Range Of Different Values Research Articles

Experimental investigation of pressure losses in a co-rotating cavity with radial inflow employing tubed vortex reducers with varied nozzles

Modern aero-engines require a high cycle temperature for effective performance. Particular attention is paid to the ICAS (internal cooling air system), particularly the air-bleed system, where the cooling air is bled from the compressor platform to cool down the turbine discs but faces an internal losses problem. Turbines are the elemental power supply of aero-engine and always exposed to high temperature. Internal pressure losses will lead to shortage of air from compressor to turbine disk for cooling purpose, thus deteriorating turbine’s performance and finally limiting their lifespan.To simulate the flow in the air-bleed system in an aero-engine, a co-rotating cylindrical cavity with two steel discs is used as a simplified model. In the present study, we found that oblong nozzles at the shroud improved flow conditions and are 30–50% better than circular ones at reducing pressure losses. Furthermore, we discuss the combined effect of vortex reducers and nozzles under a range of different values of λT (which decided by inertial factor of internal flow and rotational factor of disks), and found them to have a positive effect only when λT is in a specific range. Compared with the whole vortex reducer configuration (long tubes ×15), particular attention is focused on the combined vortex reducer configuration with long-short matched tubes, (long tubes ×10 and short tubes ×5 arranged interlacely in turbine cavity) which is designed to reduce weight and vibration but still has high potential capability to reduce pressure losses. To analyse the experimental data, Ro is adopted to describe the pressure losses instead of the conventional use of λT. This is suitable particularly in the cavity with tubes. Test rig results concerning the pressure drop for different configurations can be referenced by aero-engine designers for convenient and optimized industrial manufacture.

Effects of Turbulent Reynolds Number on Turbulent Scalar Flux Modeling in Premixed Flames Using Reynolds-Averaged Navier–Stokes Simulations

The influence of turbulent Reynolds number (Re t ) on the statistical behavior and modeling of turbulent scalar flux (TSF) has been analyzed using a direct numerical simulation database of freely propagating turbulent premixed flames. A range of different values of Re t is considered in which the Damköhler and Karlovitz numbers are modified independent of each other to bring about the variation of Re t . It has been found that the qualitative behavior of the various terms of the TSF transport equation does not change by the variation of Re t , but their relative contributions to the transport of TSF are affected to some extent. The effects of Re t on the modeling of the TSF using both algebraic and transport equation-based closures are addressed in detail. It is demonstrated that model parameters for an existing algebraic model, and the models for turbulent transport, pressure gradient and the reaction rate terms in the TSF transport equation, all exhibit Re t dependence for small values of Re t but all assume asymptotic values for Re t ≥ 50. By contrast, the model parameters for the combined molecular diffusion term are found to be insensitive to the variation of turbulent Re t . Existing models for algebraic and transport equation-based closures of TSF have been modified to account for the observed Re t dependence.

Assessment of sub-grid scalar flux modelling in premixed flames for Large Eddy Simulations: A-priori Direct Numerical Simulation analysis

The performances of different models for sub-grid scalar flux for premixed turbulent combustion in the context of Large Eddy Simulations (LES) have been assessed based on a Direct Numerical Simulation (DNS) database of freely propagating turbulent premixed flames with a range of different values of Ret where Damköhler and Karlovitz numbers are altered independently of each other to bring about the variation of Ret, whereas the heat release parameter τ is kept unaltered. It has been found that the sub-grid scalar flux exhibits local counter-gradient transport for all cases considered here. However, the extent of counter-gradient transport decreases with decreasing values of filter width Δ and for increasing values of the ratio of the root-mean-square turbulent velocity fluctuation to the unstrained laminar burning velocity u′/SL. The performance of several algebraic models has been assessed with respect to explicitly filtered DNS data. The standard gradient hypothesis based model does not adequately capture both the qualitative and quantitative behaviours of sub-grid scalar flux for all cases for all filter widths. The models which account for local flame normal acceleration perform better than the standard gradient hypothesis model. In general the performance of the models, which account for the alignment of local resolved velocity and scalar gradients, remains relatively better than the performance of the other existing models. Detailed physical explanations have been provided for the observed model performances.

