Efficient Certified RAT Verification

Clausal proofs have become a popular approach to validate the results of SAT solvers. However, validating clausal proofs in the most widely supported format (DRAT) is expensive even in highly optimized implementations. We present a new format, called LRAT, which extends the DRAT format with hints that facilitate a simple and fast validation algorithm. Checking validity of LRAT proofs can be implemented using trusted systems such as the languages supported by theorem provers. We demonstrate this by implementing two certified LRAT checkers, one in Coq and one in ACL2

Nanoscale Electronic Order in Iron Pnictides

The charge distribution in RFeAs (R=La, Sm) iron pnictides is probed using As NQR. Whereas undoped and optimally-doped/overdoped compounds feature a single charge environment, two charge environments are detected in the underdoped region. Spin- lattice relaxation measurements show their coexistence at the nanoscale. Together with the quantitative variations of the spectra with doping, they point at a local electronic order in the iron layers, where low- and high-doping-like regions would coexist. Implications for the interplay of static magnetism and superconductivity are discussed

Computational reconstruction and analysis of structural models of avian cryptochrome 4

A recent study by Xu et al. (Nature,2021, 594, 535−540) provided strongevidence that cryptochrome 4 (Cry4) is a key protein to endow migratory birds with the magneticcompass sense. The investigation compared the magneticfield response of Cry4 from migratoryand nonmigratory bird species and suggested that a difference in magnetic sensitivity could exist.Thisfinding prompted an in-depth investigation into Cry4 protein differences on the structuraland dynamic levels. In the present study, the pigeon Cry4 (ClCry4) crystal structure was used toreconstruct the missing avian Cry4 protein structures via homology modeling for carefullyselected bird species. The reconstructed Cry4 structure from European robin, Eurasian blackcap,zebrafinch, chicken, and pigeon were subsequently simulated dynamically and analyzed. Thestudied avian Cry4 structures showflexibility in analogous regions pointing to similar activationmechanisms and/or signaling interaction partners. It can be concluded that the experimentallyrecorded difference in the magneticfield sensitivity of Cry4 from different birds is unlikely to bedue to solely intrinsic dynamics of the proteins but requires additional factors that have not yet been identified

Continuous Coupling of Ultracold Atoms to an Ionic Plasma via Rydberg Excitation

We characterize the two-photon excitation of an ultracold gas of Rubidium atoms to Rydberg states analysing the induced atomic losses from an optical dipole trap. Extending the duration of the Rydberg excitation to several ms, the ground state atoms are continuously coupled to the formed positively charged plasma. In this regime we measure the $n$-dependence of the blockade effect and we characterise the interaction of the excited states and the ground state with the plasma. We also investigate the influence of the quasi-electrostatic trapping potential on the system, confirming the validity of the ponderomotive model for states with $20\leq n\leq 120$

Electronic properties of LaO1-xFxFeAs in the normal state probed by nmr/nqr

We report 139La, 57Fe and 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on powders of the new LaO1−xFxFeAs superconductor for x=0 and 0.1 at temperatures up to 480 K, and compare our measured NQR spectra with local density approximation (LDA) calculations. For all three nuclei in the x=0.1 material, it is found that the local Knight shift increases monotonically with an increase in temperature, and scales with the macroscopic susceptibility, suggesting a single magnetic degree of freedom. Surprisingly, the spin lattice relaxation rates for all nuclei also scale with one another, despite the fact that the form factors for each site sample different regions of q-space. This result suggests a lack of any q-space structure in the dynamical spin susceptibility that might be expected in the presence of antiferromagnetic correlations. Rather, our results are more compatible with simple quasi-particle scattering. Furthermore, we find that the increase in the electric field gradient at the As cannot be accounted for by LDA calculations, suggesting that structural changes, in particular the position of the As in the unit cell, dominate the NQR response

