Multi-Length-Scale Morphologies Driven by Mixed Additives in Porphyrin-Based Organic Photovoltaics.
Gao, Ke; Miao, Jingsheng; Xiao, Liangang; Deng, Wanyuan; Kan, Yuanyuan; Liang, Tianxiang; Wang, Cheng; Huang, Fei; Peng, Junbiao; Cao, Yong; Liu, Feng; Russell, Thomas P; Wu, Hongbin; Peng, Xiaobin
2016-06-01
A new category of deep-absorbing small molecules is developed. Optimized devices driven by mixed additives show a remarkable short-circuit current of ≈20 mA cm(-2) and a highest power conversion efficiency of 9.06%. A multi-length-scale morphology is formed, which is fully characterized by resonant soft X-ray scattering, high-angle annular dark film image transmission electron microscopy, etc. PMID:27062394
Wang, Lingle; Friesner, Richard A.; Berne, B. J.
2011-01-01
The binding affinities between a united-atom methane and various model hydrophobic enclosures were studied through high accuracy free energy perturbation methods (FEP). We investigated the non-additivity of the hydrophobic interaction in these systems, measured by the deviation of its binding affinity from that predicted by the pairwise additivity approximation. While only small non-additivity effects were previously reported in the interactions in methane trimers, we found large cooperative effects (as large as −1.14 kcal mol−1 or approximately a 25% increase in the binding affinity) and anti-cooperative effects (as large as 0.45 kcal mol−1) for these model enclosed systems. Decomposition of the total potential of mean force (PMF) into increasing orders of multi-body interactions indicates that the contributions of the higher order multi-body interactions can be either positive or negative in different systems, and increasing the order of multi-body interactions considered did not necessarily improve the accuracy. A general correlation between the sign of the non-additivity effect and the curvature of the solute molecular surface was observed. We found that implicit solvent models based on the molecular surface area (MSA) performed much better, not only in predicting binding affinities, but also in predicting the non-additivity effects, compared with models based on the solvent accessible surface area (SASA), suggesting that MSA is a better descriptor of the curvature of the solutes. We also show how the non-additivity contribution changes as the hydrophobicity of the plate is decreased from the dewetting regime to the wetting regime. PMID:21043426
Softness Correlations Across Length Scales
NASA Astrophysics Data System (ADS)
Ivancic, Robert; Shavit, Amit; Rieser, Jennifer; Schoenholz, Samuel; Cubuk, Ekin; Durian, Douglas; Liu, Andrea; Riggleman, Robert
In disordered systems, it is believed that mechanical failure begins with localized particle rearrangements. Recently, a machine learning method has been introduced to identify how likely a particle is to rearrange given its local structural environment, quantified by softness. We calculate the softness of particles in simulations of atomic Lennard-Jones mixtures, molecular Lennard-Jones oligomers, colloidal systems and granular systems. In each case, we find that the length scale characterizing spatial correlations of softness is approximately a particle diameter. These results provide a rationale for why localized rearrangements--whose size is presumably set by the scale of softness correlations--might occur in disordered systems across many length scales. Supported by DOE DE-FG02-05ER46199.
Li, Hua; Somers, Anthony E; Howlett, Patrick C; Rutland, Mark W; Forsyth, Maria; Atkin, Rob
2016-03-01
The efficacy of ionic liquids (ILs) as lubricant additives to a model base oil has been probed at the nanoscale and macroscale as a function of IL concentration using the same materials. Silica surfaces lubricated with mixtures of the IL trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate and hexadecane are probed using atomic force microscopy (AFM) (nanoscale) and ball-on-disc tribometer (macroscale). At both length scales the pure IL is a much more effective lubricant than hexadecane. At the nanoscale, 2.0 mol% IL (and above) in hexadecane lubricates the silica as well as the pure IL due to the formation of a robust IL boundary layer that separates the sliding surfaces. At the macroscale the lubrication is highly load dependent; at low loads all the mixtures lubricate as effectively as the pure IL, whereas at higher loads rather high concentrations are required to provide IL like lubrication. Wear is also pronounced at high loads, for all cases except the pure IL, and a tribofilm is formed. Together, the nano- and macroscales results reveal that the IL is an effective lubricant additive - it reduces friction - in both the boundary regime at the nanoscale and mixed regime at the macroscale. PMID:26865399
The NIST Length Scale Interferometer
Beers, John S.; Penzes, William B.
1999-01-01
The National Institute of Standards and Technology (NIST) interferometer for measuring graduated length scales has been in use since 1965. It was developed in response to the redefinition of the meter in 1960 from the prototype platinum-iridium bar to the wavelength of light. The history of the interferometer is recalled, and its design and operation described. A continuous program of modernization by making physical modifications, measurement procedure changes and computational revisions is described, and the effects of these changes are evaluated. Results of a long-term measurement assurance program, the primary control on the measurement process, are presented, and improvements in measurement uncertainty are documented.
LENGTH SCALE OF TURBULENCE ABOVE ROUGH SURFACES
Results of analyses of data for two urban sites and a rural site suggest that the mixing length can be represented by the integral length scale of the turbulence derived from vertical velocity spectra. The result is apparently universal and permits the shear production of turbule...
Coupled length scales in eroding landscapes
Chan, Kelvin K.; Rothman, Daniel H.
2001-05-01
We report results from an empirical study of the anisotropic structure of eroding landscapes. By constructing a novel correlation function, we show quantitatively that small-scale channel-like features of landscapes are coupled to the large-scale structure of drainage basins. We show additionally that this two-scale interaction is scale-dependent. The latter observation suggests that a commonly applied effective equation for erosive transport may itself depend on scale.
The length-scaling properties of topography
NASA Technical Reports Server (NTRS)
Weissel, Jeffrey K.; Pratson, Lincoln F.; Malinverno, Alberto
1994-01-01
The scaling properties of synthetic topographic surfaces and digital elevation models (DEMs) of topography are examined by analyzing their 'structure functions,' i.e., the qth order powers of the absolute elevation differences: delta h(sub q) (l) = E((absolute value of h(x + l) - h(x))(exp q)). We find that the relation delta h(sub 1 l) approximately equal cl(exp H) describes well the scaling behavior of natural topographic surfaces, as represented by DEMs gridded at 3 arc sec. Average values of the scaling exponent H between approximately 0.5 and 0.7 characterize DEMs from Ethiopia, Saudi Arabia, and Somalia over 3 orders of magnitude range in length scale l (approximately 0.1-150 km). Differences in appparent topographic roughness among the three areas most likely reflect differences in the amplitude factor c. Separate determination of scaling properties in the x and y coordinate directions allows us to assess whether scaling exponents are azimuthally dependent (anisotropic) or whether they are isotropic while the surface itself is anisotropic over a restricted range of length scale. We explore ways to determine whether topographic surfaces are characterized by simple or multiscaling properties.
Relevant length scale of barchan dunes.
Hersen, Pascal; Douady, Stéphane; Andreotti, Bruno
2002-12-23
A new experiment can create small scale barchan dunes under water: some sand is put on a tray moving periodically and asymmetrically in a water tank, and barchans rapidly form. We measure basic morphological and dynamical properties of these dunes and compare them to field data. These favorable results demonstrate experimentally the relevance of the so-called "saturation length" for the control of the dunes physics. PMID:12484824
Quantum criticality with two length scales
NASA Astrophysics Data System (ADS)
Shao, Hui; Guo, Wenan; Sandvik, Anders W.
2016-04-01
The theory of deconfined quantum critical (DQC) points describes phase transitions at absolute temperature T = 0 outside the standard paradigm, predicting continuous transformations between certain ordered states where conventional theory would require discontinuities. Numerous computer simulations have offered no proof of such transitions, instead finding deviations from expected scaling relations that neither were predicted by the DQC theory nor conform to standard scenarios. Here we show that this enigma can be resolved by introducing a critical scaling form with two divergent length scales. Simulations of a quantum magnet with antiferromagnetic and dimerized ground states confirm the form, proving a continuous transition with deconfined excitations and also explaining anomalous scaling at T > 0. Our findings revise prevailing paradigms for quantum criticality, with potential implications for many strongly correlated materials.
Quantum criticality with two length scales.
Shao, Hui; Guo, Wenan; Sandvik, Anders W
2016-04-01
The theory of deconfined quantum critical (DQC) points describes phase transitions at absolute temperature T = 0 outside the standard paradigm, predicting continuous transformations between certain ordered states where conventional theory would require discontinuities. Numerous computer simulations have offered no proof of such transitions, instead finding deviations from expected scaling relations that neither were predicted by the DQC theory nor conform to standard scenarios. Here we show that this enigma can be resolved by introducing a critical scaling form with two divergent length scales. Simulations of a quantum magnet with antiferromagnetic and dimerized ground states confirm the form, proving a continuous transition with deconfined excitations and also explaining anomalous scaling at T > 0. Our findings revise prevailing paradigms for quantum criticality, with potential implications for many strongly correlated materials. PMID:26989196
Determining multiple length scales in rocks
NASA Astrophysics Data System (ADS)
Song, Yi-Qiao; Ryu, Seungoh; Sen, Pabitra N.
2000-07-01
Carbonate reservoirs in the Middle East are believed to contain about half of the world's oil. The processes of sedimentation and diagenesis produce in carbonate rocks microporous grains and a wide range of pore sizes, resulting in a complex spatial distribution of pores and pore connectivity. This heterogeneity makes it difficult to determine by conventional techniques the characteristic pore-length scales, which control fluid transport properties. Here we present a bulk-measurement technique that is non-destructive and capable of extracting multiple length scales from carbonate rocks. The technique uses nuclear magnetic resonance to exploit the spatially varying magnetic field inside the pore space itself-a `fingerprint' of the pore structure. We found three primary length scales (1-100µm) in the Middle-East carbonate rocks and determined that the pores are well connected and spatially mixed. Such information is critical for reliably estimating the amount of capillary-bound water in the rock, which is important for efficient oil production. This method might also be used to complement other techniques for the study of shaly sand reservoirs and compartmentalization in cells and tissues.
Determining multiple length scales in rocks
Song; Ryu; Sen
2000-07-13
Carbonate reservoirs in the Middle East are believed to contain about half of the world's oil. The processes of sedimentation and diagenesis produce in carbonate rocks microporous grains and a wide range of pore sizes, resulting in a complex spatial distribution of pores and pore connectivity. This heterogeneity makes it difficult to determine by conventional techniques the characteristic pore-length scales, which control fluid transport properties. Here we present a bulk-measurement technique that is nondestructive and capable of extracting multiple length scales from carbonate rocks. The technique uses nuclear magnetic resonance to exploit the spatially varying magnetic field inside the pore space itself--a 'fingerprint' of the pore structure. We found three primary length scales (1-100 microm) in the Middle-East carbonate rocks and determined that the pores are well connected and spatially mixed. Such information is critical for reliably estimating the amount of capillary-bound water in the rock, which is important for efficient oil production. This method might also be used to complement other techniques for the study of shaly sand reservoirs and compartmentalization in cells and tissues. PMID:10910355
Introducing artificial length scales to tailor magnetic properties
NASA Astrophysics Data System (ADS)
Fassbender, J.; Strache, T.; Liedke, M. O.; Markó, D.; Wintz, S.; Lenz, K.; Keller, A.; Facsko, S.; Mönch, I.; McCord, J.
2009-12-01
Magnetism is a collective phenomenon. Hence, a local variation on the nanoscale of material properties, which act on the magnetic properties, affects the overall magnetism in an intriguing way. Of particular importance are the length scales on which a material property changes. These might be related to the exchange length, the domain wall width, a typical roughness correlation length, or a length scale introduced by patterning of the material. Here we report on the influence of two artificially created length scales: (i) ion erosion templates that serve as a source of a predefined surface morphology (ripple structure) and hence allow for the investigation of roughness phenomena. It is demonstrated that the ripple wave length can be easily tuned over a wide range (25-175 nm) by varying the primary ion erosion energy. The effect of this ripple morphology on the induced uniaxial magnetic anisotropy in soft magnetic Permalloy films is studied. Only below a ripple wavelength threshold (≈60 nm) is a significant induced magnetic anisotropy found. Above this threshold the corrugated Permalloy film acts as a flat film. This cross-over is discussed in the frame of dipolar interactions giving rise to the induced anisotropies. (ii) Ion implantation through a lithographically defined mask, which is used for a magnetic property patterning on various length scales. The resulting magnetic properties are neither present in non-implanted nor in homogeneously implanted films. Here new insight is gained by the comparison of different stripe patterning widths ranging from 1 to 10 μm. In addition, the appearance of more complicated magnetic domain structures, i.e. spin-flop domain configurations and head-on domain walls, during hard axis magnetization reversal is demonstrated. In both cases the magnetic properties, the magnetization reversal process as well as the magnetic domain configurations depend sensitively on the artificially introduced length scale.
Critical length scale controls adhesive wear mechanisms
Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois
2016-01-01
The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270
Critical length scale controls adhesive wear mechanisms.
Aghababaei, Ramin; Warner, Derek H; Molinari, Jean-Francois
2016-01-01
The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270
Critical length scale controls adhesive wear mechanisms
NASA Astrophysics Data System (ADS)
Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois
2016-06-01
The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients.
Optimal Length Scale for a Turbulent Dynamo
NASA Astrophysics Data System (ADS)
Sadek, Mira; Alexakis, Alexandros; Fauve, Stephan
2016-02-01
We demonstrate that there is an optimal forcing length scale for low Prandtl number dynamo flows that can significantly reduce the required energy injection rate. The investigation is based on simulations of the induction equation in a periodic box of size 2 π L . The flows considered are the laminar and turbulent A B C flows forced at different forcing wave numbers kf, where the turbulent case is simulated using a subgrid turbulence model. At the smallest allowed forcing wave number kf=kmin=1 /L the laminar critical magnetic Reynolds number R mclam is more than an order of magnitude smaller than the turbulent critical magnetic Reynolds number Rmc turb due to the hindering effect of turbulent fluctuations. We show that this hindering effect is almost suppressed when the forcing wave number kf is increased above an optimum wave number kfL ≃4 for which Rmc turb is minimum. At this optimal wave number, Rmc turb is smaller by more than a factor of 10 than the case forced in kf=1 . This leads to a reduction of the energy injection rate by 3 orders of magnitude when compared to the case where the system is forced at the largest scales and thus provides a new strategy for the design of a fully turbulent experimental dynamo.
Optimal Length Scale for a Turbulent Dynamo.
Sadek, Mira; Alexakis, Alexandros; Fauve, Stephan
2016-02-19
We demonstrate that there is an optimal forcing length scale for low Prandtl number dynamo flows that can significantly reduce the required energy injection rate. The investigation is based on simulations of the induction equation in a periodic box of size 2πL. The flows considered are the laminar and turbulent ABC flows forced at different forcing wave numbers k_{f}, where the turbulent case is simulated using a subgrid turbulence model. At the smallest allowed forcing wave number k_{f}=k_{min}=1/L the laminar critical magnetic Reynolds number Rm_{c}^{lam} is more than an order of magnitude smaller than the turbulent critical magnetic Reynolds number Rm_{c}^{turb} due to the hindering effect of turbulent fluctuations. We show that this hindering effect is almost suppressed when the forcing wave number k_{f} is increased above an optimum wave number k_{f}L≃4 for which Rm_{c}^{turb} is minimum. At this optimal wave number, Rm_{c}^{turb} is smaller by more than a factor of 10 than the case forced in k_{f}=1. This leads to a reduction of the energy injection rate by 3 orders of magnitude when compared to the case where the system is forced at the largest scales and thus provides a new strategy for the design of a fully turbulent experimental dynamo. PMID:26943538
Going up in time and length scales in modeling polymers
NASA Astrophysics Data System (ADS)
Grest, Gary S.
Polymer properties depend on a wide range of coupled length and time scales, with unique macroscopic viscoelastic behavior stemming from interactions at the atomistic level. The need to probe polymers across time and length scales and particularly computational modeling is inherently challenging. Here new paths to probing long time and length scales including introducing interactions into traditional bead-spring models and coarse graining of atomistic simulations will be compared and discussed. Using linear polyethylene as a model system, the degree of coarse graining with two to six methylene groups per coarse-grained bead derived from a fully atomistic melt simulation were probed. We show that the degree of coarse graining affects the measured dynamic. Using these models we were successful in probing highly entangled melts and were able reach the long-time diffusive regime which is computationally inaccessible using atomistic simulations. We simulated the relaxation modulus and shear viscosity of well-entangled polyethylene melts for scaled times of 500 µs. Results for plateau modulus are in good agreement with experiment. The long time and length scale is coupled to the macroscopic viscoelasticity where the degree of coarse graining sets the minimum length scale instrumental in defining polymer properties and dynamics. Results will be compared to those obtained from simple bead-spring models to demonstrate the additional insight that can be gained from atomistically inspired coarse grained models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
How Cells Measure Length on Subcellular Scales.
Marshall, Wallace F
2015-12-01
Cells are not just amorphous bags of enzymes, but precise and complex machines. With any machine, it is important that the parts be of the right size, yet our understanding of the mechanisms that control size of cellular structures remains at a rudimentary level in most cases. One problem with studying size control is that many cellular organelles have complex 3D structures that make their size hard to measure. Here we focus on linear structures within cells, for which the problem of size control reduces to the problem of length control. We compare and contrast potential mechanisms for length control to understand how cells solve simple geometry problems. PMID:26437596
Hierarchy of Bone Microdamage at Multiple Length Scales
Vashishth, Deepak
2007-01-01
Microdamage formation is a critical determinant of bone fracture and the nature and type of damage formed in bone depends on the interaction of its extracellular matrix (ECM) with the applied loading. More importantly, because bone is a hierarchical composite with multiple length scales linked to each other, the nature and type of damage in bone could also be hierarchical. In this review article, based on new unpublished data and a reanalysis of literature reports on in vivo and in vitro observations of microdamage, three length scales including mineralized collagen fibrils, lamellar and osteonal levels have been identified as the key contributors to microdamage hierarchy and energy dissipation in bone. Inherent hierarchy in bone’s ECM therefore has specific microstructural features and energy dissipation mechanisms at different length scales that allow the bone to effectively resist the different components of the applied physiological loading. Furthermore, because human bones experience multiaxial cyclic loading and its ECM is subjected to variation with aging and disease, additional emphasis is placed on investigating how the nature of applied loading and the quality of ECM affect the hierarchy of microdamage formation with age. PMID:18516216
Length Scales in Bayesian Automatic Adaptive Quadrature
NASA Astrophysics Data System (ADS)
Adam, Gh.; Adam, S.
2016-02-01
Two conceptual developments in the Bayesian automatic adaptive quadrature approach to the numerical solution of one-dimensional Riemann integrals [Gh. Adam, S. Adam, Springer LNCS 7125, 1-16 (2012)] are reported. First, it is shown that the numerical quadrature which avoids the overcomputing and minimizes the hidden floating point loss of precision asks for the consideration of three classes of integration domain lengths endowed with specific quadrature sums: microscopic (trapezoidal rule), mesoscopic (Simpson rule), and macroscopic (quadrature sums of high algebraic degrees of precision). Second, sensitive diagnostic tools for the Bayesian inference on macroscopic ranges, coming from the use of Clenshaw-Curtis quadrature, are derived.
Drift wave transport scalings introduced by varying correlation length
Weiland, J.; Holod, I.
2005-01-01
Scalings of the correlation length of drift wave turbulence with magnetic current q, shear, elongation, and temperature ratio have been introduced into a drift wave transport model. The correlation length is calculated from linear scaling of the fastest growing mode. Such a procedure is supported by previous turbulence simulations with absorbing boundaries for short and long wavelengths. The resulting q and s scalings are now in better agreement with experimental scalings. In particular, the simulation results for transport barrier shots improve.
Localization length scales of triplet excitons in singlet fission materials
NASA Astrophysics Data System (ADS)
Bayliss, Sam L.; Thorley, Karl J.; Anthony, John E.; Bouchiat, Hélène; Greenham, Neil C.; Chepelianskii, Alexei D.
2015-09-01
We measure the dielectric confinement length scales of triplet excitons in organic semiconductors by jointly measuring their microwave-domain electric and magnetic susceptibilities. We apply this technique to characterize triplet excitons in two singlet fission materials with distinct solid-state packing and correlate the extracted localization length scales with the role of the excitonic environment. By using the magnetic susceptibility simultaneously determined through our experiments, we compare the independently extracted dielectric and spin-spin localization length scales, highlighting the role of local anisotropy on the properties of excitonic triplet states.
Length scale effects on percolation of geometrically complex nanocomposites
NASA Astrophysics Data System (ADS)
Hoffman, T. J.; Stevens, D. R.; Roberts, W. A.; Gorga, R. E.; Clarke, L. I.
2008-10-01
With growing interest in materials that include nanostructures the focus on nanocomposites (a polymer-based matrix that is enhanced by a nanometer sized particle) has grown. Electrospun nanocomposites contain a complex geometry including fiber sizes of 200 nm arranged in a random mat with a porosity of >= 70%. Composites utilize connected paths of particles throughout the sample to enhance the mechanical and electrical properties of the matrix. Previous literature has shown, in the case of continuous films, that this percolation phenomenon is affected by the sample size. This work aims to investigate these length scale effects within a complex morphology, such as a nanofiber mat. For a clear understanding of the change in percolation vs. length scale we fabricated interdigitated electrodes (IDEs) with a finger spacing of 10 to 100 μm, electrospun mats onto the IDEs, and performed electrical conductance measurements. In addition, computation simulations of the experimental systems were undertaken. I will discuss our results and the role sample size/shape plays on 1) the percolation threshold and 2) the conductivity vs. doping fraction curve.
Hydrodynamic length-scale selection in microswimmer suspensions
NASA Astrophysics Data System (ADS)
Heidenreich, Sebastian; Dunkel, Jörn; Klapp, Sabine H. L.; Bär, Markus
2016-08-01
A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms.
DHS Internship Summary-Crystal Assembly at Different Length Scales
Mishchenko, L
2009-08-06
I was part of a project in which in situ atomic force microscopy (AFM) was used to monitor growth and dissolution of atomic and colloidal crystals. At both length scales, the chemical environment of the system greatly altered crystal growth and dissolution. Calcium phosphate was used as a model system for atomic crystals. A dissolution-reprecipitation reaction was observed in this first system, involving the conversion of brushite (DCPD) to octacalcium phosphate (OCP). In the second system, polymeric colloidal crystals were dissolved in an ionic solvent, revealing the underlying structure of the crystal. The dissolved crystal was then regrown through an evaporative step method. Recently, we have also found that colloids can be reversibly deposited in situ onto an ITO (indium tin oxide) substrate via an electrochemistry setup. The overall goal of this project was to develop an understanding of the mechanisms that control crystallization and order, so that these might be controlled during material synthesis. Controlled assembly of materials over a range of length scales from molecules to nanoparticles to colloids is critical for designing new materials. In particular, developing materials for sensor applications with tailorable properties and long range order is important. In this work, we examine two of these length scales: small molecule crystallization of calcium phosphate (whose crystal phases include DCPD, OCP, and HAP) and colloidal crystallization of Poly(methyl methacrylate) beads. Atomic Force Microscopy is ideal for this line of work because it allows for the possibility of observing non-conducting samples in fluid during growth with high resolution ({approx} 10 nm). In fact, during atomic crystal growth one can observe changes in atomic steps, and with colloidal crystals, one can monitor the individual building blocks of the crystal. Colloids and atoms crystallize under the influence of different forces acting at different length scales as seen in Table 1
SQUID magnetometry from nanometer to centimeter length scales
NASA Astrophysics Data System (ADS)
Hatridge, Michael Jonathan
Information stored in magnetic fields plays an important role in everyday life. This information exists over a remarkably wide range of sizes, so that magnetometry at a variety of length scales can extract useful information. Examples at centimeter to millimeter length scales include measurement of spatial and temporal character of fields generated in the human brain and heart, and active manipulation of spins in the human body for non-invasive magnetic resonance imaging (MRI). At micron length scales, magnetometry can be used to measure magnetic objects such as flux qubits; at nanometer length scales it can be used to study individual magnetic domains, and even individual spins. The development of Superconducting QUantum Interference Device (SQUID) based magnetometer for two such applications, in vivo prepolarized, ultra-low field MRI of humans and dispersive readout of SQUIDs for micro- and nanoscale magnetometry, are the focus of this thesis. Conventional MRI has developed into a powerful clinical tool for imaging the human body. This technique is based on nuclear magnetic resonance of protons with the addition application of three-dimensional magnetic field gradients to encode spatial information. Most clinical MRI systems involve magnetic fields generated by superconducting magnets, and the current trend is to higher magnetic fields than the widely used 1.5-T systems. Nonetheless, there is ongoing interest in the development of less expensive imagers operating at lower fields. The prepolarized, SQUID detected ultra-low field MRI (ULF MRI) developed by the Clarke group allows imaging in very weak fields (typically 132 muT, corresponding to a resonant frequency of 5.6 kHz). At these low field strengths, there is enhanced contrast in the longitudinal relaxation time of various tissue types, enabling imaging of objects which are not visible to conventional MRI, for instance prostate cancer. We are currently investigating the contrast between normal and cancerous
Length scales and self-organization in dense suspension flows
NASA Astrophysics Data System (ADS)
Düring, Gustavo; Lerner, Edan; Wyart, Matthieu
2014-02-01
Dense non-Brownian suspension flows of hard particles display mystifying properties: As the jamming threshold is approached, the viscosity diverges, as well as a length scale that can be identified from velocity correlations. To unravel the microscopic mechanism governing dissipation and its connection to the observed correlation length, we develop an analogy between suspension flows and the rigidity transition occurring when floppy networks are pulled, a transition believed to be associated with the stress stiffening of certain gels. After deriving the critical properties near the rigidity transition, we show numerically that suspension flows lie close to it. We find that this proximity causes a decoupling between viscosity and the correlation length of velocities ξ, which scales as the length lc characterizing the response to a local perturbation, previously predicted to follow lc˜1/√zc-z ˜p0.18, where p is the dimensionless particle pressure, z is the coordination of the contact network made by the particles, and zc is twice the spatial dimension. We confirm these predictions numerically and predict the existence of a larger length scale lr˜√p with mild effects on velocity correlation and of a vanishing strain scale δγ ˜1/p that characterizes decorrelation in flow.
Procedure for Determining Turbulence Length Scales Using Hotwire Anemometry
NASA Technical Reports Server (NTRS)
El-Gabry, Lamyaa A.; Thurman, Douglas R.; Poinsatte, Philip E.
2014-01-01
Hotwire anemometers are used to measure instantaneous velocity from which the mean velocity and the velocity fluctuation can be determined. Using a hotwire system, it is possible to deduce not only the velocity components and their fluctuation but to also analyze the energy spectra and from that the turbulence length scales. In this experiment, hotwire anemometry is used to measure the flow field turbulence for an array of film cooling holes. The objective of this paper is to document the procedure that is used to reduce the instantaneous velocity measurements to determine the turbulence length scales using data from the film-cooling experiments to illustrate the procedure.
Process length scales and longitudinal damping in karst conduits
NASA Astrophysics Data System (ADS)
Covington, M. D.; Luhmann, A. J.; Wicks, C. M.; Saar, M. O.
2012-03-01
Simple mathematical models often allow an intuitive grasp of the function of physical systems. We develop a mathematical framework to investigate reactive or dissipative transport processes within karst conduits. Specifically, we note that for processes that occur within a characteristic timescale, advection along the conduit produces a characteristic process length scale. We calculate characteristic length scales for the propagation of thermal and electrical conductivity signals along karst conduits. These process lengths provide a quantitative connection between karst conduit geometry and the signals observed at a karst spring. We show that water input from the porous/fractured matrix is also characterized by a length scale and derive an approximation that accounts for the influence of matrix flow on the transmission of signals through the aquifer. The single conduit model is then extended to account for conduits with changing geometries and conduit flow networks, demonstrating how these concepts can be applied in more realistic conduit geometries. We introduce a recharge density function, ϕR, which determines the capability of an aquifer to damp a given signal, and cast previous explanations of spring variability within this framework. Process lengths are a general feature of karst conduits and surface streams, and we conclude with a discussion of other potential applications of this conceptual and mathematical framework.
Estimation of Length-Scales in Soils by MRI
NASA Technical Reports Server (NTRS)
Daidzic, N. E.; Altobelli, S.; Alexander, J. I. D.
2004-01-01
Soil can be best described as an unconsolidated granular media that forms porous structure. The present macroscopic theory of water transport in porous media rests upon the continuum hypothesis that the physical properties of porous media can be associated with continuous, twice-differentiable field variables whose spatial domain is a set of centroids of Representative Elementary Volume (REV) elements. MRI is an ideal technique to estimate various length-scales in porous media. A 0.267 T permanent magnet at NASA GRC was used for this study. A 2D or 3D spatially-resolved porosity distribution were obtained from the NMR signal strength from each voxel and the spin-lattice relaxation time. A classical spin-warp imaging with Multiple Spin Echos (MSE) was used to evaluate proton density in each voxel. Initial resolution of 256 x 256 was subsequently reduced by averaging neighboring voxels and the porosity convergence was observed. A number of engineered "space candidate" soils such as Isolite(trademark), Zeoponics(trademark), Turface(trademark), and Profile(trademark) were used. Glass beads in the size range between 50 microns to 2 mm were used as well. Initial results with saturated porous samples have shown a good estimate of the average porosity consistent with the gravimetric porosity measurement results. For Profile(trademark) samples with particle sizes ranging between 0.25 to 1 mm and characteristic interparticle pore size of 100 microns the characteristic Darcy scale was estimated to be about delta(sub REV) = 10 mm. Glass beads porosity show clear convergence toward a definite REV which stays constant throughout homogeneous sample. Additional information is included in the original extended abstract.
Past and Future Blurring at Fundamental Length Scale
Neves, M. J.; Farina, C.; Cougo-Pinto, M. V.
2010-11-19
We obtain the {kappa}-deformed versions of the retarded and advanced Green functions and show that their causality properties are blurred in a time interval of the order of a length parameter q=1/(2{kappa}). The functions also indicate a smearing of the light cone. These results favor the interpretation of q as a fundamental length scale below which the concept of a point in space-time should be substituted by the concept of a fuzzy region of radius q, as proposed long ago by Heisenberg.
Progress in Long Scale Length Laser-Plasma Interactions
Glenzer, S H; Arnold, P; Bardsley, G; Berger, R L; Bonanno, G; Borger, T; Bower, D E; Bowers, M; Bryant, R; Buckman, S; Burkhart, S C; Campbell, K; Chrisp, M P; Cohen, B I; Constantin, G; Cooper, F; Cox, J; Dewald, E; Divol, L; Dixit, S; Duncan, J; Eder, D; Edwards, J; Erbert, G; Felker, B; Fornes, J; Frieders, G; Froula, D H; Gardner, S D; Gates, C; Gonzalez, M; Grace, S; Gregori, G; Greenwood, A; Griffith, R; Hall, T; Hammel, B A; Haynam, C; Heestand, G; Henesian, M; Hermes, G; Hinkel, D; Holder, J; Holdner, F; Holtmeier, G; Hsing, W; Huber, S; James, T; Johnson, S; Jones, O S; Kalantar, D; Kamperschroer, J H; Kauffman, R; Kelleher, T; Knight, J; Kirkwood, R K; Kruer, W L; Labiak, W; Landen, O L; Langdon, A B; Langer, S; Latray, D; Lee, A; Lee, F D; Lund, D; MacGowan, B; Marshall, S; McBride, J; McCarville, T; McGrew, L; Mackinnon, A J; Mahavandi, S; Manes, K; Marshall, C; Mertens, E; Meezan, N; Miller, G; Montelongo, S; Moody, J D; Moses, E; Munro, D; Murray, J; Neumann, J; Newton, M; Ng, E; Niemann, C; Nikitin, A; Opsahl, P; Padilla, E; Parham, T; Parrish, G; Petty, C; Polk, M; Powell, C; Reinbachs, I; Rekow, V; Rinnert, R; Riordan, B; Rhodes, M
2003-11-11
The first experiments on the National Ignition Facility (NIF) have employed the first four beams to measure propagation and laser backscattering losses in large ignition-size plasmas. Gas-filled targets between 2 mm and 7 mm length have been heated from one side by overlapping the focal spots of the four beams from one quad operated at 351 nm (3{omega}) with a total intensity of 2 x 10{sup 15} W cm{sup -2}. The targets were filled with 1 atm of CO{sub 2} producing of up to 7 mm long homogeneously heated plasmas with densities of n{sub e} = 6 x 10{sup 20} cm{sup -3} and temperatures of T{sub e} = 2 keV. The high energy in a NIF quad of beams of 16kJ, illuminating the target from one direction, creates unique conditions for the study of laser plasma interactions at scale lengths not previously accessible. The propagation through the large-scale plasma was measured with a gated x-ray imager that was filtered for 3.5 keV x rays. These data indicate that the beams interact with the full length of this ignition-scale plasma during the last {approx}1 ns of the experiment. During that time, the full aperture measurements of the stimulated Brillouin scattering and stimulated Raman scattering show scattering into the four focusing lenses of 6% for the smallest length ({approx}2 mm). increasing to 12% for {approx}7 mm. These results demonstrate the NIF experimental capabilities and further provide a benchmark for three-dimensional modeling of the laser-plasma interactions at ignition-size scale lengths.
Multiple-length-scale deformation analysis in a thermoplastic polyurethane
Sui, Tan; Baimpas, Nikolaos; Dolbnya, Igor P.; Prisacariu, Cristina; Korsunsky, Alexander M.
2015-01-01
Thermoplastic polyurethane elastomers enjoy an exceptionally wide range of applications due to their remarkable versatility. These block co-polymers are used here as an example of a structurally inhomogeneous composite containing nano-scale gradients, whose internal strain differs depending on the length scale of consideration. Here we present a combined experimental and modelling approach to the hierarchical characterization of block co-polymer deformation. Synchrotron-based small- and wide-angle X-ray scattering and radiography are used for strain evaluation across the scales. Transmission electron microscopy image-based finite element modelling and fast Fourier transform analysis are used to develop a multi-phase numerical model that achieves agreement with the combined experimental data using a minimal number of adjustable structural parameters. The results highlight the importance of fuzzy interfaces, that is, regions of nanometre-scale structure and property gradients, in determining the mechanical properties of hierarchical composites across the scales. PMID:25758945
Multiple-length-scale deformation analysis in a thermoplastic polyurethane
NASA Astrophysics Data System (ADS)
Sui, Tan; Baimpas, Nikolaos; Dolbnya, Igor P.; Prisacariu, Cristina; Korsunsky, Alexander M.
