Time Scale Factor Research Articles

Scale factor self-dual cosmological models

We implement a conformal time scale factor duality for Friedmann-Robertson-Walker cosmological models, which is consistent with the weak energy condition. The requirement for self-duality determines the equations of state for a broad class of barotropic fluids. We study the example of a universe filled with two interacting fluids, presenting an accelerated and a decelerated period, with manifest UV/IR duality. The associated self-dual scalar field interaction turns out to coincide with the “radiation-like” modified Chaplygin gas models. We present an equivalent realization of them as gauged Kähler sigma models (minimally coupled to gravity) with very specific and interrelated Kähler- and super-potentials. Their applications in the description of hilltop inflation and also as quintessence models for the late universe are discussed.

Barotropic FRW cosmologies with Chiellini damping in comoving time

For nonzero cosmological constant Λ, we show that the barotropic FRW cosmologies as worked out in the comoving time lead in the radiation-dominated case to scale factors of identical form as for the Chiellini dissipative scale factors in conformal time obtained recently by us in Phys. Lett. A 379, 882 (2015). This is due to the Ermakov equation which is obtained in this case. For zero cosmological constant, several textbook solutions are easily obtained as particular cases of our formulas and hypergeometric solutions are also reminded.

Scaling law of static liquefaction mechanism in geocentrifuge and corresponding hydromechanical characterization of an unsaturated silty sand having a viscous pore fluid

Fast landslides induced by rainfall impose considerable damage on infrastructure and cause major casualties worldwide. Static liquefaction is one of the triggering mechanisms mentioned frequently in the literature as a cause of this type of landslide. The scaling laws required to model this mechanism in the geotechnical centrifuge are developed, and it is shown that either a reduction in the soil pore size or use of a viscous pore fluid is needed to unify the time scaling factors of contractive volume change of the saturated voids and dissipation of the excess pore pressure generated. The latter option was used in this research; therefore, the influences of the viscous pore fluid on the hydromechanical characteristics of a silty sand were investigated. Subsequently, geocentrifuge tests were conducted to compare the behaviour of a slope having a viscous solution as the pore fluid with that of a model with water as the pore fluid. Both slopes were subjected to rainfall, and the evolution of the pore pressure and surface movements were monitored.

Derivation of the scan time requirement for maintaining a consistent PET image quality

Objectives: the image quality of PET for larger patients is relatively poor, even though the injection dose is optimized considering the NECR characteristics of the PET scanner. This poor image quality is due to the lower level of maximum NECR that can be achieved in these large patients. The aim of this study was to optimize the PET scan time to obtain a consistent PET image quality regardless of the body size, based on the relationship between the patient specific NECR (pNECR) and body weight.Methods: eighty patients (M/F=53/27, body weight: 059 ± 1 kg) underwent whole-body FDG PET scans using a Philips GEMINI GS PET/CT scanner after an injection of 0.14 mCi/kg FDG. The relationship between the scatter fraction (SF) and body weight was determined by repeated Monte Carlo simulations using a NEMA scatter phantom, the size of which varied according to the relationship between the abdominal circumference and body weight. Using this information, the pNECR was calculated from the prompt and delayed PET sinograms to obtain the prediction equation of NECR vs. body weight. The time scaling factor (FTS) for the scan duration was finally derived to make PET images with equivalent SNR levels.Results: the SF and NECR had the following nonlinear relationships with the body weight: SF=0.15 ⋅ body weight0.3 and NECR = 421.36 (body weight)−0.84. The equation derived for FTS was 0.01⋅ body weight + 0.2, which means that, for example, a 120-kg person should be scanned 1.8 times longer than a 70 kg person, or the scan time for a 40-kg person can be reduced by 30%.Conclusion: the equation of the relative time demand derived in this study will be useful for maintaining consistent PET image quality in clinics.

