Fluctuations and waves in fluidized bed systems: The influence of the air-supply system

A general model of the response of a fluidized bed to disturbances is formulated, and the information provided by the model with respect to the dynamics of the bed, the bed plus the air-plenum and the bed plus the entire air-supply system, is investigated. Expressions given in literature on the fundamental frequency of the bed-plenum system are analyzed, and it is shown that they are a special case of the general model. In order to simulate various types of interaction between the bed and the rest of the system, experiments were performed in a cold fluidized bed unit operated under both non-circulating and circulating conditions. At low velocity, three regimes were identified: the multiple bubble regime with almost no interaction between bed and air-plenum, the single bubble regime with the interaction between bed and air-plenum only, and a regime with numerous irregular bubbles, where the bed interacted with the entire air-supply system. At high fluidization velocity, the exploding bubble regime was identified, with the same dominant frequency as that of the single bubble regime (the interaction with the air-supply system remains at that frequency). The models investigated correctly reproduce the dynamics when the bed is independent of the other parts of the system, or when the bed interacts only with the air-plenum. However, the models are only partially applicable when the bed interacts with the entire air-supply system. The reasons for this are investigated. In the case of system interaction, pressure waves, generated in the bed, interact with pressure pulsations from the air-supply system. This results in a coupled system, which is not covered by the models. Pressure waves resulting from events in the bed, are recognized as the coherent part of the cross power spectra of pressure fluctuations measured in the bed and the air-plenum.     

Stabilization of fixed modes in expansions of LTI systems

The objective of this note is to propose a method for stabilization of structurally fixed modes in expansions of LTI dynamic systems in the scope of overlapping decentralized control design based on the expansion/contraction framework, enabling successful design for a broader class of problems than considered so far. The method is based on a judicious choice of complementary matrices in the expanded space. Numerical examples are provided to illustrate simplicity and efficiency of the proposed approach.     

An image watermarking based on the pdf modeling and quantization effects in the wavelet domain

An image watermarking technique based on the concept of JPEG2000 algorithm is proposed. Biorthogonal wavelet 9/7 transform is used to provide a set of coefficients suitable for watermark embedding. The statistical properties of different subbands are analyzed in order to choose the number of decomposition levels and position of subbands, which will assure the best compromise between the watermark transparency and robustness. The JPEG2000 quantization is applied to avoid insignificant wavelet coefficients, while the remaining ones are used for watermarking. The optimal and blind watermark detection is based on the nonlinear score function and appropriate model of coefficients distribution. The performance of the proposed procedure is tested on examples with various images, showing robustness under different attacks, while maintaining high image quality.     

Low level laser therapy with trigger points technique: a clinical study on 243 patients

Among the various methods of application techniques in low level laser therapy (LLLT) (HeNe 632.8 nm visible red or infrared 820-830 nm continuous wave and 904 nm pulsed emission) there are very promising "trigger points" (TPs), i.e., myofascial zones of particular sensibility and of highest projection of focal pain points, due to ischemic conditions. The effect of LLLT and the results obtained after clinical treatment of more than 200 patients (headaches and facial pain, skeletomuscular ailments, myogenic neck pain, shoulder and arm pain, epicondylitis humery, tenosynovitis, low back and radicular pain, Achilles tendinitis) to whom the "trigger points" were applied were better than we had ever expected. According to clinical parameters, it has been observed that the rigidity decreases, the mobility is restored (functional recovery), and the spontaneous or induced pain decreases or even disappears, by movement, too. LLLT improves local microcirculation and it can also improve oxygen supply to hypoxic cells in the TP areas and at the same time it can remove the collected waste products. The normalization of the microcirculation, obtained due to laser applications, interrupts the "circulus vitiosus" of the origin of the pain and its development (Melzak: muscular tension > pain > increased tension > increased pain, etc.). Results measured according to VAS/VRS/PTM: in acute pain, diminished more than 70%; in chronic pain more than 60%. Clinical effectiveness (success or failure) depends on the correctly applied energy dose--over/underdosage produces opposite, negative effects on cellular metabolism. We did not observe any negative effects on the human body and the use of analgesic drugs could be reduced or completely excluded. LLLT suggests that the laser beam can be used as monotherapy or as a supplementary treatment to other therapeutic procedures for pain treatment.     

Denoising of sparse images in impulsive disturbance environment

Multimedia Tools and Applications - The paper presents a method for denoising and reconstruction of sparse images based on a gradient-descent algorithm. It is assumed that the original (non-noisy)...     

Thermal analysis and microscopic characterization of the piston alloy AlSi13Cu4Ni2Mg

In this research paper, the phases identified by thermal and microscopic analysis of the piston alloy AlSi13Cu4Ni2Mg, which was solidified under different conditions, are presented and compared with different piston alloys. Piston alloys are a group of casting Al–Si alloys, well-known as wear resistant materials, which are widely used as the piston materials for internal combustion engines because of their low thermal expansion coefficient and high wear resistance when alloyed with other elements such as copper, magnesium and nickel. Depending on the combination of alloying elements and other impacting factors, pistons alloys with different mechanical and physical properties are obtained.     

Numerical model of gaseous fuel jet injection into a fluidized furnace

The paper presents a fluid-porous medium model, developed for stationary 2D predictions of fluidized bed. Dense phase is considered a fixed porous medium, while gas–particle interactions and bubbling phase are modeled regarding balance of friction forces between gas and particles. Like referent measurements, predictions of lateral jet injection into the bed suggest the jet penetration length is strongly affected by fluid velocity at the nozzle outlet, while influences of the nozzle vertical position and inclination angle are not significant. Also, the fluid velocity and the nozzle vertical position exert pronounced effects on mixing rate of components (fuel and oxidizer).