Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment m...Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. Recommendations for abutment modeling are made.展开更多
An efficient authenticated key agreement protocol is proposed, which makesuse of bilinear pairings and self-certificd public keys. Its security is based on the securityassumptions of the bilinear Diff ie-Hellman probl...An efficient authenticated key agreement protocol is proposed, which makesuse of bilinear pairings and self-certificd public keys. Its security is based on the securityassumptions of the bilinear Diff ie-Hellman problem and the computational Diffie-Hellman problem.Users can choose their private keys independently. The public keys and identities of users can beverified implicitly when the session key being generating in a logically single step. A trusted KeyGeneration Center is no longer requiredas in the ID-based authenticated key agreement protocolsCompared with existing authenticated key agreement protocols from pairings, the. new proposedprotocol is more efficient and secure.展开更多
In today＇s globalized digital world, networkbased, mobile, and interactive collaborations have enabled work platforms of personal computers to cross multiple geographical boundaries. The new requirements of privacy-p...In today＇s globalized digital world, networkbased, mobile, and interactive collaborations have enabled work platforms of personal computers to cross multiple geographical boundaries. The new requirements of privacy-preservation, sensitive information sharing, portability, remote attestation, and robust security create new problems in system design and implementation. There are critical demands for highly secure work platforms and security enhancing mechanisms for ensuring privacy protection, component integrity, sealed storage, and remote attestation of platforms. Trusted computing is a promising technology for enhancing the security of a platform using a trusted platform module （TPM）. TPM is a tamper-resistant microcontroller designed to provide robust security capabilities for computing platforms. It typically is affixed to the motherboard with a low pin count （LPC） bus. However, it limited in that TPM cannot be used directly in current common personal computers （PCs）, and TPM is not flexible and portable enough to be used in different platforms because of its interface with the PC and its certificate and key structure. For these reasons, we propose a portable trusted platform module （PTPM） scheme to build a trusted platform for the common PC based on a single cryptographic chip with a universal serial bus （USB） interface and extensible firmware interface （EFI）, by which platforms can get a similar degree of security protection in general-purpose systems. We show the structure of certificates and keys, which can bind to platforms via a PTPM and provide users with portability and flexibility in different platforms while still allowing the user and platform to be protected and attested. The implementation of prototype system is described in detail and the performance of the PTPM on cryptographic operations and time-costs of the system bootstrap are evaluated and analyzed. The results of experiments show that PTPM has high performances for supporting trusted computing and it can be used f展开更多
The aim of this study was to identify Aspergillus species isolated from maize kernels and soils of maize fields of Nandi County using macro and micro morphological characteristics. A cross sectional research design wa...The aim of this study was to identify Aspergillus species isolated from maize kernels and soils of maize fields of Nandi County using macro and micro morphological characteristics. A cross sectional research design was used in the study and purposive sampling was employed to determine districts of Nandi County and sub locations where sampling was done. This study was part of a larger project whose aim was to survey aflatoxin exposure in the maize value chain. Aspergillus species were isolated from maize and soil samples using quarter strength potato dextrose agar and modified Rose Bengal agar respectively. Pure cultures of the isolates were sub cultured and transferred onto differential media;malt extract agar, czapek yeast extract agar and czapek dox agar for species identification using macro morphological characteristics. Fungal slides were prepared from pure cultures on potato dextrose agar media after three days to identify micro morphological characteristics. Based on morphological characteristics, seven sections of Aspergillus namely: Flavi, Fumigati, Nigri, Circumdati, Clavati, Nidulantes and Candidi were identified. Aspergillus section Flavi was the most predominant with 57% followed by section Nigri with 27% from maize and 58% of section Flavi followed by 26% of section Nigri from the soil across the three locations. Aspergillus sections Nidulantes and Candidi were rare and only recovered from the soil samples of Kaptumo location. All the Aspergillius flavus that formed sclerotia both from the soils or maize kernels were of the L strains. In conclusion Aspergillus section Flavi was most frequent during the isolation process and dominated with Aspergillus flavus from both the maize and soil. Morphological characteristics remain the primary tool for detection and identification of Aspergillus species. The significance for high incidence of Aspergillus section Flavi is in regard to their aflatoxin production profiles that poses a health threat to the community and it is of public health concern. Morphologi展开更多
In the paper,the added tangential nonlinear springs are introduced to represent the effects of one-way and two-way shear keys. The added tangential stiffness coefficient is relative to the joint opening and the relati...In the paper,the added tangential nonlinear springs are introduced to represent the effects of one-way and two-way shear keys. The added tangential stiffness coefficient is relative to the joint opening and the relative tangential movement and determined numerically by using a refined model of shear keys.The user subroutine of nonlinear spring elements has been implemented into ABAQUS program.The seismic responses of an arch-gravity dam are mainly examined.It is shown by the results that a significant increase of about 17%-30%in joint opening can be observed for the dam with one-way shear keys;the two-way shear keys are beneficial to restrain the sliding displacement along both the radial and vertical directions,whereas the one-way shear keys mainly restrain the displacement along the radial direction;for the dam with shear keys,the maximum arch stress is increased,the cantilever stress is reduced,and the location of the maximum cantilever stress is also moved from the dam heel to the midheight of the cantilever.展开更多
