1,482 research outputs found
Limits on the HI content of the dwarf galaxy Hydra II
Sensitive 21cm HI observations have been made with the Green Bank Telescope
toward the newly-discovered Local Group dwarf galaxy Hydra II, which may lie
within the leading arm of the Magellanic Stream. No neutral hydrogen was
detected. Our 5-sigma limit of MHI < 210 solar masses for a 15 km/s linewidth
gives a gas-to-luminosity ratio MHI/L_V < 2.6 x 10^{-2} Mo / Lo. The limits on
HI mass and MHI/L_V are typical of dwarf galaxies found within a few hundred
kpc of the Milky Way. Whatever the origin of Hydra II, its neutral gas
properties are not unusual.Comment: Accepted for publication in Astronomy & Astrophysic
Deforming the metric of cognitive maps distorts memory
Entorhinal grid cells, characterized by spatially periodic activity patterns, are thought to provide a universal spatial metric. However, grid cell firing-patterns are distorted in highly polarized environments such as trapezoids. Additionally, the functional role of grid cells in guiding behavior remains elusive. Here, we leverage immersive virtual reality using a novel motion platform to test the impact of environmental geometry on spatial memory in participants navigating a trapezoid arena. Object position memory in the trapezoid was degraded compared to a square control environment. Consistent with grid pattern distortions in rodents, this effect was more pronounced in the narrow than the broad part of the trapezoid. Remarkably, even outside of the encoding environment, these distortions persistently affected both navigated and judged distance estimates of never experienced paths between remembered positions and reconstructed memory maps. These distorted memory maps in turn explained behavior better than objective maps. Our findings demonstrate that environmental geometry interacts with human spatial memory similarly to how it affects rodent grid cells − thus strengthening the putative link between grid cells and behavior as well as cognitive functions beyond navigation
The Effects of Load History and Design Variables on Performance Limit States of Circular Bridge Columns
This report discusses a research program aimed at defining accurate limit state
displacements which relate to specific levels of damage in reinforced concrete bridge
columns subjected to seismic hazards. Bridge columns are designed as ductile elements
which form plastic hinges to dissipate energy in a seismic event. To satisfy the aims of
performance based design, levels of damage which interrupt the serviceability of the
structure or require more invasive repair techniques must be related to engineering criteria.
For reinforced concrete flexural members such as bridge columns, concrete compressive and
steel tensile strain limits are very good indicators of damage.
Serviceability limit states such as concrete cover crushing or residual crack widths
exceeding 1mm may occur during smaller, more frequent earthquakes. While the
serviceability limit states do not pose a safety concern, the hinge regions must be repaired to
prevent corrosion of internal reinforcing steel. At higher ductility demands produced by
larger less frequent earthquakes, reinforcing bar buckling may lead to permanent elongation
in the transverse steel, which diminishes its effectiveness in confining the concrete core. Bar
buckling and significant damage to the core concrete represent the damage control limit
states, which when exceeded lead to significant repair costs. Furthermore, rupture of
previously buckled bars during subsequent cycles of loading leads to rapid strength loss. The
life safety or collapse prevention limit state is characterized by fracture of previously buckled
bars.
The goal of the experimental program is to investigate the impact of load history and
other design variables on the relationship between strain and displacement, performance
strain limits, and the spread of plasticity. The main variables for the thirty circular bridge
column tests included: lateral displacement history, axial load, longitudinal steel content,
aspect ratio, and transverse steel detailing. A key feature of the experiments is the high
fidelity strain data obtained through the use of an optical 3D position measurement system.Column curvature distributions and fixed-end rotations attributable to strain penetration of
reinforcement into the footing were quantified.
The following sequence of damage was observed in all of the cyclically loaded
experiments: concrete cracking, longitudinal steel yielding, cover concrete crushing,
confinement steel yielding, longitudinal bar buckling, and fracture of previously buckled
reinforcement. The first significant loss in strength occurred when previously buckled
reinforcement fractured. The measured data was used to refine strain limit recommendations.
Particular attention was paid to the limit state of longitudinal bar buckling, since it limited the
deformation capacity of all of the cyclically loaded specimens. Empirical expression were
developed to predict the compressive strain at cover crushing, the compressive strain at spiral
yielding, and the peak tensile strain prior to visible buckling after reversal of loading.
