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Four species of malaria parasite, Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium knowlesi infect humans living in the Khanh Phu commune, Khanh Hoa Province, Vietnam. The latter species also infects wild macaque monkeys in this region. In order to understand the transmission dynamics of the three species, we attempted to detect gametocytes of the three species in the blood of infected individuals, and sporozoites in the salivary glands of mosquitoes from the same region. For the detection of gametocyte-specific mRNA, we targeted region 3 of pfg377, pvs25, pmg and pks25 as indicators of the presence of P. falciparum, P. vivax, P. malariae and P. knowlesi gametocytes, respectively. Gametocyte-specific mRNA was present in 37, 61, 0 and 47% of people infected with P. falciparum (n = 95), P. vivax (n = 69), P. malariae (n = 6) or P. knowlesi (n = 32), respectively. We found that 70% of mosquitoes that had P. knowlesi in their salivary glands also carried human malaria parasites, suggesting that mosquitoes are infected with P. knowlesi from human infections.
There are several regions where a group of quasars are significantly clustered in the physical space. In the “CFHT grens survey” conducted by Crampton et al. (Crampton et al. 1989 and references therein), the 23 quasars between z=1.036 and 1.185 were found to be clustered over ~ 2° × 2° in the region denoted as 1338+27 At the mean redshift zave = 1.113, the angular extent 6000 arcsec (CHH89) of this cluster corresponds to 60 h−1Mpc(q0 = 0.5) and the dispergion of the redshift λz = 0.044 to 45 h−1Mpc.
Since the discovery of fading X-rays from Gamma-Ray Bursts (GRBs) with BeppoSAX (Piro et al. 1997, Costa et al. 1997), world-wide follow-up observations in optical band have achieved the fruitful results. The case of GRB 970228, there was an optical transient, coincides with the BeppoSAX position and faded (Paradijs et al. 1997, Sahu et al. 1997). These optical observations also confirmed the extended component, which was associated with the optical transient. The new transient are fading with a power-law function in time and the later observation of HST confirmed the extended emission is stable (Fruchter et al. 1997). This extended object seems to be a distant galaxy and strongly suggests to be the host.
We compared the calculation performance of cosmological N-body simulations with and without GRAPE-4. A modified Barnes-Hut treecode was used for these simulations. GRAPE(GRAvity piPE) is a special-purpose computer for gravitational N-body simulations. The newest hardware GRAPE-4 achieved a quite high peak performance (1.08 Tflops). In cosmological N-body simulations, a large number of particles is required and fast algorithms such as Barnes-Hut treecode or P3M/PM are usually used. GRAPE-4 can accelearte such algorithms. In paticular, the PCI interface recently completed allows us to use fast host computer, thus it improved the performance of these fast algorithms. Figure 1 shows the CPU time per one timestep as functions of force calculation error for both systems with and without GRAPE-4.
Here we present a very short review of the ASCA observation campaign of the enigmatic galactic jet system SS433. The campaign started in 1994 just after the launch, and ended in 1996. Various phases of the 162.5-day precession and 13-day orbital motion were sampled. With ASCA, the Doppler-shifted pairs from various ion species from Si to Ni were resolved for the first time (Kotani et al. 1994). The Doppler-shift parameters were determined with an accuracy comparable to optical spectroscopy (Kawai 1995). No velocity gradient was found between the X-ray emission region of the jet and the optical. The distance between them was constrained to be less than 1015 cm. Line intensity ratios of Fe XXVI/Fe XXV give the base temperature of the jet to be 20 keV (Kotani et al. 1996). The variation of the apparent base temperature of the jet can be explained in terms of the partial occultation of the jet by a precessing accretion disk (Kotani et al. 1997a). From the variation, the disk radius and the disk height in unit of the X-ray jet length were estimated to be 0.23 ± 0.10 and 0.0232 ± 0.0049, respectively. (These are an improved version of the values in Kotani et al. (1997a).) SS433 is also known as an eclipsing binary. Because the emission from each jet with ASCA, it is possible to know how much of which jet is occulted by the companion star during an eclipse. Relative size of the companion star gives Roche lobe size and thus mass ratio MX/MC = 0.22+0.09-0.16 (Kotani 1997b). With the help of Doppler modulation, compact star mass is constrained. However, the values of Doppler modulation reported from optical observations largely scatters. D'Odorico et al. (1991) reported 112 km s−1 and this gives MX = 0.68+0.43-0.53 M⊙, i.e., a white dwarf, while Fabrika and Bychkova (1990) reported 175 km s−1, which gives 2.6+1.6-2.0 M⊙. (This error includes systematic errors of the X-ray data, and will be reduced in future analysis.) On the other hand, the absolute size of the system were determined with a satisfactory precision. For example, the X-ray jet length was determined to be 2×1013 cm, ten times larger than previous estimations (Kotani et al. 1997c). Other physical parameters of the jet can be derived from the X-ray jet length. Mass outflow rate and the kinetic luminosity of both jet were determined to be 8 × 10−6 M⊙ yr−1 and 1.6 × 1040 erg s−1 (Kotani et al. 1997d), implicating a highly super critical accretion. Most of these values are first precise measurements and/or “radical” revisions of previous estimations. The new picture of SS433 drawn here is far stormy and highly energetic.
