Small-scale Factors Research Articles

Nonlocal Flügge Shell Model for Vibrations of Double-Walled Carbon Nanotubes With Different Boundary Conditions

In this paper, the vibrational behavior of double-walled carbon nanotubes (DWCNTs) is studied by a nonlocal elastic shell model. The nonlocal continuum model accounting for the small scale effects encompasses its classical continuum counterpart as a particular case. Based upon the constitutive equations of nonlocal elasticity, the displacement field equations coupled by van der Waals forces are derived. The set of governing equations of motion are then numerically solved by a novel method emerged from incorporating the radial point interpolation approximation within the framework of the generalized differential quadrature method. The present analysis provides the possibility of considering different combinations of layerwise boundary conditions. The influences of small scale factor, layerwise boundary conditions and geometrical parameters on the mechanical behavior of DWCNTs are fully investigated. Explicit expressions for the nonlocal frequencies of DWCNTs with all edges simply supported are also analytically obtained by a nonlocal elastic beam model. Some new intertube resonant frequencies and the corresponding noncoaxial vibrational modes are identified due to incorporating circumferential modes into the shell model. A shift in noncoaxial mode numbers, not predictable by the beam model, is also observed when the radius of DWCNTs is varied. The results generated also provide valuable information concerning the applicability of the beam model and new noncoaxial modes affecting the physical properties of nested nanotubes.

Water equivalence evaluation of PRESAGE® formulations for megavoltage electron beams: a Monte Carlo study

To investigate the radiological water equivalency of three different formulations of the radiochromic, polyurethane based dosimeter PRESAGE(®) for three dimensional (3D) dosimetry of electron beams. The EGSnrc/BEAMnrc Monte Carlo package was used to model 6-20MeV electron beams and calculate the corresponding doses delivered in the three different PRESAGE(®) formulations and water. The depth of 50% dose and practical range of electron beams were determined from the depth dose calculations and scaling factors were calculated for these electron beams. In the buildup region, a 1.0% difference in dose was found for all PRESAGE(®) formulations relative to water for 6 and 9MeV electron beams while the difference was negligible for the higher energy electron beams. Beyond the buildup region (at a depth range of 22-26mm for the 6MeV beam and 38mm for the 9MeV beam), the discrepancy from water was found to be 5.0% for the PRESAGE(®) formulations with lower halogen content than the original formulation, which was found to have a discrepancy of up to 14% relative to water. For a 16MeV electron beam, the dose discrepancy from water increases and reaches about 7.0% at 70mm depth for the lower halogen content PRESAGE(®) formulations and 20% at 66mm depth for the original formulation. For the 20MeV electron beam, the discrepancy drops to 6.0% at 90mm depth for the lower halogen content formulations and 18% at 85mm depth for the original formulation. For the lower halogen content PRESAGE(®), the depth of 50% dose and practical range of electrons differ from water by up to 3.0%, while the range of differences from water is between 6.5 and 8.0% for the original PRESAGE(®) formulation. The water equivalent depth scaling factor required for the original formulation of PRESAGE(®) was determined to be 1.07-1.08, which is larger than that determined for the lower halogen content formulations (1.03) over the entire beam energy range of electrons. All three of the PRESAGE(®) formulations studied require a depth scaling factor to convert depth in PRESAGE(®) to water equivalent depth for megavoltage electron beam dosimetry. Compared to the original PRESAGE(®) formulation, the lower halogen content formulations require a significantly smaller scaling factor and are thus recommended over the original PRESAGE(®) formulation for electron beam dosimetry.

