Cops and Robber Game Without Recharging

Cops & Robber is a classical pursuit-evasion game on undirected graphs, where the task is to identify the minimum number of cops sufficient to catch the robber. In this work, we consider a natural variant of this game, where every cop can make at most f steps, and prove that for each f≥2, it is PSPACE-complete to decide whether k cops can capture the robber.     

Polyethylene–Silica Nanocomposites with the Structure of Semi‐Interpenetrating Networks

Organic–inorganic nanocomposites with the structure of interpenetrating or semi‐interpenetrating networks are considered as advanced materials, since they have improved thermal and mechanical properties. An alternative approach to the preparation of such hybrid systems is proposed. It is based on the synthesis of silica from the precursor of hyperbranched polyethoxysiloxane by the hydrolytic condensation reaction in the volume of pores of a polymer matrix (bulk porosity is 40 vol%) stretched via the environmental crazing mechanism. Polyethylene–silica nanocomposites with the structure of semi‐interpenetrating networks when the content of silica is not less than 20–25 wt% are obtained. These composites can undergo an additional phase separation at a temperature of 160 °C (above the melting point of polyethylene), which is accompanied by an increase in the size of the polymer phase with the formation of macrophases. At the same time, the environment (orthophosphoric acid), in which the composite is heated, fills the pores that have appeared. As a result, the content of the third component with the new functionality increases up to 50 wt%, which allowed us to impart proton‐conducting properties to the composite material and preserve its shape stability.     

On-tip sub-micrometer Hall probes for magnetic microscopy prepared by AFM lithography

We developed a technology of sub-micrometer Hall probes for future application in scanning hall probe microscopy (SHPM) and magnetic force microscopy (MFM). First, the Hall probes of ∼9-μm dimensions are prepared on the top of high-aspect-ratio GaAs pyramids with an InGaP/AlGaAs/GaAs active layer using wet-chemical etching and non-planar lithography. Then we show that the active area of planar Hall probes can be downsized to sub-micrometer dimensions by local anodic oxidation technique using an atomic force microscope. Such planar probes are tested and their noise and magnetic field sensitivity are evaluated. Finally, the two technologies are combined to fabricate sub-micrometer Hall probes on the top of high-aspect ratio mesa for future SHPM and MFM techniques.     

Supercritical parametric wave phase conjugation as an instrument for narrowband analysis in ultrasonic harmonic imaging

Supercritical parametric wave phase conjugation (SWPC) is used for selection and phase conjugation of harmonic components of a nonlinear incident wave. The amplitude of the phase conjugate wave in a supercritical mode is high enough for acoustic nonlinearity of the propagation medium to appear. As a result, in particular, doubled and quadrupled frequencies of the incident wave become available for image formation at the same order of the medium nonlinearity. The improvement of the imaging system resolution because of harmonic analysis of the received acoustic signal and compensation of phase distortions caused by wave phase conjugation were observed simultaneously when the propagation medium was inhomogeneous.     

Approaches to Formaldehyde Measurement: From Liquid Biological Samples to Cells and Organisms

Formaldehyde (FA) is the simplest aldehyde present both in the environment and in living organisms. FA is an extremely reactive compound capable of protein crosslinking and DNA damage. For a long time, FA was considered a “biochemical waste” and a by-product of normal cellular metabolism, but in recent decades the picture has changed. As a result, the need arose for novel instruments and approaches to monitor and measure not only environmental FA in water, cosmetics, and household products, but also in food, beverages and biological samples including cells and even organisms. Despite numerous protocols being developed for in vitro and in cellulo FA assessment, many of them have remained at the “proof-of-concept” stage. We analyze the suitability of different methods developed for non-biological objects, and present an overview of the recently developed approaches, including chemically-synthesized probes and genetically encoded FA-sensors for in cellulo and in vivo FA monitoring. We also discuss the prospects of classical methods such as chromatography and spectrophotometry, and how they have been adapted in response to the demand for precise, selective and highly sensitive evaluation of FA concentration fluctuations in biological samples. The main objectives of this review is to summarize data on the main approaches for FA content measurement in liquid biological samples, pointing out the advantages and disadvantages of each method; to report the progress in development of novel molecules suitable for application in living systems; and, finally, to discuss genetically encoded FA-sensors based on existing natural biological FA-responsive elements.     

Green Lithography for Delicate Materials

A variety of unconventional materials, including biological nanostructures, organic and hybrid semiconductors, as well as monolayer, and other low-dimensional systems, are actively explored. They are usually incompatible with standard lithographic techniques that use harsh organic solvents and other detrimental processing. Here, a new class of green and gentle lithographic resists, compatible with delicate materials and capable of both top-down and bottom-up fabrication routines is developed. To demonstrate the excellence of this approach, devices with sub-micron features are fabricated on organic semiconductor crystals and individual animal's brain microtubules. Such structures are created for the first time, thanks to the genuinely water-based lithography, which opens an avenue for the thorough research of unconventional delicate materials at the nanoscale.     

Novel integrated helium extraction and natural gas liquefaction process configurations using absorption refrigeration and waste heat

Conceptual design and modeling of novel-integrated process configurations for helium extraction and natural gas liquefaction is investigated. Mixed fluid cascade (MFC) refrigeration system is considered for providing the needed refrigeration in the natural liquefaction section. Using an absorption refrigeration system as the precooling cycle is investigated in one of the introduced processes. Integrated flash and distillation method is used for helium extraction. Purity of the extracted crude helium is 50% (mole). Process streams operational condition and specifications of the devices are presented and explained. Composite curves of the heat exchangers demonstrate that thermal design has been done properly. Ratio of the power consumption to the produced liquefied natural gas (LNG) of the MFC process is 0.265 kWh per kg LNG and applying absorption refrigeration system instead of the pre-cooling cycle decreases it to 0.1849 kWh per kg LNG. For the modified process with absorption refrigeration system helium extraction rate and power consumption ratio are 0.951 and 132.9 (kWh/[kgmole Helium]) respectively. Exergy method is applied on the under consideration processes. The results show that the compressors have the highest rate of exergy destruction among the other process equipment. An extensive economic analysis is done on the proposed processes. The results show that prime cost of the product (US$/kg LNG) for MFC and modified MFC processes are 0.1939 and 0.2069, respectively. Finally, a sensitivity analysis is done based on the economic factors such as electrical energy price and prime cost of the product.