2015-03-01
Thermoplastic polyurethane elastomers enjoy an exceptionally wide range of applications due to their remarkable versatility. These block co-polymers are used here as an example of a structurally inhomogeneous composite containing nano-scale gradients, whose internal strain differs depending on the length scale of consideration. Here we present a combined experimental and modelling approach to the hierarchical characterization of block co-polymer deformation. Synchrotron-based small- and wide-angle X-ray scattering and radiography are used for strain evaluation across the scales. Transmission electron microscopy image-based finite element modelling and fast Fourier transform analysis are used to develop a multi-phase numerical model that achieves agreement with the combined experimental data using a minimal number of adjustable structural parameters. The results highlight the importance of fuzzy interfaces, that is, regions of nanometre-scale structure and property gradients, in determining the mechanical properties of hierarchical composites across the scales.
Multiple-length-scale deformation analysis in a thermoplastic polyurethane.
Sui, Tan; Baimpas, Nikolaos; Dolbnya, Igor P; Prisacariu, Cristina; Korsunsky, Alexander M
2015-01-01
Thermoplastic polyurethane elastomers enjoy an exceptionally wide range of applications due to their remarkable versatility. These block co-polymers are used here as an example of a structurally inhomogeneous composite containing nano-scale gradients, whose internal strain differs depending on the length scale of consideration. Here we present a combined experimental and modelling approach to the hierarchical characterization of block co-polymer deformation. Synchrotron-based small- and wide-angle X-ray scattering and radiography are used for strain evaluation across the scales. Transmission electron microscopy image-based finite element modelling and fast Fourier transform analysis are used to develop a multi-phase numerical model that achieves agreement with the combined experimental data using a minimal number of adjustable structural parameters. The results highlight the importance of fuzzy interfaces, that is, regions of nanometre-scale structure and property gradients, in determining the mechanical properties of hierarchical composites across the scales. PMID:25758945
Cross correlation and length scales in turbulent flows near surfaces
NASA Technical Reports Server (NTRS)
Hunt, J. C. R.; Moin, P.; Lee, M.; Moser, R. D.; Spalart, P.; Mansour, N. N.; Kaimal, J. C.; Gaynor, E.
1989-01-01
Two kinds of length scales are used in turbulent flows; 'functional length scales' such as mixing length, dissipation length L(sub epsilon), etc., and 'flow-field length scales' derived from cross correlations of velocity, pressure, etc. in the flow. Some connection between these scales are derived here. We first consider the cross correlation R(sub vv)(y,y(sub 1)) of the normal components u at two heights y, y(sub 1) above a rigid surface, normalized by the velocity y(sub 1) (greater than y). For shear-free boundary layers it is found theoretically, and in field and numerical experiments that R(sub vv) approximately equals y/y(sub 1). For shear layers it is also found that R(sub vv) approximately equals f(y/y(sub 1)) less than or equal to y,y(sub 1). This function f differs slightly between low Reynolds number numerical simulations and field experiments. The lateral structure defined by R(sub vv)(y,r(sub 3); y(sub 1),0) is also self similar and shows that the eddies centered at about y(sub 1) appear to have constant lateral width a(sub 3) above and below y(sub 1), where a(sub 3, sup +) approximately equals 7+1/(1.4dU(sup +)/dy(sup +)), when normalized on u(sub *) and v, where U is the mean velocity. Results for L(sub epsilon, sup -1) from direct numerical simulation are found to compare well with the formula L(sub epsilon, sup -1) = A(sub B)/y + A(sub S)dU/dy/v, for unidirectional and reversing turbulent boundary layers and channel flow, except near where dU/dy approximately equals 0. The conclusion is that the large-scale eddy structure and length scales in these flows are determined by a combination of shear and blocking, and that the vertical component of turbulence has a self-similar structure in both kinds of boundary layer.
Atomistic Simulation of Polymer Crystallization at Realistic Length Scales
Gee, R H; Fried, L E
2005-01-28
Understanding the dynamics of polymer crystallization during the induction period prior to crystal growth is a key goal in polymer physics. Here we present the first study of primary crystallization of polymer melts via molecular dynamics simulations at physically realistic (about 46 nm) length scales. Our results show that the crystallization mechanism involves a spinodal decomposition microphase separation caused by an increase in the average length of rigid trans segments along the polymer backbone during the induction period. Further, the characteristic length of the growing dense domains during the induction period is longer than predicted by classical nucleation theory. These results indicate a new 'coexistence period' in the crystallization, where nucleation and growth mechanisms coexist with a phase separation mechanism. Our results provide an atomistic verification of the fringed micelle model.
The length and time scales of water's glass transitions
NASA Astrophysics Data System (ADS)
Limmer, David T.
2014-06-01
Using a general model for the equilibrium dynamics of supercooled liquids, I compute from molecular properties the emergent length and time scales that govern the nonequilibrium relaxation behavior of amorphous ice prepared by rapid cooling. Upon cooling, the liquid water falls out of equilibrium whereby the temperature dependence of its relaxation time is predicted to change from super-Arrhenius to Arrhenius. A consequence of this crossover is that the location of the apparent glass transition temperature depends logarithmically on cooling rate. Accompanying vitrification is the emergence of a dynamical length-scale, the size of which depends on the cooling rate and varies between angstroms and tens of nanometers. While this protocol dependence clarifies a number of previous experimental observations for amorphous ice, the arguments are general and can be extended to other glass forming liquids.
Topology, length scales, and energetics of surfactant micelles.
Dhakal, Subas; Sureshkumar, Radhakrishna
2015-07-14
We study the morphology, energetics, and kinetics of a self-associating model cationic surfactant in water using large-scale coarse-grained molecular dynamics simulations over time scales that allow for probing micelle recombination dynamics. We develop an algorithm to track micelle contours and quantify various microstructural features such as contour length distribution, persistence length, and mesh size. We predict reliably the end-cap energy and recombination time of micelles, directly from molecular simulations for the first time. We further consider the variation of solution viscosity as a function of salt concentration and show that branched and multiconnected structures govern the experimentally observed anomalous dependence of zero-shear viscosity on salt concentration. Overall, simulation predictions are in good agreement with experiments. PMID:26178125
Emergence of Chirality from Isotropic Interactions of Three Length Scales.
Mkhonta, S K; Elder, K R; Huang, Zhi-Feng
2016-05-20
Chirality is known to play a pivotal role in determining material properties and functionalities. However, it remains a great challenge to understand and control the emergence of chirality and the related enantioselective process particularly when the building components of the system are achiral. Here we explore the generic mechanisms driving the formation of two-dimensional chiral structures in systems characterized by isotropic interactions and three competing length scales. We demonstrate that starting from isotropic and rotationally invariant interactions, a variety of chiral ordered patterns and superlattices with anisotropic but achiral units can self-assemble. The mechanisms for selecting specific states are related to the length-scale coupling and the selection of resonant density wave vectors. Sample phase diagrams and chiral elastic properties are identified. These findings provide a viable route for predicting chiral phases and selecting the desired handedness. PMID:27258877
Emergence of Chirality from Isotropic Interactions of Three Length Scales
NASA Astrophysics Data System (ADS)
Mkhonta, S. K.; Elder, K. R.; Huang, Zhi-Feng
2016-05-01
Chirality is known to play a pivotal role in determining material properties and functionalities. However, it remains a great challenge to understand and control the emergence of chirality and the related enantioselective process particularly when the building components of the system are achiral. Here we explore the generic mechanisms driving the formation of two-dimensional chiral structures in systems characterized by isotropic interactions and three competing length scales. We demonstrate that starting from isotropic and rotationally invariant interactions, a variety of chiral ordered patterns and superlattices with anisotropic but achiral units can self-assemble. The mechanisms for selecting specific states are related to the length-scale coupling and the selection of resonant density wave vectors. Sample phase diagrams and chiral elastic properties are identified. These findings provide a viable route for predicting chiral phases and selecting the desired handedness.
Instability of Stratified Shear Flow: Intermittency and Length Scales
NASA Astrophysics Data System (ADS)
Ecke, Robert; Odier, Philippe
2015-11-01
The stability of stratified shear flows which occur in oceanic overflows, wind-driven thermoclines, and atmospheric inversion layers is governed by the Richardson Number Ri , a non-dimensional balance between stabilizing stratification and destabilizing shear. For a shear flow with velocity difference U, density difference Δρ and characteristic length H, one has Ri = g (Δρ / ρ) H /U2 . A more precise definition is the gradient Richardson Number Rig =N2 /S2 where the buoyancy frequency N =√{ (g / ρ) ∂ρ / ∂z } , the mean strain S = ∂U / ∂z with z parallel to gravity and with ensemble or time averages defining the gradients. We explore the stability and mixing properties of a wall-bounded shear flow for 0 . 1 < Rig < 1 using simultaneous measurements of density and velocity fields. The flow, confined from the top by a horizontal boundary, is a lighter alcohol-water mixture injected from a nozzle into quiescent heavier salt-water fluid. The injected flow is turbulent with Taylor Reynolds number about 75. We compare a set of length scales that characterize the mixing properties of our turbulent stratified shear flow including Thorpe Length LT, Ozmidov Length LO, and Ellison Length LE.
Uncinate Process Length in Birds Scales with Resting Metabolic Rate
Tickle, Peter; Nudds, Robert; Codd, Jonathan
2009-01-01
A fundamental function of the respiratory system is the supply of oxygen to meet metabolic demand. Morphological constraints on the supply of oxygen, such as the structure of the lung, have previously been studied in birds. Recent research has shown that uncinate processes (UP) are important respiratory structures in birds, facilitating inspiratory and expiratory movements of the ribs and sternum. Uncinate process length (UPL) is important for determining the mechanical advantage for these respiratory movements. Here we report on the relationship between UPL, body size, metabolic demand and locomotor specialisation in birds. UPL was found to scale isometrically with body mass. Process length is greatest in specialist diving birds, shortest in walking birds and intermediate length in all others relative to body size. Examination of the interaction between the length of the UP and metabolic demand indicated that, relative to body size, species with high metabolic rates have corresponding elongated UP. We propose that elongated UP confer an advantage on the supply of oxygen, perhaps by improving the mechanical advantage and reducing the energetic cost of movements of the ribs and sternum. PMID:19479074
Taylor length-scale size particles in Isotropic Turbulence
NASA Astrophysics Data System (ADS)
Lucci, Francesco
The present study investigates the two-way coupling effects of finite-size solid spherical particles on decaying isotropic turbulence using an immersed boundary method. The conventional point particle assumption is valid only in the case of particles with a diameter, dp, much smaller than the Kolmogorov length scale, eta. In a simulation with particles of diameter dp > eta the flow around each particle needs to be resolved. In this study, we use a method similar to that of Uhlmann(2005) [55] that adapts the Immersed Boundary(IB) Method developed by Peskin [38] to simulate the flow around suspended spherical solid particles. The main idea of the method is to distribute a number of Lagrangian points uniformly over the surface of the particle. A force is applied at each Lagrangian point to represent the momentum exchange between the particle and the surrounding fluid. An analytic three-point delta function is used to distribute the force to the Eulerian grid points saddling the spherical surface to satisfy the no-slip condition at each Lagrangian point. Decaying turbulence is simulated in a periodic box with a uniform mesh of up to (512)3 grid points and an initial microscale Reynolds number of up to Relambda0 = 110. We compare the single phase flow (SPF) with particle-laden flows with particles of different diameters. The density of the particle varies from 2.56 to 10 times that of the fluid. The effects of the particles on the temporal development of turbulence kinetic energy E(t), its dissipation rate epsilon( t), its two-way coupling rate of change Ψp( t) and frequency spectra E(o) are discussed. In this study, in contrast to particles with dp < eta [15], particles with dp > eta always increase the dissipation rate of turbulence kinetic energy, epsilon( t). In addition, Ψp(t) is always positive, whereas it can be positive or negative for particles with dp < eta. The balance between these two effects caused E(t) to be smaller than that of the single-phase flow
Length-Scale Dependent Viscosity in Semidilute Polyelectrolyte Solutions
NASA Astrophysics Data System (ADS)
Poling-Skutvik, Ryan; Krishnamoorti, Ramanan; Conrad, Jacinta
2015-03-01
Using optical microscopy and particle tracking algorithms, we measured the mean-squared displacements (MSDs) of fluorescent polystyrene particles with diameters ranging from 300 nm to 2 μm suspended in semidilute solutions of high molecular weight partially hydrolyzed polyacrylamide. The solutions had polymer concentrations ranging from 0.67 to 67c*, where c* is the overlap concentration, and estimated correlation lengths of ~ 100 to 900 nm. At short times, the particles exhibited subdiffusive behavior characterized by MSD ~tα with α < 1 . On long time scales, the particles transitioned to Fickian diffusion (α = 1) and their diffusivity was calculated from the slope of the MSD. Whereas the large particles agreed with predictions using the Stokes-Einstein equation and bulk zero-shear viscosity, the smaller particles diffused much faster than predicted. The relative diffusivities do not collapse onto a single curve, but rather form a continuum that varies with particle size. This indicates that the particles experience a size-dependent effective viscosity mediated by the ratio of particle diameter to characteristic length scales in the polymer solution.
Length scale selects directionality of droplets on vibrating pillar ratchet
Agapov, Rebecca L.; Boreyko, Jonathan B.; Briggs, Dayrl P.; Srijanto, Bernadeta R.; Retterer, Scott T.; Collier, C. Patrick; Lavrik, Nickolay V.
2014-09-22
Directional control of droplet motion at room temperature is of interest for applications such as microfluidic devices, self-cleaning coatings, and directional adhesives. Here, arrays of tilted pillars ranging in height from the nanoscale to the microscale are used as structural ratchets to directionally transport water at room temperature. Water droplets deposited on vibrating chips with a nanostructured ratchet move preferentially in the direction of the feature tilt while the opposite directionality is observed in the case of microstructured ratchets. This remarkable switch in directionality is consistent with changes in the contact angle hysteresis. To glean further insights into the length scale dependent asymmetric contact angle hysteresis, the contact lines formed by a nonvolatile room temperature ionic liquid placed onto the tilted pillar arrays were visualized and analyzed in situ in a scanning electron microscope. As a result, the ability to tune droplet directionality by merely changing the length scale of surface features all etched at the same tilt angle would be a versatile tool for manipulating multiphase flows and for selecting droplet directionality in other lap-on-chip applications.
A Two-length Scale Turbulence Model for Single-phase Multi-fluid Mixing
Schwarzkopf, J. D.; Livescu, D.; Baltzer, J. R.; Gore, R. A.; Ristorcelli, J. R.
2015-09-08
A two-length scale, second moment turbulence model (Reynolds averaged Navier-Stokes, RANS) is proposed to capture a wide variety of single-phase flows, spanning from incompressible flows with single fluids and mixtures of different density fluids (variable density flows) to flows over shock waves. The two-length scale model was developed to address an inconsistency present in the single-length scale models, e.g. the inability to match both variable density homogeneous Rayleigh-Taylor turbulence and Rayleigh-Taylor induced turbulence, as well as the inability to match both homogeneous shear and free shear flows. The two-length scale model focuses on separating the decay and transport length scales, as the two physical processes are generally different in inhomogeneous turbulence. This allows reasonable comparisons with statistics and spreading rates over such a wide range of turbulent flows using a common set of model coefficients. The specific canonical flows considered for calibrating the model include homogeneous shear, single-phase incompressible shear driven turbulence, variable density homogeneous Rayleigh-Taylor turbulence, Rayleigh-Taylor induced turbulence, and shocked isotropic turbulence. The second moment model shows to compare reasonably well with direct numerical simulations (DNS), experiments, and theory in most cases. The model was then applied to variable density shear layer and shock tube data and shows to be in reasonable agreement with DNS and experiments. Additionally, the importance of using DNS to calibrate and assess RANS type turbulence models is highlighted.
The length scale for sub-grid-scale parameterization with anisotropic resolution
NASA Technical Reports Server (NTRS)
Lilly, Douglas K.
1989-01-01
Use of the Smagorinsky eddy-viscosity formulation and related schemes for subgrid-scale parameterization of large eddy simulation models requires specification of a single length scale, earlier related by Lilly to the scale of filtering and/or numerical resolution. An anisotropic integration of the Kolmogoroff enstrophy spectrum allows generalization of that relationship to anisotropic resolution. It is found that the Deardorff assumption is reasonably accurate for small anisotropies and can be simply improved for larger values.
Dynamic Leidenfrost Effect: Relevant Time and Length Scales.
Shirota, Minori; van Limbeek, Michiel A J; Sun, Chao; Prosperetti, Andrea; Lohse, Detlef
2016-02-12
When a liquid droplet impacts a hot solid surface, enough vapor may be generated under it to prevent its contact with the solid. The minimum solid temperature for this so-called Leidenfrost effect to occur is termed the Leidenfrost temperature, or the dynamic Leidenfrost temperature when the droplet velocity is non-negligible. We observe the wetting or drying and the levitation dynamics of the droplet impacting on an (isothermal) smooth sapphire surface using high-speed total internal reflection imaging, which enables us to observe the droplet base up to about 100 nm above the substrate surface. By this method we are able to reveal the processes responsible for the transitional regime between the fully wetting and the fully levitated droplet as the solid temperature increases, thus shedding light on the characteristic time and length scales setting the dynamic Leidenfrost temperature for droplet impact on an isothermal substrate. PMID:26918994
Dynamic Leidenfrost Effect: Relevant Time and Length Scales
NASA Astrophysics Data System (ADS)
Shirota, Minori; van Limbeek, Michiel A. J.; Sun, Chao; Prosperetti, Andrea; Lohse, Detlef
2016-02-01
When a liquid droplet impacts a hot solid surface, enough vapor may be generated under it to prevent its contact with the solid. The minimum solid temperature for this so-called Leidenfrost effect to occur is termed the Leidenfrost temperature, or the dynamic Leidenfrost temperature when the droplet velocity is non-negligible. We observe the wetting or drying and the levitation dynamics of the droplet impacting on an (isothermal) smooth sapphire surface using high-speed total internal reflection imaging, which enables us to observe the droplet base up to about 100 nm above the substrate surface. By this method we are able to reveal the processes responsible for the transitional regime between the fully wetting and the fully levitated droplet as the solid temperature increases, thus shedding light on the characteristic time and length scales setting the dynamic Leidenfrost temperature for droplet impact on an isothermal substrate.
Hybrid Supramolecular and Colloidal Hydrogels that Bridge Multiple Length Scales**
Janeček, Emma-Rose; McKee, Jason R; Tan, Cindy S Y; Nykänen, Antti; Kettunen, Marjo; Laine, Janne; Ikkala, Olli; Scherman, Oren A
2015-01-01
Hybrid nanocomposites were constructed based on colloidal nanofibrillar hydrogels with interpenetrating supramolecular hydrogels, displaying enhanced rheological yield strain and a synergistic improvement in storage modulus. The supramolecular hydrogel consists of naphthyl-functionalized hydroxyethyl cellulose and a cationic polystyrene derivative decorated with methylviologen moieties, physically cross-linked with cucurbit[8]uril macrocyclic hosts. Fast exchange kinetics within the supramolecular system are enabled by reversible cross-linking through the binding of the naphthyl and viologen guests. The colloidal hydrogel consists of nanofibrillated cellulose that combines a mechanically strong nanofiber skeleton with a lateral fibrillar diameter of a few nanometers. The two networks interact through hydroxyethyl cellulose adsorption to the nanofibrillated cellulose surfaces. This work shows methods to bridge the length scales of molecular and colloidal hybrid hydrogels, resulting in synergy between reinforcement and dynamics. PMID:25772264
Katanin contributes to interspecies spindle length scaling in Xenopus
Loughlin, Rose; Wilbur, Jeremy D.; McNally, Francis J.; Nédélec, François J.; Heald, Rebecca
2011-01-01
SUMMARY Bipolar spindles must separate chromosomes by the appropriate distance during cell division, but mechanisms determining spindle length are poorly understood. Based on a 2D model of meiotic spindle assembly, we predicted that higher localized microtubule (MT) depolymerization rates could generate the shorter spindles observed in egg extracts of X. tropicalis compared to X. laevis. We found that katanin-dependent MT severing was increased in X. tropicalis, which lacks an inhibitory phosphorylation site in the p60 catalytic subunit that is present in X. laevis p60. Katanin inhibition lengthened spindles in both species, and kinetochore fibers extended through X. tropicalis spindle poles disrupting them. In both X. tropicalis extracts and the spindle simulation, a threshold number of stable kinetochore fibers could overwhelm MT depolymerization, leading to similar phenotypes. Thus, mechanisms have evolved in different species to scale spindle size and coordinate regulation of multiple MT populations in order to generate a robust steady state structure. PMID:22153081
Additional Results of Ice-Accretion Scaling at SLD Conditions
NASA Technical Reports Server (NTRS)
Bond, Thomas H. (Technical Monitor); Anderson, David N.; Tsao, Jen-Ching
2005-01-01
To determine scale velocity an additional similarity parameter is needed to supplement the Ruff scaling method. A Weber number based on water droplet MVD has been included in several studies because the effect of droplet splashing on ice accretion was believed to be important, particularly for SLD conditions. In the present study, ice shapes recorded at Appendix-C conditions and recent results at SLD conditions are reviewed to show that droplet diameter cannot be important to main ice shape, and for low airspeeds splashing does not appear to affect SLD ice shapes. Evidence is presented to show that while a supplementary similarity parameter probably has the form of a Weber number, it must be based on a length proportional to model size rather than MVD. Scaling comparisons were made between SLD reference conditions and Appendix-C scale conditions using this Weber number. Scale-to-reference model size ratios were 1:1.7 and 1:3.4. The reference tests used a 91-cm-chord NACA 0012 model with a velocity of approximately 50 m/s and an MVD of 160 m. Freezing fractions of 0.3, 0.4, and 0.5 were included in the study.
Length scale selects directionality of droplets on vibrating pillar ratchet
Agapov, Rebecca L.; Boreyko, Jonathan B.; Briggs, Dayrl P.; Srijanto, Bernadeta R.; Retterer, Scott T.; Collier, C. Patrick; Lavrik, Nickolay V.
2014-09-22
Directional control of droplet motion at room temperature is of interest for applications such as microfluidic devices, self-cleaning coatings, and directional adhesives. Here, arrays of tilted pillars ranging in height from the nanoscale to the microscale are used as structural ratchets to directionally transport water at room temperature. Water droplets deposited on vibrating chips with a nanostructured ratchet move preferentially in the direction of the feature tilt while the opposite directionality is observed in the case of microstructured ratchets. This remarkable switch in directionality is consistent with changes in the contact angle hysteresis. To glean further insights into the lengthmore » scale dependent asymmetric contact angle hysteresis, the contact lines formed by a nonvolatile room temperature ionic liquid placed onto the tilted pillar arrays were visualized and analyzed in situ in a scanning electron microscope. As a result, the ability to tune droplet directionality by merely changing the length scale of surface features all etched at the same tilt angle would be a versatile tool for manipulating multiphase flows and for selecting droplet directionality in other lap-on-chip applications.« less
Length scales for fragile glass-forming liquids
NASA Astrophysics Data System (ADS)
Mountain, Raymond D.
1995-04-01
Molecular dynamics simulation results are used to demonstrate the existence of a growing length in supercooled, fragile glass-forming liquids. This length is the longest wavelength, propagating shear wave the fluid can support. Explicit results are reported for an equimolar soft-sphere mixture. A possible connection between this length and the size of locally rigid clusters is discussed.
Time-dependent couplings and crossover length scales in nonequilibrium surface roughening
NASA Astrophysics Data System (ADS)
Pradas, Marc; López, Juan M.; Hernández-Machado, A.
2007-07-01
We show that time-dependent couplings may lead to nontrivial scaling properties of the surface fluctuations of the asymptotic regime in nonequilibrium kinetic roughening models. Three typical situations are studied. In the case of a crossover between two different rough regimes, the time-dependent coupling may result in anomalous scaling for scales above the crossover length. In a different setting, for a crossover from a rough to either a flat or damping regime, the time-dependent crossover length may conspire to produce a rough surface, although the most relevant term tends to flatten the surface. In addition, our analysis sheds light into an existing debate in the problem of spontaneous imbibition, where time-dependent couplings naturally arise in theoretical models and experiments.
Fault zone rheology and length scales of frictional failure
NASA Astrophysics Data System (ADS)
Fagereng, A.
2011-12-01
variation in power-law exponent indicates that whether deformation occurs predominantly by continuous or discontinuous deformation may be predicted from the shape of the frequency-size distribution of competent lenses, and supports the hypothesis that bulk rheology is determined by the volume fraction of competent material. The distribution of competent material likely affects the seismic style of actively deforming fault zones. The length scales of shear discontinuities are likely to be a factor determining the possible length scales of seismic ruptures, and thus the likely range of earthquake magnitudes which may occur within a tabular fault zone segment. The power-law exponent of the distribution may be analogous to the b-value in the earthquake frequency-magnitude relationship, where a low power-law exponent, reflecting a high proportion of large phacoids or phacoid clusters, relates to a low b, reflecting a higher proportion of large earthquakes. Variation in the distribution of materials of varying rheology, both along and across strike, may therefore be a possible explanation for 3-D variability in seismic style.
Scale Length of Mantle Heterogeneities: Helium Diffusion Constraints
NASA Astrophysics Data System (ADS)
Hart, S.; Kurz, M.; Wang, Z.
2007-12-01
will be >20 Ra. In essence, slabs may lose their He signature by diffusion, but it will remain recorded in the surrounding mantle; i.e. veins may run but they can't hide! For both enriched and depleted upper mantle slabs, sampled along a spreading ridge, the 3/4He variability on 10-20 km scale lengths would be easily observed; even massive along-axis melt mixing (50-100 km) would not hide these signatures. We have evaluated 3 extant ridge-crest data sets in this context (MAR 0-47S; EPR 19-23S; SWIR 16- 24E), with a view to defining scale-lengths of He isotope variability. The average 3/4He variability for these 3 areas is 0.47, 0.19 and 0.21 Ra (±1 sigma); a well-sampled sub-area on the MAR (25.7-26.5S) is 0.13 Ra. There is a monotonic variation along the SWIR, from 6.6 to 7.3 Ra; variability about a best fit line is 0.09 Ra (maximum deviation is only 0.20 Ra). At the smallest scale, a single 20 km EPR flow field shows similar variability (0.29 Ra) to the above examples. Since these ridges range from slow to very fast-spreading, the variability in size of along- axis magma chambers will lead inevitably to various scales of melt averaging. We conclude that these ridge areas are not sampling mantle that contains enriched veins or recycled oceanic crust slabs of any significant size. This is especially clear for the 500 km domain on the SWIR, where very small He variability is observed, superimposed on a large scale He gradient. In particular, the view of the upper mantle as a ubiquitous mixture of veins and depleted matrix, with MORB always representing an averaging of this mixture, appears untenable.
A Two-length Scale Turbulence Model for Single-phase Multi-fluid Mixing
Schwarzkopf, J. D.; Livescu, D.; Baltzer, J. R.; Gore, R. A.; Ristorcelli, J. R.
2015-09-08
A two-length scale, second moment turbulence model (Reynolds averaged Navier-Stokes, RANS) is proposed to capture a wide variety of single-phase flows, spanning from incompressible flows with single fluids and mixtures of different density fluids (variable density flows) to flows over shock waves. The two-length scale model was developed to address an inconsistency present in the single-length scale models, e.g. the inability to match both variable density homogeneous Rayleigh-Taylor turbulence and Rayleigh-Taylor induced turbulence, as well as the inability to match both homogeneous shear and free shear flows. The two-length scale model focuses on separating the decay and transport length scales,more » as the two physical processes are generally different in inhomogeneous turbulence. This allows reasonable comparisons with statistics and spreading rates over such a wide range of turbulent flows using a common set of model coefficients. The specific canonical flows considered for calibrating the model include homogeneous shear, single-phase incompressible shear driven turbulence, variable density homogeneous Rayleigh-Taylor turbulence, Rayleigh-Taylor induced turbulence, and shocked isotropic turbulence. The second moment model shows to compare reasonably well with direct numerical simulations (DNS), experiments, and theory in most cases. The model was then applied to variable density shear layer and shock tube data and shows to be in reasonable agreement with DNS and experiments. Additionally, the importance of using DNS to calibrate and assess RANS type turbulence models is highlighted.« less
Physical aspects of a length scale for the Gulf Stream front
Kao, T.W.
1983-07-20
A discussion is presented of the physical interpretation of the length scale, lambda, introduced in a recent paper by Kao and Cheney (1982) to scale the sea surface height anomaly across the Gulf Stream front. Additional results of sea-surface height anomaly profiles computed from the hydrographic data from Fuglister's GULF STREAM 60 are also included. In all cases the width of the anomaly is spanned rather precisely by 2lambda. The relationship between lambda and the internal Rossby radius of deformation lambda, is discussed.
Scale length of mantle heterogeneities: Constraints from helium diffusion
NASA Astrophysics Data System (ADS)
Hart, S. R.; Kurz, M. D.; Wang, Z.
2008-05-01
A model of coupled He production/diffusion is used to constrain the question of whether Earth's peridotitic mantle contains ubiquitous mesoscale veins or slabs of other lithologies. The high diffusion rates of helium preclude survival of He isotope heterogeneities on scales smaller than a few tens of meters, especially if they represent long term in-growth of 4He in the mantle. For 1.5 Gyr residence times, and a diffusion coefficient of 10 - 10 m 2/s, 0.5 km slabs or 2 km cylinders will lose > 90% of in-grown 4He. However, substantial 3He/ 4He variations may persist in slabs or be induced in adjacent mantle, depending on initial He, U and Th contents. We have modeled three cases of 3He/ 4He equilibration between mantle domains: an ocean crust (OC) slab in depleted upper mantle (DMM) or in enriched mantle (BSE), and a BSE slab in DMM. For a 1 km OC slab in DMM (8 Ra today), the slab today will have 3He/ 4He of only 3 Ra, and will have influenced the surrounding mantle with 4He for > 7 km on either side. The average 3He/ 4He of this mixed zone will be < 7 Ra, even when sampled by melts over a total width of 20-50 km. For the case of a 1 km BSE slab in DMM (8 Ra today), the slab will be 37 Ra today, and will have infected a mantle domain > 16 km wide. Even with a 60 km melt sampling width, the average 3He/ 4He will be > 15 Ra. Slabs may lose their He signature by diffusion, but their presence will be recorded in the surrounding mantle. We have evaluated 3 along-axis N-MORB ridge-crest data sets in this context (MAR 25.7-26.5°S; EPR 19-23°S; SWIR 16-24° E), with a view to defining scale-lengths of He isotope variability. The average 3He/ 4He variability for these 3 areas is very small, and independent of spreading rate: 0.13, 0.19 and 0.21 Ra (± 1 σ). Since these ridges range from ultra-slow to very fast-spreading, the variability in size of along-axis magma chambers will lead inevitably to various scales of melt averaging. We conclude that these ridge areas are
Proton conduction in exchange membranes across multiple length scales.
Jorn, Ryan; Savage, John; Voth, Gregory A
2012-11-20
Concerns over global climate change associated with fossil-fuel consumption continue to drive the development of electrochemical alternatives for energy technology. Proton exchange fuel cells are a particularly promising technology for stationary power generation, mobile electronics, and hybrid engines in automobiles. For these devices to work efficiently, direct electrical contacts between the anode and cathode must be avoided; hence, the separator material must be electronically insulating but highly proton conductive. As a result, researchers have examined a variety of polymer electrolyte materials for use as membranes in these systems. In the optimization of the membrane, researchers are seeking high proton conductivity, low electronic conduction, and mechanical stability with the inclusion of water in the polymer matrix. A considerable number of potential polymer backbone and side chain combinations have been synthesized to meet these requirements, and computational studies can assist in the challenge of designing the next generation of technologically relevant membranes. Such studies can also be integrated in a feedback loop with experiment to improve fuel cell performance. However, to accurately simulate the currently favored class of membranes, perfluorosulfonic acid containing moieties, several difficulties must be addressed including a proper treatment of the proton-hopping mechanism through the membrane and the formation of nanophase-separated water networks. We discuss our recent efforts to address these difficulties using methods that push the limits of computer simulation and expand on previous theoretical developments. We describe recent advances in the multistate empirical valence bond (MS-EVB) method that can probe proton diffusion at the nanometer-length scale and accurately model the so-called Grotthuss shuttling mechanism for proton diffusion in water. Using both classical molecular dynamics and coarse-grained descriptions that replace atomistic
Inlet Turbulence and Length Scale Measurements in a Large Scale Transonic Turbine Cascade
NASA Technical Reports Server (NTRS)
Thurman, Douglas; Flegel, Ashlie; Giel, Paul
2014-01-01
Constant temperature hotwire anemometry data were acquired to determine the inlet turbulence conditions of a transonic turbine blade linear cascade. Flow conditions and angles were investigated that corresponded to the take-off and cruise conditions of the Variable Speed Power Turbine (VSPT) project and to an Energy Efficient Engine (EEE) scaled rotor blade tip section. Mean and turbulent flowfield measurements including intensity, length scale, turbulence decay, and power spectra were determined for high and low turbulence intensity flows at various Reynolds numbers and spanwise locations. The experimental data will be useful for establishing the inlet boundary conditions needed to validate turbulence models in CFD codes.
Recognition and assembly at multiple length-scales
NASA Astrophysics Data System (ADS)
Olmsted, Brian Keith
contours to study how symmetry and packing originates at the micron length-scale. Although much is known about assembly at the molecular level for symmetry and packing, the assembly of anisotropic particles at longer length scales, which involve different interactive forces, has not been studied. This work concludes by performing preliminary work in elucidating the general behavior towards symmetry and packing in two-dimensions of micron-sized particles by using gravitational gradients and dielectrophoresis.
Cooperative Length Scale and Fragility of Polystyrene under Confinement
NASA Astrophysics Data System (ADS)
Zhang, Chuan; Guo, Yunlong; Priestley, Rodney
2012-02-01
While thin films are an attractive model system to investigate the impact of confinement on glassy behavior, extending studies beyond thin films to geometries of higher dimensionalities is vital from both scientific and technological viewpoints. In this talk, we present the impact of confinement on the characteristic length at the glass transition as well as the fragility for confined polystyrene (PS) nanoparticles under isochoric conditions. We measure the glass transition temperature (Tg), fictive temperature (Tf) and isochoric heat capacity of silica-capped PS nanoparticles as a function of diameter via differential scanning calorimetry. From the measurement of Tf, we obtain the isochoric fragility, and via the fluctuation formula, the characteristic length at the glass transition. We illustrate that confinement under isochoric conditions for PS nanoparticles leads to a significant increase in the isochoric fragility while the characteristic length is reduced with size. At the minimum the results demonstrate a relationship between fragility and the characteristics length of isochorically-confined polymer that is not intuitive from the Adam-Gibbs theory.
