Titus Quinctius Flamininus: Imperialism and the pursuit of auctoritas

In the early second century BC, Rome built an empire that encompassed the Western Mediterranean basin and most of the Italic Peninsula. The necessity of using manpower provided by Italian treaties, the desire for economic gain, the differing treatment of Eastern and Western peoples, and especially, the political competition among the nobiles all created the Roman imperialistic war-machine. Growth had its consequences, though, as the Hannibalic War diminished the number of qualified generals, which allowed younger men to assume command of the legions. These circumstances allowed Titus Quinctius Flamininus to rise swiftly through the ranks of Roman Republican politics and develop a highly successful career by exploiting the elements of Roman imperialism. As Rome entered into a new stage of imperialistic development, Flamininus took advantage of the new situation, as Scipio had before him, to create a successful career. In accordance with standard cultural practices, Flamininus unerringly pursued auctoritas and personal benefit from the outset of his career. Throughout the Second Macedonian and Spartan Wars he manipulated military and political scenarios to retain his command and settle those conflicts before another ambitious Roman could steal his glory. Following his martial exploits, Flamininus continued to compete for political preeminence through his diplomatic work in Greece prior to the Syrian War. After serving as censor, however, Flamininus wisely curtailed his political activity to prevent himself from being the object of jealous rivals. Titus Quinctius Flamininus stands as a notable figure in Roman imperialistic history, whose involvement in Greece helped to continue the expansion of the fledgling empire. His actions in the East have been interpreted as being motivated by philhellenism and duty to allies among other reasons, but Flamininus found his motivation from the desire to effectively compete and succeed within the politico-cultural setting of the middle Republic

Large Signal Performance of the Gallium Nitride Heterostructure Field-Effect Transistor With a Graphene Heat-Removal System

The self-heating effect exerts a considerable influence on the characteristics of high-power electronic and optoelectronic devices based on gallium nitride. An extremely non-uniform distribution of the dissipated power and a rise in the average temperature in the gallium nitride heterostructure field-effect transistor lead to the formation of a hot spot near the conductive channel and result in the degradation of the drain current, power gain and device reliability. The purpose of this work is to design a gallium nitride heterostructure field-effect transistor with an effective graphene heat-removal system and to study using numerical simulation the thermal phenomena specific to it. The object of the research is the device structure formed on sapphire with a grapheme heat-spreading element placed on its top surface and a trench in the passivation layer filled with diamond grown by chemical vapor deposition. The subject of the research is the large signal performance quantities. The simulation results confirm the effectiveness of the heat-removal system integrated into the heterostructure field-effect transistor and leading to the suppression of the self-heating effect and to the improvement of the device performance. The advantage of our concept is that the heat-spreading element is structurally connected with a heat sink and is designed to remove the heat immediately from the maximum temperature area through the trench in which a high thermal conductivity material is deposited. The results of this work can be used by the electronics industry of the Republic of Belarus for developing the hardware components of gallium nitride power electronics.The self-heating effect exerts a considerable influence on the characteristics of high-power electronic and optoelectronic devices based on gallium nitride. An extremely non-uniform distribution of the dissipated power and a rise in the average temperature in the gallium nitride heterostructure field-effect transistor lead to the formation of a hot spot near the conductive channel and result in the degradation of the drain current, power gain and device reliability. The purpose of this work is to design a gallium nitride heterostructure field-effect transistor with an effective graphene heat-removal system and to study using numerical simulation the thermal phenomena specific to it. The object of the research is the device structure formed on sapphire with a grapheme heat-spreading element placed on its top surface and a trench in the passivation layer filled with diamond grown by chemical vapor deposition. The subject of the research is the large signal performance quantities. The simulation results confirm the effectiveness of the heat-removal system integrated into the heterostructure field-effect transistor and leading to the suppression of the self-heating effect and to the improvement of the device performance. The advantage of our concept is that the heat-spreading element is structurally connected with a heat sink and is designed to remove the heat immediately from the maximum temperature area through the trench in which a high thermal conductivity material is deposited. The results of this work can be used by the electronics industry of the Republic of Belarus for developing the hardware components of gallium nitride power electronics

