2,852 research outputs found
Semileptonic decays in the limit of a heavy daughter quark
The rate of the semileptonic decay b to c l v is calculated with order
alphas^2 accuracy, as an expansion around the limit of equal masses of the b
and c quarks. Recent results obtained around the limit of the c-quark much
lighter than b are confirmed. Details of the new expansion method are
described.Comment: 7 pages, 5 figure
Linear-time algorithms for testing the satisfiability of propositional horn formulae
AbstractNew algorithms for deciding whether a (propositional) Horn formula is satisfiable are presented. If the Horn formula A contains K distinct propositional letters and if it is assumed that they are exactly P1,âŠ, PK, the two algorithms presented in this paper run in time O(N), where N is the total number of occurrences of literals in A. By representing a Horn proposition as a graph, the satisfiability problem can be formulated as a data flow problem, a certain type of pebbling. The difference between the two algorithms presented here is the strategy used for pebbling the graph. The first algorithm is based on the principle used for finding the set of nonterminals of a context-free grammar from which the empty string can be derived. The second algorithm is a graph traversal and uses a âcall-by-needâ strategy. This algorithm uses an attribute grammar to translate a propositional Horn formula to its corresponding graph in linear time. Our formulation of the satisfiability problem as a data flow problem appears to be new and suggests the possibility of improving efficiency using parallel processors
Tales from the playing field: black and minority ethnic students' experiences of physical education teacher education
This article presents findings from recent research exploring black and minority ethnic (BME) studentsâ experiences of Physical Education teacher education (PETE) in England (Flintoff, 2008). Despite policy initiatives to increase the ethnic diversity of teacher education cohorts, BME students are under-represented in PETE, making up just 2.94% of the 2007/8 national cohort, the year in which this research was conducted. Drawing on in-depth interviews and questionnaires with 25 BME students in PETE, the study sought to contribute to our limited knowledge and understanding of racial and ethnic difference in PE, and to show how ârace,â ethnicity and gender are interwoven in individualsâ embodied, everyday experiences of learning how to teach. In the article, two narratives in the form of fictional stories are used to present the findings. I suggest that narratives can be useful for engaging with the experiences of those previously silenced or ignored within Physical Education (PE); they are also designed to provoke an emotional as well as an intellectual response in the reader. Given that teacher education is a place where we should be engaging students, emotionally and politically, to think deeply about teaching, education and social justice and their place within these, I suggest that such stories of difference might have a useful place within a critical PETE pedagogy
Optical interface created by laser-cooled atoms trapped in the evanescent field surrounding an optical nanofiber
Trapping and optically interfacing laser-cooled neutral atoms is an essential
requirement for their use in advanced quantum technologies. Here we
simultaneously realize both of these tasks with cesium atoms interacting with a
multi-color evanescent field surrounding an optical nanofiber. The atoms are
localized in a one-dimensional optical lattice about 200 nm above the nanofiber
surface and can be efficiently interrogated with a resonant light field sent
through the nanofiber. Our technique opens the route towards the direct
integration of laser-cooled atomic ensembles within fiber networks, an
important prerequisite for large scale quantum communication schemes. Moreover,
it is ideally suited to the realization of hybrid quantum systems that combine
atoms with, e.g., solid state quantum devices
Quantum Clock Synchronization Based on Shared Prior Entanglement
We demonstrate that two spatially separated parties (Alice and Bob) can
utilize shared prior quantum entanglement, and classical communications, to
establish a synchronized pair of atomic clocks. In contrast to classical
synchronization schemes, the accuracy of our protocol is independent of Alice
or Bob's knowledge of their relative locations or of the properties of the
intervening medium.Comment: 4 page
A Quantum Rosetta Stone for Interferometry
Heisenberg-limited measurement protocols can be used to gain an increase in
measurement precision over classical protocols. Such measurements can be
implemented using, e.g., optical Mach-Zehnder interferometers and Ramsey
spectroscopes. We address the formal equivalence between the Mach-Zehnder
interferometer, the Ramsey spectroscope, and the discrete Fourier transform.
Based on this equivalence we introduce the ``quantum Rosetta stone'', and we
describe a projective-measurement scheme for generating the desired
correlations between the interferometric input states in order to achieve
Heisenberg-limited sensitivity. The Rosetta stone then tells us the same method
should work in atom spectroscopy.Comment: 8 pages, 4 figure
Husimi's function and quantum interference in phase space
We discuss a phase space description of the photon number distribution of non
classical states which is based on Husimi's function and does not
rely in the WKB approximation. We illustrate this approach using the examples
of displaced number states and two photon coherent states and show it to
provide an efficient method for computing and interpreting the photon number
distribution . This result is interesting in particular for the two photon
coherent states which, for high squeezing, have the probabilities of even and
odd photon numbers oscillating independently.Comment: 15 pages, 12 figures, typos correcte
The impact of Covid-19 on unethical practices in global supply chains
As a result of the disruptions caused by Covid-19, this research aims to understand the current state of global textile supply chains, and what impacts the pandemic has caused to the risks of modern slavery and labour exploitation.
By taking a wide scope of literature and surveys from multiple stakeholders including: industry, governmental, international, business membership, and non-governmental organisations, we hoped to gain a broad understanding of the current issues.
Our objectives were to assess the various impacts the industry has faced, what actions were taken, and what was the reasoning behind those actions. Furthermore, we wanted to evaluate what had been the result of the actions taken and how had the structure of global textile supply chains affected their resilience to the pandemic.
From this we were able to highlight the complexity of the problems currently at play with the industry and the variety of decisions being made to try and combat them, as well as the risk to workers within the system and the unpredictability of how the pandemic will unfold
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