Simulation of electron transport in quantum well devices

Double barrier resonant tunneling diodes (DBRTD) have received much attention as possible terahertz devices. Despite impressive experimental results, the specifics of the device physics (i.e., how the electrons propagate through the structure) are only qualitatively understood. Therefore, better transport models are warranted if this technology is to mature. In this paper, the Lattice Wigner function is used to explain the important transport issues associated with DBRTD device behavior

Far-infrared imaging of tokamak plasma

A 20-channel interferometer has been developed which utilizes a linear, one-dimensional microbolometer array to obtain single-shot density profiles from the UCLA Microtor tokamak plasma. The interferometer has been used to study time-dependent phenomena in the plasma density profile. Observations of the sawtooth instability clearly show the growth of the m=0 mode from a localized oscillation (r=1 cm) on axis to an oscillation of the entire plasma. Also, measurements during the initial startup phase of the discharge show evidence of hollow density profiles. In addition, a simultaneous measurement of the poloidal magnetic field has been developed which provides 20 channels of polarimetry. Interferometry and polarimetry both use the same imaging system and the spatial resolution of both measurements has been tested using plastic and crystal-quartz test objects. The signal-to-noise ratio for the polarimeter has also proved adequate for the expected Faraday rotation angle (alphamax=7°, Ip=70 kA, n=5×10^13 cm^−3)

Interferometric fir phase imaging of a tokamak plasma

Multichannel phase imaging of dielectric objects has been demonstrated in the laboratory using a microbolometer detector array and 400 GHz carcinotron radiation cource. The application of this imaging system to perform single shot measurements of electron density profiles in a tokamak plasma is described. The primary advantages are increased spatial resolution together with a much simpler optical system

Multichannel far-infrared phase imaging for fusion plasmas

A 20-channel far-infrared imaging interferometer system has been used to obtain single-shot density profiles in the UCLA Microtor tokamak. This system differs from conventional multichannel interferometers in that the phase distribution produced by the plasma is imaged onto a single, monolithic, integrated microbolometer linear detector array and provides significantly more channels than previous far-infrared interferometers. The system has been demonstrated to provide diffraction-limited phase images of dielectric targets

Large area bolometers for millimeter-wave power calibration

An accurate monolithic power meter has been developed for millimeter-wave applications. The detector is a large-area Bismuth bolometer, integrated on a fused-Quartz substrate. It simply measures the temperature change caused by the absorption of millimeter-wave radiation. The power meter is simple to fabricate, inexpensive, and can be easily calibrated using a low-frequency network. The measured responsivity for a 50Ω bolometer, with an area of 1×1cm, at a bias of 1V. and a video modulation of 100Hz, is 1mV/W. The noise spectrum exhibits a 1/f rolloff till 1KHz, and is limited by the Johnson noise for higher frequencies. The NEP of the detector is 3μWHz −1/2 at a video modulation of 1KHz. It is possible to decrease the current NEP by fabricating bolometers with higher responsivities. Possible application areas are absolute power calibration and localized power density measurements at millimeter and submillimeter wavelengths.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44543/1/10762_2005_Article_BF01010389.pd

Chesapeake Bay National Estuarine Research Reserve in Virginia Management Plan: 2022-2027

Established through the Coastal Zone Management Act, the National Estuarine Research Reserve System (NERRS) represents a partnership program between the National Oceanic and Atmospheric Administration (NOAA) and the coastal states to promote informed management of the Nation’s estuaries and habitats. Designated in 1991, and administered by the Virginia Institute of Marine Science (VIMS) of William & Mary, the Chesapeake Bay National Estuarine Research Reserve in Virginia (CBNERR-VA or Reserve) is one of 30 protected areas, which encompass over 1.3 million acres and make up the NERRS. As the nation\u27s largest estuary, the Chesapeake Bay contains a diverse collection of habitats and salinity regimes. In order to incorporate the diversity of habitats in the lower Bay subregion, CBNERR-VA incorporates a multi-component network along the salinity gradient of the York River estuary (YRE). The Reserve’s four components are: (1) Goodwin Islands (148 ha; 366 ac), an archipelago of polyhaline saltmarsh islands surrounded by inter-tidal flats, extensive submerged aquatic vegetation beds, and shallow open estuarine waters near the mouth of the YRE; (2) Catlett Islands (220 ha; 542 ac), consisting of multiple parallel ridges of forested wetland hammocks, maritime-forest uplands, and emergent mesohaline salt marshes; (3) Taskinas Creek (433 ha; 1070 ac), containing non-tidal feeder streams that drain oak-hickory forests, maple-gum-ash swamps and freshwater marshes which transition into tidal oligo and mesohaline salt marshes; and (4) Sweet Hall Marsh (443 ha; 1094 ac), an extensive tidal freshwater-oligohaline marsh ecosystem located in the Pamunkey River, one of two major tributaries of the York River. This plan aligns with and complements the NERRS 2017-2022 Strategic Plan and VIMS\u27s 2015-2020 Strategic Plan while building upon previous accomplishments and the desire to address current priority issues and meet future challenges. Its intent is to provide a vision and framework to guide Reserve activities for program undertakings over the five-year period from 2022-2027