Gas Hole Research Articles

Computed tomographic evaluation of gas hole formation and structural quality in Gouda‐type cheese

Computed tomography (CT) was performed on Gouda‐type cheese during ripening to evaluate gas hole formation and structural quality. The cheese was exposed to different ripening conditions, including variations in ripening temperature and concentration of butyric acid bacteria. Computed tomography images were obtained every 2 weeks for 16 weeks to assess the volume, shape and location of gas holes. The results demonstrate that CT makes the nondestructive monitoring of cheese gas hole formation and evaluation of the structural features of cheese possible throughout the ripening period.

Charge localization in [1 1 2] Si/Ge and Ge/Si core–shell nanowires

We report a first-principles study of Ge/Si and Si/Ge core/shell nanowires (NWs) along the [1 1 2] direction with a diameter of ∼20 Å using density-functional theory. Our results show that for both NW structures the band gaps are indirect and are significantly larger than the gaps of the bulk crystalline Si and Ge. The quantum well confinement effect in these NWs is found to be modified by a type II lineup of band structures. Moreover, the carriers on the conduction band minimum are strongly localized in the Si region while the carriers on the valence band maximum are located mainly in the Ge region. The charge separation and localization characters make the NWs good candidates for nanochannels in field effect devices, solar cells with higher efficiency and high mobility heterostructures due to the spatial separation of one-dimensional electron gas and one-dimensional hole gas.

THE LOPSIDEDNESS OF PRESENT-DAY GALAXIES: CONNECTIONS TO THE FORMATION OF STARS, THE CHEMICAL EVOLUTION OF GALAXIES, AND THE GROWTH OF BLACK HOLES

We have used the Sloan Digital Sky Survey (SDSS) to undertake an investigation of lopsidedness in a sample of ~25,000 nearby galaxies (z < 0.06). We use the m=1 azimuthal Fourier mode between the 50% and 90% light radii as our measure of lopsidedness. The SDSS spectra are used to measure the properties of the stars, gas, and black hole in the central-most few-kpc-scale region. We show that there is a strong link between lopsidedness in the outer parts of the galactic disk and the youth of the stellar population in the central region. This link is independent of the other structural properties of the galaxy. These results provide a robust statistical characterization of the connections between accretion/interactions/mergers and the resulting star formation. We also show that residuals in the galaxy mass-metallicity relation correlate with lopsidedness (at fixed mass, the more metal-poor galaxies are more lopsided). This suggests that the events causing lopsidedness and enhanced star formation deliver lower metallicity gas into the galaxy's central region. Finally, we find that there is a trend for the more powerful active galactic nuclei to be hosted by more lopsided galaxies (at fixed galaxy mass, density, or concentration). However if we compare samples matched to have both the same structures and central stellar populations, we then find no difference in lopsidedness between active and non-active galaxies. This leads to the following picture. The presence of cold gas in the central region of a galaxy (irrespective of its origin) is essential for both star-formation and black hole growth. The delivery of cold gas is aided by the processes that produce lopsidedness. Other processes on scales smaller than we can probe with our data are required to transport the gas to the black hole.

Layer interdependence of transport in an undoped electron-hole bilayer

The layer interdependence of transport in an undoped electron-hole bilayer (UEHBL) device was studied as a function of carrier density, interlayer electric field, and temperature. The UEHBL device consisted of a density tunable, independently contacted two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) in distinct (100) GaAs quantum wells separated by a 30 nm ${\text{Al}}_{0.9}{\text{Ga}}_{0.1}\text{As}$ barrier. The 2DEG and 2DHG are induced via field effect by top and bottom gates, respectively. Transport measurements were made simultaneously on each layer using the van der Pauw method. An increase in 2DHG mobility with increasing 2DEG density was observed, while the 2DEG mobility showed minimal dependence on the 2DHG density. Changes in both surface-gate voltages for the mobility-density measurements were observed. Decreasing the interlayer electric field and thereby increasing interlayer separation also increased the 2DHG mobility with negligible effects on the 2DEG mobility. The change in interlayer separation as interlayer electric field changed was estimated using 2DHG Coulomb drag measurements. A general discussion of the results is given in which the possible sources for the apparent interlayer dependence of the hole transport are examined.

