Small animal PET image super-resolution using Tikhonov and modified total variation regularisation

Positron emission tomography (PET) is an imaging procedure used mainly in the diagnosis and treatment of diseases. PET is also used in the preclinical research studies of small animals. However, researchers may have difficulty interpreting the particularly low-resolution images obtained via this procedure. This paper presents a new method of increasing the resolution of PET images through the use of super-resolution techniques. Aside from being resistant to the noise and other degradations that plague PET images, our proposed algorithm is also capable of preserving important structures (e.g. lesions). To this end, the proposed objective function includes a term based on the modified total variation model which allows the user to preserve texture and to deal with noise without incurring the artefacts that typically arise when the total variation norm is used. The present study shows the effectiveness of the method in recovering structures and details and indicates that, in most cases, it outperforms other state-of-the-art methods.     

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.     

Computational fluid dynamic simulations of coal-fired utility boilers: An engineering tool

The objective of this study was to develop an engineering tool by which the combustion behavior of coals in coal-fired utility boilers can be predicted. We presented in this paper that computational fluid dynamic (CFD) codes can successfully predict performance of- and emission from- full-scale pulverized-coal utility boilers of various types, provided that the model parameters required for the simulation are properly chosen and validated. For that purpose we developed a methodology combining measurements in a 50 kW pilot-scale test facility with CFD simulations using the same CFD code configured for both test and full-scale furnaces. In this method model parameters of the coal processes are extracted and validated. This paper presents the importance of the validation of the model parameters which are used in CFD codes. Our results show very good fit of CFD simulations with various parameters measured in a test furnace and several types of utility boilers. The results of this study demonstrate the viability of the present methodology as an effective tool for optimization coal burning in full-scale utility boilers.     

Novel electrode materials based on ion beam induced deposition of platinum carbon composites

Untreated and thermally annealed platinum carbon (PtC) composites obtained by ion beam induced deposition (IBID) are physically and electrochemically characterized as novel patternable electrode materials. Energy dispersive X-ray spectroscopy (EDX) and Raman spectroscopy reveal that annealing in ambient atmosphere and at temperatures above 400 °C substantially reduces the amount of carbon within the deposited material. Raman spectra also show that at elevated temperatures carbon rearranges into a more structured graphitic-like phase. Atomic force microscopy (AFM) reveals that after the annealing procedure the surface structure appears more corrugated, while the dimensions of granular surface features decreases. Furthermore, it is shown that electrodes based on annealed PtC material show an improved heterogeneous electron transfer rate for the oxidation of potassium hexacyanoferrate(II) trihydrate by almost three orders of magnitude, whereas the reduction of hexaammineruthenium(III) trichloride proceeds at similar rates for both treated and untreated electrodes. The rate of electrochemical oxidation of H₂O₂, which is influenced by the composition of the electrode surface, is also improved at thermally annealed electrodes. Finally, cyclic voltammetry in sulfuric acid shows an increase in surficial platinum concentration after annealing of the material.     

Optimizing the Kinetics and Thermodynamics of DNA i‐Motif Folding

Under slightly acidic conditions, single cytidine‐rich DNA strands can form four‐stranded structures called i‐motifs. The stability of the i‐motif structure is based on the intercalation of hemiprotonated C–C⁺ base pairs. In addition, the stability of these structures is influenced by pH, temperature, salt concentration, number of cytidines per C‐rich stretch, and length of sequence; it also depends on the nucleotides in the connecting loop regions. Here, we investigated the influence of the loop nucleotides on i‐motif stability, structure, and kinetics of folding, in five structures with the same loop‐size but different adenosine and thymidine residues within the loop. The stabilities of the i‐motif structures were determined by CD melting, and structure and kinetics of folding were studied by static and time‐resolved NMR experiments.     

Unusual case of network polymer formation in anionic polymerization of monofunctional vinyl monomer

Summary Monofunctional monomers such as hydroxyalkyl (meth)acrylates can form crosslinked polymer in anionic polymerization. This unusual phenomenon relates to a plural reactivity of such type of monomers and their ability to be polymerized by the Michael addition mechanism with the formation of isomerized heterochain fragments of backbone as well as by anionic polymerization with the formation of carbon chain fragments of the main chain. This combination of reaction mechanisms results in the formation of highly branched polymer. Besides these reactions, simultaneous anionic polymerization of hydroxyalkyl (meth)acrylates, an intensive interchain exchange reaction leading to redistribution of the end functional groups and formation of polyester-ether di(meth)acrylate macromolecules result in crosslinking of the generated polymer.     

Decomposition of Fe5C2 catalyst particles in carbon nanofibers during TEM observation

The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe₃C). However, for Hägg carbide nanoparticles (χ-Fe₅C₂), explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and γ-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.     

Mineral Collecting in Russia

This brief survey of beryl, its crystallography and composition, its properties and special features, and its deposits, is based on the author's now out-of-print Emerald and Other Beryls (Chilton Book Co., 1981), to which the reader is referred for additional data and references to the extensive beryl literature as well as discussions of topics not undertaken herein. A shorter version of the above, edited by Peter G. Read, is entitled Beryl and is available from Butterworths Scientific Ltd.; it was published in 1986.     

Particle Adhesion to Drops

The adhesion of spheroidal particles to spherical drops is calculated and discussed in terms of an equilibrium-penetration index. The present study emphasizes the case of particles that are sufficiently large to affect the drop volume upon penetration. It is shown that the more elongated the particles, the steeper the dependence of the penetration index on the contact angle. The effect of line tension on nanoscale particles is considered. Positive line tensions increase the steepness of the dependence of penetration index on contact angle whereas negative line tensions decrease this dependence. In addition, the energy barrier caused by positive line tensions is presented and discussed.