12 research outputs found
Stabilization of a wheels carrying communication satellite without angle and angular velocity sensors
No full textInvestigation of resonant phenomena in a locomotive wheelset on the basis of calculation of natural frequencies and modes of their oscillations on finite element models
No full textFrom the practice of engineering design it is known that in the development of mechanical systems, the operation of which is certainly not based on the phenomena of resonance, self-synchronization, etc., one should be wary of the proximity of the frequencies of free oscillations in such mechanical systems in different forms. Transient processes are dangerous due to the excitation of significant quantities of mechanical stresses and their damage to structures before destruction. This effect can also be appeared in wheel pairs (WS) of locomotives during operation. On the finite element model (FE) of the electric locomotive wheelset, calculations of natural frequencies and vibration modes are performed, the case of torsional oscillation frequencies with the participation of the electric drive gear and bending (saddle-shaped) oscillations of the running wheels is demonstrated, which can accelerate the processes of origin and development in its fatigue cracks. Paper discusses methodical issues of performing such calculations, problems of assessing the degree of danger of proximity of vibration frequencies of structural elements. The prototype of the finite-element model considered in the article was the WS of a locomotive with an asynchronous transmission, a one-way reducer and a composite retaining wheel. Methodical issues of performing such calculations, problems of assessing the degree of danger of proximity of vibration frequencies of structural elements are discussed. The results of calculations in combination with their visualization give a fairly complete idea of the behavior of the wheelset in the traction drive, while allowing studying the stress-strain state of its parts, and also providing an opportunity to identify the damaged elements and zones. It is highly advisable to carry out similar studies on virtual models when analyzing the operation of locomotive structures and assemblies under extreme operating conditions (for example, in case of boxing), which is not practicable or dangerous by experimental methods. It is possible, as shown, and it is necessary at the design stage of the WS to conduct its frequency analysis in the manner described in the article and, based on its results, perform a resonant detuning in a constructive or software way in the frequency range of the modulation of the operation of an asynchronous drive. To this end, by analogy with the AAR S-669 standard (USA), it is necessary to develop a domestic regulatory document for the projected locomotives with an asynchronous drive
Implementation of Phase Transitions in Rb3H(SO4)2 under K Substitution
No full textA series of solid acid compounds, representing the large family MmHn(AO4)(m + n)/2·yH2O (where M = K, Rb, Cs, NH4; AO4 = SO4, SeO4, HPO4, HAsO4), is characterized by high values of own proton conductivity, which arises as a result of a phase transition through the formation of a dynamically disordered hydrogen bond network. Such superprotonic phase transitions are observed, however, not for all compounds of the family and Rb3H(SO4)2 is one of them. The occurrence of superprotonic phase transitions has been experimentally demonstrated in the (KxRb1−x)3H(SO4)2 solid solutions through cation substitution. The high-temperature phases are unstable towards decomposition reaction, and their temperature range of existence is about 1–7 °C. The implementation of superprotonic transitions is discussed in terms of hydrogen bond lengths
МИКРОСПЕКТРАЛЬНОЕ РАМАНОВСКОЕ РАССЕЯНИЕ НА УПРУГИХ ДЕФОРМАЦИЯХ БАЛКИ КАНТИЛЕВЕРА
Get PDFFlexural elastic deformations of single-crystal silicon have been studied using microspectral Raman scattering. Results are reported on nano-scaled sign-changing shifts of the main peak of the microspectral Raman scattering within the single-crystal silicon cantilever beam during exposure to flexural stress. The maximum value of Raman shift characteristic of the silicon peak 518 cm-1 at which elasticity still remains, has been found to be 8 cm−1 which corresponds to an applied deformation of 4 GPa. We report three-dimensional maps of the distribution of internal stresses at different levels of deformation up to irreversible changes and brittle fracture of the samples that clearly show compression and tension areas and an undeformed area. A qualitative explanation of the increase in the strength of the cantilever beam due to its small thickness (2 μm) has been provided that agrees with the predictions of real-world physical parameters obtained in SolidWorks software environment with the SimulationXpress module. We have defined the relative strain of the beam surface which was 2% and received a confirmation of changes in the silicon lattice parameter from 5.4307Е to 5.3195Е by the BFGS algorithm
Investigation of resonant phenomena in a locomotive wheelset on the basis of calculation of natural frequencies and modes of their oscillations on finite element models
No full text
Leukaemia Incidence in Children and Adults in the Regions of Russia Most Highly Contaminated after the Chernobyl Nuclear Power Plant Accident
No full textABSTRACT
BACKGROUND Leukaemia, especially the acute types predominant in children, may be caused by ionizing radiation. After the Chernobyl Nuclear Power Plant accident on 26 April 1986, parts of Belarus, Russia and the Ukraine were contaminated with radionuclides. To date, over 270 000 people live in such contaminated regions in Russia. This study investigates whether the leukaemia incidence rates in these regions might have increased due to the radiation.
