Uniform Distribution Model Research Articles

Effects of thermal residual stresses and thermal-induced geometrically necessary dislocations on size-dependent strengthening of particle-reinforced MMCs

The thermal residual stresses (TRSes) can noticeably increase the yield strength and flow stresses of particle-reinforced metal-matrix composites (PR-MMCs) and show size-dependence due to thermal geometrically necessary dislocations (GNDs) when the size of particles is on the order of micron. This TRSes strengthening is attributed to the conventional thermal-elasto-plastic constituent mismatch (regardless of particles’ size) and the presence of GNDs (size-dependent). A modified Taylor-based nonlocal theory (TNT) of plasticity is proposed to quantify the individual contributions of size-dependent GND strengthening. An axisymmetric unit-cell model of uniform and aligned particle distribution with various particle sizes is built to study thermal-induced non-uniformly distributed GNDs, their evolution and contributions to the stress strengthening under combined thermal and mechanical loading. The results show that the proposed methodology can effectively capture the size dependence of thermal-induced GNDs which keeps a sharp gradient variation in the zone near the matrix-inclusion interface and gradually flattens out in the zone far away from the interface. It is demonstrated that TRSes significantly improve the yield strength and flow stresses. It also revealed that the contribution of thermal-induced GNDs increased as the particle size in the PR-MMCs decreased. The simulation results were validated by experimental results reported in the literature.

A simplified model of biosonar echoes from foliage and the properties of natural foliages.

Foliage echoes could play an important role in the sensory ecology of echolocating bats, but many aspects of their sensory information content remain to be explored. A realistic numerical model for these echoes could support the development of hypotheses for the relationship between foliage properties and echo parameters. In prior work by the authors, a simple foliage model based on circular disks distributed uniformly in space has been developed. In the current work, three key simplifications used in this model have been examined: (i) representing leaves as circular disks, (ii) neglecting shading effects between leaves, and (iii) the uniform spatial distribution of the leaves. The target strengths of individual leaves and shading between them have been examined in physical experiments, whereas the impact of the spatial leaf distribution has been studied by modifying the numerical model to include leaf distributions according to a biomimetic model for natural branching patterns (L-systems). Leaf samples from a single species (leatherleaf arrowwood) were found to match the relationship between size and target strength of the disk model fairly well, albeit with a large variability part of which could be due to unaccounted geometrical features of the leaves. Shading between leaf-sized disks did occur for distances below 50 cm and could hence impact the echoes. Echoes generated with L-system models in two distinct tree species (ginkgo and pine) showed consistently more temporal inhomogeneity in the envelope amplitudes than a reference with uniform distribution. However, these differences were small compared to effects found in response to changes in the relative orientation of simulated sonar beam and foliage. These findings support the utility of the uniform leaf distribution model and suggest that bats could use temporal inhomogeneities in the echoes to make inferences regarding the relative positioning of their sonar and a foliage.

Lightweight Mashup Middleware for Coal Mine Safety Monitoring and Control Automation

Recently, the frequent coal mine safety accidents have caused serious casualties and huge economic losses. It is urgent for the global mining industry to increase operational efficiency and improve overall mining safety. This paper proposes a lightweight mashup middleware to achieve remote monitoring and control automation of underground physical sensor devices. First, the cluster tree based on ZigBee Wireless Sensor Network (WSN) is deployed in an underground coal mine, and propose an Open Service Gateway initiative (OSGi)-based uniform devices access framework. Then, propose a uniform message space and data distribution model, and also, a lightweight services mashup approach is implemented. With the help of visualization technology, the graphical user interface of different underground physical sensor devices could be created, which allows the sensors to combine with other resources easily. Besides, four types of coal mine safety monitoring and control automation scenarios are illustrated, and the performance has also been measured and analyzed. It has been proved that our lightweight mashup middleware can reduce the costs efficiently to create coal mine safety monitoring and control automation applications.

