A critical analysis of the UV-continuum slopes of high-redshift galaxies; no evidence (yet) for extreme stellar populations at z > 6

It has recently been reported that the faintest galaxies at z~6-7 display extremely blue UV continuum slopes, with a UV power-law index beta ~ -3. Such slopes are bluer than previously reported for any other galaxy population, and imply extinction-free, young, very low-metallicity stellar populations with a high ionizing photon escape fraction. Here we undertake a critical study of the evidence for such extreme values of beta, combining three new WFC3/IR-selected samples of galaxies spanning ~2 decades in UV luminosity over the redshift range z~4.5-8. We explore the impact of inclusion/exclusion of less robust high-z candidates, and use the varying depths of the samples to explore the effects of noise and selection bias. Simple data-consistency arguments suggest that artificially blue average values of beta can result when the analysis is extended into the deepest ~ 0.5-mag bin of these WFC3/IR-selected samples, regardless of the actual luminosity or z range probed. By confining attention to robust, well-detected high-z galaxy candidates, we find that the average value of beta is consistent with -2.05 +/- 0.10 for z=5-7, and -22 < M_UV < -18. We create and analyse a set of simulations which demonstrate that a bias towards artifically low/blue average values of beta is indeed expected when the UV slope analysis is extended towards the source detection threshold, and conclude that there is as yet no clear evidence for UV slopes significantly bluer than beta ~ -2, the typical value displayed by the bluest star-forming galaxies at more modest z. A robust measurement of beta for the faintest galaxies at z~7-8 remains a key observational goal, as it provides a fundamental test for high escape fractions from a potentially abundant source of reionizing photons. This goal is achievable with HST, but requires still deeper WFC3/IR imaging in the HUDF.Comment: 12 pages, 10 figures, minor modifications made to make arXiv version match the accepted/published MNRAS versio

Designer lipid-like peptides

A crucial bottleneck in membrane protein studies, particularly G-protein coupled receptors, is the notorious difficulty of finding an optimal detergent that can solubilize them and maintain their stability and function. Here we report rapid production of 12 unique mammalian olfactory receptors using short designer lipid-like peptides as detergents. The peptides were able to solubilize and stabilize each receptor. Circular dichroism showed that the purified olfactory receptors had alpha-helical secondary structures. Microscale thermophoresis suggested that the receptors were functional and bound their odorants. Blot intensity measurements indicated that milligram quantities of each olfactory receptor could be produced with at least one peptide detergent. The peptide detergents' capability was comparable to that of the detergent Brij-35. The ability of 10 peptide detergents to functionally solubilize 12 olfactory receptors demonstrates their usefulness as a new class of detergents for olfactory receptors, and possibly other G-protein coupled receptors and membrane proteins

Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3

The dielectric constant of the incipient ferroelectric EuTiO$_3$ exhibits a sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering of the Eu spins simultaneously appears, indicating coupling between the magnetism and dielectric properties. This may be attributed to the modification of the soft-phonon mode, $T_{1\mu}$, which is the main contribution to the large dielectric constant, by the Eu spins(7$\mu_B$ per Eu). By adding the coupling term between the magnetic and electrical subsystems as $-g\sum\limits_l {\sum\limits_{< {i,j}} {q_l^2}} \overrightarrow {S_i} \cdot \overrightarrow {S_j}$ we show that the variation of the frequency of soft-phonon mode depends on the spin correlation between the nearest neighbors Eu spins and is substantially changed under a magnetic field.Comment: 13 pages, 4 figure

Experimental evidence of thermal fluctuations on the X-ray absorption near-edge structure at the aluminum K-edge

After a review of temperature-dependent experimental x-ray absorption near-edge structure (XANES) and related theoretical developments, we present the Al K-edge XANES spectra of corundum and beryl for temperature ranging from 300K to 930K. These experimental results provide a first evidence of the role of thermal fluctuation in XANES at the Al K-edge especially in the pre-edge region. The study is carried out by polarized XANES measurements of single crystals. For any orientation of the sample with respect to the x-ray beam, the pre-edge peak grows and shifts to lower energy with temperature. In addition temperature induces modifications in the position and intensities of the main XANES features. First-principles DFT calculations are performed for both compounds. They show that the pre-edge peak originates from forbidden 1s to 3s transitions induced by vibrations. Three existing theoretical models are used to take vibrations into account in the absorption cross section calculations: i) an average of the XANES spectra over the thermal displacements of the absorbing atom around its equilibrium position, ii) a method based on the crude Born-Oppenheimer approximation where only the initial state is averaged over thermal displacements, iii) a convolution of the spectra obtained for the atoms at the equilibrium positions with an approximate phonon spectral function. The theoretical spectra so obtained permit to qualitatively understand the origin of the spectral modifications induced by temperature. However the correct treatment of thermal fluctuation in XANES spectroscopy requires more sophisticated theoretical tools

