696 research outputs found
Compile-Time Optimisation of Store Usage in Lazy Functional Programs
Functional languages offer a number of advantages over their imperative counterparts. However,
a substantial amount of the time spent on processing functional programs is due to
the large amount of storage management which must be performed. Two apparent reasons
for this are that the programmer is prevented from including explicit storage management
operations in programs which have a purely functional semantics, and that more readable
programs are often far from optimal in their use of storage. Correspondingly, two alternative
approaches to the optimisation of store usage at compile-time are presented in this thesis.
The first approach is called compile-time garbage collection. This approach involves determining
at compile-time which cells are no longer required for the evaluation of a program,
and making these cells available for further use. This overcomes the problem of a programmer
not being able to indicate explicitly that a store cell can be made available for further use.
Three different methods for performing compile-time garbage collection are presented in this
thesis; compile-time garbage marking, explicit deallocation and destructive allocation. Of
these three methods, it is found that destructive allocation is the only method which is of
practical use.
The second approach to the optimisation of store usage is called compile-time garbage
avoidance. This approach involves transforming programs into semantically equivalent programs
which produce less garbage at compile-time. This attempts to overcome the problem
of more readable programs being far from optimal in their use of storage. In this thesis, it is
shown how to guarantee that the process of compile-time garbage avoidance will terminate.
Both of the described approaches to the optimisation of store usage make use of the
information obtained by usage counting analysis. This involves counting the number of times
each value in a program is used. In this thesis, a reference semantics is defined against which
the correctness of usage counting analyses can be proved. A usage counting analysis is then
defined and proved to be correct with respect to this reference semantics. The information
obtained by this analysis is used to annotate programs for compile-time garbage collection,
and to guide the transformation when compile-time garbage avoidance is performed.
It is found that compile-time garbage avoidance produces greater increases in efficiency
than compile-time garbage collection, but much of the garbage which can be collected by
compile-time garbage collection cannot be avoided at compile-time. The two approaches are
therefore complementary, and the expressions resulting from compile-time garbage avoidance
transformations can be annotated for compile-time garbage collection to further optimise the
use of storage
Proletarian doctors?: the Colegio Médico de Chile under socialism and dictatorship, 1970-1980
Abstract available : p.xv-xvi
KH 15D: A Spectroscopic Binary
We present the results of a high-resolution spectroscopic monitoring program
of the eclipsing pre-main-sequence star KH 15D that reveal it to be a
single-line spectroscopic binary. We find that the best-fit Keplerian model has
a period P = 48.38 days, which is nearly identical to the photometric period.
Thus, we find the best explanation for the periodic dimming of KH 15D is that
the binary motion carries the currently visible star alternately above and
below the edge of an obscuring cloud. The data are consistent with the models
involving an inclined circumstellar disk, as recently proposed by Winn et al.
(2004) and Chiang & Murray-Clay (2004). We show that the mass ratio expected
from models of PMS evolution, together with the mass constraints for the
visible star, restrict the orbital eccentricity to 0.68 < e < 0.80 and the mass
function to 0.125 < Fm < 0.5 Msun.Comment: 8 pages, 4 figures, 3 tables, accepted for publication in September
AJ. Discussion of rotational velocity deferred to Hamilton, et al. (2004, in
prep). Previously reported vsini value in error; Replaced Table 3 with new
Figure 3; Added new Table 2 showing individual radial velocities w.r.t. each
reference star; Fixed typo in Figure
Recommended from our members
March 1965
Turf and Lawn Grass Association
Better turf through research and Educatio
Adam Smith’s Green Thumb and Malthus’ Three Horsemen: Cautionary tales from classical political economy
This essay identifies a contradiction between the flourishing interest in the environmental economics of the classical period and a lack of critical parsing of the works of its leading representatives. Its focus is the work of Adam Smith and Thomas Malthus. It offers a critical analysis of their contribution to environmental thought and surveys the work of their contemporary devotees. It scrutinizes Smith's contribution to what Karl Polanyi termed the "economistic fallacy," as well as his defenses of class hierarchy, the "growth imperative" and consumerism. It subjects to critical appraisal Malthus's enthusiasm for private property and the market system, and his opposition to market regulation. While Malthus's principal attraction to ecological economists lies in his having allegedly broadened the scope of economics, and in his narrative of scarcity, this article shows that he, in fact, narrowed the scope of the discipline and conceptualized scarcity in a reified and pseudo-scientific way
