196,580 research outputs found
"TNOs are Cool": A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations
The classical Kuiper belt contains objects both from a low-inclination,
presumably primordial, distribution and from a high-inclination dynamically
excited population. Based on a sample of classical TNOs with observations at
thermal wavelengths we determine radiometric sizes, geometric albedos and
thermal beaming factors as well as study sample properties of dynamically hot
and cold classicals. Observations near the thermal peak of TNOs using infra-red
space telescopes are combined with optical magnitudes using the radiometric
technique with near-Earth asteroid thermal model (NEATM). We have determined
three-band flux densities from Herschel/PACS observations at 70.0, 100.0 and
160.0 m and Spitzer/MIPS at 23.68 and 71.42 m when available. We have
analysed 18 classical TNOs with previously unpublished data and re-analysed
previously published targets with updated data reduction to determine their
sizes and geometric albedos as well as beaming factors when data quality
allows. We have combined these samples with classical TNOs with radiometric
results in the literature for the analysis of sample properties of a total of
44 objects. We find a median geometric albedo for cold classical TNOs of 0.14
and for dynamically hot classical TNOs, excluding the Haumea family and dwarf
planets, 0.085. We have determined the bulk densities of Borasisi-Pabu (2.1
g/cm^3), Varda-Ilmare (1.25 g/cm^3) and 2001 QC298 (1.14 g/cm^3) as well as
updated previous density estimates of four targets. We have determined the
slope parameter of the debiased cumulative size distribution of dynamically hot
classical TNOs as q=2.3 +- 0.1 in the diameter range 100<D<500 km. For
dynamically cold classical TNOs we determine q=5.1 +- 1.1 in the diameter range
160<D<280 km as the cold classical TNOs have a smaller maximum size.Comment: 22 pages, 7 figures Accepted to be published in Astronomy and
Astrophysic
Differentially Private Publication of Sparse Data
The problem of privately releasing data is to provide a version of a dataset
without revealing sensitive information about the individuals who contribute to
the data. The model of differential privacy allows such private release while
providing strong guarantees on the output. A basic mechanism achieves
differential privacy by adding noise to the frequency counts in the contingency
tables (or, a subset of the count data cube) derived from the dataset. However,
when the dataset is sparse in its underlying space, as is the case for most
multi-attribute relations, then the effect of adding noise is to vastly
increase the size of the published data: it implicitly creates a huge number of
dummy data points to mask the true data, making it almost impossible to work
with.
We present techniques to overcome this roadblock and allow efficient private
release of sparse data, while maintaining the guarantees of differential
privacy. Our approach is to release a compact summary of the noisy data.
Generating the noisy data and then summarizing it would still be very costly,
so we show how to shortcut this step, and instead directly generate the summary
from the input data, without materializing the vast intermediate noisy data. We
instantiate this outline for a variety of sampling and filtering methods, and
show how to use the resulting summary for approximate, private, query
answering. Our experimental study shows that this is an effective, practical
solution, with comparable and occasionally improved utility over the costly
materialization approach
"TNOs are Cool": A survey of the trans-Neptunian region VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects
Trans-Neptunian objects (TNO) represent the leftovers of the formation of the
Solar System. Their physical properties provide constraints to the models of
formation and evolution of the various dynamical classes of objects in the
outer Solar System. Based on a sample of 19 classical TNOs we determine
radiometric sizes, geometric albedos and beaming parameters. Our sample is
composed of both dynamically hot and cold classicals. We study the correlations
of diameter and albedo of these two subsamples with each other and with orbital
parameters, spectral slopes and colors. We have done three-band photometric
observations with Herschel/PACS and we use a consistent method for data
reduction and aperture photometry of this sample to obtain monochromatic flux
densities at 70.0, 100.0 and 160.0 \mu m. Additionally, we use Spitzer/MIPS
flux densities at 23.68 and 71.42 \mu m when available, and we present new
Spitzer flux densities of eight targets. We derive diameters and albedos with
the near-Earth asteroid thermal model (NEATM). As auxiliary data we use
reexamined absolute visual magnitudes from the literature and data bases, part
of which have been obtained by ground based programs in support of our Herschel
key program. We have determined for the first time radiometric sizes and
albedos of eight classical TNOs, and refined previous size and albedo estimates
or limits of 11 other classicals. The new size estimates of 2002 MS4 and 120347
Salacia indicate that they are among the 10 largest TNOs known. Our new results
confirm the recent findings that there are very diverse albedos among the
