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The diode effect is fundamental to electronic devices and is widely used in rectifiers and AC-DC converters. At low temperatures, however, conventional semiconductor diodes possess a high resistivity, which yields energy loss and heating during operation. The superconducting diode effect (SDE), which relies on broken inversion symmetry in a superconductor may mitigate this obstacle: in one direction a zero-resistance supercurrent can flow through the diode, but for the opposite direction of current flow, the device enters the normal state with ohmic resistance. The application of a magnetic field can induce SDE in Nb/V/Ta superlattices with a polar structure, in superconducting devices with asymmetric patterning of pinning centres, or in superconductor/ferromagnet hybrid devices with induced vortices. The need for an external magnetic field limits their practical application. Recently, a field-free SDE was observed in a NbSe2/Nb3Br8/NbSe2 junction, and it originates from asymmetric Josephson tunneling that is induced by the Nb3Br8 barrier and the associated NbSe2/Nb3Br8 interfaces. Here, we present another implementation of zero-field SDE using noncentrosymmetric [Nb/V/Co/V/Ta]20 multilayers. The magnetic layers provide the necessary symmetry breaking and we can tune the SDE by adjusting the structural parameters, such as the constituent elements, film thickness, stacking order, and number of repetitions. We control the polarity of the SDE through the magnetization direction of the ferromagnetic layers. Artificially stacked structures, as the one used in this work, are of particular interest as they are compatible with microfabrication techniques and can be integrated with devices such as Josephson junctions. Energy-loss-free SDEs as presented in this work may therefore enable novel non-volatile memories and logic circuits with ultralow power consumption., 31 pages, 11 figures

Spin–orbit torque (SOT) switching in chiral antiferromagnets, such as D019-Mn3Sn, has opened prospects in antiferromagnetic spintronics. In this paper, we investigated the critical switching voltage as a function of the voltage pulse width in order to explore the thermal stability factor Δ in the D019-Mn3Sn. Although the critical switching voltage is found to decrease with increasing the voltage pulse width as expected by the thermally activated switching process with Δ of 131.1 at 300 K, our detailed examinations reveal that the Joule heating due to the voltage pulse could induce the magnetic phase transition in the D019-Mn3Sn, which significantly alters the energy landscape relevant to the SOT switching. This assisting mechanism for the SOT switching inhibits an accurate determination of Δ but could deliver a smaller Δ than the actual. Our study provides cautionary note in estimating the thermal stability of the chiral antiferromagnets.

Recently, an ultimate diode effect, a superconducting diode where an electric current shows the superconducting state in one direction and the normal state in the other direction, has been discovered in a noncentrosymmetric Nb/V/Ta superlattice. Here, we report that the polarity of the superconducting diode shows a sign reversal as a magnetic field is increased. Such a nonlinear behavior of the diode effect is beyond the phenomenology based on the Ginzburg–Landau theory. Based on a recent microscopic study, we propose the crossover and phase transitions of the finite-momentum pairing states as a possible origin of the sign reversals.

Artificially engineered superlattice offers highly flexible control of the quantized electronic state by manipulating its lattice structure. We fabricated artificially engineered superlattices [Nb/V/Ta] n as a new class of superconducting superlattices and investigated the upper critical field H c2 in terms of the structural difference. It is found that the out-of-plane upper critical field H c 2 ⊥ significantly increases compared with that of a Nb single layer film as the thickness of the constituent Nb, V, and Ta layers becomes thin. In the case of the superlattice [Nb/V/Ta] n , the H c 2 ⊥ is basically governed by the orbital pair-breaking effect rather than Pauli pair-breaking effect and increases only when the crystalline size of the superlattice decreases by the insertion of V layers. Thus, we conclude that the shortening of the coherence length of Cooper pairs due to the crystalline disorder predominantly contributes to the increase of the H c 2 ⊥ in the superlattice [Nb/V/Ta] n .

