Applications of Circular Array Sensors

Submitted to the Department of Electrical Engineering and Computer Science on January 18, 1980 in partial fulfillment of the requirements for the Degree Master of Science in Electrical Engineering and Computer ScienceThe application of the Reticon RO-64 annular photo-diode array to the task of optical tracking of special targets, direct optical focusing, and automatic printed circuit board inspection were studied. In order to facilitate this work, a digital camera unit incorporating the array was designed and constructed. Of the three applications investigated, the tracking task proved to be the most successful, since multiple targets were tracked in real time using the array. In the focusing application, the digital approach was found to be too slow for real-time use, and suggestions were made for the analog implementation of a focusing algorithm using the array. The printed circuit board inspection algorithm detected errors successfully, but the inefficiency of image acquisition with the array is a serious drawback, leading to the conclusion that linear arrays of similar design would provide faster and less expensive inspection. Thus the annular geometry is best suited to the onetime sampling of points on a circle in an image, as in the case of the tracking and focusing tasks. The focusing task suffers mainly from the amount of computation required to achieve focus, and from its competition with more established indirect focusing techniques.MIT Artificial Intelligence Laborator

Electrochemical Investigation of Azurin Thermodynamic and Adsorption Properties at Monolayer-Protected Cluster Film Assemblies – Evidence for a More Homogeneous Adsorption Interface

Thermodynamic and adsorption properties of protein monolayer electrochemistry (PME) are examined for Pseudomonas aeruginosa azurin (AZ) immobilized at an electrode modified with a networked film of monolayer-protected clusters (MPCs) to assess if nanoparticle films of this nature offer a more homogeneous adsorption interface compared to traditional self-assembled monolayer (SAM) modified electrodes. Specifically, electrochemistry is used to assess properties of surface coverage, formal potential, peak broadening, and electron transfer (ET) kinetics as a function of film thickness. The modification of a surface with dithiol-linked films of MPCs (Au225C675) provides a more uniform binding interface for AZ that results in voltammetry with less peak broadening (mV) compared to SAMs (\u3e120–130 mV). Improved homogeneity of the MPC interface for protein adsorption is confirmed by atomic force microscopy imaging that shows uniform coverage of the gold substrate topography and by electrochemical analysis of film properties during systematic desorption of AZ, which indicates a more homogeneous population of adsorbed protein at MPC films. These results suggest MPC film assemblies may be used in PME to provide greater molecular level control of the protein adsorption interface, a development with applications for strategies to study biological ET processes as well as the advancement of biosensor technologies

Encounters with the moral economy of water: convergent evolution in Valencia

[EN] This article presents the results of comparative fieldwork on the huerta of Valencia in Spain, a successful community-managed irrigation system of medium scale, one governed collectively by thousands of small farmers organized into 10 autonomous but highly interdependent irrigator groups. The study tested a model identified previously in research on successful systems of much smaller scale in Peru, a set of principles of operation that, when affirmed by farmers and obeyed as collective-choice rules, interact to create equity among water rights and transparency in water use in an unusual way. The authors show that a nearly identical set are at work in all 10 communities of Valencia, revealing the unique manner in which these work together to promote successful and sustainable cooperation, both within and between the user groups, and arguing that their presence in Spain and the Andes is indicative, not of diffusion from one continent to another, but of independent invention. These principles together laid the foundations for separate Andean and Islamic hydraulic traditions, which were often manifested locally in robust and equitable systems of the same general type, here called the moral economy of water. This kind of communal system appears to have emerged repeatedly, and often independently, in a great many other locales and settings throughout the world; its adaptive dynamics are shown to be of great relevance to small farmers today as they face the growing scarcity of water being induced by population growth and by climate change.Trawick, P.; Ortega Reig, MV.; Palau-Salvador, G. (2014). Encounters with the moral economy of water: convergent evolution in Valencia. Wiley Interdisciplinary Reviews: Water. 1(1):87-110. doi:10.1002/wat2.1008S871101

Distance Dependence of Electron Transfer Kinetics for Azurin Protein Adsorbed to Monolayer Protected Nanoparticle Film Assemblies

