Absorption in the fractional quantum Hall regime: trion dichroism and spin polarization

We present measurements of optical interband absorption in the fractional quantum Hall regime in a GaAs quantum well in the range 0 < nu < 1. We investigate the mechanism of singlet trion absorption, and show that its circular dichroism can be used as a probe of the spin polarization of the ground state of the two-dimensional electron system (2DES). We find that at nu = 1/3 the 2DES is fully spin-polarized. Increasing the filling factor results in a gradual depolarization, with a sharp minimum in the dichroism near nu = 2/3. We find that in the range 0.5 < nu < 0.85 the 2DES remains partially polarized for the broad range of magnetic fields from 2.75 to 11 Tesla. This is consistent with the presence of a mixture of polarized and depolarized regions.Comment: 4 pages, 4 figures (Fig 4 is in color

Variation of electric shielding on virtual Frisch-grid detectors

Because of the low mobility of holes, CdZnTe (CZT) detectors operate as electron-transport-only type devices whose particular geometrical parameters and contacts configurations are specially chosen to minimize the contribution of uncollected holes into the output signal amplitudes (induction effect). Several detector configurations have been proposed to address this problem. One of them employs a large geometrical aspect ratio, parallelepiped-shaped crystal with two planar contacts on the top and bottom surfaces (anode and cathode) and an additional shielding electrode placed on a crystal\u27s side to create the virtual Frisch-grid effect. We studied the effect of the shielding electrode length, as well as its location, on the responses of 6 x 6 x 15 mm(3) virtual Frisch-grid detectors. We found that the length of the shielding electrode placed next to the anode can be reduced to 5 mm with no adverse effects on the device performance. Meanwhile, this allows for charge loss correction by reading the cathode signal

Microtomography developments on the ANATOMIX beamline at Synchrotron SOLEIL

The new ANATOMIX beamline at Synchrotron SOLEIL is dedicated to hard X-ray full-field tomography techniques. Operating in a range of photon energies from approximately 5 to 50 keV, it offers both parallel-beam projection microtomography and nanotomography using a zone-plate transmission X-ray microscope and thus covers a range of spatial resolution from 20 nm to 20 $\mu$m, expressed in terms of useful pixel size. Here we describe the microtomography instrumentation and its performance.Comment: Paper submitted for publication in the Proceedings of the 15th International Conference on X-Ray Microscopy (XRM 2020), 19--24 July 2020, Taipei, Taiwan, edited by D.-H. Wei and C.-M. Cheng and H.-W. Shiu and T.-H. Chuang, AIP Conf. Pro

Causal hierarchy within the thalamo-cortical network in spike and wave discharges

Background: Generalised spike wave (GSW) discharges are the electroencephalographic (EEG) hallmark of absence seizures, clinically characterised by a transitory interruption of ongoing activities and impaired consciousness, occurring during states of reduced awareness. Several theories have been proposed to explain the pathophysiology of GSW discharges and the role of thalamus and cortex as generators. In this work we extend the existing theories by hypothesizing a role for the precuneus, a brain region neglected in previous works on GSW generation but already known to be linked to consciousness and awareness. We analysed fMRI data using dynamic causal modelling (DCM) to investigate the effective connectivity between precuneus, thalamus and prefrontal cortex in patients with GSW discharges. Methodology and Principal Findings: We analysed fMRI data from seven patients affected by Idiopathic Generalized Epilepsy (IGE) with frequent GSW discharges and significant GSW-correlated haemodynamic signal changes in the thalamus, the prefrontal cortex and the precuneus. Using DCM we assessed their effective connectivity, i.e. which region drives another region. Three dynamic causal models were constructed: GSW was modelled as autonomous input to the thalamus (model A), ventromedial prefrontal cortex (model B), and precuneus (model C). Bayesian model comparison revealed Model C (GSW as autonomous input to precuneus), to be the best in 5 patients while model A prevailed in two cases. At the group level model C dominated and at the population-level the p value of model C was ∼1. Conclusion: Our results provide strong evidence that activity in the precuneus gates GSW discharges in the thalamo-(fronto) cortical network. This study is the first demonstration of a causal link between haemodynamic changes in the precuneus - an index of awareness - and the occurrence of pathological discharges in epilepsy. © 2009 Vaudano et al

