8,645 research outputs found
Resonant-tunneling oscillators and multipliers for submillimeter receivers
Resonant tunneling through double-barrier heterostructures has attracted increasing interest recently, largely because of the fast charge transport it provides. In addition, the negative differential resistance regions that exist in the current-voltage (I-V) curve (peak-to-valley ratios of 3.5:1 at room temperature, and nearly 10:1 at 77 K, were measured) suggest that high-speed devices based on the character of the I-V curve should be possible. For example, the negative differential resistance region is capable of providing the gain necessary for high-frequency oscillations. In the laboratory attempts were made to increase the frequency and power of these oscillators and to demonstrate several different high-frequency devices
Transverse momentum distribution of vector mesons produced in ultraperipheral relativistic heavy ion collisions
We study the transverse momentum distribution of vector mesons produced in
ultraperipheral relativistic heavy ion collisions (UPCs). In UPCs there is no
strong interaction between the nuclei and the vector mesons are produced in
photon-nucleus collisions where the (quasireal) photon is emitted from the
other nucleus. Exchanging the role of both ions leads to interference effects.
A detailed study of the transverse momentum distribution which is determined by
the transverse momentum of the emitted photon, the production process on the
target and the interference effect is done. We study the total unrestricted
cross section and those, where an additional electromagnetic excitation of one
or both of the ions takes place in addition to the vector meson production, in
the latter case small impact parameters are emphasized.Comment: 12 pages, REVTeX manuscrip
The dynamically hot stellar halo around NGC 3311: a small cluster-dominated central galaxy
An important open question is the relation between intracluster light and the
halos of central galaxies in galaxy clusters. Here we report results from an on
going project with the aim to characterize the dynamical state in the core of
the Hydra I (Abell 1060) cluster around NGC 3311. Methods: We analyze deep
long-slit absorption line spectra reaching out to ~25 kpc in the halo of NGC
3311. Results: We find a very steep increase in the velocity dispersion profile
from a central sigma_0=150 km/s to sigma_out ~450 km/s at R ~ 12 kpc. Farther
out, to ~25 kpc, sigma appears to be constant at this value, which is ~60% of
the velocity dispersion of the Hydra I galaxies. With its dynamically hot halo
kinematics, NGC 3311 is unlike other normal early-type galaxies. Conclusions:
These results and the large amount of dark matter inferred from X-rays around
NGC 3311 suggest that the stellar halo of this galaxy is dominated by the
central intracluster stars of the cluster, and that the transition from
predominantly galaxy-bound stars to cluster stars occurs in the radial range 4
to 12 kpc from the center of NGC 3311. We comment on the wide range of halo
kinematics observed in cluster central galaxies, depending on the evolutionary
state of their host clusters.Comment: 5 pages, 4 figures, 1 table, accepted for publication in A&
Scaling-up experiments of smouldering combustion as a remediation technology for contaminated soil
Self-sustaining Treatment for Active Remediation (STAR) is a novel, patent-pending process that uses smouldering combustion as a remediation technology for land contaminated with hazardous organic liquids. Compounds such as chlorinated solvents, coal tar and petroleum products, called Non-Aqueous Phase Liquids (NAPLs) for their low miscibility with water, have a long history of use in the industrialised world and are among the most ubiquitous of contaminants worldwide. These contaminants are toxic and many are suspected or known carcinogens. Existing remediation technologies are expensive and ineffective at reducing NAPL source zones sufficiently to restore affected water resources to appropriate quality levels. STAR introduces a self-sustaining smouldering reaction within the NAPL pool in the subsurface and allows that reaction to provide all of the post-ignition energy required by the reaction to completely remediate the NAPL source zone in the soil. Results from laboratory and field experiments have been very promising. Laboratory experiments have demonstrated STAR across a wide range of NAPL fuels and focused on coal tar to identify key parameters for successful remediation. Modelling has suggested that STAR efficiency will improve with scale as effects such as heat losses from boundaries become less significant. Observations from field experiments support the modelling theory - significantly lower relative air flow in a