The Hydrological Sensitivity to Global Warming and Solar Geoengineering Derived from Thermodynamic Constraints

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleidon, Alex; Kravitz, Benjamin S.; Renner, Maik

2015-01-16

We derive analytic expressions of the transient response of the hydrological cycle to surface warming from an extremely simple energy balance model in which turbulent heat fluxes are constrained by the thermodynamic limit of maximum power. For a given magnitude of steady-state temperature change, this approach predicts the transient response as well as the steady-state change in surface energy partitioning and the hydrologic cycle. We show that the transient behavior of the simple model as well as the steady state hydrological sensitivities to greenhouse warming and solar geoengineering are comparable to results from simulations using highly complex models. Many ofmore » the global-scale hydrological cycle changes can be understood from a surface energy balance perspective, and our thermodynamically-constrained approach provides a physically robust way of estimating global hydrological changes in response to altered radiative forcing.« less

An easy-to-use calculating machine to simulate steady state and non-steady-state preparative separations by multiple dual mode counter-current chromatography with semi-continuous loading of feed mixtures.

PubMed

Kostanyan, Artak E; Shishilov, Oleg N

2018-06-01

Multiple dual mode counter-current chromatography (MDM CCC) separation processes with semi-continuous large sample loading consist of a succession of two counter-current steps: with "x" phase (first step) and "y" phase (second step) flow periods. A feed mixture dissolved in the "x" phase is continuously loaded into a CCC machine at the beginning of the first step of each cycle over a constant time with the volumetric rate equal to the flow rate of the pure "x" phase. An easy-to-use calculating machine is developed to simulate the chromatograms and the amounts of solutes eluted with the phases at each cycle for steady-state (the duration of the flow periods of the phases is kept constant for all the cycles) and non-steady-state (with variable duration of alternating phase elution steps) separations. Using the calculating machine, the separation of mixtures containing up to five components can be simulated and designed. Examples of the application of the calculating machine for the simulation of MDM CCC processes are discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

Modeling Lithium Movement over Multiple Cycles in a Lithium-Metal Battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferrese, A; Newman, J

This paper builds on the work by Ferrese et al. [J. Electrochem., 159, A1615 (2012)], where a model of a lithium-metal battery with a LiyCoO2 positive electrode was created in order to predict the movement of lithium in the negative electrode along the negative electrode/separator interface during cell cycling. In this paper, the model is expanded to study the movement of lithium along the lithium-metal anode over multiple cycles. From this model, it is found that when a low percentage of lithium at the negative electrode is utilized, the movement of lithium along the negative electrode/separator interface reaches a quasimore » steady state after multiple cycles. This steady state is affected by the slope of the open-circuit-potential function in the positive electrode, the rate of charge and discharge, the depth of discharge, and the length of the rest periods. However, when a high percent of the lithium at the negative electrode is utilized during cycling, the movement does not reach a steady state and pinching can occur, where the lithium nearest the negative tab becomes progressively thinner after cycling. This is another nonlinearity that leads to a progression of the movement of lithium over multiple cycles. (C) 2014 The Electrochemical Society.« less

Steady state preparative multiple dual mode counter-current chromatography: Productivity and selectivity. Theory and experimental verification.

PubMed

Kostanyan, Artak E; Erastov, Andrey A

2015-08-07

In the steady state (SS) multiple dual mode (MDM) counter-current chromatography (CCC), at the beginning of the first step of every cycle the sample dissolved in one of the phases is continuously fed into a CCC device over a constant time, not exceeding the run time of the first step. After a certain number of cycles, the steady state regime is achieved, where concentrations vary over time during each cycle, however, the concentration profiles of solutes eluted with both phases remain constant in all subsequent cycles. The objective of this work was to develop analytical expressions to describe the SS MDM CCC separation processes, which can be helpful to simulate and design these processes and select a suitable compromise between the productivity and the selectivity in the preparative and production CCC separations. Experiments carried out using model mixtures of compounds from the GUESSmix with solvent system hexane/ethyl acetate/methanol/water demonstrated a reasonable agreement between the predictions of the theory and the experimental results. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of alternative pathway therapy on branched chain amino acid metabolism in urea cycle disorder patients.

PubMed

Scaglia, Fernando; Carter, Susan; O'Brien, William E; Lee, Brendan

2004-04-01

Urea cycle disorders (UCDs) are a group of inborn errors of hepatic metabolism caused by the loss of enzymatic activities that mediate the transfer of nitrogen from ammonia to urea. These disorders often result in life-threatening hyperammonemia and hyperglutaminemia. A combination of sodium phenylbutyrate and sodium phenylacetate/benzoate is used in the clinical management of children with urea cycle defects as a glutamine trap, diverting nitrogen from urea synthesis to alternatives routes of excretion. We have observed that patients treated with these compounds have selective branched chain amino acid (BCAA) deficiency despite adequate dietary protein intake. However, the direct effect of alternative therapy on the steady state levels of plasma branched chain amino acids has not been well characterized. We have measured steady state plasma branched chain and other essential non-branched chain amino acids in control subjects, untreated ornithine transcarbamylase deficiency females and treated null activity urea cycle disorder patients in the fed steady state during the course of stable isotope studies. Steady-state leucine levels were noted to be significantly lower in treated urea cycle disorder patients when compared to either untreated ornithine transcarbamylase deficiency females or control subjects (P<0.0001). This effect was reproduced in control subjects who had depressed leucine levels when treated with sodium phenylacetate/benzoate (P<0.0001). Our studies suggest that this therapeutic modality has a substantial impact on the metabolism of branched chain amino acids in urea cycle disorder patients. These findings suggest that better titration of protein restriction could be achieved with branched chain amino acid supplementation in patients with UCDs who are on alternative route therapy.

Preliminary design of an auxiliary power unit for the space shuttle. Volume 5: Selected system cycle performance data

NASA Technical Reports Server (NTRS)

Hamilton, M. L.; Burriss, W. L.

1972-01-01

Detailed cycle steady-state performance data are presented for the final auxiliary power unit (APU) system configuration. The selection configuration is a hydrogen-oxygen APU incorporating a recuperator to utilize the exhaust energy and using the cycle hydrogen flow as a means of cooling the component heat loads. The data are given in the form of computer printouts and provide the following: (1) verification of the adequacy of the design to meet the problem statement for steady-state performance; (2) overall system performance data for the vehicle system analyst to determine propellant consumption and hydraulic fluid temperature as a function for varying mission profiles, propellant inlet conditions, etc.; and (3) detailed component performance and cycle state point data to show what is happening in the cycle as a function of the external forcing functions.

Light-Induced resetting of the circadian pacemaker: quantitative analysis of transient versus steady-state phase shifts.

PubMed

Watanabe, K; Deboer, T; Meijer, J H

2001-12-01

The suprachiasmatic nuclei of the hypothalamus contain the major circadian pacemaker in mammals, driving circadian rhythms in behavioral and physiological functions. This circadian pacemaker's responsiveness to light allows synchronization to the light-dark cycle. Phase shifting by light often involves several transient cycles in which the behavioral activity rhythm gradually shifts to its steady-state position. In this article, the authors investigate in Syrian hamsters whether a phase-advancing light pulse results in immediate shifts of the PRC at the next circadian cycle. In a first series of experiments, the authors aimed a light pulse at CT 19 to induce a phase advance. It appeared that the steady-state phase advances were highly correlated with activity onset in the first and second transient cycle. This enabled them to make a reliable estimate of the steady-state phase shift induced by a phase-advancing light pulse on the basis of activity onset in the first transient cycle. In the next series of experiments, they presented a light pulse at CT 19, which was followed by a second light pulse aimed at the delay zone of the PRC on the next circadian cycle. The immediate and steady-state phase delays induced by the second light pulse were compared with data from a third experiment in which animals received a phase-delaying light pulse only. The authors observed that the waveform of the phase-delay part of the PRC (CT 12-16) obtained in Experiment 2 was virtually identical to the phase-delay part of the PRC for a single light pulse (obtained in Experiment 3). This finding allowed for a quantitative assessment of the data. The analysis indicates that the delay part of the PRC-between CT 12 and CT 16-is rapidly reset following a light pulse at CT 19. These findings complement earlier findings in the hamster showing that after a light pulse at CT 19, the phase-advancing part of the PRC is immediately shifted. Together, the data indicate that the basis for phase advancing involves rapid resetting of both advance and delay components of the PRC.

Simplified formula for mean cycle-slip time of phase-locked loops with steady-state phase error.

NASA Technical Reports Server (NTRS)

Tausworthe, R. C.

1972-01-01

Previous work shows that the mean time from lock to a slipped cycle of a phase-locked loop is given by a certain double integral. Accurate numerical evaluation of this formula for the second-order loop is extremely vexing because the difference between exponentially large quantities is involved. The presented article demonstrates a method in which a much-reduced precision program can be used to obtain the mean first-cycle slip time for a loop of arbitrary degree tracking at a specified SNR and steady-state phase error. It also presents a simple approximate formula that is asymptotically tight at higher loop SNR.

Initial and steady-state Ru growth by atomic layer deposition studied by in situ Angle Resolved X-ray Photoelectron Spectroscopy

NASA Astrophysics Data System (ADS)

Egorov, Konstantin V.; Lebedinskii, Yury Yu.; Soloviev, Anatoly A.; Chouprik, Anastasia A.; Azarov, Alexander Yu.; Markeev, Andrey M.

2017-10-01

The clear substrate-dependent growth and delayed film continuity are essential challenges of Ru atomic layer deposition (ALD) demanding adequate and versatile approaches for their study. Here, we report on the application of in situ Angle Resolved X-ray Phototelectron Spectroscopy (ARXPS) for investigation of initial and steady-state ALD growth of Ru using Ru(EtCp)2 and O2 as precursors. Using ARXPS surface analysis technique we determine such parameters of Ru ALD initial growth as incubation period, fractional coverage and the thickness of islands/film depending on the substrate chemical state, governed by the presence/absence of NH3/Ar plasma pretreatment. It was demonstrated that NH3/Ar plasma pretreatment allows to obtain the lowest incubation period (∼7 ALD cycles) resulting in a continuous ultrathin (∼20 Å) and smooth Ru films after 70 ALD cycles. In situ XPS at UHV was used at steady state Ru growth for analysis of half-cycle reactions that revealed formation of RuOx (x ≈ 2) layer with thickness of ∼8 Å after O2 pulse (first half-cycle). It was also shown that oxygen of RuOx layer combusts Ru(EtCp)2 ligands in the second half-cycle reaction and the observed Ru growth of ∼0.34 Å per cycle is in a good agreement with the amount of oxygen in the RuOx layer.

The Effects of Crushed Ice Ingestion Prior to Steady State Exercise in the Heat.

PubMed

Zimmermann, Matthew; Landers, Grant; Wallman, Karen E; Saldaris, Jacinta

2017-06-01

This study examined the physiological effects of crushed ice ingestion before steady state exercise in the heat. Ten healthy males with age (23 ± 3 y), height (176.9 ± 8.7 cm), body-mass (73.5 ± 8.0 kg), VO 2peak (48.5 ± 3.6 mL∙kg∙min -1 ) participated in the study. Participants completed 60 min of cycling at 55% of their VO 2peak preceded by 30 min of precooling whereby 7 g∙kg -1 of thermoneutral water (CON) or crushed ice (ICE) was ingested. The reduction in T c at the conclusion of precooling was greater in ICE (-0.9 ± 0.3 °C) compared with CON (-0.2 ± 0.2 °C) (p ≤ .05). Heat storage capacity was greater in ICE compared with CON after precooling (ICE -29.3 ± 4.8 W∙m -2 ; CON -11.1 ± 7.3 W∙m -2 , p < .05). Total heat storage was greater in ICE compared with CON at the end of the steady state cycle (ICE 62.0 ± 12.5 W∙m-2; CON 49.9 ± 13.4 W∙m -2 , p < .05). Gross efficiency was higher in ICE compared with CON throughout the steady state cycle (ICE 21.4 ± 1.8%; CON 20.4 ± 1.9%, p < .05). Ice ingestion resulted in a lower thermal sensation at the end of precooling and a lower sweat rate during the initial stages of cycling (p < .05). Sweat loss, respiratory exchange ratio, heart rate and ratings of perceived exertion and thirst were similar between conditions (p > .05). Precooling with crushed ice led to improved gross efficiency while cycling due to an increased heat storage capacity, which was the result of a lower core temperature.

A comparison of practical assessment methods to determine treadmill, cycle and elliptical ergometer VO2peak

PubMed Central

Mays, Ryan J.; Boér, Nicholas F.; Mealey, Lisa M.; Kim, Kevin H.; Goss, Fredric L.

2015-01-01

This investigation compared estimated and predicted peak oxygen consumption (VO2peak) and maximal heart rate (HRmax) among the treadmill, cycle ergometer and elliptical ergometer. Seventeen women (mean ± SE: 21.9 ± .3 yrs) exercised to exhaustion on all modalities. ACSM metabolic equations were used to estimate VO2peak. Digital displays on the elliptical ergometer were used to estimate VO2peak. Two individual linear regression methods were used to predict VO2peak: 1) two steady state heart rate (HR) responses up to 85% of age-predicted HRmax, and 2) multiple steady state/non-steady state HR responses up to 85% of age-predicted HRmax. Estimated VO2peak for the treadmill (46.3 ± 1.3 ml · kg−1 · min−1) and the elliptical ergometer (44.4 ± 1.0 ml · kg−1 · min−1) did not differ. The cycle ergometer estimated VO2peak (36.5 ± 1.0 ml · kg−1 · min−1) was lower (p < .001) than the estimated VO2peak values for the treadmill and elliptical ergometer. Elliptical ergometer VO2peak predicted from steady state (51.4 ± .8 ml · kg−1 · min−1) and steady state/non-steady state (50.3 ± 2.0 ml · kg−1 · min−1) models were higher than estimated elliptical ergometer VO2peak, p < .01. HRmax and estimates of VO2peak were similar between the treadmill and elliptical ergometer, thus cross-modal exercise prescriptions may be generated. The use of digital display estimates of submaximal oxygen uptake for the elliptical ergometer may not be an accurate method for predicting VO2peak. Health-fitness professionals should use caution when utilizing submaximal elliptical ergometer digital display estimates to predict VO2peak. PMID:20393357

Walkway Length Determination for Steady State Walking in Young and Older Adults

ERIC Educational Resources Information Center

Macfarlane, Pamela A.; Looney, Marilyn A.

2008-01-01

The primary purpose of this study was to determine acceleration (AC) and deceleration (DC) distances that would accommodate young and older adults walking at their preferred and fast speeds. A secondary purpose was to determine the minimal walkway length needed to record six steady state (SS) steps (three full gait cycles) for younger and older…

Bipolar pulse field for magnetic refrigeration

DOEpatents

Lubell, Martin S.

1994-01-01

A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies.

End-of-life flows of multiple cycle consumer products.

PubMed

Tsiliyannis, C A

2011-11-01

Explicit expressions for the end-of-life flows (EOL) of single and multiple cycle products (MCPs) are presented, including deterministic and stochastic EOL exit. The expressions are given in terms of the physical parameters (maximum lifetime, T, annual cycling frequency, f, number of cycles, N, and early discard or usage loss). EOL flows are also obtained for hi-tech products, which are rapidly renewed and thus may not attain steady state (e.g., electronic products, passenger cars). A ten-step recursive procedure for obtaining the dynamic EOL flow evolution is proposed. Applications of the EOL expressions and the ten-step procedure are given for electric household appliances, industrial machinery, tyres, vehicles and buildings, both for deterministic and stochastic EOL exit, (normal, Weibull and uniform exit distributions). The effect of the physical parameters and the stochastic characteristics on the EOL flow is investigated in the examples: it is shown that the EOL flow profile is determined primarily by the early discard dynamics; it also depends strongly on longevity and cycling frequency: higher lifetime or early discard/loss imply lower dynamic and steady state EOL flows. The stochastic exit shapes the overall EOL dynamic profile: Under symmetric EOL exit distribution, as the variance of the distribution increases (uniform to normal to deterministic) the initial EOL flow rise becomes steeper but the steady state or maximum EOL flow level is lower. The steepest EOL flow profile, featuring the highest steady state or maximum level, as well, corresponds to skew, earlier shifted EOL exit (e.g., Weibull). Since the EOL flow of returned products consists the sink of the reuse/remanufacturing cycle (sink to recycle) the results may be used in closed loop product lifecycle management operations for scheduling and sizing reverse manufacturing and for planning recycle logistics. Decoupling and quantification of both the full age EOL and of the early discard flows is useful, the latter being the target of enacted legislation aiming at increasing reuse. Copyright © 2011 Elsevier Ltd. All rights reserved.

Bipolar pulse field for magnetic refrigeration

DOEpatents

Lubell, M.S.

1994-10-25

A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies. 2 figs.

Endogenous Thrombin Potential Changes during the First Cycle of Oral Contraceptive Use

PubMed Central

Westhoff, Carolyn L.; Pike, Malcolm C.; Cremers, Serge; Eisenberger, Andrew; Thomassen, Stella; Rosing, Jan

2017-01-01

Objectives Venous thromboembolism (VTE) risk increases within months of combination oral contraceptive (COC) initiation. Because elevated endogenous thrombin potential (ETP) has been found in several studies to be a VTE risk factor, we evaluated the extent of ETP changes during the initial cycle of an ethinyl estradiol (EE) and levonorgestrel (LNG) COC. We also assessed the relationship between ETP changes and systemic EE and LNG concentrations. Study Design Participants provided multiple blood samples during a first 21-day cycle of a 30 µg EE/150 µg LNG COC and after a further 7 days without an active COC. Thrombin generation measured with and without addition of activated protein C (APC) yielded ETP+APC and ETP−APC and the normalized APC sensitivity ratio (nAPCsr). EE and LNG pharmacokinetic analyses were conducted over 24 hours after the first COC tablet and again at steady state. Results Thrombin generation was determined in 16 of the 17 women who completed the study. Mean ETP−APC increased steadily to 21% above baseline at 24 hours after the 6th COC tablet (COC624; p < 0.001) and to 28% above baseline at steady state (COC21; p < 0.001). Mean ETP+APC increased considerably more – by 54% at COC624 and by 79% at steady state. Mean nAPCsr increased by 28% at COC624 and by 41% at steady state. Higher concentrations of EE or LNG were not correlated with greater increases in ETP. Conclusions ETP increases during the first COC cycle were substantial. Implications The early increases in ETP may provide biological support for the rapid increase in VTE risk during initial COC use. The lack of association between this clotting system perturbation and the systemic EE concentration is surprising and deserves further study. PMID:28088496

Estimating Systemic Exposure to Levonorgestrel from an Oral Contraceptive

PubMed Central

Basaraba, Cale N; Westhoff, Carolyn L; Pike, Malcolm C; Nandakumar, Renu; Cremers, Serge

2017-01-01

Objective The gold standard for measuring oral contraceptive (OC) pharmacokinetics is the 24-hour steady-state area-under-the-curve (AUC). We conducted this study to assess whether limited sampling at steady state or measurements following use of one or two OCs could provide an adequate proxy in epidemiological studies for the progestin 24-hour steady-state AUC of a particular OC. Study Design We conducted a 13-sample, 24-hour pharmacokinetic study on both day 1 and day 21 of the first cycle of a monophasic OC containing 30 μg ethinyl estradiol and 150 μg levonorgestrel (LNG) in 17 normal-weight healthy white women, and a single-dose 9-sample study of the same OC after a one-month washout. We compared the 13-sample steady-state results with several steady-state and single-dose results calculated using parsimonious sampling schemes. Results The 13-sample steady-state 24-hour LNG AUC was highly correlated with the steady-state 24-hour trough value (r = 0.95; 95% CI [0.85, 0.98]) and with the steady-state 6, 8, 12 and 16-hour values (0.92 ≤ r ≤ 0.95). The trough values after one or two doses were moderately correlated with the steady-state 24-hour AUC value (r = 0.70; 95% CI [0.27, 0.90] and 0.77; 95% CI [0.40, 0.92], respectively). Conclusions Single time-point concentrations at steady-state and after administration of one or two OCs gave highly to moderately correlated estimates of steady-state LNG AUC. Using such measures could facilitate prospective pharmaco-epidemiologic studies of the OC and its side effects. PMID:28041990

Optimal tuning of a confined Brownian information engine.

PubMed

Park, Jong-Min; Lee, Jae Sung; Noh, Jae Dong

2016-03-01

A Brownian information engine is a device extracting mechanical work from a single heat bath by exploiting the information on the state of a Brownian particle immersed in the bath. As for engines, it is important to find the optimal operating condition that yields the maximum extracted work or power. The optimal condition for a Brownian information engine with a finite cycle time τ has been rarely studied because of the difficulty in finding the nonequilibrium steady state. In this study, we introduce a model for the Brownian information engine and develop an analytic formalism for its steady-state distribution for any τ. We find that the extracted work per engine cycle is maximum when τ approaches infinity, while the power is maximum when τ approaches zero.

40 CFR 1033.520 - Alternative ramped modal cycles.

Code of Federal Regulations, 2012 CFR

2012-07-01

...) Following the completion of the third test phase of the applicable ramped modal cycle, conduct the post... POLLUTION CONTROLS CONTROL OF EMISSIONS FROM LOCOMOTIVES Test Procedures § 1033.520 Alternative ramped modal... locomotive notch settings. Ramped modal cycles combine multiple test modes of a discrete-mode steady-state...

40 CFR Appendix II to Part 1054 - Duty Cycles for Laboratory Testing

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Duty Cycles for Laboratory Testing II.... 1054, App. II Appendix II to Part 1054—Duty Cycles for Laboratory Testing (a) Test handheld engines with the following steady-state duty cycle: G3 mode No. Engine speed a Torque(percent) b Weighting...

The Path of Carbon in Photosynthesis XX. The Steady State

DOE R&D Accomplishments Database

Calvin, M.; Massini, Peter

1952-09-01

The separation of the phenomenon of photosynthesis in green plants into a photochemical reaction and into the light-dependent reduction of carbon dioxide is discussed, The reduction of carbon dioxide and the fate of the assimilated carbon were investigated with the help of the tracer technique (exposure of the planks to the radioactive C{sup 14}O{sub 2}) and of paper chromatography. A reaction cycle is proposed in which phosphoglyceric acid is the first isolable assimilations product. Analyses of the algal extracts which had assimilated radioactive carbon dioxide in a stationary condition ('steady-state' photosynthesis) for a long time provided further information concerning the proposed cycle and permitted the approximate estimation, for a number of compounds of what fraction of each compound was taking part in the cycle. The earlier supposition that light influences the respiration cycle was confirmed. The possibility of the assistance of {alpha}-lipoic acid, or of a related substance, in this influence and in the photosynthesis cycle, is discussed.

Estimating systemic exposure to levonorgestrel from an oral contraceptive.

PubMed

Basaraba, Cale N; Westhoff, Carolyn L; Pike, Malcolm C; Nandakumar, Renu; Cremers, Serge

2017-04-01

The gold standard for measuring oral contraceptive (OC) pharmacokinetics is the 24-h steady-state area under the curve (AUC). We conducted this study to assess whether limited sampling at steady state or measurements following use of one or two OCs could provide an adequate proxy in epidemiological studies for the progestin 24-h steady-state AUC of a particular OC. We conducted a 13-sample, 24-h pharmacokinetic study on both day 1 and day 21 of the first cycle of a monophasic OC containing 30-mcg ethinyl estradiol and 150-mcg levonorgestrel (LNG) in 17 normal-weight healthy White women and a single-dose 9-sample study of the same OC after a 1-month washout. We compared the 13-sample steady-state results with several steady-state and single-dose results calculated using parsimonious sampling schemes. The 13-sample steady-state 24-h LNG AUC was highly correlated with the steady-state 24-h trough value [r=0.95; 95% confidence interval (0.85, 0.98)] and with the steady-state 6-, 8-, 12- and 16-h values (0.92≤r≤0.95). The trough values after one or two doses were moderately correlated with the steady-state 24-h AUC value [r=0.70; 95% CI (0.27, 0.90) and 0.77; 95% CI (0.40, 0.92), respectively]. Single time-point concentrations at steady state and after administration of one or two OCs gave highly to moderately correlated estimates of steady-state LNG AUC. Using such measures could facilitate prospective pharmaco-epidemiologic studies of the OC and its side effects. A single time-point LNG concentration at steady state is an excellent proxy for complete and resource-intensive steady-state AUC measurement. The trough level after two single doses is a fair proxy for steady-state AUC. These results provide practical tools to facilitate large studies to investigate the relationship between systemic LNG exposure and side effects in a real-life setting. Copyright © 2017 Elsevier Inc. All rights reserved.

Using CarbonTracker carbon flux estimates to improve a terrestrial carbon cycle model

NASA Astrophysics Data System (ADS)

Peters, W.; Krol, M.; Miller, J. B.; Tans, P. P.; Carvalhais, N.; Schaefer, K.

2009-12-01

Estimates of net ecosystem exchange (NEE) from NOAA’s CarbonTracker CO2 data assimilation system show patterns of annual net uptake not represented in most terrestrial carbon cycle models. This is mainly because such models lack information on the land-use history of individual ecosystems, which is the main driver of long-term mean carbon exchange. Instead, they assume the biosphere to be in steady-state, with annual gross photosynthesis equalling ecosystem respiration everywhere. This limits their use in interpreting observations of carbon dynamics such as with eddy-covariance techniques or through atmospheric CO2 records. We have implemented a method that takes the long-term mean NEE estimates from CarbonTracker to derive the size of the dominant carbon pool in each ecosystem of the SIBCASA biosphere model. With the new pool sizes, the SIBCASA model is no longer in steady-state and reproduces annual carbon uptake patterns from CarbonTracker. We will show that the non steady-state SIBCASA model is not only much more consistent with the atmospheric CO2 record, but also with independent data on standing wood biomass and forest age from the Forest Inventory and Analysis (FIA) Program of the U.S. Forest Service. Four years of CarbonTracker NEE are needed to reliably derive a long term mean for this process, and we use three other years from CarbonTracker to evaluate the non steady state SIBCASA NEE. We will furthermore show that the non steady-state SIBCASA NEE is a much better first-guess for the CarbonTracker data assimilation process, allowing more confidence in its final NEE estimate, and reducing a systematic bias in CarbonTracker modeled atmospheric CO2. This overcomes a long standing issue in inverse modeling, and opens the way for further assessment and improvement of carbon cycle models such as SIBCASA.

Modeling and Analysis of Energy Conservation Scheme Based on Duty Cycling in Wireless Ad Hoc Sensor Network

PubMed Central

Chung, Yun Won; Hwang, Ho Young

2010-01-01

In sensor network, energy conservation is one of the most critical issues since sensor nodes should perform a sensing task for a long time (e.g., lasting a few years) but the battery of them cannot be replaced in most practical situations. For this purpose, numerous energy conservation schemes have been proposed and duty cycling scheme is considered the most suitable power conservation technique, where sensor nodes alternate between states having different levels of power consumption. In order to analyze the energy consumption of energy conservation scheme based on duty cycling, it is essential to obtain the probability of each state. In this paper, we analytically derive steady state probability of sensor node states, i.e., sleep, listen, and active states, based on traffic characteristics and timer values, i.e., sleep timer, listen timer, and active timer. The effect of traffic characteristics and timer values on the steady state probability and energy consumption is analyzed in detail. Our work can provide sensor network operators guideline for selecting appropriate timer values for efficient energy conservation. The analytical methodology developed in this paper can be extended to other energy conservation schemes based on duty cycling with different sensor node states, without much difficulty. PMID:22219676

Analysis of lunar regolith thermal energy storage

NASA Technical Reports Server (NTRS)

Colozza, Anthony J.

1991-01-01

The concept of using lunar regolith as a thermal energy storage medium was evaluated. The concept was examined by mathematically modeling the absorption and transfer of heat by the lunar regolith. Regolith thermal and physical properties were established through various sources as functions of temperature. Two cases were considered: a semi-infinite, constant temperature, cylindrical heat source embedded in a continuum of lunar regolith and a spherically shaped molten zone of lunar regolith set with an initial temperature profile. The cylindrical analysis was performed in order to examine the amount of energy which can be stored in the regolith during the day. At night, the cylinder acted as a perfect insulator. This cycling was performed until a steady state situation was reached in the surrounding regolith. It was determined that a cycling steady state occurs after approximately 15 day/night cycles. Results were obtained for cylinders of various diameters. The spherical molten zone analysis was performed to establish the amount of thermal energy, within the regolith, necessary to maintain some molten material throughout a nighttime period. This surrounding temperature profile was modeled after the cycling steady state temperature profile established by the cylindrical analysis. It was determined that a molten sphere diameter of 4.76 m is needed to maintain a core temperature near the low end of the melting temperature range throughout one nighttime period.

Investigation of the Evolution of Crystal Size and Shape during Temperature Cycling and in the Presence of a Polymeric Additive Using Combined Process Analytical Technologies

PubMed Central

2017-01-01

Crystal size and shape can be manipulated to enhance the qualities of the final product. In this work the steady-state shape and size of succinic acid crystals, with and without a polymeric additive (Pluronic P123) at 350 mL, scale is reported. The effect of the amplitude of cycles as well as the heating/cooling rates is described, and convergent cycling (direct nucleation control) is compared to static cycling. The results show that the shape of succinic acid crystals changes from plate- to diamond-like after multiple cycling steps, and that the time required for this morphology change to occur is strongly related to the type of cycling. Addition of the polymer is shown to affect both the final shape of the crystals and the time needed to reach size and shape steady-state conditions. It is shown how this phenomenon can be used to improve the design of the crystallization step in order to achieve more efficient downstream operations and, in general, to help optimize the whole manufacturing process. PMID:28867966

Experimental and Analytical Performance of a Dual Brayton Power Conversion System

NASA Technical Reports Server (NTRS)

Lavelle, Thomas A.; Hervol, David S.; Briggs, Maxwell; Owen, A. Karl

2009-01-01

The interactions between two closed Brayton cycle (CBC) power conversion units (PCU) which share a common gas inventory and heat source have been studied experimentally using the Dual Brayton Power Conversion System (DBPCS) and analytically using the Closed- Cycle System Simulation (CCSS) computer code. Selected operating modes include steady-state operation at equal and unequal shaft speeds and various start-up scenarios. Equal shaft speed steady-state tests were conducted for heater exit temperatures of 840 to 950 K and speeds of 50 to 90 krpm, providing a system performance map. Unequal shaft speed steady-state testing over the same operating conditions shows that the power produced by each Brayton is sensitive to the operating conditions of the other due to redistribution of gas inventory. Startup scenarios show that starting the engines one at a time can dramatically reduce the required motoring energy. Although the DBPCS is not considered a flight-like system, these insights, as well as the operational experience gained from operating and modeling this system provide valuable information for the future development of Brayton systems.

Toward an MRI-based method to measure non-uniform cartilage deformation: an MRI-cyclic loading apparatus system and steady-state cyclic displacement of articular cartilage under compressive loading.

PubMed

Neu, C P; Hull, M L

2003-04-01

Recent magnetic resonance imaging (MRI) techniques have shown potential for measuring non-uniform deformations throughout the volume (i.e. three-dimensional (3D) deformations) in small orthopedic tissues such as articular cartilage. However, to analyze cartilage deformation using MRI techniques, a system is required which can construct images from multiple acquisitions of MRI signals from the cartilage in both the underformed and deformed states. The objectives of the work reported in this article were to 1) design an apparatus that could apply highly repeatable cyclic compressive loads of 400 N and operate in the bore of an MRI scanner, 2) demonstrate that the apparatus and MRI scanner can be successfully integrated to observe 3D deformations in a phantom material, 3) use the apparatus to determine the load cycle necessary to achieve a steady-state deformation response in normal bovine articular cartilage samples using a flat-surfaced and nonporous indentor in unconfined compression. Composed of electronic and pneumatic components, the apparatus regulated pressure to a double-acting pneumatic cylinder so that (1) load-controlled compression cycles were applied to cartilage samples immersed in a saline bath, (2) loading and recovery periods within a cycle varied in time duration, and (3) load magnitude varied so that the stress applied to cartilage samples was within typical physiological ranges. In addition the apparatus allowed gating for MR image acquisition, and operation within the bore of an MRI scanner without creating image artifacts. The apparatus demonstrated high repeatability in load application with a standard deviation of 1.8% of the mean 400 N load applied. When the apparatus was integrated with an MRI scanner programmed with appropriate pulse sequences, images of a phantom material in both the underformed and deformed states were constructed by assembling data acquired through multiple signal acquisitions. Additionally, the number of cycles to reach a steady-state response in normal bovine articular cartilage was 49 for a total cycle duration of 5 seconds, but decreased to 33 and 27 for increasing total cycle durations of 10 and 15 seconds, respectively. Once the steady-state response was achieved, 95% of all displacements were within +/- 7.42 microns of the mean displacement, indicating that the displacement response to the cyclic loads was highly repeatable. With this performance, the MRI-loading apparatus system meets the requirements to create images of articular cartilage from which 3D deformation can be determined.

Bifurcation analysis of an automatic dynamic balancing mechanism for eccentric rotors

NASA Astrophysics Data System (ADS)

Green, K.; Champneys, A. R.; Lieven, N. J.

2006-04-01

We present a nonlinear bifurcation analysis of the dynamics of an automatic dynamic balancing mechanism for rotating machines. The principle of operation is to deploy two or more masses that are free to travel around a race at a fixed distance from the hub and, subsequently, balance any eccentricity in the rotor. Mathematically, we start from a Lagrangian description of the system. It is then shown how under isotropic conditions a change of coordinates into a rotating frame turns the problem into a regular autonomous dynamical system, amenable to a full nonlinear bifurcation analysis. Using numerical continuation techniques, curves are traced of steady states, limit cycles and their bifurcations as parameters are varied. These results are augmented by simulations of the system trajectories in phase space. Taking the case of a balancer with two free masses, broad trends are revealed on the existence of a stable, dynamically balanced steady-state solution for specific rotation speeds and eccentricities. However, the analysis also reveals other potentially attracting states—non-trivial steady states, limit cycles, and chaotic motion—which are not in balance. The transient effects which lead to these competing states, which in some cases coexist, are investigated.

Differences in corticospinal excitability to the biceps brachii between arm cycling and tonic contraction are not evident at the immediate onset of movement.

PubMed

Forman, Davis A; Philpott, Devin T G; Button, Duane C; Power, Kevin E

2016-08-01

This is the first study to examine changes in corticospinal excitability to the biceps brachii during the onset of arm cycling from a resting position to a point when steady-state arm cycling was obtained. Supraspinal and spinal excitability were assessed using motor-evoked potentials (MEPs) elicited via transcranial magnetic stimulation and cervicomedullary evoked potentials (CMEPs) elicited via transmastoid electrical stimulation, respectively. Evoked responses were recorded from the biceps brachii during elbow flexion (6 o'clock relative to a clock face) for both arm cycling and an intensity-matched tonic contraction at three separate periods: (1) immediately at the onset of motor output and after completion of the (2) 4th revolution and (3) 9th revolution. There was no difference during initiation between tasks for MEP (P = 0.79) or CMEP amplitudes (P = 0.57). However, MEP amplitudes were significantly larger during arm cycling than an intensity-matched tonic contraction after the completion of the 4th (Cycling 76.48 ± 17.35 % of M max, Tonic 63.45 ± 18.45 % of M max, P < 0.05) and 9th revolutions (Cycling 72.37 ± 15.96 % of M max, Tonic 58.1 ± 24.23 % of M max, P < 0.05). There were no differences between conditions in CMEP amplitudes at the 4th (Cycling 49.6 ± 25.4 % of M max, Tonic 41.6 ± 11.2 % of M max, P = 0.31) or the 9th revolution (Cycling 47.2 ± 17.0 % of M max, Tonic 40.8 ± 13.6 % of M max, P = 0.29). These results demonstrate that corticospinal excitability is not different between arm cycling and a tonic contraction at motor output onset, but supraspinal excitability is enhanced during steady-state arm cycling. This suggests a similarity in the way the corticospinal tract initiates motor outputs in humans, regardless of the differences that present themselves in the later, steady-state stages.

Ultrahigh-resolution imaging of the human brain with phase-cycled balanced steady-state free precession at 7 T.

PubMed

Zeineh, Michael M; Parekh, Mansi B; Zaharchuk, Greg; Su, Jason H; Rosenberg, Jarrett; Fischbein, Nancy J; Rutt, Brian K

2014-05-01

The objectives of this study were to acquire ultra-high resolution images of the brain using balanced steady-state free precession (bSSFP) at 7 T and to identify the potential utility of this sequence. Eight volunteers participated in this study after providing informed consent. Each volunteer was scanned with 8 phase cycles of bSSFP at 0.4-mm isotropic resolution using 0.5 number of excitations and 2-dimensional parallel acceleration of 1.75 × 1.75. Each phase cycle required 5 minutes of scanning, with pauses between the phase cycles allowing short periods of rest. The individual phase cycles were aligned and then averaged. The same volunteers underwent scanning using 3-dimensional (3D) multiecho gradient recalled echo at 0.8-mm isotropic resolution, 3D Cube T2 at 0.7-mm isotropic resolution, and thin-section coronal oblique T2-weighted fast spin echo at 0.22 × 0.22 × 2.0-mm resolution for comparison. Two neuroradiologists assessed image quality and potential research and clinical utility. The volunteers generally tolerated the scan sessions well, and composite high-resolution bSSFP images were produced for each volunteer. Rater analysis demonstrated that bSSFP had a superior 3D visualization of the microarchitecture of the hippocampus, very good contrast to delineate the borders of the subthalamic nucleus, and relatively good B1 homogeneity throughout. In addition to an excellent visualization of the cerebellum, subtle details of the brain and skull base anatomy were also easier to identify on the bSSFP images, including the line of Gennari, membrane of Liliequist, and cranial nerves. Balanced steady-state free precession had a strong iron contrast similar to or better than the comparison sequences. However, cortical gray-white contrast was significantly better with Cube T2 and T2-weighted fast spin echo. Balanced steady-state free precession can facilitate ultrahigh-resolution imaging of the brain. Although total imaging times are long, the individually short phase cycles can be acquired separately, improving examination tolerability. These images may be beneficial for studies of the hippocampus, iron-containing structures such as the subthalamic nucleus and line of Gennari, and the basal cisterns and their contents.

40 CFR 1065.546 - Validation of minimum dilution ratio for PM batch sampling.

Code of Federal Regulations, 2010 CFR

2010-07-01

... flows and/or tracer gas concentrations for transient and ramped modal cycles to validate the minimum... mode-average values instead of continuous measurements for discrete mode steady-state duty cycles... molar flow data. This involves determination of at least two of the following three quantities: Raw...

Quasi-steady-state voltammetry of rapid electron transfer reactions at the macroscopic substrate of the scanning electrochemical microscope.

PubMed

Nioradze, Nikoloz; Kim, Jiyeon; Amemiya, Shigeru

2011-02-01

We report on a novel theory and experiment for scanning electrochemical microscopy (SECM) to enable quasi-steady-state voltammetry of rapid electron transfer (ET) reactions at macroscopic substrates. With this powerful approach, the substrate potential is cycled widely across the formal potential of a redox couple while the reactant or product of a substrate reaction is amperometrically detected at the tip in the feedback or substrate generation/tip collection mode, respectively. The plot of tip current versus substrate potential features the retraceable sigmoidal shape of a quasi-steady-state voltammogram although a transient voltammogram is obtained at the macroscopic substrate. Finite element simulations reveal that a short tip-substrate distance and a reversible substrate reaction (except under the tip) are required for quasi-steady-state voltammetry. Advantageously, a pair of quasi-steady-state voltammograms is obtained by employing both operation modes to reliably determine all transport, thermodynamic, and kinetic parameters as confirmed experimentally for rapid ET reactions of ferrocenemethanol and 7,7,8,8-tetracyanoquinodimethane at a Pt substrate with ∼0.5 μm-radius Pt tips positioned at 90 nm-1 μm distances. Standard ET rate constants of ∼7 cm/s were obtained for the latter mediator as the largest determined for a substrate reaction by SECM. Various potential applications of quasi-steady-state voltammetry are also proposed.

Nonequilibrium steady state of biochemical cycle kinetics under non-isothermal conditions

NASA Astrophysics Data System (ADS)

Jin, Xiao; Ge, Hao

2018-04-01

The nonequilibrium steady state of isothermal biochemical cycle kinetics has been extensively studied, but that under non-isothermal conditions has been much less extensively investigated. When the heat exchange between subsystems is slow, the isothermal assumption of the whole system breaks down, as is true for many types of living organisms. Here, starting with a four-state model of molecular transporter across the cell membrane, we generalize the nonequilibrium steady-state theory of isothermal biochemical cycle kinetics to the circumstances with non-uniform temperatures of subsystems in terms of general master equation models. We obtain a new thermodynamic relationship between the chemical reaction rates and thermodynamic potentials in non-isothermal circumstances, based on the overdamped dynamics along the continuous reaction coordinate. We show that the entropy production can vary up to 3% in real cells, even when the temperature difference across the cell membrane is only approximately 1 K. We then decompose the total thermodynamic driving force into its thermal and chemical components and predict that the net flux of molecules transported by the molecular transporter can potentially go against the temperature gradient in the absence of a chemical driving force. Furthermore, we demonstrate that the simple application of the isothermal transition-state rate formula for each chemical reaction in terms of only the reactant’ temperature is not thermodynamically consistent. Therefore, we mathematically derive several revised reaction rate formulas that are not only consistent with the new thermodynamic relationship but also approximate the exact reaction rate better than Kramers’ rate formula under isothermal conditions.

Effect of oral nitrate supplementation on pulmonary hemodynamics during exercise and time trial performance in normoxia and hypoxia: a randomized controlled trial

PubMed Central

Bourdillon, Nicolas; Fan, Jui-Lin; Uva, Barbara; Müller, Hajo; Meyer, Philippe; Kayser, Bengt

2015-01-01

Background: Hypoxia-induced pulmonary vasoconstriction increases pulmonary arterial pressure (PAP) and may impede right heart function and exercise performance. This study examined the effects of oral nitrate supplementation on right heart function and performance during exercise in normoxia and hypoxia. We tested the hypothesis that nitrate supplementation would attenuate the increase in PAP at rest and during exercise in hypoxia, thereby improving exercise performance. Methods: Twelve trained male cyclists [age: 31 ± 7 year (mean ± SD)] performed 15 km time-trial cycling (TT) and steady-state submaximal cycling (50, 100, and 150 W) in normoxia and hypoxia (11% inspired O2) following 3-day oral supplementation with either placebo or sodium nitrate (0.1 mmol/kg/day). We measured TT time-to-completion, muscle tissue oxygenation during TT and systolic right ventricle to right atrium pressure gradient (RV-RA gradient: index of PAP) during steady state cycling. Results: During steady state exercise, hypoxia elevated RV-RA gradient (p > 0.05), while oral nitrate supplementation did not alter RV-RA gradient (p > 0.05). During 15 km TT, hypoxia lowered muscle tissue oxygenation (p < 0.05). Nitrate supplementation further decreased muscle tissue oxygenation during 15 km TT in hypoxia (p < 0.05). Hypoxia impaired time-to-completion during TT (p < 0.05), while no improvements were observed with nitrate supplementation in normoxia or hypoxia (p > 0.05). Conclusion: Our findings indicate that oral nitrate supplementation does not attenuate acute hypoxic pulmonary vasoconstriction nor improve performance during time trial cycling in normoxia and hypoxia. PMID:26528189

ANALYSIS OF MERCURY IN VERMONT AND NEW HAMPSHIRE LAKES: EVALUATION OF THE REGIONAL MERCURY CYCLING MODEL

EPA Science Inventory

An evaluation of the Regional Mercury Cycling Model (R-MCM, a steady-state fate and transport model used to simulate mercury concentrations in lakes) is presented based on its application to a series of 91 lakes in Vermont and New Hampshire. Visual and statistical analyses are pr...

Mariner Jupiter/Saturn LCSSE thruster/valve assembly and injection propulsion unit rocket engine assemblies: 0.2-lbf T/VA development and margin limit test report

NASA Technical Reports Server (NTRS)

Clark, E. C.

1975-01-01

Thruster valve assemblies (T/VA's) were subjected to the development test program for the combined JPL Low-Cost Standardized Spacecraft Equipment (LCSSE) and Mariner Jupiter/Saturn '77 spacecraft (MJS) programs. The development test program was designed to achieve the following program goals: (1) demonstrate T/VA design compliance with JPL Specifications, (2) to conduct a complete performance Cf map of the T/VA over the full operating range of environment, (3) demonstrate T/VA life capability and characteristics of life margin for steady-state limit cycle and momentum wheel desaturation duty cycles, (4) verification of structural design capability, and (5) generate a computerized performance model capable of predicting T/VA operation over pressures ranging from 420 to 70 psia, propellant temperatures ranging from 140 F to 40 F, pulse widths of 0.008 to steady-state operation with unlimited duty cycle capability, and finally predict the transient performance associated with reactor heatup during any given duty cycle, start temperature, feed pressure, and propellant temperature conditions.

Slow-slip events on the Whillans Ice Plain, Antarctica, described using rate-and-state friction as an ice stream sliding law

NASA Astrophysics Data System (ADS)

Lipovsky, Bradley Paul; Dunham, Eric M.

2017-04-01

The Whillans Ice Plain (WIP), Antarctica, experiences twice daily tidally modulated stick-slip cycles. Slip events last about 30 min, have sliding velocities as high as ˜0.5 mm/s (15 km/yr), and have total slip ˜0.5 m. Slip events tend to occur during falling ocean tide: just after high tide and just before low tide. To reproduce these characteristics, we use rate-and-state friction, which is commonly used to simulate tectonic faulting, as an ice stream sliding law. This framework describes the evolving strength of the ice-bed interface throughout stick-slip cycles. We present simulations that resolve the cross-stream dimension using a depth-integrated treatment of an elastic ice layer loaded by tides and steady ice inflow. Steady sliding with rate-weakening friction is conditionally stable with steady sliding occurring for sufficiently narrow ice streams relative to a nucleation length. Stick-slip cycles occur when the ice stream is wider than the nucleation length or, equivalently, when effective pressures exceed a critical value. Ice streams barely wider than the nucleation length experience slow-slip events, and our simulations suggest that the WIP is in this slow-slip regime. Slip events on the WIP show a sense of propagation, and we reproduce this behavior by introducing a rate-strengthening region in the center of the otherwise rate-weakening ice stream. If pore pressures are raised above a critical value, our simulations predict that the WIP would exhibit quasi-steady tidally modulated sliding as observed on other ice streams. This study validates rate-and-state friction as a sliding law to describe ice stream sliding styles.

WASP Model Tutorials

EPA Pesticide Factsheets

Contains WASP tutorial videos. WASP Command Line, WASP, Modeling Dissolved Oxygen, Building a Steady State Example, Modeling Nutrients in Rivers, Nutrient Cycles, Interpreting Water Quality Models, Linking with LSPC, WRDB, BASINS, WCS, WASP Network Tool

Performance Benefits for Wave Rotor-Topped Gas Turbine Engines

NASA Technical Reports Server (NTRS)

Jones, Scott M.; Welch, Gerard E.

1996-01-01

The benefits of wave rotor-topping in turboshaft engines, subsonic high-bypass turbofan engines, auxiliary power units, and ground power units are evaluated. The thermodynamic cycle performance is modeled using a one-dimensional steady-state code; wave rotor performance is modeled using one-dimensional design/analysis codes. Design and off-design engine performance is calculated for baseline engines and wave rotor-topped engines, where the wave rotor acts as a high pressure spool. The wave rotor-enhanced engines are shown to have benefits in specific power and specific fuel flow over the baseline engines without increasing turbine inlet temperature. The off-design steady-state behavior of a wave rotor-topped engine is shown to be similar to a conventional engine. Mission studies are performed to quantify aircraft performance benefits for various wave rotor cycle and weight parameters. Gas turbine engine cycles most likely to benefit from wave rotor-topping are identified. Issues of practical integration and the corresponding technical challenges with various engine types are discussed.

Correcting oral contraceptive pharmacokinetic alterations due to obesity. A randomized controlled trial

PubMed Central

Edelman, Alison B; Cherala, Ganesh; Munar, Myrna Y.; McInnis, Martha; Stanczyk, Frank Z.; Jensen, Jeffrey T

2014-01-01

Objective To determine if increasing the hormone dose or eliminating the hormone-free interval improves key pharmacokinetic (PK) alterations caused by obesity during oral contraceptive (OC) use. Study design Obese (BMI ≥ 30 kg/m2), ovulatory, otherwise healthy, women received an OC containing 20 mcg ethinyl estradiol (EE)/100 mcg levonorgestrel (LNG) dosed cyclically (21 days active pills with 7-day placebo week) for two cycles and then were randomized for two additional cycles to: Continuous Cycling [CC, a dose neutral arm using the same OC with no hormone-free interval] or Increased Dose [ID, a dose escalation arm using an OC containing 30 mcg EE/150 mcg LNG cyclically]. During Cycle 2, 3, and 4, outpatient visits were performed to assess maximum serum concentration (Cmax), area under the curve (AUC0-∞), and time to steady state as well as pharmacodynamics. These key PK parameters were calculated and compared within groups between baseline and treatment cycles. Results A total of 31 women enrolled and completed the study (CC group n = 16; ID group n = 15). Demographics were similar between groups [mean BMI: CC 38kg/m2 (SD 5.1), ID 41kg/m2 (SD 7.6)]. At baseline, the key LNG PK parameters were no different between groups; average time to reach steady-state was 12 days in both groups; Cmax were CC: 3.82 ± 1.28 ng/mL and ID: 3.13 ± 0.87 ng/mL; and AUC0-∞ were CC: 267 ± 115 hr*ng/mL and ID: 199±75 hr*ng/mL. Following randomization, the CC group maintained steady-state serum levels whereas the ID group had a significantly higher Cmax (p< 0.001) but again required 12 days to achieve steady-state. However, AUC was not significantly different between CC (412 ± 255 hr*ng/mL) and ID (283 ± 130 hr*ng/mL). Forty-five percent (14/31) of the study population had evidence of an active follicle-like structure prior to randomization and afterwards this decreased to 9% (3/31). Conclusion Both increasing the OC dose and continuous dosing appear to counteract the impact of obesity on key OC PK parameters. PMID:25070547

40 CFR 1039.505 - How do I test engines using steady-state duty cycles, including ramped-modal testing?

Code of Federal Regulations, 2013 CFR

2013-07-01

.... You may extend the sampling time to improve measurement accuracy of PM emissions, using good..., you may omit speed, torque, and power points from the duty-cycle regression statistics if the... mapped. (2) For variable-speed engines without low-speed governors, you may omit torque and power points...

40 CFR 1039.505 - How do I test engines using steady-state duty cycles, including ramped-modal testing?

Code of Federal Regulations, 2012 CFR

2012-07-01

.... You may extend the sampling time to improve measurement accuracy of PM emissions, using good..., you may omit speed, torque, and power points from the duty-cycle regression statistics if the... mapped. (2) For variable-speed engines without low-speed governors, you may omit torque and power points...

Nonequilibrium life-cycles in Ocean Heat Content

NASA Astrophysics Data System (ADS)

Weiss, Jeffrey B.; Fox-Kemper, Baylor; Mandal, Dibyendu; Zia, Royce K. P.

2014-03-01

Natural climate variability can be considered as fluctuations in a nonequilibrium steady state. A fundamental property of nonequilibrium steady states is the phase space current which provides a preferred direction for fluctuations, and is manifested as preferred life-cycles for climate fluctuations. We propose a new quantity, the phase space angular momentum, to quantify the phase space rotation. In analogy with traditional angular momentum, which quantifies the rotation of mass in physical space, the phase space angular momentum quantifies the rotation of probability in phase space. It has the additional advantage that it is straightforward to calculate from a time series. We investigate the phase space angular momentum for fluctuations in ocean heat content in both observations and ocean general circulation models. We gratefully acknowledge financial support from the National Science Foundation (USA) under grant OCE 1245944.

Drive cycle analysis of butanol/diesel blends in a light-duty vehicle.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miers, S. A.; Carlson, R. W.; McConnell, S. S.

2008-10-01

The potential exists to displace a portion of the petroleum diesel demand with butanol and positively impact engine-out particulate matter. As a preliminary investigation, 20% and 40% by volume blends of butanol with ultra low sulfur diesel fuel were operated in a 1999 Mercedes Benz C220 turbo diesel vehicle (Euro III compliant). Cold and hot start urban as well as highway drive cycle tests were performed for the two blends of butanol and compared to diesel fuel. In addition, 35 MPH and 55 MPH steady-state tests were conducted under varying road loads for the two fuel blends. Exhaust gas emissions,more » fuel consumption, and intake and exhaust temperatures were acquired for each test condition. Filter smoke numbers were also acquired during the steady-state tests.« less

Effect of Surface-mantle Water Exchange Parameterizations on Exoplanet Ocean Depths

NASA Astrophysics Data System (ADS)

Komacek, Thaddeus D.; Abbot, Dorian S.

2016-11-01

Terrestrial exoplanets in the canonical habitable zone may have a variety of initial water fractions due to random volatile delivery by planetesimals. If the total planetary water complement is high, the entire surface may be covered in water, forming a “waterworld.” On a planet with active tectonics, competing mechanisms act to regulate the abundance of water on the surface by determining the partitioning of water between interior and surface. Here we explore how the incorporation of different mechanisms for the degassing and regassing of water changes the volatile evolution of a planet. For all of the models considered, volatile cycling reaches an approximate steady state after ∼ 2 {Gyr}. Using these steady states, we find that if volatile cycling is either solely dependent on temperature or seafloor pressure, exoplanets require a high abundance (≳ 0.3 % of total mass) of water to have fully inundated surfaces. However, if degassing is more dependent on seafloor pressure and regassing mainly dependent on mantle temperature, the degassing rate is relatively large at late times and a steady state between degassing and regassing is reached with a substantial surface water fraction. If this hybrid model is physical, super-Earths with a total water fraction similar to that of the Earth can become waterworlds. As a result, further understanding of the processes that drive volatile cycling on terrestrial planets is needed to determine the water fraction at which they are likely to become waterworlds.

Mitigation of near-band balanced steady-state free precession through-plane flow artifacts using partial dephasing.

PubMed

Datta, Anjali; Cheng, Joseph Y; Hargreaves, Brian A; Baron, Corey A; Nishimura, Dwight G

2018-06-01

To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing. A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects. Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets. Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med 79:2944-2953, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Inductive storage for quasi-steady MPD thrusters

NASA Technical Reports Server (NTRS)

Clark, K. E.

1978-01-01

Experiments in which a quasi-steady MPD thruster is driven by a large inductor demonstrate the feasibility of using inductive energy storage to couple an intermittent high power plasma thruster to a lower power steady state supply, such as a thermionic converter. Switching between inductor charging and MPD thrusting phases of the current cycle occurs smoothly, with the voltage spike generated during switching sufficient to initiate the arc discharge in the thruster without an auxiliary starting circuit. Further, the current waveforms delivered by the inductor are of a shape suitable for the quasi-steady thrusting process, and they agree with analytical estimates, indicating that the interaction between the thruster impedance and the inductive source is dynamically stable.

A Mechanistic Model of the Actin Cycle

PubMed Central

Bindschadler, M.; Osborn, E. A.; Dewey, C. F.; McGrath, J. L.

2004-01-01

We have derived a broad, deterministic model of the steady-state actin cycle that includes its major regulatory mechanisms. Ours is the first model to solve the complete nucleotide profile within filaments, a feature that determines the dynamics and geometry of actin networks at the leading edges of motile cells, and one that has challenged investigators developing models to interpret steady-state experiments. We arrived at the nucleotide profile through analytic and numerical approaches that completely agree. Our model reproduces behaviors seen in numerous experiments with purified proteins, but allows a detailed inspection of the concentrations and fluxes that might exist in these experiments. These inspections provide new insight into the mechanisms that determine the rate of actin filament treadmilling. Specifically, we find that mechanisms for enhancing Pi release from the ADP·Pi intermediate on filaments, for increasing the off rate of ADP-bound subunits at pointed ends, and the multiple, simultaneous functions of profilin, make unique and essential contributions to increased treadmilling. In combination, these mechanisms have a theoretical capacity to increase treadmilling to levels limited only by the amount of available actin. This limitation arises because as the cycle becomes more dynamic, it tends toward the unpolymerized state. PMID:15111391

On the Stable Limit Cycle of a Weight-Driven Pendulum Clock

ERIC Educational Resources Information Center

Llibre, J; Teixeira, M. A.

2010-01-01

In a recent paper (Denny 2002 Eur. J. Phys. 23 449-58), entitled "The pendulum clock: a venerable dynamical system", Denny showed that in a first approximation the steady-state motion of a weight-driven pendulum clock is shown to be a stable limit cycle. He placed the problem in a historical context and obtained an approximate solution using the…

Non-equilibrium steady states in supramolecular polymerization

NASA Astrophysics Data System (ADS)

Sorrenti, Alessandro; Leira-Iglesias, Jorge; Sato, Akihiro; Hermans, Thomas M.

2017-06-01

Living systems use fuel-driven supramolecular polymers such as actin to control important cell functions. Fuel molecules like ATP are used to control when and where such polymers should assemble and disassemble. The cell supplies fresh ATP to the cytosol and removes waste products to sustain steady states. Artificial fuel-driven polymers have been developed recently, but keeping them in sustained non-equilibrium steady states (NESS) has proven challenging. Here we show a supramolecular polymer that can be kept in NESS, inside a membrane reactor where ATP is added and waste removed continuously. Assembly and disassembly of our polymer is regulated by phosphorylation and dephosphorylation, respectively. Waste products lead to inhibition, causing the reaction cycle to stop. Inside the membrane reactor, however, waste can be removed leading to long-lived NESS conditions. We anticipate that our approach to obtain NESS can be applied to other stimuli-responsive materials to achieve more life-like behaviour.

An Introduction to System-Level, Steady-State and Transient Modeling and Optimization of High-Power-Density Thermoelectric Generator Devices Made of Segmented Thermoelectric Elements

NASA Astrophysics Data System (ADS)

Crane, D. T.

2011-05-01

High-power-density, segmented, thermoelectric (TE) elements have been intimately integrated into heat exchangers, eliminating many of the loss mechanisms of conventional TE assemblies, including the ceramic electrical isolation layer. Numerical models comprising simultaneously solved, nonlinear, energy balance equations have been created to simulate these novel architectures. Both steady-state and transient models have been created in a MATLAB/Simulink environment. The models predict data from experiments in various configurations and applications over a broad range of temperature, flow, and current conditions for power produced, efficiency, and a variety of other important outputs. Using the validated models, devices and systems are optimized using advanced multiparameter optimization techniques. Devices optimized for particular steady-state operating conditions can then be dynamically simulated in a transient operating model. The transient model can simulate a variety of operating conditions including automotive and truck drive cycles.

Effect of higher frequency on the classification of steady-state visual evoked potentials

NASA Astrophysics Data System (ADS)

Won, Dong-Ok; Hwang, Han-Jeong; Dähne, Sven; Müller, Klaus-Robert; Lee, Seong-Whan

2016-02-01

Objective. Most existing brain-computer interface (BCI) designs based on steady-state visual evoked potentials (SSVEPs) primarily use low frequency visual stimuli (e.g., <20 Hz) to elicit relatively high SSVEP amplitudes. While low frequency stimuli could evoke photosensitivity-based epileptic seizures, high frequency stimuli generally show less visual fatigue and no stimulus-related seizures. The fundamental objective of this study was to investigate the effect of stimulation frequency and duty-cycle on the usability of an SSVEP-based BCI system. Approach. We developed an SSVEP-based BCI speller using multiple LEDs flickering with low frequencies (6-14.9 Hz) with a duty-cycle of 50%, or higher frequencies (26-34.7 Hz) with duty-cycles of 50%, 60%, and 70%. The four different experimental conditions were tested with 26 subjects in order to investigate the impact of stimulation frequency and duty-cycle on performance and visual fatigue, and evaluated with a questionnaire survey. Resting state alpha powers were utilized to interpret our results from the neurophysiological point of view. Main results. The stimulation method employing higher frequencies not only showed less visual fatigue, but it also showed higher and more stable classification performance compared to that employing relatively lower frequencies. Different duty-cycles in the higher frequency stimulation conditions did not significantly affect visual fatigue, but a duty-cycle of 50% was a better choice with respect to performance. The performance of the higher frequency stimulation method was also less susceptible to resting state alpha powers, while that of the lower frequency stimulation method was negatively correlated with alpha powers. Significance. These results suggest that the use of higher frequency visual stimuli is more beneficial for performance improvement and stability as time passes when developing practical SSVEP-based BCI applications.

Effect of higher frequency on the classification of steady-state visual evoked potentials.

PubMed

Won, Dong-Ok; Hwang, Han-Jeong; Dähne, Sven; Müller, Klaus-Robert; Lee, Seong-Whan

2016-02-01

Most existing brain-computer interface (BCI) designs based on steady-state visual evoked potentials (SSVEPs) primarily use low frequency visual stimuli (e.g., <20 Hz) to elicit relatively high SSVEP amplitudes. While low frequency stimuli could evoke photosensitivity-based epileptic seizures, high frequency stimuli generally show less visual fatigue and no stimulus-related seizures. The fundamental objective of this study was to investigate the effect of stimulation frequency and duty-cycle on the usability of an SSVEP-based BCI system. We developed an SSVEP-based BCI speller using multiple LEDs flickering with low frequencies (6-14.9 Hz) with a duty-cycle of 50%, or higher frequencies (26-34.7 Hz) with duty-cycles of 50%, 60%, and 70%. The four different experimental conditions were tested with 26 subjects in order to investigate the impact of stimulation frequency and duty-cycle on performance and visual fatigue, and evaluated with a questionnaire survey. Resting state alpha powers were utilized to interpret our results from the neurophysiological point of view. The stimulation method employing higher frequencies not only showed less visual fatigue, but it also showed higher and more stable classification performance compared to that employing relatively lower frequencies. Different duty-cycles in the higher frequency stimulation conditions did not significantly affect visual fatigue, but a duty-cycle of 50% was a better choice with respect to performance. The performance of the higher frequency stimulation method was also less susceptible to resting state alpha powers, while that of the lower frequency stimulation method was negatively correlated with alpha powers. These results suggest that the use of higher frequency visual stimuli is more beneficial for performance improvement and stability as time passes when developing practical SSVEP-based BCI applications.

The Dynamic Earth.

ERIC Educational Resources Information Center

Siever, Raymond

1983-01-01

Discusses how the earth is a dynamic system that maintains itself in a steady state. Areas considered include large/small-scale earth motions, geologic time, rock and hydrologic cycles, and other aspects dealing with the changing face of the earth. (JN)

Fully Modulated Turbulent Diffusion Flames in Microgravity*

NASA Astrophysics Data System (ADS)

Sangras, Ravikiran; Hermanson, James C.; Johari, Hamid; Stocker, Dennis P.; Hegde, Uday G.

2001-11-01

Fully modulated, turbulent diffusion flames are studied in microgravity in 2.2 s drop-tower tests with a co-flow combustor. The fuel consists of pure ethylene or a 50/50 mixture with nitrogen; the oxidizer is either normal air or up to 40% oxygen in nitrogen. A fast solenoid valve is used to fully modulate (completely shut off) the fuel flow. The injection times range from 5 to 400 ms with a duty-cycle of 0.1 - 0.5. The fuel nozzle is 2 mm in diameter with a jet Reynolds number of 5000. The shortest injection times yield compact puffs with a mean flame length as little as 20% of that of the steady-state flame. The reduction in flame length appears to be somewhat greater in microgravity than in normal gravity. As the injection time increases, elongated flames result with a mean flame length comparable to that of a steady flame. The injection time for which the steady-state flame length is approached is shorter for lower air/fuel ratios. For a given duty-cycle, the separation between puffs is greater in microgravity than in normal gravity. For compact puffs, increasing the duty-cycle appears to increase the flame length more in microgravity than in normal gravity. The microgravity flame puffs do not exhibit the vortex-ring-like structure seen in normal gravity.

Transition from homogeneous to inhomogeneous limit cycles: Effect of local filtering in coupled oscillators

NASA Astrophysics Data System (ADS)

Banerjee, Tanmoy; Biswas, Debabrata; Ghosh, Debarati; Bandyopadhyay, Biswabibek; Kurths, Jürgen

2018-04-01

We report an interesting symmetry-breaking transition in coupled identical oscillators, namely, the continuous transition from homogeneous to inhomogeneous limit cycle oscillations. The observed transition is the oscillatory analog of the Turing-type symmetry-breaking transition from amplitude death (i.e., stable homogeneous steady state) to oscillation death (i.e., stable inhomogeneous steady state). This novel transition occurs in the parametric zone of occurrence of rhythmogenesis and oscillation death as a consequence of the presence of local filtering in the coupling path. We consider paradigmatic oscillators, such as Stuart-Landau and van der Pol oscillators, under mean-field coupling with low-pass or all-pass filtered self-feedback and through a rigorous bifurcation analysis we explore the genesis of this transition. Further, we experimentally demonstrate the observed transition, which establishes its robustness in the presence of parameter fluctuations and noise.

To Demonstrate an Integrated Solution for Plasma-Material Interfaces Compatible with an Optimized Core Plasma

NASA Astrophysics Data System (ADS)

Goldston, Robert; Brooks, Jeffrey; Hubbard, Amanda; Leonard, Anthony; Lipschultz, Bruce; Maingi, Rajesh; Ulrickson, Michael; Whyte, Dennis

2009-11-01

The plasma facing components in a Demo reactor will face much more extreme boundary plasma conditions and operating requirements than any present or planned experiment. These include 1) Power density a factor of four or more greater than in ITER, 2) Continuous operation resulting in annual energy and particle throughput 100-200 times larger than ITER, 3) Elevated surface operating temperature for efficient electricity production, 4) Tritium fuel cycle control for safety and breeding requirements, and 5) Steady state plasma confinement and control. Consistent with ReNeW Thrust 12, design options are being explored for a new moderate-scale facility to assess core-edge interaction issues and solutions. Key desired features include high power density, sufficient pulse length and duty cycle, elevated wall temperature, steady-state control of an optimized core plasma, and flexibility in changing boundary components as well as access for comprehensive measurements.

Refined elasticity sampling for Monte Carlo-based identification of stabilizing network patterns.

PubMed

Childs, Dorothee; Grimbs, Sergio; Selbig, Joachim

2015-06-15

Structural kinetic modelling (SKM) is a framework to analyse whether a metabolic steady state remains stable under perturbation, without requiring detailed knowledge about individual rate equations. It provides a representation of the system's Jacobian matrix that depends solely on the network structure, steady state measurements, and the elasticities at the steady state. For a measured steady state, stability criteria can be derived by generating a large number of SKMs with randomly sampled elasticities and evaluating the resulting Jacobian matrices. The elasticity space can be analysed statistically in order to detect network positions that contribute significantly to the perturbation response. Here, we extend this approach by examining the kinetic feasibility of the elasticity combinations created during Monte Carlo sampling. Using a set of small example systems, we show that the majority of sampled SKMs would yield negative kinetic parameters if they were translated back into kinetic models. To overcome this problem, a simple criterion is formulated that mitigates such infeasible models. After evaluating the small example pathways, the methodology was used to study two steady states of the neuronal TCA cycle and the intrinsic mechanisms responsible for their stability or instability. The findings of the statistical elasticity analysis confirm that several elasticities are jointly coordinated to control stability and that the main source for potential instabilities are mutations in the enzyme alpha-ketoglutarate dehydrogenase. © The Author 2015. Published by Oxford University Press.

A critical examination of the dual system theory in Ostrinia nubilalis.

PubMed

Skopik, S D; Takeda, M; Holyoke, C W

1981-11-01

Beck's dual system theory (DST) is examined theoretically and experimentally by investigating the oviposition rhythm of Ostrinia nubilalis and its entrainment by light cycles. Several well-known circadian phenomena are not accounted for by the DST. 1) It does not generate transient cycles when light pulses fall during the advance portion of the circadian cycle. This is also reflected in DST-predicted phase-response curves (PRC's) for both Drosophila pseudoobscura and O. nubilalis. Steady-state phase advances are predicted to occur on day 1 after the light pulses by the DST, not several cycles later as has been observed in many cases. 2) It does not account for the observation that the magnitude of a phase shift (delta phi) is often a function of pulse duration of both delays and advances. The DST predicts the same + delta phi, for example, for a 0.5-h and a 6.0-h light pulse beginning 5.0 h after dusk. 3) The DST does not accurately predict steady-state phase relationships between the light cycle and the gating oscillation (P-system) in non-24-h light cycles. 4) The driver (S-system) is given the property of being temperature sensitive whereas the driven rhythm (P-system) is temperature compensated. This is contrary to accumulated data suggesting that the circadian pacemaker is temperature compensated.

