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Large Families of Ternary Sequences with Aperiodic Zero Correlation Zone Sequences for a Multi-Carrier DS-CDMA System
A new method for generating families of ternary spreading sequences is presented. The sequences have aperiodic zero correlation zones and large families are created for a specific sequence length. The sequences are proposed as spreading sequences to provide high capacity and cancel multipath and multiple access interference (MAI) in a single carrier (SC) or multi-carrier (MC) direct-spread code division multiple access (DS-CDMA) system. A Multi-carrier DS-CDMA system is simulated that employs the new sequences as spreading sequences in a multipath channel. Bit error rates (BER) and frame error rates (FER) for a range of Eb/No values are presented and it is demonstrated that the proposed sequences improve the BER and FER performance when used in place of masked Walsh Codes for the frequency selective fading channel evaluated, when a single correlator receiver is used on each sub-carrier
Microlensing masses via photon bunching
In microlensing of a Galactic star by a brown dwarf or other compact object,
the amplified image really consists of two unresolved images with slightly
different light-travel times. The difference (of order a microsecond) is GM/c^3
times a dimensionless factor depending on the total magnification. Since
magnification is well-measured in microlensing events, a single time-delay
measurement would provide the mass of the lens, without degeneracies. The
challenge is to find an observable that varies on sub-microsecond time scales.
This paper notes that the narrow-band intensity of the unresolved image pair
will show photon bunching (the Hanbury Brown and Twiss effect), and argues that
the lensed intensity will have an auto-correlation peak at the lensing time
delay. The ultrafast photon-counting technology needed for this type of
measurement exists, but the photon numbers required to give sufficient
signal-to-noise appear infeasible at present. Preliminary estimates suggest
time-delayed photon bunching may be measurable for lensed early-type
main-sequence stars at 10 kpc, with the help of 30 m-class telescopes.Comment: To appear in MNRA
A Backend Framework for the Efficient Management of Power System Measurements
Increased adoption and deployment of phasor measurement units (PMU) has
provided valuable fine-grained data over the grid. Analysis over these data can
provide insight into the health of the grid, thereby improving control over
operations. Realizing this data-driven control, however, requires validating,
processing and storing massive amounts of PMU data. This paper describes a PMU
data management system that supports input from multiple PMU data streams,
features an event-detection algorithm, and provides an efficient method for
retrieving archival data. The event-detection algorithm rapidly correlates
multiple PMU data streams, providing details on events occurring within the
power system. The event-detection algorithm feeds into a visualization
component, allowing operators to recognize events as they occur. The indexing
and data retrieval mechanism facilitates fast access to archived PMU data.
Using this method, we achieved over 30x speedup for queries with high
selectivity. With the development of these two components, we have developed a
system that allows efficient analysis of multiple time-aligned PMU data
streams.Comment: Published in Electric Power Systems Research (2016), not available
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Amplification and stability of magnetic fields and dynamo effect in young A stars
This study is concerned with the early evolution of magnetic fields and
differential rotation of intermediate-mass stars which may evolve into Ap
stars. We report on simulations of the interplay of differential rotation and
magnetic fields, the stability limits and non-linear evolution of such
configurations, and the prospects of dynamo action from the unstable cases. The
axisymmetric problem delivers a balance between field amplification and
back-reaction of the magnetic field on the differential rotation. The
non-axisymmetric case involves also the Tayler instability of the amplified
toroidal fields. We consider limits for field amplification and apply these to
young A stars. Apart from its application to Ap stars, the instability is
scrutinized for the fundamental possibility of a dynamo. We are not looking for
a dynamo as an explanation for the Ap star phenomenon. The kinetic helicity is
concentrated near the tangent cylinder of the inner sphere of the computational
domain and is negative in the northern hemisphere. This appears to be a
ubiquitous effect not special to the Tayler instability. The latter is actually
connected with a positive current helicity in the bulk of the spherical shell
giving rise to a small, but non-vanishing alpha-effect in non-linear evolution
of the instability.Comment: 13 pages, 14 figures, accepted by Mon. Not. R. Astro
Development of Threshold Levels and a Climate-Sensitivity Model of the Hydrological Regime of the High-Altitude Catchment of the Western Himalayas, Pakistan
Water shortages in Pakistan are among the most severe in the world, and its water resources are decreasing significantly due to the prevailing hydro-meteorological conditions. We assessed variations in meteorological and hydrological variables using innovative trend analysis (ITA) and traditional trend analysis methods at a practical significance level, which is also of practical interest. We developed threshold levels of hydrological variables and developed a non-parametric climate-sensitivity model of the high-altitude catchment of the western Himalayas. The runoff of Zone I decreased, while the temperature increased and the precipitation increased significantly. In Zone II, the runoff and temperature increased but the precipitation decreased. A two-dimensional visualization of the Pardé coefficient showed extreme drought events, and indicated greater sensitivity of the hydrological regime to temperature than to precipitation. The threshold levels of runoff for Zones I and II were 320 and 363 mm using the Q80 fixed method, while the mean runoff amounts were estimated to be 79.95 and 55.61 mm, respectively. The transient threshold levels varied by month, and the duration of droughts in Zones I and II ranged from 26.39 to 78.98 days. The sensitivity of the hydrological regime was estimated based on a modified climate-elasticity model (εp = 0.11–0.23, εt = −0.04–2.39) for Zones I and II, respectively. These results highlight the sensitivity of the hydrological regime to temperature, which influences the melting process. However, it is important to establish thresholds for hydrological variables and understand the climate sensitivity of the hydrological regime of the entire basin, so that policy makers and water managers can make sustainable water-resource-management decisions for this region
A Hierarchal Planning Framework for AUV Mission Management in a Spatio-Temporal Varying Ocean
The purpose of this paper is to provide a hierarchical dynamic mission
planning framework for a single autonomous underwater vehicle (AUV) to
accomplish task-assign process in a limited time interval while operating in an
uncertain undersea environment, where spatio-temporal variability of the
operating field is taken into account. To this end, a high level reactive
mission planner and a low level motion planning system are constructed. The
high level system is responsible for task priority assignment and guiding the
vehicle toward a target of interest considering on-time termination of the
mission. The lower layer is in charge of generating optimal trajectories based
on sequence of tasks and dynamicity of operating terrain. The mission planner
is able to reactively re-arrange the tasks based on mission/terrain updates
while the low level planner is capable of coping unexpected changes of the
terrain by correcting the old path and re-generating a new trajectory. As a
result, the vehicle is able to undertake the maximum number of tasks with
certain degree of maneuverability having situational awareness of the operating
field. The computational engine of the mentioned framework is based on the
biogeography based optimization (BBO) algorithm that is capable of providing
efficient solutions. To evaluate the performance of the proposed framework,
firstly, a realistic model of undersea environment is provided based on
realistic map data, and then several scenarios, treated as real experiments,
are designed through the simulation study. Additionally, to show the robustness
and reliability of the framework, Monte-Carlo simulation is carried out and
statistical analysis is performed. The results of simulations indicate the
significant potential of the two-level hierarchical mission planning system in
mission success and its applicability for real-time implementation
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