42,513 research outputs found
Geometry and supersymmetry of heterotic warped flux AdS backgrounds
We classify the geometries of the most general warped, flux AdS backgrounds
of heterotic supergravity up to two loop order in sigma model perturbation
theory. We show under some mild assumptions that there are no
backgrounds with . Moreover the warp factor of AdS backgrounds is
constant, the geometry is a product and such solutions
preserve, 2, 4, 6 and 8 supersymmetries. The geometry of has been
specified in all cases. For 2 supersymmetries, it has been found that
admits a suitably restricted structure. For 4 supersymmetries, has
an structure and can be described locally as a circle fibration over a
6-dimensional KT manifold. For 6 and 8 supersymmetries, has an
structure and can be described locally as a fibration over a
4-dimensional manifold which either has an anti-self dual Weyl tensor or a
hyper-K\"ahler structure, respectively. We also demonstrate a new Lichnerowicz
type theorem in the presence of corrections.Comment: 34 pages. Reference adde
Introductory workshops on remote sensing as related to geological problems in Georgia
There are no author-identified significant results in this report
A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics
Several techniques were used to study pretreated Ti 6-4 surfaces including scanning electron microscopy (SEM), electron spectroscopy of chemical analysis (ESCA), and, reflectance visible spectroscopy. Each pretreatment type gave a characteristic surface morphology as seen by SEM. Elemental analysis of the Ti 6-4 surfaces was done using ESCA. Trace residual contaminants from particular chemical pretreatments were identified readily. Results indicate that reflectance visible spectroscopy using indicator dyes placed on Ti 6-4 surfaces appears to be a feasible approach to establish surface acidity. Differences in surface acidity were observed using bromthymol blue on Ti 6-4 surfaces pretreated by two different methods
An investigation of adhesive/adherend and fiber matrix interactions
Research during the report period focused on continued scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) of lap shear samples and flatwise tensile specimens and on the surface characterization of TiO2, Ti 6-4, and Ti powders with particular emphasis on their interaction with primer solutions of both polyphenylquinoxaline and LaRC-13 polyimide. The use of SEM and XPS in the analysis of Ti 6-4 adherend surfaces is described as well as differences in Ti 6-4 surface composition after different chemical pretreatments. Analysis of fractured surfaces is used to established the failure mode. The surface acidity of Ti 6-4 coupons can be established by reflectance visible spectroscopy using indicator dyes
A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics
Pretreated and primed Ti 6-4 surfaces were characterized by scanning electron microscopy/energy dispersive analysis of X-rays (SEM/EDAX) and electron spectroscopy for chemical analysis (ESCA). Fractured lap shear bonded Ti 6-4 specimens were also characterized by SEM/EDAX and ESCA. A number of surface techniques were used to characterize Ti02 powders
Application of pushbroom altimetry from space using large space antennas
The capabilities of multibeam altimetry are discussed and an interferometric multibeam technique for doing precision altimetry is described. The antenna feed horn arrangement and the resulting footprint lube pattern are illustrated. Plans for a shuttle multibeam altimetry mission are also discussed
Subsampling in Smoothed Range Spaces
We consider smoothed versions of geometric range spaces, so an element of the
ground set (e.g. a point) can be contained in a range with a non-binary value
in . Similar notions have been considered for kernels; we extend them to
more general types of ranges. We then consider approximations of these range
spaces through -nets and -samples (aka
-approximations). We characterize when size bounds for
-samples on kernels can be extended to these more general
smoothed range spaces. We also describe new generalizations for -nets to these range spaces and show when results from binary range spaces can
carry over to these smoothed ones.Comment: This is the full version of the paper which appeared in ALT 2015. 16
pages, 3 figures. In Algorithmic Learning Theory, pp. 224-238. Springer
International Publishing, 201
A search for extended radio emission from selected compact galaxy groups
Context. Studies on compact galaxy groups have led to the conclusion that a
plenitude of phenomena take place in between galaxies that form them. However,
radio data on these objects are extremely scarce and not much is known
concerning the existence and role of the magnetic field in intergalactic space.
Aims. We aim to study a small sample of galaxy groups that look promising as
possible sources of intergalactic magnetic fields; for example data from radio
surveys suggest that most of the radio emission is due to extended, diffuse
structures in and out of the galaxies. Methods. We used the Effelsberg 100 m
radio telescope at 4.85 GHz and NRAO VLA Sky Survey (NVSS) data at 1.40 GHz.
After subtraction of compact sources we analysed the maps searching for
diffuse, intergalactic radio emission. Spectral index and magnetic field
properties were derived. Results. Intergalactic magnetic fields exist in groups
HCG 15 and HCG 60, whereas there are no signs of them in HCG 68. There are also
hints of an intergalactic bridge in HCG 44 at 4.85 GHz. Conclusions.
Intergalactic magnetic fields exist in galaxy groups and their energy density
may be comparable to the thermal (X-ray) density, suggesting an important role
of the magnetic field in the intra-group medium, wherever it is detected.Comment: 13 pages, 4 figures, 3 tables, accepted for publication in A&
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The Diderot meteorite: The second chassignite
The Diderot meteorite is a dunite discovered in Sahara. The martian origin is unambiguous and Diderot shares strong petrographical similarities with Chassigny
A dynamical model for the heavily ram pressure stripped Virgo spiral galaxy NGC 4522
A dynamical model including ram pressure stripping is applied to the strongly
HI deficient Virgo spiral galaxy NGC 4522. A carefully chosen model snapshot is
compared with existing VLA HI observations. The model successfully reproduces
the large-scale gas distribution and the velocity field. However it fails to
reproduce the large observed HI linewidths in the extraplanar component, for
which we give possible explanations. In a second step, we solve the induction
equation on the velocity fields of the dynamical model and calculate the large
scale magnetic field. Assuming a Gaussian distribution of relativistic
electrons we obtain the distribution of polarized radio continuum emission
which is also compared with our VLA observations at 6 cm. The observed maximum
of the polarized radio continuum emission is successfully reproduced. Our model
suggests that the ram pressure maximum occurred only ~50 Myr ago. Since NGC
4522 is located far away from the cluster center (~1 Mpc) where the
intracluster medium density is too low to cause the observed stripping if the
intracluster medium is static and smooth, two scenarios are envisaged: (i) the
galaxy moves very rapidly within the intracluster medium and is not even bound
to the cluster; in this case the galaxy has just passed the region of highest
intracluster medium density; (ii) the intracluster medium is not static but
moving due to the infall of the M49 group of galaxies. In this case the galaxy
has just passed the region of highest intracluster medium velocity. This study
shows the strength of combining high resolution HI and polarized radio
continuum emission with detailed numerical modeling of the evolution of the gas
and the large-scale magnetic field.Comment: 15 pages, 11 figures, accepted for publication in A&
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