smouldering field experiment (330L) led to faster smouldering front propagation than observed in laboratory experiments (1L and 3L). Preliminary emissions monitoring by Fourier Transform Infrared (FTIR) spectroscopy has suggested that STAR emissions might be low enough to meet regulatory requirements, but further study is necessary. As emissions are expected to vary with each contaminant, activated carbon filters are being developed and tested in case emissions filtration is necessary. Experiments at all scales have demonstrated that STAR is controllable and self-terminating. Pilot-scale (2500L) field trials are underway to demonstrate STAR on excavated contaminated soil. The materials that will be studied in these trials are manufactured coal tar in coarse sand (which is the same material as used in the laboratory and field experiments) as well as two soils obtained from coal tar contaminated sites. This poster focuses on the scale-up to these field trials, including small scale characterisation, large scale performance, emissions monitoring and post-treatment soil analysis
Testing a simple recipe for estimating galaxy masses from minimal observational data
The accuracy and robustness of a simple method to estimate the total mass
profile of a galaxy is tested using a sample of 65 cosmological
zoom-simulations of individual galaxies. The method only requires information
on the optical surface brightness and the projected velocity dispersion
profiles and therefore can be applied even in case of poor observational data.
In the simulated sample massive galaxies ( \kms) at
redshift have almost isothermal rotation curves for broad range of radii
(RMS for the circular speed deviations from a constant value over
). For such galaxies the method recovers the
unbiased value of the circular speed. The sample averaged deviation from the
true circular speed is less than with the scatter of
(RMS) up to . Circular speed estimates of massive
non-rotating simulated galaxies at higher redshifts ( and ) are also
almost unbiased and with the same scatter. For the least massive galaxies in
the sample ( \kms) at the RMS deviation is
and the mean deviation is biased low by about . We also derive the
circular velocity profile from the hydrostatic equilibrium (HE) equation for
hot gas in the simulated galaxies. The accuracy of this estimate is about RMS
for massive objects () and the HE
estimate is biased low by , which can be traced to the presence of
gas motions. This implies that the simple mass estimate can be used to
determine the mass of observed massive elliptical galaxies to an accuracy of
and can be very useful for galaxy surveys.Comment: 15 pages, 14 figures, 1 tabl
Experimental studies of self-sustaining thermal aquifer remediation (STAR) for non-aqueous phase liquid (NAPL) sources
Self-sustaining Thermal Aquifer Remediation (STAR) is a novel technology that employs smouldering combustion for the remediation of subsurface contamination by non-aqueous phase liquids (NAPLs). Smouldering is a form of combustion that is slower and less energetic than flaming combustion. Familiar examples of smouldering involve solid fuels that are destroyed by the reaction (e.g., a smouldering cigarette or peat smouldering after a wildfire). In STAR, the NAPL serves as the fuel within an inert, porous soil medium. Results from experiments across a range of scales are very promising. Detailed characterisation has focused on coal tar, a common denser-than-water NAPL (DNAPL) contaminant. Complete remediation is demonstrated across this range of scales. Visual observations are supported bychemical extraction results. Further experiments suggest that STAR can be self-sustaining, meaning that once ignited the process can supply its own energy to propagate. Costly energy input is reduced significantly. Comparison of large scale to small scale laboratory experiments, a volume increase by a factor of 100, suggests that STAR process efficiency increases with scale. This increase in efficiency results from reduced heat losses at larger scales while maximum the temperature achieved by STAR is unaffected. The research also demonstrates the controllability of STAR, where the termination of airflow to the reaction terminates the STAR process. The scale-up process provides important guidance to the development of full scale STAR for ex situ remediation of NAPL-contaminated soil
Hardy's Inequality for the fractional powers of Grushin operator
We prove Hardy's inequality for the fractional powers of the generalized
sublaplacian and the fractional powers of the Grushin operator. We also find an
integral representation and a ground state representation for the fractional
powers of generalized sublaplacian
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