Null shift and beam squint in circularly polarized offset-reflector antenna

A formula for the null shift of the difference mode pattern of an offset-reflector antenna is derived. It is shown that this null shift and the beam squint of the sum mode pattern have different values. Such a phenomenon must be considered in the design of a two-channel tracking system.     

Solutions and properties of multi-stage stackelberg games

The inducible region concept is used to solve multistage, deterministic Stackelberg games, and to study properties of the solutions. We first delineate the inducible region by using a process similar to dynamic programming. A desired outcome is then selected from the region. To construct a Stackelberg strategy, we move forwards in time to cover various contingent situations. This approach gives a distinct picture about the nature of the problem. In particular, two aspects of the principle of the optimality are discussed. A design procedure is presented to construct a relatively robust Stackelberg strategy. The issue of credibility is also addressed.     

Carboxyfullerenes as neuroprotective agents

Two regioisomers with C3 or D3 symmetry of water-soluble carboxylic acid C60 derivatives, containing three malonic acid groups per molecule, were synthesized and found to be equipotent free radical scavengers in solution as assessed by EPR analysis. Both compounds also inhibited the excitotoxic death of cultured cortical neurons induced by exposure to N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), or oxygen-glucose deprivation, but the C3 regioisomer was more effective than the D3 regioisomer, possibly reflecting its polar nature and attendant greater ability to enter lipid membranes. At 100 microM, the C3 derivative fully blocked even rapidly triggered, NMDA receptor-mediated toxicity, a form of toxicity with limited sensitivity to all other classes of free radical scavengers we have tested. The C3 derivative also reduced apoptotic neuronal death induced by either serum deprivation or exposure to Abeta1-42 protein. Furthermore, continuous infusion of the C3 derivative in a transgenic mouse carrying the human mutant (G93A) superoxide dismutase gene responsible for a form of familial amyotrophic lateral sclerosis, delayed both death and functional deterioration. These data suggest that polar carboxylic acid C60 derivatives may have attractive therapeutic properties in several acute or chronic neurodegenerative diseases.     

Bacteremia and fungemia in patients with advanced human immunodeficiency virus (HIV) infection in Taiwan

To understand the etiology and clinical outcome of bacterial and fungal sepsis in patients with advanced human immunodeficiency virus (HIV) infection in Taiwan, we conducted a prospective study of nonmycobacterial bacteremia and fungemia in HIV-infected patients with fever who were admitted to a university hospital in Taiwan during a 42-month period. Of 210 patients, 41 (19.5%) had a total of 52 episodes of sepsis due to nonmycobacterial bacteria or fungi, or both (15.5% of 336 episodes of fever). All but one patient had acquired immunodeficiency syndrome (AIDS), and the mean CD4 lymphocyte count was 29/microL (range, 0-321/microL). A total of 57 pathogens (39 bacteria and 18 fungi) were isolated from blood; polymicrobial sepsis due to both bacteria and fungi occurred in four episodes. Nontyphoid Salmonella (NTS) was the most common cause of community-acquired bacteremia (24/30, 80%). Staphylococcus aureus bacteremia was diagnosed in three episodes while Streptococcus pneumoniae bacteremia was found in only one. Cryptococcus neoformans was the most common cause of fungemia and was responsible for 12 episodes, while fungemia due to Penicillium marneffei and Histoplasma capsulatum, two emerging fungi in Taiwan, were diagnosed in four cases and one case, respectively. Nine episodes, eight of bacteremia and one of candidemia, were nosocomial. The overall in-hospital mortality was 29%, and nosocomial sepsis was associated with a higher mortality rate (56%, p = 0.02). The mean duration of survival after recovery from initial sepsis was 426 days. We conclude that NTS bacteremia was the most common cause of sepsis in patients with advanced HIV infection in Taiwan and clinicians caring for such patients should watch for emerging fungal infections. Nosocomial sepsis was associated with a high mortality rate. The mean survival duration after recovery from sepsis of our patients was short.     

Redundant robot control using task based performance measures

The joint velocities required to move the end-effector of a redundant robot with a desired linear and angular velocity depend on its configuration. Similarly, the joint torques produced due to the force and moment at the end-effector also depend on its configuration. When the robot is near a singular configuration, the joint velocities required to attain the end-effector velocity in certain directions are extremely high. Similarly, in some configurations the joint torque produced at certain joints may be high for a relatively small magnitude of external force. An infinite number of trajectories in the joint space can be used to achieve a desired end-effector trajectory for redundant robots. However, a joint trajectory resulting in robot configurations requiring lower joint velocities or joint torques is desired. This may be achieved through a proper utilization of redundancy. Local performance measures for redundant robots are defined in this article as indicators of their ability to follow a desired end-effector trajectory and their ability to apply desired forces at the end-effector. Thus, these performance measures depend on the task to be performed. Control algorithms which can be efficiently applied to redundant robots to improve these performance measures are presented. These control algorithms are based on the gradient projection method. Gradients of the performance measures used in the control schemes result in simple symbolic expressions for “real world” robots'. Feasibility and effectiveness of these control schemes is demonstrated through the simulation of a seven-degree-of-freedom redundant robot derived from the PUMA geometry.     

