2,809 research outputs found
An Invisible Quantum Tripwire
We present here a quantum tripwire, which is a quantum optical interrogation
technique capable of detecting an intrusion with very low probability of the
tripwire being revealed to the intruder. Our scheme combines interaction-free
measurement with the quantum Zeno effect in order to interrogate the presence
of the intruder without interaction. The tripwire exploits a curious nonlinear
behaviour of the quantum Zeno effect we discovered, which occurs in a lossy
system. We also employ a statistical hypothesis testing protocol, allowing us
to calculate a confidence level of interaction-free measurement after a given
number of trials. As a result, our quantum intruder alert system is robust
against photon loss and dephasing under realistic atmospheric conditions and
its design minimizes the probabilities of false positives and false negatives
as well as the probability of becoming visible to the intruder.Comment: Improved based on reviewers comments; 5 figure
Navigating Our Past, Present, and Future using Mo‘olelo: Sitting beside Our Ancestors.
Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017
The Cyclic Connectivity of Homogeneous Arcwise Connected Continua
A continuum is cyclicly connected provided each pair of its points lie together on some simple closed curve. In 1927, G. T. Whyburn proved that a locally connected plane continuum is cyclicly connected if and only if it contains no separating points. This theorem was fundamental in his original treatment of cyclic element theory. Since then numerous authors have obtained extensions of Whyburn\u27s theorem. In this paper we characterize cyclic connectedness in the class of all Hausdorff continua
Simulations and Measurements of the Background Encountered by a High-Altitude Balloon-Borne Experiment for Hard X-ray Astronomy
We have modelled the hard X-ray background expected for a high-altitude
balloon flight of the Energetic X-ray Telescope Experiment (EXITE2), an imaging
phoswich detector/telescope for the 20--600 keV energy range. Photon and
neutron-induced contributions to the background are considered. We describe the
code and the results of a series of simulations with different shielding
configurations. The simulated hard X-ray background for the actual flight
configuration agrees reasonably well (within a factor of 2) with the
results measured on the first flight of EXITE2 from Palestine, Texas. The
measured background flux at 100 keV is 4 10 counts
cm s keV.Comment: 17 pages Latex (uses aaspp4.sty) plus 7 postscript figures: available
in file figs.tar.g
The bronchodilator response in preschool children: A systematic review
BACKGROUND: The bronchodilator response (BDR) is frequently used to support diagnostic and therapeutic decision-making for children who wheeze. However, there is little evidence-based guidance describing the role of BDR testing in preschool children and it is unclear whether published cut-off values, which are derived from adult data, can be applied to this population. METHODS: We searched MEDLINE, EMBASE, Web of Science, and Cochrane databases (inception-September 2015) for studies reporting response to a bronchodilator in healthy preschool children, response following placebo inhalation, and the diagnostic efficacy of BDR compared with a clinical diagnosis of asthma/recurrent wheezing. FINDINGS: We included 14 studies. Thirteen studies provided BDR data from healthy preschool children. Two studies reported response to placebo in preschool children with asthma/recurrent wheezing. Twelve studies compared BDR measurements from preschool children with asthma/recurrent wheeze to those from healthy children and seven of these studies reported diagnostic efficacy. Significant differences between the BDR measured in healthy preschool children compared with that in children with asthma/recurrent wheeze were demonstrated in some, but not all studies. Techniques such as interrupter resistance, oscillometry, and plethysmography were more consistently successfully completed than spirometry. Between study heterogeneity precluded determination of an optimum technique. INTERPRETATION: There is little evidence to suggest spirometry-based BDR can be used in the clinical assessment of preschool children who wheeze. Further evaluation of simple alternative techniques is required. Future studies should recruit children in whom airways disease is suspected and should evaluate the ability of BDR testing to predict treatment response
Correlated Depletion and Dilution of Lithium and Beryllium Revealed by Subgiants in M 67
The surface content of lithium (Li) and beryllium (Be) provide insights into
the mixing and circulation mechanisms in stellar interiors. The old open
cluster, M 67, has been well-studied for Li abundances in both main-sequence
and evolved stars. The Be abundances give us a probe to a deeper level in
stars. We have taken high-resolution spectra with Keck I with HIRES to
determine Be abundances along the subgiant branch of M 67, where there are
dramatic depletions of Li. These subgiants range in mass from 1.26 to 1.32
M and have evolved from main-sequence stars that would have occupied
the region of the Li-Be dip found in younger clusters. Lithium abundances have
been adjusted to the same scale for 103 stars in M 67 by Pace et al. The more
massive stars now the coolest and furthest-evolved from the main-sequence
show a drop in Li by a factor of 400 across the subgiant branch. Our new Be
abundances also show a decline, but by a factor of 50. The two elements
decline together with Li showing a steeper decline in these subgiants than it
does in the Li-Be dip stars. The relative decline in Be abundance compared to
Li is remarkably well fit by the models of Sills & Deliyannis, made
specifically for the subgiants in M 67. Those models include the effects of
mixing induced by stellar rotation. These M 67 subgiants show the effects of
both main-sequence depletion and post-main-sequence dilution of both Li and Be.Comment: 31 pages with 3 tables, 13 figures Accepted by Ap. J. 10/7/201
An Inward-Facing Conformation of a Putative Metal-Chelate–Type ABC Transporter
The crystal structure of a putative metal-chelate–type adenosine triphosphate (ATP)–binding cassette (ABC) transporter encoded by genes HI1470 and HI1471 of Haemophilus influenzae has been solved at 2.4 angstrom resolution. The permeation pathway exhibits an inward-facing conformation, in contrast to the outward-facing state previously observed for the homologous vitamin B12 importer BtuCD. Although the structures of both HI1470/1 and BtuCD have been solved in nucleotide-free states, the pairs of ABC subunits in these two structures differ by a translational shift in the plane of the membrane that coincides with a repositioning of the membrane-spanning subunits. The differences observed between these ABC transporters involve relatively modest rearrangements and may serve as structural models for inward- and outward-facing conformations relevant to the alternating access mechanism of substrate translocation
- …