We made a search of quiescent X-ray counterparts of two Gamma-Ray Bursts (GRBs), GRB930131 and GRB940217. These GRBs were detected with BATSE, EGRET, COMPTEL on board CGRO together with the GRB detector on Ulysses spacecraft, then they were localized in small error regions. These observations showed that the bursts were remarkably bright accompanying delayed high energy gamma-rays. ASCA observations have found a single X-ray source for each GRB on the possible location determined with the above instruments.
SS 433 has been observed with ASCA for three years since the launch in 1993. The excellent energy resolution of ASCA revealed the Doppler-shifted emission lines from the both jets, though it had been generally accepted that the X-ray emitting region of the receding jet is hidden behind the accretion disk. Thus the estimation on the properties of the X-ray jet, such as length, temperature, and mass outflow rate, should be revised in accordance with the ASCA data. Modeling the jet as a radiating ballistic plasma, we determined these quantities. It is also tried to determine the mass of the system from a data covering an eclipse.
We propose an X-ray all sky monitor for Japanese Experimental Module (JEM) on the space station. Considering practical circumstances, we show as a case study that the all sky monitor with slit hole cameras is most promising for monitoring the short-term and long-term X-ray transients. We call this all sky monitor as MAXI (Monitor of All-sky X-ray Image). Position determination of gamma-ray bursts could be achieved with accuracy less than one degree observing the X-ray component of the burst. Weak X-ray sources such as active galactic nuclei could be also monitored with time resolution less than one day. The X-ray all sky monitor will work to discover X-ray novae and transient phenomena and give us the alarm for further detailed observations. The obtained data will be also used for archival study.
We report on the spectral and temporal properties of the 50 ms pulsar PSR B0540–69 using ASCA archival data obtained during 1993 to 1995. From the spectral analysis it was found that the spectra of the whole (nebular and pulsed) emission and pulsed emission in the range 1-10 keV can be represented by a single power law of photon index, Γ = 2.00 ± 0.02 and Γpulsed = 1.7 ± 0.3 respectively. The parameters for pulse frequency change during 1993-1995 were obtained using the 9 pulse frequency measurements with ASCA. The parameters derived from the ASCA observations are consistent with the previous measurements, suggesting high stability of this pulsar, ΔΩ/Ω ≲ 0.5 × 10−7 over the past 10 years. These results confirm similarity of this pulsar with the Crab pulsar.
The High Energy Transient Explorer 2 is a small scientific satellite designed to detect and localize gamma-ray bursts (GRBs). The coordinates of GRBs detected by HETE-2 will be distributed to interested ground-based observers within seconds of burst detection, thereby allowing detailed observations of the initial phases of GRBs. HETE-2 was launched successfully on October 9, 2000. The GRB positions will start to be delivered after a few months of the complete testing and calibration of the spacecraft system and the science instruments.
This study presents accelerator mass spectrometry (AMS) radiocarbon dates and pollen assemblages of 400-cm core sediments collected from the Karekare Swamp in Rarotonga, Southern Cook Islands, to investigate vegetation changes on the island, in particular those induced by human impacts. Eight 14C dates of charcoal and higher plant fragment samples indicate that the sediments accumulated since ∼6.0 cal kBP, with an apparent interruption of deposition (hiatus) from 130 to 132 cm in depth, corresponding to ∼2.8 to 0.7 cal kBP. The appearance of Chenopodiaceae pollen from upland weeds, and Cucurbitaceae and Vigna pollen grains from cultivated plants suggest that human influence existed in core sediments above 130 cm in depth. The increased abundance of Pandanus pollen and monolate-type fern spores also implies the existence of human activity.