Electronic properties of LaOFFeAs in the normal state probed by NMR/NQR

We report 139La, 57Fe and 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on powders of the new LaO1-xFxFeAs superconductor for x = 0 and x = 0.1 at temperatures up to 480 K, and compare our measured NQR spectra with local density approximation (LDA) calculations. For all three nuclei in the x = 0.1 material, it is found that the local Knight shift increases monotonically with an increase in temperature, and scales with the macroscopic susceptibility, suggesting a single magnetic degree of freedom. Surprisingly, the spin lattice relaxation rates for all nuclei also scale with one another, despite the fact that the form factors for each site sample different regions of q-space. This result suggests a lack of any q-space structure in the dynamical spin susceptibility that might be expected in the presence of antiferromagnetic correlations. Rather, our results are more compatible with simple quasi-particle scattering. Furthermore, we find that the increase in the electric field gradient at the As cannot be accounted for by LDA calculations, suggesting that structural changes, in particular the position of the As in the unit cell, dominate the NQR response.Comment: 17 pages, 6 figure

Computing with quasiseparable matrices

International audienceThe class of quasiseparable matrices is defined by a pair of bounds, called the quasiseparable orders, on the ranks of the maximal sub-matrices entirely located in their strictly lower and upper triangular parts. These arise naturally in applications, as e.g. the inverse of band matrices, and are widely used for they admit structured representations allowing to compute with them in time linear in the dimension and quadratic with the quasiseparable order. We show, in this paper, the connection between the notion of quasisepa-rability and the rank profile matrix invariant, presented in [Dumas & al. ISSAC'15]. This allows us to propose an algorithm computing the quasiseparable orders (rL, rU) in time O(n^2 s^(ω−2)) where s = max(rL, rU) and ω the exponent of matrix multiplication. We then present two new structured representations, a binary tree of PLUQ decompositions, and the Bruhat generator, using respectively O(ns log n/s) and O(ns) field elements instead of O(ns^2) for the previously known generators. We present algorithms computing these representations in time O(n^2 s^(ω−2)). These representations allow a matrix-vector product in time linear in the size of their representation. Lastly we show how to multiply two such structured matrices in time O(n^2 s^(ω−2))

Electronic properties of LaOFFeAs in the normal state probed by NMR/NQR

We report 139La, 57Fe and 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on powders of the new LaO1-xFxFeAs superconductor for x = 0 and x = 0.1 at temperatures up to 480 K, and compare our measured NQR spectra with local density approximation (LDA) calculations. For all three nuclei in the x = 0.1 material, it is found that the local Knight shift increases monotonically with an increase in temperature, and scales with the macroscopic susceptibility, suggesting a single magnetic degree of freedom. Surprisingly, the spin lattice relaxation rates for all nuclei also scale with one another, despite the fact that the form factors for each site sample different regions of q-space. This result suggests a lack of any q-space structure in the dynamical spin susceptibility that might be expected in the presence of antiferromagnetic correlations. Rather, our results are more compatible with simple quasi-particle scattering. Furthermore, we find that the increase in the electric field gradient at the As cannot be accounted for by LDA calculations, suggesting that structural changes, in particular the position of the As in the unit cell, dominate the NQR response.Comment: 17 pages, 6 figure

The use of fatty acid profile as a potential marker for Brazilian coffee (Coffea arabica L.) for corn adulteration

Fatty acid methyl ester (FAME) composition of the coffee (Coffea arabica L.) varieties Catuai, Catucaí, Bourbom, Mundo Novo, Rubí and Topázio known to produce beverage of intermediate, excellent, excellent, intermediate, intermediate and poor quality, respectively, was determined for the first time. Average area % of the FAMEs of the six varieties was: palmitic (38.2), stearic (8.3), oleic (8.6), linoleic (38.5), linolenic (1.6) and arachidic (3.6) acids, respectively. The method was very quick with complete characterization (>99%) of the samples studied being possible in less than 6 min. While these values may provide insights for evaluating the coffee quality, no significant effect (p < 0.05) of coffee variety was found on area % of the FAMEs. In addition, FAMEs of six corn samples, six commercial coffee brands and one commercial coffee sample intentionally contaminated with three levels of corn were compared. Although the linoleic/stearic ratio was significantly different in coffee and corn FAMEs, this probe could not be used a marker to detect corn adulteration in commercial coffees