1,276 research outputs found
Magnetic damping of a carbon nanotube NEMS resonator
A suspended, doubly clamped single wall carbon nanotube is characterized at
cryogenic temperatures. We observe specific switching effects in dc-current
spectroscopy of the embedded quantum dot. These have been identified previously
as nano-electromechanical self-excitation of the system, where positive
feedback from single electron tunneling drives mechanical motion. A magnetic
field suppresses this effect, by providing an additional damping mechanism.
This is modeled by eddy current damping, and confirmed by measuring the
resonance quality factor of the rf-driven nano-electromechanical resonator in
an increasing magnetic field.Comment: 8 pages, 3 figure
Resolution and Efficiency of the ATLAS Muon Drift-Tube Chambers at High Background Rates
The resolution and efficiency of a precision drift-tube chamber for the ATLAS
muon spectrometer with final read-out electronics was tested at the Gamma
Irradiation Facility at CERN in a 100 GeV muon beam and at photon irradiation
rates of up to 990 Hz/square cm which corresponds to twice the highest
background rate expected in ATLAS. A silicon strip detector telescope was used
as external reference in the beam. The pulse-height measurement of the read-out
electronics was used to perform time-slewing corrections which lead to an
improvement of the average drift-tube resolution from 104 microns to 82 microns
without irradiation and from 128 microns to 108 microns at the maximum expected
rate. The measured drift-tube efficiency agrees with the expectation from the
dead time of the read-out electronics up to the maximum expected rate
Co-sputtered MoRe thin films for carbon nanotube growth-compatible superconducting coplanar resonators
Molybdenum rhenium alloy thin films can exhibit superconductivity up to
critical temperatures of . At the same time, the films are
highly stable in the high-temperature methane / hydrogen atmosphere typically
required to grow single wall carbon nanotubes. We characterize molybdenum
rhenium alloy films deposited via simultaneous sputtering from two sources,
with respect to their composition as function of sputter parameters and their
electronic dc as well as GHz properties at low temperature. Specific emphasis
is placed on the effect of the carbon nanotube growth conditions on the film.
Superconducting coplanar waveguide resonators are defined lithographically; we
demonstrate that the resonators remain functional when undergoing nanotube
growth conditions, and characterize their properties as function of
temperature. This paves the way for ultra-clean nanotube devices grown in situ
onto superconducting coplanar waveguide circuit elements.Comment: 8 pages, 6 figure
HomeScout: Anti-Stalking Mobile App for Bluetooth Low Energy Devices
Bluetooth Low Energy (BLE) personal trackers are affordable devices misused to track nonconsensual individuals. Due to the increased misuse, Apple implemented two detection applications. However, the Android application is limited to user-initiated scans with a fixed detection algorithm. This paper focuses on reducing the misuse of malicious trackers by examining current solutions, potential generic detection approaches, and improving tracker detection times. HomeScout expands detection to the Tile and Samsung Galaxy SmartTag+, and examines the misuse potential of all BLE-enabled devices. HomeScout can reliably detect devices tracking the user as quickly as 1 minute once in motion by optimizing the parameters. The optimal parameter setting for distance is 200 m due to its high recall rate, for occurrence is 2, and for time is 1 minute. Furthermore, HomeScout applies the tracking algorithm to all BLE-enabled devices
A Cosmic Ray Measurement Facility for ATLAS Muon Chambers
Monitored Drift Tube (MDT) chambers will constitute the large majority of
precision detectors in the Muon Spectrometer of the ATLAS experiment at the
Large Hadron Collider at CERN. For commissioning and calibration of MDT
chambers, a Cosmic Ray Measurement Facility is in operation at Munich
University. The objectives of this facility are to test the chambers and
on-chamber electronics, to map the positions of the anode wires within the
chambers with the precision needed for standalone muon momentum measurement in
ATLAS, and to gain experience in the operation of the chambers and on-line
calibration procedures.
