1970s and early 1980s, although this work has never resulted in a comprehensive model of the fixed abrasive grinding process. However, a recently published model describes many of the most important features of the loose abrasive machining process, for example depth of damage, surface roughness, and material removal rate. Many of the relations in the loose abrasive machining model can be readily discerned from fracture mechanics models, in terms of material properties. By understanding the mechanisms of material removal, from a material properties perspective, we can better estimate how one material will machine in relation to another. Although the fracture mechanics models may have been developed for loose abrasive machining, the principles of crack initiation and propagation are equally valuable for fixed abrasive machining. This report provides a brief review of fracture in brittle materials, the stress distribution induced by abrasives, critical indenter loads, the extension of cracks, and the relation of the fracture process to material removal.

  15. Crosstalk between focal adhesions and material mechanical properties governs cell mechanics and functions.

    PubMed

    Fusco, Sabato; Panzetta, Valeria; Embrione, Valerio; Netti, Paolo A

    2015-09-01

    Mechanical properties of materials strongly influence cell fate and functions. Focal adhesions are involved in the extremely important processes of mechanosensing and mechanotransduction. To address the relationship between the mechanical properties of cell substrates, focal adhesion/cytoskeleton assembly and cell functions, we investigated the behavior of NIH/3T3 cells over a wide range of stiffness (3-1000kPa) using two of the most common synthetic polymers for cell cultures: polyacrylamide and polydimethylsiloxane. An overlapping stiffness region was created between them to compare focal adhesion characteristics and cell functions, taking into account their different time-dependent behavior. Indeed, from a rheological point of view, polyacrylamide behaves like a strong gel (elastically), whereas polydimethylsiloxane like a viscoelastic solid. First, focal adhesion characteristics and dynamics were addressed in terms of material stiffness, then cell spreading area, migration rate and cell mechanical properties were correlated with focal adhesion size and assembly. Focal adhesion size was found to increase in the whole range of stiffness and to be in agreement in the overlapping rigidity region for the investigated materials. Cell mechanics directly correlated with focal adhesion lengths, whereas migration rate followed an inverse correlation. Cell spreading correlated with the substrate stiffness on polyacrylamide hydrogel, while no specific trend was found on polydimethylsiloxane. Substrate mechanics can be considered as a key physical cue that regulates focal adhesion assembly, which in turn governs important cellular properties and functions. PMID:26004223

  16. Effects of sintering atmosphere on the physical and mechanical properties of modified BOF slag glass

    NASA Astrophysics Data System (ADS)

    Dai, Wen-bin; Li, Yu; Cang, Da-qiang; Zhou, Yuan-yuan; Fan, Yong

    2014-05-01

    This study proposes an efficient way to utilize all the chemical components of the basic oxygen furnace (BOF) slag to prepare high value-added glass-ceramics. A molten modified BOF slag was converted from the melting BOF slag by reducing it and separating out iron component in it, and the modified BOF slag was then quenched in water to form glasses with different basicities. The glasses were subsequently sintered in the temperature range of 600-1000°C in air or nitrogen atmosphere for 1 h. The effects of different atmospheres on the physical and mechanical properties of sintered samples were studied by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) and by conducting experiment on evaluating the sintering shrinkage, water absorption and bulk density. It is found that the kinetics of the sintering process is significantly affected by sintering atmosphere. In particular, compared with sintering in air atmosphere, sintering in N2 atmosphere promotes the synergistic growth of pyroxene and melilite crystalline phases, which can contribute to better mechanical properties and denser microstructure.

  17. Structure and mechanical properties of liquid crystalline filaments

    SciTech Connect

    Eremin, Alexey; Nemes, Alexandru; Stannarius, Ralf; Schulz, Mario; Nadasi, Hajnalka; Weissflog, Wolfgang

    2005-03-01

    The formation of stable freely suspended filaments is an interesting peculiarity of some liquid crystal phases. So far, little is known about their structure and stability. Similarly to free-standing smectic films, an internal molecular structure of the mesophase stabilizes these macroscopically well-ordered objects with length to diameter ratios of 10{sup 3} and above. In this paper, we report observations of smectic liquid crystal fibers formed by bent-shaped molecules in different mesophases. Our study, employing several experimental techniques, focuses on mechanical and structural aspects of fiber formation such as internal structure, stability, and mechanical and optical properties.

  18. Decoupling polymer properties to elucidate mechanisms governing cell behavior.

    PubMed

    Wang, Xintong; Boire, Timothy C; Bronikowski, Christine; Zachman, Angela L; Crowder, Spencer W; Sung, Hak-Joon

    2012-10-01

    Determining how a biomaterial interacts with cells ("structure-function relationship") reflects its eventual clinical applicability. Therefore, a fundamental understanding of how individual material properties modulate cell-biomaterial interactions is pivotal to improving the efficacy and safety of clinically translatable biomaterial systems. However, due to the coupled nature of material properties, their individual effects on cellular responses are difficult to understand. Structure-function relationships can be more clearly understood by the effective decoupling of each individual parameter. In this article, we discuss three basic decoupling strategies: (1) surface modification, (2) cross-linking, and (3) combinatorial approaches (i.e., copolymerization and polymer blending). Relevant examples of coupled material properties are briefly reviewed in each section to highlight the need for improved decoupling methods. This follows with examples of more effective decoupling techniques, mainly from the perspective of three primary classes of synthetic materials: polyesters, polyethylene glycol, and polyacrylamide. Recent strides in decoupling methodologies, especially surface-patterning and combinatorial techniques, offer much promise in further understanding the structure-function relationships that largely govern the success of future advancements in biomaterials, tissue engineering, and drug delivery. PMID:22536977

  19. Decoupling Polymer Properties to Elucidate Mechanisms Governing Cell Behavior

    PubMed Central

    Wang, Xintong; Boire, Timothy C.; Bronikowski, Christine; Zachman, Angela L.; Crowder, Spencer W.

    2012-01-01

    Determining how a biomaterial interacts with cells (“structure-function relationship”) reflects its eventual clinical applicability. Therefore, a fundamental understanding of how individual material properties modulate cell-biomaterial interactions is pivotal to improving the efficacy and safety of clinically translatable biomaterial systems. However, due to the coupled nature of material properties, their individual effects on cellular responses are difficult to understand. Structure-function relationships can be more clearly understood by the effective decoupling of each individual parameter. In this article, we discuss three basic decoupling strategies: (1) surface modification, (2) cross-linking, and (3) combinatorial approaches (i.e., copolymerization and polymer blending). Relevant examples of coupled material properties are briefly reviewed in each section to highlight the need for improved decoupling methods. This follows with examples of more effective decoupling techniques, mainly from the perspective of three primary classes of synthetic materials: polyesters, polyethylene glycol, and polyacrylamide. Recent strides in decoupling methodologies, especially surface-patterning and combinatorial techniques, offer much promise in further understanding the structure-function relationships that largely govern the success of future advancements in biomaterials, tissue engineering, and drug delivery. PMID:22536977

  20. Basic properties of a liquidt in anode solid oxide fuel cell

    SciTech Connect

    Harry Abernathy; RandallGemmen; KirkGerdes; Mark Koslowske; ThomasTao

    2010-12-17

    An unconventional high temperature fuel cell system, the liquidt in anode solid oxide fuel cell(LTA-SOFC), is discussed. A thermodynamic analysis of a solid oxide fuel cell with a liquid metal anode is developed. Pertinent thermo chemical and thermo physical properties of liquid tin in particular are detailed. An experimental setup for analysis of LTA-SOFC anode kinetics is described, and data for a planar cell under hydrogen indicated an effective oxygen diffusion coefficient of 5.3×10−5 cm2 s−1 at 800 ◦C and 8.9×10−5 cm2 s−1 at 900 ◦C. This value is similar to previously reported literature values for liquid tin. The oxygen conductivity through the tin, calculated from measured diffusion coefficients and theoretical oxygen solubility limits, is found to be on the same order of thatofyttria-stabilizedzirconia(YSZ), a traditional SOFC electrolyte material. As such,the ohmicloss due to oxygen transport through the tin layer must be considered in practical system cell design since the tin layer will usually be at least as thick as the electrolyte.

  1. Basic Properties of Conductivity and Normal Hall Effect in the Periodic Anderson Model

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinji; Miyake, Kazumasa

    2016-04-01

    Exact formulas of diagonal conductivity σxx and Hall conductivity σxy are derived from the Kubo formula in hybridized two-orbital systems with arbitrary band dispersions. On the basis of the theoretical framework for the Fermi liquid based on these formulas, the ground-state properties of the periodic Anderson model with electron correlation and weak impurity scattering are studied on the square lattice. It is shown that imbalance of the mass-renormalization factors causes remarkable increase in σxx and σxy in the valence-fluctuation regime as the f level increases while the cancellation of the renormalization factors causes slight increase in σxx and σxy in the Kondo regime. The Hall coefficient RH shows almost constant behavior in both the regimes. Near half filling, RH is expressed by the total hole density as R{H} = 1/(bar{n}{hole}e) while RH approaches zero near quarter filling, which reflects the curvature of the Fermi surface. These results hold as far as the damping rate for f electrons is less than about 10% of the renormalized hybridization gap. From these results we discuss pressure dependence of residual resistivity and normal Hall effect in Ce- and Yb-based heavy electron systems.

  2. Chemical treatment of olive pomace: effect on acid-basic properties and metal biosorption capacity.

    PubMed

    Martín-Lara, M A; Pagnanelli, F; Mainelli, S; Calero, M; Toro, L

    2008-08-15

    In this study, olive pomace, an agricultural waste that is very abundant in Mediterranean area, was modified by two chemical treatments in order to improve its biosorption capacity. Potentiometric titrations and IR analyses were used to characterise untreated olive pomace (OP), olive pomace treated by phosphoric acid (PAOP) and treated by hydrogen peroxide (HPOP). Acid-base properties of all investigated biosorbents were characterised by two main kinds of active sites, whose nature and concentration were determined by a mechanistic model assuming continuous distribution for the proton affinity constants. Titration modelling denoted that all investigated biosorbents (OP, PAOP and HPOP) were characterised by the same kinds of active sites (carboxylic and phenolic), but with different total concentrations with PAOP richer than OP and HPOP. Single metal equilibrium studies in batch reactors were carried out to determine the capacity of these sorbents for copper and cadmium ions at constant pH. Experimental data were analysed and compared using the Langmuir isotherm. The order of maximum uptake capacity of copper and cadmium ions on different biosorbents was PAOP>HPOP>OP. The maximum adsorption capacity of copper and cadmium, was obtained as 0.48 and 0.10 mmol/g, respectively, for PAOP. Metal biosorption tests in presence of Na(+) in solution were also carried out in order to evaluate the effect of chemical treatment on biomass selectivity. These data showed that PAOP is more selective for cadmium than the other sorbents, while similar selectivity was observed for copper. PMID:18242836

  3. Chemical treatment of olive pomace: effect on acid-basic properties and metal biosorption capacity.

    PubMed

    Martín-Lara, M A; Pagnanelli, F; Mainelli, S; Calero, M; Toro, L

    2008-08-15

    In this study, olive pomace, an agricultural waste that is very abundant in Mediterranean area, was modified by two chemical treatments in order to improve its biosorption capacity. Potentiometric titrations and IR analyses were used to characterise untreated olive pomace (OP), olive pomace treated by phosphoric acid (PAOP) and treated by hydrogen peroxide (HPOP). Acid-base properties of all investigated biosorbents were characterised by two main kinds of active sites, whose nature and concentration were determined by a mechanistic model assuming continuous distribution for the proton affinity constants. Titration modelling denoted that all investigated biosorbents (OP, PAOP and HPOP) were characterised by the same kinds of active sites (carboxylic and phenolic), but with different total concentrations with PAOP richer than OP and HPOP. Single metal equilibrium studies in batch reactors were carried out to determine the capacity of these sorbents for copper and cadmium ions at constant pH. Experimental data were analysed and compared using the Langmuir isotherm. The order of maximum uptake capacity of copper and cadmium ions on different biosorbents was PAOP>HPOP>OP. The maximum adsorption capacity of copper and cadmium, was obtained as 0.48 and 0.10 mmol/g, respectively, for PAOP. Metal biosorption tests in presence of Na(+) in solution were also carried out in order to evaluate the effect of chemical treatment on biomass selectivity. These data showed that PAOP is more selective for cadmium than the other sorbents, while similar selectivity was observed for copper.

  4. Time-temperature superposition applied to PBX mechanical properties

    NASA Astrophysics Data System (ADS)

    Thompson, Darla; DeLuca, Racci; Wright, Walter J.