In design, limit state curvatures are converted to target displacements using an
equivalent curvature distribution. The Modified Plastic Hinge Method was developed to
improve the accuracy of strain-displacement predictions. Key aspects of the proposed model
which differentiate it from the current method include: (1) a decoupling of column flexure
and strain penetration deformation components, (2) a linear plastic curvature distribution
which emulates the measured curvature profiles, and (3) separate plastic hinge lengths for
tensile and compressive strain-displacement predictions.
In the experiments, the measured extent of plasticity was found to increase due to the
combined effects of moment gradient and tension shift. The proposed tension hinge length
was calibrated to match the upper bound of the measured spread of palsticity. The proposed
compressive hinge length only contains a term related to the moment gradient effect.
Expressions which describe the additional column deformation due to strain penetration of
reinforcement into the adjoining member were developed. When compared to the current
technique, the Modified Plastic Hinge Method improved the accuracy of both tensile and
compressive strain-displacement predictions.
Abstract for Volume 3:
This report presents the numerical portion of the research project on the impacts of loading history on the behavior of reinforced concrete bridge columns. In well-detailed reinforced concrete structures, reinforcing bar buckling and subsequent bar rupture serve as common failure mechanisms under extreme seismic events. Engineers often use a strain limit state which is associated with bar buckling as the ultimate limit state, but the relationship between the strain demand and resultant bar buckling is not well understood. Past research has indicated large impact of the cyclic loading history on the strain demand to achieve reinforcing bar buckling. On the other hand, sectional analysis is widely implemented by engineers to relate strain to displacement. However, the cyclic load history also has potential impact on the relationship between strain limits and displacement limits. As a result, it is important to study the seismic load history effect on the strain limit state of reinforcing bar buckling and on the relationship between local strain and structural displacement. In addition, Performance-Based Earthquake Engineering (PBEE) strongly depends on an accurate strain limit definition, so a design methodology needs to be developed to identify the strain limit for reinforcing bar buckling including the seismic load history effect.
Two independent finite element methods were utilized to accomplish the goal of this research work. First, fiber-based analysis was utilized which employed the Open System for Earthquake Engineering Simulation (OpenSees). The fiber-based method was selected because of its accuracy in predicting strains and its computational efficiency in performing nonlinear time history analysis (NTHA). The uniaxial material models in fiber-based sections were calibrated with data from material tests. In addition, strain data and force-deformation response from large scale testing assists selection of element types and integration schemes to ensure accuracy. The advanced beam-column elements and material models in OpenSees resulted in a very accurate prediction of strain at local sections as well as global dynamic response of structures. A number of nonlinear time history analyses with 40 earthquake ground motions were conducted to investigate the effect of seismic load history on relationship between structural displacement and strain of extreme fiber bars at the critical section.
The second finite element model was established with solid elements to predict bar buckling. The model included a segment of reinforcing bar and its surrounding elements, such as spiral turns and concrete. This model separates itself from previous bar buckling research by utilizing actual sectional detailing boundary conditions and plastic material models instead of the simplified bar-spring model. The strain history is considered as the demand on this model. A series of strain histories from the experimental tests and fiber-based analyses were applied to the finite element model to study their impacts on the strain limit for reinforcing bar buckling.