A mobile ad hoc network (MANET) is a collection of mobile nodes that temporarily integrate with each other to form a network. Such a network does not require the existence of a typical network infrastructure. There is...A mobile ad hoc network (MANET) is a collection of mobile nodes that temporarily integrate with each other to form a network. Such a network does not require the existence of a typical network infrastructure. There is no central entity with the authority to administer the services and configurations of the network. How to secure a MANET is an active field of study for researchers. However, most of the research on the topic of securing the MANETs has focused on adapting security mechanisms that were meant for traditional wired networks. This adaptation has resulted in security solutions that do not work efficiently or that make assumptions that are not in line with the properties and characterizations of MANETs. In this paper, we propose the use of security mechanisms for MANETs that are designed based on the characteristics, functionalities, and goals of such networks. We aim to initiate a paradigm shift in securing MANETs, in which the focus should be on building security solutions specifically developed for MANETs, and not on adapting solutions that were meant for conventional wired networks. We revisit the basics and propose a simple encryption keys creation scheme that is based on the Diffie-Hellman key agreement protocol. The work presented in this paper should mark the initiation of a research agenda designed to build security primitives that are specifically for MANETs, along the lines of the new paradigm.展开更多
The open and broadcast nature of wireless channels leads to the inherent security problem of information leakage in wireless communication.We can utilize endogenous security functions to resolve this problem.The funda...The open and broadcast nature of wireless channels leads to the inherent security problem of information leakage in wireless communication.We can utilize endogenous security functions to resolve this problem.The fundamental solution is channel-based mechanisms,like physical layer secret keys.Unfortunately,current investigations have not fully exploited the randomness of wireless channels,making secret key rates not high.Consequently,user data can be encrypted by reducing the data rate to match the secret key rate.Based on the analysis of the endogenous wireless security principle,we proposed that the channel-based endogenous secret key rate can nearly match the maximum data rate in the fast-fading environments.After that,we validated the proposition in an instantiation system with multiple phase shift keying(MPSK)inputs from the perspectives of both theoretical analysis and simulation experiments.The results indicate that it is possible to accomplish the onetime pad without decreasing the data rate via channelbased endogenous keys.Besides,we can realize highspeed endogenously secure transmission by introducing independent channels in the domains of frequency,space,or time.The conclusions derived provide a new idea for wireless security and promote the application of the endogenous security theory.展开更多
基金Supported by:U.S.National Science Foundation to the Pacifi c Earthquake Engineering Research Center(PEER)Under Grant No.EEC-9701568
文摘Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. Recommendations for abutment modeling are made.
文摘An efficient authenticated key agreement protocol is proposed, which makesuse of bilinear pairings and self-certificd public keys. Its security is based on the securityassumptions of the bilinear Diff ie-Hellman problem and the computational Diffie-Hellman problem.Users can choose their private keys independently. The public keys and identities of users can beverified implicitly when the session key being generating in a logically single step. A trusted KeyGeneration Center is no longer requiredas in the ID-based authenticated key agreement protocolsCompared with existing authenticated key agreement protocols from pairings, the. new proposedprotocol is more efficient and secure.
文摘In today＇s globalized digital world, networkbased, mobile, and interactive collaborations have enabled work platforms of personal computers to cross multiple geographical boundaries. The new requirements of privacy-preservation, sensitive information sharing, portability, remote attestation, and robust security create new problems in system design and implementation. There are critical demands for highly secure work platforms and security enhancing mechanisms for ensuring privacy protection, component integrity, sealed storage, and remote attestation of platforms. Trusted computing is a promising technology for enhancing the security of a platform using a trusted platform module （TPM）. TPM is a tamper-resistant microcontroller designed to provide robust security capabilities for computing platforms. It typically is affixed to the motherboard with a low pin count （LPC） bus. However, it limited in that TPM cannot be used directly in current common personal computers （PCs）, and TPM is not flexible and portable enough to be used in different platforms because of its interface with the PC and its certificate and key structure. For these reasons, we propose a portable trusted platform module （PTPM） scheme to build a trusted platform for the common PC based on a single cryptographic chip with a universal serial bus （USB） interface and extensible firmware interface （EFI）, by which platforms can get a similar degree of security protection in general-purpose systems. We show the structure of certificates and keys, which can bind to platforms via a PTPM and provide users with portability and flexibility in different platforms while still allowing the user and platform to be protected and attested. The implementation of prototype system is described in detail and the performance of the PTPM on cryptographic operations and time-costs of the system bootstrap are evaluated and analyzed. The results of experiments show that PTPM has high performances for supporting trusted computing and it can be used f
