10,214 research outputs found
Strongly coupled modes in a weakly driven micromechanical resonator
We demonstrate strong coupling between the flexural vibration modes of a
clamped-clamped micromechanical resonator vibrating at low amplitudes. This
coupling enables the direct measurement of the frequency response via
amplitude- and phase modulation schemes using the fundamental mode as a
mechanical detector. In the linear regime, a frequency shift of
is observed for a mode with a line width of
in vacuum. The measured response is well-described by the
analytical model based on the Euler-Bernoulli beam including tension.
Calculations predict an upper limit for the room-temperature Q-factor of
for our top-down fabricated micromechanical beam
resonators.Comment: 9 pages, 2 figure
Recommended from our members
Measuring the impact of observations on the predictability of the Kuroshio Extension in a shallow-water model
In this paper sequential importance sampling is used to assess the impact of observations on a ensemble prediction for the decadal path transitions of the Kuroshio Extension (KE). This particle filtering approach gives access to the probability density of the state vector, which allows us to determine the predictive power — an entropy based measure — of the ensemble prediction. The proposed set-up makes use of an ensemble that, at each time, samples the climatological probability distribution. Then, in a post-processing step, the impact of different sets of observations is measured by the increase in predictive power of the ensemble over the climatological signal during one-year. The method is applied in an identical-twin
experiment for the Kuroshio Extension using a reduced-gravity shallow water model. We investigate the impact of assimilating velocity observations from different locations during the elongated and the contracted meandering state of the KE. Optimal observations location correspond to regions with strong potential vorticity gradients. For the elongated state the optimal location is in the first meander of the KE. During the contracted state of the KE it is located south of Japan, where the Kuroshio separates from the coast
Somatisation and functional impairment in adolescents: longitudinal link with mothers' reactions
Adolescents' somatisation (i.e., the psychological tendency to experience and report multiple physical complaints for which no definite medical cause can be found; SOM) and functional impairment (i.e., all bothersome aftermath of somatisation; FI) were studied in relation to mothers' protection, encouraging/monitoring, and minimisation of physical functional complaints. Besides main effects, interaction effects with other child and parenting characteristics were examined. A total of 990 adolescents and their mothers filled out questionnaires when the adolescents were respectively 12-13 (T1) and 13-14 (T2) years old. At T1, there was a significant relation between mothers' higher amounts of minimisation and adolescents' higher levels of SOM. Further, the link between mothers' higher levels of T1 minimisation and adolescents' higher amounts of T1 FI was significant, but not for adolescents with high levels of depressive mood. Longitudinal analyses revealed that mothers' reactions did not significantly predict adolescents' SOM/FI, nor did adolescents' SOM/FI significantly predict mothers' reactions. Practical implications are discussed
Rivals for the crown: Reply to Opthof and Leydesdorff
We reply to the criticism of Opthof and Leydesdorff [arXiv:1002.2769] on the
way in which our institute applies journal and field normalizations to citation
counts. We point out why we believe most of the criticism is unjustified, but
we also indicate where we think Opthof and Leydesdorff raise a valid point
Towards a new crown indicator: Some theoretical considerations
The crown indicator is a well-known bibliometric indicator of research
performance developed by our institute. The indicator aims to normalize
citation counts for differences among fields. We critically examine the
theoretical basis of the normalization mechanism applied in the crown
indicator. We also make a comparison with an alternative normalization
mechanism. The alternative mechanism turns out to have more satisfactory
properties than the mechanism applied in the crown indicator. In particular,
the alternative mechanism has a so-called consistency property. The mechanism
applied in the crown indicator lacks this important property. As a consequence
of our findings, we are currently moving towards a new crown indicator, which
relies on the alternative normalization mechanism
Severe Language Effect in University Rankings: Particularly Germany and France are wronged in citation-based rankings
We applied a set of standard bibliometric indicators to monitor the
scientific state-of-arte of 500 universities worldwide and constructed a
