15,340 research outputs found
Flexible Integration of Alternative Energy Sources for Autonomous Sensing
Recent developments in energy harvesting and autonomous sensing mean that it is now possible to power sensors solely from energy harvested from the environment. Clearly this is dependent on sufficient environmental energy being present. The range of feasible environments for operation can be extended by combining multiple energy sources on a sensor node. The effective monitoring of their energy resources is also important to deliver sustained and effective operation. This paper outlines the issues concerned with combining and managing multiple energy sources on sensor nodes. This problem is approached from both a hardware and embedded software viewpoint. A complete system is described in which energy is harvested from both light and vibration, stored in a common energy store, and interrogated and managed by the node
Implications of Alternative Emission Trading Plans: Experimental Evidence
Two approaches to emissions trading are cap-and-trade, in which an aggregate cap on emissions is distributed in the form of emission allowances and baseline-and-credit, in which firms earn emission reduction credits for emissions below their baselines. Theoretical considerations suggest the long-run equilibria of the two plans will differ if baselines are proportional to output, because a variable baseline is equivalent to an output subsidy. To test this prediction we have developed a computerized environment in which subjects representing firms can adjust both their emission rates (per unit output) and capacity levels. Subjects buy or sell emission rights (allowances or credits) in a sealed bid call auction. The demand for output is simulated. All decisions are tracked through a double-entry bookkeeping system. This environment is to be used to compare short and long run responses to the alternative trading methods. Initial experiments in this environment will alternately hold emission rate and capacity choice constant. We report on six experimental sessions with variable emissions rates but fixed capacity and two pilot sessions with variable capacity but fixed emission rates.
Direct processing of structural thermoplastic composites using rapid isothermal stamp forming
A novel rapid isothermal stamp forming process is proposed which enables the rapid manufacture of structural thermoplastic composite laminate parts directly from multilayer hybrid fabrics comprising stitched unidirectional carbon fibre-thermoplastic polymer veil. The process employs rapid-response variothermal tooling, allowing macro-scale (fabric forming/draping) and micro-scale (fibre wetting/laminate consolidation) composite material transformation processes to occur isothermally above the constituent polymer matrix melt temperature (Tm), thus manufacturing a composite component directly from a hybrid dry fabric in a single press cycle in a relatively short overall cycle time. The proposed rapid isothermal stamp forming (RISF) concept is presented, and details of the process are given along with some considerations made throughout the formulation of the process. As a result of the RISF process development work, candidate manufacturing parameters were derived, delivering parts that exhibit acceptable composite laminate microstructure and mechanical performance within a press station cycle time of 330 s
Han's Bijection via Permutation Codes
We show that Han's bijection when restricted to permutations can be carried
out in terms of the cyclic major code and the cyclic inversion code. In other
words, it maps a permutation with a cyclic major code to a permutation with a cyclic inversion code . We also show that the fixed points of Han's map can be characterized by
the strong fixed points of Foata's second fundamental transformation. The
notion of strong fixed points is related to partial Foata maps introduced by
Bj\"orner and Wachs.Comment: 12 pages, to appear in European J. Combi
Fluorescence-based incision assay for human XPF-ERCC1 activity identifies important elements of DNA junction recognition
The structure-specific endonuclease activity of the human XPFāERCC1 complex is essential for a number of DNA processing mechanisms that help to maintain genomic integrity. XPFāERCC1 cleaves DNA structures such as stemāloops, bubbles or flaps in one strand of a duplex where there is at least one downstream single strand. Here, we define the minimal substrate requirements for cleavage of stemāloop substrates allowing us to develop a real-time fluorescence-based assay to measure endonuclease activity. Using this assay, we show that changes in the sequence of the duplex upstream of the incision site results in up to 100-fold variation in cleavage rate of a stem-loop substrate by XPF-ERCC1. XPFāERCC1 has a preference for cleaving the phosphodiester bond positioned on the 3ā²-side of a T or a U, which is flanked by an upstream T or U suggesting that a T/U pocket may exist within the catalytic domain. In addition to an endonuclease domain and tandem helixāhairpināhelix domains, XPF has a divergent and inactive DEAH helicase-like domain (HLD). We show that deletion of HLD eliminates endonuclease activity and demonstrate that purified recombinant XPFāHLD shows a preference for binding stemāloop structures over single strand or duplex alone, suggesting a role for the HLD in initial structure recognition. Together our data describe features of XPFāERCC1 and an accepted model substrate that are important for recognition and efficient incision activity
A Solution to the Galactic Foreground Problem for LISA
Low frequency gravitational wave detectors, such as the Laser Interferometer
Space Antenna (LISA), will have to contend with large foregrounds produced by
millions of compact galactic binaries in our galaxy. While these galactic
signals are interesting in their own right, the unresolved component can
obscure other sources. The science yield for the LISA mission can be improved
if the brighter and more isolated foreground sources can be identified and
regressed from the data. Since the signals overlap with one another we are
faced with a ``cocktail party'' problem of picking out individual conversations
in a crowded room. Here we present and implement an end-to-end solution to the
galactic foreground problem that is able to resolve tens of thousands of
sources from across the LISA band. Our algorithm employs a variant of the
Markov Chain Monte Carlo (MCMC) method, which we call the Blocked Annealed
Metropolis-Hastings (BAM) algorithm. Following a description of the algorithm
and its implementation, we give several examples ranging from searches for a
single source to searches for hundreds of overlapping sources. Our examples
include data sets from the first round of Mock LISA Data Challenges.Comment: 19 pages, 27 figure
Ringing the eigenmodes from compact manifolds
We present a method for finding the eigenmodes of the Laplace operator acting
on any compact manifold. The procedure can be used to simulate cosmic microwave
background fluctuations in multi-connected cosmological models. Other
applications include studies of chaotic mixing and quantum chaos.Comment: 11 pages, 8 figures, IOP format. To be published in the proceedings
of the Cleveland Cosmology and Topology Workshop 17-19 Oct 1997. Submitted to
Class. Quant. Gra
Complete Set of Homogeneous Isotropic Analytic Solutions in Scalar-Tensor Cosmology with Radiation and Curvature
We study a model of a scalar field minimally coupled to gravity, with a
specific potential energy for the scalar field, and include curvature and
radiation as two additional parameters. Our goal is to obtain analytically the
complete set of configurations of a homogeneous and isotropic universe as a
function of time. This leads to a geodesically complete description of the
universe, including the passage through the cosmological singularities, at the
classical level. We give all the solutions analytically without any
restrictions on the parameter space of the model or initial values of the
fields. We find that for generic solutions the universe goes through a singular
(zero-size) bounce by entering a period of antigravity at each big crunch and
exiting from it at the following big bang. This happens cyclically again and
again without violating the null energy condition. There is a special subset of
geodesically complete non-generic solutions which perform zero-size bounces
without ever entering the antigravity regime in all cycles. For these, initial
values of the fields are synchronized and quantized but the parameters of the
model are not restricted. There is also a subset of spatial curvature-induced
solutions that have finite-size bounces in the gravity regime and never enter
the antigravity phase. These exist only within a small continuous domain of
parameter space without fine tuning initial conditions. To obtain these
results, we identified 25 regions of a 6-parameter space in which the complete
set of analytic solutions are explicitly obtained.Comment: 38 pages, 29 figure
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