Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution

The larger number of models of asteroid shapes and their rotational states derived by the lightcurve inversion give us better insight into both the nature of individual objects and the whole asteroid population. With a larger statistical sample we can study the physical properties of asteroid populations, such as main-belt asteroids or individual asteroid families, in more detail. Shape models can also be used in combination with other types of observational data (IR, adaptive optics images, stellar occultations), e.g., to determine sizes and thermal properties. We use all available photometric data of asteroids to derive their physical models by the lightcurve inversion method and compare the observed pole latitude distributions of all asteroids with known convex shape models with the simulated pole latitude distributions. We used classical dense photometric lightcurves from several sources and sparse-in-time photometry from the U.S. Naval Observatory in Flagstaff, Catalina Sky Survey, and La Palma surveys (IAU codes 689, 703, 950) in the lightcurve inversion method to determine asteroid convex models and their rotational states. We also extended a simple dynamical model for the spin evolution of asteroids used in our previous paper. We present 119 new asteroid models derived from combined dense and sparse-in-time photometry. We discuss the reliability of asteroid shape models derived only from Catalina Sky Survey data (IAU code 703) and present 20 such models. By using different values for a scaling parameter cYORP (corresponds to the magnitude of the YORP momentum) in the dynamical model for the spin evolution and by comparing synthetics and observed pole-latitude distributions, we were able to constrain the typical values of the cYORP parameter as between 0.05 and 0.6.Comment: Accepted for publication in A&A, January 15, 201

Direct multiplex imaging and optogenetics of Rho GTPases enabled by near-infrared FRET

Direct visualization and light control of several cellular processes is a challenge, owing to the spectral overlap of available genetically encoded probes. Here we report the most red-shifted monomeric near-infrared (NIR) fluorescent protein, miRFP720, and the fully NIR Forster resonance energy transfer (FRET) pair miRFP670-miRFP720, which together enabled design of biosensors compatible with CFP-YFP imaging and blue-green optogenetic tools. We developed a NIR biosensor for Rac1 GTPase and demonstrated its use in multiplexed imaging and light control of Rho GTPase signaling pathways. Specifically, we combined the Rac1 biosensor with CFP-YFP FRET biosensors for RhoA and for Rac1-GDI binding, and concurrently used the LOV-TRAP tool for upstream Rac1 activation. We directly observed and quantified antagonism between RhoA and Rac1 dependent on the RhoA-downstream effector ROCK; showed that Rac1 activity and GDI binding closely depend on the spatiotemporal coordination between these two molecules; and simultaneously observed Rac1 activity during optogenetic manipulation of Rac1.Peer reviewe

Scaling slowly rotating asteroids with stellar occultations

Context. As evidenced by recent survey results, the majority of asteroids are slow rotators (spin periods longer than 12 h), but lack spin and shape models because of selection bias. This bias is skewing our overall understanding of the spins, shapes, and sizes of asteroids, as well as of their other properties. Also, diameter determinations for large (>60 km) and medium-sized asteroids (between 30 and 60 km) often vary by over 30% for multiple reasons. Aims. Our long-term project is focused on a few tens of slow rotators with periods of up to 60 h. We aim to obtain their full light curves and reconstruct their spins and shapes. We also precisely scale the models, typically with an accuracy of a few percent. Methods. We used wide sets of dense light curves for spin and shape reconstructions via light-curve inversion. Precisely scaling them with thermal data was not possible here because of poor infrared datasets: large bodies tend to saturate in WISE mission detectors. Therefore, we recently also launched a special campaign among stellar occultation observers, both in order to scale these models and to verify the shape solutions, often allowing us to break the mirror pole ambiguity. Results. The presented scheme resulted in shape models for 16 slow rotators, most of them for the first time. Fitting them to chords from stellar occultation timings resolved previous inconsistencies in size determinations. For around half of the targets, this fitting also allowed us to identify a clearly preferred pole solution from the pair of two mirror pole solutions, thus removing the ambiguity inherent to light-curve inversion. We also address the influence of the uncertainty of the shape models on the derived diameters. Conclusions. Overall, our project has already provided reliable models for around 50 slow rotators. Such well-determined and scaled asteroid shapes will, for example, constitute a solid basis for precise density determinations when coupled with mass information. Spin and shape models in general continue to fill the gaps caused by various biases

Vol de deux projectiles separes par une faible distance. Pt. 1 Visualisation des ecoulements et mesures de pression autor de projectiles de reference

