8,782 research outputs found
Probing the charge of a quantum dot with a nanomechanical resonator
We have used the mechanical motion of a carbon nanotube (CNT) as a probe of
the average charge on a quantum dot. Variations of the resonance frequency and
the quality factor are determined by the change in average charge on the
quantum dot during a mechanical oscillation. The average charge, in turn, is
influenced by the gate voltage, the bias voltage, and the tunnel rates of the
barriers to the leads. At bias voltages that exceed the broadening due to
tunnel coupling, the resonance frequency and quality factor show a double dip
as a function of gate voltage. We find that increasing the current flowing
through the CNT at the Coulomb peak does not increase the damping, but in fact
decreases damping. Using a model with energy-dependent tunnel rates, we obtain
quantitative agreement between the experimental observations and the model. We
theoretically compare different contributions to the single-electron induced
nonlinearity, and show that only one term is significant for both the Duffing
parameter and the mode coupling parameter. We also present additional
measurements which support the model we develop: Tuning the tunnel barriers of
the quantum dot to the leads gives a 200-fold decrease of the quality factor.
Single-electron tunneling through an excited state of the CNT quantum dot also
changes the average charge on the quantum dot, bringing about a decrease in the
resonance frequency. In the Fabry-P\'{e}rot regime, the absence of charge
quantization results in a spring behaviour without resonance frequency dips,
which could be used, for example, to probe the transition from quantized to
continuous charge with a nanomechanical resonator.Comment: 17 pages, 12 figure
Transillumination imaging through scattering media by use of photorefractive polymers
We demonstrate the use of a near-infrared-sensitive photorefractive polymer with high efficiency for imaging through scattering media, using an all-optical holographic time gate. Imaging through nine scattering mean free paths is performed at 800 nm with a mode-locked continuous-wave Ti:sapphire laser
Multiwavelength observations of the Be/X-ray binary 4U1145-619
We report optical and infrared observations of the massive X-ray binary
system 4U1145-619 (V801 Cen) which show that the circumstellar disc of the Be
star component is in decline. Infrared J,H,K,L magnitudes of V801Cen have been
monitored from 1993 March to 1996 April. H alpha spectra have been obtained
throughout the same period. We find that both the infrared excess and the
Balmer emission have been in decline throughout the period of observations. A
13 year optical and X-ray history of the source has been collated, revealing a
possible correlation between the optical and X-ray activity. In addition, we
have used u,v,b,y,beta indices, corrected for both circumstellar and
interstellar effects, to calculate the physical parameters of the underlying B
star.Comment: 8 pages postscript. Accepted by MNRA
Radiative Electroweak Symmetry-Breaking Revisited
In the absence of a tree-level scalar-field mass, renormalization-group
methods permit the explicit summation of leading-logarithm contributions to all
orders of the perturbative series within the effective potential for
electroweak symmetry. This improvement of the effective
potential function is seen to reduce residual dependence on the renormalization
mass scale. The all-orders summation of leading logarithm terms involving the
dominant three couplings contributing to radiative corrections is suggestive of
a potential characterized by a plausible Higgs boson mass of 216 GeV. However,
the tree potential's local minimum at is restored if QCD is
sufficiently strong.Comment: revtex, 4 pages, 1 eps figure embedded in manuscript. Updated version
contains additional comments and corrects minor error
Buffalo National River Ecosystems - Part II
The priorities were established for the Buffalo National River Ecosystem Studies through meetings and correspondence with Mr. Roland Wauer and other personnel of the Office of Natural Sciences, Southwest Region of the National Park Service. These priorities were set forth in the appendix of contract no. CX 700050443 dated May 21, 1975
Strong coupling between single-electron tunneling and nano-mechanical motion
Nanoscale resonators that oscillate at high frequencies are useful in many
measurement applications. We studied a high-quality mechanical resonator made
from a suspended carbon nanotube driven into motion by applying a periodic
radio frequency potential using a nearby antenna. Single-electron charge
fluctuations created periodic modulations of the mechanical resonance
frequency. A quality factor exceeding 10^5 allows the detection of a shift in
resonance frequency caused by the addition of a single-electron charge on the
nanotube. Additional evidence for the strong coupling of mechanical motion and
electron tunneling is provided by an energy transfer to the electrons causing
mechanical damping and unusual nonlinear behavior. We also discovered that a
direct current through the nanotube spontaneously drives the mechanical
resonator, exerting a force that is coherent with the high-frequency resonant
mechanical motion.Comment: Main text 12 pages, 4 Figures, Supplement 13 pages, 6 Figure
The impact of population-based faecal occult blood test screening on colorectal cancer mortality:a matched cohort study
BACKGROUND: Randomised trials show reduced colorectal cancer (CRC) mortality with faecal occult blood testing (FOBT). This outcome is now examined in a routine, population-based, screening programme. METHODS: Three biennial rounds of the UK CRC screening pilot were completed in Scotland (2000–2007) before the roll out of a national programme. All residents (50–69 years) in the three pilot Health Boards were invited for screening. They received a FOBT test by post to complete at home and return for analysis. Positive tests were followed up with colonoscopy. Controls, selected from non-pilot Health Boards, were matched by age, gender, and deprivation and assigned the invitation date of matched invitee. Follow-up was from invitation date to 31 December 2009 or date of death if earlier. RESULTS: There were 379 655 people in each group (median age 55.6 years, 51.6% male). Participation was 60.6%. There were 961 (0.25%) CRC deaths in invitees, 1056 (0.28%) in controls, rate ratio (RR) 0.90 (95% confidence interval (CI) 0.83–0.99) overall and 0.73 (95% CI 0.65–0.82) for participants. Non-participants had increased CRC mortality compared with controls, RR 1.21 (95% CI 1.06–1.38). CONCLUSION: There was a 10% relative reduction in CRC mortality in a routine screening programme, rising to 27% in participants
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