Single-particle stochastic heat engine.

PubMed

Rana, Shubhashis; Pal, P S; Saha, Arnab; Jayannavar, A M

2014-10-01

We have performed an extensive analysis of a single-particle stochastic heat engine constructed by manipulating a Brownian particle in a time-dependent harmonic potential. The cycle consists of two isothermal steps at different temperatures and two adiabatic steps similar to that of a Carnot engine. The engine shows qualitative differences in inertial and overdamped regimes. All the thermodynamic quantities, including efficiency, exhibit strong fluctuations in a time periodic steady state. The fluctuations of stochastic efficiency dominate over the mean values even in the quasistatic regime. Interestingly, our system acts as an engine provided the temperature difference between the two reservoirs is greater than a finite critical value which in turn depends on the cycle time and other system parameters. This is supported by our analytical results carried out in the quasistatic regime. Our system works more reliably as an engine for large cycle times. By studying various model systems, we observe that the operational characteristics are model dependent. Our results clearly rule out any universal relation between efficiency at maximum power and temperature of the baths. We have also verified fluctuation relations for heat engines in time periodic steady state.

Cell-cycle research with synchronous cultures: an evaluation

NASA Technical Reports Server (NTRS)

Helmstetter, C. E.; Thornton, M.; Grover, N. B.

2001-01-01

The baby-machine system, which produces new-born Escherichia coli cells from cultures immobilized on a membrane, was developed many years ago in an attempt to attain optimal synchrony with minimal disturbance of steady-state growth. In the present article, we put forward a model to describe the behaviour of cells produced by this method, and provide quantitative evaluation of the parameters involved, at each of four different growth rates. Considering the high level of selection achievable with this technique and the natural dispersion in interdivision times, we believe that the output of the baby machine is probably close to optimal in terms of both quality and persistence of synchrony. We show that considerable information on events in the cell cycle can be obtained from populations with age distributions very much broader than those achieved with the baby machine and differing only modestly from steady state. The data presented here, together with the long and fruitful history of findings employing the baby-machine technique, suggest that minimisation of stress on cells is the single most important factor for successful cell-cycle analysis.

Phase-exchange thermoacoustic engine

NASA Astrophysics Data System (ADS)

Offner, Avshalom; Meir, Avishai; Ramon, Guy Z.; WET Lab Team

2017-11-01

Phase-exchange thermoacoustic engines are reliable machines holding great promise in converting heat from low grade heat sources to mechanical or electrical power. In these engines the working fluid is a gas mixture containing one condensable component, decreasing the temperature difference required for ignition and steady state operation. Our experimental setup consists of a vertical acoustic resonator containing a mixture of air-water vapor. Water evaporates near the heat source, condenses at the heat sink and is drawn back down by gravity and capillary forces where it re-evaporates, sustaining a steady state closed thermodynamic cycle. We investigated the stability limit, namely the critical point at which temperature difference in the engine enables onset of self-excited oscillations, and the steady state of the engine. A simple theoretical model was derived, describing mechanisms of irreversible entropy generation and production of acoustic power in such engines. This model captures the essence in the differences between regular and phase-exchange thermoacoustic engines, and shows good agreement with experimental results of stability limit. Steady state results reveal not only a dramatic decrease in temperature difference, but also an increase in engine performances. The authors acknowledge the support from the Nancy and Stephen Grand Technion Energy Program (GTEP).

A Stress Test to Evaluate the Physical Capacity of Performing L-1 Anti-G Straining Maneuvers

DTIC Science & Technology

1988-09-01

similar to hyperventilation can produce respiratory alkalosis . Therefore, lowered G-tolerance may result from decreased cerebral blood flow. Another...VE), respiratory exchange ratio (RER) and heart rate (HR were determined for steady state exercise at AGSM duty cyclEs cf 2,, 215%, 33% and 50%. Thesc...V02, ml/kg/min), minute pulmonary ventilation (VE, I/min) and respiratory exchange ratio (RER, VCO 2/VO2) at each duty cycle of discontinuous AGSM

Nature and Stability of the Martian Seasonal Water Cycle

NASA Astrophysics Data System (ADS)

Richardson, M. I.; Wilson, R. J.

2001-12-01

Which components control the contemporary water cycle and what is the nature of the control mechanisms? These questions are at the heart of understanding how the Martian exchangeable water budget adjusts to perturbations and changes in the climate system. Analysis of a water cycle model embedded in the GFDL Mars GCM provides a paradigm for the water cycle as a feedback system, providing information on the important control points and response times. Much information on this system derives from monitoring the evolution towards steady state--one that resembles the observed water vapour and ice cloud distributions. The most important exchange balance in the system is that between the northern polar atmosphere and the rest of the planet. As the major net source for water, the northern residual water ice cap is active during summer, in the window of time between the sublimation and recondensation of the seasonal CO2 cap. At this time, water is exported from the northern polar atmosphere at a rate determined by the mixing capacity of the atmosphere and the amount of water held in the polar atmosphere. The latter is determined by the cap surface temperature. During the remainder of the year, water is returned to the pole. This return flux is determined by the atmospheric mixing capacity and the amount of water vapour held in the tropical and winter extratropical atmosphere. Steady-state is achieved when these fluxes balance. For a given climate state (and a roughly repeatable annual cycle of mixing), the outflux and influx of polar water are controlled by separate variables. Holding the cap temperature constant, the outflux will remain constant. Any perturbation to the global water budget will result in a change in the return flux that tends to oppose the sense of the perturbation--the perturbation will be damped. In the same way, a change in cap temperature (e.g. associated with a change in albedo) will result in changed water outflow. Again, this will tend to change the non-polar water vapour budget and hence the polar water influx so as to develop a new steady-state. It is important to note that only in this case is the steady-state global humidity changed: a given cap temperature and seasonal cycle of mixing capacity specifies a bulk steady-state atmospheric humidity. In all cases, the regolith acts as a damper on the system and adjusts to the global water distribution dictated ultimately by the northern cap. The model also suggests fast adjustment times, on order decades. A number of factors can affect atmospheric mixing capacity. As climate forcing factors change (associated with obliquity or greenhouse gas loading) the mixing capacity will change--an area for future study. The current mixing capacity of the atmosphere is also different from one that would obtain without atmospheric water condensation and sedimentation. Model clouds play important roles in returning water to the residual ice cap in northern summer, and significantly altering interhemispheric transport from that which would occur without clouds. As with previous studies, the southern polar cap acts as a permanent sink for water. The model and resulting paradigm for the water cycle can be used in very preliminary studies of past climate states. Forcing the model with an obliquity of 45 deg., the seasonal water ice caps become significantly more extended, reaching into the summer hemisphere. In fact, the seasonal caps "overlap" in the northern tropics, generating a year-round surface ice belt. Much work remains to be done in understanding water ice transport and exchange processes before models of paleoclimate can be of widespread utility--of which analysis of data from MGS and future missions will be key.

Time course of the uridylylation and adenylylation states in the glutamine synthetase bicyclic cascade.

PubMed Central

Varón-Castellanos, R; Havsteen, B H; García-Moreno, M; Valero-Ruiz, E; Molina-Alarcón, M; García-Cánovas, F

1993-01-01

A kinetic analysis of the glutamine synthetase bicyclic cascade is presented. It includes the dependence on time from the onset of the reaction of both the uridylylation of Shapiro's regulatory protein and the adenylylation of the glutamine synthetase. The transient phase equations obtained allow an estimation of the time elapsed until the states of uridylylation and adenylylation reach their steady-states, and therefore an evaluation of the effective sensitivity of the system. The contribution of the uridylylation cycle to the adenylylation cycle has been studied, and an equation relating the state of adenylylation at any time to the state of uridylylation at the same instant has been derived. PMID:8104399

Iterative LQG Controller Design Through Closed-Loop Identification

NASA Technical Reports Server (NTRS)

Hsiao, Min-Hung; Huang, Jen-Kuang; Cox, David E.

1996-01-01

This paper presents an iterative Linear Quadratic Gaussian (LQG) controller design approach for a linear stochastic system with an uncertain open-loop model and unknown noise statistics. This approach consists of closed-loop identification and controller redesign cycles. In each cycle, the closed-loop identification method is used to identify an open-loop model and a steady-state Kalman filter gain from closed-loop input/output test data obtained by using a feedback LQG controller designed from the previous cycle. Then the identified open-loop model is used to redesign the state feedback. The state feedback and the identified Kalman filter gain are used to form an updated LQC controller for the next cycle. This iterative process continues until the updated controller converges. The proposed controller design is demonstrated by numerical simulations and experiments on a highly unstable large-gap magnetic suspension system.

Cyclic steady state stress-strain behavior of UHMW polyethylene.

PubMed

Krzypow, D J; Rimnac, C M

2000-10-01

To increase the long-term performance of total joint replacements, finite element analyses of ultra high molecular weight polyethylene (UHMWPE) components have been conducted to predict the effect of load on the stress and strain distributions occurring on and within these components. Early models incorporated the monotonic behavior of UHMWPE without considering the unloading and cyclic loading behavior. However, UHMWPE components undergo cyclic loading during use and at least two wear damage modes (pitting and delamination) are thought to be associated with the fatigue fracture properties of UHMWPE. The objective of this study was to examine the fully reversed uniaxial tension/compression cyclic steady state stress-strain behavior of UHMWPE as a first step towards developing a cyclic constitutive relationship for UHMWPE. The hypothesis that cycling results in a permanent change in the stress-strain relationship, that is, that the cyclic steady state represents a new cyclically stabilized state, was examined. It was found that, like other ductile polymers, UHMWPE substantially cyclically softens under fully reversed uniaxial straining. More cyclic softening occurred in tension than in compression. Furthermore, cyclic steady state was attained, but not cyclic stability. It is suggested that it may be more appropriate to base a material constitutive relationship for UHMWPE for finite element analyses of components upon a cyclically modified stress-strain relationship.

Developing Exemplary Civilian-Military Relationships

DTIC Science & Technology

1989-07-01

military efforts? The implication is that community relations never The cycle never ends. Good civilian-military rela- reach a steady state; they are...the dimensions and dynamics of the civilian- qualify for in-state tuition rates at Virginia colleges ; and military relationship. What were some of...another 1,200 civilian local department chosen by the state of Mississippi to and contractor employees, and almost 8,000 students provide DARE training

The Effects of High Intensity Interval Training vs Steady State Training on Aerobic and Anaerobic Capacity

PubMed Central

Foster, Carl; Farland, Courtney V.; Guidotti, Flavia; Harbin, Michelle; Roberts, Brianna; Schuette, Jeff; Tuuri, Andrew; Doberstein, Scott T.; Porcari, John P.

2015-01-01

High intensity interval training (HIIT) has become an increasingly popular form of exercise due to its potentially large effects on exercise capacity and small time requirement. This study compared the effects of two HIIT protocols vs steady-state training on aerobic and anaerobic capacity following 8-weeks of training. Fifty-five untrained college-aged subjects were randomly assigned to three training groups (3x weekly). Steady-state (n = 19) exercised (cycle ergometer) 20 minutes at 90% of ventilatory threshold (VT). Tabata (n = 21) completed eight intervals of 20s at 170% VO2max/10s rest. Meyer (n = 15) completed 13 sets of 30s (20 min) @ 100% PVO2 max/ 60s recovery, average PO = 90% VT. Each subject did 24 training sessions during 8 weeks. Results: There were significant (p < 0.05) increases in VO2max (+19, +18 and +18%) and PPO (+17, +24 and +14%) for each training group, as well as significant increases in peak (+8, + 9 and +5%) & mean (+4, +7 and +6%) power during Wingate testing, but no significant differences between groups. Measures of the enjoyment of the training program indicated that the Tabata protocol was significantly less enjoyable (p < 0.05) than the steady state and Meyer protocols, and that the enjoyment of all protocols declined (p < 0.05) across the duration of the study. The results suggest that although HIIT protocols are time efficient, they are not superior to conventional exercise training in sedentary young adults. Key points Steady state training equivalent to HIIT in untrained students Mild interval training presents very similar physiologic challenge compared to steady state training HIIT (particularly very high intensity variants were less enjoyable than steady state or mild interval training Enjoyment of training decreases across the course of an 8 week experimental training program PMID:26664271

The Effects of High Intensity Interval Training vs Steady State Training on Aerobic and Anaerobic Capacity.

PubMed

Foster, Carl; Farland, Courtney V; Guidotti, Flavia; Harbin, Michelle; Roberts, Brianna; Schuette, Jeff; Tuuri, Andrew; Doberstein, Scott T; Porcari, John P

2015-12-01

High intensity interval training (HIIT) has become an increasingly popular form of exercise due to its potentially large effects on exercise capacity and small time requirement. This study compared the effects of two HIIT protocols vs steady-state training on aerobic and anaerobic capacity following 8-weeks of training. Fifty-five untrained college-aged subjects were randomly assigned to three training groups (3x weekly). Steady-state (n = 19) exercised (cycle ergometer) 20 minutes at 90% of ventilatory threshold (VT). Tabata (n = 21) completed eight intervals of 20s at 170% VO2max/10s rest. Meyer (n = 15) completed 13 sets of 30s (20 min) @ 100% PVO2 max/ 60s recovery, average PO = 90% VT. Each subject did 24 training sessions during 8 weeks. There were significant (p < 0.05) increases in VO2max (+19, +18 and +18%) and PPO (+17, +24 and +14%) for each training group, as well as significant increases in peak (+8, + 9 and +5%) & mean (+4, +7 and +6%) power during Wingate testing, but no significant differences between groups. Measures of the enjoyment of the training program indicated that the Tabata protocol was significantly less enjoyable (p < 0.05) than the steady state and Meyer protocols, and that the enjoyment of all protocols declined (p < 0.05) across the duration of the study. The results suggest that although HIIT protocols are time efficient, they are not superior to conventional exercise training in sedentary young adults. Key pointsSteady state training equivalent to HIIT in untrained studentsMild interval training presents very similar physiologic challenge compared to steady state trainingHIIT (particularly very high intensity variants were less enjoyable than steady state or mild interval trainingEnjoyment of training decreases across the course of an 8 week experimental training program.

ESTIMATING SYSTEMIC EXPOSURE TO ETHINYL ESTRADIOL FROM AN ORAL CONTRACEPTIVE

PubMed Central

WESTHOFF, Carolyn L.; PIKE, Malcolm C.; TANG, Rosalind; DINAPOLI, Marianne N.; SULL, Monica; CREMERS, Serge

2015-01-01

Objectives This study was conducted to compare single-dose pharmacokinetics of ethinyl estradiol in an oral contraceptive to steady-state values, and to assess whether any simpler measures could provide an adequate proxy of the ‘gold standard’ 24-hour steady-state area-under-the-curve. Identifying a simple, less expensive, measure of systemic ethinyl estradiol exposure would be useful for larger studies designed to assess the relationship between an individual’s ethinyl estradiol exposure and her side effects. Study Design We conducted a 13 samples over 24 hours pharmacokinetic analysis on day 1 and day 21 of the first cycle of a monophasic oral contraceptive containing 30 mcg ethinyl estradiol and 150 mcg levonorgestrel in 17 non-obese healthy white women. We also conducted an abbreviated single dose 9-sample pharmacokinetic analysis after a month washout. Ethinyl estradiol was measured by liquid chromatography-tandem mass spectrometry. We compared results of full 13-sample steady-state pharmacokinetic analysis with results calculated using fewer samples (9 or 5) and following the single doses. We calculated Pearson correlation coefficients to evaluate the relationships between these estimates of systemic ethinyl estradiol exposure. Results The area-under-the-curve, maximum (Cmax), and 24-hour (C24) values were similar following the two single oral contraceptive doses (area-under-the-curve, r = 0.92). The steady-state 13-sample 24-hour area-under-the-curve was highly correlated with the average 9-sample area-under-the-curve after the two single doses (r = 0.81, p = 0.0002). This correlation remained the same if the number of samples was reduced to 4, taken at time 1, 2.5, 4 and 24 hours. The C24 at steady-state was highly correlated with the 24-hour steady-state area-under-the-curve (r = 0.92, p < 0.0001). The average of the C24 values following the two single doses was also quite highly correlated with the steady-state area-under-the-curve (r = 0.72, p = 0.0026). Conclusions Limited blood sampling, including results from two single doses, gave highly correlated estimates of an oral contraceptive user’s steady-state ethinyl estradiol exposure. PMID:25511238

Estimating systemic exposure to ethinyl estradiol from an oral contraceptive.

PubMed

Westhoff, Carolyn L; Pike, Malcolm C; Tang, Rosalind; DiNapoli, Marianne N; Sull, Monica; Cremers, Serge

2015-05-01

This study was conducted to compare single-dose pharmacokinetics of ethinyl estradiol in an oral contraceptive with steady-state values and to assess whether any simpler measures could provide an adequate proxy of the "gold standard" 24-hour steady-state area under the curve (AUC) value. Identification of a simple, less expensive measure of systemic ethinyl estradiol exposure would be useful for larger studies that are designed to assess the relationship between an individual's ethinyl estradiol exposure and side-effects. We collected 13 samples over 24 hours for pharmacokinetic analysis on days 1 and 21 of the first cycle of a monophasic oral contraceptive that contained 30 μg ethinyl estradiol and 150 μg levonorgestrel in 17 nonobese healthy white women. We also conducted an abbreviated single-dose 9-sample pharmacokinetic analysis after a month washout. Ethinyl estradiol was measured by liquid chromatography-tandem mass spectrometry. We compared results of a full 13-sample steady-state pharmacokinetic analysis with results that had been calculated with the use of fewer samples (9 or 5) and after the single doses. We calculated Pearson correlation coefficients to evaluate the relationships between these estimates of systemic ethinyl estradiol exposure. The AUC, maximum, and 24-hour values were similar after the 2 single oral contraceptive doses (AUC; r=0.92). The steady-state 13-sample 24-hour AUC value was correlated highly with the average 9-sample AUC value after the 2 single doses (r=0.81; P=.0002). This correlation remained the same if the number of single-dose samples was reduced to 4, taken at time 1, 2.5, 4, and 24 hours. The 24-hour value at steady-state was correlated highly with the 24-hour steady-state AUC value (r=0.92; P<.0001). The average of the 24-hour values after the 2 single doses was also correlated quite highly with the steady-state AUC value (r=0.72; P=.0026). Limited blood sampling, including results from 2 single doses, gave highly correlated estimates of an oral contraceptive user's steady-state ethinyl estradiol exposure. Copyright © 2015 Elsevier Inc. All rights reserved.

Cardiomyocyte cell cycle control and growth estimation in vivo--an analysis based on cardiomyocyte nuclei.

PubMed

Walsh, Stuart; Pontén, Annica; Fleischmann, Bernd K; Jovinge, Stefan

2010-06-01

Adult mammalian cardiomyocytes are traditionally viewed as being permanently withdrawn from the cell cycle. Whereas some groups have reported none, others have reported extensive mitosis in adult myocardium under steady-state conditions. Recently, a highly specific assay of 14C dating in humans has suggested a continuous generation of cardiomyocytes in the adult, albeit at a very low rate. Mice represent the most commonly used animal model for these studies, but their short lifespan makes them unsuitable for 14C studies. Herein, we investigate the cellular growth pattern for murine cardiomyocyte growth under steady-state conditions, addressed with new analytical and technical strategies, and we furthermore relate this to gene expression patterns. The observed levels of DNA synthesis in early life were associated with cardiomyocyte proliferation. Mitosis was prolonged into early life, longer than the most conservative previous estimates. DNA synthesis in neonatal life was attributable to bi-nucleation, therefore suggesting that cardiomyocytes withdraw from the cell cycle shortly after birth. No cell cycle activity was observed in adult cardiomyocytes and significant polyploidy was observed in cardiomyocyte nuclei. Gene analyses identified 32 genes whose expression was predicted to be particular to day 3-4 neonatal myocytes, compared with embryonic or adult cells. These cell cycle-associated genes are crucial to the understanding of the mechanisms of bi-nucleation and physiological cellular growth in the neonatal period.

The Atacama Large Millimeter/submillimeter Array - from Early Science to Full Operations.

NASA Astrophysics Data System (ADS)

Remijan, Anthony

2017-06-01

The Atacama Large Millimeter/Submillimeter Array (ALMA) is now entering its 6th cycle of scientific observations. Starting with Cycle 3, science observations were no longer considered "Early Science" or "best efforts". Cycle 5 is now the third cycle of "steady state" observations and Cycle 7 is advertised to begin ALMA "full science" operations. ALMA Full Science Operations will include all the capabilities that were agreed upon by the international consortium after the ALMA re-baselining effort. In this talk, I will detail the upcoming ALMA Cycle 5 observing capabilities, describe the process of selecting new observing modes for upcoming cycles and provide an update on the status of the ALMA Full Science capabilities.

Experimental Validation of a Closed Brayton Cycle System Transient Simulation

NASA Technical Reports Server (NTRS)

Johnson, Paul K.; Hervol, David S.

2006-01-01

The Brayton Power Conversion Unit (BPCU) is a closed cycle system with an inert gas working fluid. It is located in Vacuum Facility 6 at NASA Glenn Research Center. Was used in previous solar dynamic technology efforts (SDGTD). Modified to its present configuration by replacing the solar receiver with an electrical resistance heater. The first closed-Brayton-cycle to be coupled with an ion propulsion system. Used to examine mechanical dynamic characteristics and responses. The focus of this work was the validation of a computer model of the BPCU. Model was built using the Closed Cycle System Simulation (CCSS) design and analysis tool. Test conditions were then duplicated in CCSS. Various steady-state points. Transients involving changes in shaft rotational speed and heat input. Testing to date has shown that the BPCU is able to generate meaningful, repeatable data that can be used for computer model validation. Results generated by CCSS demonstrated that the model sufficiently reproduced the thermal transients exhibited by the BPCU system. CCSS was also used to match BPCU steady-state operating points. Cycle temperatures were within 4.1% of the data (most were within 1%). Cycle pressures were all within 3.2%. Error in alternator power (as much as 13.5%) was attributed to uncertainties in the compressor and turbine maps and alternator and bearing loss models. The acquired understanding of the BPCU behavior gives useful insight for improvements to be made to the CCSS model as well as ideas for future testing and possible system modifications.

The interaction of excited atoms and few-cycle laser pulses

PubMed Central

Calvert, J. E.; Xu, Han; Palmer, A. J.; Glover, R. D.; Laban, D. E.; Tong, X. M.; Kheifets, A. S.; Bartschat, K.; Litvinyuk, I. V.; Kielpinski, D.; Sang, R. T.

2016-01-01

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse. We compare the observations to theoretical predictions based on the Ammosov-Delone-Krainov (ADK) theory and a solution to the time-dependent Schrödinger equation (TDSE). The TDSE provides better agreement with the experimental data than the ADK theory. We optically pump the target atomic species and measure the ionisation rate as the a function of different steady-state populations in the fine structure of the target state which shows significant ionisation rate dependence on populations of spin-polarised states. The physical mechanism for this effect is unknown. PMID:27666403

The interaction of excited atoms and few-cycle laser pulses.

PubMed

Calvert, J E; Xu, Han; Palmer, A J; Glover, R D; Laban, D E; Tong, X M; Kheifets, A S; Bartschat, K; Litvinyuk, I V; Kielpinski, D; Sang, R T

2016-09-26

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse. We compare the observations to theoretical predictions based on the Ammosov-Delone-Krainov (ADK) theory and a solution to the time-dependent Schrödinger equation (TDSE). The TDSE provides better agreement with the experimental data than the ADK theory. We optically pump the target atomic species and measure the ionisation rate as the a function of different steady-state populations in the fine structure of the target state which shows significant ionisation rate dependence on populations of spin-polarised states. The physical mechanism for this effect is unknown.

Computation of Steady-State Probability Distributions in Stochastic Models of Cellular Networks

PubMed Central

Hallen, Mark; Li, Bochong; Tanouchi, Yu; Tan, Cheemeng; West, Mike; You, Lingchong

2011-01-01

Cellular processes are “noisy”. In each cell, concentrations of molecules are subject to random fluctuations due to the small numbers of these molecules and to environmental perturbations. While noise varies with time, it is often measured at steady state, for example by flow cytometry. When interrogating aspects of a cellular network by such steady-state measurements of network components, a key need is to develop efficient methods to simulate and compute these distributions. We describe innovations in stochastic modeling coupled with approaches to this computational challenge: first, an approach to modeling intrinsic noise via solution of the chemical master equation, and second, a convolution technique to account for contributions of extrinsic noise. We show how these techniques can be combined in a streamlined procedure for evaluation of different sources of variability in a biochemical network. Evaluation and illustrations are given in analysis of two well-characterized synthetic gene circuits, as well as a signaling network underlying the mammalian cell cycle entry. PMID:22022252

Cardiorespiratory dynamics: sensitivity of the on-transition to endurance-training status.

PubMed

Taylor, N A; Osborne, M A; Bube, T L; Stocks, J M

1999-10-01

This project investigated the sensitivity of oxygen uptake (VO(2)) dynamics to training-induced physiological changes, across a broad spectrum of endurance-training histories. Forty subjects participated: sedentary (n = 10), active healthy (n = 10), regular runners (n = 10), and competitive distance runners (n = 10). Subjects completed a cycle step-function protocol, to elicit a steady state at 60% maximal work rate. Breath-by-breath data were collected for VO(2) and cardiac frequency (f(c)), and modelled mathematically, and used to determine the average response times to attain 20%, 40%, 60%, 80% and 100% of the respective steady states. The between-group comparisons for both VO(2) and f(c) revealed significantly faster response times to 40%, 60%, 80% and 100% of the induced response, for the better trained subjects (P < 0.05). In general, this technique permitted differentiation between the VO(2) and f(c) response dynamics of non-elite subjects from a broad range of endurance-training histories, with differences becoming more pronounced as subjects approached the steady state.

Revelations of X-ray spectral analysis of the enigmatic black hole binary GRS 1915+105

NASA Astrophysics Data System (ADS)

Peris, Charith; Remillard, Ronald A.; Steiner, James; Vrtilek, Saeqa Dil; Varniere, Peggy; Rodriguez, Jerome; Pooley, Guy

2016-01-01

Of the black hole binaries discovered thus far, GRS 1915+105 stands out as an exceptional source primarily due to its wild X-ray variability, the diversity of which has not been replicated in any other stellar-mass black hole. Although extreme variability is commonplace in its light-curve, about half of the observations of GRS1915+105 show fairly steady X-ray intensity. We report on the X-ray spectral behavior within these steady observations. Our work is based on a vast RXTE/PCA data set obtained on GRS 1915+105 during the course of its entire mission and 10 years of radio data from the Ryle Telescope, which overlap the X-ray data. We find that the steady observations within the X-ray data set naturally separate into two regions in a color-color diagram, which we refer to as steady-soft and steady-hard. GRS 1915+105 displays significant curvature in the Comptonization component within the PCA band pass suggesting significantly heating from a hot disk present in all states. A new Comptonization model 'simplcut' was developed in order to model this curvature to best effect. A majority of the steady-soft observations display a roughly constant inner radius; remarkably reminiscent of canonical soft state black hole binaries. In contrast, the steady-hard observations display a growing disk truncation that is correlated to the mass accretion rate through the disk, which suggests a magnetically truncated disk. A comparison of X-ray model parameters to the canonical state definitions show that almost all steady-soft observations match the criteria of either thermal or steep power law state, while the thermal state observations dominate the constant radius branch. A large portion (80%) of the steady-hard observations matches the hard state criteria when the disk fraction constraint is neglected. These results suggest that within the complexity of this source is a simpler underlying basis of states, which map to those observed in canonical black hole binaries. When represented in a color-color diagram, state assignments appear to map to ``A, B and C'' (Belloni et al. 2000) regions that govern fast variability cycles in GRS 1915+105 demonstrating a compelling link between short and long time scales in its phenomenology.

Implications of Network Topology on Stability

PubMed Central

Kinkhabwala, Ali

2015-01-01

In analogy to chemical reaction networks, I demonstrate the utility of expressing the governing equations of an arbitrary dynamical system (interaction network) as sums of real functions (generalized reactions) multiplied by real scalars (generalized stoichiometries) for analysis of its stability. The reaction stoichiometries and first derivatives define the network’s “influence topology”, a signed directed bipartite graph. Parameter reduction of the influence topology permits simplified expression of the principal minors (sums of products of non-overlapping bipartite cycles) and Hurwitz determinants (sums of products of the principal minors or the bipartite cycles directly) for assessing the network’s steady state stability. Visualization of the Hurwitz determinants over the reduced parameters defines the network’s stability phase space, delimiting the range of its dynamics (specifically, the possible numbers of unstable roots at each steady state solution). Any further explicit algebraic specification of the network will project onto this stability phase space. Stability analysis via this hierarchical approach is demonstrated on classical networks from multiple fields. PMID:25826219

Effects of friction dampers on aerodynamically unstable rotor stages

NASA Technical Reports Server (NTRS)

Griffin, J. H.; Sinha, A.

1983-01-01

Attention is given to the physical concepts and mathematical techniques useful in the analysis of the stabilizing effect of friction on aerodynamically unstable rotor stages. Results are presented for three-, four-, and five-bladed disks. In the present multidegree-of-freedom model of an aerodynamically unstable rotor stage, a harmonic steady state solution due to the friction dampers may be either a stability limit, a stable cycle limit, or neither. A criterion is established in the form of an energy function which determines whether the solution is a stability limit. In the event that the initial displacement and velocity exeed those associated with the steady state solution corresponding to a stability limit, the reponse becomes unbounded.

Adressing optimality principles in DGVMs: Dynamics of Carbon allocation changes

NASA Astrophysics Data System (ADS)

Pietsch, Stephan

2017-04-01

DGVMs are designed to reproduce and quantify ecosystem processes. Based on plant functions or species specific parameter sets, the energy, carbon, nitrogen and water cycles of different ecosystems are assessed. These models have been proven to be important tools to investigate ecosystem fluxes as they are derived by plant, site and environmental factors. The general model approach assumes steady state conditions and constant model parameters. Both assumptions, however, are wrong, since: (i) No given ecosystem ever is at steady state! (ii) Ecosystems have the capability to adapt to changes in growth conditions, e.g. via changes in allocation patterns! This presentation will give examples how these general failures within current DGVMs may be addressed.

Adressing optimality principles in DGVMs: Dynamics of Carbon allocation changes.

NASA Astrophysics Data System (ADS)

Pietsch, S.

2016-12-01

DGVMs are designed to reproduce and quantify ecosystem processes. Based on plant functions or species specific parameter sets, the energy, carbon, nitrogen and water cycles of different ecosystems are assessed. These models have been proven to be important tools to investigate ecosystem fluxes as they are derived by plant, site and environmental factors. The general model approach assumes steady state conditions and constant model parameters. Both assumptions, however, are wrong. Any given ecosystem never is at steady state! Ecosystems have the capability to adapt to changes in growth conditions, e.g. via changes in allocation patterns! This presentation will give examples how these general failures within current DGVMs may be addressed.

Open cycle traveling wave thermoacoustics: mean temperature difference at the regenerator interface.

PubMed

Weiland, Nathan T; Zinn, Ben T

2003-11-01

In an open cycle traveling wave thermoacoustic engine, the hot heat exchanger is replaced by a steady flow of hot gas into the regenerator to provide the thermal energy input to the engine. The steady-state operation of such a device requires that a potentially large mean temperature difference exist between the incoming gas and the solid material at the regenerator's hot side, due in part to isentropic gas oscillations in the open space adjacent to the regenerator. The magnitude of this temperature difference will have a significant effect on the efficiencies of these open cycle devices. To help assess the feasibility of such thermoacoustic engines, a numerical model is developed that predicts the dependence of the mean temperature difference upon the important design and operating parameters of the open cycle thermoacoustic engine, including the acoustic pressure, mean mass flow rate, acoustic phase angles, and conductive heat loss. Using this model, it is also shown that the temperature difference at the regenerator interface is approximately proportional to the sum of the acoustic power output and the conductive heat loss at this location.

Interrelations between random walks on diagrams (graphs) with and without cycles.

PubMed

Hill, T L

1988-05-01

Three topics are discussed. A discrete-state, continuous-time random walk with one or more absorption states can be studied by a presumably new method: some mean properties, including the mean time to absorption, can be found from a modified diagram (graph) in which each absorption state is replaced by a one-way cycle back to the starting state. The second problem is a random walk on a diagram (graph) with cycles. The walk terminates on completion of the first cycle. This walk can be replaced by an equivalent walk on a modified diagram with absorption. This absorption diagram can in turn be replaced by another modified diagram with one-way cycles back to the starting state, just as in the first problem. The third problem, important in biophysics, relates to a long-time continuous walk on a diagram with cycles. This diagram can be transformed (in two steps) to a modified, more-detailed, diagram with one-way cycles only. Thus, the one-way cycle fluxes of the original diagram can be found from the state probabilities of the modified diagram. These probabilities can themselves be obtained by simple matrix inversion (the probabilities are determined by linear algebraic steady-state equations). Thus, a simple method is now available to find one-way cycle fluxes exactly (previously Monte Carlo simulation was required to find these fluxes, with attendant fluctuations, for diagrams of any complexity). An incidental benefit of the above procedure is that it provides a simple proof of the one-way cycle flux relation Jn +/- = IIn +/- sigma n/sigma, where n is any cycle of the original diagram.

Dynamic Modeling of ALS Systems

NASA Technical Reports Server (NTRS)

Jones, Harry

2002-01-01

The purpose of dynamic modeling and simulation of Advanced Life Support (ALS) systems is to help design them. Static steady state systems analysis provides basic information and is necessary to guide dynamic modeling, but static analysis is not sufficient to design and compare systems. ALS systems must respond to external input variations and internal off-nominal behavior. Buffer sizing, resupply scheduling, failure response, and control system design are aspects of dynamic system design. We develop two dynamic mass flow models and use them in simulations to evaluate systems issues, optimize designs, and make system design trades. One model is of nitrogen leakage in the space station, the other is of a waste processor failure in a regenerative life support system. Most systems analyses are concerned with optimizing the cost/benefit of a system at its nominal steady-state operating point. ALS analysis must go beyond the static steady state to include dynamic system design. All life support systems exhibit behavior that varies over time. ALS systems must respond to equipment operating cycles, repair schedules, and occasional off-nominal behavior or malfunctions. Biological components, such as bioreactors, composters, and food plant growth chambers, usually have operating cycles or other complex time behavior. Buffer sizes, material stocks, and resupply rates determine dynamic system behavior and directly affect system mass and cost. Dynamic simulation is needed to avoid the extremes of costly over-design of buffers and material reserves or system failure due to insufficient buffers and lack of stored material.

A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium

NASA Astrophysics Data System (ADS)

Reed, Mark; Parker, Ronald R.; Forget, Benoit

2012-06-01

This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more proliferation-resistant than that bred by conventional fast reactors. Furthermore, it can maintain constant total hybrid power output as burnup proceeds by varying the neutron source strength.

Towards an Automated Full-Turbofan Engine Numerical Simulation

NASA Technical Reports Server (NTRS)

Reed, John A.; Turner, Mark G.; Norris, Andrew; Veres, Joseph P.

2003-01-01

The objective of this study was to demonstrate the high-fidelity numerical simulation of a modern high-bypass turbofan engine. The simulation utilizes the Numerical Propulsion System Simulation (NPSS) thermodynamic cycle modeling system coupled to a high-fidelity full-engine model represented by a set of coupled three-dimensional computational fluid dynamic (CFD) component models. Boundary conditions from the balanced, steady-state cycle model are used to define component boundary conditions in the full-engine model. Operating characteristics of the three-dimensional component models are integrated into the cycle model via partial performance maps generated automatically from the CFD flow solutions using one-dimensional meanline turbomachinery programs. This paper reports on the progress made towards the full-engine simulation of the GE90-94B engine, highlighting the generation of the high-pressure compressor partial performance map. The ongoing work will provide a system to evaluate the steady and unsteady aerodynamic and mechanical interactions between engine components at design and off-design operating conditions.

A global model of carbon-nutrient interactions

NASA Technical Reports Server (NTRS)

Moore, Berrien, III; Gildea, Patricia; Vorosmarty, Charles; Mellilo, Jerry M.; Peterson, Bruce J.

1985-01-01

The global biogeochemical model presented has two primary objectives. First, it characterizes natural elemental cycles and their linkages for the four elements significant to Earth's biota: C, N, S, and P. Second, it describes changes in these cycles due to human activity. Global nutrient cycles were studied within the drainage basins of several major world rivers on each continent. The initial study region was the Mississippi drainage basin, concentrating on carbon and nitrogen. The model first establishes the nutrient budgets of the undisturbed ecosystems in a study region. It then uses a data set of land use histories for that region to document the changes in these budgets due to land uses. Nutrient movement was followed over time (1800 to 1980) for 30 ecosystems and 10 land use categories. A geographically referenced ecological information system (GREIS) was developed to manage the digital global data bases of 0.5 x 0.5 grid cells needed to run the model: potential vegetation, drainage basins, precipitation, runoff, contemporary land cover, and FAO soil maps of the world. The results show the contributions of land use categories to river nutrient loads on a continental scale; shifts in nutrient cycling patterns from closed, steady state systems to mobile transient or open, steady state systems; soil organic matter depletion patterns in U.S. agricultural lands; changing nutrient ratios due to land use changes; and the effect of using heavy fertilizer on aquatic systems.

Replication cycle of duck hepatitis A virus type 1 in duck embryonic hepatocytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, Fangke; Chen, Yun; Shi, Jintong

Duck hepatitis A virus type 1 (DHAV-1) is an important agent of duck viral hepatitis. Until recently, the replication cycle of DHAV-1 is still unknown. Here duck embryonic hepatocytes infected with DHAV-1 were collected at different time points, and dynamic changes of the relative DHAV-1 gene expression during replication were detected by real-time PCR. And the morphology of hepatocytes infected with DHAV was evaluated by electron microscope. The result suggested that the adsorption of DHAV-1 saturated at 90 min post-infection, and the virus particles with size of about 50 nm including more than 20 nm of vacuum drying gold weremore » observed on the infected cells surface. What's more, the replication lasted around 13 h after the early protein synthesis for about 5 h, and the release of DHAV-1 was in steady state after 32 h. The replication cycle will enrich the data for DVH control and provide the foundation for future studies. - Highlights: • This is the first description of the replication cycle of DHAV-1. • Firstly find that DHAV-1 adsorption saturated at 90 min post-infection. • The replication lasted around 13 h after early protein synthesis for about 5 h. • The release of DHAV-1 was in steady state after 32 h.« less

Passive load follow analysis of the STAR-LM and STAR-H2 systems

NASA Astrophysics Data System (ADS)

Moisseytsev, Anton

A steady-state model for the calculation of temperature and pressure distributions, and heat and work balance for the STAR-LM and the STAR-H2 systems was developed. The STAR-LM system is designed for electricity production and consists of the lead cooled reactor on natural circulation and the supercritical carbon dioxide Brayton cycle. The STAR-H2 system uses the same reactor which is coupled to the hydrogen production plant, the Brayton cycle, and the water desalination plant. The Brayton cycle produces electricity for the on-site needs. Realistic modules for each system component were developed. The model also performs design calculations for the turbine and compressors for the CO2 Brayton cycle. The model was used to optimize the performance of the entire system as well as every system component. The size of each component was calculated. For the 400 MWt reactor power the STAR-LM produces 174.4 MWe (44% efficiency) and the STAR-H2 system produces 7450 kg H2/hr. The steady state model was used to conduct quasi-static passive load follow analysis. The control strategy was developed for each system; no control action on the reactor is required. As a main safety criterion, the peak cladding temperature is used. It was demonstrated that this temperature remains below the safety limit during both normal operation and load follow.

Gluconeogenesis from labeled carbon: estimating isotope dilution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kelleher, J.K.

1986-03-01

To estimate the rate of gluconeogenesis from steady-state incorporation of labeled 3-carbon precursors into glucose, isotope dilution must be considered so that the rate of labeling of glucose can be quantitatively converted to the rate of gluconeogenesis. An expression for the value of this isotope dilution can be derived using mathematical techniques and a model of the tricarboxylic acid (TCA) cycle. The present investigation employs a more complex model than that used in previous studies. This model includes the following pathways that may affect the correction for isotope dilution: 1) flux of 3-carbon precursor to the oxaloacetate pool via acetyl-CoAmore » and the TCA cycle; 2) flux of 4- or 5-carbon compounds into the TCA cycle; 3) reversible flux between oxaloacetate (OAA) and pyruvate and between OAA and fumarate; 4) incomplete equilibrium between OAA pools; and 5) isotope dilution of 3-carbon tracers between the experimentally measured pool and the precursor for the TCA-cycle OAA pool. Experimental tests are outlined which investigators can use to determine whether these pathways are significant in a specific steady-state system. The study indicated that flux through these five pathways can significantly affect the correction for isotope dilution. To correct for the effects of these pathways an alternative method for calculating isotope dilution is proposed using citrate to relate the specific activities of acetyl-CoA and OAA.« less

40 CFR 90.301 - Applicability.

Code of Federal Regulations, 2010 CFR

2010-07-01

... the test engine is operated using a steady state test cycle on an engine dynamometer. The exhaust... concentrations are converted to mass emission rates in grams per hour based on either fuel flow, fuel flow and engine intake air flow, or exhaust volume flow. Weighted emission rates are reported as grams per brake...

Long cycle life microporous spherical carbon anodes for sodium-ion batteries derived from furfuryl alcohol

DOE PAGES

Zhou, Dehua; Peer, Maryam; Yang, Zhenzhen; ...

2016-04-11

Spherical micron-sized carbon powders were synthesized from feedstock furfuryl alcohol and tested as anodes in sodium ion batteries (SIBs). A long cycle life of 1000 cycles is achievable with this carbon at C rate (3–4 mg cm –2 loading and i = 200 mA g –1) yielding a steady capacity of ca. 115 mA h g –1. Furthermore, the results from solid-state 23Na MAS NMR analyses of cycled electrodes indicate no correlation in voltage profiles with sodium site nature (graphene or nanopores), which is a new observation in SIB carbon anodes.

Core signalling motif displaying multistability through multi-state enzymes.

PubMed

Feng, Song; Sáez, Meritxell; Wiuf, Carsten; Feliu, Elisenda; Soyer, Orkun S

2016-10-01

Bistability, and more generally multistability, is a key system dynamics feature enabling decision-making and memory in cells. Deciphering the molecular determinants of multistability is thus crucial for a better understanding of cellular pathways and their (re)engineering in synthetic biology. Here, we show that a key motif found predominantly in eukaryotic signalling systems, namely a futile signalling cycle, can display bistability when featuring a two-state kinase. We provide necessary and sufficient mathematical conditions on the kinetic parameters of this motif that guarantee the existence of multiple steady states. These conditions foster the intuition that bistability arises as a consequence of competition between the two states of the kinase. Extending from this result, we find that increasing the number of kinase states linearly translates into an increase in the number of steady states in the system. These findings reveal, to our knowledge, a new mechanism for the generation of bistability and multistability in cellular signalling systems. Further the futile cycle featuring a two-state kinase is among the smallest bistable signalling motifs. We show that multi-state kinases and the described competition-based motif are part of several natural signalling systems and thereby could enable them to implement complex information processing through multistability. These results indicate that multi-state kinases in signalling systems are readily exploited by natural evolution and could equally be used by synthetic approaches for the generation of multistable information processing systems at the cellular level. © 2016 The Authors.

Revitalizing Fusion via Fission Fusion

NASA Astrophysics Data System (ADS)

Manheimer, Wallace

2001-10-01

Existing tokamaks could generate significant nuclear fuel. TFTR, operating steady state with DT might generate enough fuel for a 300 MW nuclear reactor. The immediate goals of the magnetic fusion program would necessarily shift from a study of advanced plasma regimes in larger sized devices, to mostly known plasmas regimes, but at steady state or high duty cycle operation in DT plasmas. The science and engineering of breeding blankets would be equally important. Follow on projects could possibly produce nuclear fuel in large quantity at low price. Although today there is strong opposition to nuclear power in the United States, in a 21st century world of 10 billion people, all of whom will demand a middle class life style, nuclear energy will be important. Concern over greenhouse gases will also drive the world toward nuclear power. There are studies indicating that the world will need 10 TW of carbon free energy by 2050. It is difficult to see how this can be achieved without the breeding of nuclear fuel. By using the thorium cycle, proliferation risks are minimized. [1], [2]. 1 W. Manheimer, Fusion Technology, 36, 1, 1999, 2.W. Manheimer, Physics and Society, v 29, #3, p5, July, 2000

Ribosome flow model with positive feedback

PubMed Central

Margaliot, Michael; Tuller, Tamir

2013-01-01

Eukaryotic mRNAs usually form a circular structure; thus, ribosomes that terminatae translation at the 3′ end can diffuse with increased probability to the 5′ end of the transcript, initiating another cycle of translation. This phenomenon describes ribosomal flow with positive feedback—an increase in the flow of ribosomes terminating translating the open reading frame increases the ribosomal initiation rate. The aim of this paper is to model and rigorously analyse translation with feedback. We suggest a modified version of the ribosome flow model, called the ribosome flow model with input and output. In this model, the input is the initiation rate and the output is the translation rate. We analyse this model after closing the loop with a positive linear feedback. We show that the closed-loop system admits a unique globally asymptotically stable equilibrium point. From a biophysical point of view, this means that there exists a unique steady state of ribosome distributions along the mRNA, and thus a unique steady-state translation rate. The solution from any initial distribution will converge to this steady state. The steady-state distribution demonstrates a decrease in ribosome density along the coding sequence. For the case of constant elongation rates, we obtain expressions relating the model parameters to the equilibrium point. These results may perhaps be used to re-engineer the biological system in order to obtain a desired translation rate. PMID:23720534

A pre-steady state and steady state kinetic analysis of the N-ribosyl hydrolase activity of hCD157.

PubMed

Preugschat, Frank; Carter, Luke H; Boros, Eric E; Porter, David J T; Stewart, Eugene L; Shewchuk, Lisa M

2014-12-15

hCD157 catalyzes the hydrolysis of nicotinamide riboside (NR) and nicotinic acid riboside (NAR). The release of nicotinamide or nicotinic acid from NR or NAR was confirmed by spectrophotometric, HPLC and NMR analyses. hCD157 is inactivated by a mechanism-based inhibitor, 2'-deoxy-2'-fluoro-nicotinamide arabinoside (fNR). Modification of the enzyme during the catalytic cycle by NR, NAR, or fNR increased the intrinsic protein fluorescence by approximately 50%. Pre-steady state and steady state data were used to derive a minimal kinetic scheme for the hydrolysis of NR. After initial complex formation a reversible step (360 and 30s(-1)) is followed by a slow irreversible step (0.1s(-1)) that defined the rate limiting step, or kcat. The calculated KMapp value for NR in the hydrolytic reaction is 6nM. The values of the kinetic constants suggest that one biological function of cell-surface hCD157 is to bind and slowly hydrolyze NR, possibly converting it to a ligand-activated receptor. Differences in substrate preference between hCD157 and hCD38 were rationalized through a comparison of the crystal structures of the two proteins. This comparison identified several residues in hCD157 (F108 and F173) that can potentially hinder the binding of dinucleotide substrates (NAD+). Copyright © 2014 Elsevier Inc. All rights reserved.

Transition from amplitude to oscillation death in a network of oscillators

NASA Astrophysics Data System (ADS)

Nandan, Mauparna; Hens, C. R.; Pal, Pinaki; Dana, Syamal K.

2014-12-01

We report a transition from a homogeneous steady state (HSS) to inhomogeneous steady states (IHSSs) in a network of globally coupled identical oscillators. We perturb a synchronized population of oscillators in the network with a few local negative or repulsive mean field links. The whole population splits into two clusters for a certain number of repulsive mean field links and a range of coupling strength. For further increase of the strength of interaction, these clusters collapse into a HSS followed by a transition to IHSSs where all the oscillators populate either of the two stable steady states. We analytically determine the origin of HSS and its transition to IHSS in relation to the number of repulsive mean-field links and the strength of interaction using a reductionism approach to the model network. We verify the results with numerical examples of the paradigmatic Landau-Stuart limit cycle system and the chaotic Rössler oscillator as dynamical nodes. During the transition from HSS to IHSSs, the network follows the Turing type symmetry breaking pitchfork or transcritical bifurcation depending upon the system dynamics.

Transition from amplitude to oscillation death in a network of oscillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nandan, Mauparna; Department of Mathematics, National Institute of Technology, Durgapur 713209; Hens, C. R.

2014-12-01

We report a transition from a homogeneous steady state (HSS) to inhomogeneous steady states (IHSSs) in a network of globally coupled identical oscillators. We perturb a synchronized population of oscillators in the network with a few local negative or repulsive mean field links. The whole population splits into two clusters for a certain number of repulsive mean field links and a range of coupling strength. For further increase of the strength of interaction, these clusters collapse into a HSS followed by a transition to IHSSs where all the oscillators populate either of the two stable steady states. We analytically determinemore » the origin of HSS and its transition to IHSS in relation to the number of repulsive mean-field links and the strength of interaction using a reductionism approach to the model network. We verify the results with numerical examples of the paradigmatic Landau-Stuart limit cycle system and the chaotic Rössler oscillator as dynamical nodes. During the transition from HSS to IHSSs, the network follows the Turing type symmetry breaking pitchfork or transcritical bifurcation depending upon the system dynamics.« less

Extruder system for high-throughput/steady-state hydrogen ice supply and application for pellet fueling of reactor-scale fusion experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Combs, S.K.; Foust, C.R.; Qualls, A.L.

Pellet injection systems for the next-generation fusion devices, such as the proposed International Thermonuclear Experimental Reactor (ITER), will require feed systems capable of providing a continuous supply of hydrogen ice at high throughputs. A straightforward concept in which multiple extruder units operate in tandem has been under development at the Oak Ridge National Laboratory. A prototype with three large-volume extruder units has been fabricated and tested in the laboratory. In experiments, it was found that each extruder could provide volumetric ice flow rates of up to {approximately}1.3 cm{sup 3}/s (for {approximately}10 s), which is sufficient for fueling fusion reactors atmore » the gigawatt power level. With the three extruders of the prototype operating in sequence, a steady rate of {approximately}0.33 cm{sup 3}/s was maintained for a duration of 1 h. Even steady-state rates approaching the full ITER design value ({approximately}1 cm{sup 3}/s) may be feasible with the prototype. However, additional extruder units (1{endash}3) would facilitate operations at the higher throughputs and reduce the duty cycle of each unit. The prototype can easily accommodate steady-state pellet fueling of present large tokamaks or other near-term plasma experiments.« less

Development and analysis of closed cycle circulator elements. Final report 31 Jul 978-31 May 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shih, C.C.; Karr, G.R.; Perkins, J.F.

1980-05-01

A series of experiments with various flow rates of laser gas and coolants under several levels of energy inputs has been conducted on the Army Closed Cycle Circulator for pulsed EDL to collect sufficient data for flow calibration and coefficient determination. Verification of the theoretical models depicting the functions of the heat exchangers in maintaining the thermal balance in the flow through the steady and transient states are made through comparison with results of the experimental analysis.

Otto engine beyond its standard quantum limit.

PubMed

Leggio, Bruno; Antezza, Mauro

2016-02-01

We propose a quantum Otto cycle based on the properties of a two-level system in a realistic out-of-thermal-equilibrium electromagnetic field acting as its sole reservoir. This steady configuration is produced without the need of active control over the state of the environment, which is a noncoherent thermal radiation, sustained only by external heat supplied to macroscopic objects. Remarkably, even for nonideal finite-time transformations, it largely over-performs the standard ideal Otto cycle and asymptotically achieves unit efficiency at finite power.

Measurement and Perturbation of Morphogen Lifetime: Effects on Gradient Shape

PubMed Central

Drocco, Jeffrey A.; Grimm, Oliver; Tank, David W.; Wieschaus, Eric

2011-01-01

Protein lifetime is of critical importance for most biological processes and plays a central role in cell signaling and embryonic development, where it impacts the absolute concentration of signaling molecules and, potentially, the shape of morphogen gradients. Early conceptual and mathematical models of gradient formation proposed that steady-state gradients are established by an equilibration between the lifetime of a morphogen and its rates of synthesis and diffusion, though whether gradients in fact reach steady state before being read out is a matter of controversy. In any case, this class of models predicts that protein lifetime is a key determinant of both the time to steady state and the spatial extent of a gradient. Using a method that employs repeated photoswitching of a fusion of the morphogen Bicoid (Bcd) and the photoconvertible fluorescent protein Dronpa, we measure and modify the lifetime of Dronpa-Bcd in living Drosophila embryos. We find that the lifetime of Bcd is dynamic, changing from 50 min before mitotic cycle 14 to 15 min during cellularization. Moreover, by measuring total quantities of Bcd over time, we find that the gradient does not reach steady state. Finally, using a nearly continuous low-level conversion to the dark state of Dronpa-Bcd to mimic the effect of increased degradation, we demonstrate that perturbation of protein lifetime changes the characteristic length of the gradient, providing direct support for a mechanism based on synthesis, diffusion, and degradation. PMID:22004733

Caffeinated nitric oxide-releasing lozenge improves cycling time trial performance.

PubMed

Lee, J; Kim, H T; Solares, G J; Kim, K; Ding, Z; Ivy, J L

2015-02-01

Boosting nitric oxide production during exercise by various means has been found to improve exercise performance. We investigated the effects of a nitric oxide releasing lozenge with added caffeine (70 mg) on oxygen consumption during steady-state exercise and cycling time trial performance using a double-blinded randomized, crossover experimental design. 15 moderately trained cyclists (7 females and 8 males) were randomly assigned to ingest the caffeinated nitric oxide lozenge or placebo 5 min before exercise. Oxygen consumption and blood lactate were assessed at rest and at 50%, 65% and 75% maximal oxygen consumption. Exercise performance was assessed by time to complete a simulated 20.15 km cycling time-trial course. No significant treatment effects for oxygen consumption or blood lactate at rest or during steady-state exercise were observed. However, time-trial performance was improved by 2.1% (p<0.01) when participants consumed the nitric oxide lozenge (2,424±69 s) compared to placebo (2,476±78 s) and without a significant difference in rating of perceived exertion. These results suggest that acute supplementation with a caffeinated nitric oxide releasing lozenge may be a practical and effective means of improving aerobic exercise performance. © Georg Thieme Verlag KG Stuttgart · New York.

Physical and biochemical energy balance during an isometric tetanus and steady state recovery in frog sartorius at 0 degree C

PubMed Central

1983-01-01

Frog sartorius muscle stimulated isometrically for 3 s every 256 s to attain a steady state in which initial heat (QI), recovery heat (QR), rate of O2 consumption (JO2), and isometric force (PO) generated are constant for each cycle. For a 3-s tetanus given every 256 s, JO2 was 0.106 mumol/(min . g blotted weight), approximately 71% of the maximum rate observed, whereas lactate production was negligible under these conditions. QI, QT(= QI + QR), and QT/QI were 88.2, 181.5, 2.06 mJ/g blotted weight, respectively. The high-energy phosphate breakdown (delta approximately P) breakdown during the first 3-s tetanus was not different from that during a contraction in the steady state and averaged 1.1 mumol/g blotted weight. Less than half of the initial heat could be accounted for in terms of the extent of the known chemical reactions occurring during contraction. From the stoichiometry of the theoretical biochemical pathways, the amount of ATP synthesized in the steady state exceeds delta approximately P during contraction by more than twofold, corresponding to an apparent ADP:O ratio of 1.5. If it is assumed that carbohydrate oxidation is the only net chemical reaction in the steady state, the total heat production can be explained on the basis of the measured JO2. Under this assumption, heat production during recovery was less than that expected on the basis of the oxygen consumption and delta approximately P during contraction. These observations support the hypothesis that the unexplained enthalpy production and low apparent ADP:O ratio are causally related, i.e., that the reaction(s) producing the unexplained heat during contraction is reversed during the recovery period. PMID:6601686

Disruption of the auditory response to a regular click train by a single, extra click.

PubMed

Lütkenhöner, Bernd; Patterson, Roy D

2015-06-01

It has been hypothesized that the steady-state response to a periodic sequence of clicks can be modeled as the superposition of responses to single clicks. Here, this hypothesis is challenged by presenting an extra click halfway between two consecutive clicks of a regular series, while measuring the auditory evoked field. After a solitary click at time zero, the click series sounded from 100 to 900 ms, with the extra click presented around 500 ms. The silent period between two stimulus sequences was 310-390 ms (uniformly distributed) so that one stimulation cycle lasted, on average, 1250 ms. Five different click rates between 20 and 60 Hz were examined. The disturbance caused by the extra click was revealed by subtracting the estimated steady-state response from the joint response to the click series and the extra click. The early peaks of the single-click response effectively coincide with same-polarity peaks of the 20-Hz steady-state response. Nevertheless, prediction of the latter from the former proved impossible. However, the 40-Hz steady-state response can be predicted reasonably well from the 20-Hz steady-state response. Somewhat surprisingly, the amplitude of the evoked response to the extra click grew when the click rate of the train was increased from 20 to 30 Hz; the opposite effect would have been expected from research on adaptation. The smaller amplitude at lower click rates might be explained by forward suppression. In this case, the apparent escape from suppression at higher rates might indicate that the clicks belonging to the periodic train are being integrated into an auditory stream, possibly in much the same manner as in classical stream segregation experiments.

Potential Fuel Economy Improvements from the Implementation of cEGR and CDA on an Atkinson Cycle Engine

EPA Science Inventory

Present the implementation of cEGR and CDA on an Atkinson engine and use steady state fuel consumption maps to estimate the technologies’ potential fuel economy improvements over the FTP and Highway tests. In addition to use fuel weighted modes to determine possible fuel economy...

40 CFR Appendix II to Part 1042 - Steady-State Duty Cycles

Code of Federal Regulations, 2011 CFR

2011-07-01

... the maximum test power. 3 Advance from one mode to the next within a 20-second transition phase. During the transition phase, command a linear progression from the torque setting of the current mode to... transition phase, command a linear progression from the torque setting of the current mode to the torque...

Environmental degradation of 316 stainless steel in high temperature low cycle fatigue

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Manson, S. Stanford; Halford, Gary R.

1987-01-01

Procedures based on modification of the conventional Strainrange Partitioning method are proposed to characterize the time-dependent degradation of engineering alloys in high-temperature, low-cycle fatigue. Creep-fatigue experiments were conducted in air using different waveforms of loading on 316 stainless steel at 816 C (1500 F) to determine the effect of exposure time on cyclic life. Reductions in the partitioned cyclic lives were observed with an increase in the time of exposure (or with the corresponding decrease in the steady-state creep rate) for all the waveforms involving creep strain. Excellent correlations of the experimental data were obtained by modifying the Conventional Strainrange Partitioning life relationships involving creep strain using a power-law term of either: (1) time of exposure, or (2) steady-state creep rate of the creep-fatigue test. Environmental degradation due to oxidation, material degradation due to the precipitation of carbides along the grain boundaries and detrimental deformation modes associated with the prolonged periods of creep were observed to be the main mechanisms responsible for life reductions at long exposure times.

Simulation of the pentose cycle in lactating rat mammary gland

PubMed Central

Haut, Michael J.; London, Jack W.; Garfinkel, David

1974-01-01

A computer model representing the pentose cycle, the tricarboxylic acid cycle and glycolysis in slices of lactating rat mammary glands has been constructed. This model is based primarily on the studies, with radioactive chemicals, of Abraham & Chaikoff (1959) [although some of the discrepant data of Katz & Wals (1972) could be accommodated by changing one enzyme activity]. Data obtained by using [1-14C]-, [6-14C]- and [3,4-14C]-glucose were simulated, as well as data obtained by using unlabelled glucose (for which some new experimental data are presented). Much past work on the pentose cycle has been mainly concerned with the division of glucose flow between the pentose cycle and glycolysis, and has relied on the assumption that the system is in steady state (both labelled and unlabelled). This assumption may not apply to lactating rat mammary glands, since the model shows that the percentage flow through the shunt progressively decreased for the first 2h of a 3h experiment, and we were unable to construct a completely steady-state model. The model allows examination of many quantitative features of the system, especially the amount of material passing through key enzymes, some of which appear to be regulated by NADP+ concentrations as proposed by McLean (1960). Supplementary information for this paper has been deposited as Supplementary Publication SUP 50023 at the British Museum (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1973) 131, 5. PMID:4154746

Alternative refrigerants and refrigeration cycles for domestic refrigerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sand, J.R.; Rice, C.L.; Vineyard, E.A.

1992-12-01

This project initially focused on using nonazeotropic refrigerant mixtures (NARMs) in a two-evaporator refrigerator-freezer design using two stages of liquid refrigerant subcooling. This concept was proposed and tested in 1975. The work suggested that the concept was 20% more efficient than the conventional one-evaporator refrigerator-freezer (RF) design. After considerable planning and system modeling based on using a NARM in a Lorenz-Meutzner (L-M) RF, the program scope was broadened to include investigation of a ``dual-loop`` concept where energy savings result from exploiting the less stringent operating conditions needed to satisfy cooling, of the fresh food section. A steady-state computer model (CYCLE-Z)more » capable of simulating conventional, dual loop, and L-M refrigeration cycles was developed. This model was used to rank the performance of 20 ozone-safe NARMs in the L-M refrigeration cycle while key system parameters were systematically varied. The results indicated that the steady-state efficiency of the L-M design was up to 25% greater than that of a conventional cycle. This model was also used to calculate the performance of other pure refrigerants relative to that of dichlorodifluoromethane, R-12, in conventional and dual-loop RF designs. Projected efficiency gains for these cycles were more modest, ranging from 0 to 10%. Individual compressor calorimeter tests of nine combinations of evaporator and condenser temperatures usually used to map RF compressor performance were carried out with R-12 and two candidate L-M NARMs in several compressors. Several models of a commercially produced two-evaporator RF were obtained as test units. Two dual-loop RF designs were built and tested as part of this project.« less

Exonuclease 1 is a critical mediator of survival during DNA double strand break repair in nonquiescent hematopoietic stem and progenitor cells.

PubMed

Desai, Amar; Qing, Yulan; Gerson, Stanton L

2014-02-01

Hematopoietic stem cell (HSC) populations require DNA repair pathways to maintain their long-term survival and reconstitution capabilities, but mediators of these processes are still being elucidated. Exonuclease 1 (Exo1) participates in homologous recombination (HR) and Exo1 loss results in impaired 5' HR end resection. We use cultured Exo1(mut) fibroblasts and bone marrow to demonstrate that loss of Exo1 function results in defective HR in cycling cells. Conversely, in Exo1(mut) mice HR is not required for maintenance of quiescent HSCs at steady state, confirming the steady state HSC reliance on nonhomologous end joining (NHEJ). Exo1(mut) mice sustained serial repopulation, displayed no defect in competitive repopulation or niche occupancy, and exhibited no increased sensitivity to whole body ionizing radiation. However, when Exo1(mut) HSCs were pushed into cell cycle in vivo with 5-fluorouracil or poly IC, the hematopoietic population became hypersensitive to IR, resulting in HSC defects and animal death. We propose Exo1-mediated HR is dispensable for stem cell function in quiescent HSC, whereas it is essential to HSC response to DNA damage processing after cell cycle entry, and its loss is not compensated by intact NHEJ. In HSCs, the maintenance of stem cell function after DNA damage is dependent on the DNA repair capacity, segregated by active versus quiescent points in cell cycle. © AlphaMed Press.

Preliminary results of steady state characterization of near term electric vehicle breadboard propulsion system

NASA Technical Reports Server (NTRS)

Sargent, N. B.

1980-01-01

The steady state test results on a breadboard version of the General Electric Near Term Electric Vehicle (ETV-1) are discussed. The breadboard was built using exact duplicate vehicle propulsion system components with few exceptions. Full instrumentation was provided to measure individual component efficiencies. Tests were conducted on a 50 hp dynamometer in a road load simulator facility. Characterization of the propulsion system over the lower half of the speed-torque operating range has shown the system efficiency to be composed of a predominant motor loss plus a speed dependent transaxle loss. At the lower speeds with normal road loads the armature chopper loss is also a significant factor. At the conditions corresponding to a cycle for which the vehicle system was specifically designed, the efficiencies are near optimum.

A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, Mark; Parker, Ronald R.; Forget, Benoit

2012-06-19

This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritiummore » allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more proliferation-resistant than that bred by conventional fast reactors. Furthermore, it can maintain constant total hybrid power output as burnup proceeds by varying the neutron source strength.« less

Modeling the complete Otto cycle: Preliminary version. [computer programming

NASA Technical Reports Server (NTRS)

Zeleznik, F. J.; Mcbride, B. J.

1977-01-01

A description is given of the equations and the computer program being developed to model the complete Otto cycle. The program incorporates such important features as: (1) heat transfer, (2) finite combustion rates, (3) complete chemical kinetics in the burned gas, (4) exhaust gas recirculation, and (5) manifold vacuum or supercharging. Changes in thermodynamic, kinetic and transport data as well as model parameters can be made without reprogramming. Preliminary calculations indicate that: (1) chemistry and heat transfer significantly affect composition and performance, (2) there seems to be a strong interaction among model parameters, and (3) a number of cycles must be calculated in order to obtain steady-state conditions.

Design and operation of a continuous integrated monoclonal antibody production process.

PubMed

Steinebach, Fabian; Ulmer, Nicole; Wolf, Moritz; Decker, Lara; Schneider, Veronika; Wälchli, Ruben; Karst, Daniel; Souquet, Jonathan; Morbidelli, Massimo

2017-09-01

The realization of an end-to-end integrated continuous lab-scale process for monoclonal antibody manufacturing is described. For this, a continuous cultivation with filter-based cell-retention, a continuous two column capture process, a virus inactivation step, a semi-continuous polishing step (twin-column MCSGP), and a batch-wise flow-through polishing step were integrated and operated together. In each unit, the implementation of internal recycle loops allows to improve the performance: (a) in the bioreactor, to simultaneously increase the cell density and volumetric productivity, (b) in the capture process, to achieve improved capacity utilization at high productivity and yield, and (c) in the MCSGP process, to overcome the purity-yield trade-off of classical batch-wise bind-elute polishing steps. Furthermore, the design principles, which allow the direct connection of these steps, some at steady state and some at cyclic steady state, as well as straight-through processing, are discussed. The setup was operated for the continuous production of a commercial monoclonal antibody, resulting in stable operation and uniform product quality over the 17 cycles of the end-to-end integration. The steady-state operation was fully characterized by analyzing at the outlet of each unit at steady state the product titer as well as the process (HCP, DNA, leached Protein A) and product (aggregates, fragments) related impurities. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1303-1313, 2017. © 2017 American Institute of Chemical Engineers.

40 CFR 1039.505 - How do I test engines using steady-state duty cycles, including ramped-modal testing?

Code of Federal Regulations, 2011 CFR

2011-07-01

.... You may extend the sampling time to improve measurement accuracy of PM emissions, using good...-speed engines whose design prevents full-load operation for extended periods, you may ask for approval... designed to operate for extended periods. (e) See 40 CFR part 1065 for detailed specifications of...

Effect of Semirecumbent and Upright Body Position on Maximal and Submaximal Exercise Testing

ERIC Educational Resources Information Center

Scott, Alexander; Antonishen, Kevin; Johnston, Chris; Pearce, Terri; Ryan, Michael; Sheel, A. William; McKenzie, Don C.

2006-01-01

The study was designed to determine the effect of upright-posture (UP) versus semirecumbent (SR) cycling on commonly used measures of maximal and submaximal exercise capacity. Nine healthy, untrained men (M age = 27 years, SD = 4.8 years) underwent steady-state submaximal aerobic testing followed by a ramped test to determine maximal oxygen…

Dynamics of nitrate production and removal as a function of residence time in the hyporheic zone

Treesearch

Jay P. Zarnetske; Roy Haggerty; Steven M. Wondzell; Michelle A. Baker

2011-01-01

Biogeochemical reactions associated with stream nitrogen cycling, such as nitrification and denitrification, can be strongly controlled by water and solute residence times in the hyporheic zone (HZ). We used a whole-stream steady state 15N-Iabeled nitrate and conservative tracer addition to investigate the spatial and temporal physiochemical...

40 CFR 1042.505 - Testing engines using discrete-mode or ramped-modal duty cycles.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Testing engines using discrete-mode or...-IGNITION ENGINES AND VESSELS Test Procedures § 1042.505 Testing engines using discrete-mode or ramped-modal... the Clean Air Act. (a) You may perform steady-state testing with either discrete-mode or ramped-modal...