Initial analytical investigations have shown significant impact of load history on the strain demand to lead to reinforcing bar buckling in the plastic hinge region. This is also confirmed in the experimental observation which only included a limited number of load histories. The parametric study extended the range of load history types and also studied the effect of reinforcement detailing on bar buckling. On the other hand, analyses with fiber-based models showed that the load history rarely impacts the relationship between local strain and structural displacement. A design approach was developed to include the load history effect on the strain limit state of bar buckling.Volume I:
LIST OF TABLES __________________________________________________ xv
LIST OF SELECTED NOTATIONS _________________________________ xxxii
Chapter 1: Introduction _______________________________________________ 1
1.1 Background – Performance Limit States ______________________ 1
1.2 The Need for Research ___________________________________ 3
1.3 Research Goals and Scope _________________________________ 5
Chapter 2: Test Setup, Instrumentation, Construction, and Text Matrix ______ 6
2.1 Test Setup _____________________________________________ 6
2.2 Test Matrix ____________________________________________ 13
2.3 Instrumentation ________________________________________ 16
2.4 Construction Process ____________________________________ 22
2.4.1 Construction Sequence ______________________________________ 23
2.4.2 Optotrak Target Marker Application Method _____________________ 39
Chapter 3: Experimental Observations _________________________________ 41
3.1 Contents of Report Volume 2 _____________________________ 41
Chapter 4: The Effect of Load History on Column Performance ____________ 43
4.1 Introduction ___________________________________________ 43
4.1.1 Test Setup ________________________________________________ 46
4.1.2 Instrumentation ____________________________________________ 50
4.1.3 Loading Protocol ___________________________________________ 51
4.2 Experimental Results ____________________________________ 55
4.2.1 Damage Observations _______________________________________ 55
4.2.2 Test 11 – Response to the Kobe 1995 Earthquake _________________ 55
4.2.3 The Effect of Load History on Reinforcement Bar Buckling _________ 58
4.3 Spread of Plasticity _____________________________________ 63
4.3.1 Test 16 – Deformation Components Three Cycle Set Load History with #3
Spiral at 1.5” (38mm) _______________________________________ 63
4.3.2 Measured Spread of Plasticity _________________________________ 69
4.4 Conclusions ___________________________________________ 70
Chapter 5: Impact of Steel Content, Aspect Ratio, and Axial Load Ratio on
Column Performance ________________________________________________ 72
5.1 Test Setup and Instrumentation ____________________________ 73
5.2 Symmetric Three-Cycle-Set Loading Protocol ________________ 75
5.3 Gradual Bar Buckling Mechanism with Inelastic Transverse Steel
Restraint ______________________________________________ 78
5.3.1 North Reinforcement ________________________________________ 79
5.3.2 South Reinforcement ________________________________________ 81
5.4 Transverse Steel Detailing Variable Experiments ______________ 85
5.5 Aspect Ratio Variable Experiments _________________________ 90
5.6 Longitudinal Steel Content Variable Experiments _____________ 92
5.7 Axial Load Ratio Variable Experiments _____________________ 95
5.8 Equivalent Viscous Damping _____________________________ 98
5.9 Conclusions __________________________________________ 102
Chapter 6: Bridge Column Response Prediction Techniques ______________ 104
6.1 Background and Motivation _____________________________ 104
6.1.1 Experimental Program ______________________________________ 104
6.2 Measured Deformation Components _______________________ 107
6.3 Response Prediction Methods ____________________________ 111
6.3.1 Sectional Response Prediction _______________________________ 112
6.3.2 Member Response Prediction ________________________________ 113
6.3.3 Motivation for a New Equivalent Curvature Distribution ___________ 116
Chapter 7: Modified Plastic Hinge Method _____________________________ 118
7.1 Goals for the Modified Plastic Hinge Method ________________ 118
7.2 Deformation due to Strain Penetration of Reinforcement into
Adjoining Members ____________________________________ 120
7.3 Tensile and Compressive Plastic Hinge Lengths _____________ 128
7.4 Tensile Strain-Displacement Predictions using the Modified Plastic
Hinge Method ________________________________________ 149
7.5 Compressive Strain-Displacement Predictions using the Modified
Plastic Hinge Method __________________________________ 152
