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  1. Wang, L. ; Zhang, J.-M. ; Wang, R. (Ed.)
    Observations of the dynamic loading and liquefaction response of a deep medium dense sand deposit to controlled blasting have allowed quantification of its large-volume dynamic behavior from the linear-elastic to nonlinear-inelastic regimes under in-situ conditions unaffected by the influence of sample disturbance or imposed laboratory boundary conditions. The dynamic response of the sand was shown to be governed by the S-waves resulting from blast-induced ground motions, the frequencies of which lie within the range of earthquake ground motions. The experimentally derived dataset allowed ready interpretation of the in-situ γ-ue responses under the cyclic strain approach. However, practitioners have more commonly interpreted cyclic behavior using the cyclic stress-based approach; thus this paper also presents the methodology implemented to interpret the equivalent number of stress cycles, Neq, and deduce the cyclic stress ratios, CSRs, generated during blast-induced shearing to provide a comprehensive comparison of the cyclic resistance of the in-situ and constant-volume, stress- and strain-controlled cyclic direct simple shear (DSS) behavior of reconstituted sand specimens consolidated to the in-situ vertical effective stress, relative density, and Vs. The multi-directional cyclic resistance of the in-situ deposit was observed to be larger than that derived from the results of the cyclic strain and stress interpretations of the uniaxial DSS test data, indicating the substantial contributions of natural soil fabric and partial drainage to liquefaction resistance during shaking. The cyclic resistance ratios, CRRs, computed using case history-based liquefaction triggering procedures based on the SPT, CPT, and Vs are compared to that determined from in-situ CRR-Neq relationships considering justified, assumed slopes of the CRR-N curve, indicating variable degrees of accuracy relative to the in-situ CRR, all of which were smaller than that associated with the in-situ cyclic resistance. 
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  2. This paper presents the results from a study of the role of soil fabric on the cyclic response of silty soil samples retrieved from two different sites from a series of sites investigated as a part of a larger study: one along the Willamette River (Site B) and one along the Columbia River (Site D). The soils investigated in this study were retrieved from Site B and exhibited an average 𝑃𝐼=13, and from Site D which were characterized with an average 𝑃𝐼=28. The cyclic response of the soils was evaluated by performing several constant-volume, stress-controlled, cyclic direct simple shear tests (CDSS) with varying cyclic stress ratios, CSRs, on natural, intact specimens and their reconstituted counterparts. Despite the lower void ratios of the reconstituted specimens, the cyclic resistance of the intact specimens for Sites B and D at 15 loading cycles were 19% and 37% greater than their reconstituted counterparts, respectively. For the given loading conditions, the rate of excess pore pressure development, single amplitude shear strain (𝛾) accumulation, and shear stiffness degradation in reconstituted specimens were greater than the natural intact specimens, emphasizing the role of soil fabric, as confirmed by the lower shear wave velocity (𝑉𝑠) of reconstituted specimens compared to their intact counterparts. 
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  3. Current best practices for the assessment of the cyclic response of plastic silts are centered on the careful sampling and cyclic testing of natural, intact specimens. Side-by-side evaluation of in-situ and laboratory element test responses are severely limited, despite the need to establish similarities and differences in their characteristics. In this paper, a coordinated laboratory and field-testing campaign that was undertaken to compare the strain-controlled cyclic response of a plastic silt deposit at the Port of Longview, Longview, WA is described. Following a discussion of the subsurface conditions at one of several test panels, the responses of laboratory test specimens to resonant column and cyclic torsional shear testing, and constant-volume, strain-controlled cyclic direct simple shear testing are described in terms of shear modulus nonlinearity and degradation, and excess pore pressure generation with shear strain. Several months earlier, the in-situ cyclic response of the same deposit was investigated by applying a range of shear strain amplitudes using a large mobile shaker. The in-situ response is presented and compared to the laboratory test results, highlighting similarities and differences arising from differences in mechanical (e.g., constant-volume shearing; strain rate-effects) and hydraulic (e.g., local drainage) boundary conditions and the spatial variability of natural soil deposits. 
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  4. null (Ed.)
  5. Summary

    Pathogens secrete effector proteins into host cells to suppress host immunity and promote pathogen virulence, although many features at the molecular interface of host–pathogen interactions remain to be characterized. In a yeast two‐hybrid assay, we found that thePseudomonas syringaeeffector HopZ1a interacts with the Arabidopsis transcriptional regulator Abscisic Acid Repressor 1 (ABR1). Further analysis revealed that ABR1 interacts with multipleP. syringaeeffectors, suggesting that it may be targeted as a susceptibility hub. Indeed, loss‐of‐functionabr1mutants exhibit reduced susceptibility to a number ofP. syringaestrains. The ABR1 protein comprises a conserved APETALA2 (AP2) domain flanked by long regions of predicted structural disorder. We verified the DNA‐binding activity of the AP2 domain and demonstrated that the disordered domains act redundantly to enhance DNA binding and to facilitate transcriptional activation by ABR1. Finally, we compared gene expression profiles from wild‐type andabr1plants following inoculation withP. syringae, which suggested that the reduced susceptibility ofabr1mutants is due to the loss of a virulence target rather than an enhanced immune response. These data highlight ABR1 as a functionally important component at the host–pathogen interface.

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  6. Abstract

    Pathogen pressure on hosts can lead to the evolution of genes regulating the innate immune response. By characterizing naturally occurring polymorphisms in immune receptors, we can better understand the molecular determinants of pathogen recognition. ZAR1 is an ancientArabidopsis thalianaNLR (Nucleotide‐binding [NB] Leucine‐rich‐repeat [LRR] Receptor) that recognizes multiple secreted effector proteins from the pathogenic bacteriaPseudomonas syringaeandXanthomonas campestristhrough its interaction with receptor‐like cytoplasmic kinases (RLCKs). ZAR1 was first identified for its role in recognizingP. syringaeeffector HopZ1a, through its interaction with the RLCK ZED1. To identify additional determinants of HopZ1a recognition, we performed a computational screen for ecotypes from the 1001 Genomes project that were likely to lack HopZ1a recognition, and tested ~300 ecotypes. We identified ecotypes containing polymorphisms in ZAR1 and ZED1. Using our previously establishedNicotiana benthamianatransient assay and Arabidopsis ecotypes, we tested for the effect of naturally occurring polymorphisms on ZAR1 interactions and the immune response. We identified key residues in the NB or LRR domain of ZAR1 that impact the interaction with ZED1. We demonstrate that natural diversity combined with functional assays can help define the molecular determinants and interactions necessary to regulate immune induction in response to pathogens.

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