2,563 research outputs found
Energy dissipation of a friction damper: experimental validation
Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised orcontrolled. In this work one of the positive sides of friction is investigated: friction damping. The frictioninherently present in a system can be positively used to increase the total damping or alternatively, a frictiondamper can be designed. Friction dampers can be a cheap and efficient way to reduce the vibration levels ofa wide range of mechanical systems.In the present paper the conclusions of previous analytic and numericalresults regarding friction damping are validated with results of laboratory experiments, where the energydissipated through friction is measured. The test set-up consists of a mass sliding on parallel ball-bearings,where additional friction is created by a sledge attached to the mass, which is pre-stressed against a frictionplate. No care has been taken to ensure pure dry (Coulomb) friction. Nevertheless, the measured energydissipation is in good agreement with the theoretical results for Coulomb friction
Energy dissipation of a friction damper: experimental validation
Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised orcontrolled. In this work one of the positive sides of friction is investigated: friction damping. The frictioninherently present in a system can be positively used to increase the total damping or alternatively, a frictiondamper can be designed. Friction dampers can be a cheap and efficient way to reduce the vibration levels ofa wide range of mechanical systems.In the present paper the conclusions of previous analytic and numericalresults regarding friction damping are validated with results of laboratory experiments, where the energydissipated through friction is measured. The test set-up consists of a mass sliding on parallel ball-bearings,where additional friction is created by a sledge attached to the mass, which is pre-stressed against a frictionplate. No care has been taken to ensure pure dry (Coulomb) friction. Nevertheless, the measured energydissipation is in good agreement with the theoretical results for Coulomb friction
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Development of Neutron Probes for Characterization of Hazardous Materials in the Sub-surface Medium
Neutron probes are being developed at the Idaho National Engineering and Environmental Laboratory (INEEL) for the detection, identification and quantification of hazardous materials in the ground. Such materials include plutonium, uranium, americium, chlorine and fluorine. Both a Neutron Gamma (NG) probe and a Prompt Fission Neutron (PFN) probe are being developed. The NG probe is used primarily for nuclide identification and quantification measurements. The PFN is used mostly for the detection and measurement of fissile material, but also for the determination of thermal neutron macroscopic absorption cross sections of the various elements comprising the ground matrix. Calibration of these probes will be carried out at the INEEL using an indoor facility that has been designed for this activity
Low Power CMOS Chopper Preamplifier Based on Source-Degeneration Transconductors
This paper describes the design of a low-power, low-noise flicker CMOS chopper preamplifier for sensor signal conditioning. The core amplifier and the Gm-C output low pass filter of the proposed fully differential preamplifier are based on a source degeneration transconductor. The circuit was designed in a standard 0.18µm CMOS process with 1.8V supply voltage. It shows 42dB gain, 1 kHz bandwidth and a total power consumption of 84 µW. The proposed configuration achieves a noise efficiency factor of 4.6 and a total input-referred noise of 560 nVrms integrated from 0.1 to 1 kHz
From Predicting Solar Activity to Forecasting Space Weather: Practical Examples of Research-to-Operations and Operations-to-Research
The successful transition of research to operations (R2O) and operations to
research (O2R) requires, above all, interaction between the two communities. We
explore the role that close interaction and ongoing communication played in the
successful fielding of three separate developments: an observation platform, a
numerical model, and a visualization and specification tool. Additionally, we
will examine how these three pieces came together to revolutionize
interplanetary coronal mass ejection (ICME) arrival forecasts. A discussion of
the importance of education and training in ensuring a positive outcome from
R2O activity follows. We describe efforts by the meteorological community to
make research results more accessible to forecasters and the applicability of
these efforts to the transfer of space-weather research.We end with a
forecaster "wish list" for R2O transitions. Ongoing, two-way communication
between the research and operations communities is the thread connecting it
all.Comment: 18 pages, 3 figures, Solar Physics in pres
A Discussion on Dirac Field Theory, No-Go Theorems and Renormalizability
We study Dirac field equations coupled to electrodynamics with metric and
torsion fields: we discuss how special spinorial solutions are incompatible
with torsion; eventually these results will be used to sketch a discussion on
the problem of renormalizability of point-like particles.Comment: 10 page
Self Duality and Oblique Confinement in Planar Gauge Theories
We investigate the non-perturbative structure of two planar
lattice gauge models and discuss their relevance to two-dimensional condensed
matter systems and Josephson junction arrays. Both models involve two compact
U(1) gauge fields with Chern-Simons interactions, which break the symmetry down
to . By identifying the relevant topological excitations
(instantons) and their interactions we determine the phase structure of the
models. Our results match observed quantum phase transitions in Josephson
junction arrays and suggest also the possibility of {\it oblique confining
ground states} corresponding to quantum Hall regimes for either charges or
vortices.Comment: 32 pages, harvma
Continuum theory of vacancy-mediated diffusion
We present and solve a continuum theory of vacancy-mediated diffusion (as
evidenced, for example, in the vacancy driven motion of tracers in crystals).
Results are obtained for all spatial dimensions, and reveal the strongly
non-gaussian nature of the tracer fluctuations. In integer dimensions, our
results are in complete agreement with those from previous exact lattice
calculations. We also extend our model to describe the vacancy-driven
fluctuations of a slaved flux line.Comment: 25 Latex pages, subm. to Physical Review
Macrofungal diversity in Colombian Amazon forests varies with regions and regimes of disturbance
Here we present the results of fungal biodiversity studies from some selected Colombian Amazon forests in relationship to plant biodiversity and successional stages after slash and burn agriculture. Macrofungal diversity was found to differ between forests occurring in two regions (Araracuara vs Amacayacu) as well as between flooded forests and terra firme forests in the Amacayacu region. Macrofungal biodiversity differed between regeneration states of different age in the Araracuara region. Suitable substrates, especially dead wood that occurred as a result of recent slash and burn agriculture, resulted in the formation of many sporocarps of wood-inhabiting species. Putative ectomycorrhizal species were found in a dipterocarp forest. Fifty two percent of the macrofungal species could not be identified to the species level, but could be assigned to a genus, and it is likely that a significant portion of these represent species new to science. Long term studies are needed to obtain a comprehensive and complete understanding of the diversity and functioning of mycobiota in Amazon forest ecosystems
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