220 research outputs found
The importance of scale in spatially varying coefficient modeling
While spatially varying coefficient (SVC) models have attracted considerable
attention in applied science, they have been criticized as being unstable. The
objective of this study is to show that capturing the "spatial scale" of each
data relationship is crucially important to make SVC modeling more stable, and
in doing so, adds flexibility. Here, the analytical properties of six SVC
models are summarized in terms of their characterization of scale. Models are
examined through a series of Monte Carlo simulation experiments to assess the
extent to which spatial scale influences model stability and the accuracy of
their SVC estimates. The following models are studied: (i) geographically
weighted regression (GWR) with a fixed distance or (ii) an adaptive distance
bandwidth (GWRa), (iii) flexible bandwidth GWR (FB-GWR) with fixed distance or
(iv) adaptive distance bandwidths (FB-GWRa), (v) eigenvector spatial filtering
(ESF), and (vi) random effects ESF (RE-ESF). Results reveal that the SVC models
designed to capture scale dependencies in local relationships (FB-GWR, FB-GWRa
and RE-ESF) most accurately estimate the simulated SVCs, where RE-ESF is the
most computationally efficient. Conversely GWR and ESF, where SVC estimates are
naively assumed to operate at the same spatial scale for each relationship,
perform poorly. Results also confirm that the adaptive bandwidth GWR models
(GWRa and FB-GWRa) are superior to their fixed bandwidth counterparts (GWR and
FB-GWR)
gwpcorMapper: an interactive mapping tool for exploring geographically weighted correlation and partial correlation in high-dimensional geospatial datasets
Exploratory spatial data analysis (ESDA) plays a key role in research that
includes geographic data. In ESDA, analysts often want to be able to visualize
observations and local relationships on a map. However, software dedicated to
visualizing local spatial relations be-tween multiple variables in high
dimensional datasets remains undeveloped. This paper introduces gwpcorMapper, a
newly developed software application for mapping geographically weighted
correlation and partial correlation in large multivariate datasets.
gwpcorMap-per facilitates ESDA by giving researchers the ability to interact
with map components that describe local correlative relationships. We built
gwpcorMapper using the R Shiny framework. The software inherits its core
algorithm from GWpcor, an R library for calculating the geographically weighted
correlation and partial correlation statistics. We demonstrate the application
of gwpcorMapper by using it to explore census data in order to find meaningful
relationships that describe the work-life environment in the 23 special wards
of Tokyo, Japan. We show that gwpcorMapper is useful in both variable selection
and parameter tuning for geographically weighted statistics. gwpcorMapper
highlights that there are strong statistically clear local variations in the
relationship between the number of commuters and the total number of hours
worked when considering the total population in each district across the 23
special wards of Tokyo. Our application demonstrates that the ESDA process with
high-dimensional geospatial data using gwpcorMapper has applications across
multiple fields.Comment: 18 pages, 8 figures, 2 table
Controlled structure of anatase TiO2 nanoparticles by using organic additives in a microwave process
Synthesis of anatase nanoparticles was carried out in a microwave system. Crystal morphology was controlled by organic additives including PAAc (polyacrylic acid) and PVP (polyvinylpyrrolidone). Modified TiO2 particles were compared to the bare TiO2 anatase structure. The synthesis of materials via the microwave system has great advantages due to the short reaction period and low energy requirement and is therefore an environmentally friendly process compared to the hydrothermal process. The decomposition of acetaldehyde was studied to determine the photocatalytic activity of the modified anatase TiO2 material
Spatial Domain Resource Sharing for Overlapping Cells in Indoor Environment
As microcell wireless systems become more widespread, intercell interference among the access points will increase due to the limited frequency resource. In the overlapping cell scenario, radio resources should be shared by multiple cells. Although time and frequency resource sharing has been described in many papers, there is no detailed report on dynamic spatial resource sharing among multiple cells for microcell wireless systems. Thus, we present the effectiveness of spatial resource sharing among two access points. We introduce two scenarios based on the zero forcing method; one is the primary-secondary AP scenario and the other is the cooperative AP scenario. To evaluate the transmission performance of spatial resource sharing, channel matrices are measured in an indoor environment. The simulation results using the measured channel matrices show the potential of spatial resource sharing
