Minimax approximation of a complex-valued function modulus by means of linear programming

© 2016 IEEE.The problem of approximating the complex-valued function modulus using a minimax criterion is of interest in many technical applications, such as standard process controlling systems with limiting the transient oscillations, low-side-lobe antenna arrays, or multiplexing devices having a deep channel isolation. The paper introduces approximate formulas to compute the absolute value of a complex number based on piecewise linear inequalities, thanks to which the approximation problem may be reduced to the minimax linear programming problem allowing the use of standard application packages. Computational experiments, the results of which are discussed, have proven the efficiency of the proposed computing algorithm combining high speed and good approximation accuracy

High surface area activated carbon prepared from wood-based spent mushroom substrate for supercapacitors and water treatment

Edible white-rot fungi are commonly cultivated on wood-based substrates and selectively degrade lignin to a larger extent during their growth. Spent mushroom substrate (SMS) is produced in huge amounts by the mushroom industry and today there is a lack of proven methods to valorize this kind of biomass waste, which in most cases is landfilled or used as fuel. This study demonstrates that birch wood-based SMS from the cultivation of oyster mushrooms can be converted into high-quality activated carbon (AC) with an extremely high surface area of about 3000 m2 /g. These activated carbons showed good performance when used in electrodes for supercapacitors, with energy storage parameters nearly identical to AC produced from high-quality virgin birch wood. Moreover, AC produced from SMS showed high potential as an adsorbent for cleaning reactive orange-16 azo dye from aqueous solutions as well as contaminants from synthetic effluents and from real sewage water. The kinetics of adsorption were well represented by the Avrami fractional order model and isotherms of adsorption by the Liu model. The theoretical maximum reactive orange-16 adsorption capacities were approximately 519 mg/g (SMS-based carbon) and 553 mg/g (virgin birch-based carbon). The removal of contaminants from synthetic effluents made of different dyes and inorganic compounds was around 95% and 83% depending on the effluent composition. The removal of contaminants from raw sewage water was around 84%, and from treated sewage water was around 68%. Overall, the results showed that activated carbon prepared from waste generated during cultivation of white-rot fungi is as good as activated carbon prepared from high-quality virgin wood

Covalent Organic Framework (COF-1) under High Pressure

COF-1 has a structure with rigid 2D layers composed of benzene and B3O3 rings and weak van der Waals bonding between the layers. The as-synthesized COF-1 structure contains pores occupied by solvent molecules. A high surface area empty-pore structure is obtained after vacuum annealing. High-pressure XRD and Raman experiments with mesitylene-filled (COF-1-M) and empty-pore COF-1 demonstrate partial amorphization and collapse of the framework structure above 12–15 GPa. The ambient pressure structure of COF-1-M can be reversibly recovered after compression up to 10–15 GPa. Remarkable stability of highly porous COF-1 structure at pressures at least up to 10 GPa is found even for the empty-pore structure. The bulk modulus of the COF-1 structure (11.2(5) GPa) and linear incompressibilities (k[100]=111(5) GPa, k[001]=15.0(5) GPa) were evaluated from the analysis of XRD data and cross-checked against first-principles calculations.\ua0\ua9 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei

Hydrogen storage in high surface area graphene scaffolds

Using an optimized KOH activation procedure we prepared highly porous graphene scaffoldmaterials with SSA values up to 3400m² g⁻¹ and a pore volume up to 2.2 cm³ gˉ¹, which are among the highest for carbon materials. Hydrogen uptake of activated graphene samples was evaluated in a broad temperature interval (77–296 K). After additional activation by hydrogen annealing the maximal excess H2 uptake of 7.5 wt% was obtained at 77 K. A hydrogen storage value as high as 4 wt% was observed already at 193 K (120 bar H₂), a temperature of solid CO₂, which can be easily maintained using common industrial refrigeration methods

