Testing Modified Dark Matter with Galaxy Clusters: Does Dark Matter know about the Cosmological Constant?

We discuss the possibility that the cold dark matter mass profiles contain information on the cosmological constant, and that such information constrains the nature of cold dark matter (CDM). We call this approach Modified Dark Matter (MDM). In particular, we examine the ability of MDM to explain the observed mass profiles of 13 galaxy clusters. Using general arguments from gravitational thermodynamics, we provide a theoretical justification for our MDM mass profile and successfully compare it to the NFW mass profiles both on cluster and galactic scales. Our results suggest that indeed the CDM mass profiles contain information about the cosmological constant in a non-trivial way

Testing MONDian Dark Matter with Galactic Rotation Curves

MONDian dark matter (MDM) is a new form of dark matter quantum that naturally accounts for Milgrom's scaling, usually associated with modified Newtonian dynamics (MOND), and theoretically behaves like cold dark matter (CDM) at cluster and cosmic scales. In this paper, we provide the first observational test of MDM by fitting rotation curves to a sample of 30 local spiral galaxies (z approximately 0.003). For comparison, we also fit the galactic rotation curves using MOND, and CDM. We find that all three models fit the data well. The rotation curves predicted by MDM and MOND are virtually indistinguishable over the range of observed radii (~1 to 30 kpc). The best-fit MDM and CDM density profiles are compared. We also compare with MDM the dark matter density profiles arising from MOND if Milgrom's formula is interpreted as Newtonian gravity with an extra source term instead of as a modification of inertia. We find that discrepancies between MDM and MOND will occur near the center of a typical spiral galaxy. In these regions, instead of continuing to rise sharply, the MDM mass density turns over and drops as we approach the center of the galaxy. Our results show that MDM, which restricts the nature of the dark matter quantum by accounting for Milgrom's scaling, accurately reproduces observed rotation curves.Comment: Preprint number IPMU13-0147. Accepted for publication in Ap

CLUMP-3D. Testing Λ\LambdaCDM with galaxy cluster shapes

The $\Lambda$CDM model of structure formation makes strong predictions on concentration and shape of DM (dark matter) halos, which are determined by mass accretion processes. Comparison between predicted shapes and observations provides a geometric test of the $\Lambda$CDM model. Accurate and precise measurements needs a full three-dimensional analysis of the cluster mass distribution. We accomplish this with a multi-probe 3D analysis of the X-ray regular CLASH (Cluster Lensing And Supernova survey with Hubble) clusters combining strong and weak lensing, X-ray photometry and spectroscopy, and the Sunyaev-Zel'dovich effect. The cluster shapes and concentrations are consistent with $\Lambda$CDM predictions. The CLASH clusters are randomly oriented, as expected given the sample selection criteria. Shapes agree with numerical results for DM-only halos, which hints at baryonic physics being not so effective in making halos rounder.Comment: v2: 8 pages, in press on ApJL. Extended discussion on regularity. One of three new companion papers of the CLUMP-3D project (Keiichi Umetsu et al., arxiv:1804.00664; I-Non Chiu et al., arXiv:1804.00676

Diagnostic quality assessment of compressed sensing accelerated magnetic resonance neuroimaging.

PURPOSE: To determine the efficacy of compressed sensing (CS) reconstructions for specific clinical magnetic resonance neuroimaging applications beyond more conventional acceleration techniques such as parallel imaging (PI) and low-resolution acquisitions. MATERIALS AND METHODS: Raw k-space data were acquired from five healthy volunteers on a 3T scanner using a 32-channel head coil using T2 -FLAIR, FIESTA-C, time of flight (TOF), and spoiled gradient echo (SPGR) sequences. In a series of blinded studies, three radiologists independently evaluated CS, PI (GRAPPA), and low-resolution images at up to 5× accelerations. Synthetic T2 -FLAIR images with artificial lesions were used to assess diagnostic accuracy for CS reconstructions. RESULTS: CS reconstructions were of diagnostically acceptable quality at up to 4× acceleration for T2 -FLAIR and FIESTA-C (average qualitative scores 3.7 and 4.3, respectively, on a 5-point scale at 4× acceleration), and at up to 3× acceleration for TOF and SPGR (average scores 4.0 and 3.7, respectively, at 3× acceleration). The qualitative scores for CS reconstructions were significantly better than low-resolution images for T2 -FLAIR, FIESTA-C, and TOF and significantly better than GRAPPA for TOF and SPGR (Wilcoxon signed rank test, P \u3c 0.05) with no significant difference found otherwise. Diagnostic accuracy was acceptable for both CS and low-resolution images at up to 3× acceleration (area under the ROC curve 0.97 and 0.96, respectively.) CONCLUSION: Mild to moderate accelerations are possible for those sequences by a combined CS and PI reconstruction. Nevertheless, for certain sequences/applications one might mildly reduce the acquisition time by appropriately reducing the imaging resolution rather than the more complicated CS reconstruction. J. Magn. Reson. Imaging 2016;44:433-444

