398 research outputs found
Quantum metrology beyond the classical limit under the effect of dephasing
Quantum sensors have the potential to outperform their classical
counterparts. For classical sensing, the uncertainty of the estimation of the
target fields scales inversely with the square root of the measurement time T.
On the other hand, by using quantum resources, we can reduce this scaling of
the uncertainty with time to 1/T. However, as quantum states are susceptible to
dephasing, it has not been clear whether we can achieve sensitivities with a
scaling of 1/T for a measurement time longer than the coherence time. Here, we
propose a scheme that estimates the amplitude of globally applied fields with
the uncertainty of 1/T for an arbitrary time scale under the effect of
dephasing. We use one-way quantum computing based teleportation between qubits
to prevent any increase in the correlation between the quantum state and its
local environment from building up and have shown that such a teleportation
protocol can suppress the local dephasing while the information from the target
fields keeps growing. Our method has the potential to realize a quantum sensor
with a sensitivity far beyond that of any classical sensor
The lost innocence of ethanol: power, knowledge, discourse, and U.S. biofuel policy
Doctor of PhilosophyDepartment of GeographyLisa HarringtonIn the United States, rationales for corn ethanol policies have included national energy
security, air pollution abatement, clean technology development, and climate change mitigation.
The ostensible benefits of corn ethanol have been used to justify the transfer of federal funds
toward corn and ethanol production subsidies, consumption mandates, and import restrictions,
plus substantial research and development efforts. Public and private sector funding has also
focused on efforts to commercially develop biofuels from advanced technology using cellulosic
biomass. Despite decades of public and commercial interest, cellulosic ethanol has failed to
commercialize, corn ethanol remains heavily dependent on subsidies, and each of the alleged
benefits of ethanol has been hotly disputed.
This research examines the links between interest groups and rationales for biofuel
policies. Drawing from Foucauldian discourse analysis, the research identifies key discourses
supporting and opposed to biofuel development, and their relation to broader issues in
environmental and energy politics. This approach involved a detailed review of newspaper
archives, policy documents, Congressional bills, committee hearings and debates, governmental
and non-governmental reports, and scientific research findings. It reveals how a powerful
coalition of agricultural interests succeeded in harnessing biofuel discourses to popular public
and political environmental and energy concerns.
The primary discourses identified were Environmental Bureaucracy, Free Markets,
Ecological Modernization, and Limits. A common element in the first three of these was
Techno-Optimism. A Limits discourse opposed ethanol expansion, primarily based on a narrative
of competition for agricultural land, and stood apart from other discourses in its mistrust of
science and technology to resolve environmental problems. The research concludes that
Foucauldian discourse analysis provides a useful tool for examining key shifts in policy debates,
for clarifying the relationship between scientific knowledge and discursive power, for
understanding divisions within environmental discourse, and for revealing the importance of
scale in environmental public policy process
The efficiencies of generating cluster states with weak non-linearities
We propose a scalable approach to building cluster states of matter qubits
using coherent states of light. Recent work on the subject relies on the use of
single photonic qubits in the measurement process. These schemes can be made
robust to detector loss, spontaneous emission and cavity mismatching but as a
consequence the overhead costs grow rapidly, in particular when considering
single photon loss. In contrast, our approach uses continuous variables and
highly efficient homodyne measurements. We present a two-qubit scheme, with a
simple bucket measurement system yielding an entangling operation with success
probability 1/2. Then we extend this to a three-qubit interaction, increasing
this probability to 3/4. We discuss the important issues of the overhead cost
and the time scaling. This leads to a "no-measurement" approach to building
cluster states, making use of geometric phases in phase space.Comment: 21 pages, to appear in special issue of New J. Phys. on
"Measurement-Based Quantum Information Processing
Constructing 2D and 3D cluster states with photonic modules
Large scale quantum information processing (QIP) and distributed quantum
computation require the ability to perform entangling operations on a large
number of qubits. We describe a new photonic module which prepares,
deterministically, photonic cluster states using an atom in a cavity as an
ancilla. Based on this module we design a network for constructing 2D cluster
states and then we extend the architecture to 3D topological cluster states.
Advantages of our design include a passive switching mechanism and the
possibility of using global control pulses for the atoms in the cavity. The
architecture described here is well suited for integrated photonic circuits on
a chip and could be used as a basis of a future quantum optical processor or in
a quantum repeater node
Integration of highly probabilistic sources into optical quantum architectures: perpetual quantum computation
In this paper we introduce a design for an optical topological cluster state
computer constructed exclusively from a single quantum component. Unlike
previous efforts we eliminate the need for on demand, high fidelity photon
sources and detectors and replace them with the same device utilised to create
photon/photon entanglement. This introduces highly probabilistic elements into
the optical architecture while maintaining complete specificity of the
structure and operation for a large scale computer. Photons in this system are
continually recycled back into the preparation network, allowing for a
arbitrarily deep 3D cluster to be prepared using a comparatively small number
of photonic qubits and consequently the elimination of high frequency,
deterministic photon sources.Comment: 19 pages, 13 Figs (2 Appendices with additional Figs.). Comments
welcom
Recursive quantum repeater networks
Internet-scale quantum repeater networks will be heterogeneous in physical
technology, repeater functionality, and management. The classical control
necessary to use the network will therefore face similar issues as Internet
data transmission. Many scalability and management problems that arose during
the development of the Internet might have been solved in a more uniform
fashion, improving flexibility and reducing redundant engineering effort.
