251 research outputs found
Non-contact method for measurement of the microwave conductivity of graphene
We report a non-contact method for conductivity and sheet resistance
measurements of graphene samples using a high Q microwave dielectric resonator
perturbation technique, with the aim of fast and accurate measurement of
microwave conductivity and sheet resistance of monolayer and few layers
graphene samples. The dynamic range of the microwave conductivity measurements
makes this technique sensitive to a wide variety of imperfections and
impurities and can provide a rapid non-contacting characterisation method.
Typically the graphene samples are supported on a low-loss dielectric
substrate, such as quartz, sapphire or SiC. This substrate is suspended in the
near-field region of a small high Q sapphire puck microwave resonator. The
presence of the graphene perturbs both centre frequency and Q value of the
microwave resonator. The measured data may be interpreted in terms of the real
and imaginary components of the permittivity, and by calculation, the
conductivity and sheet resistance of the graphene. The method has great
sensitivity and dynamic range. Results are reported for graphene samples grown
by three different methods: reduced graphene oxide (GO), chemical vapour
deposition (CVD) and graphene grown epitaxially on SiC. The latter method
produces much higher conductivity values than the others.Comment: 8 pages, 2 figures and 2 table
Nature behavioral responses, lipid profile and state of cardiovascular system in lead intoxication modelling on the background of hyperlipidemia in albino rats
The article describes the comparative study of the effect of lead intoxication in healthy animals and in terms of modelled hyperlipidemic condition on lipid metabolism, ECG performance, behavior in the test of the extrapolation of deliverance. The study was performed on 40 albino outbred adult male rats. Modeling hyperlipidemic condition was carried out daily by feeding natural unsalted fat at the rate of 8 grams per animal for 16 days. Lead intoxication was created after the atherogenic diet by adding lead acetate into drinking water in a dose of 50 mg/kg of body weight for 4 weeks. To investigate the lipid metabolism was measured in serum total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol. In the test of extrapolation deliverance 70 % of animals with lead intoxication on the lipid load background did not cope with the task versus 40 % of albino rats in the group with lead acetate exposure alone. All control animals successfully solved the problem of the deliverance test. The deterioration of the functioning of the cardiovascular system of rats with lead poisoning on the background of atherogenic diet was manifested by elongation of intraventricular conduction intervals on an electrocardiogram as compared with animals with lead intoxication alone. Disorders of lipid metabolism were manifested by increased levels of LDL cholesterol in rats with lead intoxication on the background of hyperlipidemia to 0.86 (0.69-1.14) mmol/l compared with the value of 0.67 (0.58-0.79) mmol/l in animals with lead intoxication
Affine spherical homogeneous spaces with good quotient by a maximal unipotent subgroup
For an affine spherical homogeneous space G/H of a connected semisimple
algebraic group G, we consider the factorization morphism by the action on G/H
of a maximal unipotent subgroup of G. We prove that this morphism is
equidimensional if and only if the weight semigroup of G/H satisfies some
simple condition.Comment: v2: title and abstract changed; v3: 16 pages, minor correction
Проточные методы, как общий подход к автоматизации химического анализа водных сред (обзор)
The article is devoted to the consideration of general approaches to automating the analysis of aqueous media, which are the main objects of chemical analysis including natural and waste waters, as well as technological media in various industries (microelectronics, biochemical industries, nuclear and thermal power engineering), which are the main consumers of high-purity water used for pre-start flushing of inline equipment to the required cleanliness of surfaces, for preparation of coolants that ensure the operation of nuclear and thermal power plants. In all these cases, the content of impurities in used or spent and intended for discharge aqueous media is strictly regulated. Changes in the content of impurities in controlled media often occur spontaneously due to equipment failure on the controlled objects. Prompt response to such changes and their timely elimination can be performed more efficiently if chemical and technological control of the normalized parameters of aqueous media of any named origin and destination is carried out in a continuous automatic, on-line, mode, which guarantees the exclusion of gaps or delays in obtaining information about equipment failure on a controlled facility in case of technological control or about unauthorized discharges of pollutants in case of environmental control. Possible methodological approaches to the development of systems for continuous chemical monitoring of quality or levels of contamination of aqueous media are considered on the basis of the above prerequisites, and applicability of various flow methods for these purposes is discussed in the order of their appearance in the arsenal of analytical chemists.Keywords: automation, chemical analysis, aqueous media, flow methods, continuous flow analysis, flow injection, cyclic injection, sequential injection.