Consequences of radioactive pollution of forests in the zone affected by the accident at the Chernobyl power plant

The effect of forests on the radionuclide primary distribution in different components of the contaminated ecosystems is considered by the example of Chernobyl accident. A basic mathematical model is developed describing 137Cs biogeochemical cycling under conditions of quasi-steady state radionuclide redistribution in the ecosystem. The radionuclide fluxes between different ecosystem components are estimated. Forest ecosystems are proved to diminish radionuclide migration in the environment, and forest should be regarded as an important sanitary factor. The contribution of contaminated forests and forest products to the total irradiation dose to local population is estimated. Special countermeasures are elaborated in order to diminish unfavorable consequences of forest radioactive contamination. A long-term dynamics of radioactive situation in the forest ecosystems is forecasted and further studies on the subject are drafted.     

Cobalt-Catalyzed Green Cross-Dehydrogenative C(sp<Superscript>2</Superscript>)-H/P-H Coupling Reactions

Joined electrolysis of arenes (benzene or coumarin derivatives) and diethyl-H-phosphonate (EtO)₂P(O)H in the presence of [CoCl₂(bpy)] catalyst (5%) in an ethanol-aqueous solution in reductive conditions allows obtaining the desired products in a single step by aromatic C–H bonds phosphonation with yields up to 70%. The only by-product is hydrogen; the reaction proceeds at room temperature and does not require specially added reducing agents and oxidants or other initiators. Radical mechanism has been confirmed for the catalytic reaction proceeding via bicobalt phosphonates with Co–P bond, the structure of which also has been identified.     

Infrared tuneable up-conversion phosphor based on Er-doped nano-glass–ceramics

Up-conversion luminescence has been studied in the Er³⁺-doped oxyfluoride glass, its daughter nano-glass–ceramics and the polycrystalline ErF₃ when excited at infrared wavelengths of either 800 or 980 nm. The mechanism of the up-conversion luminescence is shown to differ for excitations at 800 and 980 nm since the different excited levels of the Er³⁺ are involved, respectively. An order of magnitude increase of red-to-green up-conversion luminescence ratio has been observed with nano-ceramming of the precursor glass when excited at 800 nm and a full dominance of the red up-conversion luminescence has been observed in the ErF₃ at the both excitation wavelengths. Observed changes in the spectra of the up-conversion luminescence from the precursor glass to its daughter nano-glass–ceramics provide a tool for tuning the colour of the up-conversion luminescence by ceramming of the precursor glass. These changes are shown to be due to decrease of the vibration energy of phonons coupled to the Er³⁺ ions embedded to the PbF₂ nano-crystals with nano-ceramming. Hence we report for the first time that the red up-conversion luminescence from the Er³⁺-doped material can be due to the radiative transition ⁴F_5/2, ⁴F_3/2 → ⁴I_13/2 of the Er³⁺ ion, which is principally allowed only in such a low-phonon energy host as the PbF₂ nano-crystals, while such red up-conversion luminescence is almost completely non-radiatively quenched in the oxyfluoride precursor glass. The up-conversion emission spectrum of the ErF₃ is dominated by a cross-relaxation mechanism typical of hosts with a very high doping level of the Er³⁺ ions.     

Improving on Linear Scan Register Allocation

Register allocation is a major step for all compilers. Various register allocation algorithms have been developed over the decades. This work describes a new class of rapid register allocation algorithms and presents experimental data on their behavior. Our research encourages the avoidance of graphing and graph-coloring based on the fact that precise graph-coloring is nondeterministic polynomial time-complete (NP-complete), which is not suitable for real-time tasks. In addition, practical graph-coloring algorithms tend to use polynomial-time heuristics. In dynamic compilation environments, their super linear complexity makes them unsuitable for register allocation and code generation. Existing tools for code generation and register allocation do not completely fulfill the require- ments of fast compilation. Existing approaches either do not allow for the optimization of register allocation to be achieved compre- hensively with a sufficient degree of performance or they require an unjustifiable amount of time and/or resources. Therefore, we pro- pose a new class of register allocation and code generation algorithms that can be performed in linear time. These algorithms are based on the mathematical foundations of abstract interpretation and the computation of the level of abstraction. They have been implemen- ted in a specialized library for just-in-time compilation. The specialization of this library involves the execution of common intermedi- ate language (CIL) and low level virtual machine (LLVM) with a focus on embedded systems.     

