Modeling Approaches for Investigating Gas Migration from a Deep Low/Intermediate Level Waste Repository (Switzerland)

In low/intermediate-level waste (L/ILW) repositories, anaerobic corrosion of metals and degradation of organic materials produce mainly hydrogen, methane, and carbon dioxide. The Swiss reference concept for the L/ILW repository consists of parallel caverns sealed off from a single access tunnel in a deep low-permeability claystone formation. The potential buildup of excess gas pressures in the backfilled emplacement caverns was investigated in a series of two-phase flow models. In the first step, a large-scale model was constructed, implementing the 3D radial tunnel and cavern geometry with a simplified rectangular geometry. In the second step, the potential impact of the detailed geometry of the engineered barrier system (EBS) and the associated heterogeneity inside the cavern was examined using detailed models of the repository caverns, tunnel seals, access tunnel, and surrounding host rock. The simulation results from the large-scale 3D repository model show that during the early post-closure period simulated pressures can vary significantly between different parts of the repository. The simulated pressure increase in the emplacement caverns remained below the fracture pressure of the rock for realistic assumptions. Gas flow is largely limited to the EBS and the excavation disturbed zone (EDZ); thus, gas flows through and around the repository seal into the adjacent tunnel system, which is also demonstrated in the detailed repository-cavern model. The repository seal model described the detailed two-phase flow pattern of early time resaturation of the repository by water inflow from the ramp and subsequent counter flow associated with the gas flow from the repository cavern. Overall, the results of the detailed models complement and confirmed the results of the large-scale 3D model in terms of the timing of the pressure peaks and the migration of gas from the cavern into the surrounding host rock and through the repository seal.     

Microwave photon counter based on Josephson junctions

We describe a microwave photon counter based on the current-biased Josephson junction. The junction is tuned to absorb single microwave photons from the incident field, after which it tunnels into a classically observable voltage state. Using two such detectors, we have performed a microwave version of the Hanbury Brown-Twiss experiment at 4 GHz and demonstrated a clear signature of photon bunching for a thermal source. The design is readily scalable to tens of parallelized junctions, a configuration that would allow number-resolved counting of microwave photons.     

Combining TOUGH2 and FLAC3D to Solve Problems in Underground Gas Storage

This paper describes modeling studies assessing the feasibility of increasing the maximum storage pressure in several underground natural gas storage reservoirs. This required an assessment of the potential for gas transport in the caprock and the geomechanical response to pressure change in the storage reservoir. To solve this problem in an efficient manner, two-phase flow (TOUGH2) and geomechanical (FLAC3D) models were combined in series. The TOUGH2 model was calibrated to fit pressure data collected on-site, from both the reservoir and caprock. The mechanical response of the caprock to increased storage pressure was modeled using FLAC3D, allowing assessment of the induced stresses in formations surrounding the reservoirs. We focused on two sites. In the first, field data were obtained from a deep borehole above the gas reservoir, which provided indirect observations of the geomechanical response of the caprock to pressure changes in the reservoir. In the second, open boreholes intersecting two thin caprock units immediately above the reservoir allowed gas flow to a shallower unit, significantly impacting the modeled fracture gradient.     

An exponential lower bound for Cunningham’s rule

In this paper we give an exponential lower bound for Cunningham’s least recently considered (round-robin) rule as applied to parity games, Markov decision processes and linear programs. This improves a recent subexponential bound of Friedmann for this rule on these problems. The round-robin rule fixes a cyclical order of the variables and chooses the next pivot variable starting from the previously chosen variable and proceeding in the given circular order. It is perhaps the simplest example from the class of history-based pivot rules. Our results are based on a new lower bound construction for parity games. Due to the nature of the construction we are also able to obtain an exponential lower bound for the round-robin rule applied to acyclic unique sink orientations of hypercubes (AUSOs). Furthermore these AUSOs are realizable as polytopes. We believe these are the first such results for history based rules for AUSOs, realizable or not. The paper is self-contained and requires no previous knowledge of parity games.     

