965 research outputs found
MHC class II complexes sample intermediate states along the peptide exchange pathway
The presentation of peptide-MHCII complexes (pMHCIIs) for surveillance by T
cells is a well-known immunological concept in vertebrates, yet the
conformational dynamics of antigen exchange remain elusive. By combining NMR-
detected H/D exchange with Markov modelling analysis of an aggregate of 275
microseconds molecular dynamics simulations, we reveal that a stable pMHCII
spontaneously samples intermediate conformations relevant for peptide
exchange. More specifically, we observe two major peptide exchange pathways:
the kinetic stability of a pMHCIIâs ground state defines its propensity for
intrinsic peptide exchange, while the population of a rare, intermediate
conformation correlates with the propensity of the HLA-DM-catalysed pathway.
Helix-destabilizing mutants designed based on our model shift the exchange
behaviour towards the HLA-DM-catalysed pathway and further allow us to
conceptualize how allelic variation can shape an individualâs MHC restricted
immune response
The Biological Standard of Living in the two Germanies.
Physical stature is used as a proxy for the biological standard of living in the two Germanies before and after unification in an analysis of a cross-sectional sample (1998) of adult heights, as well as among military recruits of the 1990s. West Germans tended to be taller than East Germans throughout the period under consideration. Contrary to official proclamations of a classless society, there were substantial social differences in physical stature in East-Germany. Social differences in height were greater in the East among females, and less among males than in the West. The difficulties experienced by the East-German population after 1961 is evident in the increase in social inequality of physical stature thereafter, as well as in the increasing gap relative to the height of the West-German population. After unification, however, there is a tendency for East-German males, but not of females, to catch up with their West-German counterparts
Memorandum on Mississippi House Bill 1523
As legal scholars with expertise in matters of religious freedom, civil rights, and the interaction between those fields, we offer our opinion on the scope and meaning of Mississippi House Bill 1523, which was signed into law today by Governor Phil Bryant. Specifically, we wish to call attention to language in the law that we believe conflicts with the Establishment Clause of the U.S. Constitution. We share the view of Justice Kennedy when he expressed that âa bare . . . desire to harm a politically unpopular group cannot constitute a legitimate governmental interest,â and would add that neither can such a desire be justified in the name of religious liberty. HB 1523 presents a conflict with First Amendment religious freedom doctrine by providing for religious exemptions that will meaningfully harm the rights of others, particularly LGBT Mississippians
Creating nearly Heisenberg-limited matter-waves exploiting tunable interactions
The wave nature of matter implies wavepackets with minimal combined
uncertainty in position and momentum, a limit which can hardly be reached for
clouds of large atom numbers of interacting particles. Here, we report on a
high-flux source of ultra-cold atoms realizing near-Heisenberg-limited
expansion rates upon release from the trap. Depending on the value of the
scattering length, we model our system either with a scaling approach based on
the Thomas-Fermi approximation, or with a variational approach based on a
Gaussian atomic density approximation, observing the transition between the
weak and strong interaction regimes. Finally, we discuss applications of our
methods to test foundational principles of quantum mechanics such as the
superposition principle or their extension to other atomic species
Matter-wave collimation to picokelvin energies with scattering length and potential shape control
We study the impact of atomic interactions on an in-situ collimation method
for matter-waves. Building upon an earlier study with Rb, we apply a
lensing protocol to K where the atomic scattering length can be tailored
by means of magnetic Feshbach resonances. Minimizing interactions, we show an
enhancement of the collimation compared to the strong interaction regime,
realizing ballistic 2D expansion energies of 438(77) pK in our experiment. Our
results are supported by an accurate simulation, describing the ensemble
dynamics, which we further use to study the behavior of various trap
configurations for different interaction strengths. Based on our findings we
propose an advanced scenario which allows for 3D expansion energies below 16 pK
by implementing an additional pulsed delta-kick collimation directly after
release from the trapping potential. Our results pave the way to achieve
state-of-the-art quantum state in typical dipole trap setups required to
perform ultra-precise measurements without the need of complex micro-gravity or
long baselines environments
Counting Complex Disordered States by Efficient Pattern Matching: Chromatic Polynomials and Potts Partition Functions
Counting problems, determining the number of possible states of a large
system under certain constraints, play an important role in many areas of
science. They naturally arise for complex disordered systems in physics and
chemistry, in mathematical graph theory, and in computer science. Counting
problems, however, are among the hardest problems to access computationally.
Here, we suggest a novel method to access a benchmark counting problem, finding
chromatic polynomials of graphs. We develop a vertex-oriented symbolic pattern
matching algorithm that exploits the equivalence between the chromatic
polynomial and the zero-temperature partition function of the Potts
antiferromagnet on the same graph. Implementing this bottom-up algorithm using
appropriate computer algebra, the new method outperforms standard top-down
methods by several orders of magnitude, already for moderately sized graphs. As
a first application, we compute chromatic polynomials of samples of the simple
cubic lattice, for the first time computationally accessing three-dimensional
lattices of physical relevance. The method offers straightforward
generalizations to several other counting problems.Comment: 7 pages, 4 figure
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