135 research outputs found
Energy-scales convergence for optimal and robust quantum transport in photosynthetic complexes
Underlying physical principles for the high efficiency of excitation energy
transfer in light-harvesting complexes are not fully understood. Notably, the
degree of robustness of these systems for transporting energy is not known
considering their realistic interactions with vibrational and radiative
environments within the surrounding solvent and scaffold proteins. In this
work, we employ an efficient technique to estimate energy transfer efficiency
of such complex excitonic systems. We observe that the dynamics of the
Fenna-Matthews-Olson (FMO) complex leads to optimal and robust energy transport
due to a convergence of energy scales among all important internal and external
parameters. In particular, we show that the FMO energy transfer efficiency is
optimum and stable with respect to the relevant parameters of environmental
interactions and Frenkel-exciton Hamiltonian including reorganization energy
, bath frequency cutoff , temperature , bath spatial
correlations, initial excitations, dissipation rate, trapping rate, disorders,
and dipole moments orientations. We identify the ratio of \lambda T/\gamma\*g
as a single key parameter governing quantum transport efficiency, where g is
the average excitonic energy gap.Comment: minor revisions, removing some figures, 19 pages, 19 figure
Pion-Muon Asymmetry Revisited
Long ago an unexpected and unexplainable phenomena was observed. The
distribution of muons from positive pion decay at rest was anisotropic with an
excess in the backward direction relative to the direction of the proton beam
from which the pions were created. Although this effect was observed by several
different groups with pions produced by different means, the result was not
accepted by the physics community, because it is in direct conflict with a
large set of other experiments indicating that the pion is a pseudoscalar
particle. It is possible to satisfy both sets of experiments if helicity-zero
vector particles exist and the pion is such a particle. Helicity-zero vector
particles have direction but no net spin. For the neutral pion to be a vector
particle requires an additional modification to conventional theory as
discussed herein. An experiment is proposed which can prove that the asymmetry
in the distribution of muons from pion decay is a genuine physical effect
because the asymmetry can be modified in a controllable manner. A positive
result will also prove that the pion is NOT a pseudoscalar particle.Comment: 9 pages, 3 figure
Capacity to Elicit Cytotoxic CD8 T Cell Activity Against Mycobacterium avium subsp. paratuberculosis Is Retained in a Vaccine Candidate 35 kDa Peptide Modified for Expression in Mammalian Cells
Studies focused on development of an attenuated vaccine against Mycobacterium avium subsp. paratuberculosis (Map), the causative agent of paratuberculosis (Ptb) in cattle and other species, revealed that deletion of relA, a global gene regulator, abrogates the ability of Map to establish a persistent infection. In the absence of relA, cattle develop CD8 cytotoxic T cells (CTL) with the ability to kill intracellular bacteria. Analysis of the recall response to a relA mutant, Map/relA, with cells from a vaccinated steer demonstrated that a 35-kDa membrane peptide (MMP) is one of the targets of the response. This observation suggested that it might be possible to develop a peptide-based vaccine. As reported here, the gene encoding the hypothetical MMP ORF, MAP2121c, was modified for expression in mammalian cells as a first step in developing an expression cassette for incorporation into a mammalian expression vector. The modified sequence of MMP, tPA-MMP, was mutated to generate two additional sequences for the study, one with substitutions to replace five potential residues that could be glycosylated, tPA-MMP-5mut, and one with substitutions to replace the first two potential residues that could be glycosylated, tPA-MMP-2mut. The sequences were placed in an expression cassette to produce peptides for analysis. An ex vivo platform was used with flow cytometry and a bacterium viability assay to determine if modifications in the gene encoding MMP for expression in mammalian cells altered its capacity to elicit development of CD8 CTL, essential for its use in a peptide-based vaccine. Monocyte-depleted PBMC (mdPBMC) were stimulated with antigen-presenting cells (APC) pulsed with different MMP constructs. CD4 and CD8 T cells proliferated in response to stimulation with MMP (control) expressed in Escherichia coli (eMMP), tPA-MMP, and tPA-MMP-2mut. CD8 T cells retained the capacity to kill intracellular bacteria. The tPA-MMP-5mut failed to elicit a proliferative response and was not included in further studies. The data show that the expression cassettes containing MMP and MMP-2mut can be used to screen and select a mammalian expression vector for the development of an efficacious peptide-based vaccine against Ptb
