2,928 research outputs found
Analysis of regolith electromagnetic scattering as constrained by high resolution Earth-based measurements of the lunar microwave emission
When high resolution measurements of the phase variation of the lunar disk center brightness temperature revealed that in situ regolith electrical losses were larger than those measured on returned samples by a factor of 1.5 to 2.0 at centimeter wavelengths, the need for a refinement of the regolith model to include realistic treatment of scattering effects was identified. Two distinct scattering regimes are considered: vertial variations in dielectric constant and volume scattering due to subsurface rock fragments. Models of lunar regolith energy transport processes are now at the state for which a maximum scientific return could be realized from a lunar orbiter microwave mapping experiment. A detailed analysis, including the effects of scattering produced a set of nominal brightness temperature spectra for lunar equatorial regions, which can be used for mapping as a calibration reference for mapping variations in mineralogy and heat flow
Simple and fast subband de-blocking technique by discarding the high band signals
In this paper, we propose a simple and fast post-processing de-blocking technique to reduce blocking artifacts. The block-based coded image is first decomposed into several subbands. Only the low frequency subband signals are retained and the high frequency subband signals are discarded. The remaining subband signals are then reconstructed to obtain a less blocky image. The ideas are demonstrated by a cosine filter bank and a modulated sine filter bank. The simulation result shows that the proposed algorithm is effective in the reduction of blocking artifacts
Securing Internet Protocol (IP) Storage: A Case Study
Storage networking technology has enjoyed strong growth in recent years, but
security concerns and threats facing networked data have grown equally fast.
Today, there are many potential threats that are targeted at storage networks,
including data modification, destruction and theft, DoS attacks, malware,
hardware theft and unauthorized access, among others. In order for a Storage
Area Network (SAN) to be secure, each of these threats must be individually
addressed. In this paper, we present a comparative study by implementing
different security methods in IP Storage network.Comment: 10 Pages, IJNGN Journa
High resolution thermal infrared mapping of Martian channels
Viking Infrared Thermal Mapper (IRTM) high resolution (2 to 5 km) data were compiled and compared to Viking Visual Imaging Subsystem (VIS) data and available 1:5M geologic maps for several Martian channels including Dao, Harmakhis, Mangala, Shalbatana, and Simud Valles in an effort to determine the surface characteristics and the processes active during and after the formation of these channels. Results show a dominance of aeolian processes active in and around the channels. These processes have left materials thick enough to mask any genuine channel deposits. Results also indicate that very comparable Martian channels and their surrounding terrain are blanketed by deposits which are homogeneous in their thermal inertia values. However, optimum IRTM data does not cover the entire Martian surface and because local deposits of high thermal inertia material may not be large enough in areal extent or may be in an unfavorable location on the planet, a high resolution data track may not always occur over these deposits. Therefore, aeolian processes may be even more active than the IRTM data tracts can always show
An absolute calibration system for millimeter-accuracy APOLLO measurements
Lunar laser ranging provides a number of leading experimental tests of
gravitation -- important in our quest to unify General Relativity and the
Standard Model of physics. The Apache Point Observatory Lunar Laser-ranging
Operation (APOLLO) has for years achieved median range precision at the ~2 mm
level. Yet residuals in model-measurement comparisons are an order-of-magnitude
larger, raising the question of whether the ranging data are not nearly as
accurate as they are precise, or if the models are incomplete or
ill-conditioned. This paper describes a new absolute calibration system (ACS)
intended both as a tool for exposing and eliminating sources of systematic
error, and also as a means to directly calibrate ranging data in-situ. The
system consists of a high-repetition-rate (80 MHz) laser emitting short (< 10
ps) pulses that are locked to a cesium clock. In essence, the ACS delivers
photons to the APOLLO detector at exquisitely well-defined time intervals as a
"truth" input against which APOLLO's timing performance may be judged and
corrected. Preliminary analysis indicates no inaccuracies in APOLLO data beyond
the ~3 mm level, suggesting that historical APOLLO data are of high quality and
motivating continued work on model capabilities. The ACS provides the means to
deliver APOLLO data both accurate and precise below the 2 mm level.Comment: 21 pages, 10 figures, submitted to Classical and Quantum Gravit
Optimal Coded Diffraction Patterns for Practical Phase Retrieval
Phase retrieval, a long-established challenge for recovering a complex-valued
signal from its Fourier intensity measurements, has attracted significant
interest because of its far-flung applications in optical imaging. To enhance
accuracy, researchers introduce extra constraints to the measuring procedure by
including a random aperture mask in the optical path that randomly modulates
the light projected on the target object and gives the coded diffraction
patterns (CDP). It is known that random masks are non-bandlimited and can lead
to considerable high-frequency components in the Fourier intensity
measurements. These high-frequency components can be beyond the Nyquist
frequency of the optical system and are thus ignored by the phase retrieval
optimization algorithms, resulting in degraded reconstruction performances.
