20,313 research outputs found
In-vehicle vibration study of child safety seats
This paper reports experimental measurements of the in-vehicle vibrational behaviour of stage 0&1
child safety seats. Road tests were performed for eight combinations of child, child seat and
automobile. Four accelerometers were installed in the vehicles and orientated to measure as closely
as possible in the vertical direction; two were attached to the floor and two located at the human
interfaces. An SAE pad was placed under the ischial tuberosities of the driver at the seat cushion
and a child pad, designed for the purpose of this study, was placed under the child. 4 test runs were
made over a pave’ (cobblestone) surface for the driver’s seat and 4 for the child seat at both 20 km/h and 40 km/h. Power spectral densities were determined for all measurement points and
acceleration transmissibility functions (ATFs) were estimated from the floor of the vehicle to the
human interfaces. The system composed of automobile seat, child seat and child was found to
transmit greater vibration than the system composed of automobile seat and driver. The ensemble
mean transmissibility in the frequency range from 1 to 60 Hz was found to be 77% for the child seat
systems as opposed to 61% for the driver’s seats. The acceleration transmissibility for the child seat
system was found to be higher than that of the driver’s seat at most frequencies above 10 Hz for all
eight systems tested. The measured ATFs suggest that the principal whole-body vibration resonance
of the children occurred at a mean frequency of 8.5, rather than the 3.5 to 5.0 Hz typically found in the case of seated adults. It can be concluded that current belt-fastened child seats are less effective
than the vehicle primary seating systems in attenuating vibrational disturbances. The results also
suggest the potential inability of evaluating child comfort by means of existing whole-body
vibration standards
Photon spheres in Einstein and Einstein-Gauss-Bonnet theories and circular null geodesics in axially-symmetric spacetimes
In this article we extend a recent theorem proven by Hod (Phys. Lett. B, {\bf
727}, 345--348, 2013) to -dimensional Einstein and Einstein-Gauss-Bonnet
theories, which gives an upper bound for the photon sphere radii of spherically
symmetric black holes. As applications of these results we give a universal
upper bound for the real part of quasinormal modes in the WKB limit and a
universal lower bound for the position of the first relativistic image in the
strong lensing regime produced by these type of black holes. For the
axially-symmetric case, we also make some general comments (independent of the
underlying gravitational theory) on the relation between circular null
geodesics and the fastest way to circle a black hole.Comment: In this post-publisher version two typos were corrected: the
signature of the metric in eq.(1) and a factor in eq.(102). We thanks Gary
Gibbons and Chris Pope for bringing to our attention these typo
A Jacobian elliptic single-field inflation
In the scenario of single-field inflation, this field is done in terms of
Jacobian elliptic functions. This approach provides, when constrained to
particular cases, analytic solutions already known in the past, generalizing
them to a bigger family of analytical solutions. The emergent cosmology is
analysed using the Hamilton-Jacobi approach and then, the main results are
contrasted with the recent measurements obtained from the Planck 2015 data.Comment: 7 pages, 5 figure
Rapid sync acquisition system Patent
System designed to reduce time required for obtaining synchronization in data communication with spacecraft utilizing pseudonoise code
Design for a Rapid Automatic Sync Acquisition System
System provides rapid command sync acquisition between widely separated transmitter-receivers. It is based on a rapid, automatic range-adjustment approach rather than the time-consuming cycle slipping or stepping techniques of conventional phase-locked loops
Hodge polynomials of the moduli spaces of pairs
Let be a smooth projective curve of genus over the complex
numbers. A holomorphic pair on is a couple , where is a
holomorphic bundle over of rank and degree , and is
a holomorphic section. In this paper, we determine the Hodge polynomials of the
moduli spaces of rank 2 pairs, using the theory of mixed Hodge structures. We
also deal with the case in which has fixed determinant.Comment: 23 pages, typos added, minor change
Double dynamical regime of confined water
The Van Hove self correlation function of water confined in a silica pore is
calculated from Molecular Dynamics trajectories upon supercooling. At long time
in the relaxation region we found that the behaviour of the real space
time dependent correlators can be decomposed in a very slow, almost frozen,
dynamics due to the bound water close to the substrate and a faster dynamics of
the free water which resides far from the confining surface. For free water we
confirm the evidences of an approach to a crossover mode coupling transition,
previously found in Q space. In the short time region we found that the two
dynamical regimes are overimposed and cannot be distinguished. This shows that
the interplay between the slower and the faster dynamics emerges in going from
early times to the relaxation region, where a layer analysis of the
dynamical properties can be performed.Comment: 6 pages with 9 figures. RevTeX. Accepted for pulbication in J. Phys.
Cond. Mat
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