Characterization of the K2-18 multi-planetary system with HARPS: A habitable zone super-Earth and discovery of a second, warm super-Earth on a non-coplanar orbit

The bright M dwarf K2-18 at 34 pc is known to host a transiting super-Earth-sized planet orbiting within the star's habitable zone; K2-18b. Given the superlative nature of this system for studying an exoplanetary atmosphere receiving similar levels of insolation as the Earth, we aim to characterize the planet's mass which is required to interpret atmospheric properties and infer the planet's bulk composition. We obtain precision radial velocity measurements with the HARPS spectrograph and couple those measurements with the K2 photometry to jointly model the observed radial velocity variation with planetary signals and a radial velocity jitter model based on Gaussian process regression. We measure the mass of K2-18b to be $8.0 \pm 1.9$ M$_{\oplus}$ with a bulk density of $3.7 \pm 0.9$ g/cm$^3$ which may correspond to a predominantly rocky planet with a significant gaseous envelope or an ocean planet with a water mass fraction $\gtrsim 50$%. We also find strong evidence for a second, warm super-Earth K2-18c at $\sim 9$ days with a semi-major axis 2.4 times smaller than the transiting K2-18b. After re-analyzing the available light curves of K2-18 we conclude that K2-18c is not detected in transit and therefore likely has an orbit that is non-coplanar with K2-18b. A suite of dynamical integrations with varying simulated orbital eccentricities of the two planets are used to further constrain each planet's eccentricity posterior from which we measure $e_b < 0.43$ and $e_c < 0.47$ at 99% confidence. The discovery of the inner planet K2-18c further emphasizes the prevalence of multi-planet systems around M dwarfs. The characterization of the density of K2-18b reveals that the planet likely has a thick gaseous envelope which along with its proximity to the Solar system makes the K2-18 planetary system an interesting target for the atmospheric study of an exoplanet receiving Earth-like insolation.Comment: 13 pages, 8 figures including 4 interactive figures best viewed in Adobe Acrobat. Submitted to Astronomy & Astrophysics. Comments welcom

Low Energy Electron Point Projection Microscopy of Suspended Graphene, the Ultimate "Microscope Slide"

Point Projection Microscopy (PPM) is used to image suspended graphene using low-energy electrons (100-200eV). Because of the low energies used, the graphene is neither damaged or contaminated by the electron beam. The transparency of graphene is measured to be 74%, equivalent to electron transmission through a sheet as thick as twice the covalent radius of sp^2-bonded carbon. Also observed is rippling in the structure of the suspended graphene, with a wavelength of approximately 26 nm. The interference of the electron beam due to the diffraction off the edge of a graphene knife edge is observed and used to calculate a virtual source size of 4.7 +/- 0.6 Angstroms for the electron emitter. It is demonstrated that graphene can be used as both anode and substrate in PPM in order to avoid distortions due to strong field gradients around nano-scale objects. Graphene can be used to image objects suspended on the sheet using PPM, and in the future, electron holography

Nanoscale structuring of tungsten tip yields most coherent electron point-source

This report demonstrates the most spatially-coherent electron source ever reported. A coherence angle of 14.3 +/- 0.5 degrees was measured, indicating a virtual source size of 1.7 +/-0.6 Angstrom using an extraction voltage of 89.5 V. The nanotips under study were crafted using a spatially-confined, field-assisted nitrogen etch which removes material from the periphery of the tip apex resulting in a sharp, tungsten-nitride stabilized, high-aspect ratio source. The coherence properties are deduced from holographic measurements in a low-energy electron point source microscope with a carbon nanotube bundle as sample. Using the virtual source size and emission current the brightness normalized to 100 kV is found to be 7.9x10^8 A/sr cm^2

The Tyrosine Kinase Csk Dimerizes through Its SH3 Domain

The Src family kinases possess two sites of tyrosine phosphorylation that are critical to the regulation of kinase activity. Autophosphorylation on an activation loop tyrosine residue (Tyr 416 in commonly used chicken c-Src numbering) increases catalytic activity, while phosphorylation of a C-terminal tyrosine (Tyr 527 in c-Src) inhibits activity. The latter modification is achieved by the tyrosine kinase Csk (C-terminal Src Kinase), but the complete inactivation of the Src family kinases also requires the dephosphorylation of the activation loop tyrosine. The SH3 domain of Csk recruits the tyrosine phosphatase PEP, allowing for the coordinated inhibition of Src family kinase activity. We have discovered that Csk forms homodimers through interactions mediated by the SH3 domain in a manner that buries the recognition surface for SH3 ligands. The formation of this dimer would therefore block the recruitment of tyrosine phosphatases and may have important implications for the regulation of Src kinase activity

Social influence and moment-to-moment changes in young adults’ mood and psychotic symptoms

