Yokosuka, Japan

National Defense Academy of Japan , abbreviated NDA is the national, four-year university-level military academy aimed to educate and train students who will be serving as officers in the three services of the Japan Self-Defense Forces. It is located in Yokosuka, Kanagawa on the grounds close to the former Imperial Japanese Army Academy. Wikipedia.

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Tanaka H.,Japan National Defense Academy
Acta Astronautica | Year: 2011

Novel methods for the estimation and correction of antenna surface deformations are developed and investigated. Surface adjustment mechanisms, which are used for a reconfigurable antenna system, are used to estimate and correct surface errors. Relations between antenna surface errors and changes in antenna gains caused by intentional deformations are derived from the Ruze equation. In these methods, an antenna surface is deformed using the surface adjustment mechanisms, and the changes in the gains caused by the intentional deformations are measured. On the basis of the information regarding the intentional deformations and the resultant changes in the antenna gains, original deformation of the antenna surface is estimated. The deformation is corrected using the surface adjustment mechanisms. Some numerical simulations are carried out to investigate the feasibility of these methods. The results of these simulations show that the antenna deformations are estimated and corrected adequately using these methods. © 2010 Elsevier Ltd.

Yokoyama N.,Japan National Defense Academy
Journal of Guidance, Control, and Dynamics | Year: 2013

This paper describes a novel algorithm for generating flight paths in real time that avoid turbulent regions detected by an onboard Doppler lidar. Adopting the distance traveled rather than the time as the independent variable in the state equations enables an exact expression to be obtained for the point-mass dynamics and reduces the number of constraints imposed by turbulence avoidance. Moreover, the algorithm estimates the global optimum by applying second-order cone programming relaxation to the original nonconvex problem. Based on this estimate, it then applies convex quadratic programming. This algorithm is well suited for real-time applications since it is guaranteed to converge in polynomial computation time and it is expected to generate practically useful paths. The high computational speed of the algorithm is demonstrated and the physical feasibilities of the calculated paths are analyzed by numerically simulating turbulence avoidance. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Ouchi K.,Japan National Defense Academy
Remote Sensing | Year: 2013

The present article is an introductory paper in this special issue on synthetic aperture radar (SAR). A short review is presented on the recent trend and development of SAR and related techniques with selected topics, including the fields of applications, specifications of airborne and spaceborne SARs, and information contents in and interpretations of amplitude data, interferometric SAR (InSAR) data, and polarimetric SAR (PolSAR) data. The review is by no means extensive, and as such only brief summaries of of each selected topics and key references are provided. For further details, the readers are recommended to read the literature given in the references theirin. © 2013 by the author.

Kohga M.,Japan National Defense Academy
Propellants, Explosives, Pyrotechnics | Year: 2011

The burning rate of AP/HTPB composite propellant increases with increasing AP content and with decreasing AP size. In addition, the burning rate can be enhanced with the addition of Fe2O3. The burning characteristics and thermal decomposition behavior of AP/HTPB composite propellant using coarse and fine AP particles with and without Fe 2O3 at various AP contents were investigated to obtain an exhaustive set of data. As the AP content decreased, the burning rate decreased and the propellants containing less than a certain AP content self-quenched or did not ignite. The self-quenched combustion began at both lower and higher pressures. The lower limit of AP content to burn the propellant with coarse AP was lower than that with fine AP. The lower limit of AP content to burn was decreased by the addition of Fe2O3. The thermal decomposition behavior of propellants prepared with 20-80 % AP was investigated. The decrease in the peak temperature of the exothermic decomposition suggested an increased burning rate. However, a quantitative relationship between the thermochemical behavior and the burning characteristics, such as the burning rate and the lower limit of AP content to burn, could not be determined. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A single living cell (PC12), cultured on a polystyrene dish and an albumin island immobilized on glass, were successfully imaged utilizing the differential standing approach (d-SA) mode of a scanning ion conductance microscope (SICM). In the d-SA mode, the differential of the output voltage of a tuning fork (rather than its absolute value) is used as the signal for maintaining a constant distance between the probe of a scanning ion conductance microscope (SICM) and the sample. The topography and SICM images were obtained simultaneously, and approach curves, when the tip approached the immobilized albumin or the PC12 cell membrane, were also obtained. The settings for the d-SA mode were carefully determined from the PC12 cell approach curve. Furthermore, differences in the topographies of the immobilized albumin and living PC12 cell images obtained using the standing approach (SA) versus d-SA mode are discussed. It is shown that SICM in d-SA mode is capable of imaging soft samples such as living cells without damaging them. © 2014 Elsevier Ltd.

