Coherent Excitation of the 6S1/2 to 5D3/2 Electric Quadrupole Transition in 138Ba+

The electric dipole-forbidden, quadrupole 6S1/2 5D3/2 transition in Ba+ near 2051 nm, with a natural linewidth of 13 mHz, is attractive for potential observation of parity non-conservation, and also as a clock transition for a barium ion optical frequency standard. This transition also offers a direct means of populating the metastable 5D3/2 state to measure the nuclear magnetic octupole moment in the odd barium isotopes. Light from a diode-pumped, solid state Tm,Ho:YLF laser operating at 2051 nm is used to coherently drive this transition between resolved Zeeman levels in a single trapped 138Ba+ ion. The frequency of the laser is stabilized to a high finesse Fabry Perot cavity at 1025 nm after being frequency doubled. Rabi oscillations on this transition indicate a laser-ion coherence time of 3 ms, most likely limited by ambient magnetic field fluctuations.Comment: 5 pages, 5 figure

A Context-based Approach to Robot-human Interaction

AbstractCARIL (Context-Augmented Robotic Interaction Layer) is a human-robot interaction system that leverages cognitive representations of shared context as a basis for a fundamentally new approach to human-robotic interaction. CARIL gives a robot a human-like representation of context and an ability to reason about context in order to adapt its behavior to that of the humans around it. This capability is “action compliance.” A prototype CARIL implementation focuses on a fundamental form of action compliance called non-interference -- “not being underfoot or in a human's way”. Non-interference is key for the safety of human-co-workers, and is also foundational to more complex interactive and teamwork skills. CARIL is tested via simulation in a space-exploration use-case. The live CARIL prototype directs a single simulated robot in a simulated space station where four simulated astronauts are engaging in a variety of tightly-scheduled work activities. The robot is scheduled to perform background tasks away from the astronauts, but must quickly adapt and not be underfoot as astronaut activities diverge from plan and encroach on the robot's space. The robot, driven by CARIL, demonstrates non-interference action compliance in three benchmarks situations, demonstrating the viability of the CARIL technology and concept

Discrete phase space based on finite fields

The original Wigner function provides a way of representing in phase space the quantum states of systems with continuous degrees of freedom. Wigner functions have also been developed for discrete quantum systems, one popular version being defined on a 2N x 2N discrete phase space for a system with N orthogonal states. Here we investigate an alternative class of discrete Wigner functions, in which the field of real numbers that labels the axes of continuous phase space is replaced by a finite field having N elements. There exists such a field if and only if N is a power of a prime; so our formulation can be applied directly only to systems for which the state-space dimension takes such a value. Though this condition may seem limiting, we note that any quantum computer based on qubits meets the condition and can thus be accommodated within our scheme. The geometry of our N x N phase space also leads naturally to a method of constructing a complete set of N+1 mutually unbiased bases for the state space.Comment: 60 pages; minor corrections and additional references in v2 and v3; improved historical introduction in v4; references to quantum error correction in v5; v6 corrects the value quoted for the number of similarity classes for N=

Heterogeneity in Surface Sensing Suggests a Division of Labor in Pseudomonas aeruginosa Populations

The second messenger signaling molecule cyclic diguanylate monophosphate (c-di-GMP) drives the transition between planktonic and biofilm growth in many bacterial species. Pseudomonas aeruginosa has two surface sensing systems that produce c-di-GMP in response to surface adherence. Current thinking in the field is that once cells attach to a surface, they uniformly respond by producing c-di-GMP. Here, we describe how the Wsp system generates heterogeneity in surface sensing, resulting in two physiologically distinct subpopulations of cells. One subpopulation has elevated c-di-GMP and produces biofilm matrix, serving as the founders of initial microcolonies. The other subpopulation has low c-di-GMP and engages in surface motility, allowing for exploration of the surface. We also show that this heterogeneity strongly correlates to surface behavior for descendent cells. Together, our results suggest that after surface attachment, P. aeruginosa engages in a division of labor that persists across generations, accelerating early biofilm formation and surface exploration

Methionine synthase interreplacement in diatom cultures and communities : implications for the persistence of B12 use by eukaryotic phytoplankton

Author Posting. © Association for the Sciences of Limnology and Oceanography, 2013. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 58 (2013): 1431–1450, doi:10.4319/lo.2013.58.4.1431.Three proteins related to vitamin B12 metabolism in diatoms were quantified via selected reaction monitoring mass spectrometry: B12-dependent and B12-independent methionine synthase (MetH, MetE) and a B12 acquisition protein (CBA1). B12-mediated interreplacement of MetE and MetH metalloenzymes was observed in Phaeodactylum tricornutum where MetH abundance was highest (0.06 fmol µg−1 protein) under high B12 and MetE abundance increased to 3.25 fmol µg−1 protein under low B12 availability. Maximal MetE abundance was 60-fold greater than MetH, consistent with the expected ∼ 50–100-fold larger turnover number for MetH. MetE expression resulted in 30-fold increase in nitrogen and 40-fold increase in zinc allocated to methionine synthase activity under low B12. CBA1 abundance was 6-fold higher under low-B12 conditions and increased upon B12 resupply to starved cultures. While biochemical pathways that supplant B12 requirements exist and are utilized by organisms such as land plants, B12 use persists in eukaryotic phytoplankton. This study suggests that retention of B12 utilization by phytoplankton results in resource conservation under conditions of high B12 availability. MetE and MetH abundances were also measured in diatom communities from McMurdo Sound, verifying that both these proteins are expressed in natural communities. These protein measurements are consistent with previous studies suggesting that B12 availability influences Antarctic primary productivity. This study illuminates controls on expression of B12-related proteins, quantitatively assesses the metabolic consequences of B12 deprivation, and demonstrates that mass spectrometry–based protein measurements yield insight into the functioning of marine microbial communities.This work was supported by National Science Foundation (NSF) Antarctic Sciences awards 0732665, 1103503, and 0732822; NSF Division of Ocean Science awards 0752291, 0928414, and 1031271; The Gordon and Betty Moore Foundation; Center for Microbial Oceanography Research and Education; an NSF Graduate Research Fellowship (2007037200); and an Environmental Protection Agency Science To Achieve Results (EPA-STAR) Fellowship to E.M.B. (F6E720324)