In this paper we propose a domainindependent text segmentation method, which consists of three components. Latent Dirichlet allocation (LDA) is employed to compute words semantic distribution, and we measure semantic similarity by the Fisher kernel. Finally global best segmentation is achieved by dynamic programming. Experiments on Chinese data sets with the technique show it can be effective. Introducing latent semantic information, our algorithm is robust on irregular-sized segments.
Potassium (K ϩ ) 2 channels of the SLO family are the largest and most complex K ϩ channels (1, 2). These high conductance K ϩ channels are activated by voltage and modulated by intracellular ions as well as a host of different intracellular factors (3). Structurally they resemble voltage-gated K ϩ channels but have additional conserved intracellular domains appended on the C terminus that allow them to be gated by different intracellular ions (reviewed in Refs. 1, 2). Two members of this family are SLO1, which is activated by intracellular Ca 2ϩ (4) and SLO2.2 (also known as Slack), which is activated by intracellular Na ϩ (5). As with Ca 2ϩ -activated K ϩ channels, Na ϩ -activated K ϩ channels are widely expressed in the mammalian brain and other tissues, and are found in many species from Caenorhabditis elegans to humans (6, 7). Using immunohistochemistry (8) and inside-out patch recordings (9) it was shown that Na ϩ -activated K ϩ channels are present in the soma and dendrites of many different classes of neurons. Although it has been suggested that Na ϩ -activated K ϩ channels may serve a role in protecting cells from hypoxia (5, 7, 10), we (11, 12) and others (13,14) have shown that Na ϩ -activated K ϩ channels provide a major outward current component in MSN striatal neurons, tufted/mitral cells of the olfactory bulb, and a significant component in cortical pyramidal cells, and serve an important role in several aspects of normal physiology (7, 15).The activating effect of divalent ions on the Maxi-K BK channel SLO1 is well documented, and serves as a negative feedback system for calcium entry in many cell types (16 -18). On the other hand, although it is known that Na ϩ activates SLO2.2 channels the effect of divalent cations on these channels is largely unstudied. In exploring this question we were surprised to observe that all divalent ions that were reported to activate SLO1 channels have the opposite effect on SLO2.2 channels: they inhibit SLO2.2 channels. As will be shown, this inhibition by divalent cations has none of the hallmarks of a pore-blocking effect, but appears to inhibit channel activity via an allosteric site. Interestingly, we show that Ba 2ϩ is the single exception. We found that Ba 2ϩ has two distinct inhibitory effects on SLO2.2 channels; it blocks in a manner similar to other divalent ions, but has an additional pore-blocking effect that increases at higher voltages. These results contrast with the effects of Ba 2ϩ on SLO1 channels which has been reported to both activate and inhibit SLO1 channels, with the latter showing an obvious voltage-dependent pore-blocking effect (18). To investigate possible structural features in SLO2.2 channels involved with divalent cation inhibition we examined a comparative alignment of SLO2.2 with cyclic nucleotide-activated channels also known to be inhibited by divalent ions (19). The divalent cation inhibition of cyclic nucleotide gated channels involves a histidine residue located at a position immediately following the cytoplasmic end of the six...
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