51,505 research outputs found
HVAC SYSTEM AIR FILTER DIAGNOSTICS AND MONITORING
A system and method for monitoring a heating, ventilation, or air conditioning (HVAC) system of a building is provided. A monitoring server, located remotely from the building, receives operating parameter data from a monitoring device at the building that measures an operating parameter of the HVAC system. The monitoring server generates a plurality of data clusters from the operating parameter data, each data cluster corresponding to operating parameter data generated during steady-state operation of the HVAC system. The monitoring server calculates an average operating parameter value for each data cluster. The monitoring server calculates normalized operating parameter values based on normalizing the average operating parameter values for the data clusters over a predetermined normalization time period. The monitoring server compares the normalized operating parameter values with a threshold. The monitoring server determine whether an air filter of the HVAC system needs to be replaced based on the comparison and generates a notification based on the determination indicating that the air filter needs to be replaced
The 6670-Newton attitude-control thruster using hydrogen-oxygen propellant
The development of a reusable, attitude-control propulsion system for the space transportation system is discussed. A flight weight, gaseous oxygen attitude control thruster assembly was tested to obtain data on cyclic life, thermal and hydraulic characteristics, pulse response, and performance. The basic thruster components were tested in excess of 51,000 pulses and 660 seconds, steady state, with no degradation of the 93 percent characteristic exhaust velocity efficiency level. Nominal operating conditions were a chamber pressure of 207 N sq cm (300 psia), a mixture ratio of 4.0, a pulse width of 100 ms, and a pulse frequency of 2 Hz
Conclusions and implications of automation in space
Space facilities and programs are reviewed. Space program planning is discussed
Reliability assessment of microgrid with renewable generation and prioritized loads
With the increase in awareness about the climate change, there has been a
tremendous shift towards utilizing renewable energy sources (RES). In this
regard, smart grid technologies have been presented to facilitate higher
penetration of RES. Microgrids are the key components of the smart grids.
Microgrids allow integration of various distributed energy resources (DER) such
as the distributed generation (DGs) and energy storage systems (ESSs) into the
distribution system and hence remove or delay the need for distribution
expansion. One of the crucial requirements for utilities is to ensure that the
system reliability is maintained with the inclusion of microgrid topology.
Therefore, this paper evaluates the reliability of a microgrid containing
prioritized loads and distributed RES through a hybrid analytical-simulation
method. The stochasticity of RES introduces complexity to the reliability
evaluation. The method takes into account the variability of RES through Monte-
Carlo state sampling simulation. The results indicate the reliability
enhancement of the overall system in the presence of the microgrid topology. In
particular, the highest priority load has the largest improvement in the
reliability indices. Furthermore, sensitivity analysis is performed to
understand the effects of the failure of microgrid islanding in the case of a
fault in the upstream network
Analysis of turbofan engine performance deterioration and proposed follow-on tests
Data and engine parts on in-service JT3D and JT8D engines were analyzed and documented relative to engine deterioration. It is concluded that the fan-compressor system of these engines contributes to the long term engine deterioration. An engine test and instrumentation plan was formulated for a proposed follow-on program. The goal of this program is to verify the above conclusion and to attempt to identify more precisely which components of the fan-compressor system are at fault
Cytogerontology since 1881: A reappraisal of August Weismann and a review of modern progress
Cytogerontology, the science of cellular ageing, originated in 1881 with the prediction by August Weismann that the somatic cells of higher animals have limited division potential. Weismann's prediction was derived by considering the role of natural selection in regulating the duration of an organism's life. For various reasons, Weismann's ideas on ageing fell into neglect following his death in 1914, and cytogerontology has only reappeared as a major research area following the demonstration by Hayflick and Moorhead in the early 1960s that diploid human fibroblasts are restricted to a finite number of divisions in vitro.
In this review we give a detailed account of Weismann's theory, and we reveal that his ideas were both more extensive in their scope and more pertinent to current research than is generally recognised. We also appraise the progress which has been made over the past hundred years in investigating the causes of ageing, with particular emphasis being given to (i) the evolution of ageing, and (ii) ageing at the cellular level. We critically assess the current state of knowledge in these areas and recommend a series of points as primary targets for future research
Quantifying and monitoring functional Photosystem II and the stoichiometry of the two photosystems in leaf segments: Approaches and approximations
Given its unique function in light-induced
water oxidation and its susceptibility to photoinactivation
during photosynthesis, photosystem II (PS II) is often the
focus of studies of photosynthetic structure and function,
particularly in environmental stress conditions. Here we
review four approaches for quantifying or monitoring PS II
functionality or the stoichiometry of the two photosystems
in leaf segments, scrutinizing the approximations in each
approach. (1) Chlorophyll fluorescence parameters are
convenient to derive, but the information-rich signal suffers
from the localized nature of its detection in leaf tissue. (2)
The gross O2 yield per single-turnover flash in CO2-enriched
air is a more direct measurement of the functional
content, assuming that each functional PS II evolves one
O2 molecule after four flashes. However, the gross O2 yield
per single-turnover flash (multiplied by four) could overestimate
the content of functional PS II if mitochondrial
respiration is lower in flash illumination than in darkness.
(3) The cumulative delivery of electrons from PS II to P700? (oxidized primary donor in PS I) after a flash is
added to steady background far-red light is a whole-tissue
measurement, such that a single linear correlation with
functional PS II applies to leaves of all plant species
investigated so far. However, the magnitude obtained in a
simple analysis (with the signal normalized to the maximum
photo-oxidizable P700 signal), which should equal
the ratio of PS II to PS I centers, was too small to match the
independently-obtained photosystem stoichiometry. Further,
an under-estimation of functional PS II content could
occur if some electrons were intercepted before reaching
PS I. (4) The electrochromic signal from leaf segments
appears to reliably quantify the photosystem stoichiometry,
either by progressively photoinactivating PS II or suppressing
PS I via photo-oxidation of a known fraction of
the P700 with steady far-red light. Together, these
approaches have the potential for quantitatively probing PS
II in vivo in leaf segments, with prospects for application
of the latter two approaches in the field
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