Hydrogenation of canola oil in the presence of nickel and the methyl benzoate-chrome carbonyl complex

Canola oil was hydrogenated using a mixture of homogeneous methyl benzoate-Cr(CO)₃ and heterogeneous nickel catalysts. The effect of the methyl benzoate-Cr(CO)₃_to-nickel ratio on the activity, specific isomerization index, linoleate and linolenate selectivities, and fatty acid composition was evaluated, and the results compared with those obtained with commercial nickel catalyst and methyl benzoate-Cr(CO)₃ used individually. At higher chromium-to-nickel ratios the activity of nickel was inhibited and the system behaved essentially like the pure chrome complex, while at low chromium-to-nickel ratios the characteristics of the nickel predominated. In a short transition zone relatively high reaction rates were obtained with significantly reducedtrans-isomer levels in the product. In a broader sense, it may be possible to combine a homogeneous and heterogeneous catalyst while retaining the advantages of both. We may thus be able to design catalyst systems for specific applications.     

The production of salad oil by fractional crystallization with solvents

A fractional crystallization method for the winterization of cottonseed oil with solvents was developed in our laboratories and pilot plant. Small amounts of solvent (e.g., 10% by weight of acetone) were mixed with the oil. This mixture was rapidly chilled to 0°C. and kept at this temperature for 3–4 hrs.; the liquid portion was separated from the solids. After solvent evaporation a salad oil of good quality was obtained. The yield is equal to or better than that obtained with conventional methods. The method is suitable for a continuous operation since rapid chilling can be used, and only a short over-all time is necessary. Great advantages of the process are the use of low amounts of solvent and of a refrigeration system not requiring temperatures below 0°C.     

Regulation of phosphatidylinositol turnover,calcium metabolism and enzyme secretion by phorbol dibutyrate in neutrophils

The action of the tumor promoter, phorbol 12,13-dibutyrate (PDBu), on rabbit peritoneal and human neutrophils is associated with stimulation of¹⁴C-arachidonic acid incorporation into phospholipids within 1–2 min. Stimulated¹⁴C-arachidonate incorporation was relatively selective for phosphatidylinositol (PI) in rabbit neutrophils. In contrast, the secretory response of human neutrophils to PDBu coincided with stimulated label incorporation into phosphatidylserine (PS), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA) and PI. Significant increases in label incorporation were observed with PDBu concentrations as low as 2 nM, and the dose response of stimulated label incorporation paralleled that of evoked lysozyme secretion. A parallel, but partial, inhibition of PDBu-stimulated PI labeling and enzyme release was observed after exposing rabbit neutrophils to calcium-deprived medium, whereas calcium deprivation failed to significantly depress either of these stimulant actions of PDBu in human neutrophils. Further, in rabbit neutrophils PDBu elicited an increase in cell associated⁴⁵Ca. However, PDBu was unable to promote the incorporation of³²P orthophosphate into PI or enhance phospholipase A₂ activity in broken cells. These findings suggest that one expression of the interaction between phorbol esters and their receptors on neutrophils involves the turnover of arachidonic acid in phospholipids. This stimulated turnover of arachidonate may be a critical step in the cascade of events associated with neutrophil activation.     

Supported gold catalysis in the hydrogenation of canola oil

The catalytic activity of gold supported on silica orγ-alumina has been studied in the hydrogenation of canola oil. In the hydrogenation of butadiene and pentene using these catalysts, high stability, low yield oftrans-isomers and high monoene selectivity have been reported in the literature. Catalysts containing 1% and 5% Au w/w on porous silica andγ-alumina were active in hydrogenating canola oil in the range of 150 to 250 C and 3550 to 5620 kPa. The activity level of these catalysts was about 30 times lower than that shown by the standard AOCS Ni catalyst based on the concentration of metal (g Au/L oil). Up to 91% monoene content was obtained using these catalysts in comparison with a maximum of 73% for the AOCS standard Ni catalysts. Gold catalysts can be recovered easily by filtration and reused several times without a decrease in activity. The hydrogenated oil was nearly colorless. No gold was detectable in the oil. Contrary to claims in the patent literature, the gold catalyst produces higher concentrations oftrans-isomers than does nickel. However, using gold catalysts the complete reduction of linolenic acid in canola oil can be achieved at a lowertrans-isomer content in the products than that obtained by using the AOCS standard nickel catalyst.     

