Showing papers by "University of Waterloo published in 2011"
TL;DR: In this paper, a simple realization of the 3D Weyl semimetal phase was proposed, utilizing a multilayer structure, composed of identical thin films of a magnetically doped 3D topological insulator, separated by ordinary-insulator spacer layers.
Abstract: We propose a simple realization of the three-dimensional (3D) Weyl semimetal phase, utilizing a multilayer structure, composed of identical thin films of a magnetically doped 3D topological insulator, separated by ordinary-insulator spacer layers. We show that the phase diagram of this system contains a Weyl semimetal phase of the simplest possible kind, with only two Dirac nodes of opposite chirality, separated in momentum space, in its band structure. This Weyl semimetal has a finite anomalous Hall conductivity and chiral edge states and occurs as an intermediate phase between an ordinary insulator and a 3D quantum anomalous Hall insulator. We find that the Weyl semimetal has a nonzero dc conductivity at zero temperature, but Drude weight vanishing as ${T}^{2}$, and is thus an unusual metallic phase, characterized by a finite anomalous Hall conductivity and topologically protected edge states.
1,803 citations
TL;DR: A survey of speech emotion classification addressing three important aspects of the design of a speech emotion recognition system, the choice of suitable features for speech representation, and the proper preparation of an emotional speech database for evaluating system performance are addressed.
1,735 citations
TL;DR: In this paper, the authors highlight the progress made over the past 40 years with a detailed discussion of recent works in the area of non-precious metal electrocatalysts for oxygen reduction reaction, a necessary reaction at the PEM fuel cell cathode.
Abstract: With the approaching commercialization of PEM fuel cell technology, developing active, inexpensive non-precious metal ORR catalyst materials to replace currently used Pt-based catalysts is a necessary and essential requirement in order to reduce the overall system cost. This review paper highlights the progress made over the past 40 years with a detailed discussion of recent works in the area of non-precious metal electrocatalysts for oxygen reduction reaction, a necessary reaction at the PEM fuel cell cathode. Several important kinds of unsupported or carbon supported non-precious metal electrocatalysts for ORR are reviewed, including non-pyrolyzed and pyrolyzed transition metal nitrogen-containing complexes, conductive polymer-based catalysts, transition metal chalcogenides, metal oxides/carbides/nitrides/oxynitrides/carbonitrides, and enzymatic compounds. Among these candidates, pyrolyzed transition metal nitrogen-containing complexes supported on carbon materials (M–Nx/C) are considered the most promising ORR catalysts because they have demonstrated some ORR activity and stability close to that of commercially available Pt/C catalysts. Although great progress has been achieved in this area of research and development, there are still some challenges in both their ORR activity and stability. Regarding the ORR activity, the actual volumetric activity of the most active non-precious metal catalyst is still well below the DOE 2015 target. Regarding the ORR stability, stability tests are generally run at low current densities or low power levels, and the lifetime is far shorter than targets set by DOE. Therefore, improving both the ORR activity and stability are the major short and long term focuses of non-precious metal catalyst research and development. Based on the results achieved in this area, several future research directions are also proposed and discussed in this paper.
1,628 citations
TL;DR: In this paper, the authors studied the effect of perturbation of the critical point between a normal insulator and a topological insulator, which breaks either time-reversal (TR) or inversion symmetry.
Abstract: We present a study of ``nodal-semimetal'' phases in which nondegenerate conduction and valence bands touch at points (the ``Weyl semimetal'') or lines (the ``line-node semimetal'') in three-dimensional momentum space. We discuss a general approach to such states by perturbation of the critical point between a normal insulator (NI) and a topological insulator (TI), breaking either time-reversal (TR) or inversion symmetry. We give an explicit model realization of both types of states in a NI-TI superlattice structure with broken TR symmetry. Both the Weyl and the line-node semimetals are characterized by topologically protected surface states, although in the line-node case, some additional symmetries must be imposed to retain this topological protection. The edge states have the form of ``Fermi arcs'' in the case of the Weyl semimetal: these are chiral gapless edge states, which exist in a finite region in momentum space, determined by the momentum-space separation of the bulk Weyl nodes. The chiral character of the edge states leads to a finite Hall conductivity. In contrast, the edge states of the line-node semimetal are ``flat bands'': these states are approximately dispersionless in a subset of the two-dimensional edge Brillouin zone, given by the projection of the line node onto the plane of the edge. We discuss unusual transport properties of the nodal semimetals and, in particular, point out quantum critical-like scaling of the dc and optical conductivities of the Weyl semimetal and similarities to the conductivity of graphene in the line-node case.
