Probing onset of strong localization and electron-electron interactions with the presence of direct insulator-quantum Hall transition

We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator-quantum Hall transition with increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron-electron interaction effects to the observed transition in our study.Comment: 9 pages, 4 figure

Palmoplantar keratoderma along with neuromuscular and metabolic phenotypes in Slurp1-deficient mice.

Mutations in SLURP1 cause mal de Meleda, a rare palmoplantar keratoderma (PPK). SLURP1 is a secreted protein that is expressed highly in keratinocytes but has also been identified elsewhere (e.g., spinal cord neurons). Here, we examined Slurp1-deficient mice (Slurp1(-/-)) created by replacing exon 2 with β-gal and neo cassettes. Slurp1(-/-) mice developed severe PPK characterized by increased keratinocyte proliferation, an accumulation of lipid droplets in the stratum corneum, and a water barrier defect. In addition, Slurp1(-/-) mice exhibited reduced adiposity, protection from obesity on a high-fat diet, low plasma lipid levels, and a neuromuscular abnormality (hind-limb clasping). Initially, it was unclear whether the metabolic and neuromuscular phenotypes were due to Slurp1 deficiency, because we found that the targeted Slurp1 mutation reduced the expression of several neighboring genes (e.g., Slurp2, Lypd2). We therefore created a new line of knockout mice (Slurp1X(-/-) mice) with a simple nonsense mutation in exon 2. The Slurp1X mutation did not reduce the expression of adjacent genes, but Slurp1X(-/-) mice exhibited all of the phenotypes observed in the original line of knockout mice. Thus, Slurp1 deficiency in mice elicits metabolic and neuromuscular abnormalities in addition to PPK

Whole exome sequencing to identify genetic causes of short stature

BACKGROUND/AIMS: Short stature is a common reason for presentation to pediatric endocrinology clinics. However, for most patients, no cause for the short stature can be identified. As genetics plays a strong role in height, we sought to identify known and novel genetic causes of short stature. METHODS: We recruited 14 children with severe short stature of unknown etiology. We conducted whole exome sequencing of the patients and their family members. We used an analysis pipeline to identify rare non-synonymous genetic variants that cause the short stature. RESULTS: We identified a genetic cause of short stature in 5 of the 14 patients. This included cases of floating-harbor syndrome, Kenny-Caffey syndrome, the progeroid form of Ehlers-Danlos syndrome, as well as 2 cases of the 3-M syndrome. For the remaining patients, we have generated lists of candidate variants. CONCLUSIONS: Whole exome sequencing can help identify genetic causes of short stature in the context of defined genetic syndromes, but may be less effective in identifying novel genetic causes of short stature in individual families. Utilized in the clinic, whole exome sequencing can provide clinically relevant diagnoses for these patients. Rare syndromic causes of short stature may be underrecognized and underdiagnosed in pediatric endocrinology clinics

Percolation theory applied to measures of fragmentation in social networks

We apply percolation theory to a recently proposed measure of fragmentation $F$ for social networks. The measure $F$ is defined as the ratio between the number of pairs of nodes that are not connected in the fragmented network after removing a fraction $q$ of nodes and the total number of pairs in the original fully connected network. We compare $F$ with the traditional measure used in percolation theory, $P_{\infty}$, the fraction of nodes in the largest cluster relative to the total number of nodes. Using both analytical and numerical methods from percolation, we study Erd\H{o}s-R\'{e}nyi (ER) and scale-free (SF) networks under various types of node removal strategies. The removal strategies are: random removal, high degree removal and high betweenness centrality removal. We find that for a network obtained after removal (all strategies) of a fraction $q$ of nodes above percolation threshold, $P_{\infty}\approx (1-F)^{1/2}$. For fixed $P_{\infty}$ and close to percolation threshold ($q=q_c$), we show that $1-F$ better reflects the actual fragmentation. Close to $q_c$, for a given $P_{\infty}$, $1-F$ has a broad distribution and it is thus possible to improve the fragmentation of the network. We also study and compare the fragmentation measure $F$ and the percolation measure $P_{\infty}$ for a real social network of workplaces linked by the households of the employees and find similar results.Comment: submitted to PR

Wavelength Tunability of Ion-bombardment Induced Ripples on Sapphire

A study of ripple formation on sapphire surfaces by 300-2000 eV Ar+ ion bombardment is presented. Surface characterization by in-situ synchrotron grazing incidence small angle x-ray scattering and ex-situ atomic force microscopy is performed in order to study the wavelength of ripples formed on sapphire (0001) surfaces. We find that the wavelength can be varied over a remarkably wide range-nearly two orders of magnitude-by changing the ion incidence angle. Within the linear theory regime, the ion induced viscous flow smoothing mechanism explains the general trends of the ripple wavelength at low temperature and incidence angles larger than 30. In this model, relaxation is confined to a few-nm thick damaged surface layer. The behavior at high temperature suggests relaxation by surface diffusion. However, strong smoothing is inferred from the observed ripple wavelength near normal incidence, which is not consistent with either surface diffusion or viscous flow relaxation.Comment: Revtex4, 19 pages, 10 figures with JPEG forma

Recurrent 8q13.2-13.3 microdeletions associated with Branchio-oto-renal syndrome are mediated by human endogenous retroviral (HERV) sequence blocks

Background: Human endogenous retroviral (HERV) sequences are the remnants of ancient retroviral infection and comprise approximately 8% of the human genome. The high abundance and interspersed nature of homologous HERV sequences make them ideal substrates for genomic rearrangements. A role for HERV sequences in mediating human disease-associated rearrangement has been reported but is likely currently underappreciated. Methods and Results: In the present study, two independent de novo 8q13.2-13.3 microdeletion events were identified in patients with clinical features of Branchio-Oto-Renal (BOR) syndrome. Nucleotide-level mapping demonstrated the identical breakpoints, suggesting a recurrent microdeletion including multiple genes such as EYA1, SULF1, and SLCO5A1, which is mediated by HERV1 homologous sequences. Conclusions: These findings raise the potential that HERV sequences may more commonly underlie recombination of dosage sensitive regions associated with recurrent syndromes