Cloud-Based Parameter-Driven Statistical Services and Resource Allocation in a Heterogeneous Platform on Enterprise Environment

A fundamental key for enterprise users is a cloud-based parameter-driven statistical service and it has become a substantial impact on companies worldwide. In this paper, we demonstrate the statistical analysis for some certain criteria that are related to data and applied to the cloud server for a comparison of results. In addition, we present a statistical analysis and cloud-based resource allocation method for a heterogeneous platform environment by performing a data and information analysis with consideration of the application workload and the server capacity, and subsequently propose a service prediction model using a polynomial regression model. In particular, our aim is to provide stable service in a given large-scale enterprise cloud computing environment. The virtual machines (VMs) for cloud-based services are assigned to each server with a special methodology to satisfy the uniform utilization distribution model. It is also implemented between users and the platform, which is a main idea of our cloud computing system. Based on the experimental results, we confirm that our prediction model can provide sufficient resources for statistical services to large-scale users while satisfying the uniform utilization distribution.

Developing a hybrid procedure of one dimensional finite element method and CFD simulation for modeling refrigerant flow mal-distribution in parallel flow condenser

Mal-distribution of refrigerant flow in flat tubes is an important problem in parallel flow heat exchangers (PFHXs) which should be considered in heat exchanger modeling. In the present study, a hybrid method is developed for flow distribution forecasting based on simultaneous use of computational fluid dynamics (CFD) simulation for 3D analysis of flow in PFHX headers and one dimensional finite element model for solving flow within flat tubes. The experimental data of a parallel flow condenser (PFC) performance is collected to verify the developed method. The average absolute deviations of 2.8%, 4.1% and 3% from experimental data for pressure drop, capacity and outlet temperature respectively, indicate the model validity. Slight increase of mass flow rate with moving toward the bottom tubes of the inlet header shows insignificant effect of gravity when vapor-phase flow is present. Also, comparing the pressure drop data of the developed method with those of uniform-distribution model demonstrates reduction of average absolute deviation from 28.7% to 2.8%. The proposed model has the advantage of predicting PFC overall performance and can be used to accurately design and optimize headers and multiport flat tubes.

A New Radiocarbon Sequence from Lamanai, Belize: Two Bayesian Models from One of Mesoamerica’s Most Enduring Sites

AbstractThe ancient Maya community of Lamanai, Belize, is well known for its span of occupation from the Early Preclassic (before 1630 BC) to the present. Although most centers in the central and southern Maya Lowlands were abandoned during the Terminal Classic period (AD 750–1000), ceramic and stratigraphic evidence at Lamanai has shown continuous occupation from the start of the Early Preclassic to the Spanish Conquest. In this paper, we present the first complete set of radiocarbon dates from this important site, including 19 new accelerator mass spectrometry (AMS)14C dates. We use these dates to build Bayesian models for a Terminal Classic structure and an Early Postclassic structure in the site center. This method assists in the refinement of older, conventional dates and provides key chronological information about the site during this volatile time. Adjustments to the standard, uniform distribution model are made using exponential, long-tail, and trapezoidal distributions to incorporate outlier samples and more accurately portray ceramic phases. Because of changes in construction behavior in the Terminal Classic, it is difficult to acquire primary samples from this period, but there remains enough overlap between dates and ceramic phases to deduce persistent occupation at Lamanai during the transition from Late Classic to Postclassic times.

A CFD model for gas uniform distribution in turbulent flow for the production of titanium pigment in chloride process

The fluid dynamic behavior of feeding gas (TiCl4) in an annular channel affects the combination of O2 and TiCl4 in an oxidation reactor, a key piece of equipment in titanium pigment production. The numerical procedure was validated by a 3-dimensional gas flow in the annular channel. Applying the validated model, the flow characteristics of TiCl4 in the oxidation reactor with a tangential inlet were simulated and characterized. The flow distribution with five rectifying rings of different structure was simulated and analyzed. The results showed that the rectifying ring improved the distribution uniformity of the pressure and outlet velocity. Compared to the original case without a rectifying ring, the non-uniformity of the pressure and outlet velocity could be reduced by up to 91% and 69% respectively. The rectifying ring #5, which can be installed and adjusted easily, is more effective in realizing even distribution. In addition, installation of the rectifying ring effectively reduced the circulating flow in an annular channel as well as the total energy loss.

