3,980 research outputs found
An analytical and experimental assessment of flexible road ironwork support structures
This paper describes work undertaken to investigate the mechanical performance of road ironwork installations in highways, concentrating on the chamber construction. The principal aim was to provide the background research which would allow improved designs to be developed to reduce the incidence of failures through improvements to the structural continuity between the installation and the surrounding pavement. In doing this, recycled polymeric construction materials (Jig Brix) were studied with a view to including them in future designs and specifications. This paper concentrates on the Finite Element (FE) analysis of traditional (masonry) and flexible road ironwork structures incorporating Jig Brix. The global and local buckling capacity of the Jig Brix elements was investigated and results compared well with laboratory measurements. FE models have also been developed for full-scale traditional (masonry) and flexible installations in a surrounding flexible (asphalt) pavement structure. Predictions of response to wheel loading were compared with full-scale laboratory measurements. Good agreement was achieved with the traditional (masonry) construction but poorer agreement for the flexible construction. Predictions from the FE model indicated that the use of flexible elements significantly reduces the tensile horizontal strain on the surface of the surrounding asphaltic material which is likely to reduce the incidence of surface cracking
Some observations on the assimilation of atmospheric nitrogen by a free living soil organism Azotobacter Chroococcum of Beijerinck
Some years before the appearance of Hellriegel and Wilfarth's work on the sources of nitrogen of leguminous plants, and while the part played by atmospheric nitrogen in the nutrition of crops was under active discussion, Berthelot was making some exact observations on the behaviour of uncropped soils towards the free element. He found that when 50 kilograms of air-dry arable soil were exposed to the air and rain in a vessel for seven months a great increase in the nitrogen content could be observed; the total nitrogen of the original soil had increased from 50 grams to 63, or a gain of over 25 per cent, after allowing for the small amount of combined nitrogen brought down by rain; in another experiment where the soil had first been washed free from nitrates, a gain of 46 per cent, of nitrogen was proved. In many other cases, however, the gain was only from 10–15 per cent, of the original nitrogen present in the soil
Experimental characterization of thermally-activated artificial muscles based on coiled nylon fishing lines
The discovery of an innovative class of thermally activated actuators based on twisted polymeric fibres has opened new horizons toward the development of effective devices that can be easily manufactured using inexpensive materials such as fishing lines or sewing threads. These new devices show large deformations when heated together with promising performance in terms of energy and power densities. With the aim of providing information and data useful for the future engineering applications, we present the results of a thermo-mechanical characterization conducted on a specific type of twisted polymeric fibre (i.e. nylon-made coiled actuators) that is considered particularly promising. A custom experimental test-bench and procedure have been developed and employed to run isothermal and isometric tensile tests on a set of specimens that are fabricated with a simple and repeatable process. The results of the experiments highlight some important issues related to the response of these actuators such as hysteresis, repeatability, predictability and stored elastic energy
On the Gravitomagnetic Time Delay
We study the gravitational time delay in ray propagation due to rotating
masses in the linear approximation of general relativity. Simple expressions
are given for the gravitomagnetic time delay that occurs when rays of radiation
cross a slowly rotating shell and propagate in the field of a distant rotating
source. Moreover, we calculate the local gravitational time delay in the Goedel
universe. The observational consequences of these results in the case of weak
gravitational lensing are discussed.Comment: 15 pages, 1 figure, revised version submitted to Phys. Lett.