Direct observation of electron propagation and dielectric screening on the atomic length scale.
Neppl, S; Ernstorfer, R; Cavalieri, A L; Lemell, C; Wachter, G; Magerl, E; Bothschafter, E M; Jobst, M; Hofstetter, M; Kleineberg, U; Barth, J V; Menzel, D; Burgdörfer, J; Feulner, P; Krausz, F; Kienberger, R
2015-01-15
The propagation and transport of electrons in crystals is a fundamental process pertaining to the functioning of most electronic devices. Microscopic theories describe this phenomenon as being based on the motion of Bloch wave packets. These wave packets are superpositions of individual Bloch states with the group velocity determined by the dispersion of the electronic band structure near the central wavevector in momentum space. This concept has been verified experimentally in artificial superlattices by the observation of Bloch oscillations--periodic oscillations of electrons in real and momentum space. Here we present a direct observation of electron wave packet motion in a real-space and real-time experiment, on length and time scales shorter than the Bloch oscillation amplitude and period. We show that attosecond metrology (1 as = 10(-18) seconds) now enables quantitative insight into weakly disturbed electron wave packet propagation on the atomic length scale without being hampered by scattering effects, which inevitably occur over macroscopic propagation length scales. We use sub-femtosecond (less than 10(-15) seconds) extreme-ultraviolet light pulses to launch photoelectron wave packets inside a tungsten crystal that is covered by magnesium films of varied, well-defined thicknesses of a few ångströms. Probing the moment of arrival of the wave packets at the surface with attosecond precision reveals free-electron-like, ballistic propagation behaviour inside the magnesium adlayer--constituting the semi-classical limit of Bloch wave packet motion. Real-time access to electron transport through atomic layers and interfaces promises unprecedented insight into phenomena that may enable the scaling of electronic and photonic circuits to atomic dimensions. In addition, this experiment allows us to determine the penetration depth of electrical fields at optical frequencies at solid interfaces on the atomic scale. PMID:25592539
Length scales in glass-forming liquids and related systems: a review
NASA Astrophysics Data System (ADS)
Karmakar, Smarajit; Dasgupta, Chandan; Sastry, Srikanth
2016-01-01
The central problem in the study of glass-forming liquids and other glassy systems is the understanding of the complex structural relaxation and rapid growth of relaxation times seen on approaching the glass transition. A central conceptual question is whether one can identify one or more growing length scale(s) associated with this behavior. Given the diversity of molecular glass-formers and a vast body of experimental, computational and theoretical work addressing glassy behavior, a number of ideas and observations pertaining to growing length scales have been presented over the past few decades, but there is as yet no consensus view on this question. In this review, we will summarize the salient results and the state of our understanding of length scales associated with dynamical slow down. After a review of slow dynamics and the glass transition, pertinent theories of the glass transition will be summarized and a survey of ideas relating to length scales in glassy systems will be presented. A number of studies have focused on the emergence of preferred packing arrangements and discussed their role in glassy dynamics. More recently, a central object of attention has been the study of spatially correlated, heterogeneous dynamics and the associated length scale, studied in computer simulations and theoretical analysis such as inhomogeneous mode coupling theory. A number of static length scales have been proposed and studied recently, such as the mosaic length scale discussed in the random first-order transition theory and the related point-to-set correlation length. We will discuss these, elaborating on key results, along with a critical appraisal of the state of the art. Finally we will discuss length scales in driven soft matter, granular fluids and amorphous solids, and give a brief description of length scales in aging systems. Possible relations of these length scales with those in glass-forming liquids will be discussed.
Length scales in glass-forming liquids and related systems: a review.
Karmakar, Smarajit; Dasgupta, Chandan; Sastry, Srikanth
2016-01-01
The central problem in the study of glass-forming liquids and other glassy systems is the understanding of the complex structural relaxation and rapid growth of relaxation times seen on approaching the glass transition. A central conceptual question is whether one can identify one or more growing length scale(s) associated with this behavior. Given the diversity of molecular glass-formers and a vast body of experimental, computational and theoretical work addressing glassy behavior, a number of ideas and observations pertaining to growing length scales have been presented over the past few decades, but there is as yet no consensus view on this question. In this review, we will summarize the salient results and the state of our understanding of length scales associated with dynamical slow down. After a review of slow dynamics and the glass transition, pertinent theories of the glass transition will be summarized and a survey of ideas relating to length scales in glassy systems will be presented. A number of studies have focused on the emergence of preferred packing arrangements and discussed their role in glassy dynamics. More recently, a central object of attention has been the study of spatially correlated, heterogeneous dynamics and the associated length scale, studied in computer simulations and theoretical analysis such as inhomogeneous mode coupling theory. A number of static length scales have been proposed and studied recently, such as the mosaic length scale discussed in the random first-order transition theory and the related point-to-set correlation length. We will discuss these, elaborating on key results, along with a critical appraisal of the state of the art. Finally we will discuss length scales in driven soft matter, granular fluids and amorphous solids, and give a brief description of length scales in aging systems. Possible relations of these length scales with those in glass-forming liquids will be discussed. PMID:26684508
Length Scale Correlations of Cellular Microstructures in Directionally Solidified Binary System
Yunxue Shen
2002-06-27
In a cellular array, a range of primary spacing is found to be stable under given growth conditions. Since a strong coupling of solute field exists between the neighboring cells, primary spacing variation should also influence other microstructure features such as cell shape and cell length. The existence of multiple solutions is examined in this study both theoretically as well as experimentally. A theoretical model is developed that identifies and relates four important microstructural lengths, which are found to be primary spacing, tip radius, cell width and cell length. This general microstructural relationship is shown to be valid for different cells in an array as well as for other cellular patterns obtained under different growth conditions. The unique feature of the model is that the microstructure correlation does not depend on composition or growth conditions since these variables scale microstructural lengths to satisfy the relationship obtained in this study. Detailed directional solidification experimental studies have been carried out in the succinonitrile-salol system to characterize and measure these four length scales. Besides the validation of the model, experimental results showed additional scaling laws to be present. In the regime where only a cellular structure is formed, the shape of the cell, the cell tip radius and the length of the cell are all found to scale individually with the local primary spacing. The presence of multiple solutions of primary spacing is also shown to influence the cell-dendrite transition that is controlled not only by the processing variables (growth velocity, thermal gradient and composition) but also by the local cell spacing. The cell-dendrite transition was found not to be sharp, but occurred over a range of processing conditions. Two critical conditions have been identified such that only cells are present below lower critics condition, and only dendrites are formed above the upper critics condition. Between
Length Scale Correlations of Cellular Microstructures in Directionally Solidified Binary System
Yunxue Shen
2002-08-01
In a cellular array, a range of primary spacing is found to be stable under given growth conditions. Since a strong coupling of solute field exists between the neighboring cells, primary spacing variation should also influence other microstructure features such as cell shape and cell length. The existence of multiple solutions is examined in this study both theoretically as well as experimentally. A theoretical model is developed that identifies and relates four important microstructural lengths, which are found to be primary spacing, tip radius, cell width and cell length. This general microstructural relationship is shown to be valid for different cells in an array as well as for other cellular patterns obtained under different growth conditions. The unique feature of the model is that the microstructure correlation does not depend on composition or growth conditions since these variables scale microstructural lengths to satisfy the relationship obtained in this study. Detailed directional solidification experimental studies have been carried out in the succinonitrile-salol system to characterize and measure these four length scales. Besides the validation of the model, experimental results showed additional scaling laws to be present. In the regime where only a cellular structure is formed, the shape of the cell, the cell tip radius and the length of the cell are all found to scale individually with the local primary spacing. The presence of multiple solutions of primary spacing is also shown to influence the cell-dendrite transition that is controlled not only by the processing variables (growth velocity, thermal gradient and composition) but also by the local cell spacing. The cell-dendrite transition was found not to be sharp, but occurred over a range of processing conditions. Two critical conditions have been identified such that only cells are present below lower critics condition, and only dendrites are formed above the upper critics condition. Between
Experimental evidence for two thermodynamic length scales in neutralized polyacrylate gels
NASA Astrophysics Data System (ADS)
Horkay, Ferenc; Hecht, Anne-Marie; Grillo, Isabelle; Basser, Peter J.; Geissler, Erik
2002-11-01
The small angle neutron scattering (SANS) behavior of fully neutralized sodium polyacrylate gels is investigated in the presence of calcium ions. Analysis of the SANS response reveals the existence of three characteristic length scales, two of which are of thermodynamic origin, while the third length is associated with the frozen-in structural inhomogeneities. This latter contribution exhibits power law behavior with a slope of about -3.6, reflecting the presence of interfaces. The osmotically active component of the scattering signal is defined by two characteristic length scales, a correlation length ξ and a persistence length L.
SQUID magnetometry from nanometer to centimeter length scales
Hatridge, Michael J.
2010-06-01
The development of Superconducting QUantum Interference Device (SQUID)-based magnetometer for two applications, in vivo prepolarized, ultra-low field MRI of humans and dispersive readout of SQUIDs for micro- and nano-scale magnetometery, are the focus of this thesis.
Shear viscosity of strongly coupled Yukawa systems on finite length scales.
Sanbonmatsu, K Y; Murillo, M S
2001-02-12
The Yukawa shear viscosity has been calculated using nonequilibrium molecular dynamics. Near the viscosity minimum, we find exponential decay consistent with the Navier-Stokes equation, with significant deviations on finite length scales for larger viscosity values. The viscosity is determined to be nonlocal on a scale length consistent with the correlation length, revealing the length scales necessary for obtaining transport coefficients in the hydrodynamic limit by nonequilibrium molecular dynamics methods. Our results are quasiuniversal with respect to excess entropy for excess entropies well below unity. PMID:11178047
Displacement–length scaling of brittle faults in ductile shear
Grasemann, Bernhard; Exner, Ulrike; Tschegg, Cornelius
2011-01-01
Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement–distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow. PMID:26806996
Non-universal aperture-length scaling of opening mode fractures
NASA Astrophysics Data System (ADS)
Mayrhofer, Franziska; Schöpfer, Martin P. J.; Grasemann, Bernhard
2014-05-01
Opening-mode fractures, such as joints, veins and dykes, typically exhibit a power-law aperture-length scaling with a power-law exponent of about 0.5. The fracture aperture is hence proportional to the square root of fracture length, a relation which is in fact predicted by linear elastic fracture mechanics (LEFM) for an isolated Mode I fracture subjected to remote tension. The existence of such a 'universal scaling law' is however a highly debated topic. High quality outcrop data illustrate that fracture aperture-length scaling may be 'non-universal' and indicate that below a certain length-scale scaling is super-linear (power-law exponent > 1). We use a numerical model comprised of a square lattice of breakable elastic beams to investigate the aperture-length scaling that emerges in thin plates subjected to remote tension. Strength heterogeneity is introduced in the regular lattice by randomly assigning beam strengths from a Weibull probability distribution. The model fracture system evolution is characterised by two stages which are separated by the strain at which peak-stress occurs. During the pre-peak stress stage fracture aperture-length scaling is universal with a power-law exponent of about 0.5 as expected from LEFM. Shortly after the material has attained its maximum load bearing capacity, aperture-length scaling becomes non-universal, so that the average aperture-length relation plotted on a log-log graph exhibits a distinct kink. Fractures with a length less than this critical length scale exhibit super-linear aperture-length scaling, whereas fractures with a greater length exhibit sub-linear scaling. The models illustrate that the emergence of non-universal aperture-length scaling is a result of fracture clustering, which occurs after peak-stress in the form of a localised fracture zone. Given that fracture clustering is a common phenomenon in natural fracture systems, we argue that a universal scaling law may be the exception rather than the rule.
Investigation of the effect of inlet turbulence length scale on fan discrete tone noise
NASA Technical Reports Server (NTRS)
Hodder, B. K.
1973-01-01
Results of an experimental investigation at the Ames 40- by 80-Foot Wind Tunnel of fan rotor alone discrete tone noise is presented. The investigation examines rotor interaction with fan inlet turbulence. The importance of turbulence length scale is shown by comparing the fan radiated acoustic spectrum with and without modified turbulence length scales. A small-scale low pressure ratio fan was used for the experiment.
Laser profilometry and length-scale analysis of stone tools: second series experiment results.
James Stemp, W; Childs, Ben E; Vionnet, Samuel
2010-01-01
Based on the need to develop a method to reliably and objectively document and discriminate the use-wear on archaeological stone tools, Stemp et al. (2009) tested whether the surface roughness measured on experimentally worn stone tools used on different contact materials could be discriminated. Results of these initial experiments indicated that discrimination was possible and also determined the scales over which this discrimination occurred. In this article, we report the results of additional experiments using the same method on a second set of tools to test its reliability and reproducibility. In these experiments, four flint flakes were intensively used for 20 min on either conch shell or dry deer antler. The surface roughness or texture of the stone tools was measured by generating 2D profiles using a UBM laser profilometer. Relative lengths (RLs) calculated from the profiles were used directly as characterization parameters and subsequently compared statistically at each scale using the F-test to establish a level of confidence for the differentiation at each scale represented in the measured profiles. The mean square ratios of measurement data were used to determine whether the variation in roughness was statistically significant and to what level of confidence. The scales at which there was a high level of confidence were the ones at which the tools were differentiable. The results of these experiments confirm our previous findings that RLs, over certain scale ranges, can discriminate the stone tool surface wear profiles produced by the different contact materials. PMID:20853403
Radiation Damage on Multiple Length Scales in Uranium Dioxide
NASA Astrophysics Data System (ADS)
Gupta, Mahima
Radiation damage in UO2 has been well studied but there exists little correlation between point defect accumulation, lattice structure changes and microstructure. This is partly because irradiated nuclear fuel is highly radioactive and its defect chemistry is extremely complicated resulting from fission of the material and consequent fission products being embedded in the fuel matrix [Olander1976]. To adequately study the evolution of defects from point defects through to microstructure features, the resulting defects have to be intentionally simplified for characterization. Ion accelerators have the unique capability of creating simple microstructure features using specific ions, without the added complication of fission and neutron activation from nuclear reactors. As an example, H+ ions have been used to create (only) a distribution of dislocations that were studied using various techniques. The ability to tune the energy or type of the ion to achieve desirable implantation depth and ideally simple microstructure renders it a lucrative instrument for this type of analysis. X-ray diffraction (XRD) studies and transmission electron microscopy (TEM) have been utilized to study extended structure changes and microstructure evolution. Ion beam irradiations create displacements and displacement networks, voids, surface fracturing, gas bubbles and several other microstructure changes to model nuclear reactor damage [Noris1972]. Using an ion accelerator, it has been possible to isolate these radiation induced defects and study their subsequent evolution with increasing dose. Insofar, since all of the phenomena caused by radiation damage originate from point defects, the elucidation of radiation effects on the atomic scale is crucial. This is rendered complicated due to aperiodic irradiation defects. This lack of periodicity renders standard approaches, such as TEM and XRD ineffective, as these methods probe average structure over tens of Angstroms. Therefore, techniques
A large scale membrane-binding protein conformational change that initiates at small length scales
NASA Astrophysics Data System (ADS)
Grandpre, Trevor; Andorf, Matthew; Chakravarthy, Srinivas; Lamb, Robert; Poor, Taylor; Landahl, Eric
2013-03-01
The fusion (F) protein of parainfluenza virus 5 (PIV5) is a membrane-bound, homotrimeric glycoprotein located on the surface of PIV5 viral envelopes. Upon being triggered by the receptor-binding protein (HN), F undergoes a greater than 100Å ATP-independent refolding event. This refolding event results in the insertion of a hydrophobic fusion peptide into the membrane of the target cell, followed by the desolvation and subsequent fusion event as the two membranes are brought together. Isothermal calorimetry and hydrophobic dye incorporation experiments indicate that the soluble construct of the F protein undergoes a conformational rearrangement event at around 55 deg C. We present the results of an initial Time-Resolved Small-Angle X-Ray Scattering (TR-SAXS) study of this large scale, entropically driven conformational change using a temperature jump. Although we the measured radius of gyration of this protein changes on a 110 second timescale, we find that the x-ray scattering intensity at higher angles (corresponding to smaller length scales in the protein) changes nearly an order of magnitude faster. We believe this may be a signature of entropically-driven conformational change. To whom correspondence should be addressed
NASA Astrophysics Data System (ADS)
Morris, A. R.; Anderson, F. S.; Mouginis-Mark, P.; Haldemann, A.; Brooks, B.; Foster, J.
2007-12-01
The roughness of a natural surface is often defined by the topography of the surface at scales of a few tens of meters or less. To ensure the safety of rovers and scientific instruments on Mars, these scales are of critical importance during landing site selection and rover traverse operations. Published work on terrestrial and Martian topography datasets has demonstrated that statistical values such as the Hurst exponent can be used in conjunction with related statistical measures such as RMS slope or deviation to quantify the relationship between scale-dependent roughness values and the morphology of a surface. In our detailed studies of the statistical behavior of meter-scale surface roughness on Earth, we determine that the length scales used to calculate the surface roughness affect the resulting roughness statistics and must be taken into account when analyzing planetary surface roughness. Extensive airborne Light Detection and Ranging (a-LiDAR) coverage of the summit of Kilauea volcano on the Big Island of Hawaii (1 m DEM) provides an opportunity for simulating higher resolution Martian topography data such as will be obtained from photoclinometry and stereo imaging using the HiRISE camera on MRO. In addition to the a-LiDAR data, we use high-resolution topography (2 cm DEM) generated from a tripod-mounted scanning LiDAR system (t-LiDAR). Previous authors have described techniques for calculating roughness statistics in one dimension using topographic profiles. We adapt the 1D method for use with 2D topographic datasets to generate maps of the Hurst exponent of Martian analog flows in Hawaii. Results from the surface roughness analysis suggest that the calculated RMS deviation or slope and Hurst exponent exhibit systematic variations as the length of a profile segment (in 1D studies) or size of the cell (in 2D studies) changes. These new results, combined with previously described data, indicate that the length scales used to calculate roughness statistics
Plasma scale-length effects on electron energy spectra in high-irradiance laser plasmas
NASA Astrophysics Data System (ADS)
Culfa, O.; Tallents, G. J.; Rossall, A. K.; Wagenaars, E.; Ridgers, C. P.; Murphy, C. D.; Dance, R. J.; Gray, R. J.; McKenna, P.; Brown, C. D. R.; James, S. F.; Hoarty, D. J.; Booth, N.; Robinson, A. P. L.; Lancaster, K. L.; Pikuz, S. A.; Faenov, A. Ya.; Kampfer, T.; Schulze, K. S.; Uschmann, I.; Woolsey, N. C.
2016-04-01
An analysis of an electron spectrometer used to characterize fast electrons generated by ultraintense (1020W cm-2 ) laser interaction with a preformed plasma of scale length measured by shadowgraphy is presented. The effects of fringing magnetic fields on the electron spectral measurements and the accuracy of density scale-length measurements are evaluated. 2D EPOCH PIC code simulations are found to be in agreement with measurements of the electron energy spectra showing that laser filamentation in plasma preformed by a prepulse is important with longer plasma scale lengths (>8 μ m ).
Multi-plane Particle Shadow Velocimetry to Quantify Integral Length Scales
NASA Astrophysics Data System (ADS)
Harris, Jeff; Truong, Christine; Hinkle, Steven; Sinding, Kyle; Camp, Tiffany; Fontaine, Arnie; Krane, Michael; Devilbiss, David
2015-11-01
Multi-plane PIV has been used for several years to assist in quantifying the integral length scales in turbulent flow. Particle shadow velocimetry (PSV) enables illumination of a volume and is an efficient means of obtaining multi-plane illumination. The combination of two colors in the LED backlight and a dichroic mirror makes possible the imaging of two planes in space without the complexity of aligning two different light sources. The velocity fields obtained in these two vector fields are then correlated to obtain length scales using the definitions in the literature. The length scales and multi-plane measurements are compared with previous studies which used proven measurement methods.
Bridging Length Scales to Study Self-Assembly and Self-Organization
NASA Astrophysics Data System (ADS)
Kaye, Bryan; Needleman, Daniel
A variety of proteins can assemble into large polymers as an integral part of their biological function. Studying the biochemistry and biophysics of polymer formation often involves time-resolvable measurements of the amount of polymer. Non-invasive measurements of polymer can be divided into two categories: short (spectroscopy) and large (microscopy) length scale measurements. Microscopy-based estimates of polymer amount are often dependent on spatial non-uniformity of polymer, whereas spectroscopy-based estimates of polymer amount are often based on models that are difficult to test. Here we show how both large and small length scale measurements can be combined to validate the assumptions behind both measurements while incorporating both measurements to make more accurate estimates of polymer amount. We utilize this approach with two-photon microscopy and FRET to measure the amount of tubulin (monomer) in microtubules (polymer) in order to study microtubule nucleation in cell extracts. In addition, this approach may be useful to study a wide variety of polymers, including actin filaments, viruses, lipid membranes, and other protein aggregates.
2013-01-01
Background Many inpatients receive little or no rehabilitation on weekends. Our aim was to determine what effect providing additional Saturday rehabilitation during inpatient rehabilitation had on functional independence, quality of life and length of stay compared to 5 days per week of rehabilitation. Methods This was a multicenter, single-blind (assessors) randomized controlled trial with concealed allocation and 12-month follow-up conducted in two publically funded metropolitan inpatient rehabilitation facilities in Melbourne, Australia. Patients were eligible if they were adults (aged ≥18 years) admitted for rehabilitation for any orthopedic, neurological or other disabling conditions excluding those admitted for slow stream rehabilitation/geriatric evaluation and management. Participants were randomly allocated to usual care Monday to Friday rehabilitation (control) or to Monday to Saturday rehabilitation (intervention). The additional Saturday rehabilitation comprised physiotherapy and occupational therapy. The primary outcomes were functional independence (functional independence measure (FIM); measured on an 18 to 126 point scale), health-related quality of life (EQ-5D utility index; measured on a 0 to 1 scale, and EQ-5D visual analog scale; measured on a 0 to 100 scale), and patient length of stay. Outcome measures were assessed on admission, discharge (primary endpoint), and at 6 and 12 months post discharge. Results We randomly assigned 996 adults (mean (SD) age 74 (13) years) to Monday to Saturday rehabilitation (n = 496) or usual care Monday to Friday rehabilitation (n = 500). Relative to admission scores, intervention group participants had higher functional independence (mean difference (MD) 2.3, 95% confidence interval (CI) 0.5 to 4.1, P = 0.01) and health-related quality of life (MD 0.04, 95% CI 0.01 to 0.07, P = 0.009) on discharge and may have had a shorter length of stay by 2 days (95% CI 0 to 4, P = 0.1) when compared to
Kinetically engendered subspinodal length scales in spontaneous dewetting of thin liquid films
NASA Astrophysics Data System (ADS)
Kotni, Tirumala Rao; Sarkar, Jayati; Khanna, Rajesh
2014-08-01
Numerical simulations reveal emergence of subspinodal length scales in spontaneous dewetting of nonslipping unstable thin liquid films on homogeneous substrates if the liquid viscosity decreases with decrease in film thickness.
Desert bird associations with broad-scale boundary length: Applications in avian conservation
Gutzwiller, K.J.; Barrow, W.C., Jr.
2008-01-01
1. Current understanding regarding the effects of boundaries on bird communities has originated largely from studies of forest-non-forest boundaries in mesic systems. To assess whether broad-scale boundary length can affect bird community structure in deserts, and to identify patterns and predictors of species' associations useful in avian conservation, we studied relations between birds and boundary-length variables in Chihuahuan Desert landscapes. Operationally, a boundary was the border between two adjoining land covers, and broad-scale boundary length was the total length of such borders in a large area. 2. Within 2-km radius areas, we measured six boundary-length variables. We analysed bird-boundary relations for 26 species, tested for assemblage-level patterns in species' associations with boundary-length variables, and assessed whether body size, dispersal ability and cowbird-host status were correlates of these associations. 3. The abundances or occurrences of a significant majority of species were associated with boundary-length variables, and similar numbers of species were related positively and negatively to boundary-length variables. 4. Disproportionately small numbers of species were correlated with total boundary length, land-cover boundary length and shrubland-grassland boundary length (variables responsible for large proportions of boundary length). Disproportionately large numbers of species were correlated with roadside boundary length and riparian vegetation-grassland boundary length (variables responsible for small proportions of boundary length). Roadside boundary length was associated (positively and negatively) with the most species. 5. Species' associations with boundary-length variables were not correlated with body size, dispersal ability or cowbird-host status. 6. Synthesis and applications. For the species we studied, conservationists can use the regressions we report as working models to anticipate influences of boundary-length changes
NASA Astrophysics Data System (ADS)
Sohrab, Siavash
Thermodynamic equilibrium between matter and radiation leads to de Broglie wavelength λdβ = h /mβvrβ and frequency νdβ = k /mβvrβ of matter waves and stochastic definitions of Planck h =hk =mk <λrk > c and Boltzmann k =kk =mk <νrk > c constants, λrkνrk = c , that respectively relate to spatial (λ) and temporal (ν) aspects of vacuum fluctuations. Photon massmk =√{ hk /c3 } , amu =√{ hkc } = 1 /No , and universal gas constant Ro =No k =√{ k / hc } result in internal Uk = Nhνrk = Nmkc2 = 3 Nmkvmpk2 = 3 NkT and potential pV = uN\\vcirc / 3 = N\\ucirc / 3 = NkT energy of photon gas in Casimir vacuum such that H = TS = 4 NkT . Therefore, Kelvin absolute thermodynamic temperature scale [degree K] is identified as length scale [meter] and related to most probable wavelength and de Broglie thermal wavelength as Tβ =λmpβ =λdβ / 3 . Parallel to Wien displacement law obtained from Planck distribution, the displacement law λwS T =c2 /√{ 3} is obtained from Maxwell -Boltzmann distribution of speed of ``photon clusters''. The propagation speeds of sound waves in ideal gas versus light waves in photon gas are described in terms of vrβ in harmony with perceptions of Huygens. Newton formula for speed of long waves in canals √{ p / ρ } is modified to √{ gh } =√{ γp / ρ } in accordance with adiabatic theory of Laplace.
Size effects and internal length scales in the elasticity of random fiber networks
NASA Astrophysics Data System (ADS)
Picu, Catalin; Berkache, Kamel; Shahsavari, Ali; Ganghoffer, Jean-Francois
Random fiber networks are the structural element of many biological and man-made materials, including connective tissue, various consumer products and packaging materials. In all cases of practical interest the scale at which the material is used and the scale of the fiber diameter or the mean segment length of the network are separated by several orders of magnitude. This precludes solving boundary value problems defined on the scale of the application while resolving every fiber in the system, and mandates the development of continuum equivalent models. To this end, we study the intrinsic geometric and mechanical length scales of the network and the size effect associated with them. We consider both Cauchy and micropolar continuum models and calibrate them based on the discrete network behavior. We develop a method to predict the characteristic length scales of the problem and the minimum size of a representative element of the network based on network structural parameters and on fiber properties.
Virtual Testing of Large Composite Structures: A Multiple Length/Time-Scale Framework
NASA Astrophysics Data System (ADS)
Gigliotti, Luigi; Pinho, Silvestre T.
2015-12-01
This paper illustrates a multiple length/time-scale framework for the virtual testing of large composite structures. Such framework hinges upon a Mesh Superposition Technique (MST) for the coupling between areas of the structure modelled at different length-scales and upon an efficient solid-to-shell numerical homogenization which exploits the internal symmetries of Unit Cells (UCs). Using this framework, it is possible to minimize the areas of the structure modelled at the lowest- (and computationally demanding) scales and the computational cost required to calculate the homogenised to be used in the higher-scales subdomains of multiscale FE models, as well as to simulate the mechanical response of different parts of the structure using different solvers, depending on where they are expected to provide the most computationally efficient solution. The relevance and key-aspects of the multiple length/time-scale framework are demonstrated through the analysis of a real-sized aeronautical composite component.
NASA Astrophysics Data System (ADS)
Zhang, Z.; Challamel, N.; Wang, C. M.
2013-09-01
This paper presents the determination of Eringen's small length scale coefficient e0 for buckling of nonlocal Timoshenko beam from a microstructured beam model. The microstructured beam model is composed of discrete rigid elements (of equal length), which are connected by rotational and shear springs that model the bending and shearing behaviors in a beam. The exact solution of e0 is given for nonlocal Timoshenko beam with small length scale term appearing in the normal stress-strain relation only. It is shown that e0 approaches 1/√12 ≈0.289 which coincides with the one calibrated for nonlocal Euler beams.
Characteristic length scales of the secondary relaxations in glass-forming glycerol.
Gupta, S; Mamontov, E; Jalarvo, N; Stingaciu, L; Ohl, M
2016-03-01
We investigate the secondary relaxations and their link to the main structural relaxation in glass-forming liquids using glycerol as a model system. We analyze the incoherent neutron scattering signal dependence on the scattering momentum transfer, Q , in order to obtain the characteristic length scale for different secondary relaxations. Such a capability of neutron scattering makes it somewhat unique and highly complementary to the traditional techniques of glass physics, such as light scattering and broadband dielectric spectroscopy, which provide information on the time scale, but not the length scales, of relaxation processes. The choice of suitable neutron scattering techniques depends on the time scale of the relaxation of interest. We use neutron backscattering to identify the characteristic length scale of 0.7 Å for the faster secondary relaxation described in the framework of the mode-coupling theory (MCT). Neutron spin-echo is employed to probe the slower secondary relaxation of the excess wing type at a low temperature ( ∼ 1.13T g . The characteristic length scale for this excess wing dynamics is approximately 4.7 Å. Besides the Q -dependence, the direct coupling of neutron scattering signal to density fluctuation makes this technique indispensable for measuring the length scale of the microscopic relaxation dynamics. PMID:27021657
Does Scale Length Matter? A Comparison of Nine- versus Five-Point Rating Scales for the Mini-CEX
ERIC Educational Resources Information Center
Cook, David A.; Beckman, Thomas J.
2009-01-01
Educators must often decide how many points to use in a rating scale. No studies have compared interrater reliability for different-length scales, and few have evaluated accuracy. This study sought to evaluate the interrater reliability and accuracy of mini-clinical evaluation exercise (mini-CEX) scores, comparing the traditional mini-CEX…
What can we learn about a dynamical length scale in glasses from measurements of surface mobility?
NASA Astrophysics Data System (ADS)
Forrest, J. A.
2013-08-01
We consider the ability of recent measurements on the size of a liquid-like mobile surface region in glasses to provide direct information on the length scale of enhanced surface mobility. While these quantities are strongly related there are important distinctions that limit the ability of measurements to quantify the actual length over which the surface properties change from surface to bulk-like. In particular, we show that for temperatures near the bulk glass transition, measurements of a liquid-like mobile layer may have very limited predictive power when it comes to determining the temperature dependent length scale of enhanced surface mobility near the glass transition temperature. This places important limitations on the ability of measurements of such enhanced surface dynamics to contribute to discussion on the length scale for dynamical correlation in glassy materials.
Improvement of modal scaling factors using mass additive technique
NASA Technical Reports Server (NTRS)
Zhang, Qiang; Allemang, Randall J.; Wei, Max L.; Brown, David L.
1987-01-01
A general investigation into the improvement of modal scaling factors of an experimental modal model using additive technique is discussed. Data base required by the proposed method consists of an experimental modal model (a set of complex eigenvalues and eigenvectors) of the original structure and a corresponding set of complex eigenvalues of the mass-added structure. Three analytical methods,i.e., first order and second order perturbation methods, and local eigenvalue modification technique, are proposed to predict the improved modal scaling factors. Difficulties encountered in scaling closely spaced modes are discussed. Methods to compute the necessary rotational modal vectors at the mass additive points are also proposed to increase the accuracy of the analytical prediction.
Experimental observation of a fundamental length scale of waves in random media.
Barkhofen, S; Metzger, J J; Fleischmann, R; Kuhl, U; Stöckmann, H-J
2013-11-01
Waves propagating through a weakly scattering random medium show a pronounced branching of the flow accompanied by the formation of freak waves, i.e., extremely intense waves. Theory predicts that this strong fluctuation regime is accompanied by its own fundamental length scale of transport in random media, parametrically different from the mean free path or the localization length. We show numerically how the scintillation index can be used to assess the scaling behavior of the branching length. We report the experimental observation of this scaling using microwave transport experiments in quasi-two-dimensional resonators with randomly distributed weak scatterers. Remarkably, the scaling range extends much further than expected from random caustics statistics. PMID:24237521
Universality of galactic surface densities within one dark halo scale-length.
Gentile, Gianfranco; Famaey, Benoit; Zhao, HongSheng; Salucci, Paolo
2009-10-01
It was recently discovered that the mean dark matter surface density within one dark halo scale-length (the radius within which the volume density profile of dark matter remains approximately flat) is constant across a wide range of galaxies. This scaling relation holds for galaxies spanning a luminosity range of 14 magnitudes and the whole Hubble sequence. Here we report that the luminous matter surface density is also constant within one scale-length of the dark halo. This means that the gravitational acceleration generated by the luminous component in galaxies is always the same at this radius. Although the total luminous-to-dark matter ratio is not constant, within one halo scale-length it is constant. Our finding can be interpreted as a close correlation between the enclosed surface densities of luminous and dark matter in galaxies. PMID:19794488
A crystal plasticity analysis of length-scale dependent internal stresses with image effects
NASA Astrophysics Data System (ADS)
Aghababaei, Ramin; Joshi, Shailendra P.
2012-12-01
In this work, we present a stress functions approach to include image effects in continuum crystal plasticity arising from the long-range elastic interactions (LRI) between the GND density and free surfaces. The resulting length-scale dependent internal stresses augment those produced by the GND density variation. The formulation is applied to the case of a long, thin specimen subjected to uniform curvature. The analysis shows that under nominally uniform GND density distribution, internal stresses arise from two sources: (1) GND-GND LRI arising from the finite spatial extent of the uniform GND density field and (2) the LRI between the GND density and free surfaces appearing as image fields. A comparison with experimental results suggests that the length-scale for internal stresses, described as a correlation length-scale, should increase with decreasing specimen thickness. This observation is rationalized by associating the internal length-scale with the average slip-plane spacing, which may increase with decreasing specimen size due to paucity of dislocation sources. Finally, we also discuss the length-scale dependent image stress in terms of the Peach-Koehler force density proposed by Gurtin (2002).
