MOA-cam3: a wide-field mosaic CCD camera for a gravitational microlensing survey in New Zealand     

T. Sako  T. Sekiguchi  M. Sasaki  K. Okajima  F. Abe  I. A. Bond  J. B. Hearnshaw  Y. Itow  K. Kamiya  P. M. Kilmartin  K. Masuda  Y. Matsubara  Y. Muraki  N. J. Rattenbury  D. J. Sullivan  T. Sumi  P. Tristram  T. Yanagisawa  P. C. M. Yock 《Experimental Astronomy》2008,22(1-2):51-66

We have developed a wide-field mosaic CCD camera, MOA-cam3, mounted at the prime focus of the Microlensing Observations in Astrophysics (MOA) 1.8-m telescope. The camera consists of ten E2V CCD4482 chips, each having 2k×4k pixels, and covers a 2.2 deg² field of view with a single exposure. The optical system is well optimized to realize uniform image quality over this wide field. The chips are constantly cooled by a cryocooler at ??80° C, at which temperature dark current noise is negligible for a typical 1–3 min exposure. The CCD output charge is converted to a 16-bit digital signal by the GenIII system (Astronomical Research Cameras Inc.) and readout is within 25 s. Readout noise of 2–3 ADU (rms) is also negligible. We prepared a wide-band red filter for an effective microlensing survey and also Bessell V, I filters for standard astronomical studies. Microlensing studies have entered into a new era, which requires more statistics, and more rapid alerts to catch exotic light curves. Our new system is a powerful tool to realize both these requirements.  相似文献   

Visible and near-infrared spectral survey of Martian meteorites stored at the National Institute of Polar Research     

Takahiro Hiroi  Hiroshi Kaiden  Keiji Misawa  Takafumi Niihara  Hideyasu Kojima  Sho Sasaki 《Polar Science》2011,5(3):337-344

Martian meteorite chip samples stored at the National Institute of Polar Research (NIPR) have been studied by a visible and near-infrared (VNIR) spectrometer. Measured spots are about 3 × 2 mm in size, which are clearly marked on photographs of the meteorite chips. Rock types and approximate mineral compositions of studied meteorites have been identified or obtained through this spectral survey with no sample preparation required. This study demonstrates that this kind of spectral survey is effective in classifying and describing Marian meteorites, and that such a VNIR spectrometer on a Mars rover would be useful for identifying these kinds of unaltered Mars rocks. Further studies which utilize a smaller spot size are desired for improving the accuracy of identifying the clasts and mineral phases in the rocks.  相似文献   

A multidimensional horizontal-loop controlled-source electromagnetic inversion method and its use to characterize heterogeneity in aquiferous fractured crystalline rocks   总被引：1，自引：0，他引：1  

Yutaka Sasaki  Max A. Meju 《Geophysical Journal International》2006,166(1):59-66

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Impact of the equatorial Atlantic sea surface temperature on the tropical Pacific in a CGCM   总被引：1，自引：0，他引：1  

Wataru Sasaki  Takeshi Doi  Kelvin J. Richards  Yukio Masumoto 《Climate Dynamics》2014,43(9-10):2539-2552

Many coupled general circulation models (CGCMs) suffer from serious model bias in the zonal gradient of sea surface temperature (SST) in the equatorial Atlantic. The bias of the equatorial Atlantic SST (EASST) may affect the interannual variability of the equatorial Atlantic, which in turn may influence the state of the tropical Pacific. In this paper we investigate the impact of the bias and the interannual variability of the EASST on the tropical Pacific in a CGCM. To determine the impact of the interannual variability of the EASST on the tropical Pacific, we compare a run in a fully coupled mode (CTL run) and a run in which the EASST is nudged toward the climatological monthly mean of the SST in the CTL run, but full air-sea coupling is allowed elsewhere (AT_m run). We find that, when the interannual variability of the EASST is excluded, the thermocline depth in the eastern equatorial Pacific is deepened, and the amplitude of the El Niño/Southern Oscillation is reduced by 30 % compared to the CTL run. The impact of the bias of the EASST on the tropical Pacific is investigated by comparing the AT_m run and a run in which the EASST is nudged toward the observed climatological monthly mean SST (AT_o run). It is found that, when the bias of the EASST is removed (i.e. AT_o run), the Gill–Matsuno type response to the warm SST anomalies in the western equatorial Atlantic induces low-level cyclonic anomalies in the eastern South Pacific, which leads to a deeper thermocline and colder SST in the South Pacific as compared to AT_m. The colder SST in the South Pacific reduces the precipitation along the South Pacific convergence zone. Our results of the model experiments demonstrate the importance of the EASST to the tropical Pacific climate.  相似文献   

Vertical coupling and dynamical source for the intraseasonal variability in the deep Kuroshio Extension     

Yang  Yang  Liang  X. San  Sasaki  Hideharu 《Ocean Dynamics》2021,71(11-12):1069-1086

Ocean Dynamics - In the power spectrum, the upper and deep parts of the Kuroshio Extension have distinctly different peaks. The former peaks around 200 days, while the latter is mainly at the...  相似文献   

Spectral observations of impact dark spots     

B. Suzuki  H. Kurihara  T. Sasaki  J. Watanabe 《Earth, Moon, and Planets》1994,66(1):19-27

We carried out a spectral observation of traces of the comet impacts within the wavelength region between 440 and 830 nm. Three dark spots of fragments K, E, and G impact sites were investigated. The spectrum of these dark spots shows no special emission or absorption lines in this observation. The global spectral feature resembles that of Jovian zone cloud rather than that of the belt. While the continuum reflectivity of the dark spots of K and E sites is less than 0.42 at 600 nm, that of the G site is 0.33. These values should be interpreted as an upper limits because of the influence of atmospheric seeing. The equivalent width of the absorption lines at the K sites is also derived. Both the continuum reflectivity and the equivalent width of the dark spots are smaller than those of any Jovian zonal cloud. This indicates that the dark spots are low-albedo cloud formed at the upper atmosphere.  相似文献   

