Ar Values Research Articles

Surface of Maximums of AR(2) Process Spectral Densities and its Application in Time Series Statistics

Background. In the problem on probabilities of large deviations of discrete time and sub-Gaussian AR(2) noise non­li­near regression model parameter least squares estimate a constant is determined that controls the rate of exponential convergence to zero of indicated probabilities. Objective. The aim of the paper is to find the surface of maximums of AR(2) process spectral densities in the domain of its stationarity in explicit form. Methods. The results were obtained on the use of methodology developed in the works by A. Sieders, K. Dzhaparidze (1987), A.V. Ivanov (1997, 2016) and standard Calculus methods. Results. A complex formula that describes a continuous surface of maximums of AR(2) process spectral densities assig­ned on the stationary triangle of the time series of this type is obtained. Conclusions. The obtained formula of surface of maximums of noise spectral densities gives an opportunity to realize for which values of AR(2) process characteristic polynomial coefficients it is possible to look for greater rate of convergence to zero of the probabilities of large deviations of the considered estimates.

Türkiye ve Rusya Arasındaki "Uçak Krizinin" Borsa İstanbul Gıda, İçecek ve Turizm Endeksleri Üzerine Etkisi

On November 24, 2015 at the Syrian border, boundary violations of Russian combat aircraft was shot down by Turkish warplanes that has caused serious problems in terms of bilateral relations. After the incident, Russia unilaterally froze all its military and economic cooperation and has decided to apply economic sanctions to Turkey. Many of the sectors, especially tourism and food sector, were directly affected by these sanctions decisions. In this context, the purpose of the study is to reveal how the companies of BIST Food, Beverage and BIST Tourism Indexes react to this circumstance by employing the event study methodology. According to the findings, it is observed that the companies that are listed in the BIST Food, Beverage Index generally are affected negatively. Also, it has been determined that companies in the BIST Tourism Index exhibit positive AR values in the post-event period. On the other hand, it was noted that the majority of CAAR values were negative. Moreover, although there are no obvious predictable trends, the presence of statistically significant results in the event window on some days has shown that the market is not efficient in a semi-strong form.

Water-Channel Estimation of Eulerian and Lagrangian Time Scales of the Turbulence in Idealized Two-Dimensional Urban Canopies

Lagrangian and Eulerian statistics are obtained from a water-channel experiment of an idealized two-dimensional urban canopy flow in neutral conditions. The objective is to quantify the Eulerian $$(T^{\mathrm{E}})$$ and Lagrangian $$(T^{\mathrm{L}})$$ time scales of the turbulence above the canopy layer as well as to investigate their dependence on the aspect ratio of the canopy, AR, as the latter is the ratio of the width (W) to the height (H) of the canyon. Experiments are also conducted for the case of flat terrain, which can be thought of as equivalent to a classical one-directional shear flow. The values found for the Eulerian time scales on flat terrain are in agreement with previous numerical results found in the literature. It is found that both the streamwise and vertical components of the Lagrangian time scale, $$T_\mathrm{u}^\mathrm{L} $$ and $$T_\mathrm{w}^\mathrm{L} $$ , follow Raupach’s linear law within the constant-flux layer. The same holds true for $$T_\mathrm{w}^\mathrm{L} $$ in both the canopies analyzed $$(AR= 1$$ and $$AR= 2$$ ) and also for $$T_\mathrm{u}^\mathrm{L} $$ when $$AR = 1$$ . In contrast, for $$AR = 2$$ , $$T_\mathrm{u}^\mathrm{L} $$ follows Raupach’s law only above $$z=2H$$ . Below that level, $$T_\mathrm{u}^\mathrm{L} $$ is nearly constant with height, showing at $$z=H$$ a value approximately one order of magnitude greater than that found for $$AR = 1$$ . It is shown that the assumption usually adopted for flat terrain, that $$\beta =T^{\mathrm{L}}/T^{\mathrm{E}}$$ is proportional to the inverse of the turbulence intensity, also holds true even for the canopy flow in the constant-flux layer. In particular, $$\gamma /i_\mathrm{u} $$ fits well $$\beta _\mathrm{u} =T_\mathrm{u}^\mathrm{L} /T_\mathrm{u}^\mathrm{E} $$ in both the configurations by choosing $$\gamma $$ to be 0.35 (here, $$i_\mathrm{u} =\sigma _\mathrm{u} / \bar{u} $$ , where $$\bar{u} $$ and $$\sigma _\mathrm{u} $$ are the mean and the root-mean-square of the streamwise velocity component, respectively). On the other hand, $$\beta _\mathrm{w} =T_\mathrm{w}^\mathrm{L} /T_\mathrm{w}^\mathrm{E} $$ follows approximately $$\gamma /i_\mathrm{w} =0.65/\left( {\sigma _\mathrm{w} /\bar{u} } \right) $$ for $$z > 2H$$ , irrespective of the AR value. The second main objective is to estimate other parameters of interest in dispersion studies, such as the eddy diffusivity of momentum $$(K_\mathrm{{T}})$$ and the Kolmogorov constant $$(C_0)$$ . It is found that $$C_0$$ depends appreciably on the velocity component both for the flat terrain and canopy flow, even though for the latter case it is insensitive to AR values. In all the three experimental configurations analyzed here, $$K_\mathrm{{T}}$$ shows an overall linear growth with height in agreement with the linear trend predicted by Prandtl’s theory.