Robust throughput and routing for mobile ad hoc wireless networks

Flows transported across mobile ad hoc wireless networks suffer from route breakups caused by nodal mobility. In a network that aims to support critical interactive real-time data transactions, to provide for the uninterrupted execution of a transaction, or for the rapid transport of a high value file, it is essential to identify robust routes across which such transactions are transported. Noting that route failures can induce long re-routing delays that may be highly interruptive for many applications and message/stream transactions, it is beneficial to configure the routing scheme to send a flow across a route whose lifetime is longer, with sufficiently high probability, than the estimated duration of the activity that it is selected to carry. We evaluate the ability of a mobile ad hoc wireless network to distribute flows across robust routes by introducing the robust throughput measure as a performance metric. The utility gained by the delivery of flow messages is based on the level of interruption experienced by the underlying transaction. As a special case, for certain applications only transactions that are completed without being prematurely interrupted may convey data to their intended users that is of acceptable utility. We describe the mathematical calculation of a network’s robust throughput measure, as well as its robust throughput capacity. We introduce the robust flow admission and routing algorithm (RFAR) to provide for the timely and robust transport of flow transactions across mobile ad hoc wireless network systems.     

Performance evaluation of a reservation random access scheme for packetized wireless systems with call control and hand-off loading

We consider a packet switched wireless network where each cell's communication channel is shared among packet voice sources. In this paper, we present a method for the design and analysis of wireless cells using a reservation random access (RRA) scheme for packet access control. This scheme is integrated with a call admission control procedure. We model the state process of a single cell as a vector Markov chain. We compute the steady state distribution of the Markov chain. This result is used to calculate the packet dropping probability and the call blocking probability. By setting limits on maximum permissible levels for the call blocking probability and the packet dropping probability, we obtain the Erlang capacity of a single cell, with and without hand-off traffic. For an illustrative RRA scheme, the Erlang capacity of a single cell is shown to be about twice that attained by a comparable fixed assigned TDMA scheme. We show that a cellular network using this RRA scheme and which applies can be no blocking of hand-off calls, exhibits similar call capacity levels.This work is supported by a University of California MICRO and Pacific-Bell Grant No. 94-107.     

General solution for propagation, radiation and scattering inarbitrary 3D inhomogeneous structures

A versatile technique for obtaining the full-wave characteristics of structures composed of conductors and dielectrics is described. It involves the replacement of the dielectric regions by an equivalent interlocking array of thin-wall sections, to which appropriate surface impedances are then attributed. Through the use of a two-dimensional rooftop current representation and line-function testing of the electric field, matrix equations appropriate for propagation, radiation, and scattering problems are generated and solved. The focus is on the physical principles, and the usefulness of the approach is demonstrated by solving a wide variety of practical problems     

Impact of the location area structure on the performance ofsignaling channels in wireless cellular networks

The authors consider connection-oriented wireless cellular networks such as IS-54, IS-95, GSM, and wireless ATM networks. These are connection-oriented digital networks which employ separate radio channels for the transmission of signaling information. A forward signaling channel is a common signaling channel assigned to carry the multiplexed stream of paging and channel-allocation packets from a base station to mobile stations. For wireless ATM networks, paging and virtual-circuit (VC) allocation packets are multiplexed across the forward signaling channels as part of the VC setup phase. A reverse signaling channel, which employs a contention-oriented medium access algorithm, is used by mobile stations to send channel-request and location-update packets. A location area is a region which includes a specified set of adjacent cells; it is used to track the location of mobile stations. Mobile units must reregister as they cross the boundary of a location area. The channel setup and paging response times are critical performance factors in the design of the signaling subsystem. A location area structure must be suitably selected to ensure that acceptable levels of such performance functions are achieved. A network which employs small location-areas will experience a high rate of location updates, while larger location areas lead to higher traffic intensities of paging messages. The authors overview a method for calculating the performance behavior of signaling messages. Subsequently the impact of the location area structure on the performance of the signaling system is investigated