Proton MR spectroscopy after acute central nervous system injury: outcome prediction in neonates, infants, and children

PURPOSE: To evaluate the usefulness of proton magnetic resonance (MR) spectroscopy in predicting 6-12-month neurologic outcome in children after central nervous system injuries. MATERIALS AND METHODS: Localized single-voxel, 20-msec-echo-time MR spectra (including N-acetylaspartate [NAA], choline [Ch], creatine and phosphocreatine [Cr]) were obtained in the occipital gray matter in 82 patients and 24 control patients. Patient age groups were defined as neonates (< or = 1 month [n = 23]), infants (1-18 months [n = 31]), and children (> or = 18 months [n = 28]). Metabolite ratios and the presence of lactate were determined. Linear discriminant analysis-with admission clinical data, proton MR spectroscopy findings, and MR imaging score (three-point scale based on severity of structural neuroimaging changes)-was performed to help predict outcome in each patient. Findings were then compared with the actual 6-12-month outcome assigned by a pediatric neurologist. RESULTS: Outcome on the basis of proton MR spectroscopy findings combined with clinical data and MR imaging score was predicted correctly in 91% of neonates and in 100% of infants and children. Outcome on the basis of clinical data and MR imaging score alone was 83% in neonates, 84% in infants, and 93% in children. The presence of lactate was significantly higher in patients with poor outcome than in patients with good-moderate outcomes in all three age groups (neonates, 38% vs 5%; infants, 87% vs 5%; children, 64% vs 10% [chi 2 test, P < .02]). In children with poor outcomes, NAA/Cr ratios were significantly lower in infants (P = .006) and children (P < .001), and NAA/Ch ratios were significantly lower in infants (P = .001) and neonates (P = .05). CONCLUSION: Findings at proton MR spectroscopy helped predict long-term neurologic outcomes in children after central nervous system injury.     

Correlating the Mechanical Properties of a Continuous Fiber-Reinforced Ceramic-Matrix Composite to the Sliding Resistance of the Fibers

The sliding resistance of NICALON fibers (SiC) in a lithium aluminosilicate (LAS III) glass-ceramic matrix has been correlated with the mechanical properties of the composite. Push-down measurements of the sliding resistance for individual fibers show an order of magnitude increase when the ceramic composite is annealed in air for 4 h at 800°C. Such increases are correlated with a loss of toughness, a reduction in the ultimate strength, and an increase in the matrix cracking stress of the composite, as measured using tension tests and bend tests of bulk samples.     

Nested partitions for global optimization in nonlinear model predictive control

In Nonlinear Model Predictive Control (NMPC), the optimization problem may be nonconvex. It is important to find a global solution since a local solution may not be able to operate the process at desired setpoints. Also the solution must be available before the control input has to be applied to the process. In this paper, a stochastic algorithm called the Nested Partitions Algorithm (NPA) is used for global optimization. The NPA divides the search space into smaller regions and either concentrates search in one of these regions called the most promising region or backtracks to a larger region in the search space based on a performance index. To adapt the NPA to solve dynamic NMPC with continuous variables, a new partitioning scheme is developed that focuses on the first few control moves in the control horizon. The expected number of iterations taken by the NPA is presented. Convergence speed is improved by reducing the size of the starting most promising region based on a good starting point. The discrete sampling nature of the NPA may cause difficulty in finding the global solution in a continuous space. A gradient-based search is used with the NPA to overcome this difficulty. The solution quality is assessed in terms of the error from the actual global minimum. The algorithm is shown to give a feasible solution that provides asymptotic stability. Case studies are used to show the algorithm performance in terms of tracking setpoints, cost, solution quality and convergence time.     

From Overcrowded Polycyclic Aromatic Enes to Semifullerenes

Bi-9H-fluoren-9-ylidene (2) and bi-4H-cyclopenta[def]phenanthren-4-ylidene (5) are potential starting materials for the preparation of bowl-shaped fragments of fullerenes. Semiempirical MNDO-PM3 calculations of C₂₆H_n and C₃₀H_n (n = 12, 14, 16) species 2-12 are used to analyze energetic effects on the dehydrocyclization and isomerization reactions of these species. Oxidative photocyclizations on Z-2,2′-bridged derivatives of 2 and 5 are briefly outlined.     

Warranting Quality of Steel Bridge Coating

Civil infrastructure systems, particularly the highway and bridge systems, have become a focal point of attention both nationally and among researchers. Because many of the nation's bridges have been identified by the Federal Highway Administration as deficient, more attention needs to be given to the quality of bridge coatings, which act as inhibitors of bridge deterioration. This paper represents an extended study by the authors to establish and implement contract warranties for steel bridge coatings. First, the earlier activities in warranting the quality of bridge coatings are reviewed. Next, the writers focus on the basic categories of a steel bridge coating warranty, especially the warranty period and defects for which the contractor is held responsible. The paper further illustrates the functioning of a hybrid model for nondestructive quality assessment of steel bridge coatings. The model provides objective and quantitative analysis to improve the coating quality assessment process. This approach prevents potential conflicts that might arise between the state Department of Transportation and the bridge-coating contractors during the warranty implementation.