Dilatation of the High-Rise Building by Inserted Field

The dilatation of the high-rise building by inserted field is the main topic of this paper. This building contains of two “towers” with different heights (8-storey and 25-storey), which are linked by inserted field. The description of the building and applied loads are shortly mentioned. The paper is mainly focused on the importance of the dilatation and its types, the modelling of inserted field and its structural solutions. The comparisons of horizontal forces due to the wind load and seismic load are presented at the end. The solution was recalculated for four seismic areas in Slovakia, where different values of basic seismic acceleration ar are. Also, the maximum horizontal deflections calculated for three alternatives of the building (without dilatation, with continuous dilatation 50 mm located between two “towers” passing through the foundation, with dilatation by inserted field between two “towers”) due to static wind load are presented here.

Graphene Oxide/Chitosan/Polyvinyl-Alcohol Composite Sponge as Effective Adsorbent for Dyes.

Water pollution is one of the most pervasive problems afflicting people. Therefore, seeking highly efficient, low-cost methods to decontaminate water is very much in demand. In this paper, chitosan/polyvinyl-alcohol composite sponges are synthesized via foamed cross-linking method while incorporating different amount of graphene oxide, the resultant graphene oxide/chitosan/polyvinyl-alcohol composite sponges (GCS) are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR), indicating the reasonable dispersion of graphene oxide in the matrix. Furthermore, some physical properties (water absorption, water retention, apparent density, porosity) are also determined; water absorption is high up to 873%, apparent density is lower than 0.25 g/cm3, and porosity could reach 78%. The GCSs also manifest high adsorption ability, as effective adsorbent for Acid Red 37 (AR 37) solution. The relationship between adsorption capacity and independent variables (adsorbent mass, initial dye concentration, and contacting time) is obtained. The optimal adsorption capacity value of AR 37 on GCS could reach 421.5 mg/g.

Effects of axis ratio, nanoparticle volume fraction and its size on the momentum and heat transfer phenomena from an elliptic cylinder in water-based CuO nanofluids

In this study, a detailed numerical investigation has been carried on the momentum and heat transfer phenomena from an elliptic cylinder, including the limiting cases of circular cylinder and flat plates, in streaming water based CuO nanofluids over the following ranges of conditions as: Reynolds number, 1 ≤ Re ≤ 40; nanoparticle volume fraction, 0 ≤ ϕ ≤ 0.06 and cylinder axis ratio, 0.1 ≤ AR ≤ 5.0 for two sizes of the nanoparticles, namely, 30nm and 60nm. The local flow field in the vicinity of the cylinder surface is visualized in terms of the streamline profiles, whereas the gross flow and heat transfer characteristics are presented in terms of the drag coefficient and Nusselt number respectively. All else being equal, the separation of the boundary layers is accelerated in 60nm CuO nanofluids as compared to that seen in water, whereas it is decelerated in 30nm CuO nanofluids. The total drag coefficient for an elliptic cylinder is always seen to be higher in nanofluids as compared to that seen in pure water. For 60nm CuO nanofluids, the Nusselt number always increases with the increasing values of ϕ, whereas for 30nm CuO nanofluids, it first increases and then decreases. Finally, simple analytical formulas for the total drag coefficient and average Nusselt number are provided which facilitate the interpolation of the present results for the intermediate values of Re,ϕ and AR.

