227 research outputs found
A light scattering instrument for investigating cloud ice microcrystal morphology
We describe an optical scattering instrument designed to assess the shapes and sizes of microscopic atmospheric cloud particles, especially the smallest ice crystals that can profoundly affect cloud processes and radiative properties yet cannot be seen clearly using in situ cloud particle imaging probes. The new instrument captures high-resolution spatial light scattering patterns from individual particles down to ~1 μm in size passing through a laser beam. Its significance lies in the ability of these patterns to provide morphological data for particle sizes well below the optical resolution limits of current probes
INTEGRAL and XMM-Newton observations of the weak GRB 030227
We present INTEGRAL and XMM-Newton observations of the prompt gamma-ray
emission and the X-ray afterglow of GRB030227, the first GRB for which the
quick localization obtained with the INTEGRAL Burst Alert System (IBAS) has led
to the discovery of X-ray and optical afterglows. GRB030227 had a duration of
about 20 s and a peak flux of 1.1 photons cm^-2 s^-1 in the 20-200 keV energy
range. The time averaged spectrum can be fit by a single power law with photon
index about 2 and we find some evidence for a hard to soft spectral evolution.
The X-ray afterglow has been detected starting only 8 hours after the prompt
emission, with a 0.2-10 keV flux decreasing as t^-1 from 1.3x10e-12 to 5x10e-13
erg cm^-2 s^-1. The afterglow spectrum is well described by a power law with
photon index 1.94+/-0.05 modified by a redshifted neutral absorber with column
density of several 10e22 cm^-2. A possible emission line at 1.67 keV could be
due to Fe for a redshift z=3, consistent with the value inferred from the
absorption.Comment: 16 pages, 5 figures, latex, Accepted for publication in The
Astrophysical Journal Letter
A nested hierarchical perspective to enhance interpretations and communication in fluvial geomorphology for use in water resources management::Lessons from the Okavango Delta, Botswana
Scaling Laws and Transient Times in 3He Induced Nuclear Fission
Fission excitation functions of compound nuclei in a mass region where shell
effects are expected to be very strong are shown to scale exactly according to
the transition state prediction once these shell effects are accounted for. The
fact that no deviations from the transition state method have been observed
within the experimentally investigated excitation energy regime allows one to
assign an upper limit for the transient time of 10 zs.Comment: 7 pages, TeX type, psfig, submitted to Phys. Rev. C, also available
at http://csa5.lbl.gov/moretto/ps/he3_paper.p
Immunolymphoscintigraphy for Metastatic Sentinel Nodes: Test of a Model
Aim. To develop a method and obtain proof-of-principle for immunolymphoscintigraphy for identification of metastatic sentinel nodes. Methods. We selected one of four tumour-specific antibodies against human breast cancer and investigated (1), in immune-deficient (nude) mice with xenograft human breast cancer expressing the antigen if specific binding of the intratumorally injected, radioactively labelled, monoclonal antibody could be scintigraphically visualized, and (2) transportation to and retention in regional lymph nodes of the radioactively labelled antibody after subcutaneous injection in healthy rabbits. Results and Conclusion. Our paper suggests the theoretical possibility of a model of dual isotope immuno-lymphoscintigraphy for noninvasive, preoperative, malignant sentinel node imaging
OCTOPUS database (v.2)
OCTOPUS v.2 is an Open Geospatial Consortium (OGC) compliant web-enabled database that allows users to visualise, query, and download cosmogenic radionuclide, luminescence, and radiocarbon ages and denudation rates associated with erosional landscapes, Quaternary depositional landforms, and archaeological records, along with ancillary geospatial (vector and raster) data layers. The database follows the FAIR (Findability, Accessibility, Interoperability, and Reuse) data principles and is based on open-source software deployed on the Google Cloud Platform. Data stored in the database can be accessed via a custom-built web interface and via desktop geographic information system (GIS) applications that support OGC data access protocols. OCTOPUS v.2 hosts five major data collections. CRN Denudation and ExpAge consist of published cosmogenic 10Be and 26Al measurements in modern fluvial sediment and glacial samples respectively. Both collections have a global extent; however, in addition to geospatial vector layers, CRN Denudation also incorporates raster layers, including a digital elevation model, gradient raster, flow direction and flow accumulation rasters, atmospheric pressure raster, and CRN production scaling and topographic shielding factor rasters. SahulSed consists of published optically stimulated luminescence (OSL) and thermoluminescence (TL) ages for fluvial, aeolian, and lacustrine sedimentary records across the Australian mainland and Tasmania. SahulArch consists of published OSL, TL, and radiocarbon ages for archaeological records, and FosSahul consists of published late-Quaternary records of direct and indirect non-human vertebrate (mega)fauna fossil ages that have been systematically quality rated. Supporting data are comprehensive and include bibliographic, contextual, and sample-preparation- and measurement-related information. In the case of cosmogenic radionuclide data, OCTOPUS also includes all necessary information and input files for the recalculation of denudation rates using the open-source program CAIRN. OCTOPUS v.2 and its associated data curation framework allow for valuable legacy data to be harnessed that would otherwise be lost to the research community. The database can be accessed at https://octopusdata.org (last access: 1 July 2022). The individual data collections can also be accessed via their respective digital object
identifiers (DOIs) (see Table 1)
Evidence for a Geometrically Thick Self-Gravitating Accretion Disk in NGC 3079
We have mapped, for the first time, the full velocity extent of the water
maser emission in NGC 3079. The largely north-south distribution of emission,
aligned with a kpc-scale molecular disk, and the segregation of blue- and
red-shifted emission on the sky are suggestive of a nearly edge-on molecular
disk on pc-scales. Positions and line-of-sight velocities of blue- and
red-shifted maser emission are consistent with a central mass of ~2 x 10^6 Msun
enclosed within a radius of ~0.4 pc. The corresponding mean mass density of
10^6.8 Msun pc^-3 is suggestive of a central black hole, which is consistent
with the detection of hard X-ray excess (20-100 keV) and an Fe Kalpha line from
the nucleus. Because the rotation curve traced by the maser emission is flat,
the mass of the pc-scale disk is significant with respect to the central mass.