Im Rahmen der Untersuchungen zur intelligenten Zielannaeherung wurde eine mehrteilige Untersuchung ueber das Flugverhalten zweier in geringer Entfernung voneinander befindlicher Geschosse durchgefuehrt. Vorligender Bericht behandelt den ersten Teil (experimentelle Untersuchung), dessen Ziel es ist, die Bezugsgroessen fuer jedes einzelne Geschoss zu bestimmen und sicherzustellen, dass die eingesetzten Versuchsvorrichtungen fuer die Untersuchung solcher Stroemungen geeignet sind. Die Messungen wurden in einem Windkanal mit kurzen Blaszeiten bei einer Machzahl von 2,06 an zwei Modellarten durchgefuehrt: Einerseits an vorfliegenden Modellen (gerades Heck, mit oder ohne Flossen), die das Heckteil der Geschosse darstellen, andererseits an nachfliedenden Modellen (sphaerische Haube, Konus mit einer Laenge von 2 oder 3 Kalibern), die es kuenftig ermoeglichen, das Verhalten des zweiten Geschosses im Nachlauf des ersten zu untersuchen. Fuer jedes der vorfliegenden und nachfliegenden Geschosse und bei verschiedenen Anstellwinkeln (-5, 0 und +5 Grad) wurden die Stroemungen sichtbar gemacht und Druckmessungen durchgefuehrt. Bei den nachfliegenden Geschossen weisen die Ergebnisse qualitativ und quantitativ eine grosse Aehnlichkeit mit den analytischen Prognosen auf. Bei den vorfliegenden Geschossen zeigen die Ergebnisse, dass der Tragedorn dem Windkanal des ISL angepasst ist und sich keine Wechselwirkung mit der Stroemung ergibt. Ausserdem sind unseres Wissens die am Heck mit Flossen durchgefuehrten Messungen einmalig. (orig.)Within the scope of investigations into smart target homing, a series of studies of the flying characteristics of two projectiles flying at a short distance to one another was carried out. The present report covers the first part (experimental investigation) the objective of which is to determine the reference parameters for each individual projectile and to verify that the experimental facilities are appropriate for an investigation of such flows. The measurements were taken in a blowdown wind tunnel at a Mach number of 2.06 using two types of models: On the one hand leading models (straight base with or without fins) representing the tail section of the projectiles, on the other hand trailing models (spherical nose, cone having a length of 2 or 3 calibers), which in the future will permit to study the behavior of the second projectile in the wake of the first one. The flows were visualized and pressure measurements taken for each of the leading and trailing projectiles and at different angles of attack (-5, 0 and +5 degrees). The results for the trailing projectiles show great similarity to analytical forecasts in terms of quality and quantity. The results for the leading projectiles indicate that the supporting boom has been adapted to the ISL wind tunnel and that there is no interaction with the flow. In addition, as far as we know, the measurements carried out on the tail with fins are unprecedented. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Pathogenic Mechanisms of Secondary Organic Aerosols

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Photometric analysis for the spin and shape parameters of the C-type main-belt asteroids (171) Ophelia and (360) Carlova

Aims. Two C-type main-belt asteroids (171) Ophelia and (360) Carlova are studied for their spin parameters and shapes in the present paper. Although it was suspected that Ophelia was a binary system owing to the eclipse features in the light curve obtained in 1977, no direct evidence has been obtained to confirm the binarity. To verify the previous findings, the spin parameters and shape of Ophelia are derived by analyzing the photometric data. To understand the dispersion in the previous determination of Carlova’s spin parameters, new observational data and existing photometric data are reanalyzed to find a homogenous solution for its spin parameters and shape. Methods. The spin parameters and shapes of two asteroids were determined from photometric data using the convex inversion technique. The simplified virtual-observation Markov chain Monte Carlo method was applied to estimate the uncertainties of the spin parameters and to understand the divergence of derived shapes. Results. A pair of possible poles for Ophelia are derived, the spin periods corresponding to the two poles are nearly the same. The convex shape of Ophelia shows binary characteristics. For Carlova, a unique pole solution and its convex shape are ascertained together with the occultation observations. The convex shape of Carlova shows that it is a rough ellipsoid

Four new binary minor planets: (854) Frostia, (1089) Tama, (1313) Berna, (4492) Debussy

Context. Aims.We present evidence that four minor planets of the main belt are binary systems. Methods.These discoveries are based on CCD photometric measurements made by many observers coordinated in a network of observatories. Results.Orbital and physical properties are derived from a total of 134 partial light curves involving 26 stations. (854) Frostia, (1089) Tama, (1313) Berna, and (4492) Debussy show mutual eclipses features on their light curves. In all cases, rotation and revolution are synchronous. Synodic periods are 37.728, 16.444, 25.464 and 26.606 h respectively. From a simple model, we have derived their bulk densities as follows: 0.89 ± 0.14, 2.52 ± 0.30, 1.22 ± 0.15 and 0.91 ± 0.10 g cm-3 respectively. Uncertainties in the bulk densities, arising from scattering and shadow effects are not taken into account. These could increase the density estimates by a factor up to 1.6. Our method of determining bulk density is completely independent of their mass and their diameter estimates. The low rotational periods and the low bulk densities clearly imply a collisional process to explain this kind of binary asteroid. Based on our database of a few thousand light curves of minor planets, the population of similar-sized objects in the main belt is estimated to $6\pm 3$ percent in the 10–50 km diameter class. Conclusions

Multiplexing molecular tension sensors reveals piconewton force gradient across talin-1

Förster resonance energy transfer (FRET)-based tension sensor modules (TSMs) are available for investigating how distinct proteins bear mechanical forces in cells. Yet, forces in the single piconewton (pN) regime remain difficult to resolve, and tools for multiplexed tension sensing are lacking. Here, we report the generation and calibration of a genetically encoded, FRET-based biosensor called FL-TSM, which is characterized by a near-digital force response and increased sensitivity at 3–5 pN. In addition, we present a method allowing the simultaneous evaluation of coexpressed tension sensor constructs using two-color fluorescence lifetime microscopy. Finally, we introduce a procedure to calculate the fraction of mechanically engaged molecules within cells. Application of these techniques to new talin biosensors reveals an intramolecular tension gradient across talin-1 that is established upon integrin-mediated cell adhesion. The tension gradient is actomyosin- and vinculin-dependent and sensitive to the rigidity of the extracellular environment