Dynamics of Kicked and Accelerated Massive Black Holes in Galaxies

A study is made of the behavior of massive black holes in disk galaxies that have received an impulsive kick from a merger or a sustained acceleration from an asymmetric jet. The motion of the gas, stars, dark matter, and massive black hole are calculated using the GADGET-2 simulation code. The massive black hole escapes the galaxy for kick velocities above about 600 km s−1 or accelerations above about 4 × 10−8 cm s−2 over timescales of the order of 108 yr. For smaller velocity kicks or smaller accelerations, the black hole oscillates about the center of mass with a frequency that decreases as the kick velocity or acceleration increases. The black hole displacements may give rise to observable nonaxisymmetries in the morphology and dynamics of the stellar and gaseous disk of the galaxy. In some cases the dynamical center of the galaxy is seen to be displaced toward the direction of the BH acceleration with a characteristic tongue-shaped extension of the velocity contours on the side of the galaxy opposite the acceleration.

Effect of nano-CeO2 on cobalt-based alloy laser coatings

Abstract Cobalt-based alloy coatings with/without nano-CeO2 addition prepared by a 5 kW CO2 laser on Q235 low carbon steel were introduced. The effects of nanoparticles on the macro-quality, microstructure, phase composition, and wear resistance of the coatings were investigated. The microstructure and phases composition of the coatings were analyzed using Olympus-Pme-3 type microscope, Philip Xl 30 type scanning electron microscope and XD-3A type X-ray diffractometer (XRD). The wear resistance was tested using MM-200 type sliding wear machine, and the wear mechanism was analyzed by JSM-35C type scanning electron microscope (SEM). The results showed that defect (such as crack, gas hole, etc.) -free coatings were obtained. There existed γ-Co and Cr23C6 in cobalt-based alloy coatings. Another two phases of CeCo2 and ɛ-Co were identified with nanoparticles addition. Fine microstructure and equiaxed dendrite were obtained by adding nano-CeO2. The relative wear resistance is improved with the increased amount of nano-CeO2, and the coatings with the best wear resistance when laser power was 2.0 kW by adding 1.5 wt.% CeO2. The mechanism was found from abrasive/adhesive wear to fretting wear. The wear resistance decreased with 2.0 wt.% CeO2 addition.

Research on laser welding of vehicle body

Based on many experiments of CO 2 laser welding of vehicle body, joint microstructure and stress–strain curve of specimen are analyzed. The deep punching performance acquired by adopting Ar as protective gas is better than that of the one acquired by adopting N 2 as protective gas. Meanwhile the percentage of zinc in welding seam can be effectively controlled by means of blowing side protective gas. In this paper, welding penetration and width are shown to vary with laser power and speed of welding. The results indicate that some flaws such as gas hole, crack and softening of HAZ do not appear in laser welding seam in sheet steel of automobile bodies if technology parameters optimizes. The deep punching performance of tailor-welding sheet is fine.

Undoped electron-hole bilayers in a GaAs∕AlGaAs double quantum well

The authors present the fabrication details of completely undoped electron-hole bilayer devices in a GaAs∕AlGaAs double quantum well heterostructure with a 30nm barrier. These devices have independently tunable densities of the two-dimensional electron gas and two-dimensional hole gas. The authors report four-terminal transport measurements of the independently contacted electron and hole layers with balanced densities from 1.2×1011cm−2 down to 4×1010cm−2 at T=300mK. The mobilities can exceed 1×106cm2V−1s−1 for electrons and 4×105cm2V−1s−1 for holes.

Massive black holes: formation and evolution

AbstractSupermassive black holes are nowadays believed to reside in most local galaxies. Observations have revealed us vast information on the population of local and distant black holes, but the detailed physical properties of these dark massive objects are still to be proven. Accretion of gas and black hole mergers play a fundamental role in determining the two parameters defining a black hole: mass and spin. We briefly review here the basic properties of the population of supermassive black holes, focusing on the still mysterious formation of the first massive black holes, and their evolution from early times to now.

신발금형의 가스 배출량 측정 장치와 영상정보를 이용한 가스벤트 자동 교환 시스템의 개발

This paper presents a gas measurement system for deciding hole positions on a PU middle-sole mold from computed gas amount. The optimal number of holes and their positions on the shoe mold are decided from statistical experiment results to overcome the problem of excessive expenses in gas vent exchange. This paper also describes a gas vent exchange mechanism using computer vision system. The gas hole detecting process is based on computer vision algorithms represented as a simple Pattern Matching. The experimental result showed us that the system was useful to calculate the number of holes and their positions on the shoes mold.

