Search

An accident occurred when an aircraft landed at Narita International Airport, Japan, on 20 June 2012. The aircraft encountered rapid changes of winds together with strong turbulence, although the weather was fair. In the present study, a two‐domain nested regional weather prediction models are used. The results in the outer domain show that southwesterly winds associated with a synoptic extratropical cyclone were locally accelerated to the southwest of the airport resulting in strong vertical shear. The simulation in the inner domain reproduces horizontal convective rolls, which are similar to those observed by a Doppler lidar at the airport. The wind velocity component parallel to the runway had a spatial variation of about 10 m s −1. The present approach using a large eddy simulation is useful for clarifying environments and features of horizontal convective rolls and forecasting low‐level wind shear associated with them, which can be a significant risk for aircraft. Plain Language Summary: Synoptic/mesoscale fronts and downbursts (strong downdrafts from a thunderstorm and diverging winds after they hit the ground) are known to be serious threats to airplanes during takeoff and landing. However, it is less known that there is another type of danger under fair weather conditions. An aircraft landing at Narita International Airport, Japan, in the afternoon of 20 June 2012 encountered rapid changes of wind and turbulence and made a hard landing, resulting in several injuries and damage to the fuselage. A Doppler lidar, a remote sensing device for monitoring low‐level winds at the airport observed alternating regions of strong and weak winds aligned southwest–northeast, perpendicular to the runway. In order to clarify the detailed structure and mechanism of these disturbances, numerical simulations using a fine‐resolution (horizontal resolution: 100 m) nested in a coarse resolution (horizontal resolution: 1 km) are made. The simulations show that horizontal convective rolls, which occur in convective boundary layers with strong vertical shear (vertical gradient of horizontal wind speed) were prevailing. These rolls are associated with the rapid changes in wind speed and turbulence similar to those observed by the Doppler lidar and flight recorder. The present study demonstrates that the large eddy simulation is useful for clarifying the structure and mechanisms of horizontal convective rolls, which caused the aircraft accident, and also for forecasting them. Key Points: Horizontal convective rolls that caused an aircraft accident in a fair weather condition were successfully reproduced by a numerical modelCharacteristics of the rolls and turbulence as observed by a Doppler lidar and flight recorder are clarified based on the model resultsCapability of accessing and operationally predicting potentially hazardous rolls by use of a large eddy simulation is demonstrated [ABSTRACT FROM AUTHOR]

Abstract: Microstructures with well-defined micropatterns were fabricated on the surfaces of silica glass using a laser-induced backside wet etching (LIBWE) method by diode-pumped solid state (DPSS) UV laser at the repetition rate of 10kHz. For a demonstration of flexible rapid prototyping as mask-less exposure system, the focused laser beam was directed to the sample by galvanometer-based point scanning system. Additionally, a diagnostics study of plume propagation in the ablated products of toluene solid film was carried out with an intensified CCD (ICCD) camera. [Copyright &y& Elsevier]

By a laser-induced backside wet etching method using a pyrene/acetone solution, a fused silica plate was etched upon irradiation with a conventional XeCl excimer laser. The etch rate was about 50% lower than that obtained with a KrF excimer laser under the same experimental conditions. The threshold fluence for etching was estimated to be below 0.5 J cm−2 and a typical etch rate was around 10 nm pulse−1 at a fluence of 1 J cm−2. After producing the sample having the 10 μm lines and space by irradiation with the first 200 pulses, the second 400 pulses were irradiated to the target sample rotated at right angle. As a result, a square dotted pattern was given without damages for the first etched pattern. Micrographs of the etched surfaces show that this process is a remarkably gentle process free from crack and debris, and favorable for microcrack-free etching of transparent materials. [Copyright &y& Elsevier]

An organosilicon compound, hexamethylcyclotrisilazane (HMCTS), was photolyzed in a solid film at 84 K with an ArF excimer laser. A polymeric film was prepared as a result of polymerization and/or crosslinking using a reactive species such as 1-(methylsilyl)methanimine, generated by photolysis. At room temperature in air, the film changed into a polymer having siloxane units. However, fragments generated by laser irradiation of HMCTS in the frozen film made a similar polymer film having a siloxane structure on a PVA film in air. The polymeric film with siloxane units prepared by the cryogenic laser ablation method displayed hydrophobic properties. [ABSTRACT FROM AUTHOR]