    2012-03-01

    The use of plastic-bonded explosives (PBXs) in weapon applications requires that they possess and maintain a level of structural/mechanical integrity. Uniaxial tension and compression experiments are typically used to characterize the mechanical response of materials over a wide range of temperatures and strain rates, providing the basis for predictive modeling in more complex geometries. After many years of data collection on a variety of PBX formulations, we have here applied the principles of time-temperature superposition to a mechanical properties database which includes PBX 9501, PBX 9502, PBXN-110, PBXN-9, and HPP (propellant). Consistencies are demonstrated between the results of quasi-static tension and compression, dynamic Split-Hopkinson Pressure Bar (SHPB) compression, and cantilever Dynamic Mechanical Analysis (DMA). Timetemperature relationships of maximum stress and corresponding strain values are analyzed, in addition to the more conventional analysis of modulus. The extensive analysis shows adherence to the principles of time-temperature superposition and correlations of mechanical response to binder glasstransition temperature (Tg) and specimen density. Direct ties exist between the time-temperature analysis and the underlying basis of a useful existing PBX mechanical model (ViscoSCRAM). Results give confidence that, with some limitations, mechanical response can be predicted at conditions not explicitly measured.

  5. Prediction of Mechanical Properties of Polymers With Various Force Fields

    NASA Technical Reports Server (NTRS)

    Odegard, Gregory M.; Clancy, Thomas C.; Gates, Thomas S.

    2005-01-01

    The effect of force field type on the predicted elastic properties of a polyimide is examined using a multiscale modeling technique. Molecular Dynamics simulations are used to predict the atomic structure and elastic properties of the polymer by subjecting a representative volume element of the material to bulk and shear finite deformations. The elastic properties of the polyimide are determined using three force fields: AMBER, OPLS-AA, and MM3. The predicted values of Young s modulus and shear modulus of the polyimide are compared with experimental values. The results indicate that the mechanical properties of the polyimide predicted with the OPLS-AA force field most closely matched those from experiment. The results also indicate that while the complexity of the force field does not have a significant effect on the accuracy of predicted properties, small differences in the force constants and the functional form of individual terms in the force fields determine the accuracy of the force field in predicting the elastic properties of the polyimide.

  6. On the mechanical properties of selenite glass nanocomposites

    NASA Astrophysics Data System (ADS)

    Bar, Arun Kr.; Kundu, Ranadip; Roy, Debasish; Bhattacharya, Sanjib

    2016-05-01

    In this paper the room temperature micro-hardness of selenite glass-nanocomposites has been measured using a Vickers and Knoop micro hardness tester where the applied load varies from 0.01N to 0.98 N. A significant indentation size effect was observed for each sample at relatively low indentation test loads. The classical Meyer's law and the proportional specimen resistance model were used to analyze the micro-hardness behavior. It was found that the selenite glass-nanocomposite becomes harder with increasing CuI composition and the work hardening coefficient and mechanical properties like Young modulus, E, were also calculated. Our results open the way for the preparation, application and investigation of significant mechanical properties of new type of glass-nanocomposites.

  7. Synchronization properties of self-sustained mechanical oscillators.

    PubMed

    Arroyo, Sebastián I; Zanette, Damián H

    2013-05-01

    We study, both analytically and numerically, the dynamics of mechanical oscillators kept in motion by a feedback force, which is generated electronically from a signal produced by the oscillators themselves. This kind of self-sustained systems may become standard in the design of frequency-control devices at microscopic scales. Our analysis is thus focused on their synchronization properties under the action of external forces and on the joint dynamics of two to many coupled oscillators. Existence and stability of synchronized motion are assessed in terms of the mechanical properties of individual oscillators, namely, their natural frequencies and damping coefficients, and synchronization frequencies are determined. Similarities and differences with synchronization phenomena in other coupled oscillating systems are emphasized.

  8. Enhancement in mechanical properties of concrete due to blended ash

    SciTech Connect

    Naik, T.R.; Singh, S.S.; Hossain, M.M.

    1996-01-01

    This study was carried out to evaluate the effects of blended ash mixture on mechanical properties of concrete. In this study two reference mixtures were used. One of the mixtures was a no-fly ash mixture, and the other mixture contained 35% unblended Class C fly ash. Additional mixtures were composed of three blends of Class C and Class F fly ash while maintaining a total fly ash content of 40% of the total cementitious materials. Mechanical properties such as compressive strength, tensile strength, flexural strength, and modulus of elasticity were determined as a function of age ranging from 1 to 91 days. The results showed that blending of Class F fly ash with Class C fly ash showed either comparable or better results compared to either the reference mixture without fly ash or the unblended Class C fly ash concrete mixture at a fly ash concentration of 40% of total cementitious materials.

  9. Quantitative ultrasonic evaluation of mechanical properties of engineering materials

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1978-01-01

    Current progress in the application of ultrasonic techniques to nondestructive measurement of mechanical strength properties of engineering materials is reviewed. Even where conventional NDE techniques have shown that a part is free of overt defects, advanced NDE techniques should be available to confirm the material properties assumed in the part's design. There are many instances where metallic, composite, or ceramic parts may be free of critical defects while still being susceptible to failure under design loads due to inadequate or degraded mechanical strength. This must be considered in any failure prevention scheme that relies on fracture analysis. This review will discuss the availability of ultrasonic methods that can be applied to actual parts to assess their potential susceptibility to failure under design conditions.

  10. Enhanced Mechanical Properties in PVA/SWNT Composite Fibers

    NASA Astrophysics Data System (ADS)

    Sampson, William; Dalton, Alan

    2005-03-01

    Composite fibers of polyvinyl alcohol (PVA) and HiPco Single Walled Carbon Nanotubes (SWNT) have been developed at The University of Texas at Dallas that show greatly enhanced mechanical properties, with typical strengths of 1.8GPa and toughness in excess of that of spider silk, making these the toughest known fibers to date. However, the exact interactions leading to the enhanced mechanical properties are not as yet fully understood. We have used a series of Raman and DSC experiments to discover the nature of the strength-enhancing interactions in these composite materials. The results lead to the conclusion that the bulk of the improvements are due to SWNT-nucleated PVA crystallinity, with the SWNTs playing less of a direct role than we originally thought.

  11. Mechanical and thermophysical properties of hot-pressed SYNROC B

    SciTech Connect

    Hoenig, C.L.; Newkirk, H.W.; Otto, R.A.; Brady, R.L.; Brown, A.E.; Ulrich, A.R.; Lum, R.C.

    1981-05-06

    The optimal SYNROC compositons for use with commercial waste are reviewed. Large amounts of powder (about 2.5 kg) were prepared by convention al ceramic operations to test the SYNROC concept on a processing scale. Samples, 15.2 cm in diameter, were hot pressed in graphite, and representative samples were cut for microstructural evaluations. Measured mechanical and thermophysical properties did not vary significantly as a function of sample location and were typical of titanate ceramic materials.

  12. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

    NASA Astrophysics Data System (ADS)

    Aho, Johnathon M.; Qiang, Bo; Wigle, Dennis A.; Tschumperlin, Daniel J.; Urban, Matthew W.

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal-submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa-submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered esophageal

  13. Mechanical properties of D0 Run IIB silicon detector staves

    SciTech Connect

    Lanfranco, Giobatta; Fast, James; /Fermilab

    2001-06-01

    A proposed stave design for the D0 Run IIb silicon tracker outer layers featuring central cooling channels and a composite shell mechanical structure is evaluated for self-deflection and deflection due to external loads. This paper contains an introduction to the stave structure, a section devoted to composite lamina and laminate properties and finally a section discussing the beam deflections expected for assembled staves using these laminates.

  14. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

    NASA Astrophysics Data System (ADS)

    Aho, Johnathon M.; Qiang, Bo; Wigle, Dennis A.; Tschumperlin, Daniel J.; Urban, Matthew W.

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal–submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa–submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered

  15. ORMOSIL thin films: tuning mechanical properties via a nanochemistry approach.

    PubMed

    Palmisano, Giovanni; Le Bourhis, Eric; Ciriminna, Rosaria; Tranchida, Davide; Pagliaro, Mario

    2006-12-19

    The mechanical properties (hardness and elastic modulus) of organically modified silicate thin films can be finely tuned by varying the degree of alkylation and thus the fraction of six- and four-membered siloxane rings in the organosilica matrix. This opens the way to large tunability of parameters that are of crucial practical importance for films that are finding increasing application in numerous fields ranging from microelectronics to chemical sensing.

  16. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry.

    PubMed

    Aho, Johnathon M; Qiang, Bo; Wigle, Dennis A; Tschumperlin, Daniel J; Urban, Matthew W

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal-submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa-submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered esophageal

  17. The mechanical properties of density graded hemp/polyethylene composites

    NASA Astrophysics Data System (ADS)

    Dauvegis, Raphaël; Rodrigue, Denis

    2015-05-01

    In this work, the production and mechanical characterization of density graded biocomposites based on high density polyethylene and hemp fibres was performed. The effect of coupling agent addition (maleated polyethylene) and hemp content (0-30%) was studied to determine the effect of hemp distribution (graded content) inside the composite (uniform, linear, V and Λ). Tensile and flexural properties are reported to compare the structures, especially in terms of their stress-strain behaviors under tensile loading.

  18. Spectroscopic comparison of effects of electron radiation on mechanical properties of two polyimides

    NASA Technical Reports Server (NTRS)

    Long, Edward R., Jr.; Long, Sheila Ann T.

    1987-01-01

    The differences in the radiation durabilities of two polyimide materials, Du Pont Kapton and General Electric Ultem, are compared. An explanation of the basic mechanisms which occur during exposure to electron radiation from analyses of infrared (IR) and electron paramagnetic resonance (EPR) spectroscopic data for each material is provided. The molecular model for Kapton was, in part, established from earlier modeling for Ultem (pp. 1293-1298 of IEEE Transactions on Nuclear Science, December 1984). Techniques for understanding the durability of one complex polymer based on the understanding of a different and equally complex polymer are demonstrated. The spectroscopic data showed that the primary radiation-generated change in the tensile properties of Ultem (a large reduction in tensile elongation) was due to crosslinking, which followed the capture by phenyl radicals of hydrogen atoms removed from gem-dimethyl groups. In contrast, the tensile properties of Kapton remained unchanged because radical-radical recombination, a self-mending process, took place.

  19. Basic properties of transition remanent magnetizations of magnetite in relation to the ambient field using granite samples

    NASA Astrophysics Data System (ADS)

    Sato, Masahiko; Seita, Kazuhiro; Miyagawa, Takeshi; Mochizuki, Nobutatsu; Kogiso, Tetsu; Tsunakawa, Hideo

    2015-01-01

    We have investigated basic properties of transition remanent magnetization of natural magnetite in granite samples collected from the Minnesota River Valley, North America. Transition remanence was imparted during cooling and/or warming through the Verwey transition around 120 K. Depending on magnetic field conditions during cooling and warming, three types of transition remanences have been categorized: (1) TrRM, acquired during a cycle of field cooling and field warming; (2) TrWRM, acquired during zero-field cooling and field warming and (3) TrCRM, imparted during field cooling and zero-field warming. These remanences fulfil basic laws of remanent magnetization: (1) directions of the transition remanences are parallel to direction of the applied field (the law of parallelism), (2) intensities of the transition remanences are proportional to the applied field intensity (the law of proportionality) and (3) sum of the partial transition remanences is equal to the total transitional remanence, that is, TrRM = TrWRM + TrCRM. In addition, the ratio of TrRM to TRMLTD (the demagnetized component of thermoremanent magnetization by low-temperature demagnetization) shows a nearly constant value of ˜0.34. This relationship might reflect differences in equilibrium magnetic domain state at low and high temperature.

  20. Rubber-toughened cyanate composites - Properties and toughening mechanism

    NASA Technical Reports Server (NTRS)

    Yang, P. C.; Woo, E. P.; Laman, S. A.; Jakubowski, J. J.; Pickelman, D. M.; Sue, H. J.

    1991-01-01

    Earlier work by Young et al. (1990) has shown that Dow experimental cyanate ester resin XU71787.02 is readily toughenable by rubber. A particularly effective rubber for this purpose is an experimental core-shell rubber which toughens the polymer by inducing shear yielding. This paper describes an investigation into the toughening mechanism in the corresponding carbon-fiber composite systems and the effect of fibers on composite properties. Resin-fiber interfacial shear strengths have been successfully correlated to the compressive strengths after impact and other key properties of composites based on rubber-toughened cyanate and several carbon fibers. The differences in the properties are explained by the difference in the functioning of the rubber particles during the fracture process.