ranking on the basis of these indicators (Leiden Ranking 2010). We find a
dramatic and hitherto largely underestimated language effect in the
bibliometric, citation-based measurement of research performance when comparing
the ranking based on all Web of Science (WoS) covered publications and on only
English WoS covered publications, particularly for Germany and France.Comment: Short communication, 3 pages, 4 figure
Initialization by measurement of a two-qubit superconducting circuit
We demonstrate initialization by joint measurement of two transmon qubits in
3D circuit quantum electrodynamics. Homodyne detection of cavity transmission
is enhanced by Josephson parametric amplification to discriminate the two-qubit
ground state from single-qubit excitations non-destructively and with 98.1%
fidelity. Measurement and postselection of a steady-state mixture with 4.7%
residual excitation per qubit achieve 98.8% fidelity to the ground state, thus
outperforming passive initialization.Comment: 5 pages, 4 figures, and Supplementary Information (7 figures, 1
table
Numerical simulations on the motion of atoms travelling through a standing-wave light field
The motion of metastable helium atoms travelling through a standing light
wave is investigated with a semi-classical numerical model. The results of a
calculation including the velocity dependence of the dipole force are compared
with those of the commonly used approach, which assumes a conservative dipole
force. The comparison is made for two atom guiding regimes that can be used for
the production of nanostructure arrays; a low power regime, where the atoms are
focused in a standing wave by the dipole force, and a higher power regime, in
which the atoms channel along the potential minima of the light field. In the
low power regime the differences between the two models are negligible and both
models show that, for lithography purposes, pattern widths of 150 nm can be
achieved. In the high power channelling regime the conservative force model,
predicting 100 nm features, is shown to break down. The model that incorporates
velocity dependence, resulting in a structure size of 40 nm, remains valid, as
demonstrated by a comparison with quantum Monte-Carlo wavefunction
calculations.Comment: 9 pages, 4 figure
Rotation periods of late-type stars in the young open cluster IC 2602
We present the results of a monitoring campaign aimed at deriving rotation
periods for a representative sample of stars in the young (30 Myr) open cluster
IC 2602. Rotation periods were derived for 29 of 33 stars monitored. The
periods derived range from 0.2d (one of the shortest known rotation periods of
any single open cluster star) to about 10d (which is almost twice as long as
the longest period previously known for a cluster of this age). We are able to
confirm 8 previously known periods and derive 21 new ones, delineating the long
period end of the distribution. Despite our sensitivity to longer periods, we
do not detect any variables with periods longer than about 10d. The combination
of these data with those for IC 2391, an almost identical cluster, leads to the
following conclusions:
1) The fast rotators in a 30 Myr cluster are distributed across the entire
0.5 < B-V < 1.6 color range.
2) 6 stars in our sample are slow rotators, with periods longer than 6d.
3) The amplitude of variability depends on both the color and the period. The
dependence on the latter might be important in understanding the selection
effects in the currently available rotation period database and in planning
future observations.
4) The interpretation of these data in terms of theoretical models of
rotating stars suggests both that disk-interaction is the norm rather than the
exception in young stars and that disk-locking times range from zero to a few
Myr.Comment: 23 pages, 8 figures, accepted for publication in the Astrophysical
Journa
First optical images of circumstellar dust surrounding the debris disk candidate HD 32297
Near-infrared imaging with the Hubble Space Telescope recently revealed a
circumstellar dust disk around the A star HD 32297. Dust scattered light is
detected as far as 400 AU radius and the linear morphology is consistent with a
disk ~10 degrees away from an edge-on orientation. Here we present the first
optical images that show the dust scattered light morphology from 560 to 1680
AU radius. The position angle of the putative disk midplane diverges by 31
degrees and the color of dust scattering is most likely blue. We associate HD
32297 with a wall of interstellar gas and the enigmatic region south of the
Taurus molecular cloud. We propose that the extreme asymmetries and blue disk
color originate from a collision with a clump of interstellar material as HD
32297 moves southward, and discuss evidence consistent with an age of 30 Myr or
younger.Comment: 5 pages; Accepted for publication in ApJ Letter
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