Accurate Mass Determinations in Decay Chains with Missing Energy: II

We discuss kinematic methods for determining the masses of the particles in events at a hadron collider in which a pair of identical particles is produced with each decaying via a series of on-shell intermediate beyond-the-SM (BSM) particles to visible SM particles and an invisible particle (schematically, pp -> ZZ + jets with Z -> Aa -> Bba -> Ccba -> ... -> cba... + N where a,b,c,... are visible SM particles or groups of SM particles, A,B,C,... are on-shell BSM particles and N is invisible). This topology arises in many models including SUSY processes such as squark and gluino pair production and decay. We present the detailed procedure for the case of Z -> 3 visible particles + N and demonstrate that the masses obtained from the kinematic procedure are independent of the model by comparing SUSY to UED.Comment: v2, published version in PR

Proteomic analyses of plant-bacterial interactions

Proteome-level changes of both the plant growth-promoting bacterium (PGPB) Pseudomonas putida UW4 and its plant host Brassica napus (canola) were profiled using two-dimensional (2-D) difference in-gel electrophoresis (DIGE) and mass spectrometry, to elucidate the proteins’ prospective of plant-bacterial interactions. This study was undertaken in an effort to elaborate how a plant growth-promoting bacterium and its plant host biochemically and physiologically influence one another. More specifically, the effects of the PGPB P. putida UW4 on the proteome of canola and vice versa were examined. In addition, environmental stresses including heavy metal and salt were incorporated into the system. Moreover, how the presence of a functional bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase (AcdS), which can lower plant ethylene levels and hence promote plant growth under a variety of stresses, would affect protein expression in both the bacterium and the plant was investigated. First, 2-D DIGE was used to detect significantly up- or down- regulated proteins in P. putida UW4 and its AcdS minus mutant in response to the presence of 2 mM nickel. Thirty-five proteins whose expression was altered were successfully identified by mass spectrometry and sequence comparisons with related species. Nineteen of the identified proteins were detected as differentially expressed in both wild-type and AcdS minus mutant expression profiles. Functional assessment of proteins with significantly altered expression levels revealed several mechanisms involved in bacterial heavy metal detoxification, including general stress adaptation, anti-oxidative stress and heavy metal efflux proteins. In addition, by detection of bacterial protein expression changes in the presence of plant exudates, three unique P. putida UW4 proteins that mediate interactions between the bacterium and its plant host were identified. However many of the observed changes of protein expression elicited by nickel and plant exudates were similar for wild-type P. putida UW4 and the AcdS minus mutant, with the majority of identified significant protein expression changes occurring in both strains. This is not unexpected because the P. putida UW4 ACC deaminase is unlikely to be involved in bacterial perception and response to plant host signals and environmental stimuli, and it causes a noticeable difference only in plant growth. A comprehensive proteome 2-D reference map of the PGPB P. putida UW4 containing 326 2-D gel spots representing 275 different proteins was also constructed. A 2-D database containing all the mass spectrometric information of P. putida UW4 proteins has been constructed. The data set has been deposited into the World-2DPAGE database and is accessible at http://world-2dpage.expasy.org/repository/. On the plant side, ninety proteins with significantly altered expression levels in the presence of salt and/or bacteria were identified by mass spectrometry. Many of these proteins are involved in photosynthesis, anti-oxidative processes, salt transportation/accumulation and pathogenesis-related responses. Importantly, the presence of the bacterial ACC deaminase was observed to alter the plant’s protein expression in response to salt stress. The effects included enhanced photosynthesis and salt accumulation contributed by wild-type P. putida UW4. The work described in this thesis furthers our understanding of plant-bacterial interactions, and is also likely to be of importance to both organic agriculture and environmental remediation efforts

Micromechanical modeling of hollow cylinder torsional shear test on sand using discrete element method

Previous studies on the hollow cylinder torsional shear test (HCTST) have mainly focused on the macroscopic behavior, while the micromechanical responses in soil specimens with shaped particles have rarely been investigated. This paper develops a numerical model of the HCTST using the discrete element method (DEM). The method of bonded spheres in a hexagonal arrangement is proposed to generate flexible boundaries that can achieve real-time adjustment of the internal and external cell pressures and capture the inhomogeneous deformation in the radial direction during shearing. Representative angular particles are selected from Toyoura sand and reproduced in this model to approximate real sand particles. The model is then validated by comparing numerical and experimental results of HCTSTs on Toyoura sand with different major principal stress directions. Next, a series of HCTSTs with different combinations of major principal stress direction (α) and intermediate principal stress ratio (b) is simulated to quantitatively characterize the sand behavior under different shear conditions. The results show that the shaped particles are horizontally distributed before shearing, and the initial anisotropic packing structure further results in different stress–strain curves in cases with different α and b values. The distribution of force chains is affected by both α and b during the shear process, together with the formation of the shear bands in different patterns. The contact normal anisotropy and contact force anisotropy show different evolution patterns when either α or b varies, resulting in the differences in the non-coaxiality and other macroscopic responses. This study improves the understanding of the macroscopic response of sand from a microscopic perspective and provides valuable insights for the constitutive modeling of sand