Earthshine observation of vegetation and implication for life detection on other planets - A review of 2001 - 2006 works

The detection of exolife is one of the goals of very ambitious future space missions that aim to take direct images of Earth-like planets. While associations of simple molecules present in the planet's atmosphere ($O_2$, $O_3$, $CO_2$ etc.) have been identified as possible global biomarkers, we review here the detectability of a signature of life from the planet's surface, i.e. the green vegetation. The vegetation reflectance has indeed a specific spectrum, with a sharp edge around 700 nm, known as the "Vegetation Red Edge" (VRE). Moreover vegetation covers a large surface of emerged lands, from tropical evergreen forest to shrub tundra. Thus considering it as a potential global biomarker is relevant. Earthshine allows to observe the Earth as a distant planet, i.e. without spatial resolution. Since 2001, Earthshine observations have been used by several authors to test and quantify the detectability of the VRE in the Earth spectrum. The egetation spectral signature is detected as a small 'positive shift' of a few percents above the continuum, starting at 700 nm. This signature appears in most spectra, and its strength is correlated with the Earth's phase (visible land versus visible ocean). The observations show that detecting the VRE on Earth requires a photometric relative accuracy of 1% or better. Detecting something equivalent on an Earth-like planet will therefore remain challenging, moreover considering the possibility of mineral artifacts and the question of 'red edge' universality in the Universe.Comment: Invited talk in "Strategies for Life Detection" (ISSI Bern, 24-28 April 2006) to appear in a hardcopy volume of the ISSI Space Science Series, Eds, J. Bada et al., and also in an issue of Space Science Reviews. 13 pages, 8 figures, 1 tabl

Lithographically fabricated nanopore-based electrodes for electrochemistry

We report a new technique for fabricating electrodes for electrochemical applications with lateral dimensions in the range 15−200 nm and a reproducible, well-defined geometry. This technique allows determining the electrode size by electron microscopy prior to electrochemical measurements and without contamination of the metal electrode. We measured the diffusion-limited current with stepped-current voltammetry and showed that its dependence on electrode size can be quantitatively understood if the known geometry of the electrodes is explicitly taken into account

Nonconstant electronic density of states tunneling inversion for A15 superconductors: Nb3Sn

We re-examine the tunneling data on A15 superconductors by performing a generalized McMillan-Rowell tunneling inversion that incorporates a nonconstant electronic density of states obtained from band-structure calculations. For Nb3Sn, we find that the fit to the experimental data can be slightly improved by taking into account the sharp structure in the density of states, but it is likely that such an analysis alone is not enough to completely explain the superconducting tunneling characteristics of this material. Nevertheless, the extracted Eliashberg function displays a number of features expected to be present for the highest quality Nb3Sn samples.Comment: 11 pages, 11 figure

Computer‐aided photo‐identification of a rare stingray, Megatrygon microps

We have defined protocol for photo‐identification to identify individual Megatrygon microps. 104 identification photographs were taken between 2005 and 2019. Spot patterns on the dorsal surface were used to identify individuals. Unique scarring on 8 re‐observed M. microps provided an independent confirmation of pattern stability of up to 761 days. Previously, studies have lacked statistical testing to validate photo‐identification approach. The I3S photo‐matching software was proven to successfully match images, identifying 69 individuals. A photo‐matching software facilitates an open‐source platform for identifying individual M. microps, allowing for better population assessments

Triphosphate reorientation of the incoming nucleotide as a fidelity checkpoint in viral RNA-dependent RNA Polymerases

The nucleotide incorporation fidelity of the viral RNA-dependent RNA polymerase (RdRp) is important for maintaining functional genetic information but, at the same time, is also important for generating sufficient genetic diversity to escape the bottlenecks of the host's antiviral response. We have previously shown that the structural dynamics of the motifDloop are closely related to nucleotide discrimination. Previous studies have also suggested that there is a reorientation of the triphosphate of the incoming nucleotide, which is essential before nucleophilic attack from the primer RNA 3-hydroxyl. Here, we have used 31PNMRwith poliovirus RdRp to show that the binding environment of the triphosphate is different when correct versus incorrect nucleotide binds.Wealso show that amino acid substitutions at residues known to interact with the triphosphate can alter the binding orientation/environment of the nucleotide, sometimes lead to protein conformational changes, and lead to substantial changes in RdRp fidelity. The analyses of other fidelity variants also show that changes in the triphosphate binding environment are not always accompanied by changes in the structural dynamics of the motif D loop or other regions known to be important for RdRp fidelity, including motif B. Altogether, our studies suggest that the conformational changes in motifs B and D, and the nucleoside triphosphate reorientation represent separable, "tunable" fidelity checkpoints

