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Search Results: 1 - 10 of 86017 matches for " Wei-Hao Lee "
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FPGA Implementation of Generalized Hebbian Algorithm for Texture Classification
Shiow-Jyu Lin,Wen-Jyi Hwang,Wei-Hao Lee
Sensors , 2012, DOI: 10.3390/s120506244
Abstract: This paper presents a novel hardware architecture for principal component analysis. The architecture is based on the Generalized Hebbian Algorithm (GHA) because of its simplicity and effectiveness. The architecture is separated into three portions: the weight vector updating unit, the principal computation unit and the memory unit. In the weight vector updating unit, the computation of different synaptic weight vectors shares the same circuit for reducing the area costs. To show the effectiveness of the circuit, a texture classification system based on the proposed architecture is physically implemented by Field Programmable Gate Array (FPGA). It is embedded in a System-On-Programmable-Chip (SOPC) platform for performance measurement. Experimental results show that the proposed architecture is an efficient design for attaining both high speed performance andlow area costs.
Efficient Architecture for Spike Sorting in Reconfigurable Hardware
Wen-Jyi Hwang,Wei-Hao Lee,Shiow-Jyu Lin,Sheng-Ying Lai
Sensors , 2013, DOI: 10.3390/s131114860
Abstract: This paper presents a novel hardware architecture for fast spike sorting. The architecture is able to perform both the feature extraction and clustering in hardware. The generalized Hebbian algorithm (GHA) and fuzzy C-means (FCM) algorithm are used for feature extraction and clustering, respectively. The employment of GHA allows efficient computation of principal components for subsequent clustering operations. The FCM is able to achieve near optimal clustering for spike sorting. Its performance is insensitive to the selection of initial cluster centers. The hardware implementations of GHA and FCM feature low area costs and high throughput. In the GHA architecture, the computation of different weight vectors share the same circuit for lowering the area costs. Moreover, in the FCM hardware implementation, the usual iterative operations for updating the membership matrix and cluster centroid are merged into one single updating process to evade the large storage requirement. To show the effectiveness of the circuit, the proposed architecture is physically implemented by field programmable gate array (FPGA). It is embedded in a System-on-Chip (SOC) platform for performance measurement. Experimental results show that the proposed architecture is an efficient spike sorting design for attaining high classification correct rate and high speed computation.
Faint Submillimter Galaxy Counts at 450 micron
Chian-Chou Chen,Lennox L. Cowie,Amy J. Barger,Caitlin M. Casey,Nicholas Lee,David B. Sanders,Wei-Hao Wang,Jonathan P. Williams
Physics , 2012, DOI: 10.1088/0004-637X/762/2/81
Abstract: We present the results of SCUBA2 observations at 450 micron and 850 micron of the field lensed by the massive cluster A370. With a total survey area > 100 arcmin2 and 1 sigma sensitivities of 3.92 and 0.82 mJy/beam at 450 and 850 micron respectively, we find a secure sample of 20 sources at 450 micron and 26 sources at 850 micron with a signal-to-noise ratio > 4. Using the latest lensing model of A370 and Monte Carlo simulations, we derive the number counts at both wavelengths. The 450 micron number counts probe a factor of four deeper than the counts recently obtained from the Herschel Space Telescope at similar wavelengths, and we estimate that ~47-61% of the 450 micron extragalactic background light (EBL) resolved into individual sources with 450 micron fluxes greater than 4.5 mJy. The faint 450 micron sources in the 4 sigma sample have positional accuracies of 3 arcseconds, while brighter sources (signal-to-noise > 6 sigma) are good to 1.4 arcseconds. Using the deep radio map (1 sigma ~ 6 uJy) we find that the percentage of submillimeter sources having secure radio counterparts is 85% for 450 micron sources with intrinsic fluxes > 6 mJy and 67% for 850 micron sources with intrinsic fluxes > 4 mJy. We also find that 67% of the > 4 sigma 450 micron sources are detected at 850 micron, while the recovery rate at 450 micron of > 4 sigma 850 micron sources is 54%. Combined with the source redshifts estimated using millimetric flux ratios, the recovered rate is consistent with the scenario where both 450 micron and 20 cm emission preferentially select lower redshift dusty sources, while 850 micron emission traces a higher fraction of dusty sources at higher redshifts. [Abridge]
Resolving the Cosmic Far-Infrared Background at 450 and 850 Microns with SCUBA-2
Chian-Chou Chen,Lennox L. Cowie,Amy J. Barger,Caitlin. M. Casey,Nicholas Lee,David B. Sanders,Wei-Hao Wang,Jonathan P. Williams
Physics , 2013, DOI: 10.1088/0004-637X/776/2/131
Abstract: We use the SCUBA-2 submillimeter camera mounted on the JCMT to obtain extremely deep number counts at 450 and 850um. We combine data on two cluster lensing fields, A1689 and A370, and three blank fields, CDF-N, CDF-S, and COSMOS, to measure the counts over a wide flux range at each wavelength. We use statistical fits to broken power law representations to determine the number counts. This allows us to probe to the deepest possible level in the data. At both wavelengths our results agree well with the literature in the flux range over which they have been measured, with the exception of the 850um counts in CDF-S, where we do not observe the counts deficit found by previous single-dish observations. At 450um, we detect significant counts down to ~1mJy, an unprecedented depth at this wavelength. By integrating the number counts above this flux limit, we measure 113.9^{+49.7}_{-28.4} Jydeg^{-2} of the 450um extragalactic background light (EBL). The majority of this contribution is from sources with S_450um between 1-10mJy, and these sources are likely to be the ones that are analogous to the local luminous infrared galaxies (LIRGs). At 850um, we measure 37.3^{+21.1}_{-12.9} Jydeg^{-2} of the EBL. Because of the large systematic uncertainties on the COBE measurements, the percentage of the EBL we resolve could range from 48%-153% (44%-178%) at 450 (850)um. Based on high-resolution SMA observations of around half of the 4sigma 850um sample in CDF-N, we find that 12.5^{+12.1}_{-6.8}% of the sources are blends of multiple fainter sources. This is a low multiple fraction, and we find no significant difference between our original SCUBA-2 850um counts and the multiplicity corrected counts.
