Investigation of transition between spark ignition and controlled auto-ignition combustion in a V6 direct-injection engine with cam profile switching

Controlled auto-ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI) can be achieved by trapping residuals with early exhaust valve closure in a direct fuel injection in-cylinder four-stroke gasoline engines (through the employment of low-lift cam profiles). Due to the operating region being limited to low and mid-load operation for CAI combustion with a low-lift cam profile, it is important to be able to operate SI combustion at high-load with a normal cam profile. A 3.0L prototype engine was modified to achieve CAI combustion, using a Cam Profile Switching mechanism which has the capability to switch between high and low-lift cam-profiles. A strategy was used where a high-profile could be used for SI combustion and a low-lift profile was used for CAI combustion. Initial analysis showed that for transitioning from SI to CAI combustion, misfire occurred on the first CAI transitional cycle. Subsequent experiments showed that the throttle opening position and switching time could be controlled avoiding misfire. Further work investigated transitioning at different loads and from CAI to SI combustion

The number of independent sets in a graph with small maximum degree

Let ${\rm ind}(G)$ be the number of independent sets in a graph $G$. We show that if $G$ has maximum degree at most $5$ then $${\rm ind}(G) \leq 2^{{\rm iso}(G)} \prod_{uv \in E(G)} {\rm ind}(K_{d(u),d(v)})^{\frac{1}{d(u)d(v)}}$$ (where $d(\cdot)$ is vertex degree, ${\rm iso}(G)$ is the number of isolated vertices in $G$ and $K_{a,b}$ is the complete bipartite graph with $a$ vertices in one partition class and $b$ in the other), with equality if and only if each connected component of $G$ is either a complete bipartite graph or a single vertex. This bound (for all $G$) was conjectured by Kahn. A corollary of our result is that if $G$ is $d$-regular with $1 \leq d \leq 5$ then $${\rm ind}(G) \leq \left(2^{d+1}-1\right)^\frac{|V(G)|}{2d},$$ with equality if and only if $G$ is a disjoint union of $V(G)/2d$ copies of $K_{d,d}$. This bound (for all $d$) was conjectured by Alon and Kahn and recently proved for all $d$ by the second author, without the characterization of the extreme cases. Our proof involves a reduction to a finite search. For graphs with maximum degree at most $3$ the search could be done by hand, but for the case of maximum degree $4$ or $5$, a computer is needed.Comment: Article will appear in {\em Graphs and Combinatorics

Testing Bekenstein's Relativistic MOND gravity with Lensing Data

We propose to use multiple-imaged gravitational lenses to set limits on gravity theories without dark matter, specificly TeVeS (Bekenstein 2004), a theory which is consistent with fundamental relativistic principles and the phenomenology of MOdified Newtonian Dynamics (MOND) theory. After setting the framework for lensing and cosmology, we derive analytically the deflection angle for the point lens and the Hernquist galaxy profile, and fit galaxy-quasar lenses in the CASTLES sample. We do this with three methods, fitting the observed Einstein ring sizes, the image positions, or the flux ratios. In all cases we consistently find that stars in galaxies in MOND/TeVeS provide adequate lensing. Bekenstein's toy $\mu$ function provides more efficient lensing than the standard MOND $\mu$ function. But for a handful of lenses [indicated in Table 2,3, fig 16] a good fit would require a lens mass orders of magnitude larger/smaller than the stellar mass derived from luminosity unless the modification function $\mu$ and modification scale $a_0$ for the universal gravity were allowed to be very different from what spiral galaxy rotation curves normally imply. We discuss the limitation of present data and summarize constraints on the MOND $\mu$ function. We also show that the simplest TeVeS "minimal-matter" cosmology, a baryonic universe with a cosmological constant, can fit the distance-redshift relation from the supernova data, but underpredicts the sound horizon size at the last scattering. We conclude that lensing is a promising approach to differentiate laws of gravity (see also astro-ph/0512425).Comment: reduced to 17p, 16 figs, discussed cosmology and constraints on mu-function, MNRAS accepte

Number of states for nucleons in a single-jj shell

In this paper we obtain number of states with a given spin $I$ and a given isospin $T$ for systems with three and four nucleons in a single-$j$ orbit, by using sum rules of six-$j$ and nine-$j$ symbols obtained in earlier works.Comment: to be published in Physical Review

Signatures of Emerging Subsurface Structures in Acoustic Power Maps

We show that under certain conditions, subsurface structures in the solar interior can alter the average acoustic power observed at the photosphere above them. By using numerical simulations of wave propagation, we show that this effect is large enough for it to be potentially used for detecting emerging active regions before they appear on the surface. In our simulations, simplified subsurface structures are modeled as regions with enhanced or reduced acoustic wave speed. We investigate the dependence of the acoustic power above a subsurface region on the sign, depth, and strength of the wave speed perturbation. Observations from the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) prior and during the emergence of NOAA active region 10488 are used to test the use of acoustic power as a potential precursor of magnetic flux emergence.Comment: 7 pages, 5 figures, accepted for publication in Solar Physics on 21 March 201

Heat conduction in graphene flakes with inhomogeneous mass interface

Using nonequilibrium molecular dynamics simulations, we study the heat conduction in graphene flakes composed by two regions. One region is mass-loaded and the other one is intact. It is found that the mass interface between the two regions greatly decreases the thermal conductivity, but it would not bring thermal rectification effect. The dependence of thermal conductivity upon the heat flux and the mass difference ratio are studied to confirm the generality of the result. The interfacial scattering of solitons is studied to explain the absence of rectification effect.Comment: 5 pages, 4 figure