76 FR 60017 - Notice of Intent To Prepare a Supplemental Environmental Impact Statement (SEIS) for the...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-28

..., irradiation will increase from today's 544 TPBARs per fuel cycle to a projected steady state rate of... requesting authorization for TPBAR irradiation to be increased in fiscal year 2016 to a level that is beyond... the Nuclear Regulatory Commission (NRC) to permit the irradiation of a greater number of TPBARs per...

Fixed points and limit cycles in the population dynamics of lysogenic viruses and their hosts

NASA Astrophysics Data System (ADS)

Wang, Zhenyu; Goldenfeld, Nigel

2010-07-01

Starting with stochastic rate equations for the fundamental interactions between microbes and their viruses, we derive a mean-field theory for the population dynamics of microbe-virus systems, including the effects of lysogeny. In the absence of lysogeny, our model is a generalization of that proposed phenomenologically by Weitz and Dushoff. In the presence of lysogeny, we analyze the possible states of the system, identifying a limit cycle, which we interpret physically. To test the robustness of our mean-field calculations to demographic fluctuations, we have compared our results with stochastic simulations using the Gillespie algorithm. Finally, we estimate the range of parameters that delineate the various steady states of our model.

Testing of a Neon Loop Heat Pipe for Large Area Cryocooling

NASA Technical Reports Server (NTRS)

Ku, Jentung; Robinson, Franklin Lee

2014-01-01

Cryocooling of large areas such as optics, detector arrays, and cryogenic propellant tanks is required for future NASA missions. A cryogenic loop heat pipe (CLHP) can provide a closed-loop cooling system for this purpose and has many advantages over other devices in terms of reduced mass, reduced vibration, high reliability, and long life. A neon CLHP was tested extensively in a thermal vacuum chamber using a cryopump as the heat sink to characterize its transient and steady performance and verify its ability to cool large areas or components. Tests conducted included loop cool-down from the ambient temperature, startup, power cycle, heat removal capability, loop capillary limit and recovery from a dry-out, low power operation, and long duration steady state operation. The neon CLHP demonstrated robust operation. The loop could be cooled from the ambient temperature to subcritical temperatures very effectively, and could start successfully by applying power to both the pump and evaporator without any pre-conditioning. It could adapt to changes in the pump power andor evaporator power, and reach a new steady state very quickly. The evaporator could remove heat loads between 0.25W and 4W. When the pump capillary limit was exceeded, the loop could resume its normal function by reducing the pump power. Steady state operations were demonstrated for up to 6 hours. The ability of the neon loop to cool large areas was therefore successfully verified.

The steady-state mosaic of disturbance and succession across an old-growth Central Amazon forest landscape.

PubMed

Chambers, Jeffrey Q; Negron-Juarez, Robinson I; Marra, Daniel Magnabosco; Di Vittorio, Alan; Tews, Joerg; Roberts, Dar; Ribeiro, Gabriel H P M; Trumbore, Susan E; Higuchi, Niro

2013-03-05

Old-growth forest ecosystems comprise a mosaic of patches in different successional stages, with the fraction of the landscape in any particular state relatively constant over large temporal and spatial scales. The size distribution and return frequency of disturbance events, and subsequent recovery processes, determine to a large extent the spatial scale over which this old-growth steady state develops. Here, we characterize this mosaic for a Central Amazon forest by integrating field plot data, remote sensing disturbance probability distribution functions, and individual-based simulation modeling. Results demonstrate that a steady state of patches of varying successional age occurs over a relatively large spatial scale, with important implications for detecting temporal trends on plots that sample a small fraction of the landscape. Long highly significant stochastic runs averaging 1.0 Mg biomass⋅ha(-1)⋅y(-1) were often punctuated by episodic disturbance events, resulting in a sawtooth time series of hectare-scale tree biomass. To maximize the detection of temporal trends for this Central Amazon site (e.g., driven by CO2 fertilization), plots larger than 10 ha would provide the greatest sensitivity. A model-based analysis of fractional mortality across all gap sizes demonstrated that 9.1-16.9% of tree mortality was missing from plot-based approaches, underscoring the need to combine plot and remote-sensing methods for estimating net landscape carbon balance. Old-growth tropical forests can exhibit complex large-scale structure driven by disturbance and recovery cycles, with ecosystem and community attributes of hectare-scale plots exhibiting continuous dynamic departures from a steady-state condition.

Low-order models of a single-screw expander for organic Rankine cycle applications

NASA Astrophysics Data System (ADS)

Ziviani, D.; Desideri, A.; Lemort, V.; De Paepe, M.; van den Broek, M.

2015-08-01

Screw-type volumetric expanders have been demonstrated to be a suitable technology for organic Rankine cycle (ORC) systems because of higher overall effectiveness and good part-load behaviour over other positive displacement machines. An 11 kWe single-screw expander (SSE) adapted from an air compressor has been tested in an ORC test-rig operating with R245fa as working fluid. A total of 60 steady-steady points have been obtained at four different rotational speeds of the expander in the range between 2000 rpm and 3300 rpm. The maximum electrical power output and overall isentropic effectiveness measured were 7.3 kW and 51.9%, respectively. In this paper, a comparison between two low-order models is proposed in terms of accuracy of the predictions, the robustness of the model and the computational time. The first model is the Pacejka equation-based model and the second is a semi-empirical model derived from a well-known scroll expander model and modified to include the geometric aspects of a single screw expander. The models have been calibrated with the available steady-state measurement points by identifying the proper parameters.

Induction motor speed control using varied duty cycle terminal voltage via PI controller

NASA Astrophysics Data System (ADS)

Azwin, A.; Ahmed, S.

2018-03-01

This paper deals with the PI speed controller for the three-phase induction motor using PWM technique. The PWM generated signal is utilized for voltage source inverter with an optimal duty cycle on a simplified induction motor model. A control algorithm for generating PWM control signal is developed. Obtained results shows that the steady state error and overshoot of the developed system is in the limit under different speed and load condition. The robustness of the control performance would be potential for induction motor performance improvement.

Prediction and verification of creep behavior in metallic materials and components, for the space shuttle thermal protection system. Volume 1, phase 1: Cyclic materials creep predictions

NASA Technical Reports Server (NTRS)

Davis, J. W.; Cramer, B. A.

1974-01-01

Cyclic creep response was investigated and design methods applicable to thermal protection system structures were developed. The steady-state (constant temperature and load) and cyclic creep response characteristics of four alloys were studied. Steady-state creep data were gathered through a literature survey to establish reference data bases. These data bases were used to develop empirical equations describing creep as a function of time, temperature, and stress and as a basis of comparison for test data. Steady-state creep tests and tensile cyclic tests were conducted. The following factors were investigated: material thickness and rolling direction; material cyclic creep response under varying loads and temperatures; constant stress and temperature cycles representing flight conditions; changing stresses present in a creeping beam as a result of stress redistribution; and complex stress and temperature profiles representative of space shuttle orbiter trajectories. A computer program was written, applying creep hardening theories and empirical equations for creep, to aid in analysis of test data. Results are considered applicable to a variety of structures which are cyclicly exposed to creep producing thermal environments.

Characterisation of the pharmacokinetics of ethinylestradiol and drospirenone in extended-cycle regimens: population pharmacokinetic analysis from a randomised Phase III study

PubMed Central

Reif, Stefanie; Snelder, Nelleke; Blode, Hartmut

2013-01-01

Objectives The primary objective of this analysis was to characterise the steady-state pharmacokinetics (PK) of ethinylestradiol (EE) and drospirenone (DRSP) in a randomised Phase III study that investigated the contraceptive efficacy and safety of three different regimens of EE 20 µg/DRSP 3 mg. Methods Non-linear mixed-effects modelling was used to develop population PK models for EE and DRSP. EE and DRSP serum concentrations were determined in blood samples obtained from approximately 1100 healthy young women on two occasions during the first cycle (Week 3) and after 6 months (Week 27) of EE 20 µg/DRSP 3 mg use. EE 20 µg/DRSP 3 mg was administered as a flexible extended regimen [24–120 days’ active hormonal intake followed by 4 days with no tablet intake (tablet-free interval)], a conventional 28-day cyclic regimen (24 days’ active hormonal intake followed by 4 days of placebo tablets) or a fixed extended regimen (120 days’ uninterrupted active hormonal intake followed by a 4-day tablet-free interval) over 1 year. Results The population PK of EE and DRSP in this population were successfully described using the developed population models. All three regimens led to similar steady-state drug exposure during long-term treatment. Only minor changes (≤8%) in the steady-state PK of EE and DRSP were observed between Week 3 and Week 27 of an extended regimen. Body weight (BW) and age had a small, statistically significant impact on the PK of EE and DRSP (BW only) in a covariate analysis, however, these changes were not considered to be clinically relevant. Conclusions Extending the established 24/4-day regimen of EE 20 µg/DRSP 3 mg does not change the known steady-state PK of EE and DRSP, suggesting that the clinical efficacy is also similar. This is in line with the published clinical results from this study. PMID:23493606

Characterisation of the pharmacokinetics of ethinylestradiol and drospirenone in extended-cycle regimens: population pharmacokinetic analysis from a randomised Phase III study.

PubMed

Reif, Stefanie; Snelder, Nelleke; Blode, Hartmut

2013-04-01

The primary objective of this analysis was to characterise the steady-state pharmacokinetics (PK) of ethinylestradiol (EE) and drospirenone (DRSP) in a randomised Phase III study that investigated the contraceptive efficacy and safety of three different regimens of EE 20 µg/DRSP 3 mg. Non-linear mixed-effects modelling was used to develop population PK models for EE and DRSP. EE and DRSP serum concentrations were determined in blood samples obtained from approximately 1100 healthy young women on two occasions during the first cycle (Week 3) and after 6 months (Week 27) of EE 20 µg/DRSP 3 mg use. EE 20 µg/DRSP 3 mg was administered as a flexible extended regimen [24-120 days' active hormonal intake followed by 4 days with no tablet intake (tablet-free interval)], a conventional 28-day cyclic regimen (24 days' active hormonal intake followed by 4 days of placebo tablets) or a fixed extended regimen (120 days' uninterrupted active hormonal intake followed by a 4-day tablet-free interval) over 1 year. The population PK of EE and DRSP in this population were successfully described using the developed population models. All three regimens led to similar steady-state drug exposure during long-term treatment. Only minor changes (≤ 8%) in the steady-state PK of EE and DRSP were observed between Week 3 and Week 27 of an extended regimen. Body weight (BW) and age had a small, statistically significant impact on the PK of EE and DRSP (BW only) in a covariate analysis, however, these changes were not considered to be clinically relevant. Extending the established 24/4-day regimen of EE 20 µg/DRSP 3 mg does not change the known steady-state PK of EE and DRSP, suggesting that the clinical efficacy is also similar. This is in line with the published clinical results from this study.

Design and development of a ceramic radial turbine for the AGT101

NASA Technical Reports Server (NTRS)

Finger, D. G.; Gupta, S. K.

1982-01-01

An acceptable and feasible ceramic turbine wheel design has been achieved, and the relevant temperature, stress, and success probability analyses are discussed. The design is described, the materials selection presented, and the engine cycle conditions analysis parameters shown. Measured MOR four-point strengths are indicated for room and elevated temperatures, and engine conditions are analyzed for various cycle states, materials, power states, turbine inlet temperatures, and speeds. An advanced gas turbine ceramic turbine rotor thermal and stress model is developed, and cumulative probability of survival is shown for first and third-year properties of SiC and Si3N4 rotors under different operating conditions, computed for both blade and hub regions. Temperature and stress distributions for steady-state and worst-case shutdown transients are depicted.

Reynolds-Averaged Navier-Stokes Analysis of Zero Efflux Flow Control over a Hump Model

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.

2006-01-01

The unsteady flow over a hump model with zero efflux oscillatory flow control is modeled computationally using the unsteady Reynolds-averaged Navier-Stokes equations. Three different turbulence models produce similar results, and do a reasonably good job predicting the general character of the unsteady surface pressure coefficients during the forced cycle. However, the turbulent shear stresses are underpredicted in magnitude inside the separation bubble, and the computed results predict too large a (mean) separation bubble compared with experiment. These missed predictions are consistent with earlier steady-state results using no-flow-control and steady suction, from a 2004 CFD validation workshop for synthetic jets.

Reynolds-Averaged Navier-Stokes Analysis of Zero Efflux Flow Control Over a Hump Model

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.

2006-01-01

The unsteady flow over a hump model with zero efflux oscillatory flow control is modeled computationally using the unsteady Reynolds-averaged Navier-Stokes equations. Three different turbulence models produce similar results, and do a reasonably good job predicting the general character of the unsteady surface pressure coefficients during the forced cycle. However, the turbulent shear stresses are underpredicted in magnitude inside the separation bubble, and the computed results predict too large a (mean) separation bubble compared with experiment. These missed predictions are consistent with earlier steady-state results using no-flow-control and steady suction, from a 2004 CFD validation workshop for synthetic jets.

An adaptive scale factor based MPPT algorithm for changing solar irradiation levels in outer space

NASA Astrophysics Data System (ADS)

Kwan, Trevor Hocksun; Wu, Xiaofeng

2017-03-01

Maximum power point tracking (MPPT) techniques are popularly used for maximizing the output of solar panels by continuously tracking the maximum power point (MPP) of their P-V curves, which depend both on the panel temperature and the input insolation. Various MPPT algorithms have been studied in literature, including perturb and observe (P&O), hill climbing, incremental conductance, fuzzy logic control and neural networks. This paper presents an algorithm which improves the MPP tracking performance by adaptively scaling the DC-DC converter duty cycle. The principle of the proposed algorithm is to detect the oscillation by checking the sign (ie. direction) of the duty cycle perturbation between the current and previous time steps. If there is a difference in the signs then it is clear an oscillation is present and the DC-DC converter duty cycle perturbation is subsequently scaled down by a constant factor. By repeating this process, the steady state oscillations become negligibly small which subsequently allows for a smooth steady state MPP response. To verify the proposed MPPT algorithm, a simulation involving irradiances levels that are typically encountered in outer space is conducted. Simulation and experimental results prove that the proposed algorithm is fast and stable in comparison to not only the conventional fixed step counterparts, but also to previous variable step size algorithms.

Cyclic steady states in diffusion-induced plasticity with applications to lithium-ion batteries

NASA Astrophysics Data System (ADS)

Peigney, Michaël

2018-02-01

Electrode materials in lithium-ion batteries offer an example of medium in which stress and plastic flow are generated by the diffusion of guest atoms. In such a medium, deformation and diffusion are strongly coupled processes. For designing electrodes with improved lifetime and electro-mechanical efficiency, it is crucial to understand how plasticity and diffusion evolve over consecutive charging-recharging cycles. With such questions in mind, this paper provides general results for the large-time behavior of media coupling plasticity with diffusion when submitted to cyclic chemo-mechanical loadings. Under suitable assumptions, we show that the stress, the plastic strain rate, the chemical potential and the flux of guest atoms converge to a cyclic steady state which is largely independent of the initial state. A special emphasis is laid on the special case of elastic shakedown, which corresponds to the situation where the plastic strain stops evolving after a sufficiently large number of cycles. Elastic shakedown is expected to be beneficial for the fatigue behavior and - in the case of lithium-ion batteries - for the electro-chemical efficiency. We provide a characterization of the chemo-mechanical loadings for which elastic shakedown occurs. Building on that characterization, we suggest a general method for designing structures in such fashion that they operate in the elastic shakedown regime, whatever the initial state is. An attractive feature of the proposed method is that incremental analysis of the fully coupled plasticity-diffusion problem is avoided. The results obtained are applied to the model problem of a battery electrode cylinder particle under cyclic charging. Closed-form expressions are obtained for the set of charging rates and charging amplitudes for which elastic shakedown occurs, as well as for the corresponding cyclic steady states of stress, lithium concentration and chemical potential. Some results for a spherical particle are also presented.

State trajectories used to observe and control dc-to-dc converters

NASA Technical Reports Server (NTRS)

Burns, W. W., III; Wilson, T. G.

1976-01-01

State-plane analysis techniques are employed to study the voltage stepup energy-storage dc-to-dc converter. Within this framework, an example converter operating under the influence of a constant on-time and a constant frequency controller is examined. Qualitative insight gained through this approach is used to develop a conceptual free-running control law for the voltage stepup converter which can achieve steady-state operation in one on/off cycle of control. Digital computer simulation data are presented to illustrate and verify the theoretical discussions presented.

Acyl-protein thioesterase 2 catalyzes the deacylation of peripheral membrane-associated GAP-43.

PubMed

Tomatis, Vanesa M; Trenchi, Alejandra; Gomez, Guillermo A; Daniotti, Jose L

2010-11-30

An acylation/deacylation cycle is necessary to maintain the steady-state subcellular distribution and biological activity of S-acylated peripheral proteins. Despite the progress that has been made in identifying and characterizing palmitoyltransferases (PATs), much less is known about the thioesterases involved in protein deacylation. In this work, we investigated the deacylation of growth-associated protein-43 (GAP-43), a dually acylated protein at cysteine residues 3 and 4. Using fluorescent fusion constructs, we measured in vivo the rate of deacylation of GAP-43 and its single acylated mutants in Chinese hamster ovary (CHO)-K1 and human HeLa cells. Biochemical and live cell imaging experiments demonstrated that single acylated mutants were completely deacylated with similar kinetic in both cell types. By RT-PCR we observed that acyl-protein thioesterase 1 (APT-1), the only bona fide thioesterase shown to mediate deacylation in vivo, is expressed in HeLa cells, but not in CHO-K1 cells. However, APT-1 overexpression neither increased the deacylation rate of single acylated GAP-43 nor affected the steady-state subcellular distribution of dually acylated GAP-43 both in CHO-K1 and HeLa cells, indicating that GAP-43 deacylation is not mediated by APT-1. Accordingly, we performed a bioinformatic search to identify putative candidates with acyl-protein thioesterase activity. Among several candidates, we found that APT-2 is expressed both in CHO-K1 and HeLa cells and its overexpression increased the deacylation rate of single acylated GAP-43 and affected the steady-state localization of diacylated GAP-43 and H-Ras. Thus, the results demonstrate that APT-2 is the protein thioesterase involved in the acylation/deacylation cycle operating in GAP-43 subcellular distribution.

CHF Enhancement by Vessel Coating for External Reactor Vessel Cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan-Bill Cheung; Joy L. Rempe

2004-06-01

In-vessel retention (IVR) is a key severe accident management (SAM) strategy that has been adopted by some operating nuclear power plants and advanced light water reactors (ALWRs). One viable means for IVR is the method of external reactor vessel cooling (ERVC) by flooding of the reactor cavity during a severe accident. As part of a joint Korean – United States International Nuclear Energy Research Initiative (K-INERI), an experimental study has been conducted to investigate the viability of using an appropriate vessel coating to enhance the critical heat flux (CHF) limits during ERVC. Toward this end, transient quenching and steady-state boilingmore » experiments were performed in the SBLB (Subscale Boundary Layer Boiling) facility at Penn State using test vessels with micro-porous aluminum coatings. Local boiling curves and CHF limits were obtained in these experiments. When compared to the corresponding data without coatings, substantial enhancement in the local CHF limits for the case with surface coatings was observed. Results of the steady state boiling experiments showed that micro-porous aluminum coatings were very durable. Even after many cycles of steady state boiling, the vessel coatings remained rather intact, with no apparent changes in color or structure. Moreover, the heat transfer performance of the coatings was found to be highly desirable with an appreciable CHF enhancement in all locations on the vessel outer surface but with very little effect of aging.« less

Global asymptotic stability and hopf bifurcation for a blood cell production model.

PubMed

Crauste, Fabien

2006-04-01

We analyze the asymptotic stability of a nonlinear system of two differential equations with delay, describing the dynamics of blood cell produc- tion. This process takes place in the bone marrow, where stem cells differen- tiate throughout division in blood cells. Taking into account an explicit role of the total population of hematopoietic stem cells in the introduction of cells in cycle, we are led to study a characteristic equation with delay-dependent coefficients. We determine a necessary and sufficient condition for the global stability of the first steady state of our model, which describes the popula- tion's dying out, and we obtain the existence of a Hopf bifurcation for the only nontrivial positive steady state, leading to the existence of periodic solutions. These latter are related to dynamical diseases affecting blood cells known for their cyclic nature.

Spatially distributed characterization of hyporheic solute transport during baseflow recession in a headwater mountain stream using electrical geophysical imaging

Treesearch

Adam S. Ward; Michael N. Gooseff; Michael Fitzgerald; Thomas J. Voltz; Kamini Singha

2014-01-01

The transport of solutes along hyporheic flowpaths is recognized as central to numerous biogeochemical cycles, yet our understanding of how this transport changes with baseflow recession, particularly in a spatially distributed manner, is limited. We conducted four steady-state solute tracer injections and collected electrical resistivity data to characterize hyporheic...

40 CFR 1042.525 - How do I adjust emission levels to account for infrequently regenerating aftertreatment devices?

Code of Federal Regulations, 2010 CFR

2010-07-01

... this section for how to adjust discrete-mode testing. For this section, “regeneration” means an... ramped-modal cycle, or on average less than once per typical mode in a discrete-mode test. (a) Developing... modes of a discrete-mode steady-state test. You may use either of the following different approaches for...

40 CFR 86.1363-2007 - Steady-state testing with a discrete-mode cycle.

Code of Federal Regulations, 2011 CFR

2011-07-01

... The percent torque is relative to the maximum torque at the commanded test speed. 3 Upon Administrator... ±50 rpm and the specified torque must be held to within plus or minus two percent of the maximum torque at the test speed. (d) One filter shall be used for sampling PM over the 13-mode test procedure...

40 CFR 86.1363-2007 - Steady-state testing with a discrete-mode cycle.

Code of Federal Regulations, 2012 CFR

2012-07-01

... The percent torque is relative to the maximum torque at the commanded test speed. 3 Upon Administrator... ±50 rpm and the specified torque must be held to within plus or minus two percent of the maximum torque at the test speed. (d) One filter shall be used for sampling PM over the 13-mode test procedure...

40 CFR 86.1363-2007 - Steady-state testing with a discrete-mode cycle.

Code of Federal Regulations, 2013 CFR

2013-07-01

... The percent torque is relative to the maximum torque at the commanded test speed. 3 Upon Administrator... ±50 rpm and the specified torque must be held to within plus or minus two percent of the maximum torque at the test speed. (d) One filter shall be used for sampling PM over the 13-mode test procedure...

40 CFR 1065.202 - Data updating, recording, and control.

Code of Federal Regulations, 2010 CFR

2010-07-01

... means. § 1065.514, § 1065.530 Steady-state and ramped-modal duty cycle reference and feedback speeds and... mean value per test interval. § 1065.530, § 1065.545 Diluted exhaust flow rate from a CVS with a heat exchanger upstream of the flow measurement N/A 1 Hz. § 1065.530, § 1065.545 Diluted exhaust flow rate from a...

40 CFR 1033.515 - Discrete-mode steady-state emission tests of locomotives and locomotive engines.

Code of Federal Regulations, 2011 CFR

2011-07-01

... the provisions of 40 CFR part 1065, subpart F for general pre-test procedures (including engine and... 1065. (b) Begin the test by operating the locomotive over the pre-test portion of the cycle specified... Sample averagingperiod for emissions 1 Pre-test idle Lowest idle setting 10 to 15 3 Not applicable A Low...

40 CFR 1033.515 - Discrete-mode steady-state emission tests of locomotives and locomotive engines.

Code of Federal Regulations, 2014 CFR

2014-07-01

... the provisions of 40 CFR part 1065, subpart F for general pre-test procedures (including engine and... 1065. (b) Begin the test by operating the locomotive over the pre-test portion of the cycle specified... Sample averagingperiod for emissions 1 Pre-test idle Lowest idle setting 10 to 15 3 Not applicable A Low...

40 CFR 1033.515 - Discrete-mode steady-state emission tests of locomotives and locomotive engines.

Code of Federal Regulations, 2013 CFR

2013-07-01

... the provisions of 40 CFR part 1065, subpart F for general pre-test procedures (including engine and... 1065. (b) Begin the test by operating the locomotive over the pre-test portion of the cycle specified... Sample averagingperiod for emissions 1 Pre-test idle Lowest idle setting 10 to 15 3 Not applicable A Low...

40 CFR 1033.515 - Discrete-mode steady-state emission tests of locomotives and locomotive engines.

Code of Federal Regulations, 2010 CFR

2010-07-01

... the provisions of 40 CFR part 1065, subpart F for general pre-test procedures (including engine and... 1065. (b) Begin the test by operating the locomotive over the pre-test portion of the cycle specified... Sample averagingperiod for emissions 1 Pre-test idle Lowest idle setting 10 to 15 3 Not applicable A Low...

40 CFR 1033.515 - Discrete-mode steady-state emission tests of locomotives and locomotive engines.

Code of Federal Regulations, 2012 CFR

2012-07-01

... the provisions of 40 CFR part 1065, subpart F for general pre-test procedures (including engine and... 1065. (b) Begin the test by operating the locomotive over the pre-test portion of the cycle specified... Sample averagingperiod for emissions 1 Pre-test idle Lowest idle setting 10 to 15 3 Not applicable A Low...

Damage Accumulation and Failure of Plasma-Sprayed Thermal Barrier Coatings under Thermal Gradient Cyclic Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Ghosn, Louis J.; Miller, rober A.

2005-01-01

Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. A fundamental understanding of the sintering and thermal cycling induced delamination of thermal barrier coating systems under engine-like heat flux conditions will potentially help to improve the coating temperature capability. In this study, a test approach is established to emphasize the real-time monitoring and assessment of the coating thermal conductivity, which can initially increase under the steady-state high temperature thermal gradient test due to coating sintering, and later decrease under the thermal gradient cyclic test due to coating cracking and delamination. Thermal conductivity prediction models have been established for a ZrO2-(7- 8wt%)Y2O3 model coating system in terms of heat flux, time, and testing temperatures. The coating delamination accumulation is then assessed based on the observed thermal conductivity response under the combined steady-state and cyclic thermal gradient tests. The coating thermal gradient cycling associated delaminations and failure mechanisms under simulated engine heat-flux conditions will be discussed in conjunction with the coating sintering and fracture testing results.

Isotopically Nonstationary Metabolic Flux Analysis (INST-MFA) of Photosynthesis and Photorespiration in Plants.

PubMed

Ma, Fangfang; Jazmin, Lara J; Young, Jamey D; Allen, Doug K

2017-01-01

Photorespiration is a central component of photosynthesis; however to better understand its role it should be viewed in the context of an integrated metabolic network rather than a series of individual reactions that operate independently. Isotopically nonstationary 13 C metabolic flux analysis (INST-MFA), which is based on transient labeling studies at metabolic steady state, offers a comprehensive platform to quantify plant central metabolism. In this chapter, we describe the application of INST-MFA to investigate metabolism in leaves. Leaves are an autotrophic tissue, assimilating CO 2 over a diurnal period implying that the metabolic steady state is limited to less than 12 h and thus requiring an INST-MFA approach. This strategy results in a comprehensive unified description of photorespiration, Calvin cycle, sucrose and starch synthesis, tricarboxylic acid (TCA) cycle, and amino acid biosynthetic fluxes. We present protocols of the experimental aspects for labeling studies: transient 13 CO 2 labeling of leaf tissue, sample quenching and extraction, mass spectrometry (MS) analysis of isotopic labeling data, measurement of sucrose and amino acids in vascular exudates, and provide details on the computational flux estimation using INST-MFA.

Fuel economy and exhaust emissions characteristics of diesel vehicles: Test results of a prototype Chrysler Volare, 225 CID (3.7-liter) automobile

NASA Technical Reports Server (NTRS)

Walter, R. A.

1982-01-01

The results obtained from fuel economy and emission tests conducted on a prototype Chrysler Volare diesel vehicle are documented. The vehicle was tested on a chassis dynamometer over selected drive cycles and steady-state conditions. The fuel used, was a DOE/BETC referee fuel. Particulate emission rates were calculated from dilution tunnel measurements and large volume particulate samples were collected for biological and chemical analysis. The vehicle obtained 32.7 mpg for the FTP urban cycle and 48.8 mpg for the highway cycle. The emissions rates were 0.42/1.58/1.17/0.28 g/mile of HC, CO, NOx and particulates respectively.

Unifying concept of serotonin transporter-associated currents.

PubMed

Schicker, Klaus; Uzelac, Zeljko; Gesmonde, Joan; Bulling, Simon; Stockner, Thomas; Freissmuth, Michael; Boehm, Stefan; Rudnick, Gary; Sitte, Harald H; Sandtner, Walter

2012-01-02

Serotonin (5-HT) uptake by the human serotonin transporter (hSERT) is driven by ion gradients. The stoichiometry of transported 5-HT and ions is predicted to result in electroneutral charge movement. However, hSERT mediates a current when challenged with 5-HT. This discrepancy can be accounted for by an uncoupled ion flux. Here, we investigated the mechanistic basis of the uncoupled currents and its relation to the conformational cycle of hSERT. Our observations support the conclusion that the conducting state underlying the uncoupled ion flux is in equilibrium with an inward facing state of the transporter with K+ bound. We identified conditions associated with accumulation of the transporter in inward facing conformations. Manipulations that increased the abundance of inward facing states resulted in enhanced steady-state currents. We present a comprehensive kinetic model of the transport cycle, which recapitulates salient features of the recorded currents. This study provides a framework for exploring transporter-associated currents.

Unifying Concept of Serotonin Transporter-associated Currents*

PubMed Central

Schicker, Klaus; Uzelac, Zeljko; Gesmonde, Joan; Bulling, Simon; Stockner, Thomas; Freissmuth, Michael; Boehm, Stefan; Rudnick, Gary; Sitte, Harald H.; Sandtner, Walter

2012-01-01

Serotonin (5-HT) uptake by the human serotonin transporter (hSERT) is driven by ion gradients. The stoichiometry of transported 5-HT and ions is predicted to result in electroneutral charge movement. However, hSERT mediates a current when challenged with 5-HT. This discrepancy can be accounted for by an uncoupled ion flux. Here, we investigated the mechanistic basis of the uncoupled currents and its relation to the conformational cycle of hSERT. Our observations support the conclusion that the conducting state underlying the uncoupled ion flux is in equilibrium with an inward facing state of the transporter with K+ bound. We identified conditions associated with accumulation of the transporter in inward facing conformations. Manipulations that increased the abundance of inward facing states resulted in enhanced steady-state currents. We present a comprehensive kinetic model of the transport cycle, which recapitulates salient features of the recorded currents. This study provides a framework for exploring transporter-associated currents. PMID:22072712

Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization

NASA Astrophysics Data System (ADS)

Mentink-Vigier, Frederic; Akbey, Ümit; Oschkinat, Hartmut; Vega, Shimon; Feintuch, Akiva

2015-09-01

Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160 K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea -eb - n } during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle. This study also shows the complexity of the MAS-DNP process and therefore the necessity to rely on numerical simulations for understanding parametric dependencies of the enhancements. Finally an extension of the spin system up to five spins allowed us to probe the first steps of the transfer of polarization from the nuclei coupled to the electrons to further away nuclei, demonstrating a decrease in the spin-diffusion barrier under MAS conditions.

Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization.

PubMed

Mentink-Vigier, Frederic; Akbey, Ümit; Oschkinat, Hartmut; Vega, Shimon; Feintuch, Akiva

2015-09-01

Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea-eb-n} during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle. This study also shows the complexity of the MAS-DNP process and therefore the necessity to rely on numerical simulations for understanding parametric dependencies of the enhancements. Finally an extension of the spin system up to five spins allowed us to probe the first steps of the transfer of polarization from the nuclei coupled to the electrons to further away nuclei, demonstrating a decrease in the spin-diffusion barrier under MAS conditions. Copyright © 2015 Elsevier Inc. All rights reserved.

Composite load spectra for select space propulsion structural components

NASA Technical Reports Server (NTRS)

Newell, J. F.; Ho, H. W.; Kurth, R. E.

1991-01-01

The work performed to develop composite load spectra (CLS) for the Space Shuttle Main Engine (SSME) using probabilistic methods. The three methods were implemented to be the engine system influence model. RASCAL was chosen to be the principal method as most component load models were implemented with the method. Validation of RASCAL was performed. High accuracy comparable to the Monte Carlo method can be obtained if a large enough bin size is used. Generic probabilistic models were developed and implemented for load calculations using the probabilistic methods discussed above. Each engine mission, either a real fighter or a test, has three mission phases: the engine start transient phase, the steady state phase, and the engine cut off transient phase. Power level and engine operating inlet conditions change during a mission. The load calculation module provides the steady-state and quasi-steady state calculation procedures with duty-cycle-data option. The quasi-steady state procedure is for engine transient phase calculations. In addition, a few generic probabilistic load models were also developed for specific conditions. These include the fixed transient spike model, the poison arrival transient spike model, and the rare event model. These generic probabilistic load models provide sufficient latitude for simulating loads with specific conditions. For SSME components, turbine blades, transfer ducts, LOX post, and the high pressure oxidizer turbopump (HPOTP) discharge duct were selected for application of the CLS program. They include static pressure loads and dynamic pressure loads for all four components, centrifugal force for the turbine blade, temperatures of thermal loads for all four components, and structural vibration loads for the ducts and LOX posts.

Experimental Validation of a Closed Brayton Cycle System Transient Simulation

NASA Technical Reports Server (NTRS)

Johnson, Paul K.; Hervol, David S.

2006-01-01

The Brayton Power Conversion Unit (BPCU) located at NASA Glenn Research Center (GRC) in Cleveland, Ohio was used to validate the results of a computational code known as Closed Cycle System Simulation (CCSS). Conversion system thermal transient behavior was the focus of this validation. The BPCU was operated at various steady state points and then subjected to transient changes involving shaft rotational speed and thermal energy input. These conditions were then duplicated in CCSS. Validation of the CCSS BPCU model provides confidence in developing future Brayton power system performance predictions, and helps to guide high power Brayton technology development.

Propulsion system mathematical model for a lift/cruise fan V/STOL aircraft

NASA Technical Reports Server (NTRS)

Cole, G. L.; Sellers, J. F.; Tinling, B. E.

1980-01-01

A propulsion system mathematical model is documented that allows calculation of internal engine parameters during transient operation. A non-realtime digital computer simulation of the model is presented. It is used to investigate thrust response and modulation requirements as well as the impact of duty cycle on engine life and design criteria. Comparison of simulation results with steady-state cycle deck calculations showed good agreement. The model was developed for a specific 3-fan subsonic V/STOL aircraft application, but it can be adapted for use with any similar lift/cruise V/STOL configuration.

Study on the variable cycle engine modeling techniques based on the component method

NASA Astrophysics Data System (ADS)

Zhang, Lihua; Xue, Hui; Bao, Yuhai; Li, Jijun; Yan, Lan

2016-01-01

Based on the structure platform of the gas turbine engine, the components of variable cycle engine were simulated by using the component method. The mathematical model of nonlinear equations correspondeing to each component of the gas turbine engine was established. Based on Matlab programming, the nonlinear equations were solved by using Newton-Raphson steady-state algorithm, and the performance of the components for engine was calculated. The numerical simulation results showed that the model bulit can describe the basic performance of the gas turbine engine, which verified the validity of the model.

Recent studies of tire braking performance. [for aircraft

NASA Technical Reports Server (NTRS)

Mccarty, J. L.; Leland, T. J. W.

1973-01-01

The results from recent studies of some factors affecting tire braking and cornering performance are presented together with a discussion of the possible application of these results to the design of aircraft braking systems. The first part of the paper is concerned with steady-state braking, that is, results from tests conducted at a constant slip ratio or steering angle or both. The second part deals with cyclic braking tests, both single cycle, where brakes are applied at a constant rate until wheel lockup is achieved, and rapid cycling of the brakes under control of a currently operational antiskid system.

Advanced space engine powerhead breadboard assembly system study

NASA Technical Reports Server (NTRS)

Campbell, R. G.

1978-01-01

The objective of this study was to establish a preliminary design of a Powerhead Breadboard Assembly (PBA) for an 88 964-Newton (20,000-pound) thrust oxygen/hydrogen staged combustion cycle engine for use in orbital transfer vehicle propulsion. Existing turbopump, preburner, and thrust chamber components were integrated with interconnecting ducting, a heat exchanger, and a control system to complete the PBA design. Cycle studies were conducted to define starting transients and steady-state balances for the completed design. Specifications were developed for all valve applications and the conditions required for the control system integration with the facility for system test were defined.

Non-linear analysis of stick/slip motion

NASA Astrophysics Data System (ADS)

Pratt, T. K.; Williams, R.

1981-02-01

The steady state relative motion of two masses with dry (Coulomb) friction contact is investigated. The bodies are assumed to have the same mass and stiffness and are subjected to harmonic excitation. By means of a combined analytical—numerical procedure, results are obtained for arbitrary values of Coulomb friction, excitation frequency, and natural frequencies of the bodies. For certain values of these parameters, multiple lockups per cycle are possible. In this respect, the problem investigated here is a natural extension of the one considered by Den Hartog, who in obtaining his closed form solution assumed a maximum of two lockups per cycle.

How large is the subducted water flux? New constraints on mantle regassing rates

NASA Astrophysics Data System (ADS)

Parai, R.; Mukhopadhyay, S.

2012-02-01

Estimates of the subducted water (H2O) flux have been used to discuss the regassing of the mantle over Earth history. However, these estimates vary widely, and some are large enough to have reduced the volume of water in the global ocean by a factor of two over the Phanerozoic. In light of uncertainties in the hydration state of subducting slabs, magma production rates and mantle source water contents, we use a Monte Carlo simulation to set limits on long-term global water cycling and the return flux of water to the deep Earth. Estimates of magma production rates and water contents in primary magmas generated at ocean islands, mid-ocean ridges, arcs and back-arcs are paired with estimates of water entering trenches via subducting oceanic slab in order to construct a model of the deep Earth water cycle. The simulation is constrained by reconstructions of Phanerozoic sea level change, which suggest that ocean volume is near steady-state, though a sea level decrease of up to 360 m may be supported. We provide limits on the return flux of water to the deep Earth over the Phanerozoic corresponding to a near steady-state exosphere (0-100 meter sea level decrease) and a maximum sea level decrease of 360 m. For the near steady-state exosphere, the return flux is 1.4 - 2.0- 0.3+ 0.4 × 1013 mol/yr, corresponding to 2-3% serpentinization in 10 km of lithospheric mantle. The return flux that generates the maximum sea level decrease over the Phanerozoic is 3.5- 0.3+ 0.4 × 1013 mol/yr, corresponding to 5% serpentinization in 10 km of lithospheric mantle. Our estimates of the return flux of water to the mantle are up to 7 times lower than previously suggested. The imbalance between our estimates of the return flux and mantle output flux leads to a low rate of increase in bulk mantle water content of up to 24 ppm/Ga.

Dynamics of ferrofluidic flow in the Taylor-Couette system with a small aspect ratio

PubMed Central

Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

2017-01-01

We investigate fundamental nonlinear dynamics of ferrofluidic Taylor-Couette flow - flow confined be-tween two concentric independently rotating cylinders - consider small aspect ratio by solving the ferro-hydrodynamical equations, carrying out systematic bifurcation analysis. Without magnetic field, we find steady flow patterns, previously observed with a simple fluid, such as those containing normal one- or two vortex cells, as well as anomalous one-cell and twin-cell flow states. However, when a symmetry-breaking transverse magnetic field is present, all flow states exhibit stimulated, finite two-fold mode. Various bifurcations between steady and unsteady states can occur, corresponding to the transitions between the two-cell and one-cell states. While unsteady, axially oscillating flow states can arise, we also detect the emergence of new unsteady flow states. In particular, we uncover two new states: one contains only the azimuthally oscillating solution in the configuration of the twin-cell flow state, and an-other a rotating flow state. Topologically, these flow states are a limit cycle and a quasiperiodic solution on a two-torus, respectively. Emergence of new flow states in addition to observed ones with classical fluid, indicates that richer but potentially more controllable dynamics in ferrofluidic flows, as such flow states depend on the external magnetic field. PMID:28059129

Artificial neural network for suppression of banding artifacts in balanced steady-state free precession MRI.

PubMed

Kim, Ki Hwan; Park, Sung-Hong

2017-04-01

The balanced steady-state free precession (bSSFP) MR sequence is frequently used in clinics, but is sensitive to off-resonance effects, which can cause banding artifacts. Often multiple bSSFP datasets are acquired at different phase cycling (PC) angles and then combined in a special way for banding artifact suppression. Many strategies of combining the datasets have been suggested for banding artifact suppression, but there are still limitations in their performance, especially when the number of phase-cycled bSSFP datasets is small. The purpose of this study is to develop a learning-based model to combine the multiple phase-cycled bSSFP datasets for better banding artifact suppression. Multilayer perceptron (MLP) is a feedforward artificial neural network consisting of three layers of input, hidden, and output layers. MLP models were trained by input bSSFP datasets acquired from human brain and knee at 3T, which were separately performed for two and four PC angles. Banding-free bSSFP images were generated by maximum-intensity projection (MIP) of 8 or 12 phase-cycled datasets and were used as targets for training the output layer. The trained MLP models were applied to another brain and knee datasets acquired with different scan parameters and also to multiple phase-cycled bSSFP functional MRI datasets acquired on rat brain at 9.4T, in comparison with the conventional MIP method. Simulations were also performed to validate the MLP approach. Both the simulations and human experiments demonstrated that MLP suppressed banding artifacts significantly, superior to MIP in both banding artifact suppression and SNR efficiency. MLP demonstrated superior performance over MIP for the 9.4T fMRI data as well, which was not used for training the models, while visually preserving the fMRI maps very well. Artificial neural network is a promising technique for combining multiple phase-cycled bSSFP datasets for banding artifact suppression. Copyright © 2016 Elsevier Inc. All rights reserved.

RELAP5-3D Results for Phase I (Exercise 2) of the OECD/NEA MHTGR-350 MW Benchmark

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerhard Strydom

2012-06-01

The coupling of the PHISICS code suite to the thermal hydraulics system code RELAP5-3D has recently been initiated at the Idaho National Laboratory (INL) to provide a fully coupled prismatic Very High Temperature Reactor (VHTR) system modeling capability as part of the NGNP methods development program. The PHISICS code consists of three modules: INSTANT (performing 3D nodal transport core calculations), MRTAU (depletion and decay heat generation) and a perturbation/mixer module. As part of the verification and validation activities, steady state results have been obtained for Exercise 2 of Phase I of the newly-defined OECD/NEA MHTGR-350 MW Benchmark. This exercise requiresmore » participants to calculate a steady-state solution for an End of Equilibrium Cycle 350 MW Modular High Temperature Reactor (MHTGR), using the provided geometry, material, and coolant bypass flow description. The paper provides an overview of the MHTGR Benchmark and presents typical steady state results (e.g. solid and gas temperatures, thermal conductivities) for Phase I Exercise 2. Preliminary results are also provided for the early test phase of Exercise 3 using a two-group cross-section library and the Relap5-3D model developed for Exercise 2.« less

RELAP5-3D results for phase I (Exercise 2) of the OECD/NEA MHTGR-350 MW benchmark

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strydom, G.; Epiney, A. S.

2012-07-01

The coupling of the PHISICS code suite to the thermal hydraulics system code RELAP5-3D has recently been initiated at the Idaho National Laboratory (INL) to provide a fully coupled prismatic Very High Temperature Reactor (VHTR) system modeling capability as part of the NGNP methods development program. The PHISICS code consists of three modules: INSTANT (performing 3D nodal transport core calculations), MRTAU (depletion and decay heat generation) and a perturbation/mixer module. As part of the verification and validation activities, steady state results have been obtained for Exercise 2 of Phase I of the newly-defined OECD/NEA MHTGR-350 MW Benchmark. This exercise requiresmore » participants to calculate a steady-state solution for an End of Equilibrium Cycle 350 MW Modular High Temperature Reactor (MHTGR), using the provided geometry, material, and coolant bypass flow description. The paper provides an overview of the MHTGR Benchmark and presents typical steady state results (e.g. solid and gas temperatures, thermal conductivities) for Phase I Exercise 2. Preliminary results are also provided for the early test phase of Exercise 3 using a two-group cross-section library and the Relap5-3D model developed for Exercise 2. (authors)« less

Phase transformation of mixed-phase clouds

NASA Astrophysics Data System (ADS)

Korolev, Alexei; Isaac, George

2003-01-01

The glaciation time of a mixed-phase cloud due to the Wegener-Bergeron-Findeisen mechanism is calculated using an adiabatic one-dimensional numerical model for the cases of zero, ascending, descending and oscillating vertical velocities. The characteristic values of the glaciation time are obtained for different concentrations of ice particles and liquid-water content. Steady state is not possible for the ice-water content/total water content ratio in a uniformly vertically moving mixed-phase parcel. The vertical oscillation of a cloud parcel may result in a periodic evaporation and activation of liquid droplets in the presence of ice particles during infinite time. After a certain time, the average ice-water content and liquid-water content reach a steady state. This phenomenon may explain the existence of long-lived mixed-phase stratiform layers. The obtained results are important for understanding the mechanisms of formation and life cycle of mixed-phase clouds.

Structural Evaluation of a Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump Turbine Blade

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali

1996-01-01

Thermal and structural finite-element analyses were performed on the first high pressure fuel turbopump turbine blade of the space shuttle main engine (SSME). A two-dimensional (2-D) finite-element model of the blade and firtree disk attachment was analyzed using the general purpose MARC (finite-element) code. The loading history applied is a typical test stand engine cycle mission, which consists of a startup condition with two thermal spikes, a steady state and a shutdown transient. The blade material is a directionally solidified (DS) Mar-M 246 alloy, the blade rotor is forged with waspalloy material. Thermal responses under steady-state and transient conditions were calculated. The stresses and strains under the influence of mechanical and thermal loadings were also determined. The critical regions that exhibited high stresses and severe localized plastic deformation were the blade-rotor gaps.

Electrochemical disinfection of repeatedly recycled blackwater in a free-standing, additive-free toilet.

PubMed

Hawkins, Brian T; Sellgren, Katelyn L; Klem, Ethan J D; Piascik, Jeffrey R; Stoner, Brian R

2017-11-01

Decentralized, energy-efficient waste water treatment technologies enabling water reuse are needed to sustainably address sanitation needs in water- and energy-scarce environments. Here, we describe the effects of repeated recycling of disinfected blackwater (as flush liquid) on the energy required to achieve full disinfection with an electrochemical process in a prototype toilet system. The recycled liquid rapidly reached a steady state with total solids reliably ranging between 0.50 and 0.65% and conductivity between 20 and 23 mS/cm through many flush cycles over 15 weeks. The increase in accumulated solids was associated with increased energy demand and wide variation in the free chlorine contact time required to achieve complete disinfection. Further studies on the system at steady state revealed that running at higher voltage modestly improves energy efficiency, and established running parameters that reliably achieve disinfection at fixed run times. These results will guide prototype testing in the field.

Neutronic, steady-state, and transient analyses for the Kazakhstan VVR-K reactor with LEU fuel: ANL independent verification results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanan, Nelson A.; Garner, Patrick L.

Calculations have been performed for steady state and postulated transients in the VVR-K reactor at the Institute of Nuclear Physics (INP), Kazakhstan. (The reactor designation in Cyrillic is BBP-K; transliterating characters to English gives VVR-K but translating words gives WWR-K.) These calculations have been performed at the request of staff of the INP who are performing similar calculations. The selection of the transients considered started during working meetings and email correspondence between Argonne National Laboratory (ANL) and INP staff. In the end the transient were defined by the INP staff. Calculations were performed for the fresh low-enriched uranium (LEU) coremore » and for four subsequent cores as beryllium is added to maintain critically during the first 15 cycles. These calculations have been performed independently from those being performed by INP and serve as one step in the verification process.« less

Predicted performance of an integrated modular engine system

NASA Technical Reports Server (NTRS)

Binder, Michael; Felder, James L.

1993-01-01

Space vehicle propulsion systems are traditionally comprised of a cluster of discrete engines, each with its own set of turbopumps, valves, and a thrust chamber. The Integrated Modular Engine (IME) concept proposes a vehicle propulsion system comprised of multiple turbopumps, valves, and thrust chambers which are all interconnected. The IME concept has potential advantages in fault-tolerance, weight, and operational efficiency compared with the traditional clustered engine configuration. The purpose of this study is to examine the steady-state performance of an IME system with various components removed to simulate fault conditions. An IME configuration for a hydrogen/oxygen expander cycle propulsion system with four sets of turbopumps and eight thrust chambers has been modeled using the Rocket Engine Transient Simulator (ROCETS) program. The nominal steady-state performance is simulated, as well as turbopump thrust chamber and duct failures. The impact of component failures on system performance is discussed in the context of the system's fault tolerant capabilities.

State-plane trajectories used to observe and control the behavior of a voltage step-up dc-to-dc converter

NASA Technical Reports Server (NTRS)

Burns, W. W., III; Wilson, T. G.

1976-01-01

State-plane analysis techniques are employed to study the voltage step up energy storage dc-to-dc converter. Within this framework, an example converter operating under the influence of a constant on time and a constant frequency controller is examined. Qualitative insight gained through this approach is used to develop a conceptual free running control law for the voltage step up converter which can achieve steady state operation in one on/off cycle of control. Digital computer simulation data is presented to illustrate and verify the theoretical discussions presented.

Comments on Sudhakar Rao et al. on An experimental study of cyclic operation of a benzene hydrogenation reactor'

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silveston, P.L.; Hudgins, R.R.

Recently the author's attention was drawn to a note by Sudhakar Rao et al. that reports two cyclic experiments and a steady-state one and concludes that periodically turning off and on the flow of either hydrogen or benzene results in an increase in benzene conversion to cyclohexane. Although there is now a large literature documenting the possibility of conversion improvements, the data presented by the authors do not establish their claim. The authors show conversion and particle temperature measurements at what would appear to be the composition switching times. These data points are plotted against the number of completed cycles.more » Even though only data points taken after 5 to 8 cycles are shown, both conversion and particle temperatures vary irregularly. Three possible explanations come to mind for these irregular variations: sampling of the gas stream and the accompanying temperature measurement were not done at precisely the same time in each cycle, or the cycling system had not attained a stationary cycling state in which the variation of conversion and temperature within a cycle become constant and therefore reproducible, or the catalytic system is chaotic.« less

Glutamatergic and GABAergic neurotransmitter cycling and energy metabolism in rat cerebral cortex during postnatal development.

PubMed

Chowdhury, Golam M I; Patel, Anant B; Mason, Graeme F; Rothman, Douglas L; Behar, Kevin L

2007-12-01

The contribution of glutamatergic and gamma-aminobutyric acid (GABA)ergic neurons to oxidative energy metabolism and neurotransmission in the developing brain is not known. Glutamatergic and GABAergic fluxes were assessed in neocortex of postnatal day 10 (P10) and 30 (P30) urethane-anesthetized rats infused intravenously with [1,6-(13)C(2)]glucose for different time intervals (time course) or with [2-(13)C]acetate for 2 to 3 h (steady state). Amino acid levels and (13)C enrichments were determined in tissue extracts ex vivo using (1)H-[(13)C]-NMR spectroscopy. Metabolic fluxes were estimated from the best fits of a three-compartment metabolic model (glutamatergic neurons, GABAergic neurons, and astroglia) to the (13)C-enrichment time courses of amino acids from [1,6-(13)C(2)]glucose, constrained by the ratios of neurotransmitter cycling (V(cyc))-to-tricarboxylic acid (TCA) cycle flux (V(TCAn)) calculated from the steady-state [2-(13)C]acetate enrichment data. From P10 to P30 increases in total neuronal (glutamate plus GABA) TCA cycle flux (3 x ; 0.24+/-0.05 versus 0.71+/-0.07 micromol per g per min, P<0.0001) and total neurotransmitter cycling flux (3.1 to 5 x ; 0.07 to 0.11 (+/-0.03) versus 0.34+/-0.03 micromol per g per min, P<0.0001) were approximately proportional. Incremental changes in total cycling (DeltaV(cyc(tot))) and neuronal TCA cycle flux (DeltaV(TCAn(tot))) between P10 and P30 were 0.23 to 0.27 and 0.47 micromol per g per min, respectively, similar to the approximately 1:2 relationship previously reported for adult cortex. For the individual neurons, increases in V(TCAn) and V(cyc) were similar in magnitude (glutamatergic neurons, 2.7 x versus 2.8 to 4.6 x ; GABAergic neurons, approximately 5 x versus approximately 7 x), although GABAergic flux changes were larger. The findings show that glutamate and GABA neurons undergo large and approximately proportional increases in neurotransmitter cycling and oxidative energy metabolism during this major postnatal growth spurt.

Stable Density and Dynamics of Dendritic Spines of Cortical Neurons Across the Estrous Cycle While Expressing Differential Levels of Sensory-Evoked Plasticity.

PubMed

Alexander, Bailin H; Barnes, Heather M; Trimmer, Emma; Davidson, Andrew M; Ogola, Benard O; Lindsey, Sarah H; Mostany, Ricardo

2018-01-01

Periodic oscillations of gonadal hormone levels during the estrous cycle exert effects on the female brain, impacting cognition and behavior. While previous research suggests that changes in hormone levels across the cycle affect dendritic spine dynamics in the hippocampus, little is known about the effects on cortical dendritic spines and previous studies showed contradictory results. In this in vivo imaging study, we investigated the impact of the estrous cycle on the density and dynamics of dendritic spines of pyramidal neurons in the primary somatosensory cortex of mice. We also examined if the induction of synaptic plasticity during proestrus, estrus, and metestrus/diestrus had differential effects on the degree of remodeling of synapses in this brain area. We used chronic two-photon excitation (2PE) microscopy during steady-state conditions and after evoking synaptic plasticity by whisker stimulation at the different stages of the cycle. We imaged apical dendritic tufts of layer 5 pyramidal neurons of naturally cycling virgin young female mice. Spine density, turnover rate (TOR), survival fraction, morphology, and volume of mushroom spines remained unaltered across the estrous cycle, and the values of these parameters were comparable with those of young male mice. However, while whisker stimulation of female mice during proestrus and estrus resulted in increases in the TOR of spines (74.2 ± 14.9% and 75.1 ± 12.7% vs. baseline, respectively), sensory-evoked plasticity was significantly lower during metestrus/diestrus (32.3 ± 12.8%). In males, whisker stimulation produced 46.5 ± 20% increase in TOR compared with baseline-not significantly different from female mice at any stage of the cycle. These results indicate that, while steady-state density and dynamics of dendritic spines of layer 5 pyramidal neurons in the primary somatosensory cortex of female mice are constant during the estrous cycle, the susceptibility of these neurons to sensory-evoked structural plasticity may be dependent on the stage of the cycle. Since dendritic spines are more plastic during proestrus and estrus than during metestrus/diestrus, certain stages of the cycle could be more suitable for forms of memory requiring de novo formation and elimination of spines and other stages for forms of memory where retention and/or repurposing of already existing synaptic connections is more pertinent.

Stable Density and Dynamics of Dendritic Spines of Cortical Neurons Across the Estrous Cycle While Expressing Differential Levels of Sensory-Evoked Plasticity

PubMed Central

Alexander, Bailin H.; Barnes, Heather M.; Trimmer, Emma; Davidson, Andrew M.; Ogola, Benard O.; Lindsey, Sarah H.; Mostany, Ricardo

2018-01-01

Periodic oscillations of gonadal hormone levels during the estrous cycle exert effects on the female brain, impacting cognition and behavior. While previous research suggests that changes in hormone levels across the cycle affect dendritic spine dynamics in the hippocampus, little is known about the effects on cortical dendritic spines and previous studies showed contradictory results. In this in vivo imaging study, we investigated the impact of the estrous cycle on the density and dynamics of dendritic spines of pyramidal neurons in the primary somatosensory cortex of mice. We also examined if the induction of synaptic plasticity during proestrus, estrus, and metestrus/diestrus had differential effects on the degree of remodeling of synapses in this brain area. We used chronic two-photon excitation (2PE) microscopy during steady-state conditions and after evoking synaptic plasticity by whisker stimulation at the different stages of the cycle. We imaged apical dendritic tufts of layer 5 pyramidal neurons of naturally cycling virgin young female mice. Spine density, turnover rate (TOR), survival fraction, morphology, and volume of mushroom spines remained unaltered across the estrous cycle, and the values of these parameters were comparable with those of young male mice. However, while whisker stimulation of female mice during proestrus and estrus resulted in increases in the TOR of spines (74.2 ± 14.9% and 75.1 ± 12.7% vs. baseline, respectively), sensory-evoked plasticity was significantly lower during metestrus/diestrus (32.3 ± 12.8%). In males, whisker stimulation produced 46.5 ± 20% increase in TOR compared with baseline—not significantly different from female mice at any stage of the cycle. These results indicate that, while steady-state density and dynamics of dendritic spines of layer 5 pyramidal neurons in the primary somatosensory cortex of female mice are constant during the estrous cycle, the susceptibility of these neurons to sensory-evoked structural plasticity may be dependent on the stage of the cycle. Since dendritic spines are more plastic during proestrus and estrus than during metestrus/diestrus, certain stages of the cycle could be more suitable for forms of memory requiring de novo formation and elimination of spines and other stages for forms of memory where retention and/or repurposing of already existing synaptic connections is more pertinent. PMID:29615867

Exhaustive identification of steady state cycles in large stoichiometric networks

PubMed Central

Wright, Jeremiah; Wagner, Andreas

2008-01-01

Background Identifying cyclic pathways in chemical reaction networks is important, because such cycles may indicate in silico violation of energy conservation, or the existence of feedback in vivo. Unfortunately, our ability to identify cycles in stoichiometric networks, such as signal transduction and genome-scale metabolic networks, has been hampered by the computational complexity of the methods currently used. Results We describe a new algorithm for the identification of cycles in stoichiometric networks, and we compare its performance to two others by exhaustively identifying the cycles contained in the genome-scale metabolic networks of H. pylori, M. barkeri, E. coli, and S. cerevisiae. Our algorithm can substantially decrease both the execution time and maximum memory usage in comparison to the two previous algorithms. Conclusion The algorithm we describe improves our ability to study large, real-world, biochemical reaction networks, although additional methodological improvements are desirable. PMID:18616835

Steady and unsteady blade stresses within the SSME ATD/HPOTP inducer

NASA Technical Reports Server (NTRS)

Gross, R. Steven

1994-01-01

There were two main goals of the ATD HPOTP (alternate turbopump development)(high pressure oxygen turbopump). First, determine the steady and unsteady inducer blade surface strains produced by hydrodynamic sources as a function of flow capacity (Q/N), suction specific speed (Nss), and Reynolds number (Re). Second, to identify the hydrodynamic source(s) of the unsteady blade strains. The reason the aforementioned goals are expressed in terms of blade strains as opposed to blade hydrodynamic pressures is because of the interest regarding the high cycle life of the inducer blades. This report focuses on the first goal of the test program which involves the determination of the steady and unsteady strain (stress) values at various points within the inducer blades. Strain gages were selected as the strain measuring devices. Concurrent with the experimental program, an analytical study was undertaken to produce a complete NASTRAN finite-element model of the inducer. Computational fluid dynamics analyses were utilized to provide the estimated steady-state blade surface pressure loading needed as load input to the NASTRAN inducer model.

Clotting Factor Changes during the First Cycle of Oral Contraceptive Use

PubMed Central

Westhoff, Carolyn L.; Eisenberger, Andrew; Tang, Rosalind; Cremers, Serge; Grossman, Lisa V.; Pike, Malcolm C.

2016-01-01

Objectives The risk of venous thromboembolism (VTE) is highest during the initial months of oral contraceptive (OC) use. We sought to evaluate the extent of hemostatic variable changes during the initial OC cycle and if such changes are related to systemic ethinyl estradiol (EE2) exposure. Study Design Participants provided multiple blood samples during a 21-day OC cycle (30 mcg EE2; 150 mcg levonorgestrel) and after a single dose following a wash-out period. Analytes included D-dimer, factor VIII activity, protein C total antigen and the hepatic proteins corticosteroid- and sex-hormone-binding globulins (CBG and SHBG). EE2 pharmacokinetic analyses related to the 24 hours after the first OC tablet (OC1) and at steady state (OC21). Results Seventeen women completed the study. D-dimer more than doubled by OC6 (p = 0.013) and remained elevated at OC21 (p=0.012). D-dimer levels within women varied widely from day-to-day. Factor VIII increased 27% by OC2 (p < 0.001), but declined to a 9% increase by OC21. Protein C increased only 6%. EE2 steady-state area-under-the-curve ranged from 488 to 1103 pg·h/mL; higher levels were not correlated with greater increases in clotting variables. CBG and SHBG increased significantly, but were not significantly correlated with levels of EE2 or with the hemostatic variables. Conclusions D-dimer increases during the first OC cycle were at least as great as increases seen with longer OC use. These results provide support for the increased VTE risk during initial OC use. The extreme variability in D-dimer levels may be an important component of this risk. PMID:26452328

Proposed law of nature linking impacts, plume volcanism, and Milankovitch cycles to terrestrial vertebrate mass extinctions via greenhouse-embryo death coupling

NASA Technical Reports Server (NTRS)

Mclean, D. M.

1994-01-01

A greenhouse-physiological coupling killing mechanism active among mammals, birds, and reptiles has been identified. Operating via environmental thermal effects upon the maternal core-skin blood flow critical to the survival and development of embryos, it reduces the flow of blood to the uterine tract. Today, during hot summers, this phenomena kills embryos on a vast, global scale. Because of sensitivity of many mammals to modern heat, a major modern greenhouse could reduce population numbers on a global scale, and potentially trigger population collapses in the more vulnerable parts of the world. In the geological past, the killing mechanism has likely been triggered into action by greenhouse warming via impact events, plume volcanism, and Earth orbital variations (Milankovitch cycles). Earth's biosphere is maintained and molded by the flow of energy from the solar energy source to Earth and on to the space energy sink (SES). This SES energy flow maintains Earth's biosphere and its living components, as open, intermediate, dissipative, nonequilibrium systems whose states are dependent upon the rate of energy flowing through them. Greenhouse gases such as CO2 in the atmosphere influence the SES energy flow rate. Steady-state flow is necessary for global ecological stability (autopoiesis). Natural fluctuations of the C cycle such as rapid releases of CO2 from the mantle, or oceans, disrupt steady-state SES flow. These fluctuations constantly challenge the biosphere; slowdown of SES energy flow drives it toward thermodynamical equilibrium and stagnation. Fluctuations induced by impact event, mantle plume volcanism, and Milankovitch cycles can grow into structure-breaking waves triggering major perturbations of Earth's C cycle and mass extinctions. A major C cycle perturbation involves readjustment of the outer physiochemical spheres of the Earth: the atmosphere, hydrosphere, and lithosphere; and by necessity, the biosphere. A greenhouse, one manifestation of a major C cycle perturbation, is the most dangerous natural phenomenon that life on Earth can experience. Greenhouse conditions existed during the KT mass extinctions of 65 m.y. ago, and the Pleistocene-Holocene (P-H) mammalian extinctions of 10,000-12,000 yr ago. Coupling climatology to reproductive physiology via effects of ambient air temperature upon uterine blood flow to developing embryos accounts for the extinctions via established physiological principles.

Steady state estimation of soil organic carbon using satellite-derived canopy leaf area index

DOE PAGES

Fang, Yilin; Liu, Chongxuan; Huang, Maoyi; ...

2014-12-02

Soil organic carbon (SOC) plays a key role in the global carbon cycle that is important for decadal-to-century climate prediction. Estimation of soil organic carbon stock using model-based methods typically requires spin-up (time marching transient simulation) of the carbon-nitrogen (CN) models by performing hundreds to thousands years long simulations until the carbon-nitrogen pools reach dynamic steady-state. This has become a bottleneck for global modeling and analysis, especially when testing new physical and/or chemical mechanisms and evaluating parameter sensitivity. Here we report a new numerical approach to estimate global soil carbon stock that can avoid the long term spin-up of themore » CN model. The approach uses canopy leaf area index (LAI) from satellite data and takes advantage of a reaction-based biogeochemical module NGBGC (Next Generation BioGeoChemical Module) that was recently developed and incorporated in version 4 of the Community Land Model (CLM4). Although NGBGC uses the same CN mechanisms as used in CLM4CN, it can be easily configured to run prognostic or steady state simulations. In this approach, monthly LAI from the multi-year Moderate Resolution Imaging Spectroradiometer (MODIS) data was used to calculate potential annual average gross primary production (GPP) and leaf carbon for the period of the atmospheric forcing. The calculated potential annual average GPP and leaf C are then used by NGBGC to calculate the steady-state distributions of carbon and nitrogen in different vegetation and soil pools by solving the steady-state reaction-network in NGBGC using the Newton-Raphson method. The new approach was applied at point and global scales and compared with SOC derived from long spin-up by running NGBGC in prognostic mode, and SOC from the empirical data of the Harmonized World Soil Database (HWSD). The steady-state solution is comparable to the spin-up value when the MODIS LAI is close to the LAI from the spin-up solution, and largely captured the variability of the HWSD SOC across the different dominant plant functional types (PFTs) at global scale. The numerical correlation between the calculated and HWSD SOC was, however, weak at both point and global scales, suggesting that the models used in describing biogeochemical processes in CLM needs improvements and/or HWSD needs updating as suggested by other studies. Besides SOC, the steady state solution also includes all other state variables simulated by a spin-up run, such as NPP, GPP, total vegetation C etc., which makes the developed approach a promising tool to efficiently estimate global SOC distribution and evaluate and compare different aspects simulated by different CN mechanisms in the model.« less

Performance analysis and dynamic modeling of a single-spool turbojet engine

NASA Astrophysics Data System (ADS)

Andrei, Irina-Carmen; Toader, Adrian; Stroe, Gabriela; Frunzulica, Florin

2017-01-01

The purposes of modeling and simulation of a turbojet engine are the steady state analysis and transient analysis. From the steady state analysis, which consists in the investigation of the operating, equilibrium regimes and it is based on appropriate modeling describing the operation of a turbojet engine at design and off-design regimes, results the performance analysis, concluded by the engine's operational maps (i.e. the altitude map, velocity map and speed map) and the engine's universal map. The mathematical model that allows the calculation of the design and off-design performances, in case of a single spool turbojet is detailed. An in house code was developed, its calibration was done for the J85 turbojet engine as the test case. The dynamic modeling of the turbojet engine is obtained from the energy balance equations for compressor, combustor and turbine, as the engine's main parts. The transient analysis, which is based on appropriate modeling of engine and its main parts, expresses the dynamic behavior of the turbojet engine, and further, provides details regarding the engine's control. The aim of the dynamic analysis is to determine a control program for the turbojet, based on the results provided by performance analysis. In case of the single-spool turbojet engine, with fixed nozzle geometry, the thrust is controlled by one parameter, which is the fuel flow rate. The design and management of the aircraft engine controls are based on the results of the transient analysis. The construction of the design model is complex, since it is based on both steady-state and transient analysis, further allowing the flight path cycle analysis and optimizations. This paper presents numerical simulations for a single-spool turbojet engine (J85 as test case), with appropriate modeling for steady-state and dynamic analysis.

Mimicking Nonequilibrium Steady States with Time-Periodic Driving

DTIC Science & Technology

2016-08-29

nonequilibrium steady states, and vice versa, within the theoretical framework of discrete-state stochastic thermodynamics . Nonequilibrium steady states...equilibrium [2], spontaneous relaxation towards equilibrium [3], nonequilibrium steady states generated by fixed thermodynamic forces [4], and stochastic pumps...paradigm, a system driven by fixed thermodynamic forces—such as temperature gradients or chemical potential differences— reaches a steady state in

Updates on Modeling the Water Cycle with the NASA Ames Mars Global Climate Model

NASA Technical Reports Server (NTRS)

Kahre, M. A.; Haberle, R. M.; Hollingsworth, J. L.; Montmessin, F.; Brecht, A. S.; Urata, R.; Klassen, D. R.; Wolff, M. J.

2017-01-01

Global Circulation Models (GCMs) have made steady progress in simulating the current Mars water cycle. It is now widely recognized that clouds are a critical component that can significantly affect the nature of the simulated water cycle. Two processes in particular are key to implementing clouds in a GCM: the microphysical processes of formation and dissipation, and their radiative effects on heating/ cooling rates. Together, these processes alter the thermal structure, change the dynamics, and regulate inter-hemispheric transport. We have made considerable progress representing these processes in the NASA Ames GCM, particularly in the presence of radiatively active water ice clouds. We present the current state of our group's water cycle modeling efforts, show results from selected simulations, highlight some of the issues, and discuss avenues for further investigation.­

Issues in the digital implementation of control compensators. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Moroney, P.