Enumerating Constrained Non-crossing Minimally Rigid Frameworks

In this paper we present an algorithm for enumerating without repetitions all the non-crossing generically minimally rigid bar-and-joint frameworks under edge constraints, which we call constrained non-crossing Laman frameworks, on a given set of n points in the plane. Our algorithm is based on the reverse search paradigm of Avis and Fukuda. It generates each output graph in O(n ⁴) time and O(n) space, or, with a slightly different implementation, in O(n ³) time and O(n ²) space. In particular, we obtain that the set of all the constrained non-crossing Laman frameworks on a given point set is connected by flips which preserve the Laman property. D. Avis’s research was supported by NSERC and FQRNT grants. N. Katoh’s, M. Ohsaki’s and S.-i. Tanigawa’s research was supported by NEXT Grant-in-Aid for Scientific Research on priority areas of New Horizons in Computing. I. Streinu’s research was supported by NSF grant CCF-0430990 and NSF-DARPA CARGO CCR-0310661.     

A note on some computationally difficult set covering problems

Fulkerson et al. have given two examples of set covering problems that are empirically difficult to solve. They arise from Steiner triple systems and the larger problem, which has a constraint matrix of size 330 × 45 has only recently been solved. In this note, we show that the Steiner triple systems do indeed give rise to a series of problems that are probably hard to solve by implicit enumeration. The main result is that for ann variable problem, branch and bound algorithms using a linear programming relaxation, and/or elimination by dominance require the examination of a super-polynomial number of partial solutionsThis paper was written while the author was a CORE Fellow at the Université de Louvain, Louvain-la-Neuve, Belgium.     

Development of polymer-modified magnetic nanoparticles and quantum dots for Escherichia coli binding test

A rapid binding test has been developed for the detection of bacteria using polymer-modified magnetic nanoparticles. Polydopamine (PDA) can effectively act as a sorbent even in water solution, and a PDA coating on magnetic nanoparticles (MNPs) was therefore prepared to bind Escherichia coli (E. coli). Albeit non-selective, PDA-modified magnetic nanoparticles (MNPs@PDA) show nearly 100% efficiency in binding E. coli. If E. coli, grown in tryptic soy broth medium, is analyzed by capillary electrophoresis (CE) using phosphate buffer as the background electrolyte, two peaks are found, while a single peak is found with carbonate buffer containing 0.05% of poly(ethylene glycol). Self-polymerization of dopamine on E. coli at pH 9.5 is also feasible. The detection of E. coli is demonstrated by adding quantum dots (QDs) to form a QDs-PDA-E. coli aggregate for better CE analysis.

Diameter partitioning

We discuss the problem of partitioning a set of points into two subsets with certain conditions on the diameters of the subsets and on their cardinalities. For example, we give anO(n ² logn) algorithm to find the smallestt such that the set can be split into two equal cardinality subsets each of which has diameter at mostt. We also give an algorithm that takes two pairs of points (x, y) and (s, t) and decides whether the set can be partitioned into two subsets with the respective pairs of points as diameters.     

Enantioselective Pd‐Catalyzed Allylic Alkylation Reactions of Dihydropyrido[1,2‐a]indolone Substrates: Efficient Syntheses of (−)‐Goniomitine, (+)‐Aspidospermidine,and (−)‐Quebrachamine

The successful application of dihydropyrido[1,2‐a]indolone (DHPI) substrates in Pd‐catalyzed asymmetric allylic alkylation chemistry facilitates rapid access to multiple alkaloid frameworks in an enantioselective fashion. Strategic bromination at the indole C3 position greatly improved the allylic alkylation chemistry and enabled a highly efficient Negishi cross‐coupling downstream. The first catalytic enantioselective total synthesis of (−)‐goniomitine, along with divergent formal syntheses of (+)‐aspidospermidine and (−)‐quebrachamine, are reported herein.