Recently, antiferromagnetic materials have attracted increasing attention because of their large magnetotransport and thermomagnetic effects, in which the electronic band structure associated with the noncollinear spin configuration is responsible for generating Berry curvature through spin-orbit coupling 1–3. The anomalous Nernst effect (ANE) is a thermoelectric phenomenon typically observed in ferromagnets under the application of a temperature gradient, in which a transverse voltage is induced perpendicular to both the temperature gradients and the magnetization. Recent experimental studies have shown large ANE in a noncollinear antiferromagnetic metal Mn 3 Sn with a vanishingly small magnetization of 0.002 μ B per Mn atom 4, 5, whose band structure has the Weyl points near 6, 7. In previous studies, the fabrication of thermoelectric devices with the enhanced Seebeck effect has proven to be complicated, owing to the requirement for alternately aligned p- and n-type semiconductor pillars 8. On the other hand, the ANE allows the design of much simpler thermopiles composed of laterally series-connected wires. Toward realizing a thermopile made of the chiral anti-ferromagnet Mn 3 Sn, focused ion beam (FIB) lithography was employed to microfabricate a thermoelectric element consisting of a Ta/Al 2 O 3 /Mn 3 Sn layered structure 9. Figures 1(a) and (b) show a schematic illustration of the microfabricated Mn 3 Sn device structure for measuring ANE and the magnetic structure of the Mn 3 Sn when the magnetic field is applied along the [01–10] axis, where the thermal gradient is applied along the [0001] axis. In this device, the Ta layer acts as a heater producing Joule heat diffusing across the Al 2 O 3 insulating layer into the thin Mn 3 Sn layer. All measurements were performed at room temperature in vacuum. Figure 2 shows the ANE results for the configuration shown in Fig. 1(a) obtained for a dc current of ±1.5 mA applied to the Ta heater. The measured AN signal exhibits a clear hysteresis in an applied temperature gradient and magnetic field. The $V_{ANE}$ is indeed independent of the direction of the applied electrical current in the Ta heater. This indicates that the hysteresis loop in Fig. 2(a) is arising from the ANE in Mn 3 Sn. The observation of the spontaneous, zero field value is essential for construction of the thermopile element. Figure 2(b) shows the electrical current dependence of $V_{ANE}$. The voltage increases with the electrical current in the Ta heater. The sign and magnitude do not depend on the direction of the electrical current. The magnitude is also proportional to the square of the electrical current applied to the Ta heater. In addition, the angular dependence of ANE in the configuration shown in Figure 1(a) shows a small anomaly around 60° when the magnetic field is rotated from the [2-1-10] axis (0°) to the [01–10] axis (90°). On the other hand, in another ANE-measurement device of Mn 3 Sn, the shape of the hysteresis of ANE has a step structure depending on the electrical current in the Ta heater just beside the microfabricated Mn 3 Sn. According to the theoretical study, six magnetic domains that are different at each 60° are proposed in Mn 3 Sn 10. However, an additional study is required to clarify the origin of this structure. In summary, we evaluated the ANE in a microfabricated device comprised of the chiral antiferromagnet Mn 3 Sn as a first step to realize a thermopile device. The spontaneous, zero field voltage signal in the device is of the order of a few μV, which is almost the same order of magnitude as observed in the bulk single-crystal Mn 3 Sn under a temperature gradient. The anomalous Nernst coefficient ${{S}_{\text{ANE}}}$ of the microfabricated element was determined using a temperature gradient simulated by finite-element modeling. The experiment and simulation revealed that the ANE coefficient is 0.27 μV/K which is in good agreement with the bulk value. This result indicates that the FIB microfabrication does not significantly alter the thermoelectric properties of bulk Mn 3 Sn. As the chiral antiferromagnet produces almost no stray field, our study opens the avenue for the fabrication of an efficient thermopile by densely packing the microfabricated antiferromagnetic elements. In this work, the Mn 3 Sn microdevice was fabricated from a bulk crystal, rather than through the deposition of thin films. This approach enables us to investigate thermoelectric phenomena on the nanoscale in wider range of materials than conventional materials used in thin film based devices.

