Surgery on SL~×En\widetilde{\Bbb{SL}}\times\Bbb{E}^n-manifolds

We show that although closed $\widetilde{\Bbb{SL}}\times\Bbb{E}^n$-manifolds do not admit metrics of nonpositive sectional curvature, the arguments of Farrell and Jones can be extended to show that such manifolds are topologically rigid, if $n\geq2$.Comment: 7 pages, AMS-LaTeX file, To appear in the Canadian Mathematical Bulletin

Life Satisfaction: Measurement Invariance and Correlations with Adolescent Adjustment

Background Low life satisfaction during adolescence has been associated with adjustment problems. There are few well-validated measures available to assess adolescents’ life-satisfaction. The purpose of this study was to investigate the structure of the Life Satisfaction Scale, evaluate its measurement invariance across sex and race/ethnicity, and investigate its associations with related constructs. Methods Participants were 3,340 adolescents from rural middle schools in Florida. Half the participants were female, 51% were White, 15% were Black, and 22% were Latinx. Adolescents completed the Life Satisfaction Scale, the Children’s Report of Exposure to Violence scale, and the Problem Behavior Frequency Scale. Results Confirmatory factor analysis found support for a single factor representing overall life satisfaction, and strong measurement invariance across race, but not across sex. There were significant differences in item thresholds such that girls at the same level of life satisfaction as boys, were more likely to endorse higher responses to items assessing satisfaction with school, with themselves, and with their friendships. Life satisfaction had significant negative correlations with violence exposure, problem behavior, and peer pressure for drug use. Conclusion Findings suggest that the Life Satisfaction Scale may be suitable for assessing life satisfaction across different groups of adolescents. Examining sex differences must be done cautiously as life satisfaction may have different meanings to boys and girls. The inverse correlations between life satisfaction, violence exposure and problem behavior across groups highlights the importance of developing sound measures to assess this important construct and determine how it relates to youth adjustment.https://scholarscompass.vcu.edu/gradposters/1076/thumbnail.jp

A synoptic description of coal basins via image processing

An existing image processing system is adapted to describe the geologic attributes of a regional coal basin. This scheme handles a map as if it were a matrix, in contrast to more conventional approaches which represent map information in terms of linked polygons. The utility of the image processing approach is demonstrated by a multiattribute analysis of the Herrin No. 6 coal seam in Illinois. Findings include the location of a resource and estimation of tonnage corresponding to constraints on seam thickness, overburden, and Btu value, which are illustrative of the need for new mining technology

Superorbital Period in the High Mass X-ray Binary 2S 0114+650

We report the detection of a superorbital period in the high-mass X-ray binary 2S 0114+650. Analyses of data from the Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) from 1996 January 5 to 2004 August 25 reveal a superorbital period of 30.7 +/- 0.1 d, in addition to confirming the previously reported neutron star spin period of 2.7 h and the binary orbital period of 11.6 d. It is unclear if the superorbital period can be ascribed to the precession of a warped accretion disc in the system.Comment: 5 pages, 5 figures, submitted to MNRAS 27th January 2005. Manuscript expanded to include discussion of evolution of periods, and hardness ratio variability. Number of figures increased from 5 to 9. Accepted for publication 19th December 200

On Binscatter

Binscatter is very popular in applied microeconomics. It provides a flexible, yet parsimonious way of visualizing and summarizing large data sets in regression settings, and it is often used for informal evaluation of substantive hypotheses such as linearity or monotonicity of the regression function. This paper presents a foundational, thorough analysis of binscatter: we give an array of theoretical and practical results that aid both in understanding current practices (i.e., their validity or lack thereof) and in offering theory-based guidance for future applications. Our main results include principled number of bins selection, confidence intervals and bands, hypothesis tests for parametric and shape restrictions of the regression function, and several other new methods, applicable to canonical binscatter as well as higher-order polynomial, covariate-adjusted and smoothness-restricted extensions thereof. In particular, we highlight important methodological problems related to covariate adjustment methods used in current practice. We also discuss extensions to clustered data. Our results are illustrated with simulated and real data throughout. Companion general-purpose software packages for \texttt{Stata} and \texttt{R} are provided. Finally, from a technical perspective, new theoretical results for partitioning-based series estimation are obtained that may be of independent interest

Recurrent ~24 h Periods in RXTE ASM Data

Analysis of data from the Rossi X-ray Timing Explorer satellite's All Sky Monitor instrument for several X-ray binary sources has identified a recurrent \~24 h period. This period is sometimes highly significant, giving rise to the possibility of it being identified as an orbital or super-orbital period. Further analysis has revealed the same period in a number of other X-ray sources. As a result this period has been discounted as spurious, described variously as arising from daily variations in background levels and beating between the sampling period and long-term secular trends in the light curves. We present here an analysis of the spurious periods and show that the dominant mechanism is in fact spectral leakage of low-frequency power present in the light curves.Comment: 9 Pages, 10 figures, 1 table, submitted to PASA 20th December 2004. Added 1 page of text and 3 figures to clarify results and discussion. Resubmitted 16th May 2005. Accepted 25th June 200

The fibered isomorphism conjecture for complex manifolds

In this paper we show that the fibered isomorphism conjecture of Farrell and Jones corresponding to the stable topological pseudoisotopy functor is true for the fundamental groups of a large class of complex manifolds. A consequence of this result is that the Whitehead group, reduced projective class groups and the negative K-groups of the fundamental group of these manifolds vanish whenever the fundamental group is torsion free. We also prove the same results for a class of real manifolds.Comment: accepted for publication in Acta Mathematica Sinica, English Serie

Searching for X-ray sources in nearby late-type galaxies with low star formation rates

Late type non-starburst galaxies have been shown to contain X-ray emitting objects, some being ultraluminous X-ray sources. We report on XMM-Newton observations of 11 nearby, late-type galaxies previously observed with the Hubble Space Telescope (HST) in order to find such objects. We found 18 X-ray sources in or near the optical extent of the galaxies, most being point-like. If associated with the corresponding galaxies, the source luminosities range from $2 \times 10^{37}$ erg s$^{-1}$ to $6 \times 10^{39}$ erg s$^{-1}$. We found one ultraluminous X-ray source, which is in the galaxy IC 5052, and one source coincident with the galaxy IC 4662 with a blackbody temperature of $0.166 \pm 0.015$ keV that could be a quasi-soft source or a quiescent neutron star X-ray binary in the Milky Way. One X-ray source, XMMU J205206.0$-$691316, is extended and coincident with a galaxy cluster visible on an HST image. The X-ray spectrum of the cluster reveals a redshift of $z = 0.25 \pm 0.02$ and a temperature of 3.6$\pm$0.4 keV. The redshift was mainly determined by a cluster of Fe XXIV lines between the observed energy range $0.8-1.0$ keV.Comment: 8 pages, to appear in MNRA