1,333 citations
Journal Article•
TL;DR: The epidemiological distinction between the generic term "physical activity" and the specific category of "exercise", which implies activity for a specific purpose such as improvement of physical condition or competition is recognised.
Abstract: An ever-growing volume of peer-reviewed publications speaks to the recent and rapid growth in both scope and understanding of exercise immunology. Indeed, more than 95% of all peer-reviewed publications in exercise immunology (currently >2, 200 publications using search terms "exercise" and "immune") have been published since the formation of the International Society of Exercise and Immunology (ISEI) in 1989 (ISI Web of Knowledge). We recognise the epidemiological distinction between the generic term "physical activity" and the specific category of "exercise", which implies activity for a specific purpose such as improvement of physical condition or competition. Extreme physical activity of any type may have implications for the immune system. However, because of its emotive component, exercise is likely to have a larger effect, and to date the great majority of our knowledge on this subject comes from exercise studies.
1,260 citations
TL;DR: This paper aims to test the hypothesis that when viewing natural images, the optimal perceptual weights for pooling should be proportional to local information content, which can be estimated in units of bit using advanced statistical models of natural images.
Abstract: Many state-of-the-art perceptual image quality assessment (IQA) algorithms share a common two-stage structure: local quality/distortion measurement followed by pooling. While significant progress has been made in measuring local image quality/distortion, the pooling stage is often done in ad-hoc ways, lacking theoretical principles and reliable computational models. This paper aims to test the hypothesis that when viewing natural images, the optimal perceptual weights for pooling should be proportional to local information content, which can be estimated in units of bit using advanced statistical models of natural images. Our extensive studies based upon six publicly-available subject-rated image databases concluded with three useful findings. First, information content weighting leads to consistent improvement in the performance of IQA algorithms. Second, surprisingly, with information content weighting, even the widely criticized peak signal-to-noise-ratio can be converted to a competitive perceptual quality measure when compared with state-of-the-art algorithms. Third, the best overall performance is achieved by combining information content weighting with multiscale structural similarity measures.
1,147 citations
15 Aug 2011
TL;DR: DevoFlow is designed and evaluated, a modification of the OpenFlow model which gently breaks the coupling between control and global visibility, in a way that maintains a useful amount of visibility without imposing unnecessary costs.
Abstract: OpenFlow is a great concept, but its original design imposes excessive overheads. It can simplify network and traffic management in enterprise and data center environments, because it enables flow-level control over Ethernet switching and provides global visibility of the flows in the network. However, such fine-grained control and visibility comes with costs: the switch-implementation costs of involving the switch's control-plane too often and the distributed-system costs of involving the OpenFlow controller too frequently, both on flow setups and especially for statistics-gathering.In this paper, we analyze these overheads, and show that OpenFlow's current design cannot meet the needs of high-performance networks. We design and evaluate DevoFlow, a modification of the OpenFlow model which gently breaks the coupling between control and global visibility, in a way that maintains a useful amount of visibility without imposing unnecessary costs. We evaluate DevoFlow through simulations, and find that it can load-balance data center traffic as well as fine-grained solutions, without as much overhead: DevoFlow uses 10--53 times fewer flow table entries at an average switch, and uses 10--42 times fewer control messages.
1,132 citations
TL;DR: In this paper, the authors reported the creation of Greenberger-Horne-Zeilinger states with up to 14 qubits by investigating the coherence of up to 8 ions over time and observed a decay proportional to the square of the number of qubits.
Abstract: We report the creation of Greenberger-Horne-Zeilinger states with up to 14 qubits. By investigating the coherence of up to 8 ions over time, we observe a decay proportional to the square of the number of qubits. The observed decay agrees with a theoretical model which assumes a system affected by correlated, Gaussian phase noise. This model holds for the majority of current experimental systems developed towards quantum computation and quantum metrology.
1,008 citations
TL;DR: P porous nanoparticle-supported lipid bilayers (protocells) that synergistically combine properties of liposomes and nanoporous particles are reported that allow a single protocell loaded with a drug cocktail to kill a drug-resistant HCC cell, representing a 106-fold improvement over comparable liposome.
