2,918 research outputs found
New Consequences of Induced Transparency in a Double-Lambda scheme: Destructive Interference In Four-wave Mixing
We investigate a four-state system interacting with long and short laser
pulses in a weak probe beam approximation. We show that when all lasers are
tuned to the exact unperturbed resonances, part of the four-wave mixing (FWM)
field is strongly absorbed. The part which is not absorbed has the exact
intensity required to destructively interfere with the excitation pathway
involved in producing the FWM state. We show that with this three-photon
destructive interference, the conversion efficiency can still be as high as
25%. Contrary to common belief,our calculation shows that this process, where
an ideal one-photon electromagnetically induced transparency is established, is
not most suitable for high efficiency conversion. With appropriate
phase-matching and propagation distance, and when the three-photon destructive
interference does not occur, we show that the photon flux conversion efficiency
is independent of probe intensity and can be close to 100%. In addition, we
show clearly that the conversion efficiency is not determined by the maximum
atomic coherence between two lower excited states, as commonly believed. It is
the combination of phase-matching and constructive interference involving the
two terms arising in producing the mixing wave that is the key element for the
optimized FWM generation. Indeed, in this scheme no appreciable excited state
is produced, so that the atomic coherence between states |0> and |2> is always
very small.Comment: Submitted to Phys. Rev. A, 7 pages, 4 figure
Efficient Raman Sideband Generation in a Coherent Atomic Medium
We demonstrate the efficient generation of Raman sidebands in a medium
coherently prepared in a dark state by continuous-wave low-intensity laser
radiation. Our experiment is performed in sodium vapor excited in
configuration on the D line by two laser fields of resonant frequencies
and , and probed by a third field .
First-order sidebands for frequencies , and up to the
third-order sidebands for frequency are observed. The generation
starts at a power as low as 10 microwatt for each input field. Dependencies of
the intensities of both input and generated waves on the frequency difference
(), on the frequency and on the optical
density are investigated.Comment: 7 pages, 6 figure
The roles of dispositional coping style and social support in helping people with respiratory disease cope with a breathlessness crisis
© 2019 John Wiley & Sons Ltd Aim: To explore the role of coping moderators in self-management of breathlessness crises by people with advanced respiratory disease. Design: A secondary analysis of semi-structured interview data. Methods: Interviews with patients who had advanced respiratory disease, chronic breathlessness and at least one experience where they considered presenting to Emergency but self-managed instead (a ânear missâ). Participants were recruited from New South Wales, Queensland, Victoria, South Australia or Tasmania. Eligible caregivers were those who contributed to Emergency-related decision-making. Interviews were coded inductively and then deductively against the coping moderators social support and dispositional coping style, defined by the Transactional Model of Stress and Coping. Results: Interviews were conducted between October 2015 - April 2016 with 20 patients and three caregivers. Social networks offered emotional and practical support but also had potential for conflict with patients' âhardyâ coping style. Patient hardiness (characterized by a sense of âcommitmentâ and âchallengeâ) promoted a proactive approach to self-management but made some patients less willing to accept support. Information-seeking tendencies varied between patients and were sometimes shared with caregivers. An optimistic coping style appeared to be less equivocally beneficial. Conclusion: This study shows that social support and coping style may influence how people self-manage through their breathlessness crises and identified ways coping moderators can facilitate or hinder effective self-management. Impact: This study confers insights into how social-support and coping style can be supported and optimized to facilitate breathlessness self-management. Acknowledging coping moderator interactions is beneficial for developing resources and strategies that recognise patient mastery
Individual leader to interdependent leadership: A case study in leadership development and tripartite evaluation
This article is available open access through the publisherâs website at the link below. Copyright @ 2013 Sage Publications.The Problem - In this case study we see a move away from orthodox views of school leadership as âheadshipâ to a more contemporary model of educational leadership wherein we note a departure from functional, curricula-based school leadership toward more human resource development (HRD) approaches. The aim of this study was to consider the effectiveness of an educational development program for middle leaders within an educational establishment.
The Solution - We examined the impact of a bespoke higher education leadership development intervention in Leadership (and Change) on the formation and cohesiveness of a newly formed innovative leadership structure.