1979-01-01

Techniques developed for the finite-precision implementation of digital filters were used, adapted, and extended for digital feedback compensators, with particular emphasis on steady state, linear-quadratic-Gaussian compensators. Topics covered include: (1) the linear-quadratic-Gaussian problem; (2) compensator structures; (3) architectural issues: serialism, parallelism, and pipelining; (4) finite wordlength effects: quantization noise, quantizing the coefficients, and limit cycles; and (5) the optimization of structures.

Research on transient thermal process of a friction brake during repetitive cycles of operation

NASA Astrophysics Data System (ADS)

Slavchev, Yanko; Dimitrov, Lubomir; Dimitrov, Yavor

2017-12-01

Simplified models are used in the classical engineering analyses of the friction brake heating temperature during repetitive cycles of operation to determine basically the maximum and minimum brake temperatures. The objective of the present work is to broaden and complement the possibilities for research through a model that is based on the classical scheme of the Newton's law of cooling and improves the studies by adding a disturbance function for a corresponding braking process. A general case of braking in non-periodic repetitive mode is considered, for which a piecewise function is defined to apply pulse thermal loads to the system. Cases with rectangular and triangular waveforms are presented. Periodic repetitive braking process is also studied using a periodic rectangular waveform until a steady thermal state is achieved. Different numerical methods such as the Euler's method, the classical fourth order Runge-Kutta (RK4) and the Runge-Kutta-Fehlberg 4-5 (RKF45) are used to solve the non-linear differential equation of the model. The constructed model allows during pre-engineering calculations to be determined effectively the time for reaching the steady thermal state of the brake, to be simulated actual braking modes in vehicles and material handling machines, and to be accounted for the thermal impact when performing fatigue calculations.

Volatile properties of particles emitted by compressed natural gas and diesel buses during steady-state and transient driving modes.

PubMed

Jayaratne, E R; Meyer, N K; Ristovski, Z D; Morawska, L

2012-01-03

Volatile properties of particle emissions from four compressed natural gas (CNG) and four diesel buses were investigated under steady-state and transient driving modes on a chassis dynamometer. The exhaust was diluted utilizing a full-flow continuous volume sampling system and passed through a thermodenuder at controlled temperature. Particle number concentration and size distribution were measured with a condensation particle counter and a scanning mobility particle sizer, respectively. We show that while almost all the particles emitted by the CNG buses were in the nanoparticle size range, at least 85% and 98% were removed at 100 and 250 °C, respectively. Closer analysis of the volatility of particles emitted during transient cycles showed that volatilization began at around 40 °C, with the majority occurring by 80 °C. Particles produced during hard acceleration from rest exhibited lower volatility than those produced during other times of the cycle. On the basis of our results and the observation of ash deposits on the walls of the tailpipes, we suggest that these nonvolatile particles were composed mostly of ash from lubricating oil. Heating the diesel bus emissions to 100 °C removed ultrafine particle numbers by 69-82% when a nucleation mode was present and just 18% when it was not.

Preventive and Abortive Strategies for Stimulation Based Control of Epilepsy: A Computational Model Study.

PubMed

Koppert, Marc; Kalitzin, Stiliyan; Velis, Demetrios; Lopes Da Silva, Fernando; Viergever, Max A

2016-12-01

Epilepsy is a condition in which periods of ongoing normal EEG activity alternate with periods of oscillatory behavior characteristic of epileptic seizures. The dynamics of the transitions between the two states are still unclear. Computational models provide a powerful tool to explore the underlying mechanisms of such transitions, with the purpose of eventually finding therapeutic interventions for this debilitating condition. In this study, the possibility to postpone seizures elicited by a decrease of inhibition is investigated by using external stimulation in a realistic bistable neuronal model consisting of two interconnected neuronal populations representing pyramidal cells and interneurons. In the simulations, seizures are induced by slowly decreasing the conductivity of GABA[Formula: see text] synaptic channels over time. Since the model is bistable, the system will change state from the initial steady state (SS) to the limit cycle (LS) state because of internal noise, when the inhibition falls below a certain threshold. Several state-independent stimulations paradigms are simulated. Their effectiveness is analyzed for various stimulation frequencies and intensities in combination with periodic and random stimulation sequences. The distributions of the time to first seizure in the presence of stimulation are compared with the situation without stimulation. In addition, stimulation protocols targeted to specific subsystems are applied with the objective of counteracting the baseline shift due to decreased inhibition in the system. Furthermore, an analytical model is used to investigate the effects of random noise. The relation between the strength of random noise stimulation, the control parameter of the system and the transitions between steady state and limit cycle are investigated. The study shows that it is possible to postpone epileptic activity by targeted stimulation in a realistic neuronal model featuring bistability and that it is possible to stop seizures by random noise in an analytical model.

Mimicking Nonequilibrium Steady States with Time-Periodic Driving (Open Source)

DTIC Science & Technology

2016-05-18

nonequilibrium steady states, and vice versa, within the theoretical framework of discrete-state stochastic thermodynamics . Nonequilibrium steady states...equilibrium [2], spontaneous relaxation towards equilibrium [3], nonequilibrium steady states generated by fixed thermodynamic forces [4], and stochastic pumps...paradigm, a system driven by fixed thermodynamic forces—such as temperature gradients or chemical potential differences— reaches a steady state in

An intermittency route to global instability in low-density jets

NASA Astrophysics Data System (ADS)

Murugesan, Meenatchidevi; Zhu, Yuanhang; Li, Larry K. B.

2017-11-01

Above a critical Reynolds number (Re), a low-density jet can become globally unstable, transitioning from a steady state (i.e. a fixed point) to a self-excited oscillatory state (i.e. a limit cycle) via a Hopf bifurcation. In this experimental study, we show that this transition can sometimes involve intermittency. When Re is just slightly above the critical point, intermittent bursts of high-amplitude periodic oscillations emerge amidst a background of low-amplitude aperiodic fluctuations. As Re increases further, these intermittent bursts persist longer in time until they dominate the overall dynamics, causing the jet to transition fully to a periodic limit cycle. We identify this as Type-II Pomeau-Manneville intermittency by quantifying the statistical distribution of the duration of the aperiodic fluctuations at the onset of intermittency. This study shows that the transition to global instability in low-density jets is not always abrupt but can involve an intermediate state with characteristics of both the initial fixed point and the final limit cycle. This work was supported by the Research Grants Council of Hong Kong (Project No. 16235716 and 26202815).

An extensive program of periodic alternative splicing linked to cell cycle progression

PubMed Central

Dominguez, Daniel; Tsai, Yi-Hsuan; Weatheritt, Robert; Wang, Yang; Blencowe, Benjamin J; Wang, Zefeng

2016-01-01

Progression through the mitotic cell cycle requires periodic regulation of gene function at the levels of transcription, translation, protein-protein interactions, post-translational modification and degradation. However, the role of alternative splicing (AS) in the temporal control of cell cycle is not well understood. By sequencing the human transcriptome through two continuous cell cycles, we identify ~1300 genes with cell cycle-dependent AS changes. These genes are significantly enriched in functions linked to cell cycle control, yet they do not significantly overlap genes subject to periodic changes in steady-state transcript levels. Many of the periodically spliced genes are controlled by the SR protein kinase CLK1, whose level undergoes cell cycle-dependent fluctuations via an auto-inhibitory circuit. Disruption of CLK1 causes pleiotropic cell cycle defects and loss of proliferation, whereas CLK1 over-expression is associated with various cancers. These results thus reveal a large program of CLK1-regulated periodic AS intimately associated with cell cycle control. DOI: http://dx.doi.org/10.7554/eLife.10288.001 PMID:27015110

Numerical System Solver Developed for the National Cycle Program

NASA Technical Reports Server (NTRS)

Binder, Michael P.

1999-01-01

As part of the National Cycle Program (NCP), a powerful new numerical solver has been developed to support the simulation of aeropropulsion systems. This software uses a hierarchical object-oriented design. It can provide steady-state and time-dependent solutions to nonlinear and even discontinuous problems typically encountered when aircraft and spacecraft propulsion systems are simulated. It also can handle constrained solutions, in which one or more factors may limit the behavior of the engine system. Timedependent simulation capabilities include adaptive time-stepping and synchronization with digital control elements. The NCP solver is playing an important role in making the NCP a flexible, powerful, and reliable simulation package.

Evolution of probability densities in stochastic coupled map lattices

NASA Astrophysics Data System (ADS)

Losson, Jérôme; Mackey, Michael C.

1995-08-01

This paper describes the statistical properties of coupled map lattices subjected to the influence of stochastic perturbations. The stochastic analog of the Perron-Frobenius operator is derived for various types of noise. When the local dynamics satisfy rather mild conditions, this equation is shown to possess either stable, steady state solutions (i.e., a stable invariant density) or density limit cycles. Convergence of the phase space densities to these limit cycle solutions explains the nonstationary behavior of statistical quantifiers at equilibrium. Numerical experiments performed on various lattices of tent, logistic, and shift maps with diffusivelike interelement couplings are examined in light of these theoretical results.

Wave Fluid Film Bearing Tests for an Aviation Gearbox

NASA Technical Reports Server (NTRS)

Dimofte, Florin; Proctor, Margaret P.; Fleming, David P.; Keith, Theo G., Jr.

2000-01-01

An oil-lubricated wave journal-thrust bearing assembly was successfully tested at conditions found in general aviation engine gearboxes. The bearing performed well at both steady state conditions and in start-stop tests. It ran stably under all loading conditions, including zero load, at all speeds up to 16 000 rpm. The bearing carried 25 percent more load than required for the gearbox application, supporting 8900 N (94 bars average pressure), and showed very good thermal stability. 450 start-stop cycles were also performed, including 350 cycles without oil supply during starting and stopping. Test results and numerical predictions were in good agreement.

Blazar Duty-Cycle at Gamma-Ray Frequecies: Constraints From Extragalactic Background Radiation And Prospects for AGILE And GLAST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pittori, Carlotta; Cavazzuti, Elisabetta; Colafrancesco, Sergio

2011-11-29

We take into account the constraints from the observed extragalactic {gamma}-ray background to estimate the maximum duty cycle allowed for a selected sample of WMAP Blazars, in order to be detectable by AGILE and GLAST {gamma}-ray experiments. For the nominal sensitivity values of both instruments, we identify a subset of sources which can in principle be detectable also in a steady state without over-predicting the extragalactic background. This work is based on the results of a recently derived Blazar radio LogN-LogS obtained by combining several multi-frequency surveys.

Rainfall limit of the N cycle on Earth

USGS Publications Warehouse

Ewing, S.A.; Michalski, G.; Thiemens, M.; Quinn, R.C.; Macalady, J.L.; Kohl, S.; Wankel, Scott D.; Kendall, C.; McKay, C.P.; Amundson, Ronald

2007-01-01

In most climates on Earth, biological processes control soil N. In the Atacama Desert of Chile, aridity severely limits biology, and soils accumulate atmospheric NO3-. We examined this apparent transformation of the soil N cycle using a series of ancient Atacama Desert soils (>2 My) that vary in rainfall (21 to <2 mm yr-1). With decreasing rainfall, soil organic C decreases to 0.3 kg C m-2 and biological activity becomes minimal, while soil NO3- and organic N increase to 4 kg N m-2 and 1.4 kg N m-2, respectively. Atmospheric NO3- (??17O = 23.0???) increases from 39% to 80% of total soil NO3- as rainfall decreases. These soils capture the transition from a steady state, biologically mediated soil N cycle to a dominantly abiotic, transient state of slowly accumulating atmospheric N. This transition suggests that oxidized soil N may be present in an even more and and abiotic environment: Mars. Copyright 2007 by the American Geophysical Union.

L1 adaptive control of uncertain gear transmission servo systems with deadzone nonlinearity.

PubMed

Zuo, Zongyu; Li, Xiao; Shi, Zhiguang

2015-09-01

This paper deals with the adaptive control problem of Gear Transmission Servo (GTS) systems in the presence of unknown deadzone nonlinearity and viscous friction. A global differential homeomorphism based on a novel differentiable deadzone model is proposed first. Since there exist both matched and unmatched state-dependent unknown nonlinearities, a full-state feedback L1 adaptive controller is constructed to achieve uniformly bounded transient response in addition to steady-state performance. Finally, simulation results are included to show the elimination of limit cycles, in addition to demonstrating the main results in this paper. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Pseudo Steady-State Free Precession for MR-Fingerprinting.

PubMed

Assländer, Jakob; Glaser, Steffen J; Hennig, Jürgen

2017-03-01

This article discusses the signal behavior in the case the flip angle in steady-state free precession sequences is continuously varied as suggested for MR-fingerprinting sequences. Flip angle variations prevent the establishment of a steady state and introduce instabilities regarding to magnetic field inhomogeneities and intravoxel dephasing. We show how a pseudo steady state can be achieved, which restores the spin echo nature of steady-state free precession. Based on geometrical considerations, relationships between the flip angle, repetition and echo time are derived that suffice to the establishment of a pseudo steady state. The theory is tested with Bloch simulations as well as phantom and in vivo experiments. A typical steady-state free precession passband can be restored with the proposed conditions. The stability of the pseudo steady state is demonstrated by comparing the evolution of the signal of a single isochromat to one resulting from a spin ensemble. As confirmed by experiments, magnetization in a pseudo steady state can be described with fewer degrees of freedom compared to the original fingerprinting and the pseudo steady state results in more reliable parameter maps. The proposed conditions restore the spin-echo-like signal behavior typical for steady-state free precession in fingerprinting sequences, making this approach more robust to B 0 variations. Magn Reson Med 77:1151-1161, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Mechanism for multiplicity of steady states with distinct cell concentration in continuous culture of mammalian cells.

PubMed

Yongky, Andrew; Lee, Jongchan; Le, Tung; Mulukutla, Bhanu Chandra; Daoutidis, Prodromos; Hu, Wei-Shou

2015-07-01

Continuous culture for the production of biopharmaceutical proteins offers the possibility of steady state operations and thus more consistent product quality and increased productivity. Under some conditions, multiplicity of steady states has been observed in continuous cultures of mammalian cells, wherein with the same dilution rate and feed nutrient composition, steady states with very different cell and product concentrations may be reached. At those different steady states, cells may exhibit a high glycolysis flux with high lactate production and low cell concentration, or a low glycolysis flux with low lactate and high cell concentration. These different steady states, with different cell concentration, also have different productivity. Developing a mechanistic understanding of the occurrence of steady state multiplicity and devising a strategy to steer the culture toward the desired steady state is critical. We establish a multi-scale kinetic model that integrates a mechanistic intracellular metabolic model and cell growth model in a continuous bioreactor. We show that steady state multiplicity exists in a range of dilution rate in continuous culture as a result of the bistable behavior in glycolysis. The insights from the model were used to devise strategies to guide the culture to the desired steady state in the multiple steady state region. The model provides a guideline principle in the design of continuous culture processes of mammalian cells. © 2015 Wiley Periodicals, Inc.

Synthesizing Virtual Oscillators to Control Islanded Inverters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Brian B.; Sinha, Mohit; Ainsworth, Nathan G.

Virtual oscillator control (VOC) is a decentralized control strategy for islanded microgrids where inverters are regulated to emulate the dynamics of weakly nonlinear oscillators. Compared to droop control, which is only well defined in sinusoidal steady state, VOC is a time-domain controller that enables interconnected inverters to stabilize arbitrary initial conditions to a synchronized sinusoidal limit cycle. However, the nonlinear oscillators that are elemental to VOC cannot be designed with conventional linear-control design methods. We address this challenge by applying averaging- and perturbation-based nonlinear analysis methods to extract the sinusoidal steady-state and harmonic behavior of such oscillators. The averaged modelsmore » reveal conclusive links between real- and reactive-power outputs and the terminal-voltage dynamics. Similarly, the perturbation methods aid in quantifying higher order harmonics. The resultant models are then leveraged to formulate a design procedure for VOC such that the inverter satisfies standard ac performance specifications related to voltage regulation, frequency regulation, dynamic response, and harmonic content. Experimental results for a single-phase 750 VA, 120 V laboratory prototype demonstrate the validity of the design approach. They also demonstrate that droop laws are, in fact, embedded within the equilibria of the nonlinear-oscillator dynamics. This establishes the backward compatibility of VOC in that, while acting on time-domain waveforms, it subsumes droop control in sinusoidal steady state.« less

Measurement of cerebral oxidative glucose consumption in patients with type 1 diabetes and hypoglycemia unawareness using 13C nuclear magnetic resonance spectroscopy

PubMed Central

Henry, Pierre-Gilles; Criego, Amy B.; Kumar, Anjali; Seaquist, Elizabeth R.

2009-01-01

The aim of the present study was to use 13C NMR to measure the cerebral oxidative metabolic rate of glucose (CMRglc(ox)) in patients with diabetes and to compare these measurements with those collected from matched controls. We elected to study a group with type 1 diabetes and hypoglycemia unawareness, since we had previously found such patients to have higher brain glucose concentrations than normal volunteers under steady state conditions. We sought to determine if this difference in steady-state brain concentrations could be explained by a difference in CMRglc(ox). Time courses of 13C label incorporation in brain amino acids were measured in occipital cortex during infusion of [1-13C]glucose. These time courses were fitted using a one-compartment metabolic model to determine CMRglc(ox). Our results show that the TCA cycle rate (VTCA, which is twice CMRglc(ox)) in subjects with type 1 diabetes was not significantly different from normal controls (0.84 ± 0.03 vs 0.79 ± 0.03 μmol/gm/min, n=5 in each group, mean ± SEM). We conclude that the changes in steady-state brain glucose concentrations that we observed in patients with type 1 diabetes in a previous study (1) cannot be explained by changes in oxidative glucose consumption PMID:19766263

Water cycling between ocean and mantle: Super-earths need not be waterworlds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cowan, Nicolas B.; Abbot, Dorian S., E-mail: n-cowan@northwestern.edu

2014-01-20

Large terrestrial planets are expected to have muted topography and deep oceans, implying that most super-Earths should be entirely covered in water, so-called waterworlds. This is important because waterworlds lack a silicate weathering thermostat so their climate is predicted to be less stable than that of planets with exposed continents. In other words, the continuously habitable zone for waterworlds is much narrower than for Earth-like planets. A planet's water is partitioned, however, between a surface reservoir, the ocean, and an interior reservoir, the mantle. Plate tectonics transports water between these reservoirs on geological timescales. Degassing of melt at mid-ocean ridgesmore » and serpentinization of oceanic crust depend negatively and positively on seafloor pressure, respectively, providing a stabilizing feedback on long-term ocean volume. Motivated by Earth's approximately steady-state deep water cycle, we develop a two-box model of the hydrosphere and derive steady-state solutions to the water partitioning on terrestrial planets. Critically, hydrostatic seafloor pressure is proportional to surface gravity, so super-Earths with a deep water cycle will tend to store more water in the mantle. We conclude that a tectonically active terrestrial planet of any mass can maintain exposed continents if its water mass fraction is less than ∼0.2%, dramatically increasing the odds that super-Earths are habitable. The greatest source of uncertainty in our study is Earth's current mantle water inventory: the greater its value, the more robust planets are to inundation. Lastly, we discuss how future missions can test our hypothesis by mapping the oceans and continents of massive terrestrial planets.« less

Determination of Anaerobic Threshold by Heart Rate or Heart Rate Variability using Discontinuous Cycle Ergometry.

PubMed

Park, Sung Wook; Brenneman, Michael; Cooke, William H; Cordova, Alberto; Fogt, Donovan

The purpose was to determine if heart rate (HR) and heart rate variability (HRV) responses would reflect anaerobic threshold (AT) using a discontinuous, incremental, cycle test. AT was determined by ventilatory threshold (VT). Cyclists (30.6±5.9y; 7 males, 8 females) completed a discontinuous cycle test consisting of 7 stages (6 min each with 3 min of rest between). Three stages were performed at power outputs (W) below those corresponding to a previously established AT, one at W corresponding to AT, and 3 at W above those corresponding to AT. The W at the intersection of the trend lines was considered each metric's "threshold". The averaged stage data for Ve, HR, and time- and frequency-domain HRV metrics were plotted versus W. The W at the "threshold" for the metrics of interest were compared using correlation analysis and paired-sample t -test. In all, several heart rate-related parameters accurately reflected AT with significant correlations (p≤0.05) were observed between AT W and HR, mean RR interval (MRR), low and high frequency spectral energy (LF and HR, respectively), high frequency peak (fHF), and HFxfHF metrics' threshold W (i.e., MRRTW, etc.). Differences in HR or HRV metric threshold W and AT for all subjects were less than 14 W. The steady state data from discontinuous protocols may allow for a true indication of steady-state physiologic stress responses and corresponding W at AT, compared to continuous protocols using 1-2 min exercise stages.

V02 'overshoot' during moderate-intensity exercise in endurance-trained athletes: the influence of exercise modality.

PubMed

Kilding, Andrew E; Jones, Andrew M

2008-02-01

The purpose of this study was to investigate the influence of exercise modality on the 'overshoot' in V(O2) that has been reported following the onset of moderate-intensity (below the gas exchange threshold, GET) exercise in endurance athletes. Seven trained endurance cyclists and seven trained endurance runners completed six square-wave transitions to a work-rate or running speed requiring 80% of mode-specific GET during both cycle and treadmill running exercise. The kinetics of V(O2) was assessed using non-linear regression and any overshoot in V(O2) was quantified as the integrated volume (IV) of O(2) consumed above the steady-state requirement. During cycling, an overshoot in V(O2) was evident in all seven cyclists (IV = 136 +/- 41 ml) and in four runners (IV = 81 +/- 94 ml). During running, an overshoot in V(O2) was evident in four runners (IV = 72 +/- 61 ml) but no cyclists. These data challenge the notion that V(O2) always rises towards a steady-state with near-exponential kinetics in this exercise intensity domain. The greater incidence of the V(O2) overshoot during cycling (11/14 subjects) compared to running (4/14 subjects) indicates that the overshoot phenomenon is related to an interaction between high levels of aerobic fitness and exercise modality. We speculate that a transient loss in muscle efficiency as a consequence of a non-constant ATP requirement following the onset of constant-work-rate exercise or an initially excessive recruitment of motor units (relative to the work-rate) might contribute to the overshoot phenomenon.

Hygrothermal damage mechanisms in graphite-epoxy composites

NASA Technical Reports Server (NTRS)

Crossman, F. W.; Mauri, R. E.; Warren, W. J.

1979-01-01

T300/5209 and T300/5208 graphite epoxy laminates were studied experimentally and analytically in order to: (1) determine the coupling between applied stress, internal residual stress, and moisture sorption kinetics; (2) examine the microscopic damage mechanisms due to hygrothermal cycling; (3) evaluate the effect of absorbed moisture and hygrothermal cycling on inplane shear response; (4) determine the permanent loss of interfacial bond strength after moisture absorption and drying; and (5) evaluate the three dimensional stress state in laminates under a combination of hygroscopic, thermal, and mechanical loads. Specimens were conditioned to equilibrium moisture content under steady exposure to 55% or 95% RH at 70 C or 93 C. Some specimens were tested subsequent to moisture conditioning and 100 cycles between -54 C and either 70 C or 93 C.

Effects of fresh lubricant oils on particle emissions emitted by a modern gasoline direct injection passenger car.

PubMed

Pirjola, Liisa; Karjalainen, Panu; Heikkilä, Juha; Saari, Sampo; Tzamkiozis, Theodoros; Ntziachristos, Leonidas; Kulmala, Kari; Keskinen, Jorma; Rönkkö, Topi

2015-03-17

Particle emissions from a modern turbocharged gasoline direct injection passenger car equipped with a three-way catalyst and an exhaust gas recirculation system were studied while the vehicle was running on low-sulfur gasoline and, consecutively, with five different lubrication oils. Exhaust particle number concentration, size distribution, and volatility were determined both at laboratory and on-road conditions. The results indicated that the choice of lubricant affected particle emissions both during the cold start and warm driving cycles. However, the contribution of engine oil depended on driving conditions being higher during acceleration and steady state driving than during deceleration. The highest emission factors were found with two oils that had the highest metal content. The results indicate that a 10% decrease in the Zn content of engine oils is linked with an 11-13% decrease to the nonvolatile particle number emissions in steady driving conditions and a 5% decrease over the New European Driving Cycle. The effect of lubricant on volatile particles was even higher, on the order of 20%.

The decadal state of the terrestrial carbon cycle: Global retrievals of terrestrial carbon allocation, pools, and residence times

PubMed Central

Bloom, A. Anthony; Exbrayat, Jean-François; van der Velde, Ivar R.; Feng, Liang; Williams, Mathew

2016-01-01

The terrestrial carbon cycle is currently the least constrained component of the global carbon budget. Large uncertainties stem from a poor understanding of plant carbon allocation, stocks, residence times, and carbon use efficiency. Imposing observational constraints on the terrestrial carbon cycle and its processes is, therefore, necessary to better understand its current state and predict its future state. We combine a diagnostic ecosystem carbon model with satellite observations of leaf area and biomass (where and when available) and soil carbon data to retrieve the first global estimates, to our knowledge, of carbon cycle state and process variables at a 1° × 1° resolution; retrieved variables are independent from the plant functional type and steady-state paradigms. Our results reveal global emergent relationships in the spatial distribution of key carbon cycle states and processes. Live biomass and dead organic carbon residence times exhibit contrasting spatial features (r = 0.3). Allocation to structural carbon is highest in the wet tropics (85–88%) in contrast to higher latitudes (73–82%), where allocation shifts toward photosynthetic carbon. Carbon use efficiency is lowest (0.42–0.44) in the wet tropics. We find an emergent global correlation between retrievals of leaf mass per leaf area and leaf lifespan (r = 0.64–0.80) that matches independent trait studies. We show that conventional land cover types cannot adequately describe the spatial variability of key carbon states and processes (multiple correlation median = 0.41). This mismatch has strong implications for the prediction of terrestrial carbon dynamics, which are currently based on globally applied parameters linked to land cover or plant functional types. PMID:26787856

Subscale Test Methods for Combustion Devices

NASA Technical Reports Server (NTRS)

Anderson, W. E.; Sisco, J. C.; Long, M. R.; Sung, I.-K.

2005-01-01

Stated goals for long-life LRE s have been between 100 and 500 cycles: 1) Inherent technical difficulty of accurately defining the transient and steady state thermochemical environments and structural response (strain); 2) Limited statistical basis on failure mechanisms and effects of design and operational variability; and 3) Very high test costs and budget-driven need to protect test hardware (aversion to test-to-failure). Ambitious goals will require development of new databases: a) Advanced materials, e.g., tailored composites with virtually unlimited property variations; b) Innovative functional designs to exploit full capabilities of advanced materials; and c) Different cycles/operations. Subscale testing is one way to address technical and budget challenges: 1) Prototype subscale combustors exposed to controlled simulated conditions; 2) Complementary to conventional laboratory specimen database development; 3) Instrumented with sensors to measure thermostructural response; and 4) Coupled with analysis

Thermal Modelling Analysis of Spiral Wound Supercapacitor under Constant-Current Cycling

PubMed Central

Wang, Kai; Li, Liwei; Yin, Huaixian; Zhang, Tiezhu; Wan, Wubo

2015-01-01

A three-dimensional modelling approach is used to study the effects of operating and ambient conditions on the thermal behaviour of the spiral wound supercapacitor. The transient temperature distribution during cycling is obtained by using the finite element method with an implicit predictor-multicorrector algorithm. At the constant current of 2A, the results show that the maximum temperature appears in core area. After 5 cycles, the maximum temperature is 34.5°C, while in steady state, it’s up to 42.5°C. This paper further studies the relationship between the maximum temperature and charge-discharge current. The maximum temperature will be more than 60°C after 5 cycles at the current of 4A, and cooling measurements should be taken at that time. It can provide thoughts on inner temperature field distribution and structure design of the spiral wound supercapacitor in working process. PMID:26444687

Quasi-Steady-State Analysis based on Structural Modules and Timed Petri Net Predict System's Dynamics: The Life Cycle of the Insulin Receptor.

PubMed

Scheidel, Jennifer; Lindauer, Klaus; Ackermann, Jörg; Koch, Ina

2015-12-17

The insulin-dependent activation and recycling of the insulin receptor play an essential role in the regulation of the energy metabolism, leading to a special interest for pharmaceutical applications. Thus, the recycling of the insulin receptor has been intensively investigated, experimentally as well as theoretically. We developed a time-resolved, discrete model to describe stochastic dynamics and study the approximation of non-linear dynamics in the context of timed Petri nets. Additionally, using a graph-theoretical approach, we analyzed the structure of the regulatory system and demonstrated the close interrelation of structural network properties with the kinetic behavior. The transition invariants decomposed the model into overlapping subnetworks of various sizes, which represent basic functional modules. Moreover, we computed the quasi-steady states of these subnetworks and demonstrated that they are fundamental to understand the dynamic behavior of the system. The Petri net approach confirms the experimental results of insulin-stimulated degradation of the insulin receptor, which represents a common feature of insulin-resistant, hyperinsulinaemic states.

Genotoxic potential of organic extracts from particle emissions of diesel and rapeseed oil powered engines.

PubMed

Topinka, Jan; Milcova, Alena; Schmuczerova, Jana; Mazac, Martin; Pechout, Martin; Vojtisek-Lom, Michal

2012-07-07

The present study was performed to identify possible genotoxicity induced by organic extracts from particulate matter in the exhaust of two typical diesel engines run on diesel fuel and neat heated fuel-grade rapeseed oil: a Cummins ISBe4 engine tested using the World Harmonized Steady State Test Cycle (WHSC) and modified Engine Steady Cycle (ESC) and a Zetor 1505 engine tested using the Non-Road Steady State Cycle (NRSC). In addition, biodiesel B-100 (neat methylester of rapeseed oil) was tested in the Cummins engine run on the modified ESC. Diluted exhaust was sampled with high-volume samplers on Teflon coated filters. Filters were extracted with dichlormethane (DCM) and DNA adduct levels induced by extractable organic matter (EOM) in an acellular assay of calf thymus DNA coupled with (32)P-postlabeling in the presence and absence of rat liver microsomal S9 fraction were employed. Simultaneously, the chemical analysis of 12 priority PAHs in EOM, including 7 carcinogenic PAHs (c-PAHs) was performed. The results suggest that diesel emissions contain substantially more total PAHs than rapeseed oil emissions (for the ESC) or that these concentrations were comparable (for the WHSC and NRSC), while c-PAHs levels were comparable (for the ESC) or significantly higher (for the WHSC and NRSC) for rapeseed oil emissions. DNA adduct levels induced by diesel and rapeseed oil derived EOM were comparable, but consistently slightly higher for diesel than for rapeseed oil. Highly significant correlations were found between 12 priority PAHs concentrations and DNA adduct levels (0.980; p<0.001) and these correlations were even stronger for c-PAHs (0.990; p<0.001). Metabolic activation by the microsomal S9 fraction resulted in several fold higher genotoxicity, suggesting a major contribution of PAHs to genotoxicity. Directly acting compounds, other than c-PAHs, and not requiring S9 to exhibit DNA reactivity were also significant. Generally, DNA adduct levels were more dependent on the type of engine and the test cycle than on the fuel. Our findings suggest that the genotoxicity of particulate emissions from the combustion of rapeseed oil is significant and is comparable to that from the combustion of diesel fuel. A more detailed study is ongoing to verify and extent these preliminary findings. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Evaluation and Description of Friction between an Electro-Deposited Coating and a Ceramic Ball under Fretting Condition

PubMed Central

Kim, Kyungmok

2015-01-01

This article describes fretting behavior of zirconia and silicon nitride balls on an electro-deposited coating. Fretting tests are performed using a ball-on-flat configuration. The evolution of the kinetic friction coefficient is determined, along with slip ratio. Experimental results show that the steady-state friction coefficient between ceramic balls (Si3N4 and ZrO2) and an electro-deposited coating is about 0.06, lower than the value between AISI 52100 ball and the coating. After a steady-state sliding, the transition of the friction coefficient is varied with a ball. The friction coefficient for ZrO2 balls became a critical value after higher fretting cycles than those for Si3N4 and AISI 52100 balls. In addition, it is identified that two parameters can describe the transition of the friction coefficient. Finally, the evolution of the friction coefficient is expressed as an exponential or a power-law form. PMID:28793471

Thermal and hydraulic analysis of a cylindrical blanket module design for a tokamak reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, A.Y.

1978-10-01

Various existing blanket design concepts for a tokamak fusion reactor were evaluated and assessed. These included the demonstration power reactors of ORNL, GA and others. As a result of this study, a cylindrical, modularized blanket design concept was developed. The module is a double-walled, stainless steel 316 cylinder containing liquid lithium for tritium breeding and is cooled by pressurized helium. Steady state and transient thermal conditions under normal and some off-design conditions were analyzed and presented. At the steady state reference operating point the maximum structure temperature is 452/sup 0/C at the maximum stressed location and is 495/sup 0/C atmore » the less stressed location. The coolant inlet pressure is 54.4 atm, the inlet temperature is 200/sup 0/C and the exit temperature is 435/sup 0/C. The coolant could be utilized with a helium/steam turbine power conversion system with a cycle thermal efficiency of 30.8%.« less

Non-equilibrium phase transitions in a driven-dissipative system of interacting bosons

NASA Astrophysics Data System (ADS)

Young, Jeremy T.; Foss-Feig, Michael; Gorshkov, Alexey V.; Maghrebi, Mohammad F.

2017-04-01

Atomic, molecular, and optical systems provide unique opportunities to study simple models of driven-dissipative many-body quantum systems. Typically, one is interested in the resultant steady state, but the non-equilibrium nature of the physics involved presents several problems in understanding its behavior theoretically. Recently, it has been shown that in many of these models, it is possible to map the steady-state phase transitions onto classical equilibrium phase transitions. In the language of Keldysh field theory, this relation typically only becomes apparent after integrating out massive fields near the critical point, leaving behind a single massless field undergoing near-equilibrium dynamics. In this talk, we study a driven-dissipative XXZ bosonic model and discover critical points at which two fields become gapless. Each critical point separates three different possible phases: a uniform phase, an anti-ferromagnetic phase, and a limit cycle phase. Furthermore, a description in terms of an equilibrium phase transition does not seem possible, so the associated phase transitions appear to be inherently non-equilibrium.

Electrochemical disinfection of repeatedly recycled blackwater in a free‐standing, additive‐free toilet

PubMed Central

Sellgren, Katelyn L.; Klem, Ethan J. D.; Piascik, Jeffrey R.; Stoner, Brian R.

2017-01-01

Abstract Decentralized, energy‐efficient waste water treatment technologies enabling water reuse are needed to sustainably address sanitation needs in water‐ and energy‐scarce environments. Here, we describe the effects of repeated recycling of disinfected blackwater (as flush liquid) on the energy required to achieve full disinfection with an electrochemical process in a prototype toilet system. The recycled liquid rapidly reached a steady state with total solids reliably ranging between 0.50 and 0.65% and conductivity between 20 and 23 mS/cm through many flush cycles over 15 weeks. The increase in accumulated solids was associated with increased energy demand and wide variation in the free chlorine contact time required to achieve complete disinfection. Further studies on the system at steady state revealed that running at higher voltage modestly improves energy efficiency, and established running parameters that reliably achieve disinfection at fixed run times. These results will guide prototype testing in the field. PMID:29242713

Bidirectionality and compartmentation of metabolic fluxes are revealed in the dynamics of isotopomer networks.

PubMed

Schryer, David W; Peterson, Pearu; Paalme, Toomas; Vendelin, Marko

2009-04-17

Isotope labeling is one of the few methods of revealing the in vivo bidirectionality and compartmentalization of metabolic fluxes within metabolic networks. We argue that a shift from steady state to dynamic isotopomer analysis is required to deal with these cellular complexities and provide a review of dynamic studies of compartmentalized energy fluxes in eukaryotic cells including cardiac muscle, plants, and astrocytes. Knowledge of complex metabolic behaviour on a molecular level is prerequisite for the intelligent design of genetically modified organisms able to realize their potential of revolutionizing food, energy, and pharmaceutical production. We describe techniques to explore the bidirectionality and compartmentalization of metabolic fluxes using information contained in the isotopic transient, and discuss the integration of kinetic models with MFA. The flux parameters of an example metabolic network were optimized to examine the compartmentalization of metabolites and and the bidirectionality of fluxes in the TCA cycle of Saccharomyces uvarum for steady-state respiratory growth.

Modeling of Steady-state Scenarios for the Fusion Nuclear Science Facility, Advanced Tokamak Approach

NASA Astrophysics Data System (ADS)

Garofalo, A. M.; Chan, V. S.; Prater, R.; Smith, S. P.; St. John, H. E.; Meneghini, O.

2013-10-01

A Fusion National Science Facility (FNSF) would complement ITER in addressing the community identified science and technology gaps to a commercially attractive DEMO, including breeding tritium and completing the fuel cycle, qualifying nuclear materials for high fluence, developing suitable materials for the plasma-boundary interface, and demonstrating power extraction. Steady-state plasma operation is highly desirable to address the requirements for fusion nuclear technology testing [1]. The Advanced Tokamak (AT) is a strong candidate for an FNSF as a consequence of its mature physics base, capability to address the key issues with a more compact device, and the direct relevance to an attractive target power plant. Key features of AT are fully noninductive current drive, strong plasma cross section shaping, internal profiles consistent with high bootstrap fraction, and operation at high beta, typically above the free boundary limit, βN > 3 . Work supported by GA IR&D funding, DE-FC02-04ER54698, and DE-FG02-95ER43309.

Real and financial market interactions in a multiplier-accelerator model: Nonlinear dynamics, multistability and stylized facts

NASA Astrophysics Data System (ADS)

Cavalli, F.; Naimzada, A.; Pecora, N.

2017-10-01

In the present paper, we investigate the dynamics of a model in which the real part of the economy, described within a multiplier-accelerator framework, interacts with a financial market with heterogeneous speculators, in order to study the channels through which the two sectors influence each other. Employing analytical and numerical tools, we investigate stability conditions as well as bifurcations and possible periodic, quasi-periodic, and chaotic dynamics, enlightening how the degree of market interaction, together with the accelerator parameter and the intervention of the fiscal authority, may affect the business cycle and the course of the financial market. In particular, we show that even if the steady state is locally stable, multistability phenomena can occur, with several and complex dynamic structures coexisting with the steady state. Finally, simulations reveal that the proposed model is able to explain several statistical properties and stylized facts observed in real financial markets, including persistent high volatility, fat-tailed return distributions, volatility clustering, and positive autocorrelation of absolute returns.

The Influences of Airmass Histories on Radical Species During POLARIS

NASA Technical Reports Server (NTRS)

Pierson, James M.; Kawa, S. R.

1998-01-01

The POLARIS mission focused on understanding the processes associated with the decrease of polar stratospheric ozone from spring to fall at high latitudes. This decrease is linked primarily to in situ photochemical destruction by reactive nitrogen species, NO and NO2, which also control other catalytic loss cycles. Steady state models have been used to test photochemistry and radical behavior but are not always adequate in simulating radical species observations. In some cases, air mass history can be important and trajectory models give an improved simulation of the radical species. Trajectory chemistry models, however, still consistently underestimate NO and NO2 abundances compared to measurements along the ER-2 flight track. The Goddard chemistry on trajectory model has been used to test updated rate constants for NO2 + OH, NO2 + O and OH + HNO3, key reactions that affect NO and NO2 abundances. We present comparisons between the modified Goddard chemistry on trajectory model, the JPL steady state model and observations from selected flights.

Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system

NASA Technical Reports Server (NTRS)

Davis, J. W.; Cramer, B. A.

1976-01-01

A method of analysis was developed for predicting permanent cyclic creep deflections in stiffened panel structures. This method uses creep equations based on cyclic tensile creep tests and a computer program to predict panel deflections as a function of mission cycle. Four materials were investigated - a titanium alloy (Ti-6Al-4V), a cobalt alloy (L605), and two nickel alloys (Rene'41 and TDNiCr). Steady-state and cyclic creep response data were obtained by testing tensile specimens fabricated from thin gage sheet (0.025 and 0.63 cm nominal). Steady-state and cyclic creep equations were developed which describe creep as a function of time, temperature and load. Tests were also performed on subsize (6.35 x 30.5 cm) rib and corrugation stiffened panels. These tests were used to correlate creep responses between elemental specimens and panels. The panel response was analyzed by use of a specially written computer program.

Darwin and the geological controversies over the steady-state worldview in the 1830s.

PubMed

Gohau, Gabriel

2014-01-01

In the first part of this paper, I will show that although Darwin's geological works only covered the first years of his scientific career, these played a non-negligible role in the earth sciences of the mid-nineteenth century. His intellectual proximity with Charles Lyell often made him his disciple. This is indeed the case with respect to debates over 'gradual' soil movements and 'catastrophic' soil movements, and for 'steady-state' cycles as opposed to 'directionalistic' ones. This being said, it is also true that in South America Darwin saw geological processes which were incompatible with Lyell's explanations. It must therefore be recognized that Darwin held a middle-of-the-road position between uniformitarianism (Lyell) and catastrophism (Humbolt and von Buch), at least as far as some geological questions were concerned. In the second part of the paper, debates on geological issues during Darwin's active years will be put in the methodological context of the Scientific Revolution of the seventeenth century. Copyright © 2014 Elsevier Ltd. All rights reserved.

Real and financial market interactions in a multiplier-accelerator model: Nonlinear dynamics, multistability and stylized facts.

PubMed

Cavalli, F; Naimzada, A; Pecora, N

2017-10-01

In the present paper, we investigate the dynamics of a model in which the real part of the economy, described within a multiplier-accelerator framework, interacts with a financial market with heterogeneous speculators, in order to study the channels through which the two sectors influence each other. Employing analytical and numerical tools, we investigate stability conditions as well as bifurcations and possible periodic, quasi-periodic, and chaotic dynamics, enlightening how the degree of market interaction, together with the accelerator parameter and the intervention of the fiscal authority, may affect the business cycle and the course of the financial market. In particular, we show that even if the steady state is locally stable, multistability phenomena can occur, with several and complex dynamic structures coexisting with the steady state. Finally, simulations reveal that the proposed model is able to explain several statistical properties and stylized facts observed in real financial markets, including persistent high volatility, fat-tailed return distributions, volatility clustering, and positive autocorrelation of absolute returns.

Determination of biological removal of recalcitrant organic contaminants in coal gasification waste water.

PubMed

Ji, Qinhong; Tabassum, Salma; Yu, Guangxin; Chu, Chunfeng; Zhang, Zhenjia

2015-01-01

Coal gasification waste water treatment needed a sustainable and affordable plan to eliminate the organic contaminants in order to lower the potential environmental and human health risk. In this paper, a laboratory-scale anaerobic-aerobic intermittent system carried out 66 operational cycles together for the treatment of coal gasification waste water and the removal capacity of each organic pollutant. Contaminants included phenols, carboxylic acids, long-chain hydrocarbons, and heterocyclic compounds, wherein the relative content of phenol is up to 57.86%. The long-term removal of 77 organic contaminants was evaluated at different hydraulic retention time (anaerobic24 h + aerobic48 h and anaerobic48 h +aerobic48 h). Contaminant removal ranged from no measurable removal to near-complete removal with effluent concentrations below the detection limit. Contaminant removals followed one of four trends: steady-state removal throughout, increasing removal to steady state (acclimation), decreasing removal, and no removal. Organic degradation and transformation in the reaction were analysed by gas chromatography/mass spectrometry technology.

Modeling the Metabolism of Arabidopsis thaliana: Application of Network Decomposition and Network Reduction in the Context of Petri Nets.

PubMed

Koch, Ina; Nöthen, Joachim; Schleiff, Enrico

2017-01-01

Motivation: Arabidopsis thaliana is a well-established model system for the analysis of the basic physiological and metabolic pathways of plants. Nevertheless, the system is not yet fully understood, although many mechanisms are described, and information for many processes exists. However, the combination and interpretation of the large amount of biological data remain a big challenge, not only because data sets for metabolic paths are still incomplete. Moreover, they are often inconsistent, because they are coming from different experiments of various scales, regarding, for example, accuracy and/or significance. Here, theoretical modeling is powerful to formulate hypotheses for pathways and the dynamics of the metabolism, even if the biological data are incomplete. To develop reliable mathematical models they have to be proven for consistency. This is still a challenging task because many verification techniques fail already for middle-sized models. Consequently, new methods, like decomposition methods or reduction approaches, are developed to circumvent this problem. Methods: We present a new semi-quantitative mathematical model of the metabolism of Arabidopsis thaliana . We used the Petri net formalism to express the complex reaction system in a mathematically unique manner. To verify the model for correctness and consistency we applied concepts of network decomposition and network reduction such as transition invariants, common transition pairs, and invariant transition pairs. Results: We formulated the core metabolism of Arabidopsis thaliana based on recent knowledge from literature, including the Calvin cycle, glycolysis and citric acid cycle, glyoxylate cycle, urea cycle, sucrose synthesis, and the starch metabolism. By applying network decomposition and reduction techniques at steady-state conditions, we suggest a straightforward mathematical modeling process. We demonstrate that potential steady-state pathways exist, which provide the fixed carbon to nearly all parts of the network, especially to the citric acid cycle. There is a close cooperation of important metabolic pathways, e.g., the de novo synthesis of uridine-5-monophosphate, the γ-aminobutyric acid shunt, and the urea cycle. The presented approach extends the established methods for a feasible interpretation of biological network models, in particular of large and complex models.

Modeling the Metabolism of Arabidopsis thaliana: Application of Network Decomposition and Network Reduction in the Context of Petri Nets

PubMed Central

Koch, Ina; Nöthen, Joachim; Schleiff, Enrico

2017-01-01

Motivation: Arabidopsis thaliana is a well-established model system for the analysis of the basic physiological and metabolic pathways of plants. Nevertheless, the system is not yet fully understood, although many mechanisms are described, and information for many processes exists. However, the combination and interpretation of the large amount of biological data remain a big challenge, not only because data sets for metabolic paths are still incomplete. Moreover, they are often inconsistent, because they are coming from different experiments of various scales, regarding, for example, accuracy and/or significance. Here, theoretical modeling is powerful to formulate hypotheses for pathways and the dynamics of the metabolism, even if the biological data are incomplete. To develop reliable mathematical models they have to be proven for consistency. This is still a challenging task because many verification techniques fail already for middle-sized models. Consequently, new methods, like decomposition methods or reduction approaches, are developed to circumvent this problem. Methods: We present a new semi-quantitative mathematical model of the metabolism of Arabidopsis thaliana. We used the Petri net formalism to express the complex reaction system in a mathematically unique manner. To verify the model for correctness and consistency we applied concepts of network decomposition and network reduction such as transition invariants, common transition pairs, and invariant transition pairs. Results: We formulated the core metabolism of Arabidopsis thaliana based on recent knowledge from literature, including the Calvin cycle, glycolysis and citric acid cycle, glyoxylate cycle, urea cycle, sucrose synthesis, and the starch metabolism. By applying network decomposition and reduction techniques at steady-state conditions, we suggest a straightforward mathematical modeling process. We demonstrate that potential steady-state pathways exist, which provide the fixed carbon to nearly all parts of the network, especially to the citric acid cycle. There is a close cooperation of important metabolic pathways, e.g., the de novo synthesis of uridine-5-monophosphate, the γ-aminobutyric acid shunt, and the urea cycle. The presented approach extends the established methods for a feasible interpretation of biological network models, in particular of large and complex models. PMID:28713420

Quasi-steady state conditions in heterogeneous aquifers during pumping tests

NASA Astrophysics Data System (ADS)

Zha, Yuanyuan; Yeh, Tian-Chyi J.; Shi, Liangsheng; Huang, Shao-Yang; Wang, Wenke; Wen, Jet-Chau

2017-08-01

Classical Thiem's well hydraulic theory, other aquifer test analyses, and flow modeling efforts often assume the existence of ;quasi-steady; state conditions. That is, while drawdowns due to pumping continue to grow, the hydraulic gradient in the vicinity of the pumping well does not change significantly. These conditions have built upon two-dimensional and equivalent homogeneous conceptual models, but few field data have been available to affirm the existence of these conditions. Moreover, effects of heterogeneity and three-dimensional flow on this quasi-steady state concept have not been thoroughly investigated and discussed before. In this study, we first present a quantitative definition of quasi-steady state (or steady-shape conditions) and steady state conditions based on the analytical solution of two- or three-dimensional flow induced by pumping in unbounded, homogeneous aquifers. Afterward, we use a stochastic analysis to investigate the influence of heterogeneity on the quasi-steady state concept in heterogeneous aquifers. The results of the analysis indicate that the time to reach an approximate quasi-steady state in a heterogeneous aquifer could be quite different from that estimated based on a homogeneous model. We find that heterogeneity of aquifer properties, especially hydraulic conductivity, impedes the development of the quasi-steady state condition before the flow reaching steady state. Finally, 280 drawdown-time data from the hydraulic tomographic survey conducted at a field site corroborate our finding that the quasi-steady state condition likely would not take place in heterogeneous aquifers unless pumping tests last a long period. Research significance (1) Approximate quasi-steady and steady state conditions are defined for two- or three-dimensional flow induced by pumping in unbounded, equivalent homogeneous aquifers. (2) Analysis demonstrates effects of boundary condition, well screen interval, and heterogeneity of parameters on the existence of the quasi-steady, and validity of approximate quasi-steady concept. (3) Temporal evaluation of information content about heterogeneity in head observations are analyzed in heterogeneous aquifer. (4) 280 observed drawdown-time data corroborate the stochastic analysis that quasi-steady is difficult to reach in highly heterogeneous aquifers.

Effect of cycle time on polyhydroxybutyrate (PHB) production in aerobic mixed cultures.

PubMed

Ozdemir, Sebnem; Akman, Dilek; Cirik, Kevser; Cinar, Ozer

2014-03-01

The aim of this study was to investigate the effect of cycle time on polyhydroxybutyrate (PHB) production under aerobic dynamic feeding system. The acetate-fed feast and famine sequencing batch reactor was used to enrich PHB accumulating microorganism. Sequencing batch reactor (SBR) was operated in four different cycle times (12, 8, 4, and 2 h) fed with a synthetic wastewater. The system performance was determined by monitoring total dissolved organic carbon, dissolved oxygen, oxidation-reduction potential, and PHB concentration. In this study, under steady-state conditions, the feast period of the SBR was found to allow the PHB storage while a certain part of stored PHB was used for continued growth in famine period. The percentage PHB storages by aerobic microorganism were at 16, 18, 42, and 55% for the 12, 8, 4, and 2-h cycle times, respectively. The PHB storage was increased as the length of the cycle time was decreased, and the ratio of the feast compared to the total cycle length was increased from around 13 to 33% for the 12 and 2-h cycle times, respectively.

Fluid dynamics of flapping aquatic flight in the bird wrasse: three-dimensional unsteady computations with fin deformation.

PubMed

Ramamurti, Ravi; Sandberg, William C; Löhner, Rainald; Walker, Jeffrey A; Westneat, Mark W

2002-10-01

Many fishes that swim with the paired pectoral fins use fin-stroke parameters that produce thrust force from lift in a mechanism of underwater flight. These locomotor mechanisms are of interest to behavioral biologists, biomechanics researchers and engineers. In the present study, we performed the first three-dimensional unsteady computations of fish swimming with oscillating and deforming fins. The objective of these computations was to investigate the fluid dynamics of force production associated with the flapping aquatic flight of the bird wrasse Gomphosus varius. For this computational work, we used the geometry of the wrasse and its pectoral fin, and previously measured fin kinematics, as the starting points for computational investigation of three-dimensional (3-D) unsteady fluid dynamics. We performed a 3-D steady computation and a complete set of 3-D quasisteady computations for a range of pectoral fin positions and surface velocities. An unstructured, grid-based, unsteady Navier-Stokes solver with automatic adaptive remeshing was then used to compute the unsteady flow about the wrasse through several complete cycles of pectoral fin oscillation. The shape deformation of the pectoral fin throughout the oscillation was taken from the experimental kinematics. The pressure distribution on the body of the bird wrasse and its pectoral fins was computed and integrated to give body and fin forces which were decomposed into lift and thrust. The velocity field variation on the surface of the wrasse body, on the pectoral fins and in the near-wake was computed throughout the swimming cycle. We compared our computational results for the steady, quasi-steady and unsteady cases with the experimental data on axial and vertical acceleration obtained from the pectoral fin kinematics experiments. These comparisons show that steady state computations are incapable of describing the fluid dynamics of flapping fins. Quasi-steady state computations, with correct incorporation of the experimental kinematics, are useful when determining trends in force production, but do not provide accurate estimates of the magnitudes of the forces produced. By contrast, unsteady computations about the deforming pectoral fins using experimentally measured fin kinematics were found to give excellent agreement, both in the time history of force production throughout the flapping strokes and in the magnitudes of the generated forces.

From Cycling Between Coupled Reactions to the Cross-Bridge Cycle: Mechanical Power Output as an Integral Part of Energy Metabolism

PubMed Central

Diederichs, Frank

2012-01-01

ATP delivery and its usage are achieved by cycling of respective intermediates through interconnected coupled reactions. At steady state, cycling between coupled reactions always occurs at zero resistance of the whole cycle without dissipation of free energy. The cross-bridge cycle can also be described by a system of coupled reactions: one energising reaction, which energises myosin heads by coupled ATP splitting, and one de-energising reaction, which transduces free energy from myosin heads to coupled actin movement. The whole cycle of myosin heads via cross-bridge formation and dissociation proceeds at zero resistance. Dissipation of free energy from coupled reactions occurs whenever the input potential overcomes the counteracting output potential. In addition, dissipation is produced by uncoupling. This is brought about by a load dependent shortening of the cross-bridge stroke to zero, which allows isometric force generation without mechanical power output. The occurrence of maximal efficiency is caused by uncoupling. Under coupled conditions, Hill’s equation (velocity as a function of load) is fulfilled. In addition, force and shortening velocity both depend on [Ca2+]. Muscular fatigue is triggered when ATP consumption overcomes ATP delivery. As a result, the substrate of the cycle, [MgATP2−], is reduced. This leads to a switch off of cycling and ATP consumption, so that a recovery of [ATP] is possible. In this way a potentially harmful, persistent low energy state of the cell can be avoided. PMID:24957757

Enhancing emotional-based target prediction

NASA Astrophysics Data System (ADS)

Gosnell, Michael; Woodley, Robert

2008-04-01

This work extends existing agent-based target movement prediction to include key ideas of behavioral inertia, steady states, and catastrophic change from existing psychological, sociological, and mathematical work. Existing target prediction work inherently assumes a single steady state for target behavior, and attempts to classify behavior based on a single emotional state set. The enhanced, emotional-based target prediction maintains up to three distinct steady states, or typical behaviors, based on a target's operating conditions and observed behaviors. Each steady state has an associated behavioral inertia, similar to the standard deviation of behaviors within that state. The enhanced prediction framework also allows steady state transitions through catastrophic change and individual steady states could be used in an offline analysis with additional modeling efforts to better predict anticipated target reactions.

Numerical Simulations of the Steady and Unsteady Aerodynamic Characteristics of a Circulation Control Wing Airfoil

NASA Technical Reports Server (NTRS)

Liu, Yi; Sankar, Lakshmi N.; Englar, Robert J.; Ahuja, Krishan K.

2003-01-01

The aerodynamic characteristics of a Circulation Control Wing (CCW) airfoil have been numerically investigated, and comparisons with experimental data have been made. The configuration chosen was a supercritical airfoil with a 30 degree dual-radius CCW flap. Steady and pulsed jet calculations were performed. It was found that the use of steady jets, even at very small mass flow rates, yielded a lift coefficient that is comparable or superior to conventional high-lift systems. The attached flow over the flap also gave rise to lower drag coefficients, and high L/D ratios. Pulsed jets with a 50% duty cycle were also studied. It was found that they were effective in generating lift at lower reduced mass flow rates compared to a steady jet, provided the pulse frequency was sufficiently high. This benefit was attributable to the fact that the momentum coefficient of the pulsed jet, during the portions of the cycle when the jet was on, was typically twice as much as that of a steady jet.

Boom and bust in continuous time evolving economic model

NASA Astrophysics Data System (ADS)

Mitchell, L.; Ackland, G. J.

2009-08-01

We show that a simple model of a spatially resolved evolving economic system, which has a steady state under simultaneous updating, shows stable oscillations in price when updated asynchronously. The oscillations arise from a gradual decline of the mean price due to competition among sellers competing for the same resource. This lowers profitability and hence population but is followed by a sharp rise as speculative sellers invade the large un-inhabited areas. This cycle then begins again.

Instabilities and Chaotic Behavior of Active and Passive Laser Systems.

DTIC Science & Technology

1985-03-01

Some of these attractors, already well-known from elementary calculus, are the steady states of the system, i.e., configurations such that all the time ...charactaristic fundamental frequencies (the reciprocal of the round-trip time around the limit cycle) and usually a host of harmonic components, whose origin is...provided with a hybrid electro-optic device in which the delay of the feed- 2 back loop was made considerably larger than the response time of the system

The P3 Power Generation System for Advanced Missile Defense Applications

DTIC Science & Technology

2008-11-01

circuit. This increased the output power to the load resistor . The inductor couples with the piezo element to form an electrical LC tuned circuit and...of RMS power was generated with an efficiency of 40 % when an inductor of 250 mH was connected in series to a 100 ohm resistor . From power density...per cycle for generating electrical energy in a piezo -crystal membrane. Steady-state heat transfer measurements have been made previously with a

Mechanisms of Photophobia in Mild Traumatic Brain Injury in Human Subjects: Therapeutic Implications

DTIC Science & Technology

2015-10-01

R, G, B and W). FMRI Stimuli The four fMRI runs consisted of 6 cycles of: 1. 20 s of 2.5 Hz Blue/Black Flicker alternating with 20 s Steady Black...7 2. 20 s of 2.5 Hz Red/Black Flicker , alternating with 20 s Steady Black 3. 20 s of Steady Blue alternating with 20 s Steady Red 4. 20 s of Steady...Blue alternating with 20 s Steady Green The preliminary studies confirmed that we can set all flicker frequencies at 2.5Hz to match the frequency used

The Reaction Kinetics of 3-Hydroxybenzoate 6-Hydroxylase from Rhodococcus jostii RHA1 Provide an Understanding of the para-Hydroxylation Enzyme Catalytic Cycle*

PubMed Central

Sucharitakul, Jeerus; Tongsook, Chanakan; Pakotiprapha, Danaya; van Berkel, Willem J. H.; Chaiyen, Pimchai

2013-01-01

3-Hydroxybenzoate 6-hydroxylase (3HB6H) from Rhodococcus jostii RHA1 is an NADH-specific flavoprotein monooxygenase that catalyzes the para-hydroxylation of 3-hydroxybenzoate (3HB) to form 2,5-dihydroxybenzoate (2,5-DHB). Based on results from stopped-flow spectrophotometry, the reduced enzyme-3HB complex reacts with oxygen to form a C4a-peroxy flavin with a rate constant of 1.13 ± 0.01 × 106 m−1 s−1 (pH 8.0, 4 °C). This intermediate is subsequently protonated to form a C4a-hydroperoxyflavin with a rate constant of 96 ± 3 s−1. This step shows a solvent kinetic isotope effect of 1.7. Based on rapid-quench measurements, the hydroxylation occurs with a rate constant of 36 ± 2 s−1. 3HB6H does not exhibit substrate inhibition on the flavin oxidation step, a common characteristic found in most ortho-hydroxylation enzymes. The apparent kcat at saturating concentrations of 3HB, NADH, and oxygen is 6.49 ± 0.02 s−1. Pre-steady state and steady-state kinetic data were used to construct the catalytic cycle of the reaction. The data indicate that the steps of product release (11.7 s−1) and hydroxylation (36 ± 2 s−1) partially control the overall turnover. PMID:24129570

A High-Throughput Assay for Rho Guanine Nucleotide Exchange Factors Based on the Transcreener GDP Assay.

PubMed

Reichman, Melvin; Schabdach, Amanda; Kumar, Meera; Zielinski, Tom; Donover, Preston S; Laury-Kleintop, Lisa D; Lowery, Robert G

2015-12-01

Ras homologous (Rho) family GTPases act as molecular switches controlling cell growth, movement, and gene expression by cycling between inactive guanosine diphosphate (GDP)- and active guanosine triphosphate (GTP)-bound conformations. Guanine nucleotide exchange factors (GEFs) positively regulate Rho GTPases by accelerating GDP dissociation to allow formation of the active, GTP-bound complex. Rho proteins are directly involved in cancer pathways, especially cell migration and invasion, and inhibiting GEFs holds potential as a therapeutic strategy to diminish Rho-dependent oncogenesis. Methods for measuring GEF activity suitable for high-throughput screening (HTS) are limited. We developed a simple, generic biochemical assay method for measuring GEF activity based on the fact that GDP dissociation is generally the rate-limiting step in the Rho GTPase catalytic cycle, and thus addition of a GEF causes an increase in steady-state GTPase activity. We used the Transcreener GDP Assay, which relies on selective immunodetection of GDP, to measure the GEF-dependent stimulation of steady-state GTP hydrolysis by small GTPases using Dbs (Dbl's big sister) as a GEF for Cdc42, RhoA, and RhoB. The assay is well suited for HTS, with a homogenous format and far red fluorescence polarization (FP) readout, and it should be broadly applicable to diverse Rho GEF/GTPase pairs. © 2015 Society for Laboratory Automation and Screening.

Ubiquitylation and proteasomal degradation of the p21(Cip1), p27(Kip1) and p57(Kip2) CDK inhibitors.

PubMed

Lu, Zhimin; Hunter, Tony

2010-06-15

The expression levels of the p21(Cip1) family CDK inhibitors (CKIs), p21(Cip1), p27(Kip1) and p57(Kip2), play a pivotal role in the precise regulation of cyclin-dependent kinase (CDK) activity, which is instrumental to proper cell cycle progression. The stabilities of p21(Cip1), p27(Kip1) and p57(Kip2) are all tightly and differentially regulated by ubiquitylation and proteasome-mediated degradation during various stages of the cell cycle, either in steady state or in response to extracellular stimuli, which often elicit site-specific phosphorylation of CKIs triggering their degradation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burkholder, Michael B.; Litster, Shawn, E-mail: litster@andrew.cmu.edu

In this study, we analyze the stability of two-phase flow regimes and their transitions using chaotic and fractal statistics, and we report new measurements of dynamic two-phase pressure drop hysteresis that is related to flow regime stability and channel water content. Two-phase flow dynamics are relevant to a variety of real-world systems, and quantifying transient two-phase flow phenomena is important for efficient design. We recorded two-phase (air and water) pressure drops and flow images in a microchannel under both steady and transient conditions. Using Lyapunov exponents and Hurst exponents to characterize the steady-state pressure fluctuations, we develop a new, measurablemore » regime identification criteria based on the dynamic stability of the two-phase pressure signal. We also applied a new experimental technique by continuously cycling the air flow rate to study dynamic hysteresis in two-phase pressure drops, which is separate from steady-state hysteresis and can be used to understand two-phase flow development time scales. Using recorded images of the two-phase flow, we show that the capacitive dynamic hysteresis is related to channel water content and flow regime stability. The mixed-wettability microchannel and in-channel water introduction used in this study simulate a polymer electrolyte fuel cell cathode air flow channel.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Metzler, Dominik; Li, Chen; Engelmann, Sebastian

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO 2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C 4F 8 and CHF 3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32,more » 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO 2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF 3 has a lower FC deposition yield for both SiO 2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F 8. The thickness of deposited FC layers using CHF 3 is found to be greater for Si than for SiO 2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.« less

Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

NASA Astrophysics Data System (ADS)

Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.; Oehrlein, Gottlieb S.

2017-02-01

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.

An all digital phase locked loop for synchronization of a sinusoidal signal embedded in white Gaussian noise

NASA Technical Reports Server (NTRS)

Reddy, C. P.; Gupta, S. C.

1973-01-01

An all digital phase locked loop which tracks the phase of the incoming sinusoidal signal once per carrier cycle is proposed. The different elements and their functions and the phase lock operation are explained in detail. The nonlinear difference equations which govern the operation of the digital loop when the incoming signal is embedded in white Gaussian noise are derived, and a suitable model is specified. The performance of the digital loop is considered for the synchronization of a sinusoidal signal. For this, the noise term is suitably modelled which allows specification of the output probabilities for the two level quantizer in the loop at any given phase error. The loop filter considered increases the probability of proper phase correction. The phase error states in modulo two-pi forms a finite state Markov chain which enables the calculation of steady state probabilities, RMS phase error, transient response and mean time for cycle skipping.

Steady States, Fluctuation-Dissipation Theorems and Homogenization for Reversible Diffusions in a Random Environment

NASA Astrophysics Data System (ADS)

Mathieu, P.; Piatnitski, A.

2018-04-01

Prolongating our previous paper on the Einstein relation, we study the motion of a particle diffusing in a random reversible environment when subject to a small external forcing. In order to describe the long time behavior of the particle, we introduce the notions of steady state and weak steady state. We establish the continuity of weak steady states for an ergodic and uniformly elliptic environment. When the environment has finite range of dependence, we prove the existence of the steady state and weak steady state and compute its derivative at a vanishing force. Thus we obtain a complete `fluctuation-dissipation Theorem' in this context as well as the continuity of the effective variance.

Effect of the chamber wall on fluorocarbon-assisted atomic layer etching of SiO2 using cyclic Ar/C4F8 plasma

PubMed Central

Kawakami, Masatoshi; Metzler, Dominik; Li, Chen; Oehrlein, Gottlieb S.

2016-01-01

The authors studied the effect of the temperature and chemical state of the chamber wall on process performance for atomic layer etching of SiO2 using a steady-state Ar plasma, periodic injection of a defined number of C4F8 molecules, and synchronized plasma-based Ar+ ion bombardment. To evaluate these effects, the authors measured the quartz coupling window temperature. The plasma gas phase chemistry was characterized using optical emission spectroscopy. It was found that although the thickness of the polymer film deposited in each cycle is constant, the etching behavior changed, which is likely related to a change in the plasma gas phase chemistry. The authors found that the main gas phase changes occur after C4F8 injection. The C4F8 and the quartz window react and generate SiF and CO. The emission intensity changes with wall surface state and temperature. Therefore, changes in the plasma gas species generation can lead to a shift in etching performance during processing. During initial cycles, minimal etching is observed, while etching gradually increases with cycle number. PMID:27375342

Comments on the BLAG model: the carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years

NASA Technical Reports Server (NTRS)

Kasting, J. F.

1984-01-01

A self-consistent method of determining initial conditions for the model presented by Berner, Lasaga, and Garrels (1983) (henceforth, the BLAG model) is derived, based on the assumption that the CO2 geochemical cycle was in steady state at t = -100 my (million years). This initialization procedure leads to a dissolved magnesium concentration higher than that calculated by Berner, Lasaga, and Garrels and to a low ratio of dissolved calcium to bicarbonate prior to 60 my ago. The latter prediction conflicts with the geologic record of evaporite deposits, which requires that this ratio remain greater than 0.5. The contradiction is probably caused by oversimplifications in the BLAG model, such as the neglect of the cycles of organic carbon and sulfur.

Comments on the BLAG model - The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years

NASA Technical Reports Server (NTRS)

Kasting, J. F.

1984-01-01

A self-consistent method of determining initial conditions for the model presented by Berner, Lasaga, and Garrels (1983) (henceforth, the BLAG model) is derived, based on the assumption that the CO2 geochemical cycle was in steady state at t = -100 m.y. (million years). This initialization procedure leads to a dissolved magnesium concentration higher than that calculated by Berner, Lasaga, and Garrels and to a low ratio of dissolved calcium to bicarbonate prior to 60 m.y. ago. The latter prediction conflicts with the geologic record of evaporite deposits, which requires that this ratio remain greater than 0.5. The contradiction is probably caused by oversimplifications in the BLAG model, such as the neglect of the cycles of organic carbon and sulfur.

Steady state volcanism - Evidence from eruption histories of polygenetic volcanoes

NASA Technical Reports Server (NTRS)

Wadge, G.

1982-01-01

Cumulative volcano volume curves are presented as evidence for steady-state behavior at certain volcanoes and to develop a model of steady-state volcanism. A minimum criteria of five eruptions over a year was chosen to characterize a steady-state volcano. The subsequent model features a constant head of magmatic pressure from a reservoir supplied from depth, a sawtooth curve produced by the magma arrivals or discharge from the subvolcanic reservoir, large volume eruptions with long repose periods, and conditions of nonsupply of magma. The behavior of Mts. Etna, Nyamuragira, and Kilauea are described and show continuous levels of plasma output resulting in cumulative volume increases. Further discussion is made of steady-state andesitic and dacitic volcanism, long term patterns of the steady state, and magma storage, and the lack of a sufficient number of steady-state volcanoes in the world is taken as evidence that further data is required for a comprehensive model.

Demonstration of a Non-Toxic Reaction Control Engine

NASA Technical Reports Server (NTRS)

Robinson, Philip J.; Turpin, Alicia A.; Veith, Eric M.