Modeling for multi-pass parallel flow condenser with the effect of refrigerant mal-distribution

Performance of multi-pass parallel flow condenser (MPFC) is unavoidably influenced by the refrigerant-side flow mal-distribution (MD) caused by the pressure drop in headers. Thus, a numerical MD model is proposed to predict flow distribution and performance parameters of MPFC with vertical headers and horizontal tubes. The advantage of MD model over UD model (uniform distribution model, refrigerant is assumed to be distributed into each tube evenly by ignoring the effect of header pressure drop) has been indicated by achieving better agreement with experimental data measured from variably-sized condensers A–D and data derived from a published literature. The effects of condenser aspect ratio, pass arrangement (pass number and tube number of each pass) and refrigerant mass flow rate on flow distribution, heat transfer and refrigerant-side pressure drop are investigated. The prediction results indicate that heat capacity varies much less than flow distribution and pressure drop with the change of aspect ratio or pass arrangement. Moreover, for a fixed geometry, a moderate flow rate can be searched by the MD model to obtain well flow distribution, high capacity and efficiency.

The Computed Scripture: Exponentially Based Fourier Regulated Construct of Quran and its Fundamentally Important Consequences

This is a fundamental article reporting newly observed mathematical-computational manifestations in Quran. The Principle Variations (PVs) for the purpose of textual analysis will be defined and a Normal Book model based on the stochastic nature of human writing will be developed. It will be shown that chapter word frequencies in Quran fit into an exponential model, in sharp contrast to the uniform distribution model commonly observed for other books. In particular, a phenomenal cross diagonal characteristic of the PVs in Quran will be shown to completely distinguish its exponential structure from observed structures of the world literature. Graphical and Parametric effects of the exponential construct of Quran will be shown through logarithmic plots and Fourier analysis of its PVs. The couplings observed from its variations in addition to an independent analysis of the prime numbers point to π and e, as pillars of the mathematical construct of Quran. Computed parameters of a Stepwise Fourier analysis of the PVs in Quran, reveals a finely regulated Nineteen Based Fourier Structure (NBFS) highly sensitive to the textual manipulations. These observations seem sufficient to qualify Quran as a case of (Multifaceted) Mathematically Fully Constrained Writing (MFCW), a concept defined for the first time in this article. As its prime consequence, a MFCW Quran points to the nonhuman origin of the Arabic language. Interesting observations are also made through Fourier analyses of particular names which can be indicative of an astonishing futuristic vision of Quran. The importance of such mathematical investigations particularly from the MFCW point of view will be emphasized and some relevant future studies will also be outlined.

Smoothed heights of tries and patricia tries

Tries and patricia tries are two popular data structures for storing strings. Let Hn denote the height of the trie (the patricia trie, respectively) on a set of n strings. Under the uniform distribution model on the strings, it is well known that Hn/log⁡n→2 for tries and Hn/log⁡n→1 for patricia tries, when n approaches infinity. Nevertheless, in the worst case, the height of a trie can be unbounded and the height of a patricia trie is in Θ(n). To better understand the practical performance of both tries and patricia tries, we investigate these two classical data structures in a smoothed analysis model. Given a set S={s1,s2,…,sn} of n binary strings, we perturb the set by adding an i.i.d. Bernoulli random noise to each bit of every string. We show that the resulting smoothed heights of the trie and the patricia trie are both in Θ(log⁡n).

Research and Calculation of Additional Stress due to Skin Friction of Y-Section Pile Considering Abnormality Effect

The skin friction of Y-section pile is non-uniform distributed along its inverted arch arc, the calculation of additional stress for the uniform distribution can not take the resulting deviation of actual distribution into account. Combine the function expression of non-uniform distribution model and mindlin formula to establish the calculation method of additional stress coefficient by numerical integration and analyze the influences of the parameters LRθsδ, then compare the conclusion with the uniform distribution solution and Geddes solution. Additional stress factor of non-uniform distribution model is larger than that based on uniform distribution model,the additional stress decreases with the increase of R, s, δ and increases with the increase of θ and L, and the Mechanisms of the changes coursed by these parameter are also analyzed. Some significant conclusions are obtained.