The distance dependence and kinetics of the heterogeneous electron transfer (ET) reaction for the redox protein azurin adsorbed to an electrode modified with a gold nanoparticle film are investigated using cyclic voltammetry. The nanoparticle films are comprised of nonaqueous nanoparticles, known as monolayer-protected clusters (MPCs), which are covalently networked with dithiol linkers. The MPC film assembly serves as an alternative adsorption platform to the traditional alkanethiolate self-assembled monolayer (SAM) modified electrodes that are commonly employed to study the ET kinetics of immobilized redox proteins, a strategy known as protein monolayer electrochemistry. Voltammetric analysis of the ET kinetics for azurin adsorbed to SAMs of increasing chain length results in quasi-reversible voltammetry with significant peak splitting. We observed rate constants (k°ET) of 12−20 s−1 for the protein at SAMs of shorter alkanethiolates that decays exponentially (β = 0.9/CH2 or 0.8/Å) at SAMs of longer alkanethiolates (9−11 methylene units) or an estimated distance of 1.23 nm and is representative of classical electronic tunneling behavior over increasing distance. Azurin adsorbed to the MPC film platforms of increasing thickness results in reversible voltammetry with very little voltammetric peaks splitting and nearly negligible decay of the ET rate over significant distances up to 20 nm. The apparent lack of distance dependence for heterogeneous ET reactions at MPC film assemblies is attributed to a two-step mechanism involving extremely fast electronic hopping through the MPC film architecture. These results suggest that MPC platforms may be used in protein monolayer electrochemistry to create adsorption platforms of higher architecture that can accommodate greater than monolayer protein coverage and increase the Faradaic signal, a finding with significant implications for amperometric biosensor design and development

Monte-Carlo calculation of longitudinal and transverse resistivities in a model Type-II superconductor

We study the effect of a transport current on the vortex-line lattice in isotropic type-II superconductors in the presence of strong thermal fluctuations by means of 'driven-diffusion' Monte Carlo simulations of a discretized London theory with finite magnetic penetration depth. We calculate the current-voltage (I-V) characteristics for various temperatures, for transverse as well as longitudinal currents I. From these characteristics, we estimate the linear resistivities R_xx=R_yy and R_zz and compare these with equilibrium results for the vortex-lattice structure factor and the helicity moduli. From this comparison a consistent picture arises, in which the melting of the flux-line lattice occurs in two stages for the system size considered. In the first stage of the melting, at a temperature T_m, the structure factor drops to zero and R_xx becomes finite. For a higher temperature T_z, the second stage takes place, in which the longitudinal superconducting coherence is lost, and R_zz becomes finite as well. We compare our results with related recent numerical work and experiments on cuprate superconductors.Comment: 4 pages, with eps figure

Differentiated legitimacy, differentiated resilience: beyond the natural in ‘natural disasters’

This paper starts with a flood in southern Malawi. Although apparently a ‘natural’ event, those most affected argued that it was made much worse by the rehabilitation of a nearby irrigation scheme. We use this example to interrogate the current interest in resilience from a perspective informed by political ecology and political economy, arguing that a focus on resilience should not be at the expense of understanding the conditions that shape vulnerability, including the ways in which ‘communities’ are differentiated. Complex factors are at play – and the ways in which these combine can result in a ‘perfect storm’ for some individuals and households. These factors include the effects of history combining with ethnicity, of legitimacy influencing voice, and of the interplay of political dynamics at different levels. In particular, processes of commodification have played an important role in shaping how some may benefit at the cost of catastrophic harm to others

An unusual cause of granulomatous disease

BACKGROUND: Chronic granulomatous disease (CGD) is an inherited disorder of phagocytic cells caused by an inability to generate active microbicidal oxygen species required kill certain types of fungi and bacteria. This leads to recurrent life-threatening bacterial and fungal infections with tissue granuloma formation. CASE PRESENTATION: We describe a case of X-linked Chronic granulomatous disease (CGD) diagnosed in an 18-year-old male. He initially presented with granulomatous disease mimicking sarcoidosis and was treated with corticosteroids. He subsequently developed Burkholderia cepacia complex pneumonia and further investigation confirmed a diagnosis of CGD. CONCLUSION: Milder phenotypes of CGD are now being recognised. CGD should be considered in patients of any age with granulomatous diseases, especially if there is a history of recurrent or atypical infection

Cleavage of pyrene-stabilized RNA bulge loops by trans-(±)-cyclohexane-1,2-diamine

Chemical agents that cleave HIV genome can be potentially used for anti-HIV therapy. In this report, the cleavage of the upper stem-loop region of HIV-1 TAR RNA was studied in a variety of buffers containing organic catalysts. trans-(±)-Cyclohexane-1,2-diamine was found to cleave the RNA with the highest activity (31%, 37°C, 18 h). Cleavage of the RNA in trans-(±)-cyclohexane-1,2-diamine buffer was also studied when the RNA was hybridized with complementary DNAs. A pyrene-modified C3 spacer was incorporated to the DNA strand to facilitate the formation of a RNA bulge loop in the RNA/DNA duplex. In contrast, unmodified DNAs cannot efficiently generate RNA bulge loops, regardless of the DNA sequences. The results showed that the pyrene-stablized RNA bulge loops were efficiently and site-specifically cleaved by trans-(±)-cyclohexane-1,2-diamine