Structural geologic interpretation from radar imagery

Structural geologic interpretations from side- looking radar photograph

Borel Degenerations of Arithmetically Cohen-Macaulay curves in P^3

We investigate Borel ideals on the Hilbert scheme components of arithmetically Cohen-Macaulay (ACM) codimension two schemes in P^n. We give a basic necessary criterion for a Borel ideal to be on such a component. Then considering ACM curves in P^3 on a quadric we compute in several examples all the Borel ideals on their Hilbert scheme component. Based on this we conjecture which Borel ideals are on such a component, and for a range of Borel ideals we prove that they are on the component.Comment: 20 pages, shorter and more effective versio

Two-dimensiosnal electron beam charging model for polymer films

A two dimensional model was developed to describe the charging of thin polymer films exposed to a uniform mon-energetic electron beam. The study was motivated by observed anomalous behavior of geosynchronous satellites which was attributed to electrical discharges associated with the differential charging of satellite surfaces of magnetospheric electrons. Electric fields both internal and external to the irradiated specimen were calculated at steady state in order to identify regions of high electrical stress. Particular emphasis was placed on evaluating the charging characteristics near the material's edge. The model was used to identify and quantify the effects of some of the experimental parameters notably: beam energy; beam angle of incidence; beam current density; material thickness; and material width. Simulations of the following situations were also conducted: positive or negative precharging over part of the surface; a central gap in the material; and a discontinuity in the material's thickness

Study of LINER sources with broad H(alpha) emission. X-ray properties and comparision to luminous AGN and X-ray binaries

We study the X-ray properties of LINER sources with definite detection of a broad H(alpha) emission line in their optical spectra, LINER 1s from Ho et al. sample. These objects preferentially harbor a low luminosity active nucleus at the center and show small or no intrinsic absorption (<10^(22) cm^(-1)). We analyzed all available X-ray archived XMM-Newton and Chandra observations of 13 LINER 1s satisfying the above criterion in a systematic homogeneous way. We looked for any correlations between the X-ray properties and the intrinsic parameters of our sample of LINER 1s. An absorbed power-law gave a good fit to the spectra of 9 out of the 13 sources. A thermal component and an absorbed power-law were required in the remaining 4 sources. We found a photon index between 1.3\pm0.2 for the hardest source and 2.4^(+0.2)_(-0.3) for the softest one with a mean value of 1.9\pm0.2 and a dispersion sigma=0.3. The thermal component had a mean temperature kT~0.6 keV. Significant short (hours to days) time-scale variability is not common in the present sample and was observed in only 2 sources (NGC 3226 and NGC 4278). Three other sources indicate a possible variability with a low K-S test probability (2%-4%) that the nuclear emission originates from a constant source. Significant variability on months to years time-scales is detected in 7 out of the 9 sources observed more than once. No significant Fe K(alpha) emission line at 6.4 keV was detected and upper limits were derived for the 4 sources with a high enough signal to noise ratio around 6 keV. Finally, we established, for the first time for a sample of LINER 1s, that the photon index is significantly anticorrelated to L_(2-10 keV)/L_(Edd). This anticorrelation is similar to the one seen in XRBs in their low/hard state where a radiatively inefficient accretion flow is thought to be responsible for the X-ray emitted energy.Comment: 22 pages, 14 figures, accepted for publication in Astronomy and Astrophysic

Fan-spine topology formation through two-step reconnection driven by twisted flux emergence

We address the formation of 3D nullpoint topologies in the solar corona by combining Hinode/XRT observations of a small dynamic limb event, which occurred beside a non-erupting prominence cavity, with a 3D zero-beta MHD simulation. To this end, we model the boundary-driven kinematic emergence of a compact, intense, and uniformly twisted flux tube into a potential field arcade that overlies a weakly twisted coronal flux rope. The expansion of the emerging flux in the corona gives rise to the formation of a nullpoint at the interface of the emerging and the pre-existing fields. We unveil a two-step reconnection process at the nullpoint that eventually yields the formation of a broad 3D fan-spine configuration above the emerging bipole. The first reconnection involves emerging fields and a set of large-scale arcade field lines. It results in the launch of a torsional MHD wave that propagates along the arcades, and in the formation of a sheared loop system on one side of the emerging flux. The second reconnection occurs between these newly formed loops and remote arcade fields, and yields the formation of a second loop system on the opposite side of the emerging flux. The two loop systems collectively display an anenome pattern that is located below the fan surface. The flux that surrounds the inner spine field line of the nullpoint retains a fraction of the emerged twist, while the remaining twist is evacuated along the reconnected arcades. The nature and timing of the features which occur in the simulation do qualititatively reproduce those observed by XRT in the particular event studied in this paper. Moreover, the two-step reconnection process suggests a new consistent and generic model for the formation of anemone regions in the solar corona.Comment: Accepted for publication in ApJ, 11 pages and 5 figure

Simultaneously imaging of dielectric properties and topography in a PbTiO_3 crystal by near-field scanning microwave microscopy

We use a near-field scanning microwave microscope to simultaneously image the dielectric constant, loss tangent, and topography in a PbTiO_3 crystal. By this method, we study the effects of the local dielectric constant and loss tangent in the geometry of periodic domains on the measured resonant frequency, and quality factor. We also carry out theoretical calculations and the results agree well with the experimental data and reveal the anisotropic nature of dielectric constant