The host galaxy of a narrow-line Seyfert 1 galaxy RE J1034+396 with X-ray quasi-periodic oscillations
Wei-Hao Bian,Kai Huang
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15662.x
Abstract: Using simple stellar population synthesis, we model the bulge stellar contribution in the optical spectrum of a narrow-line Seyfert 1 galaxy RE J1034+396. We find that its bulge stellar velocity dispersion is $67.7\pm 8$ \kms. The supermassive black hole (SMBH) mass is about $(1-4)\times 10^6 \msun$ if it follows the well-known $\mbh-\sigma_*$ relation found in quiescent galaxies. We also derive the SMBH mass from the H$\beta$ second moment, which is consistent with that from its bulge stellar velocity dispersion. The SMBH mass of $(1-4)\times 10^6 \msun$ implies that the X-ray quasi-periodic oscillation (QPO) of RE J1034+396 can be scaled to a high-frequency QPO at 27-108 Hz found in Galactic black hole binaries with a 10 $\msun$ black hole. With the mass distribution in different age stellar populations, we find that the mean specific star formation rate (SSFR) over past 0.1 Gyr is $0.0163\pm 0.0011$ $\rm Gyr^{-1}$, the stellar mass in the logarithm is $10.155\pm 0.06$ in units of solar mass, and the current star formation rate is $0.23\pm 0.016 \msun \rm yr^{-1}$. RE J1034+396 does not follow the relation between the Eddington ratio and the SSFR suggested by Chen et al., although a larger scatter in their relation. We also suggest that about 7.0% of the total \ha luminosity and 50% of the total \oii luminosity come from the star formation process.
Star Formation Rate and Extinction in Faint z~4 Lyman-Break Galaxies
Chun-Hao To,Wei-Hao Wang,Frazer N. Owen
Physics , 2014, DOI: 10.1088/0004-637X/792/2/139
Abstract: We present a statistical detection of 1.5 GHz radio continuum emission from a sample of faint z~4 Lyman-break galaxies (LBGs). LBGs are key tracers of the high-redshift star formation history and important sources of UV photons that ionized the intergalactic medium in the early universe. In order to better constrain the extinction and intrinsic star formation rate (SFR) of high-redshift LBGs, we combine the latest ultradeep Karl G. Jansky Very Large Array 1.5 GHz radio image and the Hubble Space Telescope Advance Camera for Surveys (ACS) optical images in the Great Observatories Origins Deep Survey-North. We select a large sample of 1771 z~4 LBGs from the ACS catalogue using $\bband$-dropout color criteria. Our LBG samples have $\iband$~25-28 (AB), ~0-3 magnitudes fainter than M*_UV at z~4. In our stacked radio images, we find the LBGs to be point-like under our 2" angular resolution. We measure their mean 1.5 GHz flux by stacking the measurements on the individual objects. We achieve a statistical detection of $S_{1.5GHz}$=0.210+-0.075 uJy at ~3 sigma, first time on such a faint LBG population at z~4. The measurement takes into account the effects of source size and blending of multiple objects. The detection is visually confirmed by stacking the radio images of the LBGs, and the uncertainty is quantified with Monte Carlo simulations on the radio image. The stacked radio flux corresponds to an intrinsic SFR of 16.0+-5.7 M/yr, which is 2.8X the SFR derived from the rest-frame UV continuum luminosity. This factor of 2.8 is in excellent agreement with the extinction correction derived from the observed UV continuum spectral slope, using the local calibration of meurer99. This result supports the use of the local calibration on high-redshift LBGs for deriving the extinction correction and SFR, and also disfavors a steep reddening curve such as that of the Small Magellanic Cloud.