  1. Vibrational, mechanical, and thermal properties of III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Dow, John D.

    1989-02-01

    Theories of the mechanical, vibrational, and electronic properties of 3 to 5 semiconductors were developed and applied to: (1) help determine the feasibility of InN-based visible and ultraviolet lasers and light detectors, (2) develop a theory of phonons in semiconductor alloys, (3) understand surface reconstruction of semiconductors, (4) predict the effects of atomic correlations on the light-scattering (Raman) properties of semiconductive alloys, (5) develop a new first principles pseudo-function implementation of local-density theory, (6) study the oxidation of GaAs, (7) develop a theory of scanning tunneling microscope images, and (8) understand the electronic and optical properties of highly strained artificial semiconductors and small semiconductor particles.

  2. Protocol dependence of mechanical properties in granular systems.

    PubMed

    Inagaki, S; Otsuki, M; Sasa, S

    2011-11-01

    We study the protocol dependence of the mechanical properties of granular media by means of computer simulations. We control a protocol of realizing disk packings in a systematic manner. In 2D, by keeping material properties of the constituents identical, we carry out compaction with various strain rates. The disk packings exhibit the strain rate dependence of the critical packing fraction above which the pressure becomes non-zero. The observed behavior contrasts with the well-studied jamming transitions for frictionless disk packings. We also observe that the elastic moduli of the disk packings depend on the strain rate logarithmically. Our results suggest that there exists a time-dependent state variable to describe macroscopic material properties of disk packings, which depend on its protocol.

  3. Mechanical properties of tendons: changes with sterilization and preservation.

    PubMed

    Smith, C W; Young, I S; Kearney, J N

    1996-02-01

    Tendon allografts are commonly used to replace damaged anterior cruciate ligaments (ACL). Some of the sterilization and preservation techniques used by tissue banks with tendon allografts are thought to impair the mechanical properties of graft tissues. The tensile mechanical properties of porcine toe extensor tendons were measured using a dynamic testing machine following either freezing, freeze-drying, freezing then irradiation at 25 kGy (2.5 MRad), freeze-drying then irradiation, or freeze-drying then ethylene oxide gas sterilization. There was a small but significant difference in Young's modulus between the frozen group (0.88 GPa + 0.09 SD) and both the fresh group (0.98 GPa 1 0.12 SD) and the frozen irradiated group (0.97 GPa 1 0.08 SD). No values of Young's modulus were obtained for the freeze-dried irradiated tendons. The ultimate tensile stress (UTS) of the freeze-dried irradiated group (4.7 MPa 1 4.8 SD) was significantly different from both the fresh and the frozen irradiated groups, being reduced by approximately 90 percent. There were no significant changes in UTS or Young's modulus between any of the other groups. If irradiation is to be used to sterilize a tendon replacement for an ACL it must take place after freeze-drying to maintain mechanical properties.

  4. Structure and mechanical properties of Octopus vulgaris suckers.

    PubMed

    Tramacere, Francesca; Kovalev, Alexander; Kleinteich, Thomas; Gorb, Stanislav N; Mazzolai, Barbara

    2014-02-01

    In this study, we investigate the morphology and mechanical features of Octopus vulgaris suckers, which may serve as a model for the creation of a new generation of attachment devices. Octopus suckers attach to a wide range of substrates in wet conditions, including rough surfaces. This amazing feature is made possible by the sucker's tissues, which are pliable to the substrate profile. Previous studies have described a peculiar internal structure that plays a fundamental role in the attachment and detachment processes of the sucker. In this work, we present a mechanical characterization of the tissues involved in the attachment process, which was performed using microindentation tests. We evaluated the elasticity modulus and viscoelastic parameters of the natural tissues (E ∼ 10 kPa) and measured the mechanical properties of some artificial materials that have previously been used in soft robotics. Such a comparison of biological prototypes and artificial material that mimics octopus-sucker tissue is crucial for the design of innovative artificial suction cups for use in wet environments. We conclude that the properties of the common elastomers that are generally used in soft robotics are quite dissimilar to the properties of biological suckers. PMID:24284894

  5. Mechanical properties of human dental enamel on the nanometre scale.

    PubMed

    Habelitz, S; Marshall, S J; Marshall, G W; Balooch, M

    2001-02-01

    Atomic force microscopy (AFM) combined with a nano-indentation technique was used to reveal the structure and to perform site-specific mechanical testing of the enamel of third molars. Nano-indentations (size<500 nm) were made in the cusp area to measure the mechanical properties of single enamel rods at different orientations. The influence of etching on the physical properties was studied and etching conditions that did not significantly alter the plastic-elastic response of enamel were defined. Elasticity and hardness were found to be a function of the microstructural texture. Mean Young's moduli of 87.5 (+/-2.2) and 72.2 (+/-4.5) GPa and mean hardness of 3.9+/-0.3 and 3.3+/-0.3 GPa were measured in directions parallel and perpendicular to the enamel rods, respectively. Analysis of variance showed that the differences were significant. The observed anisotropy of enamel is related to the alignment of fibre-like apatite crystals and the composite nature of enamel rods. Mechanical properties were also studied at different locations on single enamel rods. Compared to those in the head area of the rods, Young's moduli and hardness were lower in the tail area and in the inter-rod enamel, which can be attributed to changes in crystal orientation and the higher content of soft organic tissue in these areas.

  6. Experimental study determining the mechanical properties of dental floss holders.

    PubMed

    Wolff, Anna; Pritsch, Maria; Dörfer, Christof; Staehle, Hans Jörg

    2011-06-01

    This study determined the mechanical properties of 19 dental floss holders. Eight single-use holders and 11 reusable ones were tested. An in vitro model with dental proximal contact strength of 8 N was created. Every device had to pass the proximal contact 30 times. We measured (1) the displacement of the floss [mm], (2) the force [N] necessary to pass the proximal contact after the 30th passage, (3) the loosening of the floss (offset [mm]), and (4) the change in the distance between the branches [mm]. Each measurement was repeated seven times. The results are displacement of the floss after 30 passages, 2.0 to 9.2 mm; passage force, 2.6 to 11 N; increases in branch distance, 0-2.9 mm; offset of the floss, 0-1.8 mm (all numbers are medians). Based on cleaning a full dentition (30 passages), we suggest introducing minimal requirements of <4 mm for the displacement of the floss, ≥11 N for the force, and <0.1 mm for the difference in branch distance and the offset. Only two products fulfilled our criteria. The tests show that dental floss holders vary extremely in their mechanical properties. Their effective use seems often impossible due to limited mechanical properties.

  7. Structure and mechanical properties of Octopus vulgaris suckers

    PubMed Central

    Tramacere, Francesca; Kovalev, Alexander; Kleinteich, Thomas; Gorb, Stanislav N.; Mazzolai, Barbara

    2014-01-01

    In this study, we investigate the morphology and mechanical features of Octopus vulgaris suckers, which may serve as a model for the creation of a new generation of attachment devices. Octopus suckers attach to a wide range of substrates in wet conditions, including rough surfaces. This amazing feature is made possible by the sucker's tissues, which are pliable to the substrate profile. Previous studies have described a peculiar internal structure that plays a fundamental role in the attachment and detachment processes of the sucker. In this work, we present a mechanical characterization of the tissues involved in the attachment process, which was performed using microindentation tests. We evaluated the elasticity modulus and viscoelastic parameters of the natural tissues (E ∼ 10 kPa) and measured the mechanical properties of some artificial materials that have previously been used in soft robotics. Such a comparison of biological prototypes and artificial material that mimics octopus-sucker tissue is crucial for the design of innovative artificial suction cups for use in wet environments. We conclude that the properties of the common elastomers that are generally used in soft robotics are quite dissimilar to the properties of biological suckers. PMID:24284894

  8. Mechanical Properties of a Primary Cilium Measured by Resonant Oscillation

    NASA Astrophysics Data System (ADS)

    Resnick, Andrew

    Primary cilia are ubiquitous mammalian cellular substructures implicated in an ever-increasing number of regulatory pathways. The well-established `ciliary hypothesis' states that physical bending of the cilium (for example, due to fluid flow) initiates signaling cascades, yet the mechanical properties of the cilium remain incompletely measured, resulting in confusion regarding the biological significance of flow-induced ciliary mechanotransduction. In this work we measure the mechanical properties of a primary cilium by using an optical trap to induce resonant oscillation of the structure. Our data indicate 1), the primary cilium is not a simple cantilevered beam, 2), the base of the cilium may be modeled as a nonlinear rotatory spring, the linear spring constant `k' of the cilium base calculated to be (4.6 +/- 0.62)*10-12 N/rad and nonlinear spring constant ` α' to be (-1 +/- 0.34) *10-10 N/rad2 , and 3) the ciliary base may be an essential regulator of mechanotransduction signalling. Our method is also particularly suited to measure mechanical properties of nodal cilia, stereocilia, and motile cilia, anatomically similar structures with very different physiological functions.

  9. Structure and mechanical properties of Octopus vulgaris suckers.

    PubMed

    Tramacere, Francesca; Kovalev, Alexander; Kleinteich, Thomas; Gorb, Stanislav N; Mazzolai, Barbara

    2014-02-01

    In this study, we investigate the morphology and mechanical features of Octopus vulgaris suckers, which may serve as a model for the creation of a new generation of attachment devices. Octopus suckers attach to a wide range of substrates in wet conditions, including rough surfaces. This amazing feature is made possible by the sucker's tissues, which are pliable to the substrate profile. Previous studies have described a peculiar internal structure that plays a fundamental role in the attachment and detachment processes of the sucker. In this work, we present a mechanical characterization of the tissues involved in the attachment process, which was performed using microindentation tests. We evaluated the elasticity modulus and viscoelastic parameters of the natural tissues (E ∼ 10 kPa) and measured the mechanical properties of some artificial materials that have previously been used in soft robotics. Such a comparison of biological prototypes and artificial material that mimics octopus-sucker tissue is crucial for the design of innovative artificial suction cups for use in wet environments. We conclude that the properties of the common elastomers that are generally used in soft robotics are quite dissimilar to the properties of biological suckers.

  10. Fatigue and mechanical properties of nickel-titanium endodontic instruments.

    PubMed

    Kuhn, Grégoire; Jordan, Laurence

    2002-10-01

    Shape memory alloys are increasingly used in superelastic conditions under complex cyclic deformation situations. In these applications, it is very difficult to predict the service life based on the theoretical law. In the present work, fatigue properties of NiTi engine-driven rotary files have been characterized by using differential scanning calorimetry (DSC) and mechanical testing (bending). The DSC technique was used to measure precise transformation. The degree of deformation by bending was studied with combined DSC and mechanical property measurements. In these cold-worked files, the high dislocation density influences the reorientation processes and the crack growth. Some thermal treatments are involved in promoting some changes in the mechanical properties and transformation characteristics. Annealing around 400 degrees C shows good results; the recovery allows a compromise between an adequate density for the R-Phase germination and a low density to limit the brittleness of these instruments. In clinical usage, it is important to consider different canal shapes. It could be proposed that only few cycles of use is safe for very curved canals but to follow the manufacturer's advise for straight canals. PMID:12398171

  11. Fatigue and mechanical properties of nickel-titanium endodontic instruments.

    PubMed

    Kuhn, Grégoire; Jordan, Laurence

    2002-10-01

    Shape memory alloys are increasingly used in superelastic conditions under complex cyclic deformation situations. In these applications, it is very difficult to predict the service life based on the theoretical law. In the present work, fatigue properties of NiTi engine-driven rotary files have been characterized by using differential scanning calorimetry (DSC) and mechanical testing (bending). The DSC technique was used to measure precise transformation. The degree of deformation by bending was studied with combined DSC and mechanical property measurements. In these cold-worked files, the high dislocation density influences the reorientation processes and the crack growth. Some thermal treatments are involved in promoting some changes in the mechanical properties and transformation characteristics. Annealing around 400 degrees C shows good results; the recovery allows a compromise between an adequate density for the R-Phase germination and a low density to limit the brittleness of these instruments. In clinical usage, it is important to consider different canal shapes. It could be proposed that only few cycles of use is safe for very curved canals but to follow the manufacturer's advise for straight canals.

  12. Influence of mechanical properties on the combustion of propellants

    NASA Technical Reports Server (NTRS)

    Kumar, R. N.; Culick, F. E. C.