7.6 Elastic Force-Deformation Predictions using the Modified Plastic
Hinge Method ________________________________________ 157
7.7 Conclusion ___________________________________________ 160
Chapter 8: Performance Strain Limits for Circular Bridge Columns _______ 183
8.1 Background __________________________________________ 183
8.2 Experimental Program __________________________________ 186
8.2.1 Loading Protocol __________________________________________ 188
8.3 Observed Damage Sequence _____________________________ 189
8.4 Equation to Predict Peak Tension Strain Prior to Bar Buckling Upon
Reversal of Load ______________________________________ 193
8.5 Column Deformation at Peak Tensile Strain Prior to Bar Buckling
____________________________________________________ 197
8.6 Berry (2006) Statistical Drift-Based Bar Buckling Model for Circular
Bridge Columns _______________________________________ 200
8.7 Berry (2006) Bar Buckling Model Applied to the Goodnight et al.
Dataset ______________________________________________ 202
8.8 Evaluation of Strain Based Bar Buckling Predictions for the Berry
(2006) Dataset ________________________________________ 204
8.9 Drift Based Approach Considering Combined Berry (2006) and
Goodnight et al. Datasets ________________________________ 208
8.10 Feng (2013) Bar Buckling Strain Limit Expressions from Finite
Element Analysis ______________________________________ 211
8.11 Bar Buckling Predictions for the Combined Berry (2006) and
Goodnight et al. Dataset ________________________________ 221
8.12 Evaluation for Full Scale Column Experiments by Cheok and Stone
(1989) _______________________________________________ 223
8.13 Compressive Strain at Cover Concrete Crushing _____________ 226
8.14 Compressive Strain at Spiral Yielding in Confinement Regions of the
Column ______________________________________________ 227
8.15 Residual Crack Widths _________________________________ 232
8.16 Conclusion ___________________________________________ 234
Chapter 9: Design Recommendations for Limit State Displacements ________ 238
9.1 Performance Strain Limits _______________________________ 238
9.1.1 Serviceability Limit States __________________________________ 239
9.1.2 Intermediate Compressive Limit State _________________________ 239
9.1.3 Damage Control Limit States ________________________________ 240
9.2 Modified Plastic Hinge Method ___________________________ 244
9.2.1 Strain Penetration Length and Tension/Comp. Plastic Hinge Lengths _ 248
9.2.2 Elastic Displacements for a Column in Single Bending ____________ 249
9.2.3 Elastic Displacements for a Column in Double Bending ___________ 249
9.2.4 Inelastic Displacements for a Column in Single Bending ___________ 250
9.2.5 Inelastic Displacements for a Column in Double Bending __________ 250
Chapter 10: Future Research on the Effects of Seismic Load Path __________ 251
10.1 Problem Statement _____________________________________ 251
10.2 Background __________________________________________ 251
10.3 Brief Load Path Literature Review ________________________ 260
10.3.1 Yuk-Lung Wong, T. Paulay, and M. J. Nigel Priestley (1993). “Response
of Circular Reinforced Concrete Columns to Multi-Directional Seismic
Attack” __________________________________________________ 260
10.3.2 E. Osorio, J.M. Bairán, and A.R. Marí (2012). “Effects of Biaxial Shear
Loading on the Seismic Response of RC Columns” _______________ 261
10.3.3 Kazuhiro Tsuno and Robert Park (2004). “Experimental Study of
Reinforced Concrete Bridge Piers Subjected to Bi-Directional Quasi-Static
Loading” ________________________________________________ 263
10.3.4 Stathis N. Bousias, Guido Verzeletti, Michael N. Fardis, Eugenio Gutierrez
(1995). “Load Path Effects in Column Biaxial Bending with Axial Force”
266
10.4 Study Objectives ______________________________________ 268
10.5 Research Plan _________________________________________ 268
10.5.1 Task One: Detailed Literature Review _________________________ 268
10.5.2 Task Two: Load Path Analysis _______________________________ 269
10.5.3 Task Three: Experimental Studies on Columns __________________ 269
10.5.4 Task Four: Analysis of Data and Model Calibration _______________ 274
10.5.5 Task Five: Recommendations ________________________________ 274
REFERENCES ____________________________________________________ 275
Volume 2:
LIST OF TABLES ___________________________________________________ x
LIST OF SELECTED NOTATIONS __________________________________ xiv
Chapter 1: Experimental Observations __________________________________ 1
1.1 Load History Variable Tests 8-12 ___________________________ 1
1.1.1 Test 9 – Symmetric Three Cycle Set Load History __________________ 6
