9 research outputs found
A Parametric Analysis of Streamwise Vortices on a Compression Ramp at Mach 4
No full text九州工業大学博士（工学）1 Introduction|2 Mathematical modeling|3 Mesh Sensitivity and Validation Framework|4 Streamwise vortices in superosnic compression ramp flows|5 ConclusionShock-wave/boundary-layer interaction (SWBLI) over a compression ramp has been extensively studied to understand high-speed flow behavior around components such as control surfaces and engine inlets. The shock generated by wall deflection can cause boundary layer separation, with the extent of the separation bubble influenced by the upstream boundary layer state and ramp angle. Near the rear of the bubble, concave streamlines may induce Görtler-type instabilities, characterized by counter-rotating streamwise vortices that can promote transition to turbulence. Such vortices are observed in various applications, including flow over turbine blades, supercritical airfoils, and forebody compression surfaces in hypersonic inlets. In this work, Large-eddy simulations (LES) of supersonic flow over a compression ramp are conducted to investigate the formation of streamwise vortices and their impact on flow dynamics. The simulations are performed at a freestream Mach number of M∞ = 4.0 and unit Reynolds number of 4.56 × 10 6 per meter. Two ramp angles (15° and 18°) and three ramp corner positions(P1–P3) are examined. Initial 2D simulations across six configurations (15P1–3 and 18P1–3) help identify cases prone to Görtler instability. Results show that increasing the ramp angle or moving the ramp corner downstream leads to greater separation length and enhanced streamline curvature, promoting Görtler-type instabilities and the emergence of longitudinal vortices. For the 15° cases, no streaks are observed at P1–P2, but they begin to appear at P3. In contrast, all 18° cases exhibit longitudinal streaks, with the strongest spanwise interactions observed in the 18P3 case. Spanwise fluctuations intensify downstream due to both linear and nonlinear amplification of streamwise vortices. Notably, the vortex wavelength decreases by ~15% as plate length increases by 80% from 18P1 to 18P3. In the most extreme configuration (18P3), unsteady wall pressure data and iso-surfaces of the Qcriterion reveal intermittent high-frequency fluctuations—hallmarks of transitional flow. Further time-resolved analysis highlights the presence of secondary spanwise instabilities that give rise to turbulent spots propagating at about 60% of the freestream velocity. These findings provide clear evidence of the route to transition being driven by centrifugal instabilities in separated curved flows.
Another key result of this study is derived from space-time plots of the Stanton number (St), which visualize wall heat flux behavior across time and span. These plots reveal distinct, streamwisealigned, counter-rotating vortices that enhance local wall heating. In the 18P3 case, the peak St value is approximately 27% higher than its time- and span-averaged value, compared to ~17% for the 15P3 case highlighting stronger downwash and heat flux concentration in the steeper ramp configuration. Additionally, a negative correlation is observed between the flow reattachment location and local St near the reattachment point. Earlier reattachment corresponds to higher localheating rates, while delayed reattachment reduces the St value, resulting in up to 40% variation relative to the mean. These findings underscore the critical influence of ramp geometry and surface length on the formation and amplification of streamwise vortices. They also reveal important implications for wall heat transfer and transition prediction in hypersonic flows—two aspects crucial for thermal protection system (TPS) design and reliability of high-speed flight vehicles. The coupling between geometric parameters, instability growth, and thermal response provides a deeper physical understanding of SWBLI-induced transition mechanisms.九州工業大学博士学位論文 学位記番号:工博甲第607号 学位授与年月日:令和7年9月25日令和7年度doctoral thesi
Kalash Religion
No full textIn the essay the author sketches the Indian influence of the religious system in the Hindukush region. The document is an excerpt of the author's article "The Ṛgvedic Religious System and its Central Asian and Hindukush Antecedents", published 2004 in the book "The Vedas: Texts, Language and Ritual"
How does excess cash affect corporate financial performance?