Frequency tables for the coding-invariant quality assessment of factorial designs

ABSTRACTQuality assessment of factorial designs, particularly mixed-level factorial designs, is a nontrivial task. Existing methods for orthogonal arrays include generalized minimum aberration, a modification thereof that was proposed by Wu and Zhang for mixed two- and four-level arrays, and minimum projection aberration. For supersaturated designs, E(s2) or χ2-based criteria are widely used. Based on recent insights by Grömping and Xu regarding the interpretation of the projected aR values used in minimum projection aberration, this article proposes three new types of frequency tables for assessing the quality of level-balanced factorial designs. These are coding invariant, which is particularly important for designs with qualitative factors. The proposed tables are used in the same way as those used in minimum projection aberration and behave more favorably when used for mixed-level arrays. Furthermore, they are much more manageable than the above-mentioned approach by Wu and Zhang. The article justifies the proposed tables based on their statistical information content, makes recommendations for their use, and compares them with each other and with existing criteria. As a byproduct, it is shown that generalized minimum aberration refines the established expected χ2 criterion for level-balanced supersaturated designs.

Assessment of Lyme disease risk by using the ecological risk index in the parks of Belgrade

Background/Aim. Factors determining the risk of Lyme disease (LD) may be followed in terms of the type of habitat. The evaluation of the risk of Borrelia burgdorferi (B. burgdorferi) transmission in humans on Ixodes ricinus (I. ricinus) tick habitats is done by means of the ecological risk index, which determines the tick habitat, abundance and infection rate. The aim of this paper was to determine the value of ecological risk index (potential and actual risk ? PR and AR) on green areas in 9 p?rks in Belgrade and establish the correlation of this index with tick bites in humans. Methods. Ticks were collected in parks by means of the flag hour method and examined for the presence of LD cause in dark-field microscopic analysis. Point values were assigned to certain parameters and potential and actual risk index evaluated for each habitat. The data on tick bites from the surveyed habitats were obtained from the Protocol of patients bitten by ticks of the Sector for Preventive Medicine, Institute of Epidemiology, Military Medical Academy in Belgrade. Analysis of variance (ANOVA), Tukey test and Pearson ?s coefficient were used in statistical analysis of data. Results. In Belgrade?s park habitats a high PR of B. burgdorferi transmission was determined, while AR for 4 habitats was categorised as PR, and limited for other 5 habitats. Statistically, in terms of AR values the following habitats were significantly different (p < 0.05): H?jd P?rk and T?sm?jd?n; H?jd P?rk and K?lemegd?n; H?jd P?rk and Pionirski P?rk; H?jd P?rk and B?novo Brdo; Topcider and T?sm?jd?n; Topcider and K?lemegd?n; Topcider and Pionirski P?rk; Topcider and B?novo Brdo Park. A statistically significant correlation (p < 0.05) between bites of adults and the number of bites of infected adults with the AR value was established. Conclusion. In parks of Belgrade, there is a limited AR of B. burgdorferi transmission on the average. The AR values vary from limited to the potential, depending on the ecological features of habitat, the number of collected ticks and their infection rate. In view of the correlation of AR with the bites in humans, this index is significant for assessing LD risk.

The Effect of the Degree of Astigmatism on Optical Quality in Children.

Purpose To investigate the effect of the degree of astigmatism on optical quality in children. The important objective evaluation parameters we focus on include the RMS of the high-order aberrations, MTF, and PSF. Methods The children, age ranging from 7 to 10 years old, underwent an optometry examination. Fifty-nine children who met the inclusion criteria were divided into three groups: A (1.0 D ≤ astigmatism < 2.0 D), B (2.0 D ≤ astigmatism < 3.0 D), and C (3.0 D ≤ astigmatism < 4.0 D). The OPD-SCAN-III aberrometer was used to measure PSF, MTF, and other optical parameters. Total higher-order aberrations, total coma aberrations, total spherical aberrations, and total trefoil aberrations corresponding to the RMS value, the AR value of MTF, and the SR value of PSF with a 4 mm pupil diameter were assessed. Results RMS-HO, RMS-T.Coma, RMS-T.Tre, and RMS-T.Sph in the three groups were significantly increased with increasing the degree of astigmatism, while there were no significant differences in RMS-T.Sph between the groups. The AR value and the SR value decreased with increasing degree of astigmatism, and there were significant differences in the AR value and the SR value. Conclusion Astigmatism has a significant influence on the higher-order aberrations, MTF, and PSF in the children. The effect of astigmatism value on the optical quality is mainly reflected in the change in these three parameters.

