Cascade Parameters Research Articles

Analysis of Interference Factors of Air Turbine Cascades

This paper reports viscous compressible aerodynamics analysis of two-dimensional cascades (arrays of aerofoils). The study elucidates the effect of cascade parameters such as solidity, σ and angle of attack, α, on the interference between blades. Understanding the interference behaviour is important in the performance analysis of air turbines such as Wells turbine commonly used in oscillating water column (OWC) - wave energy converter (WEC) system. The present analysis shows that isolated two-dimensional lift coefficient modified by interference factors, ko, based on inviscid flow theory is acceptable for low solidity cascades, i.e. σ ≤ 0.5, and that stall occurs at lower angle of attack in cascade compared to isolated aerofoil. When σ > 0.5, ko is shown to depend on both α and σ especially in the post-stall flow. The result suggests that interference factors that is applicable for wide range of flow conditions as in Wells turbines should also include the α effect in the modifier.

Isotopically Selective Mass Transfer in the Q-Cascade with Losses of Working Substance

The theory of the model Q-cascade is generalized for the case of presence of losses of working substance. Analytical solutions are obtained to determine the cascade parameters for specified rates of losses. Calculations to reveal the effect of the losses on the total and feed flows for given concentrations of a target component in the product and waste flows are carried out. The dependence of the total and feed flows on the losses for multi- and binary isotope mixtures is defined.

Thawed serum is more affected by non-mixing errors than thawed plasma

It is demonstrated that the total flow in the optimum cascade composed of three different types of gas centrifuges with varied separative performance levels and overall separation factors varying over the cascade stages is less than that in the corresponding ideal (non-mixing) cascade. The data obtained make it possible to use the parameters of the optimum cascade to find the operational mode for the cascade stages that provides the minimum total flow in a separation cascade.

The Q-Cascade Explanation

The physical meaning of a continuous profile cascade, which is frequently used in the study of multicomponent isotope separation and named as the Q-cascade is explained. It is found that the parameter Q for a component at a stage is nothing but the relative increase of the concentration of the component, and is constant at all cascade stages. The Q-cascade is classified as the quasi-ideal cascade playing an importantrole for fast evaluation of the separation cascade parameters for multi-isotope mixture separation.

3-pentanone fluorescence yield measurements and modeling at elevated temperatures and pressures

Measurements of 3-pentanone fluorescence quantum yield (FQY) over a wide range of temperatures and pressures in air and nitrogen bath gases are reported and a comprehensive FQY model in support of quantitative planar laser-induced fluorescence diagnostics at elevated pressures and temperatures is presented. Measurements were made of the FQY for 20 mbar of 3-pentanone in nitrogen and air for pressures between 1 and 25 bar in a high-pressure and high-temperature cell for excitation wavelengths of 248, 266, 277, and 308 nm. The measurements were performed in nitrogen from 298 to 745 K and in air from 298 to 567 K. The 3-pentanone FQY data were used to optimize FQY model parameters, including the oxygen and nitrogen quenching rates and vibrational relaxation cascade parameters for nitrogen and oxygen. This work introduces vibrational energy dependence for cascade parameters, as well as a nitrogen quenching rate. The new 3-pentanone FQY model agrees with the measurements within 10%, as well as with fluorescence signal measurements from optical internal combustion engines at pressures and temperatures up to 28 bar and 1100 K.

Analytical model for electromagnetic cascades in rotating electric field

Electromagnetic cascades attract a lot of attention as an important quantum electrodynamics effect that will reveal itself in various electromagnetic field configurations at ultrahigh intensities. We study cascade dynamics in rotating electric field analytically and numerically. The kinetic equations for the electron-positron plasma and gamma-quanta are formulated. The scaling laws are derived and analyzed. For the cascades arising far above the threshold the dependence of the cascade parameters on the field frequency is derived. The spectra of high-energy cascade particles are calculated. The analytical results are verified by numerical simulations.

The chemopreventive effect of dimethylthiourea against carmustine-induced myelotoxicity in rats

The possible chemopreventive role of dimethylthiourea (DMTU) against carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU)-induced myelotoxicity was assessed through evaluation of apoptosis, lipid peroxidation, glutathione (GSH) content and some antioxidant enzymes activities in bone marrow cells of rats. Thirty-six rats were randomly classified into four groups. The first group was injected i.p. with ethanol and served as a control. The second group was treated with BCNU. The third group was given DMTU, while the fourth group was co-administered with DMTU prior to BCNU administration. BCNU treatment in a single dose of 30mg/kg significantly decreased the normal counts of RBCs, WBCs and platelets as well as hemoglobin level. In addition, BCNU exhibited marked apoptotic effect associated with significant alterations in the oxidative cascade parameters. Treatment of animals with DMTU in a single dose of 500mg/kg 1h before BCNU injection, followed by 125mg/kg twice daily for 5 consecutive days significantly mitigated the induced changes in the hematological parameters. The induced alterations in the oxidant and antioxidant parameters as well as apoptosis were also improved. Conclusively, DMTU treatment exhibited marked chemopreventive effect against BCNU-induced myelotoxicity; an effect which may be partially attributed to its inherently antioxidant potential.

