Multidimensional multirate filters derived from one dimensional filters

A method by which every multidimensional filter with parallelepiped passband can be designed and implemented efficiently, derived from an appropriate one dimensional filter, is presented. With this method, Nyquist constraint and zero-phase requirement can be satisfied easily. A design example is also given.<>     

Biorthogonal partners and applications

Two digital filters H(z) and F(z) are said to be biorthogonal partners of each other if their cascade H(z)F(z) satisfies the Nyquist or zero-crossing property. Biorthogonal partners arise in many different contexts such as filterbank theory, exact and least squares digital interpolation, and multiresolution theory. They also play a central role in the theory of equalization, especially, fractionally spaced equalizers in digital communications. We first develop several theoretical properties of biorthogonal partners. We also develop conditions for the existence of biorthogonal partners and FIR biorthogonal pairs and establish the connections to the Riesz basis property. We then explain how these results play a role in many of the above-mentioned applications     

A comprehensive model for software rejuvenation

Recently, the phenomenon of software aging, one in which the state of the software system degrades with time, has been reported. This phenomenon, which may eventually lead to system performance degradation and/or crash/hang failure, is the result of exhaustion of operating system resources, data corruption, and numerical error accumulation. To counteract software aging, a technique called software rejuvenation has been proposed, which essentially involves occasionally terminating an application or a system, cleaning its internal state and/or its environment, and restarting it. Since rejuvenation incurs an overhead, an important research issue is to determine optimal times to initiate this action. In this paper, we first describe how to include faults attributed to software aging in the framework of Gray's software fault classification (deterministic and transient), and study the treatment and recovery strategies for each of the fault classes. We then construct a semi-Markov reward model based on workload and resource usage data collected from the UNIX operating system. We identify different workload states using statistical cluster analysis, estimate transition probabilities, and sojourn time distributions from the data. Corresponding to each resource, a reward function is then defined for the model based on the rate of resource depletion in each state. The model is then solved to obtain estimated times to exhaustion for each resource. The result from the semi-Markov reward model are then fed into a higher-level availability model that accounts for failure followed by reactive recovery, as well as proactive recovery. This comprehensive model is then used to derive optimal rejuvenation schedules that maximize availability or minimize downtime cost.     

Trabecular scaffolds created using micro CT guided fused deposition modeling

Free form fabrication and high resolution imaging techniques enable the creation of biomimetic tissue engineering scaffolds. A 3D CAD model of canine trabecular bone was produced via micro CT and exported to a fused deposition modeler, to produce polybutylene terephthalate (PBT) trabeculated scaffolds and four other scaffold groups of varying pore structures. The five scaffold groups were divided into subgroups (n=6) and compression tested at two load rates (49 N/s and 294 N/s). Two groups were soaked in a 25 °C saline solution for 7 days before compression testing. Micro CT was used to compare porosity, connectivity density, and trabecular separation of each scaffold type to a canine trabecular bone sample. At 49 N/s the dry trabecular scaffolds had a compressive stiffness of 4.94±1.19 MPa, similar to the simple linear small pore scaffolds and significantly more stiff (p<0.05) than either of the complex interconnected pore scaffolds. At 294 N/s, the compressive stiffness values for all five groups roughly doubled. Soaking in saline had an insignificant effect on stiffness. The trabecular scaffolds matched bone samples in porosity; however, achieving physiologic connectivity density and trabecular separation will require further refining of scaffold processing.     

Synthesis and photoluminescence properties of Yb doped Ba5(PO4)3Cl phosphor for white light-emitting diodes

Yb²⁺ ion doped Ba₅(PO₄)₃Cl phosphor was synthesized by solid state reaction. Four distinct absorption bands were observed in the Ultraviolet (UV) light region due to the electronic transitions of Yb²⁺ ion from ¹S₀ ground state to ²F_5/2(t_2g), ²F_5/2(e_g), ²F_7/2(t_2g), and ²F_7/2(e_g) excited states. The main emission wavelength of the phosphor was around 630 nm. The optimized Yb²⁺ ion concentration was 0.2 mol% (λ_exc. = 400 nm). The calculated critical distance was about 8.729 Å and the concentration quenching was observed above 0.2 mol% due to the electric dipole–dipole interaction.     

Electrochemically assisted photocatalytic degradation of methyl orange using anodized titanium dioxide nanotubes

The TiO₂ nanotubes have demonstrated potential in the photoelectrocatalytic degradation of methyl orange dye (MO). TiO₂ nanotubes were prepared using anodization of titanium foils in phosphoric acid (PA) and ethylene glycol (EG) by mechanical stirring and ultrasonic method. The TiO₂ nanotubes prepared in EG under ultrasound followed by annealing in nitrogen atmosphere showed higher activity towards dye degradation as compared to the stirring method. Dye degradation shows improved activity under an external bias compared to degradation performed in the absence of an external bias. An increase in the external bias from +0.0 to +0.1 V versus calomel electrode (SCE) is sufficient to improve the degradation rates of MO from 22% to 57% within the first 10 min. At +0.1 V, a complete degradation of 40 μM MO is observed within 30 min. The addition of oxidants such as oxygen and hydrogen peroxide demonstrate improvement in the MO degradation.     

Performance investigation of heat pipe using aqueous solution of n-Pentanol with different inclinations

The orientation of the heat pipe plays the significant role in its performance. In specific orientations, the performance of the heat pipe is directly related to the wick structure. In conventional heat pipe, the working fluid is used a negative surface-tension gradient with temperature. It is an unfavorable one and it decreases the heat transport between the evaporator section and the condenser section. An Aqueous solution of n-Pentanol having a positive surface tension gradient with temperature is suggested as a working medium for heat pipe to improve the performance of capillary limit and operating stability. The objective of this paper is to perform a comparative study of heat pipe performance using the aqueous solution of n-Pentanol with water at various inclinations. The results are presented to demonstrate the merits and suitability of the aqueous solution of n-Pentanol as a working fluid for heat pipe.     

碳纳米管增强的陶瓷基复合材料

利用聚合物前驱体热裂解工艺制备了碳纳米管增强的陶瓷基复合材料.制备了含1.3%和6.4%(体积分数)碳纳米管的硅碳氮复合材料.SEM和HRTEM微观结构表明碳纳米管被均匀地分布在陶瓷基体中.采用纳米压痕测量了材料的力学性能,结果表明碳纳米管增强陶瓷复合材料的力学性能明显提高.