An experimentally based thermo-kinetic phase transformation model for multi-pass laser heat treatment by using high power direct diode laser

Laser-based phase transformation hardening (LPTH), based on rapid heating and cooling cycles produces hard and wear-resistant layers only at the selective region of the components. However, the bulk mass of the material's core property is retained. The advantages of high power direct diode laser in comparison with other high power lasers (CO2 and Nd:YAG) have put this type of laser as a main heat source for localized heat treatment. However, a tempered zone is formed in overlapping regions of a large heat-treated area during multi-pass laser heat treatment (MPLHT) that affects the uniformity of heat-treated depth of material. This study is focused on the development of a uniform hardness distribution model to minimize the tem- pering effect during the MPLHT process. A tool steel AISI S7 is heat treated by using different levels of laser power (1,400-1,800 W) and scanning speeds (15-25 mm/s). An experimentally based finite element (FE) thermal model is developed to predict the cross-sectional as well as surface temperature history of the MPLHT process. The temperature-dependent material properties and phase change kinetics are taken into account in the model. The laser beam is considered as a moving rectangular-shaped heat source (12 mm×1 mm) with a uniform distribution (top-hat) of laser power. The temperature history acquired from the FE thermal model is coupled with thermo-kinetic (TK) equations to determine the corresponding phase trans- formations and hardness. The tempering effect of MPLHT is studied for different sizes of overlap (1 mm- 3m m) and lengths of scan (10 mm-35 mm). The TK model results are verified with experimental ones to optimize the process- ing parameters. The optimized processing parameters, in- cluding laser power, scanning speed, size of overlap, and the length of scan are used to achieve a uniform hardness distribution and an even depth of heat treatment in the MPLHT area.

Evaluation of Imbalance in Stratified Blocked Randomization

If in a clinical trial prognostic factors are known in advance, it is often recommended that randomization of patients should be stratified. The best-known method is permuted-block randomization within strata. But it suffers from the disadvantage that imbalance still occurs in the trial as a whole if there are a large number of strata, or/and the block sizes are too large for the number of patients. The results of Hallstrom and Davis are appropriate for evaluating the risk of such a troubled situation by using two special cases of their general variance formula. But it is merely generally argued for whichever practical situations these special cases are valid. Consequently, additional investigations are required to reveal the conditions for correct application. We investigated the range of validity of special cases by performing computer simulations, varying a number of trial characteristics, and discuss the application of results for practical situations. The validity of special cases is not given in each situation. Depending on block size, a binomial distribution model is valid for a permitted average maximum number of patients per stratum between 36% and 57% of considered block sizes, whereas the uniform distribution model works adequately from at least 70%. In an intermediate range of invalidity, implementation of a simulation study is necessary to compute the probability distribution of differences. Our results are important if choosing the stratified permuted-block randomization to estimate the risk for an intolerable overall imbalance when planning a trial.

Using non-uniform read distribution models to improve isoform expression inference in RNA-Seq

RNA-Seq technology based on next-generation sequencing provides the unprecedented ability of studying transcriptomes at high resolution and accuracy, and the potential of measuring expression of multiple isoforms from the same gene at high precision. Solved by maximum likelihood estimation, isoform expression can be inferred in RNA-Seq using statistical models based on the assumption that sequenced reads are distributed uniformly along transcripts. Modification of the model is needed when considering situations where RNA-Seq data do not follow uniform distribution. We proposed two curves, the global bias curve (GBC) and the local bias curves (LBCs), to describe the non-uniformity of read distributions for all genes in a transcriptome and for each gene, respectively. Incorporating the bias curves into the uniform read distribution (URD) model, we introduced non-URD (N-URD) models to infer isoform expression levels. On a series of systematic simulation studies, the proposed models outperform the original model in recovering major isoforms and the expression ratio of alternative isoforms. We also applied the new model to real RNA-Seq datasets and found that its inferences on expression ratios of alternative isoforms are more reasonable. The experiments indicate that incorporating N-URD information can improve the accuracy in modeling and inferring isoform expression in RNA-Seq.

