This paper proposes an improved free-roaming mobile agent security protocol. The scheme uses "one hop backwards and two hops forwards" chain relation as the protocol core to implement the generally accepted mobile agent security properties. This scheme defends most known attacks, especially colluded truncation attacks and several special cases.
Paywalls are a staple of the internet and seen in a vast amount of websites [1]. Encountering a paywall is always annoying, whether you’re doing work for school or just trying to catch up on the latest news [2]. To eliminate this annoyance we have created Wall Breaker, a google extension with the primary task of bypassing any paywall using a variety of methods [3]. Our extension uses methods such as opening the website in an incognito tab or acting as a new user when clicking on a link. Although not the first of its kind, our extension is truly unique in the methods and techniques used. The popup used is easy to use and simple to look at, providing the best user experience. Wall Breaker will work on most websites, both popular and lesser known ones. It makes no distinction between certain types of websites and the methods can be used on any page. While Wall Breaker might not work on every website those are few and far between.
SAS experiments at the frontier often seek to measure macromolecular components whose concentrations vary, as in ligand titrations, time-resolved methods, or chromatographic separations. These experiments produce large datasets that must be processed to extract the individual component scattering curves. Mathematically, the problem is related to matrix factorization and can be solved by singular value decomposition (SVD). However, the basis vectors from SVD are usually non-physical, and there is the additional problem of finding linear combinations that satisfy physically motivated restraints. Previously, we used evolving factor analysis (EFA) to analyze sizeexclusion chromatography (SEC) SAXS experiments with overlapping peaks [1]. The method was integrated into a well-known software package [2] and has been used by many research groups. However, EFA cannot handle severe peak overlap or changing background. To address a wider class of problems, we developed a computational method called REGALS (for REGularized Alternating Least Squares) that performs matrix factorization such that "physically-meaningful" solutions are enforced by regularization. Regularization functions chosen by the user are applied separately to each component and can include smoothness and extent of the concentration peak, smoothness of the SAXS profile, or smoothness and maximum dimension of the real-space P(r) function. We recently applied REGALS to ion-exchange (IEX) SAXS data, which cannot be analyzed by EFA because the salt gradient produces a changing background [3]. In my presentation I will describe the further development of REGALS and its performance on challenging chromatography datasets. In addition, I will explore the method's potential for other types of experiments, including equilibrium titrations and time-resolved SAXS. Finally, I will describe the REGALS software package, which is free and open-source and includes both Python and MATLAB implementations. References: [1] Meisburger SP, Taylor AB, Khan CA, Zhang S, Fitzpatrick PF, Ando N. (2016). Domain movements upon activation of phenylalanine hydroxylase characterized by crystallography and chromatography-coupled small-angle X-ray scattering.
Enzyme regulation is crucial to proper function, and the mechanisms that dictate this regulation often require allosteric transitions involving dynamic conformational change. A paradigm of complex regulation is the ribonucleotide reductase (RNR) family of enzymes, which uses a conserved, radical-based mechanism to catalyze the de novo conversion of ribonucleotides to deoxyribonucleotides. In previous work, we elucidated how the RNR of Bacillus subtilis maintains DNA metabolic homeostasis via an unprecedented regulatory mechanism in which active tetrameric complexes interconvert with inhibited filaments. Further work has since uncovered that B. subtilis has evolved yet another "tuning dial" that may be linked to the organism's stress response. SAXS nucleotide titrations and chromatography-coupled SAXS experiments were used to show that the nucleotide GTP reverses RNR inhibition by breaking down inhibited filaments. Crystal structures in turn reveal a novel GTP-binding site and further suggest the mechanism of activation. This new GTP-binding site represents the surprising genesis of not just a new allosteric site but a new allosteric activator among all RNRs, and in doing so provides an exemplar of how evolutionary pressure can rapidly create novel allosteric properties.
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