17,622 research outputs found
Software for Implementing the Sequential Elimination of Level Combinations Algorithm
Genetic algorithms (GAs) are a popular technology to search for an optimum in a large search space. Using new concepts of forbidden array and weighted mutation, Mandal, Wu, and Johnson (2006) used elements of GAs to introduce a new global optimization technique called sequential elimination of level combinations (SELC), that efficiently finds optimums. A SAS macro, and MATLAB and R functions are developed to implement the SELC algorithm.
Managing the cardiovascular complications of chronic kidney disease
Patients with chronic kidney disease have risk factors for cardiovascular disease which are additional to those found in the general population. Many patients will die of cardiovascular disease before they require dialysis for their kidney disease. While lifestyle modification is essential, it is important to manage the patient's anaemia, dyslipidaemia and hypertension. Managing heart failure can be difficult because of the need to adjust the patient's fluid balance according to renal and cardiac function. If the progression of chronic kidney disease can be slowed, cardiac risk may be reduced. (author abstract
Software for Implementing the Sequential Elimination of Level Combinations Algorithm
Genetic algorithms (GAs) are a popular technology to search for an optimum in a large search space. Using new concepts of forbidden array and weighted mutation, Mandal, Wu, and Johnson (2006) used elements of GAs to introduce a new global optimization technique called sequential elimination of level combinations (SELC), that efficiently finds optimums. A SAS macro, and MATLAB and R functions are developed to implement the SELC algorithm
The quantitative soil pit method for measuring belowground carbon and nitrogen stocks
Many important questions in ecosystem science require estimates of stocks of soil C and nutrients. Quantitative soil pits provide direct measurements of total soil mass and elemental content in depth-based samples representative of large volumes, bypassing potential errors associated with independently measuring soil bulk density, rock volume, and elemental concentrations. The method also allows relatively unbiased sampling of other belowground C and nutrient stocks, including roots, coarse organic fragments, and rocks. We present a comprehensive methodology for sampling these pools with quantitative pits and assess their accuracy, precision, effort, and sampling intensity as compared to other methods. At 14 forested sites in New Hampshire, nonsoil belowground pools (which other methods may omit, double-count, or undercount) accounted for upward of 25% of total belowground C and N stocks: coarse material accounted for 4 and 1% of C and N in the O horizon; roots were 11 and 4% of C and N in the O horizon and 10 and 3% of C and N in the B horizon; and soil adhering to rocks represented 5% of total B-horizon C and N. The top 50 cm of the C horizon contained the equivalent of 17% of B-horizon carbon and N. Sampling procedures should be carefully designed to avoid treating these important pools inconsistently. Quantitative soil pits have fewer sources of systematic error than coring methods; the main disadvantage is that because they are time-consuming and create a larger zone of disturbance, fewer observations can be made than with cores
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On-Board Sensor-Based NO x Emissions from Heavy-Duty Diesel Vehicles
Real-world
nitrogen oxides (NOx) emissions
were estimated using on-board sensor readings from 72 heavy-duty diesel
vehicles (HDDVs) equipped with a Selective Catalytic Reduction (SCR)
system in California. The results showed that there were large differences
between in-use and certification NOx emissions,
with 12 HDDVs emitting more than three times the standard during hot-running
and idling operations in the real world. The overall NOx conversion efficiencies of the SCR system on many
vehicles were well below the 90% threshold that is expected for an
efficient SCR system, even when the SCR system was above the optimum
operating temperature threshold of 250 °C. This could potentially
be associated with SCR catalyst deterioration on some engines. The
Not-to-Exceed (NTE) requirements currently used by the heavy-duty
in-use compliance program were evaluated using on-board NOx sensor data. Valid NTE events covered only 4.2–16.4%
of the engine operation and 6.6–34.6% of the estimated NOx emissions. This work shows that low cost
on-board NOx sensors are a convenient
tool to monitor in-use NOx emissions in
real-time, evaluate the SCR system performance, and identify vehicle
operating modes with high NOx emissions.
This information can inform certification and compliance programs
to ensure low in-use NOx emissions
Sensitive Instances of the Constraint Satisfaction Problem
We investigate the impact of modifying the constraining relations of a
Constraint Satisfaction Problem (CSP) instance, with a fixed template, on the
set of solutions of the instance. More precisely we investigate sensitive
instances: an instance of the CSP is called sensitive, if removing any tuple
from any constraining relation invalidates some solution of the instance.
Equivalently, one could require that every tuple from any one of its
constraints extends to a solution of the instance.
Clearly, any non-trivial template has instances which are not sensitive.
Therefore we follow the direction proposed (in the context of strict width) by
Feder and Vardi (SICOMP 1999) and require that only the instances produced by a
local consistency checking algorithm are sensitive. In the language of the
algebraic approach to the CSP we show that a finite idempotent algebra
has a variable near unanimity term operation if and only if
any instance that results from running the -consistency algorithm on
an instance over is sensitive.
A version of our result, without idempotency but with the sensitivity
condition holding in a variety of algebras, settles a question posed by G.
Bergman about systems of projections of algebras that arise from some
subalgebra of a finite product of algebras.
Our results hold for infinite (albeit in the case of idempotent)
algebras as well and exhibit a surprising similarity to the strict width
condition proposed by Feder and Vardi. Both conditions can be characterized by
the existence of a near unanimity operation, but the arities of the operations
differ by 1
Cervical brachalgia: Assessment by cervical CT epidurography post transforaminal injection
Adjunct cervical CT epidurography (CCTE) can be used to image impingement in patients with cervical brachalgia undergoing fluoroscopic-guided cervical transforaminal injection (TFI) of steroid/local anaesthetic where magnetic resonance imaging (MRI) is contraindicated. CCTE images of the 9 patients on whom the authors performed CCTE post TFI over 6 years from 1998 to 2003 were retrospectively reviewed. CCTE is able to provide good images of the cervical spinal canal and its contents. CCTE may be an alternative imaging method for impingement in patients with cervical brachalgia contraindicated for MRI
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