Abstract. The surface chemical modification of polyurethane (PU) films was performed by an UV laser-induced chemical reaction in a polysaccharide solution. This process may be applicable as hydrophilic packaging of implantable medical devices and in vivo sensors. When a PU film in contact with an aqueous alginic acid (AAC) solution was irradiated with a XeCl laser, the PU film turned hydrophilic. Contact angles of water on the film were reduced from 110 degrees to 60 degrees. Since light absorption of the AAC solution at 308 nm was negligibly small, reactive sites were generated solely on the PU surface. There, AAC could be immobilized by chemical bonds thus allowing for a nanometer-scaled grafting of this biomolecule. The mechanism was investigated by surface analyses with Fourier-transform infrared spectroscopy (FT-IR), dye staining, ultraviolet-visible (UV-VIS) spectroscopy, and scanning electron microscopy (SEM) techniques. A one-photon photochemical process could be identified. [ABSTRACT FROM AUTHOR]

Abstract. Ablation of pentafluorophenylazide (FPA) in an Ar matrix at 8-10K was carried out upon irradiation with ns-pulsed UV lasers in a vacuum. The plume of ablated products was monitored by a time-resolved imaging/spectroscopic technique using a gated and intensified CCD camera system. A large amount of pentafluorophenylnitrene (FPN) having a high kinetic energy (Is approximately equal to 6 eV) was ejected as fragments from the matrix film during ablation. A quantitative formation of triplet FPN from the photolysis of the FPA was observed by spectroscopic measurements in the IR and UV-visible regions, and was confirmed by a theoretical IR spectrum calculated according to density functional theory. A FPN beam is useful for chemical surface modification of organic materials. such as aromatic polyester and alkylthiol. A surface analysis of these materials by X-ray photoelectron spectroscopy and Fourier transform infrared reflection absorption spectroscopy showed that the FPN was immobilized onto the surface through chemical bonds. This technique for the chemical surface modification of materials is made possible by a pulsed beam of reactive fragments with a high density in the laser ablation process. [ABSTRACT FROM AUTHOR]

Abstract. We have applied laser ionization time-of-flight (TOF) mass spectrometry to ablation of polysulfone (PS) with 266 nm laser light at fluences of 20-60 mJ/cm[sup 2]. Major peaks were assigned to direct fragments and recombination products ejected from the PS surface. The arrival profiles of these ablation products varied from product to product and were fitted by using a shifted Maxwell-Boltzmann distribution with a center-of-mass flight velocity [(1.4- 5.6) x 10[sup 5] cm/s] and a Knudsen layer temperature (350-3810K). Two types of ablation products, whose velocities and temperatures showed different dependences on laser fluence, were found to exist. Dynamical aspects in the decomposition of the polymer chain, the ejection of various fragments, and their expansion am discussed on the basis of a photothermal ablation model, where a heated surface layer with a temperature gradient along its depth plays an important role. [ABSTRACT FROM AUTHOR]

Abstract. We have developed a one-step technique to fabricate a well-defined pattern of lines and spaces in fused silica with micro-sized features, using laser-induced backside wet etching (LIBWE). The etch rate ranged from 5 to 25 nm/pulse with KrF laser irradiation from 400 to 1300mJ/cm[sup 2] and an acetone solution containing pyrene at a concentration of 0.4 mol/dm[sup 3]. The threshold fluence was 240 mJ/cm[sup 2], which is about one-fortieth lower than that obtained with conventional KrF laser ablation. [ABSTRACT FROM AUTHOR]

Laser-induced backside wet etching (LIBWE) of silica glass plates was performed to fabricate an imprinting template for hot embossing in polymer substrates such as polystyrene and silicone resin. Well-defined inverse surface-micropatterns of gratings and grid arrays on the substrates were produced by the hot embossing using a surface-structured silica glass as the template. These results indicate that the LIBWE method allows us to generate robust glass molding tools that exhibit the inverse shapes of the intended microstructures. [ABSTRACT FROM AUTHOR]

