Environmental Electron Scanning Microscope
This is the term paper for the course AEP 6610, reviewing the techniques and development of environmental scanning electron microscope (ESEM). The ESEM provides the ability to image samples down to nanometer scale without the necessity of high vacuum in the chamber and sample processing procedures. Therefore, samples can be imaged in its original hydrated state, preserving its dynamics, interior structures and morphology. Secondary electrons are collected to reveal the topology of the sample while backscattered electrons are collected to distinguish the element composition. In this paper, the resolution and limitations for ESEM are presented. The applications of ESEM on both organic and inorganic materials are discussed. Finally, future prospects an comparison with competing imaging technologies conclude the paper.
Analytical Models of Interband Tunneling
Gallium Nitride, Band-to-band Tunneling, PN diode
AC and DC Conductivity of Charge Density Waves
In this final report for ECE 5390/ MSE 5472, the tunneling model for charge density waves (CDW) in the quasi-one-dimensional material will be used to derive both DC and AC conductivity. The DC conductivity in the absence of AC signals has a threshold voltage, above which the conductivity is non-zero. The AC conductivity follows the same behavior due to the photon-assisted tunneling of CDW but there is an additional resonance contribution. Finally, the conductivity for mixed DC/AC signals is shown with the photon-assisted conductivity at low field and resonant AC conductivity.
Conductance of Charge Density Waves Model
VLASS MSIP planning
and 14 collaborators
Non-cyanobacterial diazotrophs mediate dinitrogen fixation in biological soil crusts during early crust formation
and 3 collaborators
Biological soil crusts (BSC) are key components of ecosystem productivity in arid lands and they cover a substantial fraction of the terrestrial surface. In particular, BSC N2-fixation contributes significantly to the nitrogen (N) budget of arid land ecosystems. In mature crusts, N2-fixation is largely attributed to heterocystous cyanobacteria, however, early successional crusts possess few N2-fixing cyanobacteria and this suggests that microorganisms other than cyanobacteria mediate N2-fixation during the critical early stages of BSC development. DNA stable isotope probing (DNA-SIP) with 15N2 revealed that Clostridiaceae and Proteobacteria are the most common microorganisms that assimilate 15N2 in early successional crusts. The Clostridiaceae identified are divergent from previously characterized isolates, though N2-fixation has previously been observed in this family. The Proteobacteria identified share >98.5 %SSU rRNA gene sequence identity with isolates from genera known to possess diazotrophs (e.g. Pseudomonas, Klebsiella, Shigella, and Ideonella). The low abundance of these heterotrophic diazotrophs in BSC may explain why they have not been characterized previously. Diazotrophs play a critical role in BSC formation and characterization of these organisms represents a crucial step towards understanding how anthropogenic change will affect the formation and ecological function of BSC in arid ecosystems.
keywords: microbial ecology / stable isotope probing / nitrogen fixation / biological soil crusts
and 2 collaborators
identify data set
come up with quiz questions to identify suitable students
Reasoning About Knowledge: HW8
A New Actuator for On-Orbit Inspection
Small satellites can enable a new kind of mission architecture: inspecting larger satellites on orbit in close proximity without mechanical contact. Induction coupling is a new actuation technology that can augment on-orbit servicing by exploiting eddy-current forces and torques. Current technologies for applying forces and torques between two spacecraft share a glaring disadvantage: they require direct contact or propellant. By using the forces between a magnetic field and the electric currents it induces in a target, an induction coupler can control the relative position and orientation between a chaser spacecraft and a target without physical contact. A system utilizing these eddy-current effects places relatively few requirements on the target and chaser compared to other proposed electromagnetic actuation concepts. This paper presents a system overview of a contactless induction coupler, outlines those requirements through the analysis of an inspection mission on the International Space Station, and traces them to flight applications through ongoing experimental work.