Adsorption technology based on ethane‐selective materials is a promising alternative to energy‐intensive cryogenic distillation for separating ethane (C2H6) and ethylene (C2H4). We employed a pore ...engineering strategy to tune the pore environment of a metal–organic framework (MOF) through organic functional groups and boosted the C2H6/C2H4 separation of the MOF. Introduction of amino (−NH2) groups into Tb‐MOF‐76 not only decreased pore sizes but also facilitated multiple guest‐host interactions in confined pores. The NH2‐functionalized Tb‐MOF‐76(NH2) has increased C2H6 and C2H4 uptakes and C2H6/C2H4 selectivity. The results of experimental and simulated transient breakthroughs reveal that Tb‐MOF‐76(NH2) has significantly improved one‐step separation performance for C2H6/C2H4 mixtures with a high C2H4 (>99.95 %) productivity of 17.66 L kg−1 compared to 7.53 L kg−1 by Tb‐MOF‐76, resulting from the suitable pore confinement and accessible −NH2 groups on pore surfaces.
By virtue of a pore engineering strategy based on isoreticular chemistry, an amino‐functionalized metal–organic framework (MOF) with suitable pore confinement and more binding sites improved the ethane/ethylene separation performance compared to the parent MOF.
One‐step C2H4 purification from ternary C2H6/C2H4/C2H2 mixtures by a single adsorbent is of great industrial significance, but few adsorbents achieve this separation. Herein, we report a robust ...metal–organic framework (MOF) that possesses methyl‐decorated nonpolar pores and shows one‐step C2H4 purification (purity >99.9 %) from binary C2H6/C2H4 mixtures and ternary C2H6/C2H4/C2H2 mixtures. The methyl groups in pores provide a suitable pore environment to simultaneously enhance the adsorption capacity for C2H2 and C2H6 compared to C2H4. Simulations revealed the multiple interactions between C2H6 or C2H2 molecules and the pore wall, while the interactions with C2H4 molecules are weak and also unfavorable due to the repulsion from methyl groups in pores. The MOF displays high C2H6 and C2H2 uptakes and benchmark C2H6/C2H4 selectivity (2.2), surpassing all of the reported MOFs for one‐step C2H4 purification from ternary C2H6/C2H4/C2H2 mixtures.
The combination of nonpolar pore environment and accessible active sites in a metal–organic framework affords benchmark C2H6/C2H4 selectivity and realizes one‐step C2H4 purification from ternary C2H6/C2H4/C2H2 mixtures.
The authentication scheme is an important cryptographic mechanism, through which two communication parties could authenticate each other in the open network environment. To satisfy the requirement of ...practical applications, many authentication schemes using passwords and smart cards have been proposed. However, passwords might be divulged or forgotten, and smart cards might be shared, lost, or stolen. In contrast, biometric methods, such as fingerprints or iris scans, have no such drawbacks. Therefore, biometrics-based authentication schemes gain wide attention. In this paper, we propose a biometrics-based authentication scheme for multiserver environment using elliptic curve cryptography. To the best of our knowledge, the proposed scheme is the first truly three-factor authenticated scheme for multiserver environment. We also demonstrate the completeness of the proposed scheme using the Burrows-Abadi-Needham logic.
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•We demonstrate privacy breaches into two password authentication schemes for WSNs.•Public-key techniques are indispensible to achieve user untraceability.•Our principle is applicable ...to two-factor authentication for universal environments.•We discuss the viable solutions to practical realization of user anonymity.•Experimental timings of related public-key operations on small devices are reported.
Anonymity is among the important properties of two-factor authentication schemes for wireless sensor networks (WSNs) to preserve user privacy. Though impressive efforts have been devoted to designing schemes with user anonymity by only using lightweight symmetric-key primitives such as hash functions and block ciphers, to the best of our knowledge none has succeeded so far. In this work, we take an initial step to shed light on the rationale underlying this prominent issue. Firstly, we scrutinize two previously-thought sound schemes, namely Fan et al.’s scheme and Xue et al.’s scheme, and demonstrate the major challenges in designing a scheme with user anonymity.
Secondly, using these two foremost schemes as case studies and on the basis of the work of Halevi–Krawczyk (1999) 44 and Impagliazzo–Rudich (1989) 43, we put forward a general principle: Public-key techniques are intrinsically indispensable to construct a two-factor authentication scheme that can support user anonymity. Furthermore, we discuss the practical solutions to realize user anonymity. Remarkably, our principle can be applied to two-factor schemes for universal environments besides WSNs, such as the Internet, global mobility networks and mobile clouds. We believe that our work contributes to a better understanding of the inherent complexity in achieving user privacy, and will establish a groundwork for developing more secure and efficient privacy-preserving two-factor authentication schemes.
A novel strategy for the expedient construction of CF3‐embeded tertiary/quarternary carbon centers was developed by taking advantage of photoredox catalysis. Thanks to a key step of single‐electron ...oxidation, electron‐rich gem‐difluoroalkenes, which otherwise are essentially reluctant towards F‐nucleoplilic addition, now readily participate in this fluoroallylation reaction. Furthermore, this strategy provides an elegant example for the generation, as well as functionalization, of α‐CF3‐substituted benzylic radical intermediates using cheap and readily available starting materials.
Finding a gem: The fluoroallylation of gem‐difluoroalkenes with inexpensive Et3N⋅3 HF and readily available allylsulfone has been developed. The photoredox‐coupled fluoride nucleophilic addition process, combined with the radical allylation allows expedient access to a large collection of functionalized homoallylic trifluoromethane derivatives under mild visible‐light‐induced conditions at room temperature.