Abstract: Encapsulation of drugs within nanocarriers that selectively target malignant cells promises to mitigate side effects of conventional chemotherapy and to enable delivery of the unique drug combinations needed for personalized medicine. To realize this potential, however, targeted nanocarriers must simultaneously overcome multiple challenges, including specificity, stability and a high capacity for disparate cargos. Here we report porous nanoparticle-supported lipid bilayers (protocells) that synergistically combine properties of liposomes and nanoporous particles. Protocells modified with a targeting peptide that binds to human hepatocellular carcinoma exhibit a 10,000-fold greater affinity for human hepatocellular carcinoma than for hepatocytes, endothelial cells or immune cells. Furthermore, protocells can be loaded with combinations of therapeutic (drugs, small interfering RNA and toxins) and diagnostic (quantum dots) agents and modified to promote endosomal escape and nuclear accumulation of selected cargos. The enormous capacity of the high-surface-area nanoporous core combined with the enhanced targeting efficacy enabled by the fluid supported lipid bilayer enable a single protocell loaded with a drug cocktail to kill a drug-resistant human hepatocellular carcinoma cell, representing a 10(6)-fold improvement over comparable liposomes.
944 citations
TL;DR: The evidence indicates that the impact of health warnings depends upon their size and design: whereas obscure text-only warnings appear to have little impact, prominent health warnings on the face of packages serve as a prominent source of health information for smokers and non-smokers, can increase health knowledge and perceptions of risk and can promote smoking cessation.
Abstract: Objective To review evidence on the impact of health warning messages on tobacco packages. Data sources Articles were identified through electronic databases of published articles, as well as relevant ‘grey’ literature using the following keywords: health warning, health message, health communication, label and labelling in conjunction with at least one of the following terms: smoking, tobacco, cigarette, product, package and pack. Study selection and data extraction: Relevant articles available prior to January 2011 were screened for six methodological criteria. A total of 94 original original articles met inclusion criteria, including 72 quantitative studies, 16 qualitative studies, 5 studies with both qualitative and qualitative components, and 1 review paper: Canada (n¼35), USA (n¼29) Australia (n¼16), UK (n¼13), The Netherlands (n¼3), France (n¼3), New Zealand (n¼3), Mexico (n¼3), Brazil (n¼2), Belgium (n¼1), other European countries (n¼10), Norway (n¼1), Malaysia (n¼1) and China (n¼1). Results The evidence indicates that the impact of health warnings depends upon their size and design: whereas obscure text-only warnings appear to have little impact, prominent health warnings on the face of packages serve as a prominent source of health information for smokers and non-smokers, can increase health knowledge and perceptions of risk and can promote smoking cessation. The evidence also indicates that comprehensive warnings are effective among youth and may help to prevent smoking initiation. Pictorial health warnings that elicit strongemotionalreactionsaresignificantlymoreeffective. Conclusions Health warnings on packages are among the most direct and prominent means of communicating with smokers. Larger warnings with pictures are significantly more effective than smaller, text-only messages.
925 citations
Swinburne University of Technology1, New York University2, University of Western Australia3, University of Copenhagen4, University of Queensland5, Australian Astronomical Observatory6, University of Sydney7, California Institute of Technology8, University of Waterloo9, University of Chicago10, Australia Telescope National Facility11, Carnegie Institution for Science12, Monash University, Clayton campus13, Australian National University14, University of British Columbia15, University of Toronto16
TL;DR: In this paper, the authors present measurements of the baryon acoustic peak at redshifts z = 0.44, 0.6 and 0.73 in the galaxy correlation function of the final dataset of the WiggleZ Dark Energy Survey.
Abstract: We present measurements of the baryon acoustic peak at redshifts z = 0.44, 0.6 and 0.73 in the galaxy correlation function of the final dataset of the WiggleZ Dark Energy Survey. We combine our correlation function with lower-redshift measurements from the 6-degree Field Galaxy Survey and Sloan Digital Sky Survey, producing a stacked survey correlation function in which the statistical significance of the detection of the baryon acoustic peak is 4.9-σ relative to a zero-baryon model with no peak. We fit cosmological models to this combined baryon acoustic oscillation (BAO) dataset comprising six distance-redshift data points, and compare the results to similar fits to the latest compilation of supernovae (SNe) and Cosmic Microwave Background (CMB) data. The BAO and SNe datasets produce consistent measurements of the equation-ofstate w of dark energy, when separately combined with the CMB, providing a powerful check for systematic errors in either of these distance probes. Combining all datasets we determine w = 1.03 ± 0.08 for a flat Universe, consistent with a cosmological constant model. Assuming dark energy is a cosmological constant and varying the spatial curvature, we find k = 0.004± 0.006.