Recoupling of chemical shift anisotropy by R-symmetry sequences in magic angle spinning NMR spectroscopy

(13)C and (15)N chemical shift (CS) interaction is a sensitive probe of structure and dynamics in a wide variety of biological and inorganic systems, and in the recent years several magic angle spinning NMR approaches have emerged for residue-specific measurements of chemical shift anisotropy (CSA) tensors in uniformly and sparsely enriched proteins. All of the currently existing methods are applicable to slow and moderate magic angle spinning (MAS) regime, i.e., MAS frequencies below 20 kHz. With the advent of fast and ultrafast MAS probes capable of spinning frequencies of 40-100 kHz, and with the superior resolution and sensitivity attained at such high frequencies, development of CSA recoupling techniques working under such conditions is necessary. In this work, we present a family of R-symmetry based pulse sequences for recoupling of (13)C∕(15)N CSA interactions that work well in both natural abundance and isotopically enriched systems. We demonstrate that efficient recoupling of either first-rank (σ(1)) or second-rank (σ(2)) spatial components of CSA interaction is attained with appropriately chosen γ-encoded RN(n)(v) symmetry sequences. The advantage of these γ-encoded RN(n)(v)-symmetry based CSA (RNCSA) recoupling schemes is that they are suitable for CSA recoupling under a wide range of MAS frequencies, including fast MAS regime. Comprehensive analysis of the recoupling properties of these RN(n)(v) symmetry sequences reveals that the σ(1)-CSA recoupling symmetry sequences exhibit large scaling factors; however, the partial homonuclear dipolar Hamiltonian components are symmetry allowed, which makes this family of sequences suitable for CSA measurements in systems with weak homonuclear dipolar interactions. On the other hand, the γ-encoded symmetry sequences for σ(2)-CSA recoupling have smaller scaling factors but they efficiently suppress the homonuclear dipole-dipole interactions. Therefore, the latter family of sequences is applicable for measurements of CSA parameters in systems with strong homonuclear dipolar couplings, such as uniformly-(13)C labeled biological solids. We demonstrate RNCSA NMR experiments and numerical simulations establishing the utility of this approach to the measurements of (13)C and (15)N CSA parameters in model compounds, [(15)N]-N-acetyl-valine (NAV), [U-(13)C, (15)N]-alanine, [U-(13)C,(15)N]-histidine, and present the application of this approach to [U-(13)C∕(15)N]-Tyr labeled C-terminal domain of HIV-1 CA protein.

Vibration analysis of single-walled carbon nanotubes using different gradient elasticity theories

The present work aims at investigating the vibrational characteristics of single-walled carbon nanotubes (SWCNTs) based on the gradient elasticity theories. The small-size effect, which plays an essential role in the dynamical behavior of nanotubes, is captured by applying different gradient elasticity theories including stress, strain and combined strain/inertia ones. The theoretical formulations are established based upon both the Euler–Bernoulli and the Timoshenko beam theories. To validate the accuracy of the present analysis, molecular dynamics (MDs) simulations are also conducted for an armchair SWCNTs with different aspect ratios. Comparisons are made between the aforementioned different gradient theories as well as different beam assumptions in predicting the free vibration response. It is shown that implementation of the strain gradient elasticity by incorporating inertia gradients yields more reliable results especially for shorter length SWCNTs on account of two small scale factors corresponding to the inertia and strain gradients. Also, the difference between two beam models is more prominent for low aspect ratios and the Timoshenko beam model demonstrates a closer agreement with MD results.

Experimental study on scaling the explosion resistance of a one-way square reinforced concrete slab under a close-in blast loading

Full-scale experiments involving actual geometries and charges are complicated and costly in terms of both preparation and measurements. Thus, scaled-down experiments are highly desirable. The present work aims to address the scaling of the dynamic response of one-way square reinforced concrete slabs subjected to close-in blast loadings. To achieve this objective, six slabs of two groups were tested under real blast loads. Three slabs with different scale-down factors were investigated using two scaled distances. Two major damage levels were observed, namely, spallation damage from a few cracks, and moderate spallation damage. The test results show that the macrostructure damage and fracture in the experiments are almost similar. However, the local damage in concrete slabs with larger-scale factors is slightly reduced compared with that of slabs with smaller-scale factors. Two empirical equations are proposed based on the results to correct the results when scaling up from the model to the prototype.