Material-Balance Method for Dual-Porosity Reservoirs With Recovery Curves To Model the Matrix/Fracture Transfer

Summary This paper presents a material-balance (MB) method applicable to naturally fractured dual-porosity reservoirs by considering the matrix/fracture transfer. The method is based on the recognition that the performance of water and gas displacement from matrix blocks can be depicted in the form of recovery factor vs. time. These recovery curves determine the matrix/fracture oil transfer. The reservoir pressure change depends on the original fluids in place and the strength of the aquifer. Thus, a close relationship between the recovery curves and the observed reservoir state (e.g., pressure, position of the phase contacts, water cut, and gas/oil ratio), the aquifer parameters, and the matrix/fracture oil transfer exists. Concerning the matrix blocks, the surrounding fracture continuum sets the boundary conditions by acting as an injector. The injection rates are predefined by the provided recovery curves, which one can obtain with different methods. They can be calculated by fine-scale single matrix-block models (Pirker et al. 2007), derived from conventional full-field numerical models, measured in a laboratory autoclave (Mattax and Kyte 1962), or determined by theoretical means (Davis and Hill 1982). The recovery curves can be scaled and normalized, making them applicable within a certain rock type to a wide range of rock parameters, namely shape factor, permeability, and porosity (Amiry 2014). While in a full-field model, various rock types can be identified; in MB calculations, however, they must be reduced to a single rock type. MB calculations—irrespective of conventional single-porosity methods or the herein-presented approach for dual-porosity naturally fractured reservoirs—are always conducted on a homogenized reservoir model. Therefore, variations in rock and pressure/volume/temperature properties cannot be taken into account. The recovery process is governed by two parameters—the asymptotic value of the recovery function and the time-scaling factor. These two parameters can be used for matching the observed reservoir performance. The new MB method matches both the reservoir pressure and the positions of the phase contacts. It also provides aquifer and matrix/fracture fluid-transfer models. Applying the parameters of those models in prediction mode and assuming a future production strategy, reservoir-pressure decline and phase-contact movements can be forecasted. The paper presents the calculation schema and the successful application to a field with more than 500 million STB of original oil in place and a 35-year production history. For the first time, it becomes possible to realistically—this means by fully considering the governing recovery mechanisms and thus the matrix/fracture transfer—calculate MB for naturally fractured dual-porosity reservoirs.

NUMERICAL DISPERSION ANALYSIS FOR THE 3-D HIGH-ORDER WLP-FDTD METHOD

In this paper, a theoretical analysis of numerical dispersion of the three-dimensional (3-D) high-order finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLPs) is presented. The phase velocity of numerical wave modes is relevant to the direction of wave propagation, grid discretization and time-scale factor. The formula to determine a suitable time-scale factor is derived. By a theoretical evaluation, the dispersion errors for the 3-D high-order WLP-FDTD scheme with different time-scale factors are obtained. Finally, one numerical example is included to validate the effectiveness of the theoretical solution of the time-scale factor.

ANALYSIS OF NUMERICAL DISPERSION IN THE HIGH-ORDER 2-D WLP-FDTD METHOD

A theoretical analysis of numerical dispersion in the high-order finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLPs) is proposed in this paper. According to the numerical dispersion relation for the two-dimensional (2-D) case, the numerical phase velocities relevant to the direction of wave propagation, grid discretization and time-scale factor are obtained. For a fixed relative error of the numerical phase velocity, the suitable sampling point density and time- scale factor can be determined. Compared with the low-order WLP-FDTD, the high-order one shows its good dispersion characteristics while a low sampling density is used. Three numerical examples are included to validate the effectiveness of the high-order scheme.

