A physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi‐instrument observations, theoretical modeling, and basic principles. According to ...the mechanism, an equatorward neutral wind is required to produce positive ionospheric storms. The mechanical effects of the wind (1) reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, (2) raise the ionosphere to high altitudes of reduced chemical loss, and hence (3) accumulate the plasma at altitudes near and above the ionospheric peak centered at around ±30° magnetic latitudes. Daytime eastward prompt penetration electric field (PPEF), if it occurs, also shifts the equatorial ionization anomaly crests to higher than normal latitudes, up to approximately ±30° latitudes. The positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning‐noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind. The mechanism agrees with the multi‐instrument observations made during the supergeomagnetic storm of 7–8 November 2004, with 18 h long initial phase (IP) and 10 h long main phase (MP). The observations, which are mainly in the Japanese‐Australian longitudes where the MP onset was in the morning (0600 LT, 2100 UT), show (1) strong positive ionospheric storms (in Ne, Nmax, hmax, Global Positioning System–total electron content (GPS‐TEC), and 630 nm airglow intensity) in both Northern and Southern hemispheres started at the morning (0600 LT) MP onset and lasted for a day, (2) repeated occurrence of strong eastward PPEF events penetrated after the MP onset and superposed with westward electric field started before the MP onset, and (3) storm time equatorward neutral winds (inferred from 1 and 2). Repeated occurrence of an unusually strong F3 layer with large density depletions around the equator was also observed during the morning‐noon MP.
The new Horizontal Wind Model (HWM07) provides a statistical representation of the horizontal wind fields of the Earth's atmosphere from the ground to the exosphere (0–500 km). It represents over 50 ...years of satellite, rocket, and ground‐based wind measurements via a compact Fortran 90 subroutine. The computer model is a function of geographic location, altitude, day of the year, solar local time, and geomagnetic activity. It includes representations of the zonal mean circulation, stationary planetary waves, migrating tides, and the seasonal modulation thereof. HWM07 is composed of two components, a quiet time component for the background state described in this paper and a geomagnetic storm time component (DWM07) described in a companion paper.
It may be possible to construct a laser interferometer gravitational wave antenna in space with h(rms) approximately 10(-27) at f approximately 0.1 Hz in this century. Using this antenna, (1) ...typically 10(5) chirp signals of coalescing binary neutron stars per year may be detected with S/N approximately 10(4); (2) we can directly measure the acceleration of the universe by a 10 yr observation of binary neutron stars; and (3) the stochastic gravitational waves of Omega(GW) > or similar to 10(-20) predicted by the inflation may be detected by correlation analysis. Our formula for phase shift due to accelerating motion might be applied for binary sources of LISA.
Securing information in communication networks is an important challenge in today's world. Quantum Key Distribution (QKD) can provide unique capabilities towards achieving this security, allowing ...intrusions to be detected and information leakage avoided. We report here a record high bit rate prototype QKD system providing a total of 878 Gbit of secure key data over a 34 day period corresponding to a sustained key rate of around 300 kbit/s. The system was deployed over a standard 45 km link of an installed metropolitan telecommunication fibre network in central Tokyo. The prototype QKD system is compact, robust and automatically stabilised, enabling key distribution during diverse weather conditions. The security analysis includes an efficient protocol, finite key size effects and decoy states, with a quantified key failure probability of ε = 10⁻¹⁰.
Cemented carbide tools are commonly used in both cutting and forging processes associated to zipper production. In production, the tools experience many millions of repeated contacts, hence they must ...be very durable to keep the wear at acceptable levels. Although the zipper elements in this investigation are made in a relatively soft CuZn alloy, the wear becomes significant and the tool life a production limiting factor. The wear process is to a large extent unknown. To increase the understanding, forging dies used for an increasing number of forgings in actual production, have been studied in detail. Initially the Co binder is preferentially worn off, and transferred CuZn partly fills the cavities. Interestingly, the repeating forging contacts lead to modification of the composition of the transferred material, which partly separates into Cu rich and Zn rich parts, where the Zn rich parts show a high presence of oxygen. During the life span of the tool, represented by the controlled use of forging tools to different percentages of their estimated life, the WC grains are gradually worn into faceted shapes. The most severely worn region of the forging dies develops an increasing surface roughness, which act to shape a corresponding pattern on the zipper elements.
•Tools were used in zipper production to different portions of the expected lifetime.•Surface analysis enables observation of wear initiation, propagation and wear out.•Cu alloy is immediately adhered, and becomes separated into Cu and Zn during use.•Wear of WC is gradual and slow, however results in faceted grains and rough surface.•Zipper element shape is a replica of the die cavity and mirrors the tool wear state.
