6,105 research outputs found
User manual of the CATSS system (version 1.0) communication analysis tool for space station
The Communication Analysis Tool for the Space Station (CATSS) is a FORTRAN language software package capable of predicting the communications links performance for the Space Station (SS) communication and tracking (C & T) system. An interactive software package was currently developed to run on the DEC/VAX computers. The CATSS models and evaluates the various C & T links of the SS, which includes the modulation schemes such as Binary-Phase-Shift-Keying (BPSK), BPSK with Direct Sequence Spread Spectrum (PN/BPSK), and M-ary Frequency-Shift-Keying with Frequency Hopping (FH/MFSK). Optical Space Communication link is also included. CATSS is a C & T system engineering tool used to predict and analyze the system performance for different link environment. Identification of system weaknesses is achieved through evaluation of performance with varying system parameters. System tradeoff for different values of system parameters are made based on the performance prediction
Endohedral terthiophene in zigzag carbon nanotubes: Density functional calculations
The inclusion and encapsulation of terthiophene (T3) molecules inside zigzag
single-walled carbon nanotubes (CNTs) is addressed by density functional
calculations. We consider the T3 molecule inside five semiconducting CNTs with
diameters ranging from 9.6 to 12.7 Ang. Our results show that the T3 inclusion
process is exothermic for CNTs with diameters larger than 9.5 Ang. The highest
energy gain is found to be of 2 eV, decreasing as the CNT diameter increases.
This notable effect of stabilization is attributed to the positively charged
CNT inner space, as induced by its curvature, which is able to accommodate the
neutral T3 molecule. The band structure of the T3@CNT system shows that T3
preserves its electronic identity inside the CNTs, superimposing their
molecular orbitals onto the empty CNT band structure without hybridization. Our
results predict that the electronic states added by the T3 molecules would give
rise to optical effects and nonradiative relaxation from excited states.Comment: 5 pages, 5 figures, 1 table, accepted in PR
Re-entrant Layer-by-Layer Etching of GaAs(001)
We report the first observation of re-entrant layer-by-layer etching based on
{\it in situ\/} reflection high-energy electron-diffraction measurements. With
AsBr used to etch GaAs(001), sustained specular-beam intensity oscillations
are seen at high substrate temperatures, a decaying intensity with no
oscillations at intermediate temperatures, but oscillations reappearing at
still lower temperatures. Simulations of an atomistic model for the etching
kinetics reproduce the temperature ranges of these three regimes and support an
interpretation of the origin of this phenomenon as the site-selectivity of the
etching process combined with activation barriers to interlayer adatom
migration.Comment: 11 pages, REVTeX 3.0. Physical Review Letters, in press
A study of primary dental enamel from preterm and full-term children using light and scanning electron microscopy
Purpose: The aim of this study was to examine the enamel thickness of the maxillary primary incisors of preterm children with very low birth weight (< 1,500 g) compared to full-term children with normal birth weight. Methods: A total of 90 exfoliated maxillary primary central incisors were investigated using light microscopy and scanning electron microscopy (SEM). Three serial buccolingual ground sections of each tooth were examined under light microscopy, and maximum dimensions of the prenatally and postnatally formed enamel were measured. Results: The enamel of preterm teeth was approximately 20% thinner than that for fullterm teeth. Most of the reduction was observed in the prenatally formed enamel. This was 5 to 13 times thinner than that for full-term children (P < .001). The catch-up thickness of postnatally formed enamel did not compensate fully for the decrease in prenatal enamel (P < .001). Although none of the teeth used in this study had enamel defects visible to the naked eye, 52% of preterm teeth showed enamel hypoplasia under SEM, compared with only 16% found on full-term teeth (P < .001). These defects were present as pits or irregular, shallow areas of missing enamel. Conclusions: Preterm primary dental enamel is abnormal in surface quality, and is significantly thinner compared to full-term enamel. The thinner enamel is due mainly to reduced prenatal growth and results in smaller dimensions of the primary dentition
Ku-band system design study and TDRSS interface analysis
The capabilities of the Shuttle/TDRSS link simulation program (LinCsim) were expanded to account for radio frequency interference (RFI) effects on the Shuttle S-band links, the channel models were updated to reflect the RFI related hardware changes, the ESTL hardware modeling of the TDRS communication payload was reviewed and evaluated, in LinCsim the Shuttle/TDRSS signal acquisition was modeled, LinCsim was upgraded, and possible Shuttle on-orbit navigation techniques was evaluated
Space Shuttle/TDRSS communication and tracking systems analysis
In order to evaluate the technical and operational problem areas and provide a recommendation, the enhancements to the Tracking and Data Delay Satellite System (TDRSS) and Shuttle must be evaluated through simulation and analysis. These enhancement techniques must first be characterized, then modeled mathematically, and finally updated into LinCsim (analytical simulation package). The LinCsim package can then be used as an evaluation tool. Three areas of potential enhancements were identified: shuttle payload accommodations, TDRSS SSA and KSA services, and shuttle tracking system and navigation sensors. Recommendations for each area were discussed
Black-box Generalization of Machine Teaching
Hypothesis-pruning maximizes the hypothesis updates for active learning to
find those desired unlabeled data. An inherent assumption is that this learning
manner can derive those updates into the optimal hypothesis. However, its
convergence may not be guaranteed well if those incremental updates are
negative and disordered. In this paper, we introduce a black-box teaching
hypothesis employing a tighter slack term
to replace
the typical for pruning. Theoretically, we prove that, under the
guidance of this teaching hypothesis, the learner can converge into a tighter
generalization error and label complexity bound than those non-educated
learners who do not receive any guidance from a teacher:1) the generalization
error upper bound can be reduced from to approximately
, and 2) the label complexity upper bound can
be decreased from to
approximately . To be
strict with our assumption, self-improvement of teaching is firstly proposed
when loosely approximates . Against learning, we further
consider two teaching scenarios: teaching a white-box and black-box learner.
Experiments verify this idea and show better generalization performance than
the fundamental active learning strategies, such as IWAL, IWAL-D, etc
Aggregation Weighting of Federated Learning via Generalization Bound Estimation
Federated Learning (FL) typically aggregates client model parameters using a
weighting approach determined by sample proportions. However, this naive
weighting method may lead to unfairness and degradation in model performance
due to statistical heterogeneity and the inclusion of noisy data among clients.
Theoretically, distributional robustness analysis has shown that the
generalization performance of a learning model with respect to any shifted
distribution is bounded. This motivates us to reconsider the weighting approach
in federated learning. In this paper, we replace the aforementioned weighting
method with a new strategy that considers the generalization bounds of each
local model. Specifically, we estimate the upper and lower bounds of the
second-order origin moment of the shifted distribution for the current local
model, and then use these bounds disagreements as the aggregation proportions
for weightings in each communication round. Experiments demonstrate that the
proposed weighting strategy significantly improves the performance of several
representative FL algorithms on benchmark datasets
Altered membrane trafficking in activated bone marrow‐derived macrophages
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141402/1/jlb0487.pd
Tidal effects and the Proximity decay of nuclei
We examine the decay of the 3.03 MeV state of Be evaporated from an
excited projectile-like fragment following a peripheral heavy-ion collision.
The relative energy of the daughter particles exhibits a dependence on
the decay angle of the Be, indicative of a tidal effect. Comparison of
the measured tidal effect with a purely Coulomb model suggests the influence of
a measurable nuclear proximity interaction.Comment: 5 pages, 4 figure
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