Online Collaborative Time Management System using Artificial Intelligence

Online Collaborative Time Management System is a system that will plan events and help achieve goals intelligently using Partial Order Planning. This product is similar to a social networking site, which plans events for collaborative set of people. For this masters’ project, such a system is developed. Our site allows multiple people to add items to a collaborative To-Do list. The user interface for our site allows people to add actions and preconditions to the existing system, enabling the system to grow constantly. In order to generate a sequence of actions to the most complex problems, partial order generators are implemented at the back end. The planning algorithms are designed such that they will resolve conflicts by implementing backtracking whenever it comes across a conflict

Single local interneurons in the locust make central synapses with different properties of transmitter release on distinct postsynaptic neurons

Quantal analysis has been applied to the inhibitory synapses made by single spiking local interneurons onto several nonspiking local interneurons (and motorneurons) in the locust CNS. Transmission at these synapses appears to be mediated by GABA. The apparent reversal potential of the IPSP and inhibitory postsynaptic current were -80 to - 85 mV, a value similar to that of the potential evoked by pressure- applied GABA. This reversal potential was 25–30 mV more negative than the resting potential of the nonspiking interneurons in the experimental conditions. The statistical properties of release at these synapses were studied by recording simultaneously from pre- and postsynaptic interneurons with intracellular electrodes. The distribution of postsynaptic potential amplitudes could be described by a simple binomial model, implying uniformity of binomial p (probability of release at a single release site) for each synapse. The mean quantal amplitude was 290 ± 110 µV, and the mean quantal content m of the IPSPs was 6.25 ± 2.83. The mean values of binomial n (average size of the releasable pool) and p were 13.11 ± 2.8 and 0.45 ± 0.16, respectively. Numerical simulations of statistical experiments were performed to test whether the IPSP amplitude distribution histograms might be misleadingly indicative of quantal release. These simulations showed that such a hypothesis was very unlikely. When a spiking local interneuron was impaled, several of its target interneurons could sometimes be successively sampled. Quantal analysis was then performed with the different IPSPs evoked, in identical conditions, by a same presynaptic interneuron, and the quantal parameters were compared between the synapses. It was found that binomials n and p and their product m generally differed between the synapses made by a given spiking interneuron onto different target neurons. These results show that quantal contents can vary for the many synapses made centrally by one interneuron, and suggest that this variability may arise from differences in release probabilities between the sites associated with different synapses

Lyot Coronagraphy on Giant Segmented-Mirror Telescopes

We present a study of Lyot style (i.e., classical, band-limited, and Gaussian occulter) coronagraphy on extremely large, highly-segmented telescopes. We show that while increased telescope diameter is always an advantage for high dynamic range science (assuming wavefront errors have been corrected sufficiently well), segmentation itself sets a limit on the performance of Lyot coronagraphs. Diffraction from inter-segment gaps sets a floor to the achievable extinction of on-axis starlight with Lyot coronagraphy. We derive an analytical expression for the manner in which coronagraphic suppression of an on-axis source decreases with increasing gap size when the segments are placed in a spatially periodic array over the telescope aperture, regardless of the details of the arrangement. A simple Lyot stop masking out pupil edges produces good extinction of the central peak in the point-spread function (PSF), but leaves satellite images caused by inter-segment gaps essentially unaffected. Masking out the bright segment gaps in the Lyot plane with a reticulated mask reduces the satellite images'intensity to a contrast of 5x10^{-9} on a 30 m telescope with 10 mm gaps, at the expense of an increase in the brightness of the central peak. The morphology of interesting targets will dictate which Lyot stop geometry is preferable: the reticulated Lyot stop produces a conveniently uni-modal PSF, whereas a simple Lyot stop produces an extended array of satellite spots. A cryogenic reticulate Lyot stop will also benefit both direct and coronagraphic mid-IR imaging.Comment: 4 pages, 2 figure

Tip-tilt Error in Lyot Coronagraphs

The direct detection of extrasolar planets by imaging means is limited by the large flux of light from the host star being scattered into the region of interest by a variety of processes, including diffraction. Coronagraphs are devices that suppress the undesirable scattering of light caused by diffraction. In a coronagraph the sensitivity limit for high dynamic range is limited by the propagation of errors introduced by the imperfect optical system to the final image. In this paper we develop theory and simulations to understand how such errors propagate in a coronagraph. We describe the response of classical and band-limited Lyot coronagraphs to small and large errors in the placement of the central star, and identify ways of making such coronagraphs more robust to small guiding errors. We also uncover features of the decentered PSF that can lead to spurious detection of companions, especially with aggressive, high dynamic range coronagraphs dedicated to companion searches aimed at finding extrasolar terrestrial or Jovian planets.Comment: 16 pages, 8 figure

Astrometry and Photometry with Coronagraphs

We propose a solution to the problem of astrometric and photometric calibration of coronagraphic images with a simple optical device which, in theory, is easy to use. Our design uses the Fraunhofer approximation of Fourier optics. Placing a periodic grid of wires (we use a square grid) with known width and spacing in a pupil plane in front of the occulting coronagraphic focal plane mask produces fiducial images of the obscured star at known locations relative to the star. We also derive the intensity of these fiducial images in the coronagraphic image. These calibrator images can be used for precise relative astrometry, to establish companionship of other objects in the field of view through measurement of common proper motion or common parallax, to determine orbits, and to observe disk structure around the star quantitatively. The calibrator spots also have known brightness, selectable by the coronagraph designer, permitting accurate relative photometry in the coronagraphic image. This technique, which enables precision exoplanetary science, is relevant to future coronagraphic instruments, and is particularly useful for `extreme' adaptive optics and space-based coronagraphy.Comment: To appear in ApJ August 2006, 27 preprint style pages 4 figure

Fast computation of Lyot-style coronagraph propagation

We present a new method for numerical propagation through Lyot-style coronagraphs using finite occulting masks. Standard methods for coronagraphic simulations involve Fast Fourier Transforms (FFT) of very large arrays, and computing power is an issue for the design and tolerancing of coronagraphs on segmented Extremely Large Telescopes (ELT) in order to handle both the speed and memory requirements. Our method combines a semi-analytical approach with non-FFT based Fourier transform algorithms. It enables both fast and memory-efficient computations without introducing any additional approximations. Typical speed improvements based on computation costs are of about ten to fifty for propagations from pupil to Lyot plane, with thirty to sixty times less memory needed. Our method makes it possible to perform numerical coronagraphic studies even in the case of ELTs using a contemporary commercial laptop computer, or any standard commercial workstation computer.Comment: 17 pages, 9 figures, accepted for publication in Optics Expres