Interactions in mixed monolayers between dioleoyl- l-phosphatidylcholine and all- trans retinal

The surface pressure isotherms of all- trans retinal and dioleoyl- l-phosphatidylcholine at the nitrogen-water interface were studied at 20.5°C. The extrapolated limiting areas per molecule are 49 and 83 Å 2 molecule −1, respectively. The properties of seven mixtures of all- trans retinal and dioleoyl- l-phosphatidylcholine, covering the whole range of molar fractions were also measured. The results show that an almost constant collapse pressure is observed at 44 ± 1 mN m −1 for all the mixtures studied. Furthermore, an apparent collapse pressure is also observed at 16, 18, 22, 26, 32, and 35 mN m −1 at a molar fraction of dioleoyl- l-phosphatidylcholine of 0.100, 0.200, 0.400, 0.500, 0.600, and 0.800, respectively. An analysis of the results in terms of the surface phase rule shows that below the apparent collapse pressure, the components are completely miscible. Negative deviations from ideality were observed in the region of miscibility for all the systems, as shown by the negative deviations to the additivity rule and the negative excess free energies of mixing calculated for all the systems at 5, 7, 10, and 13 mN m −1. Furthermore, it is shown that above the apparent collapse pressure, all-trans retinal is rejected from the monolayer, the rejection being total at the collapse pressure

Control strategy for a monolithically integrated widely tunable laser system on InP for Optical Coherence Tomography

An InP integrated widely tunable laser is investigated for the use as a swept source in optical coherence tomography (OCT) applications. The laser is realized on a generic integration technology platform. It consists of a gain medium and a bandpass filter with 3 cascaded asymmetric Mach-Zehnder interferometers. The additional presence of a balanced Mach-Zehnder modulator as variable out-coupler is instrumental to increase the laser tuning range to 90 nm between 1480 and 1570 nm but can add to additional filtering effects in the laser cavity. In this work, we propose an optimized control strategy for the wavelength calibration of this widely tunable laser source, for a stepwise wavelength scan that is suitable for OCT. The aim is to obtain a wavelength scan with at least 1000 of 10 GHz equally spaced optical frequencies, having uniform power around 100 µW and 1 GHz accuracy. The control strategy is based on the a-priori knowledge of the coarse and the medium filter tuning and on an optimization of the fine filter tuning and the longitudinal cavity mode tuning that can be frequently updated. In this way, the calibration of the laser system can be kept sufficiently accurate and stability of the scan quality can be ensured. With this strategy, 10 GHz spaced optical lasing frequencies are obtained over 30 nm making the calibrated laser suitable as an OCT source

Geosocial Query with User-Controlled Privacy

Geosocial applications collect (and record) users’ precise location data to perform proximity computations, such as notifying a user or triggering a service when a friend is within geographic proximity. With the growing popularity of mobile devices that have sophisticated localization capability, it becomes more convenient and tempting to share location data. But the precise location data in plaintext not only exposes user’s whereabouts but also mobility pa erns that are sensitive and cannot be changed easily. This paper proposes cryptographic protocols on top of spatial cloaking to reduce the resolution of location and balance between data utility and privacy. Specifically, we interest in the setting that allows users to send periodic updates of precise coordinates and define privacy preferences to control the granularity of the location, both in an encrypted format. Our system supports three kinds of user queries — “Where is this user?”, “Who is nearby?”, and “How close is this user from another user?”. Also, we develop a new algorithm to improve the multidimensional data access by reducing significant masking error. Our prototype and various performance evaluations on different platforms demonstrated that our system is practical