Effects of an Early-Time Impact Generated Vapor Blast in the Martian Atmosphere: Formation of High-Latitude Pedestal Craters

Following impact, vapor expansion creates an intense airblast that interacts with the ambient atmosphere. The resulting hemi-spherical shock wave leaves a signature on the surface that is dependent on initial atmospheric and surface conditions. Here we propose that the formation of pedestal craters (craters surrounded by an erosion-resistant pedestal) may be a direct consequence of extreme winds and elevated temperatures generated by such an impact-induced atmospheric blast. Pedestal craters, first recognized in Mariner 9 data, are a unique feature on Mars and likely a signature of near-surface volatiles. They are found at high latitudes (small pedestals, Amazonian to Late Hesperian in age) and in thick equatorial mantling deposits (larger pedestals, early Hesperian to Noachian in age). Previously suggested mechanisms for pedestal crater formation (e.g., wind: ejecta curtain vortices or vapor blast; and ejecta dust: armoring) do not provide a complete picture. The clear evidence for near-surface volatiles at high latitudes requires a re-evaluation of these alternative models. The results presented here suggest that a combined atmospheric blast/thermal model provides a plausible formation hypothesis

Intrinsic Low Temperature Paramagnetism in B-DNA

We present experimental study of magnetization in $\lambda$-DNA in conjunction with structural measurements. The results show the surprising interplay between the molecular structures and their magnetic property. In the B-DNA state, $\lambda$-DNA exhibits paramagnetic behaviour below 20 K that is non-linear in applied magnetic field whereas in the A-DNA state, remains diamagnetic down to 2 K. We propose orbital paramagnetism as the origin of the observed phenomena and discuss its relation to the existence of long range coherent transport in B-DNA at low temperature.Comment: 5 pages, 4 figures, submitted to Physical Review Letters October 200

Electromagnetic Pulse Driven Spin-dependent Currents in Semiconductor Quantum Rings

We investigate the non-equilibrium charge and spin-dependent currents in a quantum ring with a Rashba spin orbit interaction (SOI) driven by two asymmetric picosecond electromagnetic pulses. The equilibrium persistent charge and persistent spin-dependent currents are investigated as well. It is shown that the dynamical charge and the dynamical spin-dependent currents vary smoothly with a static external magnetic flux and the SOI provides a SU(2) effective flux that changes the phases of the dynamic charge and the dynamic spin-dependent currents. The period of the oscillation of the total charge current with the delay time between the pulses is larger in a quantum ring with a larger radius. The parameters of the pulse fields control to a certain extent the total charge and the total spin-dependent currents. The calculations are applicable to nano-meter rings fabricated in heterojuctions of III-V and II-VI semiconductors containing several hundreds electrons.Comment: 15pages, 5 figure

Ionization of hydrogen and hydrogenic ions by antiprotons

Presented here is a description of the ionization of hydrogen and hydrogenic ions by antiproton-impact, based on very large scale numerical solutions of the time-dependent Schr\"odinger equation in three spatial dimensions and on analysis of the topology of the electronic eigenenergy surfaces in the plane of complex internuclear distance. Comparison is made with other theories and very recent measurements.Comment: RevTex document, 11 pages, 4 Postscript figures are available from the authors, in press Phys. Rev. Let

Chaotic exploration and learning of locomotion behaviours

We present a general and fully dynamic neural system, which exploits intrinsic chaotic dynamics, for the real-time goal-directed exploration and learning of the possible locomotion patterns of an articulated robot of an arbitrary morphology in an unknown environment. The controller is modeled as a network of neural oscillators that are initially coupled only through physical embodiment, and goal-directed exploration of coordinated motor patterns is achieved by chaotic search using adaptive bifurcation. The phase space of the indirectly coupled neural-body-environment system contains multiple transient or permanent self-organized dynamics, each of which is a candidate for a locomotion behavior. The adaptive bifurcation enables the system orbit to wander through various phase-coordinated states, using its intrinsic chaotic dynamics as a driving force, and stabilizes on to one of the states matching the given goal criteria. In order to improve the sustainability of useful transient patterns, sensory homeostasis has been introduced, which results in an increased diversity of motor outputs, thus achieving multiscale exploration. A rhythmic pattern discovered by this process is memorized and sustained by changing the wiring between initially disconnected oscillators using an adaptive synchronization method. Our results show that the novel neurorobotic system is able to create and learn multiple locomotion behaviors for a wide range of body configurations and physical environments and can readapt in realtime after sustaining damage