Scalar Dissipation Rate Transport and Its Modeling for Large Eddy Simulations of Turbulent Premixed Combustion

Statistical behavior of Favre-filtered scalar dissipation rate (SDR) transport has been analyzed using direct numerical simulations (DNS) data of freely propagating statistically planar turbulent premixed flames. The DNS data has been explicitly filtered using a Gaussian filter to obtain the unclosed terms of the Favre-filtered SDR transport equation, arising from turbulent transport (), density variation due to heat release (), strain rate contribution due to the alignment of scalar and velocity gradients (), correlation between the gradients of reaction rate and reaction progress variable (), molecular dissipation of SDR (), and diffusivity gradients . It has been found that , and are the leading order contributors to the SDR transport and the magnitude of remains smaller than the magnitudes of , and irrespective of the filter width. Models are proposed for these terms in the context of large eddy simulations (LES) and their performances have been assessed with respect to their corresponding values obtained from explicitly filtered DNS data. These newly proposed models are found to satisfactorily predict both the qualitative and quantitative behaviors of these unclosed terms for a range of different values of filter widths , heat release parameter , and turbulent Reynolds number .

Modeling of Entropy Generation in Turbulent Premixed Flames for Reynolds Averaged Navier–Stokes Simulations: A Direct Numerical Simulation Analysis

The modeling of the mean entropy generation rate S·"' gen¯ due to combined actions of viscous dissipation, irreversible chemical reaction, thermal conduction and mass diffusion (i.e., T¯1,T¯2,T¯3, and T¯4) in the context of Reynolds averaged Navier–Stokes (RANS) simulations has been analyzed in detail based on a direct numerical simulation (DNS) database with a range of different values of heat release parameter τ, global Lewis number Le, and turbulent Reynolds number Ret spanning both the corrugated flamelets (CF) and thin reaction zones (TRZ) regimes of premixed turbulent combustion. It has been found that the entropy generation due to viscous dissipation T¯1 remains negligible in comparison to the other mechanisms of entropy generation (i.e., T¯2,T¯3, and T¯4) within the flame for all cases considered here. A detailed scaling analysis has been used to explain the relative contributions of , and T¯4 on the overall volumetric entropy generation rate S·"' gen¯ in turbulent premixed flames. This scaling analysis is further utilized to propose models for T¯1,T¯2,T¯3, and T¯4 in the context of RANS simulations. It has been demonstrated that the new proposed models satisfactorily predict T¯1,T¯2,T¯3, and T¯4 for all cases considered here. The accuracies of the models for T¯1,T¯2,T¯3, and T¯4 have been demonstrated to be closely linked to the modeling of dissipation rate of turbulent kinetic energy and scalar dissipation rates (SDRs) in turbulent premixed flames.

Algebraic Closure of Scalar Dissipation Rate for Large Eddy Simulations of Turbulent Premixed Combustion

An a-priori analysis of the filtered reaction rate closure based on Favre-filtered scalar dissipation rate (SDR) for large eddy simulations (LES) of turbulent premixed combustion has been conducted using a direct numerical simulation (DNS) database of freely propagating statistically planar flames for a range of different values of heat release parameter τ, global Lewis number Le, and turbulent Reynolds number Ret. It has been found that an existing SDR based reaction rate closure for Reynolds averaged Navier–Stokes (RANS) simulations is also valid for LES, when the filter width is larger than the flame thickness. This RANS-based reaction rate closure has been extended here for LES, and a satisfactory performance of this LES closure is observed for the values of filter widths, τ, Le, and Ret investigated here. A-priori DNS assessment of the SDR closures based on passive scalar mixing model and a power-law has been conducted. Moreover, an existing algebraic model of Favre-averaged SDR for RANS simulations has been extended here for LES. The performances of the algebraic closures of have been assessed with respect to Favre-filtered SDR extracted from the DNS data. It has been found that the newly proposed model for , which was extended here for LES from an existing RANS-based closure, predicts both local and volume-averaged behaviors of SDR satisfactorily for a range of for flames with different values of τ, Le, and Ret. The sensitivity of sub-grid turbulent velocity fluctuation modeling on the newly developed algebraic SDR closure has also been analyzed and it has been observed that the modeling does not significantly affect the performance of the algebraic SDR model proposed in this study.