Capacity to Elicit Cytotoxic CD8 T Cell Activity Against Mycobacterium avium subsp. paratuberculosis Is Retained in a Vaccine Candidate 35 kDa Peptide Modified for Expression in Mammalian Cells
Studies focused on development of an attenuated vaccine against Mycobacterium avium subsp. paratuberculosis (Map), the causative agent of paratuberculosis (Ptb) in cattle and other species, revealed that deletion of relA, a global gene regulator, abrogates the ability of Map to establish a persistent infection. In the absence of relA, cattle develop CD8 cytotoxic T cells (CTL) with the ability to kill intracellular bacteria. Analysis of the recall response to a relA mutant, Map/relA, with cells from a vaccinated steer demonstrated that a 35-kDa membrane peptide (MMP) is one of the targets of the response. This observation suggested that it might be possible to develop a peptide-based vaccine. As reported here, the gene encoding the hypothetical MMP ORF, MAP2121c, was modified for expression in mammalian cells as a first step in developing an expression cassette for incorporation into a mammalian expression vector. The modified sequence of MMP, tPA-MMP, was mutated to generate two additional sequences for the study, one with substitutions to replace five potential residues that could be glycosylated, tPA-MMP-5mut, and one with substitutions to replace the first two potential residues that could be glycosylated, tPA-MMP-2mut. The sequences were placed in an expression cassette to produce peptides for analysis. An ex vivo platform was used with flow cytometry and a bacterium viability assay to determine if modifications in the gene encoding MMP for expression in mammalian cells altered its capacity to elicit development of CD8 CTL, essential for its use in a peptide-based vaccine. Monocyte-depleted PBMC (mdPBMC) were stimulated with antigen-presenting cells (APC) pulsed with different MMP constructs. CD4 and CD8 T cells proliferated in response to stimulation with MMP (control) expressed in Escherichia coli (eMMP), tPA-MMP, and tPA-MMP-2mut. CD8 T cells retained the capacity to kill intracellular bacteria. The tPA-MMP-5mut failed to elicit a proliferative response and was not included in further studies. The data show that the expression cassettes containing MMP and MMP-2mut can be used to screen and select a mammalian expression vector for the development of an efficacious peptide-based vaccine against Ptb
Measurement of ϒ production in pp collisions at √s = 2.76 TeV
The production of ϒ(1S), ϒ(2S) and ϒ(3S)
mesons decaying into the dimuon final state is studied with
the LHCb detector using a data sample corresponding to an
integrated luminosity of 3.3 pb−1 collected in proton–proton
collisions at a centre-of-mass energy of √s = 2.76 TeV. The
differential production cross-sections times dimuon branching
fractions are measured as functions of the ϒ transverse
momentum and rapidity, over the ranges pT < 15 GeV/c
and 2.0 < y < 4.5. The total cross-sections in this kinematic
region, assuming unpolarised production, are measured to be
σ (pp → ϒ(1S)X) × B
ϒ(1S)→μ+μ−
= 1.111 ± 0.043 ± 0.044 nb,
σ (pp → ϒ(2S)X) × B
ϒ(2S)→μ+μ−
= 0.264 ± 0.023 ± 0.011 nb,
σ (pp → ϒ(3S)X) × B
ϒ(3S)→μ+μ−
= 0.159 ± 0.020 ± 0.007 nb,
where the first uncertainty is statistical and the second systematic
Study of the doubly charmed tetraquark T+cc
Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the D0D0π+ mass spectrum just below the D*+D0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T+cc tetraquark with a quark content of ccu⎯⎯⎯d⎯⎯⎯ and spin-parity quantum numbers JP = 1+. Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*+ mesons is consistent with the observed D0π+ mass distribution. To analyse the mass of the resonance and its coupling to the D*D system, a dedicated model is developed under the assumption of an isoscalar axial-vector T+cc state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T+cc state. In addition, an unexpected dependence of the production rate on track multiplicity is observed
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