Quantum repeater network development is currently at the stage where we risk
similar duplication when separate systems are combined. We propose a unifying
framework that can be used with all existing repeater designs. We introduce the
notion of a Quantum Recursive Network Architecture, developed from the emerging
classical concept of 'recursive networks', extending recursive mechanisms from
a focus on data forwarding to a more general distributed computing request
framework. Recursion abstracts independent transit networks as single relay
nodes, unifies software layering, and virtualizes the addresses of resources to
improve information hiding and resource management. Our architecture is useful
for building arbitrary distributed states, including fundamental distributed
states such as Bell pairs and GHZ, W, and cluster states.Comment: 14 page
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Nucleoside supplementation modulates mitochondrial DNA copy number in the dguok -/- zebrafish.
Deoxyguanosine kinase (dGK) is an essential rate-limiting component of the mitochondrial purine nucleotide salvage pathway, encoded by the nuclear gene encoding deoxyguanosine kinase (DGUOK). Mutations in DGUOK lead to mitochondrial DNA (mtDNA) depletion typically in the liver and brain, causing a hepatocerebral phenotype. Previous work has shown that in cultured DGUOK patient cells it is possible to rescue mtDNA depletion by increasing substrate amounts for dGK. In this study we developed a mutant dguok zebrafish (Danio rerio) line using CRISPR/Cas9 mediated mutagenesis; dguok-/- fish have significantly reduced mtDNA levels compared with wild-type (wt) fish. When supplemented with only one purine nucleoside (dGuo), mtDNA copy number in both mutant and wt juvenile animals was significantly reduced, contrasting with previous cell culture studies, possibly because of nucleotide pool imbalance. However, in adult dguok-/- fish we detected a significant increase in liver mtDNA copy number when supplemented with both purine nucleosides. This study further supports the idea that nucleoside supplementation has a potential therapeutic benefit in mtDNA depletion syndromes by substrate enhancement of the purine nucleoside salvage pathway and might improve the liver pathology in patients
Primate cognition in zoos : reviewing the impact of zoo-based research over 15 years
This work was supported by the European Research Council under the European Union’s Seventh Framework Program (FP7/2007-2013)/ERC grant agreement no. 609819, SOMICS (EM, EW, ST), UK Economic and Social Research Council studentship 2267016 and the St Leonard’s Research Scholarship from the University of St Andrews (KD).Primate cognition research is reliant on access to members of the study species and logistical infrastructures to conduct observations and experiments. Historically founded in research centers and private collections, and spreading to modern zoos, sanctuaries, and the field, primate cognition has been investigated in diverse settings, each with benefits and challenges. In our systematic review of 12 primatology, animal behavior, and animal cognition journals over the last 15 years, we turn a spotlight on zoos to quantify their current impact on the field and to highlight their potential as robust contributors to future work. To put zoo-based research in context, we compare zoos to three other site types: university-owned or independent research centers, sanctuaries, and field sites. We assess the contributions of zoos across several critical considerations in primate cognition research, including number of investigations, species diversity, sample size, research topic diversity, and methodology. We identified 1,119 publications reporting studies of primate cognition, almost 25% of which report research conducted in zoos. Across publications, zoo-based research has greater species diversity than research centers and covers a diverse range of research topics. Although our review is merely a snapshot of primate cognition research, our findings suggest that zoos may present advantages to researchers regarding species diversity, and lack some of the methodological constraints of field sites, allowing greater ease of access to a diverse range of subjects for cognition investigations. We suggest that zoos have great potential as key contributors for future investigations in primate cognition. Finally, we shed light on the symbiotic relationship that can emerge between researchers and zoos, forming partnerships that bring unique advantages to both parties.Publisher PDFPeer reviewe
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RNA exosome mutations in pontocerebellar hypoplasia alter ribosome biogenesis and p53 levels.
The RNA exosome is a ubiquitously expressed complex of nine core proteins (EXOSC1-9) and associated nucleases responsible for RNA processing and degradation. Mutations in EXOSC3, EXOSC8, EXOSC9, and the exosome cofactor RBM7 cause pontocerebellar hypoplasia and motor neuronopathy. We investigated the consequences of exosome mutations on RNA metabolism and cellular survival in zebrafish and human cell models. We observed that levels of mRNAs encoding p53 and ribosome biogenesis factors are increased in zebrafish lines with homozygous mutations of exosc8 or exosc9, respectively. Consistent with higher p53 levels, mutant zebrafish have a reduced head size, smaller brain, and cerebellum caused by an increased number of apoptotic cells during development. Down-regulation of EXOSC8 and EXOSC9 in human cells leads to p53 protein stabilisation and G2/M cell cycle arrest. Increased p53 transcript levels were also observed in muscle samples from patients with EXOSC9 mutations. Our work provides explanation for the pathogenesis of exosome-related disorders and highlights the link between exosome function, ribosome biogenesis, and p53-dependent signalling. We suggest that exosome-related disorders could be classified as ribosomopathies
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