To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Causes of ice-sheet layering at ice depths greater than about 900 mina transect between Dome C and the Transantarctic Mountains are examined using 60 MHz radar data, collected in the 1970s by the U.K.–U.S.–Danish collaboration. Normally, a dual-frequency technique is required for accurate determination of internal reflection mechanisms. However, by extracting the depth-related features of 60 MHz radar profiles and comparing them with the dual-frequency data collected by the Japanese Antarctic Research Expedition, we have identified a simple method to estimate internal reflection mechanisms. Two zones can be distinguished: (1) the CA zone, where change in electrical conductivity due to variation in acidity is the major cause of internal reflection, and (2) the PCOF zone, where change in dielectric permittivity due to crystal-orientation fabrics is the major cause of internal reflections. Our analysis shows that the radar data reveal the development of PCOF zones in regions where large amounts of ice shearing are expected. This analysis shows how a similar interpretation of the full radar-data archive may reveal information on internal reflection mechanisms across a large part of the East Antarctic ice sheet.
In the summers of 2001 and 2002, glacio-climatological research was performed at 4110–4120 m a.s.l. on the Belukha snow/firn plateau, Siberian Altai. Hundreds of samples from snow pits and a 21 m snow/firn core were collected to establish the annual/seasonal/monthly depth–accumulation scale, based on stable-isotope records, stratigraphic analyses and meteorological and synoptic data. The fluctuations of water stable-isotope records show well-preserved seasonal variations. The δ18O and δD relationships in precipitation, snow pits and the snow/firn core have the same slope to the covariance as that of the global meteoric water line. The origins of precipitation nourishing the Belukha plateau were determined based on clustering analysis of δ18O and d-excess records and examination of synoptic atmospheric patterns. Calibration and validation of the developed clusters occurred at event and monthly timescales with about 15% uncertainty. Two distinct moisture sources were shown: oceanic sources with d-excess <12‰, and the Aral–Caspian closed drainage basin sources with d-excess >12‰. Two-thirds of the annual accumulation was from oceanic precipitation, of which more than half had isotopic ratios corresponding to moisture evaporated over the Atlantic Ocean. Precipitation from the Arctic/Pacific Ocean had the lowest deuterium excess, contributing one-tenth to annual accumulation.
Theoretical arguments indicate that the ISM is inhomogeneous; Mathews estimated that the ~ 1M⊙ of metal ejected by each supernova event into the ISM is trapped locally within the hot bubbles. Since in elliptical galaxies, there is no overlapping of expanding supernova remnants after galactic wind period, it is expected that this inhomogeneity persists for a long time. The observations also suggests that the ISM of elliptical galaxies is inhomogeneous. Based on these arguments, we studied the evolution of the multiphase (inhomogeneous) ISM.
Material for this report was collected by the President, Vice-President and Members of the Organizing Committee. The President is, however, responsible for the form in which the report now appears. A number of special abbreviations in the references are explained in the report of Committee 27a. In addition, 3rd Harvard = 3rd Harvard-Smithsonian Conference on Stellar Atmospheres (1968). The field of Commission 29 overlaps particularly with those of 9, 27a, 36, 44 and 45 whose reports should be consulted. Since the last IAU meeting 29 has co-sponsored the following meetings: IAU Colloquium No. 4 on Stellar Rotation (Columbus, Ohio, September 1969); IAU Symposium No. 36, Ultraviolet Stellar Spectra and Related Ground-Based Observations (Lunteren, June, 1969); Second Trieste Colloquium, Mass Loss from Stars (September, 1968). We are also co-sponsoring IAU Symposium No. 42 on White Dwarfs to be held in Scotland (August, 1970). The thanks of the commission are due to their representatives on the organizing committees of these meetings. Reports from some working groups are appended. The working group with Commission 44 has not felt it necessary to submit a report (its main activity was the organization of Symposium No. 36). Miss Underhill (Chairman) recommends that the working group on Tracings of High Dispersion Stellar Spectra be dissolved.