    1973-01-01

    Experimental study of the effects of minor compositional variables upon the combustion behavior of composite solid propellants. More specifically, it was attempted to determine the influence of ingredients that improve the mechanical properties upon the oscillatory combustion characteristics. Tests were carried out in the familiar Crawford bomb, a low-pressure L-star burner, and a high-pressure T-burner. Two families of propellants were investigated; each family consists of two propellants with a minor compositional variation between them. In the family that shows a decreasing (steady state) pressure index (n) with increasing pressures, all of the combustion characteristics are found to be very similar although the mechanical properties are widely different. In the other family, which shows an increasing n with increasing pressures, unmistakable differences are found between the two propellants in the low-pressure L-star instability behavior (along with the differences in the mechanical properties), while the other combustion characteristics are almost identical. The results are interpreted to be consistent with a theory that highlights the importance of condensed phase heat-transfer effects.

  13. Reconstruction of Sedimentary Rock Based on MechanicalProperties

    SciTech Connect

    Jin, Guodong; Patzek, Tad W.; Silin, Dmitry B.

    2004-05-04

    We describe a general, physics-based approach to numericalreconstruction of the geometrical structure and mechanical properties ofnatural sedimentary rock in 3D. Our procedure consists of three mainsteps: sedimentation, compaction, and diagenesis, followed by theverification of rock mechanical properties. The dynamic geologicprocesses of grain sedimentation and compaction are simulated by solvinga dimensionless form of Newton's equations of motion for an ensemble ofgrains. The diagenetic rock transformation is modeled using a cementationalgorithm, which accounts for the effect of rock grain size on therelative rate of cement overgrowth. Our emphasis is on unconsolidatedsand and sandstone. The main input parameters are the grain sizedistribution, the final rock porosity, the type and amount of cement andclay minerals, and grain mechanical properties: the inter-grain frictioncoefficient, the cement strength, and the grain stiffness moduli. We usea simulated 2D Fontainebleau sandstone to obtain the grain mechanicalproperties. This Fontainebleau sandstone is also used to study theinitiation, growth, and coalescence of micro-cracks under increasingvertical stress. The box fractal dimension of the micro-crackdistribution, and its variation with the applied stress areestimated.

  14. Bulk Mechanical Properties of Single Walled Carbon Nanotube Electrodes

    NASA Astrophysics Data System (ADS)

    Giarra, Matthew; Landi, Brian; Cress, Cory; Raffaelle, Ryne

    2007-03-01

    The unique properties of single walled carbon nanotubes (SWNTs) make them especially well suited for use as electrodes in power devices such as lithium ion batteries, hydrogen fuel cells, solar cells, and supercapacitors. The performances of such devices are expected to be influenced, at least in part, by the mechanical properties of the SWNTs used in composites or in stand alone ``papers.'' Therefore, the elastic moduli and ultimate tensile strengths of SWNT papers were measured as functions of temperature, SWNT purity, SWNT length, and SWNT bundling. The SWNTs used to produce the papers were synthesized in an alexandrite laser vaporization reactor at 1100^oC and purified using conventional acid-reflux conditions. Characterization of the SWNTs was performed using SEM, BET, TGA, and optical and Raman spectroscopy. The purified material was filtered and dried to yield papers of bundled SWNTs which were analyzed using dynamic mechanical analysis (DMA). It was observed that the mechanical properties of acid-refluxed SWNT papers were significantly improved by controlled thermal oxidation and strain-hardening. Elastic moduli of SWNT papers were measured between 3 and 6 GPa. Ultimate (breaking) tensile stresses were measured between 45 and 90 MPa at 1-3% strain. These results and their implications in regard to potential applications in power devices will be discussed.

  15. Dielectric breakdown properties of hot SF{sub 6}/He mixtures predicted from basic data

    SciTech Connect

    Wang, Weizong; Tu, Xin; Mei, Danhua; Rong, Mingzhe

    2013-11-15

    Sulfur hexafluoride (SF{sub 6}) gas has a quite high global warming potential and hence it is required that applying any substitute for SF{sub 6} gas. Much interest in the use of a mixture of helium and SF{sub 6} as arc quenching medium was investigated indicating a higher recovery performance of arc interruption than that of pure SF{sub 6}. It is known that the electrical breakdown in a circuit breaker after arc interruption occurs in a hot gas environment, with a complicated species composition because of the occurrence of dissociation and other reactions. The likelihood of breakdown relies on the electron interactions with all these species. The critical reduced electric field strength (the field at which breakdown can occur, relative to the number density) of hot SF{sub 6}/He mixtures related to the dielectric recovery phase of a high voltage circuit breaker is calculated in the temperature range from 300 K to 3500 K. The critically reduced electric field strength of these mixtures was obtained by balancing electron generation and loss mechanisms. These were evaluated using the electron energy distribution function derived from the Boltzmann transport equation under the two-term approximation. Good agreement was found between calculations for pure hot SF{sub 6} and pure hot He and experimental results and previous calculations. The addition of He to SF{sub 6} was found to decrease the critical reduced electric field strength in the whole temperature range due to a lack of electron impact attachment process for helium regardless its high ionization potential. This indicates that not the behaviour of dielectric strength but possibly the higher energy dissipation capability caused mainly by light mass and high specific heat as well as thermal conductivity of atomic helium contributes most to a higher dielectric recovery performance of arc interruption for SF{sub 6}/He mixtures.

  16. Dielectric breakdown properties of hot SF6/He mixtures predicted from basic data

    NASA Astrophysics Data System (ADS)

    Wang, Weizong; Tu, Xin; Mei, Danhua; Rong, Mingzhe

    2013-11-01

    Sulfur hexafluoride (SF6) gas has a quite high global warming potential and hence it is required that applying any substitute for SF6 gas. Much interest in the use of a mixture of helium and SF6 as arc quenching medium was investigated indicating a higher recovery performance of arc interruption than that of pure SF6. It is known that the electrical breakdown in a circuit breaker after arc interruption occurs in a hot gas environment, with a complicated species composition because of the occurrence of dissociation and other reactions. The likelihood of breakdown relies on the electron interactions with all these species. The critical reduced electric field strength (the field at which breakdown can occur, relative to the number density) of hot SF6/He mixtures related to the dielectric recovery phase of a high voltage circuit breaker is calculated in the temperature range from 300 K to 3500 K. The critically reduced electric field strength of these mixtures was obtained by balancing electron generation and loss mechanisms. These were evaluated using the electron energy distribution function derived from the Boltzmann transport equation under the two-term approximation. Good agreement was found between calculations for pure hot SF6 and pure hot He and experimental results and previous calculations. The addition of He to SF6 was found to decrease the critical reduced electric field strength in the whole temperature range due to a lack of electron impact attachment process for helium regardless its high ionization potential. This indicates that not the behaviour of dielectric strength but possibly the higher energy dissipation capability caused mainly by light mass and high specific heat as well as thermal conductivity of atomic helium contributes most to a higher dielectric recovery performance of arc interruption for SF6/He mixtures.

  17. Mechanical properties and failure behaviors of the interface of hybrid graphene/hexagonal boron nitride sheets

    PubMed Central

    Ding, Ning; Chen, Xiangfeng; Wu, Chi-Man Lawrence

    2016-01-01

    Hybrid graphene/h-BN sheet has been fabricated recently and verified to possess unusual physical properties. During the growth process, defects such as vacancies are unavoidably present at the interface between graphene and h-BN. In the present work, typical vacancy defects, which were located at the interface between graphene and h-BN, were studied by density functional theory. The interface structure, mechanical and electronic properties, and failure behavior of the hybrid graphene/h-BN sheet were investigated and compared. The results showed that the formation energy of the defective graphene/h-BN interface basically increased with increasing inflection angles. However, Young’s modulus for all graphene/h-BN systems studied decreased with the increase in inflection angles. The intrinsic strength of the hybrid graphene/h-BN sheets was affected not only by the inflection angles, but also by the type of interface connection and the type of defects. The energy band structure of the hybrid interface could be tuned by applying mechanical strain to the systems. These results demonstrated that vacancies introduced significant effects on the mechanical and electronic properties of the hybrid graphene/h-BN sheet. PMID:27527371

  18. Influence of Water Content on Mechanical Properties of Rock in Both Saturation and Drying Processes

    NASA Astrophysics Data System (ADS)

    Zhou, Zilong; Cai, Xin; Cao, Wenzhuo; Li, Xibing; Xiong, Cheng

    2016-08-01

    Water content has a pronounced influence on the properties of rock materials, which is responsible for many rock engineering hazards, such as landslides and karst collapse. Meanwhile, water injection is also used for the prevention of some engineering disasters like rock-bursts. To comprehensively investigate the effect of water content on mechanical properties of rocks, laboratory tests were carried out on sandstone specimens with different water contents in both saturation and drying processes. The Nuclear Magnetic Resonance technique was applied to study the water distribution in specimens with variation of water contents. The servo-controlled rock mechanics testing machine and Split Hopkinson Pressure Bar technique were used to conduct both compressive and tensile tests on sandstone specimens with different water contents. From the laboratory tests, reductions of the compressive and tensile strength of sandstone under static and dynamic states in different saturation processes were observed. In the drying process, all of the saturated specimens could basically regain their mechanical properties and recover its strength as in the dry state. However, for partially saturated specimens in the saturation and drying processes, the tensile strength of specimens with the same water content was different, which could be related to different water distributions in specimens.

  19. Mechanical properties and failure behaviors of the interface of hybrid graphene/hexagonal boron nitride sheets

    NASA Astrophysics Data System (ADS)

    Ding, Ning; Chen, Xiangfeng; Wu, Chi-Man Lawrence

    2016-08-01

    Hybrid graphene/h-BN sheet has been fabricated recently and verified to possess unusual physical properties. During the growth process, defects such as vacancies are unavoidably present at the interface between graphene and h-BN. In the present work, typical vacancy defects, which were located at the interface between graphene and h-BN, were studied by density functional theory. The interface structure, mechanical and electronic properties, and failure behavior of the hybrid graphene/h-BN sheet were investigated and compared. The results showed that the formation energy of the defective graphene/h-BN interface basically increased with increasing inflection angles. However, Young’s modulus for all graphene/h-BN systems studied decreased with the increase in inflection angles. The intrinsic strength of the hybrid graphene/h-BN sheets was affected not only by the inflection angles, but also by the type of interface connection and the type of defects. The energy band structure of the hybrid interface could be tuned by applying mechanical strain to the systems. These results demonstrated that vacancies introduced significant effects on the mechanical and electronic properties of the hybrid graphene/h-BN sheet.

  20. Acidic and basic properties of zeolite-containing cracking catalyst in the process of butene-1 isomerization

    NASA Astrophysics Data System (ADS)

    Mursalova, L. A.; Guseinova, E. A.; Adzhamov, K. Yu.

    2016-08-01

    The process of butene-1 isomerization in the presence of two groups of samples of zeolite-containing catalyst (ZCC) that earlier participated in the traditional and oxidative catalytic cracking of vacuum gasoil is investigated. It is established that the nature of the reaction mixture and conditions of the cracking process are key factors in forming the acidic and basic properties of the catalyst. It is shown that the highest activity in the butene-1 isomerization into cis-/ trans-butene-2 is demonstrated by ZCC samples that participated in the oxidative catalytic cracking (oxycracking). It is suggested that the enhanced catalytic activity of this group of ZCC samples was related to the availability of acid-base centers in the form of radical-like oxygen along with protic- and aprotic-type acidic centers in the structure of the oxidative compaction products.

  1. Do Stretch Durations Affect Muscle Mechanical and Neurophysiological Properties?

    PubMed

    Opplert, J; Genty, J-B; Babault, N

    2016-08-01

    The aim of the study was to determine whether stretching durations influence acute changes of mechanical and neurophysiological properties of plantar flexor muscles. Plantar flexors of 10 active males were stretched in passive conditions on an isokinetic dynamometer. Different durations of static stretching were tested in 5 randomly ordered experimental trials (1, 2, 3, 4 and 10×30-s). Fascicle stiffness index, evoked contractile properties and spinal excitability (Hmax/Mmax) were examined before (PRE), immediately after (POST0) and 5 min after (POST5) stretching. No stretch duration effect was recorded for any variable. Moreover, whatever the stretching duration, stiffness index, peak twitch torque and rate of force development were significantly lower at POST0 and POST5 as compared to PRE (P<0.05). Electromechanical delay was longer at POST0 and POST5 as compared to PRE (P<0.05). Whatever the stretch duration, no significant changes of Hmax/Mmax ratio were recorded. In conclusion, 30 s of static stretching to maximum tolerated discomfort is sufficient enough to alter mechanical properties of plantar flexor muscles, but 10×30 s does not significantly affect these properties further. Stretching does not impair spinal excitability. PMID:27191211

  2. Measurement of the Mechanical Properties of Intact Collagen Fibrils

    NASA Astrophysics Data System (ADS)

    Mercedes, H.; Heim, A.; Matthews, W. G.; Koob, T.