Abstract. Ablation of pentafluorophenylazide (FPA) on an Ag plate at 10 K was carried out upon irradiation with a ns-pulsed UV laser at 248 nm in vacuum. The plume of ablated products was monitored by a time-resolved imaging/spectroscopic technique using a time-gated and intensified CCD camera system. The emission spectrum of the plume at gate times of between 1.0 and 2.0 micro s after the laser irradiation was attributed to blackbody radiation. The blackbody temperature upon irradiation at 100 mJ cm[sup -2] pulse[sup -1] was estimated to be 2900 K. This high-temperature emission is explained by an exothermic reaction of FPA photolysis, which was supported by a theoretical calculation of formation enthalpy based on density functional theory. [ABSTRACT FROM AUTHOR]

Abstract. The KrF laser ablation of polyarylsulfone (PAS) was investigated for fluences between 90 and 200 mJ/cm[sup 2]. Neutral fragments were probed using laser post ionization (193 nm) time-of-flight (TOF) mass spectrometry. Decomposition of PAS was found to occur mainly through scission of C-S and C-O bonds as well as via decomposition of the phenylene rings in the chain. The dependencies of both the flight velocities and the Knudsen layer temperature of the fragments on fluence suggest that PAS ablation is a photothermal process. In contrast, the high average translational energies (up to a few tens of eV) indicate the existence of a non-thermal component in the process. In terms of the plume dynamics, the fitting of the arrival profiles of the fragments with a shifted Maxwell-Boltzmann distribution over the full fluence range indicates the existence of a collision during the adiabatic expansion process. [ABSTRACT FROM AUTHOR]

Abstract. We fabricated a well-defined pattern of lines and spaces on the surface of a quartz crystal plate (c-SiO[sub 2]) with micron-sized features, using laser-induced backside wet etching (LIBWE). The line patterns obtained using LIBWE showed a high aspect ratio of about 3. The etch rates of fused silica (a-SiO[sub 2]) ranged from 5 to 25 nm/pulse with KrF laser irradiation from 0.4-1.3 J/cm[sup 2]. Threshold fluences for a-SiO[sub 2] and c-SiO[sub 2] were 0.23 and 0.34J/cm[sup 2], respectively. The single-pulse etch depth was not affected by the repetition rates of laser pulses from 1-50 Hz. [ABSTRACT FROM AUTHOR]

Laser-induced backside wet etching of fusedsilica plates using an aqueous solution of naphthalene-1,3,6trisulfonic acid trisodium salt (Np(SO[sub 3]Na)[sub 3]) is reported. A KrF excimer laser was employed as a light source. The etch rate varied greatly with the concentration of the solution and the laser fluence. For lower concentration solutions, the etch rate increased linearly with laser fluence. For highly concentrated solutions, however, the etch rate increased abruptly at higher fluence. Well-defined line-and-space and grid micropatterns were fabricated using a low etch rate. The etched surface was as flat as the surface of the virgin plates and the etched pattern was free of debris and microcracks. The formation and propagation of shockwaves and bubbles in the solution during the etch process were monitored. High pressure, as well as the high temperature generated by the photothermal process, plays a key role in the etching process. [ABSTRACT FROM AUTHOR]

The preparation of TiO2, In2O3, SnO2 doped In2O3 (ITO) and PbZr0.5Ti0.5O3 (PZT) films have been investigated by the metallorganic (MO) laser photolysis. TiO2 anatase phase was successfully obtained from Ti-2-ethylhexanolate by a two-step irradiation method, while rutile was formed from TiOacac under the same irradiation conditions. In2O3 and ITO films were crystallized by ArF irradiation above the laser fluence of 10 mJ/cm2. The resistivity of the In2O3 film irradiated by further ArF laser in a vacuum and air atmosphere was 2.2×10−2 and 2.2×10−1 Ω cm, respectively. The lowest resistivity of the ITO film irradiated by the ArF laser in a vacuum was 6.0×10−4 Ω cm. Epitaxial PZT film on a SrTiO3 substrate was successfully obtained by MO laser photolysis. [Copyright &y& Elsevier]

