Renewable energy in competitive electricity markets

A restructured electricity system may undervalue renewable energy. We remain wary of unregulated markets, but urge the renewable energy community to begin considering how they could adapt to increasing customer choice.     

Temperature and modulation characteristics of resonant-cavitylight-emitting diodes

Resonant-cavity light-emitting diodes (RCLED) are novel, high-efficiency light-emitting diodes which employ optical microcavities. These diodes have higher intensities and higher spectral purity as compared to conventional LEDs. Analytical formulas are derived for the enhancement of the spontaneous emission along the optical axis of the cavity. The design rules for high-efficiency operation of RCLEDs are established. The temperature dependence of the emission intensity is analyzed in the range 20-80° and it is described by an exponential dependence with a characteristic temperature of 112 K. The modulation characteristics of RCLEDs exhibit 3 dB frequencies of 580 MHz. Eye diagrams at transmission rates of 622 Mb/s are wide open indicating the suitability of RCLEDs for high-speed data transmission     

Polarisation insensitive semiconductor optical amplifier withintegrated electroabsorption modulators

The authors demonstrate a 1.55 μm wavelength multiquantum well semiconductor optical amplifier, integrated with bulk layer electroabsorption modulators and passive waveguide beam expanders at the input and output ports. The device has a fibre to fibre gain of 9 dB, an extinction ratio of 15 dB per modulator, a spectral range >35 nm, and polarisation sensitivity <1 dB     

A 16-Kbit Θ-search associative memory

The design of a high-capacity Θ-search associative memory (Θ∈{<,>,⩽,⩾,=≠}) is presented. PSPICE simulation and layouts show that the proposed Θ-search associative memory chip consisting of 256 words, each 64-b long, can fit on a 13.5-mm×9.5-mm chip. It can perform maskable Θ-search operations over its contents in 110 ns     

Rat and human pancreatic islet cells contain a calcium ion independent phospholipase A2 activity selective for hydrolysis of arachidonate which is stimulated by adenosine triphosphate and is specifically localized to islet beta-cells

The recent demonstration that myocardial Ca(2+)-independent phospholipase A2 exists as a complex of catalytic and regulatory polypeptides that is modulated by ATP has suggested a novel mechanisms through which alterations in glycolytic flux can be coupled to the generation of eicosanoids which facilitate insulin secretion. To determine the potential relevance of this mechanism, we examined the kinetic characteristics, substrate specificities, and cellular locus of phospholipase A2 activity in pancreatic islets. Rat pancreatic islets contain a Ca(2+)-independent phospholipase A2 activity which is optimal at physiologic pH, preferentially hydrolyzes phospholipid substrates containing a vinyl ether linkage at the sn-1 position, and prefers arachidonic acid compared to oleic acid in the sn-2 position. Rat islet Ca(2+)-independent phospholipase A2 activity is inhibited by the mechanism-based inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one and is stimulated by ATP. Purification of beta-cells from dispersed pancreatic islet cells by fluorescence-activated cell sorting demonstrated that beta-cells (but not non-beta-cells) contain Ca(2+)-independent, ATP-stimulated phospholipase A2 activity. Remarkably, clonal RIN-m5f insulinoma cells, which possess a defect in glucose-induced insulin secretion, contain a Ca(2+)-independent phospholipase A2 which is not modulated by alterations in ATP concentration. Collectively, these results and those of an accompanying paper [Ramanadham et al. (1993) Biochemistry (following paper in this issue)] implicate Ca(2+)-independent phospholipase A2 as a putative glucose sensor which can couple alterations in glycolytic metabolism to the generation of biologically active eicosanoids and thereby facilitate glucose-induced insulin secretion.     

Adaptive detection of DS/CDMA signals in fading channels

This paper examines the behavior of the minimum mean-squared error (MMSE) receiver in frequency-nonselective-fading channels. It is noted that the MMSE receiver will often lose phase lock on the desired signal when the desired signal dips into a deep fade. A modification to the MMSE receiver is presented which is demonstrated to function quite nicely in flat-fading channels. Analytical results for the modified MMSE receiver are presented and found to agree very well with simulation results. These analytical results are then compared to the theoretical performance of the conventional (i.e., correlator) receiver in terms of both bit-error rate (BER) and capacity. As expected, the modified MMSE receiver was found to offer a substantial improvement in both BER and capacity. Finally, a simple empirically derived formula is given which will give a good approximation to the BER of the modified MMSE receiver in a Rayleigh-fading environment. This formula can also be used to determine the number of users a given system can support. It is noted that as E_b/N₀ grows, it is quite feasible to approach 100% channel utilization with the MMSE receiver, whereas a conventional receiver is typically limited to a utilization of 10%-20%     

Routine microbiological testing in sudden and unexpected infant death

We reviewed 187 depth recorded seizures in 33 patients with non-lesional temporal lobe complex partial seizures. All patients had a minimum of 1 year follow-up following temporal lobectomy. We classified seizure onset pattern as rhythmic activity, attenuation, or repetitive spikes or spike wave complexes. The most common pattern of seizure onset was rhythmic activity and the next most common pattern was repetitive spikes. Seventy-five seizures (49%) had only one seizure onset pattern, and 79 seizures (51%) had a combination of seizure onset patterns. The degree of hippocampal gliosis strongly predicted the type of seizure onset pattern (Chi square = 24.07, 2 d.f., P < 0.01). The rhythmic activity pattern was associated with mild gliosis, and the repetitive spike pattern was associated with severe gliosis. We classified seizure onset as focal or regional based on the number of electrode contacts that were involved by the ictal EEG. A focal seizure onset was associated with an excellent outcome following temporal lobectomy.     

Deletions in one domain of the Friend virus-encoded membrane glycoprotein overcome host range restrictions for erythroleukemia

Although the Friend virus-encoded membrane glycoprotein (gp55) activates erythropoietin receptors (EpoR) to cause erythroblastosis only in certain inbred strains of mice but not in other species, mutant viruses can overcome aspects of mouse resistance. Thus, mice homozygous for the resistance allele of the Fv-2 gene are unaffected by gp55 but are susceptible to mutant glycoproteins that have partial deletions in their ecotropic domains. These and other results have suggested that proteins coded for by polymorphic Fv-2 alleles might directly or indirectly interact with EpoR and that changes in gp55 can overcome this defense. A new viral mutant with an exceptionally large deletion in its ecotropic domain is now also shown to overcome Fv-2rr resistance. In all cases, the glycoproteins that activate EpoR are processed to cell surfaces as disulfide-bonded dimers. To initiate analysis of nonmurine resistances, we expressed human EpoR and mouse EpoR in the interleukin 3-dependent mouse cell line BaF3 and compared the abilities of Friend virus-encoded glycoproteins to convert these cells to growth factor independence. Human EpoR was activated in these cells by erythropoietin but was resistant to gp55. However, human EpoR was efficiently activated in these cells by the same viral mutants that overcome Fv-2rr resistance in mice. By construction and analysis of human-mouse EpoR chimeras, we obtained evidence that the cytosolic domain of human EpoR contributes to its resistance to gp55 and that this resistance is mediated by accessory cellular factors. Aspects of host resistance in both murine and nonmurine species are targeted specifically against the ecotropic domain of gp55.