1,460 research outputs found
Nearest neighbor vector analysis of sdss dr5 galaxy distribution
We present the Nearest Neighbor Distance (NND) analysis of SDSS DR5 galaxies.
We give NND results for observed, mock and random sample, and discuss the
differences. We find that the observed sample gives us a significantly stronger
aggregation characteristic than the random samples. Moreover, we investigate
the direction of NND and find that the direction has close relation with the
size of the NND for the observed sample.Comment: Natural Science, Vol.5, No.1 in January 201
Multi-Scale Morphological Analysis of SDSS DR5 Survey using the Metric Space Technique
Following novel development and adaptation of the Metric Space Technique
(MST), a multi-scale morphological analysis of the Sloan Digital Sky Survey
(SDSS) Data Release 5 (DR5) was performed. The technique was adapted to perform
a space-scale morphological analysis by filtering the galaxy point
distributions with a smoothing Gaussian function, thus giving quantitative
structural information on all size scales between 5 and 250 Mpc. The analysis
was performed on a dozen slices of a volume of space containing many newly
measured galaxies from the SDSS DR5 survey. Using the MST, observational data
were compared to galaxy samples taken from N-body simulations with current best
estimates of cosmological parameters and from random catalogs. By using the
maximal ranking method among MST output functions we also develop a way to
quantify the overall similarity of the observed samples with the simulated
samples
Synchronous Retreat of Southeast Greenland\u27s Peripheral Glaciers
Recently, scientific attention has focused on estimating Greenland\u27s dynamic mass loss through changes to flow speeds, thickness, and length on its marine outlet glaciers. For the ice sheet outlet glaciers, dynamic mass loss has been found to be highly sensitive to changes in climate and individual glacier geometry. For the ice-sheet-independent marine glaciers around Greenland\u27s periphery, dynamic mass loss is presently overlooked. Here, we apply an open-source, automated method of measuring glacier length changes using satellite imagery, to produce highly detailed records of length changes for 135 peripheral marine glaciers in southeast Greenland. We find evidence for anomalous retreat across 56 glaciers coincident with elevated surface melt in 2016, with melt 22% above the 2013–2019 average. Our detailed observations resolve the widespread, rapid, and synchronous response of these independent marine glaciers to increased meltwater input in 2016, indicating that their dynamics may be more sensitive to atmospheric warming than currently thought
Automated Detection of Coronal Loops using a Wavelet Transform Modulus Maxima Method
We propose and test a wavelet transform modulus maxima method for the au-
tomated detection and extraction of coronal loops in extreme ultraviolet images
of the solar corona. This method decomposes an image into a number of size
scales and tracks enhanced power along each ridge corresponding to a coronal
loop at each scale. We compare the results across scales and suggest the
optimum set of parameters to maximise completeness while minimising detection
of noise. For a test coronal image, we compare the global statistics (e.g.,
number of loops at each length) to previous automated coronal-loop detection
algorithms
Wavelet-based tracking of bacteria in unreconstructed off-axis holograms
We propose an automated wavelet-based method of tracking particles in unreconstructed off-axis holograms to provide rough estimates of the presence of motion and particle trajectories in digital holographic microscopy (DHM) time series. The wavelet transform modulus maxima segmentation method is adapted and tailored to extract Airy-like diffraction disks, which represent bacteria, from DHM time series. In this exploratory analysis, the method shows potential for estimating bacterial tracks in low-particle-density time series, based on a preliminary analysis of both living and dead Serratia marcescens, and for rapidly providing a single-bit answer to whether a sample chamber contains living or dead microbes or is empty
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