Quantum Gravity and Dark Matter

We propose a connection between global physics and local galactic dynamics via quantum gravity. The salient features of cold dark matter (CDM) and modified Newtonian dynamics (MOND) are combined into a unified scheme by introducing the concept of MONDian dark matter which behaves like CDM at cluster and cosmological scales but emulates MOND at the galactic scale.Comment: This paper has been awarded the Fifth Prize in the 2011 Essay Competition of the Gravity Research Foundatio

Echocardiographic Manifestations in Patients with Cardiac Sarcoidosis

BackgroundCardiac sarcoidosis is a life-threatening disease with protean clinical manifestations, including congestive heart failure (CHF), conduction disturbance, ventricular arrhythmia and sudden death. Nonetheless, it is difficult to diagnose cardiac sarcoidosis in the clinical setting. Some echocardiographic findings of cardiac sarcoidosis associated with other diagnostic tools (201thallium scintigraphy, 67gallium citrate scan, serum markers and others) may be helpful upon early suspicion and diagnosis of cardiac sarcoidosis.Materials and MethodsFifty-two patients (36 female) with cardiac sarcoidosis, with a mean age of 48 ± 14 years (range, 21–70 yr), underwent a series of echocardiographic follow-up (mean, 88 ± 48 mo) examinations, and important echocardiographic parameters and findings were recorded.ResultsThere were left ventricular (LV) regional wall motion abnormalities (RWMAs) noted in 40 (localized in 16, multiple in 24), dilatation of the LV with impaired LV contractility in 28, thinning of the basal interventricular septum (IVS) in 27, thinning of LV free wall in 18, apical aneurysm in 12, apical thrombus in two, mimicking hypertrophic cardiomyopathy (HCM) in two, pericardial effusion (PE) in two (with cardiac tamponade in one), and LV wall thinning and aneurysm formation after steroid therapy for cardiac sarcoidosis in two of 43 patients.ConclusionThinning of the basal IVS or LV free wall is a specific echocardiographic finding of cardiac sarcoidosis. Other echocardiographic findings of cardiac sarcoidosis may mimic coronary artery disease (LV RWMA or apical aneurysm), CHF, or HCM. PE and thinning of the LV wall after steroid therapy were also noted in rare situations

Solving the Interpretational-Confounding and Interpretational-Ambiguity Problems of Formative Construct Modeling in Behavioral Research: Proposing a Two-Stage Fixed-Weight Redundancy Approach

Recently, information systems research has devoted increasing attention to formative measurements. However, current approaches to modeling formative constructs have potential validity problems and thus limited applicability. Here, we highlight two major problems in formative measurement—interpretational confounding and interpretational ambiguity—and propose a novel resolution. Interpretational confounding occurs when using the traditional free-estimation approach, because the weights of different formative indicators vary as the dependent variable changes, resulting in the distortion of the measurement weights of the focal formative construct and thus jeopardizing the generalizability of empirical tests. Another way to alleviate the interpretational-confounding issue is to include the multiple indicators multiple causes (MIMIC) construct in the path model (i.e., MIMIC-path). Unfortunately, this method has led to the second major problem of interpretational ambiguity, the existence of more than one potential explanation of the formative model. More specifically, reflective indicators in the MIMIC model can be viewed as (1) indicators of the MIMIC construct, (2) dependent variables of the formative construct, or (3) indicators of a reflective construct affected by independent variables (formative indicators). To resolve these issues, we propose a two-stage fixed-weight redundancy model (FWRM) approach. We demonstrate the applicability of the FWRM approach with a set of survey data. We conducted a simulation study evaluating the FWRM approach by comparing it with the commonly used free-estimation and MIMIC-path methods. The results indicate that our FWRM approach can indeed improve the validity of formative construct modeling by mitigating confounding and ambiguity issues

Exploring Individuals’ Loyalty To Online Support Groups From the Perspective Of Social Support

Prior research indicates that social support allows individuals to have additional skills to handle stresses, enhance self-esteem, and increase psychological well-being. Online social networks have become an emerging and important source of social support. However, little research has been done to explore how IT usage may improve the well-being and life quality of individuals, especially patients. Little research has been done to empirically examine individuals’ loyalty toward online social groups from the perspective of social support. This study aims to develop an integrated research model to the impact of online social support on psychological well-being and group identification, and individuals’ subsequent loyalty toward online social groups. Online social support group was operationalized as a second-order construct with four components: informational, emotional, esteem, and network supports. Data collected from 537 users of online support groups for mothers in Taiwan provide strong support for the research model. The results indicate that online social support is positively associated with psychological well-being and group identification, which in turn have a positive effect on moms’ loyalty toward online social groups. Implications for theory and practice and suggestions for future research are provided

Spacetime Emergence and General Covariance Transmutation

Spacetime emergence refers to the notion that classical spacetime "emerges" as an approximate macroscopic entity from a non-spatio-temporal structure present in a more complete theory of interacting fundamental constituents. In this article, we propose a novel mechanism involving the "soldering" of internal and external spaces for the emergence of spacetime and the twin transmutation of general covariance. In the context of string theory, this mechanism points to a critical four dimensional spacetime background.Comment: 11 pages, v2: version to appear in MPL