Finite Sample Performance of Small Versus Large Scale Dynamic Factor Models

We examine the finite-sample performance of small versus large scale dynamic factor models. Our Monte Carlo analysis reveals that small scale factor models out-perform large scale models in factor estimation and forecasting for high levels of cross-correlation across the idiosyncratic errors of series belonging to the same category, for oversampled categories and, especially, for high persistence in either the common factor series or the idiosyncratic errors. Using a panel of 147 US economic indicators, which are classified into 13 economic categories, we show that a small scale dynamic factor model that uses one representative indicator of each category yields satisfactory or even better forecasting results than a large scale dynamic factor model that uses all the economic indicators.

SU-E-T-473: Errors Introduced by Dose Scaling for Relative Dosimetry

Purpose: To quantify errors introduced by rescaling measured dose to compare measured dose distributions with calculated dose distributions for relative dosimetry. Methods: Some dosimeters such as radiographic films require a relationship between dosimeter readings and actually delivered doses. The relationship (or characteristic curves) depends on the manufacturing and environmental conditions under which the dosimeters are made or stored. To compensate for the difference in radiation response among different batches of dosimeters, the measured dose is often rescaled by normalizing the measured dose to a specific dose. This procedure allows us to skip the time‐consuming dosimeter calibration. In this study we derived a mathematical formula of the error in the dose estimated from measurements when this dose scaling procedure is applied to the original dose data. To quantify the errors, we used the characteristic curves experimentally obtained for four different batches of BANG3 polymergels. A linear equation was used to relate a spin‐spin relaxation rate to a known dose. We chose single calibration equation to estimate doses. The scaled doses were then compared with correct doses which were obtained by using the true calibration equation specific to each batch of polymergel. Results: The error was smaller than 2% for doses within 1 Gy of the 5‐Gy normalization dose. The error considerably increased as the dose decreased below 5 Gy; but the error was almost constant for doses higher than 5 Gy. The error for a batch requiring a dose scaling factor of 0.87 was larger than the errors for other batches requiring smaller dose scaling factors of 0.93 or 1.02. Conclusions: Dose scaling introduces a large error for doses far from the dose used for normalization. The error is larger for doses lower than the normalization dose. The error increases as the dose scaling factor deviates more from unity.

Image and video upscaling from local self-examples

We propose a new high-quality and efficient single-image upscaling technique that extends existing example-based super-resolution frameworks. In our approach we do not rely on an external example database or use the whole input image as a source for example patches. Instead, we follow alocal self-similarityassumption on natural images and extract patches from extremely localized regions in the input image. This allows us to reduce considerably the nearest-patch search time without compromising quality in most images. Tests, that we perform and report, show that the local self-similarity assumption holds better for small scaling factors where there are more example patches of greater relevance. We implement these small scalings using dedicated novel nondyadic filter banks, that we derive based on principles that model the upscaling process. Moreover, the new filters are nearly biorthogonal and hence produce high-resolution images that are highly consistent with the input image without solving implicit back-projection equations. The local and explicit nature of our algorithm makes it simple, efficient, and allows a trivial parallel implementation on a GPU. We demonstrate the new method ability to produce high-quality resolution enhancement, its application to video sequences with no algorithmic modification, and its efficiency to perform real-time enhancement of low-resolution video standard into recent high-definition formats.

Hořava–Lifshitz dark energy

We formulate Horava-Lifshitz cosmology with an additional scalar field that leads to an effective dark energy sector. We find that, due to the inherited features from the gravitational background, Horava-Lifshitz dark energy naturally presents very interesting behaviors, possessing a varying equation-of-state parameter, exhibiting phantom behavior and allowing for a realization of the phantom divide crossing. In addition, Horava-Lifshitz dark energy guarantees for a bounce at small scale factors and it may trigger the turnaround at large scale factors, leading naturally to cyclic cosmology.