Optimizing load transfer in multiwall nanotubes through interwall coupling: Theory and simulation

An analytical model is developed to determine the length scales over which load is transferred from outer to inner walls of multiwall carbon nanotubes (MWCNTs) as a function of the amount of bonding between walls. The model predicts that the characteristic length for load transfer scales as ℓ∼tE/μ¯, where t is the CNT wall spacing, E is the effective wall Young’s modulus, and μ¯ is the average interwall shear modulus due to interwall coupling. Molecular dynamics simulations for MWCNTs with up to six walls, and with interwall coupling achieved by interwall sp3 bonding at various densities, provide data against which the model is tested. For interwall bonding having a uniform axial distribution, the analytic and simulation models agree well, showing that continuum mechanics concepts apply down to the atomic scale in this problem. The simulation models show, however, that load transfer is sensitive to natural statistical fluctuations in the spatial distribution of the interwall bonding between pairs of walls, and such fluctuations generally increase the net load transfer length needed to fully load an MWCNT. Optimal load transfer is achieved when bonding is uniformly distributed axially, and all interwall regions have the same shear stiffness, implying a linear decrease in the number of interwall bonds with distance from the outer wall. Optimal load transfer into an n-wall MWCNT is shown to occur over a length of ∼1.5nℓ. The model can be used to design MWCNTs for structural materials, and to interpret load transfer characteristics deduced from experiments on individual MWCNTs.

Effect of Voxel Size and Computation Method on Tc-99m MAA SPECT/CT-Based Dose Estimation for Y-90 Microsphere Therapy

The use of selective internal radiation therapy for treatment of hepatocellular carcinoma and liver metastases using Y-90 labeled microspheres has become an effective and widely used treatment regimen. However, dosimetric evaluations of this treatment are still primitive as uniform distribution models based only on injected activity are often used. This investigation attempts to quantify the effectiveness of several sophisticated patient-specific techniques which utilize the source distribution of Tc-99m MAA simulation studies to perform voxelized dosimetric computations. Among these techniques are complete Monte-Carlo radiation transport computation in patient-specific CT-based voxel phantoms, local energy deposition in patient specific phantoms and kernel transport techniques in water. Each technique was evaluated using three different phantom voxel dimensions and SPECT reconstruction matrix sizes. Dose evaluation results using all methods were compared to the exact solution, obtained using fully 3-D Monte-Carlo simulations with source distribution based not on SPECT data, but on the injected activity and exact boundaries of the anthropomorphic phantom used in the study. The results of this study show that at large voxel sizes and using SPECT reconstructions with a small matrix size (64 x 64), Monte-Carlo and local deposition methods are nearly equivalent. However, using a large SPECT reconstruction matrix (256 x 256) the local deposition method is significantly more accurate than full 3-D Monte-Carlo transport, and with a negligible computational burden.

Predicting alfalfa hay production as related to water distribution functions

AbstractThe present study was carried out to evaluate two crop water production models for estimating the effects of irrigation uniformity on alfalfa hay yields. The models included the ratio of actual to maximum hay yield, two parameters of the sprinkler water uniformity, and the ratio of gross to required irrigation. Measured data from three experimental plots of a farm located in Varamin, Iran, were used for the evaluation of the proposed models. Comparisons showed that the results from both models were in good agreement with experimental results. However, the results obtained from the normal water distribution model were more accurate than those from the uniform water distribution model. The higher predictive accuracy of the normal distribution model may be due to the fact that it follows a normal pattern in terms of irrigation distribution and crop yield. The accuracy of models in estimating alfalfa hay yield improved with an increasing uniformity coefficient. The results indicate that the optimum gross to required irrigation depth ratio decreases with increasing sprinkler water uniformity value. The findings demonstrate the importance of economic constraints in determining the optimum irrigation amount. It was further found that the optimum irrigation depth increased with increasing value of the product to irrigation cost ratio. The results illustrate that normal and uniform models overestimate and underestimate the values of hay yield compared to measured values, respectively. The average difference in the yield estimation compared to measured data was 130 kg ha−1 for the uniform distribution model and 87 kg ha−1 for the normal distribution model. The average alfalfa hay yield over growing period was estimated at 24 400 kg ha−1 for the ranges of CUch between 80 and 90% in the study region. Copyright © 2008 John Wiley & Sons, Ltd.

