Modeling Delays of Microwave Transistors and Transmission Lines by the 2nd Order Bessel Function

At present, most of simulation programs can characterize gate delays of microwave transistors. However, the delay is mostly approximated by means of first-order differential equations. In the paper, a more accurate way is suggested which is based on an appropriate second-order differential equation. Concerning the transmission line delay, majority of the simulation programs use both Branin (for lossless lines) and LCRG (for lossy lines) models. However, the first causes extreme simulation times, and the second causes well-known spurious oscillations in the simulation results. In the paper, an unusual way for modeling the transmission line delay is defined, which is also based on the second-order Bessel function. The proposed model does not create the spurious oscillations and the simulation times are comparable with those obtained with the classical models. Properties of the implementation of the second-order Bessel function are demonstrated by analyses of both digital and analog microwave circuits

Constitutive description of creep behavior of Mg-4 Al-1Ca alloy

Creep behavior of an advanced magnesium alloy AX41 (4 wt.% Al, 1 wt.% Ca, Mg balanced) was investigated in temperature interval from 343 to 673 K and stresses from 2 to 200 MPa. Compressive creep experiments with stepwise loading were used in order to obtain stress dependence of the creep rate in interval from 10~9 to 10~3 iT 1 fo r a given temperature. All stress dependences can be well described by the Garofalo sinh relationship with natural exponent n = 5. An analysis ofthe parameters of this relationship has shown that lattice diffusion controls creep at all experimental conditions. While climb-controlled creep mechanism is decisive at lower stresses and higher temperatures, glide-controlled mechanisms act at higher stresses and lower temperatures. A typical power-law breakdown is observed at intermediate stresses and temperatures.Выполнены исследования ползучести оптимизированного магниевого сплава AX41 (4 вес.% Al, 1 вес.% Ca, Mg - баланс) в температурном диапазоне 343...673 K и уровнях напряжений 2...200 МПа. Были проведены испытания на ползучесть при ступенчатом нагружении сжимающей нагрузкой с целью определения зависимости скорости ползучести от напряжения в диапазоне 10-9...10-3 с-1 для данной температуры. Все вышеуказанные зависимости хорошо описывались уравнением Барафоло (типа sinh) с показателем степени n = 5. Анализ параметров этого уравнения показал, что ползучесть во всех проведенных экспериментах определяется диффузией решетки. При низких уровнях напряжений и высоких температурах определяющим является механизм восхождения, а при высоких уровнях напряжений и более низких температурах - механизм скольжения. В промежуточном диапазоне напряжений и температур наблюдается характерное отклонение экспериментальных точек от степенной зависимости

Constitutive description of creep behavior of Mg-4 Al-1Ca alloy

Creep behavior of an advanced magnesium alloy AX41 (4 wt.% Al, 1 wt.% Ca, Mg balanced) was investigated in temperature interval from 343 to 673 K and stresses from 2 to 200 MPa. Compressive creep experiments with stepwise loading were used in order to obtain stress dependence of the creep rate in interval from 10~9 to 10~3 iT 1 fo r a given temperature. All stress dependences can be well described by the Garofalo sinh relationship with natural exponent n = 5. An analysis ofthe parameters of this relationship has shown that lattice diffusion controls creep at all experimental conditions. While climb-controlled creep mechanism is decisive at lower stresses and higher temperatures, glide-controlled mechanisms act at higher stresses and lower temperatures. A typical power-law breakdown is observed at intermediate stresses and temperatures.Выполнены исследования ползучести оптимизированного магниевого сплава AX41 (4 вес.% Al, 1 вес.% Ca, Mg - баланс) в температурном диапазоне 343...673 K и уровнях напряжений 2...200 МПа. Были проведены испытания на ползучесть при ступенчатом нагружении сжимающей нагрузкой с целью определения зависимости скорости ползучести от напряжения в диапазоне 10-9...10-3 с-1 для данной температуры. Все вышеуказанные зависимости хорошо описывались уравнением Барафоло (типа sinh) с показателем степени n = 5. Анализ параметров этого уравнения показал, что ползучесть во всех проведенных экспериментах определяется диффузией решетки. При низких уровнях напряжений и высоких температурах определяющим является механизм восхождения, а при высоких уровнях напряжений и более низких температурах - механизм скольжения. В промежуточном диапазоне напряжений и температур наблюдается характерное отклонение экспериментальных точек от степенной зависимости

Compressive creep of Fe3Al-type iron aluminide with Zr additions

High-temperature creep ofa Fe3Al-type iron aluminide alloyed by zirconium was studied in the temperature range 873-1073 K. The alloy contained (wt.%) 31.5% Al, 3.5% Cr, 0.25% Zr, 0.19% C (Fe balance). It was tested in two states: (i) as received after hot rolling and (ii) heat treated (1423 K/ 2 h/air). Creep tests were performed in compression at constant load with stepwise loading: in each step, the load was changed to a new value after steady state creep rate had been established. Stress exponent and activation energy of the creep rate were determined and possible creep mechanisms were discussed in terms ofthe threshold stress concept. A rapidfall ofthe stress exponent and ofthe threshold stress with the increasing temperature indicates that creep is impeded by the presence of precipitates only at temperature 873 K. The results were compared with the results oflong-term creep tests in tension performed recently on the same alloy. Изучена высокотемпературная ползучестьИзучена высокотемпературная ползучесть алюминида железа типа Fe3Al, легирован­ного цирконием в диапазоне температур 873...1073 К. Сплав содержал (ат.%) 31,5 Al, 3,5 Сг, 0,25 Zг, 0,19 С (остальное Fе). Испытания проводили в двух состояниях: в состоя­нии поставки после горячей прокатки и после термообработки (1423 К/2 ч/воздух). Испытания на ползучесть выполняли при постоянной сжимающей нагрузке при сту­пенчатом нагружении: на каждой ступени использовали нагрузку другой величины после того, как наступала стадия установив­шейся скорости ползучести. Определена экс­понента напряжения и энергия активации для скорости ползучести, обсуждены возмож­ные механизмы ползучести с позиций кон­цепции порогового напряжения. Резкое умень­шение экспоненты напряжения и порогового напряжения при увеличении температуры свидетельствует о том, что наличие вторич­ных фаз снижает скорость ползучести толь­ко при температуре 873 К. Полученные ре­зультаты сравнивали с данными длительных испытаний на ползучесть при растяжении, выполненных на том же сплаве