Recently, our team developed a binary green noise masking scheme that can
significantly reduce the high-frequency components in the measurement. However,
the scheme cannot be extended to generate multiple-level aperture masks. This
paper proposes a two-stage optimization algorithm to generate multi-level
random masks named that can also significantly reduce
high-frequency components in the measurements but achieve higher accuracy than
the binary masking scheme. Extensive experiments on a practical optical
platform were conducted. The results demonstrate the superiority and
practicality of the proposed over the existing masking
schemes for CDP phase retrieval
Enhancing Semantic Code Search with Multimodal Contrastive Learning and Soft Data Augmentation
Code search aims to retrieve the most semantically relevant code snippet for
a given natural language query. Recently, large-scale code pre-trained models
such as CodeBERT and GraphCodeBERT learn generic representations of source code
and have achieved substantial improvement on code search task. However, the
high-quality sequence-level representations of code snippets have not been
sufficiently explored. In this paper, we propose a new approach with multimodal
contrastive learning and soft data augmentation for code search. Multimodal
contrastive learning is used to pull together the representations of code-query
pairs and push apart the unpaired code snippets and queries. Moreover, data
augmentation is critical in contrastive learning for learning high-quality
representations. However, only semantic-preserving augmentations for source
code are considered in existing work. In this work, we propose to do soft data
augmentation by dynamically masking and replacing some tokens in code sequences
to generate code snippets that are similar but not necessarily
semantic-preserving as positive samples for paired queries. We conduct
extensive experiments to evaluate the effectiveness of our approach on a
large-scale dataset with six programming languages. The experimental results
show that our approach significantly outperforms the state-of-the-art methods.
We also adapt our techniques to several pre-trained models such as RoBERTa and
CodeBERT, and significantly boost their performance on the code search task
Network coding meets TCP
We propose a mechanism that incorporates network coding into TCP with only
minor changes to the protocol stack, thereby allowing incremental deployment.
In our scheme, the source transmits random linear combinations of packets
currently in the congestion window. At the heart of our scheme is a new
interpretation of ACKs - the sink acknowledges every degree of freedom (i.e., a
linear combination that reveals one unit of new information) even if it does
not reveal an original packet immediately. Such ACKs enable a TCP-like
sliding-window approach to network coding. Our scheme has the nice property
that packet losses are essentially masked from the congestion control
algorithm. Our algorithm therefore reacts to packet drops in a smooth manner,
resulting in a novel and effective approach for congestion control over
networks involving lossy links such as wireless links. Our experiments show
that our algorithm achieves higher throughput compared to TCP in the presence
of lossy wireless links. We also establish the soundness and fairness
properties of our algorithm.Comment: 9 pages, 9 figures, submitted to IEEE INFOCOM 200
Detecting mutations in mixed sample sequencing data using empirical Bayes
We develop statistically based methods to detect single nucleotide DNA
mutations in next generation sequencing data. Sequencing generates counts of
the number of times each base was observed at hundreds of thousands to billions
of genome positions in each sample. Using these counts to detect mutations is
challenging because mutations may have very low prevalence and sequencing error
rates vary dramatically by genome position. The discreteness of sequencing data
also creates a difficult multiple testing problem: current false discovery rate
methods are designed for continuous data, and work poorly, if at all, on
discrete data. We show that a simple randomization technique lets us use
continuous false discovery rate methods on discrete data. Our approach is a
useful way to estimate false discovery rates for any collection of discrete
test statistics, and is hence not limited to sequencing data. We then use an
empirical Bayes model to capture different sources of variation in sequencing
error rates. The resulting method outperforms existing detection approaches on
example data sets.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS538 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Correlations of mutual positions of charge density waves nodes in side-by-side placed InAs wires measured with scanning gate microscopy
We investigate the correlations of mutual positions of charge density waves
nodes in side-by-side placed InAs nanowires in presence of a conductive atomic
force microscope tip served as a mobile gate at helium temperatures. Scanning
gate microscopy scans demonstrate mutual correlation of positions of charge
density waves nodes of two wires. A general mutual shift of the nodes positions
and "crystal lattice mismatch" defect were observed. These observations
demonstrate the crucial role of Coulomb interaction in formation of charge
density waves in InAs nanowires
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