3,781 research outputs found
Extended range harmonic filter
Two types of filters, leaky-wall and open-guide, are combined into single component. Combination gives 10 db or greater additional attenuation to fourth and higher harmonics, at expense of increasing loss of fundamental frequency by perhaps 0.05 to 0.08 db. Filter is applicable to all high power microwave transmitters, but is especially desirable for satellite transmitters
Case Feedback in Support of Learning a Systems Development Methodology
While the proliferation of computer-aided systems engineering (CASE) tools in the professional world mandates their exposure to information systems (IS) students, many IS faculty may be reluctant to introduce CASE due to the seeming paradox of learning a CASE tool before acquiring a thorough knowledge of a systems development methodology. Unfortunately, an unproven tenet of CASE implementation is that a thorough knowledge of a systems development methodology is necessary before attempting to use CASE. By adhering to this tenet we may be precluding students from using CASE technology in their infonnation systems curricula. Researchers in the field of education, however, view technology as a useful tool in learning. Studies in computer-aided instruction indicate that the feedback provided by software can be especially useful during the learning process. By applying what is known about computer feedback to CASE tools it may be possible to use CASE as a tool for learning a systems development methodology as well as producing quality systems
Debye mass and heavy quark potential in a PNJL quark plasma
We calculate the Debye mass for the screening of the heavy quark potential in
a plasma of massless quarks coupled to the temporal gluon background governed
by the Polyakov loop potential within the PNJL model in RPA approximation. We
give a physical motivation for a recent phenomenological fit of lattice data by
applying the calculated Debye mass with its suppression in the confined phase
due to the Polyakov-loop to a description of the temperature dependence of the
singlet free energy for QCD with a heavy quark pair at infinite separation. We
compare the result to lattice data.Comment: 6 pages, 1 figure, contribution to Proceedings of the 6th
International Conference on "Critical Point and Onset of Deconfinement", to
appear in Phys. At. Nucl., vol. 7
Alloying, de-alloying and reentrant alloying in (sub-)monolayer growth of Ag on Pt(111)
An in-situ nanoscopic investigation of the prototypical surface alloying
system Ag/Pt(111) is reported. The morphology and the structure of the
ultrathin Ag-Pt film is studied using Low Energy Electron Microscopy during
growth at about 800 K. An amazingly rich dynamic behaviour is uncovered in
which stress relieve plays a governing role. Initial growth leads to surface
alloying with prolonged and retarded nucleation of ad-islands. Beyond 50%
coverage de-alloying proceeds, joined by partial segregation of Pt towards the
centre of large islands in violent processes. Upon coalescence the irregularly
shaped vacancy clusters are filled by segregating Pt, which then take a compact
shape (black spots). As a result at around 85% coverage the strain of the
initially pseudo-morphological film is almost completely relieved and
Pt-segregation is at its maximum. Further deposition of Ag leads to transient
re-entrant alloying and recovery of the pseudo-morphological layer. The black
spots persist even in/on several layers thick films. Ex-situ atomic force
microscopy data confirm that these are constituted by probably amorphous
Pt(-rich) structures. The (sub-)monolayer films are very much heterogeneous
Shuttle/spacelab MMAP/electromagnetic environment experiment phase B definition study
Progress made during the first five months of the Phase B definition study for the MMAP/Electromagnetic Environment Experiment (EEE) was described. An antenna/receiver assembly has been defined and sized for stowing in a three pallet bay area in the shuttle. Six scanning modes for the assembly are analyzed and footprints for various antenna sizes are plotted. Mission profiles have been outlined for a 400 km height, 57 deg inclination angle, circular orbit. Viewing time over 7 geographical areas are listed. Shuttle interfaces have been studied to determine what configuration the antenna assembly must have to be shared with other experiments of the Microwave Multi-Applications Payload (MMAP) and to be stowed in the shuttle bay. Other results reported include a frequency plan, a proposed antenna subsystem design, a proposed receiver design, preliminary outlines of the experiment controls and an analysis of on-board and ground data processing schemes
Limits on the Mass, Velocity and Orbit of PSR J19336211
We present a high-precision timing analysis of PSR J19336211, a
millisecond pulsar (MSP) with a 3.5-ms spin period and a white dwarf (WD)
companion, using data from the Parkes radio telescope. Since we have accurately
measured the polarization properties of this pulsar we have applied the matrix
template matching approach in which the times of arrival are measured using
full polarimetric information. We achieved a weighted root-mean-square timing
residuals (rms) of the timing residuals of 1.23 , 15.5
improvement compared to the total intensity timing analysis. After studying the
scintillation properties of this pulsar we put constraints on the inclination
angle of the system. Based on these measurements and on mapping we put
a 2- upper limit on the companion mass (0.44 M). Since this
mass limit cannot reveal the nature of the companion we further investigate the
possibility of the companion to be a He WD. Applying the orbital period-mass
relation for such WDs, we conclude that the mass of a He WD companion would be
about 0.260.01 M which, combined with the measured mass function
and orbital inclination limits, would lead to a light pulsar mass
1.0 M. This result seems unlikely based on current neutron star
formation models and we therefore conclude that PSR J19336211 most likely
has a CO WD companion, which allows for a solution with a more massive pulsar
Visualization of steps and surface reconstructions in Helium Ion Microscopy with atomic precision
Helium Ion Microscopy is known for its surface sensitivity and high lateral
resolution. Here, we present results of a Helium Ion Microscopy based
investigation of a surface confined alloy of Ag on Pt(111). Based on a change
of the work function of 25\,meV across the atomically flat terraces we can
distinguish Pt rich from Pt poor areas and visualize the single atomic layer
high steps between the terraces. Furthermore, dechanneling contrast has been
utilized to measure the periodicity of the hcp/fcc pattern formed in the 2--3
layers thick Ag/Pt alloy film. A periodicity of 6.65\,nm along the
surface direction has been measured. In terms of
crystallography a hcp domain is obtained through a lateral displacement of a
part of the outermost layer by of a nearest neighbour spacing
along . This periodicity is measured with atomic
precision: coincidence between the Ag and the Pt lattices is observed for 23 Ag
atoms on 24 Pt atoms. The findings are perfectly in line with results obtained
with Low Energy Electron Microscopy and Phase Contrast Atomic Force Microscopy.Comment: 15 pages, 7 figure
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