Traditional intumescent coatings are widely used as passive fire-protective coatings for steel structures as they are capable of expanding in the range of 20–50 times the original thickness thereby providing excellent insulation. However, the fragile nature of such residue and susceptibility to thermo-oxidation given their carbonaceous nature are key problematic issues. The concept of in situ ceramization is explored in this work as a means to form inorganic cohesive char with improved rigidity and thermo-oxidative stability. Coating samples were prepared by incorporating ammonium polyphosphate, talc, Mg(OH)2, and polydimethylsiloxane as additives into acrylic resin at different weight fractions. Thermal analysis and x-ray diffraction have confirmed the reactions between the additives to form various crystalline magnesium phosphate phases, and to a small extent, silicon phosphate, thereby ensuring the thermo-oxidative stability of the residue. This is reiterated by the fire performance tests (by exposing the coatings to a temperature profile in a furnace similar to ISO 834 fire curve). Despite the advantages of rigid char and its thermo-oxidative stability as a result of formation of inorganic phosphates, the lack of swelling has resulted in relatively poor insulation capabilities of the char, and subsequently, compromised the fire protection times (that are in the range of 45–55 min). However, pyrolysis flow combustion calorimeter results of the coatings are promising and have shown a significant drop of up to 70% in the peak of heat release rate values as compared to neat resin. 相似文献
In General, Mobile Ad-Hoc Network (MANET) has limited energy resources, and it cannot recharge itself. This research goal focuses on building a power management scheme that saves energy in the MANET. Due to power instability, there is a chance that cluster heads fail and function incorrectly in cluster-based routing. As a result, instability occurs with the cluster heads while collecting data and communicating with others effectively. This work focuses on detecting the unstable cluster heads, which are replaced by other nodes implementing the envisaged self-configurable cluster mechanism. A self-configurable cluster mechanism with a k-means protocol approach is proposed to designate cluster heads effectively. The proposed k-means procedure is based on periodic irregular cluster head rotations or altering the number of clusters. We also propose a trust management mechanism in this research to detect and avoid MANET vulnerabilities. Because of the continuously changing topology and limited resources (power, bandwidth, computing), the trust management algorithm should only use local data. Consequently, compared to traditional protocols, the proposed approach with the k-means procedure and its experimental results show lower power usage and provide an optimal system for trust management.
We present polylogarithmic approximations for the R|prec|Cmax and R|prec|∑jwjCj problems, when the precedence constraints are “treelike”—i.e., when the undirected graph underlying the precedences is a
forest. These are the first non-trivial generalizations of the job shop scheduling problem to scheduling with precedence constraints
that are not just chains. These are also the first non-trivial results for the weighted completion time objective on unrelated
machines with precedence constraints of any kind. We obtain improved bounds for the weighted completion time and flow time for the case of chains with restricted assignment—this
generalizes the job shop problem to these objective functions. We use the same lower bound of “congestion + dilation”, as
in other job shop scheduling approaches (e.g. Shmoys, Stein and Wein, SIAM J. Comput. 23, 617–632, 1994). The first step in our algorithm for the R|prec|Cmax problem with treelike precedences involves using the algorithm of Lenstra, Shmoys and Tardos to obtain a processor assignment
with the congestion + dilation value within a constant factor of the optimal. We then show how to generalize the random-delays
technique of Leighton, Maggs and Rao to the case of trees. For the special case of chains, we show a dependent rounding technique
which leads to a bicriteria approximation algorithm for minimizing the flow time, a notoriously hard objective function.
A preliminary version of this paper appeared in the Proc. International Workshop on Approximation Algorithms for Combinatorial Optimization Problems (APPROX), pages 146–157, 2005.
V.S. Anil Kumar supported in part by NSF Award CNS-0626964. Part of this work was done while at the Los Alamos National Laboratory,
and supported in part by the Department of Energy under Contract W-7405-ENG-36.
M.V. Marathe supported in part by NSF Award CNS-0626964. Part of this work was done while at the Los Alamos National Laboratory,
and supported in part by the Department of Energy under Contract W-7405-ENG-36.
Part of this work by S. Parthasarathy was done while at the Department of Computer Science, University of Maryland, College
Park, MD 20742, and in part while visiting the Los Alamos National Laboratory. Research supported in part by NSF Award CCR-0208005
and NSF ITR Award CNS-0426683.
Research of A. Srinivasan supported in part by NSF Award CCR-0208005, NSF ITR Award CNS-0426683, and NSF Award CNS-0626636. 相似文献
A new elegant and simple algorithm for mutual exclusion of N processes is proposed. It only requires shared variables in a memory model where shared variables need not be accessed atomically.
We prove mutual exclusion by reformulating the algorithm as a transition system (automaton), and applying simulation of automata.
The proof has been verified with the higher-order interactive theorem prover PVS. Under an additional atomicity assumption,
the algorithm is starvation free, and we conjecture that no competing process is passed by any other process more than once.