The Stakeholders - The leadership development intervention was designed through a tripartite collaboration including a university, senior school leaders, and staff. The intervention was designed to shift leadership from individual leader agency to interdependent human leadership agency. Through tripartite evaluation we uncover leadership development praxis that transcends the boundaries of conventional educational leadership and reemphasizes the benefits of bridging the academic/practitioner divide and the application of theory to praxis
Spatial evolution of short pulses under coherent population trapping
Spatial and temporal evolution is studied of two powerful short laser pulses
having different wavelengths and interacting with a dense three-level
Lambda-type optical medium under coherent population trapping. A general case
of unequal oscillator strengths of the transitions is considered. Durations of
the probe pulse and the coupling pulse () are assumed to be
shorter than any of the relevant atomic relaxation times. We propose analytical
and numerical solutions of a self-consistent set of coupled Schr\"{o}dinger
equations and reduced wave equations in the adiabatic limit with the account of
the first non-adiabatic correction. The adiabaticity criterion is also
discussed with the account of the pulse propagation. The dynamics of
propagation is found to be strongly dependent on the ratio of the transition
oscillator strengths. It is shown that envelopes of the pulses slightly change
throughout the medium length at the initial stage of propagation. This distance
can be large compared to the one-photon resonant absorption length. Eventually,
the probe pulse is completely reemitted into the coupling pulse during
propagation. The effect of localization of the atomic coherence has been
observed similar to the one predicted by Fleischhauer and Lukin (PRL, {\bf 84},
5094 (2000).Comment: 16 pages revtex style, 7 EPS figures, accepted to Physical Review
Poor Sleep and Impaired Self-Care: Towards a Comprehensive Model Linking Sleep, Cognition, and Heart Failure Outcomes
Background: Persons with heart failure (HF) have significantly lower sleep quantity and quality than persons without HF. The purpose of this article is to propose a conceptual model describing how poor sleep may contribute to inadequate self-care and untoward outcomes in persons with HF. Aims: Our overarching hypothesis is that sleep affects self-care and outcomes through its effects on cognition. Building on the work of others, we outline a conceptual model that illustrates that even transient sleep disruption prevents sleep-related restorative processes and contributes to cognitive dysfunctionâespecially in the 25â50% of HF patients with existing cognitive impairment. Poor sleep may be sufficient to impair cognition to a level that interferes with higher order functions involved in effective HF self-care practices. Through these mechanisms, inadequate sleep may contribute to poor outcomes such as low health-related quality of life and greater risk of unplanned hospitalization. Conclusion: The proposed model (1) bridges physical, neuropsychological and behavioral phenomena, (2) suggests a mechanism by which poor sleep affects daytime behavior, and (3) is empirically testable. Exploring factors that interfere with sleep may improve self-care and outcomes in persons with HF
Learning physics in context: a study of student learning about electricity and magnetism
This paper re-centres the discussion of student learning in physics to focus
on context. In order to do so, a theoretically-motivated understanding of
context is developed. Given a well-defined notion of context, data from a novel
university class in electricity and magnetism are analyzed to demonstrate the
central and inextricable role of context in student learning. This work sits
within a broader effort to create and analyze environments which support
student learning in the sciencesComment: 36 pages, 4 Figure
Developing reading-writing connections; the impact of explicit instruction of literary devices on the quality of children's narrative writing
The purpose of this collaborative schools-university study was to investigate how the explicit instruction of literary devices during designated literacy sessions could improve the quality of children's narrative writing. A guiding question for the study was: Can children's writing can be enhanced by teachers drawing attention to the literary devices used by professional writers or âmentor authorsâ? The study was conducted with 18 teachers, working as research partners in nine elementary schools over one school year. The research group explored ways of developing children as reflective authors, able to draft and redraft writing in response to peer and teacher feedback. Daily literacy sessions were complemented by weekly writing workshops where students engaged in authorial activity and experienced writers' perspectives and readers' demands (Harwayne, 1992; May, 2004). Methods for data collection included video recording of peer-peer and teacher-led group discussions and audio recording of teacher-child conferences. Samples of children's narrative writing were collected and a comparison was made between the quality of their independent writing at the beginning and end of the research period. The research group documented the importance of peer-peer and teacher-student discourse in the development of children's metalanguage and awareness of audience. The study suggests that reading, discussing, and evaluating mentor texts can have a positive impact on the quality of children's independent writing
Review of post-process optical form metrology for industrial-grade metal additive manufactured parts
The scope of this review is to investigate the main post-process optical form measurement technologies available in industry today and to determine whether they are applicable to industrial-grade metal additive manufactured parts. An in-depth review of the operation of optical three-dimensional form measurement technologies applicable to metal additive manufacturing is presented, with a focus on their fundamental limitations. Looking into the future, some alternative candidate measurement technologies potentially applicable to metal additive manufacturing will be discussed, which either provide higher accuracy than currently available techniques but lack measurement volume, or inversely, which operate in the appropriate measurement volume but are not currently accurate enough to be used for industrial measurement
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