Particle composition measurements during CLOUD7

The chemical composition of >8 nm diameter aerosol was measured using the Timeof-Flight Thermal Desorption Chemical Ionization Mass Spectrometer (TOF-TDCIMS) during CLOUD7 particle nucleation experiments in Fall 2012 at the CLOUD chamber at CERN in Geneva, Switzerland. Sulfate dominated the negative ion particle spectra during all events with enough particle mass to observe, both in experiments with amine and alpha-pinene. Ammonium was also a major particle constituent during all observable events, though gaseous ammonia was present in the chamber only as a contaminant. During nucleation events following the oxidation of alpha-pinene, highly oxidized organic acids such as oxalic and oxoacetic acid were observed to be significant components of the collected aerosol

Overcoming Clonal Interference in Escherichia coli Using Genderless High Frequency Recombination Strains

Adaptive laboratory evolution (ALE) is a powerful tool for strain improvement, and has been applied successfully to improve a range of desirable phenotypes in model organisms through continuous cultivation under a selective pressure of interest. Despite its demonstrable utility, one limiting factor for the effectiveness of ALE is competition between beneficial mutants that exist contemporaneously within an evolving population. This phenomenon of clonal interference arises from the fact that the majority of microbes are obligate asexual organisms that cannot exchange DNA between cells. Mutants that arise must therefore compete for resources until the fittest mutant drives the others to extinction. The resulting loss of genetic information from the population slows the overall rate of adaptation, and decreases the amount of information that can be extracted from a given ALE experiment. To overcome these limitations, we have developed a novel in situ mating system based on the F plasmid to allow continuous DNA exchange between E. coli cells in liquid culture, allowing mutants to potentially combine their mutations into a single genetic background. The utility and limitations of an existing recombination method, genome shuffling, are also explored to demonstrate the advantages of this new method. The design and initial testing of the in situ mating system is first validated, and the system is used for a subsequent evolution experiment under osmotic stress to validate the industrial applicability of the mating system. Adaptive mutants generated in the course of these experiments are then used to test whether tolerant mutants can be formed via conjugation. Finally, additional side projects focusing on strain or population characterization tools are discussed, followed by recommendations for future work

Visualizing evolution in real-time method for strain engineering

The adaptive landscape for an industrially relevant phenotype is determined by the effects of the genetic determinants on the fitness of the microbial system. Identifying the underlying adaptive landscape for a particular phenotype of interest will greatly enhance our abilities to engineer more robust microbial strains. Visualizing evolution in real-time (VERT) is a recently developed method based on in vitro adaptive evolution that facilitates the identification of fitter mutants throughout the course of evolution. Combined with high-throughput genomic tools, VERT can greatly enhance the mapping of adaptive landscapes of industrially relevant phenotypes in microbial systems, thereby expanding our knowledge on the parameters that can be used for strain engineering

Proposal for a minimal surface code experiment

Current quantum technology is approaching the system sizes and fidelities required for quantum error correction. It is therefore important to determine exactly what is needed for proof-of-principle experiments, which will be a major step towards fault-tolerant quantum computation. Here we propose a surface code based experiment that is the smallest, both in terms of code size and circuit depth, that would allow errors to be detected and corrected for both the X and Z bases of a qubit. This requires 17 physical qubits initially prepared in a product state, on which 16 two-qubit entangling gates are applied before a final measurement of all qubits. A platform agnostic error model is applied to give some idea of the noise levels required for success. It is found that a true demonstration of quantum error correction will require fidelities for the preparation and measurement of qubits and the entangling gates to be above 99%

Energetic proton spectra in the 11 June 1991 solar flare

The June 11, 1991 gamma-ray flare seen by the Compton Gamma-ray Observatory (CGRO) displays several features that make it a dynamic and rich event. It is a member of a class of long duration gamma-ray events with both 2.223 MeV and greater than 8 MeV emission for hours after the impulsive phase. It also contains an inter-phase between the impulsive and extended phases that presents a challenge to the standard gamma-ray line (GRL) flare picture. This phase has strong 2.223 MeV emission and relatively weak 4.44 MeV emission indicative of a very hard parent proton spectrum. However, this would indicate emission greater than 8 MeV, which is absent from this period. We present the application of new spectroscopy techniques to this phase of the flare in order to present a reasonable explanation for this seemly inconsistent picture

Atypicalities and Apartment Rent Concessions

This paper examines the use and value of rental concession using a 1988 sample of apartment rents in the Greensboro/High Point/Winston-Salem (North Carolina) MSA. The first section develops an approach to the problem and the second section estimates a logit model to predict the use of concessions as a pricing strategy based on characteristics of the apartment. The third section employs a hedonic pricing model to measure the average value of rental concessions in the Greensboro market. The final section summarizes relevant findings.

Co_3O_4 Nanoparticle Water-Oxidation Catalysts Made by Pulsed-Laser Ablation in Liquids

Surfactant-free, size- and composition-controlled, unsupported, <5-nm, quantum-confined cobalt oxide nanoparticles with high electrocatalytic oxygen-evolution activity were synthesized by pulsed laser ablation in liquids. These crystalline Co_3O_4 nanoparticles have a turnover frequency per cobalt surface site among the highest ever reported for Co_3O_4 nanoparticle oxygen evolution catalysts in base and overpotentials competitive with the best electrodeposited cobalt oxides, with the advantage that they are suitable for mechanical deposition on photoanode materials and incorporation in integrated solar water-splitting devices