706 research outputs found
Volume and surface propellant heating in an electrothermal radio-frequency plasma micro-thruster
The temporal evolution of neutral gas temperature over the first 5 min of operation for an electrothermal radio-frequency micro-thruster with nitrogen (N2) propellant was measured using rovibrational band matching of the second positive N2 system. Three distinct periods of gas heating were identified with time constants of Ï 1â=â8âĂâ10â»â” s, Ï 2â=â8âs, and Ï 3â=â100âs. The fast heating (Ï 1) is attributed to volumetric heating processes within the discharge driven by ion-neutral collisions. The slow heating (Ï 3) is from ion neutralization and vibrational de-excitation on the walls creating wall heating. The intermediate heating mechanism (Ï 2) is yet to be fully identified although some theories are suggested.This research was partially funded by the Australian
Space Research Program (APT project) and the Australian
Research Council Discovery Project (No. DP140100571)
Experimental Study of Environment Friendly Mixed Refrigerant to Replace R-134a in a VCR System with Testing and Training of ANN
This work presents an experimental study on environment friendly mixed refrigerant to replace R134a in vapour compression refrigeration (VCR) System. The mixed refrigerants investigated are propane (R290), butane (R600), isobutene (R600a) and R134a. Even though the ozone depletion potentials of R134a relative to CFC-11 are very low; the global warming potentials are extremely high and also expensive. For this reason, the production and use of R134a will be terminated in the near future. Hydrocarbons are free from ozone depletion potential and have negligible global warming potential. The results showed that, mixed refrigerant with charge of 80 g satisfy the required freezer air temperature, when R134a with a charge of 110 g is used as refrigerant. The actual COP of refrigerator using mixed refrigerant was almost nearer that of the system using R134a as refrigerant. The coefficient of performance of the vapour compression refrigeration system using mixed refrigerant MR-3 [R134a/R290/ R600a/ R600 (20/35/40/5)] is having very close value with R134a and the Global warming potential of MR-3 is negligible when compared with R134a. ĂÂ Hence the mixed refrigerant MR-3 is chosen as an environmental friendly alternate refrigerant to R134a. Also the back propagation algorithm is implemented for training artificial neural network (ANN) to find out the optimum mixture having higher COP.Ă
The POINT-AGAPE survey II: An Unrestricted Search for Microlensing Events towards M31
An automated search is carried out for microlensing events using a catalogue
of 44554 variable superpixel lightcurves derived from our three-year monitoring
program of M31. Each step of our candidate selection is objective and
reproducible by a computer. Our search is unrestricted, in the sense that it
has no explicit timescale cut. So, it must overcome the awkward problem of
distinguishing long-timescale microlensing events from long-period stellar
variables. The basis of the selection algorithm is the fitting of the
superpixel lightcurves to two different theoretical models, using variable star
and blended microlensing templates. Only if microlensing is preferred is an
event retained as a possible candidate. Further cuts are made with regard to
(i) sampling, (ii) goodness of fit of the peak to a Paczynski curve, (iii)
consistency of the microlensing hypothesis with the absence of a resolved
source, (iv) achromaticity, (v) position in the colour-magnitude diagram and
(vi) signal-to-noise ratio. Our results are reported in terms of first-level
candidates, which are the most trustworthy, and second-level candidates, which
are possible microlensing but have lower signal-to-noise and are more
questionable. The pipeline leaves just 3 first-level candidates, all of which
have very short full-width half-maximum timescale (<5 days) and 3 second-level
candidates, which have timescales of 31, 36 and 51 days respectively. We also
show 16 third-level lightcurves, as an illustration of the events that just
fail the threshold for designation as microlensing candidates. They are almost
certainly mainly variable stars. Two of the 3 first-level candidates correspond
to known events (PA 00-S3 and PA 00-S4) already reported by the POINT-AGAPE
project. The remaining first-level candidate is new.Comment: 22 pages, 18 figures, MNRAS, to appea
Locally Perturbed Random Walks with Unbounded Jumps
In \cite{SzT}, D. Sz\'asz and A. Telcs have shown that for the diffusively
scaled, simple symmetric random walk, weak convergence to the Brownian motion
holds even in the case of local impurities if . The extension of their
result to finite range random walks is straightforward. Here, however, we are
interested in the situation when the random walk has unbounded range.
Concretely we generalize the statement of \cite{SzT} to unbounded random walks
whose jump distribution belongs to the domain of attraction of the normal law.