2007-01-01

T:hree non-toxic demonstration reaction control engines (RCE) were successfully tested at the Aerojet Sacramento facility under a technology contract sponsored by the National Aeronautics and Space Administration's (NASA) Marshall Space Flight Center (MSFC). The goals of the NASA MSFC contract (NAS8-01109) were to develop and expand the technical maturity of a non-toxic, on-orbit auxiliary propulsion system (APS) thruster under the auspices of the Exploration Systems Mission Directorate. The demonstration engine utilized Liquid Oxygen (LOX) and Ethanol as propellants to produce 870 lbf thrust. The Aerojet RCE's were successfully acceptance tested over a broad range of operating conditions. Steady state tests evaluated engine response to varying chamber pressures and mixture ratios. In addition to the steady state tests, a variety of pulsing tests were conducted over a wide range of electrical pulse widths (EPW). Each EPW condition was also tested over a range of percent duty cycles (DC), and bit impulse and pulsing specific impulse were determined for each of these conditions. Subsequent to acceptance testing at Aerojet, these three engines were delivered to the NASA White Sands Test Facility (WSTF) in April 2005 for incorporation into a cryogenic Auxiliary Propulsion System Test Bed (APSTB). The APSTB is a test article that will be utilized in an altitude test cell to simulate anticipated mission applications. The objectives of this APSTB testing included evaluation of engine performance over an extended duty cycle map of propellant pressure and temperature, as well as engine and system performance at typical mission duty cycles over extended periods of time. This paper provides acceptance test results and a status of the engine performance as part of the system level testing.

Demonstration of a Non-Toxic Reaction Control Engine

NASA Technical Reports Server (NTRS)

Robinson, Philip J.; Veith, Eric M.; Turpin, Alicia A.

2006-01-01

Three non-toxic demonstration reaction control engines (RCE) were successfully tested at the Aerojet Sacramento facility under a technology contract sponsored by the National Aeronautics and Space Administration s (NASA) Marshall Space Flight Center (MSFC). The goals of the NASA MSFC contract (NAS8-01109) were to develop and expand the technical maturity of a non-toxic, on-orbit auxiliary propulsion system (APS) thruster under the auspices of the Exploration Systems Mission Directorate. The demonstration engine utilized Liquid Oxygen (LOX) and Ethanol as propellants to produce 870 lbf thrust. The Aerojet RCE s were successfully acceptance tested over a broad range of operating conditions. Steady state tests evaluated engine response to varying chamber pressures and mixture ratios. In addition to the steady state tests, a variety of pulsing tests were conducted over a wide range of electrical pulse widths (EPW). Each EPW condition was also tested over a range of percent duty cycles (DC), and bit impulse and pulsing specific impulse were determined for each of these conditions. White Sands Test Facility (WSTF) in April 2005 for incorporation into a cryogenic Auxiliary Propulsion System Test Bed (APSTB). The APSTB is a test article that will be utilized in an altitude test cell to simulate anticipated mission applications. The objectives of this APSTB testing included evaluation of engine performance over an extended duty cycle map of propellant pressure and temperature, as well as engine and system performance at typical mission duty cycles over extended periods of time. This paper provides acceptance test results and a status of the engine performance as part of the system level testing. Subsequent to acceptance testing at Aerojet, these three engines were delivered to the NASA

Projecting High Beta Steady-State Scenarios from DIII-D Advanced Tokamk Discharges

NASA Astrophysics Data System (ADS)

Park, J. M.

2013-10-01

Fusion power plant studies based on steady-state tokamak operation suggest that normalized beta in the range of 4-6 is needed for economic viability. DIII-D is exploring a range of candidate high beta scenarios guided by FASTRAN modeling in a repeated cycle of experiment and modeling validation. FASTRAN is a new iterative numerical procedure coupled to the Integrated Plasma Simulator (IPS) that integrates models of core transport, heating and current drive, equilibrium and stability self-consistently to find steady state (d / dt = 0) solutions, and reproduces most features of DIII-D high beta discharges with a stationary current profile. Separately, modeling components such as core transport (TGLF) and off-axis neutral beam current drive (NUBEAM) show reasonable agreement with experiment. Projecting forward to scenarios possible on DIII-D with future upgrades, two self-consistent noninductive scenarios at βN > 4 are found: high qmin and high internal inductance li. Both have bootstrap current fraction fBS > 0 . 5 and rely on the planned addition of a second off-axis neutral beamline and increased electron cyclotron heating. The high qmin > 2 scenario achieves stable operation at βN as high as 5 by a very broad current density profile to improve the ideal-wall stabilization of low-n instabilities along with confinement enhancement from low magnetic shear. The li near 1 scenario does not depend on ideal-wall stabilization. Improved confinement from strong magnetic shear makes up for the lower pedestal needed to maintain li high. The tradeoff between increasing li and reduced edge pedestal determines the achievable βN (near 4) and fBS (near 0.5). This modeling identifies the necessary upgrades to achieve target scenarios and clarifies the pros and cons of particular scenarios to better inform the development of steady-state fusion. Supported by the US Department of Energy under DE-AC05-00OR22725 & DE-FC02-04ER54698.

Factors affecting the CD34+ cell yields from the second donations of healthy donors: The steady-state lymphocyte count is a good predictive factor.

PubMed

Guo, Zhi-Ping; Wang, Tao; Xu, Lan-Ping; Zhang, Xiao-Hui; Wang, Yu; Huang, Xiao-Jun; Chang, Ying-Jun

2016-12-01

A second allogeneic hematopoietic stem-cell transplantation and donor lymphocyte infusion using cells from the same donor is a therapeutic option in the case of stem-cell graft failure or disease relapse, but little is known about the factors associated with the CD34 + cell yields from second donations. One-hundred healthy donors who underwent a second mobilization treatment and peripheral blood stem-cell (PBSC) collection were studied. For both mobilization processes, 5 µg of granulocyte colony-stimulating factor per kg per day was administered. The blood counts of the donors were monitored during the processes. The second donations from the same donors provided lower apheresis yields than did the initial collections. The number of CD34 + cells collected from normal donors after a second cycle of PBSC mobilization was associated with their steady-state lymphocyte counts and the intertransplantation interval. Female sex negatively affected the CD34 + cell yields. The cutoff value for the steady-state absolute lymphocyte count was 2.055 × 10 9 /L. To harvest greater numbers of CD34 + cells from second collections, male donors and those with intervals of longer than 9 months between donations should be selected. The lymphocyte counts prior to the first donations may predict the content of CD34 + cells in the allografts prepared using the second donations. Copyright © 2016 Elsevier Ltd. All rights reserved.

Intrinsic diffusion sensitivity of the balanced steady-state free precession (bSSFP) imaging sequence.

PubMed

Bär, Sébastien; Weigel, Matthias; von Elverfeldt, Dominik; Hennig, Jürgen; Leupold, Jochen

2015-11-01

The purpose of this work was to analyze the intrinsic diffusion sensitivity of the balanced steady-state free precession (bSSFP) imaging sequence, meaning the observation of diffusion-induced attenuation of the bSSFP steady-state signal due to the imaging gradients. Although these diffusion effects are usually neglected for most clinical gradient systems, such strong gradient systems are employed for high resolution imaging of small animals or MR Microscopy. The impact on the bSSFP signal of the imaging gradients characterized by their b-values was analyzed with simulations and experiments at a 7T animal scanner using a gradient system with maximum gradient amplitude of approx. 700 mT/m. It was found that the readout gradients have a stronger impact on the attenuation than the phase encoding gradients. Also, as the PE gradients are varying with each repetition interval, the diffusion effects induce strong modulations of the bSSFP signal over the sequence repetition cycles depending on the phase encoding gradient table. It is shown that a signal gain can be obtained through a change of flip angle as a new optimal flip angle maximizing the signal can be defined. The dependency of the diffusion effects on relaxation times and b-values were explored with simulations. The attenuation increases with T2. In conclusion, diffusion attenuation of the bSSFP signal becomes significant for high resolution imaging voxel size (roughly < 100 μm) of long T2 substances. Copyright © 2015 John Wiley & Sons, Ltd.

Centric scan SPRITE for spin density imaging of short relaxation time porous materials.

PubMed

Chen, Quan; Halse, Meghan; Balcom, Bruce J

2005-02-01

The single-point ramped imaging with T1 enhancement (SPRITE) imaging technique has proven to be a very robust and flexible method for the study of a wide range of systems with short signal lifetimes. As a pure phase encoding technique, SPRITE is largely immune to image distortions generated by susceptibility variations, chemical shift and paramagnetic impurities. In addition, it avoids the line width restrictions on resolution common to time-based sampling, frequency encoding methods. The standard SPRITE technique is however a longitudinal steady-state imaging method; the image intensity is related to the longitudinal steady state, which not only decreases the signal-to-noise ratio, but also introduces many parameters into the image signal equation. A centric scan strategy for SPRITE removes the longitudinal steady state from the image intensity equation and increases the inherent image intensity. Two centric scan SPRITE methods, that is, Spiral-SPRITE and Conical-SPRITE, with fast acquisition and greatly reduced gradient duty cycle, are outlined. Multiple free induction decay (FID) points may be acquired during SPRITE sampling for signal averaging to increase signal-to-noise ratio or for T2* and spin density mapping without an increase in acquisition time. Experimental results show that most porous sedimentary rock and concrete samples have a single exponential T2* decay due to susceptibility difference-induced field distortion. Inhomogeneous broadening thus dominates, which suggests that spin density imaging can be easily obtained by SPRITE.

Agents' beliefs and economic regimes polarization in interacting markets

NASA Astrophysics Data System (ADS)

Cavalli, F.; Naimzada, A. K.; Pecora, N.; Pireddu, M.

2018-05-01

In the present paper, a model of a market consisting of real and financial interacting sectors is studied. Agents populating the stock market are assumed to be not able to observe the true underlying fundamental, and their beliefs are biased by either optimism or pessimism. Depending on the relevance they give to beliefs, they select the best performing strategy in an evolutionary perspective. The real side of the economy is described within a multiplier-accelerator framework with a nonlinear, bounded investment function. We study the effect of market integration, in particular, of the financialization of the real market. We show that strongly polarized beliefs in an evolutionary framework can introduce multiplicity of steady states, which, consisting in enhanced or depressed levels of income, reflect and reproduce the optimistic or pessimistic nature of the agents' beliefs. The polarization of these steady states, which coexist with an unbiased steady state, positively depends on that of the beliefs and on their relevance. Moreover, with a mixture of analytical and numerical tools, we show that such static characterization is inherited also at the dynamical level, with possibly complex attractors that are characterized by endogenously fluctuating pessimistic and optimistic prices and levels of national income, with the effect of having several coexisting business cycles. This framework, when stochastic perturbations are included, is able to account for stylized facts commonly observed in real financial markets, such as fat tails and excess volatility in the returns distributions, as well as bubbles and crashes for stock prices.

Agents' beliefs and economic regimes polarization in interacting markets.

PubMed

Cavalli, F; Naimzada, A K; Pecora, N; Pireddu, M

2018-05-01

In the present paper, a model of a market consisting of real and financial interacting sectors is studied. Agents populating the stock market are assumed to be not able to observe the true underlying fundamental, and their beliefs are biased by either optimism or pessimism. Depending on the relevance they give to beliefs, they select the best performing strategy in an evolutionary perspective. The real side of the economy is described within a multiplier-accelerator framework with a nonlinear, bounded investment function. We study the effect of market integration, in particular, of the financialization of the real market. We show that strongly polarized beliefs in an evolutionary framework can introduce multiplicity of steady states, which, consisting in enhanced or depressed levels of income, reflect and reproduce the optimistic or pessimistic nature of the agents' beliefs. The polarization of these steady states, which coexist with an unbiased steady state, positively depends on that of the beliefs and on their relevance. Moreover, with a mixture of analytical and numerical tools, we show that such static characterization is inherited also at the dynamical level, with possibly complex attractors that are characterized by endogenously fluctuating pessimistic and optimistic prices and levels of national income, with the effect of having several coexisting business cycles. This framework, when stochastic perturbations are included, is able to account for stylized facts commonly observed in real financial markets, such as fat tails and excess volatility in the returns distributions, as well as bubbles and crashes for stock prices.

Multimode optical fibers: steady state mode exciter.

PubMed

Ikeda, M; Sugimura, A; Ikegami, T

1976-09-01

The steady state mode power distribution of the multimode graded index fiber was measured. A simple and effective steady state mode exciter was fabricated by an etching technique. Its insertion loss was 0.5 dB for an injection laser. Deviation in transmission characteristics of multimode graded index fibers can be avoided by using the steady state mode exciter.

An equation to predict the maximal lactate steady state from ramp-incremental exercise test data in cycling.

PubMed

Iannetta, Danilo; Fontana, Federico Y; Maturana, Felipe Mattioni; Inglis, Erin Calaine; Pogliaghi, Silvia; Keir, Daniel A; Murias, Juan M

2018-05-23

The maximal lactate steady state (MLSS) represents the highest exercise intensity at which an elevated blood lactate concentration ([Lac] b ) is stabilized above resting values. MLSS quantifies the boundary between the heavy-to-very-heavy intensity domains but its determination is not widely performed due to the number of trials required. This study aimed to: (i) develop a mathematical equation capable of predicting MLSS using variables measured during a single ramp-incremental cycling test and (ii) test the accuracy of the optimized mathematical equation. The predictive MLSS equation was determined by stepwise backward regression analysis of twelve independent variables measured in sixty individuals who had previously performed ramp-incremental exercise and in whom MLSS was known (MLSS obs ). Next, twenty-nine different individuals were prospectively recruited to test the accuracy of the equation. These participants performed ramp-incremental exercise to exhaustion and two-to-three 30-min constant-power output cycling bouts with [Lac] b sampled at regular intervals for determination of MLSS obs . Predicted MLSS (MLSS pred ) and MLSS obs in both phases of the study were compared by paired t-test, major-axis regression and Bland-Altman analysis. The predictor variables of MLSS were: respiratory compensation point (Wkg -1 ), peak oxygen uptake (V˙O 2peak ) (mlkg -1 min -1 ) and body mass (kg). MLSS pred was highly correlated with MLSS obs (r=0.93; p<0.01). When this equation was tested on the independent group, MLSS pred was not different from MLSS obs (234±43 vs. 234±44W; SEE 4.8W; r=0.99; p<0.01). These data support the validity of the predictive MLSS equation. We advocate its use as a time-efficient alternative to traditional MLSS testing in cycling. Copyright © 2018 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Cadmium cycling in the water column of the Kuroshio-Oyashio Extension region: Insights from dissolved and particulate isotopic composition

NASA Astrophysics Data System (ADS)

Yang, Shun-Chung; Zhang, Jing; Sohrin, Yoshiki; Ho, Tung-Yuan

2018-07-01

We measured dissolved and particulate Cd isotopic composition in the water column of a meridional transect across the Kuroshio-Oyashio Extension region in a Japanese GEOTRACES cruise to investigate the relative influence of physical and biogeochemical processes on Cd cycling in the Northwestern Pacific Ocean. Located at 30-50°N along 165°E, the transect across the extension region possesses dramatic hydrographic contrast. Cold surface water and a relatively narrow and shallow thermocline characterizes the Oyashio Extension region in contrast to a relatively warm and highly stratified surface water and thermocline in the Kuroshio Extension region. The contrasting hydrographic distinction at the study site provides us with an ideal platform to investigate the spatial variations of Cd isotope fractionation systems in the ocean. Particulate samples demonstrated biologically preferential uptake of light Cd isotopes, and the fractionation effect varied dramatically in the surface water of the two regions, with relatively large fractionation factors in the Oyashio region. Based on the relationship of dissolved Cd concentrations and isotopic composition, we found that a closed system fractionation model can reasonably explain the relationship in the Kuroshio region. However, using dissolved Cd isotopic data, either a closed system or steady-state open system fractionation model may explain the relationship in the surface water of the Oyashio region. Particulate δ114/110Cd data further supports that the surface water of the Oyashio region matches a steady-state open system model more closely. Contrary to the surface water, the distribution of potential density exhibits comparable patterns with Cd elemental and isotopic composition in the thermocline and deep water in the two extension regions, showing that physical processes are the dominant forcing controlling Cd cycling in the deep waters. The results demonstrate that Cd isotope fractionation can match either a closed or open system Rayleigh fractionation model, depending on the relative contribution of physical and biogeochemical processes on its cycling.

System-state and operating condition sensitive control method and apparatus for electric power delivery systems

NASA Technical Reports Server (NTRS)

Burns, III, William Wesley (Inventor); Wilson, Thomas George (Inventor)

1978-01-01

This invention provides a method and apparatus for determining a precise switching sequence for the power switching elements of electric power delivery systems of the on-off switching type and which enables extremely fast transient response, precise regulation and highly stable operation. The control utilizes the values of the power delivery system power handling network components, a desired output characteristic, a system timing parameter, and the externally imposed operating conditions to determine where steady state operations should be in order to yield desired output characteristics for the given system specifications. The actual state of the power delivery system is continuously monitored and compared to a state-space boundary which is derived from the desired equilibrium condition, and from the information obtained from this comparison, the system is moved to the desired equilibrium condition in one cycle of switching control. Since the controller continuously monitors the power delivery system's externally imposed operating conditions, a change in the conditions is immediately sensed and a new equilibrium condition is determined and achieved, again in a single cycle of switching control.

Orbit Transfer Vehicle (OTV) advanced expander cycle engine point design study. Volume 2: Study results

NASA Technical Reports Server (NTRS)

1980-01-01

Detailed computer models of the engine were developed to predict both the steady state and transient operation of the engine system. Mechanical design layout drawings were prepared for the following components: thrust chamber and nozzle; extendible nozzle actuating mechanism and seal; LOX turbopump and boost pump; hydrogen turbopump and boost pump; and the propellant control valves. The necessary heat transfer, stress, fluid flow, dynamic, and performance analyses were performed to support the mechanical design.

Modelling the balance between quiescence and cell death in normal and tumour cell populations.

PubMed

Spinelli, Lorenzo; Torricelli, Alessandro; Ubezio, Paolo; Basse, Britta

2006-08-01

When considering either human adult tissues (in vivo) or cell cultures (in vitro), cell number is regulated by the relationship between quiescent cells, proliferating cells, cell death and other controls of cell cycle duration. By formulating a mathematical description we see that even small alterations of this relationship may cause a non-growing population to start growing with doubling times characteristic of human tumours. Our model consists of two age structured partial differential equations for the proliferating and quiescent cell compartments. Model parameters are death rates from and transition rates between these compartments. The partial differential equations can be solved for the steady-age distributions, giving the distribution of the cells through the cell cycle, dependent on specific model parameter values. Appropriate formulas can then be derived for various population characteristic quantities such as labelling index, proliferation fraction, doubling time and potential doubling time of the cell population. Such characteristic quantities can be estimated experimentally, although with decreasing precision from in vitro, to in vivo experimental systems and to the clinic. The model can be used to investigate the effects of a single alteration of either quiescence or cell death control on the growth of the whole population and the non-trivial dependence of the doubling time and other observable quantities on particular underlying cell cycle scenarios of death and quiescence. The model indicates that tumour evolution in vivo is a sequence of steady-states, each characterised by particular death and quiescence rate functions. We suggest that a key passage of carcinogenesis is a loss of the communication between quiescence, death and cell cycle machineries, causing a defect in their precise, cell cycle dependent relationship.

Illustrating the Steady-State Condition and the Single-Molecule Kinetic Method with the NMDA Receptor

ERIC Educational Resources Information Center

Kosman, Daniel J.

2009-01-01

The steady-state is a fundamental aspect of biochemical pathways in cells; indeed, the concept of steady-state is a definition of life itself. In a simple enzyme kinetic scheme, the steady-state condition is easy to define analytically but experimentally often difficult to capture because of its evanescent quality; the initial, constant velocity…

Steady state and a general scale law of deformation

NASA Astrophysics Data System (ADS)

Huang, Yan

2017-07-01

Steady state deformation has been characterized based on the experimental results for dilute single-phase aluminium alloys. It was found that although characteristic properties such as flow stress and grain size remained constant with time, a continuous loss of grain boundaries occurred as an essential feature at steady state. A physical model, which takes into account the activity of grain boundary dislocations, was developed to describe the kinetics of steady state deformation. According to this model, the steady state as a function of strain rate and temperature defines the limit of the conventional grain size and strength relationship, i.e., the Hall-Petch relation holds when the grain size is larger than that at the steady state, and an inverse Hall-Petch relation takes over if grain size is smaller than the steady state value. The transition between the two relationships relating grain size and strength is a phenomenon that depends on deformation conditions, rather than an intrinsic property as generally perceived. A general scale law of deformation is established accordingly.

An Irreversible Constitutive Law for Modeling the Delamination Process using Interface Elements

NASA Technical Reports Server (NTRS)

Goyal, Vinay K.; Johnson, Eric R.; Davila, Carlos G.; Jaunky, Navin; Ambur, Damodar (Technical Monitor)

2002-01-01

An irreversible constitutive law is postulated for the formulation of interface elements to predict initiation and progression of delamination in composite structures. An exponential function is used for the constitutive law such that it satisfies a multi-axial stress criterion for the onset of delamination, and satisfies a mixed mode fracture criterion for the progression of delamination. A damage parameter is included to prevent the restoration of the previous cohesive state between the interfacial surfaces. To demonstrate the irreversibility capability of the constitutive law, steady-state crack growth is simulated for quasi-static loading-unloading cycle of various fracture test specimens.

An Irreversible Constitutive Law for Modeling the Delamination Process Using Interface Elements

NASA Technical Reports Server (NTRS)

Goyal, Vinay K.; Johnson, Eric R.; Davila, Carlos G.; Jaunky, Navin; Bushnell, Dennis M. (Technical Monitor)

2002-01-01

An irreversible constitutive law is postulated for the formulation of interface elements to predict initiation and progression of delamination in composite structures. An exponential function is used for the constitutive law such that it satisfies a multi-axial stress criterion for the onset of delamination, and satisfies a mixed mode fracture criterion for the progression of delamination. A damage parameter is included to prevent the restoration of the previous cohesive state between the interfacial surfaces. To demonstrate the irreversibility capability of the constitutive law, steady-state crack growth is simulated for quasi-static loading-unloading cycle of various fracture test specimens.

Phased array ghost elimination (PAGE) for segmented SSFP imaging with interrupted steady-state.

PubMed

Kellman, Peter; Guttman, Michael A; Herzka, Daniel A; McVeigh, Elliot R

2002-12-01

Steady-state free precession (SSFP) has recently proven to be valuable for cardiac imaging due to its high signal-to-noise ratio and blood-myocardium contrast. Data acquired using ECG-triggered, segmented sequences during the approach to steady-state, or return to steady-state after interruption, may have ghost artifacts due to periodic k-space distortion. Schemes involving several preparatory RF pulses have been proposed to restore steady-state, but these consume imaging time during early systole. Alternatively, the phased-array ghost elimination (PAGE) method may be used to remove ghost artifacts from the first several frames. PAGE was demonstrated for cardiac cine SSFP imaging with interrupted steady-state using a simple alpha/2 magnetization preparation and storage scheme and a spatial tagging preparation.

Identification of critical equipment and determination of operational limits in helium refrigerators under pulsed heat load

NASA Astrophysics Data System (ADS)

Dutta, Rohan; Ghosh, Parthasarathi; Chowdhury, Kanchan

2014-01-01

Large-scale helium refrigerators are subjected to pulsed heat load from tokamaks. As these plants are designed for constant heat loads, operation under such varying load may lead to instability in plants thereby tripping the operation of different equipment. To understand the behavior of the plant subjected to pulsed heat load, an existing plant of 120 W at 4.2 K and another large-scale plant of 18 kW at 4.2 K have been analyzed using a commercial process simulator Aspen Hysys®. A similar heat load characteristic has been applied in both quasi steady state and dynamic analysis to determine critical stages and equipment of these plants from operational point of view. It has been found that the coldest part of both the cycles consisting JT-stage and its preceding reverse Brayton stage are the most affected stages of the cycles. Further analysis of the above stages and constituting equipment revealed limits of operation with respect to variation of return stream flow rate resulted from such heat load variations. The observations on the outcome of the analysis can be used for devising techniques for steady operation of the plants subjected to pulsed heat load.

Steady state or non-steady state? Identifying driving mechanisms of oxygen isotope signatures of leaf transpiration in functionally distinct plant species

NASA Astrophysics Data System (ADS)

Dubbert, Maren; Kübert, Angelika; Cuntz, Matthias; Werner, Christiane

2015-04-01

Isotope techniques are widely applied in ecosystem studies. For example, isoflux models are used to separate soil evaporation from transpiration in ecosystems. These models often assume that plant transpiration occurs at isotopic steady state, i.e. that the transpired water shows the same isotopic signature as the source water. Yet, several studies found that transpiration did not occur at isotopic steady state, under both controlled and field conditions. Here we focused on identifying the internal and external factors which drive the isotopic signature of leaf transpiration. Using cavity ring-down spectroscopy (CRDS), the effect of both environmental variables and leaf physiological traits on δ18OT was investigated under controlled conditions. Six plant species with distinct leaf physiological traits were exposed to step changes in relative air humidity (RH), their response in δ18OT and gas exchange parameters and their leaf physiological traits were assessed. Moreover, two functionally distinct plant types (tree, i.e. Quercus suber, and grassland) of a semi-arid Mediterranean oak-woodland where observed under natural conditions throughout an entire growth period in the field. The species differed substantially in their leaf physiological traits and their turn-over times of leaf water. They could be grouped in species with fast (<60 min.), intermediate (ca. 120 min.) and slow (>240 min.) turn-over times, mostly due to differences in stomatal conductance, leaf water content or a combination of both. Changes in RH caused an immediate response in δ18OT, which were similarly strong in all species, while leaf physiological traits affected the subsequent response in δ18OT. The turn-over time of leaf water determined the speed of return to the isotopic steady or a stable δ18OT value (Dubbert & Kübert et al., in prep.). Under natural conditions, changes in environmental conditions over the diurnal cycle had a huge impact on the diurnal development of δ18OT in both observed plant functional types. However, in accordance with our findings in the lab, species specific differences in the leaf water turn over time, significantly influenced the amount of time plants transpired at non-steady state during the day (Dubbert et al., 2013, 2014). Our results emphasize the significance of considering isotopic non-steady state of transpiration and specifically to account for the specific differences of plant species resulting from distinct physiological traits of their leaves when applying isoflux models in ecosystem studies. Dubbert, M; Cuntz, M; Piayda, A; Maguas, C; Werner, C: Partitioning evapotranspiration - Testing the Craig and Gordon model with field measurements of oxygen isotope ratios of evaporative fluxes. J Hydrol (2013) Dubbert, M; Piayda, A; Cuntz, M; Correia, AC; Costa e Silva, F; Pereira, JS; Werner, C: Stable oxygen isotope and flux partitioning demonstrates understory of an oak savanna contributes up to half of ecosystem carbon and water exchange, Frontiers in Plant Science (2014a)

Conformational state interactions provide clues to the pharmacochaperone potential of serotonin transporter partial substrates

PubMed Central

Bhat, Shreyas; Hasenhuetl, Peter S.; Kasture, Ameya; El-Kasaby, Ali; Baumann, Michael H.; Blough, Bruce E.; Sucic, Sonja; Sandtner, Walter; Freissmuth, Michael

2017-01-01

Point mutations in SLC6 transporters cause misfolding, which can be remedied by pharmacochaperones. The serotonin transporter (SERT/SLC6A4) has a rich pharmacology including inhibitors, releasers (amphetamines, which promote the exchange mode), and more recently, discovered partial substrates. We hypothesized that partial substrates trapped the transporter in one or several states of the transport cycle. This conformational trapping may also be conducive to folding. We selected naphthylpropane-2-amines of the phenethylamine library (PAL) including the partial substrate PAL1045 and its congeners PAL287 and PAL1046. We analyzed their impact on the transport cycle of SERT by biochemical approaches and by electrophysiological recordings; substrate-induced peak currents and steady-state currents monitored the translocation of substrate and co-substrate Na+ across the lipid bilayer and the transport cycle, respectively. These experiments showed that PAL1045 and its congeners bound with different affinities (ranging from nm to μm) to various conformational intermediates of SERT during the transport cycle. Consistent with the working hypothesis, PAL1045 was the most efficacious compound in restoring surface expression and transport activity to the folding-deficient mutant SERT-601PG602-AA. These experiments provide a proof-of-principle for a rational search for pharmacochaperones, which may be useful to restore function to clinically relevant folding-deficient transporter mutants. PMID:28842491

Control of Growth Rate by Initial Substrate Concentration at Values Below Maximum Rate

PubMed Central

Gaudy, Anthony F.; Obayashi, Alan; Gaudy, Elizabeth T.

1971-01-01

The hyperbolic relationship between specific growth rate, μ, and substrate concentration, proposed by Monod and used since as the basis for the theory of steady-state growth in continuous-flow systems, was tested experimentally in batch cultures. Use of a Flavobacterium sp. exhibiting a high saturation constant for growth in glucose minimal medium allowed direct measurement of growth rate and substrate concentration throughout the growth cycle in medium containing a rate-limiting initial concentration of glucose. Specific growth rates were also measured for a wide range of initial glucose concentrations. A plot of specific growth rate versus initial substrate concentration was found to fit the hyperbolic equation. However, the instantaneous relationship between specific growth rate and substrate concentration during growth, which is stated by the equation, was not observed. Well defined exponential growth phases were developed at initial substrate concentrations below that required for support of the maximum exponential growth rate and a constant doubling time was maintained until 50% of the substrate had been used. It is suggested that the external substrate concentration initially present “sets” the specific growth rate by establishing a steady-state internal concentration of substrate, possibly through control of the number of permeation sites. PMID:5137579

Bioaccumulation factors and the steady state assumption for cesium isotopes in aquatic foodwebs near nuclear facilities.

PubMed

Rowan, D J

2013-07-01

Steady state approaches, such as transfer coefficients or bioaccumulation factors, are commonly used to model the bioaccumulation of (137)Cs in aquatic foodwebs from routine operations and releases from nuclear generating stations and other nuclear facilities. Routine releases from nuclear generating stations and facilities, however, often consist of pulses as liquid waste is stored, analyzed to ensure regulatory compliance and then released. The effect of repeated pulse releases on the steady state assumption inherent in the bioaccumulation factor approach has not been evaluated. In this study, I examine the steady state assumption for aquatic biota by analyzing data for two cesium isotopes in the same biota, one isotope in steady state (stable (133)Cs) from geologic sources and the other released in pulses ((137)Cs) from reactor operations. I also compare (137)Cs bioaccumulation factors for similar upstream populations from the same system exposed solely to weapon test (137)Cs, and assumed to be in steady state. The steady state assumption appears to be valid for small organisms at lower trophic levels (zooplankton, rainbow smelt and 0+ yellow perch) but not for older and larger fish at higher trophic levels (walleye). Attempts to account for previous exposure and retention through a biokinetics approach had a similar effect on steady state, upstream and non-steady state, downstream populations of walleye, but were ineffective in explaining the more or less constant deviation between fish with steady state exposures and non-steady state exposures of about 2-fold for all age classes of walleye. These results suggest that for large, piscivorous fish, repeated exposure to short duration, pulse releases leads to much higher (137)Cs BAFs than expected from (133)Cs BAFs for the same fish or (137)Cs BAFs for similar populations in the same system not impacted by reactor releases. These results suggest that the steady state approach should be used with caution in any situation where reactor releases are episodic or pulse in nature, even if the magnitude of these releases is small. Copyright © 2012. Published by Elsevier Ltd.

Steady shape analysis of tomographic pumping tests for characterization of aquifer heterogeneities

USGS Publications Warehouse

Bohling, Geoffrey C.; Zhan, Xiaoyong; Butler, James J.; Zheng, Li

2002-01-01

Hydraulic tomography, a procedure involving the performance of a suite of pumping tests in a tomographic format, provides information about variations in hydraulic conductivity at a level of detail not obtainable with traditional well tests. However, analysis of transient data from such a suite of pumping tests represents a substantial computational burden. Although steady state responses can be analyzed to reduce this computational burden significantly, the time required to reach steady state will often be too long for practical applications of the tomography concept. In addition, uncertainty regarding the mechanisms driving the system to steady state can propagate to adversely impact the resulting hydraulic conductivity estimates. These disadvantages of a steady state analysis can be overcome by exploiting the simplifications possible under the steady shape flow regime. At steady shape conditions, drawdown varies with time but the hydraulic gradient does not. Thus transient data can be analyzed with the computational efficiency of a steady state model. In this study, we demonstrate the value of the steady shape concept for inversion of hydraulic tomography data and investigate its robustness with respect to improperly specified boundary conditions.

Thermal Non-equilibrium Revealed by Periodic Pulses of Random Amplitudes in Solar Coronal Loops

NASA Astrophysics Data System (ADS)

Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.; Solomon, J.

2016-08-01

We recently detected variations in extreme ultraviolet intensity in coronal loops repeating with periods of several hours. Models of loops including stratified and quasi-steady heating predict the development of a state of thermal non-equilibrium (TNE): cycles of evaporative upflows at the footpoints followed by falling condensations at the apex. Based on Fourier and wavelet analysis, we demonstrate that the observed periodic signals are indeed not signatures of vibrational modes. Instead, superimposed on the power law expected from the stochastic background emission, the power spectra of the time series exhibit the discrete harmonics and continua expected from periodic trains of pulses of random amplitudes. These characteristics reinforce our earlier interpretation of these pulsations as being aborted TNE cycles.

Thermal Non-Equilibrium Revealed by Periodic Pulses of Random Amplitudes in Solar Coronal Loops

NASA Astrophysics Data System (ADS)

Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.; Solomon, J.

2016-10-01

We recently detected variations in extreme ultraviolet intensity in coronal loops repeating with periods of several hours. Models of loops including stratified and quasi-steady heating predict the development of a state of thermal non-equilibrium (TNE): cycles of evaporative upflows at the footpoints followed by falling condensations at the apex. Based on Fourier and wavelet analysis, we demonstrate that the observed periodic signals are indeed not signatures of vibrational modes. Instead, superimposed on the power law expected from the stochastic background emission, the power spectra of the time series exhibit the discrete harmonics and continua expected from periodic trains of pulses of random amplitudes. These characteristics reinforce our earlier interpretation of these pulsations as being aborted TNE cycles.

Performance and Operational Characteristics for a Dual Brayton Space Power System With Common Gas Inventory

NASA Technical Reports Server (NTRS)

Johnson, Paul K.; Mason, Lee S.

2006-01-01

This paper provides an analytical evaluation on the operation and performance of a dual Brayton common gas system. The NASA Glenn Research Center in-house computer program Closed Cycle System Simulation (CCSS) was used to construct a model of two identical 50 kWe-class recuperated closed-Brayton-cycle (CBC) power conversion units that share a common gas inventory and single heat source. As operating conditions for each CBC change, the total gas inventory is redistributed between the two units and overall system performance is affected. Several steady-state off-design operating points were analyzed by varying turbine inlet temperature and turbo-alternator shaft rotational speed to investigate the interaction of the two units.

Ceramic thermal-barrier coatings for cooled turbines

NASA Technical Reports Server (NTRS)

Liebert, C. H.; Stepka, F. S.

1976-01-01

Coating systems consisting of a plasma sprayed layer of zirconia stabilized with either yttria, magnesia or calcia over a thin alloy bond coat have been developed, their potential was analyzed and their durability and benefits evaluated in a turbojet engine. The coatings on air cooled rotating blades were in good condition after completing as many as 500 two-minute cycles of engine operation between full power at a gas temperature of 1644 K and flameout, or as much as 150 hours of steady state operation on cooled vanes and blades at gas temperatures as high as 1644 K with 35 start and stop cycles. On the basis of durability and processing cost, the yttria stabilized zirconia was considered the best of the three coatings investigated.

An extended life and performance test of a low-power arcjet

NASA Technical Reports Server (NTRS)

Curran, Francis M.; Haag, Thomas W.

1988-01-01

An automated, cyclic life test was performed to demonstrate the reliability and endurance of a low power dc cycle arcjet thruster. Over 1000 hr and 500 on-off cycles were accumulated which would represent the requirements for about 15 years of on-orbit lifetime. A hydrogen/nitrogen propellant mixture was used to simulate decomposed hydrazine propellant and the power level was nominally 1.2 kW after the burn-in period. The arcjet operated in a very repeatable fashion from cycle to cycle. The steady state voltage increased by approximately 6 V over the first 300 hr, and then by only 3 V through the remainder of the test. Thrust measurements taken before, during, and after the test verified that the thruster performed in a consistent fashion throughout the tests at a specific impulse of 450 to 460 sec. Post-test component evaluation revealed limited erosion on both the anode and cathode. Other thruster components, including graphite seals, appeared undamaged.

On the need of mode interpolation for data-driven Galerkin models of a transient flow around a sphere

NASA Astrophysics Data System (ADS)

Stankiewicz, Witold; Morzyński, Marek; Kotecki, Krzysztof; Noack, Bernd R.

2017-04-01

We present a low-dimensional Galerkin model with state-dependent modes capturing linear and nonlinear dynamics. Departure point is a direct numerical simulation of the three-dimensional incompressible flow around a sphere at Reynolds numbers 400. This solution starts near the unstable steady Navier-Stokes solution and converges to a periodic limit cycle. The investigated Galerkin models are based on the dynamic mode decomposition (DMD) and derive the dynamical system from first principles, the Navier-Stokes equations. A DMD model with training data from the initial linear transient fails to predict the limit cycle. Conversely, a model from limit-cycle data underpredicts the initial growth rate roughly by a factor 5. Key enablers for uniform accuracy throughout the transient are a continuous mode interpolation between both oscillatory fluctuations and the addition of a shift mode. This interpolated model is shown to capture both the transient growth of the oscillation and the limit cycle.

The role of water ice clouds in the Martian hydrologic cycle

NASA Technical Reports Server (NTRS)

James, Philip B.

1990-01-01

A one-dimensional model for the seasonal cycle of water on Mars has been used to investigate the direction of the net annual transport of water on the planet and to study the possible role of water ice clouds, which are included as an independent phase in addition to ground ice and water vapor, in the cycle. The calculated seasonal and spatial patterns of occurrence of water ice clouds are qualitatively similar to the observed polar hoods, suggesting that these polar clouds are, in fact, an important component of water cycle. A residual dry ice in the south acts as a cold trap which, in the absence of sources other than the caps, will ultimately attract the water ice from the north cap; however, in the presence of a source of water in northern midlatitudes during spring, it is possible that the observed distribution of vapor and ice can be in a steady state even if a residual CO2 cap is a permanent feature of the system.

Investigation of the effect of ambient conditions on the performance of solid desiccant cooling cycles

NASA Astrophysics Data System (ADS)

Panaras, G.; Mathioulakis, E.; Belessiotis, V.

2018-01-01

The operation of desiccant air-conditioning systems is characterised by processes implemented to the moist air of the environment; it is, thus, expected to be affected by ambient conditions. The present work aims at quantifying this influence on the basis of an easy-to-implement, steady-state model of the system, presenting an efficiency factors approach, which has been experimentally validated. The analysis examines the behaviour of the ventilation and the recirculation cycles, which constitute the marginal cases regarding the achieved values of the outside air fraction, given the ambient conditions, the desired regeneration temperature and the efficiency of the involved components. The fact of a desiccant cycle undergoing a set of changing ambient conditions by its actual operation is also considered in the analysis. The results provide useful information for the selection of the optimum configuration to the designer of a desiccant air-conditioning system.

A numerical study of latent thermal energy storage in a phase change material/carbon panel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mekaddem, Najoua, E-mail: mekaddem.najoua@gmail.com; Ali, Samia Ben, E-mail: samia.benali@enig.rnu.tn; Hannachi, Ahmed, E-mail: ahmed.hannachi@enig.rnu.tn

2016-07-25

To reduce the energetic dependence of building, it has become necessary to explore and develop new materials promoting energy conservation. Because of their high storage capacity, phase change materials (PCMs) are efficient to store thermal energy. In this paper, a 3D model was studied for simulation of energy storing cycles to predict the performances of PCM loaded panels. Carbon was used as supporting material for the PCM. The simulation was based on the enthalpy method using Ansys Fluent software. The panel was exposed to a daily heat flow including the effects of convection and radiation. The results show that themore » temperature decreased of approximately 2.5°C with a time shift about 2 hours. The steady state was reached after four cycles. Thus, after four cycles the PCM showed its effects on the temperature conditioning.« less

Advanced Shock Position Control for Mode Transition in a Turbine Based Combined Cycle Engine Inlet Model

NASA Technical Reports Server (NTRS)

Csank, Jeffrey T.; Stueber, Thomas J.

2013-01-01

A dual flow-path inlet system is being tested to evaluate methodologies for a Turbine Based Combined Cycle (TBCC) propulsion system to perform a controlled inlet mode transition. Prior to experimental testing, simulation models are used to test, debug, and validate potential control algorithms. One simulation package being used for testing is the High Mach Transient Engine Cycle Code simulation, known as HiTECC. This paper discusses the closed loop control system, which utilizes a shock location sensor to improve inlet performance and operability. Even though the shock location feedback has a coarse resolution, the feedback allows for a reduction in steady state error and, in some cases, better performance than with previous proposed pressure ratio based methods. This paper demonstrates the design and benefit with the implementation of a proportional-integral controller, an H-Infinity based controller, and a disturbance observer based controller.

Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens.

PubMed

Yeo, Wee Kian; Paton, Carl D; Garnham, Andrew P; Burke, Louise M; Carey, Andrew L; Hawley, John A

2008-11-01

We determined the effects of a cycle training program in which selected sessions were performed with low muscle glycogen content on training capacity and subsequent endurance performance, whole body substrate oxidation during submaximal exercise, and several mitochondrial enzymes and signaling proteins with putative roles in promoting training adaptation. Seven endurance-trained cyclists/triathletes trained daily (High) alternating between 100-min steady-state aerobic rides (AT) one day, followed by a high-intensity interval training session (HIT; 8 x 5 min at maximum self-selected effort) the next day. Another seven subjects trained twice every second day (Low), first undertaking AT, then 1-2 h later, the HIT. These training schedules were maintained for 3 wk. Forty-eight hours before and after the first and last training sessions, all subjects completed a 60-min steady-state ride (60SS) followed by a 60-min performance trial. Muscle biopsies were taken before and after 60SS, and rates of substrate oxidation were determined throughout this ride. Resting muscle glycogen concentration (412 +/- 51 vs. 577 +/- 34 micromol/g dry wt), rates of whole body fat oxidation during 60SS (1,261 +/- 247 vs. 1,698 +/- 174 micromol.kg(-1).60 min(-1)), the maximal activities of citrate synthase (45 +/- 2 vs. 54 +/- 1 mmol.kg dry wt(-1).min(-1)), and beta-hydroxyacyl-CoA-dehydrogenase (18 +/- 2 vs. 23 +/- 2 mmol.kg dry wt(-1).min(-1)) along with the total protein content of cytochrome c oxidase subunit IV were increased only in Low (all P < 0.05). Mitochondrial DNA content and peroxisome proliferator-activated receptor-gamma coactivator-1alpha protein levels were unchanged in both groups after training. Cycling performance improved by approximately 10% in both Low and High. We conclude that compared with training daily, training twice every second day compromised high-intensity training capacity. While selected markers of training adaptation were enhanced with twice a day training, the performance of a 1-h time trial undertaken after a 60-min steady-state ride was similar after once daily or twice every second day training programs.

ODECS -- A computer code for the optimal design of S.I. engine control strategies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arsie, I.; Pianese, C.; Rizzo, G.

1996-09-01

The computer code ODECS (Optimal Design of Engine Control Strategies) for the design of Spark Ignition engine control strategies is presented. This code has been developed starting from the author`s activity in this field, availing of some original contributions about engine stochastic optimization and dynamical models. This code has a modular structure and is composed of a user interface for the definition, the execution and the analysis of different computations performed with 4 independent modules. These modules allow the following calculations: (1) definition of the engine mathematical model from steady-state experimental data; (2) engine cycle test trajectory corresponding to amore » vehicle transient simulation test such as ECE15 or FTP drive test schedule; (3) evaluation of the optimal engine control maps with a steady-state approach; (4) engine dynamic cycle simulation and optimization of static control maps and/or dynamic compensation strategies, taking into account dynamical effects due to the unsteady fluxes of air and fuel and the influences of combustion chamber wall thermal inertia on fuel consumption and emissions. Moreover, in the last two modules it is possible to account for errors generated by a non-deterministic behavior of sensors and actuators and the related influences on global engine performances, and compute robust strategies, less sensitive to stochastic effects. In the paper the four models are described together with significant results corresponding to the simulation and the calculation of optimal control strategies for dynamic transient tests.« less

SM-1 REACTOR VESSEL COVER AND FLANGE STRESS ANALYSIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sayre, M.F.

1962-02-19

The maximum stress calculated for the SMl-1 reactor vessel closure studs occurs during operation at full power. This value is 27,180 psi of which 19,800 psi is tension and 7380 psi bending. This stress does not include a stress concentration factor for effect of threads. It was eonservatively assumed the studs were initially tightened to a code allowable stress of 20,000 psi as specified in the ASME Code rather than the lesser stress obtained by the normal operating procedure. The maximum calculated stress occurs at the outside surface of the cover where the stress ranges from 318 psi in tensionmore » to 90,660 psi in compression. The alternating stress is 50,000 psi. According to the Navy Code for a stress range of 50,000 psi, the eover material ean safely undergo a maximum of 1600 cycles. It was estimated that the SM-1 will go through approximately 000 startup and shutdown cycles during a 20-yr life period, so the calculated stress is regarded as safe. For a transient eondition of 30 deg F/hr during heat-up, approximate temperature differences between the inside and outside surfaces of the cover were obtained. Temperature differentials between the inside and outside surfaces of the cover are increased by roughly 10%; above the steady state condition. More exact calculations of the transient stresses did not appear necessary siuce they would be not more than 10% greater than the steady state thermal stress. (auth)« less

Oxidation of [U-13 C]glucose in the human brain at 7T under steady state conditions.

PubMed

Cheshkov, Sergey; Dimitrov, Ivan E; Jakkamsetti, Vikram; Good, Levi; Kelly, Dorothy; Rajasekaran, Karthik; DeBerardinis, Ralph J; Pascual, Juan M; Sherry, A Dean; Malloy, Craig R

2017-12-01

Disorders of brain energy metabolism and neurotransmitter recycling have been implicated in multiple neurological conditions. 13 C magnetic resonance spectroscopy ( 13 C MRS) during intravenous administration of 13 C-labeled compounds has been used to measure turnover rates of brain metabolites. This approach, however, requires prolonged infusion inside the magnet. Proton decoupling is typically required but may be difficult to implement with standard equipment. We examined an alternative approach to monitor glucose metabolism in the human brain. 13 C-enriched glucose was infused in healthy subjects outside the magnet to a steady-state level of 13 C enrichment. Subsequently, the subjects were scanned at 7T for 60 min without 1 H decoupling. Metabolic modeling was used to calculate anaplerosis. Biomarkers of energy metabolism and anaplerosis were detected. The glutamate C5 doublet provided information about glucose-derived acetyl-coenzyme A flux into the tricarboxylic acid (TCA) cycle via pyruvate dehydrogenase, and the bicarbonate signal reflected overall TCA cycle activity. The glutamate C1/C5 ratio is sensitive to anaplerosis. Brain 13 C MRS at 7T provides information about glucose oxidation and anaplerosis without the need of prolonged 13 C infusions inside the scanner and without technical challenges of 1 H decoupling, making it a feasible approach for clinical research. Magn Reson Med 78:2065-2071, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Modeled Seasonal Variations of Firn Density Induced by Steady State Surface Air Temperature Cycle

NASA Technical Reports Server (NTRS)

Jun, Li; Zwally, H. Jay; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Seasonal variations of firn density in ice-sheet firn layers have been attributed to variations in deposition processes or other processes within the upper firn. A recent high-resolution (mm scale) density profile, measured along a 181 m core from Antarctica, showed small-scale density variations with a clear seasonal cycle that apparently was not-related to seasonal variations in deposition or known near-surface processes (Gerland and others 1999). A recent model of surface elevation changes (Zwally and Li, submitted) produced a seasonal variation in firn densification, and explained the seasonal surface elevation changes observed by satellite radar altimeters. In this study, we apply our 1-D time-dependent numerical model of firn densification that includes a temperature-dependent formulation of firn densification based on laboratory measurements of grain growth. The model is driven by a steady-state seasonal surface temperature and a constant accumulation rate appropriate for the measured Antarctic ice core. The modeled seasonal variations in firn density show that the layers of snow deposited during spring to mid-summer with the highest temperature history compress to the highest density, and the layers deposited during later summer to autumn with the lowest temperature history compress to the lowest density. The initial amplitude of the seasonal difference of about 0.13 reduces to about 0.09 in five years and asymptotically to 0.92 at depth, which is consistent with the core measurements.

Computational multiple steady states for enzymatic esterification of ethanol and oleic acid in an isothermal CSTR.

PubMed

Ho, Pang-Yen; Chuang, Guo-Syong; Chao, An-Chong; Li, Hsing-Ya

2005-05-01

The capacity of complex biochemical reaction networks (consisting of 11 coupled non-linear ordinary differential equations) to show multiple steady states, was investigated. The system involved esterification of ethanol and oleic acid by lipase in an isothermal continuous stirred tank reactor (CSTR). The Deficiency One Algorithm and the Subnetwork Analysis were applied to determine the steady state multiplicity. A set of rate constants and two corresponding steady states are computed. The phenomena of bistability, hysteresis and bifurcation are discussed. Moreover, the capacity of steady state multiplicity is extended to the family of the studied reaction networks.

Quasispecies in population of compositional assemblies.

PubMed

Gross, Renan; Fouxon, Itzhak; Lancet, Doron; Markovitch, Omer

2014-12-30

The quasispecies model refers to information carriers that undergo self-replication with errors. A quasispecies is a steady-state population of biopolymer sequence variants generated by mutations from a master sequence. A quasispecies error threshold is a minimal replication accuracy below which the population structure breaks down. Theory and experimentation of this model often refer to biopolymers, e.g. RNA molecules or viral genomes, while its prebiotic context is often associated with an RNA world scenario. Here, we study the possibility that compositional entities which code for compositional information, intrinsically different from biopolymers coding for sequential information, could show quasispecies dynamics. We employed a chemistry-based model, graded autocatalysis replication domain (GARD), which simulates the network dynamics within compositional molecular assemblies. In GARD, a compotype represents a population of similar assemblies that constitute a quasi-stationary state in compositional space. A compotype's center-of-mass is found to be analogous to a master sequence for a sequential quasispecies. Using single-cycle GARD dynamics, we measured the quasispecies transition matrix (Q) for the probabilities of transition from one center-of-mass Euclidean distance to another. Similarly, the quasispecies' growth rate vector (A) was obtained. This allowed computing a steady state distribution of distances to the center of mass, as derived from the quasispecies equation. In parallel, a steady state distribution was obtained via the GARD equation kinetics. Rewardingly, a significant correlation was observed between the distributions obtained by these two methods. This was only seen for distances to the compotype center-of-mass, and not to randomly selected compositions. A similar correspondence was found when comparing the quasispecies time dependent dynamics towards steady state. Further, changing the error rate by modifying basal assembly joining rate of GARD kinetics was found to display an error catastrophe, similar to the standard quasispecies model. Additional augmentation of compositional mutations leads to the complete disappearance of the master-like composition. Our results show that compositional assemblies, as simulated by the GARD formalism, portray significant attributes of quasispecies dynamics. This expands the applicability of the quasispecies model beyond sequence-based entities, and potentially enhances validity of GARD as a model for prebiotic evolution.

An Intuitive Approach to Steady-State Kinetics.

ERIC Educational Resources Information Center

Raines, Ronald T.; Hansen, David E.

1988-01-01

Attempts to provide an intuitive understanding of steady state kinetics. Discusses the meaning of steady state and uses free energy profiles to illustrate and follow complex kinetic and thermodynamic relationships. Provides examples with explanations. (MVL)

Effect of flaw size and temperature on the matrix cracking behavior of a brittle ceramic matrix composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anandakumar, U.; Webb, J.E.; Singh, R.N.

The matrix cracking behavior of a zircon matrix - uniaxial SCS 6 fiber composite was studied as a function of initial flaw size and temperature. The composites were fabricated by a tape casting and hot pressing technique. Surface flaws of controlled size were introduced using a vicker`s indenter. The composite samples were tested in three point flexure at three different temperatures to study the non steady state and steady state matrix cracking behavior. The composite samples exhibited steady state and non steady matrix cracking behavior at all temperatures. The steady state matrix cracking stress and steady state crack size increasedmore » with increasing temperature. The results of the study correlated well with the results predicted by the matrix cracking models.« less

Differences between automatically detected and steady-state fractional flow reserve.

PubMed

Härle, Tobias; Meyer, Sven; Vahldiek, Felix; Elsässer, Albrecht

2016-02-01

Measurement of fractional flow reserve (FFR) has become a standard diagnostic tool in the catheterization laboratory. FFR evaluation studies were based on pressure recordings during steady-state maximum hyperemia. Commercially available computer systems detect the lowest Pd/Pa ratio automatically, which might not always be measured during steady-state hyperemia. We sought to compare the automatically detected FFR and true steady-state FFR. Pressure measurement traces of 105 coronary lesions from 77 patients with intermediate coronary lesions or multivessel disease were reviewed. In all patients, hyperemia had been achieved by intravenous adenosine administration using a dosage of 140 µg/kg/min. In 42 lesions (40%) automatically detected FFR was lower than true steady-state FFR. Mean bias was 0.009 (standard deviation 0.015, limits of agreement -0.02, 0.037). In 4 lesions (3.8%) both methods lead to different treatment recommendations, in all 4 cases instantaneous wave-free ratio confirmed steady-state FFR. Automatically detected FFR was slightly lower than steady-state FFR in more than one-third of cases. Consequently, interpretation of automatically detected FFR values closely below the cutoff value requires special attention.

Finite volume method and multigrid acceleration in modelling of rapid crack propagation in full-scale pipe test

NASA Astrophysics Data System (ADS)

Ivankovic, A.; Muzaferija, S.; Demirdzic, I.

1997-07-01

Rapid Crack Propagation (RCP) along pressurised plastic pipes is by far the most dangerous pipe failure mode. Despite the economic benefits offered by increasing pipe size and operating pressure, both strategies increase the risk and the potential consequences of RCP. It is therefore extremely important to account for RCP in establishing the safe operational conditions. Combined experimental-numerical study is the only reliable approach of addressing the problem, and extensive research is undertaken by various fracture groups (e.g. Southwest Research Institute - USA, Imperial College - UK). This paper presents numerical results from finite volume modelling of full-scale test on medium density polyethylene gas pressurised pipes. The crack speed and pressure profile are prescribed in the analysis. Both steady-state and transient RCPs are considered, and the comparison between the two shown. The steady-state results are efficiently achieved employing a full multigrid acceleration technique, where sets of progressively finer grids are used in V-cycles. Also, the effect of inelastic behaviour of polyethylene on RCP results is demonstrated.

Dynamic Characteristics of a Simple Brayton Cryocycle

NASA Astrophysics Data System (ADS)

Kutzschbach, A.; Kauschke, M.; Haberstroh, Ch.; Quack, H.

2006-04-01

The goal of the overall program is to develop a dynamic numerical model of helium refrigerators and the associated cooling systems based on commercial simulation software. The aim is to give system designers a tool to search for optimum control strategies during the construction phase of the refrigerator with the help of a plant "simulator". In a first step, a simple Brayton refrigerator has been investigated, which consists of a compressor, an after-cooler, a counter-current heat exchanger, a turboexpander and a heat source. Operating modes are "refrigeration" and "liquefaction". Whereas for the steady state design only component efficiencies are needed and mass and energy balances have to be calculated, for the dynamic calculation one needs also the thermal masses and the helium inventory. Transient mass and energy balances have to be formulated for many small elements and then solved simultaneously for all elements. Starting point of the simulation of the Brayton cycle is the steady state operation at design conditions. The response of the system to step and cyclic changes of the refrigeration or liquefaction rate are calculated and characterized.

c-Myb is required for progenitor cell homeostasis in colonic crypts

PubMed Central

Malaterre, Jordane; Carpinelli, Marina; Ernst, Matthias; Alexander, Warren; Cooke, Michael; Sutton, Susan; Dworkin, Sebastian; Heath, Joan K.; Frampton, Jon; McArthur, Grant; Clevers, Hans; Hilton, Douglas; Mantamadiotis, Theo; Ramsay, Robert G.

2007-01-01

The colonic crypt is the functional unit of the colon mucosa with a central role in ion and water reabsorption. Under steady-state conditions, the distal colonic crypt harbors a single stem cell at its base that gives rise to highly proliferative progenitor cells that differentiate into columnar, goblet, and endocrine cells. The role of c-Myb in crypt homeostasis has not been elucidated. Here we have studied three genetically distinct hypomorphic c-myb mutant mouse strains, all of which show reduced colonic crypt size. The mutations target the key domains of the transcription factor: the DNA binding, transactivation, and negative regulatory domains. In vivo proliferation and cell cycle marker studies suggest that these mice have a progenitor cell proliferation defect mediated in part by reduced Cyclin E1 expression. To independently assess the extent to which c-myb is required for colonic crypt homeostasis we also generated a novel tissue-specific mouse model to allow the deletion of c-myb in adult colon, and using these mice we show that c-Myb is required for crypt integrity, normal differentiation, and steady-state proliferation. PMID:17360438

Relationship between composition of mixture charged and that in circulation in an auto refrigerant cascade and a J-T refrigerator operating in liquid refrigerant supply mode

NASA Astrophysics Data System (ADS)

Sreenivas, Bura; Nayak, H. Gurudath; Venkatarathnam, G.

2017-01-01

The composition of the refrigerant mixture in circulation during steady state operation of J-T and allied refrigerators is not the same as that charged due to liquid hold up in the heat exchangers and phase separators, as well as the differential solubility of different refrigerant components in the compressor lubricating oil. The performance of refrigerators/liquefiers operating on mixed refrigerant cycles is dependent on the mixture composition. It is therefore important to charge the right mixture that results in an optimum composition in circulation during steady state operation. The relationship between the charged and circulating composition has been experimentally studied in a J-T refrigerator operating in the liquid refrigerant supply (LRS) mode and an auto refrigerant cascade refrigerator (with a phase separator) operating in the gas refrigerant supply (GRS) mode. The results of the study are presented in this work. The results show that the method presented earlier for J-T refrigerators operating in GRS mode is also applicable in the case of refrigerators studied in this work.

Experimental correlations for transient soot measurement in diesel exhaust aerosol with light extinction, electrical mobility and diffusion charger sensor techniques

NASA Astrophysics Data System (ADS)

Bermúdez, Vicente; Pastor, José V.; López, J. Javier; Campos, Daniel

2014-06-01

A study of soot measurement deviation using a diffusion charger sensor with three dilution ratios was conducted in order to obtain an optimum setting that can be used to obtain accurate measurements in terms of soot mass emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement settings in steady-state operating conditions; evaluation of the proposed setting under the New European Driving Cycle; and a study of correlations for different measurement techniques. These correlations provide a reliable tool for estimating soot emission from light extinction measurement or from accumulation particle mode concentration. There are several methods and correlations to estimate soot concentration in the literature but most of them were assessed for steady-state operating points. In this case, the correlations are obtained by more than 4000 points measured in transient conditions. The results of the new two correlations, with less than 4% deviation from the reference measurement, are presented in this paper.

Steady-state temperature distribution within a Brayton rotating unit operating in a power conversion system using helium-xenon gas

NASA Technical Reports Server (NTRS)

Johnsen, R. L.; Namkoong, D.; Edkin, R. A.

1971-01-01

The Brayton rotating unit (BRU), consisting of a turbine, an alternator, and a compressor, was tested as part of a Brayton cycle power conversion system over a side range of steady state operating conditions. The working fluid in the system was a mixture of helium-xenon gases. Turbine inlet temperature was varied from 1200 to 1600 F, compressor inlet temperature from 60 to 120 F, compressor discharge pressure from 20 to 45 psia, rotative speed from 32 400 to 39 600 rpm, and alternator liquid-coolant flow rate from 0.01 to 0.27 pound per second. Test results indicated that the BRU internal temperatures were highly sensitive to alternator coolant flow below the design value of 0.12 pound per second but much less so at higher values. The armature winding temperature was not influenced significantly by turbine inlet temperature, but was sensitive, up to 20 F per kVA alternator output, to varying alternator output. When only the rotational speed was changed (+ or - 10% of rated value), the BRU internal temperatures varied directly with the speed.

Steady-State Thermal-Hydraulics Analyses for the Conversion of BR2 to Low Enriched Uranium Fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Licht, J.; Bergeron, A.; Dionne, B.

The code PLTEMP/ANL version 4.2 was used to perform the steady-state thermal-hydraulic analyses of the BR2 research reactor for conversion from Highly-Enriched to Low Enriched Uranium fuel (HEU and LEU, respectively). Calculations were performed to evaluate different fuel assemblies with respect to the onset of nucleate boiling (ONB), flow instability (FI), critical heat flux (CHF) and fuel temperature at beginning of cycle conditions. The fuel assemblies were characteristic of fresh fuel (0% burnup), highest heat flux (16% burnup), highest power (32% burnup) and highest burnup (46% burnup). Results show that the high heat flux fuel element is limiting for ONB,more » FI, and CHF, for both HEU and LEU fuel, but that the high power fuel element produces similar margin in a few cases. The maximum fuel temperature similarly occurs in both the high heat flux and high power fuel assemblies for both HEU and LEU fuel. A sensitivity study was also performed to evaluate the variation in fuel temperature due to uncertainties in the thermal conductivity degradation associated with burnup.« less

Oxygen uptake kinetics of constant-load work - Upright vs. supine exercise

NASA Technical Reports Server (NTRS)

Convertino, V. A.; Goldwater, D. J.; Sandler, H.

1984-01-01

Supine and upright positions were used in a comparitive study of the effects of constant load exercise on oxygen uptake (VO2), O2 deficit, steady-state VO2 and VO2 following recovery from constant load work. Ten male subjects (36-40 yr.) performed one submaximal exercise test in the supine and one test in the upright position consisting of 5 min rest and 5 min cycle ergometer exercise at 700 kg/min followed by ten minutes of recovery. It is found that the significant difference in VO2 kinetics during exercise in the upright compared to supine position resulted from changes in oxygen transport and utilization mechanisms rather than changes in mechanical efficiency. To the extent that data measured in the supine position can be used to estimate physiological responses to zero gravity, it is suggested that limitation of systemic O2 consumption may be the result of slow rates of oxygen uptake during transient periods of muscular work. Significant reductions in the rate of steady-state VO2 attainment at submaximal work intensities may produce an onset of muscle fatigue and exhaustion.

On the time to steady state: insights from numerical modeling

NASA Astrophysics Data System (ADS)

Goren, L.; Willett, S.; McCoy, S. W.; Perron, J.

2013-12-01

How fast do fluvial landscapes approach steady state after an application of tectonic or climatic perturbation? While theory and some numerical models predict that the celerity of the advective wave (knickpoint) controls the response time for perturbations, experiments and other landscape evolution models demonstrate that the time to steady state is much longer than the theoretically predicted response time. We posit that the longevity of transient features and the time to steady state are controlled by the stability of the topology and geometry of channel networks. Evolution of a channel network occurs by a combination of discrete capture events and continuous migration of water divides, processes, which are difficult to represent accurately in landscape evolution models. We therefore address the question of the time to steady state using the DAC landscape evolution model that solves accurately for the location of water divides, using a combination of analytical solution for hillslopes and low-order channels together with a numerical solution for higher order channels. DAC also includes an explicit capture criterion. We have tested fundamental predictions from DAC and show that modeled networks reproduce natural network characteristics such as the Hack's exponent and coefficient and the fractal dimension. We define two steady-state criteria: a topographic steady state, defined by global, pointwise steady elevation, and a topological steady state defined as the state in which no further reorganization of the drainage network takes place. Analyzing block uplift simulations, we find that the time to achieve either topographic or topological steady state exceeds by an order of magnitude the theoretical response time of the fluvial network. The longevity of the transient state is the result of the area feedback, by which, migration of a divide changes the local contributing area. This change propagates downstream as a slope adjustment, forcing further divide migrations and area change in adjacent tributaries and basins. In order to characterize the evolution of the drainage network on its way to steady state, we define a proxy to steady state elevation, χ, which is also the characteristic parameter of the transient stream power PDE. Through simulations of tectonic tilting we find that reorganization tends to minimize moments of the χ distribution of the landscape and of Δχ across divides.

Cyclosporin A and doxorubicin-ifosfamide in resistant solid tumours: a phase I and an immunological study.

PubMed Central

González-Manzano, R.; Cid, J.; Brugarolas, A.; Piasecki, C. C.

1995-01-01

In order to test whether circumvention of clinical resistance can be obtained in common solid tumours by targeting different drug resistance mechanisms, a phase I clinical and immunological study was designed. The purpose of the study was to determine the dose of cyclosporin A (CsA), in combination with doxorubicin (DOX) and ifosfamide (IFX), needed to achieve steady-state whole-blood levels of 2000 ng ml-1 and the associated toxicity of this combination. Treatment consisted of CsA 5 mg kg-1 as a 2 h loading infusion, followed by a CsA 3 day continuous infusion (c.i.) (days 1-3) at doses that were escalated from 10 to 18 mg kg-1 day-1. Chemotherapy consisted of DOX 55 mg m-2 by i.v. 24 h c.i. (day 2) and IFX 2 g m-2 i.v. over 1 h on days 1 and 3. Treatments were repeated every 4 weeks. Eighteen patients with previously treated resistant solid tumours received 39 cycles. Mean steady-state CsA levels > or = 2000 ng ml-1 were reached at 5 mg kg-1 loading dose followed by a 3 day c.i. of 16 mg kg-1 day-1 or greater. Haematological toxicity was greater than expected for the same chemotherapy alone. One patient died of intracranial haemorrhage due to severe thrombopenia. Other observed toxicities were: asymptomatic hyperbilirubinaemia (46% cycles), mild nephrotoxicity (20% cycles), hypomagnesaemia (72% cycles), mild increase in body weight (100% cycles), hypertension (15% cycles) and headache (15% cycles). Overall the toxicity was acceptable and manageable. No alterations in absolute lymphocyte number, the lymphocyte subsets studied (CD3, CD4, CD8, CD19) or CD4/CD8 ratio were observed in patients receiving more than one treatment cycle, although there were significant and non-uniform variations in the values of the different lymphocyte subsets studied when pre- and post-treatment values were compared. There was also a significant increase in the CD4/CD8 ratio. Tumour regressions were observed in two patients (epidermoid carcinoma of the cervix and Ewing's sarcoma). The CsA dose recommended for phase II trials is a 5 mg kg-1 loading dose followed by a 3-day c.i. of 16 mg kg-1 day-1 simultaneously with DOX and IFX at the doses administered in this study. PMID:7577485

75 FR 79286 - Designated Reserve Ratio

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-20

... help prevent sharp fluctuations in deposit insurance premiums over the course of the business cycle. In... economic and credit cycles; and (2) maintain a positive fund balance even during a banking crisis by..., steady assessment rates throughout economic and credit cycles. At a September 24, 2010 roundtable...

Quantitative broadband absorption and scattering spectroscopy in turbid media by combined frequency-domain and steady state methodologies

DOEpatents

Tromberg, Bruce J [Irvine, CA; Berger, Andrew J [Rochester, NY; Cerussi, Albert E [Lake Forest, CA; Bevilacqua, Frederic [Costa Mesa, CA; Jakubowski, Dorota [Irvine, CA

2008-09-23

A technique for measuring broadband near-infrared absorption spectra of turbid media that uses a combination of frequency-domain and steady-state reflectance methods. Most of the wavelength coverage is provided by a white-light steady-state measurement, whereas the frequency-domain data are acquired at a few selected wavelengths. Coefficients of absorption and reduced scattering derived from the frequency-domain data are used to calibrate the intensity of the steady-state measurements and to determine the reduced scattering coefficient at all wavelengths in the spectral window of interest. The absorption coefficient spectrum is determined by comparing the steady-state reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined frequency-domain and steady-state technique, agree well with expected reference values.

