4,164 research outputs found
Quantum Non-Barking Dogs
Quantum weak measurements with states both pre- and postselected offer a
window into a hitherto neglected sector of quantum mechanics. A class of such
systems involves time dependent evolution with transitions possible. In this
paper we explore two very simple systems in this class. The first is a toy
model representing the decay of an excited atom. The second is the tunneling of
a particle through a barrier. The postselection criteria are chosen as follows:
at the final time, the "atom" remains in its initial excited state for the
first example and the particle remains behind the barrier for the second. We
then ask what weak values are predicted in the physical environment of the
"atom" (to which no net energy has been transferred) and in the region beyond
the barrier (to which the particle has not tunneled). Previous work suggests
that very large weak values might arise in these regions for long durations
between pre- and postselection times. Our calculations reveal some distinct
differences between the two model systems.Comment: 8 pages, 3 figure
Clean Water for Less Integrated Planning Reduces the Cost of Meeting Water Quality Goals in New Hampshire
Rising populations and increased development in New Hampshire coastal communities have led to a decline in water quality in the Great Bay Estuary. Responding effectively and affordably to new federal permit requirements for treating and discharging stormwater and wastewater will require innovative solutions from communities in the area. The Water Integration for Squamscott-Exeter (WISE) project developed an integrated planning framework through which the coastal communities of Exeter, Stratham, and Newfields could significantly reduce the cost of meeting permit requirements. In this brief, authors Alison Watts, Robert Roseen, Paul Stacey, Renee Bourdeau, and Theresa Walker report that integrated planning could save these communities over $100 million (in fifty-year lifecycle costs) by prioritizing high-impact, low-cost mitigation strategies across permit type and town boundaries. The project, which has received an Environmental Merit award from Environment Protection Agency, also found that attainment of water quality standards in the Exeter–Squamscott River will not be possible without substantial cooperation and investment from upstream communities, which are not currently subject to EPA permit requirements. Collaboration among communities in planning and implementing projects to meet clean water regulations can have significant cost and effectiveness benefits
Risk Perceptions of Arsenic in Tap Water and Consumption of Bottled Water
The demand for bottled water has increased rapidly over the past decade, but bottled water is extremely costly compared to tap water. The convenience of bottled water surely matters to consumers, but are others factors at work? This manuscript examines whether purchases of bottled water are associated with the perceived risk of tap water. All of the past studies on bottled water consumption have used simple scale measures of perceived risk that do not correspond to risk measures used by risk analysts. We elicit a probability-based measure of risk and find that as perceived risks rise, expenditures for bottled water rise.Environmental Economics and Policy, Risk and Uncertainty, Q25, Q53, I12,
16S rRNA gene-based profiling of the human infant gut microbiota is strongly influenced by sample processing and PCR primer choice
Acknowledgements The authors acknowledge the assistance of Grietje Holtrop (RINH-BioSS) with the statistical analysis of the data and the Wellcome Trust Sanger Institute’s 454 pyrosequencing team for generating 16S rRNA gene data. AWW, PS and JP received core funding support from the Wellcome Trust [grant number 098051]. AWW, JCM, HJF and KPS are funded by the Scottish Government (SG-RESAS).Peer reviewedPublisher PD
An analysis of the normal accelerations and airspeeds of a two-engine type of transport airplane in commercial operations on routes in the central United States from 1948 to 1950
Evolutionary Transitions and Top-Down Causation
Top-down causation has been suggested to occur at all scales of biological
organization as a mechanism for explaining the hierarchy of structure and
causation in living systems. Here we propose that a transition from bottom-up
to top-down causation -- mediated by a reversal in the flow of information from
lower to higher levels of organization, to that from higher to lower levels of
organization -- is a driving force for most major evolutionary transitions. We
suggest that many major evolutionary transitions might therefore be marked by a
transition in causal structure. We use logistic growth as a toy model for
demonstrating how such a transition can drive the emergence of collective
behavior in replicative systems. We then outline how this scenario may have
played out in those major evolutionary transitions in which new, higher levels
of organization emerged, and propose possible methods via which our hypothesis
might be tested.Comment: 8 pages, 4 figure
Stress in the Patella Following Autologous Chondrocyte Implantation - A Finite Element Study
Bovine patella cartilage shows signs of damage and cell death when subjected to a compressive cyclic load of 6 MPa, which results in a shear stress of 5.6 MPa. The aim of this research was to investigate the effect of activities of daily living (descending stairs, bicycling and deep flexion) on the contact stresses in the patellofemoral compartment following an articular chondrocyte implantation (ACI). A finite element (FE) model of the patellar femoral joint was created and dynamic non-linear analyses were carried out for this purpose. A shear stress of 5.6 MPa was used as the threshold that cartilage can tolerate without resulting in damage. The FE model was verified numerically. Our results show that, for a 70 kg individual at 50% recovery, (i) contact stress in the patella is 11% higher than that in the femur; (ii) shear stress in the host cartilage reaches 4.75 MPa at 50° of flexion; (iii) shear stress in the patella host cartilage is twice that in a healthy cartilage during deep flexion approaching 70°; (iv) maximum shear stress value was 2.75 MPa during cycling at 60% load; (v) stress shielding still occurs through the host cartilage even when the implanted cartilage reaches 97.5% the Young’s modulus of a healthy cartilage. Based on these results, (i) using an exercise bicycle is recommended for rehabilitation; (ii) deep knee flexion should be avoided; (iii) obese people with a BMI of over 42 kg/m2 should not undertake vigorous weight-bearing exercises involving deep knee flexion
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