Practical applicability of high frequency correction theories to CO<Subscript>2</Subscript> flux measured by a closed-path system     

Takanori Shimizu 《Boundary-Layer Meteorology》2007,122(2):417-438

The theoretical correction of CO₂ fluxes for high frequency attenuation in closed-path systems was re-summarized and its applicability examined using both measurements obtained at an Asiaflux forest site and empirical transfer functions used in previous studies. For our measurement system, the theoretical transfer function was applicable to high frequency correction, even when condensation occurred in the sampling line. Further, in respect to some measurement systems described in previous studies, it was found that the theoretical function was potentially applicable along with the empirical functions used. Meanwhile, in some systems significant errors could not be resolved by re-estimation of the theories. In these systems, because of undefined buffering effects, the actual response lag time decided by the maximum covariance method or by measurement of the system response time using tracer gas was significantly different from the lag time calculated from the tube dimensions and the measured flow rate. If the average flow rate calculated by the actual lag time was used to determine the theoretical function, the theoretical function became closer to, and sometimes agreed with, the empirical function. Any remaining deviation from each function might be associated with pressure fluctuations, but this problem was unable to be examined here. The results suggested that an empirical formulation for each site is considered applicable rather than a theoretical approach, although the theories are being developed to practical application.  相似文献   

Petrological variation of large-volume felsic magmas from Hakkoda-Towada caldera cluster: Implications for the origin of high-K felsic magmas in the Northeast Japan Arc     

Takashi  Kudo  Minoru  Sasaki  Yoshihiro  Uchiyama  Akifumi  Nozawa  Hisashi  Sasaki  Takeshi  Tokizawa  Shinji  Takarada 《Island Arc》2007,16(1):133-155

Abstract The Hakkoda‐Towada caldera cluster (HTCC) is a typical Late Cenozoic caldera cluster located in the northern part of the Northeast Japan Arc. The HTCC consists of five caldera volcanoes, active between 3.5 Ma and present time. The felsic magmas can be classified into high‐K (HK‐) type and medium‐ to low‐K (MLK‐) type based on their whole‐rock chemistry. The HK‐type magmas are characterized by higher K₂O and Rb contents and higher ⁸⁷Sr/⁸⁶Sr ratios than MLK‐type magmas. Both magmas cannot be derived from fractional crystallization of any basaltic magma in the HTCC. Assimilation‐fractional crystallization model calculations show that crustal assimilation is necessary for producing the felsic magmas, and HK‐type magmas are produced by higher degree of crustal assimilation with fractional crystallization than MLK‐type magmas. Although MLK‐type magmas were erupted throughout HTCC activity, HK‐type magmas were erupted only during the initial stage. The temporal variations of magma types suggest the large contribution of crustal components in the initial stage. A major volcanic hiatus of 3 my before the HTCC activity suggests a relatively cold crust in the initial stage. The cold crust probably promoted crustal assimilation and fractional crystallization, and caused the initial generation of HK‐type magmas. Subsequently, the repeated supply of mantle‐derived magmas raised temperature in the crust and formed relatively stable magma pathways. Such a later system produced MLK‐type magmas with lesser crustal components. The MLK‐type magmas are common and HK‐type magmas are exceptional during the Pliocene–Quaternary volcanism in the Northeast Japan Arc. This fact suggests that exceptional conditions are necessary for the production of HK‐type magmas. A relatively cold crust caused by a long volcanic hiatus (several million years) is considered as one of the probable conditions. Intensive crustal assimilation and fractional crystallization promoted by the cold crust may be necessary for the generation of highly evolved HK‐type felsic magmas.  相似文献   

Determination of Stress State from Focal Mechanisms of Microseismic Events Induced During Hydraulic Injection at the Hijiori Hot Dry Rock Site     

S. Sasaki  H. Kaieda 《Pure and Applied Geophysics》2002,159(1-3):489-516

—?The stress state at the Hijiori hot dry rock site was estimated based on the inversion from focal mechanisms of microseismic events induced during hydraulic injection experiments. The best fit stress model obtained by inverting 58 focal mechanisms of seismic events simultaneously indicates that the maximum principal stress σ₁ is vertical, while the minimum principal stress σ₃ is horizontal and trends north-south. The average misfit between the stress model and all the data is 6.8°. The inversion results show that the average misfit is small enough to satisfy the assumption of homogeneity in the focal mechanism data and that the 95% confidence regions of σ₁ and σ₃ are well constrained, i.e., they do not overlap, suggesting that the inversion results are acceptable. The stress estimates obtained by the focal mechanism inversion essentially agree with other stress estimates previously obtained. It is therefore concluded that the focal mechanism inversion method provides a useful tool for estimating the stress state. The hypocentral distributions of microseismic events associated with the hydraulic fracturing experiments are distributed around the plane that spreads to almost east–west from the injection wells and declines to the north at a high angle. The vertical orientation and east–west strike of the seismic events are essentially coplanar with the caldera ring-fault structure in the southern portion of the Hijiori Caldera. This indicates that tensile fractures of intact rock were not being created, but pre-existing fractures were being re-opened and developed in the direction of the maximum horizontal principal stress, although microseismic events were caused by shear failures.  相似文献   

Immobilization of Se(VI) in mine drainage by permeable reactive barriers: column performance     

K. Sasaki  D.W. Blowes  C.J. Ptacek  W.D. Gould 《Applied Geochemistry》2008

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