On column density thresholds and the star formation rate

We present the results of a numerical study designed to address the question of whether there is a column density threshold for star formation within molecular clouds. We have simulated a large number of different clouds, with volume and column densities spanning a wide range of different values, using a state-of-the-art model for the coupled chemical, thermal and dynamical evolution of the gas. We show that star formation is only possible in regions where the mean (area-averaged) column density exceeds 1021 cm−2. Within the clouds, we also show that there is a good correlation between the mass of gas above a K-band extinction AK = 0.8 and the star formation rate (SFR), in agreement with recent observational work. Previously, this relationship has been explained in terms of a correlation between the SFR and the mass in dense gas. However, we find that this correlation is weaker and more time dependent than that between the SFR and the column density. In support of previous studies, we argue that dust shielding is the key process: the true correlation is one between the SFR and the mass in cold, well-shielded gas, and the latter correlates better with the column density than the volume density.

Novel Recognition Method of Blast Furnace Dust Composition by Multifeature Analysis Based on Comprehensive Image-Processing Techniques

The traditional artificial recognition methods for the blast furnace dust composition have several disadvantages, including a great deal of information to dispose, complex operation, and low working efficiency. In this article, a multifeature analysis method based on comprehensive image-processing techniques was proposed to automatically recognize the blast furnace dust composition. First, the artificial recognition and feature analysis, which included image preprocessing, Harris corner feature, Canny edge feature, and Ruffle feature analysis, was designed to build the template image, so that any unknown dust digital image could be tested. Second, the composition of coke, microvariation pulverized coal, vitric, ash, and iron from dust would be distinguished according to their different range of values based on the multifeature analysis. The method is valid for recognizing the blast furnace dust composition automatically, and it is fast and has a high recognition accuracy.

Modelling of the Curvature Term in the Flame Surface Density Transport Equation: A Direct Numerical Simulations Based Analysis

A simple chemistry based three-dimensional Direct Numerical Simulations (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different values of Karlovitz number Ka, turbulent Reynolds number Re t, heat release parameter τ and global Lewis number Le has been used for the modelling of the curvature term of the generalised Flame Surface Density (FSD) transport equation in the context of Reynolds Averaged Navier Stokes (RANS) simulations. The curvature term has been split into the contributions arising due to the reaction and normal diffusion components of displacement speed (i.e. T1) and the term arising due to the tangential diffusion component of displacement speed (i.e. T2). Subsequently, the sub-terms (i.e. T1 and T2) of the curvature contribution to the FSD transport have been split into the closed (i.e. T1 r and T2 r) and unclosed (i.e. T1 ur and T2 ur) components. It has been found that T2 remains deterministically negative throughout the flame brush. However, the qualitative behaviour of T1 changes significantly depending upon the values of Ka, Re t and Le. Detailed physical explanations have been provided for the observed behaviours of the components of the curvature term. Moreover, it has been observed that the closed contributions of T1 and T2 (i.e. T1 r and T2 r) remains negligible in comparison to the unclosed contributions (i.e. T1 ur and T2 ur). Suitable model expressions have been identified for T1 ur and T2 ur in the context of RANS simulations, which are shown to perform satisfactorily in all cases considered in the current analysis, accounting for the variations in Ka, Re t, τ and Le.