No full textPurposeThis article analyzes the moderating role of investment opportunities, business risk and agency costs in shaping the nexus between excess cash and corporate performance.Design/methodology/approachThis research uses dynamic regression models (two-step system generalized method of moments) to analyze the data related to 200 Turkish companies listed on Borsa Istanbul (BIST) for the years between 2009 and 2020.FindingsThe findings indicate that when excess cash increases, the financial performance deteriorates only for firms with lower investments compared to firms with more investments. In addition, investment contributes to better financial performance for firms that hold cash surplus, whereas the influence of investment is insignificant for firms that have insufficient cash. Agency costs of equity exacerbate the adverse impact of excess cash on financial performance while agency costs of debt mitigate this effect. Excess cash reduces the financial performance of highly leveraged firms. However, this impact becomes insignificant when debt ratio decreases. The findings also show that investment has more significant role than business risk in building the precautionary motive to hold cash.Research limitations/implicationsThe findings of this article are limited to the Turkish market. Future research is still needed in other emerging markets to compare the results and reveal more about the effect of excess cash on firm performance, and how other factors can change this effect.Practical implicationsThe findings verify the increased significance of excess cash in the presence of investment opportunities and difficulties in accessing external funds. Nevertheless, the role of the equity related agency problem in reducing the benefits of cash surplus confirms the necessity of policies that support corporate governance, especially in emerging markets.Originality/valueThis article, according to the knowledge of author, is the first to examine the role of agency costs associated with debt and equity, and the compound effect of investment opportunities and business risk on the nexus between excess internal funds and corporate financial performance in emerging markets
The dynamic relationship between firms' cash reserves and financial leverage: evidence from MENA emerging markets
No full textPurpose This paper investigates the impact of financial leverage on corporate cash holdings in the Middle East and North African (MENA) emerging markets. Design/methodology/approach The author applies the dynamic modeling approach to data from nonfinancial firms listed in 10 MENA countries between 2010 and 2019. The empirical model avoids the shortcomings of the prior literature by including indicators of the dynamics of the financial leverage to account for its persistence in the corporate cash holdings reserves. Findings This research reports a significant negative relationship between corporate cash holdings and financial leverage. The results support the pecking order model, suggesting that leverage can be regarded as a substitute for holding a larger amount of cash and marketable securities. The author argues that the negative relationship between financial leverage and corporate cash holdings reinforces the precautionary motive to have internal cash reserves rather than external debt to support capital and investment activities by firms in the MENA emerging markets. Practical implications The results of this research provide important insights into cash and capital structure management for nonfinancial listed firms in the MENA emerging markets. Specifically, the paper will help managers to understand the dynamic financial leverage determinants of holding cash in corporations in the MENA emerging markets and encourage policymakers to financially determine the corporate capital structure and cash holdings based on cost and benefits. Managing the firm's capital structure and cash holdings based on trade-offs between costs and benefits would enhance operating cash flow which may play an important role in creating value for shareholders. Originality/value Prior studies have commonly been concerned with the determinants of corporate cash holdings, but few have investigated the dynamic financial leverage determinants of corporate cash holdings. This paper draws attention to this issue within the context of MENA emerging markets. To the authors' best knowledge, this is the first study that explores the relationship between cash holdings and financial leverage in MENA emerging markets
Biosorption Technique for Naphthalene Removal from Aqueous Solution By Chara sp., Algae
No full textThese instructions give guidelines for preparing the article to be published in the Engineering& Technology Journal using MS World 7.0 or later. A short abstract should open the paper and give a clear indication of the aims, scope and the main results of the paper. The reader may decide from the abstract that the full text is of particular interest or not. The author should consider that the abstract is an indication of the scope of the topic and the obtained results and not a way of condensing the problem in a few words for quick reading. It should be no more than 200 words. It is placed under the title with a single space from the title. The paper titles should be concise and definitive. The length of the title should not exceed three lines. The abbreviations and formulae should be avoided. Papers titles should be written in uppercase and lowercase letters, not all uppercase. Capitalize the words of the paper title. Avoid writing a long formula and define all symbols used in the abstract and do not cite the references here