General Ripple Mobility Model: A Novel Mobility Model of Uniform Spatial Distribution and Diverse Average Speed

Simulations are often deployed to evaluate proposed mechanisms or algorithms in Mobile Ad Hoc Networks (MANET). In MANET, the impacts of some simulation parameters are noticeable, such as transmission range, data rate etc. However, the effect of mobility model is not clear until recently. Random Waypoint (RWP) is one of the most applied nodal mobility models in many simulations due to its clear procedures and easy employments. However, it exhibits the two major problems: decaying average speed and border effect. Both problems will overestimate the performance of the employed protocols and applications. Although many recently proposed mobility models are able to reduce or eliminate the above-mentioned problems, the concept of Diverse Average Speed (DAS) has not been introduced. DAS aims to provide different average speeds within the same speed range. In most mobility models, the average speed is decided when the minimum and maximum speeds are set. In this paper, we propose a novel mobility model, named General Ripple Mobility Model (GRMM). GRMM targets to provide a uniform nodal spatial distribution and DAS without decaying average speed. The simulations and analytic results have demonstrated the merits of the outstanding properties of the GRMM model.

Enzyme–inorganic nanoporous materials: Differential scanning calorimetric studies and protein stability

Direct assessment of the thermodynamic stabilities of enzymes bound to solids is essential to understand the factors that control bound enzyme stability. Here, the first reports of the thermodynamic stabilities of enzymes/proteins which are bound to an inorganic solid [α-Zr(HPO 4) 2 · H 2O, abbreviated as α-ZrP] are described. The thermal denaturation of hen egg white lysozyme (Lys), met-myoglobin (Mb) and met-hemoglobin (Hb) bound to α-ZrP occurs over a wide range of temperatures (50–100 °C). This is in contrast to the behavior of the free enzyme/proteins in the solution, which indicated sharp transitions at their respective denaturation temperatures. Denaturation of the bound protein depended on the scan rate and the denaturation process was kinetically controlled. At rapid scan rates (2 °C/min), for example, the thermal profiles of the intercalated proteins became sharper while the free proteins indicated little or no changes. Careful analysis of the calorimetric data provided a clear distinction between the moving-boundary model and the uniform distribution model for protein binding. Calorimetric data also revealed that a distribution of thermodynamic states or kinetically-slow forming states are important in the denaturation. While the thermal denaturation of Mb bound to α-ZrP indicated a significant extent of reversibility, Lys and Hb did not. The solid stabilized a fraction of the intercalated protein, and efforts will be focused to maximize this portion. Improved thermal stabilities are important for biosensor or biocatalysis applications of enzyme–inorganic materials.

Isothermal adsorption kinetics on heterogeneous surfaces

Adsorption kinetics on energetically heterogeneous surfaces under isothermal conditions is analyzed using the uniform energy distribution model. Considering the quasi-equilibrium of surface diffusion between the adsorption sites with different energy, the kinetic equations d Θ / d t = ( k a p − A d K diff ) ( 1 − Θ ) for first-order adsorption and d Θ / d t = k a p ( 1 − Θ ) 2 − A d K diff Θ ( 1 − Θ ) for dissociative adsorption are obtained, where K diff is a coefficient describing the surface diffusion equilibrium, which depends on the coverage and the energy distribution. Under isochoric conditions with p decreasing due to adsorption, surface diffusion accelerates the rate towards equilibrium significantly, as observed in static calorimetric adsorption experiments. An approximate solution in Lagergren form is derived for this condition.