3,403 research outputs found
Interference effects during burning in air for stationary n-heptane, ethyl alcohol, and methyl alcohol droplets
Experiments have been conducted for the determination
of the evaporation constant and flame shapes of two and
of five closely spaced droplets burning in air. Droplets of
approximately the same and of different diameters were
used at various distances between the droplet centers.
The apparent flame shape, which was observed only for n-heptane droplets, changes very little during burning.
The square of the droplet diameter decreases linearly with
time for fixed spacing between droplet centers, at least
within the experimental limits of accuracy. In general,
the average evaporation constant for two droplets, K',
must be assumed either to vary continuously during burning
or else to be a function of average initial drop diameter,
D^0. The change of K' with time corresponds to the second
derivative in plots of the square of the diameter vs. time.
These second derivatives are not defined in our work because
of unavoidable scatter of the experimental data. Attempts at understanding the observed results by considering
published theories for single droplets, as well as groupings obtained from dimensional analysis, have been
unsuccessful. It appears that the diffusion model for
the heterogeneous burning of single fuel droplets will require serious revision and extension before the burning of
droplets arrays and sprays can be understood quantitatively.
Furthermore, the effective value of K' for a spray
probably depends not only on the fuel-oxidizer system but
also on the injection pattern. For this reason additional
studies had best be carried out under conditions corresponding to those existing in service models
Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps
A density functional theory for colloidal dynamics is presented which
includes hydrodynamic interactions between the colloidal particles. The theory
is applied to the dynamics of colloidal particles in an optical trap which
switches periodically in time from a stable to unstable confining potential. In
the absence of hydrodynamic interactions, the resulting density breathing mode,
exhibits huge oscillations in the trap center which are almost completely
damped by hydrodynamic interactions. The predicted dynamical density fields are
in good agreement with Brownian dynamics computer simulations
The far-infrared/submillimeter properties of galaxies located behind the Bullet cluster
The Herschel Lensing Survey (HLS) takes advantage of gravitational lensing by massive galaxy clusters to sample a population of high-redshift galaxies which are too faint to be detected above the confusion limit of current far-infrared/submillimeter telescopes. Measurements from 100â500 ÎŒm bracket the peaks of the far-infrared spectral energy distributions of these galaxies, characterizing their infrared luminosities and star formation rates. We introduce initial results from our science demonstration phase observations, directed toward the Bullet cluster (1E0657-56). By combining our observations with LABOCA 870 ÎŒm and AzTEC 1.1 mm data we fully constrain the spectral energy distributions of 19 MIPS 24 ÎŒm-selected galaxies which are located behind the cluster. We find that their colors are best fit using templates based on local galaxies with systematically lower infrared luminosities. This suggests that our sources are not like local ultra-luminous infrared galaxies in which vigorous star formation is contained in a compact highly dust-obscured region. Instead, they appear to be scaled up versions of lower luminosity local galaxies with star formation occurring on larger physical scales
CMB map derived from the WMAP data through Harmonic Internal Linear Combination
We are presenting an Internal Linear Combination (ILC) CMB map, in which the
foreground is reduced through harmonic variance minimization. We have derived
our method by converting a general form of pixel-space approach into spherical
harmonic space, maintaining full correspondence. By working in spherical
harmonic space, spatial variability of linear weights is incorporated in a
self-contained manner and our linear weights are continuous functions of
position over the entire sky. The full correspondence to pixel-space approach
enables straightforward physical interpretation on our approach. In variance
minimization of a linear combination map, the existence of a cross term between
residual foregrounds and CMB makes the linear combination of minimum variance
differ from that of minimum foreground. We have developed an iterative
foreground reduction method, where perturbative correction is made for the
cross term. Our CMB map derived from the WMAP data is in better agreement with