Until the start of muon chamber installation in ATLAS, 88 chambers built at
the Max Planck Institute for Physics in Munich have to be commissioned and
calibrated. With a data taking period of one day individual wire positions can
be measured with an accuracy of 8.3 micrometers in the chamber plane and 27
micrometers in the direction perpendicular to that plane.Comment: 14+1 pages, 11 figures, contributed paper to the EPS2003 conference,
Aache
Flow-Based Detection of IPv6-specific Network Layer Attacks
With a vastly different header format, IPv6 introduces new vulnerabilities not possible in IPv4, potentially requiring new detection algorithms. While many attacks specific to IPv6 have proven to be possible and are described in the literature, no detection solutions for these attacks have been proposed. In this study we identify and characterise IPv6-specific attacks that can be detected using flow monitoring. By constructing flow-based signatures, detection can be performed using available technologies such as NetFlow and IPFIX. To validate our approach, we implemented these signatures in a prototype, monitoring two production networks and injecting attacks into the production traffic
Incidence and survival of childhood bone cancer in northern England and the West Midlands, 1981–2002
There is a paucity of population-based studies examining incidence and survival trends in childhood bone tumours. We used high quality data from four population-based registries in England. Incidence patterns and trends were described using Poisson regression. Survival trends were analysed using Cox regression. There were 374 cases of childhood (ages 0–14 years) bone tumours (206 osteosarcomas, 144 Ewing sarcomas, 16 chondrosarcomas, 8 other bone tumours) registered in the period 1981–2002. Overall incidence (per million person years) rates were 2.63 (95% confidence interval (CI) 2.27–2.99) for osteosarcoma, 1.90 (1.58–2.21) for Ewing sarcoma and 0.21 (0.11–0.31) for chondrosarcoma. Incidence of Ewing sarcoma declined at an average rate of 3.1% (95% CI 0.6–5.6) per annum (P=0.04), which may be due to tumour reclassification, but there was no change in osteosarcoma incidence. Survival showed marked improvement over the 20 years (1981–2000) for Ewing sarcoma (hazard ratio (HR) per annum=0.95 95% CI 0.91–0.99; P=0.02). However, no improvement was seen for osteosarcoma patients (HR per annum=1.02 95% CI 0.98–1.05; P=0.35) over this time period. Reasons for failure to improve survival including potential delays in diagnosis, accrual to trials, adherence to therapy and lack of improvement in treatment strategies all need to be considered
HOCl chemistry in the Antarctic stratospheric vortex 2002, as observed with the Michelson interferometer for passive atmospheric sounding (MIPAS)
In the 2002 Antarctic polar vortex enhanced HOCl mixing ratios were detected by the Michelson Interferometer for Passive Atmospheric Sounding both at altitudes of around 35 km (1000K potential temperature), where HOCl abundances are ruled by gas phase chemistry and at around 18–24 km (475–625 K), which belongs to the altitude domain where heterogeneous chlorine chemistry is relevant. At altitudes of 33 to 40 km polar vortex HOCl mixing ratios were found to be around 0.14 ppbv as long as the polar vortex was intact, centered at the pole, and thus received relatively little sunlight. This is the altitude region where in midlatitudinal and tropic atmospheres peak HOCl mixing ratios significantly above 0.2 ppbv (in terms of daily mean values) are observed. After deformation and displacement of the polar vortex in the course of a major warming, ClO-rich vortex air was more exposed to sunlight, where enhanced HOx abundances led to largely increased HOCl mixing ratios (up to 0.3 ppbv), exceeding typical midlatitudinal and tropical amounts significantly. The HOCl increase was preceded by an increase of ClO. Model runs could reproduce these measurements only when the Stimpfle et al. (1979) rate constant for the reaction ClO+HO2→HOCl+O2 was used but not with the current JPL recommendation. At an altitude of 24 km, HOCl mixing ratios of up to 0.15 ppbv were detected. This HOCl enhancement, which is already visible in 18 September data, is attributed to heterogeneous chemistry, which is in agreement with observations of polar stratospheric clouds. The measurements were compared to a model run where no polar stratospheric clouds appeared during the observation period. The fact that HOCl still was produced in the model run suggests that a significant part of HOCl was generated from ClO rather than directly via heterogeneous reaction. Excess ClO, lower ClONO2 and earlier loss of HOCl in the measurements are attributed to ongoing heterogeneous chemistry which is not reproduced by the model. On 11 October, polar vortex mean daytime mixing ratios were only 0.03 ppbv