COSMOLOGY WITH MINIMAL LENGTH UNCERTAINTY RELATIONS

We study the effects of the existence of a minimal observable length in the phase space of classical and quantum de Sitter (dS) and anti-de Sitter (AdS) cosmology. Since this length has been suggested in quantum gravity and string theory, its effects in the early universe might be expected. Adopting the existence of such a minimum length results in the generalized uncertainty principle (GUP), which is a deformed Heisenberg algebra between minisuperspace variables and their momenta operators. We extend these deformed commutating relations to the corresponding deformed Poisson algebra in the classical limit. Using the resulting Poisson and Heisenberg relations, we then construct the classical and quantum cosmology of dS and AdS models in a canonical framework. We show that in classical dS cosmology this effect yields an inflationary universe in which the rate of expansion is larger than that of the usual dS universe. Also, for the AdS model it is shown that the GUP might change the oscillatory nature of the corresponding cosmology. We also study the effects of the GUP in quantized models through approximate analytical solutions to the Wheeler–DeWitt (WD) equation, in the limit of a small scale factor for the universe, and compare the results with the ordinary quantum cosmology in each case.

Historic landscape change and habitat loss: the case of black grouse in Lower Saxony, Germany

The declines of many specialist bird species in the agricultural landscapes of Central Europe have resulted in small and isolated populations. In the case of the black grouse, a ground-nesting bird species with large spatial requirements, empiric evidence about underlying landscape changes is scarce. In this study, we examined land cover and land cover changes in a farmland-forest mosaic in eastern Lower Saxony, Germany and how they affect occurrence and persistence of black grouse. Spatial information came from historic topographic maps from 1958 to 1975. The results show profound conversions of habitat to forest and farmland but also an increase in settlement area. Habitat conversions and suburbanization were negative correlates of black grouse persistence. Habitat models from before and after a decline period differed in some of the predictors and suggest black grouse habitat to be more diverse before the land cover changes. Our study confirms that land use factors at a landscape scale extent contribute to explain black grouse occurrence and thus can complement important small scale factors like the quality and size of individual habitat patches. Results also show that landscape factors affect black grouse distribution predominantly from an area much greater than an individual black grouse home range. Our models may be further evaluated on present-day landscapes and might be used to evaluate large-scale habitat availability for black grouse.

The consistent result of cosmological constant from quantum cosmology and inflation with Born–Infeld scalar field

Quantum cosmology with a Born–Infeld (BI) type scalar field is considered. In the extreme limits of a small cosmological scale factor the wave function of the universe can also be obtained by applying the methods developed by Hartle–Hawking (HH) and Vilenkin. The HH wave function approach predicts that the most probable cosmological constant Λ equals $\frac{1}{\eta}$ ( $\frac{1}{2\eta}$ equals the maximum of the kinetic energy of the scalar field). It is different from the original results (Λ=0) for the cosmological constant obtained by Hartle–Hawking. The Vilenkin wave function predicts a nucleating universe with the largest possible cosmological constant, and it is larger than 1/η. The conclusions can nicely be reconciled with cosmic inflation. We investigate the inflation model with the BI type scalar field and find that η depends on the amplitude of the tensor perturbation δh, having the form $\frac{1}{\eta}$ $\simeq$ $\frac{m^2}{12\pi[(\frac{9\delta^2_{\Phi}}{N\delta^2_h})^2-1]}.$ The vacuum energy in the inflation epoch depends on the tensor-to-scalar ratio δh/δΦ. The amplitude of the tensor perturbation δh may, in principle, be large enough to be discovered. However, it is only on the border of detectability in future experiments. If it will have been observed in the future, this will be very interesting as regards determining the vacuum energy in the inflation epoch.

