3,741 research outputs found
Massively parallel approximate Gaussian process regression
We explore how the big-three computing paradigms -- symmetric multi-processor
(SMC), graphical processing units (GPUs), and cluster computing -- can together
be brought to bare on large-data Gaussian processes (GP) regression problems
via a careful implementation of a newly developed local approximation scheme.
Our methodological contribution focuses primarily on GPU computation, as this
requires the most care and also provides the largest performance boost.
However, in our empirical work we study the relative merits of all three
paradigms to determine how best to combine them. The paper concludes with two
case studies. One is a real data fluid-dynamics computer experiment which
benefits from the local nature of our approximation; the second is a synthetic
data example designed to find the largest design for which (accurate) GP
emulation can performed on a commensurate predictive set under an hour.Comment: 24 pages, 6 figures, 1 tabl
Combustion and emission studies of a common-rail direct injection diesel engine with various injector nozzles
Fuel injection has a critical role in an internal combustion engine and a significant
effect on the quality of the fuel spray. In turn, fuel spray directly affects an engine´s combustion,
efficiency, power and emissions. This study evaluated three different injector nozzles in a highspeed, non-road diesel engine. It was run on diesel fuel oil (DFO) and testing was conducted at
three different engine loads (100%, 75% and 50%) and at two engine speeds (2,200 rpm and
1,500 rpm). The nozzles had 6, 8 and 10 holes and a relatively high mass flow rate (HF). The
study investigated and compared injection and combustion characteristics, together with gaseous
emissions. The combustion parameters seemed to be very similar with all studied injector nozzles.
The emission measurements indicated general reductions in hydrocarbons (HC), carbon
monoxide (CO) and nitrogen oxides (NOx) at most load/speed points when using the 6- and
10-hole nozzles instead of the reference 8-hole nozzles. However, smoke number increased when
the alternative nozzles were used
Exact Path Integrals by Equivariant Cohomology
It is a common belief among field theorists that path integrals can be
computed exactly only in a limited number of special cases, and that most of
these cases are already known. However recent developments, which generalize
the WKBJ method using equivariant cohomology, appear to contradict this folk
wisdom. At the formal level, equivariant localization would seem to allow exact
computation of phase space path integrals for an arbitrary partition function!
To see how, and if, these methods really work in practice, we have applied them
in explicit quantum mechanics examples. We show that the path integral for the
1-d hydrogen atom, which is not WKBJ exact, is localizable and computable using
the more general formalism. We find however considerable ambiguities in this
approach, which we can only partially resolve. In addition, we find a large
class of quantum mechanics examples where the localization procedure breaks
down completely.Comment: LATE
Equivariance, BRST and Superspace
The structure of equivariant cohomology in non-abelian localization formulas
and topological field theories is discussed. Equivariance is formulated in
terms of a nilpotent BRST symmetry, and another nilpotent operator which
restricts the BRST cohomology onto the equivariant, or basic sector. A
superfield formulation is presented and connections to reducible (BFV)
quantization of topological Yang-Mills theory are discussed.Comment: (24 pages, report UU-ITP and HU-TFT-93-65
BRST extension of the Faddeev model
The Faddeev model is a second class constrained system. Here we construct its
nilpotent BRST operator and derive the ensuing manifestly BRST invariant
Lagrangian. Our construction employs the structure of Stuckelberg fields in a
nontrivial fashion.Comment: 4 pages, new references adde
Waste fish oil as an alternative renewable fuel for IC engines
Received: January 31st, 2021 ; Accepted: April 10th, 2021 ; Published: April 30th, 2021 ; Correspondence: [email protected] are potential fuels for internal combustion engines because of they have
advantageous properties such as biodegradability, renewability, high oxygen content and low
sulphur. However, the high viscosity, surface tension, and density of crude bio-oils pose
challenges for engine use. Those properties affect fuel spray characteristics, mixture formation
and combustion. In turn, these impact engine, efficiency, power and emissions. This study
investigated the use of crude fish oil (FO) at medium and low engine-loads at two engine speeds
in an off-road engine. The injectors had 6-hole high flow rate tips. The results were compared
with those of fossil diesel fuel oil (DFO). Fish oil increased hydrocarbon (HC), carbon monoxide
(CO) and partly oxides of nitrogen (NOx) emissions. Smoke number, however, decreased. Crude
fish oil also showed lowered total particle number (TPN) at low load at low engine-speed
compared with DFO
Alternatives to Animal Experimentation
Alternatives to animal experimentation are highly touted today by animal welfare advocates. Their campaign for adopting alternatives has caused much discussion and debate within and outside the biomedical community. This paper aimed to examine the controversy and assess the more common alternatives, including the bacterial mutagenicity assay or Ames test, cell culture, and mathematical models for toxicity prediction. Chemical safety testing is the most promising of the fields for alternatives where laboratory animals are used, and incorporating alternatives with live-animal assays is increasing. However, due to the limitations of alternatives in use currently, there is still a considerable need for in vivo systems. The veterinarian is central to the alternatives question regarding humane considerations and the usefulness of animals in science. An influential role for the veterinarian is to serve as an educator and mediator between the scientist using laboratory animals and the animal welfare proponent
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