Estimation of anisotropy of mechanical properties in Mg alloys by means of compressive creep tests

A detailed knowledge of dependence of mechanical properties on orientation in materials prepared by directional processes may present an important factor influencing the design of construction parts. Toward this end, the compressive creep testing of short specimens may be useful. Three different magnesium-based materials were subjected to this testing: (i) pure magnesium, (ii) magnesium matrix composite reinforced with 10 vol.% of titanium, and (iii) magnesium alloy WE54. All three materials were prepared through a powder metallurgical route with final hot extrusion. The specimensfor creep tests were cut in such a way that their longitudinal axis (i.e., the direction of compressive creep stress) and the axis of extruded bar contained a predestined angle. Two extreme cases can be observed: In pure Mg and in Mg-Ti composite, the dependence of the creep rate is very sensitive to the orientation especially at small inclinations from extrusion axis. The greatest creep resistance is observed in specimens with stress axis parallel to the extrusion axis, the lowest at declinationsfrom 45 to 90°. On the other hand, in WE54 no orientation dependence was observed. Possible explanations of the behaviour based on microstructural observations are discussed.Глубокое понимание зависимости механи­ческих свойств от ориентации волокон в материалах, полученных методами направ­ленного воздействия, может быть важным фактором в создании структурных элемен­тов. Исходя из этого, испытания коротких образцов на ползучесть при сжатии могут дать полезную информацию. Испытания проводили на трех различных материалах на основе магния: чистый магний; композит с магниевой матрицей, упрочненный 10 об.% титана; магниевый сплав WES4. Все три материала были получены методами порош­ковой металлургии и горячей экструзии. Образцы вырезали таким образом, чтобы их продольная ось (т.е. направление напряже­ния ползучести при сжатии) и ось экстру­дированного образца имели заданный угол. Для чистого магния и Mg-Ti композита за­висимость скорости ползучести существен­ но зависит от ориентации, особенно при не­ большом отклонении от оси экструзии. Наи­большее сопротивление ползучести имели образцы с осью напряжений, параллельной оси экструзии, наименьшее - при отклонении на 45°-90°. В сплаве WES4 не наблю­далось зависимости от ориентации. Подоб­ное поведение может быть связано с микро­структурой материала

Patient-Powered Research Networks of the Autoimmune Research Collaborative: Rationale, Capacity, and Future Directions

Patient-Powered Research Networks (PPRNs) are US-based registry infrastructures co-created by advocacy groups, patient research partners, academic investigators, and other healthcare stakeholders. Patient-Powered Research Networks collect information directly from patients to conduct and disseminate the results of patient-centered/powered research that helps patients make more informed decisions about their healthcare. Patient-Powered Research Networks gather and utilize real-world data and patient-reported outcomes to conduct comparative effectiveness, safety, and other research, and leverage the Internet to accomplish this effectively and efficiently. Four PPRNs focused on autoimmune and immune-mediated conditions formed the Autoimmune Research Collaborative: ArthritisPower (rheumatoid arthritis, spondyloarthritis, and other rheumatic and musculoskeletal diseases), IBD Partners (inflammatory bowel disease), iConquerMS (multiple sclerosis), and the Vasculitis PPRN (vasculitis). The Autoimmune Research Collaborative aims to inform the healthcare decision making of patients, care partners, and other stakeholders, such as clinicians, regulators, and payers. Illustrated by practical applications from the Autoimmune Research Collaborative and its constituent PPRNs, this article discusses the shared capacities and challenges of the PPRN model, and the opportunities presented by collaborating across autoimmune conditions to design, conduct, and disseminate patient-centered outcomes research

A schematic model for QCD at finite temperature

The simplest version of a class of toy models for QCD is presented. It is a Lipkin-type model, for the quark-antiquark sector, and, for the gluon sector, gluon pairs with spin zero are treated as elementary bosons. The model restricts to mesons with spin zero and to few baryonic states. The corresponding energy spectrum is discussed. We show that ground state correlations are essential to describe physical properties of the spectrum at low energies. Phase transitions are described in an effective manner, by using coherent states. The appearance of a Goldstone boson for large values of the interaction strength is discussed, as related to a collective state. The formalism is extended to consider finite temperatures. The partition function is calculated, in an approximate way, showing the convenience of the use of coherent states. The energy density, heat capacity and transitions from the hadronic phase to the quark-gluon plasma are calculated.Comment: 33 pages, 11 figure

Use of small specimen creep data in component life management: a review

Small specimen creep testing techniques are novel mechanical test techniques that have been developed over the past 25 years. They mainly include the sub-size uniaxial test, the small punch creep test, the impression creep test, the small ring creep test and the two-bar creep test. This paper outlines the current methods in practice for data interpretation as well as the state-of-the-art procedures for conducting the tests. Case studies for the use of impression creep testing and material strength ranking of creep resistant steels are reviewed along with the requirement for the standardisation of the impression creep test method. A database of small specimen creep testing is required to prove the validity of the tests