5,277 research outputs found
Scalable Exact Parent Sets Identification in Bayesian Networks Learning with Apache Spark
In Machine Learning, the parent set identification problem is to find a set
of random variables that best explain selected variable given the data and some
predefined scoring function. This problem is a critical component to structure
learning of Bayesian networks and Markov blankets discovery, and thus has many
practical applications, ranging from fraud detection to clinical decision
support. In this paper, we introduce a new distributed memory approach to the
exact parent sets assignment problem. To achieve scalability, we derive
theoretical bounds to constraint the search space when MDL scoring function is
used, and we reorganize the underlying dynamic programming such that the
computational density is increased and fine-grain synchronization is
eliminated. We then design efficient realization of our approach in the Apache
Spark platform. Through experimental results, we demonstrate that the method
maintains strong scalability on a 500-core standalone Spark cluster, and it can
be used to efficiently process data sets with 70 variables, far beyond the
reach of the currently available solutions
A method of approximating propellant requirements of low-thrust trajectories
Method of approximating propellant requirements of low thrust trajectorie
Single thrust period missions to Uranus for unmanned nuclear-electric propulsion systems
The effects of trip time, propulsion time, and specific powerplant mass are studied for optimized unmanned probe spacecraft on missions to Uranus with nuclear-electric propulsion systems. Electric propulsion is confined to a single thrust period at the beginning of each mission. Mission profiles include both high-thrust and electric-propulsion Earth-departure modes for planet flyby and orbital capture. Effects of propulsion time and propulsion system parameters are evaluated, and typical design features of the nuclear-electric spacecraft are outlined. Payload capability comparisons are made with systems employing ballistic transfer and solar-electric propulsion
Optimising for energy or robustness? Trade-offs for VM consolidation in virtualized datacenters under uncertainty
The final publication is available at Springer via http://dx.doi.org/10.1007/s11590-016-1065-xReducing the energy consumption of virtualized datacenters and the Cloud is very important in order to lower CO2 footprint and operational cost of a Cloud operator. However, there is a trade-off between energy consumption and perceived application performance. In order to save energy, Cloud operators want to consolidate as many Virtual Machines (VM) on the fewest possible physical servers, possibly involving overbooking of resources. However, that may involve SLA violations when many VMs run on peak load. Such consolidation is typically done using VM migration techniques, which stress the network. As a consequence, it is important to find the right balance between the energy consumption and the number of migrations to perform. Unfortunately, the resources that a VM requires are not precisely known in advance, which makes it very difficult to optimise the VM migration schedule. In this paper, we therefore propose a novel approach based on the theory of robust optimisation. We model the VM consolidation problem as a robust Mixed Integer Linear Program and allow to specify bounds for e.g. resource requirements of the VMs. We show that, by using our model, Cloud operators can effectively trade-off uncertainty of resource requirements with total energy consumption. Also, our model allows us to quantify the price of the robustness in terms of energy saving against resource requirement violations.Peer ReviewedPostprint (author's final draft
Solar-Electric Propulsion Probes for Exploring the Solar System
Payload capability of unmanned interplanetary probes using solar electric propulsio
SV Cen reveals its mystery
Our very-first high resolution spectra of SV Cen close binary system obtained
in the H alpha line reveal its absorption and emmision components, changing
with orbital phase. An accretion disk surrounding the component eclipsed at the
primary minimum is the most plausible explanation of this complex structure.Comment: To appear in ASP Conference Series special issue: "Binaries: Key to
Comprehension of the Universe
A study of contact binaries with large temperature differencies between components
We present an extensive analysis of new light and radial-velocity (RV)
curves, as well as high-quality broadening-function (BF) profiles of twelve
binary systems for which a contact configuration with large temperature
differencies between components has been reported in the literature. We find
that six systems (V1010 Oph, WZ Cyg, VV Cet, DO Cas, FS Lup, V747 Cen) have
near-contact configurations. For the remaining systems (CX Vir, FT Lup, BV Eri,
FO Hya, CN And, BX And), our solutions of the new observations once again
converge in a contact configuration with large temperature differencies between
the components. However, the bright regions discovered in the BFs for V747 Cen,
CX Vir, FT Lup, BV Eri, FO Hya, and CN And, and further attributed to hot
spots, shed new light on the physical processes taking place between the
components and imply the possibility that the contact configurations obtained
from light- and RV-curve modelling are a spurious result.Comment: Submited to Acta Astronomic
Applications and Challenges of Real-time Mobile DNA Analysis
The DNA sequencing is the process of identifying the exact order of
nucleotides within a given DNA molecule. The new portable and relatively
inexpensive DNA sequencers, such as Oxford Nanopore MinION, have the potential
to move DNA sequencing outside of laboratory, leading to faster and more
accessible DNA-based diagnostics. However, portable DNA sequencing and analysis
are challenging for mobile systems, owing to high data throughputs and
computationally intensive processing performed in environments with unreliable
connectivity and power.
In this paper, we provide an analysis of the challenges that mobile systems
and mobile computing must address to maximize the potential of portable DNA
sequencing, and in situ DNA analysis. We explain the DNA sequencing process and
highlight the main differences between traditional and portable DNA sequencing
in the context of the actual and envisioned applications. We look at the
identified challenges from the perspective of both algorithms and systems
design, showing the need for careful co-design
Determination of characteristics of newly discovered eclipsing binary 2MASS J18024395 +4003309 = VSX J180243.9+400331
During processing the observations of the intermediate polar 1RXS
J180340.0+401214, obtained 26.05.2012 at the 60-cm telescope of the Mt. Suhora
observatory (Krakow, Poland), variability of 2MASS J18024395+4003309 was
discovered. As this object was not listed in the "General Catalogue of Variable
Stars" or "Variable Stars Index", we registered it as VSX J180243.9+400331.
Additionally we used 189 separate observations from the Catalina Sky Survey
spread over 7 years. The periodogram analysis yields the period of
0d.3348837{\pm}0d.0000002.The object was classified as the Algol-type eclipsing
binary with a strong effect of ellipticity. The depths of the primary and
secondary minima are nearly identical, which corresponds to a brightness (and
maybe) mass ratio close to 1. The statistically optimal degree of the
trigonometric polynomial n=4. The most recent minimum occurred at HJD
2456074.4904. The brightness range from our data is 16.56-17.52 (V),
16.18-17.08 (R). The NAV ("New Algol Variable") algorithm was applied for
statistically optimal phenomenological modeling and determination of
corresponding parameters
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