15,522 research outputs found
Secret objectives: promoting inquiry and tackling preconceptions in teaching laboratories
In its most general form, a `secret objective' is any inconsistency between
the experimental reality and the information provided to students prior to
starting work on an experiment. Students are challenged to identify the secret
objectives and then given freedom to explore and understand the experiment,
thus encouraging and facilitating genuine inquiry elements in introductory
laboratory courses. Damping of a simple pendulum is used as a concrete example
to demonstrate how secret objectives can be included. We also discuss the
implications of the secret objectives method and how this can provide a link
between the concepts of problem based learning and inquiry style labs
Active control of spacecraft charging on ATS-5 and ATS-6
Effects on spacecraft ground potential of active emission of charged particles are being investigated through experiments using the ATS-5 and ATS-6 spacecraft. Each spacecraft is equipped with ion engine neutralizers which emit low energy charged particles. Despite great differences in design between the two spacecraft, they attain similar potentials in similar environments. Therefore, effects on spacecraft potential of neutralizer operations can be used to compare the effects of operating the two different neutralizers (hot wire filament and plasma bridge). The neutralizers on both spacecraft were operated in eclipse. Results of these operations are presented and spacecraft responses compared
Ultrahigh Error Threshold for Surface Codes with Biased Noise
We show that a simple modification of the surface code can exhibit an
enormous gain in the error correction threshold for a noise model in which
Pauli Z errors occur more frequently than X or Y errors. Such biased noise,
where dephasing dominates, is ubiquitous in many quantum architectures. In the
limit of pure dephasing noise we find a threshold of 43.7(1)% using a tensor
network decoder proposed by Bravyi, Suchara and Vargo. The threshold remains
surprisingly large in the regime of realistic noise bias ratios, for example
28.2(2)% at a bias of 10. The performance is in fact at or near the hashing
bound for all values of the bias. The modified surface code still uses only
weight-4 stabilizers on a square lattice, but merely requires measuring
products of Y instead of Z around the faces, as this doubles the number of
useful syndrome bits associated with the dominant Z errors. Our results
demonstrate that large efficiency gains can be found by appropriately tailoring
codes and decoders to realistic noise models, even under the locality
constraints of topological codes.Comment: 6 pages, 5 figures, comments welcome; v2 includes minor improvements
to the numerical results, additional references, and an extended discussion;
v3 published version (incorporating supplementary material into main body of
paper
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Motion adaptation and attention: A critical review and meta-analysis
The motion aftereffect (MAE) provides a behavioural probe into the mechanisms underlying motion perception, and has been used to study the effects of attention on motion processing. Visual attention can enhance detection and discrimination of selected visual signals. However, the relationship between attention and motion processing remains contentious: not all studies find that attention increases MAEs. Our meta-analysis reveals several factors that explain superficially discrepant findings. Across studies (37 independent samples, 76 effects) motion adaptation was significantly and substantially enhanced by attention (Cohen's d = 1.12, p < .0001). The effect more than doubled when adapting to translating (vs. expanding or rotating) motion. Other factors affecting the attention-MAE relationship included stimulus size, eccentricity and speed. By considering these behavioural analyses alongside neurophysiological work, we conclude that feature-based (rather than spatial, or object-based) attention is the biggest driver of sensory adaptation. Comparisons between naïve and non-naïve observers, different response paradigms, and assessment of 'file-drawer effects' indicate that neither response bias nor publication bias are likely to have significantly inflated the estimated effect of attention
Quantum computational renormalization in the Haldane phase
Single-spin measurements on the ground state of an interacting spin lattice
can be used to perform a quantum computation. We show how such measurements can
mimic renormalization group transformations and remove the short-ranged
variations of the state that can reduce the fidelity of a computation. This
suggests that the quantum computational ability of a spin lattice could be a
robust property of a quantum phase. We illustrate our idea with the ground
state of a spin-1 chain, which can serve as a quantum computational wire not
only at the Affleck-Kennedy-Lieb-Tasaki point, but within the
rotationally-invariant Haldane phase.Comment: v2: 4 pages, 3 figures; improved description of buffering scheme and
connection to string operators. v3: final published versio
Differential Privacy and the Fat-Shattering Dimension of Linear Queries
In this paper, we consider the task of answering linear queries under the
