868 research outputs found
Integrated vehicle dynamics control using active steering, driveline and braking
This thesis investigates the principle of integrated vehicle dynamics control through proposing a new control configuration to coordinate active steering subsystems and
dynamic stability control (DSC) subsystems. The active steering subsystems include Active Front Steering (AFS) and Active Rear Steering (ARS); the dynamic stability control subsystems include driveline based, brake based and driveline plus brake based DSC subsystems.
A nonlinear vehicle handling model is developed for this study, incorporating the load transfer effects and nonlinear tyre characteristics. This model consists of 8 degrees of freedom that include longitudinal, lateral and yaw motions of the vehicle and body roll motion relative to the chassis about the roll axis as well as the rotational dynamics of four wheels. The lateral vehicle dynamics are analysed for the entire handling region and two distinct control objectives are defined, i.e. steerability and stability which correspond to yaw rate tracking and sideslip motion bounding, respectively.
Active steering subsystem controllers and dynamic stability subsystem controller are designed by using the Sliding Mode Control (SMC) technique and phase-plane method, respectively. The former is used as the steerability controller to track the reference yaw rate and the latter serves as the stability controller to bound the sideslip
motion of the vehicle. Both stand-alone controllers are evaluated over a range of different handling regimes. The stand-alone steerability controllers are found to be
very effective in improving vehicle steering response up to the handling limit and the stand-alone stability controller is found to be capable of performing the task of maintaining vehicle stability at the operating points where the active steering subsystems cannot.
Based on the two independently developed stand-alone controllers, a novel rule based integration scheme for AFS and driveline plus brake based DSC is proposed to optimise the overall vehicle performance by minimising interactions between the two subsystems and extending functionalities of individual subsystems. The proposed integrated control system is assessed by comparing it to corresponding combined
control. Through the simulation work conducted under critical driving conditions, the proposed integrated control system is found to lead to a trade-off between stability and limit steerability, improved vehicle stability and reduced influence on the longitudinal vehicle dynamics
Entanglement and chaos in warped conformal field theories
Various aspects of warped conformal field theories (WCFTs) are studied
including entanglement entropy on excited states, the Renyi entropy after a
local quench, and out-of-time-order four-point functions. Assuming a large
central charge and dominance of the vacuum block in the conformal block
expansion, (i) we calculate the single-interval entanglement entropy on an
excited state, matching previous finite temperature results by changing the
ensemble; and (ii) we show that WCFTs are maximally chaotic, a result that is
compatible with the existence of black holes in the holographic duals. Finally,
we relax the aforementioned assumptions and study the time evolution of the
Renyi entropy after a local quench. We find that the change in the Renyi
entropy is topological, vanishing at early and late times, and nonvanishing in
between only for charged states in spectrally-flowed WCFTs.Comment: 31 pages; v2: corrected typos, matches published versio
Sneutrino DM in the NMSSM with inverse seesaw mechanism
In supersymmetric theories like the Next-to-Minimal Supersymmetric Standard
Model (NMSSM), the lightest neutralino with bino or singlino as its dominant
component is customarily taken as dark matter (DM) candidate. Since light
Higgsinos favored by naturalness can strength the couplings of the DM and thus
enhance the DM-nucleon scattering rate, the tension between naturalness and DM
direct detection results becomes more and more acute with the improved
experimental sensitivity. In this work, we extend the NMSSM by inverse seesaw
mechanism to generate neutrino mass, and show that in certain parameter space
the lightest sneutrino may act as a viable DM candidate, i.e. it can annihilate
by multi-channels to get correct relic density and meanwhile satisfy all
experimental constraints. The most striking feature of the extension is that
the DM-nucleon scattering rate can be naturally below its current experimental
bounds regardless of the higgsino mass, and hence it alleviates the tension
between naturalness and DM experiments. Other interesting features include that
the Higgs phenomenology becomes much richer than that of the original NMSSM due
to the relaxed constraints from DM physics and also due to the presence of
extra neutrinos, and that the signatures of sparticles at colliders are quite
different from those with neutralino as DM candidate.Comment: 33 page
Higgs Phenomenology in the Minimal Dilaton Model after Run I of the LHC
The Minimal Dilaton Model (MDM) extends the Standard Model (SM) by a singlet
scalar, which can be viewed as a linear realization of general dilaton field.
This new scalar field mixes with the SM Higgs field to form two mass
eigenstates with one of them corresponding to the 125 GeV SM-like Higgs boson
reported by the LHC experiments. In this work, under various theoretical and
experimental constrains, we perform fits to the latest Higgs data and then
investigate the phenomenology of Higgs boson in both the heavy dilaton scenario
and the light dilaton scenario of the MDM. We find that: (i) If one considers
the ATLAS and CMS data separately, the MDM can explain each of them well, but
refer to different parameter space due to the apparent difference in the two
sets of data. If one considers the combined data of the LHC and Tevatron,
however, the explanation given by the MDM is not much better than the SM, and
the dilaton component in the 125-GeV Higgs is less than about 20% at 2 sigma
level. (ii) The current Higgs data have stronger constrains on the light
dilaton scenario than on the heavy dilaton scenario. (iii) The heavy dilaton
scenario can produce a Higgs triple self coupling much larger than the SM
value, and thus a significantly enhanced Higgs pair cross section at hadron
colliders. With a luminosity of 100 fb^{-1} (10 fb^{-1}) at the 14-TeV LHC, a
heavy dilaton of 400 GeV (500 GeV) can be examined. (iv) In the light dilaton
scenario, the Higgs exotic branching ratio can reach 43% (60%) at 2 sigma (3
sigma) level when considering only the CMS data, which may be detected at the
14-TeV LHC with a luminosity of 300 fb^{-1} and the Higgs Factory.Comment: 27 pages, 13 figures, discussions added, to appear in JHE
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