Abstract
We present detailed modelling of the recently discovered, quadruply lensed quasar J0408−5354, with the aim of interpreting its remarkable configuration: besides three quasar images (A,B,D) ...around the main deflector (G1), a fourth image (C) is significantly reddened and dimmed by a perturber (G2) which is not detected in the Dark Energy Survey imaging data. From lens models incorporating (dust-corrected) flux ratios, we find a perturber Einstein radius 0.04 arcsec ≲ RE, G2 ≲ 0.2 arcsec and enclosed mass Mp(RE, G2) ≲ 1.0 × 1010 M⊙. The main deflector has stellar mass $\log _{10}(M_{\star }/\mathrm{M}_{{\odot }})=11.49^{+0.46}_{-0.32}$, a projected mass Mp(RE, G1) ≈ 6 × 1011 M⊙ within its Einstein radius RE, G1 = (1.85 ± 0.15) arcsec and predicted velocity dispersion 267–280 km s−1. Follow-up images from a companion monitoring campaign show additional components, including a candidate second source at a redshift between the quasar and G1. Models with free perturbers, and dust-corrected and delay-corrected flux ratios, are also explored. The predicted time-delays (ΔtAB = (135.0 ± 12.6) d, ΔtBD = (21.0 ± 3.5) d) roughly agree with those measured, but better imaging is required for proper modelling and comparison. We also discuss some lessons learnt from J0408−5354 on lensed quasar finding strategies, due to its chromaticity and morphology.
We measure the weak lensing masses and galaxy distributions of four massive galaxy clusters observed during the Science Verification phase of the Dark Energy Survey (DES). This pathfinder study is ...meant to (1) validate the Dark Energy Camera (DECam) imager for the task of measuring weak lensing shapes, and (2) utilize DECam's large field of view to map out the clusters and their environments over 90 arcmin. We conduct a series of rigorous tests on astrometry, photometry, image quality, point spread function (PSF) modelling, and shear measurement accuracy to single out flaws in the data and also to identify the optimal data processing steps and parameters. We find Science Verification data from DECam to be suitable for the lensing analysis described in this paper. The PSF is generally well behaved, but the modelling is rendered difficult by a flux-dependent PSF width and ellipticity. We employ photometric redshifts to distinguish between foreground and background galaxies, and a red-sequence cluster finder to provide cluster richness estimates and cluster–galaxy distributions. By fitting Navarro–Frenk–White profiles to the clusters in this study, we determine weak lensing masses that are in agreement with previous work. For Abell 3261, we provide the first estimates of redshift, weak lensing mass, and richness. In addition, the cluster–galaxy distributions indicate the presence of filamentary structures attached to 1E 0657−56 and RXC J2248.7−4431, stretching out as far as 1°(approximately 20 Mpc), showcasing the potential of DECam and DES for detailed studies of degree-scale features on the sky.
We report the observation and confirmation of the first group- and cluster-scale strong gravitational lensing systems found in Dark Energy Survey data. Through visual inspection of data from the ...Science Verification season, we identified 53 candidate systems. We then obtained spectroscopic follow-up of 21 candidates using the Gemini Multi-object Spectrograph at the Gemini South telescope and the Inamori-Magellan Areal Camera and Spectrograph at the Magellan/Baade telescope. With this follow-up, we confirmed six candidates as gravitational lenses: three of the systems are newly discovered, and the remaining three were previously known. Of the 21 observed candidates, the remaining 15 either were not detected in spectroscopic observations, were observed and did not exhibit continuum emission (or spectral features), or were ruled out as lensing systems. The confirmed sample consists of one group-scale and five galaxy-cluster-scale lenses. The lensed sources range in redshift z~ 0.80-3.2 and in i-band surface brightness i sub(SB)~ 23-25 mag arcsec super(-2)(2'' aperture). For each of the six systems, we estimate the Einstein radius theta sub(E) and the enclosed mass M sub(enc), which have ranges theta sub(E)~ 5''-9'' and M sub(enc)~ 8 x 10 super(12) to 6 x 10 super(13)M sub(middot in circle), respectively.
Lactate dehydrogenase from the malarial parasite
Plasmodium falciparum has many amino acid residues that are unique compared to any other known lactate dehydrogenase. This includes residues that ...define the substrate and cofactor binding sites. Nevertheless, parasite lactate dehydrogenase exhibits high specificity for pyruvic acid, even more restricted than the specificity of human lactate dehydrogenases M
4 and H
4. Parasite lactate dehydrogenase exhibits high catalytic efficiency in the reduction of pyruvate,
k
cat/
K
m=9.0×10
8 min
−1 M
−1. Parasite lactate dehydrogenase also exhibits similar cofactor specificity to the human isoforms in the oxidation of
l-lactate with NAD
+ and with a series of NAD
+ analogs, suggesting a similar cofactor binding environment in spite of the numerous amino acid differences. Parasite lactate dehydrogenase exhibits an enhanced
k
cat with the analog 3-acetylpyridine adenine dinucleotide (APAD
+) whereas the human isoforms exhibit a lower
k
cat. This differential response to APAD
+ provides the kinetic basis for the enzyme-based detection of malarial parasites. A series of inhibitors structurally related to the natural product gossypol were shown to be competitive inhibitors of the binding of NADH. Slight changes in structure produced marked changes in selectivity of inhibition of lactate dehydrogenase. 7-
p-Trifluoromethylbenzyl-8-deoxyhemigossylic acid inhibited parasite lactate dehydrogenase,
K
i=0.2
μM, which was 65- and 400-fold tighter binding compared to the M
4 and H
4 isoforms of human lactate dehydrogenase. The results suggest that the cofactor site of parasite lactate dehydrogenase may be a potential target for structure-based drug design.
