35 research outputs found
Searching for sub-millisecond pulsars: A theoretical view
No full textSub-millisecond pulsars should be triaxial (Jacobi ellipsoids), which may not spin down to super-millisecond periods via gravitation wave radiation during their lifetimes if they are extremely low mass bare strange quark stars. It is addressed that the spindown of sub-millisecond pulsars would be torqued dominantly by gravitational wave radiation (with braking index n similar or equal to 5). The radio luminosity of sub-millisecond pulsars could be high enough to be detected in advanced radio telescopes. Sub-millisecond pulsars, if detected, should be very likely quark stars with low masses and/or small equatorial ellipticities.Astronomy & AstrophysicsCPCI-S(ISTP)
A Fission-Powered Interstellar Precursor Mission
No full textAn 'interstellar precursor mission' lays the groundwork for eventual interstellar exploration by studying the interstellar medium and by stretching technologies that have potential application for eventual interstellar exploration. The numerous scientific goals for such a mission include generating a 3-D stellar map of our galaxy, studying Kuiper-belt and Oort cloud objects, and observing distant objects using the sun's gravitational lens as the primary of an enormous telescope. System equations are developed for a space tug which propels a 2500-kg scientific payload to 550 astronomical units in about 20 years. The tug to transport this payload uses electric propulsion with an Isp of 15,000 seconds and a fission reactor with a closed Brayton cycle to genemte the electricity. The optimal configuration may be to thrust for only about 6 years and then coast for the remaining 14 pars. This spacecraft does not require any physics breakthroughs or major advances in technology. The fission power syslem can be engineered and built by drawing upon known technologies developed for relatgd systems over the past 40 years. The tug system would eventually reach 1000 a.u in 33 years, and would have adequate power to relay large amounts of data throughout its journey
A Gas-Cooled Reactor Surface Power System
No full textA human outpost on Mars requires plentiful power to assure survival of the astronauts. Anywhere from 50 to 500 kW of electric power (kWe) will be needed, depending on the number of astronauts, level of scientific activity, and life- cycle closure desired. This paper describes a 250-kWe power system based on a gas-cooled nuclear reactor with a recuperated closed Brayton cycle conversion system. The design draws upon the extensive data and engineering experience developed under the various high-temperature gas cooled reactor programs and under the SP-100 program. The reactor core is similar in power and size to the research reactors found on numerous university campuses. The fuel is uranium nitide clad in Nb 1 %Zr, which has been extensively tested under the SP-I 00 program The fiel rods are arranged in a hexagonal array within a BeO block. The BeO softens the spectrum, allowing better use of the fbel and stabilizing the geometty against deformation during impact or other loadings. The system has a negative temperature feedback coefficient so that the power level will automatically follow a variable load without the need for continuous adjustment of control elements. Waste heat is removed by an air-cooled heat exchanger using cold Martian air. The amount of radioactivity in the reactor at launch is very small (less than a Curie, and about equal to a truckload of uranium ore). The system will need to be engineered so that criticality cannot occur for any launch accident. This system is also adaptable for electric propulsion or life-support during transit to and from Mars
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A Gas-Cooled Reactor Surface Power System
Get PDFA human outpost on Mars requires plentiful power to assure survival of the astronauts. Anywhere from 50 to 500 kW of electric power (kWe) will be needed, depending on the number of astronauts, level of scientific activity, and life- cycle closure desired. This paper describes a 250-kWe power system based on a gas-cooled nuclear reactor with a recuperated closed Brayton cycle conversion system. The design draws upon the extensive data and engineering experience developed under the various high-temperature gas cooled reactor programs and under the SP-100 program. The reactor core is similar in power and size to the research reactors found on numerous university campuses. The fuel is uranium nitide clad in Nb 1 %Zr, which has been extensively tested under the SP-I 00 program The fiel rods are arranged in a hexagonal array within a BeO block. The BeO softens the spectrum, allowing better use of the fbel and stabilizing the geometty against deformation during impact or other loadings. The system has a negative temperature feedback coefficient so that the power level will automatically follow a variable load without the need for continuous adjustment of control elements. Waste heat is removed by an air-cooled heat exchanger using cold Martian air. The amount of radioactivity in the reactor at launch is very small (less than a Curie, and about equal to a truckload of uranium ore). The system will need to be engineered so that criticality cannot occur for any launch accident. This system is also adaptable for electric propulsion or life-support during transit to and from Mars
Principles of application of high temperature superconductors to electromagnetic launch technology