Genetic diversity and population structure of the Spanish Murciano–Granadina goat breed according to pedigree data

The genetic diversity and population structure of the Spanish Murciano–Granadina goat breed were assessed by pedigree data analysis, which is essential for addressing conservation and improvement breed programs. We analysed 24,444 pedigree data records for the Murciano–Granadina goat breed (797 males and 23,647 females), distributed across 49 herds, for the period from 1992 to 2006. The average generation interval based on the age of the parents at the birth of offspring was 2.77±1.33years. Although the study did not identify a genetic bottleneck (fa/fe=1.00), 50% of the genetic variability was provided by only 366 ancestors, which may contribute to future genetic bottlenecks if the current mating policy is maintained. The number of equivalent generations increased from 1995 to 1997, followed by a decrease until 1999, when returned to growth. This oscillation could have been affected by difficulties in recording the genealogical data for young animals. The average values of F and AR for the entire analysed pedigree were 0.180% and 0.03%, respectively. Only 0.74% of the animals were inbred, but a high average (24.68%) was observed. The average GCI was very low (1.64), indicating a small, unbalanced contribution of the founders in the population. The average inbreeding was lower than the AR value during the studied period for the entire population, which indicates low genetic variation between populations but large intra-herd genetic diversity.

PIV measurements of the flow patterns in a CANDU-6 model

Particle image velocimetry (PIV) measurements of the flow patterns in a pressurized heavy water reactor (PHWR) were made in a 1/4 scaled-down model of the Canadian deuterium uranium (CANDU) reactor. Archimedes’ number (Ar) was introduced to evaluate the dynamic similarities between the isothermal (Ar=0) and heating conditions. Small and large PIV fields of view were used to measure the overall flow field. Flow patterns were analyzed by measuring the spatial velocity distributions and the impingement positions of the inlet jet. The momentum-dominated flow patterns were measured under isothermal conditions (Ar=0). The impingement position bias increased as Ar increased due to buoyancy effects. The overall moderator circulation characteristics were explored for various Ar values up to 0.157.

Comparison Of Cointegration Tests For Near Integrated Time Series Data With Structural Break

Sample size of data, presence of structural break, location and magnitude of potential break, and having with near integrated process might affect the performance of cointegration tests. Engle-Granger (EG) and Johansen Cointegration tests may have erroneous results since they do not take into account possible structural break unlike Gregory – Hansen (GH) cointegration test. In this study, it is argued that the suitable choice of cointegration tests is quite complex, since outcomes of these tests are very sensitive to specifying these properties. The performance of cointegration tests is compared to each other underlying properties. This study presents how standard residual based tests- Engle-Granger and Gregory-Hansen- for cointegration can be implemented if series is near integrated, that is close to a unit root process. For assessing the finite sample performance of these tests, a Monte-Carlo experiment showed that both cointegration tests have relatively better size and power properties depend on break point, break magnitude, sample size of time series and the hypothesized value of AR(1) parameter. To illustrate the findings of the paper, a financial data is analyzed. The practitioners should be careful about the hypothesized value of AR(1) parameter which represents dependency degree of the data. If the autoregressive parameters is very close to one and the break magnitude is high, any test is acceptable for moderate to large sample size. However, one might need very large sample size to have a good power and actual size of the test. Additionally, GH test becomes liberal test unlike EG test as the magnitude of structural break increases.

Inhaled loxapine for the treatment of agitation in borderline personality disorder

Introductioninhaled loxapine has shown efficiency in the treatment of the mild-moderate agitation syndrome of schyzophrenia and mania patients. Its rapid response and calming effect non-sedative allow to hypothesize reasonable efficiency and tolerability in borderline personality disorder diagnosed patients.aimsanalyze the efficiency and tolerability of inhaled loxapine as a pharmacological approach in the treatment of agitation in borderline personality disorder (BPD) clinical diagnosed patients.Materials and methodan application was administered for every agitation episode in BPD patients treated with inhaled loxapine in the emergency room or the psychiatric ward, which included B aRS and CGI-S scales for the evaluation of each episode and its severity, before and after its use. Other secondary measures of efficiency were taken into account, such as requirement of physical restrain.Resultsin the majority of evaluated episodes inhaled loxapine decreased notably initial B aRS and CGI-S values and no serious clinical side effects attributable to this medication were observed.Conclusionin our sample, inhaled loxapine was efficiency and well tolerated pharmacological intervention for agitation in BPD patients.Disclosure of interestThe authors have not supplied their declaration of competing interest.