University of Colorado Boulder1, University of Toronto2, Pierre-and-Marie-Curie University3, University of Oxford4, University of Paris5, Centre national de la recherche scientifique6, Aix-Marseille University7, INAF8, Las Cumbres Observatory Global Telescope Network9, University of California, Santa Barbara10, Defence Research and Development Canada11, University of Victoria12, California Institute of Technology13, Centra14, Lawrence Berkeley National Laboratory15, University of Waterloo16, Australian Astronomical Observatory17, University of California, Berkeley18
TL;DR: In this article, the authors combine high redshift Type Ia supernovae from the first 3 years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-$z, 93 SDSS, 242 SNLS, and 14 {\it Hubble Space Telescope}).
Abstract: We combine high redshift Type Ia supernovae from the first 3 years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-$z$, 93 SDSS, 242 SNLS, and 14 {\it Hubble Space Telescope}). SN data alone require cosmic acceleration at >99.9% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least $z=1.4$) in a flat universe, we find $w = -0.91^{+0.16}_{-0.20}(\mathrm{stat}) ^{+0.07}_{-0.14} (\mathrm{sys})$ from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematics covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems.
TL;DR: A new concept to mitigate the problem of dissolution of intermediate polysulphide reaction species into the electrolyte is reported, which relies on the design principles of drug delivery and functions as an internal polysULphide reservoir during the reversible electrochemical process to give rise to long-term stabilization and improved coulombic efficiency.
Abstract: The possibility of achieving high-energy, long-life storage batteries has tremendous scientific and technological significance. An example is the Li-S cell, which can offer a 3-5-fold increase in energy density compared with conventional Li-ion cells, at lower cost. Despite significant advances, there are challenges to its wide-scale implementation, which include dissolution of intermediate polysulphide reaction species into the electrolyte. Here we report a new concept to mitigate the problem, which relies on the design principles of drug delivery. Our strategy employs absorption of the intermediate polysulphides by a porous silica embedded within the carbon-sulphur composite that not only absorbs the polysulphides by means of weak binding, but also permits reversible desorption and release. It functions as an internal polysulphide reservoir during the reversible electrochemical process to give rise to long-term stabilization and improved coulombic efficiency. The reservoir mechanism is general and applicable to Li/S cathodes of any nature.
TL;DR: Nanocrystalline cellulose (NCC) is an emerging renewable nanomaterial that holds promise in many different applications, such as in personal care, chemicals, foods, pharmaceuticals, etc as discussed by the authors.
Abstract: Nanocrystalline cellulose (NCC) is an emerging renewable nanomaterial that holds promise in many different applications, such as in personal care, chemicals, foods, pharmaceuticals, etc. By appropriate modification of NCC, various functional nanomaterials with outstanding properties, or significantly improved physical, chemical, biological, as well as electronic properties can be developed. The nanoparticles are stabilised in aqueous suspension by negative charges on the surface, which are produced during the acid hydrolysis process. NCC suspensions can form a chiral nematic ordered phase beyond a critical concentration, i.e. NCC suspensions transform from an isotropic to an anisotropic chiral nematic liquid crystalline phase. Due to its nanoscale dimension and intrinsic physicochemical properties, NCC is a promising renewable biomaterial that can be used as a reinforcing component in high performance nanocomposites. Many new nanocomposite materials with attractive properties were obtained by the physical incorporation of NCC into a natural or synthetic polymeric matrix. Simple chemical modification on NCC surface can improve its dispersability in different solvents and expand its utilisation in nano-related applications, such as drug delivery, protein immobilisation, and inorganic reaction template. This review paper provides an overview on this emerging nanomaterial, focusing on the surface modification, properties and applications of NCC.
TL;DR: The genetic regulation and molecular components involved in biofilm formation and maturation in the context of the Gram-positive cocci, Staphylococcus aureus, are explored.
Abstract: Increasing attention has been focused on understanding bacterial biofilms and this growth modality's relation to human disease. In this review we explore the genetic regulation and molecular components involved in biofilm formation and maturation in the context of the Gram-positive cocci, Staphylococcus aureus. In addition, we discuss diseases and host immune responses, along with current therapies associated with S. aureus biofilm infections and prevention strategies.