Dark matter in elliptical galaxies - II. Estimating the mass within the virial radius

Elliptical galaxies are modelled with a a 4-component model: Sersic stars, LCDM dark matter (DM), hot gas and central black hole. DM is negligible in the inner regions, which are dominated by stars and the central black hole. This prevents any kinematical estimate (using a Jeans analysis) of the inner slope of the DM density profile. The gas fraction rises, but the baryon fraction decreases with radius, at least out to 10 effective radii (R_e). Even with line-of-sight velocity dispersion (VD) measurements at 4 to 6 R_e with 20 km/s accuracy and perfectly known velocity anisotropy, the total mass within the virial radius (r_v) is uncertain by a factor over 3. The DM distributions found in LCDM simulations are consistent with the stellar VD profiles, but appear inconsistent with the low VDs measured by Romanowsky et al. (2003) of planetary nebulae between 2 and 5 R_e, which imply such low M/Ls that the baryon fraction within r_v must be greater than the universal value. Replacing the NFW DM model by the new model of Navarro et al. (2004) decreases slightly the VD at a given radius. So, given the observed VD measured at 5 R_e, the inferred M/L within r_v is 40% larger than predicted with the NFW model. Folding in the slight (strong) radial anisotropy found in LCDM (merger) simulations, which is well modelled (much better than with the Osipkov-Merritt formula) with beta(r) = 1/2 r/(r+a), the inferred M/L within r_v is another 1.6 (2.4) times higher than for the isotropic NFW model. Thus, the DM model and radial anisotropy can partly explain the low PN VDs, but not in full. In an appendix, single integral expressions are derived for the VDs in terms of the tracer density and total mass profiles, for 3 anisotropic models: radial, Osipkov-Merritt, and the model above, for general radial profiles of luminosity density and mass.

Study on a Pre-mixed Charge Compression Ignition Engine by Dimethoxymethane Port Injection

This paper presents a study of premixed combustion in a compression ignition (CI) engine. An electrically controlled fuel injection system was installed in the intake manifold of the engine. Dimethoxymethane (DMM) fuel with a low cetane number and low boiling point was injected into the manifold. The homogeneous mixture was formed in the compression stroke and ignited by a small amount of injected diesel fuel near the TDC (top dead centre). The effects of pre-mixed fuel ratio, engine load, CO2 concentration in the intake gas and nozzle hole diameter on the engine combustion and emissions were investigated. The results show that the pre-mixed combustion by DMM fuel port injection exhibits a substantial reduction of NOx and smoke emissions simultaneously, which might make it possible to develop a technique for controlling diesel engine exhaust emissions.

Prediction of Gas Hole by Mold-Filling Simulation with Consideration of Surface Tension

The algorithm for mold-filling simulation with consideration of surface tension has been developed based on the CIP method. As a test problem, a squeeze casting simulation was taken up. As an application to a practical casting problem, we also applied this scheme to a die-casting simulation and compared the numerical results with the experimental data on the size and the position of blow holes. Numerical results both with and without surface tension indicated the existence of blow holes. However, the simulation without surface tension tended to underestimate the size of blow holes. Through these numerical results, it is confirmed that the consideration of surface tension is very important for predicting the size and the position of gas trapped in mold cavities. Furthermore, we propose a criterion for estimating whether the gas remaining in the cavity is compressed or expanded during mold filling, and adopt it to a practical die-casting problem.

Quasi-lateral 2DEG–2DHG junction in AlGaAs/GaAs

We report on an electrical and electroluminescence (EL) investigation of a quasi-lateral two-dimensional electron gas and two-dimensional hole gas junction based on an AlGaAs/GaAs heterostructure. Current bistability is demonstrated, leading to bistability in the EL efficiency.

Fabrication and microstructure of in situ Al 2O 3 decomposed from Al 2(SO 4) 3-reinforced aluminum matrix composites

In situ Al 2O 3 decomposed from Al 2(SO 4) 3-reinforced aluminum matrix composites was fabricated through stirring cast by adding Al 2(SO 4) 3 to the molten alloy which is the raw and processed materials from which industrial high-purity Al 2O 3 is made. Not only production cost may be reduced but also SO 3 decomposed from Al 2(SO 4) 3 may refine and remove the gas from the molten composites as stated before. The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As a result, Al 2O 3 and matrix bonded well, no cast defects being found, such as gas hole, porosity and particles segregation in in situ Al 2O 3 decomposed from Al 2(SO 4) 3-reinforced aluminum matrix composites. It is considered the key factor of particulate-reinforced aluminum matrix composites really being produced in industrial that SO 3 decomposed from Al 2(SO 4) 3 may refine and remove the gas from the molten composites.