Dynamical profiles of the reactive components in direct and revert Liesegang patterns
No full textIn periodic precipitation (Liesegang banding), the overwhelmingly common trend is the increase in spacing between consecutive bands as we move away from the interface. Revert spacing is a rare trend observed in a few systems, wherein the spacing decreases with distance from the interface. In this Letter, we compare the spatial profiles of the aqueous components in two chromate Liesegang precipitates: CuCrO4 and PbCrO4, displaying direct and revert spacing, respectively. The profiles are measured using UV-Vis spectrophotometry. The formation of a Pb2+-PbCrO4 complex in equilibrium with the free Pb2+, seems to play a key role in the revert spacing scenario. © 2013 Elsevier B.V. All rights reserved.Ahamed MAR, 2010, IRAN POLYM J, V19, P635; Al-Ghoul M, 2001, J PHYS CHEM A, V105, P8053, DOI 10.1021-jp011158o; Badr L, 2008, CHEM PHYS LETT, V453, P40, DOI 10.1016-j.cplett.2008.01.008; Bellamy L.J., 1975, INFRARED SPECTRA COM; BUKI A, 1995, J CHEM PHYS, V103, P10387; Chatterji AC, 1926, KOLLOID Z, V40, P97, DOI 10.1007-BF01424476; DAS I, 1987, J PHYS CHEM-US, V91, P747, DOI 10.1021-j100287a051; DAS I, 1987, J CRYST GROWTH, V82, P361, DOI 10.1016-0022-0248(87)90326-5; DEE GT, 1986, PHYS REV LETT, V57, P275, DOI 10.1103-PhysRevLett.57.275; Dhar N., 1922, KOLLOID Z, V2, P15; Dhar N., 1925, J PHYS CHEM-US, V28, P41; Dhar NR, 1925, KOLLOID Z, V37, P2, DOI 10.1007-BF01436228; FEENEY R, 1983, J CHEM PHYS, V78, P1293, DOI 10.1063-1.444867; FLICKER M, 1974, J CHEM PHYS, V60, P3458, DOI 10.1063-1.1681560; Ghosh D. N., 1930, J INDIAN CHEM SOC, V7, P509; Hedges E. S., 1932, LIESEGANG RINGS OTHE; Henisch H., 1988, CRYSTALS GELS LIESEG; Isemura T., 1933, Bulletin of the Chemical Society of Japan, V8, DOI 10.1246-bcsj.8.11; Isemura T., 1933, Bulletin of the Chemical Society of Japan, V8, DOI 10.1246-bcsj.8.108; Jablczynski CK, 1923, B SOC CHIM FR, V33, P1592; KANNIAH N, 1981, J COLLOID INTERF SCI, V80, P369, DOI 10.1016-0021-9797(81)90195-8; KANNIAH N, 1984, P INDIAN AS-CHEM SCI, V93, P801; Karam T, 2011, J PHYS CHEM A, V115, P2994, DOI 10.1021-jp200619g; Liesegang R. E., 1896, LIESEG PHOT ARCH, V21, P221; Liesegang R. E., 1896, NATURWISS WOCHENSCHR, V11, P353; Mathur P. B., 1957, KOLLOID Z, V159, P143; Molnar F, 2008, PHYS CHEM CHEM PHYS, V10, P2368, DOI 10.1039-b715775d; Ostwald W., 1899, LEHRBUCH ALLGEMEINEN, VII, P779; Polezhaev AA, 1994, CHAOS, V4, P631, DOI 10.1063-1.166040; DAS I, 1988, J NON-EQUIL THERMODY, V13, P209, DOI 10.1515-jnet.1988.13.3.209; Ratke L., 2002, GROWTH COARSENING OS; Sakka S., 2003, HDB SOL GEL SCI TECH, V1; Stern K., 1954, CHEM REV, V54, P810
Effects of Reynolds Number and Ramp Angle on Görtler Vortices over a Compression Ramp
No full textWe investigate the supersonic flow over a compression corner using Large-eddy simulations (LES) with the objective of capturing Görtler vortices and their associated effects over the ramp. Simulations are carried out at a freestream Mach number, M∞ = 4, and a reference Reynolds number of 1.16 × 105. The formation of these Görtler vortices is sensitive to the Reynolds number and ramp angles, which once formed can potentially impact the transition and wall heating rate distribution. Two ramp angles of 15◦ and 18◦ and three different positions of the ramp corner (P1-P3) are considered in this study. Our results show that the strength of the Görtler vortices increases with an increase in both the ramp angle and the position of the ramp corner. This is observed to promote early transition due to primary centrifugal instability and secondary instabilities. For the extreme test case of 18◦-P3, the peak value of the Stanton number is found to be ≈ 26% higher than the time and span-averaged value, indicating that the effect of downwash on the wall heating rate distribution is significant.conference pape
Atorvastatin increases the production of proinflammatory cytokines and decreases the survival of Escherichia coli-infected mice
No full textTo assess whether the immunosuppressive effects of atorvastatin outweigh its antibacterial ones in an infection, mice were infected with Escherichia coli and administered atorvastatin; survival rates were then monitored. Mice treated with atorvastatin post-infection showed a remarkable decrease in their survival rate. On the other hand, the higher the level of serum IFN-γ in the infected mice treated with atorvastatin, the lower was the survival rate. Levels of IL-4 were markedly depressed in all groups infected with E. coli and treated with atorvastatin. Since atorvastatin inhibits IFN-γ expression in the absence of bacterial infection, we examined whether bacterial lipopolysaccharide (LPS) was the element capable of overriding this inhibition. Mouse peripheral blood mononuclear cells were treated with atorvastatin and lipopolysaccharide ex vivo then proinflammatory (IFN-γ, TNFα, IL-6) and prohumoral/regulatory (IL-4, IL-13, IL-10) cytokine levels were analyzed in culture supernatants. While proinflammatory cytokine levels were decreased upon treatment with atorvastatin alone, their levels were markedly elevated by treatment with LPS, bacterial lysate or bacterial culture supernatant. On the other hand, atorvastatin exerted an inhibitory effect on production of the prohumoral/regulatory cytokines. Our data indicates that any consideration for statins as antimicrobial treatment should assess the possible adverse outcomes. © 2019, The Author(s)