We investigate the effect of sample size on the anomalous Nernst effect (ANE) in a device formed from chiral antiferromagnetic Mn3Sn. We also investigate its magnetic domains by employing focused ion beam lithography. Mn3Sn is a suitable material for studying the thermoelectric effect in the presence of antiferromagnetic domains because it exhibits a large ANE. In the Mn3Sn device used in this study, a Ta layer acts as a heater; the heat produced via Joule heating diffuses through a sapphire substrate into the thin flake of Mn3Sn. The Nernst signal exhibits a stepwise hysteresis when the sample is subjected to a temperature gradient and magnetic field at 290 K. The stepwise hysteresis depends on the sample shape and size—which affect nucleation, pinning, and depinning processes—but the temperature difference also has a significant effect on the switching process. The domain ratios calculated using the ANE results indicate that the domain size is smaller than 20 μm2. This obtained domain size is in good agreement with the reported experimental values of 10–100 μm2 for the magneto-optical Kerr effect in bulk single-crystal Mn3Sn. Thus, the ANE is a powerful means of obtaining information about the magnetic domains in samples under a temperature gradient, thereby promising a reliable approach to study magnetic domains and spintronics using antiferromagnets.

NICT carried out the first calibration of the GPS link between Koganei and Kobe by using GPS, TWSTFT and Clock Transport (CT). We presented the result of the calibration in EFTF 2015. The differential correction of GPS link by GPS, TWSTFT and CT were 102.5, 102.1 and 104.9 ns respectively. The CT result showed a discrepancy of 2 ns. By applying the relativistic effect correction for CT, we confirmed a good agreement of the results obtained by their three techniques.

Reflected signals of the Global Navigation Satellite System (GNSS) from the sea or land surface can be utilized to deduce and monitor physical and geophysical parameters of the reflecting area. Unlike most other remote sensing techniques, GNSS-Reflectometry (GNSS-R) operates as a passive radar that takes advantage from the increasing number of navigation satellites that broadcast their L-band signals. Thereby, most of the GNSS-R receiver architectures are based on dedicated hardware solutions. Software-defined radio (SDR) technology has advanced in the recent years and enabled signal processing in real-time, which makes it an ideal candidate for the realization of a flexible GNSS-R system. Additionally, modern commodity graphic cards, which offer massive parallel computing performances, allow to handle the whole signal processing chain without interfering with the PC’s CPU. Thus, this paper describes a GNSS-R system which has been developed on the principles of software-defined radio supported by General Purpose Graphics Processing Units (GPGPUs), and presents results from initial field tests which confirm the anticipated capability of the system.

Antarctic ice cores could preserve ancient airborne microorganisms. We examined bacteria in two Antarctic ice core samples, an interglacial age sample from Mizuho Base and a glacial age sample from the Yamato Mountains, by 16S rRNA gene sequencing analysis. Bacterial density, the number of bacterial OTUs and Simpson’s diversity index was larger in the Mizuho sample than in the Yamato sample. The 16S rDNA clone library from the Mizuho sample was dominated by the phylum Firmicutes, while the large part of that from the Yamato sample was composed of the Gamma proteobacteria group. Major sources of these identified bacteria estimated from their database records also differed between the samples: in the Mizuho sample bacterial species recorded from animals were higher than that of the Yamato sample, while in the Yamato sample bacteria from aquatic and snow-ice environments were higher than that of the Mizuho sample. The results suggest that these bacteria were past airborne bacteria that would vary in density, diversity and species composition depending on global environmental change. Our results imply that bacteria in Antarctic ice cores could be used as new environmental markers for past environmental studies.

The Antarctic ice sheet preserves paleo-climate information in the form of physical and chemical stratigraphy. A deep ice core was continuously drilled down to a depth of 2,503 m at Dome Fuji station, East Dronning Maud Land, Antarctica, during the 1993-97 JARE inland operations. Oxygen isotope measurements were conducted on 7 to 50 cm-long ice core samples selected from the entire core depth. A time scale for the Dome Fuji core is calculated from past accumulation rates and an ice flow model. Past accumulation rates were converted from oxygen isotope values by using an empirical equation obtained in the Dome Fuji area. A steady-state flow model was preciously developed for a time scale calculation of the Summit ice core, Greenland. Using reference depth points from volcanic signals and annual layer thickness values measured on the Dome Fuji core allows for tuning of the calculated time scale. A depth-age profile was obtained for the past 320 kyr. The obtained paleo-temperature profile shows the characteristics of the past three glacial and interglacial periods. The power spectrum of ƒÂ18O change over an interval of 320 kyr reveals three dominant cycles. The paleo-temperature profile coincides quite well with the Vostok ice core data in general but not in detail, suggesting that further studies are needed both for chronological investigations and a multi-factor, cross-correlation analysis between deep ice cores for climatological understanding.

