50 research outputs found
Generation of quasi-monoenergetic protons from a double-species target driven by the radiation pressure of an ultraintense laser pulse
No full textIn laser-driven proton acceleration, generation of quasi-monoenergetic proton beams has been considered a crucial feature of the radiation pressure acceleration (RPA) scheme, but the required difficult physical conditions have hampered its experimental realization. As a method to generate quasi-monoenergetic protons under experimentally viable conditions, we investigated using double-species targets of controlled composition ratio in order to make protons bunched in the phase space in the RPA scheme. From a modified optimum condition and three-dimensional particle-in-cell simulations, we showed by varying the ion composition ratio of proton and carbon that quasi-monoenergetic protons could be generated from ultrathin plane targets irradiated with a circularly polarized Gaussian laser pulse. The proposed scheme should facilitate the experimental realization of ultrashort quasi-monoenergetic proton beams for unique applications in high field science. © 2016 AIP Publishing LLC1441sciescopu
Low-divergence relativistic proton jet from a thin solid target driven by an ultra-intense circularly polarized Laguerre–Gaussian laser pulse
No full text© 2020 IOP Publishing Ltd.We propose a new ion acceleration scheme of irradiating a thin solid target with an ultraintense circularly polarized Laguerre-Gaussian (LG) laser pulse. Three-dimensional particle-in-cell simulations are performed to demonstrate that this scheme can generate a low-divergence high-density relativistic proton jet. By this scheme, the number of protons emitted with a small angle (<1°) from the laser axis can be more than tens of times as high as that of the protons accelerated by a circularly polarized Gaussian pulse. The inward ponderomotive force of the LG pulse drives such a proton beam along the laser axis11Nsciescopu
Direct laser acceleration of electrons from a plasma mirror by an intense few-cycle Laguerre-Gaussian laser and its dependence on the carrier-envelope phase
No full text© 2022 IOP Publishing Ltd.A direct acceleration scheme to generate high-energy, high-charge electron beams with an intense few-cycle Laguerre-Gaussian (LG) laser pulse was investigated using three-dimensional particle-in-cell simulations. In this scheme, an intense LG laser pulse was irradiated onto a solid density plasma slab. When the laser pulse is reflected, electrons on the target front surface are injected into the longitudinal electric field of the laser and accelerated further. We found that the carrier-envelope phase (CEP) of the few-cycle laser pulse plays a key role in the electron injection and acceleration process. Using a three-cycle LG laser pulse with a0=2 and an appropriate CEP, an about 60 pC electron beam could be obtained at a maximum energy of 16 MeV. In comparison, when a laser pulse with mismatched CEP was used, a total of 4 pC electron beam with a maximum energy of 3.5 MeV was obtained. Linear scaling of electron energy to the laser strength was shown up to a0=100 at which a quasi-monoenergetic electron beam of 850 MeV energy with a charge equal to 600 pC could be obtained. These results demonstrate that high-energy electron beams can be stably generated through direct laser acceleration using a CEP-controlled intense few-cycle LG laser pulse.11Nsciescopu
Generation of low-order Laguerre-Gaussian beams using hybrid-machined reflective spiral phase plates for intense laser-plasma interactions
No full text© 2020 The Author(s). In laser-plasma interactions (LPI), the laser beam mode is a critical parameter when trying to explore new physical phenomena. Of the various spatial beam modes, the Laguerre-Gaussian (LG) mode with vortex phase has attracted considerable attention due to its unique features, including the ability to carry an orbital angular momentum. Due to this, it has been actively applied to LPI, which mainly utilize ultrashort intense laser pulses. However, existing transmissive phase-manipulating optical elements have several limitations when applied in LPI due to critical issues such as pulse broadening, attenuation, and beam shape–all of which have an influence on the beam quality, as well as, geometry, size, simplicity, and cost–all of which are related to processing technologies. In this paper, we present a series of procedures to obtain high-quality low-order (l = 1 and 2) LG vortex beams from