Quadratic soliton collisions

The details of two soliton collision processes were investigated in detail in a 1 cm long periodically poled KTP crystal for the case when the solitons were excited by inputting only the fundamental beam. The effects on the collision outcomes of the distance of the collision into the sample, collision angle and phase mismatch were measured for different relative phases between the input beams. At small angles ( around 0.4(0)) fusion, repulsion and energy transfer processes were observed, while at the collision angles approaching 3.2(0) the two output soliton beams were essentially unaffected by the interaction. The phase mismatch was varied from 3.5 to - 1.5pi for the 0.4(0) collision angle case. The output soliton separation at p input phase difference showed strongly asymmetric behavior with phase mismatch. In general, the measurements indicate a decrease in the interaction strength with increasing phase mismatch. All collision processes were performed in the vicinity of a non-critical phase matching

The role of lysine palmitoylation/myristoylation in the function of the TEAD transcription factors

The TEAD transcription factors are the most downstream elements of the Hippo pathway. Their transcriptional activity is modulated by different regulator proteins and by the palmitoylation/myristoylation of a specific cysteine residue. In this report, we show that a conserved lysine present in these transcription factors can also be acylated, probably following the intramolecular transfer of the acyl moiety from the cysteine. Using Scalloped (Sd), the Drosophila homolog of human TEAD, as a model, we designed a mutant protein (Glu352Gln Sd ) that is predominantly acylated on the lysine (Lys350 Sd ). This protein binds in vitro to the three Sd regulators-Yki, Vg and Tgi-with a similar affinity as the wild type Sd, but it has a significantly higher thermal stability than Sd acylated on the cysteine. This mutant was also introduced in the endogenous locus of the sd gene in Drosophila using CRISPR/Cas9. Homozygous mutants reach adulthood, do not present obvious morphological defects and the mutant protein has both the same level of expression and localization as wild type Sd. This reveals that this mutant protein is both functional and able to control cell growth in a similar fashion as wild type Sd. Therefore, enhancing the lysine acylation of Sd has no detrimental effect on the Hippo pathway. However, we did observe a slight but significant increase of wing size in flies homozygous for the mutant protein suggesting that a higher acylation of the lysine affects the activity of the Hippo pathway. Altogether, our findings indicate that TEAD/Sd can be acylated either on a cysteine or on a lysine, and suggest that these two different forms may have similar properties in cells

A dp53-Dependent Mechanism Involved in Coordinating Tissue Growth in Drosophila

A study in the Drosophila wing suggests a crucial role of p53 in the coordination of growth between adjacent cell populations to maintain organ proportions and shape

Nightside condensation of iron in an ultra-hot giant exoplanet

Ultra-hot giant exoplanets receive thousands of times Earth's insolation. Their high-temperature atmospheres (>2,000 K) are ideal laboratories for studying extreme planetary climates and chemistry. Daysides are predicted to be cloud-free, dominated by atomic species and substantially hotter than nightsides. Atoms are expected to recombine into molecules over the nightside, resulting in different day-night chemistry. While metallic elements and a large temperature contrast have been observed, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ("evening") and night-to-day ("morning") terminators could, however, be revealed as an asymmetric absorption signature during transit. Here, we report the detection of an asymmetric atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this signature thanks to the combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. Iron must thus condense during its journey across the nightside.Comment: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11 figures, 3 table

ESPRESSO at VLT. On-sky performance and first results

Context. ESPRESSO is the new high-resolution spectrograph of ESO's Very Large Telescope (VLT). It was designed for ultra-high radial-velocity (RV) precision and extreme spectral fidelity with the aim of performing exoplanet research and fundamental astrophysical experiments with unprecedented precision and accuracy. It is able to observe with any of the four Unit Telescopes (UTs) of the VLT at a spectral resolving power of 140 000 or 190 000 over the 378.2 to 788.7 nm wavelength range; it can also observe with all four UTs together, turning the VLT into a 16 m diameter equivalent telescope in terms of collecting area while still providing a resolving power of 70 000. Aims: We provide a general description of the ESPRESSO instrument, report on its on-sky performance, and present our Guaranteed Time Observation (GTO) program along with its first results. Methods: ESPRESSO was installed on the Paranal Observatory in fall 2017. Commissioning (on-sky testing) was conducted between December 2017 and September 2018. The instrument saw its official start of operations on October 1, 2018, but improvements to the instrument and recommissioning runs were conducted until July 2019. Results: The measured overall optical throughput of ESPRESSO at 550 nm and a seeing of 0.65″ exceeds the 10% mark under nominal astroclimatic conditions. We demonstrate an RV precision of better than 25 cm s-1 during a single night and 50 cm s-1 over several months. These values being limited by photon noise and stellar jitter shows that the performance is compatible with an instrumental precision of 10 cm s-1. No difference has been measured across the UTs, neither in throughput nor RV precision. Conclusions: The combination of the large collecting telescope area with the efficiency and the exquisite spectral fidelity of ESPRESSO opens a new parameter space in RV measurements, the study of planetary atmospheres, fundamental constants, stellar characterization, and many other fields. Based on GTOs collected at the European Southern Observatory under ESO program(s) 1102.C-0744, 1102.C-0958 and 1104.C-0350 by the ESPRESSO Consortium

DNA recognition by the brinker repressor--an extreme case of coupling between binding and folding.

International audienceThe Brinker (Brk) nuclear repressor is a major element of the Drosophila Decapentaplegic morphogen signaling pathway. Its N-terminal part has weak homology to the Antennapedia homeodomain and binds to GC-rich DNA sequences. We have investigated the conformation and dynamics of the N-terminal 101 amino acid residues of Brk in the absence and in the presence of cognate DNA by solution NMR spectroscopy. In the absence of DNA, Brk is unfolded and highly flexible throughout the entire backbone. Addition of cognate DNA induces the formation of a well-folded structure for residues R46 to R95. This structure consists of four helices forming a helix-turn-helix motif that differs from homeodomains, but has similarities to the Tc3 transposase, the Pax-6 Paired domain, and the human centromere-binding protein. The GC-rich DNA recognition can be explained by specific major groove hydrogen bonds from the N-terminal end of helix alpha3. The transition from a highly flexible, completely unfolded conformation in the absence of DNA to a well-formed structure in the complex presents a very extreme case of the "coupling of binding and folding" phenomenon

Postcolonial perspectives on aid systems in multicultural contexts: Palestine and Uganda

n/