898 research outputs found
Brewing of filter coffee
We report progress on mathematical modelling of coffee grounds in a drip filter coffee machine. The report focuses on the evolution of the shape of the bed of coffee grounds during extraction with some work also carried out on the chemistry of extraction. This work was sponsored by Philips who are interested in understanding an observed correlation between the final shape of the coffee grounds and the quality of the coffee. We used experimental data gathered by Philips and ourselves to identify regimes in the coffee brewing process and relevant regions of parameter space. Our work makes it clear that a number of separate processes define the shape of the coffee bed depending on the values of the parameters involved e.g. the size of the grains and the speed of fluid flow during extraction. We began work on constructing mathematical models of the redistribution of the coffee grounds specialised to each region and on a model of extraction. A variety of analytic and numerical tools were used. Furthermore our research has progressed far enough to allow us to begin to exploit connections between this problem and other areas of science, in particular the areas of sedimentology and geomorphology, where the processes we have observed in coffee brewing have been studied
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Separation science and technology
The focus of this project is the demonstration and advancement of membrane-based separation and destruction technologies. The authors are exploring development of membrane systems for gas separations, selective metal ion recovery, and for separation or destruction of hazardous organics. They evaluated existing polymers and polymer formulations for recovery of toxic oxyanionic metals such as chromate and arsenate from selected waste streams and developed second-generation water-soluble polymeric systems for highly selective oxyanion removal and recovery. They optimized the simultaneous removal of radioactive strontium and cesium from aqueous solutions using the new nonhazardous separations agents, and developed recyclable, redox-active extractants that permitted recovery of the radioactive ions into a minimal waste volume. They produced hollow fibers and fabricated prototype hollow-fiber membrane modules for applications to gas separations and the liquid-liquid extraction and recovery of actinides and nuclear materials from process streams. They developed and fabricated cyclodextrin-based microporous materials that selectively absorb organic compounds in an aqueous environment; the resultant products gave pure water with organics at less than 0.05 parts per billion. They developed new, more efficient, membrane-based electrochemical reactors for use in organic destruction in process waste treatment. They addressed the need for advanced oxidation technologies based on molecular-level materials designs that selectively remove or destroy target species. They prepared and characterized surface-modified TiO{sub 2} thin films using different linking approaches to attach ruthenium photosensitizers, and they started the measurement of the photo-degradation products generated using surface modified TiO{sub 2} films in reaction with chlorophenol
The BEST study - a prospective study to compare business class versus economy class air travel as a cause of thrombosis
Background. As many as 10% of airline passengers travelling without prophylaxis for long distances may develop a venous thrombosis. There is, however, no evidence that economy class travellers are at increased risk of thrombosis.Objectives. A suitably powered prospective study, based on the incidence of deep-vein thrombosis (DVT) reported in previous studies on long-haul flights, was designed to determine the incidence of positive venous duplex scans and D-dimer elevations in low and intermediate-risk passengers, comparing passengers travelling in business and economy class.Patients/methods. Eight hundred and ninety-nine passengers were recruited (180 travelling business class and 719 travelling economy). D-dimers were measured before and after the flight. A value greater than 500 ng/ml was accepted as abnormal. A thrombophilia screen was conducted which included the factor V Leiden mutation, the prothombin 20210A mutation, protein C and S levels, antithrombin levels, and anticardiolipin antibodies immunoglobulin G (IgG) and immunoglobulin M (IgM). On arrival, lower limb compression ultrasonography of the deep veins was performed. Logistical regression analysis was used to determine the risk factors related to abnormally high D-dimer levels.Results. Only 434 subjects had a full venous duplex scan performed. None had ultrasonic evidence of venous thrombosis. Nine passengers tested at departure had elevated D-dimer levels and these volunteers were excluded from further study. Seventy-four of the 899 passengers had raised D-dimers on arrival. Twenty-two of 180 business class passengers (12%) developed elevated D-dimers compared with 52 of 719 economy class passengers (7%). There was no significant association between elevation of D-dimers and the class flown (odds ratio (OR) 0.61, p = 0.109). The factor V Leiden mutation, factor VIII levels and the use of aspirin were, however, associated with raised D-dimers (OR 3.36, p = 0.024; OR 1.01, p = 0.014; and OR 2.04, p = 0.038, respectively). Five hundred and five passengers were contacted within 6 months and none reported any symptoms of a clinical thrombosis or pulmonary embolus.Conclusion. The incidence of ultrasonically proven DVT is much lower than previously reported. However, more than 10% of all passengers developed raised D-dimers, which were unrelated to the class flown. A rise in D-dimers is associated with an inherent risk of thrombosis and/ or thrombophilia, demonstrates activation of both the coagulation and fibrinolytic systems during long-haul flights, and may indicate the development of small thrombi
The PL calibration for Milky Way Cepheids and its implications for the distance scale
The rationale behind recent calibrations of the Cepheid PL relation using the
Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent
conclusions regarding a possible change in slope of the PL relation for
short-period and long-period Cepheids are tied to a pathological distribution
of HST calibrators within the instability strip. A recalibration of the
period-luminosity relation is obtained using Galactic Cepheids in open clusters
and groups, the resulting relationship, described by log L/L_sun =