Soil hydraulic properties as ecological indicators in forested watersheds impacted by mechanized military training

Abstract Soil hydraulic properties were characterized on a ridgetop training site and other sites not impacted by training at Fort Benning, a military installation in southwestern, GA to: (1) examine the influence of mechanized training on soil hydraulic properties and (2) evaluate the utility of soil hydraulic properties as disturbance-level indicators related to ecosystem integrity. Ridgetop surface soils impacted by mechanized military training exhibited a reduction in the mean pore size, as indicated by smaller scaling factors, an increase in the soil bulk density and a decrease in saturated hydraulic conductivity for training locations versus non-training locations. Soil bulk density, saturated hydraulic conductivity and scaling factors exhibited lower population variance in the training sites, indicating repetitive training cycles that progressively mix and homogenize the soil. Surface soils (0–3 cm below ground surface) at all sites were predominantly loamy sands. The observed differences in measured soil properties at training and non-training sites characterize the endpoints of an ecosystem disturbance gradient where relatively un-impacted forest transitions to barren, churned sand. They also help explain the visual evidence of increased overland flow and significant soil erosion in the training areas. While results from this research showed a marked difference in measured soil properties between the two extreme types of land management, more work is needed to establish threshold levels for soil properties related to mechanized vehicle training cycles and training intensity and corresponding ecosystem degradation/integrity. It is noted that for assessment of immediate erosion potential and ecosystem integrity, remote sensing techniques paired with watershed-scale numerical modeling may be more valuable and that greater research emphasis be given to characterizing the indirect, yet more widespread, down-slope impacts of mechanized training activities localized on the ridgetops.

Experimental and analytical investigation into crack strength determination of infilled steel frames

This paper presents the results of further development of a new analytical approach for the evaluation of shear strength and cracking patterns of infill panels. This method is based on the minimum evaluated strength with reference to the failure surfaces. This paper also presents the results of an experimental investigation of small and medium scale masonry and concrete infilled frames. Eleven specimens, with and without horizontal reinforcement and bond beams, were subjected to static cyclic loads. The tests are categorized in two groups, based on their surrounding frames and scale. In the first group a small scale factor is used, and the frames have pinned connections with very stiff beams and columns representing the lower stories of tall buildings. In the second group a medium scale factor is used, and the frames have rigid connections. Both experiments and analysis have confirmed that the efficiency of horizontal reinforcement and bond beams depends on the dominant pattern of cracking. The results also indicate that as opposed to masonry infills, the corner crushing is the dominant mode of failure in concrete infills.

Viral impacts upon marine bacterioplankton assemblage structure

This study examined the relationship between viral infection and the richness, diversity and composition of bacterial assemblages in the water column. Viruses were enriched by ultrafiltration, added to water column incubation experiments at 15 locations in the North Atlantic, North Pacific, Gulf of Mexico and Southern California. In a separate experiment, viruses were removed from bacterioplankton by diafiltration at the San Pedro Ocean Time Series Station. Bacterial assemblage composition was observed using a high throughput and sensitive molecular fingerprinting analysis, automated rRNA intergenic spacer analysis (ARISA). Diazotrophs were used as a model functional group to represent rare organisms hypothesized to benefit from viral activity, and their richness and diversity was determined by terminal restriction fragment length polymorphism of a nitrogenase gene fragment (nifH). The enrichment and removal experiments demonstrated mixed impacts of viral pressure upon bacterial communities, and we observed significant effects of viruses on several microbial parameters in all but two experiments. However, there was no consistent response of viral enrichment on total bacterial and diazotroph assemblages at stations with similar environmental conditions, suggesting that untested variables, small spatial scale factors, or stochastic processes influence the outcome of viral activities. Across all experiments, the relative abundance of the more common operational taxonomic units (OTUs) in fingerprints were not significantly impacted compared to the abundance of rare OTUs. These data indicate that viruses may have significant influence upon community structure of bacterioplankton; however, effects were not consistent between sampling locations nor water masses.

Color image retrieval techniques for a global localization of an indoor mobile robot

In this paper we propose a both spatial and colorimetric distance D for a two dimensional color pallet built from the baker's transformation. The baker's transformation provides a quantization of the image into a space where colors that are nearby in the original space are also nearby in the output space, thereby providing dimensionality reduction and invariance to minor changes in the image. Whereas, the distance D provides for partial invariance to translation, sight point small changes and scale factor. Our feature is used in an image retrieval process that has to help a missing robot in an indoor environment. We built a structured image database corresponding to the flat where the robot works. When the robot is lost, it takes an image of its environment that we call request image and the system looks for the closest image in the database witch indicates its position (room and orientation). A hierarchical approach is then conceived by describing in the off line phase each room with a color feature. In a first search phase, we eliminate rooms whose colors are far from those of the request image and then we achieve the search by our distance D. Results obtained with this approach are better than those of the classical color histograms.

