Zhen Hou, A. J. Banday, Krzysztof M. Gorski, Franz Elsner, Benjamin D. Wandelt
May 31, 2010·astro-ph.CO·PDF We present skeleton studies of non-Gaussianity in the CMB temperature anisotropy observed in the WMAP5 data. The local skeleton is traced on the 2D sphere by cubic spline interpolation which leads to more accurate estimation of the intersection positions between the skeleton and the secondary pixels than conventional linear interpolation. We demonstrate that the skeleton-based estimator of non-Gaussianity of the local type (f_NL) - the departure of the length distribution from the corresponding Gaussian expectation - yields an unbiased and sufficiently converged f_NL-likelihood. We analyse the skeleton statistics in the WMAP5 combined V- and W-band data outside the Galactic base-mask determined from the KQ75 sky-coverage. The results are consistent with Gaussian simulations of the the best-fitting cosmological model, but deviate from the previous results determined using the WMAP1 data. We show that it is unlikely that the improved skeleton tracing method, the omission of Q-band data, the modification of the foreground-template fitting method or the absence of 6 extended regions in the new mask contribute to such a deviation. However, the application of the Kp0 base-mask in data processing does improve the consistency with the WMAP1 results. The f_NL-likelihoods of the data are estimated at 9 different smoothing levels. It is unexpected that the best-fit values show positive correlation with the smoothing scales. Further investigation argues against a point-source or goodness-of-fit explanation but finds that about 30% of either Gaussian or f_NL samples having better goodness-of-fit than the WMAP5 show a similar correlation. We present the estimate f_NL=47.3+/-34.9 (1sigma error) determined from the first four smoothing angles and f_NL=76.8+/-43.1 for the combination of all nine. The former result may be overestimated at the 0.21sigma-level because of point sources.
Zhen Hou, A. J. Banday, K. M. Gorski, N. E. Groeneboom, H. K. Eriksen
Oct 19, 2009·astro-ph.CO·PDF We present local extrema studies of two models that introduce a preferred direction into the observed cosmic microwave background (CMB) temperature field. In particular, we make a frequentist comparison of the one- and two-point statistics for the dipole modulation and ACW models with data from the five-year Wilkinson Microwave Anisotropy Probe (WMAP). This analysis is motivated by previously revealed anomalies in the WMAP data, and particularly the difference in the statistical nature of the temperature anisotropies when analysed in hemispherical partitions. The analysis of the one-point statistics indicates that the previously determined hemispherical variance difficulties can be apparently overcome by a dipole modulation field, but new inconsistencies arise if the mean and the l-dependence of the statistics are considered. The two-point correlation functions of the local extrema, the temperature pair product and the point-point spatial pair-count, demonstrate that the impact of such a modulation is to over-`asymmetrise' the temperature field on smaller scales than the wave-length of the dipole or quadrupole, and this is disfavored by the observed data.The results from the ACW model predictions, however, are consistent with the standard isotropic hypothesis. The two-point analysis confirms that the impact of this type of violation of isotropy on the temperature extrema statistics is relatively weak. From this work, we conclude that a model with more spatial structure than the dipole modulated or rotational-invariance breaking models are required to fully explain the observed large-scale anomalies in the WMAP data.
Zhen Hou, A. J. Banday, K. M. Gorski
Mar 25, 2009·astro-ph.CO·PDF We present an extensive frequentist analysis of the one-point statistics (number, mean, variance, skewness and kurtosis) and two-point correlation functions determined for the local extrema of the cosmic microwave background temperature field observed in five-years of Wilkinson Microwave Anisotropy Probe (WMAP) data. Application of a hypothesis test on the one-point statistics indicates a low-variance of hot and cold spots in all frequency bands of the WMAP data. The consistency of the observations with Gaussian simulations of the the best-fitting cosmological model is rejected at the 95% C.L. outside the WMAP KQ75 mask and the northern hemispheres in the Galactic and ecliptic coordinate frames. We demonstrate that it is unlikely that residual Galactic foreground emission contributes to the observed non-Gaussianities. However, the application of a high-pass filter that removes large angular scale power does improve the consistency with the best-fitting cosmological model. Two-point correlation functions of the local extrema are calculated for both the temperature pair product (T-T) and spatial pair-counting (P-P). The T-T observations demonstrate weak correlation on scales below 20 degree and lie completely below the lower 3-sigma confidence region once various temperature thresholds are applied to the extrema determined for the KQ75 mask and northern sky partitions. The P-P correlation structure corresponds to the clustering properties of the temperature extrema, and provides evidence that it is the large angular-scale structures, and some unusual properties thereof, that are intimately connected to the properties of the hot and cold-spots observed in the WMAP five-year data.
