Preparation and decomposition of potassium alkalide-lipophilic crown ether complexes in tetrahydrofuran

Cyclohexano-15-crown-5, cyclohexano-18-crown-6, dicyclohexano-15-crown-5, and dicyclohexano-18-crown-6, but not dicylohexano-16-crown-5, in THF dissolve potassium metal to form dark blue potassium alkalide solutions at ambient temperature. On standing, the potassium alkalide complexes decompose and the solutions turn colorless at differing rates. Identification of the products provides insight into the decomposition mechanism.     

Double-resonance decoupling for resolution enhancement of 31P solid-state MAS and 27Al --> 31P MQHETCOR NMR

27Al decoupling has been used to remove residual J-coupling interactions between 31P and 27Al in microporous aluminophosphates AlPO4-14 and AlPO4-40. In combination with 1H high-power decoupling, 27Al adapted decoupling yields 31P spectra with optimal sensitivity and resolution. The importance of double-resonance decoupling is further demonstrated by incorporating this technique in the MQHETCOR sequence. Unambiguous assignment of all the AlPO4-14 nuclear magnetic resonances is achieved by combining multiple-quantum evolution in the 27Al dimension and double-resonance decoupling in the 31P acquisition domain.     

Experimental analysis of wireless data transmission systems in space platforms

This paper presents an experimental analysis of the use of wireless data-transmission systems in manned space platforms. Previous studies have analyzed the general advantages of substituting radio systems for some of the harnesses in the platforms. This paper presents a detailed experimental characterization of the radio channel in the environment of a space platform at frequency bands of 2.5 GHz and 17 GHz. For this purpose, a mockup, based on the Columbus Space Laboratory, was built. The probability distribution functions of the fading have been obtained for narrow-band as well as wideband parameters, such as the mean square delay and the coherence bandwidth of the channel. Moreover, a study of the operating mode of a commercial wireless system, based on the IEEE 802.11b standard, has been performed, by monitoring the bit-error rate. The error rates of the IEEE 802.11b system in the typical environment of a small or medium-sized office are compared with those of a space-platform environment. The results and conclusions can be extended to other environments that present geometrical and structural characteristics similar to those of a space platform, such as ships and submarines.     

Dynamic QoS Provisioning in DiffServ Domains Using Fuzzy Logic Controllers

Most work on Differentiated Services (DiffServ) handles Quality of Service (QoS) provisioning on a per node basis, which assumes that this strategy would provide QoS in the entire domain. Nevertheless, this approach could fail in large domains with multiple flow aggregation and unexpected input traffic. Therefore, provisioning techniques should be used to avoid unexpected overloads that result in QoS fluctuations. A proposal using fuzzy controllers to reconfigure DiffServ nodes according to both incoming traffic and the actual QoS is given. However, it is not easy to specify fuzzy rule bases and membership functions that optimize controller performance. Thus, we also propose a methodology to choose fuzzy controller parameters using the Wang–Mendel and genetic algorithms. Finally, we evaluate the performance of this model by simulation of an IP Telephony application in a DiffServ domain.     

The computation of the adjoint generator for a singular neutral equation

We compute the adjoint generator for the infinitesimal generator A of a C₀-semigroup. The operator A is associated with a particular scalar nonatomic neutral equation.