We investigated a simple and productive micromachining method of silica glass by ablation using a TEA CO laser (10.6 μm) with a spatial resolution down to sub-wavelength scale. The silica glass was irradiated by the TEA CO laser light through a copper grid mask with square apertures of 20×20 μm attached to the silica glass surface. After the irradiation, circular holes with a diameter of several μm were formed on the silica glass surface at the centers of the apertures due to the Fresnel diffraction effect. The minimum diameter of the holes was 3.4 μm. The characteristics of the micromachining are discussed based on the electric field distributions of the CO laser light under the mask using a three-dimensional full-wave electromagnetic field simulation. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated ablation of silica glass using pulsed laser plasma soft X-rays. For generating a plasma that emits pulsed soft X-rays, a Ta target was irradiated with focused 532nm Nd:YAG laser light with a pulse duration of 7ns at a fluence of 104 J/cm2. The soft X-rays were focused on the surfaces of silica glass using a Au-coated ellipsoidal mirror. The energy density of the soft X-rays can be roughly estimated to be 0.1J/cm2, which is sufficiently enough for heating silica glass beyond the boiling point. We found that silica glass is smoothly ablated at 40nm/shot. The processes induced by X-ray irradiation have been discussed based on transient-absorption measurements after X-ray irradiation. [Copyright &y& Elsevier]

Transient processes of laser ablation of a highly laser-absorbing liquid, toluene, were investigated by directly measuring (by using a fast-response pressure gauge) the transient pressure caused by toluene ablation under KrF laser irradiation . The results were compared with time-resolved images . The peak pressure P due to a shock wave decreased slowly with increasing distance d for d=100-1000 µm:P?d-0.33. By extrapolating P to d=8.9 µm, the optical penetration depth of toluene at ?=248 nm, the estimated initial pressure due to toluene ablation was 65 MPa at 1.0 J cm-2 pulse-1. The estimated initial pressure increased linearly with the fluence. These results help clarify the mechanism of laser-induced backside wet etching. [ABSTRACT FROM AUTHOR]

Study Objective: The purpose of this study was to examine the uptake rates of (18)F-fluorodeoxyglucose (FDG) and (11)C-choline in patients with lung cancer, pulmonary tuberculosis, and atypical mycobacterial infection of the lung by positron emission tomography (PET) scanning with relation to their tumor size.Design: Ninety-seven patients with untreated lung cancer, 14 patients with untreated pulmonary tuberculosis, and 5 patients with untreated atypical mycobacterial infection were examined. The diagnosis of lung cancer was confirmed pathologically after biopsy and surgery. The diagnosis of tuberculosis and atypical mycobacterial infection was confirmed by bacterial culture. The uptake rates of FDG and (11)C-choline were presented quantitatively as the standardized uptake value (SUV).Setting: International Medical Center of Japan.Results: In lung cancer patients, the SUV of FDG increased with increasing tumor size, whereas the SUV of (11)C-choline was almost constant at around 3.5 for every tumor size. In tuberculosis patients, the SUV of FDG increased with increasing tumor size, whereas the SUV of (11)C-choline was almost constant at around 2 for every tumor size. In atypical mycobacterial infection patients, the SUV of FDG and the SUV of (11)C-choline were equally low at around < or = 2.Conclusion: The differences in the SUVs of FDG and (11)C-choline in patients with lung cancer, tuberculosis, and atypical mycobacterial infection for the same tumor size (tumor size, > 1.5 cm) were distinct. In lung cancer patients, the SUVs of both FDG and (11)C-choline were high. In tuberculosis patients, the SUV of FDG was high, but the SUV of (11)C-choline was low. In atypical mycobacterial infection patients, the SUVs of both FDG and (11)C-choline were low. It may be possible to apply this principle to make a presumptive diagnosis of a solitary pulmonary nodule if it is too small to make a definitive diagnosis pathologically and bacteriologically. [ABSTRACT FROM AUTHOR]