The use of underground geological repositories, such as in radioactive waste disposal (RWD) and in carbon capture (widely known as Carbon Capture and Storage; CCS), constitutes a key environmental priority for the 21st century. Based on the identification of key scientific questions relating to the geophysics, geochemistry and geobiology of geodisposal of wastes, this paper describes the possibility of technology transfer from high-technology areas of the space exploration sector, including astrobiology, planetary sciences, astronomy, and also particle and nuclear physics, into geodisposal. Synergies exist between high technology used in the space sector and in the characterization of underground environments such as repositories, because of common objectives with respect to instrument miniaturization, low power requirements, durability under extreme conditions (in temperature and mechanical loads) and operation in remote or otherwise difficult to access environments.
Changes in critical current properties depending on growth temperature (Ts) were clarified for Ba-Nb-O-doped YBa2Cu3Oy (Y123) films deposited by YAG- and excimer-PLD. Due to the introduction of Ba-Nb-O-nanorods, a vortex-Bose-glass-like behavior emerged as irreversibility lines and in-field critical current densities (Jcs) were improved. Crossover magnetic fields (Bcr) and in-field Jcs increased with the increase in Ts for the Y123 films with nanorods. These Ts-dependent critical current properties were attributable to the changes in morphology of the nanorods with Ts and were independent of laser source in PLD apparatuses. For the fabrication of RE123 coated conductors containing nanorods, optimization of Ts with taking both materials of RE123 matrix and nanorod into account is necessary to achieve higher in-field Jc.
Epitaxial Fe-Te-Se thin films were deposited by pulsed laser deposition at 250 ~ 600 °C on SrTiO3 (100, STO), MgO (100), LaAlO3 (100, LAO) and CaF2 (100) single crystal substrates. Best superconducting film was grown on CaF2: Tconset = 20.0 K and Tc0 = 16.18 K with Tdep = 300 °C, 45000 pulses, 3 Hz. The critical current density Jc at 4.2 K was 0.41×106A/cm2 at 0 T and 0.23×106 A/cm2 at 9 T. Angular dependence of Jc showed broad c-axis correlated peak when B ≥ 3 T.
We have examined the change of mechanical characteristics of silicon nanocontacts with and without the pre-treatment by flowing current through the contact. The silicon nanocontact formed between silicon tips by a mechanical contact was quickly deformed during its tensile test under a transmission electron microscope, after applying over 100 μA at a high bias voltage around 15 V between tips for a short duration. In the tensile experiment, the diameter of the nanocontact easily decreased from the initial diameter of 98 nm to 30 nm and the length increased from 11 nm to 66 nm. At 30 nm in diameter, it was suddenly fractured without further elongation and became round tips with smooth surfaces. According to the close observation, the silicon nanocontact seemed amorphous. In the retraction process of the silicon nanocontact, steps moved along the surface from the neck of the nanocontact to the tip side at the speed of 7.0 nm/s. Nano-scaled round step propagations were repeated from the neck to the tip. The step propagation caused the fast thinning of the nanocontact. On the other hand, the silicon nanocontact formed at 1 V in bias voltage was gradually thinned from 42.5 nm to 1.6 nm in diameter and elongated from 2.9 nm to 61.9 nm in length. From the comparison of silicon nanocontacts with and without the pre-treatment, the silicon nanocontact after flowing substantial current showed quick deformation and had different mechanical characteristics from the silicon nanocontact without the pre-treatment.
