26 research outputs found
Symmetric-Asymmetric transition in mixtures of Bose-Einstein condensates
We propose a new kind of quantum phase transition in phase separated mixtures
of Bose-Einstein condensates. In this transition, the distribution of the two
components changes from a symmetric to an asymmetric shape. We discuss the
nature of the phase transition, the role of interface tension and the phase
diagram. The symmetric to asymmetric transition is the simplest quantum phase
transition that one can imagine. Careful study of this problem should provide
us new insight into this burgeoning field of discovery.Comment: 6 pages, 3 eps figure
An Alternative Method to Deduce Bubble Dynamics in Single Bubble Sonoluminescence Experiments
In this paper we present an experimental approach that allows to deduce the
important dynamical parameters of single sonoluminescing bubbles (pressure
amplitude, ambient radius, radius-time curve) The technique is based on a few
previously confirmed theoretical assumptions and requires the knowledge of
quantities such as the amplitude of the electric excitation and the phase of
the flashes in the acoustic period. These quantities are easily measurable by a
digital oscilloscope, avoiding the cost of expensive lasers, or ultrafast
cameras of previous methods. We show the technique on a particular example and
compare the results with conventional Mie scattering. We find that within the
experimental uncertainties these two techniques provide similar results.Comment: 8 pages, 5 figures, submitted to Phys. Rev.
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Frost Growth in Laminar Channel Flows with Streamwise Vortices
An experimental study of frost growth under the influence of streamwise vortices in a laminar
channel flow is presented. A new model of frost growth is developed to normalize the growth
rate of frost with respect to the effects of environmental parameters and time. This
normalization and a scale analysis show that the dimensionless frost thickness grows with the
square root of environmental time, a single parameter capturing environmental and temporal
effects. Experimental plain-channel data obey this relationship to within the uncertainty of the
measurements. Also in agreement with the model, the data show no significant dependence on
channel location or on Reynolds number (for 5OO<Re<2500 based on hydraulic diameter).
Comparisons of model predictions to data from previous studies demonstrate good agreement
with these independent data obtained under other conditions. The growth patterns of frost
behind a delta-wing fixed to the surface of the channel are explained using flow visualization
results. The appearance of frost on the surface occurs sooner, and the frost has an internal
structure in regions where the vortices impose a flow toward the surface different from regions
unaffected by vortices. Horseshoe vortices form at the junction of the channel and wing and
the interaction of tip vortex and horseshoe vortex were qualitatively observed. The maximum
frost height behind the delta wing in the spanwise direction is compared to the plain channel
results: frost growth rate under the influence of the streamwise vortex was approximately 13%
higher than for the plain-channel case.Air Conditioning and Refrigeration Project 5
Soluble Tin(II) Macroinitiator Adducts for the Controlled Ring-Opening Polymerization of Lactones and Cyclic Carbonates
Polyesters and poly(ester carbonates) were synthesized via ring-opening polymerization with new tin(II) macroinitiator adducts containing oligomeric (L)-lactide (LLA,), rac-lactide (rac-LA), and is an element of-caprolactone (CL). The novel initiating species were synthesized by the reaction of LLA, rac-LA, or CL with Sn(OEt)(2) (monomer concentration/initiator concentration less than or equal to20) and then were dissolved in methylene chloride or toluene and stored in a stoppered flask for the subsequent ring-opening polymerization of cyclic esters and carbonates. The soluble tin alkoxide macroinitiators yielded predictable and quantitative initiation of polymerization for up to 1 month of storage time at room temperature. The resulting polymers displayed low polydispersity (less than or equal to 1.5), and a high monomer conversion (greater than or equal to95%) was obtained within relatively short polymerization times (less than or equal to2 h). Adjusting the monomer/macroinitiator ratio effectively controlled the molecular weights of the polymers. NMR was used to characterize the initiating species and polymer microstructure, and size exclusion chromatography was used to determine the molecular weight properties of the polymers. (C) 2002 Wiley Periodicals, Inc