Modelling of the Tangential Strain Rate Term in the Flame Surface Density Transport Equation in the Context of Reynolds Averaged Navier Stokes Simulations: A Direct Numerical Simulation Analysis

A direct numerical simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different values of Karlovitz number Ka, turbulent Reynolds numberRet, heat release parameterτ, and global Lewis number Le has been used to assess the models of the tangential strain rate term in the generalised flame surface density (FSD) transport equation in the context of Reynolds averaged Navier Stokes (RANS) simulations. The tangential strain rate term has been split into contributions arising due to dilatation rateTDand flame normal strain rate (-TN). Subsequently,TDand (-TN) were split into their resolved (i.e.,TD1and (-TN1)) and unresolved (TD2and (-TN2)) components. Detailed physical explanations have been provided for the observed behaviours of the components of the tangential strain rate term. This analysis gave way to the modelling of the unresolved dilatation rate and flame normal strain rate contributions. Models have been identified forTD2and (-TN2) for RANS simulations, which are shown to perform satisfactorily in all cases considered, accounting for the variations in Ka,Ret,τand Le. The performance of the newly proposed models for the FSD strain rate term have been found to be either comparable to or better than the existing models.

Patient advocacy and DSM-5

The revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM) provides a useful opportunity to revisit debates about the nature of psychiatric classification. An important debate concerns the involvement of mental health consumers in revisions of the classification. One perspective argues that psychiatric classification is a scientific process undertaken by scientific experts and that including consumers in the revision process is merely pandering to political correctness. A contrasting perspective is that psychiatric classification is a process driven by a range of different values and that the involvement of patients and patient advocates would enhance this process. Here we draw on our experiences with input from the public during the deliberations of the Obsessive Compulsive-Spectrum Disorders subworkgroup of DSM-5, to help make the argument that psychiatric classification does require reasoned debate on a range of different facts and values, and that it is appropriate for scientist experts to review their nosological recommendations in the light of rigorous consideration of patient experience and feedback.

Numerical Analysis of SHB Effects in Laterally-Coupled Distributed Feedback (LC-DFB) Lasers

In this paper the stability of Laterally-Coupled Distributed Feedback (LC-DFB) Lasers against the Spatial Hole Burning (SHB) effect is analyzed theoretically. The stability of the laser structure is evaluated using the flatness parameter F. It is shown that the LC-DFB lasers are stable in a wide range of different values ​​of ridge width and amplitude grating. The stability is sustained with increasing injection current. The results show that the flatness parameter is minimal for certain values ​​of the amplitude grating. The numerical calculations have been done by coupled wave and carrier rate equations on the basis of the transfer matrix method (TMM)

Regional variations and correlations of Gutenberg–Richter parameters and fractal dimension for the different seismogenic zones in Western Anatolia

We investigated the regional variations of Gutenberg–Richter (G–R) parameters (a and b) and fractal (correlation) dimension (DC) and relations among these parameters for the different regions in Western Anatolia (WA). The whole examined area (26–33°E, 33–40.5°N) is divided into 15 different seismogenic regions based on their tectonic and seismotectonic regimes. We used database including 69,182 earthquakes for the instrumental period from 1900 to 2011. We calculated b value, which is the slope of the frequency–magnitude Gutenberg–Richter relationship, from maximum likelihood method (ML) and DC value, which is the slope of log10C(r) versus log10r, from correlation integral using the least-squares (LS) method. Computed values for 15 different seismogenic regions are mapped using different color scale for different range of values of b and DC. Regional distributions of these parameters reveal information about regional variation of stress level and geological complexity. We concluded Aegean arc and Aegean islands, Aliağa fault and Büyük Menderes Graben the most vulnerable regions for occurrence of the large earthquakes in WA considering the computed lowest b-values and the highest DC-values in these regions. Since DC/b values are the highest in these regions, this ratio may be used as an indicator of earthquake hazard levels of different seismogenic zones in a studied region. An effort is made to find relationships between the G–R parameters and fractal dimension. We observed negative correlation between DC and b values and positive correlation between DC and a/b values for different regions of WA. We observed that the relationship between a/b and DC can be used for seismicity, earthquake risk and hazard studies because of the computed high correlation coefficient and fewer scattering of these parameters.