large-sized off-axis reflective spiral phase plates (ORSPPs). The geometric designs for various surface structures, electromagnetic wave simulations in the extra-large domain, hybrid-mechanical processing technique attempted newly, and experimental demonstrations are involved. Experimental observations of LG intensity distributions and interference fringes were verified with the simulation results of Poynting vector, phase, and angular momentum densities. The beam quality of LG intensity distributions was analyzed quantitatively through the investigation of an annular zone formed from the uniformity of the stepped and continuous surface structures of ORSPPs. Furthermore, we numerically investigated the physical phenomena on the high-intensity angular momentum transfer from light to matter, considering ORSPP–driven low-order LG vortex laser pulses, by performing 3D particle-in-cell simulations11Nsciescopu
Strong field physics pursued with petawatt lasers
No full textAbstract Recent ultra-short high-power lasers can provide ultra-high laser intensity over 1022 W/cm2. Laser fields of such extreme strengths instantaneously turn matter into plasma, which exhibits relativistic collective dynamics, thereby leading to unprecedented physical systems with potential breakthrough applications. In this article, we introduce the basic concepts and trace the progress in ultra-high intensity laser development and relativistic laser-plasma interactions, including laser-driven charged particle acceleration
Print Advertising In The Us And Hong Kong: A Comparative Analysis
No full textGiven the static condition of the global economy marketers are cutting advertising budgets commensurate with dismal sales. It is a longstanding belief that utilizing a standardized advertising approach not only controls good ideas and provides for a consistent image but it also has the benefit of controlling expenses through economies of scale. With this in mind, the purpose of the study was to determine the degree of standardization or lack thereof in advertising strategies in the cosmetics and fragrances advertising industries in the United States and Hong Kong. The findings of this study suggest that there is a high level of standardization in the advertising for perfumes because Hong Kong belonged to the British for a long time and individuals’ needs and desires for love and acceptance are the same irrespective of geography. On the other hand only a moderate form of standardization was noted in the advertising for cosmetics. This may be attributed to the fact that different beauty concepts are held among different regions. Implications of the findings are also noted.print advertising, standardization, glocalization, cosmetics and fragrance industry
Characteristics of electron beams accelerated by parallel and antiparallel circularly polarized Laguerre–Gaussian laser pulses
No full textA direct comparison of the properties of electron beam generated by antiparallel circularly polarized Laguerre–Gaussian (CPLG) laser pulse and parallel CPLG laser pulse has been performed with three-dimensional particle-in-cell simulations. It is known that the longitudinal field of an antiparallel CPLG laser pulse with opposite signs of spin and orbital quantum number preferentially accelerates electrons to high energy. However, a direct comparison of electron beam between the other combination of spin and orbital angular momentum, the parallel CPLG laser pulse with the same sign of spin and orbital angular quantum number, has not been conducted. While the two pulses have an identical transverse field envelope, the generated electron beam properties are different. Although the magnitude of the longitudinal field is about one order of magnitude less than that of the transverse field, it has a significant effect on beam divergence. For antiparallel CPLG laser pulse, collimated electron bunches are formed with small divergence ( 100 mrad) electron beam is formed. This difference in beam quality can indicate a field-induced acceleration in actual experiments. A few-cycle laser pulse and low-density plasma are used to rule out the effect of laser–plasma interaction. It is also shown that for antiparallel CPLG laser pulse, the maximum kinetic energy increases with the square root of incident laser power, consistent with the scaling law for field-induced acceleration. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.11Nsciescopu
Postantibiotic effects of anti-tuberculosis drugs on mycobacterium tuberculosis.