A direct calorimetry method was developed and used to measure the electrocaloric effect (ECE). A temperature change ΔT of over 20 °C and an entropy change ΔS of over 95 J/(kgK) were procured at 33 °C and 160 MV/m in the high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 68/32 mol% copolymers, which were larger than those of terpolymer blends (ΔT = 9 °C, ΔS=46 J/(kgK) at 180 MV/m and room temperature) and our earlier report on P(VDF-TrFE) 55/45 mol% normal ferroelectric copolymer (12 °C and 55 J/(kgK) at 80 °C). We observed that the β value ((8.7±0.6)×107 JmC-2K-1) in the equation of ΔS=1/2βΔD2 derived from ΔS - ΔD2 relation for irradiated copolymers was larger than that of the terpolymer blends ((5.4±0.5)×107 JmC-2K-1). It was also found that the irradiated copolymer showed a sharp depolarization peak at Td < Tm (maximum permittivity temperature), which is frequency independent, in the dielectric constant - temperature characteristics, a larger depolarization value at Td in the thermally stimulated depolarization current (TSDC) - temperature relationship, and a larger volume strain/longitudinal strain ratio over terpolymer blends. The giant ECE in irradiated copolymer is regarded as due to the greater randomness present in the relaxor state. In irradiated copolymers, the long all-trans chains are broken by the high-energy electrons, which make the small sized all-trans sequences more easily reorient along the electric field, more remarkably affecting the permittivity, TSDC, and volume strain.
Poly(3-hexylthiophene) (P3HT) nanofibers were fabricated with an association of poly(vinyl pyrrolidone) (PVP) by electrospinning. A mixture of P3HT/PVP in a mixed solvent of chlorobenzene and methanol was electrospun to form composite fibers with 60 nm - 2 μm in diameter, followed by getting rid of PVP by selective extraction. After extraction, pure P3HT nanofibers were obtained as a spindle-like structure with wrinkled surface. The nanofibers obtained exhibit specific features of strong interchain contribution as investigated by UV-vis, fluorescence spectroscopic, X-ray diffraction (XRD), and photo-electron investigations. Bulk heterojunction P3HT:PCBM nanofibers with ~200 nm in diameters were also successfully fabricated by using the same technique. The preliminary results from the study of P3HT:PCBM nanofiber-based photovoltaic cells with conversion efficiency over 0.2% could be achieved.
Using alloys whose initial microstructures are composed of Ni3Si(L12), Ni3Si(L12)+Ni3Ti(D024) and Ni3Si(L12)+Ni3Nb(D0a), aging phenomenon and the associated high-temperature tensile property were investigated. It was shown by micro hardness measurement that age hardening behavior due to the precipitation of the Ni3Ti(D024) phase occurs in all alloys at temperatures above 823K. It was however shown by tensile test that the precipitated Ni3Ti(D024) phase is not so much effective in improving the mechanical properties of alloys whose initial microstructures are composed of Ni3Si(L12)+Ni3Nb(D0a) or Ni3Si(L12)+Ni3Ti (D024). In alloys whose initial microstructures are composed of Ni3Si(L12)+Ni3Nb (D0a), a good combination of tensile strength and tensile elongation was found over a wide of test temperature whether or not they contain the precipitated Ni3Ti(D024) phase.
The electronic structures of some possible carbon fibers nucleated from the hemisphere of a bucky ball are presented. A one-dimensional electronic energy band structure model of such carbon fibers, having not only a principal rotational axis but also fibers with screw axes, can be derived by folding the two-dimensional energy bands of graphite. By considering the variation of the fiber diameter and helicity within a simple tight binding model calculation, we show that 1/3 of the fibers are metallic and 2/3 are semiconducting. The effect of adding multiple tubule layers is considered.
