147 research outputs found
Preparation and electrochemical characterization of Mn-Mo oxyanion pore-filled oxide layers on aerospace aluminum alloy
No full textSulphuric acid anodization process was carried out to grow oxide layers on unclad AA 2024 alloy. To enhance the corrosion resistance of plain oxide layer (PO), post treatments such as immersion in boiling water (HTO) and Mn-Mo oxyanions conversion bath (PMO) were carried out. Results obtained from electrochemical impedance spectroscopy (EIS) studies showed that the Mn-Mo infused oxide layer maintained the charge transfer resistance (Rct) value of about
106 Ωcm2 even after 7 days of immersion in 3.5% NaCl solution. Scanning vibrating electrode technique (SVET) results revealed that the plain and boiling water sealed oxide layers exhibited anodic corrosion activity immediately after the immersion into NaCl solution. Whereas, the distribution of anodic and cathodic sites over the surface of Mn-Mo infused oxide layer was insignificant even after 7 days of immersion. The EIS immersion study clearly revealed the self-healing behavior of the PMO in NaCl solution until 7 days of immersion. This corrosion inhibition mechanism was corroborated with the help of energy dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS) results
Multi-agent Coordination Based On Contract Net Protocol
No full textIn multi-agent system, agents need autonomy and collaboration to accomplish a complex task. Contract net protocol (CNP) is coordination mechanism often used in a multi-agent system. Due to the limitations inherent in the conventional CNP, this paper proposes a Norm-based CNP to improve the efficiency and effectiveness of the coordination processes in a multi-agent system. First, a three-dimensional taxonomy of norm is put forward in terms of the hierarchy, type and flexibility of norms. Then a coordination process guided by Norm-based CNP is developed under the taxonomy framework. The new coordination process consists of two principal stages and five sub-divided phases, providing a feasible solution for the optimization of the candidate selection. The merits of dividing the process into two stages are converging coordination process as soon as possible and controlling whole system effectively. In collaborative process, norms ensure to achieve global performance and agents pursuing maximal local performance to achieve satisfied result. Finally a case study is performed to illustrate the real application of the proposed approach.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000273591400089&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Computer Science, Artificial IntelligenceEngineering, Electrical & ElectronicEICPCI-S(ISTP)
FERMI BUBBLES INFLATED BY WINDS LAUNCHED FROM THE HOT ACCRETION FLOW IN SGR A*
No full textNatural Science Foundation of China [11103061, 11133005, 11121062, 11103059]; National Basic Research Program of China (973 Program) [2014CB845800]; Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences [XDB09000000]; China Scholarship Council [[2013] 3009]; NASA through Einstein Postdoctoral Fellowship by the Chandra X-ray Center [PF2-130102]; NASA [NAS8-03060]A pair of giant gamma-ray Bubbles has been revealed by Fermi-LAT. In this paper we investigate their formation mechanism. Observations have indicated that the activity of the supermassive black hole located at the Galactic center, Sgr A*, was much stronger than at the present time. Specifically, one possibility is that while Sgr A* was also in the hot accretion regime, the accretion rate should be 10(3)-10(4) times higher during the past similar to 10(7) yr. On the other hand, recent magnetohydrodynamic numerical simulations of hot accretion flows have unambiguously shown the existence and obtained the properties of strong winds. Based on this knowledge, by performing three-dimensional hydrodynamical simulations, we show in this paper that the Fermi Bubbles could be inflated by winds launched from the "past" hot accretion flow in Sgr A*. In our model, the active phase of Sgr A* is required to last for about 10 million years and it was quenched no more than 0.2 million years ago. The central molecular zone (CMZ) is included and it collimates the wind orientation toward the Galactic poles. Viscosity suppresses the Rayleigh-Taylor and Kelvin-Helmholtz instabilities and results in the smoothness of the Bubbles edge. The main observational features of the Bubbles can be well explained. Specifically, the ROSAT X-ray features are interpreted by the shocked interstellar medium and the interaction region between the wind and CMZ gas. The thermal pressure and temperature obtained in our model are consistent with recent Suzaku observations
Comparison analysis for classification algorithm in data mining and the study of model use
No full text
Optimizing performance of workflow executions under authorization control
No full text“Business processes or workflows are often used to
model enterprise or scientific applications. It has
received considerable attention to automate workflow
executions on computing resources. However, many
workflow scenarios still involve human activities and
consist of a mixture of human tasks and computing
tasks.
Human involvement introduces security and
authorization concerns, requiring restrictions on who
is allowed to perform which tasks at what time. Role-
Based Access Control (RBAC) is a popular authorization
mechanism. In RBAC, the authorization concepts such as
roles and permissions are defined, and various
authorization constraints are supported, including
separation of duty, temporal constraints, etc. Under
RBAC, users are assigned to certain roles, while the
roles are associated with prescribed permissions.
