21,684 research outputs found
The Value of Information in Invasive Species Management
Resource /Energy Economics and Policy,
The "Alter Ego" of Albumin in Cirrhosis
Albumin is a globular, multifunctional protein that is highly conserved in nature. Alpha-fetoprotein, Vitamin D and E binding proteins are part of the albumin family and these are produced exclusively in the liver. Albumin is negatively charged and this gives it the oncotic properties it is well known for. More recently, it has become clear that albumin has clinically significant effects on antioxidant status, immune and endothelial function, capillary permeability, organ function, and metabolic homeostasis
Glassy Phase of Optimal Quantum Control
We study the problem of preparing a quantum many-body system from an initial
to a target state by optimizing the fidelity over the family of bang-bang
protocols. We present compelling numerical evidence for a universal
spin-glass-like transition controlled by the protocol time duration. The glassy
critical point is marked by a proliferation of protocols with close-to-optimal
fidelity and with a true optimum that appears exponentially difficult to
locate. Using a machine learning (ML) inspired framework based on the manifold
learning algorithm t-SNE, we are able to visualize the geometry of the
high-dimensional control landscape in an effective low-dimensional
representation. Across the transition, the control landscape features an
exponential number of clusters separated by extensive barriers, which bears a
strong resemblance with replica symmetry breaking in spin glasses and random
satisfiability problems. We further show that the quantum control landscape
maps onto a disorder-free classical Ising model with frustrated nonlocal,
multibody interactions. Our work highlights an intricate but unexpected
connection between optimal quantum control and spin glass physics, and shows
how tools from ML can be used to visualize and understand glassy optimization
landscapes.Comment: Modified figures in appendix and main text (color schemes). Corrected
references. Added figures in SI and pseudo-cod
Smoothing of sandpile surfaces after intermittent and continuous avalanches: three models in search of an experiment
We present and analyse in this paper three models of coupled continuum
equations all united by a common theme: the intuitive notion that sandpile
surfaces are left smoother by the propagation of avalanches across them. Two of
these concern smoothing at the `bare' interface, appropriate to intermittent
avalanche flow, while one of them models smoothing at the effective surface
defined by a cloud of flowing grains across the `bare' interface, which is
appropriate to the regime where avalanches flow continuously across the
sandpile.Comment: 17 pages and 26 figures. Submitted to Physical Review
Some considerations on coastal processes relevant to sea level rise
The effects of potential sea level rise on the shoreline and shore environment
have been briefly examined by considering the interactions between sea level rise and
relevant coastal processes. These interactions have been reviewed beginning with a
discussion of the need to reanalyze previous estimates of eustatic sea level rise and
compaction effects in water level measurement. This is followed by considerations on
sea level effects on coastal and estuarine tidal ranges, storm surge and water level
response, and interaction with natural and constructed shoreline features. The
desirability to reevaluate the well known Bruun Rule for estimating shoreline recession
has been noted. The mechanics of ground and surface water intrusion with reference to
sea level rise are then reviewed. This is followed by sedimentary processes in the
estuaries including wetland response. Finally comments are included on some probable
effects of sea level rise on coastal ecosystems.
These interactions are complex and lead to shoreline evolution (under a sea level
rise) which is highly site-specific. Models which determine shoreline change on the
basis of inundation of terrestrial topography without considering relevant coastal
processes are likely to lead to erroneous shoreline scenarios, particularly where the
shoreline is composed of erodible sedimentary material.
With some exceptions, present day knowledge of shoreline response to hydrodynamic
forcing is inadequate for long-term quantitative predictions. A series of interrelated
basic and applied research issues must be addressed in the coming decades to
determine shoreline response to sea level change with an acceptable degree of
confidence. (PDF contains 189 pages.