1.1.2 Tests 8 and 8b – Chile 2010 Earthquake and Cyclic Aftershock LH ___ 35
1.1.3 Tests 10 and 10b – Chichi Earthquake and Cyclic Aftershock LH _____ 61
1.1.4 Test 11 – Kobe 1995 Earthquake Load History ___________________ 89
1.1.5 Test 12 – Japan 2011 Earthquake Load History __________________ 108
1.2 Load History and Transverse Steel Variable Tests 13-18 _______ 131
1.2.1 Test 13 –Three Cycle Set Load History with #4 Spiral at 2.75” (1.3%) 135
1.2.2 Test 14 –Three Cycle Set Load History with #3 Spiral at 4” (0.5%) __ 160
1.2.3 Test 15 – Three Cycle Set Load History with #3 Spiral at 2.75” (0.7%) 187
1.2.4 Test 16 – Three Cycle Set Load History with #3 Spiral at 1.5” (1.3%) 215
1.2.5 Test 17 – Chile 1985 Earthquake LH with #3 Spiral at 1.5” (1.3%) ___ 241
1.2.6 Test 18 – Darfield NZ 2010 EQ LH with #3 Spiral at 1.5” (1.3%) ____ 274
1.3 Aspect Ratio and Axial Load Variable Tests 19-24 ___________ 304
1.3.1 Test 19 – Aspect Ratio of 5.33 and 10% Axial Load ______________ 308
1.3.2 Test 20 – Aspect Ratio of 5.33 and 5% Axial Load _______________ 336
1.3.3 Test 21 – Aspect Ratio of 7.33 and 5% Axial Load _______________ 365
1.3.4 Test 22 – Aspect Ratio of 7.33 and 10% Axial Load ______________ 395
1.3.5 Test 23 – Aspect Ratio of 8.67 and 5% Axial Load _______________ 425
1.3.6 Test 24 – Aspect Ratio of 8.67 and 10% Axial Load ______________ 455
1.4 Steel Content and Axial Load Variable Tests 25-30 ___________ 488
1.4.1 Test 25 – 24” Dia. Column with 2.1% Long. Steel and 5% Axial Load 492
1.4.2 Test 26 – 24” Dia. Column with 2.1% Long. Steel and 10% Axial Load 525
1.4.3 Test 27 – 24” Dia. Column with 1.6% Long. Steel and 10% Axial Load 561
1.4.4 Test 28 – 18” Dia. Column with 1.7% Long. Steel and 15% Axial Load 598
1.4.5 Test 29 – 18” Dia. Column with 1.7% Long. Steel and 20% Axial Load 635
1.4.6 Test 30 – 18” Dia. Column with 3.1% Long. Steel and 15% Axial Load 671
Chapter 2: Weldability of A706 Reinforcing Steel _______________________ 707
2.1 Test 7 and Weldability of A706 Reinforcing Steel ____________ 707
2.2 A706 Steel Properties and Weldability for Tests 1-6 and 7-12 ___ 712
2.3 Conclusion ___________________________________________ 713
Chapter 3: Summary of Column Tests 1-6 ______________________________ 717
3.1 Test Setup and Instrumentation for Specimens 1-6 ____________ 717
3.2 Test 1: Pushover Load History ___________________________ 720
3.3 Test 2: Three-Cycle-Set with Full Cover Concrete ____________ 722
3.4 Test 3: Three-Cycle-Set with Cover Blockouts _______________ 727
3.5 Test 4: 1940 El Centro Earthquake Load History _____________ 731
3.6 Test 5: 1978 Tabas Earthquake Load History ________________ 737
3.7 Test 6: 1978 Tabas Earthquake Load History ________________ 744
REFERENCES ____________________________________________________ 748
Volume 3:
Chapter 1: Introduction ____________________________________________________ 1
1.1 Background and Scope ___________________________________________ 1
1.2 Layout of Report ________________________________________________ 2
Chapter 2: Literature Review _______________________________________________ 3
2.1 General Discussion ______________________________________________ 3
2.2 Relevant Articles on Numerical Simulation ___________________________ 3
2.2.1 Fiber-Based Modeling of Reinforced Concrete Members ____________ 3
2.2.2 Finite Element Method for Reinforcing Bar Buckling _______________ 8
2.3 Chapter Summery _______________________________________________ 9
Chapter 3: Fiber-Based Modeling of Circular Reinforced Concrete Bridge Columns 10
3.1 Introduction and Background _____________________________________ 10
3.2 Theory of Fiber-Based Modeling __________________________________ 12
3.3 Proposed methods for simulating RC bridge columns __________________ 18
3.3.1 Experimental Observation ____________________________________ 18
3.3.2 Proposed Method to Predict Strain Gradient ______________________ 22
3.3.3 Method to Include Strain Penetration ___________________________ 26
3.3.4 Benchmark Method to Capture Nonlinearity in RC Member with Fiber-Based Model 29
3.4 Calibration and Application of the Fiber Model _______________________ 30
3.4.1 Calibration on Material Constitutive Models _____________________ 31
3.4.2 Prediction on Force and Strain from Static Tests __________________ 32
3.4.3 Prediction on Response of Shake Table Tests _____________________ 42
3.5 Chapter Conclusions ____________________________________________ 44
Chapter 4: Load History Effect on Relationship between Strain and Displacement __ 45
4.1 General Discussion _____________________________________________ 45
4.2 Ground
Face-Fusion of Icosahedral Boron Hydride Increases Affinity to γ‐Cyclodextrin: closo,closo‐[B₂₁H₁₈]⁻ as an Anion with Very Low Free Energy of Dehydration