the WMAP best-fit CDM model than the WMAP team's Internal Linear
Combination map. We find that our method's capacity to clean foreground is
limited by the availability of enough spherical harmonic coefficients of good
Signal-to-Noise Ratio (SNR).Comment: The whole sky CMB map, which is derived from the WMAP 5 year data
through our method, is available in HEALPix FITS format at
http://www.nbi.dk/~jkim/hilc The paper with higher resolution images also
available at http://www.nbi.dk/~jkim/hil
Mechanisms of Ar release from Himalayan metamorphic hornblende
Changes in hornblende samples that occur during stepwise 39Ar/40Ar analysis were studied
experimentally and mineralogically. A complex succession of reactions was seen (hornblende
~ oxyhornblende ~ clinopyroxene-structured phase ~ fine-grained reaction products
~ glasses) in the temperature range 750-1300 °C. The release of Ar from hornblende
in the vacuum furnace appeared to occur by fundamentally different processes from those
resulting in Ar loss during metamorphism. Simple diffusional interpretations of the release patterns are, therefore, not capable of revealing the thermal history of samples. In principle, some useful information may be obtained if long-standing fractures andother defects control both natural Ar loss and mineral reactions within the laboratory
Revisiting Hafemeisterâs âScience and Societyâ Tests
We revisit a series of papers on science and society issues by David Hafemeister in the 1970s and 1980s. The emphasis in the present work is on world oil production limits and some consequences of various possible scenarios for the near future. Some of the data and scenarios used by Hafemeister are updated for U.S. oil production in the past two decades and extended to an analysis of a peak in world oil production in the future. We discuss some simple scenarios for future energy use patterns and look at the consequence of these scenarios as world oil production begins to decline. We also provide a list of resources for critical investigations of natural resource extraction and depletion patterns
Fresnel filtering in lasing emission from scarred modes of wave-chaotic optical resonators
We study lasing emission from asymmetric resonant cavity (ARC) GaN
micro-lasers. By comparing far-field intensity patterns with images of the
micro-laser we find that the lasing modes are concentrated on three-bounce
unstable periodic ray orbits, i.e. the modes are scarred. The high-intensity
emission directions of these scarred modes are completely different from those
predicted by applying Snell's law to the ray orbit. This effect is due to the
process of ``Fresnel filtering'' which occurs when a beam of finite angular
spread is incident at the critical angle for total internal reflection.Comment: 4 pages, 3 figures (eps), RevTeX 3.1, submitted to Phys. Rev. Lett;
corrected a minor (transcription) erro
Coupled KdV equations derived from atmospherical dynamics
Some types of coupled Korteweg de-Vries (KdV) equations are derived from an
atmospheric dynamical system. In the derivation procedure, an unreasonable
-average trick (which is usually adopted in literature) is removed. The
derived models are classified via Painlev\'e test. Three types of
-function solutions and multiple soliton solutions of the models are
explicitly given by means of the exact solutions of the usual KdV equation. It
is also interesting that for a non-Painlev\'e integrable coupled KdV system
there may be multiple soliton solutions.Comment: 19 pages, 2 figure
Language attitudes and use in a transplanted setting: Greek Cypriots in London
In this paper we explore language attitudes and use in the Greek Cypriot community in London, England. Our study is based on an earlier survey carried out in Nicosia, Cyprus and we compare attitudes to language and reported language use in the two communities. We thereby highlight the significance of sociolinguistic variables on similar groups of speakers. We further extend our investigation to include codeswitching practices in the London community.
\ud
Analysis of language attitudes and use within the Greek-Cypriot population of London, and comparisons with findings in Nicosia, reflect symbolic forces operating in the two contexts. Despite obvious differences between the two communities, (most obviously the official languages and distinct cultural backgrounds of the two nations), the Greek Cypriot Dialect continues to play an active role in both. English is however the âdefault choiceâ for young Cypriots in the UK and Standard Modern Greek occupies a much more limited role than in Cyprus. It is argued that differences in language attitudes and use can be interpreted in light of different market forces operating in the nation (i.e. Cyprus) and the Diaspora (i.e. UK)
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