1,913 research outputs found
Tapping the Unused Potential of Photosynthesis with a Heterologous Electron Sink
Increasing the efficiency of the conversion of light energy to products by photosynthesis represents a grand challenge in biotechnology. Photosynthesis is limited by the carbon-fixing enzyme Rubisco resulting in much of the absorbed energy being wasted as heat or fluorescence or lost as excess reductant via alternative electron dissipation pathways. To harness this wasted reductant, we engineered the model cyanobacterium Synechococcus PCC 7002 to express the mammalian cytochrome P450 CYP1A1 to serve as an artificial electron sink for excess electrons derived from light-catalyzed water-splitting. This improved photosynthetic efficiency by increasing the maximum rate of photosynthetic electron flow by 31.3%. A simple fluorescent assay for CYP1A1 activity demonstrated that the P450 was functional in the absence of its native reductase, that activity was light-dependent and scaled with irradiance. We show for the first time in live cells that photosynthetic reductant can be redirected to power a heterologous cytochrome P450. Furthermore, Synechococcus PCC 7002 expressing CYP1A1 degraded the herbicide atrazine, which is a widespread environmental pollutant
The diffusion of IP telephony and vendors' commercialisation strategies
This is a post-peer-review, pre-copyedit version of an article published in the Journal of Information Technology. The definitive publisher-authenticated version is available at the link below.The Internet telephony (IP telephony) has been presented as a technology that can replace existing fixed-line services and disrupt the telecommunications industry by offering new low-priced services. This study investigates the diffusion of IP telephony in Denmark by focusing on vendors’ commercialisation strategies. The theory of disruptive innovation is introduced to investigate vendors’ perceptions about IP telephony and explore their strategies that affect the diffusion process in the residential market. The analysis is based on interview data collected from the key market players. The study's findings suggest that IP telephony is treated as a sustaining innovation that goes beyond the typical voice transmission and enables provision of advanced services such as video telephony
ATLASGAL - environments of 6.7 GHz methanol masers
Using the 870 micron APEX Telescope large area survey of the Galaxy, we have identified 577 submillimetre continuum sources with masers from the methanol multibeam survey in the region 280deg lt ell lt 20deg; |b| lt 1deg.5 94 per cent of methanol masers in the region are associated with submillimetre dust emission. We estimate masses for tilde450 maser-associated sources and find that methanol masers are preferentially associated with massive clumps. These clumps are centrally condensed, with envelope structures that appear to be scale-free, the mean maser position being offset from the peak column density by 0 plusmn 4 arcsec. Assuming a Kroupa initial mass function and a star formation efficiency of tilde30 per cent, we find that over two-thirds of the clumps are likely to form clusters with masses gt20 M. Furthermore, almost all clumps satisfy the empirical mass-size criterion for massive star formation. Bolometric luminosities taken from the literature for tilde100 clumps range between tilde100 and 10 L. This confirms the link between methanol masers and massive young stars for 90 per cent of our sample. The Galactic distribution of sources suggests that the star formation efficiency is significantly reduced in the Galactic Centre region, compared to the rest of the survey area, where it is broadly constant, and shows a significant drop in the massive star formation rate density in the outer Galaxy. We find no enhancement in source counts towards the southern Scutum-Centaurus arm tangent at ell tilde 315deg, which suggests that this arm is not actively forming stars.Peer reviewe
Rods Near Curved Surfaces and in Curved Boxes
We consider an ideal gas of infinitely rigid rods near a perfectly repulsive
wall, and show that the interfacial tension of a surface with rods on one side
is lower when the surface bends towards the rods. Surprisingly we find that
rods on both sides of surfaces also lower the energy when the surface bends. We
compute the partition functions of rods confined to spherical and cylindrical
open shells, and conclude that spherical shells repel rods, whereas cylindrical
shells (for thickness of the shell on the order of the rod-length) attract
