On the performance of Dijkstra’s third self-stabilizing algorithm for mutual exclusion and related algorithms

In Dijkstra (Commun ACM 17(11):643–644, 1974) introduced the notion of self-stabilizing algorithms and presented three such algorithms for the problem of mutual exclusion on a ring of n processors. The third algorithm is the most interesting of these three but is rather non intuitive. In Dijkstra (Distrib Comput 1:5–6, 1986) a proof of its correctness was presented, but the question of determining its worst case complexity—that is, providing an upper bound on the number of moves of this algorithm until it stabilizes—remained open. In this paper we solve this question and prove an upper bound of 3\frac1318 n² + O(n){3\frac{13}{18} n^2 + O(n)} for the complexity of this algorithm. We also show a lower bound of 1\frac56 n² - O(n){1\frac{5}{6} n^2 - O(n)} for the worst case complexity. For computing the upper bound, we use two techniques: potential functions and amortized analysis. We also present a new-three state self-stabilizing algorithm for mutual exclusion and show a tight bound of \frac56 n² + O(n){\frac{5}{6} n^2 + O(n)} for the worst case complexity of this algorithm. In Beauquier and Debas (Proceedings of the second workshop on self-stabilizing systems, pp 17.1–17.13, 1995) presented a similar three-state algorithm, with an upper bound of 5\frac34n²+O(n){5\frac{3}{4}n^2+O(n)} and a lower bound of \frac18n²-O(n){\frac{1}{8}n^2-O(n)} for its stabilization time. For this algorithm we prove an upper bound of 1\frac12n² + O(n){1\frac{1}{2}n^2 + O(n)} and show a lower bound of n ²−O(n). As far as the worst case performance is considered, the algorithm in Beauquier and Debas (Proceedings of the second workshop on self-stabilizing systems, pp 17.1–17.13, 1995) is better than the one in Dijkstra (Commun ACM 17(11):643–644, 1974) and our algorithm is better than both.     

On the relation between common and distinctive feature models.

Investigates the relationship between the classificatory structure of objects and the dissimilarity between them by discussing the common and distinctive features models. Data indicate that given a feature structure, the 2 models produce different orderings of dissimilarity between objects. However, if one model holds in some feature structure, then the other model also holds, albeit in a different feature structure. It is suggested that the choice of a model and the specification of the feature structure are not always determined by the observed dissimilarity. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contingent weighting in judgment and choice.

Preference can be inferred from direct choice between options or from a matching procedure in which the decision maker adjusts one option to match another. Studies of preferences between two-dimensional options (e.g., public policies, job applicants, benefit plans) show that the more prominent dimension looms larger in choice than in matching. Thus, choice is more lexicographic than matching. This finding is viewed as an instance of a general principle of compatibility: The weighting of inputs is enhanced by their compatibility with the output. To account for such effects, we develop a hierarchy of models in which the trade-off between attributes is contingent on the nature of the response. The simplest theory of this type, called the contingent weighting model, is applied to the analysis of various compatibility effects, including the choice-matching discrepancy and the preference-reversal phenomenon. These results raise both conceptual and practical questions concerning the nature, the meaning and the assessment of preference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trichobezoars

Trichobezoars are accumulations of hair casts in the stomach associated with trichophagia. The typical patient is an adolescent female who presents with alopecia and an upper abdominal mass which on moving can cause intermittent gastric outlet obstruction. Only a minority of patients have severe psychiatric disorders. When hair strands extend from the main mass in the stomach, all along the small bowel and reaching the cecum, the condition is termed the Rapunzel syndrome. In about 5% of patients there are separate hair masses in the stomach. The clinical presentation includes abdominal pain, loss of appetite, weight-loss, vomiting, loose stools, pancreatitis, jaundice, anemia and hypoalbuminemia. These signs and symptoms raise the suspicion of malignancy. Complications of bezoars include ulcers, perforation of the bowel, obstruction and intussusception. Diagnosis can be established either by barium swallow or by CT scan. Ultrasound might suggest the diagnosis, but sonographic features are definitely not pathognomonic. Treatment is surgical, as endoscopic removal is usually unsuccessful. We present 2 children in whom trichobezoars were found.     