KrF excimer laser ablation of iron disilicide in the α phase (α-FeSi2) has been investigated using time-of-flight (TOF) mass spectroscopy to characterize the dependence of ejected neutrals and native positive ions on laser fluence. The TOF mass spectra showed that the ejection behavior was classified into three parts at low, moderate and high fluence ranges. At laser fluences below 0.7 J/cm2, the presence of only Si, Fe and Si2 neutrals was confirmed; the arrival profile of Si atoms is well described by a Maxwell–Boltzmann (MB) distribution with a translational velocity of 1.6×103 m/s, corresponding to a kinetic energy of 0.35 eV, and a target surface temperature of 4.0×103 K, indicating a thermal emission of these neutral species. With increasing the fluence, nascent positive ions, such as singly- or doubly-charged Si and Fe ions appeared; the arrival profiles of these ions are observed to fit a shifted MB distribution. Their kinetic energies range from several eV at moderate fluences to over 100 eV at high fluences up to 2.5 J/cm2. These high kinetic energies cannot be explained in terms of the FeSi2 target surface reaching a temperature that would produce such energetic ions upon ablation, suggesting the ion acceleration in a dense plasma plume. [Copyright &y& Elsevier]

We have investigated time evolution of the plume produced during laser ablation of ZnO under ArF-excimer-laser irradiation in He atmosphere. The plume luminescence is mainly due to excited Zn atoms. The plume propagates straightforwardly within 1 μs after ablation, and then it expands and forms an anchor-like shape due to the plasma confinement by the surrounding He gas. After the disappearance of the plume luminescence at high He pressure, a second excitation with a XeCl-excimer-laser causes a luminescence that can be explained in terms of condensation and formation of oxygen molecules and ZnO nanoparticles in the plume. [Copyright &y& Elsevier]

We have investigated the onset of surface optical breakdown on a polished, synthetic silica glass under KrF excimer laser irradiation. With increasing laser fluence, a transient, localized luminescence is often observed. If the fluence is increased further, the luminescence reappears and grows gradually more intense with continued exposure. Subsequent examination of damaged surfaces show small craters, about 1 μm in diameter, in the damaged region. Surfaces damaged by single laser pulses at still higher fluences show similar morphologies, suggesting that the same defects or flaws are responsible for damage under multiple pulse and single pulse conditions. [Copyright &y& Elsevier]

The laser-induced back-side wet etching of fused silica with aqueous solutions of pyranine (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt) is reported. KrF and XeF excimer lasers were employed as light sources. Well-defined line-and-space and grid micropatterns, free of debris and microcracks, were obtained. Compared with other organic solutions, the aqueous pyranine etching medium etches more slowly but produces a higher quality etched surface. With the KrF laser, the etch rate ranged from 0.02 to 0.12 nm pulse[sup -1] , depending on the dye concentration and the fluence of the laser. The etch rate decreased dramatically when the XeF laser was employed, which was partially attributed to the lower absorption efficiency of the aqueous pyranine solution at the XeF laser wavelength. [ABSTRACT FROM AUTHOR]

Abstract. KrF excimer-laser ablation of sintered-powder polytetrafluoroethylene (PTFE) targets is used for the deposition of high-quality PTFE films on metallic microstructures and metal backplates for electroacoustic applications. The films are found to be highly crystalline, consisting of large spherulites with diameters up to 1 mm. X-ray photoelectron spectroscopy of the films revealed the chemical similarity of press-sinter target pulsed-laser-deposited films with bulk PTFE. Negatively charged PTFE films on stainless steel backplates exhibit an exceptional charge stability with practically no decrease of the surface potential up to 225 Celsius in open-circuit thermally stimulated discharge. [ABSTRACT FROM AUTHOR]

Reports development related to visualization technology. Interaction of turbulent wakes with nucleation and droplet growth in the blade passage; Influence of an acoustic perturbation on the flow mixing in T junction; Emphasis on tornado-like vortex spawned by the supercell thunderstorm.

Presents pictures depicting several research on visualization. Development of two instabilities in a counterrotating vortex pair; Surface temperatures of heated inclined flat plate in natural convection; Flow visualization behind a car rearview mirror made by a light-sheet and smoke.