Quantum key distribution's (QKD's) central and unique claim is information theoretic security. However there is an increasing understanding that the security of a QKD system relies not only on ...theoretical security proofs, but also on how closely the physical system matches the theoretical models and prevents attacks due to discrepancies. These side channel or hacking attacks exploit physical devices which do not necessarily behave precisely as the theory expects. As such there is a need for QKD systems to be demonstrated to provide security both in the theoretical and physical implementation. We report here a QKD system designed with this goal in mind, providing a more resilient target against possible hacking attacks including Trojan horse, detector blinding, phase randomisation and photon number splitting attacks. The QKD system was installed into a 45 km link of a metropolitan telecom network for a 2.5 month period, during which time the system operated continuously and distributed 1.33 Tbits of secure key data with a stable secure key rate over 200 kbit/s. In addition security is demonstrated against coherent attacks that are more general than the collective class of attacks usually considered.
Muonic helium atom hyperfine structure (HFS) measurements are a sensitive tool to test the three-body atomic system and bound-state quantum electrodynamics theory, and determine fundamental constants ...of the negative muon magnetic moment and mass. The world's most intense pulsed negative muon beam at the Muon Science Facility of the Japan Proton Accelerator Research Complex allows improvement of previous measurements and testing further CPT invariance by comparing the magnetic moments and masses of positive and negative muons (second-generation leptons). We report new ground-state HFS measurements of muonic helium-4 atoms at a near-zero magnetic field, performed for the first time using a small admixture of CH_{4} as an electron donor to form neutral muonic helium atoms efficiently. Our analysis gives Δν=4464.980(20) MHz (4.5 ppm), which is more precise than both previous measurements at weak and high fields. The muonium ground-state HFS was also measured under the same conditions to investigate the isotopic effect on the frequency shift due to the gas density dependence in He with CH_{4} admixture and compared with previous studies. Muonium and muonic helium can be regarded as light and heavy hydrogen isotopes with an isotopic mass ratio of 36. No isotopic effect was observed within the current experimental precision.
We have developed a hybrid piston cylinder cell for quasielastic neutron scattering (QENS) experiments up to about 1 GPa. It consists of a fretted cylinder made of the high tensile steel (SNCM439) ...liner and the Al alloy (NA700) jacket. Performance tests revealed that the cell can withstand a pressure of 0.8 GPa without irreversible damage and has 4.4 times larger neutron transmission at 3.14 meV (5.10 Å in wavelength) than that of a conventional CuBe monobloc cylinder. Combined with the sample assembly devised for suppressing multiple scattering, high quality QENS spectra of water were obtained up to 0.8 GPa. This study illustrates the efficacy of the hybrid cylinders not only for increasing maximum available pressure but also manipulating the available pressure and the signal intensity, depending on the purpose of the experiments.
A quantum spin-liquid phase is an intriguing possibility for a system of strongly interacting magnetic units in which the usual magnetically ordered ground state is avoided owing to strong quantum ...fluctuations. It was first predicted theoretically for a triangular-lattice model with antiferromagnetically coupled S = 1/2 spins. Recently, materials have become available showing persuasive experimental evidence for such a state. Although many studies show that the ideal triangular lattice of S = 1/2 Heisenberg spins actually orders magnetically into a three-sublattice, non-collinear 120° arrangement, quantum fluctuations significantly reduce the size of the ordered moment. This residual ordering can be completely suppressed when higher-order ring-exchange magnetic interactions are significant, as found in nearly metallic Mott insulators. The layered molecular system κ-(BEDT-TTF)(2)Cu(2)(CN)(3) is a Mott insulator with an almost isotropic, triangular magnetic lattice of spin-1/2 BEDT-TTF dimers that provides a prime example of a spin liquid formed in this way. Despite a high-temperature exchange coupling, J, of 250 K (ref. 6), no obvious signature of conventional magnetic ordering is seen down to 20 mK (refs 7, 8). Here we show, using muon spin rotation, that applying a small magnetic field to this system produces a quantum phase transition between the spin-liquid phase and an antiferromagnetic phase with a strongly suppressed moment. This can be described as Bose-Einstein condensation of spin excitations with an extremely small spin gap. At higher fields, a second transition is found that suggests a threshold for deconfinement of the spin excitations. Our studies reveal the low-temperature magnetic phase diagram and enable us to measure characteristic critical properties. We compare our results closely with current theoretical models, and this gives some further insight into the nature of the spin-liquid phase.
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