54,899 research outputs found
Influence of Succinimide Dispersants on Film Formation, Friction and Antiwear Properties of Zinc Dialkyl Dithiophosphate
ZDDP (zinc dialkyldithiophosphate) is arguably the most successful antiwear additive ever
employed in crankcase engine lubricants. It was originally used as an antioxidant and shortly
afterwards recognized for its antiwear and extreme pressure properties. Unfortunately,
another critical additive polyisobutylsuccinimide-polyamine (PIBSA-PAM), which is used as
a dispersant in engine oils, is known to be antagonistic to ZDDP in terms of film formation,
friction and wear. The mechanisms of this antagonism have been widely studied, but they are
still not well understood. Furthermore, in order to protect engine exhaust catalysts from
sulphated ash, phosphorus and sulphur (SAPS) and extend drain intervals of engine lubricants,
a progressive reduction in ZDDP quantity but a growth in the use of PIBSA-PAM is required.
The aim of this study is to explore the mechanisms and practical effects of the antagonism
between ZDDP and PIBSA-PAM. Of particular interest is the impact on performance of the
ratio of ZDDP to PIBSA-PAM, as measured by P:N ratio. Since ZDDP is a very effective
antiwear additive, it produces only very low or "mild" rates of wear. To study this requires a
new way to measure mild wear behaviour of formulated oils.
Several techniques have been applied in this study to investigate the film formation, friction
and wear properties of ZDDP- and/or PIBSA-PAM-containing oils. These include a new mild
wear testing method, which is tested and developed using a range of different types of
additives.
It is found that the ratio of P:N plays a strong role in determining tribofilm formation and
friction of ZDDP/PIBSA-PAM blends. However it plays a much weaker role in determining
wear behaviour. It is found that some PIBSA-PAMs have considerable friction-reducing
properties in their own right. The results suggest that PIBSA-PAM may interfere with the
behaviour of ZDDP in several ways: by forming a ZDDP/ PIBSA-PAM complex at the metal
surfaces to reduce the local activity of ZDDP; by PIBSA-PAM partially removing the ZDDP
film; possibly also by PIBSA-PAM blocking ZDDP from metal surfaces. The newly-developed
wear testing method can be used conveniently and effectively to study mild wear
properties not just of ZDDP but of a wide range of other additives
Average-case Approximation Ratio of Scheduling without Payments
Apart from the principles and methodologies inherited from Economics and Game
Theory, the studies in Algorithmic Mechanism Design typically employ the
worst-case analysis and approximation schemes of Theoretical Computer Science.
For instance, the approximation ratio, which is the canonical measure of
evaluating how well an incentive-compatible mechanism approximately optimizes
the objective, is defined in the worst-case sense. It compares the performance
of the optimal mechanism against the performance of a truthful mechanism, for
all possible inputs.
In this paper, we take the average-case analysis approach, and tackle one of
the primary motivating problems in Algorithmic Mechanism Design -- the
scheduling problem [Nisan and Ronen 1999]. One version of this problem which
includes a verification component is studied by [Koutsoupias 2014]. It was
shown that the problem has a tight approximation ratio bound of (n+1)/2 for the
single-task setting, where n is the number of machines. We show, however, when
the costs of the machines to executing the task follow any independent and
identical distribution, the average-case approximation ratio of the mechanism
given in [Koutsoupias 2014] is upper bounded by a constant. This positive
result asymptotically separates the average-case ratio from the worst-case
ratio, and indicates that the optimal mechanism for the problem actually works
well on average, although in the worst-case the expected cost of the mechanism
is Theta(n) times that of the optimal cost
Laplacian coefficients of unicyclic graphs with the number of leaves and girth
Let be a graph of order and let be the characteristic polynomial of its
Laplacian matrix. Motivated by Ili\'{c} and Ili\'{c}'s conjecture [A. Ili\'{c},
M. Ili\'{c}, Laplacian coefficients of trees with given number of leaves or
vertices of degree two, Linear Algebra and its Applications
431(2009)2195-2202.] on all extremal graphs which minimize all the Laplacian
coefficients in the set of all -vertex unicyclic graphs
with the number of leaves , we investigate properties of the minimal
elements in the partial set of the Laplacian
coefficients, where denote the set of -vertex
unicyclic graphs with the number of leaves and girth . These results are
used to disprove their conjecture. Moreover, the graphs with minimum
Laplacian-like energy in are also studied.Comment: 19 page, 4figure
Effective potential calculation of the MSSM lightest CP-even Higgs boson mass
I summarize results of two-loop effective potential calculations of the
lightest CP-even Higgs boson mass in the minimal supersymmetric standard model.Comment: 4 pages, 1 figur
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