An alternative pathway for repair of deaminated bases in DNA triggered by archaeal NucS endonuclease

International audienc

Tunneling Magnetoresistance in Noncollinear Antiferromagnetic Tunnel Junctions

Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics driven by the advantages of antiferromagnets producing no stray fields and exhibiting ultrafast magnetization dynamics. The efficient method to detect an AFM order parameter, known as the N\'eel vector, by electric means is critical to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear AFM metals, such as Mn3Sn, exhibit a momentum dependent spin polarization which can be exploited in AFM tunnel junctions to detect the N\'eel vector. Using first-principles calculations based on density functional theory, we predict a tunneling magnetoresistance (TMR) effect as high as 300% in AFM tunnel junctions with Mn3Sn electrodes, where the junction resistance depends on the relative orientation of their N\'eel vectors and exhibits four non-volatile resistance states. We argue that the spin-split band structure and the related TMR effect can also be realized in other non-collinear AFM metals like Mn3Ge, Mn3Ga, Mn3Pt, and Mn3GaN. Our work provides a robust method for detecting the N\'eel vector in non-collinear antiferromagnets via the TMR effect, which may be useful for their application in AFM spintronic devices

Development of a fully coupled wind stress-wave-ocean coastal model system

To conserve momentum flux across the air-sea interface, a new wind stress-wave-ocean coupled coastal model system is developed. Via simulating a specific idealized tropical cyclone (TC), this model is firstly applied to study the impacts of three wave effects, including the commonly studied wave-breaking induced acceleration, wave-enhanced bottom friction and the seldom studied wave modified surface stress (WMWS), and the conservation of momentum flux across air-sea interface (MFB) on the predictions of storm surge and inundation. It is then further applied to investigate the role of above four effects in modeling the peak surge and inundation by generalizing the TC forcing with various physical parameters, including the TC intensity, size, translation speed, and bottom slope. The model results reveal that WMWS can contribute considerably to the total surge height and inundation distance in a relatively high-intensity TC and its contribution depends weakly on the varying bottom slopes, TC sizes or translation speeds. By contrast, the MFB can only considerably reduce the maximum storm surge with a small bottom slope, while its reduction on inundation distance is more significant. The present study thus highlights the importance and necessity of incorporating the commonly ignored effects of WMWS and MFB in coastal modeling

Development of a fully coupled wind stress-wave-ocean coastal model system

To conserve momentum flux across the air-sea interface, a new wind stress-wave-ocean coupled coastal model system is developed. Via simulating a specific idealized tropical cyclone (TC), this model is firstly applied to study the impacts of three wave effects, including the commonly studied wave-breaking induced acceleration, wave-enhanced bottom friction and the seldom studied wave modified surface stress (WMWS), and the conservation of momentum flux across air-sea interface (MFB) on the predictions of storm surge and inundation. It is then further applied to investigate the role of above four effects in modeling the peak surge and inundation by generalizing the TC forcing with various physical parameters, including the TC intensity, size, translation speed, and bottom slope. The model results reveal that WMWS can contribute considerably to the total surge height and inundation distance in a relatively high-intensity TC and its contribution depends weakly on the varying bottom slopes, TC sizes or translation speeds. By contrast, the MFB can only considerably reduce the maximum storm surge with a small bottom slope, while its reduction on inundation distance is more significant. The present study thus highlights the importance and necessity of incorporating the commonly ignored effects of WMWS and MFB in coastal modeling

Employing Modular Polyketide Synthase Ketoreductases as Biocatalysts in the Preparative Chemoenzymatic Syntheses of Diketide Chiral Building Blocks

SummaryChiral building blocks are valuable intermediates in the syntheses of natural products and pharmaceuticals. A scalable chemoenzymatic route to chiral diketides has been developed that includes the general synthesis of α-substituted, β-ketoacyl N-acetylcysteamine thioesters followed by a biocatalytic cycle in which a glucose-fueled NADPH-regeneration system drives reductions catalyzed by isolated modular polyketide synthase (PKS) ketoreductases (KRs). To identify KRs that operate as active, stereospecific biocatalysts, 11 isolated KRs were incubated with 5 diketides and their products were analyzed by chiral chromatography. KRs that naturally reduce small polyketide intermediates were the most active and stereospecific toward the panel of diketides. Several biocatalytic reactions were scaled up to yield more than 100 mg of product. These syntheses demonstrate the ability of PKS enzymes to economically and greenly generate diverse chiral building blocks on a preparative scale

Group Time-based One-time Passwords and its Application to Efficient Privacy-Preserving Proof of Location

Time-based One-Time Password (TOTP) provides a strong second factor for user authentication. In TOTP, a prover authenticates to a verifier by using the current time and a secret key to generate an authentication token (or password) which is valid for a short time period. Our goal is to extend TOTP to the group setting, and to provide both authentication and privacy. To this end, we introduce a new authentication scheme, called Group TOTP (GTOTP), that allows the prover to prove that it is a member of an authenticated group without revealing its identity. We propose a novel construction that transforms any asymmetric TOTP scheme into a GTOTP scheme. Our approach combines Merkle tree and Bloom filter to reduce the verifier\u27s states to constant sizes. As a promising application of GTOTP, we show that GTOTP can be used to construct an efficient privacy-preserving Proof of Location (PoL) scheme. We utilize a commitment protocol, a privacy-preserving location proximity scheme, and our GTOTP scheme to build the PoL scheme, in which GTOTP is used not only for user authentication but also as a tool to glue up other building blocks. In the PoL scheme, with the help of some witnesses, a user can prove its location to a verifier, while ensuring the identity and location privacy of both the prover and witnesses. Our PoL scheme outperforms the alternatives based on group digital signatures. We evaluate our schemes on Raspberry Pi hardware, and demonstrate that they achieve practical performance. In particular, the password generation and verification time are in the order of microseconds and milliseconds, respectively, while the computation time of proof generation is less than $1$ second