A polynomial oracle-time algorithm for convex integer minimization

In this paper we consider the solution of certain convex integer minimization problems via greedy augmentation procedures. We show that a greedy augmentation procedure that employs only directions from certain Graver bases needs only polynomially many augmentation steps to solve the given problem. We extend these results to convex $N$-fold integer minimization problems and to convex 2-stage stochastic integer minimization problems. Finally, we present some applications of convex $N$-fold integer minimization problems for which our approach provides polynomial time solution algorithms.Comment: 19 pages, 1 figur

Pressure-Induced Magnetism and Hidden Order in URu_2Si_2

We discuss the discovery of pressure-induced antiferromagnetism in URu_2Si_2, in the context of neutron, NMR and \mu SR results. The identification of a critical pressure separating mean-field and Ising phase transitions leads us to propose that the system lies close to a bicritical point associated with magnetic and (non-magnetic) hidden order. We conclude that the recent observation of an isotropic, field-independent component in the silicon NMR line-width implies that the hidden order parameter breaks time-reversal invariance and present a preliminary discussion of the underlying nature of the hidden order parameter.Comment: To appear in proceedings of SCES 200

Mean field approach to antiferromagnetic domains in the doped Hubbard model

We present a restricted path integral approach to the 2D and 3D repulsive Hubbard model. In this approach the partition function is approximated by restricting the summation over all states to a (small) subclass which is chosen such as to well represent the important states. This procedure generalizes mean field theory and can be systematically improved by including more states or fluctuations. We analyze in detail the simplest of these approximations which corresponds to summing over states with local antiferromagnetic (AF) order. If in the states considered the AF order changes sufficiently little in space and time, the path integral becomes a finite dimensional integral for which the saddle point evaluation is exact. This leads to generalized mean field equations allowing for the possibility of more than one relevant saddle points. In a big parameter regime (both in temperature and filling), we find that this integral has {\em two} relevant saddle points, one corresponding to finite AF order and the other without. These degenerate saddle points describe a phase of AF ordered fermions coexisting with free, metallic fermions. We argue that this mixed phase is a simple mean field description of a variety of possible inhomogeneous states, appropriate on length scales where these states appear homogeneous. We sketch systematic refinements of this approximation which can give more detailed descriptions of the system.Comment: 14 pages RevTex, 6 postscript figures included using eps

The metallic state in disordered quasi-one-dimensional conductors

The unusual metallic state in conjugated polymers and single-walled carbon nanotubes is studied by dielectric spectroscopy (8--600 GHz). We have found an intriguing correlation between scattering time and plasma frequency. This relation excludes percolation models of the metallic state. Instead, the carrier dynamics can be understood in terms of the low density of delocalized states around the Fermi level, which arises from the competion between disorder-induced localization and interchain-interactions-induced delocalization.Comment: 4 pages including 4 figure

The two-dimensional random-bond Ising model, free fermions and the network model

We develop a recently-proposed mapping of the two-dimensional Ising model with random exchange (RBIM), via the transfer matrix, to a network model for a disordered system of non-interacting fermions. The RBIM transforms in this way to a localisation problem belonging to one of a set of non-standard symmetry classes, known as class D; the transition between paramagnet and ferromagnet is equivalent to a delocalisation transition between an insulator and a quantum Hall conductor. We establish the mapping as an exact and efficient tool for numerical analysis: using it, the computational effort required to study a system of width $M$ is proportional to $M^{3}$, and not exponential in $M$ as with conventional algorithms. We show how the approach may be used to calculate for the RBIM: the free energy; typical correlation lengths in quasi-one dimension for both the spin and the disorder operators; even powers of spin-spin correlation functions and their disorder-averages. We examine in detail the square-lattice, nearest-neighbour $\pm J$ RBIM, in which bonds are independently antiferromagnetic with probability $p$, and ferromagnetic with probability $1-p$. Studying temperatures $T\geq 0.4J$, we obtain precise coordinates in the $p-T$ plane for points on the phase boundary between ferromagnet and paramagnet, and for the multicritical (Nishimori) point. We demonstrate scaling flow towards the pure Ising fixed point at small $p$, and determine critical exponents at the multicritical point.Comment: 20 pages, 25 figures, figures correcte

