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91.
In this paper, we propose a new parallel clustering algorithm, named Parallel Bisecting k-means with Prediction (PBKP), for message-passing multiprocessor systems. Bisecting k-means tends to produce clusters of similar sizes, and according to our experiments, it produces clusters with smaller entropy
(i.e., purer clusters) than k-means does. Our PBKP algorithm fully exploits the data-parallelism of the bisecting k-means algorithm, and adopts a prediction step to balance the workloads of multiple processors to achieve a high speedup. We implemented PBKP on a cluster of Linux
workstations and analyzed its performance. Our experimental results show that the speedup of PBKP is linear with the number
of processors and the number of data points. Moreover, PBKP scales up better than the parallel k-means with respect to the dimension and the desired number of clusters.
This research was supported in part by AFRL/Wright Brothers Institute (WBI). 相似文献
92.
Managing Role-Based Access Control Policies for Grid Databases in OGSA-DAI Using CAS 总被引:2,自引:0,他引:2
In this paper, we present a role-based access control method for accessing databases through the Open Grid Services Architecture
– Data Access and Integration (OGSA-DAI) framework. OGSA-DAI is an efficient Grid-enabled middleware implementation of interfaces
and services to access and control data sources and sinks. However, in OGSA-DAI, access control causes substantial administration
overhead for resource providers in virtual organizations (VOs) because each of them has to manage a role-map file containing
authorization information for individual Grid users. To solve this problem, we used the Community Authorization Service (CAS)
provided by the Globus Toolkit to support the role-based access control (RBAC) within OGSA-DAI. CAS uses the Security Assertion
Markup Language (SAML). Our method shows that CAS can support a wide range of security policies using role-privileges, role
hierarchies, and constraints. The resource providers need to maintain only the mapping information from VO roles to local
database roles and the local policies in the role-map files, so that the number of entries in the role-map file is reduced
dramatically. Also, unnecessary authentication, mapping and connections can be avoided by denying invalid requests at the
VO level. Thus, our access control method provides increased manageability for a large number of users and reduces day-to-day
administration tasks of the resource providers, while they maintain the ultimate authority over their resources. Performance
analysis shows that our method adds very little overhead to the existing security infrastructure of OGSA-DAI. 相似文献
93.
The effect of nonlinearity of the failure criterion on the passive thrust on smooth and rough vertical retaining walls is studied theoretically. Limit analysis upper bound estimates based on block-type failure mechanisms are constructed. An alternative, a priori linearization, approach is discussed. It is shown that for smooth walls both approaches, as well as the Rankine-type slip line solution, yield similar results. For rough walls, however, the ambiguity in the a priori linearization makes it difficult to compare the results. This deficiency is absent in the limit analysis nonlinear solutions. 相似文献
94.
The motivation for this paper is to present an approach for rating the quality of the parameters in a computer-aided design model for use as optimization variables. Parametric Effectiveness is computed as the ratio of change in performance achieved by perturbing the parameters in the optimum way, to the change in performance that would be achieved by allowing the boundary of the model to move without the constraint on shape change enforced by the CAD parameterization. The approach is applied in this paper to optimization based on adjoint shape sensitivity analyses. The derivation of parametric effectiveness is presented for optimization both with and without the constraint of constant volume. In both cases, the movement of the boundary is normalized with respect to a small root mean squared movement of the boundary. The approach can be used to select an initial search direction in parameter space, or to select sets of model parameters which have the greatest ability to improve model performance. The approach is applied to a number of example 2D and 3D FEA and CFD problems. 相似文献
95.
Cotton fabrics were treated with Biopag, which does not have any functional groups that are reactive toward cellulose, using crosslinking agents or a binder, for the purpose of imparting a durable antimicrobial finish. In this respect, it was found that the crosslinking agents were more effective than the binder. It was confirmed by FT‐IR that the characteristic split peaks of Biopag were still seen even after repeated launderings. The crosslinking agents deteriorated the whiteness and tensile strength of the Biopag‐treated cotton fabrics, while the wrinkle recovery angles (WRAs) were significantly improved. The one‐step padding of Biopag and the crosslinking agent was found to be superior to the two‐step padding method in which Biopag padding was followed by padding of crosslinking agent in respect of WRA, whereas the whiteness and tensile strength were vice versa. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
96.
Low distortion speech enhancement 总被引:5,自引:0,他引:5
An innovative approach to speech enhancement is illustrated which minimises distortion to the underlying speech during the noise-reduction process. The key to this approach lies in the identification of whether the additive noise for a particular frequency component is constructive or destructive. Once this can be identified both multiplicative and subtractive filters can be derived using the minimum mean-square error criterion. The optimal combination of the proposed multiplicative and subtractive filter is also shown 相似文献
97.
The esterification reaction of acrylic acid (AA) with 1,4‐butanediol (BD) to produce 4‐hydroxybutyl acrylate (HBA) was carried out in a batch reactive distillation mode over the Amberlyst 15 catalyst. The reactive distillation was highly desirable to increase the reaction rate of BD and eventually to obtain the high purity of HBA because the unreacted BD was not easily separable to the produced HBA after the reaction. The reaction pressure below 760 mm Hg was used to remove the by‐product water from the reaction zone. The air‐bubbling operation was successfully applied to prevent the polymerization of reactants and products under the vacuum condition (400 ~ 760 mm Hg). The reaction rates were strongly dependent on the reaction pressure, especially, the reaction rate of BD disappearance. The increased reaction rate of BD by the reactive distillation enabled to produce a high purity of HBA. 相似文献
98.
Weon Yong Joo Soon Young Yoon Hwang Soo Lee 《Electronics letters》1999,35(19):1617-1618
Weighted interference cancellation is proposed to improve the post-decoding interference cancellation detector in a convolutionally coded CDMA system. A weight determination method is presented in which the estimated information bit error probability from the soft-output Viterbi algorithm is used. Simulation results show that the proposed scheme outperforms the previous post-decoding interference cancellation detector 相似文献
99.
100.
Xin Guo Hongbo Sun Tat Soon Yeo 《Geoscience and Remote Sensing, IEEE Transactions on》2008,46(7):1879-1891
The performance of high-frequency surface wave radar (HFSWR) is known to suffer from external environmental interference and noise, such as cochannel radio-frequency interference from other radiating source, ionospheric clutter, lightning impulsive noise, etc. This paper experimentally evaluates the interference cancellation performance of various adaptive beamforming schemes with respect to the aforementioned three types of interferences in an attempt to find the most promising adaptive cancellation scheme in practical HFSWR environment. 相似文献