We have investigated effect of annealing at the interfaces of GaAs/ZnSe heterostructures, grown by OMVPE using TEGa, TBAs, DEZn and DMSe sources. For this work, we have annealed single quantum well (SQW), double quantum well (DQW) and super-lattice (SL) of GaAs/ZnSe heterostructures up to 640°C and characterized them by double crystal x-ray and photoluminescence. X-ray rocking curves of all these heterostructures showed a main peak due to diffraction from effective lattice parameters of epilayers and 5 satellite peaks in addition to one sharp peak from GaAs substrate. After annealing upto 640°C FWHM and position of these peaks remain unchanged, however peak height increases and small satellite peaks become more sharp and clear. Photoluminescence of these structures showed luminescence from Cu-Green and self-activated (SA) centers of ZnSe and an intense, sharp peak from GaAs. Annealing at up to 640°C did not much affect the PL intensities except that relative peak intensities of Cu-Green and SA centers showed variation which is interpreted in terms of migration of VZn and nearly no significant interdiffusion between GaAs and ZnSe layers. These factors suggest that these heterostructures are stable such that interdiffusion at interfaces is not very appreciable against thermal treatment upto 640°C and hence they are of potential importance for device applications.
We report, for the first time, on interface properties of the Ta2O5-Si system and on the deep level defects in Ta2O5 grown by plasma enhanced liquid source chemical vapor deposition (PE-LS-CVD) using Ta(OC2Hs)5. The capacitance voltage (C–V) measurement performed on Au/Ta2O5/n, p-Si MOS diodes resulted in very well defined C-V charactristics which compares well with the ideal C-V curve. The flat band voltage is as low as 0.15 V and the minimum density of the interface state is about 2.7 × 1011 cm−2 ev−1. In order to examine deep level defects in Ta2O5, we investigated variations of flat band voltage under application of high stress electric field (10MV/cm), by which hot carriers are injected in to deep levels. This charge transfer process results in increase of charges in Ta2O5 oxide which is attributed to the equivalent deep level defect densities, which is found to be of the order of 2 × 1011 cm−2 in the Ta2O5-Si system. These results strongly suggest low interface states and deep levels in the PE-LS-CVD grown Ta2O5-Si system, which may be brought about by low decomposed-carbon impurities in the film, confirmed by AES in our previous reports. These films can play a vital role as thin capacitors in I.C. technology.
Atmospheric pressure chemical vapor deposition (APCVD) was used to grow silicon carbide (SiC) on as-deposited and annealed polycrystalline silicon (polysilicon) films which were deposited on oxidized Si wafers. X-ray diffraction (XRD) reveals that SiC films grown on asdeposited polysilicon have a (110) orientation. XRD performed on as-deposited polysilicon before and after SiC growth reveals that the orientation of polysilicon changes from (110) to a mixture of (110) and (11) during growth of 2 μm-thick SiC films. Cross-sectional transmission electron microscopy (XTEM) images of the SiC/polysilicon interface show that the SiC appears to be unaffected by the recrystallization of the underlying polysilicon during the SiC growth. XRD from samples of SiC grown on annealed polysilicon show that both films have (110) and (111) orientations. For SiC films grown on annealed polysilicon substrates, XTEM images show that the crystallinity of the annealed polysilicon substrate does not significantly change during SiC growth. Furthermore, an investigation of the SiC/annealed-polysilicon interface using selected area diffraction (SAD) shows that an epitaxial relationship exists between the polysilicon and SiC grains.
We report a simple and mild fabrication of flexible organic field-effect transistors (OFETs) by an electrode-peeling transfer method. Firstly, fine patterns of source-drain metal electrodes were formed on a solid substrate, where a micro-patterning process such as photolithography is applicable. An organic dielectric layer (poly-chloro-p-xylylene) was deposited by a chemical vapor deposition. Then patterned gate electrode was deposited using a shadow mask. On the top surface of the gate electrode, another adhesive flexible substrate was fixed and the stack of the flexible substrate/gate electrode /dielectric layer /source-drain electrode was peeled away from the solid substrate. The peeling-transfer was completed with a help of a self-assembled monolayer of n-decyl mercaptan as a connecting buffer layer between the gold electrodes and the dielectric layer. Then an organic semiconductor material was deposited on the fresh peeled-off surface on the flexible substrate. When pentacene was used as the semiconductor material, the OFETs exhibited a hole mobility of 0.1 cm2/Vs and a current on/off ratio of 105.