Structural and Kinetic Characterization of Myoglobins from Eurythermal and Stenothermal Fish Species

Teleost myoglobin (Mb) proteins from four fish species inhabiting different temperature environments were used to investigate the relationship between protein function and thermal stability. Mb was isolated from yellowfin tuna (homeothermal warm), mackerel (eurythermal warm), and the Antarctic teleost Notothenia coriiceps (stenothermal cold). Zebrafish (stenothermal tropical) myoglobin was expressed from cloned cDNA. N. coriiceps Mb cDNA has also been cloned, expressed at 20°C , and isolated from E. coli, but was not used in any of the functional and kinetic studies. These proteins differed in oxygen affinity, as measured by O2 dissociation rates and P50 values, and thermal stability as measured by autooxidation rates. Mackerel Mb had the highest P50 value at 20°C (3.7mm Hg), corresponding to the lowest O2 affinity, followed by zebrafish ( 1.Omm Hg), yellowfin tuna (1.Omm Hg), and N. coriiceps (0.6mm Hg). Oxygen dissociation rates and Arrhenius plots were similar between all teleost species in this study, with the exception of mackerel myoglobin, which was two fold faster at all temperatures tested. Myoglobin from the Antarctic teleost had the highest autooxidation rate (0.44 h-1), followed by mackerel (0.26 h-1), zebrafish (0.22 h-1), and yellowfin tuna (0.088 h-1). Primary structural analysis revealed residue differences distributed throughout the polypeptide sequences, making it difficult to identify, which, if any, residues contribute to structural flexibility. However, analysis of molecular dynamics trajectories indicates that Mb from the eurythermal mackerel is the most flexible protein within the D loop and FG turn, which correlates with the O2 affinity and kinetic data

An imaging neutron/gamma-ray spectrometer

We present the test results of a neutron/gamma-ray imaging spectrometer for the identification and location of radioactive and special nuclear materials. Radioactive materials that could be fashioned into a radiation dispersal device typically emit gamma rays, while fissile materials such as uranium and plutonium emit both neutrons and gamma rays via spontaneous or induced fission. The simultaneous detection of neutrons and gamma rays is a clear indication of the presence of fissile material. The instrument works as a double-scatter telescope, requiring a neutron or gamma ray to undergo an interaction in two detectors to be considered a valid event. While this requirement reduces the detector efficiency, it yields information about the direction and energy of the incident particle, which is then used to reconstruct an image of the emitting source. Because of this imaging capability background events can be rejected, decreasing the number of events required for high confidence detection and thereby greatly improving its sensitivity. The instrument is optimized for the detection of neutrons with energies from 1-20 MeV and gamma rays from 0.4 to 10 MeV. Images and energy spectra for neutron and gamma rays are reported for several sources including depleted uranium and plutonium. In addition, the effect of neutron source shielding is investigated

NanoWalker: a fully autonomous highly integrated miniature robot for nanoscale measurements

The aim of this project is to develop the smallest and most sophisticated wireless fully autonomous instrumented robot capable of subatomic movements. The robot named 'NanoWalker' should bring a new paradigm in the way instruments are built while providing a sophisticated platform for a new range of applications. The project involves primarily the investigation of a new legged locomotion based on piezo-actuators with advanced micro-assembly techniques applied to complex embedded electronic systems; the development of new miniature instruments, micro-manipulators, integrated behavior for controlling, searching and scanning at the atomic scale; and the development of a subatomic navigation system. Besides all the new technologies and techniques that we intend to develop and which will be applicable to many areas and systems, the NanoWalker should provide a suitable yet more flexible and powerful platform compared to traditional macro-scaled instruments. It is anticipated that this new form of highly integrated autonomous microsystem will be used as the main building block for a new generation of measurement and inspection systems. In this paper, the main components of the NanoWalker are briefly described.Seaver Institut

Development and modeling of conducting polymer actuators and the fabrication of a conducting polymer based feedback loop

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references.Conducting polymers as a class of materials can be used to build a diverse range of devices. Conducting polymer based actuators (muscles), transistors (neurons), strain gages (muscle spindles), force sensors (Golgi tendon organs), light emitting diodes, photodetectors (eyes), batteries and supercapacitors (energy storage), and chemical sensors (noses) can all be manufactured. The range of behaviors makes conducting polymers the only class of materials that might be able to mimic the full range of functions needed to build a truly lifelike artificial system. In this thesis, a conducting polymer actuator and conducting polymer strain gage are used for the first time to build a reflex or position feedback loop that rejects position disturbances. The successful operation of the conducting polymer based reflex loop is an important step towards building an all polymer reflex loop that is directly integrated into a bulk material. Such a reflex loop could be used to control position, to control force or to dynamically change the material stiffness and viscosity. In the course of the project, an improved understanding of conducting polymer actuators has led to mathematical descriptions of the charging and discharging of long linear actuators and to equations describing the deflection and force of three layer bending beam actuators. These equations can be used as design tools to build actuators that satisfy given performance requirements. Finally, the performance of the actuators has been related to specific material properties to help direct research into new conducting polymeric materials.by Peter Geoffrey Alexander Madden.Ph.D

An imaging neutron/gamma-ray spectrometer

We present the design and development of a dual-species, neutron/γ-ray imaging spectrometer for the identification and location of radioactive and special nuclear materials (SNM). Real-time detection and identification is important for locating fissile materials. These materials, specifically uranium and plutonium, emit neutrons and γ rays via spontaneous or induced fission. Co-located neutron and γ-ray emissions are a sure sign of fissile material, requiring very few spatially correlated events for a significant detection. Our instrument design detects neutrons and γ rays from all sources in its field of view, constructs images of the emission pattern, and reports the spectra for both species. The detection principle is based upon multiple elastic neutron-proton scatters in organic scintillator for neutrons, and Compton scattering in organic scintillator followed by photoelectric absorption in inorganic scintillator for γ rays. The instrument is optimized for neutron imaging and spectroscopy in the 1-20 MeV range. We recorded images and spectra of a Cf-252 source from 0.5 - 10 MeV, and have done similarly for several γ-ray sources. We report the results of laboratory testing of this expanded instrument and compare them to detailed Monte Carlo simulations using Geant4