Reaction-bonded B4C/SiC composites synthesized by microwave heating

The reaction-bonding technique was used to synthesize boron carbide (B₄C) - silicon carbide (SiC) composites by microwave heating. Preforms of porous B₄C were obtained by compaction followed or not by partial densification. Then, the material was infiltrated by molten silicon under a microwave heating. The influence of the thermal cycles (T: 1400-1500°C, t: 5-120 minutes) is low. The hardness of boron carbide is comparable to that of alumina (15-19 GPa) for a much lower density (≈2.5 g/cm³ for B₄C-based material instead of 3.95 g/cm³ for alumina). These properties make this composite, obtained by microwave heating, a good candidate for ballistic applications.     

Role of acetylcholine in negative patterning in turtles (Chrysemys picta).

Turtles were run on a negative patterning task involving 2 positive elements, a key with white stripes on a black background, and a solid red key, and a compound stimulus combining the 2 elements, white stripes on a red background. Injections of scopolamine, methylscopolamine, or saline were started at the same time that the compound stimulus was introduced, after the animals had been autoshaped to press the key for each of the elements. Scopolamine disrupted the learning of negative patterning, but methylscopolamine had no effect. In contrast, learning of a simple discrimination between the elements was not affected by scopolamine. These results show that muscarinic cholinergic receptors are involved in the learning of negative patterning in turtles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Crack identification by ‘arrival time’ using XFEM and a genetic algorithm

A computational framework is developed in which cracks in two‐dimensional structures are identified, in conjunction with non‐destructive testing of specimens. As opposed to a previous study by the authors, which was based on time‐harmonic excitation with a single frequency, here the transient response of the structure to a short‐duration signal is measured along part of the external boundary. Crack detection is performed using the solution of an inverse time‐dependent problem. It is shown that the arrival time of the input signal to the points of measurement is a good criterion for crack identification in the time domain. The inverse problem of identification is solved using a genetic algorithm, while each forward problem is solved by the time‐dependent extended finite element method (XFEM). The XFEM scheme is efficient in that it allows the use of a single regular mesh for a large number of forward time response problems with different crack geometries. Numerical examples involving a crack in a flat membrane are presented. Identification based on ‘arrival time’ is shown to perform better than that based on time‐harmonic response. Copyright © 2008 John Wiley & Sons, Ltd.     

四基色投影显示

我们采用多芯片HTPS屏结构,已开发出一种四基色前投式投影样机。这种投影机建立在对一种现行高端品牌产品的光学平台进行改进的基础之上。在KESHETTM芯片中,用ColorPeakTM算法,把标准720p输入信号转换成所需要的多基色输入信号,结果使色域和亮度都有了显著的提高。     

Surface properties of Ca,Ti-doped CeO2 and their influence on the reverse water-gas shift reaction

CeO₂-based materials can be found in a variety of catalytic processes, including the reverse water-gas shift (RWGS) reaction. Nevertheless, the interaction of molecular gases with the surfaces of such materials is still not clear. Recently, some progress was reported on the incorporation of neodymium (Nd) and calcium (Ca) into ceria and their effect on H₂O and CO₂ adsorption. Titanium (Ti), which has a much smaller ionic radius, has the ability to change the interaction landscape, both as a co-dopant to Ca and as a sole dopant in the CeO₂ system. In this study, the interactions of environmental gases (i.e., water vapor and CO₂) on the surface of Ti-doped CeO₂ and Ca,Ti co-doped CeO₂ were investigated. Ti addition to CeO₂ was shown to decrease water vapor uptake by up to 25% all while maintaining similar heats of adsorption. In the case of CO₂ adsorption, Ti addition to CeO₂ had lowered the uptake by more than 50% as well as lowering the heat of adsorption. Co-doping with Ti and Ca showed small decrease in H₂O uptake accompanied with increased heat of adsorption. For CO₂, the changes to the uptake and energetics were small and did not indicate a specific trend. The RWGS catalytic performance showed improvement by the addition of Ti in certain levels. The relationship between the doping, surface properties, gas-surface interactions, and catalytic performance is discussed.