Prevalence, Causes and Socio-Economic Determinants of Vision Loss in Cape Town, South Africa

PURPOSE: To estimate the prevalence and causes of blindness and visual impairment in Cape Town, South Africa and to explore socio-economic and demographic predictors of vision loss in this setting. METHODS: A cross sectional population-based survey was conducted in Cape Town. Eighty-two clusters were selected using probability proportionate to size sampling. Within each cluster 35 or 40 people aged 50 years and above were selected using compact segment sampling. Visual acuity of participants was assessed and eyes with a visual acuity less than 6/18 were examined by an ophthalmologist to determine the cause of vision loss. Demographic data (age, gender and education) were collected and a socio-economic status (SES) index was created using principal components analysis. RESULTS: Out of 3100 eligible people, 2750 (89%) were examined. The sample prevalence of bilateral blindness (presenting visual acuity <3/60) was 1.4% (95% CI 0.9-1.8). Posterior segment diseases accounted for 65% of blindness and cataract was responsible for 27%. The prevalence of vision loss was highest among people over 80 years (odds ratio (OR) 6.9 95% CI 4.6-10.6), those in the poorest SES group (OR 3.9 95% CI 2.2-6.7) and people with no formal education (OR 5.4 95% CI 1.7-16.6). Cataract surgical coverage was 68% in the poorest SES tertile (68%) compared to 93% in the medium and 100% in the highest tertile. CONCLUSIONS: The prevalence of blindness among people ≥50 years in Cape Town was lower than expected and the contribution of posterior segment diseases higher than previously reported in South Africa and Sub Saharan Africa. There were clear socio-economic disparities in prevalence of vision loss and cataract surgical coverage in this setting which need to be addressed in blindness prevention programs

Bacterial Delivery of Nuclear Proteins into Pluripotent and Differentiated Cells

Numerous Gram negative pathogens possess a type III secretion system (T3SS) which allows them to inject virulent proteins directly into the eukaryotic cell cytoplasm. Injection of these proteins is dependent on a variable secretion signal sequence. In this study, we utilized the N-terminal secretion signal sequence of Pseudomonas aeruginosa exotoxin ExoS to translocate Cre recombinase containing a nuclear localization sequence (Cre-NLS). Transient exposure of human sarcoma cell line, containing Cre-dependent lacZ reporter, resulted in efficient recombination in the host chromosome, indicating that the bacterially delivered protein was not only efficiently localized to the nucleus but also retained its biological function. Using this system, we also illustrate the ability of P. aeruginosa to infect mouse embryonic stem cells (mESC) and the susceptibility of these cells to bacterially delivered Cre-NLS. A single two-hour infection caused as high as 30% of the mESC reporter cells to undergo loxP mediated chromosomal DNA recombination. A simple antibiotic treatment completely eliminated the bacterial cells following the delivery, while the use of an engineered mutant strain greatly reduced cytotoxicity. Utility of the system was demonstrated by delivery of the Cre-NLS to induced pluripotent stem cells to excise the floxed oncogenic nuclear reprogramming cassette. These results validate the use of T3SS for the delivery of transcription factors for the purpose of cellular reprogramming

Mass Treatment with Azithromycin for Trachoma Control: Participation Clusters in Households

Trachoma, an infectious disease, continues to cause blindness. A great deal of the trachoma burden is concentrated in developing countries. The World Health Organization recommends mass treatment for entire communities in trachoma-endemic regions. In 32 Tanzanian and 48 Gambian communities with trachoma, mass treatment was directly observed following a census. Community coverage was mostly greater than 80%. Larger-than-expected proportions of households where all children were treated and where none of the children were treated were found in each country. Household clustering of treatment was higher in Tanzania compared to The Gambia. However, children who were not treated were not more likely to be infected compared to children who were treated. We found that treatment and non-treatment within communities does not occur at random but rather clusters within households. These findings impact the design of future coverage surveys and suggest that further research evaluate factors that are associated with familial non-compliance