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 firstname.lastname@example.org
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.
In this study, direct numerical simulation of the flow around a rotating sphere at high Mach and low Reynolds numbers is conducted to investigate the effects of rotation rate and Mach number upon aerodynamic force coefficients and wake structures. The simulation is carried out by solving the three-dimensional compressible Navier–Stokes equations. A free-stream Reynolds number (based on the free-stream velocity, density and viscosity coefficient and the diameter of the sphere) is set to be between 100 and 300, the free-stream Mach number is set to be between 0.2 and 2.0, and the dimensionless rotation rate defined by the ratio of the free-stream and surface velocities above the equator is set between 0.0 and 1.0. Thus, we have clarified the following points: (1) as free-stream Mach number increased, the increment of the lift coefficient due to rotation was reduced; (2) under subsonic conditions, the drag coefficient increased with increase of the rotation rate, whereas under supersonic conditions, the increment of the drag coefficient was reduced with increasing Mach number; and (3) the mode of the wake structure becomes low-Reynolds-number-like as the Mach number is increased.
The ρ Oph dark cloud is located at a distance of 160 pc and is known as a site of active formation of low-mass stars. In optical photographs a central core of a ∼ 1° × 1° extent and two thin filamentary elongations of obscuring matter are apparent. The two filaments extend toward the east over ∼ 4° – 10°. The central core has been studied in the 2.6 mm CO lines (e.g., Wilking and Lada, 1980, Ap. J. 224, 698). On the other hand, the two filaments have not yet been mapped in molecular spectra. Interestingly, optical studies revealed that polarization vectors run along these remarkable filaments, suggesting that the magnetic field plays an important role in determining the structure of the filaments.
We have made 12CO(J=1-0) observations in the LMC with NANTEN, and compared the detected giant molecular clouds (GMCs) with HII regions and stellar clusters. It is found that ~ 80% of the GMCs are associated with HII regions. The results of comparisons of the GMCs with the HII regions and the stellar clusters are presented.
We have made a 12CO(J = 1−0) survey of the LMC with NANTEN. A sample of 55 giant molecular clouds has been identified and comparisons with stellar clusters, HII regions and SNRs are presented. The connection between the clouds and cluster formation is discussed.
We have made 12CO(J=1−0) observations of the LMC with NANTEN. We report the results of a comparison between CO clouds and SNRs in the LMC. Among the 35 known SNRs, only 10 are possibly associated with CO clouds. These 10 CO clouds and SNRs deserve follow-up studies for possible interactions. We present overlays of CO clouds on the optical images of some of these SNRs.
Fully sampled 12CO(J=1−0) observations of the whole extent of the LMC have been made with a linear resolution of ~ 30 pc at a detection limit of N(H2) = 2 × 1021 cm−2. In addition, several selected regions have been mapped with higher sensitivity corresponding to a detection limit of 1 × 1021 cm−2. Based on these results, a new estimate of the molecular mass in the LMC is presented.
We have made 12CO(J=1−0) observations of the LMC with the NANTEN millimeter-wave telescope and identified about 100 distinct giant molecular clouds (GMCs). A detailed comparison of the GMCs with stellar clusters and a UV image is discussed.
The kinetics of Ge lateral overgrowth on SiO2 with line-shaped Si seeds is examined. The growth process is described by the difference between the growth rates of Ge on (100) planes (GR100) and <311> facets (GR311). The theoretical calculations well reproduce the growth kinetics. It is shown that narrowing the line-seeds helps Ge coalescence and flat film formation.
We investigated particle acceleration and shock structure associated with an unmagnetized
relativistic jet propagating into an unmagnetized plasma. Strong magnetic fields generated
in the trailing shock contribute to the electrons transverse deflection and acceleration.
We have calculated, self-consistently, the radiation from electrons accelerated in these
turbulent magnetic fields. We found that the synthetic spectra depend on the bulk Lorentz
factor of the jet, its temperature and strength of the generated magnetic fields. We have
also investigated accelerated electrons in strong magnetic fields generated by kinetic
shear (Kelvin-Helmholtz) instabilities. The calculated properties of the emerging
radiation will guide our understanding of the complex time evolution and/or spectral
structure in gamma-ray bursts, relativistic jets in general, and supernova remnants.
We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly
relativistic shock propagating through an inhomogeneous medium. Simulation results show
that the postshock region becomes turbulent owing to preshock density inhomogeneity, and
the magnetic field is strongly amplified due to the stretching and folding of field lines
in the turbulent velocity field. The amplified magnetic field evolves into a filamentary
structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the
Kolmogorov spectrum and indicates that the so-called small-scale dynamo is occurring in
the postshock region.