Use of the Q-cascade in calculation and optimization of multi-isotope separation

The model Q-cascade is a useful tool for fast evaluation of the parameters of a separation cascade in the case of multi-isotope mixtures separation. Earlier the cascade key mass M is used as the optimization variable to search optimum parameters of a Q-cascade. A method is given here to determine the region for the valid values of the M parameter in the case of a Q-cascade with specified concentrations of a target component in its product and waste withdrawals. When a target isotope is contained in more than one component of a separation mixture, the idea for specifying the effective fractions of the target isotope in the withdrawals other than the concentrations of a target component is introduced and applied to the optimization of a Q-cascade. The applicability of the method in the determination of the valid values of the M parameter for specified effective fractions of a target isotope in cascade withdrawals is demonstrated. Examples of enrichment of cadmium and lead isotopes in Q-cascades are given to demonstrate the effectiveness of the suggested method.

Long Signaling Cascades Tend to Attenuate Retroactivity

Signaling pathways consisting of phosphorylation/dephosphorylation cycles with no explicit feedback allow signals to propagate not only from upstream to downstream but also from downstream to upstream due to retroactivity at the interconnection between phosphorylation/dephosphorylation cycles. However, the extent to which a downstream perturbation can propagate upstream in a signaling cascade and the parameters that affect this propagation are presently unknown. Here, we determine the downstream-to-upstream steady-state gain at each stage of the signaling cascade as a function of the cascade parameters. This gain can be made smaller than 1 (attenuation) by sufficiently fast kinase rates compared to the phosphatase rates and/or by sufficiently large Michaelis-Menten constants and sufficiently low amounts of total stage protein. Numerical studies performed on sets of biologically relevant parameters indicated that ∼50% of these parameters could give rise to amplification of the downstream perturbation at some stage in a three-stage cascade. In an n-stage cascade, the percentage of parameters that lead to an overall attenuation from the last stage to the first stage monotonically increases with the cascade length n and reaches 100% for cascades of length at least 6.

Spatial downscaling of precipitation from GCMs for climate change projections using random cascades: A case study in Italy

We present a Stochastic Space Random Cascade (SSRC) approach to downscale precipitation from a General Circulation Models (GCMs), developed for the assessment of water resources under climate change scenarios for the Oglio river (1440 km2), in the Italian Alps. The snow‐fed Oglio river displays complex physiography and high environmental gradient and statistical downscaling methods are required for climate change assessment. First, a back cast analysis is carried out to evaluate the most representative within a set of four available GCMs (R30, ECHAM4, PCM, HadCM3). Monthly precipitation for the window 1990–2000 from 270 gauging stations (one every 25 km2) in northern Italy is used and scores from objective indicators are calculated. The SSRC model is then tuned upon the Oglio river catchment for spatial downscaling (2 km2) of daily precipitation from the NCAR Parallel Climate Model, giving the comparatively best results for the area. Scale Recursive Estimation coupled with the Expectation Maximization algorithm is used for model estimation. The seasonal parameters of the multiplicative cascade are accommodated by statistical distributions conditioned upon the climatic forcing, based on a regression analysis. The SSRC approach reproduces well the spatial clustering, intermittency, self‐similarity, and spatial correlation structure of precipitation fields, with relatively low computational burden. Downscaling of future precipitation scenarios (A2 scenario from the Parallel Climate Model) is then carried out and some preliminary conclusions are drawn.

Comparative Study of the Model and Optimum Cascades for Multicomponent Isotope Separation

The possibility of estimating the minimum total flow in a cascade with concentrations of a target component given in the product and waste flows by means of a model match abundance ratio cascade (MARC) is studied. The parameters required to describe MARC characteristics are the total number of separation stages, the feed flow location, and the M* parameter, which is equal to a half-sum of mass numbers of the target and the supporting components. Specific research carried out independently in two scientific labs in China and Russia has demonstrated that the integral parameters of the MARC, optimized by the M* parameter, are very close to that of the optimum by the minimum total flow cascade found by means of numerical optimization. The calculation is performed for separation of krypton isotopes when the end component 78Kr and the intermediate component 83Kr are considered to be the targets. It paves the way to use the optimized MARC parameters for two purposes: first, for fast and easy evaluation of the real cascade parameters and second, as an initial guess in its further direct numerical optimization, thereby allowing significant savings in computation time.