Demonstration of 2.65 / 3.3 Gbit per sec X Band Radiowave Down Link Communications from LEO Small Satellite
This paper reports our new communication system and downlink demonstrations with a small satellite of 2.65 Gbps data rate with 64 APSK modulation and 3.3Gbps data rate with 256 APSK modulation by utilizing two circular polarization channels of X band. We have developed an on-board X-band transmitter, an on-board dual circularly polarized-wave antenna with 17dBi gain and \u3e37dB Cross Polarization Discrimination (XPD) and a 10m ground station with 39dB/K of G/T and \u3e37dB XPD for low-crosstalk polarization multiplexing. Since there are not real- time demodulator systems in such high communication speed, the downlinked signals are stored in a data recorder at an antenna site. Afterwards, we decode downlinked signals by using our non-real-time software demodulator. The system was demonstrated in orbit the RAPid Innovative payload demonstration Satellite (RAPIS-1) of JAXA in 2019. We have achieved 2.65 Gbps and 3.3Gbps communication speed in the X-band for LEO satellite at 300 M symbols per second (Msps) and polarization multiplexing of 64APSK (coding rate 4/5) and 256APSK (coding rate 3/4) following DVB-S2X protocol with roll-off factor α=0.05. The communication speeds correspond to of frequency efficiency 8.4 bit/s/Hz and 10.8 bit/s/Hz of frequency utilization efficiency. As far as authors know, these direct downlink communication speeds and frequency utilization efficiencies are the highest ones at present in LEO satellites, excluding bent-pipe communication systems
Experimental Results of Network-Assisted Interference Suppression Scheme Using Adaptive Beam-Tilt Switching
This paper introduces a network-assisted interference suppression scheme using beam-tilt switching per frame for wireless local area network systems and its effectiveness in an actual indoor environment. In the proposed scheme, two access points simultaneously transmit to their own desired station by adjusting angle of beam-tilt including transmit power assisted from network server for the improvement of system throughput. In the conventional researches, it is widely known that beam-tilt is effective for ICI suppression in the outdoor scenario. However, the indoor effectiveness of beam-tilt for ICI suppression has not yet been indicated from the experimental evaluation. Thus, this paper indicates the effectiveness of the proposed scheme by analyzing multiple-input multiple-output channel matrices from experimental measurements in an office environment. The experimental results clearly show that the proposed scheme offers higher system throughput than the conventional scheme using just transmit power control
Functional Image-Guided Radiotherapy Planning in Respiratory- Gated Intensity-Modulated Radiation Therapy (IMRT) for Lung Cancer Patients with chronic obstructive pulmonary disease (COPD)
(Purpose) To investigate the incorporation of functional lung image-derived low attenuation area (LAA) based on four-dimensional computed tomography (4D-CT) into respiratory-gated intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) in treatment planning for lung cancer patients with chronic obstructive pulmonary disease (COPD).
(Materials and Methods) Eight lung cancer patients with COPD were the subjects of this study. LAA was generated from 4D-CT data sets according to CT values lower than -860 Hounsfield units (HU) as a threshold. The functional lung image was defined as the area where LAA was excluded from the image of the total lung. Two respiratory-gated radiotherapy plans (70 Gy/35 fr) were designed and compared in each patient as follows: 1) Plan A: anatomical IMRTor VMAT plan based on the total lung 2) Plan F: functional IMRT or VMAT plan based on the functional lung. Dosimetric parameters (V20: the percentage of total lung volume irradiated with ≥ 20 Gy,MLD:mean dose of total lung) of the two plans were compared.
(Results) V20 was lower in Plan F than in Plan A (mean 1.5 %, p= 0.025 in IMRT, mean 1.6 %, p= 0.044 in VMAT) achieved by a reduction in MLD (mean 0.23 Gy, p= 0.083 in IMRT, mean 0.5 Gy, p= 0.042 in VMAT). No differences were noted in target volume coverage and organ-at-risk doses.
(Conclusions) Functional image-guided radiotherapy planning based on LAAin respiratory-guided IMRT or VMAT appears to be effective in preserving a functional lung in lung cancer patients with COPD.This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant no. 22591385), and a Grant-in-Aid for Scientific Research from the Association for Nuclear Technology in Medicine.
This work was partly presented at the 52nd Annual Meeting of the American Society of Radiation Oncology, San Diego, CA, Oct 31 - Nov 4, 2010
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