2,156 research outputs found
Directed evolution of Vibrio fischeri LuxR for improved response to butanoyl-homoserine lactone
LuxR is the 3-oxohexanoyl-homoserine lactone (3OC6HSL) dependent transcriptional activator of the prototypical acyl-homoserine lactone (AHL) quorum sensing system of Vibrio fischeri. Wild-type LuxR exhibits no response to butanoyl-HSL (C4HSL) in quantitative bioassays at concentrations of up to 1 µM; a previously described LuxR variant (LuxR-G2E) exhibits a broadened response to diverse AHLs, including pentanoyl-HSL (C5HSL), but not to C4HSL. Here, two rounds of directed evolution of LuxR-G2E generated variants of LuxR that responded to C4HSL at concentrations as low as 10 nM. One variant, LuxR-G4E, had only one change, I45F, relative to the parent LuxR-G2E, which itself differs from wild-type at three residues. Dissection of the four mutations within LuxR-G4E demonstrated that at least three of these changes were simultaneously required to achieve any measurable C4HSL response. The four changes improved both sensitivity and specificity towards C4HSL relative to any of the other 14 possible combinations of those residues. These data confirm that LuxR is evolutionarily pliable and suggest that LuxR is not intrinsically asymmetric in its response to quorum sensing signals with different acyl-side chain lengths
Nanoscale Torsional Optomechanics
Optomechanical transduction is demonstrated for nanoscale torsional
resonators evanescently coupled to optical microdisk whispering gallery mode
resonators. The on-chip, integrated devices are measured using a fully
fiber-based system, including a tapered and dimpled optical fiber probe. With a
thermomechanically calibrated optomechanical noise floor down to 7 fm/sqrt(Hz),
these devices open the door for a wide range of physical measurements involving
extremely small torques, as little as 4x10^-20 N*m.Comment: 4 pages, 4 figures - Accepted to APL Oct 22nd, 2012. To appear in
February 4th issue - as cover articl
Concentração de N na decomposição foliar de espécies lenhosas em sistemas agroflorestais (alley cropping) em Morretes, PR.
Nos sistemas de alley cropping a decomposição e subseqüente liberação de nutrientes das folhas e ramos podem ter importante influência na matéria orgânica e na reserva de nutrientes do solo. Coleman e Crossley (1996) resumem que, em geral, a decomposição é resultado da ação da biota em substratos com diferentes composições, em contraste com o clima.1 CD-ROM
Phase Changes in Ni-Ti Under Laser Shock Loading
Near-equiatomic Ni-Ti, known for its shape memory behavior, can decompose to martensitic phases and/or second phase compounds. This phase competition is investigated in NixTi100-x (494Ti3 but no martensite in the AQ state, consistent with resistivity and dilatometry results which showed no hysteresis indicative of first order phase changes over 1.9 K4Ti3 amounts (present in the AQ state) did change upon loading, indicating the importance of shock-induced heating. A thermodynamically complete equation of state (EOS) for NiTi in its B2 (CsCl) structure was generated by ab initio quantum mechanical calculations. This was tested by performing laser-launched flyer experiments, which showed consistency with the theoretical EOS, validating its use in the prediction of dynamic loading histories in the samples during direct drive loading
Local models for intersecting brane worlds
We describe the construction of configurations of D6-branes wrapped on
compact 3-cycles intersecting at points in non-compact Calabi-Yau threefolds.
Such constructions provide local models of intersecting brane worlds, and
describe sectors of four-dimensional gauge theories with chiral fermions. We
present several classes of non-compact manifolds with compact 3-cycles
intersecting at points, and discuss the rules required for model building with
wrapped D6-branes. The rules to build 3-cycles are simple, and allow easy
computation of chiral spectra, RR tadpoles and the amount of preserved
supersymmetry. We present several explicit examples of these constructions,
some of which have Standard Model like gauge group and three quark-lepton
generations. In some cases, mirror symmetry relates the models to other
constructions used in phenomenological D-brane model building, like D-branes at
singularities. Some simple N=1 supersymmetric configurations may lead to
relatively tractable G_2 manifolds upon lift to M-theory, which would be
non-compact but nevertheless yield four-dimensional chiral gauge field
theories.Comment: 52 pages, latex, 24 enclosed eps figures; v2. typo correcte
The Effects of Postfire Salvage Logging on Aquatic Ecosystems in the American West
Recent changes in the forest policies, regulations, and laws affecting public lands encourage postfire salvage logging, an activity that all too often delays or prevents recovery. In contrast, the 10 recommendations proposed here can improve the condition of watersheds and aquatic ecosystems
- …