Surface Texture Analysis in Milling of Mild Steel Using HSS Face and Milling Cutter

Surface finish influenced by the machining parameters on a milling machine. MOTIF-method is used for the evaluation of the primary profile. It is based on the envelope system and is suitable for alternative method to the mean line system. It determines the upper point of the surface profile and important for the functional behavior. The roughness and waviness can be evaluated directly from the surface profile curve. Cutting speed, feed rate and depth of cut effect was analyzed on the surface profile analysis. The experiments were conducted to study the machining parameter effects on milling of mild steel. The specimen was milled under different levels and analyzed R, Rx and Ar values.

Developmental process of the arcuate fasciculus from infancy to adolescence: a diffusion tensor imaging study.

We investigated the radiologic developmental process of the arcuate fasciculus (AF) using subcomponent diffusion tensor imaging (DTI) analysis in typically developing volunteers. DTI data were acquired from 96 consecutive typically developing children, aged 0–14 years. AF subcomponents, including the posterior, anterior, and direct AF tracts were analyzed. Success rates of analysis (AR) and fractional anisotropy (FA) values of each subcomponent tract were measured and compared. AR of all subcomponent tracts, except the posterior, showed a significant increase with aging (P < 0.05). Subcomponent tracts had a specific developmental sequence: First, the posterior AF tract, second, the anterior AF tract, and last, the direct AF tract in identical hemispheres. FA values of all subcomponent tracts, except right direct AF tract, showed correlation with subject's age (P < 0.05). Increased AR and FA values were observed in female subjects in young age (0–2 years) group compared with males (P < 0.05). The direct AF tract showed leftward hemispheric asymmetry and this tendency showed greater consolidation in older age (3–14 years) groups (P < 0.05). These findings demonstrated the radiologic developmental patterns of the AF from infancy to adolescence using subcomponent DTI analysis. The AF showed a specific developmental sequence, sex difference in younger age, and hemispheric asymmetry in older age.

Comparison between Fast Fourier Transform and Autoregressive Model on Analysis of Autonomic Nervous Function after Food Intake in Women

Purpose: Heart rate variability (HRV) is acknowledged as a useful tool to estimate autonomic function. Fast Fourier transform (FFT) and autoregressive model (AR) are used for power spectral analysis of HRV. However, there is little evidence of agreement between FFT and AR in relation to HRV following food intake in females. In the present study, we applied both FFT and AR after food intake during the follicular and luteal phases, and compared raw low-frequency (LF) and high- frequency (HF) powers, and LF/HF ratio obtained with the two power-spectral analytical methods. Methods: All subjects participated in two sessions: follicular phase session and luteal phase session. In each session, R-R intervals were continuously recorded before and after meals, and power spectral analysis of heart rate variability was performed. We analyzed low-frequency power (LF: 0.04 - 0.15 Hz) and high-frequency power (HF: 0.15 - 0.40 Hz) by using FFT and AR. LF and HF power were computed for each 30 sec, 1 min, 2.5 min, and 5 min of the 5-min R-R data before meal intake and at 20, 40, 60 and 80 min after meal intake. The LF/HF ratio was calculated as an index of sympathovagal balance. Results: In the present study, after 30 sec and 1 min of segment analysis, there was little interchangeability between AR and FFT in LF, HF, and LF/HF ratio in both follicular and luteal phases. In 2.5 min or 5 min of segment analysis, there was interchangeability between FFT and AR in LF and HF, but not in the LF/HF ratio in both follicular and luteal phases. Additionally, FFT underestimated HRV compared with AR, and the extent of underestimation increased with increasing AR value. Conclusion: FFT underestimated HRV compared with AR, and FFT correlated poorly with AR when the analysis segment was shortened.

Activity prediction of Schiff base compounds using improved QSAR models of cinnamaldehyde analogues and derivatives

In past work, QSAR (quantitative structure-activity relationship) models of cinnamaldehyde analogues and derivatives (CADs) have been used to predict the activities of new chemicals based on their mass concentrations, but these approaches are not without shortcomings. Therefore, molar concentrations were used instead of mass concentrations to determine antifungal activity. New QSAR models of CADs against Aspergillus niger and Penicillium citrinum were established, and the molecular design of new CADs was performed. The antifungal properties of the designed CADs were tested, and the experimental Log AR values were in agreement with the predicted Log AR values. The results indicate that the improved QSAR models are more reliable and can be effectively used for CADs molecular design and prediction of the activity of CADs. These findings provide new insight into the development and utilization of cinnamaldehyde compounds.