Generalised scaling relations for dynamic centrifuge tests

The trend toward physical modelling of larger prototypes triggers a move towards expansion of the current capability of dynamic centrifuge tests. In this paper a method based on the concept of two-stage scaling is proposed that allows expanded use of the currently available facilities. In the first stage a prototype is scaled down into an intermediate virtual model based on the scaling relations in a 1g field with a scaling factor of μ (prototype/virtual model). In the second stage this model is scaled down into a physical model using the conventional scaling relations in the centrifugal field with a scaling factor of η (virtual model/physical model). In this manner, a large scaling factor λ = μη (prototype/physical model) can be broken down into the smaller scaling factors μ and η, and thus the centrifuge model tests can be performed with the smaller scaling factor η. In effect, the limits in the scaling factor for the currently available centrifuge facilities can be expanded by a factor of μ. Validation of the proposed method is provided by algebraic derivations based on the mechanics of model tests.

Generalised scaling relations for dynamic centrifuge tests

The trend toward physical modelling of larger prototypes triggers a move towards expansion of the current capability of dynamic centrifuge tests. In this paper a method based on the concept of two-stage scaling is proposed that allows expanded use of the currently available facilities. In the first stage a prototype is scaled down into an intermediate virtual model based on the scaling relations in a 1g field with a scaling factor of μ (prototype/virtual model). In the second stage this model is scaled down into a physical model using the conventional scaling relations in the centrifugal field with a scaling factor of η (virtual model/physical model). In this manner, a large scaling factor λ = μη (prototype/physical model) can be broken down into the smaller scaling factors μ and η, and thus the centrifuge model tests can be performed with the smaller scaling factor η. In effect, the limits in the scaling factor for the currently available centrifuge facilities can be expanded by a factor of μ. Validation of the proposed method is provided by algebraic derivations based on the mechanics of model tests.

Genericness of Inflation in Isotropic Loop Quantum Cosmology

Nonperturbative corrections from loop quantum cosmology (LQC) to the scalar matter sector are already known to imply inflation. We prove that the LQC modified scalar field generates exponential inflation in the small scale factor regime, for all positive definite potentials, independent of initial conditions and independent of ambiguity parameters. For positive semidefinite potentials it is always possible to choose, without fine-tuning, a value of one of the ambiguity parameters such that exponential inflation results, provided zeros of the potential are approached at most as a power law in the scale factor. In conjunction with the generic occurrence of bounce at small volumes, particle horizon is absent, thus eliminating the horizon problem of the standard big bang model.

Modulo transforms - an alternative to lifting

This paper introduces a new paradigm for the construction of reversible transforms that map integers to integers. Transform matrices with integer entries are first considered, and the modular arithmetic properties of transform coefficients are studied. It is shown that these transform coefficients are redundant in modular arithmetic. Further, this redundancy can be exploited by quantizing transform coefficients critically so as to produce an effective scaled transformation with unit determinant. This forms the basis of a class of transforms referred to as modulo transforms that are reversible and unit determinant, conditions necessary for applications such as lossless compression and reversible image rotation. The theory of modulo transforms is examined in depth. Analysis based on modular arithmetic shows that two-dimensional rotations can be critically quantized, albeit with nonequal bin widths along axes. A construction procedure is derived for realizing a reversible transform with small or unit scaling factors, and a theorem is stated wherein certain Pythagorean triples can be scalar quantized to produce a reversible, normalized, scalefree transform matrix. Modulo transforms and lifting are compared and contrasted in theory, and in experiments. The computational aspects of modulo transforms are also discussed in this paper.