Childhood solid tumours in relation to population mixing around the time of birth
In a retrospective cohort study of 673 787 live births in the Northern Region of England, 1975 - 1994, we investigated whether a higher level of population mixing around birth was a risk factor for solid tumours, by diagnostic group (Hodgkin's disease, brain and spinal tumours, neuroblastoma, other solid tumours), diagnosed during 1975-2001 under age 15 years. Logistic regression was used to relate risk to population mixing, based on (i) all movers and (ii) incomers from outside the region. Both ward and county district level analyses were performed. There was a decreased risk of brain and spinal tumours with increasing population mixing based on incomers from outside the region (OR for trend across three categories = 0.79, 95% CI: 0.66-0.95, P = 0.01 in the ward level analysis). Although this may be because of chance, it is consistent with a role of exposure to infection and immunological response in the aetiology of these tumours. For other tumour groups, there was no consistent evidence of an association between risk and population mixing
Comparison of ECHAM5/MESSy Atmospheric Chemistry (EMAC) simulations of the Arctic winter 2009/2010 and 2010/2011 with Envisat/MIPAS and Aura/MLS observations
We present model simulations with the atmospheric chemistry–climate model
ECHAM5/MESSy Atmospheric Chemistry (EMAC) nudged toward European Centre for
Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalyses for the Arctic
winters 2009/2010 and 2010/2011. This study is the first to perform an
extensive assessment of the performance of the EMAC model for Arctic winters
as previous studies have only made limited evaluations of EMAC simulations
which also were mainly focused on the Antarctic winter stratosphere. We have
chosen the two extreme Arctic winters 2009/2010 and 2010/2011 to evaluate the
formation of polar stratospheric clouds (PSCs) and the representation of the
chemistry and dynamics of the polar winter stratosphere in EMAC. The EMAC
simulations are compared to observations by the Michelson Interferometer for
Passive Atmospheric Soundings (Envisat/MIPAS) and the observations from the
Aura Microwave Limb Sounder (Aura/MLS). The Arctic winter 2010/2011 was one
of the coldest stratospheric winters on record, leading to the strongest
depletion of ozone measured in the Arctic. The Arctic winter 2009/2010 was,
from the climatological perspective, one of the warmest stratospheric winters
on record. However, it was distinguished by an exceptionally cold
stratosphere (colder than the climatological mean) from mid-December 2009 to
mid-January 2010, leading to prolonged PSC formation and existence.
Significant denitrification, the removal of HNO3 from the
stratosphere by sedimentation of HNO3-containing polar stratospheric
cloud particles, occurred in that winter. In our comparison, we focus on PSC
formation and denitrification. The comparisons between EMAC simulations and
satellite observations show that model and measurements compare well for
these two Arctic winters (differences for HNO3 generally within
±20 %) and thus that EMAC nudged toward ECMWF ERA-Interim
reanalyses is capable of giving a realistic representation of the evolution
of PSCs and associated sequestration of gas-phase HNO3 in the polar
winter stratosphere. However, simulated PSC volume densities are smaller than
the ones derived from Envisat/MIPAS observations by a factor of 3–7. Further,
PSCs in EMAC are not simulated as high up (in altitude) as they are observed.
This underestimation of PSC volume density and vertical extension of the PSCs
results in an underestimation of the vertical redistribution of HNO3
due to denitrification/re-nitrification. The differences found here between
model simulations and observations stipulate further improvements in the EMAC
set-up for simulating PSCs
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