Facilitating Telecommuting as a Means of Congestion Reduction, MTI Report 09-14

Walls, Safirova and Jiang (2007) note the paucity of studies that examine telecommuting among individuals across organizations and studies that compare telecommuters with non-telecommuters. This study responds to this call by gaining a deeper understanding of telecommuting patterns and adoption behavior through an examination of perceived obstacles and facilitators of telecommuting. The study involved data collection using survey methodology, focus groups, and archival data collection. Respondents include telecommuters and non-telecommuters as well as supervisors from a wide variety of organizations. The study also included collecting benchmarking data regarding telecommuting policies and practices of companies in Silicon Valley in an attempt to understand factors that impact telecommuting

Metabolic engineering of yeast for the synthesis of fatty acid and polyketide-based chemicals

Polyketides and fatty acids are of critical importance as biorenewable chemical precursors, biofuels, and pharmaceuticals. Both are synthesized via complex polyketide or fatty acid synthases, with many using acetyl-CoA and malonyl-CoA as starter and extender units. We have engineered and combined multiple pathways in the yeast Saccharomyces cerevisiae for the production of these valuable compounds and to allow the synthesis of novel variants. We have combined enzyme engineering (of the pathway and synthase enzymes), extensive metabolic pathway engineering for increased cofactor and precursor pools, and cultivation strategies to substantially increase titers and yields of a variety of products, including 6-methylsalicylic acid (6-MSA), dihydromonocolin L (DML; precursor to lovastatin), fatty acids (FAs) of varying lengths, and triacetic acid lactone (TAL). S. cerevisiae was engineered for the high-level production of TAL by overexpression of native and variant Gerbera hybrida 2-pyrone synthase (2-PS), engineering of the yeast metabolic pathways, and implementation of various cultivation strategies. These interventions increased TAL titer from 0.07 g/L to 10.5 g/L and yield from \u3c1% to 44% of theoretical yield. Recent work has modified mitochondrial transport mechanisms and implemented cofactor-based driving forces as methods to enhance polyketide synthesis. Fatty acids are also of interest as both biofuel and chemical precursors. We have introduced heterologous fatty acid synthases into S. cerevisiae to allow the synthesis of short/medium chain free fatty acids (C6C12), and have done extensive pathway engineering to increase the levels and secretion of these and long-chain free fatty acids (C16-C18) to the culture medium. Pathway engineering approaches have focused on increasing carbon flux from glucose into the fatty acid and neutral lipid forming pathways, and preventing degradation and re-activation of these fatty acids. A unique combination of gene knockouts and gene overexpression resulted in extracellular long chain FFAs at a titer of 2.2 g/L. Recent work has included enhancing resistance to C6, C8, and C10 fatty acid toxicity, novel approaches for medium chain fatty acid synthesis, and engineering of native yeast regulatory systems to increase synthesis of both polyketides and fatty acids. In the presentation, we will discuss the critical pathways engineered, and examine the synergy between successful strategies for the various fatty acid and polyketide products. We will also present our current research using novel applications of CRISPR/Cas9 to both rapidly select and combine pathway interventions to further increase synthesis an

Tunable pseudogap Kondo effect and quantum phase transitions in Aharonov-Bohm interferometers

We study two quantum dots embedded in the arms of an Aharonov-Bohm ring threaded by a magnetic flux. The system can be described by an effective one-impurity Anderson model with an energy- and flux-dependent density of states. For specific values of the flux, this density of states vanishes at the Fermi energy, yielding a controlled realization of the pseudogap Kondo effect. The conductance and transmission phase shifts reflect a nontrivial interplay between wave interference and interactions, providing clear signatures of quantum phase transitions between Kondo and non-Kondo ground states.Comment: Published versio

Signatures of quantum phase transitions in parallel quantum dots: Crossover from local-moment to underscreened spin-1 Kondo physics

We study a strongly interacting "quantum dot 1" and a weakly interacting "dot 2" connected in parallel to metallic leads. Gate voltages can drive the system between Kondo-quenched and non-Kondo free-moment phases separated by Kosterlitz-Thouless quantum phase transitions. Away from the immediate vicinity of the quantum phase transitions, the physical properties retain signatures of first-order transitions found previously to arise when dot 2 is strictly noninteracting. As interactions in dot 2 become stronger relative to the dot-lead coupling, the free moment in the non-Kondo phase evolves smoothly from an isolated spin-one-half in dot 1 to a many-body doublet arising from the incomplete Kondo compensation by the leads of a combined dot spin-one. These limits, which feature very different spin correlations between dot and lead electrons, can be distinguished by weak-bias conductance measurements performed at finite temperatures.Comment: 7 pages, 7 figures. Accepted for publication in Phys. Rev.

Transmission in double quantum dots in the Kondo regime: Quantum-critical transitions and interference effects

We study the transmission through a double quantum-dot system in the Kondo regime. An exact expression for the transmission coefficient in terms of fully interacting many-body Green's functions is obtained. By mapping the system into an effective Anderson impurity model, one can determine the transmission using numerical renormalization-group methods. The transmission exhibits signatures of the different Kondo regimes of the effective model, including an unusual Kondo phase with split peaks in the spectral function, as well as a pseudogapped regime exhibiting a quantum critical transition between Kondo and unscreened phases.Comment: 4 pages, 3 figures; Submitted to Physica E (EP2DS-17 proceedings, oral presentation), updated Ref

Zero-field Kondo splitting and quantum-critical transition in double quantum dots

Double quantum dots offer unique possibilities for the study of many-body correlations. A system containing one Kondo dot and one effectively noninteracting dot maps onto a single-impurity Anderson model with a structured (nonconstant) density of states. Numerical renormalization-group calculations show that while band filtering through the resonant dot splits the Kondo resonance, the singlet ground state is robust. The system can also be continuously tuned to create a pseudogapped density of states and access a quantum critical point separating Kondo and non-Kondo phases.Comment: 4 pages, 4 figures; Accepted for publication in Physical Review Letter