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has properties different from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We present synthetic spectra to compare with the spectra obtained from Fermi observations.
A magnetically enhanced capacitively coupled plasma source was developed for sputter deposition of Cu seed layers on sub 0.25µm via or contact holes. The plasma source is of planer parallel plate configuration where the Cu target plate is one of the electrodes. For the generation of plasma, 60 MHz rf power is selected in order to increase the plasma density. Additionally, a line cusp magnetic field is used to further increase the plasma density. The film deposition rate and uniformity obtained with this plasma source is∼200 nm/min and ∼±5%, respectively. The Cu film resistivity lies around 2 µωcm. This sputtering system yields good film coverage on bottom and sidewalls of via holes with an aspect ratio > 5; therefore, a perfect Cu filling could be realized by electroplating process.
A comparison was made of gold and copper wires used in ball bonding in terms of their mechanical properties, bondability and the reliability of their bond interfaces in elevated temperature environments. The ball bondability of copper and gold was evaluated through clarification of the factors which govern ball deformability. Moreover a bonding method to suppress the generation of silicon cracks was proposed for ball bonding of copper wire. As to the reliability of the heat affected zone and the bond interfaces, copper wire was found to be superior to gold wire.
Crystalline quality of Bi-based oxide films has been evaluated by means of X-ray diffraction (XRD) and ion-channeling on the Rutherford backscattering (RBS). The films were sputter deposited 2201-phase Bi2Sr2Cu1O8-δ (BSCO) and 2212-phase Bi2Sr2Ca1Cu2O8-δ (BSCCO). They were prepared on MgO(100) and SrTiO3(100) substrates at the low temperature of 650°C during the deposition. The best quality, however thin films had poor crystallinity compared to single crystals, was obtained with the 2201-phase BSCO film that was deposited on a SrTiO3(100) substrate. The full width at half maximum (FWHM) value of the rocking curve on XRD for the film was estimated as 1560 (arc sec).
Morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics (MD) simulation. All the pair combinations of the elements Ni, Cu, Au, Ag, Pt, and Pd are considered. The final structures of united bimetallic clusters are classified into three categories: epitaxial, core-shell, and alloyed. Which type of structure appears via coalescence depends on the size and temperature of clusters, which can be summarized in an observed structure map.
We have developed a novel surface treatment process using vacuum ultraviolet (VUV) light with a wavelength of 172 nm and formic acid vapor. A previous study showed that the VUV process can help remove the organic contaminants on the bonding surfaces and improve the shear strength. This new work focuses on studying the effects of VUV/O3 and formic acid treatments. The formic acid (HCOOH) vapor removes the metal oxides from the surfaces before the bonding process. Evaporated Cu/Sn and immersion Au were used for the bonding micro-bumps and bonding pads in our evaluations. Different cleaning conditions with VUV/O3, formic acid vapor, or both were compared and evaluated. X-ray Photoelectron Spectroscopy (XPS) was used to study the surface elemental composition of the micro-bumps and pad surfaces before and after the cleaning process. The photoelectron spectra of C1s, Sn3d, and Au4f were obtained with XPS. The XPS results showed the atomic carbon concentrations were significantly decreased by the VUV/O3 treatment process, while the Sn and Au concentrations were increased by the VUV/O3 and formic acid treatment because of the removal of the organic contaminants and metal oxides from the surfaces. The bonding strength of the Cu/Sn bumps was evaluated using a shear test tool. The results shows that the combination of VUV/O3 and formic acid treatment obtains the highest average shear strength among the treatments tested, with a shear strength almost 2.5 times stronger than the untreated samples.
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has different properties from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We will present detailed spectra for conditions relevant to various astrophysical sites of collisionless shock formation. In particular we will discuss application to GRBs and SNRs.
For a long time, the Lagrangian linear perturbation (Zel'dovich approximation, ZA) is used for initial conditions for cosmological N-body simulations. Recently, Crocce et al.
(2006) proposed the improvement of the initial conditions. They applied Lagrangian second-order perturbation (2LPT) for the initial condition. Then they calculated the Lagrangian linear perturbation and showed that 2LPT initial conditions improve the evolution of non-Gaussianity for the density fluctuation in the Universe.
Here we have one question. Although 2LPT initial conditions improve the cosmological N-body simulation, is 2LPT initial conditions sufficient? To answer this question, in addition to the ZA and 2LPT, we also calculate the non-Gaussianity with the initial conditions based on third-order Lagrangian perturbation theory (3LPT). Then we show reasonable order of perturbation and redshift for the initial conditions.