Modelling of the Curvature Term of the Flame Surface Density Transport Equation for Large Eddy Simulations

A simplified chemistry based three-dimensional Direct Numerical Simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different values of turbulent Reynolds number has been used for the a priori modelling of the curvature term of the generalised Flame Surface Density (FSD) transport equation in the context of Large Eddy Simulation (LES). The curvature term has been split into the contributions arising due to the reaction and normal diffusion components of displacement speed and the term originating from the tangential diffusion component of displacement speed. Subsequently, these contributions of the curvature term have been split into the resolved and subgrid contributions. New models have been proposed for the subgrid curvature terms arising from the combined reaction and normal diffusion components and the tangential diffusion component of displacement speed. The performances of the new model and the existing models for the subgrid curvature term have been compared with the corresponding quantity extracted from the explicitly filtered DNS data. The new model for the subgrid curvature term is shown to perform satisfactorily in all cases considered in the current study, accounting for wide variations in LES filter size.

Combinatorial batch codes: A lower bound and optimal constructions

Batch codes, introduced by Ishai et al. in [11], are methods for solving the following data storage problem: $n$ data items are to be stored in $m$ servers in such a way that any $k$ of the $n$ items can be retrieved by reading at most $t$ items from each server, and that the total number of items stored in $m$ servers is $N$. A combinatorial batch code (CBC) is a batch code where each data item is stored without change, i.e., each stored data item is a copy of one of the $n$ data items.    One of the basic yet challenging problems is to find optimal CBCs, i.e., CBCs for which total storage ($N$) is minimal for given values of $n$, $m$, $k$, and $t$. In [13], Paterson et al. exclusively studied CBCs and gave constructions of some optimal CBCs.    In this article, we give a lower bound on the total storage ($N$) for CBCs. We give explicit construction of optimal CBCs for a range of values of $n$. For a different range of values of $n$, we give explicit construction of optimal and almost optimal CBCs. Our results partly settle an open problem of [13].

EFFECT OF WAVES ON THE BEHAVIOR OF OFFSHORE PILES

This paper studies the effect of wave loads on the submerged piles. The submerged piles are used widely in harbors, and offshore structures.The bottom part of the pile is buried in soil under the mud line while the upper part (free height of the pile above the mud line) is subjected to waves. The internal forces induced in the pile depend on many factors such as, pile diameter, soil type, water depth, wave period and height. A numerical model for a submerged pile was developed using a commercial Finite Element program to study the internal forces induced on submerged piles which subjected to wave action. The factors affecting the internal forces induced in the pile, due to the wave load, were studied. In the present research, range of different values for each factor was taken into consideration to establish the effect of each factor on the internal forces induced in the pile. The results were summarized in curves to highlight the effect of each factor.

An Acid-loading Chloride Transport Pathway in the Intraerythrocytic Malaria Parasite, Plasmodium falciparum

The intraerythrocytic malaria parasite exerts tight control over its ionic composition. In this study, a combination of fluorescent ion indicators and (36)Cl(-) flux measurements was used to investigate the transport of Cl(-) and the Cl(-)-dependent transport of "H(+)-equivalents" in mature (trophozoite stage) parasites, isolated from their host erythrocytes. Removal of extracellular Cl(-), resulting in an outward [Cl(-)] gradient, gave rise to a cytosolic alkalinization (i.e. a net efflux of H(+)-equivalents). This was reversed on restoration of extracellular Cl(-). The flux of H(+)-equivalents was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and, when measured in ATP-depleted parasites, showed a pronounced dependence on the pH of the parasite cytosol; the flux was low at cytosolic pH values < 7.2 but increased steeply with cytosolic pH at values > 7.2. (36)Cl(-) influx measurements revealed the presence of a Cl(-) uptake mechanism with characteristics similar to those of the Cl(-)-dependent H(+)-equivalent flux. The intracellular concentration of Cl(-) in the parasite was estimated to be approximately 48 mm in situ. The data are consistent with the intraerythrocytic parasite having in its plasma membrane a 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive transporter that, under physiological conditions, imports Cl(-) together with H(+)-equivalents, resulting in an intracellular Cl(-) concentration well above that which would occur if Cl(-) ions were distributed passively in accordance with the parasite's large, inwardly negative membrane potential.