MATERIALS & METHODS A prospective population-based cohort study with a control group was carried out. Cases of leukaemia previously not registered were actively sought for in medical and administrative institutions. Each case that had occurred in the study regions between 1980 and 1998 has been ascertained and verified. A descriptive analysis was then performed on the resulting data base which included 333 leukaemia cases.
RESULTS There is a slight secular trend in the standardized incidence rates both in the highly contaminated and in the control regions. This increase, however, is more marked in the control regions. The incidence rates in children (0-14) in the highly contaminated regions decrease between the pre-accident (1980 to 1986) and the first post-accident period (1987-1992) and show a slight increase towards the second post-accident period (1993-1998), whereas the incidence rates in the control regions show exactly the opposite dynamic. This makes a connection between the dynamics of the incidence rates and the radiological situation highly improbable.
The comparative analysis of the leukaemia incidence rates has not revealed a statistically significant difference between the population of the highly contaminated regions of the Bryansk oblast and the combined control regions of the Kaluga oblast.
CONCLUSIONS There is so far no indication of an increase in leukaemia incidence rates in the general population, neither for children nor for adults. This does not contradict the current radiobiological knowledge that cancer, especially leukaemia, can be caused by ionizing radiation. The number of expected radiation-induced cases based on the risk estimates from the Japanese cohort lies within the 95% confidence limits of the spontaneous incidence rates. It would therefore, if at all present, not be statistically detectable in a population of 222 000 with a spontaneous rate of 5.4/100 000 in men and 3.3/100 000 in women in the control regions. Considering the latency periods and the age-dependent risk-curve of radiation-induced cancers, it is highly unlikely that a radiation-related increase in leukaemia or solid tumour incidence rates will become obvious in the future.
The fear and apprehension caused by the overestimation of the radiation risks create a continuous stress situation and add to the present detrimental health conditions in the population. It is therefore of utmost importance to communicate not only the results but also the reliability of the study and the soundness of the data to the affected people.ZUSAMMENFASSUNG
HINTERGRUND Leukämien, insbesondere die akuten Formen, die im Kindesalter vorherrschen, können durch radioaktive Strahlung induziert werden. Durch den Unfall in Tschernobyl am 26. April 1986 sind Teile von Belarus, Russland und der Ukraine radioaktiv kontaminiert worden. Bis heute leben in Russland über 270.000 Menschen in solchen kontaminierten Gebieten. Die vorliegende Studie untersucht, ob die Leukämieinzidenzen in diesen Gebieten aufgrund der radioaktiven Strahlung angestiegen sind.
MATERIAL & METHODEN Zu diesem Zweck wurde eine bevölkerungsbezogene, prospektive Kohortenstudie mit einer Kontrollgruppe durchgeführt. Jeder Leukämiefall der Jahre 1980-1998 aus den Studienregionen wurde genau nacherhoben und verifiziert. Zudem wurde aktiv in Krankenhäusern und Behörden nach nicht erhobenen Fällen gesucht. Die 333 Leukämiefälle, die sich letztendlich in der Datenbank befanden, wurden deskriptiv analysiert.
ERGEBNISSE Die standardisierten Inzidenzen zeigen über die Jahre einen leicht ansteigenden Trend, sowohl in den kontaminierten als auch in den Kontrollregionen. Dieser Anstieg ist ausgeprägter in den Kontrollregionen. Die Inzidenzen bei Kindern (0-14 Jahre) fallen in den kontaminierten Regionen zwischen der Periode 1980-86 und der Periode 1987-1992 ab und steigen dann in der Periode 1993-98 wieder leicht an, wohingegen die Inzidenzen in den Kontrollregionen genau die umgekehrte Dynamik zeigen. Dies macht einen Zusammenhang mit der radioaktiven Strahlung höchst unwahrscheinlich.