University of Waterloo1, Stockholm University2, Royal Swedish Academy of Sciences3, Centre for International Governance Innovation4, University of Calgary5, Erasmus University Rotterdam6, University of Sussex7, Stockholm Environment Institute8, Catholic University of Leuven9, Université catholique de Louvain10, International Institute for Applied Systems Analysis11, Stanford University12, Hasso Plattner Institute13, Arizona State University14
TL;DR: The central question is whether social and technical innovations can reverse the trends that are challenging critical thresholds and creating tipping points in the earth system, and if not, what conditions are necessary to escape the current lock-in.
Abstract: This article explores the links between agency, institutions, and innovation in navigating shifts and large-scale transformations toward global sustainability. Our central question is whether social and technical innovations can reverse the trends that are challenging critical thresholds and creating tipping points in the earth system, and if not, what conditions are necessary to escape the current lock-in. Large-scale transformations in information technology, nano- and biotechnology, and new energy systems have the potential to significantly improve our lives; but if, in framing them, our globalized society fails to consider the capacity of the biosphere, there is a risk that unsustainable development pathways may be reinforced. Current institutional arrangements, including the lack of incentives for the private sector to innovate for sustainability, and the lags inherent in the path dependent nature of innovation, contribute to lock-in, as does our incapacity to easily grasp the interactions implicit in complex problems, referred to here as the ingenuity gap. Nonetheless, promising social and technical innovations with potential to change unsustainable trajectories need to be nurtured and connected to broad institutional resources and responses. In parallel, institutional entrepreneurs can work to reduce the resilience of dominant institutional systems and position viable shadow alternatives and niche regimes.
TL;DR: This method incorporates indexed primers to enable the characterization of multiple microbial communities in a single flow cell lane, may be modified readily to target other variable regions or genes, and demonstrates unprecedented and economical access to DNAs from organisms that exist at low relative abundances.
Abstract: Microbial communities host unparalleled taxonomic diversity. Adequate characterization of environmental and host-associated samples remains a challenge for microbiologists, despite the advent of 16S rRNA gene sequencing. In order to increase the depth of sampling for diverse bacterial communities, we developed a method for sequencing and assembling millions of paired-end reads from the 16S rRNA gene (spanning the V3 region; ∼200 nucleotides) by using an Illumina genome analyzer. To confirm reproducibility and to identify a suitable computational pipeline for data analysis, sequence libraries were prepared in duplicate for both a defined mixture of DNAs from known cultured bacterial isolates (>1 million postassembly sequences) and an Arctic tundra soil sample (>6 million postassembly sequences). The Illumina 16S rRNA gene libraries represent a substantial increase in number of sequences over all extant next-generation sequencing approaches (e.g., 454 pyrosequencing), while the assembly of paired-end 125-base reads offers a methodological advantage by incorporating an initial quality control step for each 16S rRNA gene sequence. This method incorporates indexed primers to enable the characterization of multiple microbial communities in a single flow cell lane, may be modified readily to target other variable regions or genes, and demonstrates unprecedented and economical access to DNAs from organisms that exist at low relative abundances.
TL;DR: Nutrition labels on pre-packaged foods are a cost-effective population-level intervention with unparalleled reach, however, governments will need to explore new formats and different types of information content to ensure that nutrition information is accessible and understandable.
Abstract: Objective To review research on consumer use and understanding of nutrition labels, as well as the impact of labelling on dietary habits. Design A systematic review was conducted by searching electronic databases. Relevant articles were screened by two reviewers and included if they met inclusion criteria, including eight methodological criteria. A total of 120 articles were included in the review, including cross-sectional surveys ( n 96), experimental designs ( n 17), ‘natural experiments’ ( n 7) and longitudinal population-based surveys ( n 2). Setting Articles covered seven jurisdictions: USA ( n 88), Europe ( n 12), Canada ( n 9), Australia and New Zealand ( n 4), Norway ( n 2), Thailand ( n 1) and Trinidad ( n 1). Subjects Participants were from a wide range of age groups, socio-economic strata and geographical regions. Results Nutrition labels on pre-packaged foods are among the most prominent sources of nutrition information. Nutrition labels are perceived as a highly credible source of information and many consumers use nutrition labels to guide their selection of food products. Evidence also shows a consistent link between the use of nutrition labels and healthier diets. However, the use of labels varies considerably across subgroups, with lower use among children, adolescents and older adults who are obese. Research also highlights challenges in terms of consumer understanding and appropriate use of labelling information. Conclusions Nutrition labels on pre-packaged foods are a cost-effective population-level intervention with unparalleled reach. However, to capitalize on their potential, governments will need to explore new formats and different types of information content to ensure that nutrition information is accessible and understandable.