Acute-on-chronic liver failure
Acute-on-chronic liver failure (ACLF) is a recently recognised and defined syndrome seen in patients with liver cirrhosis and carries a high short-term mortality in excess of 15% at 28 days. ACLF is defined by organ failures (OFs) and is distinct from simple ‘acute decompensation’ (AD) of cirrhosis. OFs involve the liver, kidney, brain, coagulation, respiratory system and the circulation, and are defined by the European Association for the Study of the Liver Chronic Liver Failure Consortium (CLIF-C) OF score. The central pathophysiological mechanism in the development of ACLF is intense systemic inflammation, which distinguishes this syndrome from AD. The most frequent precipitating event of ACLF in the western world is bacterial infection and active alcohol intake, whereas hepatitis B flare followed by sepsis and active alcohol intake are the common precipitating events in the east. In about 40% patients with ACLF, however, no precipitating event is found. The course of ACLF is dynamic and reversible, so early identification and early initiation of supportive therapy is of utmost importance. Unfortunately, to date, there is no known specific therapy for ACLF except for liver transplantation, so the treatment revolves around institution of early organ support. Most of the patients will have a clear prognosis between 3–7 days of hospitalisation. CLIF-C ACLF score is the best available prognostic score in patients with ACLF
Constant Rank Bimatrix Games are PPAD-hard
The rank of a bimatrix game (A,B) is defined as rank(A+B). Computing a Nash
equilibrium (NE) of a rank-, i.e., zero-sum game is equivalent to linear
programming (von Neumann'28, Dantzig'51). In 2005, Kannan and Theobald gave an
FPTAS for constant rank games, and asked if there exists a polynomial time
algorithm to compute an exact NE. Adsul et al. (2011) answered this question
affirmatively for rank- games, leaving rank-2 and beyond unresolved.
In this paper we show that NE computation in games with rank , is
PPAD-hard, settling a decade long open problem. Interestingly, this is the
first instance that a problem with an FPTAS turns out to be PPAD-hard. Our
reduction bypasses graphical games and game gadgets, and provides a simpler
proof of PPAD-hardness for NE computation in bimatrix games. In addition, we
get:
* An equivalence between 2D-Linear-FIXP and PPAD, improving a result by
Etessami and Yannakakis (2007) on equivalence between Linear-FIXP and PPAD.
* NE computation in a bimatrix game with convex set of Nash equilibria is as
hard as solving a simple stochastic game.
* Computing a symmetric NE of a symmetric bimatrix game with rank is
PPAD-hard.
* Computing a (1/poly(n))-approximate fixed-point of a (Linear-FIXP)
piecewise-linear function is PPAD-hard.
The status of rank- games remains unresolved
Quantum dynamics of a binary mixture of BECs in a double well potential: an Holstein-Primakoff approach
We study the quantum dynamics of a binary mixture of Bose-Einstein
condensates (BEC) in a double-well potential starting from a two-mode
Bose-Hubbard Hamiltonian. Focussing on the regime where the number of atoms is
very large, a mapping onto a SU(2) spin problem together with a
Holstein-Primakoff transformation is performed. The quantum evolution of the
number difference of bosons between the two wells is investigated for different
initial conditions, which range from the case of a small imbalance between the
two wells to a coherent spin state. The results show an instability towards a
phase-separation above a critical positive value of the interspecies
interaction while the system evolves towards a coherent tunneling regime for
negative interspecies interactions. A comparison with a semiclassical approach
is discussed together with some implications on the experimental realization of
phase separation with cold atoms.Comment: 12 pages, 7 figures, accepted for publication in J. Phys.
Broken symmetry in a two-qubit quantum control landscape
We analyze the physics of optimal protocols to prepare a target state with
high fidelity in a symmetrically coupled two-qubit system. By varying the
protocol duration, we find a discontinuous phase transition, which is
characterized by a spontaneous breaking of a symmetry in the
functional form of the optimal protocol, and occurs below the quantum speed
limit. We study in detail this phase and demonstrate that even though
high-fidelity protocols come degenerate with respect to their fidelity, they
lead to final states of different entanglement entropy shared between the
qubits. Consequently, while globally both optimal protocols are equally far
away from the target state, one is locally closer than the other. An
approximate variational mean-field theory which captures the physics of the
different phases is developed
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