Mechanical anisotropy of ice core samples has been observed in various uniaxial compression tests. The c-axis orientation distribution is the primary influence on the mechanical behavior of ice cores. A strong single-maximum fabric pattern is observed in the deep parts of the ice sheet. In this region, polycrystalline ice is very hard along the vertical axis; however, it easily shears along the horizontal plane. Thus, by acquiring the distribution of c-axis orientations throughout the ice sheet, the mechanical anisotropy of ice sheet flow behavior can be understood. Analysis of fabric measurements on the Dye 3, GRIP, and Dome F ice cores suggests that the c-axis orientation distribution depends primarily on vertical strain. Therefore, if the ice thickness at some point in the ice sheet is known, it should be possible to predict the distribution of c-axis orientations at that depth. Uniaxial compression tests were carried out along various directions of the Dye 3, GRIP, and Dome F ice cores. A contour map of mechanical anisotropy was then made to relate the compression direction to the vertical strain. This clarified the flow enhancement factor in every compression direction at a given vertical strain.

Oxgen isotope ratio and chemistry profiles were compared to find the corresponding interstadials during the Wisconsin Ice Age between the GRIP (Greenland) and Dome Fuji (Antarctica) deep ice core data for the past one hundred and sixty thousand years. Eight interstadials in GRIPδ18O profile were found to correspond to those in Dome Fuji δ18O profile. Eleven interstadials in GRIPδ18O profile were found to correspond to those in Dome Fuji chemistry (calcium, nitrate and sulfate) profile, which is better suited for the purpose of interstadial search than the δ18O profile at Dome Fuji. The Eemian interglacial period at Dome Fuji seems to be much shorter and more stable than that in the GRIP profile. Three major periods having higher contents of calcium, nitrate and sulfate appear at Dome Fuji, ranging (1) between interstadials number 1 and 8, (2) between interstadials number 17 and 19, and (3) before the Eemian, which correspond to relatively cold and stable periods in the GRIP δ18O profile. These findings promise a favorable outcome from more detailed bipolar comparison in the future for an understanding of climatic linkage conditions and the driving forces between northern and southern hemispheres.

Recent results of physical analyses of the Dome Fuji ice core are summarized with special attention to new methods introduced in the present studies. Microphysical processes which affect the ice core records are reviewed to better understand the paleoclimatic and paleoenvironmental signals stored.

Dating of ice cores is of important but is difficult for an ice core where there is low snow accumulation, and also for the deep part because seasonal chemical and isotopic signals are not easily preserved due to vapor migration after snow deposition and molecular diffusion in the deep part of ice sheet. In this paper, an attempt to reveal annual layer thickness is conducted on the basis of precise number density measurement of air bubbles and air hydrates. The annual layer thickness from air bubbles and hydrates agrees well with a calculated value within 10-15% at all depths of the 2500 m deep core. The obtained thickness in the interglacial period according to Eemian period in the Greenland ice core was half of the calculated value.

The second phase of the deep ice core drilling at Dome Fuji, Antarctica is planned to be carried out in three successive summer seasons starting from 2003/2004 with an improved JARE deep ice core drill. On the basis of tests, major improvements were made including extension of the core barrel to 4m, addition of a more powerful chip-collecting pump, addition of a check valve to avoid loss of collected chips while hoisting the drill in borehole liquid, and a more powerful drill motor. This report describes the improvements and results of the tests as of December 2000.

Deep ice core drilling was carried out at Dome Fuji, Antarctica in 1995 and 1996 from the bottom of the casing installed in 1993 and reached 2503.52m in December 1996. We used a JARE type electromechanical drill with a core barrel of 2.2m length. Total numbers of ice corings and chip collections were 1369 and 837 respectively. The mean coring depths per run and per day were 1.75m and 8.21m, respectively. Quality of ice cores was perfect throughout the whole depth, even in the brittle zone. We report the outline of the system, coring performance, and troubles encountered.

From 1993 to 1998,members of the Dome F project group carried out ice coring at Dome F station. They recovered a 2503-m-long ice core. Specific tasks for the ice core processing included (1) core storage, (2) cutting and packing the ice samples for transportation from the station to Japan, and (3) performing initial ice analyses that can be done at the station. In this report we outline the operation and describe our experiences related to the ice core processing to aid similar processing in the future.