No full textby Carrie Au-Yeang.Thesis (M.Phil.)--Chinese University of Hong Kong, 1997.Includes bibliographical references (leaves 45-54).Abstract also in Chinese.Chapter I. --- Abstract --- p.iiiChapter II. --- Acknowledgements --- p.ivChapter III. --- Table of Contents --- p.vChapter IV. --- List of Abbreviations --- p.viiChapter V. --- List of Figures --- p.viiiChapter VI. --- List of Tables --- p.ixChapter VII. --- Introduction --- p.1Chapter VIII. --- Literature Review --- p.3Chapter A. --- Mycobacterium tuberculosis Infections - clinical importance --- p.3Chapter B. --- Treatment of M. tuberculosis Infections - the past & present --- p.3Chapter C. --- Laboratory Supports for Treatment of Tuberculosis --- p.5Chapter D. --- The Postantibiotic Effects (PAE) --- p.6Chapter E. --- PAE of Antituberculosis Drugs Against Mycobacteria --- p.15Chapter F. --- Radiometric Measurement of growth --- p.16Chapter IX. --- Materials and Methods --- p.17Chapter A. --- Bacterial Strains and Their Maintenance --- p.17Chapter B. --- Antimicrobial Agents --- p.17Chapter C. --- Antimicrobial Susceptibility Testing --- p.18Chapter D. --- Assessment of PAE and KI In Vitro --- p.20Chapter E. --- Assessment of PAE and KI Ex Vivo --- p.22Chapter F. --- Determination of Drug Uptake --- p.25Chapter X. --- Results --- p.29Chapter A. --- In Vitro Susceptibility Testing of the M. tuberculosis Strains --- p.29Chapter B. --- PAE In Vitro - the Classical Viable Count Method --- p.29Chapter C. --- PAE Measured by the Bactec Method --- p.30Chapter D. --- PAE In Vitro - the Bactec Method --- p.30Chapter E. --- Postantibiotic Effects Ex Vivo by the Bactec Method --- p.31Chapter F. --- Bactericidal Activities In Vitro and Ex Vivo --- p.32Chapter XI. --- Discussion --- p.34Chapter A. --- Selection of M. tuberculosis isolates and Drug Susceptibility --- p.34Chapter B. --- PAE and KI In Vitro & Ex Vivo - the study methods --- p.34Chapter C. --- PAE In Vitro & Ex Vivo - single drug --- p.36Chapter D. --- PAE Ex Vivo - drug combinations --- p.38Chapter E. --- KI In vitro & Ex vivo --- p.39Chapter F. --- PAE and Clinical Therapeutic Regimens --- p.41Chapter G. --- Conclusion & Future Studies --- p.44Chapter XII. --- Literature Cited --- p.45Chapter XIII. --- Figures --- p.55Chapter IVX --- Tables --- p.6
Multi-GeV Laser Wakefield Electron Acceleration with PW Lasers
No full textLaser wakefield electron acceleration (LWFA) is an emerging technology for the next generation of electron accelerators. As intense laser technology has rapidly developed, LWFA has overcome its limitations and has proven its possibilities to facilitate compact high-energy electron beams. Since high-power lasers reach peak power beyond petawatts (PW), LWFA has a new chance to explore the multi-GeV energy regime. In this article, we review the recent development of multi-GeV electron acceleration with PW lasers and discuss the limitations and perspectives of the LWFA with high-power lasers
A 1.9-GHz CMOS RF power amplifier with stacked NMOS and PMOS using voltage combining method
No full text학위논문(석사) - 한국과학기술원 : 전기및전자공학전공, 2007.2, [ ix, 69 p. ]본 논문에서는 0.18-μm CMOS 공정을 이용하여 1.9-GHz 대역에서 동작하는 고주파 전력증폭기를 설계하였다. 고주파 전력증폭기는 무선 통신 회로인 송신단의 마지막 부분에서 큰 전력을 발생시키는 역할을 하기 때문에 동작의 신뢰성이 아주 중요하다. 설계된 전력증폭기는 회로 동작의 신뢰성을 향상시킬 수 있도록 출력 측 능동 소자의 양단에 나타나는 전압 차의 크기를 줄여주는 구조를 도입하였다. 이와 같이 능동 소자의 스트레스를 완화시켜주는 회로는 NMOS 증폭단만으로 구성되던 기존의 구조에 추가적으로 PMOS 증폭단을 연결함으로써 구현 가능하며, CMOS 소자의 낮은 항복 전압을 극복하기 위해 이러한 구조에 새롭게 전압 결합 방식을 도입하여, 설계 시 요구되는 와트(W) 급의 출력 전력을 얻을 수 있도록 하였다. 전체 회로의 모든 부분이 하나의 칩 안에 집적되었으며, 측정한 결과 구현된 칩은 28.1 dBm의 출력 전력과 15.1%의 효율(PAE)을 나타내었다. 구조의 인덕턴스를 예측하는 과정에서 세밀하게 고려되지 못했던 부분의 특성 때문에 실제 측정 결과는 기대된 성능에 미치지 못하였지만, 설계 과정에서 p-type switch와 회로 동작의 타당성을 보임으로써 본 논문에서는 제안된 구조의 가능성을 보여주었다.한국과학기술원 : 전기및전자공학전공