Abstract. In order to control both molecular structures and molecular orientation simultaneously, we investigated organic molecular beam deposition combined with a laser-induced photochemical reaction. Bis(ethynylstyryl) benzene (BESB) films of trans,trans-isomer were deposited by this new method. The cis,cis-molecules were sublimed and cis-to-trans photoisomerization was conducted upon KrF excimer laser irradiation (lambda = 248 nm) in this process. The laser irradiation after and during the deposition at the substrate temperature of 25 Celsius yielded amorphous films. In contrast, the growth of well-oriented crystalline films was achieved upon the laser irradiation during the deposition at the substrate temperature of 60 Celsius. At this substrate temperature only the trans,trans-molecules were deposited on the substrate surface, which indicated that unreacted cis,cis-isomer was re-evaporated from the substrates. It can be explained that the crystal growth proceeds favorably due to the surface migration of the trans,trans-isomer and the absence of the cis,cis-isomer. It was thus found that simultaneous progress of the laser-induced isomerization and the deposition caused the growth of the well-oriented crystalline films of trans,trans-BESB. [ABSTRACT FROM AUTHOR]

The threshold fluence, F[sub Th] , of ablation of a triazeno-polymer was measured in the low fluence range for thin films using conventional UV-spectroscopy. It was found that there is a clearly defined F[sub Th] for 308 nm irradiation between 20 and 25 mJ cm[sup -2] . In the case of 248 nm irradiation, a “threshold fluence range” between 16 and 32 mJ cm[sup -2] was found. The ablation rate for both irradiation wavelengths depends on film-thickness. For the XeCl excimer-laser, the point at which the rate becomes independent of thickness was observed to lie at a value which did not correspond to the calculated laser penetration depth, whereas for the KrF laser the independence was not reached within the applied thickness range (up to 0.35 μm). Additional transmission measurements have been performed showing that the target transmission at 248 nm increases only slightly, whereas for 308 nm the transmission increases by a factor of approximately 4. This result shows that dynamic target absorption properties are very important for describing the ablation process. The results derived from the transmission studies and etch rates were analyzed theoretically with a two-level model of chromophore absorption. For 248 nm irradiation this model can describe the transmission behavior and the ablation rate. In the case of 308 nm irradiation, it was only possible to match one data set. A good agreement with the experimental transmission ratio does not match the ablation rate and vice versa. [ABSTRACT FROM AUTHOR]

Initial stage of F2 laser ablation of LiCaAlF6 single crystal was investigated for clarifying the possibility of applying this wide bandgap fluoride crystal to vacuum ultraviolet (VUV) optical components. The ablation threshold, determined by the appearance of line emission from ablated species, was approximately 2 J cm-2pulse-1, similar to that of VUV grade CaF2 single crystal. The laser-induced damage on the front surface of LiCaAlF6 was faint, though adhesion of aggregated particulates of several microns was observed. [ABSTRACT FROM AUTHOR]

Laser irradiation of solid nitrogen containing cyanuric triazide (C3N12) could generate highly reactive carbon nitride species, NCN and dicyanocarbodiimide. These species were generated in the solid nitrogen at 20 K. After laser photolysis, generated reactive species were concentrated by removal of nitrogen, and converted into a film-like product. Thus, the obtained product was characterized by means of FTIR, SEM, and XPS measurements. The product was assigned to amorphous carbon nitride with relatively high nitrogen content (N/C=0.9∼1.3). [ABSTRACT FROM AUTHOR]

To clarify the initial stage of laser-induced backside wet etching, we directly measured transient pressure upon laser ablation of toluene under KrF excimer laser irradiation by using a fast-response pressure gauge. The propagation time of the pressure peak to the gauge agreed well with the time for the shock wave to reach the gauge on time-resolved images. The peak pressure P decreased slowly with increasing distance d: P=30.4 MPa for d=100 μm to P=11.1 MPa for d=1000 μm at a fluence F=1.0 J cm-2 pulse-1. The initial pressure, estimated to be of the order of 10–200 MPa, impinges on a transparent plate and contributes to the etching. [ABSTRACT FROM AUTHOR]