О перспективе создания элементов памяти на основе наночастиц кремния

Phase-change memory is based on a change in the optical, electrical, or other properties of a substance during a phase transition, for example, transition from the amorphous to the crystalline state. Already realized and potential applications of such memory are associated with the use for this purpose of multicomponent alloys based on metals, semiconductors. However, single-component nanoparticles, including Si ones, are also of interest in view of the prospects for their use as nanoscale memory units. In particular, possibility of creating such memory units is confirmed by the fact that the bulk phase of the amorphous silicon has an optical absorption coefficient which is by an order of magnitude greater than that of the crystalline, although, it is difficult to release this effect for an individual nanoparticle whose size does not exceed the wavelength of light. In this work, using molecular dynamics (MD) and the Stillinger-Weber potential, we studied the laws of melting and conditions of crystallization for silicon nanoparticles containing up to 100,000 atoms. It has been shown that upon cooling a silicon nanodroplet at a rate of 0.2 TK/s and higher rates, its transition into the amorphous state takes place, whereas single-component metal nanodroplets crystallize even at cooling rates of 1 TK/s. Upon subsequent heating of amorphous silicon nanoparticles containing more than 50,000 atoms, they crystallize in the definite temperature range 1300—1400 K. It is concluded that it is principally possible to create memory units based on the above phase transitions. The transition of a nanoparticle to the amorphous state is achieved by its melting and subsequent cooling to the room temperature at a rate of 0.2 TK/s, and switching to the crystalline state is achieved by heating it to 1300—1400 K at a rate of 0.2 TK/s and subsequent cooling. On the basis of results of MD experiments, a conclusion is made that there exist a minimal size of silicon nanoparticles, for which producing memory units based on the change of the phase state, is not possible. It was found that for the temperature change rate of 0.2 TK/s, the minimal size in question 12.4 nm that corresponds to 50,000 atoms.Память, связанная с изменением фазового состояния (phase–change memory), основана на изменении оптических, электрических или иных свойств вещества при фазовом переходе, например переходе из аморфного состояния в кристаллическое. На сегодняшний день уже реализованные и потенциальные применения такой памяти связаны в первую очередь с использованием многокомпонентных сплавов на основе химических элементов, относящихся к металлам и полупроводникам. Однако однокомпонентные наночастицы, включая наночастицы Si, также представляют интерес в качестве перспективных наноразмерных элементов памяти. В частности, возможность создания таких элементов памяти подтверждается тем, что у объемной фазы аморфного кремния значение коэффициента оптического поглощения на порядок больше, чем у кристаллического. Разумеется, этот эффект затруднительно реализовать для отдельной наночастицы, размер которой не превышает длину волны света. В данной работе с использованием молекулярной динамики (МД) и потенциала Стиллинджера—Вебера исследованы закономерности плавления и условия кристаллизации наночастиц кремния, содержащих до 105 атомов. Показано, что при охлаждении нанокапель кремния со скоростью 0,2 ТК/с и выше имеет место их переход в аморфное состояние, тогда как однокомпонентные металлические нанокапли кристаллизуются в МД-экспериментах даже при скоростях охлаждения 1 ТК/с. При последующем нагреве аморфных наночастиц кремния, содержащих более 5 ∙ 104 атомов, происходит их кристаллизация в определенном температурном интервале от 1300 до 1400 К. Сделан вывод о принципиальной возможности создания элементов памяти, основанных на данных фазовых переходах. Переход наночастицы в аморфное состояние достигается путем ее плавления и последующего охлаждения до комнатной температуры со скоростью 0,2 ТК/с, а переключение в кристаллическое состояние — путем ее нагрева до 1300—1400 К со скоростью 0,2 ТК/с и последующего охлаждения. На основе результатов МД-экспериментов сделан вывод о существовании минимального размера наночастиц кремния, ниже которого при заданной скорости изменения температуры создание элементов памяти, основанных на изменении фазового состояния, становится принципиально невозможным. Установлено, что для скорости изменения температуры 0,2 ТК/с такой минимальный размер составляет 12,4 нм (число атомов — порядка 5 ∙ 104 атомов)

Activated carbons with extremely high surface area produced from cones, bark and wood using the same procedure

Activated carbons have been previously produced from a huge variety of biomaterials often reporting advantages of using certain precursors. Here we used pine cones, spruce cones, larch cones and a pine bark/wood chip mixture to produce activated carbons in order to verify the influence of the precursor on properties of the final materials. The biochars were converted into activated carbons with extremely high BET surface area up to similar to 3500 m(2) g(-1) (among the highest reported) using identical carbonization and KOH activation procedures. The activated carbons produced from all precursors demonstrated similar specific surface area (SSA), pore size distribution and performance to electrodes in supercapacitors. Activated carbons produced from wood waste appeared to be also very similar to "activated graphene" prepared by the same KOH procedure. Hydrogen sorption of AC follows expected uptake vs. SSA trends and energy storage parameters of supercapacitor electrodes prepared from AC are very similar for all tested precursors. It can be concluded that the type of precursor (biomaterial or reduced graphene oxide) has smaller importance for producing high surface area activated carbons compared to details of carbonization and activation. Nearly all kinds of wood waste provided by the forest industry can possibly be converted into high quality AC suitable for preparation of electrode materials

Применение Антитромбина-III при новой коронавирусной инфекции (Covid-19) в условиях экстракорпоральной мембранной оксигенации (клиническое наблюдение)

COVID-19 is a disease that, in addition to respiratory failure, leads to thrombosis and bleeding due to coagulation disorders. Extracorporeal membrane oxygenation (ECMO), required in cases of a deterioration of gas exchange function of the lungs, contributes to changes in blood coagulation indicators, which leads to an increased risk of hemorrhagic complications and thrombosis. In the article, a clinical case of a severe course of COVID-19 is reported, which required ECMO. During the treatment, antithrombin-III was used, which allowed avoiding life-threatening complications and successfully completing the procedure. COVID-19 является заболеванием, приводящим помимо дыхательной недостаточности к тромбозам и кровотечениям вследствие нарушений в системе гемостаза. Экстракорпоральная мембранная оксигенация (ЭКМО), требующаяся при снижении газообменной функции легких, вносит свой вклад в изменения показателей свертывания крови, что ведет к увеличению риска осложнений геморрагического характера и тромбозов. В статье представлен клинический случай тяжелого течения COVID-19, потребовавший проведения ЭКМО. В ходе лечения был использован Антитромбин-III, что позволило избежать жизнеугрожающих осложнений и успешно завершить процедуру.