Steady-state entanglement in levitated optomechanical systems coupled to a higher order excited atomic ensemble

NASA Astrophysics Data System (ADS)

Chen, Aixi; Nie, Wenjie; Li, Ling; Zeng, Wei; Liao, Qinghong; Xiao, Xianbo

2017-11-01

We investigate the steady-state entanglement in an optomechanical system with a levitated dielectric nanosphere and a higher order excited atomic ensemble. The single nanosphere is trapped by an external harmonic dipole trap and coupled to the single-mode cavity field by the effective optomechanical coupling, which depends on the steady-state position of the nanosphere. We show that the steady-state optomechanical entanglement can be generated via the effective optomechanical interaction between the mechanical motion and the cavity mode. Further, these exist an optimal effective cavity detuning that maximizes the optomechanical entanglement. We also analyze in detail the influences of the excitation number of atoms, the radius of the nanosphere and the thermal noise strength on the steady-state optomechanical entanglement. It is found that the steady-state entanglement can be enhanced by increasing the excitation number of atoms and the radius of the nanosphere.

Characterizing Fluorocarbon Assisted Atomic Layer Etching of Si Using Cyclic Ar/C 4F 8 and Ar/CHF 3 Plasma

DOE PAGES

Metzler, Dominik; Li, Chen; Engelmann, Sebastian; ...

2016-09-08

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO 2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C 4F 8 and CHF 3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32,more » 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO 2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF 3 has a lower FC deposition yield for both SiO 2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F 8. The thickness of deposited FC layers using CHF 3 is found to be greater for Si than for SiO 2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.« less

Effect of the chamber wall on fluorocarbon-assisted atomic layer etching of SiO{sub 2} using cyclic Ar/C{sub 4}F{sub 8} plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawakami, Masatoshi; Metzler, Dominik; Oehrlein, Gottlieb S., E-mail: oehrlein@umd.edu

2016-07-15

The authors studied the effect of the temperature and chemical state of the chamber wall on process performance for atomic layer etching of SiO{sub 2} using a steady-state Ar plasma, periodic injection of a defined number of C{sub 4}F{sub 8} molecules, and synchronized plasma-based Ar{sup +} ion bombardment. To evaluate these effects, the authors measured the quartz coupling window temperature. The plasma gas phase chemistry was characterized using optical emission spectroscopy. It was found that although the thickness of the polymer film deposited in each cycle is constant, the etching behavior changed, which is likely related to a change inmore » the plasma gas phase chemistry. The authors found that the main gas phase changes occur after C{sub 4}F{sub 8} injection. The C{sub 4}F{sub 8} and the quartz window react and generate SiF and CO. The emission intensity changes with wall surface state and temperature. Therefore, changes in the plasma gas species generation can lead to a shift in etching performance during processing. During initial cycles, minimal etching is observed, while etching gradually increases with cycle number.« less

Customized Steady-State Constraints for Parameter Estimation in Non-Linear Ordinary Differential Equation Models

PubMed Central

Rosenblatt, Marcus; Timmer, Jens; Kaschek, Daniel

2016-01-01

Ordinary differential equation models have become a wide-spread approach to analyze dynamical systems and understand underlying mechanisms. Model parameters are often unknown and have to be estimated from experimental data, e.g., by maximum-likelihood estimation. In particular, models of biological systems contain a large number of parameters. To reduce the dimensionality of the parameter space, steady-state information is incorporated in the parameter estimation process. For non-linear models, analytical steady-state calculation typically leads to higher-order polynomial equations for which no closed-form solutions can be obtained. This can be circumvented by solving the steady-state equations for kinetic parameters, which results in a linear equation system with comparatively simple solutions. At the same time multiplicity of steady-state solutions is avoided, which otherwise is problematic for optimization. When solved for kinetic parameters, however, steady-state constraints tend to become negative for particular model specifications, thus, generating new types of optimization problems. Here, we present an algorithm based on graph theory that derives non-negative, analytical steady-state expressions by stepwise removal of cyclic dependencies between dynamical variables. The algorithm avoids multiple steady-state solutions by construction. We show that our method is applicable to most common classes of biochemical reaction networks containing inhibition terms, mass-action and Hill-type kinetic equations. Comparing the performance of parameter estimation for different analytical and numerical methods of incorporating steady-state information, we show that our approach is especially well-tailored to guarantee a high success rate of optimization. PMID:27243005

Customized Steady-State Constraints for Parameter Estimation in Non-Linear Ordinary Differential Equation Models.

PubMed

Rosenblatt, Marcus; Timmer, Jens; Kaschek, Daniel

2016-01-01

Ordinary differential equation models have become a wide-spread approach to analyze dynamical systems and understand underlying mechanisms. Model parameters are often unknown and have to be estimated from experimental data, e.g., by maximum-likelihood estimation. In particular, models of biological systems contain a large number of parameters. To reduce the dimensionality of the parameter space, steady-state information is incorporated in the parameter estimation process. For non-linear models, analytical steady-state calculation typically leads to higher-order polynomial equations for which no closed-form solutions can be obtained. This can be circumvented by solving the steady-state equations for kinetic parameters, which results in a linear equation system with comparatively simple solutions. At the same time multiplicity of steady-state solutions is avoided, which otherwise is problematic for optimization. When solved for kinetic parameters, however, steady-state constraints tend to become negative for particular model specifications, thus, generating new types of optimization problems. Here, we present an algorithm based on graph theory that derives non-negative, analytical steady-state expressions by stepwise removal of cyclic dependencies between dynamical variables. The algorithm avoids multiple steady-state solutions by construction. We show that our method is applicable to most common classes of biochemical reaction networks containing inhibition terms, mass-action and Hill-type kinetic equations. Comparing the performance of parameter estimation for different analytical and numerical methods of incorporating steady-state information, we show that our approach is especially well-tailored to guarantee a high success rate of optimization.

Sources of Water to Wells for Transient Cyclic Systems

USGS Publications Warehouse

Reilly, T.E.; Pollock, D.W.

1996-01-01

Many state agencies are currently (1995) developing wellhead protection programs. The thrust of some of these programs is to protect water supplies by determining the areas contributing recharge to water-supply wells and by specifying regulations to minimize the opportunity for contamination of the recharge water by activities at the land surface. The area contributing recharge to a discharging well is the surface area at the water table through which the water flowing to the well entered the ground-water system. In the analyses of ground-water flow systems, steady-state average conditions are commonly used to simplify the problem and make a solution tractable. However, recharge is usually cyclic in nature, with seasonal cycles and longer term climatic cycles. The effect of these cyclic stresses on the area contributing recharge to wells is quantitatively analyzed for a hypothetical alluvial valley aquifer system that is representative of a large class of ground-water systems that are extensively developed for water supply. The analysis shows that, in many cases, these cyclic changes in the recharge rates do not significantly affect the location and size of the areas contributing recharge to wells. The ratio of the mean travel time to the length of the cyclic stress period appears to be an indicator of whether the transient effects of the cyclic stress must be explicitly represented in the analysis of contributing areas to wells. For the cases examined, if the ratio of the mean travel time to the period of the cyclic stress was much greater than one, then the transient area contributing recharge to wells was similar to the area calculated using an average steady-state condition. However, cyclic stresses on systems with ratios less than one do have an effect on the location and size of the areas contributing recharge to wells.

Probing quantum and classical turbulence analogy in von Kármán liquid helium, nitrogen, and water experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saint-Michel, B.; Aix Marseille Université, CNRS, Centrale Marseille, IRPHE UMR 7342, 13384 Marseille; Herbert, E.

2014-12-15

We report measurements of the dissipation in the Superfluid helium high REynold number von Kármán flow experiment for different forcing conditions. Statistically steady flows are reached; they display a hysteretic behavior similar to what has been observed in a 1:4 scale water experiment. Our macroscopical measurements indicate no noticeable difference between classical and superfluid flows, thereby providing evidence of the same dissipation scaling laws in the two phases. A detailed study of the evolution of the hysteresis cycle with the Reynolds number supports the idea that the stability of the steady states of classical turbulence in this closed flow ismore » partly governed by the dissipative scales. It also supports the idea that the normal and the superfluid components at these temperatures (1.6 K) are locked down to the dissipative length scale.« less

Existence and instability of steady states for a triangular cross-diffusion system: A computer-assisted proof

NASA Astrophysics Data System (ADS)

Breden, Maxime; Castelli, Roberto

2018-05-01

In this paper, we present and apply a computer-assisted method to study steady states of a triangular cross-diffusion system. Our approach consist in an a posteriori validation procedure, that is based on using a fixed point argument around a numerically computed solution, in the spirit of the Newton-Kantorovich theorem. It allows to prove the existence of various non homogeneous steady states for different parameter values. In some situations, we obtain as many as 13 coexisting steady states. We also apply the a posteriori validation procedure to study the linear stability of the obtained steady states, proving that many of them are in fact unstable.

Drivers of Seasonal Variability in Marine Boundary Layer Aerosol Number Concentration Investigated Using a Steady State Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohrmann, Johannes; Wood, Robert; McGibbon, Jeremy

Marine boundary layer (MBL) aerosol particles affect the climate through their interaction with MBL clouds. Although both MBL clouds and aerosol particles have pronounced seasonal cycles, the factors controlling seasonal variability of MBL aerosol particle concentration are not well-constrained. In this paper an aerosol budget is constructed representing the effects of wet deposition, free-tropospheric entrainment, primary surface sources, and advection on the MBL accumulation mode aerosol number concentration (N a). These terms are further parameterized, and by assuming that on seasonal timescales N a is in steady state, the budget equation is rearranged to form a diagnostic equation for Nmore » a based on observable variables. Using data primarily collected in the subtropical northeast Pacific during the MAGIC campaign (Marine ARM (Atmospheric Radiation Measurement) GPCI (GCSS Pacific Cross-section Intercomparison) Investigation of Clouds), estimates of both mean summer and winter N a concentrations are made using the simplified steady-state model and seasonal mean observed variables, and are found to match well with the observed N a. To attribute the modeled difference between summer and winter aerosol concentrations to individual observed variables (e.g. precipitation rate, free-tropospheric aerosol number concentration), a local sensitivity analysis is combined with the seasonal difference in observed variables. This analysis shows that despite wintertime precipitation frequency being lower than summer, the higher winter precipitation rate accounted for approximately 60% of the modeled seasonal difference in N a, which emphasizes the importance of marine stratocumulus precipitation in determining MBL aerosol concentrations on longer time scales.« less

Drivers of Seasonal Variability in Marine Boundary Layer Aerosol Number Concentration Investigated Using a Steady State Approach

DOE PAGES

Mohrmann, Johannes; Wood, Robert; McGibbon, Jeremy; ...

2018-01-21

Marine boundary layer (MBL) aerosol particles affect the climate through their interaction with MBL clouds. Although both MBL clouds and aerosol particles have pronounced seasonal cycles, the factors controlling seasonal variability of MBL aerosol particle concentration are not well-constrained. In this paper an aerosol budget is constructed representing the effects of wet deposition, free-tropospheric entrainment, primary surface sources, and advection on the MBL accumulation mode aerosol number concentration (N a). These terms are further parameterized, and by assuming that on seasonal timescales N a is in steady state, the budget equation is rearranged to form a diagnostic equation for Nmore » a based on observable variables. Using data primarily collected in the subtropical northeast Pacific during the MAGIC campaign (Marine ARM (Atmospheric Radiation Measurement) GPCI (GCSS Pacific Cross-section Intercomparison) Investigation of Clouds), estimates of both mean summer and winter N a concentrations are made using the simplified steady-state model and seasonal mean observed variables, and are found to match well with the observed N a. To attribute the modeled difference between summer and winter aerosol concentrations to individual observed variables (e.g. precipitation rate, free-tropospheric aerosol number concentration), a local sensitivity analysis is combined with the seasonal difference in observed variables. This analysis shows that despite wintertime precipitation frequency being lower than summer, the higher winter precipitation rate accounted for approximately 60% of the modeled seasonal difference in N a, which emphasizes the importance of marine stratocumulus precipitation in determining MBL aerosol concentrations on longer time scales.« less

Drivers of Seasonal Variability in Marine Boundary Layer Aerosol Number Concentration Investigated Using a Steady State Approach

NASA Astrophysics Data System (ADS)

Mohrmann, Johannes; Wood, Robert; McGibbon, Jeremy; Eastman, Ryan; Luke, Edward

2018-01-01

Marine boundary layer (MBL) aerosol particles affect the climate through their interaction with MBL clouds. Although both MBL clouds and aerosol particles have pronounced seasonal cycles, the factors controlling seasonal variability of MBL aerosol particle concentration are not well constrained. In this paper an aerosol budget is constructed representing the effects of wet deposition, free-tropospheric entrainment, primary surface sources, and advection on the MBL accumulation mode aerosol number concentration (Na). These terms are then parameterized, and by assuming that on seasonal time scales Na is in steady state, the budget equation is rearranged to form a diagnostic equation for Na based on observable variables. Using data primarily collected in the subtropical northeast Pacific during the MAGIC campaign (Marine ARM (Atmospheric Radiation Measurement) GPCI (GCSS Pacific Cross-Section Intercomparison) Investigation of Clouds), estimates of both mean summer and winter Na concentrations are made using the simplified steady state model and seasonal mean observed variables. These are found to match well with the observed Na. To attribute the modeled difference between summer and winter aerosol concentrations to individual observed variables (e.g., precipitation rate and free-tropospheric aerosol number concentration), a local sensitivity analysis is combined with the seasonal difference in observed variables. This analysis shows that despite wintertime precipitation frequency being lower than summer, the higher winter precipitation rate accounted for approximately 60% of the modeled seasonal difference in Na, which emphasizes the importance of marine stratocumulus precipitation in determining MBL aerosol concentrations on longer time scales.

Tribology and wear of metal-on-metal hip prostheses: influence of cup angle and head position.

PubMed

Williams, Sophie; Leslie, Ian; Isaac, Graham; Jin, Zhongmin; Ingham, Eileen; Fisher, John

2008-08-01

Clinical studies have indicated that the angular position of the acetabular cup may influence wear in metal-on-metal total hip bearings. A high cup angle in comparison to the anatomical position may lead to the head being constrained by the superior lateral surface and rim of the cup, thus potentially changing the location of the contact zone between the head and the cup. The aim of this study was to test the hypothesis that both a steep cup angle and a lateralized position of the head can increase head contact on the superior rim of the cup, with the consequence of increased wear. Hip-joint simulator studies of metal-on-metal bearings were undertaken with cup angles of 45 degrees and 55 degrees . The femoral head was either aligned to the center of the cup or placed in a position of microlateralization. Wear was measured gravimetrically over 5 million cycles. A steep cup angle of 55 degrees showed significantly higher long-term steady-state wear than a standard cup angle of 45 degrees (p < 0.01). The difference was fivefold. Microlateralization of the head resulted in a fivefold increase in steady-state wear compared with a centralized head. The combination of a steep cup angle and a microlateralized head increased the steady-state wear rate by tenfold compared with a standard cup angle with a centralized head. These studies support the hypothesis that both an increased cup angle and a lateral head position increase wear in metal-on-metal hip prostheses.

Hexagonal gradient scheme with RF spoiling improves spoiling performance for high-flip-angle fast gradient echo imaging.

PubMed

Hess, Aaron T; Robson, Matthew D

2017-03-01

To present a framework in which time-varying gradients are applied with RF spoiling to reduce unwanted signal, particularly at high flip angles. A time-varying gradient spoiler scheme compatible with RF spoiling is defined, in which spoiler gradients cycle through the vertices of a hexagon, which we call hexagonal spoiling. The method is compared with a traditional constant spoiling gradient both in the transition to and in the steady state. Extended phase graph (EPG) simulations, phantom acquisitions, and in vivo images were used to assess the method. Simulations, phantom and in vivo experiments showed that unwanted signal was markedly reduced by employing hexagonal spoiling, both in the transition to and in the steady state. For adipose tissue at 1.5 Tesla, the unwanted signal in the steady state with a 60 ° flip angle was reduced from 22% with constant spoiling to 2% with hexagonal spoiling. A time-varying gradient spoiler scheme that works with RF spoiling, called "hexagonal spoiling," has been presented and found to offer improved spoiling over the traditional constant spoiling gradient. Magn Reson Med 77:1231-1237, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

ABSIM. Simulation of Absorption Systems in Flexible and Modular Form

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grossman, G.

1994-06-01

The computer code has been developed for simulation of absorption systems at steady-state in a flexible and modular form, making it possible to investigate various cycle configurations with different working fluids. The code is based on unit subroutines containing the governing equations for the system`s components. When all the equations have been established, a mathematical solver routine is employed to solve them simultaneously. Property subroutines contained in a separate data base serve to provide thermodynamic properties of the working fluids. The code is user-oriented and requires a relatively simple input containing the given operating conditions and the working fluid atmore » each state point. the user conveys to the computer an image of the cycle by specifying the different components and their interconnections. Based on this information, the program calculates the temperature, flowrate, concentration, pressure and vapor fraction at each state point in the system and the heat duty at each unit, from which the coefficient of performance may be determined. A graphical user-interface is provided to facilitate interactive input and study of the output.« less

ABSIM. Simulation of Absorption Systems in Flexible and Modular Form

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grossman, G.

1994-06-01

The computer code has been developed for simulation of absorption systems at steady-state in a flexible and modular form, making it possible to investigate various cycle configurations with different working fluids. The code is based on unit subroutines containing the governing equations for the system's components. When all the equations have been established, a mathematical solver routine is employed to solve them simultaneously. Property subroutines contained in a separate data base serve to provide thermodynamic properties of the working fluids. The code is user-oriented and requires a relatively simple input containing the given operating conditions and the working fluid atmore » each state point. the user conveys to the computer an imagev of the cycle by specifying the different components and their interconnections. Based on this information, the program calculates the temperature, flowrate, concentration, pressure and vapor fraction at each state point in the system and the heat duty at each unit, from which the coefficient of performance may be determined. A graphical user-interface is provided to fcilitate interactive input and study of the output.« less

Marine boundary layer cloud regimes and POC formation in an LES coupled to a bulk aerosol scheme

NASA Astrophysics Data System (ADS)

Berner, A. H.; Bretherton, C. S.; Wood, R.; Muhlbauer, A.

2013-07-01

A large-eddy simulation (LES) coupled to a new bulk aerosol scheme is used to study long-lived regimes of aerosol-boundary layer cloud-precipitation interaction and the development of pockets of open cells (POCs) in subtropical stratocumulus cloud layers. The aerosol scheme prognoses mass and number concentration of a single log-normal accumulation mode with surface and entrainment sources, evolving subject to processing of activated aerosol and scavenging of dry aerosol by cloud and rain. The LES with the aerosol scheme is applied to a range of steadily-forced simulations idealized from a well-observed POC case. The long-term system evolution is explored with extended two-dimensional simulations of up to 20 days, mostly with diurnally-averaged insolation. One three-dimensional two-day simulation confirms the initial development of the corresponding two-dimensional case. With weak mean subsidence, an initially aerosol-rich mixed layer deepens, the capping stratocumulus cloud slowly thickens and increasingly depletes aerosol via precipitation accretion, then the boundary layer transitions within a few hours into an open-cell regime with scattered precipitating cumuli, in which entrainment is much weaker. The inversion slowly collapses for several days until the cumulus clouds are too shallow to efficiently precipitate. Inversion cloud then reforms and radiatively drives renewed entrainment, allowing the boundary layer to deepen and become more aerosol-rich, until the stratocumulus layer thickens enough to undergo another cycle of open-cell formation. If mean subsidence is stronger, the stratocumulus never thickens enough to initiate drizzle and settles into a steady state. With lower initial aerosol concentrations, this system quickly transitions into open cells, collapses, and redevelops into a different steady state with a shallow, optically thin cloud layer. In these steady states, interstitial scavenging by cloud droplets is the main sink of aerosol number. The system is described in a reduced two-dimensional phase plane with inversion height and boundary-layer average aerosol concentrations as the state variables. Simulations with a full diurnal cycle show similar evolutions, except that open-cell formation is phase-locked into the early morning hours. The same steadily-forced modeling framework is applied to the development and evolution of a POC and the surrounding overcast boundary layer. An initial aerosol perturbation applied to a portion of the model domain leads that portion to transition into open-cell convection, forming a POC. Reduced entrainment in the POC induces a negative feedback between areal fraction covered by the POC and boundary layer depth changes. This stabilizes the system by controlling liquid water path and precipitation sinks of aerosol number in the overcast region, while also preventing boundary-layer collapse within the POC, allowing the POC and overcast to coexist indefinitely in a quasi-steady equilibrium.

Contribution of highway capital to industry and national productivity growth

DOT National Transportation Integrated Search

1973-10-01

The report contains the authors initial efforts aimed at extending the steady state freeway model for optimizing freeway traffic flow to a non-steady state model. The steady-state model does not allow reaction to continuously changing conditions whic...

Circadian manifestations of barbiturate habituation, addiction and withdrawal in the rat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ehret, C. F.; Peraino, C.; Meinert, J. C.

1979-01-01

The present study uses circadian rhythm observations on rats to include diverse habituation and drug ingestion (phenobarbital) circumstances, including a comparison of the effect of pre-entrainment cycles of programmed feeding and illumination and subsequent conditions of exposure of duration sufficient to permit a steady-state in the appearance of circadian patterns derived from core-temperature telemetry and from automated food-consumption measurements. Finally, measurements were permitted to continue long enough after the drug was withdrawn from the diet to allow characterization of an abstinence syndrome, indicative of addiction.

Water transport in limestone by X-ray CAT scanning

USGS Publications Warehouse

Mossoti, Victor G.; Castanier, Louis M.

1989-01-01

The transport of water through the interior of Salem limestone test briquettes can be dynamically monitored by computer aided tomography (commonly called CAT scanning in medical diagnostics). Most significantly, unless evaporation from a particular face of the briquette is accelerated by forced air flow (wind simulation), the distribution of water in the interior of the briquette remains more or less uniform throughout the complete drying cycle. Moreover, simulated solar illumination of the test briquette does not result in the production of significant water gradients in the briquette under steady-state drying conditions.

Thermal boundary layer due to sudden heating of fluid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurkal, K.R.; Munukutla, S.

This paper proposes to solve computationally the heat-transfer problems (introduced by Munukutla and Venkataraman, 1988) related to a closed-cycle pulsed high-power laser flow loop. The continuity and the momentum equations as well as the unsteady energy equation are solved using the Keller-Box method. The solutions were compared with the steady-state solutions at large times, and the comparison was found to be excellent. Empirical formulas are proposed for calculating the time-dependent boundary-layer thickness and mass-heat transfer, that can be used by laser flow loop designers. 6 refs.

Thermal boundary layer due to sudden heating of fluid

NASA Astrophysics Data System (ADS)

Kurkal, K. R.; Munukutla, S.

1989-10-01

This paper proposes to solve computationally the heat-transfer problems (introduced by Munukutla and Venkataraman, 1988) related to a closed-cycle pulsed high-power laser flow loop. The continuity and the momentum equations as well as the unsteady energy equation are solved using the Keller-Box method. The solutions were compared with the steady-state solutions at large times, and the comparison was found to be excellent. Empirical formulas are proposed for calculating the time-dependent boundary-layer thickness and mass-heat transfer, that can be used by laser flow loop designers.

On Animating 2D Velocity Fields

NASA Technical Reports Server (NTRS)

Kao, David; Pang, Alex; Yan, Jerry (Technical Monitor)

2001-01-01

A velocity field, even one that represents a steady state flow, implies a dynamical system. Animated velocity fields is an important tool in understanding such complex phenomena. This paper looks at a number of techniques that animate velocity fields and propose two new alternatives. These are texture advection and streamline cycling. The common theme among these techniques is the use of advection on some texture to generate a realistic animation of the velocity field. Texture synthesis and selection for these methods are presented. Strengths and weaknesses of the techniques are also discussed in conjunctions with several examples.

On Animating 2D Velocity Fields

NASA Technical Reports Server (NTRS)

Kao, David; Pang, Alex

2000-01-01

A velocity field. even one that represents a steady state flow implies a dynamical system. Animated velocity fields is an important tool in understanding such complex phenomena. This paper looks at a number of techniques that animate velocity fields and propose two new alternatives, These are texture advection and streamline cycling. The common theme among these techniques is the use of advection on some texture to generate a realistic animation of the velocity field. Texture synthesis and selection for these methods are presented. Strengths and weaknesses of the techniques are also discussed in conjunction with several examples.

Thin film heat flux sensor for Space Shuttle Main Engine turbine environment

NASA Technical Reports Server (NTRS)

Will, Herbert

1991-01-01

The Space Shuttle Main Engine (SSME) turbine environment stresses engine components to their design limits and beyond. The extremely high temperatures and rapid temperature cycling can easily cause parts to fail if they are not properly designed. Thin film heat flux sensors can provide heat loading information with almost no disturbance of gas flows or of the blade. These sensors can provide steady state and transient heat flux information. A thin film heat flux sensor is described which makes it easier to measure small temperature differences across very thin insulating layers.

Fast controller for a unity-power-factor PWM rectifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eissa, M.O.; Leeb, S.B.; Verghese, G.C.

1996-01-01

This paper presents an analog implementation of a fast controller for a unity-power-factor (UPF) PWM rectifier. The best settling times of many popular controllers for this type of converter are on the order of a few line cycles, corresponding to bandwidths under 20 Hz. The fast controller demonstrated in this paper can exercise control action at a rate comparable to the switching frequency rather than the line frequency. In order to accomplish this while maintaining unity power factor during steady-state operation, the fast controller employs a ripple-feedback cancellation scheme.

Steady-state unbalance response of a three-disk flexible rotor on flexible, damped supports

NASA Technical Reports Server (NTRS)

Cunningham, R. E.

1977-01-01

Experimental data are presented for the unbalance response of a flexible, ball bearing supported rotor to speeds above the third lateral bending critical. Values of squeeze film damping coefficients obtained from measured data are compared to theoretical values obtained from short bearing approximation over a frequency range from 5000 to 31 000 cycles/min. Experimental response for an undamped rotor is compared to that of one having oil squeeze film dampers at the bearings. Unbalance applied varied from 0.62 to 15.1 gm-cm.

Optimal flash rate and duty cycle for flashing visual indicators.

NASA Technical Reports Server (NTRS)

Markowitz, J.

1971-01-01

This experiment examined the ability of observers to determine, as quickly as possible, whether a visual indicator was steadily on or flashing. Six flash rates (periods) were combined factorially with three duty cycles (on-off ratios) to define 18 ?types' of intermittent signals. Experimental sessions were divided into six runs of 100 trials, each run utilizing one of the six flash rates. On any given trial in a run, the probability of a steady signal occurring was 0.5 and the probability of a flashing signal occurring was 0.5. A different duty cycle was employed daily for each experimental session. In all, 400 trials were devoted to each of the flash rates at each duty cycle. Accuracy and latency of response were the dependent variables of interest. The results show that the observers view the light for an interval of time appropriate to the expected flash rate and duty cycle; whether they judge the light to be steady or intermittent depends upon whether the light is extinguished during the predetermined waiting period. Adoption of this temporal criterion delays responding in comparison to those tasks involving responses to light onset. The decision or response criteria held by the observers are also sensitive to the parameters of the flashing light: observers become increasingly willing to call a flashing light ?steady' as flash duration increases.

Unsteady specific work and isentropic efficiency of a radial turbine driven by pulsed detonations

NASA Astrophysics Data System (ADS)

Rouser, Kurt P.

There has been longstanding government and industry interest in pressure-gain combustion for use in Brayton cycle based engines. Theoretically, pressure-gain combustion allows heat addition with reduced entropy loss. The pulsed detonation combustor (PDC) is a device that can provide such pressure-gain combustion and possibly replace typical steady deflagration combustors. The PDC is inherently unsteady, however, and comparisons with conventional steady deflagration combustors must be based upon time-integrated performance variables. In this study, the radial turbine of a Garrett automotive turbocharger was coupled directly to and driven, full admission, by a PDC in experiments fueled by hydrogen or ethylene. Data included pulsed cycle time histories of turbine inlet and exit temperature, pressure, velocity, mass flow, and enthalpy. The unsteady inlet flowfield showed momentary reverse flow, and thus unsteady accumulation and expulsion of mass and enthalpy within the device. The coupled turbine-driven compressor provided a time-resolved measure of turbine power. Peak power increased with PDC fill fraction, and duty cycle increased with PDC frequency. Cycle-averaged unsteady specific work increased with fill fraction and frequency. An unsteady turbine efficiency formulation is proposed, including heat transfer effects, enthalpy flux-weighted total pressure ratio, and ensemble averaging over multiple cycles. Turbine efficiency increased with frequency but was lower than the manufacturer reported conventional steady turbine efficiency.

Fuel economy and exhaust emissions characteristics of diesel vehicles: Test results of a prototype fiat 131TC 2.4 liter automobile

NASA Technical Reports Server (NTRS)

Quayle, S. S.

1982-01-01

The results obtained from fuel economy and emission tests conducted on a prototype Fiat 131 turbocharged diesel vehicle are presented. The vehicle was tested on a chassis dynamometer over selected drive cycles and steady-state conditions. Two fuels were used, a United States number 2 diesel and a European diesel fuel. Particulate emission rates were calculated from dilution tunnel measurements and large volume particulate samples were collected for biological and chemical analysis. It was determined that turbocharging accompanied by complementary modifications results in small but substantial improvements in regulated emissions, fuel economy, and performance. Notably, particulate levels were reduced by 30 percent.

Critical threshold behavior for steady-state internal transport barriers in burning plasmas.

PubMed

García, J; Giruzzi, G; Artaud, J F; Basiuk, V; Decker, J; Imbeaux, F; Peysson, Y; Schneider, M

2008-06-27

Burning tokamak plasmas with internal transport barriers are investigated by means of integrated modeling simulations. The barrier sustainment in steady state, differently from the barrier formation process, is found to be characterized by a critical behavior, and the critical number of the phase transition is determined. Beyond a power threshold, alignment of self-generated and noninductively driven currents occurs and steady state becomes possible. This concept is applied to simulate a steady-state scenario within the specifications of the International Thermonuclear Experimental Reactor.

Steady-state and transient models of groundwater flow and advective transport, Eastern Snake River Plain aquifer, Idaho National Laboratory and vicinity, Idaho

USGS Publications Warehouse

Ackerman, Daniel J.; Rousseau, Joseph P.; Rattray, Gordon W.; Fisher, Jason C.

2010-01-01

Three-dimensional steady-state and transient models of groundwater flow and advective transport in the eastern Snake River Plain aquifer were developed by the U.S. Geological Survey in cooperation with the U.S. Department of Energy. The steady-state and transient flow models cover an area of 1,940 square miles that includes most of the 890 square miles of the Idaho National Laboratory (INL). A 50-year history of waste disposal at the INL has resulted in measurable concentrations of waste contaminants in the eastern Snake River Plain aquifer. Model results can be used in numerical simulations to evaluate the movement of contaminants in the aquifer. Saturated flow in the eastern Snake River Plain aquifer was simulated using the MODFLOW-2000 groundwater flow model. Steady-state flow was simulated to represent conditions in 1980 with average streamflow infiltration from 1966-80 for the Big Lost River, the major variable inflow to the system. The transient flow model simulates groundwater flow between 1980 and 1995, a period that included a 5-year wet cycle (1982-86) followed by an 8-year dry cycle (1987-94). Specified flows into or out of the active model grid define the conditions on all boundaries except the southwest (outflow) boundary, which is simulated with head-dependent flow. In the transient flow model, streamflow infiltration was the major stress, and was variable in time and location. The models were calibrated by adjusting aquifer hydraulic properties to match simulated and observed heads or head differences using the parameter-estimation program incorporated in MODFLOW-2000. Various summary, regression, and inferential statistics, in addition to comparisons of model properties and simulated head to measured properties and head, were used to evaluate the model calibration. Model parameters estimated for the steady-state calibration included hydraulic conductivity for seven of nine hydrogeologic zones and a global value of vertical anisotropy. Parameters estimated for the transient calibration included specific yield for five of the seven hydrogeologic zones. The zones represent five rock units and parts of four rock units with abundant interbedded sediment. All estimates of hydraulic conductivity were nearly within 2 orders of magnitude of the maximum expected value in a range that exceeds 6 orders of magnitude. The estimate of vertical anisotropy was larger than the maximum expected value. All estimates of specific yield and their confidence intervals were within the ranges of values expected for aquifers, the range of values for porosity of basalt, and other estimates of specific yield for basalt. The steady-state model reasonably simulated the observed water-table altitude, orientation, and gradients. Simulation of transient flow conditions accurately reproduced observed changes in the flow system resulting from episodic infiltration from the Big Lost River and facilitated understanding and visualization of the relative importance of historical differences in infiltration in time and space. As described in a conceptual model, the numerical model simulations demonstrate flow that is (1) dominantly horizontal through interflow zones in basalt and vertical anisotropy resulting from contrasts in hydraulic conductivity of various types of basalt and the interbedded sediments, (2) temporally variable due to streamflow infiltration from the Big Lost River, and (3) moving downward downgradient of the INL. The numerical models were reparameterized, recalibrated, and analyzed to evaluate alternative conceptualizations or implementations of the conceptual model. The analysis of the reparameterized models revealed that little improvement in the model could come from alternative descriptions of sediment content, simulated aquifer thickness, streamflow infiltration, and vertical head distribution on the downgradient boundary. Of the alternative estimates of flow to or from the aquifer, only a 20 percent decrease in

A Novel Chronic Opioid Monitoring Tool to Assess Prescription Drug Steady State Levels in Oral Fluid.

PubMed

Shaparin, Naum; Mehta, Neel; Kunkel, Frank; Stripp, Richard; Borg, Damon; Kolb, Elizabeth

2017-11-01

Interpretation limitations of urine drug testing and the invasiveness of blood toxicology have motivated the desire for the development of simpler methods to assess biologically active drug levels on an individualized patient basis. Oral fluid is a matrix well-suited for the challenge because collections are based on simple noninvasive procedures and drug concentrations better correlate to blood drug levels as oral fluid is a filtrate of the blood. Well-established pharmacokinetic models were utilized to generate oral fluid steady state concentration ranges to assess the interpretive value of the alternative matrix to monitor steady state plasma oxycodone levels. Paired oral fluid and plasma samples were collected from patients chronically prescribed oxycodone and quantitatively analyzed by liquid chromatography tandem mass spectrometry. Steady state plasma concentration ranges were calculated for each donor and converted to an equivalent range in oral fluid. Measured plasma and oral fluid oxycodone concentrations were compared with respective matrix-matched steady state ranges, using each plasma steady state classification as the control. A high degree of correlation was observed between matrices when classifying donors according to expected steady state oxycodone concentration. Agreement between plasma and oral fluid steady state classifications was observed in 75.6% of paired samples. This study supports novel application of basic pharmacokinetic knowledge to the pain management industry, simplifying and improving individualized drug monitoring and risk assessment through the use of oral fluid drug testing. Many benefits of established therapeutic drug monitoring in plasma can be realized in oral fluid for patients chronically prescribed oxycodone at steady state. © 2017 American Academy of Pain Medicine. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

THERMAL NON-EQUILIBRIUM REVEALED BY PERIODIC PULSES OF RANDOM AMPLITUDES IN SOLAR CORONAL LOOPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Auchère, F.; Froment, C.; Bocchialini, K.

2016-08-20

We recently detected variations in extreme ultraviolet intensity in coronal loops repeating with periods of several hours. Models of loops including stratified and quasi-steady heating predict the development of a state of thermal non-equilibrium (TNE): cycles of evaporative upflows at the footpoints followed by falling condensations at the apex. Based on Fourier and wavelet analysis, we demonstrate that the observed periodic signals are indeed not signatures of vibrational modes. Instead, superimposed on the power law expected from the stochastic background emission, the power spectra of the time series exhibit the discrete harmonics and continua expected from periodic trains of pulsesmore » of random amplitudes. These characteristics reinforce our earlier interpretation of these pulsations as being aborted TNE cycles.« less

Analysis of closed cycle megawatt class space power systems with nuclear reactor heat sources

NASA Technical Reports Server (NTRS)

Juhasz, A. J.; Jones, B. I.

1987-01-01

The analysis and integration studies of multimegawatt nuclear power conversion systems for potential SDI applications is presented. A study is summarized which considered 3 separate types of power conversion systems for steady state power generation with a duty requirement of 1 yr at full power. The systems considered are based on the following conversion cycles: direct and indirect Brayton gas turbine, direct and indirect liquid metal Rankine, and in core thermionic. A complete mass analysis was performed for each system at power levels ranging from 1 to 25 MWe for both heat pipe and liquid droplet radiator options. In the modeling of common subsystems, reactor and shield calculations were based on multiparameter correlation and an in-house analysis for the heat rejection and other subsystems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pezeshki, Alan M.; Sacci, Robert L.; Veith, Gabriel M.

Here, we demonstrate a novel method to accelerate electrode degradation in redox flow batteries and apply this method to the all-vanadium chemistry. Electrode performance degradation occurred seven times faster than in a typical cycling experiment, enabling rapid evaluation of materials. This method also enables the steady-state study of electrodes. In this manner, it is possible to delineate whether specific operating conditions induce performance degradation; we found that both aggressively charging and discharging result in performance loss. Post-mortem x-ray photoelectron spectroscopy of the degraded electrodes was used to resolve the effects of state of charge (SoC) and current on the electrodemore » surface chemistry. For the electrode material tested in this work, we found evidence that a loss of oxygen content on the negative electrode cannot explain decreased cell performance. Furthermore, the effects of decreased electrode and membrane performance on capacity fade in a typical cycling battery were decoupled from crossover; electrode and membrane performance decay were responsible for a 22% fade in capacity, while crossover caused a 12% fade.« less

A Data Filter for Identifying Steady-State Operating Points in Engine Flight Data for Condition Monitoring Applications

NASA Technical Reports Server (NTRS)

Simon, Donald L.; Litt, Jonathan S.

2010-01-01

This paper presents an algorithm that automatically identifies and extracts steady-state engine operating points from engine flight data. It calculates the mean and standard deviation of select parameters contained in the incoming flight data stream. If the standard deviation of the data falls below defined constraints, the engine is assumed to be at a steady-state operating point, and the mean measurement data at that point are archived for subsequent condition monitoring purposes. The fundamental design of the steady-state data filter is completely generic and applicable for any dynamic system. Additional domain-specific logic constraints are applied to reduce data outliers and variance within the collected steady-state data. The filter is designed for on-line real-time processing of streaming data as opposed to post-processing of the data in batch mode. Results of applying the steady-state data filter to recorded helicopter engine flight data are shown, demonstrating its utility for engine condition monitoring applications.

Tailored parameter optimization methods for ordinary differential equation models with steady-state constraints.

PubMed

Fiedler, Anna; Raeth, Sebastian; Theis, Fabian J; Hausser, Angelika; Hasenauer, Jan

2016-08-22

Ordinary differential equation (ODE) models are widely used to describe (bio-)chemical and biological processes. To enhance the predictive power of these models, their unknown parameters are estimated from experimental data. These experimental data are mostly collected in perturbation experiments, in which the processes are pushed out of steady state by applying a stimulus. The information that the initial condition is a steady state of the unperturbed process provides valuable information, as it restricts the dynamics of the process and thereby the parameters. However, implementing steady-state constraints in the optimization often results in convergence problems. In this manuscript, we propose two new methods for solving optimization problems with steady-state constraints. The first method exploits ideas from optimization algorithms on manifolds and introduces a retraction operator, essentially reducing the dimension of the optimization problem. The second method is based on the continuous analogue of the optimization problem. This continuous analogue is an ODE whose equilibrium points are the optima of the constrained optimization problem. This equivalence enables the use of adaptive numerical methods for solving optimization problems with steady-state constraints. Both methods are tailored to the problem structure and exploit the local geometry of the steady-state manifold and its stability properties. A parameterization of the steady-state manifold is not required. The efficiency and reliability of the proposed methods is evaluated using one toy example and two applications. The first application example uses published data while the second uses a novel dataset for Raf/MEK/ERK signaling. The proposed methods demonstrated better convergence properties than state-of-the-art methods employed in systems and computational biology. Furthermore, the average computation time per converged start is significantly lower. In addition to the theoretical results, the analysis of the dataset for Raf/MEK/ERK signaling provides novel biological insights regarding the existence of feedback regulation. Many optimization problems considered in systems and computational biology are subject to steady-state constraints. While most optimization methods have convergence problems if these steady-state constraints are highly nonlinear, the methods presented recover the convergence properties of optimizers which can exploit an analytical expression for the parameter-dependent steady state. This renders them an excellent alternative to methods which are currently employed in systems and computational biology.

Evaluating litter decomposition and soil organic matter dynamics in earth system models: contrasting analysis of long-term litter decomposition and steady-state soil carbon

NASA Astrophysics Data System (ADS)

Bonan, G. B.; Wieder, W. R.

2012-12-01

Decomposition is a large term in the global carbon budget, but models of the earth system that simulate carbon cycle-climate feedbacks are largely untested with respect to litter decomposition. Here, we demonstrate a protocol to document model performance with respect to both long-term (10 year) litter decomposition and steady-state soil carbon stocks. First, we test the soil organic matter parameterization of the Community Land Model version 4 (CLM4), the terrestrial component of the Community Earth System Model, with data from the Long-term Intersite Decomposition Experiment Team (LIDET). The LIDET dataset is a 10-year study of litter decomposition at multiple sites across North America and Central America. We show results for 10-year litter decomposition simulations compared with LIDET for 9 litter types and 20 sites in tundra, grassland, and boreal, conifer, deciduous, and tropical forest biomes. We show additional simulations with DAYCENT, a version of the CENTURY model, to ask how well an established ecosystem model matches the observations. The results reveal large discrepancy between the laboratory microcosm studies used to parameterize the CLM4 litter decomposition and the LIDET field study. Simulated carbon loss is more rapid than the observations across all sites, despite using the LIDET-provided climatic decomposition index to constrain temperature and moisture effects on decomposition. Nitrogen immobilization is similarly biased high. Closer agreement with the observations requires much lower decomposition rates, obtained with the assumption that nitrogen severely limits decomposition. DAYCENT better replicates the observations, for both carbon mass remaining and nitrogen, without requirement for nitrogen limitation of decomposition. Second, we compare global observationally-based datasets of soil carbon with simulated steady-state soil carbon stocks for both models. The models simulations were forced with observationally-based estimates of annual litterfall and model-derived climatic decomposition index. While comparison with the LIDET 10-year litterbag study reveals sharp contrasts between CLM4 and DAYCENT, simulations of steady-state soil carbon show less difference between models. Both CLM4 and DAYCENT significantly underestimate soil carbon. Sensitivity analyses highlight causes of the low soil carbon bias. The terrestrial biogeochemistry of earth system models must be critically tested with observations, and the consequences of particular model choices must be documented. Long-term litter decomposition experiments such as LIDET provide a real-world process-oriented benchmark to evaluate models and can critically inform model development. Analysis of steady-state soil carbon estimates reveal additional, but here different, inferences about model performance.

The Markov process admits a consistent steady-state thermodynamic formalism

NASA Astrophysics Data System (ADS)

Peng, Liangrong; Zhu, Yi; Hong, Liu

2018-01-01

The search for a unified formulation for describing various non-equilibrium processes is a central task of modern non-equilibrium thermodynamics. In this paper, a novel steady-state thermodynamic formalism was established for general Markov processes described by the Chapman-Kolmogorov equation. Furthermore, corresponding formalisms of steady-state thermodynamics for the master equation and Fokker-Planck equation could be rigorously derived in mathematics. To be concrete, we proved that (1) in the limit of continuous time, the steady-state thermodynamic formalism for the Chapman-Kolmogorov equation fully agrees with that for the master equation; (2) a similar one-to-one correspondence could be established rigorously between the master equation and Fokker-Planck equation in the limit of large system size; (3) when a Markov process is restrained to one-step jump, the steady-state thermodynamic formalism for the Fokker-Planck equation with discrete state variables also goes to that for master equations, as the discretization step gets smaller and smaller. Our analysis indicated that general Markov processes admit a unified and self-consistent non-equilibrium steady-state thermodynamic formalism, regardless of underlying detailed models.

Requirements for rapid plasmid ColE1 copy number adjustments: a mathematical model of inhibition modes and RNA turnover rates.

PubMed

Paulsson, J; Nordström, K; Ehrenberg, M

1998-01-01

The random distribution of ColE1 plasmids between the daughter cells at cell division introduces large copy number variations. Statistic variation associated with limited copy number in single cells also causes fluctuations to emerge spontaneously during the cell cycle. Efficient replication control out of steady state is therefore important to tame such stochastic effects of small numbers. In the present model, the dynamic features of copy number control are divided into two parts: first, how sharply the replication frequency per plasmid responds to changes in the concentration of the plasmid-coded inhibitor, RNA I, and second, how tightly RNA I and plasmid concentrations are coupled. Single (hyperbolic)- and multiple (exponential)-step inhibition mechanisms are compared out of steady state and it is shown how the response in replication frequency depends on the mode of inhibition. For both mechanisms, sensitivity of inhibition is "bought" at the expense of a rapid turnover of a replication preprimer, RNA II. Conventional, single-step, inhibition kinetics gives a sloppy replication control even at high RNA II turnover rates, whereas multiple-step inhibition has the potential of working with unlimited precision. When plasmid concentration changes rapidly, RNA I must be degraded rapidly to be "up to date" with the change. Adjustment to steady state is drastically impaired when the turnover rate constants of RNA I decrease below certain thresholds, but is basically unaffected for a corresponding increase. Several features of copy number control that are shown to be crucial for the understanding of ColE1-type plasmids still remain to be experimentally characterized. It is shown how steady-state properties reflect dynamics at the heart of regulation and therefore can be used to discriminate between fundamentally different copy number control mechanisms. The experimental tests of the predictions made require carefully planned assays, and some suggestions for suitable experiments arise naturally from the present work. It is also discussed how the presence of the Rom protein may affect dynamic qualities of copy number control. Copyright 1998 Academic Press.

Implicit flux-split Euler schemes for unsteady aerodynamic analysis involving unstructured dynamic meshes

NASA Technical Reports Server (NTRS)

Batina, John T.

1990-01-01

Improved algorithms for the solution of the time-dependent Euler equations are presented for unsteady aerodynamic analysis involving unstructured dynamic meshes. The improvements have been developed recently to the spatial and temporal discretizations used by unstructured grid flow solvers. The spatial discretization involves a flux-split approach which is naturally dissipative and captures shock waves sharply with at most one grid point within the shock structure. The temporal discretization involves an implicit time-integration shceme using a Gauss-Seidel relaxation procedure which is computationally efficient for either steady or unsteady flow problems. For example, very large time steps may be used for rapid convergence to steady state, and the step size for unsteady cases may be selected for temporal accuracy rather than for numerical stability. Steady and unsteady flow results are presented for the NACA 0012 airfoil to demonstrate applications of the new Euler solvers. The unsteady results were obtained for the airfoil pitching harmonically about the quarter chord. The resulting instantaneous pressure distributions and lift and moment coefficients during a cycle of motion compare well with experimental data. The paper presents a description of the Euler solvers along with results and comparisons which assess the capability.

Implicit flux-split Euler schemes for unsteady aerodynamic analysis involving unstructured dynamic meshes

NASA Technical Reports Server (NTRS)

Batina, John T.

1990-01-01

Improved algorithm for the solution of the time-dependent Euler equations are presented for unsteady aerodynamic analysis involving unstructured dynamic meshes. The improvements were developed recently to the spatial and temporal discretizations used by unstructured grid flow solvers. The spatial discretization involves a flux-split approach which is naturally dissipative and captures shock waves sharply with at most one grid point within the shock structure. The temporal discretization involves an implicit time-integration scheme using a Gauss-Seidel relaxation procedure which is computationally efficient for either steady or unsteady flow problems. For example, very large time steps may be used for rapid convergence to steady state, and the step size for unsteady cases may be selected for temporal accuracy rather than for numerical stability. Steady and unsteady flow results are presented for the NACA 0012 airfoil to demonstrate applications of the new Euler solvers. The unsteady results were obtained for the airfoil pitching harmonically about the quarter chord. The resulting instantaneous pressure distributions and lift and moment coefficients during a cycle of motion compare well with experimental data. A description of the Euler solvers is presented along with results and comparisons which assess the capability.

Stabilization of a spatially uniform steady state in two systems exhibiting Turing patterns

NASA Astrophysics Data System (ADS)

Konishi, Keiji; Hara, Naoyuki

2018-05-01

This paper deals with the stabilization of a spatially uniform steady state in two coupled one-dimensional reaction-diffusion systems with Turing instability. This stabilization corresponds to amplitude death that occurs in a coupled system with Turing instability. Stability analysis of the steady state shows that stabilization does not occur if the two reaction-diffusion systems are identical. We derive a sufficient condition for the steady state to be stable for any length of system and any boundary conditions. Our analytical results are supported with numerical examples.

Pseudo-compressibility methods for the incompressible flow equations

NASA Technical Reports Server (NTRS)

Turkel, Eli; Arnone, A.

1993-01-01

Preconditioning methods to accelerate convergence to a steady state for the incompressible fluid dynamics equations are considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Thus the steady state of the preconditioned system is the same as the steady state of the original system. The method is compared to other types of pseudo-compressibility. For finite difference methods preconditioning can change and improve the steady state solutions. An application to viscous flow around a cascade with a non-periodic mesh is presented.

Quantum thermodynamics of nanoscale steady states far from equilibrium

NASA Astrophysics Data System (ADS)

Taniguchi, Nobuhiko

2018-04-01

We develop an exact quantum thermodynamic description for a noninteracting nanoscale steady state that couples strongly with multiple reservoirs. We demonstrate that there exists a steady-state extension of the thermodynamic function that correctly accounts for the multiterminal Landauer-Büttiker formula of quantum transport of charge, energy, or heat via the nonequilibrium thermodynamic relations. Its explicit form is obtained for a single bosonic or fermionic level in the wide-band limit, and corresponding thermodynamic forces (affinities) are identified. Nonlinear generalization of the Onsager reciprocity relations are derived. We suggest that the steady-state thermodynamic function is also capable of characterizing the heat current fluctuations of the critical transport where the thermal fluctuations dominate. Also, the suggested nonequilibrium steady-state thermodynamic relations seemingly persist for a spin-degenerate single level with local interaction.

Integration of Steady-State and Temporal Gene Expression Data for the Inference of Gene Regulatory Networks

PubMed Central

Wang, Yi Kan; Hurley, Daniel G.; Schnell, Santiago; Print, Cristin G.; Crampin, Edmund J.

2013-01-01

We develop a new regression algorithm, cMIKANA, for inference of gene regulatory networks from combinations of steady-state and time-series gene expression data. Using simulated gene expression datasets to assess the accuracy of reconstructing gene regulatory networks, we show that steady-state and time-series data sets can successfully be combined to identify gene regulatory interactions using the new algorithm. Inferring gene networks from combined data sets was found to be advantageous when using noisy measurements collected with either lower sampling rates or a limited number of experimental replicates. We illustrate our method by applying it to a microarray gene expression dataset from human umbilical vein endothelial cells (HUVECs) which combines time series data from treatment with growth factor TNF and steady state data from siRNA knockdown treatments. Our results suggest that the combination of steady-state and time-series datasets may provide better prediction of RNA-to-RNA interactions, and may also reveal biological features that cannot be identified from dynamic or steady state information alone. Finally, we consider the experimental design of genomics experiments for gene regulatory network inference and show that network inference can be improved by incorporating steady-state measurements with time-series data. PMID:23967277

Oxidation and Volatilization of Silica-Formers in Water Vapor

NASA Technical Reports Server (NTRS)

Opila, E. J.; Gray, Hugh R. (Technical Monitor)

2002-01-01

At high temperatures SiC and Si3N4 react with water vapor to form a silica scale. Silica scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming silica and the other removing silica, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved, After steady state is achieved, the oxide found on the surface is a constant thickness and recession of the underlying material occurs at a linear rate. The steady state oxide thickness, the time to achieve steady state, and the steady state recession rate can all be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate can also be determined from parameters that describe a water vapor-containing environment. Accordingly, maps have been developed to show these steady state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of silica formers in water-vapor containing environments such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si3N4

X-Ray Spectral Analysis of the Steady States of GRS1915+105

NASA Astrophysics Data System (ADS)

Peris, Charith S.; Remillard, Ronald A.; Steiner, James F.; Vrtilek, Saeqa D.; Varnière, Peggy; Rodriguez, Jerome; Pooley, Guy

2016-05-01

We report on the X-ray spectral behavior within the steady states of GRS1915+105. Our work is based on the full data set of the source obtained using the Proportional Counter Array (PCA) on the Rossi X-ray Timing Explorer (RXTE) and 15 GHz radio data obtained using the Ryle Telescope. The steady observations within the X-ray data set naturally separated into two regions in the color-color diagram and we refer to these regions as steady-soft and steady-hard. GRS1915+105 displays significant curvature in the coronal component in both the soft and hard data within the RXTE/PCA bandpass. A majority of the steady-soft observations displays a roughly constant inner disk radius ({R}{{in}}), while the steady-hard observations display an evolving disk truncation which is correlated to the mass accretion rate through the disk. The disk flux and coronal flux are strongly correlated in steady-hard observations and very weakly correlated in the steady-soft observations. Within the steady-hard observations, we observe two particular circumstances when there are correlations between the coronal X-ray flux and the radio flux with log slopes η ˜ 0.68+/- 0.35 and η ˜ 1.12+/- 0.13. They are consistent with the upper and lower tracks of Gallo et al. (2012), respectively. A comparison of the model parameters to the state definitions shows that almost all of the steady-soft observations match the criteria of either a thermal or steep power-law state, while a large portion of the steady-hard observations match the hard-state criteria when the disk fraction constraint is neglected.

Enhanced absorption cycle computer model

NASA Astrophysics Data System (ADS)

Grossman, G.; Wilk, M.

1993-09-01

Absorption heat pumps have received renewed and increasing attention in the past two decades. The rising cost of electricity has made the particular features of this heat-powered cycle attractive for both residential and industrial applications. Solar-powered absorption chillers, gas-fired domestic heat pumps, and waste-heat-powered industrial temperature boosters are a few of the applications recently subjected to intensive research and development. The absorption heat pump research community has begun to search for both advanced cycles in various multistage configurations and new working fluid combinations with potential for enhanced performance and reliability. The development of working absorption systems has created a need for reliable and effective system simulations. A computer code has been developed for simulation of absorption systems at steady state in a flexible and modular form, making it possible to investigate various cycle configurations with different working fluids. The code is based on unit subroutines containing the governing equations for the system's components and property subroutines containing thermodynamic properties of the working fluids. The user conveys to the computer an image of his cycle by specifying the different subunits and their interconnections. Based on this information, the program calculates the temperature, flow rate, concentration, pressure, and vapor fraction at each state point in the system, and the heat duty at each unit, from which the coefficient of performance (COP) may be determined. This report describes the code and its operation, including improvements introduced into the present version. Simulation results are described for LiBr-H2O triple-effect cycles, LiCl-H2O solar-powered open absorption cycles, and NH3-H2O single-effect and generator-absorber heat exchange cycles. An appendix contains the user's manual.

The belowground frontier is key to understanding terrestrial ecosystem responses to global change

NASA Astrophysics Data System (ADS)

Mackay, D. S.; Grossiord, C.; Johnson, D. M.; McDowell, N. G.; Savoy, P.; Sperry, J.

2017-12-01

Terrestrial ecosystems adapt and acclimate to global change in part because plasticity of traits helps define how individuals respond to thresholds. A threshold could be a tipping point where a small change in a forcing brings about a big change in system response, or a critical transition that shifts the system into an alternative stable or steady state. For instance, a dimorphic root system offers an individual plant the ability to use shallow water during wet periods and deeper water during dry periods. During drought this system imparts on the ecosystem a stable state as opposed to shifting to an alternative state of fewer surviving woody species. We tested this systems view within TREES, a biophysical model that integrates abiotic and biotic drivers of ecosystem response by coupling whole-plant (rhizosphere to leaf) hydraulics to carbon allocation, root-rhizosphere expansion/contraction and rhizosphere-root centric microbe-plant nitrogen dynamics. We simulated ecosystem responses to (1) seasonal drought in a blue oak woodland, (2) an unusually protracted drought in a mixed species woodland, and (3) an experimentally imposed drought with and without warming in a juniper-pinon woodland. For the blue oak, access to deep groundwater was critical for the timing of drought deciduousness. For the mixed species woodland, deeper roots reduced the risk of mortality via rhizosphere hydraulic failure. Drought induced relatively greater water uptake from bedrock water sources in both juniper and pinon, while heat promoted greater bedrock water uptake by juniper. Higher temperature forced the microbial N and plant NSC cycles to new steady states that were unfavorable for allocation of carbon to canopy and fine roots, and higher respiration costs in roots resulted in a decline in root-to-leaf area and consequent greater loss of hydraulic conductance. The results justify a deeper understanding of the belowground frontier that bridges hydrology, plant hydraulics, and biogeochemical cycles.

Postexercise hypotension in an endurance-trained population of men and women following high-intensity interval and steady-state cycling.

PubMed

Rossow, Lindy; Yan, Huimin; Fahs, Christopher A; Ranadive, Sushant M; Agiovlasitis, Stamatis; Wilund, Kenneth R; Baynard, Tracy; Fernhall, Bo

2010-04-01

The acute effect of high-intensity interval exercise (HI) on blood pressure (BP) is unknown although this type of exercise has similar or greater cardiovascular benefits compared to steady-state aerobic exercise (SS). This study examined postexercise hypotension (PEH) and potential mechanisms of this response in endurance-trained subjects following acute SS and HI. Sex differences were also evaluated. A total of 25 endurance-trained men (n = 15) and women (n = 10) performed a bout of HI and a bout of SS cycling in randomized order on separate days. Before exercise, 30 min postexercise, and 60 min postexercise, we measured brachial and aortic BP. Cardiac output (CO), stroke volume (SV), end diastolic volume (EDV), end systolic volume (ESV), and left ventricular wall-velocities were measured using ultrasonography with tissue Doppler capabilities. Ejection fraction and fractional shortening (FS), total peripheral resistance (TPR), and calf vascular resistance were calculated from the above variables and measures of leg blood flow. BP, ejection fraction, and FS decreased by a similar magnitude following both bouts but changes in CO, heart rate (HR), TPR, and calf vascular resistance were greater in magnitude following HI than following SS. Men and women responded similarly to HI. Although men and women exhibited a similar PEH following SS, they showed differential changes in SV, EDV, and TPR. HI acutely reduces BP similarly to SS. The mechanistic response to HI appears to differ from that of SS, and endurance-trained men and women may exhibit differential mechanisms for PEH following SS but not HI.

Actin isoform and alpha 1B-adrenoceptor gene expression in aortic and coronary smooth muscle is influenced by cyclical stretch.

PubMed

Lundberg, M S; Sadhu, D N; Grumman, V E; Chilian, W M; Ramos, K S

1995-09-01

The occurrence of vascular domains with specific biological and pharmacological characteristics suggests that smooth muscle cells in different arteries may respond differentially to a wide range of environmental stimuli. To determine if some of these vessel-specific differences may be attributable to mechano-sensitive gene regulation, the influence of cyclical stretch on the expression of actin isoform and alpha 1B-adrenoceptor genes was examined in aortic and coronary smooth muscle cells. Cells were seeded on an elastin substrate and subjected to maximal stretching (24% elongation) and relaxation cycles at a frequency of 120 cycles/min in a Flexercell strain unit for 72 h. Total RNA was extracted and hybridized to radiolabeled cDNA probes to assess gene expression. Stretch caused a greater reduction of actin isoform mRNA levels in aortic smooth muscle cells as compared to cells from the coronary artery. Steady-state mRNA levels of alpha 1B-adrenoceptor were also decreased by cyclical stretch in both cell types but the magnitude of the response was greater in coronary smooth muscle cells. No changes in alpha 1B-adrenoceptor or beta/gamma-actin steady-state mRNA levels were observed in H4IIE cells, a nonvascular, immortalized cell line. The relative gene expression of heat shock protein 70 was not influenced by the cyclic stretch regimen in any of these cell types. These results suggest that stretch may participate in the regulation of gene expression in vascular smooth muscle cells and that this response exhibits some degree of cell-specificity.

Partitioning of water between surface and mantle on terrestrial exoplanets: effect of surface-mantle water exchange parameterizations on ocean depth

NASA Astrophysics Data System (ADS)

Komacek, T. D.; Abbot, D. S.

2016-12-01

Terrestrial exoplanets in the canonical habitable zone may have a variety of initial water fractions due to their volatile delivery rate via planetesimals. If the total planetary water complement is high, the entire surface may be covered in water, forming a "waterworld". The habitable zone for waterworlds is likely smaller than that for planets with partial land coverage because waterworlds lack the stabilizing silicate-weathering feedback. On a planet with active tectonics, competing mechanisms act to regulate the abundance of water on the surface by determining the partitioning of water between interior and surface. We have explored how the incorporation of different mechanisms for the outgassing and regassing of water changes the volatile evolution of a planet. Specifically, we have examined three models for volatile cycling: a model with degassing and regassing both determined by the seafloor pressure, one with mantle temperature-dependent degassing and regassing rates, and a hybrid model that has the degassing rate driven by seafloor pressure and the regassing rate determined by the mantle temperature. We find that the volatile cycling in all three of these scenarios reaches a steady-state after a few billion years. Using these steady-states, we can make predictions from each model for how much water is needed to flood the surface and make a waterworld. We find that if volatile cycling is either solely temperature-dependent or pressure-dependent, exoplanets require a high abundance (more than 0.3% by mass) of water to have fully inundated surfaces. This is because the waterworld boundary for these models is regulated by how much water can be stuffed into the mantle. However, if degassing is more dependent on the seafloor pressure and regassing mainly dependent on mantle temperature, super-Earth mass planets with a total water fraction similar to that of the Earth (approximately 0.05% by mass) can become waterworlds. As a result, further understanding of the processes that drive volatile cycling on terrestrial planets is needed to determine the water fraction at which they are likely to become waterworlds.

X-ray spectral analysis of the steady states of GRS 1915+105

NASA Astrophysics Data System (ADS)

Peris, Charith; Remillard, Ronald A.; Steiner, James F.; Vrtilek, Saeqa Dil; Varniere, Peggy; Rodriguez, Jerome; Pooley, Guy G.

2016-04-01

Of the black hole binaries (BHBs) discovered thus far, GRS 1915+105 stands out as an exceptional source primarily due to its wild X-ray variability, the diversity of which has not been replicated in any other stellar-mass black hole. Although extreme variability is commonplace in its light-curve, about half of the observations of GRS1915+105 show fairly steady X-ray intensity. We report on the X-ray spectral behavior within these steady observations. Our work is based on a vast RXTE/PCA data set obtained on GRS 1915+105 during the course of its entire mission and 10 years of radio data from the Ryle Telescope, which overlap the X-ray data. We find that the steady observations within the X-ray data set naturally separate into two regions in a color-color diagram, which we refer to as steady-soft and steady-hard. GRS 1915+105 displays significant curvature in the Comptonization component within the PCA band pass suggesting significantly heating from a hot disk present in all states. A new Comptonization model 'simplcut' was developed in order to model this curvature to best effect. A majority of the steady-soft observations display a roughly constant inner disk radius, remarkably reminiscent of canonical soft state black hole binaries. In contrast, the steady-hard observations display a growing disk truncation that is correlated to the mass accretion rate through the disk, which suggests a magnetically truncated disk. A comparison of X-ray model parameters to the canonical state definitions show that almost all steady-soft observations match the criteria of either thermal or steep power law state, while the thermal state observations dominate the constant radius branch. A large portion 80 % of the steady-hard observations matches the hard state criteria when the disk fraction constraint is neglected. These results combine to suggest that within the complexity of this source is a simpler underlying basis of states, which map to those observed in canonical BHBs.

Capacity Decay Mitigation by Asymmetric Positive/Negative Electrolyte Volumes in Vanadium Redox Flow Batteries.

PubMed

Park, Jong Ho; Park, Jung Jin; Park, O Ok; Yang, Jung Hoon

2016-11-23

Capacity decay in vanadium redox flow batteries during charge-discharge cycling has become an important issue because it lowers the practical energy density of the battery. The battery capacity tends to drop rapidly within the first tens of cycles and then drops more gradually over subsequent cycles during long-term operation. This paper analyzes and discusses the reasons for this early capacity decay. The imbalanced crossover rate of vanadium species was found to remain high until the total difference in vanadium concentration between the positive and negative electrolytes reached almost 1 mol dm -3 . To minimize the initial crossover imbalance, we introduced an asymmetric volume ratio between the positive and negative electrolytes during cell operation. Changing this ratio significantly reduced the capacity fading rate of the battery during the early cycles and improved its capacity retention at steady state. As an example, the practical energy density of the battery increased from 15.5 to 25.2 Wh L -1 simply after reduction of the positive volume by 25 %. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The timing of the human circadian clock is accurately represented by the core body temperature rhythm following phase shifts to a three-cycle light stimulus near the critical zone

NASA Technical Reports Server (NTRS)

Jewett, M. E.; Duffy, J. F.; Czeisler, C. A.

2000-01-01

A double-stimulus experiment was conducted to evaluate the phase of the underlying circadian clock following light-induced phase shifts of the human circadian system. Circadian phase was assayed by constant routine from the rhythm in core body temperature before and after a three-cycle bright-light stimulus applied near the estimated minimum of the core body temperature rhythm. An identical, consecutive three-cycle light stimulus was then applied, and phase was reassessed. Phase shifts to these consecutive stimuli were no different from those obtained in a previous study following light stimuli applied under steady-state conditions over a range of circadian phases similar to those at which the consecutive stimuli were applied. These data suggest that circadian phase shifts of the core body temperature rhythm in response to a three-cycle stimulus occur within 24 h following the end of the 3-day light stimulus and that this poststimulus temperature rhythm accurately reflects the timing of the underlying circadian clock.

Modeling Non-Steady Isotopologue and Isotopomer Speciation and Fractionation during Denitrification in Soils

NASA Astrophysics Data System (ADS)

Maggi, F.; Riley, W. J.

2009-12-01

The composition and location of 15N atoms on N2O isotopomers and isotopologues during isotope speciation has been used to characterize soil biological N cycling and N2O surface emissions. Although there exist few experimental observations, no attempt has been made to model N2O isotopomer speciation. The mathematical treatment of biological kinetic reactions in isotopic applications normally makes use of first-order and quasi steady-state complexation assumptions without taking into account changes in enzyme concentration, reaction stoichiometry, and isotopologue and isotopomer speciation. When multiatomic isotopically-labeled reactants are used in a multi-molecurar reaction, these assumptions may fail since they always lead to a constant fractionation factor and cannot describe speciation of isotopologues and isotopomers. We have developed a mathematical framework that is capable of describing isotopologue and isotopmer speciation and fractionation under the assumption of non-steady complexation during biological kinetic reactions that overcome the limitations mentioned above. This framework was applied to a case study of non-steady (variable and inverse) isotopic effects observed during N2O production and consumption in soils. Our mathematical treatment has led to generalized kinetic equations which replicate experimental observations with high accuracy and help interpret non-steady isotopic effects and isotopologue and isotopomer speciation. The kinetic equations introduced and applied here have general validity in describing isotopic effects in any biochemical reactions by considering: changing enzyme concentrations, mass and isotope conservation, and reaction stoichiometry. The equations also describe speciation of any isotopologue and isotopomer product from any isotopologue and isotopmer reactant.

'Butterfly effect' in porous Bénard convection heated from below

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siri, Z.; Liew, K. Y.; Ibrahim, R. I.

2014-07-10

Transition from steady to chaos for the onset of Bénard convection in porous medium was analyzed. The governing equation is reduced to ordinary differential equation and solved using built in MATLAB ODE45. The transition from steady to chaos take over from a limit cycle followed by homoclinic explosion.

Stress-relaxation and fatigue behaviour of synthetic brow-suspension materials.

PubMed

Kwon, Kyung-Ah; Shipley, Rebecca J; Edirisinghe, Mohan; Rayment, Andrew W; Best, Serena M; Cameron, Ruth E; Salam, Tahrina; Rose, Geoffrey E; Ezra, Daniel G

2015-02-01

Ptosis describes a low position of the upper eyelid. When this condition is due to poor function of the levator palpebrae superioris muscle, responsible for raising the lid, "brow-suspension" ptosis correction is usually performed, which involves internally attaching the malpositioned eyelid to the forehead musculature using brow-suspension materials. In service, such materials are exposed to both rapid tensile loading and unloading sequences during blinking, and a more sustained tensile strain during extended periods of closure. In this study, various mechanical tests were conducted to characterise and compare some of commonly-used synthetic brow-suspension materials (Prolene(®), Supramid Extra(®) II, Silicone rods (Visitec(®) Seiff frontalis suspension set) and Mersilene(®) mesh) for their time-dependent response. At a given constant tensile strain or load, all of the brow-suspension materials exhibited stress-relaxation or creep, with Prolene(®) having a statistically different relaxation or creep ratio as compared with those of others. Uniaxial tensile cyclic tests through preconditioning and fatigue tests demonstrated drastically different time-dependent response amongst the various materials. Although the tests generated hysteresis force-strain loops for all materials, the mechanical properties such as the number of cycles required to reach the steady-state, the reduction in the peak force, and the cyclic energy dissipation varied considerably. To reach the steady-state, Prolene(®) and the silicone rod required the greatest and the least number of cycles, respectively. Furthermore, the fatigue tests at physiologically relevant conditions (15% strain controlled at 6.5 Hz) demonstrated that the reduction in the peak force during 100,000 cycles ranged from 15% to 58%, with Prolene(®) and the silicone rod exhibiting the greatest and the least value, respectively. Many factors need to be considered to select the most suitable brow-suspension material for ptosis correction. These novel data on the mechanical time-dependent performance could therefore help to guide clinicians in their decision-making process for optimal surgical outcome. Copyright © 2014 Elsevier Ltd. All rights reserved.