Modeling CaCO3 crystallization fouling on a heat exchanger surface – Definition of fouling layer properties and model parameters

Crystallization fouling occurs when dissolved salts precipitate from an aqueous solution to the walls of process equipment. In the case of inversely soluble salts, like CaCO3, this may lead to crystal growth on heated surfaces. In this study, crystallization fouling of CaCO3 on a flat-plate heat exchanger surface is studied. The mass deposition rates are determined from the measurements of the fouling thermal resistance and the properties of the porous fouling layer. The uncertainty of the fouling layer properties and the mass depositions rate are quantified with a detailed uncertainty analysis, which shows that the proposed method and experimental analysis provide values that are reasonably defined and acceptable. The obtained mass deposition rates are used to determine the kinetic parameters of different fouling models using a regression analysis. The validation of the models against the experimental data shows that the closest correspondence between the experimental and modeled results occurs when the crystallization fouling is described by the surface integration model including the time scaling factor which depends on the flow velocity.

Theoretical analysis of micro-vibration between a high moisture content rape stalk and a non-smooth surface of a reciprocating metal cleaning screen matrix

Because rape stalk has a high water content, rape materials easily adhere to the cleaning screens of combine harvesters leading to a high screen loss. Inspired by friction-reducing research on bionic non-smooth metal surfaces, a special rape cleaning screen with non-smooth surface was developed and compared with a standard screen in field experiment. It showed good anti-adhesion performance to rape components. To understand the mechanism, a reciprocating friction test between a rape stalk and non-smooth metal surface was carried out. The result was consistent with the findings of a field experiment. In the test, a vertical micro-vibration was discovered between rape stalk and the non-smooth metal surface. This did not exist in the case of a common smooth metal surface and was considered as an important factor in the mechanism. In this paper, a theoretical analysis was proposed to explain how the vertical micro-vibrations occurred during a horizontal reciprocating translation of non-smooth units. Firstly, according to the case of friction test, a geometry contact model and a dynamic equation were established. Then computing methods of vertical impact force and its action time were respectively deduced. Finally, a simulation was produced with a time-scale factor of two. The result from the simulation was consistent with basic trend of test data. Although the theoretical analysis requires improvement for further investigation, it could still provide the basis of a theoretical model and the foundation for further friction-reducing research for non-smooth surfaces.

Estimation of subsurface temperature profiles from infrared measurements during ultrasound ablation

Measurement of in situ spatiotemporal temperature profiles would be useful for developing and validating thermal ablation methods and therapy monitoring approaches. Here, finite difference and analytic solutions to Pennes’ bio-heat transfer equation were used to determine spatial correlations between temperature profiles on parallel planes. Time delays and scale factors for correlated profiles were applied to infrared surface-temperature measurements to estimate subsurface temperatures. To test this method, exvivo bovine liver tissue was sonicated by linear image-ablate arrays with 1–6 pulses of 5.0 MHz unfocused (7.5 s, 64.4–92.0 W/cm2 in situ I SPTP) or focused (1 s, 562.7–799.6 W/cm2 in situ I SPTP, focus depth 10 mm) ultrasound. Temperature was measured on the liver surface by an infrared camera at 1 fps and extrapolated to the imaging/ablation plane, 3 mm below the surface. Echo decorrelation maps were computed from pulse-echo signals captured at 118 fps during 5.0 s rest periods beginning 1.1 s after each sonication pulse. Tissue samples were frozen at −80 °C, sectioned, vitally stained, imaged, and segmented for analysis. Estimated thermal dose profiles showed correspondence with segmented tissue histology, while thresholded temperature profiles corresponded with measured echo decorrelation. These results suggest utility of this method for thermal ablation research.

Effect of Time Scaling and Mass Scaling in Numerical Simulation of Incremental Forming

In incremental sheet forming (ISF) the tool moves along the specified trajectory and deforms the sheet in to required shape. In the present paper incremental forming process is simulated using explicit finite element software LS-DYNA. The computational time for the simulation of ISF is very long due to long tool paths used in the process. To overcome this problem time scaling and mass scaling are used in the present paper. The effect of time scaling and mass scaling on forming forces, plastic strain, internal energy, kinetic energy, thickness distribution and computational time is studied. A continuously varying wall angle conical frustum is simulated for this study. Extra deep drawn steel, which is most commonly used in automotive applications, has been used as a blank material. Thickness distribution obtained with different mass and time scaling factors is compared with experimentally measured thickness distribution.