The AGN Luminosity Fraction in Merging Galaxies
Galaxy mergers are key events in galaxy evolution, often causing massive
starbursts and fueling active galactic nuclei (AGN). In these highly dynamic
systems, it is not yet precisely known how much starbursts and AGN respectively
contribute to the total luminosity, at what interaction stages they occur, and
how long they persist. Here we estimate the fraction of the bolometric infrared
(IR) luminosity that can be attributed to AGN by measuring and modeling the
full ultraviolet to far-infrared spectral energy distributions (SEDs) in up to
33 broad bands for 24 merging galaxies with the Code for Investigating Galaxy
Emission. In addition to a sample of 12 confirmed AGN in late-stage mergers,
found in the Revised Bright Galaxy Sample or
Faint Source Catalog, our sample includes a comparison sample of 12 galaxy
mergers from the Interacting Galaxies Survey, mostly early-stage. We
perform identical SED modeling of simulated mergers to validate our methods,
and we supplement the SED data with mid-IR spectra of diagnostic lines obtained
with InfraRed Spectrograph. The estimated AGN contributions to the IR
luminosities vary from system to system from 0% up to 91% but are significantly
greater in the later-stage, more luminous mergers, consistent with what is
known about galaxy evolution and AGN triggering.Comment: 26 pages, 10 figure
Dust Properties and Star-Formation Rates in Star-Forming Dwarf Galaxies
We have used the Spitzer Space Telescope to study the dust properties of a
sample of star-forming dwarf galaxies. The differences in the mid-infrared
spectral energy distributions for these galaxies which, in general, are low
metallicity systems, indicate differences in the physical properties, heating,
and/or distribution of the dust. Specifically, these galaxies have more hot
dust and/or very small grains and less PAH emission than either spiral or
higher luminosity starburst galaxies. As has been shown in previous studies,
there is a gradual decrease in PAH emission as a function of metallicity.
Because much of the energy from star formation in galaxies is re-radiated in
the mid-infrared, star-formation rate indicators based on both line and
continuum measurements in this wavelength range are coming into more common
usage. We show that the variations in the interstellar medium properties of
galaxies in our sample, as measured in the mid-infrared, result in over an
order of magnitude spread in the computed star-formation rates.Comment: 25 pages, 11 figures, 4 tables, ApJ accepte
Mid-infrared Identification of 6 cm Radio Source Counterparts in the Extended Groth Strip
A new 6-cm survey of almost 0.6 square degrees to a limit of 0.55-mJy/beam
(10-sigma) finds 37 isolated radio sources and 7 radio source pairs (not
necessarily physical companions). IRAC counterparts are identified for at least
92% of the radio sources within the area of deep IRAC coverage, which includes
31 isolated sources and 6 pairs. This contrasts with an identification rate of
<74% to R<23.95 in visible light. Eight of the IRAC galaxies have power law
spectral energy distributions, implying that the mid-infrared emission comes
from a powerful AGN. The remaining 26 IRAC galaxies show stellar emission in
the mid-infrared, probably in most of these galaxies because the stellar
emission is bright enough to outshine an underlying AGN. The infrared colors
suggest that the majority of these galaxies are bulge-dominated and have
redshifts between approximately 0.5 and 1.0. Visible spectra from the DEEP2
redshift survey, available for 11 galaxies, are consistent with this
suggestion. The IRAC galaxies fall into two distinct groups in a
color-magnitude diagram, one group (the "stripe") includes all the AGN. The
other group (the "blue clump") has blue 3.6 to 8 micron colors and a small
range of 8 micron magnitudes. This separation should be useful in classifying
galaxies found in other radio surveys.Comment: Accepted by A
Dynamic ductile to brittle transition in a one-dimensional model of viscoplasticity
We study two closely related, nonlinear models of a viscoplastic solid. These
models capture essential features of plasticity over a wide range of strain
rates and applied stresses. They exhibit inelastic strain relaxation and steady
flow above a well defined yield stress. In this paper, we describe a first step
in exploring the implications of these models for theories of fracture and
related phenomena. We consider a one dimensional problem of decohesion from a
substrate of a membrane that obeys the viscoplastic constitutive equations that
we have constructed. We find that, quite generally, when the yield stress
becomes smaller than some threshold value, the energy required for steady
decohesion becomes a non-monotonic function of the decohesion speed. As a
consequence, steady state decohesion at certain speeds becomes unstable. We
believe that these results are relevant to understanding the ductile to brittle
transition as well as fracture stability.Comment: 10 pages, REVTeX, 12 postscript figure
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