Near-Solar-Circle Method for Determination of the Galactic Constants

We propose a method to determine the galactic constants R_0 (distance to the Galactic Center) and V_0 (rotation velocity of the Sun) from measurements of distances, radial velocities and proper motions of objects near the solar circle. This is a modification of the solar-circle method to a more practical observational method. We apply the method to determine R_0 using data from the literature with known distances and radial velocities, and obtain R_0 = 7.54 +/- 0.77 kpc.Comment: 5 pages, 4 figures, accepted for PASJ (Vol. 63 No. 5

Cavitation patterns on a plano-convex hydrofoil in a highspeed cryogenic cavitation tunnel

Cavitation around a plano-convex hydrofoil has been observed using a cryogenic cavitation tunnel of a blowdown type. An approximately 300mm long test section with flow visualization was set between the 100L upper and lower tanks. The working fluids were water and liquid nitrogen. Experiments with emphasis on periodical shedding of cloud cavitation were performed for three channels, 20, 30 and 60 mm in width, and two hydrofoils, 20 and 60mm in chord length LC. Inlet velocity uin and cavitation number ? were varied between 3.8 and 19.5 m/sec, and ?1.83 and 19.35, respectively. Incident angle was fixed at 8º. Observed cavitation patterns are sorted according to the maximum cavitation length Lmax compared to LC. Type X is defined as no cavitation, type A as 02LC. Type B has either the periodical shedding mode or the steady mode, so type PB is defined as type B with periodical shedding and type SB as type B under steady condition. Apparently types A and C are almost steady. Type PB solely occurs in the case that Lmax is comparable to LC. The cavitation patterns are mapped in the diagram of the degree of subcooling Pin?Psat versus the dynamic pressure ?uin2/2 because they are not organized only by ? =(Pin?Psat )/(?uin2/2). It is suggested that the maximum cavitation thickness is controlled by the similarity laws of hydrofoils for types SB and C.http://deepblue.lib.umich.edu/bitstream/2027.42/84257/1/CAV2009-final61.pd

Two fast X-ray transients in archival Chandra data

We present the discovery of two new X-ray transients in archival Chandra data. The first transient, XRT 110103, occurred in January 2011 and shows a sharp rise of at least three orders of magnitude in count rate in less than 10 s, a flat peak for about 20 s and decays by two orders of magnitude in the next 60 s. We find no optical or infrared counterpart to this event in preexisting survey data or in an observation taken by the SIRIUS instrument at the Infrared Survey Facility 2.1 yr after the transient, providing limiting magnitudes of J>18.1, H>17.6 and Ks>16.3. This event shows similarities to the transient previously reported in Jonker et al. which was interpreted as the possible tidal disruption of a white dwarf by an intermediate mass black hole. We discuss the possibility that these transients originate from the same type of event. If we assume these events are related a rough estimate of the rates gives 1.4*10^5 per year over the whole sky with a peak 0.3-7 keV X-ray flux greater than 2*10^-10 erg cm^-2 s^-1 . The second transient, XRT 120830, occurred in August 2012 and shows a rise of at least three orders of magnitude in count rate and a subsequent decay of around one order of magnitude all within 10 s, followed by a slower quasi-exponential decay over the remaining 30 ks of the observation. We detect a likely infrared counterpart with magnitudes J=16.70+/-0.06, H=15.92+/-0.04 and Ks=15.37+/-0.06 which shows an average proper motion of 74+/-19 milliarcsec per year compared to archival 2MASS observations. The JHKs magnitudes, proper motion and X-ray flux of XRT 120830 are consistent with a bright flare from a nearby late M or early L dwarf.Comment: Accepted for publication in MNRAS, 6 pages, 5 figure

EVMDD-based analysis and diagnosis methods of multi-state systems with multi-state components

A multi-state system with multi-state components is a model of systems, where performance, capacity, or reliability levels of the systems are represented as states. It usually has more than two states, and thus can be considered as a multi-valued function, called a structure function. Since many structure functions are monotone increasing, their multi-state systems can be represented compactly by edge-valued multi-valued decision diagrams (EVMDDs). This paper presents an analysis method of multi-state systems with multi-state components using EVMDDs. Experimental results show that, by using EVMDDs, structure functions can be represented more compactly than existing methods using ordinary MDDs. Further, EVMDDs yield comparable computation time for system analysis. This paper also proposes a new diagnosis method using EVMDDs, and shows that the proposed method can infer the most probable causes for system failures more efficiently than conventional methods based on Bayesian networks.Japan Society for the Promotion of ScienceMinistry of Education, Culture, Sports, Science and Technology (MEXT)Hiroshima City UniversityGrant-in Aid No. 2500050 (MEXT)Grant no. 0206 (HCU)Grant in Aid for Scientific Research (JSPS