Предлагаемая статья посвящена рассмотрению общих подходов к автоматизации анализа водных сред, являющихся основными объектами химического анализа: природных и сбросных вод, а также технологических сред в различных областях промышленности: микроэлектронике, биохимических производствах, атомной и тепловой энергетике, являющихся главными потребителями воды высокой чистоты, необходимой для предпусковых промывок внутриконтурного оборудования до требуемых кондиций чистоты его поверхностей, для приготовления теплоносителей, обеспечивающих функционирование ядерно- и теплоэнергетических объектов. Во всех перечисленных случаях жестко регламентируется содержание примесей в используемых или отработанных и подлежащих сбросу водных средах. Поскольку изменение содержания примесей в контролируемых средах часто происходит спонтанно и связано с отказами в работе оборудования контролируемых объектов, для оперативного реагирования на них и для их своевременного устранения химико-технологический контроль нормируемых параметров водных сред любого из названных происхождения и назначения предпочтительно осуществлять в непрерывном автоматическом режиме on-line, гарантирующем исключение пропусков или задержек в получении информации об отказах оборудования в контролируемом объекте в случае технологического контроля или о несанкционированных сбросах загрязняющих веществ в случае экологического контроля. Исходя из этих предпосылок, рассматриваются возможные методические подходы к созданию систем непрерывного химического контроля качества или загрязненности водных сред, и обсуждается предпочтительность для этих целей различных вариантов проточных методов в порядке их появления в арсенале химиков-аналитиков.Ключевые слова: автоматизация, химический анализа, водные среды, проточные методы, непрерывный проточный анализ, проточно - инжекционный, циклический инжекционный, последовательный инжекционный
Pillar[5]arenes bearing amide and carboxylic groups as synthetic receptors for alkali metal ions
© ISUCT Publishing. Pillar[5]arenes bearing amide and carboxylic groups have demonstrated recognition performance for some representative alkali metal ions including Li + , Na + , K + and Cs + in series cations of s- and d-metals compared to pillar[5] arenes with hydroxyl, methoxy and acetone fragments. Their complexation abilities toward these cations were evaluated by UV–Vis technique. The complexation results revealed that pillar[5] arene, containing glicylglicyne groups, were the most efficient cation receptors for Li + , Na + , K + and Cs + over other synthesized and studied pillar[5]arenes. Introduction of long glycylglycide fragments into macrocycle structure allowed to increase the association constant logarithm in the case of Li + by 2 orders. In addition, in the set of macrocycles, incorporation of the additional amide fragments and carboxyl group into macrocycle structure leads to increasing the binding efficiency with alkali metal cations
Polyammonium derivatives of (thia)calix[4]arene: Synthesis and interaction with nucleic acids
© 2015 Nova Science Publishers, Inc. Targeted delivery of polynucleic acids in cells (transfection) for therapeutic purposesis limited by a number of obstacles, starting from the cell membrane to the geneexpression. To overcome the cell barriers, the use of gene carriers - viral and non-viralvectors are employed. One of the current approaches employed in the development ofsynthetic nonviral vectors is the functionalization of easily accessible molecularplatforms with receptor groups (amino, ammonium or guanidinium groups), capable ofinteracting with nucleic acids.In this chapter, we examine recent advances in the design and development ofsynthetic vectors, and the principles underlying their interactions with nucleic acids. Thefocus will be on recent advances in the design and synthesis of potential transfectionagents based on the (thia)calixarene platform functionalized with different polyaminofragments differing in the number of amino groups, the length of their alkyl linker chainsand the present or absent of hydroxy groups. The interaction of functionalized(thia)calixarene derivatives with DNA will also be discussed
Monoaminophosphorylated pillar[5]arenes as hosts for alkaneamines
© The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.For the first time, monofunctionalized pillar[5]arenes containing a 1-aminophosphonate fragment have been obtained and characterized. As shown by NMR spectroscopy, the replacement of the amino groups by 1-aminophosphonate units in the macrocycle structure allows switching of “self-assembling-host-guest complexation” properties of the monofunctionalized pillar[5]arenes. Thus, new synthesized aminophosphonated pillar[5]arenes form host-guest complexes with aliphatic amines contrary to monoamine macrocycles that tend to self-assemble
Dream in a mode of biological rhythms of student's youth
The healthy lifestyle of any person includes such important concepts as keeping of a mode of work and rest. For activity of a young organism importance of a dream represents special value. However in student's life as all of us know, it is very difficult to keep a constant sleep patternЗдоровый образ жизни любого человека включает такие немаловажные понятия как соблюдение режима труда и отдыха. Для жизнедеятельности молодого организма важность сна представляет особое значение. Однако, в студенческой жизни, как мы все знаем, очень трудно соблюдать постоянный режим сн
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