Zhen Hou, Ryan Keisler, Lloyd Knox, Marius Millea, Christian Reichardt
Apr 12, 2011·astro-ph.CO·PDF We explore the physical origin and robustness of constraints on the energy density in relativistic species prior to and during recombination, often expressed as constraints on an effective number of neutrino species, Neff. Constraints from current data combination of Wilkinson Microwave Anisotropy Probe (WMAP) and South Pole Telescope (SPT) are almost entirely due to the impact of the neutrinos on the expansion rate, and how those changes to the expansion rate alter the ratio of the photon diffusion scale to the sound horizon scale at recombination. We demonstrate that very little of the constraining power comes from the early Integrated Sachs-Wolfe (ISW) effect, and also provide a first determination of the amplitude of the early ISW effect. Varying the fraction of baryonic mass in Helium, Yp, also changes the ratio of damping to sound-horizon scales. We discuss the physical effects that prevent the resulting near-degeneracy between Neff and Yp from being a complete one. Examining light element abundance measurements, we see no significant evidence for evolution of Neff and the baryon-to-photon ratio from the epoch of big bang nucleosynthesis to decoupling. Finally, we consider measurements of the distance-redshift relation at low to intermediate redshifts and their implications for the value of Neff.
Z. Hou, C. L. Reichardt, K. T. Story, B. Follin, R. Keisler, K. A. Aird, B. A. Benson, L. E. Bleem, J. E. Carlstrom, C. L. Chang, H-M. Cho, T. M. Crawford, A. T. Crites, T. de Haan, R. de Putter, M. A. Dobbs, S. Dodelson, J. Dudley, E. M. George, N. W. Halverson, G. P. Holder, W. L. Holzapfel, S. Hoover, J. D. Hrubes, M. Joy, L. Knox, A. T. Lee, E. M. Leitch, M. Lueker, D. Luong-Van, J. J. McMahon, J. Mehl, S. S. Meyer, M. Millea, J. J. Mohr, T. E. Montroy, S. Padin, T. Plagge, C. Pryke, J. E. Ruhl, J. T. Sayre, K. K. Schaffer, L. Shaw, E. Shirokoff, H. G. Spieler, Z. Staniszewski, A. A. Stark, A. van Engelen, K. Vanderlinde, J. D. Vieira, R. Williamson, O. Zahn
Dec 26, 2012·astro-ph.CO·PDF We explore extensions to the $Λ$CDM cosmology using measurements of the cosmic microwave background (CMB) from the recent SPT-SZ survey, along with data from WMAP7 and measurements of $H_0$ and BAO. We check for consistency within $Λ$CDM between these datasets, and find some tension. The CMB alone gives weak support to physics beyond $Λ$CDM, due to a slight trend relative to $Λ$CDM of decreasing power towards smaller angular scales. While it may be due to statistical fluctuation, this trend could also be explained by several extensions. We consider running index (nrun), as well as two extensions that modify the damping tail power (the primordial helium abundance $Y_p$ and the effective number of neutrino species $N_{\rm eff}$) and one that modifies the large-scale power due to the ISW effect (the sum of neutrino masses $\sum m_ν$). These extensions have similar observational consequences and are partially degenerate when considered simultaneously. Of the 6 one-parameter extensions considered, we find CMB to have the largest preference for nrun with -0.046<nrun<-0.003 at 95% confidence, which strengthens to a 2.7$σ$ indication of nrun<0 from CMB+BAO+$H_0$. Detectable non-zero nrun is difficult to explain in the context of single-field, slow-roll inflation models. We find $N_{\rm eff}=3.62\pm0.48$ for the CMB, which tightens to $N_{\rm eff}=3.71\pm0.35$ from CMB+BAO+$H_0$. Larger values of $N_{\rm eff}$ relieve the mild tension between CMB, BAO and $H_0$. When the SZ selected galaxy cluster abundances ($\rm{SPT_{CL}}$) data are also included, we obtain $N_{\rm eff}=3.29\pm0.31$. Allowing for $\sum m_ν$ gives a 3$σ$ detection of $\sum m_ν$>0 from CMB+BAO+$H_0$+$\rm{SPT_{CL}}$. The median value is $(0.32\pm0.11)$ eV, a factor of six above the lower bound set by neutrino oscillation observations. ... [abridged]
Z. Hou, K. Aylor, B. A. Benson, L. E. Bleem, J. E. Carlstrom, C. L. Chang, H-M. Cho, R. Chown, T. M. Crawford, A. T. Crites, T. de Haan, M. A. Dobbs, W. B. Everett, B. Follin, E. M. George, N. W. Halverson, N. L. Harrington, G. P. Holder, W. L. Holzapfel, J. D. Hrubes, R. Keisler, L. Knox, A. T. Lee, E. M. Leitch, D. Luong-Van, D. P. Marrone, J. J. McMahon, S. S. Meyer, M. Millea, L. M. Mocanu, J. J. Mohr, T. Natoli, Y. Omori, S. Padin, C. Pryke, C. L. Reichardt, J. E. Ruhl, J. T. Sayre, K. K. Schaffer, E. Shirokoff, Z. Staniszewski, A. A. Stark, K. T. Story, K. Vanderlinde, J. D. Vieira, R. Williamson
