3,623 research outputs found
On Exact Evaluation of Path Integrals
Some mistakes have been correcte
Index Theorems and Loop Space Geometry
We investigate the evaluation of the Dirac index using symplectic geometry in
the loop space of the corresponding supersymmetric quantum mechanical model. In
particular, we find that if we impose a simple first class constraint, we can
evaluate the Callias index of an odd dimensional Dirac operator directly from
the quantum mechanical model which yields the Atiyah-Singer index of an even
dimensional Dirac operator in one more dimension. The effective action obtained
by BRST quantization of this constrained system can be interpreted in terms of
loop space symplectic geometry, and the corresponding path integral for the
index can be evaluated exactly using the recently developed localization
techniques.Comment: 15 pages, report CERN-TH-6471 and HU-TFT-92-1
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
Currents on Superconducting Strings at Finite Chemical Potential and Temperature
We consider the model giving rise to Witten's superconducting cosmic strings
at finite fermion chemical potential and temperature. We demonstrate how
various symmetries of the hamiltonian can be used to exactly compute the
fermion electric current in the string background. We show that the current
along the string is not sensitive to the profiles of the string fields, and at
fixed chemical potential and temperature depends only on the string winding
number, the total gauge flux through the vortex and, possibly, the fermion mass
at infinity.Comment: 9 page
Dual Superconductors and SU(2) Yang-Mills
We propose that the SU(2) Yang-Mills theory can be interpreted as a two-band
dual superconductor with an interband Josephson coupling. We discuss various
consequences of this interpretation including electric flux quantization,
confinement of vortices with fractional flux, and the possibility that a closed
vortex loop exhibits exotic exchange statistics
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
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