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Isolation of attosecond pulses from the attosecond lighthouse
Hammond, TJ,Balogh, Emeric,Kim, Kyung Taec Institute of Physics Publishing Ltd. 2017 Journal of Physics B: Atomic, Molecular and Optica Vol.50 No.1
<P>This paper proposes and verifies methods to improve the isolation of the attosecond pulses generated via the attosecond lighthouse technique in gases. We find that the converging fundamental field can compensate for the inherent diverging wavefront of the attosecond pulses, but is only valid over a limited portion of the spectrum and sacrifices the maximum attainable photon energy. We discuss two methods of manipulating the fundamental field to control the divergence of the attosecond pulses: the first method uses a perturbing beam that manipulates the wavefront, and the second method controls the fundamental dispersion. These methods improve the isolation of the attosecond pulses up to the cutoff photon energy.</P>
Controlling attosecond angular streaking with second harmonic radiation.
Hammond, T J,Kim, Kyung Taec,Zhang, Chunmei,Villeneuve, D M,Corkum, P B Optical Society of America 2015 Optics letters Vol.40 No.8
<P>High harmonic generation, which produces a coherent burst of radiation every half cycle of the driving field, has been combined with ultrafast wavefront rotation to create a series of spatially separated attosecond pulses, called the attosecond lighthouse. By adding a coherent second harmonic beam with polarization parallel to the fundamental, we decrease the generating frequency from twice per optical cycle to once. The increased temporal separation increases the pulse contrast. By scanning the carrier envelope phase, we see that the signal is 2π periodic.</P>
Attosecond pulses measured from the attosecond lighthouse
Hammond, T. J.,Brown, Graham G.,Kim, Kyung Taec,Villeneuve, D. M.,Corkum, P. B. Nature Publishing Group, a division of Macmillan P 2016 Nature photonics Vol.10 No.3
<P>The attosecond lighthouse is a method of using ultrafast wavefront rotation with high-harmonic generation to create a series of coherent, spatially separated attosecond pulses. Previously, temporal measurements by photoelectron streaking characterized isolated attosecond pulses created by manipulating the single-atom response(1-4). The attosecond lighthouse, in contrast, generates a series of pulses that spatially separate and become isolated by propagation. Here, we show that ultrafast wavefront rotation maintains the single-atom response (in terms of temporal character) of an isolated attosecond pulse over two octaves of bandwidth. Moreover, we exploit the unique property of the attosecond lighthouse-the generation of several isolated pulses-to measure the three most intense pulses. These pulses each have a unique spectrum and spectral phase.</P>
Politeness in Administrative Discourse: Some Perspectives from TwoInstitutions in Ghana
Christiana Hammond 세종대학교 언어연구소 2017 Journal of Universal Language Vol.18 No.1
Linguistic pragmatics studies have incorporated sociolinguistic perspectives of pragmatic variations in computer-mediated massages, and in spoken and written interactions. Rather than adhering to a strict first order participant constructed conceptions or a second order analyst constructed conceptions of politeness, this paper argues that each of them could be used to inform the other through variant methodological approaches. This paper interrogated the influence of organisational structure and cultural expectations in the contents of administrative discourses to signal (im)politeness from two institutions: University of Education, Winneba and the Ghana Police Service, Winneba. Situated in Ting-Toomey’s face negotiation theory and Fraser’s views on politeness strategies, this paper attempted to bridge the gaps between three pragmatic subfields: linguistic politeness research, organisational communication, and institutional communication pragmatics. Data was gathered through discourse completion tests, focus group discussions, observations, and a content analysis of selected written documents. One significant finding from the study was that differences exist in pragmatic variations: lexical, syntactic, and textual resources to mark (im)politeness in both institutions. The study recommends the choice of politeness strategies to be informed by the structure and cultural expectations of organisations to help reduce conflicts and confrontations inherent in human exchanges.
MODELLING THE 3 MICRON REGION IN AKARI IRC SPECTRA
MARK HAMMONDS,TAMAMI MORI,Fumihiko Usui,TAKASHI ONAKA 한국천문학회 2017 天文學論叢 Vol.32 No.1
The existence of polycyclic aromatic hydrocarbons (PAHs) astronomically is well accepted, but the specific molecular forms observed remain uncertain. To better understand the molecular structures which may be present along a given sightline, the 3.0~--~3.6\mum\ region is modelled with careful consideration given to the underlying sub-features arising from specific structures within emitting molecules.
Frequency, cyclicity, and optimality
Michael Hammond 한국음운론학회 2004 음성·음운·형태론 연구 Vol.10 No.3
This paper reconsiders cyclicity in English. Specifically the relationship of frequency to cyclic stress is examined and it is shown that more frequent derived words are less likely to exhibit cyclic effects. In addition, cyclic effects are less likely if the base form is more frequent. These effects of frequency are confirmed by the behavior of Latinate prefixes. The effects can be modeled by adopting lexically-restricted markedness constraints, arguing against previous analyses of English (Pater 2000) and against the theoretical position that only correspondence constraints can be lexically restricted (Itô and Mester 1999).
가나 북부지역의 농약 관련 토마토 재배 및 수확의 안전성 평가
아티가하몬드셀라시 ( Hammond Selassie Attigah ),홍성구 ( Seonggu Hong ) 한국농공학회 2020 한국농공학회 학술대회초록집 Vol.2020 No.-
In Ghana, farmers and consumers of tomato face immense risk of exposure owing to the application of agro-chemicals and related unhygienic farm practices. This study makes a novel attempt to assess the tomato production practices related to food safety in the Techiman North District of Ghana. The tomato farmers’ knowledge and practices were assessed on pesticide use, Integrated Pest Management, harvest sanitation, worker health and hygiene, Ghana Green Label Certification program and compared Korea best food safety policies to that of Ghana. One hundred semi-structured questionnaires were administered and data analyzed using SPSS Statistical package version 25 with chi-square for significance. Seventy five percent of the participants were males, 25% females of which 10% had no formal education. About 44% has no pest management plan as against 56%; 74 and 26% do not and do keep record of application rates and dates; 75%, 17% and 8% observe withdrawer period of 7 days, 14 days and 2-4 days before harvest respectively. Relatedly, 47% assert that they take direction from AEAs; 8% from friends; 3% use own exaggeration; 41% depend on the manufacturer’s information regarding the rate of chemical application. Although a significant difference has been found in their knowledge about biological and cultural methods of pest control for IPM by the respondents, it is not observed in their behavior during the cultivation of the crop in the farm. Majority of these farmers lack knowledge on cooling and storage of the tomato fruits. Similarly, 83% assert that they leave the tomato plants to rot in the farm after harvest compared to very few of them who reported cutting it off from the farm. About 95% of the participants are not aware of the Ghana Green Label Certification Program. Although key questions found good answers from farmers, the quality of their knowledge is limited, shows lack of information and needs reinforcement. The results indicates that capacity building and periodic updates for agro-chemical dealers and farmers are required.