When we assess resource capacities, or evaluate the
performance of workflow executions on supporting
platforms, it is often assumed that when a task is
allocated to a resource, the resource will accept the
task and start the execution once a processor becomes available. However, when the authorization policies
are taken into account,” this assumption may not be
true and the situation becomes more complex. For
example, when a task arrives, a valid and activated
role has to be assigned to a task before the task can
start execution. The deployed authorization
constraints may delay the workflow execution due to
the roles’ availability, or other restrictions on the
role assignments, which will consequently have
negative impact on application performance.
When the authorization constraints are present to
restrict the workflow executions, it entails new
research issues that have not been studied yet in
conventional workflow management. This thesis aims to
investigate these new research issues.
First, it is important to know whether a feasible
authorization solution can be found to enable the
executions of all tasks in a workflow, i.e., check the
feasibility of the deployed authorization constraints.
This thesis studies the issue of the feasibility
checking and models the feasibility checking problem
as a constraints satisfaction problem.
Second, it is useful to know when the performance of
workflow executions will not be affected by the given
authorization constraints. This thesis proposes the
methods to determine the time durations when the given
authorization constraints do not have impact.
Third, when the authorization constraints do have
the performance impact, how can we quantitatively
analyse and determine the impact? When there are multiple choices to assign the roles to the tasks,
will different choices lead to the different
performance impact? If so, can we find an optimal way
to conduct the task-role assignments so that the
performance impact is minimized? This thesis proposes
the method to analyze the delay caused by the
authorization constraints if the workflow arrives
beyond the non-impact time duration calculated above.
Through the analysis of the delay, we realize that the
authorization method, i.e., the method to select the
roles to assign to the tasks affects the length of the
delay caused by the authorization constraints. Based
on this finding, we propose an optimal authorization
method, called the Global Authorization Aware (GAA)
method.
Fourth, a key reason why authorization constraints
may have impact on performance is because the
authorization control directs the tasks to some
particular roles. Then how to determine the level of
workload directed to each role given a set of
authorization constraints? This thesis conducts the
theoretical analysis about how the authorization
constraints direct the workload to the roles, and
proposes the methods to calculate the arriving rate of
the requests directed to each role under the role,
temporal and cardinality constraints.
Finally, the amount of resources allocated to
support each individual role may have impact on the
execution performance of the workflows. Therefore, it
is desired to develop the strategies to determine the
adequate amount of resources when the authorization
control is present in the system. This thesis presents the methods to allocate the appropriate quantity for
resources, including both human resources and
computing resources. Different features of human
resources and computing resources are taken into
account. For human resources, the objective is to
maximize the performance subject to the budgets to
hire the human resources, while for computing
resources, the strategy aims to allocate adequate
amount of computing resources to meet the QoS
requirements
Multi-Step Prediction of TBM Tunneling Speed Based on Advanced Hybrid Model
No full textThe accurate prediction of tunneling speed in tunnel boring machine (TBM) construction is the basis for the timely adjustment of the operating parameters of TBM equipment to ensure safe and efficient tunneling. In this paper, a multi-step prediction model of TBM tunneling speed based on the EWT-ICEEMDAN-SSA-LSTM hybrid model is proposed. Firstly, four datasets were selected under different geological conditions, and the original data were preprocessed using the binary discriminant function and the 3σ principle; secondly, the preprocessed data were decomposed using the empirical wavelet variation (EWT) to obtain several subseries and residual series; then, Intrinsic Computing Expressive Empirical Mode Decomposition With Adaptive Noise (ICEEMDAN) was used to perform further decomposition on residual sequences. Finally, several subsequences were fed into a Long Short-Term Memory (LSTM) network optimized by the Sparrow Search Algorithm (SSA) for multi-step training and prediction, and the predicted results of each subsequence were added up to obtain the final result. A comparison with existing models showed that the performance of the prediction method proposed in this paper is superior to other models. Of the four datasets, the average accuracy from the first step prediction to the fifth step prediction reached 99.06%, 98.99%, 99.07%, and 99.03%, respectively, indicating that the proposed method has high multi-step prediction performance and generalization ability. In this sense, this paper provides a reference for other projects
Diversity and ecological distribution of endophytic fungi associated with medicinal plants
No full textGravitational Waves of Holographic QCD Phase Transition with Hyperscaling Violation
No full textIn this paper, we study the gravitational waves of holographic QCD phase transition with hyperscaling violation. We consider an Einstein–Maxwell Dilaton background and discuss the confinement–deconfinement phase transition between thermally charged AdS and AdS black holes. We find that hyperscaling violation reduces the phase transition temperature. In a further study, we discuss the effect of hyperscaling violation on the GW spectrum. We found that the hyperscaling violation exponent suppresses the peak frequency of the total GW spectrum. Moreover, the results of the GW spectrum may be detected by IPTA, SKA, BBO, and NANOGrav. We also find that the hyperscaling violation exponent suppresses the peak frequency of the bubble-collision spectrum h2Ωenv. Hyperscaling violation enhances the energy densities of the sound wave spectrum h2Ωsw and the MHD turbulence spectrum h2Ωturb. The total GW spectrum is dominated by the contribution of the bubble collision in runaway bubbles case
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