41,529 research outputs found
The use of disjunct eddy sampling methods for the determination of ecosystem level fluxes of trace gases
The concept of disjunct eddy sampling (DES)
for use in measuring ecosystem-level micrometeorological
fluxes is re-examined. The governing equations are discussed
as well as other practical considerations and guidelines concerning
this sampling method as it is applied to either the
disjunct eddy covariance (DEC) or disjunct eddy accumulation
(DEA) techniques. A disjunct eddy sampling system
was constructed that could either be combined with relatively
slow sensors (response time of 2 to 40 s) to measure
fluxes using DEC, or could also be used to accumulate samples
in stable reservoirs for later laboratory analysis (DEA
technique). Both the DEC and DEA modes of this sampler
were tested against conventional eddy covariance (EC) for
fluxes of either CO2 (DEC) or isoprene (DEA). Good agreement
in both modes was observed relative to the EC systems.
However, the uncertainty in a single DEA flux measurement
was considerable (40%) due to both the reduced statistical
sampling and the analytical precision of the concentration
difference measurements. We have also re-investigated
the effects of nonzero mean vertical wind velocity on accumulation
techniques as it relates to our DEA measurements.
Despite the higher uncertainty, disjunct eddy sampling can
provide an alternative technique to eddy covariance for determining
ecosystem-level fluxes for species where fast sensors
do not currently exist
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Linked optical and gene expression profiling of single cells at high-throughput.
Single-cell RNA sequencing has emerged as a powerful tool for characterizing cells, but not all phenotypes of interest can be observed through changes in gene expression. Linking sequencing with optical analysis has provided insight into the molecular basis of cellular function, but current approaches have limited throughput. Here, we present a high-throughput platform for linked optical and gene expression profiling of single cells. We demonstrate accurate fluorescence and gene expression measurements on thousands of cells in a single experiment. We use the platform to characterize DNA and RNA changes through the cell cycle and correlate antibody fluorescence with gene expression. The platform's ability to isolate rare cell subsets and perform multiple measurements, including fluorescence and sequencing-based analysis, holds potential for scalable multi-modal single-cell analysis
Differentiability of the Value Function in Continuous–Time Economic Models
In this paper we provide some sufficient conditions for the differentiability of the value function in a class of infinite-horizon continuous-time models of convex optimization arising in economics. We dispense with an interiority condition which is quite restrictive in constrained optimization and it is usually hard to check in applications. The differentiability of the value function is used to prove Bellman’s equation as well as the existence and continuity of the optimal feedback policy. We also establish uniqueness of the vector of dual variables under some conditions that rule out existence of asset pricing bubbles.Constrained optimization, value function, differentiability, envelope therem, duality theory.
Microbiological methods for the water recovery systems test, revision 1.1
Current microbiological parameters specified to verify microbiological quality of Space Station Freedom water quality include the enumeration of total bacteria, anaerobes, aerobes, yeasts and molds, enteric bacteria, gram positives, gram negatives, and E. coli. In addition, other parameters have been identified as necessary to support the Water Recovery Test activities to be conducted at the NASA/MSFC later this year. These other parameters include aerotolerant eutrophic mesophiles, legionellae, and an additional method for heterotrophic bacteria. If inter-laboratory data are to be compared to evaluate quality, analytical methods must be eliminated as a variable. Therefore, each participating laboratory must utilize the same analytical methods and procedures. Without this standardization, data can be neither compared nor validated between laboratories. Multiple laboratory participation represents a conservative approach to insure quality and completeness of data. Invariably, sample loss will occur in transport and analyses. Natural variance is a reality on any test of this magnitude and is further enhanced because biological entities, capable of growth and death, are specific parameters of interest. The large variation due to the participation of human test subjects has been noted with previous testing. The resultant data might be dismissed as 'out of control' unless intra-laboratory control is included as part of the method or if participating laboratories are not available for verification. The purpose of this document is to provide standardized laboratory procedures for the enumeration of certain microorganisms in water and wastewater specific to the water recovery systems test. The document consists of ten separate cultural methods and one direct count procedure. It is not intended nor is it implied to be a complete microbiological methods manual
Effective thermodynamics for a marginal observer
Thermodynamics is usually formulated on the presumption that the observer has
complete information about the system he/she deals with: no parasitic current,
exact evaluation of the forces that drive the system. For example, the
acclaimed Fluctuation Relation (FR), relating the probability of time-forward
and time-reversed trajectories, assumes that the measurable transitions suffice
to characterize the process as Markovian (in our case, a continuous-time jump
process). However, most often the observer only measures a marginal current. We
show that he/she will nonetheless produce an effective description that does
not dispense with the fundamentals of thermodynamics, including the FR and the
2nd law. Our results stand on the mathematical construction of a hidden time
reversal of the dynamics, and on the physical requirement that the observed
current only accounts for a single transition in the configuration space of the
system. We employ a simple abstract example to illustrate our results and to
discuss the feasibility of generalizations.Comment: 8 pages, 1 figur
Differentiability of the value function in continuous-time economic models.
In this paper we provide some sufficient conditions for the differentiability of the value function in a class of infinite-horizon continuous—time models of convex optimization arising in economics. We dispense with an interioiity condition which is quite restrictive in constrained optimization and it is usually hard to check in applications. The differentiability of the value function is used to prove Bellman's equation as well as the existence and continuity of the optimal feedback policy. We also establish uniqueness of the vector of dual variables under some conditions that rule out existence of asset pricing bubbles.Constrained optimization; Value function; Differentiability; Envelope theorem; Duality theory;
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