TL;DR: In this article, the state and transport mechanism of water in different components of PEMFC are elaborated in detail, and the experimental techniques have been developed to predict distributions of water, gas species, temperature and other parameters in polymer electrolyte membrane fuel cell (PEMFC).
TL;DR: An Internet of Things application, smart community, is introduced, which refers to a paradigmatic class of cyber-physical systems with cooperating objects (i.e., networked smart homes), and the smart community architecture is defined.
Abstract: In this article, we introduce an Internet of Things application, smart community, which refers to a paradigmatic class of cyber-physical systems with cooperating objects (i.e., networked smart homes). We then define the smart community architecture, and describe how to realize secure and robust networking among individual homes. We present two smart community applications, Neighborhood Watch and Pervasive Healthcare, with supporting techniques and associated challenges, and envision a few value-added smart community services.
TL;DR: In this article, a superconducting qubit was used to probe the noise spectrum of a spin system with an energy-relaxation time T 1 = 12 μs.
Abstract: Quantum coherence in natural and artificial spin systems is fundamental to applications ranging from quantum information science to magnetic-resonance imaging and identification. Several multipulse control sequences targeting generalized noise models have been developed to extend coherence by dynamically decoupling a spin system from its noisy environment. In any particular implementation, however, the efficacy of these methods is sensitive to the specific frequency distribution of the noise, suggesting that these same pulse sequences could also be used to probe the noise spectrum directly. Here we demonstrate noise spectroscopy by means of dynamical decoupling using a superconducting qubit with energy-relaxation time T1 =12 μs. We first demonstrate that dynamical decoupling improves the coherence time T 2 in this system up to the T2 =2 T1 limit (pure dephasing times exceeding 100 μs), and then leverage its filtering properties to probe the environmental noise over a frequency (f) range 0.2-20 MHz, observing a 1/fα distribution with α < 1. The characterization of environmental noise has broad utility for spin-resonance applications, enabling the design of optimized coherent-control methods, promoting device and materials engineering, and generally improving coherence. © 2011 Macmillan Publishers Limited. All rights reserved.
TL;DR: It is proved that the protocol provides an efficient and reliable estimate of the average error-rate for a set operations (gates) under a very general noise model that allows for both time and gate-dependent errors.
Abstract: In this Letter we propose a fully scalable randomized benchmarking protocol for quantum information processors. We prove that the protocol provides an efficient and reliable estimate of the average error-rate for a set operations (gates) under a very general noise model that allows for both time and gate-dependent errors. In particular we obtain a sequence of fitting models for the observable fidelity decay as a function of a (convergent) perturbative expansion of the gate errors about the mean error. We illustrate the protocol through numerical examples.
TL;DR: An experiment determined the trajectories of single photons through a two-slit interferometer and reconstructed these trajectories by performing a weak measurement of the photon momentum, postselected according to the result of a strong measurement of photon position in a series of planes.
Abstract: A consequence of the quantum mechanical uncertainty principle is that one may not discuss the path or "trajectory" that a quantum particle takes, because any measurement of position irrevocably disturbs the momentum, and vice versa. Using weak measurements, however, it is possible to operationally define a set of trajectories for an ensemble of quantum particles. We sent single photons emitted by a quantum dot through a double-slit interferometer and reconstructed these trajectories by performing a weak measurement of the photon momentum, postselected according to the result of a strong measurement of photon position in a series of planes. The results provide an observationally grounded description of the propagation of subensembles of quantum particles in a two-slit interferometer.