This conjecture was verified by model checking for systems with at most five processes. 相似文献
A simple mutual exclusion algorithm is presented that only uses nonatomic shared variables of bounded size, and that satisfies
bounded overtaking. When the shared variables behave atomically, it has the first-come-first-served property (FCFS). Nonatomic
access makes information vulnerable. The effects of this can be mitigated by minimizing the information and by spreading it
over more variables. The design approach adopted here begins with such mitigating efforts. These resulted in an algorithm
with a proof of correctness, first for atomic variables. This proof is then used as a blueprint for the simultaneous development
of the algorithm for nonatomic variables and its proof. Mutual exclusion is proved by means of invariants. Bounded overtaking
and liveness under weak fairness are proved with invariants and variant functions. Liveness under weak fairness is formalized
and proved in a set-theoretic version of temporal logic. All these assertions are verified with the proof assistant PVS. We
heavily rely on the possibility offered by a proof assistant like PVS to reuse proofs developed for one context in a different
context. 相似文献
Many web databases can be seen as providing partial and overlapping information about entities in the world. To answer queries effectively, we need to integrate the information about the individual entities that are fragmented over multiple sources. At first blush this is just the inverse of traditional database normalization problem—rather than go from a universal relation to normalized tables, we want to reconstruct the universal relation given the tables (sources). The standard way of reconstructing the entities will involve joining the tables. Unfortunately, because of the autonomous and decentralized way in which the sources are populated, they often do not have Primary Key–Foreign Key relations. While tables may share attributes, naive joins over these shared attributes can result in reconstruction of many spurious entities thus seriously compromising precision. Our system, SmartInt is aimed at addressing the problem of data integration in such scenarios. Given a query, our system uses the Approximate Functional Dependencies (AFDs) to piece together a tree of relevant tables to answer it. The result tuples produced by our system are able to strike a favorable balance between precision and recall. 相似文献
The primary aim of this paper is to provide an insight on the effect of the location of organoclay on the micro- and nano-scale deformation processes in melt-compounded nylon 66/organoclay/SEBS-g-MA ternary nanocomposites prepared by different blending sequences. In addition, the deformation processes of the ternary nanocomposites were compared to the binary nanocomposites (nylon 66/organoclay and nylon 66/SEBS-g-MA) and neat nylon 66. The incorporation of SEBS-g-MA particles toughened nylon 66 markedly; but the flexural modulus and strength were both reduced. Conversely, the use of organoclay increased the modulus but decreased the fracture toughness of nylon 66. Nylon 66/SEBS-g-MA/organoclay ternary nanocomposites exhibited balanced elastic stiffness and toughness. Stress-whitening studies of the fracture surfaces in terms of gray level were also performed and an attempt was made to correlate the optical reflectivity characteristics with fracture toughness. It was concluded that the capability of SEBS-g-MA particles to cavitate was decreased by the presence of organoclay in the SEBS-g-MA phase, resulting in reduced toughening efficiency. The best micro-structure for toughness and other mechanical properties is thus to maximize the amount of exfoliated organoclay in the nylon 66 matrix rather than to have it embedded in the finely dispersed SEBS-g-MA particles. 相似文献
Voting among different agents is a powerful tool in problem solving, and it has been widely applied to improve the performance in finding the correct answer to complex problems. We present a novel benefit of voting, that has not been observed before: we can use the voting patterns to assess the performance of a team and predict their final outcome. This prediction can be executed at any moment during problem-solving and it is completely domain independent. Hence, it can be used to identify when a team is failing, allowing an operator to take remedial procedures (such as changing team members, the voting rule, or increasing the allocation of resources). We present three main theoretical results: (1) we show a theoretical explanation of why our prediction method works; (2) contrary to what would be expected based on a simpler explanation using classical voting models, we show that we can make accurate predictions irrespective of the strength (i.e., performance) of the teams, and that in fact, the prediction can work better for diverse teams composed of different agents than uniform teams made of copies of the best agent; (3) we show that the quality of our prediction increases with the size of the action space. We perform extensive experimentation in two different domains: Computer Go and Ensemble Learning. In Computer Go, we obtain high quality predictions about the final outcome of games. We analyze the prediction accuracy for three different teams with different levels of diversity and strength, and show that the prediction works significantly better for a diverse team. Additionally, we show that our method still works well when trained with games against one adversary, but tested with games against another, showing the generality of the learned functions. Moreover, we evaluate four different board sizes, and experimentally confirm better predictions in larger board sizes. We analyze in detail the learned prediction functions, and how they change according to each team and action space size. In order to show that our method is domain independent, we also present results in Ensemble Learning, where we make online predictions about the performance of a team of classifiers, while they are voting to classify sets of items. We study a set of classical classification algorithms from machine learning, in a data-set of hand-written digits, and we are able to make high-quality predictions about the final performance of two different teams. Since our approach is domain independent, it can be easily applied to a variety of other domains. 相似文献