5,680 research outputs found
Xylan oligosaccharides and cellobiohydrolase I (TrCel7A) interaction and effect on activity
<p>Abstract</p> <p>Background</p> <p>The well-studied cellulase mixture secreted by <it>Trichoderma reesei </it>(anamorph to <it>Hypocrea jecorina</it>) contains two cellobiohydolases (CBHs), cellobiohydrolase I (<it>Tr</it>Cel7A) and cellobiohydrolase II (<it>Tr</it>CeI6A), that are core enzymes for the solubilisation of cellulose. This has attracted significant research interest because of the role of the CBHs in the conversion of biomass to fermentable sugars. However, the CHBs are notoriously slow and susceptible to inhibition, which presents a challenge for the commercial utilisation of biomass. The xylans and xylan fragments that are also present in the biomass have been suggested repeatedly as one cause of the reduced activity of CHBs. Yet, the extent and mechanisms of this inhibition remain poorly elucidated. Therefore, we studied xylan oligosaccharides (XOSs) of variable lengths with respect to their binding and inhibition of both <it>Tr</it>Cel7A and an enzyme variant without the cellulose-binding domain (CBM).</p> <p>Results</p> <p>We studied the binding of XOSs to <it>Tr</it>Cel7A by isothermal titration calorimetry. We found that XOSs bind to <it>Tr</it>Cel7A and that the affinity increases commensurate with XOS length. The CBM, on the other hand, did not affect the affinity significantly, which suggests that XOSs may bind to the active site. Activity assays of <it>Tr</it>Cel7A clearly demonstrated the negative effect of the presence of XOSs on the turnover number.</p> <p>Conclusions</p> <p>On the basis of these binding data and a comparison of XOS inhibition of the activity of the two enzyme variants towards, respectively, soluble and insoluble substrates, we propose a competitive mechanism for XOS inhibition of <it>Tr</it>Cel7A with phosphoric swollen cellulose as a substrate.</p
Ageing in bosonic particle-reaction models with long-range transport
Ageing in systems without detailed balance is studied in bosonic contact and
pair-contact processes with Levy diffusion. In the ageing regime, the dynamical
scaling of the two-time correlation function and two-time response function is
found and analysed. Exact results for non-equilibrium exponents and scaling
functions are derived. The behaviour of the fluctuation-dissipation ratio is
analysed. A passage time from the quasi-stationary regime to the ageing regime
is defined, in qualitative agreement with kinetic spherical models and p-spin
spherical glasses.Comment: Latex2e, 24 pages, with 9 figures include
Graph Orientation and Flows Over Time
Flows over time are used to model many real-world logistic and routing
problems. The networks underlying such problems -- streets, tracks, etc. -- are
inherently undirected and directions are only imposed on them to reduce the
danger of colliding vehicles and similar problems. Thus the question arises,
what influence the orientation of the network has on the network flow over time
problem that is being solved on the oriented network. In the literature, this
is also referred to as the contraflow or lane reversal problem.
We introduce and analyze the price of orientation: How much flow is lost in
any orientation of the network if the time horizon remains fixed? We prove that
there is always an orientation where we can still send of the
flow and this bound is tight. For the special case of networks with a single
source or sink, this fraction is which is again tight. We present
more results of similar flavor and also show non-approximability results for
finding the best orientation for single and multicommodity maximum flows over
time
On the Localization of Ultrasound Image Slices within Point Distribution Models
Thyroid disorders are most commonly diagnosed using high-resolution
Ultrasound (US). Longitudinal nodule tracking is a pivotal diagnostic protocol
for monitoring changes in pathological thyroid morphology. This task, however,
imposes a substantial cognitive load on clinicians due to the inherent
challenge of maintaining a mental 3D reconstruction of the organ. We thus
present a framework for automated US image slice localization within a 3D shape
representation to ease how such sonographic diagnoses are carried out. Our
proposed method learns a common latent embedding space between US image patches
and the 3D surface of an individual's thyroid shape, or a statistical
aggregation in the form of a statistical shape model (SSM), via contrastive
metric learning. Using cross-modality registration and Procrustes analysis, we
leverage features from our model to register US slices to a 3D mesh
representation of the thyroid shape. We demonstrate that our multi-modal
registration framework can localize images on the 3D surface topology of a
patient-specific organ and the mean shape of an SSM. Experimental results