them. The role of flexibility is investigated by considering chains composed of
two rigid segments.Comment: 39 pages including figures and tables. 12 eps figures. LaTeX with
REVTe
Loop-Generated Bounds on Changes to the Graviton Dispersion Relation
We identify the effective theory appropriate to the propagation of massless
bulk fields in brane-world scenarios, to show that the dominant low-energy
effect of asymmetric warping in the bulk is to modify the dispersion relation
of the effective 4-dimensional modes. We show how such changes to the graviton
dispersion relation may be bounded through the effects they imply, through
loops, for the propagation of standard model particles. We compute these bounds
and show that they provide, in some cases, the strongest constraints on
nonstandard gravitational dispersions. The bounds obtained in this way are the
strongest for the fewest extra dimensions and when the extra-dimensional Planck
mass is the smallest. Although the best bounds come for warped 5-D scenarios,
for which the 5D Planck Mass is O(TeV), even in 4 dimensions the graviton loop
can lead to a bound on the graviton speed which is comparable with other
constraints.Comment: 18 pages, LaTeX, 4 figures, uses revte
Massive IIA flux compactifications and U-dualities
We attempt to find a rigorous formulation for the massive type IIA
orientifold compactifications of string theory introduced in hep-th/0505160. An
approximate double T-duality converts this background into IIA string theory on
a twisted torus, but various arguments indicate that the back reaction of the
orientifold on this geometry is large. In particular, an AdS calculation of the
entropy suggests a scaling appropriate for N M2-branes, in a certain limit of
the compactification, though not the one studied in hep-th/0505160. The
M-theory lift of this specific regime is not 4 dimensional. We suggest that the
generic limit of the background corresponds to a situation analogous to
F-theory, where the string coupling is small in some regions of a compact
geometry, and large in others, so that neither a long wavelength 11D SUGRA
expansion, nor a world sheet expansion exists for these compactifications. We
end with a speculation on the nature of the generic compactification.Comment: JHEP3 LaTeX - 34 pages - 3 figures; v2: Added references; v3: mistake
in entropy scaling corrected, major changes in conclusions; v4: changed
claims about original DeWolfe et al. setup, JHEP versio
ATLASGAL - towards a complete sample of massive star forming clumps
By matching infrared-selected, massive young stellar objects (MYSOs) and compact HII regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ~1000 embedded young massive stars between 280{ring operator} <lPeer reviewedFinal Accepted Versio
Twisted K-Theory from Monodromies
RR fluxes representing different cohomology classes may correspond to the
same twisted K-theory class. We argue that such fluxes are related by
monodromies, generalizing and sometimes T-dual to the familiar monodromies of a
D7-brane. A generalized theta angle is also transformed, but changes by a
multiple of 2pi. As an application, NS5-brane monodromies modify the twisted
K-theory classification of fluxes. Furthermore, in the noncompact case K-theory
does not distinguish flux configurations in which dG is nontrivial in compactly
supported cohomology. Such fluxes are realized as the decay products of
unstable D-branes that wrapped nontrivial cycles. This is interpreted using the
E8 bundle formalism.Comment: 24 Pages, 6 eps figure
Spectral networks
We introduce new geometric objects called spectral networks. Spectral
networks are networks of trajectories on Riemann surfaces obeying certain local
rules. Spectral networks arise naturally in four-dimensional N=2 theories
coupled to surface defects, particularly the theories of class S. In these
theories spectral networks provide a useful tool for the computation of BPS
degeneracies: the network directly determines the degeneracies of solitons
living on the surface defect, which in turn determine the degeneracies for
particles living in the 4d bulk. Spectral networks also lead to a new map
between flat GL(K,C) connections on a two-dimensional surface C and flat
abelian connections on an appropriate branched cover Sigma of C. This
construction produces natural coordinate systems on moduli spaces of flat
GL(K,C) connections on C, which we conjecture are cluster coordinate systems.Comment: 87 pages, 48 figures; v2: typos, correction to general rule for signs
of BPS count
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