AEROSOL GROWTH IN A STEADY-STATE, CONTINUOUS FLOW CHAMBER: APPLICATION TO STUDIES OF SECONDARY AEROSOL FORMATION

EPA Science Inventory

An analytical solution for the steady-state aerosol size distribution achieved in a steady-state, continuous flow chamber is derived, where particle growth is occurring by gas-to-particle conversion and particle loss is occurring by deposition to the walls of the chamber. The s...

Analytical Solution of Steady State Equations for Chemical Reaction Networks with Bilinear Rate Laws

PubMed Central

Halász, Ádám M.; Lai, Hong-Jian; McCabe, Meghan M.; Radhakrishnan, Krishnan; Edwards, Jeremy S.

2014-01-01

True steady states are a rare occurrence in living organisms, yet their knowledge is essential for quasi-steady state approximations, multistability analysis, and other important tools in the investigation of chemical reaction networks (CRN) used to describe molecular processes on the cellular level. Here we present an approach that can provide closed form steady-state solutions to complex systems, resulting from CRN with binary reactions and mass-action rate laws. We map the nonlinear algebraic problem of finding steady states onto a linear problem in a higher dimensional space. We show that the linearized version of the steady state equations obeys the linear conservation laws of the original CRN. We identify two classes of problems for which complete, minimally parameterized solutions may be obtained using only the machinery of linear systems and a judicious choice of the variables used as free parameters. We exemplify our method, providing explicit formulae, on CRN describing signal initiation of two important types of RTK receptor-ligand systems, VEGF and EGF-ErbB1. PMID:24334389

Continental crustal growth and the supercontinental cycle: evidence from the Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Hong, Dawei; Zhang, Jisheng; Wang, Tao; Wang, Shiguang; Xie, Xilin

2004-09-01

Studies of supercontinental cycle are mainly concentrated on the assembly, breakup and dispersal of supercontinents, and studies of continental crustal growth largely on the growth and loss (recycling) of the crust. These two problems have long been studied separately from each other. The Paleozoic-Mesozoic granites in the Central Asian Orogenic Belt have commonly positive ɛNd values, implying large-scale continental crustal growth in the Phanerozoic. They coincided temporally and spatially with the Phanerozoic Pangea supercontinental cycle, and overlapped in space with the P-wave high- V anomalies and calculated positions of subducted slabs for the last 180 Ma, all this suggests that the Phanerozoic Laurasia supercontinental assembly was accompanied by large-scale continental crustal growth in central Asia. Based on these observations, this paper proposes that there may be close and original correlations between a supercontinental cycle, continental crustal growth and catastrophic slab avalanches in the mantle. In this model we suggest that rapid continental crustal growth occurred during supercontinent assembly, whereas during supercontinental breakup and dispersal new additions of the crust were balanced by losses, resulting in a steady state system. Supercontinental cycle and continental crustal growth are both governed by changing patterns of mantle convection.

Genetic progress in the UNB-2U population of popcorn under recurrent selection in Rio de Janeiro, Brazil.

PubMed

Ribeiro, R M; do Amaral Júnior, A T; Gonçalves, L S A; Candido, L S; Silva, T R C; Pena, G F

2012-05-15

As part of the Universidade Estadual do Norte Fluminense recurrent selection program of popcorn, we evaluated full-sib families of the sixth cycle of recurrent selection and estimated genetic progress for grain yield and expansion capacity. We assessed 200 full-sib families for 10 agronomic traits, in a randomized block design, with two replications within sets in two environments: Campos dos Goytacazes and Itaocara, in the State of Rio de Janeiro, Brazil. There were significant differences for families/"sets" for all traits, indicating genetic variability that could be exploited in future cycles. In the selection of superior progenies, the Mulamba and Mock index gave the best gains for popping expansion (PE) and grain yield (GY), with values of 10.97 and 15.30%, respectively, using random economic weights. By comparing the evolution of the means obtained for PE and GY in the cycles C(0), C(1), C(2), C(3), C(4), C(5), and predicted for C(6), a steady increase was observed for both PE and GY, with the addition of 1.71 mL/g (R(2) = 0.93) and 192.87 kg/ha (R(2) = 0.88), respectively, in each cycle. Given the good performance of this popcorn population in successive cycles of intrapopulation recurrent selection, we expect that a productive variety with high expansion capacity will soon be available for producers in the north and northwest regions of Rio de Janeiro State, Brazil.

Exaggerated Increases in Microglia Proliferation, Brain Inflammatory Response and Sickness Behaviour upon Lipopolysaccharide Stimulation in Non-Obese Diabetic Mice.

PubMed

McGuiness, Barry; Gibney, Sinead M; Beumer, Wouter; Versnel, Marjan A; Sillaber, Inge; Harkin, Andrew; Drexhage, Hemmo A

2016-01-01

The non-obese diabetic (NOD) mouse, an established model for autoimmune diabetes, shows an exaggerated reaction of pancreas macrophages to inflammatory stimuli. NOD mice also display anxiety when immune-stimulated. Chronic mild brain inflammation and a pro-inflammatory microglial activation is critical in psychiatric behaviour. To explore brain/microglial activation and behaviour in NOD mice at steady state and after systemic lipopolysaccharide (LPS) injection. Affymetrix analysis on purified microglia of pre-diabetic NOD mice (8-10 weeks) and control mice (C57BL/6 and CD1 mice, the parental non-autoimmune strain) at steady state and after systemic LPS (100 μg/kg) administration. Quantitative PCR was performed on the hypothalamus for immune activation markers (IL-1β, IFNγ and TNFα) and growth factors (BDNF and PDGF). Behavioural profiling of NOD, CD1, BALB/c and C57BL/6 mice at steady state was conducted and sickness behaviour/anxiety in NOD and CD1 mice was monitored before and after LPS injection. Genome analysis revealed cell cycle/cell death and survival aberrancies of NOD microglia, substantiated as higher proliferation on BrdU staining. Inflammation signs were absent. NOD mice had a hyper-reactive response to novel environments with some signs of anxiety. LPS injection induced a higher expression of microglial activation markers, a higher brain pro-inflammatory set point (IFNγ, IDO) and a reduced expression of BDNF and PDGF after immune stimulation in NOD mice. NOD mice displayed exaggerated and prolonged sickness behaviour after LPS administration. After stimulation with LPS, NOD mice display an increased microglial proliferation and an exaggerated inflammatory brain response with reduced BDNF and PDGF expression and increased sickness behaviour as compared to controls. © 2016 S. Karger AG, Basel.

Measuring the Sensitivity of Single-locus “Neutrality Tests” Using a Direct Perturbation Approach

PubMed Central

Garrigan, Daniel; Lewontin, Richard; Wakeley, John

2010-01-01

A large number of statistical tests have been proposed to detect natural selection based on a sample of variation at a single genetic locus. These tests measure the deviation of the allelic frequency distribution observed within populations from the distribution expected under a set of assumptions that includes both neutral evolution and equilibrium population demography. The present study considers a new way to assess the statistical properties of these tests of selection, by their behavior in response to direct perturbations of the steady-state allelic frequency distribution, unconstrained by any particular nonequilibrium demographic scenario. Results from Monte Carlo computer simulations indicate that most tests of selection are more sensitive to perturbations of the allele frequency distribution that increase the variance in allele frequencies than to perturbations that decrease the variance. Simulations also demonstrate that it requires, on average, 4N generations (N is the diploid effective population size) for tests of selection to relax to their theoretical, steady-state distributions following different perturbations of the allele frequency distribution to its extremes. This relatively long relaxation time highlights the fact that these tests are not robust to violations of the other assumptions of the null model besides neutrality. Lastly, genetic variation arising under an example of a regularly cycling demographic scenario is simulated. Tests of selection performed on this last set of simulated data confirm the confounding nature of these tests for the inference of natural selection, under a demographic scenario that likely holds for many species. The utility of using empirical, genomic distributions of test statistics, instead of the theoretical steady-state distribution, is discussed as an alternative for improving the statistical inference of natural selection. PMID:19744997

Dynamic balance during walking adaptability tasks in individuals post-stroke.

PubMed

Vistamehr, Arian; Balasubramanian, Chitralakshmi K; Clark, David J; Neptune, Richard R; Fox, Emily J

2018-06-06

Maintaining dynamic balance during community ambulation is a major challenge post-stroke. Community ambulation requires performance of steady-state level walking as well as tasks that require walking adaptability. Prior studies on balance control post-stroke have mainly focused on steady-state walking, but walking adaptability tasks have received little attention. The purpose of this study was to quantify and compare dynamic balance requirements during common walking adaptability tasks post-stroke and in healthy adults and identify differences in underlying mechanisms used for maintaining dynamic balance. Kinematic data were collected from fifteen individuals with post-stroke hemiparesis during steady-state forward and backward walking, obstacle negotiation, and step-up tasks. In addition, data from ten healthy adults provided the basis for comparison. Dynamic balance was quantified using the peak-to-peak range of whole-body angular-momentum in each anatomical plane during the paretic, nonparetic and healthy control single-leg-stance phase of the gait cycle. To understand differences in some of the key underlying mechanisms for maintaining dynamic balance, foot placement and plantarflexor muscle activation were examined. Individuals post-stroke had significant dynamic balance deficits in the frontal plane across most tasks, particularly during the paretic single-leg-stance. Frontal plane balance deficits were associated with wider paretic foot placement, elevated body center-of-mass, and lower soleus activity. Further, the obstacle negotiation task imposed a higher balance requirement, particularly during the trailing leg single-stance. Thus, improving paretic foot placement and ankle plantarflexor activity, particularly during obstacle negotiation, may be important rehabilitation targets to enhance dynamic balance during post-stroke community ambulation. Copyright © 2018 Elsevier Ltd. All rights reserved.

A robust and tunable mitotic oscillator in artificial cells

PubMed Central

Wang, Shiyuan; Barnes, Patrick M; Liu, Xuwen; Xu, Haotian; Jin, Minjun; Liu, Allen P

2018-01-01

Single-cell analysis is pivotal to deciphering complex phenomena like heterogeneity, bistability, and asynchronous oscillations, where a population ensemble cannot represent individual behaviors. Bulk cell-free systems, despite having unique advantages of manipulation and characterization of biochemical networks, lack the essential single-cell information to understand a class of out-of-steady-state dynamics including cell cycles. Here, by encapsulating Xenopus egg extracts in water-in-oil microemulsions, we developed artificial cells that are adjustable in sizes and periods, sustain mitotic oscillations for over 30 cycles, and function in forms from the simplest cytoplasmic-only to the more complicated ones involving nuclear dynamics, mimicking real cells. Such innate flexibility and robustness make it key to studying clock properties like tunability and stochasticity. Our results also highlight energy as an important regulator of cell cycles. We demonstrate a simple, powerful, and likely generalizable strategy of integrating strengths of single-cell approaches into conventional in vitro systems to study complex clock functions. PMID:29620527

Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic and Cyclic Indentation

NASA Astrophysics Data System (ADS)

Ghosh, Sabita; Prakash, Raghu V.

2013-01-01

Fracture toughness is the ability of a component containing a flow to resist fracture. In the current study, the Ball indentation (BI) test technique, which is well acknowledged as an alternative approach to evaluate mechanical properties of materials due to its semi-nondestructive, fast, and high accurate qualities is used to estimate damage and the fracture toughness for copper samples subjected to varying levels of creep and fatigue. The indentation fracture toughness shows the degradation of Cu samples when they are subjected to different creep conditions. Axial fatigue cycling increases the strength at the mid-gauge section compared to other regions of the samples due to initial strain hardening. The advancement of indentation depth with indentation fatigue cycles experiences transient stage, i.e., jump in indentation depth has been observed, which may be an indication of failure and followed by a steady state with almost constant depth propagation with indentation cycles.

Comparison between reverse Brayton and Kapitza based LNG boil-off gas reliquefaction system using exergy analysis

NASA Astrophysics Data System (ADS)

Kochunni, Sarun Kumar; Chowdhury, Kanchan

2017-02-01

LNG boil-off gas (BOG) reliquefaction systems in LNG carrier ships uses refrigeration devices which are based on reverse Brayton, Claude, Kapitza (modified Claude) or Cascade cycles. Some of these refrigeration devices use nitrogen as the refrigerants and hence nitrogen storage vessels or nitrogen generators needs to be installed in LNG carrier ships which consume space and add weight to the carrier. In the present work, a new configuration based on Kapitza liquefaction cycle which uses BOG itself as working fluid is proposed and has been compared with Reverse Brayton Cycle (RBC) on sizes of heat exchangers and compressor operating parameters. Exergy analysis is done after simulating at steady state with Aspen Hysys 8.6® and the comparison between RBC and Kapitza may help designers to choose reliquefaction system with appropriate process parameters and sizes of equipment. With comparable exergetic efficiency as that of an RBC, a Kaptiza system needs only BOG compressor without any need of nitrogen gas.

Benchmark notch test for life prediction

NASA Technical Reports Server (NTRS)

Domas, P. A.; Sharpe, W. N.; Ward, M.; Yau, J. F.

1982-01-01

The laser Interferometric Strain Displacement Gage (ISDG) was used to measure local strains in notched Inconel 718 test bars subjected to six different load histories at 649 C (1200 F) and including effects of tensile and compressive hold periods. The measurements were compared to simplified Neuber notch analysis predictions of notch root stress and strain. The actual strains incurred at the root of a discontinuity in cyclically loaded test samples subjected to inelastic deformation at high temperature where creep deformations readily occur were determined. The steady state cyclic, stress-strain response at the root of the discontinuity was analyzed. Flat, double notched uniaxially loaded fatigue specimens manufactured from the nickel base, superalloy Inconel 718 were used. The ISDG was used to obtain cycle by cycle recordings of notch root strain during continuous and hold time cycling at 649 C. Comparisons to Neuber and finite element model analyses were made. The results obtained provide a benchmark data set in high technology design where notch fatigue life is the predominant component service life limitation.

A prototypic mathematical model of the human hair cycle.

PubMed

Al-Nuaimi, Yusur; Goodfellow, Marc; Paus, Ralf; Baier, Gerold

2012-10-07

The human hair cycle is a complex, dynamic organ-transformation process during which the hair follicle repetitively progresses from a growth phase (anagen) to a rapid apoptosis-driven involution (catagen) and finally a relative quiescent phase (telogen) before returning to anagen. At present no theory satisfactorily explains the origin of the hair cycle rhythm. Based on experimental evidence we propose a prototypic model that focuses on the dynamics of hair matrix keratinocytes. We argue that a plausible feedback-control structure between two key compartments (matrix keratinocytes and dermal papilla) leads to dynamic instabilities in the population dynamics resulting in rhythmic hair growth. The underlying oscillation consists of an autonomous switching between two quasi-steady states. Additional features of the model, namely bistability and excitability, lead to new hypotheses about the impact of interventions on hair growth. We show how in silico testing may facilitate testing of candidate hair growth modulatory agents in human HF organ culture or in clinical trials. Copyright © 2012 Elsevier Ltd. All rights reserved.

Differentiated effect of ageing on the enzymes of Krebs' cycle, electron transfer complexes and glutamate metabolism of non-synaptic and intra-synaptic mitochondria from cerebral cortex.

PubMed

Villa, R F; Gorini, A; Hoyer, S

2006-11-01

The effect of ageing on the activity of enzymes linked to Krebs' cycle, electron transfer chain and glutamate metabolism was studied in three different types of mitochondria of cerebral cortex of 1-year old and 2-year old male Wistar rats. We assessed the maximum rate (V(max)) of the mitochondrial enzyme activities in non-synaptic perikaryal mitochondria, and in two populations of intra-synaptic mitochondria. The results indicated that: (i) in normal, steady-state cerebral cortex the values of the catalytic activities of the enzymes markedly differed in the various populations of mitochondria; (ii) in intra-synaptic mitochondria, ageing affected the catalytic properties of the enzymes linked to Krebs' cycle, electron transfer chain and glutamate metabolism; (iii) these changes were more evident in intra-synaptic "heavy" than "light" mitochondria. These results indicate a different age-related vulnerability of subpopulations of mitochondria in vivo located into synapses than non-synaptic ones.

Space shuttle main engine definition (phase B). Volume 5: Valves and interconnects. [for space shuttle

NASA Technical Reports Server (NTRS)

Schultz, D. F.

1971-01-01

The steady state thermodynamic cycle balance of the single preburner staged combustion engine, coupled with dynamic transient analyses, dictated in detail the location and requirements for each valve defined in this volume. Valve configuration selections were influenced by overall engine and vehicle system weight and failure mode determinations. Modulating valve actuators are external to the valve and are line replaceable. Development and satisfactory demonstration of a high pressure dynamic shaft seal has made this configuration practical. Pneumatic motor driven actuators that use engine pumped hydrogen gas as the working fluid are used. The helium control system is proposed as a module containing a cluster of solenoid actuated valves. The separable couplings and flanges are designed to assure minimum leakage with minimum coupling weight. The deflection of the seal surface in the flange is defined by finite element analysis that has been confirmed with test data. The seal design proposed has passed preliminary pressure cycling and thermal cycling tests.

MATHEMATICAL ANALYSIS OF STEADY-STATE SOLUTIONS IN COMPARTMENT AND CONTINUUM MODELS OF CELL POLARIZATION

PubMed Central

ZHENG, ZHENZHEN; CHOU, CHING-SHAN; YI, TAU-MU; NIE, QING

2013-01-01

Cell polarization, in which substances previously uniformly distributed become asymmetric due to external or/and internal stimulation, is a fundamental process underlying cell mobility, cell division, and other polarized functions. The yeast cell S. cerevisiae has been a model system to study cell polarization. During mating, yeast cells sense shallow external spatial gradients and respond by creating steeper internal gradients of protein aligned with the external cue. The complex spatial dynamics during yeast mating polarization consists of positive feedback, degradation, global negative feedback control, and cooperative effects in protein synthesis. Understanding such complex regulations and interactions is critical to studying many important characteristics in cell polarization including signal amplification, tracking dynamic signals, and potential trade-off between achieving both objectives in a robust fashion. In this paper, we study some of these questions by analyzing several models with different spatial complexity: two compartments, three compartments, and continuum in space. The step-wise approach allows detailed characterization of properties of the steady state of the system, providing more insights for biological regulations during cell polarization. For cases without membrane diffusion, our study reveals that increasing the number of spatial compartments results in an increase in the number of steady-state solutions, in particular, the number of stable steady-state solutions, with the continuum models possessing infinitely many steady-state solutions. Through both analysis and simulations, we find that stronger positive feedback, reduced diffusion, and a shallower ligand gradient all result in more steady-state solutions, although most of these are not optimally aligned with the gradient. We explore in the different settings the relationship between the number of steady-state solutions and the extent and accuracy of the polarization. Taken together these results furnish a detailed description of the factors that influence the tradeoff between a single correctly aligned but poorly polarized stable steady-state solution versus multiple more highly polarized stable steady-state solutions that may be incorrectly aligned with the external gradient. PMID:21936604

Coordination of Myeloid Differentiation with Reduced Cell Cycle Progression by PU.1 Induction of MicroRNAs Targeting Cell Cycle Regulators and Lipid Anabolism.

PubMed

Solomon, Lauren A; Podder, Shreya; He, Jessica; Jackson-Chornenki, Nicholas L; Gibson, Kristen; Ziliotto, Rachel G; Rhee, Jess; DeKoter, Rodney P

2017-05-15

During macrophage development, myeloid progenitor cells undergo terminal differentiation coordinated with reduced cell cycle progression. Differentiation of macrophages from myeloid progenitors is accompanied by increased expression of the E26 transformation-specific transcription factor PU.1. Reduced PU.1 expression leads to increased proliferation and impaired differentiation of myeloid progenitor cells. It is not understood how PU.1 coordinates macrophage differentiation with reduced cell cycle progression. In this study, we utilized cultured PU.1-inducible myeloid cells to perform genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) analysis coupled with gene expression analysis to determine targets of PU.1 that may be involved in regulating cell cycle progression. We found that genes encoding cell cycle regulators and enzymes involved in lipid anabolism were directly and inducibly bound by PU.1 although their steady-state mRNA transcript levels were reduced. Inhibition of lipid anabolism was sufficient to reduce cell cycle progression in these cells. Induction of PU.1 reduced expression of E2f1 , an important activator of genes involved in cell cycle and lipid anabolism, indirectly through microRNA 223. Next-generation sequencing identified microRNAs validated as targeting cell cycle and lipid anabolism for downregulation. These results suggest that PU.1 coordinates cell cycle progression with differentiation through induction of microRNAs targeting cell cycle regulators and lipid anabolism. Copyright © 2017 American Society for Microbiology.

An exact solution for the steady state phase distribution in an array of oscillators coupled on a hexagonal lattice

NASA Technical Reports Server (NTRS)

Pogorzelski, Ronald J.

2004-01-01

When electronic oscillators are coupled to nearest neighbors to form an array on a hexagonal lattice, the planar phase distributions desired for excitation of a phased array antenna are not steady state solutions of the governing non-linear equations describing the system. Thus the steady state phase distribution deviates from planar. It is shown to be possible to obtain an exact solution for the steady state phase distribution and thus determine the deviation from the desired planar distribution as a function of beam steering angle.

Preconditioning and the limit to the incompressible flow equations

NASA Technical Reports Server (NTRS)

Turkel, E.; Fiterman, A.; Vanleer, B.

1993-01-01

The use of preconditioning methods to accelerate the convergence to a steady state for both the incompressible and compressible fluid dynamic equations are considered. The relation between them for both the continuous problem and the finite difference approximation is also considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Hence, the steady state of the preconditioned system is the same as the steady state of the original system. For finite difference methods the preconditioning can change and improve the steady state solutions. An application to flow around an airfoil is presented.

Theoretical studies of solar-pumped lasers

NASA Technical Reports Server (NTRS)

Harries, W. L.

1982-01-01

Solar-pumped lasers were investigated by comparing experimental results from pulse experiments with steady state calculations. The time varying behavior of an IBr laser is studied. The analysis is only approximate, but indicates that conditions occurring in a pulsed experiment are quite different from those at steady state. The possibility of steady-state lasing in an IBr laser is determined. The effects of high temperatures on the quenching and recombination rates are examined. Although uncertainties in the values of the rate coefficients make it difficult to draw firm conclusions, it seems steady state running may be possible at high temperatures.

Open Cascades as Simple Solutions to Providing Ultrasensitivity and Adaptation in Cellular Signaling

PubMed Central

Srividhya, Jeyaraman; Li, Yongfeng; Pomerening, Joseph R.

2011-01-01

Cell signaling is achieved predominantly by reversible phosphorylation-dephosphorylation reaction cascades. Up until now, circuits conferring adaptation have all required the presence of a cascade with some type of closed topology: negative–feedback loop with a buffering node, or incoherent feedforward loop with a proportioner node. In this paper—using Goldbeter and Koshland-type expressions—we propose a differential equation model to describe a generic, open signaling cascade that elicits an adaptation response. This is accomplished by coupling N phosphorylation–dephosphorylation cycles unidirectionally, without any explicit feedback loops. Using this model, we show that as the length of the cascade grows, the steady states of the downstream cycles reach a limiting value. In other words, our model indicates that there are a minimum number of cycles required to achieve a maximum in sensitivity and amplitude in the response of a signaling cascade. We also describe for the first time that the phenomenon of ultrasensitivity can be further subdivided into three sub–regimes, separated by sharp stimulus threshold values: OFF, OFF-ON-OFF, and ON. In the OFF-ON-OFF regime, an interesting property emerges. In the presence of a basal amount of activity, the temporal evolution of early cycles yields damped peak responses. On the other hand, the downstream cycles switch rapidly to a higher activity state for an extended period of time, prior to settling to an OFF state (OFF-ON-OFF). This response arises from the changing dynamics between a feed–forward activation module and dephosphorylation reactions. In conclusion, our model gives the new perspective that open signaling cascades embedded in complex biochemical circuits may possess the ability to show a switch–like adaptation response, without the need for any explicit feedback circuitry. PMID:21566270

Thermodynamic analysis of a combined-cycle solar thermal power plant with manganese oxide-based thermochemical energy storage

NASA Astrophysics Data System (ADS)

Lei, Qi; Bader, Roman; Kreider, Peter; Lovegrove, Keith; Lipiński, Wojciech

2017-11-01

We explore the thermodynamic efficiency of a solar-driven combined cycle power system with manganese oxide-based thermochemical energy storage system. Manganese oxide particles are reduced during the day in an oxygen-lean atmosphere obtained with a fluidized-bed reactor at temperatures in the range of 750-1600°C using concentrated solar energy. Reduced hot particles are stored and re-oxidized during night-time to achieve continuous power plant operation. The steady-state mass and energy conservation equations are solved for all system components to calculate the thermodynamic properties and mass flow rates at all state points in the system, taking into account component irreversibilities. The net power block and overall solar-to-electric energy conversion efficiencies, and the required storage volumes for solids and gases in the storage system are predicted. Preliminary results for a system with 100 MW nominal solar power input at a solar concentration ratio of 3000, designed for constant round-the-clock operation with 8 hours of on-sun and 16 hours of off-sun operation and with manganese oxide particles cycled between 750 and 1600°C yield a net power block efficiency of 60.0% and an overall energy conversion efficiency of 41.3%. Required storage tank sizes for the solids are estimated to be approx. 5-6 times smaller than those of state-of-the-art molten salt systems.

Greenhouse Gas and Noxious Emissions from Dual Fuel Diesel and Natural Gas Heavy Goods Vehicles.

PubMed

Stettler, Marc E J; Midgley, William J B; Swanson, Jacob J; Cebon, David; Boies, Adam M

2016-02-16

Dual fuel diesel and natural gas heavy goods vehicles (HGVs) operate on a combination of the two fuels simultaneously. By substituting diesel for natural gas, vehicle operators can benefit from reduced fuel costs and as natural gas has a lower CO2 intensity compared to diesel, dual fuel HGVs have the potential to reduce greenhouse gas (GHG) emissions from the freight sector. In this study, energy consumption, greenhouse gas and noxious emissions for five after-market dual fuel configurations of two vehicle platforms are compared relative to their diesel-only baseline values over transient and steady state testing. Over a transient cycle, CO2 emissions are reduced by up to 9%; however, methane (CH4) emissions due to incomplete combustion lead to CO2e emissions that are 50-127% higher than the equivalent diesel vehicle. Oxidation catalysts evaluated on the vehicles at steady state reduced CH4 emissions by at most 15% at exhaust gas temperatures representative of transient conditions. This study highlights that control of CH4 emissions and improved control of in-cylinder CH4 combustion are required to reduce total GHG emissions of dual fuel HGVs relative to diesel vehicles.

Mg isotope fractionation during microbe-mineral interactions

NASA Astrophysics Data System (ADS)

Kim, Insu; Ryu, Jong-sik; Lee, Kwang-sik; Lee, Dongho

2014-05-01

Magnesium is involved in various biogeochemical processes important to the global climate change over geological time-scale. Mg isotopes allow us to directly trace the Mg cycle in the Earth's surface but the factors controlling Mg isotopic compositions have not fully understood yet. Here, we conducted a batch experiment using two bacterial species (Shewanella putrefaciens and Burkholderia fungorum) and three major Mg-bearing minerals (biotite, dolomite and hornblende). All elemental concentrations increased by 336 h and then reached to steady-state values, of which Mg concentrations varied depending on minerals and bacterial species. This result indicates that the mineral dissolution is affect by the presence of microbes, which either provide organic acids or attach onto mineral surface. The Mg isotopic compositions of initial minerals biotite, dolomite and hornblende are -0.35o of biotite, -0.99o of dolomite, and -0.24o of hornblende, in δ26Mg. Similarly, δ26Mg values increased by 336 h and reached to steady-state values, which also varied with minerals and microbes. During dissolution of three minerals, the light isotope of Mg is preferentially incorporated into the dissolved phases and then the dissolved δ26Mg values become consistent with those of minerals with the time.

Closed loop statistical performance analysis of N-K knock controllers

NASA Astrophysics Data System (ADS)

Peyton Jones, James C.; Shayestehmanesh, Saeed; Frey, Jesse

2017-09-01

The closed loop performance of engine knock controllers cannot be rigorously assessed from single experiments or simulations because knock behaves as a random process and therefore the response belongs to a random distribution also. In this work a new method is proposed for computing the distributions and expected values of the closed loop response, both in steady state and in response to disturbances. The method takes as its input the control law, and the knock propensity characteristic of the engine which is mapped from open loop steady state tests. The method is applicable to the 'n-k' class of knock controllers in which the control action is a function only of the number of cycles n since the last control move, and the number k of knock events that have occurred in this time. A Cumulative Summation (CumSum) based controller falls within this category, and the method is used to investigate the performance of the controller in a deeper and more rigorous way than has previously been possible. The results are validated using onerous Monte Carlo simulations, which confirm both the validity of the method and its high computational efficiency.

Creep of trabecular bone from the human proximal tibia

PubMed Central

Novitskaya, Ekaterina; Zin, Carolyn; Chang, Neil; Cory, Esther; Chen, Peter; D'Lima, Darryl; Sah, Robert L.; McKittrick, Joanna

2014-01-01

Creep is the deformation that occurs under a prolonged, sustained load and can lead to permanent damage in bone. Creep in bone is a complex phenomenon and varies with type of loading and local mechanical properties. Human trabecular bone samples from proximal tibia were harvested from a 71-year old female cadaver with osteoporosis. The samples were initially subjected to one cycle load up to 1% strain to determine the creep load. Samples were then loaded in compression under a constant stress for two hours and immediately unloaded. All tests were conducted with the specimens soaked in phosphate buffered saline with proteinase inhibitors at 37°C. Steady state creep rate and final creep strain were estimated from mechanical testing and compared with published data. The steady state creep rate correlated well with values obtained from bovine tibial and human vertebral trabecular bone, and was higher for lower density samples. Tissue architecture was analyzed by micro-computed tomography (μCT) both before and after creep testing to assess creep deformation and damage accumulated. Quantitative morphometric analysis indicated that creep induced changes in trabecular separation and the structural model index. A main mode of deformation was bending of trabeculae. PMID:24857486

Complex and unexpected dynamics in simple genetic regulatory networks

NASA Astrophysics Data System (ADS)

Borg, Yanika; Ullner, Ekkehard; Alagha, Afnan; Alsaedi, Ahmed; Nesbeth, Darren; Zaikin, Alexey

2014-03-01

One aim of synthetic biology is to construct increasingly complex genetic networks from interconnected simpler ones to address challenges in medicine and biotechnology. However, as systems increase in size and complexity, emergent properties lead to unexpected and complex dynamics due to nonlinear and nonequilibrium properties from component interactions. We focus on four different studies of biological systems which exhibit complex and unexpected dynamics. Using simple synthetic genetic networks, small and large populations of phase-coupled quorum sensing repressilators, Goodwin oscillators, and bistable switches, we review how coupled and stochastic components can result in clustering, chaos, noise-induced coherence and speed-dependent decision making. A system of repressilators exhibits oscillations, limit cycles, steady states or chaos depending on the nature and strength of the coupling mechanism. In large repressilator networks, rich dynamics can also be exhibited, such as clustering and chaos. In populations of Goodwin oscillators, noise can induce coherent oscillations. In bistable systems, the speed with which incoming external signals reach steady state can bias the network towards particular attractors. These studies showcase the range of dynamical behavior that simple synthetic genetic networks can exhibit. In addition, they demonstrate the ability of mathematical modeling to analyze nonlinearity and inhomogeneity within these systems.

Quantification of the memory effect of steady-state currents from interaction-induced transport in quantum systems

NASA Astrophysics Data System (ADS)

Lai, Chen-Yen; Chien, Chih-Chun

2017-09-01

Dynamics of a system in general depends on its initial state and how the system is driven, but in many-body systems the memory is usually averaged out during evolution. Here, interacting quantum systems without external relaxations are shown to retain long-time memory effects in steady states. To identify memory effects, we first show quasi-steady-state currents form in finite, isolated Bose- and Fermi-Hubbard models driven by interaction imbalance and they become steady-state currents in the thermodynamic limit. By comparing the steady-state currents from different initial states or ramping rates of the imbalance, long-time memory effects can be quantified. While the memory effects of initial states are more ubiquitous, the memory effects of switching protocols are mostly visible in interaction-induced transport in lattices. Our simulations suggest that the systems enter a regime governed by a generalized Fick's law and memory effects lead to initial-state-dependent diffusion coefficients. We also identify conditions for enhancing memory effects and discuss possible experimental implications.

Effects of predation efficiencies on the dynamics of a tritrophic food chain.

PubMed

Cassinari, Maria Paola; Groppi, Maria; Tebaldi, Claudio

2007-07-01

In this paper the dynamics of a tritrophic food chain (resource, consumer, top predator) is investigated, with particular attention not only to equilibrium states but also to cyclic behaviours that the system may exhibit. The analysis is performed in terms of two bifurcation parameters, denoted by p and q, which measure the efficiencies of the interaction processes. The persistence of the system is discussed, characterizing in the (p; q) plane the regions of existence and stability of biologically significant steady states and those of existence of limit cycles. The bifurcations occurring are discussed, and their implications with reference to biological control problems are considered. Examples of the rich dynamics exhibited by the model, including a chaotic regime, are described.

Cardiorespiratory responses and blood lactate during an experimental run-cycle transition in duathletes.

PubMed

Galy, O; Hue, O; Boussana, A; Le Gallais, D; Prefaut, C

2002-04-01

The aim of this study was to determine the effects of a prior run on the cardiorespiratory responses measured during a subsequent cycle segment. Twelve duathletes underwent three successive laboratory trials at an interval of one week: 1) an incremental cycle test, 2) 20 min of running followed by 20 min of cycling (RC), and 3) 20 min of control cycling (C) at the same intensity as the cycling segment of RC. Ventilatory data were collected every minute using a breath-by-breath automated system. Blood samples were collected to measure venous blood lactate concentration, [La], at rest, after the running and cycling segments of RC and after C. The results showed that the C segment of RC had significantly higher VE, VE/VO2, f and HR than C alone and significantly lower VT (p < 0.05) than C alone. Moreover, steady state during C of RC was reached at the 2nd min for VO2, VE, VCO2, VE/VO2, VE/VCO2, and VdT; at the 4th min for R and HR, and at the 5th min for f. The C of RC induced a significant increase in [La] in comparison with C alone. We concluded that the first minute of cycling after running during an RC trial induced specific metabolic and cardiorespiratory responses.

Modeling eutrophic lakes: From mass balance laws to ordinary differential equations

NASA Astrophysics Data System (ADS)

Marasco, Addolorata; Ferrara, Luciano; Romano, Antonio

Starting from integral balance laws, a model based on nonlinear ordinary differential equations (ODEs) describing the evolution of Phosphorus cycle in a lake is proposed. After showing that the usual homogeneous model is not compatible with the mixture theory, we prove that an ODEs model still holds but for the mean values of the state variables provided that the nonhomogeneous involved fields satisfy suitable conditions. In this model the trophic state of a lake is described by the mean densities of Phosphorus in water and sediments, and phytoplankton biomass. All the quantities appearing in the model can be experimentally evaluated. To propose restoration programs, the evolution of these state variables toward stable steady state conditions is analyzed. Moreover, the local stability analysis is performed with respect to all the model parameters. Some numerical simulations and a real application to lake Varese conclude the paper.

Performance Cycle Analysis of a Two-Spool, Separate-Exhaust Turbofan With Interstage Turbine Burner

NASA Technical Reports Server (NTRS)

Liew, K. H.; Urip, E.; Yang, S. L.; Mattingly, J. D.; Marek, C. J.

2005-01-01

This paper presents the performance cycle analysis of a dual-spool, separate-exhaust turbofan engine, with an Interstage Turbine Burner serving as a secondary combustor. The ITB, which is located at the transition duct between the high- and the low-pressure turbines, is a relatively new concept for increasing specific thrust and lowering pollutant emissions in modern jet engine propulsion. A detailed performance analysis of this engine has been conducted for steady-state engine performance prediction. A code is written and is capable of predicting engine performances (i.e., thrust and thrust specific fuel consumption) at varying flight conditions and throttle settings. Two design-point engines were studied to reveal trends in performance at both full and partial throttle operations. A mission analysis is also presented to assure the advantage of saving fuel by adding ITB.

Entropy production in mesoscopic stochastic thermodynamics: nonequilibrium kinetic cycles driven by chemical potentials, temperatures, and mechanical forces

NASA Astrophysics Data System (ADS)

Qian, Hong; Kjelstrup, Signe; Kolomeisky, Anatoly B.; Bedeaux, Dick

2016-04-01

Nonequilibrium thermodynamics (NET) investigates processes in systems out of global equilibrium. On a mesoscopic level, it provides a statistical dynamic description of various complex phenomena such as chemical reactions, ion transport, diffusion, thermochemical, thermomechanical and mechanochemical fluxes. In the present review, we introduce a mesoscopic stochastic formulation of NET by analyzing entropy production in several simple examples. The fundamental role of nonequilibrium steady-state cycle kinetics is emphasized. The statistical mechanics of Onsager’s reciprocal relations in this context is elucidated. Chemomechanical, thermomechanical, and enzyme-catalyzed thermochemical energy transduction processes are discussed. It is argued that mesoscopic stochastic NET in phase space provides a rigorous mathematical basis of fundamental concepts needed for understanding complex processes in chemistry, physics and biology. This theory is also relevant for nanoscale technological advances.

Nanoscale investigation of platinum nanoparticles on strontium titanium oxide grown via physical vapor deposition and atomic layer deposition

NASA Astrophysics Data System (ADS)

Christensen, Steven Thomas

This dissertation examines growth of platinum nanoparticles from vapor deposition on SrTiO3 using a characterization approach that combines imaging techniques and X-ray methods. The primary suite of characterization probes includes atomic force microscopy (AFM), grazing-incidence small-angle X-ray scattering (GISAXS), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and X-ray absorption spectroscopy (XAS). The vapor deposition techniques include physical vapor deposition (PVD) by evaporation and atomic layer deposition (ALD). For the PVD platinum study, AFM/XRF showed ˜10 nm nanoparticles separated by an average of 100 nm. The combination of AFM, GISAXS, and XRF indicated that the nanoparticles observed with AFM were actually comprised of closely spaced, smaller nanoparticles. These conclusions were supported by high-resolution SEM. The unusual behavior of platinum nanoparticles to aggregate without coalescence or sintering was observed previously by other researchers using transmissision electron microscopy (TEM). Platinum nanoparticle growth was also investigated on SrTiO3 (001) single crystals using ALD to nucleate nanoparticles that subsequently grew and coalesced into granular films as the ALD progresses. The expected growth rate for the early stages of ALD showed a two-fold increase which was attributed to the platinum deposition occurring faster on the bare substrate. Once the nanoparticles had coalesced into a film, steady state ALD growth proceeded. The formation of nanoparticles was attributed to the atomic diffusion of platinum atoms on the surface in addition to direct growth from the ALD precursor gases. The platinum ALD nanoparticles were also studied on SrTiO3 nanocube powders. The SrTiO3 nanocubes average 60 nm on a side and the cube faces have a {001} orientation. The ALD proceeded in a similar fashion as on the single crystal substrates where the deposition rate was twice as fast as the steady state growth rate. The Pt nanoparticle size increased linearly starting at ˜0.7 nm for 1 ALD cycle to ˜3 nm for 5 ALD cycles. The platinum chemical state was also investigated using X-ray absorption spectroscopy. Platinum nanoparticles ˜1 nm or smaller tended to be oxidized. For larger nanoparticles, the platinum state systematically approached that of bulk platinum metal as the size (number of ALD cycles) increased. The platinum loading was exceptionally low, ˜10 -3 mg cm-2.

40 CFR Appendix C to Subpart S of... - Steady-State Short Test Standards

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 2 2010-07-01 2010-07-01 false Steady-State Short Test Standards C Appendix C to Subpart S of Part 51 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED.../Maintenance Program Requirements Pt. 51, Subpt. S, App. C Appendix C to Subpart S of Part 51—Steady-State...

40 CFR Appendix C to Subpart S of... - Steady-State Short Test Standards

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 2 2014-07-01 2014-07-01 false Steady-State Short Test Standards C Appendix C to Subpart S of Part 51 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED.../Maintenance Program Requirements Pt. 51, Subpt. S, App. C Appendix C to Subpart S of Part 51—Steady-State...

40 CFR Appendix C to Subpart S of... - Steady-State Short Test Standards

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 2 2012-07-01 2012-07-01 false Steady-State Short Test Standards C Appendix C to Subpart S of Part 51 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED.../Maintenance Program Requirements Pt. 51, Subpt. S, App. C Appendix C to Subpart S of Part 51—Steady-State...

Steady-state and quench-dependent relaxation of a quantum dot coupled to one-dimensional leads

NASA Astrophysics Data System (ADS)

Nuss, Martin; Ganahl, Martin; Evertz, Hans Gerd; Arrigoni, Enrico; von der Linden, Wolfgang

2013-07-01

We study the time evolution and steady state of the charge current in a single-impurity Anderson model, using matrix product states techniques. A nonequilibrium situation is imposed by applying a bias voltage across one-dimensional tight-binding leads. Focusing on particle-hole symmetry, we extract current-voltage characteristics from universal low-bias up to high-bias regimes, where band effects start to play a dominant role. We discuss three quenches, which after strongly quench-dependent transients yield the same steady-state current. Among these quenches we identify those favorable for extracting steady-state observables. The period of short-time oscillations is shown to compare well to real-time renormalization group results for a simpler model of spinless fermions. We find indications that many-body effects play an important role at high-bias voltage and finite bandwidth of the metallic leads. The growth of entanglement entropy after a certain time scale ∝Δ-1 is the major limiting factor for calculating the time evolution. We show that the magnitude of the steady-state current positively correlates with entanglement entropy. The role of high-energy states for the steady-state current is explored by considering a damping term in the time evolution.

Steady-state pattern electroretinogram and short-duration transient visual evoked potentials in glaucomatous and healthy eyes.

PubMed

Amarasekera, Dilru C; Resende, Arthur F; Waisbourd, Michael; Puri, Sanjeev; Moster, Marlene R; Hark, Lisa A; Katz, L Jay; Fudemberg, Scott J; Mantravadi, Anand V

2018-01-01

This study evaluates two rapid electrophysiological glaucoma diagnostic tests that may add a functional perspective to glaucoma diagnosis. This study aimed to determine the ability of two office-based electrophysiological diagnostic tests, steady-state pattern electroretinogram and short-duration transient visual evoked potentials, to discern between glaucomatous and healthy eyes. This is a cross-sectional study in a hospital setting. Forty-one patients with glaucoma and 41 healthy volunteers participated in the study. Steady-state pattern electroretinogram and short-duration transient visual evoked potential testing was conducted in glaucomatous and healthy eyes. A 64-bar-size stimulus with both a low-contrast and high-contrast setting was used to compare steady-state pattern electroretinogram parameters in both groups. A low-contrast and high-contrast checkerboard stimulus was used to measure short-duration transient visual evoked potential parameters in both groups. Steady-state pattern electroretinogram parameters compared were MagnitudeD, MagnitudeD/Magnitude ratio, and the signal-to-noise ratio. Short-duration transient visual evoked potential parameters compared were amplitude and latency. MagnitudeD was significantly lower in glaucoma patients when using a low-contrast (P = 0.001) and high-contrast (P < 0.001) 64-bar-size steady-state pattern electroretinogram stimulus. MagnitudeD/Magnitude ratio and SNR were significantly lower in the glaucoma group when using a high-contrast 64-bar-size stimulus (P < 0.001 and P = 0.010, respectively). Short-duration transient visual evoked potential amplitude and latency were not significantly different between the two groups. Steady-state pattern electroretinogram was effectively able to discern between glaucomatous and healthy eyes. Steady-state pattern electroretinogram may thus have a role as a clinically useful electrophysiological diagnostic tool. © 2017 Royal Australian and New Zealand College of Ophthalmologists.

Time density curve analysis for C-arm FDCT PBV imaging.

PubMed

Kamran, Mudassar; Byrne, James V

2016-04-01

Parenchymal blood volume (PBV) estimation using C-arm flat detector computed tomography (FDCT) assumes a steady-state contrast concentration in cerebral vasculature for the scan duration. Using time density curve (TDC) analysis, we explored if the steady-state assumption is met for C-arm CT PBV scans, and how consistent the contrast-material dynamics in cerebral vasculature are across patients. Thirty C-arm FDCT datasets of 26 patients with aneurysmal-SAH, acquired as part of a prospective study comparing C-arm CT PBV with MR-PWI, were analysed. TDCs were extracted from the 2D rotational projections. Goodness-of-fit of TDCs to a steady-state horizontal-line-model and the statistical similarity among the individual TDCs were tested. Influence of the differences in TDC characteristics on the agreement of resulting PBV measurements with MR-CBV was calculated. Despite identical scan parameters and contrast-injection-protocol, the individual TDCs were statistically non-identical (p < 0.01). Using Dunn's multiple comparisons test, of the total 435 individual comparisons among the 30 TDCs, 330 comparisons (62%) reached statistical significance for difference. All TDCs deviated significantly (p < 0.01) from the steady-state horizontal-line-model. PBV values of those datasets for which the TDCs showed largest deviations from the steady-state model demonstrated poor agreement and correlation with MR-CBV, compared with the PBV values of those datasets for which the TDCs were closer to steady-state. For clinical C-arm CT PBV examinations, the administered contrast material does not reach the assumed 'ideal steady-state' for the duration of scan. Using a prolonged injection protocol, the degree to which the TDCs approximate the ideal steady-state influences the agreement of resulting PBV measurements with MR-CBV. © The Author(s) 2016.

Mantle Sulfur Cycle: A Case for Non-Steady State ?

NASA Astrophysics Data System (ADS)

Cartigny, Pierre; Labidi, Jabrane

2016-04-01

Data published over the last 5 years show that the early inference that mantle is isotopically homogeneous is no more valid. Instead, new generation data on lavas range over a significant 34S/32S variability of up to 5‰ with δ 34S values often correlated to Sr- and Nd-isotope compositions. This new set of data also reveals the Earth's mantle to have a sub-chondritic 34S/32S ratio, by about ˜ 1‰. We will present at the conference our published and unpublished data on samples characterizing the different mantle components (i.e. EM1, EM2, HIMU and LOMU). All illustrate 34S-enrichments compared to MORB with Δ 33S and Δ 36S values indistinguishable from CDT or chondrites at the 0.03‰ level. These data are consistent with the recycling of subducted components carrying sulfur with Δ 33S and Δ 36S-values close to zero. Archean rocks commonly display Δ 33S and Δ 36S values deviating from zero by 1 to 10 ‰. The lack of variations for Δ 33S and Δ 36S values in present day lava argue against the sampling of any subducted protolith of Archean age in their mantle source. Instead, our data are consistent with the occurrence of Proterozoic subducted sulfur in the source of the EM1, EM2, LOMU and HIMU endmember at the St-Helena island. This is in agreement with the age of those components early derived through the use of the Pb isotope systematic. Currently, the negative δ 34S-values of the depleted mantle seem to be associated with mostly positive values of enriched components. This would be inconsistent with the concept a steady state of sulfur. Assuming that the overall observations of recycled sulfur are not biased, the origin of such a non-steady state remains unclear. It could be related to the relatively compatible behavior of sulfur during partial melting, as the residue of present-day melting can be shown to always contain significant amounts of sulfide (50{%} of what is observed in a fertile source). This typical behavior likely prevents an efficient extraction of mantle S over time, hence inhibiting quantitative mixing between surface and mantle S. This also allows the preservation of any primitive signature of the deep sulfur cycle to be potentially recorded.

Multi-Fidelity Simulation of a Turbofan Engine With Results Zoomed Into Mini-Maps for a Zero-D Cycle Simulation

NASA Technical Reports Server (NTRS)

Turner, Mark G.; Reed, John A.; Ryder, Robert; Veres, Joseph P.

2004-01-01

A Zero-D cycle simulation of the GE90-94B high bypass turbofan engine has been achieved utilizing mini-maps generated from a high-fidelity simulation. The simulation utilizes the Numerical Propulsion System Simulation (NPSS) thermodynamic cycle modeling system coupled to a high-fidelity full-engine model represented by a set of coupled 3D computational fluid dynamic (CFD) component models. Boundary conditions from the balanced, steady state cycle model are used to define component boundary conditions in the full-engine model. Operating characteristics of the 3D component models are integrated into the cycle model via partial performance maps generated from the CFD flow solutions using one-dimensional mean line turbomachinery programs. This paper highlights the generation of the high-pressure compressor, booster, and fan partial performance maps, as well as turbine maps for the high pressure and low pressure turbine. These are actually "mini-maps" in the sense that they are developed only for a narrow operating range of the component. Results are compared between actual cycle data at a take-off condition and the comparable condition utilizing these mini-maps. The mini-maps are also presented with comparison to actual component data where possible.

GENENG: A program for calculating design and off-design performance for turbojet and turbofan engines

NASA Technical Reports Server (NTRS)

Koenig, R. W.; Fishbach, L. H.

1972-01-01

A computer program entitled GENENG employs component performance maps to perform analytical, steady state, engine cycle calculations. Through a scaling procedure, each of the component maps can be used to represent a family of maps (different design values of pressure ratios, efficiency, weight flow, etc.) Either convergent or convergent-divergent nozzles may be used. Included is a complete FORTRAN 4 listing of the program. Sample results and input explanations are shown for one-spool and two-spool turbojets and two-spool separate- and mixed-flow turbofans operating at design and off-design conditions.

The Framework for 0-D Atmospheric Modeling (F0AM) v3.1

NASA Technical Reports Server (NTRS)

Wolfe, Glenn M.; Marvin, Margaret R.; Roberts, Sandra J.; Travis, Katherine R.; Liao, Jin

2016-01-01

The Framework for 0-D Atmospheric Modeling(F0AM) is a flexible and user-friendly MATLAB-based platform for simulation of atmospheric chemistry systems. The F0AM interface incorporates front-end configuration of observational constraints and model setups, making it readily adaptable to simulation of photochemical chambers, Lagrangian plumes, and steady-state or time-evolving solar cycles. Six different chemical mechanisms and three options for calculation of photolysis frequencies are currently available. Example simulations are presented to illustrate model capabilities and, more generally, highlight some of the advantages and challenges of 0-D box modeling.

Fabrication Materials for a Closed Cycle Brayton Turbine Wheel

NASA Technical Reports Server (NTRS)

Khandelwal, Suresh; Hah, Chunill; Powers, Lynn M.; Stewart, Mark E.; Suresh, Ambady; Owen, Albert K.

2006-01-01

A multidisciplinary analysis of a radial inflow turbine rotor is presented. This work couples high-fidelity fluid, structural, and thermal simulations in a seamless multidisciplinary analysis to investigate the consequences of material selection. This analysis extends multidisciplinary techniques previously demonstrated on rocket turbopumps and hypersonic engines. Since no design information is available for the anticipated Brayton rotating machinery, an existing rotor design (the Brayton Rotating Unit (BRU)) was used in the analysis. Steady state analysis results of a notional turbine rotor indicate that stress levels are easily manageable at the turbine inlet temperature, and stress levels anticipated using either superalloys or ceramics.

Prediction of elemental creep. [steady state and cyclic data from regression analysis

NASA Technical Reports Server (NTRS)

Davis, J. W.; Rummler, D. R.

1975-01-01

Cyclic and steady-state creep tests were performed to provide data which were used to develop predictive equations. These equations, describing creep as a function of stress, temperature, and time, were developed through the use of a least squares regression analyses computer program for both the steady-state and cyclic data sets. Comparison of the data from the two types of tests, revealed that there was no significant difference between the cyclic and steady-state creep strains for the L-605 sheet under the experimental conditions investigated (for the same total time at load). Attempts to develop a single linear equation describing the combined steady-state and cyclic creep data resulted in standard errors of estimates higher than obtained for the individual data sets. A proposed approach to predict elemental creep in metals uses the cyclic creep equation and a computer program which applies strain and time hardening theories of creep accumulation.

Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System.

PubMed

Roder, H M; Perkins, R A; Laesecke, A; Nieto de Castro, C A

2000-01-01

A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy.

Quasi steady-state aerodynamic model development for race vehicle simulations

NASA Astrophysics Data System (ADS)

Mohrfeld-Halterman, J. A.; Uddin, M.

2016-01-01

Presented in this paper is a procedure to develop a high fidelity quasi steady-state aerodynamic model for use in race car vehicle dynamic simulations. Developed to fit quasi steady-state wind tunnel data, the aerodynamic model is regressed against three independent variables: front ground clearance, rear ride height, and yaw angle. An initial dual range model is presented and then further refined to reduce the model complexity while maintaining a high level of predictive accuracy. The model complexity reduction decreases the required amount of wind tunnel data thereby reducing wind tunnel testing time and cost. The quasi steady-state aerodynamic model for the pitch moment degree of freedom is systematically developed in this paper. This same procedure can be extended to the other five aerodynamic degrees of freedom to develop a complete six degree of freedom quasi steady-state aerodynamic model for any vehicle.

Technical challenges in the construction of the steady-state stellarator Wendelstein 7-X

NASA Astrophysics Data System (ADS)

Bosch, H.-S.; Wolf, R. C.; Andreeva, T.; Baldzuhn, J.; Birus, D.; Bluhm, T.; Bräuer, T.; Braune, H.; Bykov, V.; Cardella, A.; Durodié, F.; Endler, M.; Erckmann, V.; Gantenbein, G.; Hartmann, D.; Hathiramani, D.; Heimann, P.; Heinemann, B.; Hennig, C.; Hirsch, M.; Holtum, D.; Jagielski, J.; Jelonnek, J.; Kasparek, W.; Klinger, T.; König, R.; Kornejew, P.; Kroiss, H.; Krom, J. G.; Kühner, G.; Laqua, H.; Laqua, H. P.; Lechte, C.; Lewerentz, M.; Maier, J.; McNeely, P.; Messiaen, A.; Michel, G.; Ongena, J.; Peacock, A.; Pedersen, T. S.; Riedl, R.; Riemann, H.; Rong, P.; Rust, N.; Schacht, J.; Schauer, F.; Schroeder, R.; Schweer, B.; Spring, A.; Stäbler, A.; Thumm, M.; Turkin, Y.; Wegener, L.; Werner, A.; Zhang, D.; Zilker, M.; Akijama, T.; Alzbutas, R.; Ascasibar, E.; Balden, M.; Banduch, M.; Baylard, Ch.; Behr, W.; Beidler, C.; Benndorf, A.; Bergmann, T.; Biedermann, C.; Bieg, B.; Biel, W.; Borchardt, M.; Borowitz, G.; Borsuk, V.; Bozhenkov, S.; Brakel, R.; Brand, H.; Brown, T.; Brucker, B.; Burhenn, R.; Buscher, K.-P.; Caldwell-Nichols, C.; Cappa, A.; Cardella, A.; Carls, A.; Carvalho, P.; Ciupiński, Ł.; Cole, M.; Collienne, J.; Czarnecka, A.; Czymek, G.; Dammertz, G.; Dhard, C. P.; Davydenko, V. I.; Dinklage, A.; Drevlak, M.; Drotziger, S.; Dudek, A.; Dumortier, P.; Dundulis, G.; Eeten, P. v.; Egorov, K.; Estrada, T.; Faugel, H.; Fellinger, J.; Feng, Y.; Fernandes, H.; Fietz, W. H.; Figacz, W.; Fischer, F.; Fontdecaba, J.; Freund, A.; Funaba, T.; Fünfgelder, H.; Galkowski, A.; Gates, D.; Giannone, L.; García Regaña, J. M.; Geiger, J.; Geißler, S.; Greuner, H.; Grahl, M.; Groß, S.; Grosman, A.; Grote, H.; Grulke, O.; Haas, M.; Haiduk, L.; Hartfuß, H.-J.; Harris, J. H.; Haus, D.; Hein, B.; Heitzenroeder, P.; Helander, P.; Heller, R.; Hidalgo, C.; Hildebrandt, D.; Höhnle, H.; Holtz, A.; Holzhauer, E.; Holzthüm, R.; Huber, A.; Hunger, H.; Hurd, F.; Ihrke, M.; Illy, S.; Ivanov, A.; Jablonski, S.; Jaksic, N.; Jakubowski, M.; Jaspers, R.; Jensen, H.; Jenzsch, H.; Kacmarczyk, J.; Kaliatk, T.; Kallmeyer, J.; Kamionka, U.; Karaleviciu, R.; Kern, S.; Keunecke, M.; Kleiber, R.; Knauer, J.; Koch, R.; Kocsis, G.; Könies, A.; Köppen, M.; Koslowski, R.; Koshurinov, J.; Krämer-Flecken, A.; Krampitz, R.; Kravtsov, Y.; Krychowiak, M.; Krzesinski, G.; Ksiazek, I.; Kubkowska, M.; Kus, A.; Langish, S.; Laube, R.; Laux, M.; Lazerson, S.; Lennartz, M.; Li, C.; Lietzow, R.; Lohs, A.; Lorenz, A.; Louche, F.; Lubyako, L.; Lumsdaine, A.; Lyssoivan, A.; Maaßberg, H.; Marek, P.; Martens, C.; Marushchenko, N.; Mayer, M.; Mendelevitch, B.; Mertens, Ph.; Mikkelsen, D.; Mishchenko, A.; Missal, B.; Mizuuchi, T.; Modrow, H.; Mönnich, T.; Morizaki, T.; Murakami, S.; Musielok, F.; Nagel, M.; Naujoks, D.; Neilson, H.; Neubauer, O.; Neuner, U.; Nocentini, R.; Noterdaeme, J.-M.; Nührenberg, C.; Obermayer, S.; Offermanns, G.; Oosterbeek, H.; Otte, M.; Panin, A.; Pap, M.; Paquay, S.; Pasch, E.; Peng, X.; Petrov, S.; Pilopp, D.; Pirsch, H.; Plaum, B.; Pompon, F.; Povilaitis, M.; Preinhaelter, J.; Prinz, O.; Purps, F.; Rajna, T.; Récsei, S.; Reiman, A.; Reiter, D.; Remmel, J.; Renard, S.; Rhode, V.; Riemann, J.; Rimkevicius, S.; Riße, K.; Rodatos, A.; Rodin, I.; Romé, M.; Roscher, H.-J.; Rummel, K.; Rummel, Th.; Runov, A.; Ryc, L.; Sachtleben, J.; Samartsev, A.; Sanchez, M.; Sano, F.; Scarabosio, A.; Schmid, M.; Schmitz, H.; Schmitz, O.; Schneider, M.; Schneider, W.; Scheibl, L.; Scholz, M.; Schröder, G.; Schröder, M.; Schruff, J.; Schumacher, H.; Shikhovtsev, I. V.; Shoji, M.; Siegl, G.; Skodzik, J.; Smirnow, M.; Speth, E.; Spong, D. A.; Stadler, R.; Sulek, Z.; Szabó, V.; Szabolics, T.; Szetefi, T.; Szökefalvi-Nagy, Z.; Tereshchenko, A.; Thomsen, H.; Thumm, M.; Timmermann, D.; Tittes, H.; Toi, K.; Tournianski, M.; Toussaint, U. v.; Tretter, J.; Tulipán, S.; Turba, P.; Uhlemann, R.; Urban, J.; Urbonavicius, E.; Urlings, P.; Valet, S.; Van Eester, D.; Van Schoor, M.; Vervier, M.; Viebke, H.; Vilbrandt, R.; Vrancken, M.; Wauters, T.; Weissgerber, M.; Weiß, E.; Weller, A.; Wendorf, J.; Wenzel, U.; Windisch, T.; Winkler, E.; Winkler, M.; Wolowski, J.; Wolters, J.; Wrochna, G.; Xanthopoulos, P.; Yamada, H.; Yokoyama, M.; Zacharias, D.; Zajac, J.; Zangl, G.; Zarnstorff, M.; Zeplien, H.; Zoletnik, S.; Zuin, M.

2013-12-01

The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, currently under construction in Greifswald, Germany. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7-X mission is to demonstrate steady-state operation under plasma conditions relevant for a fusion power plant. Steady-state operation of a fusion device, on the one hand, requires the implementation of special technologies, giving rise to technical challenges during the design, fabrication and assembly of such a device. On the other hand, also the physics development of steady-state operation at high plasma performance poses a challenge and careful preparation. The electron cyclotron resonance heating system, diagnostics, experiment control and data acquisition are prepared for plasma operation lasting 30 min. This requires many new technological approaches for plasma heating and diagnostics as well as new concepts for experiment control and data acquisition.

Mixed-Mode Decohesion Finite Elements for the Simulation of Delamination in Composite Materials

NASA Technical Reports Server (NTRS)

Camanho, Pedro P.; Davila, Carlos G.

2002-01-01

A new decohesion element with mixed-mode capability is proposed and demonstrated. The element is used at the interface between solid finite elements to model the initiation and non-self-similar growth of delaminations. A single relative displacement-based damage parameter is applied in a softening law to track the damage state of the interface and to prevent the restoration of the cohesive state during unloading. The softening law for mixed-mode delamination propagation can be applied to any mode interaction criterion such as the two-parameter power law or the three-parameter Benzeggagh-Kenane criterion. To demonstrate the accuracy of the predictions and the irreversibility capability of the constitutive law, steady-state delamination growth is simulated for quasistatic loading-unloading cycles of various single mode and mixed-mode delamination test specimens.

Modeling soil CO2 production and transport with dynamic source and diffusion terms: testing the steady-state assumption using DETECT v1.0

NASA Astrophysics Data System (ADS)

Ryan, Edmund M.; Ogle, Kiona; Kropp, Heather; Samuels-Crow, Kimberly E.; Carrillo, Yolima; Pendall, Elise

2018-05-01

The flux of CO2 from the soil to the atmosphere (soil respiration, Rsoil) is a major component of the global carbon (C) cycle. Methods to measure and model Rsoil, or partition it into different components, often rely on the assumption that soil CO2 concentrations and fluxes are in steady state, implying that Rsoil is equal to the rate at which CO2 is produced by soil microbial and root respiration. Recent research, however, questions the validity of this assumption. Thus, the aim of this work was two-fold: (1) to describe a non-steady state (NSS) soil CO2 transport and production model, DETECT, and (2) to use this model to evaluate the environmental conditions under which Rsoil and CO2 production are likely in NSS. The backbone of DETECT is a non-homogeneous, partial differential equation (PDE) that describes production and transport of soil CO2, which we solve numerically at fine spatial and temporal resolution (e.g., 0.01 m increments down to 1 m, every 6 h). Production of soil CO2 is simulated for every depth and time increment as the sum of root respiration and microbial decomposition of soil organic matter. Both of these factors can be driven by current and antecedent soil water content and temperature, which can also vary by time and depth. We also analytically solved the ordinary differential equation (ODE) corresponding to the steady-state (SS) solution to the PDE model. We applied the DETECT NSS and SS models to the six-month growing season period representative of a native grassland in Wyoming. Simulation experiments were conducted with both model versions to evaluate factors that could affect departure from SS, such as (1) varying soil texture; (2) shifting the timing or frequency of precipitation; and (3) with and without the environmental antecedent drivers. For a coarse-textured soil, Rsoil from the SS model closely matched that of the NSS model. However, in a fine-textured (clay) soil, growing season Rsoil was ˜ 3 % higher under the assumption of NSS (versus SS). These differences were exaggerated in clay soil at daily time scales whereby Rsoil under the SS assumption deviated from NSS by up to 35 % on average in the 10 days following a major precipitation event. Incorporation of antecedent drivers increased the magnitude of Rsoil by 15 to 37 % for coarse- and fine-textured soils, respectively. However, the responses of Rsoil to the timing of precipitation and antecedent drivers did not differ between SS and NSS assumptions. In summary, the assumption of SS conditions can be violated depending on soil type and soil moisture status, as affected by precipitation inputs. The DETECT model provides a framework for accommodating NSS conditions to better predict Rsoil and associated soil carbon cycling processes.

Min-By-Min Respiratory Exchange and Oxygen Uptake Kinetics During Steady-State Exercise in Subjects of High and Low Max VO2

ERIC Educational Resources Information Center

Weltman, Arthur; Katch, Victor

1976-01-01

No statistically meaningful differences in steady-state vo2 uptake for high and low max vo2 groups was indicated in this study, but a clear tendency was observed for the high max vo2 group to reach the steady-state at a faster rate. (MB)

Quantitative controls on submarine slope failure morphology

USGS Publications Warehouse

Lee, H.J.; Schwab, W.C.; Edwards, B.D.; Kayen, R.E.

1991-01-01

The concept of the steady-state of deformation can be applied to predicting the ultimate form a landslide will take. The steady-state condition, defined by a line in void ratio-effective stress space, exists at large levels of strain and remolding. Conceptually, if sediment initially exists with void ratio-effective stress conditions above the steady-state line, the sediment shear strength will decrease during a transient loading event, such as an earthquake or storm. If the reduced shear strength existing at the steady state is less than the downslope shear stress induced by gravity, then large-scale internal deformation, disintegration, and flow will occur. -from Authors

Isotopic composition of transpiration and rates of change in leaf water isotopologue storage in response to environmental variables.

PubMed

Simonin, Kevin A; Roddy, Adam B; Link, Percy; Apodaca, Randy; Tu, Kevin P; Hu, Jia; Dawson, Todd E; Barbour, Margaret M

2013-12-01

During daylight hours, the isotope composition of leaf water generally approximates steady-state leaf water isotope enrichment model predictions. However, until very recently there was little direct confirmation that isotopic steady-state (ISS) transpiration in fact exists. Using isotope ratio infrared spectroscopy (IRIS) and leaf gas exchange systems we evaluated the isotope composition of transpiration and the rate of change in leaf water isotopologue storage (isostorage) when leaves were exposed to variable environments. In doing so, we developed a method for controlling the absolute humidity entering the gas exchange cuvette for a wide range of concentrations without changing the isotope composition of water vapour. The measurement system allowed estimation of (18)O enrichment both at the evaporation site and for bulk leaf water, in the steady state and the non-steady state. We show that non-steady-state effects dominate the transpiration isoflux even when leaves are at physiological steady state. Our results suggest that a variable environment likely prevents ISS transpiration from being achieved and that this effect may be exacerbated by lengthy leaf water turnover times due to high leaf water contents. © 2013 John Wiley & Sons Ltd.

Detection-enhanced steady state entanglement with ions.

PubMed

Bentley, C D B; Carvalho, A R R; Kielpinski, D; Hope, J J

2014-07-25

Driven dissipative steady state entanglement schemes take advantage of coupling to the environment to robustly prepare highly entangled states. We present a scheme for two trapped ions to generate a maximally entangled steady state with fidelity above 0.99, appropriate for use in quantum protocols. Furthermore, we extend the scheme by introducing detection of our dissipation process, significantly enhancing the fidelity. Our scheme is robust to anomalous heating and requires no sympathetic cooling.

Microwave-Based Oxidation State and Soot Loading Determination on Gasoline Particulate Filters with Three-Way Catalyst Coating for Homogenously Operated Gasoline Engines.

PubMed

Dietrich, Markus; Jahn, Christoph; Lanzerath, Peter; Moos, Ralf

2015-09-02

Recently, a novel method emerged to determine the oxygen storage degree of three way catalysts (TWC) by a microwave-based method. Up to now, this method has been investigated only in lab-scale reactors or under steady state conditions. This work expands those initial studies. A TWC-coated gasoline particulate filter was investigated in a dynamic engine test bench simulating a typical European driving cycle (NEDC). It could be shown that both the oxygen storage degree and the soot loading can be monitored directly, but not simultaneously due to their competitive effects. Under normal driving conditions, no soot accumulation was observed, related to the low raw emissions and the catalytic coating of the filter. For the first time, the quality factor of the cavity resonator in addition to the resonance frequency was used, with the benefit of less cross sensitivity to inconstant temperature and water. Therefore, a temperature dependent calibration of the microwave signal was created and applied to monitor the oxidation state in transient driving cycles. The microwave measurement mirrors the oxidation state determined by lambda probes and can be highly beneficial in start-stop phases (where lambda-probes do not work) and to determine the oxygen storage capacity (OSC) without unnecessary emissions.

