29,698 research outputs found
An analytical model of a longitudinal-torsional ultrasonic transducer
The combination of longitudinal and torsional (LT) vibrations at high frequencies finds many applications such as ultrasonic drilling, ultrasonic welding, and ultrasonic motors. The LT mode can be obtained by modifications to the design of a standard bolted Langevin ultrasonic transducer driven by an axially poled piezoceramic stack, by a technique that degenerates the longitudinal mode to an LT motion by a geometrical alteration of the wave path. The transducer design is developed and optimised through numerical modelling which can represent the geometry and mechanical properties of the transducer and its vibration response to an electrical input applied across the piezoceramic stack. However, although these models can allow accurate descriptions of the mechanical behaviour, they do not generally provide adequate insights into the electrical characteristics of the transducer. In this work, an analytical model is developed to present the LT transducer based on the equivalent circuit method. This model can represent both the mechanical and electrical aspects and is used to extract many of the design parameters, such as resonance and anti-resonance frequencies, the impedance spectra and the coupling coefficient of the transducer. The validity of the analytical model is demonstrated by close agreement with experimental results
A strategy for delivering high torsionality in longitudinal-torsional ultrasonic devices
A composite longitudinal-torsional vibration mode has applications in ultrasonic motors, ultrasonic welding and ultrasonic drilling. There are two ways to obtain this vibration behaviour using a single transducer, namely (i) coupling of a longitudinal and a torsional mode, which is known to be difficult; and (ii) degenerating a longitudinal mode to deliver longitudinal-torsional behaviour at the horn tip. A mode-degenerating horn is achieved by incorporating helical or diagonal slits in an otherwise traditional exponential horn driven by a Langevin transducer. However, it is often difficult with this configuration to avoid coupling of unwanted bending modes, low responsiveness, and loss of ultrasonic energy due to boundaries between tuned components. Therefore, in this study the mode-degenerating characteristics are achieved by incorporating the helical slits and exponential geometry features in the front mass of the transducer itself. Finite element analysis and vibration experimental analysis show that this strategy prevents coupling of bending modes, increases responsiveness, and reduces energy losses. Most importantly the transducer delivers a very high torsionality
Efimov Physics in Atom-Dimer Scattering of Lithium-6 Atoms
Lithium-6 atoms in the three lowest hyperfine states display universal
properties when the S-wave scattering length between each pair of states is
large. Recent experiments reported four pronounced features arising from Efimov
physics in the atom-dimer relaxation rate, namely two resonances and two local
minima. We use the universal effective field theory to calculate the atom-dimer
relaxation rate at zero temperature. Our results describe the four features
qualitatively and imply there is a hidden local minimum. In the vicinity of the
resonance at 685 G, we perform a finite temperature calculation which improves
the agreement of theory and experiment. We conclude that finite temperature
effects cannot be neglected in the analysis of the experimental data.Comment: 13 pages, 5 figures, final versio
Children’s Perceptions of Intimate Partner Violence: Causes, Consequences, and Coping
Children’s appraisals of conflictual and aggressive parental interactions mediate their effect on children’s adjustment. Previous studies have relied almost exclusively on selfreport questionnaires to assess appraisals; consequently we know little about perceptions that occur naturallywhen children witness interparental aggression. This study employed a semistructured interview to assess the thoughts and feelings of 34 children (ages 7–12) whose mothers were receiving services at domestic violence agencies, and mothers reported on interparental aggression that took place in the home. Children’s thoughts centered on consequences and efforts to understand why fights occurred. They generally viewed their mother’s partner as responsible for violence, though a significant number viewed both parents as playing a role. Sadness and anger were more common than anxiety, and children often attempted to stop or withdraw from fights or both. When asked why family violence occurs, most focused on perpetrators’ lack of control of anger or personal characteristics, but approximately onethird viewed victims as provoking aggression. These findings support the idea that children actively attempt to understand the causes and consequences of interparental violence and suggest that their perceptions and interpretations are important for understanding the development of beliefs regarding the use of violence in close relationships
Limits on chemical complexity in diffuse clouds: search for CH3OH and HC5N absorption
Context: An unexpectedly complex polyatomic chemistry exists in diffuse
clouds, allowing detection of species such as C2H, C3H2, H2CO and NH3 which
have relative abundances that are strikingly similar to those inferred toward
the dark cloud TMC-1
Aims: We probe the limits of complexity of diffuse cloud polyatomic
chemistry.
Methods: We used the IRAM Plateau de Bure Interferometer to search for
galactic absorption from low-lying J=2-1 rotational transitions of A- and
E-CH3OH near 96.740 GHz and used the VLA to search for the J=8-7 transition of
HC5N at 21.3 GHz.
Results: Neither CH3OH nor HC5N were detected at column densities well below
those of all polyatomics known in diffuse clouds and somewhat below the levels
expected from comparison with TMC-1. The HCN/HC5N ratio is at least 3-10 times
higher in diffuse gas than toward TMC-1.
Conclusions: It is possible to go to the well once (or more) too ofte
HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds
%methods {We used the EMIR receiver and FTS spectrometer at the IRAM 30m to
construct absorption spectra toward bright extra-galactic background sources at
195 kHz spectral resolution ( 0.6 \kms). We used the IRAM Plateau de
Bure interferometer to synthesize absorption spectra of \hthcop\ and HCO toward
the galactic HII region W49.} %results {HCO, \cc3h\ and CF\p\ were detected
toward the blazars \bll\ and 3C111 having \EBV\ = 0.32 and 1.65 mag. HCO was
observed in absorption from ``spiral-arm'' clouds in the galactic plane
occulting W49. The complement of detectable molecular species in the 85 - 110
GHz absorption spectrum of diffuse/translucent gas is now fully determined at
rms noise level at \EBV\ = 0.32 mag (\AV\ = 1 mag)
and /\EBV\ mag overall.} %conclusions {As
with OH, \hcop\ and \cch, the relative abundance of \cc3h\ varies little
between diffuse and dense molecular gas, with N(\cc3h)/N({\it o-c}-\c3h2)
0.1. We find N(CF\p)/N(HCO\p) , N(CF\p)/N(\cch)
0.005-0.01 and because N(CF\p) increases with \EBV\ and with the
column densities of other molecules we infer that fluorine remains in the gas
phase as HF well beyond \AV\ = 1 mag. We find N(HCO)/N(HCO\p) = 16
toward \bll, 3C111 and the 40 km/s spiral arm cloud toward W49, implying X(HCO)
, about 10 times higher than in dark clouds. The behaviour of
HCO is consistent with previous suggestions that it forms from C\p\ and \HH,
even when \AV\ is well above 1 mag. The survey can be used to place useful
upper limits on some species, for instance N(\hhco)/N(\HH CS) 32 toward
3C111, compared to 7 toward TMC-1, confirming the possibility of a gas phase
formation route to \hhco.}Comment: A\%A in pres
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