indicate slice positions can be predicted within an average of 1.2 mm of the
ground-truth slice location on the patient-specific 3D anatomy and 4.6 mm on
the SSM, exemplifying its usefulness for slice localization during sonographic
acquisitions. Code is publically available:
\href{https://github.com/vuenc/slice-to-shape}{https://github.com/vuenc/slice-to-shape}Comment: ShapeMI Workshop @ MICCAI 2023; 12 pages 2 figure
Gravity waves and the LHC: Towards high-scale inflation with low-energy SUSY
It has been argued that rather generic features of string-inspired
inflationary theories with low-energy supersymmetry (SUSY) make it difficult to
achieve inflation with a Hubble scale H > m_{3/2}, where m_{3/2} is the
gravitino mass in the SUSY-breaking vacuum state. We present a class of
string-inspired supergravity realizations of chaotic inflation where a simple,
dynamical mechanism yields hierarchically small scales of post-inflationary
supersymmetry breaking. Within these toy models we can easily achieve small
ratios between m_{3/2} and the Hubble scale of inflation. This is possible
because the expectation value of the superpotential relaxes from large to
small values during the course of inflation. However, our toy models do not
provide a reasonable fit to cosmological data if one sets the SUSY-breaking
scale to m_{3/2} < TeV. Our work is a small step towards relieving the apparent
tension between high-scale inflation and low-scale supersymmetry breaking in
string compactifications.Comment: 21+1 pages, 5 figures, LaTeX, v2: added references, v3: very minor
changes, version to appear in JHE
D-brane potentials in the warped resolved conifold and natural inflation
In this paper we obtain a model of Natural Inflation from string theory with
a Planckian decay constant. We investigate D-brane dynamics in the background
of the warped resolved conifold (WRC) throat approximation of Type IIB string
compactifications on Calabi-Yau manifolds. When we glue the throat to a compact
bulk Calabi-Yau, we generate a D-brane potential which is a solution to the
Laplace equation on the resolved conifold. We can exactly solve this equation,
including dependence on the angular coordinates. The solutions are valid down
to the tip of the resolved conifold, which is not the case for the more
commonly used deformed conifold. This allows us to exploit the effect of the
warping, which is strongest at the tip. We inflate near the tip using an
angular coordinate of a D5-brane in the WRC which has a discrete shift
symmetry, and feels a cosine potential, giving us a model of Natural Inflation,
from which it is possible to get a Planckian decay constant whilst maintaining
control over the backreaction. This is because the decay constant for a wrapped
brane contains powers of the warp factor, and so can be made large, while the
wrapping parameter can be kept small enough so that backreaction is under
control.Comment: 41 pages, 3 appendices, 1 figure, PDFLaTex; various clarifications
added along with a new appendix on b-axions and wrapped D5 branes;version
matches the one published in JHE
S3M: Scalable Statistical Shape Modeling through Unsupervised Correspondences
Statistical shape models (SSMs) are an established way to represent the
anatomy of a population with various clinically relevant applications. However,
they typically require domain expertise, and labor-intensive landmark
annotations to construct. We address these shortcomings by proposing an
unsupervised method that leverages deep geometric features and functional
correspondences to simultaneously learn local and global shape structures
across population anatomies. Our pipeline significantly improves unsupervised
correspondence estimation for SSMs compared to baseline methods, even on highly
irregular surface topologies. We demonstrate this for two different anatomical
structures: the thyroid and a multi-chamber heart dataset. Furthermore, our
method is robust enough to learn from noisy neural network predictions,
potentially enabling scaling SSMs to larger patient populations without manual
segmentation annotation.Comment: Accepted at MICCAI 2023. 13 pages, 6 figure
A novel, aerosol-nanocrystal floating-gate device for non-volatile memory applications
This paper describes the fabrication, and structural and electrical characterization of a new, aerosol-nanocrystal floating-gate FET, aimed at non-volatile memory (NVM) applications. This aerosol-nanocrystal NVM device features program/erase characteristics comparable to conventional stacked gate NVM devices, excellent endurance (>l0^5 P/E cycles), and long-term non-volatility in spite of a thin bottom oxide (55-60Å). In addition, a very simple fabrication process makes this aerosol-nanocrystal NVM device a potential candidate for low cost NVM applications
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