Microwave-Based Oxidation State and Soot Loading Determination on Gasoline Particulate Filters with Three-Way Catalyst Coating for Homogenously Operated Gasoline Engines

PubMed Central

Dietrich, Markus; Jahn, Christoph; Lanzerath, Peter; Moos, Ralf

2015-01-01

Recently, a novel method emerged to determine the oxygen storage degree of three way catalysts (TWC) by a microwave-based method. Up to now, this method has been investigated only in lab-scale reactors or under steady state conditions. This work expands those initial studies. A TWC-coated gasoline particulate filter was investigated in a dynamic engine test bench simulating a typical European driving cycle (NEDC). It could be shown that both the oxygen storage degree and the soot loading can be monitored directly, but not simultaneously due to their competitive effects. Under normal driving conditions, no soot accumulation was observed, related to the low raw emissions and the catalytic coating of the filter. For the first time, the quality factor of the cavity resonator in addition to the resonance frequency was used, with the benefit of less cross sensitivity to inconstant temperature and water. Therefore, a temperature dependent calibration of the microwave signal was created and applied to monitor the oxidation state in transient driving cycles. The microwave measurement mirrors the oxidation state determined by lambda probes and can be highly beneficial in start-stop phases (where lambda-probes do not work) and to determine the oxygen storage capacity (OSC) without unnecessary emissions. PMID:26340629

Sensor placement algorithm development to maximize the efficiency of acid gas removal unit for integrated gasification combined cycle (IGCC) power plant with CO{sub 2} capture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, P.; Bhattacharyya, D.; Turton, R.

2012-01-01

Future integrated gasification combined cycle (IGCC) power plants with CO{sub 2} capture will face stricter operational and environmental constraints. Accurate values of relevant states/outputs/disturbances are needed to satisfy these constraints and to maximize the operational efficiency. Unfortunately, a number of these process variables cannot be measured while a number of them can be measured, but have low precision, reliability, or signal-to-noise ratio. In this work, a sensor placement (SP) algorithm is developed for optimal selection of sensor location, number, and type that can maximize the plant efficiency and result in a desired precision of the relevant measured/unmeasured states. In thismore » work, an SP algorithm is developed for an selective, dual-stage Selexol-based acid gas removal (AGR) unit for an IGCC plant with pre-combustion CO{sub 2} capture. A comprehensive nonlinear dynamic model of the AGR unit is developed in Aspen Plus Dynamics® (APD) and used to generate a linear state-space model that is used in the SP algorithm. The SP algorithm is developed with the assumption that an optimal Kalman filter will be implemented in the plant for state and disturbance estimation. The algorithm is developed assuming steady-state Kalman filtering and steady-state operation of the plant. The control system is considered to operate based on the estimated states and thereby, captures the effects of the SP algorithm on the overall plant efficiency. The optimization problem is solved by Genetic Algorithm (GA) considering both linear and nonlinear equality and inequality constraints. Due to the very large number of candidate sets available for sensor placement and because of the long time that it takes to solve the constrained optimization problem that includes more than 1000 states, solution of this problem is computationally expensive. For reducing the computation time, parallel computing is performed using the Distributed Computing Server (DCS®) and the Parallel Computing® toolbox from Mathworks®. In this presentation, we will share our experience in setting up parallel computing using GA in the MATLAB® environment and present the overall approach for achieving higher computational efficiency in this framework.« less

Steady-state MR imaging sequences: physics, classification, and clinical applications.

PubMed

Chavhan, Govind B; Babyn, Paul S; Jankharia, Bhavin G; Cheng, Hai-Ling M; Shroff, Manohar M

2008-01-01

Steady-state sequences are a class of rapid magnetic resonance (MR) imaging techniques based on fast gradient-echo acquisitions in which both longitudinal magnetization (LM) and transverse magnetization (TM) are kept constant. Both LM and TM reach a nonzero steady state through the use of a repetition time that is shorter than the T2 relaxation time of tissue. When TM is maintained as multiple radiofrequency excitation pulses are applied, two types of signal are formed once steady state is reached: preexcitation signal (S-) from echo reformation; and postexcitation signal (S+), which consists of free induction decay. Depending on the signal sampled and used to form an image, steady-state sequences can be classified as (a) postexcitation refocused (only S+ is sampled), (b) preexcitation refocused (only S- is sampled), and (c) fully refocused (both S+ and S- are sampled) sequences. All tissues with a reasonably long T2 relaxation time will show additional signals due to various refocused echo paths. Steady-state sequences have revolutionized cardiac imaging and have become the standard for anatomic functional cardiac imaging and for the assessment of myocardial viability because of their good signal-to-noise ratio and contrast-to-noise ratio and increased speed of acquisition. They are also useful in abdominal and fetal imaging and hold promise for interventional MR imaging. Because steady-state sequences are now commonly used in MR imaging, radiologists will benefit from understanding the underlying physics, classification, and clinical applications of these sequences.

Thermo-Mechanical Modeling and Analysis for Turbopump Assemblies

NASA Technical Reports Server (NTRS)

Platt, Mike; Marsh, Matt

2003-01-01

Life, reliability, and cost are strongly impacted by steady and transient thermo-mechanical effect. Design cycle can suffer big setbacks when working a transient stress/deflection issue. Balance between objectives and constrains is always difficult. Requires assembly-level analysis early in the design cycle.

Time density curve analysis for C-arm FDCT PBV imaging

PubMed Central

Byrne, James V

2016-01-01

Introduction Parenchymal blood volume (PBV) estimation using C-arm flat detector computed tomography (FDCT) assumes a steady-state contrast concentration in cerebral vasculature for the scan duration. Using time density curve (TDC) analysis, we explored if the steady-state assumption is met for C-arm CT PBV scans, and how consistent the contrast-material dynamics in cerebral vasculature are across patients. Methods Thirty C-arm FDCT datasets of 26 patients with aneurysmal-SAH, acquired as part of a prospective study comparing C-arm CT PBV with MR-PWI, were analysed. TDCs were extracted from the 2D rotational projections. Goodness-of-fit of TDCs to a steady-state horizontal-line-model and the statistical similarity among the individual TDCs were tested. Influence of the differences in TDC characteristics on the agreement of resulting PBV measurements with MR-CBV was calculated. Results Despite identical scan parameters and contrast-injection-protocol, the individual TDCs were statistically non-identical (p < 0.01). Using Dunn's multiple comparisons test, of the total 435 individual comparisons among the 30 TDCs, 330 comparisons (62%) reached statistical significance for difference. All TDCs deviated significantly (p < 0.01) from the steady-state horizontal-line-model. PBV values of those datasets for which the TDCs showed largest deviations from the steady-state model demonstrated poor agreement and correlation with MR-CBV, compared with the PBV values of those datasets for which the TDCs were closer to steady-state. Conclusion For clinical C-arm CT PBV examinations, the administered contrast material does not reach the assumed ‘ideal steady-state’ for the duration of scan. Using a prolonged injection protocol, the degree to which the TDCs approximate the ideal steady-state influences the agreement of resulting PBV measurements with MR-CBV. PMID:26769736

How do fission yeast cells grow and connect growth to the mitotic cycle?

PubMed

Sveiczer, Ákos; Horváth, Anna

2017-05-01

To maintain size homeostasis in a unicellular culture, cells should coordinate growth to the division cycle. This is achieved via size control mechanisms (also known as size checkpoints), i.e. some events during the mitotic cycle supervene only if the cell has reached a critical size. Rod-shaped cells like those of fission yeast are ideal model organisms to study these checkpoints via time-lapse microphotography. By applying this method, once we can analyse the growth process between two consecutive divisions at a single (or even at an 'average') cellular level, moreover, we can also position the size checkpoint(s) at the population level. Finally, any of these controls can be abolished in appropriate cell cycle mutants, either in steady-state or in induction synchronised cultures. In the latter case, we produce abnormally oversized cells, and microscopic experiments with them clearly show the existence of a critical size above which the size checkpoint ceases (becomes cryptic). In this review, we delineate the development of our knowledge both on the growth mode of fission yeast and on the operating size control(s) during its mitotic cycle. We finish these historical stories with our recent findings, arguing that three different size checkpoints exist in the fission yeast cell cycle, namely in late G1, in mid G2 and in late G2, which has been concluded by analysing these controls in several cell cycle mutants.

Road load simulator tests of the Gould phase 1 functional model silicon controlled rectifier ac motor controller for electric vehicles

NASA Astrophysics Data System (ADS)

Gourash, F.

1984-02-01

The test results for a functional model ac motor controller for electric vehicles and a three-phase induction motor which were dynamically tested on the Lewis Research Center road load simulator are presented. Results show that the controller has the capability to meet the SAE-J227a D cycle test schedule and to accelerate a 1576-kg (3456-lb) simulated vehicle to a cruise speed of 88.5 km/hr (55 mph). Combined motor controller efficiency is 72 percent and the power inverter efficiency alone is 89 percent for the cruise region of the D cycle. Steady state test results for motoring, regeneration, and thermal data obtained by operating the simulator as a conventional dynamometer are in agreement with the contractor's previously reported data. The regeneration test results indicate that a reduction in energy requirements for urban driving cycles is attainable with regenerative braking. Test results and data in this report serve as a data base for further development of ac motor controllers and propulsion systems for electric vehicles. The controller uses state-of-the-art silicon controlled rectifier (SCR) power semiconductors and microprocessor-based logic and control circuitry. The controller was developed by Gould Laboratories under a Lewis contract for the Department of Energy's Electric and Hybrid Vehicle program.

Road load simulator tests of the Gould phase 1 functional model silicon controlled rectifier ac motor controller for electric vehicles

NASA Technical Reports Server (NTRS)

Gourash, F.

1984-01-01

The test results for a functional model ac motor controller for electric vehicles and a three-phase induction motor which were dynamically tested on the Lewis Research Center road load simulator are presented. Results show that the controller has the capability to meet the SAE-J227a D cycle test schedule and to accelerate a 1576-kg (3456-lb) simulated vehicle to a cruise speed of 88.5 km/hr (55 mph). Combined motor controller efficiency is 72 percent and the power inverter efficiency alone is 89 percent for the cruise region of the D cycle. Steady state test results for motoring, regeneration, and thermal data obtained by operating the simulator as a conventional dynamometer are in agreement with the contractor's previously reported data. The regeneration test results indicate that a reduction in energy requirements for urban driving cycles is attainable with regenerative braking. Test results and data in this report serve as a data base for further development of ac motor controllers and propulsion systems for electric vehicles. The controller uses state-of-the-art silicon controlled rectifier (SCR) power semiconductors and microprocessor-based logic and control circuitry. The controller was developed by Gould Laboratories under a Lewis contract for the Department of Energy's Electric and Hybrid Vehicle program.

Universal, computer facilitated, steady state oscillator, closed loop analysis theory and some applications to precision oscillators

NASA Technical Reports Server (NTRS)

Parzen, Benjamin

1992-01-01

The theory of oscillator analysis in the immittance domain should be read in conjunction with the additional theory presented here. The combined theory enables the computer simulation of the steady state oscillator. The simulation makes the calculation of the oscillator total steady state performance practical, including noise at all oscillator locations. Some specific precision oscillators are analyzed.

Steady state analysis of Boolean molecular network models via model reduction and computational algebra.

PubMed

Veliz-Cuba, Alan; Aguilar, Boris; Hinkelmann, Franziska; Laubenbacher, Reinhard

2014-06-26

A key problem in the analysis of mathematical models of molecular networks is the determination of their steady states. The present paper addresses this problem for Boolean network models, an increasingly popular modeling paradigm for networks lacking detailed kinetic information. For small models, the problem can be solved by exhaustive enumeration of all state transitions. But for larger models this is not feasible, since the size of the phase space grows exponentially with the dimension of the network. The dimension of published models is growing to over 100, so that efficient methods for steady state determination are essential. Several methods have been proposed for large networks, some of them heuristic. While these methods represent a substantial improvement in scalability over exhaustive enumeration, the problem for large networks is still unsolved in general. This paper presents an algorithm that consists of two main parts. The first is a graph theoretic reduction of the wiring diagram of the network, while preserving all information about steady states. The second part formulates the determination of all steady states of a Boolean network as a problem of finding all solutions to a system of polynomial equations over the finite number system with two elements. This problem can be solved with existing computer algebra software. This algorithm compares favorably with several existing algorithms for steady state determination. One advantage is that it is not heuristic or reliant on sampling, but rather determines algorithmically and exactly all steady states of a Boolean network. The code for the algorithm, as well as the test suite of benchmark networks, is available upon request from the corresponding author. The algorithm presented in this paper reliably determines all steady states of sparse Boolean networks with up to 1000 nodes. The algorithm is effective at analyzing virtually all published models even those of moderate connectivity. The problem for large Boolean networks with high average connectivity remains an open problem.

Steady state analysis of Boolean molecular network models via model reduction and computational algebra

PubMed Central

2014-01-01

Background A key problem in the analysis of mathematical models of molecular networks is the determination of their steady states. The present paper addresses this problem for Boolean network models, an increasingly popular modeling paradigm for networks lacking detailed kinetic information. For small models, the problem can be solved by exhaustive enumeration of all state transitions. But for larger models this is not feasible, since the size of the phase space grows exponentially with the dimension of the network. The dimension of published models is growing to over 100, so that efficient methods for steady state determination are essential. Several methods have been proposed for large networks, some of them heuristic. While these methods represent a substantial improvement in scalability over exhaustive enumeration, the problem for large networks is still unsolved in general. Results This paper presents an algorithm that consists of two main parts. The first is a graph theoretic reduction of the wiring diagram of the network, while preserving all information about steady states. The second part formulates the determination of all steady states of a Boolean network as a problem of finding all solutions to a system of polynomial equations over the finite number system with two elements. This problem can be solved with existing computer algebra software. This algorithm compares favorably with several existing algorithms for steady state determination. One advantage is that it is not heuristic or reliant on sampling, but rather determines algorithmically and exactly all steady states of a Boolean network. The code for the algorithm, as well as the test suite of benchmark networks, is available upon request from the corresponding author. Conclusions The algorithm presented in this paper reliably determines all steady states of sparse Boolean networks with up to 1000 nodes. The algorithm is effective at analyzing virtually all published models even those of moderate connectivity. The problem for large Boolean networks with high average connectivity remains an open problem. PMID:24965213

Inverse-model estimates of the ocean's coupled phosphorus, silicon, and iron cycles

NASA Astrophysics Data System (ADS)

Pasquier, Benoît; Holzer, Mark

2017-09-01

The ocean's nutrient cycles are important for the carbon balance of the climate system and for shaping the ocean's distribution of dissolved elements. Dissolved iron (dFe) is a key limiting micronutrient, but iron scavenging is observationally poorly constrained, leading to large uncertainties in the external sources of iron and hence in the state of the marine iron cycle. Here we build a steady-state model of the ocean's coupled phosphorus, silicon, and iron cycles embedded in a data-assimilated steady-state global ocean circulation. The model includes the redissolution of scavenged iron, parameterization of subgrid topography, and small, large, and diatom phytoplankton functional classes. Phytoplankton concentrations are implicitly represented in the parameterization of biological nutrient utilization through an equilibrium logistic model. Our formulation thus has only three coupled nutrient tracers, the three-dimensional distributions of which are found using a Newton solver. The very efficient numerics allow us to use the model in inverse mode to objectively constrain many biogeochemical parameters by minimizing the mismatch between modeled and observed nutrient and phytoplankton concentrations. Iron source and sink parameters cannot jointly be optimized because of local compensation between regeneration, recycling, and scavenging. We therefore consider a family of possible state estimates corresponding to a wide range of external iron source strengths. All state estimates have a similar mismatch with the observed nutrient concentrations and very similar large-scale dFe distributions. However, the relative contributions of aeolian, sedimentary, and hydrothermal iron to the total dFe concentration differ widely depending on the sources. Both the magnitude and pattern of the phosphorus and opal exports are well constrained, with global values of 8. 1 ± 0. 3 Tmol P yr-1 (or, in carbon units, 10. 3 ± 0. 4 Pg C yr-1) and 171. ± 3. Tmol Si yr-1. We diagnose the phosphorus and opal exports supported by aeolian, sedimentary, and hydrothermal iron. The geographic patterns of the export supported by each iron type are well constrained across the family of state estimates. Sedimentary-iron-supported export is important in shelf and large-scale upwelling regions, while hydrothermal iron contributes to export mostly in the Southern Ocean. The fraction of the global export supported by a given iron type varies systematically with its fractional contribution to the total iron source. Aeolian iron is most efficient in supporting export in the sense that its fractional contribution to export exceeds its fractional contribution to the total source. Per source-injected molecule, aeolian iron supports 3. 1 ± 0. 8 times more phosphorus export and 2. 0 ± 0. 5 times more opal export than the other iron types. Conversely, per injected molecule, sedimentary and hydrothermal iron support 2. 3 ± 0. 6 and 4. ± 2. times less phosphorus export, and 1. 9 ± 0. 5 and 2. ± 1. times less opal export than the other iron types.

The cell-in-series method: A technique for accelerated electrode degradation in redox flow batteries

DOE PAGES

Pezeshki, Alan M.; Sacci, Robert L.; Veith, Gabriel M.; ...

2015-11-21

Here, we demonstrate a novel method to accelerate electrode degradation in redox flow batteries and apply this method to the all-vanadium chemistry. Electrode performance degradation occurred seven times faster than in a typical cycling experiment, enabling rapid evaluation of materials. This method also enables the steady-state study of electrodes. In this manner, it is possible to delineate whether specific operating conditions induce performance degradation; we found that both aggressively charging and discharging result in performance loss. Post-mortem x-ray photoelectron spectroscopy of the degraded electrodes was used to resolve the effects of state of charge (SoC) and current on the electrodemore » surface chemistry. For the electrode material tested in this work, we found evidence that a loss of oxygen content on the negative electrode cannot explain decreased cell performance. Furthermore, the effects of decreased electrode and membrane performance on capacity fade in a typical cycling battery were decoupled from crossover; electrode and membrane performance decay were responsible for a 22% fade in capacity, while crossover caused a 12% fade.« less

Entrenched time delays versus accelerating opinion dynamics: are advanced democracies inherently unstable?

NASA Astrophysics Data System (ADS)

Gros, Claudius

2017-11-01

Modern societies face the challenge that the time scale of opinion formation is continuously accelerating in contrast to the time scale of political decision making. With the latter remaining of the order of the election cycle we examine here the case that the political state of a society is determined by the continuously evolving values of the electorate. Given this assumption we show that the time lags inherent in the election cycle will inevitable lead to political instabilities for advanced democracies characterized both by an accelerating pace of opinion dynamics and by high sensibilities (political correctness) to deviations from mainstream values. Our result is based on the observation that dynamical systems become generically unstable whenever time delays become comparable to the time it takes to adapt to the steady state. The time needed to recover from external shocks grows in addition dramatically close to the transition. Our estimates for the order of magnitude of the involved time scales indicate that socio-political instabilities may develop once the aggregate time scale for the evolution of the political values of the electorate falls below 7-15 months.

A systematic uncertainty analysis of an evaluative fate and exposure model.

PubMed

Hertwich, E G; McKone, T E; Pease, W S

2000-08-01

Multimedia fate and exposure models are widely used to regulate the release of toxic chemicals, to set cleanup standards for contaminated sites, and to evaluate emissions in life-cycle assessment. CalTOX, one of these models, is used to calculate the potential dose, an outcome that is combined with the toxicity of the chemical to determine the Human Toxicity Potential (HTP), used to aggregate and compare emissions. The comprehensive assessment of the uncertainty in the potential dose calculation in this article serves to provide the information necessary to evaluate the reliability of decisions based on the HTP A framework for uncertainty analysis in multimedia risk assessment is proposed and evaluated with four types of uncertainty. Parameter uncertainty is assessed through Monte Carlo analysis. The variability in landscape parameters is assessed through a comparison of potential dose calculations for different regions in the United States. Decision rule uncertainty is explored through a comparison of the HTP values under open and closed system boundaries. Model uncertainty is evaluated through two case studies, one using alternative formulations for calculating the plant concentration and the other testing the steady state assumption for wet deposition. This investigation shows that steady state conditions for the removal of chemicals from the atmosphere are not appropriate and result in an underestimate of the potential dose for 25% of the 336 chemicals evaluated.

‘Life is motion’: multiscale motility of molecular motors

NASA Astrophysics Data System (ADS)

Lipowsky, Reinhard; Klumpp, Stefan

2005-07-01

Life is intimately related to complex patterns of directed movement. It is quite remarkable that all of this movement is based on filaments and motor molecules which perform mechanical work on the nanometer scale. This article reviews recent theoretical work on the motility of molecular motors and motor particles that bind to cytoskeletal filaments and walk along these filaments in a directed fashion. It is emphasized that these systems exhibit several motility regimes which are well seperated in time. In their bound state, the motor particles move with a typical velocity of about 1 μm/s. The motor cycles underlying this bound motor movement can be understood in terms of driven Brownian ratchets and networks. On larger length and time scales, the motor particles unbind from the filaments and undergo peculiar motor walks consisting of many diffusional encounters with the filaments. If the mutual exclusion (or hardcore repulsion) of these motor particles is taken into account, one finds a variety of cooperative phenomena and self-organized processes: build-up of traffic jams; active structure formation leading to steady states with spatially nonuniform density and current patterns; and active phase transitions between different steady states far from equilibrium. A particularly simple active phase transition with spontaneous symmetry breaking is predicted to occur in systems with two species of motor particles which walk on the filaments in opposite directions.

Improvement of AEP Predictions Using Diurnal CFD Modelling with Site-Specific Stability Weightings Provided from Mesoscale Simulation

NASA Astrophysics Data System (ADS)

Hristov, Y.; Oxley, G.; Žagar, M.

2014-06-01

The Bolund measurement campaign, performed by Danish Technical University (DTU) Wind Energy Department (also known as RISØ), provided significant insight into wind flow modeling over complex terrain. In the blind comparison study several modelling solutions were submitted with the vast majority being steady-state Computational Fluid Dynamics (CFD) approaches with two equation k-epsilon turbulence closure. This approach yielded the most accurate results, and was identified as the state-of-the-art tool for wind turbine generator (WTG) micro-siting. Based on the findings from Bolund, further comparison between CFD and field measurement data has been deemed essential in order to improve simulation accuracy for turbine load and long-term Annual Energy Production (AEP) estimations. Vestas Wind Systems A/S is a major WTG original equipment manufacturer (OEM) with an installed base of over 60GW in over 70 countries accounting for 19% of the global installed base. The Vestas Performance and Diagnostic Centre (VPDC) provides online live data to more than 47GW of these turbines allowing a comprehensive comparison between modelled and real-world energy production data. In previous studies, multiple sites have been simulated with a steady neutral CFD formulation for the atmospheric surface layer (ASL), and wind resource (RSF) files have been generated as a base for long-term AEP predictions showing significant improvement over predictions performed with the industry standard linear WAsP tool. In this study, further improvements to the wind resource file generation with CFD are examined using an unsteady diurnal cycle approach with a full atmospheric boundary layer (ABL) formulation, with the unique stratifications throughout the cycle weighted according to mesoscale simulated sectorwise stability frequencies.

The effect of temperature and thermal acclimation on the sustainable performance of swimming scup.

PubMed

Rome, Lawrence C

2007-11-29

There is a significant reduction in overall maximum power output of muscle at low temperatures due to reduced steady-state (i.e. maximum activation) power-generating capabilities of muscle. However, during cyclical locomotion, a further reduction in power is due to the interplay between non-steady-state contractile properties of muscle (i.e. rates of activation and relaxation) and the stimulation and the length-change pattern muscle undergoes in vivo. In particular, even though the relaxation rate of scup red muscle is slowed greatly at cold temperatures (10 degrees C), warm-acclimated scup swim with the same stimulus duty cycles at cold as they do at warm temperature, not affording slow-relaxing muscle any additional time to relax. Hence, at 10 degrees C, red muscle generates extremely low or negative work in most parts of the body, at all but the slowest swimming speeds. Do scup shorten their stimulation duration and increase muscle relaxation rate during cold acclimation? At 10 degrees C, electromyography (EMG) duty cycles were 18% shorter in cold-acclimated scup than in warm-acclimated scup. But contrary to the expectations, the red muscle did not have a faster relaxation rate, rather, cold-acclimated muscle had an approximately 50% faster activation rate. By driving cold- and warm-acclimated muscle through cold- and warm-acclimated conditions, we found a very large increase in red muscle power during swimming at 10 degrees C. As expected, reducing stimulation duration markedly increased power output. However, the increased rate of activation alone produced an even greater effect. Hence, to fully understand thermal acclimation, it is necessary to examine the whole system under realistic physiological conditions.

Transitions between strongly correlated and random steady-states for catalytic CO-oxidation on surfaces at high-pressure

DOE PAGES

Liu, Da -Jiang; Evans, James W.

2015-04-02

We explore simple lattice-gas reaction models for CO-oxidation on 1D and 2D periodic arrays of surface adsorption sites. The models are motivated by studies of CO-oxidation on RuO 2(110) at high-pressures. Although adspecies interactions are neglected, the effective absence of adspecies diffusion results in kinetically-induced spatial correlations. A transition occurs from a random mainly CO-populated steady-state at high CO-partial pressure p CO, to a strongly-correlated near-O-covered steady-state for low p CO as noted. In addition, we identify a second transition to a random near-O-covered steady-state at very low p CO.

The steady-state visual evoked potential in vision research: A review

PubMed Central

Norcia, Anthony M.; Appelbaum, L. Gregory; Ales, Justin M.; Cottereau, Benoit R.; Rossion, Bruno

2015-01-01

Periodic visual stimulation and analysis of the resulting steady-state visual evoked potentials were first introduced over 80 years ago as a means to study visual sensation and perception. From the first single-channel recording of responses to modulated light to the present use of sophisticated digital displays composed of complex visual stimuli and high-density recording arrays, steady-state methods have been applied in a broad range of scientific and applied settings.The purpose of this article is to describe the fundamental stimulation paradigms for steady-state visual evoked potentials and to illustrate these principles through research findings across a range of applications in vision science. PMID:26024451

Energy cost of isometric force production after active shortening in skinned muscle fibres.

PubMed

Joumaa, Venus; Fitzowich, Alex; Herzog, Walter

2017-04-15

The steady-state isometric force after active shortening of a skeletal muscle is lower than the purely isometric force at the corresponding length. This property of skeletal muscle is known as force depression. The purpose of this study was to investigate whether the energy cost of force production at the steady state after active shortening was reduced compared with the energy cost of force production for a purely isometric contraction performed at the corresponding length (same length, same activation). Experiments were performed in skinned fibres isolated from rabbit psoas muscle. Skinned fibres were actively shortened from an average sarcomere length of 3.0 µm to an average sarcomere length of 2.4 µm. Purely isometric reference contractions were performed at an average sarcomere length of 2.4 µm. Simultaneously with the force measurements, the ATP cost was measured during the last 30 s of isometric contractions using an enzyme-coupled assay. Stiffness was calculated during a quick stretch-release cycle of 0.2% fibre length performed once the steady state had been reached after active shortening and during the purely isometric reference contractions. Force and stiffness following active shortening were decreased by 10.0±1.8% and 11.0±2.2%, respectively, compared with the isometric reference contractions. Similarly, ATPase activity per second (not normalized to the force) showed a decrease of 15.6±3.0% in the force-depressed state compared with the purely isometric reference state. However, ATPase activity per second per unit of force was similar for the isometric contractions following active shortening (28.7±2.4 mmol l -1  mN -1  s mm 3 ) and the corresponding purely isometric reference contraction (30.9±2.8 mmol l -1  mN -1  s mm 3 ). Furthermore, the reduction in absolute ATPase activity per second was significantly correlated with force depression and stiffness depression. These results are in accordance with the idea that force depression following active shortening is primarily caused by a decrease in the proportion of attached cross-bridges. Furthermore, these findings, along with previously reported results showing a decrease in ATP consumption per unit of force after active muscle stretching, suggest that the mechanisms involved in the steady-state force after active muscle shortening and active muscle lengthening are of distinctly different origin. © 2017. Published by The Company of Biologists Ltd.

Symmetry limit theory for cantilever beam-columns subjected to cyclic reversed bending

NASA Astrophysics Data System (ADS)

Uetani, K.; Nakamura, Tsuneyoshi

THE BEHAVIOR of a linear strain-hardening cantilever beam-column subjected to completely reversed plastic bending of a new idealized program under constant axial compression consists of three stages: a sequence of symmetric steady states, a subsequent sequence of asymmetric steady states and a divergent behavior involving unbounded growth of an anti-symmetric deflection mode. A new concept "symmetry limit" is introduced here as the smallest critical value of the tip-deflection amplitude at which transition from a symmetric steady state to an asymmetric steady state can occur in the response of a beam-column. A new theory is presented for predicting the symmetry limits. Although this transition phenomenon is phenomenologically and conceptually different from the branching phenomenon on an equilibrium path, it is shown that a symmetry limit may theoretically be regarded as a branching point on a "steady-state path" defined anew. The symmetry limit theory and the fundamental hypotheses are verified through numerical analysis of hysteretic responses of discretized beam-column models.

A general theory of kinetics and thermodynamics of steady-state copolymerization.

PubMed

Shu, Yao-Gen; Song, Yong-Shun; Ou-Yang, Zhong-Can; Li, Ming

2015-06-17

Kinetics of steady-state copolymerization has been investigated since the 1940s. Irreversible terminal and penultimate models were successfully applied to a number of comonomer systems, but failed for systems where depropagation is significant. Although a general mathematical treatment of the terminal model with depropagation was established in the 1980s, a penultimate model and higher-order terminal models with depropagation have not been systematically studied, since depropagation leads to hierarchically-coupled and unclosed kinetic equations which are hard to solve analytically. In this work, we propose a truncation method to solve the steady-state kinetic equations of any-order terminal models with depropagation in a unified way, by reducing them into closed steady-state equations which give the exact solution of the original kinetic equations. Based on the steady-state equations, we also derive a general thermodynamic equality in which the Shannon entropy of the copolymer sequence is explicitly introduced as part of the free energy dissipation of the whole copolymerization system.

Molecular control of steady-state dendritic cell maturation and immune homeostasis.

PubMed

Hammer, Gianna Elena; Ma, Averil

2013-01-01

Dendritic cells (DCs) are specialized sentinels responsible for coordinating adaptive immunity. This function is dependent upon coupled sensitivity to environmental signs of inflammation and infection to cellular maturation-the programmed alteration of DC phenotype and function to enhance immune cell activation. Although DCs are thus well equipped to respond to pathogens, maturation triggers are not unique to infection. Given that immune cells are exquisitely sensitive to the biological functions of DCs, we now appreciate that multiple layers of suppression are required to restrict the environmental sensitivity, cellular maturation, and even life span of DCs to prevent aberrant immune activation during the steady state. At the same time, steady-state DCs are not quiescent but rather perform key functions that support homeostasis of numerous cell types. Here we review these functions and molecular mechanisms of suppression that control steady-state DC maturation. Corruption of these steady-state operatives has diverse immunological consequences and pinpoints DCs as potent drivers of autoimmune and inflammatory disease.

Lineage tracing of murine adult hematopoietic stem cells reveals active contribution to steady-state hematopoiesis

PubMed Central

Chapple, Richard H.; Tseng, Yu-Jung; Hu, Tianyuan; Kitano, Ayumi; Takeichi, Makiko; Hoegenauer, Kevin A.

2018-01-01

Characterization of hematopoietic stem cells (HSCs) has advanced largely owing to transplantation assays, in which the developmental potential of HSCs is assessed generally in nonhomeostatic conditions. These studies established that adult HSCs extensively contribute to multilineage hematopoietic regeneration upon transplantation. On the contrary, recent studies performing lineage tracing of HSCs under homeostatic conditions have shown that adult HSCs may contribute far less to steady-state hematopoiesis than would be anticipated based on transplantation assays. Here, we used 2 independent HSC-lineage–tracing models to examine the contribution of adult HSCs to steady-state hematopoiesis. We show that adult HSCs contribute robustly to steady-state hematopoiesis, exhibiting faster efflux toward the myeloid lineages compared with lymphoid lineages. Platelets were robustly labeled by HSCs, reaching the same level of labeling as HSCs by 1 year of chase. Our results support the view that adult HSCs contribute to the continuous influx of blood cells during steady-state hematopoiesis. PMID:29848758

Steady State Condition in the Measurement of VO2and VCO2by Indirect Calorimetry.

PubMed

Cadena, M; Sacristan, E; Infante, O; Escalante, B; Rodriguez, F

2005-01-01

Resting Metabolic Rate (RMR) is computed using VO2and VCO2short time 15-minute window measurement with Indirect Calorimetry (IC) instruments designed with mixing chamber. Steady state condition using a 10% variation coefficient criteria is the main objective to achieve metabolic long time prediction reliability. This study address how susceptible is the steady state VO2, VCO2measurement condition to the clino-orthostatic physiological maneuver. 30 young healthy subjects were analyzed. Only 18 passed the 10% variation coefficient inclusive criteria. They were exposed to 10 minutes clino-stage and 10 minutes orthostage. The hypothesis tests show not statistical significance (p< 0.1) in the average and variance analysis. It is concluded that the steady state is not influenced by the patient position IC test, probably because IC mixing chamber instruments are insensitive to detect a mayor physiological dynamics changes that can modify the steady state definition.

Einstein's steady-state theory: an abandoned model of the cosmos

NASA Astrophysics Data System (ADS)

O'Raifeartaigh, Cormac; McCann, Brendan; Nahm, Werner; Mitton, Simon

2014-09-01

We present a translation and analysis of an unpublished manuscript by Albert Einstein in which he attempted to construct a `steady-state' model of the universe. The manuscript, which appears to have been written in early 1931, demonstrates that Einstein once explored a cosmic model in which the mean density of matter in an expanding universe is maintained constant by the continuous formation of matter from empty space. This model is very different to previously known Einsteinian models of the cosmos (both static and dynamic) but anticipates the later steady-state cosmology of Hoyle, Bondi and Gold in some ways. We find that Einstein's steady-state model contains a fundamental flaw and suggest that it was abandoned for this reason. We also suggest that he declined to explore a more sophisticated version because he found such theories rather contrived. The manuscript is of historical interest because it reveals that Einstein debated between steady-state and evolving models of the cosmos decades before a similar debate took place in the cosmological community.

Temporal evolution of continental lithospheric strength in actively deforming regions

USGS Publications Warehouse

Thatcher, W.; Pollitz, F.F.

2008-01-01

It has been agreed for nearly a century that a strong, load-bearing outer layer of earth is required to support mountain ranges, transmit stresses to deform active regions and store elastic strain to generate earthquakes. However the dept and extent of this strong layer remain controversial. Here we use a variety of observations to infer the distribution of lithospheric strength in the active western United States from seismic to steady-state time scales. We use evidence from post-seismic transient and earthquake cycle deformation reservoir loading glacio-isostatic adjustment, and lithosphere isostatic adjustment to large surface and subsurface loads. The nearly perfectly elastic behavior of Earth's crust and mantle at the time scale of seismic wave propagation evolves to that of a strong, elastic crust and weak, ductile upper mantle lithosphere at both earthquake cycle (EC, ???10?? to 103 yr) and glacio-isostatic adjustment (GIA, ???103 to 104 yr) time scales. Topography and gravity field correlations indicate that lithosphere isostatic adjustment (LIA) on ???106-107 yr time scales occurs with most lithospheric stress supported by an upper crust overlying a much weaker ductile subtrate. These comparisons suggest that the upper mantle lithosphere is weaker than the crust at all time scales longer than seismic. In contrast, the lower crust has a chameleon-like behavior, strong at EC and GIA time scales and weak for LIA and steady-state deformation processes. The lower crust might even take on a third identity in regions of rapid crustal extension or continental collision, where anomalously high temperatures may lead to large-scale ductile flow in a lower crustal layer that is locally weaker than the upper mantle. Modeling of lithospheric processes in active regions thus cannot use a one-size-fits-all prescription of rheological layering (relation between applied stress and deformation as a function of depth) but must be tailored to the time scale and tectonic setting of the process being investigated.

Gill and lung ventilation responses to steady-state aquatic hypoxia and hyperoxia in the bullfrog tadpole.

PubMed

West, N H; Burggren, W W

1982-02-01

Gill ventilation frequency (fG), the pressure amplitude (PBC) and stroke volume (VS) of buccal ventilation cycles, the frequency of air breaths (fL), water flow over the gills (VW), gill oxygen uptake (MGO2), oxygen utilization (U), and heart frequency (fH) have been measured in unanaesthetized, air breathing Rana catesbeiana tadpoles (stage XVI-XIX). The animals were unrestrained except for ECG leads or cannulae, and were able to surface voluntarily for air breathing. They were subjected to aquatic normoxia, hyperoxia and three levels of aquatic hypoxia, and their respiratory responses recorded in the steady state. The experiments were performed at 20 +/- 0.5 degrees C. In hyperoxia there was an absence of air breathing, and fG, PBC and VW fell from the normoxic values, while U increased, resulting in no significant change in MGO2. Animals in normoxia showed a very low fL which increased in progressively more hypoxic states. VW increased from the normoxic value in mild hypoxia (PO2 = 96 +/- 2 mm Hg), but fell, associated with a reduction in PBC, in moderate (PO2 = 41 +/- 1 mm Hg) and severe (PO2 = 21 +/- 3 mm Hg) hypoxia in the presence of lung ventilation. Gill MGO2 was not significantly different from the normoxic value in mild hypoxia but fell in moderate hypoxia, while in severe hypoxia oxygen was lost to the ventilating water from the blood perfusing the gills. There was no significant change in fH from the normoxic value in either hypoxia or hyperoxia. These data indicate, that in the bimodally breathing bullfrog tadpole, aquatic PO2 exerts a strong control over both gill and lung ventilation. Furthermore, there is an interaction between gill and lung ventilation such that the onset of a high frequency of lung ventilation in moderate and severe hypoxia promotes a suppression of gill ventilation cycles.

Hydroquinone-Mediated Redox Cycling of Iron and Concomitant Oxidation of Hydroquinone in Oxic Waters under Acidic Conditions: Comparison with Iron-Natural Organic Matter Interactions.

PubMed

Jiang, Chao; Garg, Shikha; Waite, T David

2015-12-15

Interactions of 1,4-hydroquinone with soluble iron species over a pH range of 3-5 in the air-saturated and partially deoxygenated solution are examined here. Our results show that 1,4-hydroquinone reduces Fe(III) in acidic conditions, generating semiquinone radicals (Q(•-)) that can oxidize Fe(II) back to Fe(III). The oxidation rate of Fe(II) by Q(•-)increases with increase in pH due to the speciation change of Q(•-) with its deprotonated form (Q(•-)) oxidizing Fe(II) more rapidly than the protonated form (HQ(•)). Although the oxygenation of Fe(II) is negligible at pH < 5, O2 still plays an important role in iron redox transformation by rapidly oxidizing Q(•-) to form benzoquinone (Q). A kinetic model is developed to describe the transformation of quinone and iron under all experimental conditions. The results obtained here are compared with those obtained in our previous studies of iron-Suwannee River fulvic acid (SRFA) interactions in acidic solutions and support the hypothesis that hydroquinone moieties can reduce Fe(III) in natural waters. However, the semiquinone radicals generated in pure hydroquinone solution are rapidly oxidized by dioxygen, while the semiquinone radicals generated in SRFA solution are resistant to oxidation by dioxygen, with the result that steady-state semiquinone concentrations in SRFA solutions are 2-3 orders of magnitude greater than in solutions of 1,4-hydroquinone. As a result, semiquinone moieties in SRFA play a much more important role in iron redox transformations than is the case in solutions of simple quinones such as 1,4-hydroquinone. This difference in the steady-state concentration of semiquinone species has a dramatic effect on the cycling of iron between the +II and +III oxidation states, with iron turnover frequencies in solutions containing SRFA being 10-20 times higher than those observed in solutions of 1,4-hydroquinone.

A Poisson-like closed-form expression for the steady-state wealth distribution in a kinetic model of gambling

NASA Astrophysics Data System (ADS)

Garcia, Jane Bernadette Denise M.; Esguerra, Jose Perico H.

2017-08-01

An approximate but closed-form expression for a Poisson-like steady state wealth distribution in a kinetic model of gambling was formulated from a finite number of its moments, which were generated from a βa,b(x) exchange distribution. The obtained steady-state wealth distributions have tails which are qualitatively similar to those observed in actual wealth distributions.

The relationship between skin aging and steady state ultraweak photon emission as an indicator of skin oxidative stress in vivo.

PubMed

Gabe, Y; Osanai, O; Takema, Y

2014-08-01

Ultraweak photon emission (UPE) is one potential method to evaluate the oxidative status of the skin in vivo. However, little is known about how the daily oxidative stress of the skin is related to skin aging-related alterations in vivo. We characterized the steady state UPE and performed a skin survey. We evaluated the skin oxidative status by UPE, skin elasticity, epidermal thickness and skin color on the inner upper arm, the outer forearm, and the buttock of 70 Japanese volunteers. The steady state UPE at the three skin sites increased with age. Correlation analysis revealed that the steady state UPE only from the buttock was related to skin elasticity, which showed age-dependent changes. Moreover, analysis by age group indicated that b* values of the inner upper arm of subjects in their 20s were inversely correlated with UPE as occurred in buttock skin. In contrast, photoaged skin did not show a clear relationship with steady state UPE because the accumulation of sun-exposure might influence the sensitivity to oxidative stress. These results suggest that steady state UPE reflects not only intrinsic skin aging and cutaneous color but also the current oxidative status independent of skin aging. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Evaporation rate of nucleating clusters.

PubMed

Zapadinsky, Evgeni

2011-11-21

The Becker-Döring kinetic scheme is the most frequently used approach to vapor liquid nucleation. In the present study it has been extended so that master equations for all cluster configurations are included into consideration. In the Becker-Döring kinetic scheme the nucleation rate is calculated through comparison of the balanced steady state and unbalanced steady state solutions of the set of kinetic equations. It is usually assumed that the balanced steady state produces equilibrium cluster distribution, and the evaporation rates are identical in the balanced and unbalanced steady state cases. In the present study we have shown that the evaporation rates are not identical in the equilibrium and unbalanced steady state cases. The evaporation rate depends on the number of clusters at the limit of the cluster definition. We have shown that the ratio of the number of n-clusters at the limit of the cluster definition to the total number of n-clusters is different in equilibrium and unbalanced steady state cases. This causes difference in evaporation rates for these cases and results in a correction factor to the nucleation rate. According to rough estimation it is 10(-1) by the order of magnitude and can be lower if carrier gas effectively equilibrates the clusters. The developed approach allows one to refine the correction factor with Monte Carlo and molecular dynamic simulations.

Perception of steady-state vowels and vowelless syllables by adults and children

NASA Astrophysics Data System (ADS)

Nittrouer, Susan

2005-04-01

Vowels can be produced as long, isolated, and steady-state, but that is not how they are found in natural speech. Instead natural speech consists of almost continuously changing (i.e., dynamic) acoustic forms from which mature listeners recover underlying phonetic form. Some theories suggest that children need steady-state information to recognize vowels (and so learn vowel systems), even though that information is sparse in natural speech. The current study examined whether young children can recover vowel targets from dynamic forms, or whether they need steady-state information. Vowel recognition was measured for adults and children (3, 5, and 7 years) for natural productions of /dæd/, /dUd/ /æ/, /U/ edited to make six stimulus sets: three dynamic (whole syllables; syllables with middle 50-percent replaced by cough; syllables with all but the first and last three pitch periods replaced by cough), and three steady-state (natural, isolated vowels; reiterated pitch periods from those vowels; reiterated pitch periods from the syllables). Adults scored nearly perfectly on all but first/last three pitch period stimuli. Children performed nearly perfectly only when the entire syllable was heard, and performed similarly (near 80%) for all other stimuli. Consequently, children need dynamic forms to perceive vowels; steady-state forms are not preferred.

A stability analysis of the power-law steady state of marine size spectra.

PubMed

Datta, Samik; Delius, Gustav W; Law, Richard; Plank, Michael J

2011-10-01

This paper investigates the stability of the power-law steady state often observed in marine ecosystems. Three dynamical systems are considered, describing the abundance of organisms as a function of body mass and time: a "jump-growth" equation, a first order approximation which is the widely used McKendrick-von Foerster equation, and a second order approximation which is the McKendrick-von Foerster equation with a diffusion term. All of these yield a power-law steady state. We derive, for the first time, the eigenvalue spectrum for the linearised evolution operator, under certain constraints on the parameters. This provides new knowledge of the stability properties of the power-law steady state. It is shown analytically that the steady state of the McKendrick-von Foerster equation without the diffusion term is always unstable. Furthermore, numerical plots show that eigenvalue spectra of the McKendrick-von Foerster equation with diffusion give a good approximation to those of the jump-growth equation. The steady state is more likely to be stable with a low preferred predator:prey mass ratio, a large diet breadth and a high feeding efficiency. The effects of demographic stochasticity are also investigated and it is concluded that these are likely to be small in real systems.

Mathematical modeling of thermal stresses in basic oxygen furnace hood tubes

NASA Astrophysics Data System (ADS)

Samarasekera, I. V.

1985-06-01

The stress-strain history of Basic Oxygen Furnace hood tubes during thermal cycling has been computed using heat flow and stress analyses. The steady-state temperature distribution in a transverse section of the tube was computed at a location where gas temperature in the hood could be expected to be a maximum. Calculations were performed for peak gas temperatures in the range 1950 to 2480 °C (3500 to 4500 °F). The stress-strain history of an element of material located at the center of the tube hot face was traced for three consecutive cycles using elasto-plastic finite-element analysis. It has been shown that the state of stress in the element alternates between compression and tension as the tube successively heats and cools. Yielding and plastic flow occurs at the end of each half of a given cycle. It was postulated that owing to repctitive yielding, plastic strain energy accumulates causing failure of the tubes by fatigue in the low cycle region. Using fatigue theory a conservative estimate for tube life was arrived at. In-plant observations support this mechanism of failure, and the number of cycles within which tube cracking was observed compares reasonably with model predictions. Utilizing the heat flow and stress models it was recommended that tube life could be enhanced by changing the tube material to ARMCO 17-4 pH or AISI 405 steel or alternatively reconstructing hoods with AISI 316L tubes of reduced thickness. These recommendations were based on the criterion that low-cycle fatigue failure could be averted if the magnitude of the cyclic strain could be reduced or if macroscopic plastic flow could be prevented.

EEMD-Based Steady-State Indexes and Their Applications to Condition Monitoring and Fault Diagnosis of Railway Axle Bearings

PubMed Central

Fan, Wei; Tsui, Kwok-Leung; Lin, Jianhui

2018-01-01

Railway axle bearings are one of the most important components used in vehicles and their failures probably result in unexpected accidents and economic losses. To realize a condition monitoring and fault diagnosis scheme of railway axle bearings, three dimensionless steadiness indexes in a time domain, a frequency domain, and a shape domain are respectively proposed to measure the steady states of bearing vibration signals. Firstly, vibration data collected from some designed experiments are pre-processed by using ensemble empirical mode decomposition (EEMD). Then, the coefficient of variation is introduced to construct two steady-state indexes from pre-processed vibration data in a time domain and a frequency domain, respectively. A shape function is used to construct a steady-state index in a shape domain. At last, to distinguish normal and abnormal bearing health states, some guideline thresholds are proposed. Further, to identify axle bearings with outer race defects, a pin roller defect, a cage defect, and coupling defects, the boundaries of all steadiness indexes are experimentally established. Experimental results showed that the proposed condition monitoring and fault diagnosis scheme is effective in identifying different bearing health conditions. PMID:29495446

Performance (Off-Design) Cycle Analysis for a Turbofan Engine With Interstage Turbine Burner

NASA Technical Reports Server (NTRS)

Liew, K. H.; Urip, E.; Yang, S. L.; Mattingly, J. D.; Marek, C. J.

2005-01-01

This report presents the performance of a steady-state, dual-spool, separate-exhaust turbofan engine, with an interstage turbine burner (ITB) serving as a secondary combustor. The ITB, which is located in the transition duct between the high- and the low-pressure turbines, is a relatively new concept for increasing specific thrust and lowering pollutant emissions in modern jet-engine propulsion. A detailed off-design performance analysis of ITB engines is written in Microsoft(Registered Trademark) Excel (Redmond, Washington) macrocode with Visual Basic Application to calculate engine performances over the entire operating envelope. Several design-point engine cases are pre-selected using a parametric cycle-analysis code developed previously in Microsoft(Registered Trademark) Excel, for off-design analysis. The off-design code calculates engine performances (i.e. thrust and thrust-specific-fuel-consumption) at various flight conditions and throttle settings.

Studies of long-life pulsed CO2 laser with Pt/SnO2 catalyst

NASA Technical Reports Server (NTRS)

Sidney, Barry D.

1987-01-01

Closed-cycle CO2 laser testing with and without a catalyst and with and without CO addition indicate that a catalyst is necessary for long-term operation. Initial results indicate that CO addition with a catalyst may prove optimal, but a precise gas mix has not yet been determined. A long-term run of 10 to the 6th power pulses using 1.3% added CO and a 2% Pt on SnO2 catalyst yields an efficiency of about 95% of open-cycle steady-state power. A simple mathematical analysis yields results which may be sufficient for determining optimum running conditions. Future plans call for testing various catalysts in the laser and longer tests, 10 to the 7th power pulses. A Gas Chromatograph will be installed to measure gas species concentration and the analysis will be slightly modified to include neglected but possibly important parameters.

Wave kinetics of random fibre lasers

PubMed Central

Churkin, D V.; Kolokolov, I V.; Podivilov, E V.; Vatnik, I D.; Nikulin, M A.; Vergeles, S S.; Terekhov, I S.; Lebedev, V V.; Falkovich, G.; Babin, S A.; Turitsyn, S K.

2015-01-01

Traditional wave kinetics describes the slow evolution of systems with many degrees of freedom to equilibrium via numerous weak non-linear interactions and fails for very important class of dissipative (active) optical systems with cyclic gain and losses, such as lasers with non-linear intracavity dynamics. Here we introduce a conceptually new class of cyclic wave systems, characterized by non-uniform double-scale dynamics with strong periodic changes of the energy spectrum and slow evolution from cycle to cycle to a statistically steady state. Taking a practically important example—random fibre laser—we show that a model describing such a system is close to integrable non-linear Schrödinger equation and needs a new formalism of wave kinetics, developed here. We derive a non-linear kinetic theory of the laser spectrum, generalizing the seminal linear model of Schawlow and Townes. Experimental results agree with our theory. The work has implications for describing kinetics of cyclical systems beyond photonics. PMID:25645177

Thread mapping using system-level model for shared memory multicores

NASA Astrophysics Data System (ADS)

Mitra, Reshmi

Exploring thread-to-core mapping options for a parallel application on a multicore architecture is computationally very expensive. For the same algorithm, the mapping strategy (MS) with the best response time may change with data size and thread counts. The primary challenge is to design a fast, accurate and automatic framework for exploring these MSs for large data-intensive applications. This is to ensure that the users can explore the design space within reasonable machine hours, without thorough understanding on how the code interacts with the platform. Response time is related to the cycles per instructions retired (CPI), taking into account both active and sleep states of the pipeline. This work establishes a hybrid approach, based on Markov Chain Model (MCM) and Model Tree (MT) for system-level steady state CPI prediction. It is designed for shared memory multicore processors with coarse-grained multithreading. The thread status is represented by the MCM states. The program characteristics are modeled as the transition probabilities, representing the system moving between active and suspended thread states. The MT model extrapolates these probabilities for the actual application size (AS) from the smaller AS performance. This aspect of the framework, along with, the use of mathematical expressions for the actual AS performance information, results in a tremendous reduction in the CPI prediction time. The framework is validated using an electromagnetics application. The average performance prediction error for steady state CPI results with 12 different MSs is less than 1%. The total run time of model is of the order of minutes, whereas the actual application execution time is in terms of days.

Steady State Advanced Tokamak (SSAT): The mission and the machine

NASA Astrophysics Data System (ADS)

Thomassen, K.; Goldston, R.; Nevins, B.; Neilson, H.; Shannon, T.; Montgomery, B.

1992-03-01

Extending the tokamak concept to the steady state regime and pursuing advances in tokamak physics are important and complementary steps for the magnetic fusion energy program. The required transition away from inductive current drive will provide exciting opportunities for advances in tokamak physics, as well as important impetus to drive advances in fusion technology. Recognizing this, the Fusion Policy Advisory Committee and the U.S. National Energy Strategy identified the development of steady state tokamak physics and technology, and improvements in the tokamak concept, as vital elements in the magnetic fusion energy development plan. Both called for the construction of a steady state tokamak facility to address these plan elements. Advances in physics that produce better confinement and higher pressure limits are required for a similar unit size reactor. Regimes with largely self-driven plasma current are required to permit a steady-state tokamak reactor with acceptable recirculating power. Reliable techniques of disruption control will be needed to achieve the availability goals of an economic reactor. Thus the central role of this new tokamak facility is to point the way to a more attractive demonstration reactor (DEMO) than the present data base would support. To meet the challenges, we propose a new 'Steady State Advanced Tokamak' (SSAT) facility that would develop and demonstrate optimized steady state tokamak operating mode. While other tokamaks in the world program employ superconducting toroidal field coils, SSAT would be the first major tokamak to operate with a fully superconducting coil set in the elongated, divertor geometry planned for ITER and DEMO.

Is steady-state capitalism viable? A review of the issues and an answer in the affirmative.

PubMed

Lawn, Philip

2011-02-01

Most ecological economists believe that the transition to a steady-state economy is necessary to ensure ecological sustainability and to maximize a nation's economic welfare. While some observers agree with the necessity of the steady-state economy, they are nonetheless critical of the suggestion made by ecological economists-in particular, Herman Daly-that a steady-state economy is compatible with a capitalist system. First, they believe that steady-state capitalism is based on the untenable assumption that growth is an optional rather than in-built element of capitalism. Second, they argue that capitalist notions of efficient resource allocation are too restrictive to facilitate the transition to an "ecological" or steady-state economy. I believe these observers are outright wrong with their first criticism and, because they misunderstand Daly's vision of a steady-state economy, are misplaced with their second criticism. The nature of a capitalist system depends upon the institutional framework that supports and shapes it. Hence, a capitalist system can exist in a wide variety of forms. Unfortunately, many observers fail to recognize that the current "growth imperative" is the result of capitalist systems everywhere being institutionally designed to grow. They need not be designed this way to survive and thrive. Indeed, because continued growth is both existentially undesirable and ecologically unsustainable, redesigning capitalist systems through the introduction of Daly-like institutions would prove to be capitalism's savior. What's more, it would constitute humankind's best hope of achieving sustainable development. © 2011 New York Academy of Sciences.

Understanding emotional transitions: the interpersonal consequences of changing emotions in negotiations.

PubMed

Filipowicz, Allan; Barsade, Sigal; Melwani, Shimul

2011-09-01

Research on the interpersonal functions of emotions has focused primarily on steady-state emotion rather than on emotional transitions, the movement between emotion states. The authors examined the influence of emotional transitions on social interactions and found that emotional transitions led to consistently different outcomes than their corresponding steady-state emotions. Across 2 computer-mediated negotiations and a face-to-face negotiation, participants negotiating with partners who displayed a "becoming angry" (happy to angry) emotional transition accepted worse negotiation outcomes yet formed better relational impressions of their partners than participants negotiating with partners who displayed steady-state anger. This relationship was mediated through 2 mechanisms: attributional and emotional contagion processes. The "becoming happy" (angry to happy) emotional transition as compared with steady-state happiness was not significantly related to differences in negotiation outcomes but was significantly related to differences in relational impressions, where perceivers of the "becoming happy" emotional transition gave their partners lower relational impression ratings than perceivers of steady-state happiness. PsycINFO Database Record (c) 2011 APA, all rights reserved.

Quantized transport and steady states of Floquet topological insulators

NASA Astrophysics Data System (ADS)

Esin, Iliya; Rudner, Mark S.; Refael, Gil; Lindner, Netanel H.

2018-06-01

Robust electronic edge or surface modes play key roles in the fascinating quantized responses exhibited by topological materials. Even in trivial materials, topological bands and edge states can be induced dynamically by a time-periodic drive. Such Floquet topological insulators (FTIs) inherently exist out of equilibrium; the extent to which they can host quantized transport, which depends on the steady-state population of their dynamically induced edge states, remains a crucial question. In this work, we obtain the steady states of two-dimensional FTIs in the presence of the natural dissipation mechanisms present in solid state systems. We give conditions under which the steady-state distribution resembles that of a topological insulator in the Floquet basis. In this state, the distribution in the Floquet edge modes exhibits a sharp feature akin to a Fermi level, while the bulk hosts a small density of excitations. We determine the regimes where topological edge-state transport persists and can be observed in FTIs.

Two-rate periodic protocol with dynamics driven through many cycles

NASA Astrophysics Data System (ADS)

Kar, Satyaki

2017-02-01

We study the long time dynamics in closed quantum systems periodically driven via time dependent parameters with two frequencies ω1 and ω2=r ω1 . Tuning of the ratio r there can unleash plenty of dynamical phenomena to occur. Our study includes integrable models like Ising and X Y models in d =1 and the Kitaev model in d =1 and 2 and can also be extended to Dirac fermions in graphene. We witness the wave-function overlap or dynamic freezing that occurs within some small/ intermediate frequency regimes in the (ω1,r ) plane (with r ≠0 ) when the ground state is evolved through a single cycle of driving. However, evolved states soon become steady with long driving, and the freezing scenario gets rarer. We extend the formalism of adiabatic-impulse approximation for many cycle driving within our two-rate protocol and show the near-exact comparisons at small frequencies. An extension of the rotating wave approximation is also developed to gather an analytical framework of the dynamics at high frequencies. Finally we compute the entanglement entropy in the stroboscopically evolved states within the gapped phases of the system and observe how it gets tuned with the ratio r in our protocol. The minimally entangled states are found to fall within the regime of dynamical freezing. In general, the results indicate that the entanglement entropy in our driven short-ranged integrable systems follow a genuine nonarea law of scaling and show a convergence (with a r dependent pace) towards volume scaling behavior as the driving is continued for a long time.

Prognostics for Electronics Components of Avionics Systems

NASA Technical Reports Server (NTRS)

Celaya, Jose R.; Saha, Bhaskar; Wysocki, Philip F.; Goebel, Kai F.

2009-01-01

Electronics components have and increasingly critical role in avionics systems and for the development of future aircraft systems. Prognostics of such components is becoming a very important research filed as a result of the need to provide aircraft systems with system level health management. This paper reports on a prognostics application for electronics components of avionics systems, in particular, its application to the Isolated Gate Bipolar Transistor (IGBT). The remaining useful life prediction for the IGBT is based on the particle filter framework, leveraging data from an accelerated aging tests on IGBTs. The accelerated aging test provided thermal-electrical overstress by applying thermal cycling to the device. In-situ state monitoring, including measurements of the steady-state voltages and currents, electrical transients, and thermal transients are recorded and used as potential precursors of failure.

Towards Prognostics for Electronics Components

NASA Technical Reports Server (NTRS)

Saha, Bhaskar; Celaya, Jose R.; Wysocki, Philip F.; Goebel, Kai F.

2013-01-01

Electronics components have an increasingly critical role in avionics systems and in the development of future aircraft systems. Prognostics of such components is becoming a very important research field as a result of the need to provide aircraft systems with system level health management information. This paper focuses on a prognostics application for electronics components within avionics systems, and in particular its application to an Isolated Gate Bipolar Transistor (IGBT). This application utilizes the remaining useful life prediction, accomplished by employing the particle filter framework, leveraging data from accelerated aging tests on IGBTs. These tests induced thermal-electrical overstresses by applying thermal cycling to the IGBT devices. In-situ state monitoring, including measurements of steady-state voltages and currents, electrical transients, and thermal transients are recorded and used as potential precursors of failure.

Crustal Growth: In Defense of the Dogma

NASA Astrophysics Data System (ADS)

Albarede, F.; Blichert-Toft, J.; Guitreau, M.

2012-12-01

Plate tectonics was not even in its teens when Armstrong suggested that mantle and crust have interacted at steady-state over Earth's history. With the help of new geochemical tools and large-scale compilations, the concept of steady-state crust (as opposed to continuous crustal growth) is being revived with the implications that the equivalent of several volumes of present-day crust (PDCV) may have been subducted through geological times. Here we argue --or recall-- that four different lines of evidence invalidate this model. (i) The subduction filter must be particularly efficient for argon, even more so than for LILE and most other volatile elements. Atmosphere collects 40Ar degassed from both the extant crust and the crust dragged down at subduction zones over geological time. Regardless of the residence time of the crust at the surface, the amount of atmospheric 40Ar limits subduction of continental crust into the mantle to < 30% of the PDCV [1]. (ii) EM II, the only component that undoubtedly represents subducted continental crust in oceanic basalts, is extremely uncommon. (iii) Crustal age histograms are irrepressibly episodic. It has been argued that erosion selectively removes the crust with the elusive ages [2]. Ages of detrital zircons, which in the selective erosion conjecture should fill the voids, do not support this view [3]. Episodicity is difficult to reconcile with a continental protolith isolated by the common geological processes working either at mid-ocean ridges or subduction zones. A role may be recognized for Wilson cycles, if they can be shown to have prevailed for the entire history of the Earth. Geochemistry demonstrates that superplume material makes up the crustal protolith of all the major juvenile provinces. (iv) The residence time in the mantle of the elements distinctive of the crust is similar to the age of the Earth or even longer [4]. Continental crust finds its source in the instabilities of the lower mantle and the irreversible extraction of its low-melting point components, not in the steady-state processing of the rather barren upper mantle. This is why we surmise that steady-state does not provide an adequate account of crustal dynamics. [1] Coltice, N. et al. Science 288 (2000) 845 [2] Gurnies, M. & Davies, G. J. Geol. 14 (1986) 396 [3] Guitreau, M. et al., Earth Planet. Sci. Lettes 337-338 (2012) 211 [4] Albarede, F. AGU Monogr. 160 (2005) 25.

Quality by design: optimization of a freeze-drying cycle via design space in case of heterogeneous drying behavior and influence of the freezing protocol.

PubMed

Pisano, Roberto; Fissore, Davide; Barresi, Antonello A; Brayard, Philippe; Chouvenc, Pierre; Woinet, Bertrand

2013-02-01

This paper shows how to optimize the primary drying phase, for both product quality and drying time, of a parenteral formulation via design space. A non-steady state model, parameterized with experimentally determined heat and mass transfer coefficients, is used to define the design space when the heat transfer coefficient varies with the position of the vial in the array. The calculations recognize both equipment and product constraints, and also take into account model parameter uncertainty. Examples are given of cycles designed for the same formulation, but varying the freezing conditions and the freeze-dryer scale. These are then compared in terms of drying time. Furthermore, the impact of inter-vial variability on design space, and therefore on the optimized cycle, is addressed. With this regard, a simplified method is presented for the cycle design, which reduces the experimental effort required for the system qualification. The use of mathematical modeling is demonstrated to be very effective not only for cycle development, but also for solving problem of process transfer. This study showed that inter-vial variability remains significant when vials are loaded on plastic trays, and how inter-vial variability can be taken into account during process design.

Dynamically triggered slip leading to sustained fault gouge weakening under laboratory shear conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Paul Allan

We investigate dynamic wave-triggered slip under laboratory shear conditions. The experiment is composed of a three-block system containing two gouge layers composed of glass beads and held in place by a fixed load in a biaxial configuration. When the system is sheared under steady state conditions at a normal load of 4 MPa, we find that shear failure may be instantaneously triggered by a dynamic wave, corresponding to material weakening and softening if the system is in a critical shear stress state (near failure). Following triggering, the gouge material remains in a perturbed state over multiple slip cycles as evidencedmore » by the recovery of the material strength, shear modulus, and slip recurrence time. This work suggests that faults must be critically stressed to trigger under dynamic conditions and that the recovery process following a dynamically triggered event differs from the recovery following a spontaneous event.« less

On the possible cycles via the unified perspective of cryocoolers. Part A: The Joule-Thomson cryocooler

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maytal, Ben-Zion; Pfotenhauer, John M.

2014-01-29

Joule-Thomson (JT) cryocoolers possess a self adjusting effect, which preserves the state of the returning stream from the evaporator as a saturated vapor. The heat load can be entirely absorbed at constant temperature by evaporation even for different sized heat exchangers. It is not possible for the steady state flow resulting from a gradual cool down to penetrate 'deeper' into the two-phase dome, and produce a two phase return flow even with a heat exchanger of unlimited size. Such behavior was implicitly taken for granted in the literature but never clearly stated nor questioned and therefore never systematically proven. Themore » discussion provided below provides such a proof via the unified model of cryocoolers. This model portrays all cryocoolers as magnifiers of their respective elementary temperature reducing mechanism through the process of 'interchanging'.« less

Dynamically triggered slip leading to sustained fault gouge weakening under laboratory shear conditions

DOE PAGES

Johnson, Paul Allan

2016-02-28

We investigate dynamic wave-triggered slip under laboratory shear conditions. The experiment is composed of a three-block system containing two gouge layers composed of glass beads and held in place by a fixed load in a biaxial configuration. When the system is sheared under steady state conditions at a normal load of 4 MPa, we find that shear failure may be instantaneously triggered by a dynamic wave, corresponding to material weakening and softening if the system is in a critical shear stress state (near failure). Following triggering, the gouge material remains in a perturbed state over multiple slip cycles as evidencedmore » by the recovery of the material strength, shear modulus, and slip recurrence time. This work suggests that faults must be critically stressed to trigger under dynamic conditions and that the recovery process following a dynamically triggered event differs from the recovery following a spontaneous event.« less

Spurious Numerical Solutions Of Differential Equations

NASA Technical Reports Server (NTRS)

Lafon, A.; Yee, H. C.

1995-01-01

Paper presents detailed study of spurious steady-state numerical solutions of differential equations that contain nonlinear source terms. Main objectives of this study are (1) to investigate how well numerical steady-state solutions of model nonlinear reaction/convection boundary-value problem mimic true steady-state solutions and (2) to relate findings of this investigation to implications for interpretation of numerical results from computational-fluid-dynamics algorithms and computer codes used to simulate reacting flows.

Electronic transport characterization of silicon wafers by spatially resolved steady-state photocarrier radiometric imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Qian; University of the Chinese Academy of Sciences, Beijing 100039; Li, Bincheng, E-mail: bcli@ioe.ac.cn

2015-09-28

Spatially resolved steady-state photocarrier radiometric (PCR) imaging technique is developed to characterize the electronic transport properties of silicon wafers. Based on a nonlinear PCR theory, simulations are performed to investigate the effects of electronic transport parameters (the carrier lifetime, the carrier diffusion coefficient, and the front surface recombination velocity) on the steady-state PCR intensity profiles. The electronic transport parameters of an n-type silicon wafer are simultaneously determined by fitting the measured steady-state PCR intensity profiles to the three-dimensional nonlinear PCR model. The determined transport parameters are in good agreement with the results obtained by the conventional modulated PCR technique withmore » multiple pump beam radii.« less

A Waved Journal Bearing Concept-Evaluating Steady-State and Dynamic Performance with a Potential Active Control Alternative

NASA Technical Reports Server (NTRS)

Dimofte, Florin

1993-01-01

Analysis of the waved journal bearing concept featuring a waved inner bearing diameter for use with a compressible lubricant (gas) is presented. The performance of generic waved bearings having either three or four waves is predicted for air lubricated bearings. Steady-state performance is discussed in terms of bearing load capacity, while the dynamic performance is discussed in terms of fluid film stability and dynamic coefficients. It was found that the bearing wave amplitude has an important influence on both the steady-state and the dynamic performance of the waved journal bearing. For a fixed eccentricity ratio, the bearing steady-state load capacity and direct dynamic stiffness coefficient increase as the wave amplitude increases.

[Specific features in realization of the principle of minimum energy dissipation during individual development].

PubMed

Zotin, A A

2012-01-01

Realization of the principle of minimum energy dissipation (Prigogine's theorem) during individual development has been analyzed. This analysis has suggested the following reformulation of this principle for living objects: when environmental conditions are constant, the living system evolves to a current steady state in such a way that the difference between entropy production and entropy flow (psi(u) function) is positive and constantly decreases near the steady state, approaching zero. In turn, the current steady state tends to a final steady state in such a way that the difference between the specific entropy productions in an organism and its environment tends to be minimal. In general, individual development completely agrees with the law of entropy increase (second law of thermodynamics).