Cholestane-derived gem-dihydroperoxides and tetraoxanes were synthesized starting from 5α- and 5β-cholestan-3-ones by acid-catalyzed addition of hydrogen peroxide to the ketone. They were ...characterized by IR, NMR, and mass spectroscopy analysis aided by molecular mechanics calculations, and, in the instance of 5β-cholestane-3α,3β-dihydroperoxide (
6
), by x-ray analysis. The synthesized compounds were tested in vitro against
Plasmodium falciparum Sierra Leone (D6) and Indochina (W2) malaria clones. All compounds were inactive to both clones, with the exception of tetraoxane
7a
, which exhibited modest activity toward D6 clone with IC
50 = 155 nM.
Context. Owing to their computational simplicity, models with elliptical potentials (pseudo-elliptical) are often used in gravitational lensing applications, in particular for mass modeling using ...arcs and for arc statistics. However, these models generally lead to negative mass distributions in some regions and to dumbbell-shaped surface density contours for high ellipticities. Aims. We revisit the physical limitations of the pseudo-elliptical Navarro-Frenk-White (PNFW) model, focusing on the behavior of the mass distribution close to the tangential critical curve, where tangential arcs are expected to be formed. We investigate the shape of the mass distribution on this region and the presence of negative convergence. We obtain a mapping from the PNFW to the NFW model with elliptical mass distribution (ENFW). We compare the arc cross section for both models, aiming to determine a domain of validity for the PNFW model in terms of its mass distribution and for the cross section. Methods. We defined a figure of merit to i) measure the deviation of the iso-convergence contours of the PNFW model to an elliptical shape, ii) assigned an ellipticity εΣ to these contours, iii) defined a corresponding iso-convergence contour for the ENFW model. We computed the arc cross section using the “infinitesimal circular source approximation”. Results. We extend previous work by investigating the shape of the mass distribution of the PNFW model for a broad range of the potential ellipticity parameter ε and characteristic convergence Ks. We show that the maximum value of ε to avoid dumbbell-shaped mass distributions is explicitly dependent on Ks, with higher ellipticities (ε ≃ 0.5, i.e., εΣ ≃ 0.65) allowed for small Ks. We determine a relation between the ellipticity of the mass distribution εΣ and ε valid for any ellipticity. We also derive the relation of characteristic convergences, obtaining a complete mapping from PNFW to ENFW models, and provide fitting formulae for connecting the parameters of both models. Using this mapping, the cross sections for both models are compared, setting additional constraints on the parameter space of the PNFW model such that it reproduces the ENFW results. We also find that the negative convergence regions occur far from the arc formation region and should therefore not be a problem for studies with gravitational arcs. Conclusions. We conclude that the PNFW model is well-suited to model an elliptical mass distribution on a larger ε–Ks parameter space than previously expected. However, if we require the PNFW model to reproduce the arc cross section of the ENFW well, the ellipticity is more restricted, particularly for low Ks. The determination of a domain of validity for the PNFW model and the mapping to ENFW models could have implications for the use of PNFW models for the inverse modeling of lenses and for fast arc simulations, for example.
Owing to their computational simplicity, models with elliptical potentials (pseudo-elliptical) are often used in gravitational lensing applications, in particular for mass modeling using arcs and for ...arc statistics. The authors revisit the physical limitations of the pseudo-elliptical Navarro-Frenk-White (PNFW) model, focusing on the behavior of the mass distribution close to the tangential critical curve, where tangential arcs are expected to be formed. They obtain a mapping from the PNFW to the NFW model with elliptical mass distribution (ENFW).They determine a relation between the ellipticity of the mass distribution epsilon capital sigma and epsilon valid for any ellipticity. They also derive the relation of characteristic convergences, obtaining a complete mapping from PNFW to ENFW models, and provide fitting formulae for connecting the parameters of both models. The determination of a domain of validity for the PNFW model and the mapping to ENFW models could have implications for the use of PNFW models for the inverse modeling of lenses and for fast arc simulations, for example.
Great advances have been made in developing rapid diagnostic tests (RDTs) for diagnosing malaria. To date, RDTs present an exceedingly practical format for malaria diagnosis that outperforms ...traditional microscopy and more experimental next generation devices in the development pipeline. However, although use of such tests is accepted in principle, their actual use has lagged. Furthermore, study of how these tests perform, what their limitations are, and how to work with these limitations to still use them effectively has stagnated. We propose that the study and implementation of such RDTs should be aggressively advanced and propose a series of questions that can guide efforts.
Lactate dehydrogenase, the terminal enzyme of anerobic Embden-Meyerhoff glycolysis, plays an important role in the carbohydrate metabolism of human malaria parasites. Based on the ability of malarial ...lactate dehydrogenase to use 3-acetylpyridine NAD as a coenzyme in a reaction leading to the formation of pyruvate from L-lactate, the enzymatic activity of fresh clinical isolates of Plasmodium falciparum and Plasmodium vivax was determined in relation to incubation time, asexual stages, and parasitemia and applied to a drug susceptibility assay. Lactate dehydrogenase activity was detectable at a parasitemia >0.4%, at a hematocrit of 1.5%, and increased with parasitemia. Maximal lactate dehydrogenase activity was generally observed between 36 and 48 hr, when the trophozoites and schizonts predominated. The results of the in vitro drug susceptibility assays based on the inhibition of lactate dehydrogenase activity and on the incorporation of tritium-labeled hypoxanthine were correlated. For an optimal performance against fresh clinical malaria isolates, however, the enzymatic assay requires an initial parasitemia between 1 and 2% at a hematocrit of 1.5%.
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