Mobility of a two-dimensional electron gas in the AlGaN/GaN heterostructure: simulation and analysis

At temperatures higher than the room temperature, a two-dimensional electron gas (2DEG) formed at the AlGaN/GaN heterointerface can be characterized by the three dominant scattering mechanisms: acoustic deformation potential, polar acoustic phonon and polar optical phonon scatterings. An analytical model describing the 2DEG mobility limited by these scattering mechanisms as a function of the carrier concentration and the temperature was developed and integrated into a device simulator package using a C language interpreter. The model should be useful for heterostructure device simulators such as Blaze

Эксплуатационные характеристики транзистора с высокой подвижностью электронов на основе нитрида галлия с теплоотводящими элементами на основе нитрида бора

A local thermal management solution for high electron mobility transistors based on GaN was developed using a BN layer as a heat-spreading element. The thermally conducting and electrically insulating nature of BN allows it to be placed close to the active area and to be in direct contact with the electrodes and the heat sink, thus introducing an additional heat-escaping route. The numerical simulations of a GaN high electron mobility transistor with the BN heat-spreading element revealed the improvement in the DC, breakdown, small-signal AC and transient characteristics. In case of sapphire substrate, the maximum temperature in the device structure operating at a power density of 3.3 W/mm was reduced by 82.4 °C, while the breakdown voltage at a gate-source voltage of 2 V was increased by 357 V. The cut-off frequency and the maximum oscillation frequency at a gate-source voltage of 6 V and a drain-source voltage of 30 V were enhanced by 1.38 and 1.49 times, respectively. We suppose that the proposed thermal management method can be adapted to other high-power devices.Предлагается метод уменьшения влияния эффекта саморазогрева в транзисторах с высокой подвижностью электронов на основе нитрида галлия, который заключается в использовании слоя нитрида бора в качестве теплоотводящего элемента. Высокая теплопроводность и низкая электрическая проводимость нитрида бора позволяют располагать слой на его основе вблизи активной области и находиться в плотном контакте с электродами и теплопоглощающим элементом, формируя таким образом дополнительный канал для отведения избыточного тепла. Результаты численного моделирования транзистора с высокой подвижностью электронов на основе нитрида галлия с теплоотводящим элементом на основе нитрида бора указывают на улучшение электрических, частотных и переходных характеристик, увеличение напряжения пробоя. В случае сапфировой подложки максимальная температура в структуре прибора, работающего на уровне 3,3 Вт/мм, снижается на 82,4 °С, при этом напряжение пробоя, рассчитанное при напряжении затвор-исток 2 В, повышается на 357 В. Граничная частота и максимальная частота генерации, определенные при напряжении затвор-исток 6 В и напряжении сток-исток 30 В, увеличиваются в 1,38 и 1,49 раз, соответственно. Предлагаемое конструктивно-технологическое решение может использоваться и для других мощных приборов

Leakage current in AlGaN Schottky diode in terms of the phonon-assisted tunneling model

The leakage current in the AlGaN Schottky diode under a reverse bias is simulated and compared within the frameworks of the thermionic emission–diffusion and phonon-assisted tunneling models. It is shown that the phonon-assisted tunneling model is suitable to describe the reverse-bias characteristic of the AlGaN Schottky contact and can also be applied to calculate the gate leakage current in the AlGaN/GaN high electron mobility transistor

Mobility of a two-dimensional electron gas in the AlGaAs/GaAs heterostructure: simulation and analysis

