Isamu Nagano

Displays of paternal mouse pup retrieval following communicative interaction with maternal mates

Compared with the knowledge of maternal care, much less is known about the factors required for paternal parental care. Here we report that new sires of laboratory mice, though not spontaneously parental, can be induced to show maternal-like parental care (pup retrieval) using signals from dams separated from their pups. During this interaction, the maternal mates emit 38-kHz ultrasonic vocalizations to their male partners, which are equivalent to vocalizations that occur following pheromone stimulation. Without these signals or in the absence of maternal mates, the sires do not retrieve their pups within 5 min. These results show that, in mice, the maternal parent communicates to the paternal parent to encourage pup care. This new paradigm may be useful in the analysis of the parental brain during paternal care induced by interactive communication.

Heating characteristics of ferromagnetic iron oxide nanoparticles for magnetic hyperthermia

Heating characteristics of Fe oxide nanoparticles designed for hyperthermia were examined. Samples with coercive forces from 50 to 280 Oe(codoped magnetite) were produced with a coprecipitation technique following by hydrothermal reaction. The maximum specific loss powers (SLPs) of 420 W/g was obtained at 117 kHz (640 Oe) for a dispersant sample with coercive force of 280 Oe (ATH9D). SLPs measured on dry powder samples at 17 kHz and measured at 117 kHz on dispersant samples were compared. The measured SLP amplitudes are lower for 17 kHz and higher for 117 kHz than those expected from ferromagnetic dc minor loops. For the 117 kHz case, friction of particles in a carrier fluid (similar mechanism to Brown relaxation in superparamagnetic dispersant samples) is considered to contribute to the heating mechanism.

Selective induction hyperthermia following transcatheter arterial embolization with a mixture of nano-sized magnetic particles (ferucarbotran) and embolic materials: feasibility study in rabbits.

PurposeTo evaluate the possibility of selective hyperthermia following transcatheter arterial embolization (TAE) with ferucarbotran using a newly developed inductive heating (IH) device.Materials and methodsTwelve Japanese white rabbits were separated into four groups: those treated with TAE using a mixture of ferucarbotran and lipiodol (F-L group); those treated with ferucarbotran and gelatin sponge powder; those treated with saline and lipiodol; and a control group. These four groups received IH. Nine rabbits with renal VX2 carcinoma were separated into three groups: IH after TAE (IH-TAE tumor), TAE without IH (TAE tumor), and no treatment (control tumor). The temperature of the tumor was kept at 45°C for 20 min. The therapeutic effect was pathologically evaluated by TUNEL staining.ResultsIn the heating rates of the kidney, the F-L group showed significantly greater values than the group in which iron was not used. In the IH-TAE tumor group, tumors could be selectively heated. In TUNEL staining, the IH-TAE tumor and TAE tumor groups showed significantly greater values of apoptosis rate than in the control tumor group.ConclusionIH following TAE with a mixture of ferucarbotran and lipiodol was capable of inducing selective hyperthermia with our device. However, further investigation is needed to confirm its safety and effectiveness in the treatment of malignant neoplasms in humans.

Full wave calculation of ELF/VLF propagation from a dipole source located in the lower ionosphere

A full wave technique has been developed to calculate the field intensities both in the upper ionosphere and on the ground when a dipole source immersed in the lower ionosphere radiates ELF/VLF waves. The radiated wave is divided into a large number of elementary plane waves, for each of which the propagation in the horizontally stratified model consisting of the ionosphere, the free space and the ground is calculated by the full wave technique. Then the plane waves are summed up to give a horizontal distribution of the radiated wave intensities at any altitudes. This technique is applied to investigate the propagation characteristics of radiation from a polar electrojet (PEJ) antenna modulated at an ELF/VLF frequency, which was created by the Tromso heating facility. Comparison between the results of experiments and the calculation is given in the companion paper [Kimura et al., this issue]. We discuss several propagation characteristics, such as the frequency dependence of the radiated wave propagation up to the upper ionosphere and down to the ground. Under the conditions that the frequency is 2.5 kHz and the ionospheric dc electric field is 5 mV/m, the calculated results are roughly consistent with the experimental results and the radiation efficiency of the PEJ antenna is found to be extremely small, 2.5×10−6 upward and 3×10−8 downward.

Measurements and analysis of antenna impedance aboard the Geotail spacecraft

A practical method of estimating the effective impedance of electric dipole antennas aboard the scientific spacecraft Geotail has been developed. The principle of the newly proposed method is to derive the complex impedance of the dipole antennas immersed in the space plasma by means of the analysis of signal waveforms captured when a calibration signal was imposed directly onto the antennas. The derived complex antenna impedance is expressed as frequency responses of its real and imaginary parts. During the flight of Geotail in the Earths magnetosphere, the impedance measurements were conducted in various regions of the magnetosphere. It has been confirmed, from the analysis of the measured data, that the impedance of the Geotail antenna forms an equivalent electric circuit consisting of a resistance and a capacitance connected in parallel. It has been found that the resistance value is easily changed by the extremely rare ambient plasma density in the magnetosphere. The validity of the measured values have been examined along a theory of probes in a sheath region, taking into account antenna potentials which are lifted up due to the photoelectron emissions from the antenna surface. The analyzed result shows that the measured values of the antenna resistance are consistent with those within the sheath calculated from the theory. Correlation plots of the capacitance values obtained from both the measurements and the calculations have shown that the major parts of the measured capacitance represent the “sheath capacitance,” but other parts might result from a combination of the sheath impedance and the plasma impedance, in addition to the free-space capacitance.