Three‐Dimensionally Controllable Synthesis of Multichannel Silica Nanotubes and Their Application as Dual Drug Carriers

Three-dimensionally controllable multichannel silica nanotubes (MC-SNTs) have been constructed. Quaternary ammonium type (Cn H2n+1 (CH3 )3 N+ ) surfactants were used as structure-directing agents (SDAs) in basic ammonia. A low concentration of block copolymer HO(CH2 CH2 O)20 [CH2 CH(CH3 )O]70 (CH2 CH2 O)20 H (P123) was employed as an additive. The length, diameter, and pore size of MC-SNTs can be finely controlled in the range of 50 nm to 5 μm, 50 nm to 350 nm, and 2 nm to 3 nm by changing the molar ratio of P123 and SDA, the concentration of ammonia, and the length of carbon chain of SDAs, respectively. Observations based on transmission electron microscopy confirmed the role of P123 and ammonia in the self-assembly of micelles of SDA. Compared with the one-pot method reported previously, the aspect ratios (ARs; length/diameter) of obtained MC-SNTs were tunable in a wide range of approximately 1 to 100. The tunable MC-SNTs were used as dual drug-delivery carriers for anticancer drug doxorubicin (Dox) and anti-inflammatory drug ibuprofen (Ibu). Results of release behavior and toxicity to cancer cells of Dox-Ibu-loaded MC-SNTs with different ARs revealed that Dox and Ibu were successfully codelivered and did not interfere with each other. The produced MC-SNTs with larger AR values of showed advantages in the amount of accumulated dual drugs, the duration time of release, and inhibition of the growth of HeLa cells.

Effects of aspect ratio on laminar Rayleigh–Bénard convection of power-law fluids in rectangular enclosures: A numerical investigation

The effects of aspect ratio AR (ratio of enclosure height to length) on Rayleigh–Bénard convection of inelastic non-Newtonian fluids obeying the power-law model of viscosity within rectangular enclosures have been numerically analysed where the horizontal walls are subjected to constant wall temperatures with the bottom wall at higher temperature. Simulations have been undertaken for the range of aspect ratio 0.25⩽AR⩽4, nominal Rayleigh number range 103⩽Ra⩽105 (Ra defined based on the enclosure height) for a single representative value of nominal Prandtl number (Pr=103). It is found that convection weakens with increasing aspect ratio and the heat transfer takes place purely due to thermal conduction for tall enclosures (i.e. AR>2) for all values of Ra and n considered here. Additionally, the flow pattern for AR⩽2 has been found to be dependent not only on Ra and n but also on the choice of initial condition used for the simulation. Although viscous resistance weakens with decreasing power-law exponent for a given set of values of Ra, AR and Pr, the mean Nusselt number Nu‾ does not exhibit a monotonic increase with decreasing n for AR⩽2 because of the change in flow pattern (i.e. number of convection rolls/cells) within the enclosure. Accordingly, it has been found that the flow pattern and the mean Nusselt number Nu‾ are dependent on initial conditions and it is possible to obtain different steady-state solutions for different initial conditions. Furthermore, it is possible to obtain a steady solution for shear-thinning (i.e. n<1) fluids only for some initial conditions, whereas other initial conditions may yield unsteady flow patterns. The key simulation results have been explained based on scaling arguments and the scaling relations have been utilised to identify different regimes of natural convection of power-law fluids accounting for aspect ratio effects.

Experimental study of the turbulent free convection over horizontal smooth or grooved surfaces in an open cavity

This study investigates the turbulent free convection in a tank of water with the bottom surface being a smooth or a grooved surface and the top of the water surface exposed to ambient. The experiments for smooth surface was done with four values of AR, 3, 2, 1 and 0.5, whereas for grooved surface, values of AR are 3, 2 and 1. Here AR is the aspect ratio (=width of fluid layer/height of fluid layer). Heat flux at the bottom surface was from electrical heating. Experiments have been carried out for modified Rayleigh number in the range of \(2.5 \times 10^{8}\le Ra\le 3 \times 10^{12}\). The experimental results indicate that AR has significant effect on heat transport and hence sensitive to the nature and structures of the large scale mean flows of the system.