Toward realizing a thermopile made of the chiral anti-ferromagnet Mn3Sn, focused ion beam (FIB) lithography was employed to microfabricate a thermoelectric element consisting of a Ta/Al2O3/Mn3Sn layered structure. In this device, the Ta layer acts as a heater producing Joule heat diffusing across the Al2O3 insulating layer into the thin Mn3Sn layer. The measured Nernst signal exhibits a clear hysteresis in an applied temperature gradient and magnetic field at 300 K, and its magnitude is proportional to the square of the electrical current applied to the Ta heater. The spontaneous, zero field voltage signal in the device is of the order of a few μV, which is almost the same order of magnitude as observed in the bulk single-crystal Mn3Sn under a temperature gradient. The anomalous Nernst coefficient SANE of the microfabricated element was determined using a temperature gradient simulated by finite-element modeling. The obtained value of SANE is 0.27 μV/K, which is in good agreement with that of the reported experimental value of SANE (0.3 μV/K) for bulk single-crystal Mn3Sn. This result indicates that FIB microfabrication does not significantly alter the thermoelectric properties of bulk Mn3Sn. As the chiral antiferromagnet produces almost no stray field, our study opens the avenue for the fabrication of an efficient thermopile by densely packing the microfabricated antiferromagnetic elements.

Laboratory experiments were done to better understand the electrical conduction mechanisms of impure, polycrystalline ice as represented by the 2503 m Dome Fuji (Antarctica) ice core. Also, two electrical measurement techniques for ice cores were compared and their usefulness for determining the acidity of ice cores was studied. We measured the electrical conductivity and complex permittivity of 167 slab-ice samples at frequencies from 20 Hz to 1 MHz. Measurements were performed at –21˚C for all samples, and at –110˚ to –20˚C for several samples, to examine the effects of temperature. We found linear relations between the AC loss factor and the molarity of sulfuric acid, and between the high-frequency-limit conductivity and the AC loss factor. Thus, the acidity levels can be determined from the AC loss factor. In contrast, the electrical conductivity measurement (ECM) current correlated weakly with the other parameters; furthermore, the correlation worsens at larger signal. In several samples containing high acidity, the dielectric properties had distinct changes near –81˚C. We argue that these changes were caused by a change from a liquid-vein-mediated conduction mechanism above the eutectic point of the solute/water/ ice system to a solid-phase conduction mechanism at lower temperatures.

Post-depositional change of isotope concentration was investigated in a temperate snow pack. Daily snow pit studies were carried out at Moshiri, Hokkaido, for about a week in April 1998. During this time the snow layers were at the melting point. Isotope analysis was conducted on snow particles and the liquid water in between the particles every 5 cm in depth, and on the precipitation and the runoff water (from the bottom of the snow pack) collected during the observation period. It was found that the oxygen isotope concentration in the liquid part was smaller by about 2‰ than the solid part of the wet snow. The difference between the isotope concentrations of the liquid and the solid was low in the surface snow layer, but increased at the bottom. The results suggested that isotope fractionation took place between the liquid and the solid, when liquid water (formed by melting at the snow surface layer) flowed groundwards. Copyright © 2002 John Wiley & Sons, Ltd.

1998年2月から4月にかけて北海道母子里で積雪調査を実施し,そのうち融雪期の湿潤積雪層の同位体比の時間変化過程を調べた.調査では,湿潤積雪から層毎に,固相試料(雪粒子)と液相試料(間隙水)とを別々に採取した.観測期間中の降水と積雪下面からの流出水もあわせて採取した.それぞれの試料についての酸素,水素の同位体比を測定した.その結果,雪粒子の同位体比は間隙水よりも大きい値をとった.その差は表面から下層にいくほど増加する傾向が認められた.また,雪粒子,間隙水ともその同位体比は時間とともに大きくなる結果を得た.これらの結果を解析したところ,積雪表面で融解してできた間隙水の流下が,雪粒子の同位体比の変化に大きな影響をもたらす事が示唆された.