DISPERSION OF OBSERVED POSITION ANGLES OF SUBMILLIMETER POLARIZATION IN MOLECULAR CLOUDS

One can estimate the characteristic magnetic field strength in GMCs by comparing submillimeter polarimetric observations of these sources with simulated polarization maps developed using a range of different values for the assumed field strength. The point of comparison is the degree of order in the distribution of polarization position angles. In a recent paper by H. Li and collaborators, such a comparison was carried out using SPARO observations of two GMCs, and employing simulations by E. Ostriker and collaborators. Here we reexamine this same question, using the same data set and the same simulations, but using an approach that differs in several respects. The most important difference is that we incorporate new, higher angular resolution observations for one of the clouds, obtained using the Hertz polarimeter. We conclude that the agreement between observations and simulations is best when the total magnetic energy (including both uniform and fluctuating field components) is at least as large as the turbulent kinetic energy.

Error in estimates of tissue material properties from shear wave dispersion ultrasound vibrometry

Shear wave velocity measurements are used in elasticity imaging to find the shear elasticity and viscosity of tissue. A technique called shear wave dispersion ultrasound vibrometry (SDUV) has been introduced to use the dispersive nature of shear wave velocity to locally estimate the material properties of tissue. Shear waves are created using a multifrequency ultrasound radiation force, and the propagating shear waves are measured a few millimeters away from the excitation point. The shear wave velocity is measured using a repetitive pulse-echo method and Kalman filtering to find the phase of the harmonic shear wave at 2 different locations. A viscoelastic Voigt model and the shear wave velocity measurements at different frequencies are used to find the shear elasticity (mu(1)) and viscosity (mu(2)) of the tissue. The purpose of this paper is to report the accuracy of the SDUV method over a range of different values of mu(1) and mu(2). A motion detection model of a vibrating scattering medium was used to analyze measurement errors of vibration phase in a scattering medium. To assess the accuracy of the SDUV method, we modeled the effects of phase errors on estimates of shear wave velocity and material properties while varying parameters such as shear stiffness and viscosity, shear wave amplitude, the distance between shear wave measurements (delta r), signal-to-noise ratio (SNR) of the ultrasound pulse-echo method, and the frequency range of the measurements. We performed an experiment in a section of porcine muscle to evaluate variation of the aforementioned parameters on the estimated shear wave velocity and material property measurements and to validate the error prediction model. The model showed that errors in the shear wave velocity and material property estimates were minimized by maximizing shear wave amplitude, pulse-echo SNR, delta r, and the bandwidth used for shear wave measurements. The experimental model showed optimum performance could be obtained for delta r = 3 - 6 mm, SNR =35 dB, with a frequency range of 100 to 600 Hz, and with a shear wave amplitude on the order of a few microns down to 0.5 microm. The model provides a basis to explore different parameters related to implementation of the SDUV method. The experiment confirmed conclusions made by the model, and the results can be used for optimization of SDUV.

Adaptive Data Hiding in Edge Areas of Images With Spatial LSB Domain Systems

This paper proposes a new adaptive least-significant- bit (LSB) steganographic method using pixel-value differencing (PVD) that provides a larger embedding capacity and imperceptible stegoimages. The method exploits the difference value of two consecutive pixels to estimate how many secret bits will be embedded into the two pixels. Pixels located in the edge areas are embedded by a k-bit LSB substitution method with a larger value of k than that of the pixels located in smooth areas. The range of difference values is adaptively divided into lower level, middle level, and higher level. For any pair of consecutive pixels, both pixels are embedded by the k-bit LSB substitution method. However, the value k is adaptive and is decided by the level which the difference value belongs to. In order to remain at the same level where the difference value of two consecutive pixels belongs, before and after embedding, a delicate readjusting phase is used. When compared to the past study of Wu et al.'s PVD and LSB replacement method, our experimental results show that our proposed approach provides both larger embedding capacity and higher image quality.