2,076 research outputs found
Dark matter, neutron stars and strange quark matter
We show that self-annihilating neutralino WIMP dark matter accreted onto
neutron stars may provide a mechanism to seed compact objects with long-lived
lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV.
This effect may trigger a conversion of most of the star into a strange star.
We use an energy estimate for the long-lived strangelet based on the Fermi gas
model combined with the MIT bag model to set a new limit on the possible values
of the WIMP mass that can be especially relevant for subdominant species of
massive neutralinos.Comment: 5 pages, 2 figures, accepted for publication in Phys. Rev. Let
An Evaluation of Uranium-Series Dating of Fossil Echinoids from Southern California Pleistocene Marine Terraces
Fossil sea urchins (Strongylocentrotus) from Pleistocene marine terraces on the southern California Channel Islands have been dated by the uranium-series method in order to test the suitability of echinoids for dating marine terraces. Results indicate that urchin plates and spines do not behave as closed systems with respect to both uranium and thorium. Calculated ages based on these data do not agree with uranium-series ages (120,000 and 127,000 yrs) obtained previously from corals from the same localities. Thus, fossil sea urchins (Strongylocentrotus) are not considered suitable for uranium-series dating of Pleistocene marine terrace deposits
Voltage Stability Analysis of Grid-Connected Wind Farms with FACTS: Static and Dynamic Analysis
Recently, analysis of some major blackouts and failures of power system shows that voltage instability problem has been one of the main reasons of these disturbances and networks collapse. In this paper, a systematic approach to voltage stability analysis using various techniques for the IEEE 14-bus case study, is presented. Static analysis is used to analyze the voltage stability of the system under study, whilst the dynamic analysis is used to evaluate the performance of compensators. The static techniques used are Power Flow, VâP curve analysis, and QâV modal analysis. In this study, Flexible Alternating Current Transmission system (FACTS) devices- namely, Static Synchronous Compensators (STATCOMs) and Static Var Compensators (SVCs) - are used as reactive power compensators, taking into account maintaining the violated voltage magnitudes of the weak buses within the acceptable limits defined in ANSI C84.1. Simulation results validate that both the STATCOMs and the SVCs can be effectively used to enhance the static voltage stability and increasing network loadability margin. Additionally, based on the dynamic analysis results, it has been shown that STATCOMs have superior performance, in dynamic voltage stability enhancement, compared to SVCs
Tracing out the Northern Tidal Stream of the Sagittarius Dwarf Spheoridal Galaxy
The main aim of this paper is to report two new detections of tidal debris in
the northern stream of the Sagittarius dwarf galaxy located at 45 arcdeg and 55
arcdeg from the center of galaxy. Our observational approach is based on deep
color-magnitude diagrams, that provides accurate distances, surface brightness
and the properties of stellar population of the studied region of this tidal
stream. The derived distances for these tidal debris wraps are 45 kpc and 54
kpc respectively.We also confirm these detections with numerical simulations of
the Sagittarius dwarf plus the Milky Way. The model reproduces the present
position and velocity of the Sagittarius main body and presents a long tidal
stream formed by tidal interaction with the Milky Way potential. This model is
also in good agreement with the available observations of the Sagittarius tidal
stream. We also present a method for estimating the shape of the Milky Way halo
potential using numerical simulations. From our simulations we obtain an
oblateness of the Milky Way dark halo potential of 0.85, using the current
database of distances and radial velocities of the Sagittarius tidal stream.
The color-magnitude diagram of the apocenter of Sagittarius shows that this
region of the stream shares the complex star formation history observed in the
main body of the galaxy. We present the first evidence for a gradient in the
stellar population along the stream, possibly correlated with its different
pericenter passages. (abridged)Comment: 43 pages (including 15 figures; for high resolution color figures,
please contact [email protected]). Submitted to Ap
Synthesis of Spherical 4R Mechanism for Path Generation using Differential Evolution
The problem of path generation for the spherical 4R mechanism is solved using
the Differential Evolution algorithm (DE). Formulas for the spherical geodesics
are employed in order to obtain the parametric equation for the generated
trajectory. Direct optimization of the objective function gives the solution to
the path generation task without prescribed timing. Therefore, there is no need
to separate this task into two stages to make the optimization. Moreover, the
order defect problem can be solved without difficulty by means of manipulations
of the individuals in the DE algorithm. Two examples of optimum synthesis
showing the simplicity and effectiveness of this approach are included.Comment: Submitted to Mechanism and Machine Theor
Wind Blade Manufacturing for the Cal Poly Wind Power Club
The Cal Poly Wind Power Club is entering the 2021 Collegiate Wind Competition (CWC) in June. Last year, three senior project teams were assigned to collaborate and assist the club with the pitching mechanism, the rotor balancing, and the manufacturing process. As the manufacturing team, the goal of our project was to design a manufacturing process for the bladegeometry given. The manufacturing process was required to meet the teamâs expectations and CWCâs performance requirements to place highly in the competition taking place in June 2021.These expectations included creating a manufacturing process that is repeatable and reliable for future competitions. The manufactured blades had to be dimensionally accurate up to less than one percent error between each of the three blades. The blades also needed to be as light as possible to be efficient, thus the blades needed to be less than half a pound each. The manufactured blades also needed to be as smooth as 0.25 microns to ensure aerodynamic performance is not compromised. Our finalized process met the requirements for almost all these requirements. The dimensional accuracy of the blades is less than one percent error between the blades, however, some additional changes will be needed for future blades which be explained later in the report. The finalized blades far surpass the goals given by the WPC, only weighing 1/8 of a pound each compared to the half pound goal. Lastly the surface roughness of the blades did not meet the 0.25-micron requirement, however, we believe that the final design reaches a smoothness that will be acceptable for the competition. Solutions to make the blades smoother are also given in the report if the WPC believes the finalized blades do not meet their requirements
The First Report on the Molecular Identification of Fresh Water Microalgae from Waterfalls of Paracelis, Mountain Province, Philippines
Microalgae belong to diverse groups of complex unicellular photosynthetic microorganisms typically found in the freshwater and marine environment. Towards the isolation and an attempt to report the first molecular identification of freshwater microalgae from the waterfalls of Paracelis, Mountain Province, Philippines, two microalgae were successfully isolated independently, purified, and cultivated for DNA extraction, polymerase chain reaction, and sequencing using gene 16s rRNA and rbcL markers. Based on the 16s rRNA sequence, one of the isolates has a 92.05% sequence similarity to Oscillatoriales cyanobacterium (KJ611413). On the other hand, one isolate has 98.27% sequence similarity with Chlorella pyrenoidosa (AB240145) using the rbcL. The morphological features of two microalgae were described and the phylogenetic trees were constructed using the gene marker
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