2,887 research outputs found
Self-gravitating spheres of anisotropic fluid in geodesic flow
The fluid models mentioned in the title are classified. All characteristics
of the fluid are expressed through a master potential, satisfying an ordinary
second order differential equation. Different constraints are imposed on this
core of relations, finding new solutions and deriving the classical results for
perfect fluids and dust as particular cases. Many uncharged and charged
anisotropic solutions, all conformally flat and some uniform density solutions
are found. A number of solutions with linear equation among the two pressures
are derived, including the case of vanishing tangential pressure.Comment: 21 page
Production of Ethylene From Ethanol Dehydration Over H3PO4-Modified Cerium Oxide Catalysts = Penghasilan Etilena Daripada Pendehidratan Etanol Dengan Mangkin Serium Oksida Terubahsuai H3PO4
Production of ethylene from ethanol dehydration was investigated over H3PO4 (10 wt.% to 30wt.%)-modified cerium oxide catalysts synthesized by wet impregnation technique. The prepared catalysts were characterized using scanning electron microscope (SEM), N2 adsorption-desorption method, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) for the physicochemical properties. The ethanol catalytic dehydration was carried out in a fixed-bed reactor at 673-773 K and at ethanol partial pressure of 33 kPa. The effects of phosphorus loading on catalyst and reaction temperatures were investigated in terms of catalytic activity towards product selectivity and yield. Overall, the
selectivity and yield of ethylene increased with the temperature and phosphorus loading. The highest ethylene selectivity and yield were 99% and 65%, respectively, at 773 K and 33 kPa over the 30 wt.% H3PO4-modified cerium oxide
Nanometer-scale patterning and individual current-controlled lithography using multiple scanning probes
Cataloged from PDF version of article.Scanning probe lithography(SPL) is capable of sub-30-nm-patterning resolution and nanometer-scale alignment registration, suggesting it might provide a solution to the semiconductor industry’s lithography challenges. However, SPL throughput is significantly lower than conventional lithography techniques. Low throughput most limits the widespread use of SPL for high resolution patterning applications. This article addresses the speed constraints for reliable patterning of organic resists. Electrons field emitted from a sharp probe tip are used to expose the resist. Finite tip-sample capacitance limits the bandwidth of current-controlled lithography in which the tip-sample voltage bias is varied to maintain a fixed emission current during exposure. We have introduced a capacitance compensation scheme to ensure continuous resist exposure of SAL601 polymerresist at scan speeds up to 1 mm/s. We also demonstrate parallel resist exposure with two tips, where the emission current from each tip is individually controlled. Simultaneous patterning with multiple tips may make SPL a viable technology for high resolution lithography.
© 1999 American Institute of Physic
Large Area Roller Embossing of Multilayered Ceramic Green Composites
In this paper, we will report our achievements in developing large area
patterning of multilayered ceramic green composites using roller embossing. The
aim of our research is to pattern large area ceramic green composites using a
modified roller laminating apparatus, which is compatible with screen printing
machines, for integration of embossing and screen printing. The instrumentation
of our roller embossing apparatus, as shown in Figure1, consists of roller 1
and rollers 2. Roller 1 is heated up to the desired embossing temperature ;
roller 2 is, however, kept at room temperature. The mould is a nickel template
manufactured by plating nickel-based micro patterns (height : 50 m) on a
nickel film (thickness : 70 m) ; the substrate for the roller embossing is
a multilayered Heraeus Heralock HL 2000 ceramic green composite. Comparing with
the conventional simultaneous embossing, the advantages of roller embossing
include : (1) low embossing force ; (2) easiness of demoulding ; (3) localized
area in contact with heater ; and etc. We have demonstrated the capability of
large area roller embossing with a panel size of 150mmx 150mm on the mentioned
substrate. We have explored and confirmed the impact of parameters (feed speed,
temperature of roller and applied pressure) to the pattern quality of roller
embossing. Furthermore, under the optimized process parameters, we
characterized the variations of pattern dimension over the panel area, and
calculated a scaling factor in order to make the panel compatible with other
processes. Figure 2 shows the embossed patterns on a 150mmx 150mm green ceramic
panel.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/handle/2042/16838
Production of photons by the parametric resonance in the dynamical Casimir effect
We calculate the number of photons produced by the parametric resonance in a
cavity with vibrating walls. We consider the case that the frequency of
vibrating wall is which is a generalization of other
works considering only , where is the fundamental-mode
frequency of the electromagnetic field in the cavity. For the calculation of
time-evolution of quantum fields, we introduce a new method which is borrowed
from the time-dependent perturbation theory of the usual quantum mechanics.
This perturbation method makes it possible to calculate the photon number for
any and to observe clearly the effect of the parametric resonance.Comment: 15 pages, RevTeX, no figure
Catalytic Performance of Commercial Zeolites Y as Catalyst for Ethylene Production from Ethanol Dehydration
Catalytic dehydration of ethanol into ethylene was studied over commercial Zeolites-Y with different Si:Al ratios between 5.1:1 and 80:1, and temperature from 573 K to 773 K. The physicochemical properties of fresh and spent catalyst of Zeolite Y Si:Al 80:1 (best performing catalyst) were investigated using N2-physisorption, TGA, SEM-EDX, NH3-TPD, FTIR and XRD. Results showed that catalysts with higher Si:Al ratios exhibit better catalytic performance in terms of higher ethanol conversion and higher selectivity to ethylene. Indeed, zeolites-Y with Si:Al ratio 5.1:1 and 12:1 demonstrated low catalytic activity with ethanol conversion of 34% and 2%, respectively. However, ethylene selectivity of NH3-Y (5) was 84%, which was considerably higher than NH3-Y (12) which was 26%, indicated that this catalyst was not promoting the formation of other hydrocarbons i.e. methane and ethane. Albeit all of the catalysts namely H-Y (30), H-Y (60) and H-Y (80) showed favorable performance in ethanol dehydration, H-Y (80) attained almost total selectivity to ethylene and highest conversion of 73.0% among all the tested catalysts
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