Exposure of metallic copper surface on Cu-Al2O3-carbon catalysts

The bifunctional nature of Cu---Al2O3-on-carbon catalysts, used in the direct catalytic conversion of ethanol to ethyl acetate, prompted an examination of the dispersion of Cu on the composite catalyst. For this, the N2O-method of Osinga et al. for estimation of bare metallic copper surface on composite copper catalysts has been adapted for use on a gravimetric adsorption unit and then applied to several promoted and supported copper catalysts. For catalysts with Cu/Al atomic ratio 0.8 to 26, all reduced at 300 °C, the copper surface is only 1–8% of the total surface of 500–560 m2/g, but 50–430 m2/g Cu. The maximum Cu dispersion is obtained for the catalyst with Cu/Al = 6, which is also one of the best catalysts for the esterification reaction. The Cu surface rapidly increases from 1 to 10% of the total surface as the temperature of reduction of the catalyst is raised from 100 to 400 °C. On a low area (32 m2/g) asbestos carrier, a relatively higher Cu coverage of 55% can be obtained, but the activity of this catalyst is very poor. On use in the esterification reaction, the carbon-supported catalyst gets a more reddish brown copper color, however there is no increase in the exposed copper area.\ud \ud X-ray microscan studies of the catalyst prove that the copper sites on the surface (in an 1 μ-thick layer) are mostly in close association with the Al sites of the alumina promoter. Results from catalyst testing show that these Cu---Al sites or junctions are necessary to catalyze the condensation to ester of the acetaldehyde formed in the primary dehydrogenation of ethanol over copper. The microscan studies on the same spot on one and the same catalyst particle indicate that the distribution of Cu and Al in the 1 μ-thick layer on the catalyst surface does undergo some alterations when the catalyst is reduced at 300 °C and subsequently used in the esterification reaction at 275 °C. The exact nature of these alterations is still not clear

Off-centred dark matter halo leading to strong central disc lopsidedness

There is increasing evidence now from simulations and observations that the centre of dark matter halo in a Milky Way type galaxy could be off-centred by a few 100 pc w.r.t. the galactic disc. We study the effect of such an offset halo on the orbits and kinematics in the central few kpc of the disc. The equations of motion in the disc plane can be written in terms of the disc and halo potentials when these two are concentric and a perturbation term due to the offset halo. This perturbation potential shows an m=1 azimuthal variation, or is lopsided, and its magnitude increases at small radii. On solving these equations, we find that the perturbed orbit shows a large deviation of ~ 40 % in radius at R = 1.5 kpc, and also strong kinematical lopsidedness. Thus even a small halo offset of 350 pc can induce surprisingly strong spatial and kinematical lopsidedness in the central region within ~ 3 kpc radius. Further, the disc would remain lopsided for several Gyr, as long as the halo offset lasts. This would have important implications for the dynamical evolution of this region.Comment: 6 pages, 6 figures, Submitted to MNRA

Addendum to `Fake Projective Planes'

The addendum updates the results presented in the paper `Fake Projective Plane, Invent Math 168, 321-370 (2007)' and makes some additions and corrections. The fake projective planes are classified into twenty six classes. Together with a recent work of Donald Cartwright and Tim Steger, there is now a complete list of fake projective planes. There are precisely one hundred fake projective planes as complex surfaces classified up to biholomorphism.Comment: A more refined classification is given in the new versio

Multiaccess Channels with State Known to Some Encoders and Independent Messages

We consider a state-dependent multiaccess channel (MAC) with state non-causally known to some encoders. We derive an inner bound for the capacity region in the general discrete memoryless case and specialize to a binary noiseless case. In the case of maximum entropy channel state, we obtain the capacity region for binary noiseless MAC with one informed encoder by deriving a non-trivial outer bound for this case. For a Gaussian state-dependent MAC with one encoder being informed of the channel state, we present an inner bound by applying a slightly generalized dirty paper coding (GDPC) at the informed encoder that allows for partial state cancellation, and a trivial outer bound by providing channel state to the decoder also. The uninformed encoders benefit from the state cancellation in terms of achievable rates, however, appears that GDPC cannot completely eliminate the effect of the channel state on the achievable rate region, in contrast to the case of all encoders being informed. In the case of infinite state variance, we analyze how the uninformed encoder benefits from the informed encoder's actions using the inner bound and also provide a non-trivial outer bound for this case which is better than the trivial outer bound.Comment: Accepted to EURASIP Journal on Wireless Communication and Networking, Feb. 200

News or Noise? Signal Extraction Can Generate Volatility Clusters From IID Shocks

We develop a framework in which information about firm value is noisily observed. Investors are then faced with a signal extraction problem. Solving this would enable them to probabilistically infer the fundamental value of the firm and, hence, price its stocks. If the innovations driving the fundamental value of the firm and the noise that obscures this fundamental value in observed data come from non-Gaussian thick-tailed probability distributions, then the implied stock returns could exhibit volatility clustering. We demonstrate the validity of this effect with a simulation study.stock returns, volatility clusters, GARCH processes, signal extraction, thick-tailed distributions, simulations

Signal Extraction can Generate Volatility Clusters

volatility clusters; GARCH processes; signal extraction; heavy-tailed distributions

The late-time development of the Richtmyer–Meshkov instability

Measurements have been made of the growth by the Richtmyer–Meshkov instability of nominally single-scale perturbations on an air/sulfur hexafluoride (SF6) interface in a large shock tube. An approximately sinusoidal shape is given to the interface by a wire mesh which supports a polymeric membrane separating the air from the SF6. A single shock wave incident on the interface induces motion by the baroclinic mechanism of vorticity generation. The visual thickness delta of the interface is measured from schlieren photographs obtained singly in each run and in high-speed motion pictures. Data are presented for delta at times considerably larger than previously reported, and they are tested for self-similarity including independence of initial conditions. Four different initial amplitude/wavelength combinations at one incident shock strength are used to determine the scaling of the data. It is found that the growth rate decreases rapidly with time, ddelta/dt[proportional]t–p (i.e., delta[proportional]t1–p), where 0.67<~p<~0.74 and that a small dependence on the initial wavelength lambda0 persists to large time. The larger value of the power law exponent agrees with the result of the late-time-decay similarity law of Huang and Leonard [Phys. Fluids 6, 3765–3775 (1994)]. The influence of the wire mesh and membrane on the mixing process is assessed

The nature of the potassium compound acting as a promoter in iron-alumina catalysts for ammonia synthesis

The chemical form of the potassium promoter on an iron-alumina catalyst during ammonia synthesis has been studied by two methods, viz, (i) the measurement of the equilibrium constant of the process KNH2 + H2 KH + NH3, and (ii) chemical analysis of the used catalyst. The equilibrium constant measurements gave K723 = (12.9 ± 0.5) × 10−3, ΔHf2980(KNH2) = −119 ± 3 kJ mol−1 and S2980(KNH2) = 109 ± 4 J mol−1 K−1. The chemical analysis showed that no KNH2 is present on the catalyst during synthesis. From these results and with the aid of thermodynamic considerations it is concluded that KNH2, K and K2O are not stable compounds under conditions of ammonia synthesis. X-Ray diffraction showed that part of the potassium reacts with Al2O3, probably leaving part of the potassium in the form of KOH which is quite stable under ammonia synthesis conditions