OP0168 Clinical Characteristics, Case-Fatality and Risk Factors for Ischemic Stroke in Prevalent Rheumatoid Arthritis

BackgroundThe risk of ischemic stroke (IS) is increased in patients with rheumatoid arthritis (RA), at least in patients with longstanding disease. Little is known about the clinical phenotype, case-fatality and...

Optimization Time for Bending Extruded Aluminum Profile

The goal of this paper is to simulate the bending process of extruded aluminum profile using ABAQUS/CAE software. Bending investigations were conducted using the finite element method. The main contents of research work include simulation software, which give in details the pre-processing steps followed to obtain an accurate model to work on. The computing time is often important, explored some ways to reduce it. The simulation give information about the location of critical areas on the profile after bending; the middle section was targeted since it is the area most deformed. This paper focus on the influence of the die mesh, initial distance, mass scaling factor and time scaling factor on the evolution of the computer time (CT), kinetic energy (KE), stress (SVMises) and strain (peeq) .

Effects of Key Simulation Parameters on Conical Ring Rolling Process

This paper established 3D coupled thermo-mechanical finite element simulation model of a conical ring rolling process. Three simulation experiments were designed and performed. The effects of key simulation parameters such as mass scaling factor, time scaling factor and remeshing sweeps per increment on simulation time and volume change of conical ring were investigated and analyzed. The reasonable values of simulation parameters in conical ring rolling process were determined for decreasing simulation time and simultaneously reducing finite element simulation error.

Correlation and Spectral Properties of a Coupled Nonlinear Dynamical System in the Context of Numerical Weather Prediction and Climate Modeling

Complex dynamical processes occurring in the earth’s climate system are strongly nonlinear and exhibit wave-like oscillations within broad time-space spectrum. One way to imitate essential features of such processes is using a coupled nonlinear dynamical system, obtained by coupling two versions of the well-known Lorenz (1963) model with distinct time scales that differ by a certain time-scale factor. This dynamical system is frequently applied for studying various aspects of atmospheric and climate dynamics, as well as for estimating the effectiveness of numerical algorithms and techniques used in numerical weather prediction, data assimilation, and climate simulation. This paper examines basic dynamic, correlative, and spectral properties of this system and quantifies the influence of the coupling strength on power spectrum densities, spectrograms, and autocorrelation functions.

Numerical Dispersion Analysis and Key Parameter Selection in Laguerre-FDTD Method

In this letter, a theoretical analysis of the numerical dispersion and key parameter selection of the finite-difference time-domain (FDTD) method with weighted Laguerre polynomials is presented. Different from the conventional FDTD method, the numerical dispersion relation is relevant not only to sampling point density in space domain but also to time-scale factor. For a fixed relative error of phase velocity, the suitable sampling point density and time-scale factor can be determined. In addition, the selection of the number of Laguerre functions is derived using the theoretical time-scale factor, and is verified in a numerical example.

AVALIAÇÃO DA ESCALA DE TEMPO EM TÚNEIS DE VENTO COM BASE NA ANÁLISE ESPECTRAL E OS CRITÉRIOS DE SEMELHANÇA

A methodology based on spectral comparisons to evaluate the time scale factor in wind tunnel tests is proposed. Obtained results shown a significant dependency of these parameters with the gust duration time. This behavior must be considered when the quasistatic approach is used to evaluate wind loads by means of peak coefficients.

