3,838 research outputs found
Filtered screens and augmented Teichm\"uller space
We study a new bordification of the decorated Teichm\"uller space for a
multiply punctured surface F by a space of filtered screens on the surface that
arises from a natural elaboration of earlier work of McShane-Penner. We
identify necessary and sufficient conditions for paths in this space of
filtered screens to yield short curves having vanishing length in the
underlying surface F. As a result, an appropriate quotient of this space of
filtered screens on F yields a decorated augmented Teichm\"uller space which is
shown to admit a CW decomposition that naturally projects to the augmented
Teichm\"uller space by forgetting decorations and whose strata are indexed by a
new object termed partially oriented stratum graphs.Comment: Final version to appear in Geometriae Dedicat
Prediction of the number of cloud droplets in the ECHAM GCM
In this paper a prognostic equation for the number of cloud droplets (CDNC) is introduced into the ECHAM general circulation model. The initial CDNC is based on the mechanistic model of Chuang and Penner [1995], providing a more realistical prediction of CDNC than the empirical method previously used. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and a shape parameter, which takes the aerosol composition and size distribution into account. The total number of aerosol particles is obtained as the sum of marine sulfate aerosols produced from dimethyl sulfide, hydrophylic organic and black carbon, submicron dust, and sea-salt aerosols. Anthropogenic sulfate aerosols only add mass to the preexisting aerosols but do not form new particles. The simulated annual mean liquid water path, column CDNC, and effective radius agree well with observations, as does the frequency distributions of column CDNC for clouds over oceans and the variations of cloud optical depth with effective radius
Optical Methods for the Determination of Combustion Temperatures
A brief survey is presented of optical methods for the determination of temperatures which can be used in rocket engines. The data are presented in outlines and include an outline of basic principles involved in application of a given technique, a sketch of the experimental arrangement, and key references which should he consulted for further details
Emissivity for CO_2 at Elevated Pressures
Total absorptivity measurements have been carried out at room temperature as a function of partial pressure of CO_2 and of total pressure using nitrogen as pressurizing gas
Interference effects during burning in air for stationary n-heptane, ethyl alcohol, and methyl alcohol droplets
Experiments have been conducted for the determination
of the evaporation constant and flame shapes of two and
of five closely spaced droplets burning in air. Droplets of
approximately the same and of different diameters were
used at various distances between the droplet centers.
The apparent flame shape, which was observed only for n-heptane droplets, changes very little during burning.
The square of the droplet diameter decreases linearly with
time for fixed spacing between droplet centers, at least
within the experimental limits of accuracy. In general,
the average evaporation constant for two droplets, K',
must be assumed either to vary continuously during burning
or else to be a function of average initial drop diameter,
D^0. The change of K' with time corresponds to the second
derivative in plots of the square of the diameter vs. time.
These second derivatives are not defined in our work because
of unavoidable scatter of the experimental data. Attempts at understanding the observed results by considering
published theories for single droplets, as well as groupings obtained from dimensional analysis, have been
unsuccessful. It appears that the diffusion model for
the heterogeneous burning of single fuel droplets will require serious revision and extension before the burning of
droplets arrays and sprays can be understood quantitatively.
Furthermore, the effective value of K' for a spray
probably depends not only on the fuel-oxidizer system but
also on the injection pattern. For this reason additional
studies had best be carried out under conditions corresponding to those existing in service models
Carbon Free Boston: Offsets Technical Report
Part of a series of reports that includes:
Carbon Free Boston: Summary Report;
Carbon Free Boston: Social Equity Report;
Carbon Free Boston: Technical Summary;
Carbon Free Boston: Buildings Technical Report;
Carbon Free Boston: Transportation Technical Report;
Carbon Free Boston: Waste Technical Report;
Carbon Free Boston: Energy Technical Report;
Available at http://sites.bu.edu/cfb/OVERVIEW:
The U.S. Environmental Protection Agency defines offsets as a specific activity or set of activities
intended to reduce GHG emissions, increase the storage of carbon, or enhance GHG removals from the
atmosphere [1]. From a city perspective, they provide a mechanism to negate residual GHG emissions—
those the city is unable to reduce directly—by supporting projects that avoid or sequester them outside
of the city’s reporting boundary.
Offsetting GHG emissions is a controversial topic for cities, as the co-benefits of the investment are
typically not realized locally. For this reason, offsetting emissions is considered a last resort, a strategy
option available when the city has exhausted all others. However, offsets are likely to be a necessity to
achieve carbon neutrality by 2050 and promote emissions reductions in the near term. While public and
private sector partners pursue the more complex systems transformation, cities can utilize offsets to
support short-term and relatively cost-effective reductions in emissions. Offsets can be a relatively
simple, certain, and high-impact way to support the transition to a low-carbon world.
This report focuses on carbon offset certificates, more often referred to as offsets. Each offset
represents a metric ton of verified carbon dioxide (CO2) or equivalent emissions that is reduced,
avoided, or permanently removed from the atmosphere (“sequestered”) through an action taken by the
creator of the offset. The certificates can be traded and retiring (that is, not re-selling) offsets can be a
useful component of an overall voluntary emissions reduction strategy, alongside activities to lower an
organization’s direct and indirect emissions. In the Global Protocol for Community-Scale Greenhouse Gas
Emissions Inventories (GPC), the GHG accounting system used by the City of Boston, any carbon offset
certificates that the City has can be deducted from the City’s total GHG emissions.http://sites.bu.edu/cfb/files/2019/06/CFB_Offsets_Technical_Report_051619.pdfPublished versio
Carbon Free Boston: Energy Technical Report
Part of a series of reports that includes:
Carbon Free Boston: Summary Report;
Carbon Free Boston: Social Equity Report;
Carbon Free Boston: Technical Summary;
Carbon Free Boston: Buildings Technical Report;
Carbon Free Boston: Transportation Technical Report;
Carbon Free Boston: Waste Technical Report;
Carbon Free Boston: Offsets Technical Report;
Available at http://sites.bu.edu/cfb/INTRODUCTION:
The adoption of clean energy in Boston’s buildings and transportation systems will produce sweeping
changes in the quantity and composition of the city’s demand for fuel and electricity. The demand for
electricity is expected to increase by 2050, while the demand for petroleum-based liquid fuels and
natural gas within the city is projected to decline significantly. The city must meet future energy demand
with clean energy sources in order to meet its carbon mitigation targets. That clean energy must be
procured in a way that supports the City’s goals for economic development, social equity, environmental
sustainability, and overall quality of life. This chapter examines the strategies to accomplish these goals.
Improved energy efficiency, district energy, and in-boundary generation of clean energy (rooftop PV)
will reduce net electric power and natural gas demand substantially, but these measures will not
eliminate the need for electricity and gas (or its replacement fuel) delivered into Boston. Broadly
speaking, to achieve carbon neutrality by 2050, the city must therefore (1) reduce its use of fossil fuels
to heat and cool buildings through cost-effective energy efficiency measures and electrification of
building thermal services where feasible; and (2) over time, increase the amount of carbon-free
electricity delivered to the city. Reducing energy demand though cost effective energy conservation
measures will be necessary to reduce the challenges associated with expanding the electricity delivery
system and sustainably sourcing renewable fuels.Published versio
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