Formation and stability of barium aluminate and cerate in NOx storage-reduction catalysts

The formation and stability of BaAl₂O₄ and BaCeO₃ in Pt-Ba/Al₂O₃ and Pt-Ba/CeO₂ based NO_x storage-reduction (NSR) catalysts has been investigated using kinetic measurements, X-ray diffraction, thermal analysis and X-ray absorption spectroscopy. In as-prepared state, the Ba-component in the NSR catalysts was made up of amorphous BaO and BaCO₃. The formation of BaAl₂O₄ started above 850 °C, whereas the formation of BaCeO₃ was already observed at 800 °C and was faster than that of BaAl₂O₄. The stability of BaAl₂O₄ and BaCeO₃ in various liquid and gaseous atmospheres was different. BaAl₂O₄ was rapidly hydrated at room temperature in the presence of water and transformed to Ba(NO₃)₂ and γ-alumina in the presence of HNO₃, whereas BaCeO₃ was decomposed to much lower extent under these conditions. Interestingly, BaCeO₃ was transformed to Ba(NO₃)₂/CeO₂ in the presence of NO₂/H₂O at 300–500 °C. Also, the presence of CO₂ led to decomposition of barium cerate, which has important consequences for the catalyst ageing under NO_x-storage conditions and can be exploited for regeneration of thermally aged NSR-catalysts.     

Role and distribution of different Ba-containing phases in supported Pt–Ba NSR catalysts

Pt–Ba/MeO (where MeO = Al₂O₃, CeO₂, SiO₂ and ZrO₂) NO _x storage-reduction catalysts with Ba-loading varying from 0 wt.% to 28 wt.% were investigated concerning stability of Ba phases and NO _x storage-reduction efficiency. For Pt–Ba/Al₂O₃ three different Ba-containing phases with different thermal stability are distinguished based on their interaction with the support. The relative concentration of these phases varies with the Ba-loading and NO _x storage tests indicated that the BaCO₃ phase decomposing between 400 °C and 800 °C (LT-BaCO₃) is the most efficient Ba containing phase for NO _x storage. Similar investigations of Pt–Ba catalysts supported on CeO₂, SiO₂ and ZrO₂ showed that the relative amount of LT-BaCO₃ phase depends also on the support material. NO _x storage measurements confirmed a correlation between the concentration of LT-BaCO₃ and NO _x storage efficiency. Basicity and textural properties of the support are identified as crucial parameters for efficient NO _x storage catalysts.     

Probabilistic resource allocation in heterogeneous distributed systems with random failures

The problem of finding efficient workload distribution techniques is becoming increasingly important today for heterogeneous distributed systems where the availability of compute nodes may change spontaneously over time. Resource-allocation policies designed for such systems should maximize the performance and, at the same time, be robust against failure and recovery of compute nodes. Such a policy, based on the concepts of the Derman–Lieberman–Ross theorem, is proposed in this work, and is applied to a simulated model of a dedicated system composed of a set of heterogeneous image processing servers. Assuming that each image results in a “reward” if its processing is completed before a certain deadline, the goal for the resource allocation policy is to maximize the expected cumulative reward. An extensive analysis was done to study the performance of the proposed policy and compare it with the performance of some existing policies adapted to this environment. Our experiments conducted for various types of task-machine heterogeneity illustrate the potential of our method for solving resource allocation problems in a broad spectrum of distributed systems that experience high failure rates.     

Generalized model of vibro-isolation systems with seated human body for single-axis transmission of vibration

A generalized model of vibration isolation systems with a human body in a seated position is developed. The system dynamics is modeled for a single-axis transmission of vibration, that is, longitudinal x, lateral y and vertical z, to limit whole-body vibration exposure. The developed model can be successfully employed to describe the propagation of vibration waves from the source to a vibrating object. The proposed mathematical model can be widely used to protect a human body against vibration.     

A Case of Aluminum Nitride Embrittlement of Heavy Wall Cast Steel

Weld cracking was observed in multiple heats of large-sized cast steel components. Fracture analysis, metallography, and mechanical testing indicated that the failure mechanism was aluminum nitride (AlN) embrittlement. Prevention of this type of embrittlement is achieved by controlling aluminum content, nitrogen content, and above all, cooling rate of the casting. A macro-etch procedure for evaluating large castings for AlN embrittlement has been available in ASTM A 703 for decades, and it was found to adequately predict embrittlement in this instance.     

