Analysis of interference effects on monopulse radars

The complete numerical analysis of angle-tracking performance of a coherent amplitude-comparison monopulse radar system in a two-target situation is described. This system, equipped with automatic gain control (AGC) and phase-locked loop (PLL), was originally invented for improving the target-tracking performance in multiple-target situation. The general behavior depends on Doppler separation of the targets relative to the bandwidths of AGC and PLL. The performance of this system has previously been roughly analyzed by using linear approximation for four extreme cases: wideband and narrowband AGC in combination with wideband and narrowband PLL. In this study, the author performs nonlinear analysis of the same system for all bandwidths of AGC and PLL, because Doppler separation varies over a wide range in actual tracker, and therefore it is indispensable to know the total system behavior. A special numerical technique called the Galerkin method is used. As a result of this analysis, the extensive target-tracking performance for all intermediate bandwidths of AGC and PLL has been clarified. The result is useful for actual target tracker design     

Evaluation of dose rate reduction in a spacecraft compartment due to additional water shield

The dose reduction rates brought about by the installation of additional water shielding in a spacecraft are calculated in the paper using the particles and heavy ion transport code system PHITS, which can deal with transport of all kinds of hadrons and heavy ions with energies up to 100 GeV/n in three-dimensional phase spaces. In the PHITS simulation, an imaginary spacecraft was irradiated isotropically by cosmic rays with charges up to 28 and energies up to 100 GeV/n, and the dose reduction rates due to water shielding were evaluated for 5 types of doses: the dose equivalents obtained from the LET and linear energy spectra, the dose equivalents to skin and red bone marrow, and the effective dose equivalent. The results of the simulation indicate that the dose reduction rates differ according to the type of dose evaluated. For example, 5 g/cm² water shielding reduces the effective dose equivalent and the LET dose equivalent by approximately 14% and 32%, respectively. Such degrees of dose reduction can be regarded to make water shielding worth the efforts required to install it.     

Comparison of the mean quality factors for astronauts calculated using the Q-functions proposed by ICRP,ICRU, and NASA

For the estimation of the radiation risk for astronauts, not only the organ absorbed doses but also their mean quality factors must be evaluated. Three functions have been proposed by different organizations for expressing the radiation quality, including the Q(L), Q(y), and Q_NASA(Z, E) relationships as defined in International Committee of Radiological Protection (ICRP) Publication 60, International Commission on Radiation Units and Measurements (ICRU) Report 40, and National Aeronautics and Space Administration (NASA) TP-2011-216155, respectively. The Q(L) relationship is the most simple and widely used for space dosimetry, but the use of the latter two functions enables consideration of the difference in the track structure of various charged particles during the risk estimation.     

An observation of snow melting process from remotely sensed data

Observations of satellite images have shown that the snow melting in mountainous area proceeds more repidly in the east-facing slope of the valley than in the west-facing one. The energy for melting snow consists of the total from the atmosphere and from the solar rays. The diurnal variation of the solar energy into the snow in the east-facing slope differs from that in the west-facing slope. This causes the heighest value of the instantaneous energy for melting snow to occur in the west-facing surface. As one of the reasons for the above tendency, the difference of the heighest value to melt snow may be taken into account.     

Detection of DNA damages and repair in human culture cells with simulated space radiation

DNA damages and its repair of cultured WI38 human fibroblast cells and T98G human glioblastoma cells were studied by exposing to carbon ion beams of HIMAC accelerator. The exposed cells were incubated at 37 °C for appropriate intervals and the damages were analyzed by alkaline comet assay and quantitative RT-PCR with p53 mRNA Highly inhomogeneous DNA damages were observed among the electrophoretic cell images of the comet assay. The degree of the damages was analyzed semi-quantitatively by using the Comet Index. The damaged fraction of WI38 cells was 85% immediately after 4 Gy (100 keV/μm) irradiation and decreased to 50% after 120 min. incubation indicating a repair of cell DNA. Time dependent p53 gene expression was also analyzed by the quantitative RT-PCR method.