Precipitation downscaling using random cascades: a case study in Italy

Abstract. We present a Stochastic Space Random Cascade (SSRC) approach to downscale precipitation from a Global Climate Model (hereon, GCMs) for an Italian Alpine watershed, the Oglio river (1440 km2). The SSRC model is locally tuned upon Oglio river for spatial downscaling (approx. 2 km) of daily precipitation from the NCAR Parallel Climate Model. We use a 10 years (1990–1999) series of observed daily precipitation data from 25 rain gages. Scale Recursive Estimation coupled with Expectation Maximization algorithm is used for model estimation. Seasonal parameters of the multiplicative cascade are accommodated by statistical distributions conditioned upon climatic forcing, based on regression analysis. The main advantage of the SSRC is to reproduce spatial clustering, intermittency, self-similarity of precipitation fields and their spatial correlation structure, with low computational burden.

Experimental-numerical investigation of the dynamic stability of flexural-torsional vibrations of compressor blades under conditions of attached and separated flow. part 3. mutual aerodynamic couplings

The paper considers the results of a study of mutual aerodynamic couplings which give rise to nonstationary aerodynamic interactions between the translational and angular components displacements of neighboring ring blades in the case of variation of attack angle, reduced vibration frequency and the geometric parameters of the blade cascade. The effect of mutual aerodynamic couplings between neighboring blades on the aerodynamic stability of flexural-torsional vibrations of the blades of the peripheral section of the shrouded fan blade ring of gas turbine engine for an attack angle of 15° has been estimated.

Mathematical description of the synthesis of butadiene rubber with allowance for the branching of a polymer under conditions of the separate supply of a reaction mixture to the reactors of a cascade

Mathematical modeling of the synthesis of butadiene rubber on a neodymium-based catalytic system under conditions of the separate supply of a reaction mixture to the apparatuses of a cascade is performed. Expressions are derived for calculating the characteristics of the branching of the polymer with allowance for the additional supply of the reaction mixture to the second apparatus of the cascade. An analysis of the influence of the flow rate of an additional stream of the reaction mixture to the second apparatus of the cascade and operating parameters on the molecular weight characteristics and branching of the polymer is performed.

Topology modeling for Adaboost-cascade based object detection

Several important issues involved in Adaboost-cascade learning still remain open problems. In this work, several novel ideas are proposed for improved Adaboost-cascade object detection. The most important one is the novel topology oriented Adaboost (TOBoost) algorithm. TOBoost immediately minimizes the classification error of each selected feature, and thus enables the final detector to be more discriminative and to converge more quickly. Moreover, a simple cascading scheme is presented for tuning the cascade parameters of TOBoost; and Gaussian kernel density estimation is introduced to enhance the generalization ability of TOBoost. Another important contribution is the topology modeling of Haar-like (HL) features, which reveals an interesting property of negative HL features and significantly avoids unnecessary training computations. Non-adjacent Haar-like features are consequently configured for more effective object representation. The above enhancements result in a more efficient and stable detector with fewer features. Extensive experiments in the application of iris detection are conducted and encouraging performance is achieved.

Acoustic resonances and trapped modes in annular plate cascades

As a stepping stone towards understanding acoustic resonances in axial flow compressors, acoustic resonances are computed numerically in fixed single and tandem plate cascades in an infinitely long annular duct. Applying perfectly matched layer absorbing boundary conditions in the form of the complex scaling method of atomic and molecular physics to approximate the radiation condition the resonance problem is transformed into an eigenvalue problem. Of particular interest are resonances with zero radiation damping (trapped modes) or very small radiation damping (nearly trapped modes). Such resonances can be excited by wakes from compressor cascades or struts. If the shedding frequency is sufficiently close to an acoustic resonant frequency, the latter may control the vortex shedding causing high-intensity tonal noise or occasionally even blade failure. All resonances are computed for zero mean flow approximating low-Mach-number flows. The influence of various cascade parameters on the resonant frequencies is studied and, whenever possible, our numerical results are compared with published experimental findings.

Theoretical Analysis To Assess the Separative Power of Reconfigured Cascades of Predesigned Gas Centrifuges

An analysis is presented that describes a theoretical approach to assess the separative power of redistributions of a fixed number of predesigned gas centrifuges in reconfigured countercurrent cascades. A parameter that indicates deviations from ideal operation is derived, and this parameter facilitates the choice of likely sets of external cascade parameters. The overall loss in separative power of redistributed systems is discussed, and configurations that correspond to a minimum loss of overall separative power are presented. The application of this methodology to a specific case study that is of importance in the field of nuclear safeguards is discussed. Sample calculations simulating higher product enrichment levels are performed to determine likely cascade configurations.