    2006-03-01

    Motivated by the genetic disorder Ehlers-Danlos syndrome (EDS), in which proper collagen synthesis is interrupted, we are investigating the structural and mechanical properties of collagen fibrils. The fibrous glycoprotein collagen is the most abundant protein found in the human body and plays a key role in the extracellular matrix of the connective tissue, the properties of which are altered in EDS. We have selected as our model system the collagen fibrils of the sea cucumber dermis, a naturally mutable tissue. This system allows us to work with native fibrils which have their proteoglycan complement intact, something that is not possible with reconstituted mammalian collagen fibrils. Using atomic force microscopy, we measure, as a function of the concentration of divalent cations, the fibril diameter, its response to force loading, and the changes in its rigidity. Through these experiments, we will shed light on the mechanisms which control the properties of the sea cucumber dermis and hope to help explain the altered connective tissue extracellular matrix properties associated with EDS.

  3. Mechanical and thermophysical properties of rare-earth monopnictides

    NASA Astrophysics Data System (ADS)

    Bhalla, Vyoma; Singh, Devraj; Jain, Sushil Kumar

    2016-08-01

    The present paper addresses the temperature dependent elastic, mechanical and thermal properties of NaCl structure (B1 type) holmium monopnictides, HoX (X = N, P, As, Sb, Bi) computed using Coulomb and Born repulsive potentials extended up to second nearest neighbors. The second-order elastic constants (SOECs) of single crystals HoX are calculated as a function of temperature in the range 0-500K. The compounds under study are found to be brittle in nature. Beside these calculations, the theoretical hardness has been obtained for various rare-earth monopnictides using the elastic properties in the polycrystalline approach. The obtained hardness values indicate HoN to be hard, but cannot be considered super hard. The anisotropic nature of the chosen single crystal is an important physical quantity in studying the directional dependent thermal properties such as Debye temperature and thermal conductivity computed using ultrasonic velocities along different crystallographic directions. The obtained results are discussed in correlation with mechanical and thermophysical properties of similar materials.

  4. Deterioration of Mechanical Properties of Discs in Chronically Inflamed TMJ

    PubMed Central

    Wang, X.D.; Cui, S.J.; Liu, Y.; Luo, Q.; Du, R.J.; Kou, X.X.; Zhang, J.N.; Zhou, Y.H.; Gan, Y.H.

    2014-01-01

    Temporomandibular joint (TMJ) discs frequently undergo degenerative changes in arthritis. However, the biomechanical properties of pathogenic discs remain to be explored. In this study, we evaluated the effects of chronic inflammation on the biomechanical properties of TMJ discs in rats. Chronic inflammation of TMJs was induced by double intra-articular injections of complete Freund’s adjuvant for 5 weeks, and biomechanical properties and ultrastructure of the discs were examined by mechanical testing, scanning electron microscopy, and transmission electron microscopy. The instantaneous compressive moduli of the anterior and posterior bands of discs in inflamed TMJs were decreased significantly compared with those in the control group. The instantaneous tensile moduli of the discs of inflamed TMJs also showed significant decreases in both the anterior-posterior and mesial-lateral directions. The relaxation moduli of the discs of inflamed TMJs showed nearly the same tendency as the instantaneous moduli. The surfaces of the discs of inflamed TMJs became rough and porous due to the loss of the superficial gel-like stratum, with many collagen fibers exposed and degradation of the sub-superficial collagen fibrils. Our results suggested that chronic inflammation of TMJ could lead to deterioration of mechanical properties and alteration of disc ultrastructure, which might contribute to TMJ disc displacement. PMID:25266714

  5. Self-cleaning and mechanical properties of modified white cement with nanostructured TiO2.

    PubMed

    Khataee, R; Heydari, V; Moradkhannejhad, L; Safarpour, M; Joo, S W

    2013-07-01

    In the present study, self-cleaning and mechanical properties of white Portland cement by addition of commercial available TiO2 nanoparticles with the average particle size of 80 nm were investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET were used to characterize TiO2 nanoparticles. For determination of self-cleaning properties of TiO2-modified white cement, colorimetric tests in decolorization of C.I. Basic Red 46 (BR46) in comparison to unmodified cement samples was applied. The results indicated that with increasing the amount of TiO2 nanoparticles in modified cement, self-cleaning property of the samples increased. The mechanical properties of TiO2-modified and unmodified cement samples, such as time of setting of hydraulic cement, compressive strength of hydraulic cement mortar and flexural strength of hydraulic cement mortar were examined. The results indicated that addition of TiO2 nanoparticles up to maximum replacement level of 1.0% improved compressive and flexural strength and decreased its setting time.

  6. One of the distinctive properties of ionic liquids over molecular solvents and inorganic salts: enhanced basicity stemming from the electrostatic environment and "free" microstructure.

    PubMed

    Yang, Qiwei; Xing, Huabin; Bao, Zongbi; Su, Baogen; Zhang, Zhiguo; Yang, Yiwen; Dai, Sheng; Ren, Qilong

    2014-04-01

    The basicity of ionic liquids (ILs) underlies many important IL-based processes including the dissolution and conversion of cellulose, the capture of CO2, and metal catalysis. In this work, we have disclosed the nature of the basicity of ILs, i.e., the difference between the basicity of IL and the basicity of the molecular solvent and inorganic salt, through a quantitative electrostatic and electronic analysis of the molecular surface for the first time. The results reveal one of the distinctive properties of ILs (enhanced basicity over molecular solvents and inorganic salts with the same basic site) stemming from their special electrostatic environment and microstructure. The enhancement is significant, from either the electrostatic aspect or the covalent aspect of basicity. The peculiar electrostatic environment of ILs leads to stronger basicity than similar molecular solvents, and the relatively freer microstructure of ILs contributes to the enhancement of basicity over their inorganic analogues. These results are highly instructive for better understanding the unique value of ILs and designing novel ILs to improve the efficiency of basicity-related processes. PMID:24620779

  7. Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties.

    PubMed

    Israël, I; Grasso, R; Georges-Francois, P; Tsuzuku, T; Berthoz, A

    1997-06-01

    According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by

  8. Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties.

    PubMed

    Israël, I; Grasso, R; Georges-Francois, P; Tsuzuku, T; Berthoz, A

    1997-06-01

    According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by

  9. Mechanical Properties of Mineralized Collagen Fibrils As Influenced By Demineralization

    SciTech Connect

    Balooch, M.; Habelitz, S.; Kinney, J.H.; Marshall, S.J.; Marshall, G.W.

    2009-05-11

    Dentin and bone derive their mechanical properties from a complex arrangement of collagen type-I fibrils reinforced with nanocrystalline apatite mineral in extra- and intrafibrillar compartments. While mechanical properties have been determined for the bulk of the mineralized tissue, information on the mechanics of the individual fibril is limited. Here, atomic force microscopy was used on individual collagen fibrils to study structural and mechanical changes during acid etching. The characteristic 67 nm periodicity of gap zones was not observed on the mineralized fibril, but became apparent and increasingly pronounced with continuous demineralization. AFM-nanoindentation showed a decrease in modulus from 1.5 GPa to 50 MPa during acid etching of individual collagen fibrils and revealed that the modulus profile followed the axial periodicity. The nanomechanical data, Raman spectroscopy and SAXS support the hypothesis that intrafibrillar mineral etches at a substantially slower rate than the extrafibrillar mineral. These findings are relevant for understanding the biomechanics and design principles of calcified tissues derived from collagen matrices.

  10. Mechanical Properties of Type IV Pili in P. Aeruginosa

    NASA Astrophysics Data System (ADS)

    Lu, Shun; Touhami, Ahmed; Scheurwater, Edie; Harvey, Hanjeong; Burrows, Lori; Dutcher, John

    2009-03-01

    Type IV pili (Tfp) are thin flexible protein filaments that extend from the cell membrane of bacteria such as Pseudomonas aeruginosa and Neisseria gonorrhoeae. The mechanical properties of Tfp are of great importance since they allow bacteria to interact with and colonize various surfaces. In the present study, we have used atomic force microscopy (AFM) for both imaging and pulling on Tfp from P. aeruginosa (PAO1) and from its PilA, PilT, and FliC mutants. A single pilus filament was mechanically stretched and the resulting force-extension profiles were fitted using the worm-like-chain (WLC) model. The statistical distributions obtained for contour length, persistence length, and number of pili per bacteria pole, were used to evaluate the mechanical properties of a single pilus and the biogenesis functions of different proteins (PilA, PilT) involved in its assembly and disassembly. Importantly, the persistence length value of ˜ 1 μm measured in the present study, which is consistent with the curvature of the pili observed in our AFM images, is significantly lower than the value of 5 μm reported earlier by Skerker et al. (1). Our results shed new light on the role of mechanical forces that mediate bacteria-surface interactions and biofilm formation. 1- J.M. Skerker and H.C. Berg, Proc. Natl. Acad. Sci. USA, 98, 6901-6904 (2001).

  11. The Upper Band of the Subscapularis Tendon in the Rat has Altered Mechanical and Histologic Properties

    PubMed Central

    Thomas, Stephen J.; Miller, Kristin S.; Soslowsky, Louis J.

    2011-01-01

    Hypothesis/Background The subscapularis is an important mover and stabilizer of the glenohumeral joint and since the advent of shoulder arthroscopy, partial tears are found in 43% of rotator cuff patients. While partial tears to the upper band occur more commonly, little is known about the structure and mechanical behavior of the individual bands. Therefore, the objective of this study was to measure tensile mechanical properties, corresponding collagen fiber alignment, and histology in the upper and lower bands of the rat subscapularis tendon. Materials and Methods Thirty, adult Sprague-Dawley rats were euthanized and subscapularis tendons dissected out for mechanical, organization (n = 24), and histologic assessment (n = 6). Collagen organization was measured with a custom device during mechanical testing. Results Linear-region modulus at the insertion site was significantly lower in the upper band compared to the lower band while no differences were found at the midsubstance location. The upper band was found to be significantly less aligned and demonstrated a more rounded cell shape than the lower band at the insertion site. Discussion This study demonstrated that the two bands of the subscapularis tendon have differential mechanical, organizational, and histological properties. This suggests that a functional deficit exists to the upper band of the subscapularis and may be contributing to the prevalence of partial subscapularis tears. Conclusions Clinicians should be aware that the upper band of the subscapularis tendon may be at higher risk of developing tears due to the decreased mechanical properties and a more disorganized collagen fiber distribution. Level of Evidence Basic Science Study, Biomechanics, Animal Model. PMID:22484390

  12. Time-Temperature Superposition Applied to PBX Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Thompson, Darla; Deluca, Racci

    2011-06-01

    The use of plastic-bonded explosives (PBXs) in weapon applications requires a certain level of structural/mechanical integrity. Uniaxial tension and compression experiments characterize the mechanical response of materials over a wide range of temperatures and strain rates, providing the basis for predictive modeling in more complex geometries. After years of data collection on a wide variety of PBX formulations, we have applied time-temperature superposition principles to a mechanical properties database which includes PBX 9501, PBX 9502, PBXN-110, PBXN-9, and HPP (propellant). The results of quasi-static tension and compression, SHPB compression, and cantilever DMA are compared. Time-temperature relationships of maximum stress and corresponding strain values are analyzed in addition to the more conventional analysis of modulus. Our analysis shows adherence to the principles of time-temperature superposition and correlations of mechanical response to the binder glass transition and specimen density. Direct ties relate time-temperature analysis to the underlying basis of existing PBX mechanical models (ViscoSCRAM). Results suggest that, within limits, mechanical response can be predicted at conditions not explicitly measured. LA-UR 11-01096.

  13. Nondestructive evaluation of hydrogel mechanical properties using ultrasound

    PubMed Central

    Walker, Jason M.; Myers, Ashley M.; Schluchter, Mark D.; Goldberg, Victor M.; Caplan, Arnold I.; Berilla, Jim A.; Mansour, Joseph M.; Welter, Jean F.