Dramatically growing shear rigidity length scale in the supercooled glass former NiZr2
NASA Astrophysics Data System (ADS)
Weingartner, Nicholas B.; Soklaski, Ryan; Kelton, K. F.; Nussinov, Zohar
2016-06-01
Finding a suitably growing length scale that increases in tandem with the immense viscous slowdown of supercooled liquids is an open problem associated with the glass transition. Here, we define and demonstrate the existence of one such length scale which may be experimentally verifiable. This is the length scale over which external shear perturbations appreciably penetrate into a liquid as the glass transition is approached. We provide simulation based evidence of its existence, and its growth by at least an order of magnitude, by using molecular dynamics simulations of NiZr2, a good fragile glass former. On the probed timescale, upon approaching the glass transition temperature Tg from above, this length scale ξ is also shown to be consistent with Ising-like scaling, ξ ∝(T/-Tg Tg)-ν , with ν ≈0.7 . Furthermore, we demonstrate the possible scaling of ξ about the temperature at which super-Arrhenius growth of viscosity, and a marked growth of the penetration depth, sets in. Our simulation results suggest that upon supercooling, marked initial increase of the shear penetration depth in fluids may occur in tandem with the breakdown of the Stokes-Einstein relation.
Microstructural characterization of transformable Fe-Mn alloys at different length scales
Liang, X.; Wang, X.; Zurob, H.S.
2009-11-15
The as-annealed and deformed Microstructure of transformable Fe-Mn alloys were, comprehensively, characterized over a wide range of length scales. Differential interference contrast optical metallography, combined with a tinting etching method, was employed to examine the grain morphology. A new specimen preparation method, involving electro-polishing and electro-etching, was developed for scanning electron microscopy and electron back-scattered diffraction analysis. This method leads to a very good imaging contrast and thus bridges the length scale gap between optical metallography and transmission electron microscopy. Moreover, it enables simultaneous scanning electron microscopy and electron backscatter diffraction analysis which allows correlations among morphology, crystal orientation and phase analysis in the length scale of microns. Transmission electron microscopy investigations were also made to evaluate the thermal and mechanical transformation products as well as defect structures.
NASA Astrophysics Data System (ADS)
Xia, Wenjie; Ruiz, Luis; Pugno, Nicola M.; Keten, Sinan
2016-03-01
Multi-layer graphene assemblies (MLGs) or fibers with a staggered architecture exhibit high toughness and failure strain that surpass those of the constituent single sheets. However, how the architectural parameters such as the sheet overlap length affect these mechanical properties remains unknown due in part to the limitations of mechanical continuum models. By exploring the mechanics of MLG assemblies under tensile deformation using our established coarse-grained molecular modeling framework, we have identified three different critical interlayer overlap lengths controlling the strength, plastic stress, and toughness of MLGs, respectively. The shortest critical length scale Lsc governs the strength of the assembly as predicted by the shear-lag model. The intermediate critical length Lpc is associated with a dynamic frictional process that governs the strain localization propensity of the assembly, and hence the failure strain. The largest critical length scale LTc corresponds to the overlap length necessary to achieve 90% of the maximum theoretical toughness of the material. Our analyses provide the general guidelines for tuning the constitutive properties and toughness of multilayer 2D nanomaterials using elasticity, interlayer adhesion energy and geometry as molecular design parameters.Multi-layer graphene assemblies (MLGs) or fibers with a staggered architecture exhibit high toughness and failure strain that surpass those of the constituent single sheets. However, how the architectural parameters such as the sheet overlap length affect these mechanical properties remains unknown due in part to the limitations of mechanical continuum models. By exploring the mechanics of MLG assemblies under tensile deformation using our established coarse-grained molecular modeling framework, we have identified three different critical interlayer overlap lengths controlling the strength, plastic stress, and toughness of MLGs, respectively. The shortest critical length scale
Surface-immobilized hydrogel patterns on length scales from micrometer to nanometer
NASA Astrophysics Data System (ADS)
Zeira, Assaf
The present work concentrates on the study of pattern generation and transfer processes of monolayer covered surfaces, deriving from the basic working concept of Constructive Lithography. As an advancement of constructive lithography, we developed a direct, one-step printing (contact electrochemical printing, CEP) and replication (contact electrochemical replication, CER) of hydrophilic organic monolayer patterns surrounded by a hydrophobic monolayer background. In addition, we present a process of transfer of metal between two contacting solid surfaces to predefined monolayer template pattern sites (contact electrochemical transfer, CET). This thesis shows that CEP, CER, and CET may be implemented under a variety of different experimental conditions, regardless of whether the initial "master" pattern was created by a parallel (fast) or serial (slow) patterning process. CEP and CER also posses the unique attractive property that each replica may equally function as master stamp in the fabrication of additional replicas. Moreover, due to a mechanism of selfcorrection patterned surfaces produced these process are often free of defects that the initial "master" stamp may had. We finally show that the electrochemical patterning of OTS monolayers on silicon can be further extended to flexible polymeric substrate materials as well as to a variety of chemical manipulations, allowing the fabrication of tridimensional (3D) composite structures made on the basis of readily available OTS compound. The results obtained suggest that such contact electrochemical processes could be used to rapidly generate multiple copies of surface patterns spanning variable length scales, this basic approach being applicable to rigid as well as flexible substrate materials.
Tests of the gravitational inverse-square law below the dark-energy length scale.
Kapner, D J; Cook, T S; Adelberger, E G; Gundlach, J H; Heckel, B R; Hoyle, C D; Swanson, H E
2007-01-12
We conducted three torsion-balance experiments to test the gravitational inverse-square law at separations between 9.53 mm and 55 microm, probing distances less than the dark-energy length scale lambda(d)=[4 -root](variant Planck's over 2pic/rho(d) approximately 85 microm. We find with 95% confidence that the inverse-square law holds (|alpha|
A grid-independent length scale for large-eddy simulations
NASA Astrophysics Data System (ADS)
Piomelli, U.; Geurts, B. J.
2009-11-01
In most large-eddy simulations a length-scale related to the grid size is used in the subgrid-scale models. Rapid variations of the mesh may cause errors and unphysical results. We propose a new length scale for small-scale turbulence models that is decoupled from the grid, and is determined dynamically from the velocity field itself. It is based on an approximation to a local integral scale used in turbulence models. The resulting eddy-viscosity model has many features of dynamic models (it vanishes near a wall or in laminar flows, and senses the local small scales of the flow) but does not require the use of spatial filtering operations, which are costly and may be difficult to perform on unstructured grids. The model coefficient is determined by a Successive Inverse Polynomial Interpolation procedure (Geurts & Meyers, 2006), in which the coefficient is optimized computationally to minimize a specified cost function. Since this procedure can be performed on coarse grids, it adds little to the computational cost of the method. A set of 4-6 coarse simulations with the new model is required to approximate the optimum with fair accuracy, and the total cost of a simulation is comparable to that of a single simulation with a dynamic model. The new length scale also has the desirable feature that refining the mesh does not result in a DNS, but in a grid-converged LES. Applications to plane channel and mixing layers will be presented.
The Venus ionopause current sheet - Thickness length scale and controlling factors
NASA Technical Reports Server (NTRS)
Elphic, R. C.; Russell, C. T.; Luhmann, J. G.; Scarf, F. L.; Brace, L. H.
1981-01-01
Data from the fluxgate magnetometer, plasma wave experiment and Langmuir probe aboard Pioneer Venus are used to investigate the characteristic thickness length scale of the ionopause current sheet, as well as how this length scale is controlled. Thickness is found to be a bistatic quality, large scales being associated with high field strengths and current sheet altitudes below 300 km, while smaller scales are found with lower field strengths and ionopause altitudes above 300 km. Ion collisions and plasma wave activity contribute to the formation of the broader, low-altitude ionopause current sheets. Although evidence suggests that the wave activity influences the thin ionopause current sheets, a simple model points to the control of the thin ionopause current sheets by ionospheric ion and electron temperatures
Xia, Wenjie; Ruiz, Luis; Pugno, Nicola M; Keten, Sinan
2016-03-17
Multi-layer graphene assemblies (MLGs) or fibers with a staggered architecture exhibit high toughness and failure strain that surpass those of the constituent single sheets. However, how the architectural parameters such as the sheet overlap length affect these mechanical properties remains unknown due in part to the limitations of mechanical continuum models. By exploring the mechanics of MLG assemblies under tensile deformation using our established coarse-grained molecular modeling framework, we have identified three different critical interlayer overlap lengths controlling the strength, plastic stress, and toughness of MLGs, respectively. The shortest critical length scale L governs the strength of the assembly as predicted by the shear-lag model. The intermediate critical length L is associated with a dynamic frictional process that governs the strain localization propensity of the assembly, and hence the failure strain. The largest critical length scale L corresponds to the overlap length necessary to achieve 90% of the maximum theoretical toughness of the material. Our analyses provide the general guidelines for tuning the constitutive properties and toughness of multilayer 2D nanomaterials using elasticity, interlayer adhesion energy and geometry as molecular design parameters. PMID:26935048
Eating disorder diagnostic scale: additional evidence of reliability and validity.
Stice, Eric; Fisher, Melissa; Martinez, Erin
2004-03-01
The authors conducted 4 studies investigating the reliability and validity of the Eating Disorder Diagnostic Scale (HDDS; E. Stice, C. F. Telch, & S. L. Rizvi, 2000), a brief self-report measure for diagnosing anorexia nervosa, bulimia nervosa, and binge eating disorder. Study 1 found that the HDDS showed criterion validity with interview-based diagnoses, convergent validity with risk factors for eating pathology, and internal consistency. Studies 2 and 3 found that the EDDS was sufficiently sensitive to detect the effects of eating disorder prevention programs. Regarding predictive validity, Studies 3 and 4 found that the EDDS predicted response to a prevention program and future onset of eating pathology and depression. Results provide additional evidence of the reliability and validity of this scale and suggest it may be useful in clinical and research applications. PMID:15023093
Infrared length scale and extrapolations for the no-core shell model
Wendt, K. A.; Forssén, C.; Papenbrock, T.; Sääf, D.
2015-06-03
In this paper, we precisely determine the infrared (IR) length scale of the no-core shell model (NCSM). In the NCSM, the A-body Hilbert space is truncated by the total energy, and the IR length can be determined by equating the intrinsic kinetic energy of A nucleons in the NCSM space to that of A nucleons in a 3(A-1)-dimensional hyper-radial well with a Dirichlet boundary condition for the hyper radius. We demonstrate that this procedure indeed yields a very precise IR length by performing large-scale NCSM calculations for 6Li. We apply our result and perform accurate IR extrapolations for bound statesmore » of 4He, 6He, 6Li, and 7Li. Finally, we also attempt to extrapolate NCSM results for 10B and 16O with bare interactions from chiral effective field theory over tens of MeV.« less
Nano-scaled graphene platelets with a high length-to-width aspect ratio
Zhamu, Aruna; Guo, Jiusheng; Jang, Bor Z.
2010-09-07
This invention provides a nano-scaled graphene platelet (NGP) having a thickness no greater than 100 nm and a length-to-width ratio no less than 3 (preferably greater than 10). The NGP with a high length-to-width ratio can be prepared by using a method comprising (a) intercalating a carbon fiber or graphite fiber with an intercalate to form an intercalated fiber; (b) exfoliating the intercalated fiber to obtain an exfoliated fiber comprising graphene sheets or flakes; and (c) separating the graphene sheets or flakes to obtain nano-scaled graphene platelets. The invention also provides a nanocomposite material comprising an NGP with a high length-to-width ratio. Such a nanocomposite can become electrically conductive with a small weight fraction of NGPs. Conductive composites are particularly useful for shielding of sensitive electronic equipment against electromagnetic interference (EMI) or radio frequency interference (RFI), and for electrostatic charge dissipation.
Infrared length scale and extrapolations for the no-core shell model
NASA Astrophysics Data System (ADS)
Wendt, K. A.; Forssén, C.; Papenbrock, T.; Sääf, D.
2015-06-01
We precisely determine the infrared (IR) length scale of the no-core shell model (NCSM). In the NCSM, the A -body Hilbert space is truncated by the total energy, and the IR length can be determined by equating the intrinsic kinetic energy of A nucleons in the NCSM space to that of A nucleons in a 3 (A -1 ) -dimensional hyper-radial well with a Dirichlet boundary condition for the hyper radius. We demonstrate that this procedure indeed yields a very precise IR length by performing large-scale NCSM calculations for 6Li. We apply our result and perform accurate IR extrapolations for bound states of 4He,6He,6Li , and 7Li . We also attempt to extrapolate NCSM results for 10B and 16O with bare interactions from chiral effective field theory over tens of MeV.
A modification in the technique of computing average lengths from the scales of fishes
Van Oosten, John
1953-01-01
In virtually all the studies that employ scales, otollths, or bony structures to obtain the growth history of fishes, it has been the custom to compute lengths for each individual fish and from these data obtain the average growth rates for any particular group. This method involves a considerable amount of mathematical manipulation, time, and effort. Theoretically it should be possible to obtain the same information simply by averaging the scale measurements for each year of life and the length of the fish employed and computing the average lengths from these data. This method would eliminate all calculations for individual fish. Although Van Oosten (1929: 338) pointed out many years ago the validity of this method of computation, his statements apparently have been overlooked by subsequent investigators.
Studying fractal geometry on submicron length scales by small-angle scattering
Wong, P.; Lin, J.
1988-08-01
Recent studies have shown that internal surfaces of porous geological materials, such as rocks and lignite coals, can be described by fractals down to atomic length scales. In this paper, the basic properties of self-similar and self-affine fractals are reviewed and how fractal dimensions can be measured by small-angle scattering experiments are discussed.
Near-wall reconstruction of higher order moments and length scales using the POD
NASA Technical Reports Server (NTRS)
Glauser, Mark N.
1992-01-01
An analysis of the near-wall behavior of the proper orthogonal decomposition (POD) eigenfunctions derived from direct numerical simulation (DNS) of channel flow is performed. Consistent with previous studies, a low order multi-mode reconstruction of the kinetic energy and Reynolds shear stress suffices. A similar reconstruction of the isotropic dissipation rate is shown to be insufficient, however. An analysis is performed of the multi-mode composition of the dissipation rate in the near-wall region, and it is shown that a significant number of higher-order modes are required to achieve the correct asymptotic consistency in the near-wall region. In an attempt to avoid this problem, a length scale definition is proposed in terms of an integration of the correlation tensor which factors in the presence of the wall. The wall is accounted for by only integrating out to 2y(+) and not over the entire domain. Viscous and inviscid estimates for the dissipation were used in the near-wall and core regions respectively, in conjunction with this length scale representation to obtain an estimate of the dissipation throughout the domain. The resulting dissipation exhibits the proper behavior near the wall and in the inertial layer. A 1 POD mode estimate of the length scale is computed and found to agree quite well with the length scale obtained when the entire correlation tensor is used.
Determining the optimal smoothing length scale for actuator line models of wind turbine blades
NASA Astrophysics Data System (ADS)
Martinez, Luis; Meneveau, Charles
2015-11-01
The actuator line model (ALM) is a widely used tool for simulating wind turbines when performing Large-Eddy Simulations. The ALM uses a smearing kernel ηɛ = 1 /ɛ3π 3 / 2 exp (-r2 /ɛ2) , where r is the distance to an actuator point, and ɛ is the smoothing length scale which establishes the kernel width, to project the lift and drag forces onto the grid. In this work, we develop formulations to establish the optimum value of the smoothing length scale ɛ, based on physical arguments, instead of purely numerical constraints. This parameter has a very important role in the ALM, to provide a length scale, which may, for example, be related to the chord of the airfoil being studied. In the proposed approach, we compare features (such as vertical pressure gradient) of a potential flow solution for flow over a lifting surface with features of the solution of the Euler equations with a body force term. The potential flow solution over a lifting surface is used as a general representation of an airfoil. The method presented aims to minimize the difference between these features of the flow fields as a function of the smearing length scale (ɛ), in order to obtain the optimum value. This work is supported by NSF (IGERT and IIA-1243482) and computations use XSEDE resources.
Length scaling of carbon nanotube electric and photo diodes down to sub-50 nm.
Xu, Haitao; Wang, Sheng; Zhang, Zhiyong; Peng, Lian-Mao
2014-09-10
Carbon nanotubes (CNTs) are promising candidates for future optoelectronics and logic circuits.1-3 Sub-10 nm channel length CNT transistors have been demonstrated with superb performance.4 Yet, the scaling of CNT p-n diodes or photodiodes, basic elements for most optoelectronic devices, is held back on a scale of micrometers.5-8 Here, we demonstrate that CNT diodes fabricated via a dopant-free technique show good rectifying characteristics and photovoltaic response even when the channel length is scaled to sub-50 nm. By making a trade-off between performance and size, a diode with both channel length and contact width around 100 nm, fabricated on a CNT with a small diameter (d ∼ 1.2 nm), shows a photovoltage of 0.24 V and a fill factor of up to 60%. Study on the dependence of turn-on voltage on scaled channel length reveals transferred charges induced potential barrier at the contact in long channel diodes and the effect of self-adjusting charge distribution. This effect could be utilized for realizing stable and high performance sub-100 nm pitch CNT diodes. As elementary building blocks, such tiny electric and photodiodes could be used in nanoscale rectifiers, photodetectors, light sources, and high-efficiency photovoltaic devices. PMID:25115287
NASA Astrophysics Data System (ADS)
Alberts, Samantha J.
The investigation of microgravity fluid dynamics emerged out of necessity with the advent of space exploration. In particular, capillary research took a leap forward in the 1960s with regards to liquid settling and interfacial dynamics. Due to inherent temperature variations in large spacecraft liquid systems, such as fuel tanks, forces develop on gas-liquid interfaces which induce thermocapillary flows. To date, thermocapillary flows have been studied in small, idealized research geometries usually under terrestrial conditions. The 1 to 3m lengths in current and future large tanks and hardware are designed based on hardware rather than research, which leaves spaceflight systems designers without the technological tools to effectively create safe and efficient designs. This thesis focused on the design and feasibility of a large length-scale thermocapillary flow experiment, which utilizes temperature variations to drive a flow. The design of a helical channel geometry ranging from 1 to 2.5m in length permits a large length-scale thermocapillary flow experiment to fit in a seemingly small International Space Station (ISS) facility such as the Fluids Integrated Rack (FIR). An initial investigation determined the proposed experiment produced measurable data while adhering to the FIR facility limitations. The computational portion of this thesis focused on the investigation of functional geometries of fuel tanks and depots using Surface Evolver. This work outlines the design of a large length-scale thermocapillary flow experiment for the ISS FIR. The results from this work improve the understanding thermocapillary flows and thus improve technological tools for predicting heat and mass transfer in large length-scale thermocapillary flows. Without the tools to understand the thermocapillary flows in these systems, engineers are forced to design larger, heavier vehicles to assure safety and mission success.
Scale and time dependence of serial correlations in word-length time series of written texts
NASA Astrophysics Data System (ADS)
Rodriguez, E.; Aguilar-Cornejo, M.; Femat, R.; Alvarez-Ramirez, J.
2014-11-01
This work considered the quantitative analysis of large written texts. To this end, the text was converted into a time series by taking the sequence of word lengths. The detrended fluctuation analysis (DFA) was used for characterizing long-range serial correlations of the time series. To this end, the DFA was implemented within a rolling window framework for estimating the variations of correlations, quantified in terms of the scaling exponent, strength along the text. Also, a filtering derivative was used to compute the dependence of the scaling exponent relative to the scale. The analysis was applied to three famous English-written literary narrations; namely, Alice in Wonderland (by Lewis Carrol), Dracula (by Bram Stoker) and Sense and Sensibility (by Jane Austen). The results showed that high correlations appear for scales of about 50-200 words, suggesting that at these scales the text contains the stronger coherence. The scaling exponent was not constant along the text, showing important variations with apparent cyclical behavior. An interesting coincidence between the scaling exponent variations and changes in narrative units (e.g., chapters) was found. This suggests that the scaling exponent obtained from the DFA is able to detect changes in narration structure as expressed by the usage of words of different lengths.
Integrated measurements of acoustical and optical thin layers II: Horizontal length scales
NASA Astrophysics Data System (ADS)
Moline, Mark A.; Benoit-Bird, Kelly J.; Robbins, Ian C.; Schroth-Miller, Maddie; Waluk, Chad M.; Zelenke, Brian
2010-01-01
The degree of layered organization of planktonic organisms in coastal systems impacts trophic interactions, the vertical availability of nutrients, and many biological rate processes. While there is reasonable characterization of the vertical structure of these phenomena, the extent and horizontal length scale of variation has rarely been addressed. Here we extend the examination of the vertical scale in the first paper of the series to the horizontal scale with combined shipboard acoustic measurements and bio-optic measurements taken on an autonomous underwater vehicle. Measurements were made in Monterey Bay, CA from 2002 to 2008 for the bio-optical parameters and during 2006 for acoustic scattering measurements. The combined data set was used to evaluate the horizontal decorrelation length scales of the bio-optical and acoustic scattering layers themselves. Because biological layers are often decoupled from the physical structure of the water column, assessment of the variance within identified layers was appropriate. This differs from other studies in that physical parameters were not used as a basis for the layer definition. There was a significant diel pattern to the decorrelation length scale for acoustic layers with the more abundant nighttime layers showing less horizontal variability despite their smaller horizontal extent. A significant decrease in the decorrelation length scale was found in bio-optical parameters over six years of study, coinciding with a documented shift in the plankton community. Results highlight the importance of considering plankton behavior and time of day with respect to scale when studying layers, and the challenges of sampling these phenomena.
NASA Astrophysics Data System (ADS)
Baglay, Roman; Roth, Connie
Polymer-polymer interfaces are ubiquitous in polymer blends and block copolymers, while opening up another avenue for the study of interfacial perturbations to the local glass transition temperature Tg(z). We have previously reported the full local Tg(z) profile across a glassy-rubbery polymer interface between polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA), an 80 K difference in bulk Tg [Baglay & Roth, J Chem Phys 2015, 143, 111101]. By using local fluorescence measurements, we revealed how the Tg(z) profile extends hundreds of nanometers away from the interface showing an asymmetric behavior penetrating deeper into the glassy PS side relative to the composition profile. Here, we extend these measurements to investigate how the local Tg profile in PS varies when in contact with a variety of immiscible polymers whose Tgs vary between +90 K and -80 K relative to the bulk Tg of PS, so-called hard vs. soft confinement. The data reveal that the onset of local Tg deviation from bulk in PS occurs at two distinct length scales, which depend on whether PS is the low Tg component (hard confinement) or the high Tg component (soft confinement). In addition, we explore the influence of finite system size on the range of dynamics by the introduction of periodic boundary conditions, as is commonly encountered in computer simulations or block copolymer systems.
Bounds on fifth forces at the sub-Å length scale
NASA Astrophysics Data System (ADS)
Salumbides, E. J.; Ubachs, W.; Korobov, V. I.
2014-06-01
Constraints on a possible fifth-force interaction between hadrons are derived based on an analysis of results from laser precision frequency measurements of antiprotonic helium atoms, both pHe+ and pHe+ species, and from experiments on resonant formation rates of ddμ+-ions in muon-catalyzed fusion processes. A comparison is made between accurate experimental data and first-principles theoretical descriptions of the exotic systems within a quantum electrodynamical framework. The agreement between theory and experiment sets general limits on a possible additional hadron-hadron interaction, written in the form of a Yukawa potential V5(r)=α5exp(-r/λ)/r, with λ representing the characteristic length scale associated with the mass of a hypothetical force-carrying particle via λ=ℏ/(m5c). The laser spectroscopic data of antiprotonic helium set a constraint of α5/αEM<10-8 for λ<1 Å, while the binding energy of the muonic molecular deuterium ion delivers a constraint of α5/αEM∼10-5 for λ<0.05 Å, where αEM represents the strength of the electromagnetic interaction or the fine structure constant.
Tricot, G; Saitoh, A; Takebe, H
2015-11-28
The structure of tin borophosphate glasses, considered for the development of low temperature sealing glasses or anode materials for Li-batteries, has been analysed at the intermediate length scale by a combination of high field standard and advanced 1D/2D nuclear magnetic resonance techniques. The nature and extent of B/P mixing were analysed using the (11)B((31)P) dipolar heteronuclear multiple quantum coherence NMR sequence and the data interpretation allowed (i) detecting the presence and analysing the nature of the B-O-P linkages, (ii) re-interpreting the 1D (31)P spectra and (iii) extracting the proportion of P connected to borate species. Interaction between the different borate species was analysed using the (11)B double quantum-simple quantum experiment to (i) investigate the presence and nature of the B-O-B linkage, (ii) assign the different borate species observed all along the composition line and (iii) monitor the borate network formation. In addition, (119)Sn static NMR was used to investigate the evolution of the chemical environment of the tin polyhedra. Altogether, the set of data allowed determining the structural units constituting the glass network and quantifying the extent of B/P mixing. The structural data were then used to explain the non-linear and unusual evolution of the glass transition temperature. PMID:26186677
Energy-Filtering Transmission Electron Microscopy on the Nanometer Length Scale
Grogger, Werner; Varela del Arco, Maria; Ristau, Roger; Schaffer, Bernhard; Hofer, Ferdinand; Krishnan, Kannan M.
2004-01-01
Energy-filtering transmission electron microscopy (EFTEM), developed about ten years ago, is now a routine analysis tool in the characterization of materials. Based on the physical principles of electron energy-loss spectrometry (EELS), but with the addition of in-column or post-column energy-filters, it forms images of microstructures using a narrow energy band of inelastically scattered electrons. Post-column energy-filters, developed commercially by Gatan (Gatan Imaging Filter, GIF) in the early 1990s, could be attached to nearly any TEM. Almost at the same time, the introduction of the EM-912 microscope with an integrated {Omega}-filter by Zeiss, made it possible to use in-column filters as well. These two developments made EFTEM possible on an almost routine basis. The operation of these filters is rather straightforward and it is now possible to acquire element specific images within a few minutes. However, the optimal setup for data acquisition, the judicious choice of experimental parameters to solve specific materials science problems and the interpretation of the results can be rather difficult. For best results, a fundamental knowledge of the underlying physics of EELS and a systematic development of the technical details is necessary. In this work, we discuss the current status of EFTEM in terms of spatial resolution and illustrate it with a few technologically relevant applications at the nanometer length scale.
Vertical length scale selection for pancake vortices in strongly stratified viscous fluids
NASA Astrophysics Data System (ADS)
Godoy-Diana, Ramiro; Chomaz, Jean-Marc; Billant, Paul
2004-04-01
The evolution of pancake dipoles of different aspect ratio is studied in a stratified tank experiment. Two cases are reported here for values of the dipole initial aspect ratio alpha_0 = L_v/L_h (where L_v and L_h are vertical and horizontal length scales, respectively) of alpha_0 = 0.4 (case I) and alpha_0 = 1.2 (case II). In the first case, the usual decay scenario is observed where the dipole diffuses slowly with a growing thickness and a decaying circulation. In case II, we observed a regime where the thickness of the dipole decreases and the circulation in the horizontal mid-plane of the vortices remains constant. We show that this regime where the vertical length scale decreases can be explained by the shedding of two boundary layers at the top and bottom of the dipole that literally peel off vorticity layers. Horizontal advection and vertical diffusion cooperate in this regime and the decrease towards the viscous vertical length scale delta = L_hRe(-1/2) occurs on a time scale alpha_0 Re(1/2) T_A, T_A being the advection time L_h/U. From a scaling analysis of the equations for a stratified viscous fluid in the Boussinesq approximation, two dominant balances depending on the parameter R = ReF_h(2) are discussed, where F_h = U/NL_h is the horizontal Froude number and Re = UL_h/nu is the Reynolds number, U, N and nu being, respectively, the translation speed of the dipole, the Brunt Väisälä frequency and the kinematic viscosity. When R≫ 1 the vertical length scale is determined by buoyancy effects to be of order L_b = U/N. The experiments presented in this paper pertain to the case of small R, where viscous effects govern the selection of the vertical length scale. We show that if initially L_v ≤ delta, the flow diffuses on the vertical (case I), while if L_v ≫ delta (case II), vertically sheared horizontal advection decreases the vertical length scale down to delta. This viscous regime may explain results from experiments and numerical simulations on
Hogstrom, L J; Guo, S M; Murugadoss, K; Bathe, M
2016-02-01
Brain function emerges from hierarchical neuronal structure that spans orders of magnitude in length scale, from the nanometre-scale organization of synaptic proteins to the macroscopic wiring of neuronal circuits. Because the synaptic electrochemical signal transmission that drives brain function ultimately relies on the organization of neuronal circuits, understanding brain function requires an understanding of the principles that determine hierarchical neuronal structure in living or intact organisms. Recent advances in fluorescence imaging now enable quantitative characterization of neuronal structure across length scales, ranging from single-molecule localization using super-resolution imaging to whole-brain imaging using light-sheet microscopy on cleared samples. These tools, together with correlative electron microscopy and magnetic resonance imaging at the nanoscopic and macroscopic scales, respectively, now facilitate our ability to probe brain structure across its full range of length scales with cellular and molecular specificity. As these imaging datasets become increasingly accessible to researchers, novel statistical and computational frameworks will play an increasing role in efforts to relate hierarchical brain structure to its function. In this perspective, we discuss several prominent experimental advances that are ushering in a new era of quantitative fluorescence-based imaging in neuroscience along with novel computational and statistical strategies that are helping to distil our understanding of complex brain structure. PMID:26855758
Probing sub-alveolar length scales with hyperpolarized-gas diffusion NMR
NASA Astrophysics Data System (ADS)
Miller, Wilson; Carl, Michael; Mooney, Karen; Mugler, John; Cates, Gordon
2009-05-01
Diffusion MRI of the lung is a promising technique for detecting alterations of normal lung microstructure in diseases such as emphysema. The length scale being probed using this technique is related to the time scale over which the helium-3 or xenon-129 diffusion is observed. We have developed new MR pulse sequence methods for making diffusivity measurements at sub-millisecond diffusion times, allowing one to probe smaller length scales than previously possible in-vivo, and opening the possibility of making quantitative measurements of the ratio of surface area to volume (S/V) in the lung airspaces. The quantitative accuracy of simulated and experimental measurements in microstructure phantoms will be discussed, and preliminary in-vivo results will be presented.
Composition dependence of charge and magnetic length scales in mixed valence manganite thin films
NASA Astrophysics Data System (ADS)
Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.
2016-07-01
Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1‑yPry)1‑xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1‑xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.
Composition dependence of charge and magnetic length scales in mixed valence manganite thin films.
Singh, Surendra; Freeland, J W; Fitzsimmons, M R; Jeen, H; Biswas, A
2016-01-01
Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1-yPry)1-xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1-xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties. PMID:27461993
Composition dependence of charge and magnetic length scales in mixed valence manganite thin films
Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.
2016-01-01
Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1−yPry)1−xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1−xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties. PMID:27461993
Natural length scales define the range of applicability of the Richards equation for capillary flows
NASA Astrophysics Data System (ADS)
Or, Dani; Lehmann, Peter; Assouline, Shmuel
2015-09-01
The rapid expansion of remotely sensed spatial information and enhanced computational capabilities fuel raising scientific and public expectations for reliable hydrologic predictions across time and spatial scales. Process-based hydrologic models often rely on the Richards equation (RE) formalism to represent unsaturated flow processes at multiple scales which raises the much debated question: does the underlying physics in the RE formulation apply at large scales of practical interest? The study analyses recent findings from different unsaturated flow processes (soil evaporation, internal redistribution, and capillary flow from point sources) revealing inherent characteristic length scales that delineate the spatial range of applicability of the RE. These length scales reflect the role of intrinsic porous medium properties that shape liquid phase continuity and interplay of forces that drive and resist unsaturated flow. The study revisits some of the key assumptions in the RE and their ramifications for numerical discretization. An intrinsic length scale for hydraulic continuity deduced from pore size distribution has been shown to control soil evaporation dynamics (i.e., stage 1 to stage 2 transition), to provide upper bounds for regional evaporative losses, and governs the dynamics of internal redistribution toward field capacity. For large-scale hydrologic applications, we show that the spatial extent of lateral flow interactions under most natural capillary gradients rarely exceed a few meters. The study provides a framework for guiding numerical and mathematical models for capillary flows across different scales considering the conditions for coexistence of stationarity, hydraulic continuity, and capillary gradients—essential ingredients for physically consistent application of the RE.
NASA Astrophysics Data System (ADS)
Mezzenga, Raffaele; Hammond, Matthew; Klok, Harm-Anton
2008-03-01
A peptide-synthetic hybrid block copolymer, poly(ethylene oxide)-block-poly(L-glutamic acid), is demonstrated to form supramolecular complexes with primary alkylamines of varying alkyl chain length (8 to 18 methylene units) in organic solvents via acid-base proton transfer and subsequent ionic bonding. The peptidic block being in the α-helical conformation, these materials behave as coil-``hairy rod'' block copolymers, and show hierarchically self-organized nanostructures in the solid state; X-ray scattering measurements show mesomorphic behavior at the length scales of both the overall block copolymer and the polypeptide-alkylammonium complex.
Scaling analysis of random walks with persistence lengths: Application to self-avoiding walks
NASA Astrophysics Data System (ADS)
Granzotti, C. R. F.; Martinez, A. S.; da Silva, M. A. A.
2016-05-01
We develop an approach for performing scaling analysis of N -step random walks (RWs). The mean square end-to-end distance,
Measurements of the Influence of Integral Length Scale on Stagnation Region Heat Transfer
NASA Technical Reports Server (NTRS)
Vanfossen, G. James; Ching, Chang Y.
1994-01-01
The purpose was twofold: first, to determine if a length scale existed that would cause the greatest augmentation in stagnation region heat transfer for a given turbulence intensity and second, to develop a prediction tool for stagnation heat transfer in the presence of free stream turbulence. Toward this end, a model with a circular leading edge was fabricated with heat transfer gages in the stagnation region. The model was qualified in a low turbulence wind tunnel by comparing measurements with Frossling's solution for stagnation region heat transfer in a laminar free stream. Five turbulence generating grids were fabricated; four were square mesh, biplane grids made from square bars. Each had identical mesh to bar width ratio but different bar widths. The fifth grid was an array of fine parallel wires that were perpendicular to the axis of the cylindrical leading edge. Turbulence intensity and integral length scale were measured as a function of distance from the grids. Stagnation region heat transfer was measured at various distances downstream of each grid. Data were taken at cylinder Reynolds numbers ranging from 42,000 to 193,000. Turbulence intensities were in the range 1.1 to 15.9 percent while the ratio of integral length scale to cylinder diameter ranged from 0.05 to 0.30. Stagnation region heat transfer augmentation increased with decreasing length scale. An optimum scale was not found. A correlation was developed that fit heat transfer data for the square bar grids to within +4 percent. The data from the array of wires were not predicted by the correlation; augmentation was higher for this case indicating that the degree of isotropy in the turbulent flow field has a large effect on stagnation heat transfer. The data of other researchers are also compared with the correlation.