The 320 kyr climatic record from the 2503 m Dome Fuji (Antarctica) ice core was analyzed using two electrical methods: AC-ECM and ECM (electrical conductivity measurements). AC-ECM is a method to detect the complex admittance between electrodes dragged on the ice surface with mm-scale resolution and uses 1V and 1 MHz. the ratio of the real to imaginary part of the admittance is the AC loss factor, which responds linearly to the amount of sulfuric acid and hydrogen ions. Both the AC loss factor and the ECM current respond to acid, but the ECM signal tends to saturate at high acidities. Dome Fuji ice was measured to be highly acidic, with background values of 2–7 μM, and had 4500 major peaks with acidities of up to 90 μM. This ice-core evidence and earlier snow-chemistry survey around the dome region indicates that Dome F may have a better connection to the stratosphere than have sites at lower altitude, which allows more stratospheric aerosol and gases to reach the snow surface. Acidity tends to be high in interglacial periods, but correlation between acidity and δ18O is not straightforward. Electrical signals decreased and smoothed out with increasing depth; the diffusion coefficients deduced from this smoothing were 10–102 times greater than in solid ice. the ice core exhibited electromechanical effects and expelling effects from sulfate peaks.

Surface snow observations were carried out on many glaciers in the Arctic. The observational sites were in Svalbard, Severnaya Zemlya, Greenland and arctic Canada. The seasonal variations of chemical constituents in snowfall remained in the surface snow on the central Greenland ice sheet where the effect of snowmelt was weak. Conversely, the chemical constituents in the snow layer changed with infiltration of melt water on the Svalbard glacier where strong snowmelt occurred, even in high latitudes. But in general, specific regional characteristics remained in all the glaciers. The concentrations of ions in snow were significantly decreased, because of percolation of melt water. But the ratio of NO_3 to Cl still had unique regional characteristic values.

210-year records of dust concentration, electrical conductivity, acidity (pH), non-sea salt sulfate (nss sulfate) and nitrate concentrations were obtained for an ice core from Site-J, Greenland. The ice core was well dated by counting annual cycles of the δ^O profile and by tuning with time markers established for tritium peaks and the Laki 1783 eruption signal. Dust records in both ice cores from Site-J and Crete suggest that dust storms occurred in 1818,1900,1919,1936 and 1943 over Greenland. Electrical conductivity shows remarkable peaks probably due to volcanic eruptions with VEI larger than 4. The anthropogenic effect on precipitation chemistry started in ca. 1860,40 years earlier than the time previously reported. Nss sulfate increased remarkably, much more than nitrate, because of the rapid increase in solid fossil fuel combustion, but by the early 1970's, the nitrate concentration exceeded the nss sulfate concentration due to the intense increase in liquid fossil fuel combustion since the 1950's. The decrease in sulfate and nitrate concentrations started in the early 1970's. This is attributed to the spread of suppression facilities for anthropogenic pollutants emitted by the combustion of solid and liquid fossil fuels.

Ice coring and snow cover observations have been carried out at 3 sites in Nordaustlandet, Svalbard since 1995. The results of stratigraphic analyses, and chemical and δ^O analyses from Vestfonna and Austfonna cores are presented here. The results from these sites show that most of the chemical constituents contained in the initial snow cover still remained in the ice cores, although re-distribution of them by melt water percolation had occurred. Anthropogenic increases in trace metals, sulfate and nitrate since about 1950 are detected. This suggests that ice-core chemistry records from Nordaustlandet, Svalbard, can be useful to reconstruct past atmospheric conditions. In addition to chemical records, δ^O records, that correlate well with the temperature records in Svalbard, can be used to reconstruct past temperature changes.

Successive snow pits were dug intensively in a melting snowcover. Water was successfully separated from snow grains in the field for the first time. By measuring δ18O values of water and snow grain samples as well as comparing isotopic profiles, it is found that meltwater percolating down in snow develops quick and clear isotopic fractionation with snow grains, but exerts no clear impact on the δ18O profile of the snowcover through which the meltwater percolates.

Physical analyses of the Dome Fuji ice core have been carried out to reveal fundamental properties of the core : (1) Stratigraphy, (2) Bulk density by a volumetric method, (3) Bulk density by an x-ray transmission method, (4) Total gas content, (5) Permeability and bubble volume, (6) Distribution of air-bubbles, (7) Distribution of clathrate hydrates, (8) Raman spectral N_2/O_2 ratios of air-bubbles and clathrate hydrates, (9) Ice fabrics, (10) Ice grain size, (11) Laser scattering tomography, (12) DC-ECM and AC-ECM, (13) Mechanical test, and (14) Crystalline structures of ice and clathrate hydrate. In the present paper the main results obtained so far are summarized.