    2012-01-01

    The feasibility of using ultrasound technology as a noninvasive, nondestructive method for evaluating the mechanical properties of engineered weight-bearing tissues was evaluated. A fixture was designed to accurately and reproducibly position the ultrasound transducer normal to the test sample surface. Agarose hydrogels were used as phantoms for cartilage to explore the feasibility of establishing correlations between ultrasound measurements and commonly used mechanical tissue assessments. The hydrogels were fabricated in 1–10% concentrations with a 2–10 mm thickness. For each concentration and thickness, six samples were created, for a total of 216 gel samples. Speed of sound was determined from the time difference between peak reflections and the known height of each sample. Modulus was computed from the speed of sound using elastic and poroelastic models. All ultrasonic measurements were made using a 15 MHz ultrasound transducer. The elastic modulus was also determined for each sample from a mechanical unconfined compression test. Analytical comparison and statistical analysis of ultrasound and mechanical testing data was carried out. A correlation between estimates of compressive modulus from ultrasonic and mechanical measurements was found, but the correlation depended on the model used to estimate the modulus from ultrasonic measurements. A stronger correlation with mechanical measurements was found using the poroelastic rather than the elastic model. Results from this preliminary testing will be used to guide further studies of native and engineered cartilage. PMID:21773854

  14. Mechanical properties of graphene on deformable patterned substrates: Experimental studies

    NASA Astrophysics Data System (ADS)

    Scharfenberg, S.; Chialvo, C.; Rocklin, D. Z.; Weaver, R.; Goldbart, P. M.; Mason, N.

    2010-03-01

    The mechanical properties of graphene can strongly influence its electronic behavior, and are relevant for implementing novel nano-mechanical devices. In this talk we present results on the mechanical behavior of few-layered graphene (FLG) placed on a patterned rubbery surface. Samples of FLG, with thicknesses ranging from 1-7 atomic layers, were deposited on micro-scale grooved polydimethylsiloxane (PDMS) substrates. AFM imaging techniques were then used to study the surface deformations, and to perform thickness measurements on the samples. AFM phase-imaging shows that the graphene strongly adheres to the substrate. The graphene also substantially deforms the substrate, with thicker pieces causing greater deformation. The results are discussed in the context of a linear elasticity theory (detailed in an accompanying paper) which can be used to explain the data and place bounds on the various interface strengths.

  15. 'Long-Cell Action' Corrosion: A Basic Mechanism Hidden Behind Components Degradation Issues in Nuclear Power Plants

    SciTech Connect

    Genn Saji

    2006-07-01

    In spite of industries' effort over the last 40 years, corrosion-related issues continue to be one of the largest unresolved problems for nuclear power plants worldwide. There are several types of strange corrosion phenomena from the point of view of our current understanding of corrosion science established in other fields. Some of these are IGSCC, PWSCC, AOA, and FAC (Erosion-Corrosion). Through studying and coping with diverse corrosion phenomena, the author believes that they share a common basis with respect to the assumed corrosion mechanism (e.g., 'local cell action' hypothesis). In general, local cell action is rarely severe since it produces a fairly uniform corrosion. The 'long cell action' that transports electrons through structures far beyond the region of local cell corrosion activities has been identified as a basic mechanism in soil corrosion. If this mechanism is assumed in nuclear power plants, the structure becomes anodic in the area where the potential is less positive and cathodic where this potential is more positive. Metallic ions generated at anodic corrosion sites are transported to remote cathodic sites through the circulation of water and deposits as corrosion products. The SCC, FAC (E-C) and PWSCC occur in the anodic sites as the structure itself acts as a short-circuiting conductor between the two sites, the action is similar to a galvanic cell but in a very large scale. This situation is the same as a battery that has been short-circuited at the terminals. No apparent external potential difference exists between the two electrodes, but an electrochemical reaction is still taking place inside the battery cell with a large internal short current. In this example what is important is the potential difference between the local coolant and the surface of the structural material. Long cell action corrosion is likely enhancing the local cell action's anodic corrosion activities, such as SCC, FAC/E-C, and PWSCC. It tends to be more hazardous

  16. Properties of M31 . I. Dust. Basic properties and a discussion about age-dependent dust heating

    NASA Astrophysics Data System (ADS)

    Montalto, M.; Seitz, S.; Riffeser, A.; Hopp, U.; Lee, C.-H.; Schönrich, R.

    2009-11-01

    Aims: Observations acquired by the Spitzer Space Telescope and improvements to theoretical modeling of dust emission properties are used to discuss the distribution of dust and its characteristics in the closest neighbor spiral galaxy M31. These data are then used with GALEX FUV, NUV, and SDSS images to study the age dependence of the dust heating process. Methods: Spitzer IRAC/MIPS maps of M31 were matched together and compared to dust emission models allowing us to constrain the dust mass, the intensity of the mean radiation field, the abundance of polycyclic aromatic hydrocarbon (PAH) particles. The total infrared emission (TIR) was analyzed as a function of UV and optical colors and compared to predictions of models that consider age-dependent dust heating. Results: We demonstrate that cold-dust component emission dominates the infrared spectral energy distribution of M31. The mean intensity of the radiation field heating the dust is low (typically U < 2, where U = 1 is the value in the solar neighborhood). Because of a lack of submillimeter observations, the dust mass (M_dust) is only weakly constrained by the infrared spectrum, but we derived a lower limit of M_dust ≳ 1.1 × 107 M⊙ with a best-fit model value of M_dust = 7.6 × 107 M⊙, in good agreement with expectations from CO and HI measurements. Across the spiral-ring structure of M31, we show that a fraction >3% of the total dust mass is in PAHs. UV and optical colors are correlated with the total infrared to far ultraviolet (TIR/FUV) ratios in ~670 pc-sized regions over the disk of M31, although deviating from the relationship between infrared excess and ultraviolet spectral slope (referred as IRX-β relationship) for starburst galaxies. In particular, redder regions have lower values of the TIR/FUV ratio for a fixed color. Considering the predictions of models that account for the dust-heating age dependence, we found that in 83% of the regions analyzed across the 10 kpc ring, more than 50% of

  17. Mechanical and hydraulic properties of rocks related to induced seismicity

    USGS Publications Warehouse

    Witherspoon, P.A.; Gale, J.E.

    1977-01-01

    Witherspoon, P.A. and Gale, J.E., 1977. Mechanical and hydraulic properties of rocks related to induced seismicity. Eng. Geol., 11(1): 23-55. The mechanical and hydraulic properties of fractured rocks are considered with regard to the role they play in induced seismicity. In many cases, the mechanical properties of fractures determine the stability of a rock mass. The problems of sampling and testing these rock discontinuities and interpreting their non-linear behavior are reviewed. Stick slip has been proposed as the failure mechanism in earthquake events. Because of the complex interactions that are inherent in the mechanical behavior of fractured rocks, there seems to be no simple way to combine the deformation characteristics of several sets of fractures when there are significant perturbations of existing conditions. Thus, the more important fractures must be treated as individual components in the rock mass. In considering the hydraulic properties, it has been customary to treat a fracture as a parallel-plate conduit and a number of mathematical models of fracture systems have adopted this approach. Non-steady flow in fractured systems has usually been based on a two-porosity model, which assumes the primary (intergranular) porosity contributes only to storage and the secondary (fracture) porosity contributes only to the overall conductivity. Using such a model, it has been found that the time required to achieve quasi-steady state flow in a fractured reservoir is one or two orders of magnitude greater than it is in a homogeneous system. In essentially all of this work, the assumption has generally been made that the fractures are rigid. However, it is clear from a review of the mechanical and hydraulic properties that not only are fractures easily deformed but they constitute the main flow paths in many rock masses. This means that one must consider the interaction of mechanical and hydraulic effects. A considerable amount of laboratory and field data is now

  18. Genetic Deletion of TREK-1 or TWIK-1/TREK-1 Potassium Channels does not Alter the Basic Electrophysiological Properties of Mature Hippocampal Astrocytes In Situ

    PubMed Central

    Du, Yixing; Kiyoshi, Conrad M.; Wang, Qi; Wang, Wei; Ma, Baofeng; Alford, Catherine C.; Zhong, Shiying; Wan, Qi; Chen, Haijun; Lloyd, Eric E.; Bryan, Robert M. Jr.; Zhou, Min

    2016-01-01

    We have recently shown that a linear current-to-voltage (I-V) relationship of membrane conductance (passive conductance) reflects the intrinsic property of K+ channels in mature astrocytes. While passive conductance is known to underpin a highly negative and stable membrane potential (VM) essential for the basic homeostatic function of astrocytes, a complete repertoire of the involved K+ channels remains elusive. TREK-1 two-pore domain K+ channel (K2P) is highly expressed in astrocytes, and covalent association of TREK-1 with TWIK-1, another highly expressed astrocytic K2P, has been reported as a mechanism underlying the trafficking of heterodimer TWIK-1/TREK-1 channel to the membrane and contributing to astrocyte passive conductance. To decipher the individual contribution of TREK-1 and address whether the appearance of passive conductance is conditional to the co-expression of TWIK-1/TREK-1 in astrocytes, TREK-1 single and TWIK-1/TREK-1 double gene knockout mice were used in the present study. The relative quantity of mRNA encoding other astrocyte K+ channels, such as Kir4.1, Kir5.1, and TREK-2, was not altered in these gene knockout mice. Whole-cell recording from hippocampal astrocytes in situ revealed no detectable changes in astrocyte passive conductance, VM, or membrane input resistance (Rin) in either kind of gene knockout mouse. Additionally, TREK-1 proteins were mainly located in the intracellular compartments of the hippocampus. Altogether, genetic deletion of TREK-1 alone or together with TWIK-1 produced no obvious alteration in the basic electrophysiological properties of hippocampal astrocytes. Thus, future research focusing on other K+ channels may shed light on this long-standing and important question in astrocyte physiology. PMID:26869883

  19. An Experimental Investigation of Shale Mechanical Properties Through Drained and Undrained Test Mechanisms

    NASA Astrophysics Data System (ADS)

    Islam, Md. Aminul; Skalle, Paal

    2013-11-01

    Shale mechanical properties are evaluated from laboratory tests after a complex workflow that covers tasks from sampling to testing. Due to the heterogeneous nature of shale, it is common to obtain inconsistent test results when evaluating the mechanical properties. In practice, this variation creates errors in numerical modeling when test results differ significantly, even when samples are from a similar core specimen. This is because the fundamental models are based on the supplied test data and a gap is, therefore, always observed during calibration. Thus, the overall goal of this study was to provide additional insight regarding the organization of the non-linear model input parameters in borehole simulations and to assist other researchers involved in the rock physics-related research fields. To achieve this goal, the following parallel activities were carried out: (1) perform triaxial testing with different sample orientations, i.e., 0°, 45°, 60°, and 90°, including the Brazilian test and CT scans, to obtain a reasonably accurate description of the anisotropic properties of shale; (2) apply an accurate interpretative method to evaluate the elastic moduli of shale; (3) evaluate and quantify the mechanical properties of shale by accounting for the beddings plane, variable confinement pressures, drained and undrained test mechanisms, and cyclic versus monotonic test effects. The experimental results indicate that shale has a significant level of heterogeneity. Postfailure analysis confirmed that the failure plane coincides nicely with the weak bedding plane. The drained Poisson’s ratios were, on average, 40 % or lower than the undrained rates. The drained Young’s modulus was approximately 48 % that of the undrained value. These mechanical properties were significantly impacted by the bedding plane orientation. Based on the Brazilian test, the predicted tensile strength perpendicular to the bedding plane was 12 % lower than the value obtained using the

  20. Size effects on mechanical and thermal properties of thin films

    NASA Astrophysics Data System (ADS)

    Alam, Md Tarekul

    Materials, from electronic to structural, exhibit properties that are sensitive to their composition and internal microstructures such as grain and precipitate sizes, crystalline phases, defects and dopants. Therefore, the research trend has been to obtain fundamental understanding in processing-structure-properties to develop new materials or new functionalities for engineering applications. The advent of nanotechnology has opened a new dimension to this research area because when material size is reduced to nanoscale, properties change significantly from the bulk values. This phenomenon expands the problem to 'size-processing-structure-propertiesfunctionalities'. The reinvigorated research for the last few decades has established size dependency of the material properties such as thermal conductivity, Young's modulus and yield strength, electrical resistivity, photo-conductance etc. It is generally accepted that classical physical laws can be used to scale down the properties up to 25-50 nm length-scale, below which their significant deviation or even breakdown occur. This dissertation probes the size effect from a different perspective by asking the question, if nanoscale size influences one physical domain, why it would not influence the coupling between two or more domains? Or in other words, if both mechanical and thermal properties are different at the nanoscale, can mechanical strain influence thermal conductivity? The hypothesis of size induced multi-domain coupling is therefore the foundation of this dissertation. It is catalyzed by the only few computational studies available in the literature while experimental validations have been non-existent owing to experimental challenges. The objective of this research is to validate this hypothesis, which will open a novel avenue to tune properties and functionalities of materials with the size induced multi-domain coupling. Single domain characterization itself is difficult at the nanoscale due to specimen

  1. The fundamental role of mechanical properties in the progression of cancer disease and inflammation

    NASA Astrophysics Data System (ADS)