Jacobs University Bremen1, Max Planck Society2, Howard Hughes Medical Institute3, University of Colorado Boulder4, Michigan State University5, Marine Biological Laboratory6, Plymouth Marine Laboratory7, Argonne National Laboratory8, University of Chicago9, National Institutes of Health10, Yonsei University11, University of Manchester12, University of Oxford13, Harvard University14, New York University15, University of Pennsylvania16, United States Department of Energy17, Los Alamos National Laboratory18, University of Maryland, Baltimore19, Ghent University20, Lawrence Berkeley National Laboratory21, University of Southern California22, National Ecological Observatory Network23, Baylor College of Medicine24, University of New Mexico25, Washington University in St. Louis26, University of Queensland27, San Diego State University28, Cornell University29, Technische Universität München30, J. Craig Venter Institute31, University of Waterloo32, Oak Ridge National Laboratory33, Vrije Universiteit Brussel34, University of Guelph35, United States Department of Veterans Affairs36, Stanford University37
TL;DR: To establish a unified standard for describing sequence data and to provide a single point of entry for the scientific community to access and learn about GSC checklists, the minimum information about any (x) sequence is presented (MIxS).
Abstract: Here we present a standard developed by the Genomic Standards Consortium (GSC) for reporting marker gene sequences—the minimum information about a marker gene sequence (MIMARKS). We also introduce a system for describing the environment from which a biological sample originates. The ‘environmental packages’ apply to any genome sequence of known origin and can be used in combination with MIMARKS and other GSC checklists. Finally, to establish a unified standard for describing sequence data and to provide a single point of entry for the scientific community to access and learn about GSC checklists, we present the minimum information about any (x) sequence (MIxS). Adoption of MIxS will enhance our ability to analyze natural genetic diversity documented by massive DNA sequencing efforts from myriad ecosystems in our ever-changing biosphere.
29 Nov 2011
TL;DR: In this article, the authors proposed a quantum-resistant public-key cryptosystem based on the conjectured difficulty of finding isogenies between supersingular elliptic curves, which allows the two parties to arrive at a common shared key despite the noncommutativity of the endomorphism ring.
Abstract: We present new candidates for quantum-resistant public-key cryptosystems based on the conjectured difficulty of finding isogenies between supersingular elliptic curves. The main technical idea in our scheme is that we transmit the images of torsion bases under the isogeny in order to allow the two parties to arrive at a common shared key despite the noncommutativity of the endomorphism ring. Our work is motivated by the recent development of a subexponential-time quantum algorithm for constructing isogenies between ordinary elliptic curves. In the supersingular case, by contrast, the fastest known quantum attack remains exponential, since the noncommutativity of the endomorphism ring means that the approach used in the ordinary case does not apply. We give a precise formulation of the necessary computational assumption along with a discussion of its validity. In addition, we present implementation results showing that our protocols are multiple orders of magnitude faster than previous isogeny-based cryptosystems over ordinary curves.
Royal Swedish Academy of Sciences1, Stockholm University2, Stockholm Environment Institute3, University of Wisconsin-Madison4, University of Alaska Fairbanks5, Stanford University6, Swedish University of Agricultural Sciences7, Indiana University8, Arizona State University9, University of Minnesota10, Australian National University11, Commonwealth Scientific and Industrial Research Organisation12, University of Waterloo13
TL;DR: It is suggested that the Millennium Development Goals need to be reframed in such a planetary stewardship context combined with a call for a new social contract on global sustainability.
Abstract: Humanity has emerged as a major force in the operation of the biosphere, with a significant imprint on the Earth System, challenging social–ecological resilience. This new situation calls for a fundamental shift in perspectives, world views, and institutions. Human development and progress must be reconnected to the capacity of the biosphere and essential ecosystem services to be sustained. Governance challenges include a highly interconnected and faster world, cascading social–ecological interactions and planetary boundaries that create vulnerabilities but also opportunities for social–ecological change and transformation. Tipping points and thresholds highlight the importance of understanding and managing resilience. New modes of flexible governance are emerging. A central challenge is to reconnect these efforts to the changing preconditions for societal development as active stewards of the Earth System. We suggest that the Millennium Development Goals need to be reframed in such a planetary stewardship context combined with a call for a new social contract on global sustainability. The ongoing mind shift in human relations with Earth and its boundaries provides exciting opportunities for societal development in collaboration with the biosphere—a global sustainability agenda for humanity.
University of Oxford1, Pierre-and-Marie-Curie University2, University of Toronto3, University of Colorado Boulder4, University of Paris5, Centre national de la recherche scientifique6, Aix-Marseille University7, INAF8, University of California, Santa Barbara9, Las Cumbres Observatory Global Telescope Network10, Defence Research and Development Canada11, University of Victoria12, California Institute of Technology13, Lawrence Berkeley National Laboratory14, University of Waterloo15, Perimeter Institute for Theoretical Physics16, Australian Astronomical Observatory17, Centra18, University of California, Berkeley19
TL;DR: In this article, the authors present observational constraints on the nature of dark energy using the Supernova Legacy Survey three-year sample (SNLS3) of Guy et al. and Conley et al., and they find that the cosmological constraints derived from these different subsamples are consistent.
