Experimental investigation of crater growth dynamics

This work is a continuation of an ongoing program whose objective is to perform experiments and to develop scaling relationships for large-body impacts onto planetary surfaces. The centrifuge technique is used to provide experimental data for actual target materials of interest. With both power and gas guns mounted on the rotor arm, it is possible to match various dimensionless similarity parameters, which have been shown to govern the behavior of large-scale impacts. The development of the centrifuge technique has been poineered by the present investigators and is documented by numerous publications, the most recent of which are listed below. Understanding the dependence of crater size upon gravity has been shown to be key to the complete determination of the dynamic and kinematic behavior of crater formation as well as ejecta phenomena. Three unique time regimes in the formation of an impact crater have been identified

Space station impact experiments

Four processes serve to illustrate potential areas of study and their implications for general problems in planetary science. First, accretional processes reflect the success of collisional aggregation over collisional destruction during the early history of the solar system. Second, both catastrophic and less severe effects of impacts on planetary bodies survivng from the time of the early solar system may be expressed by asteroid/planetary spin rates, spin orientations, asteroid size distributions, and perhaps the origin of the Moon. Third, the surfaces of planetary bodies directly record the effects of impacts in the form of craters; these records have wide-ranging implications. Fourth, regoliths evolution of asteroidal surfaces is a consequence of cumulative impacts, but the absence of a significant gravity term may profoundly affect the retention of shocked fractions and agglutinate build-up, thereby biasing the correct interpretations of spectral reflectance data. An impact facility on the Space Station would provide the controlled conditions necessary to explore such processes either through direct simulation of conditions or indirect simulation of certain parameters

Thermal evolution and activity of Comet 9P/Tempel 1 and simulation of a deep impact

We use a quasi 3-D thermal evolution model for a spherical comet nucleus, which takes into account the diurnal and latitudinal variation of the solar flux, but neglects lateral heat conduction. We model the thermal evolution and activity of Comet 9P/Tempel 1, in anticipation of the Deep Impact mission encounter with the comet. We also investigate the possible outcome of a projectile impact, assuming that all the energy is absorbed as thermal energy. An interesting result of this investigation, is that the estimated amount of dust ejected due to the impact is equivalent to 2--2.6 days of activity, during "quiet" conditions, at perihelion. We show that production rates of volatiles that are released in the interior of the nucleus depend strongly on the porous structure, in particular on the surface to volume ratio of the pores. We develop a more accurate model for calculating this parameter, based on a distribution of pore sizes, rather than a single, average pore size.Comment: 25 pages, 8 figures, accepted for publication in PASP (in press). For fig.xx (composite image, sec.4) and a better resolution of fig.6 see, http://geophysics.tau.ac.il/personal/gal%5Fsarid

Predicting language learners' grades in the L1, L2, L3 and L4: the effect of some psychological and sociocognitive variables

This study of 89 Flemish high-school students' grades for L1 (Dutch), L2 (French), L3 (English) and L4 (German) investigates the effects of three higher-level personality dimensions (psychoticism, extraversion, neuroticism), one lower-level personality dimension (foreign language anxiety) and sociobiographical variables (gender, social class) on the participants' language grades. Analyses of variance revealed no significant effects of the higher-level personality dimensions on grades. Participants with high levels of foreign language anxiety obtained significantly lower grades in the L2 and L3. Gender and social class had no effect. Strong positive correlations between grades in the different languages could point to an underlying sociocognitive dimension. The implications of these findings are discussed

Steady 10Be-derived Paleoerosion Rates across the Plio-Pleistocene Climate Transition, Fish Creek-Vallecito Basin, California

Rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution. Here we measure 10Be archived in quartz sediment from the Fish Creek-Vallecito basin to resolve a time series of catchment-averaged erosion rates and to test the hypothesis that aridity and increased climate variation after approximately 3 Ma led to an increase in erosion rates in this semiarid, ice-free setting. The Fish Creek-Vallecito basin, located east of the Peninsular Ranges in Southern California, is an ideal setting to derive a Plio-Pleistocene paleoerosion rate record. The basin has a rapid sediment accumulation rate, a detailed magnetostratigraphic age record, and its stratigraphy has been exposed through recent, rapid uplift and erosion. A well-defined source region of uniform lithology and low erosion rate provides a high, reproducible 10Be signal. We find that paleoerosion rates were remarkably consistent between 1 and 4 Ma, averaging 38 ± 24 m/Myr (2σ). Modern catchment-averaged erosion rates are similar to the paleoerosion rates. The uniformity of erosion over the past 4 Myr indicates that the landscape was not significantly affected by late Pliocene global climate change, nor was it affected by a local long-term increase in aridity

P/2010A2 LINEAR - I: An impact in the Asteroid Main Belt

Comet P/2010A2 LINEAR is a good candidate for membership with the Main Belt Comet family. It was observed with several telescopes (ESO NTT, La Silla; Gemini North, Mauna Kea; UH 2.2m, Mauna Kea) from 14 Jan. until 19 Feb. 2010 in order to characterize and monitor it and its very unusual dust tail, which appears almost fully detached from the nucleus; the head of the tail includes two narrow arcs forming a cross. The immediate surroundings of the nucleus were found dust-free, which allowed an estimate of the nucleus radius of 80-90m. A model of the thermal evolution indicates that such a small nucleus could not maintain any ice content for more than a few million years on its current orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up and electrostatic dust levitations were also rejected, leaving an impact with a smaller body as the favoured hypothesis, and ruling out the cometary nature of the object. The impact is further supported by the analysis of the tail structure. Finston-Probstein dynamical dust modelling indicates the tail was produced by a single burst of dust emission. More advanced models, independently indicate that this burst populated a hollow cone with a half-opening angle alpha~40degr and with an ejection velocity v_max ~ 0.2m/s, where the small dust grains fill the observed tail, while the arcs are foreshortened sections of the burst cone. The dust grains in the tail are measured to have radii between a=1-20mm, with a differential size distribution proportional to a^(-3.44 +/- 0.08). The dust contained in the tail is estimated to at least 8x10^8kg, which would form a sphere of 40m radius. Analysing these results in the framework of crater physics, we conclude that a gravity-controlled crater would have grown up to ~100m radius, i.e. comparable to the size of the body. The non-disruption of the body suggest this was an oblique impact.Comment: 15 pages, 11 figures, in pres

Facial expression animation through action units transfer in latent space

Automatic animation synthesis has attracted much attention from the community. As most existing methods take a small number of discrete expressions rather than continuous expressions, their integrity and reality of the facial expressions is often compromised. In addition, the easy manipulation with simple inputs and unsupervised processing, although being important to the automatic facial expression animation applications, is relatively less concerned. To address these issues, we propose an unsupervised continuous automatic facial expression animation approach through action units (AU) transfer in the latent space of generative adversarial networks. The expression descriptor which is depicted with AU vector is transferred into the input image without the need of labeled pairs of images and even without their expressions and further network training. We also propose a new approach to quickly generate input image's latent code and cluster the boundaries of different AU attributes with their latent codes. Two latent code operators, vector addition and continuous interpolation, are leveraged for facial expression animation simulating align with the boundaries in the latent space. Experiments have shown that the proposed approach is effective on facial expression translation and animation synthesis