    Mierke, Claudia Tanja

    2014-07-01

    The role of mechanical properties in cancer disease and inflammation is still underinvestigated and even ignored in many oncological and immunological reviews. In particular, eight classical hallmarks of cancer have been proposed, but they still ignore the mechanics behind the processes that facilitate cancer progression. To define the malignant transformation of neoplasms and finally reveal the functional pathway that enables cancer cells to promote cancer progression, these classical hallmarks of cancer require the inclusion of specific mechanical properties of cancer cells and their microenvironment such as the extracellular matrix as well as embedded cells such as fibroblasts, macrophages or endothelial cells. Thus, this review will present current cancer research from a biophysical point of view and will therefore focus on novel physical aspects and biophysical methods to investigate the aggressiveness of cancer cells and the process of inflammation. As cancer or immune cells are embedded in a certain microenvironment such as the extracellular matrix, the mechanical properties of this microenvironment cannot be neglected, and alterations of the microenvironment may have an impact on the mechanical properties of the cancer or immune cells. Here, it is highlighted how biophysical approaches, both experimental and theoretical, have an impact on the classical hallmarks of cancer and inflammation. It is even pointed out how these biophysical approaches contribute to the understanding of the regulation of cancer disease and inflammatory responses after tissue injury through physical microenvironmental property sensing mechanisms. The recognized physical signals are transduced into biochemical signaling events that guide cellular responses, such as malignant tumor progression, after the transition of cancer cells from an epithelial to a mesenchymal phenotype or an inflammatory response due to tissue injury. Moreover, cell adaptation to mechanical alterations, in

  2. Effect of diet on mechanical properties of horse's hair.

    PubMed

    Kania, Małgorzata; Mikołajewska, Dorota; Marycz, Krzysztof; Kobielarz, Magdalena

    2009-01-01

    The aim of this research was to assess the effect of diet supplementation with zinc and copper, in different chemical forms (organic and inorganic), on the mechanical properties of the hair of healthy English thoroughbred horses. Hairs were taken from 18 horses which had been fed with oats and hay for a period of 110 days. Twelve of the horses had been additionally given a daily dose of 700 g of highquality 44-ingredients Fohlengold St-Hippolyt muesli made by Muhle Ebert Dilheim. Six of them had received the muesli-containing organic zinc and copper (OS), while the other six horses had received the muesli-containing inorganic zinc and copper (IS). The mechanical properties of the hairs before and after the supplementation period were tested in a Synergie 100 (MTS) testing machine. Each of the hairs was loaded at a constant rate of 20 mm/min until rupture. Young modulus (E), breaking stress (Ru) and yield point (Rs) of the particular hairs were determined. No significant changes in the mechanical parameters were observed in the reference group in which the horses were fed with only oats and hay for the whole experimental period of 110 days. The supplementation of the diet with inorganic zinc and copper resulted in an increase in the elasticity and diameter of the hairs and in a simultaneous reduction in their strength. Whereas organic zinc and copper caused an increase in the elasticity and strength of the hairs and a simultaneous reduction in their diameter. It has been shown that the organic form of the supplemented trace zinc and copper (mainly copper) elements has a beneficial effect on the mechanical properties of the hairs since it results in an increase in both their elasticity and strength.

  3. Morphology, orientation, and mechanical properties of gelatin films

    SciTech Connect

    Blanton, T.N.; Tsou, A.H.

    1996-12-31

    Gelatin is a polypeptide derived from degradation and disorganization of collagen fibers and is the primary binder in photographic emulsions. Gelatin provides the mechanical integrity and strength to the photographic emulsion allowing for packaging, handling, and photofinishing operations. Gelatin films generated from aqueous-solution casting can exist in a semicrystalline or an amorphous state. When a gelatin solution is cooled below its helix-coil transition temperature, partial renaturation of gelatin to form triple helices can occur. The degree of renaturation in a coated film is dependent upon the drying temperature and the drying rate. During the drying process, gelatin crystals can be formed by lateral association of the triple helices through a mechanism of nucleation and growth of a fringed micelle structure. X-ray scattering techniques have been utilized to examine the morphology and orientation of gelatin films. Based on X-ray diffraction data, it is observed that aggregates of triple-helix rods lie parallel to the film plane but are symmetrically distributed within the film plane. Since a material`s physical and mechanical properties are related to its structure, it is necessary to understand and to characterize the morphological development in gelatin film formation. In this study, an X-ray diffractometer and pole figure goniometer were utilized to examine the structural development and orientation anisotropy in solid-state gelatin films. Also, in this study, the in-plane mechanical properties of a gelatin film were determined from a uniaxial tensile test, and the gelatin film properties in the thickness direction were extracted from an indentation test based on the finite element analysis of the indentation results using a viscoelastic material model.

  4. Mechanical properties of single electrospun drug-encapsulated nanofibres

    PubMed Central

    Chew, Sing Yian; Hufnagel, Todd C; Lim, Chwee Teck; Leong, Kam W

    2008-01-01

    The mechanical and structural properties of a surface play an important role in determining the morphology of attached cells, and ultimately their cellular functions. As such, mechanical and structural integrity are important design parameters for a tissue scaffold. Electrospun fibrous meshes are widely used in tissue engineering. When in contact with electrospun scaffolds, cells see the individual micro- or nanofibres as their immediate microenvironment. In this study, tensile testing of single electrospun nanofibres composed of poly(ε-caprolactone) (PCL), and its copolymer, poly(caprolactone-co-ethyl ethylene phosphate) (PCLEEP), revealed a size effect in the Young's modulus, E, and tensile strength, σT. Both strength and stiffness increase as the fibre diameter decreases from bulk (∼5 μm) into the nanometre region (200–300 nm). In particular, E and σT of individual PCL nanofibres were at least two-fold and an order of magnitude higher than that of PCL film, respectively. PCL films were observed to have more pronounced crystallographic texture than the nanofibres; however no difference in crystalline fraction, perfection, or texture was detected among the various fibres. When drugs were encapsulated into single PCLEEP fibres, mechanical properties were enhanced with 1–20 wt% of loaded retinoic acid, but weakened by 10–20 wt% of encapsulated bovine serum albumin. This understanding of the effect of size and drug and protein encapsulation on the mechanical properties of electrospun fibres may help in the optimization of tissue scaffold design that combines biochemical and biomechanical cues for tissue regeneration. PMID:19079553

  5. Mechanical properties of lunar regolith and lunar soil simulant

    NASA Technical Reports Server (NTRS)

    Perkins, Steven W.

    1989-01-01

    Through the Surveyor 3 and 7, and Apollo 11-17 missions a knowledge of the mechanical properties of Lunar regolith were gained. These properties, including material cohesion, friction, in-situ density, grain-size distribution and shape, and porosity, were determined by indirect means of trenching, penetration, and vane shear testing. Several of these properties were shown to be significantly different from those of terrestrial soils, such as an interlocking cohesion and tensile strength formed in the absence of moisture and particle cementation. To characterize the strength and deformation properties of Lunar regolith experiments have been conducted on a lunar soil simulant at various initial densities, fabric arrangements, and composition. These experiments included conventional triaxial compression and extension, direct tension, and combined tension-shear. Experiments have been conducted at low levels of effective confining stress. External conditions such as membrane induced confining stresses, end platten friction and material self weight have been shown to have a dramatic effect on the strength properties at low levels of confining stress. The solution has been to treat these external conditions and the specimen as a full-fledged boundary value problem rather than the idealized elemental cube of mechanics. Centrifuge modeling allows for the study of Lunar soil-structure interaction problems. In recent years centrifuge modeling has become an important tool for modeling processes that are dominated by gravity and for verifying analysis procedures and studying deformation and failure modes. Centrifuge modeling is well established for terrestrial enginering and applies equally as well to Lunar engineering. A brief review of the experiments is presented in graphic and outline form.

  6. Measurement of Mechanical Properties of Cantilever Shaped Materials

    PubMed Central

    Finot, Eric; Passian, Ali; Thundat, Thomas

    2008-01-01

    Microcantilevers were first introduced as imaging probes in Atomic Force Microscopy (AFM) due to their extremely high sensitivity in measuring surface forces. The versatility of these probes, however, allows the sensing and measurement of a host of mechanical properties of various materials. Sensor parameters such as resonance frequency, quality factor, amplitude of vibration and bending due to a differential stress can all be simultaneously determined for a cantilever. When measuring the mechanical properties of materials, identifying and discerning the most influential parameters responsible for the observed changes in the cantilever response are important. We will, therefore, discuss the effects of various force fields such as those induced by mass loading, residual stress, internal friction of the material, and other changes in the mechanical properties of the microcantilevers. Methods to measure variations in temperature, pressure, or molecular adsorption of water molecules are also discussed. Often these effects occur simultaneously, increasing the number of parameters that need to be concurrently measured to ensure the reliability of the sensors. We therefore systematically investigate the geometric and environmental effects on cantilever measurements including the chemical nature of the underlying interactions. To address the geometric effects we have considered cantilevers with a rectangular or circular cross section. The chemical nature is addressed by using cantilevers fabricated with metals and/or dielectrics. Selective chemical etching, swelling or changes in Young's modulus of the surface were investigated by means of polymeric and inorganic coatings. Finally to address the effect of the environment in which the cantilever operates, the Knudsen number was determined to characterize the molecule-cantilever collisions. Also bimaterial cantilevers with high thermal sensitivity were used to discern the effect of temperature variations. When appropriate

  7. The mechanical properties of human ribs in young adult.

    PubMed

    Pezowicz, Celina; Głowacki, Maciej

    2012-01-01

    A good understanding of thoracic biomechanics is important for complete examination and control of chest behaviour under conditions of physiological and pathological work, and under the impact of external forces leading to traumatic loading of the chest. The purpose of the study was to analyse the mechanical properties of human ribs obtained from individuals under the age of 25 with scoliosis deformation and to correlate them with geometric properties of ribs. Thirty three fragments of ribs (9th to 12th) were tested in three-point bending. Rib fragments were collected intraoperatively from female patients treated for scoliosis in the thoracic, thoracolumbar, and lumbar spine. The results were used to determine the maximum failure force, stiffness, and Young's modulus. A significant relationship was found between the age and elastic modulus of the ribs. The analysis was carried out for two age groups, i.e., between the ages of 10 and 15 and between the ages of 16 and 22, and statistically significant differences were obtained for Young's modulus (p = 0.0001) amounting to, respectively, 2.79 ± 1.34 GPa for the first group and 7.44 ± 2.85 GPa for the second group. The results show a significant impact of age on the mechanical properties of ribs.

  8. Dynamic and mechanical properties of supported lipid bilayers

    NASA Astrophysics Data System (ADS)

    Wu, Hsing-Lun; Tsao, Heng-Kwong; Sheng, Yu-Jane

    2016-04-01

    Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh2 and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts.

  9. Effects of prestresses on mechanical properties of isotropic graphite materials

    NASA Astrophysics Data System (ADS)

    Oku, T.; Kurumada, A.; Imamura, Y.; Kawamata, K.; Shiraishi, M.

    1998-10-01

    Graphite materials which are used for plasma facing components and other components are subjected to stresses due to the high heat flux from the fusion plasma. Some mechanical properties of graphite materials can change due to the prestresses. The property changes should be considered for the design of the plasma facing components. The purpose of this study is to examine the effects of prestresses on the mechanical properties of isotropic graphite materials. Compressive prestresses were applied to two kinds of isotropic fine-grained graphites (IG-430 and IG-11) at 298 K (both), 1873 K (IG-11), 2273 K (IG-11) and 2283 K (IG-430). As a result, the decrease in Young's modulus for IG-430 due to high-temperature prestressing was 56% which was much larger than the 6.4% that was due to prestressing at 298 K. The results for IG-11 were the same as those for IG-430 graphite. This finding was considered to be due primarily to a difference in degree of the preferred orientation of crystallites in the graphite on the basis of the Bacon anisotropy factor (BAF) obtained from X-ray diffraction measurement of the prestressed specimens. Furthermore, high-temperature compressive prestressing produced an increase in the strength of the isotropic graphite, although room temperature prestressing produced no such effect. The results obtained here suggest that the isotropic graphite which is subjected to high-temperature compressive stresses can become anisotropic in service.

