36,376 research outputs found
Brownian ratchets driven by asymmetric nucleation of hydrolysis waves
We propose a stochastic process wherein molecular transport is mediated by
asymmetric nucleation of domains on a one-dimensional substrate. Track-driven
mechanisms of molecular transport arise in biophysical applications such as
Holliday junction positioning and collagenase processivity. In contrast to
molecular motors that hydrolyze nucleotide triphosphates and undergo a local
molecular conformational change, we show that asymmetric nucleation of
hydrolysis waves on a track can also result in directed motion of an attached
particle. Asymmetrically cooperative kinetics between ``hydrolyzed'' and
``unhydrolyzed'' states on each lattice site generate moving domain walls that
push a particle sitting on the track. We use a novel fluctuating-frame,
finite-segment mean field theory to accurately compute steady-state velocities
of the driven particle and to discover parameter regimes which yield maximal
domain wall flux, leading to optimal particle drift.Comment: 5 pp, 6 fig
Peeling and Sliding in Nucleosome Repositioning
We investigate the mechanisms of histone sliding and detachment with a
stochastic model that couples thermally-induced, passive histone sliding with
active motor-driven histone unwrapping. Analysis of a passive loop or twist
defect-mediated histone sliding mechanism shows that diffusional sliding is
enhanced as larger portions of the DNA is peeled off the histone. The mean
times to histone detachment and the mean distance traveled by the motor complex
prior to histone detachment are computed as functions of the intrinsic speed of
the motor. Fast motors preferentially induce detachment over sliding. However,
for a fixed motor speed, increasing the histone-DNA affinity (and thereby
decreasing the passive sliding rate) increases the mean distance traveled by
the motor.Comment: 5 pp, 4 fig
New Detectors to Explore the Lifetime Frontier
Long-lived particles (LLPs) are a common feature in many beyond the Standard
Model theories, including supersymmetry, and are generically produced in exotic
Higgs decays. Unfortunately, no existing or proposed search strategy will be
able to observe the decay of non-hadronic electrically neutral LLPs with masses
above GeV and lifetimes near the limit set by Big Bang Nucleosynthesis
(BBN), ~m. We propose the MATHUSLA surface
detector concept (MAssive Timing Hodoscope for Ultra Stable neutraL pArticles),
which can be implemented with existing technology and in time for the high
luminosity LHC upgrade to find such ultra-long-lived particles (ULLPs), whether
produced in exotic Higgs decays or more general production modes. We also
advocate for a dedicated LLP detector at a future 100 TeV collider, where a
modestly sized underground design can discover ULLPs with lifetimes at the BBN
limit produced in sub-percent level exotic Higgs decays.Comment: 7 pages, 4 figures. Added more detail to discussion of backgrounds.
Various minor clarifications. Results and conclusions unchange
Mechanism of formation of half-doped stripes in underdoped cuprates
Using a variational Monte-Carlo approach with a recently proposed stripe wave
function, we showed that the strong correlation included in a t-J-type model
has essentially all the necessary ingredients to form these stripes with
modulations of charge density, spin magnetization, and pair field. If a
perturbative effect of electron-phonon coupling to renormalize the effective
mass or the hopping rate of holes is considered with the model, we find the
half-doped stripes, which has on the average one half of a hole in one period
of charge modulation, to be most stable, energetic wise in the underdoped
region, . This is in good agreement with the observation
in the neutron scattering experiments. We also find long range Coulomb
interaction to be less effective in the formation of half-doped stripes.Comment: 4 pages, 4 figure
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