Measurement of secondary colony formation after 5 weeks in long-term cultures in patients with myelodysplastic syndrome

Pancytopenia is a frequent manifestation of myelodysplastic syndromes (MDS). In the presence of an empty bone marrow, clinical distinction from aplastic anemia may be difficult. The hypoplastic marrow morphology seen in some cases of MDS raises questions about etiologic and pathophysiologic relationships between aplastic anemia and MDS. The goal of our study was to compare the degree of the hematopoietic failure in these diseases at the level of the most immature progenitor and stem cells that can be measured in vitro. In a systemic, prospective fashion, we have studied bone marrow (n = 45) and peripheral blood (n = 33) of patients with MDS for the number of long-term culture initiating cells (LTC-IC) in comparison to 17 normal controls and patients with new, untreated aplastic anemia (46 marrow; 62 blood samples). Due to the low numbers of cells available for the analysis, formal limiting dilution analysis could not be performed, instead secondary colony-forming cells (CFC) after 5 weeks of LTBMC were measured. As the number of these cells is proportional to the input number of LTC-IC, the number of secondary CFC per 10(6) mononuclear cells (MNC) initiating the LTBMC can be used as a measure of the content of immature stem cells in bone marrow and peripheral blood. The MDS group consisted of 34 RA, three RARS, eight RAEB and two RAEB-T patients with mean absolute neutrophil values of 1992, 1413, 1441, and 380 per mm3, respectively. The diagnosis was established based on bone marrow morphology and results of cytogenetic studies. In comparison to controls (147 +/- 38/10(6) MNC), significantly decreased numbers of bone marrow secondary CFC were found in MDS: in patients with RA and RARS, 21 +/- 7 secondary CFC per 10(6) bone marrow MNC (P < 0.001); patients with RAEB and RAEB-T: 39 +/- 12 CFC per 10(6) marrow MNC (P < 0.001). In all groups tested, the decrease in peripheral blood secondary CFC numbers was consistently less pronounced. In MDS patients with hypocellular bone marrow, secondary CFC were lower but not significantly different in comparison to MDS with hypercellular marrow (18 +/- 6 vs 35 +/- 11; NS; hypoplastic bone marrow also was not associated with significantly lower neutrophil counts). However, in 24% of patients with MDS, bone marrow secondary CFC were within the normal range, while in the aplastic anemia group only one of the patients showed secondary CFC number within normal range. Bone marrow and blood secondary CFC numbers in hypoplastic RA were significantly higher than those in severe aplastic anemia 919 +/- 5 in bone marrow, P < 0.01; 7 +/- 2 in blood, P < 0.05). This trend was even more pronounced in hypoplastic RA with chromosomal abnormalities. However, no significant differences were found between the secondary CFC numbers in hypoplastic RA and moderate aplastic anemia. We concluded that, although the deficiency in the stem cell compartment is less severe in MDS than in aplastic anemia, depletion of early hematopoietic cells is an essential part of the pathophysiology in both diseases.     

Repeatable generalized inverse control strategies for kinematicallyredundant manipulators

The issue of generating a repeatable control strategy which possesses the desirable physical properties of a particular generalized inverse is addressed. The technique described is fully general and only requires a knowledge of the associated mill space of the desired inverse. While an analytical representation of the null vector is desirable, ultimately the calculations are done numerically so that a numerical knowledge of the associated full vector is sufficient. This method first characterizes repeatable strategies using a set of orthonormal basis functions to describe the null space of these transformations. The optimal repeatable inverse is then obtained by projecting the null space of the desired generalized inverse onto each of these basis functions. The resulting inverse is guaranteed to be the closest repeatable inverse to the desired inverse, in an integral norm sense, from the set of all inverses spanned by the selected basis functions. This technique is illustrated for a planar, three-degree-of-freedom manipulator and a seven-degree-of-freedom spatial manipulator     

Analyzing unidentified locked-joint failures in kinematically redundant manipulators

Robots are frequently used for operations in hostile environments. The very nature of these environments, however, increases the likelihood of robot failures. Common failure-tolerance techniques rely on effective failure detection and identification. Since a failure may not always be successfully identified, or, even if identified, may not be identified soon enough, it becomes important to consider the behavior of manipulators with unidentified failures. This work investigates the behavior of robots experiencing unidentified locked-joint failures in a general class of tasks characterized by point-to-point motion. Based on the analysis, a procedure for workspace evaluation is developed that allows for the identification of regions in the manipulator's workspace in which tasks may be completed even with such failures. © 2005 Wiley Periodicals, Inc.     

Eigendecomposition of Images Correlated on $S^{1}$, $S^{2}$, and $SO(3)$ Using Spectral Theory

Eigendecomposition represents one computationally efficient approach for dealing with object detection and pose estimation, as well as other vision-based problems, and has been applied to sets of correlated images for this purpose. The major drawback in using eigendecomposition is the off line computational expense incurred by computing the desired subspace. This off line expense increases drastically as the number of correlated images becomes large (which is the case when doing fully general 3-D pose estimation). Previous work has shown that for data correlated on S ¹ , Fourier analysis can help reduce the computational burden of this off line expense. This paper presents a method for extending this technique to data correlated on S ² as well as SO(3) by sampling the sphere appropriately. An algorithm is then developed for reducing the off line computational burden associated with computing the eigenspace by exploiting the spectral information of this spherical data set using spherical harmonics and Wigner-D functions. Experimental results are presented to compare the proposed algorithm to the true eigendecomposition, as well as assess the computational savings.