1,363 research outputs found
Screening nuclear field fluctuations in quantum dots for indistinguishable photon generation
A semiconductor quantum dot can generate highly coherent and
indistinguishable single photons. However, intrinsic semiconductor dephasing
mechanisms can reduce the visibility of two-photon interference. For an
electron in a quantum dot, a fundamental dephasing process is the hyperfine
interaction with the nuclear spin bath. Here we directly probe the consequence
of the fluctuating nuclear spins on the elastic and inelastic scattered photon
spectra from a resident electron in a single dot. We find the nuclear spin
fluctuations lead to detuned Raman scattered photons which are distinguishable
from both the elastic and incoherent components of the resonance fluorescence.
This significantly reduces two-photon interference visibility. However, we
demonstrate successful screening of the nuclear spin noise which enables the
generation of coherent single photons that exhibit high visibility two-photon
interference.Comment: 5 pages, 4 figures + Supplementary Informatio
A note on conformal symmetry in projective superspace
We describe a sufficient condition for actions constructed in projective
superspace to possess an SU(2) R-symmetry. We check directly that this
condition implies that the corresponding hyperkahler varieties, constructed by
means of the generalized Legendre transform, have a Swann bundle structure.Comment: 21 pages, added reference
Analysis of lower limb internal kinetics and electromyography in elite race walking.
The aim of this study was to analyse lower limb joint moments, powers and electromyography patterns in elite race walking. Twenty international male and female race walkers performed at their competitive pace in a laboratory setting. The collection of ground reaction forces (1000 Hz) was synchronised with two-dimensional high-speed videography (100 Hz) and electromyography of seven lower limb muscles (1000 Hz). As well as measuring key performance variables such as speed and stride length, normalised joint moments and powers were calculated. The rule in race walking which requires the knee to be extended from initial contact to midstance effectively made the knee redundant during stance with regard to energy generation. Instead, the leg functioned as a rigid lever which affected the role of the hip and ankle joints. The main contributors to energy generation were the hip extensors during late swing and early stance, and the ankle plantarflexors during late stance. The restricted functioning of the knee during stance meant that the importance of the swing leg in contributing to forward momentum was increased. The knee flexors underwent a phase of great energy absorption during the swing phase and this could increase the risk of injury to the hamstring muscles
Wafer-Scale Epitaxial Modulation of Quantum Dot Density
Precise control of the properties of semiconductor quantum dots (QDs) is
vital for creating novel devices for quantum photonics and advanced
opto-electronics. Suitable low QD-density for single QD devices and experiments
are challenging to control during epitaxy and are typically found only in
limited regions of the wafer. Here, we demonstrate how conventional molecular
beam epitaxy (MBE) can be used to modulate the density of optically active QDs
in one- and two- dimensional patterns, while still retaining excellent quality.
We find that material thickness gradients during layer-by-layer growth result
in surface roughness modulations across the whole wafer. Growth on such
templates strongly influences the QD nucleation probability. We obtain density
modulations between 1 and 10 QDs/ and periods ranging from several
millimeters down to at least a few hundred microns. This novel method is
universal and expected to be applicable to a wide variety of different
semiconductor material systems. We apply the method to enable growth of
ultra-low noise QDs across an entire 3-inch semiconductor wafer
Wafer-scale epitaxial modulation of quantum dot density
Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-densities for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/”m2 and periods ranging from several millimeters down to at least a few hundred microns. This method is universal and expected to be applicable to a wide variety of different semiconductor material systems. We apply the method to enable growth of ultra-low noise QDs across an entire 3-inch semiconductor wafer
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Mitigation of Moral Hazard and Adverse Selection in Venture Capital Financing: The Influence of the Countryâs Institutional Setting
A venture capitalist (VC) needs to trade off benefits and costs when attempting to mitigate agency problems in their investor-investee relationship. We argue that signals of ventures complement the VCâs capacity to screen and conduct a due diligence during the pre-investment phase, but its attractiveness may diminish in institutional settings supporting greater transparency. Similarly, whereas a VC may opt for contractual covenants to curb potential opportunism by ventures in the post-investment phase, this may only be effective in settings supportive of shareholder rights enforcement. Using an international sample of VC contracts, our study finds broad support for these conjectures. It delineates theoretical and practical implications for how investors can best deploy their capital in different institutional settings whilst nurturing their relationships with entrepreneurs
THE ROLE OF INTERDEPENDENCE IN THE MICRO-FOUNDATIONS OF ORGANIZATION DESIGN: TASK, GOAL, AND KNOWLEDGE INTERDEPENDENCE
Interdependence is a core concept in organization design, yet one that has remained consistently understudied. Current notions of interdependence remain rooted in seminal works, produced at a time when managersâ near-perfect understanding of the task at hand drove the organization design process. In this context, task interdependence was rightly assumed to be exogenously determined by characteristics of the work and the technology. We no longer live in that world, yet our view of interdependence has remained exceedingly task-centric and our treatment of interdependence overly deterministic. As organizations face increasingly unpredictable workstreams and workers co-design the organization alongside managers, our field requires a more comprehensive toolbox that incorporates aspects of agent-based interdependence. In this paper, we synthesize research in organization design, organizational behavior, and other related literatures to examine three types of interdependence that characterize organizationsâ workflows: task, goal, and knowledge interdependence. We offer clear definitions for each construct, analyze how each arises endogenously in the design process, explore their interrelations, and pose questions to guide future research
Synthesis, Conformation and Antiproliferative Activity of Isothiazoloisoxazole 1,1-dioxides
Sixteen new isothiazoloisoxazole 1,1-dioxides, one new isothiazolotriazole and one new isothiazolopyrazole have been synthesised by using 1,3-dipolar cycloadditions to isothiazole 1,1-dioxides. One sub-set of these isothiazoloisoxazoles showed low ÎŒM activity against a human breast carcinoma cell line, whilst a second sub-set plus the isothiazolotriazole demonstrated an interesting restricted rotation of sterically hindered bridgehead substituents. A thiazete 1,1-dioxide produced from one of the isothiazole 1,1-dioxides underwent conversion into an unknown 1,2,3-oxathiazolin-2-oxide upon treatment with Lewis acids, but was inert towards 1,3-dipoles and cyclopropenones. Six supporting crystal structures are included
Fairness, envy, guilt and greed: building equity considerations into agency theory
In this article we examine the extent to which fairness considerations are salient to senior executives, and consider the implications for agency theory, tournament theory and the design of top-management incentives. We look for patterns in a unique data set of senior executive preferences and seek explanations for these patterns using a model of fairness first advanced by Fehr and Schmidt in 1999. We propose a number of amendments to Fehr and Schmidtâs model. We challenge some of the standard tenets of agency theory and tournament theory, demonstrating why equity considerations should be taken into account. We add to the growing literature on behavioural agency theory
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