We study the consistency of 150 GHz data from the South Pole Telescope (SPT) and 143 GHz data from the Planck satellite over the patch of sky covered by the SPT-SZ survey. We first visually compare the maps and find that the residuals appear consistent with noise after accounting for differences in angular resolution and filtering. We then calculate (1) the cross-spectrum between two independent halves of SPT data, (2) the cross-spectrum between two independent halves of Planck data, and (3) the cross-spectrum between SPT and Planck data. We find the three cross-spectra are well-fit (PTE = 0.30) by the null hypothesis in which both experiments have measured the same sky map up to a single free calibration parameter---i.e., we find no evidence for systematic errors in either data set. As a by-product, we improve the precision of the SPT calibration by nearly an order of magnitude, from 2.6% to 0.3% in power. Finally, we compare all three cross-spectra to the full-sky Planck power spectrum and find marginal evidence for differences between the power spectra from the SPT-SZ footprint and the full sky. We model these differences as a power law in spherical harmonic multipole number. The best-fit value of this tilt is consistent among the three cross-spectra in the SPT-SZ footprint, implying that the source of this tilt is a sample variance fluctuation in the SPT-SZ region relative to the full sky. The consistency of cosmological parameters derived from these datasets is discussed in a companion paper.
Zhijun Zeng, Zhen Hou, Ting Li, Lei Deng, Jianguo Hou, Xinran Huang, Jun Li, Meirou Sun, Yunhan Wang, Qiyu Wu, Wenhao Zheng, Hua Jiang, Qi Wang
Feb 21, 2022·q-bio.QM·PDF We develop a deep learning approach to predicting a set of ventilator parameters for a mechanically ventilated septic patient using a long and short term memory (LSTM) recurrent neural network (RNN) model. We focus on short-term predictions of a set of ventilator parameters for the septic patient in emergency intensive care unit (EICU). The short-term predictability of the model provides attending physicians with early warnings to make timely adjustment to the treatment of the patient in the EICU. The patient specific deep learning model can be trained on any given critically ill patient, making it an intelligent aide for physicians to use in emergent medical situations.
Christian L. Reichardt, Roland de Putter, Oliver Zahn, Zhen Hou
Oct 24, 2011·astro-ph.CO·PDF We present new limits on early dark energy (EDE) from the cosmic microwave background (CMB) using data from the WMAP satellite on large angular scales and South Pole Telescope (SPT) on small angular scales. We find a strong upper limit on the EDE density of Omega_e < 0.018 at 95% confidence, a factor of three improvement over WMAP data alone. We show that adding lower-redshift probes of the expansion rate to the CMB data improves constraints on the dark energy equation of state, but not the EDE density. We also explain how the small-scale CMB temperature anisotropy constrains EDE.
Yifei Xu, Jiaying Wu, Herun Wan, Yang Li, Zhen Hou, Min-Yen Kan
Hashtag trends ignite campaigns, shift public opinion, and steer millions of dollars in advertising spend, yet forecasting which tag goes viral is elusive. Classical regressors digest surface features but ignore context, while large language models (LLMs) excel at contextual reasoning but misestimate numbers. We present BuzzProphet, a reasoning-augmented hashtag popularity prediction framework that (1) instructs an LLM to articulate a hashtag's topical virality, audience reach, and timing advantage; (2) utilizes these popularity-oriented rationales to enrich the input features; and (3) regresses on these inputs. To facilitate evaluation, we release HashView, a 7,532-hashtag benchmark curated from social media. Across diverse regressor-LLM combinations, BuzzProphet reduces RMSE by up to 2.8% and boosts correlation by 30% over baselines, while producing human-readable rationales. Results demonstrate that using LLMs as context reasoners rather than numeric predictors injects domain insight into tabular models, yielding an interpretable and deployable solution for social media trend forecasting.