constraint of differential privacy. This is a general and well-studied class of
queries that captures other commonly studied classes, including predicate
queries and histogram queries. We show that the accuracy to which a set of
linear queries can be answered is closely related to its fat-shattering
dimension, a property that characterizes the learnability of real-valued
functions in the agnostic-learning setting.Comment: Appears in APPROX 201
Sulfate-Reducing Bacteria Community Analysis: ISCO/ISB Coupled Remediation
Improved techniques for remediating groundwater systems are required for the more than 500,000 contaminated sites in North America. Many of these sites are the legacy of historical industrial operations, inappropriate disposal practices and accidental releases. The most widely observed contaminant at many of these sites is petroleum hydrocarbons (PHCs). Recently, remediation efforts that involve the sequential application of treatment technologies have gained widespread interest. One specific sequential technology application or treatment train employs the aggressive nature of a chemical oxidation followed by bioremediation for polishing. When persulfate is used as the chemical oxidant its natural degradation by-product is sulfate, an electron acceptor for sulfate-reducing bacteria. Hence in this thesis, the focus is on ways to optimize the mass removal behaviour of a treatment train that involves the use of PHC biodegrading sulfate-reducing bacteria as a bioremediation tool for the ‘polishing’ of a contaminated site. Persulfate was predicted to have a multitude of effects on microbial communities, both positive and negative. It was hypothesized that the production of sulfate would enhance the sulfate-reducing community and subsequently increase biodegradation potential following a persulfate treatment. However, the use of a strong oxidant like persulfate may also have detrimental effects on microbial communities. In order to test this hypothesis, a bench-scale system was implemented to gather data for the analyses of this remediation technique. Microbiological methods and chemical analyses of geochemical parameters were used to examine diversity, richness and abundance of sulfate-reducing communities following persulfate treatments. Initially, the successful generation of anaerobic bioreactors containing an indigenous sulfate-reducing microbial community from a freshwater aquifer was completed and confirmed using colony-PCR. Approximately 3 ppm total PHC was then introduced into the reactors and the microbial community was then allowed to acclimate to the conditions. PHC biodegradation was confirmed (~ 5.7 µg/L/hr). The community was then exposed to two types of oxidants, unactivated and alkaline-activated persulfate. Immediately following exposure, culture-based methods revealed almost complete reduction of the microbial community (≤101 CFU/mL and SRB cells/mL). qPCR on a gene conserved within the sulfate-reducing phylogeny confirmed this reduction. However, by the fourth week of the recovery phase, bacterial counts and target genes rose above pre-treatment levels, indicating enhancement of the sulfate-reducing community following the oxidant exposure(s). However, the recovered community displayed differences in structure and function, as revealed by microbial community fingerprint profiles and a lowered biodegradation potential (~2.7 µg/L/hr). Overall this research illustrated the successful application of a remediation treatment train at a bench-scale level
The CAG trinucleotide repeat length in the androgen receptor does not predict the early onset of prostate cancer
Objective To relate the repeat length of the androgen-receptor CAG trinucleotide to the age of onset of prostate cancer, stage and grade of disease. Patients and methods After obtaining ethical approval, 265 patients with locally confined or locally advanced/metastatic prostate cancer were identified and evaluated for age at diagnosis (less than 65 years and greater than 75 years). DNA was extracted from peripheral blood lymphocytes and 1 mug aliquots subjected to polymerase chain reaction using fluorescently labelled primers. Samples were then run on an ABI 377 gene scan analysis gel with an internal molecular weight marker. The length of the CAG repeat was determined by comparing the gene scan product size to samples where the CAG repeat length had been quantified using direct sequencing. The Kruskal-Wallis, Mann-Whitney and Wilcoxon two sample tests were used to analyse the data. Results The mean (range) length of the CAG repeat in the androgen receptor was 22.2 (10-31) in the younger and 22.5 (16-32) in the older group, and was not statistically different. There was no significant association between the CAG repeat length and the age of onset of prostate cancer (P = 0.568) or with stage (P = 0.577) and grade (P = 0.891) of prostate cancer. Conclusion These results suggest that there is no correlation between the androgen receptor CAG repeat length and the age of onset, stage and grade of prostate cancer, confirming recent doubts from other similar studies of a suggested correlation between shorter androgen receptor CAG repeat and early onset and aggressiveness of prostate cancer
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
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