classical TNOs and that cold classicals possess a high average albedo (0.17 +/-
0.04). Diameters of classical TNOs strongly correlate with orbital inclination
in our sample. We also determine the bulk densities of six binary TNOs.Comment: 21 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
A new approach to measure reduction intensity on cores and tools on cobbles: the Volumetric Reconstruction Method
Knowing to what extent lithic cores have been reduced through knapping is an important step toward understanding the technological variability of lithic assemblages and disentangling the formation processes of archaeological assemblages. In addition, it is a good complement to more developed studies of reduction intensity in retouched tools, and can provide information on raw material management or site occupation dynamics. This paper presents a new methodology for estimating the intensity of reduction in cores and tools on cobbles, the Volumetric Reconstruction Method (VRM). This method is based on a correction of the dimensions (length, width, and thickness) of each core from an assemblage. The mean values of thickness and platform thickness of the assemblage’s flakes are used as corrections for the cores’ original dimensions, after its diacritic analysis. Then, based on these new dimensions, the volume or mass of the original blank are reconstructed using the ellipsoid volume formula. The accuracy of this method was experimentally tested, reproducing a variety of possible archaeological scenarios. The experimental results demonstrate a high inferential potential of the VRM, both in estimating the original volume or mass of the original blanks, and in inferring the individual percentage of reduction for each core. The results of random resampling demonstrate the applicability of VRM to non size-biased archaeological contexts.Introduction Methods - The Volumetric Reconstruction Method - Experimental design - Statistical procedures - Resamples Results - Geometric formulas - Reduction strategy and size - Resampling (randomly biased record) - Resampling (size bias) - Measuring the effect of number of generations Discussion and conclusion
Statistical Geometry of Packing Defects of Lattice Chain Polymer from Enumeration and Sequential Monte Carlo Method
Voids exist in proteins as packing defects and are often associated with
protein functions. We study the statistical geometry of voids in
two-dimensional lattice chain polymers. We define voids as topological features
and develop a simple algorithm for their detection. For short chains, void
geometry is examined by enumerating all conformations. For long chains, the
space of void geometry is explored using sequential Monte Carlo importance
sampling and resampling techniques. We characterize the relationship of
geometric properties of voids with chain length, including probability of void
formation, expected number of voids, void size, and wall size of voids. We
formalize the concept of packing density for lattice polymers, and further
study the relationship between packing density and compactness, two parameters
frequently used to describe protein packing. We find that both fully extended
and maximally compact polymers have the highest packing density, but polymers
with intermediate compactness have low packing density. To study the
conformational entropic effects of void formation, we characterize the
conformation reduction factor of void formation and found that there are strong
end-effect. Voids are more likely to form at the chain end. The critical
exponent of end-effect is twice as large as that of self-contacting loop
formation when existence of voids is not required. We also briefly discuss the
sequential Monte Carlo sampling and resampling techniques used in this study.Comment: 29 pages, including 12 figure
Airborne LiDAR for DEM generation: some critical issues
Airborne LiDAR is one of the most effective and reliable means of terrain data collection. Using LiDAR data for DEM generation is becoming a standard practice in spatial related areas. However, the effective processing of the raw LiDAR data and the generation of an efficient and high-quality DEM remain big challenges. This paper reviews the recent advances of airborne LiDAR systems and the use of
LiDAR data for DEM generation, with special focus on LiDAR data filters, interpolation methods, DEM resolution, and LiDAR data reduction. Separating LiDAR points into ground and non-ground is the most critical and difficult step for
DEM generation from LiDAR data. Commonly used and most recently developed LiDAR filtering methods are presented. Interpolation methods and choices of suitable interpolator and DEM resolution for LiDAR DEM generation are discussed in detail. In order to reduce the data redundancy and increase the efficiency in terms of storage
and manipulation, LiDAR data reduction is required in the process of DEM generation. Feature specific elements such as breaklines contribute significantly to DEM quality. Therefore, data reduction should be conducted in such a way that critical elements are kept while less important elements are removed. Given the highdensity
characteristic of LiDAR data, breaklines can be directly extracted from LiDAR data. Extraction of breaklines and integration of the breaklines into DEM generation are presented
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