Cognitive and neuropsychiatric correlates of EEG dynamic complexity in patients with Alzheimer's disease

This study assessed the utility of multiscale entropy (MSE), a complexity analysis of biological signals, to identify changes in dynamics of surface electroencephalogram (EEG) in patients with Alzheimer's disease (AD) that was correlated to cognitive and behavioral dysfunction. A total of 108 AD patients were recruited and their digital EEG recordings were analyzed using MSE methods. We investigate the appropriate parameters and time scale factors for MSE calculation from EEG signals. We then assessed the within-subject consistency of MSE measures in different EEG epochs and correlations of MSE measures to cognitive and neuropsychiatric symptoms of AD patients. Increased severity of AD was associated with decreased MSE complexity as measured by short-time scales, and with increased MSE complexity as measured by long-time scales. MSE complexity in EEGs of the temporal and occipitoparietal electrodes correlated significantly with cognitive function. MSE complexity of EEGs in various brain areas was also correlated to subdomains of neuropsychiatric symptoms. MSE analysis revealed abnormal EEG complexity across short- and long-time scales that were correlated to cognitive and neuropsychiatric assessments. The MSE-based EEG complexity analysis may provide a simple and cost-effective method to quantify the severity of cognitive and neuropsychiatric symptoms in AD patients.

Oscillations and chaos in the dynamics of the BCM learning rule

The BCM learning rule originally arose from experiments intended for measuring the selectivity of neurons in the primary visual cortex, and it dependence on input stimuli. This learning rule incorporates a dynamic LTP threshold, which depends on the time averaged postsynaptic activity. Although the BCM learning rule has been well studied and some experimental evidence of neuronal adherence has been found in the other areas of the brain, including the hippocampus, there is still much to be known about the dynamic behavior of this learning rule. The dynamics of BCM cell can be described as follows: τwdwdt=νxj(i)ν-θ τθdθdt=ν2-θ where x(i)=x1(i),...,xn(i) is an input stimulus pattern, and w=w1,...,wn is the synaptic weights. The postsynaptic activity is computed as ν=w.x(i), and θ is a sliding threshold for the postsynaptic activity. and are constants. In this work, a mean-field version of the BCM learning rule is studied, and it is shown that if the synaptic weights and the postsynaptic activity threshold share similar time scales, then it is possible to obtain complex dynamics. It is also shown that there exist periodic orbits for certain parametric regions of stimulus orientation and time-scale factor, as evidenced by a Hopf Bifurcation (see Figure ​Figure1).1). Consequently, it is discovered that the synaptic weights exhibit an oscillatory behavior in this region. A preliminary study of two BCM cells coupled by lateral inhibition yields a torus bifurcation, which tends to lead to chaos. Figure 1 (A) w1-vs-a, where a is the parameterizes of input stimulus. The bold curve shows the periodic orbits as a varies. (B) The green curve is θ-vs-time, the black curve is w1-vs-time, and the red curve is w2-vs-tme. Each exhibiting a stable oscillation ...

Multiscale Entropy Analysis of Electroencephalography During Sleep in Patients With Parkinson Disease

Sleep disorders are frequently seen in patients with Parkinson disease (PD), including rapid eye movement (REM) behavior disorder and periodic limb movement disorder. However, knowledge about changes in non-REM sleep in patients with PD is limited. This study explored the characteristics of electroencephalography (EEG) during sleep in patients with PD and non-PD controls. We further conducted multiscale entropy (MSE) analysis to evaluate and compare the complexity of sleep EEG for the 2 groups. There were 9 patients with PD (Hoehn-Yahr stage 1 or 2) and 11 non-PD controls. All participants underwent standard whole-night polysomnography (PSG), which included 23 channels, 6 of which were for EEG. The raw data of the EEG were extracted and subjected to MSE analysis. Patients with PD had a longer sleep onset time and a higher spontaneous EEG arousal index. Sleep stage-specific increased MSE was observed in patients with PD during non-REM sleep. The difference was more marked and significant at higher time scale factors (TSFs). In conclusion, increased biosignal complexity, as revealed by MSE analysis, was found in patients with PD during non-REM sleep at high TSFs. This finding might reflect a compensatory mechanism for early defects in neuronal network control machinery in PD.