1,701 research outputs found
Shaping Giant Membrane Vesicles in 3D-Printed Protein Hydrogel Cages
Giant unilamellar phospholipid vesicles are attractive starting points for constructing minimal living cells from the bottom-up. Their membranes are compatible with many physiologically functional modules and act as selective barriers, while retaining a high morphological flexibility. However, their spherical shape renders them rather inappropriate to study phenomena that are based on distinct cell shape and polarity, such as cell division. Here, a microscale device based on 3D printed protein hydrogel is introduced to induce pH-stimulated reversible shape changes in trapped vesicles without compromising their free-standing membranes. Deformations of spheres to at least twice their aspect ratio, but also toward unusual quadratic or triangular shapes can be accomplished. Mechanical force induced by the cages to phase-separated membrane vesicles can lead to spontaneous shape deformations, from the recurrent formation of dumbbells with curved necks between domains to full budding of membrane domains as separate vesicles. Moreover, shape-tunable vesicles are particularly desirable when reconstituting geometry-sensitive protein networks, such as reaction-diffusion systems. In particular, vesicle shape changes allow to switch between different modes of self-organized protein oscillations within, and thus, to influence reaction networks directly by external mechanical cues
Vortices on Orbifolds
The Abelian and non-Abelian vortices on orbifolds are investigated based on
the moduli matrix approach, which is a powerful method to deal with the BPS
equation. The moduli space and the vortex collision are discussed through the
moduli matrix as well as the regular space. It is also shown that a quiver
structure is found in the Kahler quotient, and a half of ADHM is obtained for
the vortex theory on the orbifolds as the case before orbifolding.Comment: 25 pages, 4 figures; references adde
Non-Abelian vortex dynamics: Effective world-sheet action
The low-energy vortex effective action is constructed in a wide class of
systems in a color-flavor locked vacuum, which generalizes the results found
earlier in the context of U(N) models. It describes the weak fluctuations of
the non-Abelian orientational moduli on the vortex worldsheet. For instance,
for the minimum vortex in SO(2N) x U(1) or USp(2N) x U(1) gauge theories, the
effective action found is a two-dimensional sigma model living on the Hermitian
symmetric spaces SO(2N)/U(N) or USp(2N)/U(N), respectively. The fluctuating
moduli have the structure of that of a quantum particle state in spinor
representations of the GNO dual of the color-flavor SO(2N) or USp(2N) symmetry,
i.e. of SO(2N) or of SO(2N+1). Applied to the benchmark U(N) model our
procedure reproduces the known CP(N-1) worldsheet action; our recipe allows us
to obtain also the effective vortex action for some higher-winding vortices in
U(N) and SO(2N) theories.Comment: LaTeX, 25 pages, 0 figure
Vortex counting from field theory
The vortex partition function in 2d N = (2,2) U(N) gauge theory is derived
from the field theoretical point of view by using the moduli matrix approach.
The character for the tangent space at each moduli space fixed point is written
in terms of the moduli matrix, and then the vortex partition function is
obtained by applying the localization formula. We find that dealing with the
fermionic zero modes is crucial to obtain the vortex partition function with
the anti-fundamental and adjoint matters in addition to the fundamental chiral
multiplets. The orbifold vortex partition function is also investigated from
the field theoretical point of view.Comment: 21 pages, no figure
Exploratory analysis of high-resolution power interruption data reveals spatial and temporal heterogeneity in electric grid reliability
Modern grid monitoring equipment enables utilities to collect detailed
records of power interruptions. These data are aggregated to compute publicly
reported metrics describing high-level characteristics of grid performance. The
current work explores the depth of insights that can be gained from public
data, and the implications of losing visibility into heterogeneity in grid
performance through aggregation. We present an exploratory analysis examining
three years of high-resolution power interruption data collected by archiving
information posted in real-time on the public-facing website of a utility in
the Western United States. We report on the size, frequency and duration of
individual power interruptions, and on spatio-temporal variability in aggregate
reliability metrics. Our results show that metrics of grid performance can vary
spatially and temporally by orders of magnitude, revealing heterogeneity that
is not evidenced in publicly reported metrics. We show that limited access to
granular information presents a substantive barrier to conducting detailed
policy analysis, and discuss how more widespread data access could help to
answer questions that remain unanswered in the literature to date. Given open
questions about whether grid performance is adequate to support societal needs,
we recommend establishing pathways to make high-resolution power interruption
data available to support policy research.Comment: Journal submission (in review), 22 pages, 8 figures, 1 tabl
Structurally Parameterized d-Scattered Set
In -Scattered Set we are given an (edge-weighted) graph and are asked to
select at least vertices, so that the distance between any pair is at least
, thus generalizing Independent Set. We provide upper and lower bounds on
the complexity of this problem with respect to various standard graph
parameters. In particular, we show the following:
- For any , an -time algorithm, where
is the treewidth of the input graph.
- A tight SETH-based lower bound matching this algorithm's performance. These
generalize known results for Independent Set.
- -Scattered Set is W[1]-hard parameterized by vertex cover (for
edge-weighted graphs), or feedback vertex set (for unweighted graphs), even if
is an additional parameter.
- A single-exponential algorithm parameterized by vertex cover for unweighted
graphs, complementing the above-mentioned hardness.
- A -time algorithm parameterized by tree-depth
(), as well as a matching ETH-based lower bound, both for
unweighted graphs.
We complement these mostly negative results by providing an FPT approximation
scheme parameterized by treewidth. In particular, we give an algorithm which,
for any error parameter , runs in time
and returns a
-scattered set of size , if a -scattered set of the same
size exists
Coherent manipulation of electronic states in a double quantum dot
We investigate coherent time-evolution of charge states (pseudo-spin qubit)
in a semiconductor double quantum dot. This fully-tunable qubit is manipulated
with a high-speed voltage pulse that controls the energy and decoherence of the
system. Coherent oscillations of the qubit are observed for several
combinations of many-body ground and excited states of the quantum dots.
Possible decoherence mechanisms in the present device are also discussed.Comment: RevTe
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