Nucleobase but not sugar fidelity is maintained in the Sabin I RNA-dependent RNA polymerase

The Sabin I poliovirus live, attenuated vaccine strain encodes for four amino acid changes (i.e., D53N, Y73H, K250E, and T362I) in the RNA-dependent RNA polymerase (RdRp). We have previously shown that the T362I substitution leads to a lower fidelity RdRp, and viruses encoding this variant are attenuated in a mouse model of poliovirus. Given these results, it was surprising that the nucleotide incorporation rate and nucleobase fidelity of the Sabin I RdRp is similar to that of wild-type enzyme, although the Sabin I RdRp is less selective against nucleotides with modified sugar groups. We suggest that the other Sabin amino acid changes (i.e., D53N, Y73H, K250E) help to re-establish nucleotide incorporation rates and nucleotide discrimination near wild-type levels, which may be a requirement for the propagation of the virus and its efficacy as a vaccine strain. These results also suggest that the nucleobase fidelity of the Sabin I RdRp likely does not contribute to viral attenuation

Nuclear dependence coefficient α(A,qT)\alpha(A,q_T) for the Drell-Yan and J/ψ\psi production

Define the nuclear dependence coefficient $\alpha(A,q_T)$ in terms of ratio of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon collisions: $\frac{d\sigma^{hA}}{dq_T^2}/ \frac{d\sigma^{hN}}{dq_T^2}\equiv A^{\alpha(A,q_T)}$. We argue that in small $q_T$ region, the $\alpha(A,q_T)$ for the Drell-Yan and J/$\psi$ production is given by a universal function:\ $a+b q_T^2$, where parameters a and b are completely determined by either calculable quantities or independently measurable physical observables. We demonstrate that this universal function $\alpha(A,q_T)$ is insensitive to the A for normal nuclear targets. For a color deconfined nuclear medium, the $\alpha(A,q_T)$ becomes strongly dependent on the A. We also show that our $\alpha(A,q_T)$ for the Drell-Yan process is naturally linked to perturbatively calculated $\alpha(A,q_T)$ at large $q_T$ without any free parameters, and the $\alpha(A,q_T)$ is consistent with E772 data for all $q_T$.Comment: latex, 28 pages, 10 figures, updated two figures, and add more discussion

Systematic study of the effect of short range correlations on the form factors and densities of s-p and s-d shell nuclei

Analytical expressions of the one- and two-body terms in the cluster expansion of the charge form factors and densities of the s-p and s-d shell nuclei with N=Z are derived. They depend on the harmonic oscillator parameter b and the parameter $\beta$ which originates from the Jastrow correlation function. These expressions are used for the systematic study of the effect of short range correlations on the form factors and densities and of the mass dependence of the parameters b and $\beta$. These parameters have been determined by fit to the experimental charge form factors. The inclusion of the correlations reproduces the experimental charge form factors at the high momentum transfers ($q\geq 2 1/fm$). It is found that while the parameter $\beta$ is almost constant for the closed shell nuclei, $^4$He, $^{16}$O and $^{40}$Ca, its values are larger (less correlated systems) for the open shell nuclei, indicating a shell effect in the closed shell nuclei.Comment: Latex, 21 pages, 6 figures, 1 tabl

Strong and weak chaos in weakly nonintegrable many-body Hamiltonian systems

We study properties of chaos in generic one-dimensional nonlinear Hamiltonian lattices comprised of weakly coupled nonlinear oscillators, by numerical simulations of continuous-time systems and symplectic maps. For small coupling, the measure of chaos is found to be proportional to the coupling strength and lattice length, with the typical maximal Lyapunov exponent being proportional to the square root of coupling. This strong chaos appears as a result of triplet resonances between nearby modes. In addition to strong chaos we observe a weakly chaotic component having much smaller Lyapunov exponent, the measure of which drops approximately as a square of the coupling strength down to smallest couplings we were able to reach. We argue that this weak chaos is linked to the regime of fast Arnold diffusion discussed by Chirikov and Vecheslavov. In disordered lattices of large size we find a subdiffusive spreading of initially localized wave packets over larger and larger number of modes. The relations between the exponent of this spreading and the exponent in the dependence of the fast Arnold diffusion on coupling strength are analyzed. We also trace parallels between the slow spreading of chaos and deterministic rheology.Comment: 15 pages, 14 figure