2,211 research outputs found
Performance of the ATLAS Precision Muon Chambers under LHC Operating Conditions
For the muon spectrometer of the ATLAS detector at the large hadron collider
(LHC), large drift chambers consisting of 6 to 8 layers of pressurized drift
tubes are used for precision tracking covering an active area of 5000 m2 in the
toroidal field of superconducting air core magnets. The chambers have to
provide a spatial resolution of 41 microns with Ar:CO2 (93:7) gas mixture at an
absolute pressure of 3 bar and gas gain of 2?104. The environment in which the
chambers will be operated is characterized by high neutron and background with
counting rates of up to 100 per square cm and second. The resolution and
efficiency of a chamber from the serial production for ATLAS has been
investigated in a 100 GeV muon beam at photon irradiation rates as expected
during LHC operation. A silicon strip detector telescope was used as external
reference in the beam. The spatial resolution of a chamber is degraded by 4 ?m
at the highest background rate. The detection efficiency of the drift tubes is
unchanged under irradiation. A tracking efficiency of 98% at the highest rates
has been demonstrated
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
Stochastic optimization of a cold atom experiment using a genetic algorithm
We employ an evolutionary algorithm to automatically optimize different
stages of a cold atom experiment without human intervention. This approach
closes the loop between computer based experimental control systems and
automatic real time analysis and can be applied to a wide range of experimental
situations. The genetic algorithm quickly and reliably converges to the most
performing parameter set independent of the starting population. Especially in
many-dimensional or connected parameter spaces the automatic optimization
outperforms a manual search.Comment: 4 pages, 3 figure
Two-point phase correlations of a one-dimensional bosonic Josephson junction
We realize a one-dimensional Josephson junction using quantum degenerate Bose
gases in a tunable double well potential on an atom chip. Matter wave
interferometry gives direct access to the relative phase field, which reflects
the interplay of thermally driven fluctuations and phase locking due to
tunneling. The thermal equilibrium state is characterized by probing the full
statistical distribution function of the two-point phase correlation.
Comparison to a stochastic model allows to measure the coupling strength and
temperature and hence a full characterization of the system
Predictors and Moderators of Quality of Life Among College Students With ADHD
Objective: The current study examines (a) whether ADHD among college students is associated with differences in perceptions of quality of life (QoL); (b) the moderating roles of comorbidity, drug use, psychopharmacological treatment, and psychosocial treatment; and (c) the total impact of these variables on QoL. Method: Participants were college students with and without ADHD (N = 372) in a longitudinal study. Results: College students with ADHD were more likely to assert negative global QoL evaluations relative to non-ADHD peers. The relationship between ADHD and QoL was not altered as a function of medication treatment, comorbid psychopathology, psychosocial treatment, or drug use. Conclusion: College students with ADHD behave similarly to other adults with ADHD in that they make lower subjective global evaluations of their QoL relative to their non-ADHD agemates. Other factors associated with ADHD and QoL do not appear to moderate this relationship
Wave packet dynamics of potassium dimers attached to helium nanodroplets
The dynamics of vibrational wave packets excited in K dimers attached to
superfluid helium nanodroplets is investigated by means of femtosecond
pump-probe spectroscopy. The employed resonant three-photon-ionization scheme
is studied in a wide wavelength range and different pathways leading to
K-formation are identified. While the wave packet dynamics of the
electronic ground state is not influenced by the helium environment,
perturbations of the electronically excited states are observed. The latter
reveal a strong time dependence on the timescale 3-8 ps which directly reflects
the dynamics of desorption of K off the helium droplets
Thermalization in a quasi-1D ultracold bosonic gas
We study the collisional processes that can lead to thermalization in
one-dimensional systems. For two body collisions excitations of transverse
modes are the prerequisite for energy exchange and thermalzation. At very low
temperatures excitations of transverse modes are exponentially suppressed,
thermalization by two body collisions stops and the system should become
integrable. In quantum mechanics virtual excitations of higher radial modes are
possible. These virtually excited radial modes give rise to effective
three-body velocity-changing collisions which lead to thermalization. We show
that these three-body elastic interactions are suppressed by pairwise quantum
correlations when approaching the strongly correlated regime. If the relative
momentum is small compared to the two-body coupling constant the
three-particle scattering state is suppressed by a factor of ,
which is proportional to , that is to the square of the
three-body correlation function at zero distance in the limit of the
Lieb-Liniger parameter . This demonstrates that in one
dimensional quantum systems it is not the freeze-out of two body collisions but
the strong quantum correlations which ensures absence of thermalization on
experimentally relevant time scales.Comment: revtex4, 3 figures. Final version of the text, accepted for
publication (see journal ref.
Miniaturization of Chemical Analysis Systems – A Look into Next Century's Technology or Just a Fashionable Craze?
Miniaturization of already existing techniques in on-line analytical chemistry is an alternative to compound-selective chemical sensors. Theory points in the direction of higher efficiency, faster analysis time, and lower reagent consumption. Micromachining, a well known photolithographic
technique for structures in the micrometer range, is introduced and documented with structures as examples for flow injection analysis, electrophoresis, and a detector cell
- …