Sharp lower bounds on the extractable randomness from non-uniform sources

Extraction of uniform randomness from (noisy) non-uniform sources is an important primitive in many security applications, e.g. (pseudo-)random number generators, privacy-preserving biometrics, and key storage based on Physical Unclonable Functions. Generic extraction methods exist, using universal hash functions. There is a trade-off between the length of the extracted bit string and the uniformity of the string. In the literature there are proven lower bounds on this length as a function of the desired uniformity. The best known bound involves a quantity known as smooth min-entropy. Unfortunately, there exist at least three definitions of smooth entropy. In this paper we compare three of these definitions, and we derive improved lower bounds on the extractable randomness.We also investigate the use of almost universal hash functions, which are slightly worse at extracting randomness than universal hash functions, but are preferable in practice because they require far less resources in devices. We show that using them has negligible effect on the extractable randomness.     

Data collection and assessment of commonly consumed foods and recipes in six geo-political zones in Nigeria: Important for the development of a National Food Composition Database and Dietary Assessment

A cross-sectional study was undertaken to collect and assess commonly consumed foods/recipes from the six geopolitical zones in Nigeria for the production of food composition database (FCDB) for dietary assessment. Communities used were selected using a multi-stage sampling plan. Focus group discussions, interviews, recipe documentation, food preparations and literature reviews were employed. Qualitative methods were used to analyse and present data. SWOT (strengths, weaknesses, opportunities, and threats) analysis was used to evaluate the project. A total of 322 recipes were collected out of which 110 were soups. Food consumption patterns across the geographical zones were found to be changing. Variations in recipes and methods of preparation of similar foods were observed. Factors to be considered in the development of a country-specific FCDB were identified. There were challenges with the use of values reported in literature for Nigerian foods. The study justifies the need for a country-specific FCDB that will include traditional recipes.     

Study of the properties of solar cells based on a-Si:H p-i-n structures by admittance spectroscopy

Properties of solar cells based on a-Si:H p-i-n structures are studied by admittance spectroscopy. The responses of the density of states in the (i)a-Si:H layers and a-SiC:H layers in the p-type region of the structure are distinguished in the admittance spectra. The density of states in the middle of the mobility gap for (i)a-Si:H is estimated to be 5 × 10¹⁶ cm^?3 eV^?1. It is shown that this value increases during the course of photoinduced degradation to ～10¹⁷ cm^?3 eV^?1. For the wide-gap a-SiC:H layers, the observed response of the density of states in the valence-band tails made it possible to estimate the lower bound for the density of states at the Fermi level (10¹⁸ cm^?3 eV^?1) and to find the Fermi level position to be 0.4 eV above the valenceband edge. The suggested procedure can be used to optimize the design of solar cells in order to improve their efficiency.     

Interaction between single walled carbon nanotube and 1D crystal in CuX@SWCNT (X = Cl,Br, I) nanostructures

CuX@SWCNT (X = Cl, Br, I) nanostructures were prepared by capillary filling of 1.4–1.6 nm single-walled carbon nanotubes (SWCNT) with copper halides. The structure of CuX@SWCNT (X = Cl, Br, I) represents a distorted two-layer hcp of halogen atoms arranged along the SWCNT. The EXAFS and the high angle angular dark field (HAADF) HRTEM data indicate that Cu is partially coordinated by C. According to the optical absorption, valence band photoemission spectroscopy and work function measurements, a Fermi level (FL) downshift as compared with the initial value for the nanotubes and a corresponding charge transfer from the nanotubes to the 1D crystals is observed for CuX@SWCNT nanostructures. The FL shift increases in the sequence CuI < CuBr < CuCl due to an increase of the electron affinity for the halogen atoms. The XPS data confirm the acceptor effect of copper halides and indicate that metallic and semiconducting nanotubes behave differently. Raman spectroscopy performed under electrochemical charging allowed estimation of the value of charge transfer between the nanotube walls and the intercalated 1D crystal. The X-ray absorption and emission spectra for carbon and copper thresholds revealed a new energy level composed of the carbon 2р_z and copper 3d-orbitals. This indicates the Cu–C bonding, which in line with the structural HAADF HRTEM and EXAFS data.     