Air bubbles trapped near the surface of an ice sheet are transformed into air hydrates below a certain depth Their volume and number varies partly with environment and climate. Air bubbles and hydrates at 120-2200 m depth in the Dome Fuji (Dome F) ice core were examined with a microscope. This depth range covers the Holocene/Last Glacial/Last Interglacial/Previous Glacial periods. No air bubbles were seen below about 1100 m depth, and air hydrates began to appear from about 600 m. The observed number of air bubbles and hydrates was similar to that found in the Vostok ice core. For the ice covering the Last Glacial Maximum period, however the hydrate concentration in the Dome F core is about half that of the Vostok core. Reference to snow metamorphism and packing does not explain this finding.

Uniaxial compression tests were performed on samples of the Greenland Ice Gore Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate (type A) and constant load (type B). Fifty-four uniaxial-compression test specimens from 1327-2922 m were selected. Each test specimen (25 mm x 25 mm x 90 mm) was prepared with its uniaxial stress axis inclined 45° from the core axis in order to examine the flow behavior of strong single-maximum ice-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow-enhancement factor increases to about 20-30 with a relatively high variability When the Schmid factor was > 0.46, the enhancement factor obtained was higher than expected from the .-axis concentrations measured. The higher values of flow-enhancement factor were obtained from specimens with a cloudy band structure. It was revealed that cloudy bands affect ice-deformation processes, but the details remain unclear.

An X-ray transmission method has been developed to obtain a continuous profile of bulk densities of ice cores. Intensities of X-rays transmitted through an ice-core sample were continuously measured by an X-ray detector during translation of the sample across the X-ray beam. A thick section of an ice core with a constant thickness was prepared by band-sawing followed by microtome planing. The X-ray intensity profile obtained was converted to a density profile using a calibration curve for X-ray absorption vs ice thickness. Using this method, spatial resolution of the density profile was down to 1 mm. X-ray radiographs were also taken on a two-dimensional detector imaging plate, in order to observe layer structures of the ice cores.The method was applied to Dome Fuji (Antarctica) ice cores from the surface to 110 m depth. From the density profile obtained we calculated the power spectrum of the density variation by the discrete Fourier transform, and obtained several peaks at different frequencies. The center period in the spectrum was close to the annual accumulation thickness at the drill site.

The heat balance of road snow was analyzed to examine ice-film formation and to determine the characteristics of heat balance on a natural snow cover. The main heat source used to melt natural snow cover is solar radiation. However, the results of the analysis indicated that the absorbed solar radiation is reduced due to the high albedo of snow and therefore cannot compensate for the heat loss by long-wave radiation. This occurrence results in negative net radiation during winter. To evaluate the heat balance on road snow, the infrared radiation from vehicles was estimated by measuring vehicle temperatures. These measurements indicated that heat input applied to snow decreased with vehicle speed and increased with traffic volume. A new index—the shading time—was developed and is defined as the amount of time a section of road is shadowed by vehicles. It was established that incoming long-wave radiation increased by 50 percent during 20 minutes of shading time and that the net radiation became positive, suggesting that snow melting occurred on roads with heavy traffic flow, even in winter.

A comprehensive study of ice-crystal fabrics and textures was conducted on the Dome F (Antarctica) ice core. Crystal ,-axis orientations, crystal sizes and crystal shape were measured on thin sections with an automatic ice-fabric analyzer. The general feature of textural and fabric development through a 2500 m long core was obtained by a 20 m interval study. Crystal size steadily increases with depth except for depths of about 500,1800, 2000, 2200 and 2300 m, at which depths crystal size decreases suddenly. There is a clear correlation between crystal-size and ´18O values. Crystals tend to elongate horizontally with depth, and the aspect ratio (long axis vs short axis of a grain) increases twofold at 1600 m depth and fluctuates below that depth. The .-axis orientation fabrics gradually change with depth from a random orientation pattern near the surface to a strong vertical single maximum at 2500 m. These are very similar to those from the GRIP (Greenland) core The observations of crystal shape and the fabric measurements indicate that nucleation-recrystallization does not take place at Dome F.