We do this first: for diffusively scaled random walks on having finite variance; and second: for random walks with distribution
belonging to the non-normal domain of attraction of the normal law. This result
can be applied to random walks with tail behavior analogous to that of the
infinite horizon Lorentz-process; these, in particular, have infinite variance,
and convergence to Brownian motion holds with the superdiffusive scaling.Comment: 16 page
The Development of the Australian Sweet Persimmon Industry
Persimmons were introduced into Australia in the 1850s, probably by Chinese gold miners. Commercial production began in the late 1800s. Small quantities, presumably of astringent varieties, were exported in the early 1900s , but markets never really developed. The first non-astringent persimmon, variety Fuyu, was grown at the Merbein Research Station, in Victoria, in 1967. Commercial plantings started in the early 1980s, and tree numbers exceeded 100 000 by 1990. In 1989 a national workshop addressed the future of the industry in Australia. As a result, a group of 12 growers committed to working together to establish an export marketing strategy. This group grew to become the Australian Persimmon Export Company, now with 40 members from five states, and established as the benchmark for the rest of the industry. APEC has developed markets in Singapore, Malaysia, Thailand and Hong Kong. Its two registered brands, 'Sweet Gold' and 'Golden Star', are recognized as the leading persimmon brands in Australia. In the future, more research is needed to address fruit softening problems and growers need to be focused on achieving higher percentages of export grade fruit. Market access to potentially lucrative markets such as Taiwan and Japan needs to be negotiated, and the industry must identify the means by which it will raise funds to invest in these key areas of R&D
Algebraic totality, towards completeness
Finiteness spaces constitute a categorical model of Linear Logic (LL) whose
objects can be seen as linearly topologised spaces, (a class of topological
vector spaces introduced by Lefschetz in 1942) and morphisms as continuous
linear maps. First, we recall definitions of finiteness spaces and describe
their basic properties deduced from the general theory of linearly topologised
spaces. Then we give an interpretation of LL based on linear algebra. Second,
thanks to separation properties, we can introduce an algebraic notion of
totality candidate in the framework of linearly topologised spaces: a totality
candidate is a closed affine subspace which does not contain 0. We show that
finiteness spaces with totality candidates constitute a model of classical LL.
Finally, we give a barycentric simply typed lambda-calculus, with booleans
and a conditional operator, which can be interpreted in this
model. We prove completeness at type for
every n by an algebraic method
Higher-Order Termination: from Kruskal to Computability
Termination is a major question in both logic and computer science. In logic,
termination is at the heart of proof theory where it is usually called strong
normalization (of cut elimination). In computer science, termination has always
been an important issue for showing programs correct. In the early days of
logic, strong normalization was usually shown by assigning ordinals to
expressions in such a way that eliminating a cut would yield an expression with
a smaller ordinal. In the early days of verification, computer scientists used
similar ideas, interpreting the arguments of a program call by a natural
number, such as their size. Showing the size of the arguments to decrease for
each recursive call gives a termination proof of the program, which is however
rather weak since it can only yield quite small ordinals. In the sixties, Tait
invented a new method for showing cut elimination of natural deduction, based
on a predicate over the set of terms, such that the membership of an expression
to the predicate implied the strong normalization property for that expression.
The predicate being defined by induction on types, or even as a fixpoint, this
method could yield much larger ordinals. Later generalized by Girard under the
name of reducibility or computability candidates, it showed very effective in
proving the strong normalization property of typed lambda-calculi..
Cross-Over between universality classes in a magnetically disordered metallic wire
In this article we present numerical results of conduction in a disordered
quasi-1D wire in the possible presence of magnetic impurities. Our analysis
leads us to the study of universal properties in different conduction regimes
such as the localized and metallic ones. In particular, we analyse the
cross-over between universality classes occurring when the strength of magnetic
disorder is increased. For this purpose, we use a numerical Landauer approach,
and derive the scattering matrix of the wire from electron's Green's function.Comment: Final version, accepted for publication in New Journ. of Physics, 27
pages, 28 figures. Replaces the earlier shorter preprint arXiv:0910.427
Characteristics tests of cerebrospinal fluid cytology, chemistry and bacteriology in invasive paediatric bacterial meningitis in Madagascar
Background: Paediatric bacterial meningitis is a major public health problem. CSF laboratory analysis is the key element to confirm the disease but remains difficult to access by clinicians or patients in low-resource settings. We described CSF biological tests results in invasive paediatric bacterial meningitis at the University Hospital Mother and Child of TsaralalĂ na (CHUMET) in Madagascar.Methods: In this retrospective and descriptive study from January 2013 to December 2018, all CSF samples that were confirmed for bacterial meningitis by triplex PCR Streptococcus pneumoniae, Haemophilus influenzae and Neisseria meningitidis were enrolled. CSF collected from eligible children were tested by microscopy, culture, soluble antigen at CHUMET laboratory. Residual CSF was referred to the regional reference laboratory (RRL) for real-time polymerase chain reaction (RT-PCR) confirmatory testing and serotyping.Results: Over the 6-year study period, 2286 CSF were tested by PCR, 141 (6.1%) were positive. The age group of (1-12 months) was the most affected (68.0%). The majority of CSF were cloudy with pleiocytosis >100/mm3. Hyperproteinorrhea >1 g/l was noted in 48.2% of cases. The sensitivity of gram stain was respectively 56.6% and 75% for Pneumococcus and Meningococcus detection while for culture it was 28.3% and 66.6%, respectively. The average white cell count was notably higher in meningococcal meningitis and changed significantly according to the pathogens identified (p=0.007).Conclusions: Paediatric bacterial meningitis diagnosis are based on CSF laboratory testing. Accessibility to multiplex PCR point-of-care tests targeting meningitis pathogens should be made easier for laboratories in low-income countries to improve patient care, monitor pathogen trends and vaccine impact program.
A New Elimination Rule for the Calculus of Inductive Constructions
Published in the post-proceedings of TYPES but actually not presented orally to the conferenceInternational audienceIn Type Theory, definition by dependently-typed case analysis can be expressed by means of a set of equations â the semantic approach â or by an explicit pattern-matching construction â the syntactic approach. We aim at putting together the best of both approaches by extending the pattern-matching construction found in the Coq proof assistant in order to obtain the expressivity and flexibility of equation-based case analysis while remaining in a syntax-based setting, thus making dependently-typed programming more tractable in the Coq system. We provide a new rule that permits the omission of impossible cases, handles the propagation of inversion constraints, and allows to derive Streicher's K axiom. We show that subject reduction holds, and sketch a proof of relative consistency
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