Strong lensing constraints on the velocity dispersion and density profile of elliptical galaxies

We use the statistics of strong gravitational lensing from the CLASS survey to impose constraints on the velocity dispersion and density profile of elliptical galaxies. This approach differs from much recent work, where the luminosity function, velocity dispersion and density profile were typically {\it assumed} in order to constrain cosmological parameters. It is indeed remarkable that observational cosmology has reached the point where we can consider using cosmology to constrain astrophysics, rather than vice versa. We use two different observables to obtain our constraints (total optical depth and angular distributions of lensing events). In spite of the relatively poor statistics and the uncertain identification of lenses in the survey, we obtain interesting constraints on the velocity dispersion and density profiles of elliptical galaxies. For example, assuming the SIS density profile and marginalizing over other relevant parameters, we find 168 km/s < sigma_* < 200 km/s (68% CL), and 158 km/s < sigma_* < 220 km/s (95% CL). Furthermore, if we instead assume a generalized NFW density profile and marginalize over other parameters, the slope of the profile is constrained to be 1.50 < beta < 2.00 (95% CL). We also constrain the concentration parameter as a function of the density profile slope in these models. These results are essentially independent of the exact knowledge of cosmology. We briefly discuss the possible impact on these constraints of allowing the galaxy luminosity function to evolve with redshift, and also possible useful future directions for exploration.Comment: Uses the final JVAS/CLASS sample, more careful choice of ellipticals, added discussion of possible biases. Final results essentially unchanged. Matches the MNRAS versio

A determination of H_0 with the CLASS gravitational lens B1608+656: II. Mass models and the Hubble constant from lensing

EDITED FROM PAPER: We present mass models of the four-image gravitational lens system B1608+656. A mass model for the lens galaxies has been determined that reproduces the image positions, two out of three flux-density ratios and the model time delays. Using the time delays determined by Fassnacht et al. (1999a), we find that the best isothermal mass model gives H_0=59^{+7}_{-6} km/s/Mpc for Omega_m=1 and Omega_l=0.0, or H_0=(65-63)^{+7}_{-6} km/s/Mpc for Omega_m=0.3 and Omega_l = 0.0-0.7 (95.4% statistical confidence). A systematic error of +/-15 km/s/Mpc is estimated. This cosmological determination of H_0 agrees well with determinations from three other gravitational lens systems (i.e. B0218+357, Q0957+561 and PKS1830-211), SNe Ia, the S-Z effect and local determinations. The current agreement on H_0 from four out of five gravitational lens systems (i) emphasizes the reliability of its determination from isolated gravitational lens systems and (ii) suggests that a close-to-isothermal mass profile can describe disk galaxies, ellipticals and central cluster ellipticals. The average of H_0 from B0218+357, Q0957+561, B1608+656 and PKS1830-211, gives H_0(GL)=69 +/-7 km/s/Mpc for a flat universe with Omega_m=1 or H_0(GL)=74 +/-8 km/s/Mpc for Omega_m=0.3 and Omega_l=0.0-0.7. When including PG1115+080, these values decrease to 64 +/-11 km/s/Mpc and 68 +/-13 km/s/Mpc (2-sigma errors), respectively.Comment: Accepted for publication in ApJ. 34 pages, 4 figure

Interferometric Phase Calibration Sources in the Declination Range 0deg to -30deg

We present a catalog of 321 compact radio sources in the declination range 0deg > delta > -30deg. The positions of these sources have been measured with a two-dimensional rms accuracy of 35 milliarcseconds using the NRAO Very Large Array. Each source has a peak flux density >50 mJy at 8.4 GHz. We intend for this catalog to be used mainly for selection of phase calibration sources for radio interferometers, although compact radio sources have other scientific uses.Comment: 9 pages. To appear in ApJS. Catalog (Table 3) is abbreviated in printed version. Complete catalog available at ftp://ftp.aoc.nrao.edu/pub/staff/jwrobel/WPW2003_ApJS.tx