[Abstract] The supramolecular recognition of closo,closo‐[B₂₁H₁₈]⁻ by cyclodextrins (CDs) has been studied in aqueous solution by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. These solution studies follow up on previous mass‐spectrometric measurements and computations, which indicated the formation and stability of CD ⋅ B₂₁H₁₈⁻ complexes in the gas phase. The thermodynamic signature of solution‐phase binding is exceptional, the association constant for the γ‐CD complex with B₂₁H₁₈⁻ reaches 1.8×10⁶ M⁻¹, which is on the same order of magnitude as the so far highest observed value for the complex between γ‐CD and a metallacarborane. The nature of the intermolecular interaction is also examined by quantum‐mechanical computational protocols. These suggest that the desolvation penalty, which is particularly low for the B₂₁H₁₈⁻ anion, is the decisive factor for its high binding strength. The results further suggest that the elliptical macropolyhedral boron hydride is another example of a CD binder, whose extraordinary binding affinity is driven by the chaotropic effect, which describes the intrinsic affinity of large polarizable and weakly solvated chaotropic anions to hydrophobic cavities and surfaces in aqueous solution.K.I.A. and W.M.N. are grateful to the DFG for grant NA-686/8 within the priority program SPP 1807 “Control of London Dispersion Interactions in Molecular Chemistry”. J.H., J.F., and D.H. thank the Czech Science Foundation (grant number 17-08045S) and M.I.F.P., M.C.L, and J.A.S.L. thank the regional government Xunta de Galicia for financial support (Project Grupo Potencial Crecemento -GPC- ED431B 2017/59). J.M.O.-E. acknowledges financial support from the Spanish MICINN through project CTQ2018-094644-B-C22German Research Foundation; NA‐686/8Czech Science Foundation; 17‐08045SXunta de Galicia; ED431B 2017/5
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Preferential binding of unsaturated hydrocarbons in aryl-bisimidazolium·cucurbit[8]uril complexes furbishes evidence for small-molecule π-π interactions.
Whilst cucurbit[n]urils (CBn) have been utilized in gas encapsulation, only the smaller CBn (n = 5 and 6) have utility given their small cavity size. In this work, we demonstrate that the large cavity of CB8 can be tailored for gaseous and volatile hydrocarbon encapsulation by restricting its internal cavity size with auxiliary aryl-bisimidazolium (Bis, aryl = phenyl, naphthyl, and biphenyl) guests. The binding constants for light hydrocarbons (C ≤ 4) are similar to those measured with CB6, while larger values are obtained with Bis·CB8 for larger guests. A clear propensity for higher affinities of alkenes relative to alkanes is observed, most pronounced with the largest delocalized naphthalene residue in the auxiliary Bis guest, which provides unique evidence for sizable small-molecule π-π interactions
A Francisella tularensis Live Vaccine Strain That Improves Stimulation of Antigen-Presenting Cells Does Not Enhance Vaccine Efficacy
Vaccination is a proven strategy to mitigate morbidity and mortality of infectious diseases. The methodology of identifying and testing new vaccine candidates could be improved with rational design and in vitro testing prior to animal experimentation. The tularemia vaccine, Francisella tularensis live vaccine strain (LVS), does not elicit complete protection against lethal challenge with a virulent type A Francisella strain. One factor that may contribute to this poor performance is limited stimulation of antigen-presenting cells. In this study, we examined whether the interaction of genetically modified LVS strains with human antigen-presenting cells correlated with effectiveness as tularemia vaccine candidates. Human dendritic cells infected with wild-type LVS secrete low levels of proinflammatory cytokines, fail to upregulate costimulatory molecules, and activate human T cells poorly in vitro. One LVS mutant, strain 13B47, stimulated higher levels of proinflammatory cytokines from dendritic cells and macrophages and increased costimulatory molecule expression on dendritic cells compared to wild type. Additionally, 13B47-infected dendritic cells activated T cells more efficiently than LVS-infected cells. A deletion allele of the same gene in LVS displayed similar in vitro characteristics, but vaccination with this strain did not improve survival after challenge with a virulent Francisella strain. In vivo, this mutant was attenuated for growth and did not stimulate T cell responses in the lung comparable to wild type. Therefore, stimulation of antigen-presenting cells in vitro was improved by genetic modification of LVS, but did not correlate with efficacy against challenge in vivo within this model system
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