Background: • Social situations can have a significant impact on young people’s mood and mental experiences. • More specifically, we want to know how someone’s perceived social influence in social situations relates to their mood and psychotic symptoms. • Past studies have found connections between lower perceived social status (rank, comparison, and related concepts) and psychotic symptoms anxiety, depression, and other mood related psychopathology. • We use experience sampling methods to capture moment-to-moment changes in mood and psychotic symptoms in a variety of social settings

SEED PRODUCTION OF SOME FIELD CROPS IN THE Bc INSTITUTE, ZAGREB

Organizirana potrošnja sjemena ratarskih kultura u Hrvatskoj u razdoblju od 1990. do 1998. godine, bila je ovisna o ekonomskom interesu poljoprivrednika za proizvodnju, klimatskim uvjetima za vrijeme sjetve i ratnim uvjetima od 1991 . do 1995. godine. Ovo se posebno odnosi na najvažniju krušaricu ozimu pšenicu koja je u 1992. godini požnjevena sa 169.000 ha. Međutim, u jesen 1998. godine dolazi do daljnjeg smanjenja sjetve ozime pšenice u Hrvatskoj na svega 160.578 ha. Ovim je smanjena potrošnja certificiranog sjemena ozime pšenice u Hrvatskoj na svega 26.687 tona, što je najniža količina u zadnjih nekoliko decenija. Smanjena je potrošnja svih kreacija pa i kreacija Bc Instituta. Kreacije ostalih strnih žitarica Bc Instituta jare zobi i jarog ječma u sjemenskoj proizvodnji imaju blagi trend rasta i na razini su od 300 tona sjemena godišnje. Sjemenarstvo krmnih kultura, poglavito višegodišnjih trava i leguminoza kreiranih u Bc Institutu Zagreb sa svojim visokim potencijalom rodnosti, adaptibilnosti, kakvoćama i stabilnim urodima, imajući u vidu velike mogućnosti i perspektivu razvoja stočarstva uz očekivane poticajne mjere države, ima veliko značenje. Sjemenarstvo krmnih kultura, danas u Hrvatskoj je zabrinjavajuće, jer domaća proizvodnja ne zadovoljava ni umanjene potrebe, pa se ovo sjeme uvozi, često sumnjivog podrijetla i kakvoće.Organized seed consumption of some field crops in Croatia in the period from 1990 to 1998 was dependent on the farmers\u27 economic interest to produce, on climatic conditions during sowing time and on the war conditions from 1991 to 1995. This particularly refers to the most important bread grain, winter wheat, which was harvested from 169.000 ha in 1992. However, in autumn of 1998, there was further reduction in the area planted to winter wheat in Croatia down to 160.578 ha. In this way consumption of certified seed of winter wheat in Croatia was reduced to mere 26.687 t, which is the lowest quantity in the last few decades. Consumption of all varieties was reduced including the Bc Institute\u27s. Seed production of other cereal crops developed by the Bc lnstitute, spring oats and spring barley, has a slight trend of growing and is on the level of 300 t of seed per year. Seed production of fodder crops, particularly perennial grasses and pulses developed by the Zagreb Bc Institute with their high yielding potential, adaptability, quality, and stable yield, is of great importance bearing in mind great possibilities and perspectives for livestock development and with expected measures of government support. Seed production of fodder crops in Croatia is of great concern because domestic production does not meet even the existing reduced needs and the seeds, often of doubtful origin and quality is being imported

Brief communication: On direct impact probability of landslides on vehicles

When calculating the risk of railway or road users of being killed by a natural hazard, one has to calculate a temporal spatial probability, i.e. the probability of a vehicle being in the path of the falling mass when the mass falls, or the expected number of affected vehicles in case such of an event. To calculate this, different methods are used in the literature, and, most of the time, they consider only the dimensions of the falling mass or the dimensions of the vehicles. Some authors do however consider both dimensions at the same time, and the use of their approach is recommended. Finally, a method considering an impact on the front of the vehicle is discussed

GJ 1252 b: A 1.2 R\u3csub\u3e⊕\u3c/sub\u3e Planet Transiting An M3 Dwarf At 20.4 pc

We report the discovery of GJ 1252 b, a planet with a radius of 1.193 ± 0.074 R⊕ and an orbital period of 0.52 days around an M3-type star (0.381 ± 0.019 M⊕, 0.391 ± 0.020 R⊕) located 20.385 ± 0.019 pc away. We use Transiting Exoplanet Survey Satellite (TESS) data, ground-based photometry and spectroscopy, Gaia astrometry, and high angular resolution imaging to show that the transit signal seen in the TESS data must originate from a transiting planet. We do so by ruling out all false-positive scenarios that attempt to explain the transit signal as originating from an eclipsing stellar binary. Precise Doppler monitoring also leads to a tentative mass measurement of 2.09 ± 0.56 M⊕. The host star proximity, brightness (V = 12.19 mag, K = 7.92 mag), low stellar activity, and the system\u27s short orbital period make this planet an attractive target for detailed characterization, including precise mass measurement, looking for other objects in the system, and planet atmosphere characterization