Gas holdup in a trayed cold-flow bubble column

An experimental study was performed to investigate the effect of sieve trays on the time-averaged gas holdup profiles and the overall gas holdup in a cold-flow bubble column that was scaled-down from a commercial unit. γ-ray computed tomography (CT) was used to scan the column at several axial locations in the presence and absence of trays from which the local variation of the gas holdup was extracted. The overall gas holdup was also determined using the same configuration by comparing the expanded and static liquid heights. Air and water were used as the gas–liquid system. The superficial gas and liquid velocities were selected to span the range of the commercial system using gas spargers having multiple lateral distributors that were also scaled-down from the commercial design. To investigate the impact of sparger hole density on the local and overall gas holdup, two difference sparger designs were used in which the hole density per lateral was varied. The gas hole velocity was maintained constant at ca. 245 m/ s , which approached that used in the commercial reactor. It is shown that the local gas holdup determined by CT is generally higher in the tray down comer region and exhibits an asymmetric pattern when trays are present. The use of increased sparger hole density at a constant gas superficial velocity leads to steeper gradient in the gas holdup near the column centerline and a higher overall gas holdup. These findings suggest that the performance of bubble column reactors for various applications is sensitive to both sparger and tray design.

Projection Velocities of Droplets in the Spray Regime of Sieve Tray Operation

A dual-electronic-probe technique and a multicolor high-speed stroboscopic photographic technique were used to measure the initial projection velocities of droplets on a 300 mm diameter sieve tray operating in the spray regime. The experimental results confirmed that both of these techniques can supplement each other for the measurements. A new correlation was obtained to express the relation among projection velocity, droplet size, and gas hole velocity.

Study of two-dimensional hole gas concentration and hole mobility in zinc delta-doped GaAs and pseudomorphic GaAs/In0.2Ga0.8As heterostructures

Zinc delta-doped GaAs and pseudomorphic GaAs/In}0.2Ga0.8As heterostructures grown by low-pressure metalorganic chemical vapour deposition have been demonstrated. The influence of delta-doping period and spacer thickness on two-dimensional hole gas concentrations and hole mobility was studied. From secondary-ion mass spectroscopy and Hall measurement, we conclude that zinc delta-doping can form an excellent abrupt profile (full-width at half maximum is of 10 nm) and offer a high two-dimensional hole gas sheet density (as high as 1×1013cm−2) By adopting a strained InGaAs material as the active channel and by carefully modulating the spacer layer thickness, one can obtain a significantly enhanced hole mobility.

Failure analysis and prevention of a brake nave on a landing gear

The leakage failure of a brake nave on a landing gear has been investigated. A crack initiating at the transitional region and propagating as deep as the blind gas hole was responsible for the leakage. Rough machining marks and an incomplete protective coating were found near the crack. Examinations revealed that brittle and tough fracture features existed alternately in the fracture surface. Analysis results show that the crack grew by transgranular stress corrosion, promoted by the stress concentration and poor surface conditions. Similar failures have been avoided by adopting the preventive actions detailed in this paper.

Study of Zinc-Delta-Doped Strained Quantum Well InGaAs/GaAs p-Channel Heterostructure Field-Effect Transistors

Zinc-delta-doped strained quantum well InGaAs/GaAs p-channel heterostructure field-effect transistor (HFET) grown by low-pressure metalorganic chemical vapor deposition has been realized. In terms of using the zinc-delta-doping technique by interrupting the growth, high concentration is carried out. The influence of spacer layer thickness on two-dimensional hole gas concentration and hole mobility is also studied. The delta-doped p-type strained InGaAs/GaAs HFET with 8 nm spacer layer thickness exhibits extrinsic transconductances of 15 mS/mm at 300 K and 24 mS/mm at 77 K. Secondary-ion mass spectrometry (SIMS) is carried out to confirm the film quality, zinc diffusion profile and sharpness of the proposed structures. Due to the smaller mobility difference in InGaAs/GaAs than in using AlGaAs barriers, the gate voltage swing in the p-channel delta-doped InGaAs/GaAs HFET exhibits a value about 1.7 V. Consequently, a wider linear amplifier application is expected in the present device.