15,713 research outputs found
Asymmetric Two-component Fermion Systems in Strong Coupling
We study the phase structure of a dilute two-component Fermi system with
attractive interactions as a function of the coupling and the polarization or
number difference between the two components. In weak coupling, a finite number
asymmetry results in phase separation. A mixed phase containing symmetric
superfluid matter and an asymmetric normal phase is favored. With increasing
coupling strength, we show that the stress on the superfluid phase to
accommodate a number asymmetry increases. Near the infinite-scattering length
limit, we calculate the single-particle excitation spectrum and the
ground-state energy at various polarizations. A picture of weakly-interacting
quasi-particles emerges for modest polarizations. In this regime near infinite
scattering length, and for modest polarizations, a homogeneous phase with a
finite population of excited quasi-particle states characterized by a gapless
spectrum should be favored over the phase separated state. These states may be
realized in cold atom experiments.Comment: 4 pages, 3 figur
Propensity to form amyloid fibrils is encoded as excitations in the free energy landscape of monomeric proteins
Protein aggregation, linked to many of diseases, is initiated when monomers
access rogue conformations that are poised to form amyloid fibrils. We show,
using simulations of src SH3 domain, that mechanical force enhances the
population of the aggregation prone () states, which are rarely populated
under force free native conditions, but are encoded in the spectrum of native
fluctuations. The folding phase diagrams of SH3 as a function of denaturant
concentration (), mechanical force (), and temperature exhibit an
apparent two-state behavior, without revealing the presence of the elusive
states. Interestingly, the phase boundaries separating the folded and
unfolded states at all [C] and fall on a master curve, which can can be
quantitatively described using an analogy to superconductors in a magnetic
field. The free energy profiles as a function of the molecular extension (),
which are accessible in pulling experiments, (), reveal the presence of a
native-like with a disordered solvent-exposed amino terminal
-strand. The structure of the state is identical to that found in
Fyn SH3 by NMR dispersion experiments. We show that the time scale for fibril
formation can be estimated from the population of the state, determined
by the free energy gap separating the native structure and the state, a
finding that can be used to assess fibril forming tendencies of proteins. The
structures of the state are used to show that oligomer formation and
likely route to fibrils occur by a domain-swap mechanism in SH3 domain.Comment: 12 pages, 8 figures, 9 supplementary figures (on 5 more pages), 2
supplementary movies (on youtube
On the ground state of gapless two flavor color superconductors
This paper is devoted to the study of some aspects of the instability of two
flavor color superconductive quark matter. We find that, beside color
condensates, the Goldstone boson related to the breaking of suffers of
a velocity instability. We relate this wrong sign problem, which implies the
existence of a Goldstone current in the ground state or of gluonic
condensation, to the negative squared Meissner mass of the gluon in
the g2SC phase. Moreover we investigate the Meissner masses of the gluons and
the squared velocity of the Goldstone in the multiple plane wave LOFF states,
arguing that in such phases both the chromo-magnetic instability and the
velocity instability are most probably removed. We also do not expect Higgs
instability in such multiple plane wave LOFF. The true vacuum of gapless two
flavor superconductors is thus expected to be a multiple plane wave LOFF state.Comment: 16 pages, RevTe3X4 styl
Energy Requirements in Size Reduction of Solids
It is no exageration to state that of the many appr-oaches to understand different aspects of process of comminution, perhaps the most important one is the search for the sound relationship between the size and the energy used. Basic Laboratory investigations of comminution have been concerned mainly with 3 phases of the problem:
1) The micro crack pattern and its progress
2) Fragment size distribution of commuted products
3) new surface production as a relation to energy inpu
Analytical and numerical evaluation of the Debye and Meissner masses in dense neutral three-flavor quark matter
We calculate the Debye and Meissner masses and investigate chromomagnetic
instability associated with the gapless color superconducting phase changing
the strange quark mass and the temperature . Based on the analytical
study, we develop a computational procedure to derive the screening masses
numerically from curvatures of the thermodynamic potential. When the
temperature is zero, from our numerical results for the Meissner masses, we
find that instability occurs for and gluons entirely in the gapless
color-flavor locked (gCFL) phase, while the Meissner masses are real for ,
, , and until exceeds a certain value that is larger than
the gCFL onset. We then handle mixing between color-diagonal gluons ,
, and photon , and clarify that, among three eigenvalues of the
mass squared matrix, one remains positive, one is always zero because of an
unbroken U(1)_\tilde{Q} symmetry, and one exhibits chromomagnetic instability
in the gCFL region. We also examine the temperature effects that bring
modifications into the Meissner masses. The instability found at large
for , , , and persists at finite into the -quark
color superconducting (uSC) phase which has - and - but no -
quark pairing and also into the two-flavor color superconducting (2SC) phase
characterized by - quark pairing only. The and instability
also goes into the uSC phase, but the 2SC phase has no instability for ,
, and . We map the unstable region for each gluon onto the phase
diagram as a function of and .Comment: 17 pages, 18 figure
Testing the Ginzburg-Landau approximation for three-flavor crystalline color superconductivity
It is an open challenge to analyze the crystalline color superconducting
phases that may arise in cold dense, but not asymptotically dense, three-flavor
quark matter. At present the only approximation within which it seems possible
to compare the free energies of the myriad possible crystal structures is the
Ginzburg-Landau approximation. Here, we test this approximation on a
particularly simple "crystal" structure in which there are only two condensates
and whose position-space dependence is that of two
plane waves with wave vectors and at arbitrary angles.
For this case, we are able to solve the mean-field gap equation without making
a Ginzburg-Landau approximation. We find that the Ginzburg-Landau approximation
works in the limit as expected, find that it correctly predicts
that decreases with increasing angle between and meaning that the phase with has the lowest
free energy, and find that the Ginzburg-Landau approximation is conservative in
the sense that it underestimates at all values of the angle between
and .Comment: 16 pages, 6 figures. Small changes only. Version to appear in Phys.
Rev.
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