Abstract: We present observational constraints on the nature of dark energy using the Supernova Legacy Survey three-year sample (SNLS3) of Guy et al. and Conley et al. We use the 472 Type Ia supernovae (SNe Ia) in this sample, accounting for recently discovered correlations between SN Ia luminosity and host galaxy properties, and include the effects of all identified systematic uncertainties directly in the cosmological fits. Combining the SNLS3 data with the full WMAP7 power spectrum, the Sloan Digital Sky Survey luminous red galaxy power spectrum, and a prior on the Hubble constant H_0 from SHOES, in a flat universe we find Ω_m = 0.269 ± 0.015 and w = –1.061^(+0.069)_(–0.068) (where the uncertainties include all statistical and SN Ia systematic errors)—a 6.5% measure of the dark energy equation-of-state parameter w. The statistical and systematic uncertainties are approximately equal, with the systematic uncertainties dominated by the photometric calibration of the SN Ia fluxes—without these calibration effects, systematics contribute only a ~2% error in w. When relaxing the assumption of flatness, we find Ω_m = 0.271 ± 0.015, Ω_k = –0.002 ± 0.006, and w = –1.069^(+0.091)_(–0.092). Parameterizing the time evolution of w as w(a) = w_0 + w_a (1–a) gives w_0 = –0.905 ± 0.196, w_a = –0.984^(+1.094)_(– 1.097) in a flat universe. All of our results are consistent with a flat, w = –1 universe. The size of the SNLS3 sample allows various tests to be performed with the SNe segregated according to their light curve and host galaxy properties. We find that the cosmological constraints derived from these different subsamples are consistent. There is evidence that the coefficient, β, relating SN Ia luminosity and color, varies with host parameters at >4σ significance (in addition to the known SN luminosity-host relation); however, this has only a small effect on the cosmological results and is currently a subdominant systematic.
TL;DR: The adsorption of 12, 18, 24, and 36-mer single-stranded DNA on graphene oxide is affected by several factors, and shorter DNAs are adsorbed more rapidly and bind more tightly to the surface of graphene, which is favored by a lower pH and a higher ionic strength.
Abstract: Being the newest member of the carbon materials family, graphene possesses many unique physical properties resulting is a wide range of applications. Recently, it was discovered that graphene oxide can effectively adsorb DNA, and at the same time, it can completely quench adsorbed fluorophores. These properties make it possible to prepare DNA-based optical sensors using graphene oxide. While practical analytical applications are being demonstrated, the fundamental understanding of binding between graphene oxide and DNA in solution received relatively less attention. In this work, we report that the adsorption of 12-, 18-, 24-, and 36-mer single-stranded DNA on graphene oxide is affected by several factors. For example, shorter DNAs are adsorbed more rapidly and bind more tightly to the surface of graphene. The adsorption is favored by a lower pH and a higher ionic strength. The presence of organic solvents such as ethanol can either increase or decrease adsorption depending on the ionic strength of the so...
University of Leeds1, National Institute of Amazonian Research2, Forestry Commission3, Wageningen University and Research Centre4, University of St Andrews5, James Cook University6, Indiana University7, Paul Sabatier University8, Forest Research Institute9, University of Edinburgh10, University of São Paulo11, University of Waterloo12, University of New Hampshire13, Hokkaido University14, Universiti Brunei Darussalam15, Forest Research Institute Malaysia16, United States Forest Service17, Oregon State University18, University of Twente19, Universidade do Estado de Mato Grosso20, University of York21, Commonwealth Scientific and Industrial Research Organisation22, National University of Colombia23, University of Cambridge24, University of Yaoundé I25
TL;DR: In this article, the authors developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries, and used this database to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap).
Abstract: . Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: 1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap). 2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A). 3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level H across all plots to within amedian −2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account.
TL;DR: In this article, the authors developed a model of community support based on the social exchange theory, which contained fourteen hypothesized relationships and was tested using the LISREL package from responses collected from residents of Grand-Baie, Mauritius.