At temperatures above 100 K, a two-dimensional electron gas generated at the AlGaAs/GaAs heterointerface can be characterized by the three dominant scattering mechanisms: acoustic deformation potential, polar acoustic phonon and polar optical phonon. An analytical model describing the two-dimensional electron gas mobility controlled by these scattering processes as a function of the electron concentration and the temperature was developed and integrated into a device simulator package using a built-in C language interpreter. The electrical characteristics of a simple AlGaAs/GaAs high electron mobility transistor were simulated using either the derived or a conventional bulk mobility model and the results were compared

Design optimization of the gallium nitride high electron mobility transistor with graphene and boron nitride heat-spreading elements

The self-heating effect has long been a persistent issue for high electron mobility transistors based on gallium nitride due to their inherently poor heat dissipation capability. Although a wide variety of thermal management solutions has to date been proposed, the problem of the extremely non-uniform heat dissipation at the micrometer scale is still challenging. It has recently been demonstrated, however, that the performance of gallium nitride high electron mobility transistors can be substantially improved by the introduction of various heat-spreading elements based on graphene, boron nitride or diamond. In this paper, using numerical simulation, we carried out a design optimization procedure for a normally-off gallium nitride high electron mobility transistor containing both graphene and cubic boron nitride layers. First, a screening experiment based on a very economical Plackett−Burman design was performed in order to find the most critical geometric parameters that influence the dc characteristics. After that, a full two-level factorial experiment consisting of three factors was implemented and an optimized parameter set was yielded. By applying this set, the output power was increased by 11.35%. The combination of the most significant parameters does not include any factors related to the heat-spreading layers

Linearizing torsion classes in the Picard group of algebraic curves over finite fields

We address the problem of computing in the group of $\ell^k$-torsion rational points of the jacobian variety of algebraic curves over finite fields, with a view toward computing modular representations.Comment: To appear in Journal of Algebr

Теплопроводность нитрида галлия с кристаллической структурой типа вюрцита

This paper reviews the theoretical and experimental works concerning one of the most important parameters of wurtzite gallium nitride – thermal conductivity. Since the heat in gallium nitride is transported almost exclusively by phonons, its thermal conductivity has a temperature behavior typical of most nonmetallic crystals: the thermal conductivity increases proportionally to the third power of temperature at lower temperatures, reaches its maximum at approximately 1/20 of the Debye temperature and decreases proportionally to temperature at higher temperatures. It is shown that the thermal conductivity of gallium nitride (depending on fabrication process, crystallographic direction, concentration of impurity and other defects, isotopical purity) varies significantly, emphasizing the importance of determining this parameter for the samples that closely resemble those being used in specific applications. For isotopically pure undoped wurtzite gallium nitride, the thermal conductivity at room temperature has been estimated as high as 5.4 W/(cm·K). The maximum room temperature value measured for bulkshaped samples of single crystal gallium nitride has been 2.79 W/(cm·K).Выполнен анализ теоретических и экспериментальных исследований одного из важнейших параметров нитрида галлия с кристаллической структурой типа вюрцита – теплопроводности. Так как перенос тепла в нитриде галлия осуществляется главным образом с помощью фононов, его теплопроводность имеет температурную зависимость, характерную для большинства неметаллических кристаллов: увеличивается пропорционально третьей степени температуры в области низких температур, достигает своего максимального значения при температуре, приблизительно равной 1/20 от дебаевской, и уменьшается пропорционально температуре в области высоких температур. Показано, что в зависимости от условий (технология изготовления образца, кристаллографическое направление, концентрация примеси и других дефектов, изотопный состав) теплопроводность нитрида галлия может находиться в большом диапазоне значений, что указывает на важность определения этого параметра именно тех образцов материала, которые используются в конкретных приложениях. Теплопроводность нелегированного изотопно-чистого нитрида галлия при комнатной температуре оценивается на уровне 5,4 Вт/(см·К). Максимальная теплопроводность, достигнутая для объемного образца из монокристаллического нитрида галлия, равна 2,79 Вт/(см·К)