Physics on the Smallest Scales: An Introduction to Minimal Length Phenomenology
ERIC Educational Resources Information Center
Sprenger, Martin; Nicolini, Piero; Bleicher, Marcus
2012-01-01
Many modern theories which try to unify gravity with the Standard Model of particle physics, such as e.g. string theory, propose two key modifications to the commonly known physical theories: the existence of additional space dimensions; the existence of a minimal length distance or maximal resolution. While extra dimensions have received a wide…
Winterhalter, Wade E.
2011-09-01
Global climate change is expected to impact biological populations through a variety of mechanisms including increases in the length of their growing season. Climate models are useful tools for predicting how season length might change in the future. However, the accuracy of these models tends to be rather low at regional geographic scales. Here, I determined the ability of several atmosphere and ocean general circulating models (AOGCMs) to accurately simulate historical season lengths for a temperate ectotherm across the continental United States. I also evaluated the effectiveness of regional-scale correction factors to improve the accuracy of these models. I found that both the accuracy of simulated season lengths and the effectiveness of the correction factors to improve the model's accuracy varied geographically and across models. These results suggest that regional specific correction factors do not always adequately remove potential discrepancies between simulated and historically observed environmental parameters. As such, an explicit evaluation of the correction factors' effectiveness should be included in future studies of global climate change's impact on biological populations.
Winterhalter, Wade E.
2011-09-01
Global climate change is expected to impact biological populations through a variety of mechanisms including increases in the length of their growing season. Climate models are useful tools for predicting how season length might change in the future. However, the accuracy of these models tends to be rather low at regional geographic scales. Here, I determined the ability of several atmosphere and ocean general circulating models (AOGCMs) to accurately simulate historical season lengths for a temperate ectotherm across the continental United States. I also evaluated the effectiveness of regional-scale correction factors to improve the accuracy of these models. I foundmore » that both the accuracy of simulated season lengths and the effectiveness of the correction factors to improve the model's accuracy varied geographically and across models. These results suggest that regional specific correction factors do not always adequately remove potential discrepancies between simulated and historically observed environmental parameters. As such, an explicit evaluation of the correction factors' effectiveness should be included in future studies of global climate change's impact on biological populations.« less
Mitotic chromosome length scales in response to both cell and nuclear size
Ladouceur, Anne-Marie; Dorn, Jonas F.
2015-01-01
Multicellular development requires that cells reduce in size as a result of consecutive cell divisions without increase in embryo volume. To maintain cellular integrity, organelle size adapts to cell size throughout development. During mitosis, the longest chromosome arm must be shorter than half of the mitotic spindle for proper chromosome segregation. Using high-resolution time-lapse microscopy of living Caenorhabditis elegans embryos, we have quantified the relation between cell size and chromosome length. In control embryos, chromosome length scaled to cell size. Artificial reduction of cell size resulted in a shortening of chromosome length, following a trend predicted by measurements from control embryos. Disturbing the RAN (Ras-related nuclear protein)-GTP gradient decoupled nuclear size from cell size and resulted in chromosome scaling to nuclear size rather than cell size; smaller nuclei contained shorter chromosomes independent of cell size. In sum, quantitative analysis relating cell, nuclear, and chromosome size predicts two levels of chromosome length regulation: one through cell size and a second in response to nuclear size. PMID:26033258
Stability of two-dimensional soft quasicrystals in systems with two length scales.
Jiang, Kai; Tong, Jiajun; Zhang, Pingwen; Shi, An-Chang
2015-10-01
The relative stability of two-dimensional soft quasicrystals in systems with two length scales is examined using a recently developed projection method, which provides a unified numerical framework to compute the free energy of periodic crystal and quasicrystals. Accurate free energies of numerous ordered phases, including dodecagonal, decagonal, and octagonal quasicrystals, are obtained for a simple model, i.e., the Lifshitz-Petrich free-energy functional, of soft quasicrystals with two length scales. The availability of the free energy allows us to construct phase diagrams of the system, demonstrating that, for the Lifshitz-Petrich model, the dodecagonal and decagonal quasicrystals can become stable phases, whereas the octagonal quasicrystal stays as a metastable phase. PMID:26565220
Structure, dynamics and multiple length-scales in network-forming materials
NASA Astrophysics Data System (ADS)
Wilson, Mark
2016-07-01
Relationships between the structural and dynamical properties of network-forming materials are investigated. A generic model is utilised for systems of stoichiometry MX2 which are linked in the sense that they can all be usefully considered as constructed from linked MX4 tetrahedra. A single model parameter (the anion polarizability) is varied systematically to control the mean MXM bond angles (and hence the network topologies). The networks evolve from those dominated by corner-sharing units to those dominated by edge-sharing structural motifs. These changes are accompanied by changes in the characteristic length-scales, with the emergence of ordering on intermediate length-scales. Key dynamical properties (the liquid relaxation just above the melting point and the liquid fragility) are studied and their relationship to the underlying static structure analysed.
Jamshidian, M.; Rabczuk, T.
2014-03-15
We establish the correlation between the diffuse interface and sharp interface descriptions for stressed grain boundary migration by presenting analytical solutions for stressed migration of a circular grain boundary in a bicrystalline phase field domain. The validity and accuracy of the phase field model is investigated by comparing the phase field simulation results against analytical solutions. The phase field model can reproduce precise boundary kinetics and stress evolution provided that a thermodynamically consistent theory and proper expressions for model parameters in terms of physical material properties are employed. Quantitative phase field simulations are then employed to investigate the effect of microstructural length scale on microstructure and texture evolution by stressed grain growth in an elastically deformed polycrystalline aggregate. The simulation results reveal a transitional behaviour from normal to abnormal grain growth by increasing the microstructural length scale.
The role of reactant unmixedness, strain rate, and length scale on premixed combustor performance
Samuelsen, S.; LaRue, J.; Vilayanur, S.; Guillaume, D.
1995-12-31
Lean premixed combustion provides a means to reduce pollutant formation and increase combustion efficiency. However, fuel-air mixing is rarely uniform in space and time. This nonuniformity in concentration will lead to relative increases in pollutant formation and decreases in combustion efficiency. The nonuniformity of the concentration at the exit of the premixer has been defined by Lyons (1981) as the ``unmixedness.`` Although turbulence properties such as length scales and strain rate are known to effect unmixedness, the exact relationship is unknown. Evaluating this relationship and the effect of unmixedness in premixed combustion on pollutant formation and combustion efficiency are an important part of the overall goal of US Department of Energy`s Advanced Turbine System (ATS) program and are among the goals of the program described herein. The information obtained from ATS is intended to help to develop and commercialize gas turbines. The contributions to the program which the University of California (Irvine) Combustion Lab (UCICL) will provide are: (1) establish the relationship of inlet unmixedness, length scales, and mean strain rate to performance, (2) determine the optimal levels of inlet unmixedness, length scales, and mean strain rates to maximize combustor performance, and (3) identify efficient premixing methods for achieving the necessary inlet conditions. The program during this reporting period is focused on developing a means to measure and qualify different degrees of temporal and spatial unmixedness. Laser diagnostic methods for planer unmixedness measurements are being developed and preliminary results are presented herein. These results will be used to (1), aid in the design of experimental premixers, and (2), determine the unmixedness which will be correlated with the emissions of the combustor. This measure of unmixedness coupled with length scale, strain rate and intensity information is required to attain the UCI goals.
Factorial Moments Analyses Show a Characteristic Length Scale in DNA Sequences
NASA Astrophysics Data System (ADS)
Mohanty, A. K.; Narayana Rao, A. V. S. S.
2000-02-01
A unique feature of most of the DNA sequences, found through the factorial moments analysis, is the existence of a characteristic length scale around which the density distribution is nearly Poissonian. Above this point, the DNA sequences, irrespective of their intron contents, show long range correlations with a significant deviation from the Gaussian statistics, while, below this point, the DNA statistics are essentially Gaussian. The famous DNA walk representation is also shown to be a special case of the present analysis.
Energy Dependence and Scaling Property of Localization Length near a Gapped Flat Band
NASA Astrophysics Data System (ADS)
Ge, Li; Tureci, Hakan
Using a tight-binding model for a one-dimensional Lieb lattice, we show that the localization length near a gapped flat band behaves differently from the typical Urbach tail in a band gap: instead of reducing monotonically as the energy E moves away from the flat band energy Ef, the presence of the flat band causes a nonmonotonic energy dependence of the localization length. This energy dependence follows a scaling property when the energy is within the spread (W) of uniformly distributed diagonal disorder, i.e. the localization length is only a function of (E-Ef)/W. Several other lattices are compared to distinguish the effect of the flat band on the localization length, where we eliminate, shift, or duplicate the flat band, without changing the dispersion relations of other bands. Using the top right element of the Green's matrix, we derive an analytical relation between the density of states and the localization length, which shines light on these properties of the latter, including a summation rule for its inverse. This work is partially supported by NSF under Grant No. DMR-1506987.
NASA Astrophysics Data System (ADS)
Chiang, Fu-Pen
Sandwich panels with foam core have gained substantial importance in marine structures for the past several decades. However, designers of ships still lack the confidence in composites when compared to traditional structural materials such as aluminum or steel. As a result, composite structures tend to be overdesigned to provide added safety. While there have been numerous studies, most investigators treat the foam cores as made of homogeneous and isotropic materials. But at the length scale of the order of millimeter or smaller, foam is neither homogeneous nor isotropic. In this paper, we present some results of the characteristics of deformation and failure mechanism of polymer foam composites at different length scales. Central to this investigation is a multiscale digital speckle photography technique whereby we can measure detailed full deformation with spatial resolution ranging from centimeters to micrometers. We first investigate the size effect on the mechanical properties of polyurethane foams with and without nanoparticles, crack tip deformation field at different length scales, and the crack propagation characteristics in a foam. Then we present results for a newly created auxetic PVC foam composite. Auxetic materials have a negative Poisson's ratio rendering them to be more resistant to shear failure, indentation, and impact damages. We describe the manufacturing process of this material and demonstrate its advantageous properties as compared to the original foam.
LPI Thresholds in Longer Scale Length Plasmas Driven by the Nike Laser*
NASA Astrophysics Data System (ADS)
Weaver, J.; Oh, J.; Phillips, L.; Afeyan, B.; Seely, J.; Kehne, D.; Brown, C.; Obenschain, S.; Serlin, V.; Schmitt, A. J.; Feldman, U.; Holland, G.; Lehmberg, R. H.; McLean, E.; Manka, C.
2010-11-01
The Krypton-Fluoride (KrF) laser is an attractive driver for inertial confinement fusion due to its short wavelength (248nm), large bandwidth (1-3 THz), and beam smoothing by induced spatial incoherence. Experiments with the Nike KrF laser have demonstrated intensity thresholds for laser plasma instabilities (LPI) higher than reported for other high power lasers operating at longer wavelengths (>=351 nm). The previous Nike experiments used short pulses (350 ps FWHM) and small spots (<260 μm FWHM) that created short density scale length plasmas (Ln˜50-70 μm) from planar CH targets and demonstrated the onset of two-plasmon decay (2φp) at laser intensities ˜2x10^15 W/cm^2. This talk will present an overview of the current campaign that uses longer pulses (0.5-4.0 ns) to achieve greater density scale lengths (Ln˜100-200 μm). X-rays, emission near ^1/2φo and ^3/2φo harmonics, and reflected laser light have been monitored for onset of 2φp. The longer density scale lengths will allow better comparison to results from other laser facilities. *Work supported by DoE/NNSA and ONR.
Spacetime with zero point length is two-dimensional at the Planck scale
NASA Astrophysics Data System (ADS)
Padmanabhan, T.; Chakraborty, Sumanta; Kothawala, Dawood
2016-05-01
It is generally believed that any quantum theory of gravity should have a generic feature—a quantum of length. We provide a physical ansatz to obtain an effective non-local metric tensor starting from the standard metric tensor such that the spacetime acquires a zero-point-length ℓ _0 of the order of the Planck length LP. This prescription leads to several remarkable consequences. In particular, the Euclidean volume V_D(ℓ ,ℓ _0) in a D-dimensional spacetime of a region of size ℓ scales as V_D(ℓ , ℓ _0) ∝ ℓ _0^{D-2} ℓ ^2 when ℓ ˜ ℓ _0, while it reduces to the standard result V_D(ℓ ,ℓ _0) ∝ ℓ ^D at large scales (ℓ ≫ ℓ _0). The appropriately defined effective dimension, D_eff , decreases continuously from D_eff=D (at ℓ ≫ ℓ _0) to D_eff=2 (at ℓ ˜ ℓ _0). This suggests that the physical spacetime becomes essentially 2-dimensional near Planck scale.
Measurement of Two-Plasmon-Decay Dependence on Plasma Density Scale Length
NASA Astrophysics Data System (ADS)
Haberberger, D.
2013-10-01
An accurate understanding of the plasma scale-length (Lq) conditions near quarter-critical density is important in quantifying the hot electrons generated by the two-plasmon-decay (TPD) instability in long-scale-length plasmas. A novel target platform was developed to vary the density scale length and an innovative diagnostic was implemented to measure the density profiles above 1021 cm-3 where TPD is expected to have the largest growth. A series of experiments was performed using the four UV (351-nm) beams on OMEGA EP that varied the Lq by changing the radius of curvature of the target while maintaining a constant Iq/Tq. The fraction of laser energy converted to hot electrons (fhot) was observed to increase rapidly from 0.005% to 1% by increasing the plasma scale length from 130 μm to 300 μm, corresponding to target diameters of 0.4 mm to 8 mm. A new diagnostic was developed based on refractometry using angular spectral filters to overcome the large phase accumulation in standard interferometric techniques. The angular filter refractometer measures the refraction angles of a 10-ps, 263-nm probe laser after propagating through the plasma. An angular spectral filter is used in the Fourier plane of the probe beam, where the refractive angles of the rays are mapped to space. The edges of the filter are present in the image plane and represent contours of constant refraction angle. These contours are used to infer the phase of the probe beam, which are used to calculate the plasma density profile. In long-scale-length plasmas, the diagnostic currently measures plasma densities from ~1019 cm-3 to ~2 × 1021 cm-3. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. In collaboration with D. H. Edgell, S. X. Hu, S. Ivancic, R. Boni, C. Dorrer, and D. H. Froula (Laboratory for Laser Energetics, U. of Rochester).
Meier, Andrea R; Schmuck, Ute; Meloro, Carlo; Clauss, Marcus; Hofmann, Reinhold R
2016-03-01
Various morphological measures demonstrate convergent evolution in ruminants with their natural diet, in particular with respect to the browser/grazer dichotomy. Here, we report quantitative macroanatomical measures of the tongue (length and width of specific parts) of 65 ruminant species and relate them to either body mass (BM) or total tongue length, and to the percentage of grass in the natural diet (%grass). Models without and with accounting for the phylogenetic structures of the dataset were used, and models were ranked using Akaike's Information Criterion. Scaling relationships followed geometric principles, that is, length measures scaled with BM to the power of 0.33. Models that used tongue length rather than BM as a body size proxy were consistently ranked better, indicating that using size proxies that are less susceptible to a wider variety of factors (such as BM that fluctuates with body condition) should be attempted whenever possible. The proportion of the freely mobile tongue tip of the total tongue (and hence also the corpus length) was negatively correlated to %grass, in accordance with concepts that the feeding mechanism of browsers requires more mobile tongues. It should be noted that some nonbrowsers, such as cattle, use a peculiar mechanism for grazing that also requires long, mobile tongues, but they appear to be exceptions. A larger corpus width with increasing %grass corresponds to differences in snout shape with broader snouts in grazers. The Torus linguae is longer with increasing %grass, a finding that still warrants functional interpretation. This study shows that tongue measures covary with diet in ruminants. In contrast, the shape of the tongue (straight or "hourglass-shaped" as measured by the ratio of the widest and smallest corpus width) is unrelated to diet and is influenced strongly by phylogeny. PMID:26647882
Physics on the smallest scales: an introduction to minimal length phenomenology
NASA Astrophysics Data System (ADS)
Sprenger, Martin; Nicolini, Piero; Bleicher, Marcus
2012-07-01
Many modern theories which try to unify gravity with the Standard Model of particle physics, such as e.g. string theory, propose two key modifications to the commonly known physical theories: the existence of additional space dimensions; the existence of a minimal length distance or maximal resolution. While extra dimensions have received a wide coverage in publications over the last ten years (especially due to the prediction of micro black hole production at the Large Hadron Collider), the phenomenology of models with a minimal length is still less investigated. In a summer study project for bachelor students in 2010, we have explored some phenomenological implications of the potential existence of a minimal length. In this paper, we review the idea and formalism of a quantum gravity-induced minimal length in the generalized uncertainty principle framework as well as in the coherent state approach to non-commutative geometry. These approaches are effective models which can make model-independent predictions for experiments and are ideally suited for phenomenological studies. Pedagogical examples are provided to grasp the effects of a quantum gravity-induced minimal length. This paper is intended for graduate students and non-specialists interested in quantum gravity.
Tritschler, V K; Zubel, M; Hickel, S; Adams, N A
2014-12-01
In this study we present direct numerical simulation results of the Richtmyer-Meshkov instability (RMI) initiated by Ma=1.05,Ma=1.2, and Ma=1.5 shock waves interacting with a perturbed planar interface between air and SF(6). At the lowest shock Mach number the fluids slowly mix due to viscous diffusion, whereas at the highest shock Mach number the mixing zone becomes turbulent. When a minimum critical Taylor microscale Reynolds number is exceeded, an inertial range spectrum emerges, providing further evidence of transition to turbulence. The scales of turbulent motion, i.e., the Kolmogorov length scale, the Taylor microscale, and the integral length, scale are presented. The separation of these scales is found to increase as the Reynolds number is increased. Turbulence statistics, i.e., the probability density functions of the velocity and its longitudinal and transverse derivatives, show a self-similar decay and thus that turbulence evolving from RMI is not fundamentally different from isotropic turbulence, though nominally being only isotropic and homogeneous in the transverse directions. PMID:25615181
Barenblatt, G. I.; Chorin, A. J.; Prostokishin, V. M.
2000-01-01
In a turbulent boundary layer over a smooth flat plate with zero pressure gradient, the intermediate structure between the viscous sublayer and the free stream consists of two layers: one adjacent to the viscous sublayer and one adjacent to the free stream. When the level of turbulence in the free stream is low, the boundary between the two layers is sharp, and both have a self-similar structure described by Reynolds-number-dependent scaling (power) laws. This structure introduces two length scales: one—the wall-region thickness—determined by the sharp boundary between the two intermediate layers and the second determined by the condition that the velocity distribution in the first intermediate layer be the one common to all wall-bounded flows and in particular coincide with the scaling law previously determined for pipe flows. Using recent experimental data, we determine both these length scales and show that they are close. Our results disagree with the classical model of the “wake region.” PMID:10760253
Measurements of the effect of free-stream turbulence length scale on heat transfer
NASA Astrophysics Data System (ADS)
Moss, R. W.; Oldfield, M. L. G.
1992-06-01
The effects of free-stream turbulence scale on heat transfer through a turbulent flat plate boundary layer have been measured. A variety of turbulence spectra were produced by parallel bar grids. The design of these was guided by previous measurements of combustion chamber turbulence. Heat transfer was measured transiently using thin film gauges. The heat transfer to the plate was found to be a function of turbulence integral length scale as well as intensity, and is of relevance to gas turbine heat transfer where airfoils are subject to high turbulence levels from the combustor. Enhancement factors of up to 40 percent were experienced and the results extend conclusions drawn by other workers to higher turbulence levels and scales.
Scaling of the critical free length for progressive unfolding of self-bonded graphene
Kwan, Kenny; Cranford, Steven W.
2014-05-19
Like filled pasta, rolled or folded graphene can form a large nanocapsule surrounding a hollow interior. Use as a molecular carrier, however, requires understanding of the opening of such vessels. Here, we investigate a monolayer sheet of graphene as a theoretical trial platform for such a nanocapsule. The graphene is bonded to itself via aligned disulfide (S-S) bonds. Through theoretical analysis and atomistic modeling, we probe the critical nonbonded length (free length, L{sub crit}) that induces fracture-like progressive unfolding as a function of folding radius (R{sub i}). We show a clear linear scaling relationship between the length and radius, which can be used to determine the necessary bond density to predict mechanical opening/closing. However, stochastic dissipated energy limits any exact elastic formulation, and the required energy far exceeds the dissociation energy of the S-S bond. We account for the necessary dissipated kinetic energy through a simple scaling factor (Ω), which agrees well with computational results.
Large-scale evidence of dependency length minimization in 37 languages
Futrell, Richard; Mahowald, Kyle; Gibson, Edward
2015-01-01
Explaining the variation between human languages and the constraints on that variation is a core goal of linguistics. In the last 20 y, it has been claimed that many striking universals of cross-linguistic variation follow from a hypothetical principle that dependency length—the distance between syntactically related words in a sentence—is minimized. Various models of human sentence production and comprehension predict that long dependencies are difficult or inefficient to process; minimizing dependency length thus enables effective communication without incurring processing difficulty. However, despite widespread application of this idea in theoretical, empirical, and practical work, there is not yet large-scale evidence that dependency length is actually minimized in real utterances across many languages; previous work has focused either on a small number of languages or on limited kinds of data about each language. Here, using parsed corpora of 37 diverse languages, we show that overall dependency lengths for all languages are shorter than conservative random baselines. The results strongly suggest that dependency length minimization is a universal quantitative property of human languages and support explanations of linguistic variation in terms of general properties of human information processing. PMID:26240370
Second-moment closures and length scales for weakly stratified turbulent shear flows
NASA Astrophysics Data System (ADS)
Baumert, Helmut; Peters, Hartmut
2000-03-01
For the special hydrodynamic situation of unbounded homogeneous shear layers, turbulence closure models of Mellor-Yamada type (MY) and k-ɛ type are put into a single canonical form. For this situation we show that conventional versions of MY and various k-ɛ versions lack a proper steady state, and are unable to simulate the most basic properties of stratified shear flows exemplified in, for example, the Rohr et al. [1988] experiments: exponential growth at sufficiently low gradient Richardson number (Rg), exponential decay at sufficiently large Rg, and a steady state in between. Proper choice of one special model parameter readily solves the problems. In the fairly general case of structural equilibrium (state of exponential evolution) in weakly to moderately stratified turbulence (Rg ≲ 0.25), the ratio between the Thorpe scale (or Ellison scale) and the Ozmidov scale varies like the gradient Richardson number (Rg) to the power 3/4, and the ratio of the Thorpe scale to the buoyancy scale varies like Rg1/2. Length scales predicted by our current model are consistent with laboratory measurements of Rohr et al. [1988], with large-eddy numerical simulations of Schumann and Gerz [1995], and with microstructure measurements from the 1987 Tropic Heat Experiment in the equatorial Pacific by Peters et al. [1995].
Enright, Ryan; Miljkovic, Nenad; Al-Obeidi, Ahmed; Thompson, Carl V; Wang, Evelyn N
2012-10-01
Water condensation on surfaces is a ubiquitous phase-change process that plays a crucial role in nature and across a range of industrial applications, including energy production, desalination, and environmental control. Nanotechnology has created opportunities to manipulate this process through the precise control of surface structure and chemistry, thus enabling the biomimicry of natural surfaces, such as the leaves of certain plant species, to realize superhydrophobic condensation. However, this "bottom-up" wetting process is inadequately described using typical global thermodynamic analyses and remains poorly understood. In this work, we elucidate, through imaging experiments on surfaces with structure length scales ranging from 100 nm to 10 μm and wetting physics, how local energy barriers are essential to understand non-equilibrium condensed droplet morphologies and demonstrate that overcoming these barriers via nucleation-mediated droplet-droplet interactions leads to the emergence of wetting states not predicted by scale-invariant global thermodynamic analysis. This mechanistic understanding offers insight into the role of surface-structure length scale, provides a quantitative basis for designing surfaces optimized for condensation in engineered systems, and promises insight into ice formation on surfaces that initiates with the condensation of subcooled water. PMID:22931378
Artan, Guleid A.; Neale, C. M. U.; Tarboton, D. G.
2000-01-01
The appropriate spatial scale for a distributed energy balance model was investigated by: (a) determining the scale of variability associated with the remotely sensed and GIS-generated model input data; and (b) examining the effects of input data spatial aggregation on model response. The semi-variogram and the characteristic length calculated from the spatial autocorrelation were used to determine the scale of variability of the remotely sensed and GIS-generated model input data. The data were collected from two hillsides at Upper Sheep Creek, a sub-basin of the Reynolds Creek Experimental Watershed, in southwest Idaho. The data were analyzed in terms of the semivariance and the integral of the autocorrelation. The minimum characteristic length associated with the variability of the data used in the analysis was 15 m. Simulated and observed radiometric surface temperature fields at different spatial resolutions were compared. The correlation between agreement simulated and observed fields sharply declined after a 10×10 m2 modeling grid size. A modeling grid size of about 10×10 m2 was deemed to be the best compromise to achieve: (a) reduction of computation time and the size of the support data; and (b) a reproduction of the observed radiometric surface temperature.
Zavadil, Kevin Robert; Wall, Frederick Douglas
2004-03-01
A key factor in our ability to produce and predict the stability of metal-based macro- to nano-scale structures and devices is a fundamental understanding of the localized nature of corrosion. Corrosion processes where physical dimensions become critical in the degradation process include localized corrosion initiation in passivated metals, microgalvanic interactions in metal alloys, and localized corrosion in structurally complex materials like nanocrystalline metal films under atmospheric and inundated conditions. This project focuses on two areas of corrosion science where a fundamental understanding of processes occurring at critical dimensions is not currently available. Sandia will study the critical length scales necessary for passive film breakdown in the inundated aluminum (Al) system and the chemical processes and transport in ultra-thin water films relevant to the atmospheric corrosion of nanocrystalline tungsten (W) films. Techniques are required that provide spatial information without significantly perturbing or masking the underlying relationships. Al passive film breakdown is governed by the relationship between area of the film sampled and its defect structure. We will combine low current measurements with microelectrodes to study the size scale required to observe a single initiation event and record electrochemical breakdown events. The resulting quantitative measure of stability will be correlated with metal grain size, secondary phase size and distribution to understand which metal properties control stability at the macro- and nano-scale. Mechanisms of atmospheric corrosion on W are dependent on the physical dimensions and continuity of adsorbed water layers as well as the chemical reactions that take place in this layer. We will combine electrochemical and scanning probe microscopic techniques to monitor the chemistry and resulting material transport in these thin surface layers. A description of the length scales responsible for driving the
NASA Astrophysics Data System (ADS)
Hunt, Allen G.
2016-04-01
Percolation theory can be used to find water flow paths of least resistance. Application of percolation theory to drainage networks allows identification of the range of exponent values that describe the tortuosity of rivers in real river networks, which is then used to generate the observed scaling between drainage basin area and channel length, a relationship known as Hack's law. Such a theoretical basis for Hack's law may allow interpretation of the range of exponent values based on an assessment of the heterogeneity of the substrate.
Explanation of the values of Hack's drainage basin, river length scaling exponent
NASA Astrophysics Data System (ADS)
Hunt, A. G.
2015-08-01
Percolation theory can be used to find water flow paths of least resistance. The application of percolation theory to drainage networks allows identification of the range of exponent values that describe the tortuosity of rivers in real river networks, which is then used to generate the observed scaling between drainage basin area and channel length, a relationship known as Hack's law. Such a theoretical basis for Hack's law allows interpretation of the range of exponent values based on an assessment of the heterogeneity of the substrate.
NASA Technical Reports Server (NTRS)
Cliff, W. C.; Skarda, J. R.
1987-01-01
NASA's Airborne Doppler Lidar System has been used to obtain a detailed 'instantaneous' mapping of horizontal spatial wind fields at 600-800 m elevations on the east side of the San Gorgonio Pass in California, in the form of checkerboard-fashion horizontal wind vectors spaced at 300 m intervals along and normal to the flight path. Spatial autocorrelations for the lateral and longitudinal components are ensemble-averaged, and integral turbulent length scales are computed for the wind fields' longitudinal and lateral directions. The flow in the region studied does not appear to be isotropic.
Horkay, Ferenc; Falus, Peter; Hecht, Anne-Marie; Geissler, Erik
2010-12-07
In solutions of the charged semirigid biopolymer hyaluronic acid in salt-free conditions, the diffusion coefficient D{sub NSE} measured at high transfer momentum q by neutron spin echo is more than an order of magnitude smaller than that determined by dynamic light scattering, D{sub DLS}. This behavior contrasts with neutral polymer solutions. With increasing salt content, D{sub DLS} approaches D{sub NSE}, which is independent of ionic strength. Contrary to theoretical expectation, the ion-polymer coupling, which dominates the low q dynamics of polyelectrolyte solutions, already breaks down at distance scales greater than the Debye-Hueckel length.
Holten-Andersen, Niels; Michael Henderson, J.; Walther, Frans J.; Waring, Alan J.; Ruchala, Piotr; Notter, Robert H.; Lee, Ka Yee C.
2011-01-01
We investigated the effects of KL4, a 21-residue amphipathic peptide approximating the overall ratio of positively charged to hydrophobic amino acids in surfactant protein B (SP-B), on the structure and collapse of dipalmitoylphosphatidylcholine and palmitoyl-oleoyl-phosphatidylglycerol monolayers. As reported in prior work on model lung surfactant phospholipid films containing SP-B and SP-B peptides, our experiments show that KL4 improves surfactant film reversibility during repetitive interfacial cycling in association with the formation of reversible collapse structures on multiple length scales. Emphasis is on exploring a general mechanistic connection between peptide-induced nano- and microscale reversible collapse structures (silos and folds). PMID:22208194
Extreme-ultraviolet radiation transport in small scale length laser-produced tin plasmas
NASA Astrophysics Data System (ADS)
Sequoia, Kevin Lamar Williams
The majority of the studies on laser-produced plasmas as an efficient extreme ultraviolet (EUV) light source have focused on relatively large plasmas produced at large laser facilities. However, to develop a commercially viable light source for EUV lithography, much smaller lasers and hence much smaller plasmas must be employed. Smaller plasmas behave quite differently than large plasmas in that the temperature and density are less uniform, and lateral expansion is more important. These differences affect the energy transport and, in particular, the radiation transport. This work studies the EUV radiation transport in small scale length tin plasmas, focusing on the effects of target geometry and laser pulse duration. Both planar and spherical tin targets were irradiated with an Nd:YAG laser operating at 1.064 microm. Conversion efficiency of laser light to 13.5 nm radiation (in-band), EUV emission spectrum, two-dimensional in-band emission profile, and the plasma electron density were measured experimentally. These measurements provide insight into where the laser is absorbed, where the in-band emission is produced, and how the radiation is transmitted. The plasma evolution in these experiments were simulated with a two-dimensional radiation hydrodynamic code, while the radiation transport and atomic kinetics where modeled with a collisional radiative code. Additional experiments were conducted using planar targets where the pulse duration was varied from 0.5 ns to 16 ns to understand the effects of laser pulse duration. It was found that the optimum plasma temperature for efficient generation and transmission of in-band emission is 20 eV. This is lower than the previously reported optimum temperature of 30 eV. The use of a 1.064 microm heating laser results in overheating of the plasma in a region that is much too dense to transmit the in-band emission. This overheating is necessary for the plasma to reach the optimum temperature in the region where the density is
Hybrid coarse-graining approach for lipid bilayers at large length and time scales.
Ayton, Gary S; Voth, Gregory A
2009-04-01
A hybrid analytic-systematic (HAS) coarse-grained (CG) lipid model is developed and employed in a large-scale simulation of a liposome. The methodology is termed hybrid analytic-systematic because one component of the interaction between CG sites is variationally determined from the multiscale coarse-graining (MS-CG) methodology, whereas the remaining component utilizes an analytic potential. The systematic component models the in-plane center-of-mass interaction of the lipids as determined from an atomistic-level MD simulation of a bilayer. The analytic component is based on the well-known Gay-Berne ellipsoid-of-revolution liquid-crystal model and is designed to model the highly anisotropic interactions at a highly coarse-grained level. The HAS CG approach is the first step in an "aggressive" CG methodology designed to model multicomponent biological membranes at very large length and time scales. PMID:19281167
Reynolds Number Effects on Boundary Layer Streamwise Velocity Statistics and Length Scales
NASA Astrophysics Data System (ADS)
Metzger, M.; Atzet, I.; Klewicki, J.
2003-11-01
Well-resolved streamwise velocity data were recently obtained in a turbulent boundary layer at R_θ ≈ 5 × 10^6. Hot-wire anemometry experiments were performed on the salt playa of Utah's western desert under conditions of near-neutral thermal stability, as verified by the Monin-Obukhov length. A distinction of the present data is the use of 20 simultaneously sampled hot-wires to cover a wall normal distance (inner normalized) spanning 5≤ y^+ ≤ 10^4. Because of inherent temporal variations in the atmosphere, simultaneous data are needed to clarify trends in the statistical profiles. The present atmospheric results are compared with wind tunnel data acquired in the range 2500 ≤ R_θ ≤ 1.5×10^4. In all cases, the inner normalized wire length is less than 10. The inner normalized mean profile at high R_θ exhibit a logarithmic region with an inverse slope less than the typical value of κ=0.41, observed at lower R_θ. Evidence for a secondary peak in the inner normalized rms profile is observed near y^+=550 at R_θ ≈ 5 × 10^6. The variation of intermediate length and time scales (Taylor microscales) as a function of Reynolds number and distance from the wall is also presented.
Relations between overturning length scales at the Spanish planetary boundary layer
NASA Astrophysics Data System (ADS)
López, Pilar; Cano, José L.