  10. Local Mechanical Properties by Atomic Force Microscopy Nanoindentations

    NASA Astrophysics Data System (ADS)

    Tranchida, Davide; Piccarolo, Stefano

    The analysis of mechanical properties on a nanometer scale is a useful tool for combining information concerning texture organization obtained by microscopy with the properties of individual components. Moreover, this technique promotes the understanding of the hierarchical arrangement in complex natural materials as well in the case of simpler morphologies arising from industrial processes. Atomic Force Microscopy (AFM) can bridge morphological information, obtained with outstanding resolution, to local mechanical properties. When performing an AFM nanoindentation, the rough force curve, i.e., the plot of the voltage output from the photodiode vs. the voltage applied to the piezo-scanner, can be translated into a curve of the applied load vs. the penetration depth after a series of preliminary determinations and calibrations. However, the analysis of the unloading portion of the force curves collected for polymers does not lead to a correct evaluation of Young's modulus. The high slope of the unloading curves is not linked to an elastic behavior, as would be expected, but rather to a viscoelastic effect. This can be argued on the basis that the unloading curves are superimposed on the loading curves in the case of an ideal elastic behavior, as for rubbers, or generally in the case of materials with very short relaxation times. In contrast, when the relaxation time of the sample is close to or even much larger than the indentation time scale, very high slopes are recorded.

  11. Optical and mechanical properties of thermally evaporated fluoride thin films

    SciTech Connect

    Zhang, K.; Fahey, R.; Jasinski, D.; Scarpino, C.; Dziendziel, R.; Burger, S.; DePoy, D.

    1998-06-08

    As a result of health and safety issues surrounding the use of radioactive materials on coated optical components, there has been renewed interest in coating materials whose optical and mechanical properties approach those offered by their radioactive counterparts. Due to the radioactive nature of ThF{sub 4} and its widespread use in optical coatings, the coating industry is examining other low index and non-radioactive fluorides as possible alternatives. In this paper, the authors present the results of an experimental study on the optical and mechanical properties of thermally evaporated ThF{sub 4}, DyF{sub 3}, CeF{sub 3}, LiF, HfF{sub 4}, IRX, and IRB thin films, where the materials were deposited at different substrate temperatures. The objective is to examine this series of fluorides under comparable deposition conditions and with respect to such material properties as: n and k, film stress, and environmental stability. The optical constants of these fluorides were evaluated over the wavelength region from 1.0 {micro}m to 12.5 {micro}m.

  12. Dynamic and mechanical properties of supported lipid bilayers.

    PubMed

    Wu, Hsing-Lun; Tsao, Heng-Kwong; Sheng, Yu-Jane

    2016-04-21

    Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh(2) and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts. PMID:27389237

  13. Monte Carlo studies of the mechanical properties of biopolymers

    NASA Astrophysics Data System (ADS)

    Sadeghi, Sara

    Biopolymers are one of the main components of living systems. Their sequence dictates their structure that ultimately determines their function. Many factors play key mechanical roles in the cell and one of the most abundant biopolymers that is involved in such tasks is the class of coiled-coil proteins. Various theoretical and experimental studies have been done to explore the mechanical properties of these proteins and there are now a number of single molecule measurements that measure their force response characteristics, making coiled-coils an excellent model system to test folding models connecting sequence to structure to function. In this thesis we have developed a coarse-grained atomistic model to study coiled-coil formation and explore both mechanical and thermal properties. Our model is able to reproduce known coiled-coil structures using only a simple hydrophobic-polar (HP) representation of their sequence and is able to explain the observed mechanical response measured in single molecule experiments. To address how common coiled-coil formation is with respect to all possible helix packs, we have evaluated the designability of the space of possible helical folds, defined as the number of sequences that can fold into a particular structure. We find that left-handed coils emerge as one of the most highly designable structures. From the designability calculation we can identify sequence patterns that design particular coiled-coil folds and mutations that lead to their instability. We also predict that designable coiled-coil structures are more mechanically stable than less designable helical packs. Keywords: Monte Carlo; coiled-coils; alpha-helices; transition force; transition temperature; designability

  14. Effect of viscosity, basicity and organic content of composite flocculant on the decolorization performance and mechanism for reactive dyeing wastewater.

    PubMed

    Wang, Yuanfang; Gao, Baoyu; Yue, Qinyan; Wang, Yan

    2011-01-01

    A coagulation/flocculation process using the composite flocculant polyaluminum chloride-epichlorohydrin dimethylamine (PAC-EPI-DMA) was employed for the treatment of an anionic azo dye (Reactive Brilliant Red K-2BP dye). The effect of viscosity (eta), basicity (B = [OH]/[Al]) and organic content (W(P)) on the flocculation performance as well as the mechanism of PAC-EPI-DMA flocculant were investigated. The eta was the key factor affecting the dye removal efficiency of PAC-EPI-DMA. PAC-EPI-DMA with an intermediate eta (2400 mPa x sec) gave higher decolorization efficiency by adsorption bridging and charge neutralization due to the co-effect of PAC and EPI-DMA polymers. The W(P) of the composite flocculant was a minor important factor for the flocculation. The adsorption bridging of PAC-EPI-DMA with eta of 300 or 4300 mPa x sec played an important role with the increase of W(P), whereas the charge neutralization of them was weaker with the increase of W(P). There was interaction between W(P) and B on the removal of reactive dye. The composite flocculant with intermediate viscosity and organic content was effective for the treatment of reactive dyeing wastewater, which could achieve high reactive dye removal efficiency with low organic dosage. PMID:22432257

  15. Atomic vacancies significantly degrade the mechanical properties of phosphorene

    NASA Astrophysics Data System (ADS)

    Sha, Zhen-Dong; Pei, Qing-Xiang; Zhang, Ying-Yan; Zhang, Yong-Wei

    2016-08-01

    Due to low formation energies, it is very easy to create atomic defects in phosphorene during its fabrication process. How these atomic defects affect its mechanical behavior, however, remain unknown. Here, we report on a systematic study of the effect of atomic vacancies on the mechanical properties and failure behavior of phosphorene using molecular dynamics simulations. It is found that atomic vacancies induce local stress concentration and cause early bond-breaking, leading to a significant degradation of the mechanical properties of the material. More specifically, a 2% concentration of randomly distributed mono-vacancies is able to reduce the fracture strength by ∼40%. An increase in temperature from 10 to 400 K can further deteriorate the fracture strength by ∼60%. The fracture strength of defective phosphorene is also found to be affected by defect distribution. When the defects are patterned in a line, the reduction in fracture strength greatly depends on the tilt angle and the loading direction. Furthermore, we find that di-vacancies cause an even larger reduction in fracture strength than mono-vacancies when the loading is in an armchair direction. These findings provide important guidelines for the structural design of phosphorene in future applications.

  16. Atomic vacancies significantly degrade the mechanical properties of phosphorene.

    PubMed

    Sha, Zhen-Dong; Pei, Qing-Xiang; Zhang, Ying-Yan; Zhang, Yong-Wei

    2016-08-01

    Due to low formation energies, it is very easy to create atomic defects in phosphorene during its fabrication process. How these atomic defects affect its mechanical behavior, however, remain unknown. Here, we report on a systematic study of the effect of atomic vacancies on the mechanical properties and failure behavior of phosphorene using molecular dynamics simulations. It is found that atomic vacancies induce local stress concentration and cause early bond-breaking, leading to a significant degradation of the mechanical properties of the material. More specifically, a 2% concentration of randomly distributed mono-vacancies is able to reduce the fracture strength by ∼40%. An increase in temperature from 10 to 400 K can further deteriorate the fracture strength by ∼60%. The fracture strength of defective phosphorene is also found to be affected by defect distribution. When the defects are patterned in a line, the reduction in fracture strength greatly depends on the tilt angle and the loading direction. Furthermore, we find that di-vacancies cause an even larger reduction in fracture strength than mono-vacancies when the loading is in an armchair direction. These findings provide important guidelines for the structural design of phosphorene in future applications.

  17. Probing mechanical properties of living cells by magnetopneumography.

    PubMed

    Möller, W; Takenaka, S; Rust, M; Stahlhofen, W; Heyder, J

    1997-01-01

    Magnetopneumography (MPG) has been used to study long-term particle clearance from human lungs as well as cellular motility of pulmonary macrophages (PMs). This study describes an extension of the method enabling the measurement of mechanical properties of PM cells in vivo. Ferromagnetic microparticles are inhaled and then retained in the alveolar region of the lungs, where they are phagocytized within hours by PMs. The magnetic particles can be rotated in weak magnetic fields, and the response to this twisting shear (force) is detected as a macroscopic magnetic field producing a measure of cytoskeletal mechanics. Cytoplasmic viscosity is very high compared with that of water and is strongly non-Newtonian. Under rotational stresses from 0.4 to 6.4 Pa, it acts like a pseudoplastic fluid showing a characteristic shear rate dependence. The viscosity as well as the stiffness of the cytoskeleton increases with increasing shear stress as seems typical for living tissue and evidence for an intact cytoskeletal matrix. The particle recoil as measured by the amount of recoverable strain following a short twisting force describes a cytoplasmic elasticity that depends on both level and duration of stress. These investigations on the mechanical properties of living human cells are promising and should lead to better understanding of cellular dysfunction in disease as well as pathways for drug administration. PMID:10174196

  18. Mechanical properties of borophene films: a reactive molecular dynamics investigation

    NASA Astrophysics Data System (ADS)

    Quy Le, Minh; Mortazavi, Bohayra; Rabczuk, Timon

    2016-11-01

    The most recent experimental advances could provide ways for the fabrication of several atomic thick and planar forms of boron atoms. For the first time, we explore the mechanical properties of five types of boron films with various vacancy ratios ranging from 0.1–0.15, using molecular dynamics simulations with ReaxFF force field. It is found that the Young’s modulus and tensile strength decrease with increasing the temperature. We found that boron sheets exhibit an anisotropic mechanical response due to the different arrangement of atoms along the armchair and zigzag directions. At room temperature, 2D Young’s modulus and fracture stress of these five sheets appear in the range 63–136 N m‑1 and 12–19 N m‑1, respectively. In addition, the strains at tensile strength are in the ranges of 9%–14%, 11%–19%, and 10%–16% at 1, 300, and 600 K, respectively. This investigation not only reveals the remarkable stiffness of 2D boron, but establishes relations between the mechanical properties of the boron sheets to the loading direction, temperature and atomic structures.

  19. Mechanical properties for irradiated face-centred cubic nanocrystalline metals

    PubMed Central

    Xiao, X. Z.; Song, D. K.; Chu, H. J.; Xue, J. M.; Duan, H. L.

    2015-01-01

    In this paper, a self-consistent plasticity theory is proposed to model the mechanical behaviours of irradiated face-centred cubic nanocrystalline metals. At the grain level, a tensorial crystal model with both irradiation and grain size effects is applied for the grain interior (GI), whereas both grain boundary (GB) sliding with irradiation effect and GB diffusion are considered in modelling the behaviours of GBs. The elastic-viscoplastic self-consistent method with considering grain size distribution is developed to transit the microscopic behaviour of individual grains to the macroscopic properties of nanocrystals (NCs). The proposed theory is applied to model the mechanical properties of irradiated NC copper, and the feasibility and efficiency have been validated by comparing with experimental data. Numerical results show that: (i) irradiation-induced defects can lead to irradiation hardening in the GIs, but the hardening effect decreases with the grain size due to the increasing absorption of defects by GBs. Meanwhile, the absorbed defects would make the GBs softer than the unirradiated case. (ii) There exists a critical grain size for irradiated NC metals, which separates the grain size into the irradiation hardening dominant region (above the critical size) and irradiation softening dominant region (below the critical size). (iii) The distribution of grain size has a significant influence on the mechanical behaviours of both irradiated and unirradiated NCs. The proposed model can offer a valid theoretical foundation to study the irradiation effect on NC materials. PMID:27547091

  20. Mechanical properties of borophene films: a reactive molecular dynamics investigation.

    PubMed

    Le, Minh Quy; Mortazavi, Bohayra; Rabczuk, Timon

    2016-11-01

    The most recent experimental advances could provide ways for the fabrication of several atomic thick and planar forms of boron atoms. For the first time, we explore the mechanical properties of five types of boron films with various vacancy ratios ranging from 0.1-0.15, using molecular dynamics simulations with ReaxFF force field. It is found that the Young's modulus and tensile strength decrease with increasing the temperature. We found that boron sheets exhibit an anisotropic mechanical response due to the different arrangement of atoms along the armchair and zigzag directions. At room temperature, 2D Young's modulus and fracture stress of these five sheets appear in the range 63-136 N m(-1) and 12-19 N m(-1), respectively. In addition, the strains at tensile strength are in the ranges of 9%-14%, 11%-19%, and 10%-16% at 1, 300, and 600 K, respectively. This investigation not only reveals the remarkable stiffness of 2D boron, but establishes relations between the mechanical properties of the boron sheets to the loading direction, temperature and atomic structures. PMID:27678335