Strain-controlled switching kinetics of epitaxial PbZr0.52Ti0.48O3 films

We investigate the effect of biaxial strain on the switching of ferroelectric thin films. The strain state of epitaxial PbZr0.52Ti0.48O3 films is controlled directly and reversibly by the use of piezoelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (001) substrates. At small external electric fields, the films show switching characteristics consistent with a creep-like domain wall motion. In this regime, we find a huge decrease of the switching time under compressive strain. For larger external electric fields, the domain wall motion is in a depinning regime. The effect of compressive strain is more moderate in this region and shows a reduction in the switching kinetics

Observations of the GRB afterglow ATLAS17aeu and its possible association with GW170104

We report the discovery and multi-wavelength data analysis of the peculiar optical transient, ATLAS17aeu. This transient was identified in the skymap of the LIGO gravitational wave event GW170104 by our ATLAS and Pan-STARRS coverage. ATLAS17aeu was discovered 23.1hrs after GW170104 and rapidly faded over the next 3 nights, with a spectrum revealing a blue featureless continuum. The transient was also detected as a fading x-ray source by Swift and in the radio at 6 and 15 GHz. A gamma ray burst GRB170105A was detected by 3 satellites 19.04hrs after GW170104 and 4.10hrs before our first optical detection. We analyse the multi-wavelength fluxes in the context of the known GRB population and discuss the observed sky rates of GRBs and their afterglows. We find it statistically likely that ATLAS17aeu is an afterglow associated with GRB170105A, with a chance coincidence ruled out at the 99\% confidence or 2.6$\sigma$. A long, soft GRB within a redshift range of $1 \lesssim z \lesssim 2.9$ would be consistent with all the observed multi-wavelength data. The Poisson probability of a chance occurrence of GW170104 and ATLAS17aeu is $p=0.04$. This is the probability of a chance coincidence in 2D sky location and in time. These observations indicate that ATLAS17aeu is plausibly a normal GRB afterglow at significantly higher redshift than the distance constraint for GW170104 and therefore a chance coincidence. However if a redshift of the faint host were to place it within the GW170104 distance range, then physical association with GW170104 should be considered.Comment: 16 pages, 6 figures, accepted to Ap

Structural, electronic, magnetic, and thermal properties of single-crystalline UNi0.5Sb2

We studied the properties of the antiferromagnetic (AFM) UNi0.5Sb2 (TN \approx 161 K) compound in Sb-flux grown single crystals by means of measurements of neutron diffraction, magnetic susceptibility ({\chi}), specific heat (Cp), thermopower (S), thermal conductivity ({\kappa}), linear thermal expansion ({\Delta}L/L), and electrical resistivity ({\rho}) under hydrostatic pressures (P) up to 22 kbar. The neutron diffraction measurements revealed that the compound crystallizes in the tetragonal P42/nmc structure, and the value of the U-moments yielded by the histograms at 25 K is \approx 1.85 \pm 0.12 {\mu}B/U-ion. In addition to the features in the bulk properties observed at TN, two other hysteretic features centered near 40 and 85 K were observed in the measurements of {\chi}, S, {\rho}, and {\Delta}L/L. Hydrostatic pressure was found to raise TN at the rate of \approx 0.76 K/kbar, while suppressing the two low temperature features. These features are discussed in the context of Fermi surface and hybridization effects.Comment: 17 pages, 8 figure

The effect of parallel static and microwave electric fields on excited hydrogen atoms

Motivated by recent experiments we analyse the classical dynamics of a hydrogen atom in parallel static and microwave electric fields. Using an appropriate representation and averaging approximations we show that resonant ionisation is controlled by a separatrix, and provide necessary conditions for a dynamical resonance to affect the ionisation probability. The position of the dynamical resonance is computed using a high-order perturbation series, and estimate its radius of convergence. We show that the position of the dynamical resonance does not coincide precisely with the ionisation maxima, and that the field switch-on time can dramatically affect the ionisation signal which, for long switch times, reflects the shape of an incipient homoclinic. Similarly, the resonance ionisation time can reflect the time-scale of the separatrix motion, which is therefore longer than conventional static field Stark ionisation. We explain why these effects should be observed in the quantum dynamics. PACs: 32.80.Rm, 33.40.+f, 34.10.+x, 05.45.Ac, 05.45.MtComment: 47 pages, 20 figure