2016-04-01
We analyze the behavior of the maximum Thorpe displacement (dT)max and the Thorpe scale LTat the atmospheric boundary layer (ABL), extending previous research with new data and improving our studies related to the novel use of the Thorpe method applied to ABL. The maximum Thorpe displacements vary between -900 m and 950 m for the different field campaigns. The maximum Thorpe displacement is always greater under convective conditions than under stable ones, independently of its sign. The Thorpe scale LT ranges between 0.2 m and 680 m for the different data sets which cover different stratified mixing conditions (turbulence shear-driven and convective regions). The Thorpe scale does not exceed several tens of meters under stable and neutral stratification conditions related to instantaneous density gradients. In contrast, under convective conditions, Thorpe scales are relatively large, they exceed hundreds of meters which may be related to convective bursts. We analyze the relation between (dT)max and the Thorpe scale LT and we deduce that they verify a power law. We also deduce that there is a difference in exponents of the power laws for convective conditions and shear-driven conditions. These different power laws could identify overturns created under different mechanisms. References Cuxart, J., Yagüe, C., Morales, G., Terradellas, E., Orbe, J., Calvo, J., Fernández, A., Soler, M., Infante, C., Buenestado, P., Espinalt, Joergensen, H., Rees, J., Vilà, J., Redondo, J., Cantalapiedra, I. and Conangla, L.: Stable atmospheric boundary-layer experiment in Spain (Sables 98). A report, Boundary-Layer Meteorology, 96, 337-370, 2000. Dillon, T. M.: Vertical Overturns: A Comparison of Thorpe and Ozmidov Length Scales, J. Geophys. Res., 87(C12), 9601-9613, 1982. Itsweire, E. C.: Measurements of vertical overturns in stably stratified turbulent flow, Phys. Fluids, 27(4), 764-766, 1984. Kitade, Y., Matsuyama, M. and Yoshida, J.: Distribution of overturn induced by internal
Additional Results of Glaze Icing Scaling in SLD Conditions
NASA Technical Reports Server (NTRS)
Tsao, Jen-Ching
2016-01-01
New guidance of acceptable means of compliance with the super-cooled large drops (SLD) conditions has been issued by the U.S. Department of Transportation's Federal Aviation Administration (FAA) in its Advisory Circular AC 25-28 in November 2014. The Part 25, Appendix O is developed to define a representative icing environment for super-cooled large drops. Super-cooled large drops, which include freezing drizzle and freezing rain conditions, are not included in Appendix C. This paper reports results from recent glaze icing scaling tests conducted in NASA Glenn Icing Research Tunnel (IRT) to evaluate how well the scaling methods recommended for Appendix C conditions might apply to SLD conditions. The models were straight NACA 0012 wing sections. The reference model had a chord of 72 in. and the scale model had a chord of 21 in. Reference tests were run with airspeeds of 100 and 130.3 kn and with MVD's of 85 and 170 micron. Two scaling methods were considered. One was based on the modified Ruff method with scale velocity found by matching the Weber number WeL. The other was proposed and developed by Feo specifically for strong glaze icing conditions, in which the scale liquid water content and velocity were found by matching reference and scale values of the nondimensional water-film thickness expression and the film Weber number Wef. All tests were conducted at 0 deg AOA. Results will be presented for stagnation freezing fractions of 0.2 and 0.3. For nondimensional reference and scale ice shape comparison, a new post-scanning ice shape digitization procedure was developed for extracting 2-D ice shape profiles at any selected span-wise location from the high fidelity 3-D scanned ice shapes obtained in the IRT.
Salmon, Philip S; Zeidler, Anita
2013-10-01
The structure of several network-forming liquids and glasses is considered, where a focus is placed on the detailed information that is made available by using the method of neutron diffraction with isotope substitution (NDIS). In the case of binary network glass-forming materials with the MX2 stoichiometry (e.g. GeO2, GeSe2, ZnCl2), two different length scales at distances greater than the nearest-neighbour distance manifest themselves by peaks in the measured diffraction patterns. The network properties are influenced by a competition between the ordering on these "intermediate" and "extended" length scales, which can be manipulated by changing the chemical identity of the atomic constituents or by varying state parameters such as the temperature and pressure. The extended-range ordering, which describes the decay of the pair-correlation functions at large-r, can be represented by making a pole analysis of the Ornstein-Zernike equations, an approach that can also be used to describe the large-r behaviour of the pair-correlation functions for liquid and amorphous metals where packing constraints are important. The first applications are then described of the NDIS method to measure the detailed structure of aerodynamically-levitated laser-heated droplets of "fragile" glass-forming liquid oxides (CaAl2O4 and CaSiO3) at high-temperatures (~2000 K) and the structure of a "strong" network-forming glass (GeO2) under pressures ranging from ambient to ~8 GPa. The high-temperature experiments show structural changes on multiple length scales when the oxides are vitrified. The high-pressure experiment offers insight into the density-driven mechanisms of network collapse in GeO2 glass, and parallels are drawn with the high-pressure behaviour of silica glass. Finally, the hydrogen-bonded network of water is considered, where the first application of the method of oxygen NDIS is used to measure the structures of light versus heavy water and a difference of approximately equal
Dupont, Virginie; Germann, Timothy C
2011-01-18
Shock compression of materials constitutes a complex process involving high strain rates, elevated temperatures and compression of the lattice. Materials properties are greatly affected by temperature, the representative length scale and the strain rate of the deformation. Experimentally, it is difficult to study the dynamic microscopic mechanisms that affect materials properties following high intensity shock loading, but they can be investigated using molecular dynamics (MD) simulations. Moreover, MD allows a better control over some parameters. We are using MD simulations to study the effect of the strain rate, representative length scale and temperature on the properties of metals during compression. A half-million-atom Cu sample is subjected to strain rates ranging from 10{sup 7} s{sup -1} to 10{sup 12} s{sup -1} at different temperatures ranging from 50K to 1500K. Single crystals as well as polycrystals are investigated. Plasticity mechanisms as well as the evolution of the micro- and macro-yield stress are observed. Our results show that the yield stress increases with increasing strain rate and decreasing temperature. We also show that the strain rate at which the transition between constant and increasing yield stress as a function of the temperature occurs increases with increasing temperature. Calculations at different grain sizes will give an insight into the grain size effect on the plasticity mechanisms and the yield stress.
New Large Length Scale Capillary Fluidics Investigations Using a Drop Tower
NASA Astrophysics Data System (ADS)
Weislogel, Mark; Wollman, Andrew; Wiles, Brentley
2013-11-01
Drop Towers provide brief terrestrial access to microgravity environments. When exploited for capillary fluidics research, the drop tower allows for unique control over an experiment's initial conditions which can enable, enhance, or otherwise improve methods to study capillary flows and phenomena at significantly larger length scales than can be achieved on the ground. In this work a new, highly accessible, 2.1 s tower is introduced for such research. Enabled in part by simple macro-fabrication methods, a variety of new demonstrative experiments are presented for purely capillarity-driven flows leading to droplet ejections, bubble ingestions, sinking flows, particle injections, and multiphase flows. Due to the repeatability of the passive flows, each experiment may be used in turn as a means to study other phenomena and forward-looking research themes are suggested that include large length scale passive phase separations, heat and mass transfer, droplet dynamics, combustion, and more. NASA NNX09AP66A Glenn Research Center, NASA NNX10AK68H Oregon Space Grant Consortium.
NASA Astrophysics Data System (ADS)
Bedingham, D. J.
2014-03-01
Working in the limit in which the localization length scale is large compared to other relevant length scales, we examine three experimental situations with the continuous-spontaneous-localization (CSL) model, a well-motivated alternative to standard quantum theory. These are the two-slit experiment, scattering from a potential barrier, and release of two noninteracting particles simultaneously from a potential trap. In each case we calculate the diagonal part of the time-evolved density matrix giving a probability density function over final measured states. The case of the two-slit experiment is already well understood and we reproduce some known conditions for observing loss of interference. The other examples have not previously been examined in the context of CSL. For scattering from a potential barrier we find that the probability of reflection is unchanged by CSL; however, the momentum state is spread in a characteristic way. For the case of two particles released simultaneously from a trap we find that it is more likely that the particles diffuse in the same direction than would happen if the particles behaved independently. We assess the possibility of observing these effects.
NASA Astrophysics Data System (ADS)
Bonini, L.; Basili, R.; Burrato, P.; Kastelic, V.; Toscani, G.; Seno, S.; Valensise, G.
2013-12-01
The scaling relation between displacement and length of faults plays a crucial role in understanding the growth history of individual faults and their possible linkage and reactivation in future ruptures. Displacement-length relations are commonly based on empirical data. The measurement of fault geometric properties, however, is generally affected by large scattering due not only to intrinsic difficulties of making observations in natural cases (outcrop availability, seismic profiles), but also to the variety of geological factors that may affect the rupture patterns. These can be the interaction between the present-day tectonic regime and an inherited structural fabric, or that between a master fault at depth and shallow structural features. As an alternative to field observations, analogue modeling provides an opportunity to investigate the faulting processes in a controlled environment. During the last decade, the ability of scaled models to properly reproduce such geological processes has greatly improved thanks to the introduction of new materials (e.g. wet kaolin) suitable for reproducing brittle deformation in the upper crust and hi-tech monitoring systems (e.g. laser scanner, particle image velocimetry) with the ability of capturing structural details and performing accurate measurements. We use a dedicated apparatus with such properties to gain insights on the evolution of extensional faults through a suite of experiments which includes (a) setups in homogeneous material to test our ability in meeting general criteria related with fault displacement-length parameters; and (b) increasing complexities attained by inserting various pre-existing fault patterns to analyze how shallow mechanical discontinuities affect our ability to characterize a major fault at depth. Our results show that pre-existing faults can either halt or favor fault development and growth depending on their location/orientation with respect to the applied stress field and suggest the
Simulation of driven self assembly of complex polymeric systems across multiple length scales
NASA Astrophysics Data System (ADS)
de Pablo, Juan
2007-03-01
The self assembly of macromolecular systems is often driven or facilitated by the application of external fields, including flow, voltage, or confinement. The structures that arise when external fields are applied often depend on the history of the sample, and it is therefore important to develop theoretical and computational methods capable of describing the order formation process across multiple length and time scales. Over the past several years we have developed several new classes of multiscale modeling techniques for study of the structure and properties of polymeric materials under external fields, including confinement or flows. For systems at equilibrium, these systems permit precise calculation of the free energy. For systems beyond equilibrium, these methods include the effects of fluctuating hydrodynamic interactions (for dilute and semidilute systems) and the effects of constraining molecules (for concentrated melts). These models and methods can be used to investigate the equilibrium structure and relaxation of a variety of fluids, including solutions of biological macromolecules. The usefulness and limitations of our proposed approach will be discussed in the context of three applications. The first application is concerned with the elongation and presentation of long DNA molecules in nanofluidic channels. A multiscale model, that includes fluctuating hydrodynamic interactions, has been used to design a gene mapping device and to interpret experimental data pertaining to the structure and dynamics of confined chromosome-length DNA. The second application is concerned with the study of liquid-crystal based biosensors. A multiscale model has been used to design a liquid-crystal based device in which nanoscale particles suspended in a liquid crystal self assemble into highly regular structures, including chains, upon exposure to proteins or virions. The third application focuses on the formation of ordered block copolymer structures on nanopatterned
Correlation Length Scales of Isotopic Variations Along Mid-Ocean Ridges and Upper Mantle Dynamics
NASA Astrophysics Data System (ADS)
Graham, D. W.; Spera, F. J.
2003-12-01
How isotopic variations in basalts erupted at the Earth's surface are linked to convective mixing in the underlying mantle is a central problem in geodynamics. The objective of this study is to quantify the length scales of upper mantle heterogeneity through spatial statistical analysis of MORB. We define a characteristic length scale, the scale of segregation L, computed from the spatial self-correlations for 3He/4He, 87Sr/86Sr, 143Nd/144Nd and 206,207,208Pb/204Pb in "zero age" lavas from mid-ocean ridges. Our working hypothesis is that small scale convection in the upper mantle controls dispersion of geochemical tracers. Differences in L between ocean basins may then be quantitatively related to unsteadiness in this convection, due to thickening of the lithosphere, plume impingement, or lateral temperature/compositional differences between continental and oceanic lithosphere induced by batholith formation. The correlation coefficient R, and the separation distance r, are calculated for every i,j pair of points. Ri,j is given by the product of the deviations in isotope composition from the population mean, normalized to the population variance, and R(r) is computed as an ensemble average. The total number of point pairs (N) for n sample locations is given by N=n(n-1)/2. For the global MORB data set (n=1265 and 735 for Sr and He, respectively), N exceeds 105 (799480 and 269745, respectively). A value of R(r) close to 1 indicates that an isotope ratio above (or below) the population average is likely to be associated with an above (or below) average value at a distance r away. A value of R(r) close to zero implies a random relationship, and a value close to -1 implies an anti-correlation. R(r) approaches unity at small r by definition, as points close together are from the same "clump" of mantle. The value of r at which R first goes to zero is denoted as r*. On a diagram of R(r) vs. r (the correlogram), the integral of R(r) from r=0 to r=r* is the scale of
A simulation procedure for light-matter interaction at different length scales
NASA Astrophysics Data System (ADS)
Leiner, Claude; Nemitz, Wolfgang; Wenzl, Franz P.; Hartmann, Paul; Hohenester, Ulrich; Sommer, Christian
2012-06-01
The development of photonic devices with tailor-made optical properties requires the control and the manipulation of light propagation within structures of different length scales, ranging from sub-wavelength to macroscopic dimensions. However, optical simulation at different length scales necessitates the combination of different simulation methods, which have to account properly for various effects such as polarization, interference, or diffraction: At dimensions much larger than the wavelength of light common ray-tracing (RT) techniques are conveniently employed, while in the subwavelength regime more sophisticated approaches, like the so-called finite-difference time-domain (FDTD) technique, are needed. Describing light propagation both in the sub-wavelength regime as well as at macroscopic length scales can only be achieved by bridging between these two approaches. In this contribution we present on the one hand a study aiming at the determination of the intermediate size range for which both simulation methods are applicable and on the other hand an approach for combining classical ray-tracing with FDTD simulation in order to handle optical elements of large sizes. Generally, the interface between RT and FDTD is restricted to very small sample areas. Nevertheless, many real world optical devices use e.g. diffractive optical elements (DOEs) having comparably large areas in the order of 1-2 mm² (or larger). Therefore, one has to develop strategies in order to handle the data transfer between FDTD and RT also for structures of such larger size scales. Our approach in this regard is based on the symmetries of the structures. In this way support programs like e.g. MATLAB can be used to replicate the near-field of a single structure and to merge it to the near-field of a larger area. Comparisons of RT and FDTD simulations in the far-field can be used to validate the physical correctness of this approach. With such procedure it is possible to optimize light
A stochastic immersed boundary method for fluid-structure dynamics at microscopic length scales
Atzberger, Paul J. . E-mail: atzberg@math.ucsb.edu; Kramer, Peter R.; Peskin, Charles S.
2007-06-10
In modeling many biological systems, it is important to take into account flexible structures which interact with a fluid. At the length scale of cells and cell organelles, thermal fluctuations of the aqueous environment become significant. In this work, it is shown how the immersed boundary method of [C.S. Peskin, The immersed boundary method, Acta Num. 11 (2002) 1-39.] for modeling flexible structures immersed in a fluid can be extended to include thermal fluctuations. A stochastic numerical method is proposed which deals with stiffness in the system of equations by handling systematically the statistical contributions of the fastest dynamics of the fluid and immersed structures over long time steps. An important feature of the numerical method is that time steps can be taken in which the degrees of freedom of the fluid are completely underresolved, partially resolved, or fully resolved while retaining a good level of accuracy. Error estimates in each of these regimes are given for the method. A number of theoretical and numerical checks are furthermore performed to assess its physical fidelity. For a conservative force, the method is found to simulate particles with the correct Boltzmann equilibrium statistics. It is shown in three dimensions that the diffusion of immersed particles simulated with the method has the correct scaling in the physical parameters. The method is also shown to reproduce a well-known hydrodynamic effect of a Brownian particle in which the velocity autocorrelation function exhibits an algebraic ({tau} {sup -3/2}) decay for long times [B.J. Alder, T.E. Wainwright, Decay of the Velocity Autocorrelation Function, Phys. Rev. A 1(1) (1970) 18-21]. A few preliminary results are presented for more complex systems which demonstrate some potential application areas of the method. Specifically, we present simulations of osmotic effects of molecular dimers, worm-like chain polymer knots, and a basic model of a molecular motor immersed in fluid
NASA Astrophysics Data System (ADS)
Kurman, Matthew; Tess, Michael; Bravo, Luis; Kweon, Chol-Bum
2014-11-01
The effect of the integral length scale on global spray diagnostics was examined for non-reacting and reacting JP-8 sprays. The scales were set by varying the nominal nozzle diameter from 90 μm, 100 μm, and 147 μm, resulting in the ranges of Re (6.7 × 104 - 9.9 × 104) and We (1.3 × 106 - 1.7 × 106) setting the spray in the fully atomization mode. A high temperature (900-1000 K) high pressure (60-100 bar) flow through chamber was used to conduct experiments at relevant compression ignition engine operating conditions. Each fuel injector was characterized with an injection analyzer to determine the rate of injection and injected fuel mass. High speed near simultaneous Mie and schlieren images were acquired to determine the liquid and vapor penetration lengths of the non-reacting spray. Ignition delay experiments were conducted by measuring the start of formation of OH radicals. A numerical investigation was also carried out to provide additional insights into the behavior of each spray with the specified conditions. The quantitative results presented will aid in the overall advancement of fuel injector designs and ultimately lead to optimized engines.
NASA Astrophysics Data System (ADS)
Rozler, Michael
It is clear that complete understanding of macroscopic properties of materials is impossible without a thorough knowledge of behavior at the smallest length scales. While the past 25 years have witnessed major advances in a variety of techniques that probe the nanoscale properties of matter, electrical transport measurements -- the heart of condensed matter research -- have lagged behind, never progressing beyond bulk measurements. This thesis describes a scanning tunneling potentiometry (STP) system developed to simultaneously map the transport-related electrochemical potential distribution of a biased sample along with its surface topography, extending electronic transport measurements to the nanoscale. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit - the Johnson noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining atomic scale STM imaging, all at scan sizes of up to 15 microns. A mm-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. Use of carefully selected model materials, combined with excellent topographic and voltage resolution has allowed us to distinguish measurement artifacts caused by surface roughness from true potentiometric features, a major problem in previous STP measurements. The measurements demonstrate that STP can produce physically meaningful results for homogeneous transport as well as non-uniform conduction dominated by material microstructures. Measurements of several physically interesting materials systems are presented as well, revealing new behaviors at the smallest length sales. The results establish scanning tunneling potentiometry as a useful tool for physics and
Eating Disorder Diagnostic Scale: Additional Evidence of Reliability and Validity
ERIC Educational Resources Information Center
Stice, Eric; Fisher, Melissa; Martinez, Erin
2004-01-01
The authors conducted 4 studies investigating the reliability and validity of the Eating Disorder Diagnostic Scale (HDDS; E. Stice, C. F. Telch, & S. L. Rizvi, 2000), a brief self-report measure for diagnosing anorexia nervosa, bulimia nervosa, and binge eating disorder. Study 1 found that the HDDS showed criterion validity with interview-based…
Small-Scale Spray Releases: Additional Aerosol Test Results
Schonewill, Philip P.; Gauglitz, Phillip A.; Kimura, Marcia L.; Brown, G. N.; Mahoney, Lenna A.; Tran, Diana N.; Burns, Carolyn A.; Kurath, Dean E.
2013-08-01
One of the events postulated in the hazard analysis at the Waste Treatment and Immobilization Plant (WTP) and other U.S. Department of Energy (DOE) nuclear facilities is a breach in process piping that produces aerosols with droplet sizes in the respirable range. The current approach for predicting the size and concentration of aerosols produced in a spray leak involves extrapolating from correlations reported in the literature. These correlations are based on results obtained from small engineered spray nozzles using pure liquids with Newtonian fluid behavior. The narrow ranges of physical properties on which the correlations are based do not cover the wide range of slurries and viscous materials that will be processed in the WTP and across processing facilities in the DOE complex. To expand the data set upon which the WTP accident and safety analyses were based, an aerosol spray leak testing program was conducted by Pacific Northwest National Laboratory (PNNL). PNNL’s test program addressed two key technical areas to improve the WTP methodology (Larson and Allen 2010). The first technical area was to quantify the role of slurry particles in small breaches where slurry particles may plug the hole and prevent high-pressure sprays. The results from an effort to address this first technical area can be found in Mahoney et al. (2012a). The second technical area was to determine aerosol droplet size distribution and total droplet volume from prototypic breaches and fluids, including sprays from larger breaches and sprays of slurries for which literature data are largely absent. To address the second technical area, the testing program collected aerosol generation data at two scales, commonly referred to as small-scale and large-scale. The small-scale testing and resultant data are described in Mahoney et al. (2012b) and the large-scale testing and resultant data are presented in Schonewill et al. (2012). In tests at both scales, simulants were used to mimic the
Large-Scale Spray Releases: Additional Aerosol Test Results
Daniel, Richard C.; Gauglitz, Phillip A.; Burns, Carolyn A.; Fountain, Matthew S.; Shimskey, Rick W.; Billing, Justin M.; Bontha, Jagannadha R.; Kurath, Dean E.; Jenks, Jeromy WJ; MacFarlan, Paul J.; Mahoney, Lenna A.
2013-08-01
One of the events postulated in the hazard analysis for the Waste Treatment and Immobilization Plant (WTP) and other U.S. Department of Energy (DOE) nuclear facilities is a breach in process piping that produces aerosols with droplet sizes in the respirable range. The current approach for predicting the size and concentration of aerosols produced in a spray leak event involves extrapolating from correlations reported in the literature. These correlations are based on results obtained from small engineered spray nozzles using pure liquids that behave as a Newtonian fluid. The narrow ranges of physical properties on which the correlations are based do not cover the wide range of slurries and viscous materials that will be processed in the WTP and in processing facilities across the DOE complex. To expand the data set upon which the WTP accident and safety analyses were based, an aerosol spray leak testing program was conducted by Pacific Northwest National Laboratory (PNNL). PNNL’s test program addressed two key technical areas to improve the WTP methodology (Larson and Allen 2010). The first technical area was to quantify the role of slurry particles in small breaches where slurry particles may plug the hole and prevent high-pressure sprays. The results from an effort to address this first technical area can be found in Mahoney et al. (2012a). The second technical area was to determine aerosol droplet size distribution and total droplet volume from prototypic breaches and fluids, including sprays from larger breaches and sprays of slurries for which literature data are mostly absent. To address the second technical area, the testing program collected aerosol generation data at two scales, commonly referred to as small-scale and large-scale testing. The small-scale testing and resultant data are described in Mahoney et al. (2012b), and the large-scale testing and resultant data are presented in Schonewill et al. (2012). In tests at both scales, simulants were used
NASA Astrophysics Data System (ADS)
Komaragiri, Uday; Agnew, Sean R.; Gangloff, Richard P.; Begley, Matthew R.
This paper quantifies the effect of strain gradient plasticity (SGP) on crack tip stress elevation for a broad range of applied loading conditions and constitutive model parameters, including both macroscopic hardening parameters and individual material length-scales controlling gradient effects. Finite element simulations incorporating the Fleck-Hutchinson SGP theory are presented for an asymptotically sharp stationary crack. Results identify fundamental scaling relationships describing (i) the physical length-scales over which strain gradients are prominent, and (ii) the degree of stress elevation over conventional Hutchinson-Rice-Rosengren (HRR) fields. Results illustrate that the three length-scale theory predicts much larger SGP effects than the single length-scale theory. Critically, the first length-scale parameter dominates SGP stress elevation: this suggests that SGP effects in fracture can be predicted using the length-scales extracted from nanoindentation, which exhibits similar behavior. Transitional loading/material parameters are identified that establish regimes of SGP relevance: this provides the foundation for the rational application of SGP when developing new micromechanical models of crack tip damage mechanisms and associated subcritical crack propagation behavior in structural alloys.
NASA Astrophysics Data System (ADS)
St. Martin, Clara M.; Lundquist, Julie K.; Handschy, Mark A.
2015-04-01
The variability in wind-generated electricity complicates the integration of this electricity into the electrical grid. This challenge steepens as the percentage of renewably-generated electricity on the grid grows, but variability can be reduced by exploiting geographic diversity: correlations between wind farms decrease as the separation between wind farms increases. But how far is far enough to reduce variability? Grid management requires balancing production on various timescales, and so consideration of correlations reflective of those timescales can guide the appropriate spatial scales of geographic diversity grid integration. To answer ‘how far is far enough,’ we investigate the universal behavior of geographic diversity by exploring wind-speed correlations using three extensive datasets spanning continents, durations and time resolution. First, one year of five-minute wind power generation data from 29 wind farms span 1270 km across Southeastern Australia (Australian Energy Market Operator). Second, 45 years of hourly 10 m wind-speeds from 117 stations span 5000 km across Canada (National Climate Data Archive of Environment Canada). Finally, four years of five-minute wind-speeds from 14 meteorological towers span 350 km of the Northwestern US (Bonneville Power Administration). After removing diurnal cycles and seasonal trends from all datasets, we investigate dependence of correlation length on time scale by digitally high-pass filtering the data on 0.25-2000 h timescales and calculating correlations between sites for each high-pass filter cut-off. Correlations fall to zero with increasing station separation distance, but the characteristic correlation length varies with the high-pass filter applied: the higher the cut-off frequency, the smaller the station separation required to achieve de-correlation. Remarkable similarities between these three datasets reveal behavior that, if universal, could be particularly useful for grid management. For high
St. Martin, Clara M.; Lundquist, Julie K.; Handschy, Mark A.
2015-04-02
The variability in wind-generated electricity complicates the integration of this electricity into the electrical grid. This challenge steepens as the percentage of renewably-generated electricity on the grid grows, but variability can be reduced by exploiting geographic diversity: correlations between wind farms decrease as the separation between wind farms increases. However, how far is far enough to reduce variability? Grid management requires balancing production on various timescales, and so consideration of correlations reflective of those timescales can guide the appropriate spatial scales of geographic diversity grid integration. To answer 'how far is far enough,' we investigate the universal behavior of geographic diversity by exploring wind-speed correlations using three extensive datasets spanning continents, durations and time resolution. First, one year of five-minute wind power generation data from 29 wind farms span 1270 km across Southeastern Australia (Australian Energy Market Operator). Second, 45 years of hourly 10 m wind-speeds from 117 stations span 5000 km across Canada (National Climate Data Archive of Environment Canada). Finally, four years of five-minute wind-speeds from 14 meteorological towers span 350 km of the Northwestern US (Bonneville Power Administration). After removing diurnal cycles and seasonal trends from all datasets, we investigate dependence of correlation length on time scale by digitally high-pass filtering the data on 0.25–2000 h timescales and calculating correlations between sites for each high-pass filter cut-off. Correlations fall to zero with increasing station separation distance, but the characteristic correlation length varies with the high-pass filter applied: the higher the cut-off frequency, the smaller the station separation required to achieve de-correlation. Remarkable similarities between these three datasets reveal behavior that, if universal, could be particularly useful for grid management. For high
Temperature and length scale dependence of solvophobic solvation in a single-site water-like liquid
NASA Astrophysics Data System (ADS)
Dowdle, John R.; Buldyrev, Sergey V.; Stanley, H. Eugene; Debenedetti, Pablo G.; Rossky, Peter J.
2013-02-01
The temperature and length scale dependence of solvation properties of spherical hard solvophobic solutes is investigated in the Jagla liquid, a simple liquid that consists of particles interacting via a spherically symmetric potential combining a hard core repulsion and a longer ranged soft core interaction, yet exhibits water-like anomalies. The results are compared with equivalent calculations for a model of a typical atomic liquid, the Lennard-Jones potential, and with predictions for hydrophobic solvation in water using the cavity equation of state and the extended simple point charge model. We find that the Jagla liquid captures the qualitative thermodynamic behavior of hydrophobic hydration as a function of temperature for both small and large length scale solutes. In particular, for both the Jagla liquid and water, we observe temperature-dependent enthalpy and entropy of solvation for all solute sizes as well as a negative solvation entropy for sufficiently small solutes at low temperature. This feature of water-like solvation is distinct from the strictly positive and temperature independent enthalpy and entropy of cavity solvation observed in the Lennard-Jones fluid. The results suggest that, compared to a simple liquid, it is the presence of a second thermally accessible repulsive energy scale, acting to increasingly favor larger separations for decreasing temperature, that is the essential characteristic of a liquid that favors low-density, open structures, and models hydrophobic hydration, and that it is the presence of this second energy scale that leads to the similarity in the behavior of water and the Jagla liquid. In addition, the Jagla liquid dewets surfaces of large radii of curvature less readily than the Lennard-Jones liquid, reflecting a greater flexibility or elasticity in the Jagla liquid structure than that of a typical liquid, a behavior also similar to that of water's hydrogen bonding network. The implications of the temperature and
The P/Halley: Spatial distribution and scale lengths for C2, CN, NH2, and H2O
NASA Technical Reports Server (NTRS)
Fink, Uwe; Combi, Michael; Disanti, Michael A.
1991-01-01
From P/Halley long slit spectroscopic exposures on 12 dates, extending from Oct. 1985 to May 1986, spatial profiles were obtained for emissions by C2, CN, NH2, and OI(1D). Haser model scale lengths were fitted to these data. The extended time coverage allowed the checking for consistency between the various dates. The time varying production rate of P/Halley severely affected the profiles after perihelion, which is shown in two profile sequences on adjacent dates. Because of the time varying production rate, it was not possible to obtain reliable Haser model scale lengths after perihelion. The pre-perihelion analysis yielded Haser model scale lengths of sufficient consistency that they can be used for production rate determinations, whenever it is necessary to extrapolate from observed column densities within finite observing apertures. Results of scale lengths reduced to 1 AU are given and discussed.
Turbulent transport and length scale measurement experiments with comfined coaxial jets
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Roback, R.
1984-01-01
A three phase experimental study of mixing downstream of swirling and nonswirling confined coaxial jets was conducted to obtain data for the evaluation and improvement of turbulent transport models currently employed in a variety of computational procedures. The present effort was directed toward the acquisition of length scale and dissipation rate data that provide more accurate inlet boundary conditions for the computational procedures and a data base to evaluate the turbulent transport models in the near jet region where recirculation does not occur, and the acquisition of mass and momentum turbulent transport data for a nonswirling flow condition with a blunt inner jet inlet configuration rather than the tapered inner jet inlet. A measurement technique, generally used to obtain approximate integral length and microscales of turbulence and dissipation rates, was computerized. Results showed the dissipation rate varied by 2 1/2 orders of magnitude across the inlet plane, by 2 orders of magnitude 51 mm from the inlet plane, and by 1 order of magnitude at 102 mm from the inlet plane for a nonswirling flow test conditions.
Transfer-matrix scaling from disorder-averaged correlation lengths for diluted Ising systems
NASA Astrophysics Data System (ADS)
de Queiroz, S. L. A.; Stinchcombe, R. B.
1994-10-01
A transfer-matrix-scaling technique is developed for randomly diluted systems, and applied to the site-diluted Ising model on a square lattice in two dimensions. For each allowed disorder configuration between two adjacent columns, the contribution of the respective transfer matrix to the decay of correlations is considered only as far as the ratio of its two largest eigenvalues, allowing an economical calculation of a configuration-averaged correlation length. Standard phenomenological-renormalization procedures are then used to analyze aspects of the phase boundary which are difficult to assess accurately by alternative methods. For magnetic site concentration p close to pc, the extent of exponential behavior of the Tc×p curve is clearly seen for over two decades of variation of p-pc. Close to the pure-system limit, the exactly known reduced slope is reproduced to a very good approximation, though with nonmonotonic convergence. The averaged correlation lengths are inserted into the exponent-amplitude relationship predicted by conformal invariance to hold at criticality. The resulting exponent η remains near the pure value (1/4) for all intermediate concentrations until it crosses over to the percolation value at the threshold.
Kelley, Shana O; Mirkin, Chad A; Walt, David R; Ismagilov, Rustem F; Toner, Mehmet; Sargent, Edward H
2014-12-01
Rapid progress in identifying disease biomarkers has increased the importance of creating high-performance detection technologies. Over the last decade, the design of many detection platforms has focused on either the nano or micro length scale. Here, we review recent strategies that combine nano- and microscale materials and devices to produce large improvements in detection sensitivity, speed and accuracy, allowing previously undetectable biomarkers to be identified in clinical samples. Microsensors that incorporate nanoscale features can now rapidly detect disease-related nucleic acids expressed in patient samples. New microdevices that separate large clinical samples into nanocompartments allow precise quantitation of analytes, and microfluidic systems that utilize nanoscale binding events can detect rare cancer cells in the bloodstream more accurately than before. These advances will lead to faster and more reliable clinical diagnostic devices. PMID:25466541
Kelley, Shana O.; Mirkin, Chad A.; Walt, David R.; Ismagilov, Rustem F.; Toner, Mehmet; Sargent, Edward H.
2015-01-01
Rapid progress in identifying disease biomarkers has increased the importance of creating high-performance detection technologies. Over the last decade, the design of many detection platforms has focused on either the nano or micro length scale. Here, we review recent strategies that combine nano- and microscale materials and devices to produce large improvements in detection sensitivity, speed and accuracy, allowing previously undetectable biomarkers to be identified in clinical samples. Microsensors that incorporate nanoscale features can now rapidly detect disease-related nucleic acids expressed in patient samples. New microdevices that separate large clinical samples into nanocompartments allow precise quantitation of analytes, and microfluidic systems that utilize nanoscale binding events can detect rare cancer cells in the bloodstream more accurately than before. These advances will lead to faster and more reliable clinical diagnostic devices. PMID:25466541
On the characteristic length scales associated with plastic deformation in metallic glasses
Murali, P.; Zhang, Y. W.; Gao, H. J.
2012-05-14
Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale l{sub c} that governs Poisson's ratio {nu}, shear band thickness t{sub SB}, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest l{sub c}, thinnest t{sub SB}, lowest {nu}, and brittle fracture; CuZr exhibits largest l{sub c}, thickest t{sub SB}, highest {nu}, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest l{sub c} as a fundamental measure of the shear transformation zone size in metallic glasses.
On the characteristic length scales associated with plastic deformation in metallic glasses
NASA Astrophysics Data System (ADS)
Murali, P.; Zhang, Y. W.; Gao, H. J.
2012-05-01
Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale ℓc that governs Poisson's ratio ν, shear band thickness tSB, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest ℓc, thinnest tSB, lowest ν, and brittle fracture; CuZr exhibits largest ℓc, thickest tSB, highest ν, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest ℓc as a fundamental measure of the shear transformation zone size in metallic glasses.
A Hybrid Coarse-graining Approach for Lipid Bilayers at Large Length and Time Scales
Ayton, Gary S.; Voth, Gregory A.