No full textThis is an open access article under the CC by licenseMany recent advances in the performance of bulk high temperature superconductors (HTSC) now permit conductor and magnet development at practical magnetic fields to be pursued for high current applications such as electromagnetic launchers (EML). While early hopes for a superconductor critical temperature (Tc) approaching room temperature have not been fulfilled, numerous HTSC with Tc between 60K and 125K exist which can be successfully processed. Some of these HTSC are well enough understood that small conductors and coils may be fabricated for operation near 20K. Numerous physics, magnetic flux mechanics, materials processing and structural support issues remain for resolution before large scale coils made of HTSC can be operated at high energy storage density at temperatures well above 20K. This paper describes our recent results on properties and materials processing of HTSC and their relation to EML applications technology. © 1991 IEEEWright-Patterson AFB; Air Force Institute of Technology, AFIT; National Research Council, NRCThe superconductor research was sponsored by the Air Force at the Wright Research and Development Center (WRDC) , Wright-Patterson AFB, Ohio. Materials processing and superconductor properties measurements were conducted primarily at the Aero Propulsion and Power Laboratories and some additional materials procesing and superconductor properties measurements were conducted in the Materials Laboratory and WRDC. One of the authors (G. Kozlowski) is supported under the auspices of the National Research Council Fellowship Program. The EML applications discussion was jointly provided by the Aero Propulsion and Power Laboratory, the Air Force Armament Laboratory at Eglin AFB, Florida, and the Strategic Defense Initiative Office, Washington, D. C. Helpful discussions on materials and the physics of superconductors were generously provided by P. Hemenger and M. Ohmer of the Materials Laboratory. The laboratory work was made possible by the industrious technical assistance of R. Leese and D. Linder of the University of Dayton Research Institute in Dayton, Ohio
Connection between the decadal variability in the Southern Ocean circulation and the Southern Annular Mode
Get PDFAuthor Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 34 (2007): L16604, doi:10.1029/2007GL030526.Previous studies demonstrated the remarkable upward trend of the Southern Annular Mode (SAM) and Southern Ocean wind stress in association with anthropogenic forcing. An oceanic reanalysis data set is used to investigate the response of the circulation in the Southern Ocean to the decadal variability of SAM. Our results indicate the strengthening and the poleward shift of the northward Ekman velocity as well as the Ekman pumping rate, which led to a corresponding strengthening trend in the Deacon Cell. This strengthening, in turn, intensified the meridional density gradient and the tilting of the isopycnal surfaces. On the interannual time scale, the Antarctic Circumpolar Currents (ACC) transport exhibits a positive correlation with SAM index as seen separately in observations. However, there is no significant trend in the total transport of ACC. Possible reasons are discussed.This work was supported by the
Chinese Academy of Sciences (Grant KZSW2-YW-214), the Natural
Science Foundation of China (Grant 40640420557) and National Basic
Research Program of China (Grant 2006CB403604) for X-Y. Yang and
D. Wang, and by W. Alan Clark Chair from Woods Hole Oceanographic
Institution for R.X. Huang
PULSARS AND GRAVITATIONAL WAVES
No full textThe relationship between pulsar-like compact stars and gravitational waves is briefly reviewed. Due to regular spins, pulsars could be useful tools for us to detect, similar to nano-Hz low-frequency gravitational waves by pulsar-timing array technique; besides, they would also be similar to kilo-Hz high-frequency gravitational wave radiators because of their compactness. The wave strain of an isolated pulsar depends on the equation state of cold matter at supra-nuclear densities. Therefore, a real detection of gravitational wave should be very meaningful in gravity physics, micro-theory of elementary strong interaction, and astronomy.Astronomy & AstrophysicsCPCI-S(ISTP)
Open Data from the Third Observing Run of LIGO, Virgo, KAGRA, and GEO
Get PDFThe global network of gravitational-wave observatories now includes five detectors, namely LIGO Hanford, LIGO Livingston, Virgo, KAGRA, and GEO 600. These detectors collected data during their third observing run, O3, composed of three phases: O3a starting in 2019 April and lasting six months, O3b starting in 2019 November and lasting five months, and O3GK starting in 2020 April and lasting two weeks. In this paper we describe these data and various other science products that can be freely accessed through the Gravitational Wave Open Science Center at https://gwosc.org. The main data set, consisting of the gravitational-wave strain time series that contains the astrophysical signals, is released together with supporting data useful for their analysis and documentation, tutorials, as well as analysis software packages. © 2023. The Author(s). Published by the American Astronomical Society.<br/
He star evolutionary channel to intermediate-mass binary pulsar PSR J1802-2124
No full textContext. The intermediate-mass binary pulsars (IMBPs) are characterized by relatively long spin periods (10-200 ms) and massive (greater than or similar to 0.4 M-circle dot) white dwarf (WD) companions. Recently, precise mass measurements have been performed for the pulsar and the WD in the IMBP PSR J1802-2124. Some observed properties, such as the low mass of the pulsar, the high mass of the WD, the moderately long spin period, and the tight orbit, imply that this system has undergone a peculiar formation mechanism. Aims. In this work, we attempt to simulate the detailed evolutionary history of PSR J1802-2124. Methods. We propose that a binary system consisting of a neutron star (NS, of mass 1.3 M-circle dot) and an He star (of mass 1.0 M-circle dot), and with an initial orbital period of 0.5 d, may have been the progenitor of PSR J1802-2124. Once the He star overflows its Roche lobe, He-rich material is transferred onto the NS at a relatively high rate of similar to 10(-7)-10(-6) M(circle dot)yr(-1), which is significantly higher than the Eddington accretion rate. A large amount of the transferred material is ejected from the vicinity of the NS by radiation pressure and results in the birth of a mildly recycled pulsar. Results. Our simulated results are consistent with the observed parameters of PSR J1802-2124. Therefore, we argue that the NS + He star evolutionary channel may be responsible for the formation of most IMBPs with orbital periods less than or similar to 3 d.Astronomy & AstrophysicsSCI(E)EI3ARTICLEnull53
