Although mind wandering occupies a large proportion of our waking life, its neural basis and relation to ongoing behavior remain controversial. We report an fMRI study that used experience sampling to provide an online measure of mind wandering during a concurrent task. Analyses focused on the interval of time immediately preceding experience sampling probes demonstrate activation of default network regions during mind wandering, a finding consistent with theoretical accounts of default network functions. Activation in medial prefrontal default network regions was observed both in association with subjective self-reports of mind wandering and an independent behavioral measure (performance errors on the concurrent task). In addition to default network activation, mind wandering was associated with executive network recruitment, a finding predicted by behavioral theories of off-task thought and its relation to executive resources. Finally, neural recruitment in both default and executive network regions was strongest when subjects were unaware of their own mind wandering, suggesting that mind wandering is most pronounced when it lacks meta-awareness. The observed parallel recruitment of executive and default network regions-two brain systems that so far have been assumed to work in oppositionsuggests that mind wandering may evoke a unique mental state that may allow otherwise opposing networks to work in cooperation. The ability of this study to reveal a number of crucial aspects of the neural recruitment associated with mind wandering underscores the value of combining subjective self-reports with online measures of brain function for advancing our understanding of the neurophenomenology of subjective experience.

A significant number of tropical cyclones move into the midlatitudes and transform into extratropical cyclones. This process is generally referred to as extratropical transition (ET). During ET a cyclone frequently produces intense rainfall and strong winds and has increased forward motion, so that such systems pose a serious threat to land and maritime activities. Changes in the structure of a system as it evolves from a tropical to an extratropical cyclone during ET necessitate changes in forecast strategies. In this paper a brief climatology of ET is given and the challenges associated with forecasting extratropical transition are described in terms of the forecast variables (track, intensity, surface winds, precipitation) and their impacts (flooding, bush fires, ocean response). The problems associated with the numerical prediction of ET are discussed. A comprehensive review of the current understanding of the processes involved in ET is presented. Classifications of extratropical transition are described and potential vorticity thinking is presented as an aid to understanding ET. Further sections discuss the interaction between a tropical cyclone and the midlatitude environment, the role of latent heat release, convection and the underlying surface in ET, the structural changes due to frontogenesis, the mechanisms responsible for precipitation, and the energy budget during ET. Finally, a summary of the future directions for research into ET is given.

In the cyanobacterium Synechococcus elongatus (PCC 7942) the kai genes A, B, and C and the sasA gene encode the functional protein core of the timing mechanism essential for circadian clock regulation of global gene expression. The Kai proteins comprise the central timing mechanism, and the sensor kinase SasA is a primary transducer of temporal information. We demonstrate that the circadian clock also regulates a chromosome compaction rhythm. This chromosome compaction rhythm is both circadian clockcontrolled and kai-dependent. Although sasA is required for global gene expression rhythmicity, it is not required for these chromosome compaction rhythms. We also demonstrate direct control by the Kai proteins on the rate at which the SasA protein autophosphorylates. Thus, to generate and maintain circadian rhythms in gene expression, the Kai proteins keep relative time, communicate temporal information to SasA, and may control access to promoter elements by imparting rhythmic chromosome compaction.cyanobacteria ͉ regulation C ircadian clocks have evolved within the cyanobacteria (an extremely diverse group of oxygenic photosynthesizing bacteria) and many, if not all, eukaryotes. These clocks effectively tune gene expression patterns, and thus metabolic activity and behavior, to distinct daily frequencies (1-3). In each of several well studied model systems, circadian gene expression patterns are generated and maintained by the combined functions of fairly small sets of proteins (1-3). Amazingly, in vitro combination of only three proteins, KaiA, KaiB, and KaiC, from the cyanobacterium Synechococcus elongatus results in a functional circadian timing mechanism (4). This phenomenon underscores recent data demonstrating that a transcription and translation feedback loop, once considered essential for circadian timing, is not required for rhythmic activity in this cyanobacterium (5). Interestingly, demonstration of this simple proteinaceous clock, and presumption of its straightforward transfer to newly formed daughter cells, explains the enigma of how a circadian (24-h) timing mechanism can function in cyanobacteria that have generation times of 8 h or less.Despite those compelling data, questions concerning how this timing mechanism connects circadian clock function to global regulation of gene expression still loom (6). Existent data show functional interactions among the three Kai proteins and the SasA sensor kinase protein as essential for this global regulation (7). For example, the KaiC protein forms a homohexamer upon binding ATP and is an autokinase. It also interacts with double-stranded DNA molecules (8, 9). Overproduction of KaiC represses gene expression on a global scale (8, 9). In an sasA-null strain, except for kai gene expression patterns, all other tested genes are arrhythmically expressed (7). SasA protein thus appears to act as temporal output regulator from the clock. In addition, clock-regulated gene expression rhythms consist of at least two temporal classes (10-12). The major class includes kaiB g...

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