Cross-group secret sharing scheme for secure usage of cloud storage over different providers and regions

With the spread of the Internet, more and more data are being stored in the cloud. Here the technique of secret sharing can be naturally applied in order to provide both security and availability of the stored data, hereby reducing the risks of data leakage and data loss. The privacy property of secret sharing ensures protection against unauthorized access, while protection against data loss may be attained by distributing shares to the servers located in different regions. However, there is still a problem: If we naively employ the secret sharing technique without regarding to whom the cloud servers belong, a dishonest provider can obtain the secret data by collecting enough shares from its servers. In this scenario, there is a need to distribute shares over cloud services operated by different providers. In this paper, we propose a simple secret sharing technique, a cross-group secret sharing (CGSS), which is suitable for storing the data on cloud storage distributed over different groups—that is, different providers and regions. By combining an \(\ell \)-out-of-m threshold secret sharing scheme with a k-out-of-n threshold secret sharing scheme using a symmetric-key encryption scheme, we construct the CGSS scheme that forces k shares to be collected from \(\ell \) groups. Compared with the previous works, our scheme attains the functionality with reasonable computation. We also formalize the problem of allocating shares over different providers and regions as an optimization problem and show the design principles, which one must follow, when applying our proposal in practical settings. An experiment on real IaaS systems shows effectiveness of our proposed scheme, CGSS.     

Color mixing in the metering zone of a single screw extruder: Numerical simulations and experimental validation

We present numerical simulations for an acrylonitrile‐butadiene‐styrene copolymer (ABS) resin extrusion in an industrial conventional single‐screw extruder. Based upon the flow field patterns obtained in the simulations, a particle tracking procedure was employed to obtain information about the spatial distribution of particle tracers of two colors. Results of the simulation were compared with experimental data obtained under similar extrusion conditions. To evaluate the degree of color mixing and color homogeneity for the system, we employ a specific index calculated based upon the Shannon entropy for two species populations. POLYM. ENG. SCI., 45:1011–1020, 2005. © 2005 Society of Plastics Engineers     

NMR microimaging of fluid flow in model string-type reactors

Magnetic resonance microimaging (MRM) was employed to obtain quantitative velocity maps of water flowing in the channels possessing unconventional cross-section shapes formed by a bundle of parallel fibers within a tubular string-type reactor. The maps obtained demonstrate the presence of large amounts of an almost stagnant liquid in the stretched corners of the cross-sections representing distorted triangles or squares. This fact together with the irregularity of the filaments packing in the model string-type reactor was demonstrated to lead to a broad residence time distributions (RTDs) for liquid flow. Next, the pulsed field gradient NMR (PFG NMR) technique was employed to compare transport of water with that of butane gas in the same model string-type reactor. The experimentally measured average propagators (travel distance probability density functions) have demonstrated that Taylor dispersion can lead to much better RTDs for gas as compared to liquid in channels with sub-millimeter equivalent diameters. The PFG NMR data were compared with the RTD obtained using the conventional tracer time-of-flight transient response method. It is concluded that due to the differences in the quantities actually measured by the two techniques, and the significant differences in the measurement length scales (microns to 1-2 cm for NMR/MRM, tens of centimeters for transient response methods), there is no reliable way of directly comparing these results. The information obtained by NMR/MRM and more conventional techniques such as time-of-flight should be considered as complementary. In particular, NMR/MRM can reveal the reasons for the observed overall reactor performance by providing access to the transport processes on short length scales inside the reactor and by revealing structure-transport interrelations.