On VLF wave scattering in plasma with density irregularities

A systematic approach to the problem of wave scattering on plasma density irregularities is developed. The scattering process is treated as a wave field spatial evolution while crossing the scattering region, without dividing the wave field into a given incident wave and the field of the scattered waves. In such an approach, the wave energy conservation in the scattering process naturally follows from general formulas. We show that a spatial modulation of the wave packet amplitude caused by spectral broadening in k space is a general consequence of wave scattering. As an example of applications of theoretical consideration in this paper, we suggest an explanation of the amplitude modulation of VLF signals observed by the Akebono satellite in the upper ionosphere. We discuss the relation between amplitude modulation and the apparent spectral broadening of VLF transmitter signals. Both effects are described by the present theory in a similar manner.

Minimally required heat doses for various tumour sizes in induction heating cancer therapy determined by computer simulation using experimental data

Purpose: Although induction heating cancer therapy (IHCT) using magnetic nanoparticles can be a promising approach to treatment-less multi-nodular cancers, the objective requirement for successful clinical application has not clearly been elucidated. We intended to define objective heat doses suitable for IHCT, especially focusing on the sizes of liver cancer nodules. Materials and methods: Alternating magnetic fields were applied to three human pancreatic cancer cell lines, the intercellular space of those cell pellets were filled with magnetic nanoparticles, and confirmed the cytotoxic effect of IHCT. Subsequently, the temperatures of liver cancer nodules in IHCT were simulated using a computer software program and the required heat dose for various sized tumours were determined. Results: Heating the cancer cells up to 50°C for 10 min was sufficient for complete cell killing and the heat dose of 1.7 W/gtumour is required for 10 mm tumour. Larger tumours require a smaller heat dose, e.g. 20 mm and 40 mm tumours require 0.7 W/gtumour and 0.6 W/gtumour, respectively, whereas smaller tumours require large amounts of heat, e.g. 5 mm and 1 mm tumours require 5.1 W/gtumour and 105 W/gtumour, respectively. Conclusions: Integrating the presently available technologies, including high-quality magnetic nanoparticles (1000 W/gmaterial) and effective drug delivery systems (1–2 mgmaterial/gtumour), treatment of a 10 mm tumour seems possible. Since treatment of smaller tumours less than 5 mm require substantial heat dose, researchers involved in IHCT should target cancer nodules of 10 mm or more, and develop a heat delivery system providing a minimum of 1.7 W/gtumour.

Complex comprised of dextran magnetite and conjugated cisplatin exhibiting selective hyperthermic and controlled-release potential.

We developed a dextran-magnetite conjugated cisplatin (DM-Cis) complex for use in thermal ablation and as a chemotherapeutic drug. To produce DM-Cis we reacted Cis with 1 mL DM (56 mg/mL iron). The temperature rise of DM-Cis was measured in vitro and in vivo under a portable induction-heating (IH) device. Platinum desorption from DM-Cis over 24 hours was measured in bovine serum. In in vivo accumulation and magnet and exothermic experiments we used four rat groups. In group 1 we delivered DM-Cis intraperitoneally (ip) and placed magnets subcutaneously (sc). In group 2 we injected saline (ip) and placed magnets (sc). In group 3 we injected DM-Cis (ip) and placed a sc incision (sham). The control (group 4) received an ip injection of saline. Rectus abdominis muscle tissue was stained with hematoxylin-eosin and iron-stained tissue areas (μm2) were calculated. The maximum platinum concentration in DM-Cis was approximately 105.6 μg/mL. Over 24 hours, 33.48% of platinum from DM-Cis was released. There was a significant difference (P < 0.05) in the iron-stained area between group 1 and the other groups. The temperature in muscle tissue registered a maximum of 56°C after about 4 min. DM-Cis may represent a magnetically-accumulated anticancer drug with hyperthermic effects.

EXOS-D (AKEBONO) very low frequency plasma wave instruments (VLF)

The Akebono (EXOS-D) satellite has been successfully observing the Earths magnetosphere since it was launched on February 21, 1989. The objectives of VLF instruments on board the satellite were to investigate the behavior of plasma waves associated with accelerated auroral particles, wave-particle interaction mechanisms, and propagation characteristics of whistler-mode waves in the magnetosphere. The instruments measured not only the dynamic spectra of VLF waves up to 15 kHz by a wideband receiver, but also their absolute field intensities, wave normal vectors, and Poynting vectors. Two electric and three magnetic components with a bandwidth of about 50 Hz up to 12.5 kHz are sent to measure the wave normal vectors and Poynting vectors. The antenna impedance is measured to determine the correct absolute electric field intensities. The instruments have successfully measured the wave spectra, the wave normal vectors. Poynting vectors, the precise wave intensities, the antenna impedance, etc. The present paper describes the unique features of the instruments, especially the Poynting flux analyzers in more detail. Obtained scientific results are also reviewed.

k vector measurements of VLF signals by the satellite EXOS‐D

On board the EXOS-D (Akebono) satellite is a five channel PFX subsystem of VLF instruments, working to determine the wave normal of {kappa} vector and Poynting vector directions by measuring two components of E and three components of B fields using wire and loop antennas. In order to confirm the characteristics or capability of determining the {kappa} vector and the Poynting vector of a coherent VLF Omega signal transmitted from Australia have been analyzed. The observed Omega signal has been found to be right-handed polarized with Poynting vector is making a small angle with the geomagnetic field and lies nearly on the plane constructed by the geomagnetic field and {kappa} vector. The refractive index deduced from the E and B fields well agrees with that calculated by Appleton Hartree formula.