Since the velocity dispersion of the maser features does not decrease with
radius and constitutes a large fraction of the orbital velocity, the disk is
probably thick and flared. The rotation curve and the physical conditions
necessary to support maser emission imply a Toomre Q-parameter that is << 1.
Thus, the disk is most likely clumpy, and we argue that it is probably forming
stars. Overall, the accretion disk in NGC 3079 stands in contrast to the
compact, thin, warped, differentially rotating disk in the archetypal maser
galaxy NGC 4258 (abridged).Comment: 41 pages, 13 figures, to appear in the 2005 January 10 issue of the
Astrophysical Journal. High resolution versions of the figures and of the
paper are available at
http://cfa-www.harvard.edu/~pkondratko/publications/NGC3079
Scalar and vector Slepian functions, spherical signal estimation and spectral analysis
It is a well-known fact that mathematical functions that are timelimited (or
spacelimited) cannot be simultaneously bandlimited (in frequency). Yet the
finite precision of measurement and computation unavoidably bandlimits our
observation and modeling scientific data, and we often only have access to, or
are only interested in, a study area that is temporally or spatially bounded.
In the geosciences we may be interested in spectrally modeling a time series
defined only on a certain interval, or we may want to characterize a specific
geographical area observed using an effectively bandlimited measurement device.
It is clear that analyzing and representing scientific data of this kind will
be facilitated if a basis of functions can be found that are "spatiospectrally"
concentrated, i.e. "localized" in both domains at the same time. Here, we give
a theoretical overview of one particular approach to this "concentration"
problem, as originally proposed for time series by Slepian and coworkers, in
the 1960s. We show how this framework leads to practical algorithms and
statistically performant methods for the analysis of signals and their power
spectra in one and two dimensions, and, particularly for applications in the
geosciences, for scalar and vectorial signals defined on the surface of a unit
sphere.Comment: Submitted to the 2nd Edition of the Handbook of Geomathematics,
edited by Willi Freeden, Zuhair M. Nashed and Thomas Sonar, and to be
published by Springer Verlag. This is a slightly modified but expanded
version of the paper arxiv:0909.5368 that appeared in the 1st Edition of the
Handbook, when it was called: Slepian functions and their use in signal
estimation and spectral analysi
Image-based Search and Retrieval for Biface Artefacts using Features Capturing Archaeologically Significant Characteristics
Archaeologists are currently producing huge numbers of digitized photographs to record and preserve artefact finds. These images are used to identify and categorize artefacts and reason about connections between artefacts and perform outreach to the public. However, finding specific types of images within collections remains a major challenge. Often, the metadata associated with images is sparse or is inconsistent. This makes keyword-based exploratory search difficult, leaving researchers to rely on serendipity and slowing down the research process. We present an image-based retrieval system that addresses this problem for biface artefacts. In order to identify artefact characteristics that need to be captured by image features, we conducted a contextual inquiry study with experts in bifaces. We then devised several descriptors for matching images of bifaces with similar artefacts. We evaluated the performance of these descriptors using measures that specifically look at the differences between the sets of images returned by the search system using different descriptors. Through this nuanced approach, we have provided a comprehensive analysis of the strengths and weaknesses of the different descriptors and identified implications for design in the search systems for archaeology
Tetrofosmin early time gated post-stress single-photon emission computed tomography imaging: Feasibility and potential benefits
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