2009-01-01
A hybrid analytic-systematic (HAS) coarse-grained (CG) lipid model is developed and employed in a large-scale simulation of a liposome. The methodology is termed hybrid analyticsystematic as one component of the interaction between CG sites is variationally determined from the multiscale coarse-graining (MS-CG) methodology, while the remaining component utilizes an analytic potential. The systematic component models the in-plane center of mass interaction of the lipids as determined from an atomistic-level MD simulation of a bilayer. The analytic component is based on the well known Gay-Berne ellipsoid of revolution liquid crystal model, and is designed to model the highly anisotropic interactions at a highly coarse-grained level. The HAS CG approach is the first step in an “aggressive” CG methodology designed to model multi-component biological membranes at very large length and timescales. PMID:19281167
NASA Astrophysics Data System (ADS)
Kelley, Shana O.; Mirkin, Chad A.; Walt, David R.; Ismagilov, Rustem F.; Toner, Mehmet; Sargent, Edward H.
2014-12-01
Rapid progress in identifying disease biomarkers has increased the importance of creating high-performance detection technologies. Over the last decade, the design of many detection platforms has focused on either the nano or micro length scale. Here, we review recent strategies that combine nano- and microscale materials and devices to produce large improvements in detection sensitivity, speed and accuracy, allowing previously undetectable biomarkers to be identified in clinical samples. Microsensors that incorporate nanoscale features can now rapidly detect disease-related nucleic acids expressed in patient samples. New microdevices that separate large clinical samples into nanocompartments allow precise quantitation of analytes, and microfluidic systems that utilize nanoscale binding events can detect rare cancer cells in the bloodstream more accurately than before. These advances will lead to faster and more reliable clinical diagnostic devices.
Multi-length scale porous polymer films from hypercrosslinked breath figure arrays.
Ding, Lei; Zhang, Aijuan; Li, Wenqing; Bai, Hua; Li, Lei
2016-01-01
Multi-length scale porous polymer (MLSPP) films were fabricated using commercially available polystyrene (PS) via static breath figure (BF) process and sequent hypercrosslinking reaction. One level of ordered pores in microscale were introduced using static BF process, and the other level in nanoscale were produced by the sequent Friedel-Crafts hypercrosslinking reaction. The chemical structure of the PS MLSPP film was investigated by Fourier transformation infrared spectrometry and solid state nuclear magnetic resonance, and the morphology of the film was observed with electron microscopes. The MLSPP films showed large specific surface areas and excellent chemical and thermal stabilities, owing to the micropores and the crosslinked chemical structure produced by the Friedel-Crafts reaction. The methodology reported in this paper is a template-free, low cost and general strategy for the preparation of MLSPP films, which has potential applications in the areas of environment and energy. PMID:26397926
Comment on {open_quotes}Magnetic-coherence-length scaling in metallic multilayers{close_quotes}
Aarts, J.
1997-10-01
In a recent paper [Phys. Rev. B {bold 54}, 515 (1996)], Koperdraad and Lodder compare calculations of the parallel critical field H{sub c2}{sup {parallel}} in superconductor{endash}normal-metal multilayers with experimental data taken from the literature. The poor agreement leads them to introduce a scaling factor {alpha} in the superconducting coherence length. The aim of this Comment is to point out the importance of the boundary conditions of the problem. Free sample surfaces will yield different results than an infinite stack of layers. The effect of free surfaces on the temperature of the dimensional crossover in H{sub c2}{sup {parallel}} is shown to be similar to the effect of {alpha}, making the need for the latter parameter questionable. {copyright} {ital 1997} {ital The American Physical Society}
Nonlinear laser-matter interaction processes in long-scale-length plasmas
NASA Astrophysics Data System (ADS)
Seka, W.; Bahr, R. E.; Short, R. W.; Simon, A.; Craxton, R. S.; Montgomery, D. S.; Rubenchik, A. E.
1992-07-01
This paper reports on nonlinear laser-plasma interaction experiments using long-scale-length plasmas produced by the 24-beam OMEGA laser system operating at 351 nm. The experiments were carried out with distributed phase plates (DPP's) in all beams and with and without smoothing by spectral dispersion (SSD). Most of the beams were used to create a large preformed plasma, which had gradient scale lengths of ≤800 μm at electron densities below a quarter of the critical density nc and temperatures in excess of 1 keV. One of the beams, the ``interaction beam,'' was timed independently and tightly focused to intensities ˜1015 W/cm2. All beams had pulse durations of ˜0.6 nsec. The interaction processes studied were mainly Raman scattering and the two-plasmon decay (TPD) instability as evidenced by its characteristic 3/2-harmonic emission. Details of the Raman and 3/2-harmonic spectra are presented. Evidence was found for the TPD instability close to its Landau cutoff density at ˜ 0.2nc. Raman emission was narrow-band and observed only from densities < 0.2nc. For late timings of the interaction beam, the Raman emission appeared to originate from near the peak of the density profile, but for earlier timings it appeared to come from densities a factor of 2 below the calculated peak. Application of SSD affected the 3/2-harmonic emission only slightly, but it strongly reduced the Raman emission. A discussion is given of some models that attempt to explain these observations.
Tiwary, C. S. Chattopadhyay, K.; Chakraborty, S.; Mahapatra, D. R.
2014-05-28
This paper attempts to gain an understanding of the effect of lamellar length scale on the mechanical properties of two-phase metal-intermetallic eutectic structure. We first develop a molecular dynamics model for the in-situ grown eutectic interface followed by a model of deformation of Al-Al{sub 2}Cu lamellar eutectic. Leveraging the insights obtained from the simulation on the behaviour of dislocations at different length scales of the eutectic, we present and explain the experimental results on Al-Al{sub 2}Cu eutectic with various different lamellar spacing. The physics behind the mechanism is further quantified with help of atomic level energy model for different length scale as well as different strain. An atomic level energy partitioning of the lamellae and the interface regions reveals that the energy of the lamellae core are accumulated more due to dislocations irrespective of the length-scale. Whereas the energy of the interface is accumulated more due to dislocations when the length-scale is smaller, but the trend is reversed when the length-scale is large beyond a critical size of about 80 nm.
Turbulence length scales in stably stratified free shear flow analyzed from slant aircraft profiles
Tjernstroem, M. )
1993-05-01
The vertical turbulence structure in the marine atmosphere close to a coastline is investigated using airborne measurements. The measurements are from a field experiment close to the coast in the southeast of Sweden, in the Baltic Sea. The Baltic Sea has two main properties that make it particularly interesting to study: significant annual lag in sea surface temperature compared to inland surface temperatures and the fact that it is surrounded by land in all directions within advection distances of from a few hours up to 10-15 hours in normal meteorological conditions. The present results are mostly from spring or early summer with mainly cool water: with a stable or neutral marine boundary layer but with substantial heating of the land area during daytime. When the daytime inland convective boundary layer is advected out over the cool sea, there is a frictional decoupling in space analogous to the same nocturnal process in time. This sometimes creates a residual layer, a remnant of the inland convective boundary layer, that can be advected for considerable distances over the sea. At the top of this layer, wind shear gives rise to a local increase in turbulent kinetic energy. These layers are used for an analysis of turbulent scales for free shear flow in stable stratification. The analysis is based on different length scales used in numerical model closures for turbulence processes and reveals the asymptotic behavior of different scales in the neutral limit and their functional form, and illustrates the nonlinear relationship between scales for different properties. The profiles from the aircraft are taken from 25 slant soundings performed in connection to low-level boundary-layer flights. The results are calculated from turbulence data extracted through filtering techniques on instantaneous time series (individual profiles). The calculated turbulence parameters from all profiles are grouped and averaged compositely over all profiles. 48 refs., 12 figs., 1 tab.
NASA Astrophysics Data System (ADS)
Zhang, Jianfei; Ma, Xuewei; Ren, Huiping; Chen, Lin; Jin, Zili; Li, Zhenliang; Shen, Jun
2016-01-01
In this article, the Ni-46.1Al-7.8Mo (at.%) alloy was directionally solidified at different growth rates ranging from 15 μm/s to 1000 μm/s under a constant temperature gradient (334 K/cm). The dependence of microstructural length scales on the growth rate was investigated. The results show that, with the growth rate increasing, the primary dendritic arm spacings (PDAS) and secondary dendritic arm spacings (SDAS) decreased. There exists a large distribution range in PDAS under directional solidification conditions at a constant temperature gradient. The average PDAS and SDAS as a function of growth rate can be given as λ1 = 848.8967 V-0.4509 and λ2 = 64.2196 V-0.4140, respectively. In addition, a comparison of our results with the current theoretical models and previous experimental results has also been made.
A phenomenological description of BslA assemblies across multiple length scales
Morris, Ryan J.; Bromley, Keith M.; Stanley-Wall, Nicola
2016-01-01
Intrinsically interfacially active proteins have garnered considerable interest recently owing to their potential use in a range of materials applications. Notably, the fungal hydrophobins are known to form robust and well-organized surface layers with high mechanical strength. Recently, it was shown that the bacterial biofilm protein BslA also forms highly elastic surface layers at interfaces. Here we describe several self-assembled structures formed by BslA, both at interfaces and in bulk solution, over a range of length scales spanning from nanometres to millimetres. First, we observe transiently stable and highly elongated air bubbles formed in agitated BslA samples. We study their behaviour in a range of solution conditions and hypothesize that their dissipation is a consequence of the slow adsorption kinetics of BslA to an air–water interface. Second, we describe elongated tubules formed by BslA interfacial films when shear stresses are applied in both a Langmuir trough and a rheometer. These structures bear a striking resemblance, although much larger in scale, to the elongated air bubbles formed during agitation. Taken together, this knowledge will better inform the conditions and applications of how BslA can be used in the stabilization of multi-phase materials. This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’. PMID:27298433
Quantifying Contributions to Transport in Ionic Polymers Across Multiple Length Scales
NASA Astrophysics Data System (ADS)
Madsen, Louis
Self-organized polymer membranes conduct mobile species (ions, water, alcohols, etc.) according to a hierarchy of structural motifs that span sub-nm to >10 μm in length scale. In order to comprehensively understand such materials, our group combines multiple types of NMR dynamics and transport measurements (spectroscopy, diffusometry, relaxometry, imaging) with structural information from scattering and microscopy as well as with theories of porous media,1 electrolytic transport, and oriented matter.2 In this presentation, I will discuss quantitative separation of the phenomena that govern transport in polymer membranes, from intermolecular interactions (<= 2 nm),3 to locally ordered polymer nanochannels (a few to 10s of nm),2 to larger polymer domain structures (10s of nm and larger).1 Using this multi-scale information, we seek to give informed feedback on the design of polymer membranes for use in, e . g . , efficient batteries, fuel cells, and mechanical actuators. References: [1] J. Hou, J. Li, D. Mountz, M. Hull, and L. A. Madsen. Journal of Membrane Science448, 292-298 (2013). [2] J. Li, J. K. Park, R. B. Moore, and L. A. Madsen. Nature Materials 10, 507-511 (2011). [3] M. D. Lingwood, Z. Zhang, B. E. Kidd, K. B. McCreary, J. Hou, and L. A. Madsen. Chemical Communications 49, 4283 - 4285 (2013).
A phenomenological description of BslA assemblies across multiple length scales.
Morris, Ryan J; Bromley, Keith M; Stanley-Wall, Nicola; MacPhee, Cait E
2016-07-28
Intrinsically interfacially active proteins have garnered considerable interest recently owing to their potential use in a range of materials applications. Notably, the fungal hydrophobins are known to form robust and well-organized surface layers with high mechanical strength. Recently, it was shown that the bacterial biofilm protein BslA also forms highly elastic surface layers at interfaces. Here we describe several self-assembled structures formed by BslA, both at interfaces and in bulk solution, over a range of length scales spanning from nanometres to millimetres. First, we observe transiently stable and highly elongated air bubbles formed in agitated BslA samples. We study their behaviour in a range of solution conditions and hypothesize that their dissipation is a consequence of the slow adsorption kinetics of BslA to an air-water interface. Second, we describe elongated tubules formed by BslA interfacial films when shear stresses are applied in both a Langmuir trough and a rheometer. These structures bear a striking resemblance, although much larger in scale, to the elongated air bubbles formed during agitation. Taken together, this knowledge will better inform the conditions and applications of how BslA can be used in the stabilization of multi-phase materials.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298433
Predicting the roughness length of turbulent flows over landscapes with multi-scale microtopography
NASA Astrophysics Data System (ADS)
Pelletier, Jon D.; Field, Jason P.
2016-05-01
The fully rough form of the law of the wall is commonly used to quantify velocity profiles and associated bed shear stresses in fluvial, aeolian, and coastal environments. A key parameter in this law is the roughness length, z0. Here we propose a predictive formula for z0 that uses the amplitude and slope of each wavelength of microtopography within a discrete-Fourier-transform-based approach. Computational fluid dynamics (CFD) modeling is used to quantify the effective z0 value of sinusoidal microtopography as a function of the amplitude and slope. The effective z0 value of landscapes with multi-scale roughness is then given by the sum of contributions from each Fourier mode of the microtopography. Predictions of the equation are tested against z0 values measured in ˜ 105 wind-velocity profiles from southwestern US playa surfaces. Our equation is capable of predicting z0 values to 50 % accuracy, on average, across a 4 order of magnitude range. We also use our results to provide an alternative formula that, while somewhat less accurate than the one obtained from a full multi-scale analysis, has an advantage of being simpler and easier to apply.
Scrape-off Layer Flows With Pressure Gradient Scale Length ~ {rho}{sub p}
Robert J. Goldston
2013-03-08
A heuristic model for the plasma scrape-off width balances magnetic drifts against parallel loss at c{sub s} /2, resulting in a SOL width ~ {rho}{sub p}. T{sub sep} is calculated from Spitzer–Härm parallel thermal conduction. This results in a prediction for the power scrape-off width in quantitative agreement both in magnitude and scaling with recent experimental data. To achieve the ~ c{sub s} /2 flow assumed in this model and measured experimentally sets requirements on the ratio of upstream to total SOL particle sources, relative to the square-root of the ratio of target to upstream temperature. The Pfisch-Schlüter model for equilibrium flows has been modified to allow near-sonic flows, appropriate for gradient scale lengths of order {rho}{sub p}, resulting in a new quadrupole radial flow pattern. The strong parallel flows and plasma charging implied by this model suggest a mechanism for H-mode transition, consistent with many observations
Zebrafish brain mapping--standardized spaces, length scales, and the power of N and n.
Hunter, Paul R; Hendry, Aenea C; Lowe, Andrew S
2015-06-01
Mapping anatomical and functional parameters of the zebrafish brain is moving apace. Research communities undertaking such studies are becoming ever larger and more diverse. The unique features, tools, and technologies associated with zebrafish are propelling them as the 21st century model organism for brain mapping. Uniquely positioned as a vertebrate model system, the zebrafish enables imaging of anatomy and function at different length scales from intraneuronal compartments to sparsely distributed whole brain patterns. With a variety of diverse and established statistical modeling and analytic methods available from the wider brain mapping communities, the richness of zebrafish neuroimaging data is being realized. The statistical power of population observations (N) within and across many samples (n) projected onto a standardized space will provide vast databases for data-driven biological approaches. This article reviews key brain mapping initiatives at different levels of scale that highlight the potential of zebrafish brain mapping. By way of introduction to the next wave of brain mappers, an accessible introduction to the key concepts and caveats associated with neuroimaging are outlined and discussed. PMID:25418847
Luscher, Darby J; Bronkhorst, Curt A; Mc Dowell, David L
2010-12-20
All nonlocal continuum descriptions of inelastic material response involve length scale parameters that either directly or implicitly quantify the physical dimensions of a neighborhood of response which influences the behavior at a particular point. The second-gradient continuum theories such as those developed by Germain, Toupin and Mindlin, and Eringen, and giving rise to strain-gradient plasticity, is becoming a common coarse-scale basis for homogenization of material response that respects the non local nature of heterogeneous material response. Ideally, the length scale parameters involved in such homogenization would be intrinsically associated with dominant aspects of the microstructure. However, these parameters, at least in some cases, are inextricably linked to the details of the coarse scale boundary value problem. Accordingly, they cannot be viewed as pure constitutive parameters. An example problem of multiscale homogenization is presented to underscore the dependence of second-gradient length scale parameters on the coarse scale boundary value problem, namely the multiscale response of an idealized porous microstructure. The fine scale (microstructure) comprises elastic perfectly plastic matrix with a periodic array of circular voids. This fine scale description of the problem is identical for two separate classes of coarse scale boundary value problem, viz. an extruded channel subject to compression and eventually developing plastic shear bands and a thin layer of material with larger (coarse scale) elliptical voids subject to shear deformation. Implications of the relationship between length scale parameters and the details of the coarse scale boundary value problem are discussed and ideas to ascertain such length parameters from evolving response fields are presented.
St. Martin, Clara M.; Lundquist, Julie K.; Handschy, Mark A.
2015-04-02
The variability in wind-generated electricity complicates the integration of this electricity into the electrical grid. This challenge steepens as the percentage of renewably-generated electricity on the grid grows, but variability can be reduced by exploiting geographic diversity: correlations between wind farms decrease as the separation between wind farms increases. However, how far is far enough to reduce variability? Grid management requires balancing production on various timescales, and so consideration of correlations reflective of those timescales can guide the appropriate spatial scales of geographic diversity grid integration. To answer 'how far is far enough,' we investigate the universal behavior of geographic diversity by exploring wind-speed correlations using three extensive datasets spanning continents, durations and time resolution. First, one year of five-minute wind power generation data from 29 wind farms span 1270 km across Southeastern Australia (Australian Energy Market Operator). Second, 45 years of hourly 10 m wind-speeds from 117 stations span 5000 km across Canada (National Climate Data Archive of Environment Canada). Finally, four years of five-minute wind-speeds from 14 meteorological towers span 350 km of the Northwestern US (Bonneville Power Administration). After removing diurnal cycles and seasonal trends from all datasets, we investigate dependence of correlation length on time scale by digitally high-pass filtering the data on 0.25–2000 h timescales and calculating correlations between sites for each high-pass filter cut-off. Correlations fall to zero with increasing station separation distance, but the characteristic correlation length varies with the high-pass filter applied: the higher the cut-off frequency, the smaller the station separation required to achieve de-correlation. Remarkable similarities between these three datasets reveal behavior that, if universal, could be particularly useful for grid management. For high
A role for self-gravity at multiple length scales in the process of star formation.
Goodman, Alyssa A; Rosolowsky, Erik W; Borkin, Michelle A; Foster, Jonathan B; Halle, Michael; Kauffmann, Jens; Pineda, Jaime E
2009-01-01
Self-gravity plays a decisive role in the final stages of star formation, where dense cores (size approximately 0.1 parsecs) inside molecular clouds collapse to form star-plus-disk systems. But self-gravity's role at earlier times (and on larger length scales, such as approximately 1 parsec) is unclear; some molecular cloud simulations that do not include self-gravity suggest that 'turbulent fragmentation' alone is sufficient to create a mass distribution of dense cores that resembles, and sets, the stellar initial mass function. Here we report a 'dendrogram' (hierarchical tree-diagram) analysis that reveals that self-gravity plays a significant role over the full range of possible scales traced by (13)CO observations in the L1448 molecular cloud, but not everywhere in the observed region. In particular, more than 90 per cent of the compact 'pre-stellar cores' traced by peaks of dust emission are projected on the sky within one of the dendrogram's self-gravitating 'leaves'. As these peaks mark the locations of already-forming stars, or of those probably about to form, a self-gravitating cocoon seems a critical condition for their existence. Turbulent fragmentation simulations without self-gravity-even of unmagnetized isothermal material-can yield mass and velocity power spectra very similar to what is observed in clouds like L1448. But a dendrogram of such a simulation shows that nearly all the gas in it (much more than in the observations) appears to be self-gravitating. A potentially significant role for gravity in 'non-self-gravitating' simulations suggests inconsistency in simulation assumptions and output, and that it is necessary to include self-gravity in any realistic simulation of the star-formation process on subparsec scales. PMID:19122636
Assink, R.A.; Jamison, G.M.; Alam, T.M.; Gillen, K.T.
1997-10-01
A fundamental understanding of aging in an organic material requires that one understand how aging affects the chemical structure of a material, and how these chemical changes are related to the material`s macroscopic properties. This level of understanding is usually achieved by examining the material on a variety of length scales ranging from atomic to meso-scale to macroscopic. The authors are developing and applying several {sup 13}C nuclear magnetic resonance (NMR) spectroscopy experiments to characterize the aging process of organic materials over a broad range of length scales. Examples of studies which range from atomic to macroscopic will be presented.
Clinical Frailty Scale in an Acute Medicine Unit: a Simple Tool That Predicts Length of Stay
Juma, Salina; Taabazuing, Mary-Margaret; Montero-Odasso, Manuel
2016-01-01
Background Frailty is characterized by increased vulnerability to external stressors. When frail older adults are admitted to hospital, they are at increased risk of adverse events including falls, delirium, and disability. The Clinical Frailty Scale (CFS) is a practical and efficient tool for assessing frailty; however, its ability to predict outcomes has not been well studied within the acute medical service. Objective To examine the CFS in elderly patients admitted to the acute medical ward and its association with length of stay. Design Prospective cohort study in an acute care university hospital in London, Ontario, Canada, involving 75 patients over age 65, admitted to the general internal medicine clinical teaching units (CTU). Measurements Patient demographics were collected through chart review, and CFS score was assigned to each patient after brief clinician assessment. The CFS ranges from 1 (very fit) to 9 (terminally ill) based on descriptors and pictographs of activity and functional status. The CFS was collapsed into three categories: non-frail (CFS 1–4), mild-to-moderately frail (CFS 5–6), and severely frail (CFS 7–8). Outcomes of length of stay and 90-day readmission were gathered through the LHSC electronic patient record. Results Severe frailty was associated with longer lengths of stay (Mean = 12.6 ± 12.7 days) compared to mild-to-moderate frailty (mean = 11.2 ± 10.8 days), and non-frailty (mean = 4.1 ± 2.1 days, p = .014). This finding was significant after adjusting for age, sex, and number of medications. Participants with higher frailty scores showed higher readmission rates when compared with those with no frailty (31.2% for severely frail, vs. 34.2% for mild-to-moderately frail vs. 19% for non-frail) although there was no significant difference in the adjusted analysis. Conclusion The CFS helped identify patients that are more likely to have prolonged hospital stays on the acute medical ward. The CFS is an easy to use tool which
Fracture length scales in human cortical bone: the necessity of nonlinear fracture models.
Yang, Q D; Cox, Brian N; Nalla, Ravi K; Ritchie, R O
2006-03-01
Recently published data for fracture in human humeral cortical bone are analyzed using cohesive-zone models to deal with the nonlinear processes of material failure. Such models represent the nonlinear deformation processes involved in fracture by cohesive tractions exerted by the failing material along a fracture process zone, rather than attributing all damage to a process occurring at a single point, as in conventional linear-elastic fracture mechanics (LEFM). The relationship between the tractions and the net displacement discontinuity across the process zone is hypothesized to be a material property for bone. To test this hypothesis, the cohesive law was evaluated by analyzing published load vs. load-point displacement data from one laboratory; the calibrated law was then used to predict similar data taken for a different source of bone using a different specimen geometry in a different laboratory. Further model calculations are presented to illustrate more general characteristics of the nonlinear fracture of bone and to demonstrate in particular that LEFM is not internally consistent for all cases of interest. For example, the fracture toughness of bone deduced via LEFM from test data is not necessarily a material constant, but will take different values for different crack lengths and test configurations. LEFM is valid when the crack is much longer than a certain length scale, representative of the length of the process zone in the cohesive model, which for human cortical bone ranges from 3 to 10mm. Since naturally occurring bones and the specimens used to test them are not much larger than this dimension for most relevant orientations, it is apparent that only nonlinear fracture models can give an internally consistent account of their fracture. The cohesive law is thus a more complete representation of the mechanics of material failure than the single-parameter fracture toughness and may therefore provide a superior measure of bone quality. The analysis of
NASA Astrophysics Data System (ADS)
Khawaja, Aly Salim
A general prismatic mesh generator capable of discretizing flow domains for arbitrary 3-D geometries is presented. The overall project objective was to be able to perform routine viscous flow simulations for engineering design and analysis. The suitability of the hybrid prismatic/tetrahedral grid generation approach for numerical computations of flow phenomena over complex bodies was to be authenticated. The prismatic elements are used in close proximity to the body surface to resolve the viscous stresses whereas tetrahedral elements tessellate the rest of the domain. Such an approach allows the exploitation of the best of both, structured and unstructured grid generation approaches. A special algorithm is developed to allow the prisms to march along general splined boundary surfaces. The method uses a 2-D marching scheme in the parametric domain and performs coordinate transfers to the real space. The inclusion of such a scheme allows the use of periodic boundary conditions to reduce solver memory requirements and broaden the range of applicability of the grid generator. The work also introduces the novel ideas of multi-zone and unstructured prismatic mesh generation to allow different levels of grid resolution within the same geometry and to treat disparate length scales. Both these developments are aimed at optimizing the discretized flow domain with the fewest elements and reducing the time step restrictions of the solver by increasing the volumes of the individual cells. Several quality enhancement and validity checks are presented along with an automatic mesh regeneration mechanism for improved overall quality. The combination of the developed algorithms allows for the discretization of realistic 3-D geometries without much user intervention. Applications of the hybrid prismatic/tetrahedral grid generator are presented from various fields such as the aerospace, turbomachinery and offshore industries. The robustness and efficiency of the prismatic grid
Stably stratified shear turbulence: A new model for the energy dissipation length scale
NASA Technical Reports Server (NTRS)
Cheng, Y.; Canuto, V. M.
1994-01-01
A model is presented to compute the turbulent kinetic energy dissipation length scale l(sub epsilon) in a stably stratified shear flow. The expression for l(sub epsilon) is derived from solving the spectral balance equation for the turbulent kinetic energy. The buoyancy spectrum entering such equation is constructed using a Lagrangian timescale with modifications due to stratification. The final result for l(sub epsilon) is given in algebraic form as a function of the Froude number Fr and the flux Richardson number R(sub f), l(sub epsilon) = l(sub epsilon)(Fr, R(sub f). The model predicts that for R(sub f) less than R(sub fc), l(sub epsilon) decreases with stratification. An attractive feature of the present model is that it encompasses, as special cases, some seemingly different models for l(sub epsilon) that have been proposed in the past by Deardorff, Hunt et al., Weinstock, and Canuto and Minotti. An alternative form for the dissipation rate epsilon is also discussed that may be useful when one uses a prognostic equation for the heat flux. The present model is applicable to subgrid-scale models, which are needed in large eddy simulations (LES), as well as to ensemble average models. The model is applied to predict the variation of l(sub epsilon) with height z in the planetary boundary layer. The resulting l(sub epsilon) versus z profile reproduces very closely the nonmonotonic profile of l(sub epsilon) exhibited by many LES calculations, beginning with the one by Deardorff in 1974.
NASA Astrophysics Data System (ADS)
Padding, J. T.; Louis, A. A.
2006-09-01
We describe in detail how to implement a coarse-grained hybrid molecular dynamics and stochastic rotation dynamics simulation technique that captures the combined effects of Brownian and hydrodynamic forces in colloidal suspensions. The importance of carefully tuning the simulation parameters to correctly resolve the multiple time and length scales of this problem is emphasized. We systematically analyze how our coarse-graining scheme resolves dimensionless hydrodynamic numbers such as the Reynolds number Re, which indicates the importance of inertial effects, the Schmidt number Sc, which indicates whether momentum transport is liquidlike or gaslike, the Mach number, which measures compressibility effects, the Knudsen number, which describes the importance of noncontinuum molecular effects, and the Peclet number, which describes the relative effects of convective and diffusive transport. With these dimensionless numbers in the correct regime the many Brownian and hydrodynamic time scales can be telescoped together to maximize computational efficiency while still correctly resolving the physically relevant processes. We also show how to control a number of numerical artifacts, such as finite-size effects and solvent-induced attractive depletion interactions. When all these considerations are properly taken into account, the measured colloidal velocity autocorrelation functions and related self-diffusion and friction coefficients compare quantitatively with theoretical calculations. By contrast, these calculations demonstrate that, notwithstanding its seductive simplicity, the basic Langevin equation does a remarkably poor job of capturing the decay rate of the velocity autocorrelation function in the colloidal regime, strongly underestimating it at short times and strongly overestimating it at long times. Finally, we discuss in detail how to map the parameters of our method onto physical systems and from this extract more general lessons—keeping in mind that there
NASA Astrophysics Data System (ADS)
Wheatland, Jonathan; Bushby, Andy; Droppo, Ian; Carr, Simon; Spencer, Kate
2015-04-01
Suspended estuarine sediments form flocs that are compositionally complex, fragile and irregularly shaped. The fate and transport of suspended particulate matter (SPM) is determined by the size, shape, density, porosity and stability of these flocs and prediction of SPM transport requires accurate measurements of these three-dimensional (3D) physical properties. However, the multi-scaled nature of flocs in addition to their fragility makes their characterisation in 3D problematic. Correlative microscopy is a strategy involving the spatial registration of information collected at different scales using several imaging modalities. Previously, conventional optical microscopy (COM) and transmission electron microscopy (TEM) have enabled 2-dimensional (2D) floc characterisation at the gross (> 1 µm) and sub-micron scales respectively. Whilst this has proven insightful there remains a critical spatial and dimensional gap preventing the accurate measurement of geometric properties and an understanding of how structures at different scales are related. Within life sciences volumetric imaging techniques such as 3D micro-computed tomography (3D µCT) and focused ion beam scanning electron microscopy [FIB-SEM (or FIB-tomography)] have been combined to characterise materials at the centimetre to micron scale. Combining these techniques with TEM enables an advanced correlative study, allowing material properties across multiple spatial and dimensional scales to be visualised. The aims of this study are; 1) to formulate an advanced correlative imaging strategy combining 3D µCT, FIB-tomography and TEM; 2) to acquire 3D datasets; 3) to produce a model allowing their co-visualisation; 4) to interpret 3D floc structure. To reduce the chance of structural alterations during analysis samples were first 'fixed' in 2.5% glutaraldehyde/2% formaldehyde before being embedding in Durcupan resin. Intermediate steps were implemented to improve contrast and remove pore water, achieved by the
Hybrid Simulation Strategy for Simulating Self-Assembled Morphologies at the Atomistic Length Scales
NASA Astrophysics Data System (ADS)
Sethuraman, Vaidyanathan; Ganesan, Venkat
In the context of Lithium-ion batteries, an enhancement in both ionic conductivity and mechanical properties, were observed for block copolymer electrolytes with increasing MW. On the contrary, when homopolymers were used as electrolytes, the ionic conductivity decreased with increasing MW. However, the origins of such increase in conductivity are unclear and are speculated to be tied to both the morphology and the atomistic details of the copolymer themselves. Motivated by such issues, we present a strategy to create ordered morphologies of block copolymers at the atomistic level using a combination of coarse-graining and inverse coarse-graining techniques. A mapping which is developed using the long-ranged structural mapping in the disordered phases will be utilized to generate self-assembled morphologies. In particular we focus on generating self-assembled morphologies of PS-PEO at the atomistic length scales. Statics and dynamics of such self-assembled morphologies will be presented and the effect of self assembly on the transport properties of ions will also be explored. Funded by NSF.
Dingreville, Rémi; Karnesky, Richard A.; Puel, Guillaume; Schmitt, Jean -Hubert
2015-11-16
With the increasing interplay between experimental and computational approaches at multiple length scales, new research directions are emerging in materials science and computational mechanics. Such cooperative interactions find many applications in the development, characterization and design of complex material systems. This manuscript provides a broad and comprehensive overview of recent trends in which predictive modeling capabilities are developed in conjunction with experiments and advanced characterization to gain a greater insight into structure–property relationships and study various physical phenomena and mechanisms. The focus of this review is on the intersections of multiscale materials experiments and modeling relevant to the materials mechanics community. After a general discussion on the perspective from various communities, the article focuses on the latest experimental and theoretical opportunities. Emphasis is given to the role of experiments in multiscale models, including insights into how computations can be used as discovery tools for materials engineering, rather than to “simply” support experimental work. This is illustrated by examples from several application areas on structural materials. In conclusion this manuscript ends with a discussion on some problems and open scientific questions that are being explored in order to advance this relatively new field of research.
NASA Astrophysics Data System (ADS)
Keys, Aaron S.; Abate, Adam R.; Glotzer, Sharon C.; Durian, Douglas J.
2007-04-01
Supercooled liquids and dense colloidal suspensions exhibit anomalous behaviour known as `spatially heterogeneous dynamics' (SHD), which becomes increasingly pronounced as the system approaches the glass transition. Recently, the observation of SHD in confined granular packings under slow shear near the onset of jamming has bolstered speculation that the two transitions are related. Here, we report measurements of SHD in a system of air-driven granular beads, as a function of both density and effective temperature. On approach to jamming, the dynamics becomes progressively slower and more spatially heterogeneous. The rapid growth of timescales and dynamical length scales characterizing the heterogeneities can be described both by mode-coupling theory and the Vogel-Tammann-Fulcher (VTF) equation, such as in glass-forming liquids. The value of the control variable at the VTF transition coincides with point J (refs 9, 10), the random close-packed jamming density at which all motion ceases, in analogy to a zero-temperature ideal glass transition. Our findings demonstrate further universality of the jamming concept and provide a significant step forward in the quest for a unified theory of jamming in disparate systems.
Dingreville, Rémi; Karnesky, Richard A.; Puel, Guillaume; Schmitt, Jean -Hubert
2015-11-16
With the increasing interplay between experimental and computational approaches at multiple length scales, new research directions are emerging in materials science and computational mechanics. Such cooperative interactions find many applications in the development, characterization and design of complex material systems. This manuscript provides a broad and comprehensive overview of recent trends in which predictive modeling capabilities are developed in conjunction with experiments and advanced characterization to gain a greater insight into structure–property relationships and study various physical phenomena and mechanisms. The focus of this review is on the intersections of multiscale materials experiments and modeling relevant to the materials mechanicsmore » community. After a general discussion on the perspective from various communities, the article focuses on the latest experimental and theoretical opportunities. Emphasis is given to the role of experiments in multiscale models, including insights into how computations can be used as discovery tools for materials engineering, rather than to “simply” support experimental work. This is illustrated by examples from several application areas on structural materials. In conclusion this manuscript ends with a discussion on some problems and open scientific questions that are being explored in order to advance this relatively new field of research.« less
The role of reactant unmixedness, strain rate, and length scale on premixed combustor performance
Samuelsen, S.; LaRue, J.; Vilayanur, S.