Fluctuating noise drives Brownian transport

The transport properties of Brownian ratchet was studied in the presence of stochastic intensity noise (SIN) in both overdamped and underdamped regimes. In the overdamped case, analytical solution using the matrix continued fraction method revealed the existence of a maximum current when the noise intensity fluctuates on intermediate time scale regions. Similar effects were observed for the underdamped case by Monte Carlo simulations. The optimal time-correlation for the Brownian transport coincided with the experimentally observed time-correlation of the extrinsic noise in Esherichia coli gene expression and implied the importance of environmental noise for molecular mechanisms.Comment: 22 pages, 8 figure

Guidelines for Sustainable Use of Mobile Instant Messaging Apps in Higher Education: A South African Case Study

Objective: The purpose of the study was to propose guidelines to facilitate the sustainable and successful use of mobile instant messaging apps for learning and teaching based on a review of the literature and perceptions of educators. Fraser’s model of redistribution, recognition, and representation served as the theoretical framework. This study provides a mechanism for the development of a socially just and inclusive online classroom environment. Method: We conducted two focus groups (n = 4 and n = 3) in November 2021 at a university of technology in South Africa to explore the perceptions of educators on using mobile instant messaging (MIM) apps for learning and teaching, to identify challenges, and to suggest solutions. The data were thematically coded and analyzed to detect themes using Saldana’s six-step process. Results: Sustainable and successful use of MIM apps for learning and teaching requires guidelines in three areas: practical management, privacy and security, and sustainable use. Key considerations include uniformity of use, student consultation, data control, operating hours, appointment of a chat moderator, language communication, access control, monitoring communication, regular feedback, and formalizing MIM app use through institutional policies. Conclusion: The proposed guidelines promote the sustainable and successful use of MIM applications in learning and teaching environments. The guidelines offer practical solutions to ensure that the use of MIM apps is ethical, inclusive, and effective in supporting student learning

Multiple-scale modeling of Pt effect on durability of aluminide coatings

The beneficial effect of Pt on the durability of aluminide coatings subjected to thermal cycling was studied by first-principles density functional theory (DFT) calculations, thermal physical analysis, atom diffusion simulation and mechanics-based modeling. This presentation will highlight these analytical approaches and research findings in three subject areas. First, the effect of doping elements (S, Pt, Cr, Y, Zr, Hf) on work adhesion, Wad, of the β-NiAl coating/Al2O3 scale interface was investigated. S was found to significantly reduce, while Y, Zr and Hf to largely increase Wad of the interface, with Pt having a minimal effect. The bonding characteristics of the interface associated with the elemental doping were used to explain the trend of Wad. Furthermore the X-S (X=Pt, Y, Zr, Hf) co-doping effects were also examined to elucidate the potential of these dopants in supressing the detrimental effects of S. Second, the beneficial effect of Pt on reducing the β-NiAl/Al2O3 interfacial tensile stress was assessed. The coefficients of thermal expansion (CTE) of Pt, β-NiAl and β-NiAl+Pt were obtained using DFT calculations and thermal physical formulas. The calculated CTE of the coatings, along with the experimentally measured CTE of Al2O3, were then incorporated to evaluate thermal cyclic tensile stress at the undulated β-NiAl/Al2O3 interface. The results showed that the addition of Pt to b-NiAl coating reduced the interfacial tensile stress, thus contributing to the improvement of thermal cyclic durability of the coating. This beneficial effect of Pt was more pronounced with a thicker oxide scale and a larger ratio of interfacial wave amplitude over wavelength. Third, the beneficial effect of Pt on lowering the diffusivity of S in b-NiAl coating was evaluated. The apparent activation energy and the pre-exponential factor of diffusivity via the next nearest neighbour (NNN) atom transportation as well as via interstitial jumps were analyzed, and the bonding characteristics of S with its surrounding atoms were calculated and compared with experimental results in the literature to elucidate the diffusion process of S. The addition of Pt in b-NiAl was found to significantly reduce the diffusivity of S, thus supressing the detrimental segregation of S to the β-NiAl coating/Al2O3 scale interface. Please click Additional Files below to see the full abstract

Gluconate Complexes of Cu(II) & Zn(II)

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