Cosolvent flushing for the remediation of PAHs from former manufactured gas plants

Cosolvent flushing is a technique that has been proposed for the removal of hydrophobic organic contaminants in the subsurface. Cosolvents have been shown to dramatically increase the solubility of such compounds compared to the aqueous solubility; however, limited data are available on the effectiveness of cosolvents for field-contaminated media. In this work, we examine cosolvent flushing for the removal of polycyclic aromatic hydrocarbons (PAHs) in soil from a former manufactured gas plant (FMGP). Batch studies confirmed that the relationship between the soil-cosolvent partitioning coefficient (Ki) and the volume fraction of cosolvent (fc) followed a standard log-linear equation. Using methanol at an fc of 0.95, column studies were conducted at varying length scales, ranging from 11.9 to 110 cm. Removal of PAH compounds was determined as a function of pore volumes (PVs) of cosolvent flushed. Despite using a high fc, rate and chromatographic effects were observed in all the columns. PAH effluent concentrations were modeled using a common two-site sorption model. Model fits were improved by using MeOH breakthrough curves to determine fitted dispersion coefficients. Fitted mass-transfer rates were two to three orders of magnitude lower than predicted values based on published data using artificially contaminated sands

Unravelling the temporal association between lameness and body condition score in dairy cattle using a multistate modelling approach

Recent studies have reported associations between lameness and body condition score (BCS) in dairy cattle, however the impact of change in the dynamics of BCS on both lameness occurrence and recovery is currently unknown. The aim of this study was to investigate in a longitudinal study the effect of change in BCS on the transitions from the non-lame to lame, and lame to non-lame states. A total of 731 cows with 6889 observations from 4 UK herds were included in the study. Mobility score (MS) and body condition score (BCS) were recorded every 13-15 days from July 2010 until December 2011. A multilevel multistate discrete time event history model was built to investigate the transition of lameness over time. There were 1042 non-lame episodes and 593 lame episodes of which approximately 50% (519/1042) of the non-lame episodes transitioned to the lame state and 81% (483/593) of the lame episodes ended with a transition to the non-lame state. Cows with a lower BCS at calving (BCS Group 1 (1.00-1.75) and Group 2 (2.00-2.25)) had a higher probability of transition from non-lame to lame and a lower probability of transition from lame to non-lame compared to cows with BCS 2.50-2.75 i.e. they were more likely to become lame and if lame, they were less likely to recover. Similarly, cows who suffered a greater decrease in BCS (compared to their BCS at calving) had a higher probability of becoming lame and a lower probability of recovering in the next 15 days. An increase in BCS from calving was associated with the converse effect i.e. a lower probability of cows moving from the non-lame to the lame state and higher probability of transition from lame to non-lame. Days of lactation, months of calving and parity was associated with both lame and non-lame transitions and there was evidence of heterogeneity among cows in lameness occurrence and recovery. This study suggests loss of BCS and increase of BCS could influence the risk of becoming lame and the chance of recovery from lameness. Regular monitoring and maintenance of BCS on farms could be a key tool for reducing lameness. Further work is urgently needed in this area to allow a better understanding of the underlying mechanisms behind these relationships

A Review of River Herring Science in Support of Species Conservation and Ecosystem Restoration

River herring—a collective name for the Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis—play a crucial role in freshwater and marine ecosystems along the Eastern Seaboard of North America. River herring are anadromous and return to freshwater habitats in the tens to hundreds of millions to spawn, supplying food to many species and providing nutrients to freshwater ecosystems. After two and a half centuries of habitat loss, habitat degradation, and overfishing, river herring are at historic lows. In 2013, National Oceanic and Atmospheric Administration Fisheries established the Technical Expert Working Group (TEWG) to synthesize information about river herring and to provide recommendations to advance the science related to their restoration. This paper was composed largely by the chairs of the TEWG subgroups and represents a review of the current state of knowledge of river herring, with an emphasis on identification of threats and discussion of recent research and management actions related to understanding and reducing these threats. Important research needs are then identified and discussed. Finally, current knowledge is synthesized, considering the relative importance of different threats. This synthesis identifies dam removal and increased stream connectivity as critical to river herring restoration. Better understanding and accounting for predation, climate change, and fisheries are also important for restoration. Finally, there is recent evidence that the effects of human development and contamination on habitat quality may be more important threats than previously recognized. Given the range of threats, an ecosystem approach is needed to be successful with river herring restoration. To facilitate this ecosystem approach, collaborative forums such as the TEWG (renamed the Atlantic Coast River Herring Collaborative Forum in 2020) are needed to share and synthesize information among river herring managers, researchers, and community groups from across the species’ range