A molecular method to discriminate between mass-reared sterile and wild tsetse flies during eradication programmes that have a sterile insect technique component

Background The Government of Senegal has embarked several years ago on a project that aims to eradicate Glossina palpalis gambiensis from the Niayes area. The removal of the animal try-panosomosis would allow the development more efficient livestock production systems. The project was implemented using an area-wide integrated pest management strategy including a sterile insect technique (SIT) component. The released sterile male flies originated from a colony from Burkina Faso. Methodology/Principal Findings Monitoring the efficacy of the sterile male releases requires the discrimination between wild and sterile male G.p. gambiensis that are sampled in monitoring traps. Before being released, sterile male flies were marked with a fluorescent dye powder. The marking was however not infallible with some sterile flies only slightly marked or some wild flies contaminated with a few dye particles in the monitoring traps. Trapped flies can also be damaged due to predation by ants, making it difficult to discriminate between wild and sterile males using a fluorescence camera and / or a fluorescence microscope. We developed a molecular technique based on the determination of cytochrome oxidase haplotypes of G. p. gambiensis to discriminate between wild and sterile males. DNA was isolated from the head of flies and a portion of the 5' end of the mitochondrial gene cytochrome oxidase I was amplified to be finally sequenced. Our results indicated that all the sterile males from the Burkina Faso colony displayed the same haplotype and systematically differed from wild male flies trapped in Senegal and Burkina Faso. This allowed 100% discrimination between sterile and wild male G. p. gambiensis. Conclusions/Significance This tool might be useful for other tsetse control campaigns with a SIT component in the framework of the Pan-African Tsetse and Trypanosomosis Eradication Campaign (PATTEC) and, more generally, for other vector or insect pest control programs

Probiotics: Finding the Right Regulatory Balance

Some products marketed as drugs should be excused from Phase I trials, but safety and efficacy claims for dietary supplements should be more tightly regulated

Epidemiological surveys of camel trypanosomosis in Al-jouf, Saudi Arabia based on PCR and ELISA

Trypanosomosis due to Trypanosoma evansi (surra) is a major enzootic disease of the dromedary camel. The present study was conducted to determine the prevalence of camel trypanosomosis in the northern part of Saudi Arabia with different methods of diagnosis (ELISA, PCR) and to compare the results to whose obtained previously with Card Agglutination Test for Trypanosomiasis (CATT/T.evansi). A total of 195 blood samples and 118 serum samples were used for molecular and serological investigation respectively. After analyses, 25% (49/195) and 3% (4/118) samples were positive using PCR and ELISA respectively. The variability of trypanosomosis was highly significant to the factor moving, location, breed and clinical signs with PCR. The discrepancy between PCR, CATT test and ELISA is likely due to antibodies degradation on spotted papers maintained several weeks at ambient temperature. This is the first molecular diagnosis report which gives a picture of camel trypanosomosis in Al-jouf, Saudi Arabia

Role of local disorder in the dielectric response of BaTaO_2N

Short-range structural disorder of the high-κ dielectric BaTaO_2N is revealed by the analysis of the extended x-ray-absorption fine-structure (EXAFS) spectroscopy measured at the Ta L_III edge. Although previous neutron, x-ray, and electron diffraction studies have shown BaTaO_2N to crystallize in a centrosymmetric, cubic structure, these EXAFS spectra show a wide distribution of first shell Ta-(O,N) distances with further implications to nonuniformity of the existing octahedral distortions. A distortion model based upon a density functional theory energy minimization for a 4×4×4 supercell of BaTaO_2N was used to successfully interpret these EXAFS data. We find that structural distortions with very short correlation lengths exist in this material and that these distortions are consistent with the large dielectric permitivity of BaTaO_2N