The Effect of NAG–thiazoline on Morphology and Surface Hydrophobicity of Escherichia Coli

The β-hexosaminidase inhibitor and structural analog of the putative oxazolium reaction intermediate of lytic transglycosylases, N-acetylglucosamine thiazoline (NAG–thiazoline), was synthesized in 46% overall yield and tested as an inhibitor of Escherichia coli growth. NAG–thiazoline, at concentrations up to 1 mg/ml, was not found to affect the viability of E. coli DH5α

Model averaging approaches to data subset selection

Model averaging is a useful and robust method for dealing with model uncertainty in statistical analysis. Often, it is useful to consider data subset selection at the same time, in which model selection criteria are used to compare models across different subsets of the data. Two different criteria have been proposed in the literature for how the data subsets should be weighted. We compare the two criteria closely in a unified treatment based on the Kullback-Leibler divergence, and conclude that one of them is subtly flawed and will tend to yield larger uncertainties due to loss of information. Analytical and numerical examples are provided.Comment: 17 pages, 2 figures. v2: updated to published versio

Improved information criteria for Bayesian model averaging in lattice field theory

Bayesian model averaging is a practical method for dealing with uncertainty due to model specification. Use of this technique requires the estimation of model probability weights. In this work, we revisit the derivation of estimators for these model weights. Use of the Kullback-Leibler divergence as a starting point leads naturally to a number of alternative information criteria suitable for Bayesian model weight estimation. We explore three such criteria, known to the statistics literature before, in detail: a Bayesian analogue of the Akaike information criterion which we call the BAIC, the Bayesian predictive information criterion (BPIC), and the posterior predictive information criterion (PPIC). We compare the use of these information criteria in numerical analysis problems common in lattice field theory calculations. We find that the PPIC has the most appealing theoretical properties and can give the best performance in terms of model-averaging uncertainty, particularly in the presence of noisy data.Comment: 69 pages, 13 figures. v2: corrections to data subset formulas for BPIC and PPIC; edits for clarity. Submitted to PR

Algorithmic approach to adiabatic quantum optimization

It is believed that the presence of anticrossings with exponentially small gaps between the lowest two energy levels of the system Hamiltonian, can render adiabatic quantum optimization inefficient. Here, we present a simple adiabatic quantum algorithm designed to eliminate exponentially small gaps caused by anticrossings between eigenstates that correspond with the local and global minima of the problem Hamiltonian. In each iteration of the algorithm, information is gathered about the local minima that are reached after passing the anticrossing non-adiabatically. This information is then used to penalize pathways to the corresponding local minima, by adjusting the initial Hamiltonian. This is repeated for multiple clusters of local minima as needed. We generate 64-qubit random instances of the maximum independent set problem, skewed to be extremely hard, with between 10^5 and 10^6 highly-degenerate local minima. Using quantum Monte Carlo simulations, it is found that the algorithm can trivially solve all the instances in ~10 iterations.Comment: 7 pages, 3 figure

Two modes of accelerated glacier sliding related to water

We present the first glacier-wide detailed measurement of basal effective pressure and related observations including bed separation to elucidate the role of water in sliding. The hard bedded glacier instrumented in our study exhibited two phases of accelerated sliding motion apparently driven by separate mechanisms. The first acceleration phase (up to 5 fold increase in speed) was closely tied to an increase in bed separation. The faster second phase (up to 9 fold increase in speed) was related to an unusually high level of connectivity of subglacial waters. We infer the first mode was related to cavity opening and the second mode was related to reduced ice contact with the bed. Glacier sliding over a hard bed is typically represented by sliding laws that include the effective basal pressure, but neither sliding phase was accompanied by a simultaneous decrease in local or regional effective pressure

Crevasse patterns and the strain-rate tensor: a high-resolution comparison

Values of the strain-rate tensor represented at a 20 m length scale are found to explain the pattern and orientation of crevasses in a 0.13 km2 reach of Worthington Glacier, Alaska, U.S.A. The flow field of the reach is constructed from surveyed displacements of 110 markers spaced 20-30 m apart. A velocity gradient method is then used to calculate values of the principal strain-rate axes at the nodes of a 20 m x 20 m orthogonal grid. Crevasses in the study reach are of two types, splaying and transverse, and are everywhere normal to the trajectories of greatest (most tensile) principal strain rate. Splaying crevasses exist where the longitudinal strain rate (Ex) is less than or equal to 0 and transverse crevasses are present under longitudinally extending flow (i.e. Ex greater than 0). The orientation of crevasses changes in the down-glacier direction, but the calculated rotation by the flow field does not account for this change in orientation. Observations suggest that individual crevasses represent local values of the regional flow field and are transient on the time-scale of 1-2 years; they are not persistent features that are translated and rotated by flow. Crevasse patterns are thus found to be a useful tool for mapping the strain-rate tensor in this reach of a temperate valley glacier

Diurnal water-pressure fluctuations: timing and pattern of termination below Bench Glacier, Alaska, USA

Observations from basal water-pressure sensors along the length of Bench Glacier, Alaska, USA, show that diurnal fluctuations of water pressure are seasonal and restricted to summer. Most notable about these fluctuations is their disappearance in the late summer and early autumn, long before the seasonal end of diurnal meltwater input. Here we present data documenting the end of diurnal water-pressure fluctuations during the 2002 and 2003 melt seasons. The end of diurnal fluctuations occurred abruptly in multiple boreholes spaced meters to kilometers apart. There was no obvious spatial progression of termination events, and a clear correlation with meteorological forcing or discharge in the outlet stream was not apparent. After diurnal pressure fluctuations ended, basal water pressure returned to a high, generally steady, value either in an irregular pattern or by a distinct increase. This high water pressure was interrupted by episodic, acyclic events throughout the autumn before becoming stable and high in winter

Diurnal fluctuations in borehole water levels: configuration of the drainage system beneath Bench Glacier, Alaska, USA

Water levels were measured in boreholes spaced along the entire length of Bench Glacier, Alaska, USA, for a period in excess of 2 years. Instrumented boreholes were arranged as nine pairs along the center line of the glacier and an orthogonal grid of 16 boreholes in a 3600 m2 region at the center of the ablation area. Dirunal fluctuations of the water levels were found to be restricted to the late melt season. Pairs of boreholes spaced along the length of the ablation area often exhibited similar fluctuations and diurnal changes in water levels. Three distinct and independent types of diurnal fluctuations in water level were observed in cluster of boreholes within the grid of boreholes. Head gradients suggest water did not flow between clusters,and a single tunnel connecting the boreholes could not explain the observed pattern of diunal water-level fluctuations. Inter-borehole and borehole-cluster connectivity suggests the cross-glacier width of influence of a segment of the drainage system connected to a borehole was limited to tens of meters. A drainage configuration whereby boreholes are connected to a somewhat distant tunnel by drainage pipes of differing lengths, often hundreds of meters, is shown with a numerical test to be a plausible explanation for the observed borehole behavior