19,197 research outputs found
Soma size distinguishes projection neurons from neurokinin 1 receptor-expressing interneurons in lamina I of the rat lumbar spinal dorsal horn
Lamina I of the spinal dorsal horn contains neurons that project to various brain regions, and ∼80% of these projection cells express the neurokinin 1 receptor (NK1r), the main receptor for substance P. Two populations of NK1r-immunoreactive neurons have been identified in lamina I: small weakly immunoreactive cells and large cells with strong immunolabelling [Cheunsuang O and Morris R (2000) Neuroscience 97:335–345]. The main aim of this study was to test the hypothesis that the large cells are projection neurons and that the small cells are interneurons. Projection neurons were identified by injection of tracers into the caudal ventrolateral medulla and lateral parabrachial area, and this was combined with immunostaining for NK1r. We found a bimodal size distribution for NK1r-immunoreactive neurons. The small cells (with somatic cross-sectional areas <200 μm2) showed weak immunoreactivity, while immunostaining intensity was variable among the large cells. Virtually all (99%) of the immunoreactive cells with soma areas >200 μm2 were retrogradely labelled, while only 10% of retrogradely labelled cells were smaller than this. Soma sizes of retrogradely labelled neurons that lacked NK1r did not differ from those of NK1r-expressing projection neurons. It has been suggested that a population of small pyramidal projection neurons that lack NK1r may correspond to cells activated by innocuous cooling, and we therefore assessed the morphology of retrogradely labelled cells that were not NK1r-immunoreactive. Fifteen percent of these were pyramidal, but these did not differ in size from pyramidal NK1r-immunoreactive projection neurons. These results confirm that large NK1r-immunoreactive lamina I neurons are projection cells, and suggest that the small cells are interneurons. Since almost all of the NK1r-immunoreactive cells with soma size >200 μm2 were retrogradely labelled, cells of this type can be identified as projection cells in anatomical studies
SSME single crystal turbine blade dynamics
A study was performed to determine the dynamic characteristics of the Space Shuttle main engine high pressure fuel turbopump (HPFTP) blades made of single crystal (SC) material. The first and second stage drive turbine blades of HPFTP were examined. The nonrotating natural frequencies were determined experimentally and analytically. The experimental results of the SC second stage blade were used to verify the analytical procedures. The analytical study examined the SC first stage blade natural frequencies with respect to crystal orientation at typical operating conditions. The SC blade dynamic response was predicted to be less than the directionally solidified blade. Crystal axis orientation optimization indicated the third mode interference will exist in any SC orientation
JT9D jet engine performance deterioration
The analytical techniques utilized to examine the effects of flight loads and engine operating conditions on performance deterioration are presented. The role of gyroscopic, gravitational, and aerodynamic loads are shown along with the effect of variations in engine build clearances. These analytical results are compared to engine test data along with the correlation between analytically predicted and measured clearances and rub patterns. Conclusions are drawn and important issues are discussed
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Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System
Background theory, a reference design, and demonstration
results are given for a Global Navigation Satellite
System (GNSS) interference localization system comprising a
distributed radio-frequency sensor network that simultaneously
locates multiple interference sources by measuring their signals’
time difference of arrival (TDOA) between pairs of nodes in
the network. The end-to-end solution offered here draws from
previous work in single-emitter group delay estimation, very long
baseline interferometry, subspace-based estimation, radar, and
passive geolocation. Synchronization and automatic localization
of sensor nodes is achieved through a tightly-coupled receiver
architecture that enables phase-coherent and synchronous sampling
of the interference signals and so-called reference signals
which carry timing and positioning information. Signal and crosscorrelation
models are developed and implemented in a simulator.
Multiple-emitter subspace-based TDOA estimation techniques
are developed as well as emitter identification and localization
algorithms. Simulator performance is compared to the CramérRao
lower bound for single-emitter TDOA precision. Results are
given for a test exercise in which the system accurately locates
emitters broadcasting in the amateur radio band in Austin, TX.Aerospace Engineering and Engineering Mechanic
A Graphical Approach to GPS Software-Defined Receiver Implementation
Global positioning system (GPS) software-defined
receivers (SDRs) offer many advantages over their hardwarebased
counterparts, such as flexibility, modularity, and upgradability.
A typical GPS receiver is readily expressible as a block
diagram, making a graphical approach a natural choice for
implementing GPS SDRs. This paper presents a real-time, graphical
implementation of a GPS SDR, consisting of two modes:
acquisition and tracking. The acquisition mode performs a twodimensional
fast Fourier transform (FFT)-based search over code
offsets and Doppler frequencies. The carrier-aided code tracking
mode consists of the following main building blocks: correlators,
code and carrier phase detectors, code and carrier phase filters,
a code generator, and a numerically-controlled oscillator. The
presented GPS SDR provides an abstraction level that enables
future research endeavors.Aerospace Engineering and Engineering Mechanic
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The Texas Spoofing Test Battery: Toward a Standard for Evaluating GPS Signal Authentication Techniques
A battery of recorded spoofing scenarios has been compiled
for evaluating civil Global Positioning System (GPS) signal
authentication techniques. The battery can be considered
the data component of an evolving standard meant to
define the notion of spoof resistance for commercial GPS
receivers. The setup used to record the scenarios is described.
A detailed description of each scenario reveals
readily detectable anomalies that spoofing detectors could target to improve GPS securityAerospace Engineering and Engineering Mechanic
Preparation of urban land use inventories by machine processing of ERTS MSS data
Spectral classes of urban phenomena identified from Earth Resources Technology Satellite (ERTS) multispectral scanner data in Milwaukee included suburban inner city, industry, grassy (open area), road, wooded suburb, water cloud, and shadow. The Milwaukee spectral class statistics were used to classify the Chicago area, within the same ERTS frame, and similar results were achieved. In another ERTS frame, Marion County (Indianapolis) data were classified into similar classes. The Marion County ERTS study was supported by a land use classification of an area near downtown Indianapolis that utilized 12-band MSS data collected by aircraft from 3000 feet. The results of the ERTS analyses suggest that satellite data will be a useful tool for the urban planner for monitoring urban land use
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