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Large gauge transformations and little group for soft photons
Hamada, Yuta,Seo, Min-Seok,Shiu, Gary American Physical Society 2017 Physical Review D Vol.96 No.10
<P>Recently, large gauge transformation(LGT), the residual gaugesymmetry after gauge fixing that survives at null infinity, has drawn much attention concerning soft theorems and the memory effect. We point out that LGT charges in quantum electrodynamics are in fact one of noncompact generators of the two dimensional Euclidean group. Moreover, by comparing two equivalent descriptions of gauge transformation, we suggest that LGT is simply another way of describing the gauged little group for massless soft photons.</P>
QUASICONFORMAL EXTENSIONS OF STARLIKE HARMONIC MAPPINGS IN THE UNIT DISC
Hamada, Hidetaka,Honda, Tatsuhiro,Shon, Kwang Ho Korean Mathematical Society 2013 대한수학회보 Vol.50 No.4
Let $f$ be a harmonic mapping on the unit disc ${\Delta}$ in $\mathbb{C}$. We give some condition for $f$ to be a quasiconformal homeomorphism on ${\Delta}$ and to have a quasiconformal extension to the whole plane $\bar{\mathbb{C}}$. We also obtain quasiconformal extension results for starlike harmonic mappings of order ${\alpha}{\in}(0,1)$.
Memory in de Sitter space and Bondi-Metzner-Sachs-like supertranslations
Hamada, Yuta,Seo, Min-Seok,Shiu, Gary American Physical Society 2017 Physical Review D Vol.96 No.2
<P>It is well known that the memory effect in flat spacetime is parametrized by the Bondi-Metzner-Sachs (BMS) supertranslation. We investigate the relation between the memory effect and diffeomorphism in de Sitter spacetime. We find that gravitational memory is parametrized by a BMS-like supertranslation in the static patch of de Sitter spacetime. We also show a diffeomorphism that corresponds to gravitational memory in the Poincare/cosmological patch. Our method does not need to assume the separation between the source and the detector to be small compared with the Hubble radius, and can potentially be applicable to other Friedmann-Lemaitre-Robertson-Walker universes, as well as 'ordinary memory' mediated by massive messenger particles.</P>
Effect of Aft-deck Length on the Performance of Serpentine Nozzle
Hamada Mohamed(하마다 모하메드),Changwook Lee(이창욱),Heeju Choi(최희주),Jeekeun Lee(이지근) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.8
Serpentine nozzle has been widely utilized in many types of aircraft to minimize the infrared radiation emitted by high temperature parts and exhaust systems. Annular mixer was used in the infrared suppressor of exhaust system to mix the cold outside air with hot gases from the engine. The most important parameters can evaluate the performance of the nozzle with lobed mixer include mixing effectiveness, pressure loss, and pumping performance. A central plug is used at the exit of the lobed nozzle to penetrate the primary stream in the nozzle. In this study a numerical investigation of flow characteristics of the serpentine nozzle with lobed mixer was conducted. The flow characteristics such as velocity, temperature, pressure of the lobed mixer were studied. The three-dimensional model of the serpentine nozzle was used in the simulations that carried out using Star CCM software. The grid system com-posed of 8,364,993 polyhedral cells. Hot gases enter the nozzle through the core that treated as stagnation inlet at a pressure and temperature of 45023 Pa and 811.8 K, respectively. While, the cold air at pressure and temperature of 48963 Pa and 334.8 K, respectively enters via the bypass that considered as stagnation inlet. The outlet of the nozzle was treated as a pressure outlet subjected to atmospheric pressure and temperature. The nozzle body was considered as adiabatic walls with no-slip boundary conditions. The results showed that the increasing aft-deck decreased the temperature inside the nozzle and at exhausted gases that reduced the infrared temperature.
Live Exhibitions in the Classroom with Mathematical Software
( Hamada Tatsuyoshi ) 한국수학교육학회 2012 수학교육 학술지 Vol.2012 No.2
Generally, we have “Intensive Course” for undergraduate and graduate students in any universities in Japan. We give credit hours with lectures of four or five days and reports. For students, it is a good system for getting new knowledge from professors of different universities intensively. In this article, I want to describe my experiences of intensive courses with mathematical software and the effectiveness of the live exhibitions in the classroom.
Wheeling Charge Reflecting the Transmission Conditions based on the Embedded Cost Method
Hamada, Hiromu,Yokoyama, Ryuichi The Korean Institute of Electrical Engineers 2011 The Journal of International Council on Electrical Vol.1 No.1
This paper proposes a practical and devised method for designing the wheeling charge based on the embedded cost method. In setting up the wheeling charge, one of the most important items is recovering the invested cost. Because the marginal cost method has the disadvantages regarding the above point, the embedded cost method is focused in this paper. By applying the proposed method, the wheeling charge that reflects the use of transmission systems not only gives an incentive for the efficient operation of power systems but also achieve the recovery of the invested cost by electric utilities. In order to verify the proposed method, several simulations have been conducted on the IEEE 30-bus test system.
Hamada, Mohanad Lateef,Alwan, Ghazwan Saud,Annaz, Abdulkader Ahmed,Irhayyim, Saif Sabah,Hammood, Hashim Shukur Materials Research Society of Korea 2021 한국재료학회지 Vol.31 No.6
Composite materials offer distinct and unique properties that are not naturally inherited in the individual materials that make them. One of the most attractive composites to manufacture is the aluminum alloy matrix composite, because it usually combines easiness of availability, light weight, strength, and other favorable properties. In the current work, Powder Metallurgy Method (PMM) is used to prepare Al2024 matrix composites reinforced with different mixing ratios of yttrium oxide (Y<sub>2</sub>O<sub>3</sub>) particles. The tests performed on the composites include physical, mechanical, and tribological, as well as microstructure analysis via optical microscope. The results show that the experimental density slightly decreases while the porosity increases when the reinforcement ratio increases within the selected range of 0 ~ 20 wt%. Besides this, the yield strength, tensile strength, and Vickers hardness increase up to a 10 wt% Y<sub>2</sub>O<sub>3</sub> ratio, after which they decline. Moreover, the wear results show that the composite follows the same paradigm for strength and hardness. It is concluded that this composite is ideal for application when higher strength is required from aluminum composites, as well as lighter weight up to certain values of Y<sub>2</sub>O<sub>3</sub> ratio.
The Anatomy of Bubble Economy in Japan
Hamada, Yasuyuki 연세대학교 산업경영연구소 1992 산업과경영 Vol.10 No.1
"Bubble Economy," describes well the scene of Japanese economy since the end of 1980's. The purpose of this paper is to try to find the core of Bubble. It leads us to some explanations to the following questions: 1. Why did "Bubble" occur in Japan typically? 2. Why did "Bubble" emerge in the second half of 1980's, especially after 1987? 3. Why did "Bubble" emerge as a stock-inflation?