Die vergleichende Analyse zeigt keinen statistisch signifikanten Unterschied in den Inzidenzen zwischen den kontaminierten Regionen und den Kontrollregionen.
SCHLUSSFOLGERUNGEN Es gibt keinen Hinweis auf einen Anstieg der Leukämieraten in der Allgemeinbevölkerung, weder bei Kindern noch bei Erwachsenen. Dies widerspricht nicht der strahlenbiologischen Erkenntnis, dass Tumoren, insbesondere Leukämien, durch radioaktive Strahlung induziert werden können. Die mittels der Risikokoeffizienten aus den japanischen Studien errechnete Anzahl der strahleninduzierten Leukämiefälle liegt innerhalb der 95% Konfidenzintervalle der jährlichen Fluktuation der Spontanraten. Solch induzierte Fälle wären daher – falls vorhanden – bei einer exponierten Bevölkerung von ca. 222.000 und einer in den Kontroll-regionen beobachteten Spontanrate von 5,4/100.000 (Männer) bzw. 3,3/100.000 (Frauen) statistisch nicht nachweisbar. Bedenkt man die Latenzzeiten und die altersabhängige Risikostruktur strahleninduzierter Tumore, ist ein Anstieg sowohl der Leukämieraten als auch der Raten solider Tumore aufgrund des Reaktorunfalls in Tschernobyl in der Zukunft extrem unwahrscheinlich.
Die Ängste und Befürchtungen, die durch die Überschätzung der Risiken durch die radioaktive Strahlung entstanden sind, haben zu einer persistierenden Stresssituation für die Betroffenen geführt. Dieser Stress wirkt sich zusätzlich zu den aktuellen ökonomischen und sozialen Faktoren negativ auf die Gesundheit der Bevölkerung aus. Es ist daher wichtig, den Betroffenen nicht nur die Ergebnisse der vorliegenden Studie, sondern insbesondere auch die Qualität der zugrunde liegenden Daten glaubwürdig zu vermitteln
Мультифокальный атеросклероз в практике семейного врача: современный взгляд на проблему и результаты личных наблюдений
No full textМетою даного огляду є аналіз можливостей діагностики
мультифокального атеросклерозу (МФА) у практиці лікаря загальної практики–сімейної медицини з урахуванням
доступних у реальній клінічній діяльності діагностичних та
лікувальних стратегій, які базуються на даних доказової
медицини. На сьогодні не існує уніфікованого керівництва
з ведення пацієнтів з МФА. Зважаючи на важкі ускладнення МФА (інсульт, інфаркт міокарда, гострий тромбоз
периферичних артерій), його діагностика на ранніх
стадіях в осіб з факторами ризику є важливим кроком
профілактики. Для ефективної співпраці зі спеціалістами
лікарю загальної практики–сімейної медицини слід широко використовувати шкали стратифікації серцево-судинного ризику та методику оцінки претестової ймовірності
ІХС. На підставі даних літератури і власного досвіду узагальнено показання до додаткового обстеження та
хірургічного лікування пацієнтів з атеросклерозом різних
судинних басейнів.The aim of this review is to analyze the possibility of diagnostics of
multifocal atherosclerosis (MFA) in the practice of the General practitioner taking into account available in real clinical activity diagnostic and treatment strategies based on evidence1based medicine. At the
moment there are no standardized guidelines for the management of
patients with MFA. Considering the severe MFA complications
(stroke, myocardial infarction, acute thrombosis of peripheral arteries)
diagnostic of this disease in early stages in patients with risk factors is
an important step in the prevention of these complications. For effective cooperation with specialists General practitioner should be widely used scales of cardiovascular risk stratification and the methodology of pre-test probability of coronary heart disease. Based on the
analysis of literature data and own experience the indications for additional observation and surgical intervention treatment of patients with
atherosclerosis of different vessels are summarized.Целью данного обзора является анализ возможностей диагностики
мультифокального атеросклероза (МФА) в практике врачей общей практики–семейной медицины с учетом доступных в реальной
клинической деятельности диагностических и лечебных стратегий,
основанных на данных доказательной медицины. На данный момент не существует унифицированного руководства по ведению
пациентов с МФА. Ввиду грозных осложнений МФА (инсульт, инфаркт миокарда, острый тромбоз периферических артерий) его диагностика на ранних стадиях у лиц с факторами риска является