Kinetic Isotope Effect in the Hydrogenation and Deuteration of Graphene

Time‐dependent photoemission spectroscopy is employed to study the kinetics of the hydro‐genation/deuteration reaction of graphene. Resulting in an unusual kinetic isotope effect, the graphene deuteration reaction proceeds faster than hydrogenation and leads to substantially higher maximum coverages of deuterium (D/C≈35% vs H/C≈25%). These results can be explained by the fact that in the atomic state H and D have a lower energy barrier to overcome in order to react with graphene, while in the molecular form the bond between two atoms must be broken before the capture on the graphene layer. More importantly, D has a higher desorption barrier than H due to quantum mechanical zero‐point energy effects related to the C–D or C–H stretch vibration. Molecular dynamics simulations based on a quantum mechanical electronic potential can reproduce the experimental trends and reveal the contribution of the constituent chemisorption, reflection, and associative desorption processes of H or D atoms onto graphene. Regarding the electronic structure changes, a tunable electron energy gap can be induced by both deuteration and hydrogenation.     

Surface texture of single-crystal silicon oxidized under a thin V<Subscript>2</Subscript>O<Subscript>5</Subscript> layer

The process of surface texturing of single-crystal silicon oxidized under a V₂O₅ layer is studied. Intense silicon oxidation at the Si–V₂O₅ interface begins at a temperature of 903 K which is 200 K below than upon silicon thermal oxidation in an oxygen atmosphere. A silicon dioxide layer 30–50 nm thick with SiO₂ inclusions in silicon depth up to 400 nm is formed at the V₂O₅–Si interface. The diffusion coefficient of atomic oxygen through the silicon-dioxide layer at 903 K is determined (D ≥ 2 × 10^–15 cm² s^–1). A model of low-temperature silicon oxidation, based on atomic oxygen diffusion from V₂O₅ through the SiO₂ layer to silicon, and SiO _x precipitate formation in silicon is proposed. After removing the V₂O₅ and silicon-dioxide layers, texture is formed on the silicon surface, which intensely scatters light in the wavelength range of 300–550 nm and is important in the texturing of the front and rear surfaces of solar cells.     

Synthesis of random copolymers of styrene and arylamino substituted styrenes and their sensitivities towards nitroaromatics

Random copolymers of styrene and substituted styrenes bearing arylamino substituents as fluorophore units have been obtained. Their photophysical properties have been investigated by measuring absorption and emission spectra as in solutions as solid-state. All copolymers proved to possess absolute quantum yields up to 0.39 in solution and up to 0.05 in solid-state, depending on their fluorophore substituents. Fluorescence studies have shown that these copolymers show a highly sensitive response towards a diversity of nitroaromatic compounds, both in solutions and in a vapor phase. The detection limits for these compounds towards model nitroaromatic explosives in dichloromethane solution proved to be in the range from 10⁻⁶ to 10⁻⁷ mol/L. The fluorescent materials prepared by electrospinning of synthesized copolymers have been evaluated as sensor materials for detecting nitrobenzene vapor for our hand-made sniffer with detection limits of 0.5 ppm during 100-s exposure to the vapor.     

Nutrient and nutritional evaluation of sinasin prepared in two ways

Mutator mutants that show an increased frequency of spontaneous mutation have led to the elucidation of the multiple pathways of spontaneous mutagenesis. 8-Oxo-dGTP (8-oxo-7,8-dihydrodeoxyguanosine triphosphate) is formed in the nucleotide pool of a cell during normal cellular metabolism, and when it is incorporated into DNA causes mutation. MutT protein of Escherichia coli and related mammalian enzymes specifically degrade 8-oxo-dGTP to 8-oxo-dGMP, thereby preventing occurrence of transversion mutation. The gene encoding the human enzyme, designated MTH1 (for mutT homologue 1), maps to chromosome 7p22. These proteins may be responsible for genomic stability.     

The structure of 1D and 3D CuI nanocrystals grown within 1.5–2.5 nm single wall carbon nanotubes obtained by catalyzed chemical vapor deposition

Catalyzed chemical vapor deposition (CCVD) grown single wall carbon nanotubes (SWCNT) with diameter of D_m = 1.5–2.5 nm were used as templates to host one-dimensional nanocrystals of CuI. The CuI@SWCNT nanocomposite was obtained using capillary filling of preopened SWCNTs by CuI melt at 650 °C. Nanocomposite structural studies were performed on a FEI Titan 60–300 at 80 kV. According to the model and image simulation CuI crystallizes within 1.5–2.0 nm SWCNTs in the form of one-dimensional crystals with zinc blende or rock salt type unit cell connected by [0 0 1] edges and translated along 〈1 1 0〉. Copper cations occupy tetrahedral or octahedral sites in the lattice. In SWCNTs with D_m > 2.0 nm 3DCuI@SWCNTs were generated. The crystals of copper halides exhibit acceptor behavior as supported by Raman spectroscopy.