Early Evidence of Dose-dependent Pharmacodynamic Activity Following Treatment with SY-5609, a Highly Selective and Potent Oral CDK7 Inhibitor, in Patients with Advanced Solid Tumors
https://jdc.jefferson.edu/medoncposters/1012/thumbnail.jp
Thinking outside the channel : modeling nitrogen cycling in networked river ecosystems
Author Posting. © Ecological Society of America, 2011. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Frontiers in Ecology and the Environment 9 (2011): 229–238, doi:10.1890/080211.Agricultural and urban development alters nitrogen and other biogeochemical cycles in rivers worldwide. Because such biogeochemical processes cannot be measured empirically across whole river networks, simulation models are critical tools for understanding river-network biogeochemistry. However, limitations inherent in current models restrict our ability to simulate biogeochemical dynamics among diverse river networks. We illustrate these limitations using a river-network model to scale up in situ measures of nitrogen cycling in eight catchments spanning various geophysical and land-use conditions. Our model results provide evidence that catchment characteristics typically excluded from models may control river-network biogeochemistry. Based on our findings, we identify important components of a revised strategy for simulating biogeochemical dynamics in river networks, including approaches to modeling terrestrial–aquatic linkages, hydrologic exchanges between the channel, floodplain/riparian complex, and subsurface waters, and interactions between coupled biogeochemical cycles.This research was supported by NSF (DEB-0111410).
Additional support was provided by NSF for BJP and
SMT (DEB-0614301), for WMW (OCE-9726921 and
DEB-0614282), for WHM and JDP (DEB-0620919), for
SKH (DEB-0423627), and by the Gordon and Betty
Moore Foundation for AMH, GCP, ESB, and JAS, and by
an EPA Star Fellowship for AMH
Concordant Gene Expression in Leukemia Cells and Normal Leukocytes Is Associated with Germline cis-SNPs
The degree to which gene expression covaries between different primary tissues within an individual is not well defined. We hypothesized that expression that is concordant across tissues is more likely influenced by genetic variability than gene expression which is discordant between tissues. We quantified expression of 11,873 genes in paired samples of primary leukemia cells and normal leukocytes from 92 patients with acute lymphoblastic leukemia (ALL). Genetic variation at >500,000 single nucleotide polymorphisms (SNPs) was also assessed. The expression of only 176/11,783 (1.5%) genes was correlated (p<0.008, FDR = 25%) in the two tissue types, but expression of a high proportion (20 of these 176 genes) was significantly related to cis-SNP genotypes (adjusted p<0.05). In an independent set of 134 patients with ALL, 14 of these 20 genes were validated as having expression related to cis-SNPs, as were 9 of 20 genes in a second validation set of HapMap cell lines. Genes whose expression was concordant among tissue types were more likely to be associated with germline cis-SNPs than genes with discordant expression in these tissues; genes affected were involved in housekeeping functions (GSTM2, GAPDH and NCOR1) and purine metabolism
Stream denitrification across biomes and its response to anthropogenic nitrate loading
Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 452 (2008): 202-205, doi:10.1038/nature06686.Worldwide, anthropogenic addition of bioavailable nitrogen (N) to the
biosphere is increasing and terrestrial ecosystems are becoming increasingly N
saturated, causing more bioavailable N to enter groundwater and surface waters.
Large-scale N budgets show that an average of about 20-25% of the N added to the
biosphere is exported from rivers to the ocean or inland basins, indicating
substantial sinks for N must exist in the landscape. Streams and rivers may be
important sinks for bioavailable N owing to their hydrologic connections with
terrestrial systems, high rates of biological activity, and streambed sediment
environments that favor microbial denitrification. Here, using data from 15N
tracer experiments replicated across 72 streams and 8 regions representing several
biomes, we show that total biotic uptake and denitrification of nitrate increase with
stream nitrate concentration, but that the efficiency of biotic uptake and
denitrification declines as concentration increases, reducing the proportion of instream
nitrate that is removed from transport. Total uptake of nitrate was related
to ecosystem photosynthesis and denitrification was related to ecosystem
respiration. Additionally, we use a stream network model to demonstrate that
excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate
that is exported to receiving waters and reduces the relative role of small versus
large streams as nitrate sinks.Funding for this research was provided by the National Science
Foundation
Partisans Without Constraint: Political Polarization and Trends in American Public Opinion
- …