Tada S.,Japan National Defense Academy
Physics in Medicine and Biology | Year: 2010

This study investigates the oxygen mass transport in the region around the human carotid bifurcation, particularly addressing the effects of bifurcation geometry and pulsatile blood flow on the oxygen transport between the blood flow and artery wall tissue, coupled with the metabolic oxygen consumption and oxygen diffusion in the artery wall tissue. The temporal variations and spatial distributions of the oxygen tension are predicted quantitatively using a geometric model of the human carotid bifurcation and realistic blood flow waveforms. Results reveal that the flow separation at the outside wall of the sinus of the internal carotid artery (ICA) can markedly alter the flow pattern, oxygen tension and the oxygen wall flux. Results also clarify that the flow unsteadiness has a secondary effect on the oxygen tension inside the wall. The non-dimensional oxygen flux, the Sherwood number Sh, at the outside wall of the ICA sinus, takes markedly lower values of about 45 than at other sites because the rates of oxygen transport by the convective flow are reduced at the outside wall of the ICA sinus. The transverse distributions of the oxygen tension inside the artery wall show parabolic profiles having minima in the middle of the wall thickness, with the lowest value of 35 mmHg. These predicted distributions of the oxygen tension inside the wall closely resemble those obtained from experiments. The results demonstrate that hypoxic zones appear inside the artery walls at locations where atherosclerotic lesions are prone to develop. © 2010 Institute of Physics and Engineering in Medicine.

Kohga M.,Japan National Defense Academy | Okamoto K.,Japan National Defense Academy
Combustion and Flame | Year: 2011

Ammonium nitrate (AN)-based propellant is plagued by several drawbacks: low burning rate, poor ignitability, and low energy. The application of an energetic binder is an effective approach to the practical use of AN-based propellants but has not been used to date because the synthesis processes are complicated and expensive. Polytetrahydrofuran (PTHF) is a raw material for rubber products and is not an energetic material. The repeating unit of PTHF has one oxygen atom, and although PTHF could not become solid with use of a curing agent alone, PTHF became rubbery with the use of glycerin as a crosslinking modifier. Thus the PTHF/glycerin mixture would be a useful binder to improve the burning characteristics of AN-based propellants, due to the oxygen atoms in the mixture. The use of PTHF/glycerin binder is theoretically effective for enhancing the performance of AN-based propellant, but the combined AN/PTHF/glycerin propellants failed to ignite; they only generated a flashing flame at the ignition event. The ignition failure of the AN/PTHF/glycerin propellant occurred because the melted binder covered the burning surface and interfered with the evolution of the AN decomposition gases and the heat flux feedback from the flame to AN. The AN/PTHF/glycerin propellant was then burned with the addition of a catalyst, and the effect of PTHF/glycerin binder on the improvement of burning characteristics was apparent. The PTHF/glycerin binder was an effective binder material for improving a performance of the AN-based composite propellant. © 2010 The Combustion Institute.

Polytetrahydrofuran (PTHF) is an effective binder ingredient for improving propellant performance, even though it is not an energetic material. PTHF becomes sufficiently rubbery for use as a binder when a triol material such as glycerin is added as a crosslinking modifier. The cured PTHF/glycerin binder had unsatisfactory mechanical characteristics for use as a propellant binder, so a more appropriate crosslinking modifier than glycerin needs to be found. In this study, glycerol propoxylate (GPO), with a molecular weight of 260, was used as a crosslinking modifier, and the curing behavior, tensile properties, and thermal decomposition behaviors of the PTHF binder using GPO were investigated. The PTHF/GPO blend did not solidify when the PTHF/GPO mole ratio (ξ) was greater than a certain value. The PTHF (Mn=650)/GPO blend with ξ≤5 and the PTHF (Mn=1400)/GPO blend with ξ≤3 were used as propellant binders. From the curing behaviors and tensile properties, it was found that the PTHF/GPO binders ensured optimal mixing of the propellant ingredients and casting of the uncured propellant into the rocket motor case, and the tensile properties of the binders changed more drastically with the variation in ξ than did those of the PTHF/glycerin binders. The thermal decomposition behaviors of the PTHF/GPO binders were hardly dependent on ξ and were almost identical to those of the PTHF/glycerin binders. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hasue K.,Japan National Defense Academy
Journal of Energetic Materials | Year: 2014

The burning rate of propellants is affected by pressure and temperature. The relation between the burning rate and pressure has been well studied. However, the effect of the initial temperature on the burning rate has not been investigated quantitatively. In this study, the burning rate of bis (1H-tetrazolyl) amine ammonium salt and potassium nitrate phase-stabilized ammonium nitrate mixtures was examined and an equation for the burning rate as a function of pressure and temperature was obtained. In general, the burning rates predicted by the regression equations were in good agreement with the observed values. The temperature sensitivities were also predicted using the regression equation and compared with the observed values and good agreement was found between the predicted and observed values. © 2014 Copyright Taylor and Francis Group, LLC.

Ozaki R.,Japan National Defense Academy | Moritake H.,Japan National Defense Academy
Optics Express | Year: 2012

The chiral smectic C phase of ferroelectric liquid crystals (FLCs) has a self-assembling helical structure which is regarded as a onedimensional pseudo-photonic crystal. It is well known that a stopband of a FLC can be tuned in wavelength domain by changing temperature or electric field. We here have demonstrated an FLC stopband with independently tunable wavelength and bandwidth by controlling temperature and incident angle. At highly oblique incidence, the stopband does not have polarization dependence. Furthermore, the bandwidth at highly oblique incidence is much wider than that at normal incidence. The mechanism of the tunable stopband is clarified by considering the reflection at oblique incidence. © 2012 Optical Society of America.

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