文摘The aim of this study was to identify Aspergillus species isolated from maize kernels and soils of maize fields of Nandi County using macro and micro morphological characteristics. A cross sectional research design was used in the study and purposive sampling was employed to determine districts of Nandi County and sub locations where sampling was done. This study was part of a larger project whose aim was to survey aflatoxin exposure in the maize value chain. Aspergillus species were isolated from maize and soil samples using quarter strength potato dextrose agar and modified Rose Bengal agar respectively. Pure cultures of the isolates were sub cultured and transferred onto differential media;malt extract agar, czapek yeast extract agar and czapek dox agar for species identification using macro morphological characteristics. Fungal slides were prepared from pure cultures on potato dextrose agar media after three days to identify micro morphological characteristics. Based on morphological characteristics, seven sections of Aspergillus namely: Flavi, Fumigati, Nigri, Circumdati, Clavati, Nidulantes and Candidi were identified. Aspergillus section Flavi was the most predominant with 57% followed by section Nigri with 27% from maize and 58% of section Flavi followed by 26% of section Nigri from the soil across the three locations. Aspergillus sections Nidulantes and Candidi were rare and only recovered from the soil samples of Kaptumo location. All the Aspergillius flavus that formed sclerotia both from the soils or maize kernels were of the L strains. In conclusion Aspergillus section Flavi was most frequent during the isolation process and dominated with Aspergillus flavus from both the maize and soil. Morphological characteristics remain the primary tool for detection and identification of Aspergillus species. The significance for high incidence of Aspergillus section Flavi is in regard to their aflatoxin production profiles that poses a health threat to the community and it is of public health concern. Morphologi
基金supported by the National Natural Science Foundation of China(Grant Nos.50539030,50779011,11132003)the National Basic Research Program of China("973"Project)(Grant No.2007CB714104)the Innovative Project for Graduate Students of Jiangsu Province (Grant No.CX10B_202Z)
文摘In the paper,the added tangential nonlinear springs are introduced to represent the effects of one-way and two-way shear keys. The added tangential stiffness coefficient is relative to the joint opening and the relative tangential movement and determined numerically by using a refined model of shear keys.The user subroutine of nonlinear spring elements has been implemented into ABAQUS program.The seismic responses of an arch-gravity dam are mainly examined.It is shown by the results that a significant increase of about 17%-30%in joint opening can be observed for the dam with one-way shear keys;the two-way shear keys are beneficial to restrain the sliding displacement along both the radial and vertical directions,whereas the one-way shear keys mainly restrain the displacement along the radial direction;for the dam with shear keys,the maximum arch stress is increased,the cantilever stress is reduced,and the location of the maximum cantilever stress is also moved from the dam heel to the midheight of the cantilever.
文摘A mobile ad hoc network (MANET) is a collection of mobile nodes that temporarily integrate with each other to form a network. Such a network does not require the existence of a typical network infrastructure. There is no central entity with the authority to administer the services and configurations of the network. How to secure a MANET is an active field of study for researchers. However, most of the research on the topic of securing the MANETs has focused on adapting security mechanisms that were meant for traditional wired networks. This adaptation has resulted in security solutions that do not work efficiently or that make assumptions that are not in line with the properties and characterizations of MANETs. In this paper, we propose the use of security mechanisms for MANETs that are designed based on the characteristics, functionalities, and goals of such networks. We aim to initiate a paradigm shift in securing MANETs, in which the focus should be on building security solutions specifically developed for MANETs, and not on adapting solutions that were meant for conventional wired networks. We revisit the basics and propose a simple encryption keys creation scheme that is based on the Diffie-Hellman key agreement protocol. The work presented in this paper should mark the initiation of a research agenda designed to build security primitives that are specifically for MANETs, along the lines of the new paradigm.
基金funded by the National Key R&D Program of China under Grant 2017YFB0801903the National Natural Science Foundation of China under Grant 61871404,61701538,61521003Doctoral Fund of Ministry of Education of China under Grant 2019M663994。
文摘The open and broadcast nature of wireless channels leads to the inherent security problem of information leakage in wireless communication.We can utilize endogenous security functions to resolve this problem.The fundamental solution is channel-based mechanisms,like physical layer secret keys.Unfortunately,current investigations have not fully exploited the randomness of wireless channels,making secret key rates not high.Consequently,user data can be encrypted by reducing the data rate to match the secret key rate.Based on the analysis of the endogenous wireless security principle,we proposed that the channel-based endogenous secret key rate can nearly match the maximum data rate in the fast-fading environments.After that,we validated the proposition in an instantiation system with multiple phase shift keying(MPSK)inputs from the perspectives of both theoretical analysis and simulation experiments.The results indicate that it is possible to accomplish the onetime pad without decreasing the data rate via channelbased endogenous keys.Besides,we can realize highspeed endogenously secure transmission by introducing independent channels in the domains of frequency,space,or time.The conclusions derived provide a new idea for wireless security and promote the application of the endogenous security theory.