Dozens of two-factor authentication schemes have been proposed to secure real-time data access in industrial wireless sensor networks (WSNs). However, more often than not, the protocol designers ...advocate the merits of their scheme, but do not reveal (or unconsciously ignoring) the facets on which their scheme performs poorly. Such lack of an objective, comprehensive measurement leads to the unsatisfactory "break-fix-break-fix" cycle in this research area. In this paper, we make an attempt toward breaking this undesirable cycle by proposing a systematical evaluation framework for schemes to be assessed objectively, revisiting two foremost schemes proposed by Wu et al. (2017) and Srinivas et al. (2017) to reveal the challenges and difficulties in designing a sound scheme, and conducting a measurement of 44 representative schemes under our evaluation framework, thereby providing the missing evaluation for two-factor schemes in industrial WSNs. This work would help increase awareness of current measurement issues and improve the scientific process in our field.
Model-free control is an important and promising topic in control fields, which has attracted extensive attention in the past few years. In this paper, we aim to solve the model-free optimal tracking ...control problem of nonaffine nonlinear discrete-time systems. A critic-only Q-learning (CoQL) method is developed, which learns the optimal tracking control from real system data, and thus avoids solving the tracking Hamilton-Jacobi-Bellman equation. First, the Q-learning algorithm is proposed based on the augmented system, and its convergence is established. Using only one neural network for approximating the Q-function, the CoQL method is developed to implement the Q-learning algorithm. Furthermore, the convergence of the CoQL method is proved with the consideration of neural network approximation error. With the convergent Q-function obtained from the CoQL method, the adaptive optimal tracking control is designed based on the gradient descent scheme. Finally, the effectiveness of the developed CoQL method is demonstrated through simulation studies. The developed CoQL method learns with off-policy data and implements with a critic-only structure, thus it is easy to realize and overcome the inadequate exploration problem.
Zipf's Law in Passwords Wang, Ding; Cheng, Haibo; Wang, Ping ...
IEEE transactions on information forensics and security,
2017-Nov., 2017-11-00, Letnik:
12, Številka:
11
Journal Article
Recenzirano
Despite three decades of intensive research efforts, it remains an open question as to what is the underlying distribution of user-generated passwords. In this paper, we make a substantial step ...forward toward understanding this foundational question. By introducing a number of computational statistical techniques and based on 14 large-scale data sets, which consist of 113.3 million real-world passwords, we, for the first time, propose two Zipf-like models (i.e., PDF-Zipf and CDF-Zipf) to characterize the distribution of passwords. More specifically, our PDF-Zipf model can well fit the popular passwords and obtain a coefficient of determination larger than 0.97; our CDF-Zipf model can well fit the entire password data set, with the maximum cumulative distribution function (CDF) deviation between the empirical distribution and the fitted theoretical model being 0.49%~4.59% (on an average 1.85%). With the concrete knowledge of password distributions, we suggest a new metric for measuring the strength of password data sets. Extensive experimental results show the effectiveness and general applicability of the proposed Zipf-like models and security metric.
A robust cluster-based Eu-MOF has been created by a tetrazolyl-carboxyl linker, which shows great chemical and thermal stability and multiple functions of fluorescent sensor for the detection of ...antibiotics (MDZ, DMZ) and pesticides (DCN).
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•A robust cluster-based Eu-MOF as a fluorescence probe.•Resistance to water, organic solvents and wide pH value range.•Selective detection of MDZ, DMZ and DCN with low detection limit, rapid response.•Detected MDZ and DMZ in calf serum and sensed DCN in lake water.•Combining experiments and calculations to study the sensing mechanism.
As a hot issue of global concern, the abuse of organic pollutants, including pesticides and antibiotics poses a great threat to the human health and ecological environment. Effective and accurate detection of these species is of profound significance in many fields. In this work, a novel 3D metal-organic framework (MOF) Eu2(dtztp)(OH)2(DMF)(H2O)2.5·2H2O (1) was solvothermally synthesized. 1 is a three-dimensional framework based on tetranuclear Eu4(μ3-OH)4(μ2-OH2)8+ clusters, and reveals the great chemical stability and excellent tolerance in water and organic solvents. The MOF also shows strong fluorescence that was undisturbed by the pH in aqueous water (pH = 3–12). Importantly, 1 can quickly detect metronidazole (MDZ) and dimetridazole (DMZ) antibiotics as well as 2,6-dichloro-4-nitroaniline (DCN) pesticide in water with good recyclability and low detection limit. MDZ, DMZ and DCN were also successfully detected in calf serum and lake water, respectively. The mechanism of fluorescence quenching was disclosed through the combination of experiments and density functional theory calculations.
In this paper, the robust control problem for a class of continuous-time nonlinear system with unmatched uncertainties is investigated using an event-based control method. First, the robust control ...problem is transformed into a corresponding optimal control problem with an augmented control and an appropriate cost function. Under the event-based mechanism, we prove that the solution of the optimal control problem can asymptotically stabilize the uncertain system with an adaptive triggering condition. That is, the designed event-based controller is robust to the original uncertain system. Note that the event-based controller is updated only when the triggering condition is satisfied, which can save the communication resources between the plant and the controller. Then, a single network adaptive dynamic programming structure with experience replay technique is constructed to approach the optimal control policies. The stability of the closed-loop system with the event-based control policy and the augmented control policy is analyzed using the Lyapunov approach. Furthermore, we prove that the minimal intersample time is bounded by a nonzero positive constant, which excludes Zeno behavior during the learning process. Finally, two simulation examples are provided to demonstrate the effectiveness of the proposed control scheme.