Continuous postoperative pericardial flushing reduces postoperative bleeding after coronary artery bypass grafting: a randomized trial

Background: Prolonged or excessive bleeding after cardiac surgery can lead to a broad spectrum of secondary complications. One of the underlying causes is incomplete wound drainage, with subsequent accumulation of blood and clots in the pericardium. We developed the continuous postoperative pericardial flushing (CPPF) therapy to improve wound drainage and reduce postoperative blood loss and bleeding-related complications after cardiac surgery. This study compared CPPF to standard care in patients after coronary artery bypass grafting (CABG).Methods: This is a single center, open label, randomized trial that enrolled patients at the Amsterdam UMC, location AMC, Amsterdam, the Netherlands. The study was registered at the 'Netherlands Trial Register', study identifier NTR5200 [1]. Adults undergoing CABG were randomly assigned to receive CPPF therapy or standard care, participants and investigators were not masked to group assignment. The primary end point was postoperative blood loss in the first 12-hours after surgery.Findings: Between the January 15, 2014 and the March 13, 2017, 169 patients were enrolled and assigned to CPPF therapy (study group; n = 83) or standard care (control group; n = 86). CPPF reduced postoperative blood loss when compared to standard care (median differences -385 ml, reduction 76% p=<= 0.001), with the remark that these results are overestimated due to a measurement error in part of the study group. None of patients in the study group required reoperation for non-surgical bleeding versus 3 (4%, 95% CI -0.4% to 7.0%) in the control group. None of the patients in the study group suffered from cardiac tamponade, versus 3 (4%, 95% CI -0,4% to 7.0%) in the control group. The incremental cost-effectiveness ratio was (sic)116.513 (95% bootstrap CI (sic)-882.068 to (sic)+897.278).Interpretation: The use of CPPF therapy after CABG seems to reduce bleeding and bleeding related complications. With comparable costs and no improvement in Qualty of Life (QoL), cost consideration for the implementation of CPPF is not relevant. None of the patients in the study group required re-interventions for nonsurgical bleeding or acute cardiac tamponade, which underlines the proof of concept of this novel therapy. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)Thoracic Surger

Modelling spectral and timing properties of accreting black holes: the hybrid hot flow paradigm

The general picture that emerged by the end of 1990s from a large set of optical and X-ray, spectral and timing data was that the X-rays are produced in the innermost hot part of the accretion flow, while the optical/infrared (OIR) emission is mainly produced by the irradiated outer thin accretion disc. Recent multiwavelength observations of Galactic black hole transients show that the situation is not so simple. Fast variability in the OIR band, OIR excesses above the thermal emission and a complicated interplay between the X-ray and the OIR light curves imply that the OIR emitting region is much more compact. One of the popular hypotheses is that the jet contributes to the OIR emission and even is responsible for the bulk of the X-rays. However, this scenario is largely ad hoc and is in contradiction with many previously established facts. Alternatively, the hot accretion flow, known to be consistent with the X-ray spectral and timing data, is also a viable candidate to produce the OIR radiation. The hot-flow scenario naturally explains the power-law like OIR spectra, fast OIR variability and its complex relation to the X-rays if the hot flow contains non-thermal electrons (even in energetically negligible quantities), which are required by the presence of the MeV tail in Cyg X-1. The presence of non-thermal electrons also lowers the equilibrium electron temperature in the hot flow model to <100 keV, making it more consistent with observations. Here we argue that any viable model should simultaneously explain a large set of spectral and timing data and show that the hybrid (thermal/non-thermal) hot flow model satisfies most of the constraints.Comment: 26 pages, 13 figures. To be published in the Space Science Reviews and as hard cover in the Space Sciences Series of ISSI - The Physics of Accretion on to Black Holes (Springer Publisher