Insulin immuno-neutralization in chicken: effects on insulin signaling and gene expression in liver and muscle

In order to evaluate the role of insulin in chicken, an insulin immuno-neutralization was performed. Fed chickens received 1 or 3 i.v. injections of anti-insulin serum (2-h intervals), while fed or fasted controls received normal serum. Measurements included insulin signaling cascade (at 1 h in liver and muscle), metabolic or endocrine plasma parameters (at 1 and 5 h), and qRT-PCR analysis (at 5 h) of 23 genes involved in endocrine regulation, metabolisms, and transcription. Most plasma parameters and food intake were altered by insulin privation as early as 1 h and largely at 5 h. The initial steps of insulin signaling pathways including insulin receptor (IR), IR substrate-1 (IRS-1), and Src homology collagen and downstream elements: phosphatidylinositol 3-kinase (PI3K), Akt, GSK3, ERK2, and S6 ribosomal protein) were accordingly turned off in the liver. In the muscle, IR, IRS-1 tyrosine phosphorylation, and PI3K activity remained unchanged, whereas several subsequent steps were altered by insulin privation. In both tissues, AMPK was not altered. In the liver, insulin privation decreased Egr1, PPAR gamma, SREBP1, THRSP alpha (spot 14), D2-deiodinase, glucokinase (GK), and fatty acid synthase (whereas D3-deiodinase and IGF-binding protein 1 transcripts were up-regulated. Liver SREBP1 and GK and plasma IGFBP1 proteins were accordingly down- and up-regulated. In the muscle, PPAR beta delta and atrogin-1 mRNA increased and Egr1 mRNA decreased. Changes in messengers were partly mimicked by fasting. Thus, insulin signaling in muscle is peculiar in chicken and is strictly dependent on insulin in fed status. The 'diabetic' status induced by insulin immuno-neutralization is accompanied by impairments of glucagon secretion, thyroid axis, and expression of several genes involved in regulatory pathways or metabolisms, evidencing pleiotropic effects of insulin in fed chicken.

Analysis of c-myc, PAI-1 and uPAR in patients with incisional hernias

Disturbed wound healing leading to alterations in collagen composition has been thought to play a key role in the pathogenesis of incisional hernia formation. The aim of the present study was to further characterise the scarring process in such patients. Mature skin scars from patients with either primary or recurrent incisional hernias were compared to mature abdominal skin scars from patients without hernias. The distribution of collagen types I and III was analysed using crosspolarisation microscopy. Expression of c-myc--a parameter for cell differentiation and proliferation--and of PAI-1 and uPAR--parameters of the proteolytic cascade in wound healing--were determined by immunohistochemistry. In agreement with previous studies, decreased collagen I/III ratios were found in patients with incisional hernias. In these patients, c-myc levels were significantly elevated whereas plasminogen activator inhibitor-1 (PAI-1) and urokinase-plasminogen activator receptor (uPAR) levels were only slightly increased. In contrast to controls, a significant correlation between c-myc, PAI-1 and uPAR expression and collagen I/III ratios was found in patients with incisional hernias. The differential correlation of collagen types and expression of c-myc, PAI-1 and uPAR within the scar tissue might represent a causal factor in incisional hernia formation.

Formation of steady state size distribution of precipitates in alloys under cascade-producing irradiation

The effect of coherency loss on the development of precipitate size distribution under cascade-producing irradiation is considered. The nucleation of coherent precipitates, their growth followed by coherency loss and cascade-induced dissolution of large incoherent precipitates can occur simultaneously resulting in formation of a quasi-stationary size distribution of semicoherent precipitates. To describe this process we consider co-evolution of a mixed population of coherent, semicoherent and incoherent precipitates. Mathematically, the problem is formulated as a set of discrete rate equations of nucleation kinetics (the Master equation approach) which is also used for later stages of evolution. To solve the corresponding large set of equations (typically, more than 10 5 equations) an efficient numerical method is developed. The simulation results obtained for material parameters and irradiation conditions typical for nuclear reactors show that the coherency loss affects considerably evolution of the precipitate population. Under certain irradiation conditions, both in solution-annealed alloys and in aged ones, the mean precipitate size and the number density during prolonged irradiation tend to steady state values, whereas the size distribution function of large precipitates narrows. The width of the quasi-stationary size distribution is controlled by cascade parameters. It was found that the asymptotic quasi-stationary state of the precipitate population may depend on initial state of the alloy.