Cucurbit[6]uril p-xylylenediammonium diiodide decahydrate inclusion complex
Wei-Hao Huang,Peter Y. Zavalij,Lyle Isaacs
Acta Crystallographica Section E , 2008, DOI: 10.1107/s1600536808018412
Abstract: The title inclusion complex, C36H36N24O12·C8H14N22+·2I ·10H2O, displays a large ellipsoidal deformation of the cucurbit[6]uril (CB[6]) skeleton upon complex formation. The benzene ring of the cation is rotationally disordered between two orientations in a ratio of 3:1. The solvent H2O molecules form a hydrogen-bonded network by interaction with the carbonyl groups of CB[6] and the I counterions. The crystal studied exhibited non-merohedral twinning. Both CB[6] and the cation are centrosymmetric.
A search for H$α$ emission in high-metallicity damped Lyman-$α$ systems at $z \sim 2.4$
Wei-Hao Wang,Nissim Kanekar,J. Xavier Prochaska
Physics , 2015, DOI: 10.1093/mnras/stv171
Abstract: We report on a sensitive search for redshifted H$\alpha$ line-emission from three high-metallicity damped Ly$\alpha$ absorbers (DLAs) at $z \approx 2.4$ with the Near-infrared Integral Field Spectrometer (NIFS) on the Gemini-North telescope, assisted by the ALTtitude conjugate Adaptive optics for the InfraRed (ALTAIR) system with a laser guide star. Within the NIFS field-of-view, $\approx 3.22" \times 2.92"$ corresponding to $\approx 25$ kpc $ \times 23$ kpc at $z=2.4$, we detect no statistically significant line-emission at the expected redshifted H$\alpha$ wavelengths. The measured root-mean-square noise fluctuations in $0.4"$ apertures are $1-3\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$. Our analysis of simulated, compact, line-emitting sources yields stringent limits on the star-formation rates (SFRs) of the three DLAs, $< 2.2$~M$_{\odot}$ yr$^{-1}$ ($3\sigma$) for two absorbers, and $< 11$~M$_{\odot}$ yr$^{-1}$ ($3\sigma$) for the third, at all impact parameters within $\approx 12.5$~kpc to the quasar sightline at the DLA redshift. For the third absorber, the SFR limit is $< 4.4$~M$_\odot$ yr$^{-1}$ for locations away from the quasar sightline. These results demonstrate the potential of adaptive optics-assisted, integral field unit searches for galaxies associated with high-$z$ DLAs.
A Ks and IRAC Selection of High-Redshift Extremely Red Objects
Wei-Hao Wang,Amy J. Barger,Lennox L. Cowie
Physics , 2011, DOI: 10.1088/0004-637X/744/2/155
Abstract: In order to find the most extreme dust-hidden high-redshift galaxies, we select 196 extremely red objects in the Ks and IRAC bands (KIEROs, [Ks-4.5um](AB)>1.6) in the 0.06 deg^2 GOODS-N region. This selection avoids the Balmer breaks of galactic spectra at z<4 and picks up red galaxies with strong dust extinction. The photometric redshifts of KIEROs are between 1.5 and 5, with ~70% at z~2-4. KIEROs are very massive, with M*~10^10-10^12 Msun. They are optically faint and usually cannot be picked out by the Lyman break selection. On the other hand, the KIERO selection includes approximately half of the known millimeter and submillimeter galaxies in the GOODS-N. Stacking analyses in the radio, millimeter, and submillimeter all show that KIEROs are much more luminous than average 4.5um selected galaxies. Interestingly, the stacked fluxes for ACS-undetected KIEROs in these wavebands are 2.5-5 times larger than those for ACS-detected KIEROs. With the stacked radio fluxes and the local radio-FIR correlation, we derive mean infrared luminosities of 2-7x10^12 Lsun and mean star formation rates of 300-1200 Msun/yr for KIEROs with redshifts. We do not find evidence of a significant subpopulation of passive KIEROs. The large stellar masses and star formation rates imply that KIEROs are $z>2$ massive galaxies in rapid formation. Our results show that a large sample of dusty ultraluminous sources can be selected in this way and that a large fraction of high-redshift star formation is hidden by dust.
Spectral variability of FIRST bright QSOs with SDSS observations
Wei-Hao Bian,Li Zhang,Richard Green,Chen Hu
Physics , 2012, DOI: 10.1088/0004-637X/759/2/88
Abstract: For some samples, it has been shown that spectra of QSOs with low redshift are bluer during their brighter phases. For the FIRST bright QSO sample, we assemble their spectra from SDSS DR7 to investigate variability between the spectra from White et al. (2000) and from the SDSS for a long rest-frame time-lag, up to 10 years. There are 312 radio loud QSOs and 232 radio quiet QSOs in this sample, up to $z \sim 3.5$. With two-epoch variation, it is found that spectra of half of the QSOs appear redder during their brighter phases. There is no obvious difference in slope variability between sub-samples of radio quiet and radio loud QSOs. This result implies that the presence of a radio jet does not affect the slope variability on 10-year timescales. The arithmetic composite difference spectrum for variable QSOs is steep at blueward of $\sim$ 2500\AA. The variability for the region blueward of 2500 \AA\ is different to that for the region redward of 2500 \AA.
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