2.415(+-0.035) + 1.148(+-0.044)log P, exhibiting only the moderate scatter
expected from color spread within the instability strip. The relationship is
confirmed by Cepheids with HST parallaxes, although without the need for
Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos
parallaxes, albeit with concerns about the cited precisions of the latter. A
Wesenheit formulation of Wv = -2.259(+-0.083) - 4.185(+-0.103)log P for
Galactic Cepheids is tested successfully using Cepheids in the inner regions of
the galaxy NGC 4258, confirming the independent geometrical distance
established for the galaxy from OH masers. Differences between the extinction
properties of interstellar and extragalactic dust may yet play an important
role in the further calibration of the Cepheid PL relation and its application
to the extragalactic distance scale.Comment: Accepted for Publication (Astrophysics & Space Science
The Accelerating Growth of Online Tagging Systems
Research on the growth of online tagging systems not only is interesting in
its own right, but also yields insights for website management and semantic web
analysis. Traditional models that describing the growth of online systems can
be divided between linear and nonlinear versions. Linear models, including the
BA model (Brabasi and Albert, 1999), assume that the average activity of users
is a constant independent of population. Hence the total activity is a linear
function of population. On the contrary, nonlinear models suggest that the
average activity is affected by the size of the population and the total
activity is a nonlinear function of population. In the current study,
supporting evidences for the nonlinear growth assumption are obtained from data
on Internet users' tagging behavior. A power law relationship between the
number of new tags (F) and the population (P), which can be expressed as F ~ P
^ gamma (gamma > 1), is found. I call this pattern accelerating growth and find
it relates the to time-invariant heterogeneity in individual activities. I also
show how a greater heterogeneity leads to a faster growth.Comment: 8 pages, 3 figure
The History of Galaxy Formation in Groups: An Observational Perspective
We present a pedagogical review on the formation and evolution of galaxies in
groups, utilizing observational information from the Local Group to galaxies at
z~6. The majority of galaxies in the nearby universe are found in groups, and
galaxies at all redshifts up to z~6 tend to cluster on the scale of nearby
groups (~1 Mpc). This suggests that the group environment may play a role in
the formation of most galaxies. The Local Group, and other nearby groups,
display a diversity in star formation and morphological properties that puts
limits on how, and when, galaxies in groups formed. Effects that depend on an
intragroup medium, such as ram-pressure and strangulation, are likely not major
mechanisms driving group galaxy evolution. Simple dynamical friction arguments
however show that galaxy mergers should be common, and a dominant process for
driving evolution. While mergers between L_* galaxies are observed to be rare
at z < 1, they are much more common at earlier times. This is due to the
increased density of the universe, and to the fact that high mass galaxies are
highly clustered on the scale of groups. We furthermore discus why the local
number density environment of galaxies strongly correlates with galaxy
properties, and why the group environment may be the preferred method for
establishing the relationship between properties of galaxies and their local
density.Comment: Invited review, 16 pages, to be published in ESO Astrophysics
Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V.
Ivanov, J. Borissov
ParIC : A Family of Parallel Incomplete Cholesky Preconditioners
A class of parallel incomplete factorization preconditionings
for the solution of large linear systems is investigated. The approach may
be regarded as a generalized domain decomposition method. Adjacent
subdomains have to communicate during the setting up of the preconÂ
ditioner, and during the application of the preconditioner. Overlap is
not necessary to achieve high performance. FillÂin levels are considered
in a global way. If necessary, the technique may be implemented as a
global reÂordering of the unknowns. Experimental results are reported
for twoÂdimensional problems
Air fluorescence measurements in the spectral range 300-420 nm using a 28.5 GeV electron beam
Measurements are reported of the yield and spectrum of fluorescence, excited
by a 28.5 GeV electron beam, in air at a range of pressures of interest to
ultra-high energy cosmic ray detectors. The wavelength range was 300 - 420 nm.
System calibration has been performed using Rayleigh scattering of a nitrogen
laser beam. In atmospheric pressure dry air at 304 K the yield is 20.8 +/- 1.6
photons per MeV.Comment: 29 pages, 10 figures. Submitted to Astroparticle Physic
A Catalogue of M51 type Galaxy Associations
A catalog of 232 apparently interacting galaxy pairs of the M51 class is
presented. Catalog members were identified from visual inspection of mult-band
images in the IRSA archive. The major findings in the compilation of this
catalog are (1) A surprisingly low number of the main galaxies in M51 systems
are early type spirals and barred spirals. (2) Over 70% of the main galaxies in
M51 systems are 2-armed spirals. (3) Some systems that were classified as M51
types in previous studies are not M51 types as defined in this catalog. There
were a number of systems previously classified as M51 systems for which the
companion is identified as an HII region within the main galaxy or a foreground
star within the Milky Way. (4) It was found that only 18% of the M51 type
companions have redshift measurements in the literature. There is a significant
need for spectroscopic study of the companions in order to improve the value of
the catalog as a sample for studying the effects of M51 type interaction on
galaxy dynamics, morphology, and star formation. Further spectroscopy will also
help constrain the statistics of possible chance projections between foreground
and background galaxies in this catalog. The catalog also contains over 430
additional systems which are classified as "possible M51" systems. The reasons
for classifying certain systems as possible M51 systems are discussed.Comment: 19 pages including 6 figures and tables 3-8, Tables 1 and 2 are found
at http://www.jorcat.com, Accepted for publication in Astrophysics and Space
Scienc
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