1995-10-01
Lean premixed combustion provides a means to reduce pollutant formation and increase combustion efficiency. However, fuel-air mixing is rarely uniform in space and time. This nonuniformity in concentration will lead to relative increases in pollutant formation and decreases in combustion efficiency. The nonuniformity of the concentration at the exit of the premixer has been defined by Lyons (1981) as the {open_quotes}unmixedness.{close_quotes} Although turbulence properties such as length scales and strain rate are known to effect unmixedness, the exact relationship is unknown. Evaluating this relationship and the effect of unmixedness in premixed combustion on pollutant formation and combustion efficiency are an important part of the overall goal of US Department of Energy`s Advanced Turbine Systems (ATS) program and are among the goals of the program described herein. The information obtained from ATS is intended to help to develop and commercialize gas turbines which have (1) a wide range of operation/stability, (2) a minimal amount of pollutant formation, and (3) high combustion efficiency. Specifically, with regard to pollutants, the goals are to reduce the NO{sub x} emissions by at least 10%, obtain less than 20 PPM of both CO and UHC, and increase the combustion efficiency by 5%.
Low frequency energy scavenging using sub-wave length scale acousto-elastic metamaterial
NASA Astrophysics Data System (ADS)
Ahmed, Riaz U.; Banerjee, Sourav
2014-11-01
This letter presents the possibility of energy scavenging (ES) utilizing the physics of acousto-elastic metamaterial (AEMM) at low frequencies (<˜3KHz). It is proposed to use the AEMM in a dual mode (Acoustic Filter and Energy Harvester), simultaneously. AEMM's are typically reported for filtering acoustic waves by trapping or guiding the acoustic energy, whereas this letter shows that the dynamic energy trapped inside the soft constituent (matrix) of metamaterials can be significantly harvested by strategically embedding piezoelectric wafers in the matrix. With unit cell AEMM model, we experimentally asserted that at lower acoustic frequencies (< ˜3 KHz), maximum power in the micro Watts (˜35µW) range can be generated, whereas, recently reported phononic crystal based metamaterials harvested only nano Watt (˜30nW) power against 10KΩ resistive load. Efficient energy scavengers at low acoustic frequencies are almost absent due to large required size relevant to the acoustic wavelength. Here we report sub wave length scale energy scavengers utilizing the coupled physics of local, structural and matrix resonances. Upon validation of the argument through analytical, numerical and experimental studies, a multi-frequency energy scavenger (ES) with multi-cell model is designed with varying geometrical properties capable of scavenging energy (power output from ˜10µW - ˜90µW) between 0.2 KHz and 1.5 KHz acoustic frequencies.
NASA Astrophysics Data System (ADS)
Dingreville, Rémi; Karnesky, Richard A.; Puel, Guillaume; Schmitt, Jean-Hubert
2016-02-01
With the increasing interplay between experimental and computational approaches at multiple length scales, new research directions are emerging in materials science and computational mechanics. Such cooperative interactions find many applications in the development, characterization and design of complex material systems. This manuscript provides a broad and comprehensive overview of recent trends where predictive modeling capabilities are developed in conjunction with experiments and advanced characterization to gain a greater insight into structure-properties relationships and study various physical phenomena and mechanisms. The focus of this review is on the intersections of multiscale materials experiments and modeling relevant to the materials mechanics community. After a general discussion on the perspective from various communities, the article focuses on the latest experimental and theoretical opportunities. Emphasis is given to the role of experiments in multiscale models, including insights into how computations can be used as discovery tools for materials engineering, rather than to "simply" support experimental work. This is illustrated by examples from several application areas on structural materials. This manuscript ends with a discussion on some problems and open scientific questions that are being explored in order to advance this relatively new field of research.
Barabash, R.I.; Bei, H.; Gao, Y.F.; Ice, G.E.
2010-10-26
Three-dimensional spatially resolved strains were mapped in a model NiAl/Mo composite after nanoindentation. The depth-dependent strain distributed in the two phases and partitioned across the composite interfaces is directly measured at submicron length scale using X-ray microdiffraction and compared with a detailed micromechanical stress analysis. It is shown that indentation-induced deformation in the composite material is distinct from deformation expected in a single-phase material. This difference arises in part from residual thermal strains in both phases of the composite in the as-grown state. Interplay between residual thermal strains and external mechanical strain results in a complex distribution of dilatational strain in the Mo fibers and NiAl matrix and is distinct in different locations within the indented area. Reversal of the strain sign (e.g., alternating tensile/compressive/tensile strain distribution) is observed in the NiAl matrix. Bending of the Mo fibers during indentation creates relatively large 1.5{sup o} misorientations between the different fibers and NiAl matrix. Compressive strain along the <0 0 1> direction reached -0.017 in the Mo fibers and -0.007 in the NiAl matrix.
Relevant time- and length scale of touch-down for drops impacting on a heated surface
NASA Astrophysics Data System (ADS)
van Limbeek, Michiel A. J.; Shirota, Minori; Sun, Chao; Prosperetti, Andrea; Lohse, Detlef
2015-11-01
The vapor generated from a liquid drop impacting a hot solid surface can prevent it to make contact, depending on the solid temperature. The minimum temperature when no contact is made between the drop and the solid is called the dynamic Leidenfrost temperature. The latent heat needed to generated the vapor is drawn from the solid, and in general the Leidenfrost temperature depends on the solid thermal properties. Here we show experiments conducted on a sapphire plate, to minimize the cooling of the solid and ensuring nearly isothermal conditions. By using high speed total internal reflection imaging, we observe the drop base during impact up to about 100nm above the substrate surface. By this technique we are able to study the processes responsible for the transition between fully wetting and fully levitating drop impact conditions as the solid temperature increases. We reveal the relevant length- and time-scales for the dimple formation under the drop and explain their relevance for the late-time dynamics. As the transition regime is traversed from low to high temperature, the liquid-solid contact gradually decreases which reduces the friction with the solid, enhancing the spreading of the drop considerably.
Comparison of friction and wear of articular cartilage on different length scales.
Kienle, Sandra; Boettcher, Kathrin; Wiegleb, Lorenz; Urban, Joanna; Burgkart, Rainer; Lieleg, Oliver; Hugel, Thorsten
2015-09-18
The exceptional tribological properties of articular cartilage are still far from being fully understood. Articular cartilage is able to withstand high loads and provide exceptionally low friction. Although the regeneration abilities of the tissue are very limited, it can last for many decades. These biomechanical properties are realized by an interplay of different lubrication and wear protection mechanisms. The deterioration of cartilage due to aging or injury leads to the development of osteoarthritis. A current treatment strategy focuses on supplementing the intra-articular fluid with a saline solution containing hyaluronic acid. In the work presented here, we investigated how changing the lubricating fluid affects friction and wear of articular cartilage, focusing on the boundary and mixed lubrication as well as interstitial fluid pressurization mechanisms. Different length and time scales were probed by atomic force microscopy, tribology and profilometry. We compared aqueous solutions with different NaCl concentrations to a viscosupplement containing hyaluronic acid (HA). In particular, we found that the presence of ions changes the frictional behavior and the wear resistance. In contrast, hyaluronic acid showed no significant impact on the friction coefficient, but considerably reduced wear. This study confirms the previous notion that friction and wear are not necessarily correlated in articular cartilage tribology and that the main role of HA might be to provide wear protection for the articular surface. PMID:26294356
Radosevich, Andrew J.; Rogers, Jeremy D.; Turzhitsky, Vladimir; Mutyal, Nikhil N.; Yi, Ji; Roy, Hemant K.; Backman, Vadim
2013-01-01
Since the early 1980’s, the enhanced backscattering (EBS) phenomenon has been well-studied in a large variety of non-biological materials. Yet, until recently the use of conventional EBS for the characterization of biological tissue has been fairly limited. In this work we detail the unique ability of EBS to provide spectroscopic, polarimetric, and depth-resolved characterization of biological tissue using a simple backscattering instrument. We first explain the experimental and numerical procedures used to accurately measure and model the full azimuthal EBS peak shape in biological tissue. Next we explore the peak shape and height dependencies for different polarization channels and spatial coherence of illumination. We then illustrate the extraordinary sensitivity of EBS to the shape of the scattering phase function using suspensions of latex microspheres. Finally, we apply EBS to biological tissue samples in order to measure optical properties and observe the spatial length-scales at which backscattering is altered in early colon carcinogenesis. PMID:24163574
Extending the length and time scales of Gram–Schmidt Lyapunov vector computations
Costa, Anthony B.; Green, Jason R.
2013-08-01
Lyapunov vectors have found growing interest recently due to their ability to characterize systems out of thermodynamic equilibrium. The computation of orthogonal Gram–Schmidt vectors requires multiplication and QR decomposition of large matrices, which grow as N{sup 2} (with the particle count). This expense has limited such calculations to relatively small systems and short time scales. Here, we detail two implementations of an algorithm for computing Gram–Schmidt vectors. The first is a distributed-memory message-passing method using Scalapack. The second uses the newly-released MAGMA library for GPUs. We compare the performance of both codes for Lennard–Jones fluids from N=100 to 1300 between Intel Nahalem/Infiniband DDR and NVIDIA C2050 architectures. To our best knowledge, these are the largest systems for which the Gram–Schmidt Lyapunov vectors have been computed, and the first time their calculation has been GPU-accelerated. We conclude that Lyapunov vector calculations can be significantly extended in length and time by leveraging the power of GPU-accelerated linear algebra.
Revealing Optical Properties of Reduced-Dimensionality Materials at Relevant Length Scales.
Ogletree, D Frank; Schuck, P James; Weber-Bargioni, Alexander F; Borys, Nicholas J; Aloni, Shaul; Bao, Wei; Barja, Sara; Lee, Jiye; Melli, Mauro; Munechika, Keiko; Whitelam, Stephan; Wickenburg, Sebastian
2015-10-14
Reduced-dimensionality materials for photonic and optoelectronic applications including energy conversion, solid-state lighting, sensing, and information technology are undergoing rapid development. The search for novel materials based on reduced-dimensionality is driven by new physics. Understanding and optimizing material properties requires characterization at the relevant length scale, which is often below the diffraction limit. Three important material systems are chosen for review here, all of which are under investigation at the Molecular Foundry, to illustrate the current state of the art in nanoscale optical characterization: 2D semiconducting transition metal dichalcogenides; 1D semiconducting nanowires; and energy-transfer in assemblies of 0D semiconducting nanocrystals. For each system, the key optical properties, the principal experimental techniques, and important recent results are discussed. Applications and new developments in near-field optical microscopy and spectroscopy, scanning probe microscopy, and cathodoluminescence in the electron microscope are given detailed attention. Work done at the Molecular Foundry is placed in context within the fields under review. A discussion of emerging opportunities and directions for the future closes the review. PMID:26332202
Barriga, H M G; Tyler, A I I; McCarthy, N L C; Parsons, E S; Ces, O; Law, R V; Seddon, J M; Brooks, N J
2015-01-21
Bicontinuous cubic structures offer enormous potential in applications ranging from protein crystallisation to drug delivery systems and have been observed in cellular membrane structures. One of the current bottlenecks in understanding and exploiting these structures is that cubic scaffolds produced in vitro are considerably smaller in size than those observed in biological systems, differing by almost an order of magnitude in some cases. We have addressed this technological bottleneck and developed a methodology capable of manufacturing highly swollen bicontinuous cubic membranes with length scales approaching those seen in vivo. Crucially, these cubic systems do not require the presence of proteins. We have generated highly swollen Im3m symmetry bicontinuous cubic phases with lattice parameters of up to 480 Å, composed of ternary mixtures of monoolein, cholesterol and negatively charged lipid (DOPS or DOPG) and we have been able to tune their lattice parameters. The swollen cubic phases are highly sensitive to both temperature and pressure; these structural changes are likely to be controlled by a fine balance between lipid headgroup repulsions and lateral pressure in the hydrocarbon chain region. PMID:25430049
Quantum electrodynamics and the electron self-energy in a deformed space with a minimal length scale
NASA Astrophysics Data System (ADS)
Silva, Apollo V.; Abreu, E. M. C.; Neves, M. J.
2016-06-01
The main motivation to study models in the presence of a minimal length is to obtain a quantum field theory free of the divergences. In this way, in this paper, we have constructed a new framework for quantum electrodynamics embedded in a minimal length scale background. New operators are introduced and the Green function method was used for the solution of the field equations, i.e. the Maxwell, Klein-Gordon and Dirac equations. We have analyzed specifically the scalar field and its one loop propagator. The mass of the scalar field regularized by the minimal length was obtained. The QED Lagrangian containing a minimal length was also constructed and the divergences were analyzed. The electron and photon propagators, and the electron self-energy at one loop as a function of the minimal length was also obtained.
NASA Astrophysics Data System (ADS)
van Duyne, Richard
2015-03-01
During the last few years, there has been an explosion of interest and activity in the field of plasmonics. The goal of plasmonics is to control and manipulate light on the nanometer length scale using the properties of the collective electronic excitations in noble metal films or nanoparticles, known as surface plasmons. An improved understanding of the interactions between adsorbed molecules and plasmonic nanostructures (i.e., molecular plasmonics) is having a significant impact in a number of research areas including electrochemistry, surface science, catalysis for energy conversion and storage, the materials science of nanoparticles, biomedical diagnostics, art conservation science, and nanolithography. In the first part of this lecture, I will provide some background material on the basic physical concepts underlying molecular plasmonics with an emphasis on surface-enhanced Raman spectroscopy (SERS), localized surface plasmon resonance (LSPR) spectroscopy, and tip-enhanced Raman spectroscopy (TERS). In the second part of this lecture, I will focus in on three recent advances in TERS which illustrate the power of this nanoscale vibrational spectroscopy. First, new insights into the nature of the relative intensity fluctuations in single molecule tip-enhanced Raman spectroscopy (SMTERS) will be discussed. Second, our current understanding of the adsorbate surface interactions involved in the low temperature (LT), ultrahigh vacuum (UHV) TERS of the Ag tip/Rhodamine 6G (R6G) /Ag(111) system will be described. Finally, an update on our new results in coupling ultrafast lasers with TERS. This last topic illuminates a path forward toward the goal of understanding chemistry at the space-time limit.
NASA Technical Reports Server (NTRS)
Smalheer, C. V.
1973-01-01
The chemistry of lubricant additives is discussed to show what the additives are chemically and what functions they perform in the lubrication of various kinds of equipment. Current theories regarding the mode of action of lubricant additives are presented. The additive groups discussed include the following: (1) detergents and dispersants, (2) corrosion inhibitors, (3) antioxidants, (4) viscosity index improvers, (5) pour point depressants, and (6) antifouling agents.
Assessing the role of static length scales behind glassy dynamics in polydisperse hard disks.
Russo, John; Tanaka, Hajime
2015-06-01
The possible role of growing static order in the dynamical slowing down toward the glass transition has recently attracted considerable attention. On the basis of random first-order transition theory, a new method to measure the static correlation length of amorphous order, called "point-to-set" (PTS) length, has been proposed and used to show that the dynamic length grows much faster than the static length. Here, we study the nature of the PTS length, using a polydisperse hard-disk system, which is a model that is known to exhibit a growing hexatic order upon densification. We show that the PTS correlation length is decoupled from the steeper increase of the correlation length of hexatic order and dynamic heterogeneity, while closely mirroring the decay length of two-body density correlations. Our results thus provide a clear example that other forms of order can play an important role in the slowing down of the dynamics, casting a serious doubt on the order-agnostic nature of the PTS length and its relevance to slow dynamics, provided that a polydisperse hard-disk system is a typical glass former. PMID:26038545
Song, Min Jae; Dean, David; Knothe Tate, Melissa L.
2010-01-01
A major hurdle to understanding and exploiting interactions between the stem cell and its environment is the lack of a tool for precise delivery of mechanical cues concomitant to observing sub-cellular adaptation of structure. These studies demonstrate the use of microscale particle image velocimetry (μ-PIV) for in situ spatiotemporal mapping of flow fields around mesenchymal stem cells, i.e. murine embryonic multipotent cell line C3H10T1/2, at the subcellular length scale, providing a tool for real time observation and analysis of stem cell adaptation to the prevailing mechanical milieu. In the absence of cells, computational fluid dynamics (CFD) predicts flow regimes within 12% of μ-PIV measures, achieving the technical specifications of the chamber and the flow rates necessary to deliver target shear stresses at a particular height from the base of the flow chamber. However, our μ-PIV studies show that the presence of cells per se as well as the density at which cells are seeded significantly influences local flow fields. Furthermore, for any given cell or cell seeding density, flow regimes vary significantly along the vertical profile of the cell. Hence, the mechanical milieu of the stem cell exposed to shape changing shear stresses, induced by fluid drag, varies with respect to proximity of surrounding cells as well as with respect to apical height. The current study addresses a previously unmet need to predict and observe both flow regimes as well as mechanoadaptation of cells in flow chambers designed to deliver precisely controlled mechanical signals to live cells. An understanding of interactions and adaptation in response to forces at the interface between the surface of the cell and its immediate local environment may be key for de novo engineering of functional tissues from stem cell templates as well as for unraveling the mechanisms underlying multiscale development, growth and adaptation of organisms. PMID:20862249
NASA Astrophysics Data System (ADS)
Newcomb, C.; Qafoku, N. P.; Grate, J. W.; Hufschmid, R.; Browning, N.; De Yoreo, J. J.
2015-12-01
With elevated levels of carbon dioxide in the atmosphere due to anthropogenic emissions and disruption to the carbon cycle, the effects of climate change are being accelerated. Approximately 80% of Earth's terrestrial organic carbon is stored in soil, and the residence time of this carbon can range from hours to millenia. Understanding the dynamics of this carbon pool in the carbon cycle is crucial to both predicting climate and sustaining ecosystem services. Soil organic carbon is known to be strongly associated with high surface area clay minerals. The nature of these interactions is not well understood primarily due to the heterogeneity of soil, as much of the current knowledge relies on experiments that take a top-down approach using bulk experimental measurements. Our work seeks to probe physical, chemical, and molecular-level interactions at the organic-mineral interface using a bottom-up approach that establishes a model system where complexity can be built in systematically. By performing in situ techniques such as dynamic force spectroscopy, a technique where organic molecules can be brought into contact with mineral surfaces in a controlled manner using an atomic force microscope, we demonstrate the ability to mechanistically probe the energy landscape of individual organic molecules with mineral surfaces. We demonstrate the ability to measure the binding energies of soil-inspired organic functional groups (including carboxylic acid, amine, methyl, and phosphate) with clay and mineral surfaces as a function of solution chemistry. This effort can provide researchers with both guiding principles about carbon dynamics at the sub-nanometer length scale and insights into early aggregation events, where organic-mineral interactions play a significant role.
Orientational dynamics of water confined on a nanometer length scale in reverse micelles
NASA Astrophysics Data System (ADS)
Tan, Howe-Siang; Piletic, Ivan R.; Fayer, M. D.
2005-05-01
The time-resolved orientational anisotropies of the OD hydroxyl stretch of dilute HOD in H2O confined on a nanometer length scale in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles are studied using ultrafast infrared polarization and spectrally resolved pump-probe spectroscopy, and the results are compared to the same experiments on bulk water. The orientational anisotropy data for three water nanopool sizes (4.0, 2.4, and 1.7nm) can be fitted well with biexponential decays. The biexponential decays are analyzed using a wobbling-in-a-cone model that involves fast orientational diffusion within a cone followed by slower, full orientational relaxation. The data provide the cone angles, the diffusion constants for motion within the cones, and the final diffusion constants as a function of the nanopool size. The two processes can be interpreted as a local angular fluctuation of the OD and a global hydrogen bond network rearrangement process. The trend in the relative amplitudes of the long and short exponential decays suggest an increasing rigidity as the nanopool size decreases. The trend in the long decay constants indicates a longer hydrogen bond network rearrangement time with decreasing reverse micelle size. The anisotropy measurements for the reverse micelles studied extrapolate to ˜0.33 rather than the ideal value of 0.4, suggesting the presence of an initial inertial component in the anisotropy decay that is too fast to resolve. The very fast decay component is consistent with initial inertial orientational motion that is seen in published molecular-dynamics simulations of water in AOT reverse micelles. The angle over which the inertial orientational motion occurs is determined. The results are in semiquantitative agreement with the molecular-dynamics simulations.
NASA Astrophysics Data System (ADS)
Han, Jaeheon
2011-12-01
Short channel GaAs Metal Semiconductor Field Effect Transistors (MESFETs) have been fabricated with gate length to 20 nm, in order to examine the characteristics of sub-50 nm MESFET scaling. Here the rise in the measured transconductance is mainly attributed to electron velocity overshoot. For gate lengths below 40 nm, however, the transconductance drops suddenly. The behavior of velocity overshoot and its degradation is investigated and simulated by using a transport model based on the retarded Langevin equation (RLE). This indicates the existence of a minimum acceleration length needed for the carriers to reach the overshoot velocity. The argument shows that the source resistance must be included as an internal element, or appropriate boundary condition, of relative importance in any model where the gate length is comparable to the inelastic mean free path of the carriers.
Additional field verification of convective scaling for the lateral dispersion parameter
Sakiyama, S.K.; Davis, P.A.
1988-07-01
The results of a series of diffusion trials over the heterogeneous surface of the Canadian Precambrian Shield provide additional support for the convective scaling of the lateral dispersion parameter. The data indicate that under convective conditions, the lateral dispersion parameter can be scaled with the convective velocity scale and the mixing depth. 10 references.
Unidirectional solidification of Zn-rich Zn-Cu peritectic alloys -- 2. Microstructural length scales
Ma, D.; Li, Y.; Ng, S.C.; Jones, H.
2000-05-11
Experimental results are presented of solidification microstructure length scale including {eta}-phase cell spacing, primary {epsilon} secondary dendrite arm spacing, size of nonaligned dendrite of primary {epsilon}, and volume fraction of primary {epsilon}, as functions of alloy concentration (containing up to 7.37 wt% Cu) and growth velocity (ranging from 0.02 to 4.82 mm/s) in the unidirectional solidification of Zn-rich Zn-Cu peritectic alloys. Intercellular spacing ({lambda}) of two-phase cellular structure decreases with increasing growth velocity (V) such that {lambda}V{sup 1/2} is constant at a fixed alloy concentration in parametric agreement with the KGT and Hunt-Lu models. The value of {lambda}V{sup 1/2} varies from 216 {+-} 10 to 316 {+-} 55 {micro}m{sup 3/2}/s{sup 1/2} with decrease in alloy concentration from 4.94 to 2.17 wt% Cu. These values are much greater than for normal eutectic systems but comparable with monotectic alloys. Dendritic secondary arm spacing ({lambda}{sub 2}) of primary {epsilon} decreases with increasing V such that {lambda}{sub 2}V{sup 1/3} is constant ranging 14.9 {+-} 0.9 to 75.6 {+-} 8.1 {micro}m{sup 4/3}/s{sup 1/3} with increase in alloy concentration (C{sub 0}) from 2.17 to 7.37 wt% Cu, which is in parametric agreement with predictions of arm-coarsening theory. The volume fraction (f{sub e}) of primary {epsilon} increases with increasing V for Zn-rich Zn-3.37, 4.94 and 7.37 wt% Cu hyperperitectic alloys. Predictions of the Scheil and Sarreal-Abbaschian models show good agreement with the observed f{sub {epsilon}} for Zn-4.94 wt% Cu at moderate V from 0.19 to 2.64 mm/s, but fail at low V of less than 0.16 mm/s and at high V of greater than 3.54 mm/s. The measured average size, {Lambda}V{sup 1/2} is constant for a given alloy, increasing from (0.98 {+-} 0.04) x 10{sup 3} to (7.2 {+-} 0.7) x 10{sup 3} {micro}m{sup 3/2}/s{sup 1/2} with increase in alloy concentration from 2.17 to 4.94 wt% Cu.
Hierarchical Self-Assembly of Peptide Amphiphiles: Form and Function at Multiple Length Scales
NASA Astrophysics Data System (ADS)
Zha, Runye Helen
Hierarchical self-assembly, the organization of molecules into supramolecular structures of increasing size and complexity, is a potent tool for materials synthesis and requires understanding the connections of structure across multiple length scales. Herein, self-assembly of peptide amphiphiles (PAs) into nanoscopic and macroscopic materials is explored, and their anti-cancer applications are investigated. First, nanoscale assembly is examined in the context of an anti-angiogenic PA bearing the G-helix motif of maspin, a tumor suppressor protein. Assembly of this maspin-mimetic PA (MMPA) stabilizes the native G-helix conformation and improves binding to endothelial cells. Furthermore, PA nanostructures significantly increase cell adhesion to fibronectin as compared to G-helix peptide alone. Combined with its inhibitory effect on cell migration, MMPA nanostructures thus show anti-angiogenic activity on par with maspin protein in vitro and in vivo. Second, assembly of cationic PAs with hyaluronic acid (HA), an anionic polyelectrolyte, into macroscopic membranes is explored using PAs with identical formal charge but systematically varied self-assembly domains. Results suggest that membrane formation is dictated by the initial moments of component aggregation and is highly sensitive to PA molecular structure via nanoscale assembly. Specifically, PAs with beta-sheet forming residues are nanofibrous and have high surface charge density, leading to robust membranes with aligned-fiber microstructure. PAs without beta-sheet forming residues are nanospherical and have low surface charge density, leading to weak membranes with non-fibrous finger-like microstructure. Lastly, the principles of PA-HA membrane assembly are applied towards development of anti-cancer therapeutic biomaterials. Here, cytotoxic PAs bearing the epitope (KLAKLAKbeta)2 are co-assembled with non-bioactive cationic PA in order to achieve varying nanoscale morphology. These nanostructures are then
Performance of four turbulence closure models implemented using a generic length scale method
Warner, J.C.; Sherwood, C.R.; Arango, H.G.; Signell, R.P.
2005-01-01
A two-equation turbulence model (one equation for turbulence kinetic energy and a second for a generic turbulence length-scale quantity) proposed by Umlauf and Burchard [J. Marine Research 61 (2003) 235] is implemented in a three-dimensional oceanographic model (Regional Oceanographic Modeling System; ROMS v2.0). These two equations, along with several stability functions, can represent many popular turbulence closures, including the k-kl (Mellor-Yamada Level 2.5), k-??, and k-?? schemes. The implementation adds flexibility to the model by providing an unprecedented range of turbulence closure selections in a single 3D oceanographic model and allows comparison and evaluation of turbulence models in an otherwise identical numerical environment. This also allows evaluation of the effect of turbulence models on other processes such as suspended-sediment distribution or ecological processes. Performance of the turbulence models and sediment-transport schemes is investigated with three test cases for (1) steady barotropic flow in a rectangular channel, (2) wind-induced surface mixed-layer deepening in a stratified fluid, and (3) oscillatory stratified pressure-gradient driven flow (estuarine circulation) in a rectangular channel. Results from k-??, k-??, and gen (a new closure proposed by Umlauf and Burchard [J. Marine Research 61 (2003) 235]) are very similar for these cases, but the k-kl closure results depend on a wall-proximity function that must be chosen to suit the flow. Greater variations appear in simulations of suspended-sediment concentrations than in salinity simulations because the transport of suspended-sediment amplifies minor variations in the methods. The amplification is caused by the added physics of a vertical settling rate, bottom stress dependent resuspension, and diffusive transport of sediment in regions of well mixed salt and temperature. Despite the amplified sensitivity of sediment to turbulence models in the estuary test case, the four
Taylor-plasticity-based analysis of length scale effects in void growth
NASA Astrophysics Data System (ADS)
Liu, J. X.; Demiral, M.; El Sayed, T.
2014-10-01
We have studied the void growth problem by employing the Taylor-based strain gradient plasticity theories, from which we have chosen the following three, namely, the mechanism-based strain gradient (MSG) plasticity (Gao et al 1999 J. Mech. Phys. Solids 47 1239, Huang et al 2000 J. Mech. Phys. Solids 48 99-128), the Taylor-based nonlocal theory (TNT; 2001 Gao and Huang 2001 Int. J. Solids Struct. 38 2615) and the conventional theory of MSG (CMSG; Huang et al 2004 Int. J. Plast. 20 753). We have addressed the following three issues which occur when plastic deformation at the void surface is unconstrained. (1) Effects of elastic deformation. Elasticity is essential for cavitation instability. It is therefore important to guarantee that the gradient term entering the Taylor model is the effective plastic strain gradient instead of the total strain gradient. We propose a simple elastic-plastic decomposition method. When the void size approaches the minimum allowable initial void size related to the maximum allowable geometrically necessary dislocation density, overestimation of the flow stress due to the negligence of the elastic strain gradient is on the order of \\frac{l\\varepsilon_Y}{R0} near the void surface, where l, ɛY and R0 are, respectively, the intrinsic material length scale, the yield strain and the initial void radius. (2) MSG intrinsic inconsistency, which was initially mentioned in Gao et al (1999 J. Mech. Phys. Solids 47 1239) but has not been the topic of follow-up studies. We realize that MSG higher-order stress arises due to the linear-strain-field approximation within the mesoscale cell with a nonzero size, lɛ. Simple analysis shows that within an MSG mesoscale cell near the void surface, the difference between microscale and mesoscale strains is on the order of (\\frac{l\\varepsilon}{R0})2 , indicating that when \\frac{l\\varepsilon}{R0}˜ 1.0 , the higher-order stress effect can make the MSG result considerably different from the TNT or CMSG
Fischer, Peter
2008-08-01
The magnetic properties of low dimensional solid state matter is of the utmost interest both scientifically as well as technologically. In addition to the charge of the electron which is the base for current electronics, by taking into account the spin degree of freedom in future spintronics applications open a new avenue. Progress towards a better physical understanding of the mechanism and principles involved as well as potential applications of nanomagnetic devices can only be achieved with advanced analytical tools. Soft X-ray microscopy providing a spatial resolution towards 10nm, a time resolution currently in the sub-ns regime and inherent elemental sensitivity is a very promising technique for that. This article reviews the recent achievements of magnetic soft X-ray microscopy by selected examples of spin torque phenomena, stochastical behavior on the nanoscale and spin dynamics in magnetic nanopatterns. The future potential with regard to addressing fundamental magnetic length and time scales, e.g. imaging fsec spin dynamics at upcoming X-ray sources is pointed out.
P. Oshkai; M. Geveci; D. Rockwell; M. Pollack
2002-12-12
Flow-acoustic interactions due to fully turbulent inflow past a shallow axisymmetric cavity mounted in a pipe are investigated using a technique of high-image-density particle image velocimetry in conjunction with unsteady pressure measurements. This imaging leads to patterns of velocity, vorticity, streamline topology, and hydrodynamic contributions to the acoustic power integral. Global instantaneous images, as well as time-averaged images, are evaluated to provide insight into the flow physics during tone generation. Emphasis is on the manner in which the streamwise length scale of the cavity alters the major features of the flow structure. These image-based approaches allow identification of regions of the unsteady shear layer that contribute to the instantaneous hydrodynamic component of the acoustic power, which is necessary to maintain a flow tone. In addition, combined image analysis and pressure measurements allow categorization of the instantaneous flow patterns that are associated with types of time traces and spectra of the fluctuating pressure. In contrast to consideration based solely on pressure spectra, it is demonstrated that locked-on tones may actually exhibit intermittent, non-phase-locked images, apparently due to low damping of the acoustic resonator. Locked-on flow tones (without modulation or intermittency), locked-on flow tones with modulation, and non-locked-on oscillations with short-term, highly coherent fluctuations are defined and represented by selected cases. Depending on which of,these regimes occur, the time-averaged Q (quality)-factor and the dimensionless peak pressure are substantially altered.
NASA Astrophysics Data System (ADS)
Moayedi, S. K.; Setare, M. R.; Khosropour, B.
2013-11-01
In the 1990s, Kempf and his collaborators Mangano and Mann introduced a D-dimensional (β, β‧)-two-parameter deformed Heisenberg algebra which leads to an isotropic minimal length (\\triangle Xi)\\min = \\hbar √ {Dβ +β '}, \\forall i\\in \\{1, 2, ..., D\\}. In this work, the Lagrangian formulation of a magnetostatic field in three spatial dimensions (D = 3) described by Kempf algebra is presented in the special case of β‧ = 2β up to the first-order over β. We show that at the classical level there is a similarity between magnetostatics in the presence of a minimal length scale (modified magnetostatics) and the magnetostatic sector of the Abelian Lee-Wick model in three spatial dimensions. The integral form of Ampere's law and the energy density of a magnetostatic field in the modified magnetostatics are obtained. Also, the Biot-Savart law in the modified magnetostatics is found. By studying the effect of minimal length corrections to the gyromagnetic moment of the muon, we conclude that the upper bound on the isotropic minimal length scale in three spatial dimensions is 4.42×10-19 m. The relationship between magnetostatics with a minimal length and the Gaete-Spallucci nonlocal magnetostatics [J. Phys. A: Math. Theor. 45, 065401 (2012)] is investigated.
Wei, Wei; Zhang, Xia; Ren, Xiaomin
2014-01-01
An asymmetric hybrid plasmonic metal-wire waveguide is proposed by combining the advantages of symmetric and hybrid plasmonic modes. The idea of asymmetric structure eliminates the adverse effect of a substrate and enhances the optical performance of the waveguide. The guiding properties of the proposed waveguide are intensively investigated using the finite elements method. The results exhibit a quite long propagation length of 2.69 cm with subwavelength confinement. More importantly, an extremely large figure of merit of 139037 is achieved. Furthermore, the proposed waveguides can be used as directional couplers. They can achieve a coupling length of only 1.01 μm at S = 0.1 μm with negligible loss. A strong dependence of coupling length on the operating wavelength makes the proposed waveguide promising for realizing wavelength-selective components at telecommunication wavelengths. PMID:25400529
2014-01-01
An asymmetric hybrid plasmonic metal-wire waveguide is proposed by combining the advantages of symmetric and hybrid plasmonic modes. The idea of asymmetric structure eliminates the adverse effect of a substrate and enhances the optical performance of the waveguide. The guiding properties of the proposed waveguide are intensively investigated using the finite elements method. The results exhibit a quite long propagation length of 2.69 cm with subwavelength confinement. More importantly, an extremely large figure of merit of 139037 is achieved. Furthermore, the proposed waveguides can be used as directional couplers. They can achieve a coupling length of only 1.01 μm at S = 0.1 μm with negligible loss. A strong dependence of coupling length on the operating wavelength makes the proposed waveguide promising for realizing wavelength-selective components at telecommunication wavelengths. PMID:25400529