важным шагом в предотвращении этих осложнений. Для эффективного сотрудничества со специалистами врачам общей практики–семейной медицины следует широко использовать шкалы стратификации сердечно-сосудистого риска и методику претестовой
вероятности ишемической болезни сердца. На основании анализа
данных литературы и собственного опыта обобщены показания к
дополнительному обследованию и хирургическому лечению пациентов с атеросклерозом различных сосудистых бассейнов
Разработка композиции на основе полимочевины с увеличенным сроком жизни
Get PDFObjectives. Improvement of the technology for obtaining polymer-sprayed coatings based on polycarbodiimides (polyureas) with high chemical, hydrolytic, and abrasive resistance and improved physical and mechanical properties, as well as obtainment of polyurea compositions with a lifetime of at least 5 min without loss performance characteristics (i.e., “hand-applied” polyureas) suitable for repair of coatings already in use.Methods. The reaction rate between isocyanate and amino groups is almost a hundred times higher than that between isocyanate and hydroxyl groups, necessitating the use of special highperformance and high-pressure installations equipped with self-cleaning mixing chambers and heating of components. The following are determined from the obtained materials: strength, elongation at break according to the standard method, Taber abrasion, and Shore hardness.Results. Three methods of slowing down the reaction are investigated: 1) the synthesis of prepolymers with the content of NCO groups from 10.5% to 18%; 2) the addition of a plasticizer into the prepolymer in the amount of 1–10 mass parts; and 3) the introduction of polyesters into the composition and radiation of the so-called “hybrid” systems. When using 14% polyesters with a molecular weight of 2000 Da, only “hybrid” systems make it possible to obtain compositions with a lifetime of more than 5 min. At the same time, the tensile strength decreases by 20%, and the abrasion increases by 40%; however, such “hybrid” systems have a higher adhesion force and are cheaper than pure polyureas, allowing them to be used as “repair” systems.Conclusions. The developed composition and technology of applying “hybrid” systems allow for the repair of existing coatings without using specialized devices. “Manual” polyurea is easy to use and does not require special training. Цели. Совершенствование технологии получения полимерных напыляемых покрытий на основе поликарбодиимидов (полимочевин), с высокой химической, гидролитической и абразивной стойкостью и улучшенными физико-механическими показателями, а также, получение полимочевинных композиций с временем жизни не менее 5 мин без потери эксплуатационных характеристик (полимочевин «ручного» нанесения), пригодных для ремонта уже эксплуатирующихся покрытий.Методы. Скорость реакции между изоцианатными и аминогруппами практически в сто раз превышает скорость реакции между изоцианатными и гидроксильными группами, что вызывает необходимость использовать специальные высокопроизводительные установки высокого давления, оснащенные самоочищающимися смесительными камерами и обогревом компонентов. У полученных материалов определяли прочность, удлинение на разрыв по стандартной методике, истираемость по Таберу и твердость по Шору.Результаты. Исследованы три способа замедления реакции: во-первых, синтез предполимеров с содержанием NCO-групп от 10.5% до 18%; во-вторых, введение в предполимер пластификатора в количестве 1–10 масс.ч.; в-третьих, введение в композицию полиэфиров и получения «гибридных» систем. Показано, что только «гибридные» системы при использовании полиэфиров с молекулярной массой 2000 Да, в количестве 14% позволяют получить композиции с временем жизни более 5 мин. При этом прочность на разрыв снижается на 20%, истираемость увеличивается на 40%, но такие «гибридные» системы имеют более высокую силу адгезии и дешевле по сравнению с чистыми полимочевинами, что позволяет использовать их в качестве «ремонтных» систем.Выводы. Разработанный состав и технология нанесения «гибридных» систем позволяют производить ремонтные работы существующих покрытий без применения специализированных устройств. Полимочевина «ручного» нанесения удобна в эксплуатации и не требует специальной подготовки.
