Inferring models of bacterial dynamics toward point sources

Experiments have shown that bacteria can be sensitive to small variations in chemoattractant (CA) concentrations. Motivated by these findings, our focus here is on a regime rarely studied in experiments: bacteria tracking point CA sources (such as food patches or even prey). In tracking point sources, the CA detected by bacteria may show very large spatiotemporal fluctuations which vary with distance from the source. We present a general statistical model to describe how bacteria locate point sources of food on the basis of stochastic event detection, rather than CA gradient information. We show how all model parameters can be directly inferred from single cell tracking data even in the limit of high detection noise. Once parameterized, our model recapitulates bacterial behavior around point sources such as the "volcano effect". In addition, while the search by bacteria for point sources such as prey may appear random, our model identifies key statistical signatures of a targeted search for a point source given any arbitrary source configuration

Lesbian brides: post-queer popular culture

The last decade has witnessed a proliferation of lesbian representations in European and North American popular culture, particularly within television drama and broader celebrity culture. The abundance of “positive” and “ordinary” representations of lesbians is widely celebrated as signifying progress in queer struggles for social equality. Yet, as this article details, the terms of the visibility extended to lesbians within popular culture often a rm ideals of hetero-patriarchal, white femininity. Focusing on the visual and narrative registers within which lesbian romances are mediated within television drama, this article examines the emergence of what we describe as “the lesbian normal.” Tracking the ways in which the lesbian normal is anchored in a longer history of “the normal gay,” it argues that the lesbian normal is indicative of the emergence of a broader post-feminist and post-queer popular culture, in which feminist and queer struggles are imagined as completed and belonging to the past. Post-queer popular culture is depoliticising in its e ects, diminishing the critical potential of feminist and queer politics, and silencing the actually existing conditions of inequality, prejudice, and stigma that continue to shape lesbian lives

Development and validation of a new glaucoma screening test using temporally modulated flicker

Purpose Describing the psychometric characteristics and diagnostic accuracy of the Accelerator 4‐Alternative Forced‐Choice Flicker Test prototype (A4FTp) for detecting chronic open angle glaucoma (COAG). Methods A4FTp measures temporally‐modulated flicker thresholds in regions of the visual field with high susceptibility to glaucomatous loss. We initially evaluated its psychometric properties on 20 normals (aged 33.8 ± 8.5 years) who were tested multiple times over a period of 3 months. All subjects underwent four repetitions for shorter (T8) and longer (T12) staircase termination criteria, to determine the most suitable threshold criterion. Four randomly selected subjects underwent a total of 10 repetitions to study test‐retest repeatability and learning effects. To determine its diagnostic accuracy, one eye of 40 participants with COAG and 38 normal controls were tested with the A4FTp in comparison with the Frequency Doubling Technology (FDT; C20‐5 programme) and iVue Spectral Domain Optical Coherence Tomography (SD‐OCT). Tests were conducted in a random order with results masked to the clinician conducting the reference ophthalmic examination. The accuracy of each test was determined by analysis of the area under the receiver operator characteristic curve (AUROC). Results A4FTp flicker thresholds were stable, with standard deviations of only 0.52 decilog (dL) for T8, increasing to 1.32 dL for T12, and no significant flicker sensitivity threshold improvement over the 10 repeat runs. T8 was superior to T12 on several other measures, so it was used for the remaining comparisons. In terms of diagnostic accuracy, the mean AUROC for the three tests were A4FTp [T8 criterion; 0.82, 95% confidence interval (0.73–0.92)]; SD‐OCT [any RNFL parameter p < 1% level; 0.90 (0.83–0.97)]; and FDT [one or more locations missed at p < 5% level; 0.91 (0.82–0.96)]. There was no statistical difference in AUROC between A4FTp and SD‐OCT (p = 0.18) or FDT (p = 0.12). The A4FTp test duration averaged just over 2 min per eye, taking approximately one‐third of the time for completion of the HFA SITA 24‐2 algorithm (conducted as part of the reference examination) and twice the time for the suprathreshold FDT. Conclusion Test accuracy for the A4FTp was comparable to those of the FDT and SD‐OCT for the detection of COAG. Time taken to complete the A4FTp was relatively short and initial results are promising. With further refinement, the A4FTp could have a future role in glaucoma detection

The New Zealand Strong Motion Earthquake Recorder Network

The network of strong-motion earthquake recorders, maintained throughout New Zealand by the Engineering Seismology Section of the Department of Scientific and Industrial Research, is described. The instruments are either deployed as ground instruments to measure potential earthquake attack on structures, or in structures, e.g. buildings, dams and industrial installations, to record structural response. Details are given of installation of instruments , maintenance, laboratory work, record retrieval and digitisation, costs and staffing for the network. Future developments mooted include an improved digitising system, the introduction of an improved version of the existing mechanical-optical instrument in 1979, and, in the long term, the introduction of an entirely new digital recorder, having an electrical output from its accelerometers, which will make possible the transmission of data by telephone or radio link

The Uncoiling of Supercoiled Plasmid DNA Over Time Observed by Atomic Force Microscopy

Long term stability of DNA structures in a cell is critical to sustaining life. The DNA structures could be degraded biologically (e.g. enzymes), chemically (e.g. drugs), and physically (e.g. thermal agitation process) with time. The DNA structures are maintained by being regenerated and/or being recovered by proteins within a cell. However, even though it is important, it is difficult to observe the time-evolution of DNA structures for extended periods at a molecular resolution. Here, we observed the time evolution of DNA structures for two months, in order to understand the long term stability of DNA structures. For this study, we used purified plasmid DNA molecules extracted from Escherichia coli (E-coli) as a sample. We also employed atomic force microscopy (AFM) to observe the plasmid DNA structures at a molecular resolution. The purified plasmid DNA molecules were diluted with pure water, deposited on a mica surface, and observed by an AFM on a regular basis in an ambient environment for two months. The sequential AFM images show the plasmid DNA formed globular structures at the beginning and transformed into uncoiled plasmid DNA network structures after two months. The globular structures appeared to be the supercoiled state of plasmid DNA, a well-known strategy to store genetic information in a confined space for bacterial systems. The observed DNA network structures are believed to be results of long periods of unwinding and rejoining processes of the supercoiled plasmid DNA. The unwinding and rejoining processes would have been caused by small residual proteins (or enzymes) possibly present in the plasmid DNA solution. This study reveals DNA stability is dramatically influenced by prolonged (~ a few months) exposure to small amounts of residual proteins (or enzymes). The result also suggests the AFM is a powerful tool in observing the biological process at the molecular level over extended periods of time

Long-term Structural Change in Plasmid DNA

Long-term stability of plasmid DNA (pDNA) conformations is critical in many research areas, especially those concerning future gene therapy. Despite its importance, the timeevolution of pDNA structures has rarely been studied at a molecular resolution. Here, the time-evolution of pDNA solutions spanning four years was observed with atomic force microscopy (AFM). The AFM data show that the pDNA molecules evolved from isolated supercoiled structures; to aggregated supercoiled structures; to thin, branched network structures; and finally to wider, branched network structures. Additional topographical analysis of the AFM data suggests the actions of residual proteins could be the main mechanism for the structural changes in our laboratory prepared pDNA