Magnetic properties of carbon phases synthesized using high pressure-high temperature treatment

Two sets of samples were synthesized at 3.5 GPa near the point of C60 cage collapse at different annealing times. A clear structural transformation from mixture of C60 polymeric phases to graphite-like hard carbon phase was confirmed by X-ray diffraction and Raman spectroscopy. Magnetic force microscopy and superconducting quantum interference device were used to characterize the magnetic properties of the synthesized samples. We found that the sample preparation conditions used in this study are not suitable to produce bulk magnetic carbon.Comment: 26 pages, 7 figure

Особенности изменений показателей системы гемостаза при экстракорпоральной мембранной оксигенации у пациентов с новой коронавирусной инфекцией

Extracorporeal membrane oxygenation (ECMO) is a method that makes it possible to compensate for critical changes caused by acute respiratory failure, with the ineffectiveness of treatment with rigid modes of artificial lung ventilation (ventilator) in patients with acute respiratory distress syndrome in intensive care units. The search for the optimal state of the hemostasis system is one of the main tasks in the treatment of critical patients in ECMO conditions.The objective: to study changes in hemostatic parameters in patients with COVID-19 undergoing ECMO and determine the need for their correction.Subjects and Methods. According to the inclusion and exclusion criteria, 100 patients were included in the study: 72 men and 28 women aged 26 to 75 years old, the median age made 55 years [47; 60]. VV-ECMO was performed in all observations. In 100% of cases, the cause of respiratory failure which required VV-ECMO was COVID-19-associated pneumonia.Results. 49 episodes of hemorrhagic complications and 76 episodes of thrombotic complications were recorded from the 1st to the 7th day from the moment of ECMO initiation. We found that the chance of developing thrombosis decreased by an average of 0.3% with an increase in the activity of antithrombin-3 by 1%. A statistically significant association of thrombosis risk was also found for prothrombin and prothrombin time.Conclusion. During the first 7 days of ECMO, patients with COVID-19 demonstrate the increase in APTT, prothrombin time and a decrease in the number of platelets, prothrombin activity, and fibrinogen concentration. The risk of thrombosis in this group of patients significantly decreases with the increasing activity of antithrombin-3 and prothrombin and increases with rising need of the higher dose of unfractionated heparin. The tactics of restrictive anticoagulant therapy when using unfractionated heparin can be taken into account as a way to reduce the risk of thrombosis and requires further research.  Экстракорпоральная мембранная оксигенация (ЭКМО) является методом, который позволяет компенсировать критические изменения, вызванные острой дыхательной недостаточностью, при неэффективности лечения жесткими режимами искусственной вентиляции легких у пациентов с острым респираторным дистресс-синдромом в отделениях реанимации и интенсивной терапии. Поиск оптимального состояния системы гемостаза является одной из основных задач при лечении пациентов в критическом состоянии в условиях ЭКМО.Цель: изучение изменений показателей системы гемостаза у пациентов с COVID-19 в условиях ЭКМО с определением необходимости их коррекции.Материалы и методы. В соответствии с критериями включения и исключения в исследование вошло 100 пациентов: 72 мужчины и 28 женщин в возрасте от 26 до 75 лет, медиана 55 лет [47; 60]. Во всех наблюдениях проводили ЭКМО в вено-венозной конфигурации (ВВ-ЭКМО). Причиной развития дыхательной недостаточности, потребовавшей проведения ВВ-ЭКМО, являлась COVID-19-ассоциированная пневмония в 100% наблюдений.Результаты. С 1-х по 7-е сут с момента подключения ЭКМО зафиксировано 49 эпизодов геморрагических и 76 эпизодов тромботических осложнений. Выявлено, что шанс развития тромбоза уменьшался в среднем на 0,3% при увеличении активности антитромбина-3 на 1%. Статистически значимая ассоциация риска тромбоза характерна также для уровня протромбина и протромбинового времени.Заключение. Пациентам с COVID-19 в первые 7 дней проведения ЭКМО свойственны увеличение активированного частичного тромбопластинового времени, протромбинового времени и снижение числа тромбоцитов, активности протромбина, концентрации фибриногена. Риск тромбозов у пациентов данной группы статистически значимо снижается при увеличении активности антитромбина-3 и протромбина и повышается при возникновении необходимости увеличения дозы нефракционированного гепарина. Тактика рестриктивной антикоагулянтной терапии при использовании нефракционированного гепарина может быть принята во внимание как способ снижения риска тромбозов.