Drexel University

About: Drexel University is a education organization based out in Philadelphia, Pennsylvania, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 26770 authors who have published 51438 publications receiving 1949443 citations. The organization is also known as: Drexel & Drexel Institute.

SPECTRA AND HUBBLE SPACE TELESCOPE LIGHT CURVES OF SIX TYPE Ia SUPERNOVAE AT 0.511 <z< 1.12 AND THE UNION2 COMPILATION ∗

Abstract: We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise HST data, and spectra of six SNe Ia that were discovered during 2001 are presented. Additionally, for the two SNe with z > 1, we present groundbased J-band photometry from Gemini and the VLT. These are among the most distant SNe Ia for which ground based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation (Kowalski et al. 2008). We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 supernovae, the Union2

Some antecedents and effects of trust in virtual communities

Abstract: This study explores several downstream effects of trust in virtual communities and the antecedents of trust in this unique type of environment. The data, applying an existing scale to measure two dimensions of trust (ability and benevolence/integrity), show that trust had a downstream effect on members' intentions to both give information and get information through the virtual community. Both these apparent dimensions of trust were increased through perceived responsive relationships in the virtual community, by a general disposition to trust, and by the belief that others confide personal information.

When Black + Lesbian + Woman ≠ Black Lesbian Woman: The Methodological Challenges of Qualitative and Quantitative Intersectionality Research

Abstract: The notion that social identities and social inequality based on ethnicity, sexual orientation, and sex/gender are intersectional rather than additive poses a variety of thorny methodological challenges. Using research with Black lesbians (Bowleg, manuscripts in preparation; Bowleg et al., Journal of Lesbian Studies, 2008; Bowleg et al., Cultural Diversity & Ethnic Minority Psychology 10:229–240, 2004; Bowleg et al., Journal of Lesbian Studies, 7:87–108, 2003) as a foundation, I examine how these challenges shape measurement, analysis, and interpretation. I argue that a key dilemma for intersectionality researchers is that the additive (e.g., Black + Lesbian + Woman) versus intersectional (e.g., Black Lesbian Woman) assumption inherent in measurement and qualitative and quantitative data analyses contradicts the central tenet of intersectionality: social identities and inequality are interdependent for groups such as Black lesbians, not mutually exclusive. In light of this, interpretation becomes one of the most substantial tools in the intersectionality researcher’s methodological toolbox.

Improving Wireless Physical Layer Security via Cooperating Relays

Abstract: Physical (PHY) layer security approaches for wireless communications can prevent eavesdropping without upper layer data encryption. However, they are hampered by wireless channel conditions: absent feedback, they are typically feasible only when the source-destination channel is better than the source-eavesdropper channel. Node cooperation is a means to overcome this challenge and improve the performance of secure wireless communications. This paper addresses secure communications of one source-destination pair with the help of multiple cooperating relays in the presence of one or more eavesdroppers. Three cooperative schemes are considered: decode-and-forward (DF), amplify-and-forward (AF), and cooperative jamming (CJ). For these schemes, the relays transmit a weighted version of a reencoded noise-free message signal (for DF), a received noisy source signal (for AF), or a common jamming signal (for CJ). Novel system designs are proposed, consisting of the determination of relay weights and the allocation of transmit power, that maximize the achievable secrecy rate subject to a transmit power constraint, or, minimize the transmit power subject to a secrecy rate constraint. For DF in the presence of one eavesdropper, closed-form optimal solutions are derived for the relay weights. For other problems, since the optimal relay weights are difficult to obtain, several criteria are considered leading to suboptimal but simple solutions, i.e., the complete nulling of the message signals at all eavesdroppers (for DF and AF), or the complete nulling of jamming signal at the destination (for CJ). Based on the designed relay weights, for DF in the presence of multiple eavesdroppers, and for CJ in the presence of one eavesdropper, the optimal power allocation is obtained in closed-form; in all